Options for Thermal Interface Materials

What are the options for Thermal Interface Materials (TIM)?

What is TIM?

This is Thermal Interface Material and is designed to bridge the gap between surfaces and hence enable a better heat transfer.

Thermal interface materials (TIMs) can be grouped and broken down in a few different ways, primarily by their product format (how they are applied) and their base chemistry or material composition:

1. Grouping by Product Format (Delivery Method)

TIMs come in various physical forms to accommodate different manufacturing processes, gap sizes, and structural requirements:

• Pre-Cured Thermal Pads: These are solid, pre-cut compliant pads applied to one substrate and compressed to a set thickness. They are easy to handle, reworkable, and great for consistent gaps, but they require higher compressive force and can struggle to conform perfectly to microscopic surface roughness, potentially trapping air.
• Liquid-Dispensed Gap Fillers (Thermal Gels): These are cure-in-place, often two-part low-viscosity systems that flow directly into microscopic valleys and uneven surfaces under low assembly force. They eliminate air entrapment, reduce mechanical stress on fragile components, and easily accommodate variable bond lines, making them ideal for high-volume automated manufacturing.
• Thermally Conductive Adhesives (TCAs): These multi-functional materials act as a thermal interface, a structural bonding agent, and a vibration-damping layer. They are increasingly used in electric vehicle (EV) cell-to-pack architectures to replace mechanical fasteners while dissipating heat.
• Phase Change Materials (PCMs): These materials absorb and release thermal energy via latent heat capacity during a phase transition (typically melting from a solid to a liquid). They act as a passive thermal buffer, absorbing sudden temperature spikes without a notable rise in their own temperature.
• Thermal Greases and Pastes: While they provide maximum wettability and minimal thermal resistance for high-power applications, they are prone to “pump-out” (being squeezed out of the bond line due to thermal cycling and vibrations) and are messy to apply.
• Thermal Tapes: These are pressure-sensitive adhesive tapes (often silicone- or acrylic-based) that provide a quick, structural bond while transferring heat.

2. Grouping by Base Chemistry

The polymer matrix or primary base material dictates a TIM’s flexibility, operating temperature, and structural strength:

• Silicone-Based: Silicone TIMs dominate the market because they offer a broad operating temperature range (-50°C to 200°C), low modulus (which absorbs stress and dampens vibrations), and strong pump-out resistance. However, they can release outgassing volatile organic compounds (siloxanes) and oil bleeding, which can occasionally interfere with sensitive electronics.
• Epoxy-Based: Epoxies provide high modulus (stiffness) and extreme structural bonding strength, making them ideal for structural battery pack assembly. However, they are generally brittle at colder temperatures, transfer mechanical stress during thermal cycling, and are difficult to rework or disassemble.
• Polyurethane (Urethane)-Based: Urethanes offer a balanced “mid-point” between silicones and epoxies, providing elastomeric flexibility along with respectable structural strength. They are lightweight and excellent moisture barriers, though they are usually limited to operating temperatures below 130°C.
• Acrylic-Based: Acrylic elastomers provide moderate conformability and tackiness without the use of added silicones, meaning there is no risk of siloxane outgassing or oil bleeding.
• Graphite-Based: Flexible graphite materials (such as natural expanded graphite sheets or synthetic pyrolytic graphite films) are used as high-performance heat spreaders. They provide excellent in-plane thermal conductivity and can help prevent thermal propagation during a cell failure.
• Metal & Ceramic-Filled Additives: Base polymers are almost always loaded with highly thermally conductive fillers like aluminium oxide, magnesium oxide, or boron nitride to give the polymer matrix its heat-transfer capabilities. In some specialized cases, indium-based solder foils are also used.

This post has been built based on the support of and sponsorship from: illumion, Custom Power, Quarto Technical Services, Eatron Technologies and About:Energy

3. Next Generation TIM Materials

Just a thought provoker maybe to think about how Thermal Interface Materials might change, develop and what future requirements might be.

• Phase Change Materials
  • Smart and Active Phase Change Materials (PCMs): PCMs that can respond to shifting loads or ambient conditions in real time. By embedding magnetic or electrically conductive particles into the material, the heat transport behaviour of these PCMs can be actively modulated using external fields.
  • Nano-Enhanced PCMs: Designed to overcome the naturally low thermal conductivity of phase change materials, future formulations will increasingly be mixed with nanomaterials such as graphene, carbon nanotubes, expanded graphite, and metal nanoparticles. This approach can boost thermal conductivity by up to an order of magnitude while maintaining the material’s ability to absorb transient heat spikes.
• Debonding-on-Demand (DoD) Adhesives: with the industry shifting toward Cell-to-Pack (CTP) designs that directly glue cells to cooling plates, permanently bonding the battery becomes a major hurdle for repairability and recycling. Future systems will transition to DoD adhesives that are thermally or electrically triggered (often using Thermally Expandable Particles) to release their bond, allowing for non-destructive pack disassembly at the end of its life.
• Sustainable and Bio-Derived TIMs: To meet stricter environmental regulations and reduce the carbon footprint of battery supply chains, future TIMs will utilize bio-derived materials. This includes using bio-based carrier resins, bio-carbons, and recycled-content fillers like recycled graphite. Additionally, fatty acids (such as stearic and lauric acids) are being developed as biodegradable alternatives to the petroleum-based paraffins currently used in PCMs.
• Multifunctional Structural TIMs: Future TIMs are being designed to serve multiple purposes to save space and weight. For example, structural PCMs can act as load-bearing supports, acoustic insulators, and vibration dampeners while also managing heat. Some formulations are also integrating expanding flame-retardant materials; if a fire occurs, the PCM melts and the retardant expands to physically build a wall between cells, stopping the fire from spreading.
• Next-Generation Dual-Phase Dielectric Liquids: Emerging refrigerants, such as proprietary hydrofluoroolefins (HFOs), are being engineered to boil and turn into gas around 50°C to cool battery components. These future fluids act as flame suppressants, have zero ozone depletion potential, and enable holistic thermal management systems that can recycle the battery’s heat to warm the vehicle cabin.
• Materials for Solid-State Batteries (SSBs): As solid-state batteries approach commercialization, they will require a completely new category of TIMs. Unlike current lithium-ion batteries that use compliant, flexible gap fillers, the ceramic and sulfide solid electrolytes in SSBs demand extremely flat, rigid, and high-conductivity interface materials.

References

1. Calborean, A.; Máthé, L.; Bruj, O. Phase Change Materials for Thermal Management in Lithium-Ion Battery Packs: A Review. Batteries 2025, 11, 432.
2. Phase change materials, e-mobility engineering
3. Thermal Interface Material for Battery Market, DataIntelo
4. Thermally Conductive Adhesives (TCAs) for EV Battery Packs: A Technical Guide for Design Engineers, GLUESPEC
5. Liu Y, Yang Z, Huang X and Tan J (2026) A review of cell-to-body (CTB) battery-structure integration design for electric vehicles. Front. Mech. Eng.