Traditional Electrolytes Research Articles

Polyoxymethylene-based solid polymer electrolyte for high-performance room-temperature all-solid-state lithium batteries

Compared with flammable liquid electrolytes, solid state electrolytes show promising potential for lithium-ion batteries with high safety and high energy density simultaneously due to their high thermal stability, mechanical strength, excellent chemical and electrochemical stability. Solid polymer electrolytes are an attractive choice to achieve high energy density due to their thinness and good manufacturability. However, traditional solid polymer electrolytes typically need to operate at above 60 °C due to the insufficient room-temperature ionic conductivity, thereby limiting its practical application in common room temperature lithium-ion batteries. Here, we report a novel design of polyoxymethylene (POM)-based solid polymer electrolytes for high-performance room-temperature all-solid-state lithium batteries. This design includes POM and lithium bis(trifluoromethylsulfonyl)amine (LiTFSI), which offers the similar structure to polyethylene oxide based solid electrolyte while with shorter chain segments to achieve higher ionic conductivity (2.8 × 10−4S cm−1) and mechanical strength at room temperature. As a result, lithium dendrites can be efficiently suppressed, and symmetrical Li-Li cells have demonstrated more than 300 h of cycling at 0.05 mA cm−2. The wide electrochemical stability window of 4.75 V also enables broader application for full cells. All-solid-state lithium batteries fabricated with POM/LiTFSI exhibit excellent cycling stability for 150 cycles at 0.2 C rate at room temperature. The design breaks through the useable temperature limit of solid polymeric electrolytes and broaden their application in all-solid-state lithium batteries.

High performance gel polymer electrolyte based on P(MMA-co-Sty) and PVDF blend for fast-charging lithium metal batteries with extended cycle life

In the quest for high-energy-density lithium metal batteries (LMBs), the stabilization of lithium (Li) metal anodes during fast charging remains a formidable challenge. In this study, a novel copolymer, Poly(methyl methacrylate-co-styrene) (namely PMS) is synthesized and blended with Poly(vinylidene fluoride) to fabricate a porous gel polymer electrolyte (GPE, namely PMS-PVDF) through the nonsolvent-induced phase separation technique, which significantly enhances the electrochemical stability and fast-charging capabilities of LMBs. The developed GPE exhibits a high ionic conductivity of 5.62 mS cm−1, thereby reducing the formation of detrimental Li dendrites and leading to over 400 h stripping/plating process at 0.5 mA cm−2. Extensive electrochemical tests show that the LMBs with the obtained PMS-PVDF GPE achieve exceptional cycle stability over 600 and 1000 cycles at the C-rates of 0.5 and 3 C, respectively, outperforming traditional electrolytes. Furthermore, the ultra-stability of the quasi-solid-state electrolyte is demonstrated in a 375 mAh pouch cell setup, suggesting an essential trait for the practical application of high-power devices. This work marks a pivotal contribution to the field of energy storage, delivering insights and a clear methodology that pave the way for the development of next-generation LMBs poised for commercial viability.

Quasi-Solid-State Na-O2 Battery with Composite Polymer Electrolyte.

Na-O2 batteries have emerged as promising candidates due to their high theoretical energy density (1,601 Wh kg-1), the potential for high energy storage efficiency, and the abundance of sodium in the earth's crust. Considering the safety issue, quasi-solid-state composite polymer electrolytes are among the promising solid-state electrolyte candidates. Their higher mechanical toughness provides superior resistance to dendritic penetration compared with traditional liquid electrolytes. The flexibility of the composite polymer electrolyte matrix allows it to conform to various battery configurations and considerably reduces safety concerns related to the combustion risks associated with conventional liquid electrolytes. In this study, we employed poly(ethylene oxide) (PEO) and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) as the polymer matrix and sodium ion-conducting agent, respectively. We incorporated nanosized NZSP (25 wt %) to create the composite polymer electrolyte membrane. This CPE design facilitates ion conduction pathways through both sodium salt and NZSP. By utilizing a liquid electrolyte infiltration method, we successfully enhanced its ionic conductivity, achieving an ionic conductivity of 10-4 S cm-1 at room temperature.

