Lithium ion batteries fabricated with ionic ladder-like polysilsesquioxane hybrid ionogels

Article abstract of DOI:10.1166/jnn.2017.14144

A new cross-linkable ionic group-functionalized ladder-like structured polysilsesquioxane was utilized as crosslinker for fabrication of hybrid ionogels. The ionic ladder-like polysilsesquioxane was completely solution processable in ionic liquid electrolytes and through chemical crosslinking, hybrid ionogel electrolytes with high ionic conductivity and electrochemical stability were obtained. Lithium ion batteries assembled with these hybrid ionogels electrolytes exhibited excellent cell cycling performance at elevated temperatures, suggesting the highly utile nature of our hybrid ionogel electrolytes.

Full text of DOI:10.1166/jnn.2017.14144

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Nanoscience and Nanotechnology
Vol. 17, 5570–5573, 2017
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Lithium Ion Batteries Fabricated with Ionic Ladder-Like
Polysilsesquioxane Hybrid Ionogels
1
1
1ꢀ2
1ꢀ2
1ꢀ2ꢀ3ꢀ∗
Jin Hong Lee , Albert S. Lee , Soon Man Hong , Seung Sang Hwang , and Chong Min Koo
1
Materials Architecturing Research Center, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea
Nanomaterials Science and Engineering, University of Science and Technology, Daejeon, 305-350, Republic of Korea
KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, Republic of Korea
2
3
A new cross-linkable ionic group-functionalized ladder-like structured polysilsesquioxane was uti-
lized as crosslinker for fabrication of hybrid ionogels. The ionic ladder-like polysilsesquioxane was
completely solution processable in ionic liquid electrolytes and through chemical crosslinking, hybrid
ionogel electrolytes with high ionic conductivity and electrochemical stability were obtained. Lithium
ion batteries assembled with these hybrid ionogels electrolytes exhibited excellent cell cycling perfor-
mance at elevated temperatures, suggesting the highly utile nature of our hybrid ionogel electrolytes.
Keywords: Polysilsesquioxane, Ionic Liquids, Lithium Ion Batteries.
1
. INTRODUCTION
2. EXPERIMENTAL DETAILS
2.1. Materials
All materials were vacumm distilled or recrystallized prior
to use. All solvents were used as received.
With increasing demands for high performance lithium ion
batteries, subsequent needs for enhanced safety have been
a key issue and challenge for engineers. To mitigate the
most common safety concerns of lithium ion batteries,
which are electrolyte leakage and explosions derived from
such leakage, are to develop solidified electrolytes.
However, completely solid polymer electrolytes without
liquid components lack the required ionic conductivities
for practical industry application. As such, gel polymer
electrolytes and solidified ionic liquids, so-called ionogels,
have received much attention. Ionogels can be fabricated
via chemical or physical crosslinking methods, but chem-
ical crosslinking with highly soluble materials have been
sought out as the most facile method.
2
.2. Synthesis of LPClSQ
1
8
The synthesis of LPClSQ followed our previous method
utilizing 3-chloropropyltrimethoxysilane as monomer.
2
2
.3. Synthesis of LVImClSQ
To a solution of LPClSQ (1 g) in DMF (20 mL), 1-vinyl
imidazole (0.2 g, 2.1 mmol) was added under Ar. The
3
–5
ꢀ
reaction mixture was heated to 60 C for 24 h and purified
through repeated precipitations in hexane.
However, a remaining problem with ionogels is their
insufficient mechanical properties. As such, the hybridiza-
6
2.4. Synthesis of LVImTFSISQ
LVImClSQ (1 g) was dissolved in deionized water (5 mL)
and precipitated in a previously prepared solution of
LiTFSI (0.72 g, 0.25 mmol) in deionized water (5 mL).
The precipitates were collected via vacuum filtration and
tion of ionogels with inorganic materials have been exten-
sively investigated in several recent reports, most notably
with the Vioux and Archer groups.
6
ꢀ7
As ladder-structured polysilsesquioxanes are known to
ꢀ
8
LPVImTFSI stored at 40 C prior to use.
exhibited superior thermal and mechanical properties over
organic-based and other hybrid materials with uncon-
trolled structure, all while having excellent solubility in
organic solvents, we sought out to develop hybrid iono-
gels through synthesis of an ionic ladder-like structured
polysilsesquioxane.
2
.5. Fabrication of Hybrid Ionogels
LVImTFSISQ was dissolved in an ionic liquid elec-
trolyte (ILE) solution of 1M LiTFSI in N -butyl-
N -methylpyrrolidiniumbis (trifluoromethylsulfonyl)imide
(
BMPTFSI) and thermally cured with AIBN as radical
∗
ꢀ
Author to whom correspondence should be addressed.
initiator (1 wt% of LVImTFSISQ) at 70 C for 3 h to
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J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 8
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doi:10.1166/jnn.2017.14144

