Lithium ion conductivity of polymer electrolytes based on insoluble lithium tetrakis(pentafluorobenzenethiolato)borate and poly(ethylene oxide)

Article abstract of DOI:10.1149/1.2116687

Lithium ion conductivity and the ion transport mechanism for heterogeneous polymer electrolytes composed of insoluble lithium tetrakis(pentafluorobenzenethiolato)borate (LiTPSB), which has weak interaction between the lithium ion and the counteranion, and

Full text of DOI:10.1149/1.2116687

Lithium Ion Conductivity of Polymer Electrolytes Based on Insoluble
Lithium Tetrakis(pentafluorobenzenethiolato)borate and
Poly(ethylene oxide)
Takahiro Aoki and Tatsuo Fujinami
J. Electrochem. Soc. 2005, Volume 152, Issue 12, Pages A2352-A2356.
doi: 10.1149/1.2116687
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A2352
Journal of The Electrochemical Society, 152 ͑12͒ A2352-A2356 ͑2005͒
0013-4651/2005/152͑12͒/A2352/5/$7.00 © The Electrochemical Society, Inc.
Lithium Ion Conductivity of Polymer Electrolytes
Based on Insoluble Lithium
Tetrakis(pentafluorobenzenethiolato)borate
and Poly(ethylene oxide)
z
*
Takahiro Aoki and Tatsuo Fujinami
Department of Materials Science and Chemical Engineering, Faculty of Engineering, Shizuoka University,
3-5-1, Johoku, Hamamatsu 432-8561, Japan
Lithium ion conductivity and the ion transport mechanism for heterogeneous polymer electrolytes composed of insoluble lithium
tetrakis͑pentafluorobenzenethiolato͒borate ͑LiTPSB͒, which has weak interaction between the lithium ion and the counteranion,
and high molecular weight poly͑ethylene oxide͒ ͑PEO͒ have been investigated. In addition, the ionic conductivity of polymer
electrolytes based on low molecular weight poly͑ethylene glycol͒ dimethyl ether ͑PEGDME͒ or amorphous poly͓tetra͑ethylene
glycol͒ methyl ether methacrylate͔ ͑PEGM͒ was also researched. LiTPSB is not soluble in any solvents and polymers, however its
composites with poly͑ether͒s exhibited ionic conductivity. The lithium ion transport mechanism in the interfacial phase between
LiTPSB and PEO was proposed. The apparent activation energy of ionic conductivity was smaller for LiTPSB/PEO ͑salt 50 wt %͒
than lithium trifluoromethanesulfonate ͑Litrif͒/PEO. A high lithium ion transference number of 0.65–0.75 was also obtained for the
insoluble LiTPSB/PEO system. A new peak of the melting point of PEO was observed in differential scanning calorimetry
measurements of LiTPSB/PEO polymer electrolytes, and it suggested the formation of a new ion conducting phase in the
interfacial region between LiTPSB and PEO.
© 2005 The Electrochemical Society. ͓DOI: 10.1149/1.2116687͔ All rights reserved.
Manuscript submitted April 25, 2005; revised manuscript received August 3, 2005. Available electronically October 24, 2005.
Lithium ion conducting dry polymer electrolytes have been at-
Experimental
tracting interest as safer alternatives to liquid electrolytes or gel
polymer electrolytes in lithium secondary batteries for hybrid ve-
hicles and electric vehicles.1-3 High dissociative property, high elec-
trochemical stability, and good thermal stability are necessary for
lithium salts in polymer electrolytes. Several high dissociative
lithium salts such as lithium orthoaluminate, lithium orthoborate,
and lithium orthophosphate have been reported.4-10
We have reported lithium ion conducting ionic liquids which
contained two methoxy ͓oligo ͑ethylene oxide͔͒ and two electron
withdrawing groups bonded to aluminate or borate complex center,
which exhibited high ionic conductivity of 5 ϫ 10−5 S cm−1 at
30°C and high lithium ion transference numbers of 0.8,11,12 and
polymer electrolytes containing fluoroalkane dicarboxylate substi-
tuted aluminate or borate backbone and two methoxy ͓oligo ͑ethyl-
ene oxide͔͒ side chains, which exhibited high single lithium ionic
conductivity of 10−5 S cm−1 at 30°C.13 The relationship between
ionic conductivity and chemical structure of electrolytes containing
a complex structure was discussed by focusing on the negative par-
tial charges in anions which were estimated by optimization calcu-
lations in MOPAC. Weak interaction between the lithium ion and the
counter anion with dispersed negative charge was necessary for high
ionic conductivity.
