A high-conductivity stainless steel foil for positive electrode current collector and its preparation method

Abstract

The application relates to the technical field of battery current collectors, and discloses a high-conductivity stainless steel foil for a positive electrode current collector and a preparation method thereof; the method comprises the following operation steps: step 1: after the stainless steel foil is pickled and dried, the stainless steel foil is immersed in an ethylene diamine tetramethylene phosphonic acid ethanol solution and stirred under a nitrogen atmosphere for 2-3 hours, taken out and washed, and cured at 120-125 DEG C for 3-4 hours; after being cooled to room temperature, the stainless steel foil is washed, dried with nitrogen, and a pre-prepared stainless steel foil is obtained; step 2: the pre-prepared stainless steel foil is immersed in an antioxidant conductive copper composite sol for 25-40 seconds, taken out and dried, coated with an aluminum grid, rolled and pressed, immersed in a graphene / carbon nanotube composite sol for 20-30 seconds, taken out, dried at 100-120 DEG C for 4-6 minutes, rolled and pressed, and dried, so that the high-conductivity stainless steel foil is obtained.

Description

Technical Field

[0001] This invention relates to the field of battery current collector technology, specifically a high-conductivity stainless steel foil for positive electrode current collectors and its preparation method. Background Technology

[0002] In electrochemical energy storage devices such as lithium-ion batteries, the positive electrode current collector is a key component of the electrode structure and must possess excellent conductivity, corrosion resistance, and mechanical properties. Although the commonly used aluminum foil current collector has a low cost, it is prone to oxidation and corrosion under high voltage systems, leading to a decline in battery cycle performance. Copper foil, on the other hand, lacks stability in the positive electrode working environment.

[0003] Stainless steel foil has become a potential alternative material due to its good corrosion resistance and mechanical properties, but its poor conductivity limits its practical application. Existing modification methods mostly improve conductivity by improving the bonding with the polymer conductive layer through surface coating or by doping with conductive phases. However, when stainless steel foil is used as a positive electrode current collector, its conductivity and capacitance retention still need to be improved.

[0004] In summary, the preparation of a high-conductivity stainless steel foil for positive electrode current collectors is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a high-conductivity stainless steel foil for positive electrode current collectors and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a high-conductivity stainless steel foil for positive electrode current collectors includes the following steps:

[0008] Step 1: Pickle and dry the stainless steel foil, then immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution and stir for 2-3 hours under a nitrogen atmosphere. Remove and clean it, then cure it at 120-125℃ for 3-4 hours. After cooling to room temperature, wash it and dry it under nitrogen to obtain the pre-made stainless steel foil.

[0009] Step 2: Immerse the pre-made stainless steel foil in an antioxidant conductive copper composite sol for 25-40 seconds, remove and dry, then cover with an aluminum mesh, roll and press, then immerse in a graphene / carbon nanotube composite sol for 20-30 seconds, remove and dry at 100-120℃ for 4-6 minutes, roll and dry to obtain a highly conductive stainless steel foil.

[0010] In a more optimized form, the stainless steel foil comprises the following components: 14~17wt%Cr, 6~8wt%Ni, 1.5~2.5wt%Cu, 0.6~0.8wt%Mn, 0.15~0.3wt%Al, 0.05~0.1wt%Ti, 0.003~0.005wt%B, 0.2~0.3wt%Nb, with the remainder being iron;

[0011] In the prefabricated stainless steel foil, the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1~1.5mM.

[0012] In the scheme, the aluminum mesh has a mesh count of 500; the stainless steel foil has a longer side length than the aluminum mesh, and the final high-conductivity stainless steel foil needs to be cut to a greater extent than the aluminum mesh; the stainless steel foil is pickled in 10wt% nitric acid and then dried.

[0013] A more optimized method for preparing the antioxidant conductive copper composite sol is as follows: (1) Add copper nitride and nickel acetate to an aqueous sodium hydroxide solution and mix evenly. Add ethylenediamine and hydrazine hydrate aqueous solution and continue mixing evenly to obtain a mixed solution; (2) Add graphite oxide to deionized water, sonicate, add hydrazine hydrate and mix evenly, reflux at 90~95℃ for 20~24 hours, cool down to 70~80℃ and add the mixed solution, heat for 1.5~2.5 hours, cool down to room temperature, adjust the pH to 4~5 with 0.05~0.1M phosphoric acid aqueous solution, add sulfonated polyaniline, stir for 2~3 hours under a nitrogen atmosphere, adjust the pH to neutral, and obtain the antioxidant conductive copper composite sol.

