High tap density silver powder, preparation method therefor, and use thereof

Abstract

A method for preparing a high tap density silver powder, comprising the following steps: dispersing a silver salt in an alkanolamine solution, adding a dispersant, and then reacting same with an organic amine solution to obtain silver particles. The method can prepare spherical powder having different particle sizes. The silver paste prepared from the spherical silver powder generally has better fluidity, and large-particle-size silver particles and small-particle-size silver particles fill the empty space within each other, thereby ensuring sufficient contact areas within the silver powder, improving the overall sintering performance, and being suitable for solar cell manufacturing. The present invention also relates to a high tap density silver powder and a use thereof.

Description

A high tap density silver powder, its preparation method and application Cross-reference to related applications This disclosure claims priority to Chinese Patent Application No. 2024114618624, filed on October 18, 2024, entitled "A High Tap Density Silver Powder and Its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field This disclosure relates to the field of metallic materials technology, and in particular to a high tap density silver powder, its preparation method, and its application. Background Technology Silver powder possesses excellent electrical and thermal conductivity and corrosion resistance, making it widely used in the electronics industry, aerospace, and materials science. In recent years, its application in the photovoltaic field has been increasing. Silver powder is used as a conductive material in heterojunction cells, and the application of high-temperature / low-temperature silver paste technology has further broadened its use in this area. The morphology, particle size, and tap density of silver powder, among other parameters, affect the printability of conductive pastes, thus determining the photoelectric conversion efficiency of solar cells. Currently, silver powder generally suffers from poor dispersibility and low tap density, resulting in poor printability after being made into silver paste. Therefore, preparing micron-sized silver powder with good dispersibility and high tap density is one of the key factors in improving the photoelectric conversion efficiency of solar cells. Currently, the method for preparing silver powder that can be mass-produced in China is the liquid-phase reduction method. This method involves adding reducing and dispersing solutions to a silver salt solution using a peristaltic pump in a multi-flow, timed, and quantitative manner. However, the dispersion of silver powder particles produced by this method is difficult to control, and the tap density is generally low. Summary of the Invention This disclosure aims to at least address one of the aforementioned technical problems existing in the prior art. Therefore, the purpose of this disclosure is to provide a high tap density silver powder, its preparation method, and its applications. To achieve the above objectives, the technical solution adopted in this disclosure is as follows: The first aspect of this disclosure provides a method for preparing silver particles, comprising the following steps: dispersing a silver salt in an alcoholic amine solution, and then reacting it with an organic amine solution to obtain the silver particles. In this disclosure, the reduction rates of the alkanolamine solution and the organic amine solution for silver salts differ, resulting in silver powder with varying particle sizes. Smaller silver powder particles fill the gaps between larger particles, reducing the inter-particle size and leading to a more compact overall structure, thus increasing the tap density of the silver powder. Furthermore, compared to individual large or small silver powder particles, the smaller particles sinter faster, while the larger particles maintain their shape well at higher temperatures, improving the structural stability of the sintered body and enhancing the overall sintering performance of the silver powder. On the other hand, the alkanolamine solution acts as a co-reducing agent, and the organic amine as the primary reducing agent; their combined action increases the reduction reaction rate, thereby accelerating the formation rate of silver powder. Moreover, the alkanolamine solution itself is weakly alkaline; adding it first provides an alkaline environment for the subsequently added organic amine solution and its reaction with the silver salt, which is beneficial