Unraveling Cation Intercalation Mechanism in MXene for Enhanced Supercapacitor Performance

Unraveling Cation Intercalation Mechanism in MXene for Enhanced Supercapacitor Performance | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Unraveling Cation Intercalation Mechanism in MXene for Enhanced Supercapacitor Performance Xiaodan Yin, Wei Zheng, Haifeng Tang, Li Yang, Chengjie Lu, Long Pan, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4161663/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 3 You are reading this latest preprint version Abstract MXenes are two-dimensional materials with high electrical conductivity, adjustable composition, and tunable surface terminations, endowing them with significant potential for supercapacitors (SCs). However, during etching preparation, the susceptibility to interlayer restacking and the attachment of inactive -F terminations reduce their capacitances and rate performance. To resolve these issues, electrochemistry-driven cation intercalation (ECI) followed by calcination is proposed to widen their interlayer spacing and modify surface chemistry simultaneously. Results show that the Mn-modified Ti 3 C 2 T z exhibits an exceptionally high volumetric capacitance (1655.5 F cm − 3 at 1 mV s − 1 , 1.5 times higher than that of pristine Ti 3 C 2 T z ) and excellent rate performance (72.3% retention from 1 to 50 A g − 1 ) due to the unblocked interlayers and the increased -O terminations. Density Functional Theory (DFT) results reveal that the intercalated Mn 2+ displayed the largest formation energy difference, manifesting a great driving force to form active -O terminations, which is crucial for improving electrochemical performance. Kinetic analysis reveals that the intercalated Mn 2+ increases the termination-related capacitances (pseudocapacitance and diffusion-controlled capacitance) significantly. The asymmetric SCs assembled with Mn-intercalated Ti 3 C 2 T z and nitrogen-doped activated carbon, show the combination of high energy densities at high powers (38.2 Wh L − 1 at 30.1 kW L − 1 ). The findings clarify how metal cation intercalation affects MXene performance, providing insights for advancing MXene-based electrodes in energy storage applications. MXene Restacking Cation intercalation Capacitance Supercapacitor Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Electrochemical energy storage devices such as batteries and supercapacitors (SCs) are becoming increasingly crucial for various applications, from portable electronics to grid-scale energy storage. SCs, distinguished by fast charging and discharging capabilities and long cycling stability, exhibit outstanding suitability for applications demanding expeditious energy delivery 1–3 . However, the current development of SCs is primarily restricted by low energy densities 4 . Developing electrodes with high capacitances is one of the keys to the breakthrough of SC practicality. Two-dimensional (2D) materials, with nanometer thickness and unique properties, have become the focus of attention. Among them, MXenes stand out in the field of SCs. MXenes, a class of 2D materials with the formula M n+1 X n T z (M represents a transition metal, X denotes C or N, n ranges from 1 to 4, and T z refers to surface terminations such as -OH, -O, -F, etc.), which possess exceptional electrical conductivity (up to ~ 24000 S cm − 1 ), high density (3–4 g cm − 3 ), good hydrophilicity (20–40° contact angles with water) and favorable mechanical properties (high Young’s modulus up to ~ 0.36 TPa) 5–10 . Particularly, the rich composition and tunable surface terminations offer MXenes great promise in SCs. However, the restacking in nanosheets caused by van der Waals forces limits the exploitation of MXene-based electrodes, by preventing the full exposure of active sites and compromising their rate performance. Additionally, the surface terminations which are closely associated with their preparation and subsequent treatment, substantially influence MXenes’ electrochemical properties. More specifically, the lack of active -O terminations (participating redox reactions) limits their specific capacitances 11, 12 . To resolve the above issues, various strategies, including compositing, atomic doping, and intercalation, have been proposed. However, compositing MXene with materials such as metal oxides or conducting polymer enhances the capacitances but increases the preparation complexity 13–16 . Atomic doping introduces nitrogen or boron, optimizing MXenes’ electronic structure and improving conductivity, though it may introduce impurities 17–20 . The intercalation strategy is a simple and effective method, addressing the issues through the “pillar effect” and “termination replace effect” 8, 21–23 . Additionally, among the commonly used intercalation agents, metal cations exhibit strong tunability, offering greater design flexibility with the ability to choose different types of metal cations based on specific requirements. Unlocking the full potential of applicable metal cation intercalation holds promise for advancing the practicality of MXene-based electrodes. Despite significant progress in current research, it only reveals the tip of the iceberg, and the lack of a clear elucidation of relevant mechanisms remains a major challenge. Hence, we thoroughly study the effect of metal cationic interlayer intercalation on the electrochemical properties of MXene. We choose the electrochemistry-driven cation intercalation (ECI) method to insert the metal cations into the Ti 3 C 2 T z interlayers followed by calcination. Taking advantage of precision and controllability, ECI allows for the precise modulation of ion intercalation quantities by applying different voltages. Besides, it is expected to enable unobstructed ion diffusion channels to guarantee fast ion diffusivity by continuous cation intercalation 23, 24 . This integrated approach of ECI and calcination holds significant importance for improving the interlayer spacing and terminations of Ti 3 C 2 T z , thereby synergetic manipulating MXene structure and composition. Next, we leverage the computational advantages of Density Functional Theory (DFT) calculations. Starting from the minimum energy principle, we investigate the impact of cation interactions with Ti 3 C 2 T z MXene. This elucidates the mechanism by which cation intercalation affects the structure and composition of Ti 3 C 2 T z . This study presents a rigorous theoretical analysis of cation intercalation effects on the structure and composition of MXene. It showcases a strategic framework for the advanced development of MXene electrodes, emphasizing its pivotal role in optimizing MXene’s structural and compositional benefits for enhanced application. Results and discussion It has been widely accepted that the surface terminations of MXene is closely related to the intercalation process, in which the -O termination is a pivotal factor in redox reactions 11, 12 . Accordingly, we propose a surface termination modulation strategy using metal cations intercalation, expecting to find suitable metal cations to make MXene surface rich in -O termination with suitable interlayer spacing. Figure S1 shows a fragment of the periodic table of elements. The metallic elements are generally considered to be proper cation elements, among which those stable and commonly used in aqueous solution are labeled in red. It should be noted that certain metallic-based salts demonstrate limited solubility, rendering them unsuitable for use as electrolytes. Ultimately, Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , MnSO 4 , ZnSO 4 , MgSO 4 , and Al 2 (SO 4 ) 3 are chosen as intercalators and cation intercalation in Ti 3 C 2 T z , labeled as Ti 3 C 2 T z -M in this work. Ti 3 C 2 T z freestanding films were prepared according to our previous work 25 . The experimental process is illustrated schematically in Figure S2. It involves selectively etching the A-layer of the homemade Ti 3 AlC 2 (in Figures S4(a)-(b)) to obtain a multi-layered Ti 3 C 2 T z (in Figures S4(c)-(d)). Subsequently, ultrasound and centrifugation were used to achieve a uniformly dispersed Ti 3 C 2 T z (in Figure S5(a)), which was further vacuum-filtered to obtain Ti 3 C 2 T z freestanding films (in Figure S5(b)). The thickness and quality of the Ti 3 C 2 T z films can be adjusted by varying the concentration of the Ti 3 C 2 T z suspension. The ECI approach was selected to adjust the interlayer space and create the favorite terminations. The treated Ti 3 C 2 T z surface not only exposes more active sites but also experiences surface termination adjustment, particularly the increase in -O terminations and a reduction in -F terminations. These changes significantly boost the redox reactions of Ti 3 C 2 T z in H 2 SO 4 electrolyte. The XRD patterns of Ti 3 AlC 2 and Ti 3 C 2 T z are shown in Fig. 1 (a). The characteristic peaks can be assigned to Ti 3 AlC 2 (JCPDS No. 50–0875), indicating its good crystallinity 28 . After selectively etching the Al layer of the precursor using HCl/LiF mixture, the (002) peak shifts to 7.05° from 9.68°, indicating the successful preparation of the Ti 3 C 2 T z . To investigate the effect of different metal cations on the Ti 3 C 2 T z interlayer distance and surface chemistry, metal cations including Li + , Na + , K + , Mn 2+ , Zn 2+ , Mg 2+ , and Al 3+ with varying valence states were selected. The comparison of ionic radii, hydrated ionic radii, and atomic weights is shown in Fig. 1 (b). Initially, the films after ECI were naturally dried at room temperature (RT), and the shift of the (002) characteristic peaks were observed in Figure S6, indicating the intercalation of metal cations into the Ti 3 C 2 T z with adjustable interlayer spacing. Considering the intercalated water may affect the interlayer distance, drying under a vacuum at 120°C was used to compare the effect of different intercalation cations more accurately. Shown in Figure S7, the (002) peak of the dried Ti 3 C 2 T z is shifted to the right by 1.01° compared to the undried Ti 3 C 2 T z , which is attributed to the removal of free water between the Ti 3 C 2 T z layers. According to the Bragg equation, the interlayer spacing decreased by 2.37 Å, approximately one layer of water molecules 29 . In addition, Figure S8 compares the XRD patterns of intercalated cations with different valence states. The (002) peaks are shifted to the left for all ECI treated Ti 3 C 2 T z -based electrodes, implying the metal cations are present in the Ti 3 C 2 T z interlayers. Due to the use of LiF salts as an etchant, the Ti 3 C 2 T z layers contain some Li + . This explains why the (002) peak of Ti 3 C 2 T z shows minimal shift after ECI in Li 2 SO 4 . The interlayer spacing of each intercalated cation can be calculated based on their respective ion diameters and the calculated interlayer distance was consistent with the actual test results for all cations except for Mg 2+ and Al 3+ listed in Table S1 . This discrepancy in Mg 2+ and Al 3+ is likely attributed to their small atomic radii with high charges, leading to a strong adsorption force on water molecules, resulting in the difficulty of water evaporation and incomplete drying at 120°C. ECI influences the redox reactions of Ti 3 C 2 T z by opening the interlayer distance and altering the terminations. Subsequently, a 400°C calcination step was employed to introduce more favorited terminations. This Ti 3 C 2 T z -Metal Cation Intercalation-Calcination process is denoted as T-M-C. The XRD patterns of T-M-C are illustrated in Fig. 1 (c). In contrast to the Ti 3 C 2 T z that underwent calcination (T-C), it can be observed that the (002) peaks of T-M-C are all shifted to the left. The intercalated cations mostly existed as Ti-O-M, resulting in increased interlayer spacing. TEM further analyzes the homogeneous structure of Ti 3 C 2 T z and T-Mn-C electrodes in Figs. 1 (d)-(e), respectively. Ti 3 C 2 T z has a monolayer structure with a lateral size of 500–600 nm in Figure S9. It is observed that the interlayer homogeneity of Ti 3 C 2 T z is poor, while the interlayers of the T-Mn-C show a smooth and flat arrangement. This difference can be attributed to the ECI, which uses an external power to facilitate the cations intercalating into the Ti 3 C 2 T z layers, thereby opening the blocked interlayer areas 23 . Additionally, a cross-sectional SEM of T-Mn-C displays a lamellar structure like Ti 3 C 2 T z in Fig. 1 (f), indicating that the ECI and calcination process does not affect the lamellar structure of Ti 3 C 2 T z . The intercalated Mn element is evenly distributed in the cross-section images (in Fig. 1 (g)), indicating good Mn 2+ intercalation during the ECI process. The comparison of the macroscopic optical morphology of Ti 3 C 2 T z with different cation intercalation and calcination is presented in Figure S10. It can be observed that the films’ surface exhibits tiny bubbles after calcination, reflecting the expansion of the films during calcination. The T-M-C films maintain flexibility, which can be used as electrodes directly without any post-treatment. It should be noted that the flexibility of the T-M-C films is slightly reduced compared with the pristine Ti 3 C 2 T z films, primarily attributed to the removal of free water between the Ti 3 C 2 T z layers during the calcination. However, this flexibility reduction does not affect the use of the T-M-C films during electrochemical testing. The cross-section images of the electrodes (in Figure S10) are comparable, indicating the layer-stacked structures of Ti 3 C 2 T z are maintained. Electrochemical tests were conducted on T-M-C electrodes in 3 M H 2 SO 4 electrolyte. Figure S11(a) exhibits the CV curves at 20 mV s − 1 in a potential window of -0.5 V to 0.2 V vs. Ag/AgCl. All samples show asymmetric oval-like shapes with one pair of broad peaks, consistent with a pseudocapacitance, PC, dominated performance in H 2 SO 4 electrolyte by H + intercalation/de-intercalation. Notably, the CV areas display that T-M-C is more significant than the rest samples, indicating its highest specific capacitance. Figures S11(b)-(c) compares the specific capacitances for all samples at different scan rates, the specific capacitances at 20 mV s − 1 and the capacitance retention rates at 50 mV s − 1 (compared with the specific capacitance at 1 mV s − 1 ). When considering monovalent cations (Li + , Na + , and K + ), the specific capacitances of the three cations at 20 mV s − 1 do not differ significantly. T-Li-C demonstrates a relatively high specific capacitance of 1151.1 F cm − 3 , while T-K-C exhibits the highest capacitance retention rate of 86.1%. This observation can be attributed to the influence of cationic radius. The relationship between the radii of Li + , Na + , and K + ions is followed by Li + < Na + < K + . The larger radius of intercalated K + ions increases interlayer distance and provides fast ion diffusion channels. It is found that the capacitance retention varies linearly with increasing monovalent cations radius, which also has been reported in previous work 23 . Among the divalent cations, T-Mn-C exhibits the highest specific capacitance at 1 mV s − 1 , with a maximum specific capacitance of 1655.5 F cm − 3 . On the other hand, T-Mg-C displays the most significant capacitance retention of 82.0%. The underlying reasons are still unknown. We speculate that it is related to the more absorbed water among the T-Mg-C interlayers, reflected from the (002) peak in Fig. 1 (c). This situation is also found in T-Al-C electrodes, which show the highest capacitance retention (86.1%) due to the larger interlayer distance. Additionally, the effect of the different valence states of the same element on electrochemical performance is considered. We selected FeSO 4 and Fe 2 (SO 4 ) 3 as the electrolytes, and their electrochemical performances are presented in Figure S12. Notably, we observe minimal disparity in the electrochemical performances between T-Fe 2+ -C and T-Fe 2+ -C. The specific capacitances of T-Fe 2+ -C are slightly higher than that of T-Fe 2+ -C. This improvement can be attributed to the higher valence state of Fe 3+ , which enhances its water adsorption capability, consequently leading to increased interlayer distance and a slight enhancement in electrochemical performance. When considering all T-M-C electrodes, T-Mn-C demonstrates the highest capacitances and impressive capacitance retention due to the more -O terminations and suitable interlayer spacing. This result is well consistent with the calculation results. Hence, the electrochemical performance of T-Mn-C electrode was further investigated. Figure 2 (a) displays the CV curves of T, T-C, T-Mn, and T-Mn-C at a scan rate of 20 mV s − 1 . It can be observed that Ti 3 C 2 T z exhibits a non-rectangular shape. Adding Mn 2+ to Ti 3 C 2 T z leads to broad oxidation peaks near − 0.2 V vs Ag/AgCl and reduction peaks around − 0.3 V vs Ag/AgCl in T-Mn-C. By analyzing the area of CV curves, T-Mn-C exhibits the largest area, indicating significantly enhanced specific capacitance. The electrochemical properties of other T-M-C electrodes are shown in Figures S13-14. The specific capacitances of the four electrodes at 20 mV s − 1 are calculated using the CV curves shown in Fig. 2 (b). The T-Mn-C demonstrates a specific capacitance of 1428.5 F cm − 3 , improving 87.3% compared with pristine Ti 3 C 2 T z . This performance surpasses that of many Ti 3 C 2 T z -based electrodes reported in Table S2. The Nyquist plots of T, T-C, T-Mn, and T-Mn-C are compared in Fig. 2 (c). The Nyquist plot has a semicircle in the high-frequency area and a linear line in the low-frequency area. The internal resistance of these electrodes (R s ) does not change much, indicating that the ECI and calcination process do not alter their R s . The semicircle radius corresponds to the charge transfer resistance (R ct ). T-Mn-C (3.59 Ω) has a smaller R ct than pure Ti 3 C 2 T z (3.64 Ω) among these electrodes. Besides, the slope of T-Mn-C is the largest in the low-frequency region, indicating its accelerated ion diffusion process. This is reasonable considering Ti-O-Mn as a ‘pillar’ to expand the interlayer distance and increase the active sites. As shown in Figure S15, T-Mn-C exhibited the largest specific capacitances than the other three electrodes. When the current densities are increased from 1 A g − 1 to 50 A g − 1 , the capacitance is still maintained at 72.3%, a 19% improvement compared to the pure Ti 3 C 2 T z at 53.3%. Generally, the total amount of charge stored in an electrode is contributed to a combination of surface-controlled and diffusion-controlled processes. The b value is near 1, demonstrating that the electrochemical mechanism is a surface-controlled process 30 . As displayed in Figure S16, the b value was calculated from the oxidation peaks of the CV curves. T-Mn-C’s b value is 0.96, indicating the fast surface charge response. To demonstrate the advance of the ECI method, we employed a self-assembly technique to fabricate the T-Mn-self assembling (T-Mn-sa) and