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

1. Investigation on additives to improve positive active material utilization in lead-acid batteries Rubha Ponraj Research seminar October 23, 2007 Department 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 Department of Chemistry

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_vehicle Department of Chemistry

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 Department of Chemistry

5. Comparison between different batteries in electric vehicle Specific energy - Wh/kg Specific power - W/kg Specific cost - $/Wh Jürgen Garche, J. Phys. Chem. Chem. Phys., 3, (2001) 356-367 Department of Chemistry

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 Department of Chemistry

7. Goal of our project • Advanced lead-acid battery for military electric vehicle - high fuel economy - provides power at remote location - stealth operation Department of Chemistry

8. Lead-acid batteries Department of Chemistry

9. History of lead-acid batteries Inventor of first rechargeable battery - 1859 Plante’s Lead–acid battery (1859) Gaston Plante (1834-1889) http://www.leadacidbatteryinfo.org/resources.htm http://www.geocities.com/bioelectrochemistry/plante.htm Department of Chemistry

10. 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. Department of Chemistry 10

11. Working principle LAB During discharge process: Link http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/PbbatteryV8web.html Department of Chemistry

12. Positive plate pack valve Negative cell connection Positive cell connector Microporous separator Grid plate casing terminal Positive plate pack Negative pole Negative plate Positive plate Lead-acid battery construction http://www.doitpoms.ac.uk/tlplib/batteries/batteries_lead_acid.php Department of Chemistry

13. 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 Department of Chemistry

14. Limitation • Low specific energy (energy to weight ratio) Department of Chemistry

15. 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 Department of Chemistry

16. What is active material utilization? • Positive electrode: lead dioxide • Negative electrode: lead • Ratio of ampere hours discharged to its stoichiometric capacity Department of Chemistry

17. Electrical conductivity • Positive electrode: PbO2 - 50 Ω-1cm-1 • Negative electrode: Pb - 5.3x104 Ω-1cm-1 • PbSO4 - Insulator Department of Chemistry

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 Department of Chemistry

19. Methods to improve positive active material utilization • 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 Department of Chemistry

20. PbSO4 Grid eֿ Electrically isolated PbO2 HSO4¯ HSO4¯ PbO2 At positive electrode 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 Department of Chemistry

21. PbSO4 Grid eֿ eֿ HSO4¯ HSO4¯ PbO2 Active material without additive Illustration on the effect of porous additive HSO4ֿ Active material with mass transport enhancing additive Department of Chemistry

22. Current collector (grid) Active material Electrically conductive material Effect of electrically conductive additives Electronic conducting matrix in active mass Jürgen Garche, J. Phys. Chem. Chem. Phys., 3, (2001) 356-367 Department of Chemistry

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. Department of Chemistry

24. 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.% 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 SEM image for glass microspheres (x 500) Department of Chemistry

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 173, 2 (2007) Department of Chemistry

26. 5µm 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 http://en.wikipedia.org/wiki/Diatomaceous_earth Department of Chemistry

27. EXPERIMENTAL Department of Chemistry

28. A B C 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 Department of Chemistry

29. Paste preparation Unsatisfactory Unsatisfactory Curing Porosity test Zero valent Pb test Satisfactory Formation Conditioning Process of positive plate preparation Department of Chemistry

30. Paste inside teflon ring Pb strip 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) Department of Chemistry

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 Department of Chemistry

32. Testing • Porosity by water absorption - >45% • Pb0 atomic absorption spectroscopy - <5wt.% • SO42- by ion-conduction chromatography If it passed the screen test…. Department of Chemistry

33. Positive plate Glass mat with 90% porosity polyethylene separator b/w negative and positive plates negative plate in between separators Formation cell (cross-sectional view) Formation cell (side view) Formation oxidation 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 . Department of Chemistry

34. Counter Electrode 20-30 cm of Pt wire Working Electrode – Positive plate Reference Electrode – Ag/AgCl 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 Department of Chemistry

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 Department of Chemistry

36. RESULTS Department of Chemistry

37. discharge PbSO4 + H2O PbO2 + HSO4- + 3H+ + 2e- • Fast discharge rate (50 mA/cm2) • Discharge capacity (mAh) • Utilization = Calculated capacity • Theoretical capacity = 0.2241 Ah/g Theoretical capacity Discharge curve Department of Chemistry

38. Utilization at fast discharge rate Department of Chemistry

39. Utilization at slow discharge rate Department of Chemistry

40. Specific capacity Specific capacity – mAh/g At fast discharge rate (50 mA/cm2) At slow discharge rate (10 mA/cm2) Department of Chemistry

41. A B C Diatomites’ structure • Diatomites are stable in the battery environment • Single diatomite elements did not perform as good as conglomerates 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) Department of Chemistry

42. Conclusions Comparison of % utilization of best performed size of diatomites with control • Statistically significant increase in performance • Specific energy – 12.69% increase relative to control Department of Chemistry

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 Department of Chemistry

44. The way forward • Test in Full sized plates 1cm2 3.65 x 3.365 x 0.050 in3 • Use electrically conductive additives Department of Chemistry

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 Department of Chemistry