Active silver powder and preparation method and application thereof

Abstract

The invention relates to silver powder, and particularly discloses active silver powder and a preparation method and application thereof. The silver powder prepared by the preparation method provided by the invention has high sintering activity and strong chemical stability, and can meet the requirements of the field of low-temperature slurry in photovoltaic cells on high-reliability and high-performance new materials.

Description

Technical Field

[0001] The present application relates to a silver powder, and in particular to an active silver powder and a preparation method 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 an active silver powder and a preparation method and application thereof. The silver powder prepared by the preparation method has high sintering activity and strong chemical stability.

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

[0007] (1) adding a reducing agent to a mixed solution containing a silver precursor and a protective agent to prepare a silver suspension;

[0008] (2) adding a reducing agent and a silver precursor to the above silver suspension to react and obtain an unactivated silver powder;

[0009] (3) placing the unactivated silver powder in a heating furnace with a reducing atmosphere, and activating the unactivated silver powder to obtain activated silver powder.

[0010] In some embodiments, in step (3), the pressure of the reducing atmosphere in the heating furnace is 0.01 MPa to 0.15 MPa;

[0011] and / or;

[0012] The temperature in the heating furnace is 25°C to 120°C;

[0013] and / or;

[0014] The activation treatment time is 10 to 100 minutes.

[0015] and / or;

[0016] The above-mentioned reducing atmosphere includes hydrogen.

[0017] In some embodiments, in step (3), the unactivated silver powder is placed in a heating furnace, and the heating furnace is evacuated to an internal pressure of less than 1×10 -3 Pa.

[0018] In some embodiments, the molar ratio between the silver precursor in step (1) and the silver precursor in step (2) is 1:(0-100);

[0019] and / or;

[0020] The molar ratio between the reducing agent in the above step (1) and the reducing agent in the step (2) is (0.1-1):(0.5-2).

[0021] In some embodiments, the above step (1) includes:

[0022] Prepare a solution: disperse a silver precursor, a first reducing agent, a second reducing agent, a first pH adjusting agent, a second pH adjusting agent, and a protective agent in a solvent to form a silver precursor solution, a first reducing agent solution, a second reducing agent solution, a first pH adjusting agent solution, a second pH adjusting agent solution, and a protective agent solution, respectively; separate the silver precursor solution into a silver precursor A solution and a silver precursor B solution; the molar ratio of the silver precursor A solution to the silver precursor B solution is 1:(1-100);

[0023] Premixing: adding a silver precursor A solution to a protective agent solution, and then adding a first pH adjusting agent solution until the system reaches a certain pH value, to obtain a mixed solution containing a silver precursor and a protective agent;

[0024] A first reducing agent solution is added to the mixed solution to obtain a silver suspension.

[0025] In some embodiments, the above step (2) includes:

[0026] A second pH adjusting agent solution is added to the above silver suspension until the system reaches a certain pH value, and the second reducing agent solution is continuously added. After mixing, the above silver precursor B solution is added to react to obtain unactivated silver powder.

[0027] In some embodiments, in the above-mentioned configuration solution, the molar ratio between the above-mentioned silver precursor, the first reducing agent, the second reducing agent and the protective agent is 1:(0.1-1):(0.5-2):(0.1-2);

[0028] The silver precursor includes any one or more of silver nitrate and silver acetate;

[0029] and / or;

[0030] The first reducing agent includes any one or more of formaldehyde, ascorbic acid, hydrazine hydrate, and sodium hypophosphite;

[0031] and / or;

[0032] The second reducing agent includes any one or more of ascorbic acid, potassium tartrate, hydrazine hydrate, and glucose;

[0033] and / or;

[0034] The protective agent includes any one or more of PVA, PVP, sodium citrate, gelatin, gum arabic, BTA, PEG, and SDBS;

[0035] and / or;

[0036] The first pH adjuster includes any one or more of sodium hydroxide, potassium hydroxide, ammonia water, nitric acid, hydrochloric acid, acetic acid, and sulfuric acid;

[0037] and / or;

[0038] The second pH adjuster includes any one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

[0039] In some embodiments, the solvent includes any one or more of water and alcohol organic solvents;

[0040] Preferably, the alcohol organic solvent includes any one or more of ethanol, ethylene glycol, and glycerol;

[0041] Preferably, the solvent comprises water and an alcohol organic solvent, and the mass ratio of the water to the alcohol organic solvent is (0.5-4):1.

[0042] The second aspect of the present application is to provide an active silver powder, which is prepared by the preparation method described in the first aspect;

[0043] The median particle size D50 of the active silver powder is 80 nm to 800 nm.

[0044] 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.

[0045] Beneficial technical effects of this application:

[0046] (1) The preparation method provided in the present application crushes and refines the silver powder particles prepared by the liquid phase reduction method and reorganizes the crystal surface, thereby breaking up the soft aggregation of the silver powder particle clusters, and automatically dehydrogenating and resisting oxidation during the sintering process, thereby achieving the technical purpose of improving the sintering activity.

