Yi Cui and Zhenan Bao from the University of Stanford have developed an electrode manufacturing technique that could improve the capacity of ultra-capacitors by 20 to 45 percent and make them compete with much more expensive batteries currently used in electric cars.
The two researchers and the team they led used managanese oxide electrodes (MnO), because manganese is abundant in nature and costs little. Manganese oxide in its raw form has a low conductivity, which makes it a poor electrode, but the team dipped it into either a carbon nanotube or a conductive polymer solution.
Both the carbon nanotube and the conductive polymer improved the MnO’s conductivity and increased its surface area, so the results were pretty amazing: the electrode’s ability to store charge has been increased by 20 and respectively 45 percent.
The performance obtained in the field of ultra-capacitors (otherwise widely used in electric buses, where you need quick and high bursts of power) could be reproduced to improve lithium ion battery electrodes.
Not only the conductive properties of manganese oxide could be enhanced by the new substances, but also the ones of sulfur, silicon and lithium manganese phosphate.
Although the storage capacity of the ultra-capacitors upgraded by Cui and Bao (155 watt-hours/kilogram) doesn’t by far match the one of lithium ion batteries, it can nevertheless compete with that of nickel-metal-hydride batteries, which is a great success for the researchers.