A pre-formed coated solder, its preparation method and application

Abstract

This invention discloses a pre-formed coated solder, its preparation method, and its application, belonging to the field of brazing technology. It includes a solder and a flux surrounding the solder. The solder comprises a zinc-aluminum alloy, and the flux comprises an activator and a film-forming substance. The activator includes fluoroaluminate; the mass ratio of the zinc-aluminum alloy to the fluoroaluminate is 100:(4-12); the film-forming substance includes a self-crosslinking emulsion, and the mass ratio of the self-crosslinking emulsion to the activator is (0.3-1):100. The pre-formed coated solder of this invention can effectively fill the battery cell tab structure, improving production yield. The flux pre-coated on the outer surface is for improving production efficiency and yield. The addition of a self-crosslinking emulsion as a film-forming substance in this invention can effectively improve welding quality, prevent flux detachment, and effectively reduce the weld void rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of brazing, in particular to a preformed coating filler metal and a preparation method and application thereof. BACKGROUND

[0002] The application scenarios of square batteries are very wide. They are widely used in electric vehicles, wireless devices, industrial devices and medical devices. In new energy power vehicles, aluminum shell square lithium batteries are very common. Its structure is simple, can be adjusted arbitrarily according to the application scenario, and is suitable for various electronic devices.

[0003] The production cost of the battery cell has been reduced to a certain extent through continuous process improvement. In the increasingly fierce competition, it is necessary to continuously reduce the cost and increase the benefit, reduce various manufacturing costs. Generally, the brazing flux and solvent are mixed and applied before induction welding, and the welding is carried out in a wet state. The cost of brazing flux is high, and a large amount of VOC is generated by solvent volatilization. The present application develops a preformed coating filler metal suitable for welding of the electrode lug of the battery cell and a preparation method thereof, which can be assembled conveniently and adapt to automation, has the characteristics of no splashing and less residue, reduces the labor cost and brazing flux cost, is relatively environmentally friendly, has high production efficiency, stable and lower cavity rate.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The present application aims to overcome the deficiencies in the prior art and provide a preformed coating filler metal and a preparation method and application thereof. The preformed coating filler metal can fill the electrode lug structure of the battery cell well, improve the production yield, improve the welding quality, avoid the falling off of the brazing flux, and effectively reduce the welding cavity rate.

[0006] To achieve the above-mentioned purpose, in the first aspect of the present application, the present application provides a preformed coating filler metal, which comprises a filler metal and a brazing flux wrapped around the outer periphery of the filler metal, the filler metal comprises a zinc-aluminum alloy, and the brazing flux comprises an active agent and a film-forming substance.

[0007] The active agent comprises fluoroaluminate;

[0008] The mass ratio of the zinc-aluminum alloy to the fluoroaluminate is 100:(4-12);

[0009] The film-forming substance comprises a self-crosslinking emulsion, and the mass ratio of the self-crosslinking emulsion to the active agent is (0.3-1):100.

[0010] As an embodiment of the present application, the mass percentage content of aluminum in the zinc-aluminum alloy is 5-22%.

[0011] As an embodiment of the present application, the self-crosslinking emulsion comprises a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion; and the mass ratio of the self-crosslinking acrylic emulsion and the self-crosslinking polyurethane emulsion is (1.5-9):1.

[0012] As an embodiment of the present application, the glass transition temperature of the crosslinking acrylic emulsion is ≤30℃.

[0013] As an embodiment of the present application, the minimum film formation temperature of the self-crosslinking polyurethane emulsion is ≤0℃.

[0014] In the second aspect of the present application, the present application provides a preparation method of a preformed solder-coated filler, comprising the following steps:

[0015] (1) mixing a soldering agent, a self-crosslinking emulsion and a solvent uniformly to obtain a mixed solution;

[0016] (2) uniformly coating the mixed solution on the surface of the soldering filler and baking to obtain a preformed solder-coated filler.

