A hot-pressing pre-bonding manufacturing process for a steel-body lithium battery cover plate

Abstract

The application discloses a hot-pressing pre-bonding manufacturing process of a steel lithium battery cover plate and relates to the technical field of lithium battery manufacturing. Maleic anhydride modified polypropylene particles are extruded into a film by using an extrusion casting compound machine, the temperature and viscosity of the unshaped film are utilized to perform hot-pressing compounding with a PET base film in the extrusion process, then, the film is cut into a ring offline, the ring is upwardly faced, a constant-temperature suction nozzle of an intelligent manipulator is utilized to perform first hot-pressing bonding with a metal sheet or a metal ring, the base film is peeled off, the metal surface is sucked by the suction nozzle of the intelligent manipulator and is transferred and accurately positioned on a three-in-one constant-temperature platform to perform three-in-one hot-pressing pre-bonding, and then, the material is discharged. The application does not use a self-adhesive any more, the advantages of a traditional offline die-cutting process are absorbed, and the influence of the self-adhesive on a die cutter is avoided. The efficiency can be greatly improved. The steel lithium battery cover plate manufactured by using the process can be used as a safety valve for explosion and combustion prevention and can also be used as a positive and negative electrode of a battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and in particular to a hot-pressing pre-bonding process for a steel lithium battery cover. Background Technology

[0002] The earliest explosion-proof technology involved using a high-precision punch press and high-precision stamping dies to locally stamp aluminum sheets, creating thin-slit explosion-proof sheets. Under the internal pressure of a steel-bodied lithium battery, these thin-slit areas would rupture preferentially within a specified pressure range, thus preventing the steel packaging from exploding under immense pressure. However, when a steel-bodied battery explodes, it will 100% ignite and burn. While traditional explosion-proof technologies effectively controlled the explosion of steel-bodied lithium batteries, they could not prevent the explosion-proof sheets from igniting and burning when they ruptured at temperatures exceeding 130°C.

[0003] Today, steel-bodied lithium batteries are becoming an inevitable trend to replace traditional aluminum-plastic film soft-pack lithium batteries. The explosion-proof method of traditional aluminum-plastic film soft-pack lithium batteries can no longer be used on steel-bodied lithium batteries with a thickness of less than 8mm or a diameter of less than 8mm.

[0004] In the manufacturing technology of steel-bodied lithium batteries, cover plates are mostly used as the main explosion-proof components. The cover plate can serve as an explosion-proof and flame-proof safety valve for steel-bodied lithium batteries, and can also serve as the positive and negative electrodes of steel-bodied lithium batteries.

[0005] In existing technologies, cover plates are manufactured using two methods: offline die-cutting and online die-cutting. In offline die-cutting process ① Throughout the entire process of bonding one side of the adhesive ring to the self-adhesive, from offline die-cutting to the final peeling off, the self-adhesive remains in close contact with the adhesive. This poses a significant risk of adhesive transfer or residue remaining on the adhesive ring, representing the most potentially fatal and highest-risk aspect of this process for such products. Specifically, residual adhesive on the adhesive ring easily forms bubbles when bonded to metal in two- or three-way bonding, reducing adhesion strength and making it susceptible to the strong corrosive penetration and corrosion of the electrolyte, thus severely compromising the product's fundamental sealing function. Even the most intelligent assembly equipment currently cannot perform full online inspection of this defect; only offline destructive sampling is possible. This easily leads to batch production scrap and the significant risk of missed inspections.

[0006] ② During the die-cutting process of the rubber ring, the die-cutting blade must cut through the entire thickness of the self-adhesive layer. The self-adhesive will accumulate on the die-cutting blade and edges. In addition to affecting the quality of the rubber ring, it is necessary to stop the machine regularly to thoroughly clean the self-adhesive accumulated on the blade and edges. In severe cases, the mold will be damaged and need to be repaired or scrapped completely. This will seriously affect production efficiency and increase direct and indirect costs.

[0007] ③ After the adhesive rings are die-cut, all the bottom film outside the adhesive rings needs to be removed as waste. At this time, a large amount of the adhesive surface is exposed on the self-adhesive tape, which will attract dust (including foreign matter generated by the die-cutting process) from the die-cutting environment, posing a certain risk. Similarly, when the adhesive rings are unwound on the three-in-one machine, the self-adhesive surface will also be exposed before the adhesive rings are peeled off, which will also pose a certain risk.

