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Lithium metal is a possible anode material for building high energy density secondary batteries, but its problems during cycling have hindered the commercialization of lithium metal secondary batteries. Until now, many sophisticated techniques have been used to obtain rich micro‐morphological and physicochemical information of the deposition layer and the solid electrolyte interface (SEI), and to develop improvement strategies based on the information and achieve remarkable results. Regulating the reaction process around key links is a classic strategy to achieve expected results. Based on this empirical fact, we artificially highlighted the differences in the apparent performance of lithium metal anode using different series of electrolytes. We used microelectrode technology to analyze the reaction mechanisms and kinetic characteristics of each elementary step under all electrolyte conditions, revealing common laws that affect apparent performance and the basic steps that have a decisive impact on apparent performance. We discussed and elucidated the relevant physical and chemical principles, providing a clear basis for improving the pertinence and efficiency of improvement strategies. [ABSTRACT FROM AUTHOR]

The demand for innovative batteries with high specific energy densities has increased. Li‐metal batteries employing Li‐metal anodes, regarded as the ultimate anodes with a high theoretical capacity, have been extensively studied over the past few decades. However, the poor reversibility and safety concerns regarding Li‐metal anodes remain unresolved. The importance of the electrode/electrolyte interface, especially the solid electrolyte interphase (SEI), for achieving reversibility of Li metal anodes has been extensively studied. Herein, we focused on the impact of the Li ion transport properties in oligoether (glyme)‐based electrolytes on the deposition/dissolution efficiency of Li metal anodes. Analysis of the low‐frequency impedance spectra of Li‐plated Cu/Li cells revealed that the diffusion resistance of Li ions (Rdiffusion) may be a dominant contributor to the internal resistance of the cells employing glyme‐based electrolytes. A higher Rdiffusion in poor‐mass‐transport electrolytes with a lower Li ion transference number resulted in larger polarization during Li deposition/dissolution, leading to more pronounced unfavorable side reactions and lower Coulombic efficiency. Rdiffusion rather than interfacial resistance affected the reversibility of the Li metal anode. Enhancing the Li ion mass transport ability of electrolytes is important for achieving highly reversible charge‐discharge performance of Li metal anodes at high current densities. [ABSTRACT FROM AUTHOR]

The current commercially used anode material, graphite, has a theoretical capacity of only 372 mAh/g, leading to a relatively low energy density. Lithium (Li) metal is a promising candidate as an anode for enhancing energy density; however, challenges related to safety and performance arise due to Li's dendritic growth, which needs to be addressed. Owing to these critical issues in Li metal batteries, all-solid-state lithium-ion batteries (ASSLIBs) have attracted considerable interest due to their superior energy density and enhanced safety features. Among the key components of ASSLIBs, solid-state electrolytes (SSEs) play a vital role in determining their overall performance. Various types of SSEs, including sulfides, oxides, and polymers, have been extensively investigated for Li metal anodes. Sulfide SSEs have demonstrated high ion conductivity; however, dendrite formation and a limited electrochemical window hinder the commercialization of ASSLIBs due to safety concerns. Conversely, oxide SSEs exhibit a wide electrochemical window, but compatibility issues with Li metal lead to interfacial resistance problems. Polymer SSEs have the advantage of flexibility; however their limited ion conductivity poses challenges for commercialization. This review aims to provide an overview of the distinctive characteristics and inherent challenges associated with each SSE type for Li metal anodes while also proposing potential pathways for future enhancements based on prior research findings. [ABSTRACT FROM AUTHOR]

This review focuses on the promising technology of solid-state batteries (SSBs) that utilize lithium metal and solid electrolytes. SSBs offer significant advantages in terms of high energy density and enhanced safety. This review categorizes solid electrolytes into four classes: polymer, oxide, hybrid, and sulfide solid electrolytes. Each class has its own unique characteristics and benefits. By exploring these different classes, this review aims to shed light on the diversity of materials and their contributions to the advancement of SSB technology. In order to gain insights into the latest technological developments and identify potential avenues for accelerating the progress of SSBs, this review examines the intellectual property landscape related to solid electrolytes. Thus, this review focuses on the recent SSB technology patent filed by the main companies in this area, chosen based on their contribution and influence in the field of batteries. The analysis of the patent application was performed through the Espacenet database. The number of patents related to SSBs from Toyota, Samsung, and LG is very important; they represent more than 3400 patents, the equivalent of 2/3 of the world's patent production in the field of SSBs. In addition to focusing on these three famous companies, we also focused on 15 other companies by analyzing a hundred patents. The objective of this review is to provide a comprehensive overview of the strategies employed by various companies in the field of solid-state battery technologies, bridging the gap between applied and academic research. Some of the technologies presented in this review have already been commercialized and, certainly, an acceleration in SSB industrialization will be seen in the years to come. [ABSTRACT FROM AUTHOR]

All‐solid‐state Li‐metal batteries (ASLMBs) represent a significant breakthrough in the quest to overcome limitations associated with traditional Li‐ion batteries, particularly in energy density and safety aspects. However, widespread implementation is stymied due to a lack of profound understanding of the complex mechano‐electro‐chemical behavior of Li metal in the ASLMBs. Herein, operando neutron imaging and X‐ray computed tomography (XCT) are leveraged to nondestructively visualize Li behaviors within ASLMBs. This approach offers real‐time observations of Li evolutions, both pre‐ and post‐ occurrence of a "soft short". The coordination of 2D neutron radiography and 3D neutron tomography enables charting of the terrain of Li metal deformation operando. Concurrently, XCT offers a 3D insight into the internal structure of the battery following a "soft short". Despite the manifestation of a "soft short", the persistence of Faradaic processes is observed. To study the elusive "soft short" , phase field modeling is coupled with electrochemistry and solid mechanics theory. The research unravels how external pressure curbs dendrite growth, potentially leading to dendrite fractures and thus uncovering the origins of both "soft" and "hard" shorts in ASLMBs. Furthermore, by harnessing finite element modeling, it dive deeper into the mechanical deformation and the fluidity of Li metal. [ABSTRACT FROM AUTHOR]

