Structural evolution of mesoporous graphene/LiNi1/3Co1/3Mn1/3O2 composite cathode for Li–ion battery

Abstract

Layered LiMO2 (M = Ni, Co, and Mn) is a type of promising cathode materials for high energy density and high work voltage lithium-ion batteries. However, the poor rate performance and low power density hinder its further applications. The capacity fade is related to the structural transformation in the layered LiMO2. In this work, the structural changes of bi-material cathode composed of mesoporous graphene and layered LiNi1/3Co1/3Mn1/3O2 (NCM) were studied via in situ X-ray diffraction (XRD). During different C-rate charge–discharge test at the voltage range of 2.5–4.1 V, the composite cathode of NCM−graphene (NCM−G) reveals better rate performances than pure NCM cathode. The NCM−G composite electrode displays a higher rate capability of 76.7 mAh·g−1 at 5C rate, compared to the pure NCM cathode of 69.8 mAh·g−1 discharge capacity. The in situ XRD results indicate that a reversible phase transition from hexagonal H1 to hexagonal H2 occurs in layered NCM material during 1C charge–discharge process. With the current increasing to 2C/5C, the structure of layered NCM material for both electrodes reveals few changes during charge and discharge processes, which indicates the less utilization of NCM component at high C-rates. Hence, the improved rate performance for bi-material electrode is attributed to the highly conductive mesoporous graphene and the synergistic effect of mesoporous graphene and NCM material.