A novel approach to improve the electrochemical performances of layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode by YPO₄ surface coating

Layered LiNi_1/3Co_1/3Mn_1/3O₂ (LNCMO) is surface coated with different contents of YPO₄ (0.5 wt.%, 1 wt.% and 3 wt.%) through simple chemical deposition method. The pristine and YPO₄-coated LNCMO are characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). It is found that the YPO₄ surface coating layers do not change the bulk structure of LNCMO. The investigation in their cycling performances demonstrates that 1 wt.% YPO₄-coated LNCMO exhibits the best cycling stability, with capacity retention ratio of 88.6% after 50 cycles, much better than that of the pristine material (only 80.1%). Furthermore, the 1 wt.% YPO₄ surface modification improves the rate performance and thermal stability of layered LNCMO. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared (FTIR) measurements of pristine and 1 wt.% YPO₄-coated LNCMO are also measured and compared. It has been proved that the coated YPO₄ inhibits the growth of solid electrolyte interfacial (SEI) film in repeated cycling, which partly explains the improved capacity retention in electrochemical tests