a Novel Sulfur Electrode for the Lithium Ion/Sulfur Battery

The lithium/sulfur battery has many attractive properties. In addition to a high theoretical energy density (about 2600 Wh/kg), it is made of relatively low-cost and non-poisonous materials. However, it has several disadvantages which result from the solubility of sulfur and of lithium polysulfides (PS) in the battery electrolyte. These include self-discharge, short cycle life and low Coulombic efficiency. In addition, the use of a metallic lithium anode poses safety and reversibility problems. The lithium-ion battery is assembled in the discharged state. Thus, in the case of the lithium ion/sulfur battery, lithium sulfide must be incorporated into the cathode prior to cell assembly. Up to now, a very limited number of papers have been published on the assembly of the lithium/sulfur battery in the discharged state (including: Scrosati, Cai, Hayash, Yang). Another problem related to this battery is the large volume changes of the cathode during cycling. The cathode material expands on discharge and contracts on charge. The molar volume of Li₂S, is about 80% greater than that of sulfur. This leads to mechanical stress at the cathode and contributes to more rapid degradation of capacity. A novel strategy to overcome the degradation of the sulfur electrode will be described and discussed. Preliminary results collected from cycling of coin cells, having 1 to 4mAh/cm² of sulfur, over a voltage range of 1.5 to 2.8V, show a very stable capacity and very high current efficiency - nearly 100%. The high current efficiency clearly Indicates a strong depression of the shuttle current resulting from the solubility of the polysulfides in common Li/S batteries.