Département de chimie moléculaire

The Li/S battery is a promising electrochem. system that has a high theor. capacity of 1675 mAh/g-1, but its discharge mechanism is known to be a complex multistep process. As the active material dissolves during cycling, this discharge mechanism was studied through the electrolyte characterization. Using HPLC, UV-visible absorption, and ESR spectroscopies, the authors studied the electrolyte compn. at different discharge potentials in a TEGDME-based electrolyte. The authors propose a possible mechanism for S redn. consisting of three steps. Long polysulfide chains are produced during the 1st redn. step (2.4-2.2 V vs. Li+/Li), such as S82- and S62-, as evidenced by UV and HPLC data. The S3·- radical can also be found in soln. because of a disproportionation reaction. S42- is produced during the 2nd redn. step (2.15-2.1 V vs. Li+/Li), thus pointing out the gradual decrease of the polysulfide chain lengths. Finally, short polysulfide species, such as S32-, S22-, and S2-, are produced at the end of the redn. process, i.e., between 2.1 and 1.9 V vs. Li+/Li. The pptn. of the poorly sol. and insulating short polysulfide compds. was evidenced, thus leading to the pos. electrode passivation and explaining the early end of discharge. [on SciFinder(R)]