A conducting medium in which the flow of electric current takes place by migration of ions. Commonly an electrolyte is defined as a substance that when dissolved in a specific solvent, usually polar, like water or ethylene glycol, produces an ionically conducting solution.
Typical electrolytes are solutions of acids, bases, salts, and molten salts. Molten salts are a special class of electrolytes in which the ions and the solvent are the same species.
In an electrolytic capacitor the electrolyte constitutes the second electrode, or plate, separated from the anode, or positive plate by the barrier layer of oxide formed on the anode surface.
The electrolyte impregnated in the element (typically the wound anode foil, paper separator, and cathode foil of an electrolytic capacitor) is referred to as driving or working electrolyte and performs the following two functions:
1. it impregnates and adheres to the surfaces of the anode and cathode foils to realize 100 % of their capacitance (essentially a cathode action).
2. repairs defects in the anode oxide film.
Important: The characteristics of the electrolyte have a great influence on the temperature characteristic, frequency characteristic, high temperature load life, reliability, etc. of the capacitor, and so an electrolyte with a composition different from that of the formation electrolyte and one that also satisfies economic, safety and other requirements is, of course, required.
Ideally, a driving electrolyte should:
* be chemically inert to all capacitor components exposed to it
* have the ability to anodize the anode material
* have good temperature stability
* have a suitable conductivity
* be free of contaminating or corrosive agents
* additionally, if there is a spacer material separating the anode and cathode structures, then the electrolyte must also impregnate or "wet" the spacer very well without unduly decreasing its effective conductivity.

This definition is in context to Capacitor. See more contextual defintions for Electrolyte.