Silver-coated copper paste matched with HJT cell for high-salt-mist environment, and preparation method and application thereof

Abstract

The application belongs to the technical field of photovoltaic cell metallization, and specifically discloses a silver-coated copper paste matched with HJT cells in a high-salt-mist environment and a preparation method and application thereof, the silver-coated copper paste comprises the following components in mass fractions: full-coated silver-coated copper powder, micron silver powder, nano silver powder, alicyclic epoxy resin, multifunctional epoxy resin, curing agent, organic solvent, acid absorbent, corrosion inhibitor, coupling agent and dispersant, and the total mass fraction of the conductive filler composed of the full-coated silver-coated copper powder, the micron silver powder and the nano silver powder is not more than 93 parts, and the full-coated silver-coated copper powder is zero-defect dense full-coated silver-coated copper powder. The silver-coated paste significantly improves the long-term reliability of the paste in a high-salt-mist, high-acid-alkali-corrosion environment through the synergistic effect of the zero-defect dense full-coated silver-coated copper powder, the multi-scale particle size grading conductive filler, the alicyclic / multifunctional composite resin system and the acid-absorbing and corrosion-resistant active defense additives.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic cell metallization technology, specifically relating to a silver-coated copper paste for HJT cells adapted to high salt spray environments, its preparation method, and its application. Background Technology

[0002] Heterojunction (HJT) solar cells have become an important development direction for next-generation silicon-based solar cells due to their advantages such as high conversion efficiency, high stability, and bifacial power generation. However, the metallization of HJT cells currently mainly relies on low-temperature curing silver paste, with a silver content typically exceeding 90%. The cost of silver paste accounts for as much as 60% of the non-silicon cost, becoming one of the main bottlenecks restricting the large-scale industrialization of HJT cells.

[0003] Silver-coated copper paste, by coating a silver layer onto the surface of copper powder and replacing part of the silver with copper, significantly reduces paste costs while maintaining good conductivity, thus becoming an ideal choice for metallization of HJT batteries. However, silver-coated copper paste still faces significant reliability issues in applications: the silver layer of conventional silver-coated copper powder inevitably contains micropores and grain boundary defects, and the high concentration of chloride ions (Cl) in seawater or salt spray environments... - It is extremely easy for it to penetrate into the copper core through defect sites, causing copper oxidation and electrochemical corrosion, leading to a decrease in battery efficiency. This problem is even more serious in applications such as offshore photovoltaics and saline-alkali land photovoltaics.

[0004] Existing technologies have some improvement solutions, such as using powders with multiple particle sizes, zinc phosphate intermediate layers, and organic silver salt repair, but none of them have systematically integrated multiple dimensions such as dense powder coating, multi-scale gradation, composite resin systems, and active defense additives.

[0005] Therefore, developing a silver-coated copper paste that can adapt to high salt spray and high acid and alkali corrosion environments has significant practical importance and market value. Summary of the Invention

[0006] The technical objective of this invention is to overcome the shortcomings of existing technologies and provide a silver-coated copper paste for HJT batteries that is suitable for high salt spray environments. Through the synergistic effect of zero-defect dense fully coated silver-coated copper powder, multi-scale particle size-graded conductive filler, alicyclic / multifunctional composite resin system, and acid-absorbing and corrosion-resistant active defense additives, the long-term reliability of the paste in high salt spray and high acid and alkali corrosion environments is significantly improved.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: The silver-coated copper paste for HJT batteries adapted to high salt spray environments, as described in this invention, comprises the following components by weight: Fully coated silver-coated copper powder: 80-92 parts Micron-sized silver powder: 0-10 parts; Nano silver powder: 0.3–5.0 parts; Alicyclic epoxy resin: 0.5–4.0 parts; Multifunctional epoxy resin: 1.0–6.0 parts; Hardener: 0.3–4.0 parts; Organic solvent: 2.0–10 parts; Acid absorbent: 0.5–3.0 parts; Corrosion resist: 0.1–1.5 parts; Coupling agent: 0.3–1.0 parts; Dispersant: 0-1.0 parts; Furthermore, the total mass fraction of the conductive filler composed of fully coated silver-coated copper powder, micron-sized silver powder, and nano-sized silver powder does not exceed 93 parts.

