The Specialty Polymers Advantage in Higher-Voltage E-Mobility

e-motec
May 25, 2022

The Specialty Polymers Advantage in Higher-Voltage E-Mobility

Brian Baleno

Fully electric vehicles (EVs) are fast winning greater market shares everywhere as the energy transformation is picking up pace. One of the major reasons is that automakers have focused on lightweighting as well as higher-power battery systems, extending the all-electrical driving range beyond 400 km while also reducing the time required for charging. High-performance specialty polymers can play a significant role in maximizing these benefits together with higher manufacturing efficiency and improved fire safety.

The automotive industry has gone electric and is increasingly taking advantage of advanced polymers offering greater flexibility for system integration, lightweighting and miniaturization in combination with superior electrical and thermal properties. The latter are instrumental in shifting from established 400 to higher-volt systems in order to enable faster charging and longer distances. High-temperature insulation materials protect against electrical breakdown, and polymers offering a high comparative tracking index (CTI) of 600 volts and above result in minimized electrical and magnetic losses.

Changing the game with 800 V systems – and thinner structures

Following the fully electric Porsche Taycan sports car, the number of EVs equipped with 800 V systems is growing. Together with fast chargers supporting such high voltages and supplying a charging power of up to 270 kW at a minimum of 300A , the average charging time from 5 to 80 percent drops to approximately 20 minutes, which corresponds to the duration of a conventional refilling stop for a petrol driven vehicle.

At the same time, 800 V units also increase the mileage that can be reached with a single charge, since they are capable of charging with a lower current, thus reducing the loss of power due to excessive heat that could otherwise be generated during the charging process. In addition, low-current charging can extend battery life. Another benefit derived from higher-voltage systems for EV motors is that their simplified design compared to combustion engines requires less copper.

Two recent developments helping EV manufacturers accelerate the introduction of high-voltage systems are slot liners injection molded in high-flow Xydar® liquid crystal polymer (LCP) and magnet wire insulation using solvent-free KetaSpire® polyetheretherketone (PEEK). “Building on our extensive and long experience in the market of specialty polymers for high-performance and cost-efficient components of internal combustion engines, we are now extending the innovation potential of these materials for electrical insulation, lightweighting through metal replacement and enhanced sustainability to e-mobility applications from power electronics to electric drive motors and battery units,” says [Brian Baleno-Head of Automotive Marketing] at Solvay. “In e-motors, this spans from insulation systems, and thermal management, to seals and lubrication. Key components include magnet wire insulation, slot liners,  busbars, and high-voltage connections.”

Slot liners are used to create an insulating barrier between the copper winding and the steel lamination of rotors in electric drive traction motors. Here, Xydar® LCP combines the high flowability needed to fill long and thin parts with zero warpage to meet tighter tolerance specifications. Besides, it lends itself as a cost-efficient alternative with higher dielectric strength at elevated temperatures, thermal endurance up to 240°C and better thermal conductivity than incumbent multi-layer films. Moreover, its high stiffness prevents breakage during assembly.

Magnet wires coated with KetaSpire® PEEK can increase the power density and torque of lightweight and downsized e-motors. The insulation must ensure resistance to harsh bending operations during winding as well as to high voltages in service to prevent electrical breakdown. The PEEK polymer combines excellent dielectric strength and long-term stress crack resistance with high heat resistance and outstanding chemical resistance for this application.

Slot liner molded in Xydar® LCP from Solvay for use as a barrier between the conductive windings and the body of electric rotors. The LCP material offers significant total cost and performance advantages to replace incumbent multi-layer films in this application. (Photo: Solvay)
Slot liner molded in Xydar® LCP from Solvay for use as a barrier between the conductive windings and the body of electric rotors. The LCP material offers significant total cost and performance advantages to replace incumbent multi-layer films in this application. (Photo: Solvay)

Electrical reliability under high voltages

Next to the introduction of higher-voltage systems, another trend in EVs is the integration of the onboard charger, the converter and the inverter into a single consolidated power electronics module – complete with thermoplastic component housings and covers, busbars and miniaturized connectors as well as overmolded capacitors or insulated-gate bipolar transistors (IGBTs), Mosfets and the cooling system. While such solutions provide weight, space and cost savings, their electrical reliability is even more critical when operating under high voltages.

