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공학석사학위논문
Pyrrolinium-based ionic liquids as
electrolytes at high temperature for
LiFePO4 cells of lithium ion batteries
고온에서의 피롤리늄 이온성 액체를 전해질로
하는 LiFePO4 리튬이온전지의 특성
2013年 2月
서울대학교 대학원
화학생물공학부
이 혜 령
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Pyrrolinium-based ionic liquids as
electrolytes at high temperature for
LiFePO4 cells of lithium ion batteries
고온에서의 피롤리늄 이온성 액체를 전해질로
하는 LiFePO4 리튬이온전지의 특성
指導敎授 : 金 榮 奎
이 論文을 工學碩士 學位論文으로 提出함
2013年 2月
서울大學校 大學院
化學生物工學部
李 惠 玲
李 惠 玲 의 工學碩士 學位論文을 認准함
2012年 12月
委 員 長 ( 印 )
副委員長 ( 印 )
委 員 ( 印 )
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Pyrrolinium-based ionic liquids as
electrolytes at high temperature for
LiFePO4 cells of lithium ion batteries
by
Hyeryoung Lee
February 2013
Thesis Adviser: Young Gyu Kim
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학위논문 원문제공 서비스에 대한 동의서
본인의 학위논문에 대하여 서울대학교가 아래와 같이 학위논문
저작물을 제공하는 것에 동의합니다.
1. 동의사항
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것에 동의합니다.
2. 개인(저작자)의 의무
본 논문의 저작권을 타인에게 양도하거나 또는 출판을 허락하는 등
동의 내용을 변경하고자 할 때는 소속대학(원)에 공개의 유보 또는
해지를 즉시 통보하겠습니다.
3. 서울대학교의 의무
①서울대학교는 본 논문을 외부에 제공할 경우 저작권
보호장치(DRM)를 사용하여야 합니다.
②서울대학교는 본 논문에 대한 공개의 유보나 해지 신청 시 즉시
처리해야 합니다.
논문제목 : Pyrrolinium-based ionic liquids as electrolytes at high
temperature for LiFePO4 cells of lithium ion batteries
학위구분 : 석사 □․박사 □
학 과 : 화학생물공학부
학 번 : 2011-21070
연 락 처 :
저 작 자 : 이혜령 (인)
제 출 일 : 2013 년 2 월 4 일
서울대학교총장 귀하
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Abstract
Pyrrolinium-based ionic liquids as
electrolytes at high temperature for
LiFePO4 cells of lithium ion batteries
Lee hyeryoung
Chemical and biological engineering
The Graduate School
Seoul National University
Due to their unusual sets of properties, ionic liquids (ILs)
have many important applications in many field. Above all the
advantages of ILs, the superior high temperature
characteristics provide a appropriate solution to high
temperature electrolyte problems related with device internal
pressure build-up, corrosion, and thermal stability.
Our group have been reported characteristics of
different kinds of ionic liquids
(ILs)bis(trifluoromethanesulfonyl)imide (TFSI) include in
imidazolium, ammonium, pyrrolidinium and piperidinium based
compounds. Several research trials have contributed to develop
the novel pyrrolinium based ionic liquid which is containing
heteroatom substituent such as ether moiety have affirmative
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effect on cathodic stability, viscosity and ionic conductivity. In
addition to this, the plane structure caused higher conductivity
different with pyrrolidinium and piperidinium based ILs.
With this target ILs, we measured the function of the
lithium salt concentration to influence on the conductivity that
has been studied with carbonate.
The E(OMe)Pyrl-FSI(6) and P(OMe)Pyrl-FSI(7)
A(OMe)Pyrl-FSI(8) had the highest conductivity of 6.56
mS/cm , 4.69 mS/cm and 5.91 mS/cm at 0.5 M / 0.8 M LiTFSI
which were described higher than values of ILs including 1 M
salt concentration. Gratifyingly we expected, they not only
presented better discharge capacity than other ILs had 1.0 M
lithium salt concentration but these results were performed at 1
C rate.
We envisaged that these ILs transcend the barrier of the
carbonate electrochemical property is known as the superior
electrolyte until now. The thermal stability is the remarkable
property of the ILs as mentioned and we embarked on the
comparison of cycling performance with carbonate at high
temperature. The results was same as we expected that ILs
could have prominent cycle life and discharge capacity,
specially the result of P(OMe)Pyrl-FSI 0.5 M LiTFSI and
A(OMe)Pyrl-FSI 0.8 M LiTFSI stands out clearly. As the
result of analysis of electrolyte after reaction, decomposition
rate led to the value of the discharge capacity which is why the
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previous ILs with lower decomposition rate had higher
discharge capacity.
keywords : Ionic liquids, pyrrolinium, electrolyte, capacity,
carbonate, high temperature, concentration, decomposition rate
Student Number : 2011-21070
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TABLE OF CONTENTS
ABSTRACT … … … … … … … … … … … … … … … … … … … … … . . . v
LIST OF FIGURES ……………………………… .…… . .………… . . .x
LIST OF TABLE ………………..…………………………..……...………xi
LIST OF SCHEME………………..…………..…………………...………xii
LIST OF ABBREVIATIONS …………… . .………………… . .…xiii
INTRODUCTION…………………………..................………...………………..1
PART 1. SYNTHETIC APPROACH……..……..…………….............10
- Experimental
Materials …………………..………….……………..................................10
Synthetic scheme…………………….………………..…..………………..….10
General Procedure for the Preparation of the Pyrrolinium – based
Ionic Liquid………………..…………………..………………………………..11
1. Gener a l pro cedur e fo r pr epar at io n o f 1-a lkyl- 2-
pyrrolidinone…………………..………………………………….……….11
2. General procedure for the anion metathesis…………………….12
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Instruments and measurements……………………………..….…………13
- Result and Discussion……………………………..……………………14
PART 2. ELECTROCHEMICAL APPROACH………...............17
- Experimental
Materials …………………..………….……………..................................17
General Procedure for the Preparat ion of Design half
Cell…………………..…….…..…………………..……………………………..17
Instruments and Measurements……………………………..….………..19
- Result and Discussion……………………………..…………………….19
Physicochemical Properties……………………………..………….…19
Elect rochemical Propert ies……… ..…………….……………22
CONCLUSION………………………..….…………………………………………..35
REFERENCES....................................……………...........………..37
APPENDICES……………………….............................………..................39
ABSTRACT IN KOREAN………………………......................................40
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LIST OF FIGURES
Figure 1. Use and application of ILs ………………………..………..2
Figure 2. Comparison of energy densities………………………. …...2
Figure 3. Various species of ILs …………………………………..….5
Figure 4. Effect of viscosity on temperature……………………..…...20
Figure 5. Cycle life test of E(OMe)Pyrl-FSI xM LiTFSI for LiFePO4/Li
cells at room temperature …………………...………….....22
Figure 6. Cycle life test of P(OMe)Pyrl-FSI xM LiTFSI for LiFePO4/Li
cells at room temperature …………….………………….23
Figure 7. Cycle life test of A(OMe)Pyrl-FSI xM LiTFSI for
LiFePO4/Li cells at room temperature..…………………………..23
Figure 8 Cycling performance of various electrolytes for LiFePO4/Li
cell at 50 oC ……………………..…………………………………………...24
Figure 9. Capacity retention ratio of various electrolytes for LiFePO4/Li
cell at 50 oC……………………..…………………………………………...24
Figure 10. 1H-NMR and 13C-NMR spectrum of E(OMe)Pyrl-FSI 0.5 M
LiTFSI after cycle at 50 oC..……………………………....26
Figure 11. 1H-NMR and 13C-NMR spectrum of P(OMe)Pyrl-FSI 0.5 M
LiTFSI after cycle at 50 oC..………………...………..27
Figure 12. 1H-NMR and 13C-NMR spectrum of A(OMe)Pyrl-FSI 0.5 M
