In recent years, the rapid adoption of electric vehicles (EVs) has underscored the critical importance of safety in high-energy lithium-ion battery packs. As an engineer specializing in electrochemical energy storage systems, I have conducted extensive research on fire suppression technologies for EV battery packs. These packs, characterized by high voltage and substantial energy capacity, pose significant safety risks, particularly thermal runaway events that can lead to fires or explosions. To ensure vehicle safety, it is essential to equip EV battery packs with effective fire suppression systems that can either prevent thermal runaway or promptly extinguish flames upon occurrence. This article presents a comprehensive experimental study on the cooling and fire suppression performance of perfluorohexanone-based extinguishing devices applied to EV battery packs. Through detailed experimentation, we aim to validate the efficacy of these systems and provide insights into their design and implementation for enhancing EV safety.
The EV battery pack is a complex assembly of multiple lithium-ion cells, typically arranged in modules and enclosed in a protective casing. During operation, factors such as overcharging, physical damage, or internal defects can trigger exothermic reactions within cells, leading to thermal runaway. This process involves the rapid release of heat and flammable gases, which can ignite, causing fires that are challenging to control due to the self-sustaining nature of the reactions. Traditional fire suppression methods often fall short in addressing these unique challenges, necessitating specialized approaches. In this study, we focus on perfluorohexanone, a clean agent fire extinguisher, known for its effectiveness in suppressing lithium-ion battery fires through both physical cooling and chemical inhibition mechanisms.
To contextualize our work, it is important to review the current state of lithium-ion battery fire suppression technologies. These can be broadly classified into water-based agents, gaseous agents, and aerosol agents. Water-based systems offer excellent cooling due to water’s high specific heat capacity, but they risk causing electrical shorts in high-voltage EV battery packs and may not effectively reach fire cores within enclosed spaces. Gaseous agents, such as heptafluoropropane and perfluorohexanone, work by physical heat absorption and chemical radical scavenging. However, heptafluoropropane has been associated with greenhouse gas effects and potential re-ignition issues after suppression. Aerosol agents are environmentally friendly and cost-effective but lack sufficient cooling capability, often leading to re-ignition. Among these, perfluorohexanone has emerged as a promising candidate due to its low global warming potential and rapid fire suppression properties. Previous studies have demonstrated its effectiveness at the cell or module level, but there is limited research on full-scale EV battery pack applications. Our study addresses this gap by evaluating perfluorohexanone systems in realistic EV battery pack scenarios.
The experimental design was meticulously planned to simulate real-world conditions. All tests were conducted in an environment maintained at a temperature of $25 \pm 10^\circ\text{C}$, relative humidity of 15% to 90%, and atmospheric pressure of 86 to 106 kPa. Measurement instruments included K-type sheathed thermocouples with an accuracy of $0.1^\circ\text{C}$ and multimeters with a precision of $0.001\,\text{V}$. The primary experimental object was an EV battery pack composed of prismatic aluminum-shell lithium iron phosphate (LFP) cells connected in series. This EV battery pack had a mass of 200 kg, dimensions of $930\,\text{mm} \times 680\,\text{mm} \times 250\,\text{mm}$, and an IP67-rated enclosure, ensuring dust and water resistance. The pack was fully charged prior to experiments, as per standard protocols, to replicate operational conditions. Inside the EV battery pack, fire detection sensors and extinguishing nozzles were installed to mimic actual safety systems.
The fire suppression system utilized perfluorohexanone as the extinguishing agent. Given the lack of comprehensive design standards for perfluorohexanone in EV battery pack applications, we referred to the Shandong provincial standard DB37/T3642—2019 for guidance. The required灭火剂用量 (extinguishing agent quantity) was calculated using the formula:
$$ W = K \times \frac{V}{S} \times \frac{C_1}{100 – C_1} $$
where $W$ is the design用量 in kg, $C_1$ is the灭火设计浓度 (design concentration) taken as $8\%$, $V$ is the net volume of the protected area (the EV battery pack interior) at $0.158\,\text{m}^3$, $S$ is the specific volume of superheated vapor at $101\,\text{kPa}$ and the minimum ambient temperature, and $K$ is the altitude correction factor, set to 1 for sea level. The specific volume $S$ is given by:
$$ S = K_1 + K_2 T = 0.05544\,\text{m}^3/\text{kg} $$
with $K_1 = 0.0664$, $K_2 = 0.000274$, and $T = -40^\circ\text{C}$ (the lowest expected temperature). Substituting values, we obtained $W = 0.248\,\text{g}$. Accounting for a safety factor of 1.5, a $5\%$ residual agent in the cylinder, and a dual-mode operation (cooling followed by fire suppression), we designed a system with two cylinders containing at least $1.3\,\text{kg}$ of perfluorohexanone, sufficient for the EV battery pack experiments.
