Understanding our customers’ needs and challenges is crucial to designing and manufacturing shielded enclosures that can withstand the toughest threats their processes might encounter.
Many of our customers work in cutting-edge industries where staying ahead of technological advancements is critical. With the rise of renewable energy, electric vehicles, and portable electronics, battery testing has become a key focus area, one that comes with significant risks. Improper safety processes can lead to catastrophic failures putting people, equipment, and facilities at risk.
That is why, for our latest blog post, we’ve reached out to Wojciech Mrozik, a Faraday Institution Senior Research Fellow with an outstanding background in safety battery research, to discuss the hazards involved with battery testing and share practical strategies for minimizing risks.
TABLE OF CONTENTS
- What is Thermal Runaway?
- Battery Testing and its Inherent Risks
- Battery Abuse Testing
- The Role of State of Charge (SOC) in Thermal Runaway
- Arc Faults: A Novel Trigger for Thermal Runaway
- Hazards from Thermal Runaway Effluent Gases
- Advanced Detection and Prevention Strategies
- Fire Suppression
- Conclusion
- References
Lithium-ion batteries (LIBs) are a cornerstone of modern technology, powering everything from electric vehicles (EVs) and smartphones to large-scale energy storage systems (ESS). Their high-energy density, long cycle life, and affordability make them the preferred choice for many applications. However, these very features also pose significant safety risks, especially during battery testing, where the boundaries of battery performance are often pushed. One of the most critical risks is thermal runaway (TR), a chain reaction that can lead to the release of hazardous gases, and subsequently to fires or even explosions.
Battery testing is a vital part of the development process to ensure that these systems perform safely under various conditions. However, testing batteries, particularly under abuse conditions such as overheating, overcharging, or mechanical stress, introduces its own set of dangers. This article briefly explores the risks associated with battery testing, especially thermal runaway, the dangers posed by arc faults, and explosion hazards from off gassing. It will also discuss advanced detection, prevention strategies, and fire suppression tissues aimed at mitigating these risks.
What is Thermal Runaway?
Thermal runaway (TR) refers to an uncontrollable chain reaction that occurs within lithium-ion batteries when internal temperatures reach critical levels.
Once triggered, TR is virtually impossible to stop. The process begins with the breakdown of internal battery components, such as the solid electrolyte interphase (SEI) layer, which is designed to protect the anode material from reacting with the electrolyte. When this layer breaks down due to excessive heat or internal damage, the highly reactive anode is exposed to the electrolyte, resulting in a series of exothermic reactions [1].
These reactions release more heat, further accelerating the process and creating a feedback loop. As temperatures rise, the cathode and electrolyte begin to decompose, releasing flammable gases like hydrogen (H2), methane (CH4), carbon monoxide (CO), and even toxic gases such as hydrogen fluoride (HF). In a confined space, such as a battery casing or testing chamber, these gases can accumulate and lead to an explosion if ignited [2 – 4].
Understanding the specific triggers (abuse) of TR is essential for developing safer battery systems and more effective testing protocols. The primary causes of thermal runaway include:
- Mechanical: Physical deformation from impacts or punctures can breach internal layers, causing short circuits.
- Thermal (Overheating): External heat sources or excessive internal heating can degrade the SEI layer, triggering TR.
- Electric (Overcharging, over-discharging): Excessive charging causes lithium plating on the anode, which can lead to internal short circuits.
Additionally, we can talk about:
- Electronic: Any faults in the Battery Management System (BMS) or other power electronics components of the battery system
All of these abuse methods lead to Internal Short Circuits. Internal short circuits can also be triggered by manufacturing defects or aging, which can lead to short circuits within the battery, initiating thermal runaway [2]. Once TR starts, it is difficult to stop, especially in large-format batteries used in EVs and energy storage systems, where the failure of one cell can trigger a cascading effect, leading to the failure of an entire battery pack [5].
