Synergistic Engineering of Fluorine Doping FexMn1-xMoO4/Graphene Heterojunction as Ultrahigh-Rate Anode for LIBs

Synergistic Engineering of Fluorine Doping FexMn1-xMoO4/Graphene Heterojunction as Ultrahigh-Rate Anode for LIBs | 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 Article Synergistic Engineering of Fluorine Doping Fe x Mn 1-x MoO 4 /Graphene Heterojunction as Ultrahigh-Rate Anode for LIBs Tianwei Liu, Xiaomin Chen, Huiling Chen, Caiyong Huang, Pu Yu, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9264724/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract The development of advanced anode materials is critical for high-energy and high-power lithium-ion batteries (LIBs). Conventional conversion-type anodes, such as transition metal molybdates, suffer from poor conductivity, severe volume expansion, and structural degradation, leading to rapid capacity fading. To overcome these limitations, we propose a synergistic design strategy that integrates heterojunction engineering with fluorine doping. A fluorine-doped, heterojunction-structured F-Fe x Mn 1−x MoO 4 /graphene (F-FMMO/G) was successfully synthesized via a facile solvothermal route. Structural characterizations confirm the formation of a well-defined FeMoO 4 /Mn 2 Mo 3 O 8 heterojunction with effective fluorine incorporation. When evaluated as an anode for LIBs, the F-FMMO/G composite exhibits an ultrahigh initial specific capacity of 1158 mAh g − 1 at 0.1 C and maintains 780 mAh g − 1 after 150 cycles, substantially outperforming the undoped counterpart. Notably, it delivers excellent rate performance, sustaining ~ 100 mAh g − 1 at 10 C and rapidly recovering to > 900 mAh g − 1 when cycled back to 0.1 C. The enhanced electrochemical performance is attributed to the synergistic effects of the built-in electric field at the heterojunction interface, which promotes rapid charge transfer, and fluorine doping, which optimizes the electronic structure and stabilizes the electrode–electrolyte interface. This study offers a rational design framework combining interfacial and bulk modifications for next-generation high-rate LIB anodes. Physical sciences/Chemistry Physical sciences/Energy science and technology Physical sciences/Materials science FexMn1−xMoO4/G anode materials fluorine doping ultrahigh rate heterojunction structure synergistic enhancement Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The growing demand for lithium-ion batteries (LIBs) with both high energy and power densities has spurred intense research into advanced anode materials beyond conventional graphite. Among the most promising candidates are transition metal oxides (TMOs) and molybdates, which offer high theoretical capacities via multi-electron conversion reactions 1 , 2 . However, their practical application is hindered by several intrinsic limitations, including low electronic conductivity, significant volume changes during lithiation/delithiation, and resulting structural pulverization and rapid capacity decay 3 , 4 . To address these challenges, heterojunction engineering has emerged as a key strategy in advanced electrode design. A heterojunction, formed at the interface between two semiconductors with distinct band structures, generates a built-in electric field that facilitates directional charge separation and transport. This interfacial electric field acts as a nanoscale ‘highway’, significantly enhancing charge-transfer kinetics and mitigating the conductivity bottleneck 5 , 6 . Additionally, the mechanical interplay between the constituent phases can relieve internal stress during cycling. One phase may serve as a structural buffer or conductive scaffold for the other, thereby reducing volume expansion and preserving structural integrity, which is critical for achieving long-term cyclability 7 , 8 . Notably, recent studies on Co 3 O 4 /ZnO, Fe 2 O 3 /SnO 2 , and NiCo 2 O 4 /MnO 2 heterostructures have demonstrated enhanced rate capability and improved mechanical stability compared to their single-phase analogs 9 – 11 . Elemental doping, particularly with anions such as fluorine (F), offers a complementary avenue for tailoring the physicochemical properties of electrode materials. F-doping induces lattice distortion, introduces oxygen vacancies, and modifies the electronic band structure, collectively improving both ionic and electronic conductivity 12 , 13 . Moreover, the formation of strong metal-fluorine (M–F) bonds at the surface generates a robust interfacial layer that stabilizes the solid-electrolyte interphase (SEI) and suppresses unwanted side reactions during extended cycling 14 , 15 . The combination of heterojunction engineering and targeted doping thus presents a synergistic strategy: the heterojunction enhances charge transport and structural resilience, while doping optimizes surface chemistry and electronic structure 16 , 17 . Iron molybdate (FeMoO 4 ) and manganese molybdate (MnMoO 4 ) are environmentally benign materials with high theoretical capacities, making them attractive for LIB anodes. Nevertheless, their individual electrochemical performance is limited by poor conductivity and structural degradation upon cycling 18 , 19 . A Fe x Mn 1−x MoO 4 -based heterojunction can leverage the benefits of both parent compounds. While molybdate-based heterostructures such as MoO 2 /MoS 2 and CoMoO 4 /NiMoO 4 have shown promise in boosting electrochemical kinetics 20 , the specific integration of a fluorine-doped FeMoO 4 /Mn 2 Mo 3 O 8 heterojunction with conductive graphene remains largely unexplored 21 . In this study, we design and synthesize a fluorine-doped, heterojunction-structured Fe x Mn 1−x MoO 4 /graphene (F-FMMO/G) nanocomposite via a facile solvothermal method. The work aims to elucidate how the combined strategies of heterojunction formation and fluorine doping jointly address the limitations of conversion-type anodes. We systematically investigate improvements in structural stability (e.g., buffered volume changes and robust SEI formation), charge transfer efficiency (e.g., reduced interfacial resistance and enhanced conductivity), and overall electrochemical kinetics. Advanced characterizations, supported by density functional theory (DFT) simulations, reveal the fundamental mechanisms underlying the ultrahigh-rate performance and superior cycling stability. This work establishes a rational design blueprint that couples interfacial and bulk modifications for next-generation high-power LIB anodes. Results and Discussions Thermal stability of the precursor Figure 1 a presents the TG-DSC curves of the FMMO precursor heated under N 2 from room temperature to 800 ℃, which reveals the thermal behavior and crystallization temperature. As the temperature increases, a gradual mass loss is observed, accompanied by endothermic behavior. A distinct exothermic peak appears at approximately 400 ℃, corresponding to the formation of crystalline phases and a sharp weight loss of over 7%, indicating a major decomposition and crystallization step associated with oxide phase formation. Following this step, a slower and continuous weight loss process ensues, resembling thermal behavior before 400 ℃. As heating continues, a second exothermic peak is detected at 730 ℃, suggesting the onset of more complex phase transformations. Based on these observations, a calcination temperature of 650 ℃ was selected to obtain well-crystallized products while avoiding the higher-temperature regime where more complex phase transformations may occur. XRD and Morphology Comparison of FMMOs Figure 1 b displays the X-ray diffraction (XRD) patterns of FMMO/G and F-FMMO/G composites calcined at 650 ℃. Both samples exhibit mixed-phase structures, indicating that neither is a single-phase material. The diffraction pattern of FMMO/G shows three prominent peaks: the reflections at 2θ ≈ 26.5° corresponding to the (220) plane of FeMoO 4 (JCPDS 22–628), while peaks at 37° and 53° corresponding to the (201) and (006) planes of Mn 2 Mo 3 O 8 (JCPDS 34–510), respectively. Upon fluorine doping, the F-FMMO/G sample exhibits enhanced crystallinity, as evidenced by increased peak intensity and additional diffraction peaks. In addition to the FeMoO 4 (220) peak, several new Mn 2 Mo 3 O 8 peaks appear at 15° (002), 25.5° (102), 36° (112), and 45° (203), indicating the formation of an improved crystallinity and ordered heterostructure. To further elucidate the structural evolution, Raman spectroscopy was conducted on both samples, as shown in Fig. 1 c. Both FMMO/G and F-FMMO/G exhibit characteristic D and G graphene bands at 1347 cm − 1 and 1597 cm − 1 , respectively. Notably, the relative intensity of these bands decreases after fluorine doping, indicating stronger coupling between the carbon framework and the fluorine-modified oxide matrix, along with changes in defect density within the carbon component. Peaks at 199 cm − 1 and 347 cm − 1 , attributed to the Fe–O stretching vibration and the triply degenerate bending vibration of the MoO 4 tetrahedra, respectively, are present in both samples. Upon fluorine doping, new peaks emerge in the Raman spectrum of F-FMMO/G: a prominent peak at 819 cm − 1 assigned to the asymmetric stretching vibration of MoO 4 tetrahedra 21 , as well as additional peaks at 931 cm − 1 and 992 cm − 1 corresponding to the symmetric stretching modes of terminal metal–oxygen (M = O) bonds. The appearance of these new peaks, combined with an overall increase in peak intensity, reflects enhanced crystallinity and a more mature phase structure in the fluorine-doped sample. Electrochemical Performance Electrochemical impedance spectroscopy (EIS) analysis of both samples is shown in Fig. 1 d. The Nyquist plots feature a depressed semicircle in the high-frequency region, indicative of charge-transfer resistance, and a linear tail in the low-frequency region, characteristic of Warburg impedance related to lithium-ion diffusion. As summarized in Table 1 , the charge-transfer resistance (R_ct) for F-FMMO/G is markedly lower (73.7 Ω) compared to FMMO/G (243 Ω). This substantial reduction in R_ct clearly demonstrates the enhanced electrical conductivity of the fluorine-doped heterostructure, consistent with the improved electronic transport indicated by Hall results and the enhanced defect signal in EPR, which contributes to its superior electrochemical performance. Table 1 Electrochemical impedance parameters and diffusion coefficients. Electrode R S (Ω) R ct (Ω) σ w Diffusion coefficient (cm 2 s − 1 ) FMMO/G 6.93 243 2.05E + 01 2.86E-14 F-FMMO/G 7.1 73.7 9.86E + 01 1.24E-15 Figure 2 a compares the cycling behavior at 0.1 C. Both samples exhibit high initial irreversible discharge capacities: 1045 mAh g − 1 for FMMO/G and 1158 mAh g − 1 for F-FMMO/G. The corresponding initial cycling curves are presented in Fig. 2 b. After the