Hierarchically Porous and Minimally Stacked Graphene Cathodes for High-Performance Lithium-Oxygen Batteries

Although lithium-oxygen batteries have attracted attention due to their extremely high energy densities, rational design, and critical evaluation of high-energy-density cathode for practical Li-O-2 batteries is still urgently needed. Herein, the multiscale, angstrom-to-millimeter, precisely controllable synthesis of binder-free cathodes with minimally stacked graphene free from edge sites is demonstrated. The proposed Li-O-2 battery, based on a hierarchically porous cathode with a practical mass loading of >4.0 mg cm(-2), simultaneously exhibits an unprecedented specific areal (>30.0 mAh cm(-2)), mass (>6300 mAh g(-1)), and volumetric (>480 mAh cm(-3)) capacities. The battery displays the optimal energy density of 793 Wh kg(-1) critically normalized to the total mass of all active materials including electrolytes and even discharge products Li2O2. Comprehensive in situ characterizations demonstrate a unique discharge mechanism in hierarchical pores which contributes to competitive battery performance. Superior rate performance in a current density range of 0.1 to 0.8 mA cm(-2) and long-cycle stability (>260 cycles) at a current density of 0.4 mA cm(-2), outperforming state-of-the-art carbon cathodes. This study yields insight into next-generation carbon cathodes, not only for use in practical Li-O-2 batteries, but also in other metal-gas batteries with high energy densities.