Influence of electrolyte additives on the gassing behaviour in silicon based lithium-ion batteries

Summary:

This conference paper shows the influence of electrolyte additives on the gassing behaviour in silicon-based lithium-ion batteries.
The stability of the electrolyte in a lithium-ion battery is an important issue when it comes to the lifetime of a battery. The decomposition of the electrolyte is noticeable through the formation of gases. By examining these gases, information is obtained about the reactions taking place in the battery and can thus help to optimise the overall performance of the battery.
The setup shown here allows gas samples to be taken in-situ from the cell. It also provides the opportunity to obtain pressure and temperature data that can be used to quantify the gas produced. The gases were analysed using a special gas chromatography system with attached mass spectrometry (GC-MS). This system allows the analysis of volatile and permanent gases via two separation columns. The indicated molar quantities were calculated using the simplified ideal gas equation.
The results show that the total gas evolution within the cell during the formation cycle depends on the electrolyte additives used. The use of 5 wt% vinylene carbonate in addition to the EC/EMC (3:7) and 1 M lithium hexafluorophosophate results in the most significant reduction in gas evolution over the entire formation cycle.
When looking at the individual gas component ratios, it is noticeable that the use of additives also has an influence on the ratios of the gas components. In particular, it can be seen that the main component of the gases when vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are used is carbon dioxide, whereas when 3-(triethoxysilyl)propionitrile (TEOSCN) is used, or in the absence of additives, ethylene is the main component.