Full text of DOI:10.1002/1097-0126(200007)49:7<703::AID-PI442>3.0.CO;2-H

Polymer International
Polym Int 49:703±711 (2000)
Polymer electrolytes based on lithium sulfonate
derived from perfluorovinyl ethers; single ion
conductors
Sami Bayoudh, Nathalie Parizel and L e´ onard Reibel*
CNRS Institut Charles Sadron, 6 rue Boussingault, 67083 Strasbourg Cedex, France
Abstract: A new lithium per¯uoroakylsulfonate has been synthesized from a commercial per¯uoro-
vinylether ®tted with a ¯uorosulfonyl group. By making use of the vinylether group, this species was
incorporated into polyurethane networks based either on a poly(ethylene oxide)glycol or on a tri-arm
star-poly(ethylene oxide)triol. The results, in terms of ionic conductivities, thermal behaviour and
1
different domains of rigidity (solid-state H NMR), are reported for these single cation conductor
polymer electrolytes. When compared to the polymer electrolytes where the same but untethered
lithium per¯uoroakylsulfonate is dissolved in the same initial networks, a loss of conductivity is
observed despite the higher mobility of the ionomers. This loss corresponds to the conductivity
attributed to the anionic species. The higher mobility of the ionomeric electrolytes is to be related to
the quasi absence of physical crosslinks.
#
2000 Society of Chemical Industry
Keywords: polymer electrolytes; lithium per¯uoroakylsulfonate; single cation conductors; crosslinked polyethers;
ionomers
8
±12
INTRODUCTION
The application of ion-conductive polymers to solid
electrolytes in high-energy batteries was suggested in
monomers;
conductive monomer which is also a carrier ion
(3) the polymerization of an ion-
13
source. Another approach is the preparation of a
polyether network with an ionizable crosslinking
1
978. Since then, a large number of studies and
1
reviews
2±4
14,15
agent.
have been devoted to this subject, and the
Most of the salts used were of sulfonate
or carboxylic acid type, and provided modest con-
pertinent parameters to achieve important conductiv-
ity have been recognized. They are based on the
solvating power of the polymer towards the lithium salt
to be used and the capability of this salt to dissociate in
a medium of low dielectric constant. This determines
the number of charge carriers. The mechanism of ion
migration requires amorphous character of the poly-
�
7
� 1
ductivities (around 10 Scm at room temperature)
due to limited solubilities and dissociation in poly-
ethers. The use of per¯uorocarbon moieties adjacent
to the sulfonate group increases conductivity because
16,17
of a better dissociation of the ion-pair.
Different
strategies have been developed to prepare and
copolymerize monomers ®tted with such salts and
5
meric system, because the mobility of the ionic
17
species is directly related to the segmental motion of
the polymer. One of the drawbacks of such systems is
the signi®cant decrease in ionic conductivity that
occurs under dc polarization, because of cation and
anion migration: no active electrode is used for the
anionic species, so the local concentration of anions
near the anode is increased and, as a consequence, the
resistance of the system becomes more important with
time.
ion-conductive monomers.
This work presents the preparation and study of a
new type of single ion-conductor obtained from a
per¯uorovinylether ®tted with a ¯uorosulfonyl end-
group, ie CF2=CFÐOÐCF ÐCF(CF )ÐOÐ
CF CF ÐSO F. This compound is used as a
comonomer in the copolymerization of tetra¯uor-
2
3
18
2
2
2
1
19
oethylene to obtain the commercialized Na®on. It
was ®rst transformed by alkaline hydrolysis into
lithium sulfonate and its performance as an electrolyte
was examined in several polymer matrixes. By making
use of the vinyl end-group, a strategy was developed to
graft the anion to a polymer and thus prepare a single
cation conductor. The vinyl function was transformed
into a hydroxyl group and submitted to polycondensa-
Several methods have been developed to achieve
single cation conductive polymers. According to
4
Tsuchida and co-workers three general approaches
can be identi®ed: (1) a blend of polyelectrolyte and
6,7
ion-conductive polymer; (2) the copolymerization
of ion-conductive monomers and carrier source
*
Correspondence to: L e´ onard Reibel, CNRS Institut Charles Sadron, 6 rue Boussingault, 67083 Strasbourg Cedex, France
Contract/grant sponsor: Electricit e´ de France
Contract/grant sponsor: Centre National de la Recherche Scientifique
Contract/grant sponsor: Bollor e´ Technologies
(
Received 5 August 1999; revised version received 2 February 2000; accepted 15 February 2000)
#
2000 Society of Chemical Industry. Polym Int 0959±8103/2000/$30.00
703

S Bayoudh, N Parizel, L Reibel
tion with different functional solvating poly(ethylene
oxide)s. To obtain thin ®lm polymer electrolytes with
good mechanical stability, polymeric networks were
prepared where the per¯uoro lithium sulfonates are
present as dangling chains attached to a crosslink.
toethanol and 0.378g of azobisisobutyronitrile
(AIBN) in 15ml of THF solvent, within a glass tube.
