Nanotech promises lithium ion battery boost

Carbon nanotubes can prevent batteries losing charge capacity

Robert Jaques, vnunet.com 14 Apr 2008

Scientists have unveiled details of how nanotechnology could improve the life of lithium ion batteries.

Research to be published in the International Journal of Nanomanufacturing demonstrates that carbon nanotubes can prevent such batteries from losing their charge capacity.

Researchers at the Shenyang National Laboratory for Materials Science in China aimed to eliminate the degradation suffered by traditional lithium ion batteries when they get too hot or too cold.

The scientists noted that the slow degradation of lithium ion batteries is usually due to the formation of a solid electrolyte interphase film that increase the batteries' internal resistance and prevents a full recharge.

Researchers have suggested using silicon in the composition of the negative electrode material to improve charge capacity.

However, this material leads to even faster capacity loss as it repeatedly alloys and then de-alloys during charge/discharge cycles.

Hui-Ming Cheng and his Shenyang colleagues have turned to carbon nanotubes to help them use silicon as the battery anode but avoid the problem of large volume change during alloying and de-alloying.

The researchers grew carbon nanotubes on the surface of tiny particles of silicon using a technique known as chemical vapour deposition in which a carbon-containing vapour decomposes and then condenses on the surface of the silicon particles forming the nanoscopic tubes.

They then coated these particles with carbon released from sugar at a high temperature in a vacuum. A separate batch of silicon particles produced using sugar but without the carbon nanotubes was also prepared.

They found that after 20 cycles of the semi-cell experiments, the sugar-coated silicon/carbon nanotubes composite material achieved a discharge capacity of 727 milliamp hours per gram.

In contrast the charge capacity of the simple sugar-coated particles had dropped to just 363 milliamp hours per gram.

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