A silver powder and a preparation method thereof

Abstract

The present invention provides a silver powder and a preparation method thereof. The silver powder is a polycrystalline silver powder composed of a number of primary particles, and the tapped density of the silver powder is ≥ 6.0 g / cm 3 , the Span of the particle size distribution of the silver powder is 0.7 to 1.0, the through-hole porosity of the silver powder is 3% to 10%, and the major axis length of the primary particle is 0.3 μm to 0.8 μm. The silver powder has a porous structure inside, high tapped density, and uniform particle size distribution, which can reduce the sintering temperature of the silver powder and improve the electrical conductivity after silver powder printing while ensuring its excellent printing performance. The present invention also provides a preparation method of the silver powder.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal powder preparation, and particularly relates to a silver powder and a preparation method thereof. Background Art

[0002] With the rapid development of the photovoltaic industry, the requirements for photovoltaic silver paste are getting higher and higher. The silver paste basically contains the following components: silver powder, glass frit, organic resin, organic solvent, and other inorganic additives. As one of the main components of the silver paste, the particle size distribution and internal structure are particularly important for the performance of the silver paste. In the industry, silver paste manufacturers generally require that the silver powder has a uniform particle size distribution and a high tapped density. The silver paste prepared from silver powder with a uniform particle size distribution can smoothly pass through the screen, and there are no breakpoints or disconnection phenomena during the printing process; the silver powder with a high tapped density has good crystal integrity, high solid content and low viscosity in the slurry under the same ratio, and the printed conductive film is dense and has good conductivity.

[0003] At present, the melting temperature of conventional glass powder is 400 - 500°C. Excessive tapped density will make it difficult for the silver powder to melt, and a higher sintering temperature is required, resulting in a large difference in the melting points of the silver powder and the glass frit, and thus printing problems occur. Therefore, how to reduce the sintering temperature of the silver powder while maintaining a high tapped density and a uniform particle size distribution is one of the great challenges faced by silver powder manufacturers. Summary of the Invention

[0004] The present invention aims to at least solve one of the above technical problems in the prior art. For this purpose, the present invention provides a silver powder and a preparation method thereof. The silver powder has a porous structure inside, high tapped density and uniform particle size distribution, and can reduce the sintering temperature of the silver powder and improve the conductivity of the printed silver powder while ensuring its excellent printing performance.

[0005] The present invention also provides a preparation method of a silver powder.

[0006] In the first aspect of the present invention, there is provided a silver powder, which is a polycrystalline silver powder composed of a number of primary particles. The tapped density of the silver powder is ≥6.0 g / cm 3 , the Span of the particle size distribution of the silver powder is 0.7 - 1.0, the through-hole porosity of the silver powder is 3% - 10%, and the major axis length of the primary particle is 0.3 μm - 0.8 μm.

[0007] One technical solution in the technical solution of the present invention regarding the silver powder has at least the following beneficial effects:

[0008] The silver powder material of the present invention is polycrystalline silver powder composed of a number of primary particles, having a polycrystalline structure. The major axis length of the primary particles is 0.3 μm to 0.8 μm. The primary particles are smaller, with higher surface energy and good silver powder activity, which is beneficial to faster softening during high-temperature sintering, forming a dense silver film and improving conductivity. The Span of the particle size distribution of the silver powder is 0.7 to 1.0, the particle size distribution is concentrated, and it has the characteristic of good particle size uniformity. The particles are uniform, and the particle uniformity is good, which can reduce the thixotropy index after preparing the silver paste, reduce the occurrence of breakpoints and broken lines during the printing process of the silver powder, and can also improve the conductivity of the conductive film after sintering.

[0009] The silver powder material of the present invention has a cut pore rate of 3% to 10%. On the premise that the silver powder can maintain a high tapped density and a uniform particle size distribution, it can also reduce the sintering temperature of the silver powder, enabling the silver powder to better match the glass powder and the organic carrier, and improving the comprehensive printing performance of the silver paste. The tapped density of the silver powder is 6.0 g / cm 3 ~6.8 g / cm 3 , and the high tapped density ensures its good filling performance, making the printed line shape of the silver paste better.

[0010] In addition, due to the silver powder having a uniform particle size distribution and an internal pore structure, the rheological properties of the silver paste are also improved. This means that the silver paste has better fluidity during the printing process and is easier to control, thereby improving the printing consistency and efficiency.

[0011] By using silver powder with a uniform particle size distribution and a polycrystalline structure inside, the prepared silver paste can be better compatible with other materials, reducing the defects and non-uniformities that may occur during the preparation process, thereby improving the production quality and stability of photovoltaic devices.

[0012] Among them, the primary particles are approximately cuboid, and the major axis is approximately the length of the cuboid. The "major axis length of the primary particles" refers to the distance between the two farthest opposite sides of the largest surface of the primary particles.

[0013] According to some embodiments of the present invention, the loose bulk density of the silver powder ≥ 3.0 g / cm 3 .

[0014] According to some embodiments of the present invention, the loose bulk density is 3.0 g / cm 3 ~3.8 g / cm 3 .

[0015] When silver powder with a relatively high tap density is used to fill a carrier (such as an organic resin), it can fill the voids more tightly, enabling the silver paste to be more evenly distributed on the surface of the substrate during the printing process. This can improve the density and conductivity of the printed product. Due to the relatively high tap density, the fluidity of the silver powder may be relatively good, making it easier to be transported and controlled during the printing process. This will help improve the printing speed and efficiency, thereby reducing production costs and increasing production capacity. Silver powder with a relatively high tap density can also be more evenly distributed on the printed substrate, reducing printing defects caused by uneven distribution of silver powder, such as breakpoints and broken lines. Therefore, the quality and stability of the product may be improved.

[0016] In addition, a relatively high tap density can reduce the amount of silver powder required, thereby reducing production costs. At the same time, due to the improved filling performance and increased printing efficiency, the scrap rate can also be reduced, further reducing production costs.

[0017] The silver powder with high tapped and loose bulk densities has a high solid content and low viscosity after being made into a paste. After printing and sintering, the formed conductive film is dense and uniform, with small and few holes in the film and a relatively low porosity, and has excellent electrical conductivity.

[0018] The cut pore rate of the silver powder is 3% - 10%, and the pore rate value is obtained by calculating the ratio of the pore area of the cross-section of the silver powder sphere to the total cross-sectional area. A certain range of pore rates can reduce the sintering temperature of the silver powder while not affecting the tapped density, and improve the printing and electrical conductivity of the silver paste.

