Measurements and application of thermal characteristics of soft-packed NCM lithium-ion power battery

The polarization resistance of lithium-ion batteries is the key parameter for irreversible heat testing. In order to obtain more precise results of polarization resistance, hybrid pulse power characterization (HPPC) test, entropy thermal coefficient test, and the temperature measurements of the cell in charging and discharging were carried out for a soft-packed NCM lithium-ion battery. Two methods were used to calculate the polarization resistance. One was obtained by dividing the amount of voltage change by the current, the other was identified by establishing a second-order RC model combined with the HPPC test condition. The temperature field simulation under 1C charging and 0.5C, 1C and 2C discharge was carried out by combining with Bernardi's heat generation rate model formula, and compared with the temperature distribution recorded by the infrared thermal imager. The results show that the polarization resistance obtained by second-order RC model is in good agreement with the experimental data, which indicates that the polarization resistance obtained by the second-order RC model is more suitable for the thermal analysis of the battery's continuous charge-discharge process. The model simulates well the temperature field information under different charge-discharge ratios of the battery, which plays a key role in the thermal analysis and thermal management of the battery.