for the reduction reaction between the organic amine and the silver salt. In some embodiments of this disclosure, the molar ratio of the alkanolamine compound to the silver ions in the silver salt in the alkanolamine solution is 0.05 to 5:1, such as 0.1:1, 0.5:1.0, 1:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, etc.; if the concentration of silver ions is too high, it may be difficult to disperse them effectively; the addition of alkanolamine can increase the rate of reduction reaction between the organic amine solution and the silver salt, accelerate the generation rate of silver powder, improve the purity of silver powder, and reduce the occurrence of side reactions. In some embodiments of this disclosure, the molar concentration of the silver salt is controlled to be 0.008–5.0 mol / L before the organic amine solution is added, such as 0.1 mol / L, 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, or 4.5 mol / L. In some embodiments of this disclosure, the molar ratio of the organic amine compound in the organic amine solution to the silver ions in the silver salt is 0.005 to 0.15:1, such as 0.008:1, 0.01:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1, 0.12:1, etc. In some embodiments of this disclosure, the silver salt includes at least one of silver sulfate, silver nitrate, silver oxide, silver acetate, silver oxalate, silver phosphate, silver hexafluorophosphate, silver tetrafluoroborate, silver hexafluoroarsenate, silver chromate, silver chloride, silver bromide, silver iodide, silver carbonate, silver bicarbonate, silver benzoate, silver tartrate, silver laurate, silver perchlorate, and silver perbromate. In some embodiments of this disclosure, the alkanolamine solution includes a solution of at least one selected from diethanolamine, methyldiethanolamine, ethanolamine, dimethylethanolamine, diethylene glycolamine, isopropanolamine, triisopropanolamine, oleic acid diethanolamide, stearic acid diethanolamide, lauric acid diethanolamide, and octadecyl diethanolamine. In some embodiments of this disclosure, the organic amine solution includes a solution of at least one of triethylamine, N,N-diisopropylethylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, cyclohexylamine, N,N-dimethyloctylamine, N,N-dimethyldecylamine, tris(3,6-dioxaheptyl)amine, and octylamine. In some embodiments of this disclosure, the pH of the organic amine solution is controlled to be 10-13, such as 10.5, 11, 11.5, 12, 12.5, etc.; at least one of the pH adjusters such as monoethanolamine, triethanolamine, and sodium hydroxide can be used to control the pH of the organic amine solution within this range, so as to facilitate the reduction reaction. The particle size of the silver powder precipitated by reduction decreases as the reaction pH increases. In some embodiments of this disclosure, the reaction is a hydrothermal reaction; the reaction temperature is 75–235°C, such as 75–170°C, 90–210°C, 90–155°C, 100–200°C, 120–180°C, etc.; the reaction time is 0.5–12 h, such as 1–10 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, etc.; the hydrothermal reaction can be controlled by methods known in the art, a common method being to place the hydrothermal reactor in an oven for temperature control; to improve the uniformity of the reaction, the hydrothermal reaction can be carried out under stirring, and the stirring rate can be controlled at 200–500 rpm. In the silver powder manufacturing method disclosed herein, the yield, purity, and particle size of the silver powder can be controlled by controlling the feeding ratio of reactants such as alcohol amine solution and organic amine solution in the hydrothermal reaction, or by controlling the temperature and time of the hydrothermal reaction, thereby regulating the tap density of the silver powder. In the silver powder manufacturing method disclosed herein, the use of an alcoholic amine solution and an organic amine solution can accelerate the reduction rate of silver salt by the organic amine without making the reaction rate too fast. Therefore, it is not necessary to strictly control the pH or temperature of the mixed solution or base solution of the alcoholic amine solution and silver salt; nor is it necessary to control the temperature of the organic amine solution. After the organic amine solution is added, the system will not immediately undergo a hydrothermal reaction or the reaction rate will be too fast, causing the reaction process to become uncontrollable and the particle size of the silver powder in the initial stage to be difficult to control effectively. After the organic amine solution