A porous hollow spherical silver powder, a preparation method and application thereof

Abstract

The application belongs to the technical field of preparation of conductive materials, and specifically discloses a porous hollow spherical silver powder, a preparation method and application thereof, and creatively adopts BPOP-2 type COF material as a configuration agent and a reducing agent for preparing the silver powder, so that the configuration of the silver powder can be realized in the reduction process of the silver powder, and after the COF material is removed through sintering, the superfine porous hollow spherical silver powder can be obtained. The superfine porous hollow spherical silver powder has the advantages of high hollow rate, good tap density, large specific surface area, low heat loss (650 DEG C), uniform particle size distribution, excellent printing property, low broken line rate, good printing line type, high sintering activity, and the like, and has a remarkable effect on the efficiency improvement of conductive silver paste. The whole process flow is simple and easy to control, the product has excellent comprehensive performance and stable quality.

Description

TECHNICAL FIELD

[0001] The present application relates to silver powder and its preparation method and application, and in particular to a kind of porous hollow spherical silver powder and its preparation method and application;Belong to the technical field of conductive material preparation. BACKGROUND

[0002] As the key material of crystalline silicon solar photovoltaic cell, conductive silver paste is mainly composed of three parts: silver powder, glass powder and organic carrier. Silver powder is widely used in this field due to its excellent electrical conductivity, and its shape is mostly spherical (or spherical-like) with a small particle size to meet the printing and electrical conductivity requirements. Silver powder can form a high-quality ohmic contact with the surface of the silicon wafer, significantly improving the photoelectric conversion efficiency of the solar cell. Glass powder plays the role of a binder in silver paste, which not only firmly adheres silver powder to the surface of the silicon wafer, but also etches the silicon nitride film on the surface of the silicon wafer, having a decisive influence on the ohmic contact performance of silver paste. The organic carrier gives the silver paste appropriate viscosity to ensure the smooth progress of the printing process. In silver paste, the content of silver powder is extremely high (about 90%), which plays a crucial role in the electrical conductivity and printing performance of silver paste.

[0003] In recent years, the technology of crystalline silicon solar photovoltaic cells has developed rapidly, and the product update iteration speed is extremely fast. From polycrystalline to single crystal, to Perc and Perc-se technology, and until the popularization of N-type solar cell wafers, the product efficiency has increased from less than 10% to about 24%. This progress is not only due to the continuous innovation of cell technology, but also closely related to the continuous development of conductive silver paste. With the increase in size of crystalline silicon wafers and the refinement of silver grid lines, the printing screen tends to be high-density and fine-grained, which requires silver powder to have higher overall performance. That is, silver powder needs to have high sintering activity, good printing performance and perfect printing line type. With the continuous narrowing of the printing screen line width, the particle size of silver powder also needs to be adjusted accordingly to ensure that the silver paste can pass through the screen hole and be printed on the surface of the silicon wafer. Compared with solid silver powder, porous hollow silver powder has obvious advantages in printing line type and sintering shrinkage, and its high aspect ratio helps to improve the current. Therefore, the research and preparation of ultra-fine porous hollow spherical silver powder has become a key direction to promote the performance improvement of silver powder. SUMMARY

[0004] In view of the problems of high broken line rate, poor line type and low photoelectric conversion efficiency of the silicon solar conductive silver paste under the condition of narrow line width screen printing due to the poor comprehensive performance of the silver powder in the prior art, the application provides a porous hollow spherical silver powder, a preparation method and application thereof, silver salt is shaped and reduced in a reducing dispersion system composed of a reducing COF material and a dispersant, a reducing COF material with a three-dimensional porous structure and an aldehyde group is introduced as a shaper and a reducing agent for preparing the silver powder, and then the ultra-fine porous hollow spherical silver powder with high hollow rate, large specific surface area and uniform particle size distribution can be directly obtained by one-step reduction. The whole process is simple and easy to control, the product has excellent comprehensive performance and stable quality.

[0005] To achieve the above technical purposes, the technical solutions adopted by the application are as follows:

[0006] According to the first embodiment of the application, a preparation method of a porous hollow spherical silver powder is provided, which comprises the following steps:

[0007] S1: Dissolve silver salt in water (preferably deionized water or distilled water) to obtain a silver salt solution, and add a reducing COF material and a dispersant into water to obtain a reducing dispersion system. Then, the silver salt solution is added into the reducing dispersion system for reaction, and after the reaction is completed, the wet silver powder can be obtained by solid-liquid separation treatment.

[0008] S2: Sintering treatment is performed on the wet silver powder to obtain the porous hollow spherical silver powder.

[0009] As preferred, the preparation method further comprises:

[0010] S3: Surface coating treatment is performed on the porous hollow spherical silver powder by using a coating liquid, and after the coating is completed, the coated porous hollow spherical silver powder can be obtained by sequentially performing drying treatment and optional scattering treatment.

