Research On Heat Generation And The Thermal Management Of The Lithium-ion Battery

Lithium batteries, due to its advantages, are widely used in electronics, electric vehicles. In the practical application, the working temperature of battery not only affects the safety of the battery, and seriously affects the life of the battery, such as aging, the utilization rate of energy performance. In order to carry out on the battery thermal management effectively, three ways: the experiment test, simulation and analytic calculation,are combined to study the heat production distribution and the thermal management of the battery. The main contents and conclusions are as follows:1.Heat Generation AnalysisBased on Manganese Acid lithium battery, a one-dimensional batteries model is established using COMSOL software, which is used to calculate the heat production rate of batteries. The heat generation of tabs and collectors are calculated by the analytic calculation. A new analytical method is used to calculate the heat production rate in different positions of the collectors. Then, the heat generation of the tabs, collectors and the battery unit are imported into the thermal model which is used to calculate the temperature distribution of the battery. The experiment test was carried out to verify the accuracy of the model. Both the model and the analytical method to calculate the heat production are reasonable and accurate.Based on this model, this thesis analyzed the heat production rate at different positions of electrolytes, positive electrode and negative electrode. The results show that the heat production rate of the negative electrode is greater than the positive electrode, and the highest heat production rate locate in the surface between the negative electrode and the electrolyte.In addition, this paper analyzed the influence of the reversible reaction heat and the irreversible ohm heat to the total heat generation of battery unit at different discharge rate. The results show that the reversible heat accounts for the proportion of the total heat is greater than the ohm heat at the small discharge rate. And with the increase of discharge ratio, both the reversible heat and the ohm heat grow quickly, but the increase of the ohm heat amplitude is greater than the reversible heat, eventually led to the ohm heat in the proportion of the total heat larger than the reversible heat.2.Thermal Management The battery thermal management is divided into two parts. In the first part, this thesis study the structure of the battery itself, tab positions, size and length of cells, to the influence of the temperature of the battery. The results of six tab configurations show that the tabs placed on both sides of the battery is good for reducing temperature gradient, it is not helpful in lowering maximum temperature. When the two tabs are not aligned, the maximum temperature would be lower. And more wide of tabs, more conducive to reducing the highest temperature of the battery.This thesis studies the influence of length and thickness of battery to the temperature of the battery cell. Results show that the thickness unchanged, increase cell width and height, can effectively reduce the highest temperature of the battery, but will increase the local temperature difference. And the battery area unchanged, increase the thickness to add capacity, can effectively reduce the temperature of the battery, but increasing the average temperature of the battery. When both expand the width and thickness of the battery, can not only reduce the maximum temperature of the battery, but also can reduce the local temperature of the battery.The second part is the use of external thermal management cooling process. Large-capacity lithium manganese battery and the battery pack are cooled by air-cooling, phase change cooling and the combination of the two.The results showed that:(1) the air-cooling which increase heat transfer coefficient, can effectively reduce the average temperature of the battery. But it is not very useful to reduce the local temperature difference. What’s more, if the number of cooling channels is relatively small, it will increase the local temperature difference.(2) The phase change heat dissipation can also reduce and the temperature difference and the average temperature of the battery. However, if the amount of phase change materials is not enough, which causing it to melt. Between the phase change material starts to melt and completely melted, the local temperature difference of batteries will increase rapidly, while the average temperature of the battery will be kept within the range of the phase transition temperature. However, the average temperature of the battery continues to rise after the phase change material completely melted.(3) It is more useful to cool batteries by the combination of the air cooling and the phase change cooling, which is better than the single air-cooling or the single cooing by phase change materials.