Silver powder modified with surface carboxylate silver and a method for its production

Abstract

The application provides a kind of surface carboxylic acid silver modified silver powder and its preparation method, and relates to the technical field of silver powder preparation.The application obtains the surface carboxylic acid silver modified silver powder by reacting organic carboxylic acid with silver nitrate ammonia water complex in alcohol washing stage, and the silver powder is coated with carboxylic acid silver on the surface.The silver powder after surface modification is spherical particle, has sub-micron to micron size, uniform morphology, good dispersibility, high tap density, low sintering temperature, low series resistance, good conductivity, and improves the application performance of silver powder in electronic paste.

Description

Technical Field

[0001] This invention relates to the field of silver powder preparation technology, and in particular to a silver powder with surface modified silver carboxylic acid and its preparation method. Background Technology

[0002] Due to its excellent electrical and thermal conductivity, metallic silver is widely used in electronic pastes such as thick-film conductive pastes, high- and low-temperature conductive adhesives, and electromagnetic shielding. Silver powder, as a conductive filler, is a crucial component of electronic pastes and a key material determining paste performance; therefore, it is currently the most widely used and consumed precious metal powder material. As an important component of electronic pastes, the morphology, particle size, dispersibility, and specific surface area of ​​silver powder significantly influence the electrical properties, flowability, and printability of the paste. The dispersibility of silver powder determines its uniform dispersion in the electronic paste; excellent dispersibility ensures uniform distribution of silver powder, thereby improving the conductivity and stability of the paste. The sintering performance of silver powder determines the stability and molding effect of the electronic paste under high-temperature conditions; good sintering performance ensures the formation of a dense conductive layer during sintering, improving the performance and reliability of electronic devices. Therefore, the conductivity, dispersibility, and sintering performance of silver powder play a decisive role in the quality of electronic pastes.

[0003] In the field of solar cells, electronic pastes generally require silver powder with high sphericity, narrow flowability, narrow particle size distribution, and high tap. During the synthesis and modification of silver powder, researchers generally focus on particle size, tap, specific surface area, and surface morphology, while surface modification of silver powder is often poorly studied. However, surface modification of silver powder can improve the bonding strength between silver powder and the substrate material, enhance the uniformity and density of sintering, and improve sintering performance by altering surface properties and morphology and introducing functional materials.

[0004] To adapt to the rapid sintering process of crystalline silicon solar cells, high sintering activity is required for the silver powder constituting the front-side silver paste. Especially with the development of new high-efficiency battery technologies such as PERC and HJT, silver powder needs to exhibit higher sintering activity at lower temperatures. The application of nano-silver powder is one option to solve these application challenges. By combining micron-sized silver powder with a small amount of nano-sized silver powder, the comprehensive performance requirements of the front-side silver paste for crystalline silicon solar cells in terms of screen printing suitability, sintering activity, and electrical performance can be met. However, the use of nano-silver powder increases the cost of the paste, and there are operational complexities and quality risks regarding the uniform dispersion of nano-silver powder in the paste. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a silver powder with surface-modified silver carboxylic acid and its preparation method. This invention involves reacting an organic carboxylic acid with a silver nitrate ammonia complex to coat the surface of the silver powder with silver carboxylic acid. The surface-modified silver powder consists of spherical particles with submicron to micron particle sizes, uniform morphology, good dispersibility, high tap density, excellent sintering performance, low crosstalk resistance, and good electrical conductivity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] On the one hand, a method for preparing silver powder with surface modified silver carboxylate includes the following steps:

[0008] Silver powder is dispersed in ethanol, silver nitrate ammonia complex is added and dispersed evenly, then organic silver carboxylic acid is added, and the mixture is stirred to react and generate silver carboxylic acid, which coats the surface of the silver powder, thus obtaining silver powder with silver carboxylic acid surface modification.

[0009] Furthermore, the silver powder is spherical with a particle size of 0.5–4.0 μm, preferably 1.0–3.0 μm.