[0011] It should be noted that in the application, "optionally" means "performing" or "not performing".

[0012] As preferred, in step S1, the reducing COF material is prepared by condensation reaction of tris(4-aldehyde biphenyl)amine and phenylenediamine or hydroquinone. Preferably, the phenylenediamine is p-phenylenediamine, o-phenylenediamine and / or m-phenylenediamine, and the hydroquinone is p-hydroquinone, o-hydroquinone and / or m-hydroquinone; further preferably, the phenylenediamine is p-phenylenediamine and / or m-phenylenediamine, and the hydroquinone is p-hydroquinone and / or m-hydroquinone. More preferably, the phenylenediamine is p-phenylenediamine, and the hydroquinone is p-hydroquinone.

[0013] As preferred, the condensation reaction is specifically: tris(4-formaldehyde biphenyl) amine and phenylenediamine (or benzenediol) are dissolved in an organic solvent (preferably anhydrous ethanol), an acid catalyst (preferably acetic acid) is added, and then reacted at a temperature of 60-80°C for 5-24h (preferably at a temperature of 65-75°C for 10-20h), and after the reaction is completed, the target product can be obtained by recrystallization treatment; the average molecular weight of the obtained product is 500-700g / mol.

[0014] As preferred, in the condensation reaction, the molar ratio of tris(4-formaldehyde biphenyl) amine to phenylenediamine or benzenediol when reacting is 0.5-2:1, preferably 0.8-1.5:1. For example, one of 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1.

[0015] As preferred, in the condensation reaction, the amount of acid catalyst used is 0.01-0.3 times the molar amount of tris(4-formaldehyde biphenyl) amine, preferably 0.05-0.2 times.

[0016] As preferred, in step S1, the silver salt is silver nitrate.

[0017] As preferred, in step S1, the dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, gelatin.

[0018] As preferred, in step S1, the concentration of silver salt in the silver salt solution is 0.5-5mol / L, preferably 1-3mol / L. For example, one of 0.5mol / L, 0.8mol / L, 1.0mol / L, 1.2mol / L, 1.5mol / L, 1.8mol / L, 2.0mol / L, 2.2mol / L, 2.5mol / L, 2.8mol / L, 3.0mol / L, 3.5mol / L, 4mol / L, 4.5mol / L, 5mol / L.

[0019] As preferred, in step S1, the mass concentration of the reduced COF material in the reduced dispersion system is 12-45%, preferably 20-35%. For example, one of 12%, 13%, 14%, 15%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%.

[0020] As preferred, the mass concentration of the dispersant in the reducing dispersion system in step S1 is 0.5-5%, preferably 1-3%. For example, the mass concentration is one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5%.

[0021] As preferred, the volume ratio of the silver salt solution to the reducing dispersion system is 1:1-10, preferably 1:2-8, further preferably 1:3-6, for example, the volume ratio is one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10.

[0022] As preferred, in step S1, the reaction is a stirring reaction. The temperature of the stirring reaction is 20-60°C, preferably 25-50°C. The time length of the stirring reaction is 20-120 min, preferably 30-90 min. The stirring rate during the stirring reaction is 200-800 r / min, preferably 300-600 r / min.

[0023] As preferred, in step S1, the silver salt solution is added dropwise, and the time length of the dropwise addition of the silver salt solution is 15-60 min, preferably 20-50 min.

[0024] As preferred, in step S2, the temperature of the sintering treatment is 150-500°C, preferably 200-400°C. The time of the sintering treatment is 0.5-5 h, preferably 1-3 h.

[0025] As preferred, in step S3, the coating liquid comprises a coating agent and a solvent. The coating agent is one or more of stearic acid, oleic acid, and amino silicone oil. The solvent is ethanol and / or isopropyl alcohol. Preferably, the mass concentration of the coating agent in the coating liquid is 1-20%, preferably 5-15%, more preferably 8-12%, for example, the concentration is one of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%.

[0026] As preferred, in step S3, the drying treatment is drying at a temperature of 60-85°C for 1-12 h, preferably vacuum drying at a temperature of 65-80°C for 2-6 h.

[0027] Preferably, in step S3, the dispersing treatment is first carried out by airflow crushing, and then by ultrasonic vibration and sieving.

[0028] According to a second embodiment of the present application, a porous hollow spherical silver powder is provided.

[0029] A porous hollow spherical silver powder is prepared by the preparation method according to the first embodiment.

[0030] According to a third embodiment of the present application, an application of the porous hollow spherical silver powder is provided.

[0031] An application of the porous hollow spherical silver powder or the porous hollow spherical silver powder prepared by the preparation method according to the first embodiment is applied to the fields of conductive paint, antibacterial material and electromagnetic shielding, and preferably to solar cell conductive silver paste.

