Motions and Diffusion of
Ions in Polymer Electrolytes Observed by NMR Spectroscopy
Kikuko Hayamizu
National Institute of Advanced Industrial Science and Technology, Energy
Electronics Institute Ibaraki,Japan
Nippon Gomu Kyokaishi,(2003),76(9), 324-328 General Review in Japanese.
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 respectively.
Since the temperature dependences of the relaxation times,
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 (PFG) 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
Keywords:
Polymer electrolyte, Ion diffusion, Segmental motion, NMR |