High-conductivity stainless steel foil for positive current collector and preparation method of high-conductivity stainless steel foil

Abstract

The invention relates to the technical field of battery current collectors, and discloses a high-conductivity stainless steel foil for a positive current collector and a preparation method of the high-conductivity stainless steel foil. Comprising the following operation steps that 1, stainless steel foil is subjected to acid pickling and then dried, the stainless steel foil is soaked in an ethylenediamine tetramethylenephosphonic acid ethanol solution to be stirred for 2-3 h in the nitrogen atmosphere, the stainless steel foil is taken out to be cleaned and cured for 3-4 h at the temperature of 120-125 DEG C, after the stainless steel foil is cooled to the room temperature, washing and nitrogen drying are conducted, and prefabricated stainless steel foil is obtained; and 2, the prefabricated stainless steel foil is soaked in the anti-oxidation conductive copper composite sol for 25-40 s, taken out, dried, coated with an aluminum grid, ground, soaked in the graphene / carbon nanotube composite sol for 20-30 s, taken out, dried for 4-6 min at the temperature of 100-120 DEG C, ground and dried, and the high-conductivity stainless steel foil is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery current collectors, in particular to a high-conductivity stainless steel foil for a positive electrode current collector and a preparation method thereof. BACKGROUND

[0002] In electrochemical energy storage devices such as lithium ion batteries, the positive electrode current collector, as a key component of the electrode structure, needs to have 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 a high-voltage system, resulting in the attenuation of the cycle performance of the battery; and copper foil has insufficient stability in the positive electrode working environment.

[0003] The stainless steel foil becomes a potential alternative material due to good corrosion resistance and mechanical properties, but its poor conductivity limits its practical application; the existing modification methods mainly improve the combination with the polymer conductive layer or dope the conductive phase to improve the conductivity, but the conductivity and capacitance retention rate of the stainless steel foil as the positive electrode current collector still need to be improved.

[0004] In summary, it is of great significance to prepare a high-conductivity stainless steel foil for a positive electrode current collector. SUMMARY

[0005] The application aims to provide a high-conductivity stainless steel foil for a positive electrode current collector and a preparation method thereof, so as to solve the problems in the prior art.

[0006] To achieve the above-mentioned purpose, the application provides the following technical scheme: A preparation method of a high-conductivity stainless steel foil for a positive electrode current collector comprises the following operation 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 under a nitrogen atmosphere for 2-3 hours, taken out and washed, and then solidified at 120-125 DEG C for 3-4 hours; after cooling to room temperature, the stainless steel foil is washed and dried with nitrogen to obtain a pre-prepared stainless steel foil; Step 2: the pre-prepared stainless steel foil is immersed in an oxidation-resistant conductive copper composite sol for 25-40 seconds, taken out and dried, coated with an aluminum grid, and then rolled and pressed; 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 pressed to obtain a high-conductivity stainless steel foil.

[0007] More preferably, the stainless steel foil comprises the following components: 14-17 wt% Cr, 6-8 wt% Ni, 1.5-2.5 wt% Cu, 0.6-0.8 wt% Mn, 0.15-0.3 wt% Al, 0.05-0.1 wt% Ti, 0.003-0.005 wt% B, 0.2-0.3 wt% Nb, and the balance is iron. The concentration of the ethylene diamine tetramethylene phosphonic acid ethanol solution in the prefabricated stainless steel foil is 1-1.5 mM.

[0008] In the scheme, the mesh number of the aluminum grid is 500 meshes; the side length of the stainless steel foil is longer than that of the aluminum grid, and the high-conductivity stainless steel foil obtained finally needs to be cut to be longer than the aluminum grid; the stainless steel foil is pickled in 10 wt% nitric acid and then dried.

[0009] More preferably, the preparation method of the anti-oxidation conductive copper composite sol is as follows: (1) uniformly mix copper nitride and nickel acetate in a sodium hydroxide aqueous solution, continuously mix ethylene diamine and a hydrazine hydrate aqueous solution to obtain a mixed solution; (2) add graphite oxide to deionized water, ultrasonically treat, uniformly mix the hydrazine hydrate, reflux at 90-95℃ for 20-24 hours, cool to 70-80℃, add the mixed solution, heat for 1.5-2.5 hours, cool to room temperature, adjust the pH to 4-5 with a 0.05-0.1M phosphoric acid aqueous solution, add sulfonated polyaniline, stir for 2-3 hours in a nitrogen atmosphere, adjust the pH to neutral to obtain the anti-oxidation conductive copper composite sol.

