Composite silver powder with surface nano-coating structure and preparation method of composite silver powder

Abstract

The invention discloses composite silver powder with a surface nano-coating structure and a preparation method of the composite silver powder. The composite silver powder comprises a micron-sized spherical silver powder core and a nano-silver shell layer coating the surface of the core, and the nano-silver shell layer comprises nano-silver particles making contact with one another; the D50 particle size of the core body is 1-2 microns, and the particle size D50 of the nano-silver particles is 10-100 nm; the composite spherical silver powder with micron-sized silver coated with nano-silver is prepared through a liquid phase chemical reduction method, the D50 particle size of the composite spherical silver powder is 1.67-1.70 microns, the tap density can reach 5.94 g / cm < 3 >, the specific surface area can reach 0.47 m < 2 > / g, and compared with micron-sized spherical silver powder of a single structure, the conductive performance of the silver powder can be improved by 32%, and the sintering activity is higher.

Description

Technical Field

[0001] This invention relates to the field of silver powder preparation technology, and in particular to a surface nano-coated composite silver powder and its preparation method. Background Technology

[0002] Conductive silver powder, as a core functional material in electronic pastes, is widely used in photovoltaic cells, printed circuit boards (PCBs), flexible electronics, and other fields. Currently, micron-sized spherical silver powder has become the mainstream choice due to its good flowability and printability. However, its high sintering temperature and reliance on point contacts for the conductive network result in insufficient electrode conductivity and sintering activity, making it difficult to meet the requirements of photovoltaic silver pastes for BC cells.

[0003] To address these issues, some research has turned to silver nanoparticles, leveraging their high specific surface area and low-temperature sintering properties to improve performance. However, silver nanoparticles are prone to agglomeration, and their preparation processes are complex and costly, making large-scale application difficult. Furthermore, simply mixing micron-sized and nano-sized silver powders (physical mixing) cannot achieve effective synergy; the nano-silver is prone to becoming free or oxidized, which reduces the stability of the slurry.

[0004] In view of the shortcomings of existing technologies, there is an urgent need to develop a new composite silver powder structure that can retain the processing advantages of micron-sized silver powder while improving its sintering activity and conductivity. Summary of the Invention

[0005] In view of this, this application provides a surface nano-coated composite silver powder and its preparation method, which is used to solve the problem of how to simultaneously improve the conductivity and sintering activity of micron-sized silver powder.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a surface nano-coated composite silver powder, which includes a micron-sized spherical silver powder core and a nano-silver shell layer coated on the surface of the core. The nano-silver shell layer includes nano-silver particles in contact with each other. The D50 particle size of the core is 1-2 μm, and the particle size D50 of the nano-silver particles is 10-100 nm.

[0007] Secondly, this application provides a method for preparing surface nano-coated composite silver powder, comprising the following steps: S1. Micron-sized spherical silver powder is added to an aqueous solution of a surfactant to obtain a dispersion of micron-sized spherical silver powder; silver salt is added to an aqueous solution of the dispersant, and then ammonia is added to obtain a silver ammonia solution; S2. The aqueous solution of the reducing agent and the silver ammonia solution are simultaneously and uniformly added to the micron-sized spherical silver powder dispersion to carry out a liquid-phase reduction reaction and obtain a mixture; S3. Add the alcohol solution of the coating agent to the mixture and stir to react, thus obtaining the surface nano-coated composite silver powder.

[0008] Preferably, the temperature of the aqueous solution of the surfactant is 35-40°C, and the pH value of the aqueous solution of the surfactant is 10-12.

[0009] Preferably, the surfactant includes one or more of polyvinylpyrrolidone, ethanol, glycerol, polyethylene glycol, Tween series, Span series, silane coupling agent, sodium citrate, oleic acid, cetyltrimethylammonium bromide, and lecithin; the mass of the surfactant is 20-30% of the mass of the micron-sized spherical silver powder.

[0010] Preferably, the dispersant comprises polyvinylpyrrolidone, and the mass of the dispersant is 10-20% of the mass of the silver salt; the silver salt comprises silver nitrate.

