Process for producing low-residual-stress functional current collector by two-step annealing method

Abstract

The invention relates to the technical field of current collector materials, and particularly discloses a process for producing a low-residual-stress functional current collector by a two-step annealing method, which comprises the following steps of: compounding copper on the surface of a polypropylene film or a composite polypropylene film by using a magnetron sputtering technology, annealing for the first time, and thickening a copper layer by using an electroplating method; the functional current collector produced by using the two-step annealing method is low in residual stress, so that the cycle life of the battery is prolonged, the fracture risk in the use process is reduced, and the overall safety of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of current collector materials, and specifically to a process for producing a low-residual stress functional current collector by a two-step annealing method. Background Art

[0002] With the rapid development of new energy and advanced manufacturing industries, the key performance of batteries such as cycle life, safety performance, and energy density urgently needs to be improved. The current collector is a key component in the battery, which plays the role of collecting current. At the same time, the quality of the current collector directly affects technical indicators such as the cycle life, energy density, and safety of the battery.

[0003] Currently, the common positive and negative current collectors in the battery industry are mostly made of copper foil and aluminum foil. The current collector made of pure metal has high cost and quality. At the same time, its performance in battery safety is often not satisfactory. In addition, the pure metal current collector also has a high "dead weight", which is not conducive to improving the energy density of the battery. At this time, the composite conductive foil shows high advantages. The functional current collector made of the composite foil is usually a "sandwich" structure, with a polymer polymer layer in the inner layer and metal conductive layers on both sides. The metal layer on the surface of the current collector is relatively thin, and the density of the middle polymer is significantly lower than that of pure metal, so that the weight of the current collector can be well reduced, and then the energy density of the battery can be improved. When thermal runaway occurs, the functional current collector is easier to disconnect compared with the traditional current collector, thus isolating the connection between the active material and the current collector and preventing the continuous progress of battery thermal runaway.

[0004] Although the functional current collector has the advantages of low cost and high safety, during the production process of the functional current collector, various internal stresses often occur. Coupled with a large amount of heat generated during battery cycling, which causes volume changes in the functional current collector, excessive thermal shrinkage will cause large thermal deformation of the current collector, thus seriously reducing the safety and cycle life of the battery and also bringing safety problems to the battery. The functional current collector made of polypropylene material is the current major development trend, so it is necessary to develop a new process to reduce the residual stress of the functional current collector. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for producing a low-residual stress functional current collector by a two-step annealing method, so as to solve the problem of high residual stress in the production process of the functional current collector.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A process for producing a low-residual stress functional current collector by a two-step annealing method, specifically as follows:

[0008] (1) Take the current collector base film, perform magnetron sputtering on the surface to form a seed layer, and then perform annealing treatment;

[0009] (2) Hydroelectroplating is adopted to thicken the metal on the surface of the seed layer, and then annealing treatment is carried out.

[0010] As a limitation of the present invention, the specific parameters of magnetron sputtering are as follows: When magnetron sputtering, the cavity is evacuated, the vacuum degree is 4×10 -3 ~6×10 -3 Pa, the argon gas flow rate is 120~140 sccm, the cooling temperature is -20~-10 °C, and the copper target power is 11~13 KW.

[0011] As a limitation of the present invention, the annealing temperature for both annealings is 80~150 °C, the holding time for the first annealing is 1.5~2.5 h, and the holding time for the second annealing is 7~9 h.

[0012] As a limitation of the present invention, in the copper plating solution used for hydroelectroplating, the concentration of copper sulfate is 50~70 g / L, the concentration of hydrochloric acid is 40~90 mg / L, the concentration of sulfuric acid is 120~150 g / L, the additive is sodium poly(dithiopropanesulfonate), the concentration is 0.01~0.04 g / L, and the solvent is deionized water.

[0013] As a limitation of the present invention, the thickness of the copper layer obtained by hydroelectroplating is 0.9~1.5 μm.

[0014] As a limitation of the present invention, the preparation method of the composite polypropylene film is as follows:

[0015] By mass, 0.3~0.5 parts of tannic acid, 0.18~0.22 parts of sodium periodate, and 195~205 parts of tris(hydroxymethyl)aminomethane buffer solution are mixed and stirred evenly to obtain a tannic acid solution. The intercalation-modified montmorillonite composite polypropylene film is immersed in the tannic acid solution and reacted at 25~30 °C for 5~10 h. After the reaction is completed, it is dried at 50~70 °C to obtain the composite polypropylene film.

