Electrochemical Impedance Spectroscopy – High-Tech with REGATRON Power

With the widespread use of high-performance batteries in electric vehicles, the demand for more detailed monitoring of the operation and condition of battery stacks is growing rapidly. Electrochemical Impedance Spectroscopy (EIS) provides insights into the details of the electrochemical reaction down to the level of ions - with the precision and reliability of REGATRON devices!

Electrochemical Impedance Spectroscopy (EIS) is a modern tool for the assessment of electrochemical processes, which can extend the exploration of the conventional parameters of cell voltage, current and internal cell resistance by a significant step. With a sophisticated measurement methodology, the EIS provides reliable information on the kinetics of ion movement, the condition of cell components as well as drift, ageing phenomena and abnormal behaviour of the process. In addition to monitoring and characterising battery cells, the method is also suitable for the monitoring of fuel cells, electrolysers, electrochemical sensors and applications of all kinds.

 

Functional principle

The EIS is based on the determination of the impedance curve of the DUT at different measuring frequencies. An alternating current of low amplitude is modulated onto the working current of the stack, the fuel cell or the electrolysis tank and the corresponding impedance is calculated in real time from the phase angle between the cell voltage and the current. This procedure is repeated per measurement cycle with a larger number of predetermined frequencies and then builds up an impedance spectrum. 

 

Legende: Typical EIS measurement setup with a fuel cell stack, a bidirectional DC power supply unit for loading the device under test and integrated AC modulation as well as a measurement periphery with data acquisition and analysis tools.

 

It is interesting to note that each electrochemical process has its own characteristic spectrogram. In this way, the cells in a stack, for example, can be compared with each other; even very slight deviations within the electrochemical process result in significant deviations in the spectrogram. This fact can be used for test purposes, for research and development, but also for close monitoring of a process.

 

The advantages of EIS

The EIS method offers a whole range of advantages over the methods most commonly used today based on the determination of the cell resistance and its limit value monitoring:  

• Significantly more precise and versatile insights into the electrochemical system, including statements about the charge flow, condition of the electrodes, condition of the electrolyte, internal resistance and complex impedances
• High sensitivity: Even small process deviations at ion level cause a footprint in the EIS spectrogram and thus enable analyses in the area of electrode/electrolyte interactions
• The EIS method is non-destructive for the analysed process and runs parallel to the actual main electrochemical process
• Good transferability of the method to a variety of electrochemical processes in the fields of batteries, fuel cells, electrolysers, coatings and electrochemical sensors
• EIS works in both liquid and solid-state media
• The high reproducibility of the results enables quantitative data to be obtained for further analysis by chemists and R&D specialists
• EIS is the method of choice when it comes to fine-meshed monitoring of electrochemical processes, the determination of degradation and drift as well as the identification of failure mechanisms

Legende: Nyquist diagram of an EIS with deviating impedance of a cell

 

Why REGATRON devices for the EIS

EIS requires a particularly high level of modulation capability from the load current source. In the interests of good signal quality, it must be able to work fully bidirectionally and have an integrated function generator with a very wide frequency range. It must be system-capable in order to handle the extensive data traffic from and to the test environment. The REGATRON G5 device family has established itself as a recommended system source in practical EIS applications thanks to its proverbial accuracy and electrical stability as well as the large number of useful interfaces.

 

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