Wood Nanobattery Could Be Ideal To Store Huge Amount Of Energy

sodium-ion battery contains wood fibers

If you are talking about your smartphone then Li-ion batteries may be ok but when it comes to large-scale energy storage, the priorities suddenly shift from compactness and cycling performance (at which Li-ion batteries excel) to low cost and environmental feasibility (in which Li-ion batteries still have much room for improvement). A new "wood battery", a sliver of wood coated with tin could make a tiny, long-lasting, efficient and environmentally friendly battery for large-scale energy storage.

Teng Li and Liangbing Hu of the University of Maryland have described how wood might be used to make one class of batteries cheaper by permitting the lithium now employed in them to be replaced with sodium. The components in the battery tested by scientists at the University of Maryland are a thousand times thinner than a piece of paper.

Scientists are speculating that sodium-ion batteries could suit large-scale energy storage for rechargeable batteries much better than Li-ion batteries because sodium is cheap and plentiful and because sodium is environmentally benign. But for Na-ion batteries to become a viable energy-storage option there are still many obstacles to overcome.

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 that can literally pulverize the anode after only 20 cycles, rendering the battery extremely short-lived. Liangbing Hu, Teng Li and their team found that wood fibers are supple enough to let their sodium-ion battery last more than 400 charging cycles, which puts it among the longest lasting nanobatteries.

The wood fibers are first coated with single-walled carbon nanotubes to make them electrically conductive, and then with tin (Sn) so they behave as the battery's anode 

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 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 Univ. of Maryland nanobattery is based on cellulose.

The wooden battery was not perfect. Its initial capacity was 339 milliamp hours per gram (mAH/g), but that fell to 145 mAH/g over the course of the 400 cycles. This, however, was not bad for a prototype, and far better than the copper-framed batteries managed. They had an initial capacity of 50 mAH/g. That fell to 22 mAH/g after just 100 cycles. Wood, then, seems a plausible candidate for battery frames.

"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."

Wood fibers are hollow, elongated cells that transport water and minerals

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Write by: RC - Sunday, July 7, 2013