Conductive silver-coated copper micropowder for photovoltaics and method for preparing same

Abstract

This invention relates to the field of photovoltaic technology and discloses a conductive silver-coated copper micropowder for photovoltaic applications and its preparation method. This preparation method aims to solve the problem of balancing performance and cost in existing silver-coated copper micropowders for photovoltaic applications. In this invention, during the pretreatment stage, the base copper powder is acid-washed but not water-washed. It undergoes pH adjustment, organic pre-bonding treatment, and gradient ammoniation to retain the activity of the copper powder and construct a uniform copper-ammonia complex layer. In the chemical silver plating stage, the pretreatment solution is added to a composite base liquid containing a complexing agent, organic amine, dispersant, and combined reducing agent. A silver-ammonia solution is then added dropwise under ultrasonic dispersion and nitrogen protection. In the post-treatment stage, the product undergoes ethanol reflux desorption, antioxidant treatment, vacuum drying, and low-temperature plasma activation, followed by sieving to obtain the final product. This method can achieve uniform and complete silver coating even with low silver content, providing a feasible path for the large-scale replacement of pure silver powder for photovoltaic applications with silver-coated copper micropowder.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and in particular to a conductive silver-coated copper micropowder for photovoltaic applications and its preparation method. Background Technology

[0002] In the photovoltaic industry, conductive paste is a key component of photovoltaic cell electrodes. Traditionally, it is prepared using pure silver powder, but silver resources are scarce and expensive. Therefore, silver-coated copper micropowder has gradually gained attention as an alternative material to silver powder. Silver-coated copper micropowder combines the low cost of copper with the high conductivity and oxidation resistance of silver by coating a silver layer on the surface of copper powder. Its preparation is mostly carried out using chemical plating processes, including pretreatment, silver plating, and post-treatment. It is widely used in conductive pastes in electronics, photovoltaics, and other fields. The photovoltaic field has more stringent performance requirements for silver-coated copper micropowder, which must simultaneously meet the requirements of low silver content, high conductivity, strong oxidation resistance, and good dispersibility.

[0003] However, the fundamental contradiction in adapting existing silver-coated copper micropowder technology to the photovoltaic field lies in the difficulty of balancing performance and cost. The fundamental goal of using silver-coated copper micropowder is to replace pure silver powder to reduce material costs, which necessitates controlling the silver content of the silver-coated copper micropowder within a low-cost range. However, under low silver content conditions, existing processes struggle to form a complete and uniform silver coating layer, directly resulting in insufficient oxidation resistance and poor conductivity of the product. Conversely, to meet photovoltaic application standards, existing technologies often require increasing the silver content to improve the integrity of the silver coating and conductivity. However, this also weakens the cost advantage of silver-coated copper micropowder. Low silver content leads to substandard performance, while high silver content lacks cost advantage, thus hindering the large-scale replacement of pure silver powder by silver-coated copper micropowder. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that the existing technology has the disadvantage of difficulty in balancing performance and cost. To this end, we propose a method for preparing conductive silver-coated copper micropowder for photovoltaic applications, as well as the conductive silver-coated copper micropowder for photovoltaic applications prepared by using the method.

[0005] To achieve the above objectives, the first aspect of this application adopts the following technical solution: a method for preparing conductive silver-coated copper micropowder for photovoltaic applications, comprising the following steps: S1: the base copper powder is acid-washed without water washing, ammonia water is added dropwise to adjust the pH of the system, and then organic prebonding treatment is used to form a monolayer. Subsequently, it is transferred to a composite ammoniation system for gradient pH adjustment, and after ultrasonic treatment, the waste liquid is removed by standing to obtain a pretreated solution; S2: the pretreated solution is added to a composite base liquid containing a complexing agent, an organic amine, a dispersant, and a reducing agent. After ultrasonic dispersion and nitrogen protection, a silver ammonia solution containing an organic amine is added dropwise to complete the silver plating reaction. Then, a directional guiding agent is added and the pH of the system is adjusted. After standing, the waste liquid is removed to obtain a crude silver-coated copper powder; S3: the crude silver-coated copper powder is filtered and washed with water until neutral. After ethanol reflux desorption to remove residual impurities, it is subjected to antioxidant protection, and then vacuum drying, low-temperature plasma activation, and sieving to obtain the finished product.

[0006] Preferably, the ammonia water mentioned in S1 is a 5% by mass dilute ammonia water, and the pH of the system is adjusted to 2-3.

[0007] Preferably, the prebonding solution used in the organic prebonding treatment in S1 is a solution prepared by dissolving 12-hydroxystearic acid in anhydrous ethanol, wherein the mass of 12-hydroxystearic acid is 0.5%-0.6% of the mass of the matrix copper powder.

