Key Takeaways & Executive Findings
- •• Relay response of bi-layered coating achieved fast response and extended protection. • 320-µm coating achieved over 900 s of burn-through resistance. • 320-µm coating achieved extended electrochemical stability for battery under fire. • Bi-layered coating with fast response endows polyurethane foam with rapid self-extinguishing.
Abstract
Developing high-efficient flame-retardant coatings is crucial for fire safety polymer and battery fields. Traditional intumescent coatings and ceramifiable coatings struggle to provide immediate and prolonged protection simultaneously, which limits the applicability. To address this, an innovative bi-layered coating with organic/nano-inorganic additives is inspired by differential response behaviors, enabling relay response effect with both fast-acting and extended protection. Specifically, two layers function continuously in the form of a relay. With a mere 320 microns, the bi-layered coating withstands fire temperatures of up to 1400 °C for at least 900 s. Consequently, the coating effective prevented burn through in aluminum plates and glass fabric-reinforced epoxy resin, which otherwise were burned through in 135 and 173 s, respectively. Meanwhile, the bi-layered coating suppressed the formation and decomposition of solid interface layer in lithium soft-package batteries, leading to prolonged electrochemical stability and fire safety. Additionally, the bi-layered coating with a fast response endows polyurethane foam with rapid self-extinguishing, preventing ignition even under exposure to strong fire of 1400 °C. Shortly, our work offers new insights into the design and development of thin, high-performance, and multi-application flame-retardant coatings.
1. Introduction
Flame-retardant coatings are effective for enhancing the fire resistance of materials in various industries, including construction, transportation, and electronics [1–4]. Coating flame-retardant technology offers a range of advantages, particularly in its ability to provide surface-level fire protection without significantly altering the underlying properties of the material. By applying a flame-retardant coating, the material is enveloped in a protective layer that acts as a barrier against heat and oxygen, two critical elements needed for combustion [5, 6]. This approach is especially valuable in applications where preserving the original characteristics of the material is required.
Primarily, coating technology is undoubtedly the optimal solution for metal-based materials, such as aluminum and its alloy [7–11]. In particular, in the field of batteries, aluminum is frequently used for the fabrication of integral pack battery enclosures and laminated pouches for soft-package batteries (SPB). Owing to their relatively low melting temperature around 660 °C and high thermal conductivity of aluminum, it is extremely susceptible to the risk of thermal runaway and explosion of batteries under fire conditions [12–16]. Therefore, the development of high-performance fire-resistant coatings is essential for high safety batteries. Apart from that, for some polymer materials, the advantages of coating technology are also evident. For instance, rigid polyurethane (PU) foam is often used as a thermal insulation material, and the traditional additive flame-retardant method is feasible to raise the flame retardancy efficiency, but significantly weakened the thermal insulation performance, density, and other physical and mechanical properties [17, 18]. Also, applying polymeric coating on the laminate surface has been one of the most popular flame-retardant approaches for fireproofing fiber-reinforced polymer composites [19, 20]. Another example is the fiber-reinforced polymer composites, slowing heat transfer and temperature rise-up through the thickness direction of greater importance than simply lowering fire hazards such as heat and smoke release due to their widely use in structural loading applications [21]. Up to now, several efforts have been made to tackle this challenge with thickness more than one millimeter, which indirectly lowered the strength-to-weight ratio of materials [22–25]. To the best of our knowledge, the research for ultra-thin and highly efficient polymeric coating for metal and polymer materials is still in its infancy with more efforts needing to be made.
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Wei Tang, Qi Chen, Junxiao Li, Xiang Ao, Yunhuan Liu, Lijun Qian, Silvia González Prolongo, Yong Qiu, De-Yi Wang (2025). Bi-Layered, Ultrathin Coating Initiated Relay Response to Impart Superior Fire Resistance for Polymeric and Metallic Substrates. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01739-8
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Frequently Asked Questions
What is the main innovation of this bi-layered coating?
The bi-layered coating features a relay response mechanism, combining fast-acting and extended protection, achieving superior fire resistance with an ultra-thin thickness of only 320 microns.
How does the bi-layered coating perform under fire conditions?
It withstands fire temperatures up to 1400 °C for at least 900 seconds, preventing burn-through in aluminum plates and glass fabric-reinforced epoxy resin, and providing rapid self-extinguishing for polyurethane foam.
What are the potential applications of this coating?
The coating is suitable for fire safety in polymers and batteries, including aluminum battery enclosures, soft-package batteries, and thermal insulation materials like polyurethane foam.
How does the coating enhance battery safety?
It suppresses the formation and decomposition of the solid interface layer in lithium soft-package batteries, leading to prolonged electrochemical stability and improved fire safety.
What is the significance of the ultra-thin thickness?
The ultra-thin thickness (320 µm) minimizes weight and preserves the mechanical properties of the substrate, addressing a key limitation of thicker conventional coatings.
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