High-purity micron-sized solid sphere-like silver powder, preparation method and low-temperature silver paste

Abstract

The invention provides high-purity micron-sized solid sphere-like silver powder, a preparation method and low-temperature silver paste, and belongs to the technical field of conductive silver paste. The preparation method comprises the following steps: respectively obtaining an oxidation solution and a first reduction solution; pVP is dissolved in an ascorbic acid solution to form a second reduction solution; the second reduction solution is added into the reaction container to be stirred, the silver nitrate solution is rapidly guided into the reaction container to react, the water buffer solution is added into the reaction container, and silver crystal nucleuses with the uniform particle size are obtained; deionized water, a dispersing agent and silver crystal nucleuses are added into a reaction kettle, a pH adjusting solution is added to adjust the pH to be 4-6, the first reduction solution and the oxidation solution are added into the reaction kettle at the temperature of 35-40 DEG C at the equal speed, stirring, centrifuging, soaking, suction filtration, drying, crushing and screening are conducted, and the silver powder is obtained. The silver powder is synthesized on a large crystal nucleus, micron-sized powder is obtained, the particle size distribution of the silver powder is narrow, the maximum particle size can be controlled to be 5.5 microns or below, and the printing performance is better while good conductivity is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive silver paste, and in particular relates to a high-purity micron-level solid spherical silver powder and a preparation method thereof, and a low-temperature silver paste. Background Art

[0002] In the past, the evolution of photovoltaic cells seemed to be a technological replacement, but in fact it was also an extension of technology. For example, in the past, the battery was an aluminum back surface field solar cell (BSF cell), and the emitter and rear passivated cell (PERC cell) superimposed passivation and grooving technology on the BSF cell technology, reducing the back surface recombination rate and improving conversion efficiency. On the basis of PERC cells, TOPCON cells changed the cell substrate and added tunneling silicon oxide passivation technology, which increased the minority carrier lifetime on the one hand and further reduced the back surface recombination rate on the other hand. It can be seen that absolute technological replacement did not exist in the past photovoltaic development. The actual replacement was mainly the production line replacement brought about by technological extension, and the future may usher in a real technological iteration. HJT technology that prepares different PN junctions on both sides of the battery, or forms BC battery technology that transfers the grid line to the back of the battery, and even thin-film perovskite cells and stacked cells, these new technologies are very different from the original batteries in structure and have become the focus of enterprises.

[0003] However, HJT amorphous silicon can only be prepared in a low-temperature environment of less than 200°C, so the high-temperature silver paste of traditional crystalline silicon cells is not suitable for HJT cells. At present, the HJT industry uses resin-cured low-temperature silver paste to make battery electrodes. The high cost of silver paste is mainly caused by two reasons: 1) The low-temperature silver paste does not undergo high-temperature sintering, and other components remaining in the electrode under the low-temperature process lead to high resistivity and conductivity deviation, so it is necessary to increase the amount of silver paste to reduce resistance; 2) HJT has a double-sided structure and pure silver is required on both sides, unlike PERC cells, which can use silver-aluminum paste on the back, so HJT cells have a higher silver consumption. According to PV-Tech data, the silver consumption of HJT batteries in 2022 will be around 18-20mg / W, which is significantly higher than the silver consumption of PERC batteries of 10mg / W and TOPCon batteries of 13mg / W.

[0004] The heterojunction battery process needs to be carried out below 200°C, so the silver paste used in heterojunction batteries is different from the high-temperature silver paste used in other crystalline silicon batteries. It needs to use low-temperature silver paste. Among them, heterojunction silver paste is generally composed of conductive fillers and organic polymers. The conductive filler is generally silver powder, and occasionally other alloy conductive fillers, which mainly play the role of conducting electrons and determine the electrical properties of the heterojunction silver paste. In the HJT silver paste system, silver powder and silver-coated copper powder are conductive functional phases, which directly affect the volume resistance and contact resistance of the silver paste. In order to reduce the cost of paste and improve the conversion efficiency of solar cells, the opening of the paste printing line width is gradually narrowed. The main factors affecting the printing line width opening include the morphology and particle size of the silver powder, the characteristics of the organic polymer, etc.

