A silver powder with a twin structure, its preparation method and applications

Abstract

The present invention provides a silver powder with a twin crystal structure, a preparation method thereof and an application. The preparation method includes: firstly, mixing a silver nitrate solution, a dispersant, an initiator, a surfactant and a reducing agent to obtain a primary product; secondly, mixing the primary product with a coating agent and performing a stirring treatment to obtain a reaction suspension; finally, performing a sedimentation treatment on the reaction suspension to obtain a precipitate. Thereafter, the precipitate is washed and dried to obtain the silver powder with a twin crystal structure. In the process of redox reaction between the silver nitrate solution and the reducing agent to generate the silver powder with a twin crystal structure, through the synergistic effect of the dispersant, the initiator and the surfactant on the silver powder particles, the silver powder with a twin crystal structure is prepared, further enabling the conductive paste prepared from the above silver powder with a twin crystal structure to have a low resistance and excellent conductivity. At the same time, the synthesis process of the present invention has the characteristics of rapid reaction, simple operation, green and harmless, and is suitable for mass production.

Description

Technical Field

[0001] The present invention relates to the technical field of noble metal powder materials, and particularly relates to a silver powder with a twin structure, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of the photovoltaic industry and emerging electronic industries, electronic conductive pastes have been increasingly widely used. As the most important conductive component, the performance of metal powders has a crucial impact on the quality of electronic pastes. Due to its good electrical conductivity and relatively low price, metallic silver has become the main raw material for preparing powder for pastes. In industrial production, the 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] Currently, among the invention patents on silver powder for photovoltaic cells that have been publicly disclosed, the prepared silver powder is mainly spherical silver powder. However, it has been found that during the actual use process at the downstream paste end, the electrical properties, printing linearity, and sintering activity of spherical silver powder are poor during the application process at the paste end, and it is difficult to meet the application requirements of the client. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that the spherical silver powder produced by the existing preparation method of silver powder is difficult to meet the application requirements of the client.

[0005] To solve the above technical problem, the present invention first provides a preparation method of a silver powder with a twin structure, including:

[0006] S1, mixing a silver nitrate solution, a dispersant, an initiator, a surfactant, and a reducing agent to obtain a primary product;

[0007] S2, mixing the primary product with a coating agent and performing a stirring treatment to obtain a reaction suspension;

[0008] S3, performing a sedimentation treatment on the reaction suspension to obtain a precipitate. Thereafter, the precipitate is washed and dried to obtain a silver powder with a twin structure.

[0009] Preferably, the S1 step specifically includes:

[0010] S11, mixing the surfactant and the reducing agent, and adjusting the pH value to 4.5 - 5.5 to obtain a first mixed solution;

[0011] S12, mixing the first mixed solution, the dispersant, and the initiator, and placing the mixture in a reaction kettle for stirring to obtain a second mixed solution;

[0012] S13, adding the silver nitrate solution to the second mixed solution for stirring treatment to obtain a primary product;

[0013] Among them, in step S13, the feeding time for adding the silver nitrate solution to the second mixed solution is 5 to 10 minutes.

[0014] Preferably, in step S11, the surfactant is one or more of sodium dodecyl sulfonate, cetyltrimethylammonium bromide, and betaine.

[0015] Preferably, in step S11, the reducing agent is any one of ascorbic acid, glucose, formaldehyde, triethanolamine, and hydrazine hydrate; the dosage of the reducing agent exceeds 10% of the theoretical value of the stoichiometric ratio.

[0016] Preferably, in step S12, the dispersant is one of polyethylene glycol, polyvinylpyrrolidone, gelatin, and gum arabic; the dosage of the dispersant is 10 to 15% of the mass of the silver powder obtained by the reaction.

[0017] Preferably, in step S12, the initiator is sodium borohydride.

[0018] Preferably, in step S2, the coating agent includes one or more of oleic acid, lauric acid, stearic acid, and palmitic acid.