After oxygen removal, the reaction was run under
static vacuum at 70°C for 8h. A ®rst distillation under
vacuum (10mmHg) allowed the solvent and non-
reacted species to be removed. A colourless, viscous
product was obtained at about 80% yield by distilla-
�
4
EXPERIMENTAL
Materials
The per¯uorovinylether ®tted with a ¯uorosulfonyl
tion under 10 mmHg vacuum and characterized as
follows:
ꢀ
c†
CF3
j
group is abbreviated as RFSO F. It was graciously
given by Dupont and corresponds to the following
2
ꢀ
1†; ꢀ2† ꢀ3†
HO CH2CH2
S
CF2 CFH
O
CF2 CF
O
CF2CF2 SO2 F
ꢀb† ꢀe† ꢀa†
developed
formula:
CF2
=
CFÐOÐCF Ð
CF(CF )ÐOÐCF CF ÐSO F. LiOH, mercapto-
ꢀd†
ꢀf†
2
3
ethanol, azobisisobutyronityrile and poly(ethylene
1
oxide)glycol (M =600g mol ) were purchased from
2
2
2
1
�
HNMR (CDCl ) d (ppm): 6 (dt, 1H, ÐCFHÐ);
.57 (t, 2H, ÐCH OÐ); 3.08 (t, 2H, ÐCH SÐ).
3
n
3
Aldrich.
Desmodur RFE) was purchased from Bayer. A
trihydroxyl star-shaped PEO [PEO(OH)3,
Tris(4-isocyanatophenyl)thiophosphate
2
2
19
FNMR (CDCl ) d (ppm): ‡47.88 (m, 1F,
(
3
ÐSO F, a); � 77 (m, 2F, b); � 77.6 (m, 3F, c); � 82
2
�
1
(
m, 2F, d); � 86.5 (m, 2F, F1‡F2); � 109.6 (m, 2F,
M =3300g mol ] was graciously prepared by Y
n
Gnanou (Laboratoire de Chimie des Polym eÁ res
Organiques, Bordeaux). All solvents were distilled
before used.
e); � 136.9 (d, 1F, 3); � 142.6 (m, 1F, f).
�
1
IR (®lm): (SO ) asym vibr 1415cm (strong), sym
2
vibr 982cm (strong).
�
1
Mass spectrum: M/e =524, parent peak for
C H O F S
Syntheses
Preparation of RFSO F derivatives and characterization
9
6
5 14 2
2
RFSO Li (per¯uorovinylether lithium sulfonate) was
Synthesis of the polymer electrolyte network
NTPEO RFSO Li (O/Li=18)
3
�
3
obtained by reacting 1.16g (2.6Â10 mol) of
6
The reaction was carried out in a glove box under
3
RFSO F dissolved in 5ml of THF and 1.7ml of
2
�
1
� 3
aqueous LiOH (3.4moll ). The solution was con-
tinuously stirred at room temperature for 15h. After
evaporation of the solvent, the product was again
dissolved in tetrahydrofuran (THF), centrifuged and
nitrogen atmosphere. 1.38g (2.3Â10 mol) of
PEG600 (poly(ethylene oxide)glycol), M =600g
mol
n
�
1
� 3
)
(Aldrich), 0.75g (1.43Â10 mol) of
�
3
HOÐRFSO F and 1.00g (2.15Â10 mol) of
2
tris(4-isocyanatophenyl)thiophosphate
®
evaporation of THF, the product was dried under
ltered to eliminate the excess of LiOH and LiF. After
(Desmodur
O)3 were dis-
RFE, Bayer) S
=
P(OC H N
=
C
=
6
4
�
3
vacuum (10 mmHg) for 48hours. A yellow solid was
obtained (about 92% yield) and washed with chloro-
form to extract unreacted RFSO F. It was character-
solved in THF. 1,4-Diazo-[2,2,2]-bicyclooctane cata-
lyst was added at 0.3% of the total mass of PEG and
monohydroxylated HOÐRFÐSO F. The critical
2
2
ized as follows:
conversion p to reach the gel point was previously
calculated
c
20
to be 0.84 using the equation
ꢀ
c†
0.5
pc =1/[r(f
[NCO]=0.935, and f
w,OH
� 1) (f
w,NCO
� 1)] , where r =[OH]/
w,NCO
ꢀ
ꢀ
1† F
2† F
O
!