[0008] ④ During the process of using the suction nozzle to hold the rubber ring and transfer and position it, trace amounts of moisture and oil inside the suction nozzle cavity and on the suction nozzle will contaminate the surface of the rubber ring, which will form air bubbles and reduce the sealing performance.

[0009] ⑤ If the suction hole on the suction nozzle is held in place, the rubber ring will be uneven and concave. This is not conducive to the high flatness required for the two-in-one process, which is to remove the air between the rubber ring and the hot-melt metal bonding surface. Air bubbles are easily generated in the concave area.

[0010] ⑥ This stacked three-in-one process refers to heating the metal rings on the same workstation platform, then stacking the rubber rings on top of each other, and finally placing the metal sheet to complete the three-in-one hot melt and hot press pre-bonding. Before the three-in-one process, due to the lack of pressure but the presence of temperature, the rubber rings will shrink and deform, which seriously affects the accurate positioning and positioning effect deviation during the three-in-one process. At the same time, it affects the flatness of the adhesive surface before the three-in-one process and is prone to generating air bubbles.

[0011] Online die-cutting process ①The advantage is that it completely eliminates the most fatal and highest risk of residual or transferred self-adhesive during the offline die-cutting process.

[0012] ②However, the high risks in the suction nozzle, suction ring, and stacked two-in-one and three-in-one processes have not been improved.

[0013] ③ The online die-cutting process is difficult, and the equipment cost is more than three times that of offline die-cutting, while the efficiency is only 10-20% of that of offline die-cutting. The overall efficiency of the three-in-one equipment is 30ppm to 40ppm, while the cost of the equipment is between 8 million and 10 million. The cost amortization of this equipment accounts for about 30% of the total product cost. In other words, the downtime losses caused by the online die-cutting process will be huge and unbearable, or the unit price of the product will remain high. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by proposing a hot-pressing pre-bonding process for steel lithium battery cover plates that improves explosion-proof and fire-proof effects, simplifies the manufacturing process, and significantly reduces costs.

[0015] The technical problem to be solved by the present invention is achieved through the following technical solution: a hot-pressing pre-bonding process for manufacturing steel lithium battery cover plates, characterized by: Step 1: Maleic anhydride modified polypropylene particles are extruded into a film using an extrusion casting laminating machine. At the die of the extrusion casting laminating machine, the temperature and viscosity of the unshaped film are used to laminate the freshly extruded unshaped film onto the PET base film through a hot-pressing laminating process to form a composite film. After cooling, crystallization and shaping, the film is then wound up. Step 2: The above-mentioned rolled composite film is die-cut using a die-cutting machine. The adhesive film on the PET base film is die-cut into adhesive rings according to the design specifications, and then the waste adhesive film is removed to form an adhesive ring composite film. Place the adhesive ring composite film on the laminating equipment with the adhesive ring facing upwards and the PET base film in contact with the platform of the laminating equipment; use the constant temperature suction nozzle of the intelligent robotic arm to pick up the metal sheet or metal ring and accurately position it with the adhesive ring for two-in-one hot pressing pre-lamination. Step 3: After the two-in-one hot-press pre-lamination process, the adhesive ring composite film is conveyed to the peeling station for PET base film peeling. After peeling, the PET base film is rolled up, and the adhesive ring with the metal sheet or metal ring is left on the platform. The adhesive ring is in contact with the platform, and the metal surface of the metal sheet or metal ring is facing up. The suction nozzle of the intelligent robotic arm picks up the metal surface for transfer and accurately positions it on the metal ring or metal sheet on the three-in-one constant temperature platform for three-in-one hot-press pre-lamination. In the two-in-one hot press pre-bonding process, the thermostatic nozzle picks up a metal ring, and in the three-in-one hot press pre-bonding process, the corresponding metal sheet is placed on the thermostatic platform; conversely, if the thermostatic nozzle picks up a metal sheet in the two-in-one hot press pre-bonding process, the corresponding metal ring is placed on the thermostatic platform in the three-in-one hot press pre-bonding process. After the two-in-one and three-in-one hot press pre-bonding processes, a three-layer structure of metal ring / adhesive ring / metal sheet is formed.

[0016] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: in step 1, the instantaneous temperature of the composite of the unshaped adhesive film and the PET base film is 180~210℃, and the composite pressure is 0.4~0.6MPa.

[0017] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: the hot pressing composite process in step 1 includes a cooling roller set below the outlet of the extrusion casting composite machine, and an elastic composite roller set on the side of the cooling roller. When the film extruded from the outlet of the extrusion casting composite machine wraps the cooling roller, the temperature and viscosity of the unshaped film are used to drive the PET base film to complete instantaneous pressing and bonding between the elastic composite roller and the cooling roller. Then the cooling roller cools and shapes the film and exports it.