T-Mn-self assembling-calcination (T-Mn-sa-C) sample to make a comparison. The electrochemical properties of these samples are depicted in Figure S17. The results demonstrate that the electrodes after ECI exhibit higher capacitances than the electrodes with the self-assembling technique, except a slightly lower at 50 mV s − 1 . This enhancement is ascribed to the more uniform pathways and more active sites created by ECI. Figure 2 (d) illustrates the CV plots of T-Mn-C at different scan rates with a potential window of -0.5 V to 0.2 V vs Ag/AgCl. With increasing scan rates, CV curves show no significant distortions, indicating that T-Mn-C has fast ion diffusion/migration processes 31 . Figure 2 (e) depicts the GCD curves of T-Mn-C at different current densities, showing symmetric charge/discharge processes without obvious plateaus, indicating good electrochemical reversibility. Even under high current densities, the GCD curves maintain symmetrical triangles without significant IR drop. The kinetic processes from the CV curves were analyzed to gain deeper insights into the energy storage mechanism of T-Mn-C. Electrode charge storage typically involves a capacitive-controlled process and a diffusion-controlled process. As the calculation of the b value in Figure S16, the contribution of the capacitive-control process is determined at different scan rates. From Figure S18, it can be observed that with increasing scan rates, the capacitive-controlled contribution rises from 63–92%. This higher capacitive-controlled contribution from 1 to 50 mV s − 1 indicates that T-Mn-C possesses rapid charge storage kinetics, which is advantageous for achieving good rate performance. Additionally, the T-Mn-C electrode exhibits excellent long-term cycling performance, as shown in Fig. 2 (f). After 10000 cycles at 10 A g − 1 , it has a capacitance retention rate of 101.1% and an averaged Coulombic efficiency of 100.1%, outstanding among previous reports, as shown in Figure S19 and Table S2. Ex-situ XRD and XPS analyses were conducted to investigate T-Mn-C's phase changes and charge storage mechanism, as depicted in Figs. 2 (g)-(j), respectively. During the charging process from − 0.5 V to 0.2 V (point A to C in Fig. 2 (g)), the (002) peak of T-Mn-C shifts towards higher angles, indicating a reduction in interlayer spacing. Conversely, during discharging from 0.2 V to -0.5 V, the (002) peak turns towards lower degrades due to the increased interlayer spacing. Ex-situ XPS analysis revealed that the Ti peaks shift to higher binding energies during charging, suggesting oxidation. Conversely, the Ti peaks shift to lower binding energies during discharging, indicating reduction. This phenomenon is primarily attributed to the intercalation and deintercalation of H + in the H 2 SO 4 electrolyte during the charging/discharging process, which is in line with previous report 32 . XPS was further utilized to analyze the surface chemistries of the T-Mn-C electrode to reveal the role of the intercalated Mn. Figure 3 (a) presents the XPS curves of T, T-C, T-Mn, and T-Mn-C electrodes. T-C, T-Mn, and T-Mn-C’s peaks are similar to Ti 3 C 2 T z , indicating that the structure of Ti 3 C 2 T z remains following the ECI and calcination process. The Mn 2p peak at 640.8 eV is observed in T-Mn and T-Mn-C, indicating the successful intercalation of Mn 2+ into the Ti 3 C 2 T z interlayers. The elemental percentages of O, F, and Mn were calculated based on XPS results. As shown in Fig. 3 (b), the ECI increases the O and decreases the F content, which is ascribed to the intercalated cations and is in line with the calculation results. The calcination process is also employed to reduce the inactive -F further. The increased O content after calcination may be ascribed to the slight surface oxidation, which has been reported previously 21 . The fitted result for the Mn 2p of T-Mn-C is shown in Fig. 3 (c), revealing the presence of Mn 3+ besides Mn 2+ . This indicates the oxidation of Mn 2+ from the oxidizing agent originating from Ti 3 C 2 T z or oxygen in the atmosphere 29 . Further analysis of the Mn 2p in the XPS of T-Mn and T-Mn-C at different depths are in Figs. 3 (d)-(e). It is observed that the Mn 2p can still be found inside the electrode, which is consistent with the EDS mapping of the cross-sectional image in Fig. 3 (g). Although Mn 2p peaks exist on the surface and inside the T-Mn-C before testing, it is speculated that H + might replace them during pre-cycling. To verify this, ICP analysis was performed on the T-Mn-C before and after pre-cycling. Figure 3 (f) shows that the Mn content before pre-cycling is 3.4 wt%. In contrast, after pre-cycling (50 cycles), it is 0.35 wt%. This confirms that the Ti-O-Mn bonds break during pre-cycling, and Mn cations extract from the Ti 3 C 2 T z interlayer through H + exchange. Moreover, this phenomenon provides a reasonable explanation for the continuing expansion of CV areas (in Figure S20). In short, the intercalated Mn cations exist in the form of Ti-O-Mn, which increase the -O terminations, decrease the -F terminations, serve as active sites and pillar up the interlayer. These combinations enhance the electrochemical performance of T-Mn-C electrodes. The Ti 2p of T, T-C, T-Mn, and T-Mn-C electrodes are analyzed as shown in Figure S21. It can be observed that the Ti-C binding is lowest for the T-Mn-C electrode, indicating the inactive sites are minimized in the four electrodes, thereby increasing the specific capacitances. To systematically study how the intercalated cations affect the surface terminations and the interlayer spacing. DFT simulation has been primarily performed for a comprehensive understanding of the Ti 3 C 2 T z -M, with the corresponding atomic scheme illustrated in Fig. 4 (a). It can be seen that three possible accommodation sites exist in the interlayer space of Ti 3 C 2 T z , namely, Top, Hollow, and Mid. The formation energy computation results imply that the optimal intercalation configuration of each cation species might be different, as demonstrated in detail in Figure S22: taking Li, Mg, and Al elements for example, the formation energy plots in Fig. 4 (b) imply that Li exhibits a strong interaction with substrate Ti 3 C 2 T z , with the largest formation energy calculated to be -0.68eV/-2.59 eV for Mid-Ti 3 C 2 F 2 /Mid-Ti 3 C 2 O 2 , respectively. While in the case of Mg and Al, the energetically favorable configurations are determined to be Top/Hollow (-0.28 eV/-2.11 eV) and Top/Top (-0.05 eV/-1.76 eV), respectively. It is interesting to find that the formation energy of M-Ti 3 C 2 O 2 is generally much higher than that of M-Ti 3 C 2 F 2 , suggesting an overall strong interaction between the -O termination and metal cations. Consequently, the presence of metal cation in solution is proposed to possibly induce termination alternation in solution, according to Eq. ( 1 ): $${\text{T}\text{i}}_{3}{\text{C}}_{2}{\text{F}}_{z}-\text{M}+ \text{*}\text{O} \rightleftharpoons {\text{T}\text{i}}_{3}{\text{C}}_{2}{\text{O}}_{z}-\text{M}+ \text{*}\text{F}$$ 1 where Ti 3 C 2 F z -M and Ti 3 C 2 O z -M refer to the cation intercalated Ti 3 C 2 T z , * O and * F refer to the active oxygen and fluorine existing in the solution during the intercalation process, In order to raise the content of -O termination, which plays a significant role in the surface redox reactions of Ti 3 C 2 T z , a well combination of strong interaction between cation and -O termination and weak interaction between the cation and -F is expected 11, 12 . Considering that the free energy difference between * O and * F is constant in a dilute solution, the reaction enthalpy of the above equation can be calculated by the formation energy difference, which evaluates the termination preference of cation element species according to Eq. ( 2 ): $$\varDelta {E}_{\text{d}\text{i}\text{f}\text{f}}={E}_{{\text{T}\text{i}}_{3}{\text{C}}_{2}{\text{F}}_{z}-\text{M}}^{\text{o}\text{p}\text{t}\text{i}\text{m}\text{a}\text{l}}-{E}_{{\text{T}\text{i}}_{3}{\text{C}}_{2}{\text{O}}_{z}-\text{M}}^{\text{o}\text{p}\text{t}\text{i}\text{m}\text{a}\text{l}}$$ 2 Correspondingly, the Li cation with a formation energy difference of \({\varDelta E}_{\text{d}\text{i}\text{f}\text{f}}^{\text{L}\text{i}}\) of 1.90 eV is suggested to possess stronger termination preference than Na and Mg cations with the values of 1.83 eV and 1.67 eV, respectively. Then, a high-throughput DFT simulation is conducted to find out the element with the strongest termination preference for Ti 3 C 2 T z . After the energy calculation of Ti 3 C 2 T z -M (T=-F, -O) at various interlayer distances (ranging from 10 to Å to 15 Å), the optimal configuration of each Ti 3 C 2 T z -M is determined, thereby the theoretical interlayer distance as well as the formation energy difference can be obtained, displayed in Figs. 4 (c)-(d), respectively. After considering accommodation sites, it is notable that the interlayer distance of Ti 3 C 2 T z -M is not simply dominated by the ionic radius of the cation element, for example, that of Ti 3 C 2 T z -Zn is much larger than that of Ti 3 C 2 T z -Mg despite their similar cation ionic radius (Zn-0.74 Å versus Mg-0.72 Å) 26, 27 . The formation energy calculation results demonstrate that Mn cation exhibits the strongest termination preference in this work, with the largest formation energy difference calculated to be 2.46 eV. Therefore, combined with the previous experimental results, the Ti 3 C 2 T z -Mn shows outstanding electrochemical performance with a high contribution from surface redox reactions. The contribution from capacitive-controlled and diffusion-controlled behaviors is shown in Fig. 5 (a). The capacitive-controlled component in each electrode typically remains consistent as scan rates increase, suggesting that the decrease in total specific capacitance at high scan rates is mainly due to a lower contribution from the diffusion-controlled behavior. Furthermore, it is observed that all the T-M-C electrodes exhibit a higher contribution from capacitive-controlled behavior compared to the pure Ti 3 C 2 T z electrode. Capacitive-controlled behavior is responsive to the surface composition. It can be broadly categorized into two components: EDLC, associated with the intercalation of hydrated ions between Ti 3 C 2 T z layers, and PC, linked to redox reactions involving surface absorption and functional groups 33, 34 . Additionally, based on the electrochemical active surface area (ECSA), capacitive capacitance can be quantitative in Figure S23. The slope of the current per unit area against the corresponding scan rate of T-M-C is used to calculate the electrochemical double-layer capacitances ( C dl ) in Fig. 5 (b). EDLC was measured by cycling the electrode in the non-Faradaic regions. These regions are characterized by potentials where no charge-transfer reactions occur, but only absorption/desorption processes take place. In our case, this potential range was 0.1–0.2 V vs Ag/AgCl. This surface area is proportional to the C dl of the solid-liquid interface 35, 36 . At the center of the potential range (0.15 V vs RHE), the difference in current densities ( Δ j ) between the anodic ( j a ) and cathodic ( j c ) current densities was calculated for each scan rate. The value of C dl can be determined from the slop of this linear fitting diagram according to the following Eq. ( 3 ): $${C}_{dl}=S\varDelta j/V$$ 3 Therefore, capacitance is divided into three parts, and their specific capacitance values are presented in Fig. 5 (c) and Table S3. The variations in capacitive EDLC values are not substantial, indicating that the disparity in electrode performance is primarily attributed to PCs and diffusion-controlled capacitances. With the division of total capacitance into three contributing parts, specifically, capacitive EDLC, capacitive PC, and diffusion-controlled capacitance, it is then possible to disclose the dominating factors of energy storage mechanisms by combining the experimental results and our previous DFT simulation. The hydrated radius of intercalation cations is generally proposed to play a significant role in the delamination of MXene 7, 37, 38 , while in the present work however, better consistency between theoretical ILD and that related capacitance can be found in Fig. 5 (d), suggesting that the intercalation position of cations is an essential factor affecting the ILD of MXene which has not been carefully discussed before. Notably, the experimental ILD value of T-M-C obtained by XRD analysis is not totally covered by the theoretical range from DFT simulation, which might be mainly attributed to the complex microstructure evolution (for example, dehydration, change of intercalation site, etc.) during sample preparation. Figure 5 (e) demonstrates the relationship between termination-related capacitance (sum of capacitive PC and diffusion-controlled capacitance) and calculated formation energy difference. The excellent liner distribution indicates that our tailor strategy, changing the termination composition of Ti 3 C 2 T z by introducing cations during ECI, is feasible, and the formation energy difference is soundly proved to be the critical factor dominating the content of -O termination: as expected, Mn 2+ which possesses the largest formation energy difference among all investigated cations is proved to significantly favor the electrochemical performance of T-Mn-C, with a large termination-related capacitance contribution up to 1230 F cm − 3 . Figure 5 (f) shows the map of charge density difference of T-Mn. The energetically optimal interaction site is computed to be the Mid site, and apparent charge exchange can be observed along the Mn-O and O-Ti bonds. In other words, the -O termination plays a significant role in realizing the charge transfer between Mn and Ti, which is important in the contributing mechanism of diffusion-controlled capacitance. While ILD impacts the capacitive EDLC, the effect is limited. Different ion intercalation sites result in distinct electron exchange energies for Ti, -O, and M atoms, thereby -O terminations giving rise to varied termination-related capacitance in T-M-C electrodes. This variance is the crucial factor contributing to the enhancement of T-Mn-C electrochemical performance. It has also been observed that diffusion-controlled capacitance is partly influenced by the size of the layer spacing and is caused by the relatively slow movement in bulky electrodes. Essentially, this means that the ion diffusion rate inside the electrodes is lower than that consumed by the electrode reactions. The highest PC values for T-Mn-C are ascribed to the high content of -O terminations and the rapid ion migration in interlayers since the reaction mechanism in MXene can be expressed as Eq. (4) 11 : $${Ti}_{3}{C}_{2}{O}_{x}{\left(OH\right)}_{y}{F}_{z}+\delta {H}^{+}+\delta {e}^{-}\underleftrightarrow{ }{Ti}_{3}{C}_{2}{O}_{x-\delta }{\left(OH\right)}_{y+\delta }{F}_{z}$$ 4 Generally, the larger diffusion-controlled capacitance of the electrode results in the worse rate performance. Therefore, the relationship between diffusion-controlled capacitance ratio and capacitance retention is shown in Figure S24. The diffusion-controlled capacitance of T-M-C at different scan rates correlates with changes in the layer spacing. In the case of monovalent metal cations such as Li + , Na + , and K + , the largest layer spacing of K + processes the smallest diffusion capacitance. For bivalent metals like Mn 2+ , Zn 2+ , and Mg 2+ , T-Mg-C has the largest interlayer spacing, which promotes electrolyte diffusion. In the case of trivalent Al 3+ , the situation is like that of Mg 2+ . Based on the outstanding electrochemical performance of T-Mn-C, symmetrical supercapacitors (SSCs) with a voltage window ranging from 0 V to 0.7 V were assembled, as illustrated in Figure S25(a). The CV curves of SSCs are presented in Figure S25(b), displaying nearly rectangular shapes with no significant changes even at 100 mV s − 1 . This indicates that the T-Mn-C electrodes possess excellent reversibility. Figure S25(c) shows the GCD curves of the SSCs at current densities from 0.1 A g − 1 to 10 A g − 1 . These curves exhibit an almost inclined straight line and near-symmetric triangle, confirming the superior electrochemical reversibility of T-Mn-C. The volumetric capacitance (C v ) values at current densities of 0.1, 0.2, 0.5, 1, 2, and 10 A g − 1 are measured as 343.4, 305.0, 272.3, 237.4, 190.4, and 182.7 F cm − 3 , respectively. The capacitance retention rate remains 17.2% at 100 mV s − 1 , as demonstrated in Figure S25(d). Furthermore, Figure S25(e) presents the Nyquist plots of SSCs, which further validates the low internal resistance. And the self-discharge performance of the device was tested in Figure S25(f). After 10 hours, the voltage of the cells is observed to stabilize at 0.16 V, indicating a retention rate of 22.9%. It is hereby acknowledged that the self-discharge rates need to be further reduced before applications. The Ragone plot of SSCs based on T-Mn-C is illustrated in Figure S25(g). The SSCs show an energy density of 23.3 Wh L − 1 at a power density of 112.2 W L − 1 , while the energy density remains at 6.5 Wh L − 1 at 7350.1 W L − 1 . Moreover, T-Mn-C exhibits excellent cycling performance, as demonstrated in Figures S25(h)-(i). It retains a capacitance retention of 107.6% after 20000 cycles at 10 A g − 1 and 90.4% after 2000 cycles at 1 A g − 1 . The Columbic efficiency remains nearly 100.0% during the 10 A g − 1 and 1 A g − 1 cycling tests. To further explore the practical application of T-Mn-C, all-solid-state supercapacitors (ASSSCs) were constructed using a PVA/H 2 SO 4 gel electrolyte, as depicted in Figure S26(a). The CV and GCD curves of three 0.7 V flexible ASSSCs connected in series and parallel under practical conditions are presented in Figures S26(b)-(c). It was observed that three flexible ASSSCs connected in series could power a 1.6 V thermohygrometer and a 1.8 V small bulb. To expand voltages and improve the energy densities in aqueous SCs, we assembled an asymmetric SC by pairing nitrogen-doped activated carbon film (NAC, 0 to 1 V vs Ag/AgCl) with T-Mn-C film (-0.5 to 0.2 V vs Ag/AgCl) in Fig. 6 (a). Figure 6 (b) displays the potential windows of the NAC (0–1 V vs Ag/AgCl) and T-Mn-C (-0.5-0.2 V vs Ag/AgCl) electrodes at the same scan rate of 20 mV s − 1 . The morphologies and electrochemical performance of the NAC are shown in Figure S27. It follows that the potential window of NAC//T-Mn-C ASSC is from 0 to 1.5 V. Figure 6 (c) shows CV of NAC//T-Mn-C ASCs, where a pair of pronounced redox peaks is observed. Increasing the scan rates does not appear to distort the curves, indirectly demonstrating the fast charge/discharge processes and excellent rate performances. The GCD curves at different current densities (1–20 A g − 1 ) in Fig. 6 (d). As shown in Fig. 6 (e), at a scan rate of 0.5 A g − 1 , the device delivers a capacitance of 176.8 F cm − 3 and maintains a capacitance of 122.1 F cm − 3 when the scan rate