Enhanced electrochemical performance and thermal stability of a CePO4-coated Li1.2Ni0.13Co0.13Mn0.54O2 cathode material for lithium-ion batteries

Abstract

A layered Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode is coated with a CePO₄ layer via a simple precipitation method. The pristine and CePO₄-coated Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS), and the results indicate that CePO₄ has been uniformly coated on the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂. Charge–discharge tests show that the CePO₄-coated Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ has an obviously enhanced electrochemical performance compared with the pristine sample: the initial coulombic efficiency from 88.26% to 92.19%, rate capability from 6 to 110 mA h g⁻¹ at 10 C, high-temperature performance from 59.5 to 219.6 mA h g⁻¹ at 55 °C after 20 cycles, and low-temperature performance from 128.3 to 246.7 mA h g⁻¹ at −20 °C. According to the analysis from dc impedance and electrochemical impedance spectra, the improvements on the electrochemical performance are mainly because the coated CePO₄ layer can reduce side reactions of Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ with the electrolyte, and thus form the cathode–electrolyte interface (CEI) layer with enhanced Li⁺ diffusion. In addition, the CePO₄ layer significantly improves the thermal stability of the coexisting systems of the charged cathode with the electrolyte. Therefore, CePO₄ coating will be a promising approach to improve the electrochemical performance and thermal stability of Li-rich layered oxide cathode materials.