Monodisperse spherical micro-nano silver powder and preparation method thereof

Abstract

The invention provides monodisperse spherical micro-nano silver powder and a preparation method thereof, and belongs to the technical field of metal powder preparation. The silver nitrate solution is used as a silver source, polyvinylpyrrolidone is used as a dispersing agent, ascorbic acid is used as a reducing agent, and the micro-nano silver powder which is narrow in particle size distribution and high in sphericity degree is prepared at the low temperature. The kinetics of hydrolysis and reduction nucleation are effectively slowed down at low temperature, thermal motion of a polyvinylpyrrolidone molecular chain is weakened, the polyvinylpyrrolidone molecular chain can be more orderly and stably adsorbed on a specific crystal face of a silver crystal nucleus, anisotropic growth of the crystal nucleus is inhibited, low-temperature Ostwald ripening among particles is also effectively prevented, and uniformity of the particle size is guaranteed; at a low temperature, the reducing ability of ascorbic acid is moderated. The'mild reduction 'is perfectly matched with the'ordered guiding', so that good balance between reaction kinetics and thermodynamics is realized. And the prepared silver powder is excellent in morphology, ultrahigh in sphericity degree and good in monodispersity, and can be applied to high-end electronic paste.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal powder and its preparation, in particular to a kind of monodisperse spherical micro-nano silver powder and its preparation method. BACKGROUND

[0002] Spherical silver powder, especially sub-micron to nanometer scale spherical silver powder, because it has the highest tap density, excellent fluidity and sintering activity, becomes the ideal material for preparing high-performance, high-resolution electronic paste. Monodisperse ultra-fine spherical silver powder can form a highly dense conductive network after low-temperature sintering, thereby achieving excellent conductivity and line fineness, which is crucial for the current development of electronic devices towards miniaturization and high integration.

[0003] The existing chemical reduction technology, especially in the face of high-end electronic paste application, still has the following significant technical bottlenecks and defects. 1. Difficulty in controlling morphology and particle size: wide particle size distribution and irregular morphology will reduce the tap density of silver powder, leading to unstable rheological properties when preparing paste, and easy to produce defects after printing, uneven sintering shrinkage, which seriously affects the performance of the final device; 2. Process complexity and environmental pollution caused by morphology control: In order to achieve strong reduction and stable morphology, many methods still rely on hydrazine hydrate, sodium borohydride and other toxic or strongly corrosive reducing agents, which pose a threat to the environment and operating personnel safety, and are contrary to the development concept of green chemistry; 3. It is difficult to balance product performance: existing methods are difficult to achieve "high sphericity", "small particle size", "narrow distribution" (monodisperse) and "adjustable particle size" under simple process conditions. For example, when using ascorbic acid as a mild reducing agent, the reaction rate is slow at room temperature, and the product is prone to Ostwald ripening, resulting in uneven particle size; while small particle size can be obtained through severe reaction conditions, but the morphology is difficult to control. SUMMARY

[0004] In view of the technical problems in the background art, the present application provides a kind of monodisperse spherical micro-nano silver powder and its preparation method, to solve the problem that the preparation of existing silver powder is difficult to achieve "high sphericity", "small particle size", "narrow distribution" (monodisperse) and "adjustable particle size" under simple process conditions.

[0005] In one aspect, the present application provides a method for preparing a monodisperse spherical micro-nano silver powder, characterized in that it comprises the following steps: S1. Mix silver nitrate solution and polyvinylpyrrolidone solution at 0-10℃, stir uniformly, and obtain a mixed solution; S2. Under stirring conditions, add ascorbic acid solution pre-cooled to the same temperature as the mixed solution to the mixed solution, continue to react, and obtain silver powder material; S3. The silver powder material is subjected to solid-liquid separation, washing, and drying to obtain the target silver powder.

