High power is the main reason for applying electrochemical capacitors. Power is limited by the inner resistance of the capacitor. However, there are many definitions for the inner resistance; data sheets, impedance spectroscopy measurements and cycling experiments give quite different numbers for the resistance.
The alternating current (AC) resistance is rather easily determined by measuring the impedance at 100 Hz frequency. The AC resistance value corresponds to the contact resistance of tabs, welds, current feeders and aluminum/carbon contacts. Additionally, the electrolyte resistance inside the separator causes contact resistance.
The direct current (DC) resistance includes the AC resistance and the electrolyte resistance in the porous carbon structure. The measurement is less straightforward, and the result depends on current and time.
In this presentation, various components of the resistance are discussed:
- aluminum foil
- aluminum/carbon contact
- electrolyte in the separator
- electrolyte in the porous carbon.
Some methods for resistance measurement are shown:
- 10ms method
- 5s method
- impedance spectroscopy
- capacitor cycling
Finally, the importance of resistance for different applications is discussed.