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The Glue Talk Blog

Navigating Electric Vehicle Battery Design Trends

A decade ago, road-tripping in an electric vehicle (EV) may have sounded strange. That is no longer the case thanks to innovations like battery swapping stations (in certain countries) and EVs with ranges similar to gas-powered engines. Driving around the northern coast of Scotland or from Paris to London and back without stopping to recharge is now possible.

Innovations in materials and design increase EV range. However, each change must be balanced to ensure the vehicle remains safe and functions well over time. Here, we’ll unpack the differences between cell-to-module, cell-to-pack, and cell-to-chassis EV battery designs, discuss emerging trends in EV batteries, and explore how adhesives support the form and function of EV batteries.

What is Cell-to-Module EV Battery Design?

Electric vehicle batteries traditionally include individual cells encased within a module. Manufacturers assemble multiple modules onto a pack, which is attached to the vehicle’s chassis. This nesting-doll configuration provides the structure necessary to hold the cells in place during use. The cell-to-module design also enables easier repairs. For example, if the battery management system notices a failed cell, a repair person can open the battery pack and replace the faulty module with a functioning one.

How Adhesives Enhance EV Battery Repairability

Compared to other designs, cell-to-module batteries require more production steps (Table 2). The module casings add weight to the battery, which impacts mileage. However, the repairability of modules within the design cements its place in the EV world.

Availability is more important than mileage for some types of EVs, such as public service vehicles. When vehicles are equipped with cell-to-module batteries, workers can easily repair or replace malfunctioning modules so the vehicle can continue operating with minimal downtime.

Table 2. Comparing Cell-to-Module, Cell-to-Pack, and Cell-to-Chassis EV Batteries.

Quality Cell to Module Cell to Pack Cell to Chassis
Reduces weight ✓ ✓
Lowers production complexity ✓ ✓
Easily repairable ✓
Swappable ✓ ✓
Requires structural adhesives or additional structural support ✓ ✓

H.B. Fuller’s EV Seal adhesive line allows for resealable EV battery packs. When sealed, the hot-melt, butyl-based adhesives protect the battery pack assembly from moisture, humidity, and environmental exposure. However, the adhesives can be removed and reapplied, allowing manufacturers to open the pack and repair or replace modules.

What is Cell-to-Pack EV Battery Design?

A cell-to-pack EV battery design eliminates the need for modules. Instead, manufacturers place battery cells directly onto the battery pack and install the pack onto the chassis. Removing the module casing reduces the battery’s weight and frees space for additional cells. Lighter, stronger batteries improve mileage, an increasingly important feature for consumers. Cell-to-pack designs also remove many steps from assembling a battery, increasing production speed and (potentially) decreasing costs.

“Manufacturers are trying to remove as much weight and complexity in a battery as possible,” explains Michael Cooper, Global Business Development Manager at H.B. Fuller, “The transition from module to pack removes a significant portion of the material weight and increases the battery’s power density.”

Switching from cell-to-pack simplifies production for automakers and provides consumers with more powerful, lighter vehicles. However, the design requires creative engineering solutions to maintain structural integrity. Manufacturers may add metal structural elements to the battery pack or use structural adhesives, such as H.B. Fuller’s EV Bond line, to unify the battery to withstand vibration and other environmental stressors during use.

Powerful EV Batteries Require Powerful Thermal Management Adhesives

Cell-to-pack EV batteries require innovative solutions to keep them within ideal operating temperature ranges because the cells are packed closely together. If EV battery cells get too cold, their performance suffers; when too hot, they age more rapidly and risk thermal runaway events (e.g., fires). Maintaining temperatures below 65°C (149°F) within cell-to-pack EV batteries prevents overheating.

“As batteries and battery-related electronics become more powerful, they generate more heat during operation,” says Florian Schloegl, Global Market Manager ePower/Storage at H.B. Fuller, “There’s a need for improved thermal management and stronger thermally conductive adhesives and encapsulants to remove heat from the electronic components.”

H.B. Fuller’s EV Protect line of flame retardant encapsulants isolates thermal runaway so fires don’t spread. Manufacturers apply the foam encapsulant as a liquid, which expands to surround battery cells. The lightweight foam is less dense than competitive products and helps unify the battery with its semi-structural properties. The H.B. Fuller® EV Protect 4006 SFR adhesive is also the first of its kind and isolates thermal propagation incredibly quickly compared with competitors.

