Lithium ion conductors with novel polymeric matrices have been developed for rechargeable lithium batteries operating at ambient temperature. The polymeric electrolytes were prepared by photo-induced radical co-polymerization of mixtures of ethylmethacryl-methyl carbonate (EMMC) and diethyleneglycol dimethacrylate (DEGDM) dissolving LiClO4 with propylene carbonate (PC) as plasticizing solvent. The resulting composite films were homogeneous, flexible and self-standing. The ionic conductivity depended much on the polymer matrix structure. The conductivity increased with decreasing the degree of cross-linking and with increasing the PC content in the composite. A high conductivity of about 10(-3) S cm(-1) at room temperature was obtained for the composite containing 70 wt.% of PC-LiClO4. The Li+ transport number was measured as a function of the electrolyte composition. The electrochemical and thermal stabilities of the composites also depended on the polymer matrix structure as well as the PC content.