Surface-Modification of Doping and Coating Li1.2Ni0.2Co0.08Mn0.52O2 as a Long Life Cathode Material of Lithium-Ion Battery by Sodium Salt Treatment

Abstract

Lithium-rich layered oxides are considered to be the most promising next-generation lithium-ion cathode materials due to their high specific capacity and energy density. However, its commercialization is limited due to its poor cycling stability and severe voltage decay. A NaH2PO4 molten salt treatment is designed, which simultaneously realizes Na+ doping and phosphate coating to improve the defects of lithium-rich materials. Sodium dihydrogen phosphate is of good contact with lithium-rich materials in the process of high temperature melting to facilitate surface sodium doping which is conducive to stabilizing the surface structure through lithium-sodium exchange. At the same time, the phosphate coating produced by lithium-sodium exchange and dehydration on the outer surface of the material can effectively inhibit the corrosion of the electrolyte. The modified material obtained by the synergistic effect of doping and coating has a capacity of 262.4 mAh·g−1 at 0.1 C and 169.6 mAh·g−1 at 5 C, the capacity retention rate of 73.6% after 500 cycles, and the voltage decay is significantly improved. A simple and effective method for improving the electrochemical performance of Li-rich layered materials is provided.