Spherical nano silver powder and preparation method thereof

Abstract

The invention relates to the technical field of silver powder, in particular to spherical nano silver powder and a preparation method thereof. The silver paste comprises a first reaction solution and a second reaction solution, the first reaction solution comprises silver salt, pure water, a pH regulator and a dispersing agent, and the second reaction solution comprises a reducing agent; the content of silver salt in the first reaction liquid is less than 0.4 mol / L. The prepared spherical nano silver powder is uniform in morphology, high in sphericity degree, high in crystallization, high in tap density and high in dispersion, can be better matched with an organic carrier in the application of conductive paste, realizes low-temperature sintering and high adhesive force of the paste, and can comprehensively meet the requirements of viscosity, rheological property, conductivity and the like of silver paste in TOPCon batteries and HJT batteries; the method is simple in process, high in silver powder recovery rate, stable in silver powder batch quality and suitable for large-scale production in factories.

Description

Technical Field

[0001] The present invention relates to the technical field of silver powder, and specifically, to a spherical nano silver powder and a preparation method thereof. Background Art

[0002] There are various preparation methods for spherical nano silver powder, including physical methods and chemical methods. Physical methods such as mechanical ball milling, laser ablation, ultrasonic waves, and irradiation, etc. These methods usually have high requirements for instrument equipment, but the prepared silver nanoparticles have high purity and excellent performance. Chemical methods are to prepare spherical nano silver powder through chemical reactions. Its preparation process is relatively complex, and it is not easy to simultaneously meet the usage requirements for the uniformity, sphericity, crystallinity, tap density, and dispersibility of the silver powder.

[0003] Chinese invention patent CN111940760B discloses a spherical nano silver powder. The preparation raw materials include: silver salt, dispersant, reducing agent, regulator, additive; the mass ratio of the dispersant to the reducing agent is (1.2 - 1.6):1. In the feeding sequence, the dispersant is added to the silver salt solution first and then the reducing agent is added, and the type and content of the added dispersant are controlled, and at the same time, the reaction conditions are controlled, so as to effectively control the morphology and size of the silver powder. However, the particle size of the silver powder prepared by this invention exceeds 1μm. Summary of the Invention

[0004] The first aspect of the present invention provides a spherical nano silver powder, the components of which include: a first reaction solution and a second reaction solution. The first reaction solution includes a silver salt, pure water, a pH regulator, and a dispersant. The second reaction solution includes a reducing agent and pure water; the content of the silver salt in the first reaction solution is less than 0.4 mol / L; the D90 particle size of the nano silver powder is less than 1000 nm.

[0005] Preferably, the content of the silver salt in the first reaction solution is less than 0.2 mol / L.

[0006] Preferably, the content of the silver salt in the first reaction solution is 0.05 - 0.15 mol / L.

[0007] The silver salt includes at least one of silver nitrate, silver acetate, and silver chloride.

[0008] The dispersant includes at least one of gelatin, gum ghatti, polyvinylpyrrolidone (PVP), and sodium dodecylbenzenesulfonate.

[0009] Preferably, the dispersant includes PVP.

[0010] The reducing agent includes at least one of citric acid, ascorbic acid, formic acid, formaldehyde, hydrazine hydrate, glycerol, triethanolamine, sodium borohydride, glucose, D-glucopyranose, D-glucal, fructose, and xylose.

[0011] Preferably, the reducing agent includes at least one of citric acid, formic acid, formaldehyde, glycerol, triethanolamine, sodium borohydride, glucose, D-pyranose, D-glucal, fructose and xylose.

[0012] The pH adjuster includes at least one of sodium hydroxide, ammonia water, potassium hydroxide, anhydrous sodium carbonate and calcium hydroxide.

[0013] The mass ratio of the silver salt to the dispersant in the first reaction solution is (500-12000):1.

[0014] Preferably, the mass ratio of the silver salt to the dispersant in the first reaction solution is (5000-12000):1.

[0015] Preferably, the mass ratio of the silver salt to the dispersant in the first reaction solution is (8000-12000):1.

[0016] The molar ratio of the reducing agent to the silver salt is (1-2):1.

[0017] Preferably, the molar ratio of the reducing agent to the silver salt is (1.5-2):1.

[0018] The present application has found that by selecting a specific reducing agent and limiting the molar ratio of the reducing agent to the silver salt to (1-2):1, the sphericity of the nano silver powder can be improved and the D90 particle size of the silver powder can be less than 1000nm. It is possible that the molar ratio affects the reaction rate, thereby affecting the balance between nucleation and growth, and determining the particle size; an excess of reducing agent may provide more nucleation sites, resulting in small particles; while an insufficient amount may result in large particles; at the same time, the concentration of the reducing agent may affect the stability of the particle surface, prevent aggregation, or promote the growth of specific crystal faces, thereby changing the morphology and resulting in different intermediates or by-products, affecting the crystal growth path.

