Significant improvement of electrochemical properties of AlF3-coated LiNi0.5Co0.2Mn0.3O2 cathode materials

The uniform and spherical LiNi0.5Co0.2Mn0.3O2 particles were successfully coated with AlF3. The structures and electrochemical properties of AlF3-coated LiNi0.5Co0.2Mn0.3O2 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 LiNi0.5Co0.2Mn0.3O2. The AlF3-coated LiNi0.5Co0.2Mn0.3O2/Li cell had capacity retention of 98% after 100 cycles even at 4 C over 2.8–4.5 V, while the pristine LiNi0.5Co0.2Mn0.3O2 exhibited capacity retention of only 89%. Moreover, the rate capability and cyclic performance at elevated temperature (55 °C) were also improved. Electrochemical impedance spectroscopy testing revealed the improved electrochemical performance, which could be considered that the AlF3 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.