A composite current collector electrode welding method for laminated battery

Abstract

The present invention relates to the field of electrode welding technology, and specifically to a method for welding composite current collector electrodes for laminated batteries. The specific method comprises the following steps: (1) coating the surfaces of a plurality of composite current collectors with electrode paste, leaving a blank area for the electrode tabs, to obtain composite current collector electrodes; (2) welding a transfer foil to the blank area for the electrode tabs of the composite current collector electrodes; (3) stacking the composite current collector electrodes welded in (2) in sequence, and after the stacking is completed, welding the composite current collector electrodes of the upper and lower stacks to obtain a semi-finished laminated current collector electrode; (4) performing a pressure-fusion welding process on the welded areas on the semi-finished laminated current collector electrode to complete the welding and obtain a laminated current collector electrode. In the present invention, a no-cleaning flux is coated on the blank area for the electrode tabs of the composite current collector electrodes before welding. Under the synergistic effect of the welding process and the flux, the quality of the welded areas is greatly improved, and defects such as voids at the welds are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of pole piece welding, in particular to a method for welding composite current collector pole pieces of a laminated battery. Background Art

[0002] Composite current collectors have attracted widespread attention in the lithium battery industry because they can improve battery energy density and safety while also reducing costs. Existing composite current collectors primarily consist of copper / aluminum metal layers deposited on the surface of a PET / PP substrate. The two metal layers are not in direct contact, but are bonded to a polymer-based film, forming a "sandwich structure." Therefore, when applied to lithium-ion batteries, these current collectors require a transfer weld process. By extending a layer of conventional metal foil from each metal layer, the two metal layers are electrically conductive, ensuring proper battery performance.

[0003] The existing composite current collector welding solution mainly involves transferring and welding a layer of traditional foil (usually copper / aluminum foil) on both sides of the electrode. Compared with traditional electrodes, the number of foil layers required for welding in the composite current collector pre-welding process is often doubled, which undoubtedly increases the difficulty of the welding process and increases the loss of copper / aluminum foil to a certain extent.

[0004] Based on this, the present invention will provide a composite current collector electrode welding method for a laminated battery, which can reduce the waste of metal foil in the current composite current collector transfer welding process and reduce the burden of subsequent pre-welding processes. Summary of the Invention

[0005] The object of the present invention is to provide a method for welding composite current collector pole pieces of a laminated battery to solve the problems raised in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for welding composite current collector electrodes of a laminated battery, specifically comprising:

[0008] (1) Applying electrode paste on both surfaces of several composite current collectors, leaving a blank area for the tabs, and drying to obtain composite current collector electrodes;

[0009] (2) Welding the transfer foil in the blank area of ​​the tab of the composite current collector electrode to be laminated;

[0010] (3) stacking the composite current collector electrodes welded in (2) in sequence. After the stacking is completed, welding the upper and lower laminated composite current collector electrodes so that the transfer foil is in complete contact with the blank areas of the tabs of the upper and lower composite current collector electrodes, thereby obtaining a semi-finished laminated current collector electrode.

[0011] (4) The welding parts of the semi-finished laminated current collector electrode are subjected to pressure fusion welding to ensure that each layer of the composite current collector electrode is in full contact with the transfer foil to achieve the purpose of current conduction, complete the welding, and obtain the laminated current collector electrode.

[0012] Furthermore, the composite current collector is any one of a composite copper current collector and a composite aluminum current collector.

[0013] Furthermore, the electrode paste is prepared by mixing lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 95.6:2.1:2.3, and adding appropriate amounts of N-methylpyrrolidone thereto in batches and stirring and mixing.

[0014] Furthermore, the specific method of welding in (2) is: welding a layer of transition foil on both sides of the blank area of ​​the tab of the composite current collector electrode placed in the first layer from bottom to top of the laminated battery, specifically as follows Figure 1 As shown; the composite current collector electrodes at other locations are welded with a layer of transfer foil on one side of the blank area of ​​the tab, as shown in FIG. Figure 2 shown.

[0015] Furthermore, the specific method of welding in (3) is: welding the transfer foil of the tab blank area of ​​the composite current collector electrode in the lower layer to the tab blank area of ​​the composite current collector electrode in the upper layer, specifically as follows: Figure 3 shown.

[0016] Furthermore, the welding in (2) and (3) is performed by an ultrasonic welding machine, and its working parameters are: the mode is energy mode, the welding energy is 20~40J, the welding amplitude is 20~50μm, and the welding pressure is 10~40psi.