CF2 CF3
O
CF2CF2 SO3Li
ꢀb† ꢀe†
!C
and f
are the weight-
ꢀ
d†
j
w,OH
C
average functionalities of the hydroxyl and isocyanate
containing molecules. Thus, it is established that a
network can be formed that would fully incorporate
the monohydroxy derivative of the ¯uorosulfonyl
per¯uorovinylether.
CF
ꢀ
ꢀ3†F
f†
1
9
F NMR (acetone-d ) d (ppm): � 72.8 (m, 5F,
6
b‡c); � 77.7 (m, 2F, d); � 106.9 (dd, 1F, CF =, 1);
2
�
111.1 (m, 2F, e); � 115 (dd, 1F, CF =, 2); � 129.3
The solution was poured in a Te¯on mould to
obtain a thin ®lm. It was kept at ambient temperature
for 48h and then raised to 60°C and kept at this
temperature for 3h. The resulting gel was washed in
methanol until constant weight was obtained: 2% by
weight of soluble species were extracted and showed to
be mainly isocyanate oligomers. Thus one can
consider that practically all PEG600 and HOÐRFÐ
2
(
dd, 1F, CF=, 3); � 138.3 (m, 1F, f).
�
1
IR: (SO ) asym vibr 1309cm (strong), sym vibr
2
82cm (weak).
�
1
9
The elemental analysis was made on a sample that
could not be dried completely because of its very high
hygroscopy: C (%) 18.95 (calculated 18.66), Li (%)
1
.66 (calculated 1.55). However, the slight excess of Li
and C is to be attributed to traces of impurities,
presumably lithine or LiF and organic by-products.
SO F are present and reacted in stoichiometric
amounts with the triisocyanate.
2
HOÐRFÐSO F
(o-hydroxy
derivative
RFSO F) was obtained by reacting 5.14g
of
Subsequently the gel was swollen in water in the
presence of LiOH ([LiOH]/[HOÐRFÐSO F]=2.2)
2
2
0.015mol) of RFSO F, 1.8g (0.023mol) of mercap-
2
for 2h to transform the pendant ÐSO F group into
(
2
2
704
Polym Int 49:703±711 (2000)

Polymer electrolytes based on lithium sulfonate
ÐSO Li. It was washed with water to remove LiOH
and LiF and then with methanol. The ®lm obtained
The resonance ®eld was monitored with a ®eld
frequency lock (Drusch, NMR gaussmeter and reg-
ulation unit TAO2) within 2mT. The free induction
decay (FID) signal, following a p/2 pulse of 4ms
generated by a Hewlett-Packard pattern generator
8175A, was digitized with a LeCroy 6810 with 12 bits
(accuracy 1/2000) at a fastest sampling rate of 5MHz,
and ®nally averaged and treated on an IBM-PC
compatible ACER-1100. Numerical computations
were performed in Asyst language. The FID can be
®tted with a linear combination of exponential
functions. Extrapolation of the signal to the middle
of the pulse (t =0) through the dead time of the
receiver (5ms) provides the relative amount of each
component. Owing to a ratio of at least three for the
time constants, the fractions deduced from the FID
can be considered as signi®cant.
3
�
3
was dried under vacuum (10 mmHg) at 80°C for
4h.
2
Synthesis of the polymer electrolyte network
NTPEO RFSO Li (O/Li=17.5)
3
The same procedure was used to obtain the
3
3
NTPEO RFSO Li network. A trihydroxyl star-
�
3
3
3
shaped PEO [PEO(OH) , M =3300g mol ] was
1
3
prepared by Y Gnanou using the anionic polymeriza-
n
21
� 5
tion technique. 0.23g (7Â10 mol) of this func-
tional polymer was reacted with 0.15g
2.86Â10 mol) of HOÐRFÐSO F and 0.080g
�
�
4
(
(
2
4
1.72Â10 mol) of tris(4-isocyanatophenyl)thiopho-
sphate in THF solution. The critical conversion p to
reach the gel point was calculated to be 0.78, so that
HOÐRFÐSO F should be fully incorporated into the
c
2
network. By washing, some 2% by weight of soluble
species [isocyanate oligomers and some tri-star
PEO(OH) ] were extracted, so that again one can
RESULTS AND DISCUSSION
Various polymer electrolytes were synthesized in order
to achieve an O/Li ratio (molar ratio of solvating ether
oxygens to lithium salt) of around 18, which corre-
sponds to a domain of salt concentration showing
usually high conductivity values, and thus allow
comparison at the same or close salt content. A limited
availability of the starting material (per¯uorovinyl-
ether) did not allow us to explore a larger range of
lithium salt concentration.
3
consider that practically all PEO(OH)3 and HOÐ
RFÐSO F are present and reacted in stoichiometric
2
amounts with the triisocyanate. The alkaline hydro-
lysis was run in the same way as previously.
