A Series of Hybrid Multifunctional Interfaces as Artificial SEI Layer for Realizing Dendrite Free,and Long-Life Sodium Metal Anodes (Adv. Funct. Mater. 42/2023)

Sodium metal (Na) anodes are considered the most promising anode for high-energy-density sodium batteries because of their high capacity and low electrochemical potential. However, Na metal anode undergoes uncontrolled Na dendrite growth, and unstable solid electrolyte interphase layer (SEI) formation during cycling, leading to poor coulombic efficiency, and shorter lifespan. Herein, a series of Na-ion conductive alloy-type protective interface (Na-In, Na-Bi, Na-Zn, Na-Sn) is studied as an artificial SEI layer to address the issues. The hybrid Na-ion conducting SEI components over the Na-alloy can facilitate uniform Na deposition by regulating Na-ion flux with low overpotential. Furthermore, density functional study reveals that the lower surface energy of protective alloys relative to bare Na is the key factor for facilitating facile ion diffusion across the interface. Na metal with interface layer facilitates a highly reversible Na plating/stripping for ≈790 h, higher than pristine Na metal (100 h). The hybrid self-regulating protective layers exhibit a high mechanical flexibility to promote dendrite free Na plating even at high current density (5 mA cm⁻²), high capacity (10 mAh cm⁻²), and good performance with Na₃V₂(PO₄)₃ cathode. The current study opens a new insight for designing dendrite Na metal anode for next generation energy storage devices.     

Glassy/Ceramic Li2TiO3/LixByOz Analogous “Solid Electrolyte Interphase” to Boost 4.5 V LiCoO2 in Sulfide-Based All-Solid-State Batteries

Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) are the widely recognized approach toward high safety owing to excellent ionic conductivity and nonflammable nature of solid-state electrolytes (SSEs). However, narrow potential window of SSEs brings about serious interfacial parasitic reactions, resulting in fast degradation of the battery. Herein, a glassy/ceramic analogous solid electrolyte interface (SEI) is constructed on LiCoO₂ (LCO) to enhance interfacial stability between LCO and the Li₁₀GeP₂S₁₂ (LGPS) SSEs. In which, ceramic Li₂TiO₃ guarantees good mechanical toughness of analogous SEI, while glassy LixByOz reinforces the coverage to avoid parasitic reactions. Analogous SEI endows ASSLIBs with excellent cycling and rate performance under an upper charge voltage of 4.3 V with 82.3% capacity retention after 300 cycles at 0.2 C. When pushing charge voltage to 4.5 V, analogous SEI also enables desirable performance with an initial capacity of 172.7 mAh g⁻¹ and long lifespan of 200 cycles at 0.2 C. Both experiments and theoretical computation reveal excellent stability between analogous SEI and LGPS, which endows ASSLIBs with small polarization and improved performance. This work provides an insight on glassy/ceramic analogous SEI strategy to boost the interfacial stability of ASSLIBs.     

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).     

Stable Na Metal Anode Enabled by a Reinforced Multistructural SEI Layer

Metallic sodium (Na) is one of the most promising anode candidates for next‐generation secondary batteries. The development of Na metal batteries with a high energy density and low cost is desirable to meet the requirements of both portable and stationary electrical energy storage. Unfortunately, several problems caused by the unstable Na metal anode severely hinder the practical applications of these batteries. Here reported is a facile but effective methodology to form a multistructural interphase layer containing a sodium fluoride‐rich solid electrolyte interphase (SEI) and crisscrossed Na₃Sb bars on the Na electrode surface. The reinforced Na‐alloy network and chemically/electrochemically complementary SEI formation greatly improve the interphase strength and Na⁺ conductivity. The well‐protected Na metal electrode in symmetric Na|Na cells is stable and dendrite‐free in the plating and stripping cycling processes with a negligible voltage divergence, even at a large current density of 5 mA cm^?2 or with a high deposition capacity of 10 mAh cm^?2. Moreover, this anode is especially compatible with different cathodes and demonstrates outstanding cycle performance in the full cells. It is believed that this approach provides a practical solution toward stable Na metal anodes and related battery systems.     

