Polyurethane adhesives play a significant role in lithium battery manufacturing due to their unique properties, mainly used for the packaging and structural bonding of battery cells.
1. Main applications
(1)Cell packaging (pouch battery) : This is its most core application. Polyurethane adhesives (usually in the form of heat-sealing films) are used to bond the multi-layer structures (nylon, aluminum foil, polypropylene) of aluminum-plastic encapsulation films. It must provide extremely high bonding strength between the PP layers, forming a reliable heat-sealed edge to effectively prevent the intrusion of external moisture and the leakage of internal electrolyte, ensuring the safety and lifespan of the battery during long-term use.
(2)Structural bonding: It is used for bonding the tabs, insulating materials, protective films inside the battery cells, as well as the battery cells and end plates, and the battery cells and foam in the module. It offers excellent adhesion, elasticity and electrolyte resistance, and can buffer the stress caused by the volume change of electrode materials during charging and discharging, enhancing the structural stability and impact resistance of the battery pack.
2. Key performance requirements:
(1)Excellent adhesion: It can firmly bond various materials (metals, plastics, ceramics, etc.).
(2)Extremely low water vapor transmission rate: Ensures the long-term sealing of pouch batteries and prevents failure.
(3)Good resistance to electrolyte and chemical stability: It can resist the erosion of electrolyte (especially ester solvents), without decomposition or swelling.
(4)Appropriate flexibility and elastic modulus: Adapt to volume changes and avoid stress cracking.
(5)High insulation: Ensures electrical safety.
(6)Reliable processability: such as appropriate hot melt temperature, curing speed, etc., to meet the requirements of automated production.
3. Precautions
(1)The performance of polyurethane adhesives (such as adhesion and electrolyte resistance) is closely related to their chemical structure (such as polyester type/polyether type), and strict screening and evaluation should be carried out according to specific application scenarios.
(2)Moisture control during the curing process is of vital importance. Moisture can react with isocyanate groups to produce carbon dioxide bubbles, which can affect the quality and appearance of the seal.
(3)Attention should be paid to its durability and anti-aging ability under long-term high and low temperature cycles to ensure that it is in line with the battery life.
With the development, polyurethane adhesives have gradually become one of the key materials for ensuring the safety, reliability and long service life of lithium batteries, especially pouch batteries. With the development of battery technology, higher requirements have been put forward for its high-temperature resistance, high thermal conductivity and other properties.
