Web edition: June 26, 2012
Print edition: July 28, 2012; Vol.182 #2 (p. 12)
A rechargeable battery patented by Thomas Edison more than a century ago is staging a comeback. The nickel-iron battery may yet prove to be a viable power source for electric cars, as the inventor had intended.
Thanks to a redesign, Edison’s battery can now store almost as much energy, gram for gram, as the lithium-ion battery in Nissan’s all-electric car, the Leaf. But the redesigned battery charges faster and promises to be cheaper and safer, researchers report online June 26 in Nature Communications.
“People abandoned this type of battery in the 1970s because there were better batteries at the time,” says Hongjie Dai, a chemist at Stanford University. “We have made the Edison battery interesting again by drastically increasing the ability to charge and discharge it.”
Edison’s original design, patented in 1901, calls for two metal electrodes. A mixture of iron compounds and carbon gives off electricity that flows to a sheet of nickel, discharging the battery. Though hardy, it didn’t usher in the revolution in electric cars that Edison had hoped for. Ultimately it was eclipsed by other technologies, including the lithium-ion battery, that stored and delivered more energy.
To resurrect Edison’s battery, Dai and colleagues reshaped its electrodes at nanometer scales. Instead of simply mixing iron and carbon, the researchers grew iron pellets on top of atom-thick sheets of carbon chicken wire called graphene. Tiny plates of nickel perched atop carbon tubes formed the other electrode.
This attention to detail united each metal and its carbon counterpart with chemical bonds that provided a superhighway for electrons. A small prototype battery charged in about two minutes and discharged within 30 seconds, nearly 1,000 times faster than traditional nickel-iron designs. That speediness could be useful for juicing up a car in a hurry or storing and releasing the energy flowing through the larger power grid.
If scaled up for use in cars, nickel-iron batteries may be cheaper than batteries made from lithium, which is less abundant in Earth’s crust. Also, the fluid electrolyte between iron and nickel electrodes isn’t flammable, so the battery won’t have the safety problems that have caused lithium-ion batteries to explode, says Dai.
Despite its advantages, the Edison reboot still has a ways to go to prove itself. It faces competition from new lithium technologies under development that promise to store more than twice the energy in current lithium-ion batteries. And the researchers still need to show that their laboratory battery can scale up to larger sizes.
“Quoting power and energy density from small lab cells is not realistic,” says M. Stanley Whittingham, a chemist at Binghamton University in New York. “Real cells typically have capacities of only 20 percent of the numbers calculated in the lab.”Building a bigger battery may be the only way that Edison’s 20th-century scheme will come of age in the 21st century.
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