Unraveling the evolution of Cathode–Solid electrolyte interface using operando X-ray Photoelectron spectroscopy

Understanding the evolution of the solid electrolyte-electrode interface is currently one of the most challenging obstacles in the development of solid-state batteries (SSBs). Here, we develop an X-ray Photoelectron Spectroscopy (XPS) that allows for operando measurement during cycling. Based on theoretical analysis and the modulated electrode and detector co-grounding mode, the displacement of binding energy can be correlated with the surface electrostatic potential of the material, revealing the charge distribution and composition evolution of the space charge layer between the cathode and the electrolyte. In the investigation of typical LiCoO₂ (LCO)/Li₆PS₅Cl (LPSC)/Li–In batteries, we observed the static potential difference and oxidative decomposition between LPSC and LCO, and the effectiveness of the LiNbO₃ coating in reducing potential difference and inhibiting the diffusion of Co and oxidation of S species. Furthermore, our study also revealed that the potential drop between LiNi_0·8Co_0·1Mn_0·1O₂ and LPSC is smaller than that of LCO, whilst that between Li₃InCl₆ and LCO remains near zero. The proposed operando XPS method offers a novel approach for real-time monitoring of interface potential and species formation, providing rational guidance for the interface engineering in SSBs.