Fires in electric vehicles (EVs) and Battery Energy Storage Systems (BESS) have gained significant media attention in recent years. In a high-profile move, GM recalled Bolt batteries in 2020 and 2021, costing the company $1.9 billion. Lithium-ion battery defects were contributing to thermal runaway, but GM was not alone. Hyundai and Ford also recalled batteries for causing fires, costing the companies hundreds of millions of dollars each.
Likewise, there is a risk of building fires from residential, commercial, and utility-scale energy storage batteries. For example, due to fire hazard concerns, LG Energy Solutions recalled roughly 10,000 RESU 10H storage batteries in 2021. In addition, in 2019, a battery energy storage system (BESS) caused an explosion at an Arizona Public Service (ASP) site, injuring several firefighters.
Although manufacturer defects have contributed to the issue, clean energy technicians must develop a thermal management strategy to prevent the risk of thermal runaway. What is thermal runaway? It is a chain reaction that results in uncontrolled temperature increases in battery cells, potentially leading to fires and explosions.
What Is Thermal Runaway?
Thermal runaway is a dangerous process characterized by an uncontrolled rise in temperature. As the temperature increases, it releases energy, which in turn causes further temperature spikes in a self-perpetuating cycle. This feedback loop can lead to catastrophic outcomes if not addressed.
This phenomenon can occur in various fields: in chemical engineering, it arises from exothermic reactions; in electrical engineering, it is linked to increased current flow and power dissipation; in civil engineering, it can happen during the curing of concrete; and in astrophysics, it occurs with runaway nuclear fusion reactions in stars.
What Is Thermal Runaway In BESS?
Thermal runaway in BESS occurs when damage to a lithium-ion battery cell causes it to release toxic or flammable gases. This thermal runaway process initiates a dangerous chain reaction, where the decomposition of one cell exacerbates the situation, leading to further reactions.
As thermal runaway progresses, it generates additional heat and gases, significantly increasing the risk of fires or explosions. Managing thermal runaway is crucial; effective thermal management systems, early fault detection, and enhanced battery designs are essential to prevent these catastrophic failures.
How BESS Thermal Runaway Occurs
In the process, heat builds up more quickly than it can dissipate. Finally, the battery ignites or even explodes. One critical component in a lithium-ion battery is the separator, a porous membrane separating the anode and cathode sides of the battery while allowing ion transfer. However, separator breakdown, often caused by heat, can lead to thermal runaway.
Risks of Thermal Runaway in BESS
Thermal runaway poses significant risks to property, the environment, and human safety. If not properly prevented, thermal runaway in BESS can lead to fires and explosions, toxic gas release, physical damage, and even loss of life. These incidents can be difficult to contain and extinguish once they occur, making prevention through proper safety procedures and mitigation strategies critical to ensuring battery safety and minimizing potential consequences.
Factors Contributing to BESS Thermal Runaway
Abuse factors on batteries are also often the trigger of thermal runaway. Common abuse factors include overcharging, overheating, battery misuse, manufacturer defects, and short circuits.
Often, excess heat accumulates faster than it is expelled. This causes the electrolyte in the battery to turn from a liquid into a gas. As the gas expands, it increases the internal pressure in the battery faster than it can be vented.
Preventing BESS Thermal Runaway
If there is intervention at this point and the abuse factor stops, this can prevent thermal runaway. However, if the separator in the battery is damaged, the positive and negative sides of the battery start mixing. The cracking of the separator causes smoke, which signals that failure is imminent and thermal runaway in BESS occurs.
Thermal Runaway Containment And Prevention
Unfortunately, thermal runaway can happen very quickly and for many different reasons, causing extremely high temperatures and fires that are difficult to extinguish.
Dangers of Thermal Runaway In Lithium-ion Batteries
When a chain reaction creates cascading thermal runaway, containment can be difficult. An investigation into the ASP example referenced above found a battery cell defect likely caused thermal runaway in BESS. Once set in motion, thermal runaway was difficult to stop, causing significant property damage and exposing the need for more extensive prevention and mitigation training.
Although the total flooding clean agent fire suppression system at the ASP worked as designed, it is only capable of handling a beginning-stage fire and could not contain cascading thermal runaway. However, the chain reaction started in the defective cell and occurred in every cell and module in one rack within the lithium-ion BESS.
The uncontrolled cascading thermal runaway led to the production of a large quantity of flammable gases. When the firefighters opened the door, it agitated the gases and allowed them to make contact with a heat source or spark, causing an explosion. First responders and BESS operators need adequate training in BESS safety, or their actions could make the situation more dangerous.
