University of Maryland scientists say they\'ve developed an environmentally friendly battery that uses wood as its backbone. The device uses a sliver of wood coated with tin as its substrate, an advantage over current batteries that often use stiff, non-flexible substrates that are too rigid to release the stress that occurs as ions flow through the battery. Writing in the journal Nano Letters, Liangbing Hu, Teng Li and colleagues said they turned to wood fibers from trees that are supple and naturally designed to hold mineral-rich water, similar to the electrolyte in batteries. They used wood as the base of an experimental sodium-ion battery, choosing sodium over lithium to make the device more environmentally friendly. In lab experiments, they said, the device performed successfully though 400 charge-discharge cycles, putting it among the longest-lasting of all sodium-ion nanobatteries. Batteries of this type would be best suited for large-scale energy storage applications such as wind farms or solar energy installations, the researchers said.