[0017] Furthermore, the specific location of the welding part in (4) is Figure 3 At the dotted line position.

[0018] Furthermore, the parameters of the pressure fusion welding process are: welding pressure of 80-100N, welding current of 25-130A, and welding time of 1-2s.

[0019] Furthermore, if the composite current collector is a composite copper current collector, the transfer foil is copper foil; if the composite current collector is a composite aluminum current collector, the transfer foil is aluminum foil.

[0020] Furthermore, in order to promote welding and improve welding strength, in (2) and (3), before welding, the blank area of ​​the tab of the composite current collector electrode is coated with flux.

[0021] Furthermore, the soldering flux is obtained by mixing the following components: calculated by mass percentage, rosin 1-5%, modified rosin 0.5-2%, activator 0.2-1.5%, surfactant 0.2-4%, antioxidant 0.5-1%, film former 0.1-1%, and solvent 86-93%.

[0022] Furthermore, the preparation method of the modified rosin is as follows: (1) under nitrogen protection, rosin amine and N,N'-carbonyldiimidazole are dissolved in dimethyl sulfoxide, stirred and heated to 65-85°C for reaction for 1-5 hours, and the reaction is terminated to obtain reaction liquid A; (2) the container containing reaction liquid A is evacuated to a vacuum degree of 0.08-0.1 MPa; then the reaction liquid A is heated to 100-110°C, ethylene oxide is added, and then the reaction liquid is continued to be stirred and heated to 150-160°C for a period of time until the pressure in the container no longer changes, and finally the temperature is cooled to 100-110°C to obtain reaction liquid B; (3) potassium hydroxide and ethylene oxide are added to the reaction liquid B, Then, the mixture was stirred and heated to 150-160°C for a period of time until the pressure in the container no longer changed, and the reaction was terminated. After the reaction system was naturally cooled to room temperature, deionized water was added, and the lower organic phase was collected after extraction. The organic phase was washed with brine for 1-5 times, and then dried with anhydrous sodium sulfate to obtain product A. (4) Product A and 5-carboxybenzotriazole were dissolved in dimethyl sulfoxide, stirred and heated to 65-85°C for 12-36 hours, and the reaction was terminated. After the reaction system was naturally cooled to room temperature, dimethyl sulfoxide was removed by vacuum distillation, and the organic phase was washed with brine for 1-5 times. Finally, the modified rosin was obtained.

[0023] Furthermore, the components required for preparing the product A are: 10-14 parts of rosin amine, 6-8 parts of N,N'-carbonyldiimidazole, 40 parts of dimethyl sulfoxide, 16-22 parts of ethylene oxide, and 0.01-0.03 parts of potassium hydroxide, calculated by weight.

[0024] Furthermore, the components required for preparing the modified rosin are: 16-20 parts of product A, 10-14 parts of 5-carboxybenzotriazole, and 50 parts of dimethyl sulfoxide, in parts by weight.

[0025] Furthermore, the active agent is an organic acid.

[0026] Furthermore, the organic acid includes but is not limited to a combination of one or more of succinic acid, adipic acid, azelaic acid, glutaric acid, citric acid, malic acid, tartaric acid, and salicylic acid.

[0027] Furthermore, the surfactant includes but is not limited to any one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, dodecylphenol polyoxyethylene ether, and fatty alcohol polyoxyethylene ether.

[0028] Furthermore, the antioxidant includes but is not limited to any one of benzotriazole, hydroquinone, and butylated hydroxytoluene.

[0029] Furthermore, the film-forming agent is a silicone-modified polyurethane, and its preparation method is: adding terminal hydroxyl silicone oil and acetone to the terminal isocyanate polyurethane prepolymer, stirring and heating to 70-85°C for reaction for 1-6 hours, terminating the reaction, waiting for it to naturally cool to room temperature, and separating and purifying to obtain the silicone-modified polyurethane.

[0030] Furthermore, the mass ratio of the terminal hydroxyl silicone oil to the terminal isocyanate polyurethane prepolymer is (0.2-0.3):1.

[0031] Furthermore, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 24-28%; it was purchased from Shandong Jiaying Chemical Technology Co., Ltd.

[0032] Furthermore, the solvent includes but is not limited to any one of ethanol, ethylene glycol, propylene glycol, glycerol, and isopropyl alcohol.