formation cycle, the fluorinated composite stabilizes at ~ 860 mAh g − 1 , which is the more representative reversible capacity for subsequent cycling. For FMMO/G, the capacity maintains a relatively stable capacity of 1016 mAh g − 1 , then gradually decays at a rate of approximately 0.2% per cycle over the first 80 cycles. After this point, the decay accelerates to 0.9% per cycle, resulting in a sharp capacity decline. By the 150th cycle, the capacity drops to 360 mAh g − 1 , which corresponds to only 35% of its initial value. In contrast, the fluorine-doped F-FMMO/G shows a different trend. After the initial capacity drop, the specific capacity gradually increases over the next 50 cycles, at a rate of 0.1% per cycle. This improvement is attributed to enhanced electrolyte infiltration and gradual activation of the electrode surface. Following this activation phase, a slow and steady capacity decay is observed. However, the F-FMMO/G retains significantly better stability than its undoped counterpart. After 150 cycles, it maintains a capacity of 780 mAh g − 1 , which is approximately 90% of its initial value and demonstrates excellent cycling durability. The rate performance of both samples is depicted in Fig. 2 c, where the behavior under varying current densities appears comparable. The F-FMMO/G electrode exhibits superior rate performance under the same testing conditions. To further evaluate high-rate capabilities, the F-FMMO/G electrode was subjected to extended cycling at 10 C, as shown in Fig. 2 d. During initial cycles at 0.1 C, the specific capacity exceeds 900 mAh g − 1 . Upon increasing the current density to 10 C, the capacity drops rapidly from 480 mAh g − 1 to 180 mAh g − 1 within 25 cycles and then stabilizes around 100 mAh g − 1 . Impressively, this stabilized capacity is sustained for over 200 cycles. When the current density is returned to 0.1 C, the capacity recovers to over 900 mAh g − 1 , indicating excellent structural robustness and rate-reversible capacity. These results confirm that F-FMMO/G exhibits outstanding rate capability and high structural integrity under extreme cycling conditions. Figure 3 a presents the cyclic voltammetry (CV) curves of FMMO/G and F-FMMO/G electrodes measured at a scan rate of 1 mV s − 1 within a voltage window of 0.01–3.0 V. FMMO/G exhibits no distinct redox peaks, showing only broad humps, which is characteristic of pseudocapacitive or amorphous-like behavior, consistent with our previous findings 22 . In contrast, the F-FMMO/G electrode displays two well-defined reduction peaks at 1.51 V and 1.26 V, along with corresponding oxidation peaks at 1.54 V and 1.78 V. These redox couples can be identified as follows: the pair at 1.78 V (oxidation) and 1.51 V (reduction) yields a potential separation (ΔV) of 0.27 V, while the pair at 1.54 V (oxidation) and 1.26 V (reduction) yields a ΔV of 0.28 V. The redox features in this voltage range can be attributed to stepwise conversion of the molybdate-containing phases involving reduction/oxidation of transition-metal centers (Fe/Mn/Mo) together with Li 2 O formation/decomposition and interfacial lithium storage on the graphene-coupled composite framework. The appearance of distinct and symmetric redox peaks in F-FMMO/G confirms improved electrochemical reversibility and well-defined redox kinetics after fluorine doping. Table 2 Hall effect results comparison of FMMO/G and F-FMMO/G. Anode Material Temperature (K) Resistivity (ohm·cm) Electron Mobility (cm 2 V − 1 S − 1 ) Carrier Concentration (1/cm 3 ) R H (cm 3 C − 1 ) FMMO/G 300 3.77E + 01 8.71E + 01 1.90E + 15 -3.29E + 03 F-FMMO/G 300 3.10E + 01 9.30E + 01 1.88E + 15 -3.72E + 03 To elucidate the intrinsic electronic structure modifications induced by fluorine doping, electron paramagnetic resonance (EPR) spectroscopy and Hall effect measurements were performed. As shown in Fig. 3 b, both samples exhibit a prominent EPR signal at g ≈ 2.001, typically attributed to unpaired electrons associated with oxygen vacancies and other defect states. Notably, the F-FMMO/G sample displays a significantly stronger signal than FMMO/G, indicating a higher concentration of paramagnetic centers, primarily oxygen vacancies, introduced by F − incorporation. This finding is consistent with the XPS analysis, which revealed modulation of Fe valence states, suggesting that fluorine doping effectively engineers the defect chemistry of the material. Complementary Hall effect measurements (Table 2 ) provide quantitative insight into the electronic transport properties. Both FMMO/G and F-FMMO/G exhibit negative Hall coefficients (R H ), confirming n-type semiconductor behavior with electrons as the dominant charge carriers. Following fluorine doping, the room-temperature resistivity of F-FMMO/G decreases from 3.77 × 10 1 Ω·cm to 3.10 × 10 1 Ω·cm, while electron mobility increases from 8.71 × 10 1 cm 2 V − 1 s − 1 to 9.30 × 10¹ cm² V − 1 s − 1 , while the carrier concentration remains relatively constant (~ 1.9 × 10 15 cm − 3 ). These results indicate that the primary role of fluorine doping is not to increase carrier density but to enhance carrier mobility within the lattice. This mobility enhancement is attributed to two key factors: (i) F-induced oxygen vacancies act as donor sites, donating electrons to the conduction band and reducing scattering events; and (ii) local electronic structure modification weakens Fe–O bonds, as evidenced by XPS, thereby lowering the energy barrier for electron hopping. Together, the EPR and Hall effect analyses confirm that fluorine doping functions as an effective electronic modulator. It simultaneously increases the density of active defect states and improves the efficiency of charge transport. This intrinsic conductivity enhancement, coupled with the built-in electric field at the heterojunction interface, underpins the significantly reduced charge-transfer resistance and outstanding high-rate capability observed in the F-FMMO/G anode. X-ray photoelectron spectroscopy (XPS) was employed to investigate survey results of F-FMMO/G and the changes in the oxidation states of Fe in FMMO/G and F-FMMO/G, as shown in Fig. 4 , with the corresponding quantitative data summarized in the inset table of Fig. 4 a and Table 3 . The F1s signal is detected with an atomic concentration of 0.9 at. %, confirming successful fluorine incorporation into the material. The Fe/Mn atomic ratio is approximately 1.05, consistent with the nominal stoichiometry of FeₓMn₁₋ₓMoO 4 (x ≈ 0.5). The relatively high carbon content (61.77 at. %) originates from both the intrinsic graphene component and surface-adsorbed adventitious carbon, which is commonly observed in air-exposed carbon-containing samples. The Fe 2p spectra of both samples can be deconvoluted into characteristic Fe 2+ and Fe 3+ doublets, indicating the coexistence of mixed valence states. Notably, the Fe 2+ /Fe 3+ ratio increases from 1.59 in FMMO/G to 1.71 in F-FMMO/G, demonstrating that fluorine doping effectively modulates the Fe valence distribution. This increase in the Fe 2+ fraction is consistent with the higher initial specific capacity observed for the fluorine-doped sample. In addition to the change in valence states, a systematic shift of Fe 2p binding energies toward lower values is observed after fluorine doping, indicating a weakened Fe–O bonding environment. The reduced bond strength lowers the energy barrier for Li⁺ insertion and extraction, thereby facilitating lithium-ion intercalation kinetics. Furthermore, the modified surface electronic structure is expected to promote more favorable interfacial charge-transfer processes, contributing to the enhanced electrochemical performance of the F-FMMO/G electrode. Table 3 Fe 2p XPS valence distribution. Electrode orbit B.E. XPS AREA AREA RATIO FMMO/G Fe 2+ 2p 3/2 710.8 10300 Fe 2+ /Fe 3+ =1.59 Fe 2+ 2p 1/2 724 5150 Fe 3+ 2p 3/2 712.8 6468 Fe 3+ 2p 1/2 726.5 3234 F-FMMO/G Fe 2+ 2p 3/2 710.46 5724 Fe 2+ /Fe 3+ =1.71 Fe 2+ 2p 1/2 723.46 2862 Fe 3+ 2p 3/2 712.53 3346 Fe 3+ 2p 1/2 726.02 1673 The high-resolution transmission electron microscopy (HR-TEM) images in Fig. 5 reveal the stacked nanosheet structure of the F-FMMO/G composite. Despite being composed of two heterophase structures, well-defined crystalline fringes are clearly observed, indicating the high crystallinity of the final product. In Fig. 5 a, lattice fringes corresponding to the (101) and (112) planes of Mn 2 Mo 3 O 8 (JCPDS 34–510) are observed, intersecting at an angle of approximately 89°, consistent with the expected crystallographic orientation. Figure 5 b shows the presence of the (220) plane of FeMoO 4 (JCPDS 22–628), while Fig. 5 c reveals the (002) and (101) planes of Mn 2 Mo 3 O 8 . Selected area electron diffraction (SAED) analysis, shown in Fig. 5 d, further supports these findings. The diffraction pattern exhibits clear and distinct spots arranged in concentric rings, which, together with other evidence provided earlier, confirms the polycrystalline nature of the heterostructure. Specifically, the first and third rings correspond to the (002) and (112) planes of Mn 2 Mo 3 O 8 , while the second ring is assigned to the (220) plane of FeMoO 4 . These results collectively validate the coexistence of both crystalline phases in the fluorine-doped composite, which can provide abundant contact regions for charge transfer and mechanical buffering during cycling. In addition, a thin amorphous layer is observed at the outer edge of the HR-TEM images. This layer is expected to facilitate lithium-ion insertion and extraction by providing a more accessible surface and flexible interface between the electrode and electrolyte, potentially contributing to the improved electrochemical kinetics of the F-FMMO/G anode. Theoretical Calculation Results To investigate the atomic-scale charge redistribution and electronic structure at the heterojunction interface, we constructed an interface model between the FeMoO 4 (220) and Mn 2 Mo 3 O 8 (112) planes. Differential charge density analysis, shown in Fig. 6 a, illustrates the spatial distribution of electron transfer at the interface. The cyan and yellow isosurfaces represent regions of electron depletion and accumulation, respectively. A clear electron accumulation is observed on the Mn 2 Mo 3 O 8 side, while electron depletion occurs on the adjacent FeMoO 4 region. This asymmetric charge redistribution indicates spontaneous electron transfer from FeMoO 4 to Mn 2 Mo 3 O 8 upon contact, generating a built-in electric field directed from the electron-rich Mn 2 Mo 3 O 8 to the electron-deficient FeMoO 4 . This interfacial electric field is critical for enhancing charge separation and facilitating Li⁺ migration during electrochemical cycling. It also contributes to the reduced interfacial charge-transfer resistance, in agreement with the EIS