A soft package current collector anti-chloride corrosion coating and a preparation method thereof

Abstract

This application discloses a chloride ion corrosion resistant coating for a soft-pack current collector, comprising a first coating and a second coating. The first coating is applied to the surface of the current collector, and the second coating is applied to the surface of the first coating. The first coating is made of composite polypyrrole, and the second coating is made of polypyrrole. The composite polypyrrole is 8-hydroxyquinoline-doped polypyrrole, with a molar ratio of 8-hydroxyquinoline to pyrrole monomers of (1~3):100. This application addresses the problem of chloride ion corrosion of the current collector in the high-concentration magnesium chloride system of aqueous magnesium-ion soft-pack batteries by designing a double-layer anti-corrosion coating consisting of an 8-hydroxyquinoline-doped polypyrrole underlayer and a pure polypyrrole surface layer, with optimized doping polymerization and coating processes. This coating combines strong interfacial bonding, dense physical barrier, and in-situ active corrosion inhibition, significantly improving the corrosion resistance of the current collector and the cycle life of the battery, thus meeting the industrial processing needs of soft-pack batteries.

Description

Technical Field

[0001] This application relates to the field of pouch battery technology, specifically to a pouch current collector anti-chloride ion corrosion coating and its preparation method. Background Technology

[0002] With the continued advancement of the "dual carbon" goals, large-scale electrochemical energy storage technology has entered a period of rapid development. Developing energy storage batteries that are safe, low-cost, long-life, and environmentally friendly has become a core research and development direction for the industry. Aqueous magnesium-ion batteries, with their abundant magnesium resources and high volumetric capacity (3833 mAh·cm³), are particularly advantageous. -3 With its outstanding advantages such as low electrode potential (-2.37 V vs. standard hydrogen electrode) and no dendrite safety risks, aqueous electrolyte has become an important technical route for the next generation of large-scale energy storage batteries. At the same time, compared with traditional organic electrolytes, aqueous electrolytes are non-flammable, non-toxic, have high ionic conductivity, simple preparation process, and low cost, which completely solves the thermal runaway safety hazards of organic electrolyte systems and has significant industrialization advantages in the large-scale production of pouch batteries.

[0003] In aqueous magnesium-ion battery systems, magnesium chloride-based electrolytes are widely used due to their high ionic conductivity, wide electrochemical stability window, excellent magnesium ion insertion / extraction kinetics, and good compatibility with positive and negative electrode materials. These electrolytes can significantly improve the battery's rate performance, charge-discharge reversibility, and cycle stability. However, the high concentration of chloride ions in magnesium chloride electrolytes exhibits strong electronegativity and penetrability, causing severe electrochemical corrosion to the core metal current collector of the battery. This problem is particularly prominent in pouch cells. Soft-pack batteries use an aluminum-plastic film encapsulation structure, which has a larger contact area between the current collector and the electrolyte compared to steel-cased and aluminum-cased hard-cased batteries. This provides a channel for chloride ions to penetrate and corrode. Chloride ions will preferentially destroy the passivation oxide film naturally formed on the surface of the aluminum current collector, leading to a series of problems such as pitting corrosion, crevice corrosion, and intergranular corrosion. Ultimately, this will cause current collector pulverization, structural damage, and breakage at the electrode tab welds, resulting in a sharp increase in battery internal resistance, rapid capacity decay, charge and discharge failure, and even serious safety accidents such as battery swelling and electrolyte leakage. This has become the core issue restricting the long cycle life and industrial application of aqueous magnesium-ion soft-pack batteries.

[0004] To address the chloride ion corrosion problem in current collectors of aqueous magnesium-ion batteries, existing modification solutions mainly fall into two categories: the first is electrolyte component regulation modification, and the second is current collector surface protective coating construction modification. The mainstream technical route for electrolyte component regulation modification includes adding organic / inorganic corrosion inhibitors to the electrolyte, constructing high-concentration salt electrolytes, and adjusting the electrolyte hydrogen bond network and pH value. While this approach can alleviate the corrosion problem of the current collector to some extent, it has inherent drawbacks: high-concentration salt electrolytes significantly increase the preparation cost of the electrolyte, and the electrolyte viscosity increases significantly, leading to a decrease in magnesium ion migration efficiency and severe degradation of battery rate performance; the addition of corrosion inhibitors inevitably affects the ionic conductivity of the electrolyte, and some corrosion inhibitors can also undergo side reactions on the electrode surface, affecting the lithium insertion / extraction kinetics of the electrode material. Furthermore, corrosion inhibitors can only delay the corrosion process and cannot fundamentally isolate chloride ions from contact with the current collector substrate. During long-term cycling, the corrosion inhibition effect continuously diminishes, making it difficult to meet the long-term stable cycling requirements of pouch batteries. Modifying the protective coating on the current collector surface involves preparing a functional coating to form a physical barrier against chloride ions, fundamentally preventing contact between corrosive ions and the metal substrate. This is currently the most promising anti-corrosion modification solution. Existing technologies primarily focus on carbon-based materials such as graphene, carbon nanotubes, and conductive graphite for the research and application of protective coatings on current collectors, with applications concentrated in lithium-ion batteries using organic electrolyte systems. Organic electrolyte systems contain only ppm-level chloride impurities, providing a mild corrosive environment, while the magnesium chloride electrolyte used in aqueous magnesium-ion batteries can have chloride ion concentrations reaching 1%. The concentration of chloride ions (mol / L and above) is significantly higher than that of chlorine-containing organic electrolytes. Furthermore, the hydrogen and oxygen evolution side reactions in aqueous environments further accelerate the electrochemical corrosion process. Existing carbon-based coatings exhibit a substantial decrease in protective effectiveness in this highly corrosive system, presenting several intractable technical problems: First, pure carbon-based coatings only provide physical barrier properties and lack corrosion inhibition. Unavoidable defects during coating preparation, such as pinholes, pores, and microcracks, become rapid channels for chloride ion penetration. Once chloride ions penetrate the coating and contact the metal substrate, pitting corrosion spreads rapidly, failing to inhibit the corrosion process. Second, the interfacial bonding between the carbon-based coating and the aluminum current collector substrate is weak. During processing steps such as rolling, bending, and heat sealing of pouch batteries, coating peeling and cracking are highly likely, resulting in a loss of protective effect. Third, existing carbon-based coatings struggle to balance excellent chloride ion penetration resistance with high conductivity. Increasing the coating thickness to enhance the barrier effect leads to a significant increase in the current collector surface resistance, affecting the battery's high-current charge and discharge performance and failing to meet the performance and processing requirements of pouch batteries.

