Silver powder and its preparation method and application

Abstract

The present invention discloses a silver powder, its preparation method, and its application, belonging to the technical field of silver powder. The silver powder has a surface nanostructure, a grain size of ≤150nm, a shrinkage rate of ≥11%, and a sintering temperature corresponding to the maximum shrinkage rate of the silver powder of ≤550°C. The silver powder has a small grain size and high sintering activity, enabling it to maintain a high shrinkage rate while maintaining a low temperature corresponding to the maximum shrinkage rate, thereby achieving excellent sintering performance and meeting the efficiency requirements of surface metallization of crystalline silicon solar cells. The preparation method of the silver powder is simple, easy to operate, and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of silver powder, and in particular to silver powder and a preparation method and application thereof. Background Art

[0002] Solar cell backside silver paste is a major component of solar cell electronic paste. It is primarily used to create the backside busbar in solar cell production, serving to channel current collected by the aluminum backside field. Solar cell backside silver paste is primarily composed of silver powder, glass powder, and an organic carrier.

[0003] At present, conventional silver powder is mainly micron-sized, with large size, poor morphology regularity, and low sintering activity, resulting in low conductivity of the material and poor printing performance.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a silver powder and a preparation method and application thereof, so as to solve or improve the above-mentioned technical problems.

[0006] The present invention can be implemented like this:

[0007] In a first aspect, the present invention provides a silver powder having a nanostructure on its surface;

[0008] The grain size of the silver powder is ≤150nm, the shrinkage rate of the silver powder is ≥11%, and the sintering temperature corresponding to the maximum shrinkage rate of the silver powder is ≤550°C.

[0009] In an optional embodiment, the silver powder further comprises at least one of the following features:

[0010] Feature 1: The nanostructure includes at least one of a block structure, a sheet structure, a prism structure, a strip structure, a rod structure, a spherical structure, a pore structure, and a hole structure at the nanoscale;

[0011] Feature 2: The specific surface area of ​​silver powder is 0.4m 2 / g~1.1m 2 / g;

[0012] Feature 3: The burnout of silver powder is 0.4% to 1.5%;

[0013] Feature 4: Silver powder D 10 0.7μm~1.7μm;

[0014] Feature 5: Silver powder D 50 1.1μm~3.2μm;

[0015] Feature 6: Silver powder D 90It is 1.7μm~5.8μm.

[0016] In a second aspect, the present invention provides a method for preparing silver powder as described in the aforementioned embodiment, comprising the following steps: mixing a nanosilver seed solution with a dispersant to obtain a first mixed solution; mixing the first mixed solution with a reducing solution and a surface conditioner solution to obtain a second mixed solution; and mixing the second mixed solution with a precursor solution containing silver ions for reaction.

[0017] In an optional embodiment, the particle size of the nanosilver seeds in the nanosilver seed solution is 10 nm to 80 nm;

[0018] and / or, the mass fraction of the nanosilver seeds in the nanosilver seed solution is 0.1% to 5%;

[0019] and / or, the shape of the nanosilver seed crystals is spherical;

[0020] And / or, the silver ion concentration in the silver ion-containing precursor solution is 0.5 mol / L to 2.5 mol / L.

[0021] In an alternative embodiment, the dispersant comprises at least one of gum arabic, gelatin, polyethylene glycol, polyoxyethylene ether, polyvinyl alcohol, polyvinyl pyrrolidone and Tween;

[0022] And / or, the amount of the dispersant used is 0.5% to 20% of the mass of the silver ions in the precursor solution containing silver ions, preferably 5% to 10%.

[0023] In an optional embodiment, the concentration of the reducing agent contained in the reducing solution is 0.2 mol / L to 2.0 mol / L;

[0024] and / or, the reducing agent contained in the reducing solution includes at least one of ascorbic acid, glucose, erythorbic acid, sodium erythorbate, sodium ascorbate and sodium gluconate;

[0025] And / or, based on the theoretical molar ratio of transferred electrons in the reaction between the reducing agent and the silver ions, the molar ratio of the reducing agent contained in the reducing solution to the silver ions in the silver ion-containing precursor solution is 1.02:1 to 2.0:1.

[0026] In an alternative embodiment, the surface conditioner solution is an organic conditioner containing carboxylic acid functional groups;

[0027] and / or, the mass fraction of the surface conditioner in the surface conditioner solution is 0.5% to 10%;

[0028] And / or, the mass of the surface conditioner in the surface conditioner solution is 0.1% to 5% of the mass of the silver ions in the precursor solution containing silver ions.

[0029] In an optional embodiment, when the temperature of the mixing reaction is 15°C to 40°C, the surface regulator is a carboxylic acid substance with a carbon number of ≤8; when the temperature of the mixing reaction exceeds 40°C and does not exceed 60°C, the surface regulator is a fatty acid substance with a carbon number of ≥12.

[0030] In an optional embodiment, when the temperature of the mixing reaction is 15°C to 40°C, the surface regulator includes at least one of malonic acid, acrylic acid, tartronic acid, fumaric acid, succinic acid, malic acid, maleic acid, citric acid, tartaric acid, sorbic acid and mandelic acid; when the temperature of the mixing reaction exceeds 40°C and does not exceed 60°C, the surface regulator includes at least one of lauric acid, myristic acid, palmitic acid, oleic acid, 731A and polyacrylic acid.

