A Flexible Solid Electrolyte Interphase Layer for Long‐Life Lithium Metal Anodes

Trinitarian Design of Gradient Artificial Interphase Enables Colossal Granular Li Deposits for Stable Li-Metal Batteries

The cycling lifespan of Li-metal batteries is compromised by the unstable solid electrolyte interphase (SEI) and the continuous Li dendrites, restricting their practical implementations. Given these challenges, establishing an artificial SEI holds promise. Herein, a trinitarian gradient interphase is innovatively designed through composite coatings of magnesium fluoride (MgF2), N-hexadecyltrimethylammonium chloride (CTAC), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) on Li-metal anode (LMA). Specifically, the MgF2/CTAC/PVDF-HFP SEI spontaneously forms a lithium fluoride (LiF)-rich PVDF-HFP-based SEI, along with lithium-magnesium (Li-Mg) alloy substrate as lithiophilic electronic conductor and positively charged CTAC during plating. Noticeably, the Li-Mg alloy homogenizes the distribution of electric field and reduce the internal resistance, while the electronically insulated LiF/PVDF-HFP composite SEI offers fast ion-conducting and mechanical flexibility, accommodating the volumetric expansion and ensuring stable Li-ion flux. Additionally, CTAC at the dendritic tip is pivotal for mitigating dendrites through its electrostatic shield mechanism. Innovatively, this trinitarian synergistic mechanism, which facilitates colossal granular Li deposits, constructs a dendrite-free LMA, leading to stable cycling performances in practical Li||LFP, popular Li||NCM811, and promising Li||S full cells. This work demonstrates the design of multifunctional composite SEI for comprehensive Li protection, thereby inspiring further advancements in artificial SEI engineering for alkali-metal batteries.

Noncovalent Interactions-Driven Self-Assembly of Polyanionic Additive for Long Anti-Calendar Aging and High-Rate Zinc Metal Batteries

Zinc anodes of zinc metal batteries suffer from unsatisfactory plating/striping reversibility due to interfacial parasitic reactions and poor Zn2+ mass transfer kinetics. Herein, methoxy polyethylene glycol-phosphate (mPEG-P) is introduced as an electrolyte additive to achieve long anti-calendar aging and high-rate capabilities. The polyanionic of mPEG-P self-assembles via noncovalent-interactions on electrode surface to form polyether-based cation channels and in situ organic-inorganic hybrid solid electrolyte interface layer, which ensure rapid Zn2+ mass transfer and suppresses interfacial parasitic reactions, realizing outstanding cycling/calendar aging stability. As a result, the Zn//Zn symmetric cells with mPEG-P present long lifespans over 9000 and 2500 cycles at ultrahigh current densities of 120 and 200 mA cm-2, respectively. Besides, the coulombic efficiency (CE) of the Zn//Cu cell with mPEG-P additive (88.21%) is much higher than that of the cell (36.4%) at the initial cycle after the 15-day calendar aging treatment, presenting excellent anti-static corrosion performance. Furthermore, after 20-day aging, the Zn//MnO2 cell exhibits a superior capacity retention of 89% compared with that of the cell without mPEG-P (28%) after 150 cycles. This study provides a promising avenue for boosting the development of high efficiency and durable metallic zinc based stationary energy storage system.

Overcoming Chemical and Mechanical Instabilities in Lithium Metal Anodes with Sustainable and Eco-Friendly Artificial SEI Layer

Construction of a robust artificial solid-electrolyte interphase (SEI) layer has proposed an effective strategy to overcome the instability of the lithium (Li). However, existing artificial SEI layers inadequately controlled ion distribution, leading to dendritic growth and penetration. Furthermore, the environmental impact of the manufacturing process and materials of the artificial layer is often overlooked. In this work, a chemically and physically reinforced membrane (C-Li@P) composed of the biocompatible Li+ coordinated carboxymethyl guar gum (CMGG) and polyacrylamide (PAM) polymers serves as an artificial SEI membrane for dendrite-free Li. This membrane with hollow channels not only directs ion flux along the interspace of fibers, fostering uniform Li plating but also induces a desirable interface chemistry. Consequently, artificial SEI membrane-covered Li exhibits stable electrochemical plating/stripping reactions, surpassing the cycle life of ≈750% of bare Li. It demonstrates exceptional capacity retention of ≈93.9%, ≈88.1%, and ≈79.18% in full cells paired with LiNi0.8Mn0.1Co0.1O2 (NMC811), LiNi0.6Mn0.2Co0.2O2 (NMC622) and S cathodes, respectively over 200 cycles at 1 C rate. Additionally, the water-based green manufacturing and biodegradability of the membrane demonstrated the sustainable development and disposal of electrodes. This work provides a comprehensive framework for the design of an artificial layer chemically and physically regulating dendritic growth.

Construction of Hierarchical Conductive Networks for LiNi0.8Mn0.1Co0.1O2 Cathode toward Stable Cycling at High Areal Mass Loadings

Realizing high-performance thick electrodes is considered as a practical strategy to promote the energy density of lithium-ion batteries. However, establishing effective transport pathways for both lithium-ions and electrons in a thick electrode is very challenging. This study develops a hierarchical conductive network structure for constructing high-performance NMC811 (LiNi0.8Mn0.1Co0.1O2) cathode toward stable cycling at high areal mass loadings. The hierarchical conductive networks are composed of a Li+/e- mixed conducting interface (lithium polyacrylate/hydroxyl-functionalized multiwalled carbon nanotubes) on NMC811 particles, and a segregated network of single-walled carbon nanotubes in the electrode, without any additional binders or carbon black. Such strategy endows the NMC811 cathode (up to 250 µm and 50 mg cm-2) with low porosity/tortuosity, ultrahigh Li+/e- conductivities and excellent mechanical property at low carbon nanotube content (1.8 wt%). It significantly improves the electrochemical reaction homogeneity along the electrode depth, meanwhile effectively inhibits the side reactions at the electrode/electrolyte interface and cracks in the NMC particles during cycling. This work emphasizes the crucial role of the electronic/ionic cooperative transportation in the performance deterioration of thick cathodes, and provide guidance for architecture optimization and performance improvement of thick electrodes toward practical applications, not just for the NMC811 cathode.

In Situ Electrochemical Atomic Force Microscopy: From Interfaces to Interphases

The electrochemical interface formed between an electrode and an electrolyte significantly affects the rate and mechanism of the electrode reaction through its structure and properties, which vary across the interface. The scope of the interface has been expanded, along with the development of energy electrochemistry, where a solid-electrolyte interphase may form on the electrode and the active materials change properties near the surface region. Developing a comprehensive understanding of electrochemical interfaces and interphases necessitates three-dimensional spatial resolution characterization. Atomic force microscopy (AFM) offers advantages of imaging and long-range force measurements. Here we assess the capabilities of AFM by comparing the force curves of different regimes and various imaging modes for in situ characterizing of electrochemical interfaces and interphases. Selected examples of progress on work related to the structures and processes of electrode surfaces, electrical double layers, and lithium battery systems are subsequently illustrated. Finally, this review provides perspectives on the future development of electrochemical AFM.