[0019] The pores inside the silver powder are beneficial for its rapid softening during the sintering process of the silver paste, reducing the sintering temperature, thus achieving good printability and increasing its electrical conductivity. The pore structure inside the silver powder also helps to increase the contact area between the silver powder and the organic resin, thereby enhancing the electrical conductivity. This means that when preparing devices such as photovoltaic cells, the required conductive layer can be more evenly covered on the surface of the substrate, improving the electrical conductivity and stability of the device.

[0020] According to some embodiments of the present invention, the average particle size D50 of the silver powder is 1.2 μm - 2.0 μm.

[0021] A moderate average particle size enables the silver powder to better fill the microstructure of printed circuit boards or solar cells, thereby improving the filling performance and encapsulation effect of the silver paste. With a moderate average particle size of the silver powder, it can also promote the formation of conductive paths, thus enhancing the conductivity of the silver paste and being beneficial to the performance of electronic devices. Further, a moderate average particle size enables the silver powder to be more evenly distributed during the printing and sintering processes, contributing to the formation of a more uniform and dense silver film, thereby improving the performance and stability of the device. A moderate average particle size can improve the rheological properties of the silver paste, making it easier to flow and control during the printing process, thus enhancing the printing consistency and efficiency. Finally, a moderate average particle size can reduce the loss of silver powder during the printing and sintering processes, improve the utilization rate of silver powder, and reduce production costs.

[0022] The second aspect of the present invention provides a method for preparing silver powder, comprising the following steps:

[0023] S1: Prepare 4 - 5 parts of a reaction bottom solution containing a dispersant and a reducing agent;

[0024] S2: Add 0.01 - 0.02 parts of a first silver source solution containing a reducing agent to 0.8 - 1.2 parts of a second silver source solution to obtain a precursor solution;

[0025] S3: Add the precursor solution to the reaction bottom solution for reaction, and after the feeding is completed, add a coating agent for coating to obtain the silver powder.

[0026] One technical solution in the method for preparing silver powder according to the present invention has at least the following beneficial effects:

[0027] The preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are easily available, the production cost is low, and it is easy to be industrially produced.

[0028] The core steps of the method for preparing silver powder according to the present invention lie in the preparation of the precursor solution and the redox reaction process.

[0029] By controlling the ratio of the reducing agent to the silver source solution, the conditions for preparing precursor microcrystals of a certain size are achieved; meanwhile, by controlling the existence time of the precursor solution, the silver powder microcrystals inside the solution can grow appropriately.

[0030] Adopting the process mode of adding the precursor solution to the reducing agent / dispersant mixed solution (i.e., the reaction bottom solution) enables the silver powder microcrystals in the precursor solution to continuously grow in the reaction kettle, and finally silver powder with a certain particle size distribution is obtained.

[0031] By controlling the molar concentration ratio of the oxidizing agent (silver source, specifically silver nitrate) to the reducing agent and controlling the reaction time, silver microcrystal clusters are rapidly formed during the reaction to reach a supersaturated state. When the cluster state breaks through the critical nucleation radius, large clusters will grow into large crystal nuclei. Pores of different sizes are formed inside it.

[0032] According to some embodiments of the present invention, the dispersant includes at least one of polyvinylpyrrolidone (PVP), Tween 80, and oleic acid.

[0033] According to some embodiments of the present invention, the dispersant is polyvinylpyrrolidone (PVP).

[0034] According to some embodiments of the present invention, in the reaction bottom liquid, the mass percentage of the dispersant is 1.0 wt% - 1.2 wt%.

[0035] According to some embodiments of the present invention, the reducing agent includes at least one of glucose, formaldehyde, hydrazine hydrate, and ascorbic acid.

[0036] According to some embodiments of the present invention, in the reaction bottom liquid, the mass percentage of the reducing agent is 3.5 wt% - 4.2 wt%.

[0037] According to some embodiments of the present invention, in step S1, the method for preparing the reaction bottom liquid can be:

[0038] Add 400 - 500 L of pure water into the reaction kettle, add 3.5 wt% - 4.2 wt% of the reducing agent and 1.0 wt% - 1.2 wt% of the dispersant, stir at a speed of 180 rpm - 260 rpm for about 30 minutes to mix evenly, and an appropriate amount of ammonia water can be added to control the pH of the mixed solution between 3.0 and 4.5.

[0039] According to some embodiments of the present invention, the components of the first silver source solution include a reducing agent and a first silver source.

[0040] According to some embodiments of the present invention, the reducing agent includes at least one of glucose, formaldehyde, hydrazine hydrate, and ascorbic acid.

[0041] According to some embodiments of the present invention, the reducing agent is ascorbic acid.

[0042] According to some embodiments of the present invention, the first silver source includes silver nitrate.

[0043] According to some embodiments of the present invention, in the first silver source solution, 0.005 to 0.01 parts of a reducing agent are included, the molar concentration of the reducing agent is 0.03 to 0.08 mol / L, and the molar concentration of silver ions in the first silver source solution is 1.00 to 3.00 mol / L.

[0044] According to some embodiments of the present invention, in the first silver source solution, the molar concentration ratio of the reducing agent to the first silver source is 1:25.0 to 37.5.

[0045] According to some embodiments of the present invention, the components of the second silver source solution include a second silver source.

[0046] According to some embodiments of the present invention, the second silver source includes silver nitrate.

[0047] According to some embodiments of the present invention, in the second silver source solution, the mass percentage of silver nitrate is 30 wt% to 38 wt%.

[0048] According to some embodiments of the present invention, the preparation method of the second silver source solution may be:

[0049] At room temperature, silver nitrate with a mass percentage of 30 wt% to 38 wt% is added to 80 to 120 L of pure water with a conductivity ≤ 2 μS / cm.

[0050] According to some embodiments of the present invention, in step S2, the method for obtaining the precursor solution may be:

[0051] Prepare 0.5 L to 1.0 L of a reducing agent solution with a concentration of 0.03 mol / L to 0.08 mol / L, add it to 0.5 L to 1.0 L of a silver nitrate solution with a concentration of 1.0 to 3.0 mol / L to form a first silver source solution; add the first silver source solution to 80 to 120 L of a second silver source solution with a nitric acid mass percentage of 30 to 38 wt% to obtain a precursor.

[0052] According to some embodiments of the present invention, starting from preparing the precursor solution in step S2 (specifically, starting from adding the first silver source solution to the second silver source solution), until the precursor solution is added to the reaction bottom liquid in step S3 for reaction, the interval time is 3 min to 10 min, that is, the interval time from the start of forming the precursor solution to the precursor solution participating in the reaction is 3 min to 10 min.

[0053] Add the precursor solution to the reaction bottom liquid for reaction, and maintain a stirring speed of 180 rpm to 260 rpm during the reaction process.