[0006] In the technical solution of this application embodiment, silver nitrate solution is used as the silver source, polyvinylpyrrolidone (PVP) as the dispersant, and ascorbic acid as the reducing agent. At low temperatures, micro / nano silver powder with a narrow particle size distribution and high sphericity is prepared. At low temperatures, the kinetics of hydrolysis and reduction nucleation are effectively slowed down, reducing the thermal motion of the PPVP molecular chains. This allows the PPVP molecules to be more orderly and stably adsorbed onto specific crystal faces of the silver nuclei, effectively inhibiting anisotropic growth of the nuclei and strongly guiding silver atoms to uniformly deposit along isotropic directions. This results in extremely high sphericity, a smooth surface, and good monodispersity of the silver powder. Simultaneously, the stable encapsulation by PPVP effectively prevents low-temperature Ostwald ripening between particles, ensuring uniform particle size. At low temperatures, the reducing power of ascorbic acid is moderated. This perfect match between "mild reduction" and "orderly guidance" achieves a good balance between reaction kinetics and thermodynamics. The prepared silver powder has an excellent morphology, with high sphericity, smooth surface, good monodispersity, narrow particle size distribution, and good consistency, and can be applied to high-end electronic pastes.

[0007] In some embodiments, in step S1, the concentration of the silver nitrate solution is 0.1~1.0 mol / L, the concentration of the polyvinylpyrrolidone solution is 0.1~0.5 mol / L, and the volume ratio of the silver nitrate solution to the polyvinylpyrrolidone solution is 1:1~100.

[0008] In this embodiment, the particle size of silver powder can be controlled by adjusting the ratio of silver nitrate solution to polyvinylpyrrolidone solution. Polyvinylpyrrolidone acts as a steric hindrance stabilizer, and adjusting the ratio can directly affect the number of silver crystal nuclei and the growth space, thereby determining the final particle size. At this ratio, the polyvinylpyrrolidone molecules can quickly and fully encapsulate each crystal nucleus at the moment of silver crystal nucleus formation, forming a dense protective layer. This protective layer can effectively prevent the crystal nuclei from colliding, agglomerating, and merging, ultimately resulting in silver powder with smaller particle size and more uniform distribution. In addition, under the synergistic effect of a low-temperature environment, the ultra-high sphericity of the silver powder can be induced and maintained.

[0009] In some embodiments, in step S2, the concentration of the ascorbic acid solution is 0.1~1.0 mol / L; the volume ratio of the silver nitrate solution to the ascorbic acid solution is 1:1~100.

[0010] In this embodiment, by controlling the ratio of silver nitrate solution to ascorbic acid solution, the completeness of the reduction reaction and the purity of the product can be controlled, ensuring that all silver ions are fully and thoroughly reduced, thereby obtaining the highest silver powder yield and a high-purity product. Regulating the reaction rate, by controlling the reduction kinetics, affects the nucleation density and growth environment of silver crystal nuclei.

[0011] In some embodiments, in step S2, the reaction temperature is 1~3℃; the reaction time is 0.5~2h.

[0012] In this embodiment, the reduction reaction is carried out at a specific low temperature, and the in-situ crystallization guiding effect is effective at low temperatures. High temperatures will intensify the reaction and atomic migration, leading to excessively rapid nucleation and growth, causing polyvinylpyrrolidone to lose its morphology control ability.

[0013] In some embodiments, the drying temperature in step S3 is 50~70°C.

[0014] Secondly, this application provides a monodisperse spherical micro / nano silver powder, which is prepared by the method described above. The monodisperse spherical micro / nano silver powder has a D50 particle size of 200~900nm, a particle size distribution range that satisfies (D90~D10) / D50<0.8, and a particle size ratio between 1.0 and 1.1 accounts for more than 95% of the total.

[0015] In the technical solution of this application embodiment, the prepared silver powder has an extremely excellent morphology, with ultra-high sphericity, smooth surface, good monodispersity, narrow particle size distribution range, good uniformity, and adjustable particle size. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0017] Figure 1 This is a SEM image of the silver powder prepared in Example 1.

[0018] Figure 2 SEM images of the silver powders prepared in Examples 2-3 and Comparative Examples 1-2.

[0019] Figure 3 The images shown are SEM images of the silver powders prepared in Examples 4-7.