results (Table 1 ). Furthermore, the electronic band structure of the heterojunction was analyzed, as shown in Fig. 6 b. Notably, the calculated band gap for the integrated FeMoO 4 /Mn 2 Mo 3 O 8 heterojunction is approximately 0 eV, indicating a quasi-metallic character. The valence band maximum (VBM, − 0.9884 eV) and conduction band minimum (CBM, − 0.9854 eV) are nearly degenerate, resulting in an almost negligible energy barrier for electron excitation. This near-zero band gap is of critical importance for charging transport, as it allows thermal excitation of electrons from the valence band to the conduction band with minimal energy input. Consequently, the intrinsic carrier concentration is expected to be several orders of magnitude higher than that of conventional semiconductors with typical band gaps exceeding 1 eV. This dramatically enhanced bulk electronic conductivity offers a fundamental explanation for the superior rate performance of the F-FMMO/G composite, enabling rapid and efficient electron transport throughout the electrode under high-current operating conditions. Collectively, the DFT results reveal a dual enhancement mechanism that underlies the exceptional electrochemical performance of the F-FMMO/G composite. First, interfacial engineering plays a critical role: the spontaneous charge transfer at the FeMoO 4 /Mn 2 Mo 3 O 8 interface establishes a built-in electric field, which effectively facilitates both ion and electron transport across the heterojunction and significantly lowers interfacial resistance. Second, bulk property modulation is achieved through heterostructure formation, which induces a quasi-metallic electronic structure characterized by a near-zero band gap. This leads to a substantial increase in intrinsic electronic conductivity throughout the bulk material. The synergistic interplay between interfacial charge modulation and enhanced bulk conductivity, enabled by the rational design of the heterojunction architecture, is the key to the ultrahigh-rate capability demonstrated by the F-FMMO/G anode. This dual mechanism provides a compelling design strategy for the development of next-generation high-performance lithium-ion battery materials. Conclusions In summary, a fluorine-doped Fe x Mn 1−x MoO 4 /graphene (F-FMMO/G) heterojunction nanocomposite was successfully developed as an ultrahigh-rate anode material for lithium-ion batteries (LIBs) through a synergistic design strategy. This approach effectively combines the advantages of heterojunction engineering and fluorine anion doping to address the intrinsic limitations of conventional conversion-type anodes. The in-situ formation of a heterojunction between FeMoO 4 and Mn 2 Mo 3 O 8 phases generates a built-in electric field that significantly enhances charge-transfer kinetics, as evidenced by the substantial reduction in charge-transfer resistance (73.7 Ω for F-FMMO/G vs. 243 Ω for the undoped sample). Simultaneously, fluorine doping modulates the local bonding environment by weakening Fe–O interactions, thereby facilitating Li + diffusion and improving both structural robustness and interfacial stability during cycling. As a result, the F-FMMO/G anode delivers outstanding electrochemical performance, including an ultrahigh reversible capacity of 1158 mAh g − 1 at 0.1 C, excellent cycling stability with 90% capacity retention after 150 cycles, and superior rate capability, maintaining structural integrity under prolonged operation at 10 C with rapid capacity recovery. Complementary density functional theory (DFT) calculations reveal a dual enhancement mechanism: spontaneous interfacial charge transfer generates a favorable electric field for ion/electron transport, while heterostructure formation leads to a quasi-metallic electronic structure with a near-zero band gap, significantly improving bulk conductivity. This work not only introduces a high-performance anode material but also elucidates the synergistic mechanism between interfacial and bulk-level modifications. The design principle demonstrated here—integrating interfacial charge modulation with electronic structure engineering via elemental doping—offers a powerful and generalizable strategy for the development of next-generation high-power energy storage systems. Experimental Material Synthesis Fe x Mn 1−x MoO 4 /G and F-Fe x Mn 1−x MoO 4 /G composites were synthesized via a solvothermal method. First, 1 mmol of (NH 4 ) 6 Mo 7 O 24 (Fisher Chemical, Laboratory Grade) was dissolved in a mixed solvent of ethylene glycol (EG) and deionized water (EG: H₂O = 2:1 by volume) to prepare solution A, followed by stirring for 30 minutes. Separately, 3.5 mmol of FeCl 2 ·4H 2 O (Sigma-Aldrich, 99.5%) and 3.5 mmol of MnCl 2 ·H 2 O (Sigma-Aldrich, 99.5%) were dissolved in 30 mL of distilled water to form solution B. After stirring solution B for 1 hour, it was added dropwise to solution A under vigorous stirring. The mixture was then stirred continuously for 4 hours. Subsequently, 10 mL of a pre-prepared graphene oxide (GO) dispersion (2 mg mL − 1 ) was added dropwise to the resulting solution, followed by an additional hour of stirring. The GO was synthesized according to a previously reported method 23 . Then, 0.48 mmol of NH 4 F (Fisher Chemical, > 98%) was added, and the mixture was stirred for another 5 minutes to ensure homogeneity before the solvothermal reaction. The final solution was transferred into a 100 mL Teflon-lined stainless-steel autoclave, sealed, and maintained at 180 ℃ for 20 hours. After the reaction, the autoclave was allowed to cool naturally to room temperature. The resulting precipitate was collected, washed thoroughly with deionized water several times, and dried at 60 ℃ under vacuum for 12 hours. The dried product was then sintered at 650 ℃ for 8 hours in an argon atmosphere to obtain the fluorine-doped heterojunction composite, designated as F-FMMO/G. For comparison, a non-doped control sample (FMMO/G) was synthesized using the same procedure, excluding the addition of NH 4 F. Material Characterization Thermal stability was assessed using thermogravimetric-differential scanning calorimetry (TG-DSC) on a NETZSCH STA 449C instrument. Samples were heated in an N₂ atmosphere at a rate of 5 ℃ min − 1 . Crystal structure analysis was conducted via powder X-ray diffraction (XRD) using a Bruker D8 Advance diffractometer with Cu Kα radiation (λ = 0.154 nm) over a 2θ range of 10° to 80°. Electrochemical properties were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), performed on a Chenhua CHI660E workstation. The EIS tests used an AC amplitude of ± 5 mV over a frequency range of 10 2 to 10 6 Hz. X-ray photoelectron spectroscopy (XPS) was carried out on a ThermoFisher ESCALAB Xi+ instrument with Al Kα radiation (hv = 1486.6 eV), under a base pressure of 8 × 10 − 10 Pa. All binding energies were referenced to the C 1s peak at 284.8 eV. Raman spectra were obtained using a Thermo DXi confocal Raman spectrometer with a 532 nm excitation source at 300 K. Electron paramagnetic resonance (EPR) spectra were recorded on a Bruker E500 system. The microwave frequency: X-band, ranging from 9.3 GHz to 9.9 GHz (with automatic tuning). Magnetic field range: 0 to 1.4 Tesla (0–14,000 Gauss). All measurements were conducted at room temperature unless otherwise specified. Electrochemical Performance Characterization The electrochemical performance of FMMO/G and F-FMMO/G was evaluated using 2032-type coin half-cells. The electrolyte consisted of 1.0 M LiPF 6 in a 1:1 (v/v) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). A polypropylene microporous membrane (Celgard 2500) was used as the separator. Electrodes were prepared by blending active material, Super P conductive carbon, and poly (vinylidene fluoride) (PVDF) binder in a weight ratio of 8:1:1. The resulting slurry was coated onto copper foil, dried overnight at 65 ℃ under vacuum, and punched into circular electrodes with a diameter of 14 mm. The weight of active material per anode is 5 ~ 6 mg. Coin cells were assembled in an argon-filled glovebox. Galvanostatic charge–discharge tests were carried out on a LAND CT2001A multichannel battery tester (Wuhan, China) at various current densities within a voltage window of 0.01–3 V (vs. Li + /Li) at room temperature. Theoretical Calculation All first-principles calculations were performed within the framework of density functional theory (DFT) using the Vienna Ab initio Simulation Package (VASP 6.3.0) 24–26 . The exchange-correlation interactions were treated using the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) functional 27 . Interactions between core and valence electrons were described using the projector augmented wave (PAW) method with standard pseudopotentials 28 . A 3 × 2 × 1 Monkhorst–Pack k-point grid was used for Brillouin zone sampling, and a plane-wave cutoff energy of 500 eV was applied. The atomic structures were fully relaxed until the total energy convergence threshold reached 10 − 6 eV and the maximum residual force on each atom was less than 0.03 eV/Å. To account for the localized nature of d-electrons in the transition metals, the DFT + U method was employed. Effective Hubbard U values were set to 2.5 eV for both Mn and Fe, and 2.0 eV for Mo. Declarations Acknowledgments We would like to thank the funding support from Excellent Youth Project of Hunan Provincial Department of Education (Project No.: 23B0772). Author contributions statement T.L. conceived and designed the experiments; T.L., X.C., H.C., and C.H. performed the synthesis and characterization; T.L., P.Y., and W.T. conducted the electrochemical measurements and analyzed the data; T.L. and W.T. performed the DFT calculations; T.L. and W.T. wrote the manuscript; T.L. and W.T. supervised the project. All authors reviewed and approved the final manuscript. Data availability: Data will be made available on request from the corresponding author upon reasonable request. Competing interests: The authors declare no conflicts of interest. References Zhang, D. et al. MnO Nanoparticles Attached to S, N Co-Doped Carbon Skeleton as a High-Rate Performance Anode Material. Molecules 29 , 4306. 10.3390/molecules29184306 (2024). Concisely Constructing S, F Co-Modified. Du, J. et al. Graphene Doped with Transition Metal Oxides: Enhancement of Anode Performance in Lithium-Ion Batteries. Metals 15 , 387. 10.3390/met15040387 (2025). 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Highly reversible lithium storage in porous SnO 2 nanotubes with coaxially grown carbon nanotube overlayers. Adv. Mater. 18 , 645–649. 10.1002/adma.200501883 (2006). Hoster, H. E., Zhang, G., Yu, L., Wu, H. B. & Lou, D. X. W. Formation of ZnMn 2 O 4 ball-in-ball hollow microspheres as a high-performance anode for lithium-ion batteries. Adv. Mater. 24 , 4609–4613. 