Lithium polyelectrolyte-ionic liquid systems

Novel lithium polyelectrolyte-ionic liquid systems, using poly(lithium 2-acrylamido-2-methyl propanesulfonate) and its copolymer with N-vinyl formamide, have been developed in this work. The ionic liquid used in this work is from a novel family of methanesulfonate ionic liquids, specifically N-hexyl-N,N,N-tributyl ammonium methanesulfonate, which is chosen because of the similarity with the anionic functionality of the polymer. The ionic liquid thereby acts as a good solvating medium for the polyelectrolyte. It was found that the copolymer-based polyelectrolyte-ionic liquid system exhibits two to three times higher conductivity than that of the homopolymer system. The results of solid-state Li-7-NMR have shown that lithium cations in the copolymer system are mobile whereas in the homopolymer, only a fraction appears to be mobile even at 80 degreesC. This supports the hypothesis that separation of the charged groups on the polymer backbone via the co-monomer encourages the dissociation of lithium cations from the sulfonate groups bonded to the polymer chains, and hence, results in an increase in conductivity of the polyelectrolyte material. (C) 2002 Elsevier Science B.V. All rights reserved.