Silver-coated copper powder with low silver content as well as preparation method and application of silver-coated copper powder

Abstract

The invention discloses low-silver-content silver-coated copper powder and a preparation method and application thereof.The preparation method includes the steps that copper powder is pretreated and then mixed with water, a dispersing agent and sodium tartrate to be stirred, and a copper precursor solution is obtained; slowly dropwise adding a small amount of silver-ammonia solution into the copper precursor solution for reaction; and mixing a complexing agent with the residual silver-ammonia solution, dropwise adding the mixture into the reaction solution, raising the temperature, continuously reacting for a period of time, dropwise adding a reducing agent into the reaction system, continuously reacting, and after the reaction is finished, carrying out solid-liquid separation, washing and drying to obtain the silver-coated copper. According to the method, firstly, gradient control is conducted on the concentration of silver ions, a layer of uniform silver crystals are replaced on the copper surface, then the residual silver ions are adsorbed to the surface through the double-face adsorption effect of the complexing agent and then are replaced, and therefore the uniform silver shell is formed. A reducing agent is utilized to drive silver crystals to grow under low concentration, and the structure of a silver layer is improved in the preparation process, so that the silver layer has good oxidation resistance and conductivity.

Description

Technical Field

[0001] The invention relates to a metal composite material powder and a preparation method and application thereof, in particular to a silver-coated copper powder with a low silver content and a preparation method and application thereof, belonging to the field of metal composite materials. Background Art

[0002] Heterojunction solar cells (HJT cells) have the remarkable performance of low-temperature manufacturing, fewer production processes, high conversion efficiency, high bifaciality, low attenuation rate, and high stability due to their unique double-sided symmetrical structure and excellent passivation effect of amorphous silicon layer. Silver paste has been limited by the high cost of silver powder when used as its conductive paste, and it is urgently needed to be replaced by other powders. Therefore, silver-coated copper was proposed, which combines the advantages of Ag and Cu and is considered to be the most promising choice. It can maintain high conductivity while resisting oxidation. However, obtaining a uniform and dense silver coating on the copper surface usually requires a higher silver content, which increases the cost. In order to overcome this problem, low-silver-content Cu@Ag composites face huge challenges, and innovative methods and routes are needed to achieve uniform and dense coating.

[0003] At present, there are some problems in the application of Cu@Ag powder in HJT solar cells, which hinder its large-scale industrial application. First, Cu@Ag is prone to solid-state dewetting behavior, which causes the silver shell to disintegrate and the copper core to be exposed, resulting in an increase in resistance. Anti-wetting performance mainly occurs at the grain boundaries and is more common in silver layers with smaller grain sizes. Secondly, the resistivity of Cu@Ag powder is high, which is because the grain refinement in the metal material introduces a large number of grain boundaries, which enhance electron scattering and thus reduce conductivity. In addition, Cu@Ag with a low silver content has a thinner silver layer, and its oxidation resistance is bound to be affected.

[0004] Silver-coated copper powder with low silver content, which has low cost, good long-term weather resistance and significant conductivity, is the key development direction of silver-coated copper powder. Therefore, it is imperative to consider the grain size during the synthesis process and dynamically control the growth process of the silver layer to ensure optimal conductivity and alleviate anti-wetting behavior. Summary of the invention

[0005] Purpose of the invention: The first purpose of the present invention is to provide a densely coated silver-coated copper powder with low silver content, which has low resistivity and high oxidation resistance. The second purpose of the present invention is to provide a method for preparing the silver-coated copper powder with low silver content. The third purpose of the present invention is to provide the application of the silver-coated copper powder with low silver content as silver paste in preparing conductive materials.

