Burr spherical rough silver powder and preparation method and application thereof

Abstract

The invention discloses burr spherical rough silver powder and a preparation method and application thereof. The preparation method of the silver powder comprises the following steps: respectively preparing a silver nitrate solution, a first reducing agent solution and a second reducing agent solution; uniformly mixing a dispersing agent solution with the silver nitrate solution, adding the first reducing agent solution, and stirring to react for 1-3 minutes; then adding a molding agent, adjusting the pH value of the system to 5-8, then adding a second reducing agent solution, and continuously stirring and reacting for 5-15 minutes; and carrying out centrifugal separation, washing and drying on the obtained reaction product. The silver powder with thorn-shaped spherical protrusions on the surface is prepared through the technology of one-stage rapid nucleation and two-stage molding agent induced growth, the surface roughness and interface bonding force of the silver powder are remarkably improved, a compact conductive network can be formed when the silver powder is used for TOPCon battery silver paste, Isc and FF are effectively improved, and the problem that the conductivity of traditional silver paste is insufficient is solved.

Description

Technical Field

[0001] This invention belongs to the field of silver powder preparation and photovoltaic materials technology, and particularly relates to a burr-like spherical rough silver powder, its preparation method and application. Background Technology

[0002] Silver powder, as a key conductive component in conductive silver paste for crystalline silicon solar cells, directly affects the printing performance, sintering characteristics, and photoelectric conversion efficiency of the paste. With the development of N-type high-efficiency cell technology, especially the large-scale application of TOPCon cells, higher requirements are placed on the conductivity and sintering characteristics of silver paste.

[0003] In existing technologies, silver powder is mostly prepared by liquid-phase reduction, resulting in silver powder with a smooth surface and a predominantly spherical or near-spherical morphology. However, this process suffers from defects such as small specific surface area and insufficient surface activity. The small specific surface area limits the formation of conductive pathways between silver powder particles; insufficient surface activity leads to weak interfacial bonding with glass powder and organic carriers. During sintering, it is difficult to form a dense and low-resistance conductive network, affecting carrier collection efficiency and consequently resulting in lower short-circuit current (Isc) and fill factor (FF) of the battery, thus restricting further improvements in battery performance.

[0004] Therefore, developing a silver powder with high specific surface area, good surface activity and low true density is of great significance for improving the performance of conductive silver paste for next-generation high-efficiency batteries (such as TOPCon batteries) and meeting industrialization needs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a rough, spherical silver powder with burrs, its preparation method, and its application, thereby solving the problems of small specific surface area and insufficient surface activity of existing silver powders.

[0006] The objective of this invention is achieved through the following technical solution: A method for preparing burr-like, spherical, coarse silver powder includes the following steps: S1. Prepare silver nitrate solution with a concentration of 0.5~2.0 mol / L, a first reducing agent solution with a concentration of 0.05~0.6 mol / L, and a second reducing agent solution with a concentration of 0.2~1.5 mol / L, respectively; S2. Mix the dispersant solution and the silver nitrate solution evenly, add the first reducing agent solution, and stir the reaction for 1-3 min; then add the plasticizer, adjust the pH of the system to 5-8, add the second reducing agent solution, and continue stirring the reaction for 5-15 min; S3. The reaction product obtained in step S2 is centrifuged, washed and dried to obtain the burr-like spherical rough silver powder.

[0007] Preferably, in step S1, the solute in the first reducing agent solution is selected from at least one of hydrazine hydrate, sodium borohydride, ascorbic acid, formaldehyde, and ethylene glycol.

[0008] Preferably, in step S2, the solute in the second reducing agent solution is selected from at least one of ascorbic acid, glucose, and hydrazine hydrate.

[0009] In this invention, the first reducing agent needs to meet the nucleation requirement of "generating a large number of uniform primary silver nuclei in a short time." Therefore, strong reducing agents such as hydrazine hydrate and sodium borohydride are preferred. These agents can rapidly reduce Ag within a short period of 2-10 seconds of feeding and 1-3 minutes of reaction. + The first reducing agent is reduced to Ag atoms to avoid insufficient number or uneven size of crystal nuclei due to a slow reduction rate, thus laying a uniform "seed" foundation for subsequent growth stages. The second reducing agent needs to work in conjunction with a plasticizer to achieve "directional growth." Therefore, reagents with moderate reducing power and slow reaction rates, such as ascorbic acid and glucose, are chosen. Their mild reducing properties synergize with the selective adsorption of plasticizers (such as citric acid and tartaric acid): the plasticizer preferentially adsorbs onto specific crystal faces of the primary silver nuclei, restricting growth on some crystal faces. Simultaneously, the slow reaction rate ensures that Ag atoms are deposited orderly on unadsorbed crystal faces, ultimately forming a rough, spherical structure. Using a strong reducing agent would lead to Ag... + Rapid excessive reduction and disordered accumulation of silver atoms disrupt the directional control effect of the plasticizer. Through the synergy of "strong reduction nucleation and mild reduction shaping", the morphology and performance (high specific surface area and low true density) of silver powder are precisely controlled, which meets the requirements of subsequent conductive silver paste for silver powder structure in TOPCon batteries.