[0011] Preferably, the reducing agent includes one or more of ascorbic acid, glucose, hydrazine hydrate, sodium borohydride, formaldehyde, and sodium hypophosphite; the mass of the reducing agent is 60-70% of the mass of the silver salt.

[0012] Preferably, the coating agent includes one or more of oleic acid, lauric acid, and stearic acid; the mass of the coating agent is 0.5-2% of the sum of the mass of the silver salt and the micron-sized spherical silver powder.

[0013] Preferably, the addition time for both the aqueous solution of the reducing agent and the silver ammonia solution is 30-40 min, and the temperature of the liquid-phase reduction reaction is 35-40℃.

[0014] Preferably, the stirring reaction time is 5-10 minutes and the stirring reaction temperature is 35-40℃.

[0015] Preferably, the mass ratio of micron-sized spherical silver powder to silver salt is 100:15-35.

[0016] The beneficial effects of this application are as follows: This application prepares composite spherical silver powder with nano-silver coated with micron-sized silver by liquid-phase chemical reduction method, with a D50 particle size of 1.67-1.70 μm and a tap density of up to 5.94 g / cm³. 3 Its specific surface area can reach 0.47 m². 2 / g, the silver powder of this application has a 32% higher conductivity than micron-sized spherical silver powder with a single structure, and also has higher sintering activity. Attached Figure Description

[0017] Figure 1 SEM image (×5000x) of the silver powder obtained in Example 1. Figure 2 SEM image (×5000x) of the silver powder obtained in Example 2. Figure 3 SEM image (×5000x) of the silver powder obtained in Example 3. Figure 4 SEM image of micron-sized spherical silver powder (×5000x). Detailed Implementation

[0018] 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.

[0019] This application provides a surface nano-coated composite silver powder, which includes a micron-sized spherical silver powder core and a nano-silver shell layer coated on the surface of the core. The nano-silver shell layer includes nano-silver particles in contact with each other. The D50 particle size of the core is 1-2 μm, and the particle size D50 of the nano-silver particles is 10-100 nm.

[0020] In this application, a composite structure of nano-silver and micron-sized silver powder is formed. The micron-sized core provides structural support, while the nano-shell enhances surface activity. The two are tightly coated by liquid-phase reduction. Compared with single nano-silver or single micron-sized silver powder, its conductivity and sintering activity are improved. The specific mechanism is as follows: the sintering temperature of nano-silver is much lower than that of micron-sized silver powder. Therefore, the sintering temperature of the composite silver powder is lower than that of single micron-sized silver powder. Furthermore, during sintering, the nano-silver in the composite silver powder with nano-coating structure of this application forms additional conductive pathways. The nano-silver particles play a bridging role, increasing the conductive pathways between spherical silver powders in addition to point contact, thereby improving the conductivity of the silver electrode.

[0021] The size and surface effects of the nano-silver in this application improve electron mobility and reduce interfacial resistance; while the micron core helps maintain the good flowability and printability of silver powder, and using micron-sized silver powder as the core overcomes the disadvantage of easy agglomeration of single nano-silver powder.

[0022] This application uses an aqueous solution reaction to avoid introducing excessive alcohol into the entire system, thereby avoiding the safety hazard of excessive ethanol causing volatilization and explosion.

[0023] The purpose of introducing nano-silver particles in this application is to improve activity, because the inherent properties of nano-silver are high activity and high specific surface area. The smaller the particle size, the higher the activity and specific surface area. Introducing nano-silver into the slurry can effectively reduce the sintering temperature of the slurry.

[0024] In some embodiments, the micron-sized spherical silver powder is prepared in-house, and the preparation method is as follows: Ingredient preparation stage: 320g silver nitrate was dissolved in 1.8L water to prepare an oxidizing agent solution; 200g ascorbic acid was dissolved in 1.8L water to prepare a reducing agent solution; 56g polyvinylpyrrolidone was dissolved in 2.2L water to prepare a dispersant solution; 1.5g oleic acid was dissolved in 40ml anhydrous ethanol to prepare a coating agent solution. Reaction stage: The reducing agent solution and oxidizing agent solution are simultaneously added to the dispersant solution at the same rate through a peristaltic pump within 5 minutes; after the reducing agent solution and oxidizing agent solution are added, the coating agent solution is added and stirring is continued for 5 minutes; after solid-liquid separation process, wet silver powder is obtained, and the wet silver powder is dried at 90℃ for 8 hours, and then subjected to crushing and air milling post-processing to obtain the micron-sized spherical silver powder used in this film.

