Stable Non-flammable Phosphate Electrolyte for Lithium Metal Batteries via Solvation Regulation by the Additive

The application of lithium metal batteries (LMBs) is impeded by safety concerns. Employing non-flammable electrolytes can improve battery reliability while the cost and performance deterioration limit their popularization. Herein, a high-performance non-flammable electrolyte is designed, 1.5 m LiTFSI in propylene carbonate (PC)/triethyl phosphate (TEP) (4:1 by vol.) with 4-nitrophenyl trifluoroacetate (TFANP) as the additive, which can facilitate the construction of LiF-rich solid electrolyte interphase (SEI) on Li anode surface and cathode electrolyte interphase (CEI) on cathode surface through its prioritized decomposition. In TFANP-containing electrolyte, the decreased TEP coordination number in the solvation sheath relieves the adverse effect of active TEP on both the SEI and CEI for suppressing the growth of Li dendrites and reducing the continuous electrolyte consumption. Thus, the Li||LiNi_0.6Co_0.2Mn_0.2O₂ battery with such an electrolyte can deliver 132 mAh g⁻¹ after 150 cycles with high coulombic efficiency (99.5%) and superior rate performance (110 mAh g⁻¹ at 5 C, 1 C = 200 mA g⁻¹). This work provides a new additive insight on non-flammable electrolyte for reliable LMBs.     

Hexafluoroisopropyl Trifluoromethanesulfonate-Driven Easily Li+ Desolvated Electrolyte to Afford Li||NCM811 Cells with Efficient Anode/Cathode Electrolyte Interphases

Solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) with optimized components and structures are considered to be crucial for lithium-ion batteries. Here, gradient lithium oxysulfide (Li₂SO_x, x = 0, 3, 4)/uniform lithium fluoride (LiF)-type SEI is designed in situ by using hexafluoroisopropyl trifluoromethanesulfonate (HFPTf) as electrolyte additive. HFPTf is more likely to be reduced on the surface of Li anode in electrolytes due to its high reduction potential. Moreover, HFPTf can make Li⁺ desolvated easily, leading to the increase in the flux of Li⁺ on the surface of Li anode to avoid the growth of Li dendrites. Thus, the cycling stability of Li||Li symmetric cells is improved to be 1000 h at 0.5 mA cm⁻². In addition, HFPTf-contained electrolyte could make Li||NCM811 batteries with a capacity retention of 70% after 150 cycles at 100 mA g⁻¹, which is attributed to the formation of uniform and stable CEI on the cathode surface for hindering the dissolvation of metal ions from the cathode. This study provides effective insights on the strong ability of additives to adjust electrolytes in “one phase and two interphases” (electrolyte and SEI/CEI).     

Catalytically Induced Robust Inorganic-Rich Cathode Electrolyte Interphase for 4.5 V Li||NCM622 Batteries

Tailoring inorganic components of cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) is critical to improving the cycling performance of lithium metal batteries. However, it is challenging due to complicated electrolyte reactions on cathode/anode surfaces. Herein, the species and inorganic component content of the CEI/SEI is enriched with an objectively gradient distribution through employing pentafluorophenyl 4-nitrobenzenesulfonate (PFBNBS) as electrolyte additive guided by engineering bond order with functional groups. In addition, a catalytic effect of LiNi_0.6Mn_0.2Co_0.2O₂ (NCM622) cathode is proposed on the decomposition of PFBNBS. PFBNBS with lower highest occupied molecular orbital can be preferentially oxidized on the NCM622 surface with the help of the catalytic effect to induce an inorganic-rich CEI for superior electrochemical performance at high voltage. Moreover, PFBNBS can be reduced on the Li surface due to its lower lowest unoccupied molecular orbital , increasing inorganic moieties in SEI for inhibiting Li dendrite generation. Thus, 4.5 V Li||NCM622 batteries with such electrolyte can retain 70.4% of initial capacity after 500 cycles at 0.2 C, which is attributed to the protective effect of the excellent CEI on NCM622 and the inhibitory effect of its derived CEI/SEI on continuous electrolyte decomposition.     

