Micron-sized silver-coated copper powder, and preparation method and application thereof

Abstract

The application discloses a low-temperature curing type micron-level spherical silver-coated copper powder and a preparation method thereof, and comprises the following steps: (1) preparation of a modified bonding layer: micron-level spherical copper powder is dispersed in a modified solution composed of a high polymer modifier and a coordination type pre-reducing agent to react, and then the copper powder filter cake with a uniform composite bonding layer on the surface is obtained by filtration; (2) silver plating reaction: after the copper powder filter cake is pre-dispersed and swelled in a solvent, a reducing agent and a silver source solution are added to perform chemical silver plating, so that a silver-coated copper powder crude product is obtained; (3) post-treatment: the crude product is subjected to hydrothermal densification treatment, and the target product is obtained. Through the construction of an active interface of "pre-reduction-coordination anchoring", the application solves the problem of weak bonding force between the silver layer and the copper matrix; the hydrothermal densification process is used to repair the coating defects, and the density and oxidation resistance of the material are significantly improved. The method is controllable, the prepared silver-coated copper powder is low in resistance and complete in coating, and is suitable for the production of high-performance electronic conductive paste and photovoltaic paste.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to a low-temperature curing micron-sized spherical silver-coated copper powder, its preparation method and application, and is particularly suitable for low-temperature electronic pastes, photovoltaics and other fields. Background Technology

[0002] With the rapid development of the electronic information industry and photovoltaic technology, the market demand for conductive pastes, as key basic materials for preparing electrodes and interconnect circuits of electronic components, is growing daily. Conductive fillers play a decisive role in the composition of conductive pastes. Currently, commercially available conductive pastes mainly use silver powder as the conductive filler due to its excellent conductivity and chemical stability. However, the high cost and price fluctuations of silver, as well as the "silver migration" phenomenon under a DC electric field, severely restrict its application in low-cost, large-scale industrial production.

[0003] In contrast, copper powder has similar conductivity to silver and is inexpensive, making it an ideal alternative. However, copper powder is chemically reactive and readily oxidizes in air. The formation of copper oxide or cuprous oxide films leads to a sharp decline in the conductivity of the slurry, limiting its practical application. Combining the oxidation resistance of silver with the low cost of copper, "silver-coated copper powder" has emerged. This structural material theoretically offers a balance between high conductivity, high oxidation resistance, and low cost.

[0004] Currently, the main methods for preparing silver-coated copper powder include chemical reduction and displacement methods. However, existing chemical silver plating processes still face the following serious technical bottlenecks: 1) Weak interfacial bonding and loose coating: Due to the difference in lattice parameters between copper and silver, and the fact that copper is corroded during the substitution reaction, the deposition of silver atoms on the copper surface often results in island-like growth, making it difficult to form a continuous and dense coating. This loose structure not only makes the silver layer easy to peel off, but also leaves a large number of pinhole structures, leaving the internal copper nuclei exposed to the environment and unable to effectively prevent oxygen penetration.

[0005] 2) Rough coating surface: The surface of silver-coated copper powder prepared by traditional reduction method often adsorbs a large number of fine silver nanoparticles, with a large specific surface area and high oil absorption value, which is not conducive to its high filling amount dispersion in conductive paste and increases the contact resistance.

[0006] 3) Poor process stability: In existing technologies, dispersants (such as PVP) are often used to directly mix into the plating solution. Although this improves the dispersibility to some extent, it fails to fundamentally solve the affinity problem of the silver-copper interface, resulting in large fluctuations in conductivity between product batches.

[0007] Therefore, there is an urgent need to develop a method for preparing silver-coated copper powder that can significantly enhance the bonding force between silver and copper, achieve high-density coating, and obtain low resistance and high oxidation resistance through a simple process, so as to meet the urgent demand of high-performance electronic pastes and the photovoltaic industry for low-cost conductive fillers. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects of the existing technology and provide a low-temperature curing micron-sized spherical silver-coated copper powder. By constructing an active modification layer, optimizing the dispersion process and hydrothermal densification treatment, the silver coating of the obtained micron-sized spherical silver-coated copper powder is dense, completely coated, and has low resistance, exhibiting excellent oxidation resistance and conductivity.

