LITHIUM SULFUR BATTERY - OXIDATION REDUCTION-MECHANISMS OF POLYSULFIDES IN THF SOLUTIONS

The redox processes of Li//2S//n (6 less than equivalent to n less than equivalent to 12) at a glassy carbon electrode in THF was studied by programmed cyclic voltammetry in the range of plus 1300 to minus 2000 mV (vs. polysulfide reference electrode) at sweep rates of 2-200 mV/s. One anodic and up to three cathodic peaks were detected. The anodic peak seems to result from the oxidation of all PS's through the same intermediate to elemental sulfur. The first cathodic peak is caused by the reduction of all PS (n greater than 6) to Li//2S//6 in a diffusion controlled reaction. The second reduction peak most likely arises from the reduction of S//6**2** minus to S//5**2** minus . This is apparently preceded by a chemical step. The third reduction peak is caused by the reduction of S//5**2** minus to S//2**2** minus or S**2** minus or a mixture of both in a diffusion-controlled reaction.