Method for chromium-free passivation of lithium battery copper foil

Abstract

Disclosed in the present invention is a method for chromium-free passivation of a lithium battery copper foil. The method comprises the following specific steps: step 1: first, stripping a lithium battery copper foil from a cathode roller and allowing the lithium battery copper foil to enter a passivation tank via a transition roller; step 2: adding chromium-free passivation liquid in the passivation tank; step 3: impregnating the lithium battery copper foil in the passivation tank and applying a cathode passivation current; step 4: passing the lithium battery copper foil through a liquid squeezing roller to evenly squeeze the passivation liquid on the surface of the foil, and then, blow-drying the liquid on the surface of the foil by means of an air-drying device; and step 5: finally drying the lithium battery copper foil in a drying oven, winding the lithium battery copper foil onto a winding roller to form a finished lithium battery foil, and warehousing after passing inspection and testing. The rigidity of a passivation film is improved while the compactness of the passivation film is improved, durability and stability problems of the lithium battery copper foil during long-term storage after passivation are solved, local color change abnormity caused upon the baking of the passivated copper foil is improved, the problem that the surface of the foil is sticky when the lithium battery copper foil is passivated is solved, and the odor problem in a copper foil coil sample is solved.

Description

A method for chromium-free passivation of lithium battery copper foil

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410056957.1, filed on January 16, 2024, entitled “A method for chromium-free passivation of lithium battery copper foil”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of copper foil, in particular to a method for chromium-free passivation of lithium battery copper foil. Background Art

[0004] Achieving higher energy density, higher rate performance, and greater safety has always been a key development direction for lithium-ion batteries. As the negative electrode current collector in lithium-ion batteries, copper foil is responsible for carrying the negative electrode active material and evenly transferring current to the negative electrode material. Therefore, lithium battery copper foil must not only have high mechanical properties and strong conductivity, but also good oxidation resistance.

[0005] In the production process of electrolytic copper foil, in order to make the copper foil have antioxidant properties, surface passivation treatment is an important part of the copper foil production process. Qualified passivated copper foil not only has good antioxidant properties, but also its original surface properties will not change, which is conducive to further processing at the battery end.

[0006] The most commonly used passivation system for lithium battery copper foil is a chromium-containing passivation system. This system forms a dense protective chromium oxide film on the copper foil surface, insulating it from air and preventing oxidation. However, this method introduces chromium, which is not only present on the surface of the copper foil product but also introduced during various steps of the production process. The World Health Organization and other organizations have classified hexavalent chromium as a carcinogen. For the sake of human health and environmental protection, countries around the world have implemented strict restrictions on chromium use. Therefore, a chromium-free passivation method for lithium battery copper foil is needed, ensuring the same excellent oxidation and corrosion resistance.

[0007] Existing chromium-free passivation processes for copper materials vary, with common ones including inorganic and organic passivators. Inorganic passivators primarily utilize molybdates, tungstates, and other agents, utilizing their coordination with copper to form a passivation film. Organic passivators utilize organic groups such as heterocyclic rings in the solution to coordinate with copper to form a passivation film. However, these passivators are primarily targeted at individual components such as pipes. There are very few passivation processes specifically designed for multi-layer, wound copper foil. Furthermore, existing chromium-free passivation processes suffer from issues such as localized discoloration of the copper foil after passivation, a short antioxidant lifespan, and an odor on the foil surface.

[0008] In order to solve the problems existing in the above-mentioned technology. The present invention provides a passivating agent using a composite of organic and inorganic materials, which enables the copper foil to have strong antioxidant properties after passivation. The composite passivating agent includes four functional agents: a film-forming agent, a film-forming aid, a chelating agent, and a wetting agent. The passivation method can form a dense oxide film during the passivation process, effectively improving the antioxidant capacity of the copper foil. Compared with the existing technology, the new method has the advantages of being environmentally friendly, having strong corrosion resistance and high durability. In addition, the present invention also proposes a comprehensive set of detection methods for detecting the antioxidant and corrosion resistance of lithium battery copper foil after chromium-free passivation.

[0009] Summary of the Invention

[0010] The object of the present invention is to provide a method for chromium-free passivation of lithium battery copper foil. The specific steps of the method for chromium-free passivation of lithium battery copper foil are as follows:

[0011] Step 1: First, peel the lithium battery copper foil from the cathode roller, pass through the transition roller, and enter the passivation tank;

[0012] Step 2: Add chromium-free passivation solution into the passivation tank;

[0013] Step 3: Immerse the lithium battery copper foil in a passivation tank and apply a cathode passivation current;

[0014] Step 4: After the lithium battery copper foil passes through the liquid squeezing roller to squeeze the passivation liquid on the foil surface evenly, it passes through the air drying device to dry the liquid on the foil surface;

[0015] Step 5: The lithium battery copper foil is finally dried in an oven and wound onto a winding roller to become the finished lithium battery foil. It is then put into storage after passing inspection and testing.

[0016] Preferably, the chromium-free passivation passivator is a passivation agent aqueous solution prepared by adding a passivation agent of an organic and inorganic complex and pure water. The passivation agent includes four functional agents: a film-forming agent, a film-forming aid, a chelating agent, and a wetting agent. This passivation method can form a dense oxide film during the passivation process, thereby improving the oxidation resistance of the copper foil.

