Nanowire from recycled silicon

The technology world produces a lot of silicon - after all most of our computer powered gadgets are awash with the stuff.

However, once the product reaches end-of-life, the silicon is very difficult to recycle.  Most likely it will end up contributing to the shameful waste mountains polluting our world.

There is, though, a very novel use for this computer junk and one that could usher in the next generation of nanotechnology-driven products.   Battery technology is making great inroads into game-changing advances in the electrode design for the next generation of lithium ion batteries.  By replacing the solid graphite (carbon) anode with a 3 dimensional array of silicon nanowires, various teams of researchers are increasing the energy density (power to volume capability) by up to 10 times that of the very best current generation lithium ion batteries.  Silicon is a much better conductor than carbon and it absorbs up to 10 times more lithium ions. It can handle 10 times the electrical current of carbon, allowing for more amps to made available to the power-hungry devices of today.

Nanowires of silicon, anchored and spaced to allow expansion 

Unfortunately the nanowires that make up these next generation electrodes are a very fragile commodity and silicon does have some inherent problems that scientists have needed to overcome.  When used as an electrode, silicon expands about 4 times more than the equivalent carbon based one would and that has led to issues with cracking.  Unless the wires are anchored they quickly disintegrate and become useless.   However, by using colloidal nanosphere lithography manufacturing processes, they can now fabricate perfect "forests" of 50 - 70 micron thick nanowires that are spaced sufficiently to allow for expansion and are coated with a thin layer of copper to improve ion absorption and to protect the fragile structure. This process of using masks to shape materials is not new but its application to the burgeoning nanowire sector brings us a reliable and relatively cheap manufacturing process with huge potential.  It's all very well coming up with great ideas but commercial success is dependent on being able to actually turn that idea into a tangible product.

Check out the battery tech provided by promising start-ups like Amprius, who are using silicon nanowires in their almost-ready-for-market battery that will power some cellphones as early as 2014.  Take a look at the great work that Prieto Battery are doing with the use of copper coated anode sponges - another very clever and demonstrable manufacturing process.

http://cleantechnica.com/2012/09/10/discarded-silicon-gets-new-life-in-lithium-ion-batteries/

How nanowires work (HowStuffWorks)