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11/02/2005
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Tom Shelley discovers that slightly unconventional lead acid batteries currently look to be the best bet for hybrid vehicles
Nickel hydride and lithium may offer the best energy densities for secondary batteries, but enhanced lead acid offers the best bet if cost is taken into account.
Dr David Stone, who is a member of the University of Sheffield Electrical Machines and Drives Research Group, explained to Eureka that nickel hydride and even more, lithium, batteries are so expensive that it is cheaper to take weight out of a car by giving it a carbon fibre body than by adopting them for battery use. Added to that, in the light of the requirements of WEEE, lead is a lot easier to recycle than nickel, and very much easier to recycle than lithium.
Conventional lead acid batteries still have considerable room for improvement. Dr Stone has been involved in a project called RHOLAB - Reliable, Highly Optimised Lead Acid Battery, funded as a DTI/ESPRC Foresight Vehicle LINK project.
He told us that conventional lead acid batteries make poor use of their lower regions, so the team has come up with batteries with electrodes both top and bottom. Furthermore, use in hybrid vehicles, which is fairly arduous, requiring operation at about 50% state of charge, is liable to result in large sulphate crystal formation and poor battery life. The team's solution to this problem is to employ packs of 19 cells. 18 are used normally at any moment, but one additional cell is from time to time, cycled up to a full state of charge to break down the large lead sulphate crystals.
Partners are the Advanced Lead-Acid Battery Consortium, ALABC, Provector, the University of Sheffield, Hawker Energy Products and the Warwick Manufacturing Group. A full sized battery is currently on test in a Honda Insight at the Milbrook proving ground.
University of Sheffield Electrical Machines and Drives Research Group
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Author
Tom Shelley
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