Facile synthesis of nano-flower shaped NiCo₂O₄ and hexagonal prism shaped MoO₃ composite materials as high-performance cathode materials for lithium-oxygen batteries

The development of lithium-oxygen batteries has a considerable positive impact on environmental protection and energy conservation. The cycling performance of lithium-oxygen batteries can be greatly improved by using a bifunctional cathode catalyst. In this study, composites of NiCo₂O and h-MoO₃ (named h-MoO₃/NiCo₂O₄) were synthesized by a simple hydrothermal method and used as cathode catalysts for lithium-oxygen batteries. The h-MoO₃/NiCo₂O₄ has large specific surface area (120 m² g⁻¹), low proportions of Ni²⁺/Ni³⁺ (0.41) and Co²⁺/Co³⁺ (0.91) and high proportions of Mo⁵⁺/Mo⁶⁺ (0.20) compared with those of h-MoO₃/NiO and h-MoO₃/Co₃O₄. The h-MoO₃/NiCo₂O₄ composite provided a larger effective area for Li₂O₂ storage, resulting in low overpotential and high capacity. The first discharge capacities of h-MoO₃/NiCo₂O₄ electrodes reached up to 9981.4 mA h g⁻¹ and 8971.6 mA h g⁻¹ at the current density of 500 mA g⁻¹ and 700 mA g⁻¹, respectively. The h-MoO₃/NiCo₂O₄ electrodes exhibited good cyclic stability (133 cycles under a limited capacity of 500 mA h g⁻¹ at 500 mA g⁻¹) and low charge-discharge overpotential (only 0.84 V for the first cycle).