Investigation on the fire-induced hazards of Li-ion battery cells by fire calorimetry

The use of the high energy Li-ion battery technology for emerging markets like electromobility requires precise appraisal of their safety levels in abuse conditions. Combustion tests were performed on commercial pouch cells by means of the Fire Propagation Apparatus also called Tewarson calorimeter in the EU, so far used to study flammability parameters of polymers and chemicals. Well-controlled conditions for cell combustion are created in such an apparatus with the opportunity to analyse standard decomposition/combustion gases and therefore to quantify thermal and toxic threat parameters governing the fire risk namely the rate of heat release and the effective heat of combustion as well as the toxic product releases. Using the method of O2 consumption, total combustion heats and its kinetic of production were determined as a function of the cell state of charge unveiling an explosion risk in the case of a charged cell. The resulting combustion heat is revealed to be consistent with cumulated contribution values pertaining to each organic part of the cell (polymers and electrolytes) as calculated from thermodynamic data. The first order evaluation of the dangerousness of toxic gases resulting from fire induced combustion such as HF, CO, NO, SO2 and HCl was undertaken and stressed the fact that HF is the most critical gas originating from F-containing cell components in our test conditions.