57Fe Mossbauer study of the electrochemical reaction of lithium with triclinic iron vanadate

The electrochemical reaction of lithium with triclinic FeVO4 (a = 6.714(1) Angstrom, b = 8.060(2) Angstrom, c = 9.352(2) Angstrom, alpha = 96.678(1)degrees, beta = 106.641(1)degrees, and gamma = 101.523(1)degrees, P-1) has been investigated by means of Fe-57 Mossbauer spectroscopy in order to complement the previous X-ray diffraction and X-ray absorption near edge structure studies on the same system. A complex Fe-III --> Fe-II --> Fe-0 or Fe-III --> Fe-II, Fe-0 reduction process has been detected upon the first discharge of the battery down to 0.02 V, with in addition the iron reoxidation during the next charge step. A mechanism based on lithium adsorption is proposed in order to explain this unexpected behavior.