[0054] According to some embodiments of the present invention, the coating agent includes at least one of stearic acid, lauric acid, gelatin, and gum arabic.

[0055] According to some embodiments of the present invention, the dosage of the coating agent is 0.13 wt% to 0.18 wt% of the total mass of silver nitrate.

[0056] According to some embodiments of the present invention, the time for adding the coating agent for coating is 5 min to 10 min.

[0057] According to some embodiments of the present invention, the method further includes post-treating the product after adding the coating agent for coating.

[0058] According to some embodiments of the present invention, the post-treatment includes: cleaning, dewatering, emulsifying, drying, and crushing.

[0059] Cleaning and dewatering can be carried out by a centrifuge or a press dryer. After cleaning and dewatering, a wet silver powder material with a water content of 10 - 25% is obtained.

[0060] Emulsification can be carried out with alcohol 1.0 times the mass of silver powder and a modifying agent with a mass fraction of 0.1% - 0.5% of silver powder. The modifying agent can be stearic acid, lauric acid, gelatin, gum arabic, or a substance selected from amide substances or alcohol substances. It is carried out in an emulsifier. The rotation speed of the emulsifier is 1000 - 2000 r / min. The emulsification temperature can be 30 - 40 °C. The emulsification time is 30 min - 60 min. After emulsification, a press dryer or a centrifuge is used for dehydration.

[0061] After emulsification, the dehydrated silver powder is placed on a tray and put into an oven. The drying temperature is controlled at 60 - 70 °C, and the drying time is 6 - 10 hours.

[0062] Finally, the dried silver powder is crushed using a jet mill, and the crushing air pressure is 0.5 - 1.0 Mpa to obtain silver powder with good dispersibility and high tapped density.

[0063] According to some embodiments of the present invention, the method for preparing silver powder can be:

[0064] Step 1, preparation of silver nitrate solution: Prepare a solution of 80 L to 120 L with a silver nitrate mass fraction of 30 - 38 wt%, and control the solution temperature at 20 - 30 °C;

[0065] Step 2, preparation of bottom liquid: Add 400 L to 500 L of pure water to the reaction kettle, add a reducing agent and a dispersant, where the mass fraction of the reducing agent is 3.5 - 4.2 wt% and the mass fraction of the dispersant is 1.0 - 1.2 wt%; then add an appropriate amount of ammonia water to control the pH of the mixed solution between 3.0 - 4.5;

[0066] Step 3. Preparation of precursor solution: Prepare 0.5 - 1.0 L of a reducing agent solution with a concentration of 0.03 - 0.08 mol / L, add 0.5 - 1.0 L of a silver nitrate solution with a concentration of 2.0 - 3.0 mol / L, and control the molar concentration ratio of silver nitrate to the reducing agent at (25 - 37.5):1. Mix them evenly to obtain a mixed solution, and add it to the silver nitrate solution in Step 1 to form a precursor solution. Control the interval time from the addition of the mixed solution to the silver nitrate solution until the next redox reaction at 3 - 10 min, that is, the time for the formation and standing of the precursor solution is 3 - 10 min.

[0067] Step 4. Redox reaction: Keep the reaction kettle at a constant temperature of 20 - 25 °C, maintain a constant value between 180 - 260 r / min during the process reaction stirring, and stop temperature control after reaching the requirement. Add the prepared precursor solution evenly into the reaction kettle within 300 - 360 s;

[0068] Step 5: After the feeding is completed, add a coating agent (such as stearic acid, lauric acid, gelatin, gum arabic, etc.) (0.13 - 0.18% of the mass of silver nitrate) to coat it, control the coating time at 5 - 10 min, then discharge the material, and obtain silver powder after at least one post-treatment such as centrifugation, pressing dry, drying, and air milling. Description of the Drawings

[0069] Figure 1 It is the microscopic morphology diagram of the silver powder prepared in Example 1.

[0070] Figure 2 It is the microscopic morphology diagram of the commercially available silver powder.

[0071] Figure 3 It is the microscopic morphology diagram of the cross-section of the silver powder prepared in Example 1.

[0072] Figure 4 It is the microscopic morphology diagram of the cross-section of the silver powder prepared in Comparative Example 1.

[0073] Figure 5 It is the electron microscope image of the silver powder in Example 1 at 20,000 times magnification.

[0074] Figure 6 It is the electron microscope image of the silver powder in Comparative Example 1 at 20,000 times magnification.

[0075] Figure 7 It is the electron microscope image of the silver powder in Comparative Example 3.

[0076] Figure 8 It is the electron microscope image of the silver powder in Comparative Example 4. Detailed Embodiments

[0077] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in combination with the embodiments, but the present invention is not limited to these embodiments.

[0078] In an embodiment of the first aspect of the present invention, a silver powder is provided. The silver powder is a polycrystalline silver powder composed of a number of primary particles, and the tapped density of the silver powder is ≥6.0 g / cm 3 , the Span of the particle size distribution of the silver powder is 0.7 to 1.0, the through-hole porosity of the silver powder is 3% to 10%, and the major axis length of the primary particle is 0.3 μm to 0.8 μm.

[0079] It should be noted that the silver powder material of the present invention is a polycrystalline silver powder composed of a number of primary particles, having a polycrystalline structure. The major axis length of the primary particle is 0.3 μm to 0.8 μm. The primary particles are smaller, with higher surface energy and good silver powder activity, which is beneficial to faster softening during high-temperature sintering, forming a dense silver film and improving conductivity. The Span of the particle size distribution of the silver powder is 0.7 to 1.0, the particle size distribution is concentrated, with the characteristic of good particle size uniformity. The particles are uniform, with good particle uniformity, which can reduce the thixotropy index after preparing the silver paste, reduce the occurrence of breakpoints and broken lines during the printing process of the silver powder, and can also improve the conductivity of the sintered conductive film.

[0080] It can be understood that the silver powder material of the present invention has a through-hole porosity of 3% to 10%, enabling the silver powder to maintain a high tapped density and uniform particle size distribution, while also reducing the sintering temperature of the silver powder, making the silver powder better match the glass powder and organic carrier, and improving the comprehensive printing performance of the silver paste.

[0081] In addition, due to the silver powder having a uniform particle size distribution and internal pore structure, the rheological properties of the silver paste are also improved. This means that the silver paste has better fluidity during the printing process and is easier to control, thereby improving the printing consistency and efficiency.

[0082] It should also be noted that by using silver powder with a uniform particle size distribution and an internal polycrystalline structure, the prepared silver paste can be better compatible with other materials, reducing the defects and non-uniformities that may occur during the preparation process, thereby improving the production quality and stability of photovoltaic devices.

