Monodisperse smooth spherical silver powder, its preparation method and use

Abstract

The application discloses monodisperse smooth spherical silver powder, a preparation method and application thereof, wherein the silver powder has a particle size distribution parameter D100 of less than or equal to 4.0 microns, a sphericity ratio range of 0.85 to 1.15, and a specific surface area range of 0.60 to 0.75 m 2 / g. In view of the trend of narrow line width of the metalized printing of the crystalline silicon solar cell, the silver powder as the conductive phase of the silver paste needs to have a smaller D100 value and higher monodispersity. The application realizes high sphericity of the silver particles by constructing high supersaturation, inhibits agglomeration by combining two types of surface adsorbents with adsorption effect, and then adjusts the D100 value and optimizes the smoothness of the surface by Ostwald ripening process, so as to obtain the silver powder with excellent monodispersity, small D100 value, high sphericity and smooth surface, which effectively meets the high-precision requirement of the narrow line width printing of the photovoltaic cell, and is suitable for the field of high-performance conductive paste preparation.

Description

Technical Field

[0001] This invention relates to the field of conductive silver powder technology, and in particular to a monodisperse, smooth-surfaced spherical silver powder, its preparation method, and its uses. Background Technology

[0002] In the field of crystalline silicon solar cell manufacturing, as metallization printing processes develop towards narrower linewidths, the screen design linewidth has shrunk to 6.0~4.0 μm. Silver powder, as the conductive phase of silver paste, needs to possess a smaller maximum particle size distribution (D100) and higher monodispersity to meet the stringent requirements of printing accuracy and electrode line uniformity. However, existing methods for preparing monodisperse spherical silver powder still have significant technical shortcomings: most patents do not explicitly disclose the maximum particle size distribution (D100), only qualitatively describing the particle dispersion state through scanning electron microscopy (SEM) morphology images. However, SEM images are limited by the observation area and magnification, making it difficult to quantitatively reflect the overall particle size distribution dispersion, resulting in insufficient reliability of monodispersity. Furthermore, there is a lack of systematic data on particle sphericity (such as size ratio or roundness), which cannot effectively characterize the influence of silver powder geometry on printing performance (such as line edge smoothness and grid breakage rate).

[0003] Specifically, prior art CN115055690A achieves spherical silver particle preparation by controlling pH, but the reaction process relies on real-time pH adjustment and involves numerous side reactions; CN118699389A uses a high molecular weight dispersant requiring prolonged swelling, resulting in larger silver particles without providing particle size distribution data; CN118848011A requires prolonged high-temperature holding at 120℃, leading to high energy consumption and a complex process; CN117415327A synthesizes silver particles with a high D50 value and does not specify the maximum particle size D100. None of the above patents effectively control the crucial parameter D100, and quantitative data on sphericity are generally lacking, making it difficult to guarantee line uniformity and printing stability in narrow-linewidth printing applications for photovoltaic cells. Summary of the Invention

[0004] This invention addresses the shortcomings of existing methods for preparing monodisperse spherical silver powder, such as the lack of clear control over the D100 parameter, reliance on SEM for qualitative description of monodispersity, and insufficient sphericity data. It focuses on the key parameter D100 in silver powder particle size distribution. Through the synergistic effect of formulation optimization (e.g., using composite adsorbents to regulate silver particle agglomeration and high supersaturation nucleation to construct high sphericity) and post-processing (e.g., Ostwald curing to induce surface smoothing), it aims to prepare silver powder with a reduced D100 value (≤4.0 μm), excellent monodispersity, high sphericity (size ratio 0.85~1.15), and a smooth surface (specific surface area 0.60~0.75 m²). 2This invention provides a silver powder product (g) that quantitatively characterizes particle dispersion and addresses the lack of sphericity parameters, meeting the high precision and consistency requirements of conductive silver powder for narrow linewidth printing in photovoltaic cells. The technical solution provided by this invention is as follows:

[0005] In a first aspect, the present invention provides a monodisperse, smooth-surfaced spherical silver powder, wherein the silver powder has a particle size distribution parameter D100 ≤ 4.0 μm, a sphericity ratio ranging from 0.85 to 1.15, and a specific surface area ranging from 0.60 to 0.75 m². 2 / g.

[0006] In some specific embodiments, the particle size distribution parameters of the silver powder are: D10 value of 0.70~0.95 μm, D50 value of 1.05~1.65 μm, and D90 value of 1.55~2.55 μm.