[0047] (2) The silver powder provided in this application has excellent sintering activity and strong chemical stability, which can effectively solve the problem that the silver powder is easy to agglomerate and oxidize, and can meet the demand for high-reliability and high-performance new materials in the field of low-temperature slurries for photovoltaic cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a process flow chart for preparing silver powder in some embodiments of this application;

[0049] Figure 2A Scanning electron microscope (SEM) images of silver powder obtained in some examples of this application;

[0050] Figure 2B Scanning electron microscope (SEM) images of sintered silver powder obtained for some examples of this application;

[0051] Figure 2C X-ray diffraction patterns (XRD) of silver powders obtained for some examples of this application;

[0052] Figure 2D The particle size distribution diagram of the silver powder obtained in some embodiments of the present application;

[0053] Figure 3A Scanning electron microscope (SEM) images of silver powder obtained for some comparative examples of this application;

[0054] Figure 3B Scanning electron microscope (SEM) images of silver powder after sintering obtained for some comparative examples of this application;

[0055] Figure 3C X-ray diffraction pattern (XRD) of silver powder obtained for some comparative examples of this application;

[0056] Figure 3D This is the particle size distribution diagram of the silver powder obtained in some comparative examples of this application. DETAILED DESCRIPTION

[0057] 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.

[0058] 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.

[0059] Unless expressly stated to the contrary, all ranges cited herein are inclusive.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] With the rapid development of the photovoltaic industry, the performance requirements for electronic pastes are becoming higher and higher. For example, HJT batteries require that the process temperature must not exceed 200°C, and the process temperature of crystalline silicon-perovskite stacked batteries is further reduced to below 130°C. Among them, silver powder needs to have a lower sintering temperature and better reliability. Nano silver powder has size effects, surface and interface effects, quantum tunneling effects, etc., which make nano silver powder show a trend of high diffusion sintering driving force and significantly reduced melting point. At the same time, due to its high surface energy and low chemical reaction energy barrier, nano powders are prone to agglomeration or oxidation problems, which affect the conductivity, density and porosity of the film layer after sintering, and reduce the reliability and service life of functional devices. Low-temperature silver paste technology below 130°C for stacked batteries is still blank worldwide. The balance between the intrinsic properties of nano silver powder and sintering activity is the main reason restricting its development.

[0067] In order to solve the above technical problems, the present application provides a method for preparing active silver powder, which comprises the following preparation process:

[0068] (1) adding a reducing agent to a mixed solution containing a silver precursor and a protective agent to prepare a silver suspension;

[0069] (2) adding a reducing agent and a silver precursor to the above silver suspension to react and obtain an unactivated silver powder;

[0070] (3) placing the unactivated silver powder in a heating furnace with a reducing atmosphere, and activating the unactivated silver powder to obtain activated silver powder.

[0071] The present application adopts a liquid phase chemical reduction method to prepare silver powder. Specifically, the growth rate of silver particles is controlled by a seed crystal method during the growth of the metal, and the size, morphology and microstructure of the particles are precisely regulated. The silver powder agglomerates are further broken and the grains are refined by hydrogen explosion crushing. A small amount of hydrogen atoms permeate the surface lattice of the grains, which reduces the oxygen content and increases the driving force for powder sintering, thereby efficiently realizing the preparation of high-activity silver powder for low-temperature slurry.

[0072] In some embodiments, in step (3), the pressure of the reducing atmosphere in the heating furnace is 0.01 MPa to 0.15 MPa.

[0073] In these embodiments, the present application discloses that the pressure of the reducing atmosphere in the heating furnace in step (3) is any one of 0.01 MPa, 0.02 MPa, 0.03 MPa, 0.04 MPa, 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.10 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, and 0.15 MPa, or any one of the ranges satisfying any two of the above ranges.

[0074] In some embodiments, the temperature in the heating furnace is 25°C to 120°C.

[0075] In these embodiments, the present application discloses that the temperature in the heating furnace in step (3) is any one of 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or any one of any two ranges mentioned above.

[0076] In some embodiments, the activation treatment time is 10 min to 100 min.

[0077] In these embodiments, the present application discloses that the time for the activation treatment in step (3) is any one of 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min or any one of the ranges satisfying any two of the above ranges.

[0078] In some embodiments, the reducing atmosphere includes hydrogen. The present application only schematically lists the reducing atmosphere including hydrogen, and in fact, it may also include other reducing gases.

[0079] In some embodiments, in step (3), the unactivated silver powder is placed in a heating furnace, and the heating furnace is evacuated to an internal pressure of less than 1×10 -3 Pa.

[0080] In some embodiments, the molar ratio of the silver precursor in step (1) to the silver precursor in step (2) is 1:(0-100).

[0081] The present application discloses in these embodiments that the molar ratio between the silver precursor in the above step (1) and the silver precursor in the step (2) is 1:0, that is, the silver precursor is added in the step (1) and the silver precursor is not added in the step (2). This design method is convenient for preparing silver powder in one step.

