Negative electrode column and preparation method thereof, and secondary battery

Abstract

The present invention provides a negative electrode column and a preparation method thereof, and a secondary battery, belonging to the field of battery technology. The preparation method of the negative electrode column of the present invention comprises the following steps: coating a solder flux on the surface of a soldering sheet to obtain a preformed soldering sheet, assembling the preformed soldering sheet between a copper plate and an aluminum column, and performing high-frequency induction brazing on the copper plate and the aluminum column to form a negative electrode column. The present invention improves the yield rate and solder joint strength of the negative electrode column by controlling the composition and coating amount of the solder flux.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a negative electrode column and a preparation method thereof, and a secondary battery. Background Art

[0002] As the global demand for clean energy continues to increase, the market demand for electric vehicles (EVs) as an environmentally friendly means of transportation continues to grow. As the core component of electric vehicles, the performance of power batteries directly affects the range and safety of electric vehicles. The connection of the negative pole of the power battery cell is one of the key steps in the battery assembly process, which directly affects the electrical connection and mechanical strength of the battery. In the field of welding technology, induction brazing is an efficient and energy-saving welding method, especially suitable for the welding of non-ferrous metals such as aluminum and copper. Induction brazing uses the principle of electromagnetic induction to heat the workpiece, and by controlling the current and frequency, the surface of the workpiece is quickly heated to the brazing temperature, thereby achieving welding. The existing power battery cell negative pole connection usually adopts mechanical crimping or laser welding. Mechanical crimping is to press the negative pole onto the cell by external force. Although this method is simple, it is easy to loosen, affecting the electrical connection and mechanical strength of the battery. Laser welding uses a high-energy laser beam to melt the copper and aluminum negative poles together. This method has high welding strength, but the equipment cost is high, the energy consumption is high, and the operator's skills are high. In addition, aluminum and copper are highly reflective materials and have low laser absorption efficiency. Therefore, laser welding has problems such as loose welding, electrode damage, and spark splashing. The existing power battery cell negative pole connection technology has the following problems: First, the mechanical crimping connection strength is insufficient and easy to loosen, affecting the performance and safety of the battery. Second, the equipment cost of laser welding is high, the energy consumption is high, and the operation is complex, which is not suitable for large-scale production.

[0003] Patent CN110120490A discloses a method for processing negative poles of lithium-ion batteries. The invention uses furnace brazing to weld aluminum-copper composite negative poles. Compared with laser brazing, furnace brazing can reduce costs to a certain extent, but the heating time is long, the process cycle is long, the efficiency is low, and it is not suitable for large-scale production. Patent CN118352746A discloses a method and equipment for making negative poles. The yield rate and solder joint strength of the negative poles prepared by this method are low.

[0004] Therefore, there is an urgent need for a novel, efficient, economical method for preparing a negative electrode column with good yield and solder joint strength. Summary of the invention

[0005] The purpose of the present disclosure is to overcome the deficiencies of the prior art. The present invention provides a negative electrode column and a preparation method thereof, and a secondary battery.

[0006] To achieve the above objectives, the technical solution adopted by the present disclosure is as follows: In a first aspect, a method for preparing a negative electrode column is provided, comprising the following steps:

[0007] Coat the soldering flux on the surface of the solder sheet to obtain a preformed solder sheet.

[0008] Assemble the solder preform between the copper plate and the aluminum column.

[0009] Performing high-frequency induction brazing on the copper plate and the aluminum column to form a negative electrode column;

[0010] Wherein, the coating amount of the soldering flux is 5-35wt%, and the soldering flux includes an activator, a self-crosslinking emulsion and a solvent;

[0011] The mass ratio of the self-crosslinking emulsion to the active agent is 0.5-1.2:100;

[0012] The mass ratio of the solvent to the active agent is 0.5-2.5:1;

[0013] The self-crosslinking emulsion includes a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion.

