Structural Characterization and Electrochemical Reactions with Lithium of Cu2CoTixSn3-xS8 Solid Solutions

The synthesis, structural determination, and electrochemical studies of Cu{sub 2}CoTi{sub x}Sn{sub 3 {minus}x}S{sub 8} solid solutions are reported. The evolution of the cubic spinel unit cell parameter with x shows two regions which are defined by the increasing covalency of the Ti-S bonds and the radii of the metal ions present in the solid. An increase in the isomer shift of the {sup 119}Sn Moessbauer spectra of these solids agrees with this interpretation. The solid solutions are used as active cathode materials in lithium cells. The discharge shows a complex reduction effect which is associated with the decrease in the oxidation state of Sn{sup 4+} and Ti{sup 4+} ions, accompanied by deep structural changes which end in the complete amorphization of the solid and the occurrence of tin in the metallic state. The extended discharge of the lithium cells leads to a good cycling behavior in galvanostatic experiments carried out in the 0--2.3 V interval, with capacities close to 400 mAh/g after 10 cycles.