Safe or Slow? The Illusion of Thermal Stability Under Reduced-Velocity Nail Intrusion

Abstract

This study investigates the effects of nail penetration speed on the safety outcomes of large-format automotive lithium-ion pouch cells. Through six controlled tests varying the speed of nail insertion, we observed that lower penetration speeds did not induce thermal runaway; instead, the cells exhibited self-discharge while the nail remained embedded. These findings suggest that penetration speed is a critical factor in the onset of thermal runaway, providing valuable insights for the development of safer battery systems and more effective safety testing protocols.

Figures (18)

• Figure 1: Test setup showing the SH mounted on the NPA inside the reactor. The reactor is open in the render picture.
• Figure 2: TC positions on the cell surface (red dots) and schematic of the stacked setup inside the casket.
• Figure 3: Drawings of different nail formats. Long nail was used in the test series.
• Figure 4: Cell before test.
• Figure 5: Picture of the cell inside the SH. TCs are fixated on the cell by placing them inside a steel comb. Cell terminals are elongated with copper sheets to feed through the stacked SH.