Causes of thermal runaway in lithium-ion batteries
Essentially, thermal runaway in lithium-ion batteries is a positive energy feedback loop: rising temperatures cause the system to heat up, which in turn raises the temperature, making the system even hotter. Thermal runaway is a common phenomenon, occurring in everything from concrete curing to stellar explosions.
1. Frequent overcharging.
2. Unauthorized modification of the outer shell.
3. The ambient temperature exceeds 60°C.
4. Tearing of the separator separating the negative and positive electrodes of a lithium-ion battery can lead to a short circuit, which in turn often causes thermal collapse.
Thermal runaway in lithium-ion batteries primarily occurs because the rate of internal heat generation far exceeds the rate of heat dissipation. This leads to a buildup of heat inside the battery, triggering a chain reaction that results in fire and explosion. The cobalt oxide chemical in lithium-ion batteries is involved in the thermal runaway reaction. When this chemical is heated to a certain temperature, it begins to self-heat, eventually leading to fire and explosion. In some cases, the release of pressure from this organic electrolyte can cause the battery to rupture. Exposure to high temperatures or sparks can also cause it to ignite.
Thermal runaway and its intensity are related to the size, configuration, and number of cells in a lithium-ion battery. Small lithium-ion battery packs have only a few cells, so the chance of thermal runaway propagating from a faulty cell to others is relatively low. The massive battery packs in the Boeing 787 are a different story: they are housed in sealed metal enclosures that cannot dissipate heat, so when one cell heats up enough to ignite the electrolyte, the rest of the cells quickly follow suit.