[0007] Secondly, the present invention also provides a method for preparing monodisperse, surface-smooth spherical silver powder, comprising the following steps:

[0008] (1) Solution preparation: Prepare silver nitrate solution, dispersant solution containing reducing agent, first adsorbent solution, second adsorbent solution and aging agent solution containing chloride ions respectively;

[0009] (2) Generation of monodisperse silver particles: The silver nitrate solution and the first adsorbent solution are added to the dispersant solution containing the reducing agent within a first preset time to carry out a reduction reaction; the second adsorbent solution is added within a second preset time and the reaction continues for a third preset time to obtain monodisperse silver particles;

[0010] (3) Solid-liquid separation: The silver particles are subjected to solid-liquid separation, washing and centrifugation to obtain wet powder;

[0011] (4) Surface curing: The wet powder is mixed with a curing agent solution containing chloride ions and an alcohol solvent, and heated under stirring to carry out Ostwald curing. Then, it is centrifuged and washed to obtain spherical silver powder with a smooth surface.

[0012] (5) Particle size control: The spherical silver powder after aging is dried and crushed to control the final silver powder's D100≤4.0 μm, sphericity of 0.85~1.15, and specific surface area of ​​0.60~0.75 m². 2 / g.

[0013] In some specific embodiments, the silver nitrate solution is an aqueous solution with a concentration of 0.15~2.45 mol / L;

[0014] The dispersant solution containing reducing agent comprises a dispersant and a reducing agent; wherein the dispersant is selected from at least one of polyvinylpyrrolidone, Tween, and polyethylene glycol, and the reducing agent is selected from at least one of ascorbic acid, glucose, and stannous chloride, and the content of the dispersant is 1.0% to 20.0% of the mass of silver ions.

[0015] In some specific embodiments, the molar ratio of the reducing agent to the silver nitrate solution is 0.52 to (1.05:1).

[0016] In some specific embodiments, the first adsorbent solution is selected from at least one of citric acid, gluconic acid, tartaric acid, tartaric acid, acrylic acid, maleic acid, malic acid, lactic acid, glycolic acid, sorbic acid, fumaric acid, and pyruvic acid, and its molar ratio with the silver nitrate solution is 1.0:(5.0~40.0).

[0017] The second adsorbent solution is a substance that promotes the surface modification of silver powder into a prismatic shape, and is selected from at least one of lauric acid and its sodium salt, oleic acid and its sodium salt, sodium polycarboxylate, imidazole, stearic acid and its sodium salt, and palmitic acid and its sodium salt; its mass concentration is 1% to 10%, and the amount used is 0.1% to 5% of the mass of silver ions.

[0018] In some specific embodiments, the chloride-containing curing agent solution is an alcoholic or aqueous solution of sodium chloride or potassium chloride, with a mass concentration of 10% to 40%, and the amount used is 0.2% to 0.6% of the mass of silver ions;

[0019] The first adsorbent solution is mixed with the dispersant solution containing the reducing agent before the reduction reaction, or mixed with the silver nitrate solution and then added to the dispersant solution containing the reducing agent;

[0020] The first preset time is 1~10s, the second preset time is 0~120s, and the third preset time is 5~10min.

[0021] In some specific implementations, in step (3), the electrical conductivity of the wet powder is <200 μS / cm and the water content is <50% of the theoretical mass of silver powder produced.

[0022] In some specific implementations, in step (4), the aging treatment temperature is greater than 50 ℃ and the action time is 30~120 min;

[0023] The alcohol solvent is 100% to 150% of the mass of the wet powder.

[0024] In some specific implementations, in step (5), the aged silver powder is dried at 60~70℃ for 2~4h.

[0025] Thirdly, the present invention also provides a use of monodisperse, surface-smooth spherical silver powder, which is used as a conductive paste for the fine grid on the front side of a crystalline silicon solar cell.

[0026] By adopting the above technical solution, the monodisperse, surface-smooth spherical silver powder, its preparation method, and its uses provided by the present invention have the following beneficial effects:

[0027] 1. The spherical silver powder of this invention possesses significant characteristics such as smooth surface, strong monodispersity, and a cumulative particle size distribution D100 value ≤ 4.0 μm, which can precisely meet the high-precision requirements of narrow linewidth metallization printing on the surface of crystalline silicon solar cells in the photovoltaic field. Its high sphericity (quasi-spherical structure, with a size 1 to size 2 ratio ranging from 0.85 to 1.15) has been statistically verified by SEM. Its regular geometric shape is beneficial for improving the leveling and printing uniformity of the silver paste. Surface smoothness, measured by dynamic method, shows a specific surface area ranging from 0.60 to 0.75 μm. 2 The / g parameter is used for quantitative characterization. This parameter is directly related to the dispersion state of silver powder in the paste and the printing performance. It can effectively reduce line defects caused by the roughness of the particle surface during the printing process and improve the conductivity and yield of the battery cell electrode.

