A new “wood battery” could allow the emerging sodium-ion battery technology to fit the bill as a long-lasting, efficient and environmentally friendly battery for large-scale energy storage. The stiff bases often used in existing batteries are too brittle to withstand the swelling and shrinking caused by sodiation, so the researchers turned to the much softer wood fibers. These have evolved to withstand these forces extremely well as they use capillary forces to transfer the sodium ions from the soil around them to the leaves of their tree. The resulting sodium-ion battery that uses wood fibers increases durability twenty-fold compared with previous designs. The researchers coated a sliver of wood fibers with a thin layer (10 nm) of single-walled carbon nanotubes to make it electrically conductive, and then deposited a tin film over it. The soft wood fibers effectively neutralized the strong mechanical stresses of the sodiation process. Even after charging and discharging the battery hundreds of times, the wood ended up
wrinkled but remarkably intact. In their testing, the researchers measured a stable cycling performance of 400 cycles with an initial capacity of 339 mAh/g, which is a marked improvement over previous designs. Because sodium doesn’t store energy quite as efficiently as lithium, there is little chance of this technology eventually finding its way to your next-generation gadget. However, because of their low cost and use of environmentally benign common materials, sodium-ion batteries could be used to store large amounts of energy from renewable energy sources, such as wind and solar.