Hierarchical carbon-free NiCo₂O₄ cathode for Li–O₂ batteries

Li–oxygen battery provides much higher specific energy density compared to conventional Li–ion batteries, but there is a lack of desired cathodes which show lower over-potential during the charging cycle. Here, we report the effect of surface morphology of carbon-free spinel-like NiCo₂O₄ nanowires and nanosheets on Ni foam on cathode performance in Li–O₂ battery. Two hierarchical structured NiCo₂O₄ cathodes were synthesized by using a hydrothermal method. Physical, chemical, and electrochemical properties of NiCo₂O₄ were characterized using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, BET surface area, electrochemical AC impedance spectroscopy, and linear sweep voltammetry. Scale-like NiCo₂O₄ electrode showed the highest specific capacity, compared to that of rod-like morphology, which seems due to a superior catalytic activity for oxygen reduction reaction, with lower charging over-potential, high discharge capacity, and excellent cycle performance.