Method for preparing silver-coated copper powder by using waste liquid recovered from retired photovoltaic cell pieces

Abstract

The present application relates to the technical field of decommissioned photovoltaic resource utilization and photovoltaic metallized powder preparation, and discloses a method for preparing silver-coated copper powder by using decommissioned photovoltaic cell recycling waste liquid, which comprises the following steps: preparation of precursor solution, photovoltaic silver leaching, pH regulation and impurity removal, and preparation of silver-coated copper powder.The present application uses decommissioned photovoltaic cell recycling waste liquid as a silver source, leaches silver through a dilute sulfuric acid-hydrogen peroxide system, and realizes impurity adjustment and silver-coated copper powder morphology control by using pH regulation, so that silver-coated copper powder with granular protrusions on the surface can be prepared, and the resource utilization of silver and lead in the waste liquid can be realized.The present application has a short process and low cost, and the preparation process is shortened by about 50% compared with the traditional preparation process, and can be used in the field of photovoltaic slurry and the like.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of decommissioned photovoltaic cells and preparation of photovoltaic metallized powder, specifically to a method for preparing silver-coated copper powder from recycled waste liquid of decommissioned photovoltaic cells. Background Technology

[0002] Silver-coated copper powder is a composite metal powder that combines the high conductivity of silver with the low cost of copper. It is used in photovoltaic pastes, electronic packaging, electromagnetic shielding, and other fields. With the rapid development of the photovoltaic industry, a large number of photovoltaic modules are entering their retirement period. The leachate from these solar cells contains valuable elements such as aluminum, iron, silver, and lead, and has high recycling value.

[0003] Currently, the mainstream preparation method for silver-coated copper powder is the displacement-reduction method. The displacement reaction refers to the reduction of silver ions in silver nitrate by copper, while the reduction reaction refers to the reduction of silver ions in silver nitrate by an external reducing agent. High-purity silver nitrate is typically used as the silver source, and silver-coated copper powder is obtained through a displacement-reduction reaction. This method has the following problems: high cost of the silver source, lengthy preparation process, and direct discharge of silver-containing waste liquid can easily lead to the loss of precious metals and environmental pollution.

[0004] Chinese patent application CN121295155A discloses a conductive silver-coated copper micropowder for photovoltaic applications and its preparation method. This method aims to address the challenge of balancing performance and cost in existing silver-coated copper micropowders for photovoltaic applications. The method includes: a pretreatment stage where the copper powder matrix is ​​acid-washed but not water-washed, followed by pH adjustment, organic pre-bonding treatment, and gradient ammoniation to retain copper powder activity and construct a uniform copper-ammonia complex layer; a chemical silver plating stage where the pretreatment solution is added to a composite base liquid containing a complexing agent, organic amine, dispersant, and combined reducing agent, and a silver-ammonia solution is added dropwise under ultrasonic dispersion and nitrogen protection; and a post-treatment stage where 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 achieves 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. The above method is complex and takes more than 10 hours. Summary of the Invention

[0005] This invention aims to solve the problems of high silver source cost, lengthy process and uncontrollable product morphology in existing silver-coated copper powder preparation methods. It provides a method for preparing silver-coated copper powder using recycled waste liquid from decommissioned photovoltaic cells, which has a short process and controllable morphology, using photovoltaic decommissioned waste as the silver source.

[0006] To solve the above-mentioned technical problems, the technical solution is as follows:

[0007] A method for preparing silver-coated copper powder using waste liquid from decommissioned photovoltaic cells includes: S10. Preparation of precursor solution: Copper powder is placed in dilute sulfuric acid and stirred. After washing with deionized water, complexing agent, dispersant and reducing agent are added in sequence and stirred until a uniformly dispersed precursor solution is formed. S20. Photovoltaic silver leaching: Take the waste material of retired photovoltaic cells containing silver, add dilute sulfuric acid for acidification treatment, then add hydrogen peroxide solution dropwise, stir and react to dissolve the silver in the waste material to obtain the waste liquid of retired photovoltaic cells containing silver ions, wherein the pH of the waste liquid of retired photovoltaic cells containing silver ions is less than 0.5. S30, pH adjustment and impurity removal: The waste liquid containing silver ions from the decommissioned photovoltaic cells obtained in step S20 is filtered to remove insoluble residues, and a filtrate containing silver ions and impurity ions is obtained; the impurity ions include aluminum, iron and lead; impurities are removed by filtration, the pH value of the filtrate is adjusted to 1-2, and it is filtered again to obtain a filtrate containing silver ions and lead ions. S40, Preparation of silver-coated copper powder: The filtrate containing silver and lead ions obtained in step S30 is added dropwise to the precursor solution prepared in step S10. The silver-coated copper powder is prepared by stirring at room temperature. Silver and lead ions are deposited on the surface of copper powder. After the reaction is completed, the powder is filtered, washed and dried to obtain silver-coated copper powder.

