Thermal Runaway — A Staircase Climbed on Its Own Heat

Why Battery Fires Are Unusually Hard to Put Out

We often hear that fires in electric vehicle batteries are hard to put out. Three reasons are cited: heat pours out extremely rapidly, the box enclosing the battery traps the heat making it hard to cool from the outside, and oxygen is generated inside the battery so the fire does not rely solely on outside air (DOI: 10.1016/j.firesaf.2025.104503). Fires that have quieted down springing back to life also makes response tricky (DOI: 10.3390/su172310578).

Two of the three reasons come from inside the battery. The reactions that produce heat and oxygen happen inside the battery. Thermal runaway is a loop that cannot stop on its own, where if the temperature inside the battery rises, a chemical reaction that produces heat occurs, and the heat produced by that reaction raises the temperature again to trigger even more reactions (DOI: 10.1016/j.ecmx.2022.100310; DOI: 10.1002/bte2.70149).

This article follows how that loop starts, in what order it escalates, and how it spreads sideways. It also follows where designs aimed at breaking that loop are built in. The target is the liquid-filled lithium-ion battery used in mobile phones and electric vehicles today. Batteries using other chemistries are outside the scope of this article.

What Lies Inside a Cell

Cell phone batteries and electric vehicle batteries are made from the same basic units. A cell is the smallest single compartment making up a battery, containing a positive electrode, a negative electrode, the electrolyte filling the space between them, and a separator dividing the two inside a single container. An electric vehicle battery is a clump of many such cells bound together.

The main character moving back and forth inside the cell is lithium. A lithium ion is a + electrically charged particle formed when a lithium atom gives up an electron. The places where lithium ions stay are the two electrodes. The positive electrode is the + side electrode of the cell, where lithium ions return and settle during discharge. The negative electrode is the − side electrode of the cell, where lithium ions cross over and stay during charging. Which paths the lithium ions and electrons take respectively is covered in detail by another piece in this series, the one dealing with the structure inside the cell and charging and discharging.

What matters in the story of thermal runaway is the nature of these components. The materials of a cell are highly reactive and flammable, so if placed under strained conditions, unwanted reactions can occur in a chain between the electrodes and the electrolyte (DOI: 10.3390/app9122483).

Let us start with what fills the space between the two electrodes. An electrolyte is a substance filling the space between the two electrodes that lets lithium ions pass through while preventing electrons from crossing. The electrolyte is usually a flammable liquid. The gas emitted by a cell contains a heavy mixture of evaporated electrolyte solvent, and that gas makes the gas as a whole more flammable (DOI: 10.1016/j.jlp.2024.105488).

There is also a membrane between the two electrodes. A separator is a thin membrane dividing the positive and negative electrodes so they do not touch, with many tiny pores through which lithium ions pass. The separator lets ions pass while blocking electrons, keeping the two electrodes from connecting directly inside the cell. However, commonly used plastic separators shrink at high temperatures (DOI: 10.1002/adma.202106335).

The two electrodes store energy under normal conditions, and when the temperature rises, the cell's materials—down to the electrolyte and the separator—react with one another to become fuel that releases heat.

The Speed at Which Heat Accumulates and Escapes

There are tests in laboratories that intentionally create worst-case conditions. A cell is placed in a container that allows no heat to escape and is heated up. This condition mimics a single cell in the middle of a large battery pack that has lost its path to cool down (DOI: 10.1149/ma2014-01/1/76).

The reason this test is the worst case lies in the arithmetic of heat. A cell generates heat while it is in use, some of that heat escapes to the outside, and the rest accumulates inside the cell (DOI: 10.1109/access.2018.2824838). When the escaping heat catches up to the generated heat, the temperature stops at a certain line. If the generated heat pulls ahead, the temperature rises, and because chemical reactions speed up at higher temperatures, heat is generated even faster. Inside a container with no path for heat to escape, this pulling ahead happens most easily.

This loop can be pictured as a staircase. Each step of the staircase is a single reaction that begins only when a certain temperature is reached. When the heat generated by that reaction pushes the cell up to the starting temperature of the next step, the cell climbs to the next step without anyone pushing it. The explanation that views thermal runaway as a phenomenon where a chain of exothermic reactions steeply raises the temperature inside the cell matches this picture (DOI: 10.1016/j.ecmx.2022.100310). A study analyzing two cells using a cathode mixed with nickel, cobalt, and manganese also concludes that the reaction generating the most heat begins when a critical temperature is reached (DOI: 10.3389/fenrg.2018.00126). Actual reactions sometimes intertwine and proceed together (DOI: 10.1002/advs.76228). The staircase is a picture that shows those main branches.

