Insights into Ion Occupancy Manipulation of Fe-Co Oxide Free-Standing Cathodes for Li-O Batteries with Enhanced Deep Charge Capability and Long-Term Capability.

The merits of Li-O batteries due to the huge energy density are shadowed by the sluggish kinetics of oxygen redox and massive side reactions caused by conductive carbon and a binder. Herein, Fe-Co inverse spinel oxide nanowires grown on Ni foam are fabricated as carbon-free and binder-free cathodes for Li-O batteries. Superior high rate cycle durability and deep charge capability are obtained. For example, 300 cycles with a low overpotential under a fixed capacity of 500 mAh g are achieved at a high current density of 500 mA g. In the deep discharge/charge mode at 500 mA g, the optimized Fe-Co oxide cathode can stably work for more than 30 cycles with the capacity maintained at about 2100 mAh g. Owing to the appreciable incorporation of Fe into the surface of stable inverse spinel oxides, the regulated Fe-Co oxide cathodes possess a more stable and higher ratio of Co/Co, which offers improved adsorption ability of reactive oxygen intermediates and thus achieves the enhanced electrocatalytic performance in the higher current density. In addition, the morphology evolution from array to pyramid-like structure of nanowires further provides assurance in the superior cycle capability. By coupling pyramid-shaped nanowires with binary inverse spinel, the obtained Fe-Co oxide becomes a promising material for practical applications in Li-O batteries. This work offers a general strategy to design efficient mixed metal oxide-based electrodes for the critical energy storage fields.