Thermal Property Measurements of a Large Prismatic Lithium-ion Battery for Electric Vehicles

Because of the high cost of measuring the specific heat capacity and the difficulty in measuring the thermal conductivity of prismatic lithium-ion batteries, two devices with a sandwiched core of the sample-electric heating film-sample were designed and developed to measure the thermal properties of the batteries based on Fourier's thermal equation. Similar to electrical circuit modeling, two equivalent thermal circuits were constructed to model the heat loss of the self-made devices, one thermal-resistance steady circuit for the purpose of measuring the thermal conductivity, the other thermal-resistance-capacitance dynamic circuit for the purpose of measuring the specific heat capacity. Using the analytic method and recursive least squares, the lumped model parameters of these two thermal circuits were extracted to estimate the heat loss and correct the measured values of the self-made devices. Compared to the standard values of the reference samples of the glass and steel plates, the measured values were corrected to improve the measurement accuracies beyond 95% through steady thermal-circuit modeling. Compared to the measured value of the specific heat capacity of the battery sample at 50% state of charge using the calorimeter, the measured value using the self-made device was corrected in order to elevate the measurement accuracy by about 90% through dynamic thermal-circuit modeling. As verified through the experiments, it was reliable, convenient, and low cost for the proposed methodology to measure the thermal properties of prismatic lithium-ion batteries.