10.1002/adma.201201779 (2012). Yuan, C. et al. Ultrathin mesoporous NiCo 2 O 4 nanosheets supported on Ni foam as advanced electrodes for supercapacitors. Adv. Funct. Mater. 22 , 4592–4597. 10.1002/adfm.201200994 (2012). Liu, T. et al. Approaching theoretical specific capacity of iron-rich lithium iron silicate using graphene-incorporation and fluorine-doping. J. Mater. Chem. A . 10 , 4006–4014. 10.1039/D1TA09417C (2022). Wang, J., Zhang, Q., Han, P., Luo, J. & Peng, K. Q. An S-Infused/S, F-Codoped PVDF-Derived Carbon as a High-Performance Anode for Sodium-Ion Batteries. Materials 18 , 4018. 10.3390/ma18174018 (2025). Etacheri, V., Marom, R., Elazari, R., Salitra, G. & Aurbach, D. Challenges in the development of advanced Li-ion batteries: a review. Energy Environ. Sci. 4 , 3243–3262. 10.1039/clee01598b (2011). Xu, K. Electrolytes and interphases in Li-ion batteries and beyond. Chem. Rev. 114 , 11503–11618. 10.1021/cr500003w (2014). Wu, H. B., Chen, J. S., Hng, H. H. & Lou, X. W. D. Nanostructured metal oxide-based materials as advanced anodes for lithium-ion batteries. Nanoscale 4 , 2526–2542. 10.1039/C2NR11966H (2012). Bruce, P. G., Scrosati, B. & Tarascon, J. M. Nanomaterials for rechargeable lithium batteries. Angew. Chem. Int. Ed. 47 , 2930–2946. 10.1002/anie.200702505 (2008). Massé, R. C., Liu, C., Li, Y., Mai, L. & Cao, G. Energy storage through intercalation reactions: electrodes for rechargeable batteries. Natl. Sci. Rev. 4 , 26–53. 10.1093/nsr/nww093 (2017). Yadav, J. K., Rani, B., Saini, P. & Dixit, A. Rechargeable iron-ion (Fe-ion) batteries: recent progress, challenges, and perspectives. Energy Adv. 3 , 927–944. 10.1039/D4YA00101J (2024). Yuan, L. et al. High-performance electrodes based on metal-organic framework-templated bimetallic molybdate on graphene-decorated nickel foam. J. Electroanal. Chem. 119791 10.1016/j.jelechem.2026.119791 (2026). Huu, H. T. & Im, W. B. Facile green synthesis of pseudocapacitance-contributed ultrahigh capacity Fe 2 (MoO 4 ) 3 as an anode for lithium-ion batteries. ACS Appl. Mater. Interfaces . 12 , 35152–35163. 10.1021/acsami.0c11862 (2020). Liu, T., Liu, Y., Niu, C. & Chao, Z. S. Pseudocapacitive contribution in amorphous FeVO 4 cathode for lithium-ion batteries. ChemElectroChem 9, e202101493, (2022). 10.1002/celc.202101493 Li, Z. F. et al. Fabrication of high-surface-area graphene/polyaniline nanocomposites and their application in supercapacitors. ACS Appl. Mater. Interfaces . 5 , 2685–2691. 10.1021/am4001634 (2013). Vienna, U. o. Vienna Ab initio Simulation Package (VASP 6.2.0) , (2020). https://www.vasp.at/ Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B . 54 , 11169. 10.1103/PhysRevB.54.11169 (1996). Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B . 59 , 1758. 10.1103/PhysRevB.59.1758 (1999). Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77 , 3865 (1996). Blochl, P., Blöchl, E. & Blöchl, P. E. Projected augmented-wave method. Phys. Rev. B . 50 , 17953–17979. 10.1103/PhysRevB.50.17953 (1994). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 24 Apr, 2026 Reviews received at journal 23 Apr, 2026 Reviewers agreed at journal 11 Apr, 2026 Reviews received at journal 06 Apr, 2026 Reviewers agreed at journal 06 Apr, 2026 Reviewers invited by journal 02 Apr, 2026 Editor invited by journal 02 Apr, 2026 Editor assigned by journal 31 Mar, 2026 Submission checks completed at journal 31 Mar, 2026 First submitted to journal 30 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-9264724","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":617997409,"identity":"3bf732d8-d45b-4b55-a92d-71682a6a4564","order_by":0,"name":"Tianwei Liu","email":"","orcid":"","institution":"Xiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Tianwei","middleName":"","lastName":"Liu","suffix":""},{"id":617997410,"identity":"5fa97e67-b58f-4524-85a5-66cde971a48f","order_by":1,"name":"Xiaomin Chen","email":"","orcid":"","institution":"Xiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Xiaomin","middleName":"","lastName":"Chen","suffix":""},{"id":617997411,"identity":"295a40f3-74c7-45b3-bf16-f78356a57343","order_by":2,"name":"Huiling Chen","email":"","orcid":"","institution":"Xiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Huiling","middleName":"","lastName":"Chen","suffix":""},{"id":617997412,"identity":"41eaa212-30f1-4476-96f6-7e3d466dfc3a","order_by":3,"name":"Caiyong Huang","email":"","orcid":"","institution":"Central Blood Station","correspondingAuthor":false,"prefix":"","firstName":"Caiyong","middleName":"","lastName":"Huang","suffix":""},{"id":617997413,"identity":"27c057ca-645a-4a1d-bd1b-f13536964749","order_by":4,"name":"Pu Yu","email":"","orcid":"","institution":"Xiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Pu","middleName":"","lastName":"Yu","suffix":""},{"id":617997414,"identity":"da71dd41-df25-4f4d-828a-aaa2ca806558","order_by":5,"name":"Wei Tang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6klEQVRIie3PsUoDQRDG8VkG5lJMcu3BFums5xIQIUd8lZODra7IG7iQVrQ938I38JLF2GgfMMXBQeqkSxGCWhtutbPYX/39GQYgCP4jjNtmfzrdPr/OF81Osqm34IgprahW9m1VpNXMFP4kZtC972RdXmjeLZX1JdfYr8fAG1S2JJ1JjRC5l6fOKzjI21myJYR3NyllMwA2Zt2dgIwrQSZ1f/NRyhYh4UtvojnHhJFFX4lT1p98Lbl2khCPNPwqcWTSR2tyYSrSOzEF+X6JHpxr9jbLZdgumsMxm8aRW3UmP9Hf5kEQBME5n+CgR+PVLduQAAAAAElFTkSuQmCC","orcid":"","institution":"Xiangnan University","correspondingAuthor":true,"prefix":"","firstName":"Wei","middleName":"","lastName":"Tang","suffix":""}],"badges":[],"createdAt":"2026-03-30 09:12:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9264724/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9264724/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106366774,"identity":"956b4e6c-fe16-45af-a559-41032e21b9d5","added_by":"auto","created_at":"2026-04-08 00:17:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":150636,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Thermogravimetric-Differential Scanning Calorimetry (TG-DSC) of the precursor. (b) X-ray diffraction (XRD) patterns of FMMO/G and F-FMMO/G sintered at 650 ℃ and standard patterns (FeMoO\u003csub\u003e4\u003c/sub\u003e JCPDS 22-628 and Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e JCPDS 34-510). Increment: 0.02°, scan rate: 5° min\u003csup\u003e-1\u003c/sup\u003e. (c) Raman spectroscopy of FMMO/G and F-FMMO/G. (d) Electrochemical impedance spectroscopy (EIS) of FMMO's new cells. Amplitude: 5 mV, frequency range: 1MHz-0.01Hz. The inset is the equivalent electrical circuit of all the fittings used in the software ZSimpWin.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/f5e580b285b7b08b8436ea76.png"},{"id":108490524,"identity":"f55c020c-c5ed-40fb-9f29-b72e3559c8e4","added_by":"auto","created_at":"2026-05-05 09:43:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":130752,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical performance. (a) Cycle life comparison as specific capacity of FMMO/G and F-FMMO/G at 0.1 C. (b) Cycle curve comparison of FMMO/G and F-FMMO/G at 0.1 C after initial cycles. (c) Rate performance of FMMO/G and F-FMMO/G. (d) 10C rate performance of F-FMMO/G.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/a78e1689efa9f7bba5021e75.png"},{"id":106366776,"identity":"1d90e343-41e6-4c7e-8ca5-a40b04335036","added_by":"auto","created_at":"2026-04-08 00:17:14","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":85903,"visible":true,"origin":"","legend":"\u003cp\u003e(a)\u003cstrong\u003e \u003c/strong\u003eCV curves of FMMO/G and F-FMMO/G at the scan rate of 1 mV s\u003csup\u003e-1\u003c/sup\u003e. Voltage window: 0.01-3.0 V. (b)\u003cstrong\u003e \u003c/strong\u003eEPR spectroscopy analysis results of FMMO/G and F-FMMO/G.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/8d218b6235e9398ea37e988a.png"},{"id":106366777,"identity":"702179f9-4053-4bfb-baff-76ef0b2f3af3","added_by":"auto","created_at":"2026-04-08 00:17:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":123044,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectroscopy analysis results. (a) XPS survey of F-FMMO/G. Inset table is the atomic percentage comparison. (b) Fe 2p XPS spectrum comparison of FMMO/G and F-FMMO/G.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/1e7180aaafa2a114f7b315d7.png"},{"id":106366778,"identity":"6f558a8b-20ef-4f11-bc1a-eb3bfd62a67c","added_by":"auto","created_at":"2026-04-08 00:17:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1211836,"visible":true,"origin":"","legend":"\u003cp\u003eHRTEM of F-FMMO/G (a-c). Scale: 2 nm. (d) SAED of F-FMMO/G. Scale: 5 1/nm.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/0b85747240d6ce390d751934.png"},{"id":106366779,"identity":"b73ad902-063e-49bb-aefc-c1c58a01104d","added_by":"auto","created_at":"2026-04-08 00:17:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":361974,"visible":true,"origin":"","legend":"\u003cp\u003eDFT results of\u003cstrong\u003e \u003c/strong\u003eF-FMMO/G composite. (a)\u003cstrong\u003e \u003c/strong\u003eDifferential charge density of the FeMoO\u003csub\u003e4\u003c/sub\u003e (220)/ Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (112) heterojunction interface. (b)\u003cstrong\u003e \u003c/strong\u003eEnergy bands of FeMoO\u003csub\u003e4\u003c/sub\u003e (220) and Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (112) planes.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/0533f1f1e886fa9fefe8175c.png"},{"id":108804563,"identity":"9a28efca-b9a2-42b0-89a1-473ed23fa4d1","added_by":"auto","created_at":"2026-05-08 15:21:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2301724,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9264724/v1/5788af48-a2ce-4fd9-8da3-db6ca81ec469.