Improved Electrochemical Performance of Al 2 O 3 -Coated @ K and Cl Dual-Doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 Cathode Materials at High Cut-Off Voltage

The irreversible phase transition of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathode materials easily occurs in high voltage (> 4.5 V) charging processes, which aggravates the corrosion of electrolyte on the materials and seriously affects the safety and cycling performance of lithium-ion batteries. In this paper, K and Cl ions were dual-doped into NCM523 by a high-temperature solid state method, and then Al 2 O 3 was coated on the surface of the NCM523 by a hydrothermal method to obtain the modified cathode materials. The crystal structure, morphology and surface state of the modified materials were analyzed, and the electrochemical performance was tested under high cut-off voltage (4.6 V). The results show that when the content of K and Cl dual-doping and Al 2 O 3 coating are 1 mol.% and 2 wt.%, respectively, the comprehensive properties of the materials are excellent. The first discharge capacity of 0.1 C is 210 mAh g −1 , and the irreversible capacity loss is reduced. Compared with pristine materials, the specific discharge capacity at 5 C was increased by 26 mAh g −1 , and the capacity retention rate was improved by 16% after 100 cycles at 1 C. The dual-doping of K and Cl ions can inhibit the mixing of cations, enhance the bond strength between transition metal cations and O 2− , and improve the structural stability and the Li + transport rate. The Al 2 O 3 coating separates the cathode materials from the electrolyte and inhibits the corrosion of the electrolyte to the cathode materials. Therefore, the electrochemical properties of the modified cathode materials are significantly improved.