Preparation method of silver powder, silver powder and application

Abstract

The invention relates to silver powder, and particularly discloses a preparation method of the silver powder, the silver powder and application. The silver powder prepared through the preparation method has the advantage of being high in specific surface area, meanwhile, the sinterability in the low-temperature environment is good, the technological process is simple, and therefore the silver powder has good application prospects in the field of photovoltaic cells.

Description

Technical Field

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

[0002] The photovoltaic industry is an important development direction for the transformation of the global energy structure. Countries around the world attach great importance to the development of the photovoltaic industry. Photovoltaic silver paste is a key material for making electrodes for photovoltaic cells. The metal electrodes of solar cells are formed by printing photovoltaic silver paste on both sides of the silicon wafer through screen printing, drying and sintering. As the electrode material of photovoltaic crystalline silicon cells, photovoltaic silver paste mainly plays the role of collecting and conducting photogenerated carriers.

[0003] Silver powder is the most important material for producing photovoltaic silver paste. The morphology, structure, particle size and distribution characteristics, tap density, specific surface area, sintering performance, corrosion resistance, etc. of silver powder will directly affect the performance of the paste. The morphology, particle size characteristics and sintering performance are the most critical characteristics, which directly or indirectly determine the photoelectric conversion efficiency of crystalline silicon cells.

[0004] However, the performance of existing silver powders needs to be improved. Summary of the invention

[0005] In view of the defects or shortcomings of the prior art, the purpose of this application is to provide a method for preparing silver powder, silver powder and application. The silver powder prepared by the preparation method has a high specific surface area and good sintering properties.

[0006] The first aspect of the present application is to disclose a method for preparing silver powder, comprising the following preparation process:

[0007] (1) preparing reaction raw materials: respectively preparing a salt solution of a silver precursor, a reducing agent solution, a protective agent solution and a pH adjuster of a certain concentration;

[0008] (2) premixing: mixing a portion of the silver precursor salt solution with the protective agent solution, adding a pH adjuster until the system reaches a certain pH value, and obtaining a mixed solution;

[0009] (3) Reduction reaction: adding a portion of the reducing agent solution to the mixed solution of step (2) to obtain a mixture through a first reduction reaction;

[0010] Adding the remaining solution of the silver precursor salt solution and the remaining solution of the reducing agent solution to the mixture, adding a pH adjuster until the system reaches a certain pH value, adding a surface treatment agent and continuing the reaction to obtain a silver powder dispersion;

[0011] (4) Post-treatment: The silver powder dispersion is post-treated to obtain silver powder.

[0012] In some embodiments, in the salt solution of the silver precursor in step (2), the volume of the partial solution is 1 / 20 to 2 / 3 of the volume of the salt solution of the silver precursor.

[0013] In some embodiments, in the reducing agent solution of step (3), the volume of the partial solution is 1 / 6 to 2 / 3 of the volume of the reducing agent solution.

[0014] In some embodiments, in the step (3), the remaining portion of the silver precursor salt solution and the remaining portion of the reducing agent solution are added to the mixture simultaneously;

[0015] The remaining portion of the silver precursor salt solution is added at time t1;

[0016] The remaining part of the reducing agent solution is added at time t2;

[0017] Satisfy t1:t2=1.5~2:1;

[0018] Preferably, the above t1 is 10 min to 40 min.

[0019] In some embodiments, the surface treatment agent includes any one or more of an organic acid or an organic amine;

[0020] and / or;

[0021] The amount of the surface treatment agent added is 0.1% to 2% of the theoretical mass of the silver powder;

[0022] and / or;

[0023] The organic acid includes any one or more of oleic acid, caprylic acid, linoleic acid, linolenic acid, ascorbic acid, malic acid, citric acid, formic acid, adipic acid, lauric acid, palmitic acid, and stearic acid;

[0024] and / or;

[0025] The organic amines include any one or more of octylamine, oleylamine, triethanolamine, hexadecylamine and octadecylamine.

[0026] In some embodiments, in the above step (3),

[0027] The temperature of the first reduction reaction is 15°C to 50°C, and the time is no more than 10 minutes;

[0028] and / or;

[0029] The temperature for continuing the reaction after adding the surface treatment agent is 20°C to 40°C, and the reaction time is 30min to 90min.