[0009] This invention also provides a method for preparing and applying the above-mentioned low-temperature curing micron-sized spherical silver-coated copper powder.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing micron-sized spherical silver-coated copper powder includes the following steps: S1. Preparation of modified adhesive layer: Micron-sized spherical copper powder is dispersed in a modified solution and reacted at 60-95 ℃ for 0.5-4 h. Solid-liquid separation (such as vacuum filtration) is performed to obtain micron-sized spherical copper powder filter cake with a uniform adhesive layer on the surface. S2. Silver plating reaction: Disperse the micron-sized spherical copper powder filter cake with a uniform bonding layer on the surface in a solvent and react at 20-75 ℃ for 20-90 min. Then add reducing agent solution and silver source solution to continue the reaction for 0.5-2 h to obtain micron-sized spherical silver-coated copper powder crude product. S3. Post-processing: The prepared micron-sized spherical silver-coated copper powder crude product is densified and then washed and dried to obtain the micron-sized spherical silver-coated copper powder.

[0011] Specifically, in step S1, the modified solution is composed of a modifier and a pre-reducing agent; wherein the modifier can be one or a combination of two or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyethylene oxide (PEO), gelatin, and hydroxyethyl cellulose; the mass ratio of the micron-sized spherical copper powder to the modifier is 4:1 to 1:1. The concentration of the modifier is 5 g / L to 20 g / L.

[0012] Specifically, in step S1, the pre-reducing agent is a reducing, coordinating compound containing amine, carboxyl, and aldehyde groups, preferably including one or more of hydrazine hydrate, diethylamine, triethanolamine, citric acid, glucose, formaldehyde, and formic acid; the mass ratio of the micron-sized spherical copper powder to the pre-reducing agent is 2:5-2:7. The concentration of the pre-reducing agent is 0.1 kg / L-0.5 kg / L.

[0013] Furthermore, in step S2, the solvent includes one or more of water, ethanol, ethylene glycol, ethylene glycol monomethyl ether, etc.

[0014] Specifically, in step S2, the reducing agent includes one or more of ascorbic acid, glucose, formaldehyde, potassium sodium tartrate, hydrazine hydrate, etc., and the molar ratio of the reducing agent to silver ions is 1:2-2:1, preferably 1-3:2.

[0015] Specifically, in step S2, the mass ratio of silver to copper powder in the silver-coated copper powder is 1:9-1:1.

[0016] Specifically, in step S2, the silver source solution comprises silver nitrate and a complexing agent; wherein the complexing agent comprises one or more of the following: ammonia, triethylenetetramine, ethylenediaminetetraacetic acid, sodium citrate, and disodium ethylenediaminetetraacetate. Preferably, the concentration of silver nitrate is 0.05 mol / L to 1 mol / L. The molar ratio of silver ions to the complexing agent is 2:1 to 2:4, more preferably around 2:3.

[0017] Specifically, the densification treatment in step S3 is a hydrothermal treatment, preferably at 160℃-300℃ for 0.5-8 h. The temperature can be 160℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃ or 300℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] The present invention also provides micron-sized spherical silver-coated copper powder prepared by the above preparation method.

[0019] This invention also provides the application of the above-mentioned micron-sized spherical silver-coated copper powder in the production of electronic silver-coated copper conductive paste, photovoltaic paste, etc.

[0020] This invention solves the problem of weak adhesion between the silver layer and the copper substrate by constructing a "pre-reduction-coordination anchoring" active interface; it also significantly improves the density and oxidation resistance of the material by using a hydrothermal densification process to repair coating defects. This method offers process control, producing silver-coated copper powder with low resistance and complete coating, making it suitable for producing high-performance electronic conductive pastes and photovoltaic pastes. Compared with existing technologies, the advantages and beneficial effects of this invention are as follows: (1) Innovative construction of a dual-effect active interface of "pre-reduction-coordination anchoring" breaks through the bottleneck of binding force in traditional physical adsorption. Unlike existing technologies that rely solely on polymers such as PVP for physical adsorption, this invention employs a composite modification system in step S1 consisting of "modifier (such as PVP / PVA) + pre-reducing agent (such as hydrazine hydrate / citric acid)". The pre-reducing agent is firmly "anchored" to the copper powder surface through its coordination groups (such as carboxyl and amino groups), while the reducing groups are locked in the adhesive layer as "in-situ initiators". This design produces unexpected technical effects: when a silver source is added in step S2, the anchored pre-reducing agent can induce silver ions to preferentially undergo "in-situ reduction nucleation" on the copper surface, rather than random self-nucleation in the solution. This "chemical bonding + in-situ growth" mechanism greatly enhances the interfacial bonding force between the silver layer and the copper substrate, eliminating the defects of easy silver layer detachment, uneven coating, and "island" growth from the root.

