Skalenübergreifende Modellierung und Simulation des thermischen Verhaltens einer Lithium-Ionen-Batterie

Kurzfassung

With the rapid development of high-power lithium-ion cells, there are growing demands for the safety of lithium-ion batteries. Heat generation in the cells is one of the key aspects responsible for thermal risks. In this study, a one-dimensional, thermal model is developed to calculate heat generation and heat transport mechanisms in the radial coordinate of cylindrical lithium iron phosphate cell. This model is based on an electrochemical multi-scale approach and was implemented in the in-house simulation environment DENIS. The transient, thermal model couples macroscopic phenomena such as heat conduction with processes of microscopic nature, which are responsible for heat production in the cell. Furthermore, the multi-scale model includes charge, mass and energy conservation of the battery. The transport and reaction mechanisms are considered as temperature dependent. Model reduction is modeled with physically-based assumptions that allow to reduce a three-dimensional battery geometry into one-dimensional quasi-homogeneous solid with eective thermal parameters. The key idea of the thermal model is the separation of heat conduction and heat production into two separate scales which eectively couples electrochemistry and thermal management. This methodology allows dierent ne discretizations for thermal conductivity and heat source terms. Results show, that computation time is dramatically saved without signicantly reducing the solution accuracy. Therefore only 5 instead of 72 electrochemical repeat units are required for heat source calculation compared to the experimental cell. By means of the model, the electrochemical and thermal behavior of a lithium-iron-phosphate cell is studied for various C-rates and ambient temperatures. In addition, important information in reference to the time progress of the temperature and the discharge/charge curves are derived from the analysis of local temperature gradients. It was found that the local temperature rise and the irreversible heat production increases with increasing C-rates and decreasing temperature. Inverse behavior applies to low C-rates and high temperatures. In this case the electrochemical reactions and the species transport in the electrolyte are improved and therefore the irreversible and joule heat sources are distinctly lower compared to the reversible thermodynamic heat.