A passivation method for aluminum foil and a passivation method for aluminum-plastic film

Abstract

The present invention provides a passivation method for aluminum foil, comprising the following steps: A) mixing fluoride, water and aqueous polyurethane to obtain a coating liquid; the fluoride is one or more of NF4F, LiF and ZnF2; B) coating the coating liquid on a carrier to form a coating; C) contacting the coating with the aluminum foil in the aluminum-plastic film, and performing a passivation treatment at 40 to 60° C. for 150 to 180 hours to obtain a passivated aluminum-plastic film. ‑ The coating contacts the aluminum foil and a surface reaction occurs under passivation conditions, namely F ‑ The ions react with Al or Al2O3 to eventually form an AlF3 passivation protective layer, in which the H2O or H2 will be released during the passivation reaction, thereby preventing the HF in the electrolyte from corroding the aluminum foil.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a passivation method for aluminum foil and a passivation method for aluminum-plastic film. Background Art

[0002] With the promotion of electronic products and electric vehicles, the use of lithium batteries, a key component, is expected to increase significantly. Aluminum-plastic film is the outer packaging material for lithium batteries. The film is in direct contact with the interior of the lithium battery, primarily serving to wrap the entire battery and block moisture and electrolyte.

[0003] Over time, a series of chemical reactions occur within lithium batteries. Components such as lithium hexafluoride, commonly found in the electrolyte, cause hydrofluoric acid to form inside the battery. Hydrofluoric acid is an extremely corrosive acid that can penetrate the heat-sealing and adhesive layers of the aluminum-plastic film and directly corrode the aluminum foil. Prolonged contact can cause delamination of the aluminum foil within the film, leading to the risk of bulging and leakage in lithium batteries. Therefore, the aluminum foil layer must possess a certain degree of resistance to corrosion from both the electrolyte and hydrofluoric acid.

[0004] Aluminum foil is typically passivated using a chromium-containing passivation solution. Treating aluminum foil with trivalent or hexavalent chromium significantly improves its hydrofluoric acid corrosion resistance. However, hexavalent chromium is toxic and carcinogenic, and trivalent chromium also pollutes the environment to a certain extent. Summary of the Invention

[0005] The purpose of the present invention is to provide a passivation method for aluminum foil and a passivation method for aluminum-plastic film. The passivation method of the present invention does not contain chromium, and the aluminum-plastic film after passivation has excellent electrolyte resistance.

[0006] The present invention provides a passivation method for aluminum foil, comprising the following steps:

[0007] A) mixing a fluoride, water and an aqueous polyurethane to obtain a coating solution;

[0008] The fluoride is one or more of NH4F, LiF and ZnF2;

[0009] B) applying the coating liquid on the support to form a coating;

[0010] C) contacting the coating with aluminum foil and performing passivation treatment at 40-60° C. for 150-180 hours to obtain a passivated aluminum foil.

[0011] Preferably, the aqueous polyurethane is 100 parts, the fluoride is 0.1 to 10 parts, and the water is 50 to 80 parts.

[0012] Preferably, the carrier is a polyester film, and the thickness of the polyester film is 50 to 200 μm.

[0013] Preferably, the coating has a thickness of 1 to 5 μm.

[0014] Preferably, the step B) is specifically:

[0015] The coating liquid is applied on the support, dried to form a coating layer, and then aged at 30 to 50° C. for 60 to 80 hours to form a coating layer.

[0016] Preferably, the coating is dried at a temperature of 80-95°C.

[0017] Preferably, a rewinder is used to roll the composite coated carrier and the aluminum foil together so that the coating is in contact with the aluminum foil.

[0018] Preferably, the humidity of the environment during the passivation treatment is 30-50%.

[0019] Preferably, after the passivation treatment in step C), an aluminum fluoride layer is formed on the surface of the aluminum foil to obtain a passivated aluminum foil.