[0017] The film-forming agent mainly uses benzotriazole or methylbenzotriazole with a concentration of 3-10g / L, which can form a coordination bond with copper atoms to form a protective film on the surface of the copper foil, so that the copper foil is not oxidized by oxygen in the air. The film-forming agent in the passivator also includes one or more of molybdate, tungstate or silicate, and its preparation concentration is 1-5g / L;

[0018] The film-forming agent in the passivation agent is an inorganic phosphate with a concentration of 1-3g / L;

[0019] The chelating agent is an organic acid, specifically one or more of benzoic acid, oxalic acid, tannic acid, tartaric acid or citric acid, with a concentration of 5-10 ml / L;

[0020] The wetting agent is one or a combination of sodium dodecylsulfonate or hexadecyltrimethylammonium bromide. In order to ensure that the passivation solution is in full contact with the copper foil, the concentration is prepared to be 0.5-1g / L.

[0021] Preferably, the passivation agent aqueous solution is prepared by adding a composite passivation agent including four functional agents, namely, a film former, a film-forming aid, a chelating agent, and a wetting agent, into pure water, and controlling the pH of the passivation agent to be between 3 and 5 by adding sodium hydroxide solution.

[0022] Preferably, two or more submersible rollers are installed in the passivation tank to fully immerse the copper foil in the passivator.

[0023] Preferably, in the passivation tank, an anode plate is installed on each of the smooth and matte surfaces close to the lithium battery copper foil, so that the chromium-free passivation solution can form a firm oxide film on the smooth and matte surfaces of the lithium battery copper foil through the passivation current.

[0024] Preferably, when passivating the anode plate in the passivation tank, the passivation current applied near the smooth surface of the lithium battery copper foil is 3-8A, and the passivation current applied near the rough surface of the lithium battery copper foil is 5-10A.

[0025] Preferably, the outlet of the passivation tank is designed with a liquid squeezing roller to squeeze out excess passivation liquid on the surface of the copper foil.

[0026] Preferably, the passivation air-drying device is a device installed at the rear end of the passivation tank, which uses an air knife to air-dry the smooth and rough surfaces of the copper foil.

[0027] Preferably, the heating oven is composed of multiple heating resistance wires, which are installed at the front end of the lithium battery copper foil roll. Combined with air knife and electric heat energy, the surface of the copper foil is dried to prevent discoloration, adhesion and odor problems caused by insufficient surface drying of the copper foil.

[0028] Preferably, the heating oven can be set to a baking temperature of 100-150° C. to accelerate the drying of the copper foil surface.

[0029] Preferably, the inspection test includes the appearance inspection of the passivation film of the lithium battery copper foil, the surface wettability test of the lithium battery copper foil, the anti-oxidation test of the lithium battery copper foil in a constant temperature and humidity environment, and the corrosion resistance test of the lithium battery copper foil in a salt spray environment;

[0030] The appearance inspection of the passivation film of lithium battery copper foil is to put the lithium battery copper foil roll that has been passivated with a chromium-free passivator into a blast drying oven and bake it at a temperature of 60-100℃ for 20-30 hours. After baking, the foil surface of the lithium battery copper foil roll should not change color, the surface should not be sticky, and the passivation film should not have any odor.

[0031] After the lithium battery copper foil is passivated with a chromium-free passivator, the surface wettability test method is to use an optical water drop angle tester to drop water onto the passivation film of the lithium battery copper foil. The test contact angle must reach the range of 40-60 degrees.

[0032] After the lithium battery copper foil is passivated with a chromium-free passivator, the anti-oxidation test method in a constant temperature and humidity environment is to place the A4 sample of copper foil in a constant temperature and humidity test chamber, set the temperature at 40-60°C, set the humidity at 90%-95%, and let it stand for 24 hours. The surface of the copper foil sample must be free of oxidation points and corrosion points;

[0033] After the lithium battery copper foil is passivated with a chromium-free passivator, the corrosion resistance test method in a salt spray environment is to place the chromium-free passivated lithium battery copper foil roll sample in a salt spray test chamber, and use a salt spray tester to spray sodium chloride solution in a mist form onto the copper foil surface. The salt spray concentration is 5%-10%, the test machine temperature is 30-50℃, and the test time is 72 hours. After the test is completed, the lithium battery copper foil roll is taken out for observation. Its surface must be free of discoloration, oxidation points, and corrosion points.

[0034] Compared with the existing technology, the present invention has the following beneficial effects: the present invention adds nitrogen-containing heterocyclic benzotriazole or methylbenzotriazole to a molybdate-silicate compound as a film-forming agent for the initial film formation of the copper foil, and then adds phosphate as a film-forming aid, thereby improving the density of the passivation film while also improving the rigidity of the passivation film. This solves the durability and stability issues of long-term storage of lithium battery copper foil after passivation, improves the local discoloration abnormalities that occur when the copper foil is baked after passivation, and solves the problem of stickiness on the foil surface after passivation of lithium battery copper foil and the odor problem of copper foil rolls. Compared with conventional technologies, this technical solution mainly solves the environmental pollution problems caused by passivants and the problem of chromium on the copper foil surface.