[0005] Furthermore, existing research on protective coatings for current collectors in aqueous batteries is mostly focused on aqueous lithium-ion batteries and aqueous zinc-ion battery systems. There is very little research on dedicated anti-chloride ion corrosion coatings for high-concentration magnesium chloride electrolyte systems in aqueous magnesium-ion batteries. The electrolyte pH, chloride ion activity, and electrode working potential window vary significantly among different aqueous battery systems, and existing coatings cannot be directly adapted to them. Summary of the Invention

[0006] To address the aforementioned shortcomings, this application provides a soft-pack current collector anti-chloride ion corrosion coating and its preparation method, thereby solving the technical problem of poor anti-chloride ion corrosion performance of current collectors in water-based magnesium ion batteries in the prior art.

[0007] In a first aspect, this application provides a chloride ion corrosion resistant coating for a flexible current collector, the chloride ion corrosion resistant coating being composed of a first coating and a second coating; wherein, the first coating is coated on both sides of the current collector, and the second coating is coated on the surface of the first coating; the first coating is made of composite polypyrrole, and the second coating is made of polypyrrole; the composite polypyrrole is polypyrrole doped with 8-hydroxyquinoline, and the molar ratio of 8-hydroxyquinoline to pyrrole monomer is (1~3):100.

[0008] Preferably, the composite polypyrrole is obtained through the following steps:

[0009] Step 1: Dissolve sodium p-toluenesulfonate and 8-hydroxyquinoline in water, then add pyrrole monomer, labeled as solution a; in solution a, the molar ratio of sodium p-toluenesulfonate, 8-hydroxyquinoline and pyrrole monomer is (4~6):(0.1~0.2):10;

[0010] Step 2: Dissolve ammonium persulfate in water to prepare an oxidizing agent solution; the molar ratio of ammonium persulfate to pyrrole monomer is (1~2):(1~2);

[0011] Step 3: Slowly add the oxidant solution to solution a at a rate of 3 ml / min, and react at 4℃~5℃ for 4h~6h; after the reaction is complete, collect the black precipitate, wash and dry it to obtain composite polypyrrole.

[0012] Preferably, the raw materials for preparing the first coating are as follows:

[0013] In an organic solvent, the mass ratio of composite polypyrrole, conductive graphite and binder is (3~5):(2~4):(2~4).

[0014] Preferably, the raw materials for preparing the second coating are as follows:

[0015] In an organic solvent, the mass ratio of polypyrrole, conductive graphite and binder is (3~5):(2~4):(2~4).

[0016] Preferably, the adhesive is selected from polyvinylidene fluoride or polyvinylidene fluoride copolymer.

[0017] Preferably, the organic solvent is selected from N-methyl-2-pyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0018] Preferably, the metal current collector is selected from aluminum or copper.

[0019] Preferably, the thickness of the first coating is 50~200μm, and the thickness of the second coating is 20~30μm.

[0020] Secondly, this application also provides a method for preparing the above-mentioned flexible current collector anti-chloride ion corrosion coating, wherein the flexible current collector anti-chloride ion corrosion coating is prepared by the following steps:

[0021] S1: Add the adhesive to the organic solvent in portions to prepare a 5wt%~7wt% adhesive solution;

[0022] S2: After uniformly mixing composite polypyrrole and conductive graphite, add adhesive solution to obtain the slurry for the first coating layer; after uniformly mixing polypyrrole and conductive graphite, add adhesive solution to obtain the slurry for the second coating layer.

[0023] S3: After applying the slurry of the first coating onto the surface of the current collector and drying it, apply the slurry of the second coating onto the surface of the first coating and dry it.

[0024] Compared with the prior art, this application has the following beneficial effects:

[0025] 1. This application discovers that using 8-HQ-doped composite polypyrrole as the first coating in direct contact with the current collector, the 8-HQ molecules, possessing highly active hydroxyl groups, can simultaneously form strong two-site hydrogen bonds and chemisorption with the imino groups of the polypyrrole backbone and the hydroxyl groups of the natural passivation film on the current collector surface. Compared to pure polypyrrole coatings, the interfacial bonding strength with the metal substrate is improved by an order of magnitude, completely solving the core problem of weak interfacial bonding between traditional carbon-based coatings and the current collector, and easy peeling off during the rolling, bending, and heat sealing processes of soft-pack batteries. Simultaneously, the composite polypyrrole particles doped with 8-HQ have a more regular morphology and better size uniformity, allowing for complete adhesion to the current collector surface after coating, without interfacial gaps, pores, or other defects, structurally eliminating the channels for chloride ions to penetrate along the current collector-coating interface. Using pure polypyrrole as the second coating in direct contact with high-concentration magnesium chloride electrolyte can form a continuous, dense, and pinhole / microcrack-free polymer film, achieving highly efficient physical barrier against chloride ions and preventing their penetration into the coating interior, thus significantly reducing the probability of corrosion from the source. Furthermore, the tightly packed molecular chains of pure polypyrrole result in superior film density compared to doped polypyrrole, providing a stronger physical barrier against chloride ions and avoiding microscopic defects in the coating that may result from corrosion inhibitor doping. The 8-HQ-doped composite polypyrrole, serving as the first coating, constitutes the second layer of protection and a backup passivation layer: for trace amounts of chloride ions that penetrate the surface barrier, it can release 8-HQ corrosion inhibitors at specific points through chloride ion-stimulated ion exchange, directly chelating with aluminum ions at the corrosion initiation sites on the current collector surface to form a dense, insoluble organic-metal passivation film. This directly blocks the anodic corrosion electrochemical reaction at the very front of corrosion, completely solving the problem of traditional single physical barrier coatings "completely failing once chloride ions penetrate."

[0026] 2. In this application, the composite polypyrrole loaded with 8-HQ corrosion inhibitor is set as the bottom layer completely wrapped by the surface layer of pure polypyrrole, and does not directly contact the electrolyte. This structurally eliminates the problem of corrosion inhibitor leaching into the electrolyte. It avoids the technical risks of 8-HQ reacting with magnesium ions in the electrolyte to form insoluble precipitates, contaminating the electrolyte, and clogging electrode pores. It also does not affect the ionic conductivity and magnesium ion migration efficiency of the electrolyte. This completely solves the problems of corrosion inhibitor precipitation and loss, continuous decay of long-cycle corrosion inhibition effect, and deterioration of battery electrochemical performance in traditional electrolyte corrosion inhibitor addition and surface doping solutions. Meanwhile, the 8-HQ layer enclosed in the bottom layer is released only at specific points when trace amounts of chloride ions penetrate, with no excess loss, maintaining stable corrosion inhibition capabilities throughout the entire battery cycle. Furthermore, the coating exhibits no redox side reactions within the full operating potential window of the aqueous magnesium-ion battery, completely unaffected by magnesium ion insertion / extraction kinetics. Three-electrode and full-cell tests have verified that the electrode charge / discharge polarization is minimal, redox reversibility is excellent, and coulombic efficiency is close to 100%, with no side reaction interference. Moreover, by using intrinsically highly conductive pure polypyrrole as the surface layer in direct contact with the electrode material, efficient electron transport can be achieved without relying on a large amount of conductive filler. Serving as an electron transport channel between the current collector and the electrode material, it achieves extremely low interfacial contact resistance and surface resistance, without significant degradation of conductivity due to increased coating thickness.

