Base membrane for composite current collector, preparation method of base membrane, composite current collector, pole piece and battery

Abstract

The invention relates to the technical field of batteries, and provides a base membrane for a composite current collector, a preparation method of the base membrane, the composite current collector, a pole piece and a battery. The preparation method comprises the following steps: carrying out orientation treatment on the porous organic base membrane; carrying out activating treatment on the porous organic base membrane subjected to the orientation treatment so as to form active sites on the surface of the porous organic base membrane and the inner walls of holes; and placing the activated porous organic base membrane in a reactor, adding a polar monomer, a cross-linking agent and a catalyst, maintaining a supercritical carbon dioxide state, and carrying out a polymerization grafting reaction so as to graft polar groups in the polar monomer to the surface of the porous organic base membrane and the inner walls of holes, thereby preparing the base membrane for the composite current collector. The binding force between the composite current collector base film and the metal layer is high, and the processing stability is good.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to the base film for composite current collectors and its preparation method, composite current collectors, electrodes and batteries. Background Technology

[0002] Composite current collectors use lightweight polymer materials (such as polyethylene or polypropylene) as the intermediate support base film, and form micron-scale metal layers on both sides through physical vapor deposition (such as magnetron sputtering) and electroplating processes, forming a "sandwich"-like structure. This structure can not only significantly reduce weight and increase energy density, but also utilize the melting and breaking properties of polymer materials to quickly cut off the current in the event of battery thermal runaway, greatly improving battery safety.

[0003] Among them, most composite current collectors use PE (polyethylene) porous membranes and PP (polypropylene) porous membranes as base membranes. PE and PP are typical non-polar and low surface energy polymer materials, lacking active sites that form strong interactions with metals. This results in extremely poor adhesion between the directly deposited copper layer and the PP or PE base membrane, making it very easy to peel off during subsequent processing or battery cycling, which seriously affects the conductivity reliability and mechanical integrity of the composite current collector. Summary of the Invention

[0004] Therefore, it is necessary to provide a base film for composite current collectors that can improve the adhesion and uniformity of metal layers, as well as a method for preparing the same, composite current collectors, electrodes, and batteries.

[0005] In a first aspect, this application provides a method for preparing a base film for composite current collectors, the method comprising:

[0006] Orientation treatment of porous organic-based membranes;

[0007] The porous organic base film after orientation treatment is activated to form active sites on the surface of the porous organic base film and the inner wall of the pores;

[0008] The activated porous organic base membrane is placed in a reactor, and polar monomers, crosslinking agents and catalysts are added. The polymerization and grafting reaction is carried out under supercritical carbon dioxide conditions to graft polar groups from the polar monomers onto the surface and inner walls of the pores of the porous organic base membrane, thus preparing a composite current collector base membrane.

[0009] In some embodiments, the preparation method also satisfies at least one of the following conditions:

[0010] (1) The activation treatment includes: introducing an oxidizing gas into the oriented porous organic base membrane in a closed reaction chamber to activate the porous organic base membrane;

[0011] (2) The reaction system is kept in a supercritical carbon dioxide state by introducing liquid carbon dioxide and increasing the pressure gradually; and / or, the pressure of the reaction system is reduced to atmospheric pressure by increasing the pressure gradually after the polymerization and grafting reaction.

[0012] In some embodiments, the orientation process includes sequentially performing a first stretching process, a second stretching process, and a shaping process on the porous organic base film.

[0013] The first stretching process includes stretching along the length of the porous organic base film, the stretching ratio of the first stretching process is 1.05~1.75, and the temperature of the first stretching process is lower than the melting point of the porous organic base film.

[0014] The second stretching process includes stretching along the width direction of the porous organic base film, the stretching ratio of the second stretching process is 1.5~2.5, and the temperature of the second stretching process is lower than the melting point of the porous organic base film.

[0015] The forming process includes applying tension to the porous organic base film after the second stretching treatment. The tension applied to the porous organic base film during the forming process is 5 N / m to 10 N / m, the temperature of the forming process is lower than the melting point of the porous organic base film, and the time is 30 min to 60 min.

[0016] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0017] (1) The material of the porous organic base membrane includes at least one of polyethylene and polypropylene;

[0018] (2) The polar monomer contains oxyvinyl groups;

[0019] (3) The polar monomers include at least one of acrylic acid and hydroxyethyl methacrylate;

[0020] (4) The polar monomers include acrylic acid and hydroxyethyl methacrylate, and the mass ratio of acrylic acid to hydroxyethyl methacrylate is 1:(0.5~1.0).

[0021] (5) For an area of ​​1m 2 The porous organic-based membrane has a polar monomer mass of 0.5g~2.5g;

[0022] (6) The catalyst includes at least one of benzoyl peroxide and dicumyl peroxide;

[0023] (7) The mass of the catalyst is 0.5% to 1.0% of the mass of the polar monomer;

[0024] (8) The temperature of the polymerization grafting reaction is 40℃~60℃, the pressure is 15MPa~30MPa, and the time is 2h~24h.

[0025] In some embodiments, the crosslinking agent also satisfies at least one of the following conditions:

[0026] (1) The crosslinking agent includes at least one of trimethylolpropane triacrylate, pentaerythritol triacrylate and dipentaerythritol hexaacrylate;

[0027] (2) The mass of the crosslinking agent is 0.1% to 0.3% of the mass of the polar monomer.

[0028] In some embodiments, the activation treatment satisfies at least one of the following conditions:

[0029] (1) The oxidizing gas contains ozone and protective gas, and the volume percentage of ozone in the oxidizing gas is 50%~70%;

[0030] (2) The activation treatment temperature is 25℃~35℃, and the time is 1min~3min;

[0031] (3) During the activation process, the oxidizing gas flows through the porous organic base membrane along the thickness direction, and the gas pressure difference on both sides of the porous organic base membrane is 30Pa~80Pa.

[0032] In some implementations, gradient boost includes a first boost stage, a second boost stage, and a third boost stage performed sequentially.

[0033] After the first pressurization stage, the pressure inside the reactor is 2.5MPa~3.5MPa, and the pressurization rate of the first pressurization stage is 0.2MPa / min~0.4MPa / min.