Inorganic Filler Enhanced Formation of Stable Inorganic-Rich Solid Electrolyte Interphase for High Performance Lithium Metal Batteries

Lithium metal (LM) is a promising anode material for next generation lithium ion based electrochemical energy storage devices. Critical issues of unstable solid electrolyte interphases (SEIs) and dendrite growth however still impede its practical applications. Herein, a composite gel polymer electrolyte (GPE), formed through in situ polymerization of pentaerythritol tetraacrylate with fumed silica fillers, is developed to achieve high performance lithium metal batteries (LMBs). As evidenced theoretically and experimentally, the presence of SiO₂ not only accelerates Li⁺ transport but also regulates Li⁺ solvation sheath structures, thus facilitating fast kinetics and formation of stable LiF-rich interphase and achieving uniform Li depositions to suppress Li dendrite growth. The composite GPE-based Li||Cu half-cells and Li||Li symmetrical cells display high Coulombic efficiency (CE) of 90.3% after 450 cycles and maintain stability over 960 h at 3 mA cm⁻² and 3 mAh cm⁻², respectively. In addition, Li||LiFePO₄ full-cells with a LM anode of limited Li supply of 4 mAh cm⁻² achieve capacity retention of 68.5% after 700 cycles at 0.5 C (1 C = 170 mA g⁻¹). Especially, when further applied in anode-free LMBs, the carbon cloth||LiFePO₄ full-cell exhibits excellent cycling stability with an average CE of 99.94% and capacity retention of 90.3% at the 160th cycle at 0.5 C.     

Unlocking the Potential of Lithium Metal Batteries With a Sulfite-Based Electrolyte

Lithium metal batteries (LMBs) have the potential to significantly increase the energy density of advanced batteries in the future. Nonetheless, the dendritic lithium structures and low Coulombic efficiency (CE) of LMBs currently impede their applied implementation. Herein, a sulfite-based electrolyte (SBE/FEC), including 1.0 m lithium bis(fluorosulfonyl)imide in a blend of ethylene sulfite and diethyl sulfite, and 5 wt% fluoroethylene carbonate is proposed. SBE/FEC is a highly efficient inhibitor against the growth of lithium dendrites through the formation of robust solid electrolyte interphase (SEI) layer. Raman spectroscopy and theoretical calculation indicate that in SBE/FEC, a significant portion of FSI⁻ exists in associated complexes, playing a vital role in the creation of LiF-rich passivation. Besides, the sulfite solvents decompose and yield polysulfide complexes in the SEI layer. A direct correlation between the proportion of cation–anion complexes and the contact angle between electrolyte and separator is elucidated through molecular dynamics simulations. The SBE/FEC system exhibits high CEs (98.3%) with Li||Cu cells, along with a steady discharge capacity of ≈137 mA h g⁻¹ in Li||LiFePO₄ cell. This study presents an effective approach for enhancing LMBs with sulfite-based electrolytes, which can lead to high-energy-density next-generation rechargeable batteries.     

Phosphonium Bromides Regulating Solid Electrolyte Interphase Components and Optimizing Solvation Sheath Structure for Suppressing Lithium Dendrite Growth

Electrolyte additives play important roles in suppressing lithium dendrite growth and improving the electrochemical performance of long-life lithium metal batteries (LMBs), however, it is still challenging to design individual additive for adjusting the solid electrolyte interphase (SEI) components and changing lithium ion solvation sheath in the electrolyte at the same time for optimizing electrochemical performance. Herein, alkyl-triphenyl-phosphonium bromides (alkyl-TPPB) are designed as the electrolyte additive to enhance the stability of metallic Li anode under the guidance of multi-factor principle for electrolyte additive molecule design (EDMD). Both alkyl-TPP cations and Br⁻ anions produce positive influences on suppressing Li dendrite growth and stabilizing the unstable interphase between metallic Li anode/electrolyte. As expected, the optimized solvation sheath structure, and the stable SEI suppress Li dendrite growth. As a result, the Li||Li₄Ti₅O₁₂ cell reveals a long stable life over 1000 cycles with high Coulombic efficiency (99.9%). This work provides an insight on stabilizing SEI and optimizing solvation sheath structure with novel approach to develop long-term stability and safety LMBs.     

