Simultaneous Acquisition of Differential Electrochemical Mass Spectrometric and Infrared Spectroscopic Data for in Situ Characterization of Gassing Processes in Lithium-Ion Batteries

A considerably contributing process to the capacity fading of lithium-ion batteries is gas evolution. The understanding of its mechanism is inevitable to develop better battery components. These are especially tailor-made electrolyte mixtures and additives, as well as cathode and anode structures/composites.

In the past, differential electrochemical mass spectrometry (DEMS) already served us with important facts on the gassing behavior of electrochemical systems, particularly in lithium-ion batteries. However, it cannot always unambiguously unveil certain important features of the ongoing gas evolution reactions. In the case of overlapping m/z values, like 28, the species can be either assigned to C₂H₄, CO as an individual reaction product or as a fragment of CO₂ too. Furthermore, the quantification of the gaseous products might be extremely difficult due to matrix effects caused by the volatile electrolyte components. A hands-on supplementary technique is infrared spectroscopy (IR), since the majority of the products in question have characteristic absorption bands. Simultaneously acquired with the DEMS measurements, they give a more complete and unequivocal picture on the nature of gases. Additionally, with the help of IR, the quantification of the products is straightforward and more precise.

In this talk, we present the results on the development of a novel, combined in-situ DEMS-IR (DEIRS) analysis method. We show that our approach is unique with regard to long-term battery cycling tests as well. We compare different cathode materials or modified versions of the given material and demonstrate the effect of chemical composition/structure on the gassing behavior. The effect of solvent mixtures and some additives, like vinylene carbonate, on the stability of the electrolyte is elucidated. With the help of our setup, a method to optimize the amount of additives is suggested. Supported by precise pressure measurements, we give a comprehensive picture on the gassing processes in closed systems and compare those with the continuous flow DEMS-IR results. The quantification of the gaseous reaction products together with versatile, potential resolved electrochemical tests enables the establishment of kinetic models of the gas evolution, which will be illuminated. Unanticipated gas formation in certain cycling steps will be manifested too.