[0032] In the present application, the silver powder is a super-fine porous hollow spherical silver powder, which has a super-fine small particle size structure to ensure excellent printability, and a porous hollow structure to facilitate excellent aspect ratio of printed linear metallization. In order to realize the porous hollow structure of the silver powder, a COF material (BPOP-2 type) with a reducing group aldehyde group is innovatively introduced as a reducing agent and a configuration agent for preparing the silver powder. Since the COF material has a three-dimensional porous structure and strong adsorption, the silver powder formed after reduction of the silver salt will be wrapped around it. After high-temperature heat treatment, the COF material in the silver powder escapes, and a porous hollow spherical or spherical structure with uniform particle size distribution is formed.

[0033] In the present application, the reducing COF material is a BPOP-2 type COF material generated by condensation reaction of tris(4-aldehyde diphenyl) amine as a monomer with p-phenylenediamine or with hydroquinone. The COF material has a strong adsorption effect on other ions, and has a three-dimensional porous structure. In the process of reducing silver salt to form silver powder, it becomes the crystal nucleus of the silver powder, so that the silver powder is wrapped around it, and then a super-fine porous spherical silver powder is formed. In addition, the pyrolysis temperature of the BPOP-2 type COF material is much lower than the melting point of silver, so it can be sintered at a relatively low temperature for removal, and will not affect the structure of the silver powder which has been formed. Finally, a high-purity porous hollow spherical silver powder material with uniform particle size distribution, high hollow rate, high specific surface area and excellent sintering performance is obtained.

[0034] It should be further noted that the reducing COF material is obtained by self-preparation. In the preparation process, the amount of tris(4-aldehyde biphenyl) amine as a monomer is such that the molar amount of aldehyde group is excessive relative to the molar amount of amine group or hydroxyl group of phenylenediamine or hydroquinone, that is, it is necessary to make the resulting reducing COF material also have a considerable amount of unreacted aldehyde group, thereby ensuring that the reducing COF material has a network structure while also having good reducibility. In a preferred embodiment of the present application, it has been found through research that when the molar ratio of tris(4-aldehyde biphenyl) amine to aniline or phenol in the condensation reaction is between 0.5 and 2:1, the overall performance of the resulting reducing COF material is relatively good, and when the molar ratio of tris(4-aldehyde biphenyl) amine to aniline or phenol in the condensation reaction is between 0.8 and 1.5:1, the overall performance of the reducing COF material is basically optimal.

[0035] In the present application, after obtaining the reducing COF material, a silver salt solution (i.e., silver nitrate solution) and a reducing dispersion system composed of the reducing COF material and a dispersant, i.e., water, are then respectively configured, and then the silver salt solution is added dropwise into the reducing dispersion system for reaction in the process of stirring. Through continuous stirring, the silver nitrate is quickly and uniformly dispersed in the reducing dispersion system, and the agglomeration of the silver powder generated by reduction during the deposition process in the local area is prevented, ensuring that the generated silver powder is uniformly deposited on the reducing COF material. After the addition of the silver salt solution is completed, the reaction needs to continue to stir for a period of time to ensure the formation of a stable and uniform silver powder dispersion system. After the reaction is completed, the solid product is separated by suction filtration and washed with deionized water for 2-5 times to remove residual impurities to obtain wet silver powder. Finally, the wet silver powder is subjected to sintering treatment to remove impurities such as the reducing COF material and residual dispersant, the sintering temperature is controlled at 150-500°C, and the sintering time is 0.5-5 hours, to obtain high-purity ultrafine porous hollow spherical silver powder.

[0036] It should be noted that the inventors have found through further experimental research and verification that the type and amount of the reducing COF material directly affect the hollow rate, specific surface area, tap density, heat loss, and particle size distribution of the porous hollow spherical silver powder during the reaction process. In a preferred embodiment of the present application, when the reducing COF material is synthesized from tris(4-aldehyde biphenyl) amine and p-phenylenediamine or hydroquinone as raw materials, the resulting reducing COF material has the best configuration reduction effect, which is reflected in that the comprehensive performance of the resulting spherical silver powder is basically optimal: the hollow rate of the resulting porous hollow spherical silver powder can be as high as 95% or more, the specific surface area is significantly improved, the tap density is more uniform, the heat loss is further reduced, the particle size distribution is more concentrated, and the overall performance basically reaches the ideal state.

[0037] In the present application, the prepared superfine porous hollow spherical silver powder is further subjected to surface coating treatment by using a coating agent, and the coated porous hollow spherical silver powder is obtained after drying. The coating treatment prevents the porous hollow spherical silver powder from being exposed to oxidation for a long time, improves the stability of the porous hollow spherical silver powder, and further improves the optical effect of the porous hollow spherical silver powder.

