Electrochemical Investigation of Compatibility Between Chloride- and Sulfide-Based Solid Electrolytes Using...

The use of solid electrolytes (SEs) allows for the construction of solid-state cells with bilayer-to-multilayer architectures. By appropriate choice of electrolytes for the positive- and negative-electrode sides, electrolyte degradation can be mitigated, thus considerably increasing the design flexibility. However, certain electrolyte combinations lead to nonideal chemical compatibility, increasing the heteroelectrolyte interfacial resistance. Precise measurement of the interfacial resistance is necessary for quantitatively evaluating the compatibility of solid electrolytes. In this work, we employed a solid-state four-electrode cell to investigate the compatibility between three chloride-based SEs-(Li₃InCl₆ (LIC), Li₃ScCl₆ (LSC), and Li₃YCl₆ (LYC))-and the sulfide-based Li₇P₂S₈I (LPSI). Electrochemical impedance spectroscopy (EIS) analysis reveals that the growth rate of the interfacial resistance is the highest in LIC, but the activation energies of the interfacial resistances are identical in all three SEs. Temperature-dependent synchrotron X-ray diffraction and density functional theory calculations strongly suggest that Li₄PS₄I, whose activation energy is similar to those measured by EIS, is the common interfacial product among the three cells, and that its relative degree of formation is consistent with the difference in interfacial resistance growth. This study demonstrates that electrochemical measurements using solid-state four-electrode cells constitute a promising technique for precisely investigating unstable heteroelectrolyte interfaces.