[0031] In an optional embodiment, the temperature of the mixing reaction is 15° C. to 60° C.; and the time of the mixing reaction is 5 min to 20 min.

[0032] In an optional embodiment, a precursor solution containing silver ions is added to the second mixed solution to perform a mixing reaction.

[0033] In an optional embodiment, the precursor solution containing silver ions is added to the second mixed solution within 15 seconds.

[0034] In an optional embodiment, the method further comprises: coating the solid matter obtained from the mixed reaction.

[0035] In an optional embodiment, the coating process includes mixing the solid object with a coating liquid.

[0036] In an optional embodiment, the mass fraction of the coating agent contained in the coating liquid is 10% to 40%.

[0037] In an optional embodiment, the solution contained in the coating liquid is water and / or alcohol.

[0038] In an optional embodiment, the amount of the coating agent is 0.1% to 5% of the mass of the silver ions in the precursor solution containing silver ions.

[0039] In a third aspect, the present invention provides use of the silver powder according to the aforementioned embodiment in preparing a solar cell.

[0040] The beneficial effects of the present invention include:

[0041] The present invention provides silver powder with a nanostructured surface. This silver powder exhibits excellent sintering properties at a low grain size, such as high sintering activity, enabling sintering at relatively low temperatures. This allows for a high shrinkage rate while maintaining a low temperature corresponding to the maximum shrinkage rate. This silver powder also exhibits excellent conductivity and printability, meeting the efficiency requirements for surface metallization of crystalline silicon solar cells.

[0042] The present invention provides a method for preparing silver powder, wherein a first mixed solution serves as a reaction base solution, and seed crystals can serve as sites for heterogeneous nucleation during the silver preparation process, thereby obtaining silver particles with a narrow size distribution and uniform dispersion. A reducing agent in the reducing solution is used to reduce silver ions in silver nitrate to elemental silver; a surface conditioner solution, combined with the reaction temperature and material addition time, can adjust and control the surface nanostructure of the silver particles; and a precursor solution containing silver ions is used to react with the reducing agent. This method can effectively produce silver powder with a surface nanostructure, a grain size ≤150nm, a shrinkage rate ≥11%, and a sintering temperature corresponding to the maximum shrinkage rate ≤550°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is a SEM image of the silver powder product prepared in Example 1;

[0045] Figure 2 This is a SEM image of the silver powder product prepared in Example 2;

[0046] Figure 3 This is a SEM image of the silver powder product prepared in Example 3;

[0047] Figure 4 This is a SEM image of the silver powder product prepared in Example 4;

[0048] Figure 5 This is a SEM image of the silver powder product prepared in Example 5;

[0049] Figure 6 This is a SEM image of the silver powder product prepared in Example 6;

[0050] Figure 7 This is a SEM image of the silver powder product prepared in Example 7;

[0051] Figure 8 This is a SEM image of the silver powder product prepared in Example 8;

[0052] Figure 9 This is a SEM image of the silver powder product prepared in Example 9;

[0053] Figure 10This is a SEM image of the silver powder product prepared in Example 10;

[0054] Figure 11 This is a SEM image of the silver powder product prepared in Example 11;

[0055] Figure 12 This is the SEM image of the silver powder product prepared in Comparative Example 1;

[0056] Figure 13 This is the SEM image of the silver powder product prepared in Comparative Example 2;

[0057] Figure 14 This is the SEM image of the silver powder product prepared in Comparative Example 3;

[0058] Figure 15 This is the SEM image of the silver powder product prepared in Comparative Example 4;

[0059] Figure 16 This is the SEM image of the silver powder product prepared in Comparative Example 5;

[0060] Figure 17 This is the SEM image of the silver powder product prepared in Comparative Example 6;

[0061] Figure 18 is the inverse pole figure of the silver powder product corresponding to Example 1 in the test example;

[0062] Figure 19 This is the inverse pole figure of the silver powder product corresponding to Comparative Example 3 in the test example;

[0063] Figure 20 This is a TMA test shrinkage curve of the silver powder products corresponding to Example 1, Example 2, Comparative Example 1 and Comparative Example 2 in the test examples;

[0064] Figure 21 This is a TMA test shrinkage rate curve of the silver powder products corresponding to Example 1 and Comparative Example 1 in the test example. DETAILED DESCRIPTION

[0065] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0066] The silver powder provided by the present invention and its preparation method and application are described in detail below.

[0067] The present invention provides a silver powder, the surface of which has a nanostructure;

[0068] The grain size of the silver powder is ≤150nm, the shrinkage rate of the silver powder is ≥11%, and the sintering temperature corresponding to the maximum shrinkage rate of the silver powder is ≤550°C.

[0069] The aforementioned "nano-microstructure" refers to a nanoscale microstructure, whereby "microstructure" may, by way of example but not limitation, include at least one of a block structure, a flaky structure, a prismatic structure, a strip structure, a rod structure, a spherical structure, a porous structure, and a hole structure. Specifically, the silver powder may have only one of these specific structures, or may simultaneously contain two or more of these specific structures. Furthermore, when the surface of the silver powder contains two or more microstructures, each microstructure may exist independently or form a composite structure formed by rotation, entanglement, or combination.

[0070] The nanostructure on the surface of the silver powder can improve the sintering performance of the silver particles, achieve sintering at a lower temperature, and meet the efficiency requirements of the surface metallization of crystalline silicon solar cells.

