ECO SPECIAL...Old red dye powers new green battery

Old red dye powers new green battery

Cathodes used in phone batteries are made of cobalt, which is expensive and toxic. But an ancient low-cost dye could replace them to make cheap green versions

Rose madder - a natural plant dye once prized throughout the Old World to make fiery red textiles - has found a second life as the basis for a new “green” battery. Chemists from The City College of New York teamed with researchers from Rice University and the US Army Research Lab to develop a non-toxic and sustainable lithium-ion battery powered by purpurin, a dye extracted from the roots of the madder plant (Rubia species). More than 3,500 years ago, civilizations in Asia and the Middle East first boiled madder roots to colour fabrics in vivid oranges, reds and pinks. In its latest incarnation, the climbing herb could lay the foundation for an ecofriendly alternative to traditional lithium-ion (Li-ion) batteries. These batteries charge everything from your mobile phone to electric vehicles, but carry with them risks to the environment during production, recycling and disposal. “Purpurin,” on the other hand, said team member George John, “comes from nature and it will go back to nature.” The team reports their results in the journal Nature’s online and open access publication, Scien-tific Reports. Most Li-ion batteries today rely on finite supplies of mined metal ores, such as cobalt. “Thirty per cent of globally produced cobalt is fed into battery technology,” noted Leela Reddy, lead author and a scientist at Rice University. The cobalt salt and lithium are combined at high temperatures to make a battery’s cathode, the electrode through which the electric current flows. Mining cobalt metal and transforming it, however, is expensive, Reddy explained. Fabricating and recycling standard Li-ion batteries demands high temperatures, guzzling energy, especially during recycling. “In 2010, almost 10 billion lithium-ion batteries had to be recycled,” he said . Fortunately, biologically based color molecules, like purpurin and its relatives, seem preadapted to act as a battery’s electrode. In the case of purpurin, the molecule’s six-membered (aromatic) rings are festooned with carbonyl and hydroxyl groups adept at passing electrons back and forth, just as traditional electrodes do. “These aromatic systems are electron-rich molecules that easily coordinate with lithium,” explained John. Moreover, growing madder or other biomass crops to make batteries would soak up carbon dioxide and eliminate the disposal problem - without its toxic components, a lithium-ion battery could be thrown away. Best of all, purpurin also turns out to be a no-fuss ingredient. Made and stored at room temperature, the purpurin electrode is made in just a few easy steps: dissolve the purpurin in an alcohol solvent and add lithium salt. When the salt’s lithium ion binds with purpurin the solution turns from reddish yellow to pink. Remove the solvent and it’s ready. “The chemistry is quite simple,” coauthor Subbiah Nagarajan explained. The team estimates that a commercial green Li-ion battery may be only a few years away.

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