[0028] 2. This invention utilizes the synergistic regulation of two composite adsorbents at specific addition points and times to construct a prismatic structure on the surface of silver particles, improving their monodispersity, effectively inhibiting particle agglomeration, and reducing the D100 value. Simultaneously, the silver powder particles undergo high-temperature Ostwald curing, transforming their surface structure from prismatic to smooth during drying, further reducing the D100 value and optimizing surface smoothness. When used with pastes, the viscosity is moderate, reducing the breakage rate of printed lines. This invention achieves integrated control of silver powder particle size distribution, sphericity, and surface morphology, solving the problems of insufficient quantitative characterization of monodispersity, missing sphericity parameters, and uncontrollable surface smoothness in existing technologies. It improves the applicability and reliability of silver powder in narrow-linewidth printing applications for photovoltaic cells, providing crucial material support for the preparation of high-precision conductive pastes. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram illustrating the constraint dimensions of high sphericity silver powder in two diameter directions provided in an embodiment of the present invention;

[0031] Figure 2This is a microscopic morphology diagram of the silver powder with a prismatic state on the intermediate surface provided in Embodiment 1 of the present invention;

[0032] Figure 3 This is a microscopic morphology diagram of the silver powder in the final smooth state provided in Embodiment 1 of the present invention;

[0033] Figure 4 This is a microscopic morphology diagram of the silver powder in the final smooth state provided in Embodiment 2 of the present invention;

[0034] Figure 5 This is a microscopic morphology diagram of the silver powder in the final smooth state provided in Embodiment 3 of the present invention;

[0035] Figure 6 This is a microscopic morphology diagram of the silver powder in the final smooth state provided in Embodiment 5 of the present invention;

[0036] Figure 7 This is a microscopic morphology diagram of the silver powder in the final smooth state provided in Embodiment 6 of the present invention;

[0037] Figure 8 This is a microscopic morphology diagram of Comparative Example 1;

[0038] Figure 9 This is a microscopic morphology diagram of Comparative Example 2;

[0039] Figure 10 This is a microscopic morphology diagram of Comparative Example 3;

[0040] Figure 11 This is a microscopic morphology diagram of Comparative Example 4;

[0041] Figure 12 This is a microscopic morphology diagram of Comparative Example 5. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0044] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0045] This invention provides a monodisperse, smooth-surfaced spherical silver powder. The silver powder has a particle size distribution parameter D100 ≤ 4.0 μm, a sphericity ratio ranging from 0.85 to 1.15, and a specific surface area ranging from 0.60 to 0.75 m². 2 / g. Specifically, D100≤4.0 μm ensures that 90% of the silver powder particles have a diameter not exceeding 4.0 μm, meeting the stringent requirements of screen design linewidths of 6.0~4.0 μm under the trend of narrowing printing linewidths. This effectively avoids short circuits or broken lines caused by large particles, ensuring the applicability of silver paste in fine pattern printing; the sphericity ratio ranges from 0.85 to 1.15. It is quantitatively characterized by the ratio of the two largest dimensions (labeled as size 1 and size 2) in the diameter direction of spherical silver powder obtained by scanning electron microscopy (SEM). Please refer to [link to relevant documentation]. Figure 1The sphericity within this range indicates that the silver powder particles are close to ideal spherical in shape and have high morphological regularity, which helps to improve the fluidity of the silver paste and the uniformity of printing; the specific surface area ranges from 0.60 to 0.75 m². 2 The / g value, obtained using dynamic methods (such as continuous flow chromatography or dynamic gas adsorption), refers to the total surface area per unit mass of material. For metal powders such as silver powder, this value directly reflects the microstructure and activity of the particle surface. A specific surface area within this range indicates that the silver powder surface is smooth, has low agglomeration, and weak interparticle interaction. This is beneficial for improving the dispersion stability and wettability of silver paste, and also enhances the compatibility of conductive fillers and organic carriers, thereby meeting the comprehensive performance requirements of high-end electronic pastes for monodisperse, smooth-surfaced spherical silver powder in terms of conductivity, process adaptability, and long-term reliability.

[0046] In some specific implementations, the particle size distribution parameters of the silver powder are: D10 value of 0.70~0.95 μm, D50 value of 1.05~1.65 μm, and D90 value of 1.55~2.55 μm.

[0047] This invention also provides a method for preparing monodisperse, surface-smooth spherical silver powder, comprising the following steps:

[0048] (1) Solution preparation: Prepare silver nitrate solution, dispersant solution containing reducing agent, first adsorbent solution, second adsorbent solution, and aging agent solution containing chloride ions, respectively. Among them, silver nitrate solution is used as the silver ion (Ag) aging agent solution. + The source of the silver particles is preferably an aqueous solution with a concentration of 0.15~2.45 mol / L. The dispersant solution containing the reducing agent contains both a dispersant and a reducing agent, used to regulate the surface charge of silver particles, inhibit agglomeration, and stabilize suspension. The first adsorbent solution is used to regulate the local concentration of silver atoms through complexation adsorption before or in the early stage of the redox reaction, inhibiting particle agglomeration in the initial nucleation stage (controlling the size of agglomerates ≤ 5 particles), and simultaneously participating in the construction of the initial morphological basis of silver particles. The second adsorbent solution is used after the formation of silver particles to induce the formation of a branched structure (intermediate state) on the particle surface by selectively adsorbing onto specific crystal faces (such as high-energy crystal faces), enhancing electrostatic repulsion and steric hindrance between particles, and further inhibiting agglomeration. The aging agent solution containing chloride ions is an alcohol (preferably ethanol) or aqueous solution of sodium chloride or potassium chloride. Chloride ions, as key surface regulating ions, can participate in surface smoothing in the subsequent Ostwald aging process by inducing surface diffusion and lattice reconstruction of silver atoms.