The lower and upper parts of the staircase have different characteristics. In an experiment that watched thermal runaway by putting a fiber-optic sensor inside a commercially available cylindrical cell, the section where the curves of the cell's temperature and pressure increase suddenly bend overlapped with the spot where reversible reactions cross over into irreversible reactions (DOI: 10.1038/s41467-023-40995-3). When three types of cells were pushed to their limits and the stress was stopped the moment a very small amount of hydrogen was detected, in all tested cases they did not go to thermal runaway (DOI: 10.1016/j.xcrp.2025.102859, laboratory test). Cells whose stress was stopped on the lower steps did not go to thermal runaway, but once they passed a certain step, the cell climbed all the way up on its own.

The height and size of the steps differ from cell to cell. Even when cells of the same design are tested under the same conditions, their thermal responses diverge widely (DOI: 10.1016/j.jpowsour.2024.234106), and large cylindrical cells can have a part of the cell significantly exceed the common starting temperature determined by a laboratory calorimeter (DOI: 10.1016/j.est.2024.111275). The process that thermal runaway goes through also varies greatly depending on the materials making up the cell (DOI: 10.1016/j.nxener.2024.100186). Exactly how many degrees each step is must be measured separately for each cell.

Three Forks Pushing It Up to the First Step

The force that lifts it onto the first step splits into three forks: mechanical damage like crushing or piercing, electrical strain such as charging past designated limits, and heat coming from the outside (DOI: 10.1016/j.jechem.2020.10.017; DOI: 10.1002/aenm.71302). All three can cause reactions inside the cell to generate heat much too quickly, which can end in thermal runaway (DOI: 10.1016/j.aets.2024.06.002).

There is a spot where the three forks often meet. Let us first name the outside path. A circuit is a closed path with no breaks where electricity comes out of a battery, passes through a device, and returns to the battery. The electricity a cell releases is supposed to travel this external circuit. An internal short circuit is when the positive and negative electrodes connect directly across the separator inside the cell, causing electricity to flow without going through the external circuit. Internal shorts frequently happen when the separator shrinks from heat or is crushed and breaks (DOI: 10.1149/ma2019-01/6/582).

Internal shorts rank among the hardest lithium-ion battery failures to handle. They can lead to thermal runaway and are difficult to detect in advance. Their causes span broadly, including defects arising at various stages of the manufacturing process (DOI: 10.1016/j.jpowsour.2025.238265). The test of driving an iron nail into a cell in a laboratory imitates cases where external shocks like car accidents create a short inside the cell (DOI: 10.1149/ma2014-01/1/76). Although the nail test is easy to perform, many conditions change its results (DOI: 10.1016/j.jpowsour.2025.238265).

The electrical path also has a route that takes time. Lithium plating is when lithium ions fail to enter the negative electrode and instead accumulate as metallic lithium on the electrode's surface. Lithium plating can happen when charging too quickly or charging at low temperatures. If the plating worsens, lithium can grow in branch-like shapes, pierce the separator, and create an internal short, which can end in thermal runaway (DOI: 10.3390/en17235930). The conditions that cause plating and the side of the story about making batteries age are handled by another piece in this series, the one covering why batteries age.

Even if the three forks start from different places, they arrive at the same destination. The moment somewhere inside the cell heats up faster than it cools down, the first step begins.

One Step at a Time — A Cell Warming Up

Now let us imagine slowly heating a single cell from the outside. The steps follow four stages outlined in a review paper. The boundary where the negative electrode and the electrolyte meet breaks down first, the separator shrinks, the electrolyte decomposes, and the positive electrode releases oxygen (DOI: 10.1002/advs.76228).

The first step begins at the surface of the negative electrode. The SEI is an extremely thin film that forms on the surface of the negative electrode; it is created as part of the electrolyte decomposes during the first few charge cycles and continues to grow little by little afterward. The breakdown of this film, which separated the negative electrode and the electrolyte, is the first stage of the steps (DOI: 10.1002/advs.76228). When the film breaks down, the negative electrode and the electrolyte meet and react directly. The film appears in more detail in another piece in this series, the one covering why batteries age.

The second step is the separator. The ways in which a separator fails are puncturing, melting, and thermal shrinkage (DOI: 10.70322/gct.2024.10006). The shrinking, melting, and collapsing of the separator are reported to occur alongside minor and major short circuits, leading to thermal runaway. Which of those triggers the start of thermal runaway is the question that research aims to settle (DOI: 10.1149/ma2021-015303mtgabs, conference abstract).

