Published on Monday February 11, 2008
The efficient use of electrical energy generated from low-emission or renewable sources such as solar, wind or moving equipment is often limited by inadequate batteries having a short lifetime.
As a recent article in the January 31st issue of The Economist points out, capacitive energy storage devices, so-called supercapacitors or ultracapacitors, are beginning to supplant, rather than just supplement batteries in applications that have grown tired of the long and expensive search for the better battery. The growing popularity of supercapacitors in hybrid electric vehicles, home appliances and back-up power sources is due to a number of desirable properties including: an order of magnitude higher power than batteries, short charging times, and, maybe most importantly, nearly infinite cycle life – far longer than the devices they are powering. Work continues, however, to increase the energy stored in supercapacitors.
A group of researches led by Prof. Yury Gogotsi from Drexel University and Prof. Patrice Simon from the Université Paul Sabatier in France recently published an article in a leading chemistry journal, Journal of the American Chemical Society, that raises the bar for energy storage in supercapacitors and points to new avenues for further energy increases.
In a supercapacitor, energy is stored via the electrostatic adsorption of ions into a charged porous carbon electrode. The energy of the devices increases with the square of the operating voltage of the supercapacitor and linearly with capacitance.
In the work published in the Journal of the American Chemical Society, a solvent-free ionic liquid was investigated as the electrolyte and a series of nanoporous carbons with average pore size tuned to be smaller than 1 nm was used as the electrodes. Ionic liquids offer the possibility to work with a higher voltage than traditional electrolytes (it means, higher energy) and at much higher temperature, for example, in the engine compartment of a car. This work showed that by decreasing the pore size of the carbon electrode to the electrolyte ion size, it is possible to double the amount of energy stored, as compared to the state-of-the art for ionic liquid supercapacitors. It means that, for example, electric cars using such supercapacitors can go further on a single charge.
Careful design of the carbon pore size and an understanding of the atomistic mechanisms of capacitance can potentially lead to tremendous improvement in the performance of electrical double-layer capacitors and their wide use in a variety of applications ranging from public transportation, such as trains and buses, to electric cars, home appliances, and even toys and flashlights.
The development of this technology was supported in part by the US Department of Energy and is being currently commercialized by Drexel spin-off company Y-Carbon.
C. Largeot, C. Portet, J. Chmiola, P. L. Taberna, Y. Gogotsi and P. Simon, "Relation between the Ion Size and Pore Size for an Electric Double Layer Capacitor," The Journal of the American Chemical Society, ASAP Article 10.1021/ja7106178 S0002-7863(71)00617-6 , Web Release Date: February 8, 2008
For more information contact Yury Gogotsi at firstname.lastname@example.org
R. F. Service, “New ‘Supercapacitor’ Promises to Pack More Electrical Punch,” Science 313, 902 (2006).
J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, and P. L. Taberna, "Anomalous Increase in Carbon Capacitance at Pore Sizes Less
Than 1 Nanometer," Science, 313, 1760-1763 (2006).
J. Chmiola, Y. Gogotsi, "Supercapacitors as Advanced Energy Storage Devices," Nanotechnology Law and Business, 4(1), 577-584 (2007).