High-performance lithium ion batteries today use anodes made from carbon (graphite). Silicon has been proposed as a substitute for graphite since it offers a theoretical improvement of 10-times in capacity over graphite, but so far prototypes have proven too unstable for creating lithium batteries with a long lifetime.
The problem is that silicon particles crack when they are formed at the same granularity of graphite particles—about 15 to 20 microns. The new nanocomposite material solves that problem by hanging 30 nanometer sized silicon particles on trees of carbon black which then self-assemble into porous spheres about 10-to-30 microns in diameter. The resulting electrode remains stable due to the durable carbon-superstructure that prevents cracking, but benefits from the increased surface area afforded by the smaller silicon nanoparticles.
Common chemical vapor deposition processes allow the new hybrid silicon-carbon electrodes to be mass produced economically. As the tiny silicon nanoparticles are permanently attached to the micron-sized carbon black trees, they avoid the health hazards of processes that require handling of nanoscale particles.
So far Georgia Tech has fabricated experimental anode electrodes, which it is testing for use in standard manufacturing processes for lithium batteries. Their prototype has survived over one hundred recharge cycles without any degradation, leading the researchers to predict they will last for thousands of recharges.
