Lithium intercalation and copper extraction in spinel sulfides of general formula Cu2MSn3S8(M = Mn, Fe, Co, Ni)

Abstract

Cu₂MSn₃S₈(M = Mn, Fe, Co, Ni) and Cu_2–yMSn₃S₈(M = Fe, Co) spinel compounds have been studied and used as cathode materials in Li/LiClO₄(PC)/spinel sulfide cells. The pristine compounds and electrochemically inserted products have been characterized by X-ray powder diffraction (XRPD) and ¹¹⁹Sn, ⁵⁷Fe Mössbauer spectroscopy (MS). Rietveld analysis and ⁵⁷Fe MS of the copper extracted phases show that copper extraction takes place from the 8a sites of the spinel structure with oxidisation of the M element. The lithiation process involves a loss of crystallinity and a slight reduction of the host materials. Discharge–charge curves of lithium cells using pristine and deintercalated spinels as cathode materials have been compared. A better performance for the Ni- and Co-containing spinels is observed. After extraction of copper, a significant increase in cell voltage and reversibility is obtained for Co.