Experimental Characterization of Li-ion Battery cells for Thermal Management in Heavy Duty Hybrid Applications

Abstract

The performance and lifetime of lithium ion (Li-ion) batteries are highly dependent on the internal operating temperature which makes thermal characterization of battery cells necessary. Therefore, the main focus of this thesis work was to characterize pouch and prismatic Li-ion cells by designing and conducting experiments to measure thermal parameters. The specific heat capacity was quantified as well as the heat conductivity in three dimensions. In addition, the heat generation from the cells was measured for different load cycles. Subsequently, the determined thermal parameters were inputs in a simulation model to determine the internal peak temperature of the cell during different load cycles. The experiments were carried out by using a custom-designed isothermal heat conduction calorimeter (IHC). This calorimeter was modified for measurement of individual thermal parameters. The modified setup was verified using available sample materials and subsequently applied for measurements on the Li-ion cells. The heat generated within the cells was measured for constant current rates and a dynamic operation cycle. The through-plane thermal conductivity for the provided pouch cell was measured to be lower than the in-plane (0.7Wm−1 K−1 compared to 20-30Wm−1 K−1). In addition, the specific heat capacity was measured to be 1100 J kg−1 K−1 for a pouch cell and a prismatic cell. Lastly, the heat generated by the cells was measured between 10mW to 30W. To conclude, the heat generation and specific heat capacity was measured successfully for both the pouch and prismatic Li-ion cell. The methods for thermal conductivity in through-plane and in-plane were utilized for the pouch cell. However, the proposed methods for thermal conductivities were found to be inapplicable for prismatic cells due to the conduction through the aluminum casing. Nevertheless, this opens up opportunities within the thermal characterization of Li-ion batteries.