LiTFSI after cycle at 50 oC..…………………………………………..28
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LIST OF TABLES
Table 1. Comparison data of various lithium based batteries……….…4
Table 2. Reagents………………………………………….…………...9
Table 3. Yield of 1-alkyl pyrrolidinone…...………………………..…..9
Table4. Yield of 1-alkyl-2-alkoxy-pyrrolinium bis(fluorosulfonyl)imide
.........................................................................................................................10
Table 5. Components of the half cell……………………………………………..16
Table 6. Physical properties of E(OMe)Pyrl-FSI(6) electrolytes as a
function of LiTFSI concentration…………………………………..18
Table 7. Physical properties of P(OMe)Pyrl-FSI(7) electrolytes as a
function of LiTFSI concentration ……...................................19
Table 8. Physical properties of A(OMe)Pyrl-FSI(8) electrolytes as a
function of LiTFSI concentration ………………………..............19
Table 9. Decomposition rate of three ILs after reaction at 50 oC
according to 1H-NMR………………………………….……..............32
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LIST OF SCHEMES
Scheme 1. Synthesis of 1-alkyl pyrrolidinone………………...........9
Sc he me 2 . S ynt he s is o f 1 - a lk y l- 2 - a lk o xy- p yr r o l i n iu m bis(fluorosulfonyl)imide……………………………………………..10
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LIST OF ABBREVIATIONS
[E(OMe)]Pyrl 1-ethyl-2-methoxy-pyrrolinium
[P(OMe)]Pyrl 1-propyl-2-methoxy-pyrrolinium
[A(OMe)]Pyrl 1-allyl-2-methoxy-pyrrolinium
d chemical shift
d doublet
dd doublet of doublet
DMC dimethyl carbonate
DSC differential scanning calometry
h viscosity
EC ethylene carbonate
EMC ethyl methyl carbonate
h hour(s)
Hz hertz
IL ionic liquid
J coupling constant(s)
LIB lithium ion battery
M mole(s) per liter
m multiplet
ND not detected
NMR nuclear magnetic resonance spectroscopy
PC propylene carbonate
q quartet
quant. quantitative
RT room temperature
RTIL room temperature ionic liquid
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s ionic conductivity
s singlet
SEI solid electrolyte interphase
sext sextet
T temperature
t time
t triplet
Tc crystallization temperature
Td decomposition temperature
TFSI bis(trifluoromethanesulfonyl)imide
FSI bis(fluorosulfonyl)imide
TGA thermogravimetric analysis
Tm melting point
VC vinyl carbonate
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Introduction
Room temperature ionic liquids or RTILs have been
investigated since Walden identified and analyzed
physicochemical properties of ethylammonium nitrate in 1914.
RTILs are as salts that exist as liquid at or below room
temperature as the word presents.[1] Their remarkable
properties such as high ionic conductivity, non-flammability
and non-volatility as well as wide voltage window, wide liquid
range are interest to electrochemists. However, not only these
properties, ILs have attractive characteristics which are useful
to chemical reaction. In contrast to organic solvents, the low
vapor pressures of ILs could be green solvent to the
environmental problem and they are actually used in reactions
as excellent solvents or catalysts.
As the below Figure 1. ILs are significant part for
batteries as electrolytes that would be focused on this paper. In
our experiment, ILs applied to lithium ion batteries (LIBs).
Lithium ion battery (LIB) is the type of secondary
rechargeable battery in which lithium ions moves from the
negative electrode to the positive electrode during discharge,
and back when charging. LIB is composed the lightest metal and
the metal that has the highest electrochemical potential.
Because of its lightness, high energy density and better charge
efficiency than other types of batteries, LIBs are ideal for
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portable devices, such as notebook and computers. Moreover,
LIBs are environmentally friendly and not poisonous unlike
other metals such as lead, mercury and cadmium. The only
disadvantage of LIBs is that they are currently more expensive
than NiCd and NiMH batteries.
Figure 1. Use and application of ILs
Chemfiles Volume 5 Article 6 in SigmaAldrich
Figure 2. Comparison of energy densities
Journal of the Korean Electrochemical Society, 11, 2008, 197-210
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The positive electrode materials are essential part
which are lithium cobalt oxide (LCO), lithium iron phosphate
(LFP), lithium manganese oxide (LMO) and lithium nickel
manganese cobalt oxide (NMC) for rechargeable lithium
batteries. The excellent candidate for the material of a
rechargeable LIB is inexpensive, nontoxic, and environmentally
benign, that is LFP. Below table 1. shows summarized
properties of lithium based batteries.
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Table 1. Comparison data of various lithium based batteries
Cathode
materials LiCoO2 LiMn2O4 Li(NiCoMn)O2 LiFePO4
Reversible
capacity
(mAh/g)
140
100
150
145
Working
voltage
plateau (V)
3.7
3.8
3.6
3.2
Charge
termination
voltage (V)
4.25
4.35
4.3
4.2
Overcharge
tolerance (V) 0.1 0.1 0.2 0.7
R.T. Cycle
life (cycles) 400 300 400 1000
55 oC Cycle
life (cycles) 300 100 300 800
Heat Flow by
DSC (kJ/g) 650 150 600 10
Overcharge
without PCB
4.9/3C
Explosion
8V/3C
Firing 8V/3C Firing
25V/3C
Pass
Price
(US$/kg) 30 15 22 12
Battery
energy
density
(Wh/kg)
180
100
170
130
General Electronics Bsttery Co., Ltd. 1-4
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ILs are extremely suitable material for electrolyte as
previous mentioned advantages. Not only those properties they
could be also capable of diverse selection of cations and anions
that is readily adjust to their constituents based on properties
of functional groups[2-4].
Figure 3. Various species of ILs
N
N
R
+N
R R
+1 2
NR R
+
1 2N
R
+
NN R
R
+2
1
NN
NR +1
SNR + N+
S+
B
F
F
FF P
F
F FF
FFF S
F
F
O
O
N S
O
O
F
F
F
BF4 PF6 TFSI
pyrrolidinium piperidinium pyridinium pyrazinium
pyrazolium triazolium thiazolium ammonium sulfonium
Halide
R2
S
O
O
N S
O
O
FF
FSI
Cl-, I- , Br-
N+
pyrrolinium
R
Imidazolium-based ILs with many kinds of substituent as
electrolyte have been widely known as low viscosity, high
conductivity and relatively wide electrochemical window,
especially the ILs with unsaturated substituent was shown
improved electrochemical stability[5-7]. Nevertheless,
imidazolium-based ILs had electrochemical stability problem
under cathodic polarization because of C-2 acidic proton and
alkyl substituent on C-2 position enhanced stable behavior,
after that[8]. This idea led to pyrrolidinium and piperidinium
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6
with allyl functional group to be expected to better
electrochemical, physicochemical properties, however, these
had low conductivity owing to cyclopentane and cyclohexane
molecules which are not flat different with imidazolium
structure[9]. The adoption of heteroatoms such as ether or
sulfide enhanced physicochemical properties due to flexibility
of substituent.
Selection of anion was considered with physical
property that most of pyrrolinium
bis(trifluoromethanesulphonyl)imide (TFSI) salts are solid
state even though ILs with the TFSI anion usually show
relatively low viscosity and high conductivity, due to the highly
delocalized charge which reduces the interactions with
neighboring cations [10,11]. Studies on ionic liquid electrolytes
based on bis(fluorophonyl)imide (FSI) containing lithium
bis(trifluoromethanesulphonyl)imide (LiTFSI) showed excellent
cycle performance without any solvent [12,13]. The SEI layers
in LiTFSI systems are more thermally stable than other salts
such as LiBF4, LiPF6 results compact surface layer that largely
covers the negative electrode and the layer has higher thermal
stability of the lithiated phases [10]. That result corresponded
with our cell test at high temperature.
The effect of LiTFSI salt concentration on the
conductivity of organic solvents has been studied for a long
time[14-16]. According to these papers, the conductivity has
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the highest point with different results on general idea that the
conductivity of a solution is proportional to its ion concentration.
Understanding of the theory applied to our ILs with different
designs including LiTFSI salt and the results was interesting
that [A(OMe)Pyrl-FSI] (8) had the highest conductivity at 0.8
M salt concentration, whereas [E(OMe)Pyrl-FSI](6) and
[P(OMe)Pyrl-FSI] (7) showed that at 0.5 M salt concentration.
Cycling performance of those electrolytes for LiFePO4 cells was
carried out at room temperature and 1C rate to compare with 1
M salt concentration of each ILs and carbonate (EC : DMC = 1 :
2) electrolyte with 1 M LiPF6. The operating cycling condition
with 1C rate in coin cell have been rarely reported, meanwhile
there are almost cycling performance results at 0.1 C / 0.2 C
rate. Furthermore, we have already gotten the results at 0.5 C
rate with same ILs. If it is supposed that the performance at 1 C
rate shows the results as much as that at lower C-rates, it
would be valuable.
As expected, better cycle capacity was slightly
observed in those ILs as electrolyte than other ILs as
electrolyte with 1 M LiTFSI salt concentration but not worse
than capacity of carbonate. The results is a task of great
significance in terms of cycling performance at 1 C rate
compared to 0.1 C / 0.2 C rate results which have been
reported until now.
In reference to the electrochemical analysis for cycle
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8
performance and capacity of carbonate based lithium ion battery
cycled at elevated temperature, we focused on cycling
performance of ILs with 0.5 M / 0.8 M salt concentration as
electrolyte at high temperature [17].
There were three factors to decide the temperature on
50 oC. The first term, cycling tests at temperatures above 50 oC
have been rarely reported in the literature, most likely owing to
the chemical instability of LiPF6 in the organic solvents at
elevated temperature. Carbonate at high temperature 55 oC is
decomposed and gave negative effect the already formed SEI,
resulting in more irreversible reactions during charging and
consequently a loss from the capacity. On the other hand, vinyl
carbonate (VC) as addictive effects formation of the ‘Good’
SEI layers and that improves the cell cycling life with scarcely
fading capacity [17,18].
As mentioned before, ILs have remarkable thermal stability
different with organic solvents. Nevertheless, there is no help
for ILs at high temperature that ILs induce aluminum corrosion
by oxidative electrolyte decomposition over 55 oC [30].
The last term in decision was the results of variation of the
viscosity of 0.5 M [E(OMe)Pyrl-FSI] and [P(OMe)Pyrl-FSI],
0.8 M [A(OMe)Pyrl-FSI] solutions with temperature from 25
oC to 50 oC. As the phenomenon, the temperature dependence
of liquid viscosity, the lowest viscosity showed at 50 oC.
Because of these, we decided to compare with discharging
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9
capacity and retention ratio of carbonate for 60 cycles at 1C
rate on 50 oC. After the experiment, we observed properties of
ILs after reaction at 50 oC by NMR spectra.
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10
Part 1. Synthetic approach
Experimental
Materials
Table 2. Reagents
Reagents Company
Ethyl pyrrolidinone Alfa asear, 100g
1-Iodopropane Alfa asear, 500g
Allyl bromide Alfa asear, 1kg
Sodium hydroxide OCI, 1kg
Dimethyl sulfate Junsei, 500 ml
Lithium
bis(fluorosulfonyl)imide(LiFSI)/
Potassium
bis(fluorosulfonyl)imide(KFSI)
PANAX,
SK innovation
Lithium
bis(trifluoromethanesulfonyl)imide
(LiTFSI)
PANAX
Synthetic scheme
Scheme 1. Synthesis of 1-alkyl pyrrolidinone
Table 3. Yield of 1-alkyl pyrrolidinone
No. ILs Yield
1 1-propyl-2-pyrrolidinone 95
2 1-allyl-2-pyrrolidinone 91
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11
Scheme 2. Synthesis of 1-alkyl-2-alkoxy-pyrrolinium
bis(fluorosulfonyl)imide
Table 4. Yield of 1-alkyl-2-alkoxy-pyrrolinium
bis(fluorosulfonyl)imide
No. ILs 1st step (%) 2nd step (%)
6 [E(OMe)]Pyrl-FSI quant. 87
7 [P(OMe)]Pyrl-FSI 88 67
8 [A(OMe)]Pyrl-FSI quant. 79
General Procedure for the Preparation of the
Pyrrolinium-based Ionic Liquids
1. General procedure for preparation of 1-alkyl-2-
pyrrolidinone
Among various alkyl-pyrrolidin-2-one, the
reason of choose propyl and allyl group as the alkyl
substituent is that pyrrolidinones substituted other
groups are commercially available. The synthetic
process is not required professional skills but reagents
purification could affect reactivity, so 1-iodopropane or
allyl bromide is performed simple distillation better
than nothing. The propyl and allyl pyrrolidin-2-one
were synthesized by reaction between pyrrolidin-2-
one (1 eq, 80mmol) and alkyl halide (1.5 eq, 120 mmol)
such as 1-iodopropane or allyl bromide in
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12
tetrahydrofuran (THF) (200 ml) solvent with sodium
hydroxide (1.5 eq, 150 mmol). The reaction mixture
was stirred for 12 h at 120 oC. Filtration of the
resulting mixture followed by removal of the solvent
under reduced pressure, and purification by column
chromatography (methylene chloride) afforded 1-
alkyl-2-pyrrolidinone, starting material as a pale
yellow liquid(80-90%).
