Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures

Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures | 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 Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures Kai Liu, Weili Zhang, Qingqing Feng, Yang Lu, Hao Wang, Guangyu Cheng, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5474223/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 08 Apr, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Ultra-low temperature lithium metal batteries face significant challenges, particularly sluggish ion transport and uncontrolled lithium dendrite formation, especially under high power. An ideal electrolyte requires high carrier ion concentration, low viscosity, rapid desolvation, and stable interfaces. However, harmonizing these attributes remains a formidable task. Here, we designed and synthesized a multifunctional additive, perfluoroalkylsulfonyl quaternary ammonium nitrate (PQA-NO 3 ), which features both cationic (PQA + ) and anionic (NO 3 - ) components. PQA + reacts in situ with lithium metal to form an inorganic-rich solid-electrolyte interphase (SEI) that enhances Li + transport through the SEI film. NO 3 - creates an anion-rich, solvent-poor solvation structure, improving oxidation stability at the cathode/electrolyte interface and reducing Li + -solvent interactions. This allows ether-based electrolytes to achieve high voltage tolerance, increased ionic conductivity, and lower desolvation energy barriers. The Li (40 µm)||NMC811 (3 mAh cm -2 ) cells with the developed electrolyte exhibited stable cycling at -60 ℃ and a 450 Wh kg -1 pouch cell retained 48.1% capacity at -85 ℃, achieving a remarkable energy density of 171.8 Wh kg -1 . Additionally, the pouch cell demonstrated a high discharge rate of 3.0 C at -50 ℃, reaching a power density of 938.5 W kg -1 , highlighting the electrolyte's potential for high-rate lithium metal batteries in extreme low-temperature environments. Physical sciences/Energy science and technology/Energy storage/Batteries Physical sciences/Chemistry/Energy ultra-low temperatures lithium metal batteries multifunctional electrolyte additive Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction The development of lithium metal batteries (LMBs) has garnered significant attention due to their potential to deliver high energy density. However, the thermodynamic instability of lithium metal and the significant volume changes during deposition and stripping processes lead to the fragility of the solid electrolyte interphase (SEI) on the lithium metal anode surface. This instability results in the growth of dendritic lithium and the formation of dead lithium during repeated deposition/stripping cycles, ultimately causing low Coulombic efficiency (CE) and poor cycling performance. These issues are exacerbated under low-temperature conditions due to sluggish kinetics. [ 1 – 4 ] Therefore, their practical application, especially under low-temperature conditions, faces several challenges, particularly concerning the choice of electrolytes. [ 5 – 8 ] The electrolyte plays a crucial role in the performance and safety of LMBs, influencing factors such as ionic conductivity, solid electrolyte interphase (SEI) formation, and overall electrochemical stability. [ 9 – 12 ] Recent advancements have identified ether-based weakly solvating solvents, such as diethyl ether (DEE), as preferred choices for low-temperature LMB electrolytes due to their excellent reduction stability and compatibility with lithium metal. More importantly, DEE offers advantages like rapid desolvation and the formation of anion-derived SEI. Previous studies have shown that inorganic rich SEI has unique advantages in inhibiting the growth of lithium dendrites due to its effective blocking of electron tunneling, promoting uniform Li + transport and superior mechanical properties. However, its low dissociation degree of lithium salts results in low ionic conductivity, and its poor high-voltage stability limits compatibility with high-voltage cathodes. [ 6 , 13 – 15 ] Conversely, strongly solvating solvents like dimethoxyethane (DME) exhibit high lithium salt dissociation, allowing DME based electrolytes to achieve high ionic conductivity, especially at low temperatures. In addition, they can address high-voltage issues with the help of specific additives. Nevertheless, strong solvents face challenges such as difficult desolvation and large voltage drops, which can lead to uncontrolled growth of lithium dendrites at low temperatures, and will ultimately pose safety risks. [ 16 – 18 ] Many recent reports on low-temperature electrolytes focus on combining strongly and weakly solvating solvents to balance ion conductivity and desolvation ability. However, due to the strong coupling between ion transport and desolvation, it is challenging to simultaneously attain high ion conductivity and low desolvation energy. [ 19 , 20 ] Therefore, there is a need for a more advanced approach to electrolyte design that can harness the advantages of both strong and week solvents while mitigating their respective drawbacks. Here, we chose a binary solvent system consisting of a mixture of strong (DME) and weak solvating solvents (DEE) for the electrolyte. We demonstrated that introducing a small amount of a strongly solvating solvent into a weakly solvating solvent significantly enhances the ionic conductivity of the electrolyte without notably altering the solvation structure of the weak solvent (DEE: DME = 9:1 vol%). Furthermore, we designed and synthesized a multifunctional additive, perfluoroalkylsulfonyl quaternary ammonium nitrate (PQA-NO 3, note as PN), containing both cations (PAQ + ) and anions (NO 3 - ). Based on the frontier orbital theory and the calculation results of reaction energy, PAQ + can be preferentially reduced on the surface of Li metal to form LiF with high interface energy and Li 3 N, Li 2 O, Li 2 S with high ionic conductivity, ensuring rapid transport of Li + through SEI and inhibiting the growth of lithium dendrites at ultra-low temperatures. In addition, NO 3 - enters the Li + solvation shell and repels the solvent, weakening the interaction between Li + and the solvent, accelerating the process of Li + de-solvation, and greatly alleviating the inevitable increase in de-solvation energy barrier caused by the introduction of strong solvents DME. Besides, NO 3 - constructs a high oxidation stability cathode/electrolyte interface with poor-solvent and rich-anions, enabling the ether based solvent system to match the NMC811 cathode for stable cycling at a high operating voltage of 4.3 V. As a result, the Li||NMC811 full cell using the designed electrolyte exhibits stable long-term cycling performance under extremely low temperature conditions of -60 ℃. The actual industrialized pouch cell can stably discharge at -85°C, maintaining 45% of its room temperature capacity and achieving an impressive energy density of 171.8 Wh kg -1 (except taps and packing foil, same hereafter) at -85°C. Remarkably, the pouch cell can discharge at a high rate of 3.0 C at -50°C, achieving a record-breaking power density of 938.5 W kg -1 . 2. Results and Discussion According to molecular frontier orbital theory, electrolyte components with lower LUMO energy levels are thermodynamically more inclined to undergo reductive decomposition. Figure 1 a calculated the molecular orbital energy levels of different components in the electrolyte, and the results show that the PN additive molecules have lower LUMO energy levels, leading to preferential decomposition on the lithium metal surface and participation in SEI formation. Furthermore, we immersed lithium metal in a DME solution containing 0.1 M PN for 2 hours, then tested its surface composition using X-ray photoelectron spectroscopy (XPS). Commercial lithium metal foil typically exhibits a native passivation layer rich in Li 2 CO 3 and LiOH (Fig. 1 c-e), which increases the impedance and overpotential of the electrode, and also affects the subsequent construction of SEI on the electrode surface. [ 21 , 22 ] However, after soaking, the surface of the lithium metal showed significant amounts of inorganic compounds such as LiF, Li 2 CO 3 , Li 2 O, Li 2 S and Li 3 N, demonstrating that PN can react in situ with lithium metal to form an inorganic-rich SEI film, altering the structure of the native passivation layer. The abundant inorganic components are typically considered to enhance the mechanical strength of the SEI, allowing it to accommodate repeated volume changes and inhibit dendrite growth, thereby promoting stable cycling of the lithium metal anode at low temperatures. [ 6 , 8 ] We further employed the ab initio molecular dynamic (AIMD) calculations to elucidate the interfacial reaction mechanism between the PN additive and the Li metal anode. [ 8 , 23 , 24 ] Fig. 1 f and Fig. S1 -S3 shows snapshots of AIMD simulations at different simulation timescales. PN was found to automatically adsorb to the surface of lithium metal, and the NO 3 - anions decompose first, forming Li 3 N and Li 2 O components. At the same time, the S = O bond of PAQ + breaks and generates Li 2 S components on the surface of lithium metal. As the reactants were exposed to more Li 0 by diffusion, the PN underwent a rapid defluororination process via C-F cleavage, leading to a substantial amount of LiF formation. However, the DME solvent is relatively stable with the Li metal, and no decomposition reaction occurs on the lithium metal surface in the simulated time scale. Therefore, the simulation results demonstrate that PN can preferentially undergo in-situ chemical reactions with lithium metal over the solvent, resulting in the formation of an inorganic-rich SEI layer with strong mechanical strength and rapid lithium-ion conduction capability, consistent with the experimental observations. Additionally, the ion transport properties, desolvation ability, and film-forming characteristics of 1.0 M LiFSI/DEE (note as DEE), 1.0 M LiFSI/DEE + DME DEE: DME = 9:1 vol%, note as DDE), and DDE + 0.1 M PN (DDE-PN) electrolytes were investigated and compared. As shown in the Fig. 2 a, the measured ionic conductivity of the electrolyte using a single DEE solvent is relatively low, only 0.22 mS cm -1 at -60°C, due to insufficient dissociation of lithium salts by weak solvents. However, the introduction of 10% vol of the strong solvent DME increased the conductivity of the entire electrolyte system by an order of magnitude, with the conductivity of the DDE electrolyte reaching 2.32 mS cm -1 at -60°C. The presence of 0.1 M PN additive did not significantly affect the conductivity of the mixed solvent electrolyte system, with the DDE-PN electrolyte showing a high conductivity of 2.11 mS cm -1 at -60°C. Further classical molecular dynamics (MD) simulations were conducted (Fig. S4), utilizing