[0034] After the second pressurization stage, the pressure inside the reactor is 7.25 MPa to 7.75 MPa, and the pressurization rate of the second pressurization stage is 0.3 MPa / min to 0.5 MPa / min.

[0035] After the third pressurization stage, the pressure inside the reactor is 15MPa~30MPa, and the pressurization rate of the third pressurization stage is 0.8MPa / min~1MPa / min.

[0036] In some implementations, gradient decompression includes a first decompression phase, a second decompression phase, and a third decompression phase performed sequentially.

[0037] After the first decompression stage, the pressure inside the reactor is 7.25 MPa to 7.75 MPa, and the decompression rate during the first decompression stage is 0.8 MPa / min to 1 MPa / min.

[0038] After the second decompression stage, the pressure inside the reactor is 2.5MPa~3.5MPa, and the decompression rate during the second decompression stage is 0.3MPa / min~0.5MPa / min.

[0039] After the third decompression stage, the pressure inside the reactor is at atmospheric pressure, and the decompression rate during the third decompression stage is 0.2 MPa / min to 0.4 MPa / min.

[0040] In some embodiments, the preparation method further includes: sequentially cleaning and drying the porous organic base membrane after the polymerization grafting reaction.

[0041] The cleaning process includes Soxhlet extraction with ethanol to remove unreacted polar monomers, crosslinking agents, and catalysts from the reaction system.

[0042] During the drying process, tension is applied to the porous organic base membrane. The tension applied to the porous organic base membrane during the drying process is 5 N / m to 10 N / m, the temperature is 50℃ to 60℃, and the time is 1h to 3h.

[0043] Secondly, this application also provides a base film for composite current collectors, which is prepared using the preparation method for composite current collector base films as described in the first aspect.

[0044] Thirdly, this application also provides a composite current collector, which includes a base film for the composite current collector as described in the second aspect, and a metal layer disposed on at least one side surface of the base film for the composite current collector.

[0045] Fourthly, this application also provides an electrode, which includes a composite current collector as described in the third aspect.

[0046] Fifthly, this application also provides a battery, which includes the electrode as described in the fourth aspect.

[0047] Compared with traditional technologies, this application has at least the following beneficial effects:

[0048] This application sequentially performs orientation treatment, activation treatment, and supercritical carbon dioxide-assisted polymerization grafting reaction on a porous organic base membrane, thereby modifying the surface and inner walls of the pores of the porous organic base membrane through grafting, and thus improving the bonding force between the metal layer and the porous organic base membrane.

[0049] This application improves the orientation degree of the porous organic base membrane by performing orientation treatment, thereby forming a stable orientation structure of the molecular chains in the material and enhancing the high-pressure resistance of the porous organic base membrane. Simultaneously, this application adds polar monomers, crosslinking agents, and catalysts to the polymerization grafting reaction system to uniformly graft polar groups onto the surface and pore walls of the porous organic base membrane, forming a molecular chain network to lock the orientation structure of the porous organic base membrane and further enhance its structural stability. Therefore, this application not only achieves uniform grafting of polar groups onto the surface and pore walls of the porous organic base membrane through the above methods, but also avoids a decrease in the elongation at break and pore size shrinkage of the base membrane, thereby improving the deposition uniformity of the metal layer and increasing the bonding force, thus enhancing the processing stability of the base membrane for composite current collectors. Detailed Implementation

[0050] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0051] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0052] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0053] In this application, "porous organic base membrane" refers to a polyethylene (PE) porous membrane or a PP (polypropylene) porous membrane.

[0054] Traditional techniques employ physical roughening and activation methods, such as plasma treatment. High-energy plasma (oxygen or argon plasma, etc.) bombards the surface of porous organic films, etching the surface to increase micro-roughness and enhancing the mechanical interlocking force between the porous organic film and the metal layer through an "anchoring effect." Simultaneously, oxygen-containing groups can be introduced onto the surface of the porous organic film to increase its surface energy, thereby improving wettability and enhancing the adhesion between the metal layer and the porous organic film. However, this method struggles to activate and etch the inner walls of the pores, resulting in poor adhesion of the metal layer within the pores and a risk of detachment. Furthermore, the oxygen-containing groups introduced in this method are in a metastable state; if the metal layer is not deposited within the specified time, the activation effect on the film surface may deteriorate, affecting processing stability. Alternatively, wet chemical oxidation can be used, immersing the porous organic film in a strong oxidizing solution (such as chromic acid, concentrated sulfuric acid / hydrogen peroxide, or other strong oxidants). Through a chemical reaction, the surface of the porous organic film is etched, introducing oxygen-containing polar groups. However, wet chemical oxidation methods are difficult to control the degree of reaction, which may result in over-etching or poor etching uniformity; moreover, the large-scale use of strong oxidizing solutions is environmentally unfriendly and has poor safety.

[0055] In addition, supercritical carbon dioxide-assisted grafting modification can be used on the surface of porous organic base films. First, the porous organic base film is oxidized with oxidizing gases such as ozone. Then, materials such as acrylic acid are polymerized and grafted onto the surface and pore walls of the porous organic base film using supercritical carbon dioxide as the mass transfer medium. However, the supercritical carbon dioxide-assisted grafting process requires high pressure (7.39 MPa~50 MPa). Under this high pressure, the tensile orientation structure of the porous organic base film may be damaged, resulting in molecular chain disorientation and a 15%~30% decrease in elongation at break, affecting the subsequent processing performance of the composite current collector, such as cutting and winding. Simultaneously, the high pressure can also cause the membrane pore structure to shrink (pore size reduction of 5%~10%), indirectly reducing the uniformity of copper layer deposition.

[0056] The first aspect of this application provides a method for preparing a base film for composite current collectors, the method comprising:

[0057] Orientation treatment of porous organic-based membranes;

[0058] The porous organic base film after orientation treatment is activated to form active sites on the surface of the porous organic base film and the inner wall of the pores;

[0059] The activated porous organic base membrane is placed in a reactor, and polar monomers, crosslinking agents, and catalysts are added. A polymerization grafting reaction is carried out while maintaining a supercritical carbon dioxide state to graft polar groups from the polar monomers onto the surface and inner walls of the pores of the porous organic base membrane, thus preparing a composite current collector base membrane. It should be understood that atmospheric pressure refers to standard atmospheric pressure.

