Capacity degradation analysis of the rechargeable iron ion batteries using post-mortem analysis and the impedance spectroscopy

We fabricated rechargeable iron ion batteries (RIIBs) using mild steel (MS) as a negative electrode, vanadium penta oxide as a positive electrode, and ferrous perchlorate hydrate in tetra-ethylene glycol dimethyl ether (TGDME)-based solvent under ambient conditions without any inert atmosphere and investigated the performance degradation. The cell exhibits similar to 120 mAh g(-1) specific capacity at a 33 mAg(-1) current density. The initial capacity fades to about 41% in 30 cycles. The cell was disassembled, and post-mortem characterizations were carried out for both electrodes. The performance degradation is attributed to the corrosion of the mild steel and the formation of multiphase iron-vanadium-based oxides at the cathode end, reducing the iron ion concentration. Thus, the present studies provide a microscopic understanding of capacity fading in iron ion batteries and may assist in designing suitable electrode materials for the improved electrochemical response.

Automated summary

Rechargeable iron ion batteries were fabricated using mild steel as the negative electrode and vanadium penta oxide as the positive electrode. The performance degradation was investigated without the need for an inert atmosphere. The capacity of the battery decreased to 41% after 30 cycles due to corrosion of the mild steel and the formation of iron-vanadium-based oxides at the cathode end.