Silver-coated copper powder with compact coating and preparation method of silver-coated copper powder

Abstract

The preparation method comprises the following steps that pretreated copper powder, a dispersing agent and water are mixed to obtain a copper powder mixed solution, first silver salt, a first complexing agent and water are mixed to obtain a first silver complexing solution, the first silver complexing solution is dropwise added into the copper powder mixed solution, a replacement reaction is conducted, and the silver-coated copper powder with the compact coating is obtained. Intermediate-state silver-coated copper powder is obtained; second silver salt, ammonia water and a second complexing agent are mixed, a second silver complexing solution is obtained, the second silver complexing solution and the reducing agent solution are dropwise added into the intermediate-state silver-coated copper powder at the same time, an oxidation-reduction reaction is carried out, then solid-liquid separation and washing are carried out, and silver-coated copper powder is obtained; through raw material control and step-by-step reaction of first replacement and second reduction, under the condition of low silver content, the uniformity and compactness of a silver layer are improved, the conductivity / oxidation resistance of the silver-coated copper powder is guaranteed, and finally the photoelectric conversion efficiency of the photovoltaic silver paste is improved.

Description

Technical Field

[0001] This invention relates to the field of silver-coated copper technology, and more particularly to a densely coated silver-coated copper powder and its preparation method. Background Technology

[0002] Heterojunction (HJT) solar cells have become one of the core directions of next-generation high-efficiency photovoltaic technologies due to their high conversion efficiency (theoretical value exceeding 27.5%) and low-temperature process compatibility. However, silver paste accounts for as much as 25%-30% of the manufacturing cost of HJT cells, becoming a major bottleneck restricting their large-scale commercial application. Traditional low-temperature silver paste mainly uses high-purity silver powder, but silver resources are scarce and their prices fluctuate wildly, necessitating cost reduction and efficiency improvement through material innovation. Silver-coated copper powder, as a high-performance composite material, uses copper as the matrix and coats the surface with a nano-silver layer. It combines the excellent conductivity and oxidation resistance of silver with the low-cost advantages of copper. Through process optimization, it can maintain a photoelectric conversion efficiency similar to that of pure silver powder paste, making silver-coated copper powder an ideal alternative to pure silver powder. At the same time, silver-coated copper powder also has important application value in electronic components, catalysis, conductive adhesives, and other fields.

[0003] Currently, the main methods for preparing silver-coated copper powder include mechanical mixing, displacement, and chemical reduction. Mechanical mixing requires complex equipment and an inert atmosphere. Displacement utilizes the potential difference between silver and copper; in solution, copper particles lose electrons to become copper ions, while silver ions gain electrons and deposit on the copper particle surface. However, this silver layer is porous, has weak bonding strength, and is relatively thin. Chemical reduction involves the reaction of a reducing agent with silver coordinating ions to form a silver layer on the copper powder surface. While this method can achieve a high silver content, silver ions easily nucleate and grow into free silver nanoparticles, making it difficult to obtain a uniformly coated silver layer. These defects lead to insufficient electrochemical performance of silver-coated copper powder.

[0004] Therefore, a technical solution is needed to improve the uniformity and density of copper-coated silver powder while maintaining a low silver content, and to ensure the conductivity and oxidation resistance of the silver-coated copper powder, so as to ultimately improve the photoelectric conversion efficiency of photovoltaic silver paste. Summary of the Invention

[0005] In view of this, this application provides a densely coated silver-coated copper powder and its preparation method, which is used to solve the problem of how to improve the conductivity and oxidation resistance of silver-coated copper powder with low silver content.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for preparing densely coated silver-coated copper powder, comprising the following steps: S1. Mix pretreated copper powder, dispersant, and water to obtain a copper powder mixture. Mix the first silver salt, the first complexing agent, and water to obtain a first silver complexing solution. Add the first silver complexing solution dropwise to the copper powder mixture to carry out a displacement reaction and obtain intermediate silver-coated copper powder. S2. Mix the second silver salt, ammonia water, and the second complexing agent to obtain the second silver complexing solution. Add the second silver complexing solution and the reducing agent solution dropwise to the intermediate silver-coated copper powder to carry out the redox reaction. Then, separate the solid and liquid and wash to obtain the silver-coated copper powder.

