investigation of ion conduction mechanism and relaxation...

Investigation of Ion Conduction Mechanism and Relaxation

Dynamics in Polymer Nano-Composite Electrolytes

IMESD – 2018

Dillip Kumar Pradhan †, * and Tapabrata Dam†, ‡

† Ferroics Laboratory, Department of Physics and Astronomy, NIT, Rourkela, Odisha-769008, India. ‡ School of Physical Sciences, IACS, Kolkata-700032, India

*e-mail: [email protected]

2

PLAN OF PRESENTATOIN

• Importance: Why stilll R and D on Battery?

• Introduction to Polymer Electrolyte

• State of the Art Achievements

• State of the Art Challenges

• Objectives

• Methodology

• Ion conduction mechanism in polymer electrolyte

• Conclusions & Future prospects

3

WHY STILL BATTERY R & D?

4

WHY STILL BATTERY R & D?

Depletion of Fossil

fuel reserves

Growing demand of

Portable Power Sources

Reduce Dependency

on OPEC Nations

Pollution Control

Environmental Protection

Global Adoption of

ZERO Emission

Vehicles

ELECTROCHEMICAL CELL

A typical ELECTROCHEMICAL CELL

TOTAL VOLTAGE = ANODE VOLTAGE + CATHODE VOLTAGE

+ -

ANODE

CATHODE

LOAD

ELECTROLYTE

Active Passive

Current Voltage

C. Vincent and ‎B, Scrosati, Modern Batteries 2nd Edition (1997), Elsevier Publications

6

ELECTROLYTE: DEFINITION & CLASSIFICATION

High ionic conductivity (~10-3S/cm) at room temperature

Negligible electronic conductivity (~10-8S/cm)

The activation energy should be very low (below ~ 0.3 eV)

Properties of Electrolyte

Electrolyte - Dissociates in solution

Cl- Na+

Electrolyte

Liquid Electrolyte

Solid Electrolyte

Framework crystalline/poly crystalline materials (AgI)

Amorphous-glassy electrolytes (Li2SiO3)

Composite or dispersed phase electrolytes

(LiI+Al2O3)

POLYMER ELECTROLYTES

Classification of Electrolyte

Fiona M. Gray, Polymer Electrolytes, ‎Royal Society of Chemistry (Great Britain) - 1997

7

TOWARDS POLYMER ELECTROLYTE SYSTEMS

Disadvantages of Liquid Electrolyte

Leakage

Low energy density

Limited temperature range of operation

Electrode corrosion by electrolytic solution

Polymer electrolytes are ionically conducting solid phases formed by the dissolution of alkali metal salts in ion-

coordinating macromolecules.

Polymer Electrolyte

LiCF3SO3

+

PEO

COMPLEXATION

Advantages of Polymer Electrolyte

Free from leakage

Design flexibility and shape mouldability

Wide temperature range of operation

Free from internal shorting

Electrochemically, Mechanically and Thermally

stable

High energy and power density

Interfacial Stability

J.R. MacCallum, C.A. Vincent, Polymer electrolyte reviews Vol I & II , Elsevier Applied Science, New York, 1987.

8

COMPLEXATION : POLYMER SALT COMPLEX FORMATION

Enthalpy change on dissolution

Dissociation of salt:- A positive enthalpy change

Cationic solvation:- A negative enthalpy change

Entropy change during dissolution

Breaking of crystal :- A positive entropy change

Ordering of solvent molecule:- A negative entropy change

Change in Gibb’s free energy ∆ 𝑮 = ∆𝑯 − 𝑻∆𝑺

J.R. MacCallum, C.A. Vincent, Polymer electrolyte reviews Vol I & II , Elsevier Applied Science, New York, 1987.

9

POLYMER ELECTROLYTE: CLASSIFICATION

Classification of Polymer Electrolyte

Polymer Electrolyte

Conventional Polymer Salt Complex

Plasticized Polymer Electrolyte

Polyelectrolyte Membranes

COMPOSITE POLYMER ELECTROLYTE

GEL POLYMER ELECTROLYTE

Fiona M. Gray, Polymer Electrolytes, ‎Royal Society of Chemistry, Great Britain (1997) Polymer Electrolytes: Fundamentals and Applications

10

STATE OF THE ART CHALLANGES

Ionic conductivity of solid electrolytes are of the order 10-5 S/cm to 10-7 S/cm. Ionic

conductivity of polymer electrolytes should be in around 10-3 S/cm or better to be used

in various energy storage/conversion device.

