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Penn State researchers developing methods to prolong operating life of valve regulated lead-acid batteries; electric locomotive as example

6 January 2013

A team of Penn State researchers is developing more cost-effective ways to prolong the life of valve regulated lead-acid (VRLA) batteries, such as those applied in Norfolk Southern Railway No. 999—the first all-electric, battery-powered locomotive in the United States. (Earlier post.)

A leading cause of damage and death in lead-acid batteries is sulfation, a degradation of the battery caused by frequent charging and discharging that creates an accumulation of lead sulfate. In a recent study, the researchers looked for ways to improve regular battery management practices. The methods had to be nondestructive, simple and cheap—using as few sensors, electronics and supporting hardware as possible while still remaining effective at identifying and decreasing sulfation.

Christopher Rahn, professor of mechanical engineering, along with mechanical engineering research assistants Ying Shi and Christopher Ferone, cycled a lead-acid battery for three months in the same way it would be used in a locomotive. They used electroimpedance spectroscopy and full charge/discharge to identify the main aging mechanisms. Through this, the researchers identified sulfation in one of the six battery cells.

They then designed a charging algorithm that could charge the battery and reduce sulfation, but was also able to stop charging before other forms of degradation occurred. The algorithm successfully revived the dead cell and increased the overall capacity. The researchers, who report their results in the current issue of the Journal of Power Sources, then compared the battery to a new battery. They found that they increased the cell capacity by 41% and the overall battery capacity by 30%.

The operating environment, manufacturing variability, and use can cause different degradation mechanisms to dominate capacity loss inside valve regulated lead-acid (VRLA) batteries. If an aging mechanism for each cell can be identified in real-time, cell usage can be adjusted by the battery management system to optimize the performance and service life of the energy storage system. In this paper, the cell voltage and pressure of new and dead VRLA batteries are monitored during testing to determine the cause of death of the cells. The new cells have fairly uniform performance with limited signs of degradation while the cells in the dead battery have widely ranging performance, especially at the end of discharge and charge. Based on the measurement data, it appears that one cell died from sulfation and another three died of dehydration. The battery capacity is mainly dictated by the sulfated cell. A desulfation charging control scheme with pressure feedback is designed to break up hard sulfate and recover capacity while minimizing water loss by using low current charging.

—Shi et al.

Even better results might have occurred if sulfation were the only aging mechanism at play, but the researchers found other factors reduced capacity, as well, such as water loss.

Other mechanisms that can damage lead-acid batteries include positive electrode corrosion, irreversible hard sulfation, positive electrode softening or shedding, electrolyte stratification, internal short-circuiting and mechanical damage.

The researchers are now developing alternative models to replace the electroimpedance spectroscopy model that would allow charging right up to, but not past, sulfation in batteries where sulfation is not yet present, hoping to prevent it from occurring in the first place.

Penn State and Norfolk Southern, which operates 21,000 route-miles in 22 states, began developing locomotive No. 999 in 2008 to evaluate the application of battery technologies for railroad motive power, with particular interest in energy savings and emissions reduction.

The US Department of Energy funded this most recent study.

Resources

  • Ying Shi, Christopher A. Ferone, Christopher D. Rahn (2013) Identification and remediation of sulfation in lead-acid batteries using cell voltage and pressure sensing, Journal of Power Sources, Volume 221, Pages 177-185, doi: 10.1016/j.jpowsour.2012.08.013

January 6, 2013 in Brief | Permalink | Comments (3) | TrackBack (0)

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Comments

This research could be cost effective, yet one wonders if this charging mod, nanotech(the bankrupt Firefly battery), capacitor-cross, various configurations, etc. hasn't been already been tried on lead-acid.

With all the decades of reported battery breakthroughs, only Tesla seems to have found a way to break the 200 mile EV acceptability range.

Many years ago a pulsing circuit was developed and reported in HOME POWER magazine for the repair of sulphated batteries, and modern computerized versions have been reported in recent years. much of the problem is eliminated if it is possible to replace individual cells. The Atraverda bipolar battery may avoid much of the problem, and they also may be able to use the FIREFLY method of reducing the problem with carbon foams and thin dispersed reactants. It must be remembered that the liquid in a lead-acid battery has about seven times the volume of the actually used lead active materials.

The ZEBRA battery is a very good highly tested choice for motive power in a locomotive. GE is making its version, the durathon, after extensive testing of the ZEBRA in locomotives and buying the research company that invented most of the technolgy. Most of their cells now seem to be going to cell tower power systems.

They can be used in automobiles and have been for range as good per pound as lithium batteries.

Lead batteries are good enough for hybrids, but hydraulic hybrids can be far cheaper and more energy saving as demonstrated by the ARTEMIS vehicles which ought to be renamed Quixote.

Modern electronics are cheap enough so that individual cells can have their own computer controller and monitor.

This is important because Pb/Acids will enable the start stop Hybrid to be inexpensive enough for ever car to get a 20-30% millage boost.

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