Spherical silver powder with nano shell structure and preparation method and application thereof

Abstract

The invention discloses spherical silver powder with a nanometer shell layer structure and a preparation method and application of the spherical silver powder. The method comprises the following steps: simultaneously adding an oxidant solution accounting for 30-35% of the total mass of the oxidant solution and a reducing agent solution accounting for 30-35% of the total mass of the reducing agent solution into a dispersant solution to obtain a first reaction solution; simultaneously adding the residual reducing agent solution and an oxidant solution which accounts for 20-65% of the total mass of the oxidant solution into the first reaction solution to obtain a second reaction solution; adding the rest oxidant solution accounting for 5-45% of the total mass of the oxidant solution into the second reaction solution to obtain a third reaction solution; and the coating agent solution is added into the third reaction solution, then stirring, solid-liquid separation, cleaning and drying are conducted, and the spherical silver powder of the nanometer shell structure is obtained. According to the invention, the problems of difficult printing and agglomeration caused by high specific surface area of nano-silver particles are greatly reduced; the method is simple to operate, low in cost and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of silver powder preparation technology, and in particular to a spherical silver powder with a nanoshell structure, its preparation method, and its application. Background Technology

[0002] With the rapid development of photovoltaic devices, conductive silver paste, as a key material in the preparation process of photovoltaic electronic components, has diversified applications in many fields. Conductive silver paste is widely used in photovoltaic cells, medical devices, touch screen electrodes, flexible electronics, printed circuit boards (PCBs), and other fields.

[0003] Silver powder, as the conductive functional phase in conductive silver paste, plays a decisive role in the paste's conductivity, sintering performance, and printability. It also accounts for over 90% of the cost of conductive silver paste. In recent years, nano-silver powder has become a research hotspot due to its unique surface effects and high sintering activity. However, its high agglomeration tendency and high specific surface area lead to poor printability, and the high cost and complex processing of nano-silver powder preparation severely restrict its industrial application.

[0004] Therefore, there is an urgent need to propose a new silver powder and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a spherical silver powder with a nanoshell structure, its preparation method and application, thereby solving the technical problems of high agglomeration tendency, poor printability due to high specific surface area, high cost and complex process of preparing nanosilver powder in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing spherical silver powder with a nanoshell structure, comprising the following steps: S1. Prepare oxidizing agent solution, reducing agent solution, dispersant solution and coating agent solution; S2. Add 30% to 35% of the total mass of the oxidant solution and 30% to 35% of the total mass of the reducing agent solution to the dispersant solution simultaneously to obtain the first reaction solution; S3. Add the remaining reducing agent solution and the oxidizing agent solution accounting for 20%~65% of the total mass of the oxidizing agent solution to the first reaction solution simultaneously to obtain the second reaction solution; S4. Add the remaining oxidant solution, which accounts for 5% to 45% of the total mass of the oxidant solution, to the second reaction solution to obtain the third reaction solution; S5. Add the coating agent solution to the third reaction solution, and then stir, separate the solid and liquid, wash and dry to obtain spherical silver powder with a nano-shell structure.

[0007] In a second aspect, the present invention provides a spherical silver powder with a nanoshell structure, which is obtained by the preparation method of the spherical silver powder with a nanoshell structure provided in the first aspect of the present invention.

[0008] Thirdly, the present invention provides the application of the above-mentioned spherical silver powder with a nanoshell structure in the preparation of conductive silver paste.

[0009] Compared with the prior art, the beneficial effects of the present invention include: The spherical silver powder of the present invention forms a shell-like structure in the nanoscale silver particles, which greatly reduces the printing difficulties and agglomeration problems caused by the high specific surface area of ​​the nanoscale silver particles. The spherical silver powder of the present invention is prepared by liquid phase chemical reduction method, which has the advantages of simple operation and low cost, and is suitable for industrial production. Attached Figure Description

[0010] Figure 1 Here is an SEM image of the silver powder prepared in Example 2 of this invention; Figure 2 This is a SEM image of the silver powder prepared in Comparative Example 2 of this invention. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] In a first aspect, the present invention provides a method for preparing spherical silver powder with a nanoshell structure, comprising the following steps: S1. Prepare oxidizing agent solution, reducing agent solution, dispersant solution and coating agent solution; S2. Add 30%~35% (including but not limited to 30%, 31%, 32%, 33%, 34%, 35%, etc.) of oxidant solution and 30%~35% (including but not limited to 30%, 31%, 32%, 33%, 34%, 35%, etc.) of reducing agent solution to dispersant solution simultaneously to obtain the first reaction solution; S3. Add the remaining reducing agent solution and an oxidizing agent solution accounting for 20% to 65% (including but not limited to 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%) of the total mass of the oxidizing agent solution to the first reaction solution to obtain the second reaction solution. S4. Add the remaining oxidant solution, which accounts for 5% to 45% of the total mass of the oxidant solution (including but not limited to 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, etc.), to the second reaction solution to obtain the third reaction solution. S5. Add the coating agent solution to the third reaction solution, and then stir, separate the solid and liquid, wash and dry to obtain spherical silver powder with a nano-shell structure.