When the separator collapses, an internal short circuit can occur right then and there. An internal short circuit is something that happens alongside the collapse of the separator, which is difficult to count as a single step of the stairs. Evidence is divided over its role. There is a conference abstract that heated a single flat cell, much larger than a phone battery, in an insulated container. In the fully charged cell, the signal for an internal short circuit was caught at about 181 degrees, and thermal runaway came 343 seconds later at about 213 degrees. The thermal shrinkage of the separator was the cause of the short circuit, and the speed at which the cell heated up did not accelerate the moment the short circuit happened. In this cell, the internal short circuit came before thermal runaway but generated little heat, and the major heat was produced by the reaction between the negative electrode and the electrolyte, and the reaction between the positive and negative electrodes. In tests where cell components were mixed and heated, the reaction between the positive and negative electrodes produced the greatest heat. The authors explain that the short circuit produced little heat because the electrolyte inside the cell had dried out, increasing resistance, and write that the role of the short circuit in thermal runaway initiated by heat needs to be clarified further (DOI: 10.1149/ma2019-01/6/582, conference abstract, single cell type).

Other evidence assigns a larger role to the short circuit. A study analyzing two nickel-cobalt-manganese cells views the short circuit as decisive in driving the large reaction between the positive and negative electrodes, while also listing the relationship between short circuits and thermal runaway as a task to be tackled in the future (DOI: 10.3389/fenrg.2018.00126). There are studies that view short circuits caused by a ruptured separator as the main cause of major failures (DOI: 10.1149/ma2021-015303mtgabs, conference abstract), and a review paper lists separator failure as the direct cause of thermal runaway (DOI: 10.70322/gct.2024.10006). When a nail is driven in or a cell is crushed so that a major short circuit occurs all at once, the short circuit directly triggers thermal runaway (DOI: 10.1149/ma2019-01/6/582).

The third step is the electrolyte, and the fourth is the positive electrode. The electrolyte decomposes, and the positive electrode releases oxygen (DOI: 10.1002/advs.76228). When a nickel-blended oxide positive electrode is heated, its crystal structure changes and oxygen is released. This observation came from an experiment that separately heated positive electrode material that had been charged beyond its limit (DOI: 10.1002/adfm.201200693). Reactive gases such as released oxygen crossing the separator and reacting with the opposite electrode are pointed to as a path that invites thermal runaway (DOI: 10.1002/adma.202106335). The main heat source that bakes the cell to over 800 degrees is identified as the oxidation-reduction reaction between the positive and negative electrodes (DOI: 10.3389/fenrg.2018.00126). "Oxygen generated inside the battery," which we saw at the beginning, comes from this exact step.

Gas also builds up inside the cell while climbing the steps. Gas venting is when pressure rises due to gas generated inside the cell, and that gas bursts out of the cell. Cylindrical cells have a passageway prepared in advance to open at this time (DOI: 10.1016/j.jlp.2024.105488). Gas venting comes before thermal runaway (DOI: 10.1016/j.xcrp.2025.102859). The pressure inside the cell, measured with a fiber-optic sensor, formed two peaks: the first matched gas venting, and the second matched the start of thermal runaway (DOI: 10.1038/s41467-023-40995-3). The vented gas is a mixture of hydrogen, methane, carbon monoxide, carbon dioxide, hydrogen fluoride, and electrolyte solvent vapor (DOI: 10.1016/j.jlp.2025.105657). Because this gas is flammable and toxic, the risks of fire, explosion, and poisoning emerge together (DOI: 10.1016/j.est.2024.111288). If gas is generated rapidly but cannot escape sufficiently, the cell can rupture (DOI: 10.1002/advs.201700369).

From One Cell to the Next

Even if a single cell reaches the top of the stairs, the accident stops at that one cell unless the heat travels to the neighbors. The problem is when it travels. Thermal runaway propagation is when the heat and hot gases released by a cell in thermal runaway heat up the neighboring cell, driving that cell into thermal runaway as well. Propagation rapidly spreads the failure to multiple cells, amplifying the danger (DOI: 10.3390/batteries11060216). In terms of our staircase picture, it is when the heat released by the cell that climbed to the top pushes the neighboring cell up past the first step of its own.

There are three paths for heat to cross over to a neighboring cell: heat conducted directly through touching surfaces, heat carried by vented hot gases, and flames along with their radiant heat. Which path dominates changes depending on the stage (DOI: 10.1002/aenm.71302). In models and experiments using large cylindrical cells, blocking the path where hot gas delivers heat to neighboring cells first was the most important. Conduction heat passing through contact was managed next by adjusting the spacing between cells, and cells with larger diameters needed to be spaced further apart (DOI: 10.1016/j.est.2024.111275). Propagation varies depending on the spacing between cells, the materials placed between them, and the way the cells are stacked (DOI: 10.1016/j.etran.2023.100305).

