A coated preform solder, its preparation and use

Abstract

The application discloses a coated preformed filler metal and a preparation method and application thereof, and belongs to the technical field of brazing. The coated preformed filler metal comprises a filler metal and a flux wrapped around the filler metal. The filler metal comprises an aluminum-silicon alloy, and the flux comprises a fluoroaluminate. The mass ratio of the aluminum-silicon alloy to the fluoroaluminate is (75-96):(4-25). The fluoroaluminate is coated on the outer surface of the aluminum-silicon alloy, the flux can effectively remove the oxide film on the surface of the filler metal and the oxide film on the welding interface, the welding quality is improved, and the product yield is improved.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, specifically to a coated preformed brazing filler metal, its preparation method, and its application. Background Technology

[0002] With the booming development of the new energy vehicle industry, the lithium battery market has also grown year by year. Among them, the production capacity and yield of battery cells, as the core component of lithium batteries, are of great concern, as they ultimately affect the price trend of new energy vehicles.

[0003] While continuous process improvements have reduced production costs to a certain extent in battery cell manufacturing, the encapsulation of the electrolyte filling port remains a pain point, with a persistently high defect rate. The yield rate for some models is even below 70%. This is because existing encapsulation technology uses laser welding, which can produce defects such as spatter, porosity, and cracks. Although these defects can be addressed through rework, they increase production costs. In response, some have considered using induction welding technology to replace laser welding. However, the efficiency and yield of existing induction welding technology are unsatisfactory. Therefore, there is an urgent need for a coated pre-formed solder suitable for sealing the electrolyte filling port of battery cells to solve the problem of low one-time sealing yield of the electrolyte filling port in new energy battery cells.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a coated preformed solder, its preparation method and application, which can effectively improve the welding yield and welding speed.

[0006] To achieve the above objectives, in a first aspect of this application, this application provides a coated preformed solder, comprising a solder and a flux surrounding the solder, wherein the solder comprises an aluminum-silicon alloy and the flux comprises a fluoroaluminate;

[0007] The mass ratio of the aluminum-silicon alloy to the fluoroaluminate is (75-96):(4-25).

[0008] As an embodiment of this application, the silicon content in the aluminum-silicon alloy is 11-13% by mass.

[0009] As an embodiment of this application, the mass ratio of the self-crosslinking emulsion to fluoroaluminate is (0.3-2):100.

[0010] As an embodiment of this application, the self-crosslinking emulsion includes a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion; the mass ratio of the self-crosslinking acrylic emulsion and the self-crosslinking polyurethane emulsion is (1.5~9):1.

[0011] As an embodiment of this application, the glass transition temperature of the crosslinked acrylic emulsion is ≤30°C.

[0012] As an embodiment of this application, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is ≤0℃.

[0013] In a second aspect, this application provides a method for preparing a coated preformed solder, comprising the following steps:

[0014] The flux, self-crosslinking emulsion, and solvent are mixed evenly to obtain a mixture.

[0015] The mixture is uniformly coated onto the surface of the solder, and then dried to remove the solvent, resulting in a coated preformed solder.

[0016] As an embodiment of this application, the solvent includes at least one of water, ethanol, n-propanol, propylene glycol, propylene glycol butyl ether, ethylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether.

[0017] As an embodiment of this application, the mass ratio of the solvent to the flux is (0.8-2):1.

[0018] In a third aspect of this application, we provide an application of a coated preformed solder in sealing the electrolyte filling port of a battery cell.

[0019] As an embodiment of this application, the coated preformed brazing filler metal is placed above the weld formed by the sealing nail and the top cover of the battery cell. During the high-frequency induction welding process, after the brazing filler metal melts, the molten liquid flows downward to fill the weld.

[0020] As an implementation scheme of this application, at least one of the following (1) to (3) is satisfied:

[0021] (1) The volume of the weld is a1, and the volume of the coated preformed brazing filler metal is a2, satisfying: 2.17≤a2 / a1≤10;

[0022] (2) The cross-sectional area of ​​the weld is b1, and the cross-sectional area of ​​the coated preformed brazing filler metal is b2, satisfying: 2≤b2 / b1≤5;

[0023] (3) The height of the coated preformed brazing filler metal is ≤5mm.

