Enhanced electrochemical properties and thermal stability of Zr4+ doped Li1.20Mn0.54Ni0.13Co0.13O2 cathode material by a Li ion conductor of Li3PO4 surface coating

Abstract

Li-excess layered oxide Li1.20Mn0.54Ni0.13Co0.13O2 and Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 were synthesized via a co-precipitation method, and then different contents of Li3PO4 were successfully coated on the surface of Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 by using the wet process. The influences of the Zr4+ doping and Li3PO4 coating on the crystal structures and particles morphology were systematically analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the Zr4+ doping enlarged the Li+ diffusion channel of the cathode structure and the 2 wt% Li3PO4 coated Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 was covered by the Li3PO4 coating layer with a thickness of 50 nm. The charge and discharge tests revealed that the Zr4+ doping and Li3PO4 coating could obviously enhance the electrochemical properties of cathode. Especially, the 2 wt% Li3PO4 coated Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 delivered a discharge capacity of 200.9 mAh g−1 after 300 cycles and the corresponding capacity retention is 92.1%. While only a discharge capacity of 163.7 mAh g−1 and a capacity retention of 83.9% are obtained after 300 cycles for the pristine Li1.20Mn0.54Ni0.13Co0.13O2. The Nyquist plots implied that the Zr4+ doping and Li3PO4 coating could effectively inhibit the increasing of the electrolyte/electrode interface charge transfer resistance during cycling.