Graphene-coated silver powder and heterojunction low-temperature silver paste, and preparation methods therefor

Abstract

A graphene-coated silver powder and a heterojunction low-temperature silver paste, and preparation methods therefor. The graphene-coated silver powder is prepared by utilizing the following method: adding graphene and a dispersing agent to a silver powder, and conducting ball milling, so as to obtain the graphene-coated silver powder. The raw materials of the heterojunction low-temperature silver paste comprise, in percentages by weight: 86-93% of a silver powder mixture, 7-10% of an organic carrier, and 0.5-1% of a curing agent, wherein the silver powder mixture comprises a flaky silver powder, a spherical silver powder and the graphene-coated silver powder. Compared with the prior art, the surfaces of silver particles are coated with graphene in one step by means of a high-energy ball-milling process, thereby achieving effective combination of the graphene with the surfaces of the silver particles and further improving the overall conductivity of the silver particles and the conductivity of the heterojunction low-temperature silver paste.

Description

Graphene-coated silver powder, heterojunction low-temperature silver paste and preparation method thereof Technical Field

[0001] The present invention relates to the technical field of silver paste preparation, and in particular to graphene-coated silver powder, heterojunction low-temperature silver paste and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of heterojunction (HJT) solar cells, the demand for low-temperature curing conductive silver paste has also increased rapidly, attracting widespread attention from researchers. Heterojunction cells are the solar cell structure with the highest relative efficiency among known industrial cells. At present, the conversion efficiency of traditional crystalline silicon cells is 20.2%, and the efficiency of high-efficiency crystalline silicon cells can only reach 22%, while the efficiency of heterojunction cells can reach up to 27%. However, the actual mass production efficiency of heterojunction cells is basically the same as that of high-efficiency crystalline silicon cells. The main technical difficulty is that the conductivity of low-temperature silver paste is relatively low, and the paste product accounts for more than 50% of the non-silicon products in battery manufacturing. Therefore, breakthroughs in heterojunction silver paste are crucial to the industrialization of batteries, and how to improve the overall conductivity of silver paste has become one of the focuses of silver paste developers.

[0003] The key conductive raw materials for silver paste have expanded from single-source silver powder to include silver powder and graphene, nanotubes, silver-coated copper powder, and more. Because composite nanographene possesses a nanoscale microstructure and extremely high conductivity, it holds great potential for improving the conductivity of low-temperature silver paste. Therefore, efficiently incorporating highly conductive materials like graphene is crucial to fully realizing the conductive properties of silver paste.

[0004] CN116833406A discloses a method for modifying graphene composite silver powder, in which graphene oxide is modified by a fluorinated surfactant, but the modified graphene destroys the π-π structure of the graphene sheet, reduces the conductivity of graphene, and even causes graphene to become an insulator. Patent CN116779211A discloses a heterojunction low-temperature silver paste doped with graphene microemulsion, which improves the conductivity of the silver paste by introducing graphene microemulsion. However, the excessive introduction of graphene in an organic solvent will cause agglomeration, resulting in poor dispersion effect and a limited number of graphenes introduced. The method of using graphene / carbon tube composite nanosilver at nanoscale also has dispersibility problems, and the process is complicated, the cost is high, and the industrial application prospects are still under consideration. Therefore, how to efficiently introduce highly conductive materials such as graphene to give play to the technical problem of the conductive effect of heterojunction low-temperature silver paste remains to be solved.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a graphene-coated silver powder, a heterojunction low-temperature silver paste and a preparation method thereof, so as to efficiently introduce highly conductive materials such as graphene and give full play to the conductive effect of the heterojunction low-temperature silver paste.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A graphene-coated silver powder is prepared by the following method: graphene and a dispersant are added to silver powder, and the graphene-coated silver powder is obtained by ball milling.

[0009] Furthermore, the mass ratio of the silver powder, graphene and dispersant is 100:(1-3):(0.5-1.5), preferably 100:2:1.

[0010] Furthermore, the silver powder is purified in advance, and the specific steps are: adding the silver powder into an acidic solution, stirring and ultrasonic cleaning, and then washing with water and drying to obtain purified silver powder.

[0011] Furthermore, the acidic solution is dilute hydrochloric acid with a concentration of 0.1-0.5 mol / L.

[0012] Furthermore, the particle size of the silver powder is 2-7 μm.

[0013] Furthermore, the graphene is unmodified graphene, and the graphene is sieved with 450-550 mesh, preferably 500 mesh.

[0014] Furthermore, the dispersing aid includes one or more of fatty acid, triethanolamine or anhydrous ethanol.

