Method for preparing silver powder having adjustable sintering activity, and conductive silver powder and use thereof

Abstract

The present disclosure belongs to the technical field of silver powder preparation, and particularly relates to a method for preparing a silver powder having adjustable sintering activity, and a conductive silver powder and the use thereof. The preparation method comprises the following steps: S1, subjecting a reducing agent, a sintering regulator, a dispersing agent and water to primary mixing, then adding an oxidizing agent solution under stirring conditions, and reacting same after the addition is finished, wherein a surfactant is introduced during the primary mixing and / or the surfactant is introduced into the oxidizing agent solution; and S2, filtering the material obtained in S1, then subjecting the material and a coating liquid containing a coating agent to secondary mixing, and then drying the mixture, so as to obtain a silver powder. The present disclosure can result in a silver powder having different sintering activities, and can satisfy usage scenarios of carrying out sintering in different temperature sections, such as the use in different temperature scenarios including low-temperature sintering and high-temperature sintering; and during the silver powder preparation process of the present disclosure, no slurry is formulated, and the sintering activity of the silver powder is directly tested by means of a thermal mechanical analyzer, such that the development process is more convenient, and characterization is more accurate.

Description

Method for preparing silver powder with adjustable sintering activity, conductive silver powder and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 2023110338371 filed with the Patent Office of China on August 15, 2023, entitled “A method for preparing silver powder with adjustable sintering activity,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the field of silver powder preparation, and in particular to a method for preparing silver powder with adjustable sintering activity, conductive silver powder and applications thereof. Background Art

[0004] Silver powder has broad application prospects, including in the fields of low-temperature RFID, flexible printed electronics, high-temperature photovoltaic cells, ceramic filters, etc., so its preparation technology has made great progress.

[0005] However, the related art has the following problems:

[0006] First, the correlation mechanism between sintering activity and formula materials is still unclear, and the required sintering activity cannot be adjusted, which cannot meet the application requirements of related technologies for silver powders with different sintering activities;

[0007] Secondly, it is generally impossible to directly provide representative data of sintering activity, such as sintering temperature, shrinkage rate, etc. This is because in related technologies, sintering activity is generally characterized by preparing silver powder into a slurry, printing it, and curing it during the temperature increase process, and then testing the resistance value. The process is cumbersome and requires the preparation of slurry, and can only be characterized by resistance, which is the final electrical performance result. The characterization process is complicated, and the sintering activity of silver powder is indirectly characterized by the electrical properties of the slurry after curing and the density of the slurry after printing and forming a film. The process is cumbersome, has many influencing factors, and takes a long time, and has poor accuracy.

[0008] Summary of the Invention

[0009] The purpose of the present disclosure includes, for example, providing a method for preparing silver powder with adjustable sintering activity, conductive silver powder and applications thereof, so as to improve the defect of related technologies in that the required sintering activity cannot be accurately adjusted. The preparation method can obtain silver powder with different sintering activities to meet application scenarios of sintering in different temperature ranges, such as low-temperature sintering and high-temperature sintering. In addition, in the silver powder preparation process of the present disclosure, no slurry is prepared, and the sintering activity of the silver powder is directly tested by a thermomechanical analyzer (TMA), which is more convenient for the development process and more accurate in characterization.

[0010] In order to achieve the above object, the present disclosure provides a method for preparing silver powder with adjustable sintering activity, comprising the following steps:

[0011] S1. A reducing agent, a sintering regulator, a dispersant, and water are first mixed, and then an oxidant solution is added under stirring, and the mixture is reacted after the addition is completed; wherein a surfactant is introduced during the first mixing and / or a surfactant is introduced into the oxidant solution;

[0012] S2. After filtering the material obtained in S1, the material is mixed with a coating liquid containing a coating agent for a second time, and then dried to obtain silver powder.

[0013] Wherein, the sintering regulator includes at least one of tartronic acid, fumaric acid, malic acid, maleic acid, succinic acid and malonic acid.

[0014] Wherein, the oxidant in the oxidant solution is a soluble silver salt.

[0015] When the required silver powder is high-temperature silver powder, the coating agent is controlled to be fatty acid, and the mass amount of the sintering regulator is controlled to be 0.1%-4% of the mass of the oxidant; when the required silver powder is low-temperature silver powder, the coating agent is controlled to be an organic alkaline substance, and the mass amount of the sintering regulator is controlled to be 4.1%-10% of the mass of the oxidant; the starting sintering temperature of the high-temperature silver powder measured by a thermomechanical analyzer is ≥400°C, and the starting sintering temperature of the low-temperature silver powder measured by a thermomechanical analyzer is ≥200°C and <400°C.

[0016] In some optional embodiments of the present disclosure, the amount of the coating agent is 0.1%-2% of the mass of the oxidant, optionally 0.1%-0.5%.

[0017] In some optional embodiments of the present disclosure, the mass concentration of the coating agent in the coating solution is 1%-10%, and the concentration of the oxidant in the oxidant solution is 0.05-1 mol / L.

[0018] In some optional embodiments of the present disclosure, the fatty acid includes at least one of lauric acid, palmitic acid, oleic acid, stearic acid, linoleic acid, linolenic acid and arachidonic acid.

[0019] Further optionally, the fatty acid includes at least one of oleic acid, linoleic acid, and lauric acid.

[0020] In some optional embodiments of the present disclosure, the organic alkaline substance includes at least one of sodium tripolyphosphate, benzotriazole, sodium oleate, sodium laurate, hexadecylamine, and dodecylamine.

[0021] Further optionally, the organic alkaline substance is benzotriazole.

[0022] In some optional embodiments of the present disclosure, the soluble silver salt is silver nitrate.

[0023] In some optional embodiments of the present disclosure, the mass of the surfactant is 0.5%-10% of the mass of the oxidant, and the molar ratio of the reducing agent to the oxidant is 1-1.5:1 based on transferred electrons.

[0024] In some optional embodiments of the present disclosure, the mass of the dispersant in S1 is 5%-20% of the mass of the oxidant.

[0025] Optionally, the dispersant includes at least one of polyvinyl pyrrolidone, gum arabic, gelatin, polyvinyl alcohol, polyethylene glycol and β-dextrin.

[0026] More optionally, the process of first mixing the reducing agent, the sintering regulator, the dispersant and the water in S1 includes: mixing a reducing liquid containing the reducing agent with a reaction base liquid containing the dispersant and the sintering regulator.

