Investigation on additives to improve
positive active material utilization in
lead-acid batteries
Rubha Ponraj
Research seminar
October 23, 2007
Department of Chemistry
Outline
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Introduction to Electric vehicle (EV)
Our choice of battery in EV
Goal of our project
Working principle
Advantages and limitation
How to overcome the limitation?
Our effort
Results
Conclusion
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Alternative fuel for vehicles
• Gas emissions and its ecology impact
• Electric vehicle
• California Air Resources Board (CARB) –Zero
emission vehicle – 1995
http://en.wikipedia.org/wiki/Electric_vehicle
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Battery powered electric vehicles
Batteries – Lead acid batteries,
Nickel metal Hydride (Ni-MH) and Lithium-ion
• Problem of recharging
(7-10 hours)
• Limited range – type and weight
• Batteries are bulky
• Safety issues
• High initial cost
http://www.naftc.wvu.edu/NAFTC/data/indepth/Electric/HybridElectric.HTML
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Comparison between different batteries in
electric vehicle
Comparison between different batteries (++: very good,
+ : good, 0: satisfactory, : poor, : very poor)
Safety
Specific energy
Specific power
Specific cost
Recycling
Lead–acid
Ni–MH
+
0
+
++
+
+
++
0
Li-ion
++
+
0
0
Specific energy - Wh/kg
Specific power - W/kg
Specific cost
- $/Wh
Jürgen Garche, J. Phys. Chem. Chem. Phys., 3, (2001) 356-367
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Feasibility of lead acid batteries
Can lead acid battery compete in modern times?
Yes
• Dominant position due to low cost - automobile applications
• Cost efficient technologies – to improve the performance
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Goal of our project
Advanced lead-acid battery for military
electric vehicle
- high fuel economy
- provides power at remote location
- stealth operation
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Lead-acid batteries
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History of lead-acid batteries
Inventor of first rechargeable
battery - 1859
Plante’s Lead–acid
battery (1859)
Gaston Plante
(1834-1889)
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http://www.leadacidbatteryinfo.org/resources.htm
http://www.geocities.com/bioelectrochemistry/plante.htm
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Reaction mechanism
• Reaction at positive electrode:
Pb(IV)O2 + HSO4- + 3H+ + 2e-
discharge
charge
Pb(II)SO4 + 2H2O Eo = 1.805 V
• Reaction at negative electrode:
Pb(0) + HSO4-
discharge
charge
Pb(II)SO4 + H+ + 2e-
Eo = -0.340 V
• Total cell reaction:
PbO2 + Pb + 2HSO4- + 4H+
discharge
charge
2PbSO4 + 2H2O
Eocell = 2.145 V
E0 – in 1.3 specific gravity H2SO4
H. Bode, Lead-Acid Batteries, translated by R.J. Brodd and K.V. Kordesch, Wiley
Interscience, New York, 1997, page 4.
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Working principle LAB
During discharge process:
Link
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/PbbatteryV8web.html
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Lead-acid battery construction
Positive plate
valve
pack
Negative cell
Positive cell connection
connector
Microporous
separator
Grid plate
casing
terminal
Positive plate pack
Negative pole
Negative plate
Positive plate
http://www.doitpoms.ac.uk/tlplib/batteries/batteries_lead_acid.php
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Advantages
• Low cost.
• Reliable.
• Indefinite shelf life – compared to
modern batteries
• Deliver high currents
• Low self-discharge
• Low maintenance requirements
• Many suppliers world wide.
• The world's most recycled product.
http://en.wikipedia.org/wiki/Lead-acid_battery
http://www.lead-battery-recycling.com/lead battery-recycling.html
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Limitation
• Low specific energy (energy to weight ratio)
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Reasons for the reduction of the theoretical
specific energy
Specific energy of Plante’s battery- 9 Wh/kg
Jürgen Garche, J. Phys. Chem. Chem. Phys., 3, (2001) 356-367
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What is active material utilization?
• Positive electrode: lead dioxide
• Negative electrode: lead
- Ratio of ampere hours discharged to its
stoichiometric capacity
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Electrical conductivity
• Positive electrode:
PbO2 - 50 Ω-1cm-1
• Negative electrode:
Pb - 5.3x104 Ω-1cm-1
• PbSO4 - Insulator
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Positive electrode - reaction limiting
Positive plate reaction
Pb(IV)O2 + HSO4- + 3H+ + 2e-
discharge
charge
Pb(II)SO4 + 2H2O Eo = 1.805 V
Discharge capacity (Ah) depends on this reaction
To sustain this reaction:
• Supply of acid
• Supply of electrons
P.T. Moseley, J. of Power Sources 64 (1997) 47-50
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Methods to improve positive active
material utilization
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Increasing energy – weight ratio
Increasing mass transport of H+ and HSO4ֿ inside
active material
Increasing electrical conductivity of active material
H.Dietz, J.Garche, K.Weisner, J. Power Sources, 14 (1985) 305.