[0008] Preferably, the composite ammoniation system in S1 is composed of 15%-18% by mass of ammonia water, 4%-6% by mass of ammonium sulfate, tannic acid and organic amine, wherein the mass of tannic acid is 0.05%-0.1% of the mass of the copper powder matrix.

[0009] Preferably, the gradient pH adjustment process in S1 includes: in the first stage, adding 5%-8% by mass of dilute ammonia water to raise the pH of the system to 8-9; and in the second stage, adding 18%-20% by mass of concentrated ammonia water to adjust the pH of the system to 10-11.

[0010] Preferably, the complexing agent in S2 is one or a combination of several of the following: disodium ethylenediaminetetraacetate, sodium aminotriacetate, disodium HEDP, trisodium citrate, glycine, cysteine, and glutamic acid, and the total mass of the complexing agent is 5%-10% of the mass of the copper matrix powder.

[0011] Preferably, the reducing agent in S2 is a compound system of glucose and ascorbic acid with a mass ratio of 1:1 to 1:2, and the mass ratio of the total mass of the reducing agent to the mass of the copper matrix powder is 1:5 to 1:10.

[0012] Preferably, the silver ammonia solution in S2 is composed of silver nitrate, organic amine, and ammonia water with a mass fraction of 25%, and the mass ratio of silver nitrate to the copper matrix powder is 1:6-1:10.

[0013] Preferably, the organic amines in the S1 composite ammonia system, the S2 composite base liquid, and the S2 silver ammonia solution are of the same type, namely one or a combination of ethylenediamine, dimethylaminopropylamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0014] The second aspect of this application adopts the following technical solution: a conductive silver-coated copper micropowder for photovoltaic applications, prepared by the above-mentioned preparation method.

[0015] The technical effects and advantages of this invention are as follows:

[0016] In this invention, a synergistic front-end process of acid pickling residue control, organic prebonding, and gradient ammoniation, combined with a combined reducing agent system, is used to construct a silver ion directional deposition mechanism. The monomolecular prebonding layer formed by 12-hydroxystearic acid provides precise anchoring points for silver ions. The gradient ammoniation process optimizes the uniformity of the copper-ammonia complex layer, avoiding local reaction imbalances. The combined reducing agent of glucose and ascorbic acid balances the reduction rate, preventing discontinuity in the silver layer and reducing the generation of free silver particles. This synergistic mechanism achieves dense and complete coating of the silver layer with low silver content, solving the core contradiction of existing technologies where low silver content results in substandard performance and high silver content leads to a loss of cost advantage. It also reduces raw material loss and material costs, laying the foundation for the large-scale replacement of pure silver powder with silver-coated copper micropowder. Attached Figure Description

[0017] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0018] Figure 1 This is a schematic diagram of the preparation process of the photovoltaic conductive silver-coated copper micro powder of the present invention;

[0019] Figure 2 This is an SEM image of the silver-coated copper micropowder prepared in Example 1 of the present invention;

[0020] Figure 3 SEM image of the silver-coated copper micropowder prepared in Example 2 of the present invention;

[0021] Figure 4 SEM image of the silver-coated copper micropowder prepared in Example 3 of the present invention;

[0022] Figure 5 This is an SEM image of the silver-coated copper micropowder prepared in Example 4 of the present invention. Detailed Implementation

[0023] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0024] Reference Figure 1 As shown, the present invention provides a technical solution: a method for preparing conductive silver-coated copper micropowder for photovoltaic applications, specifically including the following steps:

[0025] S1: The copper powder matrix is ​​acid-washed but not washed with water. A small amount of ammonia is added dropwise to adjust the pH of the system. Then, an organic pre-bonding treatment is used to form a monolayer. Subsequently, it is transferred to a composite ammoniation system for gradient pH adjustment to optimize the copper-ammonia complex layer structure and obtain the pretreated solution.

[0026] S2: The pretreatment solution is added to a composite base solution containing complexing agent, organic amine, dispersant and reducing agent. The solution is ultrasonically dispersed and protected by nitrogen at 40-50℃. After the silver plating reaction is completed by adding silver ammonia solution containing organic amine, a directional guiding agent is added. The upper waste liquid is removed by standing to obtain crude silver-coated copper powder.

[0027] S3: The crude silver-coated copper powder is filtered and washed with water until neutral. It is then desorbed by ethanol reflux to remove residual impurities, followed by antioxidant protection. Finally, it is vacuum dried, activated by low-temperature plasma, and sieved to obtain the finished product.

[0028] In some specific embodiments, step S1 includes the following technical features:

[0029] The base copper powder is selected with a particle size D50 of 3.3-3.7μm, a particle size distribution range of ≤0.9, a purity of ≥99.5%, and is dry without caking.

