Mesoporous Fe3O4@C nanoarrays as high-performance anode for rechargeable Ni/Fe battery

Rechargeable aqueous batteries with high power density and energy density are highly desired for electrochemical energy storage. Despite the recent reports of various cathode materials with ultrahigh pseudocapacitance exceeding 3000 F g−1 (or 800 mA h g−1), the development of anode materials is relatively insufficient, which limits the whole performance of the devices far from practical applications. Herein, we report the preparation of mesoporous Fe3O4@C nanoarrays as high-performance anode for rechargeable Ni/Fe battery by a self-generated sacrificial template method. ZnO/Fe3O4 composite was first synthesized by a co-deposition process, and ZnO was subsequently removed by alkali etching to construct the mesoporous structure. A thin carbon film was introduced onto the surface of the electrode by the carbonization of glucose to increase the structural stability of the electrode. The unique mesoporous nanoarray architecture endows the electrode with larger specific surface area, faster charge/mass transport and higher utilization of Fe3O4, which shows an ultrahigh specific capacity (292.4 mA h g−1 at a current density of 5 mA cm−2) and superior stability in aqueous electrolyte (capacitance retention of 90.8% after 5000 cycles). After assembled with hierarchical mesoporous NiO nanoarray as a cathode, an optimized rechargeable Ni/Fe battery with double mesoporous nanoarray electrodes was fabricated, which provided high energy/power densities (213.3 W h kg−1 at 0.658 kW kg−1 and 20.7 kW kg−1 at 113.9 W h kg−1, based on the total mass of the active materials) in the potential window of 1.5 V with excellent cyclability (81.7% retention after 5000 charge/discharge cycles).