Highly adhesive functional current collectors based on gradient adhesive layers and methods of making the same

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a high-bonding-strength functional current collector based on a gradient adhesive layer and its preparation method. The functional current collector of this invention includes a polymer base film, a functionally graded adhesive layer disposed on at least one surface of the polymer base film, and a copper layer disposed on the surface of the functionally graded adhesive layer. The functionally graded adhesive layer sequentially includes a first adhesive layer, a transition layer, and a second adhesive layer along a direction away from the polymer base film. This invention improves the bonding performance between the copper layer and the surface of the polymer base film by disposing of a functionally graded adhesive layer on the surface of the polymer base film, wherein the first adhesive layer is chemically compatible with the polymer base film, the second adhesive layer can form coordination bonds or chemical bonds with copper, and the transition layer serves as an intermediate layer, its material being a blend of the materials of the first and second adhesive layers.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-bonding-strength functional current collector based on a gradient bonding layer and its preparation method. Background Technology

[0002] Functional current collectors, as key components of lithium-ion batteries, are widely used in electric vehicles and energy storage systems. Meanwhile, the sandwich structure of functional current collectors achieves significant weight reduction, improves the mass energy density of lithium-ion batteries, and allows for thinner designs to optimize space utilization.

[0003] The structural design of functional current collectors not only helps suppress lithium dendrite growth and extend cycle life, but also improves electrode processing and cycle stability by enhancing flexibility and fatigue resistance. Furthermore, reducing the use of metals such as copper and aluminum lowers raw material costs, which is conducive to the development trend of green manufacturing.

[0004] However, the sandwich structure of functional current collectors suffers from a technical defect: insufficient adhesion between the copper metal layer and the polymer base film such as polypropylene (PP). The bonding interface mainly relies on physical bonding and limited surface roughness for anchoring, resulting in generally low bonding strength. During battery cycling, the metal layer may peel off from the polymer base film due to the volume expansion and contraction of the electrode active material or electrolyte penetration, leading to a sharp increase in internal resistance, battery performance degradation, and even failure.

[0005] Existing technologies improve interfacial adhesion by increasing surface energy through corona or plasma treatment of the polymer-based film, or by coating with a thicker adhesive. The former offers limited improvement and has a short-lived effect; the latter, while enhancing adhesion, significantly increases the thickness of the inactive material in the current collector, reducing the battery's energy density. Therefore, developing a functional current collector structure that achieves ultra-high interlayer adhesion strength with extremely low thickness increments is of significant research importance and application value. Summary of the Invention

[0006] The purpose of this invention is to provide a high-bonding-strength functional current collector based on a gradient bonding layer and its preparation method, so as to solve the related technical problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following specific technical solutions: A high-bonding-strength functional current collector based on a gradient adhesive layer includes the following structure: a polymer base film, a functional gradient adhesive layer disposed on at least one surface of the polymer base film, and a copper layer disposed on the surface of the functional gradient adhesive layer.

[0008] In a more optimized manner, the functionally graded adhesive layer sequentially comprises a first adhesive layer, a transition layer, and a second adhesive layer along the direction away from the polymer base film.

[0009] Ideally, the first adhesive layer is made of a polyolefin polymer containing carboxylic acid groups, anhydride groups, or hydroxyl groups.

[0010] More preferably, the material of the second adhesive layer is a polymer containing at least one functional group selected from pyrrolidone, amino, thiol or carboxyl groups.

[0011] More preferably, the material of the transition layer is a blend of the material of the first adhesive layer and the material of the second adhesive layer, and the mass ratio of the material of the first adhesive layer to the material of the second adhesive layer is (1~9)∶(9~1).

[0012] Ideally, the transition layer can be either a single-layer structure or a multi-layer structure.

[0013] In a more optimized manner, when the transition layer is a multi-layer structure, each layer is made by blending the first adhesive layer material and the second adhesive layer material in different mass ratios.

[0014] Ideally, the material of the first adhesive layer is maleic anhydride-grafted polypropylene (MAH-g-PP), with a grafting rate of 0.5~2.0%.

[0015] More preferably, the material of the second adhesive layer is one or more of polyvinylpyrrolidone (PVP), polyethyleneimine (PEI), polyacrylamide, and polyethylene glycol-polypropylene glycol block copolymer.

