What‘s the factor affect the overall safety design of the energy storage battery cell?

Strengthen the overall safety design of the energy storage battery cell.The battery cell is the link that combines various substances of the energy storage battery. It is the integration of the positive electrode, negative electrode, diaphragm, tab and packaging film. The structural design of the battery cell not only affects the performance of various materials, but also affects the overall battery. Electrochemical performance and safety performance have an important impact. The selection of materials and the design of the cell structure are exactly the relationship between the part and the whole. In the design of the cell, a reasonable structural model should be formulated in combination with the material properties.

In addition, some additional protection devices can also be considered in the structure of lithium batteries. Common protection mechanisms are designed as follows:

1 Using a switching element, when the temperature in the battery rises, its resistance value rises, and when the temperature is too high, it will automatically stop power supply;

2 Set the safety valve (that is, the vent hole on the top of the battery), when the internal pressure of the battery rises to a certain value, the safety valve will automatically open to ensure the safety of the battery.

The following are some examples of the safety design of the cell structure:

a) Positive and negative capacity ratio and design size

Select the appropriate capacity ratio of positive and negative electrodes according to the characteristics of the positive and negative materials. The ratio of the positive and negative capacities of the cells is an important link related to the safety of lithium-ion batteries. If the positive capacity is too large, metal lithium will appear on the surface of the negative electrode. If the negative electrode is too large, the capacity of the battery will be greatly lost. Generally speaking, N/P=1.05～1.15, and make an appropriate choice according to the actual battery capacity and safety requirements. Design large and small pieces so that the position of the negative electrode paste (active material) covers (greater than) the position of the positive electrode paste. Generally, the width should be 1-5 mm larger and the length should be 5-10 mm larger.

b) There is a margin for the width of the diaphragm

The general principle of diaphragm width design is to prevent internal short circuit due to direct contact of positive and negative electrodes. Due to the thermal shrinkage of the diaphragm during the charging and discharging process of the battery and in the environment of thermal shock, the diaphragm is deformed in the direction of length and width, and the diaphragm is deformed in the direction of length and width. The wrinkled area increases the polarization due to the increase of the distance between the positive and negative electrodes; the stretched area of ​​the diaphragm increases the possibility of micro-short circuit due to the thinning of the diaphragm; the shrinkage of the edge area of ​​the diaphragm may lead to the direct connection of the positive and negative electrodes. Contact and internal short-circuits occur, which can make the battery dangerous due to thermal runaway. Therefore, when designing a battery, the use of the area and width of the separator must consider its shrinkage characteristics, and the separator is larger than the anode and cathode. Considering the process error, the isolation film must be at least 0.1mm longer than the outer edge of the pole piece.

c) Insulation treatment

Internal short circuit is an important factor for the potential safety hazards of lithium-ion energy storage batteries. There are many potentially dangerous parts that cause internal short circuit in the structural design of the battery cell. Therefore, necessary measures or insulation should be set at these key positions to prevent abnormal conditions. In the event of a short circuit in the battery, for example: maintain the necessary distance between the positive and negative ears; place insulating tape in the middle without paste on one side of the end, and cover all the exposed parts; stick insulating tape between the positive aluminum foil and the negative active material; application Insulating tape will cover all the welding parts of the tabs; insulating tape is used on the top of the cell.

d) Set safety valve (pressure relief device)

Lithium-ion batteries are dangerous, often due to excessive internal temperature or excessive pressure, causing explosions and fires; setting a reasonable pressure relief device can quickly release the pressure and heat inside the battery when danger occurs, reducing the risk of explosion. A reasonable pressure relief device is required to not only meet the internal pressure of the battery during normal operation, but also automatically open to relieve the pressure when the internal pressure reaches the dangerous limit. Deformation characteristics to design; the design of safety valve can be achieved by lamellae, edges, seams and notches.

3 Improve the level of craftsmanship

Efforts to do a good job in the standardization and standardization of the energy storage battery cell production process. In the steps of mixing, coating, baking, compacting, slitting and winding, formulate standardization (such as diaphragm width, electrolyte injection volume, etc.), and improve process methods (such as low-pressure injection method, centrifugal Shell method, etc.), do a good job in process control, ensure process quality, and reduce the difference between products; set up special steps in key steps that have an impact on safety (such as deburring, powder sweeping, and different welding for different materials). methods, etc.), implement standardized quality monitoring, eliminate defective parts, and exclude defective products (such as pole piece deformation, diaphragm puncture, active material shedding and electrolyte leakage, etc.); keep the production site tidy and clean, and implement 5S management and 6 -Sigma quality control to prevent impurities and moisture from being mixed in production and minimize the impact of unexpected situations in production on safety.