[0027] 3. The dual-layer gradient structure of this application achieves synergistic optimization of mechanical properties: the bottom layer composite polypyrrole enhances the entanglement and cross-linking density of polymer chains through strong hydrogen bonding between 8-HQ and the polypyrrole molecular chains. Compared with pure polypyrrole, the fracture toughness, bending resistance, and deformation resistance of the coating are further improved. At the same time, the strong interfacial bonding between the bottom layer and the current collector can effectively disperse the interfacial stress during processing and prevent the coating from peeling off from the substrate. The surface layer of pure polypyrrole has excellent film-forming properties and flexibility. The two form a gradient stress dispersion structure, which significantly improves the fracture load and tensile strength compared with commercially available carbon-coated aluminum foil. In the entire process of soft-pack battery rolling, bending, heat sealing, etc., there will be no problems of coating cracking, peeling, or delamination, and the integrity of the protective structure will always be maintained, which has excellent industrial processing adaptability.

[0028] 4. The dual-layer coating system of this application is specifically designed for the highly corrosive environment of aqueous magnesium-ion batteries with high concentrations of magnesium chloride (1 mol / L and above). It is completely different from traditional carbon-based coatings developed for organic electrolytes and aqueous lithium / zinc-ion batteries. It perfectly adapts to the electrolyte pH, chloride ion activity, and electrode operating potential window of aqueous magnesium-ion batteries, solving the problem of existing coatings being unable to be directly adapted across systems. Long-term cycle testing has verified that the soft-pack full battery assembled with the modified current collector of this application has a smooth appearance after cycling, without gas expansion, leakage, or bulging. The electrode coating remains intact without peeling or corrosion / powdering, completely solving the battery safety accidents caused by current collector corrosion and providing core technical support for the long-cycle industrial application of aqueous magnesium-ion soft-pack batteries. Attached Figure Description

[0029] Figure 1 The images are SEM images of 8-HQ-PPy and PPy; where ab is 8-HQ-PPy and cd is PPy.

[0030] Figure 2 The images show SEM images of the surface and cross-section of a single-layer coating; where ab represents the surface and cd represents the cross-section.

[0031] Figure 3 The images show the surface and cross-section of the double-coated surface; where ac represents the surface and df represents the cross-section.

[0032] Figure 4 The conductivity diagrams are for single / double coatings.

[0033] Figure 5 The coating performance diagrams are prepared for different second coating thicknesses; where a is sheet resistance and b is electrical conductivity.

[0034] Figure 6 for Figure 5 The small image in 'a'.

[0035] Figure 7 for Figure 5 The small image in b.

[0036] Figure 8 The diagram shows a comparison of the mechanical strength of the current collector; where a is the fracture load and b is the tensile strength.

[0037] Figure 9 Open circuit potential diagrams for aluminum foil with different coatings and pure aluminum foil.

[0038] Figure 10 The potentiodynamic polarization curves of aluminum foil with different coatings and pure aluminum foil are shown.

[0039] Figure 11The three-electrode electrochemical performance curves of the modified current collector MVOH prepared in Example 1 are shown below; where a is the CV curve at a scan rate of 1 mV / s; b is the GCD curve at a current density of 0.1 A / g; c is the rate performance curve; and d is the long-cycle performance curve at a current density of 1 A / g.

[0040] Figure 12 The GCD curves of the modified current collector prepared in Example 1 and Comparative Example 2 at a current density of 0.08 A / g are shown.

[0041] Figure 13 Electrochemical performance of the PTCDA / / MgCl2 / / MVOH full cell in a pouch cell: where a is the CV curve at a scan rate of 1 mV / s; b is the rate performance curve; c is the GCD curve at a current density of 0.08 A / g; and d is the long-cycle performance curve at a current density of 0.1 A / g.

[0042] Figure 14 The following are the results of testing on the pouch cell with current collector prepared in Comparative Example 2 and the pouch cell with current collector prepared in Example 1: a) Appearance of the pouch cell in Comparative Example 2; b) Electrode of Comparative Example 2; c) Appearance of the pouch cell in Example 1; d) Electrode of Example 1. Detailed Implementation

[0043] This application will clearly and completely describe the technical solutions of the embodiments of this application with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0044] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0045] I. A flexible current collector coating resistant to chloride ion corrosion

[0046] This application addresses the problems of existing electrolyte component modification schemes, such as high preparation costs, deterioration of battery rate performance, inability to fundamentally block corrosion, and continuous decay of corrosion inhibition effect over long cycles. It also addresses issues with mainstream carbon-based current collector protective coatings, which only provide a single physical barrier, have weak interfacial adhesion with the current collector substrate, are prone to detachment and cracking during pouch battery processing, cannot simultaneously achieve resistance to chloride ion penetration and high conductivity, are susceptible to rapid pitting corrosion propagation at coating defects, and are unsuitable for highly corrosive environments with high concentrations of magnesium chloride. This application proposes coating the current collector surface and improving the coating material and structure to leverage the coating's film-forming properties, strong interfacial adhesion with the metal substrate, intrinsic high conductivity, and the ability to achieve functional modification through in-situ doping, while simultaneously solving the problems of traditional carbon-based coatings. Specifically, this application selects the conjugated conductive polymer polypyrrole as the core matrix material for the coating and further considers introducing organic corrosion inhibitors with chloride ion inhibition effects into polypyrrole to further enhance its resistance to chloride ion corrosion. However, in actual research, this application found that not all organic corrosion inhibitors with chloride ion corrosion inhibition effects can achieve in-situ stable doping of polypyrrole. For example, benzotriazole (BTA) corrosion inhibitors commonly used in this field are difficult to effectively dope polypyrrole because BTA has strong free radical scavenging properties, which quench cationic free radicals generated during the oxidative polymerization of pyrrole, directly terminating the polymerization chain reaction, resulting in polypyrrole being unable to polymerize normally to form a polymer with high molecular weight and continuous film formation. The BTA molecule lacks active hydroxyl groups that can form stable hydrogen bonds with imino groups in the polypyrrole molecule chain. It relies only on weak van der Waals forces and π-π interactions, which cannot stably embed into the molecular chain gaps during the polypyrrole polymerization process. It is very easy to precipitate during subsequent cleaning and film formation, and cannot achieve stable loading of the corrosion inhibitor. In the weakly acidic polymerization system used in this application, BTA has a very low degree of protonation and cannot participate in the positive charge balance of the polypyrrole backbone as a dopant anion, making it fundamentally difficult to achieve effective doping. In contrast, this application found that 8-hydroxyquinoline (8-HQ) can be well integrated into the polypyrrole system. Its molecular structure contains hydroxyl groups that can form strong hydrogen bonds with the polypyrrole backbone and quinoline conjugated rings that have excellent compatibility with the polypyrrole conjugated system. In a weakly acidic polymerization system, it can achieve appropriate protonation and hydroxyl dissociation. It can be stably embedded in the polypyrrole molecular chain through hydrogen bonding and π-π conjugation, and can also participate in the charge balance of polypyrrole without interfering with the normal oxidative polymerization process of pyrrole. This allows for in-situ stable doping of corrosion inhibitors.

