Interconnecting 3D Conductive Networks with Nanostructured Iron/Iron Oxide Enables a High-Performance Flexible Battery

Aqueous Ni/Fe alkaline batteries with features of low cost and high safety show great potential for application in portable and wearable electronics. However, the poor kinetics of the Fe-based anode greatly limits the large-scale applications of Ni/Fe batteries. Herein, we report an interconnected 3D conductive network with carbon-coated nanostructured iron/iron oxide (3D-Fe/Fe2O3@C) as an efficient anode for a flexible Ni/Fe battery. A hydrogel precursor is used to molecularly link and confine Fe3+ to spatial networks, resulting in a uniform dispersion of Fe/Fe2O3-heterostructured nanoparticles. Theoretical investigations reveal regulated potential loss and improved delocalized carrier density as a result of carbon coating and the mixed metal/metal oxide structure. In addition to these merits, due to the regulated wettability and electroactive surface areas, the 3D-Fe/Fe2O3@C anode with a high mass loading delivers an extraordinary areal capacity of 3.07 mA h cm-2, as well as the boosted rate capability and Coulombic efficiency. When coupled with the NiCo2O4 cathode, the flexible quasi-solid-state Ni/Fe battery exhibits an admirable energy density of 15.53 mW h cm-3 and a maximum power density of 761.91 W h cm-3. The good stability after 20,000 cycles and severe mechanical deformations of the as-fabricated Ni/Fe battery imply it as a promising flexible energy storage device for practical applications.