Dynamic Ion Sieve as the Buffer Layer for Regulating Li+ Flow in Lithium Metal Batteries

How to realize uniform Li⁺ flow is the key to achieve even Li deposition for lithium metal batteries (LMBs). In this study, a concept of dynamic ion sieve is proposed to design the buffer layer nearby Li anode surface to regulate Li⁺ spatial arrangement by introducing tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (TMPB) into the carbonate electrolyte. The buffer layer induced by TMP⁺ can adjust the velocity of arriving solvated Li⁺ that gives solvated Li⁺ sufficient time to redistribute and accumulate on Li anode surface, resulting in a uniform and higher concentrated Li⁺ flow. Besides, TFSI⁻ can participate in the generation of inorganic component-rich solid electrolyte interphase (SEI) with Li₃N, which can facilitate the Li⁺ conductivity of SEI. Consequently, the stable and uniform Li deposition can be obtained, achieving the excellent cycling performance up to 1000 h at 0.5 mA cm⁻² in the Li||Li symmetric cell. Besides, the Li||NCM622 full cell also possesses excellent cycling stability with a high-capacity retention rate of 66.7% after 300 cycles.     

A Salt-in-Metal Anode: Stabilizing the Solid Electrolyte Interphase to Enable Prolonged Battery Cycling

Metallic lithium (Li) is the ultimate anode candidate for high-energy-density rechargeable batteries. However, its practical application is hindered by serious problems, including uncontrolled dendritic Li growth and undesired side reactions. In this study a concept of “salt-in-metal” is proposed, and a Li/LiNO₃ composite foil is constructed such that a classic electrolyte additive, LiNO₃, is embedded successfully into the bulk structure of metallic Li by a facile mechanical kneading approach. The LiNO₃ reacts with metallic Li to generate Li⁺ conductive species (e.g., Li₃N and LiN_xO_y) over the entire electrode. These derivatives afford a stable solid electrolyte interphase (SEI) and effectively regulate the uniformity of the nucleation/growth of Li on initial plating, featuring a low nucleation energy barrier and large crystalline size without mossy morphology. Importantly, these derivatives combined with LiNO₃ can in-situ repair the damaged SEI from the large volume change during Li plating/stripping, enabling a stable electrode-electrolyte interface and suppressing side reactions between metallic Li and electrolyte. Stable cycling with a high capacity retention of 93.1% after 100 cycles is obtained for full cells consisting of high-loading LiCoO₂ cathode (≈20 mg cm⁻²) and composite metallic Li anode with 25 wt% LiNO₃ under a lean electrolyte condition (≈12 µL) at 0.5 C.     

Multiscale Structural Gel Polymer Electrolytes with Fast Li+ Transport for Long-Life Li Metal Batteries

Li metal batteries (LMBs) are considered as promising candidates for future rechargeable batteries with high energy density. However, Li metal anode (LMA) is extensively sensitive to general liquid electrolytes, leading to unstable interphase and dendrites growth. Herein, a novel gel polymer electrolyte consisting of a micro-nanostructured poly(vinylidene fluoride-co-hexafluoropropylene) matrix and inorganic fillers of Zeolite Socony Mobil-5 (ZSM-5) and SiO₂ nanoparticles, is fabricated to expedite Li⁺ ions transport and suppress Li dendrite growth. Due to the Lewis acid interaction, SiO₂ can absorb amounts of PF₆⁻ and promote the dissociation of LiPF₆. The specific sub-nanometer pore structure of ZSM-5 greatly enhances the Li⁺ ion transference number. These structures can restrain the decomposition of electrolytes and build stable interphase on LMA. Therefore, the Li||Ni_0.8Co_0.1Mn_0.1O₂ full cell maintains 92% capacity retention after 300 cycles at 1 C (1 C ≈190 mAh g⁻¹) in carbonate electrolyte. This multiscale design provides an effective strategy for electrolyte exploration in high-performance LMBs.     