[0016] As a limitation of the present invention, the preparation method of the intercalation-modified montmorillonite composite polypropylene film is as follows:

[0017] Montmorillonite and deionized water are mixed, stirred evenly, ultrasonically dispersed, octadecyltrimethylammonium chloride is added, and the reaction is carried out at 55~65 °C for 13~17 h. After the reaction is completed, it is cooled, centrifuged, washed with deionized water, and vacuum dried at 50~70 °C to obtain organic montmorillonite. Organic montmorillonite, ethanol, and deionized water are mixed, stirred until there are no obvious particles, methyl methacrylate and azobisisobutyronitrile are added, nitrogen is introduced for replacement for 10~20 min, the reaction is carried out at 70~90 °C for 6 h, filtered by suction, and dried to obtain polymethyl methacrylate-modified montmorillonite;

[0018] Mix polymethyl methacrylate modified montmorillonite, styrene-butadiene rubber latex adhesive, sodium carboxymethyl cellulose, deionized water and ethanol, and stir evenly to obtain a coating slurry. Coat the slurry on a corona-roughened polypropylene film and dry and cure it at 50-70°C for 5-7 hours to obtain an intercalated modified montmorillonite composite polypropylene film.

[0019] As a limitation of the present invention, when preparing polymethyl methacrylate modified montmorillonite, the amounts of each component are as follows by mass: 4-6 parts of organic montmorillonite, 4.5-5.5 parts of methyl methacrylate, and 0.02-0.03 parts of azobisisobutyronitrile.

[0020] As a limitation of the present invention, when preparing polymethyl methacrylate modified montmorillonite, the mass ratio of organic montmorillonite, methyl methacrylate, and azobisisobutyronitrile is (4-6):(4.5-5.5):(0.02-0.03).

[0021] As a limitation of the present invention, when preparing the coating slurry used for the intercalated modified montmorillonite composite polypropylene film, the amounts of each component are as follows by mass: 0.05-0.15 parts of polymethyl methacrylate grafted montmorillonite, 0.2-0.4 parts of styrene-butadiene rubber latex adhesive, 0.1-0.3 parts of sodium carboxymethyl cellulose, 45-55 parts of deionized water, and 35-45 parts of ethanol.

[0022] As a limitation of the present invention, a low-residual stress functional current collector obtained by the process according to any one of the above limitations.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] Through the two-step annealing method, the present invention successfully reduces the residual stress generated by the deformation of the current collector base film during magnetron sputtering, facilitating subsequent processing. At the same time, it reduces the residual stress of the finished film after electroplating, thereby reducing the appearance of defects such as white spots, holes, and wrinkles on the film material during electroplating. When this current collector is applied to a battery, it can further improve the cycle life of the battery, reduce the risk of fracture during use, and improve the overall safety of the battery.

[0025] By coating the surface of the polypropylene film with polymethyl methacrylate intercalated modified montmorillonite, the present invention improves the mechanical properties and thermal stability of the polypropylene film, weakens the heat shrinkage of the polypropylene film, and forms a dense tannic acid coating through the hydrogen bond action between tannic acid and oxygen on the modified montmorillonite, making the surface of the composite polypropylene film more stable. In addition, tannic acid can undergo a coordination reaction with copper, and the copper deposited by magnetron sputtering can be firmly bonded to the surface of the polypropylene film to form a copper layer, which is beneficial to the further deposition of electroplated copper.

[0026] In the present invention, the surface copper layer of the current collector is passivated with an ascorbic acid solution. The oxygen atom of the hydroxyl group of ascorbic acid coordinates with copper to form a dense passivation film, enhancing the antioxidant performance of the surface copper layer of the current collector and contributing to improving the service life of the current collector. Detailed implementation manners

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] The polypropylene film (Nanyang HMP-1b type, thickness 6 μm) was purchased from the market. Montmorillonite (K-10), methyl methacrylate (M813512), tris(hydroxymethyl)aminomethane buffer solution (pH = 6.8), tannic acid (T776062), styrene-butadiene rubber latex adhesive (≥2000 mPa·S), 3-mercapto-1-propanesulfonic acid sodium salt (S817708), 2-mercaptopyridine (P914145), 2-mercaptobenzimidazole (M813614) were provided by Shanghai Macklin.