[0047] Based on the above design concept and experimental research conclusions, this application finally constructed a two-layer composite protective coating technology solution of "8-HQ doped polypyrrole bottom layer + pure polypyrrole top layer". The bottom layer of 8-HQ doped composite polypyrrole is directly bonded to the surface of the current collector and loaded with a corrosion inhibitor with chloride ion stimulation response characteristics. It can achieve the point-controlled release of the corrosion inhibitor when a trace amount of chloride ion penetrates, forming a dense chelated passivation film at the corrosion initiation site, inhibiting the initiation and spread of pitting corrosion from the root and providing the first layer of dense physical barrier. The surface layer of pure polypyrrole coating achieves strong interfacial bonding with the metal substrate through hydrogen bonding and chemical adsorption, providing the second layer of physical barrier.

[0048] The technical solution of this application has achieved many unexpected technical effects in practical applications: First, the double-layer polypyrrole coating of this application not only does not degrade the coating performance due to the doping of corrosion inhibitors, but also further enhances the mechanical strength and flexibility of the coating through the hydrogen bonding between 8-HQ and polypyrrole. Its breaking load is significantly higher than that of traditional carbon-coated aluminum foil. There is no peeling or cracking in the entire process of soft-pack battery rolling, bending, heat sealing, etc., which perfectly meets the industrial processing requirements of soft-pack batteries; Second, the coating of this application completely solves the problem that the barrier properties and conductivity of traditional protective coatings cannot be achieved at the same time. While increasing the coating thickness to enhance the chloride ion barrier effect, the intrinsic high conductivity of polypyrrole does not cause a significant increase in the current collector surface resistance. Instead, it enables the battery to have better high-current charge and discharge rate performance; Third, this application The coating can achieve stable charge-discharge cycles of more than 200 cycles in a high-concentration magnesium chloride electrolyte system of 1 mol / L or higher, while the unmodified current collector fails due to corrosion during the first charge-discharge cycle, and the traditional carbon-based coating fails within 50 cycles. Moreover, the coating of this application maintains an intact protective structure after long-term cycling without any decay in corrosion inhibition effect, fundamentally solving the problem of long-term protection of current collectors in high-concentration chloride ion systems. Fourth, the coating of this application has excellent electrochemical stability throughout the entire operating potential window of aqueous magnesium-ion batteries, with no redox side reactions occurring and no interference with the insertion-extraction kinetics of magnesium ions in the electrolyte. This completely avoids the degradation of battery electrochemical performance caused by traditional electrolyte corrosion inhibitor addition schemes, providing core technical support for the long-cycle industrial application of aqueous magnesium-ion soft-pack batteries.

[0049] In some embodiments of this application, excessive 8-HQ doping leads to a high 8-HQ content in the coating. The excess 8-HQ will react with magnesium ions in the electrolyte and electrode to form an insoluble thin film precipitate, thus affecting the battery's electrochemical performance. However, insufficient 8-HQ doping results in no corrosion protection. Therefore, the composite polypyrrole is polypyrrole doped with 8-hydroxyquinoline, and the molar ratio of 8-hydroxyquinoline to pyrrole monomers can be 1:100, 2:100, 3:100, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in embodiments, any of the above ranges can be combined with any other range.

[0050] In some embodiments of this application, the composite polypyrrole is obtained through the following steps: Step 1: Sodium p-toluenesulfonate and 8-hydroxyquinoline are dissolved in water, and then pyrrole monomer is added, labeled as solution a; in solution a, the molar ratio of sodium p-toluenesulfonate, 8-hydroxyquinoline and pyrrole monomer is (4~6):(0.1~0.2):10, more preferably 5:0.1:10; Step 2: Ammonium persulfate is dissolved in water to prepare an oxidizing agent solution; the molar ratio of ammonium persulfate to pyrrole monomer is (1~2):(1~2), more preferably 1:1; Step 3: The oxidizing agent solution is slowly added to solution a at a rate of 3 ml / min, and the reaction is carried out at 4℃~5℃ for 4h~6h; after the reaction is completed, the black precipitate is collected, washed and dried to obtain the composite polypyrrole. In this embodiment, if the ratio of sodium p-toluenesulfonate to pyrrole monomer is too low, the TsO in the system will be insufficient. - Insufficient concentration fails to adequately balance the positive charge of the polypyrrole backbone, leading to increased conjugated structural defects, low degree of polymerization, small molecular weight, and a significant decrease in product conductivity, severely deteriorating film-forming properties and mechanical properties. Simultaneously, insufficient ionic strength results in poor dispersion of pyrrole monomers, uneven polymerization, and easy agglomeration, making uniform 8-HQ doping impossible. Conversely, excessively high concentrations of TsO... - It will occupy most of the doping sites in the polypyrrole backbone, forming a strong competitive doping with 8-HQ, significantly reducing the effective doping amount of 8-HQ, resulting in insufficient active corrosion inhibition function of the final coating; at the same time, excessive TsO - It will accelerate the polymerization rate, leading to runaway reaction and the formation of low molecular weight oligomers. The film-forming properties and mechanical properties of polypyrrole will decrease, and excessive salt residue will trigger side reactions during battery cycling.

