investigation on additives to improve positive active material utilization in lead-acid batteries

Investigation on additives to improve positive active material utilization in

lead-acid batteries

Rubha Ponraj Research seminar October 23, 2007

Department of ChemistryDepartment of Chemistry

2

Outline

• 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


3

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_vehiclehttp://en.wikipedia.org/wiki/Electric_vehicle

4

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


5

Comparison between different batteries in electric vehicle

Lead–acid

Ni–MH

Li-ion

Safety + 0 Specific energy + ++

Specific power + ++ +

Specific cost + 0

Recycling ++ 0 0

Comparison between different batteries (++: very good, + : good, 0: satisfactory, : poor, : very poor)

Jürgen Garche, J. Phys. Chem. Chem. Phys., 3, (2001) 356-367

Specific energy - Wh/kg

Specific power - W/kg

Specific cost - $/Wh


6

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


7

Goal of our project

Advanced lead-acid battery for military electric vehicle

- high fuel economy

- provides power at remote location

- stealth operation


Lead-acid batteries


9

History of lead-acid batteries

Inventor of first rechargeable battery - 1859

Gaston Plante (1834-1889)

http://www.geocities.com/bioelectrochemistry/plante.htm

Plante’s Lead–acid battery (1859)


http://www.leadacidbatteryinfo.org/resources.htmhttp://www.leadacidbatteryinfo.org/resources.htm

1010

Reaction mechanism• Reaction at positive electrode:

• Reaction at negative electrode:

• Total cell reaction:

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.


Pb(IV)O2 + HSO4- + 3H+ + 2e- discharge

charge Pb(II)SO4 + 2H2O Eo = 1.805 V

Pb(0) + HSO4- discharge

charge Pb(II)SO4 + H+ + 2e- Eo = -0.340 V

PbO2 + Pb + 2HSO4- + 4H+ discharge

charge 2PbSO4 + 2H2O Eocell = 2.145 V

11

Working principle LAB

During discharge process:

Link

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/PbbatteryV8web.html


http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/PbbatteryV8web.html

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Lead-acid battery construction


Positive plate pack

Positive plate pack

Microporous separator

Positive plate

Grid plate

Negative plate

Negative pole

Positive cell connector

valve

terminal

casing

Negative cell connection

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


14

Limitation

• Low specific energy (energy to weight ratio)


15

Reasons for the reduction of the theoretical specific energy


Specific energy of Plante’s battery- 9 Wh/kgSpecific energy of Plante’s battery- 9 Wh/kg


16

What is active material utilization?

• Positive electrode: lead dioxide

• Negative electrode: lead

- Ratio of ampere hours discharged to its stoichiometric capacity


17

Electrical conductivity

• Positive electrode:

PbO2 - 50 Ω-1cm-1

• Negative electrode: Pb - 5.3x104 Ω-1cm-1

• PbSO4 - Insulator


18

Positive electrode - reaction limiting

Positive plate reaction

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


Pb(IV)O2 + HSO4- + 3H+ + 2e- discharge

charge Pb(II)SO4 + 2H2O Eo = 1.805 V

19

Methods to improve positive active material utilization

• Increasing energy – weight ratio• Increasing mass transport of H+ and HSO4 ֿ 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) 297Tokunaga, M. Tsubota, K. Yonezu, K. Ando, J. Electrochem. Soc., 13 (1987) 525-529


20

Effect of discharge rates on active material utilization

• During discharge – permanent layer of PbSO4

• 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


HSO4¯

HSO4¯

e ֿ

Grid

At positive electrode

PbO2

PbSO4

Electrically Electrically isolated PbOisolated PbO22

21

Active material with mass transport enhancing additive

e ֿ

Illustration on the effect of porous additive

HSO4 ֿ

HSO4¯

HSO4¯

e ֿ

Grid

Active material without additive

PbO2

PbSO4


22

Effect of electrically conductive additives


Current collectorCurrent collector

(grid)(grid)

Active Active materialmaterial

Electrically conductive Electrically conductive materialmaterial

Electronic conducting matrix in active massElectronic conducting matrix in active mass


23

Survey on positive plate additives

Carboxymethyl cellulose (0.2 wt.%)• 9.9% increase in utilization (at 1 h discharge rate)• Initial capacity was high• Not stable – carbon oxidized

Carbon black (0.1 wt.%)• 3.3% increase in utilization (at 1 h discharge rate)• Not stable – carbon oxidized

H.Dietz, J.Garche, K.Weisner, J. Power Sources, 14 (1985) 305.