[0027] Further optionally, in S1, the mass concentration of the reducing agent in the reducing solution is 4%-10%, and the mass concentration of the dispersant in the reaction base solution is 5%-30%.

[0028] In the present disclosure, the surfactant is optionally introduced into the reaction base solution in advance, or the surfactant is introduced into the oxidant solution. More optionally, the surfactant is introduced into the oxidant solution.

[0029] In some optional embodiments of the present disclosure, the reducing agent includes at least one of hydroquinone, hydrazine hydrate, sodium hypophosphite, glucose, ascorbic acid, formaldehyde and sodium borohydride; and the surfactant is selected from non-ionic surfactants.

[0030] Further optionally, the nonionic surfactant includes at least one of Tween, Span, palmityl alcohol, cyclohexanol, polyoxyethylene ether and polyoxyethylene fatty acid ester.

[0031] Further optionally, the reducing agent includes at least one of hydrazine hydrate, formaldehyde and ascorbic acid, the surfactant includes at least one of Span, Tween and polyoxyethylene ether, and the sintering regulator includes at least one of tartronic acid, maleic acid and malic acid.

[0032] In some optional embodiments of the present disclosure, the stirring conditions in S1 include: a stirring speed of 100-400 r / min, a temperature maintained at 20-30° C., and an addition time of 5-40 s.

[0033] In some optional embodiments of the present disclosure, the reaction conditions in S1 include: reaction temperature of 20-30° C., and reaction time of 5-20 min.

[0034] In some optional embodiments of the present disclosure, stirring is performed during or after the second mixing in S2, and the conditions of the stirring include: a stirring speed of 100-500 r / min and a stirring time of 5-10 min.

[0035] In some optional embodiments of the present disclosure, the microstructure of the high-temperature silver powder is an open-pore structure, the particle size D50 of the high-temperature silver powder is 2.56 μm-4.69 μm, and the shrinkage rate is 9.6%-17.8%.

[0036] In some optional embodiments of the present disclosure, the microstructure of the low-temperature silver powder is a closed structure, the particle size D50 of the low-temperature silver powder is 1.89 μm, and the shrinkage rate is 11.9%.

[0037] The present disclosure also provides a conductive silver paste, characterized in that it comprises high-temperature silver powder or low-temperature silver powder prepared by the above-mentioned method for preparing silver powder with adjustable sintering activity.

[0038] The present disclosure also provides the use of the above-mentioned conductive silver paste in preparing the grid lines required for photovoltaic Topcon cells, RFID antennas based on ceramic substrates, photovoltaic HJT cells or RFID antennas based on flexible substrates.

[0039] The beneficial effects brought about by the embodiments of the present disclosure include, for example:

[0040] The present disclosure can achieve good sphericity, uniform surface, small particle size and narrow particle size distribution of the silver powder obtained by controlling the feeding process and formula, especially the specific feeding sequence, controlling the ratio of sintering regulator and oxidant, and coordinating the coating process of a specific type of coating agent in the later stage and other materials. It can also achieve the purpose of regulating the sintering activity of the silver powder, and obtain silver powders with different sintering activities to meet the application scenarios of sintering in different temperature ranges, such as low-temperature sintering and high-temperature sintering. At the same time, the shrinkage curve of the obtained silver powder is basically convergent (i.e., it can basically shrink completely). The silver powder obtained by the present disclosure has broad application prospects, including in the fields of low-temperature RFID, flexible printed electronics, high-temperature photovoltaic cells, ceramic filters, etc.; it is particularly suitable for conductive silver powder in the field of solar cells. The high-temperature silver powder obtained by the present disclosure can be used, for example, for the grid lines required for photovoltaic Topcon cells and RFID antennas based on ceramic substrates; the low-temperature silver powder obtained can be used, for example, for photovoltaic HJT cells and RFID antennas based on flexible substrates, and the production and application stages are both in a low-temperature environment (<300°C).

[0041] The disclosed oxidizing agent and reducing agent nucleate within a short period of time after mixing, undergoing a process of nanoclusters, atomic nuclei, nanoscale primary subcrystals, and diffusion and aggregation to form polycrystalline particles. The anisotropic effect of the sintering regulator and the appropriate ratio ensure the formation of a spherical powder with different microscopic morphologies and high sintering activity. For example, under the same conditions, when the sintering regulator dosage is appropriately low (0.1%-4% by weight of the oxidizing agent), the surface micromorphology of the resulting silver powder is an open-pore structure. Silver powders with open-pore surface structures have poor sintering activity and only exhibit sinterability at high temperatures (≥400°C) according to TMA testing, making them suitable for high-temperature silver powders. When the sintering regulator dosage is appropriately high (4.1%-10% by weight of the oxidizing agent), the surface micromorphology of the resulting silver powder is a closed structure, with pores existing only within the powder. It exhibits high sintering activity during temperature increases. According to TMA testing, sintering begins in a relatively low temperature range (≥200°C and <400°C), and the powder begins to shrink, making it suitable for low-temperature silver powders.