[0082] In these embodiments, the present application discloses that the molar ratio between the reducing agent in the above step (1) and the reducing agent in the step (2) is any one of 0.1:0.5, 0.1:1, 0.1:1.5, 0.1:2, 0.5:1, 0.5:1.5, 0.5:2, 1:0.5, 1:1, 1:1.5 or any one of the above two ranges.

[0083] In some embodiments, the above step (1) includes:

[0084] Prepare a solution: disperse a silver precursor, a first reducing agent, a second reducing agent, a first pH adjusting agent, a second pH adjusting agent, and a protective agent in a solvent to form a silver precursor solution, a first reducing agent solution, a second reducing agent solution, a first pH adjusting agent solution, a second pH adjusting agent solution, and a protective agent solution, respectively; separate the silver precursor solution into a silver precursor A solution and a silver precursor B solution; the molar ratio of the silver precursor A solution to the silver precursor B solution is 1:(1-100);

[0085] Premixing: adding a silver precursor A solution to a protective agent solution, and then adding a first pH adjusting agent solution until the system reaches a certain pH value, to obtain a mixed solution containing a silver precursor and a protective agent;

[0086] A first reducing agent solution is added to the mixed solution to obtain a silver suspension.

[0087] In some embodiments, in the premixing of step (1), the silver precursor A solution is added to the protective agent solution at a certain stirring speed. The present application discloses in these embodiments that the stirring speed is 200 r / min to 500 r / min.

[0088] The present application discloses in these embodiments that in the premixing of step (1), the stirring speed is any one of 200 r / min, 300 r / min, 400 r / min, 500 r / min or any one of the values ​​within the range of any two of the above.

[0089] In some embodiments, in the premixing of step (1), the silver precursor A solution is added to the protective agent solution, and then the first pH adjuster solution is added until the system reaches a pH of 3-12.

[0090] The present application discloses in these embodiments that, in the premixing of step (1), a first pH adjusting agent solution is added until the system reaches pH=3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12 or any one of the values ​​in the range of any two of the above.

[0091] In some embodiments, in the premixing of step (1), the first reducing agent solution is added to the mixed solution at a certain stirring speed and set temperature, and the mixture is stirred for a certain period of time to obtain a silver suspension. The present application discloses in these embodiments that the stirring speed is 200 r / min to 800 r / min, the set temperature is 10° C. to 50° C., the addition speed of the first reducing agent solution is 1 mL / min to 1000 mL / min, and the stirring is 5 min to 30 min.

[0092] The present application discloses in these embodiments that in the premixing of step (1), the stirring speed is any one of 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min or any one of the ranges satisfying any two of the above values.

[0093] The present application discloses in these embodiments that in the premixing of step (1), the temperature is set to any one of 10°C, 20°C, 30°C, 40°C, 50°C or any one of the values ​​within the range of any two of the above.

[0094] The present application discloses in these embodiments that in the premixing of step (1), the addition rate of the first reducing agent solution is any one of 1 mL / min, 5 mL / min, 10 mL / min, 50 mL / min, 100 mL / min, 500 mL / min, 1000 mL / min or any one of the ranges of any two of the above.

[0095] The present application discloses in these embodiments that in the premixing of step (1), the first reducing agent solution is added and stirred for any one of 5 min, 10 min, 15 min, 20 min, 25 min, 30 min or any one of the ranges of any two of the above.

[0096] In these embodiments, the present application discloses that the molar ratio between the silver precursor A solution and the silver precursor B solution is any one of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100 or any one of the ranges satisfying any two of the above.

[0097] In some embodiments, the above step (2) includes:

[0098] A second pH adjusting agent solution is added to the above silver suspension until the system reaches a certain pH value, and the second reducing agent solution is continuously added. After mixing, the above silver precursor B solution is added to react to obtain unactivated silver powder.

[0099] In some embodiments, in step (2), a second pH adjuster solution is added to the above silver suspension until the pH of the system is 3-8.

[0100] The present application discloses in these embodiments that, in step (2), a second pH adjusting agent solution is added to the above silver suspension until the system pH is any one of 3, 4, 5, 6, 7, 8 or any one of the values ​​within the range of any two of the above.

[0101] In some embodiments, in step (2), a second pH adjusting agent solution is added to the above silver suspension until the system reaches a certain pH value, stirred for a period of time, and the above silver precursor B solution is poured or dripped at a certain speed at a certain stirring speed and set temperature, and the pH value of the reaction system is controlled by adding the second pH adjusting agent solution, so that a heterogeneous reaction occurs and the reaction continues for a period of time to obtain a silver powder wet powder. The present application discloses in these embodiments that the stirring speed is 200r / min to 800r / min, the addition speed of the silver precursor B solution is 5mL / min to 100mL / min, the pH value of the reaction system is controlled to be 1 to 10 by adding the second pH adjusting agent solution, and the heterogeneous reaction time is 15min to 120min.

[0102] The present application discloses in these embodiments that in step (2), the stirring speed is any one of 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min or any one of the ranges of any two of the above.