[0038] In the present application, the prepared porous hollow spherical silver powder has excellent optical performance and outstanding chemical stability by using a specific process and selecting a specific configuration reducing agent. 2 / g, a tap density of 5.2-5.8 g / cm 3 , a thermal loss (650℃) of 0.1-0.8%, a particle size distribution of D10≤0.6 μm, D50≤1.0 μm, and D90≤2.0 μm. The sintering activity is high (the sintering temperature is reduced by 5-10 degrees compared with the reference), the photoelectric conversion efficiency is improved by 0.18-0.32% compared with the reference, the printing performance is excellent, the line breaking rate is low, the printed line type is good, the sintering activity is high, and the efficiency of the conductive silver paste is significantly improved.

[0039] Compared with the prior art, the technical scheme provided by the present application has the following technical effects:

[0040] 1. The BPOP-2 type COF material is used as the configuration agent and reducing agent for preparing the silver powder, so that the configuration of the silver powder can be realized in the reduction process of the silver powder, and the superfine porous hollow spherical silver powder can be obtained after removing the COF material by a simple sintering process. The present application has the advantages of short overall process, convenient operation, high production efficiency, stable product quality, etc.

[0041] 2. The present application optimizes the process mechanism, adjusts the appropriate reduction and dispersion system according to the amount of silver salt in advance, and then obtains the porous hollow spherical silver powder with the expected structure and performance index, so that the obtained porous hollow spherical silver powder has excellent sphericity and porosity, improves the conductivity and antibacterial effect, is suitable for high-performance solar cell conductive silver paste, and significantly improves the photoelectric conversion efficiency.

[0042] 3. The prepared porous hollow spherical silver powder has significantly improved conductivity, antibacterial property and electromagnetic shielding performance, especially in the application of solar cell conductive silver paste, which significantly improves the battery efficiency and stability. The prepared submicron hollow silver powder has high sintering activity, the photoelectric conversion efficiency is improved by 0.18-0.32% compared with the solid silver powder, and the printing processability is good with basically no line breaking. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Scanning electron microscope image of the porous hollow spherical silver powder obtained in Example 5 of the present application.

[0044] Figure 2 Scanning electron microscope image of the solid spherical silver powder obtained in Comparative Example 1.

[0045] Figure 3 Printed line profile of the conductive silver paste prepared using the porous hollow spherical silver powder obtained in Example 5.

[0046] Figure 4 Printed line profile of the conductive silver paste prepared using the solid spherical silver powder obtained in Comparative Example 1. DETAILED DESCRIPTION

[0047] The technical solutions of the present application are illustrated below, and the scope of protection requested by the present application includes but is not limited to the following examples.

[0048] Example 1

[0049] Preparation of the reducing COF material I: 1 mol of tris(4-formaldehyde biphenyl) amine and 1 mol of o-phenylenediamine were dissolved in anhydrous ethanol, then 0.1 mol of acetic acid was added, and then the reaction was carried out at a temperature of 60°C for 12 h. After the reaction was completed, recrystallization treatment was carried out to obtain a reducing COF material I with an average molecular weight of about 550 g / mol.

[0050] Preparation of the silver nitrate solution: silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L.

[0051] Preparation of the reducing dispersion system: the reducing COF material I and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a mass concentration of the reducing COF material I of 25% and a mass concentration of the polyvinylpyrrolidone of 1%.

[0052] First, 3 L of the reducing dispersion system was placed in a stirring reactor; then 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system under the conditions of a temperature of 25°C and a stirring rate of 450 r / min, the dropwise adding speed of the silver nitrate solution was controlled so that the time taken for the silver nitrate solution to be completely added to the reducing dispersion system was 30 min; after the silver nitrate solution was added dropwise, the stirring and temperature control equipment was continued for 30 min; after the reaction was completed, the stirring and temperature control equipment was turned off, the reaction system was subjected to suction filtration, and then washed with deionized water for 3 times to obtain wet silver powder; finally, the wet silver powder was heat treated at a temperature of 200°C for 1 h in a sintering furnace to obtain the porous hollow spherical silver powder.

[0053] Example 2

[0054] Preparation of the reducing COF material II: 1 mol of tris(4-formaldehyde biphenyl) amine and 1 mol of p-phenylenediamine were dissolved in anhydrous ethanol, then 0.1 mol of acetic acid was added, and then reacted at a temperature of 60°C for 12 h. After the reaction was completed, recrystallization treatment was performed to obtain the reducing COF material II with an average molecular weight of about 550 g / mol.

[0055] Preparation of the silver nitrate solution: silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L.

[0056] Preparation of the reducing dispersion system: the reducing COF material II and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a mass concentration of the reducing COF material II of 25% and a mass concentration of polyvinylpyrrolidone of 1%.