[0029] Example 1: A process for producing a low-residual-stress functional current collector by a two-step annealing method, specifically:

[0030] Step 1: Magnetron sputtering

[0031] Clean the polypropylene film and each roller system of the magnetron sputtering equipment with anhydrous ethanol. After unwinding the roll, evacuate the sputtering chamber, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15 °C, the copper target power is 12 KW, the winding speed is 8 m / min, and after magnetron sputtering is completed, wind up to obtain a magnetron film.

[0032] Step 2: Primary annealing

[0033] Heat the magnetron film in a constant-temperature drying environment in the furnace to 120 °C, keep it at 120 °C for 2 h, and then cool it to room temperature in the furnace to obtain a primary annealed film.

[0034] Step 3: Electroplating with water

[0035] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, stir evenly to obtain an electroplating solution, and thicken the copper foil of the primary annealed film by electroplating with water to obtain a composite copper foil. The rate of the primary annealed film on the electroplating line is 9 m / min, and the thickness of the obtained metal copper layer is 1 μm.

[0036] Step 4: Secondary annealing

[0037] Place the composite copper foil in a constant-temperature drying oven and heat it in the furnace to 120 °C. Keep it at 120 °C for 8 h, and then cool it in the furnace to room temperature to obtain a functional current collector with low residual stress.

[0038] Example 2: A process for producing a functional current collector with low residual stress by a two-step annealing method, specifically:

[0039] Step 1: Magnetron sputtering

[0040] Clean the polypropylene film and each roller system of the magnetron sputtering equipment with absolute ethanol. After unwinding the roll, evacuate the sputtering chamber, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15 °C, the copper target power is 12 KW, the winding speed is 8 m / min, and after magnetron sputtering is completed, wind up to obtain a magnetron film.

[0041] Step 2: Primary annealing

[0042] Heat the magnetron film in a constant-temperature drying environment in the furnace to 85 °C. Keep it at 85 °C for 2 h, and then cool it in the furnace to room temperature to obtain a primary annealed film.

[0043] Step 3: Electroplating with water

[0044] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, and stir evenly to obtain an electroplating solution. Treat the primary annealed film by electroplating with water to thicken the copper foil and obtain a composite copper foil. The rate of the primary annealed film on the electroplating line is 9 m / min, and the thickness of the obtained copper metal layer is 1 μm.

[0045] Step 4: Secondary annealing

[0046] Place the composite copper foil in a constant-temperature drying oven and heat it in the furnace to 85 °C. Keep it at 85 °C for 8 h, and then cool it in the furnace to room temperature to obtain a functional current collector with low residual stress.

[0047] Example 3: A process for producing a functional current collector with low residual stress by a two-step annealing method, specifically:

[0048] Step 1: Magnetron sputtering

[0049] Clean the polypropylene film and each roller system of the magnetron sputtering equipment with absolute ethanol. After unwinding the roll, evacuate the sputtering chamber, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15 °C, the copper target power is 12 KW, the winding speed is 8 m / min, and after magnetron sputtering is completed, wind up to obtain a magnetron film.

[0050] Step 2: Primary annealing

[0051] Heat the magnetron film in a constant-temperature drying environment in the furnace to 95 °C, hold it at 95 °C for 2 h, and then cool it in the furnace to room temperature to obtain the primary annealed film.

[0052] Step 3: Electroplating with water

[0053] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, stir evenly to obtain an electroplating solution, and thicken the copper foil of the primary annealed film by electroplating with water to obtain a composite copper foil. The speed of the primary annealed film on the electroplating line is 9 m / min, and the thickness of the obtained copper metal layer is 1 μm.

[0054] Step 4: Secondary annealing

[0055] Place the composite copper foil in a constant-temperature drying oven and heat it in the furnace to 95 °C, hold it at 95 °C for 8 h, and then cool it in the furnace to room temperature to obtain a low-residual stress functional current collector.

[0056] Example 4: A process for producing a low-residual stress functional current collector by a two-step annealing method, specifically:

[0057] Step 1: Magnetron sputtering

[0058] Clean the polypropylene film and each roller system of the magnetron sputtering equipment with anhydrous ethanol. After unwinding, evacuate the sputtering chamber, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15 °C, the copper target power is 12 KW, the winding speed is 8 m / min, and after magnetron sputtering is completed, wind it up to obtain a magnetron film.

[0059] Step 2: Primary annealing

[0060] Heat the magnetron film in a constant-temperature drying environment in the furnace to 150 °C, hold it at 150 °C for 2 h, and then cool it in the furnace to room temperature to obtain the primary annealed film.

