Silver powder and preparation method therefor, conductive silver paste, electronic device and electric equipment

Abstract

A method for preparing a silver powder, comprising: subjecting a first silver salt, a first dispersing agent and a first reducing agent to a first treatment, so as to obtain silver crystal nucleuses; and subjecting the silver crystal nucleus, a second silver salt, a second dispersing agent, a second reducing agent and a modifying agent to a second treatment, so as to obtain a silver powder, wherein the modifying agent comprises lauric acid, decanoic acid and undecanoic acid. The silver powder prepared by means of the method has good dispersity and wettability, a narrow particle size distribution, a small particle size and high sintering activity, and is not prone to agglomeration in a conductive silver paste, thereby enabling the conductive silver paste to have a high solid content and endowing the conductive silver paste with good conductivity. The present invention further relates to a silver powder, a conductive silver paste, an electronic device and electric equipment.

Description

Silver powder, preparation method thereof, conductive silver paste, electronic device and electrical equipment

[0001] Priority information

[0002] The present disclosure claims priority to the Chinese patent application No. 202411077786.7, filed on August 7, 2024, entitled "Silver powder, preparation method thereof, conductive silver paste, electronic device and electrical equipment", and incorporates it herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, in particular to a silver powder, a preparation method thereof, a conductive silver paste, an electronic device and an electrical equipment. BACKGROUND

[0004] The conductive silver paste prepared based on the ultra-fine spherical silver powder has the advantages of good fluidity, easy printing, small sintering shrinkage, and dense film formation, and is widely used in the fields of photovoltaic, electronics, metallurgy, etc.

[0005] At present, the method for industrializing preparing ultra-fine silver powder mainly adopts liquid phase chemical reduction method. The traditional liquid phase reduction method for preparing silver powder has the following problems: easy to appear agglomeration phenomenon in the process of synthesizing silver powder, low sintering activity of silver powder, and difficult to clean and remove the dispersant or modifier after the synthesis of silver powder, etc. Moreover, the low-temperature conductive silver paste often faces the challenges of low solid content and high resistivity, and these performance limitations affect its efficiency and reliability in electronic and photovoltaic applications.

[0006] Therefore, the current silver powder and conductive silver paste still need to be developed. SUMMARY

[0007] The present disclosure aims to at least solve one of the technical problems in the related art. To this end, one object of the present disclosure is to propose a silver powder, a preparation method thereof, a conductive silver paste, an electronic device and an electrical equipment. The silver powder of the present disclosure has good dispersibility and wettability, high particle size concentration, small particle size, high sintering activity, and can be used for low-temperature conductive silver paste. The silver powder is not easy to appear agglomeration phenomenon in the conductive silver paste, has high solid content, and endows the conductive silver paste with excellent conductive performance.

[0008] The first aspect of the present disclosure proposes a method for preparing a silver powder. According to the embodiments of the present disclosure, the method comprises: performing a first treatment on a first silver salt, a first dispersant and a first reducing agent to obtain a silver nucleus;

[0009] performing a second treatment on the silver nucleus, a second silver salt, a second dispersant, a second reducing agent and a modifier to obtain a silver powder;

[0010] wherein the modifier comprises lauric acid, sunflower acid and undecanoic acid.

[0011] According to the method of the embodiments of the present disclosure, by separating the nucleation stage and the growth stage in the crystal formation process in two systems, the silver powder nuclei formed have substantially consistent nucleation ages, effectively avoiding secondary nucleation in the growth stage, thereby making the particle size distribution of the finally formed silver powder more uniform. In addition, in the growth stage, by using lauric acid, sunflower acid and undecanoic acid to modify and coat the surface of the silver particles, the wettability of the silver powder is enhanced, making it have good dispersibility in the conductive silver paste, thereby improving the conductivity and solid content of the conductive silver paste.

[0012] According to the embodiments of the present disclosure, the method can also have the following additional technical features:

[0013] According to the embodiments of the present disclosure, the mass ratio of the lauric acid, the sunflower acid and the undecanoic acid is (0.5-50):1:(0.03-3).

[0014] According to the embodiments of the present disclosure, the mass ratio of the lauric acid, the sunflower acid and the undecanoic acid is (1-10):1:(0.1-1).

[0015] According to the embodiments of the present disclosure, the mass of the modifier is 0.1%-1% of the mass of the second silver salt.

[0016] According to the embodiments of the present disclosure, the mass of the modifier is 0.4%-0.6% of the mass of the second silver salt.

[0017] According to the embodiments of the present disclosure, the first reducing agent and the second reducing agent each independently includes at least one of ascorbic acid and hydrazine hydrate.

[0018] According to the embodiments of the present disclosure, the mass ratio of the ascorbic acid and the hydrazine hydrate is (0.5-2):1;

[0019] And / or, the molar ratio of the first reducing agent to the first silver salt is (0.1-1):1;

[0020] And / or, the mass of the second reducing agent is 0.5-1 times the mass of the second silver salt.

[0021] According to the embodiments of the present disclosure, the first dispersing agent and the second dispersing agent each independently includes at least one of oleic acid, polyvinylpyrrolidone, gum arabic, gelatin, polyvinyl alcohol, polyethylene glycol and Tween 80.

[0022] According to the embodiments of the present disclosure, the first dispersing agent includes polyvinylpyrrolidone;

[0023] And / or, the second dispersing agent includes oleic acid.

[0024] According to an embodiment of the present disclosure, the mass of the first dispersant is 10% to 60% of the mass of the first silver salt.

[0025] And / or, the mass of the second dispersant is 0.01 to 0.1 times of the mass of the second silver salt.

[0026] According to an embodiment of the present disclosure, the first silver salt and the second silver salt each independently comprises at least one of silver chloride, silver nitrate or silver carbonate.

[0027] According to an embodiment of the present disclosure, the first treatment comprises:

[0028] adding a solution containing the first silver salt to the mixed solution containing the first dispersant and the first reducing agent, and mixing to obtain the silver crystal nucleus.

[0029] According to an embodiment of the present disclosure, the solution containing the first silver salt is added to the mixed solution at one time.