Review of the Real-Time Monitoring Technologies for Lithium Dendrites in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have the advantage of high energy density, which has attracted the wide attention of researchers. Nevertheless, the growth of lithium dendrites on the anode surface causes short life and poor safety, which limits their application. Therefore, it is necessary to deeply understand the growth mechanism of lithium dendrites. Here, the growth mechanism of lithium dendrites is briefly summarized, and the real-time monitoring technologies of lithium dendrite growth in recent years are reviewed. The real-time monitoring technologies summarized here include in situ X-ray, in situ Raman, in situ resonance, in situ microscopy, in situ neutrons, and sensors, and their representative studies are summarized. This paper is expected to provide some guidance for the research of lithium dendrites, so as to promote the development of LIBs.

Bipolar Polymeric Protective Layer for Dendrite-Free and Corrosion-Resistant Lithium Metal Anode in Ethylene Carbonate Electrolyte

The unstable interface between Li metal and ethylene carbonate (EC)-based electrolytes triggers continuous side reactions and uncontrolled dendrite growth, significantly impacting the lifespan of Li metal batteries (LMBs). Herein, a bipolar polymeric protective layer (BPPL) is developed using cyanoethyl (-CH2CH2C≡N) and hydroxyl (-OH) polar groups, aiming to prevent EC-induced corrosion and facilitating rapid, uniform Li+ ion transport. Hydrogen-bonding interactions between -OH and EC facilitates the Li+ desolvation process and effectively traps free EC molecules, thereby eliminating parasitic reactions. Meanwhile, the -CH2CH2C≡N group anchors TFSI- anions through ion-dipole interactions, enhancing Li+ transport and eliminating concentration polarization, ultimately suppressing the growth of Li dendrite. This BPPL enabling Li|Li cell stable cycling over 750 cycles at 10 mA cm-2 for 2 mAh cm-2. The Li|LiNi0.8Mn0.1Co0.1O2 and Li|LiFePO4 full cells display superior electrochemical performance. The BPPL provides a practical strategy to enhanced stability and performance in LMBs application.

Cationic charge effect of glutamine repulsion adsorbate on Li metal surfaces for highly stable lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are superior next-generation batteries compared to commercial lithium-ion batteries (LiBs) because of their gravimetric energy densities, which provide longer battery life in a lighter package. However, the biggest hurdle for commercializing LSBs is their poor long-term cycling performance, which stems from polysulfide shuttling. To address this issue, we propose a novel approach: the use of glutamine, an amino acid, as an electrolyte additive to increase the cycling stability. Due to its molecular structure containing amines, the formation of Li dendrites was obstructed by homogenizing the Li-ion flux to shield the exceedingly active Li surfaces with glutamine, thereby reducing the overvoltage during Li plating and stripping. Additionally, the redox reactions of lithium polysulfides were enhanced, which helped to alleviate the shuttling of lithium polysulfides. Therefore, the addition of glutamine improved the stability and reduced the cell degradation rate by approximately 0.066% during high C-rate long-term cycling tests.

Molecular Engineering toward Robust Solid Electrolyte Interphase for Lithium Metal Batteries

Lithium-metal batteries (LMBs) with high energy density are becoming increasingly important in global sustainability initiatives. However, uncontrollable dendrite seeds, inscrutable interfacial chemistry, and repetitively formed solid electrolyte interphase (SEI) have severely hindered the advancement of LMBs. Organic molecules have been ingeniously engineered to construct targeted SEI and effectively minimize the above issues. In this review, multiple organic molecules, including polymer, fluorinated molecules, and organosulfur, are comprehensively summarized and insights into how to construct the corresponding elastic, fluorine-rich, and organosulfur-containing SEIs are provided. A variety of meticulously selected cases are analyzed in depth to support the arguments of molecular design in SEI. Specifically, the evolution of organic molecules-derived SEI is discussed and corresponding design principles are proposed, which are beneficial in guiding researchers to understand and architect SEI based on organic molecules. This review provides a design guideline for constructing organic molecule-derived SEI and will inspire more researchers to concentrate on the exploitation of LMBs.

Toward maximum energy density enabled by anode-free lithium metal batteries: Recent progress and perspective

Owing to the emergenceof energy storage and electric vehicles, the desire for safe high-energy-density energy storage devices has increased research interest in anode-free lithium metal batteries (AFLMBs). Unlike general lithium metal batteries (LMBs), in which excess Li exists to compensate for the irreversible loss of Li, only the current collector is employed as an anode and paired with a lithiated cathode in the fabrication of AFLMBs. Owing to their unique cell configuration, AFLMBs have attractive characteristics, including the highest energy density, safety, and cost-effectiveness. However, developing AFLMBs with extended cyclability remains an issue for practical applications because the high reactivity of Li with limited inventory causes severely low Coulombic efficiency (CE), poor cyclability, and dendrite growth. To address these issues, tremendous effort has been devoted to stabilizing Li metal anodes for AFLMBs. In this review, the importance and challenges of AFLMBs are highlighted. Then, diverse strategies, such as current collectors modification, advanced electrolytes, cathode engineering, and operation protocols are thoroughly reviewed. Finally, a future perspective on the strategy is provided for insight into the basis of future research. It is hoped that this review provides a comprehensive understanding by reviewing previous research and arousing more interest in this field.

Designing an Air-Stable Interphase on Lithium Metal Anode to Improve Cycling Performance

The application of rechargeable lithium metal batteries is challenged by intractable issues of uncontrollable Li dendrite growth that result in poor cycle life and safety risks. In this work, an air-stable interphase is developed to protect the lithium metal anode (LMA) via a facile solution-based approach. The Ag-embedded fluoride-rich interphase not only creates abundant lithiophilic sites for homogenizing Li nucleation and growth but also resists severe air erosion to protect the LMA beneath and enable decent cycling stability. As a result, the Ag-F-rich interphase enables flat Li deposition on LMA, which is clearly observed in the operando Li plating experiments. Paired with a LiFePO4 cathode (11.8 mg cm-2), the Ag-F-rich interphase-modified LMA enables 300 stable cycles at 0.5 C, delivering a capacity retention ratio as high as 91.4%. Even after being exposed to air for 1 h, the modified LMA still runs smoothly for over 120 cycles with ignorable capacity decay, exhibiting great air stability. This work proves the concept of functionalizing the interphase on the LMA to enable good cycling performance even under severe air erosion.

