Wood and tin could make a miniscule, long-lasting battery, according to researchers at the University of Maryland.
Efficient and environmentally-friendly, the components in the battery created and tested by scientists at the school are 1,000 times thinner than a piece of paper.
One of the problems facing existing batteries is that they are often created on stiff bases too brittle to withstand the swelling and shrinking that occurs as electrons are stored in and used up from the battery.
For this reason, the university's Liangbing Hu, Ten Li and their team of researchers opted for wood fiber when developing their battery. The choice proved to be a good one as their sodium-ion battery turned out to be supple enough to endure more than 400 charging cycles, putting it among the longest lasting nanobatteries out there.
Using sodium instead of lithium, as many rechargeable batteries do, renders the battery environmentally benign; however, sodium doesn't store energy as efficiently as lithium, meaning they are rarely seen in cell phones. Instead, its low cost and common materials mean it's perfect for storing huge amounts of energy at once, such as solar energy at a power plant.
When it came to their muse, the researchers said they said it was simply a matter of observing their surroundings.
"The inspiration behind the idea comes from the trees," Hu, an assistant professor of materials science, said in a press release. "Wood fibers that make up a tree once held mineral-rich water, and so are ideal for storing liquid electrolytes, making them not only the base but an active part of the battery."
After charging and discharging the battery hundreds of times, lead author Hongli Zhu and other team members noticed the wood ended up wrinkled, but still intact. Sure enough, computer models showed the wrinkles effectively relax the stress in the battery during charging and recharging, so that the battery can survive many cycles.
"Pushing sodium ions through the anodes often weaken the tin's connection to its base material," Li, an associate professor mechanical engineering, said. "But the wood fibers are soft enough to serve as a mechanical buffer, and thus can accommodate tin's changes. This is the key to our long-lasting sodium-ion batteries."
The research was funded by the University of Maryland and the National Science Foundation.
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