We recently reported the molecular design and synthesis of
lithium tetrakis͑pentafluorobenzenethiolato͒borate ͑LiTPSB͒ which
had weak interaction between the lithium ion and the counter-
anion. Lithium ion conductivity of LiTPSB/poly͑vinylidene
fluoride͒ ͑PVDF͒ or LiTPSB/poly͑vinylidene fluoride-co-
hexafluoropropylene͒ ͑PVDF-HFP͒ polymer electrolytes was higher
than the LiTFSI/PVDF system.14
In this paper, we report the ionic conductivity and ion transport
mechanism for heterogeneous polymer electrolytes composed of
insoluble LiTPSB and high molecular weight poly͑ethylene oxide͒
͑PEO͒. In addition, the ionic conductivity of polymer electrolytes
based on low molecular weight poly͑ethylene glycol͒ dimethyl ether
͑PEGDME͒ or amorphous poly͑ethylene glycol͒ methyl ether meth-
acrylate ͑PEGM͒ was also investigated.
Materials
.— Lithium borohydride ͑LiBH4, 2.0 M solution in
͓tetrahydrofuran ͑THF͒, Aldrich͔, pentafluorothiophenol ͑Lan-
caster͒, and azobisisobutyronitrile ͑AIBN, Wako͒ were used as sup-
plied. Lithium trifluoromethanesulfonate ͑Litrif, Tokyo Kasei Ko-
gyou͒ was dried at 100°C for 24 h under vacuum. Poly͑ethylene
oxide͒ ͑PEO, Mw 5.0 ϫ 106, Aldrich͒ and poly͑ethylene glycol͒
dimethyl ether ͑PEGDME, Mw 1000, Tm = 42°C, Aldrich͒ were
dried at 50°C for 24 h under vacuum. Tetra͑ethylene glycol͒ methyl
ether methacrylate ͑Shin-Nakamura Chemical͒ was dried under re-
duced pressure after removing the polymerization inhibitor using
activated alumina. THF was dried by refluxing over sodium before
use. Unless otherwise stated, all materials were handled on a dry
nitrogen line or in an argon glove box in order to rigorously exclude
moisture.
LiTPSB was synthesized from LiBH4 and pentafluorothiophenol
by refluxing in THF. Purified LiTPSB was dried at 100°C for 24 h
under vacuum after washing repeatedly with dry THF. The structure
of LiTPSB was confirmed by Fourier transform infrared and el-
emental analysis. Detail synthesis process has been described in
another report.14
Preparation of polymer electrolytes.— LiTPSB/PEO ͑LiTPSB
10, 20, 40, 50, 60, and 80 wt %͒ polymer electrolyte films were
prepared by hot pressing at 90°C between poly͑tetrafluorethylene͒
͑PTFE͒ disks using a PTFE or a poly͑ethylene͒ ͑PE͒ spacer to con-
trol film thickness ͑400 ␮m͒ after mixing PEO with LiTPSB in an
agate mortar. LiTPSB/PEGDME ͑LiTPSB 20, 40, 50, and 60 wt %͒
polymer electrolytes were prepared by mixing PEGDME with
LiTPSB using magnetic stirring at 50°C. LiTPSB/PEGM ͑LiTPSB
30, 50, and 70 wt %͒ polymer electrolyte films were prepared by
radical polymerization at 80°C after mixing tetra͑ethylene glycol͒
methyl ether methacrylate with LiTPSB and AIBN.
Measurements.— Ionic conductivity was determined by ac im-
pedance measurement in the frequency 1 MHz to 0.1 Hz ͑signal
amplitude 10 mV͒ using a Solartron 1260 frequency response ana-
lyzer and 1287 electrochemical interface. Samples of thickness, con-
trolled using a PTFE or a PE spacer, were sandwiched between
stainless steel electrodes in an argon glove box.
*
Electrochemical Society Active Member.
z E-mail: r5345010@ipc.shizuoka.ac.jp
Lithium ion transference number was determined for the sample
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Journal of The Electrochemical Society, 152 ͑12͒ A2352-A2356 ͑2005͒
A2353
Figure 1. Partial charges of TPSB anion and TPOB anion from the optimi-
zation calculations in MOPAC ͑PM5͒.
sandwiched between lithium metal electrodes using the ac
impedance–dc polarization combined technique of Evans15 modified
by Abraham.16
The surface of LiTPSB/PEO polymer electrolyte films was
observed by scanning electron microscopy ͑SEM͒ on a JEOL
JSM-5600.
