A method for preparing a metal electrode using an electrochemical method

Abstract

The application provides a method for preparing a metal electrode by using an electrochemical method, and the method comprises the following steps: preparing a mask plate by laser etching a molecular film according to a required electrode shape; preparing a metal slurry; the metal slurry comprises, in percentage by mass, 5-30% of a first metal salt, 5-35% of a second metal salt and 0.1-10% of a thickening agent, and the rest is a solvent; fixing the mask plate on a substrate, and sequentially depositing a non-metal buffer layer and a metal plating film on the mask plate by using a vapor deposition method, so as to deposit a metal electrode on the substrate; and finally removing the mask plate. The method has low manufacturing cost, and the prepared electrode has high conductivity, small light shielding area and high photoelectric conversion rate.

Description

Technical Field

[0001] This application relates to the field of electrode manufacturing technology, and in particular to a method for preparing metal electrodes using electrochemical methods. Background Technology

[0002] Currently, the fabrication of solar cell electrodes commonly employs screen printing silver paste, resulting in electrode linewidths exceeding 30 μm. Since silver paste is primarily composed of silver, and its high silver content leads to high costs, and given that silver paste has significantly lower conductivity than metallic silver, relatively thick electrode grid lines are required to achieve a certain conductivity. This necessitates a larger quantity of raw materials, further increasing costs, and placing high demands on equipment and processes. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in related technologies. This application proposes a method for preparing metal electrodes using an electrochemical approach, which has low manufacturing costs and produces electrodes with high conductivity and high photoelectric conversion efficiency.

[0004] To achieve the above objectives, this application proposes a method for preparing a metal electrode using an electrochemical method, comprising the following steps:

[0005] A mask is prepared by laser etching of a molecular thin film according to the required electrode shape;

[0006] Prepare a metal paste; based on the metal paste, the metal paste comprises, by mass percentage, 5-30% of a first metal salt, 5-35% of a second metal salt, and 0.1-10% of a thickener, with the remainder being a solvent;

[0007] A mask is fixed on a substrate, and a non-metallic buffer layer and a metal film are deposited sequentially on the mask using a vapor deposition method to deposit a metal electrode on the substrate; then the mask is removed.

[0008] In some embodiments, the thickness of the molecular film is 10 μm-200 μm.

[0009] In some embodiments, the process of fabricating the mask includes using an ultrafast laser to create slits of the desired electrode shape on a molecular thin film.

[0010] In some embodiments, the slit width is 1μm-1000μm.

[0011] In some embodiments, the substrate is a solar cell.

[0012] In some embodiments, the method of fixing a mask onto a substrate includes one or more combinations of double-sided tape, adhesive, fixing slots, and a stage.

[0013] In some embodiments, the first metal salt is at least one of copper salt, nickel salt, tin salt, aluminum salt, or silver salt;

[0014] And / or, the first metal salt is selected from at least one of copper sulfate, copper nitrate, copper chloride, nickel nitrate, nickel chloride, nickel sulfate, or aluminum sulfate;

[0015] And / or, the second metal salt is a potassium salt and / or a sodium salt;

[0016] The second metal salt is selected from at least one of potassium nitrate, potassium chloride, potassium sulfate, sodium nitrate, sodium chloride, or sodium sulfate.

[0017] In some embodiments, the amount of thickener added, based on the metal slurry, is 1-2% by mass percentage;

[0018] And / or, the thickener is selected from at least one of xanthan gum, guar gum, cationic guar gum, hydroxypropyl guar gum, magnesium aluminum silicate, silica, sodium magnesium silicate, hydrated silica, montmorillonite, sodium magnesium lithium silicate, and hydropyrite.

[0019] In some embodiments, the solvent is selected from at least one of water, methanol, ethanol, isopropanol, formic acid, acetic acid, or diethyl ether;

[0020] And / or, the solvent comprises 70-100% water and 0-30% isopropanol by mass percentage.

[0021] In some embodiments, the viscosity of the metal slurry is 30,000-50,000 mPa·s.