[0014] More preferably, the raw materials of the mixed solution include the following components by mass: 2 parts copper nitride, 1.8-2.5 parts nickel acetate, 10-15 parts sodium hydroxide aqueous solution, 6-12 parts ethylenediamine, and 1-2.5 parts hydrazine hydrate aqueous solution; the concentration of the sodium hydroxide aqueous solution is 7-10M; the concentration of the hydrazine hydrate aqueous solution is 30-35wt%; the raw materials of the antioxidant conductive copper composite sol include the following components by mass: 4-6 parts graphite oxide, 2-4 parts hydrazine hydrate, 3-5 parts sulfonated polyaniline, 18-20 parts mixed solution, and 100-120 parts deionized water.

[0015] In the scheme, the sulfonated polyaniline is prepared by adding 2 parts aniline, 0.3 parts 3-aminophenylboronic acid, and 1 part p-hydroxybenzenesulfonic acid to 40 parts 1M hydrochloric acid solution and mixing them evenly. Then, 2.3 parts ammonium persulfate are added, and the mixture is stirred at 0°C for 8 hours. After centrifugation, washing, and drying, sulfonated polyaniline is obtained. The parts are by weight.

[0016] A more optimized method for preparing the graphene / carbon nanotube composite sol is as follows: (1) Disperse carbon nanotubes ultrasonically in a 30-40 wt% nitric acid aqueous solution, reflux for 2-3 hours, filter and wash until neutral, disperse ultrasonically in deionized water, add NHS and EDC nitrogen atmosphere and stir for 2-3 hours, add p-phenylenediamine and 3-aminophenylboronic acid and continue mixing for 6-8 hours, wash and dry to obtain modified carbon nanotubes; (2) Add modified carbon nanotubes, aniline and p-hydroxybenzenesulfonic acid to a 1-2M HCl solution and mix evenly, add ammonium persulfate, and centrifuge, wash and dry under ice-water bath conditions for 4-6 hours to obtain carbon nanotube-based polyaniline; (3) Add graphene oxide to deionized water, sonicate, add hydrazine hydrate, reflux at 90-95℃ for 15-20 hours, add carbon nanotube-based polyaniline and continue stirring for 3-5 hours to obtain graphene / carbon nanotube composite sol.

[0017] In a more optimized form, the modified carbon nanotube raw material comprises the following components: by mass parts, 1-3 parts carbon nanotubes, 0.18-0.25 parts NHS, 0.3-0.4 parts EDC, 0.4-0.8 parts p-phenylenediamine, 0.3-0.5 parts 3-aminophenylboronic acid, and 40-50 parts deionized water; the carbon nanotube-based polyaniline raw material comprises the following components: by mass parts, 0.7-1.2 parts modified carbon nanotubes, 1-2 parts aniline, 1.5-2 parts ammonium persulfate, and 1-1.7 parts p-hydroxybenzenesulfonic acid; the graphene / carbon nanotube composite sol raw material comprises the following components: by mass parts, 4-6 parts graphite oxide, 2-4 parts hydrazine hydrate, 100-120 parts deionized water, and 3-5 parts carbon nanotube-based polyaniline.

[0018] The optimized rolling process conditions are as follows: under nitrogen conditions, the pressure is 5~15MPa, the temperature is 40~60℃, and the rolling time is 10~15min.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention incorporates a composite design with multiple conductive layers on the surface of stainless steel foil to improve the conductivity and capacity retention of the stainless steel foil.

[0021] In this solution, to address the issue of poor conductivity in stainless steel foil, ethylenediaminetetramethylenephosphonic acid (EDTA) is used to pretreat the stainless steel foil surface. This enhances the interfacial bonding between the substrate and the subsequent antioxidant conductive copper composite sol. Combined with a specific rolling process, the bond between the aluminum mesh and the antioxidant copper layer is further strengthened, effectively preventing detachment during use and thus improving the conductivity of the stainless steel foil.

