Polymeric Materials in Automotive: The Increasing Importance of Plastics for EVs and Autonomous Driving

 

In this blog post I cover six areas which deal with the increasing importance of plastics for Electric Vehicles (EVs) and autonomous driving starting from 2020.

Table 1: overview of key focus areas for plastics in EVs and autonomous driving

Let us walk through all the six areas:

Light-weighting – range extension and efficiency for electric cars

Light-weighting plays in several areas of the EV an importance and aims to provide smaller and lighter components. In a standard internal combustion engine car, plastics represent over 50% of the volume, however only 10% of the car weight.  The battery pack is the heaviest part of the whole electric car and plastics light-weighting solutions have the potential to lower the overall weight situation. Current battery housings are made using an aluminum cast solution [1]. Furthermore, battery housings need to fulfill several requirements such as crash protection, battery cooling and ease of maintenance. Thermoset based composites, as well as step by step thermoplastic composites show potential to replace aluminum castings and fulfill the afore mentioned requirements.

Amorphous materials for sensors and LEDs

LED-based lighting technology is already state of the art in cars and it offers many possibilities for the design and functionality of classic front and rear lamp applications. There are already diffractive seamless lens structures which integrate a holographic film into a polycarbonate rear-end structure. Ongoing is the integration of electronics and driving sensors such as LiDAR and radars into one operating unit. The integration of LiDAR systems into invisible components is achieved by using black-panel-based polycarbonate color technology. This solution guarantees the highest IR transmission based on the required IR laser wavelength. Polycarbonate will play a key role for so-called people mover which have large transparent structures. Realizing these structures can be done via the polycarbonate glazing technology (360° glazing concepts).

Electroactive Polymers

In a previous post I highlighted already the importance of electroactive polymers. Polyvinylidene fluoride (PVDF) has piezoelectric as well as ferroelectric properties which can be used to make car speaker systems. The integration of vibrating surfaces all over the car (dashboard; turning headrests into resonating chambers) evolves the car into an entertainment center. Piezoelectric polylactic acid is another potential material solution for such new applications.

System integration

Injection moulding allows the production of complex geometries. Furthermore, system function integration with engineering polymers (e.g. integration of damping elements for noise and vibration reduction) will further reduce costs and weight in electric cars. Metal replacement of transmission housings of electric cars are an example for integration of different materials and technologies: local reinforcement is achieved by thermoplastic composite tapes (unidirectional tapes based on PPA or PPS with carbon fiber) and overmoulded with short fiber reinforced PPA or PPS. Since transmission and power electronic housings need to have EMI shielding, placing the tapes in a 0° and 90° orientation will lead to a filtering effect and as a consequence EMI shielding can be achieved. Another integration field is the two component moulding using a hard component (PA, ASA, POM) and combining it with a soft component (thermoplastic elastomer). In particular for sealing of power electronic parts and housings in electric cars, two component solutions where a flame retardant TPE is moulded on a flame retardant PP are already existing.

Interpolymer substitution and recycling

In several areas of the internal combustion engine (ICE) car, replacement of established plastics takes place. This trend will continue in electric cars as well. Polypropylene blended with polystyrene is replacing ABS in interior decorative parts. Another example is polyketone. It is an engineering polymer which shows higher heat performance compared to polyamide 6 and 6.6. Polyketone has excellent wear resistance and impact strength, outperforming POM. Furthermore, they have a low moisture absorption (similar to PBT) and have an excellent chemical resistance, in particular toward automotive fluids, hydrocarbon solvents and salts. Commercially it is attractive to replace aliphatic polyamides, POM and PBT in the automotive market, as well as other markets. Future aim of the automotive industry is to minimize the amount of different grades and simplify the polymer chemistries in electric cars. This will accelerate recycling efforts and re-usability. Key focus area is the recycling of the battery chemistry and polymers used for making cathode and anode binders.

