Plastics - Battery Design

A vast array of plastics are used across the battery pack for structure, sealing, isolation and protection.

Acrylonitrile Butadiene Styrene (ABS) – thermoplastic known for its high impact resistance, durability, and ease of processing.

Ethylene Propylene Diene Monomer (EPDM) – a synthetic rubber with a saturated backbone that resists ozone, UV and heat ageing, giving it a broad thermal operating range and good resistance to glycol-based coolants. It is the dominant elastomer for automotive sealing and is widely used for battery pack enclosure gaskets, seals and grommets, where it also helps damp vibration [1].

Nylon – polyamides, characterized by their strength, durability, and flexibility.

Polyamide (PA)

Electrical Creepage
- Polyamides (Nylon): While strong, nylons absorb moisture. This absorbed water acts as a plasticizer that dramatically increases ionic conductivity, severely degrading the material’s Comparative Tracking Index. Consequently, standard nylons are generally unsuitable for high-voltage barrier insulation in 800V+ battery platforms.

Polyimide Films (eg Kapton)

Electrical Creepage
- Though polyimide films have incredible dielectric strength and heat resistance (often used for cell wrapping), they actually have a relatively low tracking resistance (Comparative Tracking Index ≈ 150 V, Material Group IIIb). Designers must compensate for this by maintaining larger surface creepage distances when using Kapton in unsealed areas.

Polybutylene Terephthalate (PBT)

Electrical Creepage
- Polybutylene Terephthalate (PBT) & Fluoropolymers: Specialized flame-retardant PBT and fluoropolymers (like PTFE) offer exceptional Comparative Tracking Index ratings (≥ 600 V, Material Group I) and do not absorb moisture. They are heavily favored for critical high-voltage connectors, busbar wraps, and insulation sleeves.

Polycarbonate (PC) – easily worked, moulded, and thermoformed.

Electrical Creepage
- Commonly used for large structural covers, unfilled PC typically has a lower Comparative Tracking Index (175 V to 250 V, Material Group IIIa), meaning it requires wider spacing between conductive nodes.

Polyethylene Terephthalate

Polyethylene Terephthalate (PET) is a thin, tough, electrically insulating film used to wrap cylindrical and prismatic cells (the printed outer sleeve seen on most Li-ion cells) and to insulate busbars, acting as a barrier that prevents short circuits between cells and adjacent conductive surfaces [2].

Polypropylene (PP) – chemical resistance, durability and light weight means it is often used in battery pack housings. It is also used in separators.

Polyvinyl chloride (PVC) – high resistance to chemicals, flame retardant, durable. Used in insulation, protective housings and cable covers.

V0 Plastics – sometimes used as an abbreviation to describe a plastic that meets the UL94:V-0 certification. The tested material has to self extinguish within 10 seconds on a vertical part allowing for drops of plastic that are not inflamed.