ＮＭＲで観測する高分子電解質中のイオンの運動と拡散

Abstract

PEO-based polymer electrolytes doped with LiN (SO2CF3)2 were studied by multinuclear NMR, where the motions and diffusion of the polymer, lithium ion and anion were independently measured by 1H, 7Li and 19F NMR, respectively. Since the temperature dependences of the relaxation times, T1, of the 1H and 7Li NMR showed minima, the correlation times of the polymer segmental and lithium hopping motions were obtained. The diffusion phenomena were observed by the pulsed field-gradient spin-echo (PEG) NMR method. Without doping the salt, the branched polymer chains having the methyl terminals diffuse free and the self-diffusion coefficients obtained were time dependent (anomalous diffusion). After doping the lithium salt, the polymer chains showed restricted diffusion. The anion self-diffusion coefficients can be determined and the values are also time dependent. The lithium ion clearly showed the restricted diffusion and the barrier height and the size of the sphere are fluctuating. The lithium ions are located near the PEO chains and can make the cross-linking between the chains which forms a transient sphere of the restricted diffusion of lithium ions and polymer terminals.