[0042] Furthermore, the silver powder generated in S1 of the present disclosure is coated with an acidic coating agent (fatty acid) or an organic alkaline substance in the latter stage of S2, so that the surface of the powder is coated with the coating agent, further changing the surface state, achieving the purpose of further dispersion and improving the sintering activity, thereby synergistically regulating its sintering activity and particle size, especially regulating its initial sintering temperature, in the process of preventing agglomeration. Specifically, the present invention adopts fatty acids as the coating agent when high-temperature silver powder is required, and adopts organic alkaline substances as the coating agent when low-temperature silver powder is required. This is because the silver powder starts sintering preferentially on the powder surface at the beginning of the sintering process, and the coating agents with different surfaces have the function of initiating sintering activity; the fatty acid coating agent coats the powder under acidic conditions, and the carboxyl functional groups contained in the fatty acid coating agent adsorb on the silver powder surface, causing a certain corrosion effect on the surface morphology of the silver powder, resulting in an increase in the proportion of surface open pore structure, and the regulation of the high-temperature silver powder sintering activity is achieved by fine-tuning the surface structure; the organic alkaline substance is used as the coating agent for the low-temperature silver powder, and its organic alkaline functional groups act on the surface of the silver particles to achieve dispersion and prevent agglomeration, and can further enhance the dispersibility of the synthesized silver powder, ensuring monodispersity between the particles, especially facilitating the dispersion of small-sized silver particles, thereby ensuring low-temperature sintering activity. Under the same conditions, using alkaline coating agents for high-temperature silver powders can lead to the appearance of small particles on the silver powder surface, resulting in poor sphericity and a wide overall particle size distribution. This can lead to certain sintering properties at low temperatures, resulting in adverse effects in applications requiring high-temperature silver powders. Using acidic coating agents for low-temperature silver powders can lead to severe agglomeration of silver particles, reducing the sintering activity of the silver powder, increasing shrinkage, raising the initial sintering temperature, and widening the particle size distribution. If, under the same conditions, a fatty acid is used as a coating agent when high-temperature silver powder is required, and the corresponding ratio of the sintering regulator to the oxidant is too large (greater than 4%), the surface morphology of the silver powder will change to a closed structure, the sintering activity will be improved, and it will change to a low-temperature silver powder. However, the use of fatty acid as a coating agent cannot play a good dispersing role in this case, resulting in the obtained silver powder particles tending to become larger, which will affect the sintering activity of the low-temperature silver powder and the desired high-temperature silver powder cannot be obtained; when an organic alkaline substance is used as a coating agent when low-temperature silver powder is required, and the corresponding ratio of the sintering regulator to the oxidant is too small (less than 4%) or too large (greater than 10%), the surface structure of the silver powder will change, and the particle size of the silver particles will increase, resulting in a decrease in sintering activity and an increase in the initial sintering temperature. The shrinkage rate is difficult to fully express or does not shrink completely, that is, the shrinkage rate cannot be fully reflected during the temperature increase test, resulting in poor sintering properties.

[0043] Among them, the surfactant is specially introduced to interact with the silver ions in the oxidant, and the dispersant is introduced to adsorb the silver atoms to prevent the silver powder from agglomerating. At the same time, the surfactant adsorbs and wets the surface of the silver during the nucleation and growth process, enhancing the effect of the sintering regulator and silver during the reaction process.

[0044] The present disclosure allows for the sintering activity characteristics of silver powder to be clearly defined during the silver powder preparation stage. Specifically, the sintering activity of the silver powder can be characterized by factors such as sintering temperature and shrinkage, allowing for the production of high-temperature or low-temperature silver powders as required. The silver powder produced by the disclosed preparation method can be screened for sintering properties before preparing the corresponding conductive silver paste, simplifying the silver powder screening process during paste preparation, reducing development costs, and improving the efficiency of combining silver powder and silver paste. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0046] FIG1 is a SEM image of the microstructure of the high-temperature silver powder having an open-pore structure obtained in Example 1 of the present disclosure;

[0047] FIG2 is a SEM image of the microstructure of the low-temperature silver powder having a closed-pore structure obtained in Example 2 of the present disclosure;

[0048] FIG3 is a graph showing the shrinkage rate of the silver powder obtained in Example 1 and Example 2 of the present disclosure as the temperature changes;

[0049] FIG4 a is a SEM image of the microstructure of the high-temperature silver powder obtained in Example 3 of the present disclosure;

[0050] FIG4 b is a graph showing the shrinkage rate of the high-temperature silver powder obtained in Example 3 of the present disclosure as the temperature changes;

[0051] FIG5 is a SEM image of the microstructure of the high-temperature silver powder obtained in Example 4 of the present disclosure;

[0052] FIG6 is a SEM image of the microstructure of the high-temperature silver powder obtained in Example 5 of the present disclosure;

[0053] FIG7 is a SEM image of the microstructure of the high-temperature silver powder obtained in Example 6 of the present disclosure;

[0054] FIG8 a is a SEM image of the microstructure of the high-temperature silver powder obtained in Example 7 of the present disclosure;

[0055] FIG8 b is a graph showing the shrinkage rate of the high-temperature silver powder obtained in Example 7 of the present disclosure as the temperature changes;

[0056] Figure 9a is a SEM image of the microstructure of the silver powder obtained in Comparative Example 1;

[0057] FIG9b is a graph showing the shrinkage rate of the silver powder obtained in Comparative Example 1 as a function of temperature;

[0058] Figure 10a is a SEM image of the microstructure of the silver powder obtained in Comparative Example 2;

[0059] FIG10b is a graph showing the shrinkage rate of the silver powder obtained in Comparative Example 2 as a function of temperature;

[0060] Figure 11a is a SEM image of the microstructure of the silver powder obtained in Comparative Example 3;

[0061] FIG11b is a graph showing the shrinkage rate of the silver powder obtained in Comparative Example 3 as a function of temperature;

[0062] FIG12a is a SEM image of the microstructure of the low-temperature silver powder obtained in Comparative Example 4;

[0063] FIG12b is a graph showing the shrinkage rate of the silver powder obtained in Comparative Example 4 as a function of temperature;

[0064] FIG13 is a SEM image of the microstructure of the silver powder obtained in Comparative Example 5;

[0065] FIG14a is a SEM image of the microstructure of the high-temperature silver powder obtained in Comparative Example 6;

[0066] FIG14 b is a graph showing the shrinkage rate of the silver powder obtained in Comparative Example 6 as the temperature changes. DETAILED DESCRIPTION

[0067] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Among them, the terms "optional" and "optional" all mean that they may be included or not (or may be present or not).

[0068] The definitions of terms in this disclosure are as follows:

[0069] Sintering: refers to the transformation of powdered materials into dense bodies at temperatures below the melting point, which can be characterized by mass density, water absorption, apparent porosity and shrinkage.

[0070] Sintering activity: refers to the performance of the polycrystalline material tending to be stable after sintering due to the grain boundary energy replacing the surface energy of the powder. High sintering activity means that it can be sintered at a lower temperature and achieve a very high degree of densification. The present disclosure uses a thermomechanical analyzer (TMA) to test the sintering activity of the powder (the initial sintering temperature, the shrinkage rate and whether it can shrink completely can characterize the sintering activity), thereby quantifying the sintering activity of the silver powder and characterizing it with real data. The initial sintering temperature refers to the temperature when the powder shrinks and sintering just occurs. The initial sintering temperature is the main basis for distinguishing different sintering activities. This is because the powder has a small particle size, a large specific surface area and a high surface energy. According to the principle of minimum energy, it will spontaneously change to the lowest energy state, accompanied by a reduction in the surface energy of the system. The surface energy of the powder material is greater than the grain boundary energy of the polycrystalline sintered body, which is the driving force of the sintering process. Therefore, the grain boundary energy of the powder replaces the surface energy after sintering, so the polycrystalline material tends to be stable after sintering.