[0010] More preferably, the raw materials of the mixed solution include 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 30-35 wt%; the raw materials of the anti-oxidation conductive copper composite sol include 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.

[0011] In the scheme, the preparation method of the sulfonated polyaniline is as follows: uniformly mix 2 parts of aniline, 0.3 parts of 3-aminobenzoic acid, and 1 part of p-hydroxybenzenesulfonic acid in 40 parts of a 1M hydrochloric acid solution, add 2.3 parts of ammonium persulfate, stir at 0℃ for 8 hours, centrifuge, wash, and dry to obtain the sulfonated polyaniline; the parts are mass parts.

[0012] The more optimized preparation method of the graphene / carbon nanotube composite sol is as follows: (1) ultrasonically dispersing carbon nanotubes in a 30-40 wt% nitric acid aqueous solution, reflux for 2-3 hours, filtering and washing until neutral, ultrasonically dispersing in deionized water, adding NHS and EDC and stirring under a nitrogen atmosphere for 2-3 hours, adding p-phenylenediamine and 3-aminophenylboronic acid and continuing to mix for 6-8 hours, washing and drying to obtain modified carbon nanotubes; (2) adding modified carbon nanotubes, aniline and p-hydroxybenzenesulfonic acid to a 1-2 M HCl solution and uniformly mixing, adding ammonium persulfate, incubating in an ice-water bath for 4-6 hours, centrifuging, washing and drying to obtain carbon nanotube-based polyaniline; (3) adding graphite oxide to deionized water, ultrasonically treating, adding hydrazine hydrate, refluxing at 90-95°C for 15-20 hours, adding carbon nanotube-based polyaniline and continuing to stir for 3-5 hours to obtain a graphene / carbon nanotube composite sol.

[0013] More optimally, the raw materials of the modified carbon nanotubes include the following components, by mass: 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-aminophenylboric acid, and 40-50 parts of deionized water; the raw materials of the carbon nanotube-based polyaniline include the following components, by mass: 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 include the following components, by mass: 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.

[0014] The more optimized process conditions of the rolling treatment are: under nitrogen conditions, the pressure is 5~15MPa, the temperature is 40~60℃, and the rolling time is 10~15min.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts a composite design of a multi-level conductive layer on the surface of the stainless steel foil to improve the conductivity and capacity retention rate of the stainless steel foil.

[0016] In the plan, in order to solve the problem of poor conductivity of stainless steel foil, ethylenediaminetetramethylenephosphonic acid is used to pretreat the surface of the stainless steel foil to enhance the interfacial bonding strength between the substrate and the subsequent antioxidant conductive copper composite sol. Combined with a specific rolling process, the bonding between the aluminum grid and the antioxidant copper layer is further strengthened, effectively avoiding the problem of falling off during use, thereby improving the conductivity of the stainless steel foil.

[0017] In order to improve the oxidation resistance of copper, in the scheme, copper nitride is co-reduced with nickel acetate to form Cu / Ni alloy to inhibit the oxidation of copper; wherein, in the graphene sol, ethylenediamine is used as a capping agent, hydrazine hydrate is used as a reducing agent, copper nitride and nickel acetate are reduced at a certain temperature to obtain Cu / Ni / GO; and in the graphene sol, 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, and then sulfonated polyaniline is added for continuous stirring to adjust the pH to neutral to obtain an oxidation-resistant conductive copper composite sol.

