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Structural Batteries: The Cars of the Future Are Glued

authorIcon By Stéphane Melançon on January 26, 2022 topicIcon Batteries

The technology behind electric vehicles is evolving quickly, and one of the most promising innovations is the structural battery pack. 

Structural battery packs are multifunctional materials that serve both for energy storage and structure. As a result, redundant structural elements can be removed, eliminating weight from other parts of the vehicle. They are said to offer “massless energy storage” because their effective weight is lower than the total weight of the cells (considering the parts they replace). 

Structural batteries are changing the way electric cars are assembled. Structural adhesives are replacing screws and welds to “glue” components together using a process called adhesive bonding. This process requires additional surface preparation and creates new challenges for automakers and battery makers.

Traditional vs. Structural Battery Packs 

Traditional battery packs are mainly used to provide electrical energy, but they also help strengthen the car’s frame. Structural battery packs take this role much further and are an important part of the load-bearing structure.   

Let’s look at two examples to better understand the difference. 

Tesla’s traditional battery packs are made of cylindrical cells enclosed in modules. These modules provide a rigid enclosure for the battery cells, protecting them to make sure they are under no stress. 

But in Tesla’s structural batteries, cylindrical cells are not enclosed in modules. Instead, the cells are first bonded to each other, then they are bonded to an upper metal sheet and a lower metal sheet. This creates a solid structure that strengthens the vehicle’s body and chassis while providing torsional rigidity and shear transfer. 

Improvements brought by structural batteries are impressive:

These improvements [for Tesla’s Model Y] result in a 10% weight reduction, a 14% increase in range, a significant reduction in the number of parts, and the overall increased structural integrity of the vehicle.

Excerpt from Tesla Model Y with Structural Battery May Already Be in Production, Owner’s Manual Hints

GM has a different approach. In their Hummer EV, they are using pouch cells protected by modules, and the battery packs are installed in the chassis.

The Ultium battery packs are installed in - and help stiffen - the vehicle’s chassis. This, in turn, improves ride and handling while reducing vibration and harshness.

Excerpt from Next step for EVs: Design batteries to strengthen car, extend range

These are different approaches to structural batteries, but in all cases, they serve an additional function in the vehicle’s structure. They also have a better energy density (Watt-hours per kilogram) than traditional batteries, improving the battery’s range. 

What Companies Manufacture Structural Batteries? 

Companies that manufacture structural batteries include automakers like Tesla and GM as well as battery makers like BYD and Contemporary Amperex Technology. Some automakers partner up with battery makers to produce their battery packs. Examples include Volvo and Northvolt as well as BMW and ONE (Our Next Energy). ​

What Is Adhesive Bonding and Why Is It Important? 

Adhesive bonding is a critical process for structural batteries. It is used to join surfaces together, creating a structure that distributes the stress load evenly, which provides more strength. It is done using structural adhesives, such as epoxy resin mixed with a hardener, adhesive tapes, or double-sided adhesive sheets.

Adhesives serve many purposes. By replacing mechanical fasteners, they reduce the battery’s weight and hence improve its range. Adhesives also protect the battery from environmental factors, such as water, dust, road salt, and automotive fluids. They improve the battery’s mechanical properties as well, offering protection against shocks and vibrations. Finally, they can act as thermal conductors or insulators, helping regulate the battery’s temperature for improved safety and durability.

If you’re interested in learning more about the adhesive bonding process, you can watch the following video. 

 

To ensure the success of adhesive bonding, surfaces to be joined need to be cleaned by removing contaminants such as dusts, oxides, oils, battery electrolytes, and coatings. This improves the chemical properties that hold the surfaces together. 

For a structural battery, the cleaning step represents a challenge because the total surface area that needs to be cleaned and bonded is very high compared to traditional batteries. This means that there is even less room for errors or inconsistencies in the cleaning and bonding processes, or else batteries will fail.  

To ensure this, manufacturers need a reliable and precise cleaning process. This is where industrial laser cleaning can help. 

Laser Technology to Prepare Batteries for Adhesive Bonding 

Laser technology offers two key processes to prepare batteries for adhesive bonding: laser cleaning and laser texturing. 

  • Laser cleaning removes surface contaminants to prevent them from interfering with the bonding process. Unlike other cleaning technologies, laser cleaning does not introduce contaminants in the process, such as abrasives or chemicals. 
  • Laser texturing improves the surface texture and roughness, improving properties like wettability for a better adhesion during assembly. The process can be customized for personalized surface patterns and roughness values. 

Watch this video to see both processes performed at the same time. 

 

Laser technology is well suited to prepare structural batteries for adhesive bonding because of its high precision and repeatability. It is fast, easily automated, and generates little maintenance, making it ideal for the demanding requirements of battery production lines. 

If you think you could benefit from laser technology, contact a laser expert to discuss your application. 

Title photo: @shortword/Twitter

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Stéphane Melançon's picture

Stéphane Melançon

Technical expert and consultant in batteries and electrical propulsion systems, Stéphane holds a Physics degree with specializations in Photonics, Optics, Electronics, Robotics, and Acoustics. Invested in the EV transformation, he has designed industrial battery packs for electrical bikes. In his free time, he runs a YouTube channel on everything electrical.