Nano silver powder with high specific surface area and preparation method thereof

Abstract

The invention provides nano silver powder with a high specific surface area and a preparation method thereof, and belongs to the technical field of photovoltaic silver powder, and the preparation method comprises the following steps: adding a silver nitrate solution and a reducing agent solution with a specific pH into a reaction base solution containing a dispersing agent and an auxiliary agent for reaction, adding a coating agent after charging is completed, and stirring to obtain the nano silver powder with the high specific surface area. A silver-containing solution is obtained after the reaction time is over, and the silver-containing solution is subjected to the procedures of filtering, cleaning, drying, air milling and the like. According to the method, through process optimization, the problem that the particle size, the tap density, the high dispersion performance and the specific surface area of an existing chemical reduction method cannot be considered in the nano silver powder preparation process is well solved, and a new synthesis strategy is provided for industrial production of the nano silver powder suitable for high-end electronic paste.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic silver powder technology, specifically to a nano-silver powder with a high specific surface area and its preparation method. Background Technology

[0002] As a core functional material in high-end electronic materials and photovoltaic devices, the specific surface area of ​​nano-silver powder directly determines the sintering activity of conductive paste, electrode density, and the photoelectric conversion efficiency of the final device. In the manufacturing of crystalline silicon solar cells, the conductive phase silver powder content in the positive silver paste is as high as 80-90%. During high-temperature sintering, some of the silver powder dissolves in the molten glass powder, forming an ohmic contact between the silver electrode and the silicon substrate. At this point, parameters such as the surface morphology, particle size distribution, and specific surface area of ​​the silver powder have a decisive influence on the conductivity and density of the electrode after sintering, and thus directly affect the photoelectric conversion efficiency of the solar cell.

[0003] With the rapid development of heterojunction (HJT) solar cell technology, its highest laboratory conversion efficiency has reached 26.81%, setting a new record for silicon-based solar cells. However, HJT cells require efficient sintering at temperatures below 250°C, which places entirely new demands on silver powder. Existing high-temperature silver powders are no longer suitable, necessitating the development of novel nano-silver powders that combine high specific surface area, low-temperature sintering activity, and high dispersibility. This silver powder must meet the requirements of ultra-fine line printing technology to avoid grid clogging and grid breakage, while ensuring the rapid formation of a highly dense conductive network at low temperatures. This presents unprecedented challenges to the physicochemical properties of silver powder.

[0004] The preparation of high-performance silver powder often relies on multi-step reactions or high-end equipment (such as supercritical drying and physical vapor deposition), resulting in high production costs. Chemical reduction, due to its advantages of mild process, simple equipment, and controllable cost, has become the mainstream technical route for the industrial production of nano-silver powder. This method typically uses silver nitrate as the silver source, ascorbic acid (vitamin C) or citrate as the reducing agent, and polyvinylpyrrolidone (PVP) as a dispersant. The reduction and nucleation growth of silver ions are achieved in an aqueous system by controlling the reaction conditions. Despite the widespread application of chemical reduction methods, industrial production still faces numerous technical bottlenecks: 1. When pursuing small-sized nanoparticles (<300nm), the tap density of the powder decreases significantly (often <4.0g / cm³), while increasing the tap density requires increasing the particle size or changing the morphology; 2. The specific surface area of ​​silver powder prepared by conventional liquid-phase reduction methods is generally low, resulting in poor sintering activity and requiring higher temperatures to achieve densification; although the specific surface area can be effectively increased by surface roughening or morphology control (such as "alternating large and small spheres" structure), the difficulty of process control increases dramatically. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a nano-silver powder with high specific surface area and its preparation method, which only solves the technical problem that the existing chemical reduction method cannot simultaneously achieve small size, high specific surface area and high tap density.

[0006] The specific technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing nano-silver powder with high specific surface area, comprising the following steps: S1. Adding silver nitrate to deionized water yields an oxidizing agent solution. Adding reducing agent and auxiliary agent a to deionized water yields a reducing agent solution. Adding dispersant and auxiliary agent b to deionized water yields a reaction base solution. S2. Under stirring, the oxidant solution and the reducing agent solution are added to the reaction base solution at a uniform rate. After completion, the coating agent is added. S3. Separate the silver powder, wash and dry it, and then obtain nano silver powder by air milling; Among them, additive a is sodium hydroxide or ammonia water, which is used to adjust the pH of the reducing agent solution to 7-11; additive b is anhydrous sodium carbonate, and the dispersant contains polyvinylpyrrolidone K90 and nonylphenol polyoxyethylene ether.

[0007] Preferably, in the above preparation method, the reducing agent is one or two of ascorbic acid, sodium ascorbate, hydrazine hydrate, and glucose, with ascorbic acid being the best.

