Electrochemical lithium insertion in a cation deficient thiospinel Cu3.31GeFe4Sn12S32
Abstract
We present the characterization and the electrochemical study of the cation deficient thiospinel Cu3.31GeFe4Sn12S32 as a cathodic material in lithium cells. The pristine compound has a spinel-related structure, where the copper defect in the tetrahedral site induces a partial oxidation of FeII to FeIII. The discharge curve shows the presence of several insertion steps. The reduction of FeIII to FeII and a copper extraction takes place during the first and second steps, respectively. Moreover, the lithium insertion originates a first-order spinel to rocksalt transition, indicated by the third step of the discharge curve. Finally, at low voltages (<1.65 V) a SnIV to SnII reduction takes place.