Optimizing Atomic and Electronic Structure of Antiperovskite Solid Electrolytes for Electrochemically Stable Interface of Lithium Metal Anodes

Abstract Solid‐state batteries (SSBs) employing Li‐metal anodes (LMAs) show significant potential for overcoming the energy density limitations inherent in conventional Li‐ion batteries with graphite anodes. In the past decade, diverse approaches have tried to improve the cycling performance of SSBs, including chemical modifications of solid electrolytes (SEs) and designs of multifunctional interlayers. However, knowledge gaps regarding the physical characteristics of Li‐ion conducting inorganic SEs and the interfacial stability of LMAs are impeding advancements in battery technology. Herein, a practical strategy is developed to facilitate Li‐ion mobility and mitigate current constriction at the interfaces via manganese substitution into antiperovskite SEs, inspired by how liquid electrolyte additives modify the surface characteristics of LMAs. Due to the stable half‐filled 3d shell of manganese, the physically modified SE can achieve structural endurance and electrochemical compatibility with LMA. The Li symmetric cell employing this advanced SE demonstrates outstanding electrochemical performance at room temperature without external pressure. This cell configuration exhibits a high critical current density of 10.5 mA cm⁻² and maintains its stable charge–discharge process over 4000 cycles at 10.0 mA cm⁻². The findings here will advance the commercialization of SSBs by providing insights into the complicated solid‐solid interactions during battery operation.