[0024] In a fourth aspect, this application provides a battery cell liquid injection port, including the coated preformed solder described above.

[0025] The beneficial effects of the present invention are as follows: (1) In this application, fluoroaluminate is coated on the outer surface of aluminum-silicon alloy, and the flux can effectively remove the oxide film on the surface of the solder and the oxide film at the welding interface, thereby improving the welding quality and thus improving the product yield.

[0026] (2) This application incorporates a self-crosslinking emulsion containing self-crosslinking acrylic emulsion and self-crosslinking polyurethane emulsion. The self-crosslinking emulsion replaces the adhesive in the flux, thereby reducing the decomposition of organic matter and spatter during the welding process. Therefore, after welding, there is no need to clean the weldment, welding equipment, and fixtures. At the same time, it can reduce the decomposition of organic matter and the amount of smoke during the welding process, improving safety and environmental protection. The self-crosslinking acrylic acid is easy to connect with the hydroxyl groups in the flux during the film formation process, forming a coating on the metal surface. The self-crosslinking polyurethane emulsion and the self-crosslinking acrylic emulsion work together to improve the adhesion of the flux to the metal and the welding performance, effectively avoiding the decline in coating firmness and welding performance, and effectively improving the product yield. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of welding the weld seam of the battery cell injection port using the coated preformed solder of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0030] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0031] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0032] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0033] The inventors of this invention have discovered that pre-forming the brazing filler metal into a specific shape is to better fill the weld seam and improve production yield. The flux pre-coated on the outer surface is to improve production efficiency and yield. Existing induction welding technology generally involves applying a mixture of flux and solvent before induction welding and welding in a wet state. However, the evaporation of the solvent and the instability of the coating amount can both lead to a decrease in production yield.

[0034] Therefore, in order to solve the above-mentioned technical problems, this application provides a coating type preformed solder, including solder and flux wrapped around the outside of the solder, wherein the solder includes an aluminum-silicon alloy and the flux includes fluoroaluminate;

[0035] The mass ratio of the aluminum-silicon alloy to the fluoroaluminate is (75-96):(4-25), for example, it can be 75:25, 76:24, 78:22, 80:20, 82:18, 85:15, 88:12, 90:10, 92:8, 95:5, 96:4 or any two of these values.

[0036] This application coats the outer surface of aluminum-silicon alloy with fluoroaluminate. The flux can effectively remove the oxide film on the surface of the solder and the oxide film at the welding interface, improve the welding quality, and thus improve the product yield. However, excessive flux will not improve the welding quality, but will instead lead to increased costs. Currently, the cost of cesium fluoroaluminate flux is about 1 yuan / g, which is not allowed in the cost-sensitive new energy vehicle industry chain.

[0037] In one embodiment, the silicon mass percentage in the aluminum-silicon alloy is 11-13%, for example, it can be 11%, 11.2%, 11.5%, 11.8%, 12%, 12.2%, 12.5%, 13% or any two of these values.

[0038] In one embodiment, the mass ratio of the self-crosslinking emulsion to fluoroaluminate is (0.3-2):100, for example, it can be 0.3:100, 0.5:100, 0.6:100, 0.8:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100 or any two of these values. By controlling the mass ratio of the self-crosslinking emulsion to fluoroaluminate within this range, the coating adhesion and welding performance can be improved, powder shedding during the coating process can be avoided, and the amount of welding fumes can be effectively reduced.

[0039] In one embodiment, the self-crosslinking emulsion includes a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion; the mass ratio of the self-crosslinking acrylic emulsion and the self-crosslinking polyurethane emulsion is (1.5 to 9):1, for example, it can be 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or any two of these values.

[0040] This application creatively incorporates a self-crosslinking emulsion comprising self-crosslinking acrylic emulsion and self-crosslinking polyurethane emulsion. The self-crosslinking emulsion replaces the adhesive in the flux, thereby reducing organic matter decomposition and spatter during welding. Therefore, after welding, there is no need to clean the workpiece, welding equipment, and fixtures. Simultaneously, it reduces organic matter decomposition and fumes during welding, improving safety and environmental friendliness. The self-crosslinking acrylic readily bonds with the hydroxyl groups in the flux during film formation, forming a coating on the metal surface. The combined effect of the self-crosslinking polyurethane emulsion and self-crosslinking acrylic emulsion enhances the flux's adhesion to the metal and welding performance, effectively preventing a decline in coating adhesion and welding performance, and significantly improving product yield.

