Flexible all-solid-state fiber-shaped Ni–Fe batteries with high electrochemical performance

High-performance fiber-shaped energy storage devices (FESDs) based on Ni–Fe batteries are indispensable for the development of portable and wearable electronics. Construction of highly capacitive pseudocapacitance cathode/anode materials holds great potential for the fabrication of high-performance FESDs. In this study, CoP@Ni(OH) 2 nanowire arrays (NWAs) with hierarchical core–shell heterostructure, directly grown on carbon nanotube fiber (CNTF), are prepared by a facile and environmentally friendly hydrothermal method, followed by phosphorization and chemical bath deposition process. CoP NWAs possess excellent electrical conductivity, and the core material and secondarily grown substrate can provide fast charge transfer and reaction kinetics between electrolyte and pseudocapacitance material. 3D spindle-like α-Fe 2 O 3 (S-α-Fe 2 O 3 ) architecture is well-dispersed and directly grown on CNTF via solvothermal method and post-annealing process. An FESD consisting of a CoP@Ni(OH) 2 NWAs/CNTF as the positive electrode, a S-α-Fe 2 O 3 /CNTF as the negative electrode, and KOH-PVA as the gel electrolyte is fabricated. The FESD achieves a maximum capacity of 0.203 mA h cm −2 and highest energy density of 81.0 mW h cm −3 , which are mainly attributable to the uniquely hierarchical core–shell and spindle-like nanostructure. Furthermore, the device shows a high power density of 12 000 mW cm −3 and a long cycle life with 85.3% retention after 3000 cycles at the current density of 30 mA cm −2 .