Nanometric amorphous iron-based oxides of bacterial origin show a great potential as an Fe3+/Fe0 conversion anode material for lithium-ion batteries. By means of in situ Mössbauer spectroscopy, chemical states of Fe ions were examined under the discharge-charge process of the bacterial iron-oxide electrode in a lithium-ion half-cell. As for the first discharge process, the successive reduction of Fe3+ → Fe2+ → Fe0 occurred in the electrode as a function of the cell voltage. While on the charge process, Fe0 in the electrode was oxidized directly to Fe3+ without going through Fe2+.
