Rechargeable batteries are still imperfect. Those made from lithium-ion tend to catch fire and blow up and those made from other materials tend to lose their their recharging capabilities quickly.
In a move that will make potato-battery makers jealous, scientists from the University of Maryland and the National Center for Nanoscience and Technology in Beijing made a rechargeable battery from a baked oak leaf. Why jealous? Because potatoes aren't rechargeable.
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To make the oak leaf battery, the scientists first dried the leaf using a special process called pyrolysis, which requires temps of 1,832 degrees Fahrenheit.
Next, they soaked it in hydrogen chloride for six hours to remove impurities. Finally, they pumped it full of sodium.
Theoretically, sodium should be able to hold more charge than lithium. But it has been difficult to find a material that allows sodium ions, which are much bigger than lithium ions, to pass back and forth through pores - a process essentially to recharging.
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The leaf's natural structure makes for an ideal material.
"The natural shape of a leaf already matches a battery's needs: a low surface area, which decreases defects; a lot of small structures packed closely together, which maximizes space; and internal structures of the right size and shape to be used with sodium electrolyte," said Fei Shen, a visiting student working on the project.
The scientists used the leaf as the anode, the part of a rechargeable battery that serves as the negative pole during discharge and the positive pole when charged.
In tests, the leaf held 90 percent of its charge after 200 cycles and its charge efficiency remained around 75 percent. Not too shabby.
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Stacking multiple leaves could provide greater energy storage. At the moment, there are no plans to start selling leaf batteries in stores. This was only an experiment. But it does show that it's possible to make energy storage from natural, environmentally friendly materials.
The team published their findings in January through ACS Applied Materials & Interfaces.