A sliver of wood coated with tin could make a tiny,
long-lasting, efficient and environmentally friendly battery. But don’t try it
at home yet – the components in the battery tested by scientists at the
University of Maryland 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. Sodium doesn’t store
energy as efficiently as lithium, so you won’t see this battery in your cell
phone - instead, its low cost and common materials would make it ideal 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
Idea from trees
"The inspiration behind the idea comes from the
trees," said Hu, an assistant professor of materials science. "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."
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, an 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
The team’s research was supported by the University of
Maryland and the US National Science Foundation.