Si NWs as anodes in Li-ions batteries: electrochemical properties of different morphologies

Silicon is one of the most interesting candidates to replace graphite as anode in Li-ion batteries for its high theoretical capacity (4200mAh/g, more than 10 times larger than graphite) and because it is an abundant, low-cost and environmental-friendly material. Despite these promising aspects, Si structure still suffers from huge volume changes (300%) on alloying with Li, which determines a structural deformation and a rapid degradation of the electrode [1]. Nanostructures and particularly nanowires can better sustain the volume variation avoiding material degradation [2,3]. We have grown Si-NWs by Cu-catalysed CVD (Chemical Vapor Deposition) [4,5]. Despite the promising electrochemical performances obtained using SiNWs based anodes, the stability of the cell was not satisfying. By an accurate morphological characterization, we have observed [6] the presence of a thick silicon layer below the nanowires which could to be responsible of the lack of the electrical contact between the active material and the current collector upon cycling. In this work the role of the growing parameters is investigated with the aim to reduce the silicon thick layer under the nanowires and tune the dimension of the nanowires. How the morphology and the NWs dimensions affect the electrochemical performances was also investigated.