2. General procedure for the anion metathesis
The solution, 1-alkyl-pyrrolidin-2-one (1 eq,
100 mmol), obtained from above procedure reacted with
dimethyl sulfate (1.5 eq, 150 mmol) in neat condition.
The reaction mixture was stirred for 12 h at 40 oC in
dry condition by inert gas (argon or nitrogen).
Completion of the reaction recognized by their distinct
coloration and purification process for removing organic
impurities in crude solution performed by diethyl ether
and ethyl acetate several times to give 1-alkyl-2-
alkoxy-pyrrolinium sulfate (70-80%)
The intermediate salt composed of 1-alkyl-2-
alkoxy-pyrrolinium cation and the methyl sulfate anion,
and the anion converted readily into
bis(fluorosulfonyl)imide(FSI) anion. 1-alkyl-2-
alkoxy-pyrrolinium sulfate (1 eq, 100 mmol) added in
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13
water with potassium bis(fluorosulfonyl)imide (1.2 eq,
150 mmol) or lithium bis(fluorosulfonyl)imide. After
being stirred for 10 minutes at room temperature, the
reaction mixture was diluted with dichloromethane (150
ml) and extracted with water (150 ml). The organic
layer dried with MgSO4 and celite, then the volatiles
were evaporated in vacuo. Above the procedure
afforded final product 1-alkyl-2-alkoxy-pyrrolinium
bis(trifluoromethanesulfonyl)imide (80-90%).
Instruments and Measurements
All laboratory glassware are applied dried-oven (120 oC)
to remove water or any solvent for 12 hours and stored in the
glass desiccators to cool off before use them. Solvent contained
in every ILs removed under reduced pressure and applied
vacuum drying oven (65-70 oC) for complete drying without
residues and oxidation for 12 hours. Storage performed in the
desiccators cabinet to prevent atmospheric moisture.
1H and 13C NMR spectra were obtained using CDCl3 as a
solvent on a Bruker Advance III spectrometer (400 MHz for 1H
and 100 MHz for 13C NMR). The 1H NMR data were reported as
follows in ppm (d) from the internal standard (TMS, 0.0 ppm).
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14
Elemental analysis (C, H, O), a LECO CHNS-932 was
used and it (within ± 0.5 of the calculated value) is required to
confirm ( %) sample purity.
Result and Discussion
1. 1-propyl-2-pyrrolidinone
1H NMR 0.88-0.92 (t, J=7.2, 3H), 1.49-1.59 (m,
2H), 1.98-2.06 (m, 2H), 2.37-2.42 (t, J=8.4, 2H),
3.22-3.26 (t, J=7.6, 2H), 3.36-3.40 (t, J=6.8, 2H);
13C NMR d 11.3, 17.9, 20.6, 31.1, 44.1, 47.1,
174.9
2. 1-allyl-2-pyrrolidinone
1H NMR 1.98-2.07 (m, 2H), 2.40-2.44 (t, J=8.0,
2H), 3.34-3.37 (t, J=2.4, 2H), 3.89-3.91 (t, J=6.0,
2H), 5.16-5.21 (m, 2H), 5.68-5.78 (m, 1H); 13C
NMR d 17.8, 31.0, 45.2, 46.7, 117.8, 132.5, 174.7
3. 1-ethyl-o-methyl-pyrrolinium methylsulfate
[E(OMe)Pyrl][MeSO4]
1H NMR 1.29-1.33 (t, J=7.5, 3H), 2.38-2.46(m,
2H), 3.35-3.39 (t, J=7.6, 2H) 3.60-3.65 (q, J=7.2,
2H), 3.69 (s, 3H), 3.97-4.02 (t, J=7.6, 2H), 4.37 (s,
3H); 13C NMR d 11.2, 17.1, 29.5, 41.1, 51.8, 54.2,
62.5, 180.2.
-
15
4. 1-propyl-o-methylpyrrolinium methylsulfate
[P(OMe)Pyrl][MeSO4]
1H NMR 0.92-0.98 (t, J=7.2, 3H), 1.66-1.76 (m,
2H), 2.39-2.47 (m, 2H), 3.33-3.38(t, J=7.6, 2H),
3.49-3.54(q, J=3.2, 2H), 3.73 (s, 3H), 3.95-3.98 (t,
J=8.0, 2H), 4.37 (s, 3H), 13C NMR d 11.1, 17.2,
19.5, 47.9, 52.7, 55.1, 62.8, 180.6
5.1-allyl-o-methylpyrrolinium methylsulfate
[A(OMe)Pyrl][MeSO4]
1H NMR 2.35-2.43 (m, 2H), 3.37-3.41 (t, J=2.4,
2H), 3.67 (s, 3H), 3.90-3.94(t, J=7.2, 2H), 4.16-
4.18 (t, J=5.6, 3H), 4.37 (s, 3H), 5.35-5.42 (m, 2H),
5.79-5.89 (m, 1H) 13C NMR d 17.2, 29.6, 48.5, 52.2,
54.5, 62.8, 121.7, 128.2, 180.8.
6. 1-ethyl-o-methylpyrrolinium
bis(fluorosulfonyl)imide [E(OMe)Pyrl][FSI]
1H NMR 1.09-1.14 (t, J=7.32, 2H), 2.36-2.47
(m, 2H), 3.20-3.26 (t, J=7.9, 2H), 3.58-3.65 (t,
J=7.5, 2H), 3.93-4.06 (t, J=7.2, 2H), 4.32 (s, 3H);
13C NMR d 11.2, 16.9, 29.3, 41.9, 51.9, 62.6, 179.7
Anal. calcd for C7H14F2N2O5S2: C, 27.27; H, 4.58; N,
9.09;. Found: C, 27.27; H, 4.58; N, 9.09.
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16
7. 1-propyl-o-methylpyrrolinium
bis(fluorosulfonyl)imide [P(OMe)Pyrl][FSI]
1H NMR 0.95-0.99 (t, J=7.6, 3H), 1.67-1.76 (m,
2H), 2.37-2.44 (m, 2H), 3.21-3.25 (t, J=8.0, 2H),
3.48-3.51 (t, J=7.6, 2H), 3.92-3.96 (t, J=4, 2H),
4.31 (s, 3H); 13C NMR d 11.1, 17.0, 19.5, 29.2, 48.1,
52.6, 62.7, 180.1 Anal. calcd for C8H16F2N2O5S2: C,
29.81; H, 5.00; N, 8.69;. Found: C, 29.59; H, 5.03; N,
8.69.
8. 1-allyl-o-methylpyrrolinium bis(fluorosulfonyl)imide
[A(OMe)Pyrl][FSI]
1H NMR 2.36-2.44 (m, 2H), 3.23-3.27 (t, J=8.4,
2H), 3.88-3.92 (t, J=7.6, 2H), 4.14-4.16 (d, J=6.4,
2H), 4.33 (s, 3H), 5.39-5.45 (m, 2H), 5.74-5.84 (m,
1H); 13C NMR d 14.4,17.1, 29.6, 48.8, 51.8, 73.9,
122.8, 127.4, 179.3 Anal. calcd for C8H14F2N2O5S2:
C, 30.00; H, 4.41; N, 8.75;. Found: C,29.61; H, 4.41;
N, 8.65.
