Although they are currently in use for small devices (1 farad to 10 farads), leading ultracapacitor manufacturers are targeting transport applications such as hybrid vehicles, trolleys and buses.
Researchers and companies are inching ahead to solve challenges such as series resistance, cell resistance and low energy density to use ultracapacitors in transport applications. Researchers at the Universite Paul Sabatier, Toulouse, France, are focusing on activated carbon ultracapacitors and working on the current collector/active material film interface to address the issue of decreasing the series resistance.
Furthermore, the research team is experimenting on areas such as the synthesis of new activated carbons or new forms of carbons to store more energy, and the improvement of the energy density of the ultracapacitors by associating a battery-type electrode to an activated carbon electrode.
“A significant difference that distinguishes this research team's work is that they apply the surface treatment science to the current collector/active material interface in ultracapacitor electrodes, to improve the power,” says Frost and Sullivan’s research analyst Viswanathan Krishnan. “This concept is rather novel since it requires a material/corrosion/surface science culture in addition to an electrochemical/energy storage culture.”
Ultracapacitors suffer from low energy densities when compared to rechargeable batteries. Since energy density is correlated with the morphological characteristics of the porous carbon electrodes such as the surface area and pore size distribution of the carbon, researchers and industry participants have been working on tailoring the porosity of carbon so as to achieve a higher energy density.
Apart from working on the development of capacitor modules for hybrid cars, researchers at the Electrochemistry Laboratory, Paul Scherrer Institut, Switzerland, have carried out fundamental research on capacitance limits of activated carbon and their degradation mechanisms and lifetime aspects. The findings of this research indicate that carbons with surface area greater than 1500m2/g do not increase capacitance and gas evolution, and dimensional changes affect lifetime.
Among the European ultracapacitor manufacturers, ESMA’s third-generation ultracapacitor design uses a polarisable carbon electrode and a non-polarisable electrode made of nickel oxyhydroxide.
“Advantages such as high power density, high recharging cycles, reliability and easy recyclability have attracted various applications for ultracapacitors ranging from portable applications to automobiles,” says Krishnan. “However, the ability of ultracapacitors to compete with the conventional batteries in terms of cost and energy density are crucial to determine the pace of technology adoption.”
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