[0025] This application provides a method for preparing surface nano-coated composite silver powder, comprising the following steps: S1. Micron-sized spherical silver powder is added to an aqueous solution of a surfactant to obtain a dispersion of micron-sized spherical silver powder; silver salt is added to an aqueous solution of the dispersant, and then ammonia is added to obtain a silver ammonia solution; S2. The aqueous solution of the reducing agent and the silver ammonia solution are simultaneously and uniformly added to the micron-sized spherical silver powder dispersion to carry out a liquid-phase reduction reaction and obtain a mixture; S3. Add the alcohol solution of the coating agent to the mixture and stir to react, thus obtaining the surface nano-coated composite silver powder.

[0026] This application first disperses the micron-sized silver powder core, then simultaneously adds silver ammonia solution and a reducing agent to ensure that the nano-silver is generated in situ and uniformly coated on the surface of the micron-sized silver (rather than free agglomeration), forming a tight core-shell structure. After the nano-silver is generated, coating agents such as oleic acid are added to stabilize the nano-silver shell layer and prevent particle migration or oxidation during sintering. In this application, the in-situ coating of nano-silver reduces interface defects, and the nano-silver particles preferentially melt during sintering, filling the gaps between the micron-sized silver particles and forming a continuous conductive network. Therefore, the conductivity and sintering activity of a single micron-sized spherical silver powder are improved.

[0027] In some embodiments, the temperature of the aqueous solution of the surfactant is 35-40°C, and the pH value of the aqueous solution of the surfactant is 10-12.

[0028] In this embodiment, the pH is within a defined range, meeting the particle size requirements for preparing silver nanoparticles and avoiding Ag... + Premature reduction leads to uneven nucleation. Within a defined temperature range, it is beneficial to optimize the reduction reaction rate and avoid excessive growth or aggregation of nano-silver caused by high temperature. However, exceeding the pH or temperature range specified in this application will result in insignificant improvement in sintering activity and conductivity.

[0029] In some embodiments, the surfactant includes one or more of polyvinylpyrrolidone, ethanol, glycerol, polyethylene glycol, Tween series, Span series, silane coupling agent, sodium citrate, oleic acid, cetyltrimethylammonium bromide, and lecithin; the mass of the surfactant is 20-30% of the mass of the micron-sized spherical silver powder.

[0030] In this embodiment, the steric hindrance effect of the surfactant prevents the agglomeration of silver nanoparticles, while its hydrophilic groups maintain the stability of the aqueous phase. The surfactant adsorbs on the surface of the micron-sized silver, reduces the interfacial tension of the solution, avoids the individual nucleation of silver nanoparticles, and promotes the directional adhesion of silver nanoparticles. If the amount used is too small, it will lead to uneven dispersion of silver nanoparticles. If the amount used is too large, it will lead to higher organic residues on the surface of the silver powder and abnormally increased viscosity, which are all negative effects on sintering activity and conductivity.

[0031] In some embodiments, the dispersant comprises polyvinylpyrrolidone, and the mass of the dispersant is 10-20% of the mass of the silver salt; the silver salt comprises silver nitrate.

[0032] In this embodiment, the dispersant helps to regulate the reduction rate, ensuring that the size of the silver nanoparticles is between 10-100 nm. If the silver nanoparticles are too small, they are prone to sintering but also oxidation; if they are too large, their activity will decrease. The amount of dispersant helps to control the thickness of the silver nanoparticle shell. If too much is used, the silver nanoparticle layer will be too thick, leading to an increase in free silver nanoparticles, which is detrimental to improving conductivity. The thicker the shell, the higher the temperature required for sintering, and the lower the improvement in electrical performance.

[0033] In some embodiments, the reducing agent includes one or more of ascorbic acid, glucose, hydrazine hydrate, sodium borohydride, formaldehyde, and sodium hypophosphite; the mass of the reducing agent is 60-70% of the mass of the silver salt.