[0014] In a second aspect, a negative electrode column is provided, wherein the negative electrode column is prepared by the negative electrode column preparation method.

[0015] According to a third aspect, a secondary battery is provided, wherein the secondary battery includes the negative electrode column.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention improves the yield rate and solder joint strength of the negative electrode column by controlling the composition and coating amount of the flux; wherein, the copper plate and aluminum column with a specific roughness make the surface of the copper plate and the aluminum column have an uneven microstructure, so that the self-crosslinking emulsion forms a network structure on the surface of the copper plate and the aluminum column, thereby improving the brazing performance of the flux on the copper plate and the aluminum column, and at the same time can increase the welding area of ​​the copper plate and the aluminum column, effectively increasing the yield rate and solder joint strength of the negative electrode column; the self-crosslinking acrylic acid is easily connected with the hydroxyl group in the active agent during the film forming process to form a coating coated on the metal surface, and the self-crosslinking polyurethane emulsion and the self-crosslinking acrylic emulsion work together to improve the adhesion and welding performance of the flux to the copper plate and the aluminum column, thereby improving the yield rate and solder joint strength of the negative electrode column. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the interface of the welded surface of the negative electrode column of the present invention;

[0018] Figure 2 The present invention is a flow chart of the preparation process of the negative electrode column. DETAILED DESCRIPTION

[0019] In order to facilitate understanding of the present disclosure, the present disclosure will be described more fully below. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present disclosure more thorough and comprehensive.

[0020] As used herein:

[0021] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0022] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0023] When amount, concentration or other value or parameter is represented by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1-5", described range should be interpreted as including range "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0024] In these examples, parts and percentages are by mass unless otherwise indicated.

[0025] "Parts by mass" refers to the basic unit of measurement for expressing the mass ratio of multiple components. 1 part can represent any unit mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass of all components is not limited to 100 parts.

[0026] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0027] like Figure 1-2 As shown, the present invention provides a method for preparing a negative electrode column, comprising the following steps:

[0028] Coat the soldering flux on the surface of the solder sheet to obtain a preformed solder sheet.

[0029] Assemble the solder preform between the copper plate and the aluminum column.

[0030] Performing high-frequency induction brazing on the copper plate and the aluminum column to form a negative electrode column;

[0031] Wherein, the coating amount of the soldering flux is 5-35wt%, and the soldering flux includes an activator, a self-crosslinking emulsion and a solvent;

[0032] The mass ratio of the self-crosslinking emulsion to the active agent is 0.5-1.2:100;

[0033] The mass ratio of the solvent to the active agent is 0.5-2.5:1;

[0034] The self-crosslinking emulsion includes a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion.

[0035] The present invention improves the yield rate and solder joint strength of the negative electrode column by controlling the composition and coating amount of the flux; wherein, the copper plate and aluminum column of a specific roughness make the surface of the copper plate and aluminum column have an uneven microstructure, so that the self-crosslinking emulsion forms a network structure on the surface of the copper plate and aluminum column, improves the brazing performance of the flux to the copper plate and aluminum column, and can increase the welding area of ​​the copper plate and aluminum column, effectively increasing the yield rate and solder joint strength of the negative electrode column; the self-crosslinking acrylic acid is easily connected to the hydroxyl group in the active agent during the film forming process to form a coating coated on the metal surface, and the self-crosslinking polyurethane emulsion and the self-crosslinking acrylic emulsion work together to improve the adhesion and welding performance of the flux to the copper plate and aluminum column, thereby improving the yield rate and solder joint strength of the negative electrode column. If the coating amount of the flux is too low or too high, the yield rate and solder joint strength of the negative electrode column will decrease.

[0036] For example, in different embodiments, the mass ratio of the self-crosslinking emulsion to the active agent can be 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1.0:100, 1.1:100, or 1.2:100.

[0037] For example, in different embodiments, the mass ratio of the solvent to the active agent can be but is not limited to 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1.