[0021] (2) A pioneering "swelling-equilibrium" pre-dispersion process strategy was developed to establish batch stability and coating uniformity. Addressing the issue of polymer layer shrinkage and deactivation in the dried / semi-dried state of the modified filter cake, this invention introduces a specific "20-90 min" pre-dispersion and swelling-equilibrium stage before S2 silver plating. This process allows solvent molecules to fully penetrate the modified layer, causing it to swell and re-expose the encapsulated active sites. Simultaneously, this process establishes a chemical equilibrium between the pre-reducing agent and the solvent environment, preventing excessively high local concentrations caused by the direct addition of reactants. This strategy ensures that a uniform and stable reaction microenvironment is formed on the surface of each copper powder particle, significantly improving the dispersibility of silver-coated copper powder and the batch stability of the finished product.

[0022] (3) A hydrothermal densification post-treatment technique is introduced to achieve coating defect repair and deep purification. Unlike traditional atmosphere calcination, this invention uses "160-300 °C hydrothermal treatment" in step S3. Utilizing the liquid-phase fluid environment under high temperature and pressure, the "Oswald ripening" effect and liquid-phase pressure-assisted sintering effect of silver grains are induced. This process not only promotes the migration and rearrangement of silver atoms at the microscopic level, effectively filling the micropores of the coating and significantly improving the crystallinity and density of the silver layer; at the same time, the supercritical / subcritical water environment has extremely strong penetration and dissolution capabilities, which can deeply clean away the organic polymers remaining deep in the grain boundaries, preventing them from carbonizing and causing an increase in resistance in subsequent applications. The final silver-coated copper powder has extremely low resistivity and excellent oxidation resistance.

[0023] (4) Excellent overall performance and great industrialization value. Through the whole process improvement of interface design, process control and structural optimization, the present invention prepares micron-sized spherical silver-coated copper powder that combines the high conductivity of silver with the low cost of copper; its powder has good sphericity, dense silver layer without pinholes and smooth surface, and has excellent dispersibility and filling properties in electronic pastes; it can be used as an ideal substitute for pure silver powder, significantly reducing the production cost of electronic pastes and photovoltaic pastes.

[0024] (5) This invention also provides an application of silver-coated copper powder in conductive pastes. After mixing with a resin matrix, curing agent, accelerator, coupling agent, diluent, etc., and curing at low temperature, it exhibits excellent conductivity. The sheet resistance is as low as 0.015 Ω / □. The resin matrix, when used in combination with various additives, allows for precise control of the viscosity of the conductive paste system. Simultaneously, it effectively improves the volume shrinkage characteristics during the paste curing process, significantly enhancing the interfacial bonding strength between the conductive paste and the substrate, thereby ensuring and optimizing the conductivity of the paste film. Attached Figure Description

[0025] Figure 1 SEM images of the micron-sized spherical silver-coated copper powder obtained in Example 1; a is low magnification (left), b is high magnification (right). Figure 2 SEM images of the micron-sized spherical silver-coated copper powder obtained in Example 2; a is low magnification (left), b is high magnification (right). Figure 3 SEM images of the micron-sized spherical silver-coated copper powder obtained in Example 3; a is low magnification (left), b is high magnification (right). Figure 4 SEM images of micron-sized spherical silver-coated copper powder obtained in Comparative Example 1; a is low magnification (left), b is high magnification (right). Figure 5 The image shows the XRD pattern of the micron-sized spherical silver-coated copper powder obtained in Example 2. Figure 6 EDS image of the micron-sized spherical silver-coated copper powder obtained in Example 2; a1 is the scan image of silver-coated copper, a2 is the elemental distribution map of silver-coated copper, a3 is the elemental distribution map of copper, and a4 is the elemental distribution map of silver. Figure 7 The particle size distribution of the micron-sized spherical silver-coated copper powder obtained in Example 2 is shown in the following diagrams: quantity distribution frequency diagram (left) and cumulative distribution curve (right). Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0027] In the following examples, all raw materials used were commercially available products that could be purchased directly, or were prepared using conventional techniques in the art. For example, the micron-sized spherical copper powder was purchased from Henan Hebei University Nanomaterials Engineering Research Center Co., Ltd., and its model was DN Cu-3 with a purity ≥99.9%. Example 1

[0028] The method for preparing a micron-sized spherical silver-coated copper powder includes the following steps: S1: Weigh 10 g PVA and 50 g glucose and disperse and dissolve them in 500 mL of water. Then add 16 g of micron-sized spherical copper powder and stir evenly. React at 95 °C for 2 h and filter to obtain micron-sized spherical copper powder filter cake with a bonding layer on the surface.