Realization of Long-Life Proton Battery by Layer Intercalatable Electrolyte.

Proton batteries have attracted increasing interests because of their potential for grid-scale energy storage with high safety and great low-temperature performances. However, their development is significantly retarded by electrolyte design due to free water corrosion. Herein, we report a layer intercalatable electrolyte (LIE) by introducing trimethyl phosphate (TMP) into traditional acidic electrolyte. Different from conventional role in batteries, the presence of TMP intriguingly achieves co-intercalation of solvent molecules into the interlayer of anode materials, enabling a new working mechanism for proton reactions. The electrode corrosion was also strongly retarded with expanded electrochemical stability window. The half-cell therefore showed an outstanding long-term cycling stability with 91.0 % capacity retention at 5 A g-1 after 5000 cycles. Furthermore, the assembled full batteries can even deliver an ultra-long lifetime with a capacity retention of 74.9 % for 2 months running at -20 °C. This work provides new opportunities for electrolyte design of aqueous batteries.

Realization of Long‐Life Proton Battery by Layer Intercalatable Electrolyte

Proton batteries have attracted increasing interests because of their potential for grid‐scale energy storage with high safety and great low‐temperature performances. However, their development is significantly retarded by electrolyte design due to free water corrosion. Herein, we report a layer intercalatable electrolyte (LIE) by introducing trimethyl phosphate (TMP) into traditional acidic electrolyte. Different from conventional role in batteries, the presence of TMP intriguingly achieves co‐intercalation of solvent molecules into the interlayer of anode materials, enabling a new working mechanism for proton reactions. The electrode corrosion was also strongly retarded with expanded electrochemical stability window. The half‐cell therefore showed an outstanding long‐term cycling stability with 91.0% capacity retention at 5 A g−1 after 5000 cycles. Furthermore, the assembled full batteries can even deliver an ultra‐long lifetime with a capacity retention of 74.9% for 2 months running at ‐20 °C. This work provides new opportunities for electrolyte design of aqueous batteries.

Enhanced Stability-Based Hydroxymethyl Cellulose/Polyacrylamide Interpenetrating Dual Network Hydrogel Electrolyte for Flexible Yarn Zinc-Ion Batteries

As the field of wearable electronics continues to boom, the demand for flexible energy storage devices continues to grow. However, the development of soft energy supply devices with excellent stability is still a challenging task. Traditional hydrogel electrolytes are prone to mechanical deformation, which makes it difficult to maintain the functional stability of flexible yarn due to its short battery life and low wear resistance. Here, we developed a reversible energy-dissipating dual-network hydrogel electrolyte. The hydroxymethyl cellulose (CMC)/polyacrylamide (PAM) hydrogel electrolyte has a tensile deformation of 2700% and a high ionic conductivity of 6.37 × 10−2 S cm−1. The specific capacity of the assembled CMC/PAM-based yarn cell was 170 μAh cm−1 at 1 mA cm−1 and 73.14% after 100 cycles. The excellent performance is attributed to the crosslinked double network structure, in which the introduction of carboxyl groups is conducive to the improvement of hydrophilicity and ionic conductivity. The hydrogen bond and reversible CMC macromolecular chain can be restored after stress relief, which greatly improves the toughness of the material. Even under different bending angles and repeated bending conditions, zinc yarn batteries still have outstanding mechanical properties and cycle stability (71.28% specific capacity after 100 cycles), showing broad application prospects in wearable smart textiles.

Earth-Abundant Kaolinite Nanoplatelet Gel Electrolytes for Solid-State Lithium Metal Batteries.

