A compact silver layer coated silver-coated copper powder, a preparation method and application thereof

Abstract

The application discloses a kind of dense silver layer coated silver-coated copper powder and its preparation method and application, belong to surface engineering technical field, copper powder after pretreatment is mixed with dispersant solution, and copper powder dispersion liquid is obtained;After adding first complexing agent tannic acid solution, after stirring uniformly, tannic acid modified copper powder precursor solution is obtained;After adding the mixed solution of second complexing agent histidine solution and silver ammonia solution, then adding reducing agent solution, stirring reaction, after solid-liquid separation, washing and drying, dense silver layer coated silver-coated copper powder is obtained.Silver ion network structure is constructed by tannic acid and histidine cooperation, silver layer is slowly and orderly deposited in low silver concentration, and the silver-coated copper powder prepared has dense and uniform silver coating layer, and has excellent conductivity and oxidation resistance.Silver ion utilization rate is high, preparation process is simple, high-quality coating can be realized without multiple silver plating, production cost is effectively reduced, suitable for large-scale production, and can be applied in electronic paste, conductive coating and other fields.

Description

Technical Field

[0001] This invention belongs to the field of surface engineering technology, specifically relating to a dense silver layer coated silver-plated copper powder, its preparation method, and its application. Background Technology

[0002] Conductive silver paste is a key material in the manufacture of electronic devices such as solar cells, printed circuit boards, and flexible circuits. Its overall performance mainly depends on the conductive filler used. Commonly used conductive fillers include silver powder, copper powder, carbon powder, graphite, and metal nanoparticles. Among them, silver powder is widely used in the preparation of conductive materials due to its excellent conductivity and chemical stability. Silver powder has excellent conductivity and oxidation resistance, but as a precious metal, its high cost limits the large-scale application of conductive silver paste. Copper powder, due to its large reserves and low price, has become an ideal substitute for silver powder. However, its chemical reactivity makes it easily oxidized in air to form copper oxide with high resistivity, leading to a sharp decline in conductivity. To address the problem of copper powder's easy oxidation and resulting decline in material electrical performance, current technologies mainly focus on modifying copper powder through surface silver plating. The advantage of this method is that it can significantly improve the oxidation resistance and conductivity of copper powder, but it has disadvantages such as complex processes and high costs.

[0003] The main technical challenge in preparing silver-plated copper powder lies in how to create a dense, uniform, and strongly bonded silver coating to prevent long-term use from affecting conductivity. The primary method for preparing silver-plated copper powder is chemical plating. Chemical plating is a method that deposits a metal coating on a substrate surface through the redox reaction between a reducing agent and metal ions in solution. Compared to other methods, it has advantages such as simple process, low preparation cost, and good coating effect. Chemical plating is divided into reduction and displacement methods. The basic principle of the displacement method is that silver ions in the solution diffuse to the copper surface and undergo a displacement reaction with copper atoms, replacing a layer of silver atoms on the copper surface, thus completing the silver coating. This method uses copper itself as a reducing agent, but if the large potential difference of the reaction cannot be controlled, the displacement reaction process is extremely fast, and the reduced silver ions grow dendrites, leading to coating failure. The basic principle of the reduction method is to add a reducing agent to the plating solution to reduce silver ions and deposit them on the copper surface to form a silver shell. The advantage of this method is that it can effectively reduce the consumption of copper by the displacement reaction. The disadvantage is that silver ions react with the reducing agent in the solution environment to form free silver particles, making it difficult to accurately control the deposition of silver on the copper surface.