“We have developed an entirely new generation of Amodel® PPA resins to meet the needs of high-voltage connectors, busbars, and IGBT and Mosfet capacitors in these application with best-in-class CTI ratings, optimized thermal cycling capability and chemical resistance,” explains Baleno. Considered a breakthrough in polyphthalamide chemistry, new Amodel® Supreme grades will even retain their CTI over time even after temporary exposure to peak temperatures above 150°C. A special Amodel® Bios material designed for reflow soldering of surface mounted connectors without blistering offers enhanced impact resistance and weld-line strength, enabling further wall thickness reductions and saving up to 50 percent of space on the printed board. Exhibiting a partially long-chain molecular structure, the Amodel® Bios range also outperforms incumbent bio-sourced long-chain PPAs in terms of glass transition temperature (Tg), while it features the lowest global warming potential (GWP) in this polymer class.

Magnet wires coated with Solvay’s solvent-free KetaSpire® PEEK. The high-performance specialty polymer can dramatically enhance the environmental compatibility in the manufacturing of EV motors. (Photo: Solvay)
Magnet wires coated with Solvay’s solvent-free KetaSpire® PEEK. The high-performance specialty polymer can dramatically enhance the environmental compatibility in the manufacturing of EV motors. (Photo: Solvay)

Another specialty polymer replacing lower-performing polyamides and metals to boost the reliability of integrated power electronics is Ryton® polyphenylene sulfide (PPS). As a proven solution in demanding automotive fluid handling systems, the material shows high resistance to glycol-based and silicone-containing coolants, and maintains its dielectric strength even at elevated temperatures. This property profile is of particular importance in EVs, where increased electronics and large battery units generate excess heat. Typical application examples are extruded cooling tubes complete with injection molded connectors.

Further specialty polymers in Solvay’s portfolio for more reliable e-motor designs include high-heat Torlon® polyamide imide (HHPAI) as a higher-performance alternative to existing ICN-PAI enamel coatings; Ajedium™ PEEK slot liners with superior conformability and lubricity vs. traditional laminates; Xencor™ long fiber thermoplastics (LFT) for slot wedges holding the magnet wire and slot insulation in place; Fomblin® perfluoropolyether (PFPE) for high-performance lubrication of motor bearings; and Tecnoflon® fluoroelastomers (FKM) for seals with enhanced friction and wear resistance in motors running at higher speeds.

Cooling lines with lightweight extruded coolant tubes and injection molded line connectors in Ryton® PPS from Solvay, replacing lower-performing polyamides and metals. The material provides the enhanced thermal, chemical, and flammability performance required for more demanding automotive fluid handling systems. (Photo: Solvay)
Cooling lines with lightweight extruded coolant tubes and injection molded line connectors in Ryton® PPS from Solvay, replacing lower-performing polyamides and metals. The material provides the enhanced thermal, chemical, and flammability performance required for more demanding automotive fluid handling systems. (Photo: Solvay)

Maximizing fire safety

One of the most critical challenges associated with high-voltage EVs is the fire safety of onboard electrical systems and battery units. At present, with most components still designed for 400 V, there are only a few manufacturers who specify the use of plastics with UL94 V-0 rated flame retardancy. If a car catches fire when on the road, passengers normally have sufficient time to escape. However, the switch to 800 V creates a paradigm change. The higher voltage comes with a greater potential risk of sparks and short circuits, so the fire safety must be maximized to prevent ignition and flame propagation also when the car is left unattended to charge.

“Ryton® PPS and most of our other specialty polymers for use in electrical automotive systems combine high glow wire ignition temperature and tracking resistance with UL94 V0 flammability ratings at low wall thickness,” states Baleno.

For next-generation batteries in solid-state technology, Solvay is developing new polymer systems in which the liquid electrolyte is replaced by fully inorganic sintered powders. Without the risk of liquid leakage and subsequent ignition of volatile components, these systems can make a significant contribution to enhancing the safety management of high-voltage EV batteries while at the same time enabling more compact designs with higher energy density. Along with its comprehensive portfolio of specialty polymers for innovations in e-mobility, the company supports OEMs and Tier 1 suppliers in optimizing and validating the performance and productivity of tomorrow’s designs from concept to approval at its Materials Science Application Center (MSAC) in Brussels, Belgium. The Center provides ultramodern equipment for material testing, virtual engineering and prototyping under one roof, helping customers reinvent EV technology for enhanced efficiency, higher ranges and faster charging

Brian Baleno Head of Marketing-Automotive [E-Mobility solutions, Solvay

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