NMR, conductivity and DSC study of Li transport in ethylene glycol/citric acid polymer gel

In this present paper the influence of viscosity on the ionic dynamics of polymer gel electrolytes prepared by the Pechini polymeric precursor method is investigated by impedance spectroscopy, differential scanning calorimetric (DSC) and NMR techniques. Polymer gel electrolytes are formed by ethylene glycol (EG) and citric acid (CA) and lithium perchlorate. Room temperature conductivity of the order of 2.3 × 10⁻⁴ S/cm was obtained for the sample of EG/CA:LiClO₄ with lower viscosity (η = 197 cP). The results show that the ionic conductivity of the electrolytes increases for decreasing viscosity. Proton (¹H) and Lithium (⁷Li) NMR lineshapes and spin-lattice relaxation times were measured as a function of temperature and viscosity (197-868 cP). The ⁷Li relaxation process was found to be dominated by quadrupolar couplings. The activation energy extracted from the ¹H and ⁷Li relaxation data (∼0.23 eV) was found to be independent of the viscosity of the gel electrolyte. The ⁷Li NMR relaxation results indicate an increase of the lithium ion mobility with decreasing viscosity.