[0019] Preferably, step S3 specifically includes:

[0020] S31, performing sedimentation treatment on the reaction suspension, removing the supernatant to obtain a precipitate;

[0021] S32, mixing the precipitate with acetone and then performing stirring treatment, and after solid-liquid separation, obtaining a filter residue;

[0022] S33, washing the filter residue with deionized water and absolute ethanol respectively until the conductivity is less than 20 μS / m to obtain a wet powder;

[0023] S34, performing drying treatment on the wet powder to obtain silver powder with a twin crystal structure.

[0024] Correspondingly, the present invention further provides a silver powder with a twin crystal structure, which is prepared by the preparation method of the silver powder with a twin crystal structure as described above;

[0025] Among them, the silver powder with a twin crystal structure has a spherical-like structure or a dumbbell-like structure.

[0026] Correspondingly, the present invention further provides an application of the above silver powder with a twin crystal structure in the preparation of a conductive paste.

[0027] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a silver powder with a twin crystal structure, a preparation method thereof, and an application. The above preparation method includes: First, a silver nitrate solution, a dispersant, an initiator, a surfactant, and a reducing agent are mixed to obtain a primary product. Second, the primary product is mixed with a coating agent and then subjected to a stirring treatment to obtain a reaction suspension. Finally, the reaction suspension is subjected to a sedimentation treatment to obtain a precipitate. Thereafter, the precipitate is washed and dried to obtain a silver powder with a twin crystal structure. In the process of redox reaction between the silver nitrate solution and the reducing agent to generate a silver powder with a twin crystal structure, the dispersant can be adsorbed on the surface of the silver powder particles, providing electrostatic or steric hindrance repulsion to prevent particle aggregation, so that the silver powder can maintain a good dispersion state. The presence of the initiator can improve the efficiency of the reduction reaction and reduce the occurrence of side reactions, thereby improving the yield and purity of the silver powder. The surfactant can control the particle size and morphology of the silver powder, making it have a more uniform size distribution and a specific shape, such as spherical, flaky, or rod-shaped, etc. Furthermore, through the synergistic effect of the dispersant, initiator, and surfactant on the silver powder particles, a silver powder with a twin crystal structure is prepared, further enabling the conductive paste prepared from the above silver powder with a twin crystal structure to have a low resistance and excellent electrical conductivity. At the same time, the synthesis process of the present invention has the characteristics of rapid reaction, simple operation, green and harmless, and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flowchart of the preparation method of the silver powder with a twin crystal structure provided by the embodiment of the present invention;

[0029] Figure 2 It is a scanning electron microscope image of the silver powder with a twin crystal structure provided by Embodiment 1 of the present invention;

[0030] Figure 3 It is a scanning electron microscope image of the silver powder provided in Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] In view of the technical problems that the spherical silver powder produced by the existing silver powder preparation method has poor electrical properties, printing linearity and sintering activity during the slurry end application process, the present invention provides a silver powder with a twin crystal structure, its preparation method and application. The silver powder with a twin crystal structure prepared by this method has the characteristics of good dispersibility, controllable proportion of spherical and flaky shapes, and the whole process is obtained by one preparation, with a fast, simple, green and harmless operation method, suitable for large-scale production.

[0033] To achieve the above technical objectives, the present application adopts the following technical solutions:

[0034] In the first aspect, please refer to Figure 1 , Figure 1 which is the flow chart of the preparation method of the silver powder with a twin crystal structure provided by the embodiment of the present invention; among them, the above preparation method adopts the chemical reduction method, which specifically includes:

[0035] S1, Mix silver nitrate solution, dispersant, initiator, surfactant and reducing agent to obtain a primary product.

[0036] Specifically, step S1 further includes:

[0037] S11, Mix the surfactant and the reducing agent, and adjust the pH value to 4.5 - 5.5 to obtain a first mixed solution;

[0038] S12, Mix the first mixed solution, the dispersant and the initiator, and place them in a reaction kettle for stirring to obtain a second mixed solution;

[0039] S13, Add the silver nitrate solution to the second mixed solution for stirring treatment to obtain a primary product;

[0040] Among them, in step S13, the feeding time of the silver nitrate solution into the second mixed solution is 5 - 10 min, and the primary product is unpurified silver powder.

