How to test thermally conductive materials for EV battery ?

n their overall approach to improving the performance of electric vehicles, automotive manufacturers have focused on several related issues, in particular, power efficiency of engine control systems, fast-charging batteries for greater autonomy and vehicle weight reduction. In this presentation, we will summarize the main test methods that enable designers and carmakers to assess and test their thermally conductive materials.

Engineers need to be aware of the most adequate thermally conductive materials, as well as how to test them to assess performances. This is a mandatory step to each battery pack design for EVs, HEVs or even PHEVs. Here are some fundamental aspects battery engineers must examine: Temperature Range, Elasticity, Modulus, Mechanical Strength, Adhesion Strength, UV Resistance, Fire ResistanceDielectric Stability, Coefficient of Thermal Expansion, Volatile amount

Testing is a very critical and technical exercise that involves covering a wide range of parameters. To help designers, manufacturers, and decision-makers, Elkem Silicones recently published a comprehensive White Paper on testing methods and procedures entitled Effects of Silicone Test Methods on Thermal Conductivity Results, written by Michael Watson, R&D Senior Staff Scientist, and Jackie Nguyen, Business Development Manager.

Nb: You may wonder why this paper only focuses on silicone materials? Of course, silicone innovations and manufacturing is our core activity, at Elkem Silicones. That being said, to learn more about why you should look closer to silicone materials instead of competitive technologies, we made this eBook that explains to you how to differentiate silicones from polyurethane or epoxy.

Please take the time to read a quick summary of its scope and main testing techniques:

Heat dissipation is critical for electronics and batteries to function for their intended lifetime and to enable them to reach the desired levels of performance and reliability in EV and HEV applications throughout their intended lifecycle. Much of the industry is moving to lithium-ion batteries, requiring proper thermal management to prevent overheating during charging or discharging and ensure uniform temperature distribution, ranging between 15°C and 35°C.

Various thermal management systems (TMS) are used in EVs and HEVs, including:

  • Liquid cooling
  • Direct refrigerant cooling air cooling
  • Thermo-electric cooling.

Knowledge of thermally conductive materials and the best option to evaluate their performances is the key to determine how well these materials will perform in a specific application (nb: your battery pack design!). Thermal Interface Materials (TIMs) play a key role in the effectiveness of the TMS to ensure efficient conductivity by filling air gaps and reducing interfacial thermal resistance between the TMS and heat generation or heat insulation of electric components. A good solution supplier should work closely with end-users to determine the materials best suited for the intended application, providing expertise to control the entire value chain from silicon metals to silicone adhesives and to design and provide customized and scaled systems.

It is important to work with suppliers having full control of their technology value chain, with strong expertise and broad offer. For instance, the Elkem Silicones portfolio includes thermally conductive silicone products, with liquid (or pasty) gap fillers, low viscosity thermally conductive options (like potting materials), with varying adhesion strengths and the tests associated to these. Our teams work directly with customers to identify the testing correlations with specific test equipment and methods

As an example to measure the Thermal Conductivity, we recommend the Thermtest Hot Disk Method (TPS) using ISO/DIS 22007-2.2 test standard.technologies.

To better orient Battery Engineers on the most appropriate test method for their thermally conductive materials, we’ve been running triplicate testing on the exact same product. Surprisingly, these results show differences in thermal conductivity of 20% or higher depending on the test conditions. This highlights the need to work closely with your material supplier to determine together which test method is best suited to reflect the real condition of your application. Read more about this topic in our White Paper Effects of Silicone Test Methods on Thermal Conductivity Results, including a case study on a customer application and the different results we had depending on test methods and equipment.