Ultra-long KFeS2 nanowires grown on Fe foam as a high-performance anode for aqueous solid-state energy storage.

The development of low-cost and high-activity Fe-based anodic materials is very promising for the present solid-state energy storage. In this work, we successfully synthesize ultra-long KFeS₂ nanowires on an Fe foam substrate via a simple hydrothermal strategy. Physical characterization shows that the as-synthesized KFeS₂ nanowires possess merits of good morphological uniformity, considerable mass loading (∼76 mg cm⁻²) and strong affinity for the substrate. As an anode for solid-state energy storage, the areal capacity of the KFeS₂ electrode can reach 21.1 mA h cm⁻² (at 50 mA cm⁻²), which is greatly enhanced as compared to the previous best result (<2 mA h cm⁻²), and the durability test indicates that the electrode only shows a small working potential shift after long-time cycling. The assembled KFeS₂//NiO single solid-state battery exhibits an enhanced energy density of 175.2–135.8 W h m⁻² at a power range of 436.5–1750 W m⁻². By using in situ Raman and in situ electrochemical impedance spectroscopy (EIS) technologies, the dynamics of the electrode and the energy storage mechanism of the KFeS₂ nanowires are revealed. This work achieves a milestone in the development of high-performance Fe-based film anodes for solid-state energy storage, especially aiming for low-cost and large-scale application. [ABSTRACT FROM AUTHOR]