[0071] In the present invention, the grain size of the silver powder is obtained by testing using an EBSD device, and the grain size does not exceed 150 nm. For example, the grain size may be 130 nm to 150 nm, such as 132.2 nm, 135.2 nm, 135.8 nm, 139.1 nm, 141.9 nm, 144.9 nm, 145.3 nm, 147.5 nm, 147.7 nm, 148.1 nm or 148.8 nm, or other values ​​within the range of 130 nm to 150 nm.

[0072] In some optional embodiments, the specific surface area of ​​the silver powder is 0.4 m 2 / g~1.1m 2 / g, such as 0.411m 2 / g, 0.414m 2 / g, 0.438m 2 / g, 0.537m 2 / g, 0.691m 2 / g, 0.814m 2 / g, 0.822m 2 / g, 0.841m 2 / g, 0.894m 2 / g, 0.924m 2 / g or 1.037m 2 / g, etc., can also be 0.4m 2 / g~1.1m 2 Other values ​​within the range of / g.

[0073] In the present invention, the yield rate of silver powder is not less than 11%, for example, it can be 12% to 18.5%, such as 12.11%, 14.21%, 14.48%, 14.97%, 15.42%, 15.82%, 16.13%, 16.40%, 16.79%, 17.13% or 18.33%, etc., and can also be other values ​​within the range of 12% to 18.5%.

[0074] Moreover, the sintering temperature corresponding to the maximum shrinkage rate of the silver powder is ≤550°C, for example, it can be 495°C to 550°C, such as 498°C, 506°C, 511°C, 512°C, 533°C, 536°C, 539°C, 544°C, 545°C or 549°C, etc., or it can be other values ​​within the range of 495°C to 550°C.

[0075] That is, the silver powder provided by the present invention has a high sintering activity, and can have a high shrinkage rate while making the temperature corresponding to the maximum shrinkage rate low.

[0076] In some optional embodiments, the silver powder has a loss on burn of 0.4% to 1.5%. In some typical embodiments, the silver powder has a loss on burn of 0.5% to 1.3%, such as 0.52%, 0.68%, 0.71%, 0.84%, 0.88%, 0.91%, 0.92%, 0.93%, 1.17%, or 1.24%, or other values ​​within the range of 0.5% to 1.3%.

[0077] In some optional embodiments, the D of the silver powder 10 It can be 0.7 μm to 1.7 μm. In some typical embodiments, the D 10 It can be 0.7437 μm to 1.691 μm.

[0078] In some optional embodiments, the D of the silver powder 50 In some typical embodiments, the D 50 1.1052μm~3.148μm;

[0079] In some optional embodiments, the D of the silver powder 90 In some typical embodiments, the D 90 It is 1.7445μm~5.610μm.

[0080] The silver powder having the above-mentioned particle size has regular morphology and uniform size, which is beneficial to improving the sintering performance of the silver powder.

[0081] As mentioned above, silver powder has a small grain size and a spherical or quasi-spherical structure. The particle size and particle size distribution are within a suitable range. The resulting silver powder product has a moderate specific surface area, excellent printability, and high sintering activity in applications. Furthermore, the nanostructure on the silver powder surface can further enhance the sintering activity of the silver particles.

[0082] Correspondingly, the present invention also provides a method for preparing the above-mentioned silver powder, comprising the following steps: mixing a nanosilver seed solution with a dispersant to obtain a first mixed solution; mixing the first mixed solution with a reducing solution and a surface conditioner solution to obtain a second mixed solution; and mixing the second mixed solution with a precursor solution containing silver ions for reaction.

[0083] The first mixed solution serves as the reaction base solution, and the seed crystals act as sites for heterogeneous nucleation during the silver production process, resulting in uniformly dispersed silver particles with a narrow size distribution. The reducing agent in the reducing solution is a substance that reduces the silver ions in silver nitrate to elemental silver. The surface conditioner solution is obtained by dissolving the surface conditioner in water. The combination of reaction temperature and material addition time can adjust and control the surface nanostructure of the silver particles. The precursor solution containing silver ions is used to react with the reducing agent.

[0084] In some optional embodiments, the nanosilver seeds are spherical in shape. The particle size of the nanosilver seeds in the nanosilver seed solution is 10 nm to 80 nm, such as 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm or 80 nm, or other values ​​within the range of 10 nm to 80 nm.

[0085] The mass fraction of the nanosilver seeds in the nanosilver seed solution can be 0.1% to 5%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., or other values ​​within the range of 0.1% to 5%.

[0086] In some optional embodiments, the dispersant may illustratively but not limitatively include at least one of gum arabic, gelatin, polyethylene glycol, polyoxyethylene ether, polyvinyl alcohol, polyvinyl pyrrolidone and Tween.

[0087] The amount of the dispersant can be 0.5% to 20% of the mass of the silver ions in the precursor solution containing silver ions, such as 0.5%, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18% or 20%, etc., or other values ​​within the range of 0.5% to 20%. In some preferred embodiments, the amount of the dispersant can be 5% to 10% of the mass of the silver ions in the precursor solution containing silver ions, such as 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0088] The silver ion-containing precursor solution can be obtained by dissolving a silver source in water. The silver source can include, by way of example but not limitation, silver nitrate. The silver ion concentration in the silver ion-containing precursor solution can be 0.5 mol / L to 2.5 mol / L, such as 0.5 mL / min, 1.0 mL / min, 1.5 mL / min, 2.0 mL / min, or 2.5 mL / min, or other values ​​within the range of 0.5 mol / L to 2.5 mol / L.

