Carbon nanotubes¿tiny tubular structures composed of a single layer of carbon atoms¿could lengthen the life of batteries, according to new research. Findings published in the current issue of Physical Review Letters suggest that the diminutive tubes can hold twice as much energy as graphite, the form of carbon currently used as an electrode in many rechargeable lithium batteries.
The reduction and oxidation reactions that occur at the electrodes of batteries produce a flow of electrons that generate and store energy. Conventional graphite electrodes can reversibly store one lithium ion for every six carbon atoms. To investigate the storage capacity of carbon nanotubes, Otto Zhou and colleagues at the University of North Carolina, Chapel Hill, first created bundles of the single-walled straws. They then shortened the tubes and opened their ends by immersing them in strong acids. Subsequent tests of their energy-holding potential, conducted using electrochemistry and nuclear magnetic resonance spectroscopy, revealed an electrical storage capacity approximately double that of graphite. In explanation, the scientists note that the tubes' open ends facilitated the diffusion of lithium atoms into their interiors. Indeed, the tiny straws managed to reversibly store one charged ion for every three carbon atoms.
As with many findings in the nascent field of nanotechnology, commercial devices based on the work remain a ways off. "We'll have to work on and overcome other practical issues before we can make real devices," Zhou says, "but we are very optimistic."