Hongli Zhu and colleagues looked to Mother Nature in their quest to seek a viable alternative to conventional rechargeable batteries, which are increasingly costly to use on a large scale due to the scarcity of the lithium required to power them. Regular batteries are typically built on a lithium base, although such foundations must be replaced regularly, as the resultant swelling and shrinking that takes place during the charging process. The team hoped to replace lithium with sodium electrolyte, which are a much cheaper and plentiful in supply. However, sodium ions are several times larger than lithium ions, causing greater damage to the battery’s anode during the charging process. The use of a tin anode as the main foundations for the battery was also eliminated as a viable option, as, unlike lithium, a sodium-tin alloy caused the battery to swell, quickly damaging the battery beyond use.
The team’s response is both innovative and resourceful: they discovered that a tin anode could be bypassed completely, and replaced instead by natural wood fibres, which are capable of transporting the larger sodium ions without resulting in the same ‘structural pulverisation’ as the sodium-tin alloy. By covering a 50-nanometre-thick layer of tin onto a 2500-nanometre-thick wood fibres, the researchers were able to eliminate lithium from the equation completely.
Liangbing Hu, assistant professor of material science at the University of Maryland, stated in the press release that “the inspiration behind the idea comes from the trees. 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.” These wood fibres, which are made up of hollow cells which are used to transport water and minerals around the living organism, are advantageous in several ways. They are much more supple than conventional battery anodes, meaning that the degradation process is much slower. Whereas a sodium-tin alloy anode wears out within 20 charging cycles, the flexible and porous wood anode was shown to endure over 400 charging cycles, after which it remained intact, if not somewhat wrinkled.
The wood fibre anodes, are not only much more durable than regular rechargeable batteries, but are also much cheaper to process, not to mention environmentally friendly. The team hopes to use the wood anode in the manufacturing of low-cost batteries, as well as producing the batteries on a much larger scale for use in renewable storage applications: a challenging, but ultimately rewarding for science and for the environment.
Sources include New Scientist, Forbes
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