Dying to make greener batteries

Plant molecule a replacement for cobalt

A common and ancient plant dye could replace cobalt and help deliver greener lithium-ion batteries, according to a study out of America.

Purpurin, an extract of the common Madder plant, turns out to have the right characteristics to use as a cathode, according to research led by The City College of New York (along with Rice University and the US Army Research Laboratory).

In a paper in Nature (abstract here), the researchers observe “reversible lithium ion storage properties of a naturally occurring and abundant organic compound purpurin, which is non-toxic and derived from the plant madder.”

More simply, purpurin’s molecule has aromatic rings with carbonyl and hydroxyl groups that can perform the cathode’s task of passing electrons around – meaning that it can serve in the place of cobalt in the lithium battery.

According to Phys.org, it’s easy to process as well: the purpurin is dissolved in alcohol, and lithium salts are added, allowing the lithium ions to bind with the purpurin - at room temperature.

The researchers say getting rid of cobalt would have a bunch of green benefits: it would remove a toxin from the batteries, and remove the high-temperature processing required to combine cobalt ions with lithium to make the batteries.

Li-ion batteries are also energy-hungry to recycle, according to Rice University’s Dr Leela Reddy, with the result that the fabrication and recycling of batteries costs 72 kilos of CO₂ per kilowatt-hour of battery energy.

The study suggests purpurin could either be extracted from farmed madden, or the molecule synthesized. ®