[0004] Given the technical defects of the aforementioned electroless plating process, the selection of complexing agents is crucial for controlling the silver plating effect. By selecting suitable complexing agents, the binding force between the complexing agent and the copper substrate and silver ions can be strengthened, the spontaneous reduction reaction of silver ions can be inhibited, and the deposition behavior of silver ions on the copper surface can be controlled, thereby achieving effective control over the morphology and performance of the plating layer. Chinese patent application CN116550974A discloses a method for preparing silver-coated copper powder with a core-shell structure and low silver content. This method uses tannic acid as a complexing agent and employs a two-step method to prepare the silver-coated copper powder. However, this scheme mainly relies on the reduction mechanism, with tannic acid primarily playing a reducing role. Silver ions are easily and rapidly reduced and nucleated individually, resulting in the appearance of independently growing silver spheres or particles on the copper powder surface. This leads to uneven silver coating, rough surface, and insufficient density, making it difficult to achieve a smooth, uniform, and dense silver coating under low silver content conditions. Ammonia, as a commonly used complexing agent, can improve the uniformity of the silver layer, but it has poor stability and easily generates [Cu(NH3)4], which hinders silver plating. 2+ RE-608 copper-specific extractant needs to be used as a complexing agent to form a chelate compound with copper ions, which is then extracted into the organic phase to prevent the formation of [Cu(NH3)4]. 2+ Therefore, it is difficult to obtain a uniform silver coating by silver plating with ammonia solution alone. EDTA can construct a stable complexing system, which can improve the coating uniformity and the material's oxidation resistance, but it easily causes an increase in solution viscosity and has a high cost. Although tartaric acid can form a stable coordination structure and improve the coating uniformity, the silver plating reaction stability is insufficient, making it difficult to obtain a smooth coating with uniform morphology. Tannic acid, as a complexing agent, produces silver-plated copper powder with good thermal stability and conductivity, but the high silver concentration used results in a noticeable grainy texture on the coating surface, making it difficult to form a smooth and dense coating. Compared with a single complexing agent, the dual complexing agent system formed by sodium tartrate and histidine can significantly improve the coating effect and form a uniform and complete silver coating on the copper powder surface. However, this system still has the problem of low silver loading in a single plating and inability to achieve a dense silver coating, requiring multiple silver plating processes to increase the silver content, making the process relatively complex. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a dense silver layer coated silver-plated copper powder, its preparation method and application, so as to solve the technical problem that traditional complexing agents cannot achieve a dense silver layer coated silver-plated copper powder at low silver concentrations.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing dense silver-coated silver-plated copper powder, comprising: The pretreated copper powder was mixed with a dispersant solution to obtain a copper powder dispersion. The first complexing agent was added to the copper powder dispersion and stirred evenly to obtain a tannic acid modified copper powder precursor solution. Then, a mixture of the second complexing agent and silver ammonia solution was added, followed by the addition of a reducing agent solution. After stirring and reacting, the mixture was separated into solid and liquid phases, washed, and dried to obtain a dense silver-coated silver-plated copper powder. The first chelating agent is a tannic acid solution; the second chelating agent is a histidine solution.

[0007] Preferably, the pretreatment of copper powder includes: ultrasonic cleaning using at least two of the following: a mixed solution of acetone, ammonium sulfate and ammonia, dilute sulfuric acid, sodium hydroxide, ethanol and deionized water; the ultrasonic treatment time is 10-30 min.

[0008] Preferably, the dispersant solution is at least one of polyethylene glycol-400, polyethylene glycol-600, and polyvinylpyrrolidone-K30; the mass ratio of copper powder to dispersant solution is 100:(5~10), and the mixture is mechanically stirred at a speed of 250~350 r / min.

[0009] Preferably, the concentration of the first complexing agent is 10-20 mmol / L; the temperature of stirring the first complexing agent into the copper powder dispersion is 20-50℃, the time is 15-45 min, and the pH value is adjusted to 8-9; the solution used to adjust the pH value is any one of potassium carbonate solution, sodium hydroxide solution and sodium carbonate solution, with a concentration of 5-15 wt%.

[0010] Preferably, the concentration of the second complexing agent is 50~200 mmol / L, and the volume ratio of the second complexing agent to the first complexing agent is (3~1):1.

[0011] Preferably, the reducing agent solution is any one of L-ascorbic acid, glucose, and sodium borohydride; the concentration of the reducing agent solution is 100~300 mmol / L.

[0012] Preferably, the dropping rate of the mixture of the second complexing agent and the silver ammonia solution is 4.5~5.5 mL / min; the dropping rate of the reducing agent solution is 4.5~5.5 mL / min.

[0013] Preferably, 60-90 minutes after the initial addition of the mixture of the second complexing agent and silver ammonia solution, the mixture is separated into solid and liquid by centrifugation, washed at least 3 times with water and ethanol, and then vacuum dried at 40-60°C for 10-15 hours.

[0014] This invention discloses a dense silver layer coated silver-plated copper powder, which is prepared by the above-mentioned method for preparing dense silver layer coated silver-plated copper powder.

[0015] This invention discloses the application of the above-mentioned dense silver layer coated silver-plated copper powder in the preparation of solar cells, printed circuit boards or flexible circuits.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a dense silver-coated copper powder. The method utilizes a dual complexing agent to achieve this dense silver-coated copper powder. The complexing agent, tannic acid, has numerous phenolic hydroxyl groups, which form a tannic acid layer on the copper surface, inhibiting the displacement reaction between copper and silver ions. The remaining vacant phenolic hydroxyl groups coordinate with silver ions, allowing free silver ions that histidine could not coordinate to be utilized. Furthermore, tannic acid has reducing properties under alkaline conditions, which can reduce the silver ions coordinated with it in situ, ensuring precise reduction of silver ions on the copper surface. Histidine, by forming a stable complex with silver ions, reduces the concentration of free silver ions in the solution, controlling the release rate of silver ions and forming a dense, uniform coating. By improving the silver plating process, the dense silver-coated copper powder prepared by this invention can produce a complete, uniform, and dense silver layer even at low silver concentrations. The dense silver-coated copper powder exhibits excellent electrical properties and oxidation resistance. The raw materials of this invention are readily available, the preparation conditions are mild, the preparation method is simple, suitable for large-scale production, and the cost is low.

