Composite oxygen barrier coating and preparation method thereof

Abstract

The preparation method comprises the following steps that cobalt salt and 2-methylimidazole are dissolved in a solvent to form a first mixed solution, a base material is soaked in the first mixed solution, then the taken-out base material is washed, dried, calcined and cooled in sequence, a transition layer is formed on the surface of the base material, and a first intermediate is obtained; dissolving carboxylic acid and ammonium borate in water to form a second mixed solution, heating the second mixed solution, dipping the first intermediate in the heated second mixed solution, and then heating the taken first intermediate in stages to obtain a second intermediate; phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form a third mixed solution, the second intermediate is soaked in the third mixed solution, then the taken-out second intermediate is dried, calcined and cooled in sequence, an oxygen barrier layer is formed on the surface of the transition layer, and the needed composite oxygen barrier coating is obtained.

Description

Technical Field

[0001] The present invention relates to the field of oxygen barrier technology, in particular to a composite oxygen barrier coating and a preparation method thereof. Background Art

[0002] In areas such as high-temperature protection, electronic packaging, and energy storage, the performance of oxygen-barrier coatings directly impacts device reliability and service life. Traditional oxygen-barrier materials (such as Al2O3 and SiO2 coatings) face the following technical bottlenecks: poor interfacial adhesion with the substrate, prone to delamination during thermal cycling; and the inability to self-heal microcracks, resulting in a sharp increase in oxygen permeability.

[0003] Taking graphene as an example, due to its excellent electrical conductivity and electrothermal conversion efficiency, graphene has broad application prospects in areas such as electric heating plates, flexible electronic devices, electric heating elements, and smart wearable devices. However, as a heating material, graphene is easily oxidized in high temperature or humid environments, resulting in increased resistivity, reduced heating efficiency, and reduced product quality. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies in the prior art, the purpose of the present invention is to provide a composite oxygen barrier coating and a preparation method thereof, which realizes the organic combination of self-repair function and oxygen barrier performance, and solves the problems of low repair efficiency and poor oxygen barrier properties of traditional coatings.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for preparing a composite oxygen barrier coating, which is used to be provided on a substrate surface, comprises the following steps:

[0007] Dissolving a cobalt salt and 2-methylimidazole in a solvent to form a first mixed solution, immersing a substrate in the first mixed solution, and then washing, drying, calcining, and cooling the substrate to form a transition layer on the surface of the substrate to obtain a first intermediate;

[0008] dissolving carboxylic acid and ammonium borate in water to form a second mixed solution, heating the second mixed solution, immersing the first intermediate in the heated second mixed solution, and then heating the first intermediate in sections so that the transition layer is loaded with boron trioxide to obtain a second intermediate;

[0009] Phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form a third mixed solution. The second intermediate is immersed in the third mixed solution, and then the taken-out second intermediate is dried, calcined and cooled in sequence to form an oxygen barrier layer on the surface of the transition layer to obtain the desired composite oxygen barrier coating.

[0010] Furthermore, the cobalt salt includes cobalt nitrate hexahydrate, and the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:3.

[0011] Furthermore, the specific process of calcining the substrate includes:

[0012] The dried substrate is placed in a heating furnace, a protective gas is introduced, and the substrate is heated to 500-600°C at a heating rate of 2-5°C / min and kept warm for 5-6 hours.

[0013] Furthermore, the second mixed solution is heated in a water bath to a temperature of 75-85° C.

[0014] Furthermore, the carboxylic acid includes citric acid, and the molar ratio of citric acid to ammonium borate is (1.5:1) to (3:1).

[0015] Furthermore, the specific process of heating the first intermediate taken out in stages includes:

[0016] The first intermediate is placed in a vacuum oven, heated to 100-150° C. and kept warm for 1-2 hours, then heated to 200-250° C. and kept warm for 3-4 hours, and finally heated to 300-350° C. and kept warm for 2-3 hours.

[0017] Furthermore, the molar ratio of the phosphoric acid to aluminum dihydrogen phosphate is 20:9.

[0018] Furthermore, the specific process of sequentially drying, calcining and cooling the taken-out second intermediate includes:

[0019] The second intermediate is placed in a vacuum drying oven and dried at 80-100° C. and 150-200° C. in sequence. The second intermediate is then placed in a heating furnace and heated to 250-300° C. at a rate of 4-5° C. / min, then heated to 500-600° C. at a rate of 2-3° C. / min and kept at this temperature for 1-3 hours before naturally cooling to room temperature.