[0035] After passivation with the passivating agent of the present invention, the copper foil for lithium batteries exhibits no discoloration after being baked in a constant temperature oven at 180°C for 15 minutes. After being placed in a 5% salt spray mist according to national standards for 72 hours, the copper foil exhibits normal surface properties, good wettability, and good conductivity. The passivated copper foil can be used normally in the lithium-ion battery field. The chromium-free passivating agent for lithium battery copper foil of the present invention does not use toxic substances such as chromium and arsenic, resulting in a simple passivation process. The passivation agent byproducts are environmentally friendly, and the passivation cost is low, contributing to sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic diagram of the chromium-free passivation process for lithium battery copper foil.

[0037] In the figure: 1. Anode tank; 2. Cathode roller; 3. Lithium battery copper foil; 4. Stripping roller; 5. Transition roller; 6. Passivation tank; 7. Front passivation roller; 8. Anode plate; 9. Rear passivation roller; 10. Squeeze roller; 11. Air knife; 13. Rear tension roller; 14. Winding roller. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] In order to improve the oxidation resistance of copper foil, the present invention provides a chromium-free passivating agent, a passivating solution and a chromium-free passivation method for lithium battery copper foil.

[0040] The first embodiment of the present application provides a chromium-free passivator, which includes a film-forming agent, a film-forming aid, a chelating agent and a wetting agent. The film-forming agent includes a first film-forming agent and a second film-forming agent. The first film-forming agent includes any one or more of benzotriazole and its derivatives, and the second film-forming agent includes one or more of molybdate, tungstate or silicate.

[0041] The first film-forming agent forms coordination bonds with copper atoms, forming a protective film on the surface of the copper foil, protecting it from oxidation by oxygen in the air. The second film-forming agent can then form a corresponding oxide, filling the gaps formed by the combination of benzotriazole and Cu, making the film denser. Therefore, the passivating agent of the present application is not only environmentally friendly, but also has a strong corrosion resistance and high durability due to the oxide layer it forms on the surface of the copper foil.

[0042] In some embodiments, the first film-forming agent includes benzotriazole and / or methylbenzotriazole, and the weight portion of the first film-forming agent is preferably 3-10 parts; the weight portion of the second film-forming agent is preferably 1-5 parts.

[0043] In some embodiments, the chromium-free passivation agent satisfies any one or more of the following conditions: the film-forming agent includes an inorganic phosphate, preferably the weight portion of the inorganic phosphate is 1-3 parts; the chelating agent includes an organic acid, preferably the organic acid includes one or more of benzoic acid, oxalic acid, tannic acid, tartaric acid or citric acid, preferably the weight portion of the chelating agent is 5-10 parts, preferably 5-7 parts; the wetting agent includes one or both of sodium lauryl sulfate or hexadecyltrimethylammonium bromide; preferably the weight portion of the wetting agent is 0.5-1 part.

[0044] The wetting agent can make various reagents evenly dispersed in the passivation solution, so that the passivation layer formed on the foil surface is uniform; the active groups in the chelating agent can combine with Cu to form a strong adsorption layer and enhance the oxidation resistance; the auxiliary film-forming agent can form corresponding oxides and fill the gaps formed by the combination of benzotriazole and Cu, making the film denser.

[0045] The second embodiment of the present application provides a passivation solution, including a passivator, a solvent and an acid-base regulator. The passivator is any one of the chromium-free passivators provided in the first embodiment. The pH value of the passivation solution is preferably 3-5.

[0046] The first film-forming agent in the passivation agent forms a coordination bond with copper atoms, forming a protective film on the surface of the copper foil, which protects the copper foil from oxidation by oxygen in the air. The second film-forming agent can then form a corresponding oxide, which fills the gaps formed by the combination of benzotriazole and Cu, making the film more dense. Therefore, the passivation solution of the present application is not only environmentally friendly, but also the oxide layer formed has strong corrosion resistance and high durability.

[0047] In some embodiments, the pH of the passivating agent is controlled by adding sodium hydroxide solution.

[0048] In some embodiments, in order to improve the effects of each component and the effect of mutual cooperation, it is preferred that in the passivation solution, the concentration of the first film-forming agent is 3g / L-10g / L, preferably 5g / L-6g / L; the concentration of the second film-forming agent is 1g / L-5g / L (it should be noted that when there are two or more second film-forming agents, the above-mentioned concentration of 1g / L-5g / L is the concentration of each second film-forming agent); the concentration of the co-film-forming agent is 1g / L-3g / L; the concentration of the chelating agent is 5ml / L-10ml / L, preferably 5ml / L-7ml / L; the concentration of the wetting agent is 0.5g / L-1g / L.

[0049] A second embodiment of the present application further provides a method for chromium-free passivation of copper foil, the method comprising:

[0050] The copper foil is subjected to surface electrodeposition passivation treatment in a passivation solution to obtain a copper foil with an oxide film on the surface. The passivation solution is any one of the passivation solutions provided in the second embodiment above. The passivation solution in the copper foil with the passivation layer on the surface is removed.