[0015] Furthermore, the ball milling is carried out in a ball mill, and the rotation speed of the ball mill is 400-500 rpm.

[0016] Furthermore, the ball milling time is 4-6 hours.

[0017] Furthermore, the graphene-coated silver powder can be used for the preparation of low-temperature silver paste after drying without the need for purification.

[0018] The present invention also provides a heterojunction low-temperature silver paste, the raw materials of which are the following components and weight percentages: 86-93% of silver powder mixture, 7-10% of organic vehicle, and 0.5-1% of curing agent;

[0019] The silver powder mixture includes flaky silver powder, spherical silver powder and graphene-coated silver powder.

[0020] Furthermore, the mass ratio of the flaky silver powder, the spherical silver powder and the graphene-coated silver powder is (8-12):(2-4):(4-6).

[0021] Furthermore, the average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm 3 , bulk density is 0.8-1.2g / cm3 .

[0022] Furthermore, the average particle size of the spherical silver powder is 1.7-2.2 μm, and the tap density is 3.8-5.0 g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

[0023] Furthermore, the organic vehicle comprises the following components and their weight percentages: 60-70% organic resin, 0-20% solvent, and 0-20% auxiliary agent.

[0024] Furthermore, the organic resin includes one or more of ethyl cellulose, phenolic resin, epoxy resin, thermosetting acrylic resin or silane-modified polyurethane resin.

[0025] Furthermore, the solvent includes one or more of terpineol, turpentine, diethylene glycol butyl ether, diethylene glycol dibutyl ether, butyl carbitol acetate, dipropylene glycol monomethyl ether or tripropylene glycol monomethyl ether.

[0026] Furthermore, the auxiliary agent is a silane coupling agent.

[0027] Furthermore, the curing agent includes one or more of an imidazole curing agent, a polyamide curing agent, a methyl hexachloride curing agent, a methyl tetrachloride curing agent or a blocked isocyanate.

[0028] The present invention also provides a method for preparing a heterojunction low-temperature silver paste, comprising the following steps:

[0029] Weigh the organic carrier and curing agent in proportion, stir evenly at 800-1200 rpm at 65-75°C, add graphene-coated silver powder, continue stirring for 2-4 hours and then cool; continue to add flaky silver powder and spherical silver powder, grind 2-4 times in a three-roll mill, and pass through a 250-350 mesh sieve to obtain heterojunction low-temperature silver paste.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention adopts a ball milling process and a one-pot method to prepare graphene-coated silver powder. The effective bonding of graphene to the surface of silver particles is successfully achieved through mechanical force. The bonding strength is high and the actual operation is simple, which is suitable for large-scale applications.

[0032] (2) In the process of preparing heterojunction low-temperature silver paste, the present invention adds graphene-coated silver powder to ordinary silver powder. Compared with directly dispersing and mixing graphene, the addition of graphene-coated silver powder can significantly improve the conductivity of silver powder.

[0033] (3) The post-processing process of the present invention is simple, and the additives and products in the ball milling process can be directly used for the preparation of slurry without additional purification treatment, thereby achieving efficient utilization of process raw materials, simple process and low cost. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below. The following embodiments are implemented based on the technical solutions of the present invention, and provide detailed implementation methods and specific operating processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0035] Example 1

[0036] A heterojunction low-temperature silver paste containing graphene-coated silver powder is obtained by the following steps:

[0037] (1) Preparation of graphene-coated silver powder:

[0038] a. Add silver powder to 0.1 mol / L dilute hydrochloric acid and stir ultrasonically for 30 minutes. Then, centrifuge at 8000 rpm to precipitate the solution. Wash three times with deionized water and dry at 70°C.

[0039] b. The silver powder, graphene (pre-sieved to 500 mesh), and dispersant in step a were weighed in a mass ratio of 100:2:1 and ball milled in a QM-3SP4J ball mill at a rotation speed of 500 rpm for 6 h to obtain graphene-coated silver powder 1#.

[0040] The silver powder has an average particle size of 2-7 μm, a tap density of 1.5-2.0 g / mL, and an apparent density of 0.8-1.3 g / mL. The graphene used has a purity of ≥98%, a flake size range of 8-16 μm, and is sieved through a 500-mesh screen.

[0041] The dispersant is octadecanoic acid with a purity of ≥95%.

[0042] (2) Preparation of heterojunction low-temperature silver paste using graphene-coated silver powder 1#:

[0043] a. Weigh the materials according to the following mass percentages:

[0044] Flake silver powder 50%, spherical silver powder 15%, graphene-coated silver powder 1# 25%, ethyl cellulose 4%, terpineol 4%, silane coupling agent 1%, imidazole curing agent 1%.