Battery materials

Here, different polymers play a role for developing improved lithium-ion battery systems by optimizing the binder materials for anode and cathode (PVDF basis) and to develop robust solid-state batteries. Solid-state batteries will allow the customer to recharge the battery in a short period of time and offer more mileage range too. Furthermore, metal replacement of battery housings and module parts will continue, as already highlighted in section one. Engineering polymers are more and more used as battery module separators and end plates.

How electrification influences plastics manufacturing

The next five years will show an increase of plastics demand from the automotive industry. Demand increase will be seen in certain polymer types, combined with application focus. Polyolefins such as polypropylene will grow due to expanding exterior and interior applications. Also, thermal conditions are much lower in electric cars (60-80°C) allowing polypropylene to replace engineering polymers, as well as engineering polymers replacing high heat polymers in certain areas.

Higher growth rates are expected in the Asia-Pacific regions compared to established automotive markets. Focus on innovation will allow manufacturers to meet the upcoming application requirements. Also focus will be on the establishment of a circular economy and structured recycling. 

Thank you for reading and #findoutaboutplastics

Greetings,

Herwig Juster

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Literature

[1] https://www.spotlightmetal.com/solutions-for-ev-battery-housing-at-euroguss-2020-a-900422/

[2] https://www.composites.media/the-future-of-thermoplastics/

[3] G. Pilz, et al. : Dynamic Mechanical Profile of Polyketone Compared to Conventional Technical Plastics, AIP Conference Proceedings 1779, 070008 (2016); https://doi.org/10.1063/1.4965540

[4] http://www.poketone.com/en/applications/automotive_index.do

[5] https://www.kraiburg-tpe.com/en/flame-retardant-tpe-electrical-sector

[6] https://www.solvay.com/en/article/future-of-mobility-is-light?utm_medium=social&utm_source=linkedin&utm_campaign=Stories+or+Medium&utm_content=100001741732062&linkId=100000034561877

[7] https://doi.org/10.3144/expresspolymlett.2021.25

EMI Shielding for EVs: Thermoplastic Compounds vs. Coatings – What is Better?

EMI Shielding: Thermoplastic Compounds vs. Coatings – What is Better? I Findoutaboutplastics.com

The topic of electromagnetic interference (EMI) gains more and more importance in the electrification of cars. In this blog post, we discuss the EMI shielding using either modified thermoplastic compounds and/or standard thermoplastics with coating. 

Fresh-up on the basics of EMI

The radio frequency range of the electromagnetic spectrum (ranging from 10 KHz to 77 GHz) is mainly responsible for electromagnetic interference. As a consequence, device failures can happen by such interference. Looking at electric cars, the overall number of sensitive electronic components increases and with this the need for electromagnetic “noise” protection increases too. 

When electromagnetic waves hit a material, three different reactions of the waves may happen [1]: 

1) Absorption (energy transformation as the electromagnetic waves pass through the materials)

2) Reflection (the electromagnetic waves are reflected by the materials)

3) Transmission (the electromagnetic waves pass through the material without any energy transformation)

In general, the higher the power of a system, the higher EMI becomes (right thumb rule of current). Also, with higher power, the temperature in the enclosed housing will increase.

What are the main sources of electro-magnetic interference?

There are three different categories of EMI sources: 

1. Inverters (low frequency), 

2. DC Motors (low frequency), 

3. In-car radio frequency (RF) as well as out-of car RF (high frequency).

Which parts need to be protected (EMI receptors)?

There are several parts of an EV which need protection: battery housings, housings for automotive electronics, infotainment enclosures, ADAS housings, and LIDAR housings.

Polymer Material requirements in EVs:

New applications in Electric Vehicles lead to an increase of electrical properties such as Comparative Tracking Index (CTI), flame retardant levels, and chemical properties. Those new requirements need to be considered in the material selection of the before shown applications.  

