The flammability of solvents and electrolytes is an important aspect of the thermal safety behavior of Li-ion batteries. The inherent safety of a cell is determined by the safety of each component as well as by the interactions between the single components. At present, most of the commercial lithium battery cells utilize organic solvents to dissolve the lithium salts. To obtain a complete picture of these chemical systems, safety should be assessed on multiple levels. The flashpoints have been measured according to the Abel closed-cup methods using the pure liquids and bottled propane-butane gas flame. The effect of the mixing of two-flammable solvents is analyzed. As an alternative to their experimental determination, the flashpoints of the pure solvents have been calculated from other physical and chemical properties of the substance, and the flashpoints of the solvent mixtures and electrolytes from the flashpoints of their flammable constituents. The most important results from evaluated experiments are the values of flashpoints for methanol-ethanol, methanol-1-propanol, methanol-1-butanol, ethanol-1-butanol, propanol-1-butanol–air mixtures. These values are used to be compared with the currently available physical-chemical models describe the effect of isomer blends on a deflagration process and to rate the effects of an explosion.