3D hierarchical Co/CoO/C nanocomposites with mesoporous microsheets grown on nickel foam as cathodes for Li-O₂ batteries

Li-O₂ batteries are of great promise for next generation electrochemical power sources. However, they are significantly restricted by their low charge/discharge efficiency, inferior rate capability and poor cycle stability. Herein, a hierarchically porous Co/CoO/carbon nanocomposite is in situ grown on three dimensional nickel foam (denoted as Co/CoO/C@Ni) by the solvothermal deposition and subsequent pyrolysis of metal organic framework. This nanocomposite is found to be composed of free-standing microsheets with abundant mesopores. In comparison with Super P cathode, the Co/CoO/C@Ni architecture as a unique bifunctional cathode for Li-O₂ batteries shows enhanced electrochemical performances: the charge overpotential dramatically drops by 0.5 V; the discharge capacity reaches 8000 mAh g⁻¹ at a current density of 0.1 mA cm⁻²; the superior cycle stability of up to 70 cycles as well as good rate capability is obtained. This enhancement is mainly ascribed to the 3D hierarchically porous structure, which facilitates the diffusion of oxygen and electrolyte, and provides large space for Li₂O₂ deposition. Meanwhile, the synergy of Co and CoO contributes positively to the reaction kinetics. In addition, the high electronic conductivity of 3D Ni foam substrate ensures fast electron transport. Accordingly, the hierarchically porous Co/CoO/C@Ni architecture is a promising cathode for Li-O₂ batteries.