[0020] Furthermore, before preparing the first intermediate, the preparation method further comprises: cleaning the substrate. The specific process of the cleaning comprises: immersing the substrate in acetone for ultrasonic treatment for 5 to 10 minutes, and then rinsing with deionized water.

[0021] The present invention also provides a composite oxygen barrier coating, which is prepared by the preparation method described above. The composite oxygen barrier coating includes a transition layer and an oxygen barrier layer. The transition layer is used to be arranged on the surface of the substrate, and the oxygen barrier layer is arranged on the surface of the transition layer.

[0022] The beneficial effects of the present invention are as follows: based on the metal organic framework, a transition layer (loaded with boron oxide) with the function of a self-repairing layer is designed and prepared: the transition layer comprises a porous carbon skeleton inlaid with ultrafine nano-metal particles (cobalt particles) and nano-boron oxide particles contained in the pores of the porous carbon skeleton. The porous carbon skeleton is embedded in the pores of the substrate to improve physical adhesion, and the porous carbon skeleton can buffer the volume changes caused by thermal expansion and contraction; the controllable exposure of the metal particle active sites in the transition layer provides a directional anchoring point for the self-repairing material, guides the self-repairing design through chemical coordination, and forms a uniformly dispersed system in the transition layer. This structural design not only improves the self-repairing response efficiency of the transition layer, but its orderly distributed active sites can also effectively block the oxygen diffusion path, thereby significantly enhancing the oxygen barrier performance of the composite oxygen barrier coating (transition layer + oxygen barrier layer). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a schematic structural diagram of the composite oxygen barrier coating of the present invention covering a substrate;

[0025] Figure 2 This is a schematic diagram of the orderly arrangement of the metal organic framework in the transition layer;

[0026] Figure 3 is a schematic diagram of boron oxide loaded on a porous carbon framework;

[0027] Figure 4a is a TEM image of the porous carbon skeleton embedded with cobalt particles in the transition layer in Example 1;

[0028] Figure 4b is an SEM image of the porous carbon skeleton embedded with cobalt particles in the transition layer in Example 1;

[0029] Figure 5 This is an SEM image of the surface of the oxygen barrier layer in Example 1. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a composite oxygen barrier coating, which is used to be arranged on the surface of a substrate to play an oxygen barrier role and prevent internal substrate oxidation. The preparation method comprises the following steps:

[0031] Dissolving a cobalt salt and 2-methylimidazole in a solvent to form a first mixed solution, immersing a substrate in the first mixed solution, and then washing, drying, calcining, and cooling the substrate to form a transition layer on the surface of the substrate to obtain a first intermediate;

[0032] dissolving carboxylic acid and ammonium borate in water to form a second mixed solution, heating the second mixed solution, immersing the first intermediate in the heated second mixed solution, and then heating the first intermediate in sections to load boron trioxide on the transition layer, thereby obtaining a second intermediate;

[0033] Phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form a third mixed solution. The second intermediate is immersed in the third mixed solution, and then the taken-out second intermediate is dried, calcined and cooled in sequence to form an oxygen barrier layer on the surface of the transition layer to obtain the desired composite oxygen barrier coating.

[0034] In this embodiment, a composite oxygen-barrier coating is constructed by a three-step method, in which a metal-organic framework is generated by a coordination reaction between cobalt salt and 2-methylimidazole on the surface of the substrate. During calcination, the metal-organic framework decomposes and carbonizes at high temperature to obtain a porous carbon skeleton embedded with nano-cobalt particles, forming a transition layer. Carboxylic acid and ammonium borate are then further heated to react on the surface of the transition layer to generate boron oxide. Nano-boron oxide particles are loaded in the pores of the porous carbon skeleton and repair microcracks by capillary action with the assistance of cobalt active sites. Finally, phosphoric acid and aluminum dihydrogen phosphate are further reacted on the surface of the transition layer to form an oxygen-barrier layer containing an aluminum phosphate (AlPO4) crystal structure, so that the composite oxygen-barrier coating has both electrical conductivity and oxidation resistance.

