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

Lithium-rich transition-metal layered oxides (LROs), such as Li1.2Mn0.6Ni0.2O2, 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 Li1.2Mn0.6Ni0.2O2/graphene membrane was synthesized as a binder-free cathode for Li-ion batteries. Integrating the graphene membrane with Li1.2Mn0.6Ni0.2O2 forming a Li1.2Mn0.6Ni0.2O2/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 Li1.2Mn0.6Ni0.2O2/graphene membrane is ∼270 mA h g-1 (∼240 mA h g-1 for Li1.2Mn0.6Ni0.2O2) and its initial coulombic efficiency is 90% (72% for Li1.2Mn0.6Ni0.2O2) at a current density of 40 mA g-1. The capacity retention of the Li1.2Mn0.6Ni0.2O2/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 Li1.2Mn0.6Ni0.2O2. The improved performance of the Li1.2Mn0.6Ni0.2O2/graphene membrane is ascribed to the lower charge-transfer resistance and solid electrolyte interphase resistance of the Li1.2Mn0.6Ni0.2O2/graphene membrane compared to that of Li1.2Mn0.6Ni0.2O2. Moreover, the lithium ion diffusion of the Li1.2Mn0.6Ni0.2O2/graphene membrane is enhanced by three orders of magnitude compared to that of Li1.2Mn0.6Ni0.2O2. This work may provide a new avenue to improve the electrochemical performance of LROs through tuning the oxygen redox progress during cycling.