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^-7 S cm ^-1 was obtained for the PAE₈-co-E₃SO ₃Li with a salt concentration of EO/Li = 40. The conductivity of PAE₈-g-E₃SO₃Li is lower than that of PAE ₈-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 50 wt.% of plasticizer, PC/EMC (1/1, v/v), to PAE₈-g-E₂SO ₃Li 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 75 wt.% PC/EMC (1/1, v/v) was cycled at a current density of 100 μA cm^-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.