[0057] First, 3 L of the reducing dispersion system was placed in a stirring reactor. Then, 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system at a temperature of 25°C and a stirring rate of 450 r / min. The dropwise addition speed of the silver nitrate solution was controlled so that the time taken for the silver nitrate solution to be completely added to the reducing dispersion system was 30 min. After the dropwise addition of the silver nitrate solution, stirring was continued for 30 min. After the reaction was completed, the stirring and temperature control devices were turned off, the reaction system was suction-filtered, and then washed with deionized water three times to obtain wet silver powder. Finally, the wet silver powder was heat-treated at a temperature of 200°C for 1 h in a sintering furnace to obtain porous hollow spherical silver powder.

[0058] Example 3

[0059] Preparation of the reducing COF material III: 1 mol of tris(4-formaldehyde biphenyl) amine and 1 mol of m-phenylenediamine were dissolved in anhydrous ethanol, then 0.1 mol of acetic acid was added, and then reacted at a temperature of 60°C for 12 h. After the reaction was completed, recrystallization treatment was performed to obtain the reducing COF material III with an average molecular weight of about 550 g / mol.

[0060] Preparation of the silver nitrate solution: silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L.

[0061] Preparation of the reducing dispersion system: the reducing COF material III and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a mass concentration of the reducing COF material III of 25% and a mass concentration of polyvinylpyrrolidone of 1%.

[0062] First, 3 L of the reducing dispersion system was taken and placed in a stirring reactor; then 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system under the condition that the temperature was 25°C and the stirring rate was 450 r / min, the dropwise adding speed of the silver nitrate solution was controlled so that the time consumed for the silver nitrate solution to be completely added to the reducing dispersion system was 30 min; after the silver nitrate solution was added dropwise, the stirring was continued for 30 min; after the reaction was completed, the stirring and temperature control equipment were turned off, the reaction system was suction filtered, and then washed with deionized water for 3 times to obtain wet silver powder; finally, the wet silver powder was heat treated in a sintering furnace at a temperature of 200°C for 1 h to obtain the porous hollow spherical silver powder.

[0063] Example 4

[0064] Preparation of the reducing COF material IV: 1 mol of tris(4-formylphenyl)amine and 1 mol of catechol were dissolved in anhydrous ethanol, then 0.1 mol of acetic acid was added, and then the reaction was carried out at a temperature of 60°C for 12 h; after the reaction was completed, recrystallization treatment was carried out to obtain the reducing COF material IV with an average molecular weight of about 570 g / mol.

[0065] Preparation of the silver nitrate solution: the silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0066] Preparation of the reducing dispersion system: the reducing COF material IV and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a mass concentration of the reducing COF material IV of 25% and a mass concentration of the polyvinylpyrrolidone of 1%.

[0067] First, 3 L of the reducing dispersion system was taken and placed in a stirring reactor; then 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system under the condition that the temperature was 25°C and the stirring rate was 450 r / min, the dropwise adding speed of the silver nitrate solution was controlled so that the time consumed for the silver nitrate solution to be completely added to the reducing dispersion system was 30 min; after the silver nitrate solution was added dropwise, the stirring was continued for 30 min; after the reaction was completed, the stirring and temperature control equipment were turned off, the reaction system was suction filtered, and then washed with deionized water for 3 times to obtain wet silver powder; finally, the wet silver powder was heat treated in a sintering furnace at a temperature of 200°C for 1 h to obtain the porous hollow spherical silver powder.

[0068] Example 5

[0069] Preparation of the reducing COF material V: 1 mol of tris(4-formylphenyl)amine and 1 mol of p-benzoquinone were dissolved in anhydrous ethanol, then 0.1 mol of acetic acid was added, and then the reaction was carried out at a temperature of 60°C for 12 h; after the reaction was completed, recrystallization treatment was carried out to obtain the reducing COF material V with an average molecular weight of about 570 g / mol.

[0070] Preparation of silver nitrate solution: silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0071] Preparation of reducing dispersion system: reducing COF material V and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a mass concentration of 25% of reducing COF material V and a mass concentration of 1% of polyvinylpyrrolidone.

[0072] First, 3 L of the reducing dispersion system was placed in a stirring reactor; then 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system under the condition of a temperature of 25°C and a stirring rate of 450 r / min, the dropwise adding speed of the silver nitrate solution was controlled so that the silver nitrate solution was completely added to the reducing dispersion system for 30 min; after the silver nitrate solution was added, the stirring was continued for 30 min; after the reaction was completed, the stirring and temperature control equipment were turned off, the reaction system was suction filtered, and then washed with deionized water for 3 times to obtain wet silver powder; finally, the wet silver powder was heat treated in a sintering furnace at a temperature of 200°C for 1 h to obtain porous hollow spherical silver powder.