[0006] Technical solution: The method for preparing a silver-coated copper powder with a low silver content described in the present invention comprises the following steps:

[0007] (1) Pre-treating copper powder;

[0008] (2) adding the pretreated copper powder into deionized water, adding a dispersant and sodium tartrate, and stirring to obtain a copper precursor solution;

[0009] (3) controlling the reaction temperature, and adding the silver ammonia solution dropwise to the copper precursor solution to obtain solution A;

[0010] (4) mixing the complexing agent solution and the silver ammonia solution to obtain solution B, and adding solution B dropwise to solution A to continue the reaction;

[0011] (5) adding a reducing agent solution, continuing the reaction, solid-liquid separation, washing, and drying to obtain the product silver-coated copper powder.

[0012] Furthermore, in step (1), the copper powder pretreatment process is at least one of acetone cleaning, dilute sulfuric acid cleaning, NaOH cleaning, EDTA cleaning, mixed solution of ammonium sulfate and ammonia water cleaning, ethanol cleaning, and deionized water cleaning.

[0013] Furthermore, the concentration of ammonium sulfate in the mixed solution of ammonium sulfate and ammonia water is 0.1 mol / L-0.5 mol / L.

[0014] Furthermore, in step (2), the dispersant is at least one of PEG600, PEG400, PVP, and polyvinyl alcohol.

[0015] Furthermore, in step (2), the mass ratio of copper powder to dispersant is 20:1-5:1, the mass ratio of copper powder to deionized water is 1:150-1:50, and the mass ratio of copper powder to sodium tartrate is 1:10-1:5.

[0016] Furthermore, in step (2), the concentration of sodium tartrate is 0.3-0.6 mol / L.

[0017] Furthermore, in step (2), the stirring temperature is 20-50° C., and the stirring time is more than 10 min.

[0018] Furthermore, in step (3), the reaction temperature is controlled to be 20-50°C.

[0019] Furthermore, in step (3), the dropping speed of the silver ammonia solution is 0.1-1 mL / min.

[0020] Furthermore, in step (3), the volume ratio of the silver ammonia solution to the copper precursor solution is 1:250-1:100.

[0021] Furthermore, in step (3), the reaction time is 15-50 min.

[0022] Furthermore, in step (4), the complexing agent is at least one of malic acid, tryptophan, L-arginine, L-histidine, glutamic acid, and L-lysine.

[0023] Furthermore, in step (4), the concentration of the complexing agent solution is 0.1-0.3 mol / L.

[0024] Furthermore, in step (4), the volume ratio of solution B to solution A is 1:8-1:4.

[0025] Furthermore, in step (4), the temperature for continuing the reaction is 30-70°C, and the time for continuing the reaction is 0-50 min.

[0026] Furthermore, the mass of the silver ammonia solution added in step (3) is 5-25% of the mass of the total silver ammonia solution of step (3) and step (4), the mass ratio of the pretreated copper powder to the silver nitrate in the total silver ammonia solution is 10:1-5:1; and the concentration of silver nitrate in the silver ammonia solution is 0.1-0.5 mol / L.

[0027] Furthermore, in step (4), the dropping speed of solution B is 2-10 mL / min.

[0028] Furthermore, in step (5), the reducing agent is at least one of L-ascorbic acid, hydrazine hydrate, sodium borohydride, and citric acid.

[0029] Furthermore, in step (5), the volume ratio of the reducing agent solution to solution B is 1:10-1:5, and the concentration of the reducing agent solution is 0.2 mol / L-0.8 mol / L.

[0030] Furthermore, the mass ratio of the complexing agent to the silver nitrate in the total silver ammonia solution of step (3) and step (4) is 1:1-50:1; the mass ratio of the reducing agent to the silver nitrate in the total silver ammonia solution of step (3) and step (4) is 1:1-50:1.

[0031] Furthermore, in step (5), the reaction temperature is 30-70°C, and the reaction time is 10-60 min.

[0032] Furthermore, in step (5), the dropping speed of the reducing agent is 1-10 mL / min.

[0033] The silver-coated copper powder with low silver content is obtained by the preparation method of the invention.

[0034] The low-silver-content silver-coated copper powder of the present invention is used as a silver paste material in the preparation of a conductive material.