[0030] In some embodiments, the silver precursor salt solution comprises a silver precursor salt and a solvent;

[0031] The reducing agent solution comprises a reducing agent and a solvent;

[0032] The protective agent solution comprises a protective agent and a solvent;

[0033] The above-mentioned solvent includes any one or more of water and organic solvent.

[0034] In some embodiments, the salt of the silver precursor comprises silver nitrate;

[0035] and / or;

[0036] The reducing agent includes any one or more of formaldehyde, ascorbic acid, potassium tartrate, hydrazine hydrate, hydrazine carbonate, and sodium hypophosphite;

[0037] and / or;

[0038] The protective agent includes any one or more of citric acid, PVA, PEG, PVP, sorbitol, gelatin, and gum arabic;

[0039] and / or;

[0040] The pH adjuster includes any one or more of nitric acid, sodium hydroxide, sodium bicarbonate, and ammonia water.

[0041] The second aspect of the present application is to provide a silver powder, which is prepared by the preparation method described in the first aspect;

[0042] The median particle size Dv50 of the above silver powder is 0.3 μm to 0.8 μm;

[0043] and / or;

[0044] The specific surface area of ​​the silver powder is 3m 2 / g~20m 2 / g;

[0045] and / or;

[0046] The silver powder comprises spherical or quasi-spherical particles, and the surface of the particles has roughness.

[0047] The third aspect of the present application is to provide an application of the silver powder prepared by the preparation method described in the first aspect or the silver powder described in the second aspect in a photovoltaic cell.

[0048] Beneficial technical effects of this application:

[0049] The silver powder prepared by the preparation method provided in this application has the advantage of high specific surface area. At the same time, it has good sintering properties under low temperature environment and simple process flow. Therefore, the silver powder has good application prospects in the field of photovoltaic cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a process flow chart for preparing silver powder in some embodiments of this application.

[0051] Figure 2A This is a scanning electron microscope (SEM) image of the silver powder prepared in some examples of this application;

[0052] Figure 2B This is a scanning electron microscope (SEM) image of the silver powder prepared in some examples of this application;

[0053] Figure 3 This is a scanning electron microscope (SEM) image of the silver powder prepared in some embodiments of the present application after sintering under certain conditions. DETAILED DESCRIPTION

[0054] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0055] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0056] Unless expressly stated to the contrary, all ranges cited herein are inclusive.

[0057] The term "a" or "an" used in this application is used to describe the elements and components described in this application. This is done only for convenience and to provide a general sense of the scope of this application. This description should be understood to include one or at least one, and the singular also includes the plural, unless it is obvious that it is otherwise intended. "Multiple" means two or more.

[0058] The numbers in this application are approximate, regardless of whether the words "about" or "approximately" are used. The numerical values ​​of the numbers may vary by 1%, 2%, 5%, 7%, 8%, 10%, etc. Whenever a number with a value of N is disclosed, any number with a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8% or N+ / -10% will be explicitly disclosed, where "+ / -" means plus or minus, and the range between N-10% and N+10% is also disclosed.

[0059] The photovoltaic industry is an important development direction for the transformation of the global energy structure, and countries around the world attach great importance to the development of the photovoltaic industry. Photovoltaic silver paste is a key material for making photovoltaic cell electrodes, the largest auxiliary material for photovoltaic cells, and the second largest component of cell costs, accounting for about 33% of the non-silicon cost of cells.

[0060] Solar cells are mainly composed of silicon wafers, passivation films and metal electrodes. The metal electrodes are formed by printing photovoltaic silver paste on both sides of the silicon wafer through screen printing, drying and sintering. Photovoltaic silver paste, as the electrode material of photovoltaic crystalline silicon cells, mainly plays the role of collecting and conducting photogenerated carriers. It is often used on the light-receiving side of P-type cells and both sides of N-type cells.

[0061] Photovoltaic silver powder is the most important material for producing photovoltaic silver paste. Silver powder accounts for about 90% of the silver paste composition and more than 95% of the silver paste cost. The morphology, particle size and distribution characteristics, tap density, specific surface area, sintering performance, and corrosion resistance of silver powder will directly affect the performance of the paste, and the morphology, particle size and sintering performance are the most critical characteristics, which directly or indirectly determine the photoelectric conversion efficiency of crystalline silicon cells.