[0008] As a further improvement to the above technology, the fully coated silver-coated copper powder includes spherical silver-coated copper powder and flake silver-coated copper powder, wherein the mass ratio of spherical silver-coated copper powder to flake silver-coated copper powder is (70-90):(10-30); the D50 particle size of the spherical silver-coated copper powder is 1-5 μm, the particle thickness of the flake silver-coated copper powder is 0.2-1.5 μm, and the aspect ratio is 40:1-185:1. The fully coated silver-coated copper powder is a zero-defect, dense, fully coated silver-coated copper powder, the surface of which is completely coated by a layer of silver that is free of pinholes and gaps, continuous, uniform, and highly dense.

[0009] As a further improvement to the above technology, the micron-sized silver powder is shaped as one or two of spherical, near-spherical, or flake-like forms, with a D50 particle size of 1–5 μm; the nano-sized silver powder is shaped as spherical, with an average particle size of 50–500 nm.

[0010] As a further improvement to the above technology, the multifunctional epoxy resin is selected from one or more of phenolic epoxy resin, glycidyl triglyceride epoxy resin, glycidyl triglyceride amine epoxy resin, and cyanate ester resin; the curing agent is selected from one or a combination of several of amine-blocked hexafluoroantimonate, boron trifluoride-monoethylamine complex, blocked isocyanate, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, and 2-phenylimidazole; the organic solvent is selected from one or a combination of several of diethylene glycol butyl ether acetate, diethylene glycol butyl ether, dodecyl alcohol ester, terpineol, ethylene glycol phenyl ether, diethylene glycol diethyl ether, and dimethyl phthalate.

[0011] As a further improvement to the above technology, the acid absorbent is selected from one or both of magnesium oxide (MgO) or calcium oxide (CaO) with a particle size <1μm; the corrosion inhibitor is selected from one or more of benzotriazole (BTA) and its derivatives; the coupling agent is an epoxy silane coupling agent; and the dispersant is one or more of cationic and anionic wetting and dispersing agents.

[0012] This invention also discloses a method for preparing fully coated silver-coated copper powder in the silver-coated copper paste for HJT batteries adapted to high salt spray environments, the specific steps of which are as follows: (1) Copper powder pretreatment: The copper powder is subjected to acid washing, alkali washing and secondary acid washing in sequence to remove surface oxides and oil stains, and then dried to obtain pretreated copper powder; (2) Formation of zinc phosphate conversion film: The pretreated copper powder is placed in a conversion solution containing zinc phosphate and zinc nitrate and reacted at 40-60℃ for 30-60 min to form a zinc phosphate conversion film on the surface of the copper powder; (3) Displacement silver plating: copper powder with zinc phosphate conversion film is added to silver ammonia solution and displacement reaction is carried out under the control of tetraethylenepentamine (TEPA) and disodium ethylenediaminetetraacetate (EDTA-2Na) dual complexing agent system. The reaction temperature is controlled at 20-40℃ so that silver ions are uniformly reduced and deposited on the surface of copper powder to form a dense silver layer. (4) Defect repair treatment: The silver-plated copper powder semi-finished product is immersed in an organic silver salt solution and reacted at 50-70℃ for 30-60 minutes under ultrasonic assistance. The organic silver salt fills the defect sites by thermal decomposition or reduction reaction at the micropores and grain boundary defects of the silver layer. (5) Self-assembled monolayer passivation: The repaired silver-coated copper powder is immersed in a solution containing mercaptopropionic acid or mercaptosilane coupling agent and ultrasonically dispersed for 10-30 minutes, so that organic molecules form self-assembled monolayers (SAMs) through coordination bonds on the exposed copper defect sites that are not completely covered by the silver layer, thus obtaining a defect-dense fully coated silver-coated copper powder.

[0013] Specifically: In step (2) above, the mass concentration of zinc phosphate in the conversion solution is 0.5% to 5%, the mass concentration of zinc nitrate is 1% to 10%, and the pH value of the conversion solution is 2.0 to 3.5; In step (3) above, the concentration of silver ions in the silver ammonia solution is 0.01 to 0.1 mol / L. In the tetraethylenepentamine (TEPA) and ethylenediaminetetraacetic acid disodium salt (EDTA–2Na) dual complexing agent system, the molar ratio of TEPA to EDTA–2Na is 1:0.5 to 1:2, and the total molar concentration of the dual complexing agent is 2 to 5 times the molar concentration of silver ions. In step (4) above, the concentration of the organic silver salt solution is 0.005 to 0.05 mol / L, the organic silver salt is selected from one or more of silver citrate, silver acetate, and silver propionate, and the ultrasonic frequency is 40 to 80 kHz.

