Li-Ion Cell Safety Monitoring Using Mechanical Parameters: Part I. Normal Battery Operation

The normal operation of a 18650 lithium-ion cells has been monitored using rectangular rosette strain gauge and a pair of piezoelectric transducers. The sensors for mechanical measurements provide information about the cell deformation mechanism and electrodes structure during the cycling. The strain gauge signal revealed three type of mechanical processes. The predominant deformation pattern during galvanostatic discharge process is an isotropic cylindrical shrinkage relevant to the extraction of lithium ions from the graphite negative electrode. In the case of low-rate discharge in cyclic voltammetry mode, the deformation pattern changes to spherical growth when the state of charge falls below 40. In contrast, the thermal shrinkage and growth of the cell corresponds to simple decrease of the cell diameter with much smaller hysteresis effect. The ultrasound interrogation is able to detect repeatable progressive change of the acoustic waveform transferred across the cell in direction of the jellyroll diameter, which depends on the state of charge and does not undergo any significant changes at different cycling rates. The impact of the state of health under 2 h—rated charge/discharge cycling at 25 °C reveals slow progressive drift of the strain and acoustic signals corresponding to the growth of the cell size.