The behavior of lithium ions in a comb-like polymer electrolyte with a nitrile group has been characterized by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), ac impedance, Fourier transform infrared (FTIR) spectroscopy, and 7 Li solid-state NMR measurements. The comb-like copolymer is synthesized by poly(ethylene glycol-methyl ether methacrylate) (PEGMEM) and acrylonitrile (AN). FTIR spectra reveal the interactions of Li+ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the AN segments. 7 Li solid-state NMR spectra demonstrate the interactions of Li+ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the AN segments. Moreover, 7 Li solid-state NMR shows that the lithium ions are preferentially coordinated to the PEGMEM segment. The T g increases for the copolymers doped with LiClO4. These results indicate the interactions of Li+ with both PEGMEM and AN segments form transient cross-links. The dependence of the maximum conductivity on the doping lithium ion concentration was determined. The AN unit in the copolymer improves the dissociation of the lithium salt, and the mechanical strength.