Lithium-ion batteries are the leading energy storage technology for portable electronics and vehicle electrification. However, demands for enhanced energy density, safety, and scalability necessitate solid-state alternatives to traditional liquid electrolytes. Moreover, the rapidly increasing utilization of lithium-ion batteries further requires that next-generation electrolytes are derived from earth-abundant raw materials in order to minimize supply chain and environmental concerns. Toward these ends, clay-based nanocomposite electrolytes hold significant promise since they utilize earth-abundant materials that possess superlative mechanical, thermal, and electrochemical stability, which suggests their compatibility with energy-dense lithium metal anodes. Despite these advantages, nanocomposite electrolytes rarely employ kaolinite, the most abundant variety of clay, due to strong interlayer interactions that have historically precluded efficient exfoliation of kaolinite. Overcoming this limitation, here we demonstrate a scalable liquid-phase exfoliation process that produces kaolinite nanoplatelets (KNPs) with high gravimetric surface area, thus enabling the formation of mechanically robust nanocomposites. In particular, KNPs are combined with a succinonitrile (SN) liquid electrolyte to form a nanocomposite gel electrolyte with high room-temperature ionic conductivity (1 mS cm-1), stiff storage modulus (>10 MPa), wide electrochemical stability window (4.5 V vs Li/Li+), and excellent thermal stability (>100 °C). The resulting KNP-SN nanocomposite gel electrolyte is shown to be suitable for high-rate rechargeable lithium metal batteries that employ high-voltage LiNi0.8Co0.15Al0.05O2 (NCA) cathodes. While the primary focus here is on solid-state batteries, our strategy for kaolinite liquid-phase exfoliation can serve as a scalable manufacturing platform for a wide variety of other kaolinite-based nanocomposite applications.

Reviving Cost-Effective Organic Cathodes in Halide-Based All-Solid-State Lithium Batteries.

The evolution of inorganic solid electrolytes has revolutionized the field of sustainable organic cathode materials, particularly by addressing the dissolution problems in traditional liquid electrolytes. However, current sulfide-based all-solid-state lithium-organic batteries still face challenges such as high working temperatures, high costs, and low voltages. Here, we design an all-solid-state lithium battery based on a cost-effective organic cathode material phenanthrenequinone (PQ) and a halide solid electrolyte Li2ZrCl6. Thanks to the good compatibility between PQ and Li2ZrCl6, the PQ cathode achieved a high specific capacity of 248 mAh g-1 (96 % of the theoretical capacity), a high average discharge voltage of 2.74 V (vs. Li+/Li), and a good capacity retention of 95 % after 100 cycles at room temperature (25 °C). Furthermore, the interactions between the high-voltage carbonyl PQ cathode and both sulfide and halide solid electrolytes, as well as the redox mechanism of the PQ cathode in all-solid-state batteries, were carefully studied by a variety of advanced characterizations. We believe such a design and the corresponding investigations into the underlying chemistry give insights for the further development of practical all-solid-state lithium-organic batteries.

Reviving Cost‐Effective Organic Cathodes in Halide‐Based All‐Solid‐State Lithium Batteries

AbstractThe evolution of inorganic solid electrolytes has revolutionized the field of sustainable organic cathode materials, particularly by addressing the dissolution problems in traditional liquid electrolytes. However, current sulfide‐based all‐solid‐state lithium‐organic batteries still face challenges such as high working temperatures, high costs, and low voltages. Here, we design an all‐solid‐state lithium battery based on a cost‐effective organic cathode material phenanthrenequinone (PQ) and a halide solid electrolyte Li2ZrCl6. Thanks to the good compatibility between PQ and Li2ZrCl6, the PQ cathode achieved a high specific capacity of 248 mAh g−1 (96 % of the theoretical capacity), a high average discharge voltage of 2.74 V (vs. Li+/Li), and a good capacity retention of 95 % after 100 cycles at room temperature (25 °C). Furthermore, the interactions between the high‐voltage carbonyl PQ cathode and both sulfide and halide solid electrolytes, as well as the redox mechanism of the PQ cathode in all‐solid‐state batteries, were carefully studied by a variety of advanced characterizations. We believe such a design and the corresponding investigations into the underlying chemistry give insights for the further development of practical all‐solid‐state lithium‐organic batteries.