radial distribution functions (RDF) to describe the average local solute-solute interaction environment (Fig. 2 d-f). The analysis indicates that the DEE electrolytes exhibit a characteristic contact ion pair (CIP) structure, where the Li + solvation shell contains FSI–rich anions with little DEE molecules, with an average coordination number of 3.2 FSI - and 1.0 DEE, consistent with previous studies. [ 6 ] With the introduction of the DME solvent, due to the strong interaction between Li + and DME, DME enters the Li + solvation shell, replacing some DEE solvent molecules. The average coordination number becomes 3.2 FSI - , 0.88 DEE, and 0.48 DME, indicating that DME entered the solvation shell and squeezed out some DEE solvents. However, when the PN additive is introduced into the mixed solvent system, NO 3 - enters the Li + solvation shell due to its stronger binding ability with Li + , displacing the solvent. The average coordination number becomes 3.0 FSI - , 0.46 NO 3 - , 0.58 DEE, and 0.4 DME. The overall decrease in solvents appeared in the Li + solvation shell effectively alleviates the adverse impact of DME on desolvation kinetics. By evaluating the binding energies of Li + (solvent) n complexes, the binding energies of the Li + (DEE) 1 , Li + (DEE) 0.88 (DME) 0.48 , and Li + (DEE) 0.58 (DME) 0.4 complexes were determined to be 219.19 kJ mol -1 , 316.81 kJ mol -1 , and 238.01 kJ mol -1 , respectively. Therefore, although the introduction of DME significantly increases the desolvation barrier for lithium ions, the presence of NO 3 - in DDE-PN substantially mitigates the adverse effects caused by strong solvation solvents. The kinetics of different interfacial processes were studied using temperature-variable electrochemical impedance spectroscopy (EIS). [ 25 , 26 ] The energy barrier of the desolvation process depends on the number and coordination ability of solvent molecules in the Li + solvation shell. By measuring the charge transfer resistance of Li||Li symmetric cells at different temperatures, the desolvation activation energy E a,ct of Li + in different electrolytes was determined. Figure 2 c shows that the activation energies for the DEE system and the DDE binary system are 56.89 kJ mol -1 and 62.68 kJ mol -1 , respectively. The higher desolvation energy in the DDE system is due to the stronger complexation ability of DME with Li + , significantly increasing the difficulty of Li + desolvation. However, the PN additive introduces NO 3 - ions, which can enter the first solvation shell, altering the Li + solvation structure and weakening the Li + -solvent interactions (E a,ct =57.68 kJ mol -1 for the DDE-PN), consistent with the MD results. To study the SEI formation mechanism, XPS was employed to characterize the composition and structure of the SEI on the cycled lithium metal surface. [ 27 – 29 ] The peak intensity of C–O and C = O in the SEI formed in DEE is significantly lower than that in DDE (Fig. 2 g), indicating that solvent decomposition in DEE is suppressed compared to that in DDE. Therefore, in DEE, the SEI mainly consists of a large amount of inorganic substances generated by anion reduction, while the introduction of DME disrupts the anion-enriched solvation structure in the weak solvent, greatly increasing the organic content in the SEI (Fig. 2 h and 2 i). Interestingly, the SEI formed in the DDE-PN electrolyte contains more inorganic components such as LiF and Li 3 N, because the inorganic rich SEI derived from the decomposition of PN on the lithium metal surface effectively inhibits the solvent decomposition in the mixed binary solvent system. The SEI structure was further studied by XPS spectra at different etching depths, as shown in Fig. S5-S7. The SEI in DDE-PN contains less carbon components with more inorganic components detected with sputtering time. This gradient double-layer SEI structure, where the organic layer is located at the top and the inorganic layer is rich close to the lithium surface, has been proven to be an ideal SEI structure for lithium metal anodes. [ 10 , 30 ] Similarly, the kinetic process of interface Li + transport through SEI was evaluated using variable temperature EIS. As shown in the Fig. 2 b, in the DEE system, the activation energy for Li + transport through the SEI (E a,SEI ) is 23.94 kJ mol -1 , approximately 5 kJ mol -1 lower than that of the mixed solvent system, DDE. This is because the weakly coordinating solvent DEE can form an anion-enriched solvation structure, promoting the formation of an anion-derived, inorganic-rich SEI. The inorganic substances dispersed in the anion-derived SEI create abundant phase boundaries and vacancies, facilitating rapid Li + diffusion and significantly reducing the energy barrier. In contrast, the E a,SEI of DDE-PN decreases to 20.86 kJ mol -1 , indicating that the SEI derived from the PN additive reduces the Li + diffusion barrier, even lower than that from DEE. This has greatly accelerated the Li ion diffusion kinetics, which should be attributed to the in-situ reaction of the PN additive with lithium metal, forming LiF, an electronic insulator, and Li 3 N, a fast ion conductor. This heterogeneous synergistic effect is considered an effective strategy to achieve rapid Li + transport. [ 30 , 31 ] Therefore, the PN additive allows the DDE binary solvent to combine the advantages of each component while getting rid of their disadvantages: the DDE-PN exhibits better kinetics at the interface (high quality SEI and rapid desolvation process) inherited from weak solvents, while showing high ionic conductivity in the electrolyte bulk solution brought by the strong solvents. To test the long-term cycling stability of Li metal anode in different electrolytes, Li||Li symmetric cells were assembled. It was found that the DDE-PN electrolyte effectively extended the cycle life of the Li||Li symmetric cells (Fig. 3 a, Fig. S8). Especially at high current densities, the DDE-PN electrolyte exhibited the lowest overpotential, indicating better lithium metal reversibility. Lithium metal deposition morphology at different current densities (Fig. S9, S10) showed that lithium deposition in the DEE system displayed uniformly distributed blocky lithium with minimal gaps at low current densities. However, the introduction of DME resulted in lithium metal depositing in smaller particles with larger gaps, significantly increasing the contact area between lithium metal and the electrolyte and enhancing interfacial side reactions. In contrast, lithium deposition in the DDE-PN electrolyte displayed a smooth, film-like surface morphology, considered as the preferred one for long-term cycling of lithium metal anodes. More importantly, as the current density increased, lithium metal in the DEE and DDE electrolyte systems tended to deposit as loose small particles with significantly larger gaps (Fig. 3 b and 3 c). Remarkably, lithium metal in the DDE-PN electrolyte still formed dense (Fig. 3 d), compact aggregates even at a high current density of 10 mA cm -2 , closely related to the superior lithium ion transport kinetics of the DDE-PN system. We further assembled Li||Cu cells to study the effects of different temperatures on lithium deposition behavior. At room temperature, the Li||Cu cells exhibit a remarkable CE of 99% during the first 80 cycles in three different electrolytes, as shown in the Fig. S11. However, with extended cycling, the DDE-PN electrolyte demonstrates the most stable cycling performance, maintaining a high Coulombic efficiency (CE) of 99.1% (the average value of 100 to 200 cycles). This result proves the high compatibility of the DDE-PN with lithium metal and the long-term reversibility of lithium deposition/stripping. Subsequently, we investigated the electrochemical performance of lithium metal anodes at low temperatures. As shown in the Fig. 3 e and Fig. S12, the CE values of the DEE, measured by the Aurbach’s method, were 98.89% and 97.1% at 25°C and − 60°C, respectively. For the DDE binary system, although the ionic conductivity of the electrolyte was high at -60°C as discussed before, the CE was measured to be only 71.2% at -60°C, which should be ascribed to the increased desolvation energy barrier and unstable SEI caused by the introduction of strong solvent, DME. However, the DDE-PN electrolyte exhibited the lowest overpotential, smooth lithium deposition/stripping curves, and stable operating voltage at -60°C, achieving the highest CE (97.5%). This demonstrated that the DDE-PN electrolyte had excellent Li deposition/stripping reversibility at extremely low temperatures, attributed to superior interfacial transport kinetics properties. The Li||Li symmetric cell at -60°C, as shown in Fig. 3 f, short-circuited after ~ 150 h of cycling with the DEE electrolyte. The Li||Li cell with the DDE short-circuited at the initial stage of cycling. In contrast, the Li||Li cell with the DDE-PN stably cycled for over 300 hours. This improvement is due to enhanced ionic conductivity, reduced desolvation energy barriers, and the construction of high-quality SEI, which significantly improved the long-term cycling performance of lithium metal anodes at extremely low temperatures. Additionally, the surface morphology of lithium metal anodes was characterized using scanning electron microscopy (SEM). At -60°C and a fixed capacity of 1 mAh cm -2 , lithium metal in the DEE electrolyte maintained uniform deposition without dendrite formation (Fig. 3 g). However, in the DDE electrolyte, the Li metal surface showed a large number of unevenly distributed mossy and needle-like dendrites, consistent with previous studies. The difficulty in desolvation led to a substantial increase in local charge transfer impedance, naturally driving Li deposition kinetics in a tip-driven manner. [ 6 , 8 ] The introduction of the PN additive into the DDE electrolyte resulted in oval-shaped, dendrite-free lithium metal surfaces at -60°C, with a flat interfacial structure. This demonstrated the good compatibility between the DDE-PN electrolyte and the lithium anode, especially at extremely low temperatures. A major challenge hindering the application of ether based dilute solution electrolytes is the poor oxidation stability at high voltages (<4.0 V vs. Li/Li + ), which deteriorates the compatibility of ether based electrolytes with high-voltage NMC811 cathodes. [ 32 – 34 ] Linear sweep voltammetry (LSV) was used to evaluate the electrochemical stability window of the electrolytes, as shown in the Fig. 4 a. The electrochemical windows of the DEE and DDE electrolyte did not exceed 4.0 V, whereas the DDE-PN electrolyte successfully extended the electrochemical window of the mixed ether-based electrolyte system to 4.5 V (with a cutoff current density of 0.05 mA/cm 2 ). We then evaluated the compatibility of the three electrolytes with NCM811 cathodes. Firstly, the static leakage