Stable Silicon Anodes by Molecular Layer Deposited Artificial Zincone Coatings

A stable interface between silicon anodes and electrolytes is vital to realizing reversible electrochemistry cycling for lithium-ion batteries. Herein, a zincone polymer coating is controllably deposited on a silicon electrode using the molecular layer deposition to serve as an artificial solid electrolyte interphase (SEI). Enhanced electrochemical cycling depends on the thickness of zincone coating. The optimal zincone coating of ≈3 nm markedly improves the lithium storage performance of silicon anodes, resulting in a high reversible capacity (1741 mA h g⁻¹ after 100 cycles at 200 mA g⁻¹), outstanding cycling stability (1011 mA h g⁻¹ after 500 cycles), and superior rate capability (1580 mA h g⁻¹ at 2 A g⁻¹). Such remarkable electrochemical reversibility stems from the in situ conversion of the zincone coating and a zincone-driven thin lithium fluoride (LiF)-rich SEI, which endow the silicon electrode with superior electron/ion transport and structural stability. Meanwhile, the zincone coating demonstrates good compatibility with ether-based electrolytes (893 mA h g⁻¹ after 200 cycles, 970 mA h g⁻¹ at 5 A g⁻¹). Additionally, in situ conversion of artificial zincone coating also opens a door for constructing a functional interface on other electrode surfaces, such as lithium/sodium metal.     

3D Ordered Porous Hybrid of ZnSe/N-doped Carbon with Anomalously High Na+ Mobility and Ultrathin Solid Electrolyte Interphase for Sodium-Ion Batteries

Transition metal selenides have been widely used in alkali metal ion batteries owing to their high specific capacities and low cost. However, their reaction kinetics and structural stability are usually poor during cycling, along with ambiguous differences in Li/Na/K-storage behaviors. Herein, it is revealed that ZnSe possesses better Na⁺-diffusion kinetics (including lower diffusion barrier, smaller activation energy, and higher diffusion coefficients) in comparison with Li⁺ and K⁺, as evidenced by theoretical calculations and electrochemical studies. The architectural designs of ZnSe-based anode, including nitrogen-doped carbon (N,C) and 3D ordered hierarchical pores (3DOHP) to form a 3DOHP ZnSe@N,C hybrid combined with regulating solid electrolyte interphase (SEI), significantly enhance Na⁺ reaction kinetics and accommodate volume changes. The resulting 3DOHP ZnSe@N,C electrodes exhibit outstanding rate capability and good cycling stability (241.6 mAh g⁻¹ in sodium-ion batteries (SIBs) at 10 A g⁻¹ after 800 cycles), originating from improved electrical conductivity and shortened ion diffusion paths, accompanied by ultrathin and stable SEI with less Na₂CO₃/NaF in organic components and boosted Na₂Se adsorption as sodiation. Moreover, the Na-storage mechanism in 3DOHP ZnSe@N,C hybrid is further revealed by in situ studies. Accordingly, this study provides a new perspective for designing high-performance electrode materials for SIBs.     

Regulating Na-ion Solvation in Quasi-Solid Electrolyte to Stabilize Na Metal Anode

Sodium metal batteries are promising for cost-effective energy storage, however, the sluggish ion transport in electrolytes and detrimental sodium-dendrite growth stall their practical applications. Herein, a cross-linking quasi-solid electrolyte with a high ionic conductivity of 1.4 mS cm⁻¹ at 25 °C is developed by in-situ polymerizing poly (ethylene glycol) diacrylate-based monomer. Benefiting from the refined solvation structure of Na⁺ with a much lower desolvation barrier, random Na⁺ diffusion on the Na surface is restrained, so that the Na dendrite formation is suppressed. Consequently, symmetrical Na||Na cells employing the electrolyte can be cycled >2000 h at 0.1 mA cm⁻². Na₃V₂(PO₄)₃||Na batteries reveal a high discharge specific capacity of 66.1 mAh g⁻¹ at 15 C and demonstrate stable cycling over 1000 cycles with a capacity retention of 83% at a fast rate of 5 C.     

In Situ Formation of Li3P Layer Enables Fast Li+ Conduction across Li/Solid Polymer Electrolyte Interface

Solid‐state polymer electrolytes provide better flexibility and electrode contact than their ceramic counterparts, making them a worthwhile pursuit for all‐solid‐state lithium‐metal batteries. However, their large Li/solid state electrolyte interfacial resistance, small critical current density, and rapid lithium dendrite growth during cycling still limit their viability. Owing to these restrictions, all‐solid‐state cells with solid polymer electrolytes must be cycled above room‐temperature and with a small current density. These problems can be mitigated with an in situ formed artificial solid electrolyte interphase that rapidly conducts Li⁺ ions. Herein, a Li₃P layer formed in situ at the Li‐metal/solid polymer electrolyte interphase is reported that significantly reduces the electrode/electrolyte interfacial resistance. Additionally, this layer increases the wettability of the solid polymer by the metallic lithium anode, allowing for the critical current density of lithium symmetric cells to be doubled by homogenizing the current density at the interface. All‐solid‐state Li/Li symmetric cells and Li/LiFePO₄ cells with the Li₃P layer show improved cycling performance with a high current density.     