[0033] To reduce welding difficulty and improve weld strength, the present invention incorporates flux during the welding process. Considering the difficulty of cleaning the laminated parts after welding, conventional flux inevitably leaves some residue at the weld site. This residual flux, over time, can corrode the electrode, compromising welding reliability and, in more serious cases, causing short circuits and personal safety hazards. Furthermore, to enhance the flux's activity, organic acid activators must be added. However, organic acid activators are highly corrosive and, after clearing the oxide layer, can easily damage the current collector.

[0034] Therefore, in the present invention, modified rosin is prepared by reacting the amino groups of rosin amine with the imidazole groups of N,N'-carbonyldiimidazole, grafting polyoxyethylene ether onto the product, and finally reacting it with the carboxyl groups of 4-carboxybenzotriazole. This modified rosin is then mixed with rosin, an active agent, a surfactant, an antioxidant, a film-forming agent, a solvent, and other components to create a no-clean soldering flux. This no-clean soldering flux eliminates the need for post-soldering cleaning and does not significantly damage the electrode. The polyoxyethylene ether chain ends and benzotriazole structures in the modified rosin act as corrosion inhibitors, significantly reducing the impact of the active agent on the current collector. Furthermore, the polyoxyethylene ether chain ends in the modified rosin synergize with the surfactant to reduce the flux's surface tension, enhance its wettability, and ultimately improve solderability and weld quality. The benzotriazole structure also synergizes with the antioxidant to provide an antioxidant effect.

[0035] In order to further promote the dispersion of the active agent and enhance the effect of the flux, the invention further reacts terminal hydroxyl silicone oil and terminal isocyanate polyurethane prepolymer to prepare a silicone-modified polyurethane; the silicone-modified polyurethane can cooperate with modified rosin and surfactant to promote the welding ability of the flux and improve the welding quality of the welding part; in addition, the silicone-modified polyurethane contains silicone oil chains, which can promote thermal conductivity, make the welding part evenly heated, reduce the generation of bubbles in the welding part, further enhance the welding ability, and improve the welding quality of the welding part.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The welding method (ultrasonic welding, pressure fusion welding) of the present invention can use less transition foil and reduce the burden of subsequent pre-welding process;

[0038] 2. The welding method of the present invention can greatly reduce the void rate of the welding part and improve the welding quality;

[0039] 3. The flux in the present invention is a no-clean type flux, which avoids the tedious process of cleaning the current collector and does not cause corrosion to the electrode, greatly improving the welding reliability; under the synergistic effect of the welding method combined with the flux, it can greatly improve the quality of the welding part and reduce the void rate of the welding part. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of welding on both sides of the blank area of ​​the tab of the composite current collector at the first layer of the laminated current collector electrode;

[0041] Figure 2 A schematic diagram of single-side welding of the blank area of ​​the tab of the composite current collector at the rest of the laminated current collector electrode;

[0042] Figure 3 Schematic diagram of the laminated composite current collector electrode;

[0043] Attachment Figure 2 Middle: 1 is the transfer foil; 2 is the electrode paste; 3 is the blank area of ​​the tab. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0045] It should be noted that the purchasers of all raw materials involved in the present invention include, without any special restrictions, illustratively:

[0046] Rosin with a purity of 99%, rosin amine with a purity of 99%, N,N'-carbonyldiimidazole with a purity of 99%, dimethyl sulfoxide with a purity of 99%, ethylene oxide with a purity of 99%, potassium hydroxide with a purity of 99%, 5-carboxybenzotriazole with a purity of 99%, CAS number 23814-12-2, benzotriazole with a purity of 99%, and isopropyl alcohol with a purity of 99% were all purchased from Hubei Yongkuo Technology Co., Ltd.

[0047] Nonylphenol polyoxyethylene ether with a purity of 99%, product number: TX-10, purchased from Guangzhou Shuangmen Chemical Co., Ltd.

[0048] The molecular weight of the hydroxyl-terminated silicone oil was 1000 and was purchased from Shanghai Tangui New Material Technology Co., Ltd.

[0049] The mass percentage of isocyanate groups in the isocyanate-terminated prepolymer was 24-28%, and it was purchased from Shandong Jiaying Chemical Technology Co., Ltd.