current was measured. As shown in the Fig. 4 b, by holding the cathode at 4.3 V over 10,000 s, the leakage currents in DEE and DDE electrolytes gradually decreased and kept stable at about 0.02 mA and 0.008 mA, respectively. In contrast, the leakage current in the DDE-PN electrolyte rapidly decayed and stabilized at only 0.001 mA, indicating a better interfacial electrochemical stability. Secondly, we tested the self-discharge behaviors of the Li||NMC811 cells in the three different electrolytes. After charging the cells to 4.3 V and resting for 20 hours, there were significant differences in the self-discharge behavior of the cells. As shown in Fig. 4 c, the cell voltage in the DDE-PN electrolyte system stabilized at 4.21 V after 20 hours of rest. However, the cell voltage in the DDE electrolyte dropped to 3.8 V after 20 hours, and in the pure DEE electrolyte, the cell voltage quickly dropped below 3.5 V within only 12 hours. This indicates that the introduction of the PN additive effectively prevented the decomposition of the ether-based electrolyte at high voltage, thereby suppressing the self-discharge behavior of the cell. [ 35 ] Thirdly, Li||NCM811 cells were gavanostatic cycled with different electrolytes. As shown in Fig. S13, the Li||NCM811 half-cell with DDE-PN electrolyte demonstrated superior rate performance, with a specific capacity of 142 mAh g -1 even at a high rate of 20.0 C. In contrast, the cells with electrolytes without the PN additive showed poor rate performance, with specific capacities dropping below 50 mAh g -1 at 20.0 C for both DEE and DDE electrolytes. Similarly, the Li||NMC811 half-cell with DDE-PN electrolyte exhibited the best long-term cycling and the most stable Coulombic efficiency (CE). As shown in Fig. 4 d and 4 e, the Li||NMC811 half-cell with DDE-PN electrolyte retained 80% of its capacity after 400 cycles at 1.0 C and 76% after 1000 cycles at 5.0 C, demonstrating excellent fast charge-discharge capability at high voltage (Fig. S14 and S15). In contrast, the cells with DEE and DDE electrolytes showed rapid decay at both slow and fast charge-discharge rates during the initial cycles, as ether solvent could not withstand such high working voltages. Additionally, the introduction of the PN additive significantly reduced the interfacial impedance and showed a slower increase in impedance after cycling (Fig. S16 and S17), further confirming the effective improvement in electrode/electrolyte interfacial stability. The comparison of CV curves of Li||NMC811 half-cell after cycling also proves the long-term stability of the cathode/electrolyte interface in DDE-PN electrolyte (Fig. S18 and S19). Therefore, the introduction of the PN additive significantly inhibited the decomposition of the ether-based electrolyte at high voltage, thereby markedly enhancing the compatibility of the ether solvent with the high-voltage NMC811 cathode. SEM images showed that the NMC811 cathode suffered severe fragmentation after 50 cycles in both DEE (Fig. 4 i, Fig. S20a) and DDE (Fig. 4 j, Fig. S20b) electrolytes. Particle breakage can cause the shedding of active materials or poor electronic contact, leading to increased battery polarization, reduced content of active substances, and decreased reversible capacity of the battery. [ 36 ] In contrast, the cathode particles remained mostly intact after cycling in the DDE-PN electrolyte (Fig. 4 k, Fig. S20c). HRTEM also revealed that the CEI on the NMC811 cathode surface after cycling in the designed electrolyte was thinner, denser, and maintained better secondary particle integrity with no apparent cracks (Fig. 4 n, Fig. S21c). However, significant cracks were found within the NMC811 particles after cycling in both DEE (Fig. 4 l, Fig. S21a) and DDE (Fig. 4 m, Fig. S21b) electrolytes, indicating that the CEI formed in commercial electrolytes was not dense enough. This leads to ongoing electrochemical-stress corrosion between the electrolyte and the high-voltage cathode material, causing phase changes in the cathode material, dissolution of transition metals, and cracking of secondary particles. [ 5 , 11 ] To find out the origin of the improved compatibility of ether based electrolytes with high-voltage NMC811, In-depth XPS analysis was conducted to examine the chemical composition of the cathode electrolyte interphase (CEI) formed on the surface of NMC811 cathode material after 50 cycles in different electrolytes. A new peak at 283.1 eV in the C 1s spectrum, corresponding to the C-X metal bond, [ 37 ] was observed in DEE and DDE, indicating severe electrolyte decomposition at the NMC811 cathode interface (Fig. 5 a and Fig. S22). This is attributed to the poor anodic stability of ether-based electrolytes. With the introduction of the PN additive, the C-X metal peak almost disappeared (Fig. 5 a), indicating that the side reactions at the cathode interface were greatly suppressed. As sputtering progressed, a significant decrease in the C 1s intensity was observed in DDE-PN (Fig. S22), accompanied by a higher content of inorganic compounds such as LiF, Li 2 S, and Li x S y within the inner layer of the CEI formed in the DDE-PN electrolyte. Notably, the CEI generated from the DDE-PN electrolyte exhibited the strongest LiF peak, with an internal LiF content exceeding 39.8%, compared to 32% and 2.4% for the CEIs formed from DDE and DEE electrolytes, respectively (Fig. 5 d). This gradient distribution from organic to inorganic components within the CEI imparts excellent electronic blocking capabilities, reducing electron penetration into the CEI and thus ensuring the cycling stability of the battery. Unfortunately, the inner layer of the CEI formed in DEE revealed a higher content of carbonaceous organic compounds (from solvent decomposition) and fluorinated organic species (due to incomplete decomposition of the FSI - anion), but lower amounts of inorganic compounds such as LiF and Li 2 S (Fig. 5 a- 5 d, Fig. S22-S24). This indicates that the SEI film may be insufficiently stable and possess poor ion transport properties, rendering it unable to effectively prevent highly reactive free solvents from penetrating the CEI and undergoing continuous degradation. [ 38 , 39 ] Considering that the stability of the electrolyte depends on the aggregation state of ions and solvent molecules in the electric double layer (EDL), we further used in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) to more clearly reveal the evolution of the solvation structure in the interfacial microenvironment during charging/discharing. [ 39 , 40 ] The interface of the working electrode and electrolyte was measured by ATR-SEIRAS in-situly during the charging/discharging under the potentiostatic mode. The voltage was settled between 3.0 and 3.6 V to ensure purely capacitive behavior throughout the test and to avoid the influence of irreversible decomposition products of the electrolyte. As shown in Fig.s 5a and 5b, the intensity of the peak at 1588 cm -1 , corresponding to NO 3 - , increased with charging (Fig. S25), indicating that NO 3 - ions preferentially adsorb in the inner Helmholtz layer (IHP). The is probably due to the smaller ionic size of NO 3 - ions, consistent with previous studies. [ 5 , 41 ] Meanwhile, there are several Raman bands in the 800–900 cm -1 range. The bands at 821 cm -1 and 849 cm -1 correspond to free ether solvents with different isomers, and the band at 879 cm -1 corresponds to Li + -solvated ether solvent. The area ratio of the free solvent peak to the coordination solvent peak reflects the proportion of the bounding state of the solvent to the total volume (Fig. 5 e- 5 g). By fitting the relationship between the ratio of coordination ether solvent and the voltage at the cathode/electrolyte interface, as shown in Fig. S26, in the electrolyte without the PN additive, most ether molecules at the cathode interface exist in a free state, and the proportion of Li + -solvated ether solvents decreases with increasing voltage. Consequently, an EDL composed of a large amount of anodic unstable, free ether solvents will undoubtedly degrade at high voltage. For the DDE-PN electrolyte system, however, the proportion of Li + -solvated ether solvent increases significantly with increasing voltage, indicating that the introduction of NO 3 - allows more ether to participate in the solvation shell, forming an anodic stable EDL capable of withstanding the high-voltage environment at the cathode. Therefore, the preferential adsorption of NO 3 - leads to the displacement of the solvent, and Li + is attracted in large quantities to the electrode interface due to the strong interaction between NO 3 - and Li + . As a result, the ether present in the EDL layer is extensively bounded with Li + , constructing a highly oxidative-stable EDL. Thus, by reducing the content of active ether solvents in the initially formed EDL, the PN additive is able to altering the stability of ether solvents at the cathode interface. Overall, the DDE-PN electrolyte offers a dual protection mechanism by forming a thin, inorganic-rich CEI and establishing a thermodynamically favorable EDL. This effectively mitigates ether-based electrolyte decomposition and cathode material structural degradation, significantly enhancing the compatibility of ether-based electrolytes with high-voltage cathodes. Therefore, by reducing the content of active ether solvents in the initially formed EDL, the risk of free solvent degradation by the high-voltage cathode is minimized. Additionally, this solvent-poor, anion-rich EDL promotes the formation of an inorganic-rich CEI, which, through dual protection, significantly enhances the electrochemical stability of the cathode/electrolyte interface in ether-based electrolyte systems (Fig. 5 h- 5 j). Lastly, we investigated the electrochemical properties of these three electrolytes in Li||NMC811 full cells and practical LMBs, respectively. The gavanostatic cycling was conducted under room temperature and ultra-low temperature conditions. As shown in Fig. 6 a, the DDE-PN electrolyte enabled the Li (40 µm)||NMC811 (3.0 mAh cm -2 ) full cell to exhibit excellent cycling performance at room temperature, with a capacity retention rate of 84% after 300 cycles. In contrast, the DDE and DEE electrolytes showed poor cycling performance, with severe capacity degradation occurring at the initial cycle and after 70 cycles, respectively, due to the suboptimal high-voltage compatibility of ether-based solvents. Additionally, under harsh ultra-low temperature conditions (-60°C), the Li||NMC811 full cell was able to stably charge and discharge, providing a high reversible capacity of 110 mAh g -1 over 100 cycles with a capacity retention of 93.3%, indicating excellent cycling stability (Fig. 6 c). The corresponding charge/discharge curves with temperature variation also exhibited distinct voltage plateaus, indicating good charge/discharge capability at low temperatures (Fig. 6 d). Further, 500 mAh Li||NMC811 pouch cells were also evaluated in DDE-PN electrolyte under ultra-low temperature scenarios. As shown in the Fig. 6 e, the pouch cells were able to deliver energy densities of 337.3 mAh, 257.4 mAh, and 245.4 mAh at -60°C, -80°C, and − 85°C, respectively, corresponding to capacity retention rates of 66.1%, 50.5% and 48.1% relative to room temperature. Excitingly, even at -85°C, the pouch cell could achieve an impressive energy density of 171.8 Wh kg -1 . Remarkably, the pouch cell with DDE-PN electrolyte could discharge at a high rate of 3.0 C at -50°C, demonstrating a record-breaking power density of 938.5 W kg -1 at such harsh low-temperature condition (Fig. 6 f, Fig. S27). Compared to previously reported low-temperature lithium metal batteries, [ 6 , 42 – 45 ] our practical pouch cell exhibits significant advantages in energy density and power density under extremely low temperatures (Table S1 ), which is promising to provide reliable power for high-power devices in ultra-low temperature environments. 