[0018] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: the temperature of the cooling roller during the compounding process is 20~40℃.

[0019] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: the temperature of the feeding section of the extrusion casting composite machine in step 1 is 140~180℃, the temperature of the compression section is 180~220℃, and the temperature of the extrusion nozzle is 220~250℃.

[0020] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: in step 2, the temperature of the constant temperature nozzle is 90-130℃ and the two-in-one hot press pre-bonding time is 1-6 seconds.

[0021] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: in step 3, the temperature of the three-in-one hot press pre-bonding platform is 90-130℃, and the three-in-one hot press pre-bonding time is 1-6 seconds.

[0022] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: at least the composite surface of the metal sheet or metal ring is subjected to anti-corrosion treatment to form a nano-anti-corrosion layer.

[0023] The technical problem to be solved by the present invention can also be further achieved by the following technical solution, wherein the anti-corrosion treatment is a nano-chromiumized surface treatment.

[0024] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: the outer edge of the rubber ring is not greater than the outer edge boundary of the metal sheet or the metal ring.

[0025] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: the inner edge of the rubber ring is not less than the inner edge boundary of the metal ring.

[0026] Compared with existing technologies, this invention utilizes the online temperature of the extruded cast film for direct hot-press lamination, eliminating the need for self-adhesive labels. Its key advantages are: ① It absorbs the advantages of traditional offline die-cutting processes (high process maturity, low difficulty, inexpensive equipment, and high efficiency) while avoiding the influence of self-adhesive labels on the die-cutting blades in traditional die-cut products. ② It eliminates the most critical risk of adhesive ring transfer or residue in online die-cutting processes while still allowing the use of traditional offline die-cutting techniques. Offline die-cutting significantly reduces the difficulty and cost of online die-cutting equipment in the three-in-one process. It also greatly improves efficiency and significantly reduces the cost of the finished product. ③ It completely eliminates the high risk of contamination from moisture and oil in the nozzle's inner cavity during the three-in-one processing, where the nozzle directly picks up the adhesive ring. ④ The positioning of the two-in-one and three-in-one processes in this invention is easier and more precise, and the three-in-one effect is significantly superior to the stacked hot-press pre-lamination process. Attached Figure Description

[0027] Figure 1 This is a diagram of the hot-pressing composite process for composite films. Detailed Implementation

[0028] The specific technical solutions of the present invention are further described below. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, and to facilitate a better understanding of the present invention by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, and do not constitute a limitation on its rights. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] A hot-pressing pre-lamination process for manufacturing steel lithium battery cover plates. Step 1: Maleic anhydride modified polypropylene particles are extruded into a film using an extrusion casting laminating machine. At the die of the extrusion casting laminating machine, the temperature and viscosity of the unshaped film are used to laminate the freshly extruded unshaped film onto the PET base film through a hot-pressing laminating process to form a composite film. After cooling, crystallization and shaping, the film is then wound up. Polypropylene plastic particles modified primarily with maleic anhydride. These particles can form high-strength thermoplastic seals with metals; they can also form high-strength thermoplastic seals with metals that have undergone nano-chromium plating surface treatment, resisting the penetration of electrolytes inside lithium batteries and in highly corrosive environments; when the internal temperature of a lithium battery rises to between 100°C and 130°C, the thermoplastic bond strength between the particles and the metal rapidly decreases, causing the metal sheets in stamped structural parts to quickly rupture, thus releasing pressure and preventing further heating, thereby preventing explosion and fire.

[0030] The hot-pressing lamination process described in step 1 includes a cooling roller installed below the outlet of the extrusion casting laminator, and an elastic lamination roller installed on the side of the cooling roller. When the film extruded from the outlet of the extrusion casting laminator wraps around the cooling roller, the temperature and viscosity of the unshaped film are used to drive the PET base film to complete instantaneous pressure lamination between the elastic lamination roller and the cooling roller. Then, the cooling roller cools and shapes the film before exporting it.

[0031] As shown in the figure: 1. Extrusion casting laminating machine die head, 2. Unshaped film, 3. Base film, 4. Elastic composite roller, 5. Cooling roller, 6. Guide roller, 7. Composite film after cooling and shaping.

[0032] The instantaneous temperature for laminating the adhesive film and the PET base film is 180~210℃, and the lamination pressure is 0.4~0.6MPa. The temperature of the cooling roller during lamination is 20~40℃.

