Preparation method and application of bipolar current collector

Abstract

This invention discloses a method for preparing and applying a bipolar current collector, relating to the field of bipolar current collector technology. The method includes the following steps: cleaning the current collector, subjecting it to laser irradiation, and then performing post-processing to obtain the bipolar current collector. The laser irradiation process parameters are: laser power 20W~50W, pulse width 300ns~800μs, pulse frequency 900Hz~1500Hz, scanning speed 15mm / s~25mm / s, and scanning spacing 50μm~150μm. The bipolar current collector prepared in this application utilizes the high energy density characteristics of a specific laser to improve elongation and tensile strength, thereby enhancing the overall performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of bipolar current collector technology, specifically a method for preparing and applying a bipolar current collector. Background Technology

[0002] With the rapid development of new energy and electronic technology, the demand for battery cycle life, energy density and safety performance is becoming increasingly important. Among them, current collectors, as an important component of batteries, are widely used to collect the current generated by the battery's active materials in order to form a larger external current output. Their performance directly affects the battery's cycle life, energy density and safety.

[0003] Currently, copper and aluminum foil are commonly used as current collectors for the positive and negative electrodes of lithium / sodium batteries. While these materials offer good conductivity, they suffer from high cost and weight, limiting further improvements in battery cost control and energy density. In contrast, bipolar current collectors offer the following significant advantages: Firstly, bipolar current collectors generally adopt a lighter and thinner design, which can maintain good conductivity while reducing the area and weight of the current collector itself in the battery. This allows for sufficient space for active materials inside the battery, thereby improving the overall energy density of the battery and extending its usage time. Secondly, bipolar current collectors typically possess excellent conductivity and low interfacial contact resistance, providing an efficient channel for charge transport and promoting rapid electron migration between the current collector and the active material, as well as between different electrodes. This reduces the battery's internal resistance, decreases energy loss during charging and discharging, and improves charging and discharging efficiency. Third, bipolar current collectors can be optimized in terms of structure and materials to better adapt to changes in the volume and stress of electrode materials during battery cycling, reducing the shedding and pulverization of electrode materials, thereby maintaining the integrity of the electrode structure, extending the cycle life of the battery, and enabling the battery to maintain good performance after multiple charge and discharge cycles. However, despite the advantages of bipolar current collectors compared to traditional current collectors, issues such as low tensile strength and elongation have gradually emerged during battery production and use. On the one hand, insufficient tensile strength of bipolar current collectors makes them prone to breakage and microcracks during processing or cycling, leading to internal short circuits and active material shedding, directly impacting battery safety and lifespan. On the other hand, during charging and discharging, the active material of the electrodes undergoes volume expansion and contraction. Due to the insufficient elongation of bipolar current collectors, they cannot adapt to these volume changes, easily causing interfacial delamination between the current collector and the active material layer, increasing resistance, and degrading overall battery performance.

[0004] In summary, the preparation method and application of a bipolar current collector are of great significance in order to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying a bipolar current collector, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a bipolar current collector includes the following steps: cleaning the current collector, subjecting it to laser irradiation treatment, and performing post-treatment to obtain the bipolar current collector; The process parameters for the laser irradiation treatment are as follows: laser power 20W~50W, pulse width 300ns~800μs, pulse frequency 900Hz~1500Hz, scanning speed 15mm / s~25mm / s, scanning spacing 50μm~150μm, and laser wavelength 1000~1100nm.

[0007] In a further proposed solution, a 1064nm Nd:YAG laser is used for copper and aluminum current collectors. This wavelength laser exhibits a significant thermal effect, rapidly heating copper and aluminum materials to achieve rapid melting and solidification. It can be used for welding and cutting copper and aluminum current collectors, as well as for surface strengthening treatment, improving the material's grain structure through rapid melting and solidification. When using a scanning laser irradiation method, the scanning spacing affects the treatment coverage and uniformity of the current collector surface. A suitable scanning spacing should ensure adequate overlap between adjacent scanning lines to ensure effective treatment of the entire current collector surface.