[0060] This application sequentially performs orientation treatment, activation treatment, and supercritical carbon dioxide-assisted polymerization grafting reaction on a porous organic base membrane, thereby modifying the surface and inner walls of the pores of the porous organic base membrane through grafting, and thus improving the bonding force between the metal layer and the porous organic base membrane.

[0061] This application improves the orientation degree of the porous organic base membrane by performing orientation treatment, thereby forming a stable orientation structure of the molecular chains in the material and enhancing the high-pressure resistance of the porous organic base membrane. Simultaneously, this application adds polar monomers, crosslinking agents, and catalysts to the polymerization grafting reaction system to uniformly graft polar groups onto the surface and pore walls of the porous organic base membrane, forming a molecular chain network to lock the orientation structure of the porous organic base membrane and further enhance its structural stability. Therefore, this application not only achieves uniform grafting of polar groups onto the surface and pore walls of the porous organic base membrane through the above methods, but also avoids a decrease in the elongation at break and pore size shrinkage of the base membrane, thereby improving the deposition uniformity of the metal layer and increasing the bonding force, thus enhancing the processing stability of the base membrane for composite current collectors.

[0062] Specifically, this application employs orientation treatment, activation treatment, and supercritical carbon dioxide-assisted grafting to graft polar groups onto a porous organic substrate membrane. During the supercritical carbon dioxide process, activation grafting can be achieved on the surface and inner walls of the porous organic substrate membrane, ensuring uniform modification of the surface and pores. Compared to traditional plasma activation and wet chemical oxidation methods, this application significantly reduces damage to the porous organic substrate membrane. Furthermore, the polar groups are covalently grafted onto the porous organic substrate membrane, resulting in good structural stability and consequently, good consistency of the deposited metal layer. Therefore, the key physical properties of the composite current collector substrate membrane in this application, such as its microporous structure, tensile strength, and puncture strength, are well preserved without any risk of damage.

[0063] In some embodiments, the reaction system is maintained in a supercritical carbon dioxide state by introducing liquid carbon dioxide and gradually increasing the pressure; and / or, the pressure of the reaction system is reduced to atmospheric pressure by gradually decreasing the pressure after the polymerization and grafting reaction. This application uses a gradual pressure increase method to slowly increase the pressure inside the reactor to the required reaction pressure, and then uses a gradual pressure decrease method to slowly reduce the pressure inside the reactor to atmospheric pressure after the reaction, effectively avoiding the impact of instantaneous pressure increase on the porous organic base membrane, which could lead to molecular chain disorientation and thus affect the mechanical properties of the porous organic base membrane. Furthermore, the reaction system described in this application uses specific catalysts and crosslinking agents that enable the polar monomers to fully crosslink and form a molecular chain network, thereby locking the orientation structure of the porous organic base membrane and further improving the elongation at break of the base membrane.

[0064] It is understood that the pressure inside the reactor can be increased to the pressure required for the polymerization grafting reaction using at least two pressurization steps. The appropriate pressurization rate can be selected based on the properties of the porous organic membrane. In some embodiments, the gradient pressurization includes a first pressurization stage, a second pressurization stage, and a third pressurization stage performed sequentially.

[0065] The pressure inside the reactor after the first pressurization stage is 2.5 MPa to 3.5 MPa, for example, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa, 3.0 MPa, 3.1 MPa, 3.2 MPa, 3.3 MPa, 3.4 MPa, or 3.5 MPa; the pressurization rate of the first pressurization stage is 0.2 MPa / min to 0.4 MPa / min, for example, 0.20 MPa / min, 0.25 MPa / min, 0.30 MPa / min, 0.35 MPa / min, or 0.40 MPa / min.

[0066] After the second pressurization stage, the pressure inside the reactor is 7.25 MPa to 7.75 MPa, for example, 7.25 MPa, 7.35 MPa, 7.45 MPa, 7.55 MPa, 7.65 MPa or 7.75 MPa; the pressurization rate of the second pressurization stage is 0.3 MPa / min to 0.5 MPa / min, for example, 0.30 MPa / min, 0.35 MPa / min, 0.40 MPa / min, 0.45 MPa / min or 0.50 MPa / min.

[0067] After the third pressurization stage, the pressure inside the reactor can be the pressure of the polymerization grafting reaction, for example, it can be 15MPa, 16MPa, 17MPa, 18MPa, 19MPa, 20MPa, 21MPa, 22MPa, 23MPa, 24MPa, 25MPa, 26MPa, 27MPa, 28MPa, 29MPa or 30MPa. The pressurization rate of the third pressurization stage is 0.8MPa / min to 1.0MPa / min, for example, it can be 0.80MPa / min, 0.85MPa / min, 0.90MPa / min, 0.95MPa / min or 1.00MPa / min.

[0068] It is understood that the pressure inside the reactor can be reduced to atmospheric pressure through at least two decompression cycles. The appropriate decompression rate can be selected based on the properties of the porous organic membrane. In some embodiments, gradient decompression includes a first decompression stage, a second decompression stage, and a third decompression stage performed sequentially.

[0069] The pressure inside the reactor after the first decompression stage is 7.25 MPa to 7.75 MPa, for example, 7.25 MPa, 7.35 MPa, 7.45 MPa, 7.55 MPa, 7.65 MPa or 7.75 MPa; the decompression rate of the first decompression stage is 0.8 MPa / min to 1 MPa / min, for example, 0.80 MPa / min, 0.85 MPa / min, 0.90 MPa / min, 0.95 MPa / min or 1.00 MPa / min.

[0070] After the second decompression stage, the pressure inside the reactor is 2.5 MPa to 3.5 MPa, for example, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa, 3.0 MPa, 3.1 MPa, 3.2 MPa, 3.3 MPa, 3.4 MPa, or 3.5 MPa; the decompression rate of the second decompression stage is 0.3 MPa / min to 0.5 MPa / min, for example, 0.30 MPa / min, 0.35 MPa / min, 0.40 MPa / min, 0.45 MPa / min, or 0.50 MPa / min.

