Characterization of defect thiospinels Cu1-x[Ti2 ]S4 (0<x≤0.93)

Article abstract of DOI:10.1016/0025-5408(89)90118-9

The thiospinel framework [Ti₂]S₄ represents a metastable host selective to Li insertion/extraction reactions in three dimensions that is of technical interest as a battery-cathode material. Synthesis is performed by oxidative extraction of copper from Cu[Ti₂]S₄, but complete extraction of copper from a stoichiometric starting material has not been possible. The authors report structural, transport, magnetic, ⁶⁵Cu NMR, and electrochemical data for the defect-thiospinel systems Cu_1-x[Ti₂]S₄, 0 < × ≤ 0.93, obtained by extracting copper with I₂ at 45°C. X-ray data show a linear decrease in lattice parameter with increasing x up to 2.4% (7.2% by volume) at Cu_0.07[Ti₂]S₄. Neutron diffraction shows that the residual copper atoms of the x = 0.92 sample remain in the tetrahedral 8a sites of the spinel framework. Electrochemical lithiation of Cu[Ti₂]S₄ and Cu_0.07[Ti₂]S₄ gave an open-circuit voltage versus lithium that is higher in the former than it is in the latter. These several properties, including the limiting composition x = 0.93, are accounted for by constructing semi-empirical band diagrams for Cu[Ti₂]S₄ and Cu_0.07[Ti₂]S₄.