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eSynergistic Engineering of Fluorine Doping Fe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1-x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e/Graphene Heterojunction as Ultrahigh-Rate Anode for LIBs\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe growing demand for lithium-ion batteries (LIBs) with both high energy and power densities has spurred intense research into advanced anode materials beyond conventional graphite. Among the most promising candidates are transition metal oxides (TMOs) and molybdates, which offer high theoretical capacities via multi-electron conversion reactions\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. However, their practical application is hindered by several intrinsic limitations, including low electronic conductivity, significant volume changes during lithiation/delithiation, and resulting structural pulverization and rapid capacity decay\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eTo address these challenges, heterojunction engineering has emerged as a key strategy in advanced electrode design. A heterojunction, formed at the interface between two semiconductors with distinct band structures, generates a built-in electric field that facilitates directional charge separation and transport. This interfacial electric field acts as a nanoscale \u0026lsquo;highway\u0026rsquo;, significantly enhancing charge-transfer kinetics and mitigating the conductivity bottleneck\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Additionally, the mechanical interplay between the constituent phases can relieve internal stress during cycling. One phase may serve as a structural buffer or conductive scaffold for the other, thereby reducing volume expansion and preserving structural integrity, which is critical for achieving long-term cyclability\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Notably, recent studies on Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/ZnO, Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e/SnO\u003csub\u003e2\u003c/sub\u003e, and NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/MnO\u003csub\u003e2\u003c/sub\u003e heterostructures have demonstrated enhanced rate capability and improved mechanical stability compared to their single-phase analogs\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Elemental doping, particularly with anions such as fluorine (F), offers a complementary avenue for tailoring the physicochemical properties of electrode materials. F-doping induces lattice distortion, introduces oxygen vacancies, and modifies the electronic band structure, collectively improving both ionic and electronic conductivity\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Moreover, the formation of strong metal-fluorine (M\u0026ndash;F) bonds at the surface generates a robust interfacial layer that stabilizes the solid-electrolyte interphase (SEI) and suppresses unwanted side reactions during extended cycling\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. The combination of heterojunction engineering and targeted doping thus presents a synergistic strategy: the heterojunction enhances charge transport and structural resilience, while doping optimizes surface chemistry and electronic structure\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Iron molybdate (FeMoO\u003csub\u003e4\u003c/sub\u003e) and manganese molybdate (MnMoO\u003csub\u003e4\u003c/sub\u003e) are environmentally benign materials with high theoretical capacities, making them attractive for LIB anodes. Nevertheless, their individual electrochemical performance is limited by poor conductivity and structural degradation upon cycling\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. A Fe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e-based heterojunction can leverage the benefits of both parent compounds. While molybdate-based heterostructures such as MoO\u003csub\u003e2\u003c/sub\u003e/MoS\u003csub\u003e2\u003c/sub\u003e and CoMoO\u003csub\u003e4\u003c/sub\u003e/NiMoO\u003csub\u003e4\u003c/sub\u003e have shown promise in boosting electrochemical kinetics\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, the specific integration of a fluorine-doped FeMoO\u003csub\u003e4\u003c/sub\u003e/Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e heterojunction with conductive graphene remains largely unexplored\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this study, we design and synthesize a fluorine-doped, heterojunction-structured Fe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e/graphene (F-FMMO/G) nanocomposite via a facile solvothermal method. The work aims to elucidate how the combined strategies of heterojunction formation and fluorine doping jointly address the limitations of conversion-type anodes. We systematically investigate improvements in structural stability (e.g., buffered volume changes and robust SEI formation), charge transfer efficiency (e.g., reduced interfacial resistance and enhanced conductivity), and overall electrochemical kinetics. Advanced characterizations, supported by density functional theory (DFT) simulations, reveal the fundamental mechanisms underlying the ultrahigh-rate performance and superior cycling stability. This work establishes a rational design blueprint that couples interfacial and bulk modifications for next-generation high-power LIB anodes.\u003c/p\u003e"},{"header":"Results and Discussions","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eThermal stability of the precursor\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea presents the TG-DSC curves of the FMMO precursor heated under N\u003csub\u003e2\u003c/sub\u003e from room temperature to 800 ℃, which reveals the thermal behavior and crystallization temperature. As the temperature increases, a gradual mass loss is observed, accompanied by endothermic behavior. A distinct exothermic peak appears at approximately 400 ℃, corresponding to the formation of crystalline phases and a sharp weight loss of over 7%, indicating a major decomposition and crystallization step associated with oxide phase formation. Following this step, a slower and continuous weight loss process ensues, resembling thermal behavior before 400 ℃. As heating continues, a second exothermic peak is detected at 730 ℃, suggesting the onset of more complex phase transformations. Based on these observations, a calcination temperature of 650 ℃ was selected to obtain well-crystallized products while avoiding the higher-temperature regime where more complex phase transformations\u003c/p\u003e \u003cp\u003e may occur.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eXRD and Morphology Comparison of FMMOs\u003c/h3\u003e\n\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb displays the X-ray diffraction (XRD) patterns of FMMO/G and F-FMMO/G composites calcined at 650 ℃. Both samples exhibit mixed-phase structures, indicating that neither is a single-phase material. The diffraction pattern of FMMO/G shows three prominent peaks: the reflections at 2θ\u0026thinsp;\u0026asymp;\u0026thinsp;26.5\u0026deg; corresponding to the (220) plane of FeMoO\u003csub\u003e4\u003c/sub\u003e (JCPDS 22\u0026ndash;628), while peaks at 37\u0026deg; and 53\u0026deg; corresponding to the (201) and (006) planes of Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (JCPDS 34\u0026ndash;510), respectively. Upon fluorine doping, the F-FMMO/G sample exhibits enhanced crystallinity, as evidenced by increased peak intensity and additional diffraction peaks. In addition to the FeMoO\u003csub\u003e4\u003c/sub\u003e (220) peak, several new Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e peaks appear at 15\u0026deg; (002), 25.5\u0026deg; (102), 36\u0026deg; (112), and 45\u0026deg; (203), indicating the formation of an improved crystallinity and ordered heterostructure. To further elucidate the structural evolution, Raman spectroscopy was conducted on both samples, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. Both FMMO/G and F-FMMO/G exhibit characteristic D and G graphene bands at 1347 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1597 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Notably, the relative intensity of these bands decreases after fluorine doping, indicating stronger coupling between the carbon framework and the fluorine-modified oxide matrix, along with changes in defect density within the carbon component. Peaks at 199 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 347 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to the Fe\u0026ndash;O stretching vibration and the triply degenerate bending vibration of the MoO\u003csub\u003e4\u003c/sub\u003e tetrahedra, respectively, are present in both samples. Upon fluorine doping, new peaks emerge in the Raman spectrum of F-FMMO/G: a prominent peak at 819 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e assigned to the asymmetric stretching vibration of MoO\u003csub\u003e4\u003c/sub\u003e tetrahedra\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, as well as additional peaks at 931 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 992 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to the symmetric stretching modes of terminal metal\u0026ndash;oxygen (M\u0026thinsp;=\u0026thinsp;O) bonds. The appearance of these new peaks, combined with an overall increase in peak intensity, reflects enhanced crystallinity and a more mature phase structure in the fluorine-doped sample.\u003c/p\u003e\n\u003ch3\u003eElectrochemical Performance\u003c/h3\u003e\n\u003cp\u003eElectrochemical impedance spectroscopy (EIS) analysis of both samples is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed. The Nyquist plots feature a depressed semicircle in the high-frequency region, indicative of charge-transfer resistance, and a linear tail in the low-frequency region, characteristic of Warburg impedance related to lithium-ion diffusion. As summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the charge-transfer resistance (R_ct) for F-FMMO/G is markedly lower (73.7 Ω) compared to FMMO/G (243 Ω). This substantial reduction in R_ct clearly demonstrates the enhanced electrical conductivity of the fluorine-doped heterostructure, consistent with the improved electronic transport indicated by Hall results and the enhanced defect signal in EPR, which contributes to its superior electrochemical performance.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectrochemical impedance parameters and diffusion coefficients.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eσ\u003c/em\u003e\u003csub\u003ew\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDiffusion coefficient\u003c/p\u003e \u003cp\u003e(cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFMMO/G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e243\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.05E\u0026thinsp;+\u0026thinsp;01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.86E-14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eF-FMMO/G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e7.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e73.