[0049] (2) Generation of monodisperse silver particles: Silver nitrate solution and the first adsorbent solution are added to a dispersant solution containing a reducing agent within a first preset time to carry out a reduction reaction; a second adsorbent solution is added within a second preset time and the reaction continues for a third preset time to obtain monodisperse silver particles. Specifically, the method of adding the first adsorbent solution is not specifically limited. It can be pre-dissolved in the dispersant solution containing the reducing agent to form a homogeneous system, or it can be pre-mixed with the silver nitrate solution to form a composite solution before being added to the dispersant solution simultaneously. Regardless of the method used, it is ensured that the first adsorbent solution is completely dissolved and uniformly dispersed in the reaction system before the reduction reaction starts. By rapidly introducing the silver nitrate solution and the first adsorbent solution into the dispersant solution containing the reducing agent within a very short time (1~10s), a highly supersaturated environment is constructed, triggering a transient nucleation reaction and generating a large number of tiny silver nuclei. The high supersaturation condition encourages silver atoms to preferentially deposit on the surface of existing crystal nuclei rather than forming new nuclei, thus effectively inhibiting excessive nucleus proliferation and laying the foundation for the formation of monodisperse silver particles. Simultaneously, the first adsorbent precisely regulates the local concentration of silver atoms through complexation adsorption, further optimizing the nucleation density and reducing the tendency to aggregate. After silver nuclei are generated, the second adsorbent solution is added immediately or after a specific time window of 1–120 s (e.g., 1 s, 5 s, 30 s, 60 s, 120 s), and the reaction continues for 5–10 min. The second adsorbent selectively adsorbs onto high-energy crystal faces (such as angular crystal faces) on the surface of the silver particles, reducing the surface energy of these faces and guiding the particle surface to preferentially grow towards lower energy directions, forming intermediate-state silver particles with a prismatic structure on the surface (microscopically appearing as regular spherical particles with attached micro-protrusions). This prismatic structure not only significantly reduces direct contact and agglomeration between particles through steric hindrance but also provides a reconfigurable morphological basis for the subsequent surface smoothing process.

[0050] (3) Solid-liquid separation: The silver particles are subjected to solid-liquid separation, washing, and centrifugation to obtain wet powder. Specifically, the silver particle system generated by the reaction is filtered (e.g., by vacuum filtration or centrifugal filtration), washed with deionized water (to remove residual reactants, unreacted dispersants, and adsorbents), and centrifuged to obtain wet powder with controllable water content (the water content after solid-liquid separation after centrifugation must be less than 50% of the theoretically generated silver powder mass). The conductivity of the wet powder after washing is less than 200 μS / cm (to ensure that there is no residual electrolyte interfering with subsequent processes), providing a pure particle substrate for surface curing.

[0051] (4) Surface curing: The wet powder is mixed with a curing agent solution containing chloride ions and an alcohol solvent, and heated under stirring to perform Ostwald curing. Then, it is centrifuged and washed to obtain spherical silver powder with a smooth surface. Specifically, the Ostwald curing effect under high temperature conditions is used to transform the surface structure of silver particles from a prismatic to a smooth state, and the particle size distribution is precisely controlled. The specific operation is as follows: the wet powder is mixed with a curing agent solution containing chloride ions and an alcohol solvent (such as ethanol, the amount of which is 100%~150% of the mass of the wet powder) to form a uniform suspension; the temperature is gradually increased to above 50°C (preferably 55~65°C) under stirring, and the curing treatment is carried out at this temperature for 30~120 min. Under high-temperature conditions, chloride ions induce silver atoms on the surface of silver particles to diffuse into the particle interior (accelerating the surface atom migration rate). Simultaneously, silver atoms in high-surface-energy, orthorhombic structural regions (such as protruding corners) preferentially dissolve and migrate to the low-energy particle bulk surface for redeposition, gradually shaping the particle surface into a smoother, curved structure. Alcohol solvents reduce the surface tension of the solution, inhibiting particle aggregation during the aging process and assisting in removing residual moisture adsorbed on the surface. Ultimately, the silver particle surface transforms from an initial orthorhombic shape into a spherical structure with a certain curvature, improving surface smoothness (dynamic method measurement shows a specific surface area reduced to 0.60–0.75 m²). 2 / g corresponds to a lower surface roughness).

