Ultra-Thin Lithium Silicide Interlayer for Solid-State Lithium-Metal Batteries

Recent advances in garnet-based electrolytes for solid-state lithium metal batteries: interfacial challenges and engineering strategies

Solid-state lithium metal batteries (SSLMBs) are recognized as the most efficient and promising energy storage devices due to their enhanced safety and high energy density. As a key component in solid-state lithium metal batteries, solid-state electrolytes (SSEs) are critical for the development of batteries. Garnet-type SSEs have been employed as the most critical component of inorganic electrolytes and fillers for composite electrolytes. To date, significant research on garnet-based electrolytes has been carried out and numerous breakthrough results have been achieved. However, poor interfacial contacts between garnet-based electrolytes and electrodes still lead to Li dendrite growth and unsatisfactory electrochemical performance of batteries. Herein, recent developments of the interfaces for garnet based SSLMBs, including the strategies of garnet types and composite electrolytes as well as Li metal anode stabilizations are presented. Moreover, interfacial engineering strategies between electrolytes and cathodes are also discussed. Meanwhile, advanced techniques and electrochemical approaches for interfacial characterization are also introduced. This work provides insights into the interfacial engineering of garnet-based electrolytes, contributing to the understanding of interfaces in solid-state batteries.

Exploring the Potential of SnHPO3 and Ni3.4Sn4 as Anode Materials in Argyrodite-Based All-Solid-State Lithium-Ion Batteries

All-solid-state batteries have garnered significant attention due to their potential to exceed the energy density of conventional lithium-ion batteries, particularly when alloying-based materials or lithium metal anodes are used. However, achieving compatibility with lithium metal remains a persistent bottleneck. In this study, we shed light on the potential of SnHPO3 tin phosphite and Ni3.4Sn4 intermetallic as novel conversion/alloying anode materials for all-solid-state lithium batteries using Li6PS5Cl as the solid electrolyte. The two Sn-based active materials were nanostructured by ball-milling to demonstrate considerable promise for application in all-solid-state half-cells. Galvanostatic cycling at room temperature revealed electrochemical behavior based on conversion/alloying reactions akin to those observed in conventional lithium-ion batteries. Promisingly, both materials exhibited satisfying electrochemical stability, with coulombic efficiencies exceeding 97%. These findings indicate that Li6PS5Cl solid electrolyte is compatible with Sn-based alloying anodes.

Ductile Inorganic Solid Electrolytes for All-Solid-State Lithium Batteries

Solid electrolytes, as the core of all-solid-state batteries (ASSBs), play a crucial role in determining the kinetics of ion transport and the interface compatibility with cathodes and anodes, which can be subdivided into catholytes, bulk electrolytes, and anolytes based on their functional characteristics. Among various inorganic solid electrolytes, ductile solid electrolytes, distinguished from rigid oxide electrolytes, exhibit excellent ion transport properties even under cold pressing, thus holding greater promise for industrialization. However, the challenge lies in finding a ductile solid electrolyte that can simultaneously serve as catholyte, bulk electrolyte, and anolyte. Fortunately, due to the immobility of solid electrolytes, combining multiple types of solid electrolytes allows for leveraging their respective advantages. In this review, we discuss five types of solid electrolytes, sulfides, halides, nitrides, antiperovskite-type, and complex hydrides, and the challenges and superiorities for these electrolytes are also addressed. The impact of pressure on ASSBs has been systematically discussed. Furthermore, the suitability of electrolytes as the catholyte, bulk electrolyte, and anolyte is discussed based on their functional characteristics and physicochemical properties. This discussion aims to deepen our understanding of solid electrolytes, enabling us to harness the advantages of various types of solid electrolytes and develop practical, high-performance ASSBs.

