Composite oil removal process for coating carbon on aluminum foil of lithium battery

Abstract

The invention relates to the field of gravure prime coat of a lithium battery positive electrode current collector, in particular to a composite oil removal process for coating carbon on an aluminum foil for a lithium battery. Through improvement of structures and parameters in the heating oil removal process and the corona oil removal process, the two oil removal processes are compounded, and the problems that in the prior art, pure high-temperature oil removal is prone to causing aluminum foil wrinkling, and consequently the follow-up intaglio printing quality is affected are solved; the problems of high energy consumption and difficulty in cleaning oil stains of the corona mechanisms caused by high-power operation of a plurality of corona mechanisms in pure corona oil removal in the prior art are also solved, and meanwhile, the online oil removal is realized by integrating with a gravure carbon coating process. The dyne value of the surface of the aluminum foil subjected to composite oil removal can be up to 45, the rolling oil on the surface of the aluminum foil is greatly removed, the defects of missed coating, coating spots and patterns are reduced, the gravure coating quality is improved, the charge rate of the aluminum foil subjected to carbon coating is reduced, and meanwhile the service life of a coating rubber roller is prolonged.

Description

Technical Field

[0001] This invention patent relates to the field of gravure undercoating for the positive current collector of lithium batteries, and particularly to a composite degreasing process for carbon-coated aluminum foil used in lithium batteries. Background Art

[0002] The structure of a lithium-ion battery consists of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery case (square case, soft package, cylinder, etc.). The current collectors used for the positive and negative electrodes mainly function to carry the positive or negative electrode materials. In a lithium-ion battery, aluminum foil is used as the current collector for the positive electrode due to its good characteristics. Before becoming the positive electrode, it needs to undergo a carbon coating process using a gravure coating process to first become carbon-coated aluminum foil.

[0003] Carbon-coated aluminum foil disperses nano conductive carbon / graphite particles and an adhesive in a certain proportion and evenly and finely coats them on the aluminum foil. It can provide excellent static conductivity, collect the microcurrent of the active material, thereby significantly reducing the contact resistance between the positive / negative electrode materials and the current collector, and can improve the adhesion ability between the two, reduce the usage amount of the bonding electrode, and thus significantly improve the overall performance of the battery.

[0004] During the rolling process of aluminum foil, a large amount of rolling oil is required for lubrication and cooling, resulting in a large amount of rolling oil adhering to the surface and penetrating into the interior of the rolled aluminum foil. Before the aluminum foil leaves the factory, the foil factory will undergo degreasing treatment, such as annealing degreasing, chemical degreasing, physical degreasing, etc. However, during the carbon coating process in the battery factory, there are phenomena of rolling oil overflow and incomplete removal of surface rolling oil on the aluminum foil, which affect the quality of the gravure undercoating. The residual or overflowing rolling oil on the aluminum foil is likely to contaminate the coating rubber roller and cause cracking; during coating, it affects the transfer of the slurry, and there are defects such as large-area missed coating, coating spots, and patterns in the oily areas. Missed coating directly affects the conductivity of the positive current collector and reduces the adhesion ability of the positive electrode material.

[0005] In the field of aluminum foil gravure undercoating, the aluminum foil degreasing process uses a single method of corona degreasing or high-temperature degreasing. In the single corona degreasing process, the equipment investment cost is high, the energy consumption is high, the electrodes and the corona roller are easily contaminated by oil, the cleaning frequency is high, the electrode structure is complex and inconvenient to maintain. At the same time, the electrodes, as consumable parts, all need to be imported from Germany and are expensive. In the single high-temperature degreasing process, aluminum foil with a thickness of 8 - 20 μm is prone to thermal expansion and generate wrinkles. After leaving the high-temperature (150 °C) environment, the temperature drops rapidly, the wrinkles shrink, the foil material is wrinkled and cannot be restored, and coating cannot be carried out. At the same time, the wrinkles are likely to cause tape breakage and shutdown.

[0006] The battery aluminum foil degreasing system proposed in utility model patent CN 221336023 U uses only high-temperature degreasing. The high-temperature baking causes the aluminum foil to expand in the oven, causing severe vibration. After leaving the oven, the temperature drops, causing the aluminum foil to wrinkle and cannot be coated normally. In addition, the lithium battery substrate pre-coating degreasing mechanism and coating production line proposed in utility model patent CN219943938U has an aluminum foil that undergoes multiple up and down turns. Also, due to being in high-temperature baking, it will cause the aluminum foil to wrinkle, which is an unsolvable problem. At the same time, simply removing oil through high temperature will only remove the oil on the surface of the foil. The oil that penetrates into the interior will replace the oil on the surface, resulting in incomplete removal.

