The EVB space is developing fast, and so are innovations in design, materials and (adhesive) chemistries. The best solution depends on the design and its purpose.

How do different types of EV battery impact the need for different adhesive solutions?

Before we take a look at the various types of batteries and the tape solutions suited for their respective challenges, let’s address the previous question straight out of the gate. 

As automotive and battery OEMs and suppliers work on different solutions to meet pack performance targets, the EVB has become more complex. Battery cells, their connecting busbars, the battery management system and all the thermal management, flame propagation and electrical insulation solutions call for the assembly of many different components and materials. Different specifications for different types of cells and their chemistries will result in a different battery design with different materials.

PSA solutions can address all of these challenges, even allowing design changes as needed. Whatever the type of EV battery, PSAs can meet their needs, from insulation and gasket and sealing to flame retardancy and thermal runaway protection. 

What kind of EV batteries are there?

For starters, there are three main types of lithium-ion (Li-ion) battery formats: cylindrical cells, prismatic cells, and pouch cells. In the EVB space, the first two are most prevalent – with the cylindrical format as current champion and the prismatic cell as runner-up, poised to take over. Regardless of the format, there are six major Li-ion technologies (chemistries): 

• lithium nickel manganese cobalt oxide (NMC)

• lithium iron phosphate (LFP)

• lithium nickel cobalt aluminium oxide (LNC)

• lithium cobalt oxide (LCO)

• lithium manganese oxide (LMO)

• lithium titanium oxide (LTO)

The first three are by far the most commonly used in EVs, due to their price-performance ratio. For high performance or long range, cells with high energy density are preferred, such as NMC and LNC. As they are more expensive than LFP, the latter is the more economical option (but with lower energy density), suitable for vehicles with modest performance and range. There is a trend towards solid-state batteries (SSBs) too, but they still have some liquid electrolytes that make them the riskier choice. We will however be seeing more All-solid-state batteries (ASSBs) in the future. They have more cell expansion, manageable through compression pads – which is one of the many challenges that PSA solutions can address.

What kind of tape solutions are available for EVB?

PSA tapes can be found anywhere, addressing a variety of challenges, from inside the cells to their exterior surface, between cells and their end plates, around modules, on conducting components and surfaces, module and pack sealing, fixing mica and other barrier materials, under pack lid, to outside the pack for thermal management material. Which is why there is a wide range of Avery Dennison PSA tape solutions available. 

Adhesive formulation, carrier, facestock and liner are selected based on the materials to be bonded, the application method and the operating conditions. This makes them an excellent option for bonding the various materials used in the battery module and pack construction, ranging from foams to fibrous materials, metals, ceramics and plastics.

Basically, there are three main categories of PSA solutions:

• transfer tape for laminating and bonding material layers;

• single coated tape – protecting surfaces from external influences;

• double coated tapes – for added functions to material layer bonding

Single and double coated tapes can be used for electrical insulation, encapsulating fragile TR and TP materials, or adding stability to weak or elastic materials (such as foams). 

The role of PSA solutions in EV batteries

PSAs for the EVB space are specifically designed for everything from battery pack & seal gasketing, cell to cell bonding and wrapping, compression pads, electrode fixing tape and electrical insulation to thermal interface materials and thermal runaway protection.

For the purpose of this article, there are five roles for PSA solutions in the EVB space:

• to protect and assemble thermal runaway and propagation materials (the selection of these materials and the specifications of the adhesives, encapsulation and labels varies depending on cell chemistry (and corresponding risk of heat, fire, explosion), battery design, and more);

• to electrically insulate (all packs are High Voltage, which means electrical insulation will be needed for the cells, conducting supports, cooling plates and ribbons, and so on);

• to bond for assembly and battery lifetime (note here that lifetime is extending; in the US, it is now at 160,000km warranty – and the pack must be durable to deliver this);

• track and trace (e.g. smart labels)

• labelling (warnings, necessary information)

There are many new applications on the horizon as new technologies are introduced. 

How does battery type influence adhesive choices?

Generally speaking, the following factors impact adhesive selection:

• thermal runaway (TR) and thermal propagation (TP) materials;

• cooling and heat transport;

• expansion of the cells;

• the type of compression pads that change depending on cell format chemistry 

For instance, pouch cells require more intracell layers to manage TR and TP and the ejection of hot particles, as their PET outer covering is not nearly as robust as the aluminium cans of prismatic and cylindrical cells. Heat distribution and flow is done via additional heat spreaders – again, as the PET is not an efficient heat conductor. Also, they swell more during use, which is why more is needed from compression pads. 

Prismatic cells on the other hand are more stable. They can be attached to each other to produce cell stacks that can bear some load. Still, some compression pads are needed, as well as some TR and TP materials, and electrical insulation.