[0008] In a further embodiment, during laser irradiation, when a high-energy laser beam is focused on the surface of the bipolar current collector, the surface temperature rises rapidly within a very short time, causing the material to melt and vaporize quickly. After the laser treatment ends, the current collector surface cools and solidifies rapidly. During this process, parameters such as laser power (energy), pulse width, and frequency all affect the surface properties of the material. This application, by limiting specific process parameters, facilitates the generation of refined grains, the introduction of specific stress states, and the improvement of surface chemical composition, thereby positively impacting the performance of the bipolar current collector.

[0009] In a more optimized manner, the method includes the following steps: after cleaning the current collector, it is subjected to laser irradiation treatment and post-treatment; then, a conductive protective slurry is used for surface treatment to form a conductive protective layer; thus, a bipolar current collector containing a conductive protective layer is obtained. The conductive protective slurry comprises conductive materials and adhesives in a mass ratio of (1~5):(1~3); the conductive materials comprise modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of (1~5):(0.5~2).

[0010] In a further embodiment, the vinylsilane-modified silver nanowires are obtained by modifying silver nanowires with a vinylsilane coupling agent (KH-570).

[0011] A more optimized method for preparing the modified multi-walled carbon nanotubes is as follows: Step 1: Carboxylated multi-walled carbon nanotubes and thionyl chloride were added to DMF (N,N-dimethylformamide) and reacted at 65-75℃ for 12-16 h. After cooling, the mixture was purified and dried to obtain acyl chloride multi-walled carbon nanotubes. Subsequently, polyethylene glycol and triethylamine were added and reacted at 45-55℃ for 0.5-1.5 days. After cooling, the mixture was purified and dried to obtain hydroxylated multi-walled carbon nanotubes. Step 2: Add hydroxylated multi-walled carbon nanotubes and 3-boron benzoic acid to DMF, react at 30~60℃ for 1~3 days, and dry to obtain boron-modified multi-walled carbon nanotubes; Step 3: Add boron-modified multi-walled carbon nanotubes, phosphate ester silane coupling agent, and mercaptosilane coupling agent to an ethanol aqueous solution, react at 50~70℃ for 4~6h, cool, and obtain modified multi-walled carbon nanotubes.

[0012] In a further embodiment, the preparation process of the carboxylated multi-walled carbon nanotubes is as follows: multi-walled carbon nanotubes are added to a mixed acid (composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1) (solid-liquid ratio of 1:40), reacted at 55~65℃ for 10~20 min, washed, and dried to obtain carboxylated multi-walled carbon nanotubes.

[0013] In a more optimized manner, the mass ratio of carboxylated multi-walled carbon nanotubes to thionyl chloride in the raw materials of the acyl chloride multi-walled carbon nanotubes is 1:(70~75); and the mass ratio of acyl chloride multi-walled carbon nanotubes, polyethylene glycol, and triethylamine in the raw materials of the hydroxylated multi-walled carbon nanotubes is (2~3):(1~2):(0.08~0.12). In the raw materials for the boron-modified multi-walled carbon nanotubes, the mass ratio of hydroxylated multi-walled carbon nanotubes to 3-boron benzoic acid is (1.2~2.2):(0.4~0.7). In the raw materials for the modified multi-walled carbon nanotubes, the mass ratio of boron-modified multi-walled carbon nanotubes, phosphate ester silane coupling agent, and mercaptosilane coupling agent is (3~5):(0.1~0.2):(0.03~0.05).

[0014] Ideally, the molecular weight of the polyethylene glycol is 200-500.

[0015] In a more optimized manner, the diameter of the multi-walled carbon nanotubes in the raw material of the modified multi-walled carbon nanotubes is 20~50nm and the length is 10~30μm; the diameter of the silver nanowires in the raw material of the vinylsilane modified silver nanowires is 10~30nm and the length is 10~20μm.

[0016] In a more optimized manner, the conductive protective slurry has a solid content of 15-25 wt%, the solvent is an aqueous solution of N,N-dimethylacetamide with a concentration of 15-35 wt%, and the adhesive includes one or two of polyvinylidene fluoride and sodium carboxymethyl cellulose.

[0017] Ideally, the thickness of the conductive protective layer is 0.5~1μm.

