© Copyright 2010 by Philadelphia Scientific LLC Lead Purity: The Mother of all VRLA Problems Harold Vanasse Dan Jones Will Jones

© Copyright 2010 by Philadelphia Scientific LLC Presentation Outline Lead purity makes a difference Lead purity and battery life Measuring lead purity Solutions for managing lead purity Conclusion

© Copyright 2010 by Philadelphia Scientific LLC Why Lead Purity is Important In the early 1980’s a European battery company made the 1 st VRLA starter battery for cars. Imagine – no more watering of car batteries! –This was a wildly anticipated product. The first European built prototypes worked great. –Tests were conducted in the hot southern USA. USA factory was built to produce these batteries. –The same European specification and tooling was used.

© Copyright 2010 by Philadelphia Scientific LLC What Happened? Catastrophe! Many batteries were produced and they failed all over the country. The financial losses were in the millions! The factory was closed. The resulting investigation could not determine the cause of the failure.

© Copyright 2010 by Philadelphia Scientific LLC The Rest of the Story 20 years later the cause was determined. It all had to do with the purity of the lead. The prototype batteries used lead from Europe. The production batteries used lead from US. Both Euro and US lead was in spec. –But not in the same place within the spec. But how could this happen when spectrometry was used to measure the lead purity? –Maybe they are not the right tool to use?

© Copyright 2010 by Philadelphia Scientific LLC Lead Purity and Battery Life

© Copyright 2010 by Philadelphia Scientific LLC Time for Some Science There is a direct and scientific link between battery life and lead purity. There is a delicate voltage balance within a VRLA cell. –Voltage is shared between positive and negative plates. Too many impurities in negative active material throw off the balance leading to: –Excessive gassing –Increased current draw –Short life

© Copyright 2010 by Philadelphia Scientific LLC Voltage Evenly Split This is the ideal – it is what we want! Reactions are in balance. Unfortunately it is not what is typical for VRLA. Negative Plate Voltage Positive Plate Voltage

© Copyright 2010 by Philadelphia Scientific LLC Voltage All on Positive Plate Typical VRLA problem Negative plate discharges while on float charge. Leads to: –Increased gassing –Capacity loss –Increased float current & cell temperature –Cell dryout –Corrosion of positive plate –Early failure. Negative Plate Voltage Positive Plate Voltage

© Copyright 2010 by Philadelphia Scientific LLC VRLA on Float Charge Oxygen is produced on positive plate and recombined with hydrogen on negative plate. –This pulls down voltage of negative plate Impurities cause greater gassing on negative plate. –Lead + Acid + Impurities = Hydrogen Gas If the rate of gassing is too high the see saw shifts off balance leading to cell failure. –Negative plate self discharges.

© Copyright 2010 by Philadelphia Scientific LLC Key Points to Remember There are multiple reactions to keep in balance within VRLA cells. Impurities in the lead drive the self discharge of the negative active material. If there was a way to prevent the gas from depolarizing the negative plate then lead purity would not matter so much.

© Copyright 2010 by Philadelphia Scientific LLC Measuring Lead Purity

© Copyright 2010 by Philadelphia Scientific LLC Mass Spectrometry Used to measure purity A computerized detector counts where ions are in the e/m spectrum. –Location on the spectrum identifies the element. –Count of ions determines purity.

© Copyright 2010 by Philadelphia Scientific LLC Mass Spectrometry Spectrometry is used to measure the amount of individual impurities. Each individual impurity has a specification that limits maximum amount allowed. Sum total of impurities or net effect is not addressed. Not all impurities are created equal!

© Copyright 2010 by Philadelphia Scientific LLC Culpin’s Clever Contraption Measures self discharge based on gassing rate. –More impurities = more gas Charge a single negative plate. Put it under acid in a graduated beaker. Collect evolved gas.

© Copyright 2010 by Philadelphia Scientific LLC What is Good About It? It is better than mass spectrometry because it measures the combined effect all of the impurities. It is the net effect of all the impurities that we are ultimately concerned about. We ran this test for VRLA cells from multiple manufactures.

© Copyright 2010 by Philadelphia Scientific LLC What we found

© Copyright 2010 by Philadelphia Scientific LLC Lessons from the Test Worst battery produced 10 times more gas than best battery. All batteries claimed to use “pure” lead. There is large variability in the purity of the lead used. Disparities in test are what we see in real world performance of VRLA cells.

© Copyright 2010 by Philadelphia Scientific LLC The Bottom Line Controlling total amount of impurities is the key to VRLA performance. A mass spectrometer may not give the full picture for measuring VRLA lead purity. Lead purity is not being managed adequately for VRLA batteries.

© Copyright 2010 by Philadelphia Scientific LLC Solutions for Managing Lead Purity

© Copyright 2010 by Philadelphia Scientific LLC What Can Be Done? Three options exist: –Use very pure primary lead. –Use super refined secondary lead. –Use a catalyst None of these solutions are new.

© Copyright 2010 by Philadelphia Scientific LLC History Mid 1990’s: VRLA problems abound. Will Jones and Dr. Dave Feder repeatedly show that VRLA batteries won’t deliver design life. Various solutions presented to correct the problems. Root cause always the same: Lead purity not exact enough for VRLA.

© Copyright 2010 by Philadelphia Scientific LLC Use Very Pure Primary Lead Primary lead comes directly from mines. Worldwide demand is increasing. It is getting harder to obtain. It is becoming more expensive. –The greater the purity the greater the price. May not be sustainable.

© Copyright 2010 by Philadelphia Scientific LLC Use Super Refined Secondary Lead Secondary lead has been used before and then recycled. Refining to a higher purity standard is a must for VRLA. The very things that we need to add to other battery types are poisons to VRLA. –E.g. Silver from automotive batteries.

© Copyright 2010 by Philadelphia Scientific LLC Use Super Refined Secondary Lead Impurities from lead recycling stream are expensive to remove. –The greater the purity the greater the price. More exact purity standards and testing are needed to ensure a practical purity level is constantly maintained. Concern: How do you know which battery is made with good lead and which manufacturer cuts cost and quality?

© Copyright 2010 by Philadelphia Scientific LLC Use a Catalyst A catalyst will recombine hydrogen & oxygen to make water in the cell. It prevents gas from depolarizing the negative plate so that it does not self discharge. Cell stays in balance –See saw is in the good middle position. Compensates for fluctuations and variations in lead purity. May be the most cost effective.

© Copyright 2010 by Philadelphia Scientific LLC Will’s Experiments Early experimentation showed that VRLA cells gassed too much. Oxygen and Hydrogen leaving cell had to be reduced to obtain long life. A catalyst reduced gassing to good levels. Proof that this problem could be solved.

© Copyright 2010 by Philadelphia Scientific LLC Conclusion

© Copyright 2010 by Philadelphia Scientific LLC The Mother of all Problems Managing lead purity is the main problem with VRLA cells today. Most of the other problems have already been solved. Until this problem is solved VRLA cells will not live up to their design life. The sad part is that the information is not new. It is all about lead purity!

© Copyright 2010 by Philadelphia Scientific LLC Which is the best solution? The solutions are: –Primary lead –Super refined secondary lead –Catalyst All three solutions will increase cost of the battery but the longer life will justify it. Battery buyers/users must specify what they want! –Battery companies build what users specify.