Thickness dependence of carbon electrode on space charge of electric double layer capacitor

The space charge distribution in an Electric Double Layer Capacitor (EDLC) for energy storage has been examined by a Pulsed Electro-Acoustic (PEA) method. The EDLC in this experiment consists of aluminum as a current collector with the thickness of 30 mum, cellulose as a separator with the thickness of 20 mum, activated carbon sheet as a polarized electrode. Each component has section area of 30x30 mm². The organic electrolyte was a mixed solution of propylene carbonate (C₄H₅O₃) and tetra ethyl ammonium tetra fluoro borate (C₂Hs)₄NBF₄ in the molar ratio of 1:0.8. The dc voltage of 2.5 V, for electrical charge formation, was applied to the EDLC sample. In this research, thickness of activated carbon sheet was changed from 150 mum to 300 mum to observe the state of space charge in polarized electrode. Space charge distributions of EDLC were measured and maximum charge density and cumulative charge density on various thickness of polarized electrode were investigated. As the results, it can be found that the maximum charge density was high in case of thin polarized electrode and cumulative charge density was great in case of thick polarized electrode. Therefore, activated carbon sheet that thickness is thin is effective for development of high power density type EDLC, which has rapid charge and discharge performance. Also, activated carbon sheet that thickness is thick is effective for development of high energy density type EDLC, which has long time charge and discharge.