Core Conclusion:
1. The EV battery pack nano fireproof coating system integrates three functional layers—an aerogel nano insulation layer (0.013-0.018 W/mK, 1300°C/2h), an intumescent fireproof coating (1200°C, delays thermal runaway by 51%), and ceramicized silicone rubber encapsulation (1300°C/>30min).
2. Nanjing Tech University's ceramic aerogel 'firewall' is only 0.09 inches (2.3mm) thick, exposed to 1000°C/5 min, the backside temperature stays below 100°C—already adopted for mass production by CATL, BYD, and Xiaomi SU7.
3. GB 38031-2025 mandates a minimum 5-minute escape time after battery pack thermal runaway; next-generation regulations target extending this to 120 minutes—driving nano fireproof materials from "optional" to "mandatory".
The widespread adoption of electric vehicles has turned "battery thermal runaway" from a laboratory safety testing topic into a real-world risk of public concern. When a lithium-ion battery is triggered into thermal runaway due to internal short circuit, overcharging, or mechanical damage, the temperature of a single cell can surge to 600-1000°C within seconds, and trigger a chain reaction of adjacent cells through three pathways—thermal conduction, thermal radiation, and ejection of high-temperature particles—known as "thermal runaway propagation". Nano insulating fireproof coating for electric vehicle battery packs is the core material system for constructing thermal barriers between cells and between modules.
Physical mechanisms of thermal runaway propagation — how harsh conditions must fireproof coatings withstand?
Direct answer: The peak temperature of a single-cell thermal runaway can reach 800-1200°C (NCM ternary lithium batteries can reach 1200°C, LFP lithium iron phosphate about 600-800°C), with a duration of 30 seconds to several minutes. The fireproof coating between adjacent cells needs to maintain structural integrity and thermal insulation function under the impact of flames and high-temperature gas flows of at least 1000°C, preventing heat transfer to adjacent cells and triggering cascading thermal runaway. This requirement far exceeds the working conditions of traditional building fireproof coatings (typically <800°C/30 min).
Mechanism Details—Three Paths of Thermal Runaway Propagation.(1)Thermal Conduction—The high-temperature cell casing transfers heat to adjacent cells through direct contact or thermally conductive structural components (aluminum busbars, copper busbars). Blocking strategy: Insert ultra-low thermal conductivity nano thermal insulation pads (aerogel or SUPHIP® nanocomposite material, thermal conductivity 0.013-0.04 W/mK, only 1/2-1/4 of still air, 1/5000 of aluminum alloy) between cells. (2)Thermal Radiation—The radiant heat flux density of a cell surface at 1200°C can reach about 200 kW/m² (Stefan-Boltzmann law Q=εσT⁴, assuming ε=0.8). Blocking strategy: Add infrared reflective/absorptive nano fillers (nano TiO₂, ATO, SiC) to the nano thermal insulation coating. (3)High-temperature Particle Ejection—After the safety valve of a thermally runaway cell opens, it ejects high-temperature electrolyte vapor, molten aluminum foil (>660°C) and copper foil (>1085°C) particles. Blocking strategy: Intumescent fireproof coating rapidly expands at high temperature (volume expansion 20-50 times) to form a porous carbonized layer, physically intercepting high-temperature particles and absorbing impact energy.
Data support: GB 38031-2025 "Safety Requirements for Power Batteries of Electric Vehicles" stipulates: after thermal runaway is triggered, the battery pack must not exhibit external flames or explosion for at least 5 minutes, providing a time window for occupant escape. The UN GTR No.20 and EU ECE R100.03 have similar requirements. The next-generation regulations (expected to be implemented in 2027-2028) aim to extend the escape time to 30-120 minutes — which poses a qualitative leap requirement for the performance of fireproof coatings.