[0005] At present, the silver powder in the low-temperature silver paste for HJT solar cells is a mixture of flake silver powder and spherical silver powder. Its particle size distribution is relatively wide, and as the line width opening is gradually narrowed, for example, the line width opening of the low-temperature silver paste for HJT solar cells has been narrowed to 24μm, and will be further narrowed to below 20μm. This combination of flake powder and spherical powder cannot meet the conditions for high-resolution precision printing. Summary of the invention

[0006] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and provides a high-purity micron-level solid spherical silver powder and a preparation method, and a low-temperature silver paste.

[0007] In one aspect of the present disclosure, a method for preparing high-purity micron-sized solid spherical silver powder is provided, the preparation method comprising:

[0008] S110, dissolving silver nitrate in deionized water at room temperature, adding a pH adjusting solution to adjust the pH to 4-6, and stabilizing the temperature at 35-40° C. to obtain an oxidizing solution;

[0009] S120, dissolving ascorbic acid in deionized water at room temperature, adding a pH adjusting solution to adjust the pH to 4-5, and stabilizing the temperature at 35-40° C. to obtain a first reducing solution;

[0010] S130, dissolving silver nitrate in deionized water to form a silver nitrate solution; weighing ascorbic acid and dissolving it in deionized water to form an ascorbic acid solution, dissolving PVP in the ascorbic acid solution, and adjusting the pH of the solution to 4-5 with an ammonia solution to form a second reducing solution; adding the second reducing solution to a reaction container and stirring, and quickly introducing the silver nitrate solution into the reaction container for reaction, and adding an aqueous buffer solution to the reaction container to obtain silver crystal nuclei with uniform particle size;

[0011] S140, adding deionized water, a dispersant and the silver crystal nuclei into a reaction kettle, adding a pH adjusting solution to adjust the pH to 4-6, controlling the temperature at 35-40°C, adding the first reducing solution and the oxidizing solution into the reaction kettle at an equal rate, and subjecting the mixture to stirring, centrifuging, soaking, filtering, drying, crushing and screening to obtain a high-purity micron-level solid spherical silver powder.

[0012] Optionally, in step S110, the mass ratio of the silver nitrate to deionized water at room temperature is 1:(20-40).

[0013] Optionally, in step S120, the mass ratio of ascorbic acid to deionized water at room temperature is 1:(25-50).

[0014] Optionally, in step S130, the concentration of the silver nitrate solution is 2.5-5 g / L; and / or,

[0015] The concentration of the ascorbic acid solution is 1.67-3.33 g / L; and / or,

[0016] The concentration of the ammonia solution is 4-6%.

[0017] Optionally, in step S130, the mass ratio of the ascorbic acid to the PVP is (0.05-0.1):(2-5).

[0018] Optionally, in step S130, the volume ratio of the second reducing solution, the silver nitrate solution and the aqueous buffer solution is 1:1:2.

[0019] Optionally, in step S140, the dispersant is a fatty acid; and / or,

[0020] The amount of the dispersant added is 0.3-5% of the weight of the silver nitrate added in step S110.

[0021] Optionally, in step S140, the oxidizing solution and the first reducing solution are added at a rate of 300-500 L / min, and the addition time of each batch is 1-2 min; and / or,

[0022] The stirring speed of the reactor is 300-500r / min.

[0023] In another aspect of the present disclosure, a high-purity micron-sized solid quasi-spherical silver powder is provided. The high-purity micron-sized solid quasi-spherical silver powder is prepared by the preparation method described above.

[0024] In another aspect of the present disclosure, a low-temperature silver paste is provided, wherein the low-temperature silver paste comprises the high-purity micron-sized solid spherical silver powder described above, an organic polymer, and a solvent.

