A method for preparing spherical silver powder with controllable particle size

Abstract

This invention proposes a method for preparing spherical silver powder with controllable particle size, relating to the field of photovoltaic silver powder preparation technology. The preparation method includes: Step S1, adding pure water and a dispersant to a first reaction vessel to prepare a base solution with a dispersant concentration of 7-9 g / L and starting stirring; Step S2, nucleation process: adding a prepared silver nitrate solution dropwise into the base solution; after the addition is complete, adding a prepared reducing agent solution dropwise into the base solution and continuing stirring; Step S3, growth process: adding the prepared silver nitrate solution, reducing agent solution, and dispersant solution in a parallel flow to the first reaction vessel using a peristaltic pump and starting the reaction, continuously stirring until the reaction is complete; Step S4, washing the spherical silver powder, centrifuging, and drying to obtain the target spherical silver powder. This invention can achieve precise control of the particle size of spherical silver powder, preparing particles as small as a few micrometers without requiring external control.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic silver powder preparation technology, and particularly relates to a spherical silver powder with controllable particle size and its preparation method. Background Technology

[0002] With the increasing depletion of non-renewable energy sources such as fossil fuels, renewable energy has received widespread attention. Solar photovoltaic (PV) power generation, as a new generation of clean energy, possesses advantages such as being pollution-free, having unlimited energy resources, being unrestricted by geographical location, and being suitable for both centralized and distributed power generation, making it particularly important in the energy sector. Meanwhile, the growth rate of PV cell modules has exceeded 30% over the past decade, and over 50% in the last three years. Despite such a large demand, significant amounts of PV silver powder need to be imported, especially the front-side silver powder, which determines photoelectric conversion efficiency. Therefore, preparing high-performance front-side silver powder is a core disruptive technology, requiring high dispersibility, high tap density, uniform particle size, and narrow particle size distribution.

[0003] The main methods for preparing silver powder include liquid-phase chemical reduction, physical methods, electrochemical methods, and gas-phase methods. Among these, liquid-phase chemical reduction is the mainstream method. This method mainly uses silver salts or corresponding precipitates or complexes as oxidants, and obtains silver powder through oxidation-reduction by selecting appropriate reducing agents. To obtain the spherical silver powder required for positive-side silver powder, a dispersant needs to be added during the preparation process to prevent agglomeration. Furthermore, the liquid-phase reduction method involves both nucleation and growth of silver powder. Currently, the spherical silver powder prepared domestically undergoes short-term nucleation and growth, making it difficult to control the nucleation amount and growth rate. This results in difficulty in accurately controlling the physicochemical properties such as particle size distribution, uniformity, and tap density, and also leads to low silver powder production capacity. Summary of the Invention

[0004] To solve the above-mentioned technical problems, this invention proposes a spherical silver powder with controllable particle size and its preparation method. Compared with the prior art, (1) this invention improves the sphericity and particle size uniformity of the spherical silver powder by separating the nucleation and growth stages of the silver powder, and makes it less prone to agglomeration; (2) at the same time, during the growth of silver grains, the flow rates of the three solutions, namely silver nitrate solution, reducing agent solution and dispersant solution, are controlled to achieve precise control of the silver powder particle size; (3) by using an intermittent method, the continuous and stable growth of the silver powder particle size can be achieved, and it can be prepared even if it is only a few micrometers in size, without the need for external control.

[0005] The first aspect of this invention discloses a method for preparing spherical silver powder with controllable particle size. The preparation method includes:

[0006] Step S1: Add pure water and dispersant to the first reaction vessel to prepare a bottom liquid with a volume of half the volume of the first reaction vessel and a concentration of 7-9 g / L, and start stirring for 0.5-1.5 h;

[0007] Step S2, nucleation process: After the base liquid is stirred, the prepared silver nitrate solution is added dropwise to the first reaction vessel containing the base liquid at a rate of 90-110 mL / min for 10-15 min; after the addition is completed, the prepared reducing agent solution is added dropwise to the first reaction vessel at a rate of 135-170 mL / min for 10-15 min, and stirring is continued for 0.5-1.5 h.