[0010] Preferably, in step S2, the mass ratio of the dispersant in the dispersant solution to the silver nitrate in the silver nitrate solution is 0.03~0.3:1.

[0011] Preferably, in step S2, the mass ratio of the first reducing agent in the first reducing agent solution to the silver nitrate in the silver nitrate solution is 0.001~0.1:1.

[0012] Preferably, in step S2, the mass ratio of the second reducing agent in the second reducing agent solution to the silver nitrate in the silver nitrate solution is 0.1~0.8:1.

[0013] Preferably, in step S2, the first reducing agent solution is added within 2 to 10 seconds.

[0014] Preferably, in step S2, the second reducing agent solution is added within 1 to 5 minutes.

[0015] Preferably, the stirring rate of the stirring reaction in step S2 is 200~400 r / min.

[0016] Preferably, the concentration of the dispersant solution in step S2 is 0.12~0.15 g / mL.

[0017] Preferably, the dispersant in step S2 is at least one of anhydrous ethanol, polyethylene glycol, gelatin, gum arabic, and polyvinylpyrrolidone.

[0018] Preferably, the mass ratio of the plasticizer in step S2 to the silver nitrate in the silver nitrate solution is 0.0005~0.12:1.

[0019] Preferably, the plasticizer in step S2 is at least one of formic acid, acetic acid, propionic acid, succinic acid, glutaric acid, oxalic acid, citric acid, maleic acid, tartaric acid, and their sodium salts.

[0020] Preferably, the pH adjustment of the system to 5-8 in step S2 is achieved by adding an acidic or alkaline substance, wherein the acidic substance is at least one of nitric acid and acetic acid; and the alkaline substance is at least one of sodium carbonate, sodium bicarbonate, sodium acetate, ammonia and sodium hydroxide.

[0021] Preferably, the centrifugation speed in step S3 is 3000~5000 r / min, and the centrifugation time is 10~15 min.

[0022] Preferably, the washing method in step S3 is as follows: wash with deionized water and anhydrous ethanol alternately 3 to 4 times until the conductivity of the supernatant is <20μs / cm.

[0023] Preferably, the drying temperature in step S3 is 75~95℃, and the drying time is 7~10h.

[0024] The above-described method for preparing burr-like spherical coarse silver powder yields burr-like spherical coarse silver powder.

[0025] The application of the above-mentioned burr-shaped coarse silver powder in the preparation of TOPCon battery conductive paste.

[0026] Compared with the prior art, the beneficial effects of the present invention include: (1) This invention uses a two-step process of “rapid reduction nucleation in one stage + growth induced by plasticizing agent in the second stage” to precisely control the morphology of silver powder. In the first stage, a reducing agent is rapidly added to form a large number of uniform primary silver nuclei. In the second stage, the plasticizing agent (small molecule organic acid, etc.) selectively acts on the silver crystal surface to induce silver atoms to grow in a specific direction, forming a unique burr-like rough structure. This effectively overcomes the defects of traditional silver powder with smooth surface and few active sites, and significantly improves the surface roughness and interfacial bonding ability of silver powder.

[0027] (2) The properties of silver powder can be flexibly adjusted by controlling the type of dispersant, the proportion of plasticizer, and the pH value, making it suitable for large-scale continuous production. The resulting silver powder has an average particle size of 1.0~2.5μm and a specific surface area of ​​0.4~0.9m². 2 / g, true density ≤9.95g / cm³ 3 It also has a suitable particle size distribution, which makes the silver powder more dispersed in the silver paste. During sintering, it can form a continuous and dense conductive network, reduce contact resistance, and lay the foundation for high conductivity.

[0028] (3) When the silver powder prepared by the present invention is applied to the conductive silver paste of TOPCon battery, the burr-shaped spherical structure increases the contact area with the silicon wafer, which helps to release the active ingredients. Combined with a good conductive network, it significantly improves the battery short-circuit current (Isc) and fill factor (FF), solving the problem of insufficient conductivity of traditional silver paste in high-efficiency batteries. Attached Figure Description

[0029] Figure 1 SEM image of the rough, spherical silver powder with burrs prepared in Example 1.