[0016] Ideally, the polymer base film is any one of PP, polyethylene, or polyethylene terephthalate film.

[0017] Ideally, the total thickness of the functionally graded adhesive layer is 30-500 nm, preferably 50-300 nm.

[0018] Ideally, the thickness of the copper layer is 0.3~3μm.

[0019] Ideally, the thickness of the polymer-based film is 1~6μm.

[0020] Ideally, the total thickness of the functionally graded adhesive layer accounts for 1 to 10% of the thickness of the polymer base film.

[0021] In a more optimized manner, the method for preparing the copper layer includes forming a copper seed layer by physical vapor deposition and thickening it to the target thickness by electrochemical deposition.

[0022] Ideally, the thickness of the copper seed layer is 10~100nm.

[0023] The method for preparing a high-bonding-strength functional current collector based on a gradient bonding layer includes the following steps: Step 1: Clean and activate the surface of the polymer base film; Step 2: Prepare the first adhesive layer solution, the second adhesive layer solution, and the transition layer solution formed by mixing the two; Step 3: On the surface of the activated polymer base film, the first adhesive layer solution, the transition layer solution, and the second adhesive layer solution are sequentially coated; after each layer is coated, the first stage of drying is performed; after all coatings are completed, the second stage of heat treatment is performed to form a functionally graded adhesive layer. Step 4: Deposit a copper layer on the surface of the functionally graded adhesive layer to obtain a functional current collector.

[0024] In a more optimized manner, the specific process for depositing the copper layer in step 4 is as follows: using magnetron sputtering, the polymer base film obtained in the previous step is placed in the cavity, and the deposition is carried out at a pressure of 5 × 10⁻⁶. -4 ~5×10 -3 Under an argon (Ar) atmosphere, copper target material is sputtered at a power of 150~300W for a deposition time of 1~3min to obtain a copper seed layer; Then, the polymer-based film with the copper seed layer is used as the cathode and placed in an electroplating solution at a temperature of 20~30℃, with an A / dm². 2 Electroplating is performed at a current density of 4-6 minutes to thicken the copper layer to the target thickness.

[0025] More preferably, the electroplating solution comprises the following components by mass: copper sulfate pentahydrate (CuSO4·5H2O) 180~220 g / L, sulfuric acid (H2SO4) 50~70 g / L, and chloride ions (Cl... - 55~65ppm.

[0026] In a more optimized manner, the Cl - It is derived from hydrochloric acid.

[0027] In a more optimized manner, the functional current collector is subjected to post-treatment by impregnation with chromic anhydride solution.

[0028] In a more optimized manner, the specific process steps of the post-treatment are as follows: immerse the functional current collector in a 1~3g / L chromic anhydride solution, hold for 8~12s, then wash with water, and dry in an oven at 55~65℃ for 2~3h.

[0029] More preferably, the activation treatment method is at least one of corona treatment, low-temperature plasma treatment, and ultraviolet light treatment.

[0030] Ideally, the surface tension of the activated polymer-based film is 28~36 mN / m.

[0031] Ideally, the coating method is any one of spin coating, slot coating, scraping coating, or spraying.

[0032] In a more optimized manner, in step 3, the drying process conditions for the first stage are: drying at a temperature of 50~90℃ for 10~120s.

[0033] In a more optimized manner, in step 3, the process conditions for the second stage heat treatment are: heat treatment temperature of 80~140℃ and time of 1~30min.

[0034] In the above technical solution, the present invention improves the adhesion performance between the copper layer and the polymer base film by setting a functionally graded adhesive layer on the surface of the base film. The first adhesive layer is chemically compatible with the polymer base film, the second adhesive layer can form coordination bonds or chemical bonds with copper, and the transition layer serves as an intermediate layer. Its material is a blend of the materials of the first adhesive layer and the second adhesive layer.

[0035] The first stage of drying causes the coating to form a gel state but not fully cure. The second stage of heat treatment causes the polymer molecular chains of each layer to diffuse into each other and finally cure, forming an integrated functional gradient adhesive layer without clear interfaces.

[0036] Post-processing can improve the oxidation and corrosion resistance of functional current collectors, reduce the increase in internal resistance of batteries during long-term use, and reduce the shedding of active materials, thereby improving the cycle life and safety of lithium-ion batteries.