[0071] The present disclosure provides a method for preparing silver powder with adjustable sintering activity, comprising the following steps:

[0072] S1. A reducing agent, a sintering regulator, a dispersant, and water are first mixed, and then an oxidant solution is added under stirring, and the mixture is reacted after the addition is completed; wherein a surfactant is introduced during the first mixing and / or a surfactant is introduced into the oxidant solution;

[0073] S2. After filtering the material obtained in S1, the material is mixed with a coating liquid containing a coating agent for a second time, and then dried to obtain silver powder.

[0074] The present disclosure specifically introduces a coating liquid in the final S2 step, which enables the oxidant and reducing agent, sintering regulator, dispersant, and surfactant to be evenly mixed before being coated with the coating agent on the surface. This can effectively fine-tune the surface morphology of the silver powder and enhance the dispersibility of the silver powder, resulting in a narrow particle size distribution, a small D50 value, and a small particle size, thereby helping to improve sintering activity. Under the same conditions, if the coating agent is introduced into each mixture in S1, the subsequent redox reaction to generate silver powder will be disturbed, resulting in silver powder with a messy morphology and a wide particle size distribution. A wide particle size distribution means there is a possibility of large particles, which is not conducive to application, such as the reduction of fineness when used in conductive silver paste, which has an adverse effect on printing fine lines and reduces sintering activity.

[0075] The sintering regulator includes but is not limited to at least one of tartronic acid, fumaric acid, malic acid, maleic acid, succinic acid and malonic acid.

[0076] Further optionally, the sintering regulator includes but is not limited to at least one of tartronic acid, maleic acid, and malic acid. In this alternative, the sintering regulator type is more effective than other types because it can produce silver powder with higher sphericity and narrower particle size distribution, which is more conducive to improving the printability of the slurry prepared by the end user.

[0077] Wherein, the oxidant in the oxidant solution is a soluble silver salt.

[0078] When the required silver powder is high-temperature silver powder, the coating agent is controlled to be fatty acid, and the mass amount of the sintering regulator is controlled to be 0.1%-4% of the mass of the oxidant; when the required silver powder is low-temperature silver powder, the coating agent is controlled to be an organic alkaline substance, and the mass amount of the sintering regulator is controlled to be 4.1%-10% of the mass of the oxidant; the starting sintering temperature of the high-temperature silver powder measured by a thermomechanical analyzer is ≥400°C, and the starting sintering temperature of the low-temperature silver powder measured by a thermomechanical analyzer is ≥200°C and <400°C.

[0079] The high-temperature silver powder has an initial sintering temperature of ≥400°C as measured by a thermomechanical analyzer, indicating that the silver powder begins to exhibit sintering activity at ≥400°C as measured by the thermomechanical analyzer. The low-temperature silver powder has an initial sintering temperature of ≥200°C and <400°C as measured by a thermomechanical analyzer, indicating that the silver powder begins to exhibit sintering activity at ≥200°C and <400°C as measured by the thermomechanical analyzer. The present disclosure characterizes the sintering activity of the powder using the initial sintering temperature and shrinkage rate as measured by a thermomechanical analyzer, eliminating the need for indirect characterization by preparing a slurry and then testing the slurry's properties, thereby shortening the time and cost of powder development.

[0080] In some optional embodiments of the present disclosure, when the required silver powder is high-temperature silver powder, the mass amount of the sintering regulator can be, for example, any one of 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% of the mass of the oxidizer, or a range value between any two of them; when the required silver powder is low-temperature silver powder, the mass amount of the sintering regulator can be, for example, any one of 4.1%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 8.5%, 9%, 9.5%, 10% of the mass of the oxidizer, or a range value between any two of them.

[0081] In some optional embodiments of the present disclosure, the coating agent is used in an amount of 0.1%-2% by mass of the oxidant, for example, any one of 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any range therebetween, and may optionally be 0.1%-1%, more preferably 0.1%-0.5%. In this optional solution, the coating agent is used in an appropriate amount to disperse the silver powder, prevent particle agglomeration, and enhance the sintering activity of the silver powder, thereby meeting the sintering temperature requirements of different applications.

[0082] In some optional embodiments of the present disclosure, the mass concentration of the coating agent in the coating solution is 1%-10%. For example, it can be any one of 1%, 2%, 3%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 8.5%, 9%, 9.5%, 10%, or a range between any two of them. In this optional solution, the coating agent concentration in the coating solution is appropriate, which can better dissolve the coating agent and evenly disperse the silver powder during the coating process. At the same time, it is beneficial to replace the moisture in the silver powder and reduce the moisture content of the powder.

[0083] Optionally, the oxidant concentration in the oxidant solution is 0.05-1 mol / L, more preferably 0.1-0.5 mol / L.

[0084] In some optional embodiments of the present disclosure, the fatty acid includes but is not limited to at least one of lauric acid, palmitic acid, oleic acid, stearic acid, linoleic acid, linolenic acid and arachidonic acid.

[0085] Further optionally, the fatty acid includes but is not limited to at least one of oleic acid, linoleic acid, and lauric acid. In this alternative, the type of fatty acid can appropriately fine-tune the surface morphology of the silver particles, promote complete shrinkage of the silver powder, and further facilitate the regulation of sintering activity.

[0086] In some optional embodiments of the present disclosure, the organic alkaline substance includes, but is not limited to, at least one of sodium tripolyphosphate, benzotriazole, sodium oleate, sodium laurate, hexadecylamine, and dodecylamine. Benzotriazole and / or sodium laurate are further optional. Benzotriazole or sodium laurate can further prevent silver powder agglomeration, thereby ensuring high sintering activity at low temperatures.

[0087] In some optional embodiments of the present disclosure, the soluble silver salt is silver nitrate.

[0088] In some optional embodiments of the present disclosure, the surfactant is present in an amount of 0.5% to 10% of the mass of the oxidant. In this optional embodiment, the surfactant is present in an appropriate amount to allow adsorption onto the surface of silver ions, thereby controlling the morphology of nanoscale silver crystals during the reduction of silver ions to silver atoms and their growth, thereby further stabilizing the precipitation and growth of silver particles from the solution.

