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

Abstract

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).