[0022] To improve the oxidation resistance of copper, the proposed method involves co-reduction of copper nitride and nickel acetate to form a Cu / Ni alloy, which inhibits copper oxidation. Specifically, in a graphene sol, ethylenediamine is used as a capping agent and hydrazine hydrate is used as a reducing agent to reduce copper nitride and nickel acetate at a certain temperature to obtain Cu / Ni / GO. Furthermore, in the graphene sol, a low-concentration phosphoric acid aqueous solution is used to adjust the pH to 4-5 to avoid the influence of hydrochloric acid on the pH adjustment of Cu / Ni. Then, sulfonated polyaniline is added and stirring is continued to adjust the pH to neutral, resulting in an antioxidant conductive copper composite sol.

[0023] Sulfonated polyaniline possesses excellent hydrophilicity and polarity, enabling it to adsorb onto metal (copper, nickel) surfaces. The compatibility of the sulfonyl group with the aqueous phase enhances the stability of the entire sol system. Its conjugated structure and graphene provide a certain degree of protection for metal particles, hindering the contact between oxygen, moisture, and the metal surface through steric hindrance, thus slowing down the oxidation rate of copper and nickel and improving conductivity. In this scheme, the core function of the antioxidant conductive copper composite sol is to form a bottom conductive network through the Cu / Ni alloy. The conductivity of copper is far higher than that of graphene / carbon nanotubes. Using the antioxidant conductive copper composite sol as an intermediate layer between stainless steel foil and aluminum mesh further alleviates the oxidation resistance of Cu, and the performance of the stainless steel foil is strengthened after rolling.

[0024] To further improve conductivity and capacity retention, a graphene / carbon nanotube composite sol is applied to the surface, giving the current collector excellent corrosion resistance and conductivity. Graphene and carbon nanotubes form a three-dimensional "sheet-tube" interwoven structure to reduce overall resistance. After amination and polyaniline modification, a three-dimensional conductive network is formed on the carbon nanotubes, which can synergistically work with the underlying antioxidant conductive copper composite sol. After rolling treatment, the polar groups on the surface and the reinforced interface are combined to reduce resistance and improve the conductivity and capacity retention of the stainless steel foil. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] In the following specific embodiments, "parts" refers to parts by weight. It should be noted that, in this embodiment, there are no special restrictions on the manufacturers of the raw materials involved in this invention; exemplarily, they include:

[0027] The product code for copper nitride is HC1313; the CAS number for nickel acetate is 373-02-4; the CAS number for ethylenediamine is 107-15-3; the CAS number for hydrazine hydrate is 7803-57-8; the CAS number for 3-aminophenylboronic acid is 30418-59-8; the CAS number for EDC (ethyl-(3-dimethylaminopropyl)carbodiimide) is 25952-53-8; the CAS number for NHS (N-hydroxysuccinimide) is 6066-82-6; the CAS number for ammonium persulfate is 7727-54-0; the CAS number for aniline is 62-53-3; the CAS number for p-phenylenediamine is 106-50-3; the CAS number for p-hydroxybenzenesulfonic acid is 98-67-9; and the product code for carbon nanotubes is WD3713.

[0028] Example 1: A method for preparing a high-conductivity stainless steel foil for positive electrode current collectors, comprising the following steps:

[0029] Pre-preparation: The preparation method of the antioxidant conductive copper composite sol is as follows: (1) Add 2 parts of copper nitride and 1.8 parts of nickel acetate to 12 parts of sodium hydroxide aqueous solution (the concentration of sodium hydroxide aqueous solution is 8M) and mix evenly. Add 6 parts of ethylenediamine and 1.2 parts of hydrazine hydrate aqueous solution and continue to mix evenly to obtain a mixed solution; (2) Add 5 parts of graphite oxide to 100 parts of deionized water, sonicate, add 4 parts of hydrazine hydrate and mix evenly. Reflux at 90℃ for 22 hours, cool down to 75℃ and add 18 parts of the mixed solution. Heat for 2 hours, cool down to room temperature, adjust the pH to 5 with 0.05M phosphoric acid aqueous solution, add 4 parts of sulfonated polyaniline, stir for 2 hours under nitrogen atmosphere, adjust the pH to neutral, and obtain the antioxidant conductive copper composite sol;