[0062] Common preparation methods for silver powder are divided into physical and chemical methods. Physical methods include atomization, vapor evaporation, grinding, etc. Chemical methods include sol-gel method, liquid phase reduction method, physical vapor deposition (PVD), hydrothermal method, chemical vapor deposition (CVD), etc. Currently, the most commonly used method for preparing high-temperature sintered silver powder required in the photovoltaic field is still the liquid phase reduction method.

[0063] However, the performance of existing silver powders needs to be improved.

[0064] In order to solve the above technical problems, the present application provides a method for preparing silver powder, comprising the following preparation process:

[0065] (1) preparing reaction raw materials: respectively preparing a salt solution of a silver precursor, a reducing agent solution, a protective agent solution and a pH adjuster of a certain concentration;

[0066] (2) premixing: mixing a portion of the silver precursor salt solution with the protective agent solution, adding a pH adjuster until the system reaches a certain pH value, and obtaining a mixed solution;

[0067] (3) Reduction reaction: adding a portion of the reducing agent solution to the mixed solution of step (2) to obtain a mixture through a first reduction reaction;

[0068] Adding the remaining solution of the silver precursor salt solution and the remaining solution of the reducing agent solution to the mixture, adding a pH adjuster until the system reaches a certain pH value, adding a surface treatment agent and continuing the reaction to obtain a silver powder dispersion;

[0069] (4) Post-treatment: The silver powder dispersion is post-treated to obtain silver powder.

[0070] In the preparation method provided by the present application, step (2) is mainly used to control the number of silver particles formed in a reaction and the overall reaction environment, the reduction process of step (3) is mainly used to control the nucleation and growth rate of the silver particles and thus control their particle size and surface morphology, and the roughness of the surface and the dispersibility of the silver particles are further regulated by adding a surface treatment agent, and the main purpose of step (4) is to achieve solid-liquid separation of the silver powder and then obtain the finished silver powder by drying and shaping. Therefore, the silver powder obtained by the preparation method provided by the present application has the characteristics of high specific surface area due to its high surface roughness, and the silver powder with high specific surface area can obtain a good sintering neck even under low temperature conditions during subsequent sintering, so the silver powder has good application prospects in the field of photovoltaic cells.

[0071] In some embodiments, in the salt solution of the silver precursor in step (2), the volume of the partial solution is 1 / 20 to 2 / 3 of the volume of the salt solution of the silver precursor.

[0072] In these embodiments, the present application discloses that the volume of the partial solution is any one of 1 / 20, 1 / 10, 1 / 5, 1 / 4, 1 / 3, 2 / 3 of the volume of the salt solution of the silver precursor, or any one of the values ​​within any two ranges.

[0073] In some embodiments, in the reducing agent solution of step (3), the volume of the partial solution is 1 / 6 to 2 / 3 of the volume of the reducing agent solution.

[0074] The present application discloses in these embodiments that the volume of the partial solution is any one of 1 / 6, 2 / 6, 1 / 2, 2 / 3 of the volume of the reducing agent solution, or any one of the values ​​within any two ranges.

[0075] In some embodiments, in the above step (3), the remaining portion of the silver precursor salt solution and the remaining portion of the reducing agent solution are added to the above mixture at the same time;

[0076] The remaining portion of the silver precursor salt solution is added at time t1;

[0077] The remaining part of the reducing agent solution is added at time t2;

[0078] Satisfy t1:t2=1.5~2:1;

[0079] In some embodiments, the above t1 is 10 min to 40 min.

[0080] In these embodiments, the present application discloses that the ratio between the addition time t1 of the remaining solution in the salt solution of the silver precursor and the addition time t2 of the remaining solution in the reducing agent solution is any one of 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1 or any one of the ranges of any two of the above.

[0081] In these embodiments, the present application discloses that the addition time t1 of the remaining solution in the salt solution of the silver precursor is any one of 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, and 40 min, or any one of the values ​​satisfying any two of the above ranges.

[0082] In some embodiments, in the above step (3), the remaining portion of the silver precursor salt solution and the remaining portion of the reducing agent solution are added to the above mixture at a certain speed through a peristaltic pump at the same time.