[0010] Furthermore, in the silver nitrate ammonia complex, the amount of silver nitrate used is 0.01-5% of the mass of silver powder, preferably 0.05-1%; the amount of ammonia used is 2-3 times the molar mass of silver nitrate.

[0011] Further, the organic carboxylic acid is selected from at least one of octanoic acid, dodecanoic acid, stearic acid, oleic acid, and palmitic acid; the amount of the organic carboxylic acid is 1 to 1.1 times the molar amount of silver nitrate in the silver nitrate ammonia complex, preferably 1 to 1.05 times.

[0012] Further, the conditions for the stirring reaction are: room temperature, stirring speed of 2000-4000 r / min, and time of 3-10 min; preferably, the conditions for the stirring reaction are: room temperature, stirring speed of 3000 r / min, and time of 5 min.

[0013] Furthermore, the steps also include solid-liquid separation, ethanol washing, and drying.

[0014] Furthermore, the silver powder is prepared by the following method:

[0015] The nano-silver paste was mixed with a dispersant, and then silver nitrate solution and reducing agent solution were added dropwise to the dispersant while stirring. After the addition was complete, a surfactant and a pH adjuster were added to adjust the pH to 5-6. The mixture was stirred to react, and finally silver powder was obtained by solid-liquid separation, washing, and drying.

[0016] Preferably, the dispersant is selected from at least one of polyethylene glycol, polyvinyl alcohol, gelatin, sodium dodecylbenzenesulfonate, Tween 80, polyvinylpyrrolidone (PVP), and gum arabic; the dispersant is first dissolved in water to prepare a solution before use, and the concentration of the dispersant in the solution is 100-600 g / L, more preferably 250 g / L; the amount of the dispersant used is 8-15 times the mass of the nano-silver paste, more preferably 10 times.

[0017] Preferably, the reducing agent is selected from at least one of glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, hydroquinone, alkanolamine, and hydrogen peroxide; the concentration of the reducing agent in the reducing agent solution is 0.1-5 mol / L, more preferably 1.5 mol / L; the amount of the reducing agent is 10-20 times the mass of the nano-silver paste, more preferably 17 times.

[0018] Preferably, the surfactant is selected from at least one of oleic acid, sodium oleate, palmitic acid, caprylic acid, stearic acid, etc., and the amount of the surfactant is 1 to 5% of the mass of the generated silver powder, more preferably 3%.

[0019] Preferably, the pH adjuster comprises, but is not limited to, at least one of nitric acid, citric acid, ammonia, sodium hydroxide, and sodium carbonate solution.

[0020] Preferably, the concentration of silver nitrate in the silver nitrate solution is 0.1–3 mol / L, more preferably 1 mol / L; the amount of silver nitrate used is 10–20 times the mass of the nano-silver paste, more preferably 15 times.

[0021] Preferably, the silver particles in the nano-silver paste have a particle size of 50–300 nm, a silver particle content of 0.5–4%, and the silver particles have a hydrophilic surface. Any nano-silver paste that meets the above conditions can be used as a seed crystal in this invention.

[0022] On the other hand, a silver powder with surface-modified silver carboxylate was prepared by the above method.

[0023] Furthermore, in the silver powder modified with silver carboxylate on the surface, the silver carboxylate accounts for 0.1 to 0.6% of the total mass of the silver powder modified with silver carboxylate on the surface.

[0024] The present invention also provides the application of the above-mentioned surface-nanosized silver powder in silver paste for solar cells and / or electrode silver paste for electronic components.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention reacts organic carboxylic acids with silver nitrate ammonia water complex to generate silver carboxylate, which is then coated onto the surface of silver powder. The silver powder modified with surface-carboxylate decomposes into elemental silver during sintering, allowing the silver powder to be directly welded together, making it easier to form a conductive network. Therefore, the series resistance is lower and the conductivity is better. Furthermore, the surface-carboxylic acid modified silver powder has improved surface sintering activity due to the lower decomposition temperature of silver carboxylate. During sintering, the silver powder is welded together by the decomposition of silver carboxylate, preventing the printed lines from collapsing due to the volatilization and decomposition of the organic carrier. This results in better line preservation, a better aspect ratio, and improved battery conversion efficiency.

