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 (BdmimBF(4)) 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 BdmimBF(4). 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 degrees 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.