[0007] Utility model patent CN212093552U discloses a special degreasing device for a battery foil slitting machine, wherein the preheating degreasing device described therein is only a simple heating device and is distributed around the unwinding mechanism. The unwinding mechanism is a loading station and often needs to change rolls and splice tapes. Adding a heating device around it poses a great hidden danger to the operation, and this is difficult to achieve in actual implementation.

[0008] At the same time, the above three patents all use infrared tubes or lamps for heating in preheating or high-temperature degreasing. Aluminum foil, as a heat-insulating material, has limited heat absorption for lamps and infrared heating, and the heating effect is not ideal. Summary of the invention

[0009] In order to solve and improve the above problems, the present application provides a composite degreasing process, which can be integrated with the gravure primer coating process and used for online degreasing of lithium battery aluminum foil before gravure carbon coating. After degreasing, gravure carbon coating can be performed immediately.

[0010] The purpose of the present invention can be achieved through the following technical solutions:

[0011] The present invention provides a composite degreasing process for carbon coating of aluminum foil for lithium batteries, comprising a heating degreasing process and a high-frequency and high-pressure degreasing process, wherein the heating degreasing process and the high-frequency and high-pressure degreasing process are arranged in series, and the aluminum foil after unwinding first passes through the heating degreasing process, and then passes through the high-frequency and high-pressure degreasing process, and the aluminum foil after unwinding first passes through the heating degreasing process, so that the rolling oil on the surface is vaporized at high temperature and then discharged, and most of the rolling oil is removed, and the rolling oil that has penetrated into the interior is forced out to the surface. Then, through the high-frequency and high-pressure degreasing process, the electrode discharges high voltage to impact the surface of the foil, so that the chain molecules of the surface rolling mill oil are broken, the surface oil layer is volatilized, and discharged through a fan, so as to achieve the effect of surface degreasing.

[0012] Furthermore, the heating and oil removal process is oven heating, and the heating method of the oven is at least one of thermal oil heat exchanger heating, steam heat exchanger heating, electric heating pipe heating, and electric heating plate heating.

[0013] Further, the high-frequency high-voltage oil removal process is corona oil removal or plasma oil removal.

[0014] Further, the heating oil removal process is oven heating. The hot air heated by the heating package outside the oven on the upper surface of the aluminum foil is directly blown to the slit-type air nozzle by a fan. The hot air temperature is 0 - 150 °C. The air intake volume is controlled by a variable-frequency fan and an air valve. The arrangement interval of the slit-type air nozzles is 600 - 800 mm, the distance from the slit-type air nozzle to the aluminum foil surface is 10 - 20 mm, and the width of the outlet of the slit-type air nozzle is 3 mm.

[0015] Further, the lower surface of the aluminum foil is heated by multiple electric heating devices. The arrangement interval of the electric heating devices is 100 - 200 mm, and the temperature range of the electric heating devices is 0 - 150 °C; a return air mesh hole is provided on the bottom partition of the electric heating device, and a return air cavity is provided between the bottom partition and the inner wall of the oven. The outlet of the return air cavity is connected to the exhaust pipeline; the electric heating device is a fin-type electric heating tube or a PTC ceramic heating plate. The arrangement of the electric heating devices needs to be reasonable to prevent the aluminum foil from wrinkling.

[0016] Further, an aluminum foil supporting and passing roller is provided inside the oven for supporting and driving the aluminum foil. Reverse threading is prohibited to reduce the wrinkling of the aluminum foil caused by the thermal deformation of the roller.

[0017] Further, the length of the oven is 2 - 4 m. If the oven is too long, the sheet path of the foil in the oven will be lengthened, increasing the wrinkling situation.

[0018] Further, the high-frequency high-voltage oil removal process is corona oil removal. The aluminum foil after heating oil removal is introduced into the corona oil removal mechanism. The corona oil removal mechanism is provided with 2 - 4 corona rollers with large wrap angles. The corona rollers are arranged staggeredly according to the A / B sides of the aluminum foil, and the corona rollers are driven by a servo motor.