[0027] 2. The method described in this invention can modify silver powder with silver carboxylate in the particle size range of 0.5 to 4.0 μm. The modified silver powder has no change in particle size distribution, high dispersibility, high tap density, and still maintains good rheological and thixotropic properties.

[0028] 3. The equipment and processes used in the method of the present invention are simple, the reaction conditions are mild, the production cycle is short, it is easy to operate, has good repeatability, is energy-saving and environmentally friendly, and is suitable for industrial scale-up and industrial application. Attached Figure Description

[0029] Figure 1 This is a SEM image (15000x magnification) of the surface-modified silver powder obtained in Example 3 of the present invention;

[0030] Figure 2 This is a SEM image (15000x magnification) of the surface-modified silver powder obtained in Comparative Example 1 of this invention;

[0031] Figure 3 This is a thermogravimetric curve of the surface-modified silver powder obtained in Example 3 and Comparative Example 1 of the present invention. Detailed Implementation

[0032] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following description is merely an exemplary illustration of the scope of protection of the present invention, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection of the present invention.

[0033] In this invention, nano-silver paste is used as a seed crystal. The silver particles in the nano-silver paste have a particle size of 50–300 nm and a silver content of 0.5–4%. The silver particles have a hydrophilic surface. Any nano-silver paste that meets the above conditions can be used as a seed crystal in this application. Specifically, the nano-silver paste can be prepared by the following method:

[0034] (1) First, dissolve dispersant I and silver nitrate in water to form a mixed solution I with a silver nitrate concentration of 0.01 to 20.0 mmol / L. Then, add the solution of reducing agent I while stirring and continue stirring to form nano-silver seed crystals.

[0035] Wherein, the dispersant I is at least one of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate, and sodium dodecylbenzene sulfonate; the reducing agent I is at least one of sodium borohydride, hydrazine hydrate, ascorbic acid, or hydrogen peroxide; the molar ratio of reducing agent I to silver nitrate is 0.2 to 3:1;

[0036] (2) Dissolve the complexing agent and silver nitrate in water to form a mixed solution II with a silver nitrate concentration of 0.1-2.0 mol / L. Then, dispersant II, precipitant and nano silver seeds are added to water to form a mixed solution III. Under stirring, mixed solution II is added to mixed solution III and stirred to react, forming a uniform silver-containing precursor precipitate.

[0037] Wherein, the dispersant II is at least one of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate, and sodium dodecylbenzene sulfonate; the precipitant is at least one of oxalic acid, sodium oxalate, ammonium bicarbonate, sodium carbonate, phosphoric acid, sodium phosphate, hydrochloric acid, sodium chloride, sodium hydroxide, sulfuric acid, and ammonium sulfate.

[0038] (3) Dispersant III and reducing agent II are added to water at a molar ratio of 0.1 to 10:1 to form mixed solution IV. Dispersant IV and reaction rate control agent are added to water to form mixed solution V. Mixed solution IV and mixed solution V are added to the silver-containing precursor precipitate obtained in step (2) at the same rate and stirred to generate nano silver glue.

[0039] Wherein, dispersant III is at least one of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate, and sodium dodecylbenzenesulfonate; reducing agent II is at least one of sodium borohydride, hydrazine hydrate, ascorbic acid, and hydrogen peroxide; dispersant IV is at least one of gelatin, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, citric acid, trisodium citrate, sodium oleate, and sodium dodecylbenzenesulfonate; reaction rate control agent is at least one of ammonia, nitric acid, and sodium hydroxide; the molar ratio of dispersant IV to reducing agent II in mixed solution IV is 0.1–10:1; the molar ratio of reaction rate control agent to reducing agent II in mixed solution IV is 0.1–10:1; and the concentration of reaction rate control agent in mixed solution V is 0.05–3.0 mol / L.

