Summary
The first discussion session hosted by Danish Battery Society (DBS) was held with great success at DTU Energy Conversion, Risø campus on May 30th 2013. The topic was Electrochemical Impedance Spectroscopy (EIS) and its application to batteries.
A series of presentations was given by senior scientists Søren Højgaard Jensen, Johan Hjelm and Ane Sælland Christensen. The presentations are included below together with a summary:
General electrochemistry, equivalent circuit models and measurement techniques
by Søren Højgaard Jensen
The day started with presentations by Søren on general electrochemistry such as electrode-electrolyte interfaces and basic electrochemical relations including the Nernst equations and the Butler-Volmer equation. Søren then explained the background for equivalent circuit models and how the impedance response looks for these circuits in a Nyquist plot. Throughout the presentations questions and comment from the audience was guiding the direction of the discussion and to give a better understanding of EIS measurements a practical example was shown.
Kristian Knudsen showed how to use a Gamry Reference 600 potentiostat to measure the impedance responses from simple electric circuits, based on resistors and capacitors, and a lithium-ion battery.
Chemical processes, their equivalent circuits and common pitfalls
by Johan Hjelm
After enjoying lunch outside in the sun Johan had the daunting task of overcoming what was labeled as “Death Valley” in a hot meeting room on a full stomach. Johan passed with flying colors and elaborated further on the equivalent circuits for EIS measurements and how they are linked to the chemical processes. Johan also explained some of the pitfalls of using equivalent circuits to model the impedance response, as it is always possible to construct an equivalent circuit with the right output characteristics, but that might not be a physically correct representation of your measured system.
Johan then presented how to interpret the EIS measurements from batteries followed by Andreas Christensen showing EIS data obtained from a lithium-ion battery and the data integrity of these measurements. The following discussion transitioned to the next presentation which was Johan explaining how to use Kramers-Krönig relations to verify the data integrity from impedance measurements.
EIS examples on different cathodes and Lipon
by Ane Sælland Christensen
Next up Ane Christiansen showed EIS measurements made on batteries that she herself had produced, and she also showed EIS measurements on the individual components of the battery to understand how EIS measurement are linked to the different physical components.
The presenters were thanked for their work and looking forward to the next discussion session the group talked about the next topic and venue, which most likely is going to be about synthesis at Aarhus University campus.
Finally the group was given a guided tour through the facilities at DTU Energy Conversion.
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Invitation
From 10:00 to 16:00 Meeting room 4, building 779 Risø campus Frederiksborgvej 399, 4000 Roskilde
Electrochemical impedance spectroscopy (EIS) is a valuable tool for characterizing batteries – but data interpretation can sometimes be difficult since no perfect equivalent circuit exists. At the department of Energy conversion and Storage at DTU we are planning a day for improving our fundamental understanding within this area. The setup of the day will be a series of small presentations followed by time for discussion of relevant topics.
As we believe that this topic could be interesting for other researchers in the Danish Battery Society, we will make this an open event for all. The idea is to have a relaxed and open-minded day for discussions with fellow researcher struggling with similar problems as you.
The day will start with presentations on general electrochemistry and the basic concepts of electrochemical processes such as kinetics and diffusion in 2- and 3-electrode setups. When the fundamentals have been covered we will take a look at how electrochemical impedance spectroscopy (EIS) relates to the electrochemical processes combined with discussions on the equivalent circuits. We will also look at how to verify the integrity of the EIS measurements and how to interpret the different parts of the Nyquist/Bode plot. Finally we will look at how EIS parameters can be used to characterize a battery and its performance.
The event will start at 10:00 on Thursday May 30th at Risø and depending on the level of discussion it should end around 16:00.
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