Thioacetamide Additive Homogenizing Zn Deposition Revealed by In Situ Digital Holography for Advanced Zn Ion Batteries

Zinc ion batteries are considered as potential energy storage devices due to their advantages of low-cost, high-safety, and high theoretical capacity. However, dendrite growth and chemical corrosion occurring on Zn anode limit their commercialization. These problems can be tackled through the optimization of the electrolyte. However, the screening of electrolyte additives using normal electrochemical methods is time-consuming and labor-intensive. Herein, a fast and simple method based on the digital holography is developed. It can realize the in situ monitoring of electrode/electrolyte interface and provide direct information concerning ion concentration evolution of the diffusion layer. It is effective and time-saving in estimating the homogeneity of the deposition layer and predicting the tendency of dendrite growth, thus able to value the applicability of electrolyte additives. The feasibility of this method is further validated by the forecast and evaluation of thioacetamide additive. Based on systematic characterization, it is proved that the introduction of thioacetamide can not only regulate the interficial ion flux to induce dendrite-free Zn deposition, but also construct adsorption molecule layers to inhibit side reactions of Zn anode. Being easy to operate, capable of in situ observation, and able to endure harsh conditions, digital holography method will be a promising approach for the interfacial investigation of other battery systems.

Facile Fabrication of Polymer Electrolytes with Branched Structure via Deep Eutectic Electrolyte-Enabled In Situ Polymerizations

The demand for higher energy density in energy storage devices drives further research on lithium metal batteries (LMBs) because of the high theoretical capacity and low voltage of lithium metal anode. Polymer electrolytes (PEs) exhibit obvious advantages in combating volatilization and leakage compared with liquid electrolytes, which improves the safety of LMBs. However, it is still difficult to construct PEs with a stable electrolyte-electrode interface for high-performance and long-term life LMBs. Herein, the gel polymer electrolyte (GPE-SL) containing deep eutectic electrolyte (DEE) and branchlike polymer skeleton are designed and prepared by the DEE-induced in situ cationic and radical polymerizations. The DEE provides a smooth Li+ migration pathway to ensure the electrochemical properties, and the multibrominated polymer matrix formed in situ enables a LiBr-rich solid electrolyte interphase (SEI) layer on lithium metal anode and prolongs the life span of LMBs. Hence, the Li|GPE-SL|LiFePO4 battery displays an excellent cycling stability with 84% capacity retention after 1200 cycles at 1C. This simple deep eutectic electrolyte-induced polymerization method provides a promising direction for high-performance LMBs with improved anode-electrolyte compatibility through the construction of a stable SEI layer in situ.

A corrosion inhibiting layer to tackle the irreversible lithium loss in lithium metal batteries

Reactive negative electrodes like lithium (Li) suffer serious chemical and electrochemical corrosion by electrolytes during battery storage and operation, resulting in rapidly deteriorated cyclability and short lifespans of batteries. Li corrosion supposedly relates to the features of solid-electrolyte-interphase (SEI). Herein, we quantitatively monitor the Li corrosion and SEI progression (e.g., dissolution, reformation) in typical electrolytes through devised electrochemical tools and cryo-electron microscopy. The continuous Li corrosion is validated to be positively correlated with SEI dissolution. More importantly, an anti-corrosion and interface-stabilizing artificial passivation layer comprising low-solubility polymer and metal fluoride is designed. Prolonged operations of Li symmetric cells and Li | |LiFePO4 cells with reduced Li corrosion by ~74% are achieved (0.66 versus 2.5 μAh h-1). The success can further be extended to ampere-hour-scale pouch cells. This work uncovers the SEI dissolution and its correlation with Li corrosion, enabling the durable operation of Li metal batteries by reducing the Li loss.

From Liquid to Solid-State Lithium Metal Batteries: Fundamental Issues and Recent Developments

The widespread adoption of lithium-ion batteries has been driven by the proliferation of portable electronic devices and electric vehicles, which have increasingly stringent energy density requirements. Lithium metal batteries (LMBs), with their ultralow reduction potential and high theoretical capacity, are widely regarded as the most promising technical pathway for achieving high energy density batteries. In this review, we provide a comprehensive overview of fundamental issues related to high reactivity and migrated interfaces in LMBs. Furthermore, we propose improved strategies involving interface engineering, 3D current collector design, electrolyte optimization, separator modification, application of alloyed anodes, and external field regulation to address these challenges. The utilization of solid-state electrolytes can significantly enhance the safety of LMBs and represents the only viable approach for advancing them. This review also encompasses the variation in fundamental issues and design strategies for the transition from liquid to solid electrolytes. Particularly noteworthy is that the introduction of SSEs will exacerbate differences in electrochemical and mechanical properties at the interface, leading to increased interface inhomogeneity-a critical factor contributing to failure in all-solid-state lithium metal batteries. Based on recent research works, this perspective highlights the current status of research on developing high-performance LMBs.

Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are supposed to be one of the most potential next-generation batteries owing to their high theoretical capacity and low cost. Nevertheless, the shuttle effect of firm multi-step two-electron reaction between sulfur and lithium in liquid electrolyte makes the capacity much smaller than the theoretical value. Many methods were proposed for inhibiting the shuttle effect of polysulfide, improving corresponding redox kinetics and enhancing the integral performance of Li-S batteries. Here, we will comprehensively and systematically summarize the strategies for inhibiting the shuttle effect from all components of Li-S batteries. First, the electrochemical principles/mechanism and origin of the shuttle effect are described in detail. Moreover, the efficient strategies, including boosting the sulfur conversion rate of sulfur, confining sulfur or lithium polysulfides (LPS) within cathode host, confining LPS in the shield layer, and preventing LPS from contacting the anode, will be discussed to suppress the shuttle effect. Then, recent advances in inhibition of shuttle effect in cathode, electrolyte, separator, and anode with the aforementioned strategies have been summarized to direct the further design of efficient materials for Li-S batteries. Finally, we present prospects for inhibition of the LPS shuttle and potential development directions in Li-S batteries.

Solid Electrolyte Interphase Architecture for a Stable Li-electrolyte Interface

Li metal anode has attracted extensive attention as the state-of-the-art anode material for rechargeable batteries. It is defined as the ultimate anode material for the high theoretical specific capacity (3860 mAh g-1 ) and the lowest negative electrochemical potential (-3.04 V vs. Standard Hydrogen Electrode). However, the uncontrolled Li dendrites and the spontaneous side reactions between Li and electrolytes hinder its commercialization. To overcome these obstacles, the optimized solid electrolyte interphase (SEI) with excellent performance was proposed by the artificial method. The improved performance includes high stability, ionic conductivity, compactness, and flexibility. In this review, the strategies for artificial SEI engineering in liquid and solid electrolytes are summarized. To fabricate an ideal artificial SEI, the component, distribution, and structure should be fully and reasonably considered. This review will also provide perspectives for the SEI design and lay a foundation for the future research and development of Li metal batteries.