[0008] Step S3, growth process: The prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at the same flow rate and the reaction is started. Stirring is continued until the reaction is completed.

[0009] During the nucleation and growth process, a particle size analyzer is used to monitor the particle size of the spherical silver powder in real time, and the growth rate of the spherical silver powder is controlled to be 0.001-0.1 μm / h.

[0010] Step S4: After the reaction is completed, the spherical silver powder obtained in step S3 is washed with deionized water and centrifuged. 0.3-0.8% by mass of surface coating agent and ethanol are added to the centrifuged spherical silver powder to obtain a spherical silver powder dispersion. The spherical silver powder dispersion is dispersed at high speed for 20-40 minutes using a high-speed disperser and then dried to obtain the target spherical silver powder.

[0011] According to the preparation method of the first aspect of the present invention, step S3 includes the following sub-steps:

[0012] Step S31: After the nucleation process is completed, the prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at a rate of 80-100 mL / min using a peristaltic pump to start the reaction.

[0013] Step S32: After the first reactor is full, stop spraying, release half of the liquid from the first reactor into the second reactor, and continue to add the prepared silver nitrate solution, reducing agent solution and dispersant solution in a co-current manner through a peristaltic pump at a rate of 80-100 mL / min to the first reactor and the second reactor to continue the reaction.

[0014] Step S33: If the particle size of the spherical silver powder does not reach the target particle size after the first and second reaction vessels are full, stop spraying and continue to release half of the liquid from the first and second reaction vessels into the third and fourth reaction vessels, respectively, and repeat step S32; if the particle size of the spherical silver powder reaches the target particle size, the reaction ends.

[0015] According to the preparation method of the first aspect of the present invention, in step S2, the ratio of the dropping rate of the silver nitrate solution to the dropping rate of the reducing agent solution is 1:1.2-1:1.5.

[0016] According to the preparation method of the first aspect of the present invention, the concentration of the silver nitrate solution is 0.5-2 mol / L.

[0017] According to the preparation method of the first aspect of the present invention, the concentration of the reducing agent solution is 0.5-1.5 mol / L.

[0018] According to the preparation method of the first aspect of the present invention, the concentration of the dispersant solution is 10-25 g / L.

[0019] According to the preparation method of the first aspect of the present invention, the reducing agent is one or more of ascorbic acid, glucose, hydrazine hydrate, and hydrogen peroxide. Ascorbic acid is preferred.

[0020] According to the preparation method of the first aspect of the present invention, the dispersant is one or more selected from polyvinylpyrrolidone K30, gum arabic, Tween 40 / 80, and polyethylene glycol. Preferably, it is polyvinylpyrrolidone K30, gum arabic, or Tween 40.

[0021] According to the preparation method of the first aspect of the present invention, the stirring speed is 200-400 r / min.

[0022] According to the preparation method of the first aspect of the present invention, the surface coating agent is one or more of unsaturated higher fatty acids and amines with 8 or more carbon atoms.

[0023] According to the preparation method of the first aspect of the present invention, the drying temperature is 75-85°C and the drying time is 22-26 hours.

[0024] The second aspect of the present invention discloses a spherical silver powder prepared by the aforementioned method for preparing spherical silver powder with controllable particle size, wherein the growth rate of the spherical silver powder is 0.001-0.1 μm / h.

[0025] In summary, the solution proposed in this invention has the following technical effects:

[0026] ① This invention separates the nucleation and growth stages of silver powder. After the nucleation is completed, the number of silver crystal nuclei is controllable within a specified time. Silver powder growth begins on the basis of the existing number of nuclei, and there is no process of mutual engulfment between silver crystal nuclei. At the same time, combined with a certain stirring speed, the spherical silver powder has high sphericity, good particle size dispersion and uniform particle size, and is not easy to agglomerate.

[0027] ② In the process of silver grain growth, this invention controls the flow rates of three solutions—silver nitrate solution, reducing agent solution, and dispersant solution—and uses an intermittent production method to achieve precise control of silver powder particle size (i.e., slow growth from the initial reaction particle size to the target particle size). It can produce particles as small as a few micrometers without the need for external control.

