Abstract: Power-battery safety performance is a key factor in electric vehicle applications. The inner shortcircuit
is a root cause of battery safety issues, which is usually simulated by nail-penetration tests in the
mechanical abuse tests. This paper studies the influence of nail-penetration speeds on the power battery
safety performance. Two types of lithium iron phosphate (LFP) ion batteries, cylindrical cells and soft-package
cells, were tested referring the standard of "Lithium-Ion Batteries for Electric Vehicle" for vehicle industries in
China. The nail-penetration tests were conducted at different nail-penetration speeds for nails, which can bear
high-temperature, with a diameter of 3 mm. The cell voltage and the surface temperature were monitored and
analyzed to reflect the influence of different nail speeds on the safety performance. The results show that the
nail-penetration speeds have low impact on the cylindrical cells compared with that on the soft-package cells.
As for the soft-package cells, the thermal run away becomes more serious with increasing nail speeds.

Key words: electrical vehicle, safety performance, power battery, internal short circuit, nail speed