Battery Testing and its Inherent Risks
Abuse testing of lithium-ion batteries is an essential part of the development process to ensure they are safe, reliable, and capable of performing under a wide range of conditions. However, battery abuse testing introduces significant risks. During these tests, batteries are often subjected to conditions that push them to their limits. Sometimes, triggering TR is dangerous not only to the battery itself but also to the surroundings.
Battery Abuse Testing Methods
The following testing methods evaluate a battery’s safety and performance under conditions beyond normal operating limits. The purpose is to simulate real-world scenarios or accidents to ensure the battery won’t pose undue risks.
It’s important to understand that said tests are crucial for industries such as automotive, aerospace, energy storage, and others.
Here are the key types of abuse testing performed:
Thermal Abuse Testing
In thermal abuse testing, batteries are exposed to high temperatures to evaluate their response.
This simulates real-world conditions such as exposure to high environmental temperatures or overheating during use. Thermal runaway can be triggered when the battery’s temperature exceeds the point at which its internal components can safely operate. As the temperature rises, the SEI layer degrades, leading to the release of flammable gases and potential ignition[6].
Thermal abuse tests often involve heating the battery to a point just below its known failure threshold. The goal is to understand how the battery will behave in extreme conditions without causing a catastrophic failure. However, this testing can lead to unintended thermal runaway, requiring strict safety protocols to protect the testing environment and personnel.
Electrical Abuse Testing
Electrical abuse testing includes overcharging and over-discharging the battery to evaluate how it reacts to electrical stress.
Overcharging can lead to lithium plating on the anode, which can eventually cause internal short circuits and thermal runaway. Over-discharging, on the other hand, can cause the copper current collector to dissolve, leading to internal short circuits when the battery is recharged.
The fire risks during electrical abuse testing are significant, especially in NMC batteries with high state-of-charge (SOC). As SOC increases, the energy stored in the battery rises, which means more energy is available to fuel the exothermic reactions that drive thermal runaway [7]. For this reason, testing high-SOC batteries requires additional safety precautions, such as advanced gas detection systems and robust containment chambers.
Mechanical Abuse Testing
Mechanical abuse tests simulate the physical damage that batteries might experience in accidents or rough handling. These tests include crushing, puncturing, and dropping batteries to observe how they respond to mechanical stress. Mechanical damage can breach the internal structure of the battery, leading to internal short circuits and triggering thermal runaway.
In some cases, mechanical abuse can lead to immediate failure; in others, the damage may weaken the battery, making it more susceptible to failure later. This delayed failure poses a unique challenge in testing, as batteries that appear stable immediately after a mechanical abuse test may still pose a danger later, especially if they are recharged.
The Role of State of Charge (SOC) in Thermal Runaway
The State of Charge (SOC) of a battery plays a significant role in determining its susceptibility to thermal runaway.
Batteries with higher SOC levels contain more stored energy, which can exacerbate the severity of thermal runaway if it occurs. Research has shown that batteries with high SOCs tend to generate more heat during failure events and release larger volumes of flammable gases [7, 8] [9].
There are the internal and external safety trade-offs between different lithium-ion battery chemistries, particularly LFP (lithium iron phosphate) and NCM (nickel-cobalt-manganese) cells [10]. In the case of NMC batteries, it is more likely that when TR is triggered, they will go straight to fire and jet-like flames if the SoC is> 50%. If below, a vapor cloud is produced without fire or with delayed ignition [11].
LFP batteries are internally more stable and less prone to intense thermal runaway. However, this stability comes with an increased risk of external combustion due to the rapid release of reductive gases during failure, meaning LFP rarely goes into fire, but they produce more flammable gases and are thus more prone to explosions [7, 8]. LFP’s gas mixture usually contains more (by percentage) hydrogen, carbon monoxide, and methane (compared to NMC), thus highly explosive.
It is estimated that 1 kWh of capacity can release between 500-6000L of gas regardless of chemistry (although LFP generally sits on the lower end). So, when we consider modern single cells that can easily reach 100-150Ah capacity, there is already a much higher risk involved.