In Situ Artificial Hybrid SEI Layer Enabled High-Performance Prelithiated SiOx Anode for Lithium-Ion Batteries

Considered the promising anode material for next-generation high-energy lithium-ion batteries, SiO_x has been slow to commercialize due to its low initial Coulombic efficiency (ICE) and unstable solid electrolyte interface (SEI) layer, which leads to reduced full-cell energy density, short cycling lives, and poor rate performance. Herein, a novel strategy is proposed to in situ construct an artificial hybrid SEI layer consisting of LiF and Li₃Sb on a prelithiated SiO_x anode via spontaneous chemical reaction with SbF₃. In addition to the increasing ICE (94.5%), the preformed artificial SEI layer with long-term cycle stability and enhanced Li⁺ transport capability enables a remarkable improvement in capacity retention and rate capability for modified SiO_x. Furthermore, the full cell using Li(Ni_0.8Co_0.1Mn_0.1)O₂ and a pre-treated anode exhibits high ICE (86.0%) and capacity retention (86.6%) after 100 cycles at 0.5 C. This study provides a fresh insight into how to obtain stable interface on a prelithiated SiO_x anode for high energy and long lifespan lithium-ion batteries.     

A Simple Electrode‐Level Chemical Presodiation Route by Solution Spraying to Improve the Energy Density of Sodium‐Ion Batteries

The formation of a solid electrolyte interface (SEI) on the surface of a carbon anode consumes the active sodium ions from the cathode and reduces the energy density of sodium‐ion batteries (SIBs). Herein, a simple electrode‐level presodiation strategy by spraying a sodium naphthaline (Naph‐Na) solution onto a carbon electrode is reported, which compensates the initial sodium loss and improves the energy density of SIBs. After presodiation, an SEI layer is preformed on the surface of carbon anode before battery cycling. It is shown that a large irreversible capacity of 60 mAh g^?1 is replenished and 20% increase of the first‐cycle Coulombic efficiency is achieved for a hard carbon anode using this presodiation strategy, and the energy density of a Na_0.9[Cu_0.22Fe_0.30Mn_0.48]O₂||carbon full cell is increased from 141 to 240 Wh kg^?1 by using the presodiated carbon anode. This simple and scalable electrode‐level chemical presodiation route also shows generality and value for the presodiation of other anodes in SIBs.     

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.     

Hydrofluoric Acid-Removable Additive Optimizing Electrode Electrolyte Interphases with Li+ Conductive Moieties for 4.5 V Lithium Metal Batteries

High-voltage lithium metal batteries (LMBs) are capable to achieve the increasing energy density. However, their cycling life is seriously affected by unstable electrolyte/electrode interfaces and capacity instability at high voltage. Herein, a hydrofluoric acid (HF)-removable additive is proposed to optimize electrode electrolyte interphases for addressing the above issues. N, N-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) aniline (DMPATMB) is used as the electrolyte additive to induce PF₆⁻ decomposition to form a dense and robust LiF-rich solid electrolyte interphase (SEI) for suppressing Li dendrite growth. Moreover, DMPATMB can help to form highly Li⁺ conductive Li₃N and LiBO₂, which can boost the Li⁺ transport across SEI and cathode electrolyte interphase (CEI). In addition, DMPATMB can scavenge traced HF in the electrolyte to protect both SEI and CEI from the corrosion. As expected, 4.5 V Li|| LiNi_0.6Co_0.2Mn_0.2O₂ batteries with such electrolyte deliver 145 mAh g⁻¹ after 140 cycles at 200 mA g⁻¹. This work provides a novel insight into high-voltage electrolyte additives for LMBs.     

Rechargeable Sodium-Based Hybrid Metal-Ion Batteries toward Advanced Energy Storage

Growing demands on energy storage devices have inspired a tremendous amount of research on rechargeable batteries. Future generations of rechargeable batteries are required to have high energy density, long lifespan, low cost, high safety, low environmental impact, and wide commercial affordability. To achieve these goals, significant efforts are underway to focus on electrolyte chemistry, electrode engineering, and new designs for energy storage systems. Herein, a comprehensive overview of an innovative sodium-based hybrid metal-ion battery (HMIBs) for advanced next-generation energy storage is presented. Recent advances on sodium-based HMIBs from the development of reformulated or novel materials associated with Na⁺ ions and other metal ions (such as Li⁺, K⁺, Mg²⁺, Zn²⁺, etc.), are summarized in this work. Daniell cell and “rocking-chair” type batteries are covered. Finally, the current challenges and future remedies in terms of the design and fabrication of new electrolytes, cathodes, and anodes for advanced HMIBs are discussed in this report.     

