Enhanced electrochemical properties and thermal stability of Zr~(4+) doped Li_(1.20)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2 cathode material by a Li ion conductor of Li_3PO_4 surface coating

摘要

Li-excess layered oxide Li_(1.20)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2 and Li_(1.20)Mn_(0.53)Ni_(0.13)CO_(0.13)Zr_(0.01)O_2 were synthesized via a co-precipitation method, and then different contents of Li_3PO_4 were successfully coated on the surface of Li_(1.20)Mn_(0.53)Ni_(0.13)CO_(0.13)Zr_(0.01)O_2 by using the wet process. The influences of the Zr~(4+) doping and Li_3PO_4 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 spec-troscopy (XPS). The results showed that the Zr~(4+) doping enlarged the Li~+ diffusion channel of the cathode structure and the 2 wt% Li_3PO_4 coated Li_(1.20)Mn_(0.53)Ni_(0.13)CO_(0.13)Zr_(0.01)O_2 was covered by the Li_3PO_4 coating layer with a thickness of 50 nm. The charge and discharge tests revealed that the Zr~(4+) doping and Li_3PO_4 coating could obviously enhance the electrochemical properties of cathode. Especially, the 2 wt% Li_3PO_4 coated Li_(1.20)Mn_(0.53)Ni_(0.13)CO_(0.13)Zr_(0.01)O_2 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 Li_(1.20)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2. The Nyquist plots implied that the Zr~(4+) doping and Li_3PO_4 coating could effectively inhibit the increasing of the electrolyte/ electrode interface charge transfer resistance during cycling.