[0020] Figure 4 SEM images of the silver powder prepared in comparative examples 3-6. Detailed Implementation

[0021] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0024] To address the challenge of achieving high sphericity, small particle size, narrow particle size distribution (monodispersibility), and adjustable particle size simultaneously under simple processing conditions in existing silver powder preparation methods, this application provides a monodisperse spherical micro / nano silver powder and its preparation method. Using silver nitrate solution as the silver source, polyvinylpyrrolidone (PVP) as the dispersant, and ascorbic acid as the reducing agent, micro / nano silver powder with a narrow particle size distribution and high sphericity is prepared at low temperatures. At low temperatures, the kinetics of hydrolysis and reduction nucleation are effectively slowed down, reducing the thermal motion of PPVP molecular chains. This allows for more ordered and stable adsorption onto specific crystal faces of silver nuclei, effectively inhibiting anisotropic growth of nuclei and strongly guiding silver atoms to deposit uniformly along isotropic directions. This results in extremely high sphericity, a smooth surface, and good monodispersity of the silver powder. Simultaneously, the stable encapsulation by PPVP effectively prevents low-temperature Ostwald ripening between particles, ensuring particle size uniformity. Furthermore, the reducing power of ascorbic acid is moderated at low temperatures. This perfect match between "mild reduction" and "orderly guidance" achieves a good balance between reaction kinetics and thermodynamics. Simultaneously, the low-temperature environment significantly reduces the reduction rate of silver nitrate, making the formation (nucleation) and growth of silver crystal nuclei mild and controllable. By precisely controlling the concentration ratio of silver nitrate, ascorbic acid, and polyvinylpyrrolidone, the final particle size of the silver powder can be precisely controlled within the submicron to nanoscale range, with a narrow particle size distribution and good consistency. This application requires no complex equipment or harsh reaction conditions, nor does it require pH control steps; it can be completed simply in a conventional low-temperature bath. Achieving "small particle size" and "tunable particle size" through a simple method yields silver powder with extremely excellent morphology, high sphericity, smooth surface, and good monodispersity, making it suitable for high-end electronic pastes.

[0025] On the one hand, the present invention provides a method for preparing monodisperse spherical micro / nano silver powder, comprising the following steps: S1. Mix silver nitrate solution and polyvinylpyrrolidone solution at 0~10℃ and stir until homogeneous to obtain a mixed solution; S2. Under stirring conditions, an ascorbic acid solution pre-cooled to the same temperature as the mixed solution is added to the mixed solution, and the reaction continues to obtain silver powder material; S3. The silver powder material is subjected to solid-liquid separation, washing, and drying to obtain the target silver powder.

[0026] In the technical solution of this application embodiment, silver nitrate solution is used as the silver source, polyvinylpyrrolidone (PVP) as the dispersant, and ascorbic acid as the reducing agent. At low temperatures, micro / nano silver powder with a narrow particle size distribution and high sphericity is prepared. At low temperatures, the kinetics of hydrolysis and reduction nucleation are effectively slowed down, reducing the thermal motion of the PPVP molecular chains. This allows the PPVP molecules to be more orderly and stably adsorbed onto specific crystal faces of the silver nuclei, effectively inhibiting anisotropic growth of the nuclei and strongly guiding silver atoms to deposit uniformly along isotropic directions. This results in extremely high sphericity, a smooth surface, and good monodispersity of the silver powder. Simultaneously, the stable encapsulation by PPVP effectively prevents low-temperature Ostwald ripening between particles, ensuring particle size uniformity. At low temperatures, the reducing power of ascorbic acid is moderated. This perfect match between "mild reduction" and "orderly guidance" achieves a good balance between reaction kinetics and thermodynamics. The prepared silver powder exhibits extremely excellent morphology, with ultra-high sphericity, a smooth surface, and good monodispersity, making it suitable for high-end electronic pastes.

[0027] Further, in some embodiments, in step S1, the concentration of the silver nitrate solution is 0.1~1.0 mol / L, the concentration of the polyvinylpyrrolidone solution is 0.1~0.5 mol / L, and the volume ratio of the silver nitrate solution to the polyvinylpyrrolidone solution is 1:1~100.

