As we look toward a future of more renewable energy being fed into the grid, having reliable energy storage to back up intermittent wind and solar will be necessary for everything to run smoothly. That's why researchers have been working hard to find the best type of battery for this type of large-scale storage. Lithium-ion batteries are great for gadgets and even cars, but on a larger scale they're too expensive and aren't very environmentally friendly.
Many researchers believe sodium-ion batteries are the answer. Sodium is cheap and environmentally benign and sodium-ion batteries would be well-suited for storing large amounts of renewable energy at once. The major obstacle to advancing these batteries has been a very short life due to the swelling of the anode with each charge and discharge of sodium ions, which when using a brittle base, causes the battery to fall apart after only about 20 charge cycles.
Researchers at the University of Maryland have developed a solution to this problem by using a paper-thin layer of wood fibers coated with conductive carbon nanotubes as the base in a sodium-ion nanobattery. The wood is able to withstand the swelling and contracting of the anode and allows the battery to survive more than 400 charge cycles, which makes it one of the longest lasting nanobatteries.
"The inspiration behind the idea comes from the trees," said Liangbing 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."
At the end of the charging cycles, the wood was wrinkled, but still intact. Computer models showed that those wrinkles relaxed the stress in the battery during charging and recharging, creating a flexible and long-lasting battery.
You can watch a video about the wood nanobattery below.