Ionic conductivity of gel polymer electrolytes are of the order 10-3 S/cm to 10-4 S/cm.

but mechanical stability of gel polymer electrolytes are poor.

The ion conduction mechanism of polymer electrolytes are not properly understood.

Cause behind nearly constant loss (NCL) phenomena is more speculative than

confirmative.

Coupling between ion conduction and segmental relaxation is not well studied. (The

role of segmental relaxation in ion conduction process is not clear).

Lack of complete understanding of ion transport

behavior in polymer electrolyte may be one of the reason, why the ionic conductivity up

to the desired level is not achieved

11

OBJECTIVES

Synthesis of polymer nano-composite electrolytes (PNCEs) using conventional solution

casting technique.

To study the structural and micro-structural properties of the samples.

To investigate the change in electrical conductivity as function of filler percentage in PNCEs.

To study the relaxation phenomena observed in PNCEs.

To study the first universality also known as universal dielectric response and second

universality also known as nearly constant loss phenomena in PNCEs.

The role of segmental relaxation in ion conduction process.

Examine coupling between ion conduction and segmental relaxation.

12

CHOICE OF MATERIALS

Low lattice energy

Bulky anion

Economical among lithium salts

Choice of Salt : LiCF3SO3

Polar polymer

Low glass transition temperature

Choice of Polymer : PEO (M.W. 600000)

Zirconia: Passive dispersed phase filler.

Titania: Passive dispersed phase filler weakly attract Li+ ions.

Montmorillonite Clay: Layered intercalation filler

Choice of Filler : ZrO2, TiO2, modified Montmorillonite clay

EXPERIMENTAL TECHNIQUES

14

FILLER SYNTHESIS: ZIRCONIA (ZrO2)

Flow Chart: Tetragonal Zirconia Synthesis

XRD Pattern

FE-SEM

15

FILLER SYNTHESIS: TITANIA (TiO2)

FE-SEM Flow Chart: Tetragonal Titania Synthesis

P.C. Ricci, C.M. Carbonaro, L. Stagi, M. Salis,A. Casu, S. Enzo and F. Delogu, Phys. Chem. C, 117, 7850 (2013)

16

FILLER SYNTHESIS: TITANIA (TiO2)

XRD Pattern Rietveld Refined XRD Pattern

17

FILLER MODIFICATION: MONTMORILLONITE CLAY

Flow Chart: Clay Modification

J.-M. Yeh, S.-J. Liou, C.-Y. Lin, C.-Y. Cheng, Y.-W. Chang and K.-R. Lee, Chem. Mater., 2002, 14, 154–161.

18

MATERIAL SYNTHESIS: COMPOSITE POLYMER ELECTROLYTE

Flow Chart: Solution Casting Technique

19

X-RAY DIFFRACTION: COMPOSITE AND COMPLEX FORMATION

X-Ray diffraction pattern of poly ethylene oxide(PEO), polymer salt complex (O/Li = 20) and polymer nano composite

electrolytes with different weight percentage of Zirconia (ZrO2) filler.

Complex formation

Composite nature of the samples

Observation

PEO20-LiCF3SO3- x wt.% ZrO2 ( x = 0, 3, 5, 8, 10 & 20)

20

FIRST UNIVERSALITY : UNIVERSAL DIELECTRIC RESPONSE (UDR)

Semi-Crystalline or Glass

Dispersive nature as a function of frequency

J R Macdonald and M Ahmad, J. Phys.: Condens. Matter, 2007, 19, 046215 (1-13) A. N. Papathanassiou, I. Sakellis, J. Grammatikakis, Applied Physics Letters, 2007,91, 122911 (1-3)

Conducting Polymers

𝝈(𝒇) = 𝑨 + 𝑩𝒇𝒏

21

CONDUCTIVITY AS A FUNCTION OF TEMPERATURE & FREQUENCY

Observation

Presence of UDR and NCL

DC conductivity found following VTF relation.

