Abstract: Since thermal property affects the performance, safety and longevity of the lithium-ion battery,
specific research is necessary. This paper conducts thermal modeling of a lithium-ion battery which is
simplified as a cuboid with anisotropic thermal conductivity. Experiments were made to get the anisotropic
thermal conductivity. Supposing that the thermal conductivity and the convection coefficient are unknown,
based on model simulation, relationship was found between the isotherms of characteristic points and the
modeling thermal parameters. By analyzing the relationship, a graphic method was proposed named three lines
concurrent to determine the thermal parameters in modeling. Using the results of the graphic method, simulation
results matches well with the experimental data. The results verify that the parallel-direction thermal conductivity
is higher than the perpendicular-direction thermal conductivity in punch type lithium-ion batteries.

Key words: lithium-ion battery, thermal modeling, anisotropic thermal conductivity, graphic method of “three lines concurrent”