ELECTROCHEMICAL LITHIUM INSERTION INTO IN16SN4S32 AND CU4IN20S32 SPINEL SULFIDES

Cu2In20S32 and In16Sn4S32 spinel compounds are used as cathode material in Li/LiClO4(PC)/sulphide cells. For both compounds, incremental capacity vs. voltage curves and diffusion coefficients vs. composition curves showed two consecutive steps of intercalation. The first step occurs between x=0 and x=8 for both compositions and at a higher voltage for the tin compound. For larger x values an extended plateau is observed in the voltage vs. composition curves. Cation redistribution is observed during the first insertion step leading to a displacement of In ions from either 8a or 16d sites to another set of octahedral 16c sites in the Fd(3) over bar m space group. This process is more marked in the copper compound owing to the absence of tetrahedral vacancies in the pristine phase and conditions a lower diffusivity of lithium ions.