Safe cell, safe battery? Battery fire investigation using FMEA, FTA and practical experiments

Incidents of electrical vehicle catching fire forced on a root cause analysis. Failure mode and effects analysis (FMEA) and fault tree analysis (FTA) approaches were used for failure analysis and to design experiments on the battery system level. Analysis focused on the behaviour of an internal short circuit of a cell and its effect on the battery system and the vehicle. An internal short circuit of a stand-alone cell leads to venting and the release of dense smoke, however no fire or explosion occurred which complies with manufacturer declaration and hazard assessments according to battery safety standards. When such cell venting was triggered in the battery system it could be demonstrated that electric sparks on the carbonizing cell battery management print ignite the smoke and eventually lead to a fire of the complete vehicle. It has been shown that the use of comparatively safe Lithium-Iron-Phosphate cells does not entail a safe battery. The identification of the fire root cause enabled to develop and successfully test a mitigation method preventing fire caused by this failure mode. (C) 2016 Elsevier Ltd. All rights reserved.