[0051] The above method of the present application is not only environmentally friendly, but also the formed oxide layer has strong corrosion resistance and high durability.

[0052] In some embodiments, the process of performing a surface passivation treatment on the copper foil in a passivation solution includes:

[0053] Immerse the copper foil in the passivation solution as a cathode; set an anode plate near the smooth and matte surfaces of the copper foil; apply a passivation current to form an oxide film on the smooth and matte surfaces of the copper foil; preferably, a passivation current of 3A-8A is used to form a passivation film on the smooth surface of the copper foil; preferably, a passivation current of 5A-10A is used to form a passivation film on the matte surface of the copper foil.

[0054] Since the smooth surface of the copper foil is affected by the surface morphology of the cathode roller and has a relatively high roughness, while the matte surface of the copper foil belongs to the crystal growth surface and has a relatively low roughness, different passivation currents are set to improve the consistency of the passivation film on the smooth and matte surface.

[0055] In some embodiments, in order to better prevent oxidation of the copper foil, the copper foil production process and the passivation process are implemented continuously, and the copper foil comes from the copper foil peeled off the anode roller in the copper foil electroplating process.

[0056] In some embodiments, copper foil stripped from the anode roller in the copper foil electroplating process is fed into a passivation tank via a transition roller. Preferably, the passivation tank is equipped with two or more submerged rollers to fully immerse the copper foil in the passivation agent. Preferably, a squeeze roller is provided at the outlet of the passivation tank to remove excess passivation solution from the copper foil surface. The foil surface is then dried using an air drying device. Preferably, the air drying device is installed at the rear end of the passivation tank and uses air knives to dry both the smooth and matte surfaces of the copper foil.

[0057] After drying, the copper foil is preferably dried in an oven. The heating oven for drying is preferably composed of multiple heating resistance wires, which are installed at the front end of the lithium battery copper foil reel. The air knife and electric heat energy are combined to dry the surface of the copper foil to prevent discoloration, adhesion and odor problems caused by insufficient surface drying of the copper foil.

[0058] In some embodiments, the heating oven may be set to a baking temperature of 100-150° C. to accelerate the drying of the copper foil surface.

[0059] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0060] Example 1: Prepare 200 L of passivating agent, wherein benzotriazole is prepared at a concentration of 3 g / L, sodium molybdate is prepared at a concentration of 1 g / L, sodium silicate is prepared at a concentration of 1 g / L, sodium phosphate is prepared at a concentration of 1 g / L, and citric acid is prepared at a concentration of 5 ml / L. After preparation, stir with a stirrer for 10 minutes, and after the solvent is fully dissolved, introduce it into the passivation tank.

[0061] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the foil enters a passivation tank. A passivation current of 5A is applied to the shiny side of the foil, and 8A to the matte side. After exiting the passivation tank, the foil passes through a squeezing roller to evenly squeeze the passivation solution onto the foil surface. Air knives blow the surface dry, and the passivation film on the foil surface is dried in a heating oven set at 120°C. After passing through the oven, the foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0062] According to this embodiment, 500 meters of copper foil were produced, placed in an oven and baked at 80°C for 24 hours, and then relevant tests and verifications were carried out. The first step was to observe the discoloration of the lithium battery copper foil after baking at 80°C for 24 hours, the viscosity of the foil surface, and whether the passivation film had any odor. The second step was to take an A4 sample of lithium battery copper foil and bake it at 140°C for 15 minutes to observe the discoloration of the foil surface. The third step was to take the sample after chromium-free passivation and test the surface contact angle. The fourth step was to place the A4 sample of copper foil in a constant temperature and humidity test chamber, set the temperature at 60°C and the humidity at 95%, and let it stand for 24 hours to observe the oxidation points and corrosion points on the surface of the copper foil sample. The fifth step was to place the roll sample of chromium-free passivated lithium battery copper foil in a testing machine, use 10% salt water, and use a spray test machine to spray sodium chloride solution on the copper foil surface in a mist form. The testing machine temperature was set to 40°C and the test time was 72 hours. The oxidation points and corrosion points on the surface of the copper foil sample were observed.

[0063] Example 2: 200L of passivating agent was prepared, wherein benzotriazole was prepared at a concentration of 10g / L, sodium molybdate was prepared at a concentration of 5g / L, sodium silicate was prepared at a concentration of 2g / L, sodium phosphate was prepared at a concentration of 3g / L, citric acid was prepared at a concentration of 10ml / L, and sodium laurylsulfonate was prepared at a concentration of 1g / L. After preparation, the mixture was stirred with a stirrer for 10 minutes, and the mixture was introduced into a passivating tank after the solvent was fully dissolved.

