AN FE-57 MOSSBAUER STUDY OF THE INTERMEDIATES FORMED IN THE REDUCTION OF FES2 IN THE LI/FES2 BATTERY SYSTEM

Fe-57 Mossbauer spectroscopy has been used to study the intermediates formed at the FeS2 cathode during room-temperature discharge in the Li\LiClO4-propylene carbonate\FeS2 cell. Mossbauer spectra recorded at 4.2 K provided evidence for the formation of Li3Fe2S4 and another lithiated phase, similar to but not exactly the same as Li2FeS2. Small particles of superparamagnetic iron were also formed early in the discharge. When LiAsF6 was the electrolyte, no intermediates were detectable and rapid reduction to small particles of iron occurred. Chemical lithiation of FeS2 with n-BuLi in hexane produced a mixture of reduction products similar to that observed for the Li\LiClO4-propylene carbonate\FeS2 cell.