Spherical nano silver powder and its preparation method and application

Abstract

The present invention provides a spherical nano silver powder and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing a dispersant solution and a reducing agent solution to obtain a mixed solution; (2) adding a silver nitrate solution and an alkali solution to the mixed solution in step (1) to perform a second mixing to obtain the nano silver powder. The nano silver powder prepared by the present invention has uniform particle size, low resistivity, high tap density, and low specific surface area, and can be industrialized. The silver paste prepared by the nano silver powder has low bulk resistance, high tensile force, and high photoelectric conversion rate, and can meet market demand.

Description

Technical Field

[0001] The present invention belongs to the field of solar cells, and relates to a spherical nano silver powder, a preparation method thereof and an application thereof. Background Art

[0002] In the photovoltaic industry, conductive silver paste is the highest-cost consumable except for silicon wafers, accounting for about 10-25% of the production cost of photovoltaic cells. Among them, the most important component is silver powder.

[0003] During the manufacturing process of solar cells, conductive silver paste is printed on the solar cell substrate and sintered and solidified to form conductive grid lines, which serve as conductive channels for transmitting photocurrent. In order to improve the conductivity of the silver paste, silver powders with different morphologies and particle sizes are usually selected and mixed in a certain proportion to reduce the porosity, and then substances such as binders and organic solvents are added to prepare the conductive silver paste.

[0004] It has been found that micron-sized spherical silver powder has high sintering activity and excellent conductivity. After sintering, the voids between the micron silver powders can be reduced, and the contact area between powders can be increased, thereby increasing the conductive channels and improving the photoelectron transfer efficiency. Therefore, the preparation method of micro-nano silver powder is crucial for improving the performance of photovoltaic products. At present, the chemical method is the main method for preparing micro-nano silver powder, and among them, the chemical reduction method is the most common method, which has the advantages of simple production equipment, low cost, controllable product performance, good repeatability, etc.

[0005] CN106623971A discloses a method for synthesizing silver nanoparticles, which uses a mixed solution of a reducing agent and silver nitrate to prepare stable silver nanoparticles, including two steps: first, mixing a silver source and an organic amine solution to obtain a mixed solution, and second, synthesizing silver nanoparticles. Using silver nitrate as the silver source, hydrazine hydrate or sodium borohydride as the reducing agent, and organic amine as the protective agent, this method has relatively cumbersome steps, is not easy to control, has low silver atom utilization rate, many reaction by-products, and complex post-treatment process.

[0006] CN103817754A discloses a nano silver floor. The scientific and technological wood floor is sent into a vacuum tank containing nano silver aqueous solution for pressure treatment, and finally microwave treatment is carried out, and then taken out for post-treatment. The nano silver aqueous solution uses deionized water as the solvent, dissolves nano silver as the solute in deionized water, uses acrylic resin as the complexing agent, and at the same time adds a dispersant and a reducing agent to obtain the nano silver aqueous solution. The preparation method is complex, and many chemical reagents are used in the synthesis process.

[0007] Although there have been a large number of reports on the preparation and controllability of silver nanopowders at home and abroad, there are still some defects in the preparation of silver nanopowders by chemical reduction method at present. For example, they have unstable thermodynamic properties, poor sintering activity, poor stability of silver powders, easy agglomeration during storage, and it is very difficult to break up the agglomerates by mechanical methods. Their tapped density is relatively low, the utilization rate of silver atoms is low, and it is not easy to scale up production. These problems seriously affect the function of silver nanopowders and their application in silver pastes.

[0008] Therefore, how to prepare silver nanopowders with stable thermodynamic properties, good sintering activity, good stability of silver powders, not easy to agglomerate during storage, high tapped density, high utilization rate of silver atoms and large-scale production is an important research direction in this field. Summary of the Invention

[0009] The purpose of the present invention is to provide spherical silver nanopowders with stable thermodynamic properties, good sintering activity, good stability of silver powders, not easy to agglomerate during storage, high tapped density, high utilization rate of silver atoms and large-scale production, and their preparation methods and applications.

