Central Metal Halide Bond Dependent Chemical Compatibility of Halide Solid Electrolytes with Li₆PS₅Cl for All Solid State Cell

Halide solid electrolytes have gained a lot of research attention in the past decade due to their wide electrochemical stability window, especially their high oxidative stability enables their use with high voltage cathodes. None the less their limited reduction stability against Li metal enforces a bilayer separator configuration with sulfide solid electrolytes in all solid-state batteries. However, there are indication/ concern of electrochemical incompatibility between the halide and sulfide solid electrolyte. Here, we study the chemical reactivity between sulfide SE Li₆PS₅Cl with halide SE by varying the central metal ion and their impact on cell performance in bilayer configuration. We performed operando electrochemical impedance spectroscopy, operando temperature dependent synchrotron X-ray diffraction, ex-situ X-ray photoelectron spectroscopy and differential scanning calorimetry to quantify the reactivity between the sulfide and halide SE. We infer, that the reaction kinetics is indeed determined by the central metal atom of the halide solid electrolyte with Li₃InCl₆ and Li₂ZrCl₆ being highly reactive with Li₆PS₅Cl whereas Li₃YCl₆, Li₃ScCl₆ and Li₃ErCl₆being stable. Our work provides a guideline for selecting HSE and SSE pair for bilayer all solid-state batteries.