What Does Thermal Runaway Mean?
Thermal runaway is a phenomenon in which a battery enters a state of uncontrollable self-heating.
In this situation, the rate at which heat is generated in the battery is much higher than the rate at which it is dissipated. If left uncontrolled it can cause the battery to self-destruct and create further hazards, such as an explosion or igniting a fire. Lithium-ion batteries, in particular, are known to exhibit thermal runaway that causes explosions.
Safeopedia Explains Thermal Runaway
Batteries are required to operate within a specific internal temperature range, and the safety and stability of the cell depend on it remaining within that range. A rise in temperature above critical levels can result in a thermal runaway.
Thermal runaway is one of the primary risks associated with lithium-ion batteries as it can result in very high temperatures, smoke, fire, or violent cell venting that ejects gas, shrapnel, or particulates.
Thermal Runaway Mechanism
In batteries such as lithium-ion cells, electricity is produced by the movement of electrons and lithium ions. The charging and discharging process is accompanied by a small amount of heat, which dissipates from the cell under ideal conditions. In other conditions, however, the cell can start generating heat at a rate that outpaces its ability to dissipate it. When the temperature rise rate is greater than 20°C per minute, the cell has reached thermal runaway.
When the battery reaches thermal runaway, the temperature of the cell starts rising very fast and the energy stored in it is released very suddenly. Extremely high temperatures (400°C) are generated due to the chain reaction, which can cause gassing of the battery and extremely hot fire that is very difficult to extinguish.
Causes of Thermal Runaway
Thermal runaway can be the result of a number of different failures, such as overcharging, short-circuit, mechanical deformation, and overheating. Overcharging can permanently damage the battery and rapid charging can lead to excessive currents resulting in thermal runaway. Overheating of batteries can be due to excessive Joule heating, cooling system failure, or exposure to high external temperature.
Lithium-ion batteries that are made with low-quality materials, assembled incorrectly, damaged, or recharged improperly can cause injury to the user. According to the US Consumer Product Safety Commission, there were more than 25,000 incidents involving fires or overheating attributable to lithium-ion batteries in a five-year period.
Lithium-ion batteries are now commonly used in many electronic products such as toys, phones, laptops, headphones, power tools, appliances, electric vehicles, and electrical energy storage systems. Lithium batteries are often preferred due to their compact size and energy-holding capacity. According to the United States (US) Environmental Protection Agency (EPA), lithium-ion batteries must be taken to separate recycling or hazardous waste collection points at the end of their useful life.