Thermal Runaway in Electric Vehicles

Thermal runaway in electric vehicles (EVs) represents one of the most pressing safety concerns in the emerging industry. It’s significant enough to potentially undermine the numerous environmental benefits EVs offer. 

Although incidents of “electric vehicle thermal runaway” are rare, with about 25 occurrences per 100,000 EVs sold, the potential for damage is enough to demand rigorous attention.

It’s a dangerous reaction that occurs within EV lithium-ion batteries when they experience uncontrollable temperature increases, which can rapidly escalate to the point of a fire or explosion. 

Understanding thermal runaway to ensure the safety and performance of EVs is a necessity, due to the danger it can cause. 

thermal runaway of lithium-ion batteries

What is Thermal Runaway as it Relates to Electric Vehicles?

Thermal runaway in electric vehicles is a hazardous condition where the lithium-ion battery’s temperature spirals uncontrollably, potentially leading to fires or explosions. 

It’s triggered by factors like short circuits or overcharging and this rapid temperature rise can initiate a dangerous chemical reaction within the battery cells. 

The risk of thermal runaway begins when a battery cell reaches a temperature around 150°F. If it gets even hotter, reaching 220°F, a dangerous reaction happens. The liquid electrolyte inside the battery catches fire. This damages the battery’s structure and lets out oxygen, which then combusts in temperatures reaching up to 750°F in less than a second. 

If one battery cell overheats, it can cause nearby cells to do the same, leading to a chain reaction. At a certain point, parts of the battery can collapse, touching each other and creating a big temperature spike.

This can cause gases to escape from the battery, sometimes visibly as a cloud. If these gases catch fire, it can lead to an explosion. This whole process is what we call thermal runaway, and it can happen very fast, creating a significant risk.

Causes of Thermal Runaway

Conditions such as internal short-circuiting, mechanical damage from impacts, overcharging beyond the battery’s voltage limit, inadequate cooling, and manufacturing defects can all precipitate “automotive thermal runaway.” Understanding these triggers enables manufacturers to design more resilient battery systems.

  1. Short-circuiting: Occurs when battery internal components touch, creating a path of low resistance. This abrupt electrical flow generates intense heat, starting thermal runaway.
  1. Mechanical Damage: Impacts, crushing, or penetration compromises battery structure, disrupting internal chemistry and leading to excessive heat generation.
  1. Overcharging: Exceeding the battery’s voltage limit forces too much energy into the cells, causing overheating and potential chemical imbalance.
  1. Poor Cooling: Inadequate temperature regulation allows cells to overheat during operation or charging, increasing the likelihood of thermal runaway.
  1. Manufacturing Defects: Flaws in battery construction can create weak spots where heat accumulates, disrupting normal operation and triggering runaway conditions.

How Thermal Runaway Occurs in Electric Vehicles

We breakdown the process of thermal runaway in EVs step-by-step. 

1. Battery Cell Short Circuit 

A thermal runaway event initiates when a battery cell short circuits, leading to an uncontrollable increase in heat. This can be triggered by damage, such as penetration or crushing, or by internal faults like manufacturing defects.

2. Chemical Reaction Acceleration 

Following the short circuit, abnormal chemical reactions replace the cell’s normal operations, generating significant heat and releasing toxic, flammable gases. These reactions intensify as the temperature rises.

3. Spread to Adjacent Cells 

The heat from the affected cell increases the temperature of neighboring cells beyond their heat dissipation capabilities. This domino effect can cause multiple cells to fail, amplifying the risk.

4. Ignition and Expansion 

A mix of released gases and rising heat can lead to the ignition of the battery cell. This can cause widespread damage as surrounding cells catch fire, leading to a significant thermal event.

5. Risk of (or) Explosion

 The culmination of these reactions and the breakdown of different components, such as the metal-oxide cathode, release oxygen which can ignite. This, alongside the buildup of pressure from gas release, may result in a vapor cloud explosion, posing severe safety risks.

Best Electric Vehicle Thermal Runaway Protection Methods

electrical vehicle thermal runaway

Many innovative solutions have emerged to curb the threat of thermal runaway in EVs, emphasizing active and passive safety measures. Here are the best prevention strategies. 

1. Introducing a Flame Retardant

Incorporating a flame retardant into the battery’s thermal fluid minimizes fire risks from overcharging or accidents. Bromine compounds, encapsulated and activated by excessive heat, intercept and suppress fire by halting the spread of flames. This approach, particularly relevant in EV batteries, acts quickly during critical moments to prevent thermal runaway.

2. Using Damage Initiating Devices 

University of California researchers developed mechanisms activated mechanically or thermally to halt thermal runaway early. These devices, embedded in the battery, disrupt the electrode upon detecting damage, raising internal resistance to stop overheating. Passive initiators increase electrode impedance by creating voids, while active initiators change shape or volume under stress, both effectively preventing runaway before it escalates.

