Batteries can get a ten-fold increase in power through the addition of carbon nanotubes, found a team of researchers at MIT. Scientists believe that the recent discovery may find a place in small, portable gadgets, and may even lead to improved batteries for larger devices which require greater power.
The usual lithium-ion batteries commonly found in portable electronics rely on positively-charged lithium ions for power. When recharged, an external current causes these ions to move in the opposite direction, and they become embedded in the spaces of the porous material found in the battery’s anode.
The new battery benefits from increased storage capacity and power, thanks to the addition of carbon nanotubes—a form of pure carbon in which sheets of carbon atoms are rolled up into tiny tubes which assemble themselves into a tightly bound structure that is porous at the nanometer scale (billionths of a meter). These nanotubes have several oxygen groups on their surfaces, which can store large numbers of lithium ions. This enables the carbon nanotubes to serve as the positive electrode for the first time in lithium batteries, instead of just the negative electrode.
The findings come from a team led by MIT’s Associate Professor of Mechanical Engineering and Materials Science and Engineering Yang Shao-Horn, in collaboration with Bayer Chair Professor of Chemical Engineering Paula Hammond. The discovery was reported in a paper published on June 20 in the journal, Nature Nanotechnology. The lead authors are chemical engineering student Seung Woo Lee PhD, and postdoctoral researcher Naoaki Yabuuchi.
Ordinarily, carbon nanotubes tend to clump together in bundles, leaving fewer exposed surfaces to undergo reactions. However, in a press release Hammond explains that incorporating organic molecules on the nanotubes make them assemble with a “high degree of porosity while having a great number of nanotubes present.”
The energy output for a given weight of this new electrode material was shown to be five times greater than with conventional capacitors. The total power delivery rate was 10 times that of lithium-ion batteries, the team says, and this performance can be attributed to good conduction of ions and electrons in the electrode, and efficient lithium storage on the surface of the nanotubes.
To produce the powerful new electrode material, the team used a layer-by-layer fabrication method, in which a base material is alternately dipped in solutions containing carbon nanotubes that have been treated with simple organic compounds. The compounds then give them either a positive or negative net charge. When these layers are alternated on a surface, they bond tightly together due to the complementary charges, making a stable and durable film.
In addition to their high power output, the carbon nanotube electrodes have proven to be highly stable over time. After 1,000 cycles of charging and discharging a test battery, there were no detectable changes in the material’s performance.
While the electrodes the team produced only showed improvements in energy delivery at high-power output levels, they are now developing techniques to produce thicker electrodes and extend the improved performance to low-power outputs as well.
“In its present form, the material might have applications for small, portable electronic devices,” says Shao-Horn in a statement. “But if the reported high power capability were demonstrated in a much thicker form—with thicknesses of hundreds of microns rather than just a few—it might eventually be suitable for other applications such as hybrid cars.”
While the carbon nanotubes have been produced in limited quantities so far, a number of companies are already gearing up for mass production, which could soon help to make it a viable material for large-scale battery manufacturing.
The usual lithium-ion batteries commonly found in portable electronics rely on positively-charged lithium ions for power. When recharged, an external current causes these ions to move in the opposite direction, and they become embedded in the spaces of the porous material found in the battery’s anode.
The new battery benefits from increased storage capacity and power, thanks to the addition of carbon nanotubes—a form of pure carbon in which sheets of carbon atoms are rolled up into tiny tubes which assemble themselves into a tightly bound structure that is porous at the nanometer scale (billionths of a meter). These nanotubes have several oxygen groups on their surfaces, which can store large numbers of lithium ions. This enables the carbon nanotubes to serve as the positive electrode for the first time in lithium batteries, instead of just the negative electrode.
The findings come from a team led by MIT’s Associate Professor of Mechanical Engineering and Materials Science and Engineering Yang Shao-Horn, in collaboration with Bayer Chair Professor of Chemical Engineering Paula Hammond. The discovery was reported in a paper published on June 20 in the journal, Nature Nanotechnology. The lead authors are chemical engineering student Seung Woo Lee PhD, and postdoctoral researcher Naoaki Yabuuchi.
Ordinarily, carbon nanotubes tend to clump together in bundles, leaving fewer exposed surfaces to undergo reactions. However, in a press release Hammond explains that incorporating organic molecules on the nanotubes make them assemble with a “high degree of porosity while having a great number of nanotubes present.”
The energy output for a given weight of this new electrode material was shown to be five times greater than with conventional capacitors. The total power delivery rate was 10 times that of lithium-ion batteries, the team says, and this performance can be attributed to good conduction of ions and electrons in the electrode, and efficient lithium storage on the surface of the nanotubes.
To produce the powerful new electrode material, the team used a layer-by-layer fabrication method, in which a base material is alternately dipped in solutions containing carbon nanotubes that have been treated with simple organic compounds. The compounds then give them either a positive or negative net charge. When these layers are alternated on a surface, they bond tightly together due to the complementary charges, making a stable and durable film.
In addition to their high power output, the carbon nanotube electrodes have proven to be highly stable over time. After 1,000 cycles of charging and discharging a test battery, there were no detectable changes in the material’s performance.
While the electrodes the team produced only showed improvements in energy delivery at high-power output levels, they are now developing techniques to produce thicker electrodes and extend the improved performance to low-power outputs as well.
“In its present form, the material might have applications for small, portable electronic devices,” says Shao-Horn in a statement. “But if the reported high power capability were demonstrated in a much thicker form—with thicknesses of hundreds of microns rather than just a few—it might eventually be suitable for other applications such as hybrid cars.”
While the carbon nanotubes have been produced in limited quantities so far, a number of companies are already gearing up for mass production, which could soon help to make it a viable material for large-scale battery manufacturing.
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