Thin intermetallic Li2Te–LiTe3 bilayer (0.75 µm) derived from 2D tellurene stabilizes the solid electrolyte interphase (SEI) of lithium metal and argyrodite (LPSCl, Li6PS5Cl) solid‐state electrolyte (SSE). Tellurene is loaded onto a standard battery separator and reacted with lithium through single‐pass mechanical rolling, or transferred directly to SSE surface by pressing. State‐of‐the‐art electrochemical performance is achieved, e.g., symmetric cell stable for 300 cycles (1800 h) at 1 mA cm−2 and 3 mAh cm−2 (25% DOD, 60 µm foil). Cryo‐stage focused ion beam (Cryo‐FIB) sectioning and Raman mapping demonstrate that the Li2Te–LiTe3 bilayer impedes SSE decomposition. The unmodified Li–LPSCl interphase is electrochemically unstable with a geometrically heterogeneous reduction decomposition reaction front that extends deep into the SSE. Decomposition drives voiding in Li metal due to its high flux to the reaction front, as well as voiding in the SSE due to the associated volume changes. Analysis of cycled SSE found no evidence for pristine (unreacted) lithium metal filaments/dendrites, implying failure driven by decomposition phases with sufficient electrical conductivity that span electrolyte thickness. DFT calculations clarify thermodynamic stability, interfacial adhesion, and electronic transport properties of interphases, while mesoscale modeling examines interrelations between reaction front heterogeneity (SEI heterogeneity), current distribution, and localized chemo‐mechanical stresses. [ABSTRACT FROM AUTHOR]

The design of multifunctional separators can address crucial drawbacks of the lithium‐metal batteries. Here, a novel Janus separator (JS) is developed with tunable properties to prevent internal short circuiting and improve the cathode/electrolyte interface. JS is a P(VdF‐HFP) composite with LLZO facing lithium (Li) anode (Layer A) and N‐CQDs contacting the NMC cathode. Layer A acts as Li‐ion flux regulator to hinder dendrite propagation; Layer B plays multiple roles: i) promotion of better carrier migration, ii) protection from side reactions at the NMC cathode and iii) action as physical barrier against dendrite penetration. Galvanostatic cycling of Li/NMC cells with JS including 5 wt% CQDs demonstrated that JS was effective to avoid self‐discharge and internal short‐circuiting due to dendrite perforation, resulting in enhanced cell lifespan. Specific capacity >150 mAh g−1 with capacity retention of 91 % was delivered over 130 cycles at 1C. This result contrasted with higher capacity loss (>25 %) and cell failure in case of P(VdF‐HFP) and Single Layer A separators, respectively. Post‐mortem SEM on JS confirmed that the introduced functionalities successfully intercept dendrites. ARC overheating tests on JS‐based cells demonstrated a remarkably higher thermal resistance and lower severity of the exothermic phenomena compared to Celgard separators. [ABSTRACT FROM AUTHOR]

We introduce a paradigm of solvent and binder selection for solution-processing Li6PS5Cl solid-state electrolyte particles based on Hansen solubility parameters. Treatment of the Li6PS5Cl in selected solvents results in particle morphological change, but crystallographic structure remains intact. Although solution processing reduced the Li6PS5Cl ionic conductivity, it promotes interfacial stability by alleviating reduction of the solid electrolyte in contact with Li metal. These findings have the potential to enhance the stability, structural integrity, and performance of sulfide solid-state electrolytes in practical applications. [ABSTRACT FROM AUTHOR]

Highlights: A critical assessment of electrolytes' limiting factors, which affect the low-temperature performance of Li-metal batteries. Summary of emerging strategies to improve low-temperature performance from the aspects of electrolyte design and electrolyte/electrode interphase engineering. Perspectives and challenges on how to develop creative solutions in electrolytes and correlative materials for low-temperature operation. Electrolyte design holds the greatest opportunity for the development of batteries that are capable of sub-zero temperature operation. To get the most energy storage out of the battery at low temperatures, improvements in electrolyte chemistry need to be coupled with optimized electrode materials and tailored electrolyte/electrode interphases. Herein, this review critically outlines electrolytes' limiting factors, including reduced ionic conductivity, large de-solvation energy, sluggish charge transfer, and slow Li-ion transportation across the electrolyte/electrode interphases, which affect the low-temperature performance of Li-metal batteries. Detailed theoretical derivations that explain the explicit influence of temperature on battery performance are presented to deepen understanding. Emerging improvement strategies from the aspects of electrolyte design and electrolyte/electrode interphase engineering are summarized and rigorously compared. Perspectives on future research are proposed to guide the ongoing exploration for better low-temperature Li-metal batteries. [ABSTRACT FROM AUTHOR]