D.B.Edwards, Song Zhang, J. Power Sources, 135 (2004) 297
Tokunaga, M. Tsubota, K. Yonezu, K. Ando, J. Electrochem. Soc., 13 (1987) 525-529
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Effect of discharge rates on active
material utilization
• During discharge – permanent layer of
PbSO4
Grid
• Fast discharge rate (50 mA/cm2)
- Positive active material utilization – 30%
- Not enough time (mass-transport limited)
- Porous non-conductive additives
• Slow discharge rate (10 mA/cm2)
- Positive active material utilization – 60%
(Electronic conduction limited)
- higher electrical conductive materials
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PbSO4
eֿ
Electrically
isolated PbO2
HSO4¯
HSO4¯
PbO2
At positive electrode
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Illustration on the effect of porous additive
Grid
PbSO4
HSO4ֿ
eֿ
HSO4¯
eֿ
HSO4¯
PbO2
Active material without
additive
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Active material with mass
transport enhancing additive
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Effect of electrically conductive additives
Electronic conducting matrix in active mass
Current collector
(grid)
Active
material
Electrically
conductive material
Jürgen Garche, J. Phys. Chem. Chem. Phys., 3, (2001) 356-367
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Survey on positive plate additives
Carboxymethyl cellulose (0.2 wt.%)
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9.9% increase in utilization (at 1 h discharge rate)
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Initial capacity was high
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Not stable – carbon oxidized
Carbon black (0.1 wt.%)
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3.3% increase in utilization (at 1 h discharge rate)
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Not stable – carbon oxidized
H.Dietz, J.Garche, K.Weisner, J. Power Sources, 14 (1985) 305.
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Survey on positive plate additives
Glass microspheres
• Filler material
• Utilization -11.4 % to 33.12%
( at 0.1 A/g discharge rate)
• Optimum loading – 4.4 wt.%
SEM image for glass microspheres (x 500)
Silica gel
• Particle size - 30 to 150 nm
• 0.2 wt.% addition
• Increases utilization by 10% (high discharge rate)
D.B. Edwards, V.S.Srikanth, J. Power Sources, 34 (1991) 217
Wang Qing, J. of Wuhan University of Technology--Materials Science Edition, 22 (2007) 174
H.Dietz, J.Garche, K.Weisner, J. Power Sources, 14 (1985) 305
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Selection of additives
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Stable
Good adhesion to active material
Improve positive active material utilization
Cost effective
Light weight
Simon D. McAllister, Rubha Ponraj, I. Francis Cheng and Dean B. Edwards, J. of Power Sources 173, 2 (2007)
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Our choice of additive
Diatomaceous earth particles
(SiO2)
- Fossilized remains of diatoms,
a type of hard-shelled algae
5µm
- Uses: filtration aid, insecticide, cat litter
- It is stable, light weight, porous and cost
effective
http://en.wikipedia.org/wiki/Diatomaceous_earth
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EXPERIMENTAL
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Sorting of diatomaceous earth
A
-
B
Diatomaceous earth particles sorted using Nylon screen cloth
20-30 µm
30-53 µm
53-74 µm
74-90 µm
C
SEM of diatomites of different
sizes:
(A) 20–30 µm, (B) 53–74 µm,
(C) >90 µm
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Process of positive plate preparation
Paste
preparation
Porosity test
Zero valent
Pb test
Unsatisfactory
Unsatisfactory
Curing
Satisfactory
Formation
Conditioning
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Paste Composition
• PbO-(11% Pb0), 0.5% Dynel fibers, additive - total 10 g
Mixed with H2SO4 and H2O - paste
• Density Paste inside
Pb strip
3
2.5 – 3.5 g/cm
teflon ring
• Pasted into teflon rings
(volume 0.24 ml)
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Curing
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24 hrs hydroset – 250 °F pressure cooker
Pb0→ PbO
Some formation of PbSO4
Dried overnight
Each plate - 0.6 to 0.8 g
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Testing
• Porosity by water absorption - >45%
• Pb0 atomic absorption spectroscopy - <5wt.%
• SO42- by ion-conduction chromatography
If it passed the screen test….