[0022] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0023] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0024] Figure 1 This is a flowchart of a method for preparing a metal electrode using an electrochemical method in one embodiment of this application. Detailed Implementation

[0025] Embodiments of this application are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, embodiments of this application include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0026] To achieve the above objectives, this application proposes a method for preparing metal electrodes using electrochemical methods, such as... Figure 1 As shown, it includes the following steps:

[0027] S1: Prepare a mask by laser etching of a molecular thin film according to the required electrode shape;

[0028] S2: Prepare metal paste; Based on the metal paste, the metal paste includes 5-30% first metal salt, 5-35% second metal salt and 0.1-10% thickener by mass percentage, with the remainder being solvent;

[0029] S3: Fix the mask onto the substrate, and use vapor deposition to deposit a non-metallic buffer layer and a metal film on the mask in sequence to deposit a metal electrode on the substrate; then remove the mask.

[0030] In step S1, a mask is prepared by laser etching of a molecular thin film according to the required electrode shape. The molecular thin film is made of polyethylene terephthalate (PET), polyolefin film (PO), polyimide (PI), polyvinyl chloride (PVC), or other molecular thin films with a required thickness. For example, the molecular thin film can be a non-adhesive film or a non-adhesive film; this embodiment does not impose any special limitations, but the thickness of the molecular thin film is 10μm-200μm. For example, the thickness of the molecular thin film is 10μm, 20μm, 40μm, 60μm, 70μm, 90μm, 100μm, 160μm, 200μm, etc.

[0031] The process of preparing the mask involves using an ultrafast laser to create slits of the desired electrode shape on a molecular thin film.

[0032] The process of fabricating the mask involves using an ultrafast laser (a laser with a pulse width on the order of ps or even fs) to create slits of the desired electrode shape on the molecular thin film. Using the method described in this application, finely processed molecular thin film masks can be fabricated.

[0033] The slit width (i.e., the width of the fabricated electrode lines) for laser etching of molecular thin films ranges from 1 μm to 1000 μm. For example, the slit width value is determined based on the application. For instance, when fabricating auxiliary grids or ordinary grid lines for crystalline silicon solar cells, the slit width is preferably 1 μm to 100 μm, more preferably 1 μm to 20 μm; when fabricating main grids for crystalline silicon solar cells, the slit width is preferably 100 μm to 500 μm. The specific slit width can also be determined according to the required electrode shape; the slit length is determined based on the cell electrode design.

[0034] In step S2, the metal slurry is prepared. Based on the metal slurry, the metal slurry includes 5-30% of a first metal salt, 5-35% of a second metal salt, and 0.1-10% of a thickener by mass percentage, with the remainder being a solvent. The first metal salt is at least one of copper, nickel, tin, aluminum, or silver salts. For example, the first metal salt is selected from at least one of copper sulfate, copper nitrate, copper chloride, nickel nitrate, nickel chloride, nickel sulfate, or aluminum sulfate. The mass percentage of the first metal salt is 5%, 10%, 15%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0035] The second metal salt is a potassium salt and / or a sodium salt; for example, the second metal salt is selected from at least one of potassium nitrate, potassium chloride, potassium sulfate, sodium nitrate, sodium chloride, or sodium sulfate. The mass percentage of the second metal salt is 5%, 10%, 15%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc.

[0036] The thickener is selected from at least one of xanthan gum, guar gum, cationic guar gum, hydroxypropyl guar gum, magnesium aluminum silicate, silica, sodium magnesium silicate, hydrated silica, montmorillonite, sodium magnesium lithium silicate, and hydropyrite. In some embodiments, the content of the thickener is 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., and in some embodiments, the content of the thickener is 1-2%.

[0037] In this embodiment, the solvent is selected from at least one of water, methanol, ethanol, isopropanol, formic acid, acetic acid, or diethyl ether; the solvent comprises 70-100% water and 0-30% isopropanol by mass percentage.

[0038] In this embodiment, the first metal salt, the second metal salt, and the solvent are mixed and stirred to disperse. After heating and stirring the mixed solution, it is mixed with a thickener to obtain a pre-made slurry. After crushing the pre-made slurry, it is ground, allowed to stand, and filtered to obtain a metal slurry with a viscosity of 30,000-50,000 mPa·s.