Polymer electrolyte characterization by thermal
1
analysis, ionic conductivity and solid state HNMR
measurements
The different polymer electrolytes were obtained as
®
lms or membranes from a solution of salt and
Thermal behaviour and ionic conductivity of
polymer in acetonitrile, prepared in a Te¯on mould.
After evaporation of the solvent they were dried at
polymer electrolytes containing lithium sulfonate
RFSO Li, derived from perfluorovinyl ether
3
8
0°C under vacuum for several days and then kept in a
dry nitrogen atmosphere.
The
effectiveness
of
CF(CF )ÐOÐCF CF ÐSO Li (referred to as
CF2=CFÐOÐCF Ð
2
3
RFSO Li) as an ionic conductive salt was examined
2
2
3
The thermal analysis was performed by a Perkin
Elmer DSC 7 apparatus on tight aluminium capsules
containing the polymer electrolyte samples. To deter-
mine the glass transition temperature Tg of the
amorphous systems, the samples were ®rst quenched
to � 110°C, then heated to 150°C at a rate of
3
when dissolved in a semi-crystalline high molecular
5
weight poly(ethylene oxide) (PEO) (M =9Â10 g
ꢀ
�
1
mol ). Two samples were prepared with an O/Li
content of 20 and 30, ie respectively 0.75mol and
0.56mol of salt per kilogram of polymer electrolyte.
Their DSC analysis revealed the presence of both a
�
1
2
0°Cmin . This cycle was repeated several times to
check reproducibility. When the systems were semi-
crystalline, the rate of heating was changed to
crystalline (T =67°C) and an amorphous phase
m
(T =� 35°C and � 37°C, respectively). This is re-
g
�
1
� 1
4
0°Cmin from � 110 to 30°C and to 10°Cmin
¯ected in the Arrhenius conductivity plots (Fig 1)
which exhibit a shoulder below 60°C when the
crystalline phase appears and where low conductivity
from 30°C to 220°C, to determine T and the melting
temperature T , respectively.
g
m
5
To measure the ionic conductivity, the ®lms were
sandwiched between stainless-steel electrodes and
heated at 50°C under vacuum for 48h. AC con-
ductivity measurements were carried out under
dynamic vacuum using a Solartron 1260 impedance
analyser (Schlumberger Technologies), from room
temperature up to 85°C over the frequency range 5Hz
to 32MHz. When some ¯ow was observed, the
conductivity values were corrected by using the
appropriate dimensions of the sample.
values are obtained. When measurements were run at
decreasing temperatures a retardation to crystalliza-
tion would account for the higher conductivity as
shown in the case of O/Li=20. Conductivities of about
�
4
� 1
10 Scm were obtained at 60°C which compare
with data obtained for CF SO Li, at close O/Li
22
3
ratios, although reports for the C F
3
SO Li series
3
indicate some dependence of conductivity on the size
n
2n‡1
23
of the per¯uoro entity.
To avoid the interference of crystallinity and in
To determine domains of different rigidity, solid
1
state HNMR measurements were carried out on a
1
Bruker SXP spectrometer operating at 60MHz ( H).
order to compare RFSO Li with the most performing
24
3
(CF SO ) NLi, the two salts were dissolved in an
3 2 2
amorphous polyurethane network NTPEO , prepared
6
Polym Int 49:703±711 (2000)
705

S Bayoudh, N Parizel, L Reibel
Scheme 1. Synthesis of HO—RFSO F.
2
¯uoride group into lithium sulfonate by lithium
hydroxide and subsequent extraction by water to
eliminate excess of alkali, the polymeric networks
were expected to be single cation conductors.
A ®rst sample was obtained from a HOÐRFSO F/
2
Figure 1. Dependence of conductivity on reciprocal temperature for PEO
PEG600 mixture (0.622 molar ratio) and a stoichio-
metric amount of triisocyanate to yield a molar ratio of
solvating ether oxygens over SO F groups ([O]/
5
� 1
(
M =9Â10 g mol )/RFSO Li electrolytes for two compositions during
ꢀ
3
cooling (!, O/Li=20; ^, O/Li=30) and during heating (~, O/Li=20).
2
[
the same ratio of [O]/[ÐSO Li] equal to 18 is
ÐSO F]) equal to 18. Thus after alkaline hydrolysis,
2
from stoichiometric amounts of poly(ethylene oxide)-
�
3
1
glycol (PEG) (M =600g mol ) and an aromatic
obtained, which is within the domain where best
conductivities are usually observed. If one assumes
that only one ionomer is attached to a triurethane
knot, 71% of those knots would have a pendant
n
=
triisocyanate,
two polymer
S
P(OC H N
=
C
=
O)3, yielding
NTPEO /RFSO Li
6
4
electrolytes,
6
3
(
O/Li=26; T =‡4°C) and NTPEO /(CF SO ) NLi
g
6
3
2 2
(
O/Li=27; T =‡6°C). A preliminary study showed
RFSO Li group whereas 29% would be true cross-
g
3
conductivity values about three times higher for the
sulfonimide at the same temperature. Because these
measurements were performed at close segmental
mobility of the polymeric matrix and close solvated
lithium content, the higher conductivity of the latter
salt is to be related to some better dissociation
properties.
links, ie connected to elastic poly(ethylene oxide)
chains.