increases to 20 A g − 1 . Moreover, the electrochemical performance of NAC//T-Mn-C can be compared with other recently published MXene-based aqueous ASCs 39–49 . Based on the weight of active material, our devices show the maximum energy density of 54.0 Wh L − 1 at a power density of 0.75 kW L − 1 and a power density of 30.1 kW L − 1 at an energy density of 38.2 Wh L − 1 in Fig. 6 (f). In addition, the ASC is also at a high level of energy density from the mass values perspective in Figure S28. The self-discharge performance of NAC//T-Mn-C was tested in Fig. 6 (g). After 10 hours, the voltage of the cells is observed to stabilize at 0.54 V, indicating a retention rate of 36.0%. Furthermore, the stability of NAC//T-Mn-C ASC was examined using the GCD technique for 20000 cycles at the current density of 10 A g − 1 , as shown in Fig. 6 (h). The averaged Columbic efficiency is 96.5% after 20000 cycles, and the capacitance retention is 103.6%, demonstrating competitive cycling stability. The excellent cycling performance of NAC//T-Mn-C ASCs is found to be appreciable when compared with other MXene-based devices in Table S4. Conclusion In summary, the metal cation intercalation strategy significantly enhances the performance of MXene-based electrodes by opening up blocked channels and modifying terminations. The processes of ECI and calcination not only alleviate the interlayer restacking but also alter its surface terminations. Notably, the intercalation of various cations has varying effects on capacitance. Among these, T-Mn-C electrodes reach 1655.5 F cm − 3 at 1 mV s − 1 , exhibiting a remarkable 150% increment compared to pristine Ti 3 C 2 T z . DFT calculations have elucidated the enhanced electrochemical performance, indicating that various intercalated cations prefer different terminations. Specifically, the intercalated Mn 2+ exhibits the largest formation energy difference between Ti 3 C 2 F z and Ti 3 C 2 O z ., critically enhancing the termination-related capacitances. The advantages of T-M-C electrodes are highlighted by the SSCs and ASCs with high energy densities at high powers. This approach substantially betters the electrochemical properties of MXene-based electrodes and suggests its applicability to other 2D materials, promising widespread advancements in energy storage technologies. Experimental methods With the exception of MnSO 4 and MgSO 4 (Macklin Biochemical Company), all chemical agents were purchased from Aladdin Chemical Company without any further treatment. Preparation of Ti 3 C 2 T z films The process for synthesizing Ti 3 C 2 T z films can be found in our previous work 25 . In brief, the prepared precursor MAX phase Ti 3 AlC 2 was stirred with HCl and LiF, and the Al layer was etched off to obtain multilayered Ti 3 C 2 T z , m-Ti 3 C 2 T z , followed by ultrasonication and centrifugation to obtain Ti 3 C 2 T z suspensions. The above suspension was vacuum filtrated through a membrane (Celgard 3501, 0.22 mm pore size) by using a Buchner funnel with sand core (40 mm in diameter). The membrane was then dried in a freeze dryer for 24 h. Freestanding Ti 3 C 2 T z films were peeled off from the filter membrane. Preparation of T-M and T-M-C films To fit the size of the glassy carbon current collectors, the Ti 3 C 2 T z film was first cut into discs with a 6 mm diameter and a mass loading of ~ 1.9 mg cm − 2 . Next, 1 M of Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , MnSO 4 , ZnSO 4 , MgSO 4 and Al 2 (SO 4 ) 3 were prepared as electrolytes. Then, the pure Ti 3 C 2 T z films were used as the working electrodes, and activated carbon (AC, YP50F, Kuraray, Japan) discs with a 6 mm diameter and a mass loading of ~ 20 mg cm − 2 were used as counter electrodes, which were assembled in a plastic Swagelok half-cell. Ag/AgCl in saturated KCl was used as reference electrodes. Using the cyclic voltammetry (CV) program in the electrochemical workstation (CHI 660E), the scan rate was 20 mV s − 1 from − 1 V to 0.2 V vs Ag/AgCl and the cycling number was 50. The T-M films can be obtained by natural drying at RT for 24 h. Calcination was conducted at 400 ℃ for 2 h at a heating rate of 2 ℃ min − 1 under an Ar gas atmosphere at a flow of 100 mL min − 1 to obtain T-C-M films. For comparison, the pure Ti 3 C 2 T z films without ECI were also subjected to the calcination process. Preparation of NAC films The preparation method refers to previous work 48 . In brief, 0.4 g of activated carbon (AC) was added into 10 g of urea with 60 mL DI-water. The mixture was continuously stirred for 30 minutes, transferred into Teflon-lined stainless-steel autoclave, and kept in an oven at 180 ℃ for 24 h. Then, the reaction products were cleaned by centrifuge and dried to obtain nitrogen-doped AC (NAC). The 90% AC or NAC activated materials and Poly(tetrafluoroethylene) (PTFE) were ground, where PTFE acted as a binder. Then, the mixture with the aid of DI water to form the slurry, which was later rolled into flat films and placed at 70 ℃ to dry for 24 hours. Finally, it was perforated with a punch to form 8 mm (for AC) and 6 mm (for NAC) diameter discs. Preparation of PVA/H 2 SO 4 gel electrolytes A 2 g of Polyvinyl alcohol powder (PVA, Sigma) was added into 16.7 mL of DI water. Then the mixture was heated to 90 ℃ and stirred with a magnetic bar for 3 h. The solution was cooled down to 40 ℃. A 3.3 mL of H 2 SO 4 (98%) was added into the PVA solution slowly while keeping stirring for 1 h. Then the PVA/H 2 SO 4 solution was frozen for 12 h to obtain PVA/H 2 SO 4 gel electrolytes. Materials characterizations XRD patterns were recorded by a DX-2700BH (Haoyuan) diffractometer in the range of 2 θ = 3°-70° with the step size of 0.02° and the scan rate of 0.5 sec/step. SEM and EDS mapping images were performed on the Nova Nano SEM450 with an acceleration voltage of 30 kV. TEM and HRTEM images were acquired by a Talos F200X microscope with an acceleration voltage of 200 kV. XPS measurements were performed on a K-Alpha (Thermo Scientific) spectrometer using Al Kα radiation. Inductively coupled plasma optical emission spectrometer (ICP-OES) was performed on PerkinElmer 8300. Electrochemical measurements The 6 mm Ti 3 C 2 T z -based films were tested directly in a plastic Swagelok half-cell. To prepare SSCs devices, two 6 mm working electrodes of T-C-Mn with equal mass were assembled with a separator in a Swagelok cell. Before measurement, all configurations were pre-cycled at 20 mV s − 1 for 50 cycles to stabilize the performance. For all testing, glassy carbon (CHI Instruments, China) was used as current collectors, polypropylene membranes (Celgard 3501) were used as separators, and 3 M H 2 SO 4 was used as electrolytes. All electrochemical measurement data were recorded on a CHI 660E electrochemical workstation, except the long-cycling testing, which was recorded on the SP-150 electrochemical workstation (Bio-logic, France). Techniques employed included cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The frequency range for EIS measurements was from 10 mHz to 100 kHz. All electrochemical measurements were conducted at RT. Gravimetric capacitance (C g ) was calculated by the CV technique using the following Eq. ( 5 ): $${C}_{g}=\underset{{U}_{-}}{\overset{{U}_{+}}{\int }}I\left(V\right)dV/vUm$$ 5 Where U (V) is the potential, v (mV s − 1 ) is the scan rate, m (g) is the mass of the electrode (one electrode in 3-electrode, and two electrodes in 2-electrode), I (mA) is the current. U + and U − are the positive and negative potentials, respectively. The cells’ volumetric capacitance (F cm − 3 ) was calculated by the following Eq. ( 6 )-( 7 ): $${C}_{v}={\rho C}_{g}$$ 6 $$\rho =m/Ad$$ 7 where ρ (g cm − 3 ) is the density of the film electrodes. m (g) is the mass of the Ti 3 C 2 T z -based discs, which is ~ 0.00045 g. A (cm − 2 ) is the area of the electrodes, which is 0.2826 cm − 2 . d (cm) is the thickness of the Ti 3 C 2 T z -based discs, which is measured from SEM images, ~ 5 µm. The ρ of the Ti 3 C 2 T z and NAC films is ~ 3.2 g cm − 3 and ~ 0.7 g cm − 3 . The average packing density based overall active materials (negative and positive) is 2.0 g cm − 3 . The volumetric energy ( E v ) and power densities ( P v ) were calculated assuming Eq. ( 8 )- ( 9 ): $${E}_{v}={{C}_{v}U}^{2}/7.2$$ 8 $${P}_{v}=3.6*{E}_{v}v/U$$ 9 The self-discharge testing was recorded on the Bio-logic SP-150 electrochemical workstation, by first holding the cells at specific voltages for 0.5 h and then monitoring the cell voltage as a function of time for 10 h. Calculation method The modeling in this work was performed in the framework of the Density Functional Theory (DFT) as implemented in the Vienna Ab initio Simulation Package (VASP). The Projector Augmented Wave (PAW) method was adopted to solve the Kohn-Shan equations, together with the exchange-correlation energy functional of Generalized Gradient Approximation by Perdew-Burke-Ernzerhof (GGA-PBE). A \(\varGamma\) centered Monkhorst-Pack mesh of total number of 40 was applied, with a cutoff energy of 480 eV. Moreover, the convergence criteria were set to be 10 − 4 eV for energy and 10 − 3 eV/Å for force, respectively. A high throughput investigation was performed to reveal the cation interaction behaviors in Ti 3 C 2 T z , using a bilayer model with the consideration of all possible accommodation sites. After achieving the interaction energy of each cation in Ti 3 C 2 F z and Ti 3 C 2 O z , the termination preference was then evaluated herein by calculating the energy difference. Declarations Conflicts of interest The authors declare no conflict of interest. Funding This work was financially supported by the National Natural Science Foundation of China (52301263, 52171033, and U23A20574). Author Contribution Xiaodan Yin, Wei Zheng, and Haifeng Tang researched the experimental program, designed the work, prepared the material, collected the data, and wrote the manuscript. Chengjie Lu was responsible for theoretical calculations and wrote the manuscript. Wei Zheng, Li Yang, and Long Pan reviewed the manuscript. Peigen Zhang and ZhengMing Sun revised the manuscript critically for important intellectual content. References Lukatskaya, M. R.; Dunn, B.; Gogotsi, Y., Multidimensional materials and device architectures for future hybrid energy storage. NATURE COMMUNICATIONS 2016, 7 (1), 12647. Hosseini, H.; Shahrokhian, S., Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems. APPLIED MATERIALS TODAY 2018, 10 , 72-85. Simon, P.; Gogotsi, Y.; Dunn, B., Where Do Batteries End and Supercapacitors Begin? SCIENCE 2014, 343 (6176), 1210-1211. Wang, T.; Chen, H. C.; Yu, F.; Zhao, X. S.; Wang, H. X., Boosting the cycling stability of transition metal compounds-based supercapacitors. ENERGY STORAGE MATERIALS 2019, 16 , 545-573. Dall'Agnese, Y.; Lukatskaya, M. R.; Cook, K. M.; Taberna, P. L.; Gogotsi, Y.; Simon, P., High capacitance of surface-modified 2D titanium carbide in acidic electrolyte. ELECTROCHEMISTRY COMMUNICATIONS 2014, 48 , 118-122. Zamhuri, A.; Lim, G. P.; Ma, N. L.; Tee, K. S.; Soon, C. F., MXene in the lens of biomedical engineering: synthesis, applications and future outlook. BIOMEDICAL ENGINEERING ONLINE 2021, 20 (1), 1-24. Long, Y.; Tao, Y.; Shang, T. X.; Yang, H. T.; Sun, Z. J.; Chen, W.; Yang, Q. H., Roles of Metal Ions in MXene Synthesis, Processing and Applications: A Perspective. ADVANCED SCIENCE 2022, 9 (12), 2200296. Hu, M. M.; Dai, J.; Chen, L. H.; Meng, A. L.; Wang, L.; Li, G. C.; Xie, H. J.; Li, Z. J., Selectivity for intercalated ions in MXene toward a high-performance capacitive electrode. SCIENCE CHINA-MATERIALS 2023, 66 (3), 974-981. Jin, H. L.; Wang, K.; Mao, Z. Q.; Tang, L. Y.; Zhang, J.; Chen, X., The structural, magnetic, Raman and electrical transport properties of Mn intercalated Ti3C2TX. JOURNAL OF PHYSICS-CONDENSED MATTER 2022, 34 (1), 015701. Xu, T.; Wang, Y.; Liu, K.; Zhao, Q.; Liang, Q.; Zhang, M.; Si, C., Ultralight MXene/carbon nanotube composite aerogel for high-performance flexible supercapacitor. Advanced Composites and Hybrid Materials 2023, 6 (3). Mu, X. P.; Wang, D. S.; Du, F.; Chen, G.; Wang, C. Z.; Wei, Y. J.; Gogotsi, Y.; Gao, Y.; Dall'Agnese, Y., Revealing the Pseudo-Intercalation Charge Storage Mechanism of MXenes in Acidic Electrolyte. ADVANCED FUNCTIONAL MATERIALS 2019, 29 (29), 1902953. Chen, X. F.; Zhu, Y. Z.; Zhang, M.; Sui, J. Y.; Peng, W. C.; Li, Y.; Zhang, G. L.; Zhang, F. B.; Fan, X. B., N-Butyllithium-Treated Ti3C2Tx MXene with Excellent Pseudocapacitor Performance. ACS NANO 2019, 13 (8), 9449-9456. Li, L.; Meng, J.; Bao, X. R.; Huang, Y. P.; Yan, X. P.; Qian, H. L.; Zhang, C.; Liu, T. X., Direct-Ink-Write 3D Printing of Programmable Micro-Supercapacitors from MXene-Regulating Conducting Polymer Inks. ADVANCED ENERGY MATERIALS 2023, 13 (9), 2203683. Otgonbayar, Z.; Yang, S. H. Y.; Kim, I. J.; Oh, W. C., Recent advances in 2D MXene and solid state electrolyte for energy storage applications: Comprehensive review. CHEMICAL ENGINEERING JOURNAL 2023, 472 , 144801. Shaikh, N. S.; Ubale, S. B.; Mane, V. J.; Shaikh, J. S.; Lokhande, V. C.; Praserthdam, S.; Lokhande, C. D.; Kanjanaboos, P., Novel electrodes for supercapacitor: Conducting polymers, metal oxides, chalcogenides, carbides, nitrides, MXenes, and their composites with graphene. JOURNAL OF ALLOYS AND COMPOUNDS 2022, 893 , 161998. Luo, Y. J.; Que, W. X.; Bin, X. Q.; Xia, C. J.; Kong, B. S.; Gao, B. W.; Kong, L. B., Flexible MXene-Based Composite Films: Synthesis, Modification, and Applications as Electrodes of Supercapacitors. SMALL 2022, 18 (27), 2201290. Yoon, Y.; Lee, M.; Kim, S. K.; Bae, G.; Song, W.; Myung, S.; Lim, J.; Lee, S. S.; Zyung, T.; An, K. S., A Strategy for Synthesis of Carbon Nitride Induced Chemically Doped 2D MXene for High-Performance Supercapacitor Electrodes. ADVANCED ENERGY MATERIALS 2018, 8 (15), 1703173. Cai, M.; Wei, X. C.; Huang, H. F.; Yuan, F. L.; Li, C.; Xu, S. K.; Liang, X. Q.; Zhou, W. Z.; Guo, J., Nitrogen-doped Ti 3 C 2 T x MXene prepared by thermal decomposition of ammonium salts and its application in flexible quasi-solid-state supercapacitor. CHEMICAL ENGINEERING JOURNAL 2023, 458 , 141338. Tian, Y. P.; Ju, M. M.; Luo, Y. J.; Bin, X. Q.; Lou, X. J.; Que, W. X., In situ oxygen doped Ti 3 C 2 T x MXene flexible film as supercapacitor electrode. CHEMICAL ENGINEERING JOURNAL 2022, 446 , 137451. Nasrin, K.; Sudharshan, V.; Subramani, K.; Karnan, M.; Sathish, M., In-Situ Synergistic 2D/2D MXene/BCN Heterostructure for Superlative Energy Density Supercapacitor with Super-Long Life. SMALL 2022, 18 (4), 2106051. Li, J.; Yuan, X. T.; Lin, C.; Yang, Y. Q.; Xu, L.; Du, X.; Xie, J. L.; Lin, J. H.; Sun, J. L., Achieving High Pseudocapacitance of 2D Titanium Carbide (MXene) by Cation Intercalation and Surface Modification. ADVANCED ENERGY MATERIALS 2017, 7 (15), 1602725. Chen, H. W.; Ma, H. Y.; Li, C., Host-Guest Intercalation Chemistry in MXenes and Its Implications for Practical Applications. ACS NANO 2021, 15 (10), 15502-15537. Li, Z. J.; Dai, J.; Li, Y. R.; Sun, C. L.; Meng, A. L.; Cheng, R. F.; Zhao, J.; Hu, M. M.; Wang, X. H., Intercalation-deintercalation design in MXenes for high-performance supercapacitors. NANO RESEARCH 2022, 15 (4), 3213-3221. Lyu, S. L.; Guo, C. X.; Wang, J. N.; Li, Z. J.; Yang, B.; Lei, L. C.; Wang, L. P.; Xiao, J. P.; Zhang, T.; Hou, Y., Exceptional catalytic activity of oxygen evolution reaction via two-dimensional graphene multilayer confined metal-organic frameworks. NATURE COMMUNICATIONS 2022, 13 (1), 6171. Yin, X. D.; Zheng, W.; Tang, H. F.; Zhang, P. G.; Sun, Z. M., Novel 2D/2D 1T-MoS2/Ti3C2Tz heterostructures for high-voltage symmetric supercapacitors. NANOSCALE 2023, 15 (24), 10437-10446. Nightingale, E. R., PHENOMENOLOGICAL THEORY OF ION SOLVATION - EFFECTIVE RADII OF HYDRATED IONS. JOURNAL OF PHYSICAL CHEMISTRY 1959, 63 (9), 1381-1387. Chao, D. L.; Zhou, W. H.; Xie, F. X.; Ye, C.; Li, H.; Jaroniec, M.; Qiao, S. Z., Roadmap for advanced aqueous batteries: From design of materials to applications. SCIENCE ADVANCES 2020, 6 (21), eaba4098. Mathis, T. S.; Maleski, K.; Goad, A.; Sarycheva, A.; Anayee, M.; Foucher, A. C.; Hantanasirisakul, K.; Shuck, C. E.; Stach, E. A.; Gogotsi, Y., Modified MAX Phase Synthesis for Environmentally Stable and Highly Conductive Ti3C2 MXene. ACS NANO 2021, 15 (4), 6420-6429. Li, H. S.; Xu, K.; Chen, P. H.; Yuan, Y. Y.; Qiu, Y.; Wang, L. G.; Zhu, L.; Wang, X. G.; Cai, G. H.; Zheng, L. M.; Dai, C.; Zhou, D.; Zhang, N. A.; Zhu, J. X.; Xie, J. L.; Liao, F. H.; Peng, H. L.; Peng, Y.; Ju, J.; Lin, Z. F.; Sun, J. L., Achieving ultrahigh electrochemical performance by surface design and nanoconfined water manipulation. NATIONAL SCIENCE REVIEW 2022, 9 (6), nwac079. Liang, K.; Matsumoto, R. A.; Zhao, W.; Osti, N. C.; Popov, I.; Thapaliya, B. P.; Fleischmann, S.; Misra, S.; Prenger, K.; Tyagi, M.; Mamontov, E.; Augustyn, V.; Unocic, R. R.; Sokolov, A. P.; Dai, S.; Cummings, P. T.; Naguib, M., Engineering the Interlayer Spacing by Pre-Intercalation for High Performance Supercapacitor MXene Electrodes in Room Temperature Ionic Liquid. ADVANCED FUNCTIONAL MATERIALS 2021, 31 (33), 2104007. Zhao, L.; Fan, L. Z.; Zhou, M. Q.; Guan, H.; Qiao, S. Y.; Antonietti, M.; Titirici, M. M., Nitrogen-Containing Hydrothermal Carbons with Superior Performance in Supercapacitors. ADVANCED MATERIALS 2010, 22 (45), 5202-5206. Wang, Y. M.; Wang, X.; Li, X. F.; Li, X. L.; Liu, Y.; Bai, Y.; Xiao, H. H.; Yuan, G. H., A High-Performance, Tailorable, Wearable, and Foldable Solid-State Supercapacitor Enabled by Arranging Pseudocapacitive Groups and MXene Flakes on Textile Electrode Surface. ADVANCED FUNCTIONAL MATERIALS 2021, 31 (7), 2008185. Kötz, R.; Carlen, M., Principles and applications of electrochemical capacitors. ELECTROCHIMICA ACTA 2000, 45 (15-16), 2483-2498. Chen, C. M.; Zhang, Q.; Yang, M. G.; Huang, C. H.; Yang, Y. G.; Wang, M. Z., Structural evolution during annealing of thermally reduced graphene nanosheets for application in supercapacitors. CARBON 2012, 50 (10), 3572-3584. Anjum, M. A. R.; Lee, M. H.; Lee, J. S., Boron- and Nitrogen-Codoped Molybdenum Carbide Nanoparticles Imbedded in a BCN Network as a Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution Reactions. ACS CATALYSIS 2018, 8 (9), 8296-8305. Meng, F. K.; Hu, E. Y.; Zhang, L. H.; Sasaki, K.; Muckerman, J. T.; Fujita, E., Biomass-derived high-performance tungsten-based electrocatalysts on graphene for hydrogen evolution. JOURNAL OF MATERIALS CHEMISTRY A 2015, 3 (36), 18572-18577. Zhang, Z. R.; Yao, Z. P.; Li, Y.; Lu, S. T.; Wu, X. H.; Jiang, Z. H., Cation-induced Ti 3 C 2 T x MXene hydrogel for capacitive energy storage. CHEMICAL ENGINEERING JOURNAL 2022, 433 , 134488. Rezakazemi, M.; Shamsabadi, A. A.; Lin, H. Q.; Luis, P.; Ramakrishna, S.; Aminabhavi, T. M., Sustainable MXenes-based membranes for highly energy-efficient separations. RENEWABLE & SUSTAINABLE ENERGY REVIEWS 2021, 143 , 110878. Li, K.; Wang, X. H.; Li, S.; Urbankowski, P.; Li, J. M.; Xu, Y. X.; Gogotsi, Y., An Ultrafast Conducting Polymer@MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors. SMALL 2020, 16 (4), 1906851. Cui, Y. H.; Shi, Q. S.; Liu, Z.; Lv, J. C.; Wang, C.; Xie, X. B.; Zhang, S. H., MXene/biomass/chitosan carbon aerogel (MBC) with shared cathode and anode for the construction of high-efficiency asymmetric supercapacitor. CHEMICAL ENGINEERING JOURNAL 2023, 472 , 144701. Xiong, T.; Lee, W. S. V.; Huang, X. L.; Xue, J. M., Mn3O4/reduced graphene oxide based supercapacitor with ultra-long cycling performance. JOURNAL OF MATERIALS CHEMISTRY A 2017, 5 (25), 12762-12768. Hu, Y. T.; Guan, C.; Ke, Q. Q.; Yow, Z. F.; Cheng, C. W.; Wang, J., Hybrid Fe2O3 Nanoparticle Clusters/rGO Paper as an Effective Negative Electrode for Flexible Supercapacitors. CHEMISTRY OF MATERIALS 2016, 28 (20), 7296-7303. Yue, S. H.; Tong, H.; Lu, L.; Tang, W. W.; Bai, W. L.; Jin, F. Q.; Han, Q. W.; He, J. P.; Liu, J.; Zhang, X. G., Hierarchical NiCo2O4 nanosheets/nitrogen doped graphene/carbon nanotube film with ultrahigh capacitance and long cycle stability as a flexible binder-free electrode for supercapacitors. JOURNAL OF MATERIALS CHEMISTRY A 2017, 5 (2), 689-698. Li, L.; Zhang, N.; Zhang, M. Y.; Zhang, X. T.; Zhang, Z. G., Flexible Ti3C2Tx/PEDOT:PSS films with outstanding volumetric capacitance for asymmetric supercapacitors. DALTON TRANSACTIONS 2019, 48 (5), 1747-1756. Zheng, W.; Halim, J.; El Ghazaly, A.; Etman, A. S.; Tseng, E. N.; Persson, P. O. A.; Rosen, J.; Barsoum, M. W., Flexible Free-Standing MoO3/Ti3C2Tz MXene Composite Films with High Gravimetric and Volumetric Capacities. ADVANCED SCIENCE 2021, 8 (3), 2003656. Navarro-Suarez, A. M.; Van Aken, K. L.; Mathis, T.; Makaryan, T.; Yan, J.; Carretero-Gonzalez, J.; Rojo, T.; Gogotsi, Y., Development of asymmetric supercapacitors with titanium carbide-reduced graphene oxide couples as electrodes. ELECTROCHIMICA ACTA 2018, 259 , 752-761. Zhang, L. N.; Han, D. L.; Tao, Y.; Cui, C. J.; Deng, Y. Q.; Dong, X. M.; Lv, W.; Lin, Z. F.; Wu, S. C.; Weng, Z.; Yang, Q. H., Dense organic molecules/graphene network anodes with superior volumetric and areal performance for asymmetric supercapacitors. JOURNAL OF MATERIALS CHEMISTRY A 2020, 8 (1), 461-469. Zheng, W.; Halim, J.; Etman, A. S.; El Ghazaly, A.; Rosen, J.; Barsoum, M. W., Boosting the volumetric capacitance of MoO3-x free-standing films with Ti3C2 MXene. ELECTROCHIMICA ACTA 2021, 370 , 137665. Li, J. M.; Kurra, N.; Seredych, M.; Meng, X.; Wang, H. Z.; Gogotsi, Y., Bipolar carbide-carbon high voltage aqueous lithium-ion capacitors. NANO ENERGY 2019, 56 , 151-159. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4161663","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":288566618,"identity":"587579f4-38d6-401e-aaf9-3b268c48713d","order_by":0,"name":"Xiaodan Yin","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Xiaodan","middleName":"","lastName":"Yin","suffix":""},{"id":288566620,"identity":"345c046f-666e-4380-97ba-dcaecb676d99","order_by":1,"name":"Wei Zheng","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Zheng","suffix":""},{"id":288566623,"identity":"2ed545b8-afe2-4533-bc30-47c6c0058ce7","order_by":2,"name":"Haifeng Tang","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Haifeng","middleName":"","lastName":"Tang","suffix":""},{"id":288566624,"identity":"f6aea3e6-1e1a-4077-bdaa-3219945c0b8b","order_by":3,"name":"Li Yang","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Yang","suffix":""},{"id":288566626,"identity":"3e960416-e0c6-4ee2-9e0d-769ce95e894d","order_by":4,"name":"Chengjie Lu","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Chengjie","middleName":"","lastName":"Lu","suffix":""},{"id":288566628,"identity":"bcb20375-ede3-47d5-b7f7-04a4e9d83387","order_by":5,"name":"Long Pan","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Long","middleName":"","lastName":"Pan","suffix":""},{"id":288566631,"identity":"1d85aae9-1889-403e-bf56-112a27a04c54","order_by":6,"name":"Peigen Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4UlEQVRIiWNgGAWjYDACCSBOAGJ+CJeZBC2SDSRpAQGDA8RqkZ/de/DBg182ecbnDx+TYKiwTmxgP3sArxbGOeeSDRL70orNbqSlSTCcSU9s4MlLwKuFWSLHTCKx53Diths8ZhKMbYcTGyR4DPBqYZPIMf+R2PM/cXP/+W8SjP+I0MIDtIUh4ceBxA0MOWwSjA1EaJGQyEuWSGxITpxxI83YIuFYunEbTw5+LfIzcg9+/PHHLrG///DDGx9qrGX72c/g1wJ0GjDY2qDsBJDvCKiHaGH4Q1jZKBgFo2AUjGAAAGvkRSm/0fh9AAAAAElFTkSuQmCC","orcid":"","institution":"Southeast University","correspondingAuthor":true,"prefix":"","firstName":"Peigen","middleName":"","lastName":"Zhang","suffix":""},{"id":288566632,"identity":"89d5261a-19ac-4b1a-a588-9f98e8258604","order_by":7,"name":"ZhengMing Sun","email":"","orcid":"","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"ZhengMing","middleName":"","lastName":"Sun","suffix":""}],"badges":[],"createdAt":"2024-03-25 08:12:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4161663/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4161663/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54424548,"identity":"88509340-945e-4189-9395-9df43c1594b4","added_by":"auto","created_at":"2024-04-10 09:03:58","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":111357,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) X-ray diffraction (XRD) patterns of Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eAlC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e. (b)\u003c/strong\u003e \u003cstrong\u003eComparison of the properties of different intercalated ions \u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e26, 27\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e. (c) XRD patterns of T, T-C, and T-M-C electrodes. (d)-(e) The magnified crystal lattice stripes of Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e and T-Mn. Insets of (d) and (e) illustrate the ion intercalation of Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e and T-Mn, respectively. (f) Scanning electron microscopy (SEM) images of the cross-section of T-Mn-C and (g) Energy dispersive X-ray spectroscopy (EDS) mapping of T-Mn-C.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/07829e437d9c2160a5c08228.jpg"},{"id":54424552,"identity":"d9b7f831-7e06-41de-9b6a-4b66afcfb2dd","added_by":"auto","created_at":"2024-04-10 09:03:59","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":122851,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)-(b) Cycle voltammetry (CV) curves and specific capacitances at 20 mV s\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e for the T, T-C, T-Mn, and T-Mn-C electrodes. (c)\u003c/strong\u003e \u003cstrong\u003eNyquist plots of the T, T-C, T-Mn, and T-Mn-C electrodes. Insets show the equivalent circuit diagram and magnified view in the high-frequency region. (d)-(e)The CV and galvanostatic charge/discharge (GCD) curves of the T-Mn-C electrodes. (f) Cycling performance of T-Mn-C electrodes at 10 A g\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e. Inset of (f) shows the GCD curves of the first and the last 5 cycles. (g) GCD curve of the T-Mn-C electrode at 1 A g\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e. The corresponding ex-situ XRD patterns (h)-(i) and ex-situ XPS spectra(j).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/39dea95ba2455877e78079e4.jpg"},{"id":54424549,"identity":"fe8782a4-08fb-45d8-923f-81e9509ca178","added_by":"auto","created_at":"2024-04-10 09:03:58","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":77665,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) X-ray photoelectron spectroscopy (XPS) surveys of T, T-C, T-Mn, and T-Mn-C electrodes. (b) The count of O 1s, F 1s, and Mn 2p for T, T-C, T-Mn, and T-Mn-C electrodes. (c) Mn 2p XPS spectra of T-Mn-C. (d)-(e) Mn 2p of inside and surface for T-Mn and T-Mn-C electrodes, respectively. (f) The contents of Ti and Mn for T-Mn-C and T-Mn-C after 50 cycles (T-Mn-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e50\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e), respectively, by inductively coupled plasma (ICP).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/6c0059e04c56f3182aeb7e33.jpg"},{"id":54424550,"identity":"2a196abd-12ae-4237-8ca3-7d975ae3ac12","added_by":"auto","created_at":"2024-04-10 09:03:58","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":71554,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Atomic scheme showing cation intercalated in Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e bilayer with three possible configurations. (b) The function plots of formation energy (eV) versus interlayer distance (Å) of three typical Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e-M (M = Li, Mg, Al) systems show different optimal configurations for cation species. (c) Theoretical interlayer distance of cation intercalated Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e. (d) The formation energy difference of cation intercalated Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/5ffbbdf36e48d19bd8609ddf.jpg"},{"id":54424551,"identity":"096bdf0b-104b-46cf-be3d-6792e8292ea5","added_by":"auto","created_at":"2024-04-10 09:03:59","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":141552,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Specific capacitances at 1-50 mV s\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e, with the calculated specific contributions from capacitive-controlled (bottom part) and diffusion-controlled (upper part) behaviors. (b) The determination of the slope to calculate EDLC. (c) Distinguish capacitive capacitance into capacitive EDLC and PC for T, T-C, and T-M-C electrodes. (d) Contribution analysis of interlayer distance (ILD)-related capacitance (the capacitive EDLC part labelled in orange in Figure 5 (c)) versus cation element species. (e) Contribution analysis of termination-related capacitance (the sum of diffusion-controlled capacitance and capacitive PC, labelled in purple and green in Figure 5 (c)), respectively. (f) Map of the charge density difference showing the bonding feature of Mn cation with Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ez\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/bc6f8be6dfe6bb6602216ae6.jpg"},{"id":54424553,"identity":"9cdc0573-8abf-419a-93b4-a9f4109ae65d","added_by":"auto","created_at":"2024-04-10 09:03:59","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":99859,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical characteristics of NAC//T-Mn-C ASCs. (a)\u003c/strong\u003e \u003cstrong\u003eSchematic diagram of NAC//T-Mn-C. (b) CV curves at 20 mV s\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e. (c) CV curves at different scan rates. (d)\u003c/strong\u003e \u003cstrong\u003eGCD curves at different current densities. (e) Specific capacitance at different scan rates.\u003c/strong\u003e \u003cstrong\u003e(f) Ragone plots (volumetric values). (g) Self-discharge performance. (h) Cycling performance at a current density of 10 A g\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e for 20000 cycles (inset shows GCD curves of the first and last 5 cycles).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/5f9ea0fe4a1791be3d4a2a41.jpg"},{"id":54425007,"identity":"f789826c-c19b-430f-bcda-dd17efc42299","added_by":"auto","created_at":"2024-04-10 09:12:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1436106,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/533317cd-2891-400d-ba67-86f64a3d37c5.pdf"},{"id":54424555,"identity":"db4da80d-7541-43d9-81c6-35e9e5ae4d61","added_by":"auto","created_at":"2024-04-10 09:04:01","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":37976210,"visible":true,"origin":"","legend":"","description":"","filename":"SupportinginformationACHM.docx","url":"https://assets-eu.researchsquare.com/files/rs-4161663/v1/d133825329f853e2b81d32ae.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Unraveling Cation Intercalation Mechanism in MXene for Enhanced Supercapacitor Performance","fulltext":[{"header":"Introduction","content":"\u003cp\u003eElectrochemical energy storage devices such as batteries and supercapacitors (SCs) are becoming increasingly crucial for various applications, from portable electronics to grid-scale energy storage. SCs, distinguished by fast charging and discharging capabilities and long cycling stability, exhibit outstanding suitability for applications demanding expeditious energy delivery \u003csup\u003e1\u0026ndash;3\u003c/sup\u003e. However, the current development of SCs is primarily restricted by low energy densities \u003csup\u003e4\u003c/sup\u003e. Developing electrodes with high capacitances is one of the keys to the breakthrough of SC practicality. Two-dimensional (2D) materials, with nanometer thickness and unique properties, have become the focus of attention. Among them, MXenes stand out in the field of SCs. MXenes, a class of 2D materials with the formula M\u003csub\u003en+1\u003c/sub\u003eX\u003csub\u003en\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e (M represents a transition metal, X denotes C or N, n ranges from 1 to 4, and T\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e refers to surface terminations such as -OH, -O, -F, etc.), which possess exceptional electrical conductivity (up to ~\u0026thinsp;24000 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), high density (3\u0026ndash;4 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), good hydrophilicity (20\u0026ndash;40\u0026deg; contact angles with water) and favorable mechanical properties (high Young\u0026rsquo;s modulus up to ~\u0026thinsp;0.36 TPa) \u003csup\u003e5\u0026ndash;10\u003c/sup\u003e. Particularly, the rich composition and tunable surface terminations offer MXenes great promise in SCs. However, the restacking in nanosheets caused by van der Waals forces limits the exploitation of MXene-based electrodes, by preventing the full exposure of active sites and compromising their rate performance. Additionally, the surface terminations which are closely associated with their preparation and subsequent treatment, substantially influence MXenes\u0026rsquo; electrochemical properties. More specifically, the lack of active -O terminations (participating redox reactions) limits their specific capacitances \u003csup\u003e11, 12\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo resolve the above issues, various strategies, including compositing, atomic doping, and intercalation, have been proposed. However, compositing MXene with materials such as metal oxides or conducting polymer enhances the capacitances but increases the preparation complexity \u003csup\u003e13\u0026ndash;16\u003c/sup\u003e. Atomic doping introduces nitrogen or boron, optimizing MXenes\u0026rsquo; electronic structure and improving conductivity, though it may introduce impurities \u003csup\u003e17\u0026ndash;20\u003c/sup\u003e. The intercalation strategy is a simple and effective method, addressing the issues through the \u0026ldquo;pillar effect\u0026rdquo; and \u0026ldquo;termination replace effect\u0026rdquo; \u003csup\u003e8, 21\u0026ndash;23\u003c/sup\u003e. Additionally, among the commonly used intercalation agents, metal cations exhibit strong tunability, offering greater design flexibility with the ability to choose different types of metal cations based on specific requirements. Unlocking the full potential of applicable metal cation intercalation holds promise for advancing the practicality of MXene-based electrodes. Despite significant progress in current research, it only reveals the tip of the iceberg, and the lack of a clear elucidation of relevant mechanisms remains a major challenge.\u003c/p\u003e \u003cp\u003eHence, we thoroughly study the effect of metal cationic interlayer intercalation on the electrochemical properties of MXene. We choose the electrochemistry-driven cation intercalation (ECI) method to insert the metal cations into the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e interlayers followed by calcination. Taking advantage of precision and controllability, ECI allows for the precise modulation of ion intercalation quantities by applying different voltages. Besides, it is expected to enable unobstructed ion diffusion channels to guarantee fast ion diffusivity by continuous cation intercalation \u003csup\u003e23, 24\u003c/sup\u003e. This integrated approach of ECI and calcination holds significant importance for improving the interlayer spacing and terminations of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, thereby synergetic manipulating MXene structure and composition. Next, we leverage the computational advantages of Density Functional Theory (DFT) calculations. Starting from the minimum energy principle, we investigate the impact of cation interactions with Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e MXene. This elucidates the mechanism by which cation intercalation affects the structure and composition of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThis study presents a rigorous theoretical analysis of cation intercalation effects on the structure and composition of MXene. It showcases a strategic framework for the advanced development of MXene electrodes, emphasizing its pivotal role in optimizing MXene\u0026rsquo;s structural and compositional benefits for enhanced application.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eIt has been widely accepted that the surface terminations of MXene is closely related to the intercalation process, in which the -O termination is a pivotal factor in redox reactions \u003csup\u003e11, 12\u003c/sup\u003e. Accordingly, we propose a surface termination modulation strategy using metal cations intercalation, expecting to find suitable metal cations to make MXene surface rich in -O termination with suitable interlayer spacing. Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e shows a fragment of the periodic table of elements. The metallic elements are generally considered to be proper cation elements, among which those stable and commonly used in aqueous solution are labeled in red. It should be noted that certain metallic-based salts demonstrate limited solubility, rendering them unsuitable for use as electrolytes. Ultimately, Li\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, MnSO\u003csub\u003e4\u003c/sub\u003e, ZnSO\u003csub\u003e4\u003c/sub\u003e, MgSO\u003csub\u003e4\u003c/sub\u003e, and Al\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e are chosen as intercalators and cation intercalation in Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, labeled as Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M in this work.