[0038] As in different embodiments, the coating amount of the flux can be but is not limited to 5wt%, 6wt%, 8wt%, 12wt%, 16wt%, 20wt%, 24wt%, 28wt%, 32wt%, 35wt%, preferably 8-25wt%.

[0039] In the present invention, the coating amount of the soldering flux refers to the mass percentage of the soldering flux in the preform solder sheet.

[0040] In the present invention, when the coating amount of the soldering flux is 8-25wt%, the yield rate and solder joint strength of the negative electrode column can be further improved.

[0041] In some embodiments, the roughness of the copper plate and the aluminum column is independently 0.2-7, for example, it can be but not limited to 0.2, 0.4, 0.7, 1.0, 1.3, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, preferably 0.4-6.4.

[0042] In the present invention, when the roughness of the copper plate and the aluminum column is independently 0.2-7, the yield rate and solder joint strength of the negative electrode column can be further improved.

[0043] The present invention can obtain copper plates or aluminum columns with different roughness by machining methods known in the art, such as sandpaper grinding, grinding, mechanical polishing, etc.

[0044] In some embodiments, the welding sheet is a ZnAl alloy, wherein the Al content in the ZnAl alloy is 5-22% and the balance is Zn.

[0045] For example, in different embodiments, the Al content in the ZnAl alloy may be, but is not limited to, 5%, 7%, 10%, 12%, 15%, 17%, 20%, or 22%.

[0046] When the Al content in the ZnAl alloy of the present invention is 5-22%, the yield rate and welding point strength of the negative electrode column can be further improved.

[0047] In the present invention, the thickness of the welding sheet is the thickness commonly used in induction brazing in the field. Those skilled in the art can machine the welding sheet to obtain welding sheets of different thicknesses according to actual conditions, and select different thicknesses for brazing according to actual conditions, such as 0.1-0.3 mm.

[0048] In some embodiments, Figure 1 As shown, the copper plate has a groove, the aluminum column has a convex bulge, and the groove and the convex bulge are butt-jointed.

[0049] Specifically, the method for preparing the copper plate with the groove is as follows: punching and oiling the copper plate to obtain the copper plate with the groove;

[0050] Specifically, the method for preparing the aluminum column with the convex hull is: stamping and oiling the aluminum column to obtain the aluminum column with the convex hull.

[0051] In the present invention, the shape of the welding piece is adapted to the shape of the groove of the copper plate.

[0052] In some embodiments, the glass transition temperature of the self-crosslinking acrylic emulsion is ≤30°C, for example, it can be but not limited to -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.

[0053] Specifically, the glass transition temperature of the self-crosslinking acrylic emulsion is measured with reference to GB / T 27816 standard.

[0054] In some embodiments, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is ≤0°C, for example, it can be but not limited to -45°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C.

[0055] When the glass transition temperature of the self-crosslinking acrylic emulsion is greater than 30°C or the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is greater than 0°C, the soldering void rate will increase.

[0056] Specifically, the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is tested with reference to GB / T 9267-2008 standard.

[0057] In some embodiments, the mass ratio of the self-crosslinking acrylic emulsion and the self-crosslinking polyurethane emulsion is (1.5-9):1, for example, it can be but not limited to 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1.

