Review of Electrolyte for Lithium Sulfur Battery

Of the high energy density chemical power systems currently being considered, lithium/sulfur (Li/S) batteries which use elemental sulfur as the cathode and lithium metal as the anode, are attracting increased attention in recent decades. Li/S batteries have a high energy density (2600 Wh/kg in theoretical, about 400 Wh/kg in practice nowadays), consist of abundant raw materials, are low cost and environmentally friendly. Although the rechargeable Li/S batteries possess more advantages over the conventional lithium ion batteries, the practical use faces with a variety of problems such as low utilization of sulfur and bad cycle life. Central to the operation of Li/S batteries are polysulfide anions (S-n(2-), 4 <= n <= 8)], which are intermediate products generated during the electrochemical reduction process. These anions have high solubility in organic electrolytes. On the one hand, these anions typically diffuse to the lithium anode according to a concentration gradient and directly react with the anode. This diffusion causes an internal shuttle phenomenon and significantly corrodes the anode, which decreases active material utilization during the discharge process and reduces its cycle life. On the other hand, there are residual Li2S2 and/or Li2S on the surface of sulfur cathode and Li anode even at 100% depth of charge. The formation of Li2S2 and Li2S increasing with cycling results in active material loss. These drawbacks have seriously retarded industrial production of Li/S batteries. In this paper, combining with the works of our research team, the main research directions and the latest development of the electrolyte to enhance the cycle performance of Li-S batteries are reviewed from the aspects of the composition of the liquid electrolyte, the additives in liquid electrolyte, the polymer electrolyte and the inorganic electrolyte. At the meanwhile, the principle, the preparation of electrolyte, the influence on the performance of Li-S batteries, and problem in each research are analyzed. Finally, the further development of the electrolyte in Li-S battery is discussed.