Surface-loaded nano-layer silver powder and its preparation method and application

Abstract

The present invention discloses a surface-loaded nano-layer silver powder and its preparation method and application. The surface-loaded nano-layer silver powder comprises silver powder and nano-silver particles uniformly loaded on the surface of the silver powder. The softening temperature of the surface-loaded nano-layer silver powder is 364-468°C, and the tap density of the surface-loaded nano-layer silver powder is 6.19-6.32 g / cm 3 The particle size of the nanosilver particles is 5-20 nm, and the preparation method includes the following steps: S1. adding a silver source solution and a reducing agent solution dropwise to a dispersant solution to carry out a reduction reaction to obtain a silver powder suspension; S2. adding an etching solution to the silver powder suspension to carry out an etching reaction, and then adding the silver source solution and the reducing agent solution dropwise to carry out a reaction to obtain a mixture; S3. adding a flocculant to the mixture, flocculating and stratifying, filtering, washing, and drying to obtain a surface-loaded nanolayer silver powder with high tap density and good sintering performance.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive silver paste, and in particular to a surface-loaded nano-layer silver powder and a preparation method and application thereof. Background Art

[0002] Conductive silver paste is a key raw material in the manufacture of crystalline silicon solar cells. As a metallized electrode, it directly impacts the photovoltaic performance of solar cells. Silver powder, the conductive phase of the paste, generally accounts for 80%-90% of the total paste volume. Parameters such as its particle size and distribution, micromorphology, and tap density have a significant impact on the paste's electrical properties. The surface morphology and particle size of the silver powder are the primary factors influencing the paste's electrical properties and sintering quality, further impacting the density of the silver grid lines after sintering and the solar cell's photovoltaic conversion efficiency.

[0003] In the related art, Chinese patent publication number CN110899691A discloses a method for producing silver powder with controllable sintering activity. Based on the silver powder obtained by physical condensation, a layer of silver grains with controllable grain size is deposited on the surface of the silver powder by chemical plating, which makes certain improvements to the particle size distribution and micromorphology of the silver powder.

[0004] However, in this scheme, not only is the physical vapor condensation method more complicated and has a low output, which restricts large-scale batch preparation and application, but the prepared silver powder also has poor sintering performance. At the same time, after silver grains are deposited on the surface of the silver powder, the silver powder is easy to agglomerate and the tap density decreases. Summary of the Invention

[0005] In view of this, the present application provides a surface-loaded nano-layer silver powder and a preparation method and application thereof, which has high tap density and good sintering performance.

[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions:

[0007] In the first aspect, the present application provides a surface-loaded nano-layer silver powder, which comprises silver powder and nano-silver particles uniformly loaded on the surface of the silver powder. The softening temperature of the surface-loaded nano-layer silver powder is 364-468°C, and the tap density of the surface-loaded nano-layer silver powder is 6.19-6.32 g / cm 3 The particle size of the nanosilver particles is 5-20nm.

[0008] In a second aspect, the present application provides a method for preparing a surface-loaded nano-layer silver powder, comprising the following steps:

[0009] S1. The silver source solution and the reducing agent solution are added dropwise to the dispersant solution to carry out a reduction reaction to obtain a silver powder suspension;

[0010] S2. An etching solution is added to the silver powder suspension to perform an etching reaction, and then a silver source solution and a reducing agent solution are added dropwise to react to obtain a mixture;

[0011] S3. Add a flocculant to the mixture, flocculate and separate, filter, wash, and dry to obtain surface-loaded nano-layer silver powder.

[0012] Preferably, in step S1 and step S2, the dropping method is a double dropping method.

[0013] Preferably, in step S1 and step S2, the molar ratio of the silver source to the reducing agent is 1:0.6-1.

[0014] Preferably, the etching solution is one or more of concentrated nitric acid and concentrated sulfuric acid.

[0015] Preferably, in step S1, the molar ratio of the dispersant to the silver source is 5-10:100.

[0016] Preferably, the molar amount of the silver source in step S2 is 10-40% of the molar amount of the silver source in step S1, and the molar amount of the reducing agent in step S2 is 10-40% of the molar amount of the reducing agent in step S1.

[0017] Preferably, in step S1, the temperature of the reduction reaction is 30-40°C.

[0018] Preferably, the molar ratio of the etching solution in step S2 to the silver source in step S1 is 1-2:100.

