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

A layered Li1.2Ni0.13Co0.13Mn0.54O2 cathode is coated with a CePO4 layer via a simple precipitation method. The pristine and CePO4-coated Li1.2Ni0.13Co0.13Mn0.54O2 are characterized by X-ray diffraction (XRD), fieldemission 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 Li1.2Ni0.13Co0.13Mn0.54O2. Charge-discharge tests show that the CePO4-coated Li1.2Ni0.13Co0.13Mn0.54O2 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 degrees C, high-temperature performance from 59.5 to 219.6 mA h g(-1) at 55 degrees C after 20 cycles, and low-temperature performance from 128.3 to 246.7 mA h g(-1) at -20 degrees 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 Li1.2Ni0.13Co0.13Mn0.54O2 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.