Experimental measurement of anisotropic thermal conductivity of 18650 lithium battery

The accurate thermal conductivity of the 18650 cell is essential to the thermal management of the battery pack for electronic vehicles and aircrafts. The structure of the cell makes the conductivity anisotropic. Judged from the cell structure, the azimuthal and axial conductivity are approximately the same while the radial conductivity is much different from them. The axial conductivity of a cell is calculated by supplying an axial steady heat rate through the cell and measuring the axial temperature difference over the cell. For the radial conductivity, a steady heat rate is supplied on one quarter of the cylindrical outer surface of the cell, the heat crosses the cell radially and azimuthally to the opposite quarter of the cylindrical outer surface. The temperature difference of the two quarter surfaces is measured, and the radial conductivity of the cell is determined by adjusting the radial conductivity value with known azimuthal conductivity (equals to the axial conductivity) in an accurate CFD heat transfer simulation to match the measured temperature drop.