The key to preventing battery fires may lie in understanding how they fail.
By Battery Research Team | Published: October 2023
Imagine a power source so energetic that it can violently explode, ejecting molten metal and reaching temperatures hotter than a lava flow. This isn't a scene from a disaster movie; it is a real-world phenomenon called thermal runaway that battery scientists are racing to understand and prevent. In our daily lives, we are surrounded by lithium-ion batteries—in our phones, laptops, and especially in the electric vehicles and personal devices that are becoming commonplace. Their widespread use makes their safety paramount. This article explores how researchers are using forensic simulations to recreate battery failure, uncovering the root causes of these dangerous events to build a safer, powered future.
At its core, thermal runaway is a catastrophic, self-sustaining failure within a battery. It is a vicious cycle of heat leading to more heat, culminating in fire or explosion. The process often begins when a battery is subjected to "abuse"—whether mechanical, electrical, or, most commonly, thermal.
As a battery overheats, its internal components become unstable. The thin separator meant to keep the positive and negative electrodes apart can begin to melt.
This allows internal short circuits, releasing more heat. The heat triggers the breakdown of the battery's flammable liquid electrolyte, generating gas and increasing internal pressure. This is when a battery might "vent," releasing smoke and flammable gases.
If the temperature continues to rise unchecked, the active materials in the positive and negative electrodes themselves start to break down in violent exothermic reactions, releasing immense heat and causing the battery to erupt into jet-like flames.
For NMC532 batteries, thermal runaway can be triggered at an average temperature of around 244°C 1 .
The internal temperature during runaway can exceed a staggering 1000°C, enough to melt internal components 1 .
To truly understand how to stop thermal runaway, scientists at the University of Warwick conducted a meticulous forensic study, simulating real failure scenarios on common 18650-sized cylindrical cells (the type often used in laptops and power tools) with NMC532 and graphite chemistry 1 .
Their goal was clear: determine exactly how localised heat and a battery's charge level combine to trigger a disaster.
The researchers designed an experiment to mimic a real-world case where poor design or a malfunction could cause a small part of a battery to be consistently overheated 1 . The setup was a precise recreation of such conditions:
The results were striking and pointed to a critical factor in battery safety. The experiments demonstrated that a battery's state of charge is a primary dictator of its fate under thermal stress 1 .
When the battery was at 100% charge, applying localised heat of 200°C or 250°C consistently induced catastrophic failure. This involved violent venting, melting of internal components (with temperatures over 1085°C), and the ejection of cell materials 1 .
Conversely, when the same high temperatures (200°C and 250°C) were applied to cells at a lower state of charge, catastrophic failure was not observed. The cells vented gas but did not escalate into uncontrollable thermal runaway 1 .
| State of Charge (SOC) | Applied Localised Heat | Observed Outcome |
|---|---|---|
| 100% (High SOC) | 200°C or 250°C | Catastrophic Failure & Thermal Runaway (Violent venting, ejection, temperatures >1000°C) |
| Low SOC | 200°C or 250°C | Venting Only (No catastrophic thermal runaway) |
The study offered a glimmer of hope for intervention. They found that at a high state of charge, if the heat source was rapidly removed at the moment of venting, the onset of full thermal runaway could sometimes be avoided 1 . This highlights a crucial window for safety systems to act.
The forensic investigation of battery failure relies on a suite of specialised tools that allow researchers to see the unseen. Here are some of the essential items in a battery safety scientist's toolkit 1 4 :
Creates near-adiabatic (no heat loss) conditions to precisely measure a battery's self-heating and identify the trigger temperatures for thermal runaway.
Mimics real-world hot spots on a battery, allowing scientists to study failures from localised thermal abuse rather than just overall heating.
A real-time gas analyser that "sniffs" the gases vented from a battery, identifying their composition to understand the internal chemical reactions during failure.
High-temperature sensors attached directly to the battery to monitor rapid and extreme temperature changes from the inside out.
Acts like a CAT scan for batteries, creating a 3D visualisation of the internal structure without destroying it, revealing damage like electrode melting or deformation.
The insights gained from forensic simulations are directly informing the development of next-generation safety strategies. The clear link between state of charge and thermal runaway risk is a critical data point for engineers designing Battery Management Systems (BMS). Future BMS could be programmed to implement more conservative charging strategies in high-risk environments or if an incipient failure is detected.
Moreover, understanding the "chemical crosstalk" between the cathode and anode opens new avenues for material science 6 . Researchers are now designing more thermally stable electrolytes, robust separators, and cathode materials that are less prone to releasing oxygen when heated.
Uses algorithms to monitor health and stress, potentially limiting charge in risky conditions or activating rapid cooling.
Integrating early warning signals like gas detection or internal pressure changes.
Develops innately safer components, such as solid-state electrolytes that are non-flammable or cathodes with higher thermal stability.
Creating higher-energy-density materials that do not compromise on safety.
Uses thermal barriers and robust module design to isolate a failing cell and stop propagation.
Testing new material composites that can withstand extreme temperatures and jet flames.
The path to safer batteries is not about finding a single magic solution, but about building layers of defense—from the atomic structure of the materials to the intelligent systems that manage them. Through painstaking forensic work, scientists are turning the chaos of failure into a blueprint for safety, ensuring the powerful batteries that drive our modern world are also trustworthy guardians of it.
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