[0028] ③After the preparation process of the present invention is scaled up, the process parameters do not need to be explored again, and industrial production can be directly scaled up. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the process of the present invention.

[0031] Figure 2 This is an electron microscope image of spherical silver powder with a particle size of 1 μm prepared according to specific embodiment 1 of the present invention;

[0032] Figure 3 This is an electron microscope image of spherical silver powder with a particle size of 1.4 μm prepared according to specific embodiment 1 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The first aspect of this invention discloses a method for preparing spherical silver powder with controllable particle size. In this invention, the nucleation and growth processes of silver powder preparation are innovatively separated. The growth process begins immediately after nucleation, preventing further nucleation due to subsequent reactions. Furthermore, these two processes are not the traditional process of silver crystal nuclei merging; instead, growth occurs slowly based on the nuclei generated after nucleation, without any mutual merging.

[0035] The preparation method includes:

[0036] Step S1: Add pure water and dispersant to the first reaction vessel to prepare a bottom liquid with a volume of half the volume of the first reaction vessel and a concentration of 7-9 g / L, and start stirring for 0.5-1.5 h;

[0037] Step S2, nucleation process: After the base liquid is stirred, the prepared silver nitrate solution is added dropwise to the first reaction vessel containing the base liquid at a rate of 90-110 mL / min for 10-15 min; after the addition is completed, the prepared reducing agent solution is added dropwise to the first reaction vessel at a rate of 135-170 mL / min for 10-15 min, and stirring is continued for 0.5-1.5 h.

[0038] Step S3, growth process: The prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at the same flow rate and the reaction is started. Stirring is continued until the reaction is completed.

[0039] Step S4: After the reaction is completed, the spherical silver powder obtained in step S3 is washed with deionized water and centrifuged. 0.3-0.8% by mass of surface coating agent and ethanol are added to the centrifuged spherical silver powder to obtain a spherical silver powder dispersion. The spherical silver powder dispersion is dispersed at high speed for 20-40 minutes using a high-speed disperser and then dried to obtain the target spherical silver powder.

[0040] In step S1, pure water and dispersant are added to the first reaction vessel to prepare a bottom solution with a volume of half the volume of the first reaction vessel and a concentration of 7-9 g / L, and stirring is started for 0.5-1.5 h. The stirring time is preferably 1 h.

[0041] In some embodiments, the stirring speed is 200-400 r / min.

[0042] Before preparing the silver powder, the present invention first prepares a uniform low-concentration dispersant solution as a base liquid to ensure that the silver crystal nuclei can be uniformly dispersed in the solution during the silver powder nucleation process, thus avoiding agglomeration.

[0043] In step S2, the nucleation process: After the base liquid is stirred, the prepared silver nitrate solution is added dropwise to the first reaction vessel containing the base liquid at a rate of 90-110 mL / min for 10-15 min; after the addition is completed, the prepared reducing agent solution is added dropwise to the first reaction vessel at a rate of 135-170 mL / min for 10-15 min, and stirring continues for 0.5-1.5 h. The preferred stirring time is 1 h.

[0044] In some embodiments, in step S2, the ratio of the dropping rate of the silver nitrate solution to the dropping rate of the reducing agent solution is 1:1.2-1:1.5.

[0045] The innovation of this invention lies in the fact that during the nucleation process, silver nitrate solution is added first, followed by reducing agent solution. The two are added separately (1) to avoid the initial particle size of silver powder being too large and causing serious agglomeration; (2) to accurately control the amount of silver crystal nuclei; and (3) to separate the nucleation and growth processes of silver powder so that they do not affect each other.

[0046] Furthermore, during the nucleation process, excessively high dropping rates of the silver nitrate solution and reducing agent solution can result in low tap density of the silver powder. Therefore, the dropping rate of the silver nitrate solution should be controlled at 90-110 mL / min, and the dropping rate of the reducing agent solution at 135-170 mL / min. Simultaneously, the dropping rate of the reducing agent solution must be greater than that of the silver nitrate solution to ensure an excess of reducing agent. The preparation of silver powder is a redox process, and nitric acid is a byproduct of the reaction. Excess reducing agent will inhibit the reaction between silver powder and nitric acid; generally, an excess of 20-50% is sufficient.

