The importance of Evolved Gas Analysis in the battery testing process

Improving battery performance and safety are among the major challenges in the current battery development process. In order to achieve major progress in these fields, the materials employed in the battery assembly need to be carefully designed, tested and characterized. One of the most difficult tasks that needs to be addressed in this phase is the formation of evolved gas from the different components, due to the high temperature that could be generated inside the battery environment. Evolved gas could be responsible for different issues in the battery, such as swelling and fire phenomena, but also could give crucial information on key process happening inside the battery like the Solid Electrolyte Interface (SEI) formation. For this reason, the accurate determination of their composition and the process that are involved in their generation are of fundamental importance for the development of new battery materials. To address this issue different type of information needs to be collected such as, the thermal stability of the different materials and the correct collection, separation and analysis of the evolved gas. Hyphenation system permits to obtain all this type of information in a single analysis combining more than one technique and allowing to get deeper insights on the chemistry of the battery. Typical hyphenation systems involve the conjugation of a thermal techniques such as TGA or STA with other techniques like FT-IR and/or GC/MS.

In this work we demonstrate how hyphenation systems like TGA-MS or TGA-FT/IR prove to be very helpful in addressing this challenge in the battery manufacturing. In more details, TGA-MS system was successfully employed for analysis of electrodes to determine simultaneously 1) the residual content of water and 2) CO₂ evolution. The analysis permit to determine the thermal profiles of the electrodes and determine the temperature associate to the CO₂ desorption. In addition, TG-MS and TG-FT/IR systems were employed to analyze the thermal stability and the evolved gas produced from solid state electrolytes. The two techniques shown that different gases are evolved through the thermal heating of the samples and, by choosing accurately the MS injection time it was possible to determine the structure of these molecules, allowing to acquire new insight in the degradation process of this material.