Lithium metal is regarded as the most promising anode material for next generation high energy density lithium batteries due to its high theoretical capacity and lowest potential versus standard hydrogen electrode. However, lithium dendrite growth and huge volume change during cycling hinder its practical application. It is of great importance to design advanced Li metal anodes to solve these problems. Herein, we report a ZnO-coated Zn foam as the host matrix to pre-store lithium through thermal infusing, achieving a Zn@ZnO foam supported Li composite electrode (LZO). Needlelike ZnO nanofibers grown on the Zn foam greatly increase the surface area and enhance the lithiophilicity of the Zn foam. In situ formed synaptic LiZn layer after lithium infusion can disperse local current density and lower Li diffusion barrier effectively, leading to homogeneous Li deposition behavior, thus suppressing dendrite formation. The porous Zn foam skeleton can accommodate volume variation of the electrode during long-term cycling. Benefiting from these merits, the LZO anode exhibits much better cycle stability and rate capability in both symmetrical and full cells with low voltage hysteresis than the bare Li anode. This work opens a new opportunity in designing high performance composite Li anode for lithium-metal batteries. [ABSTRACT FROM AUTHOR]

An interlayer is usually employed to tackle the interfacial instability issue between solid electrolytes (SEs) and Li metal caused by the side reaction. However, the failure mechanism of the ionic conductor interlayers, especially the influence from electron penetration, remains largely unknown. Herein, using Li1.3Al0.3Ti1.7(PO4)3 (LATP) as the model SE and LiF as the interlayer, we use metal semiconductor contact barrier theory to reveal the failure origin of Li/LiF@LATP interface based on the calculation results of density functional theory (DFT), in which electrons can easily tunnel through the LiF grain boundary with F vacancies due to its narrow barrier width against electron injection, followed by the reduction of LATP. Remarkably, an Al-LiF bilayer between Li/LATP is found to dramatically promote the interfacial stability, due to the highly increased barrier width and homogenized electric field at the interface. Consequently, the Li symmetric cells with Al-LiF bilayer can exhibit excellent cyclability of more than 2,000 h superior to that interlayered by LiF monolayer (∼ 860 h). Moreover, the Li/Al-LiF@LATP/LiFePO4 solid-state batteries deliver a capacity retention of 83.2% after 350 cycles at 0.5 C. Our findings emphasize the importance of tuning the electron transport behavior by optimizing the potential barrier for the interface design in high-performance solid-state batteries. [ABSTRACT FROM AUTHOR]

Li10GeP2S12 (LGPS) solid electrolyte with extremely high ionic conductivity is a promising candidate for all‐solid‐state lithium batteries. However, continued LGPS reduction at Li/LGPS interface is huge challenge. Thus, developing a simple and effective strategy to improve Li/LGPS interfacial stability is highly urgent. Herein, LiF‐rich multifunctional interfaces on Li metal (Li@LiF), consisting of three functional components of LiF, carbon particles, and thin CF bond top‐layer, are in situ constructed on the Li metal surface by spontaneous reaction between Li metal and poly(tetrafluoroethylene) at room temperature. LiF, as the main component, significantly suppresses the interfacial reaction due to low electronic conductivity and promotes smooth lithium plating on the Li metal surface arising from high interfacial energy against Li. Meanwhile, carbon particles with excellent Li+ affinity and thin strong polar CF bond top‐layer enable homogenous Li+ flux as well as fast Li+ migration across the LiF‐rich interface, respectively. Consequently, the LGPS‐based symmetric lithium cell possesses significantly prolonged cycling stability and increased critical current density. The LGPS‐based all‐solid‐state lithium cells employing LiCoO2 cathode and Li@LiF anode exhibit excellent rate capability and impressive cycling stability, achieving a high capacity retention of 80.9% over 300 cycles at 0.1 C under 25 °C. [ABSTRACT FROM AUTHOR]

Lithium metal anodes may allow the energy density limit of rechargeable lithium batteries to be pushed higher. However, simple and efficient processing technologies for thin Li metal are lacking, which has significantly limited its applications. Herein, the feasibility of engineering Li metal by compositing it with ferromagnetic particles (termed magnetic Li, abbr. M‐Li) is reported. Due to its magnetic response, straightforward processing of M‐Li on diverse substrates with customized patterns and desired thickness is realized. Moreover, when a garnet‐type solid‐state electrolyte Li6.5La3Zr1.5Ta0.5O12 (LLZTO) is the substrate, intimate contact between M‐Li and LLZTO is obtained, with a low interfacial resistance of ≈11 Ω cm2. In addition to facilitating movement and wetting on various substrates, magnetic transfer of M‐Li sheets to designated locations is also enabled. The intriguing and brand‐new method for Li metal engineering via magnetic actuation may be adopted by the industrial system for the fabrication of Li metal batteries, extended to other alkali metals and promises further progress. [ABSTRACT FROM AUTHOR]

The commercialization of lithium–sulfur (Li−S) batteries is still hindered by the unsatisfactory cell performance under practical working conditions, which is mainly caused by the sluggish cathode redox kinetics, severe polysulfide shuttling, and poor Li stripping/plating reversibility. Herein, we report an effective strategy by combining Se‐doped S hosted in an ordered macroporous framework with a highly fluorinated ether (HFE)‐based electrolyte to simultaneously address the aforementioned issues in both cathode and anode. A reversible and stable high areal capacity of >5.4 mAh cm−2 with high Coulombic efficiency >99.2 % can be achieved under high areal Se/S loading (5.8 mg cm−2), while the underlying mechanism was further revealed through synchrotron X‐ray probes and Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS). The practical application potential was further evaluated at low (0 °C) and high (55 °C) temperatures under high areal Se/S loading (>5.0 mg cm−2) and thin Li metal (40 μm). [ABSTRACT FROM AUTHOR]