[0033] The distance from the film outlet to the laminating machine should be controlled between 100 and 300 mm.

[0034] The feeding section temperature of the extrusion casting laminating machine is 140~180℃, the compression section temperature is 180~220℃, and the extrusion nozzle temperature is 220~250℃.

[0035] Step 2: The above-mentioned rolled composite film is die-cut using a die-cutting machine. The adhesive film on the PET base film is die-cut into adhesive rings according to the design specifications, and then the waste adhesive film is removed to form an adhesive ring composite film. The adhesive ring composite film is placed on the laminating equipment with the adhesive ring side facing up, and the PET base film is in contact with the platform of the laminating equipment. The constant temperature suction nozzle of the intelligent robotic arm picks up the metal sheet or metal ring and precisely positions it with the adhesive ring for two-in-one hot pressing pre-bonding. This invention adopts offline film cutting technology, which does not require peeling beforehand and avoids contamination during the transfer of adhesive rings.

[0036] Step 3: After the two-in-one hot-pressing pre-lamination process, the adhesive ring composite film is conveyed to the peeling station for PET bottom film peeling. After peeling, the PET bottom film is rolled up, and the adhesive ring with the metal sheet or metal ring is left on the platform. The adhesive ring is in contact with the platform, and the metal surface of the metal sheet or metal ring is facing up. The suction nozzle of the intelligent robotic arm picks up the metal surface for transfer and accurately positions it on the metal ring or metal sheet on the three-in-one constant temperature platform for three-in-one hot-pressing pre-lamination to form a three-layer composite structure of metal ring / adhesive ring / metal sheet, and then the material is discharged.

[0037] This invention employs online hot-pressing pre-bonding technology, where the suction nozzle is used only to pick up the metal surface throughout the entire process, eliminating contamination of the rubber ring surface by the suction nozzle.

[0038] In step 2, the temperature of the thermostatic nozzle is 90-130℃, and the thermostatic pre-bonding time is 1-6 seconds.

[0039] In step 3, the three-in-one hot press pre-bonding is carried out. The temperature of the three-in-one constant temperature platform is 90-130℃, and the three-in-one hot press pre-bonding time is 1-6 seconds.

[0040] In the two-in-one hot press pre-bonding process, the thermostatic nozzle picks up a metal ring, and in the three-in-one hot press pre-bonding process, the corresponding metal sheet is placed on the thermostatic platform; conversely, if the thermostatic nozzle picks up a metal sheet in the two-in-one hot press pre-bonding process, the corresponding metal ring is placed on the thermostatic platform in the three-in-one hot press pre-bonding process. After the two-in-one and three-in-one hot press pre-bonding processes, a three-layer structure of metal ring / adhesive ring / metal sheet is formed.

[0041] Metal sheets or metal rings are formed by stamping metal strips. The metal strips are a general term for various metal strips such as aluminum, nickel, titanium, or nickel-plated stainless steel used in the manufacture of lithium batteries.

[0042] Metal sheets are sheets of any shape without any perforations on their surface, including columnar sheets with a certain thickness; metal rings are rings of any shape with a perforation on their surface, and their shapes can be circular, square, elliptical, etc.

[0043] The rubber ring must be a ring corresponding to the metal ring so that an air vent is formed during hot pressing, which is also an essential hole for explosion protection.

[0044] The outer edge of the rubber ring is not greater than the outer boundary of the metal sheet or metal ring. The inner edge of the rubber ring is not less than the inner boundary of the metal ring.

[0045] The outer edge of the rubber ring is 0-1mm smaller than the outer edge boundary of the metal sheet or metal ring.

[0046] The inner edge of the rubber ring is 0-1mm larger than the inner edge of the metal ring.

[0047] The steel lithium battery cover of the present invention can be used as an explosion-proof and fire-proof safety valve, and can also be used as the positive and negative terminals of the battery.

[0048] At least the composite surface of the metal sheet or metal ring is subjected to anti-corrosion treatment to form a nano-anti-corrosion layer. The anti-corrosion treatment is a nano-chromiumizing surface treatment.

[0049] The three-layer composite structure of metal ring / plastic ring / metal sheet manufactured by the hot-press pre-bonding process of this invention has no subsequent processes that are unrelated to this invention and will not be described in detail here.