[0045] The average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm 3 , bulk density is 0.8-1.2g / cm 3 .

[0046] The average particle size of spherical silver powder is 1.7-2.2μm, and the tap density is 3.8-5.0g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

[0047] The silane coupling agent is selected from KH550, and the imidazole curing agent is selected from 2E4MI.

[0048] b. Mix ethyl cellulose, terpineol, silane coupling agent, and imidazole curing agent in appropriate proportions and stir magnetically at 1000 rpm at 70°C. Add graphene-coated silver powder #1 and continue stirring for 3 hours. Then cool. Add flaky and spherical silver powders and grind the mixture three times on a three-roll mill. Pass through a 300-mesh sieve to obtain a heterojunction low-temperature silver paste.

[0049] Example 2:

[0050] A heterojunction low-temperature silver paste containing graphene-coated silver powder is obtained by the following steps:

[0051] (1) Preparation of graphene-coated silver powder:

[0052] a. Add silver powder with a particle size of 2-7 μm to 0.1 mol / L dilute hydrochloric acid and stir ultrasonically for 30 minutes. Then centrifuge at 8000 rpm, wash three times with deionized water, and dry at 70°C.

[0053] b. The silver powder, graphene (pre-sieved to 500 mesh), and dispersant in step a were weighed in a mass ratio of 100:2:1 and ball milled in a QM-3SP4J ball mill at a rotation speed of 500 rpm for 6 h to obtain graphene-coated silver powder 2#.

[0054] The average particle size of the silver powder is 2-7 μm, the tap density is 1.5-2.0 g / mL, and the bulk density is 0.8-1.3 g / cm 3 The graphene used should have a purity of ≥98%, a flake size range of 8-16 μm, and the actual product should be sieved through 500 mesh. The dispersant used should be diethanolamine with a purity of ≥95%.

[0055] (2) Using graphene-coated silver powder 2# to prepare heterojunction low-temperature silver paste:

[0056] a. Weigh the materials according to the following mass percentages:

[0057] Flake silver powder 50%, spherical silver powder 15%, graphene-coated silver powder 2# 25%, ethyl cellulose 4%, terpineol 4%, silane coupling agent 1%, imidazole curing agent 1%.

[0058] The average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm3 , bulk density is 0.8-1.2g / cm 3 .

[0059] The average particle size of spherical silver powder is 1.7-2.2μm, and the tap density is 3.8-5.0g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

[0060] The silane coupling agent is selected from KH550, and the imidazole curing agent is selected from 2E4MI.

[0061] b. Mix ethyl cellulose, terpineol, silane coupling agent, and imidazole curing agent, stirring magnetically at 1000 rpm at 70°C. Add graphene-coated silver powder #2 and continue stirring for 3 hours. Then cool. Add flaky and spherical silver powders, grind three times on a three-roll mill, and pass through a 300-mesh sieve to obtain a heterojunction low-temperature silver paste.

[0062] Example 3:

[0063] A silver paste containing graphene-coated silver powder is obtained by the following steps:

[0064] 1) Preparation of graphene-coated silver powder:

[0065] a. Add silver powder with a particle size of 2-7 μm to 0.1 mol / L dilute hydrochloric acid, stir ultrasonically for 30 min, then centrifuge at 8000 rpm, wash three times with deionized water, and dry at 70°C.

[0066] b. The silver powder, graphene (pre-sieved to 500 mesh), and dispersant in step a were weighed in a mass ratio of 100:2:1 and ball milled in a QM-3SP4J ball mill at a rotation speed of 500 rpm for 6 h to obtain graphene-coated silver powder 3#.

[0067] The average particle size of the silver powder is 2-7 μm, the tap density is 1.5-2.0 g / mL, and the bulk density is 0.8-1.3 g / mL. The graphene is selected with a purity of ≥98%, a flake size range of 8-16 μm, and the actual product is sieved through 500 mesh.

[0068] The dispersant is anhydrous ethanol with a purity of ≥97%.

[0069] 2) Prepare silver paste using graphene-coated silver powder 3#:

[0070] a. Weigh the materials according to the following mass percentages:

[0071] Flake silver powder 50%, spherical silver powder 15%, graphene-coated silver powder 3# 25%, ethyl cellulose 4%, terpineol 4%, silane coupling agent 1%, imidazole curing agent 1%.

[0072] The average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm 3 , bulk density is 0.8-1.2g / cm 3 .