The commercialization of lithium–sulfur (Li−S) batteries is still hindered by the unsatisfactory cell performance under practical working conditions, which is mainly caused by the sluggish cathode redox kinetics, severe polysulfide shuttling, and poor Li stripping/plating reversibility. Herein, we report an effective strategy by combining Se‐doped S hosted in an ordered macroporous framework with a highly fluorinated ether (HFE)‐based electrolyte to simultaneously address the aforementioned issues in both cathode and anode. A reversible and stable high areal capacity of >5.4 mAh cm−2 with high Coulombic efficiency >99.2 % can be achieved under high areal Se/S loading (5.8 mg cm−2), while the underlying mechanism was further revealed through synchrotron X‐ray probes and Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF‐SIMS). The practical application potential was further evaluated at low (0 °C) and high (55 °C) temperatures under high areal Se/S loading (>5.0 mg cm−2) and thin Li metal (40 μm). [ABSTRACT FROM AUTHOR]

As the electrification of the transportation industry is accelerating, the energy storage markets are trying to secure more reliable and environmentally benign materials. Advanced materials are the key performance enablers of batteries as well as a key element determining the cost structure, environmental impact, and recyclability of battery cells. In this review, we analyzed the state-of-the-art cell chemistries and active electrode and electrolyte materials for electric vehicles batteries, which we believe will dominate the battery chemistry landscape in the next decade. We believe that major breakthroughs and innovations in electrode materials such as high-nickel cathodes and silicon and metallic lithium anodes, along with novel liquid electrolyte formulations and solid-state electrolytes, will significantly improve the specific capacity of lithium batteries and reduce their cost, leading to accelerated mass-market penetration of EVs. [ABSTRACT FROM AUTHOR]

Silicon (Si) is one of the most promising anode candidates to further push the energy density of lithium ion batteries. However, its practical usage is still hindered by parasitic side reactions including electrolyte decomposition and continuous breakage and (re‐)formation of the solid electrolyte interphase (SEI), leading to consumption of active lithium. Pre‐lithiation is considered a highly appealing technique to compensate for active lithium losses. A critical parameter for a successful pre‐lithiation strategy by means of Li metal is to achieve lithiation of the active material/composite anode at the most uniform lateral and in‐depth distribution possible. Despite extensive exploration of various pre‐lithiation techniques, controlling the lithium amount precisely while keeping a homogeneous lithium distribution remains challenging. Here, the thermal evaporation of Li metal as a novel pre‐lithiation technique for pure Si anodes that allows both, that is, precise control of the degree of pre‐lithiation and a homogeneous Li deposition at the surface is reported. Li nucleation, mechanical cracking, and the ongoing phase changes are thoroughly evaluated. The terms dry‐state and wet‐state pre‐lithiation (without/with electrolyte) are revisited. Finally, a series of electrochemical methods are performed to allow a direct correlation of pre‐SEI formation with the electrochemical performance of pre‐lithiated Si. [ABSTRACT FROM AUTHOR]

Solid‐electrolytes (SEs) can provide a pathway to increase energy‐density in lithium metal batteries. However, lithium metal penetration through garnet based LLZO solid electrolytes has been identified as a critical failure process. This phenomenon is related to chemo‐mechanical processes which are difficult to probe. In particular, characterizing the dynamic mechanical deformations that occur in electrode‐SE structures is very challenging. This study reports in situ curvature measurements that are thus designed to probe chemo‐mechanical phenomena that occur during lithium plating. The novel experimental cell configuration created for this work shows that pressure builds up in the Li metal during plating, up until the point where short circuits occur. The resulting data are analyzed with a detailed finite element model (FEM) to quantitatively evaluate stress evolution. The results show that Li metal plating within a surface flaw can produce stress build‐up prior to short‐circuiting. The combined results from both the experiments and the FEM suggest that it is critical to minimize surface defects and flaws during the manufacturing processes. [ABSTRACT FROM AUTHOR]

Rough Li plating, low ionic conductivity, and low thermal stability of conventional electrolytes post‐primary challenges for achieving reliable high‐capacity rechargeable lithium batteries, for which lithium metal is frequently proposed as the most promising anode material. Conventional low‐polarity commercial polypropylene/polyethylene separators fail to support the application of high‐energy‐density Li anodes due to their rigid physicochemical properties and the high reactivity of Li metal, leading to fatal dendrite formation and vigorous exothermic reaction with electrolytes. Herein, we develop a Li‐wetting, flame‐retardant binary polymer electrolyte by functionalizing poly(vinylidene fluoride) (PVDF) separators with nonflammable polybenzimidazole (PBI) to build safe room‐temperature solid‐state electrolyte membranes. A dendrite‐free LiFePO4 cell with the solid polymer electrolyte (SPE) delivers a discharge capacity of 127 mAh g−1 at 25°C with a capacity retention of 87.5% after 500 cycles at 0.5°C (0.15 mA cm−2). Phase‐field simulations and density functional theory calculations demonstrate that the negatively charged benzimidazole chains of PBI own superior affinity to lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and shares overlapping electron density with Li anode, giving rise to accelerated Li+ conduction at room temperature and uniform Li electrodeposition at the electrolyte/Li metal interface. The SPE is also flame‐retardant since heat‐resistant polytetrafluoroethylene and a dense, heat‐blocking graphitized carbon layer are formed in intense heat through dehydrogenation/fluorination of PVDF under the catalysis of Lewis base imidazole rings and the decomposition of benzimidazole rings in PBI. No such fire‐resistant mechanism is ever reported in conventional electrolytes. [ABSTRACT FROM AUTHOR]