[0008] Preferably, in the above preparation method, the dispersant further contains a small molecule dispersant, and the small molecule dispersant is sodium citrate and / or sodium tartrate.

[0009] More preferably, in the above preparation method, the mass ratio of silver nitrate, reducing agent, polyvinylpyrrolidone K90, nonylphenol polyoxyethylene ether and small molecule dispersant is 100:(50~105):(2~15):(0.1~2):(0~0.1).

[0010] Preferably, in the above preparation method, the amount of anhydrous sodium carbonate used is 1-2 g / L. Anhydrous sodium carbonate acts as a pH buffer and can adjust the pH value during the reaction process.

[0011] Preferably, in step S1 of the above preparation method, the volume ratio of deionized water in the oxidant solution, deionized water in the reducing agent solution, and deionized water in the reaction substrate is 1:1:(1~1.5). More preferably, when the total amount of deionized water is 2~2.3L, the addition time in step S2 is within 1 minute.

[0012] Preferably, in step S2 of the above preparation method, the temperature of the reaction base liquid is 20~50℃, the stirring rate is 200~700rpm, and the reaction time after adding the coating agent is 5-30min.

[0013] Preferably, in the above preparation method, the coating agent is one or more of oleic acid, lauric acid, stearic acid, ethyl laurate, and oleamide, and the mass ratio of the added coating agent to the mass of silver nitrate is 1:(200~480).

[0014] Secondly, this invention provides a silver nanoparticle powder with a high specific surface area, which is prepared by the preparation method provided by this invention. Specifically, the silver nanoparticle powder provided by this invention has a particle size of 200-400 nm and a tap density of 2.5-4 g / cm³. 3 Between 1.5 and 3 m², the specific surface area is between 1.5 and 3 m². 2 The nano-silver powder prepared by this invention has a small size, high specific surface area, and high tap density, and can be used as a positive silver paste for preparing HJT batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the process for preparing nano-silver powder by chemical reduction, effectively solving the problem that existing chemical reduction methods cannot simultaneously achieve optimal particle size, tap density, high dispersibility, and specific surface area in the preparation of nano-silver powder. Moreover, the preparation method provided by this invention features a simple process flow, rapid reaction, ease of operation, and is green and harmless. At the same time, the process is controllable, has good reproducibility, and is suitable for large-scale industrial production. Attached Figure Description

[0016] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0017] Figure 1 A scanning electron microscope image of the silver nanoparticles prepared in Example 1; Figure 2 Scanning electron microscope image of the silver nanoparticles prepared in Example 2; Figure 3 Scanning electron microscope image of the silver nanoparticles prepared in Example 3; Figure 4 The image shows a scanning electron microscope (SEM) image of the silver nanoparticles prepared in Comparative Example 1. Detailed Implementation

[0018] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the invention.

[0020] Given the demand for high-performance silver nanoparticles in heterojunction solar cells and the shortcomings of existing chemical reduction methods in preparing high-performance silver nanoparticles, this invention provides a scheme for preparing silver nanoparticles with high specific surface area. Specifically, it utilizes the synergistic mechanism between a composite dispersant (long-chain polymer dispersant + nonionic dispersant) and effective coating triggered by a specific pH to achieve controllable preparation of silver nanoparticles with small particle size, high sphericity, and high specific surface area. Furthermore, post-coating imparts excellent dispersion stability and hydrophobicity. Simultaneously, combined with a mature additive process, the particle size distribution and dispersibility of silver particles can be effectively controlled. Based on the preparation method provided by this invention, silver nanoparticles with small spherical size, high specific surface area, high tap density, high sintering activity, and high dispersibility, suitable for high-end electronic pastes, can be obtained.

[0021] The method for preparing high specific surface area nano-silver powder provided in this embodiment of the invention includes the following steps: (1) Add silver nitrate to deionized water to obtain an oxidizing agent solution, add reducing agent and auxiliary agent a to deionized water to obtain a reducing agent solution, add dispersant and auxiliary agent b to deionized water to obtain a reaction base liquid; (2) Under stirring, the oxidant solution and the reducing agent solution are added to the reaction base solution at a constant rate, and the coating agent is added after the reaction is completed; S3. Separate the silver powder, wash and dry it, and then obtain nano silver powder by air milling; Among them, auxiliary agent a is sodium hydroxide or ammonia water, which is used to adjust the pH of the reducing agent solution to 7-11; auxiliary agent b is anhydrous sodium carbonate; the dispersant contains polyvinylpyrrolidone K90, nonylphenol polyoxyethylene ether and small molecule dispersant; the reducing agent is selected from ascorbic acid, sodium ascorbate, hydrazine hydrate and glucose; the coating agent is selected from oleic acid, lauric acid, stearic acid, ethyl laurate and oleamide.