A second sample was made from a HOÐRFSO F/
2
PEO(OH)3 3300 mixture (4.09 molar ratio) and
stoichiometric amount of triisocyanate so as to yield
after hydrolysis a molar ratio [O]/[ÐSO Li] of
3
solvating ether oxygens over SO Li groups equal to
1
from PEO(OH) and are true crosslinks, whereas 71%
3
7.5. In this network 29% of the junction points stem
Polymer networks with pendant lithium
perfluoroalkyl sulfonates: synthesis, thermal
properties, ionic conductivity, structuring effect
Synthesis of ionomeric networks with pendant lithium
perfluoroalkyl sulfonates
3
come from the triisocyanate. The latter junctions are
connected to an average of 1.6 pendant RFSO Li
3
groups per knot and thus form only a small amount of
real crosslinks.
The per¯uorinated o-hydroxy-sulfonyl ¯uoride HOÐ
RFSO F was obtained from the initial per¯uorovinyl-
The features of these networks and other systems
made from by incorporation of untethered lithium
salts are reported in table 1.
2
ether RFSO F (Scheme 1) and further incorporated
2
into a solvating polymer backbone by formation of a
polyurethane network (Scheme 2). The polymer
samples were carefully extracted with methanol to
remove soluble species. After hydrolysis of the sulfonyl
Properties of the tridimensional polymer electrolytes made
from poly(ethylene oxide)glycol PEG600
The ®rst network, referred as NTPOE RFSO F
6
2
Scheme 2. Formation of the
polyurethane (PUR) networks.
706
Polym Int 49:703±711 (2000)

Polymer electrolytes based on lithium sulfonate
mol salt/kg
of polymer
Polymer network
Polymer electrolyte
Tg (°C)
O/Li
electrolyte
NTPEO RFSO F
� 13.5
� 11.5
� 4
6
2
NTPEO RFSO Li
18
15
21
15
25
0.47
1.59
1.42
1.82
1.38
6
3
NTPEO RFSO F
6
2
‡
RFSO Li
� 5
3
Table 1. Lithium salt content and glass transition
temperatures of NTPEO RFSO F and
NTPEO6RFSO2F
‡ (CF SO ) NLi
0
� 1
6
2
3
2 2
NTPEO33RFSO F polymer networks and networks
NTPEO RFSO F
� 40
� 35
� 25
2
33
2
made from them containing either tethered
NTPEO RFSO Li
17.5
16.8
0.63
0.50
33
3
(
NTPEO RFSO Li and NTPEO RFSO Li) or
6 3 33 3
NTPEO RFSO F
33 2
untethered (RFSO Li) lithium perfluorosulfonates
3
‡ RFSO Li
3
or (CF SO ) NLi
3
2 2
before
hydrolysis,
is
totally
amorphous
clear that the non-grafted salt system is about 4±8
times more conductive. Thus the anionic contribution
predominates over the cationic one for this type of salt.
Similar observations have been reported in the
(
(
T =� 13.5°C). After hydrolysis, the network
g
NTPEO RFSO Li; O/Li=18) is still amorphous
6
3
but has a slightly higher T (� 11.5°C). Its Arrhenius
g
26,27
conductivity plot is shown in Fig 2. To compare the
results with a system where the same but untethered
lithium salt is present, RFSO Li was dissolved in the
literature.
the lower solvation of the anion compared to the
This phenomenon can be related to
‡
strong solvating interaction of Li with the ether
oxygen atoms.