The experimental platform was constructed following guidelines from CCCF/XFJJ-01, a technical specification for fire control devices in electric bus battery boxes. Key steps included installing thermocouples on cell terminals and backs, placing a controllable heating plate against a test cell to induce thermal runaway, and setting up extinguishing nozzles at the farthest point from the cell module to simulate worst-case dispersion. Data acquisition systems recorded temperature readings every second via thermocouples and CAN communication modules, while video cameras documented visual events. The setup ensured comprehensive monitoring of the EV battery pack’s response during tests.
We conducted two primary experiments: a cooling test and a fire suppression test. The cooling test aimed to evaluate the preventive effect of perfluorohexanone on potential thermal runaway in the EV battery pack. When the test cell’s terminal temperature reached $80^\circ\text{C}$ and remained stable for over 10 seconds, the system automatically triggered the release of one cylinder of perfluorohexanone. Temperature data were recorded throughout the process. The fire suppression test assessed the agent’s ability to extinguish open flames during thermal runaway. After inducing thermal runaway via heating until venting occurred, an electric igniter was activated near the vent to create sustained flames. Upon confirmation of fire (lasting 3 minutes or upon the cell back temperature exceeding $150^\circ\text{C}$), the second cylinder of perfluorohexanone was manually released. Post-extinction, re-ignition checks were performed every 3 minutes using the igniter to ensure no recurrence.
The results from the cooling test are summarized in Table 1, which shows temperature changes over time. Upon agent release at $80^\circ\text{C}$, the EV battery pack’s test cell temperature decreased to $60^\circ\text{C}$ within 333 seconds, yielding a cooling rate of $3.6^\circ\text{C}/\text{min}$. After cessation, the temperature gradually dropped to $41^\circ\text{C}$ by 4000 seconds, at a slower rate of $0.45^\circ\text{C}/\text{min}$. This demonstrates that perfluorohexanone actively mitigates thermal rise, offering a preventive buffer against thermal runaway in EV battery packs. The cooling mechanism can be modeled using Newton’s law of cooling, where the temperature change is proportional to the difference between the battery temperature and the ambient temperature, enhanced by the agent’s phase-change absorption:
$$ \frac{dT}{dt} = -k (T – T_{\text{ambient}}) + Q_{\text{agent}} $$
where $k$ is the cooling constant, and $Q_{\text{agent}}$ represents the heat absorbed by perfluorohexanone vaporization.
| Time (s) | Cell Terminal Temperature (°C) | Cell Back Temperature (°C) | Event |
|---|---|---|---|
| 0 | 25 | 25 | Experiment start |
| 1123 | 80 | 75 | Agent release triggered |
| 1456 | 60 | 58 | Agent release completed |
| 4000 | 41 | 40 | Experiment end |
In the fire suppression test, thermal runaway was induced at 364 seconds, with open flames appearing at 507 seconds. Upon agent release at 693 seconds, the flames were extinguished within 18 seconds (by 711 seconds), and no re-ignition occurred during subsequent checks up to 3000 seconds. Adjacent cells in the EV battery pack did not undergo thermal runaway, indicating effective containment. Temperature profiles, as shown in Table 2, reveal a sharp drop post-suppression. The rapid extinguishment can be attributed to perfluorohexanone’s dual action: physical cooling via vaporization (absorbing heat at a rate quantified by its latent heat of vaporization, approximately $110\,\text{kJ/kg}$) and chemical inhibition through fluorine radicals that interrupt combustion chain reactions. The extinguishing time $t_{\text{ext}}$ can be related to agent concentration $C$ and fire power $P$ using an empirical formula:
$$ t_{\text{ext}} = \alpha \cdot \frac{P}{C \cdot \Delta H_{\text{vap}}} $$
where $\alpha$ is a system-dependent constant, and $\Delta H_{\text{vap}}$ is the latent heat of vaporization.
| Time (s) | Cell Terminal Temperature (°C) | Event Description |
|---|---|---|
| 0 | 25 | Experiment start |
| 364 | 120 | Thermal runaway initiated |
| 507 | 350 | Open flames observed |
| 693 | 500 | Agent release started |
| 711 | 200 | Flames extinguished |
| 3000 | 50 | No re-ignition, experiment end |
To further analyze the performance, we compared perfluorohexanone with other agents commonly used for EV battery pack fire suppression. As illustrated in Table 3, perfluorohexanone offers a balanced profile with effective cooling and minimal environmental impact, making it suitable for enclosed EV battery pack environments. Its effectiveness stems from a high volumetric expansion ratio upon release, ensuring rapid dispersion within the pack, and a low toxicity profile, enhancing safety for occupants.