Fluorinated Bifunctional Solid Polymer Electrolyte Synthesized under Visible Light for Stable Lithium Deposition and Dendrite-Free All-Solid-State Batteries

Solid polymer electrolytes (SPEs) that can offer flexible processability, highly tunable chemical functionality, and cost effectiveness are regarded as attractive alternatives for liquid electrolytes (LE) to address their safety and energy density limitations. However, it remains a great challenge for SPEs to stabilize Li⁺ deposition at the electrolyte–electrode interface and impede lithium dendrite proliferation compared with LE-based systems. Herein, a design of solid-state fluorinated bifunctional SPE (FB-SPE) that covalently tethers fluorinated chains with polyether-based segments is proposed and synthesized via photo-controlled radical polymerization (photo-CRP). In contrast to the conventional non-fluorinated polyether-derived SPEs, FB-SPE is able to provide conducting Li⁺ transport pathways up to ≈5.0 V, while simultaneously forming a Li F interaction that can enhance Li anode compatibility and prevent Li dendrites growth. As a result, the FB-SPE exhibits outstanding cycling stability in Li||Li symmetrical cells of over 1500 operating hours at as high current density as 0.2 mA cm⁻². A thin and uniform Li deposition layer and LiF-rich SEI at the surface of Li anode are found, and stable cycling with average coulombic efficiencies of 99% is demonstrated in Li||LFP and Li||NCM all-solid-state batteries based on such bifunctional fluorinated SPEs. The interesting fluorine effect and effective self-suppression of lithium dendrites will inform rational molecular design of novel electrolytes and practical development of all-solid-state Li metal batteries.     

Low Resistance and High Stable Solid–Liquid Electrolyte Interphases Enable High-Voltage Solid-State Lithium Metal Batteries

Solid-state batteries (SSBs) with addition of liquid electrolytes are considered to possibly replace the current lithium-ion batteries (LIBs) because they combine the advantages of benign interfacial contact and strong barriers for unwanted redox shuttles. However, solid electrolyte and liquid electrolyte are generally (electro)-chemically incompatible and the resistance of the newly formed solid–liquid electrolyte interphase (SLEI) appears as an additional contribution to the overall battery resistance. Herein, a boron, fluorine-donating liquid electrolyte (B, F-LE) is introduced into the interface between the high-voltage cathode and ultrathin composite solid electrolyte (CSE), which is fabricated by adhering a high content of nanosized Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), to generate a low resistance and high stable SLEI in situ, giving a stable high-voltage output with a reinforced cathode|CSE interface. B, F-LE, consisting of a highly fluorinated electrolyte with a lithium bis(oxalato)borate additive, exhibits good chemical compatibility with CSE and enables rapid and uniform transportation of Li⁺, with its electrochemically and chemically stable interface for high-voltage cathode. Eventually, the B, F-LE assisted LiNi_0.6Co_0.2Mn_0.2O₂|Li battery displays the enhanced rate capability and high voltage cycling stability. The findings provide an interfacial engineering strategy to turn SLEI from a “real culprit” into the “savior” that may pave a brand-new way to manipulate SLEI chemistry in hybrid solid–liquid devices.     

Building Artificial Solid‐Electrolyte Interphase with Uniform Intermolecular Ionic Bonds toward Dendrite‐Free Lithium Metal Anodes

Li metal has been widely regarded as a promising anode for next‐generation batteries due to its high theoretical capacity and low electrochemical potential. The unstable solid‐electrolyte interphase (SEI) and uncontrollable dendrite growth, however, incur severe safety hazards and hamper the practical application of Li metal anodes. Herein, an advanced artificial SEI layer constructed by [LiNBH]_n chains, which are crosslinked and self‐reinforced by their intermolecular Li? N ionic bonds, is designed to comprehensively stabilize Li metal anodes on a molecular level. Benefiting from its polymer‐like structure, the [LiNBH]_n layer is flexible and effectively tolerates the volume change of Li metal anodes. In addition, this layer with high polarity in its structure, helps to regulate the homogeneous distribution of the Li⁺ flux on Li electrodes via the further formation of Li? N bonds. The designed [LiNBH]_n layer is electrically nonconductive but highly ionically conductive, thus facilitating Li⁺ diffusion and confining Li deposition beneath the layer. Therefore, under the protection of the [LiNBH]_n layer, the Li metal anodes exhibit stable cycling at a 3 mA cm^?2 for more than 700 h, and the full cells with high lithium iron phosphate and sulfur cathodes mass loading also present excellent cycling stability.     