[0025] The present disclosure provides a high-purity micron-level solid quasi-spherical silver powder and a preparation method and a low-temperature silver paste. In the preparation method disclosed herein, a silver nitrate solution is used as a silver source, ascorbic acid is used as a reducing agent, and a large silver crystal nucleus is added as a basis. Under the protection of a dispersant, the reaction process is more carefully regulated, for example, the reaction conditions of an oxidizing solution and a reducing solution are controlled to obtain a high-purity micron-level solid quasi-spherical silver powder with a narrow particle size distribution and a uniform crystal morphology. The method has a fast reaction speed, and the obtained silver powder has a high purity, is quasi-spherical, has a narrow particle size distribution, and the maximum particle size can be controlled below 5.5 μm, which ensures good conductivity while making the printing performance better. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flowchart of a method for preparing high-purity micron-sized solid spherical silver powder according to an embodiment of the present disclosure;

[0027] Figure 2 is a scanning electron microscope image of the silver powder of Example 1 of the present disclosure;

[0028] Figure 3 This is a scanning electron microscope image of the silver powder of Example 2 of the present disclosure. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0030] like Figure 1 As shown, in one aspect of the present disclosure, a method S100 for preparing high-purity micron-level solid spherical silver powder is provided, which specifically comprises the following steps S110 to S140:

[0031] S110, dissolving silver nitrate in deionized water at room temperature, adding a pH adjusting solution to adjust the pH to 4-6, and stabilizing the temperature at 35-40° C. to obtain an oxidizing solution.

[0032] In step S110, the mass ratio of silver nitrate to room temperature deionized water is 1:(20-40), and may further preferably be 1:25-1:30, for example, 1:25, 1:27, 1:30, etc. Of course, in other embodiments, other mass ratios may also be selected, and this is not specifically limited.

[0033] In step S110, the pH may also preferably be 4.5-5.5, for example, 4.5, 4.7, 5.0, 5.2, 5.5, etc.

[0034] In step S110, the temperature may also preferably be 35-37°C, for example, 35°C, 36°C, 37°C, etc.

[0035] S120, dissolving ascorbic acid in deionized water at room temperature, adding a pH adjusting solution to adjust the pH to 4-5, and stabilizing the temperature at 35-40° C. to obtain a first reducing solution.

[0036] In step S120, the mass ratio of ascorbic acid to room temperature deionized water is 1:(25-50), and may further preferably be 1:30-1:40, for example, 1:30, 1:35, 1:40, etc. Of course, in other embodiments, other mass ratios may also be selected, and this is not specifically limited.

[0037] In step S120, the pH may also preferably be 4.5-5.5, for example, 4.5, 4.7, 5.0, 5.2, 5.5, etc.

[0038] In step S120, the temperature may also preferably be 35-37°C, for example, 35°C, 36°C, 37°C, etc.

[0039] It should be noted that, in step S110 and step S120, the pH adjustment solution may be nitric acid or ammonia water.

[0040] S130, crystal nucleus preparation: dissolving silver nitrate in deionized water to form a silver nitrate solution; weighing ascorbic acid and dissolving it in deionized water to form an ascorbic acid solution, dissolving PVP in the ascorbic acid solution, and adjusting the pH to 4-5 with an ammonia solution to form a second reducing solution; adding the second reducing solution to a reaction container (e.g., a three-necked flask) and stirring, and quickly introducing the silver nitrate solution into the reaction container for reaction, and adding an aqueous buffer solution to the reaction container to obtain silver crystal nuclei with uniform particle size.

[0041] In step S130, the concentration of the silver nitrate solution is 2.5-5 g / L. For example, 0.05-0.1 g of silver nitrate is weighed and dissolved in 20 mL of deionized water to prepare a silver nitrate solution with a concentration of 2.5-5 g / L.

[0042] In step S130, the concentration of the ascorbic acid solution is 1.67-3.33 g / L. For example, 0.05-0.1 g of ascorbic acid is weighed and dissolved in 30 mL of deionized water to form an ascorbic acid solution with a concentration of 1.67-3.33 g / L.

[0043] In step S130, the mass ratio of ascorbic acid to the PVP is (0.05-0.1):(2-5), wherein PVP is used as a dispersant, and when the added content of ascorbic acid is 0.05-0.1 g, the added content of PVP is preferably 2-5 g.

