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 Li_1.75ZrO_0.5Cl_4.75 (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.