Aerogel Film, CCS Hot Pressing Film & PI Film: EV Battery Materials Guide

A lithium-ion battery pack contains thousands of individual cells, a web of electrical connections, and layers of insulation—all compressed into a space where weight, thickness, and thermal behavior are measured in fractions of a millimeter. When one cell undergoes thermal runaway, the difference between a contained failure and a cascading fire often comes down to whether the right material is sitting between that cell and its neighbors. When the CCS module fails to hold its laminated layers together under vibration, voltage monitoring goes dark. When the PI substrate in a flexible circuit delaminates under soldering heat, the entire battery management system loses a signal channel.

Three categories of specialty film address these three failure modes: aerogel flame retardant packaging film, CCS hot pressing film, and PI thermosetting film. Each solves a distinct engineering problem, and each is specified differently. This guide covers all three in a single framework, with the technical parameters and procurement considerations that matter most to battery pack engineers and materials buyers.

The Three Material Challenges in a Modern EV Battery Pack

Battery pack design has converged on three persistent material challenges that no single solution resolves.

The first is thermal containment. Lithium-ion cells store significant energy in a chemically unstable state. Under abuse conditions—overcharge, internal short circuit, mechanical damage—cells can enter thermal runaway, generating temperatures that exceed 700°C at the vent. If the adjacent cell absorbs enough heat to trigger its own runaway, the failure propagates through the module. The industry standard for acceptable safety is a minimum delay of several minutes before propagation reaches a neighboring cell, giving vehicle occupants time to exit. Traditional foam and fiber insulation materials do not reliably achieve this at the thicknesses that pack designers can accommodate.

The second is electrical connection integrity. The Cell Contact System (CCS) module replaces the wiring harness in modern battery packs, integrating voltage sensing, temperature monitoring, and high-current busbars into a single laminated assembly that sits directly on top of the cell array. This assembly is produced by hot-pressing multiple layers—FPC, insulating film, and copper or aluminum busbars—into a rigid, compact module. The insulating film used in this hot-press process must bond reliably under heat and pressure, resist delamination over thousands of thermal cycles, and maintain electrical isolation between adjacent busbars at the operating voltage of the pack.

The third is flexible circuit durability. The FPC within the CCS, and elsewhere in the battery management system, is built on a substrate film that must survive both the manufacturing process—including reflow soldering temperatures above 260°C—and the service environment of a vehicle: vibration, thermal cycling from −40°C to over 100°C, and chemical exposure. Polyimide (PI) thermosetting film is the substrate of choice for these requirements, but its performance depends heavily on the curing chemistry and the bonding interface with the copper foil.

Aerogel Flame Retardant Packaging Film: Thermal Barrier at the Cell Level

Aerogel is among the most thermally insulating solid materials known, with bulk thermal conductivity values of 0.013–0.018 W/(m·K) at room temperature—roughly five to eight times lower than conventional polyurethane foam. This performance comes from the material's nanoporous structure, in which air is trapped in pores small enough to suppress gaseous heat conduction. The challenge for battery applications has historically been that bulk aerogel blankets and panels are thick, fragile, and difficult to integrate into high-precision laminated assemblies.

Aerogel flame retardant packaging film resolves this by delivering aerogel performance in a flexible, rollable format. The film composite bonds aerogel particles or layers into a thin, handleable sheet that can be die-cut, laminated, and positioned between cells or modules with the same process discipline as any other film material in the pack. Thicknesses of 1–3 mm provide meaningful thermal barrier performance; research has shown that a 2 mm PI-aerogel layer can delay thermal runaway propagation to an adjacent cell by an average of over 500 seconds compared to untreated configurations.

The flame retardancy requirement is non-negotiable in automotive applications. The relevant benchmark is UL94 V-0, which requires that a material self-extinguish within 10 seconds of flame removal and produce no burning drips. Aerogel composites designed for battery use meet or exceed this rating, with temperature resistance typically exceeding 1000°C for inorganic aerogel compositions and 400°C for PI-based variants. This thermal stability means the barrier continues to function after the initial cell vent event, rather than melting away at the moment it is most needed.

For pack engineers, the key specification parameters are thermal conductivity (lower is better, target ≤0.02 W/(m·K)), UL94 rating (V-0 minimum), maximum service temperature, compressive strength (the material must not crush under cell expansion forces), and available thickness range. For sourcing teams, rollable format, consistent thickness tolerance, and the ability to supply die-cut shapes to the assembly line are the practical differentiators.

Explore aerogel flame retardant packaging film for EV battery thermal protection in Yanhe's new energy battery materials range.

CCS Hot Pressing Film: The Insulation Layer That Holds the Pack Together

The cell contact system module is assembled by stacking an FPC, one or more insulating films, and copper or aluminum busbars, then running this stack through a heated roller press or platen press to bond the layers into a single rigid assembly. The insulating film used in this process—the CCS hot pressing film—performs two simultaneous functions: it provides electrical isolation between the conductive layers, and it acts as the adhesive that binds the assembly together under heat and pressure.

The lamination process typically operates at temperatures between 130°C and 180°C under controlled pressure, producing a module with a total thickness often below 1 mm. The hot pressing film must flow sufficiently under these conditions to wet the adjacent surfaces and form a strong bond, then cure to a stable, non-flowing state that will not creep or delaminate under the thermal cycling of vehicle operation. This is a demanding combination of properties: adequate flow before cure, but no flow after.