[0030] According to an embodiment of the present disclosure, the temperature of the mixed solution is 40°C to 60°C.

[0031] And / or, the system temperature is maintained at 40°C to 60°C during the mixing.

[0032] According to an embodiment of the present disclosure, the mixed solution is obtained by comprising the following steps:

[0033] mixing the solution containing the first dispersant and the solution containing the first reducing agent, heating to a first preset temperature, and then cooling to a second preset temperature;

[0034] The first preset temperature is 90°C to 100°C; and / or, the second preset temperature is 40°C to 60°C.

[0035] According to an embodiment of the present disclosure, the second treatment comprises:

[0036] adding a solution containing the second silver salt to the mixed solution containing the silver crystal nucleus, the second dispersant, the second reducing agent and the modifier, and mixing to obtain a mixed slurry;

[0037] collecting the crystals in the mixed slurry, and then washing and crushing the crystals to obtain the silver powder;

[0038] wherein, the washing is performed by using water and a washing liquid respectively, and the washing liquid comprises ethanol and diethylene glycol butyl ether acetate.

[0039] According to an embodiment of the present disclosure, the mass ratio of the ethanol and diethylene glycol butyl ether acetate is (0.1 to 10):1.

[0040] According to an embodiment of the present disclosure, the adding of the solution containing the second silver salt is dropwise, and the dropwise adding speed is 1 L / min to 5 L / min.

[0041] According to an embodiment of the present disclosure, the pH value of the mixed solution is 2 to 3.

[0042] According to an embodiment of the present disclosure, the temperature of the system during the mixing is maintained at 40°C to 60°C.

[0043] The second aspect of the present disclosure provides a silver powder. According to an embodiment of the present disclosure, the silver powder is obtained by the method for preparing a silver powder of the first aspect.

[0044] According to an embodiment of the present disclosure, the Dv50 value of the silver powder is 0.6 μm to 1 μm.

[0045] The third aspect of the present disclosure provides a conductive silver paste. According to an embodiment of the present disclosure, the conductive silver paste comprises the silver powder of the second aspect.

[0046] According to an embodiment of the present disclosure, the curing temperature of the conductive silver paste is 150°C to 250°C.

[0047] According to an embodiment of the present disclosure, the content of the silver powder in the conductive silver paste is 90% to 95% by mass.

[0048] The fourth aspect of the present disclosure provides an electronic device. According to an embodiment of the present disclosure, the electronic device comprises the conductive silver paste of the third aspect of the present disclosure.

[0049] The fifth aspect of the present disclosure provides an electrical equipment. According to an embodiment of the present disclosure, the electrical equipment comprises the electronic device of the fourth aspect of the present disclosure.

[0050] Additional aspects and advantages of the present disclosure will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0051] The above and / or additional aspects and advantages of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, wherein:

[0052] FIG. 1 shows a flowchart of a method for preparing a silver powder according to an embodiment of the present disclosure;

[0053] FIG. 2 shows a schematic diagram of surface modification of silver particles according to an embodiment of the present disclosure;

[0054] FIG. 3 shows a flowchart of a method for preparing a silver powder according to another embodiment of the present disclosure;

[0055] FIG. 4 shows a scanning electron microscope (SEM) image of the silver powder prepared in Comparative Example 1 of the present disclosure;

[0056] FIG. 5 shows a particle size distribution graph of the silver powder prepared in Comparative Example 1 of the present disclosure;

[0057] FIG. 6 shows a transmission electron microscope (TEM) image (left) and a high resolution transmission electron microscope (HRTEM) image (right) of the silver powder prepared in Example 1 of the present disclosure;

[0058] FIG. 7 shows scanning electron microscope (SEM) images of the silver powder prepared in Example 1 of the present disclosure at different magnifications;

[0059] FIG. 8 shows a scanning electron microscope (SEM) image of the silver powder prepared in Example 2 of the present disclosure;

[0060] FIG. 9 shows scanning electron microscope (SEM) images of the silver powder prepared in Example 3 of the present disclosure at different magnifications;

[0061] FIG. 10 shows a particle size distribution graph of the silver powder prepared in Example 3 of the present disclosure;

[0062] FIG. 11 shows a scanning electron microscope (SEM) image of the silver powder prepared in Example 4 of the present disclosure;

[0063] FIG. 12 shows a wetting contact angle graph of a solid surface;

[0064] FIG. 13 shows scanning electron microscope (SEM) images of a conductive silver paste prepared using the silver powder of Example 3 of the present disclosure before and after a curing process, (a) before the curing process; (b) after the curing process. DETAILED DESCRIPTION

[0065] Embodiments of the present disclosure are described in detail below. The embodiments described below are examples for explaining the present disclosure and should not be understood as limiting the present disclosure.

[0066] It should be noted that the terms "first", "second" are used only for the purpose of description and should not be understood as indicating or implying relative importance or implying the number of the technical features indicated. Thus, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. Further, in the description of the present disclosure, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0067] The endpoints of the ranges and any values disclosed in the present disclosure are not limited to the precise values recited as the exact range or value should be understood as being encompassed by the ranges or values near them. For ranges of values, the endpoints of each range are included in the range, the endpoints of each range are included in the range, and the individual points within the ranges are included in the range, and the individual points within the ranges are included in the present disclosure.

[0068] In the present disclosure, the term "comprising" or "including" is an open-ended expression, i.e. including the indicated contents of the present disclosure, but not excluding other aspects.

[0069] Liquid phase chemical reduction method is the most commonly used method for preparing ultra-fine silver powder, and the main principle is to reduce silver ions from silver salt solution into silver atoms by adding a reducing agent, and to grow into elemental silver particles. The ultra-fine silver powder prepared by the liquid phase chemical reduction method is easy to agglomerate, so a dispersing agent needs to be added to reduce the agglomeration of silver particles. The liquid phase chemical reduction method has become one of the most widely used production methods in industry due to its simple process, easy availability of raw materials, simple equipment, easy operation and the like.

