Synthesis of new fluorinated imidazolium ionic liquids and their prospective function as the electrolytes for lithium-ion batteries

Article abstract of DOI:10.1016/j.jfluchem.2014.05.005

Two fluorine-containing ionic liquids, 1-(2,2,2-trifluoroethyl)-3- methylimidazolium tosylate and 1-(2,2,2-trifluoroethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (TFSI anion), were obtained in good yields and high purity via a green pathway procedure free of solvent and hazardous catalyst. The incorporation of CF₃ moieties in imidazolium structure decreases the ILs TFSI melting point. The preliminary electrochemical results are very promising, a wide electrochemical stability up to 5.7 V vs Li ⁺/Li for the fluorinated imidazolium with TFSI anion.

Full text of DOI:10.1016/j.jfluchem.2014.05.005

Accepted Manuscript
Title: Synthesis of new fluorinated imidazolium ionic liquids
and their prospective function as the electrolytes for
lithium-ion batteries
Author: Anh Ngoc Tran Thanh-Nhan Van Do Loan-Phung
My Le Thach Ngoc Le
PII:
S0022-1139(14)00134-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2014.05.005
FLUOR 8317
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
29-1-2014
17-5-2014
21-5-2014
Please cite this article as: A.N. Tran, T.-N. Van Do, L.-P.M. Le, T.N. Le, Synthesis
of new fluorinated imidazolium ionic liquids and their prospective function as
the electrolytes for lithium-ion batteries, Journal of Fluorine Chemistry (2014),
http://dx.doi.org/10.1016/j.jfluchem.2014.05.005
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1
Synthesis of new fluorinated imidazolium ionic liquids and their
prospective function as the electrolytes for lithium-ion batteries
1
1
2
1
Anh Ngoc Tran , Thanh-Nhan Van Do , Loan-Phung My Le , Thach Ngoc Le
1
Department of Organic Chemistry, Faculty of Chemistry, University of Science, Vietnam National
University-Ho Chi Minh City (VNUHCM), Ho Chi Minh City, 70000, Viet Nam
2
Applied Physical Chemistry Laboratory (APCLab), Faculty of Chemistry, University of Science,
Vietnam National University-Ho Chi Minh City, Ho Chi Minh City, 70000, Viet Nam
Tel.: +84-838653212; E-mail: lenthach@yahoo.com; lmlphung@hcmus.edu.vn
Highlights
-
-
-
-
-
Green pathway to prepare fluorinated ionic liquids.
1-(2,2,2-Trifluoroethyl)-3-methylimidazolium tosylate.
1-(2,2,2-Trifluoroethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.
Both will be prospective electrolytes for lithium batteries.
[CF CH MIm][Tf N] even showed a wider electrochemical window.
3
2
2
Page 1 of 23

2
Abstract: Two fluorine-containing ionic liquids, 1-(2,2,2-trifluoroethyl)-3-methylimidazolium
tosylate and 1-(2,2,2-trifluoroethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (TFSI
anion), were obtained in good yields and high purity via a green pathway procedure free of solvent
and hazardous catalyst. The incorporation of CF moieties in imidazolium structure decreases the ILs
3
TFSI melting point. The preliminary electrochemical results are very promising, a wide
+
electrochemical stability up to 5.7 V vs Li /Li for the fluorinated imidazolium with TFSI anion.
Keywords: Fluorinated imidazolium; Ionic liquids; Lithium-ion battery; Electrolyte; Solvent-free
pathway; Electrochemical stability.
Page 2 of 23

