We got pretty excited here at ReWire the last time we heard some news about supercapacitors out of UCLA, and so did you -- almost 20,000 Facebook users "liked" our report on a breakthrough in using graphene to store electrical power.
This week, another UCLA team reports it may have found a way to address a persistent problem with supercapacitors: limitations on their effective size.
Researchers at UCLA's Henry Samueli School of Engineering and Applied Science have found a way to use niobium oxide as a matrix to allow the fabrication of supercapacitors the size of batteries, but which could conceivably charge and deliver power hundreds of times as quickly as typical batteries can.
Batteries and supercapacitors differ in the way they store electrical power. Batteries store power in the form of chemical energy, and while that's a very efficient way to store a considerable amount of power, it makes charging and power delivery relatively slow: electrons (or other charged particles, lithium ions being one common example) must work their way through a solid substance in both directions, which takes time.
Supercapacitors, on the other hand, essentially just "hang" those charged particles on a matrix without forcing them to migrate though a solid material, meaning that charging can take place as fast as the electrons can move. But the technology is limited by the fact that storage takes place only along the capacitor material's surface area, which means that once the material gets larger than wafer-thin, its storage capacity per unit of weight drops.
Think of the two storage technologies as different parts of a movie theater, with electrically charged particles as moviegoers. The ranks of seats are like a battery: you can hold a whole lot of people there, but once the aisle seats fill up it can take some time to get people to the seats in the interior. Supercapacitors are more like the aisles: you can fill them and empty them really quickly, but they don't hold nearly as many people.
The breakthrough by the team at the Samueli School of Engineering -- led by led by professor of materials science and engineering Bruce Dunn -- involved using a crystalline matrix of niobium oxide that's essentially "porous" on a molecular scale: it's got as much open space in its makeup as solid material, meaning it's got a large expanse of internal surface area on which charged particles can be stored.
"With this work, we are blurring the lines between what is a battery and what is a supercapacitor," said Veronica Augustyn, a graduate student in materials science told UCLA's Bill Kisliuk. "The discovery takes the disadvantages of capacitors and the disadvantages of batteries and does away with them." Augustyn is lead author of a paper describing the breakthrough, published April 14 in the journal Nature Materials.
The work suggests that electrodes 40 microns thick -- a bit more than a thousandth of an inch -- could be charged and discharged as efficiently as supercapacitors that are far thinner. And as Kisliuk points out, existing commercial batteries these days often use electrodes about that size.
Bruce Dunn closes Kisliuk's post with the most optimistic obligatory cautionary disclaimer we here at ReWire have seen in quite some time:
Dunn emphasizes that although the electrodes are an important first step, "further engineering at the nanoscale and beyond will be necessary to achieve practical devices with high energy density that can charge in under a minute."