[0089] In some optional embodiments, the concentration of the reducing agent contained in the reducing solution can be 0.2mol / L to 2.0mol / L, such as 0.2mol / L, 0.5mol / L, 0.8mol / L, 1mol / L, 1.2mol / L, 1.5mol / L, 1.8mol / L or 2mol / L, etc., or it can be other values ​​within the range of 0.2mol / L to 2.0mol / L.

[0090] The reducing agent contained in the reducing solution may illustratively but not limitatively include at least one of ascorbic acid, glucose, erythorbic acid, sodium erythorbic acid, sodium ascorbate, and sodium gluconate.

[0091] Based on the theoretical molar ratio of transferred electrons in the reaction between the reducing agent and the silver ions, the molar ratio of the reducing agent contained in the reducing solution to the silver ions in the silver ion-containing precursor solution can be 1.02:1 to 2.0:1, such as 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.0:1, 1.2:1, 1.5:1, 1.8:1 or 2.0:1, etc., or other values ​​within the range of 1.02:1 to 2.0:1.

[0092] In some alternative embodiments, the surface conditioner solution is an organic conditioner containing carboxylic acid functional groups.

[0093] The mass fraction of the surface conditioner in the surface conditioner solution can be 0.5% to 10%, such as 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., or other values ​​within the range of 0.5% to 10%.

[0094] The mass of the surface conditioner in the surface conditioner solution can be 0.1% to 5% of the mass of the silver ions in the silver ion-containing precursor solution, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., or it can be other values ​​within the range of 0.1% to 5%.

[0095] In some optional embodiments, the first mixed solution, the reducing solution, and the surface conditioner solution can be mixed under stirring conditions (e.g., at a stirring speed of 200 r / min) for 1 to 10 minutes (e.g., 1 minute, 2 minutes, 5 minutes, 8 minutes, or 10 minutes) to obtain a second mixed solution. Subsequently, the silver ion-containing precursor solution is quickly added to the second mixed solution to react.

[0096] In some optional embodiments, the temperature of the mixing reaction can be 15°C to 60°C, such as 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc., or other values ​​within the range of 15°C to 60°C.

[0097] The mixing reaction time can be 5 min to 20 min, such as 5 min, 10 min, 15 min or 20 min, etc., or other values ​​within the range of 5 min to 20 min.

[0098] When the temperature of the mixing reaction is 15°C to 40°C, the surface regulator is a carboxylic acid substance with a carbon number of ≤8, and illustratively may include at least one of malonic acid, acrylic acid, tartronic acid, fumaric acid, succinic acid, malic acid, maleic acid, citric acid, tartaric acid, sorbic acid and mandelic acid.

[0099] When the temperature of the mixing reaction exceeds 40°C and does not exceed 60°C, the surface regulator is a fatty acid substance with a carbon number ≥12, which can illustratively include at least one of lauric acid, myristic acid, palmitic acid, oleic acid, 731A (polycarboxylic acid) and polyacrylic acid.

[0100] It should be noted that different reaction temperature conditions require surfactants containing carboxylic acids with different carbon atoms to achieve adjustments in the surface structure of the silver particles. The C=O bonds in the carboxylic acids adsorb silver ions or atoms. In the late stage of the reaction, when the secondary silver particles are stable, the adsorption of the C=O bonds on the (111) surface of the silver atoms, combined with the Oswald ripening effect, results in the formation of nanosheets, plates, and small particles on the surface of the silver particles. The diffusion rate of silver atoms that explode and nucleate in the low-temperature section is slow, and the driving force for their aggregation and growth into secondary particles is weak. Therefore, short-chain carboxylic acids are needed to avoid affecting the growth of aggregation, in order to achieve silver particles with a spherical structure. Therefore, when the reaction temperature is 15°C to 40°C, the present invention uses carboxylic acids with a carbon number of 8 or less as surface regulators; at high temperatures, the diffusion rate of silver atoms is fast, and diffusion growth and aggregation growth exist at the same time with a strong driving force. Therefore, long-chain carboxylic acids are needed to prevent the excessive diffusion growth of silver atoms during the process of adjusting the surface structure, thereby avoiding serious agglomeration and enlargement of grain size. Therefore, when the reaction temperature exceeds 40°C and does not exceed 60°C, the present invention uses fatty acids with a carbon number of 12 or more as surface regulators.

[0101] In some optional embodiments, the precursor solution containing silver ions is added to the second mixed solution to perform a mixing reaction. Preferably, the precursor solution containing silver ions is added to the second mixed solution within 15 seconds.

[0102] The precursor solution containing silver ions can be quickly added to the second mixed solution within 15 seconds (such as 1 second to 15 seconds) by means of gravity, injection pressure, etc., thereby realizing the synthesis of nanostructures on the surface of silver particles.

