The effect of drying methods on the structure and performance of LiNi0.5Co0.2Mn0.3O2 cathode material for lithium-ion batteries

Abstract

In this paper, we investigate the effect of drying methods (freeze drying method and vacuum drying method) assisting a solvothermal method on the morphology, structure and electrochemical properties of LiNi0.5Co0.2Mn0.3O2 cathode material (which are named FD-NCM and VD-NCM respectively) for lithium-ion batteries. X-ray diffraction (XRD) results demonstrated that FD-NCM exhibited a lower degree of cation mixing and a better layered hexagonal structure than VD-NCM. The FD-NCM sample presented a uniform and homogeneous surface morphology with a higher BET surface area (20.08 m2 g−1), as confirmed by scanning electron microscopy (SEM). In addition, the FD-NCM material exhibited better electrochemical performance than the VD-NCM material. Specifically, the discharge capacities of FD-NCM were 155.8, 153.5, 146.8, 141.1, 129.3, and 111.0 mAh g−1, corresponding to the rates of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, respectively, with the capacity retention maintained at 88.80% at 0.5 C after 50 cycles, which preceded that of the VD-NCM sample (82.46%). According to electrochemical impedance spectroscopy (EIS) analysis, the charge-transfer resistance (Rct) of FD-NCM material increased from 75.31 Ω to 80.42 Ω, much smaller than that of VD-NCM from 93.85 Ω to 119.60 Ω, which demonstrated that the uniform morphology plays an important role in cathode materials for lithium ion batteries.