High-dispersity silver powder and preparation method and application thereof

Abstract

The invention provides high-dispersity silver powder and a preparation method and application thereof.According to the preparation method of the high-dispersity silver powder, a simple liquid phase reduction method is adopted for preparing the high-dispersity silver powder, polyvinylpyrrolidone is adopted as a dispersing agent and is a simple and easy-to-obtain water-soluble polymer, animal glue such as gelatin and bone glue is not adopted, and therefore the high-dispersity silver powder is prepared. And the conductivity of the silver powder is influenced. Meanwhile, the using amount of the dispersing agent is 8%-15% of the mass of the reaction silver nitrate and is far smaller than 20%-40% of the commonly-used using amount, the using amount of the dispersing agent can be remarkably reduced, the dispersity of the final silver powder is not affected, and therefore the production cost of the high-dispersity silver powder is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of metal micro-nano powder materials, and in particular to a highly dispersible silver powder and a preparation method and application thereof. Background Art

[0002] With the development of photovoltaic industry and emerging electronic industry, electronic conductive paste has more and more extensive applications. As the most important conductive component, the performance of metal powder has a crucial impact on the quality of electronic paste. Due to its good conductivity and relatively low price, metallic silver has become the main raw material for preparing paste powder. In industrial production, chemical reduction method has become the main method for producing silver powder due to its mild reaction conditions, low production cost and simple process route.

[0003] In the technical solutions for silver powder for photovoltaic cells currently disclosed, high-dispersibility silver powder can reduce the contact resistance between the electrode and the silicon wafer. If the silver powder has poor dispersibility and is prone to agglomeration, a large gap will be formed between the agglomerated silver powder particles, and the electrons will be hindered during the transmission process, resulting in increased contact resistance. The prior art generally uses an increased amount of dispersant to achieve the purpose of dispersing and adjusting the particle size of the silver powder. However, this will lead to excessively high raw material costs, greatly increase the production cost of highly dispersible silver powder, and is not conducive to expanding the production of highly dispersible silver powder.

[0004] Therefore, there is an urgent need for a highly dispersible silver powder and a preparation method and application thereof to meet client application requirements. Summary of the invention

[0005] The purpose of the present invention is to solve the technical problem that the production cost of highly dispersed silver powder prepared in the existing silver powder preparation process is low due to excessive use of dispersant.

[0006] In order to solve the above technical problems, the present invention first provides a method for preparing highly dispersible silver powder, comprising: S10, mixing a silver nitrate solution, a reducing agent, a dispersant, a coating agent solution and a solvent to obtain a reaction suspension; S20, performing sedimentation treatment on the reaction suspension to obtain a precipitate, and then washing and drying the precipitate to obtain a highly dispersible silver powder; Wherein, in step S10: the dispersant is polyvinyl pyrrolidone, and the mass content of the dispersant is 8% to 15% of the mass content of silver nitrate in the silver nitrate solution.

[0007] Preferably, step S10 specifically includes: S101, mixing a reducing agent with a portion of a solvent, stirring until dissolved, and adding an alkaline solution to obtain a first mixed solution; S102, mixing the dispersant and another part of the solvent and stirring until dissolved to obtain a second mixed solution; S103, transferring the second mixed solution to a reactor for stirring, and adding the silver nitrate solution and the first mixed solution to the reactor at the same time and stirring at a uniform speed, then adding the coating agent solution, and continuing to stir until the reaction is completed to obtain a reaction suspension.

[0008] Preferably, in step S101: the reducing agent is at least one of ascorbic acid, formaldehyde, glucose, triethanolamine and hydrazine hydrate.

[0009] Preferably, in step S102: the specifications of polyvinyl pyrrolidone used as the dispersant meet the following requirements: K value is 31.5-33, moisture content is less than 4%, pH value is 3-4, peroxide content is ≤200ppm, and weight average molecular weight is 25000-40000.

[0010] Preferably, in step S103: the coating agent solution is formed by mixing coating agent powder and anhydrous ethanol; the coating agent powder is at least one of oleic acid, lauric acid, stearic acid and palmitic acid.

[0011] Preferably, the solvent is water; and the stirring rates in step S101, step S102 and step S103 are all 400-600 r / min.