[0044] In step S130, the concentration of the ammonia solution is 4-6%. For example, a proper amount of 25-28% concentrated ammonia solution is dissolved in a certain amount of deionized water to prepare a 5% ammonia solution.

[0045] In step S130, the volume ratio of the second reducing solution, the silver nitrate solution and the aqueous buffer solution is 1:1:2. For example, 25 mL of the second reducing solution is placed in a 250 mL three-necked flask and stirred magnetically. 25 mL of the silver nitrate solution is quickly poured into the three-necked flask and reacted for a period of time. Then, 50 mL of deionized water is added to the three-necked flask as a buffer solution to obtain silver crystal nuclei with uniform particle size.

[0046] S140, adding deionized water to the reactor, starting stirring, adding a certain amount of dispersant and a certain amount of silver crystal nuclei, adding pH adjusting solution to adjust the pH to 4-6, starting temperature control, controlling the solution temperature at 35-40°C, and after the temperature stabilizes, adding the first reducing solution and the oxidizing solution to the reactor at an equal rate through a flow controller, and continuing stirring for 10 minutes after adding; then centrifuging and washing until the outlet water conductivity is less than 10μs / cm, then adding a large amount of alcohol to soak, filtering, drying, crushing with a swing crusher, sieving, crushing with a high-speed crusher, and sieving to obtain a finished powder.

[0047] In step S140, the dispersant is preferably a fatty acid and / or PVP, wherein the fatty acid is preferably one or two to three of linoleic acid, lauric acid, oleic acid, caprylic acid, stearic acid, and palmitic acid. More preferably, a mixture of stearic acid and palmitic acid is used. A mixture of PVP and palmitic acid, or a mixture of PVP and stearic acid may also be preferred.

[0048] In step S140, the amount of dispersant added is 0.3-5% of the weight of the silver nitrate added in step S110.

[0049] In step S140, the oxidizing liquid and the first reducing liquid are metered and added quickly by a high-flow peristaltic pump, the adding speed is 300-500L / min, and the adding time of each batch is 1-2min. That is, the oxidizing liquid and the first reducing liquid are added in batches, and the adding rate in each batch is the same.

[0050] In some preferred embodiments, the speed at which the oxidizing liquid and the first reducing liquid are quickly added by a large-flow peristaltic pump may preferably be 300 L / min, 350 L / min, 400 L / min, 450 L / min, 500 L / min, etc.

[0051] In step S140, the stirring speed of the reactor is 300-500 r / min, for example, 300 r / min, 400 r / min, 500 r / min, etc.

[0052] It should be understood that in order to improve the reaction efficiency, all reaction liquids should be kept at 35-40°C before the reaction.

[0053] It is worth noting that the effect of temperature changes on the reaction system during the reaction process cannot be ignored, because the temperature change directly has a great impact on the Brownian thermal motion of particles in the liquid, thereby controlling the chemical reaction, crystal formation and crystal growth process in the system. In the ultrafine powder preparation process of this embodiment, particle nucleation and particle growth can be separated as much as possible, which is the key to preparing a particle size, morphology, and narrow particle size distribution. In order to promote the separation of nucleation and growth, the measures commonly taken are: using seed crystals to induce the precipitation process, thereby avoiding the proliferation of crystal nuclei and the process out of control; using a combined reactor, nucleation and growth are carried out in two reactors with different mixing characteristics and reaction material environments.

[0054] It should be understood that compared with nano silver powder, micron silver powder has low surface activity and complex crystal morphology, and there are large differences between different particles, so it is necessary to regulate the reaction process more carefully to obtain a more uniform crystal morphology. Therefore, in this embodiment, by regulating the reaction process more carefully, the particle nucleation and particle growth are separated as much as possible to form a larger crystal nucleus to avoid the proliferation of the crystal nucleus, and silver nitrate solution is used as the silver source, ascorbic acid is used as the reducing agent, and the formed large crystal nucleus is used as the basis. Under the protection of the dispersant, by controlling the reaction conditions of the oxidizing solution and the reducing solution, a high-purity micron-level solid spherical silver powder with a narrow particle size distribution and a relatively uniform crystal morphology is obtained. The preparation method has a fast reaction speed, the obtained silver powder has a high purity, and the silver powder particles are spherical, the particle size distribution is narrow, and the maximum particle size can be controlled below 5.5μm, while ensuring good conductivity, making the printing performance better.

