Iron anodes for rechargeable alkaline batteries
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Rechargeable low-cost alkaline batteries may become attractive non-flammable alternatives to lithium-ion (Li-ion) batteries for applications where achieving the highest energy density is less critical than safety, environmental friendliness and low cost of energy storage. The broad abundance and extremely low price of iron (Fe) make it particularly attractive as rechargeable anode material for aqueous batteries. By conducting systematic studies on Fe anodes using cyclic voltammetry and a broad range of state of the art characterization tools, four distinct stages of Fe anode evolution were revealed: development, retention, fading and failure, where each stage is associated with very specific changes in the morphology and phase of Fe anodes. The particle fragmentation with the consequent gain in the surface area resulted in the increase in the Fe anode capacity during the initial cycles of deep charge-discharge. Most importantly, it was discovered that the irreversible formation of monocrystalline maghemite (γ-Fe2O3) with low reactivity is responsible for the eventual Fe anode capacity fading. Along with the base study on Fe anodes in alkaline conditions, the extended research observed how the individual factor in cell operation influences the electrochemical behavior, morphology evolution and phase transition of electrodes. A variety of components were independently adjusted: potential range, electrolyte concentration, scan rate, and additive content. The author hopes that this study will be a cornerstone for both the fundamental understanding of Fe anodes in alkaline conditions and the future development of low-cost rechargeable alkaline batteries for grid energy storage.