Structural modifications related to lithium intercalation into iron thiospinels

Cu2FeSn3S8 and Cu2FeTi3S8 spinel compounds have been used as electrode materials in lithium cell. The lithium insertion mechanism was studied by characterization of chemically lithiated (via n-butyllithium) samples using the X-ray powder diffraction and the 57Fe Mössbauer spectroscopy. The intercalation process was correlated with the electrochemical behavior. Rietveld analysis of the tin based phase shows a weak extraction of copper between 0 and 2 lithium per formula. Along this extraction, a migration of iron cations from octahedral to tetrahedral sites was observed. Regarding titanium based thiospinel, the reduction of titanium occurs in two steps. Firstly titanium (IV) is reduced to Ti (III). Secondly, following the five already intercalated lithium, the Ti reduction process is occurring towards a lower oxidation state Ti(II).