Solid‐state batteries have been considered as promising next‐generation energy storage devices for potentially higher energy density and better safety compared with commercial lithium‐ion batteries that are based on organic liquid electrolytes. However, in terms of indispensable solid‐state electrolytes, there are remaining issues to be solved before entering the market. Most solid‐state electrolytes are air‐sensitive, which causes a complex and expensive cell assembly and impressible interface. Therefore, the solid‐state electrolytes are expected to be atmosphere‐stable, which will undoubtedly bring significant benefits to solid‐state battery manufacturing. This review covers air‐stability‐related issues of different types of inorganic solid‐state electrolytes and the corresponding strategies. First, we provide an overview of solid‐state electrolytes and solid‐state batteries, including their history and advantages/disadvantages. Then, different types of solid‐state electrolytes are selected as examples to illustrate the unfavorable interactions in air and the corresponding adverse effects. Next, according to recent advances, we summarize the effective strategies of constructing different types of air‐stable inorganic solid‐state electrolytes. Finally, perspectives on designing accessible air‐stable solid‐state electrolytes are provided, aiming to achieve the assembly of high‐performance solid‐state batteries in the atmosphere. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal is considered to be the most ideal anode for rechargeable Li-metal batteries due to its high theoretical specific capacity and low redox potential. However, the Li dendrite problem associated with Li metal anodes limits its practical application. Herein, a new chemical dealloying method that adjust the pore structure formed during chemical dealloying at room temperature to prepare a porous Copper current collector which was to enable dendrite-free Li deposition. Benefiting from the naturally formed suitable size and uniform porous structure, this current collector provides larger surface area to homogenize the Li ion distribution and promote dendrite-free Li metal anode with improved Coulombic efficiency (96% for over 210 cycles at the current density of 0.5 mA cm−2 and 95% for 80 cycles at 1.0 mA cm−2). This work provides a novel way to suppress Li dendrite. [ABSTRACT FROM AUTHOR]

The scanning droplet cell (SDC) allows for automatized electrochemical experiments leading to time‐saving and reproducible experimental conditions. Its implementation for non‐aqueous battery research is discussed, and the necessary adaptations to be operated inside an Ar‐filled glovebox in complete absence of oxygen and moisture are described. Due to the importance of the use of Li metal electrodes for next‐generation high‐energy batteries, the complex multi‐parameter optimisation of the Li plating/stripping processes are investigated by means of the SDC. In particular, the influence of pulsed Li plating protocols on the coulombic efficiency is evaluated. The results clearly show that fine tuning of the parameters of pulsed Li plating protocols, i. e. the relaxation period and Li plating duration, is required to improve Li plating efficiencies at high current densities. [ABSTRACT FROM AUTHOR]

Lithium dendrites cause battery failures and safety hazards in liquid‐electrolyte lithium‐based batteries. To address this problem, each component of the battery, such as cathode, anode, electrolyte and separator, should be well matched and engineered for the integrated battery system. The separator plays an increasingly important role owing to its gradual transformation from an inert to an active component in the battery, especially for resolving Li dendrite issues in Li‐metal batteries. Armed with advanced nanotechnology solutions, separator engineering presents a formidable strategy to suppress dendrite growth dynamics by modifying the electrolyte chemistry, regulating/trapping unwanted ionic species and redirecting dendrite growth direction. This review summarizes recent advances in separator engineering for effective dendrite suppression of Li‐metal anodes. We first introduce the challenges that the Li‐metal anode faces and the irreplaceable role of separators in the battery system. The characterization parameters and design principles of separators are also discussed. Then, the mainstream techniques for separator functionalization and their impacts on dendrite suppression are scrutinized and highlighted. Lastly, the conclusion is drawn and the future outlook for separator engineering is presented. [ABSTRACT FROM AUTHOR]

Due to an ultrahigh theoretical specific capacity of 3860 mAh g−1, lithium (Li) is regarded as the ultimate anode for high‐energy‐density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase‐field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite‐free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries. [ABSTRACT FROM AUTHOR]

Advanced high‐energy‐density energy storage systems with high safety are desperately demanded to power electric vehicles and smart grids. Li metal batteries (LMBs) can provide a considerable leap in battery energy. Nevertheless, the widespread deployment of Li metal has long been fettered by the unstable solid electrolyte interlayer and uncontrolled Li dendrite growth induced safety concerns. Herein, a flexible and conformal CTF‐LiI coating has been rationally coated on Li metal surface to stabilize metallic Li. With the CTF‐LiI coating, the Li electrodeposition exhibits a uniform, dense, and dendrite‐free manner; however, the side reactions between metallic Li and electrolyte have been effectively suppressed. The Li symmetric cells can run stably for a prolonged cycling over 2500 cycles at 10 mA cm−2, demonstrating a much lower voltage hysteresis. In addition, the Li|Li4Ti5O12 cells can deliver an improved long‐time cycling over 250 cycles at 0.05 A g−1. Furthermore, the half cells paired with the organic S cathode also demonstrate an excellent long lifespan stable cycling and a high capacity of 682.2 mAh g−1 retained over 300 cycles with an average capacity decay of ≈0.05% per cycle at 1.0 A g−1. This work demonstrates a significant step toward large‐scalable and long‐cycling stable LMBs. [ABSTRACT FROM AUTHOR]