[0103] The present application discloses in these embodiments that in step (2), the addition rate of the silver precursor B solution is 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, 80 mL / min, 85 mL / min, 90 mL / min, 95 mL / min, 100 mL / min or any one of the ranges satisfying any two of the above values.

[0104] The present application discloses in these embodiments that, in step (2), a second pH adjusting agent solution is added to control the pH value of the reaction system to any one of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any one of the values ​​within any two ranges mentioned above.

[0105] The present application discloses in these embodiments that the heterogeneous reaction time in step (2) is any one of 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min, and 120 min, or any one of the ranges satisfying any two of the above values.

[0106] In some embodiments, after completing the above step (2) and before performing the above step (3), the unactivated silver powder obtained in step (2) is post-treated, and the post-treatment includes centrifugal separation, washing and drying. The washing includes washing 3 to 4 times with any one or more of ethanol, acetone or deionized water. The drying is vacuum drying, and the vacuum drying includes controlling the temperature at 40°C to 90°C and drying for 3h to 10h.

[0107] In some embodiments, the above step (3) includes laying the unactivated silver powder prepared in step (2) flat in a material preparation box, placing it in a vacuum tube heat treatment furnace and evacuating it to a high vacuum, setting the target temperature and hydrogen pressure of the tube furnace, heating the powder with the furnace, and filling it with hydrogen to the target hydrogen pressure to ensure that the hydrogen absorption process is fully carried out under a constant hydrogen pressure. After heating, keep the temperature for a certain period of time to absorb hydrogen, evacuate, discharge hydrogen, cool the furnace charge to room temperature, open the furnace to discharge the charge, and collect the activated silver powder. The present application discloses in these embodiments that after heating, keep the temperature for a certain period of time to absorb hydrogen, evacuate to <1×10 -3 Pa, discharge hydrogen.

[0108] In some embodiments, in the above-mentioned solution, the molar ratio of the silver precursor, the first reducing agent, the second reducing agent and the protective agent is 1:(0.1-1):(0.5-2):(0.1-2).

[0109] The present application discloses in these embodiments that the molar ratios of the silver precursor, the first reducing agent, the second reducing agent and the protecting agent are 1:0.1:0.5:0.1, 1:0.5:0.5:0.1, 1:1:0.5:0.1, 1:0.1:1:0.1, 1:0.1:2:0.1, 1:0.5:1:0.1, 1:0.5:2:0.1, 1:1:1:0.1, 1:1:2:0.1, 1:0.1:0.5:0.5, 1:0.5:0.5:0.5, 1:1:0.5:0.5 Any one of the following: :0.5, 1:0.1:1:0.5, 1:0.1:2:0.5, 1:0.5:1:0.5, 1:0.5:2:0.5, 1:1:1:0.5, 1:1:2:0.5, 1:0.1:0.5:2, 1:0.5:0.5:2, 1:1:0.5:2, 1:0.1:1:2, 1:0.1:2:2, 1:0.5:1:2, 1:0.5:2:2, 1:1:1:2, 1:1:2:2, or any one of the values ​​satisfying any two of the above ranges.

[0110] In some embodiments, the silver precursor includes any one or more of silver nitrate and silver acetate.

[0111] In some embodiments, the first reducing agent includes any one or more of formaldehyde, ascorbic acid, hydrazine hydrate, and sodium hypophosphite.

[0112] In some embodiments, the second reducing agent includes any one or more of ascorbic acid, potassium tartrate, hydrazine hydrate, and glucose.

[0113] In some embodiments, the protective agent includes any one or more of PVA (polyvinyl alcohol), PVP (polyvinyl pyrrolidone), sodium citrate, gelatin, gum arabic, BTA (benzotriazole), PEG (polyethylene glycol), SDBS (sodium dodecylbenzene sulfonate)

[0114] In some embodiments, the first pH adjuster includes any one or more of sodium hydroxide, potassium hydroxide, ammonia water, nitric acid, hydrochloric acid, acetic acid, and sulfuric acid.

[0115] In some embodiments, the second pH adjuster includes any one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

[0116] In some embodiments, the solvent includes any one or more of water and alcohol organic solvents.

[0117] In some embodiments, the alcohol organic solvent includes any one or more of ethanol, ethylene glycol, and glycerol.

[0118] In some embodiments, the solvent includes water and an alcohol organic solvent, and the mass ratio of the water to the alcohol organic solvent is (0.5-4):1.

[0119] In these embodiments, the present application discloses that the above-mentioned solvent includes water and an alcohol organic solvent, and the mass ratio of the above-mentioned water to the above-mentioned alcohol organic solvent is any one of 0.5:1, 1:1, 2:1, 3:1, 4:1 or any one of the above-mentioned ranges of any two.

[0120] In some embodiments, the concentration of the silver precursor solution in step (1) above is 0.1 mol / L to 4 mol / L.

[0121] The present application discloses in these embodiments that the concentration of the silver precursor solution in the above step (1) is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 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, 4.0 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0122] In some embodiments, the concentrations of the first reducing agent and the second reducing agent in step (1) above are independently selected from 0.2 mol / L to 6 mol / L.

