Highly Stable Halide‐Electrolyte‐Based All‐Solid‐State Li–Se Batteries

Solid-state Li-S and Li-Se batteries are promising devices that can address the safety and electrochemical stability issues that arise from liquid-based systems. However, solid-state Li-Se/S batteries usually present poor cycling stability due to the high resistance interfaces and decomposition of solid electrolytes caused by their narrow electrochemical stability windows. Here, an integrated solid-state Li-Se battery based on a halide Li₃ HoCl₆ solid electrolyte with high ionic conductivity is presented. The intrinsic wide electrochemical stability window of the Li₃ HoCl₆ and its stability toward Se and the lithiated species effectively inhibit degeneration of the electrolyte and the Se cathode by suppressing side reactions. The inherent thermodynamic mechanism of the lithiation/delithiation process of the Se cathode in solid is also revealed and confirmed by theoretical calculations. The battery achieves a reversible capacity of 402 mAh g⁻¹ after 750 cycles. The electrochemical performance, thermodynamic lithiation/delithiation mechanism, and stability of metal-halide-based Li-Se batteries confer theoretical study and practical applicability that extends to other energy-storage systems.