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–O2 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–O2 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–O2 batteries, but also in other metal–gas batteries with high energy densities.