Synthesis and characterization of Al-substituted LiNi0.5Co0.2Mn0.3O2 cathode materials by a modified co-precipitation method

Abstract

An Al-substituted LiNi0.5Co0.2Mn0.3O2 (Al-NCM) cathode material was synthesized by a modified co-precipitation method followed by heat treatment process. The obtained materials were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicated that the as-prepared Al-NCM sample exhibited a well hexagonal α-NaFeO2 structure, lower cation mixing, higher crystallinity, a more homogeneous spherical structure, lower charge transfer resistance and a higher lithium ion diffusion coefficient, thus leading to enhanced electrochemical performance. The effects of Al substitution on rate capability, cycling stability and low-temperature performance of LiNi0.5Co0.2Mn0.3O2 (NCM) were evaluated by coin cells and 14500 full batteries. Specifically, the Al-NCM sample delivered discharge specific capacities of 159.7, 147.4, 139.8, 135.7, 126.9 and 111.3 mA h g-1 at 0.5C, 1C, 2C, 3C, 5C, and 10C rates, respectively, with capacity retention ratio of 86.6% after 100 cycles at 1C rate under the voltage range of 3.0-4.3 V. The 14500 battery utilizing Al-NCM material as the cathode delivered a discharge capacity of 803.55 mA h at 1C rate in the potential range of 2.7-4.2 V, with capacity retention of 89.30% after 200 cycles. Moreover, the 14500 battery fabricated with Al-NCM as the cathode delivered a discharge capacity of 590.06 mA h at 1C rate at -20 °C, much higher than 471.30 mA h of the battery assembled with NCM as the cathode.