A modified graphene composite silver powder, its preparation method and application

Abstract

The present invention discloses a modified graphene composite silver powder, comprising modified graphene, silicon dioxide, and ultrafine silver powder; the ultrafine silver powder has an average particle size of 0.2-1.2 μm and a tap density of 4-6 g / mL; the modified graphene is obtained by modifying graphene oxide with a modified fluorosurfactant; the modified fluorosurfactant has the structure shown in Formula A below. The present invention non-covalently modifies graphene oxide with a modified fluorosurfactant and then composites the ultrafine silver powder with silicon dioxide. The resulting modified graphene composite silver powder has an average particle size of 0.3-1.5 μm and a tap density of 3.5-5.6 g / mL. It exhibits excellent dispersibility, can reduce battery resistance, and improve battery photoelectric conversion efficiency. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and in particular to a modified graphene composite silver powder, a preparation method thereof, and an application thereof. Background Art

[0002] Solar energy is the source of Earth's energy. It's widely distributed, easily accessible, and inexhaustible, providing a clean energy source. Against the backdrop of the increasing depletion of non-renewable energy sources like coal and oil, the development of solar energy is urgent. Solar cells have emerged as the most direct and effective means of developing and utilizing solar energy. Silicon-based solar cells have become the most mature and widely commercialized solar cell solution.

[0003] With the rapid development of silicon-based solar cell technology, conductive silver paste has been widely used in the production of silicon-based solar cell electrodes due to its low cost and simple operation. Conductive silver paste is usually adhered and solidified on the front and back of the solar cell by printing, vacuum evaporation, electroplating or spraying to form a gate electrode. Solar cells are semiconductor devices with a "photovoltaic effect". The PN junction of the solar cell generates voltage when exposed to light, that is, the semiconductor material converts light energy into electrical energy. Based on the voltage generation, a connecting circuit is required to convert the voltage into current. After the current is drawn out, the electrical energy generated by the solar cell can be used. Since conductive silver paste has excellent conductivity, it has become a common material for the front and back electrodes of solar cells.

[0004] Conductive silver paste is generally composed of silver powder, a binder phase and an organic carrier, wherein the binder phase is glass powder. Conductive silver paste in the prior art is generally prepared by mixing silver powder and glass powder and uniformly dispersing them in an organic carrier. The physical and chemical properties of the silver powder have a significant impact on the performance of the conductive silver paste and solar cells.

[0005] Silver powder used in the conductive silver paste industry generally requires high dispersibility and tap density. Currently, silver powder products are mainly divided into two categories: spherical silver powder and flake silver powder. Spherical silver powder is mainly obtained through chemical reduction, generally mixing silver nitrate or other soluble silver salt solution with a reducing agent solution to cause a reduction reaction to precipitate silver powder particles. Flake silver powder is usually obtained by mechanically processing spherical silver powder, such as ball milling.

[0006] However, due to the small particle size of silver powder, it is very easy to agglomerate, and it is difficult to mix it evenly with glass powder during the preparation of the slurry, and additional dispersants need to be added; the silver layer after sintering the conductive silver paste has many pores and poor density, resulting in poor battery electrical performance, large battery contact resistance, and affected transmission of photogenerated electrons, resulting in low photoelectric conversion efficiency.

[0007] Therefore, there is an urgent need for a composite silver powder with excellent dispersibility that can reduce battery resistance and improve battery photoelectric conversion efficiency. Summary of the Invention

[0008] Purpose of the invention: In view of the defects of the prior art, the purpose of the present invention is to provide a modified graphene composite silver powder with excellent dispersibility, which can reduce battery resistance and improve battery photoelectric conversion efficiency, as well as its preparation method and application.

[0009] Technical solution:

[0010] A modified graphene composite silver powder comprising modified graphene, silicon dioxide and ultrafine silver powder;

[0011] The average particle size of the ultrafine silver powder is 0.2-1.2 μm, and the tap density is 4-6 g / mL;

[0012] The modified graphene is prepared by modifying graphene oxide with a modified fluorine-containing surfactant.

[0013] The present invention compounds silver powder by modified graphene and silicon dioxide, which can greatly improve the dispersibility of silver powder and reduce the problem of agglomeration. Ultrafine silver powder can be used as the main body. The silver layer after sintering has a low thickness and good density, and the battery has strong electrical performance and high silver powder utilization rate, which can reduce the use of silver powder and reduce costs.