[0007] Preferably, the first complexing agent includes one or more of tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, ammonia, and ethylenediaminetetraacetate; the molar ratio of the first complexing agent to the first silver salt is 1-1.5:1.

[0008] Preferably, the second complexing agent is a mixture of L-histidine and sodium tartrate; the mass ratio of L-histidine to sodium tartrate is 1:3-5.

[0009] Preferably, the first silver salt and the second silver salt are both nitrates; the reducing agent is ascorbic acid; and the dispersant includes one or more of PEG, PVA, PVP, and gelatin.

[0010] Preferably, the sum of the masses of silver elements in the first silver salt and the second silver salt is in a mass ratio of 1:5-10 to the mass of copper powder.

[0011] Preferably, the mass of the first silver salt is 10-15% of the total mass of the first and second silver salts.

[0012] Preferably, the preparation process of the second silver complex solution is as follows: ammonia water is added dropwise to the second silver salt under stirring. When the solution becomes transparent, the second complexing agent is added to obtain the second silver complex solution.

[0013] Preferably, the second silver complex solution and the reducing agent solution are added at the same rate, and the addition rate is 5-30 mL / min.

[0014] Preferably, the pretreated copper powder is copper powder with oxides removed.

[0015] Secondly, this application provides a densely coated silver-coated copper powder, which includes a copper core and a silver layer coating the copper core.

[0016] The beneficial effects of this application are as follows: This invention uses a combination of displacement and chemical reduction to prepare silver-coated copper powder. First, a first silver complexing solution is used to conduct a displacement reaction with copper powder, which forms silver nanoparticles on the surface of the copper powder, providing nucleation sites for the subsequent growth of the silver layer. Then, a second silver complexing solution and a reducing solution are simultaneously added to the reaction solution. Under the induction of these nucleation sites, silver particles can be uniformly deposited on the surface of the copper powder, improving the uniformity and density of the silver layer under the premise of low silver content. In this invention, a second complexing agent is added during the chemical reduction process. This agent can not only form a complex with silver ions, but also form a ligand with nano-silver. Therefore, while reducing the precipitation rate of silver ions, it can also adsorb the precipitated silver particles onto the surface of copper powder, further improving the uniformity and density of the coating.

[0017] The process of this invention is safe and environmentally friendly, requiring no introduction of cyanide and Sn. 2+ Pb 2+ The reaction conditions are easy to control, and the utilization rate of silver ions is high, which is beneficial for industrial production. Attached Figure Description

[0018] Figure 1 SEM image of the original copper powder; Figure 2 Here is a SEM image of the silver-coated copper powder in Example 1; Figure 3 Here is a SEM image of the silver-coated copper powder in Example 2; Figure 4 SEM image of the silver-coated copper powder in Comparative Example 1; Figure 5 SEM image of the silver-coated copper powder in Comparative Example 2; Figure 6 SEM image of the silver-coated copper powder in Comparative Example 3; Figure 7 This is a SEM image of the silver-coated copper powder in Comparative Example 4.

[0019] Figure 8 This is a SEM image of the silver-coated copper powder in Comparative Example 5. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] This application provides a method for preparing densely coated silver-coated copper powder, comprising the following steps: S1. Mix pretreated copper powder, dispersant, and water to obtain a copper powder mixture. Mix the first silver salt, the first complexing agent, and water to obtain a first silver complexing solution. Add the first silver complexing solution dropwise to the copper powder mixture to carry out a displacement reaction and obtain intermediate silver-coated copper powder. S2. Mix the second silver salt, ammonia water, and the second complexing agent to obtain the second silver complexing solution. Add the second silver complexing solution and the reducing agent solution dropwise to the intermediate silver-coated copper powder to carry out the redox reaction. Then, separate the solid and liquid and wash to obtain the silver-coated copper powder.

