On the Compatibility of Halide Bilayer Separators for All-Solid-State Batteries

Considering the lack of solid electrolytes that are electrochemically stable in contact with a high-voltage cathode and a low-voltage metallic anode, bilayer separators in all-solid-state batteries are gaining increasing attention. However, previous studies have shown that the chemical reactivity between the materials comprising the electrolyte bilayer is one of the contributing factors to the deterioration of battery performance during cycling. Here, we computationally screen the chemical compatibility of an extensive range of materials forming a bilayer separator using first-principles calculations. Notably, several bilayer separators are found to be thermodynamically stable, amongst them, the stability of the Li3PO4/Li3InCl6 pairing is further verified experimentally using a combination of X-ray diffraction, solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. This study underscores the importance of understanding the chemical compatibility of bilayer separators when engineering high-energy density all-solid-state batteries.