Long–Term Aging – Overdischarge Degradation Mechanisms Interplay in Li-Ion Pouch Cells

Battery Management Systems (BMS) ensure that cells within a module are cycled appropriately even though the cells may have a different capacity. For large commercial applications, modules may have a few thousand cells making it more challenging to monitor and control each cell individually. A capacity imbalance will not only affect the module performance but it can lead to an overcharge/overdischarge condition on the single cells. Overdischarge occurs when a Li-ion cell is discharged below its safe electrochemical window. If the cell is extremely overdischarged, a reverse potential condition takes place followed by the dissolution of the copper current collector. In a module without an adequate BMS, overdischarge can occur frequently. Its interaction with the natural aging degradation of the cell may pose a threat to safety issue. In this work, the interaction between aging and overdischarge in Li-ion cells is studied. The aim is accomplished by aging single pouch cells at different overdischarge levels, prior and after the onset of reverse potential. Electrochemical and morphological characterization of the abused cells will be conducted. Results will provide insights on the interaction of the two degradation mechanisms and the interaction of their corresponding effects.