The basic material of the anode for aluminum electrolytic capacitors is a foil with a thickness of ~ 20–100 μm made of aluminum with a high purity of at least 99.99%. This is etched (roughened) in an electrochemical process to increase the effective electrode surface.
Aluminium Electrolytic Capacitors: These are the most common type of aluminium capacitors. They use an aluminium electrode with a thin oxide layer as the dielectric and a liquid or gel electrolyte.
One of the major axes of research on electrolytic capacitors is the aluminum electrolytic capacitor (AEC). They have higher volume efficiency due to a significantly lower minimum dielectric thickness than all the other capacitors.
Hybrid Aluminium Electrolytic Capacitors: Combine the features of aluminium electrolytic capacitors and solid aluminium electrolytic capacitors. They have an aluminium electrode and a solid electrolyte, typically a conductive polymer or a combination of polymer and liquid electrolyte.
Electrolytic capacitors are available in several types as aluminum, tantalum, and niobium versions (Ho et al., 2010). The internal structure of an aluminum electrolytic capacitor consists of two aluminum foils, which are separated by a porous material such as paper which is impregnated with an electrolyte as shown in Fig. 6.11.
The exception is the bipolar or non-polar aluminum electrolytic capacitor, which has a back-to-back configuration of two anodes in a single case, and which can be safely used in AC applications. Electrolytic capacitors use a chemical feature of some special metals, earlier called "valve metals".