Spherical silver powder, its preparation method and application

Abstract

The application provides a kind of spheroidal silver powder and its preparation method and application, the preparation method includes the following steps: (1) emulsifying combination agent and first solvent are mixed, obtain emulsion dispersion liquid;(2) nucleating agent and the emulsion dispersion liquid are mixed, form the dispersion containing nucleating agent superfine emulsion particle dispersion solution;(3) acid liquor, reducing agent and the superfine emulsion particle dispersion solution are mixed, obtain reducing liquid;(4) oxidizing liquid and the reducing liquid are mixed, carry out liquid phase reduction reaction, obtain the spheroidal silver powder.The application utilizes the chemical action of emulsifying combination agent and nucleating agent, forms superfine silver powder containing nucleating agent liquid phase reduction reaction system, thereby obtains a kind of high-activity spheroidal silver powder.The spheroidal silver powder is unique on the surface, the morphology is consistent, the particle is uniform, can realize silver particle surface bump ordered growth, the specific surface area of silver powder significantly increases, can be widely used in photovoltaic energy and electronic printing and multiple fields.

Description

Technical Field

[0001] This invention belongs to the field of silver micro- and nanomaterials technology, specifically relating to a spherical silver powder, its preparation method, and its application. Background Technology

[0002] Silver powder, as an excellent micro / nano material, is widely used in optical materials, electronic components, medicine, and catalysis due to its superior electrical and thermal conductivity, high plasticity, low-temperature sintering ability, and oxidation resistance. With the rapid development of science and technology and the miniaturization of electronic products, the demand for ultrafine silver powder is increasing, while higher requirements are being placed on its properties. The rapid development of the electronics industry has not only promoted extensive and in-depth research on ultrafine silver powder but has also significantly driven the development of the electronic paste industry.

[0003] The morphology of silver powder is one of the most important testing items in the research and development of silver powder. It primarily affects the printing and sintering properties of silver paste, as well as the density and resistivity of the electrode, and has a significant impact on the specific surface area of ​​the silver powder. Dendritic or other complex morphologies reduce the leveling and density of the printed silver paste, thereby reducing the density of the sintered electrode and increasing the electrode resistivity. Therefore, in some sinterable silver pastes, the silver powder morphology is mainly spherical and flake-shaped, and the surface morphology should not be too complex. In silver powder used as a catalyst, the morphology affects the catalytic efficiency because it influences the specific surface area.

[0004] The morphology of silver powder depends on the preparation process. The preparation of spherical or near-spherical silver powder is mainly by chemical synthesis. For example, CN112404450B discloses a chemical synthesis method for highly dispersed, highly spherical porous silver powder, including the following steps: 1) Preparing reducing agent solution A: Adding a dispersant composed of carboxymethyl cellulose V, carboxymethyl cellulose III, and gum arabic powder to deionized water to achieve a viscosity of 400–800 mPa·s, then adding the reducing agent, and maintaining a constant temperature of 40–50℃ after complete dissolution, yields reducing agent solvent A; 2) Preparing silver-containing solution B; 3) Taking silver-containing solution B and reducing agent solution A, wherein the volume of silver-containing solution B is one-quarter the volume of reducing agent solution A, adding silver-containing solution B to reducing agent solution A, maintaining a constant temperature of 40–50℃, and continuously stirring. After the reaction is complete, continue stirring for 10–25 minutes to obtain a precipitate, which is then washed and dried to obtain the final product. Silver powder in flake or other shapes is mainly prepared by mechanical ball milling. For example, CN105478788B discloses a method for producing flake silver powder, the production steps of which include: 1. scratching the surface of zirconia grinding balls; 2. adding raw silver powder, scratched grinding balls, ball milling solvent and ball milling aid into a ball mill for ball milling; 3. cleaning with ethanol, removing the supernatant, drying and grinding into powder.