[0035] Specifically, this embodiment is based on a metal organic framework, and a transition layer (loaded with boron oxide) with a self-repairing layer function is designed and prepared: the transition layer comprises a porous carbon skeleton inlaid with ultrafine nano-metal particles (cobalt particles) and nano-boron oxide particles contained in the pores of the porous carbon skeleton. The porous carbon skeleton is embedded in the pores of the substrate to improve physical adhesion, and the porous carbon skeleton can buffer the volume changes caused by thermal expansion and contraction; the controllable exposure of the metal particle active sites in the transition layer provides a directional anchoring point for the self-repairing material, guides the self-repairing design through chemical coordination, and forms a uniformly dispersed system in the transition layer. This structural design not only improves the self-repairing response efficiency of the transition layer, but its orderly distributed active sites can also effectively block the oxygen diffusion path, thereby significantly enhancing the oxygen barrier performance of the composite oxygen barrier coating (transition layer + oxygen barrier layer). Among them, the substrate is a material that needs to be treated with antioxidants, which can be graphene, carbon black, or metal oxides, which are not limited here.

[0036] Furthermore, before preparing the first intermediate, the preparation method further includes: cleaning the substrate. The specific cleaning process includes: immersing the substrate in acetone for ultrasonic treatment for 5 to 10 minutes, and then rinsing with deionized water 3 times, 4 times or 5 times, which is not limited here.

[0037] Furthermore, the cobalt salt includes cobalt nitrate hexahydrate, and the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:3, ensuring that Co 2+ Complete coordination forms a metal-organic framework, preventing residual free metal ions from affecting performance. Of course, the cobalt salt also includes cobalt chloride or cobalt sulfate, and one or more can be selected and mixed. The cobalt salt and 2-methylimidazole are dissolved in a solvent to form a first mixed solution. The solvent can be one or more of methanol, ethanol, or water; methanol is preferred.

[0038] Furthermore, the specific process of calcining the substrate includes:

[0039] The dried substrate is placed in a heating furnace, infused with protective gas, and heated to 500-600°C at a heating rate of 2-5°C / min, where it is held for 5-6 hours. Calcination effectively removes the organic ligands (coordinated water molecules in 2-methylimidazole and cobalt nitrate), causing them to decompose and carbonize at high temperatures, forming a metal-carbon composite structure in which cobalt particles are anchored to the substrate surface. Simultaneously, the carbon skeleton of the organic ligands is transformed into a conductive carbon layer, enhancing the material's electrical conductivity.

[0040] Specifically, preparing the transition layer includes:

[0041] The substrate is immersed in acetone and ultrasonically treated for 5–10 minutes. It is then rinsed three times with deionized water to remove any residual solvent. The substrate is then immersed in a first mixed solution containing Co(NO₃)₂·6H₂O and 2-methylimidazole (at a molar ratio of 1:3) in methanol and allowed to stand for approximately 3–8 hours (preferably 5 hours). The substrate is then washed three times with deionized water and methanol. Finally, the substrate is dried in a freeze dryer for 24 hours and then calcined under a protective gas (preferably argon) stream. The calcination steps are as follows: the substrate is placed in a heating furnace, and an argon flow is introduced at room temperature for half an hour. The furnace is then heated to 500–600°C at a heating rate of 2–5°C / min (preferably 3°C / min). After reaching the target temperature, the temperature is maintained for 5–6 hours. The substrate is then cooled to room temperature to form a transition layer on the substrate surface, yielding the first intermediate.

[0042] Furthermore, the second mixed solution is heated in a water bath to 75-85°C, which can be 75°C, 80°C or 85°C, preferably 80°C.

[0043] Furthermore, the carboxylic acid includes citric acid, and the molar ratio of citric acid to ammonium borate is (1.5:1) to (3:1). Excessive citric acid ensures that the ammonium borate is completely dissolved and forms a boron-citric acid complex, generating B2O3 at high temperature. Of course, the carboxylic acid can also be selected from tartaric acid or oxalic acid, and one or more of them can be mixed. Citric acid is mainly used as a chelating agent and reducing agent in this process. By reacting with Co 2+ The metal ions form stable complexes to evenly disperse active sites. At high temperatures, they participate in reduction reactions and decompose to produce amorphous carbon, a function that can be replaced by other polycarboxylic acids (such as tartaric acid and oxalic acid). Ammonium borate, a boron source, converts to molten B2O3 at high temperatures to repair cracks.

