Separator base film for composite current collector, method for manufacturing the same, and composite current collector

Abstract

The application discloses a diaphragm base film for a composite current collector, a preparation method of the diaphragm base film and the composite current collector. Based on low initial porosity and low air permeability of the diaphragm base film, penetration of metal atoms during sputtering can be effectively blocked, substrate pollution of the composite current collector is avoided, metal atom sputtering penetration micropores form metal anchoring columns, and the substrate and the diaphragm base film are firmly locked. The three-dimensional physical interlocking structure has excellent reliability, has high puncture strength under an ultrathin thickness, significantly improves the mechanical robustness of the composite current collector, has uniform conductive performance, and can reduce the short circuit risk in battery manufacturing and use, and guarantees the safety performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a separator base film for manufacturing composite current collectors and a composite current collector structure based on the base film. Background Technology

[0002] Composite current collectors (PET / copper sandwich structure) are key components for improving the energy density and safety performance of lithium batteries. The mainstream manufacturing process is a two-step method: First, a nanoscale metal seed layer (such as a copper layer) is deposited on the surface of an insulating polymer substrate (typically a PET film) by magnetron sputtering, i.e., "magnetron sputtering seed layer deposition". Then, the thickness of the metal layer is increased by electroplating, i.e., "electroplation thickening". In this process, the separator base film, which serves as the metal deposition carrier and the isolation and protection, must meet stringent specific performance requirements. Its performance directly determines the manufacturing stability of the composite current collector and the reliability of the final product.

[0003] Existing composite current collector technologies mainly revolve around two structural paradigms, both of which have significant drawbacks: Metal-infiltrated / doped composite structures: These structures employ a polymer base film with a pre-set high porosity (usually greater than 15%), and then use chemical plating to allow metal to infiltrate and fill the pores of the base film, forming a "metal-polymer composite matrix layer." However, the pre-set high porosity of the base film results in insufficient mechanical strength, and the metal filling also alters the insulating properties of the matrix. Furthermore, relying solely on chemical bonding and physical adsorption, they lack active mechanical anchoring, leading to poor bonding stability.

[0004] Besides the two-step method, the single-carrier direct coating structure involves directly coating metal onto a single polymer base film or a traditional high-porosity battery separator. However, high-porosity battery separators are prone to metal atom penetration and contamination during magnetron sputtering, and there is an inherent contradiction between the "high porosity and high strength" of traditional separators, making them unable to withstand the stress of ultra-thin metallization.

[0005] The core design principle of traditional lithium-ion battery separators (dry or wet preparation) is to ensure lithium-ion transport, thus generally pursuing a high porosity of 35% to 55%. However, when directly applying them to the production of composite current collectors, three major adaptation challenges arise: 1. Pore structure mismatch: During the magnetron sputtering process, metal atoms in high-porosity battery separators can easily penetrate the surface micropores and deposit on the surface of the underlying polymer substrate (such as PET) or inside the sputtering chamber. This not only results in weak adhesion and poor continuity of the metal seed layer on the separator surface, but also causes equipment contamination and affects production stability. 2. Insufficient mechanical strength: The high energy density requirement of composite current collectors necessitates that the base membrane be made ultrathin, less than 3 μm. However, existing ultrathin membranes often sacrifice mechanical strength in order to maintain high porosity, especially insufficient puncture strength. They cannot withstand the physical stress of subsequent processes such as electroplating, slitting, and battery assembly, which can easily lead to membrane damage and battery short circuits. 3. Narrow process compatibility window: Currently, there is a lack of diaphragm base films specifically designed for the "magnetron sputtering pore-plating interconnect" process of composite current collectors; the ideal process compatibility requirement is that the base film is sufficient to block the sputtered metal from penetrating, while the high-energy particles of subsequent magnetron sputtering bombard the surface of the base film to controllably form through micropores, providing a channel for the electroplating solution to penetrate and the metal layer to anchor. Summary of the Invention

[0006] While some existing technologies employ wet processes to prepare polyethylene-based membranes, these technologies aim for high porosity (typically greater than 35%) and are designed for "rapid ion transport," which is fundamentally mismatched with the requirements of composite current collectors for "low porosity to prevent penetration, high stress resistance, and pore formation for anchoring." The wet process does not employ a "dual-carrier superposition" structure; its metal layer is only bonded by filling pre-defined pores, lacking a mechanical interlocking structure formed by in-situ pore formation. This results in weak bonding of the metal layer and uneven conductivity on both sides.

[0007] Therefore, there is an urgent need in this field to develop a new type of diaphragm base membrane and composite current collector structure that breaks through the traditional "ion-conducting membrane" design concept. Its core positioning is "process carrier membrane / isolation membrane + mechanical interlocking structure". It needs to have a combination of physical properties such as ultrathinness, ultra-high mechanical strength, ultra-low initial porosity and ultra-high air permeability, as well as the structural feature of "in-situ pore formation - metal anchoring" to accurately adapt to the preparation process requirements of composite current collectors.

[0008] The technical problem this invention aims to solve is as follows: Existing lithium battery separators, due to their high porosity and low strength, are unsuitable for the "magnetron sputtering-electroplating" fabrication process of composite current collectors. Furthermore, existing composite current collectors suffer from core drawbacks such as metal layer adhesion dependence on weak interfacial bonding and the difficulty in simultaneously achieving ultra-thinness and high strength. Therefore, this invention provides a dedicated separator base film for composite current collectors and a composite current collector structure based on this base film. This separator base film achieves an ultra-thin thickness of 2.0 μm-7.0 μm while possessing extremely high puncture strength, extremely low initial porosity, and high air permeability (low air volume), perfectly matching the metal penetration barrier requirements of the magnetron sputtering stage. The constructed composite current collector structure significantly enhances the metal layer adhesion through a mechanical interlocking mechanism, ensuring the reliability of subsequent processing steps.

[0009] One object of the present invention is to provide a diaphragm base membrane for composite current collectors, which is manufactured from ultra-high molecular weight copolymers and satisfies at least one or more of the following: a) Thickness is 2.0μm-7.0μm; b) Puncture strength ≥390 gf; c) Porosity ≤ 20%; d) Air permeability (Gurley value) ≥ 999 seconds / 100 ml.