[0012] Preferably, step S20 specifically includes: S201, performing sedimentation treatment on the reaction suspension, and removing the supernatant to obtain a precipitate; S202, washing the precipitate with a cleaning agent until the precipitate is washed to a conductivity of less than 20 μS / m, thereby obtaining wet silver powder; S203, drying the wet silver powder to finally obtain highly dispersible silver powder.

[0013] Preferably, in step S203: the temperature of the drying treatment is 40°C to 80°C, and the drying time is 20h to 24h.

[0014] Correspondingly, the present invention also provides a highly dispersible silver powder, which is prepared by any of the above methods for preparing highly dispersible silver powder.

[0015] Correspondingly, the present invention further provides a use of the highly dispersible silver powder as described above in the preparation of conductive silver paste.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a highly dispersible silver powder and a preparation method and application thereof. The preparation method of the highly dispersible silver powder adopts a simple liquid phase reduction method to prepare the highly dispersible silver powder, wherein the dispersant used is polyvinyl pyrrolidone, which is a simple and easily available water-soluble polymer, and no animal glue such as gelatin and bone glue is used, which is not easy to clean and affects the conductivity of the silver powder. At the same time, the amount of the dispersant used is 8% to 15% of the mass of the reacted silver nitrate, which is much less than the commonly used amount of 20% to 40%, which can significantly reduce the amount of the dispersant used, but does not affect the dispersibility of the final silver powder, thereby greatly reducing the production cost of the highly dispersible silver powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a method for preparing highly dispersible silver powder provided in an embodiment of the present invention; Figure 2 This is an electron microscope image of the highly dispersible silver powder provided in Example 1 of the present invention; Figure 3 This is an electron microscope image of the highly dispersible silver powder provided in Example 2 of the present invention; Figure 4 This is an electron microscope image of the highly dispersible silver powder provided in Example 3 of the present invention; Figure 5 This is an electron microscope image of the highly dispersible silver powder provided in Comparative Example 1. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In the currently disclosed technical solutions for silver powder for photovoltaic cells, the silver powder prepared is mainly to increase the amount of dispersant to achieve the purpose of dispersing and adjusting the particle size of the silver powder. The inventors of this application found in the actual production process that further reducing the amount of dispersant on the basis of the original dispersant to silver nitrate ratio can also produce silver powder with good dispersibility. Therefore, in combination with the actual development of the present invention, a method and application of preparing highly dispersible silver powder using a low amount of dispersant is proposed on the basis of the technology of spherical silver powder, with the focus on reducing the cost of raw materials without affecting the quality of the product.

[0020] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present invention first provides a method for preparing highly dispersible silver powder.

[0021] See also Figure 1 , Figure 1 A flow chart of a method for preparing highly dispersible silver powder provided in an embodiment of the present invention; wherein the above-mentioned preparation method specifically comprises: S10, mixing the silver nitrate solution, the reducing agent, the dispersing agent, the coating agent solution and the solvent to obtain a reaction suspension.

[0022] Specifically, step S10 includes: S101, mixing a reducing agent with a portion of a solvent, stirring until dissolved, and adding an alkaline solution to obtain a first mixed solution; S102, mixing the dispersant and another part of the solvent and stirring until dissolved to obtain a second mixed solution; S103, transferring the second mixed solution to a reactor for stirring, and adding the silver nitrate solution and the first mixed solution to the reactor at the same time and stirring at a uniform speed, then adding the coating agent solution, and continuing to stir until the reaction is completed to obtain a reaction suspension; wherein, after the reaction is completed, the pH value of the reaction suspension is about 7.

[0023] Specifically, in step S101: the reducing agent is at least one of ascorbic acid, formaldehyde, glucose, triethanolamine and hydrazine hydrate; wherein the silver nitrate solution and the reducing agent undergo a redox reaction, so that the silver ions in the solution are reduced to silver powder; the amount of the reducing agent should exceed the theoretical value of the stoichiometric ratio by 5% to 10% to achieve the effect of completely reducing the silver ions in the solution.

