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

Visualizing lithium (Li) ions and understanding Li plating/stripping processes as well as evolution of solid electrolyte interface (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 efficiently decoupled and Li ion behavior at interface between different solid‐state electrolytes (SSE) was successfully detected. The innovative combining experiments of in situ atomic force microscopy and in situ X‐ray photoelectron spectroscopy on Li metal anode revealed interfacial morphological/chemical evolution and decoupled Li plating/stripping process from SEI evolution. Though Li plating speed in Li10GeP2S12 (LGPS) was higher than Li3PS4 (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.