3. Conclusion In summary, a multifunctional electrolyte additive, PN, was designed and studied for high power lithium metal batteries at ultra-low temperatures. PN preferentially decomposes on the anode to improve the SEI, while optimize the solvation structure and improve the EDL at the cathode/electrolyte interface, which results in excellent comprehensive performance, including high voltage tolerance, high ionic conductivity, low desolvation energy, and the ability to derive an inorganic-rich SEI. Impressively, the practical industrial Li||NMC811 pouch cell cycled in binary ether based electrolyte, DDE-PN, could stably discharge at -85°C, maintaining 48.1% of its room temperature capacity, and achieving an unprecedented energy density of 171.8 Wh kg -1 at such harsh low-temperature condition. Even more remarkably, the pouch cell could discharge at a high rate of 3.0 C at -50°C, achieving a record-breaking power density of 938.5 W kg -1 . This activation of practical high-rate lithium metal batteries under extreme low-temperature conditions provides valuable design insights and theoretical background for low-temperature lithium metal battery electrolyte engineering. Declarations Conflict of Interest The authors declare no conflict of interest. Acknowledgments We gratefully acknowledge support by the Opening Project of State Key Laboratory of Space-Power Source, the National Key Research and Development Program (2023YFB2503700), the National Science Foundation of China (22071133, 22409117), Anhui Provincial Natural Science Foundation (240808QB043), the Tsinghua University-China Petrochemical Corporation Joint Institute for Green Chemical Engineering (224247), Beijing Science and Technology Plan Project (Z231100006123003), China Postdoctoral Science Foundation (2024M751747). Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. 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Research","correspondingAuthor":false,"prefix":"","firstName":"Chunyi","middleName":"","lastName":"Du","suffix":""}],"badges":[],"createdAt":"2024-11-18 08:40:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5474223/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5474223/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-58627-3","type":"published","date":"2025-04-08T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":70460784,"identity":"f8054a63-1128-4dfa-b7b6-25f8045e1896","added_by":"auto","created_at":"2024-12-03 11:31:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":499329,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSimulation and characterization of in-situ reaction between PN additive and lithium metal.\u003c/strong\u003e (a) Calculated HOMO and LUMO of the solvents, anion and additives. (b) F 1s, (c) N 1s, (d) O 1s, (e) S 2p XPS spectra of bare-lithium metal and immersed lithium metal in a DME solution containing 0.1 M PN. (f) Snapshots from AIMD simulation of decomposition reaction processes between PN with Li metal.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/b9ff7d453e988a836bc36c4f.png"},{"id":70461759,"identity":"3aea5824-1055-4ec2-9a76-52405c20ab2e","added_by":"auto","created_at":"2024-12-03 11:39:11","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":276673,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIon diffusion, charge transfer, solvation structures of electrolytes, and chemical compositions of SEI. \u003c/strong\u003e(a) Ion conductivity of different electrolytes in a wide temperature range. (b) The activation energy of Li\u003csup\u003e+\u003c/sup\u003e transport in SEI. (c) The activation energies for Li\u003csup\u003e+\u003c/sup\u003e desolvation at the anode interface. Radial distribution functions and coordination numbers in (d) DEE, (e) DDE and (f) DDE-PN. (g) C 1s, (h) N 1s, (i) F 1s XPS spectra of Li metal cycled with different electrolytes.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/ddeaa6caf668d2693065fafb.png"},{"id":70460787,"identity":"b546b5a7-7ca9-4e42-b67e-86aa5ff39399","added_by":"auto","created_at":"2024-12-03 11:31:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":506656,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe electrochemical performance of lithium metal anode under fast charging and low-temperature conditions. \u003c/strong\u003e(a) Cyclic stability of Li||Li symmetric cells at 10 mA cm\u003csup\u003e-2 \u003c/sup\u003eunder 25 ℃. The SEM morphologies of Li deposited on Cu foil cycled in (b) DEE, (c) DDE and (d) DDE-PN electrolytes under 25 ℃. (e) Li metal plating/stripping CE evaluated by Li||Cu half cells at 0.5 mA cm\u003csup\u003e-2\u003c/sup\u003e with a fixed discharge capacity of 1.0 mAh cm\u003csup\u003e-1 \u003c/sup\u003eunder -60 ℃. Cyclic stability of Li||Li symmetric cells at 0.5 mA cm\u003csup\u003e-2 \u003c/sup\u003eunder -60 ℃. SEM morphologies of Li deposited on Cu foil cycled in (g) DEE, (h) DDE and (i) DDE-PN electrolytes under -60 ℃.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/4630ab3d69fdc01de66bcdfb.png"},{"id":70461760,"identity":"96ce5894-f2c8-48e6-b7e8-5de8e803ad6d","added_by":"auto","created_at":"2024-12-03 11:39:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":619163,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEvaluation of electrolyte oxidation stability and characterization of NCM811 cathode structure.\u003c/strong\u003e (a) Oxidative stability measured via LSV for Li||Al cells. (b) Self-discharge tests after a potentiostatic hold at 4.3 V vs Li/Li\u003csup\u003e+\u003c/sup\u003e. (c) Typical current relaxation curves collected from Li||NMC811 half-cells during a potentiostatic hold at 4.3 V vs Li/Li\u003csup\u003e+\u003c/sup\u003e. Long-term cycling performance in Li||NMC811 cells at (d) 1.0 C and (e) 5.0 C. (f) SEM and (g) TEM images of NCM811 electrode cycled with different electrolytes.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/a0279c2dde8373fe15b264ea.png"},{"id":70460795,"identity":"3f4210bd-2bfd-4b2f-84d3-b5b9ada51a1a","added_by":"auto","created_at":"2024-12-03 11:31:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":384777,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of CEI compositions and electrolyte structure at the cathode surface.\u003c/strong\u003e (a) C 1s, (b) F 1s, (c) S 2p XPS spectra at depth sputtering at 15 nm of NCM811 cathode cycled with different electrolytes after 50 cycles. (d) Proportion diagram of different components at depth sputtering at 15 nm. ATR-SEIRAS of the surface layer of the working electrode under different voltages in (e) DEE, (f) DDE and (g) DDE-PN. Schematic diagram of the mechanism at the cathode/electrolyte interface in (h) DEE, (i) DDE and (j) DDE-PN.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/aea8e460a37569e21f06a85c.png"},{"id":70460791,"identity":"9129d053-50e7-4bba-8cdb-c65ea965ae5e","added_by":"auto","created_at":"2024-12-03 11:31:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":206423,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance of full cell and pouch cell at low temperatures. \u003c/strong\u003e(a) Long-term cycling performances of high-voltage Li||NMC811 full cells with 40μm Li anode. The N/P ratios of the Li||NMC811 cell was 3. The first two formation cycles were carried out at a 0.1 C rate, followed by 0.3 C charge and 1.0 C discharge. (b) The corresponding voltage profiles of high-voltage Li||NMC811 full batteries using electrolytes with DDE-PN. (c) Cycling performance of full cells at -60 ℃. (d) The corresponding voltage profiles of high-voltage Li||NMC811 full batteries using DDE-PN. (e) Discharge profiles (0.1 C) of 500 mAh Li||NMC811 cells using DDE-PN electrolyte at different temperatures. (g) Comparison of a cell-level (output) energy density and power density with state-of-the-art electrolytes and our work at ultra-low temperature.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/9c6609849f4895ab3cd5761c.png"},{"id":80202834,"identity":"1a30b5ec-3d57-4efa-984f-289ae2ff9e9e","added_by":"auto","created_at":"2025-04-09 07:07:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3236072,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/1e27bb22-ff93-4e89-a7d1-d18368138076.pdf"},{"id":70460788,"identity":"e40112d5-e6dc-449c-a157-74881b80863a","added_by":"auto","created_at":"2024-12-03 11:31:12","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5256144,"visible":true,"origin":"","legend":"SUPPLEMENTARY INFO","description":"","filename":"supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-5474223/v1/d81865c7d6139b1aa7d41ab6.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe development of lithium metal batteries (LMBs) has garnered significant attention due to their potential to deliver high energy density. However, the thermodynamic instability of lithium metal and the significant volume changes during deposition and stripping processes lead to the fragility of the solid electrolyte interphase (SEI) on the lithium metal anode surface. This instability results in the growth of dendritic lithium and the formation of dead lithium during repeated deposition/stripping cycles, ultimately causing low Coulombic efficiency (CE) and poor cycling performance. These issues are exacerbated under low-temperature conditions due to sluggish kinetics.\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e Therefore, their practical application, especially under low-temperature conditions, faces several challenges, particularly concerning the choice of electrolytes.