Precipitation of CoS vs ceramic synthesis for improved performance in lithium cells

An amorphous cobalt sulfide was synthesized by precipitation from aqueous solutions of cobalt nitrate and sodium sulfide, and its chemical composition, COS0.92.0.9H(2)O, determined from energy dispersive X-ray analysis and thermogravimetric data. X-ray photoelectron spectroscopy measurements confirmed the valence state of Co to be Co2+ bound to S2- and O in H2O Molecules. This amorphous sulfide reacts reversibly with lithium in lithium cells in several steps, which exhibited some coincidence with those observed for crystalline CoS0.89, as revealed by step potential curves. However, the cycling properties are rather different. Thus, the capacity of the cell made from the crystalline compound fades rapidly with cycling; by contrast, the amorphous compound exhibits better capacity retention upon cycling, with capacity values almost four times greater than those for cells made from CoS0.89. Supplementary experimental results are consistent with the improved performance being a result of the role played by the water content rather than the amorphous structure of the compound. (C) 2008 The Electrochemical Society.