The results of suppression studies vary depending on the subjects and methods tested. There is a study that tested five suppression methods in an 8-kilowatt-hour residential energy storage system. Fine water mist and a method adding encapsulated additives to it performed best, extending the time by which spread was delayed compared to the unsuppressed test by 179% and 167%, respectively, and lowering the risk ratio of thermal runaway by over 70%. In one residential storage system test, none of the five suppression methods completely stopped the spread. A problem was also revealed where better cooling produced more vapor clouds, increasing the risk of explosion. The authors conclude that current suppression technology can slow down propagation, but cannot stop it (DOI: 10.1007/s10694-025-01831-w). A study testing a scaled-down model of a method that injects cooling water directly into the battery pack through pre-installed pipes reports that passenger electric vehicle battery fires can be extinguished within a few minutes using about 100 kilograms of water (DOI: 10.1016/j.firesaf.2025.104503, scaled-down model experiment). There is also a review suggesting that post-thermal-runaway fire prevention and suppression technologies can effectively reduce damage (DOI: 10.1016/j.aets.2024.06.002).

Testing standards do not provide the final answer either. According to a short review gathering recorded large-scale storage system accidents, there were cases where fires and propagation occurred even in systems that passed the latest standards and their propagation tests. The authors find loopholes in the standards from those records (DOI: 10.1002/prs.12448).

The Places That Break the Chain

Ceramic-coated separators, non-flammable electrolyte additives, barrier walls between cells, and devices that watch over the cells are among the many places where countermeasures are applied. One review paper suggests setting signals for each stage of thermal runaway and matching the countermeasures for those stages to the respective layers of materials, cells, modules, packs, and systems (DOI: 10.1002/advs.76228). Countermeasures span multiple layers from materials to cells, packs, and cell-monitoring devices, and a proposal has emerged to pair these countermeasures with each step of the ladder. A review covering propagation forecasts that we must move beyond the current layered blockades toward devices that bundle multiple functions together (DOI: 10.1002/aenm.71302).

At the material layer, non-flammable electrolyte additives, heat-resistant materials, and ceramic-coated separators are used (DOI: 10.1016/j.aets.2024.06.002). In a study testing a separator that does not shrink in the heat, the steepest temperature rise when a small lab-made cell heated up dropped from 131.6 degrees per second in a cell using a normal ceramic-coated separator to 3.7 degrees per second. That separator blocked short circuits and also blocked the path for oxygen to cross over to the opposite electrode (DOI: 10.1002/adma.202106335, lab cell). A cylindrical cell using metal-coated plastic sheets as current collectors avoided thermal runaway every time in nail penetration tests, whereas normal cells went into thermal runaway every time (DOI: 10.1016/j.xcrp.2021.100360, lab test).

At the cell layer, the path for venting gas is important. A cylindrical cell with a second vent at the bottom avoided the stage leading up to cell rupture while thermal runaway was happening (DOI: 10.1002/advs.201700369, single study). At the pack layer, the gaps and barriers seen in the previous section do their work. Methods that use heat-storing materials, heat-insulating walls, and fire-suppressing substances according to each stage are organized in the literature (DOI: 10.1002/aenm.71302). One module in which cells were completely immersed in a fire-retardant liquid did not spread fire sideways in stress tests, whereas a module tested without liquid burned down with fire and explosions (DOI: 10.3390/en17102418, single study).

The top layer is the monitoring device. The battery management system is a device that monitors cell voltage, current, and temperature, estimates the state of charge and state of health, protects the cells, and balances them out among one another. The state of charge is the percentage of the amount currently remaining, the state of health indicates how old the cell is, and both are covered by other parts of this series. When anomalies are seen, this device takes action to protect the cells (DOI: 10.1002/bte2.70149), and because it cannot always prevent thermal runaway, methods to catch it before it starts are studied separately (DOI: 10.1002/bte2.70149). A systematic review of the literature concludes that temperature monitoring is suited for catching stress, while voltage monitoring is suited for catching cell failure, when paired with their respective calculation models (DOI: 10.1016/j.fub.2025.100110). An optical fiber sensor inserted inside the cell was able to sound an alarm even before gas venting (DOI: 10.1038/s41467-023-40995-3, single experiment), and methods of catching signals at lower rungs, like the hydrogen detection seen earlier, are being tested in the lab (DOI: 10.1016/j.xcrp.2025.102859). Even with the layers overlapped, gaps remain. The accident records from the previous section show those gaps.