[0103] As mentioned above, the present invention achieves the acquisition and control of the surface nanostructure of silver particles through temperature, rapid mixing time and surface conditioning agent. Among them, nano silver seeds with a particle size of 10nm to 80nm can be used as sites for heterogeneous nucleation in the process of preparing silver, and silver particles with narrow size distribution and uniform dispersion are obtained. The use of seeds can inhibit the diffusion growth of silver particles in the process of preparing silver particles under high supersaturation (silver ion precursor solution addition time <15s), thereby making the grain size less than 150nm, thereby improving the sintering activity of silver particles. Among them, the rapid addition of silver ions reacts instantly with the reducing agent, and the explosive nucleation on the surface of the seed leads to a high supersaturation of silver atoms. The short-term diffusion growth forms small-sized primary particles, which further aggregate and grow into secondary silver particles with a spherical structure under high supersaturation conditions. The spherical structure ensures that the silver particles have a suitable specific surface area, realizing basic applications in solar slurries.

[0104] Furthermore, the solid obtained from the mixed reaction can be coated. The coating process can be carried out during the final washing stage of the silver powder or the drying, pulverizing or air grinding stage.

[0105] In some optional embodiments, the coating process includes mixing the solid object with a coating liquid.

[0106] The mass fraction of the coating agent contained in the coating solution may be 10% to 40%, such as 10%, 15%, 20%, 25%, 30%, 35% or 40%, or other values ​​within the range of 10% to 40%.

[0107] The solution contained in the coating liquid may be water and / or alcohol.

[0108] In some optional embodiments, the amount of the coating agent can be 0.1% to 5% of the mass of the silver ions in the silver ion-containing precursor solution, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., or it can be other values ​​within the range of 0.1% to 5%.

[0109] Furthermore, after the coating process, the coated material may be dried and crushed.

[0110] In addition, the present invention also provides the use of the silver powder in preparing solar cells.

[0111] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0112] Example 1

[0113] This embodiment provides a silver powder product, the preparation method of which includes:

[0114] S1: 30 g of silver nitrate and 118 g of deionized water were prepared into a precursor solution containing silver ions.

[0115] 19 g of ascorbic acid and 135 g of deionized water were prepared into a reducing solution, wherein the concentration of the reducing agent in the reducing solution was about 0.8 mol / L.

[0116] Spherical nano silver seeds and deionized water are mixed to form a nano silver seed solution, wherein the mass fraction of the nano silver seeds is 1.5% and the particle size of the nano silver seeds is 10nm-50nm.

[0117] S2: 380 μL of the nanosilver seed solution, 1.5 g of a dispersant (PVP) and 244 g of deionized water were mixed to obtain a first mixed solution.

[0118] The amount of the dispersant used is 7.87% of the mass of the silver ions in the precursor solution containing silver ions.

[0119] S3: Add the reducing solution and the surface conditioner solution (1.0 g of a tartronic acid aqueous solution and 3.5 g of a citric acid aqueous solution) to the first mixed solution, and stir and mix at a speed of 200 r / min for 5 minutes to obtain a second mixed solution.

[0120] Wherein, based on the theoretical molar ratio of transferred electrons in the reaction between the reducing agent and the silver ions, the molar ratio of the reducing agent contained in the reducing solution to the silver ions in the precursor solution containing silver ions is 1.2:1.

[0121] The mass fraction of tartronic acid in the tartronic acid aqueous solution is 10%, the mass fraction of citric acid in the citric acid aqueous solution is 10%, and the mass of the surface conditioner in the surface conditioner solution is 2.36% of the mass of silver ions in the silver ion-containing precursor solution.

[0122] S4: Maintaining the temperature of the reaction solution at 25° C., the precursor solution containing silver ions was rapidly added to the second mixed solution within 10 seconds, and the mixture was reacted for 10 minutes to obtain silver powder.

[0123] S5: After the silver powder is washed and subjected to solid-liquid separation, 2.5 g of coating liquid (butyl carbitol solution) is used for coating treatment, followed by drying and crushing to obtain a silver powder product.

[0124] The mass fraction of the coating agent in the coating solution is 10%, and the amount of the coating agent used is 1.3% of the mass of the silver ions in the precursor solution containing silver ions.

[0125] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 1 As shown, the surface of the silver powder particles has obvious nanostructure and has higher sintering performance.

[0126] Example 2

[0127] This embodiment provides a silver powder product, the preparation method of which includes:

[0128] S1: 50 g of silver nitrate and 197 g of deionized water were prepared into a precursor solution containing silver ions.

[0129] 31.5 g of ascorbic acid and 225 g of deionized water were prepared into a reducing solution, wherein the concentration of the reducing agent in the reducing solution was about 0.8 mol / L.

[0130] Spherical nano silver seeds and deionized water are mixed to form a nano silver seed solution, wherein the mass fraction of the nano silver seeds is 0.5% and the particle size of the nano silver seeds is 15nm-60nm.

[0131] S2: 750 μL of the nanosilver seed solution, 4.8 g of a dispersant (Tween) and 407 g of deionized water were mixed to obtain a first mixed solution.

[0132] The amount of the dispersant used is 15% of the mass of the silver ions in the precursor solution containing silver ions.

[0133] S3: Add the reducing solution and the surface conditioner solution (3.0 g of oleic acid aqueous solution and 0.5 g of polyacrylic acid aqueous solution) to the first mixed solution, and stir and mix at a speed of 200 r / min for 2 minutes to obtain a second mixed solution.

[0134] Wherein, based on the theoretical molar ratio of transferred electrons in the reaction between the reducing agent and the silver ions, the molar ratio of the reducing agent contained in the reducing solution to the silver ions in the precursor solution containing silver ions is 1.2:1.

