Both the above mentioned gas formation processes are important to understand. First, to be able to develop novel electrolyte mixtures or tailor electrolyte additives that form a stable SEI. Second, to optimize the surface and/or structure of the cathode materials to influence their bulk oxidative properties upon delithiation and electrocatalytic activities.
Herein, we present results on the in situ gas analysis by means of differential electrochemical mass spectrometry and infrared spectroscopy (DEMS-DEIRS) of various battery systems. We analyse the SEI formation on different anode materials and the influence of various electrolyte additives. The impact of temperature and constant voltage/OCV periods on the first charge cycle (so-called formation process) is investigated. Their effect on both the gassing and electrolyte salt decomposition is described.
The stability problem of the most common electrolytes at high voltages is discussed. These are achieved either with NMC (LiNixMnyCozO2) type materials or with high voltage spinels (LiNi0.5Mn1.5O4). Beyond the decomposition of the electrolyte, oxygen evolution is the crucial factor at high cathode potentials. This effect is particularly apparent for overlithiated and high Ni content materials that will be presented as well. Monitoring gassing over 20 cycles reveals interesting changes in its characteristic being only recognizable in long term tests. We demonstrate the importance of potentiodynamic cycling tests beneath the traditional galvanostatic ones with DEMS-DEIRS in the exploration of reaction mechanisms. Pressure measurements complete the analysis in terms of validation of gas amounts and supplement them with three-electrode long term investigations.