[0061] Step 3: Electroplating with water

[0062] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, stir evenly to obtain an electroplating solution, and thicken the copper foil of the primary annealed film by electroplating with water to obtain a composite copper foil. The speed of the primary annealed film on the electroplating line is 9 m / min, and the thickness of the obtained copper metal layer is 1 μm.

[0063] Step 4: Secondary annealing

[0064] Place the composite copper foil in a constant-temperature drying oven and heat it in the furnace to 150 °C, hold it at 150 °C for 8 h, and then cool it in the furnace to room temperature to obtain a low-residual stress functional current collector.

[0065] Example 5: This example relates to the preparation of a functional current collector with low residual stress. The difference from Example 1 is only that: the polypropylene film used in the process of this comparative example is a modified composite polypropylene film, specifically:

[0066] Step 1: Magnetron sputtering

[0067] Clean the composite polypropylene film and each roller system of the magnetron sputtering equipment with absolute ethanol. After unwinding the roll, evacuate the sputtering chamber, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15°C, the power of the copper target is 12 KW, the winding speed is 8 m / min. After magnetron sputtering is completed, wind up to obtain a magnetron film.

[0068] Step 2: First annealing

[0069] Heat the magnetron film in the furnace to 120°C in a constant-temperature drying environment, keep it at 120°C for 2 h, and then cool it to room temperature with the furnace to obtain a first-annealed film.

[0070] Step 3: Electroplating with water

[0071] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, stir evenly to obtain an electroplating solution. Use the method of electroplating with water to thicken the copper foil on the first-annealed film to obtain a composite copper foil. The rate of the first-annealed film on the electroplating line is 9 m / min, and the thickness of the obtained copper metal layer is 1 μm.

[0072] Step 4: Second annealing

[0073] Place the composite copper foil in a constant-temperature drying oven and heat it to 120°C with the furnace, keep it at 120°C for 8 h, and then cool it to room temperature with the furnace to obtain a functional current collector with low residual stress.

[0074] Among them, the preparation method of the composite polypropylene film is:

[0075] Ultrasonically clean the polypropylene film in ethanol for 15 min to remove surface grease and dirt. After cleaning, rinse it with deionized water and absolute ethanol, and air-dry it at room temperature and then perform corona roughening treatment to obtain a roughened polypropylene film. The corona voltage value is 50.0 V, and the current value is 2.0 A.

[0076] By mass, 5 parts of montmorillonite and 150 parts of deionized water were mixed, stirred evenly, ultrasonically dispersed, 0.5 part of octadecyltrimethylammonium chloride was added, reacted at 60 °C for 15 h, cooled after the reaction, centrifuged, washed with deionized water, and vacuum dried at 60 °C to obtain organic montmorillonite. 5 parts of the organic montmorillonite, 64 parts of ethanol and 20 parts of deionized water were mixed, stirred until there were no obvious particles, 5 parts of methyl methacrylate and 0.025 part of azobisisobutyronitrile were added, purged with nitrogen for 15 min, reacted at 80 °C for 6 h, filtered by suction, and dried to obtain poly(methyl methacrylate)-modified montmorillonite. 0.1 part of the poly(methyl methacrylate)-modified montmorillonite, 0.3 part of styrene-butadiene rubber latex adhesive, 0.2 part of sodium carboxymethyl cellulose, 50 parts of deionized water and 40 parts of ethanol were mixed and stirred evenly to obtain a coating slurry. The slurry was coated on a roughened polypropylene film and dried and cured at 60 °C for 6 h to obtain an intercalation-modified montmorillonite composite polypropylene film.

[0077] By mass, 0.4 part of tannic acid, 0.2 part of sodium periodate and 200 parts of tris(hydroxymethyl)aminomethane buffer were mixed and stirred evenly to obtain a tannic acid solution. The intercalation-modified montmorillonite composite polypropylene film was immersed in the tannic acid solution and reacted at 27 °C for 8 h. After the reaction was completed, it was dried at 60 °C to obtain a composite polypropylene film.

[0078] The following are control experiments, specifically Comparative Example 1, Comparative Example 2 and Comparative Example 3, as described below:

[0079] Comparative Example 1: This comparative example relates to the preparation of a low-residual stress functional current collector. The difference from Example 1 is only that: annealing treatment is not carried out in the process of this comparative example. Specifically:

[0080] Step 1: Magnetron sputtering

[0081] The polypropylene film and each roller system of the magnetron sputtering equipment were cleaned with absolute ethanol. After unwinding, the sputtering chamber was evacuated, and the base vacuum of the magnetron sputtering was controlled to be 5×10 -3 Pa, the argon flow rate was 130 sccm, the cooling temperature of the sputtering main roller was -15 °C, the copper target power was 12 KW, the winding speed was 8 m / min, and after magnetron sputtering was completed, it was wound up to obtain a magnetron film.