[0010] As described above, the diaphragm base membrane includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

[0011] As described above, the first copolymer has a weight-average molecular weight of not less than 2 million, the second copolymer has a weight-average molecular weight of 1 million to 1.5 million, and the third copolymer has a weight-average molecular weight of 500,000 to 1 million.

[0012] As described above, the diaphragm base membrane contains X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5≦X / (Y+Z)≦4.0.

[0013] As described above, the diaphragm base membrane, wherein the ultra-high molecular weight copolymer satisfies at least one or more of the following: the first copolymer includes polyolefin, fluorinated polyolefin, polyether, acrylic polymer, polyester, polyol or any combination thereof; the second copolymer includes polyolefin, fluorinated polyolefin, polyether, acrylic polymer, polyester, polyol or any combination thereof; and the third copolymer includes polyolefin, fluorinated polyolefin, polyether, acrylic polymer, polyester, polyol or any combination thereof.

[0014] Another aspect of the present invention is to provide a method for preparing a diaphragm base membrane for composite current collectors, comprising the following steps: a casting step: casting a melt containing an ultra-high molecular weight copolymer and a pore-forming agent to obtain a sheet-like cast preform, wherein the melt is obtained by blending the ultra-high molecular weight copolymer and the pore-forming agent at a melting temperature; a two-dimensional stretching step: performing two-dimensional stretching of the cast preform at a stretching temperature with a stretching ratio of not less than 5 times to obtain a stretched preform, wherein the stretching temperature is not greater than the melting temperature; and an extraction step: extracting the stretched preform with a volatile solvent to remove residual pore-forming agent to obtain a diaphragm base membrane, wherein the diaphragm base membrane satisfies at least one or more of the following: a) Thickness is 2.0μm-7.0μm; b) Puncture strength ≥390 gf; c) Porosity ≤ 20%; d) Air permeability (Gurley value) ≥ 999 seconds / 100 ml.

[0015] The preparation method as described above includes: the stretching temperature includes a first stretching temperature and a second stretching temperature, and the first stretching temperature is not greater than the second stretching temperature; the two-dimensional stretching step includes: a first stretching step: at the first stretching temperature, the cast blank is stretched in a first direction to obtain a first stretched blank, with a stretching ratio of 5.0 to 20.0 times; and a second stretching step: at the second stretching temperature, the first stretched blank is stretched in a second direction to obtain the stretched blank, with a stretching ratio of 5.0 to 30.0 times, wherein the second direction is perpendicular to the first direction.

[0016] The preparation method described above, wherein the melting temperature is 180℃~260℃, the first stretching temperature is 70℃~160℃, and the second stretching temperature is 100℃~160℃.

[0017] As described above, the ultra-high molecular weight copolymer includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

[0018] As described above, in the preparation method, the weight-average molecular weight of the first copolymer is not less than 2 million, the weight-average molecular weight of the second copolymer is 1 million to 1.5 million, and the weight-average molecular weight of the third copolymer is 500,000 to 1 million.

[0019] As described above, the preparation method comprises X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5≦X / (Y+Z)≦4.0.

[0020] As described above, the ultra-high molecular weight copolymer satisfies at least one or more of the following: the first copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; the second copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; and the third copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof.

[0021] Another aspect of the present invention is to provide a composite current collector comprising: a first metal layer, a base film layer, and a second metal layer, wherein the first metal layer, the base film layer, and the second metal layer are stacked sequentially, wherein: the base film layer comprises: a substrate structure, which is manufactured from an ultra-high molecular weight copolymer and satisfies at least one or more of the following: a) a thickness of 2.0 μm-7.0 μm; b) a puncture strength ≥390 gf; c) a porosity ≤20%; d) a permeability (Gurley value) ≥999 seconds / 100 ml; a plurality of nanopores arbitrarily distributed on the substrate structure, wherein the channel of any nanopore penetrates both opposite sides of the substrate structure in the thickness direction; and a plurality of metal anchor posts, wherein any metal anchor post is inserted into any nanopore, and both ends of any metal anchor post are respectively connected to the first metal layer and the second metal layer.

[0022] The composite current collector as described above further includes a polymer substrate disposed on one side of the first metal layer relative to the base film layer, or disposed on one side of the second metal layer relative to the base film layer.

[0023] As described above, the composite current collector includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

[0024] As described above, the composite current collector has a weight-average molecular weight of not less than 2 million, a weight-average molecular weight of 1 million to 1.5 million, and a weight-average molecular weight of 500,000 to 1 million.

[0025] As described above, the composite current collector contains X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5≦X / (Y+Z)≦4.0.

[0026] As described above, in the composite current collector, the ultra-high molecular weight copolymer satisfies at least one or more of the following: the first copolymer comprises polyolefin, fluorinated polyolefin, polyether, acrylic polymer, polyester, polyol, or any combination thereof; the second copolymer comprises polyolefin, fluorinated polyolefin, polyether, acrylic polymer, polyester, polyol, or any combination thereof; and the third copolymer comprises polyolefin, fluorinated polyolefin, polyether, acrylic polymer, polyester, polyol, or any combination thereof. As described above, in the composite current collector, the ultra-high molecular weight polyethylene has a viscosity-average molecular weight of not less than 1.5 million, the nanopores have a pore size of 50 to 500 nanometers, and the areal density of the nanopores on the base film layer is 1 × 10⁻⁶. 4 ~1×10 6 pcs / cm 2 .

[0027] The advantage of this invention over previous technologies lies in its precise matching of the requirements of composite current collector preparation process, and the achievement of synergistic optimization of "product-process-application" through structural innovation of the diaphragm base membrane.

[0028] This invention proposes a composite current collector design paradigm of "dense isolation layer combined with in-situ pore formation and mechanical anchoring". It relies on an actively formed three-dimensional physical interlocking structure, which is different from the existing design paradigm of "single porous substrate combined with metal infiltration filling / plating", which relies on interfacial chemical interaction to bond the metal layer. Specifically, this invention proposes a "sandwich" five-layer complex structure of "metal layer-seed layer-base film-seed layer-metal layer", which upgrades the bonding method of the metal layer from relying on interfacial chemical interaction to relying on actively formed three-dimensional physical interlocking, fundamentally improving the bonding reliability.

