How insulation film solutions facilitate the evolution of the electric vehicle industry

Generally, there are three application scenarios for battery insulation films, starting with cell wrapping, insulating end and side plates in stacks and modules, and protecting metal components in the pack.

Variations of the cell-to-pack (CTP) design are becoming more popular as manufacturers strive to increase the energy density in the pack. The CTP design gives up the module layout by integrating batteries into groups and directly integrating the cells in the battery pack. This technological innovation brings higher requirements for the insulation performance of the battery pack and other components such as fluid cooling plates. Insulation is usually enabled by two solutions – powder coating and polymer film laminating, and the mainstream film covering processes include room temperature pressure-sensitive film application and cold lamination followed by hot pressing or a secondary cure using other energy sources such as UV light.

With performance needs such as fast charging, upstream and downstream companies along the EV industry value chain have put forward many performance requirements for battery insulation film, often featuring the following six attributes – dielectric strength, high-temperature resistance, flame retardancy, adhesive strength, durability and manufacturability.

• Dielectric strength: The common specification for the dielectric strength of insulation film materials is usually around 3.7 kV AC or 4.2 kV DC. This can be delivered by films even as thin as 23 microns, although 50-micron films are easier to handle. However, some projects, especially for higher-performance systems, require dielectric strength as high as 5 kV or even 10 kV. At the same time, the materials need to preserve their insulating properties even under high temperature and humidity conditions. Electrical surface resistance such as a tracking index can also be satisfied by these films.
• High-temperature resistance: Organic polymer materials used to make insulation film can offer insulating performance at temperatures up to 400°C. However, in the event of thermal runaway, the battery temperature can rise in some areas to as high as 800°C or even 1,200°C, which presents a huge challenge to the high-temperature resistance of polymer insulation film materials.
• Flame retardancy: Combustion and even the explosion of electric vehicle batteries have always been a serious concern for consumers, battery manufacturers and automotive OEMs. More and more industry players have begun to further prioritize the flame-retardant properties of materials. Flame retardant polymer films and adhesives are available that help the components they are insulating to reach the flammability standards as described in UL 94, commonly applied to define the flammability of pack materials.
• Adhesive strength: Self-adhesive insulating films are based on similar adhesives used for many applications in automotive engineering, that have a track record of performing under typical operating conditions such as vibrations and temperature changes. Crash-resistant pack designs however increasingly call for higher shear resistance and more durable adhesive strength of film materials. Whatever the performance needs, or the substrate material, there is an optimum adhesive that can secure the insulating film.
• Durability: Although EVs, with their increasing connectivity and use of leading-edge Human-Machine Interfaces, are being described as smartphones on wheels, actually they also require much greater longevity, and usually have a product life cycle of 8-10 years. Such an "ultra-long durability" poses challenges to the wear and environmental resistance of such insulating materials.
• Manufacturability: To achieve insulation between the cooling plate and the inside of the battery pack, a large area of insulation film needs to be bonded. Bubbles or wrinkles in the bonding process will lead to reduced thermal management performance, create production waste and adversely affect the pace of production.

Through continuous technological innovation, Avery Dennison's insulation film technologies offer solutions for suppliers in the EV industry value chain to better compete in this high-growth market and effectively respond to challenges related to electrical safety.

To address the issue of high-temperature resistance, Avery Dennison's special coating solutions can significantly improve the high-temperature resistance of polymers such as polyimides. 

Regarding the flame retardancy challenge, Avery Dennison has developed special coatings and adhesives that meet the UL® 94 VTM-0 classification criteria. Avery Dennison’s coating solutions not only meet flame-retardant requirements but also withstand the 1,000-hour aging test that is twice the Chinese national standard, delivering on the "ultra-long durability" of EVs.

For adhesive strength, Avery Dennison offers various types of adhesive solutions. For example: pressure-sensitive adhesives with a shear strength of around 2 MPa,  UV-activated adhesives with a shear strength of more than 5 MPa, and heat-activated adhesives with a shear strength of more than 7 MPa. At the same time, through special treatment, Avery Dennison has successfully improved the wetting and outgassing effect of its adhesives, delivering bubble-free bonding even on complex surfaces such as sheet metal parts to ensure the manufacturability and aesthetics of relevant processes and components.

With more than 100 years of developing pressure-sensitive adhesives, coating and laminating a wide variety of films and foils, Avery Dennison can offer superior solutions for electrical insulation. Our products can be found in automobiles across the world, including in safety-critical applications like airbags, brake systems, and durable warning labels. This competence in materials science gives us the ability to support EV battery designers and engineers in finding the optimal solution.

If you need advice on identifying the best PSA for your application, then please try our Product Selector, or talk directly to an Avery Dennison specialist at andrew.christie@eu.averydennison.com.