3
1
.
Introduction
In recent years, there have been many studies focusing on developing new electrolytes for
rechargeable lithium batteries to enhance its safety and longevity [1-3]. Some electrolytes based on
solid and gel materials were developed but their poor ion conductivity has been the main obstacle
which lessens the interest towards these materials [3-5]. Ionic liquids (ILs), alternatively, have been
considered as the promising candidates because of their extraordinary characteristics such as non-
volatility, non-flammability, high ion conductivity, and extremely thermal and electrochemical
stability [6-8]. Especially, bis(trifluoromethanesulfonyl)imide based ionic liquids have attracted a
greatest attentions due to their low viscosity as well as the broad electrochemical window [9-17]. In
this study, we proposed a green pathway to prepare 1-(2,2,2-trifluoroethyl)-3-methylimidazolium
3 2
bis(trifluoromethanesulfonyl)imide ([CF CH MIm][TFSI]) via the intermediate 1-(2,2,2-
trifluoroethyl)-3-methylimidazolium tosylate ([CF CH MIm][OTs]) and studied their thermal and
3
2
electrochemical properties for the first time to give initial evaluations on their potential of being used
as new electrolytes for lithium batteries. Compared to previous reports, in which toxic solvent
methylene chloride [18,19] or hazardous catalyst pyridine [20] was used, the procedure here in
3 2
allowed to obtain [CF CH MIm][TFSI] under very mild conditions (solvent-free, cheap and non-
hazardous catalyst, and less time-consuming). The thermal and electrochemical properties of
synthesized ILs were initially characterized. The fluorinated imidazolium ILs exhibits very high
electrochemical stability in oxidation.
2
.
Results and discussion
Page 3 of 23

4
2
.1. Synthesis of ionicliquids
In the three-step pathway illustrated in Scheme 1, the final product [CF CH MIm][TFSI] was
3
2
3 2
planned to be derived from the precursor [CF CH MIm][OTs] which had been previously synthesized
via the nucleophilic attack of 1-methylimidazole (4) to ester 3. The first step, tosylation of 2,2,2-
trifluoroethanol, was performed under ultrasound irradiation to afford the first isolatable compound 3.
The results from Table 1 showed that reaction temperature, reaction time, and molar ratio 1:2 affected
the yield of 3 at different rates. In general, there was a slight increase in yield of compound 3 along
with raising the reaction temperature or prolonging the reaction time. However, no complete
conversion could be observed unless an excess amount of reactant 2 was used. Due to the high
hydroscopic, at least 1.2 equiv. of compound 2 was used to ensure a quantitative conversion (entry 9,
Table 1).
Scheme 1
Compared to other activation methods investigated in our works (entry 12-14, Table 1) and
previous reports [21-25], sonication was the most appropriate method for such heterogeneous
reactions to afford compound 3 in the best yield. In addition, the replacement of traditional toxic bases
(
e.g. pyridine, triethylamine, 4-DMAP, and DABCO) by K CO , an environmentally benign one, was
2 3
also encouraged in the green chemistry.
Table 1
For the next step, it can be referred from Table 2 that the intermediate ionic liquid
o
[CF
3
CH
2
MIm][OTs] could be obtained in the highest yield of 77% at 120 C within 24 h (entry 9,
Table 2). Increasing the temperature or extending the reaction time did not result in better yields
entry 5 and 10, Table 2). [CF CH MIm][OTs] was then ion-exchanged with lithium
(
3
2
o
bis(trifluoromethanesulfonyl)imide (LiTFSI) to provide the final product at 40 C with a few minutes
under the ultrasound irradiation (71%, entry 2, Table 3). The microwave irradiation and the
conventional heating under the same conditions mentioned for the sonication did not further increase
the yields of product (entry 8 and 9, Table 3).
Table 2
Table 3
Page 4 of 23

