Self-standing Li1.2Mn0.6Ni0.2O2/graphene membrane as a binder-free cathode for Li-ion batteries

Abstract

Lithium-rich transition-metal layered oxides (LROs), such as Li_1.2Mn_0.6Ni_0.2O₂, are promising cathode materials for application in Li-ion batteries, but the low initial coulombic efficiency, severe voltage fade and poor rate performance of the LROs restrict their commercial application. Herein, a self-standing Li_1.2Mn_0.6Ni_0.2O₂/graphene membrane was synthesized as a binder-free cathode for Li-ion batteries. Integrating the graphene membrane with Li_1.2Mn_0.6Ni_0.2O₂ forming a Li_1.2Mn_0.6Ni_0.2O₂/graphene structure significantly increases the surface areas and pore volumes of the cathode, as well as the reversibility of oxygen redox during the charge–discharge process. The initial discharge capacity of the Li_1.2Mn_0.6Ni_0.2O₂/graphene membrane is ∼270 mA h g⁻¹ (∼240 mA h g⁻¹ for Li_1.2Mn_0.6Ni_0.2O₂) and its initial coulombic efficiency is 90% (72% for Li_1.2Mn_0.6Ni_0.2O₂) at a current density of 40 mA g⁻¹. The capacity retention of the Li_1.2Mn_0.6Ni_0.2O₂/graphene membrane remains at 88% at 40 mA g⁻¹ after 80 cycles, and the rate performance is largely improved compared with that of the pristine Li_1.2Mn_0.6Ni_0.2O₂. The improved performance of the Li_1.2Mn_0.6Ni_0.2O₂/graphene membrane is ascribed to the lower charge-transfer resistance and solid electrolyte interphase resistance of the Li_1.2Mn_0.6Ni_0.2O₂/graphene membrane compared to that of Li_1.2Mn_0.6Ni_0.2O₂. Moreover, the lithium ion diffusion of the Li_1.2Mn_0.6Ni_0.2O₂/graphene membrane is enhanced by three orders of magnitude compared to that of Li_1.2Mn_0.6Ni_0.2O₂. This work may provide a new avenue to improve the electrochemical performance of LROs through tuning the oxygen redox progress during cycling.