Solvent-Free Electrolyte for High-Temperature Rechargeable Lithium Metal Batteries

The formation of lithiophobic inorganic solid electrolyte interphase (SEI) on Li anode and cathode electrolyte interphase (CEI) on the cathode is beneficial for high-voltage Li metal batteries. However, in most liquid electrolytes, the decomposition of organic solvents inevitably forms organic components in the SEI and CEI. In addition, organic solvents often pose substantial safety risks due to their high volatility and flammability. Herein, an organic-solvent-free eutectic electrolyte based on low-melting alkali perfluorinated-sulfonimide salts is reported. The exclusive anion reduction on Li anode surface results in an inorganic, LiF-rich SEI with high capability to suppress Li dendrite, as evidenced by the high Li plating/stripping CE of 99.4% at 0.5  mA cm⁻² and 1.0 mAh cm⁻², and 200-cycle lifespan of full LiNi_0.8Co_0.15Al_0.05O₂ (2.0 mAh cm⁻²) || Li (20 µm) cells at 80 °C. The proposed eutectic electrolyte is promising for ultrasafe and high-energy Li metal batteries.     

An Ultrafast and Stable Li-Metal Battery Cycled at −40 °C

Li-metal battery (LMB) suffers from the unexpected Li dendrite growth and unstable solid-electrolyte interphase (SEI), especially in the extreme conditions, such as high rates and low temperatures (LT). Herein, a high-rate and stable LT LMB is realized by regulating electrolyte chemistry. A weak Li⁺-solvating solvent 2-methyltetrahydrofuran is used as electrolyte solvent to mitigate the kinetic barrier for Li⁺ de-solvation. Moreover, a co-solvent tetrahydrofuran with a high donor number is incorporated to improve the LT solubility of Li salts, achieving an improved ionic conductivity while maintaining the weak Li⁺-solvation effect. Furthermore, abundant FSI^- anions in contact-ion pairs are presented, facilitating the formation of a stable LiF-enriched SEI. Consequently, the Li||Li battery can be operated at 10 mA cm^-2 with a small polarization of 154 mV at −40 °C. Meanwhile, an outstanding cumulative cycling capacity of 4000 mAh cm^-2 at 8.0 mA cm^-2 is achieved, reaching a record high level in LT alkali metal symmetric batteries. Also, rechargeable high-rate and stable full batteries are achieved at −40 °C. This work demonstrates the superiority of electrolyte chemistry for synergistic regulation of both ion transfer kinetics and SEI toward ultrafast and stable rechargeable LMBs at LT.     

N-Rich Solid Electrolyte Interface Constructed In Situ Via a Binder Strategy for Highly Stable Silicon Anode

