Synthesis and characterization of single-ion graft copolymer electrolytes

A microphase-separating single-ion conductor, poly[(oxyethylene) ₉ methacrylate-ran-lithium methacrylate]-graft-poly(dimethyl siloxane), P(OEM-r-LiMA)-g-PDMS, was prepared by lithiating a precursor polymer synthesized by free radical methods using commercially available macromonomers. This material possessed a low conductivity, stemming from high ion-pairing interactions that severely restricted the number of charge carriers available for conduction. Subsequent conversion of the LiMA units via the addition of BF ₃, a Lewis acid, resulted in a 2 orders-of-magnitude rise in conductivity, a gain that could be attributed to a large increase in the number of mobile cations. By blending this material with uncharged POEM-g-PDMS, the room-temperature conductivity was optimized to 7 × 10 _-6 S/cm. With a lithium transference number of unity, these materials exhibit higher dc-measured conductivities at elevated currents than their salt-doped counterparts and are electrochemically stable to ∼4.5 V.