[0039] In step S3, the photomask is fixed onto a substrate, where the substrate is a solar cell. For example, the photomask is fixed onto the solar cell, and a metal film is deposited on the photomask using a PVD method to directly grow metal electrodes of the desired shape onto the solar cell. The substrate can also be other film plates; after depositing the metal electrodes on the substrate, they are transferred to the solar cell as solar electrodes. The method for fixing the photomask to the substrate in this application includes one or more combinations of double-sided tape, adhesive, fixing slots, and a wafer stage. If the photomask uses adhesive tape with adhesive properties, the fixing method can be direct bonding.

[0040] In addition, a non-metallic film can be pre-deposited as a buffer layer before metal deposition on the substrate, or the buffer layer may be omitted. The deposition apparatus includes an electrochemical device, wires, and electrodes, etc.; its output voltage is 1-10V.

[0041] According to the specific implementation of this application, in the method for preparing the metal electrode of the solar cell, the metal electrode of the desired shape (i.e., a fine line that is basically consistent with the shape of the slit in the mask) can be grown on the solar cell sheet, and then the mask can be removed.

[0042] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of this application, the technical solution of this application is described in detail below, but this should not be construed as limiting the scope of implementation of this application.

[0043] Example 1

[0044] This embodiment provides a method for preparing a metal electrode using an electrochemical method, which includes:

[0045] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0046] The metal slurry is prepared by mass percentage comprising 30% of a first metal salt (silver salt), 35% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol). The viscosity of the metal slurry is 50,000 mPa·s.

[0047] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0048] Example 2

[0049] This embodiment provides a method for preparing a metal electrode using an electrochemical method, which includes:

[0050] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0051] The metal slurry is prepared by mass percentage comprising 5% of a first metal salt (silver salt), 35% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 30000 mPa·s.

[0052] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0053] Example 3

[0054] This embodiment provides a method for preparing a metal electrode using an electrochemical method, which includes:

[0055] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0056] The metal slurry is prepared by mass percentage comprising 30% of a first metal salt (silver salt), 5% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 30000 mPa·s.

[0057] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0058] Example 4

[0059] This embodiment provides a method for preparing a metal electrode using an electrochemical method, which includes:

[0060] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0061] The metal slurry is prepared by mass percentage comprising 20% ​​of a first metal salt (silver salt), 25% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 30000 mPa·s.

[0062] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0063] Example 5

[0064] This embodiment provides a method for preparing a metal electrode using an electrochemical method, which includes:

[0065] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0066] The metal slurry is prepared by mass percentage comprising 30% of a first metal salt (silver salt), 35% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 40000 mPa·s.

[0067] The mask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). First, a metal film is deposited sequentially on the mask to create metal electrodes on the HIT solar cell; then the mask is removed.

[0068] Example 6

[0069] This embodiment provides a method for preparing a metal electrode using an electrochemical method, which includes:

[0070] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0071] The metal slurry is prepared by mass percentage comprising 30% of a first metal salt (tin salt), 35% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 35000 mPa·s.

[0072] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0073] Comparative Example 1

[0074] This comparative example provides a method for preparing a metal electrode using an electrochemical approach, comprising:

[0075] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0076] The metal paste is prepared by mass percentage comprising 60% of a first metal salt (silver salt) and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol).

[0077] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0078] Comparative Example 2

[0079] This comparative example provides a method for preparing a metal electrode using an electrochemical approach, comprising:

[0080] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0081] The metal paste is prepared by mass percentage, comprising 70% of a second metal salt (potassium sulfate) and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent comprises 70% water and 30% isopropanol by mass percentage).

[0082] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0083] Comparative Example 3

[0084] This comparative example provides a method for preparing a metal electrode using an electrochemical approach, comprising:

[0085] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0086] The metal slurry is prepared by mass percentage comprising 40% of a first metal salt (tin salt), 40% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 35000 mPa·s.

[0087] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. The electrochemical device, wires, and electrodes, with an output voltage of 10V, are deposited using vapor deposition (PVD). A non-metallic buffer layer and a metal film are first deposited sequentially on the photomask to deposit the metal electrodes on the HIT solar cell; then the photomask is removed.

[0088] Comparative Example 4

[0089] This comparative example provides a method for preparing a metal electrode using an electrochemical approach, comprising:

[0090] A laser is used to cut slits spaced 2 mm apart and 20 μm wide on a 30 μm thick PET or PI plastic film to obtain a PET or PI film mask. The shape of the slits is determined as needed.