[0017] Furthermore, acetone, as a highly polar organic solvent, can quickly dissolve and remove grease and organic contaminants from the surface of copper powder. A mixed solution of ammonium sulfate and ammonia can gently dissolve the oxide film on the surface of copper powder and moderately activate the copper substrate surface. Dilute sulfuric acid and sodium hydroxide can remove the oxide film on the surface of copper powder, but the concentration needs to be controlled. Ethanol, with its low surface tension and high volatility, efficiently dissolves and removes organic impurities from the surface of copper powder, and its volatility can reduce the number of drying steps. Deionized water can thoroughly rinse away residual chemical reagents and soluble salts, preventing the introduction of impurities.

[0018] Furthermore, the concentration of the first complexing agent, tannic acid solution, is 10~20 mmol / L, which can ensure coordination with silver ions while preventing excessive tannic acid from being fully utilized and the phenomenon of silver ions nucleating alone, thus reducing the silver content of the coating.

[0019] Furthermore, the water bath temperature of the tannic acid-modified copper powder precursor solution is 20~50℃, which provides a suitable temperature for the mass transfer process of silver ions. This can prevent the slow mass transfer rate caused by low temperature, which would increase the silver plating time, and also prevent the fast mass transfer rate caused by high temperature, which would result in a fast reduction rate of silver ions and uneven coating.

[0020] Furthermore, the concentration of the second complexing agent, histidine solution, is 50~200 mmol / L to ensure coordination with silver ions, thereby reducing the reduction rate of silver ions and improving the coating effect.

[0021] Furthermore, the mass ratio of copper powder to silver nitrate is 100:(6~13), which can prevent the formation of silver dendrites and uneven coating caused by high silver ion concentration, and also prevent the formation of a non-dense coating caused by low silver ion concentration.

[0022] Furthermore, different reducing agents and different addition times will have different effects on the nucleation and growth of silver particles, thus affecting the coating effect.

[0023] Furthermore, after adding the second complexing agent, a mixture of histidine solution and silver ammonia solution, for 60-90 minutes, centrifugation is used to separate the solid and liquid phases. This prevents both incomplete silver coating due to a short reaction time and excessive silver particle growth due to a long reaction time, resulting in a large-particle coating.

[0024] This invention also discloses a silver-coated copper powder with a dense silver layer obtained by the above-mentioned preparation method, which utilizes a dual complexing agent to achieve a dense silver layer. The synergistic effect of the first complexing agent, tannic acid, and the second complexing agent, histidine, achieves high utilization of silver ions, resulting in a dense silver layer, excellent electrical properties, and antioxidant properties at low silver concentrations. This invention requires no complex equipment or high-temperature, high-pressure conditions; the process is simple and cost-effective. The resulting coating has strong adhesion to the substrate, effectively avoiding peeling problems caused by physical mixing. Furthermore, by adjusting reaction parameters, product performance can be significantly improved. The prepared dense silver-coated copper powder combines the low cost of copper with the high conductivity and antioxidant properties of silver, exhibiting excellent application performance in fields such as electronic pastes and conductive coatings, significantly improving the material's cost-effectiveness and service life.

[0025] This invention discloses the application of a dense silver layer coating on silver-plated copper powder in the fabrication of solar cells, printed circuit boards, or flexible circuits. The synergistic effect of tannic acid and histidine dual complexing agents allows silver ions to be slowly released and directionally deposited on the surface of the copper powder, forming a complete, pore-free, dense silver shell. This dense silver layer can continuously and efficiently conduct current, providing conductivity similar to pure silver powder; simultaneously, the silver layer acts as an excellent physical barrier, effectively preventing oxygen and moisture from diffusing into the copper nucleus, thus inhibiting the formation of copper oxide at its source. Thermogravimetric curve of Example 2 (…) Figure 3 This study confirms that the powder exhibits minimal weight loss at high temperatures, possesses outstanding resistance to thermal oxidation, and can withstand circuit soldering and high-temperature curing processes. Furthermore, using copper as the core significantly reduces the amount of precious silver used, substantially lowering costs. The dense silver layer bonds firmly to the copper substrate, resisting detachment under mechanical stresses such as screen printing or repeated bending. This significantly improves the conductivity reliability, processing adaptability, and long-term service life of electronic devices, achieving high cost-effectiveness. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the dense silver layer coated with silver-plated copper powder prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the dense silver layer coated with silver-plated copper powder prepared in Example 2 of the present invention; Figure 3 This is the thermogravimetric curve of the dense silver layer coated silver-plated copper powder prepared in Example 2 of the present invention; Figure 4 This is a scanning electron microscope image of the dense silver layer coated with silver-plated copper powder prepared in Example 3 of the present invention; Figure 5 This is a scanning electron microscope image of the dense silver layer coated with silver-plated copper powder prepared in Example 4 of the present invention; Figure 6 This is a scanning electron microscope image of the dense silver layer coated with silver-plated copper powder prepared in Example 5 of the present invention; Figure 7 This is a scanning electron microscope image of the dense silver layer coated with silver-plated copper powder prepared in Example 6 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0029] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0030] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0031] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0032] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation for these numerical combinations.