[0035] Principle of the invention: The present invention adopts a gradient control method to prepare silver-coated copper, and dynamically regulates the concentration of the silver source so that it can cooperate with the growth of the silver layer. First, a small amount of silver ions is added to grow a uniform layer of "silver crystals" on the copper surface. At the same time, an amino acid complexing agent is used, which can both complex with silver ions and form ligands with metallic silver. Under the induction of the complexing agent, the silver crystals form double-sided adsorption, and then are coated to promote complete coating of the silver layer. Then, a reducing agent is added to drive the silver crystal particles that constitute the silver layer to grow. The growth of silver crystals can significantly reduce the dewetting behavior of the silver layer and improve the conductivity.

[0036] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0037] (1) The present invention can not only slow down the rate of copper-silver substitution by gradient-controlled addition of silver ions, but also realize dense and uniform coating of silver-coated copper through the double-sided action of the complexing agent, silver ions and silver particles. By adding a reducing agent, the silver crystals of the silver layer are driven to grow, and the performance of the silver-coated copper is improved during the preparation process.

[0038] (2) The silver-coated copper powder prepared by the present invention has a smooth coating surface and a uniformly distributed silver layer to achieve a dense coating effect. It has excellent antioxidant ability and high conductivity, and delays the solid-state dewetting behavior of the silver layer to a certain extent.

[0039] (3) The process of the present invention is simple, convenient for large-scale production, and saves costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a SEM image of the silver-coated copper powder in Examples 1-11;

[0041] Figure 2 is the SEM image of the silver-coated copper powder in Comparative Example 1;

[0042] Figure 3 is the SEM image of the silver-coated copper powder in Comparative Example 2;

[0043] Figure 4 is the SEM image of the silver-coated copper powder in Comparative Example 3;

[0044] Figure 5 The powder resistivity diagram of the silver-coated copper powder in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0045] Figure 6 is the TG-DSC curve of the silver-coated copper powder in Example 1;

[0046] Figure 7 This is the SEM picture of the silver paste used in Example 1. DETAILED DESCRIPTION

[0047] The present invention is described in further detail below.

[0048] Example 1

[0049] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0050] S2: 5 g of treated copper powder was dissolved in 500 mL of deionized water, 0.5 g of PEG600 was added thereto, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and then added to the above solution, and mechanically stirred for reaction (speed: 500 r / min), the reaction temperature was 30°C, and the reaction time was 15 min to obtain a copper precursor solution.

[0051] S3: Prepare silver ammonia solution: weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0052] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0053] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 min, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min, and reacted for 20 min.

[0054] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 25 min.

[0055] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0056] Example 2

[0057] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0058] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0059] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0060] S4: Take 6 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 2 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0061] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.1 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0062] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 2 mL / min, and continue the reaction for 45 min.

[0063] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0064] Example 3

[0065] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0066] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0067] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0068] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0069] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.3 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0070] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 8 mL / min, and continue the reaction for 45 min.

[0071] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0072] Example 4

[0073] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0074] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 15 minutes to obtain a copper precursor solution.

[0075] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0076] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 1 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0077] S5: After the reaction is completed, the reaction temperature is adjusted to 50°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 min, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0078] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0079] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0080] Example 5

[0081] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0082] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 15 minutes to obtain a copper precursor solution.

[0083] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0084] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0085] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 min, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min, and reacted for 10 min.

[0086] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 35 min.

[0087] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0088] Example 6

[0089] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0090] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 15 minutes to obtain a copper precursor solution.

[0091] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0092] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0093] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0094] S6: Continue to add 100 mL of 0.2 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 2 mL / min, and continue the reaction for 45 min.

[0095] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0096] Example 7

[0097] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0098] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0099] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0100] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0101] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0102] S6: Continue to add 100 mL of 0.8 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0103] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0104] Example 8

[0105] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0106] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0107] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0108] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0109] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0110] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0111] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0112] Example 9L - Ascorbic acid concentration is too high

[0113] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0114] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0115] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0116] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0117] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0118] S6: Continue to add 100 mL of 1 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0119] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0120] Example 10: The reducing agent dripping rate is too fast

[0121] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0122] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0123] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0124] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0125] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0126] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 15 mL / min, and continue the reaction for 45 min.

