Thermal runaway behavior of ternary lithium-ion pouch cell characterized by multi-parameters under penetration

With the rapid development of new energy vehicles, the safety issues of pouch-type lithium-ion batteries have attracted increasing attention. In this study, a 10 Ah pouch-type lithium-ion battery used in vehicles is taken as the research object. Experimental setups are designed to investigate the thermal runaway behavior under different penetration speeds, characterized by multiple parameters including voltage, temperature, gas expansion, and internal resistance. Results reveal four possible scenarios during needle puncture, with the existence of a critical penetration speed range 10-20 mm/s capable of rapidly triggering thermal runaway. Voltage variations exhibit three distinct forms, wherein higher puncture speeds corresponded to greater initial voltage drop rates and larger magnitudes, especially with the voltage dropped to 1809.15 mV in 5.62 s at 40 mm/s. Additionally, at slower puncture speeds, battery rupture location has a significant influence on the voltage drop trend, producing a deviation of about 10 s in the time of voltage plunge when the side rupture and top rupture occurred at 1 mm/s. The penetration speeds and the portions of the steel needle inside the battery being covered by elongated separator affects numbers of battery cells short-circuited within the same timeframe, altering heat generation and heat diffusion. Gas expansion during thermal runaway follows a three-stage process. The onset of expansion closely aligns with the time of the sharp voltage drop with a difference of less than 1 s, while the time difference between the sharp voltage drop and the peak gas expansion decreases with increasing penetration speed, from 4.75 s to 0.94 s. The internal resistance of the battery exhibits a consistent pattern of initial increase followed by decrease during needle puncture. These findings hold significant implications for safety design and parameter warning of pouch-type lithium-ion batteries in vehicles.