The ideal polymer compound fulfills: 

- UL 94 V0 (0.8 -1.6 mm)

- Chemical resistance toward acids and oils

- EMI shielding (> 52 dB over different frequencies - 150 kHz -100 MHz)

- High CTI (> 600 V) 

- Thermal conductivity (> 1 W/mK)

- Thermal shock resistance

- Overmoulding capability

- No electrical corrosion on overmoulded parts

- Lead-free reflow soldering (connectors)

- Cost competitive 

Testing EMI shielding and automotive standards: 

ASTM D4935 is used to estimate the shielding effectiveness (SE) of different materials. It uses a plane- and far-field electromagnetic wave. 

Furthermore, in automotive the so-called CISPR 25 was introduced in 2016 by OEMs. In this standard, different shielding levels are defined, such as CISPR 25 A2 (70-40 dB) and CISPR 25 A1 (80 dB). In automotive, shielding targets are between 40 dB and 70 dB.

Shielding compounds vs. coating of plastics

Plastics are natural insulators and do not reflect, nor absorb EMI. Modification of the compound needs to be done using different fillers such as stainless steel fibers or nickel-coated carbon fibers. As a rule of thumb, one can state that by adding 20% carbon fibers into a compound, the same EMI shielding effect as with 10% metal fibers is achieved. Another way to achieve EMI shielding is over metal based coatings. 

In a recent study conducted by RTP company [2], cost per piece of a plastic part (housing with 51 mm x 51 mm x 13 mm; wall thickness: 3.0 mm) with minimum 40 dB shielding effectiveness was shown. 

The detail requirements and results of the study: 

-Conductive coating methods: painting, metallic painting, and vacuum metallizing

-Compounds: ABS with 10% stainless steel fiber; ABS with 15% nickel-coated carbon fiber

-Part volumes: 10,000 and 100,000 pieces

-Coating costs include: apply coating; tooling/fixing/masking costs; scrape rate

-min. EMI SE: 40 dB

The cost per part for low and high volume parts can be seen in the chart below. 

Conclusions: 

Conductive coatings can be an option for higher volume parts. However, EMI shielding compounds show less costs for low and high volume parts. As we pointed out, compound requirements are changing. As soon as UL94 VO level is needed, additional flame retardants need to be added or the used resin needs to be changed to an intrinsic V0 grade such as PPS. In such a case, costs for EMI compounds will increase and conductive coatings will be more competitive.  There are also new players for conductive coating systems such as the Seal and Shield technology (Freudenberg Sealing) [3] or the Chrom-VI free process called Slotosit offered by company Schlötter [4]. 

Another innovative way of shielding is by using carbon fiber based thermoplastic composite tapes. A 0° / 90° carbon fiber PPS UD Tape allows a uniform EMI shielding while fulfilling thermal rating and mechanical stabilities. 

Thank you for reading and you interest!

Best regards and #findoutaboutplastics

Herwig Juster

More on electrification: 

High Performance Polymers in Electrification: A Must-Have Or A Nice-To-Have

Part 1: Batteries

Part 2: Traction Motors

Part 3: Autonomous Driving

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Literature: 

[1] https://incompliancemag.com/article/the-basic-principles-of-shielding/

[2] https://www.rtpcompany.com/products/emi-shielding/

[3] https://www.fst.com/corporate/newsroom/press-releases/2019/freudenberg-emshielding-press/

[4] https://schloetter.de/slotosit/

 

High Performance Polymers in Electrification: A Must-Have Or A Nice-To-Have (Part 3: Autonomous Driving)

Welcome back to the third part of the high performance plastics for electrification series. In the previous parts, we have discussed the polymeric materials used in battery systems and traction motors. Now, we a look at the high performance plastics used for autonomous driving applications.

Autonomous driving

• Connectors

Connectors need to be reliable while driving (manual and autonomous driving mode) as well as when the OEM is assembling the different parts of the car in the manufacturing line. Therefore, connectors need to fulfil different requirements:

• JEDEC MSL1 level of shelf life (=infinite);
• no corrosion (especially pins; plastic parts need to be free of halogens, red phosphor, and ionic heat stabilizers);
• continuous use temperatures of 140°C-180°C;
• high chemical resistance;
• high electric strength;
• and CTI of 600 Volts (PLC0).

