Assessment of safety characteristics for Li-ion battery cells by abuse testing
Despite the many advantages with lithium-ion batteries there can be disadvantages in form of safety
issues. 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 on
cells and electrolytes from abuse testing by overcharge, short circuiting, external heating and fire test
are presented and discussed.
The thermal runaway was studied by external heating of various commercial Li-ion cells with
cylindrical and pouch packaging. Cells with lithium cobalt based oxides showed a thermal runaway at
around 200 °C with a maximum rate of temperature increase of about 5000 °C/min. Cells with lithium
iron phosphate (LFP) showed significantly lower reactivity but a thermal runaway did still occur for
Short circuit and overcharge tests of LFP pouch cells showed in most cases temperature increases
below about 100 °C. Fires did not occur in these tests except one unexpected fire during an overcharge
test. 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 hydrogen
fluoride (HF), phosphorous oxyfluoride (POF3) and phosphorus pentafluoride (PF5) were studied by
FTIR in fire experiments conducted on electrolytes and cells. The results are extrapolated to obtain an
estimate of the possible emissions from a fire in an electric vehicle.