A H⁺/Li⁺ Ion Exchange Induced Spinel Ion‐Conductive Interphase Stabilizes 4.5 V LiCoO₂ in Sulfide‐Based All‐Solid‐State Lithium Battery

Abstract All‐solid‐state lithium batteries (ASSLIBs) show significant promise as the next‐generation energy technology due to their high energy density and inherent safety. However, the severe interface reactions between solid electrolyte and the high‐voltage cathodes pose a major challenge, particularly at higher charge voltages. Herein, a H₃PO₄‐triggered H⁺/Li⁺ exchange strategy is proposed to covert LiCoO₂ (LCO) surface to spinel Co₃O₄/Li₃PO₄ ionic‐conductive interphase. This spinel interphase presents a thickness of 15 nm and good affinity with LCO, which provides long‐lasting protection to suppress interfacial parasitic reactions. Besides, both spinel Co₃O₄ and amorphous Li₃PO₄ feature high ionic conductivity compared to bulk LCO, thereby facilitating the interfacial ionic transportation. With such modification, ASSLIBs delivers high specific capacity (146.2 mAh g⁻¹ at 0.1 C), outstanding rate performance (116.4 mAh g⁻¹ at 2 C), and long‐term cyclability (350 cycles at 0.5 C) under a cut‐off voltage of 4.3 V versus Li/Li⁺. Moreover, this robust spinel interphase further improves the stable cycling (168.9 mAh g⁻¹ at 0.1 C for 100 cycles) under elevated cut‐off voltage (4.5 V vs Li/Li⁺). This finding highlights the H⁺/Li⁺ exchange to convert LCO surface to a spinel ionic‐conductive interphase, which poses new insights for interface design in ASSLIBs.