[0037] Ideally, the solid content of the first adhesive layer solution is 0.1-5.0%, and the solvent is one of xylene, decahydronaphthalene, and toluene.

[0038] Ideally, the solid content of the second adhesive layer solution is 0.1-5.0%, and the solvent is any one or a mixture of two of ethanol and deionized water.

[0039] Ideally, in the ethanol and deionized water mixed solution, the volume ratio of ethanol to deionized water is 1:(1~2).

[0040] Compared with the prior art, the beneficial effects of the present invention are: 1. The functional current collector of the present invention, by setting a functional gradient adhesive layer, utilizes the chemical interaction between the adhesive layer and the polymer base film, and the coordination or chemical bonding with the copper layer to enhance the adhesion strength between the copper layer and the polymer base film, thereby significantly improving the peel strength of the functional current collector.

[0041] 2. The functional current collector of the present invention controls the total thickness of the functional gradient adhesive layer to the submicron level. Compared with the total thickness of conventional current collectors, the thickness increment is small and the percentage of the increment is reduced. It is far lower than the thickness required to achieve a similar effect using a single adhesive layer, and has little impact on the battery energy density.

[0042] 3. The functional gradient adhesive layer of the functional current collector of the present invention has good interface stability, reduces the interface stress caused by the difference in thermal expansion coefficient, and has a high peel strength retention rate and strong resistance to electrolyte corrosion after being soaked in electrolyte. Detailed Implementation

[0043] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. It should be understood that the embodiments described herein are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the protection scope of the present invention; unless otherwise specified, the related raw materials are all conventional settings.

[0044] In the following embodiments, a high-bond-strength functional current collector based on a gradient adhesive layer includes the following structure: a polymer base film, a functional gradient adhesive layer disposed on at least one surface of the polymer base film, and a copper layer disposed on the surface of the functional gradient adhesive layer; the functional gradient adhesive layer includes a first adhesive layer, a transition layer, and a second adhesive layer in sequence along the direction away from the polymer base film. There are no special limitations on any of the raw materials involved in this invention, and the following raw materials are included by way of example: PEI, M w 2000; PVP, model K30; MAH-g-PP, melt flow rate (MFR): 2~10g / 10min; PP, density: 0.895~0.92 g / cm³ 3 . Example

[0045] The method for preparing a high-bonding-strength functional current collector based on a gradient bonding layer includes the following steps: Step 1: Use a 4.0 μm thick biaxially oriented PP film, with a power of 150 W·min / m 2 One side of the film was subjected to corona activation treatment to obtain a polymer-based film with a surface tension of 36 mN / m. Step 2: Heat MAH-g-PP with a grafting rate of 1.0% in xylene to 100°C and stir to dissolve. After cooling to 60°C, the first adhesive layer solution is obtained and placed in a constant temperature bath for later use. The ratio of MAH-g-PP to xylene is 1g:100mL; PVP was dissolved in a mixed solution of ethanol and deionized water and stirred at room temperature until completely dissolved to obtain the second adhesive layer solution; the ratio of PVP, ethanol and deionized water was 1g:50mL:50mL. The first adhesive layer solution and the second adhesive layer solution were mixed and ultrasonically mixed for 10 minutes at a power of 200W to obtain the transition layer solution; the volume ratio of the first adhesive layer solution to the second adhesive layer solution was 1:4. Step 3: On one side of the activated polymer base film, the first adhesive layer solution is sequentially coated using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 50 nm. A transition layer solution is coated to form a transition layer with a thickness of 20 nm, and a second adhesive layer solution is coated to form a second adhesive layer with a thickness of 60 nm. After each coating layer is applied, it is immediately passed through a 1-meter-long 70℃ hot air drying channel with a wind speed of 2m / s and a stay of 60s for the first stage of drying. After the first stage of drying is completed, it is placed in a 110℃ vacuum oven with a vacuum degree of 0.08MPa for 10 minutes for the second stage of heat treatment. Step 4: On the surface of the second adhesive layer, use a magnetron sputtering device under Ar gas protection at a pressure of 5 × 10⁻⁶. -3 Pa, with a power of 200W, sputtered copper target material for 2 minutes to obtain a copper seed layer with a thickness of 30nm; It was then used as a cathode and placed in an electroplating solution at 25°C with a flux of 2 A / dm. 2 Electroplating at a current density of 5 min resulted in a copper layer with a total thickness of 1.0 μm, thus obtaining a functional current collector. The electroplating solution comprises the following components by mass: CuSO4·5H2O: 200 g / L, H2SO4: 60 g / L, Cl... - 60ppm; Cl - Derived from sodium chloride; Repeat steps 1 to 4 on the other side of the biaxially stretched PP film to obtain a functional current collector; The functional current collector from the previous step is immersed in a 2 g / L chromic anhydride solution for 10 seconds, then washed with water and dried in an oven at 60°C for 2 hours to obtain the finished product. Example