Source:GB 38031-2025, UN GTR No.20, ECE R100.03, IDTechEx Fire Protection Materials Report 2025
Four-layer protection architecture of nano fireproof coatings — engineering integration from material to system
First layer: Nanoporous aerogel thermal insulation core.SiO₂ aerogel—known as "solid smoke"—has the lowest thermal conductivity among known solid materials (0.013-0.018 W/mK, at room temperature and atmospheric pressure), with a porosity >95% and pore sizes of 2-50 nm (smaller than the mean free path of air molecules of about 70 nm, thus effectively suppressing gaseous heat conduction). The breakthrough by Nanjing Tech University in 2025 lies in: (1) reducing aerogel production cost by over 50% through an innovative supercritical CO₂ drying process (99.5% ethanol recovery); (2) solving the brittleness and powder-shedding problems of traditional aerogels through fiber reinforcement and elastic structure design (>90% elastic compression recovery)—able to withstand the repeated expansion/contraction during cell charge-discharge cycles (cell thickness variation can reach 5-10%).
Second layer: Intumescent Coating.The EP/MAP-Cu system (epoxy resin/modified ammonium polyphosphate-copper ions) is a frontier research direction supported by the National Natural Science Foundation of China from 2025 to 2026. Working principle: At high temperature, MAP decomposes into phosphoric acid → catalyzes the carbonization of epoxy resin to form an intumescent char layer → Cu²⁺ catalyzes the cross-linking and reinforcement of the char layer → the thickness of the char layer can reach 20-50 times that of the original coating. Experimental data: A 1.5mm thick coating exposed to a 1200°C butane flame has a backside temperature of only 93°C (a 36% reduction in temperature rise), and the onset time of thermal runaway is delayed by 51%.
Third layer: Ceramizable silicone rubber encapsulation. Under a flame of 800-1300°C, the nano-mica/kaolin fillers and platinum catalyst in the silicone rubber act synergistically: the methyl and vinyl side chains of the silicone rubber thermally decompose → SiO₂ residue and nano-fillers sinter at high temperature to form a dense ceramic-like protective shell — in-situ transformation from a flexible elastomer to a rigid ceramic barrier. >30 minutes of 1300°C flame penetration test with no failure.
Fourth layer (optional): Nano-aerosol fire extinguishing agent. In extreme cases (when all the first three layers are penetrated), the nano-aerosol fire extinguishing agent embedded in the coating (e.g., K₂CO₃ nanoparticles) thermally decomposes at >800°C to generate K• radicals, which efficiently capture H• and OH• radicals in the combustion chain reaction, achieving active chemical fire suppression.
Source: Nanjing Tech University/Interesting Engineering (2025), NAGASE SUPHIP® Technical Data, MDPI Gels Aerogel Review (Oct 2025)
Frequently Asked Questions
How much weight does the nano fireproof coating add to the battery pack?
The areogel insulation pad has an areal density of approximately 200-400 g/m². For an 80 kWh battery pack (~200 cells, with inter-cell surface area of about 8 m²), the added weight is approximately 1.6-3.2 kg—less than 1% of the total pack weight. Intumescent coatings add about 0.5-1.0 kg. Compared to the fire safety benefits gained for the battery pack, the weight penalty is negligible.
Will fire-resistant coatings affect the heat dissipation of batteries?
The design objective of the nano thermal insulation coating is "directional thermal insulation" — blocking thermal runaway propagation between cells (normal direction), while not affecting the normal heat dissipation paths at the cell bottom or sides (tangential direction). Precise thermal management is achieved through position-selective coating application (only between the large faces of cells).
Can existing vehicles be retrofitted with a battery fireproof coating?
The technical feasibility and safety of aftermarket installation are still under evaluation—the battery pack's ingress protection rating (IP67/IP68) and high-voltage safety must be strictly maintained during installation. Currently, nano fireproof coatings are mainly applied in the OEM original battery pack design and production stages.
Do LFP batteries still require fire-resistant coatings?
Required. Although LFP (lithium iron phosphate) has better thermal stability than NCM/NCA ternary lithium batteries (thermal runaway onset temperature ~250°C vs 180°C, peak temperature ~600–800°C vs 1000–1200°C), once thermal runaway is triggered, LFP cells likewise eject high-temperature gases and particles, and the risk of module-level thermal runaway propagation still exists. It is just that the LFP system can adopt a relatively thinner fireproof coating (1–2 mm vs 2–4 mm for NCM).
Reference sources:GB 38031-2025, Nanjing Tech University/Interesting Engineering (2025), NAGASE SUPHIP®, MDPI Gels (Oct 2025), IDTechEx Fire Protection Materials 2025-2035
Publish Date: July 6, 2026 | Category: Technical Knowledge