[0022] Furthermore, in some embodiments, the mass ratio of silver nitrate, reducing agent, polyvinylpyrrolidone K90, nonylphenol polyoxyethylene ether, and small molecule dispersant is 100:(50~105):(2~15):(0.1~2):(0~0.1). In this invention, the amount and ratio of polyvinylpyrrolidone K90 and nonylphenol polyoxyethylene ether have a crucial impact on the silver powder particle size. Based on this, an appropriate amount of small molecule dispersant can be used to fine-tune the silver powder particle size.

[0023] Furthermore, in some embodiments, the volume ratio of deionized water in the oxidant solution, deionized water in the reducing agent solution, and deionized water in the reaction substrate is 1:1:(1~1.5).

[0024] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0025] Example 1 This example provides a nano-silver powder with a high specific surface area, and its preparation method is as follows: (1) Add 160g of silver nitrate to 600ml of deionized water to obtain silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water, adjust the pH value to 8 with sodium hydroxide, and use it as a reducing agent solution and dissolve it completely; dissolve 10g of polyvinylpyrrolidone K90, 1.3g of anhydrous sodium carbonate, and 0.3g of nonylphenol polyoxyethylene ether in 880ml of deionized water as the reaction base solution; dissolve 0.5g of lauric acid and 0.1g of ethyl laurate in 10ml of anhydrous ethanol as the coating agent solution.

[0026] (2) Set the stirring speed to 500 rpm, add the silver nitrate solution and reducing agent solution to the reaction base liquid at a uniform speed, pour in the coating agent solution after the addition is completed, and react for 30 min.

[0027] (3) Silver powder was separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate was <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried silver powder was then milled by air to obtain the finished silver powder.

[0028] Example 2 This example provides a nano-silver powder with a high specific surface area, and its preparation method is as follows: (1) Add 160g of silver nitrate to 600ml of deionized water to obtain silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water and dissolve it completely, and adjust the pH value to 9 with sodium hydroxide solution as a reducing agent solution; dissolve 10g of polyvinylpyrrolidone K90, 1.3g of anhydrous sodium carbonate, 0.3g of nonylphenol polyoxyethylene ether, and 0.4g of sodium citrate in 880ml of deionized water as the reaction base solution; dissolve 0.5g of lauric acid in 10ml of anhydrous ethanol as a coating agent solution.

[0029] (2) Set the stirring speed to 500 rpm, add the silver nitrate solution and reducing agent solution to the reaction base liquid at a uniform speed, and pour in the coating agent solution after the addition is completed. The reaction time is 30 min.

[0030] (3) Silver powder was separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate was <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried silver powder was then milled to obtain the finished silver powder. Example 3 This example provides a nano-silver powder with a high specific surface area, and its preparation method is as follows: (1) Add 160g of silver nitrate to 700ml of deionized water to obtain silver nitrate solution; add 86.4g of ascorbic acid to 700ml of deionized water and dissolve it completely, and adjust the pH value to 8 with sodium hydroxide solution as a reducing agent solution; dissolve 10g of polyvinylpyrrolidone K90, 1.3g of anhydrous sodium carbonate and 0.3g of nonylphenol polyoxyethylene ether in 880ml of deionized water as the reaction base solution; dissolve 0.5g of oleic acid in 10ml of anhydrous ethanol as a coating agent solution.

[0031] (2) Set the stirring speed to 500 rpm, add the silver nitrate solution and reducing agent solution to the reaction base liquid at a uniform speed, and pour in the coating agent solution after the addition is completed. The reaction time is 5 min.

[0032] (3) Silver powder was separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate was <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried silver powder was then milled by air to obtain the finished silver powder.

[0033] Comparative Example 1 This example provides a nano-silver powder, the preparation method of which is as follows: (1) Add 160g of silver nitrate to 600ml of deionized water to obtain silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water and dissolve it completely as a reducing agent solution; dissolve 10g of polyvinylpyrrolidone K90, 1.3g of anhydrous sodium carbonate and 0.3g of nonylphenol polyoxyethylene ether in 880ml of deionized water as a reaction base solution; dissolve 0.5g of lauric acid and 0.1g of ethyl laurate in 10ml of anhydrous ethanol as a coating agent solution.

[0034] (2) Set the stirring speed to 500 rpm, add the silver nitrate solution and reducing agent solution to the reaction base liquid at a uniform speed, and pour in the coating agent solution after the addition is completed. The reaction time is 30 min.