[0022] This application improves the uniformity and density of the silver layer at low silver content through raw material control and a stepwise reaction of displacement followed by reduction, ensuring the conductivity and oxidation resistance of the silver-coated copper powder, and ultimately improving the photoelectric conversion efficiency of photovoltaic silver paste. The specific mechanism is as follows: Step S1 is a displacement process, in which silver ions undergo a displacement reaction with copper ions on the surface of copper powder, generating silver nanoparticles on the surface of copper powder. The silver nanoparticles provide nucleation sites (pre-prepared silver nuclei), preventing silver ions from growing into free silver nanoparticles on their own, while the displaced copper ions enter the solution. Step S2 is a redox process, in which newly added silver ions are gradually reduced along the nucleation sites under the action of a reducing agent, and silver is directionally deposited on the pre-prepared silver nuclei to form a dense and uniform silver layer.

[0023] In this application, the second silver complexing solution and the reducing agent solution are simultaneously added dropwise to the intermediate silver-coated copper powder, maintaining the Ag content in the reaction system. + The dynamic balance with the reducing agent concentration avoids the problem of uneven silver layer caused by excessively high local concentration, and eliminates coating defects, ultimately improving the bonding force between silver and copper and the uniformity of the silver layer.

[0024] In some embodiments, the first complexing agent includes one or more of tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, ammonia, and ethylenediaminetetraacetate.

[0025] In this embodiment, the first complexing agent is a polyamine-based multidentate ligand, taking tetraethylenepentamine as an example. It forms a tetraethylenepentamine-silver complex with silver ions. Tetraethylenepentamine (TEPA, H2N-CH2CH2-NH-CH2CH2-NH-CH2CH2-NH-CH2CH2-NH2) is a multidentate ligand containing multiple nitrogen atoms, which can simultaneously bind silver ions (Ag). + This chelation effect greatly improves the stability of the complex; the stability constant of the tetraethylenepentamine-silver complex is much higher than that of the silver ammonia complex. + When complexed, the reaction rate is mainly controlled by Ag. +The rate of dissociation from the complex; therefore, the first complexing agent of this application has higher stability and stronger chelating effect, which is beneficial to Ag. + A slower dissociation rate is achieved during the displacement reaction, resulting in more uniform formation of silver nanoparticles on the copper powder surface. In some embodiments, the molar ratio of the first complexing agent to the first silver salt is greater than or equal to 1:1, i.e., an excess of the first complexing agent is added to the first silver salt.

[0026] In some embodiments, the second complexing agent is a mixture of L-histidine and sodium tartrate; the mass ratio of L-histidine to sodium tartrate is 1:3-5.

[0027] In this embodiment, the second complexing agent is a mixture of L-histidine and sodium tartrate. During the redox process, the second complexing agent is added to the silver ammonia solution as a dual complexing agent. The imidazole, amino, and carboxyl groups in L-histidine can not only form complexes with silver ions but also form ligands with nano-silver. L-histidine adsorbs onto the copper surface, guiding the directional deposition of silver. Sodium tartrate adjusts the pH of the solution, reducing Ag. + The reduction rate reduces the continuous corrosion of copper powder in a strongly alkaline environment, thereby further improving the uniformity of silver coating.

[0028] In some embodiments, the first silver salt and the second silver salt are both nitrates; the reducing agent is ascorbic acid; and the dispersant includes one or more of PEG, PVA, PVP, and gelatin.

[0029] In some embodiments, the sum of the masses of silver elements in the first silver salt and the second silver salt is in a mass ratio of 1:5-10 to the mass of copper powder.

[0030] In this embodiment, silver and copper can achieve complete coating within a limited range. If the amount of silver used is insufficient, the coating will be incomplete; if the amount of silver used is excessive, raw materials will be wasted.

[0031] In some embodiments, the mass of the first silver salt is 10-15% of the total mass of the first and second silver salts.