[0029] The membrane base membrane provided by this invention redefines the "process-carrying membrane base membrane" for composite current collectors, breaking through the limitations of traditional lithium battery membranes that take "ion conduction" as the core design. Through a three-dimensional physical interlocking structure, it achieves ultra-thin, low porosity, and high strength physical properties, fundamentally solving the compatibility contradiction between traditional membranes and composite current collector preparation processes.

[0030] The diaphragm base membrane provided by this invention has low initial porosity (≤20%) and low air permeability (≥999 seconds / 100 ml). During the sputtering stage, it can effectively block the penetration of metal atoms, ensuring the deposition quality of the seed layer and the cleanliness of the equipment. By sputtering through micropores to form metal anchoring columns, it precisely matches the anchoring between the electroplating solution penetration and the metal layer, broadens the process adaptability window, and solves the inherent contradiction between preventing penetration during sputtering and opening holes during electroplating.

[0031] The membrane base provided by this invention has excellent structural reliability, achieving excellent puncture strength (≥390 gf) at an ultra-thin thickness (2.5 μm). Combined with the mechanical interlocking effect of the metal anchor posts, it significantly improves the mechanical robustness of the composite current collector, effectively reducing the short-circuit risk during battery manufacturing and service, and ensuring battery safety performance. At the same time, the two metal layers are interconnected through the anchor posts, exhibiting uniform conductivity.

[0032] The membrane substrate provided by this invention has high electrochemical stability. The dense membrane substrate and the closed interface formed by the metal anchoring column can suppress the side reactions between the electrolyte and the metal layer, reduce the increase of interface impedance, and improve the capacity retention rate of the battery by more than 10% after 1000 cycles.

[0033] The diaphragm base membrane provided by this invention is based on a mature wet-process diaphragm preparation route. Product upgrades can be achieved by adjusting key process parameters such as stretching ratio, without the need for large-scale modification of production equipment, which facilitates rapid industrialization and promotion.

[0034] The diaphragm base membrane provided by this invention is clearly distinguishable from products of similar processes. Compared with the industry's "single porous substrate combined with metal infiltration filling / plating", it achieves a leapfrog improvement in high bonding strength and uniform conductivity on the basis of the same wet process through the mechanical interlocking of dual carrier superposition and metal anchoring columns, realizing a systematic innovation at the three levels of materials, structure and performance. Attached Figure Description

[0035] Figure 1 A flowchart illustrating the preparation method of the diaphragm base membrane for composite current collectors; Figure 2 A flowchart illustrating the detailed process of the two-dimensional stretching procedure. Figure 3 A cross-sectional schematic diagram illustrating the laminated structure of the diaphragm base membrane used for composite current collectors; Figure 4 A flowchart illustrating the preparation method of the composite current collector; Figures 5A-5B These are scanning electron microscope images, showing the cross-sectional thickness and surface porosity of the diaphragm base membrane, respectively. Figure 6 Cartoon illustrations illustrating practical examples of composite current collector preparation methods; Figures 7A-7B The images are scanning electron microscope images, showing the cross-sectional structures of Example 1 and the conventional PET-based film composite metal layer, respectively; and Figures 8A-8B The images are scanning electron microscope images, showing the surface appearance of Example 1 and conventional PET base films after magnetron sputtering. Detailed Implementation

[0036] The following examples, illustrated with figures, illustrate specific embodiments of the present invention.

[0037] The present invention will be described in detail below with reference to specific embodiments. It should be noted that the embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0038] The first embodiment of the present invention is to provide a diaphragm base membrane for composite current collectors, which is manufactured from ultra-high molecular weight copolymers. The term "ultra-high molecular weight" refers to a viscosity-average molecular weight of not less than 500,000, 1.5 million, 2 million, 2.5 million or more.

[0039] In some embodiments, the ultra-high molecular weight copolymer includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

[0040] In a specific embodiment, the weight-average molecular weight of the first copolymer is not less than 2 million, the weight-average molecular weight of the second copolymer is 1 million to 1.5 million, and the weight-average molecular weight of the third copolymer is 500,000 to 1 million; preferably, the weight-average molecular weight of the first copolymer is 2 million to 3 million, the weight-average molecular weight of the second copolymer is 1.5 million to 2 million, and the weight-average molecular weight of the hydrocarbon in the third copolymer is 500,000 to 1 million.

[0041] In a specific embodiment, the ultra-high molecular weight copolymer comprises X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5≦X / (Y+Z)≦4.0; preferably, X is any value between 60 and 80, Y is any value between 10 and 20, and Z is any value between 10 and 20; according to the ratio of ultra-high molecular weight copolymers with different molecular weights, the stability of the material during equipment processing can be effectively improved, the initial plasticizing performance of the material can be guaranteed, and the product thickness design requirements can be taken into account while ensuring that the product has good overall mechanical strength.

[0042] In this embodiment, the first copolymer includes, but is not limited to, polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof, preferably polyolefins; the second copolymer includes, but is not limited to, polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof, preferably polyolefins; the third copolymer includes, but is not limited to, polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof, preferably polyolefins.

[0043] Specifically, the polyolefin is such as polypropylene (PP) or polyethylene (PE), the fluoropolymer is such as polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), the polyether is such as polyethylene oxide (PEO), the acrylic polymer is such as polymethyl methacrylate (PMMA), the polyester is such as polyethylene terephthalate (PET), and the polyol is such as polyvinyl alcohol (PVA); preferably, the polyolefin is polyethylene (PE).

[0044] In several embodiments, the membrane base membrane satisfies at least one or more of the following physical properties: a) The thickness is 2.0μm-7.0μm, which can be 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3.0μm, 4.0μm, 5.5μm, 6.0μm or 7.0μm. All values ​​in the aforementioned range are not exhaustively listed here, but 2.0μm-3.0μm is preferred. b) Puncture strength ≥390 gf, which can be greater than 390 gf, greater than 400 gf, greater than 500 gf, greater than 600 gf, greater than 700 gf, greater than 800 gf, greater than 900 gf, greater than 1000 gf or greater than 1000 gf, preferably 400 gf to 500 gf; c) Porosity ≤20%, which can be 1% to 20%, or 10% to 20%, preferably 11% to 18%; d) Air permeability (Gurley value) ≥ 999 seconds / 100 ml, which can be at least 999 seconds / 100 ml or at least 9999 seconds / 100 ml.