[0024] Furthermore, the reason for adding an alkaline solution to the reducing agent is that the activity of the reducing agent can be increased to a suitable level. If the pH is too high or too low, the reaction rate between the reducing agent and the silver nitrate may be too fast or too slow.

[0025] In one embodiment, the amount of reducing agent added is 54% of the mass of the reacted silver nitrate.

[0026] Furthermore, the role of the dispersant is mainly reflected in preventing silver powder particles from agglomerating, improving particle dispersibility, controlling particle morphology, and stabilizing the solution system. By selecting a suitable dispersant, the quality, uniformity, and processing performance of silver powder can be significantly improved, thereby optimizing its application in photovoltaics, electronics, and other fields.

[0027] In an embodiment of the present invention, the dispersant is polyvinyl pyrrolidone (PVP), and the mass content of the dispersant is 8% to 15% of the mass content of silver nitrate in the silver nitrate solution; wherein, within this content range, PVP can be effectively adsorbed on the surface of the silver powder particles to play a dispersing role. When the PVP content is low, such as less than 8%, it may not provide enough molecules to wrap the silver powder particles, causing the silver powder to easily agglomerate during the formation process. When the PVP content is too high, exceeding 15%, although the silver powder can be well dispersed, it may introduce too many organic impurities and increase costs.

[0028] Specifically, the specifications of polyvinyl pyrrolidone used as the dispersant meet the following requirements: K value is 31.5-33, moisture content is less than 4%, pH value is 3-4, peroxide content is ≤200ppm, and weight average molecular weight is 25000~40000.

[0029] Furthermore, the molecular chain length of PVP corresponding to the K value of 31.5-33 is moderate. The K value mainly reflects the average molecular weight of PVP. The appropriate K value means that the molecular chain length can provide a good steric hindrance effect. When dispersing silver powder, the molecular chain can be wrapped on the surface of the silver powder particles to prevent the particles from approaching each other and agglomerating. If the K value is too small, the molecular chain is short and cannot fully cover the silver powder particles, and cannot play a good dispersing role; if the K value is too large, the molecular chain is too long, the viscosity of the solution will increase, and it is not conducive to the dispersion of silver powder.

[0030] Furthermore, the moisture content of PVP is less than 4%, because too much moisture will affect the performance of PVP. High moisture content may change the structure and state of PVP molecules and reduce its adsorption capacity for silver powder particles. Moreover, too much moisture may also cause PVP to undergo hydrolysis reaction, changing its chemical properties, thereby affecting the dispersion effect of silver powder. For example, when the moisture content of PVP is too high, the adsorption on the surface of silver powder will be unstable and the dispersibility of silver powder will deteriorate.

[0031] Furthermore, the pH value of PVP is 3-4, and this acidic range helps maintain the chemical stability of PVP. Within this pH range, the structure of PVP molecules is relatively stable, and can better play its dispersing role. At the same time, the appropriate pH value is also conducive to better matching the charge state on the surface of the silver powder particles with the adsorption properties of PVP, enhancing the adsorption effect and improving the dispersibility of the silver powder. If the pH value is too high, PVP may undergo a chemical reaction, destroying its structure and resulting in a decrease in dispersibility.

[0032] Furthermore, the peroxide content of PVP is ≤200ppm, because peroxide is a strong oxidant. Too much peroxide may trigger an oxidation reaction, oxidize the surface of the silver powder, change its surface properties, and affect the dispersibility and conductivity of the silver powder. In addition, peroxide will also cause oxidative degradation of PVP molecules, reduce the molecular weight of PVP, break the molecular chain, thereby affecting its steric hindrance effect and adsorption performance, and cannot effectively play the role of a dispersant.

[0033] Furthermore, the weight average molecular weight of PVP is 25000-40000. This molecular weight range is related to the K value and directly affects the dispersion performance of PVP. Within this range, the PVP molecule has a suitable length and size, which can provide good steric hindrance effect and adsorption performance. If the molecular weight is too low, the molecular chain is short and the silver powder particles cannot be effectively wrapped, resulting in poor dispersion effect; if the molecular weight is too high, the viscosity of the solution will increase, which is also not conducive to dispersion.

