High Performance Iron Electrodes with Metal Sulfide Additives

Iron-based alkaline rechargeable batteries are promising candidates for large-scale energy storage applications owing to their low cost, robustness and environmental-friendliness. However, the widespread deployment of iron-based batteries has been limited by the low charging efficiency and poor discharge rate capability of the iron electrode. Our previous efforts on iron electrodes based on carbonyl iron powder and iron (II) sulfide have shown promise in overcoming these limitations. With the goal of understanding the role of sulfide additives, in this study, we have compared the performance of iron electrodes with iron (II) sulfide, iron (II) disulfide, copper (I) sulfide and zinc sulfide. The electrode containing zinc sulfide outperformed all other electrodes with a remarkable faradaic efficiency of 95% at C/2 rate and a specific discharge capacity close to 0.24 Ah g −1 at 1 C rate. The electrode did not lose any capacity for 750 cycles of repeated deep discharge at C/2 charge and discharge rates. Further, these electrodes could be cycled at 55 degrees Celsius with no noticeable change in performance. We attributed the excellent performance of zinc sulfide containing electrode to the low solubility of zinc sulfide in the electrolyte and the stability of zinc sulfide towards electro-reduction under the operating conditions of the iron electrode. These insights indicate that zinc sulfide is a promising additive for designing highly efficient and robust iron electrodes for alkaline nickel-iron and iron-air batteries.