Phone and car batteries could use silicon made from rice

Jul 09, 2013 by Marcia Malory report
In clockwise direction from the top left: rice plant, rice husks, white silica powder extracted from rice husks, yellowish silicon powder converted from the silica powder, an electron microscope image of the interconnected porous structure of the silicon, an example of electric vehicles where silicon anodes are expected to play critical roles in reducing the weight of rechargeable batteries. Credit: Dae Soo Jung.

( —Silicon is in great demand. When used in lithium-ion batteries (LIBs), which power smartphones and electric and hybrid cars, silicon anodes have a much greater theoretical capacity than conventional graphite anodes. However, anodes made from silicon alloys suffer from capacity fading, which makes them inefficient. Jang Wook Choi and his colleagues at several Korean universities have found a way to convert silica from rice husks, a cheap and widely available resource, into silicon for use in high-performance LIBs. This silicon has a naturally occurring nanoporous structure that prevents capacity fading. The research appears in the Proceedings of the National Academy of Sciences.

Rice is a for more than one third of the world's population. Every year, rice growers produce about 422 million metric tons. Rice husks, a waste product produced during cultivation, make up about 20 percent of this. Because these husks are very abrasive, agricultural manufacturers use them in cheap items, such as fertilizer additives, stockbreeding rugs and bed soil, which take advantage of this quality.

Choi and his team believe that rice husks could have a more valuable use. They contain large amounts of , which engineers can convert to silicon for use in LIBs. Silica comprises between 15 and 20 percent of a rice husk's weight. This silica has evolved to be nanoporous, so that air and moisture can enter rice kernels but bacteria and insects cannot.

The researchers extracted pure silicon from rice husk silica by adding acid and heat to remove metallic impurities and and then using magnesium to reduce the silica to silicon. This treatment preserved the three-dimensional porous . They then coated this silicon with carbon and used it in anodes in lithium coin cells.

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.

Explore further: The latest fashion: Graphene edges can be tailor-made

More information: Recycling rice husks for high-capacity lithium battery anodes, PNAS, Published online before print July 8, 2013, doi: 10.1073/pnas.1305025110

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, we 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.

Related Stories

Unzipped nanotubes unlock potential for batteries

Jun 13, 2013

( —Researchers at Rice University have come up with a new way to boost the efficiency of the ubiquitous lithium ion (LI) battery by employing ribbons of graphene that start as carbon nanotubes.

Researchers boost silicon-based batteries

Nov 01, 2012

(—Researchers at Rice University have refined silicon-based lithium-ion technology by literally crushing their previous work to make a high-capacity, long-lived and low-cost anode material with ...

Toughened silicon sponges may make tenacious batteries

Jul 16, 2012

( -- Researchers at Rice University and Lockheed Martin reported this month that they've found a way to make multiple high-performance anodes from a single silicon wafer. The process uses simple silicon ...

Recommended for you

The latest fashion: Graphene edges can be tailor-made

Jan 23, 2015

Theoretical physicists at Rice University are living on the edge as they study the astounding properties of graphene. In a new study, they figure out how researchers can fracture graphene nanoribbons to get ...

Nanotechnology changes behavior of materials

Jan 23, 2015

One of the reasons solar cells are not used more widely is cost—the materials used to make them most efficient are expensive. Engineers are exploring ways to print solar cells from inks, but the devices ...

Gold 'nano-drills'

Jan 22, 2015

Spherical gold particles are able to 'drill' a nano-diameter tunnel in ceramic material when heated. This is an easy and attractive way to equip chips with nanopores for DNA analysis, for example. Nanotechnologists ...

The importance of building small things

Jan 22, 2015

Strong materials, such as concrete, are usually heavy, and lightweight materials, such as rubber (for latex gloves) and paper, are usually weak and susceptible to tearing and damage. Julia R. Greer, professor ...

Graphene brings quantum effects to electronic circuits

Jan 22, 2015

Research by scientists attached to the EC's Graphene Flagship has revealed a superfluid phase in ultra-low temperature 2D materials, creating the potential for electronic devices which dissipate very little ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jul 09, 2013
First the battery made with wood ( ), now rice.

Sounds like after a billion of years of evolution, plants have got this "solvent in a reactive solid container" thing down pat. Who'da thunk?
5 / 5 (1) Jul 09, 2013
"...and then using magnesium to reduce the silicon to silica. "

Oooops! Other way around: silica, SiO2 is reduced to silicon, Si.
not rated yet Jul 09, 2013
This should bump rice exports/imports since rice has recently been suffering at the market because of grain products ha!
not rated yet Jul 11, 2013
@hemtite. Thank you. Fixed. Silly error.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.