Safety technical measures: Screen out unqualified (positive and negative poles inside the battery core are short-circuited) batteries, and the target value is greater than 99.999%. Danger: Once a serious internal short circuit occurs, control cannot be prevented, external insurance does not work, and smoke or burning will definitely occur. However, if the battery manufacturer has sufficient support capabilities, the probability of occurrence is very low. Even if it does happen, the vehicle manufacturer and the automatic fire extinguishing device must play a protective role. 2. Battery cells leak, and the implementation of process discipline is the key direct cause: external force damage; collision and improper installation causing damage to the sealing structure; welding defects and insufficient sealing glue causing poor sealing performance, etc. Failure analysis: Compared with soft-packed and plastic-cased batteries, metal-cased cells are more prone to leakage, leading to insulation failure. After the battery leaks, the insulation of the entire battery pack will fail. Single-point insulation failure is not a big problem. If there are two or more insulation failures, an external short circuit will occur. Safety technical measures: Strict process discipline and improve production automation level. Risk: Very dangerous; the probability of a car fire caused by battery leakage is several orders of magnitude greater than the probability of a short circuit between the positive and negative poles inside the battery cell. For this kind of external short circuit, external insurance must play a role. 3. The battery core is bulging and the environment (air) indicators at the production site are not up to standard. This is the key direct reason: it is mainly because side reactions occur inside the battery to produce gas, the most typical side reaction is with water. Failure analysis: The production line environment deviates from specified requirements. Safety technical measures: Strict control of moisture during the battery production process can be avoided. Risk: Once the battery is inflated, leakage and other situations may occur. This is a serious quality problem in product production quality. Preventive measures can be formulated, and unqualified products are strictly prohibited from leaving the factory. 4. The capacity consistency is poor, and the automated production line is the key direct reason: insufficient battery production and manufacturing process technology capabilities, battery storage time, temperature differences during battery pack charge and discharge, charge and discharge current, etc. Failure analysis: There are specific technical indicators for consistency. Once the consistency is lower than the specification, it indicates that the production line quality assurance system has serious problems and improvement measures must be taken. Improving product capacity consistency is a process of continuous improvement. Safety technical measures: Strengthen process management and review measures to continuously improve the capabilities of the enterprise's quality management system. Danger: The danger will not occur immediately. Due to poor capacity consistency, manufacturers must promptly improve quality and strictly prohibit unqualified products from leaving the factory. 2. Battery Management System (BMS) Safety Failure Mode Analysis and Technical Support Measures 1. Voltage detection line failure and measures Phenomenon: overcharging of the battery may cause fire or explosion; most lithium iron phosphates will smoke if overcharged to above 5V, and Once the ternary battery is overcharged, it will explode. Reason: The BMS voltage (connection, crimping process or poor contact) voltage detection line fails, causing the battery to be overcharged or overdischarged. a) The electrolyte decomposes and releases gas, causing the battery to bulge, or even smoke and catch fire in severe cases; b) Over-discharging of the battery will damage the molecular structure of the positive electrode material of the battery, resulting in inability to charge; c) The battery voltage is too low, causing The electrolyte decomposes and dries out to cause lithium precipitation, causing a short circuit in the battery. Measures: Technically, use high-reliability voltage collection lines to prevent improper contact of the collection lines; in terms of management, formulate a charging measure system and assign responsibilities to each person. 2. Current detection failure and countermeasures: BMS cannot collect current, SOC cannot be calculated, and the deviation is large. Reason: The Hall sensor fails, the charging current is large, and the internal heat of the battery core is large, which will reduce the curing capacity of the separator. Measures: Choose high-quality Hall sensors to ensure qualified installation quality. 3. Temperature detection failure and countermeasures: If the battery operating temperature is too high, it is prone to bulging, leakage, and explosion. Reason: Temperature detection failed. Measures: Strictly control the operating temperature of the battery between 20-45 degrees Celsius to avoid short circuits and high-temperature thermal runaway caused by lithium deposition during low-temperature charging of the battery. 4. Insulation monitoring failure and measures: personnel may get electric shock. Reason: Insulation failure will occur when the power battery is deformed or leaks. Measures: For monitoring sensors, high-quality and highly reliable products must be selected.

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