Lee et al.
Lithium Ion Batteries Fabricated with Ionic Ladder-Like Polysilsesquioxane Hybrid Ionogels
yield hybrid ionogels. The hybrid ionogels were named
LIE-5, LIE-10 and LIE-20 according to LVImTFSISQ
crosslinker weight percentage of 5 wt%, 10 wt%, and
synthetic scheme shown in Figure 1. As shown, the
ladder-structured polymer backbone with chloropropyl
groups was first obtained by our previously devel-
8
–11
2
0 wt%, respectively.
oped method
and the vinylimidazolium groups intro-
duced through quaternization reaction in DMF media.
Through simple anion exchange in water, LVImTFSISQ
was obtained as a viscous brown liquid with excellent
yields (∼88%).
2
.6. Electrochemical Measurements
The ionic conductivity was determined using a complex
impedance analyzer (Bio-Logics, VMP3) over frequency
range from 1 Hz to 1 MHz at AC amplitude of 10 mV.
The electrochemical stability of the hybrid ionogel elec-
trolytes was examined using a linear sweep voltammetry
system. In the experiments, a stainless steel working elec-
trode was used with lithium metal as both the counter and
reference electrodes. The voltage was swept at a scan rate
Figure 2 shows the characterization results for the vari-
ous intermediary products and final ionic ladder-like struc-
tured polysilsesquioxane, LVImTFSISQ. As shown, all of
the chloropropyl groups were quantitatively substituted
with the vinyl imidazolium group as indicated by the shift
ꢁ
in –CH -peak characterized as c to c , as well as the
2
ꢁ
−1
new peak d and d attributed aromatic proton of vinyl
imidazolium in Figure 1(a). Moreover, the C NMR of
LVImTFSISQ in Figure 1(b) revealed the presence of
of 1.0 mV s . Electrochemical measurements of the gel
polymer electrolyte were conducted using 2032 coin cells
consisting of a separator, Li metal and a LiFePO cathode
1
3
4
−
TFSI anion as shown by the new sharp peaks at 113,
(
90 wt% LiFePO , 5 wt% carbon black, 5 wt% PVDF). All
4
1
18, 122, and 127 ppm and the trifluorosulfonyl vibra-
the cells were assembled in argon-charged glove box. After
fabrication, the cells with pre-gel solution were subjected
to thermal cross-linking for 3 h at 70 C. The galvanostatic
charge–discharge experiments were carried out with volt-
age range of 2.5–4.2 V using a battery cycler (Wonatech,
WBCS3000) at 50 C.
−1
−1
tions (1193 cm and 1043 cm ) in the FTIR spectra in
Figure 1(c).
ꢀ
FT-IR analysis was also carried out to characterize the
chemical structures of the cured ionogels. As presented
−1
ꢀ
in Figure 3, the characteristic peak around 1640 cm
from the C C stretching mode of the vinyl group of
LVImTFSI disappeared after thermal treatment, indicating
the crosslinking reaction was complete.
3
. RESULTS AND DISCUSSION
The synthesis of ionic ladder-like polysilsesquiox-
ane with crosslinkable functional groups followed the
The room temperature ionic conductivities of the fabri-
cated hybrid ionogels were shown in Figure 4 as a function
Cl
Cl
Cl
K CO /H O/THF
in-situpolycondensation
H
Si
O
2
3
2
O
OH
OH
S i
Si
H
at 25 ºC
Hydrolysis
Si
H CO
OCH3
HO
OH
O
3
n
OCH3
OH
C l
LPClSQ
N
+
N
C l
N
N+
Cl-
TFSI-
OH
OH
N
N
H
O
Si
O
LiTFSI/H O
H
Si
O
Si
O
H
2
OH
OH
O
O
OH
H
O
Si
at 60ºC
DMF
H
Si
H
Si
n
O
O
OH
n
n
N+
N+
Cl-
TFSI-
Cl
N
N
LVImClSQ
LVImTFSISQ
Figure 1. Synthetic scheme for LPClSQ, LVImClSQ and LVImTFSISQ.
J. Nanosci. Nanotechnol. 17, 5570–5573, 2017
5571

Lithium Ion Batteries Fabricated with Ionic Ladder-Like Polysilsesquioxane Hybrid Ionogels
Lee et al.
Figure 2. (a) H NMR, (b) 13C NMR, and (c) FTIR spectra for LPClSQ, LVImClSQ and LVImTFSISQ.
1
of crosslinkable ionic ladder-like polysilsesquioxane.
As shown, the ionic conductivities for the hybrid
ionogels decreased as a function of ionic ladder-like
polysilsesquioxane due to the increasing rigidity of the
network structure. However, LIE-10 hybrid ionogel elec-
trolyte fabricated with only 10 wt% of ionic ladder-like
polysilsesquioxane, LVImTFSISQ, exhibited high ionic
conductivity (∼0.3 mS/cm), a most practical value for
application in lithium ion battery cells.
Next, the electrochemical stability of the LIE-10 was
measured through linear sweep voltammetry in Figure 5.
As shown, the hybrid ionogels fabricated with crosslink-
able ionic ladder-like polysilsesquioxane exhibited high
electrochemical stability (up to 5 V vs. Li+/Li) which led
Figure 4. Room temperature ionic conductivities of hybrid ionogels as
a function of ionic ladder-like polysilsesquioxane crosslinker.
Figure 3. FTIR spectra of LIE-10 before and after thermal treatment.
Figure 5. Linear sweep voltammetry curves for LIE-10.
J. Nanosci. Nanotechnol. 17, 5570–5573, 2017
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Lee et al.
Lithium Ion Batteries Fabricated with Ionic Ladder-Like Polysilsesquioxane Hybrid Ionogels
ion battery performance revealed promising cycling
behavior.
Acknowledgment: This work was financially supported
by a grant from the Fundamental R&D Program for Core
Technology of Materials and the Industrial Strategic Tech-
nology Development Program funded by the Ministry of
Knowledge Economy, Republic of Korea. Partial funding
was given by the Materials Architecturing Research Cen-
ter of Korea Institute of Science and Technology and the
Korea Research Fellowship Program funded by the Min-
istry of Science, ICT, and Future Planning through the
National Research Foundation of Korea.
Figure 6. Cyclability of hybrid ionogels LIE-10 at 0.1C–0.2C (charge–
ꢀ
discharge) at 80 C.
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Received: 25 May 2016. Accepted: 1 September 2016.
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