Thermal analysis and modelization of li-ion batteries used in electric and hybrid vehicles

Resumen

In the last years, the lithium-ion technology rapidly gained a lot of importance in our daily life. It allows storing energy for our cell phones, notebook, tools and also for electric or hybrid vehicles. Based on the motivation to lower the CO2 emissions many countries have set limits to the fleet emissions for every car manufacturer. For this reason more and more electrified vehicles were developed to lower the fleet emissions as optimizing the combustion engine does not provide the necessary CO2 savings. Most of these electrified vehicles use a lithium-ion battery to store the necessary energy, because nowadays only this technology covers the required properties necessary for the automotive sector: Gravimetric and volumetric energy density, power density, security and low price. To move the car with the specified performance the battery has to be capable of providing around 300V and 300A (90kW). The high power heats up the batteries. High temperatures have a big influence on the performance and ageing of the batteries. To keep the clients satisfied, the producers have to guarantee the safety, performance and life endurance requirements of the battery, because a bad reputation would decrease the motivation of potential clients to choose such car. To be able to design the cooling system for the vehicle, it is important to know how much heat the battery is generating. This PhD thesis contains a brief historical overview of electric vehicles and an explanation of how some energy storage technologies work. This work will explain how to do the electrical characterization of the cell in a fast way and how to measure the specific heat of a lithium-ion cell without possessing a calorimeter based on the electrical characterization. The core of the thesis is the modeling of a cell and cell-module of a battery for an electric vehicle with scope on their electrical and thermal model. In addition, it will show a model to simulate the use of phase-change material as passive refrigerant in batteries.