Flammability of Gel Polymer Electrolytes

Gel polymer electrolytes are promising technology for next-generation lithium batteries, offering a balance between the high ionic conductivity of liquids and the safety of polymers. Although it is often suggested that gel polymer electrolytes are safer than traditional organic electrolytes, there is a lack of systematic research available on the flammability of this type of electrolyte. Flammability testing for liquids, including flash point measurement, is well-established. The flash point temperature represents the minimum temperature at which a vapor-air mixture ignites in the presence of an ignition source. This measurement is standardized and allows flammability to be quantified. The use of a closed-cup flash point apparatus typically requires 2 mL of liquid. However, a single gel polymer electrolyte sample normally contains only 15 to 300 µL of liquid. This limited volume complicates flash point testing, as the resulting flame is often too small to be visible to the naked eye. This challenge has been addressed via the development of a novel methodology that combines thermal imaging and computer vision to automatically detect the flash point in gel polymer electrolytes [1]. The adapted flash point detection apparatus will be presented along with insights into how intermolecular interactions between the solvent, polymer, and salt affect the flash point of gel polymer electrolytes. Balancing low flammability with high ionic conductivity poses significant challenges. While increasing solvent content can enhance the ionic conductivity of the electrolyte, it often compromises safety by raising flammability. Multi-objective Bayesian optimization enables the fine-tuning of electrolyte composition to balance ionic conductivity and flammability, even with a limited number of data points. St-Antoine, C., et al., Novel method to automatize flash point detection in small volumes of liquid by computer vision using thermal images. Submitted.