Connectors need to have a high ductility level too. Easy identification of high voltage connectors, insulators, and circuit breakers is achieved by coloring polymers in orange (color coding compulsory above 60 V). Polymers such as polyphthalamide (PPA) with a Tg of 120°C and above (Tg of 140 up to 180°C are possible) can handle the requirements listed above offering high mechanical strength with low moisture uptake, similarly to polyesters. Apart of aliphatic polyamides and polyesters, semi-aromatic polyamides such as PPA and polyarylamide (PARA) can be obtained in a non-halogenated flame retardant compound. Advantages of PARA are the high stiffness, excellent low creep, low moisture uptake and impact properties.

• Light Detection and Ranging (LiDAR) and Radio Detection and Ranging (Radar) sensors

High performance plastics play an important role in connectors on the one hand as well as in sensors for autonomous driving on the other. An aliphatic polyamide absorbs water and moisture. This absorption is linked to a dimensional and mechanical change. LiDAR and radar housings need to be dimensional stable since their job is to scan the environment and create an accurate picture of the surrounding. Therefore, using polymers such as polycarbonate (PC), polyethersulfones (PESU), and polyphenylene sulfide (PPS) ensure the high dimensional stability combined with nearly no moisture uptake. Those polymers ensure safe communication of the different sensors over the life time of the vehicle.

• Battery temperature sensors

Minimal temperature changes (+/- 1 °C) in the Li-ion batteries can impact their loading efficiency. Therefore, accurate management of the temperature by sensors is essential for keeping the batteries at their highest effectiveness level. For this type of sensors, polyethersulfones are best suited since their Tg is around 220°C and they show excellent dimensional stability. Furthermore, this stability is needed for keeping the sealing performance of the sensor’s O-ring seals.

• 5G communication sensors

With the arrival of 5G mobile technology, our cars will be able to communicate with each other and the environment. Requirements for 5G related applications are mainly high speed data transmission, infrared transmission, retention of environmental influences and dimensional stability. Polymers such as polyether imides (PEI) and polysulfones are suitable to fulfill these requirements since their amorphous structure allows for tight tolerances and low CLTE, creep resistance and good IR transmission.

• Outlook

In next steps, automotive exterior designers start to seamlessly integrate LED lighting systems with infrared transparency for LiDAR sensor systems [1]. In such application concepts, polycarbonates can play an important role. The integration of LiDAR systems into the car bumper will lead to another challenge: having clean lenses. This may be ensured by using fluorinated coatings which are based on fluoropolymer chemistry (e.g.  perfluoropolyether - PFPE).

• Wrap-up

Electrification brings a whole mix of performance plastics in several applications. I have listed the material requirements and applications we discussed in this post including the previous two parts in two tables, which can serve as guidance through selecting the optimal polymer for your application.

Electrification application matrix for supporting polymer material selection



Material requirements of high voltage components in electric vehicles

Thank you for reading this third part of the electrification blog series! If you enjoyed it please do like and share it with your network.

Till next time!

best regards,

Herwig Juster

If you liked this post, share and like! Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section.
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Literature:

[1] https://www.magnetimarelli.com/press_room/news/magneti-marelli-showcase-its-latest-technology-and-innovation-electronics-lighting

Polyphenylene sulfide (PPS) – The Conquering of Electric Car Parts



In this blog post I explain why polyphenylene sulfide (PPS) is conquering more and more key parts in higher voltage electric cars. In my electrification series, I have discussed the requirements of certain parts already in detail as well as which advanced polymers can be used. A major one is PPS.

Currently, a typical internal combustion engine (ICE) has around 700 grams of PPS polymer on board. New numbers form Asia reveal that there will be 3 to 4 kg of PPS in electric vehicles (EVs) and hybrid electric vehicles (HEVs). This is a huge increase. Let’s find out why it is so heavily in use.

