Thermal adhesives ensure electric vehicle (EV) systems operate safely and efficiently by maintaining thermal conductivity and mechanical stability. This article discusses thermal adhesives’ important role in key EV components such as lithium-ion (Li-ion) battery traction packs, highlighting their placement in crucial locations and reviewing various design implementations. It also explores how thermal adhesives prevent additional EV systems, including electric motors and regenerative braking, from overheating.
The importance of thermal conductivity
Conventional adhesives typically provide ~0.3 watts per meter Kelvin (W/m.K) thermal conductivity. Specialized thermal adhesives, however, achieve 1 W/m.K to 5 W/m.K (and even higher for specific applications), facilitating efficient heat transfer from battery cells to cooling loops, heat sinks, and exchangers.
These adhesives are available in various forms, including liquids, pastes, gels, tapes, and pads. Although manufacturers use many different types of thermal adhesives, solutions based on silicone, epoxy, acrylic, and polyurethane are particularly common in EV batteries (Figure 1).
Figure 1. An expanded view of an EV battery module, illustrating the cooling system, battery cells, and thermal adhesives. (Image: DeepMaterial Technologies)
Silicone, for example, withstands high temperatures, providing reliable thermal conductivity and flexible bonds to accommodate expanding and contracting battery pack components. Epoxy offers solid bonding and high levels of thermal conductivity. It’s a popular choice for EV battery applications that necessitate durable, heat-resistant connections to maintain structural integrity and implement effective thermal management.
With faster curing times than epoxies, acrylics support adhesive EV battery use cases requiring quick assembly and an optimal balance of mechanical strength and thermal conductivity. Known for its durability and flexibility, polyurethane reliably maintains bonding during thermal cycling, protecting sensitive battery electronics and interfaces.
Notably, thermal adhesives significantly contribute to battery packs’ structural integrity, sealing, and dielectric isolation, which are continuously exposed to vibrations, shocks, and other mechanical stresses. They firmly bond battery cells, preventing movement, misalignment, and excessive thermal expansion that could lead to physical degradation, permanent damage, and even fires.
From battery cell casings to enclosures
Manufacturers strategically apply thermal adhesives to critical areas within li-ion battery traction packs, including:
- Cell casings: Placed between battery cells, thermal adhesives ensure optimal thermal contact and heat distribution. They also bolster structural integrity by creating a robust bond and uniformly distributing mechanical stress across the vehicle floor.
- Cooling plates: Crucial for heat transfer and dissipation, thermal adhesives facilitate bonding battery modules — or individual cells — to cooling plates. They also improve thermal interface contact between various components.
- Enclosures: Thermal adhesives establish strong, secure bonds to withstand mechanical stress and harsh environmental conditions. Additionally, they provide a moisture-resistant seal for EV batteries, shielding sensitive electronic components from humidity and temperature fluctuations.
- Ancillary components: Thermal adhesives secure EV battery heat spreaders, thermal pads, and sensors — providing conductivity and an insular layer between components.
Bolstering thermal dissipation and structural resilience
Thermal adhesives are essential in various EV battery designs, such as cell-module-pack (CMP), cell-to-pack (CTP), and cell-to-chassis (CTC). In CMP configurations, battery cells are grouped and integrated with thermal adhesives and other materials to form modules that efficiently transfer heat to cooling plates. Applied within (and between) battery cells and module housing, these adhesives significantly improve thermal dissipation and bolster structural resilience.
CTP designs use thermal adhesives to bond battery cells to cooling plates, simplifying Li-ion traction pack assembly and bolstering energy density while ensuring optimal thermal management. Lastly, CTC implementations (Figure 2) bond battery cells directly to the vehicle chassis with thermal adhesives, minimizing component count, weight, and cost while improving thermal efficiency and structural rigidity.
Figure 2. A depiction of a CTC configuration, with individual battery cells directly integrated into the EV chassis for enhanced structural support and thermal efficiency. (Image: BatteryTechOnline)
The chemical composition of EV thermal adhesives
Several types of thermal adhesives are applied throughout EVs. Epoxy-based thermal adhesives, for example, bind critical EV motor components such as magnets to rotors and stators, reducing eddy currents and minimizing efficiency losses.
Silicone-based thermal adhesives help maintain optimal operating temperatures and signal integrity in power electronics with efficient insulation and high heat conductivity. Polyurethane-based thermal adhesives, providing elasticity and durability, absorb vibrations and resist wear in panels and suspension systems.
Acrylic-based thermal adhesives create strong bonds for advanced driver-assistance systems (ADAS) sensors, connectors, thermal pads, and electronic control units (ECUs). They’re also crucial in systems such as powertrain, drivetrain, and regenerative braking. In powertrain and drivetrain systems, acrylic-based thermal adhesives facilitate heat dissipation while ensuring components securely bond — reducing the risk of misalignment and mechanical failure under high stress.
Similarly, these adhesives protect sensitive regenerative braking system components, including sensors and electronic circuits, maintaining an optimal temperature range during high-heat energy recapture.
Acrylic thermal adhesives effectively boost heat conduction between surfaces. They’re applied in EV thermal management systems (TMS), heating, ventilation, air conditioning (HVAC) units, onboard chargers, and dc-to-dc converters. Establishing a reliable bond, these adhesives resist extreme temperature cycles and help prevent short circuits with their inherent electrical insulation properties.
Evolving chemical formulas
Automotive and battery manufacturers continue to improve existing thermal adhesives and develop new chemical formulas. DuPont, in collaboration with Audi, recently debuted a new polyurethane thermal adhesive for Audi’s e-tron SUV. Facilitating efficient bidirectional heat transfer between the battery and heat sink, the thermal adhesive maintains an optimal battery temperature of 77° F (25° C) even during rapid 150-kW charging.
Meanwhile, Permabond’s two-component adhesive (Figure 3) forms a foamy structure that fills all spaces within battery packs. Producing a dense, conductive layer, this thermal adhesive effectively channels heat to cooling plates. In addition to minimizing the risk of thermal runaway, the two-component adhesive simplifies disassembly and increases recyclability.
Figure 3. A cross-section illustration of an EV battery module, showcasing Permabond’s lightweight expanding foam adhesive filling the gaps between battery cells and cooling plates. (Image: e-Motec)
Conclusion
Thermal adhesives help EVs operate safely and efficiently by maintaining thermal conductivity and mechanical stability in key vehicle systems. These adhesives are available in various forms, from liquids, pastes and gels to tapes and pads. Thermal adhesive solutions based on silicone, epoxy, acrylic, and polyurethane are particularly common in EV batteries and other crucial components, such as electric motors, powertrain, drivetrain, and TMS.
References
- Why Adhesives Technology for EV Batteries Matters More Than Ever, BatteryTechOnline
- Top Thermally Conductive Adhesives for Battery Packs, C-Therm
- Seven Ways Adhesives Push EV Design Forward, DuPont
- EV Battery Module Adhesives: Everything You Need to Know, LaserAX
- A Technological Breakthrough in Battery Bonding & Thermal Management, e-Motec
- Adhesives & Sealants in Battery & Hybrid Electric Vehicles, e-Motec
- EV Thermal Management: How Adhesives Play a Crucial Role, Permabond
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