Efficiencies of Various in situ Polymerizations of Liquid Electrolytes and the Practical Implications for Quasi Solid-state Batteries

In situ polymerization of liquid electrolytes is currently the most feasible way for constructing solid-state batteries, which, however, is affected by various interfering factors of reactions and so the electrochemical performance of cells. To disclose the effects from polymerization conditions, two types of generally used in situ polymerizing reactions of ring-opening polymerization (ROP) and double bond radical polymerization (DBRP) were investigated on the aspects of monomer conversion and electrochemical properties (Li+ -conductivity and interfacial stability). The ROP generated poly-ester and poly-carbonate show a high monomer conversion of ≈90 %, but suffer a poor Li+ -conductivity of lower than 2×10-5  S cm-1 at room temperature (RT). Additionally, the terminal alkoxy anion derived from the ROP is not resistant to high-voltage cathodes. While, the DBRP produced poly-VEC(vinyl ethylene carbonate) and poly-VC(vinylene carbonate) show lower monomer conversions of 50-80 %, delivering relatively higher Li+ -conductivities of 2×10-4  S cm-1 at RT. Compared two polymerizing reactions and four monomers, the VEC-based F-containing copolymer possesses advantages in Li+ -conductivity and antioxidant capacity, which also shows simultaneous stability towards Li-metal with the help of LiF-based passivating layer, allowing a long-term stable cycling of high-voltage quasi solid-state cells.

A hybrid polymer protective layer with uniform Li+ flux and self-adaption enabling dendrite-free Li metal anodes

Lithium (Li) metal is considered as an ideal negative electrode material for next-generation secondary batteries; however, the hideous dendrite growth and parasitic reactions hinder the practical applications of Li metal batteries. Herein, a hybrid polymer film composed of polyvinyl alcohol (PVA) and polyacrylic acid (PAA) is adopted as an artificial protective layer to inhibit the dendritic formation and side reactions in Li metal anodes. PVA with large quantities of polar functional groups can induce even distribution of Li ions (Li+). Alternatively, PAA can in situ react with Li metal to form highly elastic and ionic conducting lithium polyacrylic acid (LiPAA), thereby enabling tight contact and flexible self-adaption with Li metal anodes. Therefore, such a rationally designed functional composite layer, with good binding ability and relatively high Li+ conductivity, as well as excellent capability of homogenizing Li+ flow, accordingly enables Li metal anodes to reveal dendrite-free plating/stripping behaviours and minimum volume variation. As a result, the PVA-PAA modified Li metal anode delivered stable cycling for 700 and 250 h, respectively, at current densities of 1 and 3 mA cm-2 under an areal capacity of 1 mA h cm-2, in a carbonate ester-based electrolyte without any additive, exhibiting boosted cycling and rate performances. The Li anode with a functional PVA-PAA hybrid interlayer can maintain the dense and smooth texture without dendrite formation after long cycles. The full cell of Li|LiFeO4 with our modified Li anode and a cathode with a high areal capacity of 2.45 mA h cm-2 delivers, change to achieved a long-term lifespan of 180 cycles at 1.0 C, with a capacity retention of 96.7%. This work demonstrates a simple and effective strategy of designing multi-functional artificial protective layers, targeting dendrite-free Li anodes.

Lithiated Phosphoryl Cellulose Nanocrystals Enhance Cycling Stability and Safety of Quasi-Solid-State Lithium Metal Batteries

Cycling stability and safety are two of the main challenges facing lithium metal batteries with metallic lithium as anodes. Quasi-solid-state lithium metal batteries based on gel polymer electrolytes are one of the important development directions for lithium metal batteries addressing those challenges. Herein, we prepare lithiated phosphoryl cellulose nanocrystals (PCNC-Li) as a modification material for poly(vinylidene fluoride) (PVDF) gel polymer electrolyte to improve cycling stability and safety of quasi-solid-state lithium metal batteries. The synthesized PCNC-Li tends to form a uniform network structure on the surface of the PVDF membrane, in which the phosphoryl groups grafted regularly on celluloses can regulate the transport of lithium ions. As a result, a more uniform ion flux and more stable lithium anode interface support an obviously improved cycling stability for lithium metal batteries. Moreover, the introduction of the PCNC-Li coating layer makes the modified PVDF membranes have a better thermal stability and an enhanced mechanical strength, which is beneficial for improvement of safety of lithium metal batteries. This work provides a new alternative to fabricating a better composite gel polymer electrolyte for lithium metal batteries.

In Situ Formed Gradient Composite Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes

Lithium (Li) metal anode (LMA) is highly considered as a desirable anode material for next-generation rechargeable batteries because of its high specific capacity and the lowest reduction potential. However, uncontrollable growth of Li dendrites, large volume change, and unstable interfaces between LMA and electrolyte hinder its practical application. Herein, a novel in situ formed artificial gradient composite solid electrolyte interphase (GCSEI) layer for highly stable LMAs is proposed. The inner rigid inorganics (Li2 S and LiF) with high Li+ ion affinity and high electron tunneling barrier are beneficial to achieve homogeneous Li plating, while the flexible polymers (poly(ethylene oxide) and poly(vinylidene fluoride)) on the surface of GCSEI layer can accommodate the volume change. Furthermore, the GCSEI layer demonstrates fast Li+ ion transport capability and increased Li+ ion diffusion kinetics. Accordingly, the modified LMA enables excellent cycling stability (over 1000 h at 3 mA cm-2 ) in the symmetric cell using carbonate electrolyte, and the corresponding Li-GCSEI||LiNi0.8 Co0.1 Mn0.1 O2 full cell demonstrates 83.4% capacity retention after 500 cycles. This work offers a new strategy for the design of dendrite-free LMAs for practical applications.

Construction of a Bis(benzene sulfonyl)imide-Based Single-ion Polymer Artificial Layer for a Steady Lithium Metal Anode

Dendrite growth and parasitic reactions with liquid electrolyte are the two key factors that restrict the practical application of the lithium metal anode. Herein, a bis(benzene sulfonyl)imide based single-ion polymer artificial layer for a lithium metal anode is successfully constructed, which is prepared via blending the as-prepared copolymer of lithiated 4, 4'-dicarboxyl bis(benzene sulfonyl)imide and 4,4'-diaminodiphenyl ether on the surface of lithium foil. This single-ion polymer artificial layer enables compact structure with unique continuous aggregated Li+ clusters, thus reducing the direct contact between lithium metal and electrolyte simultaneously, ensuring Li+ transport is fast and homogeneous. Based on which, the coulombic efficiency of the Li|Cu half-cell is effectively improved, and the cycle stability of the Li|Li symmetric cell can be prolonged from 160 h to 240 h. Surficial morphology and elemental valence analysis confirm that the bis(benzene sulfonyl)imide based single-ion polymer artificial layer effectively facilitates the Li+ uniform deposition and suppresses parasitic reactions between lithium metal anode and liquid electrolyte in the LFP|Li full-cell. This strategy provides a new perspective to achieve a steady lithium metal anode, which can be a promising candidate in practical applications.

