A flexible rechargeable quasi-solid-state Ni–Fe battery based on surface engineering exhibits high energy and long durability

With the rapid development of portable and wearable electronics, energy storage devices featuring high energy and power densities, long-cycle lifetime, environment friendliness, safe operation, lightweight, ultrathin thickness and flexibilityl have become increasingly important. Herein, a high-performance flexible quasi-solid-state Ni–Fe battery was rationally developed by engineering the surfaces of α-Fe2O3 nanorods (NRs) and NiCo2O4 nanowire arrays (NWAs) as the anode and cathode, respectively. Benefiting from the flexible current collector, fast charge transport, rapid ion diffusion, and sufficient electroactive sites, this flexible quasi-solid-state Ni–Fe battery presents outstanding capacity as high as 134.5 mA h g−1. Furthermore, this battery also has long cycling life, and could be cycled up to 2600 times with 82.7% capacity retention. Most importantly, the as-fabricated flexible quasi-solid-state Ni–Fe battery achieves an admirable energy density of 227 W h kg−1, together with a peak power density of 23.4 kW kg−1, thus outperforming the most recently reported Ni–Fe batteries and other flexible energy storage devices. Coupled with the advantages of admirable energy density and durability, this highly flexible and rechargeable Ni–Fe battery will greatly enrich the energy storage technologies for future flexible electronic device applications.