[0089] Further optionally, the molar ratio of the reducing agent to the oxidizing agent is 1-1.5:1 based on the transferred electrons.

[0090] In S1, a dispersant is introduced into the first mixing. Optionally, the present disclosure introduces a dispersant in addition to a surfactant. Due to the presence of the dispersant, it is adsorbed on the surface of silver atoms, making it difficult for silver to diffuse and aggregate when it becomes nano-sized crystals. This can play a synergistic adsorption role on silver atoms, control the entire silver nucleation and growth process, and further help prevent silver powder agglomeration.

[0091] Optionally, the mass of the dispersant is 5%-20% of the mass of the oxidant. For example, it can be any one of 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any range therebetween. In this alternative, the amount of dispersant is appropriate to prevent silver powder agglomeration and ensure sintering activity.

[0092] Optionally, the dispersant includes, but is not limited to, at least one of polyvinyl pyrrolidone, gum arabic, gelatin, polyvinyl alcohol, polyethylene glycol, and β-dextrin. The degree of polymerization of the polyvinyl pyrrolidone may, for example, be 8,000-30,000. The degree of polymerization of the polyvinyl alcohol may, for example, be 25,000-35,000. The degree of polymerization of the polyethylene glycol may, for example, be 400-2,000.

[0093] The water in S1 can be deionized water.

[0094] More optionally, the first mixing of the reducing agent, sintering regulator, dispersant, and water in S1 includes mixing a reducing solution containing the reducing agent with a reaction base solution containing the sintering regulator and dispersant. It is understood that the solvents of the reducing solution and the reaction base solution are both water.

[0095] Further optionally, in S1, the mass concentration of the reducing agent in the reducing solution is 4%-10%, for example, any one of 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 8.5%, 9%, 9.5%, 10%, or a range between any two of them.

[0096] Optionally, the mass concentration of the dispersant in the reaction base solution is 5%-30%, for example, any one of 5%, 8%, 10%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or a range between any two of them.

[0097] In the present disclosure, the surfactant is optionally introduced into the reaction base solution in advance, or the surfactant is introduced into the oxidant solution. Of course, the surfactant may be partially present in the reaction base solution and partially present in the oxidant solution.

[0098] Alternatively, a surfactant may be introduced into the oxidant solution. In this solution, UV characterization indicates that the addition of a surfactant to the silver ion solution (i.e., the oxidant solution) is more conducive to the surfactant's adsorption of silver ions. UV spectroscopy testing shows a significant increase in the absorbance of silver ions at 300 nm, indicating that the surfactant's adsorption of silver ions in the presence of the surfactant can prevent agglomeration during the reduction process.

[0099] In some optional embodiments of the present disclosure, the reducing agent includes but is not limited to at least one of hydroquinone, hydrazine hydrate, sodium hypophosphite, glucose, ascorbic acid, formaldehyde and sodium borohydride.

[0100] Further optionally, the reducing agent includes but is not limited to at least one of hydrazine hydrate, formaldehyde and ascorbic acid.

[0101] Optionally, the surfactant is selected from a nonionic surfactant. In this alternative, the nonionic surfactant can adsorb on the surface of silver ions, controlling the morphology of nanoscale silver crystals during the process of silver ions being reduced to silver atoms and growing, thereby further stabilizing the precipitation and growth of silver particles from the solution.

[0102] Further optionally, the nonionic surfactant includes but is not limited to at least one of Tween, Span, palmityl alcohol, cyclohexanol, polyoxyethylene ether and polyoxyethylene fatty acid ester. The degree of polymerization of polyoxyethylene ether can be, for example, 17-110. The degree of polymerization of polyoxyethylene fatty acid ester can be, for example, 100-2000.

[0103] Further optionally, the surfactant includes but is not limited to at least one of Span, Tween, and polyoxyethylene ether.

[0104] In some optional embodiments of the present disclosure, the stirring conditions described in S1 include: a stirring speed of 100-400 r / min, optionally 100-250 r / min, a temperature maintained at 20-30°C (optionally room temperature), and an addition time of 5-40s, optionally 5-20s. In this optional scheme, the oxidant solution needs to be quickly added to the material obtained by the first mixing in a short period of time, which can provide a higher supersaturation for the formation of the powder, and nucleation, growth and aggregation are completed in a short period of time. At the same time, the anisotropic effect of the sintering regulator is synergistically obtained to obtain spherical silver powder, so that the generated powder has a richer micromorphology and pore structure, which is more conducive to improving the sintering activity.

[0105] In some optional embodiments of the present disclosure, the reaction conditions in S1 include: reaction temperature of 20-30° C., and reaction time of 5-20 min.

[0106] In some optional embodiments of the present disclosure, the preparation method further includes: performing a stirring process during or after the second mixing in S2. That is, the second mixing can be performed under stirring conditions or after the second mixing; the stirring process is used to promote coating of the silver powder surface with a coating agent to adjust sintering activity and increase dispersibility.

[0107] More optionally, the stirring conditions include: a stirring speed of 100-500 r / min and a stirring time of 5-10 min. This option allows the coating agent to act more thoroughly on the powder surface, thereby being more conducive to improving sintering activity.

[0108] In some optional embodiments of the present disclosure, the high-temperature silver powder has an open-pore microstructure, a particle size D50 of 2.56 μm to 4.69 μm, and a shrinkage rate of 9.6% to 17.8%. The low-temperature silver powder has a closed-pore microstructure, a particle size D50 of 1.89 μm, and a shrinkage rate of 11.9%.

[0109] The present disclosure also provides a conductive silver paste comprising high-temperature silver powder or low-temperature silver powder prepared by the aforementioned method for preparing silver powder with adjustable sintering activity. This conductive silver paste can be widely used in the preparation of grid lines for photovoltaic Topcon cells, ceramic-based RFID antennas, photovoltaic HJT cells, or flexible substrate-based RFID antennas.

[0110] The following detailed description of the embodiments of the present disclosure is for illustrative purposes only and is intended to explain the present disclosure, and should not be construed as limiting the present disclosure. The shrinkage rate is obtained using a thermomechanical analyzer at a heating rate of 10° C. / min.

