Electrolytic capacitor is a type of capacitors,the foil is positive (aluminum or tantalum), the metal foil(aluminum or tantalum) is a positive electrode, and the oxide film (Alumina or tantalum pentoxide) close to the positive electrode is a dielectric; The cathode is composed of conductive materials, electrolytes (electrolyte may be a liquid or a solid) and other materials, electrolytes are the main part of the cathode, hence the name called electrolytic capacitor.