[0020] The invention provides a passivation method for an aluminum-plastic film. The aluminum foil is passivated according to the passivation method described above and then compounded with a nylon layer and a polypropylene layer to obtain the passivated aluminum-plastic film.

[0021] The present invention provides a passivation method for aluminum foil in an aluminum-plastic film, comprising the following steps: A) mixing fluoride, water and aqueous polyurethane to obtain a coating liquid; the fluoride is one or more of NF4F, LiF and ZnF2; B) coating the coating liquid on a carrier to form a coating; C) contacting the coating with the aluminum foil in the aluminum-plastic film, and performing a passivation treatment at 40 to 60° C. for 150 to 180 hours to obtain a passivated aluminum-plastic film. - The coating contacts the aluminum foil and a surface reaction occurs under passivation conditions, namely F - The ions react with Al or Al2O3 to eventually form an AlF3 passivation protective layer, in which the H2O or H2 will be released during the passivation reaction, thereby preventing the HF in the electrolyte from corroding the aluminum foil. DETAILED DESCRIPTION

[0022] The present invention provides a passivation method for aluminum foil, comprising the following steps:

[0023] A) mixing a fluoride, water and an aqueous polyurethane to obtain a coating solution;

[0024] The fluoride is one or more of NF4F, LiF and ZnF2;

[0025] B) applying the coating liquid on the support to form a coating;

[0026] C) contacting the coating with the aluminum foil in the aluminum-plastic film, and performing a passivation treatment at 40-60° C. for 150-180 hours to obtain a passivated aluminum foil.

[0027] The present invention first mixes fluoride, waterborne polyurethane and water to obtain a coating liquid.

[0028] In the present invention, the weight proportion of the aqueous polyurethane is preferably 100 parts. The present invention has no special limitation on the aqueous polyurethane, and the aqueous polyurethane resin commonly used by those skilled in the art can be used. Specifically, in the embodiment of the present invention, the aqueous polyurethane resin of model ETERANE8916A provided by Changxing Chemical is used.

[0029] The fluoride is preferably one or more of NH4F, LiF and ZnF2, and the weight fraction of the fluoride is preferably 0.1 to 10 parts, more preferably 0.5 to 7 parts, such as 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5 parts, 5.2 parts, 55 parts, 5.8 parts, 6 parts, 6.2 parts, 6.5 parts, 6.8 parts, 7 parts, 7.2 parts, 7.5 parts, 7.8 parts, 8 parts, 8.2 parts, 8.5 parts, 8.8 parts, 9 parts, 9.2 parts, 9.5 parts, 9.8 parts, 10 parts, preferably a range value with any of the above numerical values as the upper or lower limit.

[0030] The weight portion of the water is preferably 50 to 80 parts, more preferably 60 to 70 parts.

[0031] The present invention applies the mixed coating liquid on the surface of the carrier, dries it, and then matures it to obtain a coating.

[0032] In the present invention, the coating method is not particularly limited, and the coating liquid can be applied to the surface of the carrier. Specifically, in an embodiment of the present invention, micro-dimpled coating can be used. The carrier is preferably a polyester film (PET), and the thickness of the polyester film is preferably 50 to 200 μm, more preferably 100 to 150 μm.

[0033] In the present invention, the drying temperature is preferably 80-95°C, more preferably 85-90°C; the aging temperature is preferably 30-50°C, more preferably 35-45°C, most preferably 35-40°C; the aging time is preferably 60-80 hours, more preferably 65-75 hours, most preferably 70-72 hours.

[0034] In the present invention, the aging is specifically to place the dried coating at 35-45°C for aging to obtain an aging coating. The aging temperature is preferably 38-40°C, and the aging time is preferably 68-78 hours, more preferably 72-74 hours.

[0035] In the present invention, the thickness of the coating layer is preferably 1 to 5 μm.

[0036] After obtaining the coating, the present invention will use a rewinder to roll the composite coated carrier and aluminum foil together, so that the coating and the aluminum foil are in contact, and perform a passivation treatment under a specific environment to form an aluminum fluoride layer on the surface of the aluminum foil, separate the coating and the aluminum foil, and complete the passivation treatment.

