Application Description

Supercapacitors, also known as ultracapacitors or electrochemical capacitors, are promising energy storage devices that bridge the gap between electrolytic capacitors and batteries. Thanks to their high power and long lifespan, supercapacitors are widely used in applications ranging from SRAM to high-speed trains. The key to such high performance is often a low equivalent series resistance (ESR), which reduces the energy wasted via Ohmic heating during charging and discharging cycles. Characterization of the supercapacitor impedance at different frequencies is thus important to determine the ESR and other critical device parameters. At low frequencies, such characterization sets a unique measurement challenge that requires an instrument capable of measuring current and voltage directly and of measuring impedance with high accuracy.

Measurement Strategies

Traditionally, the galvanostatic charging/discharging method gives the ESR as a static value independent of frequency and test voltage, and the result can thus differ significantly depending on the operating conditions. Further, if the used current is high, irreversible electrochemical processes may greatly shorten the lifespan of the device.

With the Zurich Instruments MFIA Impedance Analyzer, it is possible to avoid the above drawbacks by measuring supercapacitors over a wide frequency range, from 1 mHz to 5 MHz, with a small AC test signal. In the four-terminal configuration shown in Figure 1, voltage and current on the device are monitored simultaneously and can be displayed together with calculated impedance parameters in the Sweeper module of the LabOne instrument control software.

‍