The Steps That Change With Cathode Materials

The steepness of the steps varies greatly depending on what is used for the cathode. LFP cathodes are cathodes made of lithium, iron, and phosphate, while nickel-based cathodes are cathodes made of oxides combining nickel with cobalt and manganese or aluminum. How the crystal structures of the cathodes differ is covered in the installment dealing with the structure inside the cell.

LFP is known as a cathode that is very stable against heat. In tests where commercial cells were heated from the outside, cobalt-based laptop cells caught fire and exceeded 700 degrees, while the reaction of the LFP cells was much milder. Still, thermal runaway was observed in some of the LFP cells, and while overcharged tests mostly went without incident, one ended in a fierce fire. The authors note that while there has been progress in making safer cells, thermal runaway can still occur under extreme conditions (DOI: 10.1149/2.0311410jes).

In a study comparing cells taken from two vehicle models, when matched for the energy the cells held, the thermal runaway reaction of the high-nickel cell was 9 times faster than that of the LFP cell, and looking at the entire phase spreading to neighboring cells, it was 5 times faster. Instead, LFP cells hold less energy for the same weight and volume. That study analyzes that, when judged by averages, refining the way cells are bundled into a pack can narrow that gap to 16% on a weight basis, and the volume basis can be bridged. The authors report that the safety requirements are much higher for high-nickel cells and add that this trade-off needs further study (DOI: 10.1016/j.etran.2023.100305). In data compiling abuse tests of hundreds of commercial cells, when adjusted per capacity (ampere-hours), the heat released by the cells was greater the higher the energy density and power density of the cell (DOI: 10.1016/j.jpowsour.2024.234106). This is an observation that they move together, and this data does not single out the cause.

The gas side paints a different picture. In a review collecting the literature, nickel-manganese-cobalt cells generated more gas on average, and the gas produced by LFP cells had greater toxicity and flammability risks (DOI: 10.1016/j.est.2024.111288). One study that fully charged and heated three types of commercial cylindrical cells measured gas hazards simply by the speed at which flames spread. By that standard, for LFP cells and nickel-manganese-cobalt cells, the hydrogen-rich venting stage gas was most dangerous, while for nickel-cobalt-aluminum cells, the carbon dioxide-rich thermal runaway stage gas was most dangerous (DOI: 10.1016/j.jlp.2025.105657, single study). There are results showing that in packs made with LFP cells, even if a single cell shorted, propagation did not occur even up to extreme conditions, but this is the result of a single two-dimensional computer model (DOI: 10.1016/j.egyr.2020.03.024, modeling study).

LFP cells heat up less violently and more slowly, but thermal runaway can still occur, and gas-related risks remain distinct.

How Often Does It Happen

Since 2011, fires in electric vehicles and plug-in hybrids are estimated at roughly 5,718 cases (95% confidence interval 2,866 to 10,846 cases). Fires in these cars have been growing by roughly 45% (±11.3%) each year. The report by the U.S. National Institute of Standards and Technology (NIST) that produced this estimate notes that lithium-ion battery fire data is fragmented and mostly incomplete, and that current tallies are significantly lower than reality (DOI: 10.6028/nist.tn.2365). The NFIRS and CPSC fire data cited by the abstract as sources are American, and the abstract does not separately specify which region's tally this estimate covers. The number is an estimated sum of everything since 2011.

This number is a count of cases. How many electric cars were on the road during the same period and how far they drove are not placed alongside it. When cars are multiplying rapidly, even if the number of fires increases, it is impossible to tell whether a single car has become more dangerous. While the number of fires can be counted, unless how many cases occurred out of how many cars is placed alongside it, this number alone cannot tell us whether they are happening more or less often.

Researchers' evaluations also point to this empty space. A review gathering gas literature describes thermal runaway as a rare event (DOI: 10.1016/j.est.2024.111288). A study broadly examining battery accident risks notes that accident statistics are lacking, so it has not yet been properly evaluated whether these new risks are acceptable (DOI: 10.3390/su172310578). The evaluation that it is rare and the evaluation that statistics are lacking stand together as the current evidence.

Where to Look Next

The "circuit" appearing in this article is a term first defined in "Voltage, Current, Power — What Goes All the Way Around Undiminished". Seen against that picture where electricity must make a complete loop along the outside path, why an internal short circuit is a shortcut becomes even clearer. Energy units like "8 kilowatt-hours" used when writing about storage devices are covered in "Watts and Watt-Hours — Reading Electricity's Two Numbers Like a Speedometer and an Odometer".

