Polymer/Ionic Liquid Electrolytes and Their Potential in Lithium Batteries presented by Allyson Palker and Dean Tigelaar of NASA's Glenn Research Center at an energy workshop on 7/20/2010.

1. National Aeronautics and Space Administration!
Recent Research in Lithium Batteries and Fuel
Cells
Dean Tigelaar
Polymers Branch
NASA Glenn Research Center
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Polymer/Ionic Liquid Electrolytes and Their
Potential in Lithium Batteries
Allyson Palker, Dean Tigelaar
Polymers Branch
William Bennett
Electrochemistry Branch
NASA Glenn Research Center
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3. Lithium Polymer/Ionic Liquid Batteries
 Motivated by PERS program
 Polymer Energy Rechargeable System.
 Advantages
 Safety
 Commercial batteries contain flammable
solvents.
 Li metal anodes
 Disadvantages
 Lithium ion conductivity
 Maximum conductivity ~10-4 S/cm
*Gaston Narada International Ltd
*
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4. Our Objective
 Prepare polymer separator that has:
 High lithium ion conductivity (~10-3 S/cm)
 No volatile components
 High long term stability with lithium metal
electrodes
 Strategy: Polymer gel electrolyte that
contains ionic liquids
 Nonvolatile, nonflammable, wide ESW.
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GRC Polymer Electrolyte
 Rod segment provides mechanical strength.
 PEO coil segment helps conduct lithium ions.
 High degree of crosslinking.
 Can hold large amounts of liquid additives (>400%).
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6. Variables:
A. Amount of Room Temperature Ionic Liquid (RTIL)
~ 200, 300, 400%
B. Concentration of Lithium Bis(trifluoromethane)
sulfonimide (LiTFSi)
~ .5, .75, 1.0 mol/kg
C. Addition of Alumina (Al203)
~ 0, 5, 10, 15%

10. Cycling Data
Experiment 1: Amount of IL added
200% IL with .5 mol/kg 300% IL with .5 mol/kg
400% IL is the most
compatible with the
Lithium electrodes
at a current density
of .25 mA/cm2, 60°C
10
400% IL with .5 mol/kg

11. Experiment 2: Concentration of LiTFSi
400% IL with .5 mol/kg 400% IL with .75 mol/kg
The concentration of Lithium
salt that was the most
compatible with the Lithium
electrodes was the 1.0 mol/
kg.
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400% IL with 1.0 mol/kg

