Sulfonium-Based Ionic Liquids

Ionic liquids, also known as room temperature ionic liquids, room temperature molten salts, organic ionic liquids, etc., refer to salts that are liquid at room temperature or low temperature only composed of ions. With the deepening of the research and application of ionic liquids, the designability of ionic liquids has brought new opportunities for the application and development of various fields. Among many types of ionic liquids, most of the cations of ionic liquids have nitrogen atoms, phosphorus atoms and sulfur atoms as the central atoms. Among them, cation ionic liquids with sulfur atoms as the central atom are rarely studied. Sulfonium-based ionic liquids are mostly trialkylsulfoniums, which have the advantages of low viscosity, high conductivity, and strong stability, and have a wide range of applications in the electrochemical field.

Figure 1. Structure of sulfonium-based ionic liquids

Applications:

• Lithium secondary battery: Lithium secondary batteries are a complex system composed of positive electrode materials, negative electrode materials, separators and electrolytes. The performance of electrode materials, electrolytes and the compatibility of battery components will all affect the overall performance of the battery. The study of the compatibility between the electrolyte and the electrode is of great significance for optimizing the structure of the electrode and selecting a compatible electrolyte system for the development of high-performance lithium-ion batteries. As a component of lithium secondary battery electrolyte, ionic liquid has the following application methods: (1) ionic liquid + lithium salt; (2) ionic liquid + lithium salt + organic additives; (3) organic solvent + lithium salt + ionic liquid (liquid content of ionic liquid, used as an additive); (4) organic solvent + lithium salt + ionic liquid (liquid content of more ionic liquid, used as a flame retardant). Trialkylsulfonium ionic liquids have the characteristics of low viscosity and high conductivity. According to the characteristics of the matte-based ionic liquid, adding organic additives to it can enhance the charge-discharge rate and obtain better battery performance.
• Solar cell: The sulfonium-based ionic liquid has the advantages of high boiling point, low vapor pressure, wide electrochemical window, non-combustibility, high conductivity, etc., and can be used in the preparation of dye-sensitized solar cells. The addition of sulfonium-based ionic liquid will greatly improve the photoelectric conversion efficiency of the dye-sensitized solar cell and improve the cell performance.

Reference

• ShiChun Luo,ZhengXi Zhang,Li Yang. Lithium secondary batteries using an asymmetric sulfonium-based room temperature ionic liquid as a potential electrolyte[J]. Chinese Science Bulletin. 2008, 53, 1337-1342.