[0019] In a third aspect, the present application provides an application of surface-loaded nano-layer silver powder in a conductive silver paste.

[0020] The beneficial effects of the present application are as follows: compared with silver powder with a smooth surface, the surface-loaded nano-layer silver powder of the present solution still has a higher tap density and good dispersion performance. At the same time, the surface-loaded nano-layer silver powder of the present solution has good sintering activity, and the silver grid lines are dense after sintering; the process for preparing surface-loaded nano-layer silver powder of the present solution is simple, the output is high, the raw materials are environmentally friendly and non-irritating, and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the SEM analysis diagram of Example 1;

[0022] Figure 2 This is the SEM analysis diagram of Example 2;

[0023] Figure 3 This is the SEM analysis diagram of Comparative Example 1;

[0024] Figure 4 This is the SEM analysis diagram of Comparative Example 2;

[0025] Figure 5 1-2 and the TMA curve of Comparative Example 1;

[0026] Figure 6 These are the effects of sintering different silver wires. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The present application provides a surface-loaded nano-layer silver powder, which comprises silver powder and nano-silver particles uniformly loaded on the surface of the silver powder. The softening temperature of the surface-loaded nano-layer silver powder is 364-468°C, and the tap density of the surface-loaded nano-layer silver powder is 6.19-6.32 g / cm 3 The particle size of the nano silver particles is 5-20nm. The softening temperature of the surface-loaded nano layer silver powder is low, and the silver grid lines obtained after sintering are dense.

[0029] The present application provides a method for preparing a surface-loaded nano-layer silver powder, comprising the following steps:

[0030] S1. The silver source solution and the reducing agent solution are added dropwise to the dispersant solution to carry out a reduction reaction to obtain a silver powder suspension;

[0031] S2. An etching solution is added to the silver powder suspension to perform an etching reaction, and then a silver source solution and a reducing agent solution are added dropwise to react to obtain a mixture;

[0032] S3. Add a flocculant to the mixture, flocculate and separate, filter, wash, and dry to obtain surface-loaded nano-layer silver powder.

[0033] Step S1 is to obtain silver powder by wet reduction, and step S2 is to adjust the surface morphology of the silver powder by etching, directly grow a silver nanolayer in liquid phase reduction, so that the surface of the silver powder is loaded with nanolayer silver particles. If the etching in step S2 is not performed, the silver powder surface cannot be loaded with the nanolayer, but uneven small particles are generated in the solution. By loading silver nanoparticles on the surface of the silver powder, the sintering activity is improved, and the silver powder loaded with silver nanoparticles by the etching method has a higher tap density and better dispersion performance.

[0034] In step S1 and step S2, the dropping method is a double dropping method. Compared with the forward dropping method or the reverse dropping method, the double dropping method can improve the dispersion performance of the product and make the particle size more uniform.

[0035] In step S1 and step S2, the molar ratio of the silver source to the reducing agent is 1:0.6-1. After the reaction is completed within this range, there is little residual silver source or reducing agent, which reduces the step of processing unreacted raw materials. In some embodiments, the reducing agent can be one or more of ascorbic acid, formaldehyde, and hydrazine hydrate, and the silver source can be silver nitrate or other reducible silver salts.

[0036] The etching solution is one or more of concentrated nitric acid and concentrated sulfuric acid; the molar ratio of the etching solution in step S2 to the silver source in step S1 is 1-2:100.

[0037] In step S1, the molar ratio of the dispersant to the silver source is 5-10:100. If the amount of dispersant is too little, the dispersion effect is insufficient and the generated silver powder will agglomerate. If the amount of dispersant is too much, the raw materials will be wasted. In some embodiments, the dispersant can be one or more of gum arabic, polyethylene glycol, polyvinyl alcohol, and polyvinyl pyrrolidone.

[0038] The molar amount of the silver source in step S2 is 10-40% of the molar amount of the silver source in step S1, the molar amount of the reducing agent in step S2 is 10-40% of the molar amount of the reducing agent in step S1, and the dropping speed is 10-20 ml / min. Within this range, the nanosilver particles can be evenly loaded on the silver powder. If the silver source or reducing agent is added in excess in step S2, the nanoparticle layer on the surface of the silver powder grows unevenly.

[0039] In step S1, the temperature of the reduction reaction is 30-40° C. Within this temperature range, the etching reaction can be achieved. If the reaction temperature is too high, the particle size of the obtained silver powder will be too small.

