Rational Construction of Self-Standing Sulfur-Doped Fe₂O₃ Anodes with Promoted Energy Storage Capability for Wearable Aqueous Rechargeable NiCo-Fe Batteries

Aqueous rechargeable Ni-Fe batteries featuring an ultra-flat discharge plateau, low cost, and outstanding safety characteristics show promising prospects for application in wearable energy storage. In particular, fiber-shaped Ni-Fe batteries will enable textile-based energy supply for wearable electronics. However, the development of fiber-shaped Ni-Fe batteries is currently challenged by the performance of fibrous Fe-based anode materials. In this context, this study describes the fabrication of sulfur-doped Fe₂O₃ nanowire arrays (S-Fe₂O₃ NWAs) grown on carbon nanotube fibers (CNTFs) as an innovative anode material (S-Fe₂O₃ NWAs/CNTF). Encouragingly, first-principle calculations reveal that S-doping in Fe₂O₃ can dramatically reduce the band gap from 2.34 to 1.18 eV and thus enhance electronic conductivity. The novel developed S-Fe₂O₃ NWAs/CNTF electrode is further demonstrated to deliver a very high capacity of 0.81 mAh cm⁻² at 4 mA cm⁻². This value is almost sixfold higher than that of the pristine Fe₂O₃ NWAs/CNTF electrode. When a cathode containing zinc-nickel-cobalt oxide (ZNCO)@Ni(OH)₂ NWAs heterostructures is used, 0.46 mAh cm⁻² capacity and 67.32 mWh cm⁻³ energy density are obtained for quasi-solid-state fiber-shaped NiCo-Fe batteries, which outperform most state-of-the-art fiber-shaped aqueous rechargeable batteries. These findings offer an innovative and feasible route to design high-performance Fe-based anodes and may inspire new development for the next-generation wearable Ni-Fe batteries.