[0030] Pickling is performed using a 5%-10% sulfuric acid solution, supplemented by ultrasonic treatment at 200-400W and 40-60Hz for 5-10 minutes. The pickling temperature is controlled at 20-30℃. After pickling, the mixture is allowed to stand for 1-2 hours. Once the copper powder has completely settled, the upper layer of sulfuric acid waste liquid is removed by siphoning. The volume-to-mass ratio of the residual acid solution to the copper powder is 0.2-0.3 mL / g.

[0031] After acid washing, do not rinse with water. Immediately add 5% (w / w) dilute ammonia solution to the system dropwise while stirring until the pH of the system stabilizes at 2-3.

[0032] Subsequently, an organic pre-bonding solution is added, which is a 50 g / L ethanol solution prepared by dissolving 12-hydroxystearic acid in anhydrous ethanol. The mass of 12-hydroxystearic acid is 0.5%-0.6% of the mass of the copper powder matrix. The mixture is stirred at 200 r / min for 2-3 min at room temperature to allow the hydroxyl groups of 12-hydroxystearic acid to form coordinate bonds with the active sites on the surface of the copper powder, and the carboxyl groups to be oriented outward to form a dense monomolecular pre-bonding layer. The residual trace amount of sulfuric acid is neutralized and removed by subsequent ammoniation solution.

[0033] The composite ammoniation system is an alkaline ammoniation solution, comprising 15%-18% ammonia water, 4%-6% ammonium sulfate, 0.05%-0.1% tannic acid (by mass of copper powder), and 0.5%-1.05% organic amine (by total mass of ammoniation solution). The organic amine is one or a combination of ethylenediamine, dimethylaminopropylamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, and is consistent with the type of organic amine in the S2 composite base solution to ensure compatibility of the entire process system.

[0034] The solid-liquid ratio of the matrix copper powder to the alkaline ammoniation solution is 1:4-1:6. During the ammoniation process, ultrasonic treatment at 200W-400W is applied for 8-12 minutes. A gradient pH adjustment process is adopted. For the first 4 minutes, 5%-8% dilute ammonia solution is added dropwise to control the pH to rise slowly to 8-9. Subsequently, 18%-20% concentrated ammonia solution is added dropwise to raise the pH to 10-11.

[0035] Organic amines achieve pH buffering through the reversible interaction of amino and hydrogen ions. If the pH is below 10, a small amount of concentrated ammonia can be added. If the pH is above 11, a small amount of dilute sulfuric acid can be added for fine adjustment. This pH value needs to be locked after the ammoniation ultrasonication is completed and before standing. After standing for 1-2 hours, the upper ammoniation waste liquid is removed and directly transferred to S2 without water washing, retaining the uniform copper-ammonia complex layer and pre-bonded layer on the surface of the copper powder.

[0036] In some specific embodiments, step S2 includes the following technical features:

[0037] The composite base liquid contains a complexing agent, an organic amine, a dispersant, and a reducing agent, and the amounts of each component meet the following conditions:

[0038] The complexing agent is one or a combination of several of the following: disodium ethylenediaminetetraacetate, sodium aminotriacetate, disodium HEDP, trisodium citrate, glycine, cysteine, and glutamic acid, with a mass of 5%-10% of the copper matrix powder, used to complex free Cu. 2+ To avoid Cu 2+ It competes with silver ions for reduction sites, ensuring that the silver layer is deposited directionally on the surface of copper powder.

[0039] The organic amine is the same as that in the S1 composite ammoniation system, accounting for 2%-5% of the total mass of the composite base solution. It not only stabilizes the silver ions in the silver ammonia solution to form a complex system, but also adjusts the pH of the base solution to 9-11 to adapt to the silver ion reduction reaction.

[0040] The dispersant is a PEG-b-polylactic acid block copolymer, accounting for 0.5-1.0% of the mass of the copper powder matrix. Its PEG segments form hydrogen bonds with the hydroxyl groups of 12-hydroxystearic acid in the pre-bonded layer, and the lactic acid segments encapsulate the copper powder through hydrophobic interaction, forming a core-shell dispersion structure. This structure can both inhibit particle agglomeration and slowly release the encapsulated reducing agent, thereby regulating the reduction rate of silver ions.

[0041] The reducing agent uses a combination system of glucose and ascorbic acid with a mass ratio of 1:1 to 1:2. The mass ratio of the total mass of the reducing agent to the mass of the copper powder matrix is ​​1:5 to 1:10. When a weak reducing agent is used alone, the reaction rate is too slow, which can easily lead to discontinuous silver layer. When a strong reducing agent is used alone, silver ions will be over-reduced to generate free silver particles. The combined system can ensure that silver ions are continuously and uniformly deposited on the surface of copper powder.