[0017] As an embodiment of the present application, the solvent comprises 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, dipropylene glycol dimethyl ether; and / or

[0018] The mass ratio of the solvent and the active agent is (0.8-1.5):1.

[0019] As an embodiment of the present application, the step (2) is specifically: coating the mixed solution on the surface of the soldering filler in batches, and the coating amount of each batch is not more than 1% of the total mass of the mixed solution; and baking after each coating to obtain a preformed solder-coated filler.

[0020] The baking temperature of each batch is greater than or equal to 0.8 times the boiling point of the solvent and less than or equal to 1.2 times the boiling point of the solvent.

[0021] The baking time of each batch is 5-120s.

[0022] As an embodiment of the present application, the step (2) is specifically: coating the mixed solution on the surface of the soldering filler in batches, and the coating amount of each batch is not more than 1% of the total mass of the mixed solution; and baking during the coating process to obtain a preformed solder-coated filler.

[0023] The baking temperature of each batch is greater than or equal to 0.8 times the boiling point of the solvent and less than or equal to 1.2 times the boiling point of the solvent.

[0024] In the third aspect of the present application, the present application provides an application of the preformed solder-coated filler in the sealing of the tab structure of a battery cell.

[0025] As an embodiment of the present application, the preformed coated filler metal is placed in the middle of the weld formed by the pole and the cell, and during the high-frequency induction welding process, the filler metal melts and the molten liquid flows to fill the weld.

[0026] In a fourth aspect of the present application, the present application provides a battery cell tab, comprising the preformed coated filler metal described above.

[0027] The present application has the following beneficial effects: (1) the preformed coated filler metal described in the present application can fill the battery cell tab structure well and improve the production yield, and the flux wrapped on the outer surface is to improve the production efficiency and yield, the addition of self-crosslinking emulsion as a film-forming material in the present application can effectively improve the welding quality, avoid the falling of the flux, and effectively reduce the welding cavity rate.

[0028] (2) The self-crosslinking emulsion of the self-crosslinking acrylic emulsion and the self-crosslinking polyurethane emulsion added creatively in the present application can effectively improve the film-forming performance, effectively reduce the decomposition and spatter of organic matter during welding, so that the welding parts, welding equipment and fixtures do not need to be cleaned after welding, and the decomposition and smoke amount of organic matter during welding can be reduced, the safety and environmental protection are improved; the self-crosslinking acrylic is easy to connect with the hydroxyl group in the flux during film-forming, forming a coating wrapped on the metal surface, and 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, and effectively reduce the welding cavity rate. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] In the present application, the technical features described in an open manner include both the closed technical scheme consisting of the listed features and the open technical scheme containing the listed features.

[0031] In the present application, if no special description is made, the numerical range is regarded as continuous and includes the minimum value and the maximum value of the range and every value between the minimum value and the maximum value. Further, when the range refers to an integer, every integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0032] In the present application, the specific dispersion, stirring treatment method is not particularly limited.

[0033] The components raw materials or instruments used in the embodiments and comparative examples of the present application are commercially available raw materials or instruments unless otherwise specified, and the component raw materials used in each parallel experiment are the same.

[0034] The inventors of the present application found that the existing induction welding technology generally uses flux and solvent mixture for smearing before induction welding, and the welding is carried out in a wet state, and the volatilization of the solvent and the unstable smearing amount will cause low production efficiency and unstable cavity rate.

[0035] Therefore, in order to solve the above technical problems, the present application provides a preformed coated filler metal, which comprises a filler metal and a flux wrapped around the outer periphery of the filler metal, the filler metal comprises a zinc-aluminum alloy, and the flux comprises an active agent and a film-forming substance.

[0036] The active agent comprises fluoroaluminate;

[0037] The mass ratio of the zinc-aluminum alloy and the fluoroaluminate is 100:(4-12), for example, it can be 100:4, 100:5, 100:6, 100:8, 100:10, 100:12 or a range consisting of any two thereof;

[0038] The film-forming substance comprises a self-crosslinking emulsion, and the mass ratio of the self-crosslinking emulsion to the active agent is (0.3-1):100, for example, it can be 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.8:100, 1:100 or a range consisting of any two thereof, by controlling the mass ratio of the self-crosslinking emulsion to the fluoroaluminate in this range, the coating firmness and welding performance can be improved, the phenomenon of powder falling during coating can be avoided, and the welding smoke amount can be effectively reduced.