[0040] The present application provides an application of surface-loaded nano-layer silver powder in a conductive silver paste.

[0041] The present invention is further described below through specific examples.

[0042] Example 1

[0043] A method for preparing a surface-loaded nano-layer silver powder comprises the following steps:

[0044] S1. 1 L of a 1 mol / L silver nitrate aqueous solution and 1 L of a 0.6 mol / L ascorbic acid aqueous solution were added dropwise to 1 L of a 0.05 mol / L polyvinyl pyrrolidone aqueous solution by double addition, and the reaction was stirred at a dropping rate of 20 ml / min, a stirring speed of 400 rpm, and a reaction temperature of 30 ° C to obtain a silver powder suspension;

[0045] S2. After the addition step in step S1 is completed, 0.01 mol of concentrated sulfuric acid is added to etch the silver powder in the silver powder suspension. After stirring for 10 min, 1 L of a 0.1 mol / L silver nitrate aqueous solution and 1 L of a 0.06 mol / L ascorbic acid aqueous solution are added dropwise at a rate of 10 ml / min to obtain a mixture.

[0046] S3. Add 5 ml of 1% polyacrylamide solution to the mixture for flocculation and stratification. Filter and wash the mixture five times and then dry it to obtain surface-loaded nano-layer silver powder.

[0047] The surface loaded nano-layer silver powder of this embodiment was characterized and analyzed by SEM. Figure 1 As shown, the silver powder surface is loaded with a nanolayer of about 5 nm, and the tap density of the silver powder is 6.19 g / cm 3 , laser particle size analysis results: D10 is 0.77um; D50 is 1.21um; D90 is 1.91um, through TMA analysis, such as Figure 5 As shown, its softening temperature is 468℃.

[0048] Example 2

[0049] A method for preparing a surface-loaded nano-layer silver powder, wherein the other steps are the same as those in Example 1, except that in step S2, the amount of concentrated sulfuric acid added is 0.02 mol, the concentration of the silver nitrate aqueous solution is 0.4 mol / L, and the concentration of the ascorbic acid aqueous solution is 0.24 mol / L.

[0050] The surface loaded nano-layer silver powder of this embodiment was characterized and analyzed by SEM. Figure 2 As shown, the surface of the silver powder is loaded with a nanolayer of about 20 nm, and the tap density of the silver powder is 6.32 g / cm 3 , laser particle size analysis results: D10 is 0.81um; D50 is 1.25um; D90 is 1.92um, through TMA analysis, such as Figure 5 As shown, its softening temperature is 364℃.

[0051] Example 3

[0052] A method for preparing surface-loaded nano-layer silver powder, wherein the other steps are the same as those in Example 1, except that in step S1, the concentration of the ascorbic acid aqueous solution is 1 mol / L; and in step S2, the concentration of the ascorbic acid aqueous solution is 0.1 mol / L.

[0053] The surface-loaded nano-layer silver powder of this embodiment was characterized and analyzed by SEM. The silver powder surface was loaded with a nano-layer of about 20 nm, and the tap density of the silver powder was 6.22 g / cm 3The results of laser particle size analysis are as follows: D10 is 0.69um; D50 is 1.14um; D90 is 2.12um. Through TMA analysis, its softening temperature is 346℃. As the amount of reducing agent increases, the particle size will decrease.

[0054] Example 4

[0055] A method for preparing a surface-loaded nano-layer silver powder, wherein the other steps are the same as those in Example 1, except that in step S2, the concentration of the silver nitrate aqueous solution is 0.2 mol / L, and the concentration of the ascorbic acid aqueous solution is 0.1 mol / L.

[0056] The surface-loaded nanolayer silver powder of this embodiment was characterized and analyzed by SEM. The silver powder surface was loaded with a nanolayer of about 5 nm, the tap density of the silver powder was 6.33 g / cm3, and the laser particle size analysis results showed that D10 was 0.79 μm; D50 was 1.26 μm; and D90 was 2.04 μm. The softening temperature was 446°C according to TMA analysis. As the amount of silver nitrate and reducing agent in step S2 increased excessively, the nanolayer would tend to be flat.

[0057] Comparative Example 1

[0058] A method for preparing silver powder, wherein the other steps are the same as those in Example 1, except that the etching process in step S2 is not included, but the silver nitrate aqueous solution and the ascorbic acid aqueous solution are directly added dropwise.

