Improved electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode material by double-layer coating with graphene oxide and V2O5 for lithium-ion batteries

Abstract

LiNi0.5Co0.2Mn0.3O2 cathode material synthesized by a sol-gel method was surface-modified by double-layer coating. The results of X-ray diffraction (XRD) confirm that the intrinsic structure was no change after surface modification. A double-layer structure consisting of an inner V2O5 (VO) layer and an outer conductive graphene oxide (GO) layer was coated on the surface of active material, as confirmed by transmission electron microscopy (TEM). The results of field emission scanning electron microscope (FE-SEM) equipped with an energy dispersive spectroscope (EDS) show that both graphene oxide and V2O5 uniformly covered LiNi0.5Co0.2Mn0.3O2 cathode material. The double-layer-coated LiNi0.5Co0.2Mn0.3O2 cathode material shows improved electrochemical performance with a capacity retention of 74.2% after 50 cycles in a range of 2.5–4.5V at 55°C, compared with only 67.8% capacity retention for the pristine material. In addition, the double-layer-coated LiNi0.5Co0.2Mn0.3O2 releases 116.6mAhg−1 under a high current rate, while the pristine material only remains at 105.7mAhg−1. The results can be ascribed to the double coating layer not only avoids the side reaction between electrolyte and active material but also promotes Li+ and electronic conductivity. Differential capacity (dQ/dV) and electrochemical impedance spectroscopy (EIS) measurements reveal that the double coating layer effectively suppresses the increase of the electrode polarization during cycling.