\u003c/p\u003e \u003cp\u003eTi\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e freestanding films were prepared according to our previous work \u003csup\u003e25\u003c/sup\u003e. The experimental process is illustrated schematically in Figure S2. It involves selectively etching the A-layer of the homemade Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e (in Figures S4(a)-(b)) to obtain a multi-layered Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e (in Figures S4(c)-(d)). Subsequently, ultrasound and centrifugation were used to achieve a uniformly dispersed Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e (in Figure S5(a)), which was further vacuum-filtered to obtain Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e freestanding films (in Figure S5(b)). The thickness and quality of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e films can be adjusted by varying the concentration of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e suspension. The ECI approach was selected to adjust the interlayer space and create the favorite terminations. The treated Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e surface not only exposes more active sites but also experiences surface termination adjustment, particularly the increase in -O terminations and a reduction in -F terminations. These changes significantly boost the redox reactions of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e in H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe XRD patterns of Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). The characteristic peaks can be assigned to Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e (JCPDS No. 50\u0026ndash;0875), indicating its good crystallinity \u003csup\u003e28\u003c/sup\u003e. After selectively etching the Al layer of the precursor using HCl/LiF mixture, the (002) peak shifts to 7.05\u0026deg; from 9.68\u0026deg;, indicating the successful preparation of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eTo investigate the effect of different metal cations on the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e interlayer distance and surface chemistry, metal cations including Li\u003csup\u003e+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Mn\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, and Al\u003csup\u003e3+\u003c/sup\u003e with varying valence states were selected. The comparison of ionic radii, hydrated ionic radii, and atomic weights is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b). Initially, the films after ECI were naturally dried at room temperature (RT), and the shift of the (002) characteristic peaks were observed in Figure S6, indicating the intercalation of metal cations into the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e with adjustable interlayer spacing.\u003c/p\u003e \u003cp\u003eConsidering the intercalated water may affect the interlayer distance, drying under a vacuum at 120\u0026deg;C was used to compare the effect of different intercalation cations more accurately. Shown in Figure S7, the (002) peak of the dried Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e is shifted to the right by 1.01\u0026deg; compared to the undried Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, which is attributed to the removal of free water between the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e layers. According to the Bragg equation, the interlayer spacing decreased by 2.37 \u0026Aring;, approximately one layer of water molecules \u003csup\u003e29\u003c/sup\u003e. In addition, Figure S8 compares the XRD patterns of intercalated cations with different valence states. The (002) peaks are shifted to the left for all ECI treated Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-based electrodes, implying the metal cations are present in the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e interlayers.\u003c/p\u003e \u003cp\u003eDue to the use of LiF salts as an etchant, the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e layers contain some Li\u003csup\u003e+\u003c/sup\u003e. This explains why the (002) peak of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e shows minimal shift after ECI in Li\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. The interlayer spacing of each intercalated cation can be calculated based on their respective ion diameters and the calculated interlayer distance was consistent with the actual test results for all cations except for Mg\u003csup\u003e2+\u003c/sup\u003e and Al\u003csup\u003e3+\u003c/sup\u003e listed in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e. This discrepancy in Mg\u003csup\u003e2+\u003c/sup\u003e and Al\u003csup\u003e3+\u003c/sup\u003e is likely attributed to their small atomic radii with high charges, leading to a strong adsorption force on water molecules, resulting in the difficulty of water evaporation and incomplete drying at 120\u0026deg;C.\u003c/p\u003e \u003cp\u003eECI influences the redox reactions of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e by opening the interlayer distance and altering the terminations. Subsequently, a 400\u0026deg;C calcination step was employed to introduce more favorited terminations. This Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-Metal Cation Intercalation-Calcination process is denoted as T-M-C. The XRD patterns of T-M-C are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c). In contrast to the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e that underwent calcination (T-C), it can be observed that the (002) peaks of T-M-C are all shifted to the left. The intercalated cations mostly existed as Ti-O-M, resulting in increased interlayer spacing.\u003c/p\u003e \u003cp\u003eTEM further analyzes the homogeneous structure of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e and T-Mn-C electrodes in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d)-(e), respectively. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e has a monolayer structure with a lateral size of 500\u0026ndash;600 nm in Figure S9. It is observed that the interlayer homogeneity of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e is poor, while the interlayers of the T-Mn-C show a smooth and flat arrangement. This difference can be attributed to the ECI, which uses an external power to facilitate the cations intercalating into the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e layers, thereby opening the blocked interlayer areas \u003csup\u003e23\u003c/sup\u003e. Additionally, a cross-sectional SEM of T-Mn-C displays a lamellar structure like Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(f), indicating that the ECI and calcination process does not affect the lamellar structure of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e. The intercalated Mn element is evenly distributed in the cross-section images (in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(g)), indicating good Mn\u003csup\u003e2+\u003c/sup\u003e intercalation during the ECI process.\u003c/p\u003e \u003cp\u003eThe comparison of the macroscopic optical morphology of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e with different cation intercalation and calcination is presented in Figure S10. It can be observed that the films\u0026rsquo; surface exhibits tiny bubbles after calcination, reflecting the expansion of the films during calcination. The T-M-C films maintain flexibility, which can be used as electrodes directly without any post-treatment. It should be noted that the flexibility of the T-M-C films is slightly reduced compared with the pristine Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e films, primarily attributed to the removal of free water between the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e layers during the calcination. However, this flexibility reduction does not affect the use of the T-M-C films during electrochemical testing. The cross-section images of the electrodes (in Figure S10) are comparable, indicating the layer-stacked structures of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e are maintained.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eElectrochemical tests were conducted on T-M-C electrodes in 3 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte. Figure S11(a) exhibits the CV curves at 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in a potential window of -0.5 V to 0.2 V \u003cem\u003evs.\u003c/em\u003e Ag/AgCl. All samples show asymmetric oval-like shapes with one pair of broad peaks, consistent with a pseudocapacitance, PC, dominated performance in H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte by H\u003csup\u003e+\u003c/sup\u003e intercalation/de-intercalation. Notably, the CV areas display that T-M-C is more significant than the rest samples, indicating its highest specific capacitance.\u003c/p\u003e \u003cp\u003eFigures S11(b)-(c) compares the specific capacitances for all samples at different scan rates, the specific capacitances at 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the capacitance retention rates at 50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (compared with the specific capacitance at 1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). When considering monovalent cations (Li\u003csup\u003e+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, and K\u003csup\u003e+\u003c/sup\u003e), the specific capacitances of the three cations at 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e do not differ significantly. T-Li-C demonstrates a relatively high specific capacitance of 1151.1 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, while T-K-C exhibits the highest capacitance retention rate of 86.1%. This observation can be attributed to the influence of cationic radius. The relationship between the radii of Li\u003csup\u003e+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, and K\u003csup\u003e+\u003c/sup\u003e ions is followed by Li\u003csup\u003e+\u003c/sup\u003e \u0026lt; Na\u003csup\u003e+\u003c/sup\u003e \u0026lt; K\u003csup\u003e+\u003c/sup\u003e. The larger radius of intercalated K\u003csup\u003e+\u003c/sup\u003e ions increases interlayer distance and provides fast ion diffusion channels. It is found that the capacitance retention varies linearly with increasing monovalent cations radius, which also has been reported in previous work \u003csup\u003e23\u003c/sup\u003e. Among the divalent cations, T-Mn-C exhibits the highest specific capacitance at 1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with a maximum specific capacitance of 1655.5 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. On the other hand, T-Mg-C displays the most significant capacitance retention of 82.0%. The underlying reasons are still unknown. We speculate that it is related to the more absorbed water among the T-Mg-C interlayers, reflected from the (002) peak in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c). This situation is also found in T-Al-C electrodes, which show the highest capacitance retention (86.1%) due to the larger interlayer distance.\u003c/p\u003e \u003cp\u003eAdditionally, the effect of the different valence states of the same element on electrochemical performance is considered. We selected FeSO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e as the electrolytes, and their electrochemical performances are presented in Figure S12. Notably, we observe minimal disparity in the electrochemical performances between T-Fe\u003csup\u003e2+\u003c/sup\u003e-C and T-Fe\u003csup\u003e2+\u003c/sup\u003e-C. The specific capacitances of T-Fe\u003csup\u003e2+\u003c/sup\u003e-C are slightly higher than that of T-Fe\u003csup\u003e2+\u003c/sup\u003e-C. This improvement can be attributed to the higher valence state of Fe\u003csup\u003e3+\u003c/sup\u003e, which enhances its water adsorption capability, consequently leading to increased interlayer distance and a slight enhancement in electrochemical performance.\u003c/p\u003e \u003cp\u003eWhen considering all T-M-C electrodes, T-Mn-C demonstrates the highest capacitances and impressive capacitance retention due to the more -O terminations and suitable interlayer spacing. This result is well consistent with the calculation results. Hence, the electrochemical performance of T-Mn-C electrode was further investigated. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) displays the CV curves of T, T-C, T-Mn, and T-Mn-C at a scan rate of 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. It can be observed that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e exhibits a non-rectangular shape. Adding Mn\u003csup\u003e2+\u003c/sup\u003e to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e leads to broad oxidation peaks near \u0026minus;\u0026thinsp;0.2 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl and reduction peaks around \u0026minus;\u0026thinsp;0.3 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl in T-Mn-C. By analyzing the area of CV curves, T-Mn-C exhibits the largest area, indicating significantly enhanced specific capacitance. The electrochemical properties of other T-M-C electrodes are shown in Figures S13-14. The specific capacitances of the four electrodes at 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are calculated using the CV curves shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). The T-Mn-C demonstrates a specific capacitance of 1428.5 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, improving 87.3% compared with pristine Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e. This performance surpasses that of many Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-based electrodes reported in Table S2.\u003c/p\u003e \u003cp\u003eThe Nyquist plots of T, T-C, T-Mn, and T-Mn-C are compared in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c). The Nyquist plot has a semicircle in the high-frequency area and a linear line in the low-frequency area. The internal resistance of these electrodes (R\u003csub\u003es\u003c/sub\u003e) does not change much, indicating that the ECI and calcination process do not alter their R\u003csub\u003es\u003c/sub\u003e. The semicircle radius corresponds to the charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e). T-Mn-C (3.59 Ω) has a smaller R\u003csub\u003ect\u003c/sub\u003e than pure Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e (3.64 Ω) among these electrodes. Besides, the slope of T-Mn-C is the largest in the low-frequency region, indicating its accelerated ion diffusion process. This is reasonable considering Ti-O-Mn as a \u0026lsquo;pillar\u0026rsquo; to expand the interlayer distance and increase the active sites. As shown in Figure S15, T-Mn-C exhibited the largest specific capacitances than the other three electrodes. When the current densities are increased from 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 50 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the capacitance is still maintained at 72.3%, a 19% improvement compared to the pure Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e at 53.3%.\u003c/p\u003e \u003cp\u003eGenerally, the total amount of charge stored in an electrode is contributed to a combination of surface-controlled and diffusion-controlled processes. The \u003cem\u003eb\u003c/em\u003e value is near 1, demonstrating that the electrochemical mechanism is a surface-controlled process \u003csup\u003e30\u003c/sup\u003e. As displayed in Figure S16, the \u003cem\u003eb\u003c/em\u003e value was calculated from the oxidation peaks of the CV curves. T-Mn-C\u0026rsquo;s \u003cem\u003eb\u003c/em\u003e value is 0.96, indicating the fast surface charge response.\u003c/p\u003e \u003cp\u003eTo demonstrate the advance of the ECI method, we employed a self-assembly technique to fabricate the T-Mn-self assembling (T-Mn-sa) and T-Mn-self assembling-calcination (T-Mn-sa-C) sample to make a comparison. The electrochemical properties of these samples are depicted in Figure S17. The results demonstrate that the electrodes after ECI exhibit higher capacitances than the electrodes with the self-assembling technique, except a slightly lower at 50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This enhancement is ascribed to the more uniform pathways and more active sites created by ECI.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(d) illustrates the CV plots of T-Mn-C at different scan rates with a potential window of -0.5 V to 0.2 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl. With increasing scan rates, CV curves show no significant distortions, indicating that T-Mn-C has fast ion diffusion/migration processes \u003csup\u003e31\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(e) depicts the GCD curves of T-Mn-C at different current densities, showing symmetric charge/discharge processes without obvious plateaus, indicating good electrochemical reversibility. Even under high current densities, the GCD curves maintain symmetrical triangles without significant \u003cem\u003eIR\u003c/em\u003e drop. The kinetic processes from the CV curves were analyzed to gain deeper insights into the energy storage mechanism of T-Mn-C. Electrode charge storage typically involves a capacitive-controlled process and a diffusion-controlled process. As the calculation of the \u003cem\u003eb\u003c/em\u003e value in Figure S16, the contribution of the capacitive-control process is determined at different scan rates. From Figure S18, it can be observed that with increasing scan rates, the capacitive-controlled contribution rises from 63\u0026ndash;92%. This higher capacitive-controlled contribution from 1 to 50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicates that T-Mn-C possesses rapid charge storage kinetics, which is advantageous for achieving good rate performance.\u003c/p\u003e \u003cp\u003eAdditionally, the T-Mn-C electrode exhibits excellent long-term cycling performance, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(f). After 10000 cycles at 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, it has a capacitance retention rate of 101.1% and an averaged Coulombic efficiency of 100.1%, outstanding among previous reports, as shown in Figure S19 and Table S2.\u003c/p\u003e \u003cp\u003eEx-situ XRD and XPS analyses were conducted to investigate T-Mn-C's phase changes and charge storage mechanism, as depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(g)-(j), respectively. During the charging process from \u0026minus;\u0026thinsp;0.5 V to 0.2 V (point A to C in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(g)), the (002) peak of T-Mn-C shifts towards higher angles, indicating a reduction in interlayer spacing. Conversely, during discharging from 0.2 V to -0.5 V, the (002) peak turns towards lower degrades due to the increased interlayer spacing. Ex-situ XPS analysis revealed that the Ti peaks shift to higher binding energies during charging, suggesting oxidation. Conversely, the Ti peaks shift to lower binding energies during discharging, indicating reduction. This phenomenon is primarily attributed to the intercalation and deintercalation of H\u003csup\u003e+\u003c/sup\u003e in the H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e electrolyte during the charging/discharging process, which is in line with previous report \u003csup\u003e32\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eXPS was further utilized to analyze the surface chemistries of the T-Mn-C electrode to reveal the role of the intercalated Mn. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) presents the XPS curves of T, T-C, T-Mn, and T-Mn-C electrodes. T-C, T-Mn, and T-Mn-C\u0026rsquo;s peaks are similar to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, indicating that the structure of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e remains following the ECI and calcination process. The Mn 2p peak at 640.8 eV is observed in T-Mn and T-Mn-C, indicating the successful intercalation of Mn\u003csup\u003e2+\u003c/sup\u003e into the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e interlayers. The elemental percentages of O, F, and Mn were calculated based on XPS results. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b), the ECI increases the O and decreases the F content, which is ascribed to the intercalated cations and is in line with the calculation results. The calcination process is also employed to reduce the inactive -F further. The increased O content after calcination may be ascribed to the slight surface oxidation, which has been reported previously \u003csup\u003e21\u003c/sup\u003e. The fitted result for the Mn 2p of T-Mn-C is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c), revealing the presence of Mn\u003csup\u003e3+\u003c/sup\u003e besides Mn\u003csup\u003e2+\u003c/sup\u003e. This indicates the oxidation of Mn\u003csup\u003e2+\u003c/sup\u003e from the oxidizing agent originating from Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e or oxygen in the atmosphere \u003csup\u003e29\u003c/sup\u003e. Further analysis of the Mn 2p in the XPS of T-Mn and T-Mn-C at different depths are in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d)-(e). It is observed that the Mn 2p can still be found inside the electrode, which is consistent with the EDS mapping of the cross-sectional image in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(g).\u003c/p\u003e \u003cp\u003eAlthough Mn 2p peaks exist on the surface and inside the T-Mn-C before testing, it is speculated that H\u003csup\u003e+\u003c/sup\u003e might replace them during pre-cycling. To verify this, ICP analysis was performed on the T-Mn-C before and after pre-cycling. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(f) shows that the Mn content before pre-cycling is 3.4 wt%. In contrast, after pre-cycling (50 cycles), it is 0.35 wt%. This confirms that the Ti-O-Mn bonds break during pre-cycling, and Mn cations extract from the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e interlayer through H\u003csup\u003e+\u003c/sup\u003e exchange. Moreover, this phenomenon provides a reasonable explanation for the continuing expansion of CV areas (in Figure S20). In short, the intercalated Mn cations exist in the form of Ti-O-Mn, which increase the -O terminations, decrease the -F terminations, serve as active sites and pillar up the interlayer. These combinations enhance the electrochemical performance of T-Mn-C electrodes.\u003c/p\u003e \u003cp\u003eThe Ti 2p of T, T-C, T-Mn, and T-Mn-C electrodes are analyzed as shown in Figure S21. It can be observed that the Ti-C binding is lowest for the T-Mn-C electrode, indicating the inactive sites are minimized in the four electrodes, thereby increasing the specific capacitances.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo systematically study how the intercalated cations affect the surface terminations and the interlayer spacing. DFT simulation has been primarily performed for a comprehensive understanding of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M, with the corresponding atomic scheme illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a). It can be seen that three possible accommodation sites exist in the interlayer space of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, namely, Top, Hollow, and Mid. The formation energy computation results imply that the optimal intercalation configuration of each cation species might be different, as demonstrated in detail in Figure S22: taking Li, Mg, and Al elements for example, the formation energy plots in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b) imply that Li exhibits a strong interaction with substrate Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, with the largest formation energy calculated to be -0.68eV/-2.59 eV for Mid-Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e2\u003c/sub\u003e/Mid-Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, respectively. While in the case of Mg and Al, the energetically favorable configurations are determined to be Top/Hollow (-0.28 eV/-2.11 eV) and Top/Top (-0.05 eV/-1.76 eV), respectively. It is interesting to find that the formation energy of M-Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is generally much higher than that of M-Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e2\u003c/sub\u003e, suggesting an overall strong interaction between the -O termination and metal cations. Consequently, the presence of metal cation in solution is proposed to possibly induce termination alternation in solution, according to Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${\\text{T}\\text{i}}_{3}{\\text{C}}_{2}{\\text{F}}_{z}-\\text{M}+ \\text{*}\\text{O} \\rightleftharpoons {\\text{T}\\text{i}}_{3}{\\text{C}}_{2}{\\text{O}}_{z}-\\text{M}+ \\text{*}\\text{F}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M refer to the cation intercalated Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, \u003csub\u003e*\u003c/sub\u003eO and \u003csub\u003e*\u003c/sub\u003eF refer to the active oxygen and fluorine existing in the solution during the intercalation process, In order to raise the content of -O termination, which plays a significant role in the surface redox reactions of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, a well combination of strong interaction between cation and -O termination and weak interaction between the cation and -F is expected \u003csup\u003e11, 12\u003c/sup\u003e. Considering that the free energy difference between \u003csub\u003e*\u003c/sub\u003eO and \u003csub\u003e*\u003c/sub\u003eF is constant in a dilute solution, the reaction enthalpy of the above equation can be calculated by the formation energy difference, which evaluates the termination preference of cation element species according to Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\varDelta {E}_{\\text{d}\\text{i}\\text{f}\\text{f}}={E}_{{\\text{T}\\text{i}}_{3}{\\text{C}}_{2}{\\text{F}}_{z}-\\text{M}}^{\\text{o}\\text{p}\\text{t}\\text{i}\\text{m}\\text{a}\\text{l}}-{E}_{{\\text{T}\\text{i}}_{3}{\\text{C}}_{2}{\\text{O}}_{z}-\\text{M}}^{\\text{o}\\text{p}\\text{t}\\text{i}\\text{m}\\text{a}\\text{l}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eCorrespondingly, the Li cation with a formation energy difference of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\varDelta E}_{\\text{d}\\text{i}\\text{f}\\text{f}}^{\\text{L}\\text{i}}\\)\u003c/span\u003e\u003c/span\u003e of 1.90 eV is suggested to possess stronger termination preference than Na and Mg cations with the values of 1.83 eV and 1.67 eV, respectively. Then, a high-throughput DFT simulation is conducted to find out the element with the strongest termination preference for Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e. After the energy calculation of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M (T=-F, -O) at various interlayer distances (ranging from 10 to \u0026Aring; to 15 \u0026Aring;), the optimal configuration of each Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M is determined, thereby the theoretical interlayer distance as well as the formation energy difference can be obtained, displayed in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c)-(d), respectively. After considering accommodation sites, it is notable that the interlayer distance of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-M is not simply dominated by the ionic radius of the cation element, for example, that of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-Zn is much larger than that of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-Mg despite their similar cation ionic radius (Zn-0.74 \u0026Aring; versus Mg-0.72 \u0026Aring;) \u003csup\u003e26, 27\u003c/sup\u003e. The formation energy calculation results demonstrate that Mn cation exhibits the strongest termination preference in this work, with the largest formation energy difference calculated to be 2.46 eV. Therefore, combined with the previous experimental results, the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-Mn shows outstanding electrochemical performance with a high contribution from surface redox reactions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe contribution from capacitive-controlled and diffusion-controlled behaviors is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a). The capacitive-controlled component in each electrode typically remains consistent as scan rates increase, suggesting that the decrease in total specific capacitance at high scan rates is mainly due to a lower contribution from the diffusion-controlled behavior. Furthermore, it is observed that all the T-M-C electrodes exhibit a higher contribution from capacitive-controlled behavior compared to the pure Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e electrode.\u003c/p\u003e \u003cp\u003eCapacitive-controlled behavior is responsive to the surface composition. It can be broadly categorized into two components: EDLC, associated with the intercalation of hydrated ions between Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e layers, and PC, linked to redox reactions involving surface absorption and functional groups \u003csup\u003e33, 34\u003c/sup\u003e. Additionally, based on the electrochemical active surface area (ECSA), capacitive capacitance can be quantitative in Figure S23. The slope of the current per unit area against the corresponding scan rate of T-M-C is used to calculate the electrochemical double-layer capacitances (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003edl\u003c/em\u003e\u003c/sub\u003e) in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b). EDLC was measured by cycling the electrode in the non-Faradaic regions. These regions are characterized by potentials where no charge-transfer reactions occur, but only absorption/desorption processes take place. In our case, this potential range was 0.1\u0026ndash;0.2 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl. This surface area is proportional to the \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003edl\u003c/em\u003e\u003c/sub\u003e of the solid-liquid interface \u003csup\u003e35, 36\u003c/sup\u003e. At the center of the potential range (0.15 V \u003cem\u003evs\u003c/em\u003e RHE), the difference in current densities (\u003cem\u003eΔ\u003c/em\u003e\u003csub\u003e\u003cem\u003ej\u003c/em\u003e\u003c/sub\u003e) between the anodic (\u003cem\u003ej\u003c/em\u003e\u003csub\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sub\u003e) and cathodic (\u003cem\u003ej\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e) current densities was calculated for each scan rate. The value of C\u003csub\u003e\u003cem\u003edl\u003c/em\u003e\u003c/sub\u003e can be determined from the slop of this linear fitting diagram according to the following Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e):\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${C}_{dl}=S\\varDelta j/V$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eTherefore, capacitance is divided into three parts, and their specific capacitance values are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c) and Table S3. The variations in capacitive EDLC values are not substantial, indicating that the disparity in electrode performance is primarily attributed to PCs and diffusion-controlled capacitances.\u003c/p\u003e \u003cp\u003eWith the division of total capacitance into three contributing parts, specifically, capacitive EDLC, capacitive PC, and diffusion-controlled capacitance, it is then possible to disclose the dominating factors of energy storage mechanisms by combining the experimental results and our previous DFT simulation. The hydrated radius of intercalation cations is generally proposed to play a significant role in the delamination of MXene \u003csup\u003e7, 37, 38\u003c/sup\u003e, while in the present work however, better consistency between theoretical ILD and that related capacitance can be found in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d), suggesting that the intercalation position of cations is an essential factor affecting the ILD of MXene which has not been carefully discussed before. Notably, the experimental ILD value of T-M-C obtained by XRD analysis is not totally covered by the theoretical range from DFT simulation, which might be mainly attributed to the complex microstructure evolution (for example, dehydration, change of intercalation site, etc.) during sample preparation. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(e) demonstrates the relationship between termination-related capacitance (sum of capacitive PC and diffusion-controlled capacitance) and calculated formation energy difference. The excellent liner distribution indicates that our tailor strategy, changing the termination composition of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e by introducing cations during ECI, is feasible, and the formation energy difference is soundly proved to be the critical factor dominating the content of -O termination: as expected, Mn\u003csup\u003e2+\u003c/sup\u003e which possesses the largest formation energy difference among all investigated cations is proved to significantly favor the electrochemical performance of T-Mn-C, with a large termination-related capacitance contribution up to 1230 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(f) shows the map of charge density difference of T-Mn. The energetically optimal interaction site is computed to be the Mid site, and apparent charge exchange can be observed along the Mn-O and O-Ti bonds. In other words, the -O termination plays a significant role in realizing the charge transfer between Mn and Ti, which is important in the contributing mechanism of diffusion-controlled capacitance.\u003c/p\u003e \u003cp\u003eWhile ILD impacts the capacitive EDLC, the effect is limited. Different ion intercalation sites result in distinct electron exchange energies for Ti, -O, and M atoms, thereby -O terminations giving rise to varied termination-related capacitance in T-M-C electrodes. This variance is the crucial factor contributing to the enhancement of T-Mn-C electrochemical performance.\u003c/p\u003e \u003cp\u003eIt has also been observed that diffusion-controlled capacitance is partly influenced by the size of the layer spacing and is caused by the relatively slow movement in bulky electrodes. Essentially, this means that the ion diffusion rate inside the electrodes is lower than that consumed by the electrode reactions. The highest PC values for T-Mn-C are ascribed to the high content of -O terminations and the rapid ion migration in interlayers since the reaction mechanism in MXene can be expressed as Eq.\u0026nbsp;(4) \u003csup\u003e11\u003c/sup\u003e:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$${Ti}_{3}{C}_{2}{O}_{x}{\\left(OH\\right)}_{y}{F}_{z}+\\delta {H}^{+}+\\delta {e}^{-}\\underleftrightarrow{ }{Ti}_{3}{C}_{2}{O}_{x-\\delta }{\\left(OH\\right)}_{y+\\delta }{F}_{z}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eGenerally, the larger diffusion-controlled capacitance of the electrode results in the worse rate performance. Therefore, the relationship between diffusion-controlled capacitance ratio and capacitance retention is shown in Figure S24. The diffusion-controlled capacitance of T-M-C at different scan rates correlates with changes in the layer spacing. In the case of monovalent metal cations such as Li\u003csup\u003e+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, and K\u003csup\u003e+\u003c/sup\u003e, the largest layer spacing of K\u003csup\u003e+\u003c/sup\u003e processes the smallest diffusion capacitance. For bivalent metals like Mn\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, and Mg\u003csup\u003e2+\u003c/sup\u003e, T-Mg-C has the largest interlayer spacing, which promotes electrolyte diffusion. In the case of trivalent Al\u003csup\u003e3+\u003c/sup\u003e, the situation is like that of Mg\u003csup\u003e2+\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the outstanding electrochemical performance of T-Mn-C, symmetrical supercapacitors (SSCs) with a voltage window ranging from 0 V to 0.7 V were assembled, as illustrated in Figure S25(a). The CV curves of SSCs are presented in Figure S25(b), displaying nearly rectangular shapes with no significant changes even at 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This indicates that the T-Mn-C electrodes possess excellent reversibility. Figure S25(c) shows the GCD curves of the SSCs at current densities from 0.1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These curves exhibit an almost inclined straight line and near-symmetric triangle, confirming the superior electrochemical reversibility of T-Mn-C. The volumetric capacitance (C\u003csub\u003e\u003cem\u003ev\u003c/em\u003e\u003c/sub\u003e) values at current densities of 0.1, 0.2, 0.5, 1, 2, and 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are measured as 343.4, 305.0, 272.3, 237.4, 190.4, and 182.7 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, respectively. The capacitance retention rate remains 17.2% at 100 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, as demonstrated in Figure S25(d). Furthermore, Figure S25(e) presents the Nyquist plots of SSCs, which further validates the low internal resistance. And the self-discharge performance of the device was tested in Figure S25(f). After 10 hours, the voltage of the cells is observed to stabilize at 0.16 V, indicating a retention rate of 22.9%. It is hereby acknowledged that the self-discharge rates need to be further reduced before applications. The Ragone plot of SSCs based on T-Mn-C is illustrated in Figure S25(g). The SSCs show an energy density of 23.3 Wh L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a power density of 112.2 W L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while the energy density remains at 6.5 Wh L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 7350.1 W L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Moreover, T-Mn-C exhibits excellent cycling performance, as demonstrated in Figures S25(h)-(i). It retains a capacitance retention of 107.6% after 20000 cycles at 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 90.4% after 2000 cycles at 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The Columbic efficiency remains nearly 100.0% during the 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cycling tests. To further explore the practical application of T-Mn-C, all-solid-state supercapacitors (ASSSCs) were constructed using a PVA/H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e gel electrolyte, as depicted in Figure S26(a). The CV and GCD curves of three 0.7 V flexible ASSSCs connected in series and parallel under practical conditions are presented in Figures S26(b)-(c). It was observed that three flexible ASSSCs connected in series could power a 1.6 V thermohygrometer and a 1.8 V small bulb.