'Cotton-ball' shaped porous iron-nickel sulfide: a high-rate cathode for long-life aqueous rechargeable battery

Aqueous rechargeable batteries (ARB) offer reasonably higher energy density and cycle life than their non-aqueous counterparts. Yet, the bottleneck is a limited choice of positive electrodes coupled with low-rate capability and inadequate cycle life. We report here a wet chemical approach to synthesize in-situ three-dimensional (3D) ‘cotton-ball’ shaped porous iron-nickel sulfide (FeNi₂S₄) (henceforth referred to as PINS) as a diffusion-controlled ARB electrode. It shows a high specific capacity of 177 mA h g⁻¹ at 1 A g⁻¹ vs Pt in the alkaline electrolyte with excellent rate capability (89 mA h g⁻¹ at 40 A g⁻¹) and ultra-long cycle life (10,000 cycles). Furthermore, a pouch-type full-cell ARB (FeNi₂S₄//AC) delivers an energy density of 56.7 Wh kg⁻¹ at a power density of 871.5 W kg⁻¹ with high cycling stability (10,000 cycles). The present study offers a straightforward and efficient approach for developing nanostructured transition metal sulfide-based cathode materials for practical ARB.