[0039] The preformed coated filler metal of the present application can well fill the battery cell tab structure and improve the production yield, and the flux wrapped on the outer surface is for the improvement of production efficiency and yield, the addition of the self-crosslinking emulsion as the film-forming substance can effectively improve the welding quality, avoid the falling of the flux, and effectively reduce the welding cavity rate.

[0040] By wrapping the flux containing active agent in the outer periphery of the filler metal, the active agent mainly removes the oxide film on the surface of the filler metal and the oxide film at the welding interface. Too low content of the flux will limit the removal ability, which will affect the welding quality, and then affect the product yield. Too high flux will not improve the welding quality, but will lead to cost increase. At present, the cost of cesium fluoroaluminate flux is high (about 1.8 yuan / g), which is particularly important in the cost-sensitive new energy automobile industry chain.

[0041] In one embodiment, the zinc-aluminum alloy contains 5-22% of aluminum by mass, for example, 5%, 8%, 10%, 12%, 15%, 16%, 18%, 20%, 22%, or a range defined by any two of them.

[0042] In one embodiment, the self-crosslinking emulsion includes self-crosslinking acrylic emulsion and self-crosslinking polyurethane emulsion; the mass ratio of the self-crosslinking acrylic emulsion and the self-crosslinking polyurethane emulsion is (1.5-9):1, for example, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or a range defined by any two of them. The application creatively adds self-crosslinking emulsion containing self-crosslinking acrylic emulsion and self-crosslinking polyurethane emulsion, which can effectively improve the film forming performance, effectively reduce the decomposition and spatter of organic matter during welding, so that the welding parts, welding equipment, fixtures and the like do not need to be cleaned after welding, while the decomposition and smoke amount of organic matter during welding is reduced, the safety and environmental protection are improved; the self-crosslinking acrylic is easily connected with the hydroxyl group in the flux during film forming, forming a coating to cover the metal surface, and the self-crosslinking polyurethane emulsion and the self-crosslinking acrylic emulsion jointly act to improve the adhesion of the flux to the metal and the welding performance, and effectively reduce the welding cavity rate.

[0043] In one embodiment, the glass transition temperature of the crosslinking acrylic emulsion is ≤30℃.

[0044] In one embodiment, the glass transition temperature of the crosslinking acrylic emulsion is -40-30℃, for example, -40℃, -35℃, -30℃, -25℃, -20℃, -15℃, -10℃, -5℃, 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, or a range defined by any two of them.

[0045] The glass transition temperature of the self-crosslinking acrylic emulsion is measured according to the GB / T 27816 standard.

[0046] In one embodiment, the minimum film forming temperature of the self-crosslinking polyurethane emulsion is ≤0℃.

[0047] 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.

[0048] In one embodiment, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is tested with reference to the GB / T9267-2008 standard.

[0049] 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.

[0050] One embodiment of this application provides a method for preparing a pre-formed coated solder, comprising the following steps:

[0051] (1) Mix the flux, self-crosslinking emulsion and solvent evenly to obtain a mixture;

[0052] (2) The mixture is evenly coated onto the surface of the brazing filler metal and baked to obtain a pre-formed coated brazing filler metal.

[0053] In one embodiment, the solvent includes at least one selected from 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; and / or

[0054] The mass ratio of the solvent to the surfactant is (0.8 to 1.5):1, for example, it can be 0.8:1, 1:1, 1.2:1, 1.5:1 or any two of these values.

[0055] In one embodiment, step (2) specifically involves coating the solder surface with the mixture in multiple applications, with each application amount not exceeding 1% of the total mass of the mixture. After each application, the solder is baked to obtain a pre-formed coated solder.