3
24,26±28
same initial network ie NTPEO RFSO F, at two
different O/Li ratios (15 and 21) which raise its T to
6
2
g
�
4°C and � 5°C, respectively. Figure 2 shows that the
Properties of the tridimensional polymer electrolytes made
from the three-arm trihydroxypoly(ethylene oxide)
PEO(OH) 3300
latter polymer electrolytes are more effective in the
same range of temperature and O/Li ratio. To check
whether this can be related to the absence of the
anionic contribution, the conductivity values were
3
The second network, referred to as NTPOE RFSO F
33
2
before hydrolysis, was designed to improve the
mobility of the polymeric segments by the increase of
the average length of the polymer chains joining two
crosslinks. Therefore PEG600 was replaced by a
hydroxy-terminated three-arm poly(ethylene oxide)
plotted versus 100/(T� T ), ie at reduced temperature
g
Fig 3). Indeed, the ionic conductivity of an amor-
(
phous system, above glass transition temperature, is
related to its free volume: it was shown that the
logarithm of conductivity is inversely proportional to
�
1
star PEO(OH) 3300 (M =3300g mol ), which was
reacted with the same triisocyanate in the presence of
HOÐRFSO F. The network NTPOE RFSO F ob-
3
n
(
T � T ), as postulated by the Williams, Landel and
g
25
Ferry equation. Now comparison can be made at
equivalent mobility between the grafted and non-
grafted sulfonates, in the same range of O/Li ratio. It is
2
33
2
tained also differs from the previous one because some
of the polar urethane crosslinks are changed to non-
Figure 3. Comparison of conductivities at reduced temperature between
NTPEO RFSO F/RFSO Li network with untethered perfluorinated lithium
Figure 2. Dependence of conductivity on reciprocal temperature for
ionomeric network NTPEO RFSO Li (&, O/Li=18) and NTPEO RFSO F/
6
2
3
6
3
6
2
sulfonate added (6&, O/Li=15; &, O/Li=21) and NTPEO RFSO Li
6
3
RFSO Li network with untethered perfluorinated lithium sulfonate added
ionomeric network, made from the previous one by hydrolysis of —SO2F
3
(6&, O/Li=15; &, O/Li=21).
groups into —SO Li (&, O/Li=18).
3
Polym Int 49:703±711 (2000)
707

S Bayoudh, N Parizel, L Reibel
network but with untethered salt (NTPOE RFSO F/
RFSO Li;O/Li=16.8). Assuming that the ionomeric
33
2
3
system represents the cationic conductivity of the
latter, the anionic transport number of the
NTPOE RFSO F/RFSO Li electrolyte can be cal-
33
2
3
culated to be in the range 0.7±0.8, which compares
well to the values reported in the literature.
26,27
Effect of tethered and untethered lithium sulfonates on
polymer electrolyte structure
When the initial networks (containing the ¯uorosulfo-
nyl groups) are hydrolyzed to form ionomeric electro-
lytes only a slight increase in T is observed. Similar
g
behaviour was reported for other ionomeric net-
17
works. However, when a non-bonded salt such as
RFSO Li or (CF SO ) NLi is added to the same
Figure 4. Dependence of conductivity on reciprocal temperature for
3
3
2 2
PEO(OH) 3330- and PEG600-based networks containing either tethered
3
initial network, this increase becomes several times
more important for similar O/Li ratios (Table 1). An
important increase of T has also been reported by
NTPEO33RFSO Li (*, O/Li=17.5) and NTPEO RFSO Li (&, O/Li=18) or
3
6
3
untethered NTPEO33RFSO F/RFSO Li (*, O/Li=16.8) lithium sulfonates.
2
3
g
28
Lenest et al when untethered salts are dissolved in
polymeric networks. It was related to the presence of
ionic associations playing the role of a physical
crosslink; these crosslinks are reversible and disappear
above 40°C. However, there is no de®nite explanation
polar ones. It appears to be amorphous, although the
poly(ethylene oxide) star is semicrystalline, and is
much more ¯exible than the previous network (Table
1). The ionomeric network NTPOE RFSO Li
33 3
O/Li=17.5) obtained after hydrolysis shows only a
(
for the rather slight increase in T observed for the
g
slightly increased T (from � 40°C to � 35°C). Figure
polymer electrolytes with tethered salts. The major
difference in the present system is the reduced mobility
of the anion attached to a junction point between two
polymer segments and the steric hindrance generated
by its enhanced bulkiness, thus preventing a closer
approach of neighbouring chains to solvate the cation.
This might also affect the equilibria between the
different ionic species (simple ions, triplets, etc) and
paired species, and as a consequence the association
process of polymer chains by the electrolyte.
g
compares the Arrhenius conductivity plots of the two
4
ionomeric
systems
NTPOE RFSO Li) at very similar O/Li ratios
(NTPOE RFSO Li
and
3
3
3
6
O/Li=17.5 and 18, respectively, for the PEG3300-
3
(
and PEG600-based networks). The conductivities are
highest for the most ¯exible system and reach values of
�
5
� 1
around 2Â10 Scm at 80°C, comparable to that of
17
networks bearing other lithium per¯uorosulfonates.