[0111] Example 1

[0112] A method for preparing silver powder with adjustable sintering activity comprises the following steps:

[0113] 1) preparing a solution comprising an oxidizing agent (silver nitrate) solution containing a surfactant (specifically Span), a reaction base solution containing a dispersant (PVP, with a degree of polymerization of 10,000) and a sintering regulator (malonic acid), a reducing solution containing a reducing agent (hydrazine hydrate), and a coating solution containing a coating agent; the solvent of each solution is deionized water; and the coating agent is oleic acid;

[0114] The silver nitrate concentration in the oxidant solution is 0.2 mol / L, and the surfactant content is 2% of the mass of the silver nitrate used; the reaction base liquid contains a dispersant and a sintering regulator, the mass concentration of the dispersant is 10%, and the amount of the dispersant used is 8% of the mass of the silver nitrate used; the concentration of the reducing agent in the reducing solution is 4%, and the molar ratio of the reducing agent to the oxidant based on transferred electrons is 1.04:1; the concentration of the coating agent in the coating solution is 2%, and the amount of the coating agent used is 0.2% of the mass of the silver nitrate used.

[0115] 2) adding the reducing solution containing the reducing agent to the reaction base solution containing the dispersant and the sintering regulator, and adding the oxidizing agent solution containing the surfactant at room temperature under stirring (stirring speed of 200 r / min) for 6 seconds. The reaction was stopped 10 minutes after the addition was completed; and controlling the sintering regulator content to 1% by weight of the silver nitrate to obtain an intermediate silver powder.

[0116] 3) After filtering and washing the generated intermediate silver powder, the intermediate silver powder was added to a coating solution containing a coating agent and stirred at a stirring speed of 200 r / min for 8 minutes to coat the powder surface with the coating agent to achieve further dispersion and improve sintering activity, and then dried to obtain silver powder.

[0117] The obtained silver powder has an open-pore structure, and its microscopic morphology SEM image is shown in Figure 1. It has a high sphericity. The particle size D50 tested by a laser particle size analyzer is 2.56 μm. Its shrinkage rate tested by a thermomechanical analyzer is shown in Figure 3. The obtained silver powder only begins to sinter at 420°C.

[0118] Example 2

[0119] The method used in Example 1 was followed, except that the sintering modifier content was controlled to 5% of the mass of silver nitrate and the coating agent was benzotriazole. The resulting powder exhibited sintering activity at a relatively low temperature. The resulting silver powder had a closed-pore structure, as shown in the SEM micromorphology in Figure 2. The sphericity was high, and the particle size D50 was 1.89 μm. Its shrinkage, as measured by a thermomechanical analyzer, is shown in Figure 3.

[0120] As shown in Figure 3, compared to Example 1, Example 2 exhibits a lower shrinkage onset temperature and a greater shrinkage rate, with shrinkage occurring at 200°C, indicating sintering at this temperature. In contrast, the silver powder obtained in Example 1 only begins sintering at 420°C. Furthermore, the shrinkage rate for Example 1 is 9.6%, while that for Example 2 is 11.9%. This demonstrates that the present disclosure can produce silver powders with varying shrinkage rates through the use of sintering modifiers, coatings, and other methods, further demonstrating the adjustable sintering activity.

[0121] Example 3

[0122] The method of Example 1 was used, except that the type of coating agent was different, specifically palmitic acid.

[0123] The microscopic morphology of the obtained silver powder is shown in Figure 4a, which is an SEM image of the obtained silver powder. It has a spherical surface with a microscopic void structure, high sphericity, a relatively wide particle size distribution, and a particle size D50 of 2.72 μm. Its initial sintering temperature is 400°C, and the shrinkage rate is 17.8%. The silver powder shrinkage curve shown in Figure 4b shows complete shrinkage.

[0124] Example 4

[0125] The method of Example 1 was followed, except that the amount of coating agent used was 2% of the mass of the oxidant.

[0126] The microscopic morphology of the obtained silver powder is shown in Figure 5. It is a spherical structure with a blocky specific surface area and microscopic voids. The sphericity is average, the particle size D50 is 2.63 μm, and there is a small amount of agglomeration. Its initial sintering temperature is 520°C, the shrinkage rate is 10.8%, and the shrinkage is complete.

[0127] Example 5

[0128] The method of Example 1 is referred to, except that the reducing solution containing the reducing agent and the reaction base solution containing the dispersant and the sintering regulator in steps 1)-2) are mixed and prepared in a different manner. Specifically, the reducing agent, dispersant, sintering regulator and deionized water are directly mixed, and the amount of deionized water used is the sum of the solvent amounts of the reducing solution and the reaction base solution in Example 1.

[0129] The microscopic morphology of the obtained silver powder is a spherical surface block open-pore structure, as shown in Figure 6. The sphericity is relatively poor, the morphology is uneven, the particle size D50 is 3.21 μm, and the particle size distribution is relatively wide; its initial sintering temperature is 500°C, the shrinkage rate is 16.5%, and the shrinkage is complete.

[0130] Example 6

[0131] The method of Example 1 was followed, except that the oxidant solution was added for 40 seconds.

[0132] The spherical structure of the obtained silver powder micromorphology is not obvious compared with Example 1, and more independent flake structures appear, as shown in Figure 7. The sphericity is relatively poor, and the particle size distribution is relatively wide, with D50 of 3.65 μm; its initial sintering temperature is 550°C, the shrinkage rate is 9.8%, and the shrinkage is complete.

[0133] Example 7

[0134] The method of Example 1 was used, except that the surfactant was added to the reaction base solution instead of being added to the oxidant solution as in Example 1.

[0135] The microstructure of the obtained silver powder is a spherical structure with open pores on the surface and a large particle size, as shown in Figures 8a and 8b. The sphericity is good, the particle size D50 is 4.69 μm, and the particle size distribution is relatively wide. The initial sintering temperature is 410°C and the shrinkage rate is 11.2%.

[0136] Comparative Example 1

[0137] The method of Example 1 was followed, except that no sintering regulator was added.

[0138] The microscopic morphology of the obtained silver powder is shown in Figure 9a, which has poor sphericity, a strip-like surface structure, large particle size, uneven morphology, a particle size D50 of 5.23 μm, and severe agglomeration. As shown in Figure 9b, its initial sintering temperature is 700°C, the shrinkage rate is 10.7%, and there is a case of incomplete shrinkage, and the sintering activity is poor.

[0139] Comparative Example 2

[0140] The method of Example 1 was followed, except that the coating step in step 3) was not performed, that is, the coating liquid was not introduced for stirring, but the product was directly dried after filtration and washing.