[0070] The traditional liquid phase reduction method for preparing silver powder has the following problems: 1) Agglomeration phenomenon is easy to occur during the synthesis of silver powder; 2) The sintering activity of silver powder is low, and during the low-temperature curing or sintering of conductive silver paste, the silver powder particles cannot be well sintered and welded together, so that effective conductive paths cannot be formed, resulting in poor conductivity; 3) The dispersing agent or modifier is difficult to wash and remove to a reasonable value after the synthesis of silver powder, resulting in too much organic matter on the surface of silver powder particles, which affects the conductivity of the silver paste.

[0071] Low-temperature conductive silver paste is usually prepared by stirring conductive phase silver powder, organic solvent, binder, additive and the like. Compared with high-temperature conductive silver paste, it has a lower curing temperature, which is conducive to avoiding the adverse effects of high temperature on device materials. The requirements for the composition of low-temperature conductive silver paste are very strict, and the quality, content, morphology, uniformity and particle size of silver powder have important influence on the performance of silver paste. The current low-temperature conductive silver paste has the problems of low solid content and high resistivity.

[0072] Therefore, in the present disclosure, the nucleation stage and the growth stage in the crystal formation process are separated and carried out in two systems, so that the silver powder crystal nucleus formed has a substantially uniform nucleation age, effectively avoiding secondary nucleation in the growth stage, so that the particle size distribution of the finally formed silver powder is more uniform. In addition, in the growth stage, specific modifiers (lauric acid, sunflower acid and undecanoic acid) are used to modify and coat the surface of silver particles to enhance the wettability of silver powder, so that it has good dispersibility in conductive silver paste, thereby improving the conductivity and solid content of the conductive silver paste. In addition, the silver powder has small particles and high sintering activity, so that the curing temperature of the conductive silver paste is low.

[0073] To this end, the first aspect of the present disclosure provides a method for preparing silver powder, and a flow chart of the method for preparing silver powder is shown in FIG. 1. The method comprises S100 obtaining silver crystal nucleus and S200 obtaining silver powder. Step S100 comprises performing first treatment on a first silver salt, a first dispersant and a first reducing agent. Step S200 comprises performing second treatment on the silver crystal nucleus, a second silver salt, a second dispersant, a second reducing agent and a modifier. Each step will be described in detail below.

[0074] The principle of the method for preparing silver powder of the present disclosure to achieve the aforementioned beneficial effects will be described below.

[0075] The preparation of powder materials by liquid phase method is a complex heat and mass transfer process. Different crystallization modes will be produced under different physicochemical conditions. Klaus Borho et al. consider that the reaction and crystallization process occurs in the following order: micro-mixing, physicochemical reaction, nucleation, reversible agglomeration, irreversible agglomeration, crystal nucleus growth and aging. The process of powder preparation by liquid phase method can also be simplified into two main steps of crystal nucleation and growth. The size of the above-mentioned effects is affected by the supersaturation of solute.

[0076] In the liquid phase system, nucleation will occur when the concentration of crystal-forming substances reaches a certain supersaturation. Therefore, the first step in preparing ultrafine powder in the liquid phase is to generate crystal-forming substances (such as molecules, atoms or ions, etc.) through chemical reactions between reactants, and to accumulate their concentration to the supersaturation required for nucleation. In some local small areas in the system, the nucleus of the new phase is first formed, so that the interface of two phases will appear in the system, and the new phase will gradually grow by pushing the old area through the phase interface. Therefore, this process can be divided into two stages of nucleation and growth.

[0077] In the silver powder preparation process, the nucleation stage and the growth stage of crystal formation are carried out separately in two different systems, realizing the independent control and optimization of the two key steps. Specifically, in the nucleation stage, by precisely controlling the reaction conditions, silver powder crystal nuclei with basically consistent nucleation age can be generated. The consistency of nucleation age is crucial for the morphology of silver powder, because it can make the crystal nucleus grow uniformly in the subsequent growth stage, avoiding the secondary nucleation phenomenon caused by the difference in crystal nucleus age in the growth stage. Secondary nucleation will lead to uneven particle size distribution of silver powder, affecting the quality and performance of silver powder. By avoiding secondary nucleation, the final silver powder has a more uniform particle size distribution, which is beneficial to improve the conductivity of silver powder, and can form a more dense and stable conductive network, thereby improving the performance of the final product. In addition, due to the difficulty of agglomeration during the preparation of silver powder, the particle size of silver powder is small, which can be submicron. Compared with large particle size materials, due to the high activity of silver atoms on the surface of silver submicron particles, long-range diffusion between particles is easy to occur, which makes silver particles connect with the surrounding silver particles to realize "welding", so that the melting point of silver submicron particles will also be reduced.

[0078] In addition, in order to improve the solid content of low-temperature conductive silver paste and reduce the resistivity, the present disclosure introduces a modifier in the growth stage of silver powder. Specifically, by using lauric acid, sunflower acid and undecylic acid, these organic carboxylic acid compounds are used to modify and coat the surface of silver particles. These modifiers have carboxylic acid groups -COOH which will react with silver, so that organic matter will be adsorbed on the surface of silver powder, as shown in Figure 2. This modification not only enhances the interaction between silver powder and organic solvent, but also significantly improves the wettability of silver powder, thereby achieving better dispersion in conductive silver paste. Because the silver powder is more uniformly distributed in the silver paste, and the contact between silver particles is more close, which directly leads to the improvement of the conductivity, and also increases the solid content of the silver paste. The increase of solid content means that the mass of silver powder in the same volume is more, which is crucial for improving the conductivity of silver paste and reducing the resistivity. In addition, silver powder in conductive silver paste is not easy to agglomerate, which further helps to reduce the curing temperature of conductive silver paste. Moreover, silver powder is not easy to appear sedimentation and agglomeration phenomenon in the storage and use process of conductive silver paste, prolonging the service life of conductive silver paste.

