Charge/discharge characteristics of prototype aluminum electrolytic capacitors

Aluminum anode foils were subjected to constant current charge/discharge cycling in an electrolytic cell. From the voltage-time data, the charge and discharge energies and energy loss were calculated. The loss has a minimum value equal to the dissipation factor of the oxide dielectric and increases with the charge field. It depends on the oxide structure and details of the oxide formation process. A surprising observation is a significant dependence on the substrate morphology (etch structure). It is proposed that the high energy loss observed during this operating mode, and also during pulse discharge, is the result of frictional loss in the oxide film resulting from expansion of the oxide at high field and contraction at low field.