**Abstract**

A chemical analysis was carried out before and after a constant voltage hold test (applied at 2.5, 2.8, 3.0, and 3.2 V individually for 1 week) that was an acceleration deterioration examination to clarify the deterioration factors of electric doublelayer capacitors. The results showed that the stress test slightly raised the internal resistances and decreased the capacitances. It was also confirmed that a range of fluorochemicals was formed on the electrode surface for approximately 10–13 nm in depth using electron spectroscopy for chemical analysis. From a chemical analysis of the electrolyte using an inductively coupling plasma-optical emission spectrometer (ICP-OES), it was confirmed that the electrolyte included Si, which is an ingredient element of an electrode, and that the increase in the holding voltage during the stress test decreased the Si density in the electrolyte.

**Keywords:** deterioration factor, electric double-layer capacitors, voltage hold test