[0058] In some embodiments, the active agent is a fluoroaluminate; fluoroaluminates include potassium fluoroaluminate such as KAlF4, K2AlF5, K3AlF6, K2AlF5·H2O, cesium fluoroaluminate such as CsAlF4, Cs2AlF5, Cs3AlF6, cesium potassium fluoroaluminate such as KCs2Al3F 12, CsK2AlF6, and alkali zinc fluoroaluminates such as KZnAlF6, K2ZnAlF7, KZn2AlF8, KZnAl2F9, CsZnAlF6, Cs2ZnAlF7, CsZn2AlF8 and CsZnAl2F9. Each of the foregoing may be amorphous and / or partially or completely in the form of one or more XRD distinguishable phases. Conventional activators and their manufacture are known: for example, potassium fluoroaluminate can be manufactured from HAlF4 (obtained from HF and Al(OH)3 or Al2O3) and KOH. This is described, for example, in US4,428,920, US4,579,605 and US5,968,288. US 3,951,328, US6,221,129 or US3,971,501 describe fluxes based on KAlF4 and K3AlF6. US 4,689,092 describes a flux based on potassium fluoroaluminate and cesium fluoroaluminate. CN 104822488A describes a flux based on the general formula K w Zn x Al y F z An alkali metal zinc fluoroaluminate flux represented by: wherein w, x, y and z are positive integers, and the greatest common divisor of w, x, y and z is 1.

[0059] In one embodiment, the average particle size of the active agent is preferably 80 μm or less. For example, the average particle size of the active agent can be but is not limited to 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 37 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, 52 μm, 55 μm, 57 μm, 60 μm, 63 μm, 65 μm, 68 μm, 70 μm, 72 μm, 75 μm, 78 μm, preferably 1 to 50 μm, particularly preferably 1-20 μm. When the average particle size of the activator is within the above range, the activator shows high reactivity with the aluminum alloy and improves the inhibitory effect of the chemical reaction with oxygen; the soldering wettability of the flux is improved, thereby improving the soldering bonding strength.

[0060] Specifically, the average particle size of the active agent is obtained by testing according to GB / T 19077-2016 standard.

[0061] In some embodiments, the solvent is at least one of water, alcohol, and ether.

[0062] As mentioned herein, "alcohol" refers to a compound in which a hydrogen atom in a side chain of an aliphatic alkane, alicyclic alkane or aromatic alkane is replaced by a hydroxyl group, and the general structure is that a hydroxyl group is connected to a saturated sp3 hybridized carbon atom.

[0063] Specifically, the present disclosure prefers fatty alcohols, which may be, but are not limited to, fatty monohydric alcohols and fatty dihydric alcohols.

[0064] In one embodiment, the alcohol is a fatty monohydric alcohol, the number of carbon atoms in the fatty monohydric alcohol is ≤12, and specific examples of fatty monohydric alcohols may include methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; n-propanol is preferred as the fatty monohydric alcohol in the present disclosure.

[0065] In one embodiment, the alcohol is a fatty diol, and the number of carbon atoms in the fatty diol is ≤6. Specific examples of fatty diols include ethylene glycol, propylene glycol, trimethyl glycol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. In the present disclosure, propylene glycol is preferred as the fatty diol.

[0066] In one embodiment, the ether is at least one of 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.

[0067] Specifically, the present disclosure prefers water as the solvent. Compared with alcohol and / or ether, water has better solubility and dispersibility for active agents and self-crosslinking emulsions. In addition, water is an inorganic substance, non-toxic, environmentally friendly and safe, and has lower cost.

[0068] In some embodiments, the induced current of the high-frequency induction brazing is 20-120A; for example, it can be but not limited to 20A, 40A, 60A, 80A, 100A, 120A.

[0069] In some embodiments, the frequency of the high-frequency induction brazing is 10-200 kHz; for example, it can be but not limited to 10 kHz, 30 kHz, 50 kHz, 80 kHz, 100 kHz, 120 kHz, 150 kHz, 170 kHz, 200 kHz.

[0070] In some embodiments, the number of turns of the induction coil of the high-frequency induction brazing is 1-5 turns, for example, but not limited to 1 turn, 2 turns, 3 turns, 4 turns, 5 turns;

[0071] In some embodiments, the distance between the welding surface of the copper plate and the aluminum column and the bottom of the induction coil is 0-8 mm, for example, but not limited to 0 mm, 2 mm, 4 mm, 6 mm, and 8 mm.

[0072] In a second aspect, a negative electrode column is provided, wherein the negative electrode column is prepared by the negative electrode column preparation method.