3. Redefining Battery Design 

Tesla’s innovative battery design emphasizes a controlled thermal energy release during runaway events, ensuring safety without compromising functionality. This design directs thermal energy efficiently, preventing cell rupture and maintaining cell cap integrity as the positive terminal. By managing how and where thermal energy is released, the risk of dangerous outcomes is significantly reduced.

4. Implementing Advanced BTMS

Incorporating effective Battery Thermal Management Systems (BTMS) proactively prevents thermal runaway, as detailed by ScienceDirect. These systems regulate temperature across battery cells, ensuring they remain within safe operational limits to prevent overheating. Materials like mica, renowned for its thermal insulation and electrical resistivity, are highly compatible with BTMS. Its use within BTMS can significantly augment the battery’s resilience against heat and sparks that can start a fire, consequently stopping thermal runaway in its tracks. 

Can Thermal Runaway Be Prevented?

Thermal runaway is a critical concern in the management of electronic devices and battery systems, particularly in lithium-ion batteries, which power a vast array of modern technology. The phenomenon refers to a self-accelerating reaction that generates heat, potentially leading to fires or explosions if not adequately controlled. The question of its preventability is not just about whether we can stop it, but how we can intelligently integrate safety measures to minimize the risk.

Thermal runaway can indeed be prevented through several measures:

Monitoring: Implement continuous temperature and voltage monitoring to detect any irregularities early.

Temperature Control: Use cooling systems to maintain optimal operating temperatures and prevent overheating.

Design: Opt for battery designs and materials that reduce the likelihood of short circuits and overheating.

Protection Circuits: Install protective circuits to interrupt current flow in case of overcharging or excessive temperature rise.

Regular Maintenance: Conduct periodic inspections and maintenance to ensure systems are functioning correctly and to replace any deteriorating components.

Utilizing Mica insulation: Particularly Axim Mica’s phlogopite sheets, helps control these risks. These sheets, capable of enduring continuous temperatures up to 1292°F, can insulate the battery pack, delaying thermal propagation and enhancing passenger safety by providing more time for evacuation.

By adopting these strategies, the risk of thermal runaway can be significantly reduced.

How Axim mica can help

In the electric vehicle industry, battery safety cannot be overstated, especially with the looming threat of thermal runaway. Axim Mica brings to the table not just ISO 9001:2015 certified phlogopite mica sheets, but a commitment to excellence and reliability. Capable of withstanding temperatures up to 1292°F, our mica sheets are instrumental in mitigating the risks of thermal runaway. 

By integrating mica battery insulation sheets capable of withstanding extreme temperatures, Axim Mica provides an essential component in the thermal management, consequently reducing the risk of thermal runaway.This pivotal safety feature provides critical evacuation time, ensuring passenger safety in critical situations. 

Choose Axim Mica for your EV battery solutions—where certified quality meets unparalleled efficiency—to navigate the future of electric mobility with confidence.

Thermal runaway and the importance of EV battery safety

In facing the threat of thermal runaway, the importance of EV battery safety is paramount. Preventive measures ranging from integrating flame retardants and damage-initiating devices to redefining battery design and implementing Battery Thermal Management Systems (BTMS) offer a multi-faceted defense. 

Axim Mica’s contribution, through its high-grade, certified phlogopite mica sheets, exemplifies innovation meeting safety. Withstanding temperatures up to 1292°F, these sheets are a cornerstone in safeguarding against thermal runaway, ensuring not just the endurance of battery cells, but fundamentally preserving the well-being of passengers. 

As we drive towards a sustainable future with electric vehicles, ensuring battery integrity isn’t just an option—it’s essential. Axim Mica not only promises, but provides the reliability needed to face these challenges head-on, marking a crucial step forward in the evolution of EV safety.


How do you stop a thermal runaway in an EV? 

Implementing advanced thermal management systems and using mica insulation materials can significantly reduce the risk of thermal runaway in EVs by maintaining temperature control.

How does Tesla prevent thermal runaway? 

Tesla incorporates a comprehensive cooling system and uses phlogopite mica sheets for insulation to manage battery temperatures and prevent thermal runaway.

Can lithium batteries have thermal runaway? 

Yes, lithium batteries can experience thermal runaway, especially if subjected to excessive heat, overcharging, or physical damage.

What is thermal runaway in a battery? 

Thermal runaway in batteries refers to a rapid, uncontrollable temperature increase leading to potential fires or explosions.

What voltage does thermal runaway start? 

Thermal runaway can begin at different voltages, but it typically triggers when the internal conditions disrupt the battery’s thermal balance.

What are the solutions for thermal runaway? 

Using mica sheet battery insulation and active cooling strategies are effective solutions to mitigate thermal runaway in electric vehicles.


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