[0019] Further, ceramic electrodes are provided at a position 2 - 5 mm away from the roller surface at the wrap angle of the corona roller. The number of electrode distributions is 8 - 10 groups. The electrodes are connected to a transformer through wires, and high-voltage discharge is realized through a control cabinet; the corona roller is connected to a film temperature controller to control the temperature of the corona roller, so that the surface temperature of the corona roller remains at 58 - 62 °C. One is to prevent the aluminum foil after high-temperature oil removal from deforming due to thermal expansion and contraction, and the other is to protect the corona roller. The stains attached to the corona roller are easily removed by the exhaust system. An exhaust pipeline is provided above the electrode and connected to a high-pressure centrifugal fan for quickly exhausting the ozone generated by corona.

[0020] Further, the composite degreasing process is linked with the gravure carbon coating process. The servo motor in the corona degreasing process is linked and controlled with the traction unit in the gravure carbon coating process, and is controlled by the gravure coater. After startup, it can run automatically and the parameters can be set, the temperature can be monitored, and the abnormal alarm can be processed on the gravure coater. At the same time, the process parameters can be uploaded through the MES system, and the aluminum foil after corona degreasing directly enters the gravure carbon coating process.

[0021] Further, the process after the composite degreasing process is linked with the gravure carbon coating process includes the unwinding process, the heating degreasing process, the corona degreasing process, the A-side gravure carbon coating process, the A-side drying process, the B-side gravure carbon coating process, the B-side coating process, and the winding process.

[0022] The beneficial effects that can be produced by this application are as follows:

[0023] Through the improvement of the structure and parameters in the heating degreasing process and the corona degreasing process, the present invention realizes the combination of two degreasing processes, solves the problem that simple high-temperature degreasing in the prior art is prone to cause wrinkling of the aluminum foil, thereby affecting the subsequent gravure printing quality, and also solves the problem that simple corona degreasing in the prior art requires multiple corona units to operate at high power, resulting in high energy consumption and difficult cleaning of the oil stains on the corona units. At the same time, it is integrated with the gravure carbon coating process to realize online degreasing. The surface dyne value of the aluminum foil after composite degreasing can be as high as 45, which greatly removes the rolling oil on the surface of the aluminum foil, reduces the occurrence of missed coating, coating spots, and pattern defects, improves the quality of gravure coating, reduces the rejection rate of the aluminum foil after carbon coating, and at the same time extends the service life of the coating rubber roller. Description of the Drawings

[0024] Figure 1 It is the process flow chart after the composite degreasing process is linked with the gravure carbon coating process in Example 1 (Note: 101, unwinding process; 102, heating degreasing process; 103, corona degreasing process; 104, feeding traction; 105, A-side coating process; 106, A-side drying process; 107, B-side coating process; 108, B-side drying process; 109, winding process).

[0025] Figure 2 Picture of the aluminum foil after carbon coating with the composite degreasing process in Example 1.

[0026] Figure 3 Picture of the aluminum foil after simple high-temperature degreasing process in Comparative Example 1.

[0027] Figure 4 Picture of the aluminum foil after carbon coating after simple high-temperature degreasing in Comparative Example 1.

[0028] Figure 5 Picture of the aluminum foil after simple corona degreasing process in Comparative Example 2.

[0029] Figure 6 It is a picture of the coating rubber roller after the simple corona degreasing process in Comparative Example 2.

[0030] Figure 7 It is a picture of carbon coating on the aluminum foil after the simple corona degreasing process in Comparative Example 2. Specific Embodiments

[0031] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0032] Embodiment 1

[0033] A composite degreasing process for carbon coating on aluminum foil of lithium batteries, the composite degreasing process is in online linkage with the gravure carbon coating process, and the process flow chart is as Figure 1 shown, including the unwind process, the heating degreasing process, the corona degreasing process, the A-side gravure carbon coating process, the A-side drying process, the B-side gravure carbon coating process, the B-side coating process, and the winding process. The process flow chart after the composite degreasing process is in linkage with the gravure carbon coating process is as Figure 1 shown.

[0034] The composite degreasing process includes an oven heating degreasing process and a corona degreasing process. The oven heating degreasing process and the corona degreasing process are arranged in series. The aluminum foil after unwinding first passes through the oven heating degreasing process, and then through the corona degreasing process. The aluminum foil after unwinding first passes through the oven heating degreasing process, so that the rolling oil on the surface is vaporized at high temperature and discharged, removing most of the rolling oil, and at the same time forcing the rolling oil infiltrated into the interior to the surface. Then, through the corona degreasing process, the electrode discharges at high voltage to impact the surface of the foil material, break the chain-like molecules of the surface rolling oil, volatilize the surface oil layer, and discharge it through the fan to achieve the effect of surface degreasing.