[0123] The present application discloses in these embodiments that the concentrations of the first reducing agent and the second reducing agent in the above step (1) are independently selected from 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, 4.5 mol / L, 5.0 mol / L, 5.5 mol / L, 6.0 mol / L or any one of the values ​​satisfying any two of the above ranges.

[0124] In some embodiments, the concentration of the first pH adjuster is 0.02 mol / L to 1 mol / L.

[0125] In these embodiments, the present application discloses that the concentration of the first pH adjuster is any one of 0.02 mol / L, 0.03 mol / L, 0.04 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, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1.0 mol / L, or any one of the values ​​satisfying any two of the above ranges.

[0126] In some embodiments, the concentration of the second pH adjuster is 0.1 mol / L to 5 mol / L.

[0127] The present application discloses in these embodiments that the concentration of the second pH adjuster is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L,

[0128] Any one of 1.5mol / L, 2.0mol / L, 2.5mol / L, 3.0mol / L, 3.5mol / L, 4.0mol / L, 4.5mol / L, 5.0mol / L or any one of the values ​​satisfying any two of the above ranges.

[0129] In some embodiments, the concentration of the protective agent solution is 0.1 mol / L to 4 mol / L.

[0130] The present application discloses in these embodiments that the concentration of the protective agent solution is 0.1 mol / L, 0.2 mol / L, 0.3 mol / L,

[0131] 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L,

[0132] 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L,

[0133] 2.0mol / L, 2.1mol / L, 2.2mol / L, 2.3mol / L, 2.4mol / L, 2.5mol / L, 2.6mol / L, 2.7mol / L,

[0134] 2.8mol / L, 2.9mol / L, 3.0mol / L, 3.1mol / L, 3.2mol / L, 3.3mol / L, 3.4mol / L, 3.5mol / L,

[0135] Any one of 3.6mol / L, 3.7mol / L, 3.8mol / L, 3.9mol / L, 4.0mol / L or any one of the values ​​satisfying any two of the above ranges.

[0136] The second aspect of the present application is to provide an active silver powder, which is prepared by the preparation method described in the first aspect;

[0137] The median particle size D50 of the active silver powder is 80 nm to 800 nm.

[0138] The median particle size D50 in this application refers to the number of particles with a particle size greater than it accounting for 50%, and the number of particles with a particle size less than it also accounting for 50%, which is also called the median diameter, or the median particle size, and is usually used to represent the average particle size of the 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 a particle size distribution diagram, and then obtains it by calculation.

[0139] In these embodiments, the present application discloses that the median particle size D50 of the active silver powder is any one of 80nm, 90nm, 100nm, 120nm, 185nm, 200nm, 220nm, 286nm, 300nm, 311nm, 400nm, 500nm, 525nm, 600nm, 700nm, and 800nm, or any one of the values ​​satisfying any two of the above ranges.

[0140] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0141] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0142] 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.

[0143] Example 1

[0144] A method for preparing active silver powder is provided, wherein the flow chart of the preparation method is shown in the accompanying drawing of the specification Figure 1 Hint.

[0145] The preparation method comprises the following preparation process:

[0146] (1) Take 50g (0.2943mol) silver nitrate, 4g (0.0317mol) sodium hypophosphite, 42g (0.2385mol)

[0147] Ascorbic acid and 33 g (0.3 mol) PVP were dispersed and dissolved in 500 mL pure water, and 6 mL concentrated nitric acid and 8

[0148] g of sodium hydroxide were dispersed and dissolved in 100 mL of pure water to obtain silver nitrate solution, sodium hypophosphite solution, ascorbic acid solution, PVP solution, nitric acid solution and sodium hydroxide solution respectively; (2) 5 mL of silver nitrate solution was added to the PVP solution at a stirring speed of 500 rpm, and the pH of the reaction environment of the system was maintained at 3 by dropping the nitric acid solution;

[0149] (3) adding sodium hypophosphite solution to the mixed solution of step (2) at the same stirring speed and room temperature, with a pouring speed of 1000 mL / min, and stirring for 10 min to obtain a silver suspension;

[0150] (4) Adding sodium hydroxide solution to the suspension prepared in step (3) to maintain the pH of the reaction environment at 4.

[0151] (5) adding ascorbic acid solution to the solution obtained in step (4), stirring evenly, pouring or dropping 495 mL of silver nitrate solution at a rate of 10 mL / min at room temperature with a stirring speed of 800 rpm, and controlling the pH value of the reaction system to 4 by adding sodium hydroxide solution, so that a heterogeneous reaction occurs and the reaction is continued for 40 min to obtain wet silver powder.

[0152] (6) The wet powder obtained in step (5) is subjected to static sedimentation separation, and is dried in a vacuum drying oven at 60° C. for 5 h to obtain a silver dry powder.