Electrochemical polishing properties of AlMgScZr alloy produced by laser powder bed fusion in NaNO3 and NaCl solutions

Electrochemical polishing (ECP) is a potential process to improve the surface quality of AlMgScZr alloy components produced by laser powder bed fusion (LPBF). Replacing traditional acid electrolytes with environment-friendly electrolytes is of great significance to the environment and safety. This work aims to study the ECP properties of LPBF AlMgScZr alloy in environment-friendly electrolytes (NaNO3 and NaCl solutions). In ECP, the electrochemical dissolution behavior of anode materials determines the polished surface quality. To this end, the effect of electrolyte type, uneven microstructure and applied current density on the anodic dissolution behavior of LPBF AlMgScZr alloy was examined experimentally. The results provide information about the suitability of the electrolytes selected for the ECP of LPBF AlMgScZr alloy, the dissolved surface quality in NaNO3 solution is significantly better because of the existence of a dense passive film. In addition, a microstructure analysis reveals that the bimodal distribution of grain size is the main factor leading to an uneven dissolved surface. Finally, the inner surface of LPBF AlMgScZr alloy channel was successfully polished in NaNO3 solution, the semi-welding particles were completely removed, and the surface roughness Sa was reduced from 20.73 μm to 2.48 μm.

Designing Advanced Electrolytes for High-Safety and Long-Lifetime Sodium-Ion Batteries via Anion-Cation Interaction Modulation.

Safety hazards caused by flammable electrolytes have been major obstacles to the practical application of sodium-ion batteries (SIBs). The adoption of nonflammable all-phosphate electrolytes can effectively improve the safety of SIBs; however, traditional low-concentration phosphate electrolytes are not compatible with carbon-based anodes. Herein, we report an anion-cation interaction modulation strategy to design low-concentration phosphate electrolytes with superior physicochemical properties. Tris(2,2,2-trifluoroethyl) phosphate (TFEP) is introduced as a cosolvent to regulate the ion-solvent-coordinated (ISC) structure through enhancing the anion-cation interactions, forming the stable anion-induced ISC (AI-ISC) structure, even at a low salt concentration (1.22 M). Through spectroscopy analyses and theoretical calculations, we reveal the underlying mechanism responsible for the stabilization of these electrolytes. Impressively, both the hard carbon (HC) anode and Na4Fe2.91(PO4)2(P2O7) (NFPP) cathode work well with the developed electrolytes. The designed phosphate electrolyte enables Ah-level HC//NFPP pouch cells with an average Coulombic efficiency (CE) of over 99.9% and a capacity retention of 84.5% after 2000 cycles. In addition, the pouch cells can operate in a wide temperature range (-20 to 60 °C) and successfully pass rigorous safety testing. This work provides new insight into the design of the electrochemically compatibility electrolyte for high-safety and long-lifetime SIBs.

Constructing a raincoat-like protective layer on sulfur cathode for aqueous Zn–S batteries

The unwanted disproportionation reactions between sulfur and water seriously deteriorate the cycling performance of aqueous Zn−S batteries, but there is not yet effective strategy to address this dilemma. Here, we proposed a concept of putting a “raincoat” on the S cathode to suppress the aforementioned side reactions. Via adding trace amounts of rationally selected organic ligands to the ZnSO4-based electrolyte, a layer of hundreds nanometer thick metal−organic complexes can be in-situ formed on the cathode surface during the charging process. Although the as-formed raincoat-like protecting layer is much thicker than traditional cathode electrolyte interphase (CEI), it has similar functions with CEI, which can not only block the contact between sulfur and aqueous electrolyte, but also effectively transfer Zn2+ during the charging/discharging process. As a result, the obtained aqueous Zn−S batteries delivered a high specific capacity of 1478 mAh g−1 at 0.1 A g−1, and much-improved stability over 300 cycles at 2 A g−1. Moreover, they also delivered an extremely high areal capacity of 4.2 mAh cm−2 and extraordinary cyclic stability even under harsh condition (E/S ratio, 8 μL mg−1, N/P ratio, ∼1.5). We also prove the universality of this strategy to different kinds of S-based cathodes for aqueous Zn−S batteries.