[0071] After the third decompression stage, the pressure inside the reactor is at atmospheric pressure, for example, it can be 0.101325 MPa; the decompression rate of the third decompression stage is 0.2 MPa / min to 0.4 MPa / min, for example, it can be 0.20 MPa / min, 0.25 MPa / min, 0.30 MPa / min, 0.35 MPa / min or 0.40 MPa / min.

[0072] This application employs gradient pressurization and gradient depressurization as described above, which can further reduce the impact of pressure mutations on the molecular linkage orientation of the basement membrane.

[0073] In some embodiments, the orientation treatment includes sequentially performing a first stretching treatment, a second stretching treatment, and a shaping treatment on the porous organic base film. Optionally, the elongation at break of the porous organic base film after the orientation treatment is more than 95% of the elongation at break of the porous organic base film before the orientation treatment, and the degree of orientation is improved by 10% to 15%.

[0074] It is understandable that the stretching directions of the first stretching treatment and the second stretching treatment can be different. For example, the first stretching treatment stretches along the length direction of the porous organic base film, and the second stretching treatment stretches along the width direction of the porous organic base film; or, the first stretching treatment stretches along the width direction of the porous organic base film, and the second stretching treatment stretches along the length direction of the porous organic base film.

[0075] Optionally, the first stretching process includes stretching along the length of the porous organic base film, i.e., longitudinal stretching. The stretching ratio of the first stretching process is 1.05 to 1.75, for example, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.75; the temperature of the first stretching process is lower than the melting point of the porous organic base film. The second stretching process includes stretching along the width of the porous organic base film, i.e., transverse stretching. The stretching ratio of the second stretching process is 1.5 to 2.5, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5; the temperature of the second stretching process is lower than the melting point of the porous organic base film. This application first uses a lower stretching ratio for longitudinal stretching, and then uses a higher stretching ratio for transverse stretching. This can form a more stable and uniform micro-orientation inside the porous membrane, thereby controlling the decrease in elongation at break to a very small range (≤5%). This allows the base membrane to withstand pressure changes during subsequent gradient pressurization / depressurization processes, thus ensuring that the final composite current collector has good performance in cutting, winding, battery cycling, and other processes.

[0076] The forming process includes applying tension to the porous organic base film after the second stretching treatment. The tension applied to the porous organic base film during the forming process is 5 N / m to 10 N / m, for example, 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, or 10 N / m. The temperature of the forming process is lower than the melting point of the porous organic base film, and the time is 30 min to 60 min. The application of tension in the forming process, as described above, is beneficial for the orderly arrangement of molecular chains, further forming a stable and enhanced microstructure from the initial molecular weight orientation of the porous organic base film obtained through stretching, which is beneficial for the uniformity of subsequent metal deposition.

[0077] Understandably, the processing temperature for each step in the orientation process can be selected based on the material of the porous organic base membrane. For example, taking a polyethylene porous membrane as an example, the temperatures for the first stretching treatment, the second stretching treatment, and the molding treatment are independently 60℃~80℃, for example, 60℃, 65℃, 70℃, 75℃, or 80℃.

[0078] This application performs orientation treatment on porous organic base films as described above, enabling the molecular chains in the porous organic base film to form a stable orientation structure, thereby improving the high-pressure resistance of the base film and further reducing the molecular chain disorientation problem and pore shrinkage phenomenon during supercritical carbon dioxide-assisted polymerization grafting reaction. Furthermore, this application improves the orientation degree of the porous organic base film through orientation treatment, forming an alternating orientation structure of crystalline and amorphous regions on the porous organic base film, reducing excessive oxidation of the porous organic base film, and exposing more amorphous oxidation sites in the thickness direction of the porous organic base film, thereby forming more active sites during the activation treatment process and synergistically improving the activation treatment effect.

[0079] The active sites formed on the porous organic base membrane after activation treatment in this application can be peroxy groups and carbonyl groups, etc., which can provide grafting sites for subsequent polymerization and grafting reactions. In some embodiments, the activation treatment includes: introducing an oxidizing gas into the oriented porous organic base membrane in a closed reaction chamber to activate the porous organic base membrane.

[0080] It is understood that oxidizing gas refers to a gas with oxidizing properties. For example, oxidizing gas may contain ozone. In some embodiments, the oxidizing gas contains ozone and a protective gas, and the volume percentage of ozone in the oxidizing gas is 50% to 70%, for example, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, or 70%. The protective gas refers to a gas that does not react with the porous organic substrate membrane or ozone, such as nitrogen. This application selects the ozone percentage in the oxidizing gas as described above to slow down the oxidation rate during the activation process and prevent excessive oxidation of the porous organic substrate membrane, which could lead to material degradation.

[0081] In some embodiments, the activation treatment temperature is 25°C to 35°C, for example, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, or 35°C. The time is 1 min to 3 min, for example, 1.0 min, 1.5 min, 2.0 min, 2.5 min, or 3.0 min. The activation treatment temperature selected above in this application ensures both the efficiency of the oxidation reaction and that ozone can penetrate the porous organic membrane for uniform activation. If the temperature is relatively low, the reaction rate may be slow, significantly prolonging the treatment time; if the temperature is relatively high, it may accelerate ozone self-decomposition, easily leading to uneven treatment and waste.

[0082] In some embodiments, during the activation process, the oxidizing gas flows through the porous organic base membrane along its thickness direction. Optionally, the gas pressure difference across the porous organic base membrane is 30 Pa to 80 Pa, for example, 30 Pa, 35 Pa, 40 Pa, 45 Pa, 50 Pa, 55 Pa, 60 Pa, 65 Pa, 70 Pa, 75 Pa, or 80 Pa. Exemplarily, the porous organic base membrane can be fixed in a sealed cavity with a porous support plate. By introducing oxidizing gas into one side of the sealed cavity and evacuating the other side, the oxidizing gas passes through the pores of the porous organic base membrane, rather than only flowing through the surface of the porous organic base membrane, ensuring that both the surface of the porous organic base membrane and the inner walls of the pores are uniformly activated.