[0046] In the preparation method of high bonding strength functional current collector based on gradient bonding layer, in step S3, a transition layer solution is prepared by mixing the first bonding layer solution and the second bonding layer solution and ultrasonically stirring at 200W for 10 minutes to obtain the transition layer solution; the volume ratio of the first bonding layer solution to the second bonding layer solution is 1:1; the remaining component ratios and process steps are the same as in Example 1. Example

[0047] In the preparation method of high bonding strength functional current collector based on gradient bonding layer, in step S3, a transition layer solution is prepared by mixing the first bonding layer solution and the second bonding layer solution and ultrasonically stirring at 200W for 10 minutes to obtain the transition layer solution; the volume ratio of the first bonding layer solution to the second bonding layer solution is 4:1; the remaining component ratios and process steps are the same as in Example 1. Example

[0048] In the preparation method of high bonding strength functional current collector based on gradient adhesive layer, in step 3, a first adhesive layer solution is sequentially coated on the surface of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 25 nm. A transition layer solution is coated to form a transition layer with a thickness of 20 nm, and a second adhesive layer solution is coated to form a second adhesive layer with a thickness of 60 nm. After each coating layer is applied, it is immediately passed through a 1m long 70℃ hot air drying channel with a wind speed of 2m / s and a stay of 60s for the first stage of drying. After the first stage of drying is completed, it is placed in a 110℃ vacuum oven with a vacuum degree of 0.08MPa for 10min for the second stage of heat treatment. The remaining component ratios and process steps are the same as in Example 1. Example

[0049] In the preparation method of high bonding strength functional current collector based on gradient adhesive layer, in step 3, a first adhesive layer solution is sequentially coated on one side surface of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 100 nm. A transition layer solution is coated to form a transition layer with a thickness of 20 nm, and a second adhesive layer solution is coated to form a second adhesive layer with a thickness of 60 nm. After each coating layer is applied, it is immediately passed through a 1m long 70℃ hot air drying channel with a wind speed of 2m / s and a stay of 60s for the first stage of drying. After the first stage of drying is completed, it is placed in a 110℃ vacuum oven with a vacuum degree of 0.08MPa for 10min for the second stage of heat treatment. The remaining component ratios and process steps are the same as in Example 1. Example

[0050] In the preparation method of high bonding strength functional current collector based on gradient bonding layer, in step S2, the second bonding layer solution is prepared by dissolving PEI in a mixed solution of ethanol and deionized water and stirring at room temperature until completely dissolved to obtain the second bonding layer solution; the remaining component ratios and process steps are the same as in Example 1. Example

[0051] In the preparation method of high bonding strength functional current collector based on gradient adhesive layer, in step 3, a first adhesive layer solution is sequentially coated on one side surface of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 50 nm. A transition layer solution is coated to form a transition layer with a thickness of 20 nm, and a second adhesive layer solution is coated to form a second adhesive layer with a thickness of 30 nm; the remaining component ratios and process steps are the same as in Example 1. Example

[0052] In the preparation method of high bonding strength functional current collector based on gradient adhesive layer, in step 3, a first adhesive layer solution is sequentially coated on one side surface of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 80 nm. A transition layer solution is coated to form a transition layer with a thickness of 60 nm, and a second adhesive layer solution is coated to form a second adhesive layer with a thickness of 80 nm; the remaining component ratios and process steps are the same as in Example 1. Example

[0053] In the preparation method of high bonding strength functional current collector based on gradient adhesive layer, in step 2, the grafting rate of the first adhesive layer material MAH-g-PP is 0.5%; the remaining component ratios and process steps are the same as in Example 1.

[0054] Example 10: In the preparation method of high bonding strength functional current collector based on gradient adhesive layer, in step 2, the grafting rate of the first adhesive layer material MAH-g-PP is 2.0%; the remaining component ratios and process steps are the same as in Example 1.