Hydrated eutectic electrolyte promotes the preferential growth of Zn (0 0 2) plane and suppresses side reaction for high-stability zinc anodes

Using deep eutectic solvent (DES) electrolytes is an efficient way to suppress the Zn dendrite growth and the side reactions resulting from the high activity of H2O in aqueous zinc-ion batteries (ZIBs). However, most DESs consist of expensive/explosive zinc salts or flammable/toxic organic ligands, which hinders their practical application in ZIBs. Herein, a low-cost and high-safety hydrated eutectic electrolyte based on ZnCl2, urea, and a small amount of H2O is prepared. Due to the low content of H2O and the strong intermolecular interaction between urea and H2O, the activity of H2O is greatly restricted and therefore H2O-induced side reactions are improved. In addition, X-ray photoelectron spectroscopy spectra and density functional theory calculations reveal that the adsorption of urea molecules on the zinc surface forms an organic protective layer, which can induce the preferential growth of the Zn (0 0 2) plane. As a result, with the optimal electrolyte, the Zn||Zn symmetric cell shows a long cyclic life of 1200 h, and the Zn||Cu half-cell delivers a high average Coulombic efficiency of 99.7 % for 2500 cycles. Meanwhile, the Zn||Bi2Te3 and Zn||polyaniline full cells with DES exhibit improved cycling performances compared to those using traditional ZnSO4 electrolyte. This work offers a new perspective to explore low-cost, non-toxic, and high-security DESs for ZIBs.

Zincophilic and hydrophobic groups of surfactant-type electrolyte additive enabled stable anode/electrolyte interface toward long-lifespan aqueous zinc ion batteries

Rechargeable aqueous zinc-ion batteries, while promising in terms of safety, cost-effectiveness, and eco-friendliness, face challenges such as zinc dendrite growth and parasitic reactions at the anode/electrolyte interface. Herein, a low-cost cationic surfactant, dodecyltrimethyl ammonium chloride (DTAC) is deployed as a competitive additive in traditional ZnSO4 electrolyte to stabilize the zinc anode. Firstly, the DTAC additive disrupts the hydrogen bonding network and regulates the solvation structure. Secondly, the DTA+ cations preferentially adsorb onto the anode surface vertically, forming a dodecyl chain hydrophobic layer that suppresses the side reactions. Thirdly, the hydrophobic layer not only elevates the nucleation overpotential of Zn2+ ions but also limits their 2D diffusion at the anode surface, triggering oriented deposition of metal zinc and inhibiting dendrite growth. Leveraging these triple-regulation effects, the Zn//Zn symmetric cell with DTAC additives achieves an ultra-long cycle life of 2000 h at a current density of 1 mA cm−2 with 1 mAh cm−2. Furthermore, the Zn//MnO2 full cell with DTAC additive demonstrates promising performance, delivering an initial capacity of 149.44 mAh g−1 at 5 A g−1 and retaining 83.02 % of its capacity after 2000 cycles. These results underscore the potential of DTAC additives in advancing the industrialization of AZIBs.

