A New Differential Electrochemical Mass Spectrometry (DEMS) Setup and Its Application in Sodium Ion Batteries

Many processes in alkali ion batteries lead to the formation of gases. These can be SEI formation, electrolyte decomposition, oxygen release from certain cathodes to name some. These gas formations are relevant for lifetime and safety of the battery cells. Having information about these side reactions is important to fully understand the cell chemistry. This can be the behavior of single parts, like electrode materials or electrolyte solvents, or the more complex interplay in a full cell.<br/> <br/>Differential electrochemical mass spectrometry (DEMS) is a powerful method to understand these processes. By measuring the electrochemical behavior and the gases evolving from the cell at the same time, information is gained under which conditions side reactions occur ^[1]. This can be state of charge, resting times or temperature changes. While it is such a powerful method, not many DEMS studies have been made on sodium ion batteries (NIBs) ^[2]. A better understanding of these side reactions in NIBs is still needed. Therefore, we developed a new DEMS system in our group.<br/> <br/>This setup was designed to be comparable to other lab scale cells. So, the results would be comparable over different systems. To do so we took the carrier gas based design of Berkes <i>et al. </i>as a starting point for our design ^[3]. From there we did some optimizations to make the system suit our requirements.<br/> <br/>In the first part of the talk, we want to present the new DEMS system. Here we want to go into detail about the setup and highlight some key features, which can be advantageous compared to other systems. Besides the instrument the way we analyze our measurement data to calculate the gas evolution from full mass spectra is new in the field of DEMS for batteries. This data evaluation algorithm leads to a better signal to gas attribution and more possibilities to verify the results ^[4].<br/> <br/>In the second part of the talk, we will present results measured with the new system. Here we will show our work on sodium manganese nickel oxide cathodes and hard carbon anodes in half cells and full cells thereof. Comparing the results from half to full cells gives insight into the interplay of the whole cell. The stepwise oxidation of the electrolyte solvent, as well as the cross talk of side products between the electrodes, leads to a complex reaction behavior. To show similarities and differences for different electrolytes, we will present data on carbonate and glyme based electrolytes ^[4].<br/> <br/> <br/>[1] B. Rowden, N. Garcia-Araez, <i>Energy Reports</i> <b>2020</b>, <i>6</i>, 10.<br/>[2] L. Zhang, C. Tsolakidou, S. Mariyappan, J.-M. Tarascon, S. Trabesinger, <i>Energy Storage Materials</i> <b>2021</b>, <i>4</i>, 1616.<br/>[3] B. B. Berkes, A. Jozwiuk, M. Vračar, H. Sommer, T. Brezesinski, J. Janek, <i>Analytical chemistry</i> <b>2015</b>, <i>87</i>, 5878.<br/>[4] J. Geisler, L. Pfeiffer, P. Axmann, P. Adelhelm, "Gas evolution in sodium ion batteries – DEMS setup, data evaluation and a study on sodium nickel manganese oxide cathodes.", <i>To be submitted.</i>