[0014] This invention also discloses a method for preparing the above-mentioned silver-coated copper paste for HJT batteries adapted to high salt spray environments, which includes the following steps: Step 1: Prepare fully coated silver-coated copper powder according to the aforementioned steps (1)-(5); Step 2: Mix the alicyclic epoxy resin, the multifunctional epoxy resin and the organic solvent, and stir them in a water bath at 20℃~60℃ until completely dissolved. After cooling to room temperature, filter to obtain the organic carrier. Step 3: Weigh out the zero-defect dense fully coated silver-coated copper powder, micron silver powder, nano silver powder, organic carrier, curing agent, acid absorber, corrosion inhibitor and coupling agent according to the ratio, stir in a mixer, grind and disperse on a three-roll mill 3 to 6 times until the fineness is ≤10μm, discharge the material to obtain the HJT battery matching silver-coated copper paste suitable for high salt spray environment.

[0015] The present invention also discloses the application of the above-mentioned HJT battery-compatible silver-coated copper paste adapted to high salt spray environment in the preparation of metal electrodes for heterojunction solar cells, including: printing the silver-coated copper paste onto the surface of the transparent conductive oxide layer of the HJT battery by screen printing, and then curing it at a low temperature of 150℃~250℃ for 5~30 minutes after printing to form conductive grid lines.

[0016] Furthermore, the metal electrode of the HJT battery is a front-side sub-grid line, and the silver-coated copper paste and the high water-resistant encapsulating film are used in conjunction to form an end-to-end overall protection solution; the water vapor transmission rate of the high water-resistant encapsulating film is <3g / (m²·day).

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Zero-defect dense coating: Through four processes of zinc phosphate transition layer, double complexing agent dense silver plating, organic silver salt repair and mercapto SAMs passivation, the silver-coated copper powder is fully coated with zero defects, which fundamentally blocks the penetration of chloride ions. (2) Multi-scale gradation of conductive filler: zero-defect dense full coating, micron silver powder and nano silver powder three-scale compounding to form a dense conductive network and nano sintered neck, reduce resistance and fill voids; (3) Composite resin system: Alicyclic epoxy resin and multifunctional epoxy resin work together to ensure high crosslinking density barrier properties and improve flexibility and UV aging resistance. (4) Active defense: acid absorber neutralizes acidic substances, corrosion resist forms a protective film, and coupling agent enhances interfacial bonding to form a chemical active defense layer.

[0018] (5) Excellent salt spray resistance: After testing, the resistance change rate after 1000 hours of salt spray test is <10%, the adhesion decay is <13%, and the resistance change rate after 168 hours of acid and alkali immersion is <11%, which is significantly better than the existing technology. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the four-layer collaborative protection architecture of the silver-coated copper paste of the present invention; 10 is the outer silver layer fully coated with silver-coated copper powder, 20 is the copper powder particles inside the silver-coated copper powder, 30 is the corrosion inhibitor adsorbed on the surface of the silver-coated copper powder, 40 is the acid absorbent, 50 is the cured epoxy resin + curing agent composition, 60 is the TCO layer of the HJT battery, and 70 is the HJT battery substrate.

[0020] Figure 2 This is a SEM image of the fully coated silver-coated copper powder in this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and comparative examples. It should be noted that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0022] The silver-coated copper paste for HJT batteries adapted to high salt spray environments, as described in this invention, comprises the following components by weight: Fully coated silver-coated copper powder: 80-92 parts Micron-sized silver powder: 0-10 parts; Nano silver powder: 0.3–5.0 parts; Alicyclic epoxy resin: 0.5–4.0 parts; Multifunctional epoxy resin: 1.0–6.0 parts; Hardener: 0.3–4.0 parts; Organic solvent: 2.0–10 parts; Acid absorbent: 0.5–3.0 parts; Corrosion resist: 0.1–1.5 parts; Coupling agent: 0.3–1.0 parts; Dispersant: 0-1.0 parts; The total mass fraction of the conductive filler composed of fully coated silver-coated copper powder, micron-sized silver powder, and nano-sized silver powder does not exceed 93 parts, and the fully coated silver-coated copper powder is a zero-defect, dense, fully coated silver-coated copper powder, the surface of which is completely coated by a layer of silver layer that is free of pinholes and gaps, continuous, uniform, and highly dense.

