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−1 and 87.1% capacity retention over 300 cycles at 0.5C. 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.