Modelling specific capacitance of D.C. etched aluminium foil for aluminium electrolytic capacitor

Abstract

The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cubic tunnel etch model and a trench tunnel etch model. With these two modes, the theoretical maximum specific capacitance values for the anode foil used in aluminum electrolytic capacitors were calculated with Matlab at various formation voltages. The corresponding optimum values for tunnel size, density, distribution and geometrical shape were also given as a function of oxide thickness. The experimental and theoretical capacitance values are compared. It is concluded that the theoretical maximum specific capacitance for trench etch tunnel model is higher than that for cubic etch tunnel one at fixed formation voltage. Promoting tunnel-merging in rows rather than in clusters is preferred during electro-etching process, leading to formation of trench tunnels on the Al foil. For high formation voltages, measured capacitances approach the optimum values and enlargement of surface area by electrochemical etching was faced with the limit. But for low formation voltages, the experimental capacitance value obtained is far behind the optimized one and the tunnels size, distribution, shape and density must be optimized to achieve high capacitance.