The diffusion coefficient and conductivity of the chemically cross-linked polymer gel electrolyte composed of poly(ethylene glycol) dimethacrylate and LiBF 4 -EC/EMC were measured in order to investigate the effect of the polymer on the nature of carrier migration in the gel. With an increase of the polymer fraction in the gel, the dissociation degree of the salt in the gel increased. This indicates that the polymer accelerated the dissociation of the salt in the progress of gelation. The dissociated cation and anion showed a different manner of change in the activation energy of diffusion with gelation. The cation, through Coulombic interaction, showed a decrease in activation energy, revealing a change in the migration mechanism to hopping on the oxygen sites linked with the segmental motion of the chains. The anion, on the other hand, showed an increase in the activation energy of diffusion. This means that the conduction mechanism essentially follows, as in solution, the mobility of the solvent correlated with enhanced viscosity due to gelation.

The development of new materials for energy conversion systems is a pressing need for dealing with the energy problem and environmental preservation of the earth. On the basis of these demands, a new type of polymer gel electrolyte for lithium secondary batteries was prepared in this research using the concept of restricting the anion mobility with the chemical interactive effect of a specific site of the polymer in the gel. The polymer having the urea group CBMEU was designed to use the electron donating and withdrawing effect of the urea group for attracting the cation and anion, respectively, for the demands of promoting the dissociation of the salt and reducing the anion mobility. To quantitatively confirm the interactive effect of the polymer site, a theoretical model was set up based on the observed dynamic values to estimate the dissociation degree of the salt and interactive force. Application of the model to the new polymer gel electrolyte (CBMEU gel) and the PEO-type gel for comparison showed that, during the progress of gelation, the interactive effect of the polymer on the ionic species promoted the dissociation of the salt and reduced the ionic mobility. The absolute value of the interactive force of the cation, γ cation, was greater than that of the anion, γ anion, for both gels. The ratio, γ cation/γ anion, of the PEO-type gel was three times larger than that of the new polymer gel electrolyte. This is attributed to the anion-attracting effect of the urea group of the CBMEU gel in contrast to only the cation-attracting behavior of the ether oxygen of the PEO-type gel. From this investigation, we proposed an idea to design the polymer gel electrolyte which provides a high dissociation degree and cation transport number based on the investigation of the dynamic properties.

Salt dissociation conditions and dynamic properties of ionic species in liquid crystal electrolytes of lithium were investigated by a combination of NMR spectra and diffusion coefficient estimations using the pulsed gradient spin-echo NMR techniques. Activation energies of diffusion (Ea) of ionic species changed with the phase transition of the electrolyte. That is, Ea of the nematic phase was lower than that of the isotropic phase. This indicates that the aligned liquid crystal molecules prepared efficient conduction pathways for migration of ionic species. The dissociation degree of the salt was lower compared with those of the conventional electrolyte solutions and polymer gel electrolytes. This is attributed to the low concentration of polar sites, which attract the dissolved salt and promote salt dissociation, on the liquid crystal molecules. Furthermore, motional restriction of the molecules due to high viscosity and molecular oriented configuration in the nematic phase caused inefficient attraction of the sites for the salt. With a decreased dissolved salt concentration of the liquid crystal electrolyte, salt dissociation proceeded, and two diffusion components attributed to the ion and ion pair were detected independently. This means that the exchange rate between the ion and the ion pair is fairly slow once the salt is dissociated in the liquid crystal electrolytes due to the low motility of the medium molecules that initiate salt dissociation.