[0010] To achieve the purpose of this invention, the following technical solutions are adopted:

[0011] One of the purposes of the present invention is to provide a preparation method of silver nanopowders, and the preparation method includes the following steps:

[0012] (1) First mix a dispersant solution and a reducing agent solution to obtain a mixed solution;

[0013] (2) Add a silver nitrate solution and an alkali solution to the mixed solution in step (1) simultaneously for a second mixing to obtain the silver nanopowders.

[0014] The silver nanopowders prepared by the present invention have uniform particle size, low resistivity, high tapped density, low specific surface area, and can be industrially produced. The silver paste prepared with this silver nanopowder has low volume resistance, high tensile strength, and high photoelectric conversion rate, and can meet the market demand.

[0015] In step (1) of the present invention, mixing the dispersant solution and the reducing agent solution can fully protect the silver powders by the dispersant, and the substances on the surface of the silver powders are more uniform. In step (2), adding the silver nitrate solution and the alkali solution simultaneously can effectively control the reaction and make the particle size of the silver powders more uniform. Adding the silver nitrate solution and the alkali solution separately will result in non-uniform particle size of the silver powders and a decrease in the tapped density of the silver powders.

[0016] As a preferred technical solution of the present invention, the solvent of the dispersant solution in step (1) is water.

[0017] Preferably, the solute of the dispersant solution in step (1) includes any one or a combination of at least two of oleic acid, linoleic acid, glycerol monooleate, glycerol trioleate, or Span 80. Typical but non-limiting examples of the combination include: the combination of oleic acid and linoleic acid, the combination of linoleic acid and glycerol monooleate, the combination of glycerol monooleate and glycerol trioleate, or the combination of glycerol trioleate and Span 80, etc.

[0018] Preferably, the solvent of the reducing agent solution in step (1) includes water.

[0019] Preferably, the solute of the reducing agent solution in step (1) includes any one or a combination of at least two of kojic acid, formic acid, sodium formate, xylose, or glucose. Typical but non-limiting examples of the combination include: the combination of kojic acid and formic acid, the combination of formic acid and sodium formate, the combination of sodium formate and xylose, or the combination of xylose and glucose, etc.

[0020] As a preferred technical solution of the present invention, after the dispersant solution in step (1) is prepared, ultrasonic vibration emulsification is carried out.

[0021] Through ultrasonic vibration emulsification of the present invention, the distribution of the dispersant solution is more uniform, and the particle size of the generated silver nanoparticles is also more uniform, enabling industrial production.

[0022] Preferably, the temperature of the first mixing in step (1) is 25 - 35 °C, where the temperature can be 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, or 35 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] As a preferred technical solution of the present invention, the concentration of the silver nitrate solution in step (2) is 100 - 200 g / L, where the concentration can be 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, or 200 g / L, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] Preferably, the solvent of the silver nitrate solution in step (2) includes water.

[0025] Preferably, the lye in step (2) includes sodium hydroxide solution.

[0026] Preferably, the concentration of the alkali solution in step (2) is 0.08 - 0.12%, where the concentration can be 0.08%, 0.09%, 0.10%, 0.11% or 0.12%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] As a preferred technical solution of the present invention, the solute of the silver nitrate solution is silver nitrate, the solute of the reducing agent is the reducing agent, and the solute of the dispersant is the dispersant;

