This paper analyzes the external failure mode of power battery system and analyzes the consequences and proposes corresponding measures. 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. Various failure modes are considered in the design of the power battery system to improve the safety of the power battery.
This article refers to the address: http://
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.
The non-safety failure of the battery cell only affects the performance. The main points are as follows:
1. Poor capacity consistency:
The inconsistency of the power battery usually means that the difference in the remaining capacity of the battery in a group of batteries is too large, and the voltage difference is too large, causing the battery life to deteriorate. The reasons for the deterioration of the consistency between the batteries are various, including the manufacturing process of the battery, the storage time of the battery, the temperature difference during charging and discharging of the battery, and the magnitude of the charge and discharge current.
At present, the solution is mainly to improve the control level of the manufacturing process of the battery, and to ensure the consistency of the battery as much as possible from the production, and use the same batch of batteries for the matching. This method has certain effects, but it cannot be cured. The problem of poor consistency after using the battery pack for a period of time will occur. After the battery pack is inconsistent, if it cannot be processed in time, the problem will become more serious and even dangerous.
2. Self-discharge is too large:
The irreversible reaction caused by micro-shorts caused by impurities during battery manufacturing is the most important cause of the large self-discharge of individual batteries. In most battery manufacturers, the self-discharge of the battery can be neglected. Because the battery reacts with the environmental conditions during the long-term charging and discharging and shelving process, the battery is self-discharged, which causes the battery to decrease in power and performance. Low, can not meet the needs of use.
3. Low temperature discharge capacity reduction:
As the temperature decreases, the low temperature performance of the electrolyte is not good, the participation reaction is insufficient, the electrolyte conductivity decreases, and the battery resistance increases, the voltage platform decreases, and the capacity also decreases. At present, the discharge capacity of each manufacturer's battery at -20 degrees is basically 70% to 75% of the rated capacity. The battery discharge capacity is reduced at low temperatures, and the discharge performance is poor, which affects the performance and driving range of the electric vehicle.
4, battery capacity attenuation:
The battery accommodation attenuation is mainly due to the loss of active lithium ions and the loss of electrode active materials. The regularity of the layered structure of the positive electrode active material decreases, and a passivation film is deposited on the negative electrode active material, the degree of graphitization is lowered, and the porosity of the separator is decreased, resulting in an increase in charge transfer resistance of the battery. The ability to deintercalate lithium is reduced, resulting in a loss of capacity.
Battery capacity degradation is an inevitable problem with batteries. However, battery manufacturers should first solve the problem of safety failure and battery consistency in the first place. On this basis, consider extending the cycle life of the battery.
Second, BMS failure mode
The failure of the battery cell is not only related to the battery itself, but also to the failure of the battery management system BMS. BMS failure modes can also cause serious accidents in the following categories:
1. BMS voltage detection failure causes the battery to overcharge or over discharge:
The connection, crimping process or poor contact causes the voltage detection line to fail. The BMS has no voltage information and does not stop when charging. If the battery is overcharged, it will catch fire and explode. Most of the lithium iron phosphate overcharged to 5V is only smoke, but once the ternary battery is overcharged, it will explode.
Moreover, overcharging easily leads to decomposition of the electrolyte in the lithium ion battery to release gas, thereby causing the battery to swell, and in severe cases, even smoke and fire; the overdischarge of the battery may cause damage to the molecular structure of the positive electrode material of the battery, thereby causing charging and no charging; At the same time, the battery voltage is too low, causing the electrolyte to decompose, and the dryness of the electrolyte occurs, and the problem of short circuit inside the battery is returned. When designing the system, a reliable voltage acquisition line should be selected, which should be strictly controlled during the production process to prevent the failure of the voltage collection line.
2, BMS current detection failure
The Hall sensor fails, the BMS does not collect current, the SOC cannot be calculated, and the deviation is large. Failure of current detection can result in excessive charging current. The charging current is large, the internal heat of the battery core is large, and the temperature exceeds a certain temperature, which will attenuate the curing capacity of the diaphragm and seriously affect the battery life.
3, BMS temperature detection failure
The temperature detection failure causes the battery to work at an excessively high temperature, and the battery has an irreversible reaction, which has a great influence on the battery capacity and internal resistance. The life of the battery calendar is directly related to the temperature. The cycle number at 45 degrees is half of that at 25 degrees. In addition, if the temperature is too high, the battery is prone to bulging, liquid leakage, explosion, etc. Therefore, the battery temperature should be strictly controlled during battery use. In addition to effectively improving the service life and reliability of the battery between 20-45 degrees Celsius, it can effectively avoid short circuit caused by low-temperature battery lithium deposition and high temperature thermal runaway.
Residential Energy Storage System
electricity backup for home,5kw solar system,solar for home,house backup power supply,15kw solar system,off grid life
EMoreShare International Trade (Suzhou) Co., Ltd , https://www.emoreshare.com