[0040] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of the present invention are obtained through conventional commercial means.

[0041] Example 1: Preparation of silver powder with surface-modified silver stearate and a particle size of 1.0 μm

[0042] (1) Synthetic silver powder

[0043] Prepare a 250 g / L PVP solution by dispersing 2.2 kg of PVP solution into a PVP solution, add 210 g of nano silver paste (silver particles with a diameter of 100 nm and a silver particle content of about 2 g) and disperse evenly to obtain a mixed solution.

[0044] Dissolve 3.16 kg of silver nitrate in water to prepare a 1 mol / L silver nitrate solution, and adjust the pH to 2 with a pH adjuster; weigh 3.5 kg of ascorbic acid to prepare a 1.5 mol / L reducing agent solution, and adjust the pH to 5 with a pH adjuster;

[0045] Then, the silver nitrate solution and the reducing agent solution are added dropwise to the mixed solution in a co-current manner. After the addition is complete, 3% of the silver powder mass of surfactant oleic acid is added, and the pH is adjusted to 5 with a pH adjuster to obtain silver powder with a particle size of 1μm.

[0046] (2) Silver carboxylate surface modification

[0047] The silver powder synthesized in step (1) was allowed to settle naturally, washed twice with deionized water, and then dispersed with ethanol to obtain a silver powder-ethanol mixture.

[0048] Dissolve 2,6-dimethylsilver nitrate in 5g of deionized water, add 3g of ammonia (ammonia content 25%) and mix well to prepare a silver nitrate ammonia complex.

[0049] Under stirring conditions, silver nitrate ammonia complex was added to a silver powder-ethanol mixture and mixed thoroughly. Then, 4.7 g of stearic acid (dissolved in 100 g of ethanol) was added, and the mixture was stirred for 5 min. After solid-liquid separation, washing with ethanol, and drying, silver powder with surface-modified silver carboxylic acid was obtained. The amount of silver nitrate used was 0.13% of the mass fraction of the silver powder, and the mass of silver stearate modified on the silver powder surface was 0.3% of the mass of the silver powder.

[0050] Example 2: Preparation of surface-modified silver powder with a particle size of 1.0 μm and silver oleate.

[0051] (1) Synthetic silver powder

[0052] Prepare a 250 g / L PVP solution by dispersing 2.2 kg of PVP solution into a PVP solution, add 210 g of nano silver paste (silver particles with a diameter of 100 nm and a silver particle content of about 2 g) and disperse evenly to obtain a mixed solution.

[0053] Dissolve 3.16 kg of silver nitrate in water to prepare a 1 mol / L silver nitrate solution, and adjust the pH to 2 with a pH adjuster; weigh 3.5 kg of ascorbic acid to prepare a 1.5 mol / L reducing agent solution, and adjust the pH to 5 with a pH adjuster;

[0054] Then, the silver nitrate solution and the reducing agent solution are added dropwise to the mixed solution in a co-current manner. After the addition is complete, 3% of the silver powder mass of surfactant oleic acid is added, and the pH is adjusted to 5 with a pH adjuster to obtain silver powder with a particle size of 1μm.

[0055] (2) Silver carboxylate surface modification

[0056] The silver powder synthesized in step 1) was allowed to settle naturally, washed twice with deionized water, and then dispersed with ethanol to obtain a silver powder-ethanol mixture.

[0057] Dissolve 2,6-dimethylsilver nitrate in 5g of deionized water, add 3g of ammonia (ammonia content 25%) and mix well to prepare a silver nitrate ammonia complex.

[0058] Under stirring conditions, silver nitrate ammonia complex was added to a silver powder-ethanol mixture and mixed thoroughly. Then, 4.7 g of oleic acid was added, and the mixture was stirred for 5 min. After solid-liquid separation, washing with ethanol, and drying, silver powder with surface-modified silver carboxylate was obtained. The amount of silver nitrate used was 0.17% of the mass of the silver powder, and the mass of silver oleate modified on the silver powder surface was 0.4% of the mass of the silver powder.