[0028] Preferably, the molar ratio of silver nitrate, reducing agent, dispersant and alkali solution is 1:(0.3 - 10):(0.001 - 0.8):(0.0001 - 0.01). The molar ratio can be 1:0.3:0.001:0.0001, 1:0.3:0.8:0.0001, 1:0.3:0.001:0.01, 1:10:0.001:0.0001, 1:10:0.8:0.0001, 1:0.3:0.001:0.01 or 1:5:0.4:0.005, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] As a preferred technical solution of the present invention, the rate of adding the silver nitrate solution in step (2) to the mixed solution is 0.5 - 20 mL / min, where the rate can be 0.5 mL / min, 1 mL / min, 2 mL / min, 4 mL / min, 6 mL / min, 8 mL / min, 10 mL / min, 12 mL / min, 14 mL / min, 16 mL / min, 18 mL / min or 20 mL / min, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] Preferably, the rate of adding the alkali solution in step (2) to the mixed solution is 0.1 - 4.0 mL / min, where the rate can be 0.1 mL / min, 0.5 mL / min, 1.0 mL / min, 1.5 mL / min, 2.0 mL / min, 2.5 mL / min, 3.0 mL / min, 3.5 mL / min or 4.0 mL / min, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] As a preferred technical solution of the present invention, the temperature of the second mixing in step (2) is 5 - 35 °C, where the temperature can be 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C or 35 °C, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0032] Preferably, the time for the second mixing in step (2) is 25 to 35 min. The time can be 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0033] As a preferred technical solution of the present invention, after the second mixing in step (2), cooling and sample post-treatment are carried out in sequence to obtain the nano silver powder.

[0034] Preferably, the temperature for cooling is 25 to 35 °C. The temperature can be 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0035] Preferably, the method for sample post-treatment includes washing, drying, and grinding carried out in sequence.

[0036] Preferably, the temperature for drying is 45 to 55 °C. The temperature can be 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the time for drying is 6 to 15 h. The time can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0038] Preferably, after grinding, the particle size of the nano silver powder is 200 to 800 nm. The particle size can be 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0039] The second object of the present invention is to provide a nano silver powder, which is prepared by the preparation method of the nano silver powder as described in the first object.

[0040] The morphology of the nano silver powder is spherical, and the particle size of the nano silver powder is 200 to 800 nm. The particle size can be 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0041] The third object of the present invention is to provide an application of the nano silver powder as described in the second object, and the nano silver powder is applied to the field of solar cells.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The nano silver powder prepared by the present invention has uniform particle size, low resistivity, high tap density and low specific surface area, and can be industrially produced. The silver paste prepared with this nano silver powder has low bulk resistance, high tensile strength and high photoelectric conversion rate, and can meet the market demand.

[0044] (2) The resistivity of the nano silver powder of the present invention is as low as below 20 μΩ·cm, the loose bulk density is as high as 3.4 g / cm 3 or above, and the tap density is as high as 5.7 g / cm 3 or above. Description of the Drawings

[0045] Figure 1 is the scanning electron microscope image of the nano silver powder prepared in Example 1 of the present invention.

[0046] Figure 2 is the scanning electron microscope image of the nano silver powder prepared in Example 2 of the present invention.

[0047] Figure 3 is the scanning electron microscope image of the nano silver powder prepared in Example 3 of the present invention.

[0048] Figure 4 is the scanning electron microscope image of the nano silver powder prepared in Example 4 of the present invention.

[0049] Figure 5 is the scanning electron microscope image of the nano silver powder prepared in Example 5 of the present invention. Detailed Embodiments

[0050] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0051] Example 1

[0052] This example provides a nano silver powder with a particle size distribution range of 200-800 nm.

[0053] This example also provides a preparation method of the above nano silver powder. First, the reaction raw materials are prepared:

[0054] Silver nitrate solution: Weigh 10 g of silver nitrate and dissolve it in 100 mL of water; Reducing agent solution: Dissolve 50 g of glucose in 300 mL of water; Dispersant solution: Weigh 0.5 g of oleic acid and 0.5 g of linoleic acid, mix them with 100 mL of normal temperature water and ultrasonically emulsify; NaOH solution: Prepare 5 mL of 0.1% NaOH aqueous solution.