[0030] Figure 2 SEM image of the rough, spherical silver powder with burrs prepared in Example 2.

[0031] Figure 3 SEM image of the rough, spherical silver powder with burrs prepared in Example 3.

[0032] Figure 4 SEM image of the silver powder prepared for Comparative Example 1. Detailed Implementation

[0033] 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.

[0034] The specific steps for preparing conductive silver paste from the silver powder prepared in the examples or comparative examples are as follows: 82%wt silver powder and 6% borosilicate glass powder were dry-mixed and then added to 12% organic carrier (containing 15% STD 4-ethyl cellulose, 82% terpineol, 2% hydrogenated castor oil and 1% BYK-352 additive by mass percentage). After initial stirring, the mixture was ground by a three-roll mill until the slurry D50 ≤ 3μm and then filtered to obtain conductive silver paste.

[0035] The test steps for the short-circuit current (Isc) and fill factor (FF) of the TOPCon solar cell are as follows: The above silver paste is screen-printed onto the TOPCon solar cell, dried at 120°C for 30 min to remove organic solvents, and then placed in a sintering furnace for sintering at 450°C for 30 s. After cooling, the electrical performance is tested and evaluated.

[0036] Example 1 A method for preparing burr-like, spherical, coarse silver powder, the specific steps of which are as follows: S1. Weigh 160g of silver nitrate and dissolve it in 1.8L of deionized water to obtain a silver nitrate solution for later use; dissolve 0.2g of sodium borohydride in 100mL of deionized water to prepare the first reducing agent solution; dissolve 80g of ascorbic acid in 1L of deionized water to prepare the second reducing agent solution. S2. Weigh 24g of polyvinylpyrrolidone and dissolve it in 200mL of deionized water. After complete dissolution, mix it evenly with silver nitrate solution. Quickly pour the first reducing agent solution into the mixture at 300r / min (addition time is 3s), and react for 1min. Continue stirring, add 0.1g of citric acid to the reaction system, adjust the pH of the reaction system to 5.5, and then add the second reducing agent solution dropwise to the system at 1min. Continue to react for 10min. S3. After the reaction is complete, the product is centrifuged at 3000 r / min for 10 min, and washed 3-4 times alternately with deionized water and anhydrous ethanol until the conductivity of the supernatant is <20 μs / cm. Then, it is dried in a forced-air drying oven at 90℃ for 8 h to obtain the burr-like spherical rough silver powder.

[0037] The rough, spherical silver powder prepared in Example 1 has a D50 of 1.32 μm, a specific surface area of ​​0.52 m² / g, and a true density of 9.94 g / cm³. Its electron micrograph is shown below. Figure 1 As shown, this silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 16.072 A and its FF was 82.36%.

[0038] Example 2 A method for preparing burr-like, spherical, coarse silver powder, the specific steps of which are as follows: S1. Weigh 160g of silver nitrate and dissolve it in 1L of deionized water to obtain a silver nitrate solution for later use; dissolve 1.5g of hydrazine hydrate in 100mL of deionized water to prepare the first reducing agent solution; dissolve 80g of ascorbic acid in 1L of deionized water to prepare the second reducing agent solution. S2. Weigh 30g of polyethylene glycol and dissolve it in 200mL of deionized water. After complete dissolution, mix it evenly with silver nitrate solution. Quickly pour the first reducing agent solution into the mixture at 300r / min (addition time is 3s), and react for 2min. Continue stirring, add 0.16g of tartaric acid to the reaction system, adjust the pH of the reaction system to 6.1, and then add the second reducing agent solution dropwise to the system at a time of 2min. Continue to react for 10min. S3. After the reaction is complete, the product is centrifuged at 3000 r / min for 10 min, and washed 3-4 times alternately with deionized water and anhydrous ethanol until the conductivity of the supernatant is <20 μs / cm. Then, it is dried in a forced-air drying oven at 85℃ for 10 h to obtain the burr-like spherical rough silver powder.

[0039] The rough, spherical silver powder prepared in Example 2 has a D50 of 1.45 μm, a specific surface area of ​​0.62 m² / g, and a true density of 9.92 g / cm³. Its electron micrograph is shown below. Figure 2 As shown, the silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 16.235A and its FF was 82.41%.