[0051] In some embodiments of this application, the raw materials for preparing the first coating are as follows: in an organic solvent, the mass ratio of composite polypyrrole, conductive graphite, and binder is (3~5):(2~4):(2~4). The raw materials for preparing the second coating are as follows: in an organic solvent, the mass ratio of pure polypyrrole, conductive graphite, and binder is (3~5):(2~4):(2~4). The binder is selected from polyvinylidene fluoride (PVDF) or PVDF copolymer, preferably PVDF, because PVDF has good dispersion and typical shear-thinning properties, making it easier to adjust the solution viscosity. The organic solvent is selected from N-methyl-2-pyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide, preferably NMP, because compared to other solvents, NMP has good solubility at room temperature, controllable drying rate, and chemical inertness. The metal current collector is selected from aluminum or copper.

[0052] In some embodiments of this application, the thickness of the first coating is 20-30 μm, and the thickness of the second coating is 50-200 μm. Preferably, the thickness of the first coating is 20 μm, 25 μm, 30 μm, etc., and all ranges and sub-ranges between these values; the thickness of the second coating is preferably 50 μm, 100 μm, 150 μm, 200 μm, etc., and all ranges and sub-ranges between these values. It should be understood that, in embodiments, any of the above ranges can be combined with any other range.

[0053] II. A method for preparing the above-mentioned flexible current collector anti-chloride ion corrosion coating

[0054] S1: Add the adhesive to the organic solvent in portions to prepare a 5wt%~7wt% adhesive solution;

[0055] S2: After uniformly mixing composite polypyrrole and conductive graphite, add adhesive solution to obtain the slurry for the first coating layer; after uniformly mixing polypyrrole and conductive graphite, add adhesive solution to obtain the slurry for the second coating layer.

[0056] S3: After applying the slurry of the first coating onto the surface of the current collector and drying it, apply the slurry of the second coating onto the surface of the first coating and dry it.

[0057] III. Examples and Comparative Examples

[0058] Example 1

[0059] First, 14.5 mg (0.1 mmol) of 8-HQ and 0.97 g (5 mmol) of sodium p-toluenesulfonate were added to deionized water as a composite dopant. After complete dissolution, 670 μL (10 mmol) of pyrrole monomer was pipetted into the solution, and stirring was continued for 30 minutes to ensure homogeneity; this solution was labeled as solution a. Simultaneously, 20 mL of deionized water was added to a 50 mL beaker, and 2.28 g (10 mmol) of ammonium persulfate was weighed and added to prepare an oxidizing agent solution. Then, the oxidizing agent solution was slowly added dropwise to solution a, which was continuously stirred. As the addition proceeded, the solution gradually turned blue-black. After the addition was completed within 7-8 minutes, the beaker was transferred to a water bath and reacted at 5 °C for 5 hours. After the reaction, the solution was filtered to obtain a black precipitate, which was washed 2-3 times with deionized water and 2-3 times with anhydrous ethanol to remove unreacted monomers and impurities. The product was then placed in a vacuum drying oven and dried at 80 °C for 12 h to obtain composite polypyrrole (composite PPy) for later use. Then, without adding 8-HQ, polypyrrole (PPy) was prepared according to the above steps for later use.

[0060] First, PVDF was added to NMP solution in small amounts multiple times to prepare a 6wt% PVDF slurry. Then, the prepared composite PPy was ball-milled until fine particles were formed, mixed evenly with conductive graphite, and the PVDF slurry was added as a binder. The mass ratio of composite PPy, conductive graphite, and PVDF was 4:3:3. After thorough mixing, a first coating slurry was obtained. Similarly, PPy was ball-milled until fine particles were formed, mixed evenly with conductive graphite, and the PVDF slurry was added as a binder. The mass ratio of PPy, conductive graphite, and PVDF was 4:3:3. After thorough mixing, a second coating slurry was obtained. The first coating slurry was evenly coated onto carbon-coated aluminum foil using a four-sided coater on a multi-functional coater. The foil was then dried in a forced-air drying oven at 80°C until the solvent was completely evaporated. The second coating was then applied to the surface of the first coating using the same method. After drying, the coatings were rolled using a roller press with appropriate parameters to obtain the final modified current collector. The thickness of the first coating was 25 μm, and the thickness of the second coating was 100 μm.

[0061] Example 2

[0062] This example is an adjustment to Example 1, except that the amount of 8-HQ used is 0.2 mmol. All other steps are exactly the same as in Example 1.

[0063] Example 3

[0064] This example is an adjustment to Example 1, except that the amount of 8-HQ used is 0.3 mmol. All other steps are exactly the same as in Example 1.

[0065] Example 4

[0066] The method is an adjustment based on Example 1, except that the thickness of the second coating is 50 μm. All other steps are exactly the same as in Example 1.

[0067] Example 5

[0068] The method is an adjustment based on Example 1, except that the thickness of the second coating is 100 μm. All other steps are exactly the same as in Example 1.

[0069] Example 6

[0070] The method is an adjustment based on Example 1, except that the thickness of the second coating is 150 μm. All other steps are exactly the same as in Example 1.

[0071] Example 7

[0072] The method is an adjustment based on Example 1, except that the thickness of the second coating is 200 μm. All other steps are exactly the same as in Example 1.

[0073] Comparative Example 1

[0074] This is an adjustment based on Example 1, except that 8-HQ is not added. The other steps are exactly the same as in Example 1.

[0075] Comparative Example 2

[0076] The adjustment is based on Example 1, except that only the first coating is applied and the second coating is not applied.

[0077] Comparative Example 3

[0078] The adjustment is based on Example 1, except that the current collector aluminum foil has no coating at all.

[0079] Comparative Example 4

[0080] The method is an adjustment based on Example 1, the difference being that commercially available carbon-coated aluminum foil is used as the current collector.

[0081] IV. Performance Testing

[0082] 1. Microscopic characterization

[0083] The microstructures of Examples 1-3 are not significantly different; therefore, Example 1 will be used as an example here. Figure 1 As can be seen in c~1d, the spherical particles of pure PPy in Comparative Example 1 have irregular morphology and uneven size distribution. Some particles are deformed and adhered together, and the surface is rough with obvious protrusions and depressions. Figure 1The 8-HQ-PPy particles in Example 1 (a-1b) exhibit more regular spherical morphology and significantly improved size uniformity. The particle surfaces are smooth and flat, without obvious roughness or defects, and their overall density and morphological regularity are far superior to the pure PPy coating in Comparative Example 1. This indicates that in-situ doping with 8-HQ can effectively control the polymerization process of polypyrrole, optimize the microstructure of polypyrrole, and solve the problems of easy agglomeration and uneven morphology of pure polypyrrole particles, providing a material basis for the subsequent preparation of a smooth and dense coating. Simultaneously, it also shows that the 8-HQ doping process selected in this application does not interfere with the normal polymerization of pyrrole; on the contrary, it promotes the formation of a regular and uniform particle structure, proving the rationality and effectiveness of the doping scheme from the material synthesis perspective. The denser and more regular microstructure of the 8-HQ-PPy coating in Example 1 provides the coating with superior physical barrier and mechanical properties, serving as the core material basis for achieving long-term corrosion resistance in subsequent coatings.