[0052] (5) Particle size control: The spherical silver powder after aging is dried and crushed to control the final silver powder's D100≤4.0 μm, sphericity of 0.85~1.15, and specific surface area of ​​0.60~0.75 m². 2 / g. Specifically, through the synergistic effect of drying and mechanical crushing, the cumulative particle size distribution D100 value of the silver powder is strictly controlled within the range of ≤4.0 μm, while maintaining high sphericity (0.85~1.15) and surface smoothness. First, a drying treatment is performed, where the matured spherical silver powder is dried at 60~70℃ (e.g., 60℃, 65℃, 70℃) for 2~4 h (e.g., 2h, 3h, 4h) to remove residual moisture and solvent, obtaining dried silver powder. Subsequently, the dried silver powder is moderately crushed using mechanical grinding or air jet milling (controlling the crushing intensity to avoid excessive fineness leading to the destruction of monodispersity), ultimately obtaining a D100 ≤4.0 μm, sphericity 0.85~1.15, and specific surface area 0.60~0.75 m². 2 / g silver powder product. The particle size distribution of the crushed silver powder is detected by a laser particle size analyzer to ensure that it meets the stringent requirements for uniformity of silver powder particle size and maximum particle size in narrow linewidth printing of photovoltaic cells (screen linewidth 6.0~4.0 μm).

[0053] This method achieves integrated control of silver powder monodispersity, low D100 value, high sphericity, and surface smoothness through a complete process design of "high supersaturation nucleation → adsorbent synergistic inhibition of agglomeration → Ostwald curing surface trimming → drying and crushing particle size control". It solves the technical problems of wide silver powder particle size distribution, insufficient quantitative characterization of monodispersity, and printing defects caused by surface roughness in the existing technology. It is particularly suitable for the preparation of high-precision conductive paste for metallization of photovoltaic cells.

[0054] In some specific embodiments, the silver nitrate solution is an aqueous solution with a concentration of 0.15~2.45 mol / L (e.g., 0.15 mol / L, 1.8 mol / L or 2.45 mol / L). This concentration range can meet both the process requirements of large-scale production and the economic needs of industrial production.

[0055] The dispersant solution containing a reducing agent comprises a dispersant and a reducing agent; wherein the dispersant is selected from at least one of polyvinylpyrrolidone, Tween, and polyethylene glycol, and the reducing agent is selected from at least one of ascorbic acid, glucose, and stannous chloride. The content of the dispersant is determined to be 1.0% to 20.0% (e.g., 1.0%, 5.0%, 10.0%, 15.0%, or 20.0%) of the mass of silver ions, based on the dissolving effect and steric hindrance of different dispersants. The dispersant regulates the surface charge and steric hindrance of silver particles to inhibit aggregation and maintain dispersion stability, while the reducing agent reduces silver ions to metallic silver, driving nucleation and growth reactions. The two work synergistically to precisely control the nucleation and growth process of silver particles.

[0056] In some specific implementations, to ensure complete reduction of silver ions, the molar ratio of reducing agent to silver nitrate solution is (0.52~1.05):1 (e.g., 0.52:1, 0.8:1, 0.9:1, 1.0:1 or 1.05:1).

[0057] In some specific embodiments, the first adsorbent solution is selected from at least one of citric acid, gluconic acid, tartaric acid, tartaric acid, acrylic acid, maleic acid, malic acid, lactic acid, glycolic acid, sorbic acid, fumaric acid, and pyruvic acid, and its molar ratio with the silver nitrate solution is 1.0:(5.0~40.0) (e.g., 1.0:5.0, 1.0:10.0, 1.0:20.0, 1.0:30.0, 1.0:40.0). Through the complexation and adsorption of silver atoms by the organic acid, the size of the spherical silver particle aggregates (≤5 particles) is limited during the reaction, inhibiting excessive aggregation.

[0058] The second adsorbent solution is a substance that promotes the surface modification of silver powder into a prismatic shape, selected from at least one of lauric acid and its sodium salt, oleic acid and its sodium salt, sodium polycarboxylate, imidazole, stearic acid and its sodium salt, and palmitic acid and its sodium salt; its mass concentration is 1%~10% (e.g., 1%, 3%, 5%, 7%, 10%), and its amount is 0.1%~5% of the mass of silver ions (e.g., 0.1%, 0.5%, 1%, 3%, 5%). Insufficient concentration will lead to poor dispersion and easy agglomeration of silver particles; excessive concentration will cause disorder of the surface structure of silver particles, resulting in an abnormally large specific surface area. This second adsorbent selectively adsorbs onto specific crystal faces of spherical silver particles, promoting the formation of a raised prismatic transitional structure on the surface, which not only strengthens the spatial restraint between silver particles and improves dispersion stability, but also effectively controls the particle size distribution of silver particles and significantly reduces the D100 value.

[0059] In some specific embodiments, the chloride-containing curing agent solution is an alcoholic or aqueous solution of sodium chloride or potassium chloride, with a mass concentration of 10% to 40% (e.g., 10%, 20%, 30%, 40%), and the amount used is 0.2% to 0.6% of the mass of silver ions (e.g., 0.2%, 0.3%, 0.4%, 0.5%, 0.6%), preferably an ethanol solution. By inducing silver atoms to diffuse from the particle surface to the interior at high temperature, the surface structure of the silver particles is repaired and smoothed, reducing the D100 value of the silver powder and improving the surface smoothness.

