Waxberry-like hierarchical NiCo2O4-decorated carbon microspheres as efficient catalyst for Li-O2 batteries

Rechargeable Li-O-2 batteries have aroused wide concern due to the theoretically high value for specific energy density. However, exploring suitable catalysts holds the key to their development and commercialization. In this work, unprecedented waxberry-like hierarchical NiCo2O4 (NCO) nanorods deposited on carbon microspheres (CMs) (NCO@CMs) were synthesized by a hydrothermal method and heat treatment. When applied as the cathode catalysts, the Li-O-2 batteries with NCO@CMs show a high initial discharge capacity of 6489.5mAhg(-1) and predominant coulombic efficiency of 93.7% at a current density of 200mAg(-1). Meanwhile, significantly prolonged cycle lifespan (over 90 cycles with a cutoff capacity of 1000mAhg(-1)) and stable platforms have been maintained in the charge/discharge process. The improved electrochemical performance is attributed to the unique spatial structure of NCO@CMs which is favorable for the transport of Li+ and oxygen and provides more space for the deposition and dissolution of discharged products. The combination of the carbon base and the NCO nanorods can guarantee high conductivity and retain the structural integrity of the catalyst during the cycle.