[0050] Example 1: A method for welding a composite current collector electrode of a laminated battery:

[0051] 1. Preparation of flux:

[0052] 1. Preparation of modified rosin: (1) Under nitrogen protection, dissolve 12 parts of rosin amine and 7 parts of N,N'-carbonyldiimidazole in 40 parts of dimethyl sulfoxide, stir and heat to 75℃ for 3 hours, terminate the reaction, and obtain reaction solution A; (2) evacuate the container containing reaction solution A to a vacuum degree of 0.08MPa; then heat reaction solution A to 105℃, add 3 parts of ethylene oxide, continue stirring and heating to 155℃ for a period of time until the pressure in the container no longer changes, and finally cool to 105℃ to obtain reaction solution B; (3) add 0.02 parts of potassium hydroxide and 15 parts of ethylene oxide to reaction solution B, and then stir Heat to 155 ° C for a period of time until the pressure in the container no longer changes, terminate the reaction, wait for the reaction system to cool naturally to room temperature, add 100 parts of deionized water, extract, collect the lower organic phase, wash with brine for 5 times, and then dry it with anhydrous sodium sulfate to obtain product A; (4) Dissolve 18 parts of product A and 12 parts of 5-carboxybenzotriazole in 50 parts of dimethyl sulfoxide, stir and heat to 75 ° C for 24 hours, terminate the reaction, wait for the reaction system to cool naturally to room temperature, remove dimethyl sulfoxide by vacuum distillation, wash with brine for 5 times, and finally dry it with anhydrous sodium sulfate to obtain modified rosin;

[0053] 2. Preparation of organosilicon-modified polyurethane: Add 2.5 parts of hydroxyl-terminated silicone oil and 20 parts of acetone to 10 parts of isocyanate-terminated polyurethane prepolymer, stir and heat to 80°C for 5 hours, terminate the reaction, allow to cool naturally to room temperature, and separate and purify to obtain organosilicon-modified polyurethane;

[0054] 3. Prepare soldering flux: Mix rosin 4%, modified rosin 1.5%, succinic acid 1%, nonylphenol polyoxyethylene ether 2.5%, benzotriazole 0.6%, silicone modified polyurethane 0.8%, and isopropyl alcohol 89.6% by mass to obtain soldering flux;

[0055] 2. Welding:

[0056] (1) The electrode paste is evenly coated on both surfaces of four composite copper current collectors (PET double-sided composite copper foil, with a total thickness of 7 μm, of which the PET layer thickness is 4 μm), leaving a blank area for the tabs, and dried to obtain composite copper current collector electrodes;

[0057] (2) Evenly apply flux to the blank area of ​​the tab of the composite copper collector electrode, then place it in a vacuum dryer and dry it at 90°C for 3 hours to complete the flux coating;

[0058] (3) Using an ultrasonic welding machine (the working parameters of the ultrasonic welding machine are: energy mode, welding energy of 30J, welding amplitude of 35μm, welding pressure of 35psi), weld a 20μm thick copper foil to the blank area of ​​the tab of the composite copper collector electrode; wherein, a layer of copper foil is welded on both sides of the blank area of ​​the tab of the composite copper collector placed in the first layer from the bottom to the top of the stacked battery, such as Figure 1 As shown, the composite copper current collectors at other locations are welded with a layer of copper foil on one side of the blank area of ​​the tab, as shown in FIG. Figure 2 As shown;

[0059] (4) stacking the composite copper current collectors welded in step (3) in sequence. After stacking, an ultrasonic welding machine is used to weld the upper and lower laminated composite copper current collectors with the same parameters, so that the copper foil is in complete contact with the blank areas of the tabs of the upper and lower composite current collector electrodes, thereby obtaining a semi-finished laminated current collector electrode.

[0060] (5) The laminated current collector electrode semi-finished product is subjected to pressure fusion welding (pressure fusion welding parameters are: welding pressure is 90N, welding current is 50A, welding time is 1s) so that each layer of composite copper collector and copper foil are in full contact to achieve the purpose of current conduction, complete welding, and obtain the laminated current collector electrode.

[0061] Based on Example 1, Examples 2 to 3 and Comparative Examples 1 to 6 are provided below, specifically as follows:

[0062] Example 2: Example 2 is based on Example 1, with the following adjustments made: the amount of flux components used, and other processes remain unchanged, specifically:

[0063] Preparation of soldering flux: According to mass percentage, rosin 4%, modified rosin 0.5%, succinic acid 1%, nonylphenol polyoxyethylene ether 2.5%, benzotriazole 0.6%, silicone modified polyurethane 0.1%, and isopropyl alcohol 91.3% are mixed to obtain the soldering flux.

