Multicomponent Protective Layers for All-Solid-State Li Metal Batteries

The advancement of electric vehicles has stimulated extensive research into lithium-ion batteries (LIBs) with higher energy densities and improved safety. Consequently, all-solid-state Li metal batteries (ASLMBs) have emerged as a promising alternative due to the exceptional theoretical capacity (3,860 mA h g^-1) and low electrochemical potential (-3.04 V vs SHE) of Li metal anode, as well as their improved safety resulting from the utilization of nonflammable inorganic solid electrolytes (SEs) compared to conventional lithium-ion batteries employing liquid electrolytes. Especially, sulfide solid electrolytes (SEs) have been one of the most promising candidates thanks to their high ionic conductivities (maximum ~2.0 × 10^-2 S cm^-1) and mechanically ductile property. Nevertheless, the implementation of ASLMBs has been hindered by the unstable interfaces between Li metal and SEs, leading to severe decomposition of sulfide SEs and the formation of dendrites. To address the challenges related to interfacial instability, researchers have proposed various materials, such as lithiophilic metals and inorganics, as protective layers for Li metal. Nevertheless, no single protective coating has achieved acceptable interfacial stability between Li metal and SEs. Recently, the concept of multi-component protective layers comprising lithiophilic metals and robust inorganic materials has been introduced. However, there remains a lack of comprehensive analysis regarding the configuration or structure of the protective layer and its influence on the performance of ASLMBs.<br/>In this study, we present our recent investigation into the configuration of protective layers for Li metal and their impact on the performance of ASLMBs. Additionally, we discuss different mechanisms of Li metal plating and stripping based on variations in the protective layer's structure.