[0029] S2: The modified copper powder filter cake was redispersed in 200 mL of water, ultrasonically dispersed until uniform, and stirred at 50 ℃ for 30 min. 12.5 g of glucose was weighed, dissolved in 50 mL of water, stirred until uniform, and then added to the copper solution.

[0030] S3: Weigh 17 g of silver nitrate and dissolve it in water to prepare a 500 mL solution; then weigh 56 g of disodium ethylenediaminetetraacetate and dissolve it in water to prepare a 500 mL solution. Mix the two solutions thoroughly to form a silver complex solution. Slowly add the silver complex solution to the copper mixture at a rate of 20 mL / min and stir for 2 hours.

[0031] S4: After the reaction is complete, crude silver-coated copper powder is obtained. It is then subjected to hydrothermal treatment at 280℃ for 3 h. After washing and drying, micron-sized spherical silver-coated copper powder is finally obtained. Example 2

[0032] The method for preparing a micron-sized spherical silver-coated copper powder includes the following steps: S1: Weigh 5 g PVA, 25 g glucose and 25 g citric acid and disperse and dissolve them in 500 mL water. Then add 16 g micron-sized spherical copper powder and stir evenly. React at 95℃ for 4 h and filter to obtain micron-sized spherical copper powder filter cake with a bonding layer on the surface.

[0033] S2: The modified copper powder filter cake was redispersed in 200 mL of water, ultrasonically dispersed until uniform, and stirred at 50℃ for 30 min. 12.5 g of glucose was weighed, dissolved in 50 mL of water, stirred until uniform, and then added to the copper solution.

[0034] S3: Weigh 17 g of silver nitrate and dissolve it in water to prepare a 1000 mL solution. Then add 12 mL of triethylenetetramine solution (AR, 70%). The white precipitate will turn into a clear solution. Stir until homogeneous to form a silver complex solution. Slowly add the silver complex solution to the copper mixture at a rate of 20 mL / min and stir for 2 h. S4: After the reaction, crude silver-coated copper powder was obtained. It was then subjected to hydrothermal treatment at 200 °C for 3 h. After washing and drying, micron-sized spherical silver-coated copper powder was finally obtained. Example 3

[0035] The method for preparing a micron-sized spherical silver-coated copper powder includes the following steps: S1: Weigh 5 g PVA + 5 g PEG, 10 g hydrazine hydrate and 40 g citric acid and disperse and dissolve them in 500 mL of water. Then add 16 g of micron-sized spherical copper powder and stir evenly. React at 95℃ for 2 h and filter to obtain micron-sized spherical copper powder filter cake with a bonding layer on the surface.

[0036] S2: The modified copper powder filter cake was redispersed in 200 mL of water, ultrasonically dispersed until uniform, and stirred at 50℃ for 60 min. 14.1 g of potassium sodium tartrate was weighed, dissolved in 50 mL of water, stirred until uniform, and then added to the copper solution.

[0037] S3: Weigh 17 g of silver nitrate and add water to prepare a 1000 mL solution. Then add 15 mL of ammonia (AR, 25%-28%). The white precipitate will change into a clear solution. Stir until a silver complex solution is formed. Slowly add the silver nitrate solution to the copper mixture at 20 mL / min and stir for 2 h. S4: After the reaction, crude silver-coated copper powder was obtained. It was then subjected to hydrothermal treatment at 260 °C for 3 h. After washing and drying, micron-sized spherical silver-coated copper powder was finally obtained. Example 4

[0038] This embodiment provides a method for preparing micron-sized spherical silver-coated copper powder, which differs from Example 1 in that: in step S1, the modifier is hydroxyethyl cellulose and PVP (mass ratio 1:1), the pre-reducing agent is formic acid, and in step S2, the mass ratio of silver to copper powder in the silver-coated copper powder is 2:8, and the remaining steps are the same. Example 5

[0039] This embodiment provides a method for preparing micron-sized spherical silver-coated copper powder, which differs from Example 1 in that: in step S1, the modifier is gelatin and the pre-reducing agent is triethanolamine, while the other steps are the same. Example 6