“H.B. Fuller® EV Protect 4006 SFR is the benchmark for anyone producing batteries, whether they’re looking to provide hermetic sealing, electrical insulation, and facilitate the prevention of thermal runaway,” says Cooper.

What is Cell-to-Chassis EV Battery Design?

Automakers attach battery cells directly onto the vehicle’s chassis when making cell-to-chassis EV batteries. This configuration further simplifies battery production, eliminates the weight of the pack and module, and optimizes battery space. The chassis also provides some structural integrity to the battery.

However, materials used within the battery, such as adhesives and cells, must be designed to bear weight in addition to their other functions. The cell-to-chassis configuration is also the most difficult to repair or replace, as the entire underbody of the vehicle must be disassembled to reach the battery. EV batteries typically decline in performance after seven to eight years, meaning automakers would have to take apart the vehicle multiple times throughout its lifespan to replace the battery.

Adhesives Provide Structure and Manage Heat in Cell-to-Chassis Designs

Adhesive materials used in the cell-to-chassis design often perform multiple functions. The encapsulant keeping the cells in place must also provide structural integrity and, ideally, mitigate thermal propagation in the battery. H.B. Fuller’s EV Bond line has robust structural strength and can bond dissimilar substrates (e.g., metal and plastic). EV Bond 300, specifically, can compensate thermal expansion and contraction as the battery cells heat up and cool down. This capability helps keep the cells in place without affecting the performance of the adhesive.

The closely packed cells within the cell-to-chassis battery design require heavy-duty thermal management. Adhesives, including H.B. Fuller’s EV Therm product line, transfer heat between cells and cooling systems, helping minimize heat retention to optimize battery performance.

The EV Therm product line also includes dielectric coating products that isolate electricity between battery components. This prevents short-circuiting and arching and improves safety. The products are spray-applied, simplifying production significantly, and require only a thin application layer, reducing material costs.

Additional Trends in EV Energy Storage

Consumer demand for electric vehicles has soared in the last decade, and experts predict that sales of battery-powered EVs will continue to grow. Much of the innovation in the EV space stems from consumer demand for more affordable, safer, and functional vehicles. Consumers want EVs that can drive as far as gas-powered vehicles and take less time to charge. Trends include:

  • Light weighting through design or material changes to increase vehicle range
  • Immersion cooling to improve safety and thermal management in Lithium-ion batteries
  • Rapid charging by replacing encapsulants with dielectric fluid
  • Debonding on demand to make EV production more sustainable
  • Standardizing battery design to drive down the costs of each battery pack

Although end-of-life questions for EV batteries are less relevant to consumers, they are top-of-mind for adhesive manufacturers and automakers. What happens to batteries once they reach the end of their lifespan? Can batteries be recycled? How can batteries be dismantled to reuse cells in other applications?

One solution to a more sustainable end-of-life for EV batteries is reusing modules or packs once they reach the end of their automotive lifespan but still store sufficient electricity to make them viable. Vehicle batteries are often replaced when they still have 80% capacity. These “old” batteries could be directly reused for power grid stabilization or ESS (home energy storage systems), where space is less of an issue than a vehicle.

Solutions for EV Battery Design Challenges

No matter which trend emerges next in EV energy storage, innovative adhesives that protect, seal, bond, or manage heat within the battery will always be needed. Consider rapid cooling. If automakers encase battery cells with dielectric fluid instead of foam to cool cells quickly, the batteries will require chemically resistant adhesives with high adhesion strength and structural properties to keep units together. Adhesives will always be needed, even if their form and function change.

H.B. Fuller develops adhesives and sealants that meet battery design challenges today and tomorrow. Today, through our product offerings (like the groundbreaking H.B. Fuller® EV Protect 4006 SFR), and tomorrow, through customer partnerships. H.B. Fuller engineers work closely with customers, often starting with the battery concept phase (years before production). We can also help customers make running changes to overcome unexpected challenges pre-production or during production.

“At H.B. Fuller, we have the capability to do modifications, and we have the expertise and experience to engage with customers early in projects,” says Schloegl, “We help customers with finite element analysis (FEA), material cards, adhesive-friendly design, laboratory testing, and process development.”

Partnering with H.B. Fuller provides access to dispensing manufacturers and worldwide production facilities. In addition to the commonly used polyurethanes and acrylates, H.B. Fuller maintains a full range of adhesive technologies in-house to test out-of-the-box solutions for customers. We work to find the optimized fit for each application.

With H.B. Fuller, you can overcome your battery design challenges. Email [email protected] for more information on adhesive solutions for your EV energy storage needs.

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