DC conductivity increases with increasing filler

concentration and after reaching maxima for

8wt.% it again decrease.

𝝈 = 𝑨 + 𝑩𝒇𝒏 + 𝑪𝒇

Double Power Law

Cause Behind NCL

𝝈 𝑻 = 𝑨 𝑻−𝟏

𝟐 𝐞𝐱𝐩 −𝑬𝒂

𝒌𝑩 𝑻−𝑻𝟎

VTF Equation

𝝈 = 𝑨 + 𝑩𝒇𝒏

Power Law


22

𝜺′′ AS A FUNCTION OF TEMPERATURE & FREQUENCY

Observation

At low temperature dielectric loss become nearly

constant.

Low frequency electrode polarization phenomenon

and intermediate frequency segmental relaxation

can be observed. (Using the technique of DC

conduction free dielectric loss approach)

Relaxation time for segmental relaxation is calculated from DC

conduction free dielectric loss plots.

Ion hopping region and NCL region are separated as a function of

temperature.

DC conduction free dielectric loss

𝜺𝒅𝒆𝒓′′ = −

𝝅

𝟐

𝝏 𝜺′

𝝏 𝒍𝒏 𝝎

D Fragiadakis, S Dou, RH Colby, J Runt, J Chem. Phys. 130, 064907 (2009)


23

CAGED ION DYNAMICS

Observation

Value of m at T = 193K is 0.9975 and at T = 223K

become 0.9865.

Activation energy for NCL region found

𝑬𝑵𝑪𝑳

≈ 𝟎. 𝟎𝟒𝟓 𝐞𝐕 as compared to 𝑬𝒅𝒄

≈ 𝟎. 𝟏𝟐𝟖 𝐞𝐕.

For 8wt.% Composition.

Kramer Krönig Representation

𝜺′𝒇 = 𝑩𝒇𝒎

Value of m if close to unity NCL dominates over UDR.

With decreasing value of m UDR dominated over NCL.

A. Das, A. K. Thakur, K. Kumar, Solid State Ionics 268, 185 (2014).

PEO20-LiCF3SO3- 8 wt.% ZrO2

24

ELECTRICAL MODULUS ANALYSIS AND DE-CONVOLUTED SCALING

Observation

with decreasing temperature the position of segmental relaxation

peak is shifting towards higher frequency values.

Modulus data are analysed using

Bergman modified KWW approach.

With decreasing temperature peak is

shifting towards low frequency side.

Segmental and Conductivity relaxation

can be observed.

𝜷 value found in the range 0.45 to 0.65.

Bergman Modified KWW Equation

B. K. Money, K. Hariharan, J. Swenson, J. Phys. Chem. B,116, 7762 (2012).

PEO20-LiCF3SO3- 8 wt.% ZrO2

25

CONDUCTIVITY AND SEGMENTAL RELAXATION TIME

Observation

Relaxation times are following VTF

relationship.


26

X-RAY DIFFRACTION: COMPOSITE AND COMPLEX FORMATION

Modified clay show larger interlayer spacing

With increasing clay concentration peak intensity

of (001) peak increases

Complex formation

Composite nature of the samples

Semi-crystalline nature of samples

Observation

PEO20-LiCF3SO3- x wt.% mMMT ( x = 2, 3, 5, 8, 10 & 15)

27

AC CONDUCTIVITY : COMPARATIVE STUDY

RFEBM

Jeppe C. Dyre, J. Appl. Phys. 64, 2456 (1988)

Assumption

Ion hopping distance is uniform.

Physical interaction between mobile

ion and fixed lattice points are causing

a random potential landscape.

PEO20-LiCF3SO3- x wt.% mMMT ( x = 2, 3, 5, 8, 10 & 15)

Modified Almond-West Fromalism

28

ELECTRICAL MODULUS ANALYSIS

Observation

Modulus data are analysed using Bergman

modified KWW approach and Havriliak-Negami

formalism.

With decreasing temperature peak is shifting

towards low frequency side.

Relationship between KWW and HN

29

DIELECTRIC RELAXATION ANALYSIS

𝜺′ shows nearly constant value in high

frequency regions and with decreasing

frequency its value increases gradually.

𝜺′′ increases monotonically with

decreasing frequency.

DC conduction free dielectric loss clearly

mark EP and segmental relaxation.