[0127] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0128] Example 11 L-Histidine concentration is too high

[0129] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0130] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 10 min to obtain a copper precursor solution.

[0131] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0132] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0133] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 400 mL of 0.5 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 minutes, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min.

[0134] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0135] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50° C. for 8 h to obtain silver-coated copper powder with a low silver content.

[0136] The low silver content silver-coated copper powder prepared in Examples 1-11 was tested by scanning electron microscope. The results are as follows: Figure 1 As shown, Figure 1 The SEM images of the silver-coated copper powder in Examples 1-11, wherein (1)-(11) correspond to Examples 1-11, respectively. Figure 1It can be seen that under the experimental conditions of the above-mentioned Examples 1-8, Cu@Ag was successfully synthesized, and the synthesized powders all had a complete coated silver layer, good powder dispersibility, and a good spherical shape. However, in Example 9, the concentration of L-ascorbic acid was too high, resulting in an excessive amount of L-ascorbic acid, which resulted in a rough final coated surface, and an excessively high organic content, or resulted in adhesion on the Cu@Ag surface, thereby affecting performance. In Example 10, when the reducing agent solution was added dropwise, the drop rate was too fast, resulting in a very uneven coated surface and a loose silver layer. In Example 11, the concentration of L-histidine was too high, resulting in an excessive amount of L-histidine, and the Cu@Ag finally prepared had poor sphericity, and the copper powder had been etched in large quantities.

[0137] Comparative Example 1: No complexing agent is used

[0138] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0139] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 15 minutes to obtain a copper precursor solution.

[0140] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0141] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0142] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, and all the remaining silver ammonia solution is added dropwise to the reaction system obtained in step S4 at a rate of 0.5 mL / min.

[0143] S6: Continue to add 100 mL of 0.5 mol / L L-ascorbic acid solution to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0144] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50°C for 8 hours to obtain silver-coated copper powder.

[0145] Comparative Example 2: No reducing agent is used

[0146] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0147] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 15 minutes to obtain a copper precursor solution.

[0148] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0149] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0150] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 min, and then all of it is added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min, and reacted for 45 min.

[0151] S6: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50°C for 8 hours to obtain silver-coated copper powder.

[0152] Comparative Example 3: Complexing agent is used, and gum arabic solution is used as reducing agent

[0153] S1: First, take 5g of copper powder, add it to 50mL of acetone to remove organic matter, ultrasonically oscillate for 30min, and filter; then add 50mL of a mixed solution of ammonium sulfate and ammonia water (the mixed solution contains 0.5mol / L ammonium sulfate + 1mol / L ammonia water) to the copper powder to remove surface oxides, ultrasonically oscillate for 30min, and filter; then, add 1% sodium hydroxide solution to the copper powder, ultrasonically oscillate for 10min, and filter; finally, wash the copper powder repeatedly with water, filter, and obtain pretreated copper powder.

[0154] S2: 5 g of pretreated copper powder was dissolved in 500 mL of deionized water, to which 0.5 g of PEG600 was added, 17.5 g of sodium tartrate was weighed and dissolved in 200 mL of deionized water, and after dissolution, it was added to the copper solution to obtain a copper precursor solution, and the reaction was mechanically stirred (speed: 500 r / min), the reaction temperature was 30°C, and the reaction was carried out for 15 minutes to obtain a copper precursor solution.

[0155] S3: Prepare a silver ammonia solution, weigh 1.2 g of silver nitrate, dissolve it in 20 mL of water, and add diluted ammonia water (volume ratio of ammonia water: deionized water = 1:2) dropwise until it becomes clear and transparent to obtain a silver ammonia solution.