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.86E\u0026thinsp;+\u0026thinsp;01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.24E-15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea compares the cycling behavior at 0.1 C. Both samples exhibit high initial irreversible discharge capacities: 1045 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for FMMO/G and 1158 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for F-FMMO/G. The corresponding initial cycling curves are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. After the formation cycle, the fluorinated composite stabilizes at ~\u0026thinsp;860 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is the more representative reversible capacity for subsequent cycling. For FMMO/G, the capacity maintains a relatively stable capacity of 1016 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, then gradually decays at a rate of approximately 0.2% per cycle over the first 80 cycles. After this point, the decay accelerates to 0.9% per cycle, resulting in a sharp capacity decline. By the 150th cycle, the capacity drops to 360 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which corresponds to only 35% of its initial value. In contrast, the fluorine-doped F-FMMO/G shows a different trend. After the initial capacity drop, the specific capacity gradually increases over the next 50 cycles, at a rate of 0.1% per cycle. This improvement is attributed to enhanced electrolyte infiltration and gradual activation of the electrode surface. Following this activation phase, a slow and steady capacity decay is observed. However, the F-FMMO/G retains significantly better stability than its undoped counterpart. After 150 cycles, it maintains a capacity of 780 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is approximately 90% of its initial value and demonstrates excellent cycling durability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe rate performance of both samples is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, where the behavior under varying current densities appears comparable. The F-FMMO/G electrode exhibits superior rate performance under the same testing conditions. To further evaluate high-rate capabilities, the F-FMMO/G electrode was subjected to extended cycling at 10 C, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. During initial cycles at 0.1 C, the specific capacity exceeds 900 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Upon increasing the current density to 10 C, the capacity drops rapidly from 480 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 180 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e within 25 cycles and then stabilizes around 100 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Impressively, this stabilized capacity is sustained for over 200 cycles. When the current density is returned to 0.1 C, the capacity recovers to over 900 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating excellent structural robustness and rate-reversible capacity. These results confirm that F-FMMO/G exhibits outstanding rate capability and high structural integrity under extreme cycling conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea presents the cyclic voltammetry (CV) curves of FMMO/G and F-FMMO/G electrodes measured at a scan rate of 1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e within a voltage window of 0.01\u0026ndash;3.0 V. FMMO/G exhibits no distinct redox peaks, showing only broad humps, which is characteristic of pseudocapacitive or amorphous-like behavior, consistent with our previous findings\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. In contrast, the F-FMMO/G electrode displays two well-defined reduction peaks at 1.51 V and 1.26 V, along with corresponding oxidation peaks at 1.54 V and 1.78 V. These redox couples can be identified as follows: the pair at 1.78 V (oxidation) and 1.51 V (reduction) yields a potential separation (ΔV) of 0.27 V, while the pair at 1.54 V (oxidation) and 1.26 V (reduction) yields a ΔV of 0.28 V. The redox features in this voltage range can be attributed to stepwise conversion of the molybdate-containing phases involving reduction/oxidation of transition-metal centers (Fe/Mn/Mo) together with Li\u003csub\u003e2\u003c/sub\u003eO formation/decomposition and interfacial lithium storage on the graphene-coupled composite framework. The appearance of distinct and symmetric redox peaks in F-FMMO/G confirms improved electrochemical reversibility and well-defined redox kinetics after fluorine doping.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eHall effect results comparison of FMMO/G and F-FMMO/G.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnode Material\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTemperature (K)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eResistivity (ohm\u0026middot;cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eElectron Mobility (cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e S\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCarrier Concentration (1/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR\u003csub\u003eH\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(cm\u003csup\u003e3\u003c/sup\u003e C\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFMMO/G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.77E\u0026thinsp;+\u0026thinsp;01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.71E\u0026thinsp;+\u0026thinsp;01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.90E\u0026thinsp;+\u0026thinsp;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-3.29E\u0026thinsp;+\u0026thinsp;03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eF-FMMO/G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.10E\u0026thinsp;+\u0026thinsp;01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.30E\u0026thinsp;+\u0026thinsp;01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.88E\u0026thinsp;+\u0026thinsp;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-3.72E\u0026thinsp;+\u0026thinsp;03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTo elucidate the intrinsic electronic structure modifications induced by fluorine doping, electron paramagnetic resonance (EPR) spectroscopy and Hall effect measurements were performed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, both samples exhibit a prominent EPR signal at g\u0026thinsp;\u0026asymp;\u0026thinsp;2.001, typically attributed to unpaired electrons associated with oxygen vacancies and other defect states. Notably, the F-FMMO/G sample displays a significantly stronger signal than FMMO/G, indicating a higher concentration of paramagnetic centers, primarily oxygen vacancies, introduced by F\u003csup\u003e\u0026minus;\u003c/sup\u003e incorporation. This finding is consistent with the XPS analysis, which revealed modulation of Fe valence states, suggesting that fluorine doping effectively engineers the defect chemistry of the material. Complementary Hall effect measurements (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) provide quantitative insight into the electronic transport properties. Both FMMO/G and F-FMMO/G exhibit negative Hall coefficients (R\u003csub\u003eH\u003c/sub\u003e), confirming n-type semiconductor behavior with electrons as the dominant charge carriers. Following fluorine doping, the room-temperature resistivity of F-FMMO/G decreases from 3.77 \u0026times; 10\u003csup\u003e1\u003c/sup\u003e Ω\u0026middot;cm to 3.10 \u0026times; 10\u003csup\u003e1\u003c/sup\u003e Ω\u0026middot;cm, while electron mobility increases from 8.71 \u0026times; 10\u003csup\u003e1\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 9.30 \u0026times; 10\u0026sup1; cm\u0026sup2; V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while the carrier concentration remains relatively constant (~\u0026thinsp;1.9 \u0026times; 10\u003csup\u003e15\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e). These results indicate that the primary role of fluorine doping is not to increase carrier density but to enhance carrier mobility within the lattice. This mobility enhancement is attributed to two key factors: (i) F-induced oxygen vacancies act as donor sites, donating electrons to the conduction band and reducing scattering events; and (ii) local electronic structure modification weakens Fe\u0026ndash;O bonds, as evidenced by XPS, thereby lowering the energy barrier for electron hopping. Together, the EPR and Hall effect analyses confirm that fluorine doping functions as an effective electronic modulator. It simultaneously increases the density of active defect states and improves the efficiency of charge transport. This intrinsic conductivity enhancement, coupled with the built-in electric field at the heterojunction interface, underpins the significantly reduced charge-transfer resistance and outstanding high-rate capability observed in the F-FMMO/G anode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eX-ray photoelectron spectroscopy (XPS) was employed to investigate survey results of F-FMMO/G and the changes in the oxidation states of Fe in FMMO/G and F-FMMO/G, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, with the corresponding quantitative data summarized in the inset table of Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The F1s signal is detected with an atomic concentration of 0.9 at. %, confirming successful fluorine incorporation into the material. The Fe/Mn atomic ratio is approximately 1.05, consistent with the nominal stoichiometry of FeₓMn₁₋ₓMoO\u003csub\u003e4\u003c/sub\u003e (x\u0026thinsp;\u0026asymp;\u0026thinsp;0.5). The relatively high carbon content (61.77 at. %) originates from both the intrinsic graphene component and surface-adsorbed adventitious carbon, which is commonly observed in air-exposed carbon-containing samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Fe 2p spectra of both samples can be deconvoluted into characteristic Fe\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e doublets, indicating the coexistence of mixed valence states. Notably, the Fe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e ratio increases from 1.59 in FMMO/G to 1.71 in F-FMMO/G, demonstrating that fluorine doping effectively modulates the Fe valence distribution. This increase in the Fe\u003csup\u003e2+\u003c/sup\u003e fraction is consistent with the higher initial specific capacity observed for the fluorine-doped sample. In addition to the change in valence states, a systematic shift of Fe 2p binding energies toward lower values is observed after fluorine doping, indicating a weakened Fe\u0026ndash;O bonding environment. The reduced bond strength lowers the energy barrier for Li⁺ insertion and extraction, thereby facilitating lithium-ion intercalation kinetics. Furthermore, the modified surface electronic structure is expected to promote more favorable interfacial charge-transfer processes, contributing to the enhanced electrochemical performance of the F-FMMO/G electrode.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFe 2p XPS valence distribution.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eorbit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eB.E.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eXPS AREA\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAREA RATIO\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eFMMO/G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e2p\u003csub\u003e3/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e710.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e=1.59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e2p\u003csub\u003e1/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e724\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5150\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e3/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e712.