[0056] Each baking temperature is greater than or equal to 0.8 times the solvent boiling point and less than or equal to 1.2 times the solvent boiling point;

[0057] Each baking time is 5 to 120 seconds.

[0058] In one embodiment, step (2) specifically involves coating the solder surface with the mixture in multiple applications, with each application amount not exceeding 1% of the total mass of the mixture. The solder is kept baked during the coating process to obtain a pre-formed coated solder.

[0059] Each baking temperature is greater than or equal to 0.8 times the solvent boiling point and less than or equal to 1.2 times the solvent boiling point.

[0060] The inventors of this invention have discovered that baking after coating is detrimental to the formation of a film-forming substance on the surface of the solder, making it easy for the flux to fall off. This makes it difficult to effectively remove the oxide film on the surface of the solder and the oxide film at the welding interface during the welding process, resulting in an increased welding void rate, a higher rate of defective tab welding, and low production efficiency. By adopting the specific coating and baking process of this invention, welding quality can be effectively improved, flux can be prevented from falling off, and the welding void rate can be effectively reduced.

[0061] The drying process evaluation method is as follows: After the drying process is completed, five pre-formed coated solder pieces are randomly selected and placed in a pre-weighed flat weighing bottle. The weighing bottle is recorded as m0, and the total weight of the pre-formed coated solder and the weighing bottle before drying is recorded as m1. The pre-formed coated solder pieces are not stacked. They are dried at 100℃~105℃ for 10 minutes, then removed and cooled at room temperature in a desiccator for 5 minutes. The total weight before drying is recorded as m2, and the weight loss rate is (m2-m0) / (m1-m0). The same batch of five pre-formed coated solder pieces is measured three times. The absolute difference in weight loss rate obtained under repeatability conditions should not exceed 1% to be considered as a feasible drying process.

[0062] One embodiment of this application provides the application of the pre-formed coated solder in the sealing of battery cell tab structure.

[0063] In one embodiment, the pre-formed coated brazing filler metal is placed in the middle of the weld seam formed by the electrode post and the battery cell. During the high-frequency induction welding process, after the brazing filler metal melts, the molten liquid flows and fills the weld seam.

[0064] One embodiment of this application provides a battery cell tab, including the pre-formed coated solder described above.

[0065] The sources of raw materials used in the examples and comparative examples are shown in Table 1.

[0066] Table 1

[0067]

[0068]

[0069] The following embodiments are provided to facilitate understanding of the invention. These embodiments are not intended to limit the scope of the claims.

[0070] Example 1

[0071] A method for sealing battery cell tabs with pre-formed solder coating includes the following steps:

[0072] (1) Prepare a solvent with an azeotropic point of 80°C by mixing ethanol and water;

[0073] Preparation of pre-formed coated solder: Cesium fluoroaluminate (CsAlF4), self-crosslinking emulsion and solvent are mixed evenly to obtain a mixture;

[0074] The mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is 0.5:100; the self-crosslinking emulsion includes self-crosslinking acrylic emulsion 1 and self-crosslinking polyurethane emulsion 1 in a mass ratio of 9:1.

[0075] The mass ratio of the solvent to cesium fluoroaluminate is 1.5:1;

[0076] The mass ratio of cesium fluoroaluminate to ZnAl10 is 8:100.

[0077] The mixture was applied evenly to the surface of the brazing filler metal (ZnAL10) in multiple applications, with each application amount being 0.5% of the total mass of the brazing filler metal. After each application, the filler metal was baked in an oven at 80°C for 30 seconds to obtain a pre-formed coated brazing filler metal.

[0078] (2) Place the pre-formed coated brazing filler metal (0.4 mm in height) in the middle of the weld formed by the electrode and the cell. During the high-frequency induction welding process, after the brazing filler metal melts, the molten liquid flows and fills the weld. The high-frequency induction welding parameters are automatic control of induction current heating, current 75A, duration 3S.

[0079] Examples 2-5

[0080] The difference between Examples 2-5 and Example 1 is that the baking temperature is changed.

