Sulfur-aluminum supercharges a new battery.
The new battery uses sulfur and aluminum to store charge, more than doubling the discharge time of a typical D-cell flashlight battery, says Stuart Licht, a chemist at Clark University in Worcester, Mass. Compared to other consumer batteries, such as those used in cars or radios, the experimental sulfur-aluminum aqueous cell holds more energy per pound, discharges longer, weighs less, and uses fewer noxious chemicals, Licht told a meeting of the American Chemical Society in Chicago last week. Licht and Dharmasena Peramunage, now at EIC Laboratories in Norwood, Mass., also report on the new battery in the Aug. 20 SCIENCE.
"This battery stores 220 watt-hours per kilogram and discharges up to 17 hours," says Licht. "In comparison, a good quality alkaline battery -- a D-cell for a flashlight -- stores 95 watt-hours per kilogram and discharges for about 6.5 hours. So far, we've only accessed 25 percent of our battery's theoretical capacity, which is over 900 watt-hours per kilogram. But we're confident we can get much more" than 25 percent.
The new battery uses a solid sulfur cathode to supply positive charge and an aluminum anode for negative charge. But there's a trick involved: To get solid sulfur (an insulator at room temperature) to conduct electricity, Licht and Peramunage bathed it in an aqueous polysulfide solution saturated with sulfur. To help the aluminum anode, they used a strong alkaline solution. The result: large stored charges and strong current flow.
"Sulfur and aluminum are wonderful chemicals for batteries," Licht says. "Aluminum is the most abundant metal in the Earth's crust, and we have piles of sulfur extracted from fossil fuels. They're both plentiful, cheap, lightweight, environmentally safe, and easy to work with."
Other types of batteries--such as lead-acid, nickel-cadmium, lithium, and sodium-sulfur systems--all have drawbacks, Licht contends. "Lead-acid and nickel-cadmium pose environmental problems, and they're heavy, so a car can't go far between recharges. Both sodium and lithium batteries explode if water touches them. And sodium-sulfur batteries operate above 600 [degrees] F, with safety and cost constraints." In contrast, he adds, the sulfur-aluminum cell runs at room temperature, storing seven times as much charge per pound as a lead-acid battery.
To be useful for electric vehicles, says Licht, a battery must win on two fronts: energy and power. The energy storage capacity measures how much charge it holds--the automotive equivalent of the size of the gas tank. Power measures how well the battery delivers "juice" to the engine for quick starts and fast acceleration. Licht says that, in theory, his battery does well in both areas, "with enough energy per pound to move a car several hundred miles before recharging--much farther than the 80 miles now possible with other batteries."
This galvanic tale is still unfolding. "We're only in the beginning stages, building tiny experimental cells," Licht says. "There's a long way to go before our battery reaches the marketplace."
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|Title Annotation:||new battery stores more energy and discharges longer|
|Article Type:||Brief Article|
|Date:||Sep 4, 1993|
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