Synthesis of poly(ionic liquids) both in solution and on surface of silica nanoparticles as novel quasi-solid state electrolytes.

摘要

Ionic liquids (ILs) are compounds composed of cations and anions with low melting point, usually below room temperature. ILs have some unique properties, such as high intrinsic ionic conductivity, non-volatility, non-flammability, thermal and chemical stability. Based on these properties, ILs have been considered as promising electrolyte materials. However, the sealing and fabrication of IL electrolytes remained a challenge in industry applications due to their liquid property. One way to solve this problem was to polymerize the ILs. Compared to ILs, poly(ionic liquids) (PILs) have enhanced mechanical stability, improved processability and durability. However, PILs have their own drawback, which is that once polymerized, the ionic conductivity of PILs drops a lot, usually several orders of magnitude lower than that of their monomers. To successfully apply PILs as electrolyte materials, the ionic conductivity must be improved.;To have high conductivity, the PILs synthesized must have low Tgs. A series of low Tg polymer polyepichlorohydrin (polyEPCH) with molecular weight ranging from 22,000 to 76,000 were synthesized by anionic ring-opening polymerization. After quaternarization and ion exchange, a novel family of PIL electrolytes were synthesized and characterized. The PILs obtained showed not only low T g, high conductivity and good thermal stability, but also a high viscosity, which is beneficial in fabricating process.;To get even higher conductivity, another low T g monomer, 2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl)oxirane (ME 3MO), was synthesized and randomly copolymerized with EPCH by cationic ring-opening polymerization. The resulting copolymer (polyEPCH-co -polyME3MO) was quaternarized and ion exchanged to form a PIL copolymer (polyGBIMTFSI-co-polyME3MO). By tuning the monomer composition, a series of PIL copolymers from polyGBIMTFSI- co-polyME3MO-8/1 to polyGBIMTFSI-co-polyME 3MO-1/4 were synthesized. All PIL copolymer samples showed higher ionic conductivity than PIL homopolymer. Among them, polyGBIMTFSI-co-polyME 3MO-1/1 showed the highest ionic conductivity (around 1.2 x 10 -4 S/cm at 25 °C), which was more than 1 order of magnitude higher than PIL homopolymer (9.3 x 10-6 S/cm at 25 °C).;We also synthesized PILs on the surface of silica nanoparticles via surface initiated atom transfer radical polymerization (ATRP). A gel electrolyte was formed by dispersing the PIL/silica nanocomposites in 1-methyl-3-propylimidazolium iodide and heating for 1 h. The gel electrolyte was used as a quasi-solid state electrolyte in DSSC and a 0.37 % conversion efficiency was achieved.