While the recent news about carbon has been touted as something that can drastically improve the overall performance of the flooded lead acid battery, the facts should be completely understood before buying these types of batteries with any carbon additives, especially if they are sold as a value added feature.
Finding Solutions For Battery Sulfation Issues In Renewable Energy Applications
Fred Wehmeyer | U.S. Battery Manufacturing
Battery manufacturers are always looking for ways to improve battery longevity, especially in renewable energy applications where sulfation can result from operating in a partial state of charge (POSC). Recently, there has been some talk about the use of carbon additives to reduce the effects of sulfation in renewable energy batteries.
It's important to first understand that sulfation is common when batteries are charged with solar cells, wind turbines and other unpredictable power sources. Even though these systems regularly recharge the batteries, they don't always provide a sufficient level of overcharge. The effect of continual undercharge can, over time, cause "hard sulfate" crystals to form on both the positive and negative battery plates. These crystals reduce the capacity of the battery and make it even more difficult to fully charge, resulting in a shortened battery life.
Sulfation related to PSOC applications is a phenomenon that was first observed in electric vehicle and hybrid electric vehicle applications using sealed VRLA (valve regulated lead acid) batteries. When AGM (or GEL) VRLA batteries are used in PSOC applications, the recombination process occurring at the negative plate disproportionately discharges the negatives in relation to the positives and creates an imbalance in their relative states of charge. Normally this imbalance is corrected by providing enough overcharge during normal charge and/or equalization charge to bring them back into balance. In PSOC applications, the batteries are not overcharged or equalized enough to rebalance the state of charge and the negatives become severely sulfated.
The new discussions about carbon additives come from studies conducted by several battery research groups. They found that by using various new types of carbon in the negative plates of VRLA batteries, the sulfation issue could be addressed. These new carbons are often referred to as smart carbon, hyper carbon, ultra carbon, graphene or nano-carbon. These carbons may or may not be composed of carbon nano-tubes that are still too expensive for use in large scale applications.
The significance of this is that negative plate sulfation is a phenomenon that applies specifically to VRLA (AGM & GEL) batteries. Smart carbon technologies intended to address negative plate sulfation in VRLA batteries do nothing to address sulfation of the positive plates in a flooded deep-cycle battery, which is the primary issue when these batteries are undercharged or used in PSOC applications.
Other technologies that have been developed to address sulfation issues in flooded deep-cycle batteries utilize Outside Positive Plate battery design. The OSP™ plate construction is designed to balance the capacity of the positive plates versus the negative plates. This balanced active material ratio allows the positive and negative plates to reach full charge at the same time, thus preventing sulfation of one plate versus the other. Most batteries with conventional OSN (outside negative) plate construction end up with an excess of negative active material. Balancing the active materials with OSP™ addresses the disparate sulfation problem in addition to the other benefits.
While the recent news about carbon has been touted as something that can drastically improve the overall performance of the flooded lead acid battery, the facts should be completely understood before buying these types of batteries with any carbon additives, especially if they are sold as a value added feature.
Fred Wehmeyer
Fred is Senior VP/Engineering at U.S. Battery Manufacturing, and has 35 years of experience, as well as a Bachelor of Science Degree in Electrochemistry.
The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag
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