[0141] The microstructure of the obtained silver powder is a spherical open-pore structure with severe agglomeration, as shown in Figure 10a. The sphericity is poor and the particle size D50 is 3.85 μm. The severe agglomeration between particles leads to an initial sintering temperature of 600°C, as shown in Figure 10b, and a shrinkage rate of 10.1%.

[0142] Comparative Example 3

[0143] The method of Example 1 was used, except that the coating agent was an alkaline substance: benzotriazole.

[0144] The obtained silver powder has a spherical microstructure, as shown in Figure 11a, with flake-like and strip-like micro-nanostructures on the surface. The sphericity is average, and the particle size D50 is 2.87 μm. As shown in Figure 11b, its initial sintering temperature is 410°C, and the shrinkage rate is 18.5%. The microstructure on the surface leads to a low sintering temperature, making it impossible to obtain high-temperature silver powder. In addition, the powder does not shrink completely and has poor sintering activity.

[0145] Comparative Example 4

[0146] The method of Example 2 is referred to, except that the coating agent is an acidic substance: oleic acid.

[0147] As shown in Figure 12a, the resulting silver powder exhibits a quasi-spherical closed structure with small nanoparticles on the surface, exhibiting high sphericity, a particle size D50 of 2.03 μm, and a wide particle size distribution. The initial sintering temperature was 300°C, and as shown in Figure 12b, the shrinkage was 18%. Compared to Example 2, the initial sintering temperature in this comparative example was significantly increased because the use of an acidic coating agent has poor coating and dispersion properties for low-temperature silver powder, leading to agglomeration of some silver particles and excessive shrinkage, resulting in reduced sintering activity.

[0148] Comparative Example 5

[0149] The method of Example 1 was followed, except that no surfactant was added.

[0150] The microstructure of the obtained silver powder is a spherical open-pore structure, as shown in FIG13 . The sphericity is low and the particle size is extremely uneven. The particle size D50 is 3.12 μm and the particle size distribution is wide. The initial sintering temperature is 500° C. and the shrinkage rate is 13.5%.

[0151] Comparative Example 6

[0152] The method of Example 1 was followed, except that no dispersant was introduced.

[0153] The microscopic morphology of the obtained silver powder is a disordered structure with various shapes, including small flakes, strips, and spherical shapes, as shown in Figure 14a. The particle size distribution of the silver powder is wide and the morphology is uneven. As shown in Figure 14b, its initial sintering temperature is 500°C and the shrinkage rate is 12.1%, which means that the shrinkage is not complete. That is, although the initial sintering temperature is 500°C, there is no platform stage (i.e., no convergence) in the latter part of the shrinkage rate curve during the test, indicating that the sintering activity is very poor.

[0154] It can be seen from the above examples and comparative examples that the silver powder obtained by the embodiment scheme of the present disclosure has good sphericity, uniform surface, small particle size and narrow particle size distribution, and can be precisely adjusted to obtain silver powder with different sintering activities, and can basically shrink completely. However, in the comparative example, under the conditions of changing the key process, the morphology and initial sintering temperature of the silver powder will change. The presence or absence of raw materials will especially have a significant effect on the morphology of the silver powder, thereby affecting the sintering activity and the printability after being prepared into a slurry; and the comparative example has no obvious trending effect on the regulation of sintering activity. The comparative example is difficult to accurately control the sintering activity while ensuring the sphericity and particle size of the silver powder, and some of the sintering activities cannot be completely shrunk and the sintering activity is very poor. Among them, according to Example 1 and Comparative Examples 2 and 3 of the present disclosure, it can be seen that the use of a sintering regulator and a suitable coating agent is conducive to maintaining the sphericity of the silver powder, a narrow particle size distribution, and is more conducive to reducing the initial sintering temperature of the silver powder and shrinking completely, that is, the sintering activity is fully reflected. Complete shrinkage refers to the plateau at the end of the shrinkage curve, indicating full sintering activity. As shown in Example 1 and Comparative Example 6, the addition of a dispersant in this disclosure facilitates the production of silver powder with high sphericity and a narrow particle size distribution. Without a dispersant, the silver powder exhibits a disorganized morphology, lacks a clear structure, and struggles to achieve complete shrinkage.

[0155] Furthermore, according to Examples 1 and 3-4 of the present disclosure, the use of an optional coating agent and its dosage is more conducive to obtaining spherical silver powder with good sphericity, small silver particles and narrow particle size distribution, which is beneficial to improving the sintering activity of the silver powder.

[0156] Furthermore, according to Examples 1 and 5-7 of the present disclosure, it can be seen that the use of optional mixing methods and feeding time schemes is more conducive to maintaining the sphericity of silver powder, small silver particles and narrow particle size distribution, or is more conducive to reducing the initial sintering temperature of silver powder.

[0157] The following application is performed using Example 1 and Example 2 as examples.

[0158] Application Example 1

[0159] 820 g of the silver powder obtained in Example 1, 20 g of glass powder, 46 g of resin (20 wt% of acrylic resin, 80 wt% of chloroacetic resin), and 95 g of organic solvent (the mass ratio of butyl carbitol to carbitol acetate is 1:1) were mixed and stirred, and then 10 g of organic additives were added. The organic additives were specifically 5 g of polyamide wax thixotropic agent, 3 g of silicone oil, and 2 g of BYK-190 dispersant. The mixture was mixed and degassed using a revolution-type vacuum degassing machine, and dispersed and ground multiple times using a three-roll grinder to obtain a conductive silver paste. A 1 mm × 100 mm line was printed using a screen printer, and the mixture was dried at 867 ° C for 1 min. The resistivity was tested to be 4.22 × 10 -6 Ω·cm.

[0160] For the 10μm wide lines on solar photovoltaic cells, the conductive silver paste is used for printing. After curing, the line width is 25.4μm and the height is 9.7μm. The line reproducibility is good after multiple printings, and it can be used for fine grid printing of photovoltaic solar cells.

[0161] Application Example 2

[0162] 45 g of the silver powder obtained in Example 2 was mixed with 35 g of resin and 18 g of solvent and coarsely ground twice using a three-roll grinder. 2 g of additives (0.5 g of Wanlinglong 400599 curing agent, 0.5 g of BYK-345 leveling agent, and 1 g of BYK-190 dispersant) were added and finely ground five times. The mixture was allowed to stand and exhaust to obtain a conductive silver paste for RFID, wherein the resin was 90 wt % of trihydroxychloroacetic acid resin and 10 wt % of acrylic resin, and the solvent included 15 wt % of DBE dibasic ester solvent, 10 wt % of isophorone, 82 % of 783 slow-drying water (purchased from Dongguan Dawei Chemical Co., Ltd.), and 3 % of defoamer KSZ-169 (Shin-Etsu).

