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SYNTHESIS AND CHARACTERIZATION OF CHOLINE CHLORIDE–BASED DEEP EUTECTIC SOLVENT FOR POTENTIAL APPLICATION AS ELECTROLYTES IN LITHIUM-ION BATTERIES PREPARED BY: INTAN QHUZAIRIN BINTI ZAHARUDDIN (AS222) UNDER SUPERVISION OF: DR NABILAH AKEMAL MUHD ZAILANI DR RIZANA YUSOF

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INTRODUCTION

Energy storage system Efficient & ecologically benign energy storage system Batteries Fuel cells Supercapacitors Advantage: Highest specific energy ( Zhong et al., 2015)

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Batteries ( Abruna et al., 2008) Lithium-ion batteries Nickel-metal-hydride batteries Nickel-cadmium batteries Advantages: *Higher energy densities *Less expensive *Safer

K-ion Na-ion Ni-MH Ni-Cd Smaller Siæ Volumetric energy density / Wh

Kharbaci et al., 2020

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Liquid electrolyte in Lithium-ion batteries Organic solvent-based LE Ionic liquid (IL)-based LE Deep eutectic solvent (DES)-based LE Disadvantages: *Flammable *Volatile *Low thermal stability Disadvantages: *High cost *Tedious preparation *Toxicity *Poor biodegradability

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Liquid electrolyte in Lithium-ion batteries Organic solvent-based LE Ionic liquid (IL)-based LE Deep eutectic solvent (DES)-based LE Disadvantages: *Flammable *Volatile *Low thermal stability Disadvantages: *High cost *Tedious preparation *Toxicity *Poor biodegradability

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DES-BASED LE DES: Mixture consists of Hydrogen Bond Acceptor (HBA) and Hydrogen Bond Donor (HBD) which are able to self-associate to form a new eutectic mixture at melting point lower than melting point of each constituent in the mixture (Tome et al., 2018).

HBA Choline Chloride ( ChCl ) Biodegradable Able to interrupt hydrogen bonding HBD 1,4-butanediol Shorter alkyl chain Fewer hydroxyl group Salt Lithium triflate ( LiTf ) Strong metal reducing agent Charging-discharging process No significant specific interaction

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DES-BASED LE Advantages over IL-based LE: *Lower cost *Easy to prepare *Non-toxic *High biodegradability Disadvantages: Viscous Reduce free mobility of ion Low ionic conductivity

This has been supported by study done by Al Omar et al . (2015)

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PROBLEM STATEMENT IL-based LE presents toxicity, having poor biodegradability as well as involves expensive cost and tedious preparation. OBJECTIVE OF STUDY To synthesize DES from ChCl and different amount of 1,4-butanediol.

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PROBLEM STATEMENTS Amount of HBD influence the structure, viscosity and ionic conductivity of DES due to the excessive amount of hydrogen bonding between HBA and HBD. Thus, result in increasing of viscosity, reduce the free mobility of ion and hence decrease the ionic conductivity of DES. OBJECTIVE OF STUDY To determine the effect of various amount of 1,4-butanediol on the structure, viscosity and ionic conductivity of DES using Fourier transform infrared spectroscopy (FTIR), tensiometer and ionic conductivity meter respectively.

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PROBLEM STATEMENTS Addition of LiTf is to provide additional conducting species and is a requirement for fabrication of lithium ion batteries, however addition of excessive amount of lithium salt might increase the viscosity, restrict the free mobility of lithium ion and hence decrease the ionic conductivity of LE. OBJECTIVE OF STUDY To fabricate liquid electrolyte by adding various weight percent of LiTf salt into the highest ionic conductivity of DES. To determine the effect of various weight percent of LiTf on the structural and ionic conductivity of liquid electrolyte using FTIR and ionic conductivity meter respectively.

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SIGNIFICANCE OF STUDY This study will explain the effect of various amount of HBD (1,4-butanediol) and LiTf salt towards the properties of DES and LE respectively (i.e.: structure, viscosity and ionic conductivity). Also, the research will contribute to the production of highly conducting and environmental-friendly liquid electrolyte for application in lithium ion batteries.

