Xencor? XTreme Enables Thermal Runaway Protection, Light-weighting, and Improved Economics for Battery End Plates

By Jiwen Wu, Benoit Devaux, Han Yan, Gaurav Amarpuri, Cléa Chollier, Gill Biesold, Philipp Stelzer, Coleman Hellyer, Victoria Lee, Brian Baleno

Syensqo Materials

Four key design drivers for battery engineers are safety, performance, light weighting, and cost savings. Specifically, for safety, identifying ways to address thermal runaway or thermal runaway propagation is essential to meeting new global regulations designed to protect consumers. Some examples of these global regulatory bodies include the IEC (International Electrotechnical Commission), UL (Underwriters Laboratories), and the UN (United Nations), among others.?

To meet these criteria, Syensqo developed Xencor? XTreme LFT (long fiber technology) which can now be considered for metal replacement in battery structural parts such as module end plates. In addition to replacing metal, Xencor? XTreme LFT can eliminate the need for insulation plates or coatings, as well as aerogel, due to its excellent electrical insulation properties. In effect, Xencor? XTreme LFT goes beyond metal replacement, ultimately enabling component consolidation.

Xencor? XTreme LFT is based on a combination of bio-based PPA (polyphthalamide) resin and long glass fiber. This new injection-moldable LFT PPA opens the design envelope for metal replacement in battery systems. Figure 1 below shows the metal design of the battery module end plate of Volkswagen ID X.

Figure 1: Volkswagen ID6 (source: A2Mac1)

There are multiple design considerations to factor in when replacing metal with plastic. One of the first things to assess is the loads the component needs to withstand during operation, including factors like temperature and vibration. The high specific strength and stiffness of LFT materials enable metal replacement for components operating under a maximum end-of-life swelling force of 30 kN.? In addition to Xencor? XTreme LFT’s mechanical performance, it also offers a combination of electrical insulation across a wide temperature range, chemical compatibility with battery fluids, and the ability to withstand thermal runaway conditions. Table 2 below highlights the mechanical properties, and torch and grit properties of Xencor? XTreme LFT.

Table 1: Xencor? XTreme LFT Material Properties

Due to the need for module end plates to provide strength, pre-tightening, and constrain cell swelling throughout the battery's lifecycle, an essential step in evaluating the suitability of Xencor? XTreme LFT as an end plate material is to simulate and minimize the deflection of the component. For example, if the deflection of the Xencor? XTreme LFT end plate, made with the same design as the metal end plate, is estimated to be 1.35 mm under the maximum end-of-life cell swelling load, further design modifications could be adopted to reduce that deflection. One such approach is modifying the fixturing and using multiple straps instead of a single one, as shown in Figure 2 below. Two straps, with the same weight as the original single strap, allow for better distribution of the load, reducing the deflection to 0.84 mm as shown in Figure 2A.

Evaluating different design options through simulation is highly valuable, and using a coupled approach that connects processing and structural aspects (such as fiber orientation) is key to obtaining accurate predictions. For this reason, Xencor? XTreme LFT material cards have been characterized to support injection molding and structural simulations.

Figure 2: Initial maximum load deflection on Xencor? XTreme end plate with single strap

Figure 2A: Decreased deflection on Xencor? XTreme end plate with 2 straps versus 1

Converting from metal to plastic can result in not only weight savings but also space savings. The design shown in Figure 3 below demonstrates the benefits outlined in Table 2.

Table 2: Technical Benefits of Xencor? XTreme end plate?

Figure 3: Xencor? XTreme LFT end plate

Beyond weight and space savings, replacing die cast aluminum with Xencor? XTreme LFT can also lead to cost savings ranging from 27% to 37%. Secondary materials such as insulation coatings and aerogel can be eliminated, resulting in better economics.?

Another factor contributing to a lower total cost of ownership (TCO) is the reduction of secondary processes and operations. Injection molding, as opposed to die casting, can eliminate the need for welding, machining, painting, or finishing the end plate.?

Ultimately, this can also lead to ease of assembly benefits. Figure 4 illustrates the TCO savings. Additionally, further savings are expected through integration with other separate plastic components, such as supports for CCS and brackets for terminals.

Figure 4: Total Cost of Ownership with Xencor? XTreme LFT end plate

Xencor? XTreme was developed based on the UL 2596 torch and grit (TAG) requirements. Figure 5 provides an overview of the TAG testing protocol, while figures 6 and 7 present the test results, demonstrating that Xencor? XTreme can provide battery protection during thermal runaway events, whether as a stand-alone injection-molded component or a metal-backed injection-molded component.

Figure 5: UL 2596 test protocol

Figure 6: UL 2596 TAG Results

Figure 7: UL 2596 TAG Visual Results

In conclusion, Syensqo’s Xencor? XTreme LFT can be considered a viable metal replacement solution for die-cast aluminum battery end plates. Xencor? XTreme not only provides thermal runaway protection that meets UL 2596 TAG requirements but also offers benefits such as weight reduction, a decrease in battery module components, and cost savings.