Silicon (Si) is regarded as a promising anode material for high-energy-density lithium-ion batteries due to its high specific capacity (4200 mAh g⁻¹) and low potential (0.3 V vs Li⁺/Li). However, the large volume change (over 300%) of Si during the lithiation/delithiation process leads to severe pulverization, electrode structure destruction, and finally capacity fading, which slows down its step to practical application. Herein, a poly(vinylamine) (PVAm) binder containing amino ( NH₂) and amide ( NH CHO) is proposed to improve the stability of Si anodes from particle to electrode structure. The N-containing functional groups show strong interaction with the Si particles and form a uniform and thin layer on the surface, which would decompose and form an N-rich inorganic solid electrolyte interphase (SEI) layer during discharging. The high mechanical stability N-rich SEI helps relieve the pulverization of Si particles through stress dissipation, maintains electrode structural stability, and reduces the loss of active materials. Thus, the Si anode with PVAm binder exhibits high capacity of ≈2000 mAh g⁻¹ after 200 cycles, which is much higher than that of using Poly(vinylidene fluoride) (PVDF) binder (66 mAh g⁻¹) and Poly(vinyl alcohol) PVA binder (820 mAh g⁻¹). This facile and practical strategy provides a new perspective for the application of Si anodes in advanced batteries.     

Controlling Solvation and Solid-Electrolyte Interphase Formation to Enhance Lithium Interfacial Kinetics at Low Temperatures

Operation of lithium-based batteries at low temperatures (<0 °C) is challenging due to transport limitations as well as sluggish Li⁺ kinetics at the electrode interface. The complicated relationships among desolvation, charge transfer, and transport through the solid electrolyte interphase (SEI) at low temperatures are not well understood, hindering electrolyte development. Here, an ether/hydrofluoroether and fluoroethylene carbonate (FEC)-based ternary solvent electrolyte is developed to improve Li cycling at low temperatures (Coulombic efficiency of 93.3% at -40 °C), and the influence of the local solvation structure on interfacial Li⁺ kinetics and SEI chemistry is further revealed. The hydrofluoroether cosolvent allows for modulation of the solvation structure, thereby enabling facile Li⁺ desolvation while forming an inorganic-rich SEI, which are both beneficial for lowering Li⁺ kinetic barriers at the interface. This cosolvent also increases the oxidative stability of the electrolyte to over 4.0 V versus Li/Li⁺, thereby enabling cycling of NMC-based full cells at −40 °C. This study advances the understanding of the influence of Li⁺ solvation structure, SEI chemistry, and interfacial Li⁺ kinetics on Li electrochemistry at low temperatures, providing new design considerations for creating effective low-temperature electrolyte systems.     

Perfluoro Macrocyclic Ether as an Ambifunctional Additive for High-Performance SiO and Nickel 88%-Based High-Energy Li-ion Battery

State-of-the-art lithium (Li)-ion batteries employ silicon anode active material at a limited fraction while strongly relying on fluoroethylene carbonate (FEC) electrolyte additive exceeding 10 wt.% to enable stable cycling. The swelling issue of silicon in the aspect of solid electrolyte interphase (SEI) instability and a risk of safety hazards and high manufacturing cost due to FEC has motivated the authors to design a well-working fluorinated additive substitute. High-capacity cells employing nickel-rich oxide cathode are pursued by operating at > 4.2 V versus Li/Li⁺, for which anodic stability of electrolyte is required. Herein, a highly effective new ambifunctional additive of icosafluoro-15-crown 5-ether is proposed at a little fraction of 0.4 wt.% for the stabilized interfaces and reduced swelling of high capacity (3.5 mAh cm⁻²) 5 wt.% SiO-graphite anode and LiNi_0.88Co_0.08Mn_0.04O₂ cathode. Utilizing together with a lowered fraction of FEC, reversible long 300 cycles at 4.35 V and 1 C (225 mA g⁻¹) are achieved. Material characterization results reveal that such stabilization is derived from the surface passivation of both anode and cathode with perfluoro ether, LiF, and Li_xPF_y species. The present study gives insight into electrolyte formulation design with lower cost and both-side stabilization strategies for silicon and nickel-rich active materials and their interfaces.     