| Agent Type | Cooling Efficiency | Environmental Impact | Re-ignition Risk | Suitability for EV Battery Packs |
|---|---|---|---|---|
| Water-based | High | Low | Low | Moderate (risk of short circuits) |
| Heptafluoropropane | Moderate | High (GWP) | High | Limited |
| Aerosol | Low | Low | High | Low (insufficient cooling) |
| Perfluorohexanone | High | Low (low GWP) | Low | High |
The experimental findings highlight several key insights. First, the cooling test confirms that early intervention with perfluorohexanone can delay or prevent thermal runaway in EV battery packs, buying critical time for safety systems to engage. The cooling rate of $3.6^\circ\text{C}/\text{min}$ during agent release is substantial, considering the high thermal mass of an EV battery pack. This can be modeled using heat transfer equations, where the heat removal rate $\dot{Q}$ is given by:
$$ \dot{Q} = m_{\text{agent}} \cdot \Delta H_{\text{vap}} + h A (T_{\text{battery}} – T_{\text{agent}}) $$
where $m_{\text{agent}}$ is the agent mass flow rate, $h$ is the convective heat transfer coefficient, $A$ is the surface area, and $T_{\text{agent}}$ is the temperature of the vaporized agent. Second, the fire suppression test demonstrates that perfluorohexanone can quickly extinguish flames without re-ignition, a crucial advantage for EV battery pack safety where fire spread could lead to catastrophic failures. The chemical inhibition mechanism involves fluorine radicals (e.g., $\text{CF}_3$, $\text{CF}_2$) reacting with combustion radicals like $\text{H}^\cdot$ and $\text{OH}^\cdot$, effectively terminating chain reactions:
$$ \text{CF}_3 + \text{H}^\cdot \rightarrow \text{CF}_3\text{H} $$
$$ \text{CF}_2 + \text{OH}^\cdot \rightarrow \text{CF}_2\text{O} + \text{H}^\cdot $$
These reactions reduce the flame temperature and prevent re-ignition, ensuring sustained protection for the EV battery pack.
From a design perspective, our experiments underscore the importance of proper agent dosing and nozzle placement in EV battery packs. Using the calculated quantity of $1.3\,\text{kg}$ for a pack volume of $0.158\,\text{m}^3$, we achieved a design concentration exceeding the minimum required $8\%$, which aligns with findings from other studies on lithium-ion battery fire suppression. However, for larger EV battery packs or multi-pack systems, scaling equations must be applied. The agent quantity $W_{\text{total}}$ for multiple packs can be estimated as:
$$ W_{\text{total}} = N \cdot W \cdot \left(1 + \beta \cdot \frac{V_{\text{extra}}}{V}\right) $$
where $N$ is the number of packs, $W$ is the quantity per pack, $\beta$ is a dispersion factor, and $V_{\text{extra}}$ accounts for additional void spaces. This ensures adequate coverage in complex EV battery pack configurations.
Moreover, the integration of perfluorohexanone systems with battery management systems (BMS) can enhance responsiveness. By coupling temperature and voltage sensors in the EV battery pack with automated release triggers, the system can act preemptively during early warning signs, such as abnormal temperature rises or voltage drops. This proactive approach could further reduce the incidence of thermal runaway in EV battery packs, contributing to overall vehicle safety. In our experiments, the automatic trigger at $80^\circ\text{C}$ proved effective, but optimizing this threshold based on cell chemistry and pack design warrants further study. For instance, nickel-manganese-cobalt (NMC) cells in some EV battery packs may have lower thermal runaway onset temperatures, necessitating adjusted parameters.
The environmental and economic aspects of perfluorohexanone are also favorable. With a global warming potential (GWP) of approximately 1, compared to heptafluoropropane’s GWP of 3500, it aligns with sustainability goals for EVs. Although the cost per kilogram is higher than traditional agents, the reduced quantity needed due to high efficiency and the avoidance of costly fire damages in EV battery packs justify its adoption. Lifecycle analyses suggest that perfluorohexanone systems can lower total ownership costs for EV manufacturers by enhancing reliability and safety.
Looking ahead, future research should explore hybrid suppression systems combining perfluorohexanone with other agents, such as water mist, to leverage synergistic effects for EV battery packs. Additionally, real-world testing in moving vehicles under varying conditions (e.g., vibration, temperature extremes) is essential to validate laboratory findings. Computational fluid dynamics (CFD) simulations can model agent dispersion within EV battery pack geometries, optimizing nozzle designs for faster coverage. Standardization efforts should also be intensified to establish universal guidelines for perfluorohexanone application in EV battery packs, ensuring consistency across the industry.
In conclusion, our experimental study demonstrates that perfluorohexanone fire suppression systems are highly effective for EV battery packs, offering both preventive cooling and rapid fire extinguishment. The cooling test showed a significant temperature reduction rate of $3.6^\circ\text{C}/\text{min}$, capable of mitigating incipient thermal runaway. The fire suppression test confirmed extinction within 18 seconds without re-ignition, preventing fire spread in the EV battery pack. These results provide a solid foundation for designing safety systems in commercial EVs, where protecting high-energy battery packs is paramount. As EV adoption grows, advancing such technologies will be crucial for ensuring public confidence and sustainable transportation. Through continued innovation and collaboration, we can further enhance the safety and performance of EV battery packs, paving the way for a safer electric future.