What Is Thermal Runaway?

Against the backdrop of the global electrification of transportation, lithium-ion batteries are the core power source for electric vehicles (EVs), and their energy density and charge/discharge efficiency are rapidly improving. This progress has significantly extended driving range, but it has also placed higher demands and new challenges on vehicle safety technology. Among the many potential safety hazards, thermal runaway has consistently been a focus of engineers' discussions. So what is thermal runaway as it relates to EVs? Preventing thermal runaway has become a primary concern for automakers, fleet operators, and end users. This phenomenon is not only about technical compliance, but also about passenger safety and the future of brands. This article will provide a detailed analysis of all aspects of thermal runaway in electric vehicles, from its basic definition and root causes to practical prevention strategies.

Ⅰ. What is thermal runaway as it relates to EVs?

Thermal runaway refers to an uncontrolled, continuous exothermic chain reaction occurring inside a lithium-ion battery, causing the battery to heat up abnormally rapidly. When the battery temperature exceeds its critical threshold, thermal runaway occurs, triggering a series of chain chemical reactions that release large amounts of heat, flammable gases, and toxic emissions.

This chain reaction occurs when the rate at which the battery generates heat exceeds its rate of heat dissipation to the surrounding environment. This imbalance causes a sudden, exponential increase in temperature, peaking at over 1000 degrees Celsius. During this process, the battery releases toxic and highly flammable gases. The greatest risk is not the failure of a single battery, but thermal diffusion. The heat generated by a runaway battery can spread to adjacent batteries, causing their temperatures to exceed the critical threshold and triggering a domino effect that can engulf the entire battery pack within seconds, leading to fire, explosion, and irreversible damage.

For electric vehicles, this is not merely a theoretical risk, but a real threat that jeopardizes vehicle safety and consumer trust.

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