[0083] In some embodiments, the porous organic-based membrane is made of at least one of polyethylene and polypropylene. Optionally, the porosity of the porous organic-based membrane is 30% to 50%, for example, 30%, 35%, 40%, 45% or 50%; the pore diameter is 0.01 μm to 1 μm, for example, 0.01 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1.0 μm.

[0084] In some embodiments, the polar monomer contains oxyvinyl groups. The polar monomer includes at least one of acrylic acid and hydroxyethyl methacrylate. This application employs a polar monomer containing oxyvinyl groups and grafts oxygen-containing polar groups onto a porous organic substrate membrane via polymerization. The oxygen atoms in this polymer have strong electronegativity, resulting in an uneven electron cloud density distribution on the membrane surface. This allows for strong dipole-dipole interactions with subsequent metal atoms, and even the formation of coordination bonds, thereby fundamentally enhancing the interfacial adhesion between the metal layer and the porous organic substrate membrane.

[0085] Optionally, the polar monomers include acrylic acid and hydroxyethyl methacrylate, with a mass ratio of acrylic acid to hydroxyethyl methacrylate of 1:(0.5~1.0), for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, or 1:1.0. This application uses acrylic acid and hydroxyethyl methacrylate as polar monomers, which have high grafting efficiency. The synergistic effect of these two monomers improves the adhesion between the porous organic-based membrane and the metal layer. The carboxyl groups of acrylic acid can react efficiently with the free radicals generated on the porous membrane, resulting in high grafting efficiency. Furthermore, the carboxyl groups can form strong chemical interactions with subsequently deposited metal atoms. If the content of acrylic acid is relatively high, it may lead to increased brittleness of the interfacial layer, thus affecting the flexibility of the membrane. Excessive acidity may also cause localized corrosion of the membrane surface. The long chain and ester groups of hydroxyethyl methacrylate can prevent excessive grafting of acrylic acid, which could lead to localized stress concentration. However, a relatively high amount of hydroxyethyl methacrylate may also negatively impact the adhesion between the membrane and the metal layer.

[0086] In some embodiments, for an area of ​​1m 2 The porous organic-based membrane has a polar monomer mass of 0.5g to 2.5g, for example, it can be 0.5g, 0.75g, 1g, 1.25g, 1.5g, 1.75g, 2g, 2.25g or 2.5g.

[0087] In some embodiments, the catalyst comprises at least one of benzoyl peroxide and dicumyl peroxide. Optionally, the mass of the catalyst is 0.5% to 1.0% of the mass of the polar monomer, for example, it may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%.

[0088] In some embodiments, the crosslinking agent includes at least one selected from trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate. Optionally, the mass of the crosslinking agent is 0.1% to 0.3% of the mass of the polar monomer, for example, 0.10%, 0.15%, 0.20%, 0.25%, or 0.30%. The addition of the crosslinking agent in this application allows the crosslinking agent and the polar monomer to fully polymerize to form a molecular chain network, grafting polar groups onto the surface and inner walls of the porous membrane, while simultaneously locking the orientation structure of the porous organic base membrane, further improving the elongation at break of the base membrane.

[0089] In some embodiments, the temperature of the polymerization grafting reaction is 40°C to 60°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C, or 60°C. The pressure is 15MPa to 30MPa, for example, 15MPa, 16MPa, 18MPa, 20MPa, 22MPa, 24MPa, 26MPa, 28MPa, or 30MPa. The time is 2h to 24h, for example, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h. The above-selected temperature and pressure of the polymerization grafting reaction ensure grafting stability and avoid damage to the porous organic base membrane.

[0090] In some embodiments, the preparation method further includes: sequentially cleaning and drying the porous organic base membrane after the polymerization grafting reaction.

[0091] Optionally, the cleaning process includes: Soxhlet extraction with ethanol to remove unreacted polar monomers, cross-linking agents, and catalysts from the reaction system. The extraction time can be 36 h to 60 h.

[0092] Optionally, tension is applied to the porous organic base film during the drying process. The tension applied to the porous organic base film during drying is 5 N / m to 10 N / m, for example, 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, or 10 N / m. The drying temperature is 50℃ to 60℃, for example, 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, or 60℃. The drying time is 1 hour to 3 hours, for example, 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours, or 3.0 hours. This application applies tension to the porous organic base film during the drying process to prevent shrinkage and deformation, ensuring a smooth surface and stable dimensions after drying, fully meeting the requirements of subsequent winding and cutting processes.

[0093] Exemplarily, a method for preparing the above-mentioned composite current collector base film is provided, comprising the following steps:

[0094] Orientation treatment: The porous organic base film is subjected to a first stretching treatment along the length direction, and then a second stretching treatment along the width direction. Then, a tension of 5 N / m to 10 N / m is applied to the porous organic base film after the second stretching treatment, and the shaping treatment is carried out for 30 min to 60 min.

[0095] Activation treatment: The porous organic base membrane after the above orientation treatment is transferred to a sealed cavity, and an oxidizing gas containing ozone flows through the porous organic base membrane along its thickness direction to form active sites on the surface and inner walls of the pores of the porous organic base membrane. The ozone volume percentage in the oxidizing gas is 50%–70%, the activation temperature is 25℃–35℃, and the time is 1 min–3 min.

[0096] Supercritical carbon dioxide-assisted grafting: The activated porous organic membrane was placed in a reactor, and a mixture containing polar monomers, catalysts, and crosslinking agents was added. Liquid carbon dioxide was then added to the reactor, and the pressure was gradually increased to the required pressure for the polymerization grafting reaction (15 MPa–30 MPa). The mixture was heated to 40–60 °C and subjected to a polymerization grafting reaction for 2–24 hours to graft polar monomers onto the surface and inner walls of the pores of the porous organic membrane. After the polymerization grafting reaction, the pressure was gradually reduced to atmospheric pressure. The porous organic membrane was then cleaned and dried after the polymerization grafting reaction to prepare a composite current collector membrane.

[0097] The second aspect of this application also provides a base film for composite current collectors, which is prepared using the preparation method for composite current collector base films as described in the first aspect.

