Additive-Driven Alternative Redox of Iron Oxides for High-Capacity and Reversible Aqueous Batteries

Aqueous alkaline iron (Fe) batteries (AIBs) are promising energy storage systems because of the distinctive merits of Fe materials, including high abundance, low cost, nontoxicity, and multiple valent states. Conventional AIBs relying on a conversion storage mechanism at the Fe anode have limited faradaic efficiency and storage capacity due to the formation of electrochemically inert Fe₃O₄ upon discharging Fe(OH)₂ in the alkaline solution. Herein, we report the study of the redox behavior of iron (II, III) oxide materials containing α-FeOOH and Fe₃O₄ in NaOH solution with a low concentration silicate introduced to enable the one-charge transfer Fe(OH)₂/FeOOH reaction in the AIB anode and mitigate Fe₃O₄ formation. The system with silicate added exhibits an enhanced storage capacity and cycling life. Supported by experimental evidence, molecular dynamics simulations reveal that silicate additives strongly interacted with Fe(OH)₂ surface, inhibiting the water transport and favoring Fe(OH)₂/FeOOH over Fe(OH)₂/Fe₃O₄ conversion. This study paves a path to realizing green battery systems for efficient energy storage.