\u003csup\u003e[\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e The electrolyte plays a crucial role in the performance and safety of LMBs, influencing factors such as ionic conductivity, solid electrolyte interphase (SEI) formation, and overall electrochemical stability. \u003csup\u003e[\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eRecent advancements have identified ether-based weakly solvating solvents, such as diethyl ether (DEE), as preferred choices for low-temperature LMB electrolytes due to their excellent reduction stability and compatibility with lithium metal. More importantly, DEE offers advantages like rapid desolvation and the formation of anion-derived SEI. Previous studies have shown that inorganic rich SEI has unique advantages in inhibiting the growth of lithium dendrites due to its effective blocking of electron tunneling, promoting uniform Li\u003csup\u003e+\u003c/sup\u003e transport and superior mechanical properties. However, its low dissociation degree of lithium salts results in low ionic conductivity, and its poor high-voltage stability limits compatibility with high-voltage cathodes.\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e Conversely, strongly solvating solvents like dimethoxyethane (DME) exhibit high lithium salt dissociation, allowing DME based electrolytes to achieve high ionic conductivity, especially at low temperatures. In addition, they can address high-voltage issues with the help of specific additives. Nevertheless, strong solvents face challenges such as difficult desolvation and large voltage drops, which can lead to uncontrolled growth of lithium dendrites at low temperatures, and will ultimately pose safety risks.\u003csup\u003e[\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e Many recent reports on low-temperature electrolytes focus on combining strongly and weakly solvating solvents to balance ion conductivity and desolvation ability. However, due to the strong coupling between ion transport and desolvation, it is challenging to simultaneously attain high ion conductivity and low desolvation energy.\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e Therefore, there is a need for a more advanced approach to electrolyte design that can harness the advantages of both strong and week solvents while mitigating their respective drawbacks. Here, we chose a binary solvent system consisting of a mixture of strong (DME) and weak solvating solvents (DEE) for the electrolyte. We demonstrated that introducing a small amount of a strongly solvating solvent into a weakly solvating solvent significantly enhances the ionic conductivity of the electrolyte without notably altering the solvation structure of the weak solvent (DEE: DME\u0026thinsp;=\u0026thinsp;9:1 vol%). Furthermore, we designed and synthesized a multifunctional additive, perfluoroalkylsulfonyl quaternary ammonium nitrate (PQA-NO\u003csub\u003e3,\u003c/sub\u003e note as PN), containing both cations (PAQ\u003csup\u003e+\u003c/sup\u003e) and anions (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e). Based on the frontier orbital theory and the calculation results of reaction energy, PAQ\u003csup\u003e+\u003c/sup\u003e can be preferentially reduced on the surface of Li metal to form LiF with high interface energy and Li\u003csub\u003e3\u003c/sub\u003eN, Li\u003csub\u003e2\u003c/sub\u003eO, Li\u003csub\u003e2\u003c/sub\u003eS with high ionic conductivity, ensuring rapid transport of Li\u003csup\u003e+\u003c/sup\u003e through SEI and inhibiting the growth of lithium dendrites at ultra-low temperatures. In addition, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e enters the Li\u003csup\u003e+\u003c/sup\u003e solvation shell and repels the solvent, weakening the interaction between Li\u003csup\u003e+\u003c/sup\u003e and the solvent, accelerating the process of Li\u003csup\u003e+\u003c/sup\u003e de-solvation, and greatly alleviating the inevitable increase in de-solvation energy barrier caused by the introduction of strong solvents DME. Besides, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e constructs a high oxidation stability cathode/electrolyte interface with poor-solvent and rich-anions, enabling the ether based solvent system to match the NMC811 cathode for stable cycling at a high operating voltage of 4.3 V. As a result, the Li||NMC811 full cell using the designed electrolyte exhibits stable long-term cycling performance under extremely low temperature conditions of -60 ℃. The actual industrialized pouch cell can stably discharge at -85\u0026deg;C, maintaining 45% of its room temperature capacity and achieving an impressive energy density of 171.8 Wh kg\u003csup\u003e-1\u003c/sup\u003e(except taps and packing foil, same hereafter) at -85\u0026deg;C. Remarkably, the pouch cell can discharge at a high rate of 3.0 C at -50\u0026deg;C, achieving a record-breaking power density of 938.5 W kg\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e"},{"header":"2. Results and Discussion","content":"\u003cp\u003eAccording to molecular frontier orbital theory, electrolyte components with lower LUMO energy levels are thermodynamically more inclined to undergo reductive decomposition. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea calculated the molecular orbital energy levels of different components in the electrolyte, and the results show that the PN additive molecules have lower LUMO energy levels, leading to preferential decomposition on the lithium metal surface and participation in SEI formation. Furthermore, we immersed lithium metal in a DME solution containing 0.1 M PN for 2 hours, then tested its surface composition using X-ray photoelectron spectroscopy (XPS). Commercial lithium metal foil typically exhibits a native passivation layer rich in Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and LiOH (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec-e), which increases the impedance and overpotential of the electrode, and also affects the subsequent construction of SEI on the electrode surface.\u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e However, after soaking, the surface of the lithium metal showed significant amounts of inorganic compounds such as LiF, Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, Li\u003csub\u003e2\u003c/sub\u003eO, Li\u003csub\u003e2\u003c/sub\u003eS and Li\u003csub\u003e3\u003c/sub\u003eN, demonstrating that PN can react in situ with lithium metal to form an inorganic-rich SEI film, altering the structure of the native passivation layer. The abundant inorganic components are typically considered to enhance the mechanical strength of the SEI, allowing it to accommodate repeated volume changes and inhibit dendrite growth, thereby promoting stable cycling of the lithium metal anode at low temperatures.\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e We further employed the ab initio molecular dynamic (AIMD) calculations to elucidate the interfacial reaction mechanism between the PN additive and the Li metal anode.\u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef and Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e-S3 shows snapshots of AIMD simulations at different simulation timescales. PN was found to automatically adsorb to the surface of lithium metal, and the NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e anions decompose first, forming Li\u003csub\u003e3\u003c/sub\u003eN and Li\u003csub\u003e2\u003c/sub\u003eO components. At the same time, the S\u0026thinsp;=\u0026thinsp;O bond of PAQ\u003csup\u003e+\u003c/sup\u003e breaks and generates Li\u003csub\u003e2\u003c/sub\u003eS components on the surface of lithium metal. As the reactants were exposed to more Li\u003csup\u003e0\u003c/sup\u003e by diffusion, the PN underwent a rapid defluororination process via C-F cleavage, leading to a substantial amount of LiF formation. However, the DME solvent is relatively stable with the Li metal, and no decomposition reaction occurs on the lithium metal surface in the simulated time scale. Therefore, the simulation results demonstrate that PN can preferentially undergo in-situ chemical reactions with lithium metal over the solvent, resulting in the formation of an inorganic-rich SEI layer with strong mechanical strength and rapid lithium-ion conduction capability, consistent with the experimental observations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAdditionally, the ion transport properties, desolvation ability, and film-forming characteristics of 1.0 M LiFSI/DEE (note as DEE), 1.0 M LiFSI/DEE\u0026thinsp;+\u0026thinsp;DME DEE: DME\u0026thinsp;=\u0026thinsp;9:1 vol%, note as DDE), and DDE\u0026thinsp;+\u0026thinsp;0.1 M PN (DDE-PN) electrolytes were investigated and compared. As shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, the measured ionic conductivity of the electrolyte using a single DEE solvent is relatively low, only 0.22 mS cm\u003csup\u003e-1\u003c/sup\u003e at -60\u0026deg;C, due to insufficient dissociation of lithium salts by weak solvents. However, the introduction of 10% vol of the strong solvent DME increased the conductivity of the entire electrolyte system by an order of magnitude, with the conductivity of the DDE electrolyte reaching 2.32 mS cm\u003csup\u003e-1\u003c/sup\u003e at -60\u0026deg;C. The presence of 0.1 M PN additive did not significantly affect the conductivity of the mixed solvent electrolyte system, with the DDE-PN electrolyte showing a high conductivity of 2.11 mS cm\u003csup\u003e-1\u003c/sup\u003e at -60\u0026deg;C. Further classical molecular dynamics (MD) simulations were conducted (Fig. S4), utilizing radial distribution functions (RDF) to describe the average local solute-solute interaction environment (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed-f). The analysis indicates that the DEE electrolytes exhibit a characteristic contact ion pair (CIP) structure, where the Li\u003csup\u003e+\u003c/sup\u003e solvation shell contains FSI\u0026ndash;rich anions with little DEE molecules, with an average coordination number of 3.2 FSI\u003csup\u003e-\u003c/sup\u003e and 1.0 DEE, consistent with previous studies.