Material selection for CCS hot pressing film involves a choice between PET-based and PI-based substrates. PET-based films are cost-effective and suitable for applications where the maximum operating temperature remains below approximately 130°C. They are the dominant choice for most passenger vehicle battery packs operating in temperate climates. PI-based films are specified where higher thermal loads are anticipated—performance vehicles, bus and truck applications, or packs that operate in high-ambient-temperature environments—because PI maintains dimensional stability and electrical insulation properties at temperatures where PET begins to soften.

The electrical isolation requirement is governed by the pack's operating voltage and the creepage distances designed into the busbar layout. At 400V pack voltages, standard in current passenger EVs, the dielectric strength requirement for the insulating film is typically 3–5 kV/mm or higher, with a finished assembly withstand voltage test in the 2–4 kV range. At 800V architectures, which are increasingly common in newer platforms, these requirements increase proportionally.

For the assembly process, the film must be supplied in roll format with dimensional consistency sufficient for automated cutting and placement. Thickness tolerance, surface energy (which affects bonding uniformity), and the temperature-pressure-time window for the lamination process are the key parameters that need to be aligned between the film supplier and the CCS manufacturer before production qualification.

See CCS hot pressing film for cell contact system assembly from Yanhe's battery supporting materials line.

PI Thermosetting Film for FPC: Flexibility Without Compromise

Polyimide film has been the substrate of choice for flexible printed circuits since the technology was commercialized, for a straightforward reason: it is the only common flexible substrate that simultaneously offers continuous service temperatures above 200°C, dimensional stability through reflow soldering at 260°C+, and the mechanical flexibility needed for a circuit that must bend, route through tight spaces, and survive mechanical vibration over a vehicle's service life.

In battery applications specifically, the PI film serves as the dielectric base layer of the FCCL (Flexible Copper Clad Laminate) from which the FPC is fabricated. The copper foil—rolled-annealed (RA) copper for dynamic bending applications, electrolytic deposited (ED) copper for static configurations—is bonded to the PI film either with a thermosetting adhesive layer or, in adhesiveless constructions, directly through a casting or sputtering process.

The "thermosetting" specification is significant. Unlike thermoplastic adhesives, which soften reversibly on heating, thermosetting adhesives cure irreversibly to form a cross-linked network. This means the bond between the copper foil and the PI substrate strengthens during the initial lamination process and does not re-soften during subsequent soldering, component mounting, or service temperature excursions. For FPCs in battery management systems—where the assembly is exposed to repeated thermal cycling and occasional elevated temperatures during fast charging—this thermal stability is a functional requirement, not a premium feature.

Key parameters for PI thermosetting film selection include: dielectric constant and loss tangent (relevant for high-frequency signal integrity in BMS circuits), peel strength of the copper-PI interface (typically measured in N/cm per IPC standards), dimensional change under thermal cycling (a tight CTE match between the PI layer and the copper foil minimizes stress at the interface), and flammability rating. For automotive applications, UL94 V-0 is the standard requirement, and most qualified PI films for FPC applications meet this rating.

The film is typically supplied in roll format with standard widths of 250 mm or 500 mm. Working with a supplier who can provide consistent thickness (commonly 12.5 µm, 25 µm, or 50 µm for FPC applications), verified electrical properties, and documentation suitable for automotive qualification programs significantly reduces the process development burden at the FPC fabricator.

Find PI thermosetting film for FPC copper foil bonding in Yanhe's battery materials portfolio.

Comparing the Three: Where Each Material Fits in the Battery Pack

These three materials are not alternatives to each other—they address different layers of the same system. A fully specified battery pack typically needs all three: aerogel film at the cell-to-cell interface for thermal protection, CCS hot pressing film to build the module that monitors every cell, and PI thermosetting film as the flexible circuit backbone that carries the signals. Browse the full range of new energy battery supporting materials to see specifications across all three categories.

What to Specify When Sourcing These Films

Sourcing specialty films for battery applications is different from sourcing commodity materials. Automotive supply chains require documented material traceability, qualification testing records, and the ability to maintain consistent lot-to-lot properties over multi-year production runs. Here is what to confirm before placing a qualification order for any of these three film types.

Performance documentation. Request test reports for the parameters that determine functional performance in your application: thermal conductivity and UL94 rating for aerogel film; peel strength, dielectric breakdown voltage, and lamination process window for CCS hot pressing film; copper peel strength, dimensional stability under thermal cycling, and flammability certification for PI thermosetting film. These should be from accredited third-party laboratories, not internal tests only.

Compliance certifications. RoHS and REACH compliance documentation is baseline for any material entering an automotive supply chain. For aerogel and CCS films, confirm whether the formulation contains any halogenated flame retardants—halogen-free formulations are increasingly specified by OEMs due to toxicity concerns during end-of-life processing. For PI thermosetting film used in FPCs destined for automotive OEM programs, IPC-4204 compliance is the relevant industry standard for flexible base materials.

Customization capability. Battery pack designs are not standardized across platforms. Cell formats, module geometries, and assembly processes vary by manufacturer and model generation. A film supplier that can produce custom widths, adjust adhesive coat weights, modify thickness, and supply die-cut shapes to a customer-provided drawing removes a significant engineering burden from the pack integrator. Confirm that the supplier has in-house coating and conversion capability rather than relying entirely on commodity film stock.

Lead time and volume flexibility. Battery pack programs ramp from prototype to series production over a compressed timeline. Suppliers who can supply small qualification lots (typically 50–200 meters) under the same formulation and process conditions as future production volumes reduce the risk of performance drift between validation and production.

For custom specifications, mixed-material requirements, or volume inquiries, explore custom film solutions for battery and electronics applications from Yanhe's OEM/ODM service program.