Asian Scientist (Jul. 10, 2013) – Korean researchers have demonstrated that rice husks, a major by-product in rice harvest, can be used to produce nano-porous silicon for use in high-capacity lithium-ion batteries.
The rice husk is the outer covering of a rice kernel that protects it from attack by insects and bacteria. Because it is removed during the harvesting of rice, over 100 million tons of rice husks are produced annually worldwide. Although efforts have been made to recycle rice husks for other uses, these have been limited to low-value agricultural applications.
Now, in a study published in the Proceedings of the National Academy of Sciences, Korean researchers have described how they took advantage of the unique characteristics of rice husks to produce high-capacity anodes for lithium-ion batteries.
The researchers found that rice husks have unique nano-porous silica (silicon dioxide) layers. These layers, found in the outer shell of the husk, likely evolved because of the need to protect the inner ingredients of the rice kernel while allowing air and moisture to pass through.
Because silicon has high electrical capacity, it is thought to be an ideal material for making lithium-ion battery anodes. An anode is an electrode through which electric current flows into a polarized electrical device like a battery. Silicon has a theoretical capacity that is 10 times higher than that of conventional graphite anodes.
In their study, the researchers found a way to convert the silica in the rice husks to silicon while retaining its unique nano-porous structure. They then tested this nano-porous silicon material and found that it exhibits excellent electrochemical performance as a lithium battery anode.
It turns out that that the interconnected nano-porous structure of rice husks is instrumental for this excellent performance as an anode: anodes made of silicon are unstable and are prone to deterioration after repeated charging, but the unique structure of silicon anodes made from rice husks allow them to avoid such problems.
Since rice husks can be recycled to make lithium-ion battery anodes with excellent cycling and power performance, the researchers hope that rice husk ‘waste’ can become a resource that helps meet the ever-increasing demands for silicon in advanced batteries.
The article can be found at: Jung et al. (2013) Recycling Rice Husks For High-Capacity Lithium Battery Anodes.
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Copyright: Asian Scientist Magazine; Photo: Alex Valavanis/Flickr.
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