[0023] The specific steps for preparing the fully coated silver-coated copper powder are as follows: (1) Copper powder pretreatment: The copper powder is subjected to acid washing, alkali washing and secondary acid washing in sequence to remove surface oxides and oil stains, and then dried to obtain pretreated copper powder; (2) Formation of zinc phosphate conversion film: The pretreated copper powder is placed in a conversion solution containing zinc phosphate and zinc nitrate and reacted at 40-60℃ for 30-60 min to form a zinc phosphate conversion film on the surface of the copper powder; (3) Displacement silver plating: copper powder with zinc phosphate conversion film is added to silver ammonia solution and displacement reaction is carried out under the control of tetraethylenepentamine (TEPA) and disodium ethylenediaminetetraacetate (EDTA-2Na) dual complexing agent system. The reaction temperature is controlled at 20-40℃ so that silver ions are uniformly reduced and deposited on the surface of copper powder to form a dense silver layer. (4) Defect repair treatment: The silver-plated copper powder semi-finished product is immersed in an organic silver salt solution and reacted at 50-70℃ for 30-60 minutes under ultrasonic assistance. The organic silver salt fills the defect sites by thermal decomposition or reduction reaction at the micropores and grain boundary defects of the silver layer. (5) Self-assembled monolayer passivation: The repaired silver-coated copper powder is immersed in a solution containing mercaptopropionic acid or mercaptosilane coupling agent and ultrasonically dispersed for 10-30 minutes, so that organic molecules form self-assembled monolayers (SAMs) through coordination bonds on the exposed copper defect sites that are not completely covered by the silver layer, thus obtaining zero-defect dense fully coated silver-coated copper powder.

[0024] The following uses spherical copper powder as an example to illustrate the preparation steps of fully coated silver-coated copper powder: (1) First, take 100g of spherical copper powder with D50=2.5μm, soak it in 5% hydrochloric acid for 10min, 5% sodium hydroxide for 10min, and then soak it in 5% hydrochloric acid for 10min. Wash it with deionized water until neutral, and dry it in vacuum at 60℃. (2) Then, add 1L of conversion solution containing 3% zinc phosphate, 5% zinc nitrate, and pH=2.8, react at 50℃ for 45min, and then separate, wash and dry.

[0025] (3) Next, prepare 1L of 0.05mol / L silver ammonia solution, add 0.05mol of TEPA and 0.05mol of EDTA-2Na, add the above copper powder, react at 30℃ for 30min, filter, wash and dry.

[0026] (4) Immerse in 0.01 mol / L silver citrate solution, sonicate at 60°C for 45 min, wash and dry.

[0027] (5) Finally, immerse in 0.5% mercaptopropionic acid aqueous solution, sonicate at room temperature for 20 min, wash and dry to obtain zero-defect dense fully coated silver-coated copper powder (silver content 15%).

[0028] The preparation of flake-shaped powders is similar to that of other powders.

[0029] This invention also discloses a method for preparing the above-mentioned silver-coated copper paste for HJT batteries adapted to high salt spray environments, which includes the following steps: Step 1: Prepare zero-defect, dense, fully coated silver-coated copper powder according to the aforementioned preparation steps for fully coated silver-coated copper powder; Step 2: Mix the alicyclic epoxy resin, the multifunctional epoxy resin and the organic solvent, and stir them in a water bath at 20℃~60℃ until completely dissolved. After cooling to room temperature, filter to obtain the organic carrier. Step 3: Weigh out the zero-defect dense fully coated silver-coated copper powder, micron silver powder, nano silver powder, organic carrier, curing agent, acid absorber, corrosion inhibitor and coupling agent according to the ratio, stir in a mixer, grind and disperse on a three-roll mill 3 to 6 times until the fineness is ≤10μm, discharge the material to obtain the HJT battery matching silver-coated copper paste suitable for high salt spray environment.

[0030] This invention also discloses the application of the aforementioned HJT battery-compatible silver-coated copper paste, adapted to high salt spray environments, in the preparation of metal electrodes for heterojunction solar cells. The method includes: screen printing the silver-coated copper paste onto the surface of the transparent conductive oxide layer of the HJT battery; curing the paste at a low temperature of 150℃~250℃ for 5~30 minutes after printing to form conductive grid lines; the metal electrode of the HJT battery is a front-side sub-grid line; the silver-coated copper paste is used in conjunction with a high water-resistant encapsulating film to form an end-to-end overall protection solution; the water vapor transmission rate of the high water-resistant encapsulating film is <3g / (m²·day).

