If you've ever used a smartphone and complained about the battery life, you've experienced one of the limiting factors on gadget design. Supercapacitors, which store charge rather than generate current with a chemical reaction the way batteries do, might offer a solution, but they tend to be bulkier than batteries and store less energy in the same size.
But now a team of scientists thinks they may have found a way to create a compact, graphene-based super capacitor that lasts as long as a battery. Graphene, which is a single layer of carbon molecules, could lead to lightweight supercapacitors for electric cars and supplement traditional batteries both in electronic devices and renewable power systems. The study, lead by Dan Li of Australia's Monash University, is detailed in the Aug. 1 issue of Science.
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At its basic structure, a classic capacitor is comprised of two plates, usually metal, separated by some other material, sometimes a solution or simply air. When a charge is applied, electrons gathers on the surface of the plates but are limited by the plate's total surface area. Add more plates, gets more charge capacity.
Li's team made their version of a supercapacitor by folding sheets of graphene into corrugated shapes. Then they put the sheets into an electrolyte solution that kept the layers separated by a few nanometers and provided a path for moving electrons. To test how much charge the sheets could hold, they applied a current. Because of graphene's unique honeycomb lattice structure and because it was corrugated, there was more surface area for the electrons to gather upon, and thus the super capacitor could hold more charge in a smaller space.
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In fact, more electrons packed together than anyone had managed before. Supercapacitors are typically made from porous graphite, and can hold about 5 Watt-hours per liter. Li's team managed an energy density of about 60 Watt-hours per liter, or about the same as a car battery. That isn't as good as lithium-ion batteries, which range anywhere between 250 and 750 Watt-hours, but it's still a big jump over current capacitor technology.
An added bonus is that making the graphene sheets to larger scales won't demand exotic new production technologies. In fact, Li adopted techniques from traditional paper-making, so commercializing the technology could be simple and inexpensive.
Photo: What it looks like between two sheets of graphene. Credit: iStockPhoto