[0041] In step S11, the surfactant is one or several of sodium dodecyl sulfonate, cetyltrimethylammonium bromide and betaine; among them, the surfactant can adsorb on the surface of silver crystal nuclei and affect the crystal growth and aggregation process. By selecting a suitable surfactant, the particle size and morphology of silver powder can be controlled to have a more uniform size distribution and a specific shape, such as spherical, flaky or rod-shaped, etc.; in addition, the surfactant can improve the interfacial contact between reactants, increase the reaction rate and efficiency. They can promote the reaction between the reducing agent and silver nitrate and accelerate the formation of silver powder.

[0042] In step S11, the reducing agent is any one of ascorbic acid, glucose, formaldehyde, triethanolamine and hydrazine hydrate; the dosage of the reducing agent exceeds 10% of the theoretical value of the stoichiometric ratio, and such setting can ensure that all silver ions in the silver nitrate solution are reduced.

[0043] In step S11, the pH value is adjusted to 4.5 - 5.5 to make the entire redox system under acidic conditions, and there are several reasons for this:

[0044] First, controlling the reaction rate: Under acidic conditions, the activity of the reducing agent may increase, thereby accelerating the reduction reaction of silver nitrate and promoting the formation of silver powder;

[0045] Second, preventing side reactions: Under alkaline conditions, some side reactions may occur to silver nitrate, such as forming precipitates or decomposing. Adjusting the pH value to acidic can reduce the occurrence of these side reactions and improve the purity of silver powder.

[0046] Third, affecting the particle size and morphology of silver powder: Acidic conditions may affect the growth and aggregation processes of silver powder, thereby affecting its particle size and morphology. By adjusting the pH value, the particle size distribution and shape of silver powder can be controlled.

[0047] Fourth, improving the stability of silver powder: In an acidic environment, silver powder may be more stable and less likely to oxidize or undergo other chemical reactions.

[0048] In step S12, the dispersant is one of polyethylene glycol (PEG - 1000), polyvinylpyrrolidone (K30), gelatin, and gum arabic; among them, silver powder particles are prone to attracting and agglomerating with each other during the preparation process, forming larger particle clusters. This will result in an uneven particle size distribution of silver powder and affect its performance and applications. The dispersant can adsorb on the surface of silver powder particles, providing electrostatic or steric hindrance repulsion to prevent particle agglomeration and enable silver powder to maintain a good dispersed state; at the same time, the dispersant can affect the growth process of silver powder. By adjusting its adsorption and desorption behavior, the particle size and morphology of silver powder can be controlled. A suitable dispersant can promote the uniform growth of silver powder and obtain silver powder particles with smaller particle sizes and regular morphologies. Well - dispersed silver powder can form a more compact conductive network and improve the electrical conductivity of the material.

[0049] Furthermore, by using an appropriate amount of dispersant, the interaction force between particles can be reduced, making it easier for silver powder to disperse in the solution and maintain a good suspension state.

[0050] Furthermore, the dosage of the dispersant is 10 - 15% of the mass of the silver powder obtained from the reaction; among them, when the dosage of the dispersant is less than 10% of the mass of the silver powder obtained from the reaction, it will cause silver powder particles to agglomerate together, making it difficult to control the particle size and morphology of silver powder particles; when the dosage of the dispersant is greater than 15% of the mass of the silver powder obtained from the reaction, it will cause silver powder particles to be too dispersed, making it difficult to form silver powder with a twin crystal structure (twin crystal is a special structure in crystals, formed by the inter - nesting of two or more crystals).

[0051] In step S12, the initiator can provide active free radicals or ions, which can react with silver nitrate to accelerate the reduction process. By adding the initiator, more silver powder products can be obtained in a shorter time; in addition, the choice and dosage of the initiator can also affect the properties of the silver powder, such as particle size, morphology, dispersibility, etc. By optimizing the conditions of the initiator, silver powder products with specific performance requirements can be obtained.

[0052] In this embodiment, the initiator is preferably sodium borohydride, and sodium borohydride quickly reduces AgNO 3 to a large number of silver crystal nuclei as a reaction initiator, and then the silver crystal nuclei gradually grow under the action of the reducing agent.