[0031] Figure 1 The four-layer synergistic protective architecture of the silver-coated copper paste of the present invention is shown, which includes: an outer silver layer 10 fully covering the silver-coated copper powder, copper powder particles 20 inside the silver-coated copper powder, a corrosion inhibitor 30 adsorbed on the surface of the silver-coated copper powder, an acid absorbent 40, a cured epoxy resin and curing agent composition 50, a TCO layer 60 of the HJT battery, and an HJT battery substrate 70.

[0032] Figure 2 This is an SEM image of the fully coated silver-coated copper powder in this invention. The particles are completely coated, and the silver layer is dense and uniform, which can achieve zero-defect and dense full coating of silver-coated copper powder.

[0033] The following examples illustrate the process in detail, and the formulations for each example are shown in the table below. All examples meet the requirement of a total volume of 100 parts and a total volume of conductive filler powder composed of fully coated silver-coated copper powder, micron-sized silver powder, and nano-sized silver powder ≤ 93 parts. All examples utilize zero-defect, dense, fully coated silver-coated copper powder obtained through the aforementioned general preparation method, and the slurry is prepared according to the aforementioned method for preparing silver-coated copper paste for HJT batteries adapted to high salt spray environments.

[0034] Example 1: Formula (taking the median value of the range)

[0035] Table 1 Example 2 formulation (maximum 92 parts of fully coated silver and copper powder, total powder volume 92.8 parts)

[0036] Table 2 Example 3 Formula (minimum 80 parts of fully encapsulated silver-coated copper powder, maximum 10 parts of micronized silver powder, maximum 5 parts of nano-silver powder, total powder volume 93 parts)

[0037] Table 3 Example 4 Formulation (upper limit 4 parts of alicyclic epoxy resin, lower limit 1 part of multifunctional epoxy resin)

[0038] Table 4 Example 5 Formulation (Curing agent maximum 4 parts, organic solvent maximum 10 parts)

[0039] Table 5 Example 6 Formulation (maximum of acid absorbent 3 parts, maximum of corrosion resist 1.5 parts, maximum of coupling agent 1.0 part)

[0040] Table 6 Example 7 Formulation (lower limits of each component: 80 for fully coated silver-coated copper powder, 0 for micron-sized silver powder, 0.3 for nano-sized silver powder, 0.5 for alicyclic epoxy, 1 for multifunctional group, 0.3 for curing agent, 2 for organic solvent, 0.5 for acid scavenger, 0.1 for corrosion resist, 0.3 for coupling agent, and 0 for dispersant)

[0041] Table 7 Example 8 Formulation (Dispersant upper limit 1.0 part, the rest are taken as the middle to upper values)

[0042] Table 8 The following comparison uses four pairs of proportions to illustrate this: Comparative Example 1 (conventional spherical silver-coated copper powder, without any reinforcement treatment)

[0043] Table 9 Comparative Example 2 (zinc phosphate treatment only for silver-coated copper powder, no remediation or SAMs)

[0044] Table 10 Comparative Example 3 (Full coating of silver and copper powder, without the addition of micron / nano silver powder)

[0045] Table 11 Comparative Example 4 (Full-coverage silver-coated copper powder + micron / nano silver powder, but no additives)

[0046] Table 12 IV. Performance Testing Methods The slurries from each embodiment and comparative example were screen-printed onto the TCO layer of the HJT battery and cured at 180°C for 15 minutes to form test samples. Test method: 1. Initial resistivity: Four-probe method.

[0047] 2. Salt spray test: IEC 61701, 5% NaCl, 35℃, 1000h, calculate the rate of change of resistivity.

[0048] 3. Acid and alkali soaking: 5% HCl and 5% NaOH, 25℃, 168h, calculate the rate of change of resistance.

[0049] 4. Adhesion: 3M tape peel test, test the peel strength attenuation rate before and after salt spray.

[0050] V. Performance test results (see Tables 13 and 14 below) Performance test results

[0051] Table 13

[0052] Table 14 Results analysis: 1. The resistivity change rate after salt spray in Examples 1-8 of the present invention is less than 10%, which is significantly better than that in Comparative Examples 1-2 (>28%), indicating that the zero-defect dense full coverage, multi-scale gradation and active defense are synergistically effective.

[0053] 2. Example 6 (upper limit of additives) has the best performance, with a resistivity change rate of only 6.6%.

