Researchers use ionic liquid electrolyte additives to extend Li/S battery cycle life

　　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 electrolyte additives 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 (4mg/cm?) lithium-sulfur battery exhibits a stable capacity of 600mAh/g, and its cycle period is twice that of batteries using LiNO3 additives (300:150).

　　Lithium-sulfur batteries are popular due to their high energy density. At the same time, their materials are low-toxic, abundant and low-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 common electrolytes and have the potential to migrate to and from the lithium electrode during the shuttling process. During the "shuttle" process, polysulfides are continuously reduced and oxidized on the electrode without increasing capacity. This shuttling mechanism can cause many problems, including loss of active species, parasitic reactions, and the formation of insulating interfaces on lithium metal anodes.

　　To overcome these problems, it is necessary to use additives to change the electrolyte properties. These additives prevent shuttle processes by forming a stable solid electrolyte interface. The most common additive is LiNO3. However, during the circulation process, LiNO3 is continuously consumed and becomes a victim. Using ionic liquid additives can significantly reduce shuttle reactions and improve Coulombic efficiency. At the same time, the thermal stability of the electrolyte is improved and the flammability is reduced. In addition, Py1,4TFSI can promote the formation of solid electrolyte polymerization interface instead of inorganic interface, which helps to reduce sulfur deposition and improve lithium-sulfur battery life.

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