Dominance of NCL over UDR at low

temperature regime.

Observation

UDR and NCL together only can represent

the ion conduction process in this class of

material.

Outcome

30

VTF RELATIONSHIP

Observation

Temperature dependent DC conductivity and Relaxation times are following VTF relationship.

31

COUPLING: RATNER’S CLASSICAL APPROACH

Ion diffusivity is calculated using the MacDonald–

Trukhan model along with the Nernst–Einstein (NE)

relation.

The relation between free ion concentration and dc

conductivity

For coupled systems according to the Stokes–Einstein

relation, D is inversely proportional to the polymer

segmental relaxation time

R. J. Klein, S. Zhang, S. Dou, B. H. Jones, R. H. Colby, J. Runt, J. Chem. Phys., 124, 144903 (2006)

32

COUPLING: RATNER’S CLASSICAL APPROACH

Ionic conduction and Segmental relaxation in coupled in composite polymer electrolyte.

Outcome

If the effect of free ion concentration

is neglected

M. A. Ratner and D. F. Shriver, Chem. Rev., 88, 109–124 (1988)

33

MIGRATION CONCEPT BASED DC CONDUCTIVITY ANALYSIS

VTF equation is an empirical relation and also posses a

divergence at Vogel temperature 𝑻 = 𝑻𝟎.

The key feature causing the non-Arrhenius behaviour of the dc conductivity is the constancy of the crossover angular

frequency at the end of the dispersive regime.

Displacive activation energy, obtained from fitted results 𝐄∗ = 𝟎. 𝟏𝟏𝟓𝟏𝒆𝑽 represents the existence of coupling between

segmental motion of polymer host and ionic conduction.

Limitation of VTF

Temperature Dependent DC conductivity in

MIGRATION

Outcome

MIsmatch Generated Relaxation for the Accommodation

and Transport of IONs

MIGRATION

R.D. Banhatti, K. Funke, Solid State Ionics, 175, 661(2004)

PEO20-LiCF3SO3- 8 wt.% TiO2

34

SUMMARY & CONCLUSION

Three series of PNCEs containing ZrO2, TiO2 and modified montmorillonite clay as filler are synthesized

using conventional solution casting technique.

XRD patterns and FE-SEM micro-graphs of PNCEs suggest the proper complexation of polymer-salt and

the composite nature of PNCEs.

In PNCEs existence of first and second universality is shown using complex ac conductivity spectra and

complex dielectric spectra. Cause behind the presence of second universality or nearly constant loss

phenomenon is proposed to be the caged ion dynamics movement.

The temperature dependent dc conductivity, conductivity and segmental relaxation time in PNCE obey VTF

relation. This indicates that the polymer segmental relaxation do play crucial role in ion transport

mechanism in PNCEs. Ratner’s classical coupling analysis is used to investigate the coupled nature of ionic

conduction process and segmental relaxation process in PNCEs.

Ion conduction mechanism in PNCEs are successfully fitted with the concept developed using MIGRATION

concept. It suggest ion hopping can be considered as a collection of successful as well as unsuccessful

forward-backward hopping over a larger period of time, which is the cause behind the observed dispersion

in the complex conductivity isotherms. This model also rule out the singularity on temperature scale found

in VTF relation.

On comparison of dc conductivity values at T=303K, it can be observed for 8wt.% filler ZrO2 and TiO2

based PNCEs show maximum conductivity and for 3wt.% filler mMMT based PNCEs show maximum

conductivity.

35

SUMMARY & CONCLUSION

36

THE FUTURE

Consumers are in constant demand for thinner, lighter, space effective, shape flexibility

and cost-effective batteries with larger autonomy.

Further research related to the increase the conductivity to the desired level on the

electro active polymers needs to be done.

As Li-rechargeable batteries enter their teenage years, scientists and engineers predicts:

AN EVEN BRIGHT FUTURE LIES AHEAD.

Background:

Battery research results in annual capacity gains of approximately 6%

Moore’s Law: The number of transistors on a computer microchip will double every two years. (50 years of proof!)

Idea: If battery technology had developed at the same rate, a heavy duty car battery would be the size of a penny.

Thank You

investigation of ion conduction mechanism and relaxation...

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