Monobloc Batteries: High Temperatures, Life and Catalysts

1. Philadelphia Scientific Monobloc Batteries: High Temperatures, Life and Catalysts Harold A. Vanasse Daniel Jones

2. Outline • What does design life mean? • How does temperature affect design life? • How does actual life compare with design life? • Does a catalyst impact actual life at high temperature?

3. Introduction • We have been approached by people concerned about life of their 12-volt Monobloc VRLA batteries. • They are very popular in outside plant (OSP) applications. • Easy to install & support. • High power density. • Shorter than expected life is becoming an issue. • Can we apply our experience in larger 2-volt cells to the Monobloc design?

4. Life Expectations Definitions: • Design Life = The life of the battery as expected by the battery producer. • Actual Life = The life of the battery as experienced by the battery owner.

5. Problems happen when Design Life Actual Life

6. Designer’s Toolbox Factors used by battery designer: • Positive grid corrosion rate (purity). • Positive grid thickness. • Electrolyte reserve. • Others: Strap corrosion, post seals, jar to cover seals & vent design.

7. Positive Plate Life • For a long lived plate: • Minimize corrosion rate and … • Maximize plate thickness … • Within cost constraints. • The above parameters determine how long the positive plate lasts. • The plate life is based on 25°C (77°F).

8. Battery Life • Positive plate life has been determined. • Design is always a function of the particular application with inherent tradeoffs. • 10 year design has thicker plates than 5 year design. • No other factors should have a shorter life expectancy than positive plate. • Competent design should eliminate these. • Design Life = Positive Plate Life at 25°C.

9. But … The real world does not run at 25°C!

10. Number of Days > 90° F 15 to 30 days 60 days or more

11. Temperature • OSPs are exposed to high environmental temperature in summer. • Cabinet temperatures are higher than ambient. • Past Battcon papers identify ill effects of high temperature on Monobloc batteries: • Vacarro (2004) & McCluer (2003) • High temperatures drastically shorten life of Monobloc batteries. • Failure modes: Dry out & grid growth/corrosion.

12. Impact of High Temperature on Batteries

13. Temperature vs. Float Current

14. Arrhenius who? • Dr. Svante Arrhenius • Swedish scientist in late 1800’s quantifies impact of temperature rise on rate of chemical reactions. • Nobel prize in 1903. • His equation (generalized): • For every increase of 10°C, reaction (corrosion) rate doubles. • Life of positive plate is cut in half with each 10°C rise in temperature.

15. What does this tell us? • The theory and the data both indicate that high temperature is bad for batteries. • But how bad? • What can we expect for Design Life?

16. Design Life at Temperature

17. Design Life Summary Design life at high temperatures is MUCH shorter than at 25°C.

18. Actual Life • Only you know what your actual life is. • How does it compare to the table of Design Life at Temperature? • Our sources and testing indicate that real batteries are coming up short.

19. Closing the Gap What is the effect of a catalyst on Monobloc batteries at high temperature?

20. Catalyst Refresher • VRLA batteries can become unbalanced leading to a depolarized negative plate. • The catalyst affects the polarization of both plates. • Negative polarization increases. • Positive polarization decreases. • Lander curve describes affect on corrosion rate. • Optimum positive polarization minimizes corrosion rate.

21. Lander Curve

22. Catalyst Refresher • Oxygen and Hydrogen recombine on the negative plate and reduce it’s polarization. • The catalyst prevents a small amount of O2 from reaching the negative plate. • The negative stays polarized. • The positive polarization is reduced. • The float current of the cell is lowered. • We generally find current reduced by half.

23. Proof of Concept Testing • Four 12 V (100 Ah) Monobloc batteries. • 10-Year Design. • Two Monobloc batteries equipped with catalysts. • One catalyst per cell (6 per battery). • Microcat™ catalysts used for test. • Too large for Monobloc batteries. • Float charged at 2.27 VPC.

24. Proof of Concept Testing • Batteries run at 3 different temperatures: • 14 days @ 30°C • 14 days @ 40°C • 328 days @ 50°C • Average test temperature = 48.8°C • Parameters measured: current, capacity & conductance.

25. Float Current vs. Temperature Float current reduced by half at all temperatures.

26. Capacity at Day 356

27. Estimated Time to Failure 40% Increase in life from Catalyst Batteries

28. Tear Down Results • Observations from non-catalyst batteries: • Dry out • Positive grid corrosion & growth • Internal shorting • Battery jar cracks • Observations from catalyst batteries: • Sufficiently wet • Minimal positive grid corrosion & growth

29. Conclusions • Design life = Positive plate life at 25°C. • Significant reduction in design life at higher temperature. • 10 year design at 45°C (113°F) = 2.5 years • Only you know actual life. • Preliminary proof-of-concept catalyst test showed promising result.