Cell to Carrier Bonding for EV Battery Assembly

Cost reduction in battery assembly is best achievable by shortening the cycle times and contributing to high-speed automated processes. One of those applications where speed, precision, and automation are important is the cell to carrier bonding for cylindrical cells.

In cell to carrier bonding, a multitude of cylindrical cells are bonded onto the plastic carrier, where cells are kept stationary at very short distances from each other. This allows the cells to maintain their structural integrity and prevents them from vibrating or rotating during the welding process or during the life of the product. 
 

Getting to high production efficiency requires the cell to carrier bonding to meet expectations in speed, precision, and repeatability, while still assuring a solid bond between cell and carrier. The selection of adhesive and equipment plays an important role in meeting these application expectations. 
 

Cell carriers and the outside layer of cylindrical cells are often made out of low surface energy plastic. Bonding them together is generally done with acrylics as they provide proper adhesion between two plastics or between plastics and metal.

Based on preference or application requirements, a selection between two acrylic types is common: UV-cure acrylics or two-part acrylics (MMAs). Both have their unique benefits and challenges.

UV-Cure Acrylics

Although expensive, UV-cure acrylics offer the quickest and most efficient solution. A major reason is that this adhesive only cures when exposed to UV light. This provides more flexibility in the bonding process and doesn’t make the application dependent on the adhesives curing time.

The challenge is that all cells need to be exposed to UV light to start the curing process. Clear carriers are used to solve this challenge as this will transmit the light to all cells, but if there are any “shadow areas” where the UV light didn’t shine, these cells will not be bonded at all unless a dual-cure acrylic is used.

Two-Part Acrylics (MMAs)

Methyl methacrylate adhesive (MMA) is a type of acrylic that is not bound to UV lights; the cells will always be bonded even if they are in “shadow areas.”

The curing time of a two-part acrylic can be a challenge in bonding a large number of cells onto a carrier.

• If the curing time of the adhesive is too short, you may not have sufficient time of applying the cell before it cures.
• If the curing time is too long, you waste valuable production time waiting for the adhesive to cure.

Whichever adhesive you select, automation plays a significant role in successful cell to carrier bonding. To achieve acceptable cycle times and a robust process, it’s critical to choose dispensing equipment that can handle the speed, repeatability, and precision that is required.

At Graco, we take great pride in the precision and quality our equipment can offer in applying one component or two-component adhesives.

UV cure materials are the fastest to apply, as they can be jetted easily. We offer solutions that consistently apply small dots at the speed you need. With the range of Advanjet jet valves you’ll be able to apply up to 300 drops/sec with outstanding repeatability and this for adhesives up to 400,000 centipoise.

Fast speeds can still be achieved with two-part acrylic material, though a perfect mix and dispense are imperative for optimal results. Our two-component dispense valves are specifically designed to apply accurate shots as small as 0.005 cc repeatably.