Roasted rice husk ash provides a lasting boost to battery performance
Researchers at the University of Michigan have discovered that ash from burned rice husks contains a unique form of carbon capable of nearly doubling the energy density of lithium-ion and sodium-ion batteries. This innovation could provide a sustainable, high-performance alternative to graphite in battery electrodes.
This new ‘hard’ carbon, revealed through advanced spectroscopy techniques, significantly outperforms commercial hard carbon and graphite. It offers a storage capacity of more than 700 milliamp-hours (mAh) per gram, almost double that of graphite. “In this case, combustion can produce hard carbon because when you burn the carbon from rice husks you create a shell of silica around the remaining carbon and bake it like a cake,” explains Richard Laine, a professor at the University of Michigan. out. and corresponding author of the study published in *Advanced Sustainable Systems*.
It was previously thought that hard carbon required heating biomass to extreme temperatures of around 1200 C in an oxygen-free environment. The discovery that combustion can produce hard carbon opens the way to harnessing agricultural waste for battery materials.
Rice husks, which are usually discarded in landfills, are an untapped domestic resource. Approximately 20 billion pounds of rice are grown annually in the US alone, creating significant potential for scaling up the process. Furthermore, burning rice hulls for electricity, such as Wadham Energy in California, generates 200,000 megawatt hours annually while remaining carbon neutral. “The CO2 released when burning rice husks comes from the same CO2 that the rice plant absorbed from the atmosphere during photosynthesis, making the electricity produced green and carbon neutral,” Laine added.
The process involves partially removing silica, which makes up about 90% of rice husk ash, leaving 60% to 70% carbon behind. Although initially thought to be amorphous, the material contains nanoscale graphite islands in an amorphous carbon matrix, giving rise to the superior “hard” carbon structure.
In battery applications, the nanoporous structure of hard carbon from rice hull ash increases lithium storage capacity, providing a crucial advantage for energy-dense batteries. This could help meet the growing demand for batteries in electric vehicles and renewable energy storage, while lowering costs and reducing environmental impact.
The team, with collaborators from the Karlsruhe Institute of Technology in Germany and supported by the National Science Foundation and Mercedes-Benz Research and Development North America, is working to bring this innovation to market. Patent protection has been applied for through UM Innovation Partnerships and the researchers are looking for industrial partners.
