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Scientists at Rice University and the City College of New York have discovered that the madder plant, aka Rubia tinctorum, is a good source of purpurin, an organic dye that can be turned into a highly effective, natural cathode for lithium-ion batteries. The plant has been used since ancient times to create dye for fabrics.

The goal, according to lead author Arava Leela Mohana Reddy, a research scientist in the Rice lab of materials scientist Pulickel Ajayan, is to create environmentally friendly batteries that solve many of the problems with lithium-ion batteries in use today.

“Green batteries are the need of the hour, yet this topic hasn’t really been addressed properly,” Reddy said. “This is an area that needs immediate attention and sustained thrust, but you cannot discover sustainable technology overnight. The current focus of the research community is still on conventional batteries, meeting challenges like improving capacity. While those issues are important, so are issues like sustainability and recyclability.”

While lithium-ion batteries have become standard in conventional electronics since their commercial introduction in 1991, the rechargeable units remain costly to manufacture, Reddy said. “They’re not environmentally friendly. 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. There are a lot of costs.

Recent work by the Ajayan Group combines silicon and a porous nickel current collector in a way that has proven effective as a high-capacity anode, the other electrode in a lithium-ion battery. That research was reported recently in the American Chemical Society journal Nano Letters.

But Reddy hopes to formulate completely green batteries. The team is looking for organic molecules suitable for anodes and for an electrolyte that doesn’t break the molecules down. He fully expects to have a working prototype of a complete organic battery within a few years. “What we’ve come up with should lead to much more discussion in the scientific community about green batteries,” he said.

Co-authors of the paper are visiting scholar Porramate Chumyim and former graduate student Sanketh Gowda of Rice; postdoctoral researcher Subbiah Nagarajan, facilities manager Padmanava Pradhan and graduate student Swapnil Jadhav of the City College of New York; and Madan Dubey of the U.S. Army Research Laboratory.