[0073] Example 6

[0074] Preparation of reducing COF material VI: 1 mol of tris(4-aldehyde biphenyl) amine and 1 mol of resorcinol were dissolved in anhydrous ethanol, then 0.1 mol of acetic acid was added, and then the reaction was carried out at a temperature of 60°C for 12 h; after the reaction was completed, recrystallization treatment was carried out to obtain reducing COF material V with an average molecular weight of about 570 g / mol.

[0075] Preparation of silver nitrate solution: silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0076] Preparation of reducing dispersion system: reducing COF material VI and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a mass concentration of 25% of reducing COF material VI and a mass concentration of 1% of polyvinylpyrrolidone.

[0077] First, 3 L of the reducing dispersion system was placed in a stirring reactor; then 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system under the condition of a temperature of 25°C and a stirring rate of 450 r / min, the dropwise adding speed of the silver nitrate solution was controlled so that the silver nitrate solution was completely added to the reducing dispersion system for 30 min; after the silver nitrate solution was added, the stirring was continued for 30 min; after the reaction was completed, the stirring and temperature control equipment were turned off, the reaction system was suction filtered, and then washed with deionized water for 3 times to obtain wet silver powder; finally, the wet silver powder was heat treated in a sintering furnace at a temperature of 200°C for 1 h to obtain porous hollow spherical silver powder.

[0078] Example 7

[0079] Example 2 was repeated, except that the molar ratio of tris(4-formylphenyl)amine to p-phenylenediamine was 1.5:1.

[0080] Example 8

[0081] Example 2 was repeated, except that the molar ratio of tris(4-formylphenyl)amine to p-phenylenediamine was 0.8:1.

[0082] Example 9

[0083] Example 2 was repeated, except that the porous hollow spherical silver powder obtained in the preparation was subjected to surface coating treatment, the coating agent was an isopropyl alcohol solution of stearic acid, the concentration of stearic acid was 8%, and after the coating treatment was completed, the porous hollow spherical silver powder was baked in a vacuum drying oven at 70°C for 4h. Then, the porous hollow spherical silver powder was subjected to breaking treatment using an air flow pulverizer, and then was sieved (400 mesh screen) by ultrasonic vibration, to obtain coated porous hollow spherical silver powder.

[0084] Example 10

[0085] Example 2 was repeated, except that the porous hollow spherical silver powder obtained in the preparation was subjected to surface coating treatment, the coating agent was an isopropyl alcohol solution of oleic acid, the concentration of oleic acid was 10%, and after the coating treatment was completed, the porous hollow spherical silver powder was baked in a vacuum drying oven at 75°C for 3.5h. Then, the porous hollow spherical silver powder was subjected to breaking treatment using an air flow pulverizer, and then was sieved (400 mesh screen) by ultrasonic vibration, to obtain coated porous hollow spherical silver powder.

[0086] Example 11

[0087] Example 2 was repeated, except that the temperature during stirring reaction was 30°C, and the stirring rate was 400r / min.

[0088] Example 12

[0089] Example 2 was repeated, except that the sintering temperature was 240°C, and the sintering time was 1.5h.

[0090] Example 13

[0091] Example 2 was repeated, except that the time for completely adding the silver nitrate solution into the reducing dispersion system was 40min.

[0092] Example 14

[0093] Example 2 was repeated, except that the reducing COF material IV and the polyvinylpyrrolidone were added into the deionized water to obtain a reducing dispersion system with a mass concentration of the reducing COF material IV of 20% and a mass concentration of the polyvinylpyrrolidone of 1.2%.

[0094] Comparative Example 1

[0095] Preparation of silver nitrate solution: silver nitrate was dissolved in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0096] Preparation of reducing dispersion system: citric acid and polyvinylpyrrolidone were added to deionized water to obtain a reducing dispersion system with a concentration of ascorbic acid of 0.67 mol / L and a concentration of polyvinylpyrrolidone of 0.17 mol / L.

[0097] First, 3 L of the reducing dispersion system was placed in a stirring reactor; then, 1 L of the silver nitrate solution was added dropwise to the reducing dispersion system under the conditions of a temperature of 25°C and a stirring rate of 450 r / min, the dropwise adding speed of the silver nitrate solution was controlled so that the time taken for the silver nitrate solution to be completely added to the reducing dispersion system was 30 min; after the dropwise adding of the silver nitrate solution, the stirring was continued for 30 min; after the reaction was completed, the stirring and temperature control devices were turned off, the reaction system was filtered, washed with deionized water for 3 times, and finally dried in a vacuum drying oven at 75°C for 4 h to obtain the solid spherical silver powder.

[0098] The porous hollow spherical silver powder prepared in each of Examples 1-8 and the solid spherical silver powder prepared in Comparative Example 1 were detected, and the detection results are shown in the following table:

[0099]

[0100] In the present application, the specific surface area, the tap density were tested according to the provisions of GB / T 1774-2009, the heat loss was tested according to GB / T 5150, the particle size distribution was tested according to GB / T 19077-2016, and the hollow rate was calculated by scanning electron microscope observation.