Encapsulating lithium at the microscale: selective deposition in carbon-doped graphitic carbon nitride spheres

For stable lithium deposition without dendrites, three-dimensional (3D) porous structure has been intensively investigated. Here, we report the use of carbon-doped graphitic carbon nitride (C-doped g-C3N4) microspheres as a 3D host for lithium to suppress dendrite formation, which is crucial for stable lithium deposition. The C-doped g-C3N4microspheres have a high surface area and porosity, allowing for efficient lithium accommodation with high accessibility. The carbon-doping of the g-C3N4microspheres confers lithiophilic properties, which facilitate the regulation of Li+flux and dense filling of cavities with nucleated lithium, thereby preventing volume expansion and promoting dendrite-free Li deposition. The electrochemical performance was improved with cyclic stability and high Coulombic efficiency over 260 cycles at 1.0 mA cm-2for 1.0 mAh cm-2, and even over 70 cycles at 5.0 mA cm-2for 3.0 mAh cm-2. The use of C-doped g-C3N4microspheres as a 3D Li host shows promising results for stable lithium deposition without dendrite formation.

3D Porous Cu-Composites for Stable Li-Metal Battery Anodes

Lithium (Li) metal is a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical specific capacity of 3860 mAh g-1 and the low potential of -3.04 V versus the standard hydrogen electrode (SHE). However, these anodes rely on repeated plating and stripping of Li, which leads to consumption of Li inventory and the growth of dendrites that can lead to self-discharge and safety issues. To address these issues, as well as problems related to the volume change of these anodes, a number of different porous conductive scaffolds have been reported to create high surface area electrode on which Li can be plated reliably. While impressive results have been reported in literature, current processes typically rely on either expensive or poorly scalable techniques. Herein, we report a scalable fabrication method to create robust 3D Cu anodes using a one-step electrodeposition process. The areal loading, pore structure, and electrode thickness can be tuned by changing the electrodeposition parameters, and we show how standard mechanical calendering provides a way to further optimize electrode volume, capacity, and cycling stability. Optimized electrodes achieve high Coulombic efficiencies (CEs) of 99% during 800 cycles in half cells at a current density of 0.5 mA cm-2 with a total capacity of 0.5 mAh cm-2. To the best of our knowledge, this is the highest value ever reported for a host for Li-metal anodes using lithium bis(trifluoromethanesulfonyl)imide LITFSI based electrolyte.

Production of high-energy 6-Ah-level Li | |LiNi0.83Co0.11Mn0.06O2 multi-layer pouch cells via negative electrode protective layer coating strategy

Stable lithium metal negative electrodes are desirable to produce high-energy batteries. However, when practical testing conditions are applied, lithium metal is unstable during battery cycling. Here, we propose poly(2-hydroxyethyl acrylate-co-sodium benzenesulfonate) (PHS) as negative electrode protective layer. The PHS contains soft poly (2-hydroxyethyl acrylate) and poly(sodium p-styrene sulfonate), which improve electrode flexibility, connection with the Cu current collector and transport of Li ions. Transmission electron cryomicroscopy measurements reveal that PHS induces the formation of a solid electrolyte interphase with a fluorinated rigid and crystalline internal structure. Furthermore, theoretical calculations suggest that the -SO₃^- group of poly(sodium p-styrene sulfonate) promotes Li-ion motion towards interchain migration through cation-dipole interaction, thus, enabling uniform Li-ion diffusion. Electrochemical measurements of Li | |PHS-coated-Cu coin cells demonstrate an average Coulombic efficiency of 99.46% at 1 mA/cm², 6 mAh/cm² and 25 °C. Moreover, when the PHS-coated Li metal negative electrode is paired with a high-areal-capacity LiNi_0.83Co_0.11Mn_0.06O₂-based positive electrode in multi-layer pouch cell configuration, the battery delivers an initial capacity of 6.86 Ah (corresponding to a specific energy of 489.7 Wh/kg) and, a 91.1% discharge capacity retention after 150 cycles at 2.5 mA/cm², 25 °C and 172 kPa.

Electrochemical Imaging of Interfaces in Energy Storage via Scanning Probe Methods: Techniques, Applications, and Prospects

Developing a deeper understanding of dynamic chemical, electronic, and morphological changes at interfaces is key to solving practical issues in electrochemical energy storage systems (EESSs). To unravel this complexity, an assortment of tools with distinct capabilities and spatiotemporal resolutions have been used to creatively visualize interfacial processes as they occur. This review highlights how electrochemical scanning probe techniques (ESPTs) such as electrochemical atomic force microscopy, scanning electrochemical microscopy, scanning ion conductance microscopy, and scanning electrochemical cell microscopy are uniquely positioned to address these challenges in EESSs. We describe the operating principles of ESPTs, focusing on the inspection of interfacial structure and chemical processes involved in Li-ion batteries and beyond. We discuss current examples, performance limitations, and complementary ESPTs. Finally, we discuss prospects for imaging improvements and deep learning for automation. We foresee that ESPTs will play an enabling role in advancing EESSs as we transition to renewable energies.

The inhibited Li dendrite growth via bulk/liquid dual-phase modulation

Li metal is a potential anode material for the next generation high-energy-density batteries because of its high theoretical specific capacity. However, the inhomogeneous lithium dendrite growth restrains corresponding electrochemical performance and brings safety concerns. In this contribution, the Li₃Bi/Li₂O/LiI fillers are generated by the in-situ reaction between Li and BiOI nanoflakes, which promises corresponding Li anodes (BiOI@Li) showing favorable electrochemical performance. This can be attributed to the bulk/liquid dual modulations: (1) The three-dimensional Bi-based framework in the bulk-phase lowers the local current density and accommodates the volume variation; (2) The LiI dispersed within Li metal is slowly released and dissolved into the electrolyte with the consumption of Li, which will form I^-/I₃^- electron pair and further reactivate the inactive Li species. Specifically, the BiOI@Li//BiOI@Li symmetrical cell shows small overpotential and enhanced cycle stability over 600 h at 1 mA cm^-2. Matched with an S-based cathode, the full Li-S battery demonstrates desirable rate performance and cycling stability.