\u003c/p\u003e \u003cp\u003eTo expand voltages and improve the energy densities in aqueous SCs, we assembled an asymmetric SC by pairing nitrogen-doped activated carbon film (NAC, 0 to 1 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl) with T-Mn-C film (-0.5 to 0.2 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl) in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a). Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b) displays the potential windows of the NAC (0\u0026ndash;1 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl) and T-Mn-C (-0.5-0.2 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl) electrodes at the same scan rate of 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The morphologies and electrochemical performance of the NAC are shown in Figure S27. It follows that the potential window of NAC//T-Mn-C ASSC is from 0 to 1.5 V. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c) shows CV of NAC//T-Mn-C ASCs, where a pair of pronounced redox peaks is observed. Increasing the scan rates does not appear to distort the curves, indirectly demonstrating the fast charge/discharge processes and excellent rate performances. The GCD curves at different current densities (1\u0026ndash;20 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(e), at a scan rate of 0.5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the device delivers a capacitance of 176.8 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and maintains a capacitance of 122.1 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e when the scan rate increases to 20 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Moreover, the electrochemical performance of NAC//T-Mn-C can be compared with other recently published MXene-based aqueous ASCs \u003csup\u003e39\u0026ndash;49\u003c/sup\u003e. Based on the weight of active material, our devices show the maximum energy density of 54.0 Wh L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a power density of 0.75 kW L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a power density of 30.1 kW L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at an energy density of 38.2 Wh L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(f). In addition, the ASC is also at a high level of energy density from the mass values perspective in Figure S28. The self-discharge performance of NAC//T-Mn-C was tested in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(g). After 10 hours, the voltage of the cells is observed to stabilize at 0.54 V, indicating a retention rate of 36.0%. Furthermore, the stability of NAC//T-Mn-C ASC was examined using the GCD technique for 20000 cycles at the current density of 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(h). The averaged Columbic efficiency is 96.5% after 20000 cycles, and the capacitance retention is 103.6%, demonstrating competitive cycling stability. The excellent cycling performance of NAC//T-Mn-C ASCs is found to be appreciable when compared with other MXene-based devices in Table S4.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, the metal cation intercalation strategy significantly enhances the performance of MXene-based electrodes by opening up blocked channels and modifying terminations. The processes of ECI and calcination not only alleviate the interlayer restacking but also alter its surface terminations. Notably, the intercalation of various cations has varying effects on capacitance. Among these, T-Mn-C electrodes reach 1655.5 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e at 1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, exhibiting a remarkable 150% increment compared to pristine Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e. DFT calculations have elucidated the enhanced electrochemical performance, indicating that various intercalated cations prefer different terminations. Specifically, the intercalated Mn\u003csup\u003e2+\u003c/sup\u003e exhibits the largest formation energy difference between Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e., critically enhancing the termination-related capacitances. The advantages of T-M-C electrodes are highlighted by the SSCs and ASCs with high energy densities at high powers. This approach substantially betters the electrochemical properties of MXene-based electrodes and suggests its applicability to other 2D materials, promising widespread advancements in energy storage technologies.\u003c/p\u003e"},{"header":"Experimental methods","content":"\u003cp\u003eWith the exception of MnSO\u003csub\u003e4\u003c/sub\u003e and MgSO\u003csub\u003e4\u003c/sub\u003e (Macklin Biochemical Company), all chemical agents were purchased from Aladdin Chemical Company without any further treatment.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of Ti\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eC\u003c/b\u003e \u003csub\u003e \u003cb\u003e2\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eT\u003c/b\u003e \u003csub\u003e \u003cb\u003ez\u003c/b\u003e \u003c/sub\u003e \u003cb\u003efilms\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe process for synthesizing Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e films can be found in our previous work \u003csup\u003e25\u003c/sup\u003e. In brief, the prepared precursor MAX phase Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e was stirred with HCl and LiF, and the Al layer was etched off to obtain multilayered Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, m-Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, followed by ultrasonication and centrifugation to obtain Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e suspensions. The above suspension was vacuum filtrated through a membrane (Celgard 3501, 0.22 mm pore size) by using a Buchner funnel with sand core (40 mm in diameter). The membrane was then dried in a freeze dryer for 24 h. Freestanding Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e films were peeled off from the filter membrane.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of T-M and T-M-C films\u003c/h2\u003e \u003cp\u003eTo fit the size of the glassy carbon current collectors, the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e film was first cut into discs with a 6 mm diameter and a mass loading of ~\u0026thinsp;1.9 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Next, 1 M of Li\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, MnSO\u003csub\u003e4\u003c/sub\u003e, ZnSO\u003csub\u003e4\u003c/sub\u003e, MgSO\u003csub\u003e4\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e were prepared as electrolytes. Then, the pure Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e films were used as the working electrodes, and activated carbon (AC, YP50F, Kuraray, Japan) discs with a 6 mm diameter and a mass loading of ~\u0026thinsp;20 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e were used as counter electrodes, which were assembled in a plastic Swagelok half-cell. Ag/AgCl in saturated KCl was used as reference electrodes. Using the cyclic voltammetry (CV) program in the electrochemical workstation (CHI 660E), the scan rate was 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e from \u0026minus;\u0026thinsp;1 V to 0.2 V \u003cem\u003evs\u003c/em\u003e Ag/AgCl and the cycling number was 50. The T-M films can be obtained by natural drying at RT for 24 h. Calcination was conducted at 400 ℃ for 2 h at a heating rate of 2 ℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e under an Ar gas atmosphere at a flow of 100 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to obtain T-C-M films. For comparison, the pure Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e films without ECI were also subjected to the calcination process.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of NAC films\u003c/h2\u003e \u003cp\u003eThe preparation method refers to previous work \u003csup\u003e48\u003c/sup\u003e. In brief, 0.4 g of activated carbon (AC) was added into 10 g of urea with 60 mL DI-water. The mixture was continuously stirred for 30 minutes, transferred into Teflon-lined stainless-steel autoclave, and kept in an oven at 180 ℃ for 24 h. Then, the reaction products were cleaned by centrifuge and dried to obtain nitrogen-doped AC (NAC).\u003c/p\u003e \u003cp\u003eThe 90% AC or NAC activated materials and Poly(tetrafluoroethylene) (PTFE) were ground, where PTFE acted as a binder. Then, the mixture with the aid of DI water to form the slurry, which was later rolled into flat films and placed at 70 ℃ to dry for 24 hours. Finally, it was perforated with a punch to form 8 mm (for AC) and 6 mm (for NAC) diameter discs.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of PVA/H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e gel electrolytes\u003c/h2\u003e \u003cp\u003eA 2 g of Polyvinyl alcohol powder (PVA, Sigma) was added into 16.7 mL of DI water. Then the mixture was heated to 90 ℃ and stirred with a magnetic bar for 3 h. The solution was cooled down to 40 ℃. A 3.3 mL of H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e (98%) was added into the PVA solution slowly while keeping stirring for 1 h. Then the PVA/H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution was frozen for 12 h to obtain PVA/H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e gel electrolytes.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eMaterials characterizations\u003c/h2\u003e \u003cp\u003eXRD patterns were recorded by a DX-2700BH (Haoyuan) diffractometer in the range of 2\u003cem\u003eθ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3\u0026deg;-70\u0026deg; with the step size of 0.02\u0026deg; and the scan rate of 0.5 sec/step. SEM and EDS mapping images were performed on the Nova Nano SEM450 with an acceleration voltage of 30 kV. TEM and HRTEM images were acquired by a Talos F200X microscope with an acceleration voltage of 200 kV. XPS measurements were performed on a K-Alpha (Thermo Scientific) spectrometer using Al Kα radiation. Inductively coupled plasma optical emission spectrometer (ICP-OES) was performed on PerkinElmer 8300.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eElectrochemical measurements\u003c/h2\u003e \u003cp\u003eThe 6 mm Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-based films were tested directly in a plastic Swagelok half-cell. To prepare SSCs devices, two 6 mm working electrodes of T-C-Mn with equal mass were assembled with a separator in a Swagelok cell. Before measurement, all configurations were pre-cycled at 20 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 50 cycles to stabilize the performance. For all testing, glassy carbon (CHI Instruments, China) was used as current collectors, polypropylene membranes (Celgard 3501) were used as separators, and 3 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was used as electrolytes. All electrochemical measurement data were recorded on a CHI 660E electrochemical workstation, except the long-cycling testing, which was recorded on the SP-150 electrochemical workstation (Bio-logic, France). Techniques employed included cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The frequency range for EIS measurements was from 10 mHz to 100 kHz. All electrochemical measurements were conducted at RT.\u003c/p\u003e \u003cp\u003eGravimetric capacitance (C\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e) was calculated by the CV technique using the following Eq.\u0026nbsp;(\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e):\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$${C}_{g}=\\underset{{U}_{-}}{\\overset{{U}_{+}}{\\int }}I\\left(V\\right)dV/vUm$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eU\u003c/em\u003e (V) is the potential, \u003cem\u003ev\u003c/em\u003e (mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is the scan rate, \u003cem\u003em\u003c/em\u003e (g) is the mass of the electrode (one electrode in 3-electrode, and two electrodes in 2-electrode), \u003cem\u003eI\u003c/em\u003e (mA) is the current. \u003cem\u003eU\u003c/em\u003e\u003csub\u003e\u003cem\u003e+\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eU\u003c/em\u003e\u003csub\u003e\u003cem\u003e\u0026minus;\u003c/em\u003e\u003c/sub\u003e are the positive and negative potentials, respectively.\u003c/p\u003e \u003cp\u003eThe cells\u0026rsquo; volumetric capacitance (F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) was calculated by the following Eq.\u0026nbsp;(\u003cspan refid=\"Equ6\" class=\"InternalRef\"\u003e6\u003c/span\u003e)-(\u003cspan refid=\"Equ7\" class=\"InternalRef\"\u003e7\u003c/span\u003e):\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$${C}_{v}={\\rho C}_{g}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ7\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ7\" name=\"EquationSource\"\u003e\n$$\\rho =m/Ad$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e7\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eρ\u003c/em\u003e (g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) is the density of the film electrodes. \u003cem\u003em\u003c/em\u003e (g) is the mass of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-based discs, which is ~\u0026thinsp;0.00045 g. \u003cem\u003eA\u003c/em\u003e (cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) is the area of the electrodes, which is 0.2826 cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. \u003cem\u003ed\u003c/em\u003e (cm) is the thickness of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e-based discs, which is measured from SEM images, ~\u0026thinsp;5 \u0026micro;m. The \u003cem\u003eρ\u003c/em\u003e of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e and NAC films is ~\u0026thinsp;3.2 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and ~\u0026thinsp;0.7 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. The average packing density based overall active materials (negative and positive) is 2.0 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe volumetric energy (\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003ev\u003c/em\u003e\u003c/sub\u003e) and power densities (\u003cem\u003eP\u003c/em\u003e\u003csub\u003e\u003cem\u003ev\u003c/em\u003e\u003c/sub\u003e) were calculated assuming Eq.\u0026nbsp;(\u003cspan refid=\"Equ8\" class=\"InternalRef\"\u003e8\u003c/span\u003e)- (\u003cspan refid=\"Equ9\" class=\"InternalRef\"\u003e9\u003c/span\u003e):\u003cdiv id=\"Equ8\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ8\" name=\"EquationSource\"\u003e\n$${E}_{v}={{C}_{v}U}^{2}/7.2$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e8\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ9\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ9\" name=\"EquationSource\"\u003e\n$${P}_{v}=3.6*{E}_{v}v/U$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e9\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe self-discharge testing was recorded on the Bio-logic SP-150 electrochemical workstation, by first holding the cells at specific voltages for 0.5 h and then monitoring the cell voltage as a function of time for 10 h.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eCalculation method\u003c/h2\u003e \u003cp\u003eThe modeling in this work was performed in the framework of the Density Functional Theory (DFT) as implemented in the Vienna \u003cem\u003eAb initio\u003c/em\u003e Simulation Package (VASP). The Projector Augmented Wave (PAW) method was adopted to solve the Kohn-Shan equations, together with the exchange-correlation energy functional of Generalized Gradient Approximation by Perdew-Burke-Ernzerhof (GGA-PBE). A \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\varGamma\\)\u003c/span\u003e\u003c/span\u003e centered Monkhorst-Pack mesh of total number of 40 was applied, with a cutoff energy of 480 eV. Moreover, the convergence criteria were set to be 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e eV for energy and 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e eV/\u0026Aring; for force, respectively. A high throughput investigation was performed to reveal the cation interaction behaviors in Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, using a bilayer model with the consideration of all possible accommodation sites. After achieving the interaction energy of each cation in Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e, the termination preference was then evaluated herein by calculating the energy difference.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflicts of interest\u003c/h2\u003e \u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (52301263, 52171033, and U23A20574).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eXiaodan Yin, Wei Zheng, and Haifeng Tang researched the experimental program, designed the work, prepared the material, collected the data, and wrote the manuscript. Chengjie Lu was responsible for theoretical calculations and wrote the manuscript. Wei Zheng, Li Yang, and Long Pan reviewed the manuscript. Peigen Zhang and ZhengMing Sun revised the manuscript critically for important intellectual content.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLukatskaya, M. R.; Dunn, B.; Gogotsi, Y., Multidimensional materials and device architectures for future hybrid energy storage. \u003cem\u003eNATURE COMMUNICATIONS \u003c/em\u003e\u003cstrong\u003e2016,\u003c/strong\u003e \u003cem\u003e7\u003c/em\u003e (1), 12647.\u003c/li\u003e\n\u003cli\u003eHosseini, H.; Shahrokhian, S., Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems. \u003cem\u003eAPPLIED MATERIALS TODAY \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e10\u003c/em\u003e, 72-85.\u003c/li\u003e\n\u003cli\u003eSimon, P.; Gogotsi, Y.; Dunn, B., Where Do Batteries End and Supercapacitors Begin? \u003cem\u003eSCIENCE \u003c/em\u003e\u003cstrong\u003e2014,\u003c/strong\u003e \u003cem\u003e343\u003c/em\u003e (6176), 1210-1211.\u003c/li\u003e\n\u003cli\u003eWang, T.; Chen, H. C.; Yu, F.; Zhao, X. S.; Wang, H. X., Boosting the cycling stability of transition metal compounds-based supercapacitors. \u003cem\u003eENERGY STORAGE MATERIALS \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e16\u003c/em\u003e, 545-573.\u003c/li\u003e\n\u003cli\u003eDall\u0026apos;Agnese, Y.; Lukatskaya, M. R.; Cook, K. M.; Taberna, P. L.; Gogotsi, Y.; Simon, P., High capacitance of surface-modified 2D titanium carbide in acidic electrolyte. \u003cem\u003eELECTROCHEMISTRY COMMUNICATIONS \u003c/em\u003e\u003cstrong\u003e2014,\u003c/strong\u003e \u003cem\u003e48\u003c/em\u003e, 118-122.\u003c/li\u003e\n\u003cli\u003eZamhuri, A.; Lim, G. P.; Ma, N. L.; Tee, K. S.; Soon, C. F., MXene in the lens of biomedical engineering: synthesis, applications and future outlook. \u003cem\u003eBIOMEDICAL ENGINEERING ONLINE \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e20\u003c/em\u003e (1), 1-24.\u003c/li\u003e\n\u003cli\u003eLong, Y.; Tao, Y.; Shang, T. X.; Yang, H. T.; Sun, Z. J.; Chen, W.; Yang, Q. H., Roles of Metal Ions in MXene Synthesis, Processing and Applications: A Perspective. \u003cem\u003eADVANCED SCIENCE \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e9\u003c/em\u003e (12), 2200296.