[0064] Example 3: Example 3 is based on Example 1, with the following adjustments made: the amount of flux components used, and other processes remain unchanged, specifically:

[0065] Preparation of soldering flux: Mix 4% of rosin, 2% of modified rosin, 1% of succinic acid, 2.5% of nonylphenol polyoxyethylene ether, 0.6% of benzotriazole, 1% of organosilicon-modified polyurethane, and 88.9% of isopropyl alcohol in proportion by mass to obtain the soldering flux.

[0066] Comparative Example 1: Comparative Example 1 is based on Example 1, with the following adjustments: no modified rosin is added, and other processes remain unchanged, specifically:

[0067] Preparation of soldering flux: 5.5% of rosin, 1% of succinic acid, 2.5% of nonylphenol polyoxyethylene ether, 0.6% of benzotriazole, 0.8% of organosilicon-modified polyurethane, and 89.6% of isopropyl alcohol are mixed to obtain the soldering flux.

[0068] Comparative Example 2: Comparative Example 2 is based on Example 1, with the following adjustments: no silicone-modified polyurethane is added, and other processes remain unchanged, specifically:

[0069] Preparation of soldering flux: Mix 4% of rosin, 1.5% of modified rosin, 1% of succinic acid, 2.5% of nonylphenol polyoxyethylene ether, 0.6% of benzotriazole, and 90.4% of isopropyl alcohol in proportion by mass to obtain the soldering flux.

[0070] Comparative Example 3: Comparative Example 3 is based on Example 1, with the following adjustments: modified rosin and silicone-modified polyurethane are not added, and other processes remain unchanged, specifically:

[0071] Preparation of soldering flux: According to mass percentage, 5.5% of rosin, 1% of succinic acid, 2.5% of nonylphenol polyoxyethylene ether, 0.6% of benzotriazole, and 90.4% of isopropyl alcohol are mixed to obtain the soldering flux.

[0072] Comparative Example 4: Comparative Example 4 is based on Example 1, with the following adjustments: no flux is applied to the blank area of ​​the tab of the composite copper current collector, and other processes remain unchanged, specifically:

[0073] welding:

[0074] (1) The electrode paste is evenly coated on both surfaces of four composite copper current collectors (PET double-sided composite copper foil, with a total thickness of 7 μm, of which the PET layer thickness is 4 μm), leaving a blank area for the tabs, and dried to obtain composite copper current collector electrodes;

[0075] (2) Using an ultrasonic welding machine (the working parameters of the ultrasonic welding machine are: energy mode, welding energy of 30J, welding amplitude of 35μm, welding pressure of 35psi), a 20μm thick copper foil is welded to the blank area of ​​the tab coated; wherein, a layer of copper foil is welded on both sides of the tab blank area of ​​the composite copper current collector placed in the first layer from bottom to top of the stacked battery, and a layer of copper foil is welded on one side of the tab blank area of ​​the composite copper current collector in the remaining positions;

[0076] (3) stacking the composite copper current collectors welded in (2) in sequence. After the stacking is completed, an ultrasonic welding machine is used to weld the composite copper current collectors of the upper and lower stacks with the same parameters, so that the copper foil is in complete contact with the blank areas of the tabs of the upper and lower composite current collector pole pieces, thereby obtaining a semi-finished laminated current collector pole piece.

[0077] (4) The laminated current collector electrode semi-finished product is subjected to pressure fusion welding (pressure fusion welding parameters are: welding pressure is 90N, welding current is 50A, welding time is 1s) so that each layer of composite copper collector and copper foil are in full contact to achieve the purpose of current conduction, complete welding, and obtain the laminated current collector electrode.