[0032] In this embodiment, a small amount of silver salt is first used for a substitution reaction to provide sufficient nucleation sites without wasting silver. Then, a large amount of silver salt is used for a redox reaction to prevent silver ions from growing into free silver nanoparticles on their own, which is beneficial to improving the uniformity of the silver layer coating. If the amount of the first silver salt is too small, there will be insufficient nucleation sites, the silver layer will be discontinuous, and the coating rate will decrease. If the amount of the first silver salt is too large, the substitution layer will be too thick and the silver layer will be easy to peel off, resulting in a decrease in the bonding force between the silver layer and copper.

[0033] In some embodiments, the preparation process of the second silver complex solution is as follows: ammonia water is added dropwise to the second silver salt under stirring. When the solution becomes transparent, the second complexing agent is added to obtain the second silver complex solution.

[0034] In some embodiments, the second silver complex solution and the reducing agent solution are added at the same rate, and the addition rate is 5-30 mL / min.

[0035] In some embodiments, the pretreated copper powder is copper powder with oxides removed.

[0036] In this embodiment, the process of pretreating copper powder is as follows: soaking the copper powder in at least one of the following solutions to remove oxides from the surface of the copper powder: dilute sulfuric acid, acetone, ethanol, a mixture of ammonium sulfate and ammonia, and deionized water.

[0037] In some embodiments, the mass ratio of copper powder to dispersant is 100:1-100:5, the concentration of the copper powder mixture is 0.1-2.0 mol / L, the concentrations of the first silver salt and the second silver salt are both 0.1-1.5 mol / L, the concentration of the reducing agent is 0.1-1.5 mol / L, the stirring rate of the redox reaction is 300-600 rad / min, and the reaction temperature is 25-60℃.

[0038] In some embodiments, solid-liquid separation is performed by obtaining a solid product through vacuum filtration, washing the solid product with deionized water and ethanol until the conductivity of the filtrate is less than or equal to 20 μS / cm, and then placing it in a vacuum drying oven for drying at 60°C for 6 hours.

[0039] The following specific embodiments further illustrate this solution.

[0040] Example 1 A method for preparing densely coated silver-coated copper powder includes the following steps: S1. Weigh 85g of copper powder, add 1000mL of deionized water and 50g of concentrated sulfuric acid, stir for 30min, then filter and wash with deionized water to obtain pretreated copper powder. Add 1000mL of deionized water to the washed copper powder, then add 3g of PEG-600 as a dispersant and mix evenly to obtain a copper powder mixture. Weigh 2.5g of silver nitrate (the mass of the first silver salt is 10% of the total mass of the first and second silver salts) and dissolve it in 50mL of water. Add excess tetraethylenepentamine dropwise until the solution becomes clear and transparent to obtain the first silver complex solution. Then add the first silver complex solution dropwise to the copper powder mixture for 5min. After the dropwise addition is completed, continue the displacement reaction at 25℃ for 25min to obtain intermediate silver-coated copper powder. S2. Weigh 22.5g of silver nitrate (the sum of the mass of silver in the first and second silver salts and the mass ratio of copper powder to copper powder is 1:5.35) and dissolve it in 450mL of water. Add ammonia until the solution becomes clear. Then weigh 15g of sodium tartrate and 3.38g of L-histidine and add them to the silver ammonia solution to obtain the second silver complex solution. Weigh 15g of vitamin C and dissolve it in 500mL of water to obtain the reducing agent solution. Add the second silver complex solution and the reducing agent solution dropwise to the intermediate silver-coated copper powder. Carry out the redox reaction at 30℃. The dropping rates of the second silver complex solution and the reducing agent solution are the same, and the dropping rate is 10mL / min. After the reaction is completed, obtain the solid product by vacuum filtration. Wash the solid product with deionized water and ethanol until the conductivity of the filtrate is less than or equal to 20uS / cm. Then put it into a vacuum drying oven for drying at 60℃ for 6h to obtain silver-coated copper powder.

[0041] Example 2 A method for preparing densely coated silver-coated copper powder is the same as in Example 1, except that 10g of sodium tartrate and 2.26g of L-histidine are weighed and added to the silver ammonia solution.