[0045] The second embodiment of the present invention provides a method for preparing a diaphragm base membrane for composite current collectors; please refer to [link to relevant documentation]. Figure 1 The preparation method includes the following steps: Casting step (S1): The melt containing the ultra-high molecular weight copolymer and the pore-forming agent is cast to obtain a sheet-like cast preform, wherein the melt is obtained by blending the ultra-high molecular weight copolymer and the pore-forming agent at a melting temperature; Two-dimensional stretching step (S2): At the stretching temperature, the cast blank is subjected to two-dimensional stretching with a stretching ratio of not less than 5 times to obtain a stretched blank, wherein the stretching temperature is not greater than the melting temperature; Extraction step (S3): The stretched preform is extracted with a volatile solvent to remove the residual pore-forming agent and obtain a diaphragm base film.

[0046] In several embodiments, the melt is obtained by mixing an ultra-high molecular weight copolymer and a pore-forming agent at a solid content of 20% to 30% and then melting them together at a melting temperature; specifically, the weight percentage of the ultra-high molecular weight copolymer and the pore-forming agent is (20 to 30):(80 to 70); the melting temperature can be 180°C to 260°C, for example 180°C to 190°C, 190°C to 200°C, 200°C to 210°C, 210°C to 220°C, 220°C to 230°C, 230°C to 240°C, 240°C to 250°C, or 250°C to 260°C, preferably 220°C to 230°C or 230°C to 240°C.

[0047] The pore-forming agent can be a hydrocarbon that exhibits excellent solubility for ultra-high molecular weight copolymers (such as polyhydrocarbons) at high temperatures. Aliphatic, alicyclic, and aromatic hydrocarbons and their mixtures can also be used as pore-forming agents. The pore-forming agent can be a pure hydrocarbon, such as decane or homologues with higher boiling points, or a mixed hydrocarbon commonly found in petroleum fractions, such as kerosene or fuel oil. Mineral oil or a mixture of mineral oil and dibutyl sebacate can also be used. The pore-forming agent can also be a high-boiling-point hydrocarbon, such as liquid paraffin or solid paraffin. Preferably, the pore-forming agent is a high-boiling-point hydrocarbon.

[0048] In a preferred embodiment, the stretching temperature includes a first stretching temperature and a second stretching temperature, and the first stretching temperature is not greater than the second stretching temperature; please refer to [link / reference]. Figure 2 The two-dimensional stretching step includes: First stretching step (S21): At the first stretching temperature, the cast blank is stretched in a first direction to obtain a first stretched blank, with a stretching ratio of 5.0 to 20.0 times; and Second stretching step (S22): At the second stretching temperature, the first stretching blank is stretched in a second direction to obtain the stretching blank, with a stretching ratio of 5.0 to 30.0 times, wherein the second direction is perpendicular to the first direction.

[0049] In a specific implementation, the first stretching step (S21) is mechanical stretching (MD), with a stretching ratio preferably of 5.0 to 15.0 times; the second stretching step (S22) is transverse stretching (TD), with a stretching ratio preferably of 15.0 to 20.0 times; more preferably, the stretching ratio in the TD direction is greater than the stretching ratio in the MD direction, and the MD stretching ratio is 8.0 to 12.0 times, while the TD stretching ratio is 16.0 to 18.0 times.

[0050] In a specific implementation, the first stretching temperature is 70℃~160℃, which can be 70℃~80℃, 80℃~90℃, 90℃~100℃, 100℃~110℃, 110℃~120℃, 120℃~130℃, 130℃~140℃, 140℃~150℃, or 150℃~160℃, preferably 110℃~120℃ or 120℃~130℃; the second stretching temperature is 100℃~160℃, which can be 100℃~110℃, 110℃~120℃, 120℃~130℃, 130℃~140℃, 140℃~150℃, or 150℃~160℃, preferably 120℃~130℃ or 130℃~140℃; more preferably, the first stretching temperature is lower than the second stretching temperature.

[0051] In several embodiments, the volatile solvent is preferably dichloromethane to extract and remove residual pore-forming agent from the stretched preform, which is then dried and wound up to obtain the diaphragm base membrane.

[0052] A third embodiment of the present invention provides a composite current collector (100), such as... Figure 3 As shown, the composite current collector (100) includes: a first metal layer (1), a base film layer (2) and a second metal layer (3), wherein the first metal layer (1), the base film layer (2) and the second metal layer (3) are stacked sequentially.

[0053] In a general implementation, the base film layer (2) includes a substrate structure (20), a plurality of nanopores (21) and a plurality of metal anchor posts (22), wherein the substrate structure (20) is made of ultra-high molecular weight copolymer and satisfies at least one or more of the following: a) thickness of 2.0 μm-7.0 μm; b) puncture strength ≥390 gf; c) porosity ≤20%; d) air permeability (Gurley value) ≥999 seconds / 100 ml; the plurality of nanopores (21) are arbitrarily distributed on the substrate structure (20), and the channel of any nanopore (21) penetrates through the opposite sides of the substrate structure (20) in the thickness direction; any metal anchor post (22) is inserted into any nanopore (21), and the two ends of any metal anchor post (22) are respectively connected to the first metal layer (1) and the second metal layer (3) to ensure the conductivity of the base film layer (2).

[0054] Specifically, the base film layer (2) is formed in situ on the diaphragm base film by high-energy particles bombarding the diaphragm base film provided in the first embodiment, forming nanopores (21). After being etched by high-energy particles, the residual structure of the diaphragm base film forms a substrate structure (20). High-energy particles are deposited on the two opposite surfaces of the base film layer (2) to form a first metal layer (1) and a second metal layer (3), respectively. The high-energy particles accumulated in the channels of the nanopores (21) gradually grow to form metal anchor pillars (22).

[0055] In various embodiments, the pore size of the nanopores (21) varies, generally falling between 50 and 500 nanometers, to serve as through-holes for the metal anchor post (22), preferably between 100 and 300 nanometers; it is understood that the nanopores (21) can be through holes or blind holes. A "through hole" refers to a pore of the nanopore (21) that connects two opposing surfaces of the substrate structure (20), and a "blind hole" refers to a pore of the nanopore (21) that has an opening at one end on either surface of the substrate structure (20), while the other end extends into the interior of the substrate structure (20) but does not touch the other surface.

[0056] In these embodiments, the areal density of the nanopores (21) on the base film layer (2) is 1×10⁻⁶. 4 ~1×10 6 pcs / cm 2 Preferably 5×10 4 ~5×10 5 pcs / cm 2 .

[0057] In a preferred embodiment, the composite current collector (100) employs a dual-carrier laminated structure; please refer to [further details]. Figure 3 The composite current collector (100) further includes a polymer substrate (4), which is disposed on one side of the first metal layer (1) relative to the base film layer (2), or on one side of the second metal layer (3) relative to the base film layer (2). The material of the polymer substrate (4) is not particularly limited, and can be a PET film, PP film or PI film commonly used in the art. It is directly and tightly bonded to the diaphragm base film, and there is no additional adhesive layer between the two. The two functions work together, with the polymer substrate providing a rigid support skeleton, and the diaphragm base film bearing metal deposition and isolating and protecting the polymer substrate (4) from metal contamination.

[0058] In a preferred embodiment, the base film layer (2) is uniformly distributed with nanopores (21) that completely penetrate its upper and lower surfaces; the nanopores (21) are formed by in-situ etching on the surface of the diaphragm base film, specifically by sputtering to drive high-energy particles to bombard the diaphragm base film; during the high-energy particle bombardment, the seed layer of the first metal layer (1) gradually accumulates and covers the base film layer (2), forming the interface between the base film layer (2) and the polymer substrate (4); the seed layer of the second metal layer (3) gradually accumulates and covers the other outer surface of the base film layer (2) relative to the polymer substrate (4); furthermore, during the thickening of the metal layer, the above-mentioned seed layer... The layers gradually thicken into a first metal layer (1) and a second metal layer (3), while metal ions continue to grow in the channels of the nanopores (21) generated by etching, eventually forming a metal anchor post (22) connecting the first metal layer (1) and the second metal layer (3). The metal anchor post (22) forms a strong mechanical interlocking structure with the dense substrate structure (20). Its length is equivalent to the thickness of the base film layer (2), and its diameter matches the nanopores (21). Through the metal anchor post (22), the first metal layer (1) and the second metal layer (3) achieve a direct and low-resistance physical connection, ensuring the uniformity and integrity of the conductive network on both sides of the composite current collector (100).

[0059] Please refer to the specific implementation plan. Figure 4 The method for preparing the composite current collector (100) includes: Dual-carrier lamination step (A1): The diaphragm base film provided in the first embodiment is directly laminated with the polymer substrate to form a dual-carrier composite preform without an adhesive layer; Sputtering step (A2): Using the surface of the diaphragm base film relative to the polymer substrate as the metal deposition side, high-energy particles are used to bombard the metal deposition side to form a seed layer. Simultaneously, the high-energy particles are continuously used to bombard the metal deposition side to etch the diaphragm base film, forming a substrate structure and multiple nanopores distributed within the substrate structure. The seed layer simultaneously covers the surface of the polymer substrate, the surface of the substrate structure, and the inner walls of the nanopores, forming a seed layer-dual-carrier composite preform; and Electroplating thickening and anchoring step (A3): The seed layer-dual carrier composite preform is brought into contact with the electroplating solution, so that the metal ions contained in the electroplating solution permeate through the nanopores to both sides of the substrate structure. The metal ions are plated on the surface of the seed layer and the inner wall of the nanopores to form a first metal layer, a second metal layer and a metal anchoring post penetrating the nanopores. The two ends of the metal anchoring post are respectively connected to the first metal layer and the second metal layer.

[0060] The term "sputtering" refers to Physical Vapor Deposition (PVD) technology, which uses ions in plasma to bombard a target material, causing the target atoms or molecules to be sputtered and deposited on the substrate surface to form a thin film.

[0061] In specific implementations, the sputtering may include, but is not limited to, DC sputtering, RF sputtering, magnetron sputtering, reactive sputtering, ion beam sputtering, pulsed DC sputtering, and high power impulse magnetron sputtering (HiPIMS), or any combination thereof; preferably, the sputtering is performed by magnetron sputtering.

[0062] In these embodiments, the high-energy particles can be plasma derived from highly conductive metals, such as gold, silver, copper, or aluminum; the metal ions can be derived from the same metal as the target material or a different metal, preferably the same metal, such as copper.

[0063] In this embodiment, the ultra-low initial porosity (≤20%) of the separator base film can effectively block metal atoms from penetrating into the polymer substrate during the initial sputtering stage, thus avoiding contamination of the polymer substrate; the ultra-high puncture strength (≥400gf) of the separator base film ensures the structural integrity of the dual carrier structure throughout the entire process of sputtering, electroplating, slitting, and battery assembly; the in-situ formed nanopores provide a seed layer embedded with the nanopores to be accumulated on the surface of the separator base film during the growth of the metal anchoring column, further connecting the channels of the two metal layers, realizing the integrated anchoring interconnection structure of "first metal layer (1) - seed layer - separator base film / metal anchoring column (22) - seed layer - second metal layer (3)"; in terms of the overall structure, the composite current collector (100) forms an integrated three-dimensional physical interlocking structure of "polymer substrate (4) - first metal layer (1) - separator base film / metal anchoring column (22) - second metal layer (3)", solving the problems of weak metal bonding and uneven conductivity of traditional single carrier current collectors.

[0064] The following examples illustrate the technical effects achieved by the present invention. However, these examples are not intended to limit the implementation of the present invention, and the interpretation of the scope of the claims shall be based on the contents of the claims.

[0065] Preparation of diaphragm-based membranes for composite assemblies Example 1:

[0066] (1) Raw materials: Ultra-high molecular weight polyethylene (UHMW-PE) and medical-grade liquid paraffin (pore-forming agent) are prepared and blended at a mass ratio of 25:75. Among them, UHMW-PE is a ternary compound formula containing 60%~80% 2×10 6 Ultra-high molecular weight polyethylene (UHMWPE) with a specification of g / mol, containing 10%~20% 1.5×10 6 Ultra-high molecular weight polyethylene (UHMWPE) with specifications of g / mol, 10%~20% of 0.6×10 6 Ultra-high molecular weight polyethylene with a g / mol specification and an average weight-average molecular weight of 1.62 million to 1.81 million.