[0008] In one embodiment, the mass fraction of the dilute sulfuric acid in step S10 is 5-30%, the liquid-solid ratio of the dilute sulfuric acid to the copper powder is 5:1-20:1 mL / g, and the stirring rate is 100-500 r / min.

[0009] In one embodiment, the complexing agent is selected from at least one of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, trisodium citrate, and potassium sodium tartrate, and the mass concentration of the complexing agent in the precursor solution is 5-15 g / L.

[0010] In one embodiment, the dispersant is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, and polyacryl alcohol, and the mass concentration of the dispersant in the precursor solution is 2-10 g / L.

[0011] In one embodiment, the reducing agent is selected from at least one of anhydrous glucose, ascorbic acid, sodium hypophosphite, and formaldehyde, and the mass concentration of the reducing agent in the precursor solution is 60-120 g / L.

[0012] In one embodiment, the mass fraction of the dilute sulfuric acid is 5-30%, and the liquid-solid ratio of the dilute sulfuric acid solution to the recycled waste from decommissioned photovoltaic cells is 5:1-15:1 mL / g.

[0013] In one embodiment, the hydrogen peroxide solution has a mass fraction of 3-15%, and the amount added is 5-20% of the volume of the dilute sulfuric acid solution.

[0014] In one embodiment, the stirring reaction time in step S20 is 60-120 min, the reaction temperature is 40-95℃, and the stirring rate is 100-500 r / min.

[0015] In one embodiment, the stirring rate for preparing the silver-coated copper powder in step S40 is 150-400 r / min, the reaction time is 60-180 min, and the drying temperature is 40-100℃.

[0016] Compared with existing technologies, the beneficial effects of this application are as follows: The method for preparing silver-coated copper powder from recycled waste liquid of retired photovoltaic cells in this invention abandons the conventional practice of using high-purity silver nitrate as the silver source, instead directly using recycled waste from retired photovoltaic cells as the silver source. This achieves the recovery and utilization of precious metal silver from photovoltaic waste, while simultaneously solving the problem of precious metal loss and environmental pollution caused by the direct discharge of silver-containing photovoltaic waste liquid. Utilizing a three-step core process of "acid leaching - pH control - reduction deposition," the multiple coating and ripening steps in traditional processes are eliminated, reducing the preparation time from 7 hours in traditional methods to 3.5-3.7 hours, thus lowering energy consumption and labor costs. By controlling the pH value, the morphology and impurity ion state of the silver-coated copper powder can be controlled, resulting in silver-coated copper powder with granular protrusions on the surface and good coating properties, with performance comparable to silver-coated copper powder prepared by traditional methods. The entire preparation process uses dilute sulfuric acid-hydrogen peroxide as the leaching system, generating no complex pollutants. Furthermore, the process is simple to operate, requires low-level equipment, and does not require specialized precision equipment, making it easy to achieve industrial-scale production. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A process flow diagram for preparing silver-coated copper powder from waste liquid recovered from retired photovoltaic cells.

[0019] Figure 2 The image is a scanning electron microscope image (magnification of ×5000) of the silver-coated copper powder prepared in Example 1 of this invention.

[0020] Figure 3 The image shows the energy dispersive spectroscopy (EDS) results of the silver-coated copper powder prepared in Example 1.

[0021] Figure 4 The image is a scanning electron microscope image (magnification of ×5000) of the silver-coated copper powder prepared in Example 2 of this invention.

