Charged EVs | Developments in thermal adhesives: enhancing battery cell-to-pack and cell-to-ribbon efficiency for EVs

A key to the development of excessive energy-density, lithium-ion, battery packs is efficient administration of warmth generated throughout cost and discharge cycles. Warmth is commonly managed by connecting battery cells and/or modules to a cooling plate or pack by way of thermally conductive supplies (hole fillers or adhesives). Sometimes, they’re two-component polymeric resins with ceramic fillers. These promote warmth conduction by displacing air from not solely microscopic surfaces however massive gaps as nicely. 

Electrical Automobile (EV) battery pack structure is pushed by cell type issue: Pouch, Cylindrical, and Prismatic. The cell kind is the primary guiding affect module/pack design and thermal administration materials wants. 

Pouch and cylindrical cells are sometimes constructed into modules, and modules are linked collectively within the pack. Pouch cells require one of these building as a consequence of their lack of structural rigidity, while cylindrical cells want this as a result of excessive piece rely (>1000). Beforehand, prismatic cells had been dealt with in the identical method, however with the arrival of cell to pack/plate structure, there isn’t any longer a necessity for modules.

Typically, pouch cells stacks are fashioned into modules in 3 ways, sometimes utilizing a thermal adhesive or hole filler after which both ambiently cooled or put in touch with a cooling system:

1. Inserted right into a can with no adhesives or thermal administration
2. Inserted right into a can with thermal adhesives
3. Stacked with an aluminum warmth spreader between every cell with and with out thermal materials

Cylindrical cell module designs fall into three classes previous to being inserted into the pack and linked to the cooling loop:

1. Inserted into plastic carriers utilizing interference match or structural adhesives
2. Facet bonded to a cooling ribbon with thermal adhesives
3. Fixtured into an array after which the cell bottoms are bonded to a housing or cooling plate utilizing a thermal adhesive

Prismatic cells are used to type modules or packs (modules are inserted into the pack) sometimes utilizing a thermal adhesive or hole filler:

1. Modules are fashioned by grouping the cells right into a stack after which both inserted right into a module housing or onto a cooling plate, each utilizing thermal adhesives or hole fillers
2. Packs are straight fashioned by bonding massive format cells (~1m size) on to the underside plate utilizing thermal adhesives or hole fillers

Alternatives and Challenges

Many design and manufacturing alternatives and challenges exist for every type issue.

Pouch cell challenges embrace:

1. Minimal structural rigidity, requiring further housing
2. Use of low floor vitality polyethylene movies because the outermost layer of the foil pouch, which limits the last word power of adhesive-based stack-ups
3. Marginal floor space for warmth removing when stacked with out warmth spreaders (i.e., edge cooling)

Cylindrical cell challenges embrace:

1. Smaller cell dimension, requiring many cells to realize car vary
2. Excessive cell rely necessitating actual positioning to make sure correct finding for downstream processes
3. Important mechanical fixturing necessities
4. Nickel-plated metal surfaces that may be tough to bond
5. A cell can stay when PVC shrink-wrap sleeves are usually not used

Prismatic cell challenges embrace:

1. Greater particular person cell floor space in comparison with cylindrical or pouch cells, resulting in tolerance points for each the cell and the cooling plate/pack
2. Use of low floor vitality shrink-wrap movies or tapes for dielectric safety, which limits the last word power of adhesive-based stack-ups
3. Higher want for flexibility as a consequence of bigger areas leading to extra tolerance stacking and bigger stress from thermal growth. 

Many of those challenges will be mitigated utilizing thermal hole fillers or thermal adhesives.

Early EV battery pack purposes relied on a small variety of extremely specialised formulations. As we speak, EV battery programs profit from a broader portfolio of thermally conductive supplies which might be nonetheless engineered particularly for battery pack necessities however supply a wider vary of efficiency and processing choices.

At Parker Lord, the excellence between hole fillers and adhesives relies on power. Hole fillers sometimes exhibit lap shear strengths under 7 MPa (1015psi), whereas adhesives are usually nicely above this threshold.

Thermal adhesives formulated for electrical car battery manufacturing

Two-component acrylic structural adhesives have been used for the final 50 years to bond automotive panels. Their capability to bond straight to varied metals and finishes, together with room-temperature curing, has dramatically decreased the quantity of mechanical fixturing and/or welding required. Likewise, two-component, thermally conductive potting and encapsulation supplies have been used for the final 60 years to guard digital elements and take away warmth.

As an business chief in each classes, scientists at Parker Lord had been capable of mix these two applied sciences, creating a brand new class of adhesives: thermally conductive structural adhesives.

Parker Lord’s CoolTherm TC-2002 Thermally Conductive Structural Adhesive was the primary business product on this class. Its excessive power and thermal conductivity, mixed with the power to bond nickel-plated metal to powder-coated aluminum and treatment at room temperature with a comparatively brief fixture time, enabled vital design freedom for cylindrical battery modules.

As new cell-to-pack and cell-to-plate designs are commercialized in electrical car (EV) powertrains, the function of thermal adhesives has turn into more and more vital. There’s a rising want for progressive thermal adhesives that successfully bond battery cells to pack elements whereas addressing efficiency and manufacturing challenges.

Key enhancements in acrylic and urethane thermal adhesives embrace:

• Tailorable bond power for structural or reworkable pack designs
• Elevated elongation for enhanced sturdiness
• Tailored treatment speeds
• Strategies to facilitate high-throughput manufacturing.

The most recent launch from Parker Lord is CoolTherm TC-850 Thermally Conductive Acrylic Adhesive, which builds on the capabilities of CoolTherm TC-2002. Leveraging latest structural adhesive improvements has enabled 4 occasions greater elongation, in addition to elevated adhesion to plastics and coatings.

One notice concerning bondline – normally, adhesives present greater ranges of power with thinner bondlines. A normal bondline is 250 µm, however when decreasing thermal resistance is vital, thinner bondlines are all the time higher. For these merchandise, 100 µm was decided to be best. This thickness permits for ample breakdown power, reduces materials utilization, and lowers the required thermal conductivity.

See under for an illustration demonstrating {that a} 0.5 W/m∙Okay with a 100um bondline achieves decrease thermal resistance in comparison with a 1 W/m∙Okay materials with a 250um bondline.

Wrapping it up

In conclusion, deciding on a thermal adhesive that aligns with particular cell-to-pack designs and desires will equip battery pack designers and materials engineers with the data to optimize pack efficiency, reliability, and cost-effectiveness.

Parker Lord has a wealth of experience and data that will help you together with your EV battery design. If you wish to join with one among their software engineers to get began, then attain out as we speak.