[0042] Add the pretreatment solution to the composite base solution, control the copper powder concentration to 50-80 g / L, mix and then ultrasonically disperse at 200-400 W and 40-60 Hz. Maintain the ultrasonication throughout the process and purge with nitrogen gas for protection. The flow rate is 0.3-0.5 L / min. Remove air to avoid oxidation. Control the system temperature at 40-50℃. Too low a temperature will result in a low reaction rate, while too high a temperature will cause the base solution components to decompose.

[0043] Silver nitrate was dissolved in an organic amine, and 25% ammonia solution was added dropwise until the white precipitate was completely dissolved. The solution was then diluted with deionized water to obtain a silver ammonia solution. The mass ratio of silver nitrate to copper powder matrix was 1:6-1:10, and the organic amine was the same as that in the composite base solution.

[0044] The silver ammonia solution was added dropwise at a rate of 1.5-2.0 mL / min for a total dropping time of 4-4.5 h. The concentration gradient of silver ions was controlled by slow dropping to avoid the excessive generation of free silver particles in some areas. During the dropping process, the system was kept in a homogeneous emulsion state to ensure that the surface of each copper powder could contact silver ions and form a continuous silver layer.

[0045] After the silver ammonia solution is added dropwise, maintain the reaction conditions of ultrasound, nitrogen purging, and 40℃-50℃ for 1-1.5 hours to ensure complete deposition of residual silver ions. After the reaction is complete, add silane coupling agent KH-550 dropwise as a directional guide agent to the system at a dosage of 0.05%-0.1% of the total mass of the silver ammonia solution. During the dropwise addition, adjust the pH of the system to 8-9 with 5% (w / w) dilute ammonia water to avoid hydrolysis of KH-550. After stirring for 30 minutes, turn off the ultrasound, heating, and nitrogen purging devices and let it stand for 0.5-1 hours until the silver-coated copper powder is completely settled. Remove the upper waste liquid to obtain crude silver-coated copper powder.

[0046] In some specific embodiments, step S3 includes the following technical features:

[0047] The crude silver-coated copper powder was filtered under vacuum of 0.08-0.09 MPa until no obvious liquid dripping occurred from the wet powder. During the filtration process, the powder was rinsed with deionized water at a rate of 5-10 mL / min. The filtration was continued until the pH of the effluent stabilized at 6-7 to remove residual complexing agents, organic amine salts, and unreacted soluble impurities, thus avoiding any impact on conductivity.

[0048] The washed wet silver-coated copper powder was transferred to a round-bottom flask, and anhydrous ethanol with a volume-to-mass ratio of 1:1 to the wet powder was added. A reflux condenser was then assembled, and the mixture was refluxed at 70-75°C for 30 minutes to desorb the dispersant, organic amines, and other impurities physically adsorbed on the surface, thereby improving the purity of the powder. After reflux, the mixture was filtered under a vacuum of 0.08-0.09 MPa to remove excess ethanol.

[0049] Subsequently, an antioxidant treatment is carried out, and the antioxidant is selected from one or more combinations of dodecyl acid, oleic acid, stearic acid, benzotriazole, 5-methyltetrazazole, 5-aminotetrazazole, hexadecyl mercaptan, and octadecyl mercaptan.

[0050] After dissolving the antioxidant in anhydrous ethanol, add the silver-coated copper powder after reflux desorption and sonicate at 200-300W and 50-60Hz for 5-10 minutes at room temperature. The volume-to-mass ratio of the silver-coated copper powder after reflux desorption to anhydrous ethanol and antioxidant is 200g:200mL:1-2g.

[0051] After ultrasonication, the mixture was filtered and then washed twice with anhydrous ethanol. The volume-to-mass ratio of ethanol to wet powder was 1:1 each time. After each wash, the mixture was filtered until no obvious liquid dripped, thus removing excess unadsorbed antioxidants.

[0052] After secondary filtration, the silver-coated copper powder is transferred to a vacuum drying oven. The temperature is set at 55-65℃, the vacuum degree is 0.08-0.09MPa, and the drying time is 2.5-3.5h. This avoids high-temperature deformation of the silver layer and oxidation of the copper core, while ensuring rapid evaporation of ethanol and maintaining powder dispersibility. After drying, the moisture content of the silver-coated copper powder is ≤0.5%.

