Ultrafast charging/discharging and highly stable non-aqueous iron-ion batteries using iron oxide (Fe3O4) microspheres as an efficient cathode material†

Rechargeable iron-ion batteries (RIIBs) are considered one of the alternatives to lithium-ion batteries (LIBs) owing to their high volumetric energy density and low-cost fabrication under ambient conditions. A crucial aspect of RIIBs lies in developing high-performance cathode materials with high cycling stability and fast charge–discharge characteristics. We developed highly stable iron oxide microspheres (Fe₃O₄-MS) via solvothermal synthesis. Various electrochemical measurements were performed, including cyclic voltammetry (CV) to understand the redox mechanism and diffusion characteristics of iron-ions, galvanostatic charging discharging (GCD) for cycling stability analysis, and electrochemical impedance spectroscopy (EIS) for different electrode resistance analyses. RIIBs exhibit a high specific capacity of 155 mA h g⁻¹ at 25 mA g⁻¹ and 60 mA h g⁻¹ at a higher current density of 500 mA g⁻¹ (∼8C), with 92% retention capacity and fast charge–discharge characteristics. Electronically powered gadgets were used to demonstrate the practical utility of RIIBs. The remarkable electrochemical performance observed due to highly stable Fe₃O₄-MS is confirmed by ex situ characterization after the complete cycling of the cell compared to pristine electrodes, and these results strongly correlated with impedance analysis. Thus, the present work facilitates the development of an efficient cathode material for RIIBs.