[0041] The inventors of this application discovered that when a common solvent, such as ethanol, is used for pre-coating, the flux pre-coated on the surface easily peels off after drying, which reduces product yield. Therefore, a self-crosslinking emulsion is needed for fixation. An excessively high proportion of self-crosslinking emulsion also leads to a decrease in product yield, while the solvent proportion has little effect within a certain range.

[0042] In one embodiment, the glass transition temperature of the crosslinked acrylic emulsion is ≤30°C.

[0043] In one embodiment, the glass transition temperature of the crosslinked acrylic emulsion is -40 to 30°C, for example, it can be -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, or any two of these values.

[0044] The glass transition temperature of the self-crosslinking acrylic emulsion was determined with reference to the GB / T 27816 standard.

[0045] In one embodiment, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is ≤0°C.

[0046] In one embodiment, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is -45°C to 0°C, for example, it can be -45°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C or any two of these values.

[0047] In one embodiment, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is tested with reference to the GB / T9267-2008 standard.

[0048] In one embodiment, the fluoroaluminate includes CsAlF4, Cs2AlF5, Cs3AlF6, KAlF4, K2AlF5, K3AlF6, K2AlF5·H2O, and KCs2Al3F. 12 At least one of CsK2AlF6, KZnAlF6, K2ZnAlF7, KZn2AlF8, KZnAl2F9, CsZnAlF6, Cs2ZnAlF7, CsZn2AlF8, and CsZnAl2F9.

[0049] One embodiment of this application provides a method for preparing a coated preformed solder, comprising the following steps:

[0050] The flux, self-crosslinking emulsion, and solvent are mixed evenly to obtain a mixture.

[0051] The mixture is uniformly coated onto the surface of the solder, and then dried to remove the solvent, resulting in a coated preformed solder.

[0052] In one embodiment, the solvent includes at least one of water, ethanol, n-propanol, propylene glycol, propylene glycol butyl ether, ethylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether.

[0053] In one embodiment, the mass ratio of the solvent to the flux is (0.8 to 2):1, for example, it can be 0.8:1, 1:1, 1.2:1, 1.5:1, 1.6:1, 1.8:1, 2:1 or any two of these values.

[0054] like Figure 1 As shown, one embodiment of this application provides an application of a coated preformed solder in sealing the electrolyte injection port of a battery cell.

[0055] In one embodiment, the coated preformed brazing filler metal is placed above the weld formed by the sealing pin and the top cover of the battery cell. During the high-frequency induction welding process, after the brazing filler metal melts, the molten liquid flows downward to fill the weld.

[0056] In conventional induction welding, the solder is placed at the weld seam. In the sealing of the battery cell filling port, the sealing weld seam area is located between the sealing pin and the outside of the filling port. However, this reduces welding efficiency due to the distance of the induced magnetic field. If the induction power is increased, the sealing pin, which is above the solder, will burn out due to the close melting points of the sealing pin and the solder. Therefore, the solder of this invention is placed above the sealing pin and is preferentially heated by induction, which improves production efficiency and yield.

[0057] The coated preformed brazing filler metal needs to match the shape of the weld, such as a ring, a square, or other shapes.

[0058] In one embodiment, the volume of the weld is a1, and the volume of the coated preformed brazing filler metal is a2, satisfying 2.17 ≤ a2 / a1 ≤ 10. For example, it can be a range of 2.17, 3, 4, 5, 6, 7, 8, 9, 10, or any two of these values. The inventors of this application have discovered that the volumes of the weld and the coated preformed brazing filler metal are directly and significantly correlated with the welding process. By controlling 2.17 ≤ a2 / a1 ≤ 10, welding quality and yield can be effectively improved. Too low a filler metal volume cannot adequately fill the weld. After melting, the filler metal will wet several interface materials at the weld, forming a certain wetting angle, and cannot completely fill the weld. Therefore, setting the shape of the preformed filler metal to pre-fill the weld volume is completely unreasonable, as it will cause sealing failure due to missing filler metal flow in some areas. Too high a filler metal volume will cause solder overflow and also increase the cost of filler metal and flux. Additionally, the filler metal height exceeds 5mm. This can cause the brazing filler metal to fall into the filler weld without being perpendicular during the melting process, resulting in the brazing filler metal failing to perform its sealing function and reducing product yield.

