Abstract
The base component in aluminum electrolytic capacitors gradually concentrates on the cathode terminal end, irrespective of the dc bias. If the electrolyte is a salt with a strong base component, such as quaternary alkyl ammonium, this tendency may affect the sealing. The concentration is caused by the obvious different in electrochemical characteristics between the cathode foil and the tab used for the cathode terminal end of capacitors. A cathode foil and a tab with different rest potentials together form a galvanic couple.
Therefore, reversing the potential relationship between foil and tab gives the fundamental solution against this problem. For the method, we developed a new method of using a cathode foil-formed titanium nitride (TiN) coating on the surface by an arc ion plating method. The order of the rest potential, the polarization behaviors of the cathode terminal side while applying voltage in a capacitor and also the durability were investigated. The rest potential shifted from −1.20V to −0.30V due to the TiN coatings and consequently became nobler than that of the tab, −0.75V. Even while applying the rated voltage, the potential of the cathode terminal did not cross over the rest potential of the tab. In addition, the performance was maintained even after 5000h under 378K condition. Liquid leakage evaluation tests demonstrated that this method provides an excellent advantage in preventing leakage. TiN-coated foil has been already mass-produced for this purpose by NIPPON CHEMI-CON Corp.
