In recent years, new energy vehicles have rapidly become popular, but occasional spontaneous combustion incidents have also attracted public attention.

Many people wonder: why do new energy vehicles still catch fire without engines and fuel?

In fact, most new energy vehicle fire accidents are related to thermal runaway of the power battery.

1.What is battery thermal runaway

During normal operation, a large number of electrochemical reactions occur inside the power battery.

But when the battery is subjected to abnormal stimuli, such as:

Internal short circuit, overcharge and overdischarge, high temperature environment, mechanical collision

May cause a rapid increase in internal temperature of the battery.

When the temperature exceeds a certain range, continuous side reactions will occur inside the battery, releasing a large amount of heat and ultimately forming an uncontrollable heating process, which is called thermal runaway.

2. Why did the battery suddenly catch fire

The interior of a lithium battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

When an internal short circuit occurs, the positive and negative poles come into direct contact, generating a large amount of heat.

As the temperature increases:

Firstly, the SEI film begins to decompose;

Subsequently, the electrolyte undergoes a violent reaction;

After further heating, the positive electrode material may release oxygen;

Ultimately, a large amount of heat and combustible gases are rapidly released, triggering combustion.

This is also why lithium battery fires often have the characteristics of suddenness and rapid diffusion.

3. What situations can easily lead to thermal runaway

The battery is impacted

When a new energy vehicle experiences a serious collision, the battery pack may be compressed, causing damage to the internal structure and triggering a short circuit.

Therefore, battery packs usually require the design of anti-collision protection structures.

Long term high temperature use

High temperatures can accelerate internal side reactions in batteries.

If the cooling system is insufficient and the battery temperature continues to rise, it will increase the risk of thermal runaway.

Battery aging

As the number of cycles increases, there will be:

SEI film repeatedly generates and destroys;

Damage to electrode structure;

Internal resistance increases.

Aging batteries are more prone to local heating problems.

Unreasonable fast charging

During fast charging, a large amount of lithium ions need to be quickly embedded into the negative electrode.

If the charging conditions are not suitable, lithium deposition may occur, forming lithium dendrites and increasing the risk of short circuits.

4. How to prevent spontaneous combustion of new energy vehicles

At present, power batteries mainly improve safety through various ways:

The Battery Management System (BMS) monitors voltage, temperature, and current in real-time;

Thermal management system controls battery temperature;

Optimization of battery cell structure to improve heat resistance;

Use more stable positive electrode materials.

For example, lithium iron phosphate batteries have certain advantages in terms of safety due to their stable structure and high thermal decomposition temperature.

In conclusion

The spontaneous combustion of new energy vehicles is not due to the fact that the battery will definitely burn, but rather the result of thermal runaway of the battery in extreme situations.

The safety of power batteries is the result of the combined action of materials, cell design, battery management systems, and manufacturing processes.

In the future, with the development of solid-state batteries, new materials, and intelligent monitoring technology, the safety level of new energy vehicles will continue to improve, making electric vehicles a more reliable mode of transportation.