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SUMMARY Chemical analysis was carried out before and after the constant voltage hold test that was an acceleration deterioration examination to clarify deterioration factors of electric double‐layer capacitor (EDLC). The results showed that the stress test slightly caused the increase of internal resistance. It was also confirmed that the range of fluorochemicals was formed on the electrode surface for approximately 10 nm in depth using electron spectroscopy for chemical analysis (ESCA). From the chemical analysis of the electrolyte using an inductively coupling plasma emission analyzer (ICP‐OES), it was confirmed that the electrolyte included silicon which is one of the ingredient elements of an electrode and that the increase in holding voltage in the stress test decreased the silicon density in the electrolyte.

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In this study, capacitance behavior of Electric Double Layer Capacitor (EDLC) with nanocomposite electrode for energy storage has been examined by charge-discharge characteristics. Also, internal resistance of EDLC was evaluated using two kinds of conducting filler. The one is acetylene black (AB) and the other is Ketjenblack (KB). KB was used for polarized electrodes instead of conventionally used AB in order to improve the capacitance and to decrease the internal resistance of EDLC. Usually, KB exhibits higher electronic conductivity compared to AB, and KB could be considered as conducting filler. The temperature dependence of capacitance and internal resistance of prepared EDLC using aqueous electrolyte, organic electrolyte and 2 kinds of ionic liquid was evaluated. Also, adsorbed ion numbers on the surface of KB and pore utilization of KB on each electrolyte was evaluated. As the results, it was found that the KB containing EDLC showed fairly high capacitance compared to AB containing one on all electrolyte. In addition, temperature dependence of EDLC containing KB and AB were measured on temperature from 0 °C to 50 °C. It was understood that KB was superior to AB in all temperature and all electrolyte on capacitance and internal resistance. Moreover, adsorbed ion numbers on the surface of KB and pore utilization of KB was high using aqueous electrolyte.