A Bat­tery Made of Wood?

COL­LEGE PARK, Md. — A sliv­er of wood coated with tin could make a tiny, long-last­ing, effi­cient and envir­on­ment­ally friendly bat­tery. But don’t try it at home yet – the com­pon­ents in the bat­tery tested by sci­ent­ists at the Uni­ver­sity of Mary­land are a thou­sand times thin­ner than a piece of paper. Using sodi­um instead of lith­i­um, as many rechargeable bat­ter­ies do, makes the bat­tery envir­on­ment­ally benign. Sodi­um doesn’t store energy as effi­ciently as lith­i­um, so you won’t see this bat­tery in your cell phone — instead, its low cost and com­mon mater­i­als would make it ideal to store huge amounts of energy at once, such as sol­ar energy at a power plant. 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. 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 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.” 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 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 team’s research was sup­por­ted by the Uni­ver­sity of Mary­land and the U.S. Nation­al Sci­ence Found­a­tion. The full paper is avail­able here. Source: Uni­ver­sity of Maryland