[0101] Application Example

[0102] The porous hollow spherical silver powder prepared in each of Examples 1-8 and the solid spherical silver powder prepared in Comparative Example 1 were respectively prepared into conductive silver paste at the same proportion: the content of silver powder was 90%, the content of glass powder was 2%, and the content of organic carrier was 8%. After the paste was uniformly stirred, the paste was rolled 5 times by a three-roll machine to make the fineness of the paste meet the standard (≤6 μm). The viscosity of each paste was controlled to be basically the same by adjusting the viscosity of the organic carrier. Various pastes were respectively printed on Perc-se silicon wafer by narrow line width screen, and after the battery piece was sintered by a sintering furnace, the electrical performance data were tested after the temperature decreased to room temperature. The organic carrier was composed of 3% ethyl cellulose, 2% polyamide wax thixotropic agent, 4% dispersant TDO and 91% mixed solvent (alcohol ester twelve: butyl carbitol = 2:1).

[0103] The electrical performance data and printing conditions of each silver powder are shown in the following table:

[0104]

[0105] From the above table, the slurry made of the porous hollow spherical silver powder of the present application examples 1-8 has an efficiency improvement of 0.18-0.32% compared to the slurry made of the solid silver powder of the comparative example 1, which is a great improvement on the crystalline silicon solar photovoltaic silicon wafer. The slurry made of the porous hollow spherical silver powder of the examples 1-8 has basically no broken lines in printing, which is significantly less than the slurry made of the solid silver powder of the comparative example 1. This is mainly due to the smaller particle size of the porous hollow spherical silver powder, which is beneficial for printing, and the slurry prepared has a higher filling factor. In addition, the Isc (short circuit current) of the slurry made of the porous hollow spherical silver powder of the examples 1-8 is significantly improved compared to the slurry made of the solid silver powder of the comparative example 1, which is due to the porous hollow structure of the silver powder.

[0106] In the examples of the present application, part of the substances are as follows: Tris(4-formaldehyde biphenyl) amine is purchased from Beijing Huaweiruke Chemical Co., Ltd.; o-phenylenediamine, p-phenylenediamine, m-phenylenediamine are purchased from Nanjing Jirui Chemical Co., Ltd.; o-diphenol, p-diphenol, m-diphenol are purchased from Langfang Qianyao Technology Co., Ltd.; oleic acid is purchased from Shanghai Lisen Chemical Co., Ltd., with a purity of 99.5%. Stearic acid is provided by Guangzhou Gongsin Chemical Co., Ltd., with a purity of 98.8%. Isopropyl alcohol is purchased from Shandong Qilu Chemical Co., Ltd., with a purity of 99.7%. The experimental water is deionized water, with a purity of 99.9%. Citric acid is purchased from Jiangsu Suhua Group, with a purity of 99.5%. Polyvinylpyrrolidone (CAS: 9003-39-8) is purchased from Jinhua Bicknew Material Technology Co., Ltd., PVP-K25, number average molecular weight 32000, resin content (wt%) > 95, viscosity (mps.s-25℃ / 5%ap) 1.7-2.1, pH 3.0-7.0, K value 22.4-27.0, purity 99.3%. Polyvinyl alcohol is purchased from Anhui Longyang Environmental Protection Technology Co., Ltd. Anhydrous ethanol, purity 99.9%, is purchased from Hunan Xianghua Biological Technology Co., Ltd. Acetic acid, purity 99.9%, is purchased from Jinan Chengyijing Chemical Technology Co., Ltd. Each raw material has undergone strict quality testing to ensure the accuracy and reliability of the experimental results.

Claims

1. A method for preparing a porous hollow spherical silver powder, characterized by: The preparation method comprises the following steps: S1: dissolving silver salt in water to obtain a silver salt solution, adding a reducing COF material and a dispersant into water to obtain a reducing dispersion system, then adding the silver salt solution into the reducing dispersion system to react, and after the reaction is completed, performing solid-liquid separation treatment to obtain wet silver powder; The reducing COF material is prepared by condensation reaction of tris(4-aldehyde biphenyl) amine and phenylenediamine, or the reducing COF material is prepared by condensation reaction of tris(4-aldehyde biphenyl) amine and hydroquinone; the phenylenediamine is p-phenylenediamine, o-phenylenediamine or m-phenylenediamine, and the hydroquinone is p-hydroquinone, o-hydroquinone or m-hydroquinone; the condensation reaction is specifically as follows: tris(4-aldehyde biphenyl) amine and phenylenediamine are dissolved in an organic solvent or tris(4-aldehyde biphenyl) amine and hydroquinone are dissolved in an organic solvent, an acid catalyst is added, then the reaction is carried out at a temperature of 60-80 DEG C for 5-24 hours, and after the reaction is completed, the target product is obtained by recrystallization treatment; the average molecular weight of the obtained product is 500-700 g / mol; the molar ratio of tris(4-aldehyde biphenyl) amine to phenylenediamine or the molar ratio of tris(4-aldehyde biphenyl) amine to hydroquinone is 0.5-2:1; The mass concentration of the reducing COF material in the reducing dispersion system is 12-45%; S2: performing sintering treatment on the wet silver powder to obtain porous hollow spherical silver powder.