[0013] The purpose of this invention is to prepare spherical silver powder with a nanoshell structure, while avoiding the formation of nano-silver particles during the preparation process. This invention solves this problem by strictly controlling the addition of the oxidizing and reducing agent solutions. In this invention, the addition process of the oxidizing and reducing agent solutions is divided into three stages, with the specific functions as follows: The first stage involves simultaneously adding the oxidizing agent solution and the reducing agent solution at the same low rate. The purpose of this low rate is to avoid excessively high local concentrations, ensuring a smooth reduction reaction and the formation of uniform, micron-sized spherical silver nuclei.

[0014] Second stage: The feeding rate of the reducing agent solution is increased to rapidly consume the Ag on the surface of the silver nucleus. + This puts the surface of the silver nucleus in a "passivated" state to prevent the formation of new silver nuclei.

[0015] Third stage: When excess reducing agent is present in the reaction solution, and the remaining 5%–45% silver nitrate solution is added, Ag… + Upon contact with the silver nucleus, the nanoparticles are instantly reduced and deposited on its surface. During the experiment, the inventors discovered that adding a reducing agent solution simultaneously at this stage generates a large number of independent silver nanoparticles. In this stage, insufficient silver nitrate solution results in an excessively thin silver nanoparticle shell, leading to discontinuous coverage; excessive silver nitrate solution results in an excessively thick silver nanoparticle shell, which may even detach easily.

[0016] In this embodiment, the oxidant is silver nitrate.

[0017] In this embodiment, the concentration of the oxidant solution is 260~400g / L, and the solvent is water.

[0018] In this embodiment, the reducing agent is at least one of formaldehyde, sodium borohydride, hydrazine hydrate, glucose, ascorbic acid, and sodium citrate.

[0019] In this embodiment, the amount of reducing agent added is 60% to 70% of the mass of the oxidizing agent.

[0020] In this embodiment, the concentration of the reducing agent solution is 170~260g / L, and the solvent is water.

[0021] In this embodiment, the pH of the reducing agent solution is 5~9, including but not limited to 5, 6, 7, 8, 9, etc.

[0022] In this embodiment, the preparation process of the reducing agent solution includes: adding the reducing agent to water, adjusting the pH to 5-9 using a pH adjuster, and obtaining the reducing agent solution.

[0023] Specifically, the pH adjuster is at least one of sodium hydroxide, ammonia, sodium carbonate, ethylenediamine, tetramethylammonium hydroxide, triethylamine, trisodium phosphate, potassium hydroxide, and choline.

[0024] Specifically, the mass fraction of the pH adjuster is 6% to 8%.

[0025] In this embodiment, the dispersant is at least one of polyvinylpyrrolidone, polyethylene glycol, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyvinyl alcohol.

[0026] In this embodiment, the amount of dispersant added is 10% to 22% of the mass of the oxidant.

[0027] In this embodiment, the concentration of the dispersant solution is 12~48 g / L, and the solvent is water.

[0028] In this embodiment, the coating agent is at least one of lauric acid, oleic acid, and palmitic acid.

[0029] In this embodiment, the amount of coating agent added is 0.5% to 2% of the mass of the oxidant.

[0030] In this embodiment, the concentration of the coating agent solution is 40~160g / L, and the solvent is ethanol.

[0031] In this embodiment, the feeding time in step S2 is 3~5 minutes.

[0032] In this embodiment, the feeding time in step S3 is 3~5 minutes.

[0033] In this embodiment, the feeding time in step S4 is 1~3 minutes.

[0034] In this embodiment, the feeding time in step S5 is 10~60s.

[0035] In this embodiment, the stirring time in step S5 is 10~20 min.

[0036] In this embodiment, peristaltic pumps are used to feed materials at a constant speed in steps S2 to S4.

[0037] In this embodiment, the reactions in steps S2 to S5 are all carried out at room temperature and under stirring conditions.

