New LCP (Xydar® G-330 HH) material for Battery Module Insulation
Designed to Mitigate Thermal Runaway, Improve Electrical Insulation, & Provide Space Savings
Jiwen Wu, Nicolas Batailley, Brian Baleno
Next generation battery electric vehicles (BEVs) are launching with much higher voltages than many of the current 400 Volts systems on the market today. Driven by the need to increase range and enable direct current (DC) fast charging, automotive car makers are introducing battery systems that operate above 800 Volts. The addition of more battery cells as part of the overall battery system is a key driver to increasing the battery power density and performance.
A result of increased battery power increases is greater current and higher voltages. While enabling greater range and DC fast charging, these new high voltage battery systems pose new design challenges. Battery engineers take into account safety of the battery system which includes thermal events such as thermal runaway and thermal propagation.
When a battery cell’s temperature gets too hot, a thermal event commonly referred to as thermal runaway may occur. This outcome produces an exothermic reaction in a lithium-ion cell that can lead to the release of gasses and particles. The release of either the gasses or particles has the potential to ignite and spread to the other cells within the battery pack. Thermal runaway events can pose a serious risk to those within or around a BEV.
To ensure consumers are safe, new legislation in countries like China, Europe, Japan, and the United States, is being developed. As a result of the legislation, battery engineers are working to identify materials that withstand temperatures (300 – 1000 °C) for a given period of time (5 minutes or greater) which allows passengers to safely exit the vehicle. Battery designers are seeking material solutions that can mitigate thermal runaway in a range of components inside the pack such as the insulation as shown in Figure 1 below:
Figure 1: Battery Pack Module Insulation Plate Material Comparison
Battery Insulation Material Selection
There are multiple requirements that battery engineers take into consideration for selecting a battery material insulator. Some of the design considerations include thermal insulation, flame resistance, electrical performance, and thickness. Finding a suitable material to mitigate thermal runaway starts with identifying a material that can inhibit thermal propagation. That is a key first step. Commonly used materials for battery module thermal insulation plates range from polycarbonate (PC) to polyimide (PI).
Materials like PC or PI came in different forms with different assembly methods. As an example, PC films can be glued to the inside of the metal endplate. This is the case in many of the prismatic cell designs. A primary function of the insulator is to increase the efficiency of the battery by preventing heat loss. One of the largest technical issues with PC films is that PC melts in a few minutes at the high temperatures (> 300 °C) seen during a thermal runaway event. Once the PC melts, it’s likely to lead to degradation and carbonization. These two factors combined could result in short circuiting the module or even the entire battery pack. Beyond PC and PI, there are other materials such as epoxies and aerogels that also have their own limitations.
Engineers are faced with a broad range of materials to select with trademarks that occur when needing to have high thermal stability at temperatures exceeding 300 °C. Table 1 below gives a detailed overview of existing battery module insulator materials and compares the strengths and weaknesses of each material.
Table 1: Comparison of different types of insulation materials
| Existing Technologies | Avg Size (mm) | Pros | Cons |
| Polycarbonate Film | 100 X 150 X 0.5 | Widely known solution | Risk of thermal runaway (degradation loss of electric insulation) |
| Epoxy + GF Resin + Asbestos | 100 X 150 X 0.5 | In commercial use | High cost & manufacturing cycle time and risk of loss of electric insulation during thermal runaway |
| Aerogel-SiO2 + PET Frame | 100 X 150 X 1.0 | Excellent heat insulation | High cost, rigid/fragile, complex assembly, & risk of loss of electric insulation during thermal runaway (break under cell swelling force) |
| Polyimide Film | 100 X 150 X 1.0 | Used by several OEMs. Good electric insulation | High cost, risk of loss of electric insulation during thermal runaway (tear or break on film) |
| New Solvay Solution | |||
| Xydar® LCP G-330 HH | 100 X 150 X 0.5 | Competitive costs, ease of assembly, electrical property retention after thermal runaway | Minor dimensional change after thermal runaway |
Thermal Stability
Figure 2 below shows the thermogravimetric analysis (TGA) of two commonly used insulators, PC films and epoxies as well as a newly developed liquid crystal polymer by Solvay called Xydar® LCP. The TGA was completed with TA Q50 equipment. The testing protocol started with equilibration at 50 °C followed by a ramp of 20 °C/min until a temperature of 800 °C was reached. The results below highlight how Xydar® LCP maintained thermal stability up to 544 °C while PC was limited to 448 °C and 338 °C for epoxy.
Figure 2: Thermal propagation Material Comparison
Thermal Aging
Regulation is leading to new material requirements to address the challenge of battery thermal runaway. As a result, many material suppliers are testing their materials under these harsh temperature conditions. Among one of the new tests is the need to evaluate the form of the material as well as the electrical insulation properties after heat exposure at 400 °C for 30 minutes. Figures 4A and 4B extruded PC film and injection molded Xydar® LCP before and after heat exposure. Figure 4B highlights how Xydar® LCP G-330 is able to maintain its form (shape is intact) while PC film decarbonizes.
Figure 4A: PC Film after 400 °C for 30 Minutes
Figure 4B: Xydar® G-330 HH after 400 °C for 30 Minutes
Electrical Property Retention After Thermal Aging
Because the PC film completely degrades after 30 minutes at 400 °C, the electrical insulation could not be measured. This is where the new Xydar® LCP G-330HH still shows robust electrical insulation. Surface and volume resistance are shown in Table 2 below. As further demonstrated below, Xydar® LCP G-330HH outperforms the glass filled epoxy by an order of magnitude.
Xydar® LCP G-330HH retains electric insulation even when the voltage goes up to 1000V and 3000V but the aged Epoxy plate fails.
Table 2: Electrical Properties of Xydar® G-330 after 30 minutes for 400 °C under DC 500V, 18℃ and 22% RH
| Insulator | Surface Resistance | Volume Resistance |
| Xydar® G-330 | 1.9E+13 Ohm | 1.4E+15 Ohm.cm |
| GF Epoxy | 2.0E+12 Ohm | 7.2E+14 Ohm.cm |
| PC Film | unable to test | unable to test |
In conclusion, battery design engineers are tasked with identifying new material solutions to address thermal runaway and thermal propagation which stems from new global government legislation. These new requirements have led to the development of Xydar® LCP G-330 HH. This new LCP was designed to provide multiple benefits over incumbent module insulator materials like PC films or GF Epoxy. With robust electrical insulation performance both at room temperature and after 30 minutes exposure at 400 °C, Xydar® LCP is a novel solution for the module level insulation. Contact Solvay experts if you’re interested in more details of Xydar® LCP.
Jiwen Wu, Nicolas Batailley, Brian Baleno Solvay
