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 Li_1 + xNi_0.5Co_0.2Mn_0.3O₂ (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.