High-activity surface nanocrystallization spherical silver powder and preparation and application thereof

Abstract

The invention discloses high-activity surface nanocrystallization spherical silver powder and preparation and application thereof.The preparation method comprises the following steps that micron-sized spherical silver powder is added into a propylene glycol aqueous solution, and a first mixed solution is obtained; adding ammonia water into the silver salt aqueous solution to obtain a second mixed solution; and a reducing agent aqueous solution and the second mixed solution are added into the first mixed solution at the same time, an alcoholic solution containing a fatty acid type coating agent is added after charging is completed, stirring reaction continues, solid-liquid separation, washing and drying are conducted, and the high-activity surface nanocrystallization spherical silver powder is obtained. The micron-sized spherical silver powder is subjected to surface nanocrystallization modification through a step-by-step liquid phase reduction and coating process, the micron-sized spherical silver powder serves as a core, a uniform and compact nano-particle layer is constructed on the surface of the core, on the premise that the tap density is not affected, the specific surface area of the silver powder is remarkably increased through the structure, the burning loss is low, and the service life of the silver powder is prolonged. And the sintering activity of the silver powder is greatly improved, and slurry with excellent conductivity can be obtained subsequently.

Description

Technical Field

[0001] This invention relates to the field of silver powder technology, and in particular to a highly active surface nano-sized spherical silver powder and its preparation and application. Background Technology

[0002] In the current wave of rapid development in photovoltaic technology, back-contact (BC) cells, with their high conversion efficiency due to the absence of grid lines on the front side, have become an important direction for industrial technology iteration. As a key material in BC cell manufacturing, the performance of conductive silver paste directly determines the ohmic contact quality and final power generation efficiency of the cell. Silver powder, as the core functional phase of conductive silver paste, has a decisive influence on the printability, sintering behavior, and conductivity of the paste due to its morphology, particle size distribution, and surface properties. Therefore, developing special silver powders that combine excellent printability and superior sintering activity is one of the core material challenges in overcoming the technological bottlenecks of BC cells.

[0003] Currently, the mainstream methods for preparing silver powder in the industry mainly include physical and chemical methods. Liquid-phase chemical reduction, due to its advantages of simple operation and low cost, has become the preferred process for large-scale production. This method reduces silver ions to elemental silver using a reducing agent and uses surfactants such as polyvinylpyrrolidone (PVP) to control particle morphology and dispersibility. However, the silver powder prepared by this method has low surface energy and insufficient sintering activity; while increasing the specific surface area of ​​the silver powder to improve sintering activity often leads to a deviation from spherical particle morphology, decreased dispersion stability, and loss of tap density, making it difficult to meet the requirements of low-temperature sintering and high conductivity for BC batteries.

[0004] Therefore, it is necessary to provide a solution to improve the sintering activity of silver powder while ensuring tap density. Summary of the Invention

[0005] In view of this, this application provides a highly active surface nano-sized spherical silver powder and its preparation and application, which is used to solve the problem of how to improve the sintering activity of silver powder while ensuring tap density.

[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 highly active surface-nanosized spherical silver powder, comprising the following steps: Micron-sized spherical silver powder was added to an aqueous solution of propylene glycol to obtain a first mixture; ammonia was added to an aqueous solution of silver salt to obtain a second mixture. The reducing agent aqueous solution and the second mixture are added to the first mixture simultaneously. After the addition is complete, an alcohol solution containing a fatty acid coating agent is added, and the reaction is continued by stirring. Then, solid-liquid separation, washing, and drying are performed to obtain highly active surface nano-sized spherical silver powder.

[0007] Preferably, the fatty acid type coating agent includes one or more of oleic acid, lauric acid, and stearic acid.

[0008] Preferably, the feeding time is 3-6 minutes; the stirring time is 3-5 minutes.

[0009] Preferably, the reducing agent includes one or more of ascorbic acid, glucose, hydrazine hydrate, formaldehyde, and sodium hypophosphite.

[0010] Preferably, the silver salt is a nitrate.

[0011] Preferably, the mass of the reducing agent is 70-75% of the mass of the silver salt; the mass ratio of the silver salt to the micron-sized spherical silver powder is 15-35:100.

