Ann Arbor Times

A recent study conducted at the University of Michigan has unveiled a promising new source of hard carbon derived from burned rice hulls, which could significantly enhance the energy density of lithium-ion and sodium-ion batteries. This discovery challenges previous assumptions that hard carbon could only be produced by heating biomass to high temperatures in an oxygen-free environment.

Richard Laine, a professor at the University of Michigan and corresponding author of the study published in Advanced Sustainable Systems, explained that burning rice hulls offers a carbon-neutral electricity source. "The CO2 released while burning rice hulls comes from the same CO2 the rice plant took up from the atmosphere during photosynthesis, making the electricity produced green and carbon neutral," he said.

Rice hull ash, primarily composed of silica and carbon, has traditionally been discarded in landfills. However, it can now serve as a sustainable alternative to imported graphite for battery electrodes. The combustion process creates tiny islands of graphite within an amorphous carbon matrix, forming what is known as hard carbon. This material demonstrates superior performance compared to commercial hard carbon and graphite when used as an anode in lithium-ion batteries.

Laine described how this process works: “Hard carbon can be produced by combustion in this case because as you burn away the carbon of rice hulls, you create a shell of silica around the remaining carbon and it bakes it like a pie.”

The research highlights that rice hull ash hard carbon can store over 700 milliampere-hours (mAh) per gram—nearly double that of traditional graphite—and shows potential for widespread application in electric vehicles and renewable energy storage systems.

With annual U.S. rice production reaching approximately 20 billion pounds, there is ample opportunity to scale up this technology. The team has applied for patent protection with support from U-M Innovation Partnerships and seeks partners for commercialization.

This study involved collaboration with Karlsruhe Institute of Technology in Germany and utilized resources from Wadham Energy LP for obtaining rice hull ash. It was partly conducted at the Michigan Center for Materials Characterization with funding provided by the National Science Foundation and Mercedes-Benz Research & Development North America.