Effect of Zr doping and Al-Zr co-doping on LiNi0.5Co0.25Mn0.25O2 for lithium-ion batteries

Abstract

Cathode material Li(Ni0.5Co0.25Mn0.25)1-xZrxO2 (x = 0, 0.005, 0.01, 0.02, 0.03) and Li(Ni0.5Co0.25-yMn0.25Aly)0.99Zr0.01O2 (y = 0, 0.01, 0.02, 0.03) were synthesized by coprecipitation method. The structure and electrochemical properties of cathode materials were mainly studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), charge/discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results of XRD show that Zr doping and Al-Zr co-doping cannot destroy the crystal structure, and they are all beneficial to structural stability. Electrochemical results show that the appropriate amount of Zr4+ doping can improve the rate and cycle performance. However, there is no further increase in the rate performance and cycle stability when Co is replaced with Al. Because of the 3a site occupation of the doped ions, it is possible that the diffusion of lithium ions is hindered. And Al is low electrochemically inert. In particular, x = 0.01 exhibited the best rate performance and cycle stability in all samples. The specific discharge capacity of the material is 151.0 mAh/g at 1C, and it still up to 173.3 mAh/g at 0.1C after experiencing high-rate discharge. And the capacity retention rate is 87.53% at 0.1C after 45 cycles. When Al3+ and Zr4+ are co-doped, the performance of y = 0.01 material is the best. The specific discharge capacity at 0.1C, 0.2C, 0.5C, 1C and 0.1C are 182, 148.3, 123.5, 110.3 and 125.8 mAh/g, respectively.