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 properly.
Electrical Car (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 usually constructed into modules, and modules are linked collectively within the pack. Pouch cells require this sort of development on account of their lack of structural rigidity, while cylindrical cells want this as a result of excessive piece depend (>1000). Beforehand, prismatic cells have been dealt with in the identical method, however with the arrival of cell to pack/plate structure, there is no such thing as a longer a necessity for modules.
Usually, pouch cells stacks are shaped into modules in 3 ways, usually utilizing a thermal adhesive or hole filler after which both ambiently cooled or put in touch with a cooling system:
- Inserted right into a can with no adhesives or thermal administration
- Inserted right into a can with thermal adhesives
- 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:
- Inserted into plastic carriers utilizing interference match or structural adhesives
- Facet bonded to a cooling ribbon with thermal adhesives
- 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) usually utilizing a thermal adhesive or hole filler:
- Modules are shaped 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
- Packs are immediately shaped 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 embody:
- Minimal structural rigidity, requiring further housing
- Use of low floor power polyethylene movies because the outermost layer of the foil pouch, which limits the last word energy of adhesive-based stack-ups
- Marginal floor space for warmth elimination when stacked with out warmth spreaders (i.e., edge cooling)
Cylindrical cell challenges embody:
- Smaller cell measurement, requiring many cells to realize automobile vary
- Excessive cell depend necessitating actual positioning to make sure correct finding for downstream processes
- Vital mechanical fixturing necessities
- Nickel-plated metal surfaces that may be tough to bond
- A cell can reside when PVC shrink-wrap sleeves should not used
Prismatic cell challenges embody:
- Increased 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
- Use of low floor power shrink-wrap movies or tapes for dielectric safety, which limits the last word energy of adhesive-based stack-ups
- Higher want for flexibility on account of bigger areas leading to extra tolerance stacking and bigger stress from thermal enlargement.
Many of those challenges could be mitigated utilizing thermal hole fillers or thermal adhesives.
Early EV battery pack purposes relied on a small variety of extremely specialised formulations. Right now, EV battery techniques profit from a broader portfolio of thermally conductive supplies which are 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 energy. Hole fillers usually exhibit lap shear strengths under 7 MPa (1015psi), whereas adhesives are usually properly above this threshold.
Thermal adhesives formulated for electrical automobile battery manufacturing
Two-component acrylic structural adhesives have been used for the final 50 years to bond automotive panels. Their skill to bond immediately to numerous 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 trade chief in each classes, scientists at Parker Lord have been in a position to 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 industrial product on this class. Its excessive energy and thermal conductivity, mixed with the power to bond nickel-plated metal to powder-coated aluminum and treatment at room temperature with a comparatively quick fixture time, enabled important design freedom for cylindrical battery modules.
As new cell-to-pack and cell-to-plate designs are commercialized in electrical automobile (EV) powertrains, the function of thermal adhesives has grow to be more and more vital. There’s a rising want for revolutionary thermal adhesives that successfully bond battery cells to pack elements whereas addressing efficiency and manufacturing challenges.
Key enhancements in acrylic and urethane thermal adhesives embody:
- Tailorable bond energy 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 current structural adhesive improvements has enabled 4 instances greater elongation, in addition to elevated adhesion to plastics and coatings.
One observe relating to bondline – usually, adhesives present greater ranges of energy with thinner bondlines. A typical bondline is 250 µm, however when lowering thermal resistance is vital, thinner bondlines are all the time higher. For these merchandise, 100 µm was decided to be supreme. This thickness permits for enough breakdown energy, 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 wishes 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 can assist you along with your EV battery design. If you wish to join with certainly one of their software engineers to get began, then attain out in the present day.