\u003c/li\u003e\n\u003cli\u003eHu, M. M.; Dai, J.; Chen, L. H.; Meng, A. L.; Wang, L.; Li, G. C.; Xie, H. J.; Li, Z. J., Selectivity for intercalated ions in MXene toward a high-performance capacitive electrode. \u003cem\u003eSCIENCE CHINA-MATERIALS \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e66\u003c/em\u003e (3), 974-981.\u003c/li\u003e\n\u003cli\u003eJin, H. L.; Wang, K.; Mao, Z. Q.; Tang, L. Y.; Zhang, J.; Chen, X., The structural, magnetic, Raman and electrical transport properties of Mn intercalated Ti3C2TX. \u003cem\u003eJOURNAL OF PHYSICS-CONDENSED MATTER \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e34\u003c/em\u003e (1), 015701.\u003c/li\u003e\n\u003cli\u003eXu, T.; Wang, Y.; Liu, K.; Zhao, Q.; Liang, Q.; Zhang, M.; Si, C., Ultralight MXene/carbon nanotube composite aerogel for high-performance flexible supercapacitor. \u003cem\u003eAdvanced Composites and Hybrid Materials \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e6\u003c/em\u003e (3).\u003c/li\u003e\n\u003cli\u003eMu, X. P.; Wang, D. S.; Du, F.; Chen, G.; Wang, C. Z.; Wei, Y. J.; Gogotsi, Y.; Gao, Y.; Dall\u0026apos;Agnese, Y., Revealing the Pseudo-Intercalation Charge Storage Mechanism of MXenes in Acidic Electrolyte. \u003cem\u003eADVANCED FUNCTIONAL MATERIALS \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e29\u003c/em\u003e (29), 1902953.\u003c/li\u003e\n\u003cli\u003eChen, X. F.; Zhu, Y. Z.; Zhang, M.; Sui, J. Y.; Peng, W. C.; Li, Y.; Zhang, G. L.; Zhang, F. B.; Fan, X. B., N-Butyllithium-Treated Ti3C2Tx MXene with Excellent Pseudocapacitor Performance. \u003cem\u003eACS NANO \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e13\u003c/em\u003e (8), 9449-9456.\u003c/li\u003e\n\u003cli\u003eLi, L.; Meng, J.; Bao, X. R.; Huang, Y. P.; Yan, X. P.; Qian, H. L.; Zhang, C.; Liu, T. X., Direct-Ink-Write 3D Printing of Programmable Micro-Supercapacitors from MXene-Regulating Conducting Polymer Inks. \u003cem\u003eADVANCED ENERGY MATERIALS \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e13\u003c/em\u003e (9), 2203683.\u003c/li\u003e\n\u003cli\u003eOtgonbayar, Z.; Yang, S. H. Y.; Kim, I. J.; Oh, W. C., Recent advances in 2D MXene and solid state electrolyte for energy storage applications: Comprehensive review. \u003cem\u003eCHEMICAL ENGINEERING JOURNAL \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e472\u003c/em\u003e, 144801.\u003c/li\u003e\n\u003cli\u003eShaikh, N. S.; Ubale, S. B.; Mane, V. J.; Shaikh, J. S.; Lokhande, V. C.; Praserthdam, S.; Lokhande, C. D.; Kanjanaboos, P., Novel electrodes for supercapacitor: Conducting polymers, metal oxides, chalcogenides, carbides, nitrides, MXenes, and their composites with graphene. \u003cem\u003eJOURNAL OF ALLOYS AND COMPOUNDS \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e893\u003c/em\u003e, 161998.\u003c/li\u003e\n\u003cli\u003eLuo, Y. J.; Que, W. X.; Bin, X. Q.; Xia, C. J.; Kong, B. S.; Gao, B. W.; Kong, L. B., Flexible MXene-Based Composite Films: Synthesis, Modification, and Applications as Electrodes of Supercapacitors. \u003cem\u003eSMALL \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e18\u003c/em\u003e (27), 2201290.\u003c/li\u003e\n\u003cli\u003eYoon, Y.; Lee, M.; Kim, S. K.; Bae, G.; Song, W.; Myung, S.; Lim, J.; Lee, S. S.; Zyung, T.; An, K. S., A Strategy for Synthesis of Carbon Nitride Induced Chemically Doped 2D MXene for High-Performance Supercapacitor Electrodes. \u003cem\u003eADVANCED ENERGY MATERIALS \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e8\u003c/em\u003e (15), 1703173.\u003c/li\u003e\n\u003cli\u003eCai, M.; Wei, X. C.; Huang, H. F.; Yuan, F. L.; Li, C.; Xu, S. K.; Liang, X. Q.; Zhou, W. Z.; Guo, J., Nitrogen-doped Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003ex\u003c/sub\u003e MXene prepared by thermal decomposition of ammonium salts and its application in flexible quasi-solid-state supercapacitor. \u003cem\u003eCHEMICAL ENGINEERING JOURNAL \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e458\u003c/em\u003e, 141338.\u003c/li\u003e\n\u003cli\u003eTian, Y. P.; Ju, M. M.; Luo, Y. J.; Bin, X. Q.; Lou, X. J.; Que, W. X., In situ oxygen doped Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003cem\u003e\u003csub\u003ex\u003c/sub\u003e\u003c/em\u003e MXene flexible film as supercapacitor electrode. \u003cem\u003eCHEMICAL ENGINEERING JOURNAL \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e446\u003c/em\u003e, 137451.\u003c/li\u003e\n\u003cli\u003eNasrin, K.; Sudharshan, V.; Subramani, K.; Karnan, M.; Sathish, M., In-Situ Synergistic 2D/2D MXene/BCN Heterostructure for Superlative Energy Density Supercapacitor with Super-Long Life. \u003cem\u003eSMALL \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e18\u003c/em\u003e (4), 2106051.\u003c/li\u003e\n\u003cli\u003eLi, J.; Yuan, X. T.; Lin, C.; Yang, Y. Q.; Xu, L.; Du, X.; Xie, J. L.; Lin, J. H.; Sun, J. L., Achieving High Pseudocapacitance of 2D Titanium Carbide (MXene) by Cation Intercalation and Surface Modification. \u003cem\u003eADVANCED ENERGY MATERIALS \u003c/em\u003e\u003cstrong\u003e2017,\u003c/strong\u003e \u003cem\u003e7\u003c/em\u003e (15), 1602725.\u003c/li\u003e\n\u003cli\u003eChen, H. W.; Ma, H. Y.; Li, C., Host-Guest Intercalation Chemistry in MXenes and Its Implications for Practical Applications. \u003cem\u003eACS NANO \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e15\u003c/em\u003e (10), 15502-15537.\u003c/li\u003e\n\u003cli\u003eLi, Z. J.; Dai, J.; Li, Y. R.; Sun, C. L.; Meng, A. L.; Cheng, R. F.; Zhao, J.; Hu, M. M.; Wang, X. H., Intercalation-deintercalation design in MXenes for high-performance supercapacitors. \u003cem\u003eNANO RESEARCH \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e15\u003c/em\u003e (4), 3213-3221.\u003c/li\u003e\n\u003cli\u003eLyu, S. L.; Guo, C. X.; Wang, J. N.; Li, Z. J.; Yang, B.; Lei, L. C.; Wang, L. P.; Xiao, J. P.; Zhang, T.; Hou, Y., Exceptional catalytic activity of oxygen evolution reaction via two-dimensional graphene multilayer confined metal-organic frameworks. \u003cem\u003eNATURE COMMUNICATIONS \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e13\u003c/em\u003e (1), 6171.\u003c/li\u003e\n\u003cli\u003eYin, X. D.; Zheng, W.; Tang, H. F.; Zhang, P. G.; Sun, Z. M., Novel 2D/2D 1T-MoS2/Ti3C2Tz heterostructures for high-voltage symmetric supercapacitors. \u003cem\u003eNANOSCALE \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e15\u003c/em\u003e (24), 10437-10446.\u003c/li\u003e\n\u003cli\u003eNightingale, E. R., PHENOMENOLOGICAL THEORY OF ION SOLVATION - EFFECTIVE RADII OF HYDRATED IONS. \u003cem\u003eJOURNAL OF PHYSICAL CHEMISTRY \u003c/em\u003e\u003cstrong\u003e1959,\u003c/strong\u003e \u003cem\u003e63\u003c/em\u003e (9), 1381-1387.\u003c/li\u003e\n\u003cli\u003eChao, D. L.; Zhou, W. H.; Xie, F. X.; Ye, C.; Li, H.; Jaroniec, M.; Qiao, S. Z., Roadmap for advanced aqueous batteries: From design of materials to applications. \u003cem\u003eSCIENCE ADVANCES \u003c/em\u003e\u003cstrong\u003e2020,\u003c/strong\u003e \u003cem\u003e6\u003c/em\u003e (21), eaba4098.\u003c/li\u003e\n\u003cli\u003eMathis, T. S.; Maleski, K.; Goad, A.; Sarycheva, A.; Anayee, M.; Foucher, A. C.; Hantanasirisakul, K.; Shuck, C. E.; Stach, E. A.; Gogotsi, Y., Modified MAX Phase Synthesis for Environmentally Stable and Highly Conductive Ti\u0026lt;sub\u0026gt;3\u0026lt;/sub\u0026gt;C\u0026lt;sub\u0026gt;2\u0026lt;/sub\u0026gt; MXene. \u003cem\u003eACS NANO \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e15\u003c/em\u003e (4), 6420-6429.\u003c/li\u003e\n\u003cli\u003eLi, H. S.; Xu, K.; Chen, P. H.; Yuan, Y. Y.; Qiu, Y.; Wang, L. G.; Zhu, L.; Wang, X. G.; Cai, G. H.; Zheng, L. M.; Dai, C.; Zhou, D.; Zhang, N. A.; Zhu, J. X.; Xie, J. L.; Liao, F. H.; Peng, H. L.; Peng, Y.; Ju, J.; Lin, Z. F.; Sun, J. L., Achieving ultrahigh electrochemical performance by surface design and nanoconfined water manipulation. \u003cem\u003eNATIONAL SCIENCE REVIEW \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e9\u003c/em\u003e (6), nwac079.\u003c/li\u003e\n\u003cli\u003eLiang, K.; Matsumoto, R. A.; Zhao, W.; Osti, N. C.; Popov, I.; Thapaliya, B. P.; Fleischmann, S.; Misra, S.; Prenger, K.; Tyagi, M.; Mamontov, E.; Augustyn, V.; Unocic, R. R.; Sokolov, A. P.; Dai, S.; Cummings, P. T.; Naguib, M., Engineering the Interlayer Spacing by Pre-Intercalation for High Performance Supercapacitor MXene Electrodes in Room Temperature Ionic Liquid. \u003cem\u003eADVANCED FUNCTIONAL MATERIALS \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e31\u003c/em\u003e (33), 2104007.\u003c/li\u003e\n\u003cli\u003eZhao, L.; Fan, L. Z.; Zhou, M. Q.; Guan, H.; Qiao, S. Y.; Antonietti, M.; Titirici, M. M., Nitrogen-Containing Hydrothermal Carbons with Superior Performance in Supercapacitors. \u003cem\u003eADVANCED MATERIALS \u003c/em\u003e\u003cstrong\u003e2010,\u003c/strong\u003e \u003cem\u003e22\u003c/em\u003e (45), 5202-5206.\u003c/li\u003e\n\u003cli\u003eWang, Y. M.; Wang, X.; Li, X. F.; Li, X. L.; Liu, Y.; Bai, Y.; Xiao, H. H.; Yuan, G. H., A High-Performance, Tailorable, Wearable, and Foldable Solid-State Supercapacitor Enabled by Arranging Pseudocapacitive Groups and MXene Flakes on Textile Electrode Surface. \u003cem\u003eADVANCED FUNCTIONAL MATERIALS \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e31\u003c/em\u003e (7), 2008185.\u003c/li\u003e\n\u003cli\u003eK\u0026ouml;tz, R.; Carlen, M., Principles and applications of electrochemical capacitors. \u003cem\u003eELECTROCHIMICA ACTA \u003c/em\u003e\u003cstrong\u003e2000,\u003c/strong\u003e \u003cem\u003e45\u003c/em\u003e (15-16), 2483-2498.\u003c/li\u003e\n\u003cli\u003eChen, C. M.; Zhang, Q.; Yang, M. G.; Huang, C. H.; Yang, Y. G.; Wang, M. Z., Structural evolution during annealing of thermally reduced graphene nanosheets for application in supercapacitors. \u003cem\u003eCARBON \u003c/em\u003e\u003cstrong\u003e2012,\u003c/strong\u003e \u003cem\u003e50\u003c/em\u003e (10), 3572-3584.\u003c/li\u003e\n\u003cli\u003eAnjum, M. A. R.; Lee, M. H.; Lee, J. S., Boron- and Nitrogen-Codoped Molybdenum Carbide Nanoparticles Imbedded in a BCN Network as a Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution Reactions. \u003cem\u003eACS CATALYSIS \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e8\u003c/em\u003e (9), 8296-8305.\u003c/li\u003e\n\u003cli\u003eMeng, F. K.; Hu, E. Y.; Zhang, L. H.; Sasaki, K.; Muckerman, J. T.; Fujita, E., Biomass-derived high-performance tungsten-based electrocatalysts on graphene for hydrogen evolution. \u003cem\u003eJOURNAL OF MATERIALS CHEMISTRY A \u003c/em\u003e\u003cstrong\u003e2015,\u003c/strong\u003e \u003cem\u003e3\u003c/em\u003e (36), 18572-18577.\u003c/li\u003e\n\u003cli\u003eZhang, Z. R.; Yao, Z. P.; Li, Y.; Lu, S. T.; Wu, X. H.; Jiang, Z. H., Cation-induced Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003ex\u003c/sub\u003e MXene hydrogel for capacitive energy storage. \u003cem\u003eCHEMICAL ENGINEERING JOURNAL \u003c/em\u003e\u003cstrong\u003e2022,\u003c/strong\u003e \u003cem\u003e433\u003c/em\u003e, 134488.\u003c/li\u003e\n\u003cli\u003eRezakazemi, M.; Shamsabadi, A. A.; Lin, H. Q.; Luis, P.; Ramakrishna, S.; Aminabhavi, T. M., Sustainable MXenes-based membranes for highly energy-efficient separations. \u003cem\u003eRENEWABLE \u0026amp; SUSTAINABLE ENERGY REVIEWS \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e143\u003c/em\u003e, 110878.\u003c/li\u003e\n\u003cli\u003eLi, K.; Wang, X. H.; Li, S.; Urbankowski, P.; Li, J. M.; Xu, Y. X.; Gogotsi, Y., An Ultrafast Conducting Polymer@MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors. \u003cem\u003eSMALL \u003c/em\u003e\u003cstrong\u003e2020,\u003c/strong\u003e \u003cem\u003e16\u003c/em\u003e (4), 1906851.\u003c/li\u003e\n\u003cli\u003eCui, Y. H.; Shi, Q. S.; Liu, Z.; Lv, J. C.; Wang, C.; Xie, X. B.; Zhang, S. H., MXene/biomass/chitosan carbon aerogel (MBC) with shared cathode and anode for the construction of high-efficiency asymmetric supercapacitor. \u003cem\u003eCHEMICAL ENGINEERING JOURNAL \u003c/em\u003e\u003cstrong\u003e2023,\u003c/strong\u003e \u003cem\u003e472\u003c/em\u003e, 144701.\u003c/li\u003e\n\u003cli\u003eXiong, T.; Lee, W. S. V.; Huang, X. L.; Xue, J. M., Mn3O4/reduced graphene oxide based supercapacitor with ultra-long cycling performance. \u003cem\u003eJOURNAL OF MATERIALS CHEMISTRY A \u003c/em\u003e\u003cstrong\u003e2017,\u003c/strong\u003e \u003cem\u003e5\u003c/em\u003e (25), 12762-12768.\u003c/li\u003e\n\u003cli\u003eHu, Y. T.; Guan, C.; Ke, Q. Q.; Yow, Z. F.; Cheng, C. W.; Wang, J., Hybrid Fe2O3 Nanoparticle Clusters/rGO Paper as an Effective Negative Electrode for Flexible Supercapacitors. \u003cem\u003eCHEMISTRY OF MATERIALS \u003c/em\u003e\u003cstrong\u003e2016,\u003c/strong\u003e \u003cem\u003e28\u003c/em\u003e (20), 7296-7303.\u003c/li\u003e\n\u003cli\u003eYue, S. H.; Tong, H.; Lu, L.; Tang, W. W.; Bai, W. L.; Jin, F. Q.; Han, Q. W.; He, J. P.; Liu, J.; Zhang, X. G., Hierarchical NiCo2O4 nanosheets/nitrogen doped graphene/carbon nanotube film with ultrahigh capacitance and long cycle stability as a flexible binder-free electrode for supercapacitors. \u003cem\u003eJOURNAL OF MATERIALS CHEMISTRY A \u003c/em\u003e\u003cstrong\u003e2017,\u003c/strong\u003e \u003cem\u003e5\u003c/em\u003e (2), 689-698.\u003c/li\u003e\n\u003cli\u003eLi, L.; Zhang, N.; Zhang, M. Y.; Zhang, X. T.; Zhang, Z. G., Flexible Ti3C2Tx/PEDOT:PSS films with outstanding volumetric capacitance for asymmetric supercapacitors. \u003cem\u003eDALTON TRANSACTIONS \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e48\u003c/em\u003e (5), 1747-1756.\u003c/li\u003e\n\u003cli\u003eZheng, W.; Halim, J.; El Ghazaly, A.; Etman, A. S.; Tseng, E. N.; Persson, P. O. A.; Rosen, J.; Barsoum, M. W., Flexible Free-Standing MoO3/Ti3C2Tz MXene Composite Films with High Gravimetric and Volumetric Capacities. \u003cem\u003eADVANCED SCIENCE \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e8\u003c/em\u003e (3), 2003656.\u003c/li\u003e\n\u003cli\u003eNavarro-Suarez, A. M.; Van Aken, K. L.; Mathis, T.; Makaryan, T.; Yan, J.; Carretero-Gonzalez, J.; Rojo, T.; Gogotsi, Y., Development of asymmetric supercapacitors with titanium carbide-reduced graphene oxide couples as electrodes. \u003cem\u003eELECTROCHIMICA ACTA \u003c/em\u003e\u003cstrong\u003e2018,\u003c/strong\u003e \u003cem\u003e259\u003c/em\u003e, 752-761.\u003c/li\u003e\n\u003cli\u003eZhang, L. N.; Han, D. L.; Tao, Y.; Cui, C. J.; Deng, Y. Q.; Dong, X. M.; Lv, W.; Lin, Z. F.; Wu, S. C.; Weng, Z.; Yang, Q. H., Dense organic molecules/graphene network anodes with superior volumetric and areal performance for asymmetric supercapacitors. \u003cem\u003eJOURNAL OF MATERIALS CHEMISTRY A \u003c/em\u003e\u003cstrong\u003e2020,\u003c/strong\u003e \u003cem\u003e8\u003c/em\u003e (1), 461-469.\u003c/li\u003e\n\u003cli\u003eZheng, W.; Halim, J.; Etman, A. S.; El Ghazaly, A.; Rosen, J.; Barsoum, M. W., Boosting the volumetric capacitance of MoO3-x free-standing films with Ti3C2 MXene. \u003cem\u003eELECTROCHIMICA ACTA \u003c/em\u003e\u003cstrong\u003e2021,\u003c/strong\u003e \u003cem\u003e370\u003c/em\u003e, 137665.\u003c/li\u003e\n\u003cli\u003eLi, J. M.; Kurra, N.; Seredych, M.; Meng, X.; Wang, H. Z.; Gogotsi, Y., Bipolar carbide-carbon high voltage aqueous lithium-ion capacitors. \u003cem\u003eNANO ENERGY \u003c/em\u003e\u003cstrong\u003e2019,\u003c/strong\u003e \u003cem\u003e56\u003c/em\u003e, 151-159.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"MXene, Restacking, Cation intercalation, Capacitance, Supercapacitor","lastPublishedDoi":"10.21203/rs.3.rs-4161663/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4161663/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMXenes are two-dimensional materials with high electrical conductivity, adjustable composition, and tunable surface terminations, endowing them with significant potential for supercapacitors (SCs). However, during etching preparation, the susceptibility to interlayer restacking and the attachment of inactive -F terminations reduce their capacitances and rate performance. To resolve these issues, electrochemistry-driven cation intercalation (ECI) followed by calcination is proposed to widen their interlayer spacing and modify surface chemistry simultaneously. Results show that the Mn-modified Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e exhibits an exceptionally high volumetric capacitance (1655.5 F cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e at 1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1.5 times higher than that of pristine Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e) and excellent rate performance (72.3% retention from 1 to 50 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) due to the unblocked interlayers and the increased -O terminations. Density Functional Theory (DFT) results reveal that the intercalated Mn\u003csup\u003e2+\u003c/sup\u003e displayed the largest formation energy difference, manifesting a great driving force to form active -O terminations, which is crucial for improving electrochemical performance. Kinetic analysis reveals that the intercalated Mn\u003csup\u003e2+\u003c/sup\u003e increases the termination-related capacitances (pseudocapacitance and diffusion-controlled capacitance) significantly. The asymmetric SCs assembled with Mn-intercalated Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e and nitrogen-doped activated carbon, show the combination of high energy densities at high powers (38.2 Wh L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 30.1 kW L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The findings clarify how metal cation intercalation affects MXene performance, providing insights for advancing MXene-based electrodes in energy storage applications.\u003c/p\u003e","manuscriptTitle":"Unraveling Cation Intercalation Mechanism in MXene for Enhanced Supercapacitor Performance","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-10 09:03:53","doi":"10.21203/rs.3.rs-4161663/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorAssigned","content":"","date":"2024-04-22T07:41:53+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-08T01:11:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advanced Composites and Hybrid Materials","date":"2024-03-25T08:10:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"advanced-composites-and-hybrid-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"achm","sideBox":"Learn more about [Advanced Composites and Hybrid Materials](https://link.springer.com/journal/42114)","snPcode":"42114","submissionUrl":"https://submission.nature.com/new-submission/42114/3","title":"Advanced Composites and Hybrid Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1801bdfb-8898-41de-9d09-82748ed47161","owner":[],"postedDate":"April 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-04-10T09:03:54+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-10 09:03:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4161663","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4161663","identity":"rs-4161663","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}