is added, an additional stirring procedure can be performed before the hydrothermal reaction to improve the reaction uniformity, thereby allowing for easy control of the particle size of the silver powder. In the silver powder manufacturing method disclosed herein, to improve the uniformity of the silver salt reaction and the dispersibility of the reduced and precipitated silver powder, a dispersant is used to treat the silver salt dispersion and the silver powder. Specifically, the silver salt is dispersed in an alcoholic amine solution, a dispersant is added, and then the mixture is reacted with an organic amine solution. The mass ratio of the dispersant to the silver atoms in the silver salt is (0.05–8):1. Preferably, a hydrophobic dispersant is used, including at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, sodium citrate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, gelatin, methylcellulose, citric acid, Tween 60, propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, icosanoic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid, and ricinoleic acid. By using the above-mentioned dispersant, both the adsorption of the dispersant to silver and the dispersibility between silver particles can be considered, preventing the silver powder particles from agglomerating. In the silver powder manufacturing method disclosed herein, after obtaining a solid-liquid mixture at the end of the hydrothermal reaction, the solid-liquid mixture is washed and recycled. In the washing and recycling step, the slurry is dehydrated, and the filter cake of silver powder is washed. The washing in the washing and recycling step can be performed, for example, using pure water. The dehydration in the washing and recycling step can be performed, for example, by decantation or pressure filtration. The endpoint of washing can be determined using the conductivity of the washing water. Specifically, washing can be considered complete when the conductivity of the washing water is below a specified value, such as when its conductivity reaches 0.5 mS / m or less. After the cleaning and recycling process is completed, a drying process is carried out to dry the filter cake containing the recovered silver powder. The drying process can use a vacuum dryer or an airflow dryer. During the drying process, a high-pressure airflow can be blown onto the filter cake and the silver powder during the drying process, or the filter cake and the silver powder can be fed into a mixer with a stirring rotor or a pulverizer with a crushing rotor for stirring. This imparts a dispersing force to the filter cake and the silver powder during the drying process, promoting dispersion and drying. It should be noted that the temperature of the silver powder should be set below 70℃ during the drying process. If the temperature of the silver powder exceeds 70℃, the silver particles in the silver powder may sinter together. During or after the drying process, crushing, pulverizing, or grading operations can be performed to adjust the particle size distribution of the silver powder. Pulverizing operations can be carried out using air-jet or mechanical pulverizers. Grading operations can be performed using grading rotors, cyclone air grading, inertial grading, or sieving operations. A second aspect of this disclosure provides silver powder obtained by the method for preparing the silver particles described above. In some embodiments of this disclosure, the average particle size of the silver powder is 1.0 to 3.1 μm, such as 1.1 to 2.99 μm, 1.1 to 2.5 μm, 1.1 to 2.2 μm, etc. In some embodiments of this disclosure, the silver powder, in a volume-based particle size distribution measured by a laser diffraction scattering particle size distribution measuring device, has a cumulative 50% particle size (D50) of 3.0 μm or less, such as 2.5 μm or less, 2.0 μm or less, 1.8 μm or less, or 1.7 μm or less; and a cumulative 100% particle size (D100) of 20 μm or less, such as 18 μm or less, 15 μm or less, 12 μm or less, 10 μm or less, or 9 μm or less. The particle size distribution of the silver powder, based on volume, is determined using a laser diffraction scattering particle size distribution measuring device. In this embodiment, the following description uses the PSA1090 particle size distribution measuring device (hereinafter simply referred to as the particle size distribution measuring device) manufactured by AntonPaar. The particle size distribution of the silver powder can be determined by dispersing it in a specified dispersion medium, i.e., by wet chromatography. In this embodiment, 0.1 g of silver powder