Reason number 1: Elevated temperatures during usage over a long lifetime (over 6000 hours)

Applications such as capacitor cases, invertor cores, motor cores and housings have to withstand elevated temperatures during use and need to have excellent heat cycle performance. PPS can fulfill these set of requirements in an economic manner.

Reason number 2: Thermal management systems

Cooling of the battery and the electric motor requires water pumps. The latter need to perform when constant exposed to the water-glycol mixture. The outstanding thermal and chemical performance of PPS makes it a very suitable candidate for any application inside the water pump, e.g. impellers. Cooling of the battery is necessary when the car is charging as well. As such the lifetime expectation of (plastic) parts is also higher.

Reason number 3: Good metal overmolding capabilities

Busbars are usually thick copper lines which need to be overmoulded. Here again, processing of PPS due to good flow properties is an advantage together with its good electrical insulation properties.

Reason number 4: Dimensional stability at ambient conditions

Exterior positioning sensors in electrical vehicles need to be dimensional stable at various ambient temperatures and humidity. This ensures accurate positioning detection. In this context, PPS exhibit negligible water uptake which makes them suitable for external positioning sensors. For instances, Nylons would be less of suitable candidates here due to their inherent higher hydrophilicity.

Reason number 5: Price level suitable for automotive market

With PPS you will get a lot of value for a reasonable price, i.e. continuous use temperature of 200-240°C, UL94 V0 rating, chemically resistance up to 200°C and dimensional stability at ambient conditions. Price is a major advantage in comparison to other high performance polymers.

A short word on linear vs cross-linked PPS:

There are three major routes to obtain PPS. First one is called flash process with curing. The curing step is needed to increase molecular weight [2]. This process results in branched PPS. The second route encompasses the flash process and metal carboxylates and results in linear PPS [3]. The third route is over the quench process and results in linear PPS as well [3]. Leaders in the industrialization of the PPS polymerizations were Chevron Philips and Kureha back in the 1980s. For electric vehicles, linear types of PPS are optimal. These show superior toughness and improved weldline strength. In general, linear PPS does not process as well as cross-linked PPS. However, less moulding flash is generated by linear PPS types.

What are the potential downsides of using PPS for e-mobility applications?

One aspect to consider is the comparative tracking index of PPS which is between 250 and 275 Volts. This is low compared to PPA which can easily reach 600 Volts. Another point is its low thermal conductivity, 0.3 -0.5 W/mK and finally its brittleness.

Besides PPS, what are next best candidate materials?

In the table below, I have listed polymers which can be in competition for applications using PPS: syndiotactic polystyrene (sPS), polybutylene terephthalate (PBT), and polyphthalamide (PPA).

Conclusion:

PPS, branched or linear, are in the lead for e-mobility applications, especially for high temperature electronics. Automotive, regardless of ICE or EV, will be the main driver for using PPS. This was a wrap up on PPS used in electrification applications.

I hope you have enjoyed it!

Till next time!

best regards,

Herwig Juster

If you liked this post, share and like!

Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section.
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Literature:
[1] https://www.plasticstoday.com/automotive-and-mobility/chinaplas-pps-recording-explosive-growth-evs/50108596960874
[2] Nexant Chemical Systems
[3] Solvay Specialty Polymers – Ryton PPS https://www.solvay.com/en/brands/ryton-pps

High Performance Polymers in Electrification: A Must-Have Or A Nice-To-Have (Part 2: Traction Motors)

High Performance Polymers for E-Mobility (Part 2: Traction Motor); Source: findoutaboutplastics.com

Welcome back to the second part of the high performance plastics for electrification series. In the first part, we have discussed the polymeric materials used in battery systems. Now, we investigate the high performance plastics used in traction motors and transmission components.