[0059] Example 3: Preparation of surface-modified silver powder with a particle size of 2.0 μm and silver octoate.

[0060] (1) Synthetic silver powder

[0061] Prepare a 250 g / L PVP solution by dispersing 2.2 kg of PVP solution into a PVP solution, add 105 g of nano silver paste (silver particles with a diameter of 200 nm and a silver particle content of about 2 g) and disperse evenly to obtain a mixed solution.

[0062] Dissolve 3.16 kg of silver nitrate in water to prepare a 1 mol / L silver nitrate solution, and adjust the pH to 2 with a pH adjuster; weigh 3.5 kg of ascorbic acid to prepare a 1.5 mol / L reducing agent solution, and adjust the pH to 5 with a pH adjuster;

[0063] Then, the silver nitrate solution and the reducing agent solution are added dropwise to the mixed solution in a parallel stream. After the addition is complete, 3% of the silver powder mass of surfactant oleic acid is added, and the pH is adjusted to 5 with a pH adjuster to obtain silver powder with a particle size of 2μm.

[0064] (2) Silver carboxylate surface modification

[0065] The silver powder synthesized in step 1) was allowed to settle naturally, washed twice with deionized water, and then dispersed with ethanol to obtain a silver powder-ethanol mixture.

[0066] Dissolve 6.75g of silver nitrate in 6g of deionized water, add 8g of ammonia (ammonia content 25%) and mix well to prepare silver nitrate ammonia complex.

[0067] Under stirring conditions, silver nitrate ammonia complex was added to a silver powder-ethanol mixture and mixed thoroughly. Then, 6g of octanoic acid was added, and the mixture was stirred for 5 minutes. After solid-liquid separation, washing with ethanol, and drying, silver powder with surface-modified silver carboxylate was obtained. The amount of silver nitrate used was 0.338% of the mass of the silver powder, and the mass of the silver octanoate surface-modified silver powder was 0.5% of the mass of the silver powder.

[0068] Example 4: Preparation of surface-modified silver palmitic acid silver powder with a particle size of 3.0 μm

[0069] (1) Synthetic silver powder

[0070] Prepare a 250 g / L PVP solution by dispersing 2.2 kg of PVP solution into a PVP solution, add 70 g of nano silver paste (silver particles with a diameter of 300 nm and a silver particle content of about 2 g) and disperse evenly to obtain a mixed solution.

[0071] Dissolve 3.16 kg of silver nitrate in water to prepare a 1 mol / L silver nitrate solution, and adjust the pH to 2 with a pH adjuster; weigh 3.5 kg of ascorbic acid to prepare a 1.5 mol / L reducing agent solution, and adjust the pH to 5 with a pH adjuster;

[0072] Then, the silver nitrate solution and the reducing agent solution are added dropwise to the mixed solution in a parallel stream. After the addition is complete, 3% of the silver powder mass of surfactant oleic acid is added, and the pH is adjusted to 5 with a pH adjuster to obtain silver powder with a particle size of 3μm.

[0073] (2) Silver carboxylate surface modification

[0074] The silver powder synthesized in step 1) was allowed to settle naturally, washed twice with deionized water, and then dispersed with ethanol to obtain a silver powder-ethanol mixture.

[0075] Dissolve 4.5g of silver nitrate in 5g of deionized water, add 5g of ammonia (ammonia content 25%) and mix well to prepare silver nitrate ammonia complex;

[0076] Under stirring conditions, silver nitrate ammonia complex was added to a silver powder-ethanol mixture and mixed thoroughly. Then, 7.22 g of palmitic acid (dissolved in 100 g of ethanol) was added, and the mixture was stirred for 5 min. After solid-liquid separation, washing with ethanol, and drying, silver powder with surface-modified silver carboxylate was obtained. The amount of silver nitrate used was 0.225% of the mass of the silver powder, and the mass of the silver palmitic acid modified on the silver powder surface was 0.59% of the mass of the silver powder.