\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e With the introduction of the DME solvent, due to the strong interaction between Li\u003csup\u003e+\u003c/sup\u003e and DME, DME enters the Li\u003csup\u003e+\u003c/sup\u003e solvation shell, replacing some DEE solvent molecules. The average coordination number becomes 3.2 FSI\u003csup\u003e-\u003c/sup\u003e, 0.88 DEE, and 0.48 DME, indicating that DME entered the solvation shell and squeezed out some DEE solvents. However, when the PN additive is introduced into the mixed solvent system, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e enters the Li\u003csup\u003e+\u003c/sup\u003e solvation shell due to its stronger binding ability with Li\u003csup\u003e+\u003c/sup\u003e, displacing the solvent. The average coordination number becomes 3.0 FSI\u003csup\u003e-\u003c/sup\u003e, 0.46 NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, 0.58 DEE, and 0.4 DME. The overall decrease in solvents appeared in the Li\u003csup\u003e+\u003c/sup\u003e solvation shell effectively alleviates the adverse impact of DME on desolvation kinetics. By evaluating the binding energies of Li\u003csup\u003e+\u003c/sup\u003e(solvent)\u003csub\u003en\u003c/sub\u003e complexes, the binding energies of the Li\u003csup\u003e+\u003c/sup\u003e(DEE)\u003csub\u003e1\u003c/sub\u003e, Li\u003csup\u003e+\u003c/sup\u003e(DEE)\u003csub\u003e0.88\u003c/sub\u003e(DME)\u003csub\u003e0.48\u003c/sub\u003e, and Li\u003csup\u003e+\u003c/sup\u003e(DEE)\u003csub\u003e0.58\u003c/sub\u003e(DME)\u003csub\u003e0.4\u003c/sub\u003e complexes were determined to be 219.19 kJ mol\u003csup\u003e-1\u003c/sup\u003e, 316.81 kJ mol\u003csup\u003e-1\u003c/sup\u003e, and 238.01 kJ mol\u003csup\u003e-1\u003c/sup\u003e, respectively. Therefore, although the introduction of DME significantly increases the desolvation barrier for lithium ions, the presence of NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e in DDE-PN substantially mitigates the adverse effects caused by strong solvation solvents. The kinetics of different interfacial processes were studied using temperature-variable electrochemical impedance spectroscopy (EIS).\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e The energy barrier of the desolvation process depends on the number and coordination ability of solvent molecules in the Li\u003csup\u003e+\u003c/sup\u003e solvation shell. By measuring the charge transfer resistance of Li||Li symmetric cells at different temperatures, the desolvation activation energy E\u003csub\u003ea,ct\u003c/sub\u003e of Li\u003csup\u003e+\u003c/sup\u003e in different electrolytes was determined. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec shows that the activation energies for the DEE system and the DDE binary system are 56.89 kJ mol\u003csup\u003e-1\u003c/sup\u003e and 62.68 kJ mol\u003csup\u003e-1\u003c/sup\u003e, respectively. The higher desolvation energy in the DDE system is due to the stronger complexation ability of DME with Li\u003csup\u003e+\u003c/sup\u003e, significantly increasing the difficulty of Li\u003csup\u003e+\u003c/sup\u003e desolvation. However, the PN additive introduces NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e ions, which can enter the first solvation shell, altering the Li\u003csup\u003e+\u003c/sup\u003e solvation structure and weakening the Li\u003csup\u003e+\u003c/sup\u003e-solvent interactions (E\u003csub\u003ea,ct\u003c/sub\u003e=57.68 kJ mol\u003csup\u003e-1\u003c/sup\u003e for the DDE-PN), consistent with the MD results.\u003c/p\u003e \u003cp\u003eTo study the SEI formation mechanism, XPS was employed to characterize the composition and structure of the SEI on the cycled lithium metal surface.\u003csup\u003e[\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e The peak intensity of C\u0026ndash;O and C\u0026thinsp;=\u0026thinsp;O in the SEI formed in DEE is significantly lower than that in DDE (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg), indicating that solvent decomposition in DEE is suppressed compared to that in DDE. Therefore, in DEE, the SEI mainly consists of a large amount of inorganic substances generated by anion reduction, while the introduction of DME disrupts the anion-enriched solvation structure in the weak solvent, greatly increasing the organic content in the SEI (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei). Interestingly, the SEI formed in the DDE-PN electrolyte contains more inorganic components such as LiF and Li\u003csub\u003e3\u003c/sub\u003eN, because the inorganic rich SEI derived from the decomposition of PN on the lithium metal surface effectively inhibits the solvent decomposition in the mixed binary solvent system. The SEI structure was further studied by XPS spectra at different etching depths, as shown in Fig. S5-S7. The SEI in DDE-PN contains less carbon components with more inorganic components detected with sputtering time. This gradient double-layer SEI structure, where the organic layer is located at the top and the inorganic layer is rich close to the lithium surface, has been proven to be an ideal SEI structure for lithium metal anodes.\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e Similarly, the kinetic process of interface Li\u003csup\u003e+\u003c/sup\u003e transport through SEI was evaluated using variable temperature EIS. As shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, in the DEE system, the activation energy for Li\u003csup\u003e+\u003c/sup\u003e transport through the SEI (E\u003csub\u003ea,SEI\u003c/sub\u003e) is 23.94 kJ mol\u003csup\u003e-1\u003c/sup\u003e, approximately 5 kJ mol\u003csup\u003e-1\u003c/sup\u003e lower than that of the mixed solvent system, DDE. This is because the weakly coordinating solvent DEE can form an anion-enriched solvation structure, promoting the formation of an anion-derived, inorganic-rich SEI. The inorganic substances dispersed in the anion-derived SEI create abundant phase boundaries and vacancies, facilitating rapid Li\u003csup\u003e+\u003c/sup\u003e diffusion and significantly reducing the energy barrier. In contrast, the E\u003csub\u003ea,SEI\u003c/sub\u003e of DDE-PN decreases to 20.86 kJ mol\u003csup\u003e-1\u003c/sup\u003e, indicating that the SEI derived from the PN additive reduces the Li\u003csup\u003e+\u003c/sup\u003e diffusion barrier, even lower than that from DEE. This has greatly accelerated the Li ion diffusion kinetics, which should be attributed to the in-situ reaction of the PN additive with lithium metal, forming LiF, an electronic insulator, and Li\u003csub\u003e3\u003c/sub\u003eN, a fast ion conductor. This heterogeneous synergistic effect is considered an effective strategy to achieve rapid Li\u003csup\u003e+\u003c/sup\u003e transport.\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e Therefore, the PN additive allows the DDE binary solvent to combine the advantages of each component while getting rid of their disadvantages: the DDE-PN exhibits better kinetics at the interface (high quality SEI and rapid desolvation process) inherited from weak solvents, while showing high ionic conductivity in the electrolyte bulk solution brought by the strong solvents.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo test the long-term cycling stability of Li metal anode in different electrolytes, Li||Li symmetric cells were assembled. It was found that the DDE-PN electrolyte effectively extended the cycle life of the Li||Li symmetric cells (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, Fig. S8). Especially at high current densities, the DDE-PN electrolyte exhibited the lowest overpotential, indicating better lithium metal reversibility. Lithium metal deposition morphology at different current densities (Fig. S9, S10) showed that lithium deposition in the DEE system displayed uniformly distributed blocky lithium with minimal gaps at low current densities. However, the introduction of DME resulted in lithium metal depositing in smaller particles with larger gaps, significantly increasing the contact area between lithium metal and the electrolyte and enhancing interfacial side reactions. In contrast, lithium deposition in the DDE-PN electrolyte displayed a smooth, film-like surface morphology, considered as the preferred one for long-term cycling of lithium metal anodes. More importantly, as the current density increased, lithium metal in the DEE and DDE electrolyte systems tended to deposit as loose small particles with significantly larger gaps (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Remarkably, lithium metal in the DDE-PN electrolyte still formed dense (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed), compact aggregates even at a high current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e, closely related to the superior lithium ion transport kinetics of the DDE-PN system. We further assembled Li||Cu cells to study the effects of different temperatures on lithium deposition behavior. At room temperature, the Li||Cu cells exhibit a remarkable CE of 99% during the first 80 cycles in three different electrolytes, as shown in the Fig. S11. However, with extended cycling, the DDE-PN electrolyte demonstrates the most stable cycling performance, maintaining a high Coulombic efficiency (CE) of 99.1% (the average value of 100 to 200 cycles). This result proves the high compatibility of the DDE-PN with lithium metal and the long-term reversibility of lithium deposition/stripping.\u003c/p\u003e \u003cp\u003eSubsequently, we investigated the electrochemical performance of lithium metal anodes at low temperatures. As shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee and Fig. S12, the CE values of the DEE, measured by the Aurbach\u0026rsquo;s method, were 98.89% and 97.1% at 25\u0026deg;C and \u0026minus;\u0026thinsp;60\u0026deg;C, respectively. For the DDE binary system, although the ionic conductivity of the electrolyte was high at -60\u0026deg;C as discussed before, the CE was measured to be only 71.2% at -60\u0026deg;C, which should be ascribed to the increased desolvation energy barrier and unstable SEI caused by the introduction of strong solvent, DME. However, the DDE-PN electrolyte exhibited the lowest overpotential, smooth lithium deposition/stripping curves, and stable operating voltage at -60\u0026deg;C, achieving the highest CE (97.5%). This demonstrated that the DDE-PN electrolyte had excellent Li deposition/stripping reversibility at extremely low temperatures, attributed to superior interfacial transport kinetics properties. The Li||Li symmetric cell at -60\u0026deg;C, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, short-circuited after ~\u0026thinsp;150 h of cycling with the DEE electrolyte. The Li||Li cell with the DDE short-circuited at the initial stage of cycling. In contrast, the Li||Li cell with the DDE-PN stably cycled for over 300 hours. This improvement is due to enhanced ionic conductivity, reduced desolvation energy barriers, and the construction of high-quality SEI, which significantly improved the long-term cycling performance of lithium metal anodes at extremely low temperatures. Additionally, the surface morphology of lithium metal anodes was characterized using scanning electron microscopy (SEM). At -60\u0026deg;C and a fixed capacity of 1 mAh cm\u003csup\u003e-2\u003c/sup\u003e, lithium metal in the DEE electrolyte maintained uniform deposition without dendrite formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). However, in the DDE electrolyte, the Li metal surface showed a large number of unevenly distributed mossy and needle-like dendrites, consistent with previous studies. The difficulty in desolvation led to a substantial increase in local charge transfer impedance, naturally driving Li deposition kinetics in a tip-driven manner.