Abstract:LiNi_1/3Co_1/3Mn_1/3O₂ was coated with uniform nano-sized AlF₃ layer by chemical precipitation method to improve its rate capability. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), charge−discharge cycling, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Uniform coated layer with a thickness of about 3 nm was observed on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particle by TEM. At 0.5C and 2C rates, 1.5% (mass fraction) AlF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂/Li in 2.8−4.3 V versus Li/Li⁺ after 80 cycles showed less than 3% of capacity fading, while those of the bare one were 16.5% and 45.9%, respectively. At 5C rate, the capacity retention of the coated sample after 50 cycles maintained 91.4% of the initial discharge capacity, while that of the bare one decreased to 52.6%. EIS result showed that a little change of charge transfer resistance of the coated sample resulting from uniform thin AlF₃ layer was proposed as the main reason why its rate capability was improved obviously. CV result further indicated a greater reversibility for the electrode processes and better electrochemical performance of AlF₃-coated layer.

Key words: Li-ion battery; LiNi_1/3Co_1/3Mn_1/3O₂; coating; uniform thin AlF₃ layer; rate capability