[0077] Comparative Example 1: Preparation of silver powder with a particle size of 2.0 μm modified by adding only silver nitrate ammonia complex.

[0078] (1) Synthetic silver powder

[0079] Prepare a 250 g / L PVP solution by dispersing 2.2 kg of PVP solution into a PVP solution, add 105 g of nano silver paste (silver particles with a diameter of 200 nm and a silver particle content of about 2 g) and disperse evenly to obtain a mixed solution.

[0080] Dissolve 3.16 kg of silver nitrate in water to prepare a 1 mol / L silver nitrate solution, and adjust the pH to 2 with a pH adjuster; weigh 3.5 kg of ascorbic acid to prepare a 1.5 mol / L reducing agent solution, and adjust the pH to 5 with a pH adjuster;

[0081] Then, the silver nitrate solution and the reducing agent solution are added dropwise to the mixed solution in a parallel stream. After the addition is complete, 3% of the silver powder mass of surfactant oleic acid is added, and the pH is adjusted to 5 with a pH adjuster to obtain silver powder with a particle size of 2μm.

[0082] (2) Add silver nitrate ammonia complex during the alcohol washing of silver powder.

[0083] The silver powder synthesized in step (1) was allowed to settle naturally, washed twice with deionized water, and then dispersed with ethanol to obtain a silver powder-ethanol mixture.

[0084] Dissolve 6.75g of silver nitrate in 6g of deionized water, add 8g of ammonia (ammonia content 25%) and mix well to prepare silver nitrate ammonia complex.

[0085] Under stirring conditions, silver nitrate ammonia complex was added to the silver powder ethanol mixture and mixed well. After stirring for 5 minutes, solid-liquid separation, ethanol washing, and drying were performed to obtain silver powder with surface carboxylic acid silver modification.

[0086] Comparative Example 2: Preparation of silver powder with a particle size of 1.0 μm modified by only adding stearic acid

[0087] (1) Synthetic silver powder

[0088] Prepare a 250 g / L PVP solution by dispersing 2.2 kg of PVP solution into a PVP solution, add 210 g of nano silver paste (silver particles with a diameter of 100 nm and a silver particle content of about 2 g) and disperse evenly to obtain a mixed solution.

[0089] Dissolve 3.16 kg of silver nitrate in water to prepare a 1 mol / L silver nitrate solution, and adjust the pH to 2 with a pH adjuster; weigh 3.5 kg of ascorbic acid to prepare a 1.5 mol / L reducing agent solution, and adjust the pH to 5 with a pH adjuster;

[0090] Then, the silver nitrate solution and the reducing agent solution are added dropwise to the mixed solution in a co-current manner. After the addition is complete, 3% of the silver powder mass of surfactant oleic acid is added, and the pH is adjusted to 5 with a pH adjuster to obtain silver powder with a particle size of 1μm.

[0091] 2) Stearic acid is added during the alcohol washing of silver powder.

[0092] The silver powder synthesized in step 1) was allowed to settle naturally, washed twice with deionized water, and then dispersed with ethanol to obtain a silver powder-ethanol mixture.

[0093] Under stirring conditions, 4.7 g of stearic acid (stearic acid dissolved in 100 g of ethanol) was added to the silver powder ethanol mixture. After stirring for 5 min, solid-liquid separation, washing with ethanol, and drying were performed to obtain silver powder modified with surface carboxylic acid silver.

[0094] Experimental Example 1

[0095] The microstructure of the surface-modified silver powder obtained in Example 3 and Comparative Example 1 was observed using a scanning electron microscope (SEM). The SEM images are shown below. Figure 1 and 2 As shown.

[0096] As shown in the figure Figure 2 In Comparative Example 1, only silver powder modified with silver nitrate ammonia complex was added. Figure 1 The silver powder with surface-modified silver octoate in Example 3 is compared with... Figure 1 and Figure 2 It can be seen that both the silver powder before and after surface modification with silver carboxylic acid have spherical structures, good dispersibility, and uniform morphology.