The difference in values is even higher at lower
temperature due to the increase of the difference
To compare the stiffening in these amorphous
networks containing either tethered or untethered
T� T between the two electrolytes. Figure 4 also
g
compares the Arrhenius conductivity plots of the
1
salts, a solid-state HNMR study has been performed
on the ionomeric network NTPEO RFSO Li
ionomeric NTPOE RFSO Li network and the one
obtained when RFSO Li is added to the same initial
33
3
6
3
(O/Li=18) and on the same initial NTPEO RFSO F
6 2
3
network, ie NTPOE RFSO F at similar O/Li ratios
33
2
O/Li=17.5 for the ionomer and 16.8 for the non-
(
bonded salt). Despite its higher rigidity (T =� 25°C),
g
the untethered salt polymer is more conductive.
Plotting the conductivity values versus 100/(T� T )
g
Fig 5) allows comparison at the same mobility
(
between two ionomeric systems that differ slightly in
their O/Li ratios, but where the chemical structures of
the salt and of the polymer are identical, except that
the NTPOE RFSO Li system contains 29% of
33
3
hydrocarbon-type junctions and 71% of urethane-
type junctions. It is clear that the conductivity
increases with the number of charge carriers, which
in turn depends both on the O/Li ratio and the nature
of the junctions. Such an in¯uence of the nature of the
crosslinks on the mobility of the lithium salts has
already been mentioned and attributed to their
Figure 5. Comparison of conductivities at reduced temperature between
29,30
bulkiness or stiffness.
Figure 5 shows a conduc-
PEO(OH) 3300- and PEG600-based networks containing either tethered
3
tivity about four times lower for the NTPOE33
RFSO Li ionomeric network than for the same initial
NTPEO33RFSO3Li (*, O/Li=17.5) and NTPEO6RFSO3Li (&, O/Li=18) or
untethered NTPEO33RFSO F/RFSO Li (*, O/Li=16.8) lithium sulfonates.
2 3
3
708
Polym Int 49:703±711 (2000)

Polymer electrolytes based on lithium sulfonate
1
Figure 6. HNMR free induction decay signal of the ionomeric network NTPEO RFSO Li (O/Li=18).
6
3
network with RFSO Li added at two different con-
Li (O/Li=18) and to the NTPEO RFSO F/RFSO Li
6 2 3
3
centrations (O/Li=15 and 21). Figures 6 and 7 show
the free induction decay signals corresponding, re-
spectively, to the ionomeric network NTPEO RFSO
(O/Li=15) network with untethered salt. Their
decomposition in two domains of different mobilities
is shown in Table 2. The fast decay is to be related to
6
3-
1
Figure 7. HNMR free induction decay signal of NTPEO RFSO F network containing untethered RFSO Li (O/Li=15).
6
2
3
Polym Int 49:703±711 (2000)
709

S Bayoudh, N Parizel, L Reibel
Fast decay
domain
Slow decay
domain
1
1
Polymer electrolyte
T2 (ms)
H (%)
T2 (ms)
H (%)
1
Table 2. HNMR free induction decay
decomposition of polymer electrolyte networks with
NTPEO RFSO Li(O/Li=18)
66
49
50
34
472
303
304
66
6
3
tethered (NTPEO RFSO Li) and untethered
6
3
NTPEO RFSO F/RFSO Li (O/Li=15)
60.5
59
39.5
41
6
2
3
(
NTPEO RFSO F/RFSO Li) lithium
6 2 3
NTPEO RFSO F/RFSO Li (O/Li=21)
6 2 3
perfluorosulfonates
the rigid part of the material, whereas the slower one
represents a more mobile region, each being char-
acterized by a spin±spin relaxation time T . The
where the `rigid' protons are close to the transient
crosslinks. One can calculate that in addition to the
[CH CH O] units closest to the junctions some four
2
2
2
absence of additional spin±spin relaxation time in the
untethered system excludes any phase separation due
to some less homogeneous distribution of the per-
or ®ve supplementary units present rigid protons.
Taking into account the concentration of RFSO Li,
3
this would indicate that about 6±11 repeat units are
stiffened by one molecule of salt. Because there is a
quasi absence of stiffening for the tethered network, it
can be assumed that the formation of transient
crosslinks is notably decreased, probably due to some
steric effect of the bulky anion that would hinder the
association process.
¯
uoroalkyl groups. The percentage of protons corre-
sponding to the rigid region varies from 34% for the
ionomeric network to about 60% for the non-bonded
salt network.
