Direct growth of flower-like δ-MnO₂ on three-dimensional graphene for high-performance rechargeable Li-O₂ batteries

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 g_carbon ^-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. A highly efficient 3D graphene (G) flowerlike δ-MnO₂ (3D-G-MnO₂) air cathode is prepared by directly growing graphene and flower-like δ-MnO₂ on a skeleton of Ni foam. Li-O₂ batteries with a 3D-G-MnO₂ electrode can sustain 132 cycles at a capacity of 492 mAh g _MnO2+carbon ^-1 (1000 mAh g_carbon ^-1) and yield an average energy density of 1350 Wh Kg_MnO2+carbon ^-1 over 110 cycles at 0.333 mA cm^-2.