Experimental investigation on thermal response behaviors of lithium-ion batteries subjected to nail penetration during dynamic discharge process

The thermal response of lithium-ion batteries subjected to mechanical abuse during active discharge remains insufficiently characterized. In this work, nail penetration experiments were conducted on 25 Ah prismatic LiFePO 4 cells while the cells were under 1C discharge at 100%, 90%, 50%, and 20% SOC, with simultaneous localized internal and multi-surface temperature measurements. The embedded thermocouple recorded a localized peak temperature of 909 °C at the specified junction near the penetration region, whereas the maximum surface temperature at the same SOC was 226.0 °C, highlighting a pronounced internal-to-surface thermal gradient. Across the investigated SOC conditions, the maximum surface temperature decreased from 226.0 °C at 100% SOC to 181.7 °C, 95.5 °C, and 91.8 °C at 90%, 50%, and 20% SOC, respectively. The characteristic interval from the onset of rapid surface-temperature rise to the surface-temperature peak was 267.9 s, 312.1 s, 115.9 s, and 152.8 s, respectively, showing a non-monotonic variation among the tested conditions. Although the 50% and 20% SOC cases exhibited comparable peak surface temperatures (95.5 °C and 91.8 °C), obvious vent activation was observed only at 50% SOC, indicating that surface temperature alone is insufficient to explain the observed venting behavior. The results characterize the internal and surface thermal responses of LFP cells subjected to nail penetration during active discharge. Because each SOC condition was represented by a single test, the SOC-dependent differences are interpreted as observations under the present test conditions rather than statistically established trends.