is added to 40 mL of isopropanol as the dispersion medium, and the dispersion is prepared by dispersing it for 2 minutes using an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., US-150T; 19.5 kHz, tip diameter 18 mm). This dispersion is then used to measure the particle size distribution of the silver powder using the particle size distribution measuring device. In this specification, regarding particle size distribution, the cumulative 50% particle size refers to the so-called median particle size. The cumulative 50% particle size means the diameter at which the volumetric basis of the particle quantity from the smallest side of the particle size distribution reaches 50%. Similarly, the cumulative 100% particle size is the diameter at which the volumetric basis of the particle quantity from the smallest side of the particle size distribution reaches 100%. Hereinafter, the cumulative 50% particle size and the cumulative 100% particle size in volumetric terms are sometimes referred to as D50 and D100, respectively. In some embodiments of this disclosure, in the volume-based particle size distribution of silver powder, the ratio of the difference between the cumulative 90% particle size and the cumulative 10% particle size to the cumulative 50% particle size (Span, particle size distribution width) can be 2.20 or less, such as 2.10 or less, 2.08 or less, 2.01 or less, or 2.00 or less. The smaller the Span, the smaller the difference, indicating that the particle size distribution of the silver powder is narrower, its dispersibility is better, and the overall tap density of the formed silver powder is higher. In some embodiments of this disclosure, the tap density of the silver powder is 5.80 g / cm³ or higher, such as 5.85 g / cm³ or higher, 6.00 g / cm³ or higher, 6.30 g / cm³ or higher, 6.50 g / cm³ or higher, 6.60 g / cm³ or higher, 6.60–7.10 g / cm³, or 6.60–7.0 g / cm³. The tap density of the silver powder is the apparent density of the silver powder in the container after a predetermined amount of silver powder has been measured and placed into a container of predetermined capacity, and the container has been dropped a predetermined number of times with a predetermined drop (hereinafter referred to as "after tapping"). It is obtained by dividing the weight of the silver powder in the container by the apparent volume of the silver powder in the container. In some embodiments of this disclosure, the tap density of the silver powder is obtained as follows: using a tap density measuring device (Shibayama Scientific Co., Ltd., SS-DA-2 volumetric density measuring device), 50g of silver powder is measured and placed in a container (50mL test tube). The container is then tapped 3,000 times at a vibration frequency of 200 (i.e., 200 vibrations per minute). The value is obtained by dividing the weight of the silver powder (50g) by the apparent volume (cm³) of the tapped silver powder. It should be noted that the unit of tap density is expressed as "g / cm³". In some embodiments of this disclosure, the silver powder is spherical silver powder. Spherical means that when silver powder is observed under a scanning electron microscope (SEM), the particle sphericity is spherical or approximately spherical, and the sphericity of 100 particles is less than 1.5. Sphericity refers to the ratio of the longest diameter to the shortest diameter when the particles are observed through SEM images. A third aspect of this disclosure provides a conductive paste comprising silver powder obtained by the method for preparing the silver particles. In some embodiments of this disclosure, the conductive paste comprising the silver powder is prepared by dispersing the silver powder in a resin (binder) and a solvent, which serve as a substrate. In some embodiments of this disclosure, the conductive paste includes the silver powder, resin, and solvent. In some embodiments of this disclosure, examples of resins used in the preparation of the conductive paste include epoxy resin, acrylic resin, polyester resin, polyimide resin, polyurethane resin, phenoxy resin, silicone resin, and ethyl cellulose. Two or more resins may be used simultaneously. In some embodiments of this disclosure, examples of solvents, i.e. dispersion media, used to prepare the conductive paste are terpineol, butylcarbitol, butylcarbitol acetate, and texanol. Two or more solvents may be used simultaneously. In some embodiments of this disclosure, the conductive paste may contain components other than those described above. For example, it may contain glass frit, dispersant, surfactant, and viscosity modifier.