Traction motor with transmission – turning voltage into movement:

In the next years the power density of electric cars will increase and this is followed by an increase in voltage. We will see cars with 800 V systems, which doubles today’s system voltage. As a consequence, system temperatures (120-140°C) and torque (up to 300.000 RPM) will increase and insulation properties and safe operation will have highest priority.

-Magnet wire coating:

To ensure safe operations at increased torque and voltage system levels, traction motors and power modules require the usage of polymers such as polyphthalamides (PPA), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK). Magnet wire insulation can be achieved by using an extruded layer of PEEK on the rectangular shaped copper cable. The PEEK magnet wire coating allows for higher cable packing density and thus increased power. Furthermore, by using PEEK, high dielectric strength, chemical resistance, and thermal stability can be achieved. Abrasion resistance of magnet wires is a key property too and is fulfilled by PEEK.

In the picture below the cross section of a traction motor can be seen. In light brown, the PEEK extruded magnet wires can be seen. This example was shown at the Fakuma 2018 (Friedrichshafen, Germany) at the Solvay booth. The traction motor is from Essex Furukawa.

Magnet wire coating solution using PEEK, Solvay booth, Fakuma 2018  

Slot liners which guide the copper cables can make use of different high performance polymers such as PEEK or polyimide (PI) film solutions. Liquid crystal polymers (LCP) can be used for slot liners as well. LCP allows achieving long flow length and wall thickness down to 0.4 mm. Furthermore, LCP’s have a high relative temperature index (RTI) of 220°C combined with inherent V0 properties. Other alternatives are PI and aromatic polyamide (=aramide) sheets, which are folded and inserted in the stator as insulation.

Electronic components of the traction motor include terminals, bobbins, resolvers, and inverters. For such kind of components PPS and PPA can be used. PPA can achieve a Comparative Tracking Index of over 600 V and is available with organic-based heat stabilizers to prevent galvanic corrosion. PPS is inherently V0. However, it does not reach as high CTI values as PPA. Most PPS grades show CTI values of 280. There are PPS grades with 500 V, but the mechanical properties drop significantly, which makes them not suitable for such applications.

Traction motors can be directly cooled by using dielectric fluids such as PolyFluoroPolyEthers (PFPE). The latter, can also be used as lubricant components to prevent friction and wear. Proper lubrication ensures that traction motors can be operated up to 1.2 million kilometers with little maintenance efforts.

Power Distribution Units (PDUs)

For PDUs, the materials requirements are similar to traction motors: high dielectric strength, easy flow, weldline strength, thermal shock resistance, dimensional stability and flame retardant (V0) properties. PPA and PPS, together with PEEK fulfil this set of criteria.

– Insulated-gate bipolar transistor (IGBT):

In components like the insulated-gate bipolar transistor (IGBT), plastic components can be in direct contact with the printed circuit board (PCB). As a result, requirements for selected polymers are dimensional stability around 120°C - 150°C, CTI of 600 V, electric volume resistivity and most importantly, halogens are not allowed to gas out of the part. PPA and PPS can fulfill such stringent requirements since they have a high dielectric strength and are easy to process. Weldlines represent always a design challenge, however PPA and PPS have a good weldline strength (approx. 100 MPa). Increased current leads to temperature increase, which can also be easily handled by PPA and PPS type of polymers.

With this I will close the second part of this high performance polymers series for EV. In the third part, we will look into autonomous driving systems.

Thank you for reading!
Till next time!
Herwig Juster

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Interested in my monthly blog posts – then subscribe here.
New to my Find Out About Plastics Blog – check out the start here section.
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High Performance Polymers in Electrification: A Must-Have Or A Nice-To-Have (Part 1: Introduction and Battery Systems)

High Performance Polymers in Electrification: A Must-Have Or A Nice-To-Have (www.findoutaboutplastics.com)



In automotive industry, electrification gains traction and design engineers all over are working to increase the energy density of batteries, create higher voltage traction motors and increase allover system voltage. In this three part series, we will discuss the requirements of different system components, i.e. batteries, traction motor, power electronics and autonomous driving in terms of polymers. Let’s get started with batteries.

