Surface modification with lithium-ion conductor Li₃PO₄ to enhance the electrochemical performance of lithium-rich layered Li_1.2Ni_0.2Mn_0.6O₂

Layered lithium-rich oxide materials are regarded as one of the most promising cathode materials. However, inferior cycling stability and poor rate performance hinder their practical application prospect. In this study, Li₃PO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ cathode materials have been synthesized by sol–gel method together with a facile liquid-evaporation process. The results suggested that the Li₃PO₄ coating layer, which could not only facilitate the lithium-ion diffusion rate and accelerate the diffusion kinetics but also act as a protective layer to protect it from corrosion by HF and other side reactions. Density functional theory (DFT) calculations confirmed the essence effect on lithium-ion diffusion coefficient and electronic conductivity. After modifying with an appropriate amount of Li₃PO₄, the Li-rich layered oxides showed enhanced electrochemical performance. Especially, the capacity retention of 5 wt% Li₃PO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ was significantly enhanced from 17.7% of the bare Li_1.2Ni_0.2Mn_0.6O₂ to 73.8%. In terms of rate capabilities, 5 wt% Li₃PO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ retained capacities of 181.0, 165.9, 128.8, and 107.8 mAh g⁻¹, while the bare Li_1.2Ni_0.2Mn_0.6O₂ were only 137.4, 109.3, 75.6, and 45.9 mAh g⁻¹, respectively, at rates of 0.5 C, 1 C, 2 C, and 5 C. Our research findings show that coating with an appropriate amount of lithium-ion conductor material is one of the effective measures to obtain improved performance of Li-rich and Mn-rich layered oxide materials.