[0022] Figure 5 The image shown is a scanning electron microscope image (magnification of ×5000) of the silver-coated copper powder prepared in Example 3 of this invention.

[0023] Figure 6 Scanning electron microscope image of silver-coated copper powder prepared for Comparative Example 1 (magnification of ×5000). Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] Please see Figures 1-6 One embodiment of the method for preparing silver-coated copper powder using waste liquid from decommissioned photovoltaic cells is shown in the process flow diagram below. Figure 1 As shown, it includes the following steps: S10. Preparation of precursor solution: Copper powder is placed in a dilute sulfuric acid system and stirred to remove its surface oxide layer; after washing with deionized water, complexing agent, dispersant and reducing agent are added in sequence, and stirred to form a uniformly dispersed precursor solution for later use.

[0028] S20. Photovoltaic silver leaching: Take the waste material of retired photovoltaic cells containing silver, add dilute sulfuric acid solution for acidification treatment, then add hydrogen peroxide solution dropwise, stir and react to fully dissolve the silver in the waste material to obtain the waste liquid of retired photovoltaic cells containing silver ions, wherein the pH of the waste liquid of retired photovoltaic cells containing silver ions is less than 0.5.

[0029] In traditional methods, the preferred approach for preparing silver-coated copper powder is generally considered to be using a high-purity silver source (such as silver nitrate) to ensure product purity and controllable reaction. This invention takes the opposite approach, directly using the complex system of decommissioned photovoltaic waste liquid, which contains impurities, as the silver source.

[0030] S30, pH adjustment and impurity removal: The waste liquid containing silver ions from the decommissioned photovoltaic cells obtained in step S20 is filtered to remove insoluble residues, and a filtrate containing silver ions and impurity ions is obtained; the impurity ions include aluminum, iron and lead; impurities are removed by filtration, the pH value of the filtrate is adjusted to 1-2, and it is filtered again to obtain a filtrate containing silver ions and lead ions.

[0031] When the pH is in the range of 1-2, silver-coated copper powder with granular protrusions on the surface can be obtained. Specifically, under these acidic conditions, it is beneficial to remove the oxide layer on the surface of the copper powder, which is conducive to silver deposition. Furthermore, under these conditions, Pb²... + It cannot undergo hydrolysis and precipitation, and will follow Ag + The lead phase, reduced by copper powder, is deposited on the surface of the silver-coated copper powder in the subsequent reaction. This lead phase can form a liquid wetting layer during the curing stage of the silver-coated copper powder, thereby effectively reducing the curing temperature of the product. Simultaneously, the strongly acidic environment accelerates the curing of Ag... + The reduction deposition rate of silver atoms on the copper powder surface is high, and silver atoms undergo heterogeneous rapid nucleation and growth. + The presence of silver atoms facilitates uniform coating of copper powder, improving the oxidation resistance of silver-coated copper powder and thus enhancing the conductivity of subsequent silver-coated copper paste. The resulting silver-coated copper powder surface forms characteristic granular protrusions, while the silver layer maintains good coating. Generally, impurity elements are harmful substances that need to be removed, and pH adjustment is typically used for impurity removal. This invention revolutionarily transforms lead impurities into functional components, achieving targeted control of product morphology and ultimately improving coating and conductivity performance. Furthermore, by utilizing the lead ions present in the silver-coated copper powder, the curing temperature can be lowered.

[0032] S40. Preparation of silver-coated copper powder: The filtrate containing silver and lead ions obtained in step S30 is added dropwise to the precursor solution and stirred at room temperature to prepare silver-coated copper powder. Silver and lead ions are deposited on the surface of copper powder. After the reaction is completed, the powder is filtered, washed and dried to obtain silver-coated copper powder.

[0033] In the above preparation method, preferably, the mass fraction of the dilute sulfuric acid in step S10 is 5-30%, the liquid-solid ratio of the dilute sulfuric acid to the copper powder is 5:1-20:1 (mL / g), and the stirring rate is 100-500 r / min. Too low a concentration of dilute sulfuric acid will result in incomplete removal of the oxide layer on the surface of the copper powder, reducing the coating effect; too high a concentration will increase reagent consumption costs.

