Investigation of the Safety Related Chemistry of the Lithium Sulfur Dioxide (Li/SO2) Battery

The safety related chemistry of the Li/SO2 battery has been further investigated. The normal discharge stoichiometry, 2 Li + 2SO2 yields Li2S2O4, has been confirmed for current densities up to 8 mA/sq. cm at room temperature, and for discharges at -25 C. Experiments have revealed that Li2S2O4 in the carbon cathode decomposes at approx. 180 C producing one mole of SO2 per three moles of Li2S2O4. The other decomposition products are S, Li2SO3, and small amounts of CO2, COS and CS2. The decomposition of forced overdischarged cathodes containing Li2S2O4 and Li appears to occur at an accelerated rate at approx, 180 C, producing larger quantities of COS, CO2 and CS2, along with SO2. The higher exothermicity of the latter composition is believed to be due to the reduction of Li2S2O4 by Li. A preliminary study of the chemistry in partially discharge and stored cells has been carried out. Li-polythionates along with Li2S2O4 have been identified on the anodes of such cells. The implication of this chemistry to the safety of the system is not yet understood, The effects of parameters such as current density, depth of discharge, electrolyte composition, and storage time and temperature on the storage chemistry of the battery remain to be assessed.