The introduction of new, safe, and reliable solid‐electrolyte chemistries and technologies can potentially overcome the challenges facing their liquid counterparts while widening the breadth of possible applications. Through tech‐historic evolution and rationally analyzing the transition from liquid‐based Li‐ion batteries (LIBs) to all‐solid‐state Li‐metal batteries (ASSLBs), a roadmap for the development of a successful oxide and sulfide‐based ASSLB focusing on interfacial challenges is introduced, while accounting for five parameters: energy density, power density, longterm stability, processing, and safety. First taking a strategic approach, this review dismantles the ASSLB into its three major components and discusses the most promising solid electrolytes and their most advantageous pairing options with oxide cathode materials and the Li metal anode. A thorough analysis of the chemical, electrochemical, and mechanical properties of the two most promising and investigated classes of inorganic solid electrolytes, namely oxides and sulfides, is presented. Next, the overriding challenges associated with the pairing of the solid electrolyte with oxide‐based cathodes and a Li‐metal anode, leading to limited performance for solid‐state batteries are extensively addressed and possible strategies to mitigate these issues are presented. Finally, future perspectives, guidelines, and selective interface engineering strategies toward the resolution of these challenges are analyzed and discussed. [ABSTRACT FROM AUTHOR]

The introduction of new, safe, and reliable solid‐electrolyte chemistries and technologies can potentially overcome the challenges facing their liquid counterparts while widening the breadth of possible applications. Through tech‐historic evolution and rationally analyzing the transition from liquid‐based Li‐ion batteries (LIBs) to all‐solid‐state Li‐metal batteries (ASSLBs), a roadmap for the development of a successful oxide and sulfide‐based ASSLB focusing on interfacial challenges is introduced, while accounting for five parameters: energy density, power density, longterm stability, processing, and safety. First taking a strategic approach, this review dismantles the ASSLB into its three major components and discusses the most promising solid electrolytes and their most advantageous pairing options with oxide cathode materials and the Li metal anode. A thorough analysis of the chemical, electrochemical, and mechanical properties of the two most promising and investigated classes of inorganic solid electrolytes, namely oxides and sulfides, is presented. Next, the overriding challenges associated with the pairing of the solid electrolyte with oxide‐based cathodes and a Li‐metal anode, leading to limited performance for solid‐state batteries are extensively addressed and possible strategies to mitigate these issues are presented. Finally, future perspectives, guidelines, and selective interface engineering strategies toward the resolution of these challenges are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Garnet electrolytes (GEs) with high ion conductivity, excellent stability against lithium metal (LM) as well as wide electrochemical potential window are attracting increasing interest as they have the potential to enable all‐solid‐state Li metal batteries (ASSLMBs). However, GEs‐based ASSLMBs deeply suffer from daunting problems such as high resistance, fast short circuit, and rapid performance degradation, which can be largely attributed to unsatisfactory LM/GE interface. To this end, this minireview focuses on the LM/GE interface by summarizing the main challenges comprehensively, recapitulating emerging strategies for these challenges, and providing perspectives for future research. [ABSTRACT FROM AUTHOR]

The metallic lithium (Li) is considered as the most promising anode material for high-energy batteries. Nevertheless, the uncontrollable growth of Li dendrite and unstable electrolyte/electrode interface still hinder the development of Li-based battery. In this work, a novel strategy has been proposed to stabilize Li anode by in-situ polymerizing polypyrrole (PPy) layer on Ni foam (PPy@Ni foam) as an artificial protective layer. The PPy protective layer can effectively decrease the contact between Li metal and electrolyte during cycling. In addition, the morphology characterization shows that the PPy layer can help the even Li deposition underneath the layer, leading to a dendrite-free Li anode. As a result, when deposited 2 mAh•cm−2 Li metal, the PPy@Ni foam can keep stable Coulombic efficiency (99%) during nearly 250 cycles, much better than the pure Ni foam (100 cycles). Even in the case of the Li capacity of 10 mAh•cm−2, the stable cycling performance for 60 cycles can still be achieved. Furthermore, when assembled with LiFePO4 material as the cathode for a full cell, the PPy@Ni foam can keep high capacity retention of 85.5% at 500 cycles. In our work, we provide a simple and effective method to enhance the electrochemical performances of Li metal-based batteries, and reveal a new avenue to design three-dimensional (3D) metallic current collector for protecting the Li metal anode. [ABSTRACT FROM AUTHOR]

All-solid-state lithium metal batteries (ASSLMBs) have attracted significant attention due to their superior safety and high energy density. However, little success has been made in adopting Li metal anodes in sulfide electrolyte (SE)-based ASSLMBs. The main challenges are the remarkable interfacial reactions and Li dendrite formation between Li metal and SEs. In this work, a solid-state plastic crystal electrolyte (PCE) is engineered as an interlayer in SE-based ASSLMBs. It is demonstrated that the PCE interlayer can prevent the interfacial reactions and lithium dendrite formation between SEs and Li metal. As a result, ASSLMBs with LiFePO4 exhibit a high initial capacity of 148 mAh g-1 at 0.1 C and 131 mAh g-1 at 0.5 C (1 C = 170 mA g-1), which remains at 122 mAh g-1 after 120 cycles at 0.5 C. All-solid-state Li-S batteries based on the polyacrylonitrile-sulfur composite are also demonstrated, showing an initial capacity of 1682 mAh g-1. The second discharge capacity of 890 mAh g-1 keeps at 775 mAh g-1 after 100 cycles. This work provides a new avenue to address the interfacial challenges between Li metal and SEs, enabling the successful adoption of Li metal in SE-based ASSLMBs with high energy density. [ABSTRACT FROM AUTHOR]

