Simultaneous acquisition of differential electrochemical mass spectrometry and infrared spectroscopy data for in situ characterization of gas evolution reactions in lithium-ion batteries

Gassing in batteries is a major issue contributing to capacity fading upon cycling, and thus far, differential electrochemical mass spectrometry (DEMS) has been a suitable analytical tool to investigate such gas evolution reactions. However, the identity of molecules is ambiguous knowing only the m/z value(s) and quantification is complicated. Therefore, the setup of a novel technique for in situ gas analysis of operating lithium-ion batteries is introduced, namely, DEMS combined with infrared spectroscopy. In a “long-term” study of a Li1 + xNi0.5Co0.2Mn0.3O2 (NCM 523)/graphite cell being close to technical conditions, we monitor the CO2 evolution over more than twenty cycles and show the dependence of the amount of generated CO2 on the charge cut-off potential. Furthermore, we deconvolute the MS channel m/z = 28 and show, for the first time, the direct observation of its constituent gases. Other gaseous decomposition products (like CO2 here) can be determined unambiguously as well through both their m/z values and their characteristic IR absorptions, but are not discussed here.