[0044] Furthermore, the specific process of heating the first intermediate in stages includes: placing the first intermediate in a vacuum oven, heating it to 100-150°C for 1-2 hours, then heating it to 200-250°C for 3-4 hours, and finally heating it to 300-350°C for 2-3 hours. Specifically, the 100-150°C stage removes residual solvent and stabilizes the porous carbon skeleton; then the 200-250°C stage promotes the decomposition of organic acid (citric acid) and triggers the initial thermal decomposition of ammonium borate, while allowing the ammonium borate to completely decompose into fluid B2O3 and release NH3 gas. At the same time, the microcracks in the transition layer are repaired by capillary action with the assistance of Co active sites; finally, under vacuum treatment at 300-350°C, the melting distribution of B2O3 is further optimized and residual gas is removed to ensure the densification of the transition layer. Ammonium borate was chosen as the boron source because it efficiently decomposes into B2O3 and volatile NH3 in the 200-250°C range (without affecting the oxygen barrier layer). Compared to boric acid (which decomposes prematurely), ammonium borate is more conducive to obtaining a pure and stable self-healing coating system. The exposed cobalt particles effectively provide active sites for the boron source. B2O3 melts and flows at high temperatures, repairing cracks in the transition layer through capillary action.

[0045] Specifically, the preparation process of the transition layer loaded with boron trioxide includes:

[0046] Citric acid, tartaric acid, oxalic acid (preferably citric acid) and ammonium borate (boron source) are dissolved in water in a molar ratio of (1.5:1 to 3:1), and the mixture is stirred in a water bath at 75-85°C (preferably 80°C) to form a second mixed solution. The second mixed solution is impregnated on the transition layer, and then placed in a vacuum oven and heated in stages: first, kept at 100-150°C for 1-2 hours (preferably 1 hour), then raised to 200-250°C and kept for 3-4 hours (preferably 4 hours), and finally further kept at 300-350°C in a vacuum environment for 2-3 hours (preferably 2 hours) to obtain a transition layer with self-healing function and a second intermediate; the segmented heating process design is intended to gradually regulate the formation of the transition layer structure and the self-healing performance.

[0047] Furthermore, the molar ratio of phosphoric acid to aluminum dihydrogen phosphate is 20:9, and the optimized ratio forms dense AlPO4 crystals, fills the pores in the transition layer, and improves the oxygen barrier performance.

[0048] Furthermore, the specific process of drying, calcining and cooling the taken-out second intermediate in sequence includes:

[0049] The second intermediate is placed in a vacuum drying oven and dried at 80-100°C and 150-200°C in sequence. The second intermediate is then placed in a heating furnace and heated to 250-300°C at a rate of 4-5°C / min, then heated to 500-600°C at a rate of 2-3°C / min and kept warm for 1-3 hours before naturally cooling to room temperature. During the high-temperature calcination process at 500-600°C, the aluminum dihydrogen phosphate (Al(H2PO4)3) and phosphoric acid (H3PO4) system undergoes decomposition and reconstruction reactions. First, aluminum dihydrogen phosphate gradually removes the bound water and hydroxyl groups in its structure when heated, decomposes to form intermediate aluminum metaphosphate (Al(PO3)3) and releases H2O and P x O y Gas; simultaneously, phosphoric acid further dehydrates and condenses to form polyphosphoric acid or pyrophosphoric acid. When the temperature rises to 500°C, the aluminum ions in the system react deeply with the phosphate radicals, forming an aluminum phosphate (AlPO4) crystal structure through PO-Al bonds. This process may also be accompanied by partial oxidation of aluminum to form trace amounts of Al2O3, which forms a composite phase with the aluminum phosphate.

[0050] Specifically, preparing the oxygen barrier layer includes:

[0051] Phosphoric acid and aluminum dihydrogen phosphate are mixed with deionized water in a molar ratio of (20:9), and magnetically stirred for 2 hours until transparent to obtain a third mixed solution. The second intermediate is immersed in the third mixed solution, and after standing in the air for 1 to 3 hours (preferably 1 hour), it is dried in a vacuum drying oven at 80 to 100 ° C and 150 to 200 ° C for 30 minutes each to remove residual moisture. Thereafter, the temperature is first raised to 250 to 300 ° C at 4 to 5 ° C / min (preferably 5 ° C / min) in a heating furnace (tube furnace), and then raised to 500 to 600 ° C at 2 to 3 ° C / min (preferably 3 ° C / min), kept warm for 1 to 3 hours (preferably 2 hours), and naturally cooled to form an oxygen barrier layer; the final composite oxygen barrier coating is obtained.

