Sponsored by Parker Lord.

With the expansion and improvement of battery pack applied sciences, producers of electrical automobiles (EV) place better emphasis on pack design optimization, in search of extra compact options to enhance vitality density and cut back price. 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 group at Parker Lord developed a whitepaper “Assessing Applied sciences for Dielectric Safety of Battery System Parts.” On this whitepaper, the group mentioned their testing and comparisons of 4 totally 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 energy  
• 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, facet 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 sequence of 5 assessments have been accomplished: 

• Hipot Check: 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 fabric experiences electrical breakdown and turns into electrically conductive. 
• Adhesion: This take a look at appears to be like at how nicely the coating follow the aluminum. Crosshatch adhesion was carried out per ASTM D3359. A ranking of 5 signifies wonderful adhesion and a ranking of zero signifies poor adhesion.
• Environmental Getting older: Coated specimens for hipot and adhesion knowledge have been aged at 85°C / 85% RH for as much as 3 weeks in an ESPEC environmental chamber. One other set of specimens have 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 energy of the coating.
• Thermal Conductivity: Thermal conductivity was measured in response to ASTM D5470 utilizing 1400 TIM tester. Aluminum disks (33 mm diameter, 3 mm thick) have been coated with various movie thicknesses (50 to 200 micron) of dielectric materials. The disks have 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 answer is crucial to the choice of which to implement for a producer. Whereas every dielectric materials has its goal utility, it is very important assess every product’s utility time, ease of automation, labor and vitality prices, and the potential gear funding required for a full-rate automotive utility. 

When contemplating price and productiveness, PET movies are simple to use to geometrically easy elements however difficult for complicated elements. However, powder coating has the benefit that extra materials might be collected and reused however might be tough to realize even coating thickness on sophisticated geometries. LORD JMC coatings use customary functions and huge curing ovens whereas additionally not counting on static deposition. Which means, it’s sprayed the place it’s wished and never sprayed the place it’s not wished. In the meantime, Sipiol UV has low upfront capital funding and might 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 fabric’s electrical isolation efficiency and is measured by way of direct present hipot gear within the air. Greater 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 energy however decrease adhesion energy and is proscribed to flat surfaces.
• Powder coating has the bottom dielectric energy and requires a thicker movie to satisfy voltage face up to necessities.
• Each Sipiol UV and LORD JMC coatings can obtain excessive voltage face up to with a thickness of 90-120 microns and are beneficial for battery elements with sharper edges and radii. 

3) Edge Protection

Usually battery elements can have edges and corners that require protection for electrical isolation. As illustrated in Determine 2, electrical isolation efficiency relies 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 totally different substrates and analyzed for protection and thickness, Sipiol UV and powder coating have been efficient in uniformly coating sharp corners, however LORD JMC had problem with sharp corners and imperfections within the steel. Subsequently, a better thickness goal could also be wanted for very sharp radii to realize sufficient electrical safety.

4) Thermal Conductivity

Along with electrical isolation, thermal administration is one other crucial requirement for EV efficiency. Poor thermal administration might end in thermal runaway occasions, cut 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 fabric’s inherent thermal conductivity and the required movie thickness for electrical isolation when assessing its total warmth switch capabilities.

5) Adhesion and Surroundings

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

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

Abstract and Conclusions

The selection of dielectric supplies for particular battery elements relies on many elements, together with price and productiveness, dielectric energy, edge protection, thermal conductivity, adhesion, and electrical isolation. 

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