[0055] Use the prepared silver nitrate solution, reducing agent solution, dispersant solution and dilute NaOH solution as raw materials to prepare silver nanopowder. The specific preparation method includes the following steps:

[0056] (1) Stir the dispersant solution and the reducing agent solution evenly at 30 °C, heat the mixed solution of the dispersant and the reducing agent and keep it at 30 °C to obtain a mixed solution;

[0057] (2) Add the silver nitrate solution at a flow rate of 0.5 mL / min and the NaOH aqueous solution at a flow rate of 0.1 mL / min into the mixed solution described in step (1) together. After adding them completely, continue to stir for 30 min. After impurity removal, drying and grinding, the silver nanopowder is obtained;

[0058] The impurity removal includes: After the stirred solution has settled completely, stir and wash the lower layer of solid silver powder with 100 mL of deionized water for 20 minutes. After settling completely, extract the supernatant. Repeat the operation of washing with deionized water 4 times. Then stir and wash with 100 mL of ethanol for 10 minutes. After settling completely, extract the supernatant. Repeat the operation of washing with ethanol 2 times;

[0059] The drying includes: Place the sample after impurity removal in a vacuum oven and dry it at 45 °C for 8 hours;

[0060] Grinding includes: Crush and grind the dried sample to obtain silver nanopowder.

[0061] The scanning electron microscope image of the silver nanopowder prepared in this example is as Figure 1 shown. The silver nanopowder presents a spherical shape. The particle size distribution range measured by a laser particle size distribution analyzer is 200 - 800 nm, and the purity is high.

[0062] Example 2

[0063] This example provides silver nanopowder with a particle size distribution range of 210 - 750 nm.

[0064] This example also provides a preparation method of the above silver nanopowder. First, prepare the reaction raw materials:

[0065] Silver nitrate solution: Weigh 50 g of silver nitrate and dissolve it in 500 mL of water; Reducing agent solution: Dissolve 250 g of glucose in 500 mL of water; Dispersant solution: Weigh 0.8 g of oleic acid and 0.8 g of linoleic acid, mix them with 150 mL of normal temperature water and ultrasonically emulsify; NaOH solution: Prepare 8 mL of 0.1% NaOH aqueous solution.

[0066] Take the prepared silver nitrate solution, reducing agent solution, dispersant solution and dilute NaOH solution as raw materials to prepare silver nanopowder. The specific preparation method includes the following steps:

[0067] (1) Stir the dispersant solution and the reducing agent solution evenly at 30 °C, heat the mixed solution of the dispersant and the reducing agent and keep it at 30 °C to obtain a mixed solution;

[0068] (2) Add the silver nitrate solution at a flow rate of 0.5 mL / min and the NaOH aqueous solution at a flow rate of 0.1 mL / min to the mixed solution described in step (1) together. After adding them completely, continue to stir for 30 min. After impurity removal, drying and grinding, the silver nanopowder is obtained;

[0069] The impurity removal includes: After the stirred solution has settled completely, stir and wash the lower layer of solid silver powder with 100 mL of deionized water for 20 minutes. After settling completely, extract the supernatant. Repeat the operation of washing with deionized water 4 times. Then stir and wash with 100 mL of ethanol for 10 minutes. After settling completely, extract the supernatant. Repeat the operation of washing with ethanol 2 times;

[0070] The drying includes: Place the sample after impurity removal in a vacuum oven and dry it at 45 °C for 8 hours;

[0071] Grinding includes: Crush and grind the dried sample to obtain silver nanopowder.

[0072] The scanning electron microscope image of the silver nanopowder prepared in this example is as Figure 2 shown. The silver nanopowder presents a spherical shape. The particle size distribution range measured by a laser particle size distribution analyzer is 210 - 750 nm, and the purity is high.

[0073] Example 3

[0074] This example provides silver nanopowder with a particle size distribution range of 210 - 750 nm.