[0038] In some embodiments of this disclosure, the preparation, i.e., dispersion and mixing of conductive slurry can be carried out using ultrasonic dispersion, disperser, three-roll mill, ball mill, bead mill, twin-shaft kneader, self-rotating and revolution-type mixer, etc. In some embodiments of this disclosure, the conductive paste using the silver powder of this disclosure is suitable for forming conductive films, i.e., forming conductive patterns and electrodes on a substrate. For example, it can be applied directly to various substrates such as silicon wafers for solar cells, films for touch panels, and glass for EL elements, or, as needed, to films on which a transparent conductive film is further disposed, to form conductive films. The conductive films obtained using the conductive paste of this disclosure are suitable for applications such as current collector electrodes for solar cell units, external electrodes for chip-type electronic components, RFID, electromagnetic wave shielding, oscillator bonding, membrane switches, electroluminescence electrodes, or electrical wiring. In some embodiments of this disclosure, a conductive paste is printed onto a substrate, for example by screen printing, offset printing, photolithography, etc., thereby forming a conductive film of a desired shape. The beneficial effects of this disclosure are: 1. The silver particle preparation method disclosed herein can produce spherical powders with different particle sizes. Silver paste prepared from spherical silver powder usually has better flowability. Large and small silver particles fill each other, ensuring sufficient contact area between silver powders, which can meet the performance requirements of front-side silver paste for silver powder. 2. The silver particle preparation method disclosed herein can produce spherical powders with different particle sizes, which can be applied to high and low temperature sintering silver paste. During sintering, the silver powders of different sizes can work together with each other compared to individual large or small particles. Small particles can accelerate the sintering process, while large particles can better maintain their shape at higher temperatures, thereby improving structural stability and improving overall sintering performance. Therefore, mixed large and small powders have sintering advantages compared to single large powders or single small powders, and are suitable for solar cell manufacturing. 3. The method for preparing silver particles disclosed herein is an environmentally friendly method that can be carried out at lower temperatures and pressures, and the byproducts are generally easy to handle. Attached Figure Description Figure 1 is a SEM image of the silver powder prepared in Example 1 of this disclosure. Figure 2 is an SEM image of the silver powder prepared in Example 2 of this disclosure. Figure 3 is a SEM image of the silver powder prepared in Example 3 of this disclosure. Figure 4 is an SEM image of the silver powder prepared in Example 4 of this disclosure. Figure 5 is a SEM image of the silver powder prepared in Example 5 of this disclosure. Figure 6 is an SEM image of the silver powder prepared in Example 6 of this disclosure. Figure 7 is a SEM image of the silver powder prepared in Comparative Example 1 of this disclosure. Figure 8 is a SEM image of the silver powder prepared in Comparative Example 2 of this disclosure. Figure 9 is a SEM image of the silver powder prepared in Comparative Example 3 of this disclosure. Figure 10 is a SEM image of the silver powder prepared in Comparative Example 4 of this disclosure. Figure 11 is a SEM image of the silver powder prepared in Comparative Example 5 of this disclosure. Embodiments of the present invention The following specific embodiments further illustrate the content of this disclosure in detail. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art. Example 1 This embodiment prepares silver particles, and the specific process is as follows: 1. Preparations before the experiment: The amine solution used was dimethylethanolamine with an effective ingredient content of 98%, and the molar ratio of dimethylethanolamine to Ag was 2.25:1. The dispersant used is 98.5% oleic acid, and the mass of oleic acid is 6.14% of the mass of silver ions; The organic amine solution used was octylamine with an effective ingredient content of 98%, and the molar ratio of octylamine to Ag was 0.0798:1. Preparation of pH adjuster solution: Sodium hydroxide solution with a mass fraction of 40%, the molar amount of sodium hydroxide is approximately 0.58% of the molar amount of silver ions. 2. Weigh 2g of silver carbonate (molar amount of silver ions is 0.0145mol) and add it to the inner liner of the hydrothermal reactor. Then add 2.468g of dimethylethanolamine and 0.1246g of oleic acid to it. Place the inner liner on a magnetic stirrer and turn it on at 300rpm until it is uniform and the bottom liquid is obtained. 3. Add 0.0084g of sodium hydroxide solution to 0.152g of octylamine to adjust the pH of octylamine to 12 to obtain a reducing agent solution; 4. Pour the reducing agent solution into the inner liner of the hydrothermal reactor and mix it with the bottom liquid. Turn on the magnetic stirrer and stir for 10 minutes at 300 rpm. Then, place the inner liner into the hydrothermal reactor and put it in an oven at 105℃ for 3 hours. 5. After the reaction, once the hydrothermal reactor has cooled to room temperature (25°C), deionized water and alcohol are added sequentially to the inner liner of the hydrothermal reactor for washing and drying (drying temperature is 55°C, drying time is 2.5h) to obtain silver particles. Example 2 This embodiment prepared a silver particle, the preparation method of which differs from that of Example 1 in that the molar ratio of dimethylethanolamine to Ag is 4:1. Example 3 In this embodiment, a silver particle was prepared. The preparation method differs from that in Example 1 in that the initial molar amount of silver ions is 4.5 mol, that is, the molar ratio of dimethylethanolamine to Ag is 0.00725:1, and the molar ratio of octylamine to Ag is 0.00025:1. Example 4 This embodiment prepared silver particles, and the preparation method differed from that in Example 1 in that the mass of oleic acid was 1.8% of the mass of silver ions. Example 5 This embodiment prepared a silver particle, the preparation method of which differs from that of Example 1 in that the molar ratio of octylamine to Ag is 0.12:1. Example 6 This embodiment prepared a silver particle, the preparation method of which differs from that of Example 1 in that the molar ratio of dimethylethanolamine to Ag is 8:1. Example 7 This embodiment prepares a silver particle, the preparation method of which differs from that of Example 1 in that: the organic amine solution used is cyclohexylamine with an effective ingredient content of 99%, and the molar ratio of cyclohexylamine to Ag is 0.0926:1. Example 8 This embodiment prepares a silver particle, the preparation method of which differs from that of Example 1 in that: the amine solution used is triisopropanolamine with an effective ingredient content of 95%, and the molar ratio of triisopropanolamine to Ag is 2:1. Comparative Example 1 This comparative example prepared a silver powder, and the specific process is as follows: 1. Preparations before the experiment are the same as in Example 1;