[0034] In the above preparation method, preferably, the complexing agent in step S10 is selected from one or more of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, trisodium citrate, and potassium sodium tartrate, and the concentration of the complexing agent in the precursor solution is 5-15 g / L; the complexing agent is used to complex the impurity ions remaining on the surface of copper powder to avoid them interfering with the subsequent silver ion deposition, and at the same time improve the dispersion stability of copper powder in solution.

[0035] In the above preparation method, preferably, the dispersant in step S10 includes one or more of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, and polyacryl alcohol, and the dispersant concentration is 2-5 g / L. Too low a dispersant concentration will cause powder agglomeration, reducing coating efficiency and powder uniformity; too high a concentration will increase solution viscosity, resulting in poor flowability and increased cost.

[0036] In the above preparation method, preferably, the reducing agent in step S10 is selected from one or more of anhydrous glucose, ascorbic acid, sodium hypophosphite, and formaldehyde. The amount of reducing agent added is determined by the volume of the leaching solution and is added at 60-120 g / L. The reducing agent is used to activate the surface of copper powder, increase the reduction rate of silver ions, and at the same time reduce low-valence interfering ions that may be introduced later, thus ensuring the purity of the product.

[0037] In the above preparation method, preferably, the mass fraction of sulfuric acid in step S20 is 5-30%, and the liquid-solid ratio of dilute sulfuric acid to recycled waste is 5:1-15:1 mL / g. Too low a concentration of dilute sulfuric acid will result in a slow silver leaching rate in photovoltaic cells, reducing production efficiency; too high a concentration will result in the leaching of a large amount of metal impurities such as aluminum, iron, and lead.

[0038] In the above preparation method, preferably, the mass fraction of hydrogen peroxide in step S20 is 3-15%, and the amount of hydrogen peroxide added is 5-20% of the volume of dilute sulfuric acid. In the selective oxidation leaching system of silver composed of dilute sulfuric acid and hydrogen peroxide, hydrogen peroxide, as an oxidant, can directionally oxidize elemental silver in waste to form silver ions, and synergistically with dilute sulfuric acid to achieve efficient and selective leaching of silver, effectively avoiding excessive leaching of metal impurities such as aluminum, iron, and lead; if too little hydrogen peroxide is added, the oxidation leaching efficiency of silver will be low; if too much is added, it will cause reagent waste and easily trigger side reactions leading to the leaching of a large amount of aluminum and iron ions, increasing the difficulty of subsequent impurity removal.

[0039] In the above preparation method, preferably, the stirring time after acid washing and adding hydrogen peroxide in step S20 is 60-120 min, the water bath temperature is 40-95℃, and the stirring rate is 100-500 r / min to ensure that silver ions are fully leached out.

[0040] In the above preparation method, preferably, the stirring rate in step S40 for preparing the silver-coated copper powder is 150-400 r / min, and the reaction time is 60-180 min. Too low a stirring rate will lead to uneven mixing of the reaction system and uneven silver deposition; too high a rate may increase energy consumption. Too short a reaction time will result in incomplete displacement reaction; too long a reaction time may increase the production cycle and reduce efficiency.

[0041] In the above preparation method, preferably, the drying temperature in step S40 is 40-100℃ to ensure that the product is a fine powder.

[0042] Example 1 This embodiment describes a method for preparing silver-coated copper powder using waste liquid recovered from retired photovoltaic cells, comprising the following steps: S10. Preparation of precursor solution: Take 1g of copper powder, add 20mL of 20% (w / w) dilute sulfuric acid, and stir at 200 r / min for 5 min at room temperature for acid washing. After acid washing, wash with deionized water, and add 50 mL of deionized water, 0.7 g of disodium ethylenediaminetetraacetate (concentration 14 g / L), 0.1 g of polyvinylpyrrolidone (concentration 2 g / L), and 5.4 g of glucose (concentration 108 g / L), and stir to dissolve to obtain the precursor solution.