[0038] In a second aspect, the present invention provides a spherical silver powder with a nanoshell structure, which is obtained by the preparation method of the spherical silver powder with a nanoshell structure provided in the first aspect of the present invention.

[0039] The spherical silver powder with a nanoshell structure of the present invention comprises: a micron-sized spherical silver core and a shell formed by nano-sized silver particles. The shell structure formed by the nano-sized silver particles significantly reduces the printing difficulties and agglomeration problems caused by the high specific surface area of ​​the nano-silver particles. The present invention utilizes the inherent low melting point of the nano-silver particles, allowing the silver paste to undergo high-temperature sintering after printing. This causes the nanoshell on the surface of the silver powder to sinter and melt, forming a liquid-like phase with good fluidity. This phase first accumulates on the PN junction, forming a silver-silicon eutectic structure, thereby reducing contact resistance and achieving good ohmic contact. The present invention strictly controls the amount of silver nitrate used to prepare the coating layer, ensuring that the amount of the nano-silver layer that first undergoes sintering and melting is relatively small, thus avoiding damage to the PN junction due to high temperatures.

[0040] Thirdly, the present invention provides the application of the above-mentioned spherical silver powder with a nanoshell structure in the preparation of conductive silver paste.

[0041] Example 1 (1) Solution preparation: Dissolve 480g of silver nitrate in 1.5L of deionized water to prepare solution A; add ascorbic acid equivalent to 65% of the mass of silver nitrate to 1.5L of deionized water and adjust the pH to 7 with sodium hydroxide to prepare solution B; add polyvinylpyrrolidone equivalent to 16% of the mass of silver nitrate to 3L of deionized water to prepare solution C; add lauric acid equivalent to 0.8% of the mass of silver nitrate to 60ml of anhydrous ethanol to prepare solution D.

[0042] (2) Silver powder preparation: Solutions A and B are added at a constant rate using a peristaltic pump. Both solutions are simultaneously added to solution C, with each solution's mass added within 5 minutes. After adding 1 / 3, the reducing agent solution is added at a faster rate, with the remaining 2 / 3 added within 5 minutes. Simultaneously, the silver nitrate solution is added at the required rate. After 5 minutes, a 5% silver nitrate solution remains. After the above addition is complete, the final nanoshell coating stage is performed, adding the remaining 5% silver nitrate solution to the reaction solution within 2 minutes. After the above reaction is complete, solution D30s is added to the reaction solution, and the mixture is stirred for 15 minutes to obtain a silver powder suspension. Finally, the silver powder suspension is subjected to solid-liquid separation, washing, and drying to obtain spherical silver powder with a nanoshell structure.

[0043] Example 2 (1) Solution preparation: Dissolve 480g of silver nitrate in 1.5L of deionized water to prepare solution A; add ascorbic acid equivalent to 65% of the mass of silver nitrate to 1.5L of deionized water and adjust the pH to 7 with sodium hydroxide to prepare solution B; add polyvinylpyrrolidone equivalent to 16% of the mass of silver nitrate to 3L of deionized water to prepare solution C; add lauric acid equivalent to 0.8% of the mass of silver nitrate to 60ml of anhydrous ethanol to prepare solution D.

[0044] (2) Silver powder preparation: Solutions A and B are added to solution C at a constant rate using a peristaltic pump, with each solution being added at 1 / 3 of its mass within 5 minutes. After adding 1 / 3, the reducing agent solution is added at a faster rate, with the remaining 2 / 3 added within 5 minutes. Simultaneously, the silver nitrate solution is added at a faster rate as needed. After 5 minutes, a remaining 20% ​​of the original silver nitrate solution mass is required. Following this addition, the final nanoshell coating stage is performed, adding the remaining 20% ​​of the silver nitrate solution to the reaction solution within 2 minutes. After the reaction is complete, solution D30s is added to the reaction solution and stirred for 15 minutes to obtain a silver powder suspension. Finally, the silver powder suspension is subjected to solid-liquid separation, washing, and drying to obtain spherical silver powder with a nanoshell structure.

[0045] Example 3 (1) Solution preparation: Dissolve 480g of silver nitrate in 1.5L of deionized water to prepare solution A; add ascorbic acid equivalent to 65% of the mass of silver nitrate to 1.5L of deionized water and adjust the pH to 7 with sodium hydroxide to prepare solution B; add polyvinylpyrrolidone equivalent to 16% of the mass of silver nitrate to 3L of deionized water to prepare solution C; add lauric acid equivalent to 0.8% of the mass of silver nitrate to 60ml of anhydrous ethanol to prepare solution D.