[0097] Experimental Example 2

[0098] The particle size, specific surface area, tap density, and weight loss on ignition of silver powder before and after surface modification were tested, and the results are shown in Table 1 below.

[0099] Table 1. Parameters of surface-modified silver powder

[0100]

[0101] The results showed that, compared with the comparative example, the silver powder surface was not modified with silver carboxylate, while the silver powder prepared in this application, after surface modification with silver carboxylate, had almost no change in specific surface area. This indicates that the silver carboxylate coated on the silver powder surface is small in size and has no effect on the viscosity of the slurry, while the burn-off increases. The increase can be calculated to show that the amount of loss is consistent with the mass of organic carboxylate ions in the silver carboxylate on the silver powder surface. This indicates that the silver carboxylate prepared in the alcohol washing stage is coated on the surface of the silver powder.

[0102] Experimental Example 3

[0103] Silver powder, both before and after surface modification, was used as conductive particles to prepare silver paste in the same proportion and with the same carrier. Viscosity, rheological properties, and electrical properties were then tested. The silver paste preparation method is as follows: 92% by weight of silver powder was mixed uniformly with 6% carrier and 2% glass powder, and then rolled using a three-roll mill to obtain the silver paste. The carrier formulation is as follows: 5% by weight of ethyl cellulose, 10% by weight of JH180 thixotropic agent, 20% by weight of dibutyl phthalate, 20% by weight of diethylene glycol butyl ether acetate, 20% by weight of diethylene glycol butyl ether, 15% by weight of terpineol, and 10 parts by weight of dodecyl alcohol ester.

[0104] Viscosity test: The test was conducted using a BROOKFIELD DV-II+Pro viscometer at a temperature of 25°C. The rotation speeds were 10 rpm, 30 rpm, 50 rpm, and 100 rpm, and the test time was 1 minute.

[0105] Rheological property testing: Rheological data were tested using a BROOKFIELD R / S plus rheometer at a test temperature of 25℃. The test method was as follows: the shear rate was continuously increased from 0 to 60 / s for 60 seconds. The deceleration curve was obtained after 60 seconds, when the shear rate decreased from 60 / s to 0. Readings were taken at 1s, 10s, 60s, and 120s.

[0106] Electrical performance testing: Silver paste was printed onto the solar cell using a screen printing process, and solar cell samples were prepared using a fast burn-in process. The series electronic and other electrical properties of the samples were tested using a solar cell testing system.

[0107] The results are shown in Tables 2 and 3 below.

[0108] Table 2. Viscosity and rheological properties of surface-modified silver powder

[0109]

[0110]

[0111] The silver paste on the front side needs to have good thixotropic properties so that it can pass through the screen during printing and the printed grid lines are not easily collapsed. As can be seen from the viscosity and rheological data in the table, the viscosity and rheological changes of the silver powder after surface modification with silver carboxylic acid are not significant, and it still maintains good rheological and thixotropic properties. This indicates that the printing lines of the silver powder obtained in the example were not worsened due to surface modification.

[0112] Table 3. Silver paste series resistance and aspect ratio

[0113] Example 1 1.04 0.29 Example 2 1.03 0.30 Example 3 1.05 0.28 Example 4 1.07 0.27 Comparative Example 1 1.23 0.24 Comparative Example 2 1.11 0.26

[0114] The series resistance data in the table shows that the series resistance of Comparative Example 1 is higher than that of Example 3. This indicates that under the fast-firing process, the silver powder modified with surface carboxylate decomposes into elemental silver during sintering, allowing the silver powder to be directly welded together, making it easier to form a conductive network. Therefore, the series resistance is lower and the conductivity is better. Combined with the aspect ratio data, it can be seen that the surface carboxylate-modified silver powder has improved surface sintering activity due to the lower decomposition temperature of the carboxylate. During the sintering process, the silver powder is welded together by the decomposition of silver from the carboxylate, and the printed lines do not collapse due to the volatilization and decomposition of the organic carrier, resulting in better line preservation and a better aspect ratio.