[0018] A more optimized method for preparing bipolar current collectors is used to prepare bipolar current collectors.

[0019] An application of a bipolar current collector, used in lithium-ion batteries.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: In this application, by setting specific process parameters to perform laser irradiation on the current collector, the high energy density of the laser is utilized to improve tensile strength, elongation, and reduce resistivity, thereby reducing energy loss during charging and discharging and improving the cycle stability of the battery.

[0021] (1) Improve elongation: On the one hand, the energy of laser irradiation is concentrated on the surface and a certain depth range of the current collector. Under the action of heat, it is beneficial to optimize the grain boundary structure, so that the grains are easier to slide and deform when the material is under stress, thereby improving the elongation of the bipolar current collector; on the other hand, specific laser irradiation can introduce defects such as vacancies and interstitial atoms and dislocations that multiply. When stretched, these can serve as stress concentration points, inducing plastic deformation of the surrounding material, absorbing and dissipating external force energy, enabling the material to withstand greater deformation, thereby further improving the elongation. (2) Improve tensile strength: On the one hand, the rapid heating and cooling of laser irradiation induces recrystallization of the material and refines the grains. According to the Hall-Page formula, the reduction of grain size can increase the grain boundary density and hinder dislocation movement, thereby improving the tensile strength of the material macroscopically. On the other hand, laser irradiation heating changes the microstructure of the current collector surface material, forming a high-hardness hardened layer, which can bear more load when under stress, further enhancing the overall load-bearing capacity and tensile strength. (3) Impact on battery electrochemical performance: Laser irradiation affects battery electrochemical performance in the following three ways: First, irradiation promotes grain boundary optimization, affecting electron scattering in the material. The optimized microstructure reduces the number of grain boundaries and defects, lowers the probability of electron scattering, and allows electrons to conduct more smoothly in the material, thereby reducing resistivity and improving battery cycle life; Second, high temperature causes impurity redistribution and defect structure changes, weakening the scattering effect of impurities and defects on electrons and improving the overall performance of the battery; Third, rapid heating and cooling processes can induce phase structure transformation, transforming into a phase structure that is more conducive to electron conduction, further improving the electron transport performance of the material and improving the overall performance of the battery. (4) After laser irradiation, a certain microstructure is formed on the surface of the metal layer. However, if it comes into direct contact with the electrolyte, the electrolyte is prone to side reactions with the metal during battery cycling, forming a passivation film that affects the microstructure of the metal layer surface after laser irradiation, thereby reducing the overall performance of the battery. Therefore, adding a conductive protective layer can provide a certain degree of protection to the surface of the bipolar current collector after laser irradiation. It can effectively suppress direct contact and side reactions between the metal and the electrolyte, improve interface stability, and further enhance conductivity.

[0022] This application utilizes a conductive protective slurry coated on both sides of a bipolar current collector to form a conductive protective layer (dense conductive network). On the one hand, it can effectively suppress direct contact and side reactions between the metal and the electrolyte without affecting the microstructure, thereby improving interface stability. On the other hand, it further enhances the surface conductivity by utilizing highly conductive materials. The slurry is composed of modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a specific mass ratio, and both are of a specific size. Together with the other components, they form a three-dimensional conductive network on the surface of the bipolar current collector by enhancing interfacial bonding and stress dispersion.

[0023] In this process, modified multi-walled carbon nanotubes (MWCNTs) utilize polyethylene glycol (PEG) of a specific molecular weight as flexible connectors, reacting with acyl chlorides to form hydroxylated MWCNTs. The long PEG chains improve self-dispersion and prevent aggregation. Simultaneously, the flexible segments provide localized stress buffering, increasing elongation at break, and further preventing contact between the electrolyte and the metal layer, reducing metal corrosion. Subsequently, a carboxyl-hydroxyl esterification reaction is used to further graft the rigid benzene ring structure and boric acid groups onto the carbon nanotube surface. The rigid benzene ring structure and the flexible PEG segments synergistically enhance the interfacial bonding strength. The introduction of boric acid groups enables chemical bonding with subsequent coatings or groups on the metal surface, strengthening the adhesion between the coating and the laser-treated metal substrate, thereby improving the mechanical stability of the battery. Finally, phosphate and mercapto groups are introduced onto the carbon nanotube surface through grafting with phosphate ester silane coupling agents and mercapto silane coupling agents, providing active sites.