[0060] The first adsorbent solution is mixed with a dispersant solution containing a reducing agent before the reduction reaction, or mixed with silver nitrate solution and then added to a dispersant solution containing a reducing agent.

[0061] The first preset time is 1~10s (e.g., 1s, 3s, 5s, 7s, 10s), which aims to establish an extremely high reaction supersaturation. The second preset time is 0~120s, meaning that the second adsorbent solution can be added immediately after the silver nitrate solution is added, or it can be added after a reaction time such as 1s, 5s, 30s, 60s, 120s. The third preset time is 5~10min (e.g., 5min, 6min, 7min, 8min, 9min, 10min), to ensure that the surface of the silver particles and the second adsorbent interact fully.

[0062] In some specific embodiments, in step (3), the conductivity of the wet powder is <200 μS / cm and the water content is <50% of the theoretical mass of silver powder. By limiting the water content and conductivity of the wet powder, the residual electrolyte in the reaction is ensured to be fully removed, providing a clean reaction substrate for the surface structure trimming and smoothing of silver particles in the subsequent Ostwald ripening process, effectively inhibiting secondary agglomeration and maintaining particle dispersion stability, and improving the high monodispersity of silver powder.

[0063] In some specific embodiments, in step (4), the curing temperature is greater than 50 ℃ (e.g., 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃), and the treatment time is 30~120 min (e.g., 30 min, 60 min, 90 min, 120 min). Utilizing the Ostwald curing effect, the curing agent containing chloride ions can induce the silver powder surface particles to change from rough to a smoother structure. At the same time, the temperature greater than 50 ℃ helps the surface atoms diffuse, and the surface structure changes from an irregular prismatic structure to a spherical structure with a certain curvature.

[0064] The alcohol solvent (preferably ethanol solvent) is 100%~150% of the wet powder mass (e.g., 100%, 110%, 120%, 130%, 140%, 150%). By controlling the amount of alcohol solvent, the surface tension of the solution is reduced to inhibit particle agglomeration during the aging process. At the same time, it helps to remove residual moisture on the surface, providing a stable reaction environment for the smoothing of the silver particle surface during the Ostwald aging process.

[0065] In some specific embodiments, in step (5), the aged silver powder is dried at 60~70℃ for 2~4 hours (e.g., 60℃ for 2 hours, 60℃ for 3 hours, 60℃ for 4 hours, 65℃ for 2 hours, 65℃ for 3 hours, 65℃ for 4 hours, 70℃ for 2 hours, 70℃ for 3 hours, and 70℃ for 4 hours). This removes residual moisture and solvent from the silver powder, forming a dry silver powder substrate with suitable moisture content. This avoids oxidation or agglomeration of the silver powder due to high temperature and provides a raw material with good flowability for subsequent crushing processes.

[0066] This invention also provides an application of monodisperse, smooth-surfaced spherical silver powder, which is used as a conductive agent in the fine grid conductive paste on the front side of crystalline silicon solar cells.

[0067] The following detailed description of examples of the present invention is exemplary and is used only to explain the present invention, and should not be construed as limiting the present invention.

[0068] Example 1

[0069] A method for preparing monodisperse, smooth-surfaced spherical silver powder involves first preparing a silver nitrate solution (100 g of silver nitrate dissolved in water to prepare an aqueous solution of 1.8 mol / L), a dispersant solution containing a reducing agent (56 g of ascorbic acid and 3.2 g of polyvinylpyrrolidone dissolved in water to prepare a mixed solution, wherein the reducing agent concentration in the dispersant solution is 0.8 mol / L and the dispersant content is approximately 5.0% of the mass of silver ions), a first adsorbent solution (3.5 g of citric acid and 3.8 g of malic acid added to the dispersant solution containing the reducing agent), a second adsorbent solution (0.13 g of oleic acid dissolved in water to prepare a solution with a mass concentration of 5%), and a aging agent solution containing chloride ions (0.3 g of sodium chloride dissolved in water to prepare a solution with a mass concentration of 40%). The silver nitrate solution and the first adsorbent solution are added to the dispersant solution containing the reducing agent within 5 seconds, and a reduction reaction is carried out under stirring. Two minutes after the silver nitrate solution is completely added, the second adsorbent solution is added, and the reaction continues for 5 minutes. Min was used to obtain surface-supported spherical silver powder. The silver particles were then washed with sedimentation water and centrifuged to obtain wet powder. The wet powder was mixed with a chloride-containing curing agent solution and 100g of ethanol solvent, and heated to 55℃ for Ostwald curing with stirring for 60 min. Afterwards, it was centrifuged and washed to obtain smooth-surfaced spherical silver powder. The cured spherical silver powder was dried at 60℃ for 2 h, and finally crushed to obtain particle size distribution parameters D100 ≤ 4.0 μm, sphericity 0.85 ~ 1.15, and specific surface area 0.66 m². 2 / g of monodisperse, surface-smooth spherical silver powder. Figure 2 and Figure 3 This is a SEM image of the silver powder in this embodiment.

