December 13, 2012 | 2 Comments
Chemists from The City College of New York teamed with researchers from Rice University and the U.S. Army Research Laboratory to develop a non-toxic and environmentally sustainable lithium-ion battery. The idea is to avoid battery manufacturing based on finite supplies of mined metal ores, such as cobalt and replace them with much less costly and non-toxic organic molecules.
The team is using purpurin, a dye extracted from the roots of the madder plant (Rubia species) a natural plant dye once prized throughout the Old World to make fiery red textiles for the molecules making a new “green” battery.
More than 3,500 years ago, civilizations in Asia and the Middle East first boiled madder roots to color fabrics in vivid oranges, reds and pinks. Purpurin has carbonyl/hydroxyl groups present in its molecules to act as redox centers and react electrochemically with Lithium ions during the charge/discharge process.
There is a good chance the research of the climbing herb could lay the foundation for an eco-friendly alternative to traditional lithium-ion batteries.
Team member and corresponding author City College Professor of Chemistry George John explains, “Purpurin comes from nature and it will go back to nature.” The team reported their results in the journal Nature’s online and open access publication, Scientific Reports, on December 11, 2012.
Lead author Dr. Leela Reddy, a research scientist in Professor Pulickel Ajayan’s lab in the Department of Mechanical Engineering and Materials Science at Rice University explains 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.” The cobalt salt and lithium are combined at high temperatures to make a battery’s cathode, the electrode through which the electric current flows.
Reedy takes the explanation deeper. Mining cobalt metal and transforming it, however, is expensive. Fabricating and recycling standard Lithium ion batteries demands high temperatures, guzzling costly energy, especially during recycling. “In 2010, almost 10 billion lithium-ion batteries had to be recycled,” he said. 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 Lithium ion battery. These grim facts have fed a surging demand to develop green batteries.
Professor John explains the organic advantage – 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,” he said.
Best of all, purpurin also turns out to be a no-fuss ingredient. It’s 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 and City College postdoctoral researcher Dr. Subbiah Nagarajan explained.
On the green angle growing madder or other biomass crops to make batteries would soak up carbon dioxide and could eliminate the metallic disposal problem – without its toxic components, a lithium-ion battery could be thrown away with less effect – although that would still be an expensive metal lost to recycling.
The team estimates that a commercial green Lithium 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. “When you can generate something new or unheard of, you think of chemistry in a different way. That a natural material or dye can be used for a battery, that is exciting, even for me,” he added.
For the rest of us as well, too. The paper is open access meaning everyone can read it. What is missing is the long term multiple cycling results, something the paper might well have included if not a rush to publish. A more thorough looks at the economics could have made it to the press release. It’s not really fair to expect that in the paper, but one does look for some hints at least in the non-scientific domain.
It’s good looking work worthy of great interest, more proving up and further development. The path is now found to less nasty, good capacity and hopefully lower cost Lithium ion batteries. It’s giant organic step one, with many more to come.