[0083] In some embodiments, the surface treatment agent includes any one or more of an organic acid or an organic amine.

[0084] In some embodiments, the added amount of the surface treatment agent is 0.1% to 2% of the theoretical mass of the silver powder.

[0085] The theoretical mass of silver powder is the ideal state in which all the silver in the silver precursor is converted into silver powder without any loss. This application is only used to measure the amount of surface treatment agent added.

[0086] In these embodiments, the present application discloses that the amount of the surface treatment agent added is any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0% of the theoretical mass of the silver powder, or any one of the values ​​satisfying any two of the above ranges.

[0087] In some embodiments, the organic acid includes any one or more of oleic acid, caprylic acid, linoleic acid, linolenic acid, ascorbic acid, malic acid, citric acid, formic acid, adipic acid, lauric acid, palmitic acid, and stearic acid;

[0088] In some embodiments, the organic amine includes any one or more of octylamine, oleylamine, triethanolamine, hexadecylamine, and octadecylamine.

[0089] In some embodiments, in the above step (3), the temperature of the above first reduction reaction is 15°C to 50°C, and the time is no more than 10 minutes.

[0090] In some embodiments, in the above step (3), the time of the first reduction reaction is 3 min to 10 min.

[0091] The present application discloses in these embodiments that the temperature of the first reduction reaction is any one of 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, and 50°C, or any one of the values ​​satisfying any two of the above ranges.

[0092] The present application discloses in these embodiments that the first reduction reaction time is any one of 10 min, 9 min, 8 min, 7 min, 6 min, 5 min, 4 min, 3 min or any one of the values ​​within any two ranges above.

[0093] In some embodiments, in the above step (3), the temperature for continuing the reaction after adding the surface treatment agent is 20°C to 40°C, and the reaction time is 30min to 90min.

[0094] The present application discloses in these embodiments that in the above step (3), the temperature for continuing the reaction after adding the surface treatment agent is any one of 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C or any one of the values ​​in any two of the above ranges.

[0095] In some embodiments, the silver precursor salt solution comprises a silver precursor salt and a solvent;

[0096] The reducing agent solution comprises a reducing agent and a solvent;

[0097] The protective agent solution comprises a protective agent and a solvent;

[0098] The above-mentioned solvent includes any one or more of water and organic solvent.

[0099] In some embodiments, the organic solvent comprises an alcohol organic solvent.

[0100] In some embodiments, the alcohol organic solvent includes any one or more of ethanol, ethylene glycol, pentanediol, and glycerol.

[0101] In some embodiments, the solvent includes a mixed solvent of water and an alcohol organic solvent, in which the mass ratio of water to the alcohol organic solvent is (1-6):1.

[0102] The present application discloses in these embodiments that the mass ratio of water to the alcohol organic solvent is any one of 1:1, 2:1, 3:1, 4:1, 5:1, 6:1 or any one of the ranges of any two of the above.

[0103] In some embodiments, the water comprises pure water.

[0104] In some embodiments, the salt of the silver precursor comprises silver nitrate;

[0105] In some embodiments, the reducing agent includes any one or more of formaldehyde, ascorbic acid, potassium tartrate, hydrazine hydrate, hydrazine carbonate, and sodium hypophosphite;

[0106] In some embodiments, the protective agent includes any one or more of citric acid, PVA (polyvinyl alcohol), PEG (polyethylene glycol), PVP (polyvinyl pyrrolidone), sorbitol, gelatin, and gum arabic;

[0107] In some embodiments, the pH adjuster includes any one or more of nitric acid, sodium hydroxide, sodium bicarbonate, and ammonia water.

[0108] In some embodiments, the molar concentration of the silver precursor salt solution is 0.5 mol / L to 5 mol / L.

[0109] The present application discloses in these embodiments that the molar concentration of the salt solution of the silver precursor is any one of 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0110] In some embodiments, the molar concentration of the reducing agent solution is 0.2 mol / L to 4 mol / L.

[0111] In these embodiments, the present application discloses that the molar concentration of the reducing agent solution is any one of 0.2 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0112] In some embodiments, the molar concentration of the protective agent solution is 0.4 mol / L to 8 mol / L.

