Nanowires as Energy Materials: Batteries and Solar Cells
Professor Yi Cui
Inorganic nanowires can support electron and photon transport along the length to a macroscopic distance while maintaining a large surface-to-volume ratio and facile strain relaxation without breaking during structure transformation. These properties are attractive for batteries and solar cells. Rechargeable batteries have been attractive for applications such as portable electronics, medical devices and electrical vehicles. My group has been exploring the nanowires of materials with displacement or alloying reactions with Li ions as Li-ion battery electrodes, which can provide much higher energy density than the intercalation materials although they can not be successfully used in the form of the bulk or particle due to large structure transformation and/or poor electrical conductivity. For battery anodes, Si nanowires directly grown on metal collector substrates have been shown to have a capacity more than 10 times higher than the carbon anode used in the existing technology. The Si nanowire electrodes have been shown to overcome the issues of 400% volume change during Li insertion and extraction, which cause pulverization and capacity fading in bulk Si electrodes. I-III-VI semiconductors such as CuIn(Ga)Se2 (CIGS) have been actively studied for solar cell applications, which has resulted in highest power efficiency close to 20% in polycrystalline thin film solar cells. However, the materials property of CIGS is not well understood. Nanowires of CIGS provide well-defined nanodomains for studying the fundamental structure and property correlation. Here I will show our recent findings with nanowires, which provides better understanding towards improvement of CIGS solar cells.