[0067] (2) Preparation process: (2.1) Casting step: UHMW-PE and liquid paraffin are fed into a twin-screw extruder and melt-blended at 230°C to obtain a melt. After degassing, the melt is extruded through a T-die and cast onto a 25°C cooling roller to form a sheet-like cast preform with a thickness of about 100μm. (2.2) Longitudinal stretching (MD): The above cast blank is fed into a longitudinal stretching machine and stretched 10 times at 125°C to obtain the first stretched blank; (2.3) Transverse stretching (TD): The first stretched billet is fed into a transverse tenter frame and stretched 17 times at 135°C to obtain a stretched billet; (2.4) Extraction and drying: The stretched preform is immersed in dichloromethane solvent to extract and remove residual liquid paraffin. Then it is dried with hot air and wound up to obtain the finished diaphragm base film.

[0068] Please refer to Figures 5A-5B Scanning electron microscopy (SEM) images of the diaphragm base membrane showed that the thickness of the diaphragm base membrane was about 2.5 μm, and that the number of surface pores was small and the porosity was low.

[0069] Example 2:

[0070] The raw materials, preparation process, and process parameters used are basically the same as those in Example 1. The difference lies in the fine adjustment and reduction of the tensile tension in the MD process, and the thickness of the finished diaphragm base film is 2.6 μm.

[0071] Example 3:

[0072] The raw materials, preparation process, and process parameters used were basically the same as in Example 1. The difference was that the extraction outlet was retracted, and the thickness of the resulting diaphragm base membrane was 2.6 μm.

[0073] Comparative Example 1: The raw materials, preparation process, and process parameters used are basically the same as those in Example 1. The difference is that the longitudinal stretching (MD) ratio is 10 times and the transverse stretching (TD) ratio is 10 times, and the thickness of the finished diaphragm base film is 5 μm.

[0074] Comparative Example 2: The raw materials, preparation process, and process parameters used were basically the same as those of Comparative Example 1. The differences were that the MD stretching ratio was 9.5 times, the MD stretching temperature was 105℃, the TD stretching ratio was 10 times, the TD stretching temperature was 130℃, and the thickness of the finished diaphragm base film was 7μm.

[0075] Comparative Example 3: The raw materials, preparation process, and process parameters used were basically the same as those of Comparative Example 1. The difference was that the MD stretching ratio was 9 times, the MD stretching temperature was 100℃, the TD stretching ratio was 9 times, and the TD stretching temperature was 120℃, resulting in a finished diaphragm base film thickness of 9μm.

[0076] Comparative Example 4: The raw materials, preparation process, and process parameters used are basically the same as those in Example 1. The difference is that the average weight-average molecular weight of UHMW-PE is 400,000 to 1,200,000, and the thickness of the finished membrane base film is 3 μm.

[0077] Comparative Example 5: The raw materials, preparation process, and process parameters used are basically the same as those in Example 1. The difference is that the average weight-average molecular weight of UHMW-PE is 2 million, and the thickness of the finished membrane base film is 3 μm.

[0078] Comparative Example 6: The raw materials, preparation process, and process parameters used are basically the same as those in Example 1. The difference is that the MD stretching temperature is <100℃, the TD stretching temperature is <110℃, and the thickness of the finished diaphragm base film is 4μm.

[0079] Comparative Example 7: The preparation process and process parameters are basically the same as in Example 1, except that the ultra-high molecular weight copolymer uses a binary compound formulation containing 50% 2×10 6 g / mol specification of ultra-high molecular weight polyethylene and 50% of 1.5×10 6 Ultra-high molecular weight polyethylene with a g / mol specification and an average weight-average molecular weight of 1.75 million; it breaks down during extraction and cannot form a film.

[0080] Comparative Example 8: The preparation process and parameters are basically the same as those of Comparative Example 1, except that the ultra-high molecular weight copolymer uses a binary compound formulation containing 50% 2.5×10 6 g / mol specification of ultra-high molecular weight polyethylene and 50% of 1.5×10 6 Ultra-high molecular weight polyethylene with a g / mol specification and an average weight-average molecular weight of 2 million; it breaks down during extraction and cannot form a film.

[0081] Comparative Example 9: The preparation process and parameters are basically the same as those in Comparative Example 1, except that the ultra-high molecular weight copolymer uses a binary compound formulation containing 50% 1.5×10 6 g / mol specification of ultra-high molecular weight polyethylene and 50% of 0.6×10 6 Ultra-high molecular weight polyethylene with a g / mol specification and an average weight-average molecular weight of 1.05 million; it breaks down during extraction and cannot form a film.

[0082] Comparative Example 10: The preparation process and parameters are basically the same as in Example 1, except that the ultra-high molecular weight copolymer uses a binary compound formulation containing 50% 2.0×10 6 g / mol specification of ultra-high molecular weight polyethylene and 50% of 0.6×10 6 Ultra-high molecular weight polyethylene with a g / mol specification and an average weight-average molecular weight of 1.3 million; it breaks down during extraction and cannot form a film.

[0083] Basic Performance Testing The basic performance tests of the diaphragm base membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were conducted. The test standards and results are shown in Table 1 below. The thickness of the diaphragm base membrane was basically tested according to the test standard of GB / T 30731, the puncture strength was tested according to the test standard of GB / T 36363, the porosity was determined by the "gravimetric method", the air permeability was tested according to the test standard of GB / T 36363, the nanopore size was tested according to the test standard of GB / T 36363-2021, and the areal density was tested according to the test standard of GB / T 16594-2008.

[0084] Table 1

[0085] It should be noted that Examples 1 to 3 all used ternary compound formulations, and the test results showed that the film-forming state was good. Comparative Examples 7 to 10 all used binary compound formulations of two materials with different molecular weight specifications. Regardless of the binary combination, the technical problems of extraction film breakage and inability to form a film occurred. The two formed a significant technical comparison, which confirmed the superiority of the ternary compound system used in this invention.