[0040] This embodiment provides a method for preparing micron-sized spherical silver-coated copper powder, which differs from Example 1 in that: in step S1, the modifier is PEO and the pre-reducing agent is diethylamine, while the other steps are the same. Example 7

[0041] This embodiment provides a method for preparing micron-sized spherical silver-coated copper powder. The difference between this method and Example 1 is that the reducing agent in step S2 is ascorbic acid, and the complexing agent in step S3 is ethylenediaminetetraacetic acid. The remaining steps are the same. Example 8

[0042] This embodiment provides a method for preparing micron-sized spherical silver-coated copper powder. The difference between this method and Example 1 is that the reducing agent in step S2 is hydrazine hydrate, and the complexing agent in step S3 is sodium citrate. The remaining steps are the same.

[0043] Comparative Example 1 This comparative example provides a micron-sized spherical silver-coated copper powder. The difference between the preparation method of the micron-sized silver-coated copper powder and Example 1 is that the modification step S1 and the hydrothermal treatment step S4 are omitted in this comparative example.

[0044] Application examples This embodiment provides a method for preparing a conductive paste, the method being as follows:

[0045] S1: Weigh 10 g epoxy resin E51, 7 g methyl hexahydrophthalic anhydride, 1 g 1-cyanoethyl-2-ethyl-4-methylimidazolium, 1 g coupling agent (KH560), and 1 g phenyl glycidyl ether, and ultrasonically stir until completely dissolved to obtain an organic carrier.

[0046] S2: Mix 80 g of the micron-sized spherical silver-coated copper powder prepared in the example with 20 g of the organic carrier prepared above and disperse them evenly. Roll the mixture three times with a three-roll mill to obtain a silver-coated copper conductive paste.

[0047] S3: The conductive paste prepared above was cured at 200 °C for 30 min under nitrogen protection, and its performance was tested.

[0048] The micron-sized, near-spherical silver-coated copper powders obtained in Examples 1-4 and Comparative Example 1 were used to prepare conductive pastes according to the conductive paste formulation of the application example, and their conductivity was tested. The performance results are shown in Table 1.

[0049] Table 1 Conductivity of different embodiments

[0050] Analysis Results: As shown in Table 1, the sheet resistance of the silver-coated copper powder prepared in Example 1 of this invention, after being prepared into a conductive paste and cured at low temperature, is 0.015 Ω / □. In contrast, the sheet resistance of the silver-coated copper powder prepared in Comparative Example 1 is 0.76 Ω / □. The sharp increase in resistance indicates that the "chemical bonding + in-situ growth" mechanism of the modified copper powder before silver plating greatly enhances the interfacial bonding between the silver layer and the copper substrate, eliminating the problem of easy detachment and uneven coating of the silver layer from the root. This results in excellent conductivity and good stability of the silver-coated copper powder in conductive paste applications.

[0051] Secondly, the SEM images of Example 2, Example 1, and Example 3 are attached (see appendix). Figures 1 to 3 The comparison shows that the surface of the silver-coated copper powder in Example 2 is slightly rough and not dense; furthermore, the resistance of Example 2 is slightly higher in conductive paste applications. This is because the post-processing temperature is too low, and the rough surface leads to voids and depressions, reducing the actual contact area between particles and increasing the contact resistance. The data indicates that after high-temperature hydrothermal densification post-processing, the migration and rearrangement of silver atoms at the microscopic level effectively fills the micropores of the coating, significantly improving the crystallinity and density of the silver layer, thus resulting in lower resistance.

[0052] Figure 4 SEM images of the micron-sized spherical silver-coated copper powder obtained in Comparative Example 1 are presented. The images show that, without the PVA / glucose binder layer, the reduction of silver ions on the copper surface tends to follow an "island-like" growth pattern. Due to the lattice mismatch and surface energy difference between Cu and Ag, silver atoms tend to nucleate and aggregate locally, resulting in a discontinuous coating layer with obvious voids and exposed copper, preventing the formation of a uniform shell.

[0053] Figure 5 XRD patterns of the micron-sized near-spherical silver-coated copper powder obtained in Example 2 are shown. The figures show that the XRD curves exhibit four characteristic diffraction peaks belonging to metallic silver at 38°, 44°, 64°, and 77°, corresponding to the diffraction peaks of the (111), (200), (220), and (311) crystal planes of elemental silver, respectively; and three characteristic diffraction peaks belonging to metallic copper at 43°, 51°, and 74°, corresponding to the (111), (200), and (220) crystal planes of elemental copper, respectively. Both peak positions are consistent with those on the standard PDF card. No other oxide peaks are present, indicating good crystallinity.