Overcharging lithium-ion batteries is a common cause of thermal runaway, and it significantly affects the explosion risk during testing, particularly in high-temperature environments.
Overcharging results in a marked decrease in the lower explosion limit (LEL) of gases such as hydrogen and methane [12]. If the battery is overcharged in high-temperature environments (i.e., > 40 °C), it poses a greater risk of explosion because the reduced LEL increases the likelihood that these flammable gases will ignite. This emphasizes the critical importance of rigorous charge/discharge control during battery testing to prevent the creation of hazardous conditions.
Arc Faults: A Novel Trigger for Thermal Runaway
Arc faults are an increasingly recognized risk factor in battery safety, especially in large battery systems such as energy storage systems (BESS) or electric vehicles. An arc fault occurs when there is an electrical breakdown of the air between two conductive points, creating a plasma arc.
This arc can generate localized heating that leads to thermal runaway [13], particularly at the negative terminal of a battery, even at relatively low voltages. The arc creates a hotspot on the battery, causing the electrolyte to decompose and triggering internal short circuits. This can lead to cascading failures, where multiple cells in a battery pack undergo thermal runaway, resulting in fires or explosions. Thus, this is particularly concerning in multiple-cell battery tests, where hundreds or thousands of cells are connected in series and parallel configurations. Even a small arc can cause significant damage if it spreads to neighboring cells.
Testing for arc faults involves simulating conditions that might cause electrical breakdowns, such as loose connections or short circuits. Specialized equipment, like arc fault generators, is used to create controlled arcs and observe their effects on battery performance. Incorporating these tests into standard safety protocols is essential for identifying vulnerabilities in large battery systems and preventing arc-induced thermal runaway.
Hazards from Thermal Runaway Effluent Gases
One of the most significant hazards associated with thermal runaway is the release of effluent gases, the so-called vapor cloud (VC) [3].
These gases, which include hydrogen, methane, carbon monoxide, and a number of other species, are highly flammable and pose a serious explosion risk if they accumulate in enclosed spaces. The release of these gases can also occur rapidly, creating overpressures that can cause structural damage explosion that can be devastating to both the testing facility and its personnel [14].
The combination of high heat, flammable gases, and enclosed testing environments creates an ideal setting for explosions and fires during battery testing. One of the most significant risks is venting flammable gases during thermal runaway. If these gases are not properly ventilated, they can reach explosive concentrations, creating a serious hazard [7].
Several high-profile incidents, such as explosions in energy storage facilities and garages housing electric vehicles, have been attributed to the ignition of VC. In one notable case, accumulated gases inside a battery energy storage system in Arizona ignited when first responders opened a door to take gas measurements. The resulting explosion caused severe injuries to the responders and extensive damage to the facility (McMicken).
Recent research has focused on characterizing the explosion hazards of VC under controlled conditions. A study conducted in a typical garage setting found that even modest amounts of accumulated VC could produce overpressures well above the thresholds for structural damage and personal injury [14]. The findings highlight the need for proper ventilation, gas detection, and explosion-proof testing chambers, especially when testing large-format batteries or battery systems in enclosed spaces.
In addition to flammability, the toxic nature of some effluent gases, such as hydrogen fluoride (HF), poses additional risks. HF is released when the electrolyte in lithium-ion batteries decomposes during thermal runaway [15]. It is highly corrosive, and exposure to HF can cause severe respiratory damage, skin burns, and eye irritation, making it essential to implement rigorous gas monitoring and protective equipment during testing [14, 16].
It must be noted that the gases expelled from high-energy cells can vent at extremely high velocities (up to 399 m/s) [17]. This rapid gas release can create dangerous recoil forces, potentially spreading flames or hot gases to neighboring cells.
