Direct Growth of Flower-Like δ-MnO2on Three-Dimensional Graphene for High-Performance Rechargeable Li-O2Batteries

A challenge still remains to develop high-performance and cost-effective air electrode for Li-O2 batteries with high capacity, enhanced rate capability and long cycle life (100 times or above) despite recent advances in this field. In this work, a new design of binder-free air electrode composed of three-dimensional (3D) graphene (G) and flower-like δ-MnO2 (3D-G-MnO2) has been proposed. In this design, graphene and δ-MnO2 grow directly on the skeleton of Ni foam that inherits the interconnected 3D scaffold of Ni foam. Li-O2 batteries with 3D-G-MnO2 electrode can yield a high discharge capacity of 3660 mAh g−1 at 0.083 mA cm−2. The battery can sustain 132 cycles at a capacity of 492 mAh g−1 (1000 mAh gcarbon −1) with low overpotentials under a high current density of 0.333 mA cm−2. A high average energy density of 1350 Wh Kg−1 is maintained over 110 cycles at this high current density. The excellent catalytic activity of 3D-G-MnO2 makes it an attractive air electrode for high-performance Li-O2 batteries.