Aluminum capacitors are made of an aluminum cylinder as a negative electrode, which is filled with a liquid electrolyte, and a curved aluminum strip inserted as a positive electrode. It also needs to be processed by DC voltage, so that a layer of oxide film is formed on the positive electrode as the medium. It is characterized by large capacity, large leakage but poor stability, positive and negative polarity. Aluminum capacitors are suitable for power filtering or low-frequency circuit.