Flammability parameters of lithium-ion battery electrolytes

Abstract

Analysis of literature values of electrolyte flammability parameters does not show any correlation. This can be interpreted as a result of electrolyte flame risk being characterized by different research teams applying incomparable experimental methods. Therefore, in order to obtain a consistent set of data five different safety (flammability) parameters, i.e. flash point Fp (the open cup method), self-extinguishing time SET, flame propagation time FPT, flame propagation velocity FPV and differential scanning calorimetry (DSC) peak temperature, were measured in the same way for 33 electrolytes or solvents applied in lithium-ion batteries. No correlation was found between SET and FPV, SET and FPT, SET and Fp as well as DSC data with all the other parameters. However, on the FPT vs Fp and FPV vs Fp plots two electrolyte groups were seen. The first group consists of liquids based on dimethyl carbonate and diethyl carbonate, characterized by the lowest Fp values (Fp ≤ 29 °C). The other systems belong to the second group of liquid systems (58 °C ≤ Fp ≤ 91 °C). A general conclusion is that determination of flammability parameters in a standardized way can lead to a correlation between at least three of them: flash point, flame propagation velocity and flash propagation time.