[0059] In one embodiment, the cross-sectional area of ​​the weld is b1, and the cross-sectional area (i.e., surface area) of the coated preformed brazing filler metal is b2, satisfying: 2≤b2 / b1≤5. For example, it can be 2, 2.5, 3, 3.5, 4, 4.5, 5, or any two of these values. When the volume of the brazing filler metal is fixed, if the surface area of ​​the brazing filler metal is changed, it will affect the height of the brazing filler metal. If the surface area is too large, the brazing filler metal will not be able to gather and flow into the weld, resulting in some brazing filler metal remaining on the outside of the weld, which will not play a sealing role and will increase the product defect rate. If the surface area is too small, the brazing filler metal thickness will be too high, and the brazing filler metal may fall outside the injection port during the melting process, which will also affect the assembly accuracy and thus affect the product yield.

[0060] In one embodiment, the height of the coated preformed solder is ≤5mm.

[0061] Among them, the parameters of high-frequency induction welding are automatically controlled gradient induction current heating, with the first gradient being 100-110A for 4-10s and the second gradient being 85-95A for 1-2s.

[0062] One embodiment of this application provides a battery cell liquid injection port, including the coated preformed solder described above.

[0063] The sources of raw materials used in the examples and comparative examples are shown in Table 1.

[0064] Table 1

[0065]

[0066] The following embodiments are provided to facilitate understanding of the invention. These embodiments are not intended to limit the scope of the claims.

[0067] Example 1

[0068] A method for sealing the electrolyte injection port of a battery cell with a coated pre-formed solder includes the following steps:

[0069] (1) Preparation of coating preformed solder: Cesium fluoroaluminate (CsAlF4), self-crosslinking emulsion and solvent are mixed evenly to obtain a mixture;

[0070] The mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is 0.3:100; the self-crosslinking emulsion includes self-crosslinking acrylic emulsion 1 and self-crosslinking polyurethane emulsion 1 in a mass ratio of 3:1.

[0071] The solvent is n-propanol, and the mass ratio of n-propanol to cesium fluoroaluminate is 1.2:1;

[0072] The mass ratio of cesium fluoroaluminate to AlSi12 is 4:96.

[0073] The mixture is uniformly coated onto the surface of the solder (AlSi12), and the solvent is removed by drying to obtain a coated preformed solder.

[0074] (2) Place the coated preformed brazing filler metal (4 mm high) above the weld formed by the sealing nail and the top cover of the battery cell. During the high-frequency induction welding process, gradient induction current is used for heating, with the first gradient being 105 A for 6 s and the second gradient being 90 A for 1.5 s. After the brazing filler metal melts, the molten liquid flows downward to fill the weld.

[0075] The volume of the weld is a1, the volume of the coated preformed brazing filler metal is a2, and a2 / a1 = 3;

[0076] The cross-sectional area of ​​the weld is b1, and the cross-sectional area of ​​the coated preformed brazing filler metal is b2, where b2 / b1 = 3.

[0077] The welding parameters are shown in Table 1.

[0078] Examples 2-4, Comparative Examples 1-2

[0079] Examples 2-4 and Comparative Examples 1-2 differ from Example 1 in that the mass ratio of CsAlF4 and AlSi12 is changed.

[0080] Examples 5-8

[0081] Examples 5-8 differ from Example 1 in that the mass ratio of the self-crosslinking emulsion to CsAlF4 is changed.

[0082] Examples 9-14

[0083] Examples 9-14 differ from Example 1 in that the mass ratio or type of self-crosslinking emulsion is changed.

[0084] Examples 15-16

[0085] The difference between Examples 15 and 16 and Example 1 is that the mass ratio of solvent to CsAlF4 is changed.

[0086] Example 17

[0087] Example 17 differs from Example 1 in that the type of solvent is changed.

