Wooden batteries developed for grid storage

Wood fibers help nano-scale batteries keep their structure

Researchers in the US have made tiny batteries out of wood that are environmentally benign that they say could be used to store energy from power plants. 

A team at the University of Maryland coated slivers of wood with tin to produce a sodium-ion “nanobattery” a thousand times thinner than a piece of paper. Despite sodium not being as efficient as lithium at storing energy, the battery proved long lasting and the researchers believe its low cost and common materials could see its widespread use in the future for grid power storage.

Liangbing Hu, an assistant professor of materials science at the University of Maryland, said: "The inspiration behind the idea comes from the trees. 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."

Existing batteries are often created on stiff bases, which are too brittle to withstand the swelling and shrinking that happens as electrons are stored in and used up from the battery. The research team found that wood fibers are supple enough to let their sodium-ion battery last more than 400 charging cycles, which is longer than some lithium-ion batteries and puts it among the longest lasting nanobatteries.

After charging and discharging the battery hundreds of times, the wood ended up wrinkled but intact. Computer models showed that that 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 tin anodes often weaken the tin’s connection to its base material,” said Teng Li, an associate professor of mechanical engineering. "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."