Rice researchers discovered that the perennial climbing madder plant can be used as a source for purpurin, an organic dye that can be turned into a highly effective, natural cathode for lithium-ion batteries.
"Green batteries are the need of the hour, yet this topic hasn’t really been addressed properly," said Arava Leela Mohana Reddy, lead author of the study. "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."
Current lithium-ion batteries usually integrate lithium cobalt oxide as cathode material.
Reddy said that mining the cobalt and the entire production process is very expensive and not environmentally friendly. "And then, recycling is a big issue,” he said. “In 2010, almost 10 billion lithium-ion batteries had to be recycled, which uses a lot of energy. Extracting cobalt from the batteries is an expensive process."
The newly developed purpurin cathode includes 20 percent of carbon to add conductivity. A prototype device provided a capacity of 90 mAh per gram after 50 charge/discharge cycles. The researchers are now looking into organic molecules for anodes and for an electrolyte that does not break the molecules down. They hope to have a complete organic battery within "a few years".