5
2
2
.2. Physical chemical and electrochemical properties of synthesized ionic liquids
.2.1. Physical chemical properties
Two synthesized ionic liquids, through thermo-gravimetric analysis (TGA), were evaluated for the
o
thermal stability. The ILs exhibit a high decomposition temperature, above 340 C (Table 4). The
o
DSC analysis showed that [CF CH MIm][TFSI] presents a lower melting temperature, about -16 C
3
2
3 2 3 3
instead of -15 °C for [CH CH MIm][TFSI]. The replacement of a CH group by a CF one induces a
decrease in the IL melting point. The result is quite different with the work of M.L.P. Le et al [2,12].
However, it could be a good alternative to use CF group incorporated in the imidazolium structure in
3
order to decrease the melting point and the viscosity of ionic liquid.
Table 4
The density, viscosity and conductivity of [CF CH MIm][TFSI] was determined and compared
3
2
3 2
to the electrolyte of [CF CH MIm][TFSI] + 0.25 M LiTFSI. The addition of LiTFSI induces a
decrease of ionic conductivity. The addition of lithium salt decreases the ionic conductivity. This
behavior may be due to the increase in the viscosity or association resulting from specific interaction
involving the formation of ionic cluster [2].
Table 5
2
.2.2. Electrochemicalproperties
One of the most important requirements for the use of ILs as liquid electrolyte is that they must
have a wide electrochemical window to ensure that it is neither oxidized nor reduced in the operating
voltage range of lithium batteries. This parameter can be easily evaluated by cyclic voltammetry.
Acetonitrile (ACN) and the mixture of ethylene carbonate (EC)-dimethyl carbonate (DMC) (1:1
v/v) were used as solvents to evaluate firstly the electrochemical windows of synthesized ionic
3 2
liquids, particularly [CF CH MIm][OTs] whose melting point is fairly high above the room
temperature. Compared with a different supporting electrolyte 0.005 M TBAP/ACN, equimolar
solutions of [CF CH MIm][TFSI] and [CF CH MIm][OTs] generated similar cyclic voltammograms
3
2
3
2
in which reduction and oxidation peaks were approximately 2.7 and 4.3 V, respectively. However, for
the ionic liquid dissolved in EC-DMC, the oxidation peaks were shifted to more positive potential
(over 4.5 V) compared withthe solution containing TBAP/ACN at the same molar concentration. The
Page 5 of 23

6
electrochemical windows were expanded as the result. In addition, the presence of flat potential
plateau also confirmed the high purity of the synthesized ionic liquids (Figure 1).
Figure 1
Thus, EC-DMC was chosen as an appropriate solvent for further investigations of
[
CF CH MIm][OTs] solutions at various molar concentrations. In Figure 2, the oxidation peaks were
3 2
gradually shifted to more positive value while the reduction peaks remained almost unchanged when
increasing the concentration of [CF CH MIm][OTs] solutions. This result proved that obtained
oxidation-reduction signals were generated from ionic liquid [CF CH MIm][OTs], not from the
3
2
3
2
solvent solution.
Figure 2
In order to compare with the conventional electrolyte 1 M LiPF /EC-DMC (1:1) used in lithium
6
batteries, the cyclic voltammogram of pure [CF
3
CH
2
MIm][TFSI] was recorded. The voltammograms
+
in Figure 3 showed that the pure [CF CH MIm][TFSI] started being oxidized at 5.7 V vs Li /Li while
3
2
6
the 1 M LiPF /EC-DMC (2:1) solution was only stable within the potential range below 5.5 V vs
+
Li /Li. When scanning to more positive potential over this limit, the oxidation current of LiPF
6
solution increased so rapidly that an oxidation wall was created. Besides, the oxidation stability of
+
pure [CF
3
CH
2
MIm][TFSI] is higher than [CH
3
CH
2
MIm][TFSI] (about 5.8 V vs Li /Li). The
electrochemical stability of imidazolium-based ILs seems insufficient in lithium batteries. Thus, it can
be concluded that the incorporation of CF moieties group in imidazolium structure improve well the
3
ILs oxidation stability. The result is coherent with the work of M.L.P. Le et al [2,12].
The addition of lithium salt induces a remarkable decrease of oxidation current while the onset
+
+
oxidation potential remains about 5.8 V vs Li /Li (inset in Figure 3). The role of Li ions in the
formation of surface films on different electrodes (glassy carbon, platinum,…) in IL was already
+
discussed in the literature previously. It suggests that protective Li containing are formed on a Pt
+
metal surface due to the reduction of TFSI in the presence of Li ion [27,28]. However, the formation
of SEI film layer on the electrode materials during cycling test is still irrelevant for ILs containing Li
salt.
Figure 3
Page 6 of 23