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17
Part 2. Electrochemical approach
Experimental
Materials To measure experiment/simulation analysis aluminum
half-cell was used and that components of the coin cell were
from Welcos company except electrode, separator and lithium.
Below the table shows detailed information of these
components.
Table 5. Components of the half cell
Components Information
Positive electrode LiFePO4
Negative electrode Lithium metal
Separator Glassy carbon/ poly(propylene)
Current collector
(CC)
Aluminum foil
General Procedure for the Preparation of Design Half
Cell
Coin cell components assembly ordered can, current
collector, positive electrode, separator, lithium as a negative
electrode, spacer, gasket, cap from below. The positive
electrode consist of a thin layer of LiFePO4-containing
composite on a foil current collector (CC). The electrode was
composed a slurry mixture of LiFePO4 powder, Super-P (as a
carbon additive for conductivity enhancement) and
poly(vinylidenefluoride) (PVdF, as a binder) (75 : 15 : 10 wt. %
-
18
ratio), which was followed by drying at 120 oC for 12 hours.
Instruments and Measurements
Viscosity ( η ) was measured on a Brookfield DV-II+
cone/plate viscometer.
Measurement of ionic conductivity was performed with a
CM-30R, conductivity meter in KETI(Korean Electronics
Technology Institute). This instrument fitted with CT-57101B
conductivity cell has repeatability (+,-)0.5% F.S / (+,-)0.1 oC
digit and measuring temperature was 26~28 oC.
Galvanostatic charge-discharge cycling test was carried out
in the potential range between 3.0 and 3.9 V using constant
current mode. Cut-off voltage was determined by disadvantage
of the salt LiTFSI is that they corrode the Al current collector
used on the cathode side of Li-ion cells at high potential[23].
Two kinds of instruments were used in cycling test depending
on test temperature (50 oC / 25 oC) that are from Wonatech and
PNE(Power & energy solution). At elevated temperature, we
performed cycle life test which was composed in 1C for each
60 cycles, meanwhile 1C for 50 cycles at room
temperature carried out different capacity data depending
on the lithium salt concentration.
-
19
Results and Discussion
Physicochemical Properties
Generally, viscosity is inversely proportional to the ionic
conductivity based on Walden’s rule that the product of the
viscosity and the equivalent ionic conductance at infinite
dilution in electrolytic solutions is a constant, independent of
the solvent. Variable lithium salt concentration also effects on
viscosity and conductivity and results have been published in
papers [14-16]. In this work, the lithium salt concentrations
were 0.0 M, 0.5 M, 0.8 M, 1.0 M, 1.2 M, 1.5 M and different
data of viscosity and conductivity as a function of lithium
concentration expressed dependant on ILs. These three ILs
samples had the thing in common with tendency of
concentration and viscosity. However, each sample had
optimized concentration of LiTFSI that were 0.5 M, 0.5 M and
0.8 M. These results presented from Fig 4. to Fig 6.
Table 6. Physical properties of E(OMe)Pyrl-FSI
(6)electrolytes as a function of LiTFSI concentration
ILs Conc. of
LiTFSI (M) Viscosity (cP)
Ionic
Conductivity
(mS/cm)
0.0 18.3 8.34
0.5 24.3 6.56
0.8 27.1 5.77
1.0 29.7 5.33
1.2 34.0 4.74
1.5 46.8 4.06
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20
Table 7. Physical properties of P(OMe)Pyrl-FSI
(7)electrolytes as a function of LiTFSI concentration
ILs Conc. of
LiTFSI (M) Viscosity (cP)
Ionic
Conductivity
(mS/cm)
0.0 25.8 6.03
0.5 26.2 4.69
0.8 42.4 4.09
1.0 50.1 2.88
1.2 56.6 2.54
1.5 56.9 2.35
Table 8. Viscosity and conductivity of A(OMe)Pyrl-FSI
(8)electrolytes as a function of LiTFSI concentration
ILs Conc. of
LiTFSI (M) Viscosity (cP)
Ionic
Conductivity
(mS/cm)
0.0 16.0 7.88
0.5 29.3 3.89
0.8 23.8 5.91
1.0 34.4 5.32
1.2 40.3 3.51
1.5 44.7 3.35
Conformation of pyrrolinium cation with double bond
leads the lower viscosity than pyrrolidinium and piperidinium
based ILs by a reflection of planarity of the cation ring, this
allowing relatively facile slip of the cations. Furthermore, the
ether functional group gives free rotation that contributes lower
-
21
viscosity [19].
[A(OMe)Pyrl]-FSI (8) had different saturation
concentration of the solution with maximum value of
conductivity was 0.8 mol/L.
The impressive results was the ILs including 0.5 M / 0.8
M, lower lithium salt had higher conductivity which were 6.56
mS/cm, 4.69 mS/cm and 5.91 mS/cm than compounds with 1 M
LiTFSI which were 5.33 mS/cm, 2.88 mS/cm and 5.32 mS/cm.
In this work, the relation between concentration of lithium salt
and conductivity induced the expectation of better cycling
performance of ILs with lower salt concentration. The cycling
technique is presented on instruments and measurement part
and the ILs samples with lower lithium salt concentration had
little higher discharge capacity than 1 M at room temperature.
The data showed from (Fig 5. - Fig 7)in electrochemical
properties.
One of the outstanding properties of ILs includes good
thermal stability and the liquid viscosity dependence of
temperature is the phenomenon by which liquid viscosity tends
to decrease as its temperature increases. It means conductivity
would invariably increases with increasing temperature. 0.5 M
[E(OMe)Pyrl-FSI](6) and 0.5 M [P(OMe)Pyrl-FSI](7), 0.8 M
[A(OMe)Pyrl-FSI](8) solutions were offered a variety of
viscosity testing from 20 oC to 50 oC in range of temperature.
The range of temperature was decided to be associated in
stability of carbonate and ILs. As you know, carbonate have the
weakness of thermal stability and commercialized lithium ion
-
22
batteries can only deliver their rated capacity and power in the
temperature range -20 oC to 50 oC. In ILs case, although their
strongest is thermal stability it is necessary to try another
angle in coin cell because of inside chemical reaction. According
to the paper, Al corrosion is caused by oxidative electrolyte
decomposition over 55 oC [24].
As the result of experiments in this range of temperature, the
lowest viscosity presented at 50 oC as expected (Fig 4) which
prompted us to access to different way, comparison of cycling
performance with carbonate at high temperature. The results
and data described on electrochemical properties (Fig 8-Fig 9).