[0078] Comparative Example 5: Comparative Example 5 is based on Example 1, with the following adjustments: the laminated current collector electrode semi-finished product is not subjected to pressure welding, and other processes remain unchanged, specifically:

[0079] welding:

[0080] (1) The electrode paste is evenly coated on both surfaces of four composite copper current collectors (PET double-sided composite copper foil, with a total thickness of 7 μm, of which the PET layer thickness is 4 μm), leaving a blank area for the tabs, and dried to obtain composite copper current collector electrodes;

[0081] (2) Evenly coat the blank area of ​​the tab of the composite copper current collector with flux, then place it in a vacuum dryer and dry it at 90°C for 3 hours to complete the flux coating;

[0082] (3) Using an ultrasonic welding machine (the working parameters of the ultrasonic welding machine are: energy mode, welding energy of 30J, welding amplitude of 35μm, welding pressure of 35psi), a 20μm thick copper foil is welded to the blank area of ​​the tab coated; wherein, a layer of copper foil is welded on both sides of the tab blank area of ​​the composite copper current collector placed in the first layer from bottom to top of the stacked battery, and a layer of copper foil is welded on one side of the tab blank area of ​​the composite copper current collector in the remaining positions;

[0083] (4) The composite copper current collectors welded in (3) are stacked in sequence. After stacking, an ultrasonic welding machine is used to weld the upper and lower laminated composite copper current collectors with the same parameters, so that the copper foil is in full contact with the blank areas of the tabs of the upper and lower composite current collector electrodes, and the welding is completed to obtain a laminated current collector electrode.

[0084] Comparative Example 6: Comparative Example 6 is based on Example 1, with the following adjustments: no flux is applied to the blank area of ​​the tab of the composite copper current collector, and no pressure welding is performed. Other processes remain unchanged, specifically:

[0085] welding:

[0086] (1) The electrode paste is evenly coated on both surfaces of four composite copper current collectors (PET double-sided composite copper foil, with a total thickness of 7 μm, of which the PET layer thickness is 4 μm), leaving a blank area for the tabs, and dried to obtain composite copper current collector electrodes;

[0087] (2) Using an ultrasonic welding machine (the working parameters of the ultrasonic welding machine are: energy mode, welding energy of 30J, welding amplitude of 35μm, welding pressure of 35psi), a 20μm thick copper foil is welded to the blank area of ​​the tab coated; wherein, a layer of copper foil is welded on both sides of the tab blank area of ​​the composite copper current collector placed in the first layer from bottom to top of the stacked battery, and a layer of copper foil is welded on one side of the tab blank area of ​​the composite copper current collector in the remaining positions;

[0088] (3) The composite copper current collectors welded in (2) are stacked in sequence. After stacking, an ultrasonic welding machine is used to weld the upper and lower laminated composite copper current collectors with the same parameters, so that the copper foil is in full contact with the blank areas of the tabs of the upper and lower composite current collector electrodes, and the welding is completed to obtain a laminated current collector electrode.

[0089] Performance test: The void ratio test of the laminated current collector electrode obtained in Examples 1 to 3 and Comparative Examples 1 to 6 was performed, as described below:

[0090] 1. Void rate test: The welding parts of the laminated current collector pole pieces were scanned using an ultrasonic scanning microscope, and the void rate of the welding parts was calculated to characterize the welding quality of the welding method of the present invention.

[0091] The test results of the above test contents are shown in Table 1 below:

[0092] Table 1

[0093]