7
3
.
Experimental
.1. Chemicals and equipments
All chemical precursors and solvents were purchased from Sigma-Aldrich and employed without
3
further purification. The synthesized ionic liquids were vacuum dried at 120 °C during 24 hours. The
water contains of ILs, determined by Karl-Fisher was below 20 ppm. The ILs were stored in a
1
glovebox ([H
2
O] < 3 ppm). The structure of intermediate and final products were confirmed by H
13
1
NMR and C NMR spectra measured on a Bruker 500 spectrometer (500 MHz for H and 125 MHz
1
3
for C) in DMSO-d6 or acetone-d6, and mass spectra recorded via GC-MS and LC-HR-MS
techniques. GC-MS analyses were performed on an Agilent GC System 7890A, equipped with a mass
selective detector Agilent 5973 and a capillary column HP-5MS (30 m x 0.25 mm x 0.25 m). LC-
HRMS analyses were performed on a Bruker micrOTOF-Q II.
DSC measurements were performed using Mettler Toledo DSC1 Star. Samples of 10 mg were
sealed in aluminiumpansin a glovebox. Each sample was heated from -80 °C to 100 °C at a heating
-1
rate of 10 °C.min . Thermogravimetric measurements were carried outwitha TGA Q500 V20.10
Build. A few milligram of the sample was heated from the room temperature up to 600 °C at 10
-1
°
C.min under oxygen flow.
The ionic conductivity and viscosity of ILs in glove box was measured by using Conductimeter
OAKION CON 2700 and Ostwald viscometer CANNON.
-1
-1
Cyclic voltammetry of ILs at the scan rate of 1 mV.s and 20 mV.s was recorded on MGP2
Biologic instrument (France) by using a three-electrode cell. The counter electrode was a Pt wire and
the working electrode was a Pt electrode with a diameter 1 mm and 25 m for characterization of ILs
3
solution and pure ILs. The reference electrode was a Ag wire in AgNO 10 mM in acetonitrile + 0.1
M tetrabutylammonium perchlorate (TBAP). Preparation of electrolyte solutions was carried out in a
+
glovebox to protect the ionic liquids from hygroscopicity. Potential can be converted to the Li /Li by
adding 3.548 V [29].
Page 7 of 23

8
The oxidation stability of lithium electrolyte containing pure ILs with LiTFSI was also studied
for by cyclic voltammetry (CV). The lithium salt concentration is 0.25 M in order to compromise the
ionic conductivity and viscosity of electrolyte.
3
.2. Synthesis of ionic liquids
Ionic liquids were synthesized in a Branson 1510 ultrasonic bath, a Discover (CEM) microwave
reactor, and an IKA magnetic stirrer.
3
.2.1. 2,2,2-Trifluoroethyl tosylate (3)
3
.2.1.1. Under ultrasonic irradiation
A glass capped test tube (10 mL volume) was charged with 2,2,2-trifluoroethanol (0.500 g, 5
mmol), tosyl chloride (1.144 g, 6 mmol), and potassium carbonate (1.382 g, 10 mmol). Then it was
o
immersed into an ultrasonic bath and irradiated for 60 min at 55 C. After finishing above steps,
sodium hydroxide (0.200 g, 5 mmol) was added and the resulting mixture was continuously sonicated
for further 5 min. The mixture was subsequently cooled to the room temperature and diluted with
Et
concentrated under low pressure to afford product 3 as a white crystallized solid (92%). MS (EI) m/z
%): 254, 155, 91 (100), 65.
2 2 4
O. The ether solution was washed with water until neutralization, dried over Na SO , filtered, and
(
3
.2.1.2. Under microwave irradiation
A 10 mL pressurized vessel was charged with the same materials as in the previous section. The
o
mixture was then exposed to the microwave at 55 C for 60 min in a Discover (CEM) microwave
reactor. Upon the completion, the resulting mixture was worked up in the same manner described for
the ultrasound-assisted reaction.
3
.2.1.3. Under conventional heating
A flask (10 mL) was charged with the same materials as described above. Then it was assembled
with a condenser whose upper end was fitted with a drying tube. This assembly was immersed in an
o
oil bath, heated gently, and simultaneously stirred for 60 min at 55 C. Upon completion, the resulting
mixture was again worked up according to the procedure mentioned above.
3
.2.1.4. Under grind condition
Page 8 of 23