[0014] Furthermore, the modified fluorinated surfactant has a structure as shown in the following formula A:

[0015]

[0016] Furthermore, the modified fluorinated surfactant is prepared by the following steps:

[0017] (1) In a reactor, perfluorohexyl iodide, acetonitrile and distilled water are added in sequence, and sodium dithionite and sodium bicarbonate are added while stirring, and the mixture is reacted for 6-8 hours. After removing the acetonitrile, extraction, washing, and drying, the mixture is dissolved in concentrated sulfuric acid and distilled under reduced pressure to obtain perfluorohexylsulfinic acid;

[0018] (2) Add thionyl chloride to the reactor, add perfluorohexylsulfinic acid dropwise in an ice-water bath, react for 4-6 hours, and then distill under reduced pressure to obtain perfluorohexylsulfinyl chloride;

[0019] (3) adding perfluorohexylsulfenyl chloride, trimethyl-1,3-propylenediamine and triethylamine into a reactor, heating to 80-95° C., reflux reaction for 6-8 hours, cooling and crystallizing, filtering, washing and drying to obtain perfluorohexylsulfenamide;

[0020] (4) In a reactor, perfluorohexylsulfenamide and a solvent are added, stirred and mixed uniformly, and the temperature is raised to 40-50° C. under nitrogen protection, 1,4-dichlorobenzyl is added, and the temperature is continued to be raised to 55-65° C., stirred and kept warm for 18-24 hours, and the solvent is removed. After recrystallization, the modified fluorine-containing surfactant is obtained.

[0021] The present invention uses a modified fluorinated surfactant, which is a Gemini cationic surfactant. The modified fluorinated surfactant contains two hydrophilic groups and two lipophilic groups in its molecule, and has excellent surface activity. The fluorinated carbon chain in the molecule has excellent surface activity, thermal stability and chemical stability based on the smaller atomic radius, larger electronegativity and larger single bond energy of the fluorine atom.

[0022] Furthermore, in step (3), the molar ratio of perfluorohexylsulfenyl chloride to trimethyl-1,3-propylenediamine is 1:2-2.5; and in step (4), the molar ratio of perfluorohexylsulfenamide to 1,4-dichlorobenzyl is 2.2-2.4:1.

[0023] In the step (1), the molar ratio of perfluorohexyl iodide, sodium dithionite and sodium bicarbonate is 1:(1.2-1.5):(1.2-1.5).

[0024] In the step (2), the molar ratio of perfluorohexylsulfinic acid to thionyl chloride is 1:1.1-1.3.

[0025] Furthermore, the modified graphene is prepared by the following steps:

[0026] (1) ultrasonically dispersing graphene oxide in N,N-dimethylformamide to prepare a graphene dispersion;

[0027] (2) Adding graphene dispersion and modified fluorinated surfactant to the reactor, ultrasonically treating for 30-50 minutes, then adding hydrazine hydrate, stirring evenly, and transferring to a reactor;

[0028] (3) The reactor is heated to 100-110° C., reacted for 2-3 hours, and then filtered, washed, and dried to obtain modified graphene.

[0029] In the present invention, a modified fluorinated surfactant is used to modify graphene oxide. The modified fluorinated surfactant is adsorbed on the surface of graphene through the action of van der Waals force and hydrogen bonding. The graphene is modified by a non-covalent method. On the one hand, the interaction force between graphene sheets can be weakened, the dispersion thereof can be enhanced, and graphene agglomeration can be avoided; on the other hand, the original structure of the graphene can be retained, and its excellent electrical conductivity can be brought into play.

[0030] Furthermore, the mass ratio of the graphene oxide to the modified fluorine-containing surfactant is 1:2-3.

[0031] The method for preparing any one of the above modified graphene composite silver powders comprises the following steps:

[0032] (1) ultrasonically dispersing the modified graphene in anhydrous ethanol to prepare a modified graphene dispersion;

[0033] (2) In a reactor, add ethyl orthosilicate, anhydrous ethanol and ammonia water in sequence, stir evenly, and then let it stand for 4-6 hours to react to obtain silica sol;

[0034] (3) After stirring and mixing the ultrafine silver powder, modified graphene dispersion and silica sol for 30-50 minutes, filtering, washing and drying, adding them to anhydrous ethanol, ball milling, washing and drying to obtain the modified graphene composite silver powder.

