Silicon Nanostructures for Lithium Ion Battery Anodes

Colloidal synthetic methods have been developed for a wide variety of nanocrystal and nanowire materials.  Among these materials, silicon has been one of the most challenging to synthesize in in solution.  The general approach is to feed molecular reactants into hot solvent environment to precipitate the nanomaterial of interest.  In the case of silicon (Si), suitable reactants are needed that readily decompose in the solvent environment and the reaction must be controlled sufficiently to yield nanomaterials with the desired size and shape.  Recently, we have been developing a variety of methods for the synthesis of  Si nanomaterials, including amorphous and crystalline Si colloidal particles and Si nanorods and nanowires.  These methods can yield significant quantities of Si nanomaterials and one potential application for them is as a replacement for carbon as the anode material in lithium ion batteries.  Si has the ability to alloy with lithium (Li_4.4Si) to achieve very high charge storage capacity of as much as 4200 mAh/g, which is more than an order of magnitude higher than the storage capacity of carbon.  Lithiation, however, leads to a massive volume expansion (~400%), which leads to pulverization.  Si nanostructures have the ability to tolerate this volume expansion, while enabling significant lithiation.  Recent data of the charge storage capacity of colloidal silicon nanoparticles and nanowires will be presented.