A battery made out of wood?

A sliver of wood coated with tin could make a tiny, long-lasting, efficient and environmentally friendly battery, according to researchers at The University of Maryland.

But don’t try it at home yet - the components in the battery tested by The University of Maryland scientists are a thousand times thinner than a piece of paper. Using sodium instead of lithium, as many rechargeable batteries do, makes the battery environmentally benign. As sodium doesn’t store energy as efficiently as lithium, it is not suitable for use in mobile phones but it could be used to store huge amounts of energy at once, such as solar energy at a power plant.

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. Liangbing Hu, Teng Li and their team found that wood fibres are supple enough to let their sodium-ion battery last more than 400 charging cycles, which puts it among the longest lasting nanobatteries. “The inspiration behind the idea comes from the trees,” said Hu, Assistant Professor, Department of Materials Science and Engineering, The University of Maryland.

“Wood fibres 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.” Lead author Hongli Zhu and other team members noticed that 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 Li, Associate Professor of mechanical engineering. “But the wood fibres 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 team’s research was supported by The University of Maryland and the US National Science Foundation. The full paper is available here.