Influence of Ion Species in Electrolyte on Capacitance of EDLC

Abstract

Electric double layer capacitor (EDLC) has the power storage element. Electric double layer (EDL) is the electrochemical phenomena. EDLC consists of two electrodes and the electrolyte. EDL by ions in the electrolytes near electrodes is formed under the voltage application. Since the distance between electrode surface and EDL is extremely small, the capacitance of EDLC is huge. However, the applied voltages of EDLC must be less than the decomposition voltage. Therefore, EDLC has the problems that an energy density is small. We have been studying ions behavior in EDLC. We hope to improve the energy density of EDLC. In our reports, the influences of ion species in electrolyte on capacitance of EDLC are showed. The electrode of EDLC is the stainless steel of parallel plate electrodes. We use four kinds of electrolyte (NaCI, KCI, CsCI, and CsBr). We applied DC voltage to EDLC and estimated the capacitance from the time dependence of an electric discharge current. As the results, it was observed that the capacitance was about 7.4 μF of NaCI, about 8.4 μF of KCI, about 9.9 μF of CsCI, and about 10.4 μF of CsBr. These results showed that the quantity of ions arrangement near the electrode was limited, since the quantity of ions arrangement was influenced due to the difference in radius of the ion. the capacitance of EDLC had a major impact in the ion species.