[0073] In a third aspect, a secondary battery is provided, wherein the secondary battery comprises the negative electrode column.

[0074] The raw materials used in the embodiments and comparative examples are described below, but are not limited to these materials:

[0075] Self-crosslinking acrylic emulsion A: glass transition temperature is 0°C, LA-6162A, Zhaoqing Xinguangli Chemical Industry Co., Ltd.;

[0076] Self-crosslinking acrylic emulsion B: glass transition temperature 28°C, XK-919, Covestro;

[0077] Self-crosslinking acrylic emulsion C: glass transition temperature 42°C, XK-252, Covestro;

[0078] Self-crosslinking polyurethane emulsion A: minimum film-forming temperature is -5°C, F0415, Shenzhen Jitian Chemical Co., Ltd.;

[0079] Self-crosslinking polyurethane emulsion B: minimum film-forming temperature is 5°C, 55, Guangzhou Ruilin New Materials Co., Ltd.;

[0080] Welding piece A: ZnAl alloy, Al content is 10%, the balance is Zn;

[0081] Welding piece B: ZnAl alloy, Al content is 22%, the balance is Zn;

[0082] Solder C: ZnAl alloy, Al content is 5%, the balance is Zn;

[0083] Welding piece D: ZnAl alloy, Al content is 3%, the balance is Zn;

[0084] Solder E: ZnAl alloy, Al content is 25%, and the balance is Zn.

[0085] Example 1

[0086] This embodiment provides a method for preparing a negative electrode column, comprising the following steps:

[0087] Punching the first copper plate to obtain a second copper plate having a groove;

[0088] Punching the first aluminum column to obtain a second aluminum column having a convex hull;

[0089] The groove surface of the second copper plate and the convex surface of the second aluminum column are machined respectively to obtain a third copper plate with a roughness of 3.2 and a third aluminum column with a roughness of 3.2;

[0090] According to the groove structure of the second copper plate, a welding piece A with a thickness of 0.2 mm is processed to obtain a second welding piece, and the shape of the second welding piece is adapted to the shape of the groove of the second copper plate;

[0091] Coating flux on the surface of the second solder sheet to obtain a preformed solder sheet, wherein the coating amount of the flux is 8.9 wt %;

[0092] Assemble the preformed welding sheet between the third copper plate and the third aluminum column to obtain the welded part.

[0093] The workpiece to be welded is placed in the middle of the induction coil of the high-frequency induction brazing machine, and the height of the workpiece to be welded is 3 mm from the bottom of the induction coil. Automatic induction brazing is used. Under the conditions of induction current of 75 A and induction frequency of 32.8 kHz, induction brazing is performed for 3 seconds, and the workpiece is cooled to room temperature to obtain a negative electrode column.

[0094] The flux includes cesium fluoroaluminate, a self-crosslinking emulsion and water;

[0095] The mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is 0.5:100;

[0096] The mass ratio of water to cesium fluoroaluminate is 1.3:1;

[0097] The self-crosslinking emulsion includes self-crosslinking acrylic emulsion A and self-crosslinking polyurethane emulsion A, and the mass ratio of self-crosslinking acrylic emulsion A to self-crosslinking polyurethane emulsion A is 3:1.

[0098] Example 2

[0099] This embodiment provides a method for preparing a negative electrode column, comprising the following steps:

[0100] Punching the first copper plate to obtain a second copper plate having a groove;

[0101] Punching the first aluminum column to obtain a second aluminum column having a convex hull;

[0102] The groove surface of the second copper plate and the convex surface of the second aluminum column are machined respectively to obtain a third copper plate with a roughness of 3.2 and a third aluminum column with a roughness of 3.2;

[0103] According to the groove structure of the second copper plate, a welding piece A with a thickness of 0.2 mm is processed to obtain a second welding piece, and the shape of the second welding piece is adapted to the shape of the groove of the second copper plate;

[0104] Coating flux on the surface of the second solder sheet to obtain a preformed solder sheet, wherein the coating amount of the flux is 8.9 wt %;

[0105] Assemble the preformed welding sheet between the third copper plate and the third aluminum column to obtain the welded part.