Probing the Mechanically Stable Solid Electrolyte Interphase and the Implications in Design Strategies

The inevitable volume expansion of secondary battery anodes during cycling imposes forces on the solid electrolyte interphase (SEI). The battery performance is closely related to the capability of SEI to maintain intact under the cyclic loading conditions, which basically boils down to the mechanical properties of SEI. The volatile and complex nature of SEI as well as its nanoscale thickness and environmental sensitivity make the interpretation of its mechanical behavior many roadblocks. Widely varied approaches are adopted to investigate the mechanical properties of SEI, and diverse opinions are generated. The lack of consensus at both technical and theoretical levels has hindered the development of effective design strategies to maximize the mechanical stability of SEIs. Here, the essential and desirable mechanical properties of SEI, the available mechanical characterization methods, and important issues meriting attention for higher test accuracy are outlined. Previous attempts to optimize battery performance by tuning SEI mechanical properties are also scrutinized, inconsistencies in these efforts are elucidated, and the underlying causes are explored. Finally, a set of research protocols is proposed to accelerate the achievement of superior battery cycling performance by improving the mechanical stability of SEI.

A Critical Review on the Recycling Strategy of Lithium Iron Phosphate from Electric Vehicles

Electric vehicles (EVs) are one of the most promising decarbonization solutions to develop a carbon-negative economy. The increasing global storage of EVs brings out a large number of power batteries requiring recycling. Lithium iron phosphate (LFP) is one of the first commercialized cathodes used in early EVs, and now gravimetric energy density improvement makes LFP with low cost and robustness popular again in the market. Developments in LFP recycling techniques are in demand to manage a large portion of the EV batteries retired both today and around ten years later. In this review, first the operation and degradation mechanisms of LFP are revisited aiming to identify entry points for LFP recycling. Then, the current LFP recycling methods, from the pretreatment of the retired batteries to the regeneration and recovery of the LFP cathode are summarized. The emerging direct recovery technology is highlighted, through which both raw material and the production cost of LFP can be recovered. In addition, the current issues limiting the development of the LIBs recycling industry are presented and some ideas for future research are proposed. This review provides the theoretical basis and insightful perspectives on developing new recycling strategies by outlining the whole-life process of LFP.

Mixed Ion/Electron Conductive Li3N-Mo Interphase Enabling Stable and Ultrahigh-Rate Lithium Metal Anodes

Lithium (Li) metal is a promising anode for high-energy-density batteries; however, its practical viability is hampered by the unstable metal Li-electrolyte interface and Li dendrite growth. Herein, a mixed ion/electron conductive Li₃N-Mo protective interphase with high mechanical stability is designed and demonstrated to stabilize the Li-electrolyte interface for a dendrite-free and ultrahigh-current-density metallic Li anode. The Li₃N-Mo interphase is simultaneously formed and homogeneously distributed on the Li metal surface by the surface reaction between molten Li and MoN nanosheets powder. The highly ion-conductive Li₃N and abundant Li₃N/Mo grain boundaries facilitate fast Li-ion diffusion, while the electrochemically inert metal Mo cluster in the mosaic structure of Li₃N-Mo inhibits the long-range crystallinity and regulates the Li-ion flux, further promoting the rate capability of the Li anode. The Li₃N-Mo/Li electrode has a stable Li-electrolyte interface as manifested by a low Li overpotential of 12 mV and outstanding plating/stripping cyclability for over 3200 h at 1 mA cm^-2. Moreover, the Li₃N-Mo/Li anode inhibits Li dendrite formation and exhibits a long cycling life of 840 h even at 30 mA cm^-2. The full cell assembled with LiFePO₄ cathode exhibits stable cycling performance with 87.9% capacity retention for 200 cycles at 1C (1C = 170 mA g^-1) as well as high rate capability of 83.7 mAh g^-1 at 3C. The concept of constructing a mixed ion/electron conductive interphase to stabilize the Li-electrolyte interface for high-rate and dendrite-free Li metal anodes offers a viable strategy to develop high-performance Li-metal batteries.

Surface engineering toward stable lithium metal anodes

The lithium (Li) metal anode (LMA) is susceptible to failure due to the growth of Li dendrites caused by an unsatisfied solid electrolyte interface (SEI). With this regard, the design of artificial SEIs with improved physicochemical and mechanical properties has been demonstrated to be important to stabilize the LMAs. This review comprehensively summarizes current efficient strategies and key progresses in surface engineering for constructing protective layers to serve as the artificial SEIs, including pretreating the LMAs with the reagents situated in different primary states of matter (solid, liquid, and gas) or using some peculiar pathways (plasma, for example). The fundamental characterization tools for studying the protective layers on the LMAs are also briefly introduced. Last, strategic guidance for the deliberate design of surface engineering is provided, and the current challenges, opportunities, and possible future directions of these strategies for the development of LMAs in practical applications are discussed.

Optimizing the Fermi Level of a 3D Current Collector with Ni3 S2 /Ni3 P Heterostructure for Dendrite-Free Sodium-Metal Batteries

Rechargeable sodium-metal batteries (RSMBs) with high energy density and low cost are attracting extensive attention as promising energy-storage technologies. However, the poor cyclability and safety issues caused by unstable solid electrolyte interphase (SEI) structure and dendrite issues limit their practical application. Herein, it is theoretically predicted that constructing the Ni₃ S₂ /Ni₃ P heterostructure with high work function can lower the Fermi energy level, and therefore effectively suppressing continuous electrolyte decomposition derived from the electron-tunneling effect after long-term sodiation process. Furthermore, the Ni₃ S₂ /Ni₃ P heterostructure on 3D porous nickel foam (Ni₃ S₂ /Ni₃ P@NF) is experimentally fabricated as an advanced Na-anode current collector. The seamless Ni₃ S₂ /Ni₃ P heterostructure not only offers abundant active sites to induce uniform Na⁺ deposition and enhance ion-transport kinetics, but also facilitates the formation of stable SEI for dendrite-free sodium anode, which are confirmed by cryogenic components transmission electron microscopy tests and in situ spectroscopy characterization. As a result, the Na-composite anode (Ni₃ S₂ /Ni₃ P@NF@Na) delivers stable plating/stripping process of 5000 h and high average Coulombic efficiency of 99.7% over 2500 cycles. More impressively, the assembled sodium-ion full cell displays ultralong cycle life of 10 000 cycles at 20 C. The strategy of stabilizing the sodium-metal anode gives fundamental insight into the potential construction of advanced RSMBs.

Interface Design Enabling Stable Polymer/Thiophosphate Electrolyte Separators for Dendrite-Free Lithium Metal Batteries

Organic/inorganic interfaces greatly affect Li⁺ transport in composite solid electrolytes (SEs), while SE/electrode interfacial stability plays a critical role in the cycling performance of solid-state batteries (SSBs). However, incomplete understanding of interfacial (in)stability hinders the practical application of composite SEs in SSBs. Herein, chemical degradation between Li₆ PS₅ Cl (LPSCl) and poly(ethylene glycol) (PEG) is revealed. The high polarity of PEG changes the electronic state and structural bonding of the PS₄ ^3- tetrahedra, thus triggering a series of side reactions. A substituted terminal group of PEG not only stabilizes the inner interfaces but also extends the electrochemical window of the composite SE. Moreover, a LiF-rich layer can effectively prevent side reactions at the Li/SE interface. The results provide insights into the chemical stability of polymer/sulfide composites and demonstrate an interface design to achieve dendrite-free lithium metal batteries.