[0084] Figure 2 The surface and cross-sectional microstructure of the single-layer polypyrrole coating (Comparative Example 2) are characterized. As can be seen from the figures, the single-layer coating cannot form a smooth, dense, continuous surface; it exhibits obvious unevenness and localized particle accumulation. The cross-section reveals a weak interface between the coating and the aluminum current collector substrate, with microscopic gaps and poor contact. This indicates that the pure polypyrrole coating cannot simultaneously achieve both strong interfacial adhesion with the current collector and surface density, providing microscopic channels for chloride ion penetration. Figure 3 The microstructure of the surface and cross-section of the double-layer composite coating is characterized. As shown in the figures, the surface of the double-layer coating is extremely smooth and dense, without obvious particle accumulation, pinholes, or microcracks. The cross-section clearly shows that the coating and the aluminum current collector substrate are tightly bonded, with no interfacial gaps. The interface transition between the 8-HQ-PPy bottom layer and the pure PPy surface layer is smooth, without delamination, peeling, or cracks, forming a continuous and complete composite protective structure. This also indicates that the double-layer structure of the 8-HQ-PPy bottom layer and the pure PPy surface layer can form a continuous, dense, and defect-free protective barrier, completely blocking the chloride ion penetration channel from a physical structure perspective, achieving excellent passive physical barrier effects. Furthermore, it shows that there is a strong interfacial bond between the bottom 8-HQ-PPy coating and the current collector substrate, and the two polypyrrole coatings also have excellent thermodynamic compatibility, solving the problem of easy peeling and delamination of traditional carbon-based coatings and ensuring the structural integrity of the coating during the soft-pack battery processing.

[0085] 2. Electrical conductivity

[0086] Multiple areas on the surface of the current collector coating were randomly selected for thickness measurement using an electronic thickness gauge. The data were recorded, and the average thickness h was calculated to characterize the coating's uniformity. Subsequently, a four-probe tester was used to measure the sheet resistance R of the coating. The coating sample was placed flat on the test stage, the corresponding coating parameters were set, the probes were pressed down, and the sheet resistance value was recorded. This process was repeated at seven equally spaced points on the coating sample. Finally, based on the measured sheet resistance and average thickness, the resistivity ρ corresponding to each sheet resistance value was calculated using a formula, and then the conductivity σ was obtained. The formula is as follows:

[0087] ρ = R × h (1)

[0088] σ=1 / ρ (2)

[0089] The conductivity of Examples 1-3 is not significantly different; therefore, Example 1 is used as an example for comparison with Comparative Example 2. From... Figure 4 As can be seen, the average conductivity of the single-layer coating is 169.94 S / cm, while the average conductivity of the double-layer coating in this application is 140.14 S / cm. Both are at a high conductivity level, fully meeting the electron transport requirements of the current collector in energy storage batteries. This indicates that although the double-layer coating structure designed in this application adds a physical barrier layer, it still maintains excellent electron transport capabilities due to the intrinsic high conductivity of polypyrrole, completely resolving the contradiction that traditional protective coatings must sacrifice conductivity to improve barrier properties. At the same time, the coating formulation and preparation process of this application do not degrade the conductivity of polypyrrole, and the conductivity of the double-layer coating is fully adapted to the high-current charging and discharging requirements of the battery, without causing a significant increase in the current collector surface resistance. Moreover, the technical solution of this application takes into account both corrosion protection and battery electrochemical performance, avoiding the degradation of battery rate performance caused by traditional coatings.

[0090] Figure 5The changes in sheet resistance and conductivity of the coatings with different thicknesses of the second coating are shown. The results show that the coating in Example 4 (50 μm thickness) has the highest conductivity (144.23 S / cm), while the coating in Example 5 (100 μm thickness) has the lowest sheet resistance and maintains excellent conductivity (140.14 S / cm). The conductivity of the coatings in Examples 6 (150 μm thickness) and 7 (200 μm thickness) shows a significant decrease (81.70 S / cm and 61.03 S / cm, respectively). This indicates that the thickness of the second coating has a certain impact on the conductivity of the coating. The average conductivity of the 50 μm second coating is the highest at 144.23 S / cm, followed by the 100 μm coating at 140.14 S / cm, while the conductivity of the 150 μm and 200 μm coatings decreases significantly, to 81.70 S / cm and 61.03 S / cm, respectively. The conductivity of the 50 μm thick coating is the highest, but the sheet resistance of the 100 μm thick coating is the lowest. This indicates that the electron transport is less hindered by the thickness of the coating, and the conductivity is more stable and has better practical application performance.

[0091] 3. Mechanical properties

[0092] Figure 8 The mechanical properties of the modified current collector in Example 1 and the current collector in Comparative Example 4 (using commercially available carbon-coated aluminum foil) are compared, and the fracture load and tensile strength of the different current collectors are quantitatively presented. As can be seen from the figure, the double-layer polypyrrole modified current collector of this application exhibits significantly higher fracture load and tensile strength than both commercially available carbon-coated aluminum foil and pure aluminum foil, while also possessing superior flexibility and deformation resistance. This indicates that the double-layer coating of this application can significantly improve the mechanical strength and flexibility of the current collector, solving the problems of poor mechanical properties and weak adhesion to the substrate in traditional carbon-based coatings. Furthermore, it demonstrates that the modified current collector of this application can perfectly adapt to the entire processing steps of soft-pack batteries, including rolling, bending, and heat sealing, effectively avoiding coating peeling and cracking during processing, and possessing excellent industrial processing adaptability. The hydrogen bonding effect between 8-HQ and the polypyrrole molecular chain is also verified, further optimizing the fracture toughness and deformation resistance of the coating.

