Rice Husks Could Contribute to High Performance Batteries

Author:Energy Harvesting Journal     Source:Energy Harvesting Journal     Click:427     Publish time:2013/8/2 11:01:04

A team of researchers from several Korean universities have discovered a way of converting silica from rice husks into silicon for use in high performance lithium ion batteries. Their research was published in the Proceedings of the National Academy of Sciences.

The rice husk is the outer covering of a rice kernel which protects the inner ingredients from external attack by insects and bacteria. To perform this function while ventilating air and moisture, rice plants have developed unique nanoporous silica layers in their husks through years of natural evolution. Despite the massive amount of annual production near 108 tons worldwide, so far rice husks have been recycled only for low-value agricultural items. In an effort to recycle rice husks for high-value applications, the team converted the silica to silicon to use it for high-capacity lithium battery anodes. Taking advantage of the interconnected nanoporous structure naturally existing in rice husks, the converted silicon exhibits excellent electrochemical performance as a lithium battery anode, suggesting that rice husks can be a massive resource for use in high-capacity lithium battery negative electrodes.

The researchers, led by Jang Wook Choi, extracted pure silicon from rice husk silica by adding acid and heat to remove metallic impurities and organic components and then using magnesium to reduce the silica to silicon. This treatment preserved the three-dimensional porous nanostructure of the rice husk. They then coated this silicon with carbon and used it in anodes in lithium coin cells. Silica comprises between 15 and 20 percent of a rice husk's weight.

Choi's team found that these anodes were more efficient than anodes made with silicon alloys. The anodes made from rice husk silicon had high coulombic efficiency and excellent discharge capacity retention, which the team attributed to the interconnected porous structure of the silicon enabling the formation of stable solid electrolyte interfaces (SEIs). In comparison, anodes made from silicon alloys suffer from capacity fading because their high volume change, which can reach 300%, causes the alloys to fracture and unstable SEIs to form.

The researchers suggest that silicon extracted from rice husks could help meet the increasing demand for silicon in batteries used to run portable electronic devices and hybrid electric vehicles. This would allow a waste product from one of the world's most popular crops to contribute to the development of advanced technologies.

Keywords:Rice Husks Could Contribute to High Performance Batteries
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