[0024] Specifically, modified multi-walled carbon nanotubes of specific sizes and mass ratios synergistically form a conductive network with vinylsilane-modified silver nanowires, improving tensile strength, elongation at break, and reducing resistance, thereby enhancing battery performance. Regarding the mass ratio, excessive amounts of modified multi-walled carbon nanotubes lead to agglomeration, insufficient PEG chains, increased stress concentration points, and decreased elongation. Conversely, insufficient amounts of modified multi-walled carbon nanotubes result in a discontinuous conductive network, insufficient framework stability, decreased tensile strength, increased electrode resistivity, and reduced battery cycle life. In terms of size, excessively thick vinylsilane-modified silver nanowires cannot form a conductive network with the modified multi-walled carbon nanotubes, leading to agglomeration. Conversely, excessively thin vinylsilane-modified silver nanowires have an excessively large specific surface area, making them prone to agglomeration. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the following quantities are by weight, and there are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: in the following embodiments, the polymer film layer is a polyethylene terephthalate film (PET base film) with a thickness of 6 μm and model number XR40H; the aluminum layer is obtained by vacuum evaporation; the copper layer is obtained by magnetron sputtering; the multi-walled carbon nanotubes have a diameter of 25 nm, a length of 15 μm, and product number 105312; the silver nanowires have a diameter of 20 nm, a length of 15 μm, and product number ZC-Ag- X20; polyethylene glycol with a molecular weight of 200, catalog number P3015-1kg; 3-boron benzoic acid, CAS number 25487-66-5; phosphate ester silane coupling agent (3-(trihydroxysilyl)propylmethyl phosphate); mercaptosilane coupling agent (3-mercaptopropyltrimethoxysilane); silver nanowires with a diameter of 40nm and a length of 25μm, catalog number ZC-Ag-X35; single-walled carbon nanotubes, catalog number C805971, OD: 1.5nm, Length: 20μm, and other raw materials are all commercially available.

[0027] Example 1: A method for preparing a bipolar current collector, comprising the following steps: Step 1: Current collector pretreatment: Cleaning: Use a suitable solvent (such as ethanol, acetone) to ultrasonically clean the current collector (aluminum layer (2μm), polymer film layer (6μm), copper layer (2μm)) to remove surface oil, dust and other impurities, and ensure the consistency of laser irradiation effect; Drying: The current collector needs to be dried after cleaning. It can be dried in a vacuum drying oven at 70°C for 8 hours to avoid moisture affecting the laser irradiation process and the performance of the current collector.

[0028] Step 2: Laser irradiation setup: Obtain the laser irradiation current collector; Equipment preparation: Select appropriate laser equipment and adjust laser parameters according to the current collector material and processing requirements. Ensure the laser optical path system is clean and accurate, and the working platform is stable.

[0029] Sample positioning: The pre-treated current collector is accurately placed on the laser processing stage, and the positioning device or vision system is used to ensure that the current collector is in the precise position of the laser irradiation. Step 3: Laser irradiation treatment: Parameter settings: laser power 20W, pulse width 300ns, pulse frequency 900Hz, scanning speed 15mm / s, scanning spacing 50μm, laser wavelength 1064nm; After setting the parameters: Start the laser equipment for irradiation treatment. Continuous scanning or pulsed scanning can be used to treat the current collector surface as needed. During the treatment process, parameters such as laser power and scanning speed must be monitored in real time to ensure the stability of the process.

[0030] Step 4: Post-processing of laser-irradiated current collector: Cooling: The laser-irradiated current collector needs to be properly cooled, either naturally or by air cooling, to prevent deformation or other performance changes caused by excessive temperature.

[0031] Example 2: A method for preparing a bipolar current collector, which differs from Example 1 only in that the laser power is 50W.

[0032] Example 3: A method for preparing a bipolar current collector, which differs from Example 1 only in that the pulse width is 800 μs.