[0079] According to embodiments of the present disclosure, the mass ratio of the lauric acid, the sunflower acid and the undecanoic acid is (0.5-50):1:(0.03-3), preferably (1-10):1:(0.1-1). Exemplarily, the mass ratio of the lauric acid, sunflower acid and undecanoic acid is 5:1:0.3, 1:1:0.1, 2:1:0.2, 6:1:0.5, 7:1:0.6, 8:1:0.8, 10:1:1. Thus, a uniform and effective surface modification can be provided for the silver powder, which can further enhance the wettability of the silver powder particles, optimize the interaction of the silver powder with the organic solvent, improve the dispersibility of the silver powder in the conductive silver paste, avoid the agglomeration phenomenon, and improve the uniformity and stability of the silver paste.

[0080] According to embodiments of the present disclosure, the mass of the modifier is 0.1%-1% of the mass of the second silver salt. Exemplarily, the mass of the modifier is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, preferably 0.4%-0.6% of the mass of the second silver salt. Thus, a uniform and effective surface modification can be provided for the silver powder, which can further enhance the wettability of the silver powder particles, optimize the interaction of the silver powder with the organic solvent, improve the dispersibility of the silver powder in the conductive silver paste, avoid the agglomeration phenomenon, and improve the uniformity and stability of the silver paste.

[0081] According to embodiments of the present disclosure, the first and second reducing agents each independently comprise at least one of ascorbic acid and hydrazine hydrate. Since the redox reaction rate of ascorbic acid with silver salt is relatively slow, the chemical reaction is easy to control, and thus the obtained silver powder has good dispersibility and morphology. In some embodiments, ascorbic acid is used as the first reducing agent in the nucleation stage, which is conducive to controlling the reaction conditions to obtain crystal nuclei with suitable morphology structure.

[0082] Compared with ascorbic acid, the redox reaction rate of hydrazine hydrate and silver salt is slightly faster, the chemical reaction is short, the concentration of reduced silver atoms is easy to reach supersaturation in a short time, secondary nucleation occurs, different crystal nuclei grow at the same time, the prepared silver powder has a small particle size and a wide distribution, and the dispersibility is low. Ascorbic acid and hydrazine hydrate can cooperatively reduce silver nitrate, the chemical reaction rate is moderate, which is easy to control, and is conducive to obtaining silver powder with good morphology, good dispersibility and narrow particle size distribution, and is especially suitable for the growth stage.

[0083] According to embodiments of the present disclosure, the mass ratio of the ascorbic acid and the hydrazine hydrate is (0.5-2):1, for example, it can be 0.5:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, 2:1. Thus, the redox reaction rate is appropriate, and the secondary nucleation phenomenon in the growth process of the silver powder is reduced, which is conducive to the consistency and uniformity of the particle size of the silver powder.

[0084] According to embodiments of the present disclosure, the molar ratio of the first reducing agent to the first silver salt is (0.1-1): 1, for example, 0.1:1, 0.2:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1, 1:1. Thereby, the reduction reaction can be further promoted to proceed efficiently, reducing excessive reduction or insufficient reduction of silver ions, thereby reducing the agglomeration and irregular growth of silver powder, improving the uniformity of silver powder particles, and reducing the sedimentation and agglomeration of the conductive silver paste during storage and use, prolonging the service life of the conductive silver paste.

[0085] According to embodiments of the present disclosure, the mass of the second reducing agent is 0.5-1 times the mass of the second silver salt, for example, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times. Thereby, the reduction reaction can be further promoted to proceed efficiently, reducing excessive reduction or insufficient reduction of silver ions, thereby reducing the agglomeration and irregular growth of silver powder, improving the uniformity of silver powder particles, and reducing the sedimentation and agglomeration of the conductive silver paste during storage and use, prolonging the service life of the conductive silver paste.

[0086] According to embodiments of the present disclosure, the first dispersant and the second dispersant each independently include at least one of oleic acid, polyvinylpyrrolidone, gum arabic, gelatin, polyvinyl alcohol, polyethylene glycol, and Tween 80. Thereby, the dispersants described above can further improve the dispersibility of silver powder during synthesis.

[0087] In some embodiments, the first dispersant includes polyvinylpyrrolidone (PVP), and the second dispersant includes oleic acid. In the nucleation stage, the addition of PVP helps to obtain silver particles with better dispersibility. In the growth stage, oleic acid not only serves as a dispersant to improve the dispersing effect and avoid particle agglomeration, but also serves as a modifier to improve the wettability of silver powder and avoid agglomeration of silver powder in the silver paste.

[0088] According to embodiments of the present disclosure, the mass of the first dispersant is 10%-60% of the mass of the first silver salt. For example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%. Thereby, the dispersibility of silver particles can be further improved, reducing the occurrence of agglomeration, reducing the excessive dispersant remaining on the surface of silver nuclei, and affecting the growth of silver nuclei and the conductivity, sintering activity, and other properties of the final silver powder.

[0089] According to an embodiment of the present disclosure, the second dispersant has a mass of 0.01-0.1 times the mass of the second silver salt, for example, 0.01 times, 0.02 times, 0.03 times, 0.04 times, 0.05 times, 0.06 times, 0.07 times, 0.08 times, 0.09 times, or 0.1 times. In this way, the dispersibility of silver particles can be further improved, the occurrence of agglomeration can be reduced, the excessive dispersant remaining on the surface of silver powder can be reduced to affect the conductivity, sintering activity, and other properties of the silver powder, and the cleaning difficulty can be increased.

[0090] According to an embodiment of the present disclosure, the first silver salt and the second silver salt each independently comprises at least one of silver chloride, silver nitrate, or silver carbonate.

[0091] According to an embodiment of the present disclosure, the first treatment comprises adding a solution containing the first silver salt to a mixed solution containing the first dispersant and the first reducing agent, and mixing to obtain the silver crystal nucleus.

[0092] According to an embodiment of the present disclosure, the solution containing the first silver salt is added to the mixed solution at one time. Adding silver salt at one time is conducive to quickly reaching the required supersaturation, promoting the rapid nucleation of silver ions in a short time to generate a large number of uniform crystal nuclei. This rapid and concentrated nucleation mode helps to reduce the uneven distribution of silver ions in the solution, reduce the secondary nucleation phenomenon in the subsequent growth process, and thus obtain silver powder with more uniform particle size distribution and better dispersibility. In addition, adding silver salt at one time can also simplify the operation process, improve the production efficiency, reduce the variables in the reaction process, and improve the repeatability and consistency of the silver powder preparation process.