[0018] The sulfonated polyaniline has good hydrophilicity and polarity, can be adsorbed on the surface of the metal (copper, nickel), and the compatibility of the sulfonic group with the water phase can improve the stability of the whole sol system; the conjugated structure of the sulfonated polyaniline and the graphene has a certain protective effect on the metal particles, can hinder the contact of oxygen and water with the surface of the metal through steric hindrance, delay the oxidation rate of copper and nickel, and improve the conductivity; in the scheme, the core role of the oxidation-resistant conductive copper composite sol is to form a bottom conductive network through the Cu / Ni alloy, and the conductivity of copper is much higher than that of graphene / carbon nanotube; the oxidation resistance of Cu is further relieved by using the oxidation-resistant conductive copper composite sol as an intermediate layer of the stainless steel foil and the aluminum mesh, and the performance of the reinforced stainless steel foil after rolling is further improved. In order to further improve the conductivity and capacity retention rate, graphene / carbon nanotube composite sol is further coated on the surface to endow the current collector with good corrosion resistance and conductivity; the graphene and the carbon nanotube form a three-dimensional structure of "sheet-tube" interweaving to reduce the overall resistance; the carbon nanotube is modified by amination and polyaniline to form a three-dimensional conductive network on the carbon nanotube, and can synergistically act with the bottom oxidation-resistant conductive copper composite sol, so that the polar groups on the surface and the reinforced interface are combined while the resistance is reduced after rolling treatment, thereby improving the conductivity and capacity retention rate of the stainless steel foil. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0020] In the following specific embodiments, the parts are mass parts, and in the present embodiment, it should be noted that there is no special restriction on the purchase manufacturers of all raw materials involved in the present application, which exemplarily includes: The code number of copper nitride is HC1313; the CAS number of nickel acetate is 373-02-4; the CAS number of ethylenediamine is 107-15-3; the CAS number of hydrazine hydrate is 7803-57-8; the CAS number of 3-aminobenzoic acid is 30418-59-8; the CAS number of EDC (ethyl-(3-dimethylaminopropyl) carbodiimide) is 25952-53-8; the CAS number of NHS (N-hydroxysuccinimide) is 6066-82-6; the CAS number of ammonium persulfate (ammonium persulfate) is 7727-54-0; the CAS number of aniline is 62-53-3; the CAS number of p-phenylenediamine is 106-50-3; the CAS number of p-hydroxybenzenesulfonic acid is 98-67-9; the code number of carbon nanotube is WD3713.

[0021] Example 1: A preparation method of high-conductivity stainless steel foil for positive electrode current collector, comprising the following operation steps: Preparation: the preparation method of the antioxidant conductive copper composite sol is as follows: (1) 2 parts of copper nitride and 1.8 parts of nickel acetate are uniformly mixed into 12 parts of sodium hydroxide aqueous solution (the concentration of sodium hydroxide aqueous solution is 8M), 6 parts of ethylenediamine and 1.2 parts of hydrazine hydrate aqueous solution are continuously mixed uniformly to obtain a mixed solution; (2) 5 parts of graphite oxide are added into 100 parts of deionized water, ultrasonic treatment is performed, 4 parts of hydrazine hydrate are uniformly mixed, reflux is performed at 90℃ for 22 hours, the temperature is reduced to 75℃, 18 parts of the mixed solution is added, heating is performed for 2 hours, the temperature is reduced to room temperature, 0.05M phosphoric acid aqueous solution is used to adjust the pH to 5, 4 parts of sulfonated polyaniline is added, stirring is performed for 2 hours in a nitrogen atmosphere, the pH is adjusted to neutral, and an antioxidant conductive copper composite sol is obtained; The preparation method of the 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, washed and filtered to 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-aminobenzoic acid are continuously mixed for 6 hours, and then washed, dried to obtain modified carbon nanotubes; (2) 0.7 parts of modified carbon nanotubes, 2 parts of aniline and 1.5 parts of p-hydroxybenzenesulfonic acid are uniformly mixed into 1M HCl solution, 1.8 parts of ammonium persulfate is added, and stirring is performed for 6 hours under ice water bath condition, centrifuged, washed and dried to obtain carbon nanotube-based polyaniline; (3) 5 parts of graphite oxide are added into 100 parts of deionized water, ultrasonic treatment is performed, 3 parts of hydrazine hydrate is added, reflux is performed at 90℃ for 15 hours, 4 parts of carbon nanotube-based polyaniline is added and stirring is continuously performed for 3 hours to obtain a graphene / carbon nanotube composite sol; Step 1: The stainless steel foil was acid-washed and then dried, immersed in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution was 1.2 mM) and ultrasonicated for 2 hours, then removed and cleaned, cured at 120°C for 3 hours, cooled to room temperature, washed, and dried with nitrogen to obtain a prefabricated stainless steel foil; Step 2: The prefabricated stainless steel foil was immersed in the antioxidant conductive copper composite sol for 25 seconds, taken out and dried, then covered with an aluminum grid, and rolled (under nitrogen conditions, set the pressure to 10 MPa, the temperature to 45°C, and the time for 15 minutes), then immersed in the graphene / carbon nanotube composite sol for 20 seconds, taken out, dried at 100°C for 4 minutes, rolled (under nitrogen conditions, set the pressure to 10 MPa, the temperature to 45°C, and the time for 10 minutes), and dried to obtain a highly conductive stainless steel foil.