[0088] Examples 18-21

[0089] The difference between Examples 18-21 and Example 1 is that b2 / b1 is changed.

[0090] Examples 22-25

[0091] The difference between Examples 22-25 and Example 1 is that a2 / a1 is changed.

[0092] Comparative Example 3

[0093] The difference between Comparative Example 3 and Example 1 is that an equal amount of polyacrylic acid was used to replace the self-crosslinking emulsion.

[0094] Comparative Example 4

[0095] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 did not include a self-crosslinking emulsion.

[0096] Comparative Example 5

[0097] A method for sealing the electrolyte injection port of a battery cell with a coated pre-formed solder includes the following steps:

[0098] (1) A coated preformed solder is prepared by manual coating method, wherein the coated preformed solder is AlSi12.

[0099] (2) Place the coated preformed brazing filler metal (4 mm high) above the weld formed by the sealing nail and the top cover of the battery cell. During the high-frequency induction welding process, gradient induction current is used for heating, with the first gradient being 105 A for 6 s and the second gradient being 90 A for 1.5 s. After the brazing filler metal melts, the molten liquid flows downward to fill the weld.

[0100] The volume of the weld is a1, the volume of the coated preformed brazing filler metal is a2, and a2 / a1 = 3;

[0101] The cross-sectional area of ​​the weld is b1, and the cross-sectional area of ​​the coated preformed brazing filler metal is b2, where b2 / b1 = 3.

[0102] Table 2

[0103]

[0104]

[0105] Performance testing

[0106] Production efficiency: Number of devices produced per minute (PPM).

[0107] Yield: The soldered components are considered good if there is no obvious burn damage on the surface, the solder is completely wetted, and no obvious bubbles are generated in water after the components are introduced with gas at a pressure of 3 kPa. The yield is determined by testing 100 components.

[0108] Coating adhesion: The flux obtained in the examples and comparative examples were coated onto AlSi12 preformed solder sheets in the same manner to obtain coated sheets; 50g ± 0.2g of the coated sheet was placed in the same position in the vibratory feeder; the sheet was fed 12 times under the same parameters, and the mass of the coated sheet after 12 feedings was weighed. The powder shedding rate of the coated sheet was calculated. The formula for calculating the powder shedding rate of the coated sheet is: Powder shedding rate of the coated sheet = (Amount of flux coated before feeding - Amount of flux coated after feeding) ÷ Amount of flux coated before feeding; The smaller the powder shedding rate of the coated sheet, the better the scratch resistance and adhesion performance of the coated sheet.

[0109] Welding fume quantity and black residue: The fluxes obtained in the examples and comparative examples were coated onto AlSi12 preformed solder sheets to obtain coated sheets. The coated sheets were heated for 5 seconds at a temperature 40°C above the melting point of the activator, and aluminum parts were welded. During the welding process, the smoke size was measured 10 cm above the solder sheet using an explosion-proof dust meter. Five measurements were taken for each flux, and the average value was taken. The average smoke concentration generated when only the activator was used as the baseline value. The average smoke concentration of each flux divided by the baseline value was the welding fume quantity, which is the relative smoke size. Five coated sheets were placed on a pure aluminum plate without any other items on top, and heated for 5 seconds at a temperature 40°C above the melting point of the activator. The presence of black residue was observed.

[0110] Table 3

[0111]

[0112]

[0113] As can be seen from Table 3, the coated preformed brazing filler metal of the present invention can effectively improve the welding yield and welding speed, reduce the powder shedding rate of the coated sheet, and reduce the amount of welding fumes. It can be well applied to the welding and sealing of the filler port of battery cells and has broad application prospects.

[0114] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that by controlling the mass ratio of aluminum-silicon alloy and fluoroaluminate to (75-96): (4-25), the present invention effectively improves the welding yield, reduces the powder shedding rate of the coated sheet, and reduces the amount of welding fumes.

[0115] Comparing Example 1 with Comparative Examples 3-4, it can be seen that the present invention, by using a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion with a ratio of (1.5-9):1, effectively improves the welding yield, reduces the powder shedding rate of the coated sheet, and significantly reduces the amount of welding fumes.