[0135] The mass fraction of oleic acid in the oleic acid aqueous solution is 10%, the mass fraction of polyacrylic acid in the polyacrylic acid aqueous solution is 10%, and the mass of the surface conditioner in the surface conditioner solution is 1.1% of the mass of silver ions in the silver ion-containing precursor solution.

[0136] S4: Maintaining the temperature of the reaction solution at 45° C., the precursor solution containing silver ions was rapidly added to the second mixed solution within 15 seconds, and the mixture was reacted for 10 minutes to obtain silver powder.

[0137] S5: After the silver powder is washed and subjected to solid-liquid separation, 2.5 g of coating liquid (butyl carbitol solution) is used for coating treatment, followed by drying and crushing to obtain a silver powder product.

[0138] The mass fraction of the coating agent in the coating solution is 10%, and the amount of the coating agent used is 0.79% of the mass of the silver ions in the precursor solution containing silver ions.

[0139] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 2 As shown, the surface of the silver powder particles is closed and has block-shaped protruding nanostructures.

[0140] Example 3

[0141] The difference between this example and Example 1 is that the reducing agent in the reducing solution is replaced with 21.4 g of sodium isoascorbate to maintain the same electron transfer molar ratio.

[0142] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 3 As shown, there are ridge-like nanoplatelet structures on the surface of the silver powder particles.

[0143] Example 4

[0144] The difference between this embodiment and embodiment 1 is that the volume of the nanosilver seed solution is reduced to 250 μL.

[0145] The nucleation sites in this embodiment are reduced compared with those in Example 1, and the microstructure of the silver powder product obtained is as follows: Figure 4 As shown, the surface of the silver powder particles has a flaky and dense nanostructure.

[0146] Example 5

[0147] The difference between this embodiment and embodiment 1 is that the reaction temperature is 15°C.

[0148] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 5 As shown, there is a nanoporous structure on the surface of the silver powder particles.

[0149] Example 6

[0150] The difference between this embodiment and embodiment 1 is that the time for adding the precursor solution containing silver ions into the second mixed solution is 5 seconds.

[0151] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 6 As shown, there is a nanoparticle structure on the surface of the silver powder particles.

[0152] Example 7

[0153] The difference between this embodiment and embodiment 1 is that the surface conditioner solution is replaced by 2.23 g of a 10% by mass aqueous solution of sorbic acid and 0.56 g of a 10% by mass aqueous solution of maleic acid.

[0154] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 7 As shown, there is a nano-block structure on the surface of the silver powder particles.

[0155] Example 8

[0156] The difference between this embodiment and embodiment 1 is that 2.5 g of Tween and 1.3 g of polyvinyl alcohol are used as dispersants.

[0157] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 8 As shown, there are nano-block structures on the surface of silver powder particles.

[0158] Example 9

[0159] The difference between this embodiment and embodiment 2 is that the surface conditioner solution is replaced by 3.5 g of a 10% mass concentration lauric acid aqueous solution and 0.65 g of a 10% mass concentration 731A aqueous solution.

[0160] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 9 As shown, there is a nanosheet stacking structure on the surface of the silver powder particles.

[0161] Example 10

[0162] The difference between this embodiment and embodiment 2 is that the dispersant is replaced with 1.2 g of gum arabic and 2.5 g of PVP.

[0163] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 10 As shown, there are large nanosheet structures on the surface of silver powder particles.

[0164] Example 11

[0165] The difference between this embodiment and embodiment 2 is that the reaction temperature is 60°C.

[0166] The silver particles prepared in this embodiment are relatively large in size and have slightly poor sintering activity.

[0167] The microstructure of the silver powder product prepared in this embodiment is as follows Figure 11 As shown, there is a nanostructure on the surface of the silver powder particles, but there is an agglomeration effect.

[0168] Comparative Example 1

[0169] The difference between this comparative example and Example 1 is that the time for adding the silver ion-containing precursor solution to the second mixed solution is 30 seconds.

[0170] The microstructure of the silver powder product prepared in this comparative example is as follows Figure 12 As shown in the figure, as the time of adding silver ions increases, the concentration of silver atoms generated per unit time in the reaction decreases, that is, the supersaturation decreases, the aggregation characteristics of the generated silver powder particles are weakened, and the silver particles are plate-like, flaky, and mixed block structures. However, the morphology of the silver powder particles obtained in this comparative example is not spherical or quasi-spherical, the specific surface area and particle size of each silver powder particle vary greatly, the tap density is low, the printing performance is poor, and it is difficult to be used in solar slurry applications.

[0171] Comparative Example 2

[0172] The difference between this comparative example and Example 1 is that the surface regulator used is 3.8 g of myristic acid having ≥12 carbon atoms.

[0173] The microstructure of the silver powder product prepared in this comparative example is as follows Figure 13 As shown, there is a nano-flake microstructure on the surface of the silver powder particles, but the monodispersity of the silver particles is poor, and there are obvious large and small particles.

[0174] Comparative Example 3

[0175] The difference between this comparative example and Example 2 is that the surface conditioners used are 1.2 g of succinic acid having a carbon number ≤ 8 and 2.67 g of malic acid.

[0176] During the preparation process of this comparative example, the high temperature reaction causes the silver atoms to diffuse rapidly, and the carboxylic acid with a low carbon number has a low effect on preventing the agglomeration of silver atoms. At a high degree of supersaturation, it is easy to cause the agglomeration of silver particles, thereby reducing the sintering performance of the silver powder.