[0082] Step 2: Electroplating

[0083] Copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water were mixed and stirred evenly to obtain an electroplating solution. The magnetron film was thickened with copper foil by electroplating to obtain a low-residual stress functional current collector. The rate of the primary annealed film on the electroplating line was 9 m / min, and the thickness of the obtained copper metal layer was 1 μm.

[0084] Comparative Example 2: This comparative example relates to the preparation of a low residual stress functional current collector. The difference from Example 5 is only that: in the process of this comparative example, annealing process treatment is only carried out after the magnetron sputtering step, and annealing is not carried out after the electroplating process. Specifically:

[0085] Step 1: Magnetron sputtering

[0086] Clean the polypropylene film and each roller system of the magnetron sputtering equipment with absolute ethanol. After unwinding, evacuate the sputtering cavity, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15°C, the copper target power is 12 KW, the winding speed is 8 m / min, and after magnetron sputtering is completed, wind up to obtain a magnetron film.

[0087] Step 2: First annealing

[0088] Heat the magnetron film in a constant temperature drying environment in the furnace to 120°C, keep it at 120°C for 2 h, and then cool it to room temperature in the furnace to obtain a first annealed film.

[0089] Step 3: Electroplating

[0090] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, stir evenly to obtain an electroplating solution, and thicken the copper foil of the first annealed film by electroplating to obtain a low residual stress functional current collector. The rate of the first annealed film on the electroplating line is 9 m / min, and the thickness of the obtained copper metal layer is 1 μm.

[0091] Comparative Example 3: This comparative example relates to the preparation of a low residual stress functional current collector. The difference from Example 5 is only that: in the process of this comparative example, annealing treatment is only carried out after the electroplating process, and no annealing is carried out after magnetron sputtering. Specifically:

[0092] Step 1: Magnetron sputtering

[0093] Clean the polypropylene film and each roller system of the magnetron sputtering equipment with absolute ethanol. After unwinding, evacuate the sputtering cavity, and control the base vacuum degree of magnetron sputtering to be 5×10 -3 Pa, the argon gas flow rate is 130 sccm, the cooling temperature of the sputtering main roller is -15°C, the copper target power is 12 KW, the winding speed is 8 m / min, and after magnetron sputtering is completed, wind up to obtain a magnetron film.

[0094] Step 2: Electroplating

[0095] Mix copper sulfate, hydrochloric acid, sulfuric acid, additives and deionized water, and stir evenly to obtain an electroplating solution. Treat the magnetron film by electroplating with water to thicken the copper foil and obtain a composite copper foil. The rate of the once-annealed film on the electroplating line is 9 m / min, and the thickness of the obtained copper metal layer is 1 μm.

[0096] Step 3: Once annealing

[0097] Place the composite copper foil in a constant-temperature drying oven and heat it in the furnace to 120 °C. Keep it at 120 °C for 8 h, and then cool it in the furnace to room temperature to obtain a functional current collector with low residual stress.

[0098] Detection experiment:

[0099] Residual stress test: Prepare functional current collectors with low residual stress according to the processes in Example 1, Example 2, Example 3, Example 4, Example 5, Comparative Example 1, Comparative Example 2, and Comparative Example 3 and conduct XRD tests. Use an XRD diffractometer for the test. The test target is a Cu target, the test voltage is 40 kV, and the test current is 40 mA; Diffraction optical path: The detector is placed at the 2θ angle position to receive the diffraction signal; Scanning parameters: Scanning range 70° - 85°, scanning step 0.02°, scanning speed 2° / min; Psi angle setting: 0°, 15°, 30°, 45°, and measure 3 times at each angle. Test the residual stress of the current collector specimens.

[0100] Residual stress (N) Example 1 2 Example 2 6 Example 3 5 Example 4 5 Example 5 1.5 Comparative Example 1 10 Comparative Example 2 6 Comparative Example 3 4

[0101] Thermal shrinkage test: Prepare a composite polypropylene film according to the process of Example 5, and use the untreated polypropylene film as a comparison. Take 5 specimens of 20 mm × 20 mm size on each of the two films. Place the specimens in an oven, simulate the heating process during battery use, heat up to 150 °C, and keep it at this temperature for 5 min, and measure the average change rate of the specimen area.

