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. "These aromatic systems are electron-rich molecules that easily coordinate with lithium," explained Professor 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. "In the literature there are one or two other natural organic molecules in development for batteries, but the process to make them is much more tedious and complicated," noted Professor John.
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. "The chemistry is quite simple," coauthor and City College postdoctoral researcher Dr. Nagarajan explained.
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. "We can say it is definitely going to happen, and sometime soon, because in this case we are fully aware of the mechanism," said Professor John.
|Contact: Jessa Netting |
City College of New York