Relationship between space charge and effective pore size of nanoporous electrode in electric double-layer capacitor

The space-charge distributions of electric double-layer capacitors (EDLCs), which are energy storage devices, were examined with the pulsed electroacoustic (PEA) method. It was found that the experimental results could be influenced by the reflection and penetration of sound waves when the space-charge distributions of EDLCs were measured with the PEA method. This is because EDLCs have a five-layer structure consisting of three materials (aluminum, cellulose, and activated carbon). We calculated the reflection wave components that influenced the charge density through the acoustic impedance and the relative permittivity of the materials. In this way, we found that the changes in the space-charge distributions of EDLCs and their charge characteristics corresponded closely. We determined that measuring the space-charge distributions with the PEA method was effective for evaluating the charge accumulation of EDLCs. In this study, a polarized electrode was prepared for use in EDLCs. The ratio of the surface area to the average pore diameter of the polarized electrode was measured with the nitrogen adsorption method at 77 K. The relationship between the ratio of the surface area to the average pore size and the space-charge distributions of EDLCs is also discussed in this paper.

Charge density profile in EDLCs. This investigation revealed that the charge density of EDLCs measured with pulsed electro-acoustic method was related to the mesopores in the size range of 3–4 nm in the polarized electrode. The charge density can be improved by controlling the pore size in order to develop EDLCs with large capacitance in the future.Figure optionsDownload as PowerPoint slide