Thermal Adhesive Materials in EV Battery Design: Trends and Engineering Considerations

Battery pack design has undergone a fundamental transformation over the last decade, and with it, the role of thermal adhesive and barrier materials has expanded. From 2010 to 2019, the dominant architecture was cell-to-module, where cells were grouped into sub-assemblies before being integrated into the pack. Since 2019, with the introduction of cell-to-pack architectures in vehicles such as Tesla’s Model 3 in China and the BYD Han, pack design has shifted toward higher integration. More recently, cell-to-body and cell-to-chassis designs have emerged, further simplifying construction by removing intermediate module structures. This trend delivers gains in energy density and cost efficiency but places greater demands on thermal and safety materials, which now often serve multiple roles simultaneously.

The drive toward higher pack voltages, faster charging, and greater energy density has created new thermal and electrical challenges. Closely packed cells operating under higher loads increase the risk of local hot spots, electrical arcing, and thermal runaway propagation. At the same time, manufacturers are under pressure to reduce the number of mechanical fixings and fasteners, relying more heavily on adhesives and films for structural integrity, vibration resistance, and safety compliance. The convergence of these demands means that adhesives are no longer secondary bonding agents, but central elements of thermal management and safety engineering. This article draws on insights from the Charged EV Engineering Conference and provides an overview of the key considerations, materials, and design strategies for thermal adhesives in modern EV battery packs.

Adhesive Performance and Material Roles

Thermal adhesives and interface materials must now perform across several axes: they must conduct heat efficiently to spread or dissipate localised hot spots, provide electrical insulation at voltages up to 800 V and beyond, and maintain mechanical durability under vibration, fatigue, and thermal cycling. Unlike traditional gap fillers, which only manage heat transfer, conductive adhesives must combine thermal performance with structural strength and compliance. Bond line thickness and squeeze-flow behaviour become critical, as even modestly conductive adhesives can achieve good thermal transfer if applied in very thin, uniform layers.

The choice between indirect and direct bonding strategies also influences adhesive requirements. In indirect designs, cells are coupled to modules using one thermal interface material, while modules are bonded to a cooling plate using another. Direct bonding, which eliminates the module, requires a single adhesive to both transfer heat to the cooling plate and secure the cell structurally. While this simplifies the pack and improves thermal performance, it raises the bar for adhesive reliability. The material must withstand not only thermal stresses but also structural loads and environmental exposure over the life of the vehicle.

Beyond adhesives, insulating films and tapes are increasingly used to prevent arcing and to isolate high-voltage components from metallic casings or cooling plates. These materials must provide dielectric strength while maintaining flexibility and tear resistance, especially around sharp edges or burrs. In parallel, barrier films and composite tapes are being engineered to manage venting events. For example, Avery Dennison has an anisotropic multilayer film that can be applied between the cells and the pack vent channel. This film degrades quickly (<4s) under the heat and flame of a venting cell, but when exposed to heat from the opposite side, it insulates neighbouring cells from flame for approximately 15s. To further increase flame resistance, a non-flammable high-temperature composite tape can be used to cover the cell vent opening on the non-cell side of the pack. These short-duration protective responses are critical for mitigating cell-to-cell propagation during failure events.

Flexible thermal materials, such as graphite sheets and aramid fibres, also play a growing role. Graphite helps spread heat across a wider surface area, improving cell temperature uniformity during fast charging, while aramid fibres provide both thermal insulation and structural separation between cells or modules. In higher-risk areas of the pack, ceramic papers, aerogels, or intumescent materials are employed to delay heat transfer and contain localised failures, buying valuable time for safety systems to respond.

As safety and performance standards tighten, adhesives and barrier materials are now designed with greater emphasis on long-term durability and compliance. Materials must retain dielectric strength under humidity and temperature cycling, maintain adhesion despite mismatched thermal expansion rates, and remain flame-retardant under prolonged exposure. They also need to align with manufacturing realities—fast cure times, compatibility with automated dispensing, and reliability in high-throughput production lines are as important as thermal or structural performance.

The direction of travel is clear: as EV manufacturers push toward higher integration, greater performance, and leaner production, thermal adhesives and barrier materials are being asked to perform more functions, often simultaneously. The next generation of packs will depend on materials that are not only thermally conductive and electrically insulating but also flame-retardant, durable, and compatible with fast, scalable assembly.

Ultimately, the engineering challenge lies in balancing these competing requirements. Thinner bond lines improve heat transfer but demand greater precision in application. Flame-retardant fillers enhance safety but may compromise conductivity or flexibility. Materials must resist vibration and fatigue without becoming too rigid to absorb mechanical stresses. Successful pack designs will emerge from careful trade-offs, validated by robust testing across thermal, electrical, and mechanical domains.

The Charged EV Engineering Conference underscored that adhesives are now integral to the safety and reliability of EV batteries, not peripheral. As architectures evolve and demands intensify, engineers must approach thermal adhesive design with the same rigour as they do for core electrical and mechanical systems. Those who can integrate multifunctional materials effectively will define the benchmark for safe, high-performance battery systems in the decade ahead.