Insights into Ion Occupancy Manipulation of Fe-Co Oxide Free-Standing Cathodes for Li-O2 Batteries with Enhanced Deep Charge Capability and Long-Term Capability

The merits of Li-O-2 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-2 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(-1) are achieved at a high current density of 500 mA g(-1). In the deep discharge/charge mode at 500 mA g(-1), the optimized Fe-Co oxide cathode can stably work for more than 30 cycles with the capacity maintained at about 2100 mAh g(-1). Owing to the appreciable incorporation of Fe3+ into the surface of stable inverse spinel oxides, the regulated Fe-Co oxide cathodes possess a more stable and higher ratio of Co3+/Co2+, 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-2 batteries. This work offers a general strategy to design efficient mixed metal oxide-based electrodes for the critical energy storage fields.