Characterization of Polyiodide-Polymer Complexes by Resonance Raman Spectroscopy
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CHARACTERIZATION OF POLYIODIDE-POLYMER COMPLEXES BY RESONANCE RANAN SPECTROSCOPY MARIA FORSYTH, **HANS CONRAD ZUR LOYE, ** MICHAEL LERNER, ** ANDREW TIPTON,** DONALD C. DEGROOT,* CARL R. KANNEWURF, * MARK RATNER" AND DUWARD F. SHRIVER** Northwestern University, Department of Chemistry", Evanston, IL 60208-3113 Engineering and Computer Science, Northwestern University, Evanston, IL 60208
"*Electrical ABSTRACT
The addition of I1 to PPO/MI and MEEP/MI complexes, - poly(propylene ohmic
oxide),
conductivity.
conductivities
MEEP -
Even
are
observed
polyiodides in all cases is this peak is
in
the
in
absence
the
of
polymer/I
the
2
metal
results
iodide
complexes.
salt,
in
high
The presence 1
indicated by a Raman band at 170 cm- .
of
The width of
found to depend on the concentration of iodine and correlates with
increasing conductivity at higher 12 concentrations. the polyiodide complexes is polymer
where M - Na or Li, PPO
methoxyethoxyethoxy phosphazene
flexibility
as
An additional feature of
the apparent lack of dependence of conductivity on
indicated by T8 .
In
most polymer
electrolytes,
the
conductivity depends upon the glass transition, T., with conductivity dropping rapidly at T < T8 .
By contrast, the polyiodides show only a small inflection in
the conductivity around T. and substantial conductivity below that temperature. Apparently charge transport dynamics are only weakly coupled to the dynamics of the host polymer.
Variable temperature Raman spectroscopy has been employed to
investigate the low temperature behavior of polyiodides in
PPO/MIn systems.
Introduction Solid
polymer
electrolyte
systems
have
been
extensively
studied
as
potential substitutes for conventional liquid electrolytes in electronic devices such as high energy density batteries
[1].
The primary motivation in
such
investigations has been to increase the low temperature conductivities and this has been attempted by varying the salt type, host polymer
[2].
Recently,
it
has been
salt concentration and also the
found that addition of iodine to
conventional polymer electrolytes such as PEONaI, dramatically enhance the conductivity in observed
conductivity
is
ohmic,
in
[3] PPO,'MI [4] and MEEPXMI can
these systems (5].
marked
contrast
with
Furthermore, that
of
the
simple
electrolytes [5]. Raman spectra approximately
of these systerts is
170 cm"
1
and
115 cm'
triiodide species respectively.
1
characterized by two major bands at
corresponding
to a polyiodide
(I,-)
and
The intensity ratio of these bands at 300K is
dependent on the concentration of 12 and MI present in the polymer [6].
In this
paper we discuss the electrical properties and spectroscopic characteristics of polyiodide containing polymers both above and below T8. Mat. Res. Soc. Symp. Proc. Vol. 210. 01991 Materials Research Society
216
Experimental
Polyether-metal iodide complexes of MEEP and PPO were prepared by dissolving alkali metal salt and polymer in a common solvent (usually THF or met
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