[0053] S2. Mix the primary product with the coating agent and then perform a stirring treatment to obtain a reaction suspension.

[0054] Specifically, step S2 further includes:

[0055] After the redox reaction between the silver nitrate solution and the reducing agent is complete, mix the primary product generated after the reaction with the coating agent and then perform a stirring treatment to obtain a reaction suspension; wherein, the coating agent includes one or more of oleic acid, lauric acid, stearic acid, and palmitic acid.

[0056] Specifically, the coating agent is used to coat the primary product, and it can form a protective film on the surface of the silver powder to reduce the contact between the silver powder and air, thereby reducing the oxidation degree of the silver powder.

[0057] S3. Perform a sedimentation treatment on the reaction suspension to obtain a precipitate, and then, the precipitate is washed and dried to obtain silver powder with a twin crystal structure.

[0058] Specifically, step S3 specifically includes:

[0059] S31. Perform a sedimentation treatment on the reaction suspension, remove the supernatant to obtain a precipitate;

[0060] S32. Mix the precipitate with acetone and then perform a stirring treatment, and adjust the stirring rate to 800 - 1000 rpm, stir for 20 min, and after the stirring is completed, perform solid-liquid separation to obtain a filter residue;

[0061] S33. Wash the filter residue with deionized water and absolute ethanol respectively until the conductivity is less than 20 μS / m to obtain wet powder; wherein, by repeatedly rinsing with deionized water and absolute ethanol, the residual impurity ions are removed to make its conductivity meet the requirement of less than 20 μS / m, thereby ensuring the quality and performance of the product.

[0062] S34. Perform a drying treatment on the wet powder (dry in a 60 °C forced air drying oven for 12 h) to obtain silver powder with a twin crystal structure.

[0063] Correspondingly, the present invention also provides a silver powder with a twin structure, which is prepared by the preparation method of the silver powder with a twin structure in the previous item;

[0064] Among them, in the silver powder with a twin structure: the morphology of a single silver powder particle is spherical-like, and some silver powder particles are bonded together to form a dumbbell shape.

[0065] In one embodiment, the preparation method of a silver powder with a twin structure provided by the present invention is as follows:

[0066] Step 1, solution preparation:

[0067] First, dissolve silver nitrate in a certain amount of deionized water to obtain solution A;

[0068] Secondly, dissolve the reducing agent in a certain amount of deionized water, and add a surfactant to obtain solution B; again, dissolve the dispersant in a certain amount of deionized water, and add an initiator to obtain solution C;

[0069] Finally, dissolve the silver powder coating agent in a certain amount of absolute ethanol to obtain solution D.

[0070] Step 2, silver powder preparation:

[0071] First, transfer solution C to the reaction kettle, start mechanical stirring, and control the stirring rate between 400 - 600 rpm;

[0072] Secondly, use a 10 mol / L sodium hydroxide solution to adjust the pH value of solution B to 4.5 - 5.5, then transfer it to the reaction kettle, and stir and mix it fully with solution C;

[0073] Again, add solution A to the reaction kettle at a certain flow rate, and control the feeding time between 5 - 10 min. After the feeding is completed, stir for 5 min, add solution D, and continue to stir for 5 min to end the reaction;

[0074] Finally, sediment the reaction suspension, pour out the supernatant, then add a certain amount of acetone to the reaction kettle, adjust the stirring rate to 800 - 1000 rpm, and stir for 20 min. After the stirring is completed, perform solid-liquid separation, and wash the silver powder with deionized water and absolute ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0075] Correspondingly, the present invention also provides an application of the above silver powder with a twin structure in the preparation of conductive paste.

[0076] Now, the technical solution of the present invention will be further described in combination with specific embodiments.

[0077] 1. Test methods for each example and comparative example

[0078] Example 1:

[0079] Step 1, solution preparation:

[0080] Solution A: Take 160 g of silver nitrate and add it to a beaker. Add 600 ml of deionized water and stir to dissolve to obtain Solution A;

[0081] Solution B: Take 86.4 g of ascorbic acid and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 5 g of sodium dodecyl sulfate and stir well to dissolve to obtain Solution B;

[0082] Solution C: Take 10 g of polyethylene glycol (PEG-1000) and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 0.5 g of initiator and stir evenly to obtain Solution C;

[0083] Solution D: Take 0.5 g of oleic acid and add it to a beaker. Add 10 ml of absolute ethanol and stir to dissolve to obtain Solution C.

