Lithium-ion batteries are the preferred power source for devices ranging from smartphones to electric vehicles due to their high energy density and light weight. This concentration of energy means that a failure event can generate an intense fire fueled by an uncontrollable internal reaction. The heat produced during such an event, known as thermal runaway, is substantial and poses a significant safety hazard. This article explores the progression of a battery failure and the extreme temperatures it can reach.
The Chemical Process of Thermal Runaway
A lithium-ion battery failure begins when an internal cell temperature rises uncontrollably, often triggered by physical damage, overcharging, or an internal short circuit. This initial heat starts a highly exothermic chain reaction. The first component to break down is the Solid Electrolyte Interphase (SEI) layer on the anode, typically beginning when the cell temperature reaches 90°C to 130°C.
The breakdown of the SEI layer exposes the reactive anode material to the organic electrolyte, causing further exothermic reactions and generating gaseous compounds. As the temperature climbs to between 120°C and 190°C, the polymeric separator film melts and collapses. This failure causes a direct internal short circuit, leading to a rapid spike in temperature.
The final stage involves the decomposition of the cathode material, which releases oxygen into the cell structure. Because the fire now has an internal oxygen source, it becomes self-sustaining and difficult to extinguish. Flammable gases released earlier are then ignited by the intense heat, resulting in a violent fire.
Peak Temperatures During Lithium Battery Fires
Temperatures reached during thermal runaway vary depending on the battery’s chemistry, state of charge, and pack size. The surface temperature of a failing cell can quickly rise to between 340°C and 550°C. However, the flame temperature, which is the heat of the fire burning ejected materials, can be far more intense.
During a thermal event, the localized flame temperature can reach over 1,000°C. This heat is sufficient to melt or compromise surrounding materials, including structural metals like aluminum, which melts at about 660°C.
The venting and ignition of hot, flammable gases often precedes the larger fire and results in the highest measured temperatures. A larger battery pack increases the danger, as heat from a single failed cell can propagate the reaction to adjacent cells.
Associated Dangers Beyond Heat
While intense heat is a primary hazard, thermal runaway releases other dangers. The reaction generates and ejects a mixture of highly toxic and flammable gases. These mixtures include carbon monoxide, an asphyxiant, and hydrogen fluoride, a corrosive and toxic gas formed when the electrolyte decomposes.
The release of flammable gases creates a risk of explosion, especially in confined spaces. These gases can accumulate and, when ignited, cause a flash fire or explosion. The forceful venting of gas and burning material can also act like shrapnel, ejecting cell components at high speed.
A persistent danger is the risk of re-ignition, which can occur hours or days after visible flames are suppressed. The battery pack retains significant heat, and internal reactions can restart if the core temperature is not thoroughly reduced. This lingering hazard requires continuous monitoring and cooling.
Safe Handling and Emergency Suppression
Safe Handling
Proper storage and charging are essential, as external factors can initiate a failure. Batteries should be stored at room temperature and should not be charged below 0°C or above 40°C, as extreme temperatures accelerate degradation. Any battery showing signs of physical damage, such as swelling or bulging, should be immediately isolated and removed from use.
Emergency Suppression
In the event of an active fire, the goal is intense cooling to stop thermal runaway from spreading to adjacent cells. Applying copious amounts of water is the most effective method to rapidly cool the battery pack. Water absorbs the heat, preventing propagation, but does not extinguish the chemical reaction itself.
Standard fire extinguishers are largely ineffective against the battery’s chemical reaction. Since the fire generates its own oxygen, the smothering action of these agents is bypassed. Therefore, the immediate focus should be on using a large volume of water to reduce the temperature and contain the fire.