1404 Tokuda et al.
Macromolecules, Vol. 35, No. 4, 2002
P(EO/MEEGE) (Figure 1, kindly supplied by Daiso Co. Ltd.),
which had been dried under high vacuum at 40 °C for 72 h
and stored in the glovebox, was used as a matrix of solid
polymer electrolytes. Given amounts of lithium salts and P(EO/
MEEGE) copolymer were dissolved in anhydrous acetonitrile
(Wako) to form a highly viscous homogeneous solution. The
viscous solution was cast on a poly(tetrafluoroethylene) (PTFE)
plate. To obtain homogeneous and flat films, the solvent was
allowed to slowly evaporate at room temperature in the
glovebox for several hours and then under high vacuum for
24 h.
2.3. Ch a r a cter iza tion of a Novel P olym er ic Lith iu m
Sa lt a n d Solid P olym er Electr olytes. Gel permeation
chromatography (GPC) was conducted on a Shimadzu LC-10
HPLC system with Shodex columns with 0.01 M LiCl N,N-
dimethylformamide as the elution solvent. The columns were
calibrated by poly(ethylene glycol) (PEG) standards (Tosoh).
Potentiometic titration was carried out in order to obtain the
structural information on HPPI. An aqueous solution of HPPI
(0.0195 M based on the repeating unit, 75 mL) was titrated
with NaOH (1 M); both the amount of added NaOH solution
and the values of pH, monitored by a pH meter (HM-305 Toa
Electronics Ltd.), were recorded. Differential scanning calo-
rimetry (DSC) was carried out on a Seiko Instruments DSC
220C under a nitrogen atmosphere. Samples were sealed in
Al pans in the dry glovebox, heated to 80 °C, quenched to -130
°C, and then heated at a rate of 10 K min-1. The DSC
thermograms were recorded during the programmed heating
cycle. Thermogravimetry (TG) was measured on a Seiko
Instruments TG-DTA 6200 under a nitrogen atmosphere at a
heating rate of 10 K min-1. Dynamic mechanical analysis
(DMA) was performed on a Seiko Instruments DMS 210 under
F igu r e 1. Structure of LiPPI, LiTFSI, and P(EO/MEEGE).
characterization of LiPPI. The properties of LiPPI as
an electrolyte salt in an organic solvent and in a
polyether are revealed by comparing with LiTFSI
(Figure 1).
2. Exp er im en ta l Section
2.1. Syn th esis of a Novel P olym er ic Lith iu m Sa lt.
LiPPI was prepared according to the procedure shown in
Scheme 1. Tetrafluoroethylene and sulfuric acid anhydride
were added to a pressure-proof container and mixed. After
distilling the product, a small amount of triethylamine was
added to the product under cooling, and fluorosulfonyldifluoro-
acetyl fluoride was obtained by a ring-opening reaction.14
Fluorosulfonyldifluoroacetyl fluoride (90 g), dried diethylene
glycol dimethyl ether (60 mL), dried cesium fluoride (1.5 g),
and hexafluoropropylene oxide (90 g) were added to a 300 mL
shaker tube. This mixture was stirred for 4 h at 25-35 °C.
The obtained product was ejected from the vessel and sepa-
rated from the starting materials. After distillation, 2-(2-
fluorosulfonyltetrafluoroethoxy)tetrafluoropropyonyl fluoride
(84.7 g, yield 56%, density 1.6 g cm-3 (25 °C), bp 87-89 °C)
was obtained.
A solution, where 2-(2-fluorosulfonyltetrafluoroethoxy)-
tetrafluoropropyonyl fluoride (69.2 g, 0.2 mol) was diluted with
tetrahydrofuran (THF, 160 mL), was cooled to 0 °C, and a
potassium bis(trimethylsilyl)amide (0.2 mol)/toluene solution
(400 mL, 0.5 mol L-1) was added dropwise to the solution over
1 h. This mixture was allowed to react for 7 h at 50 °C. Once
the solvent was removed by vacuum distillation, N,N-dimethyl-
acetoamide (240 mL) was added and allowed to react for
further 24 h at 165 °C. The deposited solid was filtered and
dried at 120 °C under reduced pressure to yield a polymer
(KPPI) as a light yellow solid.