[0047] In some embodiments, the concentration of the silver nitrate solution is 0.5-2 mol / L.

[0048] In some embodiments, the concentration of the reducing agent solution is 0.5-1.5 mol / L.

[0049] In some embodiments, the reducing agent is one or more of ascorbic acid, glucose, hydrazine hydrate, and hydrogen peroxide. Ascorbic acid is preferred.

[0050] In step S3, the growth process is as follows: the prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at the same flow rate and the reaction is started. The mixture is stirred continuously until the reaction is completed.

[0051] In some embodiments, step S3 includes the following sub-steps:

[0052] Step S31: After the nucleation process is completed, the prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at a rate of 80-100 mL / min using a peristaltic pump to start the reaction.

[0053] Step S32: After the first reactor is full, stop spraying, release half of the liquid from the first reactor into the second reactor, and continue to add the prepared silver nitrate solution, reducing agent solution and dispersant solution in a co-current manner through a peristaltic pump at a rate of 80-100 mL / min to the first reactor and the second reactor to continue the reaction.

[0054] Step S33: If the particle size of the spherical silver powder does not reach the target particle size after the first and second reaction vessels are full, stop spraying and continue to release half of the liquid from the first and second reaction vessels into the third and fourth reaction vessels, respectively, and repeat step S32; if the particle size of the spherical silver powder reaches the target particle size, the reaction ends.

[0055] In some embodiments, during nucleation and growth, a particle size analyzer is used to monitor the particle size of the spherical silver powder in real time, and the growth rate of the spherical silver powder is controlled to be 0.001-0.1 μm / h.

[0056] This invention employs an intermittent method (i.e., after the reaction vessel is filled with liquid, half of it is released, the spraying continues, and then the vessel is filled again, and half of it is released again before the spraying continues) to achieve a continuous and stable increase in the particle size of silver powder. It can be prepared even if the particle size is only a few micrometers, without the need for external control.

[0057] In some embodiments, the concentration of the dispersant solution is 10-25 g / L.

[0058] In some embodiments, the dispersant is one or more selected from polyvinylpyrrolidone K30, gum arabic, Tween 40 / 80, and polyethylene glycol. Preferably, it is polyvinylpyrrolidone K30, gum arabic, or Tween 40.

[0059] In step S4, after the reaction is complete, the spherical silver powder obtained in step S3 is washed with deionized water and centrifuged. A surface coating agent and ethanol (mass percentage 0.3-0.8%) are added to the centrifuged spherical silver powder to obtain a spherical silver powder dispersion. The spherical silver powder dispersion is then dispersed at high speed for 20-40 minutes using a high-speed disperser and dried to obtain the target spherical silver powder. The preferred high-speed dispersion time is 30 minutes.

[0060] In some embodiments, the surface coating agent is one or more of unsaturated higher fatty acids and amines with 8 or more carbon atoms.

[0061] In some embodiments, the drying temperature is 75-85°C and the drying time is 22-26 hours. Preferably, the drying temperature is 80°C and the drying time is 24 hours.

[0062] The second aspect of the present invention discloses a spherical silver powder with controllable particle size, wherein the growth rate of the spherical silver powder is 0.001-0.1 μm / h.

[0063] Example 1

[0064] The first step is to prepare a 0.5 mol / L silver nitrate solution; a 0.5 mol / L ascorbic acid solution; and a 10 g / L dispersant solution.

[0065] The second step is to add 50L of pure water to the first reaction vessel (vessel A, with a volume of 100L) after the above conditions are prepared. Start the stirring and control the stirring intensity at 200r / min. At the same time, add an appropriate amount of dispersant to prepare a bottom liquid with a dispersant concentration of 7g / L and stir for 0.5-1.5h.

[0066] The third step, the nucleation process: The prepared 0.5 mol / L silver nitrate solution is added dropwise to the first reaction vessel containing the base liquid at a flow rate of 90 mL / min, with the addition time controlled at 10 min. After the addition is completed, the 0.5 mol / L ascorbic acid solution is added dropwise at a flow rate of 135 mL / min, with the addition time also controlled at 10 min. After the addition is completed, stirring is continued for 0.5-1.5 h.

