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.
Most Li-ion batteries today rely on finite supplies of mined metal ores, such as cobalt. “Thirty percent of globally produced cobalt is fed into battery technology,” noted Dr. Leela Reddy. 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, Dr. Reddy explained. Fabricating and recycling standard Li-ion batteries demands high temperatures, guzzling costly energy, especially during recycling. Production and recycling also pumps an estimated 72 kilograms of carbon dioxide – a greenhouse gas – into the atmosphere for every kilowatt-hour of energy in a Li-ion battery, he noted. These grim facts have fed a surging demand to develop green batteries, said Dr. Reddy.
Fortunately, biologically based color molecules, like purpurin and its relatives, seem pre-adapted 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.
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 team estimates that a commercial green Li-ion battery may be only a few years away, counting the time needed to ramp up purpurin’s efficiency or hunt down and synthesize similar molecules.
This story is reprinted from material from The City College of New York, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.