[0033] Example 4: A method for preparing a bipolar current collector, which differs from Example 1 only in that the pulse frequency is 1500Hz.

[0034] Example 5: A method for preparing a bipolar current collector, which differs from Example 1 only in that the scanning speed is 25 mm / s.

[0035] Example 6: A method for preparing a bipolar current collector, which differs from Example 1 only in that the scanning interval is 150 μm.

[0036] Example 7: An application of a bipolar current collector, differing from Example 2 only in that: the bipolar current collector prepared in Example 2 is further coated on both sides with a conductive protective slurry (including conductive material and binder in a mass ratio of 3:2, solid content of 20wt%, solvent of 32wt% N,N-dimethylacetamide aqueous solution; binder is polyvinylidene fluoride), and vacuum dried at 80°C for 12h to form a conductive protective layer (0.7μm); thus obtaining a bipolar current collector containing a conductive protective layer; The lithium-ion battery was fabricated by stacking the following layers in the following order from top to bottom: separator (the separator is a commercially available polyethylene separator coated with alumina ceramic), lithium iron phosphate positive electrode active layer, bipolar current collector with conductive protective layer, graphite negative electrode active layer, and separator; the electrolyte was prepared by using a 9 ml volume ratio 2:1 mixed solution of DEC (diethyl carbonate) and FEC (fluoroethylene carbonate) as the solvent; then 0.5061 g of LiBF4 (lithium hexafluorophosphate) and 0.7764 g of LiDFOB (lithium difluorooxalate borate) were weighed and added to the mixed solution, stirred and dissolved to obtain a dual-salt electrolyte with a LiBF4 concentration of 0.6 mol / L and a LiDFOB concentration of 0.6 mol / L). The raw materials for the conductive material include modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of 3:1.2. The preparation method of modified multi-walled carbon nanotubes is as follows: Step 1: Add multi-walled carbon nanotubes (with a diameter of 25 nm and a length of 15 μm) to a mixed acid (composed of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1) (solid-liquid ratio of 1:40), react at 60 °C for 15 min, wash, and dry to obtain carboxylated multi-walled carbon nanotubes. Step 2: Carboxylated multi-walled carbon nanotubes and thionyl chloride were added to DMF at a mass ratio of 1:72 and reacted at 70°C for 14 hours. After cooling, the mixture was purified and dried to obtain acyl chloride multi-walled carbon nanotubes. Subsequently, polyethylene glycol (molecular weight 200) and triethylamine were added, with a mass ratio of acyl chloride multi-walled carbon nanotubes, polyethylene glycol, and triethylamine of 2.5:1.5:0.1. The mixture was reacted at 50°C for 1 day, cooled, purified, and dried to obtain hydroxylated multi-walled carbon nanotubes. Step 3: Hydroxylated multi-walled carbon nanotubes and 3-boron benzoic acid were added to DMF at a mass ratio of 1.8:0.55, reacted at 45°C for 2 days, and dried to obtain boron-modified multi-walled carbon nanotubes. Step 4: Add boron-modified multi-walled carbon nanotubes, phosphate ester silane coupling agent and mercaptosilane coupling agent to 70wt% ethanol aqueous solution at a mass ratio of 4:0.15:0.04, react at 60℃ for 5h, cool to obtain modified multi-walled carbon nanotubes. The method for preparing vinylsilane-modified silver nanowires is as follows: silver nanowires (with a diameter of 20 nm and a length of 15 μm) and vinylsilane coupling agent (KH-570) are added to a 70 wt% ethanol aqueous solution, reacted at 60 °C for 5 h, and then cooled to obtain vinylsilane-modified silver nanowires.

[0037] Example 8: An application of a bipolar current collector, differing from Example 7 only in that the conductive material (composed of modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of 1:2).

[0038] Example 9: An application of a bipolar current collector, differing from Example 7 only in that the conductive material is composed of modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of 5:0.5.

[0039] Comparative Example 1: No laser irradiation treatment was used; otherwise, it was the same as Example 2.

[0040] Comparative Example 2: In the laser irradiation process parameters, the laser power was too high (laser power 100W); the rest were the same as in Example 2.