High‐Power Lithium Metal Batteries Enabled by High‐Concentration Acetonitrile‐Based Electrolytes with Vinylene Carbonate Additive

To enable next‐generation high‐power, high‐energy‐density lithium (Li) metal batteries (LMBs), an electrolyte possessing both high Li Coulombic efficiency (CE) at a high rate and good anodic stability on cathodes is critical. Acetonitrile (AN) is a well‐known organic solvent for high anodic stability and high ionic conductivity, yet its application in LMBs is limited due to its poor compatibility with Li metal anodes even at high salt concentration conditions. Here, a highly concentrated AN‐based electrolyte is developed with a vinylene carbonate (VC) additive to suppress Li⁺ depletion at high current densities. Addition of VC to the AN‐based electrolyte leads to the formation of a polycarbonate‐based solid electrolyte interphase, which minimizes Li corrosion and leads to a very high Li CE of up to 99.2% at a current density of 0.2 mA cm^‐2. Using such an electrolyte, fast charging of Li||NMC333 cells is realized at a high current density of 3.6 mA cm^‐2, and stable cycling of Li||NMC622 cells with a high cathode loading of 4 mAh cm^‐2 is also demonstrated.     

Manipulating Ion Transfer and Interface Stability by A Bulk Interphase Framework for Stable Lithium Metal Batteries

Lithium metal batteries (LMBs) have attracted widespread concern as the next-generation energy storage devices with high energy density. At the surface of lithium metal anodes (LMAs) toward electrolytes, lithium plating always competes with interfacial reactions. This makes interfacial reactions light shadow right behind lithium plating, leading to performance degradation. Herein, lithium plating is spatially decoupled from interfacial reactions by constructing a 3D solid electrolyte interphase framework (3D-SEIF) inside LMAs. Spontaneous while mild chemical reactions between lithium metal and lithium bisfluorosulfonimide/lithium nitrate form the robust 3D-SEIF, mainly consisting of LiF, Li₃N, and LiN_xO_y. The built-in 3D-SEIF avoids electrolyte contact but enables the diffusion and reduction of Li⁺ ions in the bulk phase, thus isolating the plating sites and electrolyte contact interface. The 3D-SEIF facilitates large granular plating and the generation of thin, inorganic-rich SEI. When assembled with high-loading LiNi_0.6Co_0.2Mn_0.2O₂ cathode (3 mAh cm⁻²), the cells present capacity retention of 92.0% after 130 cycles with barren electrolyte (≈30 µL) at 0.5 C. The conception of 3D inner interphase allows breaking the coupling of interfacial reactions with electrochemical reactions, which is taken for granted in electrochemical consortium. It also desires to inspire new thoughts to develop scalable solutions for the early industrialization of LMBs.     

Electrolytes Enriched by Crown Ethers for Lithium Metal Batteries

Lithium (Li) metal battery is considered the most promising next-generation battery due to its low potential and high theoretical capacity. However, Li dendrite growth causes serious safety problems. Herein, the 15-Crown-5 (15-C-5) is reported as an electrolyte additive based on solvation shell regulation. The strong complex effect between Li⁺ ion and 15-C-5 can reduce the concentration of Li ions on the electrode surface, thus changing the nucleation, and repressing the growth of Li dendrites in the plating process. Significantly, the strong coordination of Li⁺/15-C-5 would be able to make them aggregate around the Li crystal surface, which could form a protective layer and favor the formation of a smooth and dense solid electrolyte interphase with high toughness and Li⁺ ion conductivity. Therefore, the electrolyte system with 2.0 wt% 15-C-5 achieves excellent electrochemical performance with 170 cycles at 1.0 mA cm⁻² with capacity of 0.5 mA h cm⁻² in symmetric Li|Li cells. The obviously enhanced cycle and rate performance are also achieved in Li|LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) full cells. The 15-C-5 demonstrates to be a promising additive for the electrolytes toward safe and efficient Li metal batteries.     