[0033] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0034] The term “and / or” as used in this invention refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0035] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0036] To address the limitation of existing complexing agents in achieving a dense silver coating on silver-plated copper powder at low silver concentrations, this invention employs tannic acid and histidine as dual complexing agents. Tannic acid pre-forms a tannic acid layer on the copper powder surface via its hydroxyl groups, inhibiting the displacement reaction between copper and silver ions. Tannic acid possesses numerous phenolic hydroxyl groups, allowing for the coordination of vacant phenolic hydroxyl groups with free silver ions in solution, reducing silver ions in situ under alkaline conditions. Histidine captures silver ions in solution, forming a stable complex, reducing the concentration of free silver ions and preventing rapid, disordered deposition caused by high silver ion concentrations, which results in an uneven and non-dense coating. A bridge-like acid-base neutralization reaction between histidine and tannic acid forms a large silver ion network structure, efficiently utilizing silver ions and allowing for slow release to form a dense and uniform coating. Using copper powder as a substrate, a core-shell filler is prepared using chemical silver plating. By improving the silver plating process, the silver coating effect is enhanced, resulting in silver-plated copper powder with excellent electrical properties and oxidation resistance, achieving cost reduction and efficiency improvement. This invention combines the cost advantages of copper with the high conductivity and oxidation resistance of silver layers, and has a simple preparation process. It reduces production costs while ensuring the performance of conductive paste, thus expanding its application range in the electronics field.

[0037] This invention proposes a method for preparing silver-plated copper powder with a dense silver layer coating using dual complexing agents. The method achieves high utilization of silver ions through the synergistic effect of the first complexing agent tannic acid and the second complexing agent histidine. This method can solve the problems of silver-plated copper powder being unable to form a dense and uniform smooth coating at low silver concentrations, as well as the poor conductivity and oxidation resistance of the silver-plated copper powder.

[0038] This invention discloses a method for preparing a dense silver layer coated silver-plated copper powder, which is specifically implemented according to the following steps: Step 1: Perform surface pretreatment on the copper powder to remove the surface oxide layer; The copper powder surface pretreatment involves ultrasonic cleaning using at least two of the following: a mixed solution of acetone, ammonium sulfate and ammonia, dilute sulfuric acid, sodium hydroxide, ethanol and deionized water. The ultrasonic treatment time is 10-30 min. Step 2: Mix the pretreated copper powder with the dispersant solution and stir to obtain a copper powder dispersion; The dispersant is at least one of polyethylene glycol-400 (PEG-400), polyethylene glycol-600 (PEG-600), and polyvinylpyrrolidone-K30 (PVP-K30), and the mass ratio of copper powder to dispersant is 100:(5~10), and the mixture is mechanically stirred at a speed of 250~350 r / min. Step 3: Add the first complexing agent tannic acid solution to the copper powder dispersion from Step 2 and stir in a water bath. Adjust the pH value to 8-9 to obtain a tannic acid-modified copper powder precursor solution. The concentration of the first complexing agent, tannic acid solution, is 10–20 mmol / L; the water bath temperature is 20–50℃; the water bath time is 15–45 min; and the solution used to adjust the pH to 8–9 is any one of potassium carbonate solution, sodium hydroxide solution, and sodium carbonate solution, with a concentration of 5–15 wt%. Step 4: Add the mixed solution of the second complexing agent histidine solution and silver ammonia solution to the tannic acid modified copper powder precursor solution in Step 3, and then add the reducing agent solution. The mixture is stirred and allowed to react fully. After the reaction is complete, solid-liquid separation is performed. The product is washed and dried to obtain dense silver-coated silver-plated copper powder.

[0039] The concentration of the second chelating agent, histidine solution, is 50-200 mmol / L, and the volume ratio of the second chelating agent, histidine solution, to the first chelating agent, tannic acid solution, is (3-1):1. The silver ammonia solution is prepared by adding dilute ammonia water dropwise to silver nitrate solution until the solution color changes from brownish-black to clear and transparent. The mass ratio of copper powder to silver nitrate is 100:(6-13). The reducing agent is one of L-ascorbic acid, glucose, or sodium borohydride. The concentration of the reducing agent solution is 100-300 mmol / L. The dropping rate of the mixture of the second chelating agent, histidine solution, and silver ammonia solution, as well as the reducing agent solution, is 4.5-5.5 mL / min. After 60-90 minutes of dropping the mixture of the second chelating agent, histidine solution, and silver ammonia solution, the solution is separated by centrifugation, washed at least three times with water and ethanol, and dried in a vacuum drying oven at 40-60℃ for 10-15 minutes. h, ultimately yielding a dense silver layer coated with silver-plated copper powder.

