New gel polyelectrolytes for rechargeable lithium batteries

New polyelectrolytes were synthesized by grafting the allyl group containing lithium salt, lithium bis(allylmalonato)borate (LiBAMB), onto poly[pentaethylene glycol methyl ether acrylate-co-allyoxyethyl acrylate] through hydrosilylation chemistry. Gel polyelectrolytes were obtained by adding 50 wt.% of different 1/1 (wt/wt) mixtures of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC) and tetraethyleneglycol dimethyl ether (TEGDME). The highest ambient conductivity was 2.7 x 10(-8) S cm(-1) for the dry single ion conductors and 7.9 x 10(-6) S cm(-1) for the gel single ion conductor containing 50 wt.% of EC/DMC (1/1, wt/wt), and both are obtained for the sample with an EO/Li ratio of 40/1. The conductivity order of gel electrolytes containing the same amount of different mixed solvents suggests that the conductivity of the gel is more determined by the dielectric constant rather than by the viscosity of the solvent. The preliminary Li/Li cycling profile of a dry single ion conductor is encouraging, as almost no concentration polarization and relaxation was observed. However, some fluctuation of potential occurred, which might be due to the reactions of the electrolyte on the surface of lithium metal. (C) 2004 Elsevier B.V. All rights reserved.