[0153] (7) The silver powder prepared in step (6) is spread flat in a material preparation box and placed in a vacuum tube heat treatment furnace and evacuated to <1×10 -3 Pa. Set the target temperature of the tube furnace to 80°C, set the hydrogen pressure to 0.1MPa, heat the powder with the furnace, and fill it with hydrogen to the target hydrogen pressure.

[0154] (8) After heating, keep the temperature to absorb hydrogen for 30 minutes, evacuate, discharge hydrogen, cool the charge to room temperature, open the furnace to discharge the charge, collect the high-activity silver powder, place the obtained silver powder sample on the sample table, put it into the electron microscope chamber, evacuate, turn on the electron beam, and set appropriate parameters for characterization: the parameters for observing the morphology are 15 kV and the working distance is 10.1 mm. The powder morphology is shown in the figure. Figure 2A As shown, combined Figure 2A It can be seen that the silver powder prepared in the present application includes spherical or quasi-spherical microscopic morphology. At the same time, flaky silver powder can also be observed in the field of view of the electron microscope, but the overall particle size distribution of the silver powder is relatively uniform.

[0155] (9) The prepared high-activity silver powder was dissolved in 10 g of ethylene glycol solution and sintered in a reflux furnace at 130° C. for 6 min to obtain sintered silver powder. The sintered silver powder was placed on a sample stage, placed in an electron microscope chamber, evacuated, turned on the electron beam, and set appropriate parameters for characterization: the parameters for observing the morphology were 20 kV and the working distance was 10.6 mm. The powder morphology is shown in the figure. Figure 2B As shown in FIG. 2 , it can be seen that the silver powder prepared in the present application has an obvious sintering neck after sintering, and the sintered film layer has good density, which indicates that the silver powder prepared in the present application is completely sintered and diffused under low temperature environment, that is, the sintering property is good, which directly proves that the silver powder prepared in the present application has good sintering activity.

[0156] (10) The present application conducted an X-ray diffraction analysis on the silver powder before sintering, wherein the radiation source was Cu-Ka and the wavelength was The working voltage was 40 kV, the scanning range was 10°~80°, and the scanning speed was 6° / min. Figure 2C .

[0157] (11) The present application conducted a particle size distribution test on the silver powder before sintering, and obtained Figure 2D , combined with Figure 2D It can be seen that the silver powder prepared in this embodiment has D50=311nm, D90=724nm, and D10=66nm, so the silver powder has good dispersibility.

[0158] Comparative Example 1

[0159] A method for preparing active silver powder is provided. The difference between the preparation method and Example 1 is that steps (7) and (8) are omitted, and the rest are the same as Example 1. The powder morphology of the obtained silver powder is as follows: Figure 3A shown.

[0160] The silver powder prepared in this comparative example was dissolved in 10 g of ethylene glycol solution and sintered in a reflow furnace at 130° C. for 6 min. The sintered morphology is shown in FIG. Figure 3B As shown, combined Figure 3A , Figure 3BIt can be seen that the silver powder prepared by the preparation method provided in Comparative Example 1 was sintered at 130° C. for 6 minutes without sintering.

[0161] The present application adopts the above test method to obtain the X-ray diffraction analysis diagram of the comparative silver powder. Figure 3C , combined with Figure 2C and Figure 3C It can be seen that the design method provided in the present application adjusts the lattice on the surface of the powder. This is because a small amount of hydrogen atoms are inserted between the lattices, which expands the lattice spacing and shifts the diffraction peak to the left. At the same time, the diffraction peak height decreases and the atomic order decreases, which is beneficial to further improve the sintering diffusion driving force of the powder.

[0162] The silver powder of Comparative Example 1 was further tested for particle size, and the results were Figure 3D , combined with Figure 3D It can be seen that the D50 of the silver powder is 1253 nm. Compared with the particle size of the silver powder in the embodiment of the present application, the particle size of the silver powder in the comparative example is significantly increased, thereby indicating that the powder in the comparative example has undergone serious agglomeration during the post-treatment process.

[0163] Example 2-1

[0164] A method for preparing active silver powder is provided, which is different from that of Example 1 in that:

[0165] In step (2), 200 mL of silver nitrate solution was added to the PVP solution at a stirring speed of 500 rpm, and the pH of the reaction environment of the system was maintained at 2.6 by dropwise addition of nitric acid solution;

[0166] In step (5), add ascorbic acid solution to the solution obtained in step (4), stir evenly, pour or drop 300 mL of silver nitrate solution at a rate of 10 mL / min at room temperature with a stirring speed of 800 rpm, control the pH value of the reaction system to 7 by adding sodium hydroxide solution, make it undergo heterogeneous reaction and continue the reaction for 30 minutes to obtain wet silver powder.

[0167] Other aspects are the same as those in Example 1.

