Cation-disordered fluoride to facilitate durable interfaces in (all) solid-state Li batteries

Abstract

Nickel (Ni)-rich cathode materials such as LiNi_0.8Co_0.1Mn_0.1O₂ (NCM) have received considerable attention as potential candidates for lithium-ion batteries (LIBs) and all-solid-state batteries (ASSBs) owing to their high theoretical capacities. However, the practical application of NCM is limited by its surface instability, which is primarily attributed to its high Ni content and interfacial side reactions with sulfide-based solid electrolytes. In this study, we designed Li_2.4Ga_1.2F₆ (LGF), which exhibits high ionic conductivity and electrochemical stability, as a durable interface based on cationic disordering and vacancy concepts to reduce the interfacial resistance and improve the structural stability of NCM in LIBs and Li₆PS₅Cl (LPSCl) in ASSBs. The LGF coating layer can modulate the interfacial reactions between NCM particles, conventional liquid electrolytes, and sulfide-based solid electrolytes. The LGF coating layer significantly enhanced Li⁺ transport and surface stability, effectively suppressed interfacial side reactions, and decreased the internal resistance, resulting in improved reversibility and cycling performance of the NCM cathode. This enables the practical application of LGF, proposed by the cationic point-defect strategy, as effective coating layers for NCM cathode materials in advanced LIBs and ASSBs.