[0053] The dried silver-coated copper powder was transferred to a plasma activator. Ar gas was used to activate the powder, and the activation temperature was set to 80-90℃, the power to 100-150W, and the activation time to 5 minutes. Ar plasma removed the residual hydroxyl groups on the surface of the antioxidant layer, improving the interfacial compatibility with the photovoltaic conductive paste. After activation, nitrogen gas was introduced for protection until the powder was cooled to room temperature to prevent secondary oxidation.

[0054] After cooling, the silver-coated copper powder showed no obvious hard agglomeration. It was gently crushed with an agate mortar and sieved through a 500-mesh nylon screen. After sieving, it was collected in a sealed container, and nitrogen gas was continuously introduced during the collection process to prevent the finished product from being exposed to oxidation.

[0055] The following will explain the solution of the present invention with reference to the embodiments. It should be noted that the embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, the reagents or instruments used in the embodiments are all conventional products that can be obtained commercially.

[0056] Example 1

[0057] This embodiment provides a method for preparing conductive silver-coated copper micropowder for photovoltaic applications, specifically including the following steps:

[0058] S1: Preprocessing

[0059] Weigh 170g of matrix copper powder with a particle size of 3.5μm, add it to 1020mL of 8% H2SO4 solution, place it in an ultrasonic cleaner, set the power to 300W and the frequency to 50Hz, and ultrasonically treat it for 8min at 25℃. After ultrasonic treatment, let it stand for 1.5h until the copper powder has completely settled, remove the upper layer of sulfuric acid waste liquid, and keep the lower layer of copper powder and 42.5mL of residual acid liquid without washing with water.

[0060] Add 5% (w / w) dilute ammonia solution to the copper powder system using a pipette while stirring magnetically at 200 r / min until the pH of the system stabilizes at 2.5.

[0061] Weigh 0.935 g of 12-hydroxystearic acid, add 18.7 mL of anhydrous ethanol and stir until completely dissolved. Slowly pour the pre-bonded solution into the copper powder system and stir at 200 r / min for 2.5 min.

[0062] Prepare 850 mL of alkaline ammoniation solution by mixing 16% ammonia solution and 5% ammonium sulfate solution by volume, adding 0.136 g tannic acid and 6.9 g diethylenetriamine, and stirring until completely dissolved. Pour the alkaline ammoniation solution into the copper powder system, turn on the ultrasonic cleaner, set the power to 300 W and the frequency to 50 Hz, and add 6% dilute ammonia solution dropwise using a constant pressure dropping funnel for the first 4 minutes to slowly raise the pH of the system to 8.5. For the next 6 minutes, replace the solution with 19% concentrated ammonia solution and continue adding it dropwise until the pH of the system stabilizes at 10.5. After turning off the ultrasonic cleaner, let it stand for 1.5 hours until the copper powder has completely settled. Remove the upper layer of ammoniation waste liquid by siphon to obtain the pretreated solution.

[0063] S2: Chemical silver plating

[0064] Take 2800 mL of deionized water, and add 11.9 g of disodium ethylenediaminetetraacetate, 112.0 g of diethylenetriamine, 1.36 g of PEG-b-polylactic acid block copolymer, 17.0 g of glucose and 17.0 g of ascorbic acid in sequence. Stir magnetically for 30 min until completely dissolved to obtain the composite base solution.

[0065] Transfer all the pretreatment solution into a 5000mL three-necked flask, add the composite base liquid and stir evenly; turn on the ultrasonic cleaner, set the power to 300W and the frequency to 50Hz, and introduce nitrogen into the three-necked flask at 0.4L / min to remove air. Stabilize the system temperature at 45℃ using a water bath temperature control.

[0066] Weigh 23.8g of silver nitrate, add 47.6g of diethylenetriamine, and stir until the silver nitrate is completely dissolved. Slowly add 25% ammonia solution until the white precipitate formed in the system is completely dissolved. Then add deionized water to make up to 400mL to obtain a silver ammonia solution. Add the silver ammonia solution to a constant pressure dropping funnel and slowly add it dropwise to a three-necked flask at a rate of 1.8mL / min for a total dropping time of 4.5h. Maintain a homogeneous emulsion state in the system during the dropping process.

[0067] After the silver ammonia solution was added dropwise, the ultrasonic, nitrogen-purging, and 45°C conditions were maintained for 1.2 h. Then, 0.3 g of silane coupling agent KH-550 was added dropwise to the system, along with 5% (w / w) dilute ammonia water to adjust the pH of the system to stabilize at 8.5. After stirring for 30 min, the ultrasonic, heating, and nitrogen-purging devices were turned off, and the system was allowed to stand for 1.0 h until the silver-coated copper powder completely settled. The upper waste liquid was then removed by siphon to obtain crude silver-coated copper powder.