[0083] Among them, the primary particle is approximately a cuboid, and the major axis is approximately the length of the cuboid. The "major axis length of the primary particle" refers to the distance between the two farthest opposite sides of the largest surface of the primary particle.

[0084] Combined with the embodiment of the first aspect of the present invention, in some embodiments, the tapped density is 6.0 g / cm 3 ~6.8 g / cm 3 .

[0085] A high tap density ensures good filling performance, resulting in a better printed line shape of the silver paste.

[0086] Combined with the embodiments of the first aspect of the present invention, in some embodiments, the loose bulk density of the silver powder is ≥ 3.0 g / cm 3 .

[0087] Combined with the embodiments of the first aspect of the present invention, in some embodiments, the loose bulk density is 3.0 g / cm 3 ~3.8 g / cm 3 .

[0088] When silver powder with a relatively high loose bulk density fills the carrier (such as organic resin), it can fill the voids more tightly, enabling the silver paste to be more evenly distributed on the substrate surface during printing. This can improve the density and conductivity of the printed product. Due to the relatively high loose bulk density, the fluidity of the silver powder may be relatively better, making it easier to be transported and controlled during printing. This will help improve the printing speed and efficiency, thereby reducing production costs and increasing production capacity. Silver powder with a relatively high loose bulk density can also be more evenly distributed on the printed substrate, reducing printing defects caused by uneven distribution of silver powder, such as breakpoints and broken lines. Therefore, the quality and stability of the product may be improved.

[0089] In addition, a relatively high loose bulk density can reduce the amount of silver powder required, thereby reducing production costs. At the same time, due to the improved filling performance and increased printing efficiency, the scrap rate can also be reduced, further reducing production costs.

[0090] Silver powder with high tap and loose bulk densities has a high solid content and low viscosity after being adjusted into a paste. After printing and sintering, the formed conductive film is dense and uniform, with small and few holes in the film and a relatively low porosity, and has excellent conductive performance.

[0091] Combined with the embodiments of the first aspect of the present invention, in some embodiments, the cut pore rate of the silver powder is 3% - 10%.

[0092] The porosity value is obtained by calculating the ratio of the pore area to the total cross-sectional area of the silver powder sphere. A certain range of porosity can reduce the sintering temperature of the silver powder while not affecting the tap density, and improve the printing and conductive performance of the silver paste.

[0093] The pores inside the silver powder are beneficial for its rapid softening during the sintering process of the silver paste, reducing the sintering temperature, thereby achieving good printability and increasing its conductive ability. The pore structure inside the silver powder also helps to increase the contact area between the silver powder and the organic resin, thereby enhancing the conductive performance. This means that when preparing devices such as photovoltaic cells, the required conductive layer can cover the substrate surface more evenly, improving the conductive performance and stability of the device.

[0094] Combined with the embodiments of the first aspect of the present invention, in some embodiments, the average particle size D50 of the silver powder is 1.2 μm to 2.0 μm.

[0095] An appropriate average particle size can enable the silver powder to better fill the microstructures of printed circuit boards or solar cells, thereby improving the filling performance and encapsulation effect of the silver paste. With a moderate average particle size of the silver powder, it can also promote the formation of conductive paths, thus improving the electrical conductivity of the silver paste and being beneficial to the performance of electronic devices. Further, an appropriate average particle size can make the silver powder more evenly distributed during the printing and sintering processes, contributing to the formation of a more uniform and dense silver film, thereby improving the performance and stability of the device. An appropriate average particle size can improve the rheological properties of the silver paste, making it easier to flow and control during the printing process, thus improving the printing consistency and efficiency. Finally, an appropriate average particle size can reduce the loss of silver powder during the printing and sintering processes, improve the utilization rate of silver powder, and reduce production costs.

[0096] In the embodiments of the second aspect of the present invention, a method for preparing silver powder is provided, including the following steps:

[0097] S1: Prepare 4 to 5 parts of a reaction bottom solution containing a dispersant and a reducing agent;

[0098] S2: Add 0.01 to 0.02 parts of a first silver source solution containing a reducing agent to 0.8 to 1.2 parts of a second silver source solution to obtain a precursor solution;

[0099] S3: Add the precursor solution to the reaction bottom solution for reaction, and after the addition is completed, add a coating agent for coating to obtain silver powder.

[0100] It can be understood that the preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are easily available, the production cost is low, and it is easy to be industrially produced.

[0101] It should be noted that for the preparation method of silver powder of the present invention, the core steps lie in the preparation of the precursor solution and the redox reaction process.

[0102] It should also be noted that by controlling the ratio of the reducing agent to the silver source solution, the conditions for preparing precursor microcrystals of a certain size are achieved; at the same time, by controlling the existence time of the precursor solution, the silver powder microcrystals inside the solution can grow appropriately.

[0103] Further, by adopting the process mode of adding the precursor solution to the reducing agent / dispersant mixed solution (i.e., the reaction bottom solution), the silver powder microcrystals in the precursor solution continuously grow in the reaction kettle, and finally silver powder with a certain particle size distribution is obtained.

[0104] By controlling the molar concentration ratio of the oxidant to the reductant and controlling the reaction time, silver microcrystal clusters are rapidly formed during the reaction to reach a supersaturated state. When the cluster state breaks through the critical nucleation radius, the large clusters will grow into large crystal nuclei. Pores of different sizes are formed inside.

[0105] Combined with the embodiments of the second aspect of the present invention, in some embodiments, the dispersant includes at least one of polyvinylpyrrolidone (PVP), Tween 80, and oleic acid.

[0106] Combined with the embodiments of the second aspect of the present invention, in some embodiments, the dispersant is polyvinylpyrrolidone (PVP).

[0107] Combined with the embodiments of the second aspect of the present invention, in some embodiments, in the reaction bottom liquid, the mass percentage of the dispersant is 1.0 wt% - 1.2 wt%.

[0108] Combined with the embodiments of the second aspect of the present invention, in some embodiments, the reductant includes at least one of glucose, formaldehyde, hydrazine hydrate, and ascorbic acid.

[0109] Combined with the embodiments of the second aspect of the present invention, in some embodiments, in the reaction bottom liquid, the mass percentage of the reductant is 3.5 wt% - 4.2 wt%.

[0110] Combined with the embodiments of the second aspect of the present invention, in some embodiments, in the first silver source solution, it includes 0.005 - 0.01 parts of reductant, the molar concentration of the reductant is 0.03 - 0.08 mol / L, the molar concentration of silver ions in the first silver source solution is 1.00 - 3.00 mol / L, and the molar concentration ratio of the reductant to silver ions is 1:25.00 - 37.50.

