Graphene Oxide Gel-Derived, Free-Standing, Hierarchically Porous Carbon for High-Capacity and High-Rate Rechargeable Li-O2 Batteries

Lithium-oxygen (Li-O2) batteries are one of the most promising candidates for high-energy-density storage systems. However, the low utilization of porous carbon and the inefficient transport of reactants in the cathode limit terribly the practical capacity and, in particular, the rate capability of state-of-the-art Li-O2 batteries. Here, free-standing, hierarchically porous carbon (FHPC) derived from graphene oxide (GO) gel in nickel foam without any additional binder is synthesized by a facile and effective in situ sol-gel method, wherein the GO not only acts as a special carbon source, but also provides the framework of a 3D gel; more importantly, the proper acidity via its intrinsic COOH groups guarantees the formation of the whole structure. Interestingly, when employed as a cathode for Li-O2 batteries, the capacity reaches 11 060 mA h g-1 at a current density of 0.2 mA cm-2 (280 mA g-1); and, unexpectedly, a high capacity of 2020 mA h g-1 can be obtained even the current density increases ten times, up to 2 mA cm-2 (2.8 A g-1), which is the best rate performance for Li-O2 batteries reported to date. This excellent performance is attributed to the synergistic effect of the loose packing of the carbon, the hierarchical porous structure, and the high electronic conductivity of the Ni foam.