Silicon nanowires made via macropore etching for superior Li ion batteries

The future of electro mobility depends critically on substantially improved Li ion batteries. Si as anode material has a more than tenfold higher capacity as compared to the standard graphite anode, but needs to be nanostructured to avoid fracture. It is shown that macropore etching combined with suitable follow-up processes allows to produce nanowire arrays with optimized geometries. First tests of these anodes showed very promising results with respect to prime battery parameters like capacity and capacity losses during cycling. In particular, a first test battery showed superior performance for more than 60 cycles in comparison to an otherwise identical battery with a graphite anode. Critical processes like galvanic Cu deposition at the nanowire bottom can be avoided by using an optimized pore etching process that produces complex pore diameter profiles as a function of depth, allowing easy separation of the nanowire layer from the Si substrate and processing the nanowire surface area. In total, the production of Si nanowire anodes using this improved process should allow mass production at competitive costs. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim