Enhancing sodium-ion battery storage with novel graphite shapes

As global demand for electric vehicles and renewable energy storage surges, so does the need for affordable and sustainable battery technologies. A new study led by researchers from the Department of Materials Science and NanoEngineering at Rice University, along with collaborators from Baylor University and the Indian Institute of Science Education and Research Thiruvananthapuram, has introduced an innovative solution that could impact electrochemical energy storage technologies. The research was published in the journal Advanced Functional Materials.

Using an oil and gas industry by-product, the team worked with uniquely shaped carbon materials — tiny cones and discs — with a pure graphitic structure. These unusual forms produced via scalable pyrolysis of hydrocarbons could help address a longstanding challenge for anodes in battery research: how to store energy with elements like sodium and potassium, which are far cheaper and more widely available than lithium.

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

Breaking the graphite barrier

Traditional lithium-ion batteries rely on graphite as an anode material. However, the same graphite structure fails when it comes to sodium or potassium. Their atoms are simply too big and interactions too complex to slide in and out of graphite’s tightly packed layers.

But by rethinking the shape of carbon at the microscopic level, the team found a workaround. 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.

“We were surprised to see just how well these pure, curved graphitic structures performed,” said first author Atin Pramanik, a postdoctoral associate in Ajayan’s lab. “Even without heteroatoms, they allowed for reversible intercalation of sodium ions and did so with minimal structural stress.”

Durable, scalable and green

In lab tests, the carbon cones and discs stored about 230 milliamp-hours of charge per gram (mAh/g) using sodium ions, and they still held 151 mAh/g even after 2000 fast-charging cycles. They also worked well with potassium-ion batteries, but the performance wasn’t quite as strong as with sodium.

Atin Pramanik, a postdoctoral associate in Ajayan’s lab, examines the battery prototype. Image credit: Jeff Fitlow/Rice University.

Advanced imaging techniques like cryogenic transmission electron microscopy and solid-state nuclear magnetic resonance confirmed that ions were entering and exiting the carbon structure as expected and that the material held its shape over thousands of charge-discharge cycles.

“This is one of the first clear demonstrations of sodium-ion intercalation in pure graphitic materials with such stability,” Pramanik said. “It challenges the belief that pure graphite can’t work with sodium.”

The implications are wide ranging. Not only does this pave the way for more affordable sodium-ion batteries, but it also reduces reliance on lithium, which is becoming more expensive and geopolitically complicated to source. And because the cone/disc carbon can be synthesised from oil and gas industry by-products, it presents a more sustainable route for battery anode production.

A turning point for battery design

While most research in this area has focused on hard carbons or doped materials, the new study marks a pivot in strategy — emphasising morphology over chemical modification.

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

“We’re not just developing a better battery material,” Pramanik said. “We’re offering a real pathway to energy storage that’s cleaner, cheaper and more widely available to all.”

Top image credit: Rice University.