Envalior presents best practices to increase safety and reliability in EVs during 2023 SPE EAV Conference

The Society of Plastics Engineers (SPE) hosted the 2023 Electric & Autonomous Vehicle (EAV) conference in Troy, Michigan, in April 2023. Keith Kauffmann, application development engineer for Envalior, formerly Envalior and Lanxess Performance Materials, presented a session about Next Gen Materials to Increase Safety and Reliability in Electrical Powertrains during the three-day conference attend by more than 700 industry professionals.

Kauffmann’s presentation focused on how electric vehicles (EVs) are driving a change in the required performance of engineering thermoplastics and the ongoing research and design at Envalior to develop materials that meet EV application performance needs.

New applications and trends bring new opportunities in the industry

As the industry transitions from internal combustion engine (ICE) to EV vehicles, there is a transformation in the powertrain architecture and refueling source—from gasoline to charging. As battery packs, drive motors and high voltage connectors become the primary components of the EV powertrain, there are technical impacts on materials used in all these applications, such as:

• A drop in overall vehicle operating temperatures for EVs, leading to a decrease in the oxidative degradation of parts due to high temps
• Longer term exposure times to water/glycol solutions as battery packs typically require constant cooling even after the vehicle is not in operation
• A decrease in the amount of wear and friction concerns – there is still wear and friction in EVs with motors and bearings, but it is to a lesser extent than for ICE technology
• A decrease in the traditional oils, such as engine lubrication oils that requires oil resistance for any plastic powertrain parts.
• An increase in the use of oils for cooling high power density E-motors

Additional technical impacts for EVs include the need for high CTI (comparative tracking index) materials and higher electrical insulation capabilities because of high voltage battery systems.

The trends are faster charging speeds and moving from lower to higher voltage platforms, from 400V to 800V and greater. This has driven the need for higher insulative requirements and more effective cooling.

“Lower current decreases the heat power loss and allows you to maintain peak charging speed for a longer time, and one of the most effective ways to increase the charging speed is to increase voltage instead of current. Therefore, we are seeing higher voltage battery systems. However, as much as we try to find the balance between current and voltage to address charging power, fast charging can result in high localized heating requiring cooling and high insulative materials,” explained Kauffmann.

Another impact on technical trends is the need for oil cooling for E-motors. Plastic components within the motors need to be resistant to E-motor oils with long term exposure rates.

“When considering the fuel cell and EV architectures there are many different types of challenges that must be considered, including CTI before and after aging, oil aging, electrical corrosion, long term coolant exposure,” added Kauffmann. “It is important to maintain insulative and mechanical properties, and this requires an understanding of the effects of long-term aging over the appropriate temperature ranges.”

Solving cracks issue in high voltage component thermal shock cycling

One of the key issues for over molded bus bars is crack development due to thermal shock cycling. It is critical that cracks are prevented to stop leakage current. In many of these EV components, plastic is over molded to metal, typically copper. Cracking can occur during thermal cycling due to stress build up in the plastic because of the differences in CLTE (coefficient of linear thermal expansion) between the plastic and the copper.

The first bar chart shows CLTE of PPS (machine direction and transverse direction) and the second bar chart shows thermal stress of PPS in both directions.

“Envalior understands what causes thermal cracks and we know how to address this with optimal glass orientation, part design and mold design.” said Kauffmann.

Ensuring reliability in automotive electronic applications

Controlling the amount of halides in connectors, sensors, ECUs and PCUs is essential. As connectors play a bigger role in EV architecture, terminal reliability is critical. Factors such as high temperatures, high humidity, reactive gases, electrical potential and time can lead to corrosion. Inorganic halides and ionic additives used to improve flame retardant performance of plastics can form acids that corrode electrical contacts after long term exposure to moisture and heat. This can lead to electronic component failure that could compromise vehicle safety features.

“For connectors and sensors, keeping halides to less than 100 ppm is a target, with & 50ppm in more critical applications,” said Kauffmann. “Our FR materials are in the range of 20-30ppm (standard).”

Kauffmann added, “We see a focus on an increased need to consider UL94 flammability testing requirements for many EV plastic applications, especially when the materials are in proximity to HV components. We often see UL94 V0 burn rating required with the occasional 5VA rating required.” 

Envalior has several halogen free materials that meet V0, including PA6, PA66, PA46, PA410, PPS and PPAs.