[0113] The present application discloses in these embodiments that the molar concentration of the protective agent solution is any one of 0.4 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L, 5.5 mol / L, 6.0 mol / L, 6.5 mol / L, 7.0 mol / L, 7.5 mol / L, 8.0 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0114] In some embodiments, in step (2), the pH adjuster is dispersed in water to form a solution with a molar concentration of 0.02 mol / L to 0.6 mol / L, and the pH value of the reaction system is adjusted to 2 to 7.

[0115] The present application discloses in these embodiments that the molar concentration of the aqueous solution formed by the pH adjuster is any one of 0.02 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0116] In some embodiments, in step (3), the pH adjuster is dispersed in water to form a molar concentration of 1 mol / L to 8 mol / L, and the pH value of the reaction system is adjusted to 4 to 12.

[0117] The present application discloses in these embodiments that the molar concentration of the aqueous solution formed by the pH adjuster is any one of 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0118] In some embodiments, the post-processing of the above step (4) includes: washing, filtering, separating, drying, shaping, etc. the silver powder dispersion to finally obtain silver powder.

[0119] In some embodiments, the detergent used for washing includes any one or more of ethanol and pure water.

[0120] In some embodiments, the number of washes is 2 to 4 times.

[0121] In some embodiments, the drying temperature is 50° C. to 90° C., and the drying time is 3 h to 18 h.

[0122] In some embodiments, shaping includes airflow shaping.

[0123] The second aspect of the present application is to provide a silver powder, which is prepared by the preparation method described in the first aspect;

[0124] The median particle size Dv50 of the above silver powder is 0.3 μm to 0.8 μm;

[0125] In some embodiments, the specific surface area of ​​the silver powder is 3 m 2 / g~20m 2 / g.

[0126] In some embodiments, the silver powder comprises spherical or quasi-spherical particles, and the surface of the particles has roughness.

[0127] The median particle size Dv50 in this application refers to the particle size greater than which the volume of particles accounts for 50%, and the particle size less than which the volume of particles accounts for 50%, which is also called the median diameter, or the median particle size, which is usually used to indicate the average particle size of particles. The determination method of the median particle size includes any conventional method in the art, such as the application selects to refer to the laser diffraction particle size analysis method in these embodiments, specifically refers to the standard GB / T19077-2016 to obtain the particle size distribution diagram, and then obtains it by calculation.

[0128] The present application discloses in these embodiments that the median particle size Dv50 of the silver powder is any one of 0.3μm, 0.32μm, 0.36μm, 0.4μm, 0.5μm, 0.51μm, 0.52μm, 0.53μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.8μm or any one of the values ​​within any two ranges. The specific surface area in the present application refers to the total area per unit mass of the material, and is usually used to characterize the physical performance parameter of the outer surface size of the powder material particles. It includes two types: external surface area and internal surface area, and the unit is square meter per gram (m 2 / g). The specific surface area can be determined by any conventional method in the art. For example, the present application refers to GB / T 19587-2004, adopts nitrogen adsorption specific surface area analysis test method, and calculates the specific surface area of ​​the negative electrode active material by BET (BrunauerEmmett Teller) method. The test instrument can be TRISTAR II 3020 specific surface area and porosity analyzer produced by Micromeritics, USA.

[0129] The present application discloses in these examples that the specific surface area of ​​the silver powder is 3 m 2 / g, 3.1m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 9.0m 2 / g, 10.0m 2 / g, 11.0m 2 / g, 12.0m 2 / g, 12.1m 2 / g, 13.3m 2 / g, 13.6m 2 / g, 13.8m 2 / g, 14.1m 2 / g, 14.3m 2 / g, 15.2m 2 / g, 16.0m 2 / g, 17.0m 2 / g, 18.0m 2 / g, 19.0m 2 / g, 20.0m 2 / g or any of the values ​​satisfying any two of the above ranges.

[0130] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0131] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0132] Conventional techniques of inorganic chemistry within the art can be used in this application. In the following examples, efforts are made to ensure the accuracy of the numbers used (including amounts, temperatures, reaction times, etc.), but some experimental errors and deviations should be considered. The temperatures (in degrees Celsius) used in the following examples are expressed in ° C, and the pressure is atmospheric pressure or near atmospheric pressure. All pharmaceutical reagents are purchased at AR grade, and all reactions are carried out under argon protection. Unless otherwise noted, all reagents are obtained from commercial channels.

