Solvent molecule mobilities in propylene carbonate-based electrolyte solutions coexisting with fumed oxide nanoparticles

Non-aqueous LiClO4 solutions kneaded with various fumed oxides (fumed silica, fumed alumina, and fumed titania) were employed as model systems of lithium ion batteries. The properties of the solid phase and Li+ ions, which affect solvent molecules, were evaluated using H-1 NMR spectroscopy and H-1 NMR relaxation time (T-1, T-2) measurements. The H-1 NMR signals of propylene carbonate (PC) molecules were influenced by the coexisting solid phase in the LiClO4-PC solution/fumed oxide nanoparticle dispersion. The mobilities of the PC molecules drastically decreased in the presence of only 1-2 vol% of the solid phase (liquid phase thickness is 15-20 nm or less), regardless of the fumed oxide employed. In the IR spectra of the PC/fumed alumina systems, the vibrations at higher wavenumbers were predominantly observed because of indirect electron-donation from the solid surface. The H-1 NMR signal detection ratios depended on the fraction of the liquid phase influenced by the solid phase. In the LiClO4-PC solution/fumed alumina systems, the H-1 NMR signal detection ratios greatly decreased because of this influence; here, the large positive zeta potential of the solid phase surface of fumed alumina attracted the PC molecules, which had local negative electric fields owing to polarization. Moreover, the T-1 and T-2 results confirmed that the interaction between the solid phase and PC molecules is much smaller than that between the solid phase and water molecules. Additionally, it was seen that the PC solution system was more significantly affected than the aqueous solution system; the network structure of the entire PC solvent is greatly affected by the addition of the Li+ ion, and the relaxation time decreased significantly.