[0042] Comparative Example 1 A method for preparing silver-coated copper powder is the same as in Example 1, except that it does not include the addition of L-histidine.

[0043] Comparative Example 2 A method for preparing silver-coated copper powder is the same as in Example 1, except that it does not include the addition of sodium tartrate.

[0044] Comparative Example 3 A method for preparing silver-coated copper powder is the same as in Example 1, except that it does not include the addition of a second complexing agent.

[0045] Comparative Example 4 A method for preparing silver-coated copper powder, comprising the following steps: Weigh 85g of copper powder, add 1000mL of deionized water and 50g of concentrated sulfuric acid, stir for 30min, then filter and wash with deionized water to obtain pretreated copper powder. Add 1000mL of deionized water to the washed copper powder, then add 3g of PEG-600 as a dispersant and mix well to obtain a copper powder mixture. Weigh 25g of silver nitrate (the sum of the mass of silver in the first and second silver salts is 1:5.35 to the mass of copper powder) and dissolve in 450mL of water. Add ammonia until the solution becomes clear. Then weigh 15g of sodium tartrate and 3.38g of L-histidine and add them to the silver ammonia solution to obtain the second silver complex solution. Weigh 15g of sodium tartrate and 3.38g of L-histidine. VC was dissolved in 500 mL of water to obtain a reducing agent solution. The second silver complex solution and the reducing agent solution were simultaneously added dropwise to the copper powder mixture. A redox reaction was carried out at 30 °C. The dropping rates of the second silver complex solution and the reducing agent solution were the same, and the dropping rate was 10 mL / min. After the reaction was completed, the solid product was obtained by vacuum filtration. The solid product was washed with deionized water and ethanol until the conductivity of the filtrate was less than or equal to 20 uS / cm. Then it was placed in a vacuum drying oven for drying at 60 °C for 6 h to obtain silver-coated copper powder.

[0046] Comparative Example 5 A method for preparing silver-coated copper powder, comprising the following steps: Weigh 85g of copper powder, add 1000mL of deionized water and 50g of concentrated sulfuric acid, stir for 30min, then filter and wash with deionized water to obtain pretreated copper powder. Add 1000mL of deionized water to the washed copper powder, then add 3g of PEG-600 as a dispersant and mix evenly to obtain a copper powder mixture. Weigh 25g of silver nitrate and dissolve it in 50mL of water, then add excess tetraethylenepentamine dropwise until the solution becomes clear and transparent to obtain the first silver complex solution. Then add the first silver complex solution dropwise to the copper powder mixture over 5min. After the dropwise addition is completed, continue the displacement reaction at 25℃ for 25min. After the reaction is completed, obtain the solid product by vacuum filtration. Wash the solid product with deionized water and ethanol until the conductivity of the filtrate is less than or equal to 20uS / cm. Then place it in a vacuum drying oven at 60℃ for 6h to obtain silver-coated copper powder.

[0047] Testing and Evaluation SEM images of copper-coated silver powder obtained from different embodiments and comparative examples were tested, and the SEM image of the original copper powder was also examined. Figure 1 This is a SEM image of the original copper powder. Figure 2-7 The images shown are SEM images of the silver-coated copper powders prepared in Examples 1-2 and Comparative Examples 1-4 of this invention.

[0048] Testing revealed that the silver content in the silver-coated copper powder prepared in different embodiments and comparative examples was between 15.0% and 15.5%, showing little difference. Different methods of preparing the silver-coated copper only affected its morphology and structure. Compared to the original copper powder, the microstructure of the silver-coated copper powder changed significantly. As shown in the figures, the silver-coated copper powder in Examples 1 and 2 achieved a uniform and dense silver layer coating even with low silver content. The SEM image of Comparative Example 4 showed that the obtained product contained a large amount of silver flocs, with a silver content close to 15%, and these silver particles were not coated on the surface of the copper powder.