[0052] like Figure 1 As shown, the present invention also provides a composite oxygen barrier coating, which is prepared by the above-mentioned preparation method. The composite oxygen barrier coating includes a transition layer and an oxygen barrier layer. The transition layer is used to be arranged on the surface of the substrate, and the oxygen barrier layer is arranged on the surface of the transition layer. The transition layer includes a porous carbon skeleton and cobalt particles (not shown in the figure) and boron oxide (such as Figure 3As shown), the oxygen barrier layer 3 includes an aluminum phosphate crystal structure (not shown in the figure). Figure 2 The present invention introduces a porous carbon skeleton after high-temperature calcination (as shown). This transition layer provides directional anchoring points for boron oxide through the active sites of metal particles. B2O3 melts and flows at high temperatures, repairing cracks in the transition layer through capillary action. This organically combines self-repairing capabilities with oxygen barrier properties, addressing the low repair efficiency and insufficient durability of traditional coatings.

[0053] The present invention is further described below with reference to the following examples; a graphene substrate is selected as the substrate. Existing graphene heating films are susceptible to oxidation in high-temperature environments above 400°C, while existing self-healing coatings generally suffer from technical bottlenecks such as poor dispersion uniformity, low oxygen barrier efficiency, and lack of density.

[0054] Example 1

[0055] step:

[0056] (1) Preparation of transition layer:

[0057] The graphene substrate was immersed in acetone and ultrasonically treated for 8 minutes, then rinsed with deionized water 3 times to remove the solvent residue. It was immersed in a methanol solution containing Co(NO3)2·6H2O and 2-methylimidazole (molar ratio 1:3) and allowed to stand for 5 hours. It was washed alternately with deionized water and methanol 3 times and freeze-dried for 24 hours. Calcination in an argon flow: heating to 600℃ at 3℃ / min, keeping warm for 5 hours, and cooling naturally to obtain a porous carbon skeleton embedded with cobalt nanoparticles (TEM analysis as shown in Figure 2). Figure 4a As shown, SEM analysis Figure 4b As shown), a transition layer is formed.

[0058] (2) Transition layer loaded with boron oxide:

[0059] Dissolve citric acid and ammonium borate (molar ratio 2:1) in water, and stir in an 80° C. water bath until transparent to obtain a second mixed solution.

[0060] After the second mixed solution impregnates the transition layer, vacuum heating is performed in stages:

[0061] Keep at 120℃ for 1h (to remove the solvent and stabilize the skeleton);

[0062] Keep warm at 230℃ for 4h (decompose organic acid and generate B2O3);

[0063] Keep warm at 320℃ under vacuum for 2h (densification of molten B2O3).

[0064] (3) Preparation of oxygen barrier layer:

[0065] Phosphoric acid and aluminum dihydrogen phosphate (molar ratio 20:9) were dissolved in water and stirred for 2 h to obtain a third mixed solution.

[0066] The third mixed solution was impregnated into the transition layer loaded with boron oxide, and dried in stages after standing for 1 hour:

[0067] Vacuum drying at 90°C for 30 min;

[0068] Vacuum drying at 180℃ for 30min.

[0069] The temperature in the tubular furnace was programmed to rise at 5°C / min to 280°C, then at 3°C / min to 550°C, and kept at this temperature for 2 h.

[0070] Test results: SEM analysis (such as Figure 5 ) showed that the surface of the prepared composite oxygen barrier coating showed a dense and crack-free morphology, and the transition layer was tightly bonded to the interface of the graphene matrix, forming a stable multilayer structure. The oxygen barrier performance test showed that the oxygen diffusion rate of the composite oxygen barrier coating was significantly reduced to 0.12cm under a high temperature environment of 450°C. 3 / (m 2 The durability test data comparison shows that the oxygen barrier efficiency of the composite oxygen barrier coating prepared in Example 1 decreases by 5% after 2300 hours of testing, proving that it has excellent long-term oxygen barrier stability.

[0071] Example 2 (Optimization of calcination temperature and time): During the preparation of the transition layer, the calcination temperature was adjusted to 550°C and the holding time was extended to 6 hours (600°C for 5 hours in Example 1); the other steps were the same as in Example 1.

[0072] Test results: By optimizing the calcination process (550°C for 6 hours), the transition layer material prepared exhibited significant improvements: while the porosity of the porous carbon framework remained essentially the same as in Example 1, the pore size distribution uniformity was significantly improved, and the material density was enhanced. Performance test data showed that in long-term stability testing at 450°C, the optimized composite oxygen barrier coating exhibited superior durability. After 2500 hours of testing, the oxygen barrier efficiency of the sample in Example 2 decreased by 5%, demonstrating a substantial improvement in its high-temperature stability.

