Comb-shaped single ion conductors based on polyacrylate ethers and lithium alkyl sulfonate
Comb-shaped single ion conductors have been synthesized by (1) sulfonation of small molecule chloroethyleneglycols, which, after ion exchange to the Li+ salt were then converted to the acrylate by reaction with acryloyl chloride and copolymerized with polyethylene glycol monomethyl ether acrylate (Mn = 454, n = 8) (PAE8-co-E3SO3Li); (2) sulfonation of chloride end groups grafted on to prepolymers of polyacrylate ethers (PAE8-g-E nSO3Li, n = 2, 3). The highest conductivity at 25°C of 2.0 × 10−7Scm−1 was obtained for the PAE8-co-E3SO3Li with a salt concentration of EO/Li = 40. The conductivity of PAE8-g-E3SO3Li is lower than that of PAE8-co-E3SO3Li at similar salt concentrations, which is related to the incomplete sulfonation of the grafted polymer that leads to a lower concentration of Li+. The addition of 50wt.% of plasticizer, PC/EMC (1/1, v/v), to PAE8-g-E2SO3Li increases the ambient conductivity by three orders of magnitude, which is due to the increased ion mobility in a micro-liquid environment and an increase concentration of free ions as a result of the higher dielectric constant of the solvent. A symmetrical Li/Li cell with an electrolyte membrane consisting of 75wt.% PC/EMC (1/1, v/v) was cycled at a current density of 100μAcm−2 at 85°C. The cycling profile showed no concentration polarization after a break-in period during the first few cycles, which was apparently due to reaction of the solvent at the lithium metal surface that reacted with lithium metal to form a stable SEI layer.