Ethylene carbonate-based organic electrolytes for high performance aluminium electrolytic capacitors

The utilization of ethylene carbonate (EC)-based solutions has been examined as the electrolyte of aluminium electrolytic capacitors. The electrolytic conductivities of alkylammonium salts in the solutions containing propylene carbonate (PC), gamma-butyrolactone (BL) or sulfolane (S) as a co-solvent varied with both the solvent composition and the ion size of the salt. The maximum conductivity of 0.5 M tetraethylammonium hydrogen maleate (TEAM), 9.8 x 10(-3) S cm(-1), was obtained in a 20 mol% EC + 80 mol% BL composition. The thermal stability of the electrolyte solution varied also with the electrolyte composition; the solutions containing higher mol% EC tended to be unstable towards thermal stimulation. The anodic behaviour of the formation of aluminium oxide was briefly examined in the EC-based electrolytes containing small amounts of water. The oxide films formed in the TEAM solutions were highly resistant to corrosion, suggesting that the present electrolyte system has a high ability for the oxide film restoration in the capacitor.