[0102] Thermal shrinkage test results: The average thermal shrinkage change rate of the composite polypropylene film is 4.36%, while the average thermal shrinkage change rate of the untreated polypropylene film is 31.54%.

[0103] Conclusion: By comparing the residual stresses of the functional current collectors prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that the two-step annealing method proposed by the present invention can indeed significantly reduce the residual stress of the current collector. And by comparing the residual stresses of the functional current collectors prepared in Example 1, Example 2, Example 3, and Example 4, it is found that too high or too low annealing temperature during annealing treatment will increase the residual stress of the functional current collector; in the thermal shrinkage test, the thermal shrinkage of the modified composite polypropylene film has been significantly improved.

[0104] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

Claims

1. A process for producing a low residual stress functional current collector by a two-step annealing method, characterized in that: Specifically: (1) taking a current collector base film, performing magnetron sputtering on the surface to form a seed layer, and performing an annealing treatment; (2) Using water electroplating, metal thickening is performed on the surface of the seed layer, and a secondary annealing treatment is performed.

2. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 1, characterized in that: The specific parameters of magnetron sputtering are as follows: the chamber is evacuated during magnetron sputtering, and the vacuum degree is 4×10 -3 ~6×10 -3 Pa, argon flow rate is 120~140sccm, cooling temperature is -20~-10℃, and copper target power is 11~13KW.

3. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 1, characterized in that: The annealing temperature is 80-150°C for both annealing processes, and the first annealing process is kept at a temperature of 1.5-2.5 hours, while the second annealing process is kept at a temperature of 7-9 hours.

4. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 1, characterized in that: In the copper plating solution used for water electroplating, the concentration of copper sulfate is 50-70 g / L, the concentration of hydrochloric acid is 40-90 mg / L, the concentration of sulfuric acid is 120-150 g / L, the additive is sodium polydisulfide dipropane sulfonate, the concentration is 0.01-0.04 g / L, and the solvent is deionized water.

5. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 1, characterized in that: The copper layer obtained by water electroplating has a thickness of 0.9 to 1.5 μm.

6. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 1, characterized in that: The preparation method of the composite polypropylene film is as follows: 0.3-0.5 parts of tannic acid, 0.18-0.22 parts of sodium periodate and 195-205 parts of tris(hydroxymethyl)aminomethane) buffer were mixed by weight and stirred evenly to obtain a tannic acid solution. The intercalated modified montmorillonite composite polypropylene film was immersed in the tannic acid solution and reacted at 25-30°C for 5-10 hours. After the reaction was completed, it was dried at 50-70°C to obtain a composite polypropylene film.

7. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 6, characterized in that: The preparation method of intercalation modified montmorillonite composite polypropylene film is as follows: Mix montmorillonite and deionized water, stir evenly, disperse by ultrasonic, add octadecyltrimethylammonium chloride, react at 55-65°C for 13-17h, cool after the reaction, centrifuge, wash with deionized water, and vacuum dry at 50-70°C to obtain organic montmorillonite, mix organic montmorillonite, ethanol and deionized water, stir until no obvious particles, add methyl methacrylate and azobisisobutyronitrile, introduce nitrogen for replacement for 10-20min, react at 70-90°C for 6h, filter and dry to obtain polymethyl methacrylate modified montmorillonite; Mix polymethyl methacrylate modified montmorillonite, styrene-butadiene latex adhesive, sodium carboxymethyl cellulose, deionized water and ethanol, stir evenly to obtain a coating slurry, apply the slurry on a corona roughened polypropylene film, dry and cure at 50-70° C. for 5-7 hours to obtain an intercalated modified montmorillonite composite polypropylene film.

8. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 7, characterized in that: When preparing polymethyl methacrylate modified montmorillonite, the mass ratio of organic montmorillonite, methyl methacrylate and azobisisobutyronitrile is (4-6):(4.5-5.5):(0.02-0.03).

9. The process for producing a low residual stress functional current collector by a two-step annealing method according to claim 7, characterized in that: The amounts of the components in the coating slurry used to prepare the intercalated modified montmorillonite composite polypropylene film are as follows, by weight: 0.05-0.15 parts of polymethyl methacrylate grafted montmorillonite, 0.2-0.4 parts of styrene-butadiene latex adhesive, 0.1-0.3 parts of sodium carboxymethyl cellulose, 45-55 parts of deionized water, and 35-45 parts of ethanol.

10. A low residual stress functional current collector obtained according to the process of any one of claims 1 to 9.