Effect of cycling aging and indentation velocity on the mechanical–electrical–thermal behavior of lithium-ion pouch cells under mechanical abuse

Understanding the mechanical-abuse response of aged lithium-ion batteries is essential for life-cycle safety assessment, particularly when cells experience high-rate operation and subsequent external deformation. In this study, commercial lithium-ion pouch cells were subjected to high-rate charge–discharge cycling to obtain different aging levels, followed by quasi-static and loading-rate-dependent indentation tests (100 mm/min-500 mm/min). It is noted that the following results are confined to this specific aging protocol. The mechanical, electrical, and thermal responses were monitored simultaneously, and post-mortem disassembly was conducted to examine internal damage characteristics. The results show that high-rate cycling leads to capacity fade, cell swelling, and visible deposits on the anode and separator surfaces. Increasing the indentation rate reduces both the mechanical and electrical failure thresholds of pristine and aged cells, as reflected by lower peak force, smaller displacement at peak force, and earlier voltage drop. Compared with pristine cells, aged cells exhibit higher peak force and delayed abrupt voltage drop under the same loading conditions, indicating greater indentation resistance within the tested rate range. This difference becomes more pronounced at higher loading rates, probably due to aging-induced swelling and reduced electrolyte mobility. However, the higher failure threshold of aged cells does not necessarily imply lower overall safety risk. After discharge to the cut-off voltage, aged cells show open-circuit voltage (OCV) rebound and residual recoverable capacity, which can intensify the thermal response during subsequent mechanical failure. After repeated 1C discharge to reduce the recovered OCV, the thermal response becomes milder. These findings emphasize that both mechanical robustness and residual-capacity-driven thermal hazards are critical factors in assessing aged battery safety under mechanical abuse.