Individual batteries have their own operational temperature ranges, which shall be respected to avoid both damaging of the cells and shortening of the cycle life. In terms of the Li-Ion cells, many of them do not function well above 60 °C. Therefore, a better understanding of the thermal behavior of the batteries has its significance during designing safe and robust battery packages for automotive applications.
This study dedicates to analyze the thermal behavior of a 48 V high power battery module for automobile applications and seeks smart solutions for cooling purposes. In order to suppress self-discharge and control the capacity retention of the cells, it’s one of the primary goals to maintain the temperature of all cells not only below the maximal operational temperature, but also below app. 40 °C. The other objective of this study is to minimize the differences in cell temperature aiming at minimizing the differences of the cycle life of cells within the same battery module.
Simulative thermal analysis is employed in this study to gain knowledge of the heating of cells during operational conditions and study the cooling effect of different cooling principles. The study is carried out with following steps: Construction of the battery module in software environment of COMSOL Multiphysics. The construction of the cells and definition of the load profile are derived from the technical data of a suitable candidate for automotive applications.  Thermal analysis of the ground model, in which no cooling system is involved.  Employment and comparison of different internal cooling fin (ICF) concepts.  Employment of external water cooling systems on top of the ground model with one effective ICF concept.  Utilization of ICFs and external water cooling systems in a large and densely arranged 48 V battery module.  Combination of different cooling systems – ICF and external cooling systems (liquid and air) – to seek for smart solutions.
-RESULT- The temperature distribution in the ground model is greatly uneven, which will lead to differences in cell cycle life within the same battery module in the long term and hence a shortened cycle life of the entire module.  By involving ICFs, the temperature of the cells stabilizes earlier in comparison to the ground model.  By employing one developed ICF concept, the ∆T between the hottest and coldest cell is successfully maintained below 3 K. The temperature of the hottest cell dropped to app. 40 °C at the stable state.  By involvement of external water cooling, the ∆T between the hottest and coldest cell is kept below 2 K and the temperature of the hottest cell dropped to below 37 °C at the stable stage.  The cooling effect of ICFs and external water cooling systems in the large and densely arranged 48 V battery module is not sufficient.  A smart solution – a combination of different cooling principles – is demonstrated in this study to maintain low operational temperatures for all cells and restrict ∆T between the hottest and coldest cell with in the module.
Cooling systems for the battery module shall be considered as an indispensable component in high power battery systems for automotive applications. Combined cooling systems with different cooling principles shall be involved for large battery modules, in order to achieve a homogenous temperature distribution and ensure the function of all cells.
The authors are thankful to the Ministry of Innovation, Science and Research of North Rhine-Westphalia for funding this study under the Project “ANFAHRT”.
Autor: M.Sc. Ziyi Wu
Co-Autor: Hans Kemper