[0084] Step 2, silver powder preparation:

[0085] First, transfer Solution C to the reaction kettle, start the mechanical stirrer, and control the stirring rate at 500 rpm;

[0086] Second, use 10 mol / L sodium hydroxide solution to adjust the pH value of Solution B to 5.5, then transfer it to the reaction kettle, and stir and mix it with Solution C for 5 min;

[0087] Third, add Solution A to the reaction kettle at a certain flow rate, and control the feeding time at 5 min. After the feeding is completed, stir for 5 min, add Solution D, and continue to stir for 5 min to end the reaction;

[0088] Finally, sediment the reaction suspension, pour out the supernatant, then add 50 ml of acetone to the reaction kettle, adjust the stirring rate to 900 rpm, and stir for 20 min. After the stirring is completed, perform solid-liquid separation, and wash the silver powder with deionized water and absolute ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0089] Example 2:

[0090] Step 1, solution preparation:

[0091] Solution A: Take 160 g of silver nitrate and add it to a beaker. Add 600 ml of deionized water and stir to dissolve to obtain Solution A;

[0092] Solution B: Take 86.4 g of ascorbic acid and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 5 g of cetyltrimethylammonium bromide and stir well to obtain Solution B;

[0093] Solution C: Take 10 g of polyethylene glycol (PEG-1000) and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 0.5 g of initiator and stir evenly to obtain Solution C;

[0094] Solution D: Take 0.5 g of oleic acid and add it to a beaker. Add 10 ml of absolute ethanol and stir to dissolve to obtain Solution C.

[0095] Step 2, silver powder preparation:

[0096] First, transfer Solution C to a reaction kettle, start mechanical stirring, and control the stirring rate at 500 rpm;

[0097] Secondly, use a 10 mol / L sodium hydroxide solution to adjust the pH value of Solution B to 5.5, then transfer it to the reaction kettle, and stir and mix it with Solution C for 5 min;

[0098] Thirdly, add Solution A to the reaction kettle at a certain flow rate, and control the feeding time at 5 min. After the feeding is completed, stir for 5 min, add Solution D, and continue to stir for 5 min to end the reaction;

[0099] Finally, sediment the reaction suspension, pour out the supernatant, then add 50 ml of acetone to the reaction kettle, adjust the stirring rate to 900 rpm, and stir for 20 min. After the stirring is completed, perform solid-liquid separation, and wash the silver powder with deionized water and absolute ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0100] Example 3:

[0101] Step 1, solution preparation:

[0102] Solution A: Take 160 g of silver nitrate and add it to a beaker. Add 600 ml of deionized water and stir to dissolve to obtain Solution A;

[0103] Solution B: Take 86.4 g of ascorbic acid and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 5 g of betaine and stir well to obtain Solution B;

[0104] Solution C: Take 10 g of polyethylene glycol (PEG-1000) and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 0.5 g of initiator and stir evenly to obtain Solution C;

[0105] Solution D: Take 0.5 g of oleic acid and add it to a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve, obtaining Solution C.

[0106] Step 2, silver powder preparation:

[0107] First, transfer Solution C to a reaction kettle, start mechanical stirring, and control the stirring rate at 500 rpm;

[0108] Second, use a 10 mol / L sodium hydroxide solution to adjust the pH value of Solution B to 5.5, then transfer it to the reaction kettle, and stir and mix it with Solution C for 5 min;

[0109] Third, add Solution A to the reaction kettle at a certain flow rate, and control the feeding time at 5 min. After the feeding is completed, stir for 5 min, add Solution D, and continue to stir for 5 min to end the reaction;

[0110] Finally, sediment the reaction suspension, pour out the supernatant, then add 50 ml of acetone to the reaction kettle, adjust the stirring rate to 900 rpm, and stir for 20 min. After the stirring is completed, perform solid-liquid separation, and wash the silver powder with deionized water and anhydrous ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0111] Example 4:

