What are the causes of lithium-ion battery fires?
1. Internal short circuit: Due to the misuse of the battery, such as overcharging and over-discharging leading to dendrite formation, impurities and dust in the battery production process, etc., the battery will deteriorate and puncture the separator, resulting in a micro short circuit. The release of electrical energy leads to a temperature rise, and the chemical reaction of the material caused by the temperature rise further expands the short circuit path, forming a larger short circuit current. This mutually cumulative and mutually reinforcing damage leads to thermal runaway.
2. External Short Circuit: Taking electric vehicles as an example. The probability of a dangerous situation occurring during actual vehicle operation is very low. Firstly, the vehicle system is equipped with fuses and a Battery Management System (BMS). Secondly, the battery can withstand short-term high-current surges. In extreme cases, the short circuit point may extend beyond the vehicle's fuses, and the BMS may fail. A prolonged external short circuit generally only causes weak points in the circuit to burn out, rarely leading to thermal runaway of the battery. Currently, many battery pack companies use fuses in the circuit, which is more effective in preventing hazards caused by external short circuits.
3. External High Temperatures: Due to the structural characteristics of lithium-ion batteries, the SEI film, electrolyte, and EC will decompose under high temperatures. The decomposition products of the electrolyte will also react with the positive and negative electrodes, causing the cell separator to melt and decompose. These multiple reactions generate a large amount of heat. The melting of the separator leads to an internal short circuit, and the release of electrical energy further increases heat generation. This cumulative, mutually reinforcing destructive effect results in the rupture of the cell's explosion-proof membrane, electrolyte leakage, and subsequent combustion and fire.
As the energy source for pure electric vehicles, a major cause of lithium-ion battery fires is thermal runaway due to overheating, which is most likely to occur during battery charging and discharging. Because lithium-ion batteries have a certain internal resistance, they generate heat while supplying power to the electric vehicle, causing their temperature to rise. When this temperature exceeds their normal operating range, it will damage the battery's lifespan and safety. In pure electric vehicles, the power lithium battery system consists of multiple individual lithium battery cells. During operation, a large amount of heat accumulates within the confined battery pack. If this heat cannot be dissipated quickly and effectively, high temperatures will affect the battery's lifespan and may even lead to thermal runaway, resulting in fires and explosions.
What should you do if a lithium-ion battery catches fire?
When a lithium-ion battery catches fire and needs to be extinguished, let's look at Tesla's recommended approach:
1. In case of a small fire that has not spread to the high-voltage battery area, carbon dioxide or ABC dry powder fire extinguishers can be used to extinguish the fire.
2. When thoroughly inspecting for fire, do not come into contact with any high-voltage components, and always use insulated tools for inspection.
3. If a high-voltage battery is bent, twisted, or damaged during a fire—in short, becomes unrecognizable—or if a battery problem is suspected, then the amount of water used for firefighting must be sufficient.
4. A battery fire may take up to 24 hours to be completely extinguished. Using a thermal imaging camera can ensure that the high-voltage battery is completely cooled before the incident ends. If a thermal imaging camera is not available, the battery must be monitored for reignition. Smoke indicates that the battery is still hot; monitoring should continue for at least one hour after the battery stops smoking.
The emergency response manual for the GM Volt in the US provides the following instructions for firefighting electric vehicles: If the battery reaches a sufficiently high temperature, leaking and releasing electrolyte, the electrolyte is definitely flammable. This requires using plenty of water to cool the battery and extinguish the fire. Because DC and AC systems are not grounded, firefighters can safely use water as a primary extinguishing agent without the risk of electric shock. ABC dry powder fire extinguishers will not extinguish battery flames. Firefighters should avoid direct contact with the interior of any high-voltage components during firefighting or unblocking operations, as this could potentially result in electric shock.
A fire is an extreme event, but it receives a lot of media attention. Everyone's first reaction is that it's a problem with the battery system. Based on various analyses, a fire originating from the battery system must have a malfunction, and there must have been heat buildup that ignited it. In summary, extinguishing a lithium-ion battery fire requires a large amount of water, a considerable amount of time and patience, and cooling down is crucial. Lithium-ion batteries are not explosive and generally will not explode.