[0022] Example 2: A method for preparing a highly conductive stainless steel foil for a positive electrode current collector, comprising the following steps: Pre-preparation: The preparation method of the antioxidant conductive copper composite sol is as follows: (1) adding 2 parts of copper nitride and 1.8 parts of nickel acetate to 12 parts of sodium hydroxide aqueous solution (the concentration of the sodium hydroxide aqueous solution is 8M) and mixing them evenly, adding 6 parts of ethylenediamine and 1.2 parts of hydrazine hydrate aqueous solution and continuing to mix evenly to obtain a mixed solution; (2) adding 5 parts of graphite oxide to 100 parts of deionized water, ultrasonically treating, adding 4 parts of hydrazine hydrate and mixing evenly, refluxing at 90°C for 22 hours, cooling to 75°C, adding 18 parts of the mixed solution, heating for 2 hours, cooling to room temperature, adjusting the pH to 5 with 0.1M phosphoric acid aqueous solution, adding 4 parts of sulfonated polyaniline, stirring for 2 hours under a nitrogen atmosphere, adjusting the pH to neutral, and obtaining an antioxidant conductive copper composite sol; The preparation method of graphene / carbon nanotube composite sol is as follows: (1) 2 parts of carbon nanotubes are ultrasonically dispersed in a 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 continued to mix for 6 hours, washed and dried to obtain modified carbon nanotubes; (2) 0.7 parts of modified carbon nanotubes are added and stirred. (3) Add 5 parts of graphite oxide to 100 parts of deionized water, ultrasonically treat, add 3 parts of hydrazine hydrate, reflux at 90 ° C for 15 hours, add 4 parts of carbon nanotube-based polyaniline and continue stirring for 3 hours to obtain graphene / carbon nanotube composite sol; Step 1: stainless steel foil was cleaned by acid pickling and dried, then immersed in an ethylenediaminetetramethylene phosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylene phosphonic acid ethanol solution was 1.2 mM) for ultrasonic treatment for 2 hours, taken out and washed, cured at 120°C for 3 hours, cooled to room temperature, washed, and dried with nitrogen to obtain a pre-prepared stainless steel foil; Step 2: the pre-prepared stainless steel foil was immersed in an antioxidant conductive copper composite sol for 30 seconds, taken out and dried, then coated with an aluminum mesh and roll-pressed (under a nitrogen atmosphere, the pressure was set to 10 MPa, the temperature was 45°C, and the time was 15 minutes), then immersed in a graphene / carbon nanotube composite sol for 25 seconds, taken out, dried at 100°C for 4 minutes, roll-pressed (under a nitrogen atmosphere, the pressure was set to 10 MPa, the temperature was 45°C, and the time was 10 minutes), and dried to obtain a high-conductivity stainless steel foil.

