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10-03 :: March 2010

nanotimes

Research

7

interconnected internal pore channels. The spheres, formed in sizes ranging from 10 to 30 microns, are used to form battery anodes. The relatively large composite powder size – a thousand times larger than individual silicon nanoparticles – allows easy powder processing for anode fabrication.

The internal channels in the silicon-carbon spheres serve two purposes. They admit liquid electrolyte to allow rapid entry of lithium ions for quick battery charging, and they provide space to accommodate expansion and contraction of the silicon without cra- cking the anode. The internal channels and nanome- ter-scale particles also provide short lithium diffusion paths into the anode, boosting battery power cha- racteristics.

The size of the silicon particles is controlled by the duration of the chemical vapor deposition process and the pressure applied to the deposition system. The size of the carbon nanostructure branches and the size of the silicon spheres determine the pore size in the composite.

Production of the silicon-carbon composites could be scaled up as a continuous process amenable to ultra high-volume powder manufacturing, Yushin said. Because the final composite spheres are relatively large when they are fabricated into anodes, the self- assembly technique avoids the potential health risks of handling nanoscale powders, he added.

Top: Nanocomposite microscope image, © Gatech Background: Schematic of nanocomposite, © Gatech

“If this technology can offer a lower cost on a ca- pacity basis, or lighter weight compared to current techniques, this will help advance the market for lithium batteries,” he said. “If we are able to produce less expensive batteries that last for a long time, this could also facilitate the adoption of many ‚green‘ technologies, such as electric vehicles or solar cells.”

A. Magasinski, P. Dixon, B. Hertzberg, A. Kvit, J. Ayala & G. Yushin: High-performance lithium-ion anodes using a hierarchical bottom-up approach, In: Nature Materials, Vol. 9(2010), No. 4, April 2010, Pages 353-358, DOI:10.1038/ nmat2725:

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