[0055] Example 11: In the preparation method of high bonding strength functional current collector based on gradient bonding layer, in S3: the first bonding layer solution and the second bonding layer solution are mixed at a volume ratio of 1:4 and ultrasonically stirred for 10 min at a power of 200W. The first adhesive layer solution and the second adhesive layer solution were mixed at a volume ratio of 1:1 and ultrasonically stirred for 10 minutes at a power of 200W to obtain two transition layer solutions with different volume ratios. In step 3, a first adhesive layer solution is sequentially coated on one side of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 50 nm. Two transition layer solutions with volume ratios of 1:4 and 1:1 are coated to form a two-layer transition layer, each with a thickness of 20 nm; a second adhesive layer solution is then coated to form a second adhesive layer with a thickness of 60 nm. After each coating layer is applied, it is immediately passed through a 1m long 70℃ hot air drying channel with a wind speed of 2m / s and a stay of 60s for the first stage of drying. After the first stage of drying is completed, it is placed in a 110℃ vacuum oven with a vacuum degree of 0.08MPa for 10min for the second stage of heat treatment. The remaining component ratios and process steps are the same as in Example 1.

[0056] Example 12: In the preparation method of high-adhesion functional current collector based on gradient adhesive layer, in step 3, a first adhesive layer solution is sequentially coated on the surface of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 150 nm; a transition layer solution is coated to form a transition layer with a thickness of 120 nm; and a second adhesive layer solution is coated to form a second adhesive layer with a thickness of 180 nm. The remaining component ratios and process steps are the same as in Example 1.

[0057] Comparative Example 1: This comparative example provides a method for preparing a functional current collector, comprising the following steps: Step 1: Use a 4.0 μm thick biaxially oriented PP film, with a power of 150 W·min / m 2 One side of the film was subjected to corona activation treatment to obtain a polymer-based film with a surface tension of 36 mN / m. Step 2: On the surface of the activated polymer base film, use a magnetron sputtering device under Ar protection at a pressure of 5 × 10⁻⁶. - 3 A copper target was sputtered at 200 W for 2 min to obtain a 30 nm thick copper seed layer. This seed layer was then used as a cathode in an acidic copper sulfate electroplating solution at 2 A / dm². 2 Electroplating at a current density of 5 min resulted in a copper layer with a total thickness of 1.0 μm, thus obtaining a functional current collector. Repeat steps 1 to 2 on the other side of the biaxially stretched PP film to obtain a functional current collector; The functional current collector from the previous step is immersed in a 2 g / L chromic anhydride solution for 10 seconds, then washed with water and dried in an oven at 60°C for 2 hours to obtain the finished product.

[0058] Comparative Example 2: This comparative example provides a method for preparing a functional current collector. In step S3, the first adhesive layer solution and the second adhesive layer solution are mixed and ultrasonically stirred for 10 minutes at a power of 200W to obtain a transition layer solution. The volume ratio of the first adhesive layer solution to the second adhesive layer solution is 1:4. In step 3, a precision slit coater is used to coat only the transition layer solution on one side of the activated polymer base film at a coating speed of 5 mm / s, forming a transition layer with a thickness of 800 nm. The film is then immediately passed through a 1 m long 70 °C hot air drying channel with a wind speed of 2 m / s for 60 s for the first stage of drying. After the first stage of drying, the film is placed in a 110 °C vacuum oven with a vacuum degree of 0.08 MPa for 10 min for the second stage of heat treatment. The solid content of the transition layer solution is 5.0 wt%; the remaining component ratios and process steps are the same as in Example 1.

[0059] Comparative Example 3: This comparative example provides a method for preparing a functional current collector, in step 3, the coating and construction of a gradient adhesive layer: On one side of the activated polymer base film, a second adhesive layer solution is sequentially coated using a precision slot coater at a coating speed of 5 mm / s to form a second adhesive layer with a thickness of 50 nm. A transition layer solution is coated to form a transition layer with a thickness of 20 nm, and a first adhesive layer solution is coated to form a first adhesive layer with a thickness of 60 nm. After each coating layer is applied, it is immediately passed through a 1m long 70℃ hot air drying channel with a wind speed of 2m / s and a stay of 60s for the first stage of drying. After the first stage of drying is completed, it is placed in a 110℃ vacuum oven with a vacuum degree of 0.08MPa for 10min for the second stage of heat treatment. The remaining component ratios and process steps are the same as in Example 1.