12. Experiment 3: Addition of Alumina
400% IL with 1.0 mol/kg and 0% Alumina 400% IL with 1.0 mol/kg and 10% Alumina
The addition of 5% Alumina caused the Voltage to decrease five fold
showing there is less resistance and better stability in comparison
to the sample without Alumina.
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13. Impedance Data
• Addition of alumina results in a significant decrease in interfacial resistance
• More stable interfacial layer.
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14. Summary
 Made electrolytes by varying:
1. Amount of RTIL
2. Concentration of Li salt
3. Addition of Alumina
 Symmetric coin cells made with the polymer
electrolytes
 Improved cycling stability in coin cells from <3
hrs to >1000 hrs at 0.25 mA/cm2 current density
 400% IL with 1.0 mol/kg and 10% Alumina was
the most compatible with the Lithium electrodes
• Tigelaar, D. M.; Palker, A. P.; Meador, M. A. B.; Bennett,
W. R., J. Electrochem. Soc., 2008, 155, A768.
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Progress of Proton Exchange Membrane (PEM)
Fuel Cells
Dean Tigelaar, Allison Palker
Polymers Branch
NASA Glenn Research Center
Huan He, Christine Jackson, Kellina
Anderson, Tyler Peter, Jesse Wainright,
Robert Savinell
Case Western Reserve University
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Advantanges
• Efficient energy conversion (up to 70%)
• High energy density
• Generates water in exhaust
• No recharge needed
Potential Uses
• Propulsion
– Automotive, zero emission aircraft
• Stationary
– Power supply (Gemini V)
• Portable
– Astronaut equipment
• Regenerative
– Coupled with photovoltaic systems for energy storage
– Hydrolysis of water back into H2 and O2
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Proton Exchange Membrane must:
• Have high proton conductivity.
• Have low electrical conductivity.
• Be mechanically robust in the wet and dry state.
• Processable into thin film.
• Be stable to a high temperature, high humidity, highly acidic
environment for thousands of hours.
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Nafion-State of the art membrane
poly(perfluorosulfonic acid)
“Nafion”
Advantages: Disadvantages:
• Excellent proton conductivity • Expensive
(0.1 S/cm ) • Limited operation temperature
• Good mechanical and chemical (≤80°C)
properties •High methanol permeability.
• Long-term stability
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Sulfonated Poly(arylene ether)s (McGrath)
• High thermal and chemical stability
• Good film forming properties
• Several monomers and polymers are commercially available
• Controlled degree of sulfonation
– Controls conductivity and mechanical properties
– 30-40% sulfonated monomer
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Polybenzimidazole/H3PO4 (PBI) (CWRU)
• Excellent thermal and oxidative stability.
• Less dependant on humidification.
• Operating temperatures up to 200oC.
• High H3PO4 uptake (~200 wt%).
• But: Difficult to process into strong film.
• Produced commercially by BASF.
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Our Strategy: Synthesize Novel Polymer
• Fully Aromatic
– Thermo-oxidatively stable and mechanically strong.
• Heterocyclic
– Coordination with H3PO4 by acid-base or H-bonding.
– Similar to PBI but easier to process.
• Highly soluble in common organic solvents
– NMP, DMAc, CHCl3.
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Solution: Poly(arylene ether triazine)s
• Fully aromatic
• Soluble due to ether links and bulky pendant groups.
• Can be made conductive in 2 different ways.
1) Nitrogen groups capable of bonding with H3PO4
2) Can be sulfonated on exclusively on pendant groups
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Monomer Synthesis
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Polymer Synthesis
• High molecular weight (IV 0.6-1.0 dL/g).
• Thermo-oxidative stability (Td > 500°C in air).
• Rigid but soluble (Tg 150-290°C, soluble in CHCl3, NMP,
CF3CO2H).
• Good film forming properties.
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Glass Transition Temperature
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Polymer Sulfonation
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0.12
Conductivity of Sulfonated Films
0.1
0.08
Conductivity / S cm-1
0.06
0.04
0.02
Nafion 115 DPA-Pket DPA-diket DPA-PS
0
0 10 20 30 40 50 60 70 80 90 100
Temperature / oC
• Most conductive film is more conductive than Nafion 117.
• This film is brittle in it’s dry state, but can be fixed by changing
to a more flexible monomer.
• The most conductive polymer was the lowest water uptake and ion
exchange capacity. Why?
Tigelaar, D. M.; Palker, A. P.; Jackson, C. M.; Anderson, K. M.; Wainright, J. Savinell, R. F Macromolecules, 2009, 42,
1888.
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TEM Data
DPA-PS DPA-pket
IEC = 1.88 meq/g IEC = 2.12 meq/g
Water uptake = 131% Water uptake = 211%
σ = 0.11 S/cm at 90°C σ = 0.082 S/cm at 90°C
2-10 nm hydrophilic regions 5-15 nm hydrophilic regions
Dark background Well connected
Tigelaar, D. M.; Palker, A. P.; He, R.; Scheiman D. A.; Petek, T.; Savinell, R. F.; Yoonessi, M.
J. Membrane Science, 2011, 369, 455.
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Phosphoric Acid Uptake of DPA-PS/PBI Blends
900
800
700
600
Uptake (wt %)
500
Room Temp 50oC 90oC
400
1:1 DPA-PS:PBI
3:1 DPA-PS:PBI
300 9:1 DPA-PS:PBI
200
100
0
0 20 40 60 80 100 120 140 160 180 200 220 240 260
Time (hr)
• Uptake of PBI by this method is 200%.
• “As received” PBI can be used for 3:1, 9:1 blends.
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Phosphoric acid uptake
85% H3PO4
90°C
22 days
100% 3:1 DPA-PS:PBI blend 7% polymer
93% H3PO4
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Conclusions
• Synthesized novel poly(arylene ether)s that are fully
aromatic, soluble, and with high molecular weight.
• Polymers have high H3PO4 uptake, but lose
dimensional stability as high temperatures.
• Most conductive sulfonated polymer has the same
conductivity as Nafion 115 at 100% RH.
• Most conductive polymer is brittle when dry.
– This problem can be fixed by replacing sulfone with
isophthaloyl group or using a comonomer.
Acknowledgements
• Dan Scheiman, Mitra Yoonessi
• Robert Savinell, Jesse Wainright, Christine
Jackson, and Kellina Anderson, Huan He.
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