[0177] The microstructure of the silver powder product prepared in this comparative example is as follows Figure 14 As shown, the silver powder particles have a smooth surface and less microstructure.

[0178] Comparative Example 4

[0179] The difference between this comparative example and Example 2 is that no seed crystal is used.

[0180] The microstructure of the silver powder product prepared in this comparative example is as follows Figure 15 As shown in the figure, since no seed crystals were used, the particle size of the prepared silver powder was significantly increased.

[0181] Comparative Example 5

[0182] The difference between this comparative example and Example 2 is that the time for adding the precursor solution containing silver ions into the second mixed solution is 30 seconds.

[0183] The microstructure of the silver powder product prepared in this comparative example is as follows Figure 16 As shown, the silver powder particles have a disordered structure, which may be due to the low supersaturation leading to the diffusion growth effect of silver atoms, resulting in a significant growth of the surface structure. The silver powder particles prepared in this comparative example have poor sintering activity and poor printability, making them difficult to use in solar pastes.

[0184] Comparative Example 6

[0185] The difference between this comparative example and Example 1 is that no surface conditioner was used.

[0186] The microstructure of the silver powder product prepared in this comparative example is as follows Figure 17 As shown, the surface of the silver powder particles is smooth, there is no surface nanostructure, the particles are relatively agglomerated, and have a polyhedral structure. The sintering performance of the silver powder particles is poor.

[0187] Test example

[0188] The silver powder products prepared in Examples 1 to 11 and Comparative Examples 1 to 6 were compared, and the results are shown in Table 1.

[0189] Among them, particle size distribution: tested by laser particle size analyzer;

[0190] Silver particle grain size test: Use focused ion beam to cut silver particles to obtain cross-sectional structure, use electron backscatter diffraction to measure EBSD characterization information of silver particle cross-section and calculate grain size;

[0191] Shrinkage rate: The test was performed using a thermomechanical analyzer (TMA). Specifically, 0.5 g of silver powder was pressed into a cylinder with a diameter of 6 mm under a pressure of 125 kgf using a tablet press. The shrinkage rate and shrinkage rate of the cylindrical sintered body with increasing temperature were tested to characterize the sintering performance of the silver powder itself.

[0192] Specific surface area: Anton Paar's specific surface area meter was used for the test. Specifically, nitrogen adsorption and desorption tests were performed after degassing at 150°C for 30 minutes.

[0193] Burnout: 3.0 g of silver powder was heated to 538°C in a muffle furnace for 1 hour, and the mass loss ratio was measured to obtain the burnout data.

[0194] Taking Example 1 and Comparative Example 3 as examples, the grain size is compared, and the inverse pole figures obtained by EBSD test are compared. Figure 18 and Figure 19 shown. Figure 18 The inverse pole figure of the silver particles obtained in Example 1 was tested and statistically analyzed, and its grain size was 135.8 nm. Figure 19 This is the reverse pole figure of the silver particles obtained in Comparative Example 3. The grain size is 271.5 nm. It can be seen that the grain size of Comparative Example 3 is obviously too large.

[0195] Taking Example 1, Example 2, Comparative Example 1 and Comparative Example 4 as examples, the corresponding TMA test shrinkage curves are as follows: Figure 20 As shown in the figure, the results show that the silver powder prepared in this scheme has a small shrinkage rate and poor sintering activity. The shrinkage rate curves of Example 1 and Comparative Example 1 are shown in the figure. Figure 21 As shown, it can be seen that the silver powder obtained in Example 1 reaches a maximum shrinkage rate at about 497°C as the temperature increases, while the temperature corresponding to the maximum shrinkage rate of the silver powder obtained in Comparative Example 1 is 583°C, which proves that the silver powder obtained in Example 1 of the present invention has higher sintering activity than that in Comparative Example 1 and shrinks faster during the temperature increase process.

[0196] Table 1 Test results

[0197]

[0198]

[0199] As shown in Table 1, the silver powder provided by the present embodiment has a small grain size, a moderate specific surface area, and high sintering activity, achieving a high shrinkage ratio while maintaining a low temperature corresponding to the maximum shrinkage rate. Furthermore, the silver powder provided by this embodiment has good printability and a low burnout value, exhibiting better overall performance than the silver powder prepared in the comparative example, making it more suitable for use in slurries.

[0200] In addition, conductivity comparison was performed using Example 1 and Comparative Example 1 as examples: 4.45 g of silver particles obtained in Example 1 and Comparative Example 1 were used as conductive phases, respectively. 0.15 g of tributyl citrate and 0.175 g of diethylene glycol butyl ether acetate were mixed as a bonding phase. 0.15 g of DBE solvent and 0.075 g of dimethyl silicone oil were mixed evenly with the silver particles and the bonding phase, and ground 5 times using a three-roll grinder to obtain a precision silver paste. After the silver paste was printed and cured, its resistivity was tested using a resistivity tester, and the results were 2.28 × 10 -8 Ω·m and 1.38×10 -7 Ω·m, it can be seen that the resistivity of the silver powder prepared in Example 1 of the present invention is significantly lower than that of the comparative example 1.