An Inorganic-Rich SEI Layer by the Catalyzed Reduction of LiNO3 Enabled by Surface-Abundant Hydrogen Bonding for Stable Lithium Metal Batteries

Lithium (Li) metal anodes (LMAs) are promising anode candidates for realizing high-energy-density batteries. However, the formation of unstable solid electrolyte interphase (SEI) layers on Li metal is harmful for stable Li cycling; hence, enhancing the physical/chemical properties of SEI layers is important for stabilizing LMAs. Herein, thiourea (TU, CH₄ N₂ S) is introduced as a new catalyzing agent for LiNO₃ reduction to form robust inorganic-rich SEI layers containing abundant Li₃ N. Due to the unique molecular structure of TU, the TU molecules adsorb on the Cu electrode by forming CuS bond and simultaneously form hydrogen bonding with other hydrogen bonds accepting species such as NO₃ ^- and TFSI^- through its NH bonds, leading to their catalyzed reduction and hence the formation of inorganic-rich SEI layer with abundant Li₃ N, LiF, and Li₂ S/Li₂ S₂ . Particularly, this TU-modified SEI layer shows a lower film resistance and better uniformity compared to the electrochemically and naturally formed SEI layers, enabling planar Li growth without any other material treatments and hence improving the cyclic stability in Li/Cu half-cells and Li@Cu/LiFePO₄  full-cells.

Effect of LLZO on the in situ polymerization of acrylate solid-state electrolytes on cathodes

The comprehensive performance of the state-of-the-art solid-state electrolytes (SSEs) cannot match the requirements of commercial applications, and constructing an organic-inorganic composite electrolyte in situ on a porous electrode is an effective coping strategy. However, there are few studies focused on the influence of inorganic ceramics on the polymerization of multi-organic components. In this study, it was found that the addition of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZO) weakens the interaction between different polymers and makes organic and inorganic components contact directly in the solid electrolyte. These suppress the segregation of components in the in situ polymerized composite SSE, leading to a decrease in the polymer crystallization and improvement of electrolyte properties such as electrochemical stability window and mechanical properties. The composite solid-state electrolyte can be in situ constructed on different porous electrodes, which can establish close contact with active material particles, showing an ionic conductivity 4.4 × 10^-5 S cm^-1 at 25 °C, and afford the ternary cathode stability for 100 cycles.

Self-Healing Polymer Electrolytes for Next-Generation Lithium Batteries

The integration of polymer materials with self-healing features into advanced lithium batteries is a promising and attractive approach to mitigate degradation and, thus, improve the performance and reliability of batteries. Polymeric materials with an ability to autonomously repair themselves after damage may compensate for the mechanical rupture of an electrolyte, prevent the cracking and pulverization of electrodes or stabilize a solid electrolyte interface (SEI), thus prolonging the cycling lifetime of a battery while simultaneously tackling financial and safety issues. This paper comprehensively reviews various categories of self-healing polymer materials for application as electrolytes and adaptive coatings for electrodes in lithium-ion (LIBs) and lithium metal batteries (LMBs). We discuss the opportunities and current challenges in the development of self-healable polymeric materials for lithium batteries in terms of their synthesis, characterization and underlying self-healing mechanism, as well as performance, validation and optimization.

One-Step In Situ Polymerization: A Facile Design Strategy for Block Copolymer Electrolytes

To optimize the rapid transport of lithium ions (Li⁺ ) inside lithium metal batteries (LMBs), block copolymer electrolytes (BCPEs) have been fabricated in situ in LMBs via a one-step method combining reversible addition-fragmentation chain transfer (RAFT) polymerization and carboxylic acid-catalyzed ring-opening polymerization (ROP). The BCPEs balanced the Li⁺ coordination characteristics of the polyether- and polyester-based electrolytes to achieve a rapid Li⁺ migration in the SPEs. The carboxylic acid played a dual role since it both catalyzed the ROP and stabilized the interface. Furthermore, the in situ assembly of LMBs did effectively enable an efficient intercalation/de-intercalation of Li⁺ at the electrode/electrolyte interface. The in situ assembled Li/BCPE4/LFP exhibited high-capacity retention of 92 % after 400 cycles at 1 C. The one-step in situ fabrication of BCPEs provides a new direction for the design of polymer electrolytes.

Tailoring polymer electrolyte ionic conductivity for production of low- temperature operating quasi-all-solid-state lithium metal batteries

The stable operation of lithium-based batteries at low temperatures is critical for applications in cold climates. However, low-temperature operations are plagued by insufficient dynamics in the bulk of the electrolyte and at electrode|electrolyte interfaces. Here, we report a quasi-solid-state polymer electrolyte with an ionic conductivity of 2.2 × 10^-4 S cm^-1 at -20 °C. The electrolyte is prepared via in situ polymerization using a 1,3,5-trioxane-based precursor. The polymer-based electrolyte enables a dual-layered solid electrolyte interphase formation on the Li metal electrode and stabilizes the LiNi_0.8Co_0.1Mn_0.1O₂-based positive electrode, thus improving interfacial charge-transfer at low temperatures. Consequently, the growth of dendrites at the lithium metal electrode is hindered, thus enabling stable Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin and pouch cell operation even at -30 °C. In particular, we report a Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin cell cycled at -20 °C and 20 mA g^-1 capable of retaining more than 75% (i.e., around 151 mAh g^-1) of its first discharge capacity cycle at 30 °C and same specific current.

A Brush-like Li-Ion Exchange Polymer as Potential Artificial Solid Electrolyte Interphase for Dendrite-Free Lithium Metal Batteries

Artificial polymeric solid electrolyte interfaces (APSEIs) are an emerging material that enables use of a lithium metal anode as a lithium metal battery technique with high energy density. However, the poor ionic conductivity, low lithium transference number, and bad compatibity with lithium metal anode lead to a large dissipative loss of energy capacity. Here we report that, by properly constructing a brush-like structure in cellulose nanofibril (CNF) based APSEIs, a good ion-aggregation morphology with interconnected ionic conducting channels can be built, such that the Li-ion conduction in the APSEI layer becomes highly efficient. The optimal approach to constructing such an ionic highway is proved computationally using coarse-grained molecular dynamics (CGMD) simulations and implemented experimentally based on transmission electron microscopy (TEM) and atomic force microscopy (AFM). In addition, Li-ion exchange structures and hydroxyl-abundant structures endow the APSEIs with good ability to suppress dendrite growth and excellent compatibility with the anode surface.

