Effects of geometric, structural and operational parameters on the thermal conductivity of lithium-ion cells

The exact determination of input parameters for battery modeling has not yet been fully explored. Due to insufficient information about measurements under parametric influence in literature, a customized test stand for precisely measuring the cross-plane thermal conductivity of lithium-ion cells is developed. For the first time, non-commercially available automotive pouch cells with different geometry and structure are tested with varying pressure, state of charge and temperature. First-ever, precise information on the chemistry and the interior structure of the cells including layer thicknesses is available allowing for comparing measurement results to an analytical simulation. Hence, this work is based on experimental data and gives an extensive guideline for battery design and simulation. It is found that the influence of pressure on the thermal conductivity converges. The thermal conductivity linearly decreases over temperature whereby a parabolic slope of the SOC-dependent curve is recorded. All analyzed cells behave similarly, though having different absolute values. Since only a sparsely populated design of experiments is realized, found parametric effects require further validation. Finally, the comparison of the measurement results to the analytical model indicate that contact resistance only plays a subordinate role. However, the exact determination of active material and separator thermal conductivity remains challenging.