Transition metal sulfides as cathodes for secondary lithium batteries—II. titanium sulfides

Abstract

Titanium disulfide (Ti 1+x S 2)and trisulfide (TiS 3) were prepared by reaction of the elements. They were characterized by scanning electron microscopy and by X-ray diffraction. Both sulfides are electrochemically active and show good reversibility. Discharge cycles in propylene carbonate and methyl acetate are characterized by relatively flat voltage plateaus at about 2.0 V vs lithium. Limiting capacities approach 1 and 3 equivalents of charge per mole of TiS 2 and TiS 3, respectively. Capacities between 0.8 and 0.4 equivalents per mole of TiS x were obtained during extensive cycling ( > 300, 100% depth, C/3 rate) with unoptimized electrodes. Capacities greater than 1 eq /TiS 3were observed during the initial cycles. The reaction mechanism involves Li + ion intercalation into the layer structure of the sulfide. The measured capacities translate into energy densities of 360 and 180 Wh/kg based on active materials and actual cell voltages. TiS 2 appears to be the most attractive material for use in secondary batteries.