<scp>LiBF</scp>₄‐Derived Coating on <scp>LiCoO₂</scp> for 4.5 V Operation of Li₆<scp>PS</scp>₅Cl‐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 Li 6 PS 5 Cl are especially promising due to their superior ionic conductivity. However, interfacial degradation between sulfide electrolytes and high‐voltage cathodes, such as LiCoO 2 , limits long‐term performance. This study demonstrates that a LiBF 4 ‐derived F‐rich coating on LiCoO 2 , applied by immersing LiCoO 2 particles in a LiBF 4 solution followed by annealing, can significantly enhance performance in Li 6 PS 5 Cl‐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, CoF 2 , Li x BF y O z , and Li x BO y , which effectively suppresses side reactions at the LiCoO 2 |Li 6 PS 5 Cl 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 LiCoO 2 cathodes, offering substantial promise for next‐generation energy storage systems.