[0005] In particular, spherical silver powder with a larger specific surface area is widely used in catalyst silver powder due to its higher catalytic efficiency. For example, CN101264521A discloses an industrial preparation method for near-spherical porous silver powder. Specifically, silver carbonate raw material is first dissolved in an ammonia solution and thoroughly mixed to prepare a 5-25 wt% silver ammonium solution. The prepared silver ammonium solution is then introduced into a spray drying device for spray drying to obtain a precursor powder for near-spherical porous silver powder. The obtained precursor powder is then calcined and cooled to room temperature before being removed to obtain near-spherical porous silver powder. However, the above-mentioned existing technologies focus on reducing the particle size and improving the porosity of the powder, but do not consider improving the overall activity from the perspective of the surface shape of the silver powder. Moreover, the reduction process often directly uses a single dispersant, which does not significantly change the surface morphology of the powder.

[0006] Therefore, how to better control the morphology of silver powder, thereby increasing its specific surface area and improving its activity, is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a spherical silver powder, its preparation method, and its applications. This invention utilizes the chemical action of an emulsifying agent to capture a noble metal nucleating agent within the center of ultrafine emulsion particles, thereby forming an ultrafine reaction system containing the nucleating agent and preparing a highly active spherical silver powder. This spherical silver powder has a unique surface, consistent morphology, and uniform particle size, enabling the orderly growth of silver particles with bulges on the surface. The specific surface area of ​​the silver powder is significantly increased, making it widely applicable in photovoltaic energy, electronic printing, and other fields.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing spherical silver powder, the method comprising the following steps:

[0010] (1) Mix the emulsifying agent and the first solvent to obtain an emulsion dispersion;

[0011] (2) Mix the nucleating agent and the emulsion dispersion to form an ultrafine emulsion particle dispersion containing the nucleating agent;

[0012] (3) Mix the acid solution, reducing agent and the ultrafine emulsion particle dispersion solution to obtain a reducing solution;

[0013] (4) The oxidizing solution and the reducing solution are mixed to carry out a liquid-phase reduction reaction to obtain the spherical silver powder.

[0014] This invention utilizes an ultrafine reaction system containing a nucleating agent formed by an emulsifying agent to prepare a highly active spherical silver powder. This spherical silver powder has a unique surface, consistent morphology, and uniform particle size, enabling orderly growth of silver particles with bulging on the surface. The specific surface area of ​​the silver powder is significantly increased, and it can be widely used in photovoltaic energy, electronic printing, and other fields.

[0015] As a preferred technical solution of the present invention, the emulsifying agent in step (1) includes surfactants and thioether compounds.

[0016] Preferably, the surfactant comprises any one or a combination of at least two of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, or ethanolamine.

[0017] Preferably, the sulfide compound includes any one or a combination of at least two of dodecyl sulfide, hexadecyl sulfide, or octadecyl sulfide.

[0018] Preferably, the nucleating agent in step (2) is a noble metal salt.

[0019] Preferably, the noble metal salt includes any one or a combination of at least two of silver nitrate, chloroauric acid, chloropalladic acid, or chloroplatinic acid.

[0020] Preferably, the acid solution in step (3) includes any one or a combination of at least two of formic acid, hydrochloric acid, nitric acid or sulfuric acid.

[0021] Preferably, the reducing agent in step (3) includes any one or a combination of at least two of ascorbic acid, citric acid, formic acid or hydrazine hydrate.

[0022] As a preferred technical solution of the present invention, in steps (1)-(4), the mass ratio of the acid, the reducing agent, the nucleating agent and the emulsifying agent is (15-250):(40-800):(0.1-5):(0.1-20), wherein the acid range of "15-250" can be, for example, 15, 30, 50, 100, 150, 200 or 250, etc., and the reducing agent range of... "40-800" can be, for example, 40, 50, 100, 200, 300, 400, 500, 600, 700 or 800, etc. The nucleating agent selection range "0.1-5" can be, for example, 0.1, 0.55, 1, 2, 3, 4 or 5, etc. The emulsifying agent selection range "0.1-20" can be, for example, 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15 or 20, etc.

[0023] In this invention, if the mass ratio of acid solution to nucleating agent is too small, that is, the amount of nucleating agent is too large, the powder is too fine and the particle size distribution is wide; if the mass ratio of acid solution to nucleating agent is too large, that is, the amount of nucleating agent is too small, the powder shape is irregular and a smooth crystalline powder is formed.

