Unveiling the Growth Mechanism of the Interphase between Lithium Metal and Li₂S‐P₂S₅‐B₂S₃ Solid‐State Electrolytes

Abstract Chalcogenides with high ionic conductivity and appropriate mechanical properties are promising solid‐state electrolytes (SSEs) to substitute current liquid electrolytes in lithium‐ion batteries. Yet, their practical applications in all‐solid‐state batteries are still retarded by both the low critical current density and the inferior interfacial stability toward electrodes. In this work, a series of superior SSEs, that is, Li 2 S‐P 2 S 5 ‐B 2 S 3 electrolytes, are developed via a ball‐milling and then melt‐quenching strategy. These SSEs exhibit a high critical current density of 1.65 mA cm −2 and a long cycling life of over 300 h. In addition, the evolution mechanism of the interphase between SSEs and metallic lithium is revealed via operando electrochemical impedance spectroscopy, depth‐profiling XPS, and in situ Raman spectroscopy. The structural and chemical heterogeneities are found to be the main origins of the continual interphase evolution. The resulting “multi‐layer mosaic like” interphase facilitates the suppression of Li dendrite growth, and hence, prolongs the lifetime of lithium‐ion all‐solid‐state batteries. In addition, the preparation technique of SSEs developed in the present work is feasible for scale‐up production.