[0093] According to an embodiment of the present disclosure, the temperature of the mixed solution is 40-60°C, for example, 40°C, 42°C, 45°C, 47°C, 50°C, 52°C, 55°C, 57°C, or 60°C. According to another embodiment of the present disclosure, the system temperature is maintained at 40-60°C during the mixing process, for example, 40°C, 42°C, 45°C, 47°C, 50°C, 52°C, 55°C, 57°C, or 60°C. In this way, the nucleation rate is better, more crystal nuclei can be generated in a unit volume, and thus smaller particle sizes can be obtained. In addition, silver powder crystal nuclei with substantially uniform nucleation age can be generated, so that the crystal nuclei can grow uniformly in the subsequent growth stage, and the secondary nucleation phenomenon caused by the difference in nucleation age in the growth stage is avoided. Secondary nucleation can lead to uneven particle size distribution of silver powder, affecting the quality and performance of the silver powder. When the temperature is lower than 40°C or higher than 60°C, the morphology and dispersibility of the silver powder are slightly poor.

[0094] According to an embodiment of the present disclosure, the mixed solution is obtained by the following steps:

[0095] The solution containing the first dispersant and the solution containing the first reducing agent are mixed and heated to a first preset temperature, and then cooled to a second preset temperature.

[0096] In some embodiments, the first preset temperature is 90-100℃, for example, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, or 100℃. In this way, the first dispersant and the first reducing agent can be uniformly dissolved therein, forming a uniform mixture.

[0097] In some embodiments, the second preset temperature is 40-60℃, for example, 40℃, 42℃, 44℃, 45℃, 46℃, 48℃, 50℃, 52℃, 54℃, 55℃, 56℃, 58℃, or 60℃. In this way, nucleation is facilitated, and the reaction rate is appropriate.

[0098] According to embodiments of the present disclosure, the second processing includes:

[0099] A solution containing the second silver salt is added to the mixture containing the silver nuclei, the second dispersant, the second reducing agent, and the modifier, mixed to obtain a mixed slurry;

[0100] The crystals in the mixed slurry are collected, and the crystals are then washed and crushed to obtain the silver powder;

[0101] The washing is performed using water and a washing liquid, respectively, and the washing liquid includes ethanol and diethylene glycol butyl ether acetate. The combination of ethanol and diethylene glycol butyl ether acetate in the washing liquid can clean the dispersant, the modifier, and the reducing agent that are not physically adsorbed on the surface of the silver powder and do not participate in the reaction, and reduce the loss of silver powder, with a low weight loss rate.

[0102] It should be noted that the present disclosure does not strictly limit the number of times of washing with the two reagents, water and the washing liquid, for example, which can be 1-10 times, and the order of washing is not strictly limited, for example, one reagent can be used for multiple times of washing, and then the other reagent can be used for multiple times of washing, or the two reagents can be used alternately, which can be selected flexibly according to actual needs.

[0103] According to embodiments of the present disclosure, the mass ratio of the ethanol and diethylene glycol butyl ether acetate is (0.1-10):1, for example, 0.1:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. In this way, the washing effect can be improved, and the loss of silver powder can be reduced.

[0104] According to an embodiment of the present disclosure, the adding of the solution containing the second silver salt is carried out by dropwise adding, and the dropwise adding is carried out at a rate of 1 L / min to 5 L / min, for example, 1 L / min, 2 L / min, 3 L / min, 4 L / min, or 5 L / min. The dropwise adding is carried out at a controllable rate, which is gradually added to the reaction system, and this helps to maintain the uniformity and stability of the reaction conditions, thereby promoting the uniform growth of the silver powder crystal nucleus. The above-mentioned dropwise adding rate can avoid the rapid growth and agglomeration phenomenon caused by the excessively high concentration of silver ions in the local area, so as to make the growth of the silver powder particles more orderly. In addition, it also helps to reduce the occurrence of side reactions, improve the quality and purity of the silver powder, and at the same time improve the controllability and repeatability of the production process.

[0105] According to an embodiment of the present disclosure, the pH value of the mixed solution is 2 to 3, for example, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3. Thereby, it is helpful for the growth of the crystal nucleus. For example, the pH value of the system can be adjusted by using sodium hydroxide and nitric acid.

[0106] According to an embodiment of the present disclosure, the temperature of the system during the mixing process is maintained at 40°C to 60°C, for example, 40°C, 42°C, 44°C, 45°C, 46°C, 48°C, 50°C, 52°C, 54°C, 55°C, 56°C, 58°C, or 60°C. Thereby, it is beneficial for nucleation, and the reaction rate is appropriate. When the temperature is lower than 40°C or higher than 60°C, the morphology and dispersibility of the silver powder are slightly poor.

[0107] The second aspect of the present disclosure provides a silver powder. According to an embodiment of the present disclosure, the silver powder is obtained by the method for preparing the silver powder of the first aspect. The features and advantages described for the method for preparing the silver powder of the first aspect are also applicable to the silver powder, and will not be repeated here.

[0108] According to an embodiment of the present disclosure, the Dv50 value of the silver powder is 0.6 μm to 1 μm, for example, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm. The Dv50 is the particle size corresponding to the cumulative volume percentage of 50% of the silver powder, which can be measured by using a laser diffraction particle size distribution measuring instrument.

[0109] The silver powder of the present disclosure has small particles and high dispersibility, and is not prone to agglomeration. The silver powder with the above-mentioned particle size has a large specific surface area and surface energy, so that it has excellent properties such as good electrical conductivity and thermal conductivity, and can achieve good sintering effect at low temperature.