[0040] Example 3 A method for preparing burr-like, spherical, coarse silver powder, the specific steps of which are as follows: S1. Weigh 160g of silver nitrate and dissolve it in 600mL of deionized water to obtain a silver nitrate solution for later use; dissolve 1.5g of hydrazine hydrate in 100mL of deionized water to prepare the first reducing agent solution; dissolve 80g of ascorbic acid in 1L of deionized water to prepare the second reducing agent solution. S2. Weigh 24g of polyvinylpyrrolidone and dissolve it in 200mL of deionized water. After complete dissolution, mix it evenly with silver nitrate solution. Quickly pour the first reducing agent solution into the mixture at 300r / min (addition time is 3s), and react for 1min. Continue stirring, add 3g of tartaric acid to the reaction system, adjust the pH of the reaction system to 6.5, and then add the second reducing agent solution dropwise to the system at 1min. Continue to react for 10min. S3. After the reaction is complete, the product is centrifuged at 3000 r / min for 10 min, and washed with deionized water and anhydrous ethanol alternately 3-4 times until the conductivity of the supernatant is <20 μs / cm. Then, it is dried in a forced-air drying oven at 80℃ for 10 h to obtain the burr-like spherical rough silver powder.

[0041] The rough, spherical silver powder prepared in Example 3 has a D50 of 1.61 μm, a specific surface area of ​​0.75 m² / g, and a true density of 9.91 g / cm³. Its electron micrograph is shown below. Figure 3As shown, the silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 16.318A and its FF was 82.49%.

[0042] Example 4 Example 4 provides a method for preparing burr-like spherical coarse silver powder. Compared with Example 1, the only difference is that the plasticizer is replaced with 0.08 g formic acid, and the other steps are the same as in Example 1.

[0043] The rough, spherical silver powder prepared in Example 4 has a D50 of 1.28 μm, a specific surface area of ​​0.48 m² / g, and a true density of 9.95 g / cm³. This silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 16.098 A and its FF was 82.15%.

[0044] Example 5 Example 5 provides a method for preparing burr-like spherical coarse silver powder. Compared with Example 1, the only difference is that the plasticizer is replaced with 2.16 g of succinic acid, and the other steps are the same as in Example 1.

[0045] The rough, spherical silver powder prepared in Example 5 has a D50 of 1.42 μm, a specific surface area of ​​0.55 m² / g, and a true density of 9.92 g / cm³. This silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 16.005 A and its FF was 82.38%.

[0046] Example 6 Example 6 provides a method for preparing burr-like spherical coarse silver powder. Compared with Example 1, the only difference is that the plasticizer is replaced with 3 g of maleic acid, and the other steps are the same as in Example 1.

[0047] The rough, spherical silver powder prepared in Example 6 has a D50 of 1.37 μm, a specific surface area of ​​0.56 m² / g, and a true density of 9.93 g / cm³. This silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 16.012 A and its FF was 82.35%.

[0048] Comparative Example 1 Comparative Example 1 provides a method for preparing silver powder. The only difference from Example 1 is that no plasticizer is used, while the other steps are the same as in Example 1.

[0049] The silver powder prepared in Comparative Example 1 was spherical with a relatively smooth surface, D50 = 1.43 μm, a specific surface area of ​​0.35 m² / g, and a true density of 10.12 g / cm³. Its electron micrograph is shown below. Figure 4 As shown, the silver powder was used to prepare conductive silver paste, which was printed on TOPCon solar cells. Under standard test conditions, its Isc was 14.853A and FF was 80.47%.

[0050] Comparative Example 2 Comparative Example 2 provides a method for preparing silver powder. Compared with Example 1, the only difference is that after the plasticizer and the first reducing agent solution are mixed evenly, they are added together to the silver nitrate-dispersant system. The remaining steps are the same as in Example 1.

[0051] After the plasticizer described in Comparative Example 2 was added in advance, it did not participate in the selective adsorption of the crystal face, but instead interfered with the uniformity of the primary crystal nuclei. The prepared silver powder was spherical with no obvious burr structure, D50=1.51μm, specific surface area of ​​0.32 m² / g, and true density of 10.15g / cm³. This silver powder was used to prepare conductive silver paste and printed on TOPCon solar cells. Under standard test conditions, its Isc was 16.03A and FF was 80.02%.

[0052] Comparative Example 3 Comparative Example 3 provides a method for preparing silver powder. Compared with Example 1, the only difference is that no dispersant is added, and the remaining steps are the same as in Example 1.