[0106] The workpiece to be welded is placed in the middle of the induction coil of the high-frequency induction brazing machine, and the height of the workpiece to be welded is 0 mm from the bottom of the induction coil. Automatic induction brazing is used. Under the conditions of induction current of 20 A and induction frequency of 52.3 kHz, induction brazing is performed for 5 seconds, and then cooled to room temperature to obtain a negative electrode column.

[0107] Among them, the flux includes cesium fluoroaluminate, self-crosslinking emulsion and ethanol;

[0108] The mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is 0.8:100;

[0109] The mass ratio of ethanol to cesium fluoroaluminate is 2.5:1;

[0110] The self-crosslinking emulsion includes self-crosslinking acrylic emulsion A and self-crosslinking polyurethane emulsion A, and the mass ratio of self-crosslinking acrylic emulsion A to self-crosslinking polyurethane emulsion A is 1.5:1.

[0111] Example 3

[0112] This embodiment provides a method for preparing a negative electrode column, comprising the following steps:

[0113] Punching the first copper plate to obtain a second copper plate having a groove;

[0114] Punching the first aluminum column to obtain a second aluminum column having a convex hull;

[0115] The groove surface of the second copper plate and the convex surface of the second aluminum column are machined respectively to obtain a third copper plate with a roughness of 3.2 and a third aluminum column with a roughness of 3.2;

[0116] According to the groove structure of the second copper plate, a welding piece A with a thickness of 0.2 mm is processed to obtain a second welding piece, and the shape of the second welding piece is adapted to the shape of the groove of the second copper plate;

[0117] Coating flux on the surface of the second solder sheet to obtain a preformed solder sheet, wherein the coating amount of the flux is 8.9 wt %;

[0118] Assemble the preformed welding sheet between the third copper plate and the third aluminum column to obtain the welded part.

[0119] The workpiece to be welded is placed in the middle of the induction coil of the high-frequency induction brazing machine, and the height of the workpiece to be welded is 8 mm from the bottom of the induction coil. Automatic induction brazing is used. Under the conditions of induction current of 120 A and induction frequency of 19.5 kHz, induction brazing is performed for 1 second, and the workpiece is cooled to room temperature to obtain a negative electrode column.

[0120] Among them, the flux includes cesium fluoroaluminate, self-crosslinking emulsion and ethyl acetate;

[0121] The mass ratio of the self-crosslinking emulsion to cesium fluoroaluminate is 1.2:100;

[0122] The mass ratio of ethyl acetate to cesium fluoroaluminate is 0.5:1;

[0123] The self-crosslinking emulsion includes self-crosslinking acrylic emulsion A and self-crosslinking polyurethane emulsion A, and the mass ratio of self-crosslinking acrylic emulsion A to self-crosslinking polyurethane emulsion A is 9:1.

[0124] Example 4

[0125] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 0.2.

[0126] Example 5

[0127] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 0.4.

[0128] Example 6

[0129] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 0.8.

[0130] Example 7

[0131] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 1.6.

[0132] Example 8

[0133] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 4.

[0134] Example 9

[0135] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 6.4.

[0136] Example 10

[0137] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the roughness of the copper plate and the aluminum column are both 7.

[0138] Embodiment 11

[0139] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the coating amount of the soldering flux is 5 wt %.

[0140] Example 12

[0141] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the coating amount of the soldering flux is 15 wt %.

[0142] Example 13

[0143] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the coating amount of the soldering flux is 25 wt %.

[0144] Embodiment 14

[0145] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that the coating amount of the soldering flux is 35 wt %.

[0146] Embodiment 15

[0147] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that welding sheet B is used to replace welding sheet A.