[0081] Examples 6-7

[0082] The difference between Examples 6 and 7 and Example 1 is that the type of solvent and the baking temperature are changed.

[0083] Examples 8-9, Comparative Examples 1-2

[0084] Examples 8-9 and Comparative Examples 1-2 differ from Example 1 in that the mass ratio or types of cesium fluoroaluminate and ZnAl10 are changed.

[0085] Examples 10-11

[0086] The difference between Examples 10 and 11 and Example 1 is that the mass ratio of solvent to CsAlF4 is changed.

[0087] Examples 12-13, Comparative Examples 3-4

[0088] Examples 12-13 and Comparative Examples 3-4 differ from Example 1 in that the mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is changed.

[0089] Examples 14-19

[0090] Examples 14-19 differ from Example 1 in that the mass ratio or type of the self-crosslinking emulsion is changed.

[0091] Example 20

[0092] The difference between Example 20 and Example 1 is that the baking steps are different.

[0093] A method for sealing battery cell tabs with pre-formed solder coating includes the following steps:

[0094] (1) Prepare a solvent with an azeotropic point of 80°C by mixing ethanol and water;

[0095] Preparation of pre-formed coated solder: Cesium fluoroaluminate (CsAlF4), self-crosslinking emulsion and solvent are mixed evenly to obtain a mixture;

[0096] The mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is 0.5:100; the self-crosslinking emulsion includes self-crosslinking acrylic emulsion 1 and self-crosslinking polyurethane emulsion 1 in a mass ratio of 9:1.

[0097] The mass ratio of the solvent to cesium fluoroaluminate is 1.5:1;

[0098] The mass ratio of cesium fluoroaluminate to ZnAl10 is 8:100.

[0099] The mixture was applied evenly to the surface of the solder (ZnAL10) in multiple applications, with each application amount being 0.02% of the total mass of the solder. The coating process was carried out by baking and drying at 80°C for 2700 seconds to obtain a pre-formed coated solder.

[0100] (2) The pre-formed brazing filler metal (0.4 mm in height) is placed in the middle of the weld formed by the electrode and the cell. During the high-frequency induction welding process, the brazing filler metal melts and the molten liquid flows to fill the weld.

[0101] Table 2

[0102]

[0103]

[0104] Performance testing

[0105] Void rate testing method: In the example, the pre-formed coated brazing filler metal is placed in the middle of the weld seam formed by the electrode and the cell. After high-frequency induction welding, the welded part is obtained. The void rate of the weld surface is calculated by non-destructive ultrasonic scanning using a SONOSCAN-D9600 ultrasonic scanner. The ultrasonic probe parameters are: SK075 / 050 75MHz probe.

[0106] Mean void ratio: The void ratio of multiple samples in each embodiment was statistically analyzed by acoustic scanning, and the arithmetic square was calculated. The result is the mean void ratio of each embodiment.

[0107] Variance of void ratio: The void ratio of multiple samples in each embodiment is statistically analyzed by acoustic scanning. The average of the sum of squares of the differences between the sample void ratio and the mean void ratio is calculated. The result is the variance of void ratio for each embodiment.

[0108] Table 3

[0109]

[0110]

[0111] As can be seen from Table 3, the pre-formed coated brazing filler metal described in this invention can effectively improve welding quality, prevent flux from falling off, effectively reduce welding voids, and can well fill the battery cell tab structure, thus having broad application prospects.

[0112] Comparing Examples 1-7, it can be seen that when the baking temperature is less than 0.8 times the solvent boiling point or more than 1.2 times the solvent boiling point, both the mean and variance of the solder void rate increase. Lower baking temperatures leave solvent residue in the solder, which vaporizes during induction soldering, forming cavities that hinder the contact and reaction between the flux and the solder / solder interface, ultimately leading to an increased void rate. Higher baking temperatures result in incomplete self-crosslinking of the self-crosslinking film-forming substances in the flux, preventing proper coating of the flux onto the solder surface and causing sheet-like peeling, ultimately increasing both the solder void rate and variance. This conclusion applies to different solvent systems used in the examples.