[0034] In some embodiments, the coating agent includes one or more of oleic acid, lauric acid, and stearic acid; the mass of the coating agent is 0.5-2% of the sum of the mass of the silver salt and the micron-sized spherical silver powder.

[0035] In this embodiment, the long-chain carboxylic acid of the coating agent forms chemical bonds with the surface of the nano-silver to prevent the nano-silver from oxidizing or migrating before sintering, thereby improving conductivity. If the amount of coating agent is too small, the coating will be incomplete, and excessive coating will hinder the conductive contact between the nano-silver and the micron-sized silver. In this application, the role of the coating agent is to coat the nano-silver particles modified on the surface of the micron-sized silver powder with the micron-sized silver powder to form a whole, making the structure more stable. In this application, adding the coating agent during the feeding stage (compared to the liquid phase reduction stage) will affect the coating effect of the nanoparticles and increase the burn-off of the silver powder.

[0036] In some embodiments, the addition time for both the aqueous solution of the reducing agent and the silver ammonia solution is 30-40 min, and the temperature of the liquid-phase reduction reaction is 35-40℃.

[0037] In this embodiment, the slow feeding allows the nano-silver to be coated layer by layer, forming a dense shell. The uniform addition of the reducing agent and silver ammonia over 30-40 minutes is beneficial for the uniform coating of the nano-silver and avoids the agglomeration of the nano-silver.

[0038] In some embodiments, the stirring reaction lasts for 5-10 minutes and the stirring reaction temperature is 35-40°C.

[0039] In some embodiments, the mass ratio of micron-sized spherical silver powder to silver salt is 100:15-35.

[0040] In this embodiment, if the amount of silver salt is too small, the nano-silver coating rate will be low and the sintering activity will be insufficient. If the amount of silver salt is too large, it will cause the nano-silver to become free, reduce the tap density, and decrease the conductivity.

[0041] The following specific embodiments further illustrate this solution.

[0042] Raw material preparation In the following examples and comparative examples, the preparation method of micron-sized spherical silver powder is as follows: Dissolve 320g of silver nitrate in 1200ml of water and stir until homogeneous to obtain a silver nitrate solution; dissolve 173g of ascorbic acid in 1200ml of water and stir until homogeneous, then add a pH adjuster to adjust the pH to 7 to obtain a reducing agent solution; add 45g of polyvinylpyrrolidone to 1.76L of deionized water and stir until homogeneous, then add a pH adjuster to adjust the pH to 6, then add 0.5g of nano-silver colloid and stir until dissolved to obtain a nano-silver-dispersant mixture; add 1g of oleic acid to a beaker, add 10ml of anhydrous ethanol and stir until dissolved to obtain a coating agent solution; First, add the coating agent solution to the nano-silver-dispersant mixture and stir for 30 seconds. Then, add the silver nitrate solution and reducing agent solution to the nano-silver-dispersant mixture simultaneously. Start stirring and set the speed to 550 rpm. After the addition is completed, continue the reaction for 5 minutes. After the reaction is completed, a silver powder suspension is obtained. The obtained silver powder suspension was subjected to solid-liquid separation, and then washed and stirred with anhydrous ethanol at a stirring rate of 550 rpm for 10 min. This process was repeated until the conductivity of the washing solution was <20 μS / m, yielding wet silver powder. The wet silver powder was then dried at 80℃ for 6 h. After drying and post-treatment, micron-sized spherical silver powder was obtained, as shown in the SEM image. Figure 4 As shown.

[0043] The preparation method of the nano-silver colloid is as follows: Solution preparation: Solution A is 1 mmol / L AgNO3 aqueous solution (100 mL), Solution B is 1 mmol / L NaBH4 aqueous solution (cooled in an ice bath), and Solution C is 1% trisodium citrate aqueous solution (stabilizer). Preparation of silver colloid by reduction: Under ice bath and vigorous stirring, solution B (NaBH4) is quickly added to solution A (AgNO3). The solution color will quickly turn yellow or brown, indicating the formation of silver nanoparticles. Immediately add an appropriate amount of solution C (trisodium citrate, such as 1 mL) and continue stirring for 15-30 minutes. Citrate ions are adsorbed on the surface of silver particles, providing negative charge and stability, resulting in clear, uniformly colored silver nanoparticle colloid.

