Supercapacitor
Since capacitors' energy content increases with the square of the voltage, researchers were looking for a way to increase the electrolyte's breakdown voltage. In 1994 using the anode of a 200V high voltage tantalum electrolytic capacitor, David A. Evans developed an "Electrolytic-Hybrid Electrochemical Capacitor". These capacitors combine features of electrolytic and electrochemical capacitors. They combine the high dielectric strength of an anode from an electrolytic capacitor with the high capacitance of a pseudocapacitive metal oxide (ruthenium (IV) oxide) cathode from an electrochemical capacitor, yielding a hybrid electrochemical capacitor. Evans' capacitors, coined Capattery, had an energy content about a factor of 5 higher than a comparable tantalum electrolytic capacitor of the same size. Their high costs limited them to specific military applications.
Electrolytic capacitor
William Dubilier, whose first patent for electrolytic capacitors was filed in 1928, industrialized the new ideas for electrolytic capacitors and started the first large commercial production in 1931 in the Cornell-Dubilier (CD) factory in Plainfield, New Jersey. At the same time in Berlin, Germany, the "Hydra-Werke", an AEG company, started the production of e-caps in large quantities.
In his 1896 patent Pollak already recognized that the capacitance of the capacitor increases when roughening the surface of the anode foil. Today (2014), electrochemically etched low voltage foils can achieve an up to 200-fold increase in surface area compared to a smooth surface. Advances in the etching process are the reason for the dimension reductions in aluminum electrolytic capacitors over recent decades.