Based on nanoporous carbon electrodes electrochemical double layer capacitors (EDLC), otherwise known as supercapacitors or ultracapacitors, are currently widely used in various energy storage technologies, wherein the EDLC low internal resistance and long cycle life are at an advantage. It is still a good challenge to further reduce the internal resistance of EDLC since this can result in higher power density and higher efficiency of these promising power supply units. In this work it has been found that the EDLC internal resistance depends strongly on the electrolyte diffusion in the carbon electrode nanopores, and two techniques to measure the in-pore diffusion coefficients, namely, those based on spin-echo NMR or cyclic voltammetry with the use of porous rotating disc electrode are described. Cyclic voltammetry, impedance spectroscopy and transmission electron microscopy have also been used to select the best EDLC components. As a result, EDLC devices of very low internal resistance and high power density have been developed.

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