Advanced Detection and Prevention Strategies
Advances in battery management systems (BMS) and gas detection technologies are playing a crucial role in mitigating the risks associated with thermal runaway. Modern BMS are equipped with sensors that monitor key parameters such as temperature, pressure, and gas concentration within the battery. These systems can detect early signs of failure and take corrective action before thermal runaway occurs [18].
One promising area of research is the use of artificial intelligence (AI) and machine learning to predict battery failures. By analyzing vast amounts of data from previous battery tests, AI algorithms can identify patterns that indicate an increased risk of thermal runaway. These systems can trigger preventive measures, such as shutting down the battery or activating cooling systems before the situation escalates.
Another significant development is the integration of gas detection systems into testing environments. These systems use sensors to monitor the concentration of flammable gases in real-time, providing early warning of dangerous conditions. By detecting the release of gases before they reach explosive concentrations, these systems can help prevent fires and explosions during testing.
Read our case study on Battery Testing Chambers.
Fire Suppression
Lithium-ion battery fires are particularly challenging because of the high heat and flammable gases released during thermal runaway. One must remember that it is hardly possible to stop the thermal runaway of the cell. However, it is possible to stop propagation from cell-to-cell or module-to-module.
Moreover, it is often mistaken that fire equals thermal runaway. You don’t need a fire (e.g., the LFP case) to have a continuous TR and later propagation to adjacent cells/ modules. Therefore, traditional fire suppression methods, such as water, foam, and dry powder, have limitations when it comes to controlling battery fires.
Furthermore, during the collapse of the cathode, oxygen is released from nanometal oxides (less in the case of LFP) that can sustain smoldering/fire even without access to external sources of air. This is particularly challenging when applying a typical firefighting method, i.e., cutting off the source of the oxygen. Therefore, one must be vigilant when applying methods like fire blankets to battery fires. Yes, you would put out the fire, but you will not stop the thermal runaway, meaning that you potentially switch hazards (fire to VC – potential explosion).
Another aspect is the application of any extinguishing agent. There are a number of “dedicated” lithium-battery extinguishers on the market right now. But most of them are not verified by external, independent testing bodies, or some of the tests are not representative, i.e., applying the extinguisher after the cells are gone and claiming it prevented re-ignition.
Applying an extinguisher agent to the battery fire may result in switching hazards. Again, you would put out the fire, but you would not stop the thermal runaway, meaning that you potentially switched hazards (fire to VC—potential explosion).
The following video [19] greatly illustrates that phenomenon. So, it should be carefully considered if/when you apply any extinguisher and if you are ready to mitigate additional hazards (flammable and toxic gas in large volumes).
Conclusion
Lithium-ion batteries have revolutionized industries ranging from consumer electronics to electric vehicles and energy storage systems. However, their inherent risks, particularly those related to thermal runaway, demand rigorous safety protocols during both development and testing. As the demand for high-capacity, high-performance batteries continues to grow, so must the safety measures designed to mitigate these risks.
To mitigate these risks, testing facilities must be designed with robust explosion-proof chambers and advanced ventilation systems. These systems should be capable of quickly evacuating gases and controlling the environment to prevent the buildup of flammable concentrations. Additionally, remote monitoring of battery tests can help minimize the risk to personnel by allowing them to observe the tests from a safe distance.
By understanding the causes of thermal runaway, implementing advanced testing protocols, and utilizing state-of-the-art detection, prevention, and fire suppression technologies, the industry can continue to push the boundaries of battery performance while ensuring the safety of both personnel and the surrounding environment.
The future of lithium-ion battery safety depends on ongoing research, innovation, and the development of more robust testing protocols that account for the complex and evolving nature of battery failures.
Properly addressing the challenges of the different testing processes is not just about safety, it’s about enabling progress. By tackling these risks head-on, we empower the innovation-driving industries forward while ensuring a secure environment for transformative advancements.
If you’re looking for a battery testing chamber or enclosure, contact us. Our expert engineering team is ready to design the perfect shielding solution customized for your business needs.
Battery Testing Risks and Hazards References
REFERENCES
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