[0012] Preferably, the mass of the coating agent is 0.5-2% of the micron-sized spherical silver powder.

[0013] Preferably, the mass ratio of propylene glycol aqueous solution to micron-sized spherical silver powder is 3:1, and the concentration of propylene glycol aqueous solution is 16.7-100%.

[0014] Secondly, this application provides a highly active surface-nanosized spherical silver powder.

[0015] Thirdly, this application provides an application of highly active surface-nanosized spherical silver powder in the field of photovoltaic electronic components.

[0016] The beneficial effects of this application are as follows: This application uses a stepwise liquid-phase reduction and coating process to perform surface nano-modification on micron-sized spherical silver powder. With micron-sized spherical silver powder as the core, a uniform and dense layer of nanoparticles is constructed on the surface of the core to form a core-shell structure. Without affecting the tap density, this structure significantly increases the specific surface area of ​​the silver powder and has low burn-off, which greatly improves the sintering activity of the silver powder and helps to obtain a paste with excellent conductivity in the subsequent process. Attached Figure Description

[0017] Figure 1 Here is a SEM image of the silver powder obtained in Example 2; Figure 2 SEM image of the silver powder obtained in Comparative Example 1; Figure 3 This is a SEM image of the silver powder obtained in Comparative Example 3. 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 method for preparing highly active surface-nanosized spherical silver powder, comprising the following steps: S1. Micron-sized spherical silver powder is added to a propylene glycol aqueous solution to obtain a first mixture; ammonia is added to a silver salt aqueous solution to obtain a second mixture; S2. Add the reducing agent aqueous solution and the second mixture to the first mixture simultaneously. After the addition is complete, add the alcohol solution containing the fatty acid coating agent, continue stirring the reaction, and then separate the solid and liquid, wash and dry to obtain highly active surface nano-sized spherical silver powder.

[0020] This application employs a stepwise liquid-phase reduction and coating process to nano-modify the surface of micron-sized spherical silver powder. Using the micron-sized spherical silver powder as a core, a uniform and dense layer of nanoparticles is constructed on the core surface, forming a core-shell structure. Without affecting the tap density, this structure significantly increases the specific surface area of ​​the silver powder and exhibits low burn-off, greatly enhancing the sintering activity of the silver powder and facilitating the subsequent acquisition of a slurry with excellent electrical conductivity. Propylene glycol serves as a dispersion medium, reaction medium, and morphology control agent. Its advantages lie in its molecular structure, which allows it to effectively wet the surface of the micron-sized silver powder, creating steric hindrance and preventing the microspheres from agglomerating during the reaction. This provides a foundation for subsequent uniform nano-coating. Furthermore, compared to water or ethanol, propylene glycol provides a milder medium environment, helping to control the reduction rate of silver ammonium complex ions, allowing the nano-silver particles to slowly and orderly deposit on the surface of the microspheres, forming a dense rather than loose structure.

[0021] In some embodiments, the fatty acid type coating agent includes one or more of oleic acid, lauric acid, and stearic acid; preferably, the fatty acid type coating agent is oleic acid.

[0022] In this embodiment, short-chain fatty acids are used as coating agents. Their carboxyl groups exhibit strong chemisorption with the silver surface, forming a dense and robust monolayer. This film effectively prevents the nanoparticles from agglomerating during the reaction and drying processes, maintaining the near-spherical shape and good dispersibility of the particles, thus ensuring the high tap density of the final product. Simultaneously, this type of coating agent has a small molecular weight and is easily decomposed and volatilized completely in the early stages of sintering, without increasing burn-off.

[0023] In some embodiments, the mass of the coating agent is 0.5-2% of the micron-sized spherical silver powder.

[0024] In this embodiment, when the dosage is below 0.5%, the coating is incomplete, and the nanoparticles agglomerate, leading to a decrease in tap density and a lack of improvement in specific surface area. When the dosage is above 2%, multilayer physical adsorption occurs, resulting in a significant increase in organic residue (burn-off), which creates pores during sintering, destroys the density of the conductive film, and ultimately degrades the final conductivity. Within this range, a high specific surface area can be stably obtained while maintaining low burn-off and high tap density.