[0068] S3: Post-processing

[0069] Transfer the crude silver-coated copper powder to a Buchner funnel, connect it to a vacuum filtration device with a vacuum degree of 0.085 MPa, and slowly rinse with deionized water at a rate of 8 mL / min. Continuously filter throughout the process, and check the pH of the effluent every 5 minutes until the pH stabilizes at 6.5, then stop rinsing.

[0070] After washing with water, the wet powder was transferred to a 1000mL round-bottom flask, 200mL of anhydrous ethanol was added, and a reflux condenser was assembled. The heating device was turned on, and the system temperature was controlled at 72℃. The reflux treatment was carried out for 30 minutes. After the reflux was completed, the powder was filtered again under a vacuum of 0.085MPa to remove excess ethanol.

[0071] Weigh 1.0 g of benzotriazole, add 200 mL of anhydrous ethanol, and stir until completely dissolved. Pour the solution into the refluxed desorbed silver-coated copper powder, place it in an ultrasonic cleaner, set the power to 250 W, the frequency to 55 Hz, and sonicate at room temperature for 8 min. After sonication, filter the powder and add 200 mL of anhydrous ethanol twice for washing. After each washing, filter the powder until there is no obvious liquid dripping from the wet powder to remove excess unadsorbed benzotriazole.

[0072] After secondary filtration, the silver-coated copper powder was transferred to a vacuum drying oven, and the drying temperature was set to 60℃, the vacuum degree to 0.085MPa, and the drying time to 3.0h. After drying, a sample was taken and tested with a moisture analyzer, and the moisture content was 0.3%.

[0073] The dried silver-coated copper powder was transferred to a plasma activator, Ar gas was introduced, and the activation temperature was set to 85℃, the power to 120W, and the activation time to 5min. After activation, nitrogen gas was introduced at a rate of 0.2L / min until the powder cooled to room temperature. After cooling, the powder was gently crushed with an agate mortar and sieved through a 500-mesh nylon sieve. The sieved powder was collected in a sealed container under nitrogen protection to obtain the finished conductive silver-coated copper micro powder for photovoltaic applications.

[0074] Figure 2 This is an SEM image of the silver-coated copper micropowder prepared in this embodiment.

[0075] Example 2

[0076] This embodiment provides a method for preparing conductive silver-coated copper micropowder for photovoltaic applications. The difference between this method and Example 1 is that:

[0077] In the antioxidant treatment stage, 1.0g benzotriazole was replaced with 0.5g stearic acid and 0.5g hexadecyl mercaptan, and the ultrasonic treatment time was extended to 10min.

[0078] Figure 3 This is an SEM image of the silver-coated copper micropowder prepared in this embodiment.

[0079] Example 3

[0080] This embodiment provides a method for preparing conductive silver-coated copper micropowder for photovoltaic applications. The difference between this method and Example 1 is that:

[0081] In the chemical silver plating stage, the reducing agent was adjusted to 11.3g glucose and 22.7g ascorbic acid, the silver ammonia solution was added at a rate of 2mL / min, and the total adding time was 4h.

[0082] Figure 4 This is an SEM image of the silver-coated copper micropowder prepared in this embodiment.

[0083] Example 4

[0084] This embodiment provides a method for preparing conductive silver-coated copper micropowder for photovoltaic applications. The difference between this method and Example 1 is that:

[0085] In the pretreatment stage, diethylenetriamine in the alkaline ammonia solution is replaced with 3.45g of ethylenediamine and 3.45g of triethylenetetramine; in the electroless silver plating stage, diethylenetriamine in the composite base solution and silver ammonia solution is simultaneously replaced with an equal mass of ethylenediamine and triethylenetetramine compound system.

[0086] Figure 5 This is an SEM image of the silver-coated copper micropowder prepared in this embodiment.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing conductive silver-coated copper micropowder for photovoltaic applications, which differs from Example 1 in that:

[0089] After acid washing, rinse continuously with deionized water until the pH of the system stabilizes at 6.5, then stop to completely remove residual acid. Do not add dilute ammonia to adjust the pH, and do not add anhydrous ethanol solution of 12-hydroxystearic acid.

[0090] Comparative Example 2

[0091] This comparative example provides a method for preparing conductive silver-coated copper micropowder for photovoltaic applications, which differs from Example 1 in that:

[0092] In the pretreatment stage, diethylenetriamine is not added to the alkaline ammoniation solution. During the ammoniation process, concentrated ammonia water with a mass fraction of 19% is added dropwise to adjust the pH of the system to 10.5 in one go, without using a gradient pH adjustment process. In the chemical silver plating stage, the reducing agent system is replaced with 34.0g of glucose.