[0030] The preparation method of graphene / carbon nanotube composite sol is as follows: (1) 2 parts of carbon nanotubes are ultrasonically dispersed in 30wt% nitric acid aqueous solution, refluxed for 2 hours, filtered and washed until neutral, ultrasonically dispersed in 45 parts of deionized water, 0.18 parts of NHS and 0.3 parts of EDC are added and stirred for 1.5 hours, 0.6 parts of p-phenylenediamine and 0.4 parts of 3-aminophenylboronic acid are added and mixed for 6 hours, washed and dried to obtain modified carbon nanotubes; (2) 0.7 parts of modified carbon nanotubes 1. Add 2 parts of aniline and 1.5 parts of p-hydroxybenzenesulfonic acid to 1M HCl solution and mix evenly. Add 1.8 parts of ammonium persulfate and centrifuge, wash and dry under ice-water bath conditions for 6 hours to obtain carbon nanotube-based polyaniline; (3) Add 5 parts of graphene oxide to 100 parts of deionized water, sonicate, add 3 parts of hydrazine hydrate, reflux at 90℃ for 15 hours, add 4 parts of carbon nanotube-based polyaniline and continue stirring for 3 hours to obtain graphene / carbon nanotube composite sol;

[0031] Step 1: Pickle and dry the stainless steel foil, immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.2mM) and sonicate for 2 hours. Remove and clean it, cure it at 120℃ for 3 hours, cool it to room temperature, wash it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0032] Step 2: Immerse the pre-made stainless steel foil in an antioxidant conductive copper composite sol for 25 seconds, remove and dry, then cover with an aluminum mesh, and roll it (under nitrogen conditions, with a pressure of 10 MPa, a temperature of 45°C, and a time of 15 minutes). Then immerse it in a graphene / carbon nanotube composite sol for 20 seconds, remove it, dry it at 100°C for 4 minutes, roll it (under nitrogen conditions, with a pressure of 10 MPa, a temperature of 45°C, and a time of 10 minutes), and dry it to obtain a highly conductive stainless steel foil.

[0033] Example 2: A method for preparing a high-conductivity stainless steel foil for positive electrode current collectors, comprising the following steps:

[0034] Pre-preparation: The preparation method of the antioxidant conductive copper composite sol is as follows: (1) Add 2 parts of copper nitride and 1.8 parts of nickel acetate to 12 parts of sodium hydroxide aqueous solution (the concentration of sodium hydroxide aqueous solution is 8M) and mix evenly. Add 6 parts of ethylenediamine and 1.2 parts of hydrazine hydrate aqueous solution and continue to mix evenly to obtain a mixed solution; (2) Add 5 parts of graphite oxide to 100 parts of deionized water, sonicate, add 4 parts of hydrazine hydrate and mix evenly. Reflux at 90℃ for 22 hours, cool down to 75℃ and add 18 parts of the mixed solution. Heat for 2 hours, cool down to room temperature, adjust the pH to 5 with 0.1M phosphoric acid aqueous solution, add 4 parts of sulfonated polyaniline, stir for 2 hours under nitrogen atmosphere, adjust the pH to neutral, and obtain the antioxidant conductive copper composite sol;

[0035] The preparation method of graphene / carbon nanotube composite sol is as follows: (1) 2 parts of carbon nanotubes are ultrasonically dispersed in 30wt% nitric acid aqueous solution, refluxed for 2 hours, filtered and washed until neutral, ultrasonically dispersed in 45 parts of deionized water, 0.18 parts of NHS and 0.3 parts of EDC are added and stirred for 1.5 hours, 0.6 parts of p-phenylenediamine and 0.4 parts of 3-aminophenylboronic acid are added and mixed for 6 hours, washed and dried to obtain modified carbon nanotubes; (2) 0.7 parts of modified carbon nanotubes 1. Add 2 parts of aniline and 1.5 parts of p-hydroxybenzenesulfonic acid to 1M HCl solution and mix evenly. Add 1.8 parts of ammonium persulfate and centrifuge, wash and dry under ice-water bath conditions for 6 hours to obtain carbon nanotube-based polyaniline; (3) Add 5 parts of graphene oxide to 100 parts of deionized water, sonicate, add 3 parts of hydrazine hydrate, reflux at 90℃ for 15 hours, add 4 parts of carbon nanotube-based polyaniline and continue stirring for 3 hours to obtain graphene / carbon nanotube composite sol;