[0115] Test Example 4

[0116] The surface-modified silver powders obtained in Example 3 and Comparative Example 1 were characterized using a thermogravimetric analyzer, and the thermogravimetric curves were obtained as follows: Figure 3 As shown. From Figure 3 It can be seen that the temperature at which thermal weight loss begins in Example 3 is significantly lower than that in Comparative Example 1. This is because the silver carboxylic acid modified on the surface of the silver powder can be thermally decomposed to form elemental silver, which shortens the sintering temperature of the silver powder.

[0117] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any 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 invention should be within the protection scope of the present invention.

Claims

1. A method for preparing silver powder with surface modified silver carboxylic acid, characterized in that, Includes the following steps: Silver powder is dispersed in ethanol, silver nitrate ammonia complex is added and dispersed evenly, then organic carboxylic acid is added and stirred to react to generate silver carboxylic acid and coat the surface of silver powder, thus obtaining silver powder with silver carboxylic acid surface modification. The organic carboxylic acid is selected from at least one of octanoic acid, dodecanoic acid, stearic acid, oleic acid, and palmitic acid.

2. The preparation method according to claim 1, characterized in that, The silver powder is spherical with a particle size of 0.5–4.0 μm.

3. The preparation method according to claim 2, characterized in that, The silver powder has a particle size of 1.0–3.0 μm.

4. The preparation method according to claim 1, characterized in that, In the silver nitrate ammonia complex, the amount of silver nitrate used is 0.01-5% of the mass of silver powder, and the amount of ammonia used is 2-3 times the molar mass of silver nitrate.

5. The preparation method according to claim 4, characterized in that, In the silver nitrate ammonia complex, the amount of silver nitrate used is 0.05 to 1% of the mass of the silver powder.

6. The preparation method according to claim 1, characterized in that, The amount of the organic carboxylic acid used is 1 to 1.1 times the molar amount of silver nitrate in the silver nitrate ammonia complex.

7. The preparation method according to claim 6, characterized in that, The amount of the organic carboxylic acid used is 1 to 1.05 times the molar amount of silver nitrate in the silver nitrate ammonia complex.

8. The preparation method according to claim 1, characterized in that, The conditions for the stirring reaction are: room temperature, stirring speed of 2000-4000 r / min, and time of 3-10 min.

9. The preparation method according to claim 8, characterized in that, The conditions for the stirring reaction were: room temperature, stirring speed of 3000 r / min, and time of 5 min.

10. The preparation method according to claim 1, characterized in that, The silver powder was prepared by the following method: The nano-silver paste was mixed with a dispersant, and then silver nitrate solution and reducing agent solution were added dropwise to the dispersant while stirring. After the addition was complete, a surfactant and a pH adjuster were added to adjust the pH to 5-6. The mixture was stirred to react, and finally silver powder was obtained by solid-liquid separation, washing, and drying.

11. The preparation method according to claim 10, characterized in that, The dispersant is selected from at least one of polyethylene glycol, polyvinyl alcohol, gelatin, sodium dodecylbenzenesulfonate, Tween 80, polyvinylpyrrolidone, and gum arabic; the reducing agent is selected from at least one of glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, hydroquinone, alkanolamine, and hydrogen peroxide.

12. The preparation method according to claim 10, characterized in that, The silver particles in the nano-silver paste have a particle size of 50-300 nm and a silver content of 0.5-4%, and the silver particles have a hydrophilic surface.

13. A silver powder with a surface modified silver carboxylic acid, characterized in that, It is prepared by the preparation method according to any one of claims 1-12.

14. The silver powder with surface-modified silver carboxylate according to claim 13, characterized in that, The silver carboxylate is 0.1 to 0.6% of the total mass of the silver powder modified with surface silver carboxylate.

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