[0046] (2) Silver powder preparation: Solutions A and B are added to solution C at a constant rate using a peristaltic pump, with each solution being added at 1 / 3 of its mass within 5 minutes. After adding 1 / 3, the reducing agent solution is added at a faster rate, with the remaining 2 / 3 added within 5 minutes. Simultaneously, the silver nitrate solution is added at a rate adjusted as needed. After 5 minutes, a remaining 35% of the original silver nitrate solution mass is required. Following this addition, the final nanoshell coating stage is performed, adding the remaining 35% of the silver nitrate solution to the reaction solution within 2 minutes. After the reaction is complete, solution D30s is added to the reaction solution and stirred for 15 minutes to obtain a silver powder suspension. Finally, the silver powder suspension is subjected to solid-liquid separation, washing, and drying to obtain spherical silver powder with a nanoshell structure.

[0047] Comparative Example 1 Compared with Example 2, the only difference is that the silver powder preparation steps are different, as follows: (2) Preparation of silver powder: Solution A and solution B are added at a constant rate using a peristaltic pump. Both solutions are added to solution C simultaneously, and the addition is required to be completed within 5 minutes. After the above reaction is completed, solution D is added to the above reaction solution after 30 seconds, and the mixture is stirred for 15 minutes to obtain a silver powder suspension. Finally, the silver powder suspension is subjected to solid-liquid separation, washing, and drying to obtain silver powder.

[0048] Comparative Example 2 Compared with Example 2, the only difference is that the silver powder preparation steps are different, as follows: (2) Silver powder preparation: Solutions A and B are added at a constant rate using a peristaltic pump. Both solutions are simultaneously added to solution C, with each solution's mass added at 1 / 3 over 5 minutes. After adding 1 / 3, the reducing agent solution and silver nitrate solution are added at a faster rate, completing the addition in 5 minutes. The remaining silver nitrate solution and reducing agent solution should account for 20% of the original silver nitrate solution's mass. After the above addition is complete, the final nano-shell coating stage is performed, with the remaining 20% ​​silver nitrate solution and the remaining 20% ​​reducing agent solution added to the reaction solution simultaneously over 2 minutes. After the above reaction is complete, solution D is added to the reaction solution over 30 seconds, and the mixture is stirred for 15 minutes to obtain a silver powder suspension. Finally, the silver powder suspension is subjected to solid-liquid separation, washing, and drying to obtain silver powder.

[0049] Performance testing (1) Silver powder performance test: 1. Morphology test: SEM was used to test the morphology of the silver powder.

[0050] 2. Particle size test: GB / T 19077-2016 "Particle size analysis by laser diffraction".

[0051] 3. Burn-off test: Take a silver powder sample (accurate to 0.1 mg) and record the initial mass (m0); place the sample in nitrogen and calcine at 538℃ for 1 hour at a heating rate of 10℃ / min to simulate the high-temperature exposure conditions in actual processes; after cooling, weigh the mass of the calcined sample (m1) and calculate the burn-off rate: Burn-off rate (%) = (m0-m1) / m0×100%.

[0052] 4. Loose packing density test: GB / T 1479.1-2011 Loose packing density meter / funnel method.

[0053] 5. Tap density test: GB / T 5162-2021 Tap density meter / tap method.

[0054] 6. Specific surface area test: GB / T13390-2008 Specific surface area analyzer / nitrogen adsorption method.

[0055] 7. TMA softening inflection point temperature test: GB / T 4339-2008 "Determination of thermal expansion characteristic parameters of metallic materials".

[0056] (2) Silver electrode performance test: Sheet resistance: GB / T 17473.3-2008 "Test methods for sheet resistance of precious metal pastes for microelectronics".

[0057] Table 1. Silver Powder Properties

[0058] Table 2 Electrical properties of silver electrodes prepared by printing and sintering silver powder

[0059] Please see Figures 1-2 ,pass Figure 1 It can be seen that the silver powder prepared in Example 2 of this invention is spherical, and its surface has a nanoshell structure (corresponding to...). Figure 1 (the shiny part of the middle surface); through Figure 2 It can be seen that the silver powder prepared in Comparative Example 2 of this invention contains a large number of independently existing silver nanoparticles (corresponding to...) Figure 2 The presence of small particles indicates that the present invention, through the addition of only silver nitrate solution in the third stage, enables nano-silver to coat the surface of the micron-sized silver core in the form of a shell.