[0148] Example 16

[0149] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that welding sheet C is used to replace welding sheet A.

[0150] Embodiment 17

[0151] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that welding sheet D is used to replace welding sheet A.

[0152] Embodiment 18

[0153] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that welding sheet E is used to replace welding sheet A.

[0154] Embodiment 19

[0155] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that self-crosslinking acrylic emulsion B is used to replace self-crosslinking acrylic emulsion A.

[0156] Embodiment 20

[0157] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that self-crosslinking acrylic emulsion C is used to replace self-crosslinking acrylic emulsion A.

[0158] Embodiment 21

[0159] This embodiment provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this embodiment and that in Embodiment 1 is that self-crosslinking polyurethane emulsion B is used to replace self-crosslinking polyurethane emulsion A.

[0160] Comparative Example 1

[0161] This comparative example provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this comparative example and that in Example 1 is that the coating amount of the soldering flux is 2 wt %.

[0162] Comparative Example 2

[0163] This comparative example provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this comparative example and that in Example 1 is that the coating amount of the soldering flux is 40 wt %.

[0164] Comparative Example 3

[0165] This comparative example provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this comparative example and that in Example 1 is that the mass ratio of the self-crosslinking emulsion to the active agent is 0.3:100, and the mass ratio of water to the active agent is 3:1.

[0166] Comparative Example 4

[0167] This comparative example provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this comparative example and that in Example 1 is that the mass ratio of the self-crosslinking emulsion to the active agent is 1.5:100, and the mass ratio of water to the active agent is 0.3:1.

[0168] Comparative Example 5

[0169] This comparative example provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this comparative example and that in Example 1 is that polyacrylic acid is used to replace the self-crosslinking emulsion.

[0170] Comparative Example 6

[0171] This comparative example provides a method for preparing a negative electrode column. The difference between the method for preparing a negative electrode column in this comparative example and that in Example 1 is that the soldering flux in this comparative example is composed of 60% cesium fluoroaluminate and 40% hexadecane.

[0172] Performance Testing

[0173] The performance of the negative electrode column obtained in the embodiment and the comparative example was tested, and the testing method was as follows:

[0174] (1) Yield rate: 100 devices are tested. If there is no obvious burn damage on the device, no obvious flux residue on the solder joints, and the solder joints of the device do not fall off when it falls freely from a height of 1.5m to the ground, it is considered a good product.

[0175] (2) Pull-out force: Punch a hole in the soldered device and fix it on an electronic universal testing machine. Perform a pull-out test at a speed of 5 mm / min. Test five devices and take the average value.

[0176] The test results are shown in Table 1.

[0177] Table 1

[0178]

[0179]

[0180] It can be seen from the experimental data in Table 1 that the pull-out force of the negative electrode column of the present invention is ≥1500N, and the yield rate is ≥80%, which indicates that the negative electrode column of the present invention has higher welding point strength and yield rate.

[0181] By comparing Example 1 and Examples 4-10, it can be seen that when the roughness is 0.4-6.4, the pull-out force of the obtained negative electrode column is ≥2050N, and the yield rate is ≥96%, indicating that when the roughness is 0.4-6.4, the negative electrode column has higher weld strength and yield rate.

[0182] By comparing Example 1, Examples 11-14 and Comparative Examples 1-2, it can be seen that when the coating amount of the flux is 8-25wt%, the pull-out force of the obtained negative electrode column is ≥2030N, and the yield rate is ≥95%, indicating that when the coating amount of the flux is 8-30wt%, the negative electrode column has higher solder joint strength and yield rate.

[0183] By comparing Example 1 and Examples 15-18, it can be seen that when the Al content in the ZnAl alloy is 5-22%, the pull-out force of the obtained negative electrode column is ≥2100N, and the yield rate is ≥95%, indicating that when the Al content in the ZnAl alloy is 5-22%, the negative electrode column has higher weld strength and yield rate.

