Urchin-like NiO–NiCo2O4 heterostructure microsphere catalysts for enhanced rechargeable non-aqueous Li–O2 batteries

Abstract

Urchin-like NiO–NiCo₂O₄ microspheres with heterostructures were successfully synthesized through a facile hydrothermal method, followed by thermal treatment. The unique structure of NiO–NiCo₂O₄ with the synergetic effect between NiCo₂O₄ and NiO, and the heterostructure favour the catalytic activity towards Li–O₂ batteries. NiCo₂O₄ is helpful for boosting both the oxygen reduction reaction and oxygen evolution reaction for the Li–O₂ batteries and NiO is likely to promote the decomposition of certain by-products. The special urchin-like morphology facilitates the continuous oxygen flow and accommodates Li₂O₂. Moreover, benefitting from the heterostructure, NiO–NiCo₂O₄ microspheres are able to promote the transport of Li ions and electrons to further improve battery performance. Li–O₂ batteries utilizing a NiO–NiCo₂O₄ microsphere electrode show a much higher specific capacity and a lower overpotential than those with a Super P electrode. Moreover, they exhibit an enhanced cycling stability. The electrode can be continuously discharged and charged without obvious terminal voltage variation for 80 cycles, as the discharge capacity is restricted at 600 mA h g⁻¹, suggesting that NiO–NiCo₂O₄ is a promising catalyst for Li–O₂ batteries.