Comprehensive Analysis of Battery Thermal Management Systems: A CFD Study on Li-ion Cells with Varied Cathode Materials in 21700 Formats under Normal and Failure Operations

Abstract

This thesis presents a comprehensive analysis of battery thermal management systems using Computational Fluid Dynamics (CFD) simulations. The study focuses on lithium-ion cells with various cathode materials in the 21700 format. Which are cylindrical cells measuring 21 mm in diameter and 70 mm in height. The thermal behaviour of these cells is investigated under normal operation and fault conditions. The primary objective is to assess the effectiveness of different cooling technologies, including immersion cooling, sidewall cooling, and bottom plate cooling, in maintaining thermal stability and preventing thermal runaway. Thermal runaway describes a chain reaction within lithium-ion cells in which the temperature rises uncontrollably and exponentially. The methodology involves CAD modeling, meshing, and validation against experimental and existing simulation data, followed by parametric studies and transient simulations under various operating conditions. Results from the parametric studies indicate that temperature distribution in immersionand sidewall-cooled systems is very uniform at both module and cell levels. Conversely, bottom plate cooling demonstrates significantly poorer temperature distribution at the cell level, which negatively impacts cell aging. Further transient simulations reveal that sidewall cooling exhibits the best thermal performance regarding temperature evolution at the module level. Immersion cooling achieves slightly less efficient performance, whereas bottom plate cooling consistently shows the lowest effectiveness in heat dissipation or heat transfer. Under fault conditions, simulations demonstrate that sidewall and immersion cooling effectively limit the propagation of thermal runaway within the module. In contrast, thermal runaway propagates through the entire module in the case of bottom plate cooling. Based on these findings, bottom plate cooling is not recommended due to its inferior temperature distribution, lower performance, and reduced safety. However, when selecting a cooling system for battery powered systems, additional parameters such as overall system geometry, costs, and other application-specific factors should also be considered.

Date of Award	2025
Original language	English
Supervisor	Georg Aichinger (Supervisor)