PEO: The best-kept secret in electric vehicle manufacturing

Anyone who works in the electric vehicle (EV) industry knows one enduring challenge is producing battery pack components which balance electrical insulation with thermal conductivity and durability. Elements such as casings and heatsinks must provide safe levels of electrical isolation while preventing a dangerous build-up of heat and resisting wear and tear. EV battery components and their surface treatments must also be lightweight and compact to minimise energy usage and maximise available space.

Surely, then, if a surface treatment was available which offered exceptional dielectric resistance, heat dissipation, adherence and durability, you’d expect it to be big news in the world of automotive? PEO (Plasma Electrolytic Oxidation) combines all these properties and yet is the best-kept secret in EV production.

Read on to find out why.

What is PEO?

PEO is a surface treatment that improves the performance of alloys of aluminium, magnesium and titanium (substrate). The PEO process involves oxidising components in an alkaline electrolyte bath (much like traditional anodising). Millions of short-lived microscopic bolts of lightning transform the substrate into an oxidised ceramic layer which performs exceptionally in harsh application environments such as corrosion, wear, dielectric, fatigue, and thermal conditions.

The passing of the polymer insulation era for battery packs

Polyimide film is a commonly used solution for electrical isolation in EV battery components. This coating offers stability in a range of temperatures and has good dielectric strength. However, as consumers demand increased range and charging speed from their EV vehicles, battery voltages are increasing, ramping up the strain on surface coatings and treatments. Where polymers might have provided sufficient insulation in the past, new solutions are needed to more effectively meet the 2.4kV safety factor required on the latest 800-volt battery architectures, where coating applications need to be applied selectively and repeatedly for a high-volume driven industry.

Another drawback of using polyimide film or PET (polyester) tape is while they’re easy to apply to basic parts, more complex shapes pose a problem. Powder coatings tackle complex components better, but achieving an even application is a challenge.

PEO: perfectly suited to battery packs

The PEO process allows for the incorporation of different characteristics to suit the end requirement. PEO’s thermal characteristics can provide a barrier up to 900°C, but equally it can be used to create a coating which allows thermal transmission (0.8 – 10 W m-1 k-1). This level of thermal control is ideal for battery components, to remove the risk of thermal runaway (an uncontrolled build up of heat) which could lead to malfunctions and explosions.

PEO offers exceptional electrical insulation because of the inherent dielectric properties of the ceramic base layer, topped with a sealer to enhance the protection. In fact, Keronite PEO’s thickness (with sealer) can be tailored to provide as much as three times the dielectric strength and maximum thermal dissipation, even though it’s inherently a ceramic coating, reducing the reliance on commonly used polymer coatings. Isolation voltages of over 3 kilovolts are achievable on substrates treated with PEO.

Because components are immersed in an electrolytic bath, an even application on even the smallest, most complex shapes is possible.

PEO + aluminium alloys = a match made in heaven

EV battery manufacturers favour aluminium alloys for components such as battery pack enclosures. The preferred alloys are lightweight, have good tensile strength and excellent thermal conductivity. However, untreated aluminium is a conductive metal – hardly ideal in the construction of casings for high voltage batteries. Because PEO coatings are dense they increase dielectric breakdown without adding weight, meaning manufacturers can use this inorganic, conforming treatment to grow over the substrate, delivering better insulation.

PEO is also a more environmentally-friendly option than insulating tape. No carcinogenic materials are used in its production and it lasts around three times longer than polymer tape, which can’t be replaced – the whole part has to be removed when the polymer coating is worn or damaged.

The longevity is further increased by PEO’s excellent corrosion protection: coatings have exceeded 2000 hours in salt spray testing (ASTM B117).

Applications beyond batteries

Keronite PEO’s application within automotive isn’t limited to battery pack components. More and more system and mechanical design engineers are capitalising on its properties of dielectric resistance, ability to add strength without adding weight, thermal properties, corrosion protection, environmental credentials, and the fact it’s non-flammable. In thermal heat syncs on traction inverters, PEO can replace tape whose adhesive would melt over time. Aluminium brake discs treated with PEO are more durable, offer the same braking efficiency as steel with far less weight, and can deliver up to 78% reduction in emissions.

The best-kept secret

Back to our original question. Why is PEO the best-kept secret in EV battery pack production? It’s certainly not due to lack of uptake: here at Keronite we’ve been working with EV clients for six years and it’s one of our fastest growing areas. No – the reason no one is talking about it is simple. If you were a manufacturer who’d found a competitive edge, would you want anyone else to know?

Get in on the secret – contact us to find out how Keronite’s PEO coatings could transform your EV battery pack performance.