With the rapid development of electric vehicles, how to solve the safety problems brought by electric vehicles has become a new topic and difficulty in the automotive industry. As the power source (or one of the power sources) of electric vehicles, the power battery system has become the focus of public attention.
Studying the failure mode of a power battery system is of great significance for improving battery life, safety and reliability of electric vehicles, and reducing the cost of using electric vehicles. This paper analyzes the external failure mode of power battery system and analyzes the consequences and proposes corresponding measures. Various failure modes are considered in the design of the power battery system to improve the safety of the power battery.
The power battery system usually consists of a battery cell, a battery management system, a Pack system containing functional components, a wire harness, and a structural component. The power battery system failure mode can be divided into three different levels of failure modes, namely, cell failure mode, battery management system failure mode, and Pack system integration failure mode.
First, the battery failure mode
The failure mode of the battery can be further divided into a safety failure mode and a non-security failure mode. The main safety failures of batteries are as follows:
1. Short circuit between positive and negative poles inside the battery core:
The short circuit inside the battery is caused by the inside of the battery core. There are many reasons for the short circuit inside the battery, which may be caused by defects in the production process of the battery core or due to external force caused by long-term vibration. In the event of a serious internal short circuit, control cannot be prevented, external insurance does not work, and smoke or burning will definitely occur.
If this happens, what we can do is to inform the car personnel to escape the first time. For the problem of internal short circuit of the battery, there is no way for the battery manufacturer to screen 100% of the cells that may be internally short-circuited at the time of shipment, and the detection can be fully performed at a later stage to reduce the probability of occurrence of an internal short circuit.
2, battery cell leakage:
This is very dangerous and a very common failure mode. Many accidents of electric vehicles catching fire are caused by battery leakage. There are some reasons for leakage of the battery: external force damage; collision and installation are not standardized, resulting in damage to the sealing structure; manufacturing reasons: welding defects, insufficient sealing glue, resulting in poor sealing performance.
After the battery leaks, the insulation of the entire battery pack fails. The single-point insulation failure problem is not serious. If there are two or more insulation failures, an external short circuit will occur. From the practical application point of view, the soft case and the molded case cell are more likely to leak than the metal case monomer, resulting in insulation failure.
3, battery negative electrode lithium:
Improper use of the battery, overcharge, low temperature charge, high current charge will lead to lithium battery negative. Lithium iron phosphate or ternary batteries produced by most domestic manufacturers will be decalcified when charged below 0 degrees Celsius, and can only be charged at a low current according to the characteristics of the cell. After the lithium is decomposed by the negative electrode, the lithium metal cannot be reduced, resulting in irreversible attenuation of the battery capacity. The lithium is precipitated to a certain degree to form a lithium dendrite, and an internal short circuit occurs in the piercing diaphragm. Therefore, the power battery should not be charged at low temperature when it is used.
4, battery expansion and bulging:
There are many reasons for the flatulence, mainly due to the side reaction inside the battery to generate gas, the most typical is the side reaction with water. The problem of flatulence can be avoided by strictly controlling the moisture in the cell production process. In the event of battery flatulence, liquid leakage may occur.
The above failure modes are very serious problems and may cause casualties. Even if one battery is used for one or two years, it does not mean that there is no problem in this battery. The longer the battery is used, the greater the risk of failure.
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