Claims

1. A hot-pressing pre-bonding process for manufacturing a steel lithium battery cover, characterized in that: Step 1: Maleic anhydride modified polypropylene particles are extruded into a film using an extrusion casting laminating machine. At the die of the extrusion casting laminating machine, the temperature and viscosity of the unshaped film are used to laminate the freshly extruded unshaped film onto the PET base film through a hot-pressing laminating process to form a composite film. After cooling, crystallization and shaping, the film is then wound up. Step 2: The above-mentioned rolled composite film is die-cut using a die-cutting machine. The adhesive film on the PET base film is die-cut into adhesive rings according to the design specifications, and then the waste adhesive film is removed to form an adhesive ring composite film. Place the adhesive ring composite film on the laminating equipment with the adhesive ring facing upwards and the PET base film in contact with the platform of the laminating equipment; use the constant temperature suction nozzle of the intelligent robotic arm to pick up the metal sheet or metal ring and accurately position it with the adhesive ring for two-in-one hot pressing pre-lamination. Step 3: After the two-in-one hot-press pre-lamination process, the adhesive ring composite film is conveyed to the peeling station for PET base film peeling. After peeling, the PET base film is rolled up, and the adhesive ring with the metal sheet or metal ring is left on the platform. The adhesive ring is in contact with the platform, and the metal surface of the metal sheet or metal ring is facing up. The suction nozzle of the intelligent robotic arm picks up the metal surface for transfer and accurately positions it on the metal ring or metal sheet on the three-in-one constant temperature platform for three-in-one hot-press pre-lamination. In the two-in-one hot press pre-bonding process, the thermostatic nozzle picks up the metal ring, and in the three-in-one hot press pre-bonding process, the corresponding metal sheet is on the thermostatic platform; conversely, in the two-in-one hot press pre-bonding process, the thermostatic nozzle picks up the metal sheet, and in the three-in-one hot press pre-bonding process, the corresponding metal ring is on the thermostatic platform; after the two-in-one hot press pre-bonding process and the three-in-one hot press pre-bonding process, a three-layer structure of metal ring / adhesive ring / metal sheet is formed.

2. The hot-pressing pre-bonding process for manufacturing the steel lithium battery cover plate according to claim 1, characterized in that: The hot-pressing lamination process described in step 1 includes a cooling roller installed below the outlet of the extrusion casting laminator, and an elastic lamination roller installed on the side of the cooling roller. When the film extruded from the outlet of the extrusion casting laminator wraps around the cooling roller, the temperature and viscosity of the unshaped film are used to drive the PET base film to complete instant lamination between the elastic lamination roller and the cooling roller. Then, the cooling roller cools and shapes the film before exporting it.

3. The hot-pressing pre-bonding process for manufacturing the steel lithium battery cover plate according to claim 2, characterized in that: The instantaneous temperature for laminating the adhesive film and the PET base film is 180~210℃, and the lamination pressure is 0.4~0.6MPa.

4. The hot-pressing pre-bonding process for manufacturing the steel lithium battery cover plate according to claim 2, characterized in that: The temperature of the cooling roller during the lamination process is 20~40℃.

5. The hot-pressing pre-bonding process for manufacturing the steel lithium battery cover plate according to claim 1, characterized in that: The feeding section temperature of the extrusion casting laminator in step 1 is 140~180℃, the compression section temperature is 180~220℃, and the extrusion nozzle temperature is 220~250℃.

6. The hot-pressing pre-bonding process for manufacturing the steel lithium battery cover plate according to claim 1, characterized in that: In step 2, the temperature of the thermostatic nozzle is 90-130℃, and the thermostatic pre-bonding time is 1-6 seconds.

7. The hot-pressing pre-bonding process for manufacturing a steel lithium battery cover plate according to claim 1, characterized in that: In step 3, the three-in-one hot press pre-bonding is carried out. The temperature of the three-in-one constant temperature platform is 90-130℃, and the three-in-one hot press pre-bonding time is 1-6 seconds.

8. The hot-pressing pre-bonding process for manufacturing the steel lithium battery cover plate according to claim 1, characterized in that: In step 2, at least the composite surface of the metal sheet or metal ring is subjected to anti-corrosion treatment to form a nano-anti-corrosion layer.

9. The hot-pressing pre-bonding process for manufacturing a steel lithium battery cover plate according to claim 1, characterized in that: The outer edge of the rubber ring is not greater than the outer boundary of the metal sheet or the metal ring.

10. The hot-pressing pre-bonding process for manufacturing a steel lithium battery cover plate according to claim 1, characterized in that: The inner edge of the rubber ring is not less than the inner edge boundary of the metal ring.

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