Selection of Tab Adhesive for Polymer Lithium Batteries

Currently, the adhesives used in the production of polymer lithium batteries in China are divided into white adhesive, black adhesive, yellow adhesive, and single-layer adhesive. But which adhesive is better for sealing battery tabs? Below is a simple comparative analysis of various adhesives:

Comparison of Yellow Adhesive Tabs and Black Adhesive

Black adhesive has a functional layer and a PP layer composed of different materials, resulting in multiple interfaces. After immersion in electrolyte, it tends to delaminate. Furthermore, the PP layer of black adhesive contains three substances with different melting points: melanin (66 degrees Celsius), PE (105 degrees Celsius), and PP (137 degrees Celsius), making the interface even more unstable.

Yellow adhesive tabs have a functional layer with a melting point close to 300 degrees Celsius, making heat sealing easier. The intermediate functional layer uses a non-woven fiber layer instead of the original polyethylene terephthalate, resulting in better interface integration than black adhesive, but it still cannot completely solve the problem of complete integration between different materials. Due to the inherent limitations of its PP layer technology, yellow adhesive becomes exceptionally hard and loses its flexibility after heat sealing. This makes it prone to breakage of the tab adhesive and metal during battery encapsulation and subsequent processing (nickel transfer, plate addition), leading to battery leakage and gas expansion.

Comparison of Yellow Adhesive Tabs and White Adhesive

White adhesive is made by co-extruding three layers of PP material with different functions. Its functional layers have a wider heat-sealing temperature range of 150-180 degrees Celsius, slightly lower than the battery encapsulation temperature (180-220 degrees Celsius). This effectively prevents sectional short circuits, increases the operable temperature range during battery encapsulation, and improves the yield rate of battery production.

Yellow adhesive tabs, due to the technology of their PP layers, become extremely hard and lose flexibility after heat sealing. During battery encapsulation and subsequent processing (nickel transfer, plate addition), the tab adhesive and tab metal are prone to breakage, leading to battery leakage and gas expansion. White adhesive tabs, because the three functional layers use the same type of material (PP), maintain extremely high flexibility after heat sealing.

Comparison of White Adhesive Tabs and Single-Layer White Adhesive

Single-layer white adhesive is similar to the early aluminum-plastic film inner layer. Because it has only one melting point, if the heat-sealing temperature exceeds the melting point, it is easy to cause complete melting and short circuit. If the heat-sealing temperature is insufficient, it will soften, which will cause it to not completely melt and polymerize with the CPP layer of the aluminum-plastic film, making the battery prone to leakage and gas swelling.

The white adhesive tabs are a three-layer adhesive. The outer layer uses a material similar to the inner layer of the aluminum-plastic film, offering a wider heat-sealing temperature range and ensuring fusion with the aluminum-plastic film. The significant temperature difference between the three PP layers enhances the ease of encapsulation.

Our single-sided three-layer white adhesive series is cut from Showa master rolls. Our double-sided three-layer white adhesive uses original raw materials from Showa Denko (Japan), based on the fundamental principles of foreign white adhesives, and is produced with high-precision equipment. After nearly two years of factory trials, its performance is excellent. It can withstand electrolyte for 24 hours at 85 degrees Celsius. The material combination of each layer is more optimized, and its fusion performance with various aluminum-plastic film inner layers is better, making it more widely applicable to the encapsulation of various soft-pack lithium batteries.

In fact, the focus of battery manufacturers today—the adhesion and liquid resistance of the tab adhesive to the aluminum-plastic film, the sealing degree with the metal strip, and the tightness of the fusion edges and corners—is not only closely related to the performance of the tab adhesive, but also to the corrosion prevention and wetting treatment of the metal strip, the tab manufacturing process, and the battery sealing technology. Therefore, simply comparing tab adhesives without considering the process is a rather superficial understanding.