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Red dye plant could lead to green battery

Red dye plant could lead to green battery
Purpurin is found in the roots of the madder plant.

An organic coloring from a plant used to create dye for textiles can be turned into a highly effective, natural cathode for lithium-ion batteries.

Scientists at Rice University and the City College of New York have found that the madder plant or Rubia tinctorum can produce purpurin, an organic molecule that can electrochemically interact with lithium and bind lithium ions.

Purpurin is found in the roots of the madder plant, the same roots which have been boiled to color fabrics in civilizations in Asia and the Middle East going back more than 3,500 years ago. From these “ancient roots” the Rice and City College team believe they could find the root of a more eco-friendly lithium-ion battery.

Rechargeable lithium-ion batteries are considered a key piece of energy storage technology for many devices and gadgets of the future – including electric vehicles. However, they are made from rare materials which are often costly and are troublesome to dispose of.

“They’re not environmentally friendly,” said Arava Leela Mohana Reddy, a research scientist at Rice. “They use cathodes of lithium cobalt oxide, which are very expensive. You have to mine the cobalt metal and manufacture the cathodes in a high-temperature environment.”

Proper disposal and recycling is also a big issue as extracting cobalt from the batteries is also an expensive process. It’s estimated that in 2010, almost 10 billion lithium-ion batteries had to be recycled.

Both producing and recycling cobalt based cathodes are energy intensive processes, pumping an estimated 72 kilograms of carbon dioxide into the atmosphere for every kilowatt-hour of energy in the battery.

On the other hand, purpurin is a naturally occurring substance that is easy to extract and produce. Growing madder to make batteries would also have the additional benefit of soaking up carbon dioxide, preventing it from accumulating in the atmosphere.

The team’s battery used a cathode composed mainly of purpurin extracted from the red madder with the addition of 20 percent carbon to add conductivity. The cathode is easy to produce; purpurin is dissolved in alcohol solvent and lithium salt. Much like madder roots color fabric, the cathodes color determines whether it’s ready for use – when lithium ion binds with purpurin, the solution turns from reddish yellow to pink.

Currently the team was able to build a half-battery cell with a capacity of 90 milliamp hours per gram after 50 charge/discharge cycles. They estimate that a commercial battery using purpurin may only be a few years away, counting the time needed to ramp up its efficiency or hunt down and synthesize similar organic molecules.

The team is also looking for organic molecules suitable for use as a high-capacity anode, the other electrode in a lithium-ion battery.

The research was funded by the National Science Foundation and the U.S. Army Research Office. – EcoSeed Staff

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