Main content:
1. What is battery tab
The battery tab is a component of pouch lithium-ion battery products. The battery is divided into cathode and anode. The battery tabs are the metal conductors that lead the anode and cathode poles out of the cell.
Addoitionally, the anode and cathode poles of the batteries are colloquially said to be the contact points when charging and discharging. The anode of the battery uses aluminum (Al) material, the cathode uses nickel (Ni) material, and the cathode also has nickel-plated copper (Ni-Cu) material, which are all composed of film and metal strips.
2. Classification of battery tab
● The metal strip material of the tabs
Aluminum (AI), generally used as cathode tabs. If the battery has a lithium titanate cathode , it is also used as a cathode battery tab.
Nickel (Ni), used as anode tabs, is mainly used in lifepo4 battery. For example: phone batteries, portable power battery, tablet battery and so on.
Nickel plating (Ni-Cu) copper is used as an anode tab, mainly used in power batteries and high rate batteries.
● The tab gel
Vinyl is generally used in small digital batteries. Yellow gum is generally used in power batteries and high rate batteries. White glue is generally used in digital batteries, power batteries and high rate batteries.
● Finished product packaging
Disc type (the entire metal strip is wound into a coil after the entire metal strip is added to the film through the equipment), and is used in automated production lines.
The plate type (metal strip plus film is cut into a single piece, and then arranged in rows with two thin transparent plastic sheets sandwiched in the middle) is used in ordinary production lines.
3. Structure and properties of battery tab gels
① Battery tab gel structure
Battery tab gel is generally composed of three layers of hot pressed material together. In addition to the single-layer modified PP composition and the manufacture of five-layer battery tab plugs. Generally, battery tab gel consists of an intermediate skeleton layer and two surface modified PP layers, and the modified PP material on both surfaces is the same.
In order to pursue the adhesion strength of the ultra high adhesive layer and the metal strip, the modified PP material of the two surfaces may also be different. One side is metal-modified PP and the other surface is plastic-modified PP. However, this kind of battery tab glue, once the surface of the battery tab gel is reversed when making the battery lug, it will cause cell leakage and flatulence accidents.
At present, in the Chinese market, the battery lug glue used in the manufacture of battery tab is divided into white glue, black glue, yellow glue and single-layer glue. Among them, most of the customers of high-end battery cells use single-layer white glue. Generally, low-end customers use DNP vinyl and DNP yellow gum.
White glue with a three-layer structure is widely used in Japan and Korea. Single-layer white glue is rarely used in Japanese and Korean battery cell companies, and basically three-layer structural white glue is used. The top 10 energy storage battery cell companies in China are also gradually adopting three-layer white glue.
At present, the difficulty of battery tab glue production technology is: the molecular weight of PP materials should be controlled in a relatively narrow range, and PP glue produced by current technology is still difficult to meet the requirements.
② Battery tab gel performance
The DNP yellow gum structure is the middle functional layer UHR (nonwoven fabric structure), and the two surface layers are modified PPa.
● Yellow gum structure
Yellow rubber battery tabs are at risk of delamination. However, the packaging conditions of yellow rubber battery tabs are easier to adjust than those of white rubber. The deficiency of yellow gum is manifested in three points. The battery tab gel is hot pressed together by an middle layer of UHR and two layers of modified PP glue on the surface.
In the middle layer of non-woven fabrics, moisture will be introduced into the batteries, making the batteries flatulent Non-woven fabrics are easy to delamination, and the hot pressing effect is not good. The battery cell is easy to leak if it is used or shelved for a long time.
● Vinyl construction
The structure of DNP vinyl is an intermediate functional layer of PEN film, and the two layers of the surface are modified PPa. The functional layers of vinyl PEN and PP are compounded by different substances, and there is a risk of delamination.
● White glue structure
White glue is divided into single-layer white glue, three-layer white glue, and five-layer white glue. Single-layer white glue is generally composed of a layer of modified PP. There is no risk of delamination in a three-layer white glue structure, and power cells generally use such battery tab glue.
This kind of white glue has a anode and cathode structure in the production process of battery tab. Once the reverse is used, the battery cell will inevitably have a fatal accident of leakage.
The tabs of single-layer white rubber batteries are difficult to control when the cell is packaged, and it is easy to have overheating and short circuit quality accidents. Only hard packaging processes can be used, and the package thickness must be tightly controlled.
4. Performance comparison of tab gels
● Comparison of various battery tabs
The functional layers of vinyl PEN and PPa are composites of different substances, and they will peel off in layers after being immersed in electrolyte. There are also three substances with different melting points in the vinyl PPa layer, and the interface is more unstable.
Yellow rubber battery tabs will operate better when the functional layer is heat-sealed. Interface fusion is better than vinyl, but it still cannot solve the problem of thorough fusion between different substances. Due to technical reasons, yellow glue will become extremely hard and lose flexibility after heat sealing, and it is easy to break the battery lug glue and battery lug metal when encapsulating the batteries and post-processing, so that the battery produces leakage, flatulence, etc.
White glue can effectively prevent the problem of short-circuiting the side, increase the operating temperature range of the battery packaging, and improve the production yield of the batteries. Since the materials used in the three functional layers belong to the same substance (PP class), the white rubber battery tabs can still maintain extremely high flexibility after heat sealing.
● White gel battery tabs comparison
The single-layer white glue is similar to the inner layer of the initial aluminum plastic film, because there is only one melting point. If the heat sealing temperature exceeds the melting point, it is easy to lead to a complete short circuit melting, and the heat sealing temperature will soften when it is insufficient, which will cause the battery leaking acid.
Three-layer structure of white rubber battery tabs with a wider heat sealing temperature. This makes the package more operable. The reliability of the packaging between the battery pack glue and the aluminum plastic film is guaranteed. The surface of the battery lug glue is divided into front and back of the battery lug glue.
If it is used backwards in the process of making the battery lug, the battery cell will inevitably leak into the battery lug glue. If the production process of battery lugs is strictly controlled, the problem of using the wrong battery lug glue on the front and back will not occur. The welding strength between the battery tab glue and the metal strip is higher than that of the normal three-layer battery lug glue battery tab.
5. White glue tabs production process
Copper guarantees electrical conductivity. After surface treatment, nickel plays a role in preventing copper oxidation. If you want to ensure the solderability of the nickel-plated copper battery tab, you also need to retreat the passivation film on the surface of the battery tab.
If secondary treatment is not carried out, the electrohydraulic corrosion resistance of the battery tab will deteriorate. At present, in the industrial production of battery tab, nickel plating mainly adopts electroplating nickel and electroless nickel plating process.
When the thickness of the metal strip of the power battery tab exceeds 0.2mm, and the step thickness exceeds the thickness of PP glue, the metal strip needs to be side-trimmed, otherwise it is easy to lead to a decrease in insulation impedance and the risk of flatulence and leakage.
6. Conclusion
The battery tabs is a connected, conductive seal. Connection refers to the connection between the inside and outside of the batteries, and the connection between the battery tab glue and the aluminum plastic film. Conduction refers to the introduction of electricity through the battery tab and the generation of loops. Sealing refers to the sealing between the rubber strip and the metal strip and the sealing between the rubber strip and the aluminum plastic film.
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