Surface-Stabilized High-Entropy Layered Oxyfluoride Cathode for Lithium-Ion Batteries

High-entropy materials have been demonstrated to improve the structural stability and electrochemical performance of layered cathode materials for lithium-ion batteries (LIBs). However, structural stability at the surface and electrochemical performance of these materials are less than ideal. In this study, we show that fluorine substitution can improve both issues. Here, we report a new high-entropy layered cathode material Li_1.2Ni_0.15Co_0.15Al_0.1Fe_0.15Mn_0.25O_1.7F_0.3 (HEOF1) based on the partial substitution of oxygen with fluorine in previously reported high-entropy layered oxide LiNi_0.2Co_0.2Al_0.2Fe_0.2Mn_0.2O₂. This new compound delivers a discharge capacity of 85.4 mAh g^-1 and a capacity retention of 71.5% after 100 cycles, showing significant improvement from LiNi_0.2Co_0.2Al_0.2Fe_0.2Mn_0.2O₂ (first 57 mAh g^-1 and 9.8% after 50 cycles). This improved electrochemical performance is due to suppression of the surface M₃O₄ phase formation. Although still an early stage study, our results show an approach to stabilize the surface structure and improve the electrochemical performance of high-entropy layered cathode materials.