Designing Dendrite‐Free Zinc Anodes for Advanced Aqueous Zinc Batteries

Zn metal has been regarded as the most promising anode for aqueous batteries due to its high capacity, low cost, and environmental benignity. Zn anode still suffers, however, from low Coulombic efficiency due to the side reactions and dendrite growth in slightly acidic electrolytes. Here, the Zn plating/stripping mechanism is thoroughly investigated in 1 m ZnSO₄ electrolyte, demonstrating that the poor performance of Zn metal in mild electrolyte should be ascribed to the formation of a porous by‐product (Zn₄SO₄(OH)₆·xH₂O) layer and serious dendrite growth. To suppress the side reactions and dendrite growth, a highly viscoelastic polyvinyl butyral film, functioning as an artificial solid/electrolyte interphase (SEI), is homogeneously deposited on the Zn surface via a simple spin‐coating strategy. This dense artificial SEI film not only effectively blocks water from the Zn surface but also guides the uniform stripping/plating of Zn ions underneath the film due to its good adhesion, hydrophilicity, ionic conductivity, and mechanical strength. Consequently, this side‐reaction‐free and dendrite‐free Zn electrode exhibits high cycling stability and enhanced Coulombic efficiency, which also contributes to enhancement of the full‐cell performance when it is coupled with MnO₂ and LiFePO₄ cathodes.     

Encapsulating Sulfides into Tridymite/Carbon Reactors Enables Stable Sodium Ion Conversion/Alloying Anode with High Initial Coulombic Efficiency Over 89%

Electrode dissolution/collapses and interfacial reactions pose challenges to batteries, leading to pronounced capacity loss particularly during the initial few cycles. As high-capacity conversion/alloying anodes for sodium storage, metal sulfides generally show unsatisfactory performances like poor initial Coulombic efficiency (ICE; mostly <70% in the usual electrolyte) and inferior cyclic stability due to thick solid-electrolyte interface (SEI) layer formation and ubiquitous volume/phase changes. Using SnS₂ as an example, here, sulfides are elaborately encapsulated into functionalized amorphous tridymite/carbon reactors to address the above issues. The outer tridymite/carbon manifests good ionic permeability and superb electrochemical/mechanical tolerance against destructive Na⁺ insertion. Confining actives into tailored reactors endows SnS₂ full of nanoboundaries with an ultrahigh ICE of ≈89.13% and remarkable electrochemical attributes including large initial capacity (Max. 733.24 mAh g⁻¹), prominent stability in subsequent cycles, and excellent rate capability. Detailed investigation unveils that thin and steady SEI condition on tridymite/carbon rather than SnS₂ is key to achieving outstanding ICE. Engineered reactors always keep intact and free of valence-state changes, guaranteeing capacities running at a high level without an evident downtrend. Their peculiar functions on enlisting Na⁺ diffusion/transport and inhibiting sulfides’ release are also discussed. Packed full-cell Na-ion batteries with less irreversibility may show great potential in practical utilizations.     

Highly‐Cyclable Room‐Temperature Phosphorene Polymer Electrolyte Composites for Li Metal Batteries

Despite significant interest toward solid‐state electrolytes owing to their superior safety in comparison to liquid‐based electrolytes, sluggish ion diffusion and high interfacial resistance limit their application in durable and high‐power density batteries. Here, a novel quasi‐solid Li⁺ ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets is reported. The developed electrolyte is successfully cycled against Li metal (over 550 h cycling) at 1 mA cm^?2 at room temperature. The cycling overpotential is dropped by 75% in comparison to BP‐free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. Molecular dynamics simulations reveal that the coordination number of Li⁺ ions around (trifluoromethanesulfonyl)imide (TFSI^?) pairs and ethylene‐oxide chains decreases at the Li metal/electrolyte interface, which facilitates the Li⁺ transport through the polymer host. Density functional theory calculations confirm that the adsorption of the LiTFSI molecules at the BP surface leads to the weakening of N and Li atomic bonding and enhances the dissociation of Li⁺ ions. This work offers a new potential mechanism to tune the bulk and interfacial ionic conductivity of solid‐state electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long‐life cycling.     

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.