[0037] In the present invention, the temperature of the passivation treatment is preferably 40-60°C, more preferably 45-55°C, such as 40°C, 45°C, 50°C, 55°C, 60°C, and preferably a range value with the above arbitrary numerical values as the upper or lower limit; the ambient humidity of the passivation treatment is preferably 30-50%, more preferably 35-45%, and most preferably 35-40%; the time of the passivation treatment is preferably 150-180 hours, more preferably 160-170 hours, such as 150 hours, 155 hours, 160 hours, 165 hours, 168 hours, 170 hours, 175 hours, 180 hours, and preferably a range value with the above arbitrary numerical values as the upper or lower limit.

[0038] The present invention uses one or more of NH4F, LiF and ZnF2 to be added to the waterborne polyurethane. Since NH4F, LiF and ZnF2 are all salts, there will be free F in the waterborne polyurethane. - Compared with the method of directly eluting the aluminum foil with HF or other fluorine-containing acidic substances, the passivation method of the present invention is easier to control the reaction rate of these fluorine-containing salts on the aluminum foil during the passivation process, preventing the corrosion rate from being too fast and causing uneven surface flatness; on the other hand, F - By spreading the glue and then contacting the aluminum foil, the contact method can be further weakened, thus ensuring that the F - It reacts with the aluminum foil to form an aluminum fluoride protective layer while ensuring the flatness and uniformity of the aluminum foil surface, preventing uneven thickness or even perforation. - Under the premise that the reaction rate with aluminum foil can be controlled, high temperature and low humidity environment is used to control F - The degree of reaction with the aluminum foil is adjusted to prepare an aluminum fluoride passivation film that can protect the aluminum foil from being corroded by the electrolyte.

[0039] Based on this, the present invention also provides a passivation method for an aluminum-plastic film, wherein the aluminum foil is passivated according to the passivation method described above, and then the passivated aluminum foil is compounded with a nylon layer (PA) and a polypropylene layer (CPP) to form a nylon layer, a passivated aluminum foil layer, and a polypropylene layer that are in contact with each other in sequence, wherein the aluminum fluoride passivation film in the aluminum foil is in contact with the polypropylene layer.

[0040] In the present invention, the lamination can be performed using commonly used methods in the prior art, such as dry lamination, where the polypropylene layer is laminated to the passivated aluminum foil layer using glue, or thermal lamination, where heated polypropylene is directly coated on the surface of the passivated aluminum foil layer. The passivated aluminum foil obtained by the passivation method of the present invention is suitable for commonly used dry lamination and thermal lamination processes in the prior art, which will not be described in detail in this application.

[0041] The present invention provides a passivation method for aluminum foil, comprising the following steps: A) mixing fluoride, water and aqueous polyurethane to obtain a coating liquid; the fluoride is one or more of NF4F, LiF and ZnF2; B) coating the coating liquid on a carrier to form a coating; C) contacting the coating with the aluminum foil in the aluminum-plastic film, and performing a passivation treatment at 40 to 60° C. for 150 to 180 hours to obtain a passivated aluminum-plastic film. - The coating contacts the aluminum foil and a surface reaction occurs under passivation conditions, namely F - The ions react with Al or Al2O3 to eventually form an AlF3 passivation protective layer, in which the H2O or H2 will be released during the passivation reaction, thereby preventing the HF in the electrolyte from corroding the aluminum foil.

[0042] In order to further illustrate the present invention, a passivation method for aluminum foil and a passivation method for aluminum-plastic film provided by the present invention are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present invention.

[0043] The waterborne polyurethane in the following examples uses the ETERANE 8916A waterborne polyurethane resin provided by Changxing Chemical.

[0044] Example 1

[0045] 0.5 parts of NH4F, 100 parts of aqueous polyurethane and 70 parts of water were mixed to obtain a mixed resin coating liquid.