[0036] Step 1: Pickle and dry the stainless steel foil, immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.2mM) and sonicate for 2 hours. Remove and clean it, cure it at 120℃ for 3 hours, cool it to room temperature, wash it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0037] Step 2: Immerse the pre-made stainless steel foil in an antioxidant conductive copper composite sol for 30 seconds, remove and dry, then cover with an aluminum mesh and roll it (under nitrogen conditions, with a pressure of 10 MPa, a temperature of 45°C, and a time of 15 minutes), then immerse it in a graphene / carbon nanotube composite sol for 25 seconds, remove and dry at 100°C for 4 minutes, roll it (under nitrogen conditions, with a pressure of 10 MPa, a temperature of 45°C, and a time of 10 minutes), and dry to obtain a highly conductive stainless steel foil.

[0038] Example 3: A method for preparing a high-conductivity stainless steel foil for positive electrode current collectors, comprising the following steps:

[0039] Pre-preparation: The preparation method of the antioxidant conductive copper composite sol is as follows: (1) Add 2 parts of copper nitride and 1.8 parts of nickel acetate to 12 parts of sodium hydroxide aqueous solution (the concentration of sodium hydroxide aqueous solution is 8M) and mix evenly. Add 6 parts of ethylenediamine and 1.2 parts of hydrazine hydrate aqueous solution and continue to mix evenly to obtain a mixed solution; (2) Add 5 parts of graphite oxide to 100 parts of deionized water, sonicate, add 4 parts of hydrazine hydrate and mix evenly. Reflux at 90℃ for 22 hours, cool down to 75℃ and add 18 parts of the mixed solution. Heat for 2 hours, cool down to room temperature, adjust the pH to 5 with 0.1M phosphoric acid aqueous solution, add 4 parts of sulfonated polyaniline, stir for 2 hours under nitrogen atmosphere, adjust the pH to neutral, and obtain the antioxidant conductive copper composite sol;

[0040] The preparation method of graphene / carbon nanotube composite sol is as follows: (1) 2 parts of carbon nanotubes are ultrasonically dispersed in 30wt% nitric acid aqueous solution, refluxed for 2 hours, filtered and washed until neutral, ultrasonically dispersed in 45 parts of deionized water, 0.18 parts of NHS and 0.3 parts of EDC are added and stirred for 1.5 hours, 0.6 parts of p-phenylenediamine and 0.4 parts of 3-aminophenylboronic acid are added and mixed for 6 hours, washed and dried to obtain modified carbon nanotubes; (2) 0.7 parts of modified carbon nanotubes 1. Add 2 parts of aniline and 1.5 parts of p-hydroxybenzenesulfonic acid to 1M HCl solution and mix evenly. Add 1.8 parts of ammonium persulfate and centrifuge, wash and dry under ice-water bath conditions for 6 hours to obtain carbon nanotube-based polyaniline; (3) Add 5 parts of graphene oxide to 100 parts of deionized water, sonicate, add 3 parts of hydrazine hydrate, reflux at 90℃ for 15 hours, add 4 parts of carbon nanotube-based polyaniline and continue stirring for 3 hours to obtain graphene / carbon nanotube composite sol;

[0041] Step 1: Pickle and dry the stainless steel foil, immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.2mM) and sonicate for 2 hours. Remove and clean it, cure it at 120℃ for 3 hours, cool it to room temperature, wash it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0042] Step 2: Immerse the pre-made stainless steel foil in an antioxidant conductive copper composite sol for 35 seconds, remove and dry, then cover with an aluminum mesh, and roll it (under nitrogen conditions, with a pressure of 10 MPa, a temperature of 45°C, and a time of 15 minutes). Then immerse it in a graphene / carbon nanotube composite sol for 30 seconds, remove it, dry it at 100°C for 4 minutes, roll it (under nitrogen conditions, with a pressure of 10 MPa, a temperature of 45°C, and a time of 10 minutes), and dry it to obtain a highly conductive stainless steel foil.

