Lithium batteries are caused by fires for different reasons. Detailed accident analysis can help to avoid future risks.
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Recently, the reasons for tidying up the battery system from the inside out are analyzed. The main reason is to consider the reasons for the layer to push forward, then consider putting the previous and future accidents into the match, and then speculate on the future according to the actual design of each model. PPM for accidents (PPM: Part Per Million, parts per million). The names of all manufacturers have been removed below. The discussion of this topic is not directed at any enterprise and is not judged.
This is an experimental dimension that extends from assuming a single problem = "to the global"
Explain, because the entire analysis, just to match the extreme events of the battery system fire, we have separated the contents of mechanical abuse. The design of the battery system is based on a safer position of the vehicle to prevent problems during use. Although the whole mechanical design is a lot of experimental safety of acupuncture and extrusion, the problem caused by mechanical abuse has become a problem that everyone can easily solve.
Take Tesla as an example:
T3: Burning in Smyrna, Tennessee, USA. This electric car rushed to the trailer hook that fell off the road. A fire broke out after the chassis crashed.
T2: The driver slammed into the concrete wall after turning and finally hit a tree and stopped.
T1: The owner of the car in Seattle called the metal piece on the road, so he left the highway. After the car failed, he smelled the burning and the car was burning.
This mechanical design is also simple, and you can get immediate results by considering more protection on the perimeter of the structure and the bottom cover.
Analysis of the causes behind the fire
We removed the factory that had an accident this year. We can think about it again. Is the car fired outside the battery or the battery?
A large part is the load outside the battery
Cable overheating = "The peripheral part is lit more things
Here you can divide the basic three layers, the essential cause of the fire
1) Thermal energy release in the battery that is not designed as intended + internal and external combustion products
2) Combustible gas release + ignition point in the battery
3) Combustible liquid release + ignition point in the battery: This mainly includes two parts: electrolyte leakage and coolant leakage.
We can consider the heat release from the battery system:
1.1 Battery pack or battery unit overcharge
Overcharge is generally a common cause of heat release. The battery pack-level thermal runaway event can be subdivided into multiple batteries (module, monomer overcharge) = "battery overcharge and electrolyte evaporation = "heat event
Overcharge due to SOC calculation error (SOC: remaining battery power)
In the high SOC state, energy recovery caused by non-protection
Overcharge caused by charging control program stuck
1.2 Short-circuit overcurrent heat release
Battery pack / high voltage circuit failure causes short circuit = "heat
This is mainly caused by internal short circuit and external short circuit of the battery pack, causing overheating of the conductor & connector and overheating of the monomer to cause subsequent thermal events. Further subdivision can also be broken down into overheating of the components caused by the short circuit of the module.
Module level short circuit
One-stage short circuit in the battery pack
Short circuit caused by peripheral corrosive/conductive liquid entry
1.3 High connection impedance heating
The failure of the battery pack/high voltage circuit causes a high resistance value in the charge and discharge circuit. The temperature rises at this high resistance point, which may cause ignition of adjacent materials and subsequent heat transfer.
Poor contact at the connection point of the dry road, causing heat due to corrosion
Increased internal resistance of the battery and internal overheating
1.4 Monomer exhaust produces flammable gases, and subsequent heat sources (arc, thermal runaway of the monomer) cause excess heat in the battery system
In this case, the single-point single-point fault thermal runaway definition experiment can consider the expansion of a single unit to the overall aspect. Under the established conditions, each battery pack will be filed for the record, some reference functions, but the experimental conditions and faults. It is unlikely that the occurrence will be exactly the same.
Case review
In fact, the things that catch fire are intertwined, and the first part and the third part are often deeply combined.
2.1 Leakage and short circuit
Case 1: A car caught fire
Phenomenon 1: Two or more packets of battery cells appear in the battery compartment
Phenomenon 2: Insulation damage between battery cells and aluminum case of battery case
Running vibration = "Intermittent battery intermittent short circuit in the battery box =" Insulation damage point through the battery box and the grounding of the bracket constitutes a strong voltage short circuit = "thermal energy release, electrolyte + battery body heating ="
The fire is expanding and the interior is lit
Case 2: B car caught fire
Phenomenon 1: After a violent collision of the vehicle, the battery structure is damaged, and the cooling pipe is broken to cause coolant leakage.
Phenomenon 2: Slow chemistry caused by immersion of coolant in BMU circuit (BMU: Battery Management Unit)
After the sampling point is immersed, the board level is not completely waterproof. The slow heating triggers the cooling liquid ignition point = "The parking lot is placed after a few weeks of fire.
summary
1) Fire is a very extreme thing, but the exposure is very high. The first reaction of everyone is the battery system. From various analysis points, from the ignition of the battery system, there must be a fault, and there is heat accumulation. Ignition
2) If more public information is put together, and then the comparison is completed, the system analysis process can be improved to achieve some consensus to avoid many future fire accidents.
Foreign accident reference (details here):
1. XXXX fire burns down a garage
2. A parked XXXX combusts
3. Another XXX erupts into flames
4. A XXXX driver recounts a near brush with death
5. A damaged battery pack ignites a Seattle-area fire
6. Short circuits in batteries, due to Hurricane Sandy's storm surge, lead to a 16-car fire
7.XXX Charing fire garage
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