[0085] 2. Weigh 2g of silver carbonate (molar amount of silver ions is 0.0145mol) and add it to the inner liner of the hydrothermal reactor. Then add 2.468g of dimethylethanolamine and 0.1246g of oleic acid to it. Place the inner liner on a magnetic stirrer and turn it on at 300rpm until the mixture is homogeneous and the bottom liquid is obtained. After stirring the magnetic stirrer at 300rpm for 10min, place the inner liner in the hydrothermal reactor and place it in an oven at 105℃ for 3h. 3. After the reaction, once the hydrothermal reactor has cooled to room temperature (25°C), deionized water and alcohol are added sequentially to the inner liner of the hydrothermal reactor for washing and drying (drying temperature is 55°C, drying time is 2.5h) to obtain silver powder. Comparative Example 2 This comparative example prepared a silver powder, and the specific process is as follows: 1. Preparations before the experiment are the same as in Example 1; 2. Weigh 2g of silver carbonate (molar amount of silver ions is 0.0145mol) and add it to the inner liner of the hydrothermal reactor; add 0.0084g of sodium hydroxide solution to 0.152g of octylamine to adjust the pH value of octylamine to 12 to obtain a reducing agent solution; add the reducing agent solution and 0.1246g of oleic acid to the inner liner of the hydrothermal reactor; turn on the magnetic stirrer and stir at 300rpm for 10min, then place the inner liner in the hydrothermal reactor and place it in an oven at 105℃ for 3h; 3. After the reaction, once the hydrothermal reactor has cooled to room temperature (25°C), deionized water and alcohol are added sequentially to the inner liner of the hydrothermal reactor for washing and drying (drying temperature is 55°C, drying time is 2.5h) to obtain silver powder. Comparative Example 3 This comparative example prepared a silver powder, the preparation method of which differs from that of Example 1 in that: hydrazine hydrate is used to replace octylamine in Example 1, and the molar ratio of hydrazine hydrate to Ag is 0.0798:1. Comparative Example 4 This comparative example prepared a silver powder, the preparation method of which differs from that of Example 1 in that: cyclohexylamine was used to replace dimethylethanolamine in Example 1, and the molar ratio of cyclohexylamine to Ag was 2.25:1. Comparative Example 5 This comparative example prepared a silver powder, the preparation method of which differs from that of Example 1 in that: diethanolamine is used instead of octylamine in Example 1, and the molar ratio of diethanolamine to Ag is 0.0798:1. Test case The prepared silver powder was characterized, and the results are shown in Table 1: Table 1 Figures 1-11 are SEM images of the silver powders prepared in Examples 1-6 and Comparative Examples 1-5. Combined with Table 1 and Figures 1-11, it can be seen that the silver powders in Examples 1-6 have good dispersibility, low particle size distribution width (Span), good particle flowability, and high tap density. In Example 6, although the silver powder showed some agglomeration and the overall tap density decreased, there was still enough small-sized silver powder to fill the spaces between the large-sized silver powder particles, and the tap density still reached 5.89 g / cm3. Furthermore, agglomeration was not likely to occur during the subsequent preparation of the conductive paste. Comparative Example 1, as shown in Figure 7, had no large or small powder particles; all particles were small, resulting in a low tap density. Comparative Example 2, as shown in Figure 8, had an excessive amount of large powder particles and almost no small powder particles. During the preparation of the paste, due to the lack of small powder particles to fill the gaps, the large powder particles were prone to agglomeration, resulting in poor flowability and a decline in performance. In Comparative Example 3, the reducing agent used had a strong reducing power, which led to a significant increase in the average particle