[0067] Step 4, growth process: After stirring for 0.5-1.5 hours, simultaneously turn on the switches for silver nitrate solution, ascorbic acid solution and dispersant solution, and add the three solutions into the first reactor in parallel flow at a flow rate of 80 mL / min using a peristaltic pump to start the reaction.

[0068] After the first reactor is full (approximately 3.5 hours to reach full capacity), stop spraying. At this point, release half of the liquid from the first reactor into the second reactor (Reactor B, 100L volume). Then, turn on the switches for the silver nitrate solution, reducing agent solution, and dispersant solution, and continue spraying at a flow rate of 80mL / min. If the silver powder does not reach the target particle size after both reactors are full, release half of the liquid into two more reactors (the third and fourth reactors) and continue spraying at a flow rate of 80mL / min. The reaction ends when the spherical silver powder reaches the target particle size.

[0069] During the silver powder preparation process, a particle size analyzer was used to monitor the particle size of the spherical silver powder in real time, and the growth rate of the spherical silver powder was controlled at 0.001-0.1 μm / h. According to the process conditions of Example 1, the reaction time, silver powder particle size, and tap density were recorded as shown in Table 1. Electron micrographs of silver powder with particle sizes of 1 μm and 1.4 μm prepared using the process of Example 1 are shown below. Figure 2 and Figure 3 As shown.

[0070] Fifth step: After the reaction is completed, the spherical silver powder obtained in the fourth step is washed with deionized water and centrifuged. 0.3-0.8% by mass of surface coating agent and ethanol are added to the centrifuged spherical silver powder to obtain a spherical silver powder dispersion. The spherical silver powder dispersion is dispersed at high speed for 20-40 minutes using a high-speed disperser and then dried to obtain the target spherical silver powder.

[0071] The surface coating agent is one or more of unsaturated higher fatty acids and amines with 8 or more carbon atoms. The drying temperature is 75-85℃, and the drying time is 22-26 hours.

[0072] Table 1

[0073] 0 (Nucleation process) 0.629 - 1 0.643 - 2 0.672 - 3 0.695 - 3.5 0.711 - 4 0.715 - 5 0.751 - 6 0.782 4.2 6.5 0.820 4.7 7 0.885 5.3 10 1.061 5.7 14 1.432 6.11 17 1.703 6.45

[0074] Example 2

[0075] The difference from Example 1 is that the concentrations of silver nitrate solution and ascorbic acid solution are both 1 mol / L, and the dropping time of silver nitrate solution and ascorbic acid solution during nucleation is extended to 12 min.

[0076] Example 3

[0077] The difference from Example 1 is that the concentrations of both the silver nitrate solution and the ascorbic acid solution were 1.5 mol / L, and the dropping time of the silver nitrate solution and ascorbic acid solution during nucleation was extended to 15 min. Based on the process conditions of Example 3, the reaction time, silver powder particle size, and tap density were recorded as shown in Table 2.

[0078] Table 2

[0079] 0 (Nucleation process) 0.565 - 1 0.581 - 2 0.607 - 3 0.653 - 3.5 0.689 - 4 0.709 - 5 0.735 - 6 0.781 4.25 6.5 0.803 4.5 7 0.811 4.53 10 0.855 4.93 14 0.923 5.63 25 1.623 6.24

[0080] Example 4

[0081] The difference from Example 1 is that the concentration of the dispersant solution in the substrate is 9 g / L, the flow rate of the silver nitrate solution during nucleation is 110 mL / min, the flow rate of the reducing agent solution is 170 mL / min, and the flow rate of all three solutions is 100 mL / min during growth.

[0082] Example 5

[0083] The difference from Example 1 is that the concentration of the dispersant solution in the substrate is 8 g / L, the flow rate of the silver nitrate solution during nucleation is 100 mL / min, the flow rate of the reducing agent solution is 150 mL / min, and the flow rate of all three solutions is 90 mL / min during growth.