[0184] By comparing Example 1 and Examples 19-21, it can be seen that when the glass transition temperature of the self-cross-linking acrylic emulsion is ≤30°C; and / or the minimum film-forming temperature of the self-cross-linking polyurethane emulsion is ≤0°C, the pull-out force of the obtained negative electrode column is ≥2042N, and the yield rate is ≥88%, indicating that when the glass transition temperature of the self-cross-linking acrylic emulsion is ≤30°C; and / or the minimum film-forming temperature of the self-cross-linking polyurethane emulsion is ≤0°C, the negative electrode column has higher solder joint strength and yield rate.

[0185] It can be seen from Comparative Examples 1 and Comparative Examples 3-6 that the mass ratio of the self-crosslinking emulsion and the activator, as well as the mass ratio of water and the activator are not within the protection scope of the present invention, or when other substances are used to replace the self-crosslinking emulsion, or when a flux composed of 60% cesium fluoroaluminate and 40% hexadecane is used, the pull-out force of the obtained negative electrode column is ≤1450N, and the yield rate is ≤65%, indicating that the use of the flux added with the self-crosslinking emulsion of the present invention can obtain a negative electrode column with high solder joint strength and yield rate.

[0186] Finally, it should be noted that the above embodiments are used to illustrate the technical solution of the present disclosure rather than to limit the protection scope of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present disclosure can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present disclosure.

Claims

1. A method for preparing a negative electrode column, characterized in that: The following steps are involved: Coat the soldering flux on the surface of the solder sheet to obtain a preformed solder sheet. Assemble the solder preform between the copper plate and the aluminum column. Performing high-frequency induction brazing on the copper plate and the aluminum column to form a negative electrode column; Wherein, the coating amount of the soldering flux is 5-35wt%, and the soldering flux includes an activator, a self-crosslinking emulsion and a solvent; The mass ratio of the self-crosslinking emulsion to the active agent is 0.5-1.2:100; The mass ratio of the solvent to the active agent is 0.5-2.5:1; The self-crosslinking emulsion includes a self-crosslinking acrylic emulsion and a self-crosslinking polyurethane emulsion.

2. The method for preparing the negative electrode column according to claim 1, characterized in that: The coating amount of the soldering flux is 8-25wt%.

3. The method for preparing the negative electrode column according to claim 1, characterized in that: The roughness of the copper plate and the aluminum column are independently 0.2-7.

4. The method for preparing the negative electrode column according to claim 1, characterized in that: The welding sheet is a ZnAl alloy, wherein the Al content in the ZnAl alloy is 5-22% and the balance is Zn.

5. The method for preparing the negative electrode column according to claim 1, characterized in that: The copper plate has a groove, the aluminum column has a convex bulge, and the groove and the convex bulge are butt-jointed.

6. The method for preparing the negative electrode column according to claim 1, characterized in that: The glass transition temperature of the self-crosslinking acrylic emulsion is ≤30°C; and / or the minimum film-forming temperature of the self-crosslinking polyurethane emulsion is ≤0°C.

7. The method for preparing a negative electrode column according to claim 1, characterized in that: The active agent is fluoroaluminate; and / or the solvent is at least one of water, alcohol and ether.

8. The method for preparing the negative electrode column according to claim 7, characterized in that: The induced current of the high-frequency induction brazing is 20-120A; and / or, the frequency of the high-frequency induction brazing is 10-200kHz; and / or, the number of turns of the induction coil of the high-frequency induction brazing is 1-5 turns; and / or, the distance between the welding surface of the copper plate and the aluminum column and the bottom of the induction coil is 0-8mm.

9. A negative electrode column, characterized in that: The negative electrode column is prepared by the method for preparing the negative electrode column according to any one of claims 1 to 8.

10. A secondary battery, characterized in that: The secondary battery comprises the negative electrode column according to claim 9.

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