[0116] Comparing Examples 1 to 4, it can be seen that by controlling the mass ratio of aluminum-silicon alloy to fluoroaluminate to (8-20): (80-92), the welding yield was further improved, the powder shedding rate of the coated sheet was reduced, and the amount of welding fumes was reduced.

[0117] Comparing Examples 1 with Examples 5-8, it can be seen that by controlling the mass ratio of self-crosslinking emulsion to fluoroaluminate to (0.3-2):100, the welding yield was further improved, the powder shedding rate of the coated sheet was reduced, and the amount of welding fumes was reduced.

[0118] Comparing Example 1 with Examples 9-11, it can be seen that by controlling the mass ratio of self-crosslinking acrylic emulsion to self-crosslinking polyurethane emulsion to (3-6):1, the welding yield was further improved, the powder shedding rate of the coated sheet was reduced, and the amount of welding smoke was reduced.

[0119] Comparing Example 1 with Examples 12 and 13, it can be seen that by controlling the glass transition temperature of the crosslinked acrylic emulsion to ≤30℃ and the minimum film-forming temperature of the self-crosslinked polyurethane emulsion to ≤0℃, the welding yield was further improved, the powder shedding rate of the coated sheet was reduced, and the amount of welding smoke was reduced.

[0120] Comparing Examples 1 and 18-21, it can be seen that by controlling b2 / b1 = 2-5, the welding yield was further improved, the coating powder shedding rate was reduced, and the amount of welding fumes was reduced.

[0121] Comparing Examples 1 and Examples 22-25, it can be seen that by controlling a2 / a1 = 2.17-10, the welding yield was further improved, the coating powder shedding rate was reduced, and the amount of welding fumes was reduced.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A coated preformed solder, characterized in that, Includes a solder and a flux surrounding the solder, wherein the solder comprises an aluminum-silicon alloy and the flux comprises a fluoroaluminate; The mass ratio of the aluminum-silicon alloy to the fluoroaluminate is (75~96):(4~25); It also includes a self-crosslinking emulsion, wherein the mass ratio of the self-crosslinking emulsion to fluoroaluminate is (0.3~2):100, and the self-crosslinking emulsion includes a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion; the mass ratio of the self-crosslinking acrylic emulsion to the self-crosslinking polyurethane emulsion is (1.5~6):1; the glass transition temperature of the crosslinking acrylic emulsion is ≤30℃; and the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is ≤0℃.

2. The coated preformed solder according to claim 1, characterized in that, The silicon content in the aluminum-silicon alloy is 11-13% by mass.

3. The method for preparing the coated preformed solder according to any one of claims 1 to 2, characterized in that, Includes the following steps: The flux, self-crosslinking emulsion, and solvent are mixed evenly to obtain a mixture. The mixture is uniformly coated onto the surface of the solder, and then dried to remove the solvent, resulting in a coated preformed solder.

4. The method for preparing the coated preformed solder according to claim 3, characterized in that, The solvent includes at least one of water, ethanol, n-propanol, propylene glycol, propylene glycol butyl ether, ethylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether.

5. The method for preparing the coated preformed solder according to claim 3, characterized in that, The mass ratio of the solvent to the flux is (0.8~2):

1.

6. The application of the coated preformed solder according to any one of claims 1 to 2 in sealing the electrolyte injection port of the battery cell.

7. The application according to claim 6, characterized in that, The coated preformed brazing filler metal is placed above the weld formed by the sealing nail and the top cover of the battery cell. During the high-frequency induction welding process, after the brazing filler metal melts, the molten liquid flows downward to fill the weld.

8. The application according to claim 7, characterized in that, Satisfy at least one of the following (1) to (3): (1) The volume of the weld is a1 and the volume of the coated preformed brazing filler metal is a2, satisfying: 2.17≤a2 / a1≤10; (2) The cross-sectional area of ​​the weld is b1, and the cross-sectional area of ​​the coated preformed brazing filler metal is b2, satisfying: 2≤b2 / b1≤5; (3) The height of the coated preformed brazing filler metal is ≤5mm.

9. A battery cell electrolyte filling port, characterized in that, Includes the coated preformed solder as described in any one of claims 1 to 2.

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