An aqueous solution of the polymer was passed into a
column packed with an ion-exchange resin (Organo, Amberlite
IR-120B), and the column was washed by water. The collected
aqueous solution was dried at 60 °C, and then, a light brown
polymer (HPPI) was obtained (24 g). The obtained proton-type
polymer (1.0 g) was dissolved in methanol (50 mL), and lithium
carbonate was added with stirring over 90 min at ambient
temperature to the solution. By complete evaporation of the
solvent, a lithium salt (LiPPI) was obtained (1.1 g).
2.2. P r ep a r a tion of Electr olyte Solu tion s a n d Solid
P olym er Electr olytes. LiPPI and LiTFSI were used as
electrolyte salts for electrolyte solutions and solid polymer
electrolytes. LiTFSI (kindly supplied by IREQ) was dried
under high vacuum at 120 °C for 12 h, and both of the lithium
salts were stored in an argon atmosphere glovebox (VAC, [O2]
< 1 ppm, [H2O] < 1 ppm). For electrolyte solutions, LiPPI and
LiTFSI were dissolved in a polar aprotic solvent at different
concentrations. Ethylene carbonate (EC), kept over molecular
sieves (4 Å), was used for the solvent after distillation.
High molecular weight polyether comb polymer, poly-
[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether],
a nitrogen atmosphere at 10 Hz at a rate of 1 K min-1
.
2.4. P u lse F ield Gr a d ien t Sp in -E ch o (P GSE ) NMR
Mea su r em en t. The PGSE-NMR measurements were made
by using a J EOL GSH-200 spectrometer with a 4.7 T wide bore
superconducting magnet controlled by a TecMAG Galaxy
system equipped with J EOL pulse field gradient probes and
a current amplifier. Each electrolyte solution and polymer
electrolyte were placed in a 5 mm (outer diameter) NMR
microtube (BMS-005J , Shigemi, Tokyo) to a height of 5 mm.
The length of the sample was intentionally made short so that
it lay within the region of the constant magnetic field gradient.
In electrolyte solutions, the self-diffusion coefficients were
obtained at 40 °C and in polymer electrolytes at 60 °C. The
7
1H and Li spectra were measured with a multiple-tuned PFG
probe. The 19F spectrum was measured using a 19F/1H probe.
The gradient strength was calibrated and cross-checked using
the known self-diffusion coefficient of H2O at 30 °C (2.45 ×
10-5 cm2 s-1).15 The measurements of the diffusion coefficients
of the solvent, anion, and lithium ion were respectively made
7
by 1H, 19F, and Li NMR. The simple spin-echo pulse sequence
was used for the diffusion measurements, and the free diffu-
sion echo signal attenuation, E, is related to the experimental
parameters by
ln(E) ) ln(S/Sg)0) ) -γ2g2Dδ2(∆ - δ/3)
(1)
where S is the spin-echo signal intensity, δ is the duration of
the field gradient with magnitude g, γ is the gyromagnetic
ratio, D is the self-diffusion coefficient, and ∆ is the interval
between the two gradient pulses.16 By plotting ln(S/Sg)0) vs
γ2g2δ2(∆-δ/3), the self-diffusion coefficient can be derived from
the slope of the resulting straight line.
2.5. Electr och em ica l Mea su r em en t. Ionic conductivity
was determined by means of the complex impedance measure-
ments with stainless steel blocking electrodes, using a computer-
controlled Hewlett-Packard 4192A LF impedance analyzer
over the frequency range from 5 Hz to 13 MHz. For electrolyte
solutions, a sample was filled using a PTFE ring spacer (13
mm o.d., 7 mm i.d., 2 mm thickness). For polymer electrolytes,
a film (0.2 mm thickness) was cut into disks of 10 mm diameter
and put into a PTFE ring spacer (13 mm o.d., 10 mm i.d., 0.2
mm thickness). The electrolyte solution and polymer electro-