Figure 2. SEM image of the surface for LiTPSB/PEO ͑salt 50 wt %͒ elec-
trolyte film.
Thermal properties of the polymer electrolyte films were deter-
mined by differential scanning calorimetry ͑DSC͒ on a Perkin-Elmer
measurement. The aggregates of LiTPSB particles were also ob-
served and the size of the aggregates was distributed below 200 ␮m
by SEM images.14
Pyris
1 differential scanning calorimetry at a scan rate of
10°C min−1 in the temperature range from −80 to 200°C.
Molecular structures were depicted using CAChe version 5.0
͑Fujitsu͒. The structures and partial charges of the chemical samples
were refined by performed a pre-optimization calculation in Me-
chanics using Augmented MM3, followed by performed an optimi-
zation calculation in MOPAC using PM5 parameters.
LiTPSB/PEO ͑LiTPSB 10, 20, 40, 50, 60, and 80 wt %͒ polymer
electrolyte films were prepared by hot pressing after mixing LiTPSB
with PEO. White opaque films were obtained for all composition.
Films containing less than 40 wt % of LiTPSB were mechanically
strong, but films containing more than 40 wt % of LiTPSB were
fragile. LiTPSB/PEGDME ͑LiTPSB 20, 40, 50, and 60 wt %͒ poly-
mer electrolytes were prepared by mixing PEGDME with LiTPSB.
White opaque hard waxes were obtained for all composition.
LiTPSB/PEGM ͑LiTPSB 30, 50, and 70 wt %͒ polymer electrolytes
were prepared by radical polymerization of tetra͑ethylene glycol͒
methyl ether methacrylate with LiTPSB and AIBN. White opaque
polymer electrolytes were obtained for all composition. Polymer
electrolyte containing 30 wt % of LiTPSB was mechanically strong,
but polymer electrolytes containing more than 30 wt % of LITPSB
were fragile.
Results and Discussion
Characterizations.— LiTPSB was designed for reduced interac-
tion between the lithium ion and the counter anion in order to en-
hance the ionic conductivity of polymer electrolytes. Partial charges
on atoms in the TPSB anion and the tetrakis͑pentafluorophenolato͒
borate ͑TPOB͒ anion were estimated by optimization calculations
in MOPAC using PM5 parameters, and these results are shown in
Fig. 1. The boron atom has a negative formal charge, however a
positive charge on the boron atom and negative charges on the oxy-
gen atoms were shown for the TPOB anion. It was confirmed that
the lithium ion interacted with negative oxygen atoms in the TPOB
anion for the structure of LiTPOB by the results of optimized cal-
culations. Negative charge on the boron atom, positive charges on
sulfur atoms, and smaller negative charges on fluorine atoms were
shown for the TPSB anion. It was confirmed that the lithium ion
interacted with negative fluorine atoms in the TPSB anion for the
optimized structure of LiTPSB. From these results, interaction be-
tween the lithium ion and the negative boron atom should be weak
due to electrostatic repulsion from positive sulfur atoms around the
anion center. Therefore, it was shown that the coordination sites of
the lithium ion changed from oxygen atoms to fluorine atoms by
replacing oxygen atoms with sulfur atoms of the anion, and it is
expected that interaction between the lithium ion and the anion in
LiTPSB is weak.
SEM image.— SEM image of the surface for LiTPSB/PEO ͑salt
50 wt %͒ film is shown in Fig. 2. There were rough areas of
LiTPSB and smooth areas of PEO in the surface. LiTPSB particles
dispersed in the bulk of the polymer electrolyte film.
The lithium ion of LiTPSB complexes with THF in the ratio
of 1:1 from the results of elemental analysis. However, LiTPSB
was insoluble in polar and less polar solvents such as acetone, THF,
acetonitrile, ethanol, diethyl ether, diglyme, ␥-butyrolactone, di-
methyl sulfoxide, dimethyl formamide, 1-methyl-2-pyrrolidinone,
toluene, chloroform, hexane, 1,3-bis͑trifluoromethyl͒ benzene, and
water. This can be ascribed to the weaker interaction between the
TPSB anion and solvents due to delocalization of the negative
charge over the anion. LiTPSB was stable to hydrolysis because a
specific thiol smell was not detected after storing in a humid at-
mosphere. The particle size of LiTPSB after grinding in an agate
mortar was distributed from 100 nm to 2 ␮m by size distribution
Figure 3. DSC curves of ͑a͒ PEO, ͑b͒ LiTPSB/PEO salt 20 wt %, ͑c͒ salt
50 wt %, and ͑d͒ salt 80 wt % at a scan rate of 10°C min−1
.