[0075] This example also provides a preparation method of the above silver nanopowder. First, prepare the reaction raw materials:

[0076] Silver nitrate solution: Weigh 200 g of silver nitrate and dissolve it in 2000 mL of water; Reducing agent solution: Dissolve 500 g of glucose in 1500 mL of water; Dispersant solution: Weigh 5 g of oleic acid and mix it with 150 mL of normal temperature water and ultrasonically emulsify; NaOH solution: Prepare 30 mL of 0.1% NaOH aqueous solution.

[0077] Take the prepared silver nitrate solution, reducing agent solution, dispersant solution and dilute NaOH solution as raw materials to prepare silver nanopowder. The specific preparation method includes the following steps:

[0078] (1) Stir the dispersant solution and the reducing agent solution evenly at 30 °C, heat the mixed solution of the dispersant and the reducing agent and keep it at 30 °C to obtain a mixed solution;

[0079] (2) Add the silver nitrate solution at a flow rate of 3 mL / min and the NaOH aqueous solution at a flow rate of 2 mL / min into the mixed solution described in step (1) together. After adding completely, continue to stir for 30 min, and obtain the silver nanopowder after impurity removal, drying and grinding;

[0080] The impurity removal includes: After the stirred solution has settled completely, stir and wash the lower layer of solid silver powder with 300 mL of deionized water for 20 minutes. After settling completely, extract the supernatant. Repeat the above operation of washing with deionized water 4 times. Then stir and wash with 300 mL of ethanol for 10 minutes. After settling completely, extract the supernatant. Repeat the above operation of washing with ethanol 2 times;

[0081] The drying includes: Place the sample after impurity removal in a vacuum oven and dry it at 45 °C for 8 hours;

[0082] Grinding includes: Crush and grind the dried sample to obtain silver nanopowder.

[0083] The scanning electron microscope image of the silver nanopowder prepared in this example is as Figure 3 shown. The silver nanopowder presents a spherical shape. The particle size distribution range measured by a laser particle size distribution analyzer is 210 - 750 nm, and the purity is high.

[0084] Example 4

[0085] This example provides silver nanopowder with a particle size distribution range of 210 - 750 nm.

[0086] This example also provides a preparation method of the above silver nanopowder. First, prepare the reaction raw materials:

[0087] Silver nitrate solution: Weigh 500 g of silver nitrate and dissolve it in 4000 mL of water; Reducing agent solution: Dissolve 800 g of kojic acid in 2000 mL of water; Dispersant solution: Weigh 30 g of Span and mix it with 300 mL of normal temperature water and ultrasonically emulsify; NaOH solution: Prepare 50 mL of 0.1% NaOH aqueous solution.

[0088] Take the prepared silver nitrate solution, reducing agent solution, dispersant solution and dilute NaOH solution as raw materials to prepare silver nanopowder. The specific preparation method includes the following steps:

[0089] (1) Stir the dispersant solution and the reducing agent solution evenly at 30 °C, heat the mixed solution of the dispersant and the reducing agent and keep it at 30 °C to obtain a mixed solution;

[0090] (2) Add the silver nitrate solution at a flow rate of 20 mL / min and the NaOH aqueous solution at a flow rate of 4 mL / min to the mixed solution described in step (1) together. After adding completely, continue to stir for 30 min, and after impurity removal, drying and grinding, obtain the silver nanopowder;

[0091] The impurity removal includes: After the stirred solution has settled completely, stir and wash the lower-layer solid silver powder with 300 mL of deionized water for 10 minutes. After settling completely, extract the supernatant. Repeat the above deionized water washing operation 4 times. Then stir and wash with 300 mL of ethanol for 10 minutes. After settling completely, extract the supernatant. Repeat the above ethanol washing operation 2 times;

[0092] The drying includes: Place the sample after impurity removal in a vacuum oven and dry it at 45 °C for 8 hours;

[0093] Grinding includes: Crush and grind the dried sample to obtain silver nanopowder.