[0023] Example 3: a method for preparing a high-conductivity stainless steel foil for a positive electrode current collector, comprising the following operation steps: Preparation: the method for preparing the antioxidant conductive copper composite sol was as follows: (1) 2 parts of copper nitride and 1.8 parts of nickel acetate were uniformly mixed in 12 parts of a sodium hydroxide aqueous solution (the concentration of the sodium hydroxide aqueous solution was 8 M), 6 parts of ethylenediamine and 1.2 parts of a hydrazine hydrate aqueous solution were continuously mixed uniformly to obtain a mixed solution; (2) 5 parts of graphite oxide were added to 100 parts of deionized water and ultrasonically treated, 4 parts of hydrazine hydrate were uniformly mixed, refluxed at 90°C for 22 hours, cooled to 75°C, 18 parts of the mixed solution were added, heated for 2 hours, cooled to room temperature, the pH was adjusted to 5 with a 0.1 M phosphoric acid aqueous solution, 4 parts of sulfonated polyaniline were added, stirred for 2 hours under a nitrogen atmosphere, and the pH was adjusted to neutral to obtain an antioxidant conductive copper composite sol; The method for preparing the graphene / carbon nanotube composite sol was as follows: (1) 2 parts of carbon nanotubes were ultrasonically dispersed in 30 wt% nitric acid aqueous solution, refluxed for 2 hours, washed and dried until neutral, ultrasonically dispersed in 45 parts of deionized water, 0.18 parts of NHS and 0.3 parts of EDC were added and stirred for 1.5 hours, 0.6 parts of p-phenylenediamine and 0.4 parts of 3-aminobenzoic acid were continuously mixed for 6 hours, washed, dried, and modified carbon nanotubes were obtained; (2) 0.7 parts of modified carbon nanotubes, 2 parts of aniline, and 1.5 parts of p-hydroxybenzenesulfonic acid were uniformly mixed in a 1 M HCl solution, 1.8 parts of ammonium persulfate was added under ice water bath conditions for 6 hours, centrifuged, washed, and dried to obtain carbon nanotube-based polyaniline; (3) 5 parts of graphite oxide were added to 100 parts of deionized water and ultrasonically treated, 3 parts of hydrazine hydrate was added, refluxed at 90°C for 15 hours, 4 parts of carbon nanotube-based polyaniline was added and continuously stirred for 3 hours to obtain a graphene / carbon nanotube composite sol; Step 1: After the stainless steel foil is acid washed and dried, it is immersed in an ethylenediaminetetramethylene phosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylene phosphonic acid ethanol solution is 1.2 mM) for ultrasonic treatment for 2 hours, taken out, washed, cured at 120°C for 3 hours, cooled to room temperature, washed, and dried with nitrogen to obtain a pre-prepared stainless steel foil; Step 2: The pre-prepared stainless steel foil is immersed in the antioxidant conductive copper composite sol for 35 seconds, taken out, dried, and then covered with an aluminum grid, and then roll-pressed (under the condition of nitrogen, the pressure is set to 10 MPa, the temperature is 45°C, and the time is 15 minutes), and then immersed in the graphene / carbon nanotube composite sol for 30 seconds, taken out, dried at 100°C for 4 minutes, roll-pressed (under the condition of nitrogen, the pressure is set to 10 MPa, the temperature is 45°C, and the time is 10 minutes), and dried to obtain a high-conductivity stainless steel foil.

[0024] Comparative Example 1 is based on Example 3, and polyaniline is not added; the remaining operation steps remain unchanged. Preparation: The antioxidant conductive copper composite sol is prepared by the following method: (1) 2 parts of copper nitride and 1.8 parts of nickel acetate are uniformly mixed in 12 parts of a sodium hydroxide aqueous solution (the concentration of the sodium hydroxide aqueous solution is 8 M), 6 parts of ethylenediamine and 1.2 parts of a hydrazine hydrate aqueous solution are continuously mixed uniformly to obtain a mixed solution; (2) 5 parts of graphite oxide are added to 100 parts of deionized water, ultrasonic treatment is performed, 4 parts of hydrazine hydrate are uniformly mixed, refluxing is performed at 90°C for 22 hours, the temperature is lowered to 75°C, 18 parts of the mixed solution is added, and heating is performed for 2 hours to obtain the antioxidant conductive copper composite sol; The graphene / carbon nanotube composite sol is prepared by the following method: 5 parts of graphite oxide are added to 100 parts of deionized water, ultrasonic treatment is performed, 3 parts of hydrazine hydrate are added, refluxing is performed at 90°C for 15 hours, 4 parts of carbon nanotubes are continuously stirred for 3 hours to obtain the graphene / carbon nanotube composite sol; Step 1: After the stainless steel foil is acid washed and dried, it is immersed in an ethylenediaminetetramethylene phosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylene phosphonic acid ethanol solution is 1.2 mM) for ultrasonic treatment for 2 hours, taken out, washed, cured at 120°C for 3~4 hours, cooled to room temperature, washed, and dried with nitrogen to obtain a pre-prepared stainless steel foil; Step 2: The pre-prepared stainless steel foil is immersed in the antioxidant conductive copper composite sol for 35 seconds, taken out, dried, and then covered with an aluminum grid, and then roll-pressed, and then immersed in the graphene / carbon nanotube composite sol for 30 seconds, taken out, dried at 100°C for 4 minutes, roll-pressed, and dried to obtain a high-conductivity stainless steel foil.

[0025] Comparative Example 2 is based on Example 3, and the positions of the graphene / carbon nanotube composite sol and the antioxidant conductive copper composite sol are exchanged; the remaining operation steps remain unchanged. Step 1: The stainless steel foil was acid-washed and then dried, immersed in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution was 1.2 mM) and ultrasonicated for 2 hours, then removed and cleaned, cured at 120°C for 3-4 hours, cooled to room temperature, washed, and dried with nitrogen to obtain a prefabricated stainless steel foil; Step 2: The prefabricated stainless steel foil was immersed in the graphene / carbon nanotube composite sol for 35 seconds, taken out and dried, then covered with an aluminum grid, rolled, and then immersed in the antioxidant conductive copper composite sol for 30 seconds. The foil was taken out and dried at 100°C for 4 minutes, rolled, and dried to obtain a highly conductive stainless steel foil.