[0035] The present invention compounds silver powder with modified graphene, wherein the modified graphene uniformly covers the silver powder and fills the pores between silver layers. The excellent electrical conductivity of the graphene can accelerate the transmission of silver photogenerated electrons and improve the photoelectric conversion efficiency. The excellent surface activity of the modified fluorinated surfactant in the modified graphene can enhance the dispersibility of the silver powder, reduce the use of dispersants in the conductive silver paste, and reduce the impact on the battery resistance.

[0036] The present invention compounds silver powder with silicon dioxide, and the silicon dioxide sol can prevent the agglomeration of silver powder particles, improve the dispersibility of the silver powder, and can be evenly distributed on the surface of the substrate after sintering, thereby improving the electrical performance of the battery.

[0037] Furthermore, in step (1), the mass ratio of modified graphene to anhydrous ethanol is 0.0005-0.0015:1;

[0038] In step (2), the concentration of aqueous ammonia is 0.5-0.8 mol / L, and the mass ratio of tetraethyl orthosilicate, anhydrous ethanol and aqueous ammonia is 1:(5-8):(0.7-1);

[0039] In the step (3), the mass ratio of the ultrafine silver powder, the modified graphene dispersion and the silica sol is 1:(4-6):(0.1-0.2).

[0040] Furthermore, the modified graphene composite silver powder has an average particle size of 0.3-1.5 μm and a tap density of 3.5-5.6 g / mL.

[0041] Application of any of the above modified graphene composite silver powders in conductive silver paste.

[0042] Beneficial effects:

[0043] (1) The modified graphene composite silver powder provided by the present invention uses a modified fluorine-containing surfactant, which is a Gemini cationic surfactant. The modified fluorine-containing surfactant contains two hydrophilic groups and two lipophilic groups in its molecule and has excellent surface activity. The fluorine-carbon chain in the molecule has excellent surface activity, thermal stability and chemical stability based on the smaller atomic radius, larger electronegativity and larger single bond energy of the fluorine atom.

[0044] (2) In the modified graphene composite silver powder provided by the present invention, a modified fluorinated surfactant is used to modify graphene oxide. The modified fluorinated surfactant is adsorbed on the surface of graphene through the action of van der Waals force and hydrogen bond. The graphene is modified by a non-covalent method. On the one hand, it can weaken the interaction between graphene sheets, enhance its dispersibility and avoid graphene agglomeration; on the other hand, it can retain the initial structure of graphene and exert its excellent electrical conductivity.

[0045] (3) The modified graphene composite silver powder provided by the present invention is compounded with silver powder by modified graphene. The modified graphene uniformly covers the silver powder and fills the pores between the silver layers. The excellent conductivity of graphene can accelerate the transmission of silver photogenerated electrons and improve the photoelectric conversion efficiency. The excellent surface activity of the modified fluorinated surfactant in the modified graphene can enhance the dispersibility of the silver powder, reduce the use of dispersants in the conductive silver paste, and reduce the impact on the battery resistance.

[0046] (4) The modified graphene composite silver powder provided by the present invention is compounded with silver powder through silica. The silica sol can prevent the agglomeration between silver powder particles, improve the dispersibility of silver powder, and can be evenly distributed on the surface of the substrate after sintering, thereby improving the electrical performance of the battery.

[0047] (5) The modified graphene composite silver powder provided by the present invention can greatly improve the dispersibility of silver powder and reduce the problem of agglomeration by compounding silver powder with modified graphene and silicon dioxide. Ultrafine silver powder can be used as the main body. The silver layer after sintering has a low thickness and good density, strong battery electrical performance and high silver powder utilization rate, which can reduce the use of silver powder and thus reduce costs. DETAILED DESCRIPTION

[0048] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following examples are illustrative of the present invention and are intended only to illustrate the present invention and are not intended to limit the present invention. Other combinations and various modifications within the scope of the present invention may be made without departing from the spirit or scope of the present invention.

[0049] Graphene oxide was 796034 purchased from Merck; ultrafine silver powder was S110970 purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; commercially available silver powder was high-purity silver powder purchased from Nangong Xiangfan Alloy Materials Co., Ltd.; and the remaining reagents and equipment were conventional reagents and equipment in this technical field.

