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.