Li-Ion Cell Safety Monitoring Using Mechanical Parameters, Part 3: Battery Behaviour during Abusive Overcharge

The electrochemical and mechanical behaviour of 18,650 Li-ion cells subjected to abusive overcharge has been studied in constant current and constant voltage mode. The results from the cell deformation monitoring via a rectangular rosette strain gauges indicate an over-swelling process starting shortly after the cell voltage increases above 4.2 V. The acoustic ultrasound interrogation measurement and data treatment using clustering and mapping software, carried out in parallel, showed an abnormal evolution of the signals' power density spectral patterns, suggesting changes in the structure of the cell jellyroll induced by the overcharge reactions. The increase in cell skin temperature due to the overcharge process starts considerably later. The results suggest that the monitoring of the mechanical behaviour of cylindrical-format Li-ion cells can be used for the detection and alerting of early overcharge safety events.