[0084] In summary, the solution proposed in this invention has the following technical effects:

[0085] ① This invention separates the nucleation and growth stages of silver powder. After the nucleation is completed, the number of silver crystal nuclei is controllable within a specified time. Silver powder growth begins on the basis of the existing number of nuclei, and there is no process of mutual engulfment between silver crystal nuclei. At the same time, combined with a certain stirring speed, the spherical silver powder has high sphericity, good particle size dispersion and uniform particle size, and is not easy to agglomerate.

[0086] ② In the process of silver grain growth, this invention controls the flow rates of three solutions—silver nitrate solution, reducing agent solution, and dispersant solution—and uses an intermittent production method to achieve precise control of silver powder particle size (i.e., slow growth from the initial reaction particle size to the target particle size). It can produce particles as small as a few micrometers without the need for external control.

[0087] ③After the preparation process of the present invention is scaled up, the process parameters do not need to be explored again, and industrial production can be directly scaled up.

[0088] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing spherical silver powder with controllable particle size, characterized in that, The preparation method includes: Step S1: Add pure water and dispersant to the first reaction vessel to prepare a bottom liquid with a volume of half the volume of the first reaction vessel and a concentration of 7-9 g / L, and start stirring for 0.5-1.5 h; Step S2, nucleation process: After the base liquid is stirred, the prepared silver nitrate solution is added dropwise to the first reaction vessel containing the base liquid at a rate of 90-110 mL / min for 10-15 min; after the addition is completed, the prepared reducing agent solution is added dropwise to the first reaction vessel at a rate of 135-170 mL / min for 10-15 min, and stirring is continued for 0.5-1.5 h. Step S3, growth process: The prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at the same flow rate and the reaction is started. Stirring is continued until the reaction is completed. During the nucleation and growth process, a particle size analyzer is used to monitor the particle size of the spherical silver powder in real time, and the growth rate of the spherical silver powder is controlled to be 0.001-0.1 μm / h. Step S4: After the reaction is completed, the spherical silver powder obtained in step S3 is washed with deionized water and centrifuged. 0.3-0.8% by mass of surface coating agent and ethanol are added to the centrifuged spherical silver powder to obtain a spherical silver powder dispersion. The spherical silver powder dispersion is dispersed at high speed for 20-40 minutes using a high-speed disperser and then dried to obtain the target spherical silver powder. Step S3 includes the following sub-steps. Step S31: After the nucleation process is completed, the prepared silver nitrate solution, reducing agent solution and dispersant solution are added to the first reaction vessel in a parallel flow at a rate of 80-100 mL / min using a peristaltic pump to start the reaction. Step S32: After the first reactor is full, stop spraying, release half of the liquid from the first reactor into the second reactor, and continue to add the prepared silver nitrate solution, reducing agent solution and dispersant solution in a co-current manner through a peristaltic pump at a rate of 80-100 mL / min to the first reactor and the second reactor to continue the reaction. Step S33: If the particle size of the spherical silver powder does not reach the target particle size after the first and second reaction vessels are full, stop spraying and continue to release half of the liquid from the first and second reaction vessels into the third and fourth reaction vessels, respectively, and repeat step S32; if the particle size of the spherical silver powder reaches the target particle size, the reaction ends.

2. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, In step S2, the ratio of the dropping rate of the silver nitrate solution to the dropping rate of the reducing agent solution is 1:1.2-1:1.

5.

3. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, The concentration of the silver nitrate solution is 0.5-2 mol / L.

4. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, The concentration of the reducing agent solution is 0.5-1.5 mol / L.

5. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, The concentration of the dispersant solution is 10-25 g / L.

6. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, The reducing agent is one or more of ascorbic acid, glucose, hydrazine hydrate, and hydrogen peroxide.

7. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, The dispersant is one or more of polyvinylpyrrolidone K30, gum arabic, Tween 40 / 80, and polyethylene glycol.

8. The method for preparing spherical silver powder with controllable particle size according to claim 1, characterized in that, The stirring speed is 200-400 r / min.

9. A spherical silver powder prepared by the method for preparing spherical silver powder with controllable particle size as described in any one of claims 1-8.

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