Dynamic mechanical behavior of lithium-ion pouch cells subjected to high-velocity impact

With broad-scale deployment of lithium-ion batteries, mechanical-abuse induced failure events such as short circuits and thermal runaway have made safety a focus of attention in battery design. Most previous studies have focused on quasi-static and low-velocity impact analyses, which could not represent the mechanical behavior of lithium-ion batteries in realistic situations. Here we report a combined experimental and computational study on the dynamic response of lithium-ion pouch cells subjected to high-velocity (200-1000 m/s) impact. Dynamic finite element simulations were performed to study the effects of internal interfacial behavior and external loading and boundary conditions on the dynamic mechanical behavior of pouch cells. Specifically, mechanical resistance across interfaces between different cell components has a pronounced impact on energy distribution and absorption, thereby determining the evolution of subsequent failure events. These results have practical implications for designing cells with liquid versus gel-type electrolytes, for example. Furthermore, finite element simulations on different external loading and boundary conditions indicate that a direct interaction between the impactor and the cell boundaries lead to a significant change in residual velocity, while the response of the pouch cell is independent of the prescribed far-field boundary conditions. In other words, there is not a significant difference in the response of pouch-format cells that have stacked electrodes versus wound electrodes at such high strain rates. These results are significantly different from quasi-static simulations wherein the evolution of failure events follows a very different pathway. In addition, the impact velocity profiles under different initial impact velocities offer the ballistic limit for the pouch cell and inform subsequent propagation analyses at the battery module level. Collectively, the findings presented here not only offer new perspectives on the role of the interfacial resistances and external boundary conditions on the mechanical safety of lithium-ion pouch cells, but also have implications for further investigations on cell design, modeling approaches, and test method development to study the safety of lithium-ion batteries under extreme loading conditions.