[0049] Comparing Example 1 with Comparative Examples 1 and 2, it can be observed that the surface of the silver-coated copper powder in the comparative examples is rougher, with protrusions formed by the proliferation and growth of silver nanoparticles. This indicates that the dual complexing agents sodium tartrate and L-histidine can play a synergistic role in improving the uniformity of the silver layer. Comparing Example 1 with Comparative Example 3, it can be observed that the silver layer on the surface of the silver-coated copper powder in Comparative Example 3 is even rougher, and a small amount of silver flocculents are also present. This indicates that using only silver ammonia solution cannot guarantee the uniform deposition and growth of silver particles on the surface of copper powder. Comparing Example 1 with Comparative Example 4, it can be seen that the silver layer in Comparative Example 4 is incompletely coated, with a large amount of silver flocculents and scattered silver nanoparticles. This indicates that the displacement reaction between the silver complexing solution and the copper powder cannot obtain a uniform and dense silver layer on the surface of the copper powder.

[0050] The silver-coated copper powder obtained from different embodiments and comparative examples was made into silver-coated copper paste, which was then printed onto silicon wafers using a screen printing machine. After sintering, it was prepared into silver-coated copper electrodes. The volume resistivity of the silver-coated copper electrodes was measured in accordance with GB / T 1551-2021 "Determination of Resistivity of Silicon Single Crystals - Straight-line Four-Probe Method and DC Two-Probe Method". The test results are shown in Table 1.

[0051] Table 1. Resistivity test results of copper powder, silver-coated copper powder prepared in Examples 1-2, and Comparative Examples 1-5.

[0052] As shown in Table 1, the resistivity of the copper powder prepared from silver-coated copper powder is significantly lower than that of pure copper powder, compared to pure copper powder. The resistivity of the silver-coated copper paste prepared from examples 1 and 2 is even lower, reaching 3.63 × 10⁻⁶. -3 The result of Ω·cm is consistent with the SEM results, indicating that the addition of a dual complexing agent during the silver plating process can improve the uniformity and density of the silver plating layer, thereby improving the conductivity of the silver-coated copper powder.

[0053] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing densely coated silver-coated copper powder, characterized in that, Includes the following steps: Pretreated copper powder, dispersant, and water are mixed to obtain a copper powder mixture. A first silver salt, a first complexing agent, and water are mixed to obtain a first silver complexing solution. The first silver complexing solution is added dropwise to the copper powder mixture to carry out a displacement reaction, thereby obtaining intermediate silver-coated copper powder. The second silver salt, ammonia, and the second complexing agent are mixed to obtain a second silver complexing solution. The second silver complexing solution and the reducing agent solution are simultaneously added dropwise to the intermediate silver-coated copper powder to carry out a redox reaction. Then, the solid and liquid are separated and washed to obtain the silver-coated copper powder.

2. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The first complexing agent includes one or more of tetraethylenepentamine, diethylenetriamine, polyethylenepolyamine, ammonia, and ethylenediaminetetraacetate; the molar ratio of the first complexing agent to the first silver salt is 1-1.5:

1.

3. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The second complexing agent is a mixture of L-histidine and sodium tartrate; the mass ratio of L-histidine to sodium tartrate is 1:3-5.

4. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, Both the first silver salt and the second silver salt are nitrates; the reducing agent is ascorbic acid; and the dispersant includes one or more of PEG, PVA, PVP, and gelatin.

5. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The sum of the masses of silver elements in the first and second silver salts is in a mass ratio of 1:5-10 to the mass of the copper powder.

6. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The mass of the first silver salt is 10-15% of the total mass of the first and second silver salts.

7. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The preparation process of the second silver complex solution is as follows: under stirring, ammonia water is added dropwise to the second silver salt. When the solution becomes transparent, the second complexing agent is added to obtain the second silver complex solution.

8. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The second silver complex solution and the reducing agent solution are added at the same rate, and the addition rate is 5-30 mL / min.

9. The method for preparing densely coated silver-coated copper powder according to claim 1, characterized in that, The pretreated copper powder is copper powder with oxides removed.

10. A densely coated silver-coated copper powder obtained by the preparation method according to any one of claims 1-9, characterized in that, It includes a copper core and a silver layer covering the copper core.

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