[0050] Preparation of modified fluorinated surfactants

[0051] The modified fluorosurfactant was prepared by the following steps:

[0052] (1) In a reactor, 0.1 mol of perfluorohexyl iodide, 100 ml of acetonitrile and 200 ml of distilled water were added in sequence, 0.15 mol of sodium dithionite and 0.15 mol of sodium bicarbonate were mixed evenly, and the evenly mixed sodium dithionite and sodium bicarbonate were added under stirring, and the mixture was reacted for 8 hours. After removing the acetonitrile by rotary evaporation, the mixture was extracted, washed, dried, and dissolved in 100 ml of 75% concentrated sulfuric acid, and distilled under reduced pressure. The fraction was collected to obtain perfluorohexylsulfinic acid;

[0053] (2) Add 0.12 mol of thionyl chloride to a round-bottom flask, add 0.1 mol of perfluorohexylsulfinic acid dropwise in an ice-water bath, keep the reaction warm for 6 hours, and then distill under reduced pressure to obtain the perfluorohexylsulfinyl chloride;

[0054] (3) In a four-necked flask equipped with a spherical condenser, a mechanical stirrer, a thermometer, and a hollow stopper, 0.1 mol of perfluorohexylsulfenyl chloride, 0.2 mol of trimethyl-1,3-propylenediamine, and 100 ml of triethylamine were added, heated to 85° C., refluxed for 6 hours, cooled, crystallized, filtered, and dried to obtain the perfluorohexylsulfenamide;

[0055] (4) In a 250 mL four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen protection device, 0.22 mol of perfluorohexylsulfenamide and 100 mL of anhydrous ethanol were added and stirred to mix evenly. Under nitrogen protection, the temperature was raised to 40° C., 0.1 mol of 1,4-dichlorobenzyl was added, and the temperature was continued to rise to 55° C. After continuous stirring and heat preservation for 24 hours, the anhydrous ethanol was removed by rotary evaporation, and the modified fluorine-containing surfactant was obtained after recrystallization.

[0056] Mass spectrum data of the product: The product was analyzed by LC-MS, and the m / z of the product was 534.10 (100.0%), 534.70 (46.0%), 535.20 (11.9%), and 535.65 (2.2%).

[0057] Preparation of modified graphene-1

[0058] Modified graphene-1 was prepared by the following steps:

[0059] (1) 100 mg of graphene oxide was ultrasonically dispersed in 100 mL of N,N-dimethylformamide to prepare a graphene dispersion;

[0060] (2) In a reactor, 100 mL of graphene dispersion and 300 mg of modified fluorinated surfactant were added, and after ultrasonic treatment at 150 W for 40 minutes, 1 mL of hydrazine hydrate was added, stirred evenly, and then transferred to a reactor;

[0061] (3) The reactor was heated to 110° C., and after reacting for 3 hours, the modified graphene-1 was obtained by suction filtration, washing, and drying.

[0062] Preparation of modified graphene-2

[0063] The preparation is basically the same as that of modified graphene-1, except that the modified fluorinated surfactant is replaced by an equal amount of sodium dodecylbenzenesulfonate.

[0064] Example 1

[0065] The modified graphene composite silver powder was prepared by the following steps:

[0066] (1) ultrasonically dispersing 100 mg of modified graphene-1 in 100 g of anhydrous ethanol to prepare a modified graphene dispersion;

[0067] (2) In a reactor, 5 g of ethyl orthosilicate, 40 g of anhydrous ethanol, and 5 g of 0.6 mol / L ammonia water were added in sequence and stirred evenly, and then allowed to react for 6 hours to prepare a silica sol;

[0068] (3) 1 g of ultrafine silver powder, 6 g of modified graphene dispersion and 0.2 g of silica sol were stirred and mixed for 40 minutes, filtered, washed and dried, and added to 50 mL of anhydrous ethanol. After ball milling, washing and drying, the modified graphene composite silver powder was obtained.

[0069] Example 2

[0070] The process is basically the same as Example 1, except that in step (3), the amount of modified graphene is 5 g and the amount of silica sol is 0.15 g.

[0071] Example 3

[0072] The process is basically the same as Example 1, except that in step (3), the amount of modified graphene is 4 g and the amount of silica sol is 0.1 g.