[0044] Example 1 A composite silver powder with a surface nano-coated structure includes a micron-sized spherical silver powder core and a nano-silver shell layer coated on the surface of the core. The nano-silver shell layer includes nano-silver particles in contact with each other. The D50 particle size of the core is 1-2 μm, and the particle size D50 of the nano-silver particles is 10-100 nm.

[0045] The preparation method of surface nano-coated composite silver powder includes the following steps: S1. Add 20g of Tween-20 to 800g of water at 35℃, stir well, then add alkali to adjust the pH to 12 to obtain an aqueous solution of surfactant. Add 100g of micron-sized spherical silver powder to the surfactant aqueous solution and continue stirring and dispersing for 30min to obtain a micron-sized spherical silver powder dispersion. Take 3g of polyvinylpyrrolidone and add it to 150g of deionized water. After dissolving, obtain an aqueous solution of dispersant. Add 15g of silver nitrate to the aqueous solution of dispersant, then add ammonia water until the solution becomes clear to obtain a silver ammonia solution. S2. Take 9g of ascorbic acid and add it to 150g of deionized water. After dissolution, an aqueous solution of reducing agent is obtained. The aqueous solution of reducing agent and silver ammonia solution are added simultaneously and uniformly to the micron-sized spherical silver powder dispersion. The addition time is 30min. The liquid phase reduction reaction is carried out at 35℃ to obtain a mixture. S3. Add 1.15g of oleic acid to 20ml of anhydrous ethanol and stir until homogeneous to obtain an alcoholic solution of the coating agent. Add the alcoholic solution of the coating agent to the mixture and stir at 35℃ for 5min to obtain a silver powder suspension. Perform solid-liquid separation on the obtained silver powder suspension and wash and stir it with anhydrous ethanol at a stirring speed of 550rpm for 10min. Repeat the above operation until the conductivity of the washing solution is <20μS / m to obtain wet silver powder. Dry the wet silver powder at 80℃ for 6h. After drying and post-treatment, the surface nano-coated composite silver powder is obtained. Its SEM image is shown below. Figure 1 As shown.

[0046] Example 2 A composite silver powder with a surface nano-coated structure includes a micron-sized spherical silver powder core and a nano-silver shell layer coated on the surface of the core. The nano-silver shell layer includes nano-silver particles in contact with each other. The D50 particle size of the core is 1-2 μm, and the particle size D50 of the nano-silver particles is 10-100 nm.

[0047] The preparation method of surface nano-coated composite silver powder includes the following steps: S1. Add 20g of polyethylene glycol to 800g of water at 35℃, stir until homogeneous, then add alkali to adjust the pH to 12 to obtain an aqueous solution of surfactant. Add 100g of micron-sized spherical silver powder to the surfactant aqueous solution and continue stirring and dispersing for 30min to obtain a micron-sized spherical silver powder dispersion. Take 2.5g of polyvinylpyrrolidone and add it to 150g of deionized water. After dissolution, obtain an aqueous solution of dispersant. Add 25g of silver nitrate to the aqueous solution of dispersant, then add ammonia water until the solution becomes clear to obtain a silver ammonia solution. S2. Take 9g of hydrazine hydrate and add it to 150g of deionized water. After dissolution, an aqueous solution of reducing agent is obtained. The aqueous solution of reducing agent and silver ammonia solution are added simultaneously and uniformly to the micron-sized spherical silver powder dispersion. The addition time is 30min. The liquid phase reduction reaction is carried out at 35℃ to obtain a mixture. S3. Add 1.25g of lauric acid to 20ml of anhydrous ethanol and stir until homogeneous to obtain an alcoholic solution of the coating agent. Add the alcoholic solution of the coating agent to the mixture and stir at 35℃ for 5min to obtain a silver powder suspension. Perform solid-liquid separation on the obtained silver powder suspension and wash and stir it with anhydrous ethanol at a stirring speed of 550rpm for 10min. Repeat the above operation until the conductivity of the washing solution is <20μS / m to obtain wet silver powder. Dry the wet silver powder at 80℃ for 6h. After drying and post-treatment, the surface nano-coated composite silver powder is obtained. Its SEM image is shown below. Figure 2 As shown.