[0110] The third aspect of the present disclosure provides a conductive silver paste. According to an embodiment of the present disclosure, the conductive silver paste comprises the silver powder of the second aspect and a paste. The silver powder in the conductive silver paste of the present disclosure is not prone to agglomeration, has high solid content and excellent electrical conductivity. Moreover, due to the small particle size of the silver powder, it has high sintering activity, so that the solidification temperature of the conductive silver paste is relatively low, reducing the energy consumption and cost in the production process and reducing the damage to the device material caused by high temperature. The features and advantages described above for the silver powder of the second aspect also apply to the conductive silver paste, which will not be repeated here.

[0111] According to an embodiment of the present disclosure, the solidification temperature of the conductive silver paste is 150-250°C, for example, it can be 150°C, 160°C, 180°C, 200°C, 220°C, 240°C or 250°C. Due to the small particle size of the silver powder, it has high sintering activity, so that the solidification temperature of the conductive silver paste is relatively low, reducing the energy consumption and cost in the production process and reducing the damage to the device material caused by high temperature.

[0112] According to an embodiment of the present disclosure, the content of silver powder in the conductive silver paste is 90-95% by mass, for example, it can be 90%, 91%, 92%, 93%, 94% or 95% by mass. Since the silver powder of the present disclosure has good wettability and is not prone to agglomeration in organic solvents, the addition amount of silver powder can be increased, so that the content of silver powder in the conductive silver paste is high to improve the electrical conductivity of the conductive silver paste.

[0113] It should be noted that the paste in the conductive silver paste of the present disclosure is not strictly limited and can be a substance commonly used in the art except for the silver powder, such as an organic solvent, a binder, an additive, etc. The ratio of the components can be flexibly selected according to actual needs.

[0114] The fourth aspect of the present disclosure provides an electronic device. According to an embodiment of the present disclosure, the electronic device comprises the conductive silver paste of the third aspect of the present disclosure. Thus, the electronic device of the present disclosure has excellent electrochemical performance.

[0115] The fifth aspect of the present disclosure provides an electrical equipment. According to an embodiment of the present disclosure, the electrical equipment comprises the electronic device of the fourth aspect of the present disclosure. Thus, the electrical equipment of the present disclosure has excellent electrochemical performance.

[0116] It should be noted that the features and advantages described above for the conductive silver paste also apply to the electronic device and the electrical equipment, which will not be repeated here.

[0117] The schemes of the present disclosure will be explained below in conjunction with examples. Those skilled in the art will understand that the examples below are only for illustration of the present disclosure and should not be considered as limiting the scope of the present disclosure. If no specific technology or condition is specified in the examples, the technology or condition described in the literature in the art or according to the product instruction is used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained by purchase in the market.

[0118] Example 1

[0119] Referring to FIG. 3, the ultra-fine silver powder is prepared according to the following method:

[0120] (1) Silver crystal nucleus stage

[0121] The reducing agent solution (ascorbic acid solution and water) and the dispersant solution are added to the reaction kettle, and stirred and heated to 98℃. When the solution is cooled to 50℃, the prepared 5L silver nitrate solution with a concentration of 0.015 mol / L is poured into the reaction kettle at one time, and mechanically stirred for 30 min at 50℃ to obtain a silver crystal nucleus solution.

[0122] The molar ratio of ascorbic acid (V 溶液 = 20L) to silver nitrate is 1.5:2 (C AgNO3 = 0.015 mol / L, V 溶液 = 5L), the dispersant is polyvinylpyrrolidone (PVP K30), and the dispersant content is 45% of the mass of silver nitrate (V 溶液 = 27.5L).

[0123] (2) Crystal nucleus growth stage

[0124] Prepare 2.45Kg silver nitrate dissolved in 25L deionized water to obtain a silver nitrate solution, prepare 5.8L of a reducing agent solution containing 1.88Kg ascorbic acid, prepare 150g oleic acid dissolved in 30L alcohol solution to obtain an oleic acid alcohol solution, and prepare 15g of a modifier (mass ratio of lauric acid, sunflower acid and ethyl undecylic acid is 5:1:0.3) dissolved in 15ml of anhydrous ethanol to obtain a modifier solution.

[0125] Mix 10.5L of the above silver crystal nucleus solution, 5.8L of the reducing agent solution, 30L of the oleic acid alcohol solution, and 12.5ml of the modifier solution uniformly, and adjust the pH value of the mixed solution to 2.65 with NaOH solution; when the mixed solution is heated to 50℃, add the silver nitrate solution at a flow rate of 1.5L / min through a peristaltic pump, continue stirring for 30 min after the addition is completed; centrifuge the above reaction solution containing silver powder, and wash it with deionized water and organic cleaning solution (ethanol and diethylene glycol butyl ether acetate with a mass ratio of 1:1) in turn for 10 times each, vacuum dry at 80℃, and grind to obtain the silver powder.

[0126] Example 2

[0127] The difference from Example 1 is that ascorbic acid in step (2) is replaced by hydrazine hydrate.

[0128] Example 3

[0129] The difference from Example 1 is that 0.94 Kg ascorbic acid in step (2) is replaced by 0.94 Kg hydrazine hydrate, i.e. the mass ratio of ascorbic acid to hydrazine hydrate is 1:1.

[0130] Example 4

[0131] The difference from Example 1 is that 0.376 Kg ascorbic acid in step (2) is replaced by 0.376 Kg hydrazine hydrate, i.e. the mass ratio of ascorbic acid to hydrazine hydrate is 4:1.

[0132] Comparative Example 1

[0133] Prepare 2.45 Kg silver nitrate to be dissolved in 25 L deionized water to obtain a silver nitrate solution, prepare 5.8 L of a reducing agent solution containing 0.94 Kg of hydrazine hydrate and 0.94 Kg of ascorbic acid each, prepare 150 g of oleic acid to be dissolved in 30 L of an alcohol solution, prepare 15 g of a modifier (mass ratio of lauric acid, sunflower acid and ethyl undecanoate is 5:1:0.3) to be dissolved in 15 ml of anhydrous ethanol to obtain a modifier solution. Mix 10.5 L of the above crystal nucleus solution, 5.8 L of the reducing agent solution, 30 L of the oleic acid alcohol solution and 12.5 ml of the modifier solution uniformly and adjust the pH value to 2.65 by adjusting the NaOH solution; when the mixed solution is heated to 50℃, add the silver nitrate solution by means of a peristaltic pump at a flow rate of 1.5 L / min, and continue stirring for 30 min after the addition is completed; centrifuge the above reaction solution containing silver powder, and wash it with deionized water and organic cleaning solution (mass ratio of ethanol and diethylene glycol butyl ether acetate is 1:1) for 10 times each by means of mechanical stirring, vacuum dry, and grind to obtain the silver powder.

