Rechargeable batteries are a technological marvel that powers our modern world. Without these reuseable power packs, smartphones, tablets, and electric toothbrushes would be fantasy instead of reality. While rechargeable batteries are better for the planet than the single use kind, they’re still made from finite materials that are difficult to extract from the earth, and recycling them is energy-intensive.
Instead of simply inventing another slight variation on the batteries we’re all familiar with, collaborators from the City College of New York, Rice University and the US Army Research Laboratory decided to leave convention behind. They recently published a study that suggests its possible to make a non-toxic and sustainable lithium-ion battery powered by purpurin, a natural 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 color fabrics in vivid oranges, reds and pinks. Now this color-inducing climbing herb is being used as a substitute for mined metal ores like cobalt. 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 and bad for the environment. “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,” noted Dr. Leela Reddy, lead author and a research scientist at Rice University.
According to the researchers, organic color molecules like those found in purpurin are perfectly suited to take over cobalt’s role as a battery’s electrode. 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 City College chemistry Professor George John.
The researchers say that growing madder or other biomass crops to make batteries would soak up carbon dioxide and eliminate the disposal problem – without its toxic components, the madder-based battery would be the world first safely disposable battery.