[0024] In this invention, if the mass ratio of acid to emulsifying agent is too small, i.e., the amount of emulsifying agent is too large, the particle size distribution is wide and the morphology is irregular; if the mass ratio of acid to emulsifying agent is too large, i.e., the amount of emulsifying agent is too small, a smooth crystalline powder is generated.

[0025] As a preferred technical solution of the present invention, the preparation step of the emulsion dispersion in step (1) includes:

[0026] The surfactant, thioether compound and first solvent are blended to obtain an emulsion dispersion.

[0027] Preferably, the first solvent includes water.

[0028] As a preferred embodiment of the present invention, the mass-to-volume ratio of the emulsifying agent composed of the surfactant and the thioether compound to the first solvent is (7-150)g:(200-12000)mL. The mass range of the emulsifying agent, “(7-150)g”, can be, for example, 7g, 10g, 25g, 50g, 75g, 100g, 125g, or 150g. The volume range of the first solvent, “(200-12000)mL”, can be, for example, 200mL, 500mL, 1000mL, 2500mL, 5000mL, 7500mL, 10000mL, or 12000mL, and is preferably (10-50)g:(6000-10000)mL.

[0029] Preferably, the mass ratio of surfactant to thioether compound in the emulsifying agent is (0.5-10):(0.1-1), wherein the surfactant range of "0.5-10" can be, for example, 0.5, 1, 3, 5, 7, 9 or 10, and the thioether compound range of "0.1-1" can be, for example, 0.1, 0.3, 0.5, 0.7, 0.9 or 1.

[0030] Preferably, the blending process is accompanied by stirring.

[0031] Preferably, the blending time is 0.5-3 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0032] Preferably, the blending temperature is 20-90℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ or 90℃, etc.

[0033] As a preferred technical solution of the present invention, the preparation step of the oxidation liquid in step (4) includes:

[0034] The oxidant is dissolved in a second solvent to obtain an oxidizing solution.

[0035] Preferably, the oxidant includes silver nitrate.

[0036] Preferably, the second solvent comprises water.

[0037] Preferably, the mass-to-volume ratio of the oxidant and the second solvent is (50-1200)g:(1000-5000)mL, wherein the mass range of the oxidant "(50-1200)g" can be, for example, 50g, 100g, 250g, 500g, 750g, 1000g, 1100g or 1200g, etc., and the volume range of the second solvent "(1000-5000)mL" can be, for example, 1000mL, 1500mL, 2000mL, 2500mL, 3000mL, 3500mL, 4000mL or 5000mL, etc., preferably (100-300)g:(2000-4000)mL.

[0038] As a preferred technical solution of the present invention, the mixing method in step (2) includes: intermittently adding the oxidizing liquid to the reducing liquid.

[0039] Preferably, the dripping rate is 10-500 mL / s, for example, it can be 10 mL / s, 56 mL / s, 100 mL / s, 150 mL / s, 200 mL / s, 250 mL / s, 300 mL / s, 350 mL / s, 400 mL / s or 500 mL / s, etc., and is more preferably 100-300 mL / s.

[0040] In this invention, if the dropping rate is too low, the powder will agglomerate and have a wide particle size distribution; if the dropping rate is too high, agglomerated sponge silver will be formed.

[0041] Preferably, the reaction temperature in step (4) is 20-60°C, for example, it can be 20°C, 30°C, 40°C, 50°C or 60°C.

[0042] Preferably, the reaction time in step (4) is 5-20 min, for example, it can be 5 min, 7 min, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min.

[0043] In this invention, if the reaction time is too short, the reaction will be incomplete and the particle size distribution will be uneven; if the reaction time is too long, some silver surfaces will be acidically corroded.

[0044] Preferably, stirring is performed during the reaction in step (4).

[0045] Preferably, after the liquid-phase reduction reaction in step (4), a post-processing step is performed.

[0046] Preferably, the post-processing includes filtration and drying.