[0064] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the foil enters a passivation tank. A passivation current of 5A is applied to the shiny side of the foil, and 8A to the matte side. After exiting the passivation tank, the foil passes through a squeezing roller to evenly squeeze the passivation solution onto the foil surface. Air knives blow the surface dry, and the passivation film on the foil surface is dried in a heating oven set at 120°C. After passing through the oven, the foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0065] According to this embodiment, 500 meters of copper foil were produced, placed in an oven and baked at 80°C for 24 hours, and then relevant tests and verifications were carried out. The first step was to observe the discoloration of the lithium battery copper foil after baking at 80°C for 24 hours, the viscosity of the foil surface, and whether the passivation film had any odor. The second step was to take an A4-sized lithium battery copper foil and bake it at 140°C for 15 minutes to observe the discoloration of the foil surface. The third step was to take a sample after chromium-free passivation and test the surface wetting angle. The fourth step was to place the A4-sized copper foil in a constant temperature and humidity test chamber, set the temperature at 60°C and the humidity at 95%, and let it stand for 24 hours to observe the oxidation points and corrosion points on the surface of the copper foil sample. The fifth step was to place a roll of chromium-free passivated lithium battery copper foil in a testing machine, use a 10% concentration of salt water, and use a spray test machine to spray sodium chloride solution onto the copper foil surface in a mist form. The test chamber temperature was set to 40°C and the test time was 72 hours. The oxidation points and corrosion points on the surface of the copper foil sample were observed.

[0066] Embodiment 3: prepare 200L of passivating agent, wherein benzotriazole is prepared according to the concentration of 5g / L, sodium molybdate is prepared according to the concentration of 5g / L, sodium silicate is prepared according to the concentration of 2g / L, sodium phosphate is prepared according to the concentration of 2g / L, citric acid is prepared according to the concentration of 5ml / L, and sodium lauryl sulfate is prepared according to the concentration of 1g / L. Stir with a stirrer for 10 minutes after preparation, and import into the passivating tank after the solvent fully dissolves. In the passivating tank, add a certain amount of sodium hydroxide solution, and the pH value of the passivating agent is adjusted to 3.5.

[0067] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the foil enters a passivation tank. A passivation current of 5A is applied to the shiny side of the foil, and 8A to the matte side. After exiting the passivation tank, the foil passes through a squeezing roller to evenly squeeze the passivation solution onto the foil surface. Air knives blow the surface dry, and the passivation film on the foil surface is dried in a heating oven set at 120°C. After passing through the oven, the foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0068] According to this embodiment, 500 meters of copper foil were produced, placed in an oven and baked at 80°C for 24 hours, and then relevant tests and verifications were carried out. The first step was to observe the discoloration of the lithium battery copper foil after baking at 80°C for 24 hours, the viscosity of the foil surface, and whether the passivation film had any odor. The second step was to take an A4-sized lithium battery copper foil and bake it at 140°C for 15 minutes to observe the discoloration of the foil surface. The third step was to take a sample after chromium-free passivation and test the surface wetting angle. The fourth step was to place the A4-sized copper foil in a constant temperature and humidity test chamber, set the temperature at 60°C and the humidity at 95%, and let it stand for 24 hours to observe the oxidation points and corrosion points on the surface of the copper foil sample. The fifth step was to place a roll of chromium-free passivated lithium battery copper foil in a testing machine, use a 10% concentration of salt water, and use a spray test machine to spray sodium chloride solution onto the copper foil surface in a mist form. The test chamber temperature was set to 40°C and the test time was 72 hours. The oxidation points and corrosion points on the surface of the copper foil sample were observed.

[0069] Embodiment 4: prepare the passivating agent of 200L, wherein benzotriazole is prepared according to the concentration of 6g / L, sodium molybdate is prepared according to the concentration of 3g / L, sodium silicate is prepared according to the concentration of 2g / L, sodium phosphate is prepared according to the concentration of 1g / L, citric acid is prepared according to the concentration of 7ml / L, and sodium lauryl sulfate is prepared according to the concentration of 1g / L. Stir with a stirrer for 10 minutes after preparation, and import into the passivating tank after the solvent fully dissolves. In the passivating tank, add a certain amount of sodium hydroxide solution, and the passivating agent pH value is adjusted to 3.5.

[0070] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the foil enters a passivation tank. A passivation current of 5A is applied to the shiny side of the foil, and 8A to the matte side. After exiting the passivation tank, the foil passes through a squeezing roller to evenly squeeze the passivation solution onto the foil surface. Air knives blow the surface dry, and the passivation film on the foil surface is dried in a heating oven set at 120°C. After passing through the oven, the foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0071] According to this embodiment, 500 meters of copper foil were produced, placed in an oven and baked at 80°C for 24 hours, and then relevant tests and verifications were carried out. The first step was to observe the discoloration of the lithium battery copper foil after baking at 80°C for 24 hours, the viscosity of the foil surface, and whether the passivation film had any odor. The second step was to take an A4-sized lithium battery copper foil and bake it at 140°C for 15 minutes to observe the discoloration of the foil surface. The third step was to take a sample after chromium-free passivation and test the surface wetting angle. The fourth step was to place the A4-sized copper foil in a constant temperature and humidity test chamber, set the temperature at 60°C and the humidity at 95%, and let it stand for 24 hours to observe the oxidation points and corrosion points on the surface of the copper foil sample. The fifth step was to place a roll of chromium-free passivated lithium battery copper foil in a testing machine, use a 10% concentration of salt water, and use a spray test machine to spray sodium chloride solution onto the copper foil surface in a mist form. The test chamber temperature was set to 40°C and the test time was 72 hours. The oxidation points and corrosion points on the surface of the copper foil sample were observed.