Among the other parts of this series, "The Battery Cell — A Rocking Chair Between Two Electrodes", which covers the structure inside the cell and charging and discharging, broadens the second section of this article. "Battery Aging — Fewer Marbles, Cracked Shelves", which deals with why batteries age, details the film on the anode surface, lithium plating, and state of health. "Ampere-hours and Watt-hours — How Much It Holds, How Fast It Gives It Back", which reads battery numbers, covers energy density and state of charge.

At what temperatures each stage of thermal runaway occurs and which reaction generates the most heat vary greatly depending on the cell's materials, so researchers are still piecing them together (DOI: 10.1016/j.nxener.2024.100186).

Source Papers

• "A Review of Failure Modes and Safety Strategies of Lithium‐Ion Batteries from Materials to Systems" (2026) — DOI: 10.1002/advs.76228 — Divides thermal runaway into sequential stages of anode-electrolyte boundary collapse, separator shrinkage, electrolyte decomposition, and cathode oxygen release, analyzing multi-physics coupling. Proposes a framework linking step-by-step indicators to material-to-system-level countermeasures.
• "Understanding the risk of lithium-ion battery fires:" (2026) — DOI: 10.6028/nist.tn.2365 — Estimates roughly 5,718 electric vehicle and plug-in hybrid fires (95% CI 2,866 to 10,846) since 2011, increasing 45% annually. Data sources like NFIRS and CPSC are fragmented and undercounted.
• "Performance of Extinguishing Agents against Lithium-Ion Battery Fires" (2026) — DOI: 10.1007/s10694-025-01831-w — Tests five suppression methods in an 8kWh home storage system. Water mist and encapsulating agents delayed spread by 179% and 167%, reducing risk ratio by over 70%. None prevented propagation; vapor cloud explosion hazard exists. Suppression can delay but not prevent.
• "Breaking the Energy Cascades: Stage‐Specific Mitigation of Thermal Runaway Propagation in Lithium‐Ion Battery Systems" (2026) — DOI: 10.1002/aenm.71302 — Trigger pathways (overcharge, external heating, internal short circuit), propagation via conduction, jet convection, radiation, and flame, alongside thermal buffering, isolation, and suppression. Moving beyond layered barriers to an integrated platform.
• "Prognostic Approaches for Early Detection of Thermal Runaway in Lithium‐Ion Batteries" (2026) — DOI: 10.1002/bte2.70149 — Thermal runaway is an uncontrollable self-heating process that cannot always be prevented, prompting research into early detection. BMS-based protection actions, etc.
• "A Systematic Review of Thermal Runaway in Li-ion Batteries: Pathways, Detection Techniques, and Early Warning Models" (2025) — DOI: 10.1016/j.fub.2025.100110 — Temperature monitoring plus empirical models for abuse detection, voltage monitoring plus statistical models for cell failure detection.
• "Mitigating lithium-ion cell thermal runaway via selective trace H2 sensing" (2025) — DOI: 10.1016/j.xcrp.2025.102859 — Cells vent gas before thermal runaway, and trace hydrogen is captured. Stopping abuse upon hydrogen detection prevented thermal runaway in all tested cases (commercial NCA, NMC, and LFP cells).
• "Evaluation of the laminar burning velocity of various battery vent gases emitted during the thermal runaway of Li-ion cells" (2025) — DOI: 10.1016/j.jlp.2025.105657 — Heating three commercial cylindrical cells at 100% state of charge. Main vent gas components (H2, CH4, CO, CO2, HF, solvent vapor). Based on laminar burning velocity, LFP and NMC are most dangerous during the hydrogen-rich venting stage, while NCA is most dangerous during the carbon dioxide-rich thermal runaway stage.
• "Internal short circuits in lithium-ion batteries; origins, detection, and experimental reproduction: A review" (2025) — DOI: 10.1016/j.jpowsour.2025.238265 — Internal short circuits can trigger thermal runaway and are one of the most problematic failures to detect. Causes include manufacturing defects. Nail tests are easy but have many variables.
• "Advances in the Battery Thermal Management Systems of Electric Vehicles for Thermal Runaway Prevention and Suppression" (2025) — DOI: 10.3390/batteries11060216 — Thermal runaway propagation rapidly spreads failures between cells, increasing risk. Review of cooling methods.
• "Cooling water injection for EV battery fires: A targeted method to suppress thermal runaway" (2025) — DOI: 10.1016/j.firesaf.2025.104503 — Why electric vehicle battery fires are hard to extinguish (high heat release rate, casing insulation, oxygen generation inside cells). In reduced-scale model experiments, introducing cooling water through pre-installed pipes suppressed passenger electric vehicle battery fires within minutes using roughly 100kg of water.
