{"id":18960,"date":"2025-03-12T07:16:57","date_gmt":"2025-03-12T13:16:57","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=18960"},"modified":"2025-04-02T07:59:39","modified_gmt":"2025-04-02T13:59:39","slug":"pe-selecting-fire-protection-materials-for-an-ev-battery","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/18960\/pe-selecting-fire-protection-materials-for-an-ev-battery\/","title":{"rendered":"Selecting fire protection materials for an EV battery"},"content":{"rendered":"

\"\"What are the potential roles of polymers in EV batteries? Andy Pye reviews a report from the UK which looks at battery fire protection materials, and some research from China looking at the potential for <\/em>polyimides<\/em><\/a> for battery electrodes.<\/em><\/p>\n

Global electric vehicle (EV) sales increased year-on-year by 23% in 2024, despite significant regional disparity. EV fires are less common than those in combustion engine vehicles, but safety cannot be overlooked at any rate of occurrence and test methods and regulations continue to evolve.<\/p>\n

Many factors go into the choice of fire protection material, and it will include factors like cell form factor, pack design, thermal management approach, material costs, system costs, regulation to be met, and a wide variety of other factors. Each material has its own trade-offs and needs to be evaluated for each battery design.<\/p>\n

Cell form factor<\/strong><\/p>\n

One of the first considerations is the battery cell form factor. In 2024 around 58% of the market was using prismatic cells, followed by 22% cylindrical, and the rest pouch. While the cell form factor may not impact protection at a module or pack level, but it will certainly impact inter-cell materials.<\/p>\n

It is common to see sheet-type materials applied between the cells in prismatic or pouch cell systems, with encapsulating foams being a popular choice for cylindrical cell systems. There appears to be no technical reason why this is the case, and both are interchangeable, but it simply reflects common practice.<\/p>\n

The failure mode will also vary by cell type, with cylindrical and prismatic cells generally venting through the vents on the top of the cells, which defines the placement of fire protection materials.<\/p>\n

Thermal management<\/strong><\/p>\n

A critical factor is how the temperature of the cells is managed. A popular approach is via a cold plate that sits at the top or bottom of the cells through which water-glycol coolant is passed. Thermally insulating cells from one another helps to maintain the temperature within the cells in cold conditions but is also beneficial in preventing heat transfer between a cell in thermal runaway and the rest in the pack.<\/p>\n

A second option is to additionally cool the sides of the cells, or use heat-spreading materials between the cells to transfer as much heat away from the cells as possible. Depending on which approach is taken, this will impact what material or combination of materials are chosen to be placed between the cells. For example, foams and aerogels have a very low thermal conductivity, whereas encapsulants or phase change materials tend to have a higher thermal conductivity.<\/p>\n

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EV Battery Testing for Compliance with Regulatory Requirements and Standards, learn more here<\/a>!<\/h3>\n
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Material choices<\/strong><\/p>\n

Even once the cell form factor and thermal management strategy are decided, many different material classes and chemistries can be considered.<\/p>\n

IDTechEx has published a report entitled “Fire Protection Materials for EV Batteries 2025-2035: Markets, Trends, and Forecasts”. Materials discussed include ceramic blankets\/sheets, mica, aerogels, coatings, encapsulants, encapsulating foams, compression pads (with fire protection), phase change materials, and polymers (with fire protection). Encapsulating foams and mica currently dominate material demand.<\/p>\n

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Many materials are applicable for fire protection in EV batteries. Source – Fire Protection Materials for EV Batteries (Source: IDTechEx)<\/figcaption><\/figure>\n

Mica is a very low-cost material with strong electrical insulation properties, but is usually required in thicker (and heavier) layers to provide sufficient fire protection.<\/p>\n

On key metrics like low thermal conductivity and density, aerogels, ceramic blankets, and encapsulating foams do perform well. However, this does not tell the entire story: often, a combination of materials may be needed to meet structural requirements and\/or meet UL2596 test requirements. UL2596 tests are challenging, with the torch and grit test exposing the sample to an alternating high-temperature flame (1200\u00b0C) and alumina particle blasts; meeting them will typically increase the density required.<\/p>\n

