The NaCrS2 cathode material. IV. Effect of vanadium substitution on its physical properties and electrochemical performance in secondary Li cells

The introduction of 0.10–0.15 eq mol of V3+ into the layered structure of NaCrS2 substantially raises its conductivity and lowers its magnetic susceptibility without changing its crystal lattice parameters or nucleating a new phase, this implying considerable changes in the electron band structure of the dichalcogenide. When used as a cathode in a Li cell the partially desodiated vanadium substituted thiochromite exhibits a considerable increase in the equilibrium potential as compared to that of the nonsubstituted compound. Chemical and X-ray analysis reveal that in single phase samples (V3+⩽0.15 eq/mol) practically all the V3+ ions are incorporated into the disulfide slabs, replacing equivalent amounts of Cr3+. It is demonstrated that the partially desodiated host structure Na0.2Cr0.9V0.1S2 can reversibly intercalate up to 1 eq Li/mole. The energy density, power capability and cycle life of this layered compound make it an attractive cathode material for secondary Li cells.