High-Specific-Surface-Area Octahedral Iron–Nickel Spinel Oxides for High-Performance Li–O2 Batteries

Li–O2 batteries have attracted great attention due to their extremely high theoretical energy density. However, they suffer from a short cycle life and low capacity in practical applications. These problems stem from the inability to fully decompose the Li2O2 generated during the discharge process. In this study, NiFe2O4 catalysts with two different morphologies, octahedral and microflowers, were prepared by a simple hydrothermal method. The effects of NiFe2O4 cathodes with different morphologies on the performance of Li–O2 batteries were investigated. Theoretical calculations reveal that the overpotentials of the oxygen reduction reaction and oxygen evolution reaction of the battery with NiFe2O4 are 0.52 and 0.65 V, respectively. The results show that the octahedral Super-P/NiFe2O4 cathode exhibits high catalytic activity and shows a large specific surface area and a reasonable pore structure, resulting in the reduction in charge/discharge potential difference. The battery equipped with an octahedral Super-P/NiFe2O4 cathode exhibits the best cycle life of 125 cycles at a current density of 500 mA·g–1 and presents the highest discharge capacity of 9427 mAh·g–1 at a current density of 100 mA·g–1.