Deciphering Chemical/Electrochemical Compatibility of Li₃InCl₆ in 5.2 V High-Voltage LiCoO₂ All-Solid-State Batteries

Large interfacial resistance is a widely recognized impediment to the advancement of high-voltage, all-solid-state batteries. However, a comprehensive understanding of the fundamental cause behind the interfacial resistance between solid electrolytes and typical layered oxide cathodes has not yet been achieved. Here, we investigated the high-voltage stability of Li₃InCl₆ and elucidated the underlying interfacial electrochemical reactions between LiCoO₂ and Li₃InCl₆. The pairing of Li₃InCl₆ with LiCoO₂ exhibited a superior capacity retention of 73.6% even at 5.2 V, much higher than 28.2% charged at 4.6 V in lithium-ion batteries after 70 cycles. The enhanced high-voltage stability of ASSBs is attributed to the stable interface formed between LiCoO₂ and Li₃InCl₆ and the reinforced surface and bulk structure stability. On the other hand, the ultrahigh voltage still causes the partial decomposition of Li₃InCl₆ and generates interfacial compounds such as InClO and cobalt and indium chlorides/oxides.