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.