Advanced engineering for cathode in lithium-oxygen batteries. Flexible 3D hierarchical porous architecture design and its functional modification

Modern technology constantly requires smaller, more efficient lithium-oxygen batteries (LOBs). To meet this need, a chemical vapor deposition (CVD) method is used to create an innovative cathode design with both a hierarchical porous nanostructure and a 3D flexible macroscopical morphology. This method employs architectural optimization to further improve cathodic ORR and OER performance via heteroatom doping, surface-sprouted carbon nanofibers (CNFs) grafting, and boundary exposing. The cathode consists of a 3D hierarchical porous graphene foam (PGF), along with RuO${}_2$ nanoparticles impregnated and nitrogen doped CNFs (RuO${}_2$@NCNFs), where the PGF serves as a structural support and cathodic current collector, and the RuO${}_2$@NCNFs work as a superior bi-functional catalyst. The cathode delivers an outstanding discharge capacity of 8440 mAh g${}_{cathode}$${}^{-1}$ while maintaining a recharge plateau at ≈4.0 V, and can cycle for over 700 rounds without obvious degeneration under a fixed capacity. Notably, this free-standing cathode can be directly used in LOBs without the need for additional substrates or current collectors. Therefore, the current densities and capacities herein are calculated based on the total weight of the cathodes. These results demonstrate the RuO${}_2$@NCNFs-PGF cathode's remarkable potential for LOB applications, and this rational cathodic structure may be extended to other highly efficient catalyst applications. (© 2021 Wiley-VCH GmbH)