Sponsored by Parker Lord.

With the expansion and improvement of battery pack applied sciences, producers of electrical autos (EV) place larger emphasis on pack design optimization, looking for extra compact options to enhance vitality density and scale back value. Within the meeting of high-voltage battery packs, dielectric safety is crucial. Producers typically apply dielectric supplies to the battery cells, cooling plates, and adjoining elements. 

The crew at Parker Lord developed a whitepaper “Assessing Applied sciences for Dielectric Safety of Battery System Parts.” On this whitepaper, the crew mentioned their testing and comparisons of 4 completely different dielectric supplies (Desk 1):

• Polyethylene terephthalate (PET) movie 
• Powder coatings
• Solvent-borne coatings (LORD® JMC)
• UV-curable coatings (Sipiol® UV)

Dielectric supplies are sometimes polymeric in nature and require the next efficiency attributes:

• Excessive dielectric power  
• Good adhesion to substrates
• Sturdy after publicity to chemical, thermal, and mechanical forces
• Utilized at skinny movie thickness (50-250 microns)
• Simply utilized in a excessive throughput manufacturing course of

With functions in battery cells, bus bars, cooling plates, aspect plates, partitions, and battery lids, dielectric supplies are crucial in EV elements the place electrical isolation is required (Determine 1).

Accomplished Testing

For the research, a collection of 5 exams had been accomplished: 

• Hipot Take a look at: Excessive Potential (Hipot) gear was used to measure the breakdown voltage of dielectric supplies per ASTM D3755. The breakdown voltage is the minimal voltage the place a cloth experiences electrical breakdown and turns into electrically conductive. 
• Adhesion: This check appears to be like at how nicely the coating persist with the aluminum. Crosshatch adhesion was performed per ASTM D3359. A ranking of 5 signifies glorious adhesion and a ranking of zero signifies poor adhesion.
• Environmental Growing old: Coated specimens for hipot and adhesion knowledge had been aged at 85°C / 85% RH for as much as 3 weeks in an ESPEC environmental chamber. One other set of specimens had been uncovered to thermal chilly shock biking from -40°C to 100°C for as much as 120 cycles utilizing a Thermotron SE400 environmental chamber.
• Failure Mode: The failure mode was analyzed to find out the weakest level for the bonding meeting. A cohesive coating failure signifies that the weakest level is the cohesive power of the coating.
• Thermal Conductivity: Thermal conductivity was measured in accordance with ASTM D5470 utilizing 1400 TIM tester. Aluminum disks (33 mm diameter, 3 mm thick) had been coated with various movie thicknesses (50 to 200 micron) of dielectric materials. The disks had been compressed to 50 kPa stress within the TIM tester.

Technical Comparisons

1) Value and Productiveness 

In addition to efficiency, the economics of a dielectric materials resolution is crucial to the choice of which to implement for a producer. Whereas every dielectric materials has its goal software, it is very important assess every product’s software time, ease of automation, labor and vitality prices, and the potential gear funding required for a full-rate automotive software. 

When contemplating value and productiveness, PET movies are straightforward to use to geometrically easy elements however difficult for advanced elements. Alternatively, powder coating has the benefit that extra materials may be collected and reused however may be tough to attain even coating thickness on sophisticated geometries. LORD JMC coatings use normal functions and huge curing ovens whereas additionally not counting on static deposition. That means, it’s sprayed the place it’s needed and never sprayed the place it’s not needed. In the meantime, Sipiol UV has low upfront capital funding and may be robotically spray-applied, making it an environment friendly possibility. 

2) Electrical Isolation

Electrical isolation is a main requirement for the security and efficiency of EV battery elements. Minimal breakdown voltage is used to quantify a cloth’s electrical isolation efficiency and is measured through direct present hipot gear within the air. Increased materials breakdown voltage interprets into improved electrical isolation and improved security and efficiency of EV battery elements. 

Parker Lord discovered that:

• PET movie has the very best dielectric power however decrease adhesion power and is restricted to flat surfaces.
• Powder coating has the bottom dielectric power and requires a thicker movie to satisfy voltage stand up to necessities.
• Each Sipiol UV and LORD JMC coatings can obtain excessive voltage stand up to with a thickness of 90-120 microns and are really helpful for battery elements with sharper edges and radii. 

3) Edge Protection

Usually battery elements may have edges and corners that require protection for electrical isolation. As illustrated in Determine 2, electrical isolation efficiency will depend on movie thickness. Thus, figuring out the coating movie thickness on an edge is vital for understanding {the electrical} isolation efficiency. 

Of the 4 coatings utilized to 2 completely different substrates and analyzed for protection and thickness, Sipiol UV and powder coating had been efficient in uniformly coating sharp corners, however LORD JMC had problem with sharp corners and imperfections within the metallic. Subsequently, the next thickness goal could also be wanted for very sharp radii to attain sufficient electrical safety.

4) Thermal Conductivity

Along with electrical isolation, thermal administration is one other crucial requirement for EV efficiency. Poor thermal administration could lead to thermal runaway occasions, scale back the effectivity of digital elements, and decrease the EV’s energy. Therefore, it is very important take away warmth from battery and powertrain elements effectively. 

For EV functions requiring excessive electrical isolation and warmth switch, LORD JMC is the popular product, adopted by powder coating, Sipiol UV, and PET. It is very important think about each a cloth’s inherent thermal conductivity and the required movie thickness for electrical isolation when assessing its total warmth switch capabilities.

5) Adhesion and Atmosphere

Adhesion is one other vital issue when evaluating which dielectric supplies. As soon as the dielectric materials is utilized, it should stay on the part floor to offer dielectric safety for the product’s life. As well as, good adhesion to the metallic substrate and adhesive is vital for efficient warmth switch. The required adhesion power varies relying on the place it’s used.

Of all of the supplies examined, Sipiol UV had the very best adhesion power, adopted by powder coating and LORD JMC. PET movie had the bottom adhesion power, which might be improved with plasma therapy. The thermal shock biking had minimal damaging results on adhesion for all supplies, whereas publicity to 85°C / 85% RH situation had average reductions in adhesion power. All 4 dielectric supplies have glorious crosshatch adhesion to aluminum earlier than and after environmental publicity. 

Abstract and Conclusions

The selection of dielectric supplies for particular battery elements will depend on many elements, together with value and productiveness, dielectric power, edge protection, thermal conductivity, adhesion, and electrical isolation. 

Steady improvement of the talked about dielectric supplies is ongoing. There are merchandise which might be being developed to enhance warmth switch, adhesion, nook protection, ease of software, and value. It’s vital to determine the important thing efficiency and manufacturing attributes and work carefully with coating suppliers and manufacturing integrators to implement profitable options. In case you are considering studying extra about Lord JMC or Sipiol UV, attain out to Parker Lord at the moment. And to obtain their whitepaper, go to this hyperlink.