Figure 4. Effect of viscosity on temperature
Temperature (oC)
20 25 30 35 40 45 50
Vis
cosi
ty (cP
)
0
5
10
15
20
25
30
35
E(OMe)Pyrl-FSI 0.5 M TFSI
A(OMe)Pyrl-FSI 0.8 M TFSI
P(OMe)Pyrl-FSI 0.5 M TFSI
Electrochemical properties
Improved conductivity of solution could enhance the
capacity at discharge rate in the paper [20], so, the discharge
capacity of each three ILs solution with 0.5 M / 0.8 M lithium
salt concentration were theoretically capable of finding better
correspondence patterns than the solution with 1 M salt
-
23
concentration (Fig 5 – Fig 7). In the previous study the
optimized lithium salt concentration in carbonate is 1 M and this
condition with many kinds of ILs have been applied and studied
for several years in our laboratory [8,9]. The interesting thing
in this graph they were performed 1C rate for 50 cycles with
high discharge capacity not 0.1C / 0.2 C of usual C-rate and it
is worth. In addition, each gap of capacity in three data were
different. E(OMe)Pyrl-FSI was 3 mAh/g, P(OMe)Pyrl-FSI
was 5 mAh/g and A(OMe)Pyrl-FSI was 1 mAh/g. These could
contribute to explain the P(OMe)Pyrl-FSI was highly
influenced by lithium salt concentration.
Figure 5. Cycle life test of E(OMe)Pyrl-FSI xM LiTFSI
for LiFePO4/Li cells at room temperature
Cycle number
0 10 20 30 40 50
Spec
ific
capaci
ty (
mA
h/g
)
0
20
40
60
80
100
120
140
160
0.5 M LiTFSI1 M LiTFSI
-
24
Figure 6. Cycle life test of P(OMe)Pyrl-FSI xM LiTFSI
for LiFePO4/Li cells at room temperature
Cycle number
0 10 20 30 40 50
Spec
ific
capaci
ty (
mA
h/g
)
0
20
40
60
80
100
120
140
160
0.5 M LiTFSI
1 M LiTFSI
Figure 7. Cycle life test of A(OMe)Pyrl-FSI xM LiTFSI
for LiFePO4/Li cells at room temperature
Cycle number0 10 20 30 40 50
Spec
ific
capac
ity
(mA
h/g
)
0
20
40
60
80
100
120
140
160
0.8 M LiTFSI
1 M LiTFSI
-
25
As mentioned, the high temperature is the factor to
distinguish between carbonate and ILs. As a result of cycling
performance of ILs and carbonate showed that ILs had better
cycle life and retention ratio than carbonate with higher
discharging capacity at 50 oC (Fig 8).
According to the paper, the commercialized lithium ion
batteries are able to perform in the temperature range -20 oC
to 50 oC as mentioned [18]. However, even 50 oC causes the
irreversible reaction with lithium salt and solvent with
decomposition products, so, the discharging capacity of
carbonate faded rapidly among four samples (Fig 8).
Furthermore, the capacity retention ratio prompted the cycle
stability of ILs different with carbonate (Fig 9). The capacity
and retention ratio (Fig 8-Fig 9) provided the outstanding
properties of the P(OMe)Pyrl-FSI 0.5 M LiTFSI and
A(OMe)Pyrl-FSI 0.8 M LiTFSI compared to E(OMe)Pyrl-FSI
0.5 M LiTFSI among the ILs. This result is worth because the
cell test including superior cycling performance was performed
with 1 C rate at high temperature.
-
26
Figure 8. Cycling performance of various electrolytes for
LiFePO4/Li cell at 50 oC
Cycle number
0 10 20 30 40 50 60
Sp
ecif
ic c
ap
aci
ty (
mA
h/g
)
0
20
40
60
80
100
120
140
160
E(OMe)Pyrl-FSI 0.5 M LiTFSI
P(OMe)Pyrl-FSI 0.5 M LiTFSI
A(OMe)Pyrl-FSI 0.8 M LiTFSI
EC:DMC = 1:2, 1M LiPF6
Figure 9. Capacity retention ratio of various electrolytes
for LiFePO4/Li cell at 50 oC
Cycle number0 10 20 30 40 50 60
Cap
acit
y re
ten
tion
rati
o (%
)
0
20
40
60
80
100
E(OMe)Pyrl-FSI 0.5 M LiTFSI
P(OMe)Pyrl-FSI 0.5 M LiTFSI
A(OMe)Pyrl-FSI 0.8 M LiTFSI
EC:DMC = 1:2, 1M LiPF6
-
27
The low thermal stability could afford possible explanation
about this phenomenon but we needed different way to
illustrate about difference cycling performance of ILs.
We derived the reasonable hypothesis by the data which is the
decomposition rate could influence in cycling performance and
tried to take in the whole situation by analysis of the electrolyte
after the reaction at high temperature. Disassembling the coin
cell and dissolved the separator to extract electrolytes which
was confirmed by 1H-NMR and 13C-NMR whose information
was involved in instruments and measurements of Part 1.
The chemical decomposition reaction and thermal stability of
carbonate have been studied already studied on
paper[10,18,20]. So, we focused on the results of three ILs in
1H-NMR and 13C-NMR spectrums. These results of three ILs,
E(OMe)Pyrl-FSI 0.5 M LiTFSI, P(OMe)Pyrl-FSI 0.5 M
LiTFSI and A(OMe)Pyrl-FSI 0.8 M LiTFSI discussed in
below(Fig 10 - Fig 12).
-
28
Figure 10. 1H-NMR and 13C-NMR spectrum of
E(OMe)Pyrl-FSI 0.5 M LiTFSI after cycle at 50 oC
-
29
Figure 11. 1H-NMR and 13C-NMR spectrum of
P(OMe)Pyrl-FSI 0.5 M LiTFSI after cycle at 50 oC
-
30
Figure 12. 1H-NMR and 13C-NMR spectrum of
A(OMe)Pyrl-FSI 0.5 M LiTFSI after cycle at 50 oC
-
31
The 1H-NMR and 13C-NMR spectrums are decomposed into
a sum of components include in unreacted compound, with each
component corresponding to one or a group of peaks.
There are complicated patterns because of the decomposition
of ionic liquids as electrolytes in data, include in their starting
materials such as 1-ethyl-2-pyrrolidinone, 1-propyl-2-
pyrrolidinone (1) and 1-allyl-2-pyrrolidinone (2). However, it
is difficult to interpret every peak and unconfirmed peaks need
additional analysis.
According to the data, all ILs broke down into their starting
materials whose reason would be hydrolysis with a small
quantity of water in the air or reduction with electron transfer
during charge process. From the electron’s vantage point, there
is a question about difference with the cycling performance at
room temperature. Activation energy is required to propagate a
chemical reaction and this condition at high temperature
decreases the activation energy. According to Arrhenius
equation, the activation energy of a reaction is dependent on
temperature which would contribute to the chemical reaction in
electrolyte. However it is not clear and should be studied more.
As mentioned before, there were many kinds of
possible compounds using only NMR analysis. That is
why we tried to focus on the compounds in totally sure
with analysis and they were pyrrolinium as ILs and
pyrrolidinone. The detailed value described in below.
-
32
Table 9. Decomposition rate of three ILs after reaction
at 50 oC according to 1H-NMR
ILs Pyrrolidinone Decomposition rate
E(OMe)Pyrl-FSI
0.5 M LiTFSI
1-ethyl-2-
pyrrolidinone
1 : 4
P(OMe)Pyrl-FSI
0.5 M LiTFSI
1-propyl-2-
pyrrolidinone (1)
3 : 1
A(OMe)Pyrl-FSI
0.8 M LiTFSI
1-allyl-2-
pyrrolidinone (2)
3 : 1
Their results of decomposition rate were interesting
and showed that E(OMe)Pyrl-FSI 0.5 M LiTFSI had highest
decomposition rate unlikely P(OMe)Pyrl-FSI 0.5 M LiTFSI and
A(OMe)Pyrl-FSI 0.8 M LiTFSI. According to the combination
of decomposition rate and discharge capacity with retention
ratio, higher decomposition provided lower capacity. That is the
reason of that P(OMe)Pyrl-FSI 0.5 M LiTFSI and
A(OMe)Pyrl-FSI 0.8 M LiTFSI had good performance.