[0098] Among them, the base membrane for composite current collectors includes a porous organic base membrane, and polar monomers are grafted onto the surface of the porous organic base membrane and the inner wall of the pores.

[0099] A third aspect of this application also provides a composite current collector, which includes a base film for the composite current collector as described in the second aspect, and a metal layer disposed on at least one side surface of the base film for the composite current collector.

[0100] Understandably, the material of the metal layer can be selected based on the type of current collector. When the current collector is a negative electrode current collector, copper can be used for the metal layer; when the current collector is a positive electrode current collector, aluminum can be used for the metal layer.

[0101] In some embodiments, a metal layer may be formed by plating methods such as magnetron sputtering, vapor deposition, or electroplating.

[0102] A fourth aspect of this application also provides an electrode, which includes a composite current collector as described in the third aspect.

[0103] In this application, the electrode can be either a positive or negative electrode. The metal layer of the composite current collector in the positive electrode can be made of aluminum. The positive electrode material can be a ternary positive electrode material or a lithium iron phosphate positive electrode material. The metal layer of the composite current collector in the negative electrode material can be made of copper. The negative electrode material can be at least one of artificial graphite, natural graphite, silicon carbide, and hard carbon.

[0104] The fifth aspect of this application also provides a battery, which includes the electrode as described in the fourth aspect.

[0105] It should be noted that the battery of this application can be assembled from a positive electrode, a negative electrode, a separator, and an electrolyte. The current collectors in the positive and negative electrodes can be the composite current collectors described above. The separator can be made of polypropylene as the base material, and the electrolyte can be a commonly used electrolyte in the art, composed of organic solvents, lithium salts, and additives.

[0106] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0107] The porous organic-based membranes used in the following examples and comparative examples are made of polyethylene, with a thickness of 8 μm, a length of 1 m, a width of 1 m, a porosity of approximately 40%, an average pore diameter of approximately 0.2 μm, and an initial elongation at break of approximately 350%.

[0108] Example 1

[0109] The porous organic base film was placed in a biaxial stretching and shaping device and stretched longitudinally (along the length direction of the porous organic base film) and laterally (along the width direction of the porous organic base film) at 70℃. The longitudinal stretching ratio was 1.05 and the lateral stretching ratio was 1.5. After lateral stretching, the porous organic base film was subjected to a tension of 8 N / m and held at 60℃ for 45 min. The orientation degree of the porous organic base film was improved by 10% as measured by wide-angle X-ray diffraction.

[0110] The oriented porous organic membrane was fixed in a sealed reaction chamber, and an oxidizing gas containing ozone and nitrogen was introduced, allowing the oxidizing gas to flow through the porous organic membrane along its thickness direction to activate the surface and inner walls of the pores. The ozone volume percentage of the oxidizing gas was 60%, the activation temperature was 30℃, the activation time was 2 minutes, and the pressure difference across the porous organic membrane was 40 Pa.

[0111] The activated porous organic membrane was placed in a reactor, and 1.5g of polar monomer, 0.012g of benzoyl peroxide, and 0.003g of trimethylolpropane triacrylate were added. The polar monomer was acrylic acid and hydroxyethyl methacrylate in a mass ratio of 1:0.8. Then, liquid carbon dioxide was added, and the pressure inside the reactor was first increased to 3 MPa at a rate of 0.2 MPa / min, then increased to 7.39 MPa at a rate of 0.3 MPa / min, and then increased to 20 MPa at a rate of 0.8 MPa / min. The temperature inside the reactor was raised to 50°C, and the polymerization grafting reaction was carried out in a supercritical state of carbon dioxide for 12 hours. After the reaction was completed, the pressure inside the reactor was first reduced to 7.39 MPa at a rate of 0.8 MPa / min, then reduced to 3 MPa at a rate of 0.3 MPa / min, and finally reduced to atmospheric pressure at a rate of 0.2 MPa / min, in order to graft polar groups onto the porous organic base membrane.

[0112] The porous organic base membrane after the above polymerization and grafting reaction was subjected to Soxhlet extraction with ethanol for 48 h; then it was subjected to tension heat setting and drying at 55 °C for 2 h to prepare the composite current collector base membrane.

[0113] Example 2

[0114] The porous organic base film was placed in a biaxial stretching and shaping device and stretched longitudinally (along the length direction of the porous organic base film) and laterally (along the width direction of the porous organic base film) at 60℃. The longitudinal stretching ratio was 1.75 and the lateral stretching ratio was 2.5. After lateral stretching, a tension of 5 N / m was applied to the porous organic base film and it was kept at 60℃ for 30 min. The orientation degree of the porous organic base film was improved by 15% as measured by wide-angle X-ray diffraction.

[0115] The oriented porous organic membrane was fixed in a sealed reaction chamber, and an oxidizing gas containing ozone and nitrogen was introduced, allowing the oxidizing gas to flow through the porous organic membrane along its thickness direction to activate the surface and inner walls of the pores. The ozone volume fraction of the oxidizing gas was 70%, the activation temperature was 25℃, the activation time was 3 minutes, and the pressure difference across the porous organic membrane was 80 Pa.

[0116] The activated porous organic membrane was placed in a reactor, and 0.5g of polar monomer, 0.005g of benzoyl peroxide, and 0.0015g of trimethylolpropane triacrylate were added. The polar monomer was acrylic acid and hydroxyethyl methacrylate in a mass ratio of 1:0.5. Then, liquid carbon dioxide was added, and the pressure inside the reactor was first increased to 3.5 MPa at a rate of 0.4 MPa / min, then increased to 7.75 MPa at a rate of 0.5 MPa / min, and then increased to 30 MPa at a rate of 1 MPa / min. The temperature inside the reactor was raised to 40°C, and the polymerization grafting reaction was carried out in a supercritical state of carbon dioxide for 24 hours. After the reaction was completed, the pressure inside the reactor was first reduced to 7.75 MPa at a rate of 1 MPa / min, then reduced to 3.5 MPa at a rate of 0.5 MPa / min, and finally reduced to atmospheric pressure at a rate of 0.4 MPa / min, so as to graft polar groups onto the porous organic base membrane.