[0046] The mixed resin coating liquid is applied to the surface of a 100 μm thick polyester film using a micro-concave coating operation, a machine speed of 40 min / m, a drying tunnel temperature of 85°C, a coating dry film thickness of 1-5 μm, and cured at 40°C for 72 hours.

[0047] After aging, the polyester film and 40μm thick aluminum foil are rolled together using a rewinder. The two rolls of film are placed on the first and second unwinds of the coating machine and rewound, with the coated surface of the polyester film in contact with the aluminum foil. They are placed in a passivation treatment environment at 50°C and 40% RH for 168 hours, and the aluminum foil and polyester film are separated.

[0048] Example 2

[0049] The aluminum foil was passivated according to the method in Example 1, except that 1 part of NH4F was used.

[0050] Example 3

[0051] The aluminum foil was passivated according to the method in Example 1, except that the amount of NH4F was 5 parts.

[0052] Passivation film detection of Examples 1 to 3

[0053] After separating the aluminum foil from the polyester film, cut out 8x8 cm of the aluminum foil in Examples 1 to 3, drop 1.0 ml of pure water at 80°C on them, and let them stand for 3 minutes. - (Fluoride Ion) Rapid Qualitative Test Paper (MN, Germany) turns from pink to yellow-white when dipped in water. This indicates that the polyester film coated with polyurethane containing NH4F has been passivated, and the free fluorine ions diffuse onto the aluminum foil, allowing fluorine to be detected on the surface of the aluminum foil. This confirms that a very thin layer of aluminum fluoride has formed on the surface of the aluminum foil.

[0054] When 0.05 mol / L HF was dropped onto an unpassivated aluminum foil, hydrogen gas was emitted. This is because 6HF + 2Al → 3H2 + 2AlF3. However, when 0.05N HF was dropped onto the passivated aluminum foils of Examples 1 to 3, no bubbling reaction occurred, indicating that there was no pure aluminum layer on the surface. It also confirmed that the surface layer was no longer an aluminum foil or aluminum oxide layer, but had been fluorinated to form an aluminum fluoride layer.

[0055] The Auger electron spectrometer test showed that when the amounts of NH4F in Examples 1 to 3 were 0.5 parts, 1 parts and 5 parts, respectively, the thicknesses of the aluminum fluoride layers were 2.1 μm, 4.5 μm and 10.4 μm, respectively.

[0056] Example 4

[0057] The aluminum foil was passivated according to the method in Example 1, except that 1.5 parts of LiF were used in Example 4.

[0058] Example 5

[0059] The aluminum foil was passivated according to the method in Example 1, except that 3.5 parts of LiF were used in Example 5.

[0060] Example 6

[0061] The aluminum foil was passivated according to the method in Example 1, except that 7.0 parts of LiF was used in Example 6.

[0062] Passivation film detection of Examples 4 to 6

[0063] After separating the aluminum foil from the polyester film, cut out 8x8 cm of the aluminum foil in Examples 4 to 6, drop 1.0 ml of pure water at 80°C on them, and let them stand for 3 minutes. - When a drop of water is applied to a rapid qualitative test paper (MN, Germany), the color of the test paper changes from pink to yellow-white. This indicates that the polyester film coated with polyurethane containing LiF has been passivated, and the free fluorine ions diffuse onto the aluminum foil, allowing fluorine to be detected on the surface of the aluminum foil. This confirms that a very thin layer of aluminum fluoride has formed on the surface of the aluminum foil.

[0064] The Auger electron spectrometer test showed that when the amounts of LiF in Examples 4 to 6 were 1.5 parts, 3.5 parts, and 7 parts, respectively, the thicknesses of the aluminum fluoride layers were 1.5 μm, 3.2 μm, and 6.4 μm, respectively.

[0065] Example 7

[0066] The aluminum foil was passivated according to the method in Example 1, except that 0.5 parts of ZnF2 were used in Example 7.

[0067] Example 8

[0068] The aluminum foil was passivated according to the method in Example 1, except that 1.5 parts of ZnF2 were used in Example 8.