The development of safe lithium‐metal anodes is crucial for the next‐generation rechargeable batteries. To stabilize Li metal anodes, pre‐planting Li nucleation seeds on lithiophilic substrates is an efficient strategy to regulate initial nucleation process of Li metal. Now, activated ultrathin layered double hydroxide (U‐LDHs) are reported as a promising lithiophilic 2D material to realize the uniform deposition of Li metal. The experimental studies and DFT calculations reveal that the active oxygen on U‐LDHs provides abundant atomic‐scale active sites for Li homogeneous nucleation and plating. Moreover, the lithiophilic properties of active oxygen is also related to its coordination environments. This work opens up an opportunity to more accurate regulation and understanding of Li nucleation from atomic‐scale based on 2D ultrathin materials. Li is like oxygen: Active‐oxygen‐enriched layered double hydroxide (LDH) constructed by a facile electrochemical strategy has been proven to be an ideal lithiophilic 2D material, which realizes the uniform deposition of Li metal. This work opens up an opportunity for more accurate regulation and understanding of Li nucleation at the atomic scale based on 2D ultrathin materials. [ABSTRACT FROM AUTHOR]

Lithium metal has shown great promise as an anode material for high‐energy rechargeable batteries. However, interfacial instability caused by an unstable solid‐electrolyte interphase (SEI) and dendrite growth has impeded the realization of Li anodes for practical applications. Recently, we reported a potentiostatic stripping−galvanostatic plating electrochemical polishing method to simultaneously create atomically flat Li and a molecularly smooth SEI, leading to a near‐perfect Li anodes that exhibit much enhanced electrochemical performance. In this paper, key factors including anodic stripping potentials, cathodic plating current densities, and types of salt and solvent systems are further investigated in detail based on the understanding of electrode reactions taking place during polishing. In particular, the importance of considerations on the mutual constrains between electropolishing and SEI formation and, thus, the necessity of fine control of potential and/or current is elucidated, which serves as a general rule for the successful application of electrochemical polishing of Li as well as other metals that involve the formation of SEIs. Electrochemical polishing of Li: Key factors for the successful electrochemical polishing of Li as well as other metal surfaces that demand the formation of desirable solid‐electrolyte interphases (SEIs) are investigated based on an understanding of the fundamental electrochemistry of the systems (see picture). [ABSTRACT FROM AUTHOR]

The interface between solid electrolytes and Li metal is a primary issue for solid-state batteries. Introducing a metal interlayer to conformally coat solid electrolytes can improve the interface wettability of Li metal and reduce the interfacial resistance, but the mechanism of the metal interlayer is unknown. In this work, we used magnesium (Mg) as a model to investigate the effect of a metal coating on the interfacial resistance of a solid electrolyte and Li metal anode. The Li-Mg alloy has low overpotential, leading to a lower interfacial resistance. Our motivation is to understand how the metal interlayer behaves at the interface to promote increased Li-metal wettability of the solid electrolyte surface and reduce interfacial resistance. Surprisingly, we found that the metal coating dissolved in the molten piece of Li and diffused into the bulk Li metal, leading to a small and stable interfacial resistance between the garnet solid electrolyte and the Li metal. We also found that the interfacial resistance did not change with increase in the thickness of the metal coating (5, 10, and 100 nm), due to the transient behavior of the metal interface layer. [ABSTRACT FROM AUTHOR]

Rechargeable batteries based on lithium (Li) metal chemistry are attractive for next-generation electrochemical energy storage. Nevertheless, excessive dendrite growth, infinite relative dimension change, severe side reactions, and limited power output severely impede their practical applications. Although exciting progress has been made to solve parts of the above issues, a versatile solution is still absent. Here, a Li-ion conductive framework was developed as a stable "host" and efficient surface protection to address the multifaceted problems, which is a significant step forward compared with previous host concepts. This was fulfilled by reacting overstoichiometry of Li with SiO. The as-formed LixSi-Li2O matrix would not only enable constant electrode-level volume, but also protect the embedded Li from direct exposure to electrolyte. Because uniform Li nucleation and deposition can be fulfilled owing to the high-density active Li domains, the as-obtained nanocomposite electrode exhibits low polarization, stable cycling, and high-power output (up to 10 mA/cm²) even in carbonate electrolytes. The Li-S prototype cells further exhibited highly improved capacity retention under high-power operation (~600 mAh/g at 6.69 mA/cm²). The all-around improvement on electrochemical performance sheds light on the effectiveness of the design principle for developing safe and stable Li metal anodes. [ABSTRACT FROM AUTHOR]

Active lithium loss, lithium ion batteries, pre-lithiation, Li metal, silicon thin films Pre-Lithiation of Silicon Anodes by Thermal Evaporation of Lithium for Boosting the Energy Density of Lithium Ion Cells (Adv. Funct. Keywords: active lithium loss; Li metal; lithium ion batteries; pre-lithiation; silicon thin films EN active lithium loss Li metal lithium ion batteries pre-lithiation silicon thin films 1 1 1 05/30/22 20220525 NES 220525 B Pre-Lithiation b In article number 2201455, Aurora Gomez-Martin, Tobias Placke, and co-workers develop Li thermal evaporation as a novel pre-lithiation technique for silicon thin film anodes to achieve the most uniform Li distribution possible. [Extracted from the article]

Solid State Batteries: Solid-State Li-Metal Batteries: Challenges and Horizons of Oxide and Sulfide Solid Electrolytes and Their Interfaces (Adv. Keywords: interfacial resistance; Li metal; oxide-based cathodes; solid state batteries EN interfacial resistance Li metal oxide-based cathodes solid state batteries 1 1 1 01/09/21 20210107 NES 210107 The introduction of new, safe, and reliable solid-electrolyte chemistries and technologies can potentially overcome the challenges facing their liquid counterparts. Interfacial resistance, Li metal, oxide-based cathodes, solid state batteries. [Extracted from the article]