To identify the hydrogen atoms which belong to the
rigid part, their experimental percentage has been
compared with various calculated ones, assuming that
the closer to the crosslink the more rigid they would
be. Considering that a junction point of the ionomeric
network will not be connected to more than one
pendant per¯uorosulfonate group, one calculates that
about 29% of them constitute effective crosslinks, ie
are connected to three elastic chains: the correspond-
ing protons, resulting from the triisocyanate aromatic
groups, will be rigid in terms of NMR and will account
for about 5% of the total number of protons, which is
far below the experimental value of 34% of rigid
protons. Now, if one considers that the aromatic
protons of all the junctions are rigid, this percentage
rises to 16%. Thus, it should also be assumed that
CONCLUSIONS
Polymer electrolytes containing the lithium per¯uor-
oakylsulfonate RFSO Li, derived from a commercial
3
per¯uorovinylether ®tted with a ¯uorosulfonyl group,
show conductivity values close to those of lithium
tri¯uoromethanesulfonate. Single cation conductors
were obtained by incorporation of RFSO Li into
3
polyurethane networks where the per¯uorosulfonates
are covalently bound to the crosslinks. The best
conductivities (2Â10� Scm
5
� 1
at 80°C, for O/Li
ratios close to 18) are obtained with the ionomeric
network NTPOE RFSO Li, based on the tri-arm
star-poly(ethylene oxide)triol [PEO(OH) 3300], as
33
3
among the CH groups of the PEG elastic chains and
2
3
compared to the NTPEO RFSO Li network, based
of the per¯uorinated sulfonate branches, some will
have their movement frequency reduced due to the
vicinity of the junction with the urethane groups.
6
3
on a linear poly(ethylene oxide)glycol (PEG600). On
top of a higher mobility of the former network, this
difference is also to be related to the presence in the
Assuming that only the CH groups closest to those
2
junctions will become rigid the total amount of rigid
protons is raised to 24%. However, if the rigidity is
extended to the two CH2 groups closest to the
crosslinks, ie if the [CH CH O] units closest to the
PEO(OH) -based polymer electrolyte of a slightly
3
higher content of solvated lithium cations and a lower
amount of bulky junctions.
The conductivity values of these ionomeric systems
are below those obtained by the same but non-
hydrolysed networks, where RFSO Li is added at the
2
2
junctions become rigid, then the total number of rigid
protons would account for 32% of the total number of
protons. This value compares well with the experi-
mental one.
3
same O/Li ratio. This shows the predominant effect of
the anionic contribution. However, at lower tempera-
tures the gap of conductivity is reduced due to the
higher ¯exibility of the ionomers. The difference in
The two systems where the NTPEO RFSO F
network contains RFSO Li at two different concen-
6
2
3
trations (O/Li=15 and 21) show an almost identical
decomposition of the free induction decay, indicating
no fundamental change in the rigidity in this range of
concentration. The experimental value of rigid hydro-
gens is around 60%, meaning that a new type of
segmental stiffening has appeared and is directly due
¯exibility results from a stiffening when RFSO Li is
introduced into the non-hydrolysed networks
(NTPEO RFSO F or NTPEO RFSO F) as shown
3
6
2
33
2
1
by solid-state HNMR and thermal analysis; this
stiffening is due to the formation of physical crosslinks
that involve the untethered salt and the solvating
polymer chains. In contrast, no important stiffening is
observed in the case of ionomeric polymers, when the
SO F group is hydrolysed to SO Li: this is possibly
to the presence of the RFSO Li salt. This can be
3
related to the formation of transient physical crosslinks
between the elastic PEG chains by the electrolyte,
2
3
710
Polym Int 49:703±711 (2000)

Polymer electrolytes based on lithium sulfonate
related to the greater hindrance for neighbouring
polymer chains to solvate the lithium cation of the
bound salt.
11 Zhou G, Khan IM and Smid J, Polym Commun 30:52 (1989).
1
2 Yeh TF, Liu H, Okamoto Y, Lee HS and Skotheim TA,
Proceedings of Second International Symposium on Polymer
Electrolytes, Ed. by Scrosati B, Elsevier, London, p 83 (1990).
3 Tsuchida E, Ohno H, Kobayashi N and Ishizaka H, Macromol-
ecules 22:1771 (1989).
1
ACKNOWLEDGEMENTS
14 Le Nest J-F, Gandini A, Cheradame H and Cohen-Addad J-P,
The authors express their thanks to Electricit e de
France (EDF) which has provided ®nancial support of
part of this work in the framework of a partnership
with the French National Research Center (C N R S)
and Bollor e Technologies. The Agence de l'Envir-
onnement et de la Ma Ãõ trise de l'Energie (A D E M E) is
acknowledged for a scholarship given to SB and
Dupont de Nemours for having graciously provided
us with per¯uorovinylether samples.
Polym Commun 28:302 (1987).
5 Watanabe M, Nango S, Sanui K and Ogata N, Solid State Ionics
8/30:911 (1988).
1
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2
6 Tada Y, Sato M, Takeno N, Nakacho Y and Shigehara K,
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17 Benrabah D, Sylla S, Alloin F, Sanchez J-Y and Armand M,
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8 Dupont, US Patent 3, 282, 875 (1966).
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9 Feiring A and Smart B, Fluorine compounds, organic, in
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0 Durand D and Bruneau C-M, Makromol Chem 183:1021 (1982).
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711