[0072] Embodiment 5: prepare 200L of passivating agent, wherein benzotriazole is prepared according to the concentration of 6g / L, sodium molybdate is prepared according to the concentration of 4g / L, sodium silicate is prepared according to the concentration of 2g / L, sodium phosphate is prepared according to the concentration of 1g / L, citric acid is prepared according to the concentration of 6.5ml / L, and sodium lauryl sulfate is prepared according to the concentration of 2g / L. Stir with a stirrer for 10 minutes after preparation, and introduce into the passivating tank after the solvent fully dissolves. A certain amount of sodium hydroxide solution is added to the passivating tank, and the pH value of the passivating agent is adjusted to 3.5.

[0073] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the foil enters a passivation tank. A passivation current of 5A is applied to the shiny side of the foil, and 8A to the matte side. After exiting the passivation tank, the foil passes through a squeezing roller to evenly squeeze the passivation solution onto the foil surface. Air knives blow the surface dry, and the passivation film on the foil surface is dried in a heating oven set at 120°C. After passing through the oven, the foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0074] According to this embodiment, 500 meters of copper foil were produced, placed in an oven and baked at 80°C for 24 hours, and then relevant tests and verifications were carried out. The first step was to observe the discoloration of the lithium battery copper foil after baking at 80°C for 24 hours, the viscosity of the foil surface, and whether the passivation film had any odor. The second step was to take an A4-sized lithium battery copper foil and bake it at 140°C for 15 minutes to observe the discoloration of the foil surface. The third step was to take a sample after chromium-free passivation and test the surface wetting angle. The fourth step was to place the A4-sized copper foil in a constant temperature and humidity test chamber, set the temperature at 60°C and the humidity at 95%, and let it stand for 24 hours to observe the oxidation points and corrosion points on the surface of the copper foil sample. The fifth step was to place a roll of chromium-free passivated lithium battery copper foil in a testing machine, use a 10% concentration of salt water, and use a spray test machine to spray sodium chloride solution onto the copper foil surface in a mist form. The test chamber temperature was set to 40°C and the test time was 72 hours. The oxidation points and corrosion points on the surface of the copper foil sample were observed.

[0075] Comparative Example 1: Prepare 200 L of passivating agent, wherein benzotriazole is prepared at a concentration of 3 g / L, sodium molybdate is prepared at a concentration of 1 g / L, sodium silicate is prepared at a concentration of 1 g / L, and sodium phosphate is prepared at a concentration of 1 g / L. After preparation, stir with a stirrer for 10 minutes, and introduce the solvent into the passivation tank after it is fully dissolved.

[0076] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the copper foil enters the passivation tank. After exiting the passivation tank, it passes through a squeeze roller to evenly squeeze the passivation liquid onto the foil surface. Air knives blow the passivation liquid onto the surface, and then the passivation film on the foil surface is dried in a heated oven set at 120°C. After passing through the oven, the copper foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0077] According to this embodiment, 500 meters of copper foil were produced, placed in an oven and baked at 80°C for 24 hours, and then relevant tests and verifications were carried out. The first step was to observe the discoloration of the lithium battery copper foil after baking at 80°C for 24 hours, the viscosity of the foil surface, and whether the passivation film had any odor. The second step was to take an A4-sized lithium battery copper foil and bake it at 140°C for 15 minutes to observe the discoloration of the foil surface. The third step was to take a sample after chromium-free passivation and test the surface wetting angle. The fourth step was to place the A4-sized copper foil in a constant temperature and humidity test chamber, set the temperature at 60°C and the humidity at 95%, and let it stand for 24 hours to observe the oxidation points and corrosion points on the surface of the copper foil sample. The fifth step was to place a roll of chromium-free passivated lithium battery copper foil in a testing machine, use a 10% concentration of salt water, and use a spray test machine to spray sodium chloride solution onto the copper foil surface in a mist form. The test chamber temperature was set to 40°C and the test time was 72 hours. The oxidation points and corrosion points on the surface of the copper foil sample were observed.

[0078] Comparative Example 2: Prepare 200 L of passivating agent, wherein benzotriazole is prepared at a concentration of 3 g / L, sodium molybdate is prepared at a concentration of 1 g / L, sodium silicate is prepared at a concentration of 1 g / L, sodium phosphate is prepared at a concentration of 1 g / L, and citric acid is prepared at a concentration of 5 ml / L. After preparation, stir with a stirrer for 10 minutes, and after the solvent is fully dissolved, introduce it into the passivation tank.

[0079] 6μm lithium battery copper foil is produced at a line speed of 10m / min. After being peeled from the cathode roller, the foil enters a passivation tank. A passivation current of 5A is applied to the shiny side of the foil, and 8A to the matte side. After exiting the passivation tank, the foil passes through a squeezing roller to evenly squeeze the passivation solution onto the foil surface. Air knives blow the surface dry, and the passivation film on the foil surface is dried in a heating oven set at 120°C. After passing through the oven, the foil is wound onto a take-up reel to form a semi-finished lithium battery foil roll.