9
A mixture of the initial compounds as mentioned in previous sections was ground in a mortar for
0 min at room temperature. Upon completion, the work-up procedure was the same as above.
6
3
3 2
.2.2. [CF CH MIm][OTs]
A mixture of compound 3 (1.271 g, 5 mmol) and 1-methylimidazole (0.411 g, 5 mmol) were
charged into a flask (10 mL) assembled with a condenser. This montage was heated in an oil bath, and
o
simultaneously stirred for 24 h at 120 C. Upon completion, the resulting mixture was washed with
Et
2
O until all starting material were removed completely (checked by GC) and freeze-dried under
1
vacuum to obtain [CF CH MIm][OTs] as a yellow solid at room temperature (77%). H NMR (500
3
2
MHz, DMSO-d6): δ (ppm) 9.35 (s, 1H), 7.85 (s, 1H), 7.83 (s, 1H), 7.51 (d, J = 8.0 Hz, 2H), 7.11 (d, J
1
3
=
8.0 Hz, 2H), 5.40 (q, J = 9.0 Hz, 2H), 3.90 (s, 3H), 2.27 (s, 3H); C NMR (125 MHz, DMSO-d6): δ
(ppm) 145.3, 138.4, 137.9, 128.1, 125.4, 124.4, 123.5, 122.7 (q, J = 276 Hz), 48.3 (q, J = 35 Hz),
+
3
6.1, 20.7; HRMS (ESI ) m/z 165.0639 (165.0639 calcd. for C
6
H
8
N
2
F
3
); Anal. calcd. for C
6
H
8
N
2
F
3
:
-
(
%) C 43.62; H 4.89; N 16.97; F 34.53. Found: C 43.64; H 4.88; N 16.96; F 34.51. HRMS (ESI ) m/z
1
1
3
3
71.0116 (171.0115 calcd. for C S); Anal. calcd. for C S: (%) C 49.12; H 4.12; O 28.06; S
7
H
7
O
3
7 7 3
H O
8.70. Found: C 49.11; H 4.12; O 28.04; S 18.73.
.2.3. [CF CH MIm][TFSI]
3
2
.2.3.1. Under ultrasonic irradiation
A mixture of [CF CH MIm][OTs] (0.336 g, 1 mmol) and deionized water (1 mL) was charged
3
2
into a glass test tube (10 mL) and then immersed into an ultrasonic bath. A solution of LiTFSI (0.2871
g, 1 mmol) in deionized water (1 mL) was added dropwise to the above ionic liquid solution. The
o
mixture was irradiated for 10 min at 40 C. Upon completion, the resulting mixture consisted of two
phases, the upper aqueous phase was removed and the lower phase was diluted with dichloromethane.
This organic solution was then washed with deionized water until no remaining starting materials
3 2
(LiTFSI and [CF CH MIm][OTs]) as well as by-product (LiOTs) was detected, concentrated under
low pressure, and finally freeze-dried under vacuum to give [CF CH MIm][TFSI] as a yellow liquid
3
2
1
at room temperature (71%). H NMR (500 MHz, acetone-d6): δ (ppm) 9.23 (s, 1H), 7.85 (s, 1H), 7.82
1
3
(
s, 1H), 5.36 (q, J = 9.0 Hz, 2H), 4.12 (s, 3H); C NMR (125 MHz, acetone-d6): δ (ppm) 138.4,
+
1
24.4, 123.6 (q, J = 276 Hz), 123.4, 121.0 (q, J = 319 Hz), 50.1 (q, J = 36 Hz), 37.3. HRMS (ESI )
Page 9 of 23