[0073] Comparative Example 1: Pure SiO2 oxygen barrier layer (no transition layer)

[0074] Steps: In the experiment of preparing pure SiO2 oxygen barrier layer (without transition layer), the graphene substrate is first pretreated, and ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes each, and then vacuum dried at 80°C for use. The SiO2 coating is prepared by the sol-gel method. Tetraethoxysilane (TEOS) and anhydrous ethanol are mixed in a molar ratio of 1:4, 0.1M hydrochloric acid is added to adjust the pH to 3-4, and magnetic stirring is performed for 2 hours to form a transparent sol. Graphene is immersed in the sol by the immersion pulling method (pulling speed 2mm / s), and the gel is allowed to stand at room temperature for 30 minutes to form a preliminary gel. Then, staged temperature drying is carried out: vacuum drying at 80°C for 1 hour to remove the solvent, and annealing in air atmosphere at 300°C for 2 hours to achieve densification.

[0075] Test results: Under the same test conditions (450°C working environment), the oxygen barrier efficiency of the coating decreased by 5% after 1530 hours.

[0076] Conclusion: Pure SiO2 coating cannot meet the high-temperature oxygen barrier requirements due to the lack of the interface buffering effect of the transition layer. The transition layer plays a decisive role in improving the interface bonding strength and high-temperature stability.

[0077] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to the technical contents disclosed above without departing from the scope of the technical solution of the present invention, which are equivalent embodiments of equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a composite oxygen barrier coating, which is used to be provided on the surface of a substrate, characterized in that: The preparation method comprises the following steps: Dissolving a cobalt salt and 2-methylimidazole in a solvent to form a first mixed solution, immersing a substrate in the first mixed solution, and then washing, drying, calcining, and cooling the substrate to form a transition layer on the surface of the substrate to obtain a first intermediate; dissolving carboxylic acid and ammonium borate in water to form a second mixed solution, heating the second mixed solution, immersing the first intermediate in the heated second mixed solution, and then heating the first intermediate in sections so that the transition layer is loaded with boron trioxide to obtain a second intermediate; Phosphoric acid and aluminum dihydrogen phosphate are dissolved in water to form a third mixed solution. The second intermediate is immersed in the third mixed solution, and then the taken-out second intermediate is dried, calcined and cooled in sequence to form an oxygen barrier layer on the surface of the transition layer to obtain the desired composite oxygen barrier coating.

2. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The cobalt salt includes cobalt nitrate hexahydrate, and the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:

3.

3. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The specific process of calcining the substrate includes: The dried substrate is placed in a heating furnace, a protective gas is introduced, and the substrate is heated to 500-600°C at a heating rate of 2-5°C / min and kept warm for 5-6 hours.

4. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The second mixed solution is heated in a water bath to 75-85° C.

5. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The carboxylic acid includes citric acid, and the molar ratio of citric acid to ammonium borate is (1.5:1) to (3:1).

6. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The specific process of heating the first intermediate taken out in stages includes: The first intermediate is placed in a vacuum oven, heated to 100-150° C. and kept warm for 1-2 hours, then heated to 200-250° C. and kept warm for 3-4 hours, and finally heated to 300-350° C. and kept warm for 2-3 hours.

7. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The molar ratio of the phosphoric acid to aluminum dihydrogen phosphate is 20:

9.

8. The method for preparing the composite oxygen barrier coating according to claim 1, wherein: The specific process of drying, calcining and cooling the taken-out second intermediate in sequence includes: The second intermediate is placed in a vacuum drying oven and dried at 80-100° C. and 150-200° C. in sequence. The second intermediate is then placed in a heating furnace and heated to 250-300° C. at a rate of 4-5° C. / min, then heated to 500-600° C. at a rate of 2-3° C. / min and kept at this temperature for 1-3 hours before naturally cooling to room temperature.

9. The method for preparing the composite oxygen barrier coating according to any one of claims 1 to 8, wherein: Before preparing the first intermediate, the preparation method further includes: cleaning the substrate. The specific process of the cleaning includes: immersing the substrate in acetone for ultrasonic treatment for 5 to 10 minutes, and then rinsing with deionized water.

10. A composite oxygen barrier coating, characterized in that: The composite oxygen barrier coating is prepared by the preparation method according to any one of claims 1 to 9, and includes a transition layer and an oxygen barrier layer, wherein the transition layer is used to be arranged on the surface of the substrate, and the oxygen barrier layer is arranged on the surface of the transition layer.

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