[0070] Example 2

[0071] Following the preparation method of Example 1, except that 5.7 g of citric acid and 4.4 g of malic acid were added to the dispersant solution containing the reducing agent. The particle size distribution of the silver powder was characterized using an Anton Paar PSA9000 laser particle size analyzer; the D10 value was 0.799 μm, the D50 value was 1.197 μm, the D90 value was 1.864 μm, and the D100 value was 3.0 μm. The specific surface area was measured to be 0.68 m² using the dynamic specific surface method. 2 / g, Figure 4 This is an SEM image of the silver powder in this embodiment; the surface is smooth.

[0072] Example 3

[0073] The preparation method was the same as in Example 1, except that 3.0 g of tartaric acid and 1.5 g of glycolic acid were added to the dispersant solution containing the reducing agent. The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 0.770 μm, D50 value was 1.074 μm, D90 value was 1.695 μm, and D100 value was 3.0 μm. The specific surface area was measured to be 0.73 m² using the dynamic specific surface method. 2 / g, Figure 5 The image shows an SEM image of the silver powder in this embodiment. The silver particles have a smooth surface and high sphericity.

[0074] Example 4

[0075] The preparation method was the same as in Example 1, except that the amount of the second adsorbent was increased to 0.26 g (i.e., the amount of the second adsorbent was 0.4% of the mass of the silver ions). The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 0.735 μm, D50 value was 1.241 μm, D90 value was 2.111 μm, and D100 value was 4.0 μm. The specific surface area was measured to be 0.63 m² using the dynamic specific surface method. 2 / g.

[0076] Example 5

[0077] The preparation method was the same as in Example 1, except that the second adsorbent solution was added 30 seconds after the silver nitrate solution was added. The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 0.914 μm, D50 value was 1.515 μm, D90 value was 2.457 μm, and D100 value was 4.0 μm. The specific surface area was measured to be 0.65 m² using the dynamic specific surface method. 2 / g. Figure 6 This is a SEM image of the silver powder in this embodiment.

[0078] Example 6

[0079] Following the preparation method of Example 1, the difference was that the amount of ripening agent was reduced; 0.13 g of sodium chloride was dissolved in water to prepare a 20% (w / w) solution. The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 0.763 μm, D50 value was 1.356 μm, D90 value was 2.318 μm, and D100 value was 4.0 μm. The specific surface area was measured to be 0.72 m² using the dynamic specific surface method. 2 / g. Figure 7 The image shows an SEM image of the silver powder in this embodiment. The surface of the silver particles is relatively smooth.

[0080] Comparative Example 1

[0081] The preparation method was the same as in Example 1, except that a second adsorbent solution was not used. The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 1.604 μm, D50 value was 3.052 μm, D90 value was 5.283 μm, and D100 value was 10.0 μm. The specific surface area was measured to be 0.58 m² using the dynamic specific surface method. 2 / g. Figure 8 The image shows a SEM image of the silver powder in this comparative example, revealing obvious aggregation between particles.

[0082] Comparative Example 2

[0083] The preparation method was the same as in Example 1, except that the first adsorbent solution was not used. The particle size distribution of the silver powder was characterized using a laser particle size analyzer, with a D10 value of 1.924 μm, a D50 value of 3.344 μm, a D90 value of 5.558 μm, and a D100 value of 10.0 μm. Figure 9 The image shows a comparative example of silver powder SEM images. The silver powder exhibits a distribution of large and small particles, and the weakening of complexation leads to uneven particle size.

[0084] Comparative Example 3

[0085] The preparation method was the same as in Example 1, except that the second adsorbent was added 600 s after the silver nitrate solution was added. The particle size distribution of the silver powder was characterized using a laser particle size analyzer, with a D10 value of 1.292 μm, a D50 value of 2.112 μm, a D90 value of 3.457 μm, and a D100 value of 6.0 μm. Figure 10 The image shows a SEM image of the silver powder in this comparative example. The particle surface is relatively rough and agglomerated, and the D100 value is significantly increased.

[0086] Comparative Example 4

[0087] The preparation method was the same as in Example 1, except that no aging agent was used for surface aging. The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 0.984 μm, D50 value was 1.545 μm, D90 value was 2.440 μm, and D100 value was 4.0 μm. The specific surface area of ​​the silver powder was determined to be 0.88 m² using the dynamic specific surface method. 2 / g, rough surface Figure 11 The image shows a SEM image of the synthesized silver powder in this comparative example. The silver particles have a porous structure on their surface, which weakens the aging effect.