[0086] In the ternary compound formulation of this invention, three materials with different molecular weights each perform their respective functions to achieve synergistic effects, among which the high molecular weight specification (2×10) 6 Materials with a molecular weight of g / mol or higher serve as the main component of the system. Leveraging their high viscosity-average molecular weight, they form a strongly entangled molecular chain framework, providing core fluid structural stability for the processing. This is fundamental to suppressing fluid chain breakage and ensuring the mechanical strength of the base film, while also providing structural support for product thickness design. Medium molecular weight materials (1.5 × 10⁻⁶ g / mol) form the core component of the system. 6 Materials with a molecular weight of g / mol (g / mol) serve as transitional harmonizing components, bridging high and low molecular weight phase regions. This effectively improves the compatibility between components of different molecular weights, alleviates local shear stress concentration during processing, and prevents fluid instability caused by local molecular chain breakage, playing a crucial bridging and synergistic role. Low molecular weight specifications (0.6 × 10⁻⁶ g / mol) are used as transitional harmonizing components, connecting high and low molecular weight phase regions, effectively improving the compatibility between components of different molecular weights, alleviating the problem of local shear stress concentration during processing, and avoiding fluid instability caused by local molecular chain breakage. 6 The material (g / mol) is used as a plasticizing regulator to optimize the initial plasticizing performance of the material, broaden the processing window, improve melt ductility, avoid fluid chain breakage caused by uneven plasticizing, and ensure the continuity of the film formation process. The multi-molecular weight distribution system constructed by the above three components inhibits the phenomenon of fluid chain breakage during processing from the root. However, the binary compound system, due to the lack of any key component, cannot balance the stability of the processing fluid, component compatibility and plasticizing properties, ultimately resulting in the inability to form a film.

[0087] Application Effectiveness Verification Please refer to Figure 6 The preparation method of the composite current collector is explained in detail below: (A) Dual-carrier lamination step: The diaphragm base film prepared in Examples 1 to 3 and Comparative Examples 1 to 6 is directly laminated with a PET film with a thickness of 12 μm to form a dual-carrier composite preform without an adhesive layer; (B) Sputtering step: The side of the diaphragm base film opposite to the PET film is used as the metal deposition side. The magnetron sputtering power is set to 1000 watts to 1500 watts, so that the plasma bombards the copper target. The sputtered copper atoms continuously bombard the metal deposition side to form a seed layer with a thickness of about 50 nm. Multiple nanopores are etched in situ. The seed layer covers the surface of the PET film, the surface of the substrate structure and the inner wall of the nanopores to obtain a seed layer-dual carrier composite preform. (C) Electroplating thickening and anchoring steps: The seed layer-dual carrier composite preform is immersed in an electroplating solution containing copper ions, allowing the copper ions to penetrate through the nanopores to both sides of the substrate structure. The metal ions are plated on the surface of the seed layer and the inner wall of the nanopores, forming a copper layer with a final thickness of about 2 μm on both sides of the diaphragm substrate film, and copper pillars penetrating the nanopores. The two ends of the copper pillars are connected to the copper layers on both sides, respectively, to obtain a composite current collector.

[0088] Please refer to Table 2 below. The membrane base films of Examples 1 to 3, due to their low porosity (porosity ≤18%), can effectively block copper atoms from penetrating. The prepared composite current collectors do not show any visible metal penetration. Examples 2 and 3, due to their even lower porosity (11% to 12%) and high air permeability (9999 s / 100 ml), have even better blocking effects. The PET membrane surfaces of these examples remain clean, and the copper layer is only uniformly deposited on the membrane surface. In contrast to Examples 1 to 3, the membrane base films of Comparative Examples 1 to 6, due to their higher porosity (33% to 39%), all show varying degrees of metal penetration in the prepared composite current collectors, and obvious copper layer deposition is visible on the PET membrane surface.

[0089] Please see Figure 7A and 7B The cross-sectional structures of the composite current collector manufactured in Example 1 and the composite current collector manufactured by combining a conventional PET base film with copper foil are presented respectively; Figure 7A It is evident that after the sputtering process, multiple nanopores are etched in situ on the diaphragm base film, while the copper layer formed in the electroplating thickening and anchoring process and the in situ seed layer are embedded in the diaphragm base film and tightly connected to it.

[0090] Please see again Figure 8A and 8B They respectively demonstrate the surface metal deposition effect of the diaphragm base film of Example 1 and the traditional PET base film after magnetron sputtering; by Figure 8A It is clearly visible that, due to its low porosity, the metal deposited on the surface of the membrane base film in Example 1 is relatively uniformly distributed, while Figure 8BIt is clear that the high porosity of traditional PET base films leads to relatively concentrated metal deposition.

[0091] Furthermore, the above composite current collector was assembled into a simple stacked battery, and the following performance tests were conducted. The test results are shown in Table 2 below.

[0092] (1) Mechanical performance testing: The composite current collectors prepared from the diaphragm base membranes of Examples 1 to 3 were tested according to GB / T36363-2018, and their puncture strength remained above 390 gf; when the peel test was conducted according to GB / T 2792-2014, there was still no interfacial delamination when the strength reached 128 N / m; according to GB / T20313-2021, with the failure mode being substrate or metal layer body fracture, its bending resistance was tested to be above 500 cycles; compared with Examples 1 to 3 above, under the same test standards, the composite current collectors prepared from the diaphragm base membranes of Comparative Examples 1, 4 to 6 had a puncture strength of at most 330 gf, and a peel strength of 25 N / m to 28 N / m. When the diaphragm base membrane reaches N / m, the metal layer peels off from the surface of the diaphragm base membrane. The bending resistance does not exceed 50 times, and the metal layer also shows local cracks and detachment. In addition, although the puncture strength of the composite current collectors prepared by the diaphragm base membranes of Comparative Examples 2 and 3 reached 476 gf and 453 gf respectively, the peel strength was only 23 N / m and 19 N / m, and the bending resistance was only 50 times and 43 times.

[0093] (2) Electrical performance test: The sheet resistance coefficient of the composite current collectors prepared from the separator base film of Examples 1 to 3 was calculated with reference to the formula: CV = standard deviation / average value * 100%. Overall, it was no more than 3.2%, and the conductivity was uniform. The sheet resistance coefficient of the composite current collectors prepared from the separator base film of Comparative Examples 1 to 6 was about 4.3% to 10.5%, and the conductivity on both sides was significantly different. In addition, the cycle capacity retention rate of the batteries assembled with the above composite current collectors was tested with reference to GB / T457 ISO 626 standard. The overall battery cycle capacity retention rate of Examples 1 to 3 was maintained above 90%, while that of Comparative Examples 1 to 6 was no more than 75%.