[0113] Comparing Examples 1 and 8-9 with Comparative Examples 1 and 2, it can be seen that excessively low flux content results in limited flux removal capability, thus affecting the flux's ability to remove oxide films from the solder surface and the welding interface. Excessive flux content does not improve welding quality; instead, it leads to excessive flux residue after welding, reducing welding reliability and increasing costs.

[0114] Comparing Examples 1, 12-13, and Comparative Examples 3-4, it can be seen that when the mass ratio of the self-crosslinking emulsion of the film-forming substance to the activator is greater than 1:100, the average void ratio after soldering under this coating process is similar to that of the comparative examples. The film-forming substance does not have the ability to remove the oxide film, and a large amount of film-forming substance hinders the contact between the flux and the solder, reducing soldering reliability.

[0115] Comparing Examples 1 and 14-17, it can be seen that by controlling the mass ratio of self-crosslinking acrylic emulsion to self-crosslinking polyurethane emulsion to (1.5-9):1, the welding quality is further improved, flux detachment is avoided, and the welding void rate is further reduced.

[0116] 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 preform coated solder, characterized by, The brazing filler metal comprises a zinc-aluminum alloy, and the flux comprises an active agent and a film-forming material. The active agent comprises a fluoroaluminate. The mass ratio of the zinc-aluminum alloy to the fluoroaluminate is 100: (4-12). The film-forming material comprises a self-crosslinking emulsion, and the mass ratio of the self-crosslinking emulsion to the active agent is (0.3-1):

100. The self-crosslinking emulsion comprises a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion, and the mass ratio of the self-crosslinking acrylic emulsion to the self-crosslinking polyurethane emulsion is (1.5-9):

1. The glass transition temperature of the crosslinking acrylic emulsion is less than or equal to 30°C, and the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is less than or equal to 0°C.

2. The preform coated solder of claim 1 wherein, The mass percentage of aluminum in the zinc-aluminum alloy is 5-22%.

3. The method of producing a preform coated solder according to any one of claims 1 to 2, characterized in that, The method comprises the following steps: (1) uniformly mixing the flux, the self-crosslinking emulsion and a solvent to obtain a mixed solution; (2) uniformly coating the mixed solution on the surface of the brazing filler metal, and baking to obtain a preformed coated brazing filler metal.

4. The method of claim 3, wherein the preform coated solder is prepared by the steps of: The solvent comprises 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, and / or the mass ratio of the solvent to the active agent is (0.8-1.5):

1.

5. The method of claim 3, wherein the preform coated solder is prepared by the steps of: In step (2), the mixed solution is coated on the surface of the brazing filler metal in multiple times, and the coating amount of each time is less than or equal to 1% of the total mass of the mixed solution, and baking is performed after each coating to obtain the preformed coated brazing filler metal. The baking temperature of each time is greater than or equal to 0.8 times the boiling point of the solvent and less than or equal to 1.2 times the boiling point of the solvent. The baking time of each time is 5-120 seconds.

6. The method of claim 3, wherein the preform coated solder is prepared by the steps of: In step (2), the mixed solution is coated on the surface of the brazing filler metal in multiple times, and the coating amount of each time is less than or equal to 1% of the total mass of the mixed solution, and baking is performed during the coating to obtain the preformed coated brazing filler metal. The baking temperature of each time is greater than or equal to 0.8 times the boiling point of the solvent and less than or equal to 1.2 times the boiling point of the solvent.

7. Application of the preformed coated brazing filler metal according to any one of claims 1-2 in sealing of a battery cell tab structure.

8. Use according to claim 7, characterized in that, The preformed coated brazing filler metal is placed in the middle of a weld formed by a pole and a battery cell, and in a high-frequency induction welding process, the brazing filler metal is melted to flow and fill the weld.

9. A battery cell tab, characterized by, The method comprises the preformed coated brazing filler metal according to any one of claims 1-2.

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