[0093] Comparative Example 3

[0094] This comparative example refers to a silver-coated copper powder and its preparation method disclosed in patent CN120438614A. The silver-coated copper powder preparation method described in that patent was used, and the same batch of base copper powder was used for preparation as in Example 1.

[0095] Comparative Example 4

[0096] This comparative example uses commercially available conductive silver-coated copper micropowder for photovoltaic applications. The silver content is approximately 22.5%, and the particle size D50 is 3.5-4.0 μm. It was purchased from a regular industrial-grade commercial channel and meets the industry standards for photovoltaic conductive pastes.

[0097] The composite base solution in this comparative example contains only 8.5g of disodium ethylenediaminetetraacetate, 3.4g of PVPK30, and 21.25g of glucose, and does not contain any organic amine components.

[0098] The silver-coated copper micropowders prepared in Examples 1-4 and Comparative Examples 1-4 were sampled and subjected to performance tests. The specific test details are as follows:

[0099] The particle size distribution (unit: μm), span, and shading rate (unit: %) of silver-coated copper micropowder were tested using a laser particle size analyzer with deionized water as the dispersion medium. The results are shown in Table 1.

[0100] Table 1

[0101]

[0102] The D50 of the silver-coated copper micropowder in each embodiment is 3.48-3.52 μm, with a range of 0.74-0.76. The data proves that the technology provided by this invention can effectively suppress copper powder agglomeration and achieve uniform powder dispersion. The corresponding shading rate is 6.4%-6.55%, which is significantly lower than that of the comparative example. The reason is that the powder particles in Examples 1-4 are uniform in size and have no hard agglomerates. The light transmittance is better in the stacked state, which can meet the low shading requirements of photovoltaic cells for conductive paste.

[0103] The chemical precipitation method was used. 5g of sample was dissolved in dilute nitric acid, and excess NaCl solution was added to generate AgCl precipitate. After filtration, drying, and weighing, the silver content was calculated (unit: %). The coverage rate of silver on the copper powder surface was statistically analyzed using a scanning electron microscope by randomly selecting fields of view (unit: %). The silver source utilization rate was calculated (unit: %) based on the ratio of the total mass of silver nitrate in the silver ammonia solution to the actual mass of silver in the finished product. The direct material cost per ton was calculated based on the raw material usage for each example (unit: RMB 10,000). The results are shown in Table 2.

[0104] Table 2

[0105]

[0106] The silver content in each embodiment is 11.8%-12.2%, the silver layer coverage is 97.6%-98.2%, the silver source utilization rate is 98%-98.8%, and the cost is only 94,000-97,000 yuan. By combining reducing agents to balance the reduction rate, discontinuous silver layer or free silver formation is avoided. Pre-formed bonding layers directionally anchor silver ions, and complexing agents complex free Cu. 2+ This blocks the competition between silver ions and their reduction sites, enabling directional and dense deposition of silver ions. In Comparative Example 1, the lack of pre-bonded structures leads to disordered adsorption of silver ions, reducing the utilization rate to 86% and increasing costs. In Comparative Example 2, a single reducing agent and non-gradient ammoniation result in a vacant silver layer, with a utilization rate of only 83%. Comparative Example 4 achieves high coverage with a high amount of silver, but the cost doubles, and the silver source utilization rate is still lower than that of the examples.

[0107] 3.000g of sample was weighed and baked in an air-atmosphere oven at 300℃ for 5 hours. The mass change of the sample was measured by thermogravimetric analysis, and the high-temperature oxidation weight gain rate (unit: %) was calculated. Referring to the photovoltaic module damp heat aging standard GB / T6495.4, the sample was aged in a constant humidity chamber at 85℃ and 85% relative humidity for 1000 hours. After removal, the oxidation weight gain rate (unit: %) was measured. 2.000g of sample was weighed and added to 50mL of 25% (w / w) H2SO4 aqueous solution. The solution was allowed to stand at room temperature for 2 hours, and the solution was observed to turn blue. The copper ion concentration in the solution was measured (unit: mg / L). The results are shown in Table 3.

[0108] Table 3

[0109]

[0110] In each embodiment, the weight gain due to oxidation at 300℃ was 1.9%-2.1%, the weight gain due to humid heat oxidation was 3.0%-3.1%, and the copper ion dissolution was 0.4-0.6 mg / L. The continuous and dense silver layer forms a physical barrier, the composite antioxidant constructs a protective film through chemical adsorption, and low-temperature plasma activation enhances the bonding force between the protective layer and the silver layer. In Comparative Examples 1 and 2, due to the vacancies and defects in the silver layer, oxygen and acid can easily penetrate into the copper core, resulting in a significant increase in oxidation weight gain and dissolution.

