Rational construction of phosphate layer to optimize Cu-regulated Fe3O4 as anode material with promoted energy storage performance for rechargeable Ni-Fe batteries

Flexible aqueous energy storage devices with high security and flexibility are crucial for the progress of wearable energy storage. Particularly, aqueous rechargeable Ni-Fe batteries owning a large theoretical capacity, low cost and outstanding safety characteristics have emerged as a promising candidate for flexible aqueous energy storage devices. Herein, Cu-doped Fe3O4 (CFO) with 3D coral structure was prepared by doping Cu2+ based on Fe3O4 nanosheets (FO). Furthermore, the Fe-based anode material (CFPO) grown on carbon fibers was obtained by reconstructing the surface of CFO to form a low-crystallization shell which can enhance the ion transport. Excitingly, the newly developed CFPO electrode as an innovative anode material further exhibited a high capacity of 117.5 mAh g-1 (or 423 F g(-1)) at 1 A g(-1). Then, the assembled aqueous Ni-Fe batteries with a high cell-voltage output of 1.6 V deliver a high capacity of 49.02 mAh g(-1) at 1 A g(-1) and retention ratio of 96.8% for capacitance after 10 0 0 0 continuous cycles. What's more, the aqueous quasi-solid-state batteries present a remarkable maximal energy density of 45.6 Wh kg(-1) and a power density of 12 kW kg(-1). This work provides an innovative and feasible way and optimization idea for the design of high-performance Fe-based anodes, and may promote the development of a new generation of flexible aqueous Ni-Fe batteries. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Flexible and secure aqueous energy storage devices are crucial for wearable energy storage. This study presents a Cu-doped Fe3O4 nanosheet with a 3D coral structure and a low-crystallization shell on the surface for enhanced ion transport. The newly developed CFPO electrode exhibits high capacity, and the assembled aqueous Ni-Fe batteries show high capacity and retention ratio. The aqueous quasi-solid-state batteries demonstrate remarkable energy density and power density.