LAUSR

Abstract The LiNi0.8Co0.15Al0.05O2 (NCA) cathode material was decorated with yttrium oxide via a wet chemical-calcination method and as-prepared material was mechanically composited with graphene. Structure of bare NCA, Y2O3-decorated NCA, and graphene/Y2O3/NCA composite was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The absence of additional peaks in the XRD spectra indicated no change in the crystalline structure of the NCA material after processing. The SEM images showed that the surface of the NCA particles was decorated with Y2O3 as well as the graphene uniformly distributed among the NCA particles. Electrochemical performance of materials was evaluated by cycling test, rate capability, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The initial specific discharge capacity of all three materials was above 190 mAh g−1 at 0.5C, but capacity retention of graphene/Y2O3/NCA composite was about 48% higher than that of the bare material during 100 cycles. NCA, Y2O3/NCA, and graphene/Y2O3/NCA materials delivered specific discharge capacities of 109, 136 and 164 mAh g−1, respectively at 2C. EIS data indicated an improvement in the impedance of the electrode containing Y2O3 and graphene. The results of electrochemical tests showed that Y2O3 is an obstacle to perform side reactions between the electrode and the electrolyte by forming a protective layer on the surface of the NCA particles. By creating a three-dimensional conductive network between NCA particles, graphene reduced the impedance of the electrode and increased the kinetics of the redox process in the electrode. Thus, with the simultaneous use of Y2O3 and graphene along with the NCA material, the cycling and rate capability of the cathode electrode were improved.