Understanding the influence mechanisms of packaging form on the overcharge failure process of lithium-ion batteries

Overcharge is a common electrical abuse scenario for lithium-ion batteries and may potentially give rise to devastating consequences such as thermal runaway. Here, several in-situ techniques are employed to investigate the overcharge-induced failure mechanisms of three lithium-ion cells with different packaging forms (pouch, cylindrical, and prismatic). The overcharge and thermal behaviors throughout the entire overcharge process are briefly compared and analyzed; the state of charge (SoC) at the onset of thermal runaway and the corresponding overcharge safety limit SoC are determined. Further, the overcharge-induced degradation mechanisms and modes of the three cells at different terminal SoCs are analyzed and compared through incremental capacity analysis (ICA) and electrochemical impedance spectroscopy (EIS) results. Generally, their overcharge tolerances follow this order: cylindrical > pouch > prismatic. Under overcharge conditions, with respect to prismatic cells, the loss of active material (LAM) and the loss of lithium inventory (LLI) modes dominate the aging, whereas in cylindrical and pouch cells, the LLI and the loss of conductivity (LoC) are dominant degradation modes in the cell aging. Moreover, combined with the 3D x-ray computed tomography (XCT) results, the reasons for the distinct overcharge tolerances and failure mechanisms of cells with different packaging forms are elucidated from three perspectives: shell structure, exhaust mechanism, and heat dissipation mechanism. This paper provides deeper insights into how packaging forms affect the overcharge tolerance of lithium-ion batteries and offers key guidance for their safety design.