[0035] The hot air heated by the heating pack outside the oven on the upper surface of the aluminum foil is directly blown to the slit-type air nozzle by the fan. The hot air temperature is 150°C. The intake air volume of the hot air is controlled by a variable-frequency fan and an air valve. The arrangement interval of the slit-type air nozzles is 700 mm, the distance from the slit-type air nozzle to the surface of the aluminum foil is 15 mm, and the width of the air outlet of the slit-type air nozzle is 3 mm.

[0036] The lower surface of the aluminum foil is heated by multiple electric heating tubes. The arrangement interval of the electric heating tubes is 150 mm, and the temperature of the electric heating tubes is 150°C; a return air mesh hole is arranged on the bottom partition of the electric heating tubes, and a return air cavity is arranged between the bottom partition and the inner wall of the oven. The outlet of the return air cavity is connected to the exhaust pipeline; the arrangement of the electric heating tubes is reasonable to prevent the aluminum foil from wrinkling.

[0037] Inside the oven, there are aluminum foil supporting and guiding rollers for supporting and driving the aluminum foil. The non-return type threading is prohibited to reduce the wrinkling of the aluminum foil caused by the thermal deformation of the rollers.

[0038] The length of the oven is 4m. If the oven is too long, the path of the foil in the oven will be lengthened, increasing the possibility of wrinkling.

[0039] The aluminum foil after being heated and degreased in the oven is introduced into the corona degreasing mechanism. The corona degreasing mechanism is provided with corona rollers with 4 large wrap angles. The corona rollers are arranged staggeredly according to the A / B sides of the aluminum foil, and the corona rollers are driven by servo motors.

[0040] At a position 2mm away from the roller surface of the wrap angle of the corona roller, there are ceramic electrodes. The number of electrode distributions is 10 groups. The electrodes are connected to the transformer through wires, and high-voltage discharge is achieved through the control cabinet (for the 1600mm roller width model, the corona configuration power is 56kW); the corona roller is connected to a film temperature controller to control the temperature of the corona roller, so that the surface temperature of the corona roller remains at 60°C continuously. One is to prevent the aluminum foil after high-temperature degreasing from deforming due to thermal expansion and contraction, and the other is to protect the corona roller, and the stains attached to the corona roller are easily removed by the exhaust system. An exhaust pipeline is arranged above the electrodes and connected to a high-pressure centrifugal fan for quickly exhausting the ozone generated by corona. The composite degreasing process is linked with the gravure carbon coating process. The servo motor in the corona degreasing process is linked and controlled with the traction unit in the gravure carbon coating process, and is controlled by the gravure coater. After starting up, it can run automatically and the parameters can be set, the temperature can be monitored and the abnormal alarm can be processed on the gravure coater. At the same time, the process parameters can be uploaded through the MES system, and the aluminum foil after corona degreasing directly enters the gravure carbon coating process. The carbon-coated surface of the aluminum foil after the composite degreasing process and linked gravure carbon coating in this embodiment is as Figure 2 shown. It can be seen that the carbon coating is uniform and flat, without any phenomenon of missed coating or wrinkling.

[0041] Comparative Example 1

[0042] On the basis of the above Embodiment 1, in Comparative Example 1, the degreasing process uses a simple high-temperature (the temperature here is 150°C and the oven length is 6m) degreasing process. After the heating degreasing process, it directly enters the gravure carbon coating process. The picture of the aluminum foil after the high-temperature degreasing process is as Figure 3 shown. It can be seen that obvious wrinkling appears on the surface of the aluminum foil. The picture of the aluminum foil after gravure carbon coating is as Figure 4 shown. It can be seen that there is also wrinkling after carbon coating.

[0043] Comparative Example 2

[0044] Based on the above-mentioned Embodiment 1, in Comparative Example 2, the degreasing process uses a simple corona (for a 1600 mm roll width model, the corona configuration power is 112 kW) degreasing process, and the corona power is doubled. After corona degreasing, it directly enters the gravure carbon coating process. The aluminum foil picture after the high-power corona degreasing process is as Figure 5 shown. It can be seen that there is residual oil stain on the surface of the aluminum foil. The picture of the coating rubber roller after high-power corona degreasing is as Figure 6 shown. It can be seen that the coating rubber roller has cracks on the surface due to long-term adhesion of the oil stain of the aluminum foil. The picture of the aluminum foil after gravure carbon coating is as Figure 7 shown. It can be seen that there is a phenomenon of missed coating on the surface of the aluminum foil.