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A2354
Journal of The Electrochemical Society, 152 ͑12͒ A2352-A2356 ͑2005͒
Table I. VTF parameters and glass transition temperature „Tg…
for LiTPSB/PEO polymer electrolytes (a dash indicates “not
measured”).
VTF parameters ͑Ͼ70°C͒
Salt content
͑wt %͒
Tg ͑°C͒
A ͑K−1/2 S cm−1
͒
B ͑K͒
0
−51.6
−53.5
−53.8
−48.8
-
-
20
50
80
-
0.025
-
-
1062
-
Thermal properties.— LiTPSB was thermally stabile up to
350°C in nitrogen flow by the thermogravimetric analysis ͑TGA͒
measurement.14
Thermal properties of LiTPSB/PEO ͑salt 20, 50, and 80 wt %͒
polymer electrolyte films were also investigated by DSC measure-
ments at a scan rate of 10°C min−1 in the temperature range from
−80 to 200°C. DSC curves of PEO and LiTPSB/PEO polymer elec-
trolytes are shown in Fig. 3, and glass transition temperature ͑Tg͒ is
shown in Table I. Glass transition temperature and melting point
͑Tm͒ were determined from the second heating cycle. Pure PEO,
LiTPSB/PEO ͑salt 80 wt %͒ exhibited glass transition temperatures
of −52 and −49°C, respectively. The change of the glass transition
temperature for LiTPSB/PEO polymer electrolytes by increasing the
amount of LiTPSB was very small as compared with the general Li
salt/PEO system.17 This can be ascribed to the degree of the pseudo-
cross-linking between the lithium ion and ethylene oxide chains
of PEO. Pure PEO had a peak of the melting point at 73°C. Two
peaks at 69 and 73°C were detected for LiTPSB/PEO ͑salt
50 wt %͒. The new peak at 69°C showed the formation of a new
phase at the interface between LiTPSB and PEO. For LiTPSB/PEO
͑salt 80 wt %͒, the peak at 73°C disappeared and only a new peak at
69°C was observed.
Figure 4. Ionic conductivity of LiTPSB/PEO electrolytes: ͑a͒ relationship
between LiTPSB content and ionic conductivity at 80°C ͑᭺͒, 70°C ͑ࡗ͒,
60°C ͑᭿͒, 50°C ͑᭡͒, 40°C ͑b͒, and 30°C ͑ϫ͒; ͑b͒ temperature dependence
of ionic conductivity for LiTPSB/PEO ͑salt 50 wt %͒ ͑b͒ and Litrif/PEO
͑EO:Li = 20:1͒ ͑᭝͒.
Ionic conductivity.— The relationship between ionic conductiv-
ity and LiTPSB content for LiTPSB/PEO polymer electrolytes is
shown in Fig. 4a. Although an insoluble LiTPSB pellet exhibited
very low ionic conductivity below 10−9 S cm−1 at 200°C, its com-
posites with PEO showed good ionic conductivity at higher tem-
perature than the melting point of PEO. Optimized ionic conductiv-
ity of 2 ϫ 10−8 S cm−1 at 30°C and 4 ϫ 10−6 S cm−1 at 80°C was
obtained for LiTPSB/PEO ͑salt 50 wt %͒.
For general Li salt/PEO polymer electrolytes, the lithium ion is
usually transported in amorphous phase by the segmental motion of
the ethylene oxide chains. The ion transport mechanism for the het-
erogeneous polymer electrolytes containing insoluble LiTPSB is
tentatively shown in Scheme 1. Since LiTPSB is insoluble in PEO,
lithium ion transport is possible in the interfacial phase between
LiTPSB and PEO.
The temperature dependence of ionic conductivity for LiTPSB/
PEO ͑salt 50 wt %͒ is shown in Fig. 4b as compared with Litrif/
PEO ͑EO:Li = 20:1͒ as a general Li salt/PEO system. It is interest-
ing that heterogeneous LiTPSB/PEO polymer electrolytes show
similar ionic conductivity to homogeneous Litrif/PEO polymer elec-
trolytes below the melting point of PEO. However, the ionic con-
ductivity of LiTPSB/PEO ͑salt 50 wt %͒ is lower than that of Litrif/
PEO ͑EO:Li = 20:1͒ above 70°C. This can be ascribed to low
lithium ion carrier concentration in the interfacial phase because
inside lithium ions in insoluble LiTPSB particles cannot move. En-
hancement of the ionic conductivity based on melting of PEO
and small temperature dependence of ionic conductivity above
the melting point of PEO were observed for LiTPSB/PEO polymer
electrolytes.