\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e The introduction of the PN additive into the DDE electrolyte resulted in oval-shaped, dendrite-free lithium metal surfaces at -60\u0026deg;C, with a flat interfacial structure. This demonstrated the good compatibility between the DDE-PN electrolyte and the lithium anode, especially at extremely low temperatures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA major challenge hindering the application of ether based dilute solution electrolytes is the poor oxidation stability at high voltages (\u0026lt;4.0 V vs. Li/Li\u003csup\u003e+\u003c/sup\u003e), which deteriorates the compatibility of ether based electrolytes with high-voltage NMC811 cathodes.\u003csup\u003e[\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e Linear sweep voltammetry (LSV) was used to evaluate the electrochemical stability window of the electrolytes, as shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The electrochemical windows of the DEE and DDE electrolyte did not exceed 4.0 V, whereas the DDE-PN electrolyte successfully extended the electrochemical window of the mixed ether-based electrolyte system to 4.5 V (with a cutoff current density of 0.05 mA/cm\u003csup\u003e2\u003c/sup\u003e). We then evaluated the compatibility of the three electrolytes with NCM811 cathodes. Firstly, the static leakage current was measured. As shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, by holding the cathode at 4.3 V over 10,000 s, the leakage currents in DEE and DDE electrolytes gradually decreased and kept stable at about 0.02 mA and 0.008 mA, respectively. In contrast, the leakage current in the DDE-PN electrolyte rapidly decayed and stabilized at only 0.001 mA, indicating a better interfacial electrochemical stability. Secondly, we tested the self-discharge behaviors of the Li||NMC811 cells in the three different electrolytes. After charging the cells to 4.3 V and resting for 20 hours, there were significant differences in the self-discharge behavior of the cells. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, the cell voltage in the DDE-PN electrolyte system stabilized at 4.21 V after 20 hours of rest. However, the cell voltage in the DDE electrolyte dropped to 3.8 V after 20 hours, and in the pure DEE electrolyte, the cell voltage quickly dropped below 3.5 V within only 12 hours. This indicates that the introduction of the PN additive effectively prevented the decomposition of the ether-based electrolyte at high voltage, thereby suppressing the self-discharge behavior of the cell.\u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e Thirdly, Li||NCM811 cells were gavanostatic cycled with different electrolytes. As shown in Fig. S13, the Li||NCM811 half-cell with DDE-PN electrolyte demonstrated superior rate performance, with a specific capacity of 142 mAh g\u003csup\u003e-1\u003c/sup\u003e even at a high rate of 20.0 C. In contrast, the cells with electrolytes without the PN additive showed poor rate performance, with specific capacities dropping below 50 mAh g\u003csup\u003e-1\u003c/sup\u003e at 20.0 C for both DEE and DDE electrolytes. Similarly, the Li||NMC811 half-cell with DDE-PN electrolyte exhibited the best long-term cycling and the most stable Coulombic efficiency (CE). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee, the Li||NMC811 half-cell with DDE-PN electrolyte retained 80% of its capacity after 400 cycles at 1.0 C and 76% after 1000 cycles at 5.0 C, demonstrating excellent fast charge-discharge capability at high voltage (Fig. S14 and S15). In contrast, the cells with DEE and DDE electrolytes showed rapid decay at both slow and fast charge-discharge rates during the initial cycles, as ether solvent could not withstand such high working voltages. Additionally, the introduction of the PN additive significantly reduced the interfacial impedance and showed a slower increase in impedance after cycling (Fig. S16 and S17), further confirming the effective improvement in electrode/electrolyte interfacial stability. The comparison of CV curves of Li||NMC811 half-cell after cycling also proves the long-term stability of the cathode/electrolyte interface in DDE-PN electrolyte (Fig. S18 and S19). Therefore, the introduction of the PN additive significantly inhibited the decomposition of the ether-based electrolyte at high voltage, thereby markedly enhancing the compatibility of the ether solvent with the high-voltage NMC811 cathode. SEM images showed that the NMC811 cathode suffered severe fragmentation after 50 cycles in both DEE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ei, Fig. S20a) and DDE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ej, Fig. S20b) electrolytes. Particle breakage can cause the shedding of active materials or poor electronic contact, leading to increased battery polarization, reduced content of active substances, and decreased reversible capacity of the battery.\u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e In contrast, the cathode particles remained mostly intact after cycling in the DDE-PN electrolyte (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ek, Fig. S20c). HRTEM also revealed that the CEI on the NMC811 cathode surface after cycling in the designed electrolyte was thinner, denser, and maintained better secondary particle integrity with no apparent cracks (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003en, Fig. S21c). However, significant cracks were found within the NMC811 particles after cycling in both DEE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003el, Fig. S21a) and DDE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003em, Fig. S21b) electrolytes, indicating that the CEI formed in commercial electrolytes was not dense enough. This leads to ongoing electrochemical-stress corrosion between the electrolyte and the high-voltage cathode material, causing phase changes in the cathode material, dissolution of transition metals, and cracking of secondary particles.\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo find out the origin of the improved compatibility of ether based electrolytes with high-voltage NMC811, In-depth XPS analysis was conducted to examine the chemical composition of the cathode electrolyte interphase (CEI) formed on the surface of NMC811 cathode material after 50 cycles in different electrolytes. A new peak at 283.1 eV in the C 1s spectrum, corresponding to the C-X\u003csub\u003emetal\u003c/sub\u003e bond,\u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e was observed in DEE and DDE, indicating severe electrolyte decomposition at the NMC811 cathode interface (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and Fig. S22). This is attributed to the poor anodic stability of ether-based electrolytes. With the introduction of the PN additive, the C-X\u003csub\u003emetal\u003c/sub\u003e peak almost disappeared (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), indicating that the side reactions at the cathode interface were greatly suppressed. As sputtering progressed, a significant decrease in the C 1s intensity was observed in DDE-PN (Fig. S22), accompanied by a higher content of inorganic compounds such as LiF, Li\u003csub\u003e2\u003c/sub\u003eS, and Li\u003csub\u003ex\u003c/sub\u003eS\u003csub\u003ey\u003c/sub\u003e within the inner layer of the CEI formed in the DDE-PN electrolyte. Notably, the CEI generated from the DDE-PN electrolyte exhibited the strongest LiF peak, with an internal LiF content exceeding 39.8%, compared to 32% and 2.4% for the CEIs formed from DDE and DEE electrolytes, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). This gradient distribution from organic to inorganic components within the CEI imparts excellent electronic blocking capabilities, reducing electron penetration into the CEI and thus ensuring the cycling stability of the battery. Unfortunately, the inner layer of the CEI formed in DEE revealed a higher content of carbonaceous organic compounds (from solvent decomposition) and fluorinated organic species (due to incomplete decomposition of the FSI\u003csup\u003e-\u003c/sup\u003e anion), but lower amounts of inorganic compounds such as LiF and Li\u003csub\u003e2\u003c/sub\u003eS (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, Fig. S22-S24). This indicates that the SEI film may be insufficiently stable and possess poor ion transport properties, rendering it unable to effectively prevent highly reactive free solvents from penetrating the CEI and undergoing continuous degradation.\u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eConsidering that the stability of the electrolyte depends on the aggregation state of ions and solvent molecules in the electric double layer (EDL), we further used in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) to more clearly reveal the evolution of the solvation structure in the interfacial microenvironment during charging/discharing.\u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e The interface of the working electrode and electrolyte was measured by ATR-SEIRAS in-situly during the charging/discharging under the potentiostatic mode. The voltage was settled between 3.0 and 3.6 V to ensure purely capacitive behavior throughout the test and to avoid the influence of irreversible decomposition products of the electrolyte. As shown in Fig.s 5a and 5b, the intensity of the peak at 1588 cm\u003csup\u003e-1\u003c/sup\u003e, corresponding to NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, increased with charging (Fig. S25), indicating that NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e ions preferentially adsorb in the inner Helmholtz layer (IHP). The is probably due to the smaller ionic size of NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e ions, consistent with previous studies.