[0043] Comparative Example 1 is based on Example 3, but without the addition of polyaniline; the remaining operating steps remain unchanged.

[0044] Pre-preparation: The preparation method of the antioxidant conductive copper composite sol is as follows: (1) Add 2 parts of copper nitride and 1.8 parts of nickel acetate to 12 parts of sodium hydroxide aqueous solution (the concentration of sodium hydroxide aqueous solution is 8M) and mix evenly. Add 6 parts of ethylenediamine and 1.2 parts of hydrazine hydrate aqueous solution and continue to mix evenly to obtain a mixed solution; (2) Add 5 parts of graphite oxide to 100 parts of deionized water, sonicate, add 4 parts of hydrazine hydrate and mix evenly. Reflux at 90℃ for 22 hours, cool down to 75℃ and add 18 parts of the mixed solution. Heat for 2 hours to obtain the antioxidant conductive copper composite sol;

[0045] The preparation method of graphene / carbon nanotube composite sol is as follows: 5 parts of graphite oxide are added to 100 parts of deionized water, ultrasonic treatment is performed, 3 parts of hydrazine hydrate are added, reflux is carried out at 90°C for 15 hours, 4 parts of carbon nanotubes are added and stirring is continued for 3 hours to obtain graphene / carbon nanotube composite sol.

[0046] Step 1: Pickle and dry the stainless steel foil, immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.2mM) and sonicate for 2 hours. Remove and clean it, cure it at 120℃ for 3-4 hours, cool it to room temperature, wash it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0047] Step 2: Immerse the pre-made stainless steel foil in an antioxidant conductive copper composite sol for 35 seconds, remove and dry, then cover with an aluminum mesh, roll and immerse in a graphene / carbon nanotube composite sol for 30 seconds, remove and dry at 100℃ for 4 minutes, roll and dry to obtain a highly conductive stainless steel foil.

[0048] Comparative Example 2 is based on Example 3, except that the positions of the graphene / carbon nanotube composite sol and the antioxidant conductive copper composite sol are interchanged; the other operation steps remain the same.

[0049] Step 1: Pickle and dry the stainless steel foil, immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.2mM) and sonicate for 2 hours. Remove and clean it, cure it at 120℃ for 3-4 hours, cool it to room temperature, wash it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0050] Step 2: The pre-made stainless steel foil is immersed in graphene / carbon nanotube composite sol for 35 seconds, removed and dried, then covered with aluminum mesh, rolled, and then immersed in antioxidant conductive copper composite sol for 30 seconds. It is then removed, dried at 100℃ for 4 minutes, rolled, and dried to obtain a high conductivity stainless steel foil.

[0051] Comparative Example 3 is based on Example 3, but without the introduction of antioxidant conductive copper composite sol; the remaining operation steps remain unchanged;

[0052] Step 1: Pickle and dry the stainless steel foil, immerse it in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.2mM) and sonicate for 2 hours. Remove and clean it, cure it at 120℃ for 3-4 hours, cool it to room temperature, wash it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0053] Step 2: Coat the surface of the pre-made stainless steel foil with an aluminum mesh, roll it, then immerse it in a graphene / carbon nanotube composite sol for 30 seconds, remove it, dry it at 100°C for 4 minutes, roll it again, and dry it to obtain a highly conductive stainless steel foil.

[0054] Comparative Example 4 is based on Example 3, except that the ethylenediaminetetramethylenephosphonic acid ethanol solution is replaced with a passivation solution containing ethylenediaminetetramethylenephosphonic acid; other operating steps remain unchanged.

[0055] Step 1: Pickle and dry the stainless steel foil, immerse it in a passivation solution containing ethylenediaminetetramethylenephosphonic acid for 12 seconds, remove and clean it, and dry it with nitrogen to obtain the pre-made stainless steel foil.

[0056] The passivation solution comprises: 10 mL / L phytic acid, 5 g / L sodium phosphate aqueous solution, 2 g / L ethylenediaminetetramethylenephosphonic acid, and 5 g / L polyethylene glycol; the temperature is 45℃, and the current density is 1.5 A / dm³. 2 ;

[0057] Step 2: Immerse the pre-made stainless steel foil in an antioxidant conductive copper composite sol for 35 seconds, remove and dry, then cover with an aluminum mesh, roll and immerse in a graphene / carbon nanotube composite sol for 30 seconds, remove and dry at 100℃ for 4 minutes, roll and dry to obtain a highly conductive stainless steel foil.