[0112] Step 1, solution preparation:

[0113] Solution A: Take 160 g of silver nitrate and add it to a beaker. Add 600 ml of deionized water and stir to dissolve, obtaining Solution A;

[0114] Solution B: Take 86.4 g of ascorbic acid and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 5 g of sodium dodecyl sulfate and stir to dissolve thoroughly, obtaining Solution B;

[0115] Solution C: Take 10 g of polyvinylpyrrolidone (K30) and add it to a beaker. Add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 0.5 g of initiator and stir evenly, obtaining Solution C;

[0116] Solution D: Take 0.5 g of oleic acid and add it to a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve, obtaining Solution C.

[0117] Step 2, silver powder preparation:

[0118] First, transfer Solution C to a reaction kettle, start mechanical stirring, and control the stirring rate at 500 rpm;

[0119] Secondly, adjust the pH value of solution B to 5.5 using a 10 mol / L sodium hydroxide solution, then transfer it to a reaction kettle and stir and mix it with solution C for 5 min;

[0120] Thirdly, add solution A to the reaction kettle at a certain flow rate, and control the feeding time to be 5 min. After the feeding is completed, stir for 5 min, add solution D, and continue to stir for 5 min to end the reaction;

[0121] Finally, sediment the reaction suspension, pour out the supernatant, then add 50 ml of acetone to the reaction kettle, adjust the stirring rate to 900 rpm, and stir for 20 min. After the stirring is completed, perform solid-liquid separation, and wash the silver powder with deionized water and absolute ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0122] Example 5:

[0123] Step 1, solution preparation:

[0124] Solution A: Take 160 g of silver nitrate and add it to a beaker, add 600 ml of deionized water and stir to dissolve to obtain solution A;

[0125] Solution B: Take 86.4 g of ascorbic acid and add it to a beaker, add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 5 g of sodium dodecyl sulfonate and stir to dissolve thoroughly to obtain solution B;

[0126] Solution C: Take 10 g of gelatin and add it to a beaker, add 600 ml of deionized water and stir to dissolve. After complete dissolution, add 0.5 g of initiator and stir evenly to obtain solution C;

[0127] Solution D: Take 0.5 g of oleic acid and add it to a beaker, add 10 ml of absolute ethanol and stir to dissolve to obtain solution C.

[0128] Step 2, silver powder preparation:

[0129] Firstly, transfer solution C to the reaction kettle, start the mechanical stirrer, and control the stirring rate to be 500 rpm;

[0130] Secondly, adjust the pH value of solution B to 5.5 using a 10 mol / L sodium hydroxide solution, then transfer it to the reaction kettle and stir and mix it with solution C for 5 min;

[0131] Thirdly, add solution A to the reaction kettle at a certain flow rate, and control the feeding time to be 5 min. After the feeding is completed, stir for 5 min, add solution D, and continue to stir for 5 min to end the reaction;

[0132] Finally, sediment the reaction suspension, pour out the supernatant, then add 50 ml of acetone into the reaction kettle, adjust the stirring rate to 900 rpm, and stir for 20 min. After the stirring is completed, perform solid-liquid separation, and wash the silver powder with deionized water and absolute ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0133] Comparative example:

[0134] Step 1, solution preparation:

[0135] Solution A: Take 160 g of silver nitrate and add it to a beaker, add 600 ml of deionized water and stir to dissolve to obtain Solution A;

[0136] Solution B: Take 86.4 g of ascorbic acid and add it to a beaker, add 600 ml of deionized water and stir to dissolve to obtain Solution B;

[0137] Solution C: Take 10 g of polyvinylpyrrolidone (K30) and add it to a beaker, add 880 ml of deionized water and stir to dissolve. After complete dissolution, add 0.5 g of initiator and stir evenly to obtain Solution C;

[0138] Solution D: Take 0.5 g of oleic acid and add it to a beaker, add 10 ml of absolute ethanol and stir to dissolve to obtain Solution C.