[0069] Example 9

[0070] The aluminum foil was passivated according to the method in Example 1, except that 5 parts of ZnF2 were used in Example 9.

[0071] Passivation film detection of Examples 7 to 9

[0072] After separating the aluminum foil from the polyester film, cut out 8x8 cm of the aluminum foil in Examples 7 to 9, drop 1.0 ml of pure water at 80°C on them, and let them stand for 3 minutes. - (Fluoride Ion) Rapid Qualitative Test Paper (MN, Germany) turns from pink to yellow-white when dipped in water, indicating that the polyurethane containing ZnF2 is coated on the polyester film. After passivation, the free fluorine ions diffuse onto the aluminum foil, causing fluorine to be detected on the surface of the aluminum foil. This confirms that a very thin layer of aluminum fluoride has formed on the surface of the aluminum foil.

[0073] The Auger electron spectrometer test showed that when the dosage of LiF in Examples 7 to 9 was 0.5 parts, 1.5 parts and 5 parts respectively, the thickness of the aluminum fluoride layer was 1.8 μm, 2.7 μm and 4.3 μm respectively.

[0074] Electrolyte resistance test of passivated aluminum-plastic film

[0075] Commercial lithium hexafluorophosphate (LiPF6) electrolyte (HG / T 4067-2015) standard raw material cas.21324-40-3 was used to punch out the samples of Examples 3, 6 and 9 into a size of 151×99×95 mm in length, width and depth. After injecting the electrolyte, a 25 μm PP film was laminated to the outer surface of the passivated aluminum foil for packaging. The samples were then placed in a sealed can to prevent moisture from entering. The effect of the electrolyte on the aluminum foil was accelerated at an ambient temperature of 80°C, and the effect of the electrolyte on the aluminum-plastic film was tested. The results are shown in Table 1.

[0076] Table 1 Electrolyte resistance of aluminum-plastic film after passivation

[0077]

[0078] As can be seen from Table 1, after the aluminum foil was passivated with the materials of the three examples above, the high temperature accelerated test using commercial lithium hexafluorophosphate had little effect on it. Regardless of whether the thermal or dry manufacturing process was used, after the CPP was corroded by the electrolyte, the aluminum foil was still resistant to electrolyte corrosion. F was found in the ZnF2 of Example 3. - The effect on it is relatively slow, because Al-Zn can form a relatively stable structure, so that F - The binding of ions to Al is affected.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A passivation method for aluminum foil, comprising the following steps: A) mixing a fluoride, water and an aqueous polyurethane to obtain a coating solution; The fluoride is one or more of NH4F, LiF and ZnF2; In parts by weight, the waterborne polyurethane is 100 parts, the fluoride is 0.1 to 10 parts, and the water is 50 to 80 parts; B) applying the coating liquid on the support, drying to form a coating, and then aging at 30 to 50° C. for 60 to 80 hours to form a coating; C) contacting the coating with an aluminum foil and performing a passivation treatment at 40 to 60° C. for 150 to 180 hours to form an aluminum fluoride layer on the surface of the aluminum foil, thereby obtaining a passivated aluminum foil; The ambient humidity of the passivation treatment is 30-50%.

2. The passivation method according to claim 1, characterized in that The carrier is a polyester film, and the thickness of the polyester film is 50 to 200 μm.

3. The passivation method according to claim 2, characterized in that The thickness of the coating is 1 to 5 μm.

4. The passivation method according to claim 1, characterized in that The coating is dried at a temperature of 80-95°C.

5. The passivation method according to claim 1, characterized in that: The composite coated carrier and the aluminum foil are rolled together using a rewinding machine so that the coating is in contact with the aluminum foil.

6. A passivation method for aluminum-plastic film, characterized in that: The aluminum foil is passivated according to the passivation method according to any one of claims 1 to 5 and then compounded with a nylon layer and a polypropylene layer to obtain a passivated aluminum-plastic film.

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