LiBF₄-Derived Coating on LiCoO₂ for 4.5 V Operation of Li₆PS₅Cl-based Solid-State Batteries

Solid-state batteries are attracting considerable attention for their high energy density and improved safety over conventional lithium-ion batteries. Among solid-state electrolytes, sulfide-based options like Li₆PS₅Cl are especially promising due to their superior ionic conductivity. However, interfacial degradation between sulfide electrolytes and high-voltage cathodes, such as LiCoO₂, limits long-term performance. This study demonstrates that a LiBF₄-derived F-rich coating on LiCoO₂, applied by immersing LiCoO₂ particles in a LiBF₄ solution followed by annealing, can significantly enhance performance in Li₆PS₅Cl -based solid-state batteries. This coating enables stable high-voltage (4.5 V vs. Li⁺/Li) operation, achieving an initial specific capacity of 153.82 mAh/g and 87.1% capacity retention over 300 cycles at 0.5 C. The enhanced performance stems from the F-rich coating, composed of multiple phases including LiF, CoF₂, LixBFyOz, and LixBOy, which effectively suppresses side reactions at the LiCoO₂|Li₆PS₅Cl interface and improves lithium-ion diffusivity, thereby enabling greater Li capacity utilization. Our findings provide a practical pathway for advancing solid-state batteries with high-voltage LiCoO₂ cathodes, offering substantial promise for next-generation energy storage systems. Keywords: solid state batteries, LiCoO2, sulfide cathode, high voltage.