Thermal behavior and performance of lithium-ion batteries at low temperatures

In this thesis, the performance and thermal behavior of a commercial lithium-ion battery were investigated experimentally at low temperatures. Identical batteries are subjected to 0.5C and 1.0C charge-discharge at three different temperature settings (25 C, 4 C and -20 C). Furthermore, an in-house 1-D electrochemical-3-D thermal coupled model was utilized to simulate the low temperature conditions along with the charge-discharge tests. Experiments conducted with a battery test system show that as the temperature decreases, the available capacity of the lithium-ion batteries decreases, and heat generation inside the battery increases. The model is able to predict battery voltage and surface temperature at room temperature. However, as the operating temperature gets lower, the discrepancy between the model and the experimental data begins to increase. At low temperatures, the electrochemical properties of the lithium-ion batteries change drastically. To capture the effects of varying temperature dependent parameters, a sensitivity analysis was performed comparing the 1C experimental discharge data at -20°C with the model predictions. The sensitivity analysis indicates that decreasing temperature has negative effect especially on the electrolyte transport properties. It is demonstrated that while changing the electrolyte diffusion coefficient, electrolyte transport number, SEI film resistance, and the specific heat capacity of the battery have the largest impact on the battery voltage and temperature predicted by the model, electrode diffusion coefficient, electrolyte ionic conduction coefficient, and reaction rate constants have less impact. Results also show that the temperature dependent characterization of the model parameters is crucial for more accurate predictions.