[0040] This invention discloses a method for preparing dense silver-coated copper powder using a dual complexing agent. The method involves pretreating copper powder under ultrasonic conditions to remove the oxide layer and activate the surface. The pretreated copper powder is then thoroughly stirred with a dispersant solution to obtain a copper powder dispersion. A tannic acid solution (the first complexing agent) is added to the copper powder dispersion, and the mixture is reacted in a water bath at a constant temperature, with the pH adjusted to 8-9 to form a tannic acid-modified copper powder precursor solution. A mixture of a histidine solution and a silver ammonia solution (the second complexing agent) is slowly added dropwise to the tannic acid-modified copper powder precursor solution, along with a reducing agent solution. After sufficient reaction, the solid and liquid phases are separated. The resulting solid product is washed and dried to obtain dense silver-coated copper powder. By employing tannic acid as the first complexing agent and histidine as the second complexing agent, the utilization rate of silver ions is improved, and the cost is reduced. Adjusting the reaction parameters optimizes the silver plating effect, enabling the prepared silver-plated copper powder to combine the low cost of copper with the high conductivity and oxidation resistance of silver. This provides a new approach for preparing dense silver-coated copper powder at low silver concentrations. Furthermore, the preparation process of this invention is simple and easy to implement, facilitating large-scale applications. It exhibits excellent performance in fields such as electronic pastes and conductive coatings, and has particular practical significance for improving the cost-effectiveness and service life of materials.

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0042] Example 1 A method for preparing a dense silver-coated silver-plated copper powder includes: Add 3 g of copper powder to 30 mL of acetone and sonicate for 10 min to remove organic matter from the surface of the copper powder. Then, separate the solid and liquid phases. Add 30 mL of 3% dilute sulfuric acid solution and sonicate for 30 min to remove the oxide layer from the surface of the copper powder. After solid-liquid separation, wash with deionized water at least 3 times. Disperse the pretreated copper powder in a solution of 0.27 mL of PEG-400 and 150 mL of deionized water to prepare 20 mL of a 10 mmol / L tannic acid solution. Pour the prepared tannic acid solution into the copper powder dispersion, adjust the pH to 9 with 10 wt% sodium carbonate solution, heat in a water bath at 20°C, and mechanically stir at 350 r / min for 45 min to obtain a tannic acid-modified copper powder precursor solution. Dissolve 0.17 g of silver nitrate in 10 mL of deionized water and add dilute ammonia dropwise while stirring until the solution changes from brownish-black to transparent to obtain a silver ammonia solution. Prepare 20 mL of a 200% PEG-400 solution. A mmol / L histidine solution was prepared and mixed with silver ammonia solution for 3 min. The mixture was then added dropwise at a rate of 5.5 mL / min to a tannic acid-modified copper powder precursor solution. 20 mL of a 300 mmol / L L-ascorbic acid solution was prepared. When the mixture of histidine solution and silver ammonia solution was added for 5 min, the L-ascorbic acid solution was added dropwise at a rate of 5.5 mL / min. 60 min after the initial addition of the mixture of histidine solution and silver ammonia solution, the mixture was centrifuged to separate the solid and liquid phases. The mixture was washed at least 3 times with water and ethanol and dried in a vacuum drying oven at 40 °C for 15 h to finally obtain silver-plated copper powder.

[0043] Figure 1 The image shows a scanned image of the dense silver layer coated silver-plated copper powder prepared in Example 1 of the present invention. As can be seen from the image, the surface of the copper powder is densely coated with silver particles, and the coating is not smooth.

[0044] Example 2 A method for preparing a dense silver-coated silver-plated copper powder includes: Add 3 g of copper powder to 30 mL of acetone and sonicate for 15 min to remove organic matter from the surface of the copper powder. Then, perform solid-liquid separation. Add 30 mL of a mixed solution of 200 mmol / L ammonium sulfate and 400 mmol / L ammonia and sonicate for 15 min to remove the oxide layer from the surface of the copper powder. After solid-liquid separation, wash at least three times with ethanol and deionized water. Disperse the pretreated copper powder in 0.2 g of 150 mL of PVP solution to prepare 20 mL of 14 mmol / L tannic acid solution. Pour the prepared tannic acid solution into the copper powder dispersion solution, adjust the pH to 8.5 with 10 wt% potassium carbonate solution, heat in a water bath at 30℃, and mechanically stir at 300 r / min for 30 min to obtain a tannic acid-modified copper powder precursor solution. Dissolve 0.27 g of silver nitrate in 10 mL of deionized water and add dilute ammonia dropwise while stirring until the solution changes from brownish-black to transparent to obtain a silver ammonia solution. Prepare 40 mL of the solution. Prepare 100 mmol / L histidine solution, mix the prepared histidine solution with silver ammonia solution and react for 3 min. Add the mixture dropwise at a rate of 5 mL / min to the tannic acid-modified copper powder precursor solution. Prepare 20 mL of 200 mmol / L L-ascorbic acid solution. When the mixture of histidine solution and silver ammonia solution is added for 5 min, add the L-ascorbic acid solution dropwise at a rate of 5 mL / min. After 75 min from the start of adding the mixture of histidine solution and silver ammonia solution, separate the solid and liquid by centrifugation, wash with water and ethanol at least 3 times, and dry in a vacuum drying oven at 50 °C for 12 h to finally obtain silver-plated copper powder.