Introduction
- Plastic parts in electric vehicles (EV’s)

In 2019, we see all major OEMs and Tier-1 supplier continue their efforts toward electrification and new mobility solutions. Currently, development progress of internal combustion engines is at 1% per year [1], whereas electrification developments progress at a rate of 7 %. Industry experts predict that the connected mobility can grow according metcalfe's law with a rate of 70% (taking Facebook user rates as a baseline). The overall plastic weight per car will not change significantly with EV’s. However, there will be a slight increase in weight in total. There are currently 10 000 parts made out of plastic in an average car and these use ca. 39 different polymers. Out of the 39, 6 are used the most, i.e. polypropylene, polyurethane, polyamides, polyethylenes, acryle-butadien-sytrenes, and polyvinylchloride [2].

Check out here my infographic on “Plastics in Automotive”

Also in electrification, light weighting together with fuel economy will continue to be a megatrend. The rule of thumb says that for every 10% of weight reduction, fuel economy improves by ca. 6-8%. This additionally drives the consumption of plastics in automotive. The Chinese car market shows a lot of potential for light weighting since most cars run on old technology platforms. Furthermore, this is the largest car market today.

- What changes with EV’s?

EV’s have no longer the need for fuel tanks, AdBlue tanks, pumps and fuel connections. Here, we will see a drop in engineering polymers, together with elastomers since fuel lines and gaskets are not in demand. On the commodity side, high density polyethylene (HDPE) will also lose out since it is used for making tanks. Under the hood, combustion engine covers will not be needed either, however new engine covers for traction motor will rise.

- Which challenges are there concerning material selection?

In the past, material selection for internal combustion cars was easier since lots of experience as well as know-how were already built-up. This included the handling of specifications. For under-the-bonnet applications for example, aliphatic Nylons such as PA 6, PA 6.6., and aromatic Nylons such as polyphtalamide (PPA) are widely used. Furthermore, polyphenylene sulfide (PPS) is used where the highest heat and chemical requirements over the lifetime of the car are needed. PBT, PP, PU and POM/Acetals round up the polymers used in several exterior and interior applications.

Today, in hybrid and full EV’s, material selection tends to be much more differentiated, since applications need to fulfill specific requirements. The one-fits-all approach is no longer working in a similar sense. Standards from other industries such as electronics influence now material selection in automotive. As a result, a “wedding” between e.g. consumer electronics and automotive standards may take place.

Looking into the high performance material portfolio, semi-crystalline polymers fulfill stringent electronic requirements such as high CTI (>600), intrinsic flame retardancy, dielectric strength, creep, tracking resistance, EMI shielding, and high (140°C) Relative Temperature Index (RTI).

Lithium ion batteries – the heart of the EV

For coating the separator, fluoropolymers such as PVDF in aqueous dispersions can be used. Commodity polymers such as ultra-high-molecular-weight polyethylene (UHMWPE) can be used as separator substrate material. PVDF plays a role in making electrode binders (anode and cathode) too. In cell manufacturing, high adhesion between electrodes and separator is needed to obtain good laminates. Most common cell systems are pouch and jelly roll systems.

Battery pack and module – holding all together

Going outside the cell to the finished battery pack, several challenges need to be overcome. In general, a battery pack has between 10 to 16 modules and each module can have between 10 to 12 pouch cells.

For battery packs, three things need to be balanced:

• energy density (range),

• power (rapid charging),

• safety (non-flammable).

Every battery is connected over the pack’s housing with an electrical control unit, which protects the cells from overloading. The housing must ensure that all batteries stay in place and impact or vibration do not compromise performance. Figure 1 summarizes the potential plastic materials for cells, module, and pack.

Figure 1:  Overview of polymeric materials for battery technologies in the electrical powertrain.

.