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6468\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e1/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e726.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3234\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eF-FMMO/G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e2p\u003csub\u003e3/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e710.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5724\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e=1.71\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e2+\u003c/sup\u003e2p\u003csub\u003e1/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e723.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2862\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e3/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e712.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3346\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csup\u003e3+\u003c/sup\u003e2p\u003csub\u003e1/2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e726.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1673\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe high-resolution transmission electron microscopy (HR-TEM) images in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e reveal the stacked nanosheet structure of the F-FMMO/G composite. Despite being composed of two heterophase structures, well-defined crystalline fringes are clearly observed, indicating the high crystallinity of the final product. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, lattice fringes corresponding to the (101) and (112) planes of Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (JCPDS 34\u0026ndash;510) are observed, intersecting at an angle of approximately 89\u0026deg;, consistent with the expected crystallographic orientation. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the presence of the (220) plane of FeMoO\u003csub\u003e4\u003c/sub\u003e (JCPDS 22\u0026ndash;628), while Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec reveals the (002) and (101) planes of Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e. Selected area electron diffraction (SAED) analysis, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, further supports these findings. The diffraction pattern exhibits clear and distinct spots arranged in concentric rings, which, together with other evidence provided earlier, confirms the polycrystalline nature of the heterostructure. Specifically, the first and third rings correspond to the (002) and (112) planes of Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e, while the second ring is assigned to the (220) plane of FeMoO\u003csub\u003e4\u003c/sub\u003e. These results collectively validate the coexistence of both crystalline phases in the fluorine-doped composite, which can provide abundant contact regions for charge transfer and mechanical buffering during cycling. In addition, a thin amorphous layer is observed at the outer edge of the HR-TEM images. This layer is expected to facilitate lithium-ion insertion and extraction by providing a more accessible surface and flexible interface between the electrode and electrolyte, potentially contributing to the improved electrochemical kinetics of the F-FMMO/G anode.\u003c/p\u003e\n\u003ch3\u003eTheoretical Calculation Results\u003c/h3\u003e\n\u003cp\u003eTo investigate the atomic-scale charge redistribution and electronic structure at the heterojunction interface, we constructed an interface model between the FeMoO\u003csub\u003e4\u003c/sub\u003e (220) and Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (112) planes.\u003c/p\u003e \u003cp\u003eDifferential charge density analysis, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, illustrates the spatial distribution of electron transfer at the interface. The cyan and yellow isosurfaces represent regions of electron depletion and accumulation, respectively. A clear electron accumulation is observed on the Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e side, while electron depletion occurs on the adjacent FeMoO\u003csub\u003e4\u003c/sub\u003e region. This asymmetric charge redistribution indicates spontaneous electron transfer from FeMoO\u003csub\u003e4\u003c/sub\u003e to Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e upon contact, generating a built-in electric field directed from the electron-rich Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e to the electron-deficient FeMoO\u003csub\u003e4\u003c/sub\u003e. This interfacial electric field is critical for enhancing charge separation and facilitating Li⁺ migration during electrochemical cycling. It also contributes to the reduced interfacial charge-transfer resistance, in agreement with the EIS results (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, the electronic band structure of the heterojunction was analyzed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb. Notably, the calculated band gap for the integrated FeMoO\u003csub\u003e4\u003c/sub\u003e/Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e heterojunction is approximately 0 eV, indicating a quasi-metallic character. The valence band maximum (VBM, \u0026minus;\u0026thinsp;0.9884 eV) and conduction band minimum (CBM, \u0026minus;\u0026thinsp;0.9854 eV) are nearly degenerate, resulting in an almost negligible energy barrier for electron excitation. This near-zero band gap is of critical importance for charging transport, as it allows thermal excitation of electrons from the valence band to the conduction band with minimal energy input. Consequently, the intrinsic carrier concentration is expected to be several orders of magnitude higher than that of conventional semiconductors with typical band gaps exceeding 1 eV. This dramatically enhanced bulk electronic conductivity offers a fundamental explanation for the superior rate performance of the F-FMMO/G composite, enabling rapid and efficient electron transport throughout the electrode under high-current operating conditions.\u003c/p\u003e \u003cp\u003eCollectively, the DFT results reveal a dual enhancement mechanism that underlies the exceptional electrochemical performance of the F-FMMO/G composite. First, interfacial engineering plays a critical role: the spontaneous charge transfer at the FeMoO\u003csub\u003e4\u003c/sub\u003e/Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e interface establishes a built-in electric field, which effectively facilitates both ion and electron transport across the heterojunction and significantly lowers interfacial resistance. Second, bulk property modulation is achieved through heterostructure formation, which induces a quasi-metallic electronic structure characterized by a near-zero band gap. This leads to a substantial increase in intrinsic electronic conductivity throughout the bulk material. The synergistic interplay between interfacial charge modulation and enhanced bulk conductivity, enabled by the rational design of the heterojunction architecture, is the key to the ultrahigh-rate capability demonstrated by the F-FMMO/G anode. This dual mechanism provides a compelling design strategy for the development of next-generation high-performance lithium-ion battery materials.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, a fluorine-doped Fe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1−x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e/graphene (F-FMMO/G) heterojunction nanocomposite was successfully developed as an ultrahigh-rate anode material for lithium-ion batteries (LIBs) through a synergistic design strategy. This approach effectively combines the advantages of heterojunction engineering and fluorine anion doping to address the intrinsic limitations of conventional conversion-type anodes. The in-situ formation of a heterojunction between FeMoO\u003csub\u003e4\u003c/sub\u003e and Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e phases generates a built-in electric field that significantly enhances charge-transfer kinetics, as evidenced by the substantial reduction in charge-transfer resistance (73.7 Ω for F-FMMO/G vs. 243 Ω for the undoped sample). Simultaneously, fluorine doping modulates the local bonding environment by weakening Fe–O interactions, thereby facilitating Li\u003csup\u003e+\u003c/sup\u003e diffusion and improving both structural robustness and interfacial stability during cycling. As a result, the F-FMMO/G anode delivers outstanding electrochemical performance, including an ultrahigh reversible capacity of 1158 mAh g\u003csup\u003e− 1\u003c/sup\u003e at 0.1 C, excellent cycling stability with 90% capacity retention after 150 cycles, and superior rate capability, maintaining structural integrity under prolonged operation at 10 C with rapid capacity recovery. Complementary density functional theory (DFT) calculations reveal a dual enhancement mechanism: spontaneous interfacial charge transfer generates a favorable electric field for ion/electron transport, while heterostructure formation leads to a quasi-metallic electronic structure with a near-zero band gap, significantly improving bulk conductivity. This work not only introduces a high-performance anode material but also elucidates the synergistic mechanism between interfacial and bulk-level modifications. The design principle demonstrated here—integrating interfacial charge modulation with electronic structure engineering via elemental doping—offers a powerful and generalizable strategy for the development of next-generation high-power energy storage systems.