Researchers at MIT have developed a new method of adding carbon nanotubes to lithium-ion batteries that give the batteries the best characteristics of both capacitors and traditional lithium-ion batteries while simultaneously increasing their energy storage.
The experimental batteries, which used layered carbon nanotubes as the positive electrode (the cathode) and a lithium titanium oxide as the negative electrode (the anode), demonstrated an impressive ability to deliver power at the very fast rates of capacitors while being able to store more energy and last much longer than even the best lithium-ion batteries available today.
All batteries are made up of three components: two electrodes (the negative anode and the positive cathode) separated by an electrolyte. When lithium ion batteries are producing energy, positively charged lithium ions move through the electrolyte and deposit at the cathode, which makes electricity. Alternatively when they are recharged, an external energy source (your outlet, regen braking, etc.) causes these lithium ions to move the back across the electrolyte and embed in the anode.
Because of the humongous surface area of the carbon nanotubes, the batteries can hold much more charge than traditional cathodes, enabling carbon nanotubes for the first time to serve as the positive electrode in lithium batteries, instead of just the negative electrode.
At an energy content of about 200 Watt hours per kilogram, these experimental batteries are way up there with the most advanced forms of lithium ion batteries on the horizon, yet they also can provide very high short bursts of energy — important for EVs that need to accelerate quickly. As an added benefit, the carbon nanotubes seem to provide the batteries with an incredible durability. After 1,000 charge/discharge cycles, the research team has seen no appreciable degradation in the battery’s function.
The research was published in Nature Nanotechnology. “High-power lithium batteries from functionalized carbon nanotube electrodes.” Seung Woo Lee, Naoaki Yabuuchi, Betar M. Gallant, Shuo Chen, Byeong-Su Kim, Paula T. Hammond, & Yang Shao-Horn. Nature Nanotechnology. 19 June 2010. doi:10.1038/nnano.2010.116