Researchers use ionic liquid electrolyte additives to extend the cycle life of Li/S batteries

According to foreign media reports, researchers from Chalmers University of Technology in Sweden and Gyeongsang National University in South Korea used ionic liquid Py1,4TFSI as an electrolyte additive to extend the cycle life of lithium-sulfur batteries.

Adding ionic liquids to the electrolyte can enhance the stability of the solid electrolyte interface (SEI), reduce flammability, and improve battery safety by adjusting the concentration. Using an ionic liquid-based electrolyte, a high sulfur loading (4 mg/cm?) lithium-sulfur battery exhibits a stable capacity of 600 mAh/g, and its cycle life is twice that of a battery using LiNO3 additive (300:150).

Lithium-sulfur batteries are favored due to their high energy density. At the same time, their materials are low in toxicity, abundant and low in cost. Lithium-sulfur batteries are based on conversion reactions and consist of a sulfur-containing positive electrode and a lithium metal negative electrode. The reaction mechanism includes the formation of a series of lithium polysulfides (Li2SX, 3≤X≤8). These polysulfides, especially long-chain polysulfides, can be dissolved in ordinary electrolytes and have the potential to migrate to or from the lithium electrode during the shuttling process . During the "shuttling" process, the polysulfides are continuously reduced and oxidized on the electrode without increasing the capacity. This shuttling mechanism can cause many problems, including the loss of active materials, parasitic reactions, and the formation of insulating interfaces on the lithium metal negative electrode.

为了克服这些问题，需要使用添加剂改变电解质性质，这些添加剂通过形成稳定的固体电解质界面，防止穿梭过程产生。最常见的添加剂是LiNO3，然而在循环过程中，LiNO3不断被消耗，成为牺牲品。使用离子液体添加剂，可以显著降低穿梭反应，提高库仑效率。同时，提高电解质的热稳定性，降低可燃性。另外，Py1,4TFSI能够促进固体电解质聚合界面的形成，而不是无机界面，有助于减少硫沉积，提高锂硫电池寿命。