[0080] According to this embodiment, 500 meters of copper foil were produced and baked in an oven at 80°C for 24 hours, followed by relevant testing and verification. The first step was to observe the discoloration of the lithium battery copper foil, the viscosity of the foil surface, and the presence of odor in the passivation film after baking at 80°C for 24 hours. The second step was to bake an A4-sized lithium battery copper foil at 140°C for 15 minutes and observe the discoloration of the foil surface. The third step was to test the surface wetting angle of the chromium-free passivated sample. The fourth step was to place the A4-sized copper foil in a constant temperature and humidity test chamber at 60°C and 95% humidity for 24 hours, and observe the oxidation and corrosion points on the copper foil surface. The fifth step was to place the chromium-free passivated lithium battery copper foil roll sample in a testing machine, and use a spray test machine to spray a sodium chloride solution with a 10% concentration of salt water onto the copper foil surface in a mist form. The test chamber temperature was set to 40°C and the test time was 72 hours. The oxidation and corrosion points on the copper foil surface were observed.

[0081] Table 1: Summary of implementation results

[0082] In summary, the technical solution of the present invention, by using the aforementioned chromium-free passivating agent to form a chromium-free passivation film on the surface of lithium battery copper foil, provides the lithium battery copper foil with antioxidant properties. Furthermore, the effectiveness of the passivation film can be tested using the chromium-free passivation film effectiveness testing method.

[0083] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for chromium-free passivation of lithium-ion copper foil, characterized in that: The specific steps of the method for chromium-free passivation of lithium battery copper foil are as follows: Step 1: First, peel the lithium battery copper foil from the cathode roller, pass it through the transition roller, and enter the passivation tank; Step 2: Add a chromium-free passivation solution to the passivation tank; Step 3: Immerse the lithium battery copper foil in the passivation tank and apply a cathodic passivation current; Step 4: After the lithium battery copper foil squeezes the passivation solution on the foil surface evenly through the squeezing roller, dry the liquid on the foil surface through the air drying device; Step 5: Finally, the lithium battery copper foil is dried in the oven and wound onto the winding roller to become a finished lithium battery foil, and is stored in the warehouse after passing the inspection and testing.

2. The method for chromium-free passivation of lithium copper foil according to claim 1, characterized in that: The passivating agent for chromium-free passivation is a passivating agent aqueous solution prepared by compounding an organic and inorganic ligand passivating agent with pure water. The passivating agent includes four functional agents: a film-forming agent, a film-forming aid, a chelating agent, and a wetting agent. This passivation method can form a dense oxide film during the passivation process to improve the antioxidant property of the copper foil; For the film-forming agent, benzotriazole or methylbenzotriazole with a concentration of 3 - 10 g / L is mainly used. It can form a coordination bond with copper atoms and form a protective film on the surface of the copper foil to prevent the copper foil from being oxidized by oxygen in the air. The film-forming agent in the passivating agent also includes one or more of molybdate, tungstate, or silicate, and its preparation concentration is 1 - 5 g / L; The film-forming aid in the passivating agent is an inorganic phosphate with a concentration of 1 - 3 g / L; The chelating agent is an organic acid, specifically one or more of benzoic acid, oxalic acid, tannic acid, tartaric acid, or citric acid, and its concentration is 5 - 10 ml / L; The wetting agent is one or a combination of two of sodium dodecyl sulfonate or cetyltrimethylammonium bromide, and is formulated into a concentration of 0.5 - 1 g / L to ensure full contact between the passivation solution and the copper foil.

3. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: The passivating agent aqueous solution is prepared by adding the compound ligand passivating agent including four functional agents: a film-forming agent, a film-forming aid, a chelating agent, and a wetting agent to pure water, and controlling the pH of the passivating agent to be between 3 - 5 by adding sodium hydroxide solution.

4. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: Two or more submerged rollers are installed in the passivation tank to ensure that the copper foil is fully immersed in the passivating agent.

5. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: In the passivation tank, an anode plate is installed near the smooth surface and the matte surface of the lithium battery copper foil, so that the chromium-free passivation solution can form a firm oxide film on the smooth and matte surfaces of the lithium battery copper foil through the passivation current.

6. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: For the passivation anode plate in the passivation tank, the passivation current applied near the smooth surface of the lithium battery copper foil is 3 - 8 A, and the passivation current applied near the matte surface of the lithium battery copper foil is 5 - 10 A.

7. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: A squeezing roller is designed at the outlet of the passivation tank to squeeze off the excess passivation solution on the surface of the copper foil.

8. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: The passivation air drying device is a device installed at the rear end of the passivation tank, which dries the smooth and matte surfaces of the copper foil through an air knife.

9. A method for chromium-free passivation of lithium-ion copper foil according to claim 2, characterized in that: The heating oven is composed of multiple heating resistance wires and is installed at the front end of the winding of the lithium battery copper foil. Combining the air knife and electric heat energy, it dries the surface of the copper foil to prevent problems such as discoloration, adhesion, and peculiar smell caused by insufficient surface drying of the copper foil. The baking temperature of the heating oven can be set at 100 - 150 °C to accelerate the drying of the copper foil surface.

