Analysis of safety failure modes of 902030 polymer battery and introduction of technical guarantee measures

I. Analysis of safety failure modes of 902030 polymer battery and technical guarantee measures

1. Short circuit of positive and negative electrodes inside the battery cell, the guarantee capability of production equipment is the key

Direct cause: defects in the production process of the battery cell or deformation of the battery cell due to long-term vibration and external force.

Failure analysis: The elimination of positive and negative short circuit defects inside the battery cell during the production process is guaranteed by the relevant equipment of the production line. If the equipment cannot guarantee it, there will be quality problems of batch products. This is a basic requirement for battery manufacturers. my country has implemented catalog management for power battery manufacturers, which can basically ensure that compliant battery manufacturers will not have quality problems of batch products.

Safety technical measures: Screen out unqualified (positive and negative short circuit inside the battery cell) batteries, and the target value is greater than 99.999%.

Danger level: Once a serious internal short circuit occurs, it cannot be prevented and controlled, and the external insurance does not work, and smoke or combustion will definitely occur. However, if the battery manufacturer has sufficient protection capabilities, the probability of occurrence is very low. Even if it occurs, the vehicle manufacturer and automatic fire extinguishing device must play a protective role.

2. Battery monomer leakage, the key is to implement process discipline

Direct cause: external force damage; collision, improper installation causes the sealing structure to be destroyed; welding defects, insufficient sealing glue causes poor sealing performance, etc.

Failure analysis: Compared with soft pack and plastic shell batteries, metal shell monomers are more likely to leak, resulting in insulation failure. After the battery leaks, the insulation of the entire battery pack fails. 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 the level of production automation.

Danger level: Very dangerous; the probability of a car fire accident caused by battery leakage is several orders of magnitude greater than the probability of a short circuit between the positive and negative electrodes inside the battery. For this kind of external short circuit, external insurance must play a role.

3. The battery cell is bloated, and the key is to meet the standards of the production site environment (air) indicators

Direct cause: It is mainly because of the side reaction inside the battery that produces gas, the most typical of which is the side reaction with water.

Failure analysis: The production line environment deviates from the specified requirements.

Safety technical measures: Strictly control the water content during the battery cell production process to avoid it.

Danger level: Once the battery bloats, leakage and other situations will occur. This is a more serious quality problem in product production quality. Preventive measures can be formulated, and unqualified products are strictly prohibited from leaving the factory.

4. Poor capacity consistency, automated production line is the key

Direct cause: Insufficient battery production and manufacturing process technology capabilities, battery storage time, temperature differences during battery pack charging and discharging, charging and discharging current size, etc.

Failure analysis: Consistency has specific technical indicators. Once it is lower than the indicator regulations, it indicates that the production line quality assurance system has serious problems, and improvement measures must be taken. Improving product capacity consistency is a continuous improvement process.

Safety technical measures: Strengthen process management and review measures to continuously improve the capabilities of the enterprise quality management system.

Danger level: Danger will not occur immediately. The capacity consistency is poor, and manufacturers should make quality improvements in a timely manner, and at the same time, unqualified products are strictly prohibited from leaving the factory.

2. Analysis of safety failure modes and technical guarantee measures of battery management system (BMS)

1. Failure of voltage detection line and measures

Phenomenon: Battery overcharge leads to fire and explosion; most of the lithium iron phosphate overcharged to more than 5V will smoke, and once the ternary battery is overcharged, it will explode.

Reason: BMS voltage (connection, wire pressing process or poor contact) voltage detection line failure, resulting in battery overcharge or over discharge, charging or over discharge caused.

a) The electrolyte decomposes and releases gas, which causes the battery to swell, and in severe cases, it may even smoke and catch fire;

b) Overdischarge of the battery will cause damage to the molecular structure of the battery positive electrode material, resulting in failure to charge;

c) The battery voltage is too low, causing the electrolyte to decompose, dry up and produce lithium precipitation, causing a short circuit in the battery.

Measures: Technically, high-reliability voltage acquisition lines are selected to prevent the acquisition lines from being inadequately contacted; management formulates a charging measures system and assigns responsibilities to individuals.

2. Current detection failure and measures

Phenomenon: BMS cannot collect current, SOC cannot be calculated, and the deviation is large.

Cause: Hall sensor failure, large charging current, high heat inside the battery cell, which will cause the diaphragm solidification capacity to decay.

Measures: Select high-quality Hall sensors to ensure qualified installation quality.

3. Temperature detection failure and measures

Phenomenon: The battery operating temperature is too high, which is prone to swelling, leakage, and explosion.

Cause: Temperature detection failure.

Measures: Strictly control the battery operating temperature between 20-45 degrees Celsius to avoid short circuits caused by lithium deposition during low-temperature charging and high-temperature thermal runaway.

4. Insulation monitoring failure and measures

Phenomenon: People may be electrocuted.

Cause: 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.

5. Other failures and measures

(1) SOC estimation has a large deviation. The current inspection standard requires that it is within 5%, which is actually quite difficult. We must continue to improve accuracy.

(2) The electromagnetic compatibility is not good enough to resist electromagnetic interference, which leads to the failure of BMS communication. It is still difficult to ensure that it is in place. The product must also pass the mandatory third-party inspection.

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