[0043] S20. Photovoltaic silver leaching: Take 50 g of recycled waste from retired photovoltaic cells containing silver (mainly silicon, silver, copper and aluminum components), add 250 mL of 2 mol / L dilute sulfuric acid (liquid-solid ratio 5:1 mL / g) for acid washing, then slowly add 50 mL of 7.8% hydrogen peroxide (20% of the volume of the dilute sulfuric acid solution), and stir at 85℃ for 60 min to fully dissolve the silver in the waste into the solution. At this time, the pH value of the solution is 0.32.

[0044] S30, pH adjustment and impurity removal: The mixed solution obtained in step S20 is filtered using qualitative filter paper to remove insoluble impurities and obtain the original filtrate; pH is adjusted using 1 mol / L sodium hydroxide solution to obtain a solution with a pH value of 1 and then filtered.

[0045] S40. Preparation of silver-coated copper powder: The filtrate obtained in step S30 is added dropwise to the precursor solution at a constant rate of 350 r / min. The silver-coated copper powder is prepared by stirring at room temperature and stirring at a rate of 300 r / min for 60 min at room temperature. After the reaction is completed, the filter residue is washed three times with deionized water and once with anhydrous ethanol. After filtration, it is dried at 60℃ to obtain silver-coated copper powder.

[0046] Results Analysis: The total preparation time in this embodiment was only 3.5 hours, which is 50% shorter than the traditional multi-step method (7 hours in Comparative Example 1). Scanning electron microscopy (SEM) Figure 2 Tests show that the silver-coated copper powder prepared using the method of Example 1 of this invention has a silver layer coating, good dispersibility, and granular protrusions on the surface; energy dispersive spectroscopy results ( Figure 3The results showed that Ag elements were distributed around the copper powder particles, confirming the silver coating, and a small amount of lead was present on the powder surface. In this embodiment, the pH of the filtrate was precisely controlled to a strongly acidic environment, under which Pb² + It cannot undergo hydrolysis and precipitation, and will follow Ag + The lead phase is reduced by copper powder and deposited on the surface of the silver-coated copper powder. This lead phase allows the silver-coated copper powder to form a liquid phase during slurry curing, thus lowering the curing temperature of the silver-coated copper slurry. Simultaneously, the strongly acidic environment inhibits the growth of Ag. + The hydrolysis and precipitation of the silver powder increased its effective concentration in the solution. Silver atoms rapidly and heterogeneously nucleated on the surface of the copper powder, eventually forming characteristic granular protrusions on the surface of the silver-coated copper powder.

[0047] Example 2 This embodiment describes a method for preparing silver-coated copper powder using waste liquid recovered from retired photovoltaic cells, comprising the following steps: S10. Preparation of precursor solution: Take 1g of copper powder, add 20mL of 10% (w / w) dilute sulfuric acid, and stir at 200 r / min for 10 min at room temperature for acid washing. After acid washing, wash with deionized water, and add 50 mL of deionized water, 0.75 g (concentration 15g / L) dipotassium ethylenediaminetetraacetate, 0.5 g of polyvinylpyrrolidone (concentration 10g / L) and 3.0 g of anhydrous glucose (concentration 60g / L), and stir to dissolve to obtain the precursor solution.

[0048] S20. Photovoltaic silver leaching: Take 50 g of recycled waste photovoltaic cells containing silver, add 250 mL of 1 mol / L dilute sulfuric acid (liquid-solid ratio 5:1 mL / g) for acid washing, then slowly add 50 mL of 7.8% hydrogen peroxide (20% of the volume of the dilute sulfuric acid solution), and stir at 90℃ for 60 min to fully dissolve the silver in the waste into the solution. At this time, the pH value of the solution is 0.46.

[0049] S30, pH adjustment and impurity removal: The mixed solution obtained in step S20 is filtered using qualitative filter paper to remove insoluble impurities and obtain the original filtrate; pH is adjusted using 1 mol / L sodium hydroxide solution to obtain a solution with a pH value of 1.5 and then filtered.

[0050] S40. Preparation of silver-coated copper powder: The filtrate obtained in step S30 is added dropwise to the precursor solution at a constant rate of 350 r / min. The silver-coated copper powder is prepared by stirring at room temperature and stirring at a rate of 300 r / min for 60 min at room temperature. After the reaction is completed, the filter residue is washed three times with deionized water and once with anhydrous ethanol. After filtration, it is dried at 80℃ to obtain the silver-coated copper powder product.