[0054] Figure 6EDS images of the micron-sized spherical silver-coated copper powder obtained in Example 2 are presented. As can be seen from the figures, the copper element signal is mainly concentrated inside the particles and the signal intensity is relatively weak, while the silver element signal is uniformly and continuously distributed on the entire surface of the copper particles without any obvious blank or interrupted areas, which proves that the silver coating layer is complete and continuous and the overall coating effect is good.

[0055] Figure 7 The particle size distribution of the micron-sized near-spherical silver-coated copper powder obtained in Example 2 is shown. The figure shows that the prepared silver-coated copper powder has a relatively concentrated particle size distribution, with a median D50 particle size of 2.8 μm, and D10 and D90 values ​​of 2.3 μm and 3.4 μm, respectively. The narrow particle size distribution indicates that the powder particles are uniform in size, well-dispersed, and exhibit no obvious agglomeration. This narrow particle size distribution is beneficial for the powder to form a dense and continuous conductive network in the conductive slurry, reducing contact defects caused by excessive particle size differences and positively impacting the material's conductivity.

[0056] In summary, the silver-coated copper powder prepared using the technical solution described in this invention has a dense coating structure, low resistance, and excellent oxidation resistance. This invention also provides a novel preparation process for silver-coated copper powder used in conductive pastes. This process and the resulting silver-coated copper powder have broad practical application value and industrialization prospects in the field of conductive pastes.

Claims

1. A method for preparing micron-sized spherical silver-coated copper powder, characterized in that, Includes the following steps: S1. Disperse micron-sized spherical copper powder in a modified solution and react at 60-95 °C for 0.5-4 h. Separate the solid and liquid to obtain a micron-sized spherical copper powder filter cake with a uniform adhesive layer on the surface. S2. Disperse the micron-sized spherical copper powder filter cake with a uniform bonding layer on the surface in a solvent and react at 20-75 ℃ for 20-90 min. Then add a reducing agent solution and a silver source solution and continue the reaction for 0.5-2 h to obtain micron-sized spherical silver-coated copper powder crude product. S3. The prepared micron-sized spherical silver-coated copper powder crude product is densified, and then washed and dried to obtain the micron-sized spherical silver-coated copper powder.

2. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The modified solution in step S1 is composed of a modifier and a pre-reducing agent; wherein the modifier is one or a combination of two or more of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, polyethylene oxide, gelatin and hydroxyethyl cellulose; the pre-reducing agent includes one or a combination of two or more of hydrazine hydrate, diethylamine, triethanolamine, citric acid, glucose, formaldehyde and formic acid.

3. The method for preparing micron-sized spherical silver-coated copper powder according to claim 2, characterized in that, The mass ratio of the micron-sized spherical copper powder to the modifier is 4:1 to 1:1; the mass ratio of the micron-sized spherical copper powder to the pre-reducing agent is 2:5 to 2:

7.

4. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The solvent mentioned in step S2 includes one or more of water, ethanol, ethylene glycol, and ethylene glycol monomethyl ether; the reducing agent includes one or a combination of two or more of ascorbic acid, glucose, formaldehyde, potassium sodium tartrate, and hydrazine hydrate; the molar ratio of the reducing agent to silver ions is 1:2-2:

1.

5. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, In step S2, the mass ratio of silver to copper powder in the silver-coated copper powder is 1:9-1:

1.

6. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The silver source solution mentioned in step S2 includes silver nitrate and a complexing agent; wherein the complexing agent includes one or more of ammonia, triethylenetetramine, ethylenediaminetetraacetic acid, sodium citrate, and disodium ethylenediaminetetraacetate.

7. The method for preparing micron-sized spherical silver-coated copper powder according to claim 6, characterized in that, The concentration of silver nitrate is 0.05 mol / L to 1 mol / L; the molar ratio of silver ions to complexing agent is 2:1 to 2:

4.

8. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The densification treatment in step S3 is a hydrothermal treatment at 160-300 °C for 0.5-8 h.

9. Micron-sized spherical silver-coated copper powder prepared by any one of the preparation methods described in claims 1-8.

10. The application of the micron-sized spherical silver-coated copper powder of claim 9 in the production of electronic silver-coated copper conductive paste and photovoltaic paste.

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