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Insight of Ion Occupancy Manipulation for Fe-Co Oxide Free-Standing Cathode of Li-O2 battery with Enhanced Deep Charge and Long-Term Capability.

The merits of Li-O2 batteries on the huge energy density is covered by the sluggish kinetics of oxygen redox and massive side reactions caused by conductive carbon and binder. Herein, Fe-Co inverse spinel oxide nanowires grown on Ni foam are fabricated as the carbon-free and binder-free cathodes for Li-O2 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 deep discharge/charge mode at 500 mA g-1, the optimized Fe-Co oxide cathode can stable worked over 30 cycles with the capacity maintained at about 2100 mAh g-1. Owing to the appreciate incorporation of Fe3+ in 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 provide insurance on the superior cycle capability. Coupling pyramid-shaped nanowires with binary inverse spinel, the obtained Fe-Co oxide brings a promising material for the practical application of Li-O2 batteries. This work offers a general strategy to design efficient mixed metal oxide based electrode for the critical energy storage fields.