[0134] Test Example 1

[0135] The silver powders prepared in Examples 2-4 and Comparative Example 1 are respectively subjected to scanning electron microscope detection, and the silver crystal nucleus prepared in Example 1 is subjected to transmission electron microscope and high-resolution transmission electron microscope detection.

[0136] As shown in FIGS. 4 and 5, since the nucleation stage and the growth stage of the crystal formation process are not separated in Comparative Example 1, it is easy to cause uneven formation of the crystal nucleus, the crystal nucleus ages are inconsistent, the risk of secondary nucleation is increased, and thus the silver powder has poor particle size distribution uniformity and is prone to agglomeration. The Dv50 value of the silver powder is 5 μm.

[0137] As shown in FIGS. 6 and 7, in Example 1, because the redox reaction rate of ascorbic acid and silver nitrate is relatively slow, the chemical reaction is easy to control, and thus the silver powder obtained has good dispersity and morphology.

[0138] As shown in FIG. 8, in Example 2, because the redox reaction rate of hydrazine hydrate and silver nitrate is too fast, the chemical reaction ends very quickly, the concentration of silver atoms reduced instantaneously reaches supersaturation, leading to secondary nucleation, and the crystal nuclei of different ages grow simultaneously, and thus the silver powder prepared has a relatively small particle size and a wide distribution, and has low dispersity, but is better than that of Comparative Example 1.

[0139] As shown in FIGS. 9 and 10, in Example 3, when ascorbic acid and hydrazine hydrate are used in a mass ratio of 1:1, they can cooperatively reduce silver nitrate, the chemical reaction rate is moderate, and the chemical reaction is easy to control, and thus the silver powder obtained has good morphology, good dispersity, and narrow particle size distribution. The Dv50 value of the silver powder is 0.8 μm.

[0140] As shown in FIG. 11, in Example 4, because ascorbic acid and hydrazine hydrate are used in a mass ratio of 4:1, the amount of ascorbic acid is slightly more, and thus the overall morphology and dispersity of the silver powder obtained are slightly worse than those of Example 1.

[0141] Comparative Example 2

[0142] The difference from Example 3 is that no modifier is added.

[0143] Comparative Example 3

[0144] The difference from Example 3 is that the modifier is replaced by stearic acid.

[0145] Comparative Example 4

[0146] The difference from Example 3 is that the modifier is replaced by propylene glycol monostearate.

[0147] Comparative Example 5

[0148] The difference from Example 3 is that the modifier is replaced by palmitic acid.

[0149] Comparative Example 6

[0150] The difference from Example 3 is that the modifier is replaced by octadecylamine.

[0151] Example 5

[0152] The difference from Example 3 is that 12.5 ml of the modifier is replaced by 2.45 mL of the modifier, i.e., the modifier is 0.1% of the amount of silver nitrate.

[0153] Example 6

[0154] The difference from Example 3 is that 12.5ml of modifier is replaced by 24.5ml of modifier, i.e. the modifier is silver nitrate in an amount of 1%.

[0155] Example 7

[0156] The difference from Example 3 is that the mass ratio of lauric acid, sunflower acid and undecanoic acid is replaced by 6:1:0.03.

[0157] Test Example 2

[0158] The silver powder, acrylic resin, diethylene glycol butyl ether acetate and diethylene glycol butyl ether prepared in Example 3, Examples 5-7 and Comparative Examples 2-6 are mixed to prepare a conductive silver paste, wherein the content of silver powder is 92% by mass. The prepared conductive silver paste is manually printed on an alumina ceramic substrate, dried at 200°C, and then cured at 200°C for 20 minutes to form a conductive film.

[0159] 1. The volume resistivity of the conductive film is detected by a four-probe tester.

[0160] When the silver powder is in contact with the solvent of the organic system, an included angle, i.e. a contact angle θ (as shown in Figure 12), is formed at the solid-liquid interface, which is used to measure the degree of wetting of the liquid on the solid surface. The smaller the contact angle, the easier the liquid wets the solid surface, and the less likely the solid is to agglomerate. The larger the contact angle, the less likely the liquid wets the solid surface, and the more likely the solid is to agglomerate.

[0161] As shown in Table 1, compared with Comparative Examples 2-6, the volume resistivity of the conductive film prepared in Examples 3, 5-7 is smaller, and the conductive performance is better. This indicates that after the silver powder is modified and coated with lauric acid, sunflower acid and undecanoic acid, the wettability of the silver powder can be improved, so that the silver powder is less likely to agglomerate in the organic solvent, thereby improving the conductivity. Compared with Example 3, the addition amount of the modifier in Example 5 is slightly less, the addition amount of the modifier in Example 6 is slightly more, the addition amount of lauric acid in Example 7 is slightly more, and the addition amount of undecanoic acid in Example 7 is slightly less, which will slightly reduce the conductivity.

[0162] Table 1 Volume resistivity of different examples

[0163] 2. The silver powder prepared in Example 3 is used to prepare a conductive silver paste, and the conductive silver paste is detected by a scanning electron microscope before and after curing treatment, and the results are shown in Figure 13.

[0164] It is generally believed that the melting point of sub-micron materials will be reduced compared with large particle size materials. In theory, the melting point of silver sub-micron particles should also be reduced, because the silver atoms on the surface of the silver sub-micron particles have high activity, and the short-range diffusion between particles is easy to occur, so that the silver particles are connected with the surrounding silver particles to realize "welding".