[0094] Analysis of results: It can be seen from the data in Table 1 above that the quality of the laminated current collector pole piece obtained by welding using the welding method of the present invention is excellent, with an extremely small void rate, the lowest of which is 2.2%, which is Example 1; in addition, by comparing the examples and comparative examples 1 to 6, it can be seen that: in the present invention, both the preparation of the flux and the welding process are crucial to the quality of the laminated current collector pole piece; in particular, when the two technologies are combined and act synergistically on the laminated current collector pole piece, the best results can be obtained.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A method for welding composite current collector pole pieces of a laminated battery, characterized in that: The specific method is: (1) coating the electrode paste on the surface of several composite current collectors, leaving the blank area of ​​the tabs, to obtain composite current collector electrodes; (2) Welding the transfer foil in the blank area of ​​the tab of the composite current collector electrode to be laminated; (3) stacking the composite current collector electrodes welded in (2) in sequence. After the stacking is completed, welding the upper and lower stacked composite current collector electrodes to obtain a semi-finished laminated current collector electrode. (4) performing pressure fusion welding on the welding parts of the semi-finished laminated current collector electrode to complete the welding and obtain the laminated current collector electrode; The specific method of welding in (2) is as follows: a layer of transition foil is welded on both sides of the blank area of ​​the tab of the composite current collector electrode placed in the first layer from bottom to top of the stacked battery; a layer of transition foil is welded on one side of the blank area of ​​the tab of the composite current collector electrode placed in the remaining positions; The specific method of welding in (3) is: welding the transition foil of the tab blank area of ​​the composite current collector electrode in the lower layer to the tab blank area of ​​the composite current collector electrode in the upper layer; In (2) and (3), before welding, the blank area of ​​the tab of the composite current collector electrode is coated with flux; The soldering flux is obtained by mixing the following components: calculated by mass percentage, rosin 1-5%, modified rosin 0.5-2%, active agent 0.2-1.5%, surfactant 0.2-4%, antioxidant 0.5-1%, film-forming agent 0.1-1%, and solvent 86-93%; The preparation method of the modified rosin is as follows: (1) under nitrogen protection, rosin amine and N,N'-carbonyldiimidazole are dissolved in dimethyl sulfoxide, and the mixture is stirred and heated to 65-85°C for 1-5 hours, and the reaction is terminated to obtain a reaction solution A; (2) the container containing the reaction solution A is evacuated to a vacuum degree of 0.08-0.1 MPa; the reaction solution A is then heated to 100-110°C, ethylene oxide is added, and the mixture is stirred and heated to 150-160°C for a period of time until the pressure in the container is reduced to 0.08-0.1 MPa. The pressure no longer changes, and finally the temperature is lowered to 100-110°C to obtain reaction solution B; (3) potassium hydroxide and ethylene oxide are added to reaction solution B, and then stirred and heated to 150-160°C for a period of time until the pressure in the container no longer changes, and the reaction is terminated. After separation and purification, product A is obtained; (4) product A and 5-carboxybenzotriazole are dissolved in dimethyl sulfoxide, stirred and heated to 65-85°C for 12-36 hours, and the reaction is terminated. After separation and purification, modified rosin is obtained; The components required for the preparation of the product A are: 10-14 parts of rosin amine, 6-8 parts of N,N'-carbonyldiimidazole, 40 parts of dimethyl sulfoxide, 16-22 parts of ethylene oxide, and 0.01-0.03 parts of potassium hydroxide, calculated by weight. The components required for preparing the modified rosin are: 16-20 parts of product A, 10-14 parts of 5-carboxybenzotriazole, and 50 parts of dimethyl sulfoxide, calculated by weight.

2. The method for welding composite current collector electrodes of a laminated battery according to claim 1 is characterized in that: The welding in (2) and (3) is carried out by ultrasonic welding machine, and its working parameters are: the mode is energy mode, the welding energy is 20~40J, the welding amplitude is 20~50μm, and the welding pressure is 10~40psi; the parameters of the pressure fusion welding process in (3) are: the welding pressure is 80~100N, the welding current is 25~130A, and the welding time is 1~2s.

3. The method for welding composite current collector electrodes of a laminated battery according to claim 1, wherein: The composite current collector is any one of a composite copper current collector and a composite aluminum current collector; wherein, if the composite current collector is a composite copper current collector, the transfer foil is copper foil; if the composite current collector is a composite aluminum current collector, the transfer foil is aluminum foil.

4. The method for welding composite current collector electrodes of a laminated battery according to claim 1, wherein: The electrode paste is prepared by mixing lithium iron phosphate material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 95.6:2.1:2.3, and adding an appropriate amount of N-methylpyrrolidone thereto in batches, and stirring and mixing.

5. The method for welding composite current collector electrode sheets of a laminated battery according to claim 1, wherein: The active agent is an organic acid; the surfactant includes any one of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, dodecylphenol polyoxyethylene ether, and fatty alcohol polyoxyethylene ether; the antioxidant includes any one of benzotriazole, hydroquinone, and butylated hydroxytoluene; and the solvent includes any one of ethanol, ethylene glycol, propylene glycol, glycerol, and isopropyl alcohol.

6. The method for welding composite current collector electrodes of a laminated battery according to claim 1, wherein: The film-forming agent is an organosilicon-modified polyurethane, and its preparation method is as follows: adding hydroxyl-terminated silicone oil and acetone to an isocyanate-terminated polyurethane prepolymer, stirring and heating to 70-85°C for reaction for 1-6 hours, terminating the reaction, allowing the mixture to cool naturally to room temperature, and separating and purifying to obtain the organosilicon-modified polyurethane; The mass ratio of the hydroxyl-terminated silicone oil to the isocyanate-terminated polyurethane prepolymer is (0.2-0.3):1; the mass percentage of the isocyanate group in the isocyanate-terminated prepolymer is 24-28%.

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