[0117] The porous organic base membrane after the above polymerization and grafting reaction was subjected to Soxhlet extraction with ethanol for 48 h; then it was heat-set and dried at 60 °C with tension of 8 N / m for 2 h to prepare the base membrane for composite current collector.

[0118] Example 3

[0119] The porous organic base film was placed in a biaxial stretching and shaping device and stretched longitudinally (along the length direction of the porous organic base film) and laterally (along the width direction of the porous organic base film) at 80℃. The longitudinal stretching ratio was 1.5 and the lateral stretching ratio was 1.75. After lateral stretching, a tension of 10 N / m was applied to the porous organic base film and it was kept at 60℃ for 60 min. The orientation degree of the porous organic base film was improved by 12% as measured by wide-angle X-ray diffraction.

[0120] The oriented porous organic membrane was fixed in a sealed reaction chamber, and an oxidizing gas containing ozone and nitrogen was introduced, allowing the oxidizing gas to flow through the porous organic membrane along its thickness direction to activate the surface and inner walls of the pores. The ozone volume percentage in the oxidizing gas was 50%, the activation temperature was 35℃, the activation time was 1 min, and the pressure difference across the porous organic membrane was 60 Pa.

[0121] The activated porous organic membrane was placed in a reactor, and 2.5g of polar monomer, 0.0125g of benzoyl peroxide, and 0.0025g of trimethylolpropane triacrylate were added. The polar monomer was acrylic acid and hydroxyethyl methacrylate in a mass ratio of 1:1. Then, liquid carbon dioxide is added, and the pressure inside the reactor is first increased to 2.5 MPa at a rate of 0.3 MPa / min, then to 7.25 MPa at a rate of 0.4 MPa / min, and then to 15 MPa at a rate of 0.9 MPa / min. The temperature inside the reactor is raised to 60°C, and the polymerization grafting reaction is carried out in a supercritical state of carbon dioxide for 2 hours. After the reaction is completed, the pressure inside the reactor is first reduced to 7.25 MPa at a rate of 0.9 MPa / min, then to 2.5 MPa at a rate of 0.4 MPa / min, and finally to atmospheric pressure at a rate of 0.3 MPa / min, in order to graft polar groups onto the porous organic base membrane.

[0122] The porous organic base membrane after the above polymerization and grafting reaction was subjected to Soxhlet extraction with ethanol for 48 h; then it was heat-set and dried at 50 °C with tension of 10 N / m for 1 h to prepare the base membrane for composite current collector.

[0123] Example 4

[0124] The composite current collector base membrane was prepared according to the method of Example 1, except that after adding liquid carbon dioxide, the pressure inside the system was directly increased to 20 MPa at a rate of 0.8 MPa / min, and after the reaction was completed, the pressure inside the system was directly reduced to atmospheric pressure at a rate of 0.8 MPa / min.

[0125] Example 5

[0126] The composite current collector base film was prepared according to the method of Example 1, except that 1.5g of acrylic acid was used as the polar monomer.

[0127] Example 6

[0128] The composite current collector base film was prepared according to the method of Example 1, except that 1.5g of hydroxyethyl methacrylate was used as the polar monomer.

[0129] Comparative Example 1

[0130] The untreated porous organic base membrane from Example 1 was directly used as the base membrane for the composite current collector.

[0131] The performance of the base membranes used for composite current collectors in the above embodiments and comparative examples was tested. The testing methods included:

[0132] O / C atomic ratio: The ratio of oxygen atoms to carbon atoms in the base film for composite current collectors was analyzed using XPS. The test results are shown in Table 1.

[0133] Elongation at break: The test was conducted using a universal tensile testing machine according to the GB / T 5230-2020 standard. The test results are shown in Table 1.

[0134] The composite current collector is prepared using the base film for the composite current collector described above. The preparation method includes:

[0135] A copper seed layer with a thickness of 50 nm was formed by magnetron sputtering on the substrate film for composite current collectors; then, copper was electroplated on the copper seed layer to form a copper layer with a total thickness of 1 μm. The peel strength between the copper layer and the substrate film for composite current collectors was tested according to GB / T 2792-2014 standard, and the test results are shown in Table 1.

[0136] Table 1

[0137]

[0138] As can be seen from the table above:

[0139] (1) Compared with Example 3, Example 1 shows that this application adjusts the equipment pressure by gradient pressurization and gradient depressurization, which effectively avoids the impact damage of pressure change on porous organic base membrane and the problem of molecular chain disorientation, effectively improves the structural stability of the membrane and improves the bonding force of the metal layer.

[0140] (2) Compared with Examples 4-5, Example 1 shows that the mixture of acrylic acid and hydroxyethyl methacrylate is used as the grafted polar monomer in Example 1. Acrylic acid and hydroxyethyl methacrylate work together to further improve the structural stability of the base film and the bonding force of the metal layer.

[0141] (3) Compared with Comparative Example 1, it can be seen that this application modifies the surface and inner wall of the porous organic base film by performing orientation treatment, activation treatment and supercritical carbon dioxide assisted polymerization grafting reaction on the porous organic base film, thereby improving the bonding force between the metal layer and the base film and the mechanical properties of the base film.

[0142] In summary, the polyethylene-based film prepared using the method of this application has an elongation at break of ≥300%, maintaining or even exceeding the processing performance of the unmodified PE film, fully meeting the requirements of subsequent processes such as cutting and winding of the composite current collector. Furthermore, in the composite current collector containing a copper metal layer, the peel strength of the metal layer can reach over 0.7 kN / m.

[0143] In the preparation process of this application, supercritical carbon dioxide can be completely recycled and reused, ozone naturally decomposes into oxygen, the amount of crosslinking agent used in the grafting system is small and there is no residue, and no harmful waste liquid is generated, which is in line with the trend of green manufacturing.

[0144] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0145] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A method for producing a base film for a composite current collector, characterized by, The preparation method comprises: performing orientation treatment on a porous organic base film; performing activation treatment on the porous organic base film after the orientation treatment to form active sites on the surface and inner wall of the pores of the porous organic base film; placing the porous organic base film after the activation treatment in a reactor, adding a polar monomer, a crosslinking agent and a catalyst, maintaining a supercritical carbon dioxide state to perform a polymerization grafting reaction, and grafting polar groups in the polar monomer to the surface and inner wall of the pores of the porous organic base film to prepare the base film for the composite current collector.