[0168] Example 2-2

[0169] A method for preparing active silver powder is provided, which is different from that of Example 1 in that:

[0170] In step (2), 400 mL of silver nitrate solution was added to the PVP solution at a stirring speed of 500 rpm, and the pH of the reaction environment of the system was maintained at 3 by dropwise addition of nitric acid solution;

[0171] In step (5), an ascorbic acid solution is added to the solution obtained in step (4), and the mixture is stirred evenly. At a stirring speed of 800 rpm and room temperature, 100 mL of a silver nitrate solution is poured or added dropwise at a rate of 10 mL / min. The pH value of the reaction system is controlled to be 5 by adding a sodium hydroxide solution, so that a heterogeneous reaction occurs and the reaction is continued for 30 minutes to obtain wet silver powder.

[0172] Other aspects are the same as those in Example 1.

[0173] Example 2-3

[0174] Provides an active

[0175] The preparation method of silver powder is different from that of Example 1 in that:

[0176] In step (2), 500 mL of silver nitrate solution was added to the PVP solution at a stirring speed of 500 rpm, and the pH of the reaction environment of the system was maintained at 2.2 by dropwise addition of nitric acid solution;

[0177] 3) adding sodium hypophosphite solution to the mixed solution of step (2) at the same stirring speed and room temperature, with a pouring speed of 1000 mL / min, and stirring for 10 min to obtain a silver suspension;

[0178] (4) Adding sodium hydroxide solution to the suspension prepared in step (3) to maintain the pH of the reaction environment at 4.

[0179] (5) adding ascorbic acid solution to the solution obtained in step (4), stirring evenly, stirring evenly at a stirring speed of 800 rpm and room temperature, and controlling the pH value of the reaction system to 4 by adding sodium hydroxide solution to cause a heterogeneous reaction and continue the reaction for 40 minutes to obtain wet silver powder.

[0180] Other aspects are the same as those in Example 1.

[0181] Example 3-1

[0182] A method for preparing active silver powder is provided, which is different from that of Example 1 in that:

[0183] (7) The silver powder prepared in step (6) is spread flat in a material preparation box and placed in a vacuum tube heat treatment furnace and evacuated to <1×10 -3 Pa. Set the target temperature of the tube furnace to 120°C, set the hydrogen pressure to 0.15MPa, heat the powder with the furnace, and fill it with hydrogen to the target hydrogen pressure.

[0184] (8) After heating, keep the temperature to absorb hydrogen for 10 minutes, evacuate the furnace, discharge the hydrogen, cool the furnace charge to room temperature, open the furnace to discharge the charge, and collect the high-activity silver powder.

[0185] Other aspects are the same as those in Example 1.

[0186] Example 4-1

[0187] A method for preparing active silver powder is provided, which is different from that of Example 1 in that:

[0188] In step (1), 50 g (0.2943 mol) of silver nitrate, 36 g (0.288 mol) of sodium hypophosphite, 104 g (0.5882 mol) of ascorbic acid, and 64.7 g (0.5620 mol) of PVP are dispersed and dissolved in 500 mL of pure water, 6 mL of concentrated nitric acid and 8 g of sodium hydroxide are dispersed and dissolved in 100 mL of pure water, respectively, to obtain a silver nitrate solution, a sodium hypophosphite solution, an ascorbic acid solution, a PVP solution, a nitric acid solution, and a sodium hydroxide solution.

[0189] Other aspects are the same as those in Example 1.

[0190] Example 5-1

[0191] A method for preparing active silver powder is provided, which is different from that of Example 1 in that:

[0192] In step (1), the solvents for dispersing the reaction raw materials are water and ethanol, and the mass ratio of water to ethanol is 1:1. Other aspects are the same as those in Example 1.

[0193] Test Case

[0194] (1) Median particle size of silver powder: refer to standard GB / T19077-2016 for details.

[0195] (2) Sintering: The sample (a mixture of silver powder and ethylene glycol) was placed in a reflow furnace and heated to 130°C for 6 min to obtain sintered silver powder. The microscopic morphology of the sintered silver powder was then observed using a scanning electron microscope (SEM).

[0196] (3) Test of oxygen content in silver powder before and after sintering: Oxygen meter is used for determination. The specific steps are as follows:

[0197] ① Sample pretreatment: clean the surface of the sample with smooth surface and sample size controlled within the allowable range of the sample addition and injection holes;

[0198] ② Place the pre-treated silver powder in the oxygen meter and preheat the instrument for about 2h~3h; turn on the power gas and adjust the output pressure of the pressure reducing valve to 0.25MPa~0.3Mpa; turn on the carrier gas and adjust the output pressure of the pressure reducing valve to 0.25MPa~0.3MPa, and keep it stable for at least 15 minutes under ventilation; after the instrument is fully preheated, turn the switch to "Analysis" to power the pulse transformer; turn on the cooling water.

[0199] ③Start the computer, enter the analysis software interface, test and obtain the specific value of oxygen content.

[0200] The test results of the embodiments and comparative examples are shown in Table 1.