[0111] Combined with the embodiments of the second aspect of the present invention, in some embodiments, in step S1, the method for preparing the reaction bottom liquid can be:

[0112] Add 400 - 500 L of pure water into the reaction kettle, add 3.5 wt% - 4.2 wt% of reductant and 1.0 wt% - 1.2 wt% of dispersant, stir at a speed of 180 rpm - 260 rpm for about 30 minutes to mix evenly, and then an appropriate amount of ammonia water can be added to control the pH of the mixed solution between 3.0 and 4.5.

[0113] Combined with the embodiments of the second aspect of the present invention, in some embodiments, the components of the first silver source solution include a reductant and a first silver source.

[0114] Combined with the embodiments of the second aspect of the present invention, in some embodiments, the reductant includes at least one of glucose, formaldehyde, hydrazine hydrate, and ascorbic acid.

[0115] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the reducing agent is ascorbic acid.

[0116] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the first silver source includes silver nitrate.

[0117] In combination with the embodiments of the second aspect of the present invention, in some embodiments, in the first silver source solution, the molar concentration ratio of the reducing agent to the first silver source is 1:25.0 to 37.5.

[0118] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the components of the second silver source solution include a second silver source.

[0119] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the second silver source includes silver nitrate.

[0120] In combination with the embodiments of the second aspect of the present invention, in some embodiments, in the second silver source solution, the mass percentage of silver nitrate is 30 wt% to 38 wt%.

[0121] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the preparation method of the second silver source solution can be:

[0122] At room temperature, silver nitrate with a mass percentage of 30 wt% to 38 wt% is added to pure water with a conductivity ≤ 2 μS / cm.

[0123] In combination with the embodiments of the second aspect of the present invention, in some embodiments, in step S2, the method for obtaining the precursor solution can be:

[0124] Prepare 0.5 L to 1.0 L of a reducing agent solution with a concentration of 0.03 mol / L to 0.08 mol / L, add it to 0.5 L to 1.0 L of a silver nitrate solution with a concentration of 1.0 to 3.0 mol / L to form a first silver source solution; add the first silver source solution to 80 to 120 L of a second silver source solution with a mass percentage of silver nitrate of 30 - 38 wt% to obtain a precursor solution.

[0125] In combination with the embodiments of the second aspect of the present invention, in some embodiments, starting from preparing the precursor solution in step S2 (specifically, starting from adding the first silver source solution to the second silver source), until the precursor solution is added to the reaction bottom liquid for reaction in step S3, the interval time is 3 min to 10 min.

[0126] Add the precursor solution to the reaction bottom liquid for reaction, and maintain a stirring speed of 180 rpm to 260 rpm during the reaction process.

[0127] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the coating agent includes at least one of stearic acid, lauric acid, gelatin, and gum arabic.

[0128] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the dosage of the coating agent is 0.13 wt% - 0.18 wt% of the total mass of silver nitrate.

[0129] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the time for adding the coating agent for coating is 5 min - 10 min.

[0130] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the preparation method further includes post-treating the product after adding the coating agent for coating.

[0131] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the post-treatment includes: cleaning, dehydration, emulsification, drying, and crushing.

[0132] Cleaning and dehydration can be carried out by a centrifuge or a press dryer. After cleaning and dehydration, a wet silver powder material with a water content of 10 - 25% is obtained.

[0133] Emulsification can use alcohol with a mass 1.0 times that of the silver powder and a modified additive with a mass of 0.1% - 0.5% of the silver powder. The modified additive can be stearic acid, lauric acid, gelatin, gum arabic, or one selected from amide substances or alcohol substances, and is carried out in an emulsifier. The rotation speed of the emulsifier is 1000 - 2000 r / min. The emulsification temperature can be 30 - 40 °C. The emulsification time is 30 min - 60 min. After emulsification, dehydration is carried out using a press dryer or a centrifuge.

[0134] After emulsification, the dehydrated silver powder is loaded into a tray and placed in an oven. The drying temperature is controlled at 60 - 70 °C, and the drying time is 6 - 10 hours.

[0135] Finally, the dried silver powder is crushed using a jet mill, and the crushing air pressure is 0.5 - 1.0 Mpa to obtain silver powder with good dispersibility and high tapped density.

[0136] In combination with the embodiments of the second aspect of the present invention, in some embodiments, the preparation method of the silver powder can be:

[0137] Step 1: Preparation of silver nitrate solution: Prepare a solution of 80 L - 120 L with a silver nitrate mass fraction of 30 - 38 wt%, and control the solution temperature at 20 - 30 °C;

[0138] Step 2. Preparation of the base solution: Add 400 L to 500 L of pure water into the reaction kettle, and then add a reducing agent and a dispersant. The mass fraction of the reducing agent is 3.5 - 4.2 wt%, and the mass fraction of the dispersant is 1.0 - 1.2 wt%. Then add an appropriate amount of ammonia water to control the pH of the mixed solution between 3.0 and 4.5.

[0139] Step 3. Preparation of the precursor solution: Prepare 0.5 - 1.0 L of a reducing agent solution with a concentration of 0.03 - 0.08 mol / L, add 0.5 - 1.0 L of a silver nitrate solution with a concentration of 2.0 - 3.0 mol / L. Control the molar concentration ratio of silver nitrate to the reducing agent at (25 - 37.5):1, mix them evenly to obtain a mixed solution, and add it to the silver nitrate solution in Step 1 to form a precursor solution. Control the interval time from when the mixed solution is added to the silver nitrate solution until the next redox reaction is carried out at 3 - 10 min, that is, the time for the precursor solution to form and stand is 3 - 10 min.

[0140] Step 4. Redox reaction: Keep the reaction kettle at a constant temperature of 20 - 25 °C, and maintain a constant value of 180 - 260 r / min during the stirring of the process reaction. After reaching the requirement, stop the temperature control. Add the prepared precursor solution evenly into the reaction kettle within 300 - 360 s.

[0141] Step 5: After the feeding is completed, add a coating agent (such as stearic acid, lauric acid, gelatin, gum arabic, etc.) accounting for (0.13 - 0.18% of the total mass of silver nitrate) to coat it. Control the coating time at 5 - 10 min, then discharge the material, and obtain silver powder through at least one post-treatment such as centrifugation or pressing dry, drying, and air milling.

[0142] Next, the technical solution of the present invention will be better understood through specific embodiments.

[0143] Example 1

[0144] A kind of silver powder was prepared, and the specific steps were as follows:

[0145] Step 1. Preparation of the silver nitrate solution: Add silver nitrate crystals into 100 L of pure water (conductivity ≤ 2 uS / cm) for dissolution to prepare a solution with a concentration of 35 wt%. The conductivity of the pure water is required to be ≤ 2 um / cm, and control the temperature after dissolution at 25 °C.

