Estimating Thermal Parameters of Large-Format Laminated Lithium-Ion Batteries Using Thermal Impedance Spectroscopy

The accuracy of battery thermal parameters is crucial to the accuracy of thermal simulations for batteries. Given the structural characteristics of the large-format laminated lithium-ion battery [1], effective methods to determine multiple thermal parameters, such as the thermal conductivity and the specific heat capacity, should be developed to achieve better prediction of battery thermal behaviors.

Generally, the methods for measuring the thermal parameters of batteries can be divided into two categories, the time-domain method and the frequency-domain method. The authors developed a joint computational and experimental time-domain method to estimate the multiple thermal parameters for a 25 Ah laminated lithium-ion battery both in-situ and simultaneously [1]. However, the battery temperature changed from 25 to 35°C in the experiment, hence the estimated thermal parameters were the average properties over 25~35°C. In contrast, the change in the temperature of the sample can be greatly reduced in the frequency-domain method, making it possible to obtain the thermal parameters at different temperatures.

In this work, a frequency-domain method, the thermal impedance spectroscopy (TIS) method is used to simultaneously and in-situ determine two thermal parameters, i.e. thermal conductivity and specific heat capacity, for the large-format laminated lithium-ion battery.

In the experiment, a planar electric heater is sandwiched between two identical batteries (25 Ah, 250 mm × 220 mm × 7.2 mm，NMC-LMO/Graphite), as shown in Fig. 1(a). The electric power for the heater is adujusted at different frequencies (0.1, 0.2, 0.4, 0.6, 0.8 and 1 mHz) and the temperature response on one outer surface is recorded with the attached thermocouple. The entire set-up is placed in an environment chamber.

The heat transfer behavior between the heating power and the temperature response is examined in the frequency domain. An equivalent thermal circuit including thermal capacity and resistance is introduced to derive the analytical expression of thermal impedance, as shown in Fig. 1(b). The thermal circuit is simplified from the 1D heat conduction model, which also takes the covering aluminum-plastic film into account. The thermal conductivity and capacity of the battery core are estimated using the least-square fitting algorithm. The experimental and fitted thermal impedance are shown in Fig. 1(c).

The estimated parameters are validated against the results from the accelerating rate calorimeter (ARC), the heat flow calorimeter (HFC) and the joint computational and experimental time-domain method [1].

 

Reference

[1] Zhang J, Wu B, Li Z, et al. Simultaneous Estimation of Multiple Thermal Parameters of Large-Format Laminated Lithium-Ion Batteries[C]//Vehicle Power and Propulsion Conference (VPPC), 2013 IEEE. IEEE, 2013.