Silicon Whiskers Make Li-ion Batteries Store More Power

Nanowire anodes improve battery design

  Image of silicon nanowires
While the technological advancement in developing better electronic components goes on at blinding speeds, the humble battery which powers them hasn't had an upgrade in years. In the hope that they would succeed in creating batteries with better storing capacities, which could provide power for a greater period of time, scientists introduced nanostructures of silicon inside a conventional Li-ion battery and immediately observed an improvement in their performance.

The principle involves inserting silicon whiskers inside a conventional battery, in order to increase the charge stored at the anode of the battery. During the charging process of the battery, lithium ions receive electrons, provided by the charger through the anode terminal. When the reverse process takes place, the ions release the extra energy, and electrons travel towards the cathode terminal of the battery, through a conductive gel.

The conventional Li-ion batteries have anodes made out of carbon atoms, which bond to the lithium. Models of the reaction that takes place during this process postulate that for each lithium atom captured at least six carbon atoms are necessary to make the bond. However, scientists now believe that, by replacing the carbon anodes with silicon, batteries could become up to ten times more efficient.

Furthermore, by using silicon atoms in silicon films and particles, it cannot take the pressure of the large numbers of lithium atoms, trying to make bonds with it, and breaks contact with the metal, thus reducing the batteries power.

In order to avoid this technological flaw, the silicon anodes of the batteries were constructed in the shape of whisker-like structures that are directly bonded to a stainless steel substrate. Though during the tests the stainless steel from the substrate behaved in much the same way as the lithium ions, crowding on the silicon nanostructure, they did not produce the breaking of the anode from the substrate.

According to the inventors, this has mainly been possible due to a practice that relieves the stresses in the nanostructure material, by expanding and contracting them in radial direction, which results in longer lived anodes that remain firmly in place and do not break.

This new battery fabrication process not only would provide with greater power storage capacities, but would also enable the creation of smaller volume, and lower weight power sources.

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By    18 Dec 2007, 14:47 GMT