Li-on batteries with a nickel manganese cobalt oxide chemistry (NMC) need to have TR and TP barrier materials with good thermal resistance and flame retardancy due to higher fire and explosion risk, and may therefore require flame retardant adhesives or adhesives solutions that offer a higher temperature resistance. LFP batteries, although with lower TR risk, still need barrier materials. These may be easier to bond with adhesives with lower heat resistance (e.g. PUR foam pads instead of silicone, or ceramic layers). Both chemistries in pouch and prismatic form will require compression pads to manage the expansion.

Cylindrical cells are encased in a matrix, but TR and TP materials surround the modules to prevent flame incursion to other parts of the battery pack or entering vehicle, and this may require different types of barrier materials with specific adhesive demands.

Adhesive selection

Ultimately, the adhesive selection is guided by the substrates to be bonded, the operating conditions and environment. There is no “one size fits all”. Adhesives must be selected based on the four steps that can be found in our product selection tool:

1. what type of material will you be laminating to (what is the laminating substrate);

2. what is the surface energy of the substrate your laminated part will be bonded to;

3. are there any other end user application requirements (environmental conditions);

4. what tape construction is needed (depends on surface roughness, elasticity of the substrates, method of application, et cetera).

As our product selection tool shows, there are a variety of factors and variables for each of the four steps. For instance, substrates that are hard to bond (i.e. have low surface energies) – like many coated glass fibre textiles and silicone foams – require specific PSAs that can wet the surface and establish the required adhesion. Rubber-based PSAs have high peel strength and will bond to coated glass fibre, and are quite suitable for ceramic and mica papers and pads, while silicone adhesives and some special acrylic formulations on the other hand will work on silicone foams. When bonding PET and other dielectric layers to electrically insulate cell cans, metal cooling plates and ribbons, the end plates and pack beams may require a higher dynamic shear strength, which highly crosslinked acrylic PSAs can deliver.

Other applications may be for assembly and simple retention, where standard acrylics such as UV warm melts will demonstrate stable performance under a wide range of conditions.

There are also specialised applications, such as the electrode fixing tapes used within the cells to restrain the cell layers and insulate inside the cell can – here, the resistance to the electrolyte is most critical, and the solution must not encourage self-discharging of the cell.

Finding the right PSA solutions for your battery requirements

Selection the right adhesive material matters, as PSA tape solutions can contribute to:

• Safety
  Allowing thermal runaway and propagation materials to be assembled and retained so that they can effectively contribute to thermal stability and delay TR and TP; electrical insulation (prevent arcing, parts becoming live when they should not); warning and information labels;

• Performance
  effective integration of different materials/laminates to manage heat and extend cell life;

• Durability
  keeping everything in its place; retention, protecting TR and TP materials;

• Productivity
  contributing to efficient, high volume, six sigma output manufacturing; intelligent labels to facilitate industry 4.0, reduce cost, increase efficiency and quality.

It should be clear from the foregoing that there are many different criteria at play here. 

PSA is our materials science, combined with our expertise in adhesive formulation, coating technologies (including nanocoating). Functional bonding and protection tapes make EV batteries safer, more efficient and easier to assemble.

We offer solutions for any and all of the challenges today, but are also working on future challenges as the trend goes to higher energy density (larger modules, cell to pack/chassis), different chemistries and ultimately new batteries including various SSBs.

For instance, Cell to Pack (C2P) means more load bearing for the cell stacks –PSA tapes spread stresses (unlike mechanical fasteners), reducing stress concentrations and increasing durability. TR and TP materials not between cells but around cell stacks or other locations in the pack need to be assembled and held in place, at least during assembly. SSBs, as previously addressed, tend to swell more during charging, so cell compression pads will become critical – and will need to be assembled (perhaps made from multilayers held together with PSA to become multifunctional) and retained (kept in place for 160,000km-plus!).

Take full advantage of the flexibility and performance of our solutions

Avery Dennison's EV Battery adhesive and tape solutions empower our customers to keep pace with the ever-evolving market requirements. Our innovations are built on multiple pressure-sensitive adhesive technologies and focus on diminishing flammability, enhancing electrical insulation and safeguarding packaging components. The extensive range of functional adhesives and protective tapes for EV Batteries is based on various methodologies to elevate safety and efficiency. Indeed, Avery Dennison can help OEMs to tackle some of the most common challenges associated with electric vehicle batteries. In fact, we are well-experienced in supplying the automotive industry with solutions including demanding applications and safety critical ones and with the technology to support the industry in its transformation, now and in the future. To ensure tape compliance with OEM and battery producer specifications, we extend collaborative opportunities for creating solutions.

PSA tape solutions contribute to better product design by simplifying the use of dissimilar materials, joining irregular shapes, saving space and contributing to light-weighting. Their insulating features add to electrical safety. Adding flame retardance features to PSA tapes facilitates composites and materials to meet UL® 94 V-0 and other flame-retardant requirements. Prototyping is quick, easy and can be completed without expensive tooling and equipment. To take full advantage of the flexibility and performance of our solutions, bring your PSA expert on board early in the design stage. 

Find out how Avery Dennison can support your EVB production objectives.