[0088] Comparative Example 5

[0089] The preparation method was the same as in Example 1, except that the silver nitrate was added and dissolved over a time of 30 seconds. The particle size distribution of the silver powder was characterized using a laser particle size analyzer: D10 value was 1.434 μm, D50 value was 2.324 μm, D90 value was 3.710 μm, and D100 value was 8.0 μm. Figure 12 The image shown is a SEM image of the silver powder in this comparative example.

[0090] Table 1 Particle size distribution and specific surface area

[0091]

[0092] Based on the above test data, the test results show that the absence of adsorbent will lead to a wider distribution and larger particle size of silver powder, and cause severe agglomeration between silver particles; the addition time of silver nitrate solution and second adsorbent solution must be strictly controlled, and exceeding the required range will also cause agglomeration of silver particles and changes in morphology; in addition, aging agent can promote Ostwald aging on the surface of silver particles, thereby making the surface of silver particles smooth and reducing their specific surface area.

Claims

1. A method for preparing monodisperse, smooth-surfaced spherical silver powder, characterized in that, Includes the following steps: (1) Solution preparation: Prepare silver nitrate solution, dispersant solution containing reducing agent, first adsorbent solution, second adsorbent solution and aging agent solution containing chloride ions respectively; wherein, the first adsorbent solution is selected from at least one of citric acid, gluconic acid, tartaric acid, tartaric acid, acrylic acid, maleic acid, malic acid, lactic acid, glycolic acid, sorbic acid, fumaric acid and pyruvic acid; the second adsorbent solution is a substance that promotes the surface modification of silver powder into a prismatic shape, and is selected from at least one of lauric acid and its sodium salt, oleic acid and its sodium salt, sodium polycarboxylate, imidazole, stearic acid and its sodium salt, palmitic acid and its sodium salt; (2) Generation of monodisperse silver particles: The silver nitrate solution and the first adsorbent solution are added to the dispersant solution containing the reducing agent within a first preset time to carry out a reduction reaction; the second adsorbent solution is added within a second preset time and the reaction continues for a third preset time to obtain monodisperse silver particles; (3) Solid-liquid separation: The silver particles are subjected to solid-liquid separation, washing and centrifugation to obtain wet powder; (4) Surface curing: The wet powder is mixed with a curing agent solution containing chloride ions and an alcohol solvent, and heated under stirring to carry out Ostwald curing. Then, it is centrifuged and washed to obtain spherical silver powder with a smooth surface. (5) Particle size control: The spherical silver powder after aging is dried and crushed to control the final silver powder's D100≤4.0 μm, sphericity ratio range of 0.85~1.15, and specific surface area of ​​0.60~0.75 m². 2 / g, with particle size distribution parameters of: D10 value of 0.70~0.95 μm, D50 value of 1.05~1.65 μm, and D90 value of 1.55~2.55 μm; wherein, the ratio of sphericity refers to the ratio of the two largest dimensions in the diameter direction of the spherical silver powder.

2. The preparation method according to claim 1, characterized in that, The silver nitrate solution is an aqueous solution with a concentration of 0.15~2.45 mol / L; The dispersant solution containing reducing agent comprises a dispersant and a reducing agent; wherein the dispersant is selected from at least one of polyvinylpyrrolidone, Tween, and polyethylene glycol, and the reducing agent is selected from at least one of ascorbic acid, glucose, and stannous chloride, and the content of the dispersant is 1.0% to 20.0% of the mass of silver ions.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the reducing agent to the silver nitrate solution is (0.52~1.05):

1.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the first adsorbent solution to the silver nitrate solution is 1.0:(5.0~40.0). The mass concentration of the second adsorbent solution is 1% to 10%, and the amount used is 0.1% to 5% of the mass of silver ions.

5. The preparation method according to claim 1, characterized in that, The chloride-containing curing agent solution is an alcoholic or aqueous solution of sodium chloride or potassium chloride, with a mass concentration of 10% to 40%, and the amount used is 0.2% to 0.6% of the mass of silver ions. The first adsorbent solution is mixed with the dispersant solution containing the reducing agent before the reduction reaction, or mixed with the silver nitrate solution and then added to the dispersant solution containing the reducing agent; The first preset time is 1~10s, the second preset time is 0~120s, and the third preset time is 5~10min.

6. The preparation method according to claim 1, characterized in that, In step (3), the electrical conductivity of the wet powder is <200 μS / cm and the water content is <50% of the theoretical mass of silver powder produced.

7. The preparation method according to claim 1, characterized in that, In step (4), the aging treatment temperature is greater than 50℃ and the treatment time is 30~120min; The alcohol solvent is 100% to 150% of the mass of the wet powder.

8. The preparation method according to claim 1, characterized in that, In step (5), the aged silver powder is dried at 60~70℃ for 2~4h.

9. The use of a monodisperse, surface-smooth spherical silver powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The silver powder is used as a conductive agent in the conductive paste for the fine grid on the front side of crystalline silicon solar cells.

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