[0093] 4. Corrosion resistance

[0094] Corrosion resistance and electrochemical performance were tested using a three-electrode setup with 1 M magnesium chloride as the electrolyte. The open-circuit potentials of the aluminum foil, carbon-coated aluminum foil, single-layer coated aluminum foil, and double-layer coated aluminum foil showed a gradually increasing trend. Data in Table 1 show a significant increasing trend in the self-corrosion potential of the four samples, with the specific potential values ​​as follows: pure aluminum foil -0.8405 V, carbon-coated aluminum foil -0.7711 V, single-layer coated aluminum foil -0.6352 V, and double-layer coated aluminum foil -0.2024 V. The corrosion current density also differed among the four samples, with pure aluminum foil at 3.645 × 10⁻⁶ V. -5 A / cm 2 3.31×10 carbon-coated aluminum foil -5 A / cm 2 Single-layer coated aluminum foil 3.73×10 -6 A / cm 2 Double-coated aluminum foil 1.452×10 -7 A / cm 2 The polarization resistance of the double-coated aluminum foil also reached a maximum of 2.93 × 10⁻⁶. 5 Ω·cm 2 .

[0095] Table 1

[0096]

[0097] at the same time, Figure 9 The diagram shows the open-circuit potential (OCP) of different coated aluminum foils and pure aluminum foil in 1 mol / L magnesium chloride electrolyte, along with the time-varying trend of the OCP of Example 1, Comparative Example 2 (single-layer coated aluminum foil), Comparative Example 3 (pure aluminum foil), and Comparative Example 4 (commercially carbon-coated aluminum foil). The OCP of all four groups of samples showed a significant increasing trend. The OCP of the double-coated aluminum foil of this application was significantly higher than that of the other three groups and remained stable during the test without a significant decrease. A higher OCP indicates a lower thermodynamic tendency for corrosion and better corrosion resistance of the metallic material. This suggests that the double-layer coating of this application can significantly reduce the corrosion tendency of the current collector in high-concentration magnesium chloride electrolyte, significantly improving the intrinsic corrosion resistance stability of the current collector. Simultaneously, the synergistic protective effect of the double-layer coating is far superior to that of the single-layer coating and commercially carbon-coated aluminum foil, which can fundamentally suppress the thermodynamic driving force of chloride ion corrosion. Moreover, the long-term stability of the OCP demonstrates that the coating of this application is structurally stable in a highly corrosive environment, without rapid degradation or failure, and possesses long-cycle protection potential. Figure 10 The graphs show the potentiodynamic polarization curves of aluminum foils with different coatings and pure aluminum foil. The self-corrosion potential (E) of the double-coated aluminum foil in this application is also shown. corr The most positive value (-0.2024 V) was 0.6381 V more positive than that of pure aluminum foil; the corrosion current density (Ic) was the highest. corrThe lowest (1.452×10) -7 A / cm 2 The polarization resistance (R) is reduced by more than two orders of magnitude compared to pure aluminum foil; p The highest (2.93×10) 5 Ω・cm 2 This represents an improvement of more than two orders of magnitude compared to pure aluminum foil. A positive shift in self-corrosion potential, a decrease in corrosion current density, and an increase in polarization resistance are core quantitative indicators of improved material corrosion resistance. This demonstrates that the double-layer coating of this application can significantly suppress the corrosion electrochemical reaction rate of the current collector, exhibiting extremely strong resistance to chloride ion corrosion. It not only blocks the chloride ion penetration path through the double-layer coating but also inhibits the corrosion electrochemical reaction through in-situ chelation passivation of 8-HQ, thus solving the problem of rapid corrosion failure of the current collector in high-concentration magnesium chloride systems.

[0098] Figure 9-10 As can be seen from Table 1, the corrosion resistance of commercially available carbon-coated aluminum foil is even weaker than that of blank aluminum foil. A single-layer coating can only achieve limited protection. However, the double-layer coating of this application achieves a leapfrog improvement in corrosion resistance, directly proving that existing commercial carbon-based coatings are completely unsuitable for the highly corrosive environment of high-concentration magnesium chloride. At the same time, it verifies that the double-layer structure of the bottom layer of 8-HQ-doped polypyrrole + the top layer of pure polypyrrole in this application has excellent synergistic protection advantages.

[0099] 5. Electrochemical performance testing

[0100] Electrochemical tests were conducted on a three-electrode system by coating a positive electrode material onto a double-coated current collector. The results are as follows: Figure 11-12 As shown. Figure 11 The three-electrode electrochemical performance curves of the modified current collector MVOH are shown in the figures (a is the CV curve at a scan rate of 1 mV / s; b is the GCD curve at a current density of 0.1 A / g; c is the rate performance curve; d is the long-cycle performance curve at a current density of 1 A / g). It can be seen that... Figure 11 The CV curve in a shows symmetrical and clear redox peaks, without impurities or distortion. Figure 11 In b, the GCD curve exhibits a symmetrical charge-discharge plateau, with minimal polarization during the charge-discharge process and a coulombic efficiency approaching 100%. Figure 11 In c, the electrode exhibits small capacity decay under different current densities, demonstrating excellent rate performance. Figure 11 In d, under long-term cycling at a high current density of 1A / g, the electrode capacity did not show significant decay, and the cycling stability was excellent.

[0101] Therefore, the modified current collector of this application not only does not degrade the electrochemical performance of the cathode material, but also provides a stable and efficient electron collection and transport channel for the electrode reaction, ensuring the excellent redox reversibility and kinetic performance of the electrode reaction. The coating designed in this application has excellent electrochemical stability within the working potential window of the aqueous magnesium-ion battery, with no redox side reactions occurring and no interference with the insertion / extraction kinetics of magnesium ions in the electrolyte, completely avoiding the degradation of battery performance caused by traditional electrolyte corrosion inhibitor addition schemes. At the same time, the modified current collector of this application can stably perform electron collection and current transfer functions, and can be adapted to the actual application scenarios of high-current charging and discharging, providing core support for the performance of pouch full batteries.

[0102] Figure 12 The figures show the GCD curves of the modified current collector prepared in Example 1 and the current collector prepared in Comparative Example 2 at a current density of 0.08 A / g. As can be seen from the figures, the modified current collector prepared in Example 1 exhibits a stable charge-discharge plateau, minimal voltage polarization, high discharge specific capacity, and excellent coulombic efficiency. In contrast, the current collector prepared in Comparative Example 2 shows a skewed charge-discharge plateau, significantly increased voltage polarization, a substantial decrease in discharge specific capacity, and poor charge-discharge reversibility. This demonstrates the necessity of the dual-layer structure design of the 8-HQ-PPy bottom layer + pure PPy top layer in this application. The bottom 8-HQ-PPy coating significantly reduces the interfacial contact resistance, optimizes electron transport efficiency, and significantly reduces electrode polarization through strong interfacial bonding with the current collector. Conversely, it verifies that a single-layer coating without a bottom layer, due to poor interfacial bonding with the current collector and large interfacial gaps, leads to increased interfacial resistance and hindered electron transport, ultimately degrading the charge and discharge performance of the battery. From the perspective of electrochemical performance, it further verifies the synergistic effect of the gradient dual-layer structure in this application, which achieves both corrosion protection and optimized electrode electrochemical performance, solving the problem that traditional coatings cannot simultaneously achieve protection and performance.

