Deciphering Interfacial Stability of Sulfide and Halide-Based Electrolytes via Operando X-ray Photoelectron Spectroscopy

Combined solid electrolytes address cathode-anode compatibility in all-solid-state Li-ion batteries (ASSLBs), yet interface stability and ion transport mechanisms between different electrolytes remain unclear. Herein, we investigate Li6PS5Cl (LPSC), Li3InCl6 (LIC), and Li1.75ZrO0.5Cl4.75 (LZOC) composite electrolytes through electrochemical analysis and operando X-ray photoelectron spectroscopy. Our results reveal that the electrostatic potential difference between LPSC and LIC inhibits Li+ migration, leading to the decomposition of LIC into InCl3 and LiCl, causing battery failure. In contrast, LZOC forms an oxygen-rich interphase with LiCoO2 (LCO), showing better interfacial stability. The electrostatic potential difference between LZOC and LPSC promotes Li+ diffusion, maintaining interface stability even as LPSC decomposes, thereby preventing severe degradation of LZOC. Therefore, the LCO-LZOC composite cathode exhibits better electrochemical performance than LCO-LIC. This study elucidates the basic mechanism of interfacial reaction and ion diffusion in sulfide–halide electrolytes and emphasizes the key role of electrolyte compatibility in ASSLBs failure pathways.