Effects of Al_2O_3 coating on the structural and electrochemical performance of LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 cathode material

摘要

The pristine LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 cathode material particles were successfully coated with Al_2O_3 via a heterogeneous nucleation process and subsequent heat-treatment. The structure and electrochemical properties of Al_2O_3-coated LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 were characterized by XRD and constant-current charge/discharge cycling tests. It was found that the Al_2O_3 coating did not alter the crystal structure of the cathode material. The Al_2O_3 coating layer had a negative influence on the dicharge specific capacity and a positive effect on the cycling performance. The decreased discharge capacity of the coated sample can be attributed to the poor clectronic and ionic conductivity of Al_2O_3 layer, which interfered the Li~+ intercaltion/deintercaltion into/from the cathode material. The enhanced cycling performance can be ascribed to the suppression of the dissolution of transition metal ions by the HF acid in the eletrolyte and the side reations between electrode and electrolyte by the Al_2O_3 coating layer. The 2wt.% Al_2O_3-coated sample exhibits the optimal overall electrochemical performance, with discharge specific capacities of 157.0, 137.1 mAh/g at 0.2C and 3C rate, and capacity cycling retention rates of 97.34, 93.53% after 20 & 50 cycles, respectively.