[0025] In some embodiments, the feeding time is 3-6 minutes; the stirring time is 3-5 minutes.

[0026] In this embodiment, the short feeding time ensures that the concentrations of silver ions and reducing agents in the reaction system remain high, promoting the reduction reaction to occur preferentially on the surface of the microspheres (heterogeneous nucleation) rather than homogeneous nucleation in the solution to generate free nanoparticles, which would disrupt the tap density. The short stirring time allows the newly generated silver nanoparticles to stabilize rapidly under the action of the coating agent, thereby ensuring that the nanolayer is uniform and dense, which is beneficial for increasing the specific surface area and maintaining the tap density.

[0027] In some embodiments, the reducing agent includes one or more of ascorbic acid, glucose, hydrazine hydrate, formaldehyde, and sodium hypophosphite.

[0028] In this embodiment, a mild to moderate reducing agent is used, and the silver nanoparticles are deposited and grown in an orderly manner on the surface of the microspheres, which is conducive to the formation of a dense rather than loose nanolayer. If a strong reducing agent is used, a large number of free nanoparticles or loose structures are easily generated, thereby destroying the tap density.

[0029] In some embodiments, the silver salt is a nitrate.

[0030] In some embodiments, the mass of the reducing agent is 70-75% of the mass of the silver salt; the mass ratio of the silver salt to the micron-sized spherical silver powder is 15-35:100.

[0031] In this embodiment, the ratio of silver salt to micron-sized spherical silver powder affects the thickness of the nanocoating layer. If the ratio is too low, the nanolayer is too thin, resulting in limited improvement in specific surface area and activity; if the ratio is too high, the nanolayer is too thick, which will disrupt the overall sphericity of the microspheres, leading to a decrease in tap density.

[0032] In some embodiments, the mass ratio of propylene glycol aqueous solution to micron-sized spherical silver powder is 3:1, and the concentration of propylene glycol aqueous solution is 16.7-100%.

[0033] In this embodiment, if the liquid-to-solid ratio is too low, the dispersion and coating will be uneven. Propylene glycol, as a dispersant and morphology control agent, has mild reducing properties and suitable viscosity, which can effectively control the reaction rate, allowing the nanoparticles to be deposited slowly and orderly to form a dense coating layer. However, if the concentration is too low or too high, the above effect cannot be achieved, and it will lead to a loose coating layer and a decrease in tap density.

[0034] This application provides a highly active surface-nanosized spherical silver powder.

[0035] Compared to unmodified micron-sized spherical silver powder, this application increases the specific surface area while maintaining the tap density, thus lowering the softening inflection point temperature and increasing sintering activity. At the same time, this application maintains the tap density while minimizing burn-off, laying the foundation for obtaining highly conductive silver paste.

[0036] This application provides an application of highly active surface nano-sized spherical silver powder in the field of photovoltaic electronic components.

[0037] The silver powder of this application can be sintered at low temperature and can form a dense, highly conductive film after sintering, making it suitable for BC batteries.

[0038] The following specific embodiments further illustrate this solution.

[0039] Source of raw materials The preparation method of micron-sized spherical silver powder is as follows: Dissolve 160g of silver nitrate in 600ml of water and stir until homogeneous to obtain solution A; dissolve 96g of ascorbic acid in 600ml of water and stir until homogeneous, then add a pH adjuster to adjust the pH to 5 to obtain solution B; add 30g of polyvinylpyrrolidone to 960mL of deionized water and stir until homogeneous to obtain solution C; add 0.5g of oleic acid to a beaker and add 30ml of anhydrous ethanol and stir until homogeneous to obtain solution D; Solution A and solution B were simultaneously added to solution C using a peristaltic pump. The addition time was set to 5 minutes, and the stirrer speed was set to 550 rpm. After the addition was completed, solution D was added to solution C, and stirring was continued for another 5 minutes. The reaction was then complete, and a silver powder suspension was obtained.

[0040] 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. The above operation was repeated until the conductivity of the washing liquid was <20 μS / m to obtain wet silver powder. The wet silver powder was dried at 80℃ for 6 h. After drying and post-treatment, micron-sized spherical silver powder was obtained.