[0045] Figure 2 This is a scanning image of the dense silver layer coated silver-plated copper powder prepared in Example 2 of the present invention. As can be seen from the image, the silver particles on the surface of the copper powder are evenly distributed and densely coated, and the coating is smooth. Figure 3 The thermogravimetric analysis curve of the dense silver-coated silver-plated copper powder prepared in Example 2 of the present invention shows that the prepared silver-plated copper powder has excellent oxidation resistance.

[0046] Example 3 A method for preparing a dense silver-coated silver-plated copper powder includes: Add 3 g of copper powder to 30 mL of acetone and sonicate for 10 min to remove organic matter from the surface of the copper powder. Then, perform solid-liquid separation. Add 30 mL of a mixed solution of 200 mmol / L ammonium sulfate and 400 mmol / L ammonia and sonicate for 30 min to remove the oxide layer from the surface of the copper powder. After solid-liquid separation, wash at least three times with ethanol and deionized water. Disperse the pretreated copper powder in 0.15 g of 150 mL of PVP solution to prepare 20 mL of 20 mmol / L tannic acid solution. Pour the prepared tannic acid solution into the copper powder dispersion solution, adjust the pH to 8 with 15 wt% sodium hydroxide solution, heat in a water bath at 30°C, and mechanically stir at 300 r / min for 30 min to obtain a tannic acid-modified copper powder precursor solution. Dissolve 0.27 g of silver nitrate in 10 mL of deionized water and add dilute ammonia dropwise while stirring until the solution changes from brownish-black to transparent to obtain a silver ammonia solution. Prepare 40 mL of acetone solution. Prepare a 200 mmol / L histidine solution, mix the prepared histidine solution with silver ammonia solution and react for 3 min. Then add the mixture dropwise at a rate of 5.5 mL / min to the tannic acid-modified copper powder precursor solution. Prepare 20 mL of 100 mmol / L glucose solution. When the mixture of histidine solution and silver ammonia solution is added for 5 min, add the glucose solution dropwise at a rate of 5.5 mL / min. After 70 min from the start of adding the mixture of histidine solution and silver ammonia solution, separate the solid and liquid by centrifugation, wash with water and ethanol at least 3 times, and dry in a vacuum drying oven at 50 °C for 12 h to finally obtain silver-plated copper powder.

[0047] Figure 4 The image shows a scanned image of the dense silver layer coated silver-plated copper powder prepared in Example 3 of the present invention. As can be seen from the image, the surface of the copper powder is densely coated with silver particles, the silver particles are large in size, and the coating is not smooth.

[0048] Example 4 A method for preparing a dense silver-coated silver-plated copper powder includes: Add 3 g of copper powder to 30 mL of acetone and sonicate for 10 min to remove organic matter from the surface of the copper powder. Then, perform solid-liquid separation. Add 30 mL of a mixed solution of 200 mmol / L ammonium sulfate and 400 mmol / L ammonia and sonicate for 20 min to remove the oxide layer from the surface of the copper powder. After solid-liquid separation, wash at least three times with ethanol and deionized water. Disperse the pretreated copper powder in 0.2 g of 150 mL of PVP solution to prepare 20 mL of 14 mmol / L tannic acid solution. Pour the prepared tannic acid solution into the copper powder dispersion solution, adjust the pH to 8 with 5 wt% potassium carbonate solution, heat in a water bath at 30°C, and mechanically stir at 250 r / min for 15 min to obtain a tannic acid-modified copper powder precursor solution. Dissolve 0.27 g of silver nitrate in 10 mL of deionized water and add dilute ammonia dropwise while stirring until the solution changes from brownish-black to transparent to obtain a silver ammonia solution. Prepare 40 mL of acetone solution. Prepare a 50 mmol / L histidine solution, mix the prepared histidine solution with silver ammonia solution and react for 3 min. Then, add the mixture dropwise to the tannic acid-modified copper powder precursor solution at a rate of 4.5 mL / min. Prepare 20 mL of 200 mmol / L sodium borohydride solution. Add the sodium borohydride solution dropwise at a rate of 4.5 mL / min 5 min after adding the histidine solution and silver ammonia solution mixture. After 75 min from the start of adding the histidine solution and silver ammonia solution mixture, separate the solid and liquid components by centrifugation, wash with water and ethanol at least 3 times, and dry in a vacuum drying oven at 50 °C for 10 h to finally obtain silver-plated copper powder.