Melt-Infusion-Induced Electrolyte Surface Coating Stabilized Sulfide-Based All-Solid-State Lithium Metal Batteries

Sulfide-based all-solid-state lithium metal batteries (ASSLBs) are a potentially safe and high-energy electrochemical storage technology. The continuous interfacial degradation within sulfide solid-state electrolytes (SSEs) and Li metal however hinders Li+ transport and induces inhomogeneous Li deposition. Herein, we propose a melt-infusion method to introduce lithium trifluorosulfonylimide (LiTFSI) on Li5.5PS4.5Cl1.5 (LPSCl) particles as an artificial coating. This artificial coating can mitigate interfacial side reactions and induce the generation of the LiF/Li3N-rich solid electrolyte interphase (SEI). The combined experimental and theoretical results reveal that this LiF/Li3N-rich SEI has the merits of accelerating Li+ transport and suppressing Li dendrites. It enables the Li anode to reach a high critical current density (CCD) up to 3.1 mA cm-2. In conjunction with coated sulfide SSEs, Li-symmetric cells operate stably for 900 h at 2 mA cm-2. The ASSLBs using this coated sulfide SSEs can reversibly charge/discharge at 2C over 1000 cycles with a 90.2% capacity retention. A high LiCoO2 loading of 28.5 mg cm-2 is further demonstrated in this ASSLB with cycling stability over 100 cycles at 0.2C.

Revitalizing interphase in all-solid-state Li metal batteries by electrophile reduction

All-solid-state lithium metal batteries promise high levels of safety and energy density, but their practical realization is limited by low Li reversibility, limited cell loading and demand for high-temperature and high-pressure operation, stemming from solid-state electrolyte (SSE) low-voltage reduction and high-voltage decomposition, and from lithium dendrite growth. Here we concurrently address these challenges by reporting that a family of reductive electrophiles gain electrons and cations from metal-nucleophile materials (here a Li sulfide SSE) upon contact to undergo electrochemical reduction and form interphase layers (named solid reductive-electrophile interphase) on material surfaces. The solid reductive-electrophile interphase is electron blocking and lithiophobic, prevents SSE reduction, suppresses Li dendrites and supports high-voltage cathodes. Consequently, a reductive-electrophile-treated SSE exhibits high critical capacity and Li reversibility at the anode, and enables Li(1% Mg)/SSE/LiNi0.8Co0.15Al0.05O2 all-solid-state lithium metal batteries to achieve a high coulombic efficiency (>99.9%), long cycle life (~10,000 h) and high loading (>7 mAh cm-2) at 30 °C and 2.5 MPa. This concept also extends to cathodes of other materials (for example, metal oxides), boosting the high-nickel cathode's cycle life and expanding the operational voltage up to 4.5 V. Such solid reductive-electrophile interphase tailoring of material surfaces holds promise to accelerate all-solid-state lithium metal battery commercialization and offer solutions for a wide range of materials.

Characterizing Electrode Materials and Interfaces in Solid-State Batteries

Solid-state batteries (SSBs) could offer improved energy density and safety, but the evolution and degradation of electrode materials and interfaces within SSBs are distinct from conventional batteries with liquid electrolytes and represent a barrier to performance improvement. Over the past decade, a variety of imaging, scattering, and spectroscopic characterization methods has been developed or used for characterizing the unique aspects of materials in SSBs. These characterization efforts have yielded new understanding of the behavior of lithium metal anodes, alloy anodes, composite cathodes, and the interfaces of these various electrode materials with solid-state electrolytes (SSEs). This review provides a comprehensive overview of the characterization methods and strategies applied to SSBs, and it presents the mechanistic understanding of SSB materials and interfaces that has been derived from these methods. This knowledge has been critical for advancing SSB technology and will continue to guide the engineering of materials and interfaces toward practical performance.

Deciphering the Interfacial Li-Ion Migration Kinetics of Ni-Rich Cathodes in Sulfide-Based All-Solid-State Batteries