[0146] Step 2. Preparation of the base solution: Add 450 L of pure water (conductivity ≤ 2 μS / cm) to the reaction kettle, and then add a reducing agent (industrial-grade vitamin C, which is L-ascorbic acid, commonly purchased on the market) and a dispersant (PVP, which is polyvinylpyrrolidone, commonly purchased on the market). The mass fraction of the reducing agent is 4.0 wt%, and the mass fraction of the dispersant is 1.1 wt%. During the process, stir at a constant value between 200 r / min for 30 minutes to make it mix evenly, and control the temperature at 20 - 25 °C. After meeting the requirements, add an appropriate amount of ammonia water to control the pH of the mixed solution at 4.

[0147] Step 3. Preparation of the precursor solution: Prepare 0.7 L of a reducing agent solution with a concentration of 0.06 mol / L (the reducing agent is industrial-grade vitamin C, which is L-ascorbic acid, commonly purchased on the market), add 0.6 L of a silver nitrate solution with a concentration of 1.5 mol / L, control the molar concentration ratio of silver nitrate to the reducing agent at 25:1, then mix it evenly to obtain a mixed solution, and add it to the silver nitrate solution in Step 1 to form a precursor solution. Control the interval time from the addition of the mixed solution to the silver nitrate solution to the start of the next step of the redox reaction at 6 min, that is, the preparation and standing time of the precursor solution is 6 min.

[0148] Step 4. Redox reaction: Add the prepared precursor solution evenly to the reaction kettle within 300 s. During the process, stir at a constant value between 200 r / min. After the feeding is completed, close the relevant valves.

[0149] Step 5. After the feeding is completed, add 0.15% of the coating agent stearic acid based on the mass of silver nitrate to coat it. During the process, keep the stirring speed unchanged, and control the coating time at 8 min.

[0150] Step 6. Cleaning of silver powder: Discharge the silver powder from the reaction kettle into a centrifuge for cleaning and dehydration to obtain wet silver powder with a water content of 18%.

[0151] Step 7. Emulsification of silver powder: Add the wet silver powder to an emulsifier, and add alcohol with a mass 1.0 times that of the silver powder and 0.3% of the modified auxiliary agent stearic acid based on the mass of the silver powder. Control the rotation speed of the emulsifier at 1500 r / min, the emulsification temperature at 35 °C, and the emulsification time at 40 minutes. After emulsification, use a centrifuge for dehydration.

[0152] Step 8. Drying of silver powder: Place the dehydrated silver powder on a tray and put it into an oven. Control the drying temperature at 60 °C and the drying time at 8 hours until the water content is lower than 25%.

[0153] Step 9: Silver powder crushing: The dried silver powder is crushed using a jet mill. The feeding speed is 40 kg / h, and the crushing air pressure is 1.0 Mpa, obtaining silver powder with good dispersibility and high tapped density.

[0154] Example 2

[0155] A kind of silver powder was prepared, and the specific steps were as follows:

[0156] Step 1: Solution preparation: Silver nitrate crystals are added to 100 L of pure water (conductivity ≤ 2 μS / cm) for dissolution to prepare a solution with a concentration of 38 wt%. The conductivity of the pure water is required to be ≤ 2 μS / cm, and the temperature after dissolution is controlled at 25 °C.

[0157] Step 2: Bottom liquid preparation: Add 450 L of pure water (conductivity ≤ 2 μS / cm) to the reaction kettle, and then add a reducing agent (industrial-grade vitamin C purchased conventionally in the market, vitamin C is L-ascorbic acid) and a dispersant (PVP purchased conventionally in the market, that is, polyvinylpyrrolidone). The mass fraction of the reducing agent is 4.2 wt%, and the mass fraction of the dispersant is 1.2 wt%. During the process, the stirring is maintained at a constant value between 200 r / min, and stirred for 30 minutes to make it mix evenly, and the temperature is controlled at 20 - 25 °C. After meeting the requirements, an appropriate amount of ammonia water is added to control the pH of the mixed solution at 5.

[0158] Step 3: Preparation of precursor solution: Prepare 1 L of a reducing agent solution with a concentration of 0.08 mol / L (the reducing agent is industrial-grade vitamin C purchased conventionally in the market, vitamin C is L-ascorbic acid), add 1 L of a silver nitrate solution with a concentration of 3 mol / L, and control the molar concentration ratio of silver nitrate to the reducing agent at 37.5:1. Then mix them evenly to obtain a mixed solution, and add it to the silver nitrate solution in Step 1 to form a precursor solution. Control the interval time from the addition of the mixed solution to the silver nitrate solution to the start of the next step of redox reaction at 3 min, that is, the formation and standing time of the precursor solution is 3 min.

[0159] Step 4: Redox reaction: The prepared precursor solution is evenly added to the reaction kettle within 300 s. During the process, the reaction stirring is maintained at a constant value between 200 r / min. After the feeding is completed, close the relevant valves.

[0160] Step 5: After the feeding is completed, add a coating agent stearic acid (0.15% of the mass of silver nitrate) to coat it. During the process, maintain the stirring speed unchanged, and control the coating time at 8 min.

[0161] Step 6: Silver powder cleaning: The silver powder in the reaction kettle is discharged into a centrifuge for cleaning and dehydration to obtain wet silver powder with a water content of 18%.

[0162] Step 7: Silver powder emulsification: Add the wet silver powder into an emulsifier, along with alcohol with a mass 1.0 times that of the silver powder and stearic acid as a modified additive with a mass of 0.3% of the silver powder. Control the rotation speed of the emulsifier at 1500 r / min, the emulsification temperature at 35 °C, and the emulsification time at 40 minutes. After emulsification, use a centrifuge for dehydration.

[0163] Step 8: Silver powder drying: Place the dehydrated silver powder on a tray and put it into an oven. Control the drying temperature at 60 °C and the drying time at 8 hours until the water content is lower than 25%.

[0164] Step 9: Silver powder crushing: Crush the dried silver powder using a jet mill with a feeding speed of 40 kg / h and a crushing air pressure of 1.0 Mpa to obtain silver powder with good dispersibility and high tap density.

[0165] Example 3

[0166] A kind of silver powder was prepared, and the specific steps were as follows:

[0167] Step 1: Solution preparation: Add silver nitrate crystals into 100 L of pure water (conductivity ≤ 2 μS / cm) for dissolution to prepare a solution with a concentration of 30 wt%. The conductivity of the pure water is required to be ≤ 2 μS / cm, and control the temperature after dissolution at 25 °C.