[0073] Comparative Example 1

[0074] Commercially available silver powder.

[0075] Comparative Example 2

[0076] The process is basically the same as Example 1, except that step (1) is not performed, and the modified graphene dispersion in step (3) is replaced by an equal amount of anhydrous ethanol.

[0077] Comparative Example 3

[0078] The method is basically the same as Example 1, except that the modified graphene-1 in step (1) is replaced by an equal amount of graphene oxide.

[0079] Comparative Example 4

[0080] The process is basically the same as Example 1, except that the modified graphene-1 in step (1) is replaced by modified graphene-2.

[0081] Comparative Example 5

[0082] The process is basically the same as Example 1, except that step (2) is not performed and the silica sol in step (3) is replaced with an equal amount of anhydrous ethanol.

[0083] Performance Testing

[0084] Detection of average particle size of silver powder particles: The average particle size of the products of Examples 1-3 and Comparative Examples 1-5 was detected using a transmission electron microscope (JEM-2010 (HT), Japan Electronics).

[0085] The products of Examples 1-3 and Comparative Examples 1-5 were used to prepare conductive silver paste, which consisted of the following components in the following mass ratio: 85% of the products of Examples 1-3 and Comparative Examples 1-5, 3% of aluminum powder, 33% of B2O, and 9% of E-51 epoxy resin.

[0086] Dispersion test: A scraper fineness meter was used to test the scraper fineness of the silver powder in the conductive silver paste prepared above.

[0087] The test results are shown in the following table:

[0088] Average particle size (μm) Scraper fineness (μm) Example 1 0.9 7 Example 2 0.8 6 Example 3 0.8 6 Comparative Example 1 2.7 20 Comparative Example 2 0.6 10 Comparative Example 3 1.6 16 Comparative Example 4 1.4 12 Comparative Example 5 0.6 13

[0089] According to the comparison of the test results of Examples 1-3 with Comparative Example 1, it can be seen that the modified graphene composite silver powder provided by the present invention has a relatively low average particle size and excellent dispersibility, which can avoid the agglomeration of silver powder and improve the utilization rate of silver powder, thereby reducing costs.

[0090] According to the comparison of the test results of Examples 1-3 and Comparative Examples 2-4, it can be seen that in the modified graphene composite silver powder provided by the present invention, the ultrafine silver powder is compounded by modified graphene, and the excellent surface activity of the modified fluorinated surfactant in the modified graphene can enhance the dispersibility of the silver powder.

[0091] According to the comparison of the test results of Examples 1-3 and Comparative Example 5, it can be seen that in the modified graphene composite silver powder provided by the present invention, the ultrafine silver powder is compounded by silica, and the silica sol can prevent the agglomeration between the silver powder particles and improve the dispersibility of the silver powder.

[0092] The conductive silver paste prepared above was printed on the front surface of N-type PERC solar cells for testing.

[0093] Contact resistance detection: The commonly used TLM (transmission line model) is used to detect the contact resistance of the above-mentioned battery.

[0094] Battery photoelectric conversion efficiency test: Use TMC-PV1A solar cell tester to test IV curve and test the photoelectric conversion efficiency of the above battery.

[0095] The test results are shown in the following table:

[0096] Contact resistance (Ω) Photoelectric conversion efficiency (%) Example 1 0.47 24.1 Example 2 0.45 24.2 Example 3 0.46 24.2 Comparative Example 1 1.32 22.4 Comparative Example 2 1.13 22.6 Comparative Example 3 0.84 23.1 Comparative Example 4 0.65 23.5 Comparative Example 5 0.73 23.3

[0097] According to the comparison of the test results of Examples 1-3 with those of Comparative Example 1, it can be seen that the modified graphene composite silver powder provided by the present invention has lower contact resistance and can improve the photoelectric conversion efficiency of solar cells.

[0098] According to the comparison of the test results of Examples 1-3 and Comparative Examples 2-4, in the modified graphene composite silver powder provided by the present invention, ultrafine silver powder is compounded by modified graphene, and the modified graphene is modified by a non-covalent method, which can retain the original structure of the graphene. The modified graphene fills the pores between the silver layers, reduces the contact resistance of the battery, and accelerates the transmission of silver photogenerated electrons through the excellent electrical conductivity of graphene, thereby improving the photoelectric conversion efficiency.