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METHODOLOGY

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The synthesized DES were characterized

PREPARATION AND CHARACTERIZATION OF DES

FTIR

Tensiometer

Ionic conductivity meter

Symbol Mole ratio (ChCl:1,4-butanediol) DES1:1 1:1 DES1:2 1:2 DES1:3 1:3

OH

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The synthesized LE were characterized

PREPARATION AND CHARACTERIZATION OF LE

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DESI:I

Symbol Percentage of LiTf ( wt %) LE2.5 2.5 LE5 5 LE10 10

FTIR

Ionic conductivity meter

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RESULTS & DISCUSSIONS

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SYNTHESIS OF DES

Physical characteristics of synthesized DES Homogenous liquid Oily Unpleasant fishy odour

Mole ratio of DES Time taken to form homogenous liquid (min) 1:1 9.23 1:2 6.20 1:3 7.19

Figure 1

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STRUCTURAL STUDIES OF DES *ND = not detected

Wavenumber (cm -1 ) Peak ChCl ( Shafie et al., 2019) 1,4-butanediol (Jesus et al., 2008) DES         1:1 1:2 1:3 OH stretching 3222 3292 3297 3298 3293 C-O stretching ND 1169 1170 1172 1172 CH 2 bending 1480 1428 1441 1442 1448 CH 3 bending 1349 ND ND ND ND C-N stretching 1083 ND 1049 1046 1046

OH stretching shift to higher wavenumber along with reduced peak intensity

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(a) DES1:1

(c) DES1:3

(b) DES1:2

Peak intensity of free OH decrease

D econvolution and band-fitting of the broad O-H stretching peak (3700 – 3100 cm -1 ) Wang et al. (2019)

Figure 2

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VISCOSITY STUDIES OF DES

DES System Amount 1,4-butanediol (ml) Surface tension ( mN /m)   DES1:1 88.35 28.445 DES1:2 176.71 27.916 DES1:3 265.06 28.093

~28 mN /m (negligible difference)

Tensiometer’s limitation

Tensiometer

Surface tension result

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IONIC CONDUCTIVITY STUDIES OF DES

DES System   Amount 1,4-butanediol (ml) Ionic conductivity DES (10 -3 S cm -1 )   DES1:1 88.35 2.41 DES1:2 176.71 1.34 DES1:3 265.06 0.92

Hydrogen bond Van der Waals interaction As confirmed by FTIR analysis

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Benchmark (other DES system)

DES system Conductivity (S cm -1 ) References ChCl / EG 1.79 x 10 -3 Zhong et al . (2020) TBABr /EG 0.5285 x 10 -3 Yusof et al . ( 2014)

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FORMATION OF LIQUID ELECTROLYTE (LE)

Doped the DES1:1 (2.41 X 10 -3 S cm -1 ) with (2.5, 5 and 10 wt %) of LiTf

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FTIR STUDIES OF LE

Wavenumber (cm -1 )   Peak DES1:1 LiTf (Ramesh and Chai, 2007) LE2.5 LE5 LE10   OH 3297 ND 3303 3301 3335 C-O stretching 1170 ND 1169 1168 1169 CH 2 bending 1441 ND 1441 1441 1441 C-N stretching 1049 ND 1049 1048 1031 SO 3 (a) ND 1273 1266 1266 1253 CF 3 (a) ND 1143 ND ND ND

Appearance of salt peak in the mixture of LE

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Wavenumber (cm -1 )   Peak DES1:1 LiTf (Ramesh and Chai, 2007) LE2.5 LE5 LE10   OH 3297 ND 3303 3301 3335 C-O stretching 1170 ND 1169 1168 1169 CH 2 bending 1441 ND 1441 1441 1441 C-N stretching 1049 ND 1049 1048 1031 SO 3 (a) ND 1273 1266 1266 1253 CF 3 (a) ND 1143 ND ND ND

OH stretching shift to higher wavenumber along with reduce peak intensity

Figure 3

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IONIC CONDUCTIVITY STUDIES OF LE

LE System Ionic conductivity (10 -3 S cm -1 ) LE2.5 2.56 LE5 1.84 LE10 0.65

Free mobility of Li ion

Hydrogen bond restrict the mobility of Li ion

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Benchmark (other LE system)

LE system Conductivity (S cm -1 ) References EG/ChCl/ LiPF 6 7.95 x 10 -3 Millia et al . (2018) TFA/ LiTFSI 1.86 x 10 -3 Dinh et al . (2020)

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CONCLUSION 1. DES1:1, DES1:2 and DES1:3 were successfully synthesized 2. 3. LE2.5, LE5 and LE10 were successfully synthesized 4.

Amount of 1,4-butanediol

Hydrogen bond & Van der Waals interaction

Free mobility ion & ionic conductivity

~28 mN /m due to limitation of instrument

2.5 wt % of LiTf

Presence of lithium ion in LE

free mobility ion & ionic conductivity

5 & 10 wt % of LiTf

Hydrogen bonding

Restrict free mobility of Li ion & reduce ionic conductivity

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RECOMMENDATIONS

LE2.5 (2.56 x 10 -3 S cm -1 )

Battery cell

Investigate by using

Charge-discharge (CD) test

Cyclic voltammetry (CV)

Electrochemical impedance spectroscopy (EIS)