[0028] In the technical solution of this application embodiment, the particle size of silver powder can be controlled by controlling the ratio of silver nitrate solution and polyvinylpyrrolidone solution. Polyvinylpyrrolidone acts as a steric hindrance stabilizer, and by adjusting the ratio, it can directly affect the number of silver crystal nuclei and the growth space, thereby determining the final particle size. When the proportion of polyvinylpyrrolidone is high, at the moment the silver crystal nuclei are generated, the polyvinylpyrrolidone molecules can quickly and fully encapsulate each crystal nucleus, forming a dense protective layer. This protective layer can effectively prevent the crystal nuclei from colliding, agglomerating, and merging with each other, ultimately resulting in silver powder with smaller particle size and more uniform distribution. In addition, under the synergistic effect of a low-temperature environment, it can induce and maintain the ultra-high sphericity of the silver powder.

[0029] Furthermore, in some embodiments, in step S2, the concentration of the ascorbic acid solution is 0.1~1.0 mol / L; the volume ratio of the silver nitrate solution to the ascorbic acid solution is 1:1~100.

[0030] In the technical solution of this application embodiment, by controlling the ratio of silver nitrate solution and ascorbic acid solution, the completeness of the reduction reaction and the purity of the product can be controlled, ensuring that all silver ions are fully and thoroughly reduced, thereby obtaining the highest silver powder yield and high-purity product. Regulating the reaction rate, by controlling the speed of reduction kinetics, affects the nucleation density and growth environment of silver crystal nuclei.

[0031] Furthermore, in some embodiments, in step S2, the reaction temperature is 1~3℃; the reaction time is 0.5~2h.

[0032] In the technical solution of this application embodiment, the reduction reaction is carried out at a specific low temperature, and the in-situ crystallization guiding effect is effective at low temperatures. High temperatures will intensify the reaction and atomic migration, leading to excessively rapid nucleation and growth, causing polyvinylpyrrolidone to lose its morphology control ability.

[0033] Furthermore, in some embodiments, the drying temperature in step S3 is 50~70°C.

[0034] Secondly, this application provides a monodisperse spherical micro / nano silver powder, which is prepared by the method described above. The monodisperse spherical micro / nano silver powder has a D50 particle size of 200~900nm, a particle size distribution range that satisfies (D90~D10) / D50<0.8, and a particle size ratio between 1.0 and 1.1 accounts for more than 95% of the total.

[0035] In the technical solution of this application embodiment, the prepared silver powder has an extremely excellent morphology, with ultra-high sphericity, smooth surface, good monodispersity, narrow particle size distribution range, good uniformity, and adjustable particle size.

[0036] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0037] Example 1 This embodiment provides a method for preparing monodisperse spherical micro / nano silver powder, including the following steps: S1. Mix 0.1 mL of 0.5 mol / L silver nitrate solution with 1 mL of 0.3 mol / L polyvinylpyrrolidone solution at 2 °C and stir until homogeneous to obtain a mixed solution; S2. Under stirring conditions, 1 mL of 0.3 mol / L ascorbic acid aqueous solution was pre-cooled to 2°C in an ice-water bath and then added to the above mixed solution. The reaction was continued at 2°C for 0.5 h to obtain silver powder material. S3. The above silver powder material is filtered, washed with deionized water, and then dried in a vacuum drying oven at 50°C for 8 hours to obtain the target silver powder.

[0038] SEM image of the silver powder prepared in this embodiment, as shown below. Figure 1 As shown.

[0039] Depend on Figure 1 It can be seen that the silver powder prepared in this embodiment has high sphericity, good dispersibility and uniformity, and a particle size of about 600 nm.