[0041] Example 1 A method for preparing highly active surface-nanosized spherical silver powder includes the following steps: S1. Add 50g of propylene glycol to 250g of water and stir until homogeneous. Add 100g of micron-sized spherical silver powder and continue stirring and dispersing for 30 minutes to obtain the first mixture. Add 25g of silver nitrate to 100g of deionized water and dissolve completely. While stirring, add ammonia dropwise until the solution is clear to obtain the second mixture. Add 17.5g of ascorbic acid to 100g of deionized water and dissolve completely to obtain an ascorbic acid aqueous solution. Add 1g of oleic acid to 20ml of anhydrous ethanol and stir to dissolve to obtain an alcoholic solution containing a fatty acid-type coating agent. S2. The reducing agent aqueous solution and the second mixture are simultaneously added to the first mixture at a constant speed using a peristaltic pump. The addition time is controlled at 5 min. After the addition is completed, an alcohol solution containing a fatty acid-type coating agent is added, and stirring is continued for 5 min to obtain a suspension of nano-coated composite silver powder. The obtained silver powder suspension is subjected to solid-liquid separation, and anhydrous ethanol is used to wash and stir it. The stirring speed is set to 550 rpm and the stirring time is set to 10 min. The above operation is repeated until the conductivity of the washing liquid is <20 μS / m to obtain wet silver powder. The wet silver powder is dried at 80℃ for 6 h. After drying and post-treatment, highly active surface nano-sized spherical silver powder is obtained.

[0042] Example 2 A method for preparing highly active surface nano-sized spherical silver powder is the same as in Example 1, except that in step S1, 150g of propylene glycol is added to 150g of water. Figure 1 This is a SEM image of the silver powder obtained in Example 2.

[0043] Example 3 A method for preparing highly active surface nano-sized spherical silver powder is the same as in Example 1, except that in step S1, 300g of propylene glycol is taken.

[0044] Example 4 A method for preparing highly active surface nano-sized spherical silver powder is the same as in Example 1, except that the amount of silver nitrate is 15g and the amount of ascorbic acid is 10.5g.

[0045] Example 5 A method for preparing highly active surface nano-sized spherical silver powder is the same as in Example 1, except that the amount of silver nitrate used is 35g and the amount of ascorbic acid used is 24.5g.

[0046] Comparative Example 1 A type of silver powder, the steps of which are as follows: Step 1, preparing solutions: Solution A: Dissolve 160g of silver nitrate in 600ml of water and stir until homogeneous to obtain Solution A; Solution B: Dissolve 96g of ascorbic acid in 600ml of water and stir until homogeneous. Add a pH adjuster to adjust the pH to 5 to obtain Solution B; Solution C: Add 30g of polyvinylpyrrolidone to 960mL of deionized water and stir until homogeneous and dissolved to obtain Solution C; Solution D: Add 0.5g of oleic acid to a beaker and add 30ml of anhydrous ethanol and stir until dissolved to obtain Solution D; Step 2, silver powder preparation: Solutions A and B are simultaneously added to solution C using a peristaltic pump for 5 minutes at a stirring speed of 550 rpm. After addition, solution D is added to solution C, and stirring continues for another 5 minutes. Once the reaction is complete, a silver powder suspension is obtained. The obtained silver powder suspension is then subjected to solid-liquid separation. Anhydrous ethanol is used for washing and stirring at 550 rpm for 10 minutes. This process is repeated until the conductivity of the washing solution is <20 μS / m, yielding wet silver powder. The wet silver powder is then dried at 80°C for 6 hours. After drying and post-treatment, micron-sized spherical silver powder is obtained.

[0047] Figure 2 This is a SEM image of the silver powder obtained in Comparative Example 1.

[0048] Comparative Example 2 A silver powder, otherwise identical to Example 2, except that propylene glycol is replaced with ethanol.

[0049] Comparative Example 3 A silver powder, otherwise the same as in Example 1, except that 32.5g of polyvinylpyrrolidone is added to 250g of water. Figure 3 This is a SEM image of the silver powder obtained in Comparative Example 3.

[0050] Testing and Evaluation The burn-off, tap density, specific surface area, and TMA softening inflection point of the silver powder obtained from different embodiments and comparative examples were tested using the following methods: 1. Particle size detection method: GB / T 19077-2016 "Particle size analysis by laser diffraction".

