Failure Mode Analysis of Lithium Battery System -Lithium - Ion Battery Equipment

Failure Mode Analysis of Lithium Battery System -Lithium - Ion Battery Equipment

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 lithium battery system has become the focus of public attention for its safety and reliability.

Studying the failure mode of the power lithium battery system is of great significance to improve the battery life, the safety and reliability of electric vehicles, and reduce the cost of electric vehicles. This paper analyzes the failure mode exploration and consequences of the external performance of the power lithium battery system, and proposes corresponding measures. Various failure modes are considered in the design of the power lithium battery system to improve the safety of the power lithium battery.(Lithium - Ion Battery Equipment)

The power lithium battery system is usually composed of cells, battery management system, pack system including functional components, wiring harness, structural parts and other related components. The failure mode of the power lithium battery system can be divided into three different levels of failure modes, namely the cell failure mode, the battery management system failure mode, and the pack system integration failure mode.

1. Cell failure mode

The failure modes of cells can be further divided into safety failure modes and non-safety failure modes. The following points are important for the safety failure of the battery cell:

1. The positive and negative electrodes inside the cell are short-circuited:

The short circuit in the battery is caused by the inside of the cell. There are many reasons for the short circuit in the battery, which may be caused by defects in the production process of the battery cell or due to the deformation of the battery cell caused by long-term vibration and external force. Once a serious internal short circuit occurs, the control cannot be prevented, the external insurance cannot be used, and smoking or burning will definitely occur.

If this happens, all we can do is to notify the people in the car to escape as soon as possible. Regarding the problem of internal short circuits in batteries, so far, battery manufacturers have no way to screen out 100% of the cells that may have internal short circuits when leaving the factory.

2. Battery cell leakage:

This is very dangerous and a very common failure mode. Many electric vehicle fire accidents are caused by battery leakage. The reasons for battery leakage include: external force damage; damage to the sealing structure caused by collision and irregular installation; manufacturing reasons: welding defects, insufficient sealing glue and poor sealing performance.

After the battery leaks, the insulation of the entire battery pack fails, and the single-point insulation failure is not a big problem. If there are two or more insulation failures, an external short circuit will occur. From the perspective of practical application, soft pack and plastic case cells are more prone to leakage and insulation failure than metal shell cells.

3. Lithium precipitation in the negative electrode of the battery:

Improper use of the battery, overcharging, low-temperature charging, and high-current charging will lead to lithium precipitation in the negative electrode of the battery. Lithium iron phosphate or ternary batteries produced by most domestic manufacturers will undergo lithium precipitation when they are charged below 0 degrees Celsius. Above 0 degrees Celsius, they can only be charged with small currents according to the characteristics of the cells. After the negative electrode lithium precipitation occurs, the lithium metal cannot be reduced, which leads to the irreversible decay of the battery capacity. Lithium precipitation reaches a certain degree of severity, lithium dendrites are formed, and an internal short circuit occurs when the separator is pierced. Therefore, the power lithium battery should be strictly prohibited to be charged at low temperature when in use.

4. The battery is inflated and inflated:

There are many reasons for the occurrence of flatulence, the most important being that gas occurs in the side reaction inside the battery, the most typical one is the side reaction with water. Flatulence problems can be prevented by strictly controlling moisture during cell production. Once the battery is flattened, there will be leakage and so on.

The above failure modes are very serious problems and may cause casualties. Even if a battery cell is used without problems for 1 or 2 years, it does not mean that there will be no problems with the battery cell in the future. The longer the battery is used, the greater the risk of failure.



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