Simplified Thermal Modeling of a Lithium‐Ion Cell Considering Ambient Temperature Variations in a Closed Environment

ABSTRACT This study presents a simplified thermal model to analyze the surface temperature variation of a 2.5 Ah 18650 lithium‐ion cell under different ambient temperatures and discharge currents (5 and 10 A), considering both open and closed environments. Experimental simulations reveal that in open environments, ambient temperature changes measured at a distance of 1 m have a negligible effect on cell surface temperature, with deviations below 0.11%. However, in closed environments with measurements taken just 3 mm from the cell, the surface temperature rises significantly by approximately 8.75 K at 5 A and 15.75 K at 10 A, indicating restricted heat dissipation and increased thermal buildup. These findings confirm that higher discharge currents and enclosed conditions exacerbate cell heating, posing a risk of thermal runaway, as evidenced by the exponential rise in temperature near critical points. Incorporating ambient temperature variation into the thermal model provides a more accurate representation of real‐world operating conditions, especially within battery enclosures where thermal management is challenging.