[0156] S4: Take 3 mL of the above-prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5 mL / min. After the addition is complete, react at 30° C. for 30 min.

[0157] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 200 mL of 0.2 mol / L L-histidine solution is prepared, and all the remaining silver ammonia solution is added to the L-histidine solution, stirred for 3 min, and then added dropwise to the reaction system obtained in step S4 at a rate of 5 mL / min, and reacted for 45 min.

[0158] S6: Prepare another 100 mL of 0.5 mol / L gum arabic solution, and immediately add it dropwise to the reaction system obtained in step S5 at 5 mL / min, and continue the reaction for 45 min.

[0159] S7: After the reaction is completed, the mixture is washed with ethanol and deionized water for multiple times, filtered, placed in a vacuum drying oven, and dried at 50°C for 8 hours to obtain silver-coated copper powder.

[0160] Analysis: The silver-coated copper powders of Comparative Examples 1-3 were tested by scanning electron microscopy. Figure 2-4As shown, the electron microscope images of the silver-coated copper powder obtained in Example 1 and Comparative Example 1 are compared. In Example 1, the prepared silver-coated copper powder is completely coated and has a smooth surface, the silver layer is evenly distributed, the coating effect is good, and the actual measured silver content on the surface of the silver-copper powder is 21.9%, achieving dense coating of silver-coated copper at a low silver content. However, the surface of the copper powder in Comparative Example 1 was not successfully coated, and the silver was all free silver, and a complete silver shell was not formed. This shows that the double-sided adsorption effect of the amino acid complexing agent used in the reaction system is crucial for densely coated silver-coated copper powder. Then the electron microscope images of the silver-coated copper powder obtained in Example 1 and Comparative Example 2 were compared, and it was found that the surface silver shell of Comparative Example 2 was rough, the copper powder was corroded, and the silver shell in Example 1 was denser. Figure 4 The silver-coated copper prepared in Comparative Example 3 is incompletely coated, has a large number of voids, and the coating layer is uneven. The powder resistivity of the Cu@Ag synthesized in Example 1 and Comparative Examples 1-3 was tested. Figure 5 , the powder resistivity of Example 1 is the lowest, which also shows that its coating is denser and the silver layer is more tightly bonded.

[0161] Comprehensive comparison shows that the silver-coated copper prepared in Example 1 achieves dense coating at low silver content and exhibits excellent electrical conductivity (see Figure 5 ). From this, we can see the importance of the amino acid complexing agent and reducing agent used in the entire coating process to the coating results.

[0162] pass Figure 6 From the thermogravimetric curve, it can be observed that the silver-coated copper powder of Example 1 begins to increase in weight at around 270°C, and has good antioxidant capacity.

[0163] Example 9 Application of Silver-clad Copper

[0164] The silver-coated copper (Cu@Ag) powder synthesized in Examples 1-8 and Comparative Examples 1-3 is used as the main conductive component, spherical Ag nanoparticles (500nm) are used as the filling material, a certain proportion of acrylate and pine alcohol are added, mixed evenly, and prepared in the ratio of Cu@Ag: Ag powder: acrylate (DPHA): pine alcohol = 14:6:1:1, and ground for 30 minutes to obtain a low-temperature curing conductive silver paste. These pastes are then screen-printed onto a 25×25mm ceramic substrate, placed on an electric heating plate and heated for 60 minutes at 180°C to cure it and then evaluated. The resistivity of the low-temperature conductive silver paste was tested by four probes, and the test results are shown in Tables 1 and 2. The results show that the average resistivity of the Cu@Ag prepared in Examples 1-8 is below 50μΩ·cm, maintaining good conductive properties, and the synthesized powder can be well applied. The SEM image of the paste prepared from Example 1 (see Figure 7 ), it can be seen that there is no gap on the surface, the distance between the conductive fillers is small, the conductive fillers are bonded together, and a conductive path is formed, so it has a lower resistivity.

