The theoretical capacity of silicon (4200mAh / g), is approximately 11-fold of currently widely used graphite anode (375mAh / g). So it is now considered the most promising lithium-ion battery anode material. However, the internal tension of silicon originated from large volume changes during the cycle very likely to cause internal damage of material structures and mechanical pulverization, and to separate the electrode materials so that the practical application of silicon is hampered.

The rice husk is the outer covering of a rice kernel and 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, Prof. Jang Wook Choi and his colleagues in Korea Institute of Science and Technology convert the silica to silicon and 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.

Source: PNAS, 2013, doi: 10.1073/pnas.1305025110