[0034] Specifically, the coating agent solution is formed by mixing the coating agent powder with anhydrous ethanol, and the coating agent powder is at least one of oleic acid, lauric acid, stearic acid and palmitic acid; wherein the coating agent solution mainly forms a protective layer on the surface of the particles to prevent oxidation, control particle growth, avoid agglomeration, and improve dispersibility and sintering performance. An appropriate coating agent solution can not only improve the quality of silver powder, but also improve its performance in storage, transportation and subsequent applications.

[0035] In one embodiment, the amount of the coating agent added is 1% of the mass of the reacted silver nitrate.

[0036] Specifically, the preparation method of the silver nitrate solution in step S103 is as follows: dissolve silver nitrate in a certain amount of deionized water to prepare a silver nitrate aqueous solution with a volume concentration of 266.7 g / L, heat it up and keep it warm to 15° C.-40° C. to obtain a silver nitrate solution.

[0037] In the above embodiment, the solvent is water; the stirring rates in step S101, step S102 and step S103 are all 400-600r / min; wherein, the stirring rate range of 400-600r / min is optimized to ensure that the silver powder is evenly dispersed in the solution. During the reaction process, stirring can fully mix the reactants to avoid the occurrence of local concentrations that are too high or too low. At the same time, stirring can also promote the contact between the dispersant PVP and the silver powder particles and improve the dispersion effect. If the stirring rate is too low, such as less than 400r / min, the silver powder particles may precipitate or agglomerate in the solution, affecting the dispersibility; and if the stirring rate is too high, exceeding 600r / min, it may generate excessive shear force, destroy the structure of the silver powder particles, and is not conducive to dispersion.

[0038] S20, performing sedimentation treatment on the reaction suspension to obtain a precipitate, and then washing and drying the precipitate to obtain a highly dispersible silver powder.

[0039] Specifically, step S20 also includes: S201, performing sedimentation treatment on the reaction suspension, and removing the supernatant to obtain a precipitate; S202, washing the precipitate with a cleaning agent until the precipitate is washed to a conductivity of less than 20 μS / m, thereby obtaining wet silver powder, wherein the precipitate is washed to a conductivity of less than 20 μS / m, indicating that the ion impurity content in the precipitate is very low, and a higher purity requirement is met; S203, drying the wet silver powder to finally obtain highly dispersible silver powder.

[0040] Preferably, in step S203: the temperature of the drying process is 40°C to 80°C, and the drying time is 20h to 24h; Specifically, a lower temperature (around 40°C) can prevent the silver powder from agglomerating or oxidizing during the drying process. If the temperature is too high, the silver powder particles may collide with each other due to excessive thermal motion, resulting in agglomeration and affecting the dispersibility of the silver powder. At the same time, high temperature may also cause oxidation reaction on the surface of the silver powder to generate silver oxide, reducing the conductivity of the silver powder.

[0041] Specifically, a drying time of 20h to 24h can ensure that the moisture in the wet silver powder is fully removed. A sufficiently long drying time can enable the silver powder to reach an ideal dry state, giving it good fluidity and dispersibility. If the drying time is too short, moisture may remain in the silver powder, which will affect the performance and subsequent use of the silver powder. For example, in the subsequent electrode preparation process, silver powder containing moisture may cause bubbles or other defects in the electrode, thereby affecting the performance of the photovoltaic cell.

[0042] Correspondingly, the present invention also provides a highly dispersible silver powder, which is prepared by any of the above methods for preparing highly dispersible silver powder.

[0043] Correspondingly, the present invention further provides a use of the highly dispersible silver powder as described above in the preparation of conductive silver paste.

[0044] The technical solution of the present invention is now further described in conjunction with specific embodiments.