Nickel-rich layered oxide with high reversible capacity and high working potentials is a prevailing cathode for high-energy-density all-solid-state lithium batteries (ASSLBs). However, compared to the liquid battery system, ASSLBs suffer from poor Li-ion migration kinetics, severe side reactions, and undesired formation of space charge layers, which result in restricted capacity release and limited rate capability. In this work, we reveal that the capacity loss lies in the H2-H3 phase transition period, and we propose that the inconsistent interfacial Li-ion migration is the arch-criminal. We introduce Si doping to stabilize the bulk structure and Li4SiO4 fast ionic conductor coating to regulate the interfacial behaviors between the Ni-rich cathode and sulfide-based solid electrolyte Li6PS5Cl. The modified NCM@LSO-2||LPSCl||Li-In ASSLBs deliver a high reversible capacity of 183.5 mA h g-1 at 0.1C, 30.3% higher than the bare NCM811 electrode. Besides, the interfacial regulation strategy enables the operation at a high rate of 5.0C and achieves a high capacity retention ratio of ∼85.8% after 500 cycles at 1.0C. Furthermore, the underlying mechanisms are well investigated through kinetic analyses and theoretical simulations. This work provides an in-depth understanding on the interfacial degradations between Ni-rich cathodes and sulfide-based all-solid-state electrolytes from the view of kinetic limitations and offers potential solutions.

High-Performance Sheet-Type Sulfide All-Solid-State Batteries Enabled by Dual-Function Li4.4Si Alloy-Modified Nano Silicon Anodes

The silicon-based anodes are one of the promising anodes to achieve the high energy density of all-solid-state batteries (ASSBs). Nano silicon (nSi) is considered as a suitable anode material for assembling sheet-type sulfide ASSBs using thin free-standing Li6PS5Cl (LPSC) membrane without causing short circuit. However, nSi anodes face a significant challenge in terms of rapid capacity degradation during cycling. To address this issue, dual-function Li4.4Si modified nSi anode sheets are developed, in which Li4.4Si serves a dual role by not only providing additional Li+ but also stabilizing the anode structure with its low Young's modulus upon cycling. Sheet-type ASSBs equipped with the Li4.4Si modified nSi anode, thin LPSC membrane, and LiNi0.83Co0.11Mn0.06O2 (NCM811) cathode demonstrate exceptional cycle stability, with a capacity retention of 96.16% at 0.5 C (1.18 mA cm-2) after 100 cycles and maintain stability for 400 cycles. Furthermore, a remarkable cell-level energy density of 303.9 Wh kg-1 is achieved at a high loading of 5.22 mAh cm-2, representing a leading level of sulfide ASSBs using electrolyte membranes at room temperature. Consequently, the chemically stable slurry process implemented in the fabrication of Li4.4Si-modified nSi anode sheet paves the way for scalable applications of high-performance sulfide ASSBs.

Bottom Deposition Enables Stable All-Solid-State Batteries with Ultrathin Lithium Metal Anode

Modern strides in energy storage underscore the significance of all-solid-state batteries (ASSBs) predicated on solid electrolytes and lithium (Li) metal anodes in response to the demand for safer batteries. Nonetheless, ASSBs are often beleaguered by non-uniform Li deposition during cycling, leading to compromised cell performance from internal short circuits and hindered charge transfer. In this study, the concept of "bottom deposition" is introduced to stabilize metal deposition based on the lithiophilic current collector and a protective layer composed of a polymeric binder and carbon black. The bottom deposition, wherein Li plating ensues between the protective layer and the current collector, circumvents internal short circuits and facilitates uniform volumetric changes of Li. The prepared functional binder for the protective layer presents outstanding mechanical robustness and adhesive properties, which can withstand the volume expansion caused by metal growth. Furthermore, its excellent ion transfer properties promote uniform Li bottom deposition even under a current density of 6 mA·cm-2. Also, scanning electron microscopy analysis reveals a consistent plating/stripping morphology of Li after cycling. Consequently, the proposed system exhibits enhanced electrochemical performance when assessed within the ASSB framework, operating under a configuration marked by a high Li utilization rate reliant on an ultrathin Li.