[0073] The average particle size of spherical silver powder is 1.7-2.2μm, and the tap density is 3.8-5.0g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

[0074] The silane coupling agent is selected from KH550, and the imidazole curing agent is selected from 2E4MI.

[0075] b. Mix ethyl cellulose, terpineol, silane coupling agent, and imidazole curing agent, stirring magnetically at 1000 rpm at 70°C. Add graphene-coated silver powder #3 and continue stirring for 3 hours. Then cool. Add flaky and spherical silver powders, grind three times on a three-roll mill, and pass through a 300-mesh sieve to obtain a heterojunction low-temperature silver paste.

[0076] Comparative Example 1:

[0077] A silver paste without graphene-coated silver powder is obtained by the following steps:

[0078] 1) Preparation of comparative silver powder 1# without graphene:

[0079] a. Add silver powder with a particle size of 2-7 μm to 0.1 mol / L dilute hydrochloric acid, stir ultrasonically for 30 min, then centrifuge at 8000 rpm, wash three times with deionized water, and dry at 70°C.

[0080] b. The silver powder in step a was weighed and a dispersant was added at a mass ratio of 100:1. The mixture was ball milled in a QM-3SP4J ball mill at a rotation speed of 500 rpm for 6 h to obtain comparative silver powder 1#.

[0081] The silver powder has an average particle size of 2-7 μm, a tap density of 1.5-2.0 g / mL, and a loose density of 0.8-1.3 g / mL. The dispersant is octadecanoic acid with a purity of ≥95%.

[0082] 2) Prepare silver paste using comparative silver powder 1#:

[0083] a. Weigh the materials according to the following mass percentages:

[0084] Flake silver powder 50%, spherical silver powder 15%, comparative silver powder 1# 24.5%, graphene 0.5%, ethyl cellulose 4%, terpineol 4%, silane coupling agent 1%, imidazole curing agent 1%.

[0085] The average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm 3 , bulk density is 0.8-1.2g / cm 3 .

[0086] The average particle size of spherical silver powder is 1.7-2.2μm, and the tap density is 3.8-5.0g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

[0087] The graphene used has a purity of ≥98%, a flake size range of 8-16 μm, and the actual product is sieved through 500 mesh.

[0088] The silane coupling agent is selected from KH550, and the imidazole curing agent is selected from 2E4MI.

[0089] b. Mix ethyl cellulose, terpineol, silane coupling agent, and imidazole curing agent, stirring magnetically at 1000 rpm at 70°C. Add comparative silver powder #1 and graphene, continue stirring for 3 hours, and then cool. Add flaky and spherical silver powders, grind three times on a three-roll mill, and pass through a 300-mesh sieve to obtain a heterojunction low-temperature silver paste.

[0090] Comparative Example 2:

[0091] A silver paste without graphene-coated silver powder is obtained by the following steps:

[0092] 1) Preparation of comparative silver powder 2 without graphene:

[0093] a. Add silver powder with a particle size of 2-7 μm to 0.1 mol / L dilute hydrochloric acid, stir ultrasonically for 30 min, then centrifuge at 8000 rpm, wash three times with deionized water, and dry at 70°C.

[0094] b. The silver powder in step a was weighed and a dispersant was added at a mass ratio of 100:1. The mixture was ball milled in a QM-3SP4J ball mill at a rotation speed of 500 rpm for 6 h to obtain comparative silver powder 2#.

[0095] The silver powder has an average particle size of 2-7 μm, a tap density of 1.5-2.0 g / mL, and a loose density of 0.8-1.3 g / mL. The dispersant is octadecanoic acid with a purity of ≥95%.

[0096] 2) Prepare silver paste using comparative silver powder 2#:

[0097] a. Weigh the materials according to the following mass percentages:

[0098] Flake silver powder 50%, spherical silver powder 15%, comparative silver powder 2# 25%, ethyl cellulose 4%, terpineol 4%, silane coupling agent 1%, imidazole curing agent 1%.

[0099] The average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm 3 , bulk density is 0.8-1.2g / cm 3 .

[0100] The average particle size of spherical silver powder is 1.7-2.2μm, and the tap density is 3.8-5.0g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

[0101] The graphene used has a purity of ≥98%, a flake size range of 8-16 μm, and the actual product is sieved through 500 mesh.

[0102] The silane coupling agent is selected from KH550, and the imidazole curing agent is selected from 2E4MI.