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Experimental","content":"\u003ch2\u003eMaterial Synthesis\u003c/h2\u003e\u003cp\u003eFe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1−x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e/G and F-Fe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1−x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e/G composites were synthesized via a solvothermal method. First, 1 mmol of (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e6\u003c/sub\u003eMo\u003csub\u003e7\u003c/sub\u003eO\u003csub\u003e24\u003c/sub\u003e (Fisher Chemical, Laboratory Grade) was dissolved in a mixed solvent of ethylene glycol (EG) and deionized water (EG: H₂O = 2:1 by volume) to prepare solution A, followed by stirring for 30 minutes. Separately, 3.5 mmol of FeCl\u003csub\u003e2\u003c/sub\u003e·4H\u003csub\u003e2\u003c/sub\u003eO (Sigma-Aldrich, 99.5%) and 3.5 mmol of MnCl\u003csub\u003e2\u003c/sub\u003e·H\u003csub\u003e2\u003c/sub\u003eO (Sigma-Aldrich, 99.5%) were dissolved in 30 mL of distilled water to form solution B. After stirring solution B for 1 hour, it was added dropwise to solution A under vigorous stirring. The mixture was then stirred continuously for 4 hours. Subsequently, 10 mL of a pre-prepared graphene oxide (GO) dispersion (2 mg mL\u003csup\u003e− 1\u003c/sup\u003e) was added dropwise to the resulting solution, followed by an additional hour of stirring. The GO was synthesized according to a previously reported method\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Then, 0.48 mmol of NH\u003csub\u003e4\u003c/sub\u003eF (Fisher Chemical, \u0026gt; 98%) was added, and the mixture was stirred for another 5 minutes to ensure homogeneity before the solvothermal reaction. The final solution was transferred into a 100 mL Teflon-lined stainless-steel autoclave, sealed, and maintained at 180 ℃ for 20 hours. After the reaction, the autoclave was allowed to cool naturally to room temperature. The resulting precipitate was collected, washed thoroughly with deionized water several times, and dried at 60 ℃ under vacuum for 12 hours. The dried product was then sintered at 650 ℃ for 8 hours in an argon atmosphere to obtain the fluorine-doped heterojunction composite, designated as F-FMMO/G. For comparison, a non-doped control sample (FMMO/G) was synthesized using the same procedure, excluding the addition of NH\u003csub\u003e4\u003c/sub\u003eF.\u003c/p\u003e\n\u003ch3\u003eMaterial Characterization\u003c/h3\u003e\n\u003cp\u003eThermal stability was assessed using thermogravimetric-differential scanning calorimetry (TG-DSC) on a NETZSCH STA 449C instrument. Samples were heated in an N₂ atmosphere at a rate of 5 ℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Crystal structure analysis was conducted via powder X-ray diffraction (XRD) using a Bruker D8 Advance diffractometer with Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;0.154 nm) over a 2θ range of 10\u0026deg; to 80\u0026deg;. Electrochemical properties were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), performed on a Chenhua CHI660E workstation. The EIS tests used an AC amplitude of \u0026plusmn;\u0026thinsp;5 mV over a frequency range of 10\u003csup\u003e2\u003c/sup\u003e to 10\u003csup\u003e6\u003c/sup\u003e Hz. X-ray photoelectron spectroscopy (XPS) was carried out on a ThermoFisher ESCALAB Xi+ instrument with Al Kα radiation (hv\u0026thinsp;=\u0026thinsp;1486.6 eV), under a base pressure of 8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e Pa. All binding energies were referenced to the C 1s peak at 284.8 eV. Raman spectra were obtained using a Thermo DXi confocal Raman spectrometer with a 532 nm excitation source at 300 K. Electron paramagnetic resonance (EPR) spectra were recorded on a Bruker E500 system. The microwave frequency: X-band, ranging from 9.3 GHz to 9.9 GHz (with automatic tuning). Magnetic field range: 0 to 1.4 Tesla (0\u0026ndash;14,000 Gauss). All measurements were conducted at room temperature unless otherwise specified.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical Performance Characterization\u003c/h2\u003e \u003cp\u003eThe electrochemical performance of FMMO/G and F-FMMO/G was evaluated using 2032-type coin half-cells. The electrolyte consisted of 1.0 M LiPF\u003csub\u003e6\u003c/sub\u003e in a 1:1 (v/v) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). A polypropylene microporous membrane (Celgard 2500) was used as the separator. Electrodes were prepared by blending active material, Super P conductive carbon, and poly (vinylidene fluoride) (PVDF) binder in a weight ratio of 8:1:1. The resulting slurry was coated onto copper foil, dried overnight at 65 ℃ under vacuum, and punched into circular electrodes with a diameter of 14 mm. The weight of active material per anode is 5\u0026thinsp;~\u0026thinsp;6 mg. Coin cells were assembled in an argon-filled glovebox. Galvanostatic charge\u0026ndash;discharge tests were carried out on a LAND CT2001A multichannel battery tester (Wuhan, China) at various current densities within a voltage window of 0.01\u0026ndash;3 V (vs. Li\u003csup\u003e+\u003c/sup\u003e/Li) at room temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eTheoretical Calculation\u003c/h2\u003e \u003cp\u003eAll first-principles calculations were performed within the framework of density functional theory (DFT) using the Vienna Ab initio Simulation Package (VASP 6.3.0)\u003csup\u003e24\u0026ndash;26\u003c/sup\u003e. The exchange-correlation interactions were treated using the generalized gradient approximation (GGA) with the Perdew\u0026ndash;Burke\u0026ndash;Ernzerhof (PBE) functional\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Interactions between core and valence electrons were described using the projector augmented wave (PAW) method with standard pseudopotentials\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. A 3 \u0026times; 2 \u0026times; 1 Monkhorst\u0026ndash;Pack k-point grid was used for Brillouin zone sampling, and a plane-wave cutoff energy of 500 eV was applied. The atomic structures were fully relaxed until the total energy convergence threshold reached 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e eV and the maximum residual force on each atom was less than 0.03 eV/\u0026Aring;. To account for the localized nature of d-electrons in the transition metals, the DFT\u0026thinsp;+\u0026thinsp;U method was employed. Effective Hubbard U values were set to 2.5 eV for both Mn and Fe, and 2.0 eV for Mo.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eWe would like to thank the funding support from Excellent Youth Project of Hunan Provincial Department of Education (Project No.: 23B0772).\u003c/p\u003e\n\u003ch2\u003eAuthor\u0026nbsp;contributions statement\u003c/h2\u003e\n\u003cp\u003eT.L. conceived and designed the experiments; T.L., X.C., H.C., and C.H. performed the synthesis and characterization; T.L., P.Y., and W.T. conducted the electrochemical measurements and analyzed the data; T.L. and W.T. performed the DFT calculations; T.L. and W.T. wrote the manuscript; T.L. and W.T. supervised the project. All authors reviewed and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003eData will be made available on request from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZhang, D. et al. MnO Nanoparticles Attached to S, N Co-Doped Carbon Skeleton as a High-Rate Performance Anode Material. \u003cem\u003eMolecules\u003c/em\u003e \u003cb\u003e29\u003c/b\u003e, 4306. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/molecules29184306\u003c/span\u003e\u003cspan address=\"10.3390/molecules29184306\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2024). 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B\u003c/em\u003e. \u003cb\u003e50\u003c/b\u003e, 17953\u0026ndash;17979. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1103/PhysRevB.50.17953\u003c/span\u003e\u003cspan address=\"10.1103/PhysRevB.50.17953\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (1994).\u003c/span\u003e\u003c/li\u003e\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"FexMn1−xMoO4/G anode materials, fluorine doping, ultrahigh rate, heterojunction structure, synergistic enhancement","lastPublishedDoi":"10.21203/rs.3.rs-9264724/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9264724/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe development of advanced anode materials is critical for high-energy and high-power lithium-ion batteries (LIBs). Conventional conversion-type anodes, such as transition metal molybdates, suffer from poor conductivity, severe volume expansion, and structural degradation, leading to rapid capacity fading. To overcome these limitations, we propose a synergistic design strategy that integrates heterojunction engineering with fluorine doping. A fluorine-doped, heterojunction-structured F-Fe\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e/graphene (F-FMMO/G) was successfully synthesized via a facile solvothermal route. Structural characterizations confirm the formation of a well-defined FeMoO\u003csub\u003e4\u003c/sub\u003e/Mn\u003csub\u003e2\u003c/sub\u003eMo\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e heterojunction with effective fluorine incorporation. When evaluated as an anode for LIBs, the F-FMMO/G composite exhibits an ultrahigh initial specific capacity of 1158 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.1 C and maintains 780 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after 150 cycles, substantially outperforming the undoped counterpart. Notably, it delivers excellent rate performance, sustaining\u0026thinsp;~\u0026thinsp;100 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 10 C and rapidly recovering to \u0026gt;\u0026thinsp;900 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e when cycled back to 0.1 C. The enhanced electrochemical performance is attributed to the synergistic effects of the built-in electric field at the heterojunction interface, which promotes rapid charge transfer, and fluorine doping, which optimizes the electronic structure and stabilizes the electrode\u0026ndash;electrolyte interface. This study offers a rational design framework combining interfacial and bulk modifications for next-generation high-rate LIB anodes.\u003c/p\u003e","manuscriptTitle":"Synergistic Engineering of Fluorine Doping FexMn1-xMoO4/Graphene Heterojunction as Ultrahigh-Rate Anode for LIBs","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-08 00:17:10","doi":"10.21203/rs.3.rs-9264724/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-24T19:33:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-23T06:50:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"37528618616328894105794806175653287169","date":"2026-04-11T12:00:57+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-06T04:45:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"288696531134837842434932100321700808063","date":"2026-04-06T04:25:57+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-02T06:49:31+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-02T06:09:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-31T07:27:16+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-31T07:26:32+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-03-30T09:01:20+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"99289778-1df8-46ac-bb85-ea9fe0084695","owner":[],"postedDate":"April 8th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":65893693,"name":"Physical sciences/Chemistry"},{"id":65893694,"name":"Physical sciences/Energy science and technology"},{"id":65893695,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-05-08T03:08:21+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-08 00:17:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9264724","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9264724","identity":"rs-9264724","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}