[0047] Preferably, the drying temperature is 20-100℃, for example, it can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ or 100℃.

[0048] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0049] (I) Add the emulsifying agent to the first solvent and stir and mix for 0.5-3 hours at a temperature of 20-90°C to obtain an emulsified dispersion;

[0050] The emulsifying agent comprises a surfactant and a thioether compound, wherein the mass-volume ratio of the emulsifying agent to the first solvent is (7-150) g:(200-12000) mL, and the mass ratio of the surfactant to the thioether compound is (0.5-10):(0.1-1).

[0051] (II) Add the nucleating agent to the emulsion dispersion to form an ultrafine emulsion particle dispersion solution containing the nucleating agent, for a time of 0.5-3 hours and a temperature of 20-90°C;

[0052] The mass ratio of the nucleating agent to the emulsifying agent is (0.1-5):(0.1-20);

[0053] (III) Add the acid and reducing agent to the ultrafine emulsified particle dispersion solution and stir for 10-30 minutes to obtain the reduced solution;

[0054] The mass ratio of the acid, reducing agent, nucleating agent and emulsifying agent is (15-250):(40-800):(0.1-5):(0.1-20);

[0055] (IV) Dissolve silver nitrate in the second solvent to obtain an oxidizing solution;

[0056] The mass-to-volume ratio of silver nitrate to the second solvent is (50-1200) g:(1000-5000) mL;

[0057] (V) The oxidizing solution is intermittently added to the reducing solution at 20-60°C. After the addition is completed, the mixture is stirred at the above temperature for 5-20 minutes to obtain the reaction solution.

[0058] (VI) The reaction solution is filtered and dried at 20-100℃, then allowed to stand to settle and remove the supernatant, and washed with deionized water 2-6 times. The obtained product is then placed in an oven to dry and sieve to obtain spherical silver powder.

[0059] In a second aspect, the present invention provides a near-spherical silver powder, which is prepared by the preparation method described in the first aspect;

[0060] The surface morphology of the spherical silver powder is bulging.

[0061] Thirdly, the present invention provides a conductive silver paste, wherein the conductive silver paste comprises spherical silver powder as described in the second aspect.

[0062] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] This invention utilizes an ultrafine reaction system containing a nucleating agent formed by an emulsifying agent to prepare a highly active spherical silver powder. This spherical silver powder has a unique surface, consistent morphology, and uniform particle size, enabling orderly growth of silver particles with bulging on the surface. The specific surface area of ​​the silver powder is significantly increased, and it can be widely used in photovoltaic energy, electronic printing, and other fields. Attached Figure Description

[0065] Figure 1 This is an electron microscope image of the spherical silver powder prepared in Example 1 of the present invention.

[0066] Figure 2 This is an electron microscope image of the spherical silver powder prepared in Example 2 of the present invention.

[0067] Figure 3 This is an electron microscope image of the spherical silver powder prepared in Example 3 of the present invention. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0069] Example 1

[0070] This embodiment provides a method for preparing spherical silver powder, the method comprising the following steps:

[0071] (1) Add the emulsifying agent (including sodium dodecylbenzenesulfonate and octadecyl sulfide) to deionized water, stir and mix for 1 hour at 25°C to obtain an emulsified dispersion;

[0072] The mass-to-volume ratio of the emulsifying agent to deionized water is 10g:5000mL, and the mass ratio of sodium dodecylbenzenesulfonate to octadecyl sulfide is 1:0.1.

[0073] (2) Add chloroauric acid to the above emulsion dispersion and stir to form an ultrafine emulsion particle dispersion containing nucleating agent. The mixing time is 1 hour and the temperature is 25°C.

[0074] The mass ratio of chloroauric acid to the emulsifying agent is 0.1:5.

[0075] (3) Add sulfuric acid and ascorbic acid sequentially to the above ultrafine emulsified particle dispersion solution, stir and mix for 10 min to obtain a reducing solution;

[0076] The mass ratio of sulfuric acid, ascorbic acid, and emulsifying agent is 18:100:0.3.