[0058] Test experiment: (1) The resistance of the high conductivity stainless steel foils prepared in Examples 1-3 and Comparative Examples 1-3 was tested in the 90° direction (the meridian and the parallel are at 90°).

[0059] (2) The positive electrode current collector is a high-conductivity stainless steel foil prepared in Examples 1-3 and Comparative Examples 1-3 of this invention, NCM622 (LiNi 0.6 Mn 0.2 Co 0.2 O2) is used as the positive electrode material; the negative electrode current collector uses traditional copper foil, and artificial graphite is used as the negative electrode material; the separator is a polyolefin separator, and the electrolyte includes 1M LiPF6 carbonate mixed solvent and 5wt% fluoroethylene carbonate and 0.6wt% lithium difluorooxalate borate. The carbonate mixed solvent includes ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a mass ratio of 4:5:1. Then, the lithium-ion battery is assembled according to the relevant process; the prepared battery is subjected to 1C charge-discharge cycle test, and the battery discharge capacity of the 1000th cycle and the 1st cycle is recorded after n cycles. The discharge retention rate is calculated as follows: discharge retention rate = discharge capacity of the 1000th cycle / discharge capacity of the 1st cycle × 100%; the test results are shown in Table 1.

[0060] Table 1

[0061]

[0062] Conclusions: Comparative Example 1, based on Example 3, did not include polyaniline; the coating's toughness and conductivity decreased, making it prone to cracking during the rolling process, thus leading to performance degradation; Comparative Example 2, based on Example 3, swapped the application positions of the graphene / carbon nanotube composite sol and the antioxidant conductive copper composite sol; this resulted in a decrease in the performance of Comparative Example 3 because the core function of the antioxidant conductive copper composite sol is to form a bottom conductive network through the Cu / Ni alloy, and copper's conductivity is much higher than that of graphene / carbon nanotubes; the aluminum mesh and stainless steel foil need to be in direct contact with the copper layer to enhance conductivity through rolling; Comparative Example 3, based on Example 3, did not introduce the antioxidant conductive copper composite sol; therefore, this resulted in a decrease in the performance of Comparative Example 4; Comparative Example 4, based on Example 3, replaced the ethylenediaminetetramethylenephosphonic acid ethanol solution with a passivation solution containing ethylenediaminetetramethylenephosphonic acid; the passivation film in Comparative Example 4 resulted in increased interfacial resistance and increased energy loss during charging and discharging, thus the capacitance retention rate was lower than that of Example 3.

[0063] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for producing a high-conductivity stainless steel foil for a positive electrode current collector, characterized by: The method comprises the following steps: Step 1: After the stainless steel foil is pickled and dried, it is immersed in an ethylene diamine tetramethylene phosphonic acid ethanol solution and stirred in a nitrogen atmosphere for 2-3 hours, taken out and washed, and then cured at 120-125 DEG C for 3-4 hours; after cooling to room temperature, the stainless steel foil is washed and dried in a nitrogen atmosphere to obtain a pre-prepared stainless steel foil; Step 2: The pre-prepared stainless steel foil is immersed in an antioxidant conductive copper composite sol for 25-40 seconds, taken out and dried, coated with an aluminum grid, and then rolled and treated; the stainless steel foil is then immersed in a graphene / carbon nanotube composite sol for 20-30 seconds, taken out, dried at 100-120 DEG C for 4-6 minutes, and then rolled and treated to obtain a high-conductivity stainless steel foil; The antioxidant conductive copper composite sol is prepared by: (1) uniformly mixing copper nitride and nickel acetate in a sodium hydroxide aqueous solution, and then uniformly mixing ethylene diamine and a hydrazine hydrate aqueous solution to obtain a mixed solution; (2) adding graphite oxide to deionized water, ultrasonically treating, uniformly mixing hydrazine hydrate, refluxing at 90-95 DEG C for 20-24 hours, cooling to 70-80 DEG C, adding the mixed solution, heating for 1.5-2.5 hours, cooling to room temperature, adjusting the pH to 4-5 with a 0.05-0.1M phosphoric acid aqueous solution, and then adding sulfonated polyaniline and stirring in a nitrogen atmosphere for 2-3 hours to obtain an antioxidant conductive copper composite sol; The raw materials of the mixed solution comprise the following components: 2 parts of copper nitride, 1.8-2.5 parts of nickel acetate, 10-15 parts of a sodium hydroxide aqueous solution, 6-12 parts of ethylene diamine, and 1-2.5 parts of a hydrazine hydrate aqueous solution; the concentration of the sodium hydroxide aqueous solution is 7-10M; the concentration of the hydrazine hydrate aqueous solution is 30-35wt%; and the raw materials of the antioxidant conductive copper composite sol comprise the following components: 4-6 parts of graphite oxide, 2-4 parts of hydrazine hydrate, 3-5 parts of sulfonated polyaniline, 18-20 parts of the mixed solution, and 100-120 parts of deionized water.

