In Situ Analysis of Interfacial Morphological and Chemical Evolution in All‐Solid‐State Lithium‐Metal Batteries

Abstract In situ analysis of Li plating/stripping processes and evolution of solid electrolyte interphase (SEI) are critical for optimizing all‐solid‐state Li metal batteries (ASSLMB). However, the buried solid‐solid interfaces present a challenge for detection which preclude the employment of multiple analysis techniques. Herein, by employing complementary in situ characterizations, morphological/chemical evolution, Li plating/stripping dynamics and SEI dynamics were directly detected. As a mixed ionic‐electronic conducting interface, Li|Li 10 GeP 2 S 12 (LGPS) performed distinct interfacial morphological/chemical evolution and dynamics from ionic‐conducting/electronic‐isolating interface like Li|Li 3 PS 4 (LPS), which were revealed by combination of in situ atomic force microscopy and in situ X‐ray photoelectron spectroscopy. Though Li plating speed in LGPS was higher than LPS, speed of SSE decomposition was similar and ~85 % interfacial SSE turned into SEI during plating and remained unchanged in stripping. To leverage strengths of different SSEs, an LPS‐LGPS‐LPS sandwich electrolyte was developed, demonstrating enhanced ionic conductivity and improved interfacial stability with less SSE decomposition (25 %). Using in situ Kelvin probe force microscopy, Li‐ion behavior at interface between different SSEs was effectively visualized, uncovering distribution of Li ions at LGPS|LPS interface under different potentials.