[0168] Step 2: Bottom liquid preparation: Add 450 L of pure water (conductivity ≤ 2 μS / cm) into a reaction kettle, and then add a reducing agent (industrial-grade vitamin C that can be purchased conventionally in the market, vitamin C is L-ascorbic acid) and a dispersant (PVP that can be purchased conventionally in the market, i.e., polyvinylpyrrolidone). The mass fraction of the reducing agent is 3.5 wt%, and the mass fraction of the dispersant is 1.0 wt%. During the process, stir to maintain a constant value between 200 r / min, stir for 30 minutes to make it evenly mixed, and control the temperature at 20 - 25 °C. After meeting the requirements, add an appropriate amount of ammonia water to control the pH of the mixed solution at 3.

[0169] Step 3: Precursor solution preparation: Prepare 0.5 L of a reducing agent solution with a concentration of 0.03 mol / L (the reducing agent is industrial-grade vitamin C that can be purchased conventionally in the market, vitamin C is L-ascorbic acid), add 0.5 L of a silver nitrate solution with a concentration of 1 mol / L, control the molar concentration ratio of silver nitrate to the reducing agent at 33.33:1, then mix them evenly to obtain a mixed solution, and add it into the silver nitrate solution in Step 1 to form a precursor solution. Control the interval time from the addition of the mixed solution to the silver nitrate solution to the start of the next redox reaction at 10 min, that is, the formation and standing time of the precursor solution is 10 min.

[0170] Step 4. Redox reaction: The prepared precursor solution is evenly added into the reaction kettle within 300 s, and the stirring during the process is maintained at a constant value between 200 r / min. After the feeding is completed, the relevant valves are closed.

[0171] Step 5. After the feeding is completed, 0.15% of the coating agent stearic acid based on the mass of silver nitrate is added for coating, and the stirring speed is kept unchanged during the process. The coating time is controlled at 8 min.

[0172] Step 6. Silver powder cleaning: The silver powder in the reaction kettle is discharged into a centrifuge for cleaning and dehydration to obtain wet silver powder with a water content of 18%.

[0173] Step 7. Silver powder emulsification: The wet silver powder is added into an emulsifying machine, and alcohol with a mass 1.0 times that of the silver powder and 0.3% of the modified auxiliary agent stearic acid based on the mass of the silver powder are added. The rotation speed of the emulsifying machine is controlled at 1500 r / min, the emulsification temperature is 35 °C, and the emulsification time is 40 minutes. After emulsification, dehydration is carried out using a centrifuge.

[0174] Step 8. Silver powder drying: The dehydrated silver powder is loaded onto a tray and placed in an oven. The drying temperature is controlled at 60 °C, and the drying time is 8 hours until the water content is lower than 25%.

[0175] Step 9. Silver powder crushing: The dried silver powder is crushed using a jet mill. The feeding speed is 40 kg / h, and the crushing air pressure is 1.0 Mpa to obtain silver powder with good dispersibility and high tapped density.

[0176] Comparative Example 1

[0177] Control the preparation of the precursor solution in Step 3 as follows: Prepare 1 L of a reducing agent solution with a concentration of 0.06 mol / L (the reducing agent is PVP, i.e., polyvinylpyrrolidone, which can be conventionally purchased on the market), add 0.5 L of a silver nitrate solution with a concentration of 0.3 mol / L, control the molar concentration ratio of silver nitrate to the reducing agent at 5.0:1, then mix them evenly to obtain a mixed solution, and add it to the silver nitrate solution in Step 1 to form a precursor solution.

[0178] Other steps and conditions are the same as those in Example 1.

[0179] Comparative Example 2

[0180] Control the preparation of the precursor solution in Step 3 as follows: Prepare 1 L of a reducing agent solution with a concentration of 0.06 mol / L (the reducing agent is PVP, i.e., polyvinylpyrrolidone, which can be conventionally purchased on the market), add 0.5 L of a silver nitrate solution with a concentration of 3.3 mol / L, control the molar concentration ratio of silver nitrate to the reducing agent at 55:1, then mix them evenly to obtain a mixed solution, and add it to the silver nitrate solution in Step 1 to form a precursor solution.

[0181] The other steps and conditions are the same as those in Example 1.

[0182] Comparative Example 3

[0183] Control the interval time from the addition of silver nitrate solution to the start of the next step of redox reaction in Step 3 to be 2 min, that is, the formation and standing time of the precursor solution is 2 min.

[0184] The other steps and conditions are the same as those in Example 1.

[0185] Comparative Example 4

[0186] Control the interval time from the addition of silver nitrate solution to the start of the next step of redox reaction in Step 3 to be 12 min, that is, the formation and standing time of the precursor solution is 12 min.

[0187] The other steps and conditions are the same as those in Example 1.

[0188] Performance Test

[0189] Parameters such as the particle size of the silver powder prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0190] Table 1

[0191]

[0192] In Table 1, D10, D50, and D90 were tested using a particle size analyzer.

[0193] TD was tested using a tap density meter.

[0194] AD was tested using a loose bulk density meter.

[0195] The porosity is a simulated calculated value, which is the ratio of the pore area of the cross-section of the silver powder spheres in the view to the total cross-sectional area under a 20,000-fold electron microscope image.

[0196] D10 means that 10% of the particles have a particle size smaller than the test value; D50 means that 50% of the particles have a particle size smaller than the test value; D90 means that 90% of the particles have a particle size smaller than the test value.

[0197] SPAN = (D90 - D10) / D50, which reflects the particle size concentration. The smaller the SPAN value, the more concentrated the particle size distribution. The SPAN value of the silver powder of the present invention is 0.7 - 1, with a concentrated particle size distribution and uniform particle size. Therefore, the silver paste prepared from this silver powder can reduce the occurrence of breakpoints and broken wires during the printing process.

[0198] As Figure 1 shown, the silver powder prepared in Example 1 was observed by scanning electron microscopy.

[0199] As Figure 2 shown, the conventional silver powder on the market was also observed by scanning electron microscope.

[0200] It can be seen that the silver powder prepared in Example 1 has a polycrystalline structure, and a single silver powder particle is formed by binding together many primary particles. The size of the primary particles is 0.30 - 0.75 μm; while the conventional silver powder on the market has a single crystal structure, and the primary particles cannot be distinguished, and the particle size is above 0.8 μm. The electron microscope morphology and product parameters are basically the same.

[0201] The porosity and tap density of the silver powder in Comparative Example 1 decreased compared with those in the example.

[0202] The porosity and tap density of the silver powder in Comparative Example 2 decreased compared with those in the example.

[0203] The silver powder in Comparative Example 3 could not nucleate and needed to be dried before testing. After drying, the silver particles were connected and no data was detected.

[0204] The primary particles of the silver powder in Comparative Example 4 grew excessively and the particles were connected, and no data was detected.

