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Battery Pack Manufacturing Technologies

authorIcon By Stéphane Melançon on June 23, 2022 topicIcon Batteries

Source: Munro Live

Battery packs are key components in some of the most important technologies of the 21st century. They come in various forms to provide energy to electric vehicles, energy storage systems, medical devices, cellphones, and a lot more.

Manufacturing technologies used for battery packs vary extensively. For example, electric vehicle battery packs have complex requirements since they need to withstand large temperature ranges and vibrations. 

In this article, we will explore the complexities of EV battery manufacturing. Specifically, we will look at the following technologies:

  1. Bonding Technology: Dispensing Systems
  2. Joining Technologies: Laser Welding & Ultrasonic Bonding
  3. Surface Preparation with Laser Cleaning & Laser Texturing
  4. Traceability and Quality Control Technologies for Battery Cells
  5. Quality Control Technologies for the Final Assembly
  6. New Designs That Are Changing Battery Pack Manufacturing

Bonding Technology: Dispensing Systems

Dispensing systems are used to apply thermal interface materials (TIMs), which often take the form of liquids or pastes. TIMs are applied to the cold plate or directly to the cells before the cells are inserted into modules or cell holders. 

Due to the growing interest for structural batteries, modern battery packs are increasingly making use of TIMs such as structural adhesives and gap fillers. 

Watch the following video to see how dispensing systems work.

 

Joining Technologies: Laser Welding & Ultrasonic Bonding

Battery packs include up to thousands of electrical connections between cells and busbars. These connections are typically done using one of two technologies: ultrasonic bonding or laser welding.

Many manufacturers are looking to replace ultrasonic wire bonding with laser welding to simplify their joining process and reduce the number of machines on the shop floor. A single laser welding machine is more efficient than a dozen ultrasonic wire bonding machines. 

Ultrasonic bonding is an older technology that uses a metallic tool that vibrates at the joined area to generate heat and join surfaces without melting the surface.

 

Laser welding, a faster alternative, uses a concentrated beam of light to create a melting pool that joins metallic surfaces. 

 

Surface Preparation with Laser Cleaning & Laser Texturing

Laser technology for batteries is used to prepare surfaces for subsequent production processes, mostly bonding and welding. It is precise, consistent, and fast. 

Laser cleaning removes contaminants such as electrolytes, dust, oxides, and hydrocarbons (oil, grease, etc.) It is an essential step to ensure high-quality welds and bonds.

 

 

Laser texturing etches the surface to modify its roughness. The resulting texture improves the heat transfer between surfaces and thermal interface materials. It also improves the bonding performance of structural adhesives.

 

Traceability and Quality Control Technologies for Battery Cells

Because battery packs are expensive to produce and critical to safety, there are frequent quality control steps before assembly to validate the identity and state of each cell. To allow controlling quality, battery packs and their components need to be fully traceable. 

Laser marking is used to identify each part with a data matrix code. This is used to identify which batteries could be defective when a problem is detected.

 

Vision systems are also needed to read the DMCs and perform surface measurements.

 

Quality Control Technologies for the Final Assembly

Once the battery pack is fully assembled, several validation tests are made to ensure quality. These include hydraulic tests, electrical tests, and communication tests.

Hydraulic tests are made to ensure the quality of the cooling system. These may include pressure tests, flow tests, and leak tests.

Electrical tests include electronic measurements to see if specifications are met. These may include impedance & voltage cell tests as well as isolation tests. 

  • Isolation tests are made to ensure that there are no current leaks between the cells at high voltage and the battery casing.
  • Impedance & voltage tests measure the battery’s capacity to maintain its voltage when a current load is applied. Manufacturers use this to ensure that all cells have the same properties so that they perform better together. Similar cells can then be assembled into battery modules.

 Here is an example of a high-precision battery impedance & voltage tester.

 

 

Communications tests are made to verify that communication with the battery management system (BMS) works properly. This is done by validating the presence of all interconnected circuits.

Once all quality control tests are done, a report is generated using an inspection software system to confirm whether the battery can be assembled in the electric vehicle.

Engineering Designs That Are Changing Battery Pack Manufacturing

Engineering designs have an important effect on how battery packs are manufactured. Here is an overview of important design ideas that are turning the industry upside down.

Cell Cooling

In structural batteries, battery cells are positioned vertically, with electrical connections done at the top of the cell. Cooling then needs to be performed elsewhere, such as at the bottom and/or on the sides. This affects the way cells are designed, as they need to carry heat at the bottom or on the sides. It also affects how busbars are designed, as they need to accommodate electrical connections at the top.

Cell Manufacturing Size

There is a movement toward manufacturing bigger cells in EVs. They can store more energy with less support material. For example, the percentage of material used for the casing diminishes with larger cells. 

Bigger cells also contribute to diminishing the total number of cells in the pack, which reduces the number of electrical connections and hence the risk of manufacturing defects. You can see this evolution by looking at Tesla’s cylindrical cells, going from 18650, 21700, and 4680 (the first two numbers refer to the diameter, and the following two numbers to the height).

Repair Strategies

There are different opinions on how battery packs should be designed when it comes to maintenance and repairs. Some manufacturers prefer to design packs divided in modules that can individually be removed and replaced. Others prefer to manufacture packs held together in one piece to diminish production costs and improve performance. 

The latter type of battery packs typically needs to meet higher quality standards, as repairs are impossible without replacing the whole battery. To put it in Elon Musk’s words, these “battery packs are designed to outlast the vehicle”.

EV Battery Technologies Are Rapidly Evolving

Battery manufacturing is complex and involves lots of technologies. Laserax helps EV battery manufacturers implement laser technology to improve quality and lower production costs.

If you have an application requiring a laser, contact one of our laser experts today.

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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.