Understanding the Role of Metal Interlayers in All‐Solid‐Electrolyte Batteries Using Operando X‐Ray Photoelectron Spectroscopy

Abstract This study reports a facile and reliable operando X‐ray photoelectron spectroscopy (XPS) system for the characterization of the chemical state and electronic structure during Li‐plating/stripping in all‐solid‐state batteries (ASSBs). The measurement conditions (including manufacturing an in situ sample holder) and experimental parameters have been optimized through experimentation. The proposed system accurately defines the status of every metal interlayer component during real‐time battery operation (with simultaneous Li + ‐ion in/out migration) under a repeating Li‐plating/stripping process. Moreover, it enables elucidation of ambiguous reaction mechanisms depending on the battery performance, such as the interlayer‐material effect on the efficiency and reversibility of the Li‐plating/stripping process, and changes in the oxygen‐containing bonds due to reaction with Li. The significance of the developed system is further validated by the usefulness and reliability of the valence band structure as a criterion for the analysis of lithium‐metal alloy formation and the progress of de‐alloying reactions.