Assessing influencing factors on a passive cooling system for a Li-ion battery cell by employing the RSM methodology

This study numerically investigates the passive cooling system consisting of a compressed expanded graphite matrix combined with a phase change material (EGPCM) for a single Li-ion battery cell. The key parameters, thickness of the EGPCM (t), the bulk density of the expanded graphite matrix (BD), and the convective heat transfer coefficient (h), were examined to reveal their impact on the cooling system performance. The system responses were defined as cell temperature, liquid fraction, and the phase transition point from solid to liquid. The response surface methodology (RSM),in combination with computational fluid dynamics (CFD), was employed to determine the relationships among these factors and responses under discharge currents, 6 A, 8A, and 10 A. The results indicate that factor t is the most influential factor on the responses at each discharge current, significantly reducing both cell temperature and liquid fraction while increasing the transition point of phase change. The effects of h are also remarkable on the responses at 6A and 8A for all responses, but its effect on cell temperature disappeared at 10 A. Finally, BD exhibited the weakest impact and was statistically significant for the cell temperature at 8A and 10A. Within the considered ranges of the factors, the cell temperature remained below 313.15 K at 6 A and 8A, even with a 3 mm thickness. However, a higher temperature of 321.06 K was obtained at 10A with t=4 mm, BD= 0.25 g/cm 3 , and h= 6 W/m 2 K,because complete melting occurred before the end of the discharge period. Therefore, the cooling system should employ at least 4 mm thickness, BD below 0.25 g/cm 3 , and a h greater than 6 W/m 2 to avoid a high temperature rise, even with a 10 A discharge current.