Thermal Runaway Containment Strategies
Unfortunately, lithium-ion battery fires are extremely challenging to suppress. Often, large amounts of water need to be applied for hours or even days, which can be difficult or even impossible in certain settings.
As lithium-ion battery technology advances, there is greater knowledge about safety and thermal runaway containment. Battery manufacturers must prevent cell failures that are contributing to thermal runaway, but there are also many actions that clean energy technicians can take to mitigate risks. For example, when drawing new BESS facilities, it’s important to give extensive consideration to containment systems, ventilation, and monitoring technology.
Corrective System Shutdowns To Prevent BESS Thermal Runaway
Early detection of a cell failure is key to preventing thermal runaway before it starts, and battery management systems can help. Like our phones have a battery management system that prevents them from overcharging, this is also critical in BESS.
Battery management systems in BESS facilities track data that helps prevent thermal runaway. However, sometimes issues aren’t properly detected before it’s too late. Therefore, it is important to have other safety measures in place.
Monitoring Indicators to Prevent Thermal Runaway
Monitoring internal temperature spikes and off-gassing is a way to prevent the situation from escalating because they are critical indicators of malfunction. However, monitoring for gases often requires detecting low levels of a blend of gases, such as carbon monoxide, methane, ethane, and ethylene. Conventional gas detectors may not be suitable for detecting such low levels.
Corrective Shutdown Procedures for Thermal Runaway in BESS
When effective, the battery shuts down when the monitoring system identifies excess gases, and the gas levels can then slowly return to normal. However, the battery cell will likely be damaged and need to be replaced. In some cases, Authorities Having Jurisdiction (AHJs), insurance companies, and utility companies may require off-gas monitoring.
Enhancing BESS Safety Measures
Early detection can prevent property damage and promote safety. Now, many BESS facilities are installing off-gas detection systems and fire suppression systems for incipient fires. Likewise, a ventilation or cooling system strategy is also helpful in preventing the buildup of flammable gases.
Mitigating Dangers of BESS Thermal Runaway
Constructing BESS facilities out of non-combustible materials and having sufficient ceiling height to prevent the accumulation of combustible gases help prevent fires. In addition, local first responders need training in BESS because it requires significantly different tactics and approaches.
Thermal Runaway Prevention
Preventing thermal runaway events is much better than containing them once they’ve started. Battery manufacturers can take actions to mitigate risks, such as adding protection circuits to maintain safe operation. This helps prevent overcharging, rapid discharging, and short circuits.
There are also lessons to learn from past explosions and fires involving lithium-ion batteries. Investigations into fires and explosions at BESS facilities highlight several likely contributors.
Common contributors to BESS thermal runaway include:
Damage during construction - Damage during construction can compromise the structural integrity of battery cells, leading to internal shorts or other malfunctions. Such damage often goes unnoticed until the system is operational, increasing the risk of thermal runaway due to undetected failures.
Battery cell defects - Battery cell defects are inherent flaws in the manufacturing process that can lead to overheating or chemical reactions within the cell. These defects may not be immediately apparent but can trigger thermal runaway when the affected cells are subjected to normal operating conditions.
Operating the BESS outside of the prescribed parameters - Operating the BESS outside of the prescribed parameters—such as charge rate, state of charge, and temperature—can significantly heighten the risk of thermal runaway. Deviating from these guidelines can lead to excessive heat buildup and stress on the cells, increasing the likelihood of failure and safety hazards.
Practices to Minimize Risks of BESS Thermal Runaway
Having a detailed commissioning plan in place that can help prevent issues during construction is critical. In addition to containment strategies, such as proper ventilation and monitoring equipment, proper battery handling is essential; batteries must be protected during installation to prevent damage. Also, safe operations and maintenance practices should be taught to all facility staff.
Creating effective operations and maintenance protocols and adequate operator training helps prevent the operation of the BESS system outside safety parameters and ensures adequate testing. Likewise, BESS facilities should create plans that address extreme weather events, natural disasters, and other emergencies.
Industry Standards for Thermal Runaway Prevention
Lithium-ion batteries must undergo UL 9540A testing of fire safety hazards caused by thermal runaway to be available on the market. This testing documents the temperature at which the onset of thermal runaway is detected and the temperature at which the cell begins venting due to the internal pressure increase. This fire test report can be helpful for AHJs, insurance agents, fire departments, and building owners.
Be Mindful of BESS Thermal Runaway
Unfortunately, some high-profile incidents have increased concerns about the safety of lithium-ion batteries in numerous applications, from EVs to utility-scale BESS facilities. As a clean energy professional, it is vital to understand the threat of thermal runaway and how to prevent (or at least contain) it. This knowledge can help you earn trust in the energy storage industry and demonstrate a concern for safety.
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