[0165] Table 1 Resistivity of the silver-coated copper powder in Examples 1-8 when applied to silver paste

[0166]

[0167] Table 2 Resistivity of silver-coated copper powder in Example 1 and Comparative Examples 1-3 when applied to silver paste

[0168] Sample No. Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Slurry resistivity (μΩ·cm) 39 102 135 73

Claims

1. A method for preparing silver-coated copper powder with low silver content, characterized in that: The following steps are involved: (1) Pre-treating copper powder; (2) adding the pretreated copper powder into deionized water, adding a dispersant and sodium tartrate, and stirring to obtain a copper precursor solution; (3) controlling the reaction temperature, and adding the silver ammonia solution dropwise to the copper precursor solution to obtain solution A; (4) mixing the complexing agent solution and the silver ammonia solution to obtain solution B, and adding solution B dropwise to solution A to continue the reaction; (5) adding a reducing agent solution, continuing the reaction, solid-liquid separation, washing, and drying to obtain the product silver-coated copper powder.

2. The method for preparing the silver-coated copper powder with low silver content according to claim 1, characterized in that: In step (2), the dispersant is at least one of PEG600, PEG400, PVP, and polyvinyl alcohol, the mass ratio of copper powder to dispersant is 20:1-5:1, the mass ratio of copper powder to deionized water is 1:150-1:50, and the mass ratio of copper powder to sodium tartrate is 1:10-1:5; the concentration of sodium tartrate is 0.3-0.6 mol / L, the stirring temperature is 20-50°C, and the stirring time is more than 10 min.

3. The method for preparing the silver-coated copper powder with low silver content according to claim 1, characterized in that: In step (3), the reaction temperature is controlled to be 20-50° C., the dropping speed of the silver ammonia solution is 0.1-1 mL / min, the volume ratio of the silver ammonia solution to the copper precursor solution is 1:250-1:100, and the reaction time is 15-50 min.

4. The method for preparing the silver-coated copper powder with low silver content according to claim 1, characterized in that: In step (4), the complexing agent is at least one of malic acid, tryptophan, L-arginine, L-histidine, glutamic acid, and L-lysine, the concentration of the complexing agent solution is 0.1-0.3 mol / L, the volume ratio of solution B to solution A is 1:8-1:4, the temperature for continuing the reaction is 30-70°C, and the time for continuing the reaction is 0-50 min.

5. The method for preparing the silver-coated copper powder with low silver content according to claim 1, characterized in that: The mass of the silver ammonia solution added in step (3) is 5-25% of the mass of the total silver ammonia solution in step (3) and step (4), and the mass ratio of the pretreated copper powder to the silver nitrate in the total silver ammonia solution is 10:1-5:1; The concentration of silver nitrate in the silver ammonia solution is 0.1-0.5 mol / L. In step (4), the dropping speed of solution B is 2-10 mL / min.

6. The method for preparing the silver-coated copper powder with low silver content according to claim 1, characterized in that: In step (5), the reducing agent is at least one of L-ascorbic acid, hydrazine hydrate, sodium borohydride, and citric acid, and the volume ratio of the reducing agent solution to solution B is 1:10-1:5; the concentration of the reducing agent solution is 0.2-0.8 mol / L.

7. The method for preparing the silver-coated copper powder with low silver content according to claim 5, characterized in that: The mass ratio of the complexing agent to the silver nitrate in the total silver ammonia solution of step (3) and step (4) is 1:1-50:1; the mass ratio of the reducing agent to the silver nitrate in the total silver ammonia solution of step (3) and step (4) is 1:1-50:

1.

8. The method for preparing the silver-coated copper powder with low silver content according to claim 1, characterized in that: In step (5), the temperature for continuing the reaction is 30-70°C, the time for continuing the reaction is 10-60 min, and the dropping speed of the reducing agent is 1-10 mL / min.

9. Silver-coated copper powder with low silver content obtained by the preparation method according to claims 1-7.

10. Use of the silver-coated copper powder with low silver content as claimed in claim 9 as a silver paste material in the preparation of conductive materials.

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