Graphene modified Li_1.2Ni_0.133Co_0.133Mn_0.534O₂ cathode material for high capacity lithium-ion batteries

Abstract: Li_1.2Ni_0.133Co_0.133Mn_0.534O₂/graphene composites are prepared with Li_1.2Ni_0.133Co_0.133Mn_0.534O₂ particles and graphene oxide sol by a novel ethanol solution reduction method and an ethanol solvothermal method. The structure and morphology are characterized by X-ray diffraction, Raman spectra, scanning electron microscope, and transmission electron microscopy methods. It is found that the Li_1.2Ni_0.133Co_0.133Mn_0.534O₂ spherical secondary particles are wrapped with a graphene network. A four-probe powder conductivity measure test shows that the electrical conductivity of the materials with graphene-wrapped is significantly improved, which is further proved by the electrochemical impedance spectroscopy and ohmic polarization. In addition, the graphene network coating structure can reduce the direct contact between electrolyte and electrode active material as a physical protection. Therefore, the electrochemical properties of the two composites obtained by the two methods are all improved. By comparison, the coating effect with ethanol solution reduction method is much better than that of with ethanol solvothermal method. The composite prepared by ethanol solution reduction method can deliver an average discharge capacity of 315.1 mAh g⁻¹ at 0.05C and 281.4 mAh g⁻¹ at 0.1C, which is about 40 mAh g⁻¹ higher than that of the original material. It can deliver a capacity retention of 83.9% after 200 cycles, which is increased ~ 17% compared with that of the original material. Moreover, its discharge voltage platform and rate capability are greatly increased. Graphical abstract: [Figure not available: see fulltext.].