2. The method of claim 1, wherein the stainless steel foil is prepared by the steps of: The stainless steel foil comprises the following components: 14-17wt% Cr, 6-8wt% Ni, 1.5-2.5wt% Cu, 0.6-0.8wt% Mn, 0.15-0.3wt% Al, 0.05-0.1wt% Ti, 0.003-0.005wt% B, and 0.2-0.3wt% Nb, with the balance being iron; ​ In the pre-prepared stainless steel foil, the concentration of the ethylene diamine tetramethylene phosphonic acid ethanol solution is 1-1.5mM.

3. The method for preparing a high-conductivity stainless steel foil for a positive electrode current collector according to claim 1, characterized in that: The preparation method of the graphene / carbon nanotube composite sol comprises the following steps: (1) dispersing carbon nanotubes in 30-40wt% nitric acid aqueous solution, refluxing for 2-3 hours, washing until neutral, dispersing in deionized water, adding NHS and EDC, stirring for 2-3 hours under nitrogen atmosphere, adding p-phenylenediamine and 3-aminophenylboronic acid, continuing to mix for 6-8 hours, washing and drying to obtain modified carbon nanotubes; (2) adding the modified carbon nanotubes, aniline and p-hydroxybenzenesulfonic acid into 1-2M HCl solution, uniformly mixing, adding ammonium persulfate, centrifuging, washing and drying under ice water bath condition for 4-6 hours to obtain carbon nanotube-based polyaniline; (3) adding graphite oxide into deionized water, ultrasonic treatment, adding hydrazine hydrate, refluxing at 90-95℃ for 15-20 hours, adding carbon nanotube-based polyaniline, continuing to stir for 3-5 hours to obtain the graphene / carbon nanotube composite sol.

4. The method of claim 3, wherein the stainless steel foil is prepared by the steps of: The raw materials of the modified carbon nanotubes comprise the following components in mass fraction: 1-3 parts of carbon nanotubes, 0.18-0.25 parts of NHS, 0.3-0.4 parts of EDC, 0.4-0.8 parts of p-phenylenediamine, 0.3-0.5 parts of 3-aminophenylboronic acid and 40-50 parts of deionized water; the raw materials of the carbon nanotube-based polyaniline comprise the following components in mass fraction: 0.7-1.2 parts of modified carbon nanotubes, 1-2 parts of aniline, 1.5-2 parts of ammonium persulfate and 1-1.7 parts of p-hydroxybenzenesulfonic acid; the raw materials of the graphene / carbon nanotube composite sol comprise the following components in mass fraction: 4-6 parts of graphite oxide, 2-4 parts of hydrazine hydrate, 100-120 parts of deionized water and 3-5 parts of carbon nanotube-based polyaniline. ​ 5. The method for preparing a high-conductivity stainless steel foil for a positive electrode current collector according to claim 1, characterized in that: The process conditions of the rolling treatment are as follows: under nitrogen condition, the pressure is 5-15MPa, the temperature is 40-60℃ and the rolling time is 10-15min.

6. A high-conductivity stainless steel foil for a positive electrode current collector is prepared by the preparation method of the high-conductivity stainless steel foil according to any one of claims 1-5.

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