Significant improvement of electrochemical properties of AlF_3-coated LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 cathode materials

摘要

The uniform and spherical LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 particles were successfully coated with AlF_3. The structures and electrochemical properties of AlF_3-coated LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 were characterized by various techniques. When the coating amount was 0.5 mol%, the cathode showed enhanced cycling performance and rate capability compared to the pristine LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2. The AlF_3-coated LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2/Li cell had capacity retention of 98% after 100 cycles even at 4C over 2.8-4.5V, while the pristine LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 exhibited capacity retention of only 89%. Moreover, the rate capability and cyclic performance at elevated temperature (55℃) were also improved. Electrochemical impedance spectroscopy testing revealed the improved electrochemical performance, which could be considered that the AlF_3 coating layer can suppress the increase of impedance during the charging and discharging process by preventing directly contact of the highly delithiated active material with electrolyte.