[0051] 2. Burn-off detection method: (1) Take a certain mass of silver powder sample (accurate to 0.1 mg) and record the initial mass (m0).

[0052] (2) Place the sample in an inert atmosphere (such as nitrogen) or air environment and calcine it at a set temperature (such as 300~500℃) for 1~2 hours to simulate the high temperature exposure conditions in the actual process.

[0053] (3) After cooling, weigh the mass of the calcined sample (m1) and calculate the burn loss rate: Burn-off rate (%) = (m0−m1) / m0×100%.

[0054] 3. Test methods for loose packing density and tapped density: GB / T 1479.1-2011 Loose packing density meter / funnel method; GB / T5162-2021 Tapped density meter / tap method.

[0055] 4. Specific surface area test method: GB / T13390-2008 Specific surface area analyzer / nitrogen adsorption method.

[0056] 5. TMA softening inflection point temperature test method: GB / T 4339-2008 "Determination of thermal expansion characteristic parameters of metallic materials".

[0057] The results are shown in Table 1.

[0058] Table 1 Test Results

[0059] Examples 1, 2, and 3 adjusted the concentration of propylene glycol; Examples 2, 4, and 5 varied the amount of silver coating to obtain nano-coating layers of different thicknesses. Comparative Example 1 used unmodified micron-sized spherical silver powder; Comparative Example 2 did not use propylene glycol; Comparative Example 3 replaced propylene glycol with other dispersants; Comparative Example 4 changed the feeding order; Comparative Example 5 did not perform coating; Comparative Example 6 changed the type of coating agent; Comparative Examples 7 and 8 adjusted the amount of coating agent.

[0060] Comparing Examples 1, 2, and 3, it can be seen that both excessively low and excessively high propylene glycol concentrations will lead to a decrease in the performance of silver powder. Comparing Examples 2, 4, and 5, it can be seen that increasing the coating amount increases the specific surface area, but the tap density will decrease due to the destruction of sphericity. Compared with Example 2, Comparative Example 1 was not modified, and although it had a high tap density, it had a low specific surface area and poor sintering activity. Compared with Example 2, Comparative Examples 2 and 3 used ethanol and PVP, and their silver powder performance was not as good as that of Example 2.

[0061] 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 highly active surface-nanosized spherical silver powder, characterized in that, Includes the following steps: Micron-sized spherical silver powder was added to an aqueous solution of propylene glycol to obtain a first mixture; ammonia was added to an aqueous solution of silver salt to obtain a second mixture. The reducing agent aqueous solution and the second mixture are simultaneously added to the first mixture. After the addition is complete, an alcohol solution containing a fatty acid coating agent is added, and the reaction is continued by stirring. Then, solid-liquid separation, washing, and drying are performed to obtain the highly active surface nano-sized spherical silver powder.

2. The preparation method according to claim 1, characterized in that, The fatty acid type coating agent includes one or more of oleic acid, lauric acid, and stearic acid.

3. The preparation method according to claim 1, characterized in that, The feeding time is 3-6 minutes; the stirring time is 3-5 minutes.

4. The preparation method according to claim 1, characterized in that, The reducing agent includes one or more of ascorbic acid, glucose, hydrazine hydrate, formaldehyde, and sodium hypophosphite.

5. The preparation method according to claim 1, characterized in that, The silver salt is a nitrate.

6. The preparation method according to claim 1, characterized in that, The mass of the reducing agent is 70-75% of the mass of the silver salt; the mass ratio of the silver salt to the micron-sized spherical silver powder is 15-35:

100.

7. The preparation method according to claim 1, characterized in that, The mass of the coating agent is 0.5-2% of the micron-sized spherical silver powder.

8. The preparation method according to claim 1, characterized in that, The mass ratio of the propylene glycol aqueous solution to the micron-sized spherical silver powder is 3:1, and the concentration of the propylene glycol aqueous solution is 16.7-100%.

9. A highly active surface nano-sized spherical silver powder obtained by the preparation method according to any one of claims 1-8.

10. The application of the highly active surface nano-sized spherical silver powder as described in claim 9 in the field of photovoltaic electronic components.

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