Fire Hazards of Carbonate-Based Electrolytes for Sodium-Ion Batteries: What Changes from Lithium-Ion Batteries?

Abstract

Carbonate-based electrolytes are often employed as the preferred electrolyte for both Li-ion and Na-ion cells. To investigate the fire risk during abuse conditions in real-life scenarios covering the full value chain, not only cell-level studies but also component-level investigation is crucial. Hence, Na-ion advanced electrolyte combustion tests are performed employing the fire propagation apparatus also called Tewarson calorimeter. Heat and combustion products releases are measured, making use of fire calorimetry laws and analytical techniques such as FTIR, NDIR, FID, or paramagnetic analyzers, and optical measurement. Thermal and chemical impacts of Na-ion electrolytes combustion and fires are assessed under well-ventilated and under-ventilated environments. Data are then compared against a carbonate-based electrolyte used in Li-ion batteries to create a comparative study between these technologies. Overall, the heat released rate majorly depends upon the solvents used and is less impacted by inorganic Li or Na salts while the emitted gases depend on both solvent and salt chemistry. Another key observation lies in the different fate of the fluorine element chemically bound to the concerned salts: in similar burning conditions, F from NaPF6 decomposition is preferably converted in F-containing solid species in the residues whilst LiPF6 gives off more gaseous species such as HF.

Keywords: Na-ion battery, Electrolyte, additives, Fire Propagation Apparatus, Heat Release Rate, toxic gas