\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e Meanwhile, there are several Raman bands in the 800\u0026ndash;900 cm\u003csup\u003e-1\u003c/sup\u003e range. The bands at 821 cm\u003csup\u003e-1\u003c/sup\u003e and 849 cm\u003csup\u003e-1\u003c/sup\u003e correspond to free ether solvents with different isomers, and the band at 879 cm\u003csup\u003e-1\u003c/sup\u003e corresponds to Li\u003csup\u003e+\u003c/sup\u003e-solvated ether solvent. The area ratio of the free solvent peak to the coordination solvent peak reflects the proportion of the bounding state of the solvent to the total volume (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee-\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg). By fitting the relationship between the ratio of coordination ether solvent and the voltage at the cathode/electrolyte interface, as shown in Fig. S26, in the electrolyte without the PN additive, most ether molecules at the cathode interface exist in a free state, and the proportion of Li\u003csup\u003e+\u003c/sup\u003e-solvated ether solvents decreases with increasing voltage. Consequently, an EDL composed of a large amount of anodic unstable, free ether solvents will undoubtedly degrade at high voltage. For the DDE-PN electrolyte system, however, the proportion of Li\u003csup\u003e+\u003c/sup\u003e-solvated ether solvent increases significantly with increasing voltage, indicating that the introduction of NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e allows more ether to participate in the solvation shell, forming an anodic stable EDL capable of withstanding the high-voltage environment at the cathode. Therefore, the preferential adsorption of NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e leads to the displacement of the solvent, and Li\u003csup\u003e+\u003c/sup\u003e is attracted in large quantities to the electrode interface due to the strong interaction between NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e and Li\u003csup\u003e+\u003c/sup\u003e. As a result, the ether present in the EDL layer is extensively bounded with Li\u003csup\u003e+\u003c/sup\u003e, constructing a highly oxidative-stable EDL. Thus, by reducing the content of active ether solvents in the initially formed EDL, the PN additive is able to altering the stability of ether solvents at the cathode interface. Overall, the DDE-PN electrolyte offers a dual protection mechanism by forming a thin, inorganic-rich CEI and establishing a thermodynamically favorable EDL. This effectively mitigates ether-based electrolyte decomposition and cathode material structural degradation, significantly enhancing the compatibility of ether-based electrolytes with high-voltage cathodes. Therefore, by reducing the content of active ether solvents in the initially formed EDL, the risk of free solvent degradation by the high-voltage cathode is minimized. Additionally, this solvent-poor, anion-rich EDL promotes the formation of an inorganic-rich CEI, which, through dual protection, significantly enhances the electrochemical stability of the cathode/electrolyte interface in ether-based electrolyte systems (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eh-\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ej).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eLastly, we investigated the electrochemical properties of these three electrolytes in Li||NMC811 full cells and practical LMBs, respectively. The gavanostatic cycling was conducted under room temperature and ultra-low temperature conditions. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, the DDE-PN electrolyte enabled the Li (40 \u0026micro;m)||NMC811 (3.0 mAh cm\u003csup\u003e-2\u003c/sup\u003e) full cell to exhibit excellent cycling performance at room temperature, with a capacity retention rate of 84% after 300 cycles. In contrast, the DDE and DEE electrolytes showed poor cycling performance, with severe capacity degradation occurring at the initial cycle and after 70 cycles, respectively, due to the suboptimal high-voltage compatibility of ether-based solvents. Additionally, under harsh ultra-low temperature conditions (-60\u0026deg;C), the Li||NMC811 full cell was able to stably charge and discharge, providing a high reversible capacity of 110 mAh g\u003csup\u003e-1\u003c/sup\u003e over 100 cycles with a capacity retention of 93.3%, indicating excellent cycling stability (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The corresponding charge/discharge curves with temperature variation also exhibited distinct voltage plateaus, indicating good charge/discharge capability at low temperatures (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). Further, 500 mAh Li||NMC811 pouch cells were also evaluated in DDE-PN electrolyte under ultra-low temperature scenarios. As shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee, the pouch cells were able to deliver energy densities of 337.3 mAh, 257.4 mAh, and 245.4 mAh at -60\u0026deg;C, -80\u0026deg;C, and \u0026minus;\u0026thinsp;85\u0026deg;C, respectively, corresponding to capacity retention rates of 66.1%, 50.5% and 48.1% relative to room temperature. Excitingly, even at -85\u0026deg;C, the pouch cell could achieve an impressive energy density of 171.8 Wh kg\u003csup\u003e-1\u003c/sup\u003e. Remarkably, the pouch cell with DDE-PN electrolyte could discharge at a high rate of 3.0 C at -50\u0026deg;C, demonstrating a record-breaking power density of 938.5 W kg\u003csup\u003e-1\u003c/sup\u003e at such harsh low-temperature condition (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef, Fig. S27). Compared to previously reported low-temperature lithium metal batteries,\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan additionalcitationids=\"CR43 CR44\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/sup\u003e our practical pouch cell exhibits significant advantages in energy density and power density under extremely low temperatures (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), which is promising to provide reliable power for high-power devices in ultra-low temperature environments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Conclusion","content":"\u003cp\u003eIn summary, a multifunctional electrolyte additive, PN, was designed and studied for high power lithium metal batteries at ultra-low temperatures. PN preferentially decomposes on the anode to improve the SEI, while optimize the solvation structure and improve the EDL at the cathode/electrolyte interface, which results in excellent comprehensive performance, including high voltage tolerance, high ionic conductivity, low desolvation energy, and the ability to derive an inorganic-rich SEI. Impressively, the practical industrial Li||NMC811 pouch cell cycled in binary ether based electrolyte, DDE-PN, could stably discharge at -85\u0026deg;C, maintaining 48.1% of its room temperature capacity, and achieving an unprecedented energy density of 171.8 Wh kg\u003csup\u003e-1\u003c/sup\u003e at such harsh low-temperature condition. Even more remarkably, the pouch cell could discharge at a high rate of 3.0 C at -50\u0026deg;C, achieving a record-breaking power density of 938.5 W kg\u003csup\u003e-1\u003c/sup\u003e. This activation of practical high-rate lithium metal batteries under extreme low-temperature conditions provides valuable design insights and theoretical background for low-temperature lithium metal battery electrolyte engineering.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflict of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eWe gratefully acknowledge support by the Opening Project of State Key Laboratory of Space-Power Source, the National Key Research and Development Program (2023YFB2503700), the National Science Foundation of China (22071133, 22409117), Anhui Provincial Natural Science Foundation (240808QB043), the Tsinghua University-China Petrochemical Corporation Joint Institute for Green Chemical Engineering (224247), Beijing Science and Technology Plan Project (Z231100006123003), China Postdoctoral Science Foundation (2024M751747).\u003c/p\u003e\u003ch2\u003eData Availability Statement\u003c/h2\u003e \u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTarascon J, Armand M (2001) Nature 414:359\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu Y, Tao X, Wang Y, Jiang C, Ma C, Sheng O, Lu G, Lou XW (2022) Science 375:739\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDunn B, Kamath H, Tarascon J (2011) Science 334:928\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXia Y, Zhou P, Kong X, Tian J, Zhang W, Yan S, Hou W-H, Zhou H-Y, Dong H, Chen X, Wang P, Xu Z, Wan L, Wang B, Liu K (2023) Nat Energy 8:934\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang W, Lu Y, Wan L, Zhou P, Xia Y, Yan S, Chen X, Zhou H, Dong H, Liu K (2022) Nat Commun 13, 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65:103098\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"ultra-low temperatures, lithium metal batteries, multifunctional electrolyte additive","lastPublishedDoi":"10.21203/rs.3.rs-5474223/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5474223/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eUltra-low temperature lithium metal batteries face significant challenges, particularly sluggish ion transport and uncontrolled lithium dendrite formation, especially under high power. An ideal electrolyte requires high carrier ion concentration, low viscosity, rapid desolvation, and stable interfaces. However, harmonizing these attributes remains a formidable task. Here, we designed and synthesized a multifunctional additive, perfluoroalkylsulfonyl quaternary ammonium nitrate (PQA-NO\u003csub\u003e3\u003c/sub\u003e), which features both cationic (PQA\u003csup\u003e+\u003c/sup\u003e) and anionic (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) components. PQA\u003csup\u003e+\u003c/sup\u003e reacts in situ with lithium metal to form an inorganic-rich solid-electrolyte interphase (SEI) that enhances Li\u003csup\u003e+\u003c/sup\u003e transport through the SEI film. NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e creates an anion-rich, solvent-poor solvation structure, improving oxidation stability at the cathode/electrolyte interface and reducing Li\u003csup\u003e+\u003c/sup\u003e-solvent interactions. This allows ether-based electrolytes to achieve high voltage tolerance, increased ionic conductivity, and lower desolvation energy barriers. The Li (40 \u0026micro;m)||NMC811 (3 mAh cm\u003csup\u003e-2\u003c/sup\u003e) cells with the developed electrolyte exhibited stable cycling at -60 ℃ and a 450 Wh kg\u003csup\u003e-1\u003c/sup\u003e pouch cell retained 48.1% capacity at -85 ℃, achieving a remarkable energy density of 171.8 Wh kg\u003csup\u003e-1\u003c/sup\u003e. Additionally, the pouch cell demonstrated a high discharge rate of 3.0 C at -50 ℃, reaching a power density of 938.5 W kg\u003csup\u003e-1\u003c/sup\u003e, highlighting the electrolyte's potential for high-rate lithium metal batteries in extreme low-temperature environments.\u003c/p\u003e","manuscriptTitle":"Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-03 11:31:07","doi":"10.21203/rs.3.rs-5474223/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0ef17cfa-e90d-4716-b04e-26b80f692290","owner":[],"postedDate":"December 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":40921536,"name":"Physical sciences/Energy science and technology/Energy storage/Batteries"},{"id":40921537,"name":"Physical sciences/Chemistry/Energy"}],"tags":[],"updatedAt":"2025-04-09T07:07:46+00:00","versionOfRecord":{"articleIdentity":"rs-5474223","link":"https://doi.org/10.1038/s41467-025-58627-3","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-04-08 04:00:00","publishedOnDateReadable":"April 8th, 2025"},"versionCreatedAt":"2024-12-03 11:31:07","video":"","vorDoi":"10.1038/s41467-025-58627-3","vorDoiUrl":"https://doi.org/10.1038/s41467-025-58627-3","workflowStages":[]},"version":"v1","identity":"rs-5474223","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5474223","identity":"rs-5474223","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}