The present research aims to experimentally evaluate the safety behavior and failure mechanism of 18650 cylindrical lithium-ion battery cells under dynamic impact loading. To this end, a pneumatic impact testing apparatus was developed in accordance with the SAE J2464 standard to assess the simultaneous effects of initial temperature (25, 0, and -25 °C), state of charge (10% and 100%), and state of health (fresh and aged over 400 cycles). Experimental results derived from high-speed imaging and thermal data analysis indicated that at ambient temperature, impact with a critical velocity of 9.23 m/s on fully charged samples led to immediate separator rupture and extensive internal short circuit. Under these conditions, the cell voltage dropped to zero within 290 ms, and explosive thermal runaway occurred with a severe temperature rise reaching 662 °C. In contrast, the most significant finding of this study reveals a substantial enhancement in the cell's mechanical resistance at sub-zero temperatures; remarkably, at -25 °C, no penetration or exothermic reaction was recorded even at high impact velocities. Further analysis suggests that the partial solidification and increased viscosity of the electrolyte at low temperatures act as an internal support with quasi-solid behavior, thereby preventing local stress concentration and separator tearing.