[0041] Comparative Example 3: In the laser irradiation process parameters, the pulse width was too low (pulse width 50ns); the rest were the same as in Example 2.

[0042] Comparative Example 4: The conductive material is a single vinylsilane-modified silver nanowire; the rest is the same as in Example 7.

[0043] Comparative Example 5: Conductive material (composed of modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of 1:5), with an excess of vinylsilane-modified silver nanowires; the rest is the same as in Example 7.

[0044] Comparative Example 6: The conductive material with modified multi-walled carbon nanotubes did not contain 3-boron benzoic acid; the rest was the same as in Example 7.

[0045] Comparative Example 7: The diameter of the silver nanowire was changed to 40 nm and the length to 25 μm; the rest was the same as in Example 7.

[0046] Comparative Example 8: Multi-walled carbon nanotubes were replaced with single-walled carbon nanotubes; the rest was the same as in Example 7.

[0047] Performance Test 1: The bipolar current collectors prepared in Examples 1-6 and the bipolar current collectors with conductive protective layers prepared in Examples 7-9 and Comparative Examples 1-8 were subjected to tensile strength and elongation tests respectively, referring to GB / T1040.3-2006; the test results are shown in Table 1. Performance Test 2: The bipolar current collectors prepared in Examples 1-6 and the bipolar current collectors with conductive protective layers prepared in Examples 7-9 and Comparative Examples 1-8 were used to prepare batteries, and their cycle life was tested. The test results are shown in Table 1. Table 1

[0048] Conclusion: As shown in Table 1 above, and based on the data from Examples 1-6, this application improves elongation and tensile strength, and enhances battery cycle life by specifically setting specific laser irradiation process parameters and utilizing the high energy density characteristics of a specific laser. As shown in the data from Examples 7-9, this application, through a conductive protective layer, further achieves a specific synergistic effect with the surface of the metal layer after specific laser irradiation, thereby improving tensile strength, elongation at break, and battery cycle life.

[0049] As can be seen from the data in Comparative Example 1, without laser irradiation treatment, the grain structure of the material was not improved, and the overall performance was significantly reduced. As can be seen from the data in Comparative Example 2, excessively high laser power (100W) will lead to excessive input, coarsening of metal surface grains, and even microcracks, resulting in a decline in overall performance. As can be seen from the data in Comparative Example 3, if the pulse width is too low (50ns), the material will not melt sufficiently in time, and the grain refinement effect will not be achieved, resulting in a decrease in overall performance. As can be seen from the data of Comparative Example 4, the conductive material is a single vinyl silane modified silver nanowire, which lacks modified multi-walled carbon nanotubes and cannot play a synergistic role in the laser irradiation process. Furthermore, the single vinyl silane modified silver nanowire has poor mechanical strength and does not have a buffering effect, making it easy to break. Its tensile strength and elongation at break are significantly reduced. As can be seen from the data of Comparative Example 5, in the conductive material (composed of modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of 1:5), the excess of vinylsilane-modified silver nanowires, although the excess silver nanowires have good ductility, the lack of modified multi-walled carbon nanotubes will lead to a significant decrease in tensile strength and reduced stability. The data from Comparative Example 6 show that without the addition of 3-boron benzoic acid, the surface bonding of the modified multi-walled carbon nanotubes in the conductive material decreases, resulting in decreased stability, reduced overall mechanical strength, and decreased battery performance. As can be seen from the data in Comparative Example 7, when the diameter of the silver nanowire is changed to 40 nm and the length to 25 μm, the vinylsilane-modified silver nanowire is too thick and cannot form a conductive network with the modified multi-walled carbon nanotubes, forming agglomerates and reducing the overall performance. As can be seen from the data in Comparative Example 8, single-walled carbon nanotubes have a smaller diameter than multi-walled carbon nanotubes, making it impossible to form a conductive network with silver nanowires. Furthermore, they have fewer functional group sites, making them less suitable for grafting modification compared to multi-walled carbon nanotubes, resulting in a decrease in overall performance.

