Most lithium ion batteries use graphite electrodes, but silicon can store up to 10 times more electrons per gram of material. Unfortunately, silicon swells when absorbing the charge, often causing the electrodes to crack or break after only a handful of uses and rendering batteries using them impractical. By combining silicon nanowires and their high capacity with a core of stronger carbon nanotubes that only expand slightly when charged, these new electrodes support repeated recharging.
Assistant professor of materials science and engineering Yi Cui and his research group developed these new electrodes after earlier attempts at silicon nanowire batteries only supported limited recharging capabilities. Carbon-silicon nanowires are also easier to make than nanowires composed solely of silicon. Carbon nanofibers are commercially available in large quantities and manufacturing the combination wires doesn’t require the high temperatures needed to grow nanowires made solely of silicon. The coating process – the mechanism for attaching the silicon to the carbon nanofibers – is also easy for large scale manufacturing systems, although the speed of application could be improved.
Researchers are looking at the possibility of incorporating these batteries into automobiles but feel they must support at least 300 recharging cycles before any manufacturer would consider their use. Although the Stanford cells recharge more effectively than straight silicon nanowire electrodes (which are effective for 20 cycles at most), current versions of the hybrid cell have only been successfully used for 50 recharging cycles before degradation set in.
TFOT has previously reported on new battery and fuel cell technology including an air-fueled battery with ten times the capacity of traditional batteries, glitter sized photovoltaic cells, and high power and high capacity nanocapacitors. TFOT has also covered advances in carbon nanotube technology including the creation of the strongest nanotube ever at Los Alamos National Laboratory, carbon nanotubes that detect light in the entire visible spectrum, and nanotube based loudspeakers that can be tailored into many shapes and sizes and placed on many different types of materials.
Read more about Yi Cui and his research at this Stanford research group website.