24

Survey on positive plate additivesGlass microspheres• Filler material • Utilization -11.4 % to 33.12% ( at 0.1 A/g discharge rate)• Optimum loading – 4.4 wt.%

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) 217Wang Qing, J. of Wuhan University of Technology--Materials Science Edition, 22 (2007) 174H.Dietz, J.Garche, K.Weisner, J. Power Sources, 14 (1985) 305

SEM image for glass microspheres (x 500)


25

Selection of additives

• 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 Simon D. McAllister, Rubha Ponraj, I. Francis Cheng and Dean B. Edwards, J. of Power Sources 173173, 2 , 2 (2007)(2007)


26

Our choice of additive Diatomaceous earth particles

(SiO2)- Fossilized remains of diatoms, a type of hard-shelled algae

- Uses: filtration aid, insecticide, cat litter- It is stable, light weight, porous and cost

effective

5µm

http://en.wikipedia.org/wiki/Diatomaceous_earth


EXPERIMENTAL


28

Sorting of diatomaceous earth

- Diatomaceous earth particles -sorted using Nylon screen cloth

20-30 µm

30-53 µm

53-74 µm

74-90 µm

SEM of diatomites of different sizes: (A) 20–30 µm, (B) 53–74 µm, (C) >90 µm

BA

C


29

Paste preparation

Curing

Zero valent Pb test

Formation

Conditioning

Satisfactory

Porosity test

Unsatisfactory

Unsatisfactory

Process of positive plate preparation


30

Paste Composition• PbO-(11% Pb0), 0.5% Dynel fibers, additive - total 10 g

Mixed with H2SO4 and H2O - paste

• Density -

2.5 – 3.5 g/cm3

• Pasted into teflon rings

(volume 0.24 ml)


Pb strip Paste inside teflon ring

31

Curing

• 24 hrs hydroset – 250 °F pressure cooker

• Pb0→ PbO

• Some formation of PbSO4

• Dried overnight

• Each plate - 0.6 to 0.8 g


32

Testing

• Porosity by water absorption - >45%• Pb0 atomic absorption spectroscopy - <5wt.%

• SO42- by ion-conduction chromatography

If it passed the screen test….


33

Formation PbO + H2SO4 PbSO4 + H2O

PbSO4 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

Berndt, D. Maintenance-Free Batteries. 2nd ed. 1997, p. 106

.

negative plate in between separators

Formation cell (side view)

polyethylene separator b/w negative andpositive plates

Glass mat with 90% porosity

Formation cell (cross-sectional view)

Positive plate


oxidationoxidation

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Conditioning and cyclingChanged the electrolyte - 1.3 sp. gr. H2SO4

- Discharged at 10 mA/g

- Charged to 125% discharge

capacity

- 4 to 5 cyclesCounter Electrode 20-30 cm of Pt wire

Working Electrode – Positive plate Reference Electrode –

Ag/AgCl


35

Performance measurement• Capacity measurements are taken at a 50 mA cm-2

discharge and a 10 mA cm-2 discharge. • Diatomites - 20-30 µm, 30-53 µm, 53-74 µm and 74-90 µm, at 1 wt.%, 3 wt.% and 5 wt.% were tested.

• Our control – without additive


RESULTS


37

Discharge curve


1.20E+00

1.30E+00

1.40E+00

1.50E+00

1.60E+00

1.70E+00

1.80E+00

0 1000 2000 3000 4000

Time (s)

Vo

ltag

e (V

)

PbOPbO2 2 + HSO+ HSO44- - + 3H+ 3H+ + + 2e+ 2e- - PbSOPbSO4 4 + H+ H22OO

dischargedischarge

• Fast discharge rate (50 mA/cm2)

• Discharge capacity (mAh)

• Utilization = Calculated capacity

• Theoretical capacity = 0.2241 Ah/g

Theoretical capacityTheoretical capacity

38

Utilization at fast discharge rate

-4

-2

0

2

4

6

8

10

12

14

20-30 30-53 53-74 74-90Size (µm)

% c

han

ge in

uti

lizat

ion

3% loadings

5% loadings


39

Utilization at slow discharge rate


-10

-5

0

5

10

15

20-30 30-53 53-74 74-90

Size (µm)

% c

hang

e in

uti

liza

tion

3% loadings

5% loadings

40

Specific capacity

-12

-10

-8

-6

-4

-2

0

2

4

6

8

20-30 30-53 53-74 74-90

Size (µm)

% c

hang

e in

spe

cifi

c ca

paci

ty

3% loadings

5% loadings

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

20-30 30-53 53-74 74-90

Size (µm)

% c

hang

e in

spe

cifi

c ca

paci

ty

3% loadings

5% loadings

At fast discharge rate (50 mA/cm2) At slow discharge rate (10 mA/cm2)


Specific capacity – mAh/g

41

Diatomites’ structure A

B C

Scanning electron micrograph of diatomites: A) recovered from active material after the performance tests, B) 20-30 µm C) 53–74 µm.

• Diatomites are stable in the battery environment• Single diatomite elements did not perform as good as conglomerates


Simon D. McAllister, Rubha Ponraj, I. Francis Cheng and Dean B. Edwards, J. of Power Sources Simon D. McAllister, Rubha Ponraj, I. Francis Cheng and Dean B. Edwards, J. of Power Sources 173173, 2 , 2 (2007)(2007)

42

Conclusions

• Statistically significant increase in performance

• Specific energy – 12.69% increase relative to 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%

Comparison of % utilization of best performed size of diatomites with control

43

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


44

The way forward


• Test in Full sized plates

• Use electrically conductive additives

1cm1cm22 3.65 x 3.365 x 0.050 in3.65 x 3.365 x 0.050 in33

45

Acknowledgements

• 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: N00014-

04-1-0612


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