Enhanced Cycling Stability of All-Solid-State Lithium-Sulfur Battery through Nonconductive Polar Hosts

All-solid-state lithium-sulfur batteries (ASSLSBs) are promising next-generation battery technologies with a high energy density and excellent safety. Because of the insulating nature of sulfur/Li2S, conventional cathode designs focus on developing porous hosts with high electronic conductivities such as porous carbon. However, carbon hosts boost the decomposition of sulfide electrolytes and suffer from sulfur detachment due to their weak bonding with sulfur/Li2S, resulting in capacity decays. Herein, we propose a counterintuitive design concept of host materials in which nonconductive polar mesoporous hosts can enhance the cycling life of ASSLSBs through mitigating the decomposition of adjacent electrolytes and bonding sulfur/Li2S steadily to avoid detachment. By using a mesoporous SiO2 host filled with 70 wt % sulfur as the cathode, we demonstrate steady cycling in ASSLSBs with a capacity reversibility of 95.1% in the initial cycle and a discharge capacity of 1446 mAh/g after 500 cycles at C/5 based on the mass of sulfur.

Deeply Lithiated Carbonaceous Materials for Great Lithium Metal Protection in All-Solid-State Batteries

Protection of lithium (Li) metal electrode is a core challenge for all-solid-state Li metal batteries (ASSLMBs). Carbon materials with variant structures have shown great effect of Li protection in liquid electrolytes, however, can accelerate the solid-state electrolyte (SE) decomposition owing to the high electronic conductivity, seriously limiting their application in ASSLMBs. Here, a novel strategy is proposed to tailor the carbon materials for efficient Li protection in ASSLMBs, by in situ forming a rational niobium-based Li-rich disordered rock salt (DRS) shell on the carbon materials, providing a favorable percolating Li+ diffusion network for speeding the carbon lithiation, and enabling simultaneously improved lithiophilicity and reduced electronic conductivity of the carbon structure at deep lithiation state. Using the proposed strategy, different carbon materials, such as graphitic carbon paper and carbon nanotubes, are tailored with great ability to speed the interfacial kinetics, homogenize the Li plating/stripping processes, and suppress the SE decompositions, enabling much improved performances of ASSLMBs under various conditions approaching the practical application. This strategy is expected to create a novel roadmap of Li protection for developing reliable high-energy-density ASSLMBs.

Advances in Electrochemical Liquid-Phase Transmission Electron Microscopy for Visualizing Rechargeable Battery Reactions

This review presents an overview of the application of electrochemical liquid-phase transmission electron microscopy (ELP-TEM) in visualizing rechargeable battery reactions. The technique provides atomic-scale spatial resolution and real-time temporal resolution, enabling direct observation and analysis of battery materials and processes under realistic working conditions. The review highlights key findings and insights obtained by ELP-TEM on the electrochemical reaction mechanisms and discusses the current limitations and future prospects of ELP-TEM, including improvements in spatial and temporal resolution and the expansion of the scope of materials and systems that can be studied. Furthermore, the review underscores the critical role of ELP-TEM in understanding and optimizing the design and fabrication of high-performance, long-lasting rechargeable batteries.

Engineering the Structural Uniformity of Gel Polymer Electrolytes via Pattern-Guided Alignment for Durable, Safe Solid-State Lithium Metal Batteries

Ultrathin and super-toughness gel polymer electrolytes (GPEs) are the key enabling technology for durable, safe, and high-energy density solid-state lithium metal batteries (SSLMBs) but extremely challenging. However, GPEs with limited uniformity and continuity exhibit an uneven Li+ flux distribution, leading to nonuniform deposition. Herein, a fiber patterning strategy for developing and engineering ultrathin (16 µm) fibrous GPEs with high ionic conductivity (≈0.4 mS cm-1 ) and superior mechanical toughness (≈613%) for durable and safe SSLMBs is proposed. The special patterned structure provides fast Li+ transport channels and tailoring solvation structure of traditional LiPF6 -based carbonate electrolyte, enabling rapid ionic transfer kinetics and uniform Li+ flux, and boosting stability against Li anodes, thus realizing ultralong Li plating/stripping in the symmetrical cell over 3000 h at 1.0 mA cm-2 , 1.0 mAh cm-2 . Moreover, the SSLMBs with high LiFePO4 loading of 10.58 mg cm-2 deliver ultralong stable cycling life over 1570 cycles at 1.0 C with 92.5% capacity retention and excellent rate capacity of 129.8 mAh g-1 at 5.0 C with a cut-off voltage of 4.2 V (100% depth-of-discharge). Patterned GPEs systems are powerful strategies for producing durable and safe SSLMBs.