[0060] Please refer to Tables 1-2. As can be seen from Tables 1-2, the silver powders prepared in the embodiments of the present invention all have moderate specific surface area and TMA softening inflection point temperature. The silver electrodes made from these materials have low sheet resistance, indicating that the silver powders prepared by the method of the present invention can balance low sintering temperature and high conductivity. At the same time, the silver electrode made from the silver powder in Example 2 of the present invention has the lowest sheet resistance, indicating that the silver powder prepared when the proportion of silver nitrate solution in the third stage is around 20% has the best performance.

[0061] Compared with Example 2, the silver powder prepared in Comparative Example 1 has no shell structure and cannot form a silver-silicon eutectic structure, which is not conducive to further reducing the contact resistance and achieving good ohmic contact. At the same time, the silver powder prepared in Comparative Example 1 has a significantly higher TMA softening inflection point temperature than Examples 1 to 3, which is not conducive to reducing the sintering temperature.

[0062] Compared with Example 2, Comparative Example 2 has a higher specific surface area and a lower TMA softening inflection point temperature, but the sheet resistance is significantly increased. This is because the silver powder in Comparative Example 2 contains a large number of nano-silver particles, which leads to an increase in specific surface area and a decrease in TMA softening inflection point temperature. However, the large amount of nano-silver particles introduced will cause a significant decrease in the printing performance of the silver powder, resulting in a significant increase in the sheet resistance of the silver electrode made under the same conditions.

[0063] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing spherical silver powder with a nanoshell structure, characterized in that, Includes the following steps: S1. Prepare oxidizing agent solution, reducing agent solution, dispersant solution and coating agent solution; S2. Add 30% to 35% of the total mass of the oxidant solution and 30% to 35% of the total mass of the reducing agent solution to the dispersant solution simultaneously to obtain the first reaction solution; S3. Add the remaining reducing agent solution and the oxidizing agent solution accounting for 20% to 65% of the total mass of the oxidizing agent solution to the first reaction solution simultaneously to obtain the second reaction solution; S4. Add the remaining oxidant solution, which accounts for 5% to 45% of the total mass of the oxidant solution, to the second reaction solution to obtain the third reaction solution; S5. The coating agent solution is added to the third reaction solution, and then stirred, separated from the solid, washed and dried to obtain spherical silver powder with a nano-shell structure.

2. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, The oxidizing agent is silver nitrate; and / or, The concentration of the oxidant solution is 260~400g / L, and the solvent is water.

3. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, The reducing agent is at least one of formaldehyde, sodium borohydride, hydrazine hydrate, glucose, ascorbic acid, and sodium citrate; and / or, The amount of reducing agent added is 60% to 70% of the mass of the oxidizing agent; and / or, The concentration of the reducing agent solution is 170~260 g / L, and the solvent is water; and / or, The pH of the reducing agent solution is 5-9.

4. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, The preparation process of the reducing agent solution includes: adding the reducing agent to water, adjusting the pH to 5-9 using a pH adjuster, and obtaining the reducing agent solution; wherein, The pH adjuster is at least one selected from sodium hydroxide, ammonia, sodium carbonate, ethylenediamine, tetramethylammonium hydroxide, triethylamine, trisodium phosphate, potassium hydroxide, and choline; and / or, The pH adjuster has a mass fraction of 6% to 8%.

5. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, The dispersant is at least one of polyvinylpyrrolidone, polyethylene glycol, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyvinyl alcohol; and / or, The amount of dispersant added is 10% to 22% of the oxidant mass; and / or, The concentration of the dispersant solution is 12~48 g / L, and the solvent is water.

6. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, The coating agent is at least one of lauric acid, oleic acid, and palmitic acid; and / or, The amount of coating agent added is 0.5% to 2% of the oxidant mass; and / or, The concentration of the coating agent solution is 40~160g / L, and the solvent is ethanol.

7. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, In step S2, the feeding time is 3-5 minutes; and / or, In step S3, the feeding time is 3-5 minutes; and / or, In step S4, the feeding time is 1~3 minutes; and / or, In step S5, the feeding time is 10~60s; and / or, In step S5, the stirring time is 10~20 minutes.

8. The method for preparing spherical silver powder with a nanoshell structure according to claim 1, characterized in that, In steps S2 to S5, the reactions were carried out at room temperature and under stirring conditions.

9. A spherical silver powder with a nanoshell structure, characterized in that, The spherical silver powder with a nanoshell structure is obtained by the preparation method of the spherical silver powder with a nanoshell structure according to any one of claims 1 to 8.

10. The application of the spherical silver powder with a nanoshell structure as described in claim 9 in the preparation of conductive silver paste.

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