[0054] 3. Example 7 (lower limits of each component) still achieved acceptable performance (9.8%), proving that the formulation range was reasonable.

[0055] 4. The resistivity change rate of Comparative Example 3 (without micron / nano silver powder) was 12.8%, indicating that the multi-scale gradation further improved the corrosion resistance.

[0056] 5. Comparative Example 4 (without additives) showed a resistance change rate of 15.5%, proving that acid absorbers, corrosion inhibitors, and coupling agents are indispensable.

[0057] 6. The initial resistivity of the embodiments of the present invention is 4.8~6.0×10⁻⁶. -4 Ω·cm, indicating good electrical conductivity.

[0058] The silver-coated copper paste of the present invention can be mass-produced using conventional conductive paste production methods, and is compatible with the screen printing and low-temperature curing processes of existing HJT production lines, without the need for additional equipment modifications.

[0059] This slurry is particularly suitable for high salt spray and high acid and alkali corrosion environments such as offshore photovoltaic, tidal flat photovoltaic and saline-alkali land photovoltaic. When used in conjunction with a high water-blocking encapsulation film (water vapor transmission rate <3 g / m²·day), it can form a complete end-to-end overall protection solution, which is of great value for promoting the industrial application of HJT batteries in extreme environments.

Claims

1. A silver-coated copper paste for HJT batteries adapted to high salt spray environments, characterized in that, The silver-coated copper paste comprises the following components in parts by weight: Fully coated silver-coated copper powder: 80-92 parts Micron-sized silver powder: 0-10 parts; Nano silver powder: 0.3–5.0 parts; Alicyclic epoxy resin: 0.5–4.0 parts; Multifunctional epoxy resin: 1.0–6.0 parts; Hardener: 0.3–4.0 parts; Organic solvent: 2.0–10 parts; Acid absorbent: 0.5–3.0 parts; Corrosion resist: 0.1–1.5 parts; Coupling agent: 0.3–1.0 parts; Dispersant: 0-1.0 parts; Furthermore, the total mass fraction of the conductive filler composed of fully coated silver-coated copper powder, micron-sized silver powder, and nano-sized silver powder does not exceed 93 parts.

2. The silver-coated copper paste for HJT batteries adapted to high salt spray environments as described in claim 1, characterized in that, The fully coated silver-coated copper powder includes spherical silver-coated copper powder and flake silver-coated copper powder, wherein the mass ratio of spherical silver-coated copper powder to flake silver-coated copper powder is (70-90):(10-30); the D50 particle size of the spherical silver-coated copper powder is 1-5 μm, and the particle thickness of the flake silver-coated copper powder is 0.2-1.5 μm, with a diameter-to-thickness ratio of 40:1-185:

1.

3. The silver-coated copper paste for HJT batteries adapted to high salt spray environments as described in claim 1, characterized in that, The micron-sized silver powder has one or two of the following morphologies: spherical, near-spherical, or flake-like, with a D50 particle size of 1–5 μm; the nano-sized silver powder has a spherical morphology and an average particle size of 50–500 nm.

4. The silver-coated copper paste for HJT batteries adapted to high salt spray environments as described in claim 1, characterized in that, The alicyclic epoxy resin is selected from one or more combinations of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate, flexible alicyclic / vinylcyclohexene monoepoxy resin, bis(3,4-epoxycyclohexylmethyl)adipate, 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, and tetrahydrophthalic acid diglycidyl ester. The multifunctional epoxy resin is selected from one or more of phenolic epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, and cyanate ester resin. The organic solvent is selected from one or a combination of several of diethylene glycol butyl ether acetate, diethylene glycol butyl ether, dodecyl alcohol ester, terpineol, ethylene glycol phenyl ether, diethylene glycol diethyl ether, and dimethyl phthalate.

5. The silver-coated copper paste for HJT batteries adapted to high salt spray environments according to claim 1, characterized in that, The curing agent is selected from one or a combination of several of the following: amine-blocked hexafluoroantimonate, boron trifluoride-monoethylamine complex, blocked isocyanate, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, and 2-phenylimidazole. The acid absorbent is selected from one or both of magnesium oxide (MgO) or calcium oxide (CaO) with a particle size <1μm; the corrosion inhibitor is selected from one or more of benzotriazole (BTA) and its derivatives. The coupling agent is an epoxy silane coupling agent; The dispersant is one or more of cationic and anionic wetting and dispersing agents.