-
33
Compared to the A(OMe)Pyrl-FSI 0.8 M, although which the
causes influenced in the cycle performance of P(OMe)Pyrl-FSI
are still unknown, the reason can be inferred with differential
scanning calometry (DSC) data. In previous work, allylic
compounds had less thermal stability than compounds
containing propyl group [9]. In addition to this, n-propyl-n-
methylpyrrolidinium bis(fluorosulfonyl)imide which is the
similar structure to P(OMe)Pyrl-FSI has been reported to
superior physical and electrochemical properties[21,22]. This
ionic liquid influenced in ionic conductivity positively and
worked well in graphite/Li cell with high capacity over 100
cycles.
In summary, we have discovered the pyrrolinium-
based new ionic liquids as electrolytes were contributed to
excellent electrochemical behavior at 1 C rate over 50 cycles at
room temperature or 50 oC. The conductivity of ILs with lower
salt concentration afforded higher than ILs including 1 M
concentration approximately 1 mS/cm. This phenomenon
connected with cycling performance that P(OMe)Pyrl-FSI 0.5
M LiTFSI had the highest gap of discharge capacity almost 5
mAh/g compared to P(OMe)Pyrl-FSI 1 M LiTFSI
In high temperature condition, the discharge capacity of
P(OMe)Pyrl-FSI 0.5 M LiTFSI and A(OMe)Pyrl-FSI 0.8 M
LiTFSI maintained 150 mAh/g and 145 mAh/g with the higher
retention ratio, 99 % for 60 cycle. Meanwhile, carbonate had
-
34
the lower discharge capacity, 99 mAh/g with retention ratio,
63 %.
In accordance with 1H-NMR data, decomposition rate
were 3 parts of P(OMe)Pyrl-FSI 0.5 M LiTFSI and
A(OMe)Pyrl-FSI 0.8 M LiTFSI to 1 parts of 1-propyl-2-
pyrrolidinone (1) and 1-allyl-2-pyrrolidinone (2) which were
compared to the result 1 parts of E(OMe)Pyrl-FSI 0.5 M
LITFSI to 4 parts of 1-ethyl-2-pyrrolidinone. These results
contributed to the inverse proportional relation between
capacity and decomposition rate.
-
35
Conclusion
Commercialized lithium ion batteries, consisting of
organic solvent electrolytes have several advantages, such as a
high operating voltage, a high energy density, and good cycle
durability. However, the applications of lithium ion cells include
a drawback which is their flammability of electrolytes and it still
raise safety concerns. Ionic liquids are attracting a great deal of
attention as possible replacement to handle this problem. Low
vapor pressure is to be non-volatility, non-flammability, and
their physicochemical, electrochemical properties are suitable
for alternative electrolyte. Furthermore, by a judicious
combination of cations and anions, it is possible to create an
almost indefinitely set of designer solvents which have been
published in many papers.
We compromised in o-methylpyrrolinium
bis(fluorosulfonyl)imide with ethyl, propyl and allyl of three
different alkyl groups among several ILs which were
considered to be enhanced electrochemical and physicochemical
properties.
The lithium salt concentration influenced in viscosity
and conductivity of pyrrolinium-based ionic liquids and ILs
including lower concentration of lithium salt had higher
conductivity. The cycling performance of them compared with
their 1 M salt concentration described higher specific capacity
at room temperature as expected. Cycle life tests of the coin
-
36
cells include in ethyl, propyl and allyl pyrrolinium-base ionic
liquids with 0.5 M, 0.5 M and 0.8 M lithium salt concentration
performed at 50 oC for 60 cycles which could be compared to
carbonate electrolytes. As indicated by the theory of thermally
unstability of carbonate, the observed discharge capacity
retention ratio faded rapidly unlike ILs.
Among the ILs, P(OMe)Pyrl-FSI 0.5 M LiTFSI and
A(OMe)Pyrl 0.8 M LiTFSI showed the prominent specific
capacity and retention ratio and the reason was proposed
general foundation by 1H-NMR and 13C-NMR. A low
decomposition potential of the electrolyte to starting material,
pyrrolidinone provided better cycling performance.
The final remarkable part was that most electrochemical results
of ILs showed superior even though they were performed at 1
C rate.
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37
References
1. Tetsuya T.; Charles L.H. Electrochemical society interface.
2007, 16, 42-49.
2. Keith E.Johnson. Electrochemical society interface. 2007, 16,
42-49.
3. Colin F.et al., Journal of Chromatography A. 2004, 1037, 49-82.
4. Martyn J. Earle.; Kenneth R. Seddon. Pure Apple. Chem. 2000,
72, 1391-1398
5. (a) Min, G.H.; Yim, T.; Lee, H.Y.; Huh, D.H.; Lee, E.; Mun, J.;
Oh, S.M.; Kim, Y.G. Bull. Korean Chem. Soc. 2006, 27, 847-
852
(b) Patrick Ngoy Tshibangu.; Silindile Nomathemba
Ndwandwe.; Ezekiel Dixon Dikio. Int. J. Electrochem. Sci.
2011, 6, 2201-2213
6. Kim, J.K.; Aleksandar Matic.; Ahn, J.H.; Per Jacobsson. Journal
of Power Sources. 2010, 195, 7639-7643
7. Journal of the Korean Electrochemical Society. 2009, 12, 203-
218
8. Min, G.H.; Yim, T.; Lee, H.Y.; Kim, H.J.; Mun, J.; Kim, S.; Oh,
S.M.; Kim, Y.G. Bull. Korean Chem. Soc. 2007, 28, 1562-1566
9. Yim, T.; Lee, H.Y.; Kim, H.J.; Mun, J.; Kim, S.; Oh, S.M.; Kim,
Y.G. Bull. Korean Chem. Soc. 2007, 28, 1567-1572
10. Anna andersson. Acta Universitatis Upsaliensis Uppsala 2001.
11. I. Rey.; P. Johansson,; J. Lindgren.; J.C. Lassegues.; J. Grondin.;
L. Servant. J. Phys. Chem. A. 1998, 102, 3249-3258
-
38
12. Masashi Ishikawa,; Toshinori Sugimoto,; Manabu Kikuta.;
Eriko Ishiko.; Michiyuki Kono. Journal of Power Sources.
2006, 162, 658-662
13. Toshinori Sugimoto.; Manabu Kikuta.; Eriko Ishiko.;
Michiyuki Kono.; Masashi Ishikawa. Journal of power Sources.