[0048] Example 3 A composite silver powder with a surface nano-coated structure includes a micron-sized spherical silver powder core and a nano-silver shell layer coated on the surface of the core. The nano-silver shell layer includes nano-silver particles in contact with each other. The D50 particle size of the core is 1-2 μm, and the particle size D50 of the nano-silver particles is 10-100 nm.

[0049] The preparation method of surface nano-coated composite silver powder includes the following steps: S1. Add 20g of ethanol to 800g of water at 35℃, stir until homogeneous, then add alkali to adjust the pH to 12 to obtain an aqueous solution of surfactant. Add 100g of micron-sized spherical silver powder to the surfactant aqueous solution and continue stirring and dispersing for 30min to obtain a micron-sized spherical silver powder dispersion. Take 7g of polyvinylpyrrolidone and add it to 150g of deionized water. After dissolution, obtain an aqueous solution of dispersant. Add 35g of silver nitrate to the aqueous solution of dispersant, then add ammonia until the solution becomes clear to obtain a silver ammonia solution. S2. Take 9g of ascorbic acid and add it to 150g of deionized water. After dissolution, an aqueous solution of reducing agent is obtained. The aqueous solution of reducing agent and silver ammonia solution are added simultaneously and uniformly to the micron-sized spherical silver powder dispersion. The addition time is 40min. Liquid phase reduction reaction is carried out at 35℃ to obtain a mixture. S3. Add 1.15g of lauric acid to 20ml of anhydrous ethanol and stir until homogeneous to obtain an alcoholic solution of the coating agent. Add the alcoholic solution of the coating agent to the mixture and stir at 35℃ for 5min to obtain a silver powder suspension. Perform solid-liquid separation on the obtained silver powder suspension and wash and stir it with anhydrous ethanol at a stirring speed of 550rpm for 10min. Repeat the above operation until the conductivity of the washing solution is <20μS / m to obtain wet silver powder. Dry the wet silver powder at 80℃ for 6h. After drying and post-treatment, the surface nano-coated composite silver powder is obtained. Its SEM image is shown below. Figure 3 As shown.

[0050] Testing and Evaluation The silver powder in Examples 1-3 and Comparative Example 1 was tested. Particle size was determined according to GB / T 19077-2016 "Particle Size Analysis - Laser Diffraction Method". Loose packing density and tapped density were tested according to GB / T 1479.1-2011 "Loose Packing Density Analyzer / Funnel Method" and GB / T 5162-2021 "Tapped Density Analyzer / Tap Method", respectively. Specific surface area was measured according to GB / T13390-2008 "Specific Surface Area Analyzer / Nitrogen Adsorption Method". The burn-off test method involved taking a certain mass of silver powder sample (accurate to 0.1 g / L). The initial mass (m0) was recorded. The sample was placed in an inert atmosphere and calcined at a set temperature (e.g., 538℃) for 2 hours to simulate the high-temperature exposure conditions in the actual process. After cooling, the mass (m1) of the calcined sample was weighed, and the burn-off rate was calculated, i.e., burn-off rate (%) = (m0−m1) / m0×100%. The results are shown in Table 1.

[0051] Table 1. Test results of the physical properties of silver powder

[0052] The silver powder obtained from different embodiments and comparative examples was made into silver paste, which was then printed onto silicon wafers using a screen printing machine. After sintering, it was prepared into silver electrodes. The volume resistivity of the silver 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 2.

[0053] Table 2. Test results of silver electrode

[0054] This invention prepares a composite silver powder with a nano-coated structure. Compared with single micron-sized spherical silver powder, this composite silver powder has high conductivity and high sintering activity after the introduction of nano-silver. Compared with single nano-silver powder, it can also significantly reduce production costs.