␴ = AT −1/2 exp͓− B/͑T − T0͔͒
A and B are constants which related to the concentration of charge
carriers in the matrix and the activation energy for conduction, re-
spectively. An initial value of T0 was taken as T0 = Tg − 50°C. The
Arrhenius plots of LiTPSB/PEO ͑salt 50 wt %͒ polymer electrolyte
were well fitted to the VTF equation above the melting point of
PEO, indicating that ion motion in heterogeneous polymer electro-
lytes containing insoluble LiTPSB also depended on the segmental
motion of the ethylene oxide chains in the interfacial region. The
VTF parameters of LiTPSB/PEO ͑salt 50 wt %͒ polymer electrolyte
are shown in Table I.
It is expected for the enhancement of the ionic conductivity by
using amorphous polymers. Therefore, polymer electrolytes based
on low molecular weight PEGDME ͑Mw 1000͒ and LiTPSB were
investigated. Optimized ionic conductivity of 1 ϫ 10−6 S cm−1 at
30°C and 1 ϫ 10−5 S cm−1 at 80°C was obtained for LiTPSB/
PEGDME ͑salt 50 wt %͒. The temperature dependence of ionic con-
ductivity for LiTPSB/PEGDME ͑salt 50 wt %͒ is shown in Fig. 5 as
compared with Litrif/PEGDME ͑EO:Li = 20:1͒. Above 40°C, the
ionic conductivity of LiTPSB/PEGDME electrolytes was lower than
that of Litrif/PEGDME by two orders of magnitude, and had a
smaller temperature dependence. The large increase in the ionic con-
ductivity from 30 to 40°C was due to melting of PEGDME.
Amorphous polymer electrolytes based on PEGM with
oligo͑ethyhylene oxide͒ side chains and LiTPSB were also in-
vestigated. Optimized ionic conductivity of 1 ϫ 10−7 S cm−1 at
When ion motion depends on the relaxation phenomena of the
host polymer for the amorphous polymer electrolytes, ionic conduc-
tivity is illustrated by Vogel-Tammann-Fulcher ͑VTF͒ equation18-20
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Journal of The Electrochemical Society, 152 ͑12͒ A2352-A2356 ͑2005͒
A2355
Table II. Apparent activation energy „Ea… of ionic conduction
calculated with the Arrhenius equation in PEO, PEGDME, and
PEGM based electrolytes.
Sample
͑a͒ PEO system
Ea ͑kJ mol−1
͒
T:70–190°C
LiTPSB/PEO ͑salt 50 wt %͒
Litrif/PEO ͑EO:Li = 20:1͒
͑b͒ PEGDME system
26
41
T:40–190°C
LiTPSB/PEGDME ͑salt 50 wt %͒
Litrif/PEGDME ͑EO:Li = 20:1͒
͑c͒ PEGM system
9
23
T:30–80°C
31
LiTPSB/PEGM ͑salt 50 wt %͒
Litrif/PEGM ͑EO:Li = 20:1͒
48
glass transition temperature for polymer electrolytes containing
LiTPSB.
Lithium ion transport in the interfacial region between LiTPSB
and PEO for LiTPSB/PEO polymer electrolytes is illustrated in
Scheme 2. The composite electrolyte system of LiTPSB with Litrif/
PEO was also investigated to discuss ionic conductivity in the
interfacial phase between insoluble LiTPSB and ion conductive
Litrif/PEO instead of salt-free PEO. The relationship between
LiTPSB content ͑x͒ and ionic conductivity at 80°C of ͑x͒
͑LiTPSB͒-͑100-x͒ ͑PEO͒ and ͑x͒ ͑LiTPSB͒-͑100-x͒ ͓Litrif/PEO
͑EO:Li = 20:1͔͒ is shown in Fig. 7. Two maximum points of ionic
conductivity were observed for 5 ͑LiTPSB͒-95 ͑Litrif/PEO͒ and 50
͑LiTPSB͒-50 ͑Litrif/PEO͒ in the LiTPSB/Litrif/PEO system. This
phenomenon can be explained by the filler effect of LiTPSB to
Litrif/PEO phase for the first maximum point, and the optimized
interfacial ion conduction between LiTPSB and Litrif/PEO for the
second maximum point.
