Different mechanical-electrochemical coupled failure mechanism and safety evaluation of lithium-ion pouch cells under dynamic and quasi-static mechanical abuse

Abstract

For this study, lithium-ion pouch cells undergo quasi-static and dynamic tests and are analyzed by interdisciplinary characterization methods. These methods reveal different behaviors of the cells under mechanical-electrochemical coupled failure. The study demonstrates that the inertia effect of a cell's multilayer structure dominates the failure under dynamic loading rather than the strain rate effect of the cell's components. This finding unlocks the underlying mechanism of localized fractures near the impacted surface and counterintuitive premature failures with less critical force under dynamic loading conditions. In addition to instant failure with inflection points in force/voltage curves, this study observes an interesting delayed failure behavior without evident short-term signs in both dynamic and quasi-static tests with different mechanisms. This challenges the validity of using macroscopic inflection points in mechanical tests as indicators for failure prediction and could explain the postponed spontaneous combustion of a cell after mechanical abuse accidents. The cell's capacity and internal resistance after dynamic and quasi-static tests are also assessed. Finally, an experimental evaluation outline is proposed for lithium-ion cells under mechanical abuse. This work sheds light on the understanding of dynamic failure mechanisms and safety evaluation methods for lithium-ion cells.