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Explore the crucial role of Thermal Interface Material (TIM) in optimizing electric vehicle (EV) battery performance. Learn how TIM, including thermally conductive adhesives (TCAs) and gap fillers, helps regulate battery temperature, enhances efficiency, and prolongs lifespan. 

As the automotive industry works to increase electric vehicle (EV) options and availability, it’s important for manufacturers like you to find high-performing EV battery solutions to meet the growing demand. In particular, these batteries need to offer increasingly optimized performance, such as longer battery life, without impacting manufacturing efficiencies.

Therefore, it’s important to consider how thermal interface material (TIM) may enable high performance while allowing for efficient processes. TIM includes thermal conductive adhesives (TCAs) to address EV battery optimization needs as well as thermally conductive gap filler to protect against overheating from air gaps. Learn about TIM along with TCAs and gap filler and how they help provide the performance and efficient processes you need for effective EV batteries.

How TIM Helps EV Battery Packs

Incorporating TIM into your EV battery manufacturing is important to prolonging the overall battery life. When an EV battery is charging, discharging or in use, heat is generated inside. Lithium-ion (Li-ion) cells, which are a type of rechargeable battery commonly used for their high energy density and light weight, can degrade faster when exposed to high temperatures, resulting in a shorter lifespan. TIM conductivity, however, can transfer heat away from a battery cell to a heat sink or semiconductor device. This helps enable:

  • Battery operating temperature: When the heat is properly transferred throughout the EV battery cells, you can more easily reach the desired battery operating temperature of 86°F to 104°F (30°C to 40°C), which helps ensure stability and that the battery isn’t overheating. In particular, the battery cell temperature should never exceed 176°F (80°C), and battery charging or discharging temperatures should stay between 32°F and 140°F (0°C and 60°C).
  • Optimum battery performance: By filling air gaps and irregularities between two surfaces, such as the battery cells and a heat sink, TIM helps reduce thermal resistance and allows heat to flow more efficiently. With these imperfections filled, the TIM helps maintain a consistent temperature within the battery pack to help prevent overheating or degradation.

In order to achieve these performance features, the right TIM is comprised of both thermally conductive adhesives (TCAs) and gap filler.

How TCAs Play a Role in TIM:

TCAs help transfer heat away from a battery cell and provide electrical insulation to help prevent short circuits or overheating within the battery pack, helping extend the battery’s lifespan. As a result, they are compatible with the other materials used in battery pack assembly, such as electrode materials, current collectors and casing materials, helping to ensure that the components remain electrically isolated to reduce the risk of electrical faults. In particular, they offer:

  • Temperature resistance: TCAs can maintain performance in -40°F to 302°F (-40°C to 150°C), which allows the EV battery to operate at different temperatures for charging, discharging and operational usage.
  • Durability: TCAs protect against degradation with chemical, UV and humidity resistance. TCAs are also formulated to be compatible with metals, ceramics or plastics to prevent reactions between the adhesive and bonded materials. This helps reduce the likelihood of battery maintenance and replacement.
  • Flexibility: Some TCAs are designed to remain flexible even after curing, which helps account for expansion and contraction as battery components experience heating and cooling. Flexible TCAs have the ability to absorb the stress to reduce the likelihood of mechanical failure. However, in situations where the structural component requires stiffness, gap filling, high compression or minimal migration, a TCA with less flexibility may be preferred.
How Gap Filler Plays a Role in TIM:

In conjunction with TCAs, gap filler helps prevent air pockets to further enhance the heat transfer. Minimizing these imperfections allows the overall thermal performance to perform efficiently and extend the battery life. In particular, gap filler provides:

  • Hot spot protection: Air gaps between the battery cell and heat sink can lead to hot spots, which can damage the heat source due to inefficient heat flow. Gap filler protects the places where those hot spots would take place to help the heat flow temperatures stay consistent and avoid overheating.
  • Conformability: Using a liquid, conformable gap filler allows you to fill microscopic gaps and imperfections between the battery cells and heat sink that you may not be aware are present. Further, the gap filler enables a more uniform heat transfer by smoothing out surface irregularities.
  • Recyclability: Gap filler is removable and repositionable, helping reduce material waste if a change to the placement is needed. Further, once an EV battery is disassembled, you can remove gap filler and recycle it.

A number of technology formulations are capable of working together as TCAs and gap filler solutions to make up TIM.

For TCA bonding between the cell and cooling plate, two-part epoxy (2K EP) and two-part polyurethane 2K PUR are recommended. 

  • 2K EP TCAs are non-silicone solutions that often are chosen for high-strength bonding, with the ability to adjust the properties to your specific needs in battery design. As a low-density, non-silicone solution, they offer a variety of viscosity ranges for fast joining and automated processes. They also provide excellent chemical resistance to enhance the overall battery lifespan.
  • 2K PUR TCAs provide thermal conductivity up to 1.5 W/m.K or higher*. They are often chosen for their heat dissipation in battery pack assembly, possessing high elongation that enables elasticity for thermal expansion and contraction during heating and cooling. 2K PUR adhesives bond to substrates such as nylon, aluminum or steel and help ensure the components stay electrically isolated to help reduce electrical fault risks.

For gap filling between a module and cooling plate, 1K non-reactive or 2K silyl modified polymer (SMP) are recommended.

  • 1K non-reactive gap filler offers protection for automated processing that’s scalable for high volume production. As a non-curing, silicone-free solution, 1K gap filler offers an excellent ratio between thermal conductivity and density to help prevent air from causing hot spots. This non-hazardous, VOC-free option provides reworkability and ease of dismantling with low oil separation (~0,3%)* over the battery’s lifetime, providing long-term stability.  
  • 2K SMP gap filler provides high volume dispensing and fast compressing due to optimized viscosity levels. Further, its viscosity increases five times after 90 minutes at 95°F (35°C)*. Usable for bead applied, automated processes with applications times less than a minute, this option is silicone-free with no VOCs to reduce your environmental footprint. It provides easy processing with low compression forces.

How Bostik Can Help with 2K PUR TCAs

Bostik has designed a 2K PUR TCA specifically for heat dissipation in battery pack assemblies. Named XPUTM  TCA 202, this 2K PUR balances thermal management with high mechanical strength while maintaining flexibility, due to its high elongation properties. It provides:

  • Secure adhesion or gap filling to plastics, metals and composites; its low-monomer content helps you address the most stringent regulations without product training.
  • Room-temperature cure to reduce overall energy usage. XPUTM TCA 202 is also fast and easy to process through automatic mixing, dosing and dispensing equipment without using a primer.

Additionally, Bostik is vertically integrated to help deliver customized solutions specific to your needs, no matter where you are located.

Are you looking to enhance thermal management and other key performance levels in your EV cell-to-battery design while maintaining production efficiencies? Contact a Bostik expert to learn how 2K PUR adhesive technology can offer the capabilities you need in TCAs.

*based on internal testing

Other relevant content:

Bostik and Polytec Launch New Thermal Conductive Adhesives (TCA) Range to Accelerate Innovation in Battery Design

XPU TCA 202: 2-Part Polyurethane Thermal Conductive Adhesive

How You Can Make a More Effective EV Battery Pack

VIDEO: Thermally Conductive Adhesives for Battery Applications

XPU™ TCA 202 follows the announcement on May 17, 2023 of the planned acquisition of Polytec PT by Arkema.
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