Determination of Hydrofluoric Acid Formation During Fire Accidents of Lithium-Ion Batteries with a Direct Cooling System Based on the Refrigeration Liquids

Abstract

To avoid overheating of the batteries, which could lead to a fire, Lithium-ion batteries are provided with a thermal management system using refrigeration liquids. Since some of the commercial dielectric liquids used as refrigeration liquids contain halogens, their presence will contribute to a formation of hazardous emissions such as hydrofluoric acid during a potential fire. In this study, a simulation of a high temperature accident has been performed for lithium-ion batteries cooled with the direct immersion cooling systems using single-phase dielectric liquids to define their contribution to HF formation. Four commercial refrigeration liquids based on perfluoropolyethers, hydrofluoroether and polyalphaolefin were investigated in this work. By simulation of a fire, it was observed that the refrigeration liquids delayed the smoke formation by a factor of 2 to 2.5 in comparison to the case when the battery was burned without the cooling liquid. By analysis of the fluoride concentration in the washing system, it was determined that without the refrigeration liquid approximately 46.8 mmol/l of [F] was captured after the fire. When refrigeration liquids based on two perfluoropolyethers and hydrofluoroether were applied, the fluoride concentration in the washing system was 259 mmol/l, 173 mmol/l and 145 mmol/l, respectively. This work also proposed the reaction mechanisms of the refrigeration liquid´s decomposition during a fire. It was concluded that the refrigeration liquid based on polyalphaolefin does not contribute to the additional formation of hydrofluoric acid due to the chemical stability and low content of fluoride and can be considered as a more sustainable alternative for a direct cooling system for Lithium-ion batteries.