[0055] Another aspect of the present disclosure provides a high-purity micron-sized solid spherical silver powder, which is prepared by the preparation method described above.

[0056] The particle size distribution of the silver powder in this embodiment is D10 at 1.4-1.6 μm, D50 at 2.5-3.0 μm, D90 at 3.2-4.0 μm, D100 less than 5.5 μm, and the tap density at 6.0 g / cm 3 Above, specific surface area 0.15-0.25m 2 / g, the burning loss is 0.1-0.15%. The tap density is large, the burning loss is low, the crystal integrity is good, the particles are tightly bound, the solid content of the slurry is high under the same ratio, the viscosity is low, the conductive film formed after printing and sintering is dense and uniform, the holes in the film are small and few, the void ratio is low, and the conductive performance is excellent.

[0057] The silver powder provided in this embodiment has high purity (extremely low burn-in value) while ensuring the necessary fluidity of the powder. It is solid inside and can be used as a good conductive silver powder in combination with other silver powders with low-temperature densification characteristics in HJT silver paste.

[0058] In another aspect of the present disclosure, a low-temperature silver paste is provided, which includes the high-purity micron-sized solid spherical silver powder described above, an organic polymer, and a solvent.

[0059] It should be noted that when the silver powder of this embodiment is mixed with an organic polymer to form a low-temperature silver paste, the line width opening can be reduced to 12-14 μm, and can even be further reduced to 8-10 μm, meeting the demand for further narrowing the line width opening.

[0060] The preparation method of high-purity micron-sized solid spherical silver powder will be further described below in conjunction with specific examples:

[0061] Example 1

[0062] The method for preparing high-purity micron-level solid spherical silver powder in this example includes the following steps:

[0063] (1) Weigh 1600 g of analytical pure silver nitrate and put it into a silver salt solution preparation kettle, add 48 kg of room temperature deionized water, start stirring, and after dissolving and clarifying, add nitric acid or ammonia water to adjust the pH value of the solution to 5, start keeping warm at 35° C. to obtain an oxidizing solution.

[0064] (2) Weigh 1200 g of ascorbic acid and put it into a silver salt solution preparation kettle, add 50 kg of deionized water at room temperature, start stirring, add nitric acid or sodium hydroxide to adjust the pH value of the solution to 5 after dissolution and clarification, start keeping warm at 35° C., and obtain a first reduced solution.

[0065] (3) Weigh 0.08g of silver nitrate and dissolve it in 20mL of deionized water to prepare an acid silver solution; weigh 0.06g of ascorbic acid and dissolve it in 30mL of deionized water, weigh 3g of PVP as a dispersant and dissolve it in the ascorbic acid solution to form a second reduction solution; take an appropriate amount of 25% concentrated ammonia water and dissolve it in a certain amount of deionized water to prepare a 5% ammonia solution, and adjust the pH of the prepared second reduction solution to 4.5. Take 25mL of the second reduction solution in a 250mL three-necked flask and stir it magnetically, take 25mL of silver nitrate solution and quickly pour it into the three-necked flask to react for 1 hour, then add 50mL of deionized water as a buffer solution into the three-necked flask to obtain silver crystal nuclei with uniform particle size.

[0066] (4) Add 100L of deionized water, 60g of PVP (K value 90), and 20g of palmitic acid to a 500L reactor, start stirring, and after the dispersant is thoroughly dissolved, add 10mL of the prepared nucleus solution, add nitric acid or sodium hydroxide to adjust the pH value of the solution to 5, start keeping warm at 35°C, and set the stirring speed at 400r / min.