[0077] (4) Dissolve silver nitrate in deionized water to obtain an oxidizing solution;

[0078] The mass-to-volume ratio of silver nitrate to deionized water is 60g:2000mL;

[0079] (5) The oxidizing solution is intermittently added to the reducing solution under constant temperature and stirring at 30°C. After the addition is completed, stirring is continued at the above temperature for 10 minutes to obtain the reaction solution.

[0080] The dropping rate was 300 mL / s, the dropping time was 3 min, and the interval between intermittent dropping was 1 min.

[0081] (6) Under stirring, the reaction solution is filtered and dried at 60°C for 60 minutes. Then, it is allowed to settle to remove the supernatant and washed with deionized water three times. The obtained product is then placed in an oven to dry and sieve to obtain the spherical silver powder with a bulging surface morphology.

[0082] Figure 1 An electron microscope image of the spherical silver powder prepared in this embodiment is shown.

[0083] Example 2

[0084] This embodiment provides a method for preparing spherical silver powder, the method comprising the following steps:

[0085] (1) Add the emulsifying agent (including sodium dodecylbenzenesulfonate and octadecyl sulfide) to deionized water, stir and mix for 3 hours at 60°C to obtain an emulsified dispersion;

[0086] The mass-to-volume ratio of the emulsifying agent to deionized water is 100g:10000mL; the mass ratio of sodium dodecylbenzenesulfonate to octadecyl sulfide is 6:0.5.

[0087] (2) Chloroauric acid was added to the above emulsion dispersion and stirred and mixed to form an ultrafine emulsion particle dispersion containing nucleating agent. The mixing time was 3 hours and the temperature was 60°C.

[0088] The mass ratio of chloroauric acid to emulsifying agent is 1:20.

[0089] (3) Add sulfuric acid and ascorbic acid sequentially to the above ultrafine emulsified particle dispersion solution and stir for 15 min to obtain a reducing solution;

[0090] The mass ratio of sulfuric acid, ascorbic acid, and emulsifying agent is 18:100:0.3.

[0091] (4) Dissolve silver nitrate in deionized water to obtain an oxidizing solution;

[0092] The mass-to-volume ratio of silver nitrate to deionized water is 100g:2000mL;

[0093] (5) The oxidizing solution is intermittently added to the reducing solution under constant temperature and stirring at 30°C. After the addition is completed, stirring is continued at the above temperature for 10 minutes to obtain the reaction solution.

[0094] The dropping rate was 40 mL / s, the dropping time was 3 min, and the interval between intermittent dropping was 1 min.

[0095] (6) Under stirring, the reaction solution is filtered and dried at 80°C for 60 minutes. Then, it is allowed to settle to remove the supernatant and washed with deionized water 6 times. The obtained product is then placed in an oven to dry and sieve to obtain the spherical silver powder with a bulging surface morphology.

[0096] Figure 2 An electron microscope image of the spherical silver powder prepared in this embodiment is shown.

[0097] Example 3

[0098] This embodiment provides a method for preparing spherical silver powder, the method comprising the following steps:

[0099] (1) Add the emulsifying agent (including sodium dodecylbenzenesulfonate and octadecyl sulfide) to deionized water, stir and mix for 0.5 h at 80 °C to obtain an emulsified dispersion;

[0100] The mass-to-volume ratio of the emulsifying agent to deionized water is 20g:10000mL; the mass ratio of sodium dodecylbenzenesulfonate to octadecyl sulfide is 10:0.5.

[0101] (2) Add chloroauric acid to the above emulsion dispersion and stir to form an ultrafine emulsion particle dispersion containing nucleating agent. The mixing time is 0.5 h and the temperature is 80 °C.

[0102] The mass ratio of chloroauric acid to emulsifying agent is 1:10.

[0103] (3) Add sulfuric acid and ascorbic acid sequentially to the above ultrafine emulsified particle dispersion solution and stir for 30 min to obtain a reducing solution;

[0104] The mass ratio of sulfuric acid, ascorbic acid and emulsifying agent is 100:500:6.

