Nanotubes pack promise of battery-free energy storage

Storing and retrieving mechanical energy on the fly
To improve the performance of mechanical devices with nanotube-powered springs, Livermore's team has also imagined several novel applications that store and retrieve mechanical energy on the fly.

For instance, instead of a nanotube-powered generator running a bicycle motor, a mechanical regenerative system on a bicycle could store the energy of braking and coasting in nanotube-powered springs, then directly release that stored mechanical energy to boost acceleration when going uphill.

Eventually, Livermore's team at MIT hopes to devise ways of ganging millions of nanosprings, each of which can stretch about 5 percent of its length and snap back with no permanent deformation.

Today the team has merely tethered bundles of millimeter-long carbon nanotubes, but eventually the engineers plan to use methods that overlap the fibers, in a manner similar to ropes, to create longer springs that store and deliver mechanical energy more smoothly than current prototypes do.

"Imagine portable mechanical tools that operate without motors—like a nanotube-spring powered leaf blower," said Livermore. "We could send these mechanically powered devices into harsh environments where temperature extremes would result in poor performance by ordinary batteries."

Springs can also deliver energy faster than batteries, to power quick-release mechanisms (think "build a better mousetrap"). And with proper gearing, nanosprings can also smoothly deliver ultrasmall amounts of energy over long periods, such as for powering clockworks. A tethered spring's energy does not dissipate or leak off over time, as a battery's does, according to Livermore.

Livermore performed the work with doctoral candidates Frances Hill and Timothy Havel, as well as with John Hart, now a professor at the University of Michigan (Ann Arbor). MIT has filed for a patent on the technology. Funding was provided by the Deshpande Center for Technological Innovation Ignition and the MIT Energy Initiative.