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Formation
PbO + H2SO4
PbSO4
oxidation
PbSO4 + H2O
PbO2 + 2e-
• 1.1 sp. gr. H2SO4
• commercial negative plate with
polyethylene separator
• Theoretical capacity - 0.2241 Ah/g
• Charge positive plates to 125%
Calculation of theoretical capacity:
2F = 53.6 Ah
Positive plate
negative plate in
between separators
Glass mat with
90% porosity
polyethylene
separator b/w
negative and
positive plates
Formation cell (side view)
Formation cell (cross-sectional view)
Berndt, D. Maintenance-Free Batteries. 2nd ed. 1997, p. 106
.
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Conditioning and cycling
Changed the electrolyte - 1.3 sp. gr. H2SO4
- Discharged at 10 mA/g
- Charged to 125% discharge
capacity
- 4 to 5 cycles
Counter Electrode
20-30 cm of Pt wire
Working Electrode
– Positive plate
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Reference Electrode –
Ag/AgCl
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Performance measurement
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Capacity measurements are taken at a 50 mA cm-2
discharge and a 10 mA cm-2 discharge.
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Diatomites - 20-30 µm, 30-53 µm, 53-74 µm
and 74-90 µm, at 1 wt.%, 3 wt.% and 5 wt.% were
tested.
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Our control – without additive
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RESULTS
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Discharge curve
Voltage (V)
PbO2 + HSO4- + 3H+ + 2e-
discharge
PbSO4 + H2O
1.80E+00
• Fast discharge rate (50 mA/cm2)
1.70E+00
• Discharge capacity (mAh)
1.60E+00
• Utilization = Calculated capacity
Theoretical capacity
1.50E+00
• Theoretical capacity = 0.2241 Ah/g
1.40E+00
1.30E+00
1.20E+00
0
1000
2000
3000
4000
Tim e (s)
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Utilization at fast discharge rate
14
% change in utilization
12
10
3% loadings
5% loadings
8
6
4
2
0
-2
-4
20-30
30-53
53-74
74-90
Size (µm)
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Utilization at slow discharge rate
% change in utilization
15
3% loadings
5% loadings
10
5
0
-5
-10
20-30
30-53
53-74
74-90
Size (µm)
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Specific capacity
Specific capacity – mAh/g
At fast discharge rate (50 mA/cm2)
At slow discharge rate (10 mA/cm2)
8
12
3% loadings
3% loadings
10
6
5% loadings
5% loadings
4
% change in specific capacity
% change in specific capacity
8
6
4
2
0
-2
-4
2
0
-2
-4
-6
-6
-8
-8
-10
- 10
-12
20-30
3 0 - 53
53 - 74
Siz e (µm)
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74 - 9 0
20-30
30-53
53-74
74-90
Size (µm)
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Diatomites’ structure
A
• Diatomites are stable in the battery
environment
• Single diatomite elements did not perform
as good as conglomerates
B
C
Scanning electron micrograph of
diatomites: A) recovered from active
material after the performance tests, B)
20-30 µm C) 53–74 µm.
Simon D. McAllister, Rubha Ponraj, I. Francis Cheng and Dean B. Edwards, J. of Power Sources 173, 2 (2007)
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Conclusions
Comparison of % utilization of best performed size of
diatomites with control
Fast discharge rate
(50 mA/cm2)
Slow discharge
rate (10 mA/cm2)
Control
(without
diatomites)
33.65 ± 2.52%
58.00 ± 2.01 %
With diatomites
particle size(53-74 µm)
38 .04 ± 2.09%
58.96 ± 2.42%
• Statistically significant increase in
performance
• Specific energy – 12.69% increase relative
to control
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Summary
• Diatomites are an inexpensive filler material
• Utilization increases by 12.7% at a fast
discharge rate.
• Specific capacity increases by 9.3% at a fast
discharge rate
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The way forward
• Test in Full sized plates
1cm2
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3.65 x 3.365 x 0.050 in3
Use electrically conductive additives
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Acknowledgements
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Dr. I. Francis Cheng
Dr. Dean B. Edwards
Simon D. McAllister
Kenichi Shimizu
Derek F. Laine
Dr. Song Zhang
Dr. and Mrs. Renfrew
Office of Naval Research Award Number: N0001404-1-0612
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