2. The method of claim 1, wherein: The preparation method further comprises: S3: performing surface coating treatment on the porous hollow spherical silver powder by using a coating liquid, and after the coating is completed, sequentially performing drying treatment and scattering treatment to obtain coated porous hollow spherical silver powder.

3. The production method according to claim 1 or 2, characterized by: The condensation reaction is specifically as follows: tris(4-aldehyde biphenyl) amine and phenylenediamine are dissolved in anhydrous ethanol or tris(4-aldehyde biphenyl) amine and hydroquinone are dissolved in anhydrous ethanol, acetic acid is added, then the reaction is carried out at a temperature of 65-75 DEG C for 10-20 hours; the molar ratio of tris(4-aldehyde biphenyl) amine to phenylenediamine or the molar ratio of tris(4-aldehyde biphenyl) amine to hydroquinone is 0.8-1.5:

1.

4. The production method according to claim 1 or 2, characterized by: In step S1, the silver salt is silver nitrate; and / or In step S1, the dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol and gelatin.

5. The production method according to claim 1 or 2, characterized by: In step S1, the concentration of silver salt in the silver salt solution is 0.5-5 mol / L; and the mass concentration of the reducing COF material in the reducing dispersion system is 20-35%; The mass concentration of the dispersant in the reducing dispersion system is 0.5-5%.

6. The method of claim 5, wherein: In step S1, the concentration of silver salt in the silver salt solution is 1-3 mol / L; and the mass concentration of the dispersant in the reducing dispersion system is 1-3%.

7. The method of claim 5, wherein: The volume ratio of the amount of the silver salt solution to the amount of the reducing dispersion system is 1:1-10.

8. The method of claim 7, wherein: The volume ratio of the amount of the silver salt solution to the amount of the reducing dispersion system is 1:2-8.

9. The method of manufacturing according to claim 1 or 2, wherein: In step S1, the adding of the silver salt solution into the reducing dispersion system to react is stirring reaction; the temperature of the stirring reaction is 20-60 DEG C; the time length of the stirring reaction is 20-120 minutes; and the stirring rate during the stirring reaction is 200-800 r / min.

10. The method of claim 9, wherein: The stirring reaction temperature is 25-50℃; the stirring reaction time is 30-90min; and the stirring rate during the stirring reaction is 300-600r / min.

11. The method of claim 9, wherein: The silver salt solution is added dropwise, and the silver salt solution dropwise adding time is 15-60min.

12. The method of claim 11, wherein: The silver salt solution is added dropwise, and the silver salt solution dropwise adding time is 20-50min.

13. The method of making according to claim 1 or 2, wherein: In step S2, the sintering treatment temperature is 150-500℃; and the sintering treatment time is 0.5-5h.

14. The method of claim 13, wherein: In step S2, the sintering treatment temperature is 200-400℃; and the sintering treatment time is 1-3h.

15. The method of claim 2, wherein: In step S3, the coating liquid comprises a coating agent and a solvent; the coating agent is one or more of stearic acid, oleic acid, and amino silicon oil; and the solvent is ethanol and / or isopropyl alcohol.

16. The method of claim 15, wherein: The mass concentration of the coating agent in the coating liquid is 1-20%.

17. The method of claim 16, wherein: The mass concentration of the coating agent in the coating liquid is 5-15%.

18. The method of making of any one of claims 2, 15-17, wherein: In step S3, the drying treatment is drying at a temperature of 60-85℃ for 1-12h; and / or In step S3, the dispersing treatment is first airflow crushing treatment, and then ultrasonic vibration and sieving treatment.

19. The method of claim 18, wherein: In step S3, the drying treatment is vacuum drying at a temperature of 65-80℃ for 2-6h.

20. A porous hollow spherical silver powder, characterized by: The porous hollow spherical silver powder is prepared according to the preparation method in any one of claims 1-19.

21. Use of the porous hollow spherical silver powder obtained by the production method according to any one of claims 1 to 19, characterized in that: The porous hollow spherical silver powder is applied to the fields of conductive paint, antibacterial material, and electromagnetic shielding.

22. The use according to claim 21, characterized in that: The porous hollow spherical silver powder is applied to solar cell conductive silver paste.

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