[0019] The second aspect of the present invention provides a method for preparing spherical nano silver powder, comprising the following steps:

[0020] Dissolving silver salt in pure water, heating and stirring until the silver salt is completely dissolved, adding a pH adjuster, and then adding a dispersant to obtain a first reaction solution;

[0021] Dissolving a reducing agent in pure water to obtain a second reaction solution;

[0022] adding the second reaction liquid to the first reaction liquid, and performing a reduction reaction after the addition is completed;

[0023] After the reaction is completed, the spherical nano silver powder is obtained through filtering, washing and drying.

[0024] The temperature of the reduction reaction is 20-50° C. and the time is 10-40 min.

[0025] Preferably, the temperature of the reduction reaction is 30 - 50 °C and the time is 20 - 30 min.

[0026] The pH of the first reaction solution is 9 - 13.

[0027] Preferably, the pH of the first reaction solution is 11 - 12.

[0028] The temperature of the drying is 30 - 40 °C and the time is 6 - 12 h.

[0029] Beneficial effects

[0030] 1. By selecting a specific reducing agent and limiting the molar ratio of the reducing agent to the silver salt to (1 - 2):1, the sphericity of the nano - silver powder can be improved and the D90 particle size of the silver powder is less than 1000 nm.

[0031] 2. By limiting the content of the silver salt in the first reaction solution to less than 0.4 mol / L, the morphological uniformity of the nano - silver powder can be improved, the tap density is greater than 6.5 g / cm 3 , and the specific surface area is greater than 0.4 m 2 / g.

[0032] 3. When the dispersant is selected as PVP, the morphological uniformity of the nano - silver powder can be further improved, the tap density is greater than

[0033] 6.8 g / cm 3 , and the specific surface area is greater than 0.45 m 2 / g.

[0034] 4. The silver powder prepared in this application can better match the organic carrier in the application of conductive paste, realize the low - temperature sintering and high adhesion of the paste, and can fully meet the requirements of the viscosity, rheology, conductivity, etc. of the silver paste in TOPCon cells and HJT cells.

[0035] 5. The process of this application is simple, the recovery rate of silver powder is high, and the quality of silver powder batches is stable, which is suitable for factory - scale production. Description of the drawings

[0036] Figure 1 SEM image of the silver powder prepared in Example 1 (×30000 times)

[0037] Figure 2 SEM image of the silver powder prepared in Example 1 (×15000 times)

[0038] Figure 3 SEM image of the silver powder prepared in Comparative Example 1 (×3300 times)

[0039] Figure 4 SEM image of the silver powder prepared in Comparative Example 2 (×10000 times)

[0040] Figure 5 SEM image of the silver powder prepared in Comparative Example 3 (×30,000 magnification)

[0041] Figure 6 SEM image of the silver powder prepared in Comparative Example 9 (×10,000 magnification) Detailed implementation manners

[0042] Example 1

[0043] A spherical nano - silver powder, the preparation raw materials are shown in Table 1:

[0044] Table 1

[0045]

[0046]

[0047] A preparation method of a spherical nano - silver powder, comprising the following steps:

[0048] Preparation of the reaction solution: Dissolve the silver salt in pure water, place it in a water bath and heat it to 40 °C, stir at 300 rpm until the silver salt is completely dissolved, add a pH regulator, adjust the pH value of the solution to 11, and keep stirring for 8 min, then add a dispersant to prepare the first reaction solution; dissolve the reducing agent in pure water to prepare the second reaction solution.

[0049] Occurrence of the reduction reaction: Add the second reaction solution to the first reaction solution, and after the addition, keep stirring at a rate of 500 rpm and react at 40 °C for 20 min.

[0050] Post - reaction treatment: After the reaction ends, stop stirring. After the reaction mother liquor stands for 15 min, filter off the mother liquor to collect the silver powder, and wash the silver powder 3 times with ethanol and pure water respectively until the pH value of the filtrate is 7. Then send the washed silver powder into a vacuum drying oven and dry it at 40 °C for 12 h to obtain the product.

[0051] Comparative Example 1

[0052] The detailed implementation manners are the same as those in Example 1; the difference is that in Comparative Example 1, the second reaction solution is: 35.22 g of ascorbic acid and 400 mL of pure water.

[0053] Comparative Example 2

[0054] The detailed implementation manners are the same as those in Example 1; the difference is that in Comparative Example 2, the second reaction solution is: 9.386 g of hydrazine hydrate aqueous solution (80 wt%).