[0091] The metal slurry is prepared by mass percentage comprising 40% of a first metal salt (tin salt), 40% of a second metal salt (potassium sulfate), and 10% of a thickener (hydroxypropyl guar gum), with the remainder being a solvent (the solvent by mass percentage comprising 70% water and 30% isopropanol), wherein the viscosity of the metal slurry is 35000 mPa·s.

[0092] The photomask is fixed above the HIT solar cell with the prepared transparent conductive film using double-sided tape, ensuring the tape avoids slits. A non-metallic buffer layer and a metallized film are deposited sequentially on the photomask using a brush-coating method to deposit metal electrodes on the HIT solar cell; then the photomask is removed.

[0093] The metal electrodes obtained in the above embodiments and comparative examples were tested for the amount of paste used (g) and the efficiency Eta (conversion efficiency) of converting light energy into electrical energy. The specific test results are shown in Table 1 below.

[0094] Table 1. Performance data of the metal electrodes obtained in the examples and comparative examples.

[0095] Slurry dosage (g) Eta(%) Example 1 0.020 2.52 Example 2 0.026 2.50 Example 3 0.022 2.45 Example 4 0.029 2.46 Example 5 0.031 2.47 Example 6 0.030 2.49 Comparative Example 1 0.046 -1.22 Comparative Example 2 0.043 -1.02 Comparative Example 3 0.035 1.99 Comparative Example 4 0.073 0

[0096] As shown in Table 1, the metal electrode obtained by the method of this application has low manufacturing cost and high conductivity and photoelectric conversion efficiency.

[0097] It should be noted that in the description of this application, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0098] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the function involved, as will be understood by those skilled in the art to which embodiments of this application pertain.

[0099] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0100] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a metal electrode using an electrochemical approach, characterized in that, Includes the following steps: A mask is prepared by laser etching of a molecular thin film according to the required electrode shape; Prepare a metal paste; based on the metal paste, the metal paste comprises, by mass percentage, 5-30% of a first metal salt, 5-35% of a second metal salt, and 0.1-10% of a thickener, with the remainder being a solvent; A mask is fixed on a substrate, and a non-metallic buffer layer and a metal film are deposited sequentially on the mask using a vapor deposition method to deposit a metal electrode on the substrate; then the mask is removed.

2. The method according to claim 1, characterized in that, The thickness of the molecular film is 10μm-200μm.

3. The method according to claim 1, characterized in that, The process of fabricating the mask involves using an ultrafast laser to create slits of the desired electrode shape on a molecular thin film.

4. The method according to claim 3, characterized in that, The slit width is 1μm-1000μm.

5. The method according to claim 1, characterized in that, The substrate is a solar cell.

6. The method according to claim 1, characterized in that, Methods for fixing a mask onto a substrate include one or more combinations of double-sided tape, adhesive, fixing slots, and a stage.

7. The method according to any one of claims 1-6, characterized in that, The first metal salt is at least one of copper salt, nickel salt, tin salt, aluminum salt, or silver salt; And / or, the first metal salt is selected from at least one of copper sulfate, copper nitrate, copper chloride, nickel nitrate, nickel chloride, nickel sulfate, or aluminum sulfate; And / or, the second metal salt is a potassium salt and / or a sodium salt; The second metal salt is selected from at least one of potassium nitrate, potassium chloride, potassium sulfate, sodium nitrate, sodium chloride, or sodium sulfate.

8. The method according to claim 7, characterized in that, Based on the metal slurry, the amount of thickener added is 1-2% by mass percentage; And / or, the thickener is selected from at least one of xanthan gum, guar gum, cationic guar gum, hydroxypropyl guar gum, magnesium aluminum silicate, silica, sodium magnesium silicate, hydrated silica, montmorillonite, sodium magnesium lithium silicate, and hydropyrite.

9. The method according to claim 7, characterized in that, The solvent is selected from at least one of water, methanol, ethanol, isopropanol, formic acid, acetic acid, or diethyl ether; And / or, the solvent comprises 70-100% water and 0-30% isopropanol by mass percentage.

10. The method according to claim 7, characterized in that, The viscosity of the metal slurry is 30,000-50,000 mPa·s.

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