Cyclic Aging and Quasi-Static Indentation of Lithium-Ion Pouch Cells Under Maintained Spring-Loaded Confinement: Earlier Internal Short-Circuit Onset

Pouch cells in automotive modules age and may experience mechanical abuse while mechanically confined, yet almost all published comparisons of fresh and aged cells release the aging constraint before the abuse test. In the present work, three commercial 6 Ah pouch cells were electrochemically cycled to approximately 80% State of Health inside a spring-loaded flat-plate fixture initialized at a nominal average stack pressure of 0.11MPa and were then indented quasi-statically at nominally 100% State of Charge without releasing the confinement. Three uncycled cells were tested as fresh references in the corresponding fixture configuration. The aging state was tracked by capacity fade and Electrochemical Impedance Spectroscopy. The aged cells built up force earlier, reaching 20kN at 11% smaller intrusion, and the electrically detected Internal Short Circuit occurred at 18% lower displacement and at a 10% lower group-mean force, while peak force and displacement at peak remained within the observed cell-to-cell scatter. This differs from the right shift reported for many pouch-cell studies in which the aging constraint was released before testing and resembles the earlier onsets reported for hard-cased cylindrical cells. Following the electrically detected Internal Short Circuit onset, the aged-cell voltage reached 1V later than that of the fresh references. The results are consistent with confinement history being a contributing and experimentally controllable variable in abuse tests on aged cells.