Researchers at the Massachusetts Institute of Technology, led by Associate Professor Yang Shao-Horn, in collaboration with Professor Paula Hammond, have found that using carbon nanotubes for one of the battery’s electrodes produced up to a tenfold increase in the amount of power that a lithiun-ion battery could deliver from a given weight of material.
In the new battery electrode, carbon nanotubes are "electrostatically self-assembled" into a tightly bound structure that is porous at the nanometer scale. The carbon nanotubes have many oxygen groups on their surfaces, which can store a large number of lithium ions. This enables carbon nanotubes to serve as the positive electrode in lithium batteries.
Carbon nanotubes are a form of pure carbon in which sheets of carbon atoms are rolled up into tiny tubes. Normally, carbon nanotubes on a surface tend to clump together in bundles, leaving few exposed surfaces to undergo reactions. The "electrostatic self-assembly" process incorporates organic molecules on the nanotubes and they assemble in a way that has a many exposed surfaces.
The new batteries have some of the advantages of both capacitors and conventional lithium batteries. Like capacitors, they can produce very high power outputs in short bursts – but the energy output for a given weight of the new electrode material is five times greater than for conventional capacitors. Like conventional batteries, they can provide lower power steadily for long periods – but the total power delivery rate with the new batteries is10 times that of lithium-ion batteries
In addition to their high power output, the carbon nanotube electrodes showed very good stability over time. After 1,000 cycles of charging and discharging a test battery, there was no detectable change in the material’s performance.