Customers clearly understand the power needs of their applications that require a custom battery pack. They may also have narrowed down their choices in battery chemistry, placement of cells in the pack, the form of the cell, and battery management system (BMS) functions. Another important feature to consider is the battery enclosure.
Custom battery pack enclosures are designed to house the batteries. These enclosures may be placed into the device as a permanent fixture, or as detachable housing. The varied designs, materials, and manufacturing processes for battery enclosures have led to significant updates and innovations to promote greater levels of battery safety, thermal protection, and weight savings.
Design Updates to Battery Pack Enclosures
Additional Material Choices
Typically, the choice of materials for the enclosures comes down to either steel or aluminum. Each has its benefits and drawbacks. Steel is often chosen for its durability and strength in protecting the battery pack. Steel also has a lower carbon impact during production and can be easily repaired. However, steel can add weight to the enclosure, impacting the application's performance.
Portable medical device battery pack with plastic enclosure.
On the other hand, aluminum overcomes this weight issue by being lighter, making it an excellent choice for mobile applications. It offers better cost savings as well as recyclability at the end of the product’s life. Yet aluminum production can be harmful to the environment. It also has high thermal conductivity.
Two newer materials undergoing research involve next-generation thermoplastic and glass fiber polypropylene. Thermoplastics development focuses on creating an enclosure that keeps its lightweight properties while offering strength for durability. With long-glass fiber PP, it can lessen both weight and provide cost savings of up to 10% while also lowering CO2 emissions.
Flame Retardant Properties
An important worry for electric vehicle manufacturers is thermal runaway that can occur with battery chemistries such as lithium-based cells. When thermal runaway occurs, it could lead to fire and explosion of the battery pack. Customers who previously selected materials such as steel or aluminum for the battery enclosure would need to have a thermal blanket integrated to provide added protection.
Both thermoplastic materials and long-glass fiber materials can stand up to higher temperatures than both steel and aluminum. They also do not require a thermal blanket. This innovation leads to the design of battery enclosures that use fewer materials, creating cost savings and speeding up the production process while lowering costs.
Heat Dissipation Designs
Keeping the battery cell cool improves performance and helps to extend the battery life. Battery enclosure design has moved forward to incorporating cooling channels that are embedded into thermal plastic trays. Coolant would reside in the channels, as an aluminum plate would sit on top. As the battery builds heat, the aluminum helps transfer heat to the coolant, safely dissipating it.
While cooling channels would ideally work best with thermal plastic materials, they could also be used with steel or aluminum trays but would require using a multi-material tray to deal with the thermal conductivity that is a common characteristic for these metals.
Cell-To-Pack Configurations
For battery packs using a modular configuration with cells in a parallel placement, there are normally thermal interface materials in a module between the cooling plate and the battery. These interface materials are used to help control rises in temperatures. They also provided a safer battery pack. Yet with this placement, the added materials would increase the overall weight and take up extra space that may not be available depending on the application.
Newer cell-to-pack configurations seek to remove the thermal interface materials. Instead, a thermal conductive adhesive is applied to the battery cells and adhered directly to the cooling plate. Without the module, the number of parts and materials that are used is lower, creating a lighter battery pack. In addition, it frees up space, resulting in about 15% volume utilization. Customers can obtain higher energy density even while selecting cells with lower energy density to save on costs due to increased free space.
Summary
Testing and research are still ongoing for many manufacturers seeking to switch to alternate materials for enclosures and different configurations. While materials such as thermoplastics and glass fibers are available, the main issue with using these materials for battery enclosures is to guarantee strength for safety purposes to prevent punctures and impacts that could damage the battery cells when in operation.
Steel and aluminum far outpace these materials for strength and durability. Finding ways to integrate these properties into the newer materials will be a continued consideration. Also, steel and aluminum are still more readily available and cheaper due to long-established production lines. Switching to other materials may require new tools and equipment to produce these enclosures, which will create higher initial costs but lead to savings in the long term.
However, manufacturers are eager to pursue such changes and overcome the challenges to provide more choices for their customers. It also allows them to remain competitive in the battery manufacturing industry.