[0094] The scanning electron microscope image of the silver nanopowder prepared in this example is as Figure 4 shown. The silver nanopowder presents a spherical shape. The particle size distribution range measured by a laser particle size distribution analyzer is 210 - 750 nm, and the purity is high.

[0095] Example 5

[0096] This example provides a silver nanopowder with a particle size distribution range of 200 - 800 nm.

[0097] This example also provides a preparation method of the above silver nanopowder. First, prepare the reaction raw materials:

[0098] Silver nitrate solution: Weigh 1000 g of silver nitrate and dissolve it in 5000 mL of water; Reducing agent solution: Dissolve 2000 g of glucose in 3000 mL of water; Dispersant solution: Weigh 50 g of linoleic acid and mix it with 700 mL of normal temperature water and ultrasonically emulsify; NaOH solution: Prepare 50 mL of 0.1% NaOH aqueous solution.

[0099] Take the prepared silver nitrate solution, reducing agent solution, dispersant solution and dilute NaOH solution as raw materials to prepare silver nano-powder. The specific preparation method includes the following steps:

[0100] (1) Stir the dispersant solution and the reducing agent solution evenly at 30 °C, heat the mixed solution of the dispersant and the reducing agent and keep it at 30 °C to obtain a mixed solution;

[0101] (2) Add the silver nitrate solution at a flow rate of 20 mL / min and the NaOH aqueous solution at a flow rate of 4 mL / min into the mixed solution described in step (1) together. After adding completely, continue to stir for 30 min, and after impurity removal, drying and grinding, obtain the silver nano-powder;

[0102] The impurity removal includes: After the stirred solution has settled completely, stir and wash the lower-layer solid silver powder with 300 mL of deionized water for 10 minutes. After settling completely, extract the supernatant. Repeat the operation of washing with deionized water 4 times. Then stir and wash with 300 mL of ethanol for 10 minutes. After settling completely, extract the supernatant. Repeat the operation of washing with ethanol 2 times;

[0103] The drying includes: Place the sample after impurity removal in a vacuum oven and dry it at 45 °C for 8 hours;

[0104] Grinding includes: Crush and grind the dried sample to obtain silver nano-powder.

[0105] The scanning electron microscope image of the silver nano-powder prepared in this example is as Figure 5 shown. The silver nano-powder presents a spherical shape. The particle size distribution range measured by a laser particle size distribution analyzer is 200 - 800 nm, and the purity is high.

[0106] Example 6

[0107] In this example, except that the dispersant is not ultrasonically emulsified, other conditions are the same as those in Example 1.

[0108] Comparative Example 1

[0109] In this comparative example, except that adding the silver nitrate solution and the sodium hydroxide solution simultaneously in step (2) is replaced by adding the silver nitrate solution first and then adding the sodium hydroxide solution, other conditions are the same as those in Example 1.

[0110] Comparative Example 2

[0111] In this comparative example, except that in step (2), the simultaneous addition of silver nitrate solution and sodium hydroxide solution is replaced by the prior addition of sodium hydroxide solution followed by the addition of silver nitrate solution, other conditions are the same as those in Example 1.

[0112] Comparative Example 3

[0113] In this comparative example, except that the dispersant solution, reducing agent solution, silver nitrate solution and alkali solution are mixed simultaneously, the mixing and stirring time is 30 min, and the temperature is 30 °C, other conditions are the same as those in Example 1.