[0026] Comparative Example 3 is based on Example 3, except that the antioxidant conductive copper composite sol is not introduced; the remaining operating steps remain unchanged; Step 1: The stainless steel foil was acid-washed and then dried, immersed in an ethylenediaminetetramethylenephosphonic acid ethanol solution (the concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution was 1.2 mM) and ultrasonicated for 2 hours, then removed and cleaned, cured at 120°C for 3-4 hours, cooled to room temperature, washed, and dried with nitrogen to obtain a prefabricated stainless steel foil; Step 2: The surface of the prefabricated stainless steel foil is covered with an aluminum grid, rolled, and then immersed in the graphene / carbon nanotube composite sol for 30 seconds. The foil is taken out and dried at 100°C for 4 minutes, rolled, and dried to obtain a highly conductive stainless steel foil.

[0027] Comparative Example 4 is based on Example 3, except that the ethylenediaminetetramethylenephosphonic acid ethanol solution is replaced with a passivation solution containing ethylenediaminetetramethylenephosphonic acid; the other operating steps remain unchanged; Step 1: The stainless steel foil is pickled and dried, immersed in a passivation solution containing ethylenediaminetetramethylenephosphonic acid for electroplating for 12 seconds, taken out for cleaning, and dried with nitrogen to obtain a prefabricated stainless steel foil; The raw materials of the passivation solution include: 10mL / L phytic acid, 5g / L sodium salt of phosphoric acid aqueous solution, 2g / L ethylenediaminetetramethylenephosphonic acid, 5g / L polyethylene glycol; the temperature is 45℃, the current density is 1.5A / dm 2 ; Step 2: The prefabricated stainless steel foil was immersed in the antioxidant conductive copper composite sol for 35 seconds, taken out and dried, then covered with an aluminum grid, rolled, and then immersed in the graphene / carbon nanotube composite sol for 30 seconds. The foil was taken out and dried at 100°C for 4 minutes, rolled, and dried to obtain a highly conductive stainless steel foil.

[0028] Testing experiment: (1) The resistance of the high conductive stainless steel foils prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was tested at 90° (the warp and weft are 90°); (2) The positive electrode current collectors were made of high-conductivity stainless steel foil prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 3, NCM622 (LiNi0.6 Mn 0.2 Co 0.2 O2)as a positive electrode material; the negative electrode current collector is a 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 in a carbonate mixed solvent and 5wt% fluoroethylene carbonate, 0.6wt% lithium difluoro(oxalato)borate, and the carbonate mixed solvent includes ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a mass ratio of 4:5:1; then a lithium ion battery is assembled according to a related process; the prepared battery is subjected to 1C charge-discharge cycle test, and the discharge capacity of the battery at the 1000th time and the 1st time is recorded after n cycles of charge-discharge, and the discharge retention rate is calculated, the capacity retention rate = the discharge capacity at the 1000th time / the discharge capacity at the 1st time x 100%; the test results are shown in Table 1.

[0029] Table 1

[0030] Conclusion: Comparative Example 1 is based on Example 3, without introducing polyaniline; the toughness and conductivity of the coating are reduced, which leads to cracks during the rolling process, resulting in performance degradation; Comparative Example 2 is based on Example 3, the positions of the graphene / carbon nanotube composite sol and the oxidation-resistant conductive copper composite sol are exchanged; which leads to the performance degradation of Comparative Example 3, because the core function of the oxidation-resistant conductive copper composite sol is to form a bottom conductive network through Cu / Ni alloy, and the conductivity of copper is much higher than that of graphene / carbon nanotube; the aluminum mesh and the stainless steel foil need to be in direct contact with the copper layer to be strengthened by rolling and conductive; Comparative Example 3 is based on Example 3, without introducing the oxidation-resistant conductive copper composite sol; which leads to the performance degradation of Comparative Example 4; Comparative Example 4 is based on Example 3, replacing the ethylenediaminetetramethylene phosphonic acid ethanol solution with a passivation solution containing ethylenediaminetetramethylene phosphonic acid; the passivation film of Comparative Example 4 leads to an increase in interfacial resistance, an increase in energy loss during charge and discharge, and thus a lower capacity retention rate than Example 3.