[0040] Examples 2-3 and Comparative Examples 1-2 Examples 2-3 and Comparative Examples 1-2 respectively provide a method for preparing monodisperse spherical micro / nano silver powder. Compared with Example 1, the difference is that the volume ratio of silver nitrate solution and polyvinylpyrrolidone solution in step S1 is different, as shown in Table 1. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0041] Table 1. Volume ratios of silver nitrate solution and polyvinylpyrrolidone solution and morphology of silver powder in Examples 2-3 and Comparative Examples 1-2. SEM images of the silver powders prepared in Examples 2-3 and Comparative Examples 1-2 are shown below. Figure 2 As shown.

[0042] From Table 1 and Figure 2 It can be seen that when the volume ratio of silver nitrate solution to polyvinylpyrrolidone solution is 1:1~100, it has high sphericity. The higher the proportion of polyvinylpyrrolidone, the smaller the particle size of the prepared silver powder, which can be controlled between 200~900nm. As can be seen from the results of Comparative Example 1, when the proportion of silver nitrate solution is greater than that of polyvinylpyrrolidone solution, there are not enough polyvinylpyrrolidone molecules to uniformly cover all the newly generated silver crystal nuclei. The silver crystals will follow their own inherent crystallization habits and grow freely and anisotropically into sheets along the direction of lowest surface energy. As can be seen from the results of Comparative Example 2, when the proportion of polyvinylpyrrolidone solution continues to increase, when the content of polyvinylpyrrolidone is too high, the solution viscosity will increase significantly, which can easily produce areas with excessively high local concentrations. This causes the nucleation and growth in different areas to be asynchronous, resulting in uneven particle size, decreased sphericity, and rougher surface.

[0043] Examples 4-7 Examples 4-7 provide a method for preparing monodisperse spherical micro / nano silver powder. Compared with Example 1, the difference is that in Examples 4-5, the temperature in step S1 and the pre-cooling temperature in step S2 are different, and in Examples 6-7, the reaction temperature in step S2 is different. See Table 2 for details. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0044] Table 2. Temperature in step S1 and pre-cooling temperature in step S2, reaction temperature in step S2, and silver powder morphology in Examples 4-7. From Table 2 andFigure 3 It can be seen that the low temperature conditions of this application are beneficial to the preparation of monodisperse spherical micro / nano silver powder. The silver powder prepared under suitable low temperature conditions has high sphericity and a smooth surface.

[0045] Comparative Examples 3-6 Comparative Examples 3-6 provide methods for preparing monodisperse spherical micro / nano silver powder. The differences from Example 1 are as follows: in Comparative Example 3, the temperature in step S1 and the pre-cooling temperature in step S2 are both room temperature; in Comparative Example 4, the reaction temperature in step S2 is room temperature; in Comparative Example 5, the ascorbic acid aqueous solution is not pre-cooled; and in Comparative Example 6, the polyvinylpyrrolidone solution is replaced with stearic acid solution. The other steps are roughly the same as in Example 1 and will not be described again here.

[0046] Table 3. Particle size and morphology of silver powders prepared in Comparative Examples 3-6 SEM images of the silver powders prepared in Comparative Examples 3-6 are shown below. Figure 4 As shown.

[0047] Depend on Figure 4 As can be seen from Table 3, in Comparative Examples 3 and 4, the silver powder obtained at room temperature is irregular and agglomerated. This is because at high temperatures, the reaction tends to be in a primitive and disordered state. In Comparative Example 5, no pre-cooling was performed. When the ascorbic acid solution was added to the low-temperature mixed solution, it could not reach equilibrium with the system temperature instantly, forming a local high-temperature region. This caused silver ions to be reduced instantly and in large quantities, producing extremely high concentrations of silver crystal nuclei, resulting in irregular morphology and agglomeration of the final silver powder. In Comparative Example 6, the polyvinylpyrrolidone solution was replaced with stearic acid solution. Since stearic acid is a small molecule, it chemically adsorbs onto the silver surface through its carboxyl group (-COOH). This adsorption is usually selective and may strongly adsorb onto a specific crystal surface, thereby greatly inhibiting the growth of that crystal surface. This leads to severe anisotropic growth and the formation of flakes.