2. The method for producing a base film for a composite current collector according to claim 1, characterized by, The preparation method further satisfies at least one of the following conditions: (1) the activation treatment comprises: introducing an oxidizing gas into the porous organic base film after the orientation treatment in a closed reaction cavity to perform activation treatment on the porous organic base film; (2) the reaction system is maintained in a supercritical carbon dioxide state by introducing liquid carbon dioxide and gradually increasing the pressure; and / or, after the polymerization grafting reaction, the pressure of the reaction system is reduced to normal pressure by gradually reducing the pressure.

3. The method for preparing a base film for a composite current collector according to claim 1, characterized by, The orientation treatment comprises: sequentially performing first stretching treatment, second stretching treatment and forming treatment on the porous organic base film; the first stretching treatment comprises: stretching along the length direction of the porous organic base film, the stretching ratio of the first stretching treatment is 1.05-1.75, and the temperature of the first stretching treatment is less than the melting point of the porous organic base film; the second stretching treatment comprises: stretching along the width direction of the porous organic base film, the stretching ratio of the second stretching treatment is 1.5-2.5, and the temperature of the second stretching treatment is less than the melting point of the porous organic base film; the forming treatment comprises: applying tension to the porous organic base film after the second stretching treatment; the tension applied to the porous organic base film by the forming treatment is 5 N / m-10 N / m, the temperature of the forming treatment is less than the melting point of the porous organic base film, and the time is 30 min-60 min.

4. The method for preparing a base film for a composite current collector according to claim 1, characterized by, The preparation method satisfies at least one of the following conditions: (1) the material of the porous organic base film comprises at least one of polyethylene and polypropylene; (2) the polar monomer contains an oxygen ethylene group; (3) the polar monomer comprises at least one of acrylic acid and hydroxyethyl methacrylate; (4) the polar monomer comprises acrylic acid and hydroxyethyl methacrylate, and the mass ratio of the acrylic acid to the hydroxyethyl methacrylate is 1:(0.5-1.0); (5) for the porous organic-based film having an area of 1 m 2 2, the mass of the polar monomer is 0.5 g to 2.5 g; (6) the catalyst comprises at least one of dibenzoyl peroxide and dicumyl peroxide; (7) the mass of the catalyst is 0.5%-1.0% of the mass of the polar monomer; (8) the temperature of the polymerization grafting reaction is 40°C-60°C, the pressure is 15 MPa-30 MPa, and the time is 2 h-24 h.

5. The method for preparing a base film for a composite current collector according to claim 1, characterized by, The crosslinking agent further satisfies at least one of the following conditions: (1) the crosslinking agent comprises at least one of trimethylolpropane triacrylate, pentaerythritol triacrylate and dipentaerythritol hexaacrylate; (2) the mass of the crosslinking agent is 0.1%-0.3% of the mass of the polar monomer.

6. The method for preparing a base film for a composite current collector according to claim 2, characterized by, The activation treatment satisfies at least one of the following conditions: (1) the oxidizing gas contains ozone and a protective gas, and the volume ratio of the ozone in the oxidizing gas is 50% to 70%; (2) the temperature of the activation treatment is 25°C to 35°C, and the time is 1 min to 3 min; (3) during the activation treatment, the oxidizing gas flows through the porous organic base film along the thickness direction, and the pressure difference between the two sides of the porous organic base film is 30 Pa to 80 Pa.

7. The method for producing a base film for a composite current collector according to claim 2, characterized by, The gradient pressure increase includes a first pressure increase stage, a second pressure increase stage, and a third pressure increase stage performed in sequence; After the first pressure increase stage, the pressure in the reactor is 2.5 MPa to 3.5 MPa, and the pressure increase speed of the first pressure increase stage is 0.2 MPa / min to 0.4 MPa / min; After the second pressure increase stage, the pressure in the reactor is 7.25 MPa to 7.75 MPa, and the pressure increase speed of the second pressure increase stage is 0.3 MPa / min to 0.5 MPa / min; After the third pressure increase stage, the pressure in the reactor is 15 MPa to 30 MPa, and the pressure increase speed of the third pressure increase stage is 0.8 MPa / min to 1 MPa / min.

8. The method for preparing a base film for a composite current collector according to claim 2, characterized by, The gradient pressure decrease includes a first pressure decrease stage, a second pressure decrease stage, and a third pressure decrease stage performed in sequence; After the first pressure decrease stage, the pressure in the reactor is 7.25 MPa to 7.75 MPa, and the pressure decrease speed of the first pressure decrease stage is 0.8 MPa / min to 1 MPa / min; After the second pressure decrease stage, the pressure in the reactor is 2.5 MPa to 3.5 MPa, and the pressure decrease speed of the second pressure decrease stage is 0.3 MPa / min to 0.5 MPa / min; After the third pressure decrease stage, the pressure in the reactor is atmospheric pressure, and the pressure decrease speed of the third pressure decrease stage is 0.2 MPa / min to 0.4 MPa / min.

9. The method for producing a base film for a composite current collector according to any one of claims 1 to 8, wherein The preparation method further includes sequentially performing a cleaning treatment and a drying treatment on the porous organic base film after the polymerization grafting reaction; The cleaning treatment includes using ethanol Soxhlet extraction to remove unreacted polar monomers, cross-linking agents, and catalysts in the reaction system; During the drying treatment, tension is applied to the porous organic base film, the drying treatment applies a tension of 5 N / m to 10 N / m to the porous organic base film, the temperature is 50°C to 60°C, and the time is 1 h to 3 h.

10. A base film for a composite current collector, characterized by, The composite current collector base film is prepared by the preparation method of the composite current collector base film according to any one of claims 1 to 9.

11. A composite current collector, characterized by, The composite current collector includes the composite current collector base film according to claim 10, and a metal layer arranged on at least one side surface of the composite current collector base film.

12. A pole piece characterized by, The pole piece includes the composite current collector according to claim 11.

13. A battery, characterized by The battery includes the pole piece according to claim 12.

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