[0031] It is apparent to those skilled in the art that the present application is not limited to the details of the foregoing exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A method for preparing a highly conductive stainless steel foil for a positive electrode current collector, characterized in that: The following steps are included: Step 1: After acid washing and drying, the stainless steel foil is immersed in an ethylenediaminetetramethylenephosphonic acid ethanol solution and stirred under a nitrogen atmosphere for 2 to 3 hours, taken out and washed, and cured at 120 to 125°C for 3 to 4 hours. After cooling to room temperature, it is washed and dried under nitrogen to obtain a prefabricated stainless steel foil; Step 2: The prefabricated stainless steel foil is immersed in an antioxidant conductive copper composite sol for 25 to 40 seconds, taken out and dried, then covered with an aluminum grid, rolled, and then immersed in a graphene / carbon nanotube composite sol for 20 to 30 seconds, taken out, dried at 100 to 120°C for 4 to 6 minutes, rolled, and dried to obtain a highly conductive stainless steel foil.

2. The method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to claim 1, wherein: The stainless steel foil comprises the following components: 14-17 wt% Cr, 6-8 wt% Ni, 1.5-2.5 wt% Cu, 0.6-0.8 wt% Mn, 0.15-0.3 wt% Al, 0.05-0.1 wt% Ti, 0.003-0.005 wt% B, 0.2-0.3 wt% Nb, and the remainder is iron; The concentration of the ethylenediaminetetramethylenephosphonic acid ethanol solution in the prefabricated stainless steel foil is 1-1.5 mM.

3. The method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to claim 1, wherein: The preparation method of the antioxidant conductive copper composite sol is as follows: (1) adding copper nitride and nickel acetate to a sodium hydroxide aqueous solution and uniformly mixing, adding ethylenediamine and a hydrazine hydrate aqueous solution and continuing to uniformly mix to obtain a mixed solution; (2) adding graphite oxide to deionized water, ultrasonically treating, adding hydrazine hydrate and uniformly mixing, reflux at 90-95° C. for 20-24 hours, cooling to 70-80° 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, adding sulfonated polyaniline, stirring for 2-3 hours under a nitrogen atmosphere, adjusting the pH to neutral, and obtaining an antioxidant conductive copper composite sol.

4. The method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to claim 1, wherein: The raw materials of the mixed solution include the following components, by mass: 2 parts of copper nitride, 1.8-2.5 parts of nickel acetate, 10-15 parts of sodium hydroxide aqueous solution, 6-12 parts of ethylenediamine, and 1-2.5 parts of 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 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.

5. The method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to claim 1, wherein: The preparation method of the graphene / carbon nanotube composite sol is as follows: (1) ultrasonically dispersing carbon nanotubes in a 30-40 wt% nitric acid aqueous solution, refluxing for 2-3 hours, filtering and washing until neutral, ultrasonically dispersing carbon nanotubes in deionized water, adding NHS and EDC and stirring for 2-3 hours under a nitrogen atmosphere, adding p-phenylenediamine and 3-aminophenylboronic acid and continuing to mix for 6-8 hours, washing and drying to obtain modified carbon nanotubes; (2) adding modified carbon nanotubes, aniline and p-hydroxybenzenesulfonic acid to a 1-2 M HCl solution and uniformly mixing, adding ammonium persulfate, incubating in an ice-water bath for 4-6 hours, centrifuging, washing and drying to obtain carbon nanotube-based polyaniline; (3) adding graphite oxide to deionized water, ultrasonically treating, adding hydrazine hydrate, refluxing at 90-95° C. for 15-20 hours, adding carbon nanotube-based polyaniline and continuing to stir for 3-5 hours to obtain a graphene / carbon nanotube composite sol.

6. The method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to claim 5, wherein: The raw materials of the modified carbon nanotubes include the following components, calculated by mass: 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 include the following components, calculated by mass: 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 include the following components, calculated by mass: 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.

7. The method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to claim 1, wherein: The process conditions of the rolling treatment are as follows: under nitrogen conditions, the pressure is 5-15 MPa, the temperature is 40-60° C., and the rolling time is 10-15 minutes.

8. A highly conductive stainless steel foil prepared by the method for preparing a highly conductive stainless steel foil for a positive electrode current collector according to any one of claims 1 to 7.

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