The primary mechanisms limiting lithium sulfur (Li-S) cell cycle life and thermal stability are discussed. Two major cycle life limiting mechanisms are identified: development of rough surface morphology on the metallic lithium anode with cycling; and depletion of lithium and electrolyte components through chemical reaction. The approach taken here to mitigate these problems, by employing physical protection, including multi-functional membrane assemblies and non-isotropic pressure is presented. Sulfur utilization of 92%, at C/5 discharge rates, increased cycle life and elimination of thermal runaway in 300 mAh Li-S cells was achieved.

Rate capability improvements of Li-S cells are reported. The main goal of this work, to achieve the maximum high power benefit from the liquid polysulfide cathode system, was realized. Higher rate capability has been achieved through reduction of the electrode stack Area Specific Resistance (ASR) to below 10 Ohm*cm2, contact design improvements, and better current distribution uniformity along the electrodes and current collectors. Maximal specific power delivered by 2.5 Ah cells at 30 A pulses was 3500 W/kg. At a continuous discharge, with specific power at ~1500 W/kg, the 2.5 Ah cells delivered specific energy in excess of 200 Wh/kg.