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Safer Batteries for Electric Cars
By ANDREW BRIDGES 09/22/2002 16:39:13 EST
LOS ANGELES (AP) - Scientists have developed a variant of the batteries used in cell phones as a cheaper, safer and more compact alternative to the nickel-metal hydride cells that power electric cars.
The automotive versions of new lithium-ion batteries will be much bigger than those used in cell phones but will share other traits that make the technology popular, said Yet-Ming Chiang, of the Massachusetts Institute of Technology.
The work appeared Sunday in the electronic version of the journal Nature Materials.
Since Sony Corp. introduced lithium-ion batteries in 1991, they have become popular in many consumer electronics, including laptop computers, digital cameras and mobile phones. They're compact, lightweight and can store a lot of energy.
But they're also expensive to make, since they often contain pricey cobalt. Larger lithium-ion batteries can also be more dangerous, because of the risk of overheating.
Together, that has precluded their use in electric and hybrid-electric cars, which rely on heavier and bulkier - but safer - nickel-metal hydride batteries.
Scientists have long searched for cheaper and safer alternatives to the lithium metal oxides commonly used in the cathode, or positive electrode, of lithium-ion batteries. Among them is a material called lithium iron phosphate, which is also nontoxic.
"Iron has long been the holy grail for lithium-ion battery people as a cathode material," said Fritz Kalhammer, a Palo Alto, Calif., battery expert.
Its drawback has been its low conductivity: such batteries store a lot of energy but charge and discharge slowly. That's not a problem for cell phones, but electric cars require batteries that can be drawn down quickly to allow rapid acceleration.
Chiang and his colleagues at MIT report that modifying the composition of the material with metallic elements such as niobium or zirconium dramatically improves its conductivity. It is also safer.
"What we expect this new material to enable is larger lithium-ion batteries of higher performance," Chiang said.
MIT has patented the technology and has licensed it for commercial use, Chiang said. The new batteries could be on the market in a couple of years and could extend the limited range of electric vehicles, he added.
The discovery will not be a watershed event unless the new batteries are proven to be durable and safe in tests, said Daniel Doughty, manager of the lithium battery research and development department at Sandia National Laboratories.
Scientists designing new batteries must weigh multiple variables, including power, cost, weight, safety, durability and ease of manufacture, making it a game of trade-offs, Doughty said.
"There have been a lot of new materials proposed, and unless they solve this balance of properties, which is very hard to get, they are not going to make any impact on the industry, which is why the companies making lithium-ion batteries, in Japan and around the Pacific Rim, are using materials remarkably similar to what Sony used 10 years ago," Doughty said. |