[0060] Comparative Example 4: This comparative example provides a method for preparing a functional current collector. In step 3, a first adhesive layer solution is sequentially coated on one side surface of the activated polymer base film using a precision slit coater at a coating speed of 5 mm / s to form a first adhesive layer with a thickness of 20 nm. A transition layer solution is coated to form a transition layer with a thickness of 20 nm. A second adhesive layer solution is then coated to form a second adhesive layer with a thickness of 20 nm. After each layer is coated, the layer is immediately passed through a 1 m long 70 °C hot air drying channel with a wind speed of 2 m / s and held for 60 s for the first stage of drying. After all coatings are completed and the first stage of drying is completed, the layer is placed in a 110 °C vacuum oven with a vacuum degree of 0.08 MPa and heat-treated for 10 min for the second stage of heat treatment. The remaining component ratios and process steps are the same as in Example 1.

[0061] Experimental test: The functional current collectors prepared in Examples 1-12 and Comparative Examples 1-4 were used as samples for performance testing. Adhesion test method: A layer of 3M double-sided tape with a width of 25mm is bonded to a 3mm thick stainless steel plate with dimensions of 50mm×125mm. After rolling back and forth 3 times, the protective film of the double-sided tape is peeled off. The sample is evenly bonded on top of the double-sided tape, with no air residue between the sample and the tape. Then, the steel plate is fixed in one clamp of the tensile testing machine, and the other clamp is used to hold the free end of the sample. After fixing, the two are peeled at an angle of 180° and a speed of 5mm / min to test the peel strength, that is, the adhesion between the polymer film and the copper layer. Sheet resistance test method: Use a four-probe tester to measure the resistance of the copper layer surface; Electrolyte corrosion resistance test method: Immerse the sample in an electrolyte at 60℃ for 7 days. The electrolyte is a 1M mixed solution of LiPF6 (lithium hexafluorophosphate), EC (ethylene carbonate), and EMC (methyl ethyl carbonate), with a volume ratio of EC to EMC of 3:7. After cleaning and drying, test the peel strength. The peel strength retention rate is calculated as: peel strength of the sample before immersion / peel strength after immersion × 100%.

[0062] The experimental data are as follows: Table 1

[0063] Results and Discussion: The data in the table above show that: 1. By comparing Example 1 and Comparative Example 4, it can be seen that when the total thickness of the functionally graded adhesive layer is less than 100 nm, each layer cannot form an effective gradient adhesive structure and sufficient bonding sites. Although the peel strength is higher than that of the traditional structure, the adhesive strength is significantly lower than that of the present invention, and the stability is poor.

[0064] 2. By comparing Example 1 and Example 12, it can be seen that the best balance between peel strength, thickness increment, and stability can be achieved within the thickness range of 150~300nm. When the thickness exceeds 450nm, the performance improvement enters a plateau period, but the thickness increase has exceeded 10%, and the battery energy density decreases.

[0065] 3. By comparing Example 1 and Example 6, it can be seen that the second adhesive layer uses PEI as the adhesive material, which shows stronger adhesion than PVP, proving the technical advantage of using an amine-containing polymer as the adhesive layer to improve the adhesion to the copper layer.

[0066] 4. Comparing Examples 1-3, it can be seen that the transition layer, as an intermediate layer, has a regulatory effect on the bonding performance by the ratio of the transition layer solution. The optimal volume ratio of the first bonding layer solution to the second bonding layer solution is between 1:1 and 1:4. This indicates that controlling the volume ratio range of the first bonding layer solution to the second bonding layer solution is key to ensuring the bonding strength between the functionally graded bonding layer and the copper layer.

[0067] 5. By comparing Examples 4 and 7, it can be seen that when the total thickness is constant, excessive reduction of the first adhesive layer or the second adhesive layer will lead to a decrease in interfacial adhesion, which demonstrates the technical advantage of the present invention in constructing a functionally graded adhesive layer.