[0055] Through comparison of the above embodiments and comparative examples, the composite silver powder with nano-coated structure prepared by the present invention achieves a significant improvement in conductivity. The principle is that the sintering temperature of nano-silver is much lower than that of micron-sized silver powder. Therefore, the sintering temperature of the composite silver powder composed of the two is lower than that of single micron-sized silver powder. Furthermore, during sintering, the nano-silver in the composite silver powder with nano-coated structure prepared by the present invention forms additional conductive pathways, increasing the conductive pathways between spherical silver powders in addition to point contact, thereby improving the conductivity of the silver electrode. Therefore, the composite silver powder with nano-coated structure has better sintering activity and conductivity than single micron-sized spherical silver powder.

[0056] The nano-coated composite silver powder prepared in Example 1 exhibits good electrical conductivity, while the volume resistivity of Examples 2 and 3 did not show a significant reduction because the content of the nano-silver particles was too high. (According to the appendix...) Figure 2 and attached Figure 3 As can be seen, a large number of nano-silver particles are in a free state, and only a small amount of nano-silver forms a composite structure with micron-sized spherical silver powder. Moreover, a relatively serious nano-silver agglomeration phenomenon can be seen in the attached figure. These phenomena will cause the conductivity of the silver electrode to deteriorate. Therefore, the performance in Example 1 is the one with the greatest improvement in conductivity among the examples, which is about 32% higher than that of micron-sized spherical silver powder.

[0057] 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 composite silver powder with a surface nano-coated structure, characterized in that, It includes a micron-sized spherical silver powder core and a nano-silver shell layer covering the surface of the core, wherein the nano-silver shell layer includes nano-silver particles in contact with each other; the D50 particle size of the core is 1-2 μm, and the particle size D50 of the nano-silver particles is 10-100 nm.

2. A method for preparing surface nano-coated composite silver powder as described in claim 1, characterized in that, Includes the following steps: Micron-sized spherical silver powder is added to an aqueous solution of a surfactant to obtain a dispersion of micron-sized spherical silver powder; silver salt is added to an aqueous solution of the dispersant, and then ammonia is added to obtain a silver ammonia solution. The aqueous solution of the reducing agent and the silver ammonia solution were simultaneously and uniformly added to the micron-sized spherical silver powder dispersion to carry out a liquid-phase reduction reaction and obtain a mixture. An alcoholic solution of the coating agent is added to the mixture, and the mixture is stirred to react, thereby obtaining the surface nano-coated composite silver powder.

3. The preparation method according to claim 2, characterized in that, The temperature of the aqueous solution of the surfactant is 35-40℃, and the pH value of the aqueous solution of the surfactant is 10-12.

4. The preparation method according to claim 2, characterized in that, The surfactant includes one or more of polyvinylpyrrolidone, ethanol, glycerol, polyethylene glycol, Tween series, Span series, silane coupling agent, sodium citrate, oleic acid, cetyltrimethylammonium bromide, and lecithin; the mass of the surfactant is 20-30% of the mass of the micron-sized spherical silver powder.

5. The preparation method according to claim 2, characterized in that, The dispersant includes polyvinylpyrrolidone, and the mass of the dispersant is 10-20% of the mass of the silver salt; the silver salt includes silver nitrate.

6. The preparation method according to claim 2, characterized in that, The reducing agent includes one or more of ascorbic acid, glucose, hydrazine hydrate, sodium borohydride, formaldehyde, and sodium hypophosphite; the mass of the reducing agent is 60-70% of the mass of the silver salt.

7. The preparation method according to claim 2, characterized in that, The coating agent includes one or more of oleic acid, lauric acid, and stearic acid; the mass of the coating agent is 0.5-2% of the sum of the mass of the silver salt and the micron-sized spherical silver powder.

8. The preparation method according to claim 2, characterized in that, The addition time for both the aqueous solution of the reducing agent and the silver ammonia solution is 30-40 min, and the temperature of the liquid-phase reduction reaction is 35-40℃.

9. The preparation method according to claim 2, characterized in that, The stirring reaction lasts for 5-10 minutes and the stirring reaction temperature is 35-40℃.

10. The preparation method according to claim 2, characterized in that, The mass ratio of the micron-sized spherical silver powder to the silver salt is 100:15-35.

Images