[0165] As can be seen from Fig. 13, the sample treated at 200°C shows obvious neck-like connections between adjacent particles, and some particles are obviously enlarged, indicating that local melting occurs between silver sub-micron particles at 200°C, and the particles are connected together, thus the prepared ultra-fine silver powder particles have a low-temperature sintering effect, and sintering connection between silver particles can occur at 200°C and the particle size is enlarged.

[0166] Therefore, when the spherical silver powder particles added to the conductive silver paste are filled in the gap between the micron-level flaky silver powder or dispersed on the surface of the micron-level silver powder, the silver particles will undergo sintering reaction at a certain curing temperature, and the adjacent silver powder can be "welded" to improve the conductive performance of the cured film layer.

[0167] Example 8

[0168] The difference from Example 3 is that the organic cleaning liquid is not used.

[0169] Example 9

[0170] The difference from Example 3 is that the organic cleaning liquid is replaced by ethanol.

[0171] Test Example 3

[0172] The silver powder prepared in Example 3, Example 8 and Example 9 is respectively heated at 110°C and 538°C, and the mass of the substance before and after heating is measured to calculate the weight loss rate.

[0173] The results are shown in Table 2. Compared with using only water or using water and anhydrous ethanol cleaning, using water and an organic cleaning liquid (ethanol and diethylene glycol butyl ether acetate) to clean the silver powder has a lower weight loss rate, thereby reducing the loss of silver powder.

[0174] Table 2 Weight loss rate of silver powder

[0175] Although the embodiments of the present disclosure have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present disclosure, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A method of making silver powder, wherein, The application relates to a silver powder preparation method. The first silver salt, the first dispersant and the first reducing agent are subjected to a first treatment to obtain silver crystal nuclei; The silver crystal nuclei, the second silver salt, the second dispersant, the second reducing agent and the modifier are subjected to a second treatment to obtain silver powder; The modifier comprises lauric acid, sunflower acid and undecanoic acid.

2. The method of claim 1, wherein, The mass ratio of the lauric acid, the sunflower acid and the undecanoic acid is (0.5-50):1:(0.03-3).

3. The method of claim 1 or 2, wherein, The mass ratio of the lauric acid, the sunflower acid and the undecanoic acid is (1-10):1:(0.1-1).

4. The method according to any one of claims 1 to 3, wherein, The mass of the modifier is 0.1%-1% of the mass of the second silver salt.

5. The method according to any one of claims 1 to 4, wherein, The mass of the modifier is 0.4%-0.6% of the mass of the second silver salt.

6. The method according to any one of claims 1 to 5, wherein, The first reducing agent and the second reducing agent each independently comprise at least one of ascorbic acid and hydrazine hydrate.

7. The method of claim 6, wherein, The mass ratio of the ascorbic acid and the hydrazine hydrate is (0.5-2):

1. The molar ratio of the first reducing agent to the first silver salt is (0.1-1):

1. The mass of the second reducing agent is 0.5-1 times the mass of the second silver salt.

8. The method according to any one of claims 1 to 7, wherein, The first dispersant and the second dispersant each independently comprise at least one of oleic acid, polyvinylpyrrolidone, gum arabic, gelatin, polyvinyl alcohol, polyethylene glycol and Tween 80.

9. The method according to any one of claims 1 to 8, wherein, The first dispersant comprises polyvinylpyrrolidone. The second dispersant comprises oleic acid.

10. The method according to any one of claims 1 to 9, wherein, The mass of the first dispersant is 10%-60% of the mass of the first silver salt. The mass of the second dispersant is 0.01-0.1 times the mass of the second silver salt.

11. The method according to any one of claims 1 to 10, wherein, The first silver salt and the second silver salt each independently comprise at least one of silver chloride, silver nitrate or silver carbonate.

12. The method according to any one of claims 1 to 11, wherein, The first treatment comprises: The solution containing the first silver salt is added to the mixed solution containing the first dispersant and the first reducing agent, and mixed to obtain the silver crystal nuclei.

13. The method of claim 12, wherein, The solution containing the first silver salt is added to the mixed solution at one time; The temperature of the mixed solution is 40-60 DEG C; The system temperature is maintained at 40-60 DEG C during the mixing process.

14. The method of claim 12 or 13, wherein, The mixed solution is obtained by the following steps: The solution containing the first dispersant and the solution containing the first reducing agent are mixed, heated to a first preset temperature, and then cooled to a second preset temperature; The first preset temperature is 90-100 DEG C; and / or the second preset temperature is 40-60 DEG C.

15. The method according to any one of claims 1 to 14, wherein, The second treatment comprises: The solution containing the second silver salt is added to the mixed solution containing the silver crystal nuclei, the second dispersant, the second reducing agent and the modifier, and mixed to obtain a mixed slurry; The crystals in the mixed slurry are collected, and the crystals are cleaned and crushed to obtain the silver powder; The cleaning is respectively performed by using water and a cleaning solution, and the cleaning solution comprises ethanol and diethylene glycol butyl ether acetate.

16. The method of claim 15, wherein, The mass ratio of the ethanol and diethylene glycol butyl ether acetate is (0.1-10):

1.

17. The method of claim 15 or 16, wherein, The adding method of the solution containing the second silver salt is dropwise adding, and the dropwise adding speed is 1 L / min to 5 L / min.

18. The method of any one of claims 15-17, wherein, The pH value of the mixed solution is 2 to 3. And / or, the temperature of the system is maintained at 40°C to 60°C during the mixing.

19. A silver powder, wherein, The silver powder is obtained by the method for preparing silver powder according to any one of claims 1 to 18.

20. The silver powder of claim 19, wherein, The Dv50 value of the silver powder is 0.6 μm to 1 μm.

21. An electrically conductive silver paste, wherein, Comprising: The silver powder according to claim 19 or 20.

22. The electrically conductive silver paste of claim 21, wherein, The curing temperature of the conductive silver paste is 150°C to 250°C. And / or, the content of the silver powder in the conductive silver paste is 90 mass% to 95 mass%.

23. An electronic device, wherein, Comprising: The conductive silver paste according to claim 21 or 22.

24. An electrical device, comprising: Comprising: The electronic device according to claim 23.

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