[0035] (3) Silver powder was separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate was <20 μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12 h. The dried silver powder was then gas-milled to obtain the finished silver powder. Comparative Example 2 This example provides a nano-silver powder, the preparation method of which is as follows: (1) Add 160g of silver nitrate to 600ml of deionized water to obtain silver nitrate solution; add 86.4g of ascorbic acid to 600ml of deionized water, adjust the pH value to 8 with sodium hydroxide, and use it as a reducing agent solution and dissolve it completely; dissolve 10g of polyvinylpyrrolidone K90 and 1.3g of anhydrous sodium carbonate in 880ml of deionized water as the reaction base solution; dissolve 0.5g of lauric acid and 0.1g of ethyl laurate in 10ml of anhydrous ethanol as the coating agent solution.

[0036] (2) Set the stirring speed to 500 rpm, add the silver nitrate solution and reducing agent solution to the reaction base liquid at a uniform speed, pour in the coating agent solution after the addition is completed, and react for 30 min.

[0037] (3) Silver powder was separated by vacuum filtration, washed with deionized water until the conductivity of the filtrate was <20μS / cm, then washed with anhydrous ethanol, and dried in a drying oven at 60℃ for 12h. The dried silver powder was then milled by air to obtain the finished silver powder.

[0038] The polymer-free, highly conductive silver nanopowders prepared in each embodiment and comparative example were subjected to the following tests and evaluations: ① The particle size of silver powder was measured using a Malvern laser particle size analyzer; ② Loose packing density: Pack silver powder into a container of a certain volume, then weigh the mass of silver powder in the container, and divide the mass by the volume to obtain the loose packing density; ③ Measure the tap density of silver powder using a tap density tester; ④ Measure the specific surface area of ​​the silver powder using a surface area analyzer; ⑤ Use scanning electron microscopy to examine the morphology of the silver powder.

[0039] Test results as follows Figure 1-3As shown in the table below, the nano-silver powder prepared by the method of the present invention exhibits high dispersibility as reflected in both Malvern laser particle size analyzer test data and electron microscopy images. The tap density of the nano-silver powder, measured by a tap density meter, is ≥2.5 g / cm³, the nano-size observed under electron microscopy is 200-400 nm, the average particle size D50 measured by the Malvern laser particle size analyzer is ≤0.40 µm, and the specific surface area measured by the specific surface area analyzer is >1.5 m² / g. Therefore, the method of the present invention can effectively solve the problem of the inability to simultaneously achieve optimal particle size, tap density, high dispersibility, and specific surface area in nano-silver powder prepared by existing chemical methods. Furthermore, Comparative Example 1 shows that the particle size of the nano-silver powder significantly increases after the absence of pH adjustment; Comparative Example 2 shows that the particle size of the silver powder significantly increases even without the synergistic effect of the nonionic dispersant nonylphenol polyoxyethylene ether.

[0040]

[0041] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing nano-silver powder with high specific surface area, characterized in that, Includes the following steps: S1. Adding silver nitrate to deionized water yields an oxidizing agent solution. Adding reducing agent and auxiliary agent a to deionized water yields a reducing agent solution. Adding dispersant and auxiliary agent b to deionized water yields a reaction base solution. S2. Under stirring, the oxidant solution and the reducing agent solution are added to the reaction base solution at a uniform rate. After completion, the coating agent is added. S3. Separate the silver powder, wash and dry it, and then obtain nano silver powder by air milling; The auxiliary agent a is sodium hydroxide or ammonia, and is used to adjust the pH of the reducing agent solution to 7-11; The additive b is anhydrous sodium carbonate, and the dispersant contains polyvinylpyrrolidone K90 and nonylphenol polyoxyethylene ether.

2. The preparation method according to claim 1, characterized in that, The reducing agent is one or two of ascorbic acid, sodium ascorbate, hydrazine hydrate, and glucose.

3. The preparation method according to claim 1 or 2, characterized in that, The dispersant further comprises a small molecule dispersant, and the small molecule dispersant is sodium citrate and / or sodium tartrate; and / or, The mass ratio of silver nitrate, reducing agent, polyvinylpyrrolidone K90, nonylphenol polyoxyethylene ether, and small molecule dispersant is 100:(50~105):(2~15):(0.1~2):(0~0.1).

4. The preparation method according to claim 1, characterized in that, The concentration of anhydrous sodium carbonate in the reaction substrate is 1-2 g / L.

5. The preparation method according to claim 1, characterized in that, In step S1, the volume ratio of deionized water in the oxidant solution, deionized water in the reducing agent solution, and deionized water in the reaction substrate is 1:1:(1~1.5).

6. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the reaction substrate is 20~50℃, and the stirring speed is 200~700rpm.

7. The preparation method according to claim 1, characterized in that, The coating agent is one or more of oleic acid, lauric acid, stearic acid, ethyl laurate, and oleamide.

8. The nano-silver powder with high specific surface area prepared by the preparation method according to any one of claims 1-7.

9. The application of the high specific surface area nano-silver powder as described in claim 8 in the preparation of photovoltaic silver paste.

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