Liberating the Electrolyte via In Situ Conversion of an Amide,Sulfonate-Containing Monomer Precursor for High-Temperature Graphite/NCM Batteries

High-temperature (HT) operation and storage performance of Li-ion batteries (LIBs) are essential for applications in electric vehicles, grid storage, or defense missions. Unfortunately, severe capacity fading is witnessed due to growing instability of the electrode/electrolyte interphase at HT. Herein, the study liberates the electrolyte from the task of film-formation. Instead, it takes advantage of the favorable solid-electrolyte interphase (SEI)-forming functional groups by priorly anchoring them on graphite surface. Specifically, via molecular design, unsaturated CC bond, together with amide and sulfonate groups, are concurrently involved, namely the lithium-2-acrylamido-2-methyl-1-propanesulfonate (Li-AMPS). Upon electrochemical cycle, the unsaturated CC bond in Li-AMPS turns into a radical that induces polymerization between CC bonds to construct a polymeric network. The presence of amide and sulfonate groups endows the SEI with nitrogen, sulfur-based reduction products OSO₂Li and Li₃N, etc. As such, the designed interphase makes the use of propylene carbonate-based electrolyte possible. By assembling full cells with the modified graphite and LiNi_0.5Co_0.2Mn_0.3O₂ (cathode loading of ≈18.5 mg cm⁻²), the capacity retention of the full cell has increased from 53.2% (with pristine graphite) to 77.8% after 300 cycles under 60 °C. A 2 Ah, 265 Wh kg⁻¹ pouch cell is also able to operate for 200 cycles at an extreme temperature of 80 °C with the modified graphite.     

Establishing the Preferential Adsorption of Anion-Dominated Solvation Structures in the Electrolytes for High-Energy-Density Lithium Metal Batteries

The practical application of Li metal batteries (LMBs) is severely hindered by the unstable solid electrolyte interface (SEI). In this work, it is revealed that the unstable SEI mainly originates from the kinetic instability of Li⁺-solvation structures in the electrolyte which can result in continuous electrolyte decomposition and nonuniform Li deposition. To address this issue, preferential adsorption of anion-dominated solvation complexes (A-Coms) are established by integrating preferentially adsorbed anions (NO₃⁻ and Li₂S₈) into the Li⁺-solvation structures. In these structures, the locations of the lowest unoccupied molecular orbital energy level shift from solvents to anions, rendering a relieved electrolyte decomposition and an anion-derived SEI formation. Meanwhile, the anions in the A-coms preferentially adsorb on the Li metal surfaces due to their stronger chemisorption capability toward lithium metal anodes (LMAs) compared to the solvent molecules, effectively shielding solvent molecules from parasitic reaction with LMAs. Furthermore, the anion-derived SEI exhibits high Li-ion conductivity and low Li atom adhesion energy, which can facilitate uniform Li deposition. Consequently, this electrolyte can enable a high Li plating/stripping Coulombic efficiency of 98.5% over 500 cycles and a stable cycling under realistic testing conditions with a high-energy-density of 310 W h kg⁻¹ based on a full cell configuration.     

Electrolyte Interphase Built from Anionic Covalent Organic Frameworks for Lithium Dendrite Suppression

Lithium (Li) metal batteries hold considerable promise for numerous energy-dense applications. However, the dendritic Li anode produced during Li⁺/Li deposition-stripping endangers battery safety and shortens cycle lifespan. Herein, an electrolyte interphase built from 2D anionic covalent organic frameworks (ACOF) is coated on Li for dendrite suppression. The ACOF with Li⁺-affinity facilitates rapid and exclusive passage of Li-ions from the electrolyte, yielding near-unity Li⁺ transference number (0.82) and ionic conductivity beyond 3.7 mS cm^-1 at the interphase. Such high transport efficiency of Li-ions can fundamentally circumvent the Li⁺ deficiency that results in dendrite formation. Pairing the ACOF-coated Li against a high-voltage LiCoO₂ cathode (4.5 V) achieves exceptional cycle stability, mitigated polarization, as well as improved rate capability. Accordingly, this strategy vastly expands the pool of electrolyte interphases that can be used for coating and protecting Li anode.