Thermal fault detection by changes in electrical behaviour in lithium-ion cells

With this paper a method to detect faults of lithium-ion cells during operation is first presented and later validated by experiment. Since every cell fault will increase the cell temperature towards its process until thermal runaway the method uses the temperature-dependent change of the cell impedance as fault feature. Using a 46 Ah pouch cell the model was parameterised by electrochemical impedance spectroscopy and then validated during dynamic load. For this purpose the Worldwide harmonised Light vehicles Test Procedure (WLTP) was chosen. The presence of a fault was simulated by heating the cell once uniformly and once locally and the progression of the chosen fault feature analysed. For both test cases the method proposed was able to detect the present heat source before the thermal runaway was triggered and venting or voltage drop were observed. •A thermal fault detection concept for lithium-ion cells is proposed.•Dynamic voltage behaviour of cell changes with temperature due to impedance change.•Simple equivalent circuit model is accurate enough for detecting this change.•Detection of local and uniform thermal faults within 18 min.•Detection of thermal fault 32 min before thermal runaway of cell.