Enhanced High‐Temperature Electrochemical Performance of Layered Nickel‐Rich Cathodes for Lithium‐Ion Batteries after LiF Surface Modification

Layered nickel (Ni)‐rich materials have been widely studied as attractive cathode materials for lithium‐ion batteries, owing to their high theoretical specific capacity and low cost; however, most Ni‐rich materials have poor cycle performance, especially at high temperatures. This study reports a simple sol‐gel method for developing lithium fluoride (LiF)‐coated LiNi0.90Co0.08Al0.02O2 (NCA@LiF) by immersing NCA powder in a 1‐butyl‐2,3‐dimethylimidazolium tetrafluoroborate (BdmimBF4) solution. The residual Li compound on the surface of NCA can be converted into a uniform LiF coating layer through the in situ hydrolysis of BdmimBF4. The Li‐conducting LiF coating layer inhibits side reactions (LiPF6→PF5+LiF, PF5+H2O→POF3+HF, POF3+Li2O→LixPOFy+LiF, Li2O/LiOH+HF→H2O+2LiF) with the electrolyte and protects the electrode from HF corrosion. The NCA@LiF sample shows a high capacity retention rate of 79.9 % after 200 cycles at 1 C and an excellent capacity of 155.7 mAh g−1 at 10 C at room temperature. Additionally, the capacity retention rate of the NCA@LiF sample at high temperatures exhibited a significant improvement in comparison with the NCA sample, reaching 75.7 % after 100 cycles at 60 °C at 1 C. This simple and effective method can be used for improving the electrochemistry stability and high‐temperature performance of other Ni‐based cathode materials.