A new study by researchers from Rice University’s Department of Materials Science and NanoEngineering, Baylor University and the Indian Institute of Science Education and Research Thiruvananthapuram has introduced a solution that could help develop more affordable and sustainable sodium-ion batteries.

The findings were recently published in the journal Advanced Functional Materials.

The team worked with tiny cone- and disc-shaped carbon materials from oil and gas industry byproducts with a pure graphitic structure. The forms allow for more efficient energy storage with larger sodium and potassium ions, which is a challenge for anodes in battery research. Sodium and potassium are more widely available and cheaper than lithium.

“For years, we’ve known that sodium and potassium are attractive alternatives to lithium,” Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Engineering at Rice, said in a news release. “But the challenge has always been finding carbon-based anode materials that can store these larger ions efficiently.”

Lithium-ion batteries traditionally rely on graphite as an anode material. However, traditional graphite structures cannot efficiently store sodium or potassium energy, since the atoms are too big and interactions become too complex to slide in and out of graphite’s layers. The cone and disc structures “offer curvature and spacing that welcome sodium and potassium ions without the need for chemical doping (the process of intentionally adding small amounts of specific atoms or molecules to change its properties) or other artificial modifications,” according to the study.

“This is one of the first clear demonstrations of sodium-ion intercalation in pure graphitic materials with such stability,” Atin Pramanik, first author of the study and a postdoctoral associate in Ajayan’s lab, said in the release. “It challenges the belief that pure graphite can’t work with sodium.”

In lab tests, the carbon cones and discs stored about 230 milliamp-hours of charge per gram (mAh/g) by using sodium ions. They still held 151 mAh/g even after 2,000 fast charging cycles. They also worked with potassium-ion batteries.

“We believe this discovery opens up a new design space for battery anodes,” Ajayan added in the release. “Instead of changing the chemistry, we’re changing the shape, and that’s proving to be just as interesting.”