10
m/z 165.0639 (165.0639 calcd. for C
6
H
8
N
2
F
3
); Anal. calcd. for C
6
H
8
N
2
F
3
: (%) C 43.62; H 4.89; N
-
1
6.97; F 34.53. Found: C 43.64; H 4.88; N 16.96; F 34.51. HRMS (ESI ) m/z 279.9153 (279.9172
calcd. for C
Found: C 8.59; O 28.05; N 5.01; F 40.71; S 18.69.
.2.3.2. Under conventionalheating
2 4 6 2 2 4 6 2
O NF S ); Anal. calcd. for C O NF S : (%) C 8.57; O 28.06; N 5.00; F 40.72; S 18.70.
3
The same materials as in the previous section were charged into a flask (5 mL) which was
o
subsequently immersed in an oil bath, heated gently, and simultaneously stirred for 10 min at 40 C.
Upon completion, the resulting mixture was worked up according to the procedure mentioned above.
3
.2.3.3. Under microwave irradiation
A 10 mL pressurized vessel was charged with the same mixture as described before. The mixture
o
was then exposed to microwave at 40 C for 10 min in a Discover (CEM) microwave reactor. Upon
completion, the resulting mixture was worked up in the same manner described for previous methods.
4
.
Conclusion
We successfully synthesized [CF
3
2 3 2
CH MIm][TFSI] and its precursor, [CF CH MIm][OTs] by the
ultrasonic irradiation without using solvents, hazardous catalysts and in the short reaction time. Both
of the synthesized ionic liquids showed the good thermal and electrochemical stability. These
behaviors are crucially required for the electrolytes in lithium batteries. [CF
3
CH
2
MIm][TFSI] exhibits
/EC-
a wide electrochemical window in comparison with the conventional electrolyte (1 M LiPF
6
DMC). The primarily result is very encouraging, that the incorporation of CF group in imidazolium
3
structure enhance the oxidation stability and decrease the melting point as well as viscosity of ILs.
The electrolyte of [CF
3
CH
2
MIm][TFSI] + 0.25 M LiTFSI exhibits a remarkable decrease of oxidation
+
current even through the onset oxidation potential remains (about 5.8 V vs Li /Li). Our further works
will focus on the electrolyte – electrode interface during cycling performance.
Acknowledgements
We are grateful to NAFOSTED program (National Foundation for Science and Technology
Development, Vietnam) for financial support. The author L.M.L. Phung would like to thank the
support of Vietnam National University-Ho Chi Minh City through the Science and Technology Fund
granted for the B2011-18-01 TĐ.
Page 10 of 23

11
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13
O
S
O
S
OH
F3C
K CO
2
3
F3C
+
Cl
O
O
O
1
2
3
N
N
4
CF3
N
CF3
N
O
S
O
O
LiTFSI
N
S
S
O
F
3
C
CF
3
N
N
O
O
O
[
CF CH MIm][TFSI]
[CF CH MIm][OTs]
3 2
3
2
Scheme 1. The strategy for preparation of [CF CH MIm][TFSI]
3 2
Page 13 of 23