[0133] Example 1

[0134] A method for preparing silver powder is provided, and the process flow of the preparation method is as follows Figure 1 The process includes the following:

[0135] (1) A mixed solution of pure water and pentanediol in a mass ratio of 1:1 was used as a solvent, and 0.4 L of a 2 mol / L silver nitrate solution, 0.6 L of a 1 mol / L ascorbic acid solution, and 2 L of a 0.6 mol / L PVP solution were prepared at room temperature;

[0136] (2) at room temperature, 1 / 6 of the volume of the silver nitrate solution prepared in step (1) was separated and mixed with the PVP solution in a reaction kettle, and stirred thoroughly. A 0.2 mol / L nitric acid aqueous solution was added dropwise to the mixed solution to adjust the pH of the system to 2.6;

[0137] (3) separating 1 / 2 volume of the ascorbic acid solution prepared in step (1) and quickly adding it to the mixed solution in step (2) for reduction reaction, controlling the reaction temperature of the reactor to 35° C. and the reaction time to 5 min;

[0138] (4) using a peristaltic pump to uniformly pump the remaining 5 / 6 volume of silver nitrate solution and 1 / 2 volume of ascorbic acid solution into the reaction system at the same time, the silver salt solution is added for 30 minutes, and the ascorbic acid solution is added for 15 minutes; adding 4 mol / L sodium hydroxide aqueous solution to the reactor to adjust the pH of the entire system to 10, and then adding 100 ml of ethanol solution of octanoic acid and octylamine with a theoretical weight of 0.5% of the silver powder, the reactor temperature is maintained at 35° C. and the reaction is continued for 1 hour. After the reaction is completed, a silver powder dispersion is obtained;

[0139] (5) washing the silver powder dispersion obtained in step (4) with pure water three times and filtering and separating the dispersion, then drying at 70° C. for 10 h and performing airflow shaping treatment to finally obtain submicron silver powder with a calculated yield of 98.6%;

[0140] The obtained silver powder sample was placed on the sample stage, placed in the electron microscope chamber, evacuated, turned on the electron beam, and set appropriate parameters for characterization: the parameters for observing the morphology were 10 kV, the working distance was 7.9 mm, and the obtained Figure 2A and Figure 2B, combined table Figure 2A and Figure 2B It can be seen that the surface of the prepared silver powder is in the shape of a hair ball, that is, it has a certain degree of roughness, which makes the silver powder prepared in the present application have a higher specific surface area and is also convenient for low-temperature sintering.

[0141] The silver powder of Example 1 was sintered at 160° C. for 6 min to obtain Figure 3 , combined with Figure 3 It can be seen that the sintered silver powder has a clear sintering neck, and thus the sintering performance of the silver powder is excellent.

[0142] Comparative Example 1

[0143] A method for preparing silver powder is provided. The method is different from the above-mentioned Example 1 in that, in Comparative Example 1, steps (2), (3) and (4) of Example 1 are synthesized in one step:

[0144] At room temperature, the silver nitrate solution prepared in step (1) and the PVP solution are mixed and stirred in a reactor, and then ascorbic acid solution is added. The reaction temperature of the reactor is controlled to be 35° C. After reacting for 20 minutes, the pH of the entire system is adjusted to 10 using sodium hydroxide aqueous solution. Subsequently, 100 ml of octanoic acid and octylamine ethanol solution with a theoretical weight of 0.5% of the silver powder are added simultaneously. The temperature of the reactor is maintained at 35° C. and the reaction is continued for 1 hour. After the reaction is completed, a silver powder dispersion is obtained. Other aspects are the same as those in Example 1, and the calculated yield is 97.8%.

[0145] Comparative Example 2

[0146] A method for preparing silver powder is provided. The method is different from the above-mentioned embodiment 1 in that no octanoic acid and octylamine ethanol solution are added in step (4). Other aspects are the same as those in embodiment 1. The calculated yield is 96.5%.