Cells are connected to one another over busbars. Stability must be ensured. Busbars are usually long copper parts (up to 30 cm) overmoulded with PPS to obtain low dimensional changes. Flame-retardant plastics become increasingly important for packaging of the cells into modules. Modules have endplates and separator plates. Polymers such as PPS are a perfect candidate to be used as endplate and separator material in such environments since it ensures a best-in class thermal and chemical stability (RTI up to 220°C), inherently flame retardancy, and high dimensional stability. Selecting a linear PPS grade is beneficial since it has lower flashing during moulding. This minimizes post-processing steps after moulding and the investment of a de-flashing station. In addition, polycarbonate and their blends offer long-term capability and low-temperature impact strength which are needed for the battery modules as well.


Generally, all different assembles can benefit from thermal conductive materials which support the removal of the heat generated by the cells. Different polymer grades can be improved in this context by means of additives.


Thermal management – keep it cool
Next to the classic thermal management systems which use water-glycol, new ways of cooling are on the rise. This is driven by water-glycol reaching its performance borders with higher voltage system (>500 V). A new way is the so called “direct liquid cooling” which uses a dielectric cooling fluid and the cooling component is directly immersed in this fluid. This can be realized with fluorinated fluids such as perfluoropolyether (PFPE). These kinds of fluids have good thermal conductivity and combine a low electrical conductivity with low viscosity. Furthermore, excellent chemical resistance is given through the fluoro properties.


Heating systems for interior and battery
In contrast to traditional combustion cars, EV’S dissipate less heat to enable sufficient heating of the passenger cabin. Therefore, additional heaters need to be installed. Most of such heaters are based on the Positive Temperature Coefficient (PTC) effect. The ceramic based PTC elements can be lined up next to each other holding together via a support frame.


Here, a stringent requirement is not having ions in your polymer formulation. This is important to prevent corrosion of overmoulded metal parts and connectors. Galvanic corrosion can reduce the electric performance down to failure. Therefore, electrical friendly, halogen free stabilized semi-aromatic Nylons or PPS might be suitable here.


During operation, the battery pack temperature should be kept at 60°C. Heaters are used to keep temperatures on a certain temperature to ensure efficient charging. Heaters can operate in the high-voltage range (500V) with an output of 7 kW. High performance polymers will ensure their proper function over lifetime.


Charging Systems – high voltage with high safety
Charging the batteries of your electric vehicle in a reasonable time requires high voltage charging systems. Temperatures should be kept between 0°C to 45°C. Additionally, interconnection systems provide the power for the electric engine. Electrical properties such as dielectric strength, volume resistivity, creep, tracking resistance need to be carefully considered by design engineers.


Color coding helps safely handle parts in the event of an accident. Above 60 V, a system is considered to be high voltage and then orange color coding of connectors and cables is required.


For covering all these needs, polymeric materials need to fulfill Comparative Tracking Index (CTI) values of over 600, dielectric strength in the range of 30 kV to 35 kV, and Relative Temperature Index (RTI) of 140°C.


Aliphatic Nylons such as PA6, PA66, PA 46 fulfill this stringent criteria. Exception are certain temperature levels. Semi-aromatic Nylons such as PPA (6T/6I; 6T/6.6; 6T/6I/6.6) fulfill the temperature and electrical requirements. High mechanical strength combined with reflow soldering durability and laser welding properties make them a good choice. Important is to select types which are halogen free and free of red phosphorous which in turn allows Nylons to reach high CTI values. Electric corrosion of assembly bins is prevented by not using ionic heat stabilizers. Most Nylons have an HB flame rating and V0 rating is possible, however it might involve inorganic heat stabilizers.



With this I will close the first part of this high performance polymers series for EV.

In the second part we will look into the traction motor.


Thank you for reading!

Till next time!

Herwig Juster


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Literature:
[1] http://www.professoren.tum.de/lienkamp-markus/ and https://www.youtube.com/watch?v=5moHQFbEsDU&t=2238s
[2] A. Patil: An overview of Polymeric Materials for Automotive Applications, Materials Today: Proceedings 4 (2017) 3807-3815