[0059] Characterization analysis was performed by SEM, such as Figure 3 As shown in the figure, the surface of the silver powder is smooth. The tap density of the silver powder is 6.3g / cm3. The laser particle size analysis results show that D10 is 0.75um; D50 is 1.23um; and D90 is 1.97um. Figure 5 As shown, its softening temperature is 504℃.

[0060] Comparative Example 2

[0061] A method for preparing silver powder, wherein the other steps are the same as those in Example 1, except that the concentration of the silver nitrate aqueous solution added in step S2 is 6 mol / L, and the concentration of the ascorbic acid aqueous solution is 3 mol / L.

[0062] Characterization analysis was performed by SEM, such as Figure 4 As shown, the surface of the silver powder is smooth and a large number of small particles are generated. The tap density of the silver powder is 6.31g / cm 3 Laser particle size analysis results showed: D10 was 0.52 μm; D50 was 1.22 μm; and D90 was 1.99 μm. TMA analysis showed a softening temperature of 486°C.

[0063] The sintering performance can be characterized by TMA test data. From the above results, it can be seen that Comparative Example 1 without the etching step cannot successfully form a silver particle nanolayer on the silver powder surface, and the amount of silver nitrate and ascorbic acid used in Comparative Example 2 exceeds the specified range of this application. The silver powder surface is smooth and a large number of small particles are generated. The sintering effect is not as good as the surface-loaded nanolayer silver powder of this application; at the same time, the higher tap density and dispersibility reflect the state between the silver powder particles. Generally speaking, if the silver powder particles are severely agglomerated, the tap density will decrease. Although the silver powder surface is etched and loaded in this application, the dispersion performance of the surface-loaded nanolayer silver powder prepared therefrom is not affected, and is consistent with the dispersion performance of the unloaded silver powder in Comparative Example 1.

[0064] like Figure 6 As shown, compared with Comparative Example 1, the silver wires in Examples 1 and 2 have clear boundaries and are dense in the center after sintering.

[0065] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing surface-loaded nano-layer silver powder, characterized in that: The steps include: S1. The silver source solution and the reducing agent solution are added dropwise to the dispersant solution to perform a reduction reaction to obtain a silver powder suspension; the reducing agent comprises one or more of ascorbic acid, formaldehyde, and hydrazine hydrate, and the silver source is silver nitrate; S2. An etching solution is added to the silver powder suspension to perform an etching reaction, and then a silver source solution and a reducing agent solution are added dropwise to react to obtain a mixture; S3. A flocculant is added to the mixture, and after flocculation and delamination, the mixture is filtered, washed, and dried to obtain the surface-loaded nano-layer silver powder; The surface-loaded nano-layer silver powder comprises silver powder and nano-silver particles uniformly loaded on the surface of the silver powder. The softening temperature of the surface-loaded nano-layer silver powder is 364-468°C, and the tap density of the surface-loaded nano-layer silver powder is 6.19-6.32 g / cm 3 , the particle size of the nano silver particles is 5-20 nm; The molar amount of the silver source in step S2 is 10-40% of the molar amount of the silver source in step S1, and the molar amount of the reducing agent in step S2 is 10-40% of the molar amount of the reducing agent in step S1.

2. The method for preparing surface-loaded nano-layer silver powder according to claim 1, characterized in that: In step S1 and step S2, the dropping method is a double dropping method.

3. The method for preparing surface-loaded nano-layer silver powder according to claim 1, wherein: In step S1 and step S2, the molar ratio of the silver source to the reducing agent is 1:0.6-1.

4. The method for preparing surface-loaded nano-layer silver powder according to claim 1, wherein: The etching solution is one or more of concentrated nitric acid and concentrated sulfuric acid.

5. The method for preparing surface-loaded nano-layer silver powder according to claim 1, characterized in that: In step S1, the molar ratio of the dispersant to the silver source is 5-10:

100.

6. The method for preparing surface-loaded nano-layer silver powder according to claim 1, characterized in that: In step S1, the temperature of the reduction reaction is 30-40°C.

7. The method for preparing surface-loaded nano-layer silver powder according to claim 1, characterized in that: The molar ratio of the etching solution in step S2 to the silver source in step S1 is 1-2:

100.

8. Use of the surface-loaded nano-layer silver powder obtained by the preparation method according to claim 1 in a conductive silver paste.

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