Mechanistic insights into the thermal runaway of cylindrical lithium-ion cells with lithium plating using high speed X-ray computed tomography

As climate change accelerates, extreme weather events are becoming increasingly common, particularly in elevated latitudes where sub-zero temperatures are more frequently experienced during winter months. These evolving environmental conditions, alongside routine cold-weather and high-altitude applications, underscore the need to understand lithium-ion battery behaviour at low temperatures to ensure that both performance and safety are maintained. In this study, high-power commercial 21700-format cylindrical cells employing LiNi x Co y Al z O 2 (NCA) cathodes were aged under controlled sub-zero temperature conditions. Charging under such low-temperature regimes diverts current away from desirable lithium-ion intercalation and instead promotes the precipitation of metallic lithium onto the negative electrode surface. Cells exhibiting significant lithium plating were found to be less thermally stable and more prone to failure at lower temperatures. Moreover, when thermal runaway was triggered, these failures occurred through more violent and less predictable pathways. To investigate the failure mechanisms, high-speed X-ray computed tomography (CT) was employed to capture the internal dynamics and nucleation behaviour associated with thermal runaway. Notably, thermal runaway consistently initiated near the core of the jelly-roll structure, where winding tension is greatest, and lithium plating is most severe. This highlights a critical architectural vulnerability in the cell design under low-temperature ageing conditions.