Iron oxides or hydroxides are highly desirable “green” conversion battery electrodes owing to their abundance, multiple oxidation states, low cost, and environmental beneficence. However, their low storage capacity and poor cycling life have been lingering concerns due to the substantial hydrogen evolution on charging. Moreover, conventional AIBs relying on a conversion storage mechanism at the Fe anode have limited faradaic efficiency 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 phase information is provided by in operando synchrotron X-ray diffraction (XRD) during the redox cycling. X-ray photoelectron spectroscopy (XPS) and electrochemical measurements supplemented with the classical molecular dynamics (CMD) simulations reveal that adding Na2SiO3 results in increased Na ions in the solvation shell. Theoretical calculations (DFT) also supported that the (SiO3)* adsorption is more energetically favored than the (OH)* on the Fe(OH)2 surface. This study contributes to developing new alkaline battery systems which could pave a path to realizing green battery systems for efficient energy storage

Chemistry of improved redox performance of alkaline iron batteries by silicate additive

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