[0045] The above is a specific description of the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A composite degreasing process for carbon coating of lithium battery aluminum foil, characterized in that: The method comprises a heating degreasing process and a high-frequency and high-pressure degreasing process, wherein the heating degreasing process and the high-frequency and high-pressure degreasing process are arranged in series. The unwinding aluminum foil first passes through the heating degreasing process and then passes through the high-frequency and high-pressure degreasing process to achieve the effect of surface degreasing. After degreasing, the gravure coating process is immediately carried out.

2. According to claim 1, a composite degreasing process for carbon coating of lithium battery aluminum foil is characterized in that: The heating and oil removal process is oven heating, and the heating method of the oven is at least one of heating by a thermal oil heat exchanger, heating by a steam heat exchanger, heating by an electric heating pipe, and heating by an electric heating plate.

3. According to claim 1, a composite degreasing process for carbon coating of lithium battery aluminum foil is characterized in that: The high frequency and high pressure degreasing process is corona degreasing or plasma degreasing.

4. According to claim 2, a composite degreasing process for carbon coating of lithium battery aluminum foil is characterized in that: The upper surface of the aluminum foil is heated by a heating pack outside the oven, and the hot air is directly blown to the slit air nozzle by a fan. The hot air temperature is 0-150°C. The hot air intake is controlled by a variable frequency fan and an air valve. The slit air nozzles are arranged at intervals of 600-800mm, the distance from the slit air nozzle to the surface of the aluminum foil is 10-20mm, and the width of the slit air nozzle outlet is 3mm.

5. A composite degreasing process for carbon coating of lithium battery aluminum foil according to claim 4, characterized in that: The lower surface of the aluminum foil is heated by multiple electric heating devices, the electric heating devices are arranged at intervals of 100-200mm, and the temperature range of the electric heating devices is 0-150°C; a return air mesh is arranged on the bottom partition of the electric heating device, and a return air cavity is arranged between the bottom partition and the inner wall of the oven, and the outlet of the return air cavity is connected to the exhaust duct; the electric heating device is a fin-type electric heating tube or a PTC ceramic heating plate.

6. A composite degreasing process for carbon coating of lithium battery aluminum foil according to claim 5, characterized in that: Aluminum foil supporting rollers are arranged inside the oven for supporting and transmitting the aluminum foil. The length of the oven is 2-4 m to prevent the foil from being too long in the oven and wrinkling when heated.

7. A composite degreasing process for carbon coating of lithium battery aluminum foil according to claim 3, characterized in that: The high-frequency and high-pressure degreasing process is corona degreasing. The aluminum foil after heating and degreasing is introduced into the corona degreasing mechanism. The corona degreasing mechanism is provided with 2-4 corona rollers. The corona rollers are staggered according to the A / B surface of the aluminum foil, and the corona rollers are driven by a servo motor.

8. A composite degreasing process for carbon coating of lithium battery aluminum foil according to claim 7, characterized in that: The corona roller is provided with ceramic electrodes at the wrap angle 2-5 mm away from the roller surface, and the number of electrodes is 8-10 groups. The electrodes are connected to the transformer through wires, and high-voltage discharge is achieved through the control cabinet; the corona roller is connected to the film temperature machine to control the temperature of the corona roller, so that the surface temperature of the corona roller is continuously kept at 58-62°C.

9. A composite degreasing process for carbon coating of lithium battery aluminum foil according to claim 7, characterized in that: The composite degreasing process is linked with the gravure carbon coating process, the servo motor in the corona degreasing process is linked with the traction unit in the gravure carbon coating process, and the aluminum foil after corona degreasing directly enters the gravure carbon coating process.

10. A composite degreasing process for carbon coating of lithium battery aluminum foil according to claim 9, characterized in that: The process after the composite degreasing process is linked with the gravure carbon coating process includes an unwinding process, a heating degreasing process, a corona degreasing process, an A-side gravure carbon coating process, an A-side drying process, a B-side gravure carbon coating process, a B-side coating process, and a winding process.

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