Scientists from the University of Maryland have made a “green” battery using a sliver of wood covered with tin. While this sounds like a perfect do-it-yourself project, it isn’t; the parts in the battery tested by scientists are a thousand times thinner than a piece of paper.
Instead of using lithium, which is found in many rechargeable batteries, the scientists utilized sodium to fulfill their goal of making an environmentally friendly battery. Unlike lithium batteries, sodium doesn’t keep energy as efficiently. Instead, this battery is ideal for keeping massive amounts of energy at once just like solar energy at a power plant.
Most batteries are typically developed on stiff bases, which are too fragile to deal with the swelling and shrinking that takes place as electrons are kept in and used up from the battery. However, the scientists from the University of Maryland discovered that wood fibers are flexible enough to allow their sodium-ion battery to last more than 400 charging cycles. This battery life places it among the longest lasting nanobatteries.
“The inspiration behind the idea comes from the trees,” said Liangbing Hu, an assistant professor of materials science at the University of Maryland. “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.”
The scientists discovered that after charging and discharging the sodium-ion battery hundreds of times, the wood was wrinkled but still intact. They learned from computer models that the wrinkles help ease the stress in the battery during charging and recharging, so that the battery can last for hundreds of charging cycles.
According to Teng Li, an associate professor of mechanical engineering at the University of Maryland, “pushing sodium ions through tin anodes often weaken the tin’s connection to its base material,” but the scientists found that the wood fibers are supple enough to act as a mechanical buffer, which allows them to deal with the tin’s changes.
“The soft and mesoporous wood fiber substrate can be utilized as a new platform for low cost Na-ion batteries,” the authors write in the study’s abstract.
The study is described in greater detail in the journal Nano Letters.