[0103] b. Mix ethyl cellulose, terpineol, silane coupling agent, and imidazole curing agent, stirring magnetically at 1000 rpm at 70°C. Add comparative silver powder #2 and continue stirring for 3 hours. Then cool. Add flaky and spherical silver powders, grind three times on a three-roll mill, and pass through a 300-mesh sieve to obtain a heterojunction low-temperature silver paste.

[0104] The following performance tests were performed on Examples 1-3 and Comparative Examples 1-2: Viscosity was measured using a rotational viscometer, resistivity was measured with a line length of 350 mm, a line width of 0.6 mm, and a film thickness of 12 μm, and welding tension was measured using a standard silver-plated copper sheet.

[0105] The results are shown in Table 1:

[0106] The test data clearly demonstrates that the silver pastes prepared using graphene-coated silver powder (Examples 1-3) exhibit significantly lower resistivity than Comparative Examples 1-2, indicating significantly better conductivity. Even with the same amount of graphene introduced into Comparative Example 1, the incorporation of graphene was poor due to simple dispersion and mixing, resulting in a poor bond with the silver powder and a significantly higher resistivity. Comparative Example 2, which lacks the addition of graphene, exhibits an even higher resistivity.

[0107] Regarding other properties, such as viscosity, the silver pastes prepared using graphene-coated silver powder in Examples 1-3 exhibited higher viscosities than those in Comparative Examples 1-2, but were generally within the same range. The introduction of graphene-coated silver powder had little significant effect on the solderability of the silver paste.

[0108] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A graphene-coated silver powder, characterized in that: The preparation method is as follows: graphene and a dispersant are added to silver powder, and the silver powder coated with graphene is obtained by ball milling.

2. The graphene-coated silver powder according to claim 1, characterized in that: The mass ratio of the silver powder, graphene and dispersant is 100:(1-3):(0.5-1.5).

3. The graphene-coated silver powder according to claim 1, characterized in that: The particle size of the silver powder is 2-7 μm; The graphene is non-modified graphene, and the graphene is sieved with 450-550 mesh; The dispersing aid includes one or more of fatty acid, triethanolamine or anhydrous ethanol.

4. The graphene-coated silver powder according to claim 1, characterized in that: The rotation speed of the ball mill is 400-500 rpm, and the ball milling time is 4-6 hours.

5. A heterojunction low-temperature silver paste, characterized in that: The raw materials are as follows and their weight percentages are as follows: 86-93% silver powder mixture, 7-10% organic carrier, and 0.5-1% curing agent; The silver powder mixture comprises flaky silver powder, spherical silver powder and the graphene-coated silver powder according to any one of claims 1 to 4.

6. The heterojunction low-temperature silver paste according to claim 5, characterized in that: The mass ratio of the flaky silver powder, the spherical silver powder and the graphene-coated silver powder is (8-12):(2-4):(4-6).

7. The heterojunction low-temperature silver paste according to claim 5, characterized in that: The average particle size of the flaky silver powder is 4.0-6.2 μm, and the tap density is 1.8-2.2 g / cm 3 , bulk density is 0.8-1.2g / cm 3 ; The average particle size of the spherical silver powder is 1.7-2.2 μm, and the tap density is 3.8-5.0 g / cm 3 , bulk density is 1.8-2.3g / cm 3 .

8. The heterojunction low-temperature silver paste according to claim 5, characterized in that: The organic carrier comprises the following components and their weight percentages: 60-70% organic resin, 0-20% solvent, and 0-20% auxiliary agent; The organic resin includes one or more of ethyl cellulose, phenolic resin, epoxy resin, thermosetting acrylic resin or silane-modified polyurethane resin; The solvent includes one or more of terpineol, turpentine, diethylene glycol butyl ether, diethylene glycol dibutyl ether, butyl carbitol acetate, dipropylene glycol monomethyl ether or tripropylene glycol monomethyl ether; The auxiliary agent is a silane coupling agent.

9. The heterojunction low-temperature silver paste according to claim 5, characterized in that: The curing agent includes one or more of imidazole curing agent, polyamide curing agent, methyl hexacarboxylic anhydride curing agent, methyl tetracarboxylic anhydride curing agent or blocked isocyanate.

10. A method for preparing the heterojunction low-temperature silver paste according to claim 5, characterized in that: The following steps are involved: Weigh the organic carrier and curing agent in proportion, stir evenly at 800-1200 rpm at 65-75°C, add graphene-coated silver powder, continue stirring for 2-4 hours and then cool; continue to add flaky silver powder and spherical silver powder, grind 2-4 times in a three-roll mill, and pass through a 250-350 mesh sieve to obtain a heterojunction low-temperature silver paste.

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