Effect of low-temperature aging on the safety performance of lithium-ion pouch cells under mechanical abuse condition: A comprehensive experimental investigation

Understanding how aging affects the safety performance of lithium-ion batteries under mechanical abuse is of great importance. In this study, pouch cell batteries with four different aging levels (0%, 10%, 20% and 30% capacity fading), which respectively represent fresh, prior-scrapped, normally scrapped and over-scrapped batteries, are prepared at 0 °C and subjected to indentation loading. Mechanical-electrical-thermal responses of these batteries are compared. Results show that aged pouch cells have right-shifted force-displacement curves, higher inflection force and higher peak force. After short circuit, voltage dropping is faster and electric energy is released in a shorter duration for aged ones, leading to a higher temperature for the whole battery cell. For cells with 30% capacity fading, the voltage dropping and temperature increasing are in a steep behavior. And the generated heat after short circuit is concentrated in the indented area, resulting a localized peak temperature of 117∘C. To clarify the observations, mechanical tests in the component level are carried out. Results reveal that the response changes in cell tests are mainly from the anode. Compression test of aged anode electrode shows consistent mechanical response changes with cell test. The delay of anode fracture under compression loading lead to the enlargement of the shear fracture zone, together with the formation of sharp lithium dendrite, resulting in more severe short circuit.