[0045] Embodiment 1: This embodiment 1 provides a highly dispersible silver powder and a preparation method thereof, the preparation method comprising the following steps: Step 1, liquid preparation: Solution A: Take 160g of silver nitrate and add it into a beaker. Add 600ml of deionized water and stir to dissolve. Heat and keep it at 25℃ to obtain Solution A. Solution B: Take 86.4g of ascorbic acid and add it to a beaker. Add 600ml of deionized water and stir to dissolve. After it is completely dissolved, you will get Solution B. Solution C: Take 17.92g of polyvinyl pyrrolidone (K30) and add it into a beaker. Add 900ml of deionized water and stir to dissolve. After it is completely dissolved, solution C is obtained. The technical indicators of K30 are: K value should be 31.5-33, water content <4%, pH value 3-4, peroxide content less than or equal to 200ppm, and weight average molecular weight 25000-40000. Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: (1) Transfer solution C to the reactor, start mechanical stirring, and control the stirring rate to 500 rpm; (2) Adjust the pH value of solution B to 5.5 using a 10 mol / L sodium hydroxide solution, then transfer the solution to the reactor and mix with solution C for 5 min; (3) Add solution A and solution B into the reactor at a certain flow rate at the same time, and control the addition time to be between 1 and 3 minutes; after the addition is completed, stir for 5 minutes, and add solution D, continue stirring for 5 minutes, and the reaction is completed; (4) The reaction suspension was settled, the supernatant was poured out, and the solid-liquid separation was performed. The silver powder was washed with deionized water and anhydrous ethanol respectively until the conductivity of the filtrate was less than 20 μS / m, and dried in a 60° C. forced air drying oven for 22 h to obtain highly dispersed silver powder, such as Figure 2 shown.

[0046] Embodiment 2: Step 1, liquid preparation: Solution A: Take 160g of silver nitrate and add it into a beaker. Add 600ml of deionized water and stir to dissolve. Heat and keep it at 25℃ to obtain Solution A. Solution B: Take 86.4g of ascorbic acid and add it to a beaker. Add 600ml of deionized water and stir to dissolve. After it is completely dissolved, you will get Solution B. Solution C: Take 20.16g of polyvinyl pyrrolidone (K30) and add it into a beaker. Add 900ml of deionized water and stir to dissolve. After it is completely dissolved, solution C is obtained. The technical indicators of K30 are: K value should be 31.5-33, water content <4%, pH value 3-4, peroxide content less than or equal to 200ppm, and weight average molecular weight 25000-40000. Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: (1) Transfer solution C to the reactor, start mechanical stirring, and control the stirring rate to 500 rpm; (2) Adjust the pH value of solution B to 5.5 using a 10 mol / L sodium hydroxide solution, then transfer the solution to the reactor and mix with solution C for 5 min; (3) Add solution A and solution B into the reactor at a certain flow rate at the same time, and control the addition time to be between 1 and 3 minutes; after the addition is completed, stir for 5 minutes, and add solution D, continue stirring for 5 minutes, and the reaction is completed; (4) The reaction suspension was settled, the supernatant was poured out, and the solid-liquid separation was performed. The silver powder was washed with deionized water and anhydrous ethanol respectively until the conductivity of the filtrate was less than 20 μS / m, and dried in a 60° C. forced air drying oven for 22 h to obtain highly dispersed silver powder, such as Figure 3 shown.

[0047] Embodiment 3: Step 1, liquid preparation: Solution A: Take 160g of silver nitrate and add it into a beaker. Add 600ml of deionized water and stir to dissolve. Heat and keep it at 25℃ to obtain Solution A. Solution B: Take 86.4g of ascorbic acid and add it to a beaker. Add 600ml of deionized water and stir to dissolve. After it is completely dissolved, you will get Solution B. Solution C: Take 21.28g of polyvinyl pyrrolidone (K30) and add it into a beaker. Add 900ml of deionized water and stir to dissolve. After it is completely dissolved, solution C is obtained. The technical indicators of K30 are: K value should be 31.5-33, water content <4%, pH value 3-4, peroxide content less than or equal to 200ppm, and weight average molecular weight 25000-40000. Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: (1) Transfer solution C to the reactor, start mechanical stirring, and control the stirring rate to 500 rpm; (2) Adjust the pH value of solution B to 5.5 using a 10 mol / L sodium hydroxide solution, then transfer the solution to the reactor and mix with solution C for 5 min; (3) Add solution A and solution B into the reactor at a certain flow rate at the same time, and control the addition time to be between 1 and 3 minutes; after the addition is completed, stir for 5 minutes, and add solution D, continue stirring for 5 minutes, and the reaction is completed; (4) The reaction suspension was settled, the supernatant was poured out, and the solid-liquid separation was performed. The silver powder was washed with deionized water and anhydrous ethanol respectively until the conductivity of the filtrate was less than 20 μS / m, and dried in a 60° C. forced air drying oven for 22 h to obtain highly dispersed silver powder, such as Figure 4 shown.

