Electrolytic capacitor is a kind of capacitor. The metal foil is the positive electrode (aluminum or tantalum). The oxide film (aluminum oxide or tantalum pentoxide) that is in close contact with the positive electrode is the dielectric. The cathode is made of conductive materials and electrolytes (the electrolyte can be liquid or Solid) and other materials together. Because the electrolyte is the main part of the cathode, the electrolytic capacitor is named. At the same time, the positive and negative electrolytic capacitors cannot be connected wrongly. Aluminum electrolytic capacitors can be divided into four categories: lead aluminum electrolytic capacitors; horn-type aluminum electrolytic capacitors; bolted aluminum electrolytic capacitors; solid aluminum electrolytic capacitors.