[0051] Results Analysis: The total preparation time in this embodiment was only 3.7 hours, which is nearly 50% shorter than the traditional multi-step method (7 hours in Comparative Example 1). Scanning electron microscopy (SEM) Figure 4 Tests showed that the silver-coated copper powder prepared using the method of Example 2 of this invention had a silver coating, moderate dispersibility, and granular protrusions on the surface; energy dispersive spectroscopy results showed that Ag elements were distributed around the copper powder particles, confirming the silver coating, and a small amount of lead was present on the powder surface. In this example, the pH of the filtrate was precisely controlled to a strongly acidic environment of 1.5, under which Pb² + It cannot undergo hydrolysis and precipitation, and will follow Ag + The lead phase is reduced by copper powder and deposited on the surface of the silver-coated copper powder. This lead phase allows the silver-coated copper powder to form a liquid phase wetting layer during the curing stage, thereby effectively reducing the curing temperature of the product. At the same time, the strongly acidic environment inhibits the growth of Ag. + The hydrolysis and precipitation of the silver powder increased its effective concentration in the solution. Silver atoms rapidly and heterogeneously nucleated on the surface of the copper powder, eventually forming characteristic granular protrusions on the surface of the silver-coated copper powder.

[0052] Example 3 S10. Preparation of precursor solution: Take 1g of copper powder, add 20mL of 20% (w / w) dilute sulfuric acid, and stir at 200 r / min for 10 min at room temperature for acid washing. After acid washing, wash with deionized water, and add 50 mL of deionized water, 0.25g of disodium ethylenediaminetetraacetate (5g / L), 0.25g of polyvinylpyrrolidone (5g / L), and 6g of anhydrous glucose (120g / L). Stir to dissolve and obtain the precursor solution.

[0053] S20. Photovoltaic silver leaching: Take 50 g of recycled waste photovoltaic cells containing silver, add 250 mL of 2 mol / L dilute sulfuric acid (liquid-solid ratio 5:1 mL / g) for acid washing, then slowly add 50 mL of 7.8% hydrogen peroxide (20% of the volume of the dilute sulfuric acid solution), and stir at 90℃ for 60 min to fully dissolve the silver in the waste into the solution. At this time, the pH value of the solution is 0.24.

[0054] S30, pH adjustment and impurity removal: The mixed solution obtained in step S20 is filtered using qualitative filter paper to remove insoluble impurities and obtain the original filtrate; pH is adjusted using 1 mol / L sodium hydroxide solution to obtain a solution with a pH value of 2 and then filtered.

[0055] S40. Preparation of silver-coated copper powder: The filtrate obtained in step S30 is added dropwise to the precursor solution at a constant rate of 350 r / min. The silver-coated copper powder is prepared by stirring at room temperature and stirring at a rate of 300 r / min for 60 min at room temperature. After the reaction is completed, the filter residue is washed three times with deionized water and once with anhydrous ethanol. After filtration, it is dried at 80℃ to obtain the silver-coated copper powder product.

[0056] Results Analysis: The total preparation time in this embodiment was only 3.6 hours, which is nearly 50% shorter than the traditional multi-step method (7 hours in Comparative Example 1 below). Scanning electron microscopy (SEM) Figure 5 Test results show that the silver-coated copper powder prepared by the method of Example 1 of this invention has a silver coating, good dispersibility, and granular protrusions on the surface; energy dispersive spectroscopy results show that Ag elements are distributed around the copper powder particles, confirming the silver coating, and a small amount of lead is present on the powder surface. In this example, the pH of the filtrate was precisely controlled to a strongly acidic environment of 2, under which Pb² + It cannot undergo hydrolysis and precipitation, and will follow Ag + The lead phase is reduced by copper powder and deposited on the surface of the silver-coated copper powder. This lead phase allows the silver-coated copper powder to form a liquid phase during the curing stage, thereby effectively reducing the curing temperature of the product. At the same time, the strongly acidic environment inhibits the growth of Ag. + The hydrolysis and precipitation of the silver powder increased its effective concentration in the solution. Silver atoms rapidly and heterogeneously nucleated on the surface of the copper powder, eventually forming characteristic granular protrusions on the surface of the silver-coated copper powder.