[0105] (4) Dissolve silver nitrate in deionized water to obtain an oxidizing solution;

[0106] The mass-to-volume ratio of silver nitrate to deionized water is 200g:5000mL;

[0107] (5) The oxidizing solution is intermittently added to the reducing solution under constant temperature and stirring at 50°C. After the addition is completed, stirring is continued at the above temperature for 10 minutes to obtain the reaction solution.

[0108] The dropping rate was 200 mL / s, the dropping time was 3 min, and the interval between intermittent dropping was 1 min.

[0109] (6) Under stirring, the reaction solution is filtered and dried at 30°C for 60 minutes. Then, it is allowed to settle to remove the supernatant and washed twice with deionized water. The obtained product is then placed in an oven to dry and sieve to obtain the spherical silver powder with a bulging surface morphology.

[0110] Figure 3 An electron microscope image of the spherical silver powder prepared in this embodiment is shown.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is that chloroauric acid is not added in step (2).

[0113] The remaining preparation methods and parameters are consistent with those in Example 1.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 1 is that no emulsifying agent is added in step (2).

[0116] The remaining preparation methods and parameters are consistent with those in Example 1.

[0117] Performance testing

[0118] The specific surface area and particle size distribution of the silver powders provided in Examples 1-3 and Comparative Examples 1-2 were tested.

[0119] The test results are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123] analyze:

[0124] As shown in the table above, this invention utilizes an ultrafine reaction system containing a nucleating agent formed by an emulsifying agent to prepare a highly active spherical silver powder. This type of spherical silver powder has a unique surface, consistent morphology, and uniform particle size, enabling orderly growth of silver particles with bulging on the surface. The specific surface area of ​​the silver powder is significantly increased, and it can be widely used in multiple fields such as photovoltaic energy and electronic printing.

[0125] As can be seen from the data results of Example 1 and Comparative Example 1, if chloroauric acid is not added as a nucleating agent, the reduction process cannot control the particle size and morphology of the powder, resulting in a wide particle size distribution and a large number of irregular powders such as flat and elliptical shapes, which makes it impossible to obtain the expected target powder.

[0126] As can be seen from the data results of Example 1 and Comparative Example 2, if no emulsifying agent is added, the nucleating agent cannot play its role. Although the generated powder is spherical, it will exhibit adhesion, have a wide particle size distribution, and no bulging on the powder surface, thus failing to obtain highly active powder.

[0127] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing spherical silver powder, characterized in that, The preparation method includes the following steps: (1) Mix the emulsifying agent and the first solvent to obtain an emulsion dispersion; (2) Mix the nucleating agent and the emulsion dispersion to form an ultrafine emulsion particle dispersion solution containing the nucleating agent; (3) Mix the acid solution, reducing agent and the ultrafine emulsion particle dispersion solution to obtain a reducing solution; (4) The oxidizing solution and the reducing solution are mixed to carry out a liquid-phase reduction reaction to obtain the spherical silver powder; The emulsifying agent in step (1) includes surfactants and thioether compounds; The surfactant includes any one or a combination of at least two of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, fatty alcohol polyoxyethylene ether, or ethanolamine. The thioether compounds include any one or a combination of at least two of dodecyl sulfide, hexadecyl sulfide or octadecyl sulfide; The preparation steps of the emulsion dispersion in step (1) include: The surfactant, thioether compound and first solvent are blended to obtain an emulsion dispersion; The first solvent includes water; The mass-to-volume ratio of the emulsifying combination composed of the surfactant and the thioether compound to the first solvent is (7-150) g:(200-12000) mL; The mass ratio of surfactant to thioether compound in the emulsifying mixture is (0.5-10):(0.1-1); The nucleating agent in step (2) is a noble metal salt; The noble metal salt includes any one or a combination of at least two of silver nitrate, chloroauric acid, chloropalladic acid or chloroplatinic acid; The acid solution in step (3) includes any one or a combination of at least two of formic acid, hydrochloric acid, nitric acid or sulfuric acid; The reducing agent in step (3) includes any one or a combination of at least two of ascorbic acid, citric acid, formic acid or hydrazine hydrate; The mass ratio of the acid, the reducing agent, the nucleating agent, and the emulsifying agent is (15-250):(40-800):(0.1-5):(0.1-20); The preparation steps of the oxidation liquid in step (4) include: The oxidizing agent is dissolved in a second solvent to obtain an oxidizing solution; The mass-to-volume ratio of the oxidant to the second solvent is (50-1200) g:(1000-5000) mL.

2. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the emulsifying agent composed of the surfactant and the thioether compound to the first solvent is (10-50) g:(6000-10000) mL.

3. The preparation method according to claim 1, characterized in that, The mass ratio of surfactant to thioether compound in the emulsifying agent is (0.5-10):(0.1-1).

4. The preparation method according to claim 1, characterized in that, The blending process is accompanied by stirring.

5. The preparation method according to claim 1, characterized in that, The blending time is 0.5-3 hours.

6. The preparation method according to claim 1, characterized in that, The blending temperature is 20-90℃.

7. The preparation method according to claim 1, characterized in that, The oxidizing agent includes silver nitrate.

8. The preparation method according to claim 1, characterized in that, The second solvent includes water.

9. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the oxidant to the second solvent is (100-300) g:(2000-4000) mL.

10. The preparation method according to claim 1, characterized in that, The mixing method described in step (4) includes intermittently adding the oxidizing solution to the reducing solution.

11. The preparation method according to claim 10, characterized in that, The dripping rate is 10-500 mL / s.

12. The preparation method according to claim 11, characterized in that, The dripping rate is 100-300 mL / s.

13. The preparation method according to claim 1, characterized in that, The reaction temperature in step (4) is 20-60℃.

14. The preparation method according to claim 1, characterized in that, The reaction time in step (4) is 5-20 min.

15. The preparation method according to claim 1, characterized in that, Stirring is performed during the reaction described in step (4).

16. The preparation method according to claim 1, characterized in that, After the liquid-phase reduction reaction described in step (4), a post-processing step is also performed.

17. The preparation method according to claim 16, characterized in that, The post-processing includes filtration and drying.

18. The preparation method according to claim 17, characterized in that, The drying temperature is 30-100℃.

19. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (I) Add the emulsifying agent to the first solvent and stir and mix for 0.5-3 hours at a temperature of 20-90°C to obtain an emulsion dispersion; The emulsifying agent comprises a surfactant and a thioether compound, wherein the mass-volume ratio of the emulsifying agent to the first solvent is (7-150) g:(200-12000) mL, and the mass ratio of the surfactant to the thioether compound is (0.5-10):(0.1-1). (II) Add the nucleating agent to the emulsion dispersion to form an ultrafine emulsion particle dispersion solution containing the nucleating agent, for a time of 0.5-3 hours and a temperature of 20-90°C; The mass ratio of the nucleating agent to the emulsifying agent is (0.1-5):(0.1-20); (III) Add the acid and reducing agent to the ultrafine emulsified particle dispersion solution and stir for 10-30 minutes to obtain the reduced solution; The mass ratio of the acid, reducing agent, nucleating agent and emulsifying agent is (15-250):(40-800):(0.1-5):(0.1-20); (IV) Dissolve silver nitrate in the second solvent to obtain an oxidizing solution; The mass-to-volume ratio of silver nitrate to the second solvent is (50-1200) g:(1000-5000) mL; (V) The oxidizing solution is intermittently added to the reducing solution at 20-60°C. After the addition is completed, the mixture is stirred at the above temperature for 5-20 minutes to obtain the reaction solution. (VI) The reaction solution is filtered and dried at 20-100℃, then allowed to stand to settle and remove the supernatant, and washed with deionized water 2-6 times. The resulting product is then dried in an oven and sieved to obtain spherical silver powder.

20. A type of spherical silver powder, characterized in that, The spherical silver powder is prepared by the preparation method according to any one of claims 1-19; The surface morphology of the spherical silver powder is bulging.

21. A conductive silver paste, characterized in that, The conductive silver paste includes the spherical silver powder as described in claim 20.

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