Electrochemistry of a nonaqueous lithium/sulfur cell

The development and the electrochemistry of low-rate laboratory prototype Li/S button cells is described. The cell consists of a lithium anode, a porous catalytic current collector which is loaded with sulfur, and an organic solvent containing lithium polysulfide. The case of the cell was made from stainless steel and sealing was accomplished by the use of a combination of organic elastomer and cement (with no crimp). After 3 weeks storage at 60 °C, the button cells lost only about 1 mg of weight. The lithium polysulfide reacts with the Li anode to form a passivating layer which acts as a solid electrolyte interphase (SEI). The e.m.f. of the cells changes from 2.38 to 2.15 V depending on the composition of the solutions. Cells exhibit flat discharge curves at low drains. The energy density of the cells is 730 W h/kg or 900 W h/l at room temperature and 950 W h/kg or 1200 W h/l at 60 °C (calculated on the basis of all cell components, excluding the case). Storage and discharge tests at 60 °C show a capacity loss of 2 - 5% per month depending on solution composition. This indicates a shelf life of at least 10 years at room temperature.