Thermal Impedance Spectroscopy - A method for the thermal characterization of high power battery cells

A new approach of Thermal Impedance Spectroscopy (TIS) is introduced for thermal characterization of battery cells. It examines the transfer behavior between internal heat generation and resulting battery surface temperature in the frequency domain. Compared to previously published TIS methods the internal heat generation forced by electrical operation can be determined without any previous knowledge or assumptions on the electric/electrochemical behavior of the battery cell. The complete procedure is demonstrated by the TIS-application on a cylindrical High-Power Li-Ion cell. By the use of a thermal battery model, its theoretical transfer function can be fitted to the TIS-measurement results in the Nyquist-Plot. Consequently, the specific heat capacity and the heat conductivity of the cell's jelly roll can be derived. A comparison of the exemplary operated TIS to conventional thermal characterization methods shows a difference of 5% in the heat capacity and 12% in the heat conductivity determination. Future improvements on the experimental setup are suggested in order to reach a higher measurement accuracy and additionally, the systematic advantages of the easy to operate and non-destructive TIS-method are presented. ► Thermal Impedance Spectroscopy is used for thermal characterization of battery cells. ► Transfer function of thermal battery model is developed and fitted to TIS results. ► Heat capacity and radial heat conductivity of cylindrical Li-ion cell are determined. ► Results of TIS and of conventional thermal characterization verifies the TIS.