[0114] The resistivity, apparent density and tapped density of the nano-silver powders prepared in Examples 1-6 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0115] Table 1

[0116] Resistivity / μΩcm <![CDATA[Bulk density / g / cm 3 > <![CDATA[Tap density / g / cm 3 > Example 1 25 3.3 5.3 Example 2 24 3.4 5.5 Example 3 22 3.1 5.6 Example 4 23 3.4 5.7 Example 5 20 3.3 5.7 Example 6 29 3.0 4.9 Comparative Example 1 30 2.6 4.7 Comparative Example 2 29 2.7 4.5 Comparative Example 3 31 2.5 4.6

[0117] From the above table, it can be obtained that the silver powders obtained in Examples 1 to 5 have a smaller resistance and a larger tapped density. After ultrasonic emulsification was removed in Example 6, the resistance increased and the tapped density decreased. In Comparative Examples 1-2, adding silver nitrate first and then alkali or adding alkali first and then silver nitrate will both increase the resistance of the silver powder and decrease the tapped density. In Comparative Example 3, mixing the dispersant solution, reducing agent solution, silver nitrate solution and alkali solution simultaneously increased the resistance of the silver powder and decreased the tapped density.

[0118] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing nano silver powder for silver paste in the field of solar cells, characterized in that: The preparation method comprises the following steps: (1) mixing the dispersant solution and the reducing agent solution to obtain a mixed solution; (2) adding silver nitrate solution and alkali solution to the mixed solution in step (1) to perform a second mixing to obtain the nano silver powder; Wherein, after the dispersant solution in step (1) is prepared, ultrasonic vibration emulsification is performed; The solute of the dispersant solution in step (1) comprises any one of oleic acid, linoleic acid, monoolein, triolein or Span 80, or a combination of at least two thereof; The silver nitrate solution in step (2) is added to the mixed solution at a rate of 0.5-20 mL / min; The rate of adding the alkali solution into the mixed solution in step (2) is 0.1-4.0 mL / min; Step (2) the temperature of the second mixing is 30-35°C; The nano silver powder prepared by the preparation method is spherical in shape, and the particle size of the nano silver powder is 200-800nm; The resistivity of the nano silver powder is below 20 μΩcm and the bulk density is 3.4 g / cm 3 Above, the tap density is 5.7g / cm 3 above.

2. The preparation method according to claim 1, characterized in that: The solvent of the dispersant solution in step (1) is water.

3. The preparation method according to claim 1, characterized in that: The solvent of the reducing agent solution in step (1) includes water.

4. The preparation method according to claim 1, characterized in that: The solute of the reducing agent solution in step (1) includes any one of kojic acid, formic acid, sodium formate, xylose or glucose, or a combination of at least two thereof.

5. The preparation method according to claim 1, characterized in that: The temperature of the first mixing in step (1) is 25-35°C.

6. The preparation method according to claim 1, characterized in that: The concentration of the silver nitrate solution in step (2) is 100-200 g / L.

7. The preparation method according to claim 1, characterized in that: The solvent of the silver nitrate solution in step (2) includes water.

8. The preparation method according to claim 1, characterized in that: The alkaline solution in step (2) includes sodium hydroxide solution.

9. The preparation method according to claim 1, characterized in that: The concentration of the alkali solution in step (2) is 0.08-0.12%.

10. The preparation method according to claim 1, characterized in that: The solute of the silver nitrate solution is silver nitrate, the solute of the reducing agent solution is a reducing agent, and the solute of the dispersant solution is a dispersant.

11. The preparation method according to claim 10, characterized in that: The ratio of the amount of silver nitrate, reducing agent, dispersant and alkali solution is 1:(0.3-10):(0.001-0.8):(0.0001-0.01).

12. The preparation method according to claim 1, characterized in that: The second mixing time in step (2) is 25 to 35 minutes.

13. The preparation method according to claim 1, characterized in that: Step (2) After the second mixing, cooling and sample post-treatment are performed in sequence to obtain the nano silver powder.

14. The preparation method according to claim 13, characterized in that: The cooling temperature is 25-35°C.

15. The preparation method according to claim 13, characterized in that: The sample post-processing method includes washing, drying and grinding in sequence.

16. The preparation method according to claim 15, characterized in that: The drying temperature is 45-55°C.

17. The preparation method according to claim 15, characterized in that: The drying time is 6 to 15 hours.

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