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 Cu2–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.