Enhanced electrochemical performance of Li3PO4 modified Li[Ni0.8Co0.1Mn0.1]O2 cathode material via lithium-reactive coating

Abstract

Residue lithium is recognized as one of the critical factors affecting the electrochemical performances of LiNiO2-based cathode materials. In this paper, Li3PO4-modified LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material is successfully synthesized via a wet coating followed by a heat treatment. As a consequence, the contents of surface residual lithium are significantly reduced as confirmed by neutralization titration, which can be ascribed to the formation of a Li3PO4 coating layer by the reaction between surface residual lithium and (NH4)2HPO4. The effects of Li3PO4 coating on the surface states, crystal structure and electrochemical performances of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material are studied in detail. After 100 cycles, the capacity retention of Li3PO4-coated NCM811 is 92.6% at 25 °C at 1C, whereas the bare NCM811 is only 86.1%. Besides, the Li3PO4-coated NCM811 delivers a better rate property of 159.4 mAh·g−1 at 8C compared with 144.4 mAh·g−1 for NCM811. The prominent improvements in electrochemical performances are attribute to the fact that the formation of Li3PO4 coating layers help to remove the surface residual lithium, facilitate lithium ion diffusion, lower the level of HF and H2O in the electrolyte and suppress the deleterious side reactions between the electrolyte and active materials.