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

High-entropy materials have been demonstrated to improvethe structuralstability and electrochemical performance of layered cathode materialsfor lithium-ion batteries (LIBs). However, structural stability atthe surface and electrochemical performance of these materials areless than ideal. In this study, we show that fluorine substitutioncan improve both issues. Here, we report a new high-entropy layeredcathode material Li1.2Ni0.15Co0.15Al0.1Fe0.15Mn0.25O1.7F0.3 (HEOF1) based on the partial substitution of oxygenwith fluorine in previously reported high-entropy layered oxide LiNi0.2Co0.2Al0.2Fe0.2Mn0.2O2. This new compound delivers a discharge capacity of85.4 mAh g(-1) and a capacity retention of 71.5% after100 cycles, showing significant improvement from LiNi0.2Co0.2Al0.2Fe0.2Mn0.2O2 (first 57 mAh g(-1) and 9.8% after 50 cycles).This improved electrochemical performance is due to suppression ofthe surface M3O4 phase formation. Although stillan early stage study, our results show an approach to stabilize thesurface structure and improve the electrochemical performance of high-entropylayered cathode materials.