• "A Thorough Investigation into the Current State of the Art in Safety Management on Battery Fire and Explosion Risks" (2025) — DOI: 10.3390/su172310578 — Response is complicated by re-ignition and chemicals. Acceptance of new risks is unassessed due to a lack of statistical data.
• "Review of gas emissions from lithium-ion battery thermal runaway failure — Considering toxic and flammable compounds" (2024) — DOI: 10.1016/j.est.2024.111288 — Flammable and toxic gases from rare thermal runaway events. On average, NMC produces larger gas volumes, while LFP gas poses higher toxicity and flammability risks.
• "The battery failure databank" (2024) — DOI: 10.1016/j.jpowsour.2024.234106 — Thermal responses vary widely even under identical designs and conditions. Heat output normalized per Ah shows a strong positive correlation with energy and power density.
• "Review of prevention and mitigation technologies for thermal runaway in lithium-ion batteries" (2024) — DOI: 10.1016/j.aets.2024.06.002 — Thermal, mechanical, and electrical abuse cause excessive heat generation leading to thermal runaway. Flame-retardant electrolytes, thermally stable materials, ceramic separators. Post-thermal runaway fire prevention and suppression technologies can effectively reduce damage.
• "Time-resolved characterization of toxic and flammable gases during venting of Li-ion cylindrical cells with current interrupt devices" (2024) — DOI: 10.1016/j.jlp.2024.105488 — Burst disks in cylindrical cells open, releasing gas. DMC (electrolyte solvent) is abundant in the vented gas and contributes to the overall flammability of the gas.
• "Design guidelines to prevent thermal propagation and maximize packing density within battery systems with tabless cylindrical lithium-ion cells" (2024) — DOI: 10.1016/j.est.2024.111275 — Cylindrical cells can locally far exceed common onset temperatures. Blocking convective heat influx from hot vent gas is the priority, followed by addressing conduction through spacing. Larger diameters require greater spacing.
• "Lithium-Ion Batteries (LIBs) Immersed in Fire Prevention Material for Fire Safety and Heat Management" (2024) — DOI: 10.3390/en17102418 — Liquid-immersed modules showed no fire propagation in abuse tests, whereas standard modules experienced fire and explosion.
• "Recent Progress of High Safety Separator for Lithium-Ion Battery" (2024) — DOI: 10.70322/gct.2024.10006 — Separator failure is a direct cause of thermal runaway, consisting of three factors: puncture, melting, and thermal shrinkage.
• "Electrochemical Mechanism Underlying Lithium Plating in Batteries: Non-Invasive Detection and Mitigation" (2024) — DOI: 10.3390/en17235930 — Lithium plating is the accumulation of metallic lithium on the graphite anode surface during fast charging or low temperatures. In extreme cases, dendrites penetrate the separator, causing an internal short circuit and thermal runaway.
• "Thermal runaway process in lithium-ion batteries: A review" (2024) — DOI: 10.1016/j.nxener.2024.100186 — Thermal runaway mechanisms vary greatly by material and are complex, requiring further research.
• "Operando monitoring of thermal runaway in commercial lithium-ion cells via advanced lab-on-fiber technologies" (2023) — DOI: 10.1038/s41467-023-40995-3 — Internal fiber optic sensing in 18650 cells. Two pressure peaks (safety venting and thermal runaway onset); inflections in temperature and pressure change rate curves correspond to the transition from reversible to irreversible reactions, enabling pre-venting warnings.
• "Thermal runaway propagation in automotive lithium-ion batteries with NMC-811 and LFP cathodes" (2023) — DOI: 10.1016/j.etran.2023.100305 — Based on cell energy, NMC-811 thermal runaway reaction is 9 times faster than LFP (5 times faster across the entire propagation zone), and NMC-811 safety requirements are much higher. At the pack level, LFP's weight disadvantage can be reduced to 16% and its volume disadvantage offset. Propagation depends on spacing, interlayers, and stacking. Further research is needed.
• "Lessons learned from large‐scale lithium‐ion battery energy storage systems incidents: A mini review" (2023) — DOI: 10.1002/prs.12448 — Fire and propagation incidents occurring even in systems that passed standards and propagation tests (UL 9540A), highlighting gaps in standards.
• "A review of thermal runaway prevention and mitigation strategies for lithium-ion batteries" (2022) — DOI: 10.1016/j.ecmx.2022.100310 — Thermal runaway is a phenomenon where chain exothermic reactions inside the cell rapidly raise internal temperature.