[0057] Comparative Example 1: S10. Copper powder pickling pretreatment: Prepare a 20% concentration of dilute sulfuric acid, add 10g of commercial copper powder to the dilute sulfuric acid, stir at room temperature to pickle, and remove the oxide layer on the surface of the copper powder.

[0058] S20. Copper powder washing: After pickling, use deionized water to wash the copper powder to remove residual acid and impurities.

[0059] S30. Preparation of primary precursor solution: Weigh 1.39g of EDTA-2Na and place it together with the acid-washed copper powder in 125mL of deionized water. Stir and mix well to form a primary precursor solution for later use.

[0060] S40. Preparation of silver nitrate solution: Weigh 1.39g of silver nitrate, dissolve it in 20mL of deionized water, and then titrate to 25mL to obtain silver nitrate solution.

[0061] S50, First silver deposition reaction: Silver nitrate solution is slowly added dropwise into the reaction vessel containing the first precursor solution using a constant flow meter, while a stirrer is used to promote the reaction.

[0062] S60. First reaction ripening: After the silver nitrate solution is added, keep stirring and react for half an hour to allow the silver ions to be fully reduced and deposited on the surface of the copper powder.

[0063] S70. Post-processing of primary products: After the reaction is completed, allow the reaction system to stand and separate into layers, discard the supernatant, and then wash the product to remove unreacted ions and impurities.

[0064] S80. Preparation of secondary precursor solution: Weigh 1.39g of silver nitrate again to prepare the solution. At the same time, weigh the same mass of disodium ethylenediaminetetraacetate, 0.9g of glucose and 0.125g of PVP. Add these reagents together with the copper powder washed from the first reaction to 125mL of deionized water and stir to form a secondary precursor solution.

[0065] S90. Second silver deposition reaction: Using a constant current apparatus, the freshly prepared silver nitrate solution is added dropwise to the secondary precursor solution, and the second silver-coated copper reaction is carried out under stirring conditions.

[0066] S100, Post-processing of secondary products: After the reaction is completed, allow the product to stand and separate into layers, wash the product, and then perform vacuum filtration to remove moisture.

[0067] S110. Drying and Sample Preservation: The filtered product is dried to obtain silver-coated copper powder. Finally, the sample is preserved for subsequent testing.

[0068] The silver-coated copper powders prepared in Examples 1-3 and Comparative Example 1 were weighed and thoroughly mixed with ethylene glycol to prepare a slurry with a silver-coated copper powder content of 10% (mass fraction). Lines were then printed onto a glass plate using screen printing and cured by heating in air. The slurry was observed and the curing temperature was recorded. After curing, the volume resistivity was measured using a multimeter.

[0069] Results analysis: Performance testing was conducted on the silver-coated copper powder prepared in Comparative Example 1. Comparative Example 1 employed a traditional multi-step method to prepare the silver-coated copper powder, a process that took approximately 7 hours, double the time compared to Example 1 of this application. Furthermore, the silver-coated copper powder obtained in Comparative Example 1 was lead-free, and its curing temperature was 200°C. The electron microscopy scan of Comparative Example 1 is shown below. Figure 6 As shown, the surface of its silver-coated copper powder particles is smooth and relatively flat. The process parameters and energy efficiency comparisons of the embodiments and comparative examples are shown in Table 1.

[0070] Table 1: Comparison of Process Parameters and Energy Efficiency between Examples and Comparative Examples

[0071] In summary, the resistivity of the silver-coated copper powder obtained by adopting the technical solution of this invention is the same as or even lower than that of the prior art. The curing temperature of the silver-coated copper powder in the subsequent formation of silver-coated copper paste is lower than that of the comparative example. The technical solution of this invention can greatly shorten the product preparation time from about 7 hours to about 3.5 hours. Moreover, the raw material source is inexpensive and realizes the resource utilization of retired photovoltaic materials.

