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i

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

ii

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 )

iii

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

iv

학위논문 원문제공 서비스에 대한 동의서

본인의 학위논문에 대하여 서울대학교가 아래와 같이 학위논문

저작물을 제공하는 것에 동의합니다.

1. 동의사항

①본인의 논문을 보존이나 인터넷 등을 통한 온라인 서비스

목적으로 복제할 경우 저작물의 내용을 변경하지 않는 범위

내에서의 복제를 허용합니다.

②본인의 논문을 디지털화하여 인터넷 등 정보통신망을 통한

논문의 일부 또는 전부의 복제․배포 및 전송 시 무료로 제공하는

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

v

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

vi

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

vii

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

viii

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

ix

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

x

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

xi

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

xii

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

xiii

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

xiv

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

1

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

2

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

3

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.

4

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

5

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

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

7

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

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

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.

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

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

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

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).

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.

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.

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

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.

37

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39

APPENDICES

List of 1H-NMR and 13C-NMR Spectrum of samples

1. 1-propyl-2-pyrrolidinone

- 1H-NMR

- 13C-NMR

40

2. 1-allyl-2-pyrrolidinone

- 1H-NMR

- 13C-NMR

41

6. 1-ethyl-o-methylpyrrolinium bis(fluorosulfonyl)imide

[E(OMe)Pyrl][FSI]

- 1H-NMR

- 13C-NMR

42

7. 1-propyl-o-methylpyrrolinium bis(fluorosulfonyl)imide

[P(OMe)Pyrl][FSI]

- 1H-NMR

- 13C-NMR

43

8. 1-allyl-o-methylpyrrolinium bis(fluorosulfonyl)imide

[A(OMe)Pyrl][FSI]

- 1H-NMR

- 13C-NMR

44

l 1-ethyl-2-pyrrolidinone

- 1H-NMR

- 13C-NMR

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

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