[0048] In summary, this invention provides a monodisperse spherical micro / nano silver powder and its preparation method. Using silver nitrate solution as the silver source, polyvinylpyrrolidone (PVP) as the dispersant, and ascorbic acid as the reducing agent, micro / nano silver powder with a narrow particle size distribution and high sphericity is prepared at low temperature. At low temperature, the kinetics of hydrolysis and reduction nucleation are effectively slowed down, reducing the thermal motion of the PPVP molecular chains. This allows for more ordered and stable adsorption onto specific crystal faces of the silver nuclei, effectively inhibiting anisotropic growth of the nuclei and strongly guiding silver atoms to uniformly deposit along isotropic directions. This results in extremely high sphericity, a smooth surface, and good monodispersity of the silver powder. Simultaneously, the stable encapsulation by PPVP effectively prevents low-temperature Ostwald ripening between particles, ensuring particle size uniformity. At low temperature, the reducing power of ascorbic acid is moderated. This perfect match between "mild reduction" and "orderly guidance" achieves a good balance between reaction kinetics and thermodynamics. Meanwhile, the low-temperature environment significantly reduces the reduction rate of silver nitrate, making the formation (nucleation) and growth of silver crystal nuclei mild and controllable. By precisely controlling the concentration ratio of silver nitrate, ascorbic acid, and polyvinylpyrrolidone, the final particle size of silver powder can be precisely controlled within the submicron to nanoscale range, with a narrow particle size distribution and good consistency. This application requires no complex equipment or harsh reaction conditions, nor does it require steps such as pH control; it can be completed simply in a conventional low-temperature bath. Achieving "small particle size" and "tunable particle size" through a simple method, the prepared silver powder exhibits extremely excellent morphology, with ultra-high sphericity, a smooth surface, and good monodispersity, making it suitable for high-end electronic pastes.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing monodisperse spherical micro / nano silver powder, characterized in that, Includes the following steps: S1. Mix silver nitrate solution and polyvinylpyrrolidone solution at 0~10℃ and stir until homogeneous to obtain a mixed solution; S2. Under stirring conditions, an ascorbic acid solution pre-cooled to the same temperature as the mixed solution is added to the mixed solution, and the reaction continues to obtain silver powder material; S3. The silver powder material is subjected to solid-liquid separation, washing, and drying to obtain the target silver powder.

2. The method for preparing monodisperse spherical micro / nano silver powder according to claim 1, characterized in that, In step S1, the concentration of the silver nitrate solution is 0.1~1.0 mol / L, and the concentration of the polyvinylpyrrolidone solution is 0.1~0.5 mol / L.

3. The method for preparing monodisperse spherical micro / nano silver powder according to claim 2, characterized in that, The volume ratio of the silver nitrate solution to the polyvinylpyrrolidone solution is 1:1 to 100.

4. The method for preparing monodisperse spherical micro / nano silver powder according to claim 1, characterized in that, In step S2, the concentration of the ascorbic acid solution is 0.1~1.0 mol / L.

5. The method for preparing monodisperse spherical micro / nano silver powder according to claim 4, characterized in that, The volume ratio of the silver nitrate solution to the ascorbic acid solution is 1:1 to 100.

6. The method for preparing monodisperse spherical micro / nano silver powder according to claim 1, characterized in that, In step S2, the reaction temperature is 1~3℃.

7. The method for preparing monodisperse spherical micro / nano silver powder according to claim 1, characterized in that, In step S2, the reaction time is 0.5 to 2 hours.

8. The method for preparing monodisperse spherical micro / nano silver powder according to claim 1, characterized in that, In step S3, the drying temperature is 50~70℃.

9. A monodisperse spherical micro / nano silver powder, characterized in that, The monodisperse spherical micro / nano silver powder was prepared using the method described in any one of claims 1 to 8.

10. The monodisperse spherical micro / nano silver powder according to claim 9, characterized in that, The monodisperse spherical micro / nano silver powder has a D50 particle size of 200~900nm, a particle size distribution range that satisfies (D90~D10) / D50 < 0.8, and particles with an aspect ratio between 1.0 and 1.1 account for more than 95%.

Images