6. The method for preparing fully coated silver-coated copper powder in HJT battery silver-coated copper paste adapted to high salt spray environment according to claim 1, characterized in that, The specific steps are as follows: (1) Copper powder pretreatment: The copper powder is subjected to acid washing, alkali washing and secondary acid washing in sequence to remove surface oxides and oil stains, and then dried to obtain pretreated copper powder; (2) Formation of zinc phosphate conversion film: The pretreated copper powder is placed in a conversion solution containing zinc phosphate and zinc nitrate and reacted at 40-60℃ for 30-60 min to form a zinc phosphate conversion film on the surface of the copper powder; (3) Displacement silver plating: copper powder with zinc phosphate conversion film is added to silver ammonia solution and displacement reaction is carried out under the control of tetraethylenepentamine (TEPA) and disodium ethylenediaminetetraacetate (EDTA-2Na) dual complexing agent system. The reaction temperature is controlled at 20-40℃ so that silver ions are uniformly reduced and deposited on the surface of copper powder to form a dense silver layer. (4) Defect repair treatment: The silver-plated copper powder semi-finished product is immersed in an organic silver salt solution and reacted at 50-70℃ for 30-60 minutes under ultrasonic assistance. The organic silver salt fills the defect sites by thermal decomposition or reduction reaction at the micropores and grain boundary defects of the silver layer. (5) Self-assembled monolayer passivation: The repaired silver-coated copper powder is immersed in a solution containing mercaptopropionic acid or mercaptosilane coupling agent and ultrasonically dispersed for 10-30 minutes, so that organic molecules form self-assembled monolayers (SAMs) through coordination bonds on the exposed copper defect sites that are not completely covered by the silver layer, thus obtaining zero-defect dense fully coated silver-coated copper powder.

7. The method for preparing fully coated silver-coated copper powder in the HJT battery silver-coated copper paste adapted to high salt spray environments according to claim 6, characterized in that, The specific steps are as follows: In step (2) above, the mass concentration of zinc phosphate in the conversion solution is 0.5% to 5%, the mass concentration of zinc nitrate is 1% to 10%, and the pH value of the conversion solution is 2.0 to 3.5; In step (3) above, the concentration of silver ions in the silver ammonia solution is 0.01 to 0.1 mol / L. In the tetraethylenepentamine (TEPA) and ethylenediaminetetraacetic acid disodium salt (EDTA–2Na) dual complexing agent system, the molar ratio of TEPA to EDTA–2Na is 1:0.5 to 1:2, and the total molar concentration of the dual complexing agent is 2 to 5 times the molar concentration of silver ions. In step (4) above, the concentration of the organic silver salt solution is 0.005 to 0.05 mol / L, the organic silver salt is selected from one or more of silver citrate, silver acetate, and silver propionate, and the ultrasonic frequency is 40 to 80 kHz.

8. A method for preparing silver-coated copper paste for HJT batteries adapted to high salt spray environments, as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Prepare fully coated silver-coated copper powder according to steps (1)-(5) of claim 7; Step 2: Mix the alicyclic epoxy resin, the multifunctional epoxy resin and the organic solvent, and stir them in a water bath at 20℃~60℃ until completely dissolved. After cooling to room temperature, filter to obtain the organic carrier. Step 3: Weigh out the zero-defect dense fully coated silver-coated copper powder, micron silver powder, nano silver powder, organic carrier, curing agent, acid absorber, corrosion inhibitor and coupling agent according to the ratio, stir in a mixer, grind and disperse on a three-roll mill 3 to 6 times until the fineness is ≤10μm, discharge the material to obtain the HJT battery matching silver-coated copper paste suitable for high salt spray environment.

9. The application of the HJT battery-compatible silver-coated copper paste according to any one of claims 1-5 in the preparation of metal electrodes for heterojunction solar cells, characterized in that, The application includes: printing the silver-coated copper paste onto the surface of the transparent conductive oxide layer of the HJT battery by screen printing, and then curing it at a low temperature of 150℃~250℃ for 5~30 minutes to form conductive grid lines.

10. The application according to claim 9, characterized in that, The metal electrode of the HJT battery is a front-side sub-grid line. The silver-coated copper paste and the high water-resistant encapsulating film are used together to form an end-to-end overall protection solution. The water vapor transmission rate of the high water-resistant encapsulating film is <3g / (m²·day).

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