[0068] For those skilled in the art, it is obvious that the present invention is not limited to the details disclosed in the exemplary embodiments described above. The present invention can be implemented in other specific ways without departing from its spirit and essential characteristics. Therefore, the foregoing embodiments should be considered exemplary rather than restrictive from any perspective. The scope of protection of the present invention is defined by the appended claims. Therefore, all variations falling within the meaning and scope of the equivalent elements of the claims should be attributed to the scope of the present invention.

Claims

1. A high bond strength functional current collector based on a gradient bonding layer, characterized in that: It includes the following structure: a polymer base film, a functionally graded adhesive layer disposed on at least one surface of the polymer base film, and a copper layer disposed on the surface of the functionally graded adhesive layer; The functionally graded adhesive layer comprises, in sequence, a first adhesive layer, a transition layer, and a second adhesive layer along the direction away from the polymer base film; The first adhesive layer is made of a polyolefin polymer containing carboxylic acid groups, acid anhydride groups, or hydroxyl groups; The second adhesive layer is a polymer containing at least one functional group selected from pyrrolidone, amine, thiol, or carboxyl groups; The transition layer is a blend of the materials of the first adhesive layer and the second adhesive layer.

2. The high bond strength functional current collector based on a gradient bond layer of claim 1, wherein: In the transition layer material, the mass ratio of the first adhesive layer material to the second adhesive layer material is (1~9):(9~1); the polymer base film is any one of polypropylene, polyethylene, and polyethylene terephthalate; the total thickness of the functionally graded adhesive layer is 30~500nm.

3. The high bond strength functional current collector based on a gradient bond layer of claim 1, wherein: The first adhesive layer is made of maleic anhydride-grafted polypropylene with a grafting rate of 0.5% to 2.0%. The material of the second adhesive layer is one or more of polyvinylpyrrolidone, polyethyleneimine, polyacrylamide, and polyethylene glycol-polypropylene glycol block copolymer.

4. The high bond strength functional current collector based on a gradient bond layer of claim 1, wherein: The transition layer can be a single-layer structure or a multi-layer structure.

5. The high bond strength functional current collector based on a gradient bond layer of claim 1, wherein: The total thickness of the functionally graded adhesive layer accounts for 1 to 10% of the thickness of the polymer base film.

6. A method of making a high adhesion strength functional current collector based on a gradient adhesive layer according to any one of claims 1-5, characterized in that: Includes the following steps: Step 1: Clean and activate the surface of the polymer base film; Step 2: Prepare the first adhesive layer solution, the second adhesive layer solution, and the transition layer solution formed by mixing the two; Step 3: On the surface of the activated polymer base film, the first adhesive layer solution, the transition layer solution, and the second adhesive layer solution are sequentially coated; after each layer is coated, the first stage of drying is performed; after all coatings are completed, the second stage of heat treatment is performed to form a functionally graded adhesive layer. Step 4: Deposit a copper layer on the surface of the functionally graded adhesive layer to obtain a functional current collector.

7. The method of making a high adhesion strength functional current collector based on a gradient adhesive layer according to claim 6, characterized in that: The functional current collector is treated by impregnation with chromium anhydride solution; The specific process steps of the post-treatment are as follows: immerse the functional current collector in a 1~3g / L chromic anhydride solution, leave it for 8~12s, then wash it with water, and dry it in an oven at 55~65℃ for 2~3h.

8. The method of making a high adhesion strength functional current collector based on a gradient adhesive layer according to claim 6, wherein: The surface tension of the activated polymer-based film is 28~36 mN / m; The activation treatment method is at least one of corona treatment, low-temperature plasma treatment, and ultraviolet light treatment.

9. The method of making a high adhesion strength functional current collector based on a gradient adhesive layer according to claim 6, wherein: In step 3, the drying process conditions for the first stage are: drying at a temperature of 50~90℃ for 10~120s; The process conditions for the second stage of heat treatment are: heat treatment temperature of 80~140℃ and time of 1~30min.

10. The method of making a high adhesion strength functional current collector based on a gradient adhesive layer according to claim 6, wherein: The first adhesive layer solution has a solid content of 0.1-5.0% and the solvent is one of xylene, decahydronaphthalene, and toluene; The solid content of the second adhesive layer solution is 0.1-5.0%, and the solvent is any one or a mixture of two of ethanol and deionized water; When the solvent of the second adhesive layer solution is a mixture of ethanol and deionized water, the volume ratio of ethanol to deionized water is 1:(1~2).

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