Alternating copolymers for novel polymer electrolytes: the electrochemical properties

Gel electrolyte films were prepared on the basis of alternating copolymers of maleic anhydride (MAN) and oligo(ethylene glycol),divinyl ether ((EG)(4)DVE) by in situ photopolymerization of the monomers in the presence of oligo(ethylene glycol)(11)dimethylether ((EG)(11)DME) and LiCF3SO3. Additionally, terpolymers of MAN and (EG)(4)DVE with butylvinyl ether (BVE) or ethoxytri(ethylene glycol)methacrylate (EtO(EG)(3)MA) were used as polymer matrix for gel electrolytes because of their lower network density. All these gel electrolyte films are heterogeneous materials. The ionic association was studied by Raman spectroscopy. The content of free anions and the relative intensity of the LiO6 breathing mode was found to be comparable to the behavior detected for the corresponding liquid electrolyte. The self-diffusion of charge carriers and plasticizer was studied by PFG-NMR. The results indicate, that this technique mainly records the self-diffusion ire the liquid phase of the studied heterogeneous gel electrolyte systems, because a low correlation between conductivity and self diffusivity and a low dependence of the self-diffusivity on the composition of the system were found. Maximum conductivities of 5 x 10(-5) S cm(-1) at room temperature with an Arrhenius type temperature dependence were observed for terpolymer systems with 75 wt% of (EG)(11)DME. The cationic transference numbers were higher than 0.5. These gel electrolytes show a higher anodic decomposition voltage and an increased Li plating stripping efficiency compared with gel electrolyte systems on the basis of poly((EG)(n)DMA). (C) 2000 Elsevier Science Ltd. All rights reserved.