[0072] The above are merely preferred embodiments of the present invention. It should be noted that the present invention is not limited to the above embodiments. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing silver-coated copper powder using waste liquid from retired photovoltaic cells, characterized in that, include: S10. Preparation of precursor solution: Copper powder is placed in dilute sulfuric acid and stirred. After washing with deionized water, complexing agent, dispersant and reducing agent are added in sequence and stirred until a uniformly dispersed precursor solution is formed. S20. Photovoltaic silver leaching: Take the waste material of retired photovoltaic cells containing silver, add dilute sulfuric acid for acidification treatment, then add hydrogen peroxide solution dropwise, stir and react to dissolve the silver in the waste material to obtain the waste liquid of retired photovoltaic cells containing silver ions, wherein the pH of the waste liquid of retired photovoltaic cells containing silver ions is less than 0.

5. S30, pH adjustment and impurity removal: The waste liquid containing silver ions from the decommissioned photovoltaic cells obtained in step S20 is filtered to remove insoluble residues, and a filtrate containing silver ions and impurity ions is obtained; the impurity ions include aluminum, iron and lead; impurities are removed by filtration, the pH value of the filtrate is adjusted to 1-2, and it is filtered again to obtain a filtrate containing silver ions and lead ions. S40, Preparation of silver-coated copper powder: The filtrate containing silver and lead ions obtained in step S30 is added dropwise to the precursor solution prepared in step S10, and silver-coated copper powder is prepared by stirring at room temperature. Silver and lead ions are deposited on the surface of copper powder. After the reaction is completed, the powder is filtered, washed and dried to obtain silver-coated copper powder. In S30, a pH value within the range of 1-2 removes the oxide layer on the surface of copper powder, which is beneficial for silver deposition, and under these conditions, Pb² + It cannot undergo hydrolysis and precipitation, and will follow Ag + The lead phase, along with the reduced copper powder, is deposited on the surface of the silver-coated copper powder in the subsequent reaction as a metallic lead phase. This lead phase forms a liquid wetting layer during the curing stage of the silver-coated copper powder, thereby lowering the product's curing temperature. Simultaneously, the strongly acidic environment accelerates the curing of Ag... + The reduction deposition rate of silver atoms on the copper powder surface is high, and silver atoms undergo heterogeneous rapid nucleation and growth. + The presence of silver atoms facilitates uniform coating of copper powder, improves the oxidation resistance of silver-coated copper powder, and thus improves the conductivity of subsequent silver-coated copper paste, resulting in silver-coated copper powder with granular protrusions on the surface.

2. The method according to claim 1, characterized in that, In step S10, the mass fraction of the dilute sulfuric acid is 5-30%, the liquid-solid ratio of the dilute sulfuric acid to the copper powder is 5:1-20:1 mL / g, and the stirring rate is 100-500 r / min.

3. The method according to claim 1, characterized in that, The complexing agent is selected from at least one of disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, trisodium citrate, and potassium sodium tartrate, and the mass concentration of the complexing agent in the precursor solution is 5-15 g / L.

4. The method according to claim 1, characterized in that, The dispersant is selected from at least one of polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, and polyacryl alcohol, and the mass concentration of the dispersant in the precursor solution is 2-10 g / L.

5. The method according to claim 1, characterized in that, The reducing agent is selected from at least one of anhydrous glucose, ascorbic acid, sodium hypophosphite and formaldehyde, and the mass concentration of the reducing agent in the precursor solution is 60-120 g / L.

6. The method according to claim 1, characterized in that, The mass fraction of the dilute sulfuric acid in step S20 is 5-30%, and the liquid-solid ratio of the dilute sulfuric acid to the recycled waste from decommissioned photovoltaic cells is 5:1-15:1 mL / g.

7. The method according to claim 1, characterized in that, The hydrogen peroxide solution mentioned in step S20 has a mass fraction of 3-15%, and the amount added is 5-20% of the volume of dilute sulfuric acid.

8. The method according to claim 1, characterized in that, In step S20, the stirring time is 60-120 min, the reaction temperature is 40-95℃, and the stirring rate is 100-500 r / min.

9. The method according to claim 1, characterized in that, In step S40, the stirring rate for preparing the silver-coated copper powder is 150-400 r / min, the reaction time is 60-180 min, and the drying temperature is 40-100℃.

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