[0201] In summary, the present invention realizes the nanostructure of the surface of silver particles by using surface regulator carboxylic acid substances with different carbon atoms and different temperatures; by controlling the addition time of the silver ion-containing precursor solution to no more than 15s, a high degree of supersaturation can be achieved, and silver particles with a spherical structure are obtained to achieve control of the specific surface area; by using seed crystals to control the final size of the silver particles, silver particles with good dispersibility, moderate size, and surface microstructure can be obtained. The silver powder provided by the present invention has a smaller grain size and higher sintering activity. It can have a higher shrinkage rate while making the temperature corresponding to the maximum shrinkage rate lower, thereby obtaining better sintering performance and meeting the efficiency requirements of the surface metallization of crystalline silicon solar cells. The preparation method of the silver powder is simple, easy to operate, and can be industrialized.

[0202] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing silver powder, characterized in that: The following steps are involved: mixing the nano silver seed solution with a dispersant to obtain a first mixed solution; The first mixed solution is mixed with a reducing solution and a surface conditioner solution to obtain a second mixed solution; the precursor solution containing silver ions is added to the second mixed solution within 15 seconds to carry out a mixing reaction; the mixing reaction temperature is 15° C. to 60° C.; and the mixing reaction time is 5 minutes to 20 minutes; The particle size of the nanosilver seeds in the nanosilver seed solution is 10 nm to 80 nm; the mass fraction of the nanosilver seeds in the nanosilver seed solution is 0.1% to 5%; the shape of the nanosilver seeds is spherical; the silver ion concentration in the silver ion-containing precursor solution is 0.5 mol / L to 2.5 mol / L; When the temperature of the mixed reaction is 15°C to 40°C, the surface conditioner is a carboxylic acid substance with a carbon number of 8 or less; when the temperature of the mixed reaction is greater than 40°C and not greater than 60°C, the surface conditioner is a fatty acid substance with a carbon number of 12 or more; And / or, when the temperature of the mixing reaction is 15°C to 40°C, the surface conditioner includes at least one of malonic acid, acrylic acid, tartronic acid, fumaric acid, succinic acid, malic acid, maleic acid, citric acid, tartaric acid, sorbic acid and mandelic acid; when the temperature of the mixing reaction exceeds 40°C and does not exceed 60°C, the surface conditioner includes at least one of lauric acid, myristic acid, palmitic acid, oleic acid, 731A and polyacrylic acid.

2. The preparation method according to claim 1, characterized in that The dispersant comprises at least one of gum arabic, gelatin, polyethylene glycol, polyoxyethylene ether, polyvinyl alcohol, polyvinyl pyrrolidone and Tween; And / or, the amount of the dispersant is 0.5% to 20% of the mass of the silver ions in the silver ion-containing precursor solution.

3. The preparation method according to claim 2, characterized in that The amount of the dispersant used is 5% to 10% of the mass of the silver ions in the silver ion-containing precursor solution.

4. The preparation method according to claim 2, characterized in that The concentration of the reducing agent contained in the reducing solution is 0.2 mol / L to 2.0 mol / L; and / or, the reducing agent contained in the reducing solution includes at least one of ascorbic acid, glucose, erythorbic acid, sodium erythorbic acid, sodium ascorbate and sodium gluconate; And / or, based on the theoretical molar ratio of transferred electrons in the reaction between the reducing agent and silver ions, the molar ratio of the reducing agent contained in the reducing solution to the silver ions in the silver ion-containing precursor solution is 1.02:1 to 2.0:

1.

5. The preparation method according to claim 2, characterized in that The surface conditioner solution is an organic conditioner containing a carboxylic acid functional group; and / or, the mass fraction of the surface conditioner in the surface conditioner solution is 0.5% to 10%; And / or, the mass of the surface conditioner in the surface conditioner solution is 0.1% to 5% of the mass of the silver ions in the silver ion-containing precursor solution.

6. The preparation method according to any one of claims 1 to 5, characterized in that Also includes: The solid obtained from the mixed reaction is subjected to coating treatment.

7. The preparation method according to claim 6, characterized in that The coating process includes: mixing the solid object with a coating liquid.

8. The preparation method according to claim 7, characterized in that The mass fraction of the coating agent contained in the coating liquid is 10% to 40%.

9. The preparation method according to claim 7, characterized in that The solution contained in the coating liquid is water and / or alcohol.

10. The preparation method according to claim 8, characterized in that The amount of the coating agent is 0.1% to 5% of the mass of the silver ions in the silver ion-containing precursor solution.

11. A silver powder, characterized in that: The silver powder is prepared by the preparation method according to any one of claims 1 to 10.

12. The silver powder according to claim 11, characterized in that The surface of the silver powder has a nanostructure; The grain size of the silver powder is ≤150nm, the shrinkage rate of the silver powder is ≥11%, and the sintering temperature corresponding to the maximum shrinkage rate of the silver powder is ≤550°C.

13. The silver powder according to claim 12, characterized in that The silver powder further comprises at least one of the following features: Feature 1: The nanostructure includes at least one of a nanoscale block structure, a sheet structure, a prism structure, a strip structure, a rod structure, a spherical structure, a pore structure, and a hole structure; Feature 2: The specific surface area of ​​the silver powder is 0.4m 2 / g~1.1m 2 / g; Feature 3: The burnout of the silver powder is 0.4% to 1.5%; Feature 4: D of the silver powder 10 0.7μm~1.7μm; Feature 5: D of the silver powder 50 1.1μm~3.2μm; Feature 6: D of the silver powder 90 1.7μm~5.8μm.

14. Use of the silver powder according to any one of claims 11 to 13 in the preparation of solar cells.

Images