Maximizing thermal conductivity of EV batteries: New ORTEGOL® DA dispersing agents for highly filled thermal interface materials

In the design of state-of-the-art batteries for electric vehicles (EVs), thermal management plays a crucial role in ensuring optimal performance and longevity. During both charging and discharging cycles, battery systems are typically maintained within a narrow temperature window to maximize efficiency and extend battery life. To achieve this, standard battery configurations employ a cooling plate, onto which individual battery modules are assembled, allowing for active temperature regulation. This setup is schematically depicted in figure 1.

Figure 1: Schematical design of a state-of-the-art EV battery. 

For enhanced mechanical stability, battery modules are often adhered to the cooling plate using adhesives. Polyurethane (PU)-based adhesives are commonly utilized as thermal interface materials (TIMs) due to their favorable balance of cost and performance. In this configuration, it is essential that the adhesive exhibits high thermal conductivity, typically of at least 1.5 W/mK, to prevent it from acting as a thermal barrier and to maximize heat transfer between the battery modules and the cooling plate.

To achieve the desired high thermal conductivity, thermally conductive fillers such as aluminum trihydroxide (ATH) or aluminum oxide (Al₂O₃) are often incorporated into the adhesive formulation. Filler loadings of 80 wt.-% or more are not uncommon to meet the aforementioned thermal conductivity requirements. However, the addition of such high filler concentrations can negatively impact the viscosity and workability of the adhesive formulation. Additionally, stability issues, such as the sedimentation of the filler, may arise, posing further challenges.

In light of these challenges, there is an increasing need for dispersants that can enhance formulation properties and stability of highly filled PU-based thermal interface materials. ORTEGOL® DA 801 is a specially tailored dispersant that is ideally suited for this application. It has a high affinity for aluminum-based fillers, making it an excellent additive for formulations containing ATH and Al₂O₃. Furthermore, ORTEGOL® DA 801 is compatible with both polyols and isocyanates, providing significant flexibility during the development of PU-based adhesive formulations.

With the incorporation of ORTEGOL® DA 801, adhesive formulations can achieve filler loadings of up to 90 wt.-% while still maintaining good flowability and manageable handling characteristics. In comparison to formulations not containing dispersants, the use of ORTEGOL® DA 801 can reduce the viscosity of the adhesive system by more than an order of magnitude as depicted in figure 2. Notably, while it effectively lowers the viscosity of filled PU adhesives, ORTEGOL® DA 801 does not facilitate the settling of the filler, thereby preserving the stability of the formulation.

Figure 2: Viscosity of an ATH filled PU adhesive formulation as a function of filler loading. 

Due to their reduced viscosity, PU adhesives containing ORTEGOL® DA 801 can be more easily applied between the cooling plate and battery modules, minimizing the risk of defects in the thermal interface material, such as holes or inadequate surface coverage. Such defects can significantly reduce the effective contact area between the cooling plate and battery modules, thereby impeding heat transfer between these critical components. Therefore, it is imperative to avoid these issues to ensure optimal thermal management and the overall performance of the battery system. Next to a reduced viscosity ORTEGOL® DA 801 also helps to break down larger filler agglomerates and allows a more even distribution of the filler which as well contributes to an improve thermal conductivity.

Moreover, ORTEGOL® DA 801 is essentially free of reactive hydroxyl (OH) groups, which eliminates the risk of unwanted side reactions with isocyanates. This characteristic is of relevance, as such reactions could potentially affect the stability and shelf life of the adhesive formulation. Additionally, ORTEGOL® DA 801 does not interact with standard PU catalysts, ensuring that it has no adverse impact on the reactivity and curing behavior of PU-based adhesives. This compatibility further enhances the versatility of ORTEGOL® DA 801 in various formulations, allowing for tailored solutions that meet specific performance requirements.

In summary, the use of ORTEGOL® DA 801 in PU-based thermal interface materials not only enhances thermal conductivity but also improves formulation stability and application efficiency. By addressing the challenges associated with high filler loadings, ORTEGOL® DA 801 contributes significantly to the reliability and longevity of electric vehicle battery systems, ultimately supporting the advancement of EV technology.