Systems containing lithium bis(trifluoromethylsulfonyl)imide (TFSI), nona(ethylene glycol) dimetacrylate (EODM), and propylene carbonate (PC), or dimethyl sulfoxide (DMSO) in different concentrations were studied using H-1, Li-6, and Li-7 and C-13 1D and 2D single quantum and double quantum filtered spectra, the corresponding longitudinal, transverse, rotating frame and T-1(3) or T-2(3) relaxations, Raman spectra, and quantum mechanical (MNDO up to ab initio SCF 6-31G and DFT) calculations. The mean, local, and exchange mobilities of the lithium ion as well as the apparent equilibrium constants of coordination to EODM (two stages) and the solvent were established. According to the study, the solvent in a gel electrolyte acts not only as a plasticizer but also as a competitive ligand loosening the coordination bond of the lithium ion to the poly(ethylene oxide) moiety. DMSO was found to be substantially more effective in this respect than PC.