Carbon has long been used to enhance electrical conductivity in electrodes. To improve the Edison battery's performance, the Stanford team used graphene nanosized sheets of carbon that are only one-atom thick and multi-walled carbon nanotubes, each consisting of about 10 concentric graphene sheets rolled together.
"In conventional electrodes, people randomly mix iron and nickel materials with conductive carbon," Wang explained. "Instead, we grew nanocrystals of iron oxide onto graphene, and nanocrystals of nickel hydroxide onto carbon nanotubes."
This technique produced strong chemical bonding between the metal particles and the carbon nanomaterials, which had a dramatic effect on performance. "Coupling the nickel and iron particles to the carbon substrate allows electrical charges to move quickly between the electrodes and the outside circuit," Dai said. "The result is an ultrafast version of the nickel-iron battery that's capable of charging and discharging in seconds."
The 1-volt prototype battery developed in Dai's lab has just enough power to operate a flashlight. The researchers' goal is to make a bigger battery that could be used for the electrical grid or transportation.
Most electric cars, such as the Nissan Leaf and the Chevy Volt, run on lithium-ion batteries, which can store a lot of energy but typically take hours to charge. "Our battery probably won't be able to power an electric car by itself, because the energy density is not ideal," Wang said. "But it could assist lithium-ion batteries by giving them a real power boost for faster acceleration and regenerative braking."
The enhanced Edison battery might be especially useful in emergency situations, Dai added. "There may be applications for the military, for example, where you ha
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