Spatially Confined LiF Nanoparticles in an Aligned Polymer Matrix as the Artificial SEI Layer for Lithium Metal Anodes

The uncontrollable growth of lithium (Li) dendrites and the instability of the Li/electrolyte interface hinder the development of next-generation rechargeable lithium metal batteries. The combination of inorganic nanoparticles and polymers as the artificial SEI layer shows great potential in regulating lithium-ion flux. Here, we design spatially confined LiF nanoparticles in an aligned polymer matrix as the artificial SEI layer. A high dielectric polymer matrix homogenizes the electric field near the surface of lithium metal. Aligned pores with LiF nanoparticles promote the lithium-ion transport across the artificial SEI layer. The synergistic effect of the highly polar β-phase PVDF and LiF nanoparticles provides high stability over 900 h for the Li//Li symmetrical cell. Besides, a Li//LFP full battery equipped with this artificial layer shows good performance in the commercial carbonate electrolyte, demonstrating the great potential of this protective film in lithium metal batteries.

Multiscale Polymeric Materials for Advanced Lithium Battery Applications

Riding on the rapid growth in electric vehicles and the stationary energy storage market, high-energy-density lithium-ion batteries and next-generation rechargeable batteries (i.e., advanced batteries) have been long-accepted as essential building blocks for future technology reaching the specific energy density of 400 Wh kg^-1 at the cell-level. Such progress, mainly driven by the emerging electrode materials or electrolytes, necessitates the development of polymeric materials with advanced functionalities in the battery to address new challenges. Therefore, it is urgently required to understand the basic chemistry and essential research directions in polymeric materials and establish a library for the polymeric materials that enables the development of advanced batteries. Herein, based on indispensable polymeric materials in advanced high-energy-density lithium-ion, lithium-sulfur, lithium-metal, and dual-ion battery chemistry, the key research directions of polymeric materials for achieving high-energy-density and safety are summarized and design strategies for further improving performance are examined. Furthermore, the challenges of polymeric materials for advanced battery technologies are discussed.

Chemically Induced Activity Recovery of Isolated Lithium in Anode-free Lithium Metal Batteries

The anode-free lithium metal battery is considered to be an excellent candidate for the new generation energy storage system because of its higher energy density and safety than the traditional lithium metal battery. However, the continuous generation of SEI or isolated Li hinders its practical application. In general, the isolated Li is considered electrochemically inactive because it loses electrical connection with the current collector. Here we show an abnormal phenomenon that the lost capacity appears to be recovered after cycles when the isolated Li reconnects with a deposited Li metal layer. The isolated Li reconnection is ascribed to the chemical induction of the block copolymer coating. The migration of Li⁺ is affected by the electron delocalization and the electron cloud density of the polymer, which determine the conversion direction of Li⁺. Based on the mechanism, we propose a strategy to slow down the capacity decay of the anode-free lithium metal battery.

Stabilization of the Li metal anode through constructing a LiZn alloy/polymer hybrid protective layer towards uniform Li deposition

Constructing an artificial solid electrolyte interphase (SEI) layer is an effective strategy for solving uncontrolled Li dendrite growth resulting from an unstable and heterogeneous Li/electrolyte interface. Herein, we develop a hybrid layer of a LiZn alloy and a polyethylene oxide (PEO) polymer to protect the Li metal anode for achieving a Li dendrite-free Li metal anode surface. The LiZn alloy is advantageous for fast Li⁺ transport, and is uniformly dispersed in the PEO matrix to regulate electronic and Li⁺ ion flux distributions homogeneously. Furthermore, the flexible PEO network can alleviate the volume change during cycling. The synergistic effect enables Li deposition underneath the hybrid film. Hence, the hybrid protection film results in significantly improved cycling stability with respect to the pristine Li metal anode. A symmetric Li/Li cell with a composite protective layer can be cycled for over 1000 h at a current density of 1 mA cm^-2 with a fixed capacity of 1 mA h cm^-2, and a full cell with a high areal capacity of the LiFePO₄ (2.45 mA h cm^-2) cathode exhibits an outstanding cycling performance.

Hybrid Artificial Solid Electrolyte Interphase with Dendrite-Free Lithium Deposition and High Ion Transport Kinetics

Interfacial issues and dendritic Li deposition in lithium metal batteries (LMBs) hamper the practical application of liquid or solid-state cells. Here, a hybrid solid electrolyte interphase (SEI), based on hydroxyl-functionalized boron nitride (BN) nanosheets and poly(vinyl alcohol), is designed to solve the unstable nature of the Li anode-electrolyte interface. Rather than acquiring a rich Li halide environment through intense electrolyte decomposition, the hybrid SEI effectively regulates electrolyte decomposition and guarantees uniform Li plating via boosting interfacial Li⁺ ion transport at the interface. The Li⁺ ion boosting kinetics were deeply analyzed using simulations and spectroscopic analysis. It is revealed that the hydroxyl-functionalized BN can decrease kinetic energy barriers for Li⁺ ions and strongly holds TFSI^- ions, thereby ensuring faster Li⁺ ion migration between electrodes and electrolytes. Tailoring the interfacial Li⁺ ion dynamics with hybrid SEI renders the Li transference number enhancement from 0.391 to 0.562 and 0.178 to 0.327 in liquid and solid-state cells, respectively. Moreover, Li symmetric cells with hybrid SEI exhibit an ultrahigh stability over 3500 h at 2 mA cm^-2 with 2 mA h cm^-2, along with the improved solid-state LMB performances. Our results suggest increasing Li⁺ ion transport at the interface is an alternative to resolve Li anode issues.

Advances in Nanofibrous Materials for Stable Lithium-Metal Anodes

Lithium metal is regarded as the most potential anode material for improving the energy density of batteries due to its high specific capacity and low electrode potential. However, the practical application of lithium-metal anodes (LMAs) still faces severe challenges such as uncontrollable dendrites growth and large volume expansion. The development of functional nanomaterials has brought opportunities for the revival of LMAs. Among them, nanofibrous materials show great application potential for LMAs protection due to their distinct functional and structural features. Here, the latest research progress in nanofibrous materials for LMAs is systematically outlined. First, the problems existing in the practical application of LMAs are analyzed. Then, prospective strategies and recent research progress toward stable LMAs based on nanofibrous materials are summarized from the aspects of artificial protective layers, three-dimensional frameworks, separators, and solid-state electrolytes. Finally, the future development of nanofibrous materials for the protection of lithium-metal batteries is summarized and prospected. This review establishes a close connection between nanofibrous materials and LMA modification and provides insight for the development of high-safety lithium-metal batteries.