[0201] Table 1

[0202]

[0203]

[0204] Combining the embodiments and comparative example 1 in Table 1 above, it can be seen that the particle size of the silver powder prepared by the preparation method provided by the present application is relatively smaller. This is because the hydrogen explosion crushing in the preparation process breaks the powder agglomeration, and the oxygen content of the silver powder in the embodiment before and after sintering is lower than that in comparative example 1. At the same time, the oxygen content of the silver powder provided by the present application after sintering is lower than that before sintering, while the oxygen content of comparative example 1 increases after sintering, which shows that the preparation method provided by the present application is beneficial to reducing the oxygen content of the silver powder. Furthermore, the silver powder with a relatively smaller particle size and a relatively lower oxygen content has a greater sintering driving force during the sintering process, and has better sintering activity when sintered at a low temperature.

[0205] From Example 1 and Example 2-1 to Example 2-3 in Table 1 above, it can be seen that during the preparation process, the amount of silver precursor added and the number of additions have an impact on the particle size and oxygen content of the obtained silver powder. Among them, in Example 2-3, the silver precursor is added once, and the particle size of the obtained silver powder is relatively smaller, but the oxygen content of the silver powder is relatively higher.

[0206] Therefore, the preparation method provided in this application has an impact on the particle size and sintering activity of the silver powder. Furthermore, the preparation method provided in this application is conducive to the preparation of silver powder with excellent sintering activity and strong chemical stability, which can effectively solve the problem of easy agglomeration and oxidation of nanosilver powder, and can meet the demand for high reliability and high performance new materials in the field of low temperature slurry for photovoltaic cells.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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 active silver powder, characterized in that: The preparation process includes the following: (1) adding a reducing agent to a mixed solution containing a silver precursor and a protective agent to prepare a silver suspension; (2) adding a reducing agent and a silver precursor to the silver suspension to react and obtain an unactivated silver powder; (3) placing the unactivated silver powder in a heating furnace, wherein a reducing atmosphere is provided in the heating furnace, and activating the unactivated silver powder to obtain activated silver powder.

2. The preparation method according to claim 1, characterized in that: In step (3), the pressure of the reducing atmosphere in the heating furnace is 0.01 MPa to 0.15 MPa; and / or; The temperature in the heating furnace is 25°C to 120°C; and / or; The activation treatment time is 10min to 100min; and / or; The reducing atmosphere includes hydrogen.

3. The preparation method according to claim 1, characterized in that: In step (3), the unactivated silver powder is placed in a heating furnace, and the heating furnace is evacuated to an internal pressure of less than 1×10 -3 Pa.

4. The preparation method according to any one of claims 1 to 3, characterized in that The molar ratio between the silver precursor in step (1) and the silver precursor in step (2) is 1:(0-100); and / or; The molar ratio of the reducing agent in step (1) to the reducing agent in step (2) is (0.1-1):(0.5-2).

5. The preparation method according to any one of claims 1 to 4, characterized in that: The step (1) comprises: Prepare a solution: disperse a silver precursor, a first reducing agent, a second reducing agent, a first pH adjusting agent, a second pH adjusting agent, and a protective agent in a solvent to form a silver precursor solution, a first reducing agent solution, a second reducing agent solution, a first pH adjusting agent solution, a second pH adjusting agent solution, and a protective agent solution, respectively; separate the silver precursor solution into a silver precursor A solution and a silver precursor B solution; the molar ratio between the silver precursor A solution and the silver precursor B solution is 1:(1-100); Premixing: adding a silver precursor A solution to a protective agent solution, and then adding a first pH adjusting agent solution until the system reaches a certain pH value, to obtain a mixed solution containing a silver precursor and a protective agent; A first reducing agent solution is added to the mixed solution to obtain a silver suspension.

6. The preparation method according to claim 5, characterized in that: The step (2) comprises: A second pH adjusting agent solution is added to the silver suspension until the system reaches a certain pH value, and a second reducing agent solution is continuously added. After mixing, the silver precursor B solution is added to react to obtain unactivated silver powder.

7. The preparation method according to any one of claims 5 to 6, characterized in that: In the configuration solution, the molar ratio of the silver precursor, the first reducing agent, the second reducing agent and the protective agent is 1:(0.1-1):(0.5-2):(0.1-2); The silver precursor includes any one or more of silver nitrate and silver acetate; and / or; The first reducing agent includes any one or more of formaldehyde, ascorbic acid, hydrazine hydrate, and sodium hypophosphite; and / or; The second reducing agent includes any one or more of ascorbic acid, potassium tartrate, hydrazine hydrate, and glucose; and / or; The protective agent includes any one or more of PVA, PVP, sodium citrate, gelatin, gum arabic, BTA, PEG, and SDBS; and / or; The first pH adjuster includes any one or more of sodium hydroxide, potassium hydroxide, ammonia water, nitric acid, hydrochloric acid, acetic acid, and sulfuric acid; and / or; The second pH adjuster includes any one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The solvent includes any one or more of water and alcohol organic solvents; Preferably, the alcohol organic solvent includes any one or more of ethanol, ethylene glycol, and glycerol; Preferably, the solvent includes water and an alcohol organic solvent, and the mass ratio of the water to the alcohol organic solvent is (0.5-4):

1.

9. An active 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 D50 of the active silver powder is 80nm to 800nm.

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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