Low-Temperature Aging Effect on Safety of Lithium-Ion Batteries Subjected to Intrusion: A Comparative Study of 18650 and Pouch Cells

This study investigates the impact of cycling aging on the safety performance of lithium-ion batteries, specifically 18650 cells and pouch cells. These cells are cycled at 0 °C with charging rates of 2 C and 0.8 C, respectively, upon reaching different states-of-health, and their mechanical-electrical-thermal responses are analyzed post-indentation tests. The compressive behavior of anodes and cathodes at different states-of-health is also examined. The failure mechanisms of battery components are discussed based on indentation results at cell level, compression results of components, electrochemical impedance spectroscopy, and visual observations. The study reveals that aged 18650 cells exhibit increased stiffness (evidenced by left-shifted force-displacement curves) during cell indentation, while the compressions test results of aged electrodes show decreased stiffness (right-shifted force-displacement curves) which is similar to the stiffness behavior of the pouch cells. As aging progresses, the internal components of 18650 cells tend to fracture earlier during indentation, followed by a soft short circuit mode. A hard short circuit mode was observed at the peak force during indentation. In contrast, pouch cells, after a short circuit, demonstrate a more rapid voltage drop and release electrical energy in a shorter duration when aged. This leads to an elevated temperature throughout the entire battery cell. The changes in response for both cell types are primarily from the anode. The study confirms that low-temperature aging leads to dendrite formation on the anode, potentially causing severe short circuit or even thermal runaway. Dendrite formation is evidenced in post-mortem analysis for aged anodes of both cell types.