[0163] Use this conductive silver paste to print UHF antennas on surfaces such as paper and PET substrates, bake them at 150°C for 30 minutes, and then bind the chip. The test antenna's read range is 8-12m.

[0164] The above describes in detail the optional embodiments of the present disclosure, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure can be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present disclosure and fall within the scope of protection of the present disclosure. Industrial Applicability

[0165] In summary, the present disclosure provides a method for preparing silver powder with adjustable sintering activity, conductive silver powder and applications thereof. The preparation method can obtain silver powder with different sintering activities to meet application scenarios of sintering in different temperature ranges, such as application in different temperature scenarios of low-temperature sintering and high-temperature sintering. In addition, in the silver powder preparation process, the present disclosure does not prepare slurry, and directly tests the sintering activity of the silver powder by using a thermomechanical analyzer (TMA), which is more convenient for the development process and more accurate in characterization.

Claims

1. A method for preparing silver powder with adjustable sintering activity, characterized in that: The following steps are involved: S1, first mixing a reducing agent, a sintering regulator, a dispersant and water, then adding an oxidant solution under stirring conditions, and reacting after the addition is completed; wherein a surfactant is introduced in the first mixing and / or a surfactant is introduced in the oxidant solution; The sintering regulator includes at least one of tartronic acid, fumaric acid, malic acid, maleic acid, succinic acid and malonic acid, and the oxidant in the oxidant solution is a soluble silver salt; S2, filtering the material obtained in S1, mixing it with a coating liquid containing a coating agent, and then drying it to obtain silver powder; Among them, when the required silver powder is high-temperature silver powder, the coating agent is controlled to be fatty acid, and the mass amount of the sintering regulator is controlled to be 0.1%-4% of the mass of the oxidant; when the required silver powder is low-temperature silver powder, the coating agent is controlled to be an organic alkaline substance, and the mass amount of the sintering regulator is controlled to be 4.1%-10% of the mass of the oxidant; the initial sintering temperature of the high-temperature silver powder measured by a thermomechanical analyzer is ≥400°C, and the initial sintering temperature of the low-temperature silver powder measured by a thermomechanical analyzer is ≥200°C and <400°C.

2. The preparation method according to claim 1, characterized in that: The amount of the coating agent is 0.1%-2% of the mass of the oxidant; and / or The mass concentration of the coating agent in the coating solution is 1%-10%, and the mass concentration of the oxidant in the oxidant solution is 0.05-1 mol / L.

3. The preparation method according to any one of claims 1 to 2, characterized in that: The fatty acid comprises at least one of lauric acid, palmitic acid, oleic acid, stearic acid, linoleic acid, linolenic acid and arachidonic acid, and / or The organic alkaline substance includes at least one of sodium tripolyphosphate, benzotriazole, sodium oleate, sodium laurate, hexadecylamine and dodecylamine; and / or The soluble silver salt is silver nitrate.

4. The preparation method according to claim 3, characterized in that: The fatty acid includes at least one of oleic acid, linoleic acid and lauric acid.

5. The preparation method according to claim 3, characterized in that: The organic alkaline substance is benzotriazole.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The mass of the surfactant is 0.5%-10% of the mass of the oxidant. and / or The molar ratio of the reducing agent to the oxidizing agent is 1-1.5:1 based on the transferred electrons; and / or The reducing agent comprises at least one of hydroquinone, hydrazine hydrate, sodium hypophosphite, glucose, ascorbic acid, formaldehyde and sodium borohydride; and / or The surfactant is selected from nonionic surfactants, and the nonionic surfactant includes at least one of Tween, Span, palmityl alcohol, cyclohexanol, polyoxyethylene ether and polyoxyethylene fatty acid ester.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The reducing agent includes at least one of hydrazine hydrate, formaldehyde and ascorbic acid, the surfactant includes at least one of Span, Tween and polyoxyethylene ether, and the sintering regulator includes at least one of tartronic acid, maleic acid and malic acid.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The mass of the dispersant in S1 is 5%-20% of the mass of the oxidant; and / or The dispersant comprises at least one of polyvinyl pyrrolidone, gum arabic, gelatin, polyvinyl alcohol, polyethylene glycol and β-dextrin; and / or The process of first mixing the reducing agent, sintering regulator, dispersant and water in S1 includes: mixing a reducing solution containing the reducing agent with a reaction base solution containing the dispersant and the sintering regulator, wherein the mass concentration of the reducing agent in the reducing solution is 4%-10%, and the mass concentration of the dispersant in the reaction base solution is 5%-30%.

9. The preparation method according to claim 8, characterized in that: The surfactant is introduced into the reaction base solution in advance, or the surfactant is introduced into the oxidant solution.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The stirring conditions in S1 include: a stirring speed of 100-400 r / min, a temperature maintained at 20-30° C., and an addition time of 5-40 s; the reaction conditions include: a reaction temperature of 20-30° C., and a reaction time of 5-20 min.

11. The preparation method according to any one of claims 1 to 10, characterized in that: In S2, stirring is performed during or after the second mixing. The stirring conditions include: a stirring speed of 100-500 r / min and a stirring time of 5-10 min.

12. The preparation method according to any one of claims 1 to 11, characterized in that: The microscopic morphology of the high temperature silver powder is an open-pore structure, the particle size D50 of the high temperature silver powder is 2.56 μm-4.69 μm, and the shrinkage rate is 9.6%-17.8%.

13. The preparation method according to any one of claims 1 to 11, characterized in that: The microscopic morphology of the low-temperature silver powder is a closed structure, the particle size D50 of the low-temperature silver powder is 1.89 μm, and the shrinkage rate is 11.9%.

14. A conductive silver paste, characterized in that: The invention comprises high-temperature silver powder or low-temperature silver powder prepared by the method for preparing silver powder with adjustable sintering activity as described in any one of claims 1 to 13.

15. Use of the conductive silver paste according to claim 14 in preparing grid lines required for photovoltaic Topcon cells, RFID antennas based on ceramic substrates, photovoltaic HJT cells or RFID antennas based on flexible substrates.

Images