[0048] Comparative Example 1: Step 1, liquid preparation: Solution A: Take 160g of silver nitrate and add it into a beaker. Add 600ml of deionized water and stir to dissolve. Heat and keep it at 25℃ to obtain Solution A. Solution B: Take 86.4g of ascorbic acid and add it to a beaker. Add 600ml of deionized water and stir to dissolve. After it is completely dissolved, you will get Solution B. Solution C: Take 22.4g of polyvinyl pyrrolidone (K30) and add it into a beaker. Add 900ml of deionized water and stir to dissolve. After it is completely dissolved, solution C is obtained. The technical indicators of K30 are: K value should be 31.5-33, water content <4%, pH value 3-4, peroxide content less than or equal to 200ppm, and weight average molecular weight 25000-40000. Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: (1) Transfer solution C to the reactor, start mechanical stirring, and control the stirring rate to 500 rpm; (2) Adjust the pH value of solution B to 5.5 using a 10 mol / L sodium hydroxide solution, then transfer the solution to the reactor and mix with solution C for 5 min; (3) Add solution A and solution B into the reactor at a certain flow rate at the same time, and control the addition time to be between 1 and 3 minutes; after the addition is completed, stir for 5 minutes, and add solution D, continue stirring for 5 minutes, and the reaction is completed; (4) The reaction suspension was settled, the supernatant was poured out, and the solid-liquid separation was performed. The silver powder was washed with deionized water and anhydrous ethanol respectively until the conductivity of the filtrate was less than 20 μS / m, and dried in a 60° C. forced air drying oven for 22 h to obtain highly dispersed silver powder, such as Figure 4 shown.

[0049] Specifically, the performance of the silver powder prepared in the above Examples 1 to 3 and Comparative Example 1 was tested, and the test results are shown in Table 1: Table 1 Performance indicators of Examples 1 to 3 and Comparative Example 1

[0050] Specifically, in comparison between Comparative Example 1 and Examples 1 to 3, except for the different amount of the dispersant polyvinyl pyrrolidone (K30) used, the oxidant, the reducing agent, the reaction conditions and the added auxiliary agents were all kept the same.

[0051] It can be seen from Table 1 that the amounts of the dispersant polyvinyl pyrrolidone (K30) used in Examples 1, 2 and 3 are 80%, 90% and 95% of that in the comparative example, respectively. When the amount of the dispersant is less than 95%, the dispersibility is poor and the particle size is large, while when the amount is 95%, the dispersibility is good (such as Example 3), which is basically consistent with Comparative Example 1 and can meet the use requirements. The amount of the dispersant PVP is 13.3% of the mass of silver nitrate.

[0052] It should be noted that the amount of PVP used is also related to the weight average molecular weight of PVP. PVPs with different weight average molecular weights have different dispersing effects, and the required amount will be different. To this end, according to the steps of Comparative Example 1, except for the different weight average molecular weights of the dispersant PVP used, other conditions are basically the same, and the final PVP indicators and silver powder particle size data are shown in Table 2: Table 2 Different performance indicators corresponding to different weight average molecular weights in PVP

[0053] The present application discloses a highly dispersible silver powder and its preparation method and application, belonging to the technical field of micro-nano powder preparation. The single silver powder has a spherical shape, good dispersibility and uniform particle size. The silver powder is mainly used in solar photovoltaic cell slurry and has good electrical properties and linearity. The preparation method has a short process flow, strong operability, easy process control, low cost of raw materials and no use of hazardous chemicals, and is suitable for industrial production.

[0054] The present invention uses silver nitrate as a silver source, develops a method and application for producing silver powder using a low dispersant dosage, and reduces the raw material cost in the silver powder production process. The present invention selects a dispersant PVP with certain technical specifications, because of its specific molecular weight and specific impurity content, the steric hindrance effect can be significantly increased, the dispersion effect is improved, and the requirement of preparing highly dispersible silver powder can be achieved by reducing the amount of PVP used.