[0053] In Comparative Example 3, the lack of dispersant led to the inability of crystal nuclei to disperse stably, resulting in uncontrolled subsequent growth. The prepared silver powder exhibited severe agglomeration, forming a mixture of sheet-like and spiky morphologies. The D50 was 3.2 μm, the specific surface area was 0.12 m² / g, and the true density was 10.37 g / cm³. This silver powder was used to prepare conductive silver paste, which was then printed onto TOPCon solar cells. Under standard testing conditions, its Isc was measured to be 12.85 A and its FF was 77.35%.

[0054] As can be seen from the above comparison, the burr-shaped, rough silver powder prepared by this invention has a higher specific surface area and lower true density compared to traditional spherical silver powder. When applied to the conductive silver paste for TOPCon batteries, it can significantly improve the short-circuit current (Isc) and fill factor (FF) of the battery. This is due to its unique structure, which increases the contact area between the silver powder and the silicon wafer, thereby improving conductivity. Furthermore, by adjusting the process parameters, the performance of the silver powder can be flexibly controlled to meet different needs, making it suitable for mass production.

[0055] 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 burr-like, spherical, coarse silver powder, characterized in that, Includes the following steps: S1. Prepare silver nitrate solution with a concentration of 0.5~2.0 mol / L, a first reducing agent solution with a concentration of 0.05~0.6 mol / L, and a second reducing agent solution with a concentration of 0.2~1.5 mol / L, respectively; S2. Mix the dispersant solution and the silver nitrate solution evenly, add the first reducing agent solution, and stir the reaction for 1-3 min; then add the plasticizer, adjust the pH of the system to 5-8, add the second reducing agent solution, and continue stirring the reaction for 5-15 min; S3. The reaction product obtained in step S2 is centrifuged, washed and dried to obtain the burr-like spherical rough silver powder.

2. The method for preparing burr-like spherical coarse silver powder according to claim 1, characterized in that, Step S1: The solute in the first reducing agent solution is selected from at least one of hydrazine hydrate, sodium borohydride, ascorbic acid, formaldehyde, and ethylene glycol; and / or In step S2, the solute in the second reducing agent solution is selected from at least one of ascorbic acid, glucose, and hydrazine hydrate.

3. The method for preparing burr-like, spherical, coarse silver powder according to claim 1 or 2, characterized in that, In step S2, the mass ratio of the dispersant in the dispersant solution to the silver nitrate in the silver nitrate solution is 0.03~0.3:1; and / or In step S2, the mass ratio of the first reducing agent in the first reducing agent solution to the silver nitrate in the silver nitrate solution is 0.001~0.1:1; and / or In step S2, the mass ratio of the second reducing agent in the second reducing agent solution to the silver nitrate in the silver nitrate solution is 0.1~0.8:

1.

4. The method for preparing burr-like spherical coarse silver powder according to claim 1, characterized in that, In step S2, the first reducing agent solution is added completely within 2-10 seconds; and / or In step S2, the second reducing agent solution is added within 1 to 5 minutes.

5. The method for preparing the burr-like, spherical, coarse silver powder according to claim 1, characterized in that, The stirring rate of the stirring reaction in step S2 is 200~400 r / min; and / or The concentration of the dispersant solution in step S2 is 0.12~0.15 g / mL; and / or The centrifugation speed in step S3 is 3000~5000 r / min, and the centrifugation time is 10~15 min.

6. The method for preparing burr-like spherical coarse silver powder according to claim 1, characterized in that, The dispersant in step S2 is at least one of anhydrous ethanol, polyethylene glycol, gelatin, gum arabic, and polyvinylpyrrolidone; and / or The plasticizer mentioned in step S2 is at least one of formic acid, acetic acid, propionic acid, succinic acid, glutaric acid, oxalic acid, citric acid, maleic acid, tartaric acid and their sodium salts.

7. The method for preparing burr-like, spherical, coarse silver powder according to claim 1, characterized in that, The mass ratio of the plasticizer to the silver nitrate in the silver nitrate solution in step S2 is 0.0005~0.12:

1.

8. The method for preparing burr-like spherical coarse silver powder according to claim 1, characterized in that, The specific washing method described in step S3 is as follows: wash alternately with deionized water and anhydrous ethanol 3-4 times until the conductivity of the washing solution is <20 μS / cm; and / or The drying temperature in step S3 is 75~95℃, and the drying time is 7~10h.

9. The burr-like spherical coarse silver powder prepared by the method according to any one of claims 1 to 8.

10. The application of the burr-like spherical coarse silver powder of claim 9 in the preparation of TOPCon battery conductive paste.

Images