[0050] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bipolar current collector, characterized in that: Includes the following steps: After cleaning the current collector, it is subjected to laser irradiation treatment and post-processing to obtain a bipolar current collector; The process parameters for the laser irradiation treatment are as follows: laser power 20W~50W, pulse width 300ns~800μs, pulse frequency 900Hz~1500Hz, scanning speed 15mm / s~25mm / s, scanning spacing 50μm~150μm, and laser wavelength 1000~1100nm.

2. The method for preparing a bipolar current collector according to claim 1, characterized in that: Includes the following steps: After cleaning the current collector, it undergoes laser irradiation treatment, followed by post-processing. Then, a conductive protective slurry is used for surface treatment to form a conductive protective layer; A bipolar current collector containing a conductive protective layer was obtained; The conductive protective slurry comprises conductive materials and adhesives in a mass ratio of (1~5):(1~3); the conductive materials comprise modified multi-walled carbon nanotubes and vinylsilane-modified silver nanowires in a mass ratio of (1~5):(0.5~2).

3. The method for preparing a bipolar current collector according to claim 2, characterized in that: The method for preparing the modified multi-walled carbon nanotubes is as follows: Step 1: Carboxylated multi-walled carbon nanotubes and thionyl chloride were added to DMF and reacted at 65-75℃ for 12-16 h. After cooling, the mixture was purified and dried to obtain acyl chloride multi-walled carbon nanotubes. Subsequently, polyethylene glycol and triethylamine were added and reacted at 45-55℃ for 0.5-1.5 days. After cooling, the mixture was purified and dried to obtain hydroxylated multi-walled carbon nanotubes. Step 2: Add hydroxylated multi-walled carbon nanotubes and 3-boron benzoic acid to DMF, react at 30~60℃ for 1~3 days, and dry to obtain boron-modified multi-walled carbon nanotubes; Step 3: Add boron-modified multi-walled carbon nanotubes, phosphate ester silane coupling agent, and mercaptosilane coupling agent to an ethanol aqueous solution, react at 50~70℃ for 4~6h, cool, and obtain modified multi-walled carbon nanotubes.

4. The method for preparing a bipolar current collector according to claim 3, characterized in that: In the raw materials for the acyl chloride multi-walled carbon nanotubes, the mass ratio of carboxylated multi-walled carbon nanotubes to thionyl chloride is 1:(70~75); in the raw materials for the hydroxylated multi-walled carbon nanotubes, the mass ratio of acyl chloride multi-walled carbon nanotubes, polyethylene glycol, and triethylamine is (2~3):(1~2):(0.08~0.12). In the raw materials for the boron-modified multi-walled carbon nanotubes, the mass ratio of hydroxylated multi-walled carbon nanotubes to 3-boron benzoic acid is (1.2~2.2):(0.4~0.7). In the raw materials for the modified multi-walled carbon nanotubes, the mass ratio of boron-modified multi-walled carbon nanotubes, phosphate ester silane coupling agent, and mercaptosilane coupling agent is (3~5):(0.1~0.2):(0.03~0.05).

5. The method for preparing a bipolar current collector according to claim 4, characterized in that: The molecular weight of the polyethylene glycol is 200-500.

6. The method for preparing a bipolar current collector according to claim 2, characterized in that: The modified multi-walled carbon nanotubes have a diameter of 20-50 nm and a length of 10-30 μm in the raw materials; the vinylsilane-modified silver nanowires have a diameter of 10-30 nm and a length of 10-20 μm in the raw materials.

7. The method for preparing a bipolar current collector according to claim 2, characterized in that: The conductive protective slurry has a solid content of 15-25 wt%, the solvent is an aqueous solution of N,N-dimethylacetamide with a concentration of 15-35 wt%, and the adhesive includes one or two of polyvinylidene fluoride and sodium carboxymethyl cellulose.

8. The method for preparing a bipolar current collector according to claim 2, characterized in that: The thickness of the conductive protective layer is 0.5~1μm.

9. A bipolar current collector prepared by a method according to any one of claims 1 to 8.

10. An application of a bipolar current collector, characterized in that: The bipolar current collector as described in claim 9 is used in lithium-ion batteries.

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