[0067] (5) After the temperature stabilizes, the oxidizing liquid and the first reducing liquid are added to the reactor at an even speed of 350 L / min through a high-flow high-speed peristaltic pump. The addition time for each batch is 1 min. After the addition, stirring is continued for 10 minutes; then centrifugation is performed to clean the effluent until the conductivity is below 10 μs / cm, and the effluent is transferred to a solid-liquid separator for filtration. After filtration until there is no moisture on the surface, 200 L of alcohol is added and soaked for 1 hour, then filtered and dried. After preliminary crushing with a swing crusher and passing through an 80-mesh sieve, the effluent is processed with a high-speed powder grinder, and after processing, the effluent is passed through a 200-mesh sieve to obtain a finished powder.

[0068] As shown in Table 1 and Figure 2 As shown in the figure, the silver powder obtained in Example 1 is a solid spherical structure with the following particle size distribution: D10 = 1.47 μm, D50 = 2.85 μm, D90 = 3.92 μm, D100 = 5.21 μm, and the specific surface area is 0.19 m 2 / g, tap density is 6.36g / cm 3 , the burn loss is 0.12%.

[0069] Example 2

[0070] The method for preparing high-purity micron-level solid spherical silver powder in this example includes the following steps:

[0071] (1) Weigh 1600 g of analytical pure silver nitrate and put it into a silver salt solution preparation kettle, add 55 kg of room temperature deionized water, start stirring, and after dissolving and clarifying, add nitric acid or ammonia water to adjust the solution pH to 4.5, start keeping warm at 39° C. to obtain an oxidizing solution.

[0072] (2) Weigh 1200 g of ascorbic acid and put it into a silver salt solution preparation kettle, add 58 kg of deionized water at room temperature, start stirring, add nitric acid or sodium hydroxide to adjust the pH value of the solution to 4.5 after dissolution and clarification, start keeping warm at 39° C., and obtain a first reduced solution.

[0073] (3) Weigh 0.1g of silver nitrate and dissolve it in 20mL of deionized water to prepare an acid silver solution; weigh 0.08g of ascorbic acid and dissolve it in 30mL of deionized water, weigh 4g of PVP as a dispersant and dissolve it in the ascorbic acid solution to form a second reduction solution; take an appropriate amount of 28% concentrated ammonia water and dissolve it in a certain amount of deionized water to prepare a 5% ammonia solution, and adjust the pH of the prepared second reduction solution to 4.5. Take 25mL of the second reduction solution in a 250mL three-necked flask and stir it magnetically, take 25mL of silver nitrate solution and quickly pour it into the three-necked flask to react for 1 hour, then add 50mL of deionized water as a buffer solution into the three-necked flask to obtain silver crystal nuclei with uniform particle size.

[0074] (4) Add 100L of deionized water, 50g of PVP (K value 90), and 15g of stearic acid to a 500L reactor, start stirring, and after the dispersant is thoroughly dissolved, add 8mL of the prepared nucleus solution, add nitric acid or sodium hydroxide to adjust the pH value of the solution to 4.5, start keeping warm to 39°C, and set the stirring speed to 350r / min.

[0075] (5) After the temperature stabilizes, the oxidizing liquid and the first reducing liquid are added to the reactor at an even speed of 350 L / min through a high-flow high-speed peristaltic pump. The addition time for each batch is 1 min. After the addition, stirring is continued for 10 minutes; then centrifugation is performed to clean the effluent until the conductivity is below 10 μs / cm, and the effluent is transferred to a solid-liquid separator for filtration. After filtration until there is no moisture on the surface, 200 L of alcohol is added and soaked for 1 hour, then filtered and dried. After preliminary crushing with a swing crusher and passing through an 80-mesh sieve, the effluent is processed with a high-speed powder grinder, and after processing, the effluent is passed through a 200-mesh sieve to obtain a finished powder.

[0076] As shown in Table 1 and Figure 3 As shown in the figure, the silver powder obtained in Example 2 is a solid spherical structure with the following particle size distribution: D10 = 1.55 μm, D50 = 3.02 μm, D90 = 4.23 μm, D100 = 5.40 μm, and the specific surface area is 0.17 m 2 / g, tap density is 6.48g / cm 3 , the burning loss is 0.11%.