[0205] In addition, the polycrystalline structure of the example has smaller primary particles, higher surface energy, good activity of the silver powder, which is conducive to faster softening during high-temperature sintering, forming a dense silver film and improving conductivity.

[0206] The cross-section of the silver powder prepared in Example 1 was compared (as Figure 3 shown) with the cross-section of the silver powder in Comparative Example 1 (as Figure 4 shown). It can be seen that the inside of the silver powder sphere in Example 1 is a hollow structure with a porosity of 5.94%, and the porosity is high; while the inside of the silver powder sphere in Comparative Example 1 is a solid structure with a porosity of 0.73%, which is relatively low. The high-porosity structure of the silver powder in the example reduces the sintering softening temperature of the silver powder while maintaining the high tap density of the product, and improves the sintering activity and printability.

[0207] Figure 5 is the electron microscope image of the silver powder in Example 1 at 20,000 times magnification.

[0208] Figure 6 is the electron microscope image of the silver powder in Comparative Example 1 at 20,000 times magnification.

[0209] Comparing Figure 5 and Figure 6 it can be seen that compared with the silver powder in Example 1, the silver powder in Comparative Example 1 has the situation where the major axis of the primary particles is less than 0.3 μm and greater than 0.8 μm.

[0210] Figure 7 is the electron microscope image of the silver powder in Comparative Example 3.

[0211] Figure 8 It is the SEM image of the silver powder of Comparative Example 4.

[0212] Combining Figure 7 and Figure 8 it can be seen that, compared with the silver powder of Example 1, the silver powder of Comparative Example 3 did not nucleate, while the silver powder of Comparative Example 4 had excessive growth of primary particles and connection between particles.

[0213] The silver powders prepared in Examples 1 - 3 and Comparative Examples 1 - 2, epoxy resin added with alcohol additives, and glass fiber were mixed in a ratio of 85:12:3; after being mixed evenly with a defoamer and a three - roll mill to form a silver paste; the silver paste was printed onto the substrate of a photovoltaic cell by a screen printing machine; the substrate of the photovoltaic cell was placed in a high - temperature sintering furnace, and the sintering temperature was 700 °C (lower than the conventional high - temperature sintering temperature, the required temperature for high - temperature sintering is generally 760 - 960 °C) to sinter into a photovoltaic cell; finally, the electrical performance of the cell was tested using a HALM machine.

[0214] The commercially available conventional silver powder was prepared into a silver paste and printed onto the substrate of a photovoltaic cell in the same method as above, except that sintering was carried out at 800 °C and electrical performance testing was performed.

[0215] The preparation of silver powder into silver paste and the preparation and implementation process of electrical performance testing both adopted existing common technical means, and the required materials and equipment were all conventional equipment that could be purchased on the market. Moreover, the model of the equipment and the supplier of the materials had little impact on the test results, so no detailed description is given here. The results are shown in Table 2.

[0216] Table 2

[0217]

[0218] In Table 2:

[0219] Voc represents the open - circuit voltage; Isc represents the short - circuit current; Rs represents the series resistance; FF represents the fill factor, which is the test power / theoretical power, and the larger the value, the better; EFF represents the conversion efficiency, and 0.03% is a gradient.

[0220] The silver powder of Comparative Example 3 could not nucleate and needed to be dried before testing. After drying, the silver particles were connected and no electrical performance data was detected.

[0221] The silver powder of Comparative Example 4 had excessive growth of primary particles and connection between particles, and no electrical performance data was detected.

[0222] Compared with Comparative Examples 1-2, the pastes prepared in Examples 1-3 have better electrical properties, with a higher open-pressing current, lower resistance, and an efficiency that is 2-3 gradients higher than that of Comparative Example 2. The sintering temperature of the paste before the above performance test was 700°C, which is lower than the sintering temperature of 800°C for conventional silver powders on the market. The conversion efficiency of Examples 1-3 all reached over 22.70%, slightly higher than the efficiency of silver paste with high-temperature sintered silver powders currently on the market. Therefore, the silver powder prepared by this method has better low-temperature sintering performance.

[0223] The present invention has been described in detail above in conjunction with the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A silver powder, characterized in that, The silver powder is polycrystalline silver powder composed of a number of primary particles, and the tap density of the silver powder is ≥ 6.0 g / cm 3 , the Span of the particle size distribution of the silver powder is 0.7 - 1.0, the tangential porosity of the silver powder is 3% - 10%, the major axis length of the primary particle is 0.3 μm - 0.8 μm, and the loose density of the silver powder is ≥ 3.0 g / cm 3 , and the average particle size D50 of the silver powder is 1.2 μm - 2.0 μm.

2. A method for preparing silver powder as described in claim 1, characterized in that, It includes the following steps: S1: Prepare 4 - 5 parts of a reaction bottom solution containing a dispersant and a reducing agent; S2: Add 0.01 - 0.02 parts of a first silver source solution containing a reducing agent to 0.8 - 1.2 parts of a second silver source solution to obtain a precursor solution; S3: Add the precursor solution to the reaction bottom solution for reaction, and after the addition is completed, add a coating agent for coating to obtain the silver powder; In the first silver source solution, it includes 0.005 - 0.01 parts of a reducing agent, the molar concentration of the reducing agent is 0.03 - 0.08 mol / L, the molar concentration of silver ions in the first silver source solution is 1.00 - 3.00 mol / L, and the molar concentration ratio of the reducing agent to silver ions is 1:25.00 - 37.50; From the start of preparing the precursor solution to adding the precursor solution to the reaction bottom solution, the interval time is 3 min - 10 min.

3. The method according to claim 2, wherein In the reaction bottom solution, the mass percentage of the dispersant is 1.0 wt% - 1.2 wt%.

4. The method according to claim 2, wherein In the reaction bottom solution, the mass percentage of the reducing agent is 3.5 wt% - 4.2 wt%.

5. The method according to claim 2, wherein The silver source in the second silver source solution includes silver nitrate.

6. The method according to claim 2, characterized in that, In the second silver source solution, the mass percentage of silver nitrate is 30 wt% - 38 wt%.

7. The method according to claim 2, characterized in that The method further includes post - treating the product after adding the coating agent for coating, and the post - treatment includes one or more of washing, emulsifying, drying, and crushing.

8. The method according to any one of claims 2 to 7, characterized in that The dosage of 1 part is 100 L; the dispersant includes at least one of polyvinylpyrrolidone, Tween 80, and oleic acid; the reducing agent includes at least one of glucose, formaldehyde, hydrazine hydrate, and ascorbic acid; the silver source of the first silver source solution and the second silver source solution is silver nitrate; The coating agent includes at least one of stearic acid, lauric acid, gelatin, and gum arabic.

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