Electrochemical lithium insertion in a cation deficient thiospinel Cu3.31GeFe4Sn12S32

Abstract

We present the characterization and the electrochemical study of the cation deficient thiospinel Cu_3.31GeFe₄Sn₁₂S₃₂ 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 Fe^II to Fe^III. The discharge curve shows the presence of several insertion steps. The reduction of Fe^III to Fe^II 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 Sn^IV to Sn^II reduction takes place.