[0111] The silver-coated copper micropowders prepared in Examples 1-4 and Comparative Examples 1-4 were formulated into conductive pastes using the same formula. Grid posts were fabricated using 500-mesh screen printing. The line resistance (in Ω) at both ends of the grid posts was measured using a four-probe tester. Based on the four-probe test data and the cross-sectional area of ​​the grid posts, the line resistivity (in ×10⁻¹⁰) was calculated. -6 The conductive paste was coated onto a polyimide substrate and dried to form a 10 μm thick film. The volume resistivity of the film was measured using a four-probe tester (unit: ×10 Ω·cm). -6 Ω・cm). The results are shown in Table 4:

[0112] Table 4

[0113]

[0114] The printed grid post line resistance in each embodiment is 1.28-1.32Ω, and the line resistivity is 3.35-3.45×10⁻⁶. -6 Ω・cm, the volume resistivity of the slurry is 4.1-4.4×10⁻⁶ Ω・cm. -6 The uniform and dense silver layer, measured in Ω·cm, creates a seamless conductive path. The low agglomeration of the powder ensures the continuity of the conductive network during printing. In contrast, in Comparative Examples 1 and 2, the discontinuous silver layer and particle agglomeration result in breaks in the conductive path, leading to a significant increase in resistance.

[0115] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A process for the preparation of conductive silver-coated copper micropowder for photovoltaics, characterized in that, The method comprises the following steps: S1: After the base copper powder is pickled without water washing, ammonia water is added dropwise to adjust the pH of the system, and a monolayer is formed by organic pre-bonding treatment, wherein the organic pre-bonding treatment is carried out by using a pre-bonding liquid prepared by dissolving 12-hydroxystearic acid in anhydrous ethanol; then the system is transferred into a composite ammoniation system for gradient pH adjustment, wherein the composite ammoniation system is composed of 15%-18% ammonia water, 4%-6% ammonium sulfate, tannic acid and organic amine, and the gradient pH adjustment comprises the following steps: in the first stage, 5%-8% dilute ammonia water is added dropwise to increase the pH of the system to 8-9; in the second stage, 18%-20% concentrated ammonia water is added dropwise to adjust the pH of the system to 10-11; after ultrasonic treatment, the system is left to stand to remove waste liquid, and a pretreated liquid is obtained; S2: The pretreated liquid is added into a composite base liquid containing a complexing agent, an organic amine, a dispersant and a reducing agent, and then ultrasonic dispersion and nitrogen protection are carried out; after the plating silver reaction is completed by adding a silver-ammonia solution containing an organic amine dropwise, silane coupling agent KH-550 is added as a directional guiding agent and the pH of the system is adjusted, the system is left to stand to remove waste liquid, and a crude silver-coated copper powder is obtained; the reducing agent is a composite system of glucose and ascorbic acid, and the mass ratio is 1:1-1:2; the mass ratio of the total mass of the reducing agent to the mass of the base copper powder is 1:5-1:10; S3: The crude silver-coated copper powder is filtered and washed with water until neutral, and then the residual impurities are removed by ethanol reflux desorption; then the silver-coated copper powder is subjected to antioxidation protection, vacuum drying, low-temperature plasma activation and screening, and a finished product is obtained.

2. The method of claim 1, wherein the method is characterized by: The ammonia water in S1 is 5% dilute ammonia water, and the pH of the system is adjusted to 2-3.

3. The method of claim 1, wherein the method is characterized by: The mass of the 12-hydroxystearic acid in S1 is 0.5%-0.6% of the mass of the base copper powder.

4. The method of claim 1, wherein the method is characterized by: The mass of the tannic acid in S1 is 0.05%-0.1% of the mass of the base copper powder.

5. The method of claim 1, wherein the method is characterized by: The complexing agent in S2 is one or a combination of several of ethylenediaminetetraacetic acid disodium, sodium nitrilotriacetate, HEDP disodium, trisodium citrate, glycine, cysteine and glutamic acid, and the total mass of the complexing agent is 5%-10% of the mass of the base copper powder.

6. The method of claim 1, wherein the method is characterized by: The silver-ammonia solution in S2 is composed of silver nitrate, an organic amine and 25% ammonia water, and the mass ratio of silver nitrate to the base copper powder is 1:6-1:

10.

7. The method of claim 1, wherein the method is characterized by: The types of the organic amine in the composite ammoniation system in S1, the organic amine in the composite base liquid in S2 and the organic amine in the silver-ammonia solution in S2 are consistent, and are one or a combination of several of ethylenediamine, dimethylaminopropylamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine.

8. A conductive silver-coated copper micropowder for photovoltaics, characterized in that, The silver-coated copper powder is prepared by the method in any one of claims 1-7.

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