Elevating kinetics of passivated Fe anodes with NH4Cl regulator: Toward low-cost, long-cyclic and green cathode-free Fe-ion aqueous batteries

The environment benignity and battery cost are major concerns for grid-scale energy storage applications. The emerging dendrite-free Fe-ion aqueous batteries are promising due to the rich natural abundance, low cost and non-toxicity for Fe resources. However, serious passivation reactions on Fe anodes and poor long-term cyclability for matched cathodes still stand in the way for their practical usage. To settle above constraints, we herein use NH4Cl as the electrolyte regulator to elevate the reaction kinetics of passivated Fe anodes, and also propose a special cathode-free design to prolong the cells lifetime over 1,000 cycles. The added NH4Cl can erode/break inert passivation layers and strengthen the ion conductivity of electrolytes, facilitating the reversible Fe plating/stripping and Fe2+ shuttling. The highly puffed nano carbon foams function as current collectors and actives anchoring hosts, enabling expedite Fe2+ adsorption/desorption, FeII/FeIII redox conversions and FeIII deposition. The configured rocking-chair Fe-ion cells have good environmental benignity and decent energy-storage behaviors, including high reactivity/reversibility, outstanding cyclic stability and far enhanced operation longevity. Such economical, long-cyclic and green cathode-free Fe-ion batteries may hold great potential in near-future energy-storage power stations.