A unique hierarchical structure: NiCo2O4 nanowire decorated NiO nanosheets as a carbon-free cathode for Li–O2 battery

Abstract: The development of high-performance cathodes is critical to promoting the development of Li-O2 batteries. In this work, three-dimensional NiCo2O4 nanowire-decorated NiO nanosheets (NiO@NiCo2O4) on a Ni foam were fabricated by a two-step solvothermal process. The product exhibited efficient catalytic performance for Li-O2 batteries. This three-dimensional NiO@NiCo2O4 hierarchical structure grown on Ni foam forms a porous catalytic surface for the uniform growth of discharge products. First, NiCo2O4 is a promising catalyst for improving the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) processes for the Li-O2 batteries. Second, NiO can provide a porous scaffold for the further deposition of NiCo2O4 nanowires to avoid their aggregation. Furthermore, NiO can promote the decomposition of by-products containing carbonate/carboxylate species. As a result, the Li-O2 system with NiO@NiCo2O4 as a carbon-free cathode showed a maximum in-depth-specific discharge capacity of 9361.4 mA h g-1 at a current density of 100 mA g-1 and 176 cycles of stability under a limited capacity of 500 mA h g-1 at a current density of 200 mA g-1. The reported strategy regarding a multicomponent hierarchical structure may provide a new approach for effective electrocatalyst design for Li-O2 batteries.