Solid State Batteries: Solid-State Li-Metal Batteries: Challenges and Horizons of Oxide and Sulfide Solid Electrolytes and Their Interfaces (Adv. Keywords: interfacial resistance; Li metal; oxide-based cathodes; solid state batteries EN interfacial resistance Li metal oxide-based cathodes solid state batteries 1 1 1 02/21/22 20210101 NES 210101 The introduction of new, safe, and reliable solid-electrolyte chemistries and technologies can potentially overcome the challenges facing their liquid counterparts. Interfacial resistance, Li metal, oxide-based cathodes, solid state batteries. [Extracted from the article]

All‐solid‐state batteries are expected to enable batteries with high energy density with the use of lithium metal anodes. Although solid electrolytes are believed to be mechanically strong enough to prevent lithium dendrites from propagating, various reports today still show cell failure due to lithium dendrit growth at room temperature. While cell parameters such as current density, electrolyte porosity, and interfacial properties have been investigated, mechanical properties of lithium metal and the role of applied stack pressure on the shorting behavior are still poorly understood. Here, failure mechanisms of lithium metal are investigated in all‐solid‐state batteries as a function of stack pressure, and in situ characterization of the interfacial and morphological properties of the buried lithium is conducted in solid electrolytes. It is found that a low stack pressure of 5 MPa allows reliable plating and stripping in a lithium symmetric cell for more than 1000 h, and a Li | Li6PS5Cl | LiNi0.80Co0.15Al0.05O2 full cell, plating more than 4 µm of lithium per charge, is able to cycle over 200 cycles at room temperature. These results suggest the possibility of enabling the lithium metal anode in all‐solid‐state batteries at reasonable stack pressures. [ABSTRACT FROM AUTHOR]

Low ionic conductivity at room temperature and limited electrochemical window of poly(ethylene oxide) (PEO) are the bottlenecks restricting its further application in high‐energy density lithium metal battery. Herein, a differentiated salt designed multilayered PEO‐based solid polymer electrolyte (DSM‐SPE) is exploited to achieve excellent electrochemical performance toward both the high‐voltage LiCoO2 cathode and the lithium metal anode. The LiCoO2/Li metal battery with DSM‐SPE displays a capacity retention of 83.3% after 100 cycles at 60 °C with challenging voltage range of 2.5 to 4.3 V, which is the best cycling performance for high‐voltage (≥4.3 V) LiCoO2/Li metal battery with PEO‐based electrolytes up to now. Moreover, the Li/Li symmetrical cells present stable and low polarization plating/stripping behavior (less than 80 mV over 600 h) at current density of 0.25 mA cm−2 (0.25 mAh cm−2). Even under a high‐area capacity of 2 mAh cm−2, the profiles still maintain stable. The pouch cell with DSM‐SPE exhibits no volume expansion, voltage decline, ignition or explosion after being impaled and cut at a fully charged state, proving the excellent safety characteristic of the DSM‐SPE‐based lithium metal battery. [ABSTRACT FROM AUTHOR]

Li7La3Zr2O12 (LLZO) garnet‐based materials doped with Al, Nb, or Ta to stabilize the Li+‐conductive cubic phase are a particularly promising class of solid electrolytes for all‐solid‐state lithium metal batteries. Understanding of the intrinsic reactivity between solid electrolytes and relevant electrode materials is crucial to developing high voltage solid‐state batteries with long lifetimes. Using a novel, surface science‐based approach to characterize the intrinsic reactivity of the Li–solid electrolyte interface, it is determined that, surprisingly, some degree of Zr reduction takes place for all three dopant types, with the extent of reduction increasing as Ta < Nb < Al. Significant reduction of Nb also takes place for Nb‐doped LLZO, with electrochemical impedance spectroscopy (EIS) of Li||Nb–LLZO||Li symmetric cells further revealing significant increases in impedance with time and suggesting that the Nb reduction propagates into the bulk. Density functional theory (DFT) calculations reveal that Nb‐doped material shows a strong preference for Nb dopants toward the interface between LLZO and Li, while Ta does not exhibit a similar preference. EIS and DFT results, coupled with the observed reduction of Zr at the interface, are consistent with the formation of an "oxygen‐deficient interphase" (ODI) layer whose structure determines the stability of the LLZO–Li interface. Understanding reactivity at buried interfaces is crucial to developing next‐generation solid‐state batteries. A novel, surface science‐based approach reveals that contact with Li metal yields Zr reduction in Nb‐, Ta‐, and Al‐doped Li7La3Zr2O12, with reduction increasing as Ta < Nb < Al. This Zr reduction indicates the formation of an "oxygen‐deficient interphase," whose composition determines the stability of the Li– Li7La3Zr2O12 interface. [ABSTRACT FROM AUTHOR]

Rechargeable Li metal batteries have attracted lots of attention because they can achieve high energy densities. However, the commercialization of rechargeable Li metal batteries is delayed because Li dendrites may be generated during the batteries' electrochemical cycles, which may cause severe safety issues. In this research, a Li-B alloy is investigated as an anode for rechargeable batteries instead of Li metal. Results show that the Li-B alloy has better effects in suppressing the formation of dendritic lithium, reducing the interface impedance and improving the cycle performance. These effects may result from the unique structure of Li-B alloy, in which free lithium is embedded in the Li7B6 framework. These results suggest that Li-B alloy may be a promising anode material applicable in rechargeable lithium batteries. [ABSTRACT FROM AUTHOR]