[0147] Example 2-1

[0148] A method for preparing silver powder is provided, which is different from that of Example 1 in that:

[0149] In step (2), 1 / 20 volume of the silver nitrate solution prepared in step (1) is separated at room temperature and mixed with the PVP solution in a reaction kettle and stirred sufficiently, and 0.2 mol / L nitric acid aqueous solution is added dropwise to the mixed solution to adjust the pH of the system to 2.6;

[0150] In step (3), 1 / 6 of the volume of the ascorbic acid solution prepared in step (1) is separated and quickly added to the mixed solution of step (2) for reduction reaction, and the reaction temperature of the reactor is controlled to be 20° C. and the reaction time is 5 min;

[0151] In step (4), the remaining silver salt solution is added dropwise for 40 minutes, and the remaining ascorbic acid solution is added dropwise for 20 minutes.

[0152] Other aspects were the same as in Example 1, and the calculated yield was 98.2%.

[0153] Example 2-2

[0154] A method for preparing silver powder is provided, which is different from that of Example 1 in that:

[0155] In step (2), 2 / 3 of the volume of the silver nitrate solution prepared in step (1) is separated and mixed with the PVP solution in a reaction kettle at room temperature, and 0.2 mol / L nitric acid aqueous solution is added dropwise to the mixed solution to adjust the pH of the system to 2.6;

[0156] In step (3), 2 / 3 of the volume of the ascorbic acid solution prepared in step (1) is separated and quickly added to the mixed solution of step (2) for reduction reaction, and the reaction temperature of the reactor is controlled to be 50° C. and the reaction time is 10 min;

[0157] In step (4), the remaining silver salt solution is added dropwise for 20 minutes, and the remaining ascorbic acid solution is added dropwise for 10 minutes.

[0158] Other aspects were the same as in Example 1, and the calculated yield was 97.6%.

[0159] Example 3-1

[0160] Provided is a method for preparing silver powder, which is different from that of Example 1 in that: in step (1), a mixed solution of pure water and pentanediol in a mass ratio of 1:6 is used as a solvent, 0.4 L of a 0.5 mol / L silver nitrate solution, 0.6 L of a 0.2 mol / L ascorbic acid solution, and 2 L of a 0.4 mol / L PVP solution are prepared at room temperature;

[0161] In step (4), an ethanol solution of oleic acid and octylamine at a concentration of 0.1% of the theoretical weight of the silver powder is added.

[0162] Other aspects were the same as in Example 1, and the calculated yield was 97.9%.

[0163] Example 3-2

[0164] Provided is a method for preparing silver powder, which is different from that of Example 1 in that: in step (1), a mixed solution of pure water and pentanediol in a mass ratio of 1:6 is used as a solvent, 0.4 L of a 5 mol / L silver nitrate solution, 0.6 L of a 4 mol / L ascorbic acid solution, and 2 L of an 8 mol / L PVP solution are prepared at room temperature;

[0165] In step (4), an ethanol solution of citric acid and octadecylamine at a concentration of 2% of the theoretical mass of the silver powder is added.

[0166] Other aspects were the same as in Example 1, and the calculated yield was 96.8%.

[0167] Example 3-3

[0168] A method for preparing silver powder is provided. The method is different from that in Example 1 in that: in step (4), 0.5% of the theoretical mass of the silver powder is added with malic acid.

[0169] Other aspects were the same as those in Example 1, and the calculated yield was 97.8%.

[0170] Embodiment 3-4

[0171] A method for preparing silver powder is provided. The method is different from that in Example 1 in that: in step (4), 0.5% of the theoretical mass of the silver powder is added with triethanolamine.

[0172] Other aspects were the same as in Example 1, and the calculated yield was 98.1%.

[0173] Test Case

[0174] (1) Median particle size of silver powder: refer to standard GB / T19077-2016 for details.

[0175] (2) Specific surface area of ​​silver powder: refer to GB / T 19587-2004.

[0176] (3) Sintering: 90 wt% silver powder and 10 wt% BCA (solvent ethylene glycol butyl ether acetate) are mixed, stirred, and ground evenly, and then evenly coated on a high-temperature resistant film and placed in a sintering furnace for sintering.

[0177] Table 1 Properties of the silver powder obtained in the examples and comparative examples

[0178]

[0179] In combination with the above embodiments and comparative examples, it can be seen that the preparation process provided in the present application has a great influence on the specific surface area and sintering activity of the silver powder. Specifically, in combination with Example 1 and Comparative Example 1, it can be seen that the present application adds the reaction raw materials step by step, which is conducive to generating silver powder with a rough surface.