[0049] Figure 5 The image shows a scanned image of the dense silver layer coated silver-plated copper powder prepared in Example 4 of the present invention. As can be seen from the image, the surface of the copper powder is densely coated with silver particles, and the coating is not smooth.

[0050] Example 5 A method for preparing a dense silver-coated silver-plated copper powder includes: 3 g of copper powder was added to 30 mL of a 1:1 mixture of ethanol and deionized water and sonicated for 25 min to remove organic matter from the surface of the copper powder. Solid-liquid separation was then performed. 30 mL of a mixture of 200 mmol / L ammonium sulfate and 400 mmol / L ammonia was added, and the mixture was sonicated for 10 min to remove the oxide layer from the surface of the copper powder. After solid-liquid separation, the copper powder was washed at least three times with ethanol and deionized water. The pretreated copper powder was dispersed in 0.2 g of 150 mL of PVP solution, and 20 mL of a 14 mmol / L tannic acid solution was prepared. The prepared tannic acid solution was poured into the copper powder dispersion, and the pH was adjusted to 8 with 15 wt% potassium carbonate solution. The mixture was heated in a water bath at 50°C with mechanical stirring at 300 r / min for 30 min to obtain a tannic acid-modified copper powder precursor solution. 0.4 g of silver nitrate was dissolved in 10... Add 60 mL of deionized water and dilute ammonia dropwise while stirring until the solution changes from brownish-black to transparent to obtain silver ammonia solution. Prepare 60 mL of 100 mmol / L histidine solution. Mix the prepared histidine solution with the silver ammonia solution and react for 3 min. Add the mixture dropwise at a rate of 5 mL / min to the tannic acid modified copper powder precursor solution. Prepare 20 mL of 200 mmol / L L-ascorbic acid solution. When the mixture of histidine solution and silver ammonia solution is added for 5 min, add the L-ascorbic acid solution dropwise at a rate of 5 mL / min. After 90 min from the start of adding the mixture of histidine solution and silver ammonia solution, separate the solid and liquid by centrifugation, wash with water and ethanol at least 3 times, and dry in a vacuum drying oven at 50°C for 12 h to finally obtain silver-plated copper powder.

[0051] Figure 6 This is a scanning image of the dense silver layer coated silver-plated copper powder prepared in Example 5 of the present invention. As can be seen from the image, the surface of the copper powder is densely coated with silver particles, and the silver particles have a large particle size.

[0052] Example 6 A method for preparing a dense silver-coated silver-plated copper powder includes: Add 3 g of copper powder to 30 mL of acetone and sonicate for 10 min to remove organic matter from the surface of the copper powder. Then, perform solid-liquid separation and add 30 mL of 200 mmol / L sodium hydroxide solution. Sonicate for 30 min to remove the oxide layer from the surface of the copper powder. After solid-liquid separation, wash with deionized water at least 3 times. Disperse the pretreated copper powder in a solution of 0.13 mL of PEG-600 and 150 mL of deionized water to prepare 20 mL of 14 mmol / L tannic acid solution. Pour the prepared tannic acid solution into the copper powder dispersion solution, adjust the pH to 8 with 5 wt% potassium carbonate solution, heat in a water bath at 30℃, and mechanically stir at 250 r / min for 15 min to obtain a tannic acid-modified copper powder precursor solution. Dissolve 0.27 g of silver nitrate in 10 mL of deionized water and add dilute ammonia dropwise while stirring until the solution changes from brownish-black to transparent to obtain a silver ammonia solution. Prepare 40 mL of 50% sodium hydroxide solution. A mmol / L histidine solution was prepared and mixed with silver ammonia solution for 3 min. The mixture was then added dropwise at a rate of 4.5 mL / min to a tannic acid-modified copper powder precursor solution. 20 mL of a 200 mmol / L L-ascorbic acid solution was prepared. When the mixture of histidine and silver ammonia solutions was added for 5 min, the L-ascorbic acid solution was added dropwise at a rate of 4.5 mL / min. 75 min after the initial addition of the mixture of histidine and silver ammonia solutions, the solid and liquid phases were separated by centrifugation. The mixture was washed at least 3 times with water and ethanol and dried in a vacuum drying oven at 60 °C for 10 h to finally obtain silver-plated copper powder.

[0053] Figure 7 The image shows a scanned image of the dense silver layer coated silver-plated copper powder prepared in Example 6 of the present invention. As can be seen from the image, the surface of the copper powder is densely coated with silver particles, and the coating is not smooth.