14
Page 14 of 23

15
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16
Figure 1: Cyclic voltammograms of 0.005 M TBAP solution (a), 0.005 M [CF CH MIm][OTs]
3
2
-1
(
b) and [CF CH MIm][TFSI] (c).Cyclic voltammetry of ILs at the scan rate of 20 mV.s was
3 2
recorded by a three-electrode cell (Pt wire as counter electrode, Pt with diameter 1 mm was
used as working electrode and reference electrode was a Ag wire in AgNO 10 mM in
3
acetonitrile + 0.1 M tetrabutylammonium perchlorate). Acetonitrile (ACN) and the mixture of
ethylene carbonate (EC)-dimethyl carbonate (DMC) (1:1 v/v) were used as solvents.
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17
3 2
Figure 2. Cyclic voltammograms of [CF CH MIm][OTs] solution at different concentrations.
-1
Cyclic voltammetry of ILs at the scan rate of 20 mV.s was recorded by a three-electrode
cell (Pt wire as counter electrode, Pt with diameter 1 mm was used as working electrode and
3
reference electrode was a Ag wire in AgNO 10 mM in acetonitrile + 0.1 M
tetrabutylammonium perchlorate).
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18
Figure 3. Cyclic votammograms of pure [CF CH MIm][TFSI], [CF CH MIm][TFSI] + 0.25 M
3
2
3
2
LiTFSI vs 1 M LiPF
6
/EC – DMC (2:1) solution. Cyclic voltammetry of ILs at the scan rate of 1
-1
mV.s was recorded by a three-electrode cell (Pt wire as counter electrode, Pt with diameter
3
25 m was used as working electrode and reference electrode was a Ag wire in AgNO 10
mM in acetonitrile + 0.1 M tetrabutylammonium perchlorate).
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19
Table 1. Preparation of 2,2,2-trifluoroethyl tosylate (3)
a
b
o
Entry Method
1:2
Temp. ( C) Time (min)
Yield of 3 (%)
1
2
3
4
5
6
7
8
9
UI
UI
UI
UI
UI
UI
UI
UI
UI
UI
UI
MI
CH
G
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1.2
1:1.4
1:1.6
1:1.2
1:1.2
1:1.2
40
45
50
55
60
55
55
55
55
55
55
55
55
r.t.
30
30
30
30
30
45
60
75
60
60
60
60
60
60
33
44
58
62
61
65
74
75
92
93
95
66
26
61
1
0
1
2
3
4
1
1
1
1
a
UI: ultrasound irradiation, MI: microwave irradiation, CH: conventional
b
heating, G: grinding; Molar ratio.
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20
a
3 2
Table 2. Preparation of ionic liquid [CF CH MIm][OTs]
o
b
Entry
Temp. ( C) Time (h) Yield of [CF CH MIm][OTs] (%)
3
2
1
2
3
4
5
6
7
8
9
60
80
3
3
3
3
3
6
9
12
24
36
no reaction
11
28
46
40
50
56
64
77
77
100
120
140
120
120
120
120
120
1
0
a
Reaction conditions: conventional heating, 2,2,2-trifluoroethyl
b
tosylate:1-methylimidazole was 1:1; Isolated yield.
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21
a
3 2
Table 3. Preparation of ionic liquid [CF CH MIm][TFSI]
b
o
c
Entry
Method
UI
Temp. ( C) Time (min) Yield of [CF CH MIm][TFSI] (%)
3
2
1
2
3
4
5
6
7
8
9
35
40
45
50
40
40
40
40
40
10
10
10
10
5
15
20
10
10
b
54
71
63
58
51
68
67
61
22
UI
UI
UI
UI
UI
UI
MI
CH
a
[CF
3 2
CH MIm][OTs]:LiTFSI was 1:1; UI: ultrasound irradiation, MI: microwave
irradiation, CH: conventional heating; Isolated yield.
c
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22
a
Table 4.Properties of imidazolium ionic liquids
o
o
ILs
T / C
T / C
m
d
[
[
[
a
CF
CF
3
3
CH
CH
2
MIm][OTs]
MIm][TFSI]
35/45
-22/-12
-9
340
417
-
2
CH CH MIm][TFSI]
3
2
m d
T : melting point; T : degradation temperature.
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23
Table 5. Properties of imidazolium ionic liquids
-1
-1
Viscosity (mPa.s)
5 °C
Conductivity (mS.cm ) Density (g.ml )
3
35 °C
35 °C
[
CF CH MIm][TFSI]
55.1
-
1.92
1.56
1.54
1.67
3
2
[
CF CH MIm][TFSI] +
3
2
0
.25 M LiTFSI
Graphical Abstract
Two fluorine-containing ionic liquids, 1-(2,2,2-trifluoroethyl)-3-methylimidazolium tosylate and 1-
2,2,2-trifluoroethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (TFSI anion), were
(
obtained in good yields and high purity via a green pathway procedure free of solvent and hazardous
catalyst. The incorporation of CF moieties in imidazolium structure decreases the ILs TFSI melting
3
point. The preliminary electrochemical results are very promising, a wide electrochemical stability up
+
to 5.7 V vs Li /Li for the fluorinated imidazolium with TFSI anion.
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