[0180] Combining Example 1 and Example 3-1 to Example 3-4, it can be seen that the type and amount of the surface treatment agent added have an impact on the sintering activity of the silver powder.

[0181] Therefore, the present application obtains a product with high specific surface area and good sintering properties in a low temperature environment by adjusting the preparation process.

[0182] The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for a person skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

[0183] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0184] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0185] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0186] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing silver powder, characterized in that: The preparation process includes the following: (1) preparing reaction raw materials: respectively preparing a salt solution of a silver precursor, a reducing agent solution, a protective agent solution and a pH adjusting agent of a certain concentration; (2) premixing: mixing a portion of the salt solution of the silver precursor with the protective agent solution, adding a pH adjuster until the system reaches a certain pH value, and obtaining a mixed solution; (3) Reduction reaction: adding a portion of the reducing agent solution to the mixed solution of step (2), and performing a first reduction reaction to obtain a mixture; Adding the remaining solution of the silver precursor salt solution and the remaining solution of the reducing agent solution to the mixture, adding a pH adjuster until the system reaches a certain pH value, adding a surface treatment agent and continuing the reaction to obtain a silver powder dispersion; (4) Post-treatment: The silver powder dispersion is post-treated to obtain silver powder.

2. The preparation method according to claim 1, characterized in that: In the salt solution of the silver precursor in step (2), the volume of the partial solution is 1 / 20 to 2 / 3 of the volume of the salt solution of the silver precursor.

3. The preparation method according to any one of claims 1 to 2, characterized in that: In the reducing agent solution of step (3), the volume of the partial solution is 1 / 6 to 2 / 3 of the volume of the reducing agent solution.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In the step (3), the remaining portion of the silver precursor salt solution and the remaining portion of the reducing agent solution are added to the mixture simultaneously; The remaining portion of the silver precursor salt solution is added at a time t1; The time for adding the remaining part of the reducing agent solution is t2; Satisfy t1:t2=1.5~2:1; Preferably, the t1 is 10 min to 40 min.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The surface treatment agent includes any one or more of an organic acid or an organic amine; and / or; The added amount of the surface treatment agent is 0.1% to 2% of the theoretical mass of the silver powder; and / or; The organic acid includes any one or more of oleic acid, caprylic acid, linoleic acid, linolenic acid, ascorbic acid, malic acid, citric acid, formic acid, adipic acid, lauric acid, palmitic acid, and stearic acid; and / or; The organic amine includes any one or more of octylamine, oleylamine, triethanolamine, hexadecylamine and octadecylamine.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step (3), The temperature of the first reduction reaction is 15°C to 50°C, and the time is no more than 10 minutes; and / or; The temperature for continuing the reaction after adding the surface treatment agent is 20° C. to 40° C., and the reaction time is 30 min to 90 min.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The silver precursor salt solution comprises a silver precursor salt and a solvent; The reducing agent solution comprises a reducing agent and a solvent; The protective agent solution comprises a protective agent and a solvent; The solvent includes any one or more of water and organic solvent.

8. The preparation method according to claim 7, characterized in that: The salt of the silver precursor includes silver nitrate; and / or; The reducing agent includes any one or more of formaldehyde, ascorbic acid, potassium tartrate, hydrazine hydrate, hydrazine carbonate, and sodium hypophosphite; and / or; The protective agent includes any one or more of citric acid, PVA, PEG, PVP, sorbitol, gelatin, and gum arabic; and / or; The pH adjuster includes any one or more of nitric acid, sodium hydroxide, sodium bicarbonate, and ammonia water.

9. A silver powder, characterized in that: The silver powder is prepared by the preparation method described in any one of claims 1 to 8; The median particle size Dv50 of the silver powder is 0.3 μm to 0.8 μm; and / or; The specific surface area of ​​the silver powder is 3 m 2 / g~20m 2 / g; and / or; The silver powder includes spherical or quasi-spherical particles, and the surface of the particles has roughness.

10. Use of the silver powder obtained by the preparation method according to any one of claims 1 to 8 or the silver powder according to claim 9 in a photovoltaic cell.

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