[0055] Comparative Example 3

[0056] The specific implementation method is the same as that of Example 1; the difference is that the addition amount of silver nitrate in Comparative Example 3 is 135.896 g.

[0057] Comparative Example 4

[0058] The specific implementation method is the same as that of Example 1; the difference is that the addition amount of silver nitrate in Comparative Example 4 is 203.844 g.

[0059] Comparative Example 5

[0060] The specific implementation method is the same as that of Example 1; the difference is that the addition amount of silver nitrate in Comparative Example 5 is 271.792 g.

[0061] Comparative Example 6

[0062] The specific implementation method is the same as that of Example 1; the difference is that the addition amount of silver nitrate in Comparative Example 6 is 339.74 g.

[0063] Comparative Example 7

[0064] The specific implementation method is the same as that of Example 1; the difference is that no dispersant is added in Comparative Example 7.

[0065] Comparative Example 8

[0066] The specific implementation method is the same as that of Example 1; the difference is that the dispersant in Comparative Example 8 is PEG-400.

[0067] Comparative Example 9

[0068] The specific implementation method is the same as that of Example 1; the difference is that the dispersant in Comparative Example 9 is polyvinyl alcohol.

[0069] Performance test method

[0070] The silver powders prepared in Example 1 and the comparative examples were subjected to electron microscopy test (SEM). As shown in Figure 1 and Figure 2 , the silver powder has a uniform morphology and high sphericity; the morphology results of the silver powder in the comparative examples are shown in Table 2, and there are significant differences in the particle size distribution.

[0071] The silver powders prepared in the examples and the comparative examples were subjected to particle size distribution, tapped density, specific surface area, and composition analysis tests. The test data are listed in Table 3, where " / " indicates that the test was not performed.

[0072] The particle size distribution was measured using an LS-609 laser particle size analyzer (Omec Company).

[0073] Performance test data

[0074] Table 2

[0075] Preparation of silver powder morphology Example 1 Small particle size and high spherical-like morphology Comparative Example 1 Large particle size and irregular morphology Comparative Example 2 Large particle size and irregular morphology Comparative Example 3 Irregular morphology Comparative Example 4 Large particle size and irregular morphology Comparative Example 5 Large particle size, irregular morphology and severe agglomeration Comparative Example 6 Large particle size, irregular morphology and severe agglomeration Comparative Example 7 Severe agglomeration of powder and irregular morphology Comparative Example 8 Irregular morphology Comparative Example 9 The morphology is spherical-like, but the particle size is large

[0076] Table 3

[0077]

[0078]

Claims

1. A spherical nano silver powder, characterized in that: The components include: a first reaction liquid and a second reaction liquid, wherein the first reaction liquid includes a silver salt, pure water, a pH regulator, and a dispersant, and the second reaction liquid includes a reducing agent and pure water; the content of the silver salt in the first reaction liquid is less than 0.4 mol / L; and the D90 particle size of the nano silver powder is less than 1000 nm.

2. The spherical nano silver powder according to claim 1, characterized in that: The content of silver salt in the first reaction solution is less than 0.2 mol / L.

3. The spherical nano silver powder according to claim 2, characterized in that: The content of silver salt in the first reaction solution is 0.05-0.15 mol / L.

4. The spherical nano silver powder according to claim 1 or 3, characterized in that: The dispersant includes at least one of gelatin, guar gum, polyvinyl pyrrolidone and sodium dodecylbenzene cyclate.

5. The spherical nano silver powder according to claim 4, characterized in that: The reducing agent includes at least one of citric acid, formic acid, formaldehyde, glycerol, triethanolamine, sodium borohydride, glucose, D-pyranose, D-glucal, fructose, and xylose.

6. The spherical nano silver powder according to claim 5, characterized in that: The mass ratio of the silver salt to the dispersant in the first reaction solution is (500-12000):

1.

7. The spherical nano silver powder according to claim 6, characterized in that: The molar ratio of the reducing agent to the silver salt is (1-2):

1.

8. A method for preparing the spherical nano silver powder according to any one of claims 1 to 7, characterized in that: The following steps are involved: Dissolving silver salt in pure water, heating and stirring until the silver salt is completely dissolved, adding a pH adjuster, and then adding a dispersant to obtain a first reaction solution; Dissolving a reducing agent in pure water to obtain a second reaction solution; adding the second reaction solution to the first reaction solution to perform a reduction reaction; After the reaction is completed, the spherical nano silver powder is obtained through filtering, washing and drying.

9. The method for preparing spherical nano silver powder according to claim 8, characterized in that: The temperature of the reduction reaction is 20-50° C. and the time is 10-40 min.

10. The method for preparing spherical nano silver powder according to claim 9, characterized in that: The pH of the first reaction solution is 9-13.

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