Application of supramolecular hydrogel in supercapacitors: Opportunities and challenges

AbstractSupercapacitors (SCs) are studied and used in various fields due to their high power density, fast charging/discharging rate, as well as long cycle life. Compared to other traditional electrode and electrolyte materials, supramolecular hydrogels have great advantages in the application of SCs due to their excellent properties. Unlike covalent bonds, supramolecular systems are assembled through dynamic reversible bonds, including host–guest interactions, ion interactions, electrostatic interactions, hydrogen bonding, coordination interactions, etc. The resulting supramolecular hydrogels show some special functions, such as stretching, compression, adhesion, self‐healing, stimulus responsiveness, etc., making them strong candidates for the next generation of energy storage devices. This paper reviews the representative progress of electrodes, electrolytes, and SCs based on supramolecular hydrogels. Besides, the properties of supramolecular hydrogels, such as conductivity, extensibility, compressibility and elasticity, self‐healing, frost resistance, adhesion, and flexibility, are also reviewed to highlight the key role of excellent properties of hydrogel materials in SCs. In addition, this article also discusses the challenges faced by current technologies, hoping to continue promoting future research in this field.

Reasonable design a high-entropy garnet-type solid electrolyte for all-solid-state lithium batteries

Traditional garnet solid electrolyte (Li7La3Zr2O12) suffers from low room temperature ionic conductivity, poor air stability, high sintering temperature and energy consumption. Considering the development prospects of high-entropy materials with high structural disorder and strong component controllability in the field of electrochemical energy storage, herein, a novel high-entropy garnet-type oxide solid electrolyte, Li5.75Ga0.25La3Zr0.5Ti0.5Sn0.5Nb0.5O12 (LGLZTSNO) was constructed by partially replacing the Li and Zr sites in Li7La3Zr2O12 with Ga and Ti/Sn/Nb elements, respectively. The experimental and density functional theory (DFT) calculation results show that the high-entropy LGLZTSNO electrolyte has preferable room temperature ion conductivity, air stability, interface contact performance with lithium anode, and the ability to suppress lithium dendrites. Thanks to the improvement of electrolyte performance, the critical current density of Li/Ag@LGLZTSNO/Li symmetric cell was increased from 0.42 to 1.57 mA cm−2, and the interface area specific impedance (IASR) was reduced from 765.2 to 42.3 Ω cm2. Meanwhile, the Li/Ag@LGLZTSNO/LFP full cell also exhibits excellent rate performance and cycling performance (148 mA h g−1 at 0.1 C and 124 mA h g−1 at 0.5 C, capacity retention up to 84.8% after 100 cycles at 0.1 C), showing the application prospects of high-entropy LGLZTSNO solid electrolyte in high-performance all solid state lithium batteries.

A Hybrid-Salt Strategy for Modulating the Li+ Solvation Sheathes and Constructing Robust SEI in Non-Flammable Electrolyte Lithium Metal Batteries.

The electrode interface determines the performance of an electrochemical energy storage system. Using traditional electrolyte organic additives and high-concentration electrolyte emerging recently are two generally strategies for improving the electrode interface. Here, a hybrid-salt electrolyte strategy is proposed for constructing the stable electrode interface. Through the solubilization effect of phosphate ester on LiNO3, a hybrid-salts-based non-flammable phosphate ester electrolyte system (HSPE) with LiPF6 and LiNO3 as Li salts has been developed. By the strong interaction between NO3 - and Li+, the Li+ solvation sheath and solvent behaviors have been modulated, thus the undesirable effects of phosphate ester are eliminated and a robust SEI is formed. Experimental results and theoretical calculations illustrate that NO3 - as a kind of strongly coordinating anion can reduce the number of TEP molecules and lower the reduction reactivity of TEP. The reconfigured Li+ solvation structure allows the formation of an inorganic-rich SEI on the electrode surface. As a result, in the designed HSPE, the average coulombic efficiency of lithium plating/stripping is increased to 99.12 %. This work explored a new approach to construct the electrode interface and addressing the poor interface performance issue of phosphate esters.