Of course, a primary concern for battery designers is system cost. The addition of fire protection materials increases costs, which can vary widely between material options. Part of the calculation is determined by how much of each material is required to achieve the required performance. James Anderson, report author and research director at IDTechEx, predicts that newer emerging options will start to eat into this market share. Some of these newer options include aerogels, and intumescent polymers and coatings.<\/p>\n

Aerogels have historically been limited by cost, but in the right implementation they can provide excellent thermal insulation and fire protection. As mentioned above, if a material can provide multiple functionalities, then its additional costs can reduce its impact on overall system cost.<\/p>\n

Accordingly, suppliers are trying to produce materials that perform multiple functions and can prevent the need for multiple assembly steps. An increasingly popular option from suppliers is polymer\/composite components with fire protective and\/or intumescent properties that can be made into structural components of modules, cell holders, or an inter-cell spacer. These may be less thermally insulating and of higher density than some other candidates in normal operation, but they can replace the need for multiple other materials, while providing good insulation at high temperatures. Examples of companies active in this field include SABIC, Pyrophobic Systems and Asahi Kasei.<\/p>\n

Polyimide materials for next-generation batteries<\/strong><\/p>\n

Organic electrode materials are promising candidates for next-generation energy storage systems. However, challenges such as limited active-site density and inefficient utilization have impeded their practical application. Addressing these hurdles requires a deeper understanding of how molecular structure impacts electrochemical performance \u2014 an area where significant progress is now being made.<\/p>\n

Innovative research at Jilin University and the Chinese Academy of Sciences demonstrates how incorporating carbonyl and conjugated structures can transform lithium-ion battery performance, providing a roadmap for future advancements.<\/p>\n

By addressing key limitations of organic cathodes, the work has profound implications for the future of lithium-ion battery technology. Advanced polyimide cathodes are well-suited for applications in portable electronics, electric vehicles, and large-scale energy grids.<\/p>\n

The researchers synthesized and tested five polyimides<\/a> \u2014 PTN, PAN, PMN, PSN and PBN \u2014 each engineered with distinct molecular modifications to improve performance. Although they share a similar core (naphthalimide units), each variant used a different diamine linker to introduce more carbonyl \u201chot spots\u201d and adjust the polymer\u2019s rigidity. It turns out both factors \u2014 how many Li-ion\u2013friendly carbonyl sites each molecule has, and how neatly its backbone is arranged \u2014 are pivotal in pushing battery capacity over the 200\u202fmAh\/g threshold.<\/p>\n

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Adding carbonyl and conjugated structures to polyimides can improve the performance of lithium-ion batteries and provide a roadmap for further developments.<\/figcaption><\/figure>\n

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Schematic diagram of the main chain engineering of polyimide variants<\/figcaption><\/figure>\n

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PTN came out on top, providing a 212\u202fmAh\/g capacity at 50\u202fmA\/g, thanks to a well-tuned ratio of accessible carbonyl groups and a rigid backbone that curbed self-stacking, helping electrons move swiftly. Across the board, modifying these molecular structures also boosted other key metrics such as the rate performance \u2014 how well the batteries operate under higher current loads \u2014 and cycle life.<\/p>\n

All polyimides displayed impressive cycling stability, with capacity retention rates exceeding 97% across extended use, showcasing the robustness of this molecular engineering approach. These findings illuminate new pathways for designing high-performance organic electrode materials.<\/p>\n

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Discover Material Selection with Prospector Premium, learn more here<\/a>!<\/h3>\n
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Polyimides<\/em><\/p>\n

Polyimide<\/a> (PI) is a high-performance polymer with a ring bond in its molecular chain. It is known for its thermal stability, chemical resistance, and mechanical properties. Polyimides were originally developed by the DuPont Company. Kapton is a classic polyimide. Polyimides have excellent dielectric properties and an inherently low coefficient of thermal expansion. They can withstand extreme temperatures without significant degradation.<\/p>\n

Applications<\/em><\/p>\n