[0139] Step 2, silver powder preparation:

[0140] First, transfer Solution C to the reaction kettle, start mechanical stirring, and control the stirring rate at 500 rpm;

[0141] Secondly, use a 10 mol / L sodium hydroxide solution to adjust the pH value of Solution B to 5.5;

[0142] Then, add Solutions A and B to the reaction kettle simultaneously, and control the feeding time at 5 min. After the feeding is completed, add Solution D and continue to stir for 5 min, and the reaction ends;

[0143] Finally, perform solid-liquid separation on the reactants, and wash the silver powder with deionized water and absolute ethanol respectively until the conductivity of the filtrate < 20 μS / m, and dry it in a blast drying oven at 60 °C for 12 h.

[0144] II. Analysis of test results of each example and comparative example

[0145] Please refer to Figure 2 , Figure 2 which is the scanning electron microscope image of the silver powder with twin crystal structure provided in Example 1 of the present invention; as can be seen from Figure 2 , among the silver powder with twin crystal structure provided in Example 1 of the present invention, the morphology of a single particle is spherical-like, and some silver powder particles are bonded together to form a dumbbell shape.

[0146] Please refer to Figure 3 , Figure 3 which is the SEM image of the silver powder provided in Comparative Example 1. Among them, the silver powder prepared in the comparative example also contains silver powder with a twin structure, and the twin ratio is smaller than that of the silver powder prepared in Example 1 of the present invention. At the same time, the particle size of the silver powder provided in the comparative example is not much different from that of the silver powder in Example 1 of the present invention.

[0147] Furthermore, the physical data of the silver powders prepared in Examples 1-5 and the comparative example of the present invention are shown in Table 1:

[0148] Table 1 Physical data of the silver powders prepared in Examples 1-5 and the comparative example of the present invention

[0149]

[0150] Specifically, D10, D50, D90, and D100 respectively represent different percentiles of the particle size distribution. Among them, as can be seen from Table 1, the particle sizes of Examples 2-5 are larger, especially D100, while the particle sizes of the comparative example and Example 1 are relatively smaller.

[0151] Specifically, the burn loss refers to the loss amount of a substance under certain conditions. Among them, as can be seen from Table 1, the burn losses of Examples 2-5 are larger, while the burn losses of the comparative example and Example 1 are relatively smaller.

[0152] Specifically, the loose bulk density refers to the density of a substance in a loose state. Among them, as can be seen from Table 1, the loose bulk densities of Examples 2-5 are smaller, while the loose bulk densities of the comparative example and Example 1 are relatively larger.

[0153] Specifically, the tapped density refers to the density of a substance in a tapped state. Among them, as can be seen from Table 1, the tapped densities of Examples 2-5 are smaller, while the tapped densities of the comparative example and Example 1 are relatively larger.

[0154] Specifically, the specific surface area refers to the surface area of a unit mass of a substance. Among them, as can be seen from Table 1, the specific surface areas of Examples 2-5 are larger, while the specific surface areas of the comparative example and Example 1 are relatively smaller.

[0155] Furthermore, it can be found from Table 1 that compared with the silver powder of the comparative example, the particle sizes of the silver powders prepared in Examples 1-5 are not much different, but the specific surface area is larger. The main reason is that the twin ratio in the system increases, while the actual particle size of a single silver powder particle is smaller than that of the silver powder in the comparative example.

[0156] Further, the silver powders prepared in Example 1, BL (basic sample), and the comparative example were sent to the slurry end for performance testing. Except for the different silver powders used, the types and dosages of the organic phase, the types and dosages of the glass phase, and the dosage of the silver powder were kept consistent. The test results are shown in Table 2:

[0157] Table 2 Results of performance testing of the silver powders prepared in Example 1, BL (basic sample), and the comparative example when sent to the slurry end

[0158]

[0159] Specifically, through the comparison of the test results in Table 2, it can be seen that in terms of application performance, the silver powder of Example 1 is more excellent than BL (basic sample) in terms of current (Isc), efficiency (FF), and fill factor (Eff), and is much higher than that of the comparative example; at the same time, the parallel resistance value Rsh of Example 1 is much smaller than that of the comparative example, and the slurry aspect ratio (H / W) and series resistance value Rs of Example 1 are the same as those of BL.

