Washington, April 11 : Researchers at the Shenyang National Laboratory for Materials Science, in China, have shown that nanotechnology can boost the life of rechargeable lithium batteries, by finding that a carbon nanotube anode coating can prevent such batteries from losing their charge capacity over time.
The research team has been examining how to improve the kind of rechargeable batteries that are almost omnipresent in today's portable devices.
These lithium-ion batteries give portability to mobile phones, mp3 players, personal digital assistants (PDAs), and laptop computers. However, Li-ion batteries suffer from degradation particularly when they get too hot or too cold and ultimately lose the capacity to be fully recharged.
The problem of the slow degradation of Li-ion batteries is generally due to the formation of a solid electrolyte interphase film that increases the batteries' internal resistance and prevents a full recharge. Researchers have suggested using silicon in the composition of the negative electrode material in Li-ion batteries to improve charge capacity. owever, this material leads to even faster capacity loss as it repeatedly alloys and then de-alloys during charge-discharge cycles.
Shengyang's Hui-Ming Cheng and colleagues have turned to carbon nanotubes (CNTs) to help them use silicon (Si) as the battery anode but avoid the problem of large volume change during alloying and de-alloying.
Carbon nanotubes resemble rolled-up sheets of hexagonal chicken wire with a carbon atom at the crossover points of the wires and the wires themselves being the bonds between carbon atoms, and they can be up to a millimeter long but mere nanometers in diameter.
Hui-Ming Cheng's team grew carbon nanotubes on the surface of tiny particles of silicon using a technique described as chemical vapour deposition, in which a carbon-containing vapour decomposes and then condenses on the surface of the silicon particles forming nanoscopic tubes.
The group 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 CNTs was also prepared.
In a 20-cycle test-run, the researchers found that the sugar-coated silicon-carbon-nanotube material achieve a discharge capacity of 727 milliamp hours per gram. Without carbon nanotubes, the charge capacity had dropped to 363 mAh per gram.
The study will be published in the Inderscience publication - International Journal of Nanomanufacturing.