[0099] According to the comparison of the test results of Examples 1-3 and Comparative Example 5, it can be seen that in the modified graphene composite silver powder provided by the present invention, the ultrafine silver powder is compounded by silicon dioxide, and can be evenly distributed on the surface of the substrate after sintering the conductive silver paste, thereby improving the electrical performance of the battery.

[0100] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modified graphene composite silver powder, characterized in that: Contains modified graphene, silicon dioxide and ultrafine silver powder; The average particle size of the ultrafine silver powder is 0.2-1.2 μm, and the tap density is 4-6 g / mL; The modified graphene is prepared by modifying graphene oxide with a modified fluorine-containing surfactant; The modified fluorinated surfactant is prepared by the following steps: (1) In a reactor, perfluorohexyl iodide, acetonitrile and distilled water are added in sequence, and evenly mixed sodium dithionite and sodium bicarbonate are added under stirring. The mixture is reacted for 6-8 hours, and the acetonitrile is removed, extracted, washed, dried, dissolved in concentrated sulfuric acid, and distilled under reduced pressure to obtain perfluorohexylsulfinic acid. (2) Add thionyl chloride to the reactor, add perfluorohexylsulfinic acid dropwise in an ice-water bath, react for 4-6 hours, and then distill under reduced pressure to obtain perfluorohexylsulfinyl chloride; (3) Add perfluorohexylsulfenyl chloride, trimethyl-1,3-propylenediamine and triethylamine into the reactor, heat to 80-95°C, reflux for 6-8 hours, cool and crystallize, filter, wash and dry to obtain perfluorohexylsulfenamide; the molar ratio of perfluorohexylsulfenyl chloride to trimethyl-1,3-propylenediamine is 1:2-2.5; (4) In a reactor, perfluorohexylsulfenamide and a solvent are added, stirred and mixed uniformly, and the temperature is raised to 40-50°C under nitrogen protection, 1,4-dichlorobenzyl is added, and the temperature is continued to be raised to 55-65°C. After stirring and keeping the temperature for 18-24 hours, the solvent is removed, and the modified fluorine-containing surfactant is obtained after recrystallization; the molar ratio of perfluorohexylsulfenamide to 1,4-dichlorobenzyl is 2.2-2.4:

1.

2. The modified graphene composite silver powder according to claim 1, characterized in that The modified fluorinated surfactant has a structure shown in the following formula A: 。 3. The modified graphene composite silver powder according to claim 1, characterized in that The modified graphene is prepared by the following steps: (1) Ultrasonic dispersion of graphene oxide in N,N-dimethylformamide to obtain a graphene dispersion; (2) Add graphene dispersion and modified fluorinated surfactant to the reactor, add hydrazine hydrate after ultrasonic treatment for 30-50 minutes, stir evenly and transfer to the reactor; (3) The reactor is heated to 100-110°C, and after reacting for 2-3 hours, the modified graphene is obtained by filtration, washing, and drying.

4. The modified graphene composite silver powder according to claim 3, characterized in that The mass ratio of the graphene oxide to the modified fluorine-containing surfactant is 1:2-3.

5. The method for preparing the modified graphene composite silver powder according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Ultrasonic dispersion of modified graphene in anhydrous ethanol to prepare a modified graphene dispersion; The mass ratio of modified graphene to anhydrous ethanol is 0.0005-0.0015:1; (2) In a reactor, add ethyl orthosilicate, anhydrous ethanol and 0.5-0.8 mol / L ammonia water in sequence, stir evenly, and allow to react for 4-6 hours to prepare a silica sol; the mass ratio of ethyl orthosilicate, anhydrous ethanol and ammonia water is 1: (5-8): (0.7-1); (3) After stirring and mixing the ultrafine silver powder, modified graphene dispersion and silica sol for 30-50 minutes, filtering, washing and drying, adding them to anhydrous ethanol, ball milling, washing and drying to obtain the modified graphene composite silver powder; the mass ratio of the ultrafine silver powder, modified graphene dispersion and silica sol is 1: (4-6): (0.1-0.2).

6. The method for preparing modified graphene composite silver powder according to claim 5, wherein The modified graphene composite silver powder has an average particle size of 0.3-1.5 μm and a tap density of 3.5-5.6 g / mL.

7. Use of the modified graphene composite silver powder according to any one of claims 1 to 4 in conductive silver paste.

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