Enhancing stability in Acetonitrile-Based Supercapacitors: Implementation of Di-Pyrrolidinium ionic salts

One of the main strategies to enhance the energy density of electrochemical double layer capacitors (EDLCs) is to surpass the limitations of traditional electrolyte operating voltages. In our study, a novel high-purity di-pyrrolidine based electrolyte salt, 1-butyl-3-dimethylpyrrolidinium di[bis(trifluoromethanesulfonyl)imide] (C4di[mPyr].di[TFSI]) is synthesized, and high voltage electrolyte using acetonitrile (AN) as the sole solvent is prepared for EDLCs. The 0.5 M C4di[mPyr].di[TFSI]/AN electrolyte demonstrates an impressive electrochemical stability window of 6.04 V and a high operating voltage of 3.4 V, which is almost the highest stability reported so far for low concentration AN-based electrolytes. The impedance and conductivity of the 0.5 M C4di[mPyr].di[TFSI]/AN electrolyte are highly comparable to commercial 1.0 M TEA.BF4/AN electrolyte. EDLCs equipped with the electrolyte can maintain specific capacitance retentions of 94.92 % and 77.78 % after 2000 cycles at 3.4 V and 3.6 V, respectively. Besides, the GC–MS and XPS further prove its stability and confirm the possible electrochemical reactions of the C4di[mPyr].di[TFSI]/AN electrolyte on the electrode surface under the polarized voltages. Furthermore, the XPS also appears to show a relatively weak interaction between TFSI− and the electrode, which may serve as a potential factor in inhibiting the hydrolysis of TFSI− and the polymerization of AN.

Effect of adding K2TiF6 and K2ZrF6 to neutral electrolyte on the performance of plasma electrolytic oxidation coatings on AZ91 Mg alloy

The traditional alkaline electrolyte preparation of plasma electrolytic oxidation (PEO) coating ignites a significant spark, and the increase of micro-defects leads to a decrease in corrosion resistance. In this study, the preparation of PEO coating with neutral electrolyte was studied, and the effects of K2TiF6 and K2ZrF6 doping on the microstructure, phase composition, corrosion resistance and mechanical properties of the coating were explored. It was found that in neutral solution, the size and number of sparks decreased significantly, and the compactness of the coating increased. The phase composition was mainly MgF2. After the addition of K2TiF6 and K2ZrF6, the corrosion current density dropped from 256 to 28 and 61 nA/cm2. The long-term corrosion resistance of the coating was significantly improved. The hardness and adhesion of the coating were significantly improved.

Synergy of Weakly Solvated Electrolyte and LiF-Reinforced Interphase Enables Long-Term Operation of Li-Metal Batteries at Low Temperatures.

Hindered by the high diffusion energy barrier of Li+ in graphite anode layers, the low-temperature application of traditional Li-ion batteries is limited. Lithium metal without intercalation and with excellent specific capacity is expected to support battery operation at low temperatures. However, due to the low conductivity, high freezing point, and strong solvation energy of traditional carbonate electrolytes, the application of lithium-metal batteries at low temperatures remains challenged. In this paper, an all-ester-based ternary solvent electrolyte based on fluorinated carbonate and methyl acetate is developed to improve the cyclic efficiency of the Li-metal anode at subzero temperatures. Methyl acetate, with low viscosity and low freezing point, endows Li+ with efficient transfer in the bulk phase at low temperatures. Fluorinated cosolvent regulates the solvation structure, thereby facilitating Li+ desolvation while forming a LiF-rich solid electrolyte interphase. The electrolyte exhibits good compatibility with the Li-metal anode, as confirmed by the significantly reduced kinetic barrier of Li+ diffusion at the interface. The theoretical calculations suggest that anions occupy the dominant positions within the inner solvation sheath. The in situ/ex situ characterizations provide straightforward evidence of a dendrite-free Li-metal electrode during cycling. As a result, the symmetric Li||Li cell is able to cycle stably for thousands of hours at current densities of 0.5 mA cm-2 and 1 mAh cm-2. When paired with a LiFePO4 cathode, the battery at 0.2 C (1 C = 170 mA g-1) has a capacity retention of 95.4% after 200 cycles at -15 °C and 92.6% after 100 cycles at -20 °C, respectively.