Graphene-based surface modification on layered Li-rich cathode for high-performance Li-ion batteries

Abstract

A Li-rich cathode material Li(Li_0.2Mn_0.54Ni_0.13Co_0.13)O₂ synthesized by a sol–gel method is further modified by wrapping with graphene oxide (GO) using a simple chemical approach and post thermal annealing. X-ray diffraction (XRD), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) characterizations show that annealing of the GO-wrapped material leads to a transformation from the original layered structure to a spinel phase on the surfaces of the powder particles. The electrochemical performance, and in particular the rate capability, is observed to be significantly enhanced as a result of this unique surface-treated Li-rich cathode/graphene composite structure. The modified sample reveals a very high discharge capacity of 313 mA h g⁻¹ at a current density of 12.5 mA g⁻¹, and 201 mA h g⁻¹ charge capacity at an extremely high current density of 2500 mA g⁻¹. Such improvement is ascribed to the co-existence of reduced GO, the locally transformed spinel-like structure and the recrystallized particles on the surfaces of the primary particles.