size, D50, and D100 of the product silver powder, resulting in a decrease in the overall tap density of the silver powder. In Comparative Examples 4 and 5, only organic amine solutions or alkanolamine solutions were used for reduction. Although large and small powder particles were produced in the product silver powder, the particle size of both small and large powder particles increased significantly, resulting in obvious particle agglomeration, poor powder dispersibility, and a low tap density. The silver particles disclosed herein can be applied to conductive silver paste. First, tap density has a significant impact on the thick film microstructure of the conductive silver paste. The silver powder particles with high tap density in Examples 1-6 are more likely to form a uniform dispersion in the paste, reducing particle aggregation and resulting in a better microstructure. During thick film preparation, uniform dispersion of silver powder particles makes the film layer denser, reducing porosity and improving conductivity. Conversely, the silver powder particles with low tap density in Comparative Examples 1-5 tend to aggregate, forming an uneven microstructure, leading to increased porosity and reduced conductivity. Second, tap density also affects the electrical properties of the conductive silver paste. The silver powder particles with high tap density in Examples 1-6 have better conductivity because high tap density means a larger contact area between silver powder particles and a shorter electron conduction path. Furthermore, silver powder particles with high tap density are more likely to form interconnected networks in the film layer, providing more conductive pathways and further improving conductivity. The tap density of the silver powder also affects the rheological properties of the conductive silver paste. Rheological properties refer to the physical characteristics of conductive silver paste during processing, such as viscosity and flowability. The high-tap-density silver powder particles in Examples 1-6 are more easily and evenly dispersed in the paste, reducing viscosity, increasing flowability, and facilitating processing. Conversely, the low-tap-density silver powder particles in Comparative Examples 1-5 tend to aggregate, resulting in higher viscosity, reduced flowability, and increased processing difficulty. The above embodiments are preferred embodiments of this disclosure, but the embodiments of this disclosure are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this disclosure shall be considered equivalent substitutions and shall be included within the protection scope of this disclosure. Industrial applicability 1. The silver particle preparation method disclosed herein can produce spherical powders with different particle sizes. Silver paste prepared from spherical silver powder usually has better flowability. Large and small silver particles fill each other, ensuring sufficient contact area between silver powders, which can meet the performance requirements of front-side silver paste for silver powder. 2. The silver particle preparation method disclosed herein can produce spherical powders with different particle sizes, which can be applied to high and low temperature sintering silver paste. During sintering, the silver powders of different sizes can work together with each other compared to individual large or small particles. Small particles can accelerate the sintering process, while large particles can better maintain their shape at higher temperatures, thereby improving structural stability and improving overall sintering performance. Therefore, mixed large and small powders have sintering advantages compared to single large powders or single small powders, and are suitable for solar cell manufacturing. 3. The method for preparing silver particles disclosed herein is an environmentally friendly method that can be carried out at lower temperatures and pressures, and the byproducts are generally easy to handle.

