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]
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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
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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.
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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
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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.
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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
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FILLER SYNTHESIS: ZIRCONIA (ZrO2)
Flow Chart: Tetragonal Zirconia Synthesis
XRD Pattern
FE-SEM
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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)
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FILLER SYNTHESIS: TITANIA (TiO2)
XRD Pattern Rietveld Refined XRD Pattern
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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.
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MATERIAL SYNTHESIS: COMPOSITE POLYMER ELECTROLYTE
Flow Chart: Solution Casting Technique
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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)
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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
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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
PEO20-LiCF3SO3- x wt.% ZrO2 ( x = 0, 3, 5, 8, 10 & 20)
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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)
PEO20-LiCF3SO3- x wt.% ZrO2 ( x = 0, 3, 5, 8, 10 & 20)
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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
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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
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CONDUCTIVITY AND SEGMENTAL RELAXATION TIME
Observation
Relaxation times are following VTF
relationship.
PEO20-LiCF3SO3- x wt.% ZrO2 ( x = 0, 3, 5, 8, 10 & 20)
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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)
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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
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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
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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
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VTF RELATIONSHIP
Observation
Temperature dependent DC conductivity and Relaxation times are following VTF relationship.
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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)
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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)
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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
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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.
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SUMMARY & CONCLUSION
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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