Self-standing Li(1.2)Mn(0.6)Ni(0.2)O(2)/graphene membrane as a binder-free cathode for Li-ion batteries

Lithium-rich transition-metal layered oxides (LROs), such as Li(1.2)Mn(0.6)Ni(0.2)O(2), 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(1.2)Mn(0.6)Ni(0.2)O(2)/graphene membrane was synthesized as a binder-free cathode for Li-ion batteries. Integrating the graphene membrane with Li(1.2)Mn(0.6)Ni(0.2)O(2) forming a Li(1.2)Mn(0.6)Ni(0.2)O(2)/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(1.2)Mn(0.6)Ni(0.2)O(2)/graphene membrane is ∼270 mA h g(−1) (∼240 mA h g(−1) for Li(1.2)Mn(0.6)Ni(0.2)O(2)) and its initial coulombic efficiency is 90% (72% for Li(1.2)Mn(0.6)Ni(0.2)O(2)) at a current density of 40 mA g(−1). The capacity retention of the Li(1.2)Mn(0.6)Ni(0.2)O(2)/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(1.2)Mn(0.6)Ni(0.2)O(2). The improved performance of the Li(1.2)Mn(0.6)Ni(0.2)O(2)/graphene membrane is ascribed to the lower charge-transfer resistance and solid electrolyte interphase resistance of the Li(1.2)Mn(0.6)Ni(0.2)O(2)/graphene membrane compared to that of Li(1.2)Mn(0.6)Ni(0.2)O(2). Moreover, the lithium ion diffusion of the Li(1.2)Mn(0.6)Ni(0.2)O(2)/graphene membrane is enhanced by three orders of magnitude compared to that of Li(1.2)Mn(0.6)Ni(0.2)O(2). This work may provide a new avenue to improve the electrochemical performance of LROs through tuning the oxygen redox progress during cycling.