Claims

1. A method for preparing silver particles, characterized in that: Includes the following steps: The silver salt is dispersed in an alcoholic amine solution and then reacted with an organic amine solution to obtain the silver particles.

2. The method for preparing silver particles according to claim 1, characterized in that: The preparation method satisfies at least one of the following conditions: (I) the molar ratio of the alkanolamine compound to the silver ions in the silver salt in the alkanolamine solution is 0.05 to 5:1; (II) the molar ratio of the organic amine compound to the silver ions in the silver salt in the organic amine solution is 0.005 to 0.15:1; (III) the pH of the organic amine solution is controlled to be 10 to 13.

3. The method for preparing silver particles according to claim 1 or 2, characterized in that: The amine solution includes at least one of diethanolamine, methyldiethanolamine, ethanolamine, dimethylethanolamine, diethylene glycolamine, isopropanolamine, triisopropanolamine, oleic acid diethanolamide, stearic acid diethanolamide, lauric acid diethanolamide, and octadecyl diethanolamine.

4. The method for preparing silver particles according to any one of claims 1-3, characterized in that: The organic amine solution includes at least one of triethylamine, N-ethyldiisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, cyclohexylamine, dimethyloctylamine, dimethyldecylamine, tri(3,6-dioxaheptyl)amine, and octylamine.

5. The method for preparing silver particles according to any one of claims 1-4, characterized in that: The preparation method includes the following steps: dispersing silver salt in an alcohol amine solution, adding a dispersant, and then reacting it with an organic amine solution.

6. The method for preparing silver particles according to claim 5, characterized in that: The dispersant is a hydrophobic dispersant.

7. The method for preparing silver particles according to claim 5, characterized in that: The dispersant includes at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, sodium citrate, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, gelatin, methylcellulose, citric acid, Tween 60, propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, icosanoic acid, acrylic acid, oleic acid, linoleic acid, arachidonic acid, and ricinoleic acid.

8. The method for preparing silver particles according to any one of claims 1-7, characterized in that: The preparation method satisfies at least one of the following conditions: (I) the reaction is a hydrothermal reaction; (II) the reaction temperature is 75–235°C; (III) the reaction time is 0.5–12 h; (IV) the reaction is carried out under stirring at a stirring rate of 200–500 rpm.

9. The method for preparing silver particles according to claim 8, characterized in that: After the hydrothermal reaction is completed and a solid-liquid mixture is obtained, the solid-liquid mixture is washed and recycled. In the washing and recycling process, the slurry is dehydrated and the silver powder filter cake is washed. Pure water is used for washing. The washing is considered complete when the conductivity of the washing water reaches below 0.5 mS / m.

10. The method for preparing silver particles according to claim 9, characterized in that: After the cleaning and recycling process is completed, a drying process is carried out to dry the filter cake of the recovered silver powder.

11. The method for preparing silver particles according to claim 10, characterized in that: During the drying process, the temperature of the silver powder is set below 70°C.

12. Silver particles prepared by the method of any one of claims 1 to 11.

13. The silver particles according to claim 12, characterized in that: The silver particles satisfy at least one of the following conditions: (I) average particle size of 1.0–3.1 μm; (II) D50 of 3.0 μm or less; (III) D100 of 20 μm or less; (IV) Span of 2.20 or less; (V) tap density of 5.80 g / cm³. 3 above.

14. A conductive paste comprising silver particles prepared by the method of any one of claims 1 to 11; or, silver particles as described in claim 12 or 13.

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