[0160] In summary, different from the prior art, the present invention provides a silver powder with a twin crystal structure, its preparation method and application. The above preparation method includes: First, a silver nitrate solution, a dispersant, an initiator, a surfactant, and a reducing agent are mixed to obtain a primary product. Secondly, the primary product is mixed with a coating agent and then subjected to a stirring treatment to obtain a reaction suspension. Finally, the reaction suspension is subjected to a sedimentation treatment to obtain a precipitate. Thereafter, the precipitate is washed and dried to obtain a silver powder with a twin crystal structure; in the process of the silver nitrate solution and the reducing agent undergoing redox reaction to generate a silver powder with a twin crystal structure, the dispersant can be adsorbed on the surface of the silver powder particles to provide electrostatic or steric hindrance repulsion, preventing particle aggregation and enabling the silver powder to maintain a good dispersion state. The presence of the initiator can improve the efficiency of the reduction reaction and reduce the occurrence of side reactions, thereby improving the yield and purity of the silver powder. The surfactant can control the particle size and morphology of the silver powder, making it have a more uniform size distribution and a specific shape, such as spherical, flaky, or rod-shaped, etc. Furthermore, through the synergistic effect of the dispersant, the initiator, and the surfactant on the silver powder particles, a silver powder with a twin crystal structure is prepared, further enabling the conductive slurry prepared from the above silver powder with a twin crystal structure to have a low resistance and excellent conductivity; at the same time, the synthesis process of the present invention has the characteristics of rapid reaction, simple operation, green and harmless, and is suitable for large-scale production.

[0161] It should be noted that the above embodiments all belong to the same inventive concept. The descriptions of the embodiments have their own emphases. For the parts not described in detail in individual embodiments, reference can be made to the descriptions in other embodiments.

[0162] The above embodiments merely illustrate the implementation manners of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing silver powder having a twin structure, characterized in that: include: S1, mixing a silver nitrate solution, a dispersant, an initiator, a surfactant and a reducing agent to obtain a primary product; the dispersant is one of polyethylene glycol, polyvinyl pyrrolidone, gelatin and gum arabic, and the amount of the dispersant is 10-15% of the mass of the silver powder obtained by the reaction; the initiator is sodium borohydride; the surfactant is one or more of sodium dodecyl sulfate, hexadecyl trimethyl ammonium bromide and betaine; S2, mixing the primary product with the coating agent and stirring to obtain a reaction suspension; S3, subjecting the reaction suspension to sedimentation to obtain a precipitate, and then washing and drying the precipitate to obtain a silver powder having a twin structure; The S1 step specifically includes: S11, mixing the surfactant and the reducing agent, and adjusting the pH value to 4.5-5.5 to obtain a first mixed solution; S12, mixing the first mixed liquid, the dispersant and the initiator and placing the mixture in a reaction kettle and stirring to obtain a second mixed liquid; S13, adding the silver nitrate solution to the second mixed solution and stirring to obtain the initial product, the silver nitrate solution is added to the second mixed solution for 5 to 10 minutes.

2. The method for preparing silver powder having a twin structure according to claim 1, characterized in that: In the step S11, the reducing agent is any one of ascorbic acid, glucose, formaldehyde, triethanolamine and hydrazine hydrate; and the amount of the reducing agent exceeds the theoretical value of the stoichiometric ratio by 10%.

3. The method for preparing silver powder having a twin structure according to claim 1, characterized in that: In the step S2, the coating agent includes one or more of oleic acid, lauric acid, stearic acid and palmitic acid.

4. The method for preparing silver powder having a twin structure according to claim 1, characterized in that: The S3 step specifically includes: S31, performing sedimentation treatment on the reaction suspension, removing the supernatant, and obtaining the precipitate; S32, mixing the precipitate with acetone and stirring the mixture, and obtaining a filter residue after solid-liquid separation; S33, washing the filter residue with deionized water and anhydrous ethanol respectively until the conductivity is less than 20 μS / m to obtain wet powder; S34, drying the wet powder to obtain the silver powder with a twin structure.

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