10. A method for chromium-free passivation of lithium-ion copper foil according to claim 1, characterized in that: The inspection tests in Step 5 include the appearance inspection of the passivation film of the lithium copper foil, the wettability test of the lithium copper foil surface, the antioxidant test of the lithium copper foil in a constant temperature and humidity environment, and the corrosion resistance test of the lithium copper foil in a salt spray environment; For the appearance inspection of the passivation film of the lithium copper foil, the lithium copper foil roll passivated with the chromium-free passivating agent is placed in a forced air drying oven, the baking temperature is 60 - 100 °C, the baking time is 20 - 30 hours. After baking, the foil surface of the lithium copper foil roll shall not change color, the surface shall not be sticky, and the passivation film shall not have any peculiar smell; After the lithium copper foil is passivated with the chromium-free passivating agent, the method for the wettability test of the surface is to use an optical water contact angle tester. Drop water onto the passivation film of the lithium copper foil, and the measured contact angle shall reach the range of 40 - 60 degrees; After the lithium copper foil is passivated with the chromium-free passivating agent, the method for the antioxidant test in a constant temperature and humidity environment is to place the copper foil of A4 size in a constant temperature and humidity test chamber, set the temperature at 40 - 60 °C, set the humidity at 90% - 95%, and let it stand for 24 hours. There shall be no oxidation points and corrosion points on the surface of the copper foil sample; After the lithium copper foil is passivated with the chromium-free passivating agent, the method for the corrosion resistance test in a salt spray environment is to place the rolled sample of the lithium copper foil passivated with chromium-free in a salt spray test chamber, and use a salt water spray testing machine to spray the sodium chloride solution onto the copper foil surface in a mist form. The salt spray concentration is 5% - 10%, the temperature of the testing machine is 30 - 50 °C, the test time is 72 hours. After the test is completed, take out the lithium copper foil roll for observation, and its surface shall not change color, and there shall be no oxidation points and corrosion points.

11. A chromium-free passivator, the chromium-free passivator comprising a film-forming agent, a film-forming aid, a chelating agent, and a wetting agent, characterized in that, The film-forming agent includes a first film-forming agent and a second film-forming agent. The first film-forming agent includes any one or more of benzotriazole and its derivatives. The second film-forming agent includes one or more of molybdates, tungstates or silicates.

12. The chromium-free passivator according to claim 11, wherein, The first film-forming agent includes benzotriazole and / or methylbenzotriazole. Preferably, the weight part of the first film-forming agent is 3 - 10 parts; preferably, the weight part of the second film-forming agent is 1 - 5 parts.

13. The chromium-free passivator according to claim 11 or 12, characterized in that, The chromium-free passivating agent meets any one or more of the following conditions: The co-film-forming agent includes inorganic phosphate. Preferably, the weight part of the inorganic phosphate is 1 - 3 parts; The chelating agent includes organic acids. Preferably, the organic acids include one or more of benzoic acid, oxalic acid, tannic acid, tartaric acid or citric acid. Preferably, the weight part of the chelating agent is 5 - 10 parts, preferably 5 - 7 parts; The wetting agent includes one or both of sodium dodecyl sulfonate or cetyltrimethylammonium bromide; preferably, the weight part of the wetting agent is 0.5 - 1 part.

14. A passivation solution, comprising a passivating agent, a solvent, and an acid-base regulator, characterized in that, The passivating agent is the chromium-free passivating agent described in any one of claims 11 to 13. Preferably, the pH value of the passivating agent solution is 3 - 5.

15. The passivating agent solution according to claim 14, wherein In the passivating solution, the concentration of the first film-forming agent is 3 g / L - 10 g / L, preferably 5 g / L - 6 g / L; the concentration of the second film-forming agent is 1 g / L - 5 g / L; the concentration of the co-film-forming agent is 1 g / L - 3 g / L; the concentration of the chelating agent is 5 ml / L - 10 ml / L, preferably 5 ml / L - 7 ml / L; the concentration of the wetting agent is 0.5 ml / L - 1 ml / L.

16. A method for chromium-free passivation of copper foil, characterized in that, The method includes: The copper foil is subjected to surface electrodeposition passivation treatment in a passivation solution to obtain a copper foil with an oxide film on its surface, and the passivation solution is the passivation solution described in claim 14 or 15; Remove the passivation solution from the copper foil with a passivation layer on its surface.

17. The method according to claim 16, characterized in that, The process of subjecting the copper foil to surface passivation treatment in a passivation solution includes: Immerse the copper foil in the passivation solution as the cathode; An anode plate is respectively arranged at positions close to the shiny surface and the matte surface of the copper foil; Apply a passivation current to form an oxide film on the shiny surface and the matte surface of the copper foil respectively; preferably, a passivation current of 3A - 8A is used to form a passivation film on the shiny surface of the copper foil; preferably, a passivation current of 5A - 10A is used to form a passivation film on the matte surface of the copper foil.

18. The method according to claim 17, characterized in that, The copper foil is from the copper foil peeled off from the cathode roller in the electroplated copper foil process.

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