Figure 5. Temperature dependence of ionic conductivity for LiTPSB/
PEGDME ͑salt 50 wt %͒ ͑b͒ and Litrif/PEGDME ͑EO:Li = 20:1͒ ͑᭝͒.
30°C and 6 ϫ 10−7 S cm−1 at 80°C was obtained for LiTPSB/
PEGM ͑salt 50 wt %͒. The temperature dependence of ionic con-
ductivity of LiTPSB/PEGM ͑salt 50 wt %͒ is shown in Fig. 6 as
compared with Litrif/PEGM ͑EO:Li = 20:1͒. LiTPSB/PEGM ex-
hibited lower ionic conductivity than Litrif/PEGM by one order of
magnitude at room temperature. However, LiTPSB/PEGM showed
the same ionic conductivity as Litrif/PEGM at a low temperature.
Therefore, the ionic conductivity of amorphous LiTPSB/PEGDME
and LiTPSB/PEGM was higher than that of LiTPSB/PEO.
From the results of ionic conductivity for all host polymer sys-
tems containing insoluble LiTPSB, small activation energies of ionic
conduction were observed above the melting point of host polymers.
The apparent activation energy ͑Ea͒ was calculated with the Arrhen-
ius equation
Lithium ion transference number.— Lithium ion transference
numbers were determined using the ac impedance–dc polarization
combined technique.16 Lithium single ion conduction is expected for
polymer electrolytes containing insoluble LiTPSB, but lithium ion
transference numbers of 0.73–0.75 at 50°C and 0.65–0.70 at 80°C
were obtained for LiTPSB/PEO ͑salt 50 wt %͒. Insoluble LiTPSB
anions were not fixed in the polymer electrolytes, however these
anions were less mobile than usual anions in the general Li salt/PEO
system ͑t+ = 0.05–0.30͒.21,22 Lithium ion transference numbers of
LiTPSB/PEO ͑salt 50 wt %͒ decreased as the enhancement of tem-
perature. This can be explained by the increased mobility of in-
soluble TPSB anion aggregates in flexible ethylene oxide chains of
molten PEO at a high temperature.
␴ = A0 exp͑−Ea/RT͒
A0 and R are the pre-exponential factor and gas constant, respec-
tively. The apparent activation energies of polymer electrolytes con-
taining LiTPSB are shown in Table II as compared with those con-
taining Litrif. It is difficult to compare the activation energies among
each host polymer simply because the temperature range is different.
Polymer electrolytes containing LiTPSB showed smaller activation
energies than those containing Litrif. It is estimated that lithium ion
transport is promoted by flexible interfacial PEO phase with low
Figure 7. Relationships between ionic conductivity and LiTPSB content ͑x͒
for ͑x͒ ͑LiTPSB͒-͑100-x͒ ͓Litrif/PEO ͑EO:Li = 20:1͔͒ ͑b͒ and ͑x͒
͑LiTPSB͒-͑100-x͒ ͑PEO͒ ͑᭝͒ at 80°C.
Figure 6. Temperature dependence of ionic conductivity for LiTPSB/PEGM
͑salt 50 wt %͒ ͑b͒ and Litrif/PEGM ͑EO:Li = 20:1͒ ͑᭝͒.
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A2356
Journal of The Electrochemical Society, 152 ͑12͒ A2352-A2356 ͑2005͒
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Conclusion
Lithium ion conductivity and the ion transport mechanism for
heterogeneous polymer electrolytes composed of insoluble LiTPSB
and high molecular weight PEO have been investigated. In addition,
the ionic conductivity of polymer electrolytes based on low molecu-
lar weight PEGDME or amorphous PEGM was also researched.
LiTPSB was not soluble in poly͑ether͒s, however its composite with
poly͑ether͒s exhibited good ionic conductivity. The lithium ion
transport mechanism in the interfacial region between LiTPSB and
PEO was proposed. LiTPSB/PEO polymer electrolytes showed
small apparent activation energy for ionic conduction and high
lithium ion transference number.
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Acknowledgment
This work was supported by a Grant-in-Aid for Scientific Re-
search ͑B͒ ͑no. 16350099͒ from the Ministry of Education, Culture,
Sports, Science and Technology of Japan.
Shizuoka University assisted in meeting the publication costs of this
article.
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