What is Thermal Runaway? And Why is it Important for Electric Vehicle Adoption

What is Thermal Runaway? And Why is it Important for Electric Vehicle Adoption

Electric vehicles (EVs) are the future, and a critical step to reducing greenhouse gas (GHG) emissions and creating a more sustainable world. According to the U.S. Environmental Protection Agency (EPA), GHG emissions from the transportation sector are larger than any other sector, accounting for approximately 27% of total greenhouse gas emissions in the U.S.1

Adoption of EVs is growing fast: from 2020 to 2021, EV sales worldwide almost doubled, reaching 6.6 million. This brings the total number of EVs on the road to more than 16 million.2 The International Energy Agency (IEA) projects that, to reach Net Zero Emissions by 2050, EVs on the road must exceed 300 million in 2030 (2 billion by 2050), and electric vehicles must account for 60% of new car sales. Currently, in the U.S., less than 1% of the 250 million cars, sport utility vehicles and light-duty trucks on the road are EVs.3 To put this into perspective on a global scale, the U.S. is eighth on the list of the top 10 countries by number of EVs per capita. Norway is first, with 81 EVs per 1,000 residents. The United Kingdom has 6.7 EVs per 1,000 residents, while the U.S. has 5.2 per 1,000 and China has 3 per 1,000.4

For EV adoption to continue to rapidly accelerate, there are several key infrastructure, resource and technology challenges to address. Countries must have the EV charging infrastructure along their roadways to support electric vehicles. Battery makers must have enough lithium for lithium-ion battery-powered EVs. EVs must be equipped with technology that makes them both safe to drive and high-performing enough to be comparable to the gas-powered vehicles people are accustomed to.

Thermal runaway and the importance of EV battery safety

EV battery safety has captured public attention in recent years, particularly after events like Hurricane Ian in Florida, when EVs submerged in saltwater led to several battery fires.5 Though EV battery fires are relatively rare, occurring at a rate of roughly 25 per 100,000 EVs sold, their repercussions are serious enough to warrant focused attention to this issue.6 EV fires can be unpredictable: a recent study suggests that one third of EV fires occur when the vehicle is parked, not moving and not charging.7 And fire departments require special training to manage EV fires, as they can continue to reignite for days following being extinguished.

Fires in EV batteries are triggered by “thermal runaway” (TR) events. TR is a known safety hazard in lithium-ion batteries (LIBs) and can be caused by:

· Short-circuiting

· Mechanical stress to the EV battery from impact during an accident

· Overheating or poor cooling techniques

· Condensation and moisture in the EV battery pack

· A manufacturing defect 8

Thermal runaway is a chain of events that typically starts with the gradual breakdown of EV battery cells, causing pre-heating of the EV battery cells and pack. The elevated temperature within the EV battery cells causes the organic solvents to break down, resulting in the release of gases, increased pressure and temperature beyond its flashpoint.

As different materials within the EV battery pack break down—such as the metal-oxide cathode—oxygen is released, which can cause an ignition. The electrolyte used in EV LIBs is flammable and spreads the fire. TR may occur over a prolonged period of time before an actual fire starts, or the fire could be instantaneous.9

Addressing this challenge

Because of the drastic—and sometimes tragic—consequences of an EV battery fire, countries are developing regulations to heighten EV battery safety such as the United Nations’ Global Technical Regulation 20 on Electric Vehicle Safety (UN GTR No. 20) and China’s GB 38031-2020. GB 38031-2020 requires that EVs provide an advance warning five minutes before a hazardous situation occurs inside the passenger compartment caused by thermal runaway in the EV battery. Through the National Highway Traffic Safety Administration’s (NHTSA) Battery Safety Initiative, the U.S. aims to research and provide guidance on EV battery safety risks as well.  

To complement these regulatory actions, forward-thinking companies are developing technologies that can quickly notify drivers and workers involved in EV production, storage and transport to the risk of an EV battery fire. Honeywell’s EV battery safety sensors, integrated into EV battery packs, enable early detection of thermal runaway events to help mitigate the risk of injury, property damage or loss of life. Our BAS Series sensors, for example, detect particulate matter (smoke, liquid drops, dirt, etc.) in EV battery packs and energy storage systems, which can trigger TR events.

Honeywell has a long-standing commitment to safety. We bring significant industry experience and engineering talent to our customers in the EV sector. Our strategic advantage is not only our significant portfolio of EV solutions, but also that we are agnostic to the specific EV battery chemistry used and can help EV battery manufacturers customize a sensing solution to meet their specific needs, price sensitivities and adoption timeline.  

To learn more about Honeywell and how we are helping to drive both EV battery safety and sustainability, visit our website.


  1. www.epa.gov/transportation-air-pollution-and-climate-change/carbon-pollution-transportation
  2. www.iea.org/reports/electric-vehicles   
  3. www.reuters.com/graphics/AUTOS-ELECTRIC/USA/mopanyqxwva/
  4. www.canarymedia.com/articles/electric-vehicles/chart-these-countries-have-the-most-electric-vehicles-per-capita  
  5. www.nfpa.org/News-and-Research/Publications-and-media/Blogs-Landing-Page/NFPA-Today/Blog-Posts/2022/10/19/Experts-Warn-of-Electric-Vehicle-Fires-After-Hurricane-Ian-Damages-Lithium-Ion-Batteries
  6. www.autoinsuranceez.com/gas-vs-electric-car-fires/
  7. EV Fires: Less Common But More Problematic? | IDTechEx Research Article
  8. https://www.sciencedirect.com/science/article/abs/pii/S2405829716303464
  9. https://doi.org/10.1016/j.joule.2020.02.010
  10. https://www.nhtsa.gov/battery-safety-initiative