Effect of Nano-Porous Alumina Filler on Thermal and Electrical Transport Properties of Solid Polymer Electrolyte (PEO)12LiBF4
2008
Ionic conductivity, dielectric and thermal properties of (PEO)12LiBF4 solid polymer
electrolyte, dispersed with nanoporous Al2O3 have been studied. Out of seven different
compositions studied, the (PEO)12LiBF4 polymer-salt complex showed the highest conductivity
with σ25
o
C = 8.27 × 10-6 S cm-1. Dispersion of different weight ratio of nano-porous alumina fillers
to this electrolyte showed that the composite electrolyte composition with 15 wt. % Al2O3 gave the
highest conductivity with σ25
o
C = 6.05 × 10-5 S cm-1. The glass transition temperature, Tg decreased
from -35.3 oC to -43.2 oC and the PEO crystallite melting temperature, Tm decreased from 64.5 oC
to 58.8 oC due to the incorporation of 15 wt. % Al2O3 filler, suggesting that the interaction between
the PEO backbone and the Al2O3 filler have affected the main chain dynamics of the host polymer.
As the presence of the filler results in an increased conductivity mainly due to an increased amount
of amorphous phase in the electrolyte above Tm, another mechanism, directly associated with the
filler particles, appears to contribute to the observed conductivity enhancement. A possible
mechanism for this could be the creation of additional hopping sites and favorable conducting
pathways for migrating ionic species though Lewis acid-base type interactions between ionic
species and O/OH sites on the filler grain surface. Results of the dielectric relaxation spectroscopy
agree with the suggestion that the increased mobility is largely responsible for the obtained
conductivity enhancement caused by the nano- porous filler.
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