Influence of the state-of-charge on the mechanical behaviour of lithium-ion pouch cells under uniaxial compression

With extensive recent deployment of lithium batteries in stationary and mobility applications, integration engineers face a challenging burden for design and planning the static and dynamic external environment surrounding cells. Essential to these designs are understanding how cells respond to mechanical compression and the thresholds for initiating catastrophic failure. This study investigates how the state of charge (SOC) affects the compressive mechanical behaviour and the occurrence of internal short circuits (ISC) in lithium-ion pouch cells. NMC811 lithium-ion pouch cells were subjected to uniaxial compression tests at different SOCs, namely deep discharge, 0 %, 50 %, and 100 %. The results showed that the SOC has a minor effect on macroscopic compression behaviour and the occurrence of ISC. Engineering stress at ISC increased linearly with the SOC due to slight stiffening at higher SOC levels, while engineering strain at ISC remained constant. These findings suggest that deep-discharged cells can be used for safer mechanical testing, as their mechanical response is effectively equivalent to that of charged cells, but poses a lower safety risk. Furthermore, the results of this study align with prior research regarding the influence of SOC on the mechanical response of pouch cells. Such response is deemed to be influenced by compressive internal stresses, generated by the constrained SOC-related swelling of the jellyroll.