2008, 183, 436-440
14. Chen, H.P.; Fergus, J.W.; Jang, B.Z. Journal of The
Electrochemical Society. 2000, 147, 399-406
15. Yuichi Aihara.; Shigemasa Arai.; Kikuko Hayamizu. 2000, 45,
1321-1326
16. R. Weige.; M. Niemann.; U. Heider.; M. Jungnitz.; V. Hilarius.;
Merck KGaA, D-64271 Darnstadt, Germany
18. Kang Xu. Chem. Rev. 2004, 104, 4303-4417
19. J. Sun.; D.R. MacFarlane.; M. Forsyth. Electrochimica Acta.
2003, 48, 1707-1711
20. J. Yamaki.; S. Tobishima.; Y. Sakurai.; M. Kakuchi. Ibaraki
Electrical Communication Laboratory. 1983, 360-366
21. Claude-Montigny Benedicte.; Stefan Claudia Simona.; Violleau
David. Universite Francois Rabelais, Laboratoire PCMB
22. Abraham, D.P. The 15th International Meeting on Lithium
Batteries, IMLB 2010; Abst. No. 194
23. Krause L.J.; William Lamanna.; John Summerfield.; Mark
Engle.; Gary Korba.; Robert Loch.; Radoslav Atanasoski.
Journal of Power Sources. 1997, 68, 320-325
24. J. Mun et al., Electrochemical and Solid-State Letters. 2010, 13,
A109-A111
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APPENDICES
List of 1H-NMR and 13C-NMR Spectrum of samples
1. 1-propyl-2-pyrrolidinone
- 1H-NMR
- 13C-NMR
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40
2. 1-allyl-2-pyrrolidinone
- 1H-NMR
- 13C-NMR
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41
6. 1-ethyl-o-methylpyrrolinium bis(fluorosulfonyl)imide
[E(OMe)Pyrl][FSI]
- 1H-NMR
- 13C-NMR
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7. 1-propyl-o-methylpyrrolinium bis(fluorosulfonyl)imide
[P(OMe)Pyrl][FSI]
- 1H-NMR
- 13C-NMR
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8. 1-allyl-o-methylpyrrolinium bis(fluorosulfonyl)imide
[A(OMe)Pyrl][FSI]
- 1H-NMR
- 13C-NMR
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l 1-ethyl-2-pyrrolidinone
- 1H-NMR
- 13C-NMR
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45
국문 초록
여러 가지의 특이한 특징을 갖고 있는 이온성 액체(IL)는
여러 분야에서 중요하게 사용되고 있다. 이온성 액체의 여러 장점들
중에서 가장 우수하고 이전부터 잘 알려진 전해질, 카보네이트와 차
별되는 점은 열적으로 안정하다는 것이다.
우리는 이전부터 이미다졸리움, 암모니움, 피롤리디니움, 피
페리디니움등의 양이온과 bis(trifluoromethanesulfonyl)imide
(TFSI)의 음이온을 기반으로 한 이온성 액체를 합성하여 전해질로
서의 성능을 평가하였다. 이들의 결과들을 통해서 피롤리디니움이나
피페리디니움과 달리 이중결합을 통한 평면 구조로 인해 더 높은
이온 전도도를 갖는 피롤리니움을 양이온으로 선택하게 되었고, 음
이온의 경우 더 작은 크기의 bis(fluoromethanesulfonyl)imide
(FSI)를 타겟이 되는 이온성 액체의 기본적인 틀로 선택하게 되었
다.
이 중에서 타겟 물질은 E(OMe)Pyrl-FSI, P(OMe)Pyrl-FSI,
A(OMe)Pyrl-FSI 이 세가지 이며 우리는 이 물질들에 LiTFSI 솔
트를 몰 농도별로 녹여서 그에 따른 물리화학적, 전기화학적 성질을
측정하였고 이들 중 0.5 M 혹은 0.8 M 일 때 가장 높은 이온 전도
도를 보인 것을 확인하였으며, 이들을 각각의 1 M 농도의 리튬 솔
트를 넣은 전해질들과 셀 성능을 측정해본 결과 더 높은 방전 용량
용 보인 것을 확인 할 수 있었다. 여기서 더 흥미로운 점은 이전부
터 알려진 논문에 따르면 대부분이 0.1 C / 0.2 C 와 같이 낮은 C-
rate로 실험을 진행한 것에 비해 우리는 1 C의 빠른 속도로 50
cycle의 셀을 돌렸음에도 불구하고 꾸준히 높은 방전용량을 보였다.
이전부터 좋은 물리화학적, 전기화학적 특성을 가진 것으로
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46
알려진 카보네이트의 경우 첨가제를 넣지 않았을 때 열적으로 안정
하지 않다는 단점을 갖고 있기 때문에 이를 이용하여 낮은 몰 농도
의 리튬 솔트를 넣은 세 종류의 이온성 액체와 카보네이트의 용량
의 확실한 차이를 보이기 위해 고온, 50 oC에서 실험을 진행 하였다.
실제적으로 위의 이온성 액체들은 고온에서 60 cycle 동안 높은 사
이클 수명과 방전용량을 가졌으며 카보네이트와는 확연한 차이를
보이는 것을 확인 하였다. 이중에서도 P(OMe)Pyrl-FSI 0.5 M
LiTFSI 와 A(OMe)Pyrl-FSI 0.8 M 가 E(OMe)Pyrl-FSI 0.5 M
보다 좋은 셀 성능을 보였고 이에 대한 것을 NMR로 분석해본 결과
P(OMe)Pyrl-FSI 0.5 M LiTFSI 와 A(OMe)Pyrl-FSI 0.8 M의
분해정도가 E(OMe)Pyrl-FSI 0.5 M에 비해 차이가 나는 것을 확
인할 수 있었다. 이를 통해 셀 내의 전해질의 분해 정도는 셀의 용
량에 영향을 미친다고 말할 수 있을 것이라 판단이 된다.
학번 : 2011-21070
INTRODUCTIONPART 1. SYNTHETIC APPROACHExperimental Materials Synthetic scheme..General Procedure for the Preparation of the Pyrrolinium based Ionic Liquid1. General procedure for preparation of 1-alkyl-2-pyrrolidinone 2. General procedure for the anion metathesis
Instruments and measurements
Result and Discussion
PART 2. ELECTROCHEMICAL APPROACH Experimental Materials General Procedure for the Preparation of Design half Cell Instruments and Measurements
Result and Discussion Physicochemical Properties Electrochemical Properties
CONCLUSION REFERENCES APPENDICES ABSTRACT IN KOREAN
16INTRODUCTION 1PART 1. SYNTHETIC APPROACH 10 Experimental 10 Materials 10 Synthetic scheme.. 10 General Procedure for the Preparation of the Pyrrolinium based Ionic Liquid 11 1. General procedure for preparation of 1-alkyl-2-pyrrolidinone 11 2. General procedure for the anion metathesis 12 Instruments and measurements 13 Result and Discussion 14PART 2. ELECTROCHEMICAL APPROACH 17 Experimental 17 Materials 17 General Procedure for the Preparation of Design half Cell 17 Instruments and Measurements 19 Result and Discussion 19 Physicochemical Properties 19 Electrochemical Properties 22CONCLUSION 35REFERENCES 37APPENDICES 39ABSTRACT IN KOREAN 45