[0077] Table 1 Results of silver powder obtained in Examples 1-2

[0078]

[0079] The present disclosure provides a high-purity micron-level solid spherical silver powder and a preparation method, and a low-temperature silver paste, which have the following beneficial effects compared to the prior art:

[0080] First, the preparation method disclosed in the present invention is carried out under normal pressure reaction conditions, the process is mild, safe, and has a fast reaction speed. The obtained silver powder has high purity and a narrow particle size distribution. The maximum particle (D100) can be controlled below 5.5 μm, and no complicated processes such as airflow, classification, and high-mesh screening are required.

[0081] Second, the silver powder disclosed in the present invention has good printing performance while ensuring good conductivity, and can meet the demand for further narrowing the line width opening of low-temperature silver paste.

[0082] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A method for preparing high-purity micron-sized solid spherical silver powder, characterized in that: The preparation method comprises: S110, dissolving silver nitrate in deionized water at room temperature, adding a pH adjusting solution to adjust the pH to 4-6, and stabilizing the temperature at 35-40° C. to obtain an oxidizing solution; S120, dissolving ascorbic acid in deionized water at room temperature, adding a pH adjusting solution to adjust the pH to 4-5, and stabilizing the temperature at 35-40° C. to obtain a first reducing solution; S130, dissolving silver nitrate in deionized water to form a silver nitrate solution; weighing ascorbic acid and dissolving it in deionized water to form an ascorbic acid solution, dissolving PVP in the ascorbic acid solution, and adjusting the pH of the solution to 4-5 with an ammonia solution to form a second reducing solution; adding the second reducing solution to a reaction container and stirring, and quickly introducing the silver nitrate solution into the reaction container for reaction, and adding an aqueous buffer solution to the reaction container to obtain silver crystal nuclei with uniform particle size; S140, adding deionized water, a dispersant and the silver crystal nuclei into a reaction kettle, adding a pH adjusting solution to adjust the pH to 4-6, controlling the temperature at 35-40°C, adding the first reducing solution and the oxidizing solution into the reaction kettle at an equal rate, and subjecting the mixture to stirring, centrifuging, soaking, filtering, drying, crushing and screening to obtain a high-purity micron-grade solid spherical silver powder.

2. The preparation method according to claim 1, characterized in that: In step S110, the mass ratio of the silver nitrate to deionized water at room temperature is 1:(20-40).

3. The preparation method according to claim 1, characterized in that: In step S120, the mass ratio of ascorbic acid to deionized water at room temperature is 1:(25-50).

4. The preparation method according to claim 1, characterized in that: In step S130, the concentration of the silver nitrate solution is 2.5-5 g / L; and / or, The concentration of the ascorbic acid solution is 1.67-3.33 g / L; and / or, The concentration of the ammonia solution is 4-6%.

5. The preparation method according to claim 1, characterized in that: In step S130, the mass ratio of the ascorbic acid to the PVP is (0.05-0.1):(2-5).

6. The preparation method according to claim 1, characterized in that: In step S130, the volume ratio of the second reducing solution, the silver nitrate solution and the aqueous buffer solution is 1:1:

2.

7. The preparation method according to claim 1, characterized in that: In step S140, the dispersant is a fatty acid; and / or, The amount of the dispersant added is 0.3-5% of the weight of the silver nitrate added in step S110.

8. The preparation method according to claim 1, characterized in that: In step S140, the oxidizing solution and the first reducing solution are added at a rate of 300-500 L / min, and the addition time of each batch is 1-2 min; and / or, The stirring speed of the reactor is 300-500r / min.

9. A high-purity micron-sized solid spherical silver powder, characterized in that: The high-purity micron-sized solid spherical silver powder is prepared by the preparation method described in any one of claims 1 to 8.

10. A low-temperature silver paste, characterized in that: The low-temperature silver paste comprises the high-purity micron-sized solid spherical silver powder as described in claim 9, an organic polymer, and a solvent.

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