• "Simultaneously Blocking Chemical Crosstalk and Internal Short Circuit via Gel‐Stretching Derived Nanoporous Non‐Shrinkage Separator for Safe Lithium‐Ion Batteries" (2021) — DOI: 10.1002/adma.202106335 — Separators are ion-permeable, electron-insulating membranes. Commercial polyolefins suffer from high-temperature shrinkage, and reactive gas crosstalk such as O2 leads to thermal runaway. Non-shrinkage separators showed a maximum temperature rise rate of 3.7 vs 131.6 °C/s (1Ah pouch).
• "Prevention of lithium-ion battery thermal runaway using polymer-substrate current collectors" (2021) — DOI: 10.1016/j.xcrp.2021.100360 — Aluminum-coated polymer current collector 18650 cells prevented thermal runaway 100% of the time upon nail penetration, whereas standard cells experienced thermal runaway every time.
• "Role of High-Temperature Separator Stability on Safety and Thermal Signature of Li-Ion Pouch Cells" (2021) — DOI: 10.1149/ma2021-015303mtgabs — Conference abstract. Identifies separator rupture-induced short circuits as the primary cause of major failures, demonstrates the correlation between shrinkage, melting, collapse, and short circuits, and aims to determine what triggers the onset of thermal runaway.
• "Computational modelling of thermal runaway propagation potential in lithium iron phosphate battery packs" (2020) — DOI: 10.1016/j.egyr.2020.03.024 — 2D pack model; assuming an internal short circuit in a single cell, no propagation occurs even under extreme conditions.
• "A review of lithium-ion battery safety concerns: The issues, strategies, and testing standards" (2020) — DOI: 10.1016/j.jechem.2020.10.017 — Overview of thermal runaway focusing on the impacts of mechanical, electrical, and thermal abuse.
• "A Review on the Thermal Hazards of the Lithium-Ion Battery and the Corresponding Countermeasures" (2019) — DOI: 10.3390/app9122483 — The reactivity and flammability of traditional battery components can cause electrode-electrolyte side reactions to cascade under abuse conditions.
• "(Invited) The Role of Internal Short Circuit during the Thermal-Induced Thermal Runaway Process of Lithium-Ion Battery" (2019) — DOI: 10.1149/ma2019-01/6/582 — Conference abstract, 24Ah pouch cell. Internal short circuit occurred at 180.9 °C at 100% state of charge, followed by thermal runaway at 213.3 °C 343 seconds later. The short circuit was caused by separator shrinkage, and the resulting resistance increase from dried electrolyte meant less heat. The main heat sources are anode-electrolyte and cathode-anode reactions (cathode + anode is largest in DSC). The role of short circuits in thermally induced runaway requires further clarification. Large-scale short circuits from nails or compression lead directly to thermal runaway.
• "Time Sequence Map for Interpreting the Thermal Runaway Mechanism of Lithium-Ion Batteries With LiNixCoyMnzO2 Cathode" (2018) — DOI: 10.3389/fenrg.2018.00126 — The primary heat source is the cathode-anode redox reaction; an internal short circuit is crucial in triggering that reaction but is not the main heat source above 800 °C, and redox reactions begin at a critical temperature. The short circuit-thermal runaway relationship is presented as a future challenge.
• "An Overview on Thermal Safety Issues of Lithium-ion Batteries for Electric Vehicle Application" (2018) — DOI: 10.1109/access.2018.2824838 — Heat generation, release, and accumulation inside cells.
• "Identifying the Cause of Rupture of Li‐Ion Batteries during Thermal Runaway" (2017) — DOI: 10.1002/advs.201700369 — If gas cannot escape sufficiently, cells rupture and explode. An 18650 design featuring a second vent at the bottom avoids the rupture stage.
• "Abuse by External Heating, Overcharge and Short Circuiting of Commercial Lithium-Ion Battery Cells" (2014) — DOI: 10.1149/2.0311410jes — Under external heating, cobalt-based laptop cells caught fire and exceeded 700 °C, while LFP cells were much weaker yet still experienced some thermal runaway. LFP overcharge mostly survived safely except for one violent fire. Thermal runaway can still occur under extreme conditions.
• "Lithium-Ion Cell Safty Experiments Under Adiabatic Conditions: Nail Penetration" (2014) — DOI: 10.1149/ma2014-01/1/76 — Conference abstract. Adiabatic conditions simulate the worst-case scenario of a cell trapped within a cell stack unable to cool; nail penetration simulates an external-to-internal short circuit like a car crash.
• "Combining In Situ Synchrotron X‐Ray Diffraction and Absorption Techniques with Transmission Electron Microscopy to Study the Origin of Thermal Instability in Overcharged Cathode Materials for Lithium‐Ion Batteries" (2012) — DOI: 10.1002/adfm.201200693 — Heating overcharged NCA and NMC cathodes triggers structural changes accompanied by oxygen release.