Conductivity study of diacrylate-based gels Part III. Influence of the nature of the constituents and improvement of a theoretical model of ionic transport

Several gel electrolytes were prepared by incorporation of a liquid electrolyte in a polymer diacrylate network. The liquid electrolytes were solutions of lithium trifluoromethane sulfonate (LiTF) or lithium bis(trifluoromethane sulfone) imide (LiTFSI) in gamma butyrolactone (BL), gamma valerolactone (VL) and an optimized mixture of ethylene carbonate (EC) and 2-methoxyethyl ether (DG: diglyme) of molar percentage: EC/DG (45:55). The monomer diacrylates were: 1,3-butanediol diacrylate (131313), 1,3-butanediol dimethacrylate (BDDM), ethylene glycol dimethacrylate (EGDM) and tetraethylene glycol diacrylate (TEG). The variation of conductivity with the polymer, solvent and lithium salt contents and with temperature was studied. The volumetric weight of these gels were also determined at room temperature. The experimental results were related to the competitive salt solvent and salt polymer interactions, quantified through a theoretical model of ionic conductivity. The ionic transport in the gel electrolytes was assumed to be of the liquid type. The decrease in ionic conductivity of the liquid electrolyte, enclosed in the polymer network, relative to the "free" liquid solution, is due to the fixation of some fraction of the salt on the polymer, to increase of the viscosity of the media and to a tortuous path for the ion migration. From the proposed model, the conductivity variations with the gel composition as well as with the nature of the constituents are explained. (C) 2003 Elsevier Science B.V All rights reserved.