Rice hull. iStock
Researchers have showcased that burned rice hulls may help towards a sustainable energy future.
It turns out that properly processed rice hull ash can yield a carbon form, which could outperform graphite in battery applications.
This “hard carbon” has a unique nanostructure that allows it to store more energy than graphite — the current standard in lithium-ion batteries.
The porous carbon network left behind after removing silicon from rice hull ash, imaged with scanning transmission electron microscopy (STEM). Credit: Yu et al., 2024.
Hard carbon from burned rice hull
University of Michigan researchers made this discovery by producing hard carbon through the combustion of rice hull ash.
This method is more sustainable and efficient than traditional methods that require high temperatures and oxygen-free environments.
Moreover, it could serve as a domestic alternative to imported graphite, reducing reliance on foreign sources for making battery electrodes.
Rice hull ash is primarily composed of silica (about 90%) and carbon (about 10%).
The research team has developed a method to extract high-purity silica from rice hull ash.
“Once the silica is partially removed from the rice hull ash through a process called depolymerization, the remaining ash is about 60%-70% carbon,” the researchers noted in the press release.
Initially, the carbon residue from rice hull ash was believed to be amorphous, lacking a defined structure.
However, advanced spectroscopic analysis revealed the presence of tiny graphite structures embedded within the amorphous carbon matrix. This unique combination, known as hard carbon, exhibits enhanced properties compared to pure amorphous carbon.
This unique combination of amorphous carbon interspersed with tiny graphite structures is known as hard carbon.
“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,” explained Richard Laine, the corresponding author of this new work.
High storage capability
During testing, the hard carbon derived from rice hull ash demonstrated superior electrochemical performance than commercial hard carbon and graphite. This suggests it could be used as the anode in lithium-ion batteries.
Hard carbon batteries can store significantly more energy than traditional graphite batteries.
As per the press release, a gram of graphite can store around 370 milliampere-hours (mAh) of electrical energy. mAh is a common unit for measuring battery capacity.
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On the other hand, commercial hard carbon can store about 500 mAh per gram.
Remarkably, rice hull ash hard carbon surpasses both commercial hard carbon and graphite. It offers a storage capacity exceeding 700 mAh per gram, which is double that of graphite.
The nanoporous structure enhances the hard carbon’s lithium storage capacity.
Rice hull ash hard carbon could address the rising demand for batteries in electric vehicles and renewable energy storage.
This innovative technology offers a more sustainable and cost-effective solution, reducing both environmental impact and production costs.
The high annual U.S. rice production of 20 billion pounds provides ample opportunity for large-scale adoption of this technology.
The findings were published in the journal Advanced Sustainable Systems.
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Mrigakshi Dixit Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her work has been featured in well-known publications including Nature India, Supercluster, The Weather Channel and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.
