Properties of gel electrolytes based on crosslinked copolymers of oligo(ethylene glycol) dimethacrylate and cyanomethyl methacrylate

Abstract Gel electrolyte films were prepared from oligo(ethylene glycol) dimethacrylate ((EG) n DMA, n =23) and cyanomethyl methacrylate (CyMA) by photoinitiated in situ copolymerization in the presence of oligo(ethylene glycol) dimethylether ((EG) n -DME, n =11) and LiCF 3 SO 3 . The influence of the content of CyMA in the copolymer on the ionic association of LiCF 3 SO 3 as well as on the thermal and electrochemical properties of the gels was studied. About 80 mol% CyMA in the copolymer network causes a relatively high dissociation degree of LiCF 3 SO 3 (≈50%), cationic transference numbers t + ≈0.5 and an anodic stability up to 5 V. The ionic conductivity σ shows a maximum around 20 mol% CyMA attaining σ ≈10 −4  S/cm at ambient temperature. The decrease of σ at higher contents of CyMA in the crosslinked polymer is attributed to the insertion of substantial parts of (EG) 11 DME into the copolymer network and to a chain stiffening effect of CyMA.