Assessment of safety characteristics for Li-ion battery cells by abuse testing

Sammanfattning: Despite the many advantages with lithium-ion batteries there can be disadvantages in form of safetyissues. In an abuse situation a Li-ion cell can undergo a thermal runaway releasing excessive heat,flammable and toxic gas emissions and eventually accompanied by dissembling/explosion and fire.Abuse tests are a method for assessment of the safety characteristics of Li-ion batteries. Results oncells and electrolytes from abuse testing by overcharge, short circuiting, external heating and fire testare presented and discussed.The thermal runaway was studied by external heating of various commercial Li-ion cells withcylindrical and pouch packaging. Cells with lithium cobalt based oxides showed a thermal runaway ataround 200 °C with a maximum rate of temperature increase of about 5000 °C/min. Cells with lithiumiron phosphate (LFP) showed significantly lower reactivity but a thermal runaway did still occur forsome cells.Short circuit and overcharge tests of LFP pouch cells showed in most cases temperature increasesbelow about 100 °C. Fires did not occur in these tests except one unexpected fire during an overchargetest. The fire tests show that the reactivity of Li-ion cells in a fire are dependent on the state of charge(SOC), however, the total heat release shows a low SOC dependence. Toxic emissions of hydrogenfluoride (HF), phosphorous oxyfluoride (POF3) and phosphorus pentafluoride (PF5) were studied byFTIR in fire experiments conducted on electrolytes and cells. The results are extrapolated to obtain anestimate of the possible emissions from a fire in an electric vehicle.