[0055] Compared with the prior art, the present invention has the following beneficial effects: First, the present invention can prepare highly dispersed spherical highly conductive silver powder, which can be directly used as the conductive phase of photovoltaic silver paste.

[0056] Second, the present invention adopts a simple liquid phase reduction method to prepare highly dispersed silver powder. The dispersant used is polyvinyl pyrrolidone (PVP), which is a simple and easily available water-soluble polymer. No animal glue such as gelatin and bone glue is used, which is difficult to clean and affects the conductivity of the silver powder.

[0057] Third, the present invention adopts polyvinyl pyrrolidone PVP of specific specifications as a dispersant, and the amount of the dispersant used is 8% to 15% of the mass of the reacted silver nitrate, which is much smaller than the commonly used amount of 20% to 40%, and can significantly reduce the amount of the dispersant PVP used, but does not affect the dispersibility of the final silver powder.

[0058] Fourthly, the silver powder cleaning process of the present invention uses water and anhydrous ethanol, and this method can significantly remove the water-soluble dispersant PVP and excess reducing agent on the surface of the silver powder.

[0059] Fifth, the silver powder preparation method of the present invention has high cost performance.

[0060] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0061] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing highly dispersible silver powder, characterized in that: The steps include: S10, mixing a silver nitrate solution, a reducing agent, a dispersant, a coating agent solution and a solvent to obtain a reaction suspension; S20, performing sedimentation treatment on the reaction suspension to obtain a precipitate, and then washing and drying the precipitate to obtain highly dispersible silver powder; Wherein, in the step S10: the dispersant is polyvinyl pyrrolidone, and the mass content of the dispersant is 8% to 15% of the mass content of silver nitrate in the silver nitrate solution.

2. The method for preparing highly dispersible silver powder according to claim 1, characterized in that: The step S10 specifically includes: S101, mixing the reducing agent with a portion of the solvent and stirring until dissolved, and adding an alkaline solution to obtain a first mixed solution; S102, mixing the dispersant and another part of the solvent and stirring until dissolved to obtain a second mixed solution; S103, transferring the second mixed solution to a reactor for stirring, and adding the silver nitrate solution and the first mixed solution to the reactor at the same time and stirring at a uniform speed, then adding the coating agent solution, and continuing to stir until the reaction is completed to obtain the reaction suspension.

3. The method for preparing highly dispersible silver powder according to claim 2, characterized in that: In the step S101: the reducing agent is at least one of ascorbic acid, formaldehyde, glucose, triethanolamine and hydrazine hydrate.

4. The method for preparing highly dispersible silver powder according to claim 2, characterized in that: In the step S102: the specifications of the polyvinyl pyrrolidone used as the dispersant meet the following requirements: K value is 31.5-33, moisture <4%, pH value is 3-4, peroxide content ≤200ppm, and weight average molecular weight is 25000-40000.

5. The method for preparing highly dispersible silver powder according to claim 2, characterized in that: In the step S103: the coating agent solution is formed by mixing coating agent powder and anhydrous ethanol; the coating agent powder is at least one of oleic acid, lauric acid, stearic acid and palmitic acid.

6. The method for preparing highly dispersible silver powder according to claim 2, characterized in that: The solvent is water; the stirring rates in the step S101, the step S102 and the step S103 are all 400-600 r / min.

7. The method for preparing highly dispersible silver powder according to claim 1, characterized in that: The step S20 specifically includes: S201, performing sedimentation treatment on the reaction suspension, and removing the supernatant to obtain the precipitate; S202, washing the precipitate with a cleaning agent until the precipitate is washed to a conductivity of less than 20 μS / m, thereby obtaining wet silver powder; S203, drying the wet silver powder to finally obtain the highly dispersible silver powder.

8. The method for preparing highly dispersible silver powder according to claim 7, characterized in that: In the step S203: the temperature of the drying process is 40°C to 80°C, and the drying time is 20h to 24h.

9. A highly dispersible silver powder, characterized in that: The high-dispersibility silver powder is prepared by the preparation method of any one of claims 1 to 8.

10. Use of the highly dispersible silver powder according to claim 9 in preparing conductive silver paste.

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