Why Do Lithium Batteries Catch Fire?

[OXavier]

Lithium-ion battery fires occur when the heat inside the battery fails to dissipate as intended by the design, igniting flammable materials inside and outside the battery. The main causes include external short circuits, external high temperatures, and internal short circuits. Here is an introduction to the reasons behind lithium battery fires: Internal Short Circuit: Due to battery abuse, such as overcharging or overdischarging leading to dendrite formation, or impurities and dust during battery production, the separator may degrade and develop micro-shorts. The release of electrical energy causes a temperature rise, and the resulting chemical reactions in the materials further expand the short-circuit path, creating a larger short-circuit current. This cumulative and mutually reinforcing damage leads to thermal runaway. External Short Circuit: Taking electric vehicles as an example, the probability of danger during actual vehicle operation is very low. First, the vehicle system is equipped with fuses and a Battery Management System (BMS). Second, the battery can withstand short-term high-current surges. In extreme cases, if the short-circuit bypasses the vehicle fuse and the BMS fails, prolonged external short circuits typically cause weak points in the circuit to burn out, rarely leading to thermal runaway in the battery. Currently, many PACK companies adopt the practice of adding fuses in the circuit, which more effectively prevents hazards caused by external short circuits. External High Temperature: Due to the structural characteristics of lithium-ion batteries, high temperatures can cause decomposition reactions in the SEI film, electrolyte, EC, etc. The decomposition products of the electrolyte can also react with the cathode and anode, and the battery separator may melt and decompose. These multiple reactions generate a large amount of heat. The melting of the separator leads to internal short circuits, and the release of electrical energy further increases heat production. This cumulative and mutually reinforcing destructive effect ultimately causes the battery's explosion-proof membrane to rupture, ejecting the electrolyte and resulting in combustion and fire.