Enhanced electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode material after surface modification with graphene oxide

LiNi0.5Co0.2Mn0.3O2 powders synthesised via a citric acid assisted sol-gel method were subsequently surface-modified with graphene oxide using a wet chemical method. X-ray diffraction (XRD) results showed that the graphene-oxide-coated LiNi0.5Co0.2Mn0.3O2 powders exhibited only minor differences in their phase-structural composition compared to the original LiNi0.5Co0.2Mn0.3O2 powders. The graphene-oxide- coated LiNi0.5Co0.2Mn0.3O2 sample presented a core-shell structure, with a uniform coating layer with a thickness of about 1 nm discovered on the surface, as confirmed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) revealed that the transition metals (M = Ni, Co, Mn) maintained a high oxidation state after surface modification with graphene oxide. The cycle performance of the graphene-oxide- coated LiNi0.5Co0.2Mn0.3O2 was significantly enhanced at a high temperature of 55 degrees C, leading to a capacity retention of 72% after 100 cycles compared with only 64% for the bare LiNi0.5Co0.2Mn0.3O2. The graphene-oxide- coated LiNi0.5Co0.2Mn0.3O2 also demonstrated better performance at different rates than the pristine sample. The effect of the graphene oxide coating layer was further investigated via electro-chemical impedance spectroscopy (EIS), which indicated that this layer plays an important role in stabilising the interface between electrolyte and cathode during cycling. (C) 2017 Elsevier B.V. All rights reserved.