[0054] In summary, the present invention discloses a dense silver-coated silver-plated copper powder, its preparation method, and its application. First, commercial copper powder undergoes surface pretreatment, then is mixed with a dispersant, and a first complexing agent, tannic acid solution, is added to obtain a tannic acid-modified copper powder precursor solution. A mixture of a second complexing agent, histidine solution, and silver ammonia solution is slowly added dropwise to the obtained tannic acid-modified copper powder precursor solution under stirring. Subsequently, a reducing agent is slowly added dropwise, and the mixture reacts fully under stirring. After the reaction is complete, solid-liquid separation is performed, and the product is washed and dried to obtain a dense silver-coated silver-plated copper powder. The tannic acid and histidine complexing agents used in this invention can both coordinate with silver ions. Tannic acid has a large number of phenolic hydroxyl groups, which can increase the coordination number of silver ions. Furthermore, tannic acid and histidine undergo an acid-base neutralization-like reaction, achieving a bridging effect. Adding a reducing agent further promotes the reduction reaction of silver ions, improving the utilization rate of silver ions while reducing costs. The final result is a dense silver-coated copper powder, providing a new approach for preparing dense silver-coated copper powder at low silver ion concentrations. Through the synergistic effect of the first complexing agent, tannic acid, and the second complexing agent, histidine, efficient complexation and full utilization of silver ions are achieved. Under low silver concentration conditions, a dense, uniform silver layer, excellent electrical properties, and outstanding antioxidant properties of dense silver-coated copper powder are successfully prepared. This invention's process requires no complex production equipment or stringent reaction conditions such as high temperature and high pressure, making it simple and easy to operate and significantly reducing production costs. The resulting dense silver-coated copper powder exhibits a strong bond between the silver plating and the copper substrate, effectively solving the plating peeling problem that easily occurs with physical mixing methods. Furthermore, by controlling process parameters such as reaction temperature, reaction time, complexing agent ratio, and reducing agent addition time, the overall performance of the silver-coated copper powder is improved, meeting the needs of various application scenarios. The dense silver-coated copper powder prepared by this invention combines the low-cost characteristics of copper with the core advantages of silver, such as high conductivity and high oxidation resistance, exhibiting excellent practical application performance in the electronics field. It has significant practical importance and application value in promoting the cost-effectiveness and high-performance upgrading of related electronic functional materials.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a dense silver layer coated silver-plated copper powder, characterized in that, include: The pretreated copper powder was mixed with a dispersant solution to obtain a copper powder dispersion. First, the first complexing agent is added to the copper powder dispersion and stirred evenly to obtain a tannic acid-modified copper powder precursor solution. Then, a mixture of a second complexing agent and silver ammonia solution is added, followed by a reducing agent solution. After stirring and reacting, solid-liquid separation, washing, and drying are performed to obtain a dense silver-coated copper powder. The first complexing agent is a tannic acid solution; The second chelating agent is a histidine solution.

2. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, The pretreatment of copper powder includes ultrasonic cleaning using at least two of the following: a mixed solution of acetone, ammonium sulfate and ammonia, dilute sulfuric acid, sodium hydroxide, ethanol and deionized water; the ultrasonic treatment time is 10-30 min.

3. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, The dispersant solution is at least one of polyethylene glycol-400, polyethylene glycol-600, and polyvinylpyrrolidone-K30; the mass ratio of copper powder to dispersant solution is 100:(5~10), and the mixture is mechanically stirred at a speed of 250~350 r / min.

4. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, The concentration of the first complexing agent is 10-20 mmol / L; the temperature of the first complexing agent added to the copper powder dispersion is 20-50℃, the time is 15-45 min, and the pH value is adjusted to 8-9; the solution used to adjust the pH value is any one of potassium carbonate solution, sodium hydroxide solution and sodium carbonate solution, with a concentration of 5-15 wt%.

5. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, The concentration of the second complexing agent is 50~200 mmol / L, and the volume ratio of the second complexing agent to the first complexing agent is (3~1):

1.

6. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, The reducing agent solution is any one of L-ascorbic acid, glucose, and sodium borohydride; the concentration of the reducing agent solution is 100~300 mmol / L.

7. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, The dropping rate of the mixture of the second complexing agent and silver ammonia solution is 4.5~5.5 mL / min; the dropping rate of the reducing agent solution is 4.5~5.5 mL / min.

8. The method for preparing dense silver-coated silver-plated copper powder according to claim 1, characterized in that, After adding the mixture of the second complexing agent and silver ammonia solution dropwise for 60-90 minutes, the solid-liquid separation is performed by centrifugation, followed by washing with water and ethanol at least 3 times, and vacuum drying at 40-60℃ for 10-15 hours.

9. A dense silver layer coated with silver-plated copper powder, characterized in that, It is prepared by the method described in any one of claims 1-8 for preparing dense silver-coated silver-plated copper powder.

10. The application of the dense silver layer coated silver-plated copper powder as described in claim 9 in the preparation of solar cells, printed circuit boards or flexible circuits.

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