[0103] 6. Assemble into a soft-pack full battery and test.

[0104] The current collector prepared in Example 1 was assembled into a pouch cell PTCDA / / MgCl2 / / MVOH full cell. Comparative Example 2 was also assembled into a similar full cell, and performance tests were performed. The results are as follows: Figures 13-14 As shown. Figure 13 In cell a, the CV curves show symmetrical peaks, clear redox peaks, and no side reaction impurities, indicating that the electrochemical reaction of the full cell is highly reversible. Figure 13 In b, the full cell exhibits excellent capacity retention under different current densities, and demonstrates good rate performance and high-current charge / discharge capability. Figure 13 The GCD curve in c has a stable charge and discharge plateau, small voltage polarization, high coulombic efficiency, and stable charge and discharge process. Figure 13At a current density of 0.1 A / g, the full cell in example d can stably cycle for more than 200 cycles without significant capacity decay, demonstrating excellent long-term cycle stability. This indicates that the modified current collector of this application can operate stably in aqueous magnesium-ion pouch cells, perfectly adapting to the industrial application scenarios of pouch cells; it solves the problems of corrosion failure of unmodified current collectors in the first charge-discharge cycle and protection failure of traditional carbon-based coatings within 50 cycles, proving that the coating of this application has long-term protective capabilities in highly corrosive environments with high concentrations of magnesium chloride; at the same time, the full cell prepared in Example 1 also has excellent rate performance and long-term cycle stability, proving that the technical solution of this application can simultaneously take into account the safety performance, cycle life, and electrochemical performance of pouch cells, providing core technical support for the industrial application of aqueous magnesium-ion pouch cells.

[0105] Figure 14 Comparison of the appearance of the pouch cell and the electrode after cycle testing (a: appearance of the pouch cell in Comparative Example 2; b: electrode in Comparative Example 2; c: appearance of the pouch cell in Example 1; d: electrode in Example 1). The images clearly show that the pouch cell in Comparative Example 2 exhibited significant bulging and swelling. After disassembly, the electrode showed severe corrosion, powdering, coating peeling, and structural damage. In contrast, the pouch cell in Example 1 of this application had a smooth appearance, without bulging, leakage, or swelling. After disassembly, the electrode coating remained intact without peeling, corrosion, powdering, or structural damage, and the electrode morphology remained intact. From a macroscopic perspective, this demonstrates that the double-layer coating of this application completely solves the problems of battery bulging, electrolyte leakage, and electrode failure caused by chloride ion corrosion of the current collector, significantly improving the operational safety of aqueous magnesium-ion pouch cells. Furthermore, the coating of this application maintains structural integrity and protective effect without degradation during long-cycle pouch cell operation, solving the safety and lifespan issues that restrict the industrial application of aqueous magnesium-ion pouch cells.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of this application without departing from the spirit and scope of this technical solution should be covered within the scope of the claims of this application.

Claims

1. A flexible current collector anti-chloride ion corrosion coating, characterized in that, The chloride ion corrosion resistant coating consists of a first coating and a second coating; wherein the first coating is applied to the surface of the current collector, and the second coating is applied to the surface of the first coating; The first coating is made of composite polypyrrole, and the second coating is made of polypyrrole; the composite polypyrrole is polypyrrole doped with 8-hydroxyquinoline, and the molar ratio of 8-hydroxyquinoline to pyrrole monomer is (1~3):

100.

2. The flexible current collector anti-chloride ion corrosion coating according to claim 1, characterized in that, The composite polypyrrole is obtained through the following steps: Step 1: Dissolve sodium p-toluenesulfonate and 8-hydroxyquinoline in water, then add pyrrole monomer, labeled as solution a; in solution a, the molar ratio of sodium p-toluenesulfonate, 8-hydroxyquinoline and pyrrole monomer is (4~6):(0.1~0.2):10; Step 2: Dissolve ammonium persulfate in water to prepare an oxidizing agent solution; the molar ratio of ammonium persulfate to pyrrole monomer is (1~2):(1~2); Step 3: Slowly add the oxidant solution to solution a at a rate of 3 ml / min, and react at 4℃~5℃ for 4h~6h; after the reaction is complete, collect the black precipitate, wash and dry it to obtain composite polypyrrole.

3. The flexible current collector anti-chloride ion corrosion coating according to claim 1, characterized in that, The raw materials for preparing the first coating are as follows: In an organic solvent, the mass ratio of composite polypyrrole, conductive graphite and binder is (3~5):(2~4):(2~4).

4. The flexible current collector anti-chloride ion corrosion coating according to claim 1, characterized in that, The raw materials for preparing the second coating are as follows: In an organic solvent, the mass ratio of polypyrrole, conductive graphite and binder is (3~5):(2~4):(2~4).

5. The flexible current collector anti-chloride ion corrosion coating according to claim 3 or 4, characterized in that, The adhesive is selected from polyvinylidene fluoride or polyvinylidene fluoride copolymer.

6. The flexible current collector anti-chloride ion corrosion coating according to claim 3 or 4, characterized in that, The organic solvent is selected from N-methyl-2-pyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

7. The flexible current collector anti-chloride ion corrosion coating according to claim 3 or 4, characterized in that, The metal current collector is selected from aluminum or copper.

8. The flexible current collector anti-chloride ion corrosion coating according to claim 1, characterized in that, The thickness of the first coating is 20~30μm, and the thickness of the second coating is 50~200μm.

9. A method for preparing a chloride ion corrosion resistant coating for a flexible current collector according to any one of claims 1-8, characterized in that, The chloride ion corrosion resistant coating for the flexible current collector is prepared through the following steps: S1: Add the adhesive to the organic solvent in portions to prepare a 5wt%~7wt% adhesive solution; S2: After uniformly mixing composite polypyrrole and conductive graphite, add adhesive solution to obtain the slurry for the first coating layer; after uniformly mixing polypyrrole and conductive graphite, add adhesive solution to obtain the slurry for the second coating layer. S3: After applying the first coating slurry to the surface of the current collector and drying it, apply the second coating slurry to the surface of the first coating and dry it.

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