I. Battery safety failure mode analysis and technical safeguard measures
1. The positive and negative internal short circuit of the battery core, the production equipment support ability is the key
Direct cause: Defects in the production process of the battery core or deformation of the battery core due to long-term external vibration.
Failure analysis: The elimination of the short-circuit defects of the positive and negative electrodes inside the battery during the production process is guaranteed by the equipment of the production line. If the equipment cannot be guaranteed, the quality of the batch products will occur. This is a basic requirement for battery manufacturers. China has implemented catalog management for power battery manufacturers, which basically guarantees that the qualified battery manufacturers will not have mass product quality problems.
Safety technical measures: The unqualified (positive and negative internal and negative batteries) cells are screened out, and the target value is greater than 99.999%.
Danger: 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. However, under the sufficient guarantee capacity of the battery manufacturer, the probability of occurrence is very low. Even if it occurs, the manufacturer of the vehicle must have a guarantee function.
2. Battery cell leakage, the implementation of process discipline is the key
Direct cause: external force damage; collision, installation is not standardized, resulting in damage to the sealing structure; welding defects, insufficient sealing glue, resulting in poor sealing performance.
Failure analysis: Compared with soft packs and molded case batteries, metal shell monomers are more prone to liquid leakage, resulting in insulation failure. 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.
Safety technical measures: strict process discipline and improve production automation.
Danger: Very dangerous; the probability of a car leaking a car causing a fire accident is several orders of magnitude greater than the probability of a positive and negative short circuit inside the cell. This external short circuit, external insurance has to play a role.
3. The battery core is inflated and bulged, and the production environment (air) indicator is the key.
The direct cause: mainly due to the side reaction inside the battery to generate gas, the most typical is the side reaction with water.
Failure analysis: The production line environment deviates from the specified requirements.
Safety technical measures: Strict control of moisture during the production of batteries can be avoided.
Danger: In the event of battery flatulence, liquid leakage may occur. This is a serious quality problem in the production quality of the product. It is necessary to develop preventive measures, and it is strictly forbidden to leave the unqualified products.
4. Poor capacity consistency, automated production line is the key
Direct cause: insufficient battery manufacturing process technology, battery storage time, battery temperature difference during charge and discharge, charge and discharge current.
Failure analysis: There are specific technical indicators for consistency. Once the specifications are lower than the specifications, it indicates that the quality assurance system of the production line is serious. It is necessary to carry out improvement measures to improve the consistency of product capacity is a continuous improvement process.
Safety technical measures: Strengthen process management and review measures, and continuously improve the ability of the enterprise quality management system.
Danger: Danger does not happen immediately. The capacity consistency is poor, the manufacturer should timely improve the quality, and at the same time prohibit the unqualified products from leaving the factory.
Second, battery management system (BMS) security failure mode analysis and technical safeguards
1. Voltage detection line failure and measures
Phenomenon: The battery is overcharged, causing fire and explosion; most of the lithium iron phosphate overcharged to 5V will emit smoke, and once the ternary battery is overcharged, it will explode.
Cause: The BMS voltage (connection, crimping process or poor contact) voltage detection line is invalid, resulting in overcharging or overdischarging of the battery, charging or overdischarging.
a) decomposition of the electrolyte releases gas, which causes the battery to swell, and even if it is serious, it may cause smoke;
b) The over-discharge of the battery may cause damage to the molecular structure of the positive electrode material of the battery, resulting in no charge and no power;
c) The battery voltage is too low, causing the electrolyte to decompose, and the dryness of the electrolyte occurs, causing a short circuit inside the battery.
Measures: Technically select high-reliability voltage acquisition lines to prevent contact with the collection line from being in place; management to develop a charging system, responsibility to implement.
2. Current detection failure and measures
Phenomenon: The BMS does not collect current, the SOC cannot be calculated, and the deviation is large.
Cause: The Hall sensor fails, the charging current is large, and the internal heat of the battery core is large, which will attenuate the curing capacity of the diaphragm.
Measures: Use high-quality Hall sensors to ensure the quality of the installation.
3. Temperature detection failure and measures
Phenomenon: The operating temperature of the battery is too high, and it is prone to bulging, liquid leakage and explosion.
Cause: The temperature detection has failed.
Measures: Strictly control the operating temperature of the battery between 20-45 degrees Celsius, to avoid short circuit caused by low temperature charging of the battery and high temperature thermal runaway.
4. Insulation monitoring failure and measures
Phenomenon: A person may be exposed to electricity.
Cause: Insulation failure occurs when the power battery is deformed or leaked.
Measures: For the sensors to be monitored, high quality, highly reliable products must be used.
5. Other failures and measures
(1) The SOC estimation deviation is large, and the current inspection standard requirements are all within 5%, which is actually more difficult. To continuously improve the accuracy.
(2) Insufficient electromagnetic interference resistance of electromagnetic compatibility, resulting in failure of BMS communication, how to ensure that it is in place, there are certain difficulties. The product must also be compulsory by a third party.
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