All kinds of electric car accidents related to lithium batteries are caused by fires and even explosions.

Frankly speaking,  it is caused by battery failure (internal or external causes). The heat generation rate of the battery is much higher than that of the heat dissipation rate, and the heat is accumulated in a large amount but not released in time.

The higher the temperature of the battery will cause the system to become hot and damaged.

When the system gets hot, the temperature will rise, which in turn will make the system hotter, and then there will be no more…..

There is an official name for this kind of battery accident - Thermal runaway.

In fact, the probability of battery thermal runaway in electronic products is one in ten million, and events like Samsung note 7 are also rare.

But it's a little different in electric vehicles. The battery pack of an electric car needs hundreds or even thousands of batteries (Tesla 18650), which greatly increases the probability of thermal runaway.

And if the electric car heat out of control, the consequences are very serious, because it’s really terrible that so many batteries blow up.

The consequences will be grievous if the heat runaway occurs because of so many batteries.

OK, Let’s see:

What are the reasons cause Electric vehicle batteries' thermal runaway?

1, Firing when charging

The accident was caused by the manufacturer's own "unreliable", either the design reason or the manufacturing assembly quality. There are only three reasons for charging fire: BMS failure, thermal management failure, and battery short circuit.

The so-called BMS is the brain of battery, which is the abbreviation of the battery management system. It plays an important role in improving the utilization of battery, preventing the battery from overcharge and over-discharge, etc.

It can be understood that if the brain is out of order, such as its algorithm, sampling, diagnosis, etc., it is close to the accident.

The battery thermal management, which we often mention, is mainly based on the reasonable design of materials, electrochemistry, heat transfer, molecular dynamics, and other disciplines to solve the problem of thermal runaway and thermal efficiency caused by the battery working at too high or too low temperature.

Yes, the battery will explode when the temperature is high, but it will also lose power very fast when the temperature is too low.

Battery short-circuited

In the design, if there is no clear understanding of the system's high voltage, insulation, core material, an electrochemical process, it will be close to the accident.

Charging fire is mainly a matter of design, but it does not rule out that the designer is put together by the small partners in the manufacturing process. For example, the assembly is not rigorous, or some impurities fall into the battery, which may cause thermal management failure and battery short circuit.

2, Spontaneous combustion

If it is not charged, the electric vehicle will burn when it is moving or parked, which is the cause of thermal management failure and battery short circuit.

But the cause of spontaneous combustion may also be that the car just came back after charging, resulting in the abnormal temperature rise of the battery. 

For example, in April last year, the "Tesla spontaneous combustion door" in an underground garage of a community in the Xuhui District of Shanghai China used a supercharging pile for charging shortly before the incident. Fortunately, there were no casualties.

In the same way, spontaneous combustion may also be caused by thermal management failures and short circuits caused by assembly or impurities in battery production.

3, Fire caused by water immersion

There are two reasons for the fire of battery immersed in water: structure failure and battery leakage.

The design of the vehicle power battery is to fix the battery pack in the battery box.

If the material and structure of the whole system are not up to standard, it will cause trouble, and the welding and assembly in the manufacturing process will not be rigorous. 

Finally, if the battery box encounters collision and stone impact, it will also lead to structural failure.

In addition to the above reasons, there is a very important point that the sealing design is not well done.

In fact, the batteries of mainstream electric vehicles are treated with waterproof treatment, which can meet the protection standard of IP67.

IP67 standard means that even if you soak in water for a short time, there will be no problem. Of course, don't soak too long.

4, A collision fire

It is easy to understand that collision, like immersion in water, will lead to structural failure and leakage of battery, and eventually lead to thermal runaway.

However, in terms of anti-collision, the major electric car manufacturers pay important attention to it, and the more solid the battery case is. 

But one thing to remind you is that most of the batteries of electric vehicles are designed at the bottom of the car, which is also one of the parts most vulnerable to the collision, 

Therefore, it’s very necessary to have regular checking the battery case in a certain time.