[0094] (3) Needle penetration safety test: The needle penetration safety test was conducted in accordance with GB 38031-2020. The composite current collectors assembled with the separator base film of Examples 1 to 3 showed no voltage drop or significant temperature rise during the needle penetration process and no thermal runaway occurred. The batteries of Examples 2 and 3 showed better stability. The batteries assembled with the composite current collectors prepared with the separator base film of Comparative Examples 1 to 2 showed a slight voltage drop and a small temperature rise after needle penetration, but no serious thermal runaway occurred. The battery assembled with the composite current collector prepared with Comparative Example 3 showed a sharp voltage drop and a significant temperature rise after needle penetration, and short-circuit thermal runaway occurred. The batteries assembled with the composite current collectors prepared with Comparative Examples 4 to 6 also failed the needle penetration safety test.

[0095] Table 2

[0096] The beneficial effects of the diaphragm base membrane provided by this invention on the performance of the composite current collector are summarized as follows: (1) Suppressing metal penetration: The membrane substrate provided by the present invention has low porosity (not greater than 20%), which can block metal atoms from penetrating during magnetron sputtering and avoid contamination of polymer substrate; the porosity of traditional substrate membranes is generally around 35%, and metal can easily penetrate and deposit on the surface of polymer substrate, resulting in contamination.

[0097] (2) Improved mechanical strength: The diaphragm base membrane provided by the present invention has high puncture strength, making the overall strength of the composite current collector not less than 390 gf, the peel strength not less than 128 N / m, and the bending resistance is also greatly improved, fundamentally solving the problem of easy delamination and damage of current collectors made by traditional base membranes.

[0098] (3) Optimization of conductivity uniformity: The diaphragm base membrane provided by the present invention has a mechanical interlocking structure formed by low porosity and metal anchoring columns, so that the sheet resistance variation coefficient of the composite current collector is no more than 3%, which is far superior to the current collector manufactured by traditional high porosity wet process base membrane (sheet resistance variation coefficient is no less than 4.3%).

[0099] (4) Safety and Cyclic Performance Guarantee: The separator base membrane provided by this invention has high air permeability (Gurley value not less than 999 s / 100ml), and combined with the metal anchoring structure formed by magnetron sputtering, the battery cycle capacity is not less than 90%, and the battery thermal runaway is effectively prevented, solving the problems of capacity decay and thermal runaway of traditional base membranes.

[0100] The above content involving common knowledge will not be described in detail, as those skilled in the art will understand.

[0101] The embodiments described above are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A diaphragm base membrane for composite current collectors, characterized in that, Made from ultra-high molecular weight copolymers, and satisfying at least one or more of the following: a) Thickness is 2.0μm-7.0μm; b) Puncture strength ≥390 gf; c) Porosity ≤ 20%; d) Air permeability (Gurley value) ≥ 999 seconds / 100 ml.

2. The diaphragm base membrane according to claim 1, characterized in that, The ultra-high molecular weight copolymer includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

3. The diaphragm base membrane as described in claim 2, characterized in that, The first copolymer has a weight-average molecular weight of not less than 2 million, the second copolymer has a weight-average molecular weight of 1 million to 1.5 million, and the third copolymer has a weight-average molecular weight of 500,000 to 1 million.

4. The diaphragm base membrane as described in claim 2, characterized in that, The ultra-high molecular weight copolymer comprises X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5 ≦ X / (Y+Z) ≦ 4.

0.

5. The diaphragm base membrane according to claim 2, characterized in that, The ultra-high molecular weight copolymer satisfies at least one or more of the following: The first copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; The second copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; The third copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof.

6. A method for preparing a diaphragm-based membrane for composite current collectors, characterized in that, Includes the following steps: Casting step: The melt containing the ultra-high molecular weight copolymer and the pore-forming agent is cast to obtain a sheet-like cast preform, wherein the melt is obtained by mixing the ultra-high molecular weight copolymer and the pore-forming agent at a melting temperature; Two-dimensional stretching step: At a stretching temperature, the cast preform is subjected to two-dimensional stretching with a stretching ratio of not less than 5 times to obtain a stretched preform, wherein the stretching temperature is not greater than the melting temperature; Extraction step: The stretched preform is extracted with a volatile solvent to remove residual pore-forming agent, thereby obtaining a diaphragm base membrane, wherein the diaphragm base membrane satisfies at least one or more of the following: a) Thickness is 2.0μm-7.0μm; b) Puncture strength ≥390 gf; c) Porosity ≤ 20%; d) Air permeability (Gurley value) ≥ 999 seconds / 100 ml.

7. The preparation method according to claim 6, characterized in that: The stretching temperature includes a first stretching temperature and a second stretching temperature, and the first stretching temperature is not greater than the second stretching temperature. The two-dimensional stretching step includes: First stretching step: At the first stretching temperature, the cast blank is stretched in a first direction to obtain a first stretched blank with a stretching ratio of 5.0 to 20.0 times; Second stretching step: At the second stretching temperature, the first stretching blank is stretched in a second direction to obtain the stretching blank, with a stretching ratio of 5.0 to 30.0 times, wherein the second direction is perpendicular to the first direction.

8. The preparation method according to claim 7, characterized in that... The melting temperature is 180℃~260℃, the first stretching temperature is 70℃~160℃, and the second stretching temperature is 100℃~160℃.

9. The preparation method according to claim 7, characterized in that, The ultra-high molecular weight copolymer includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

10. The preparation method according to claim 9, characterized in that, The first copolymer has a weight-average molecular weight of not less than 2 million, the second copolymer has a weight-average molecular weight of 1 million to 1.5 million, and the third copolymer has a weight-average molecular weight of 500,000 to 1 million.

11. The preparation method according to claim 9, characterized in that, The ultra-high molecular weight copolymer comprises X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5 ≦ X / (Y+Z) ≦ 4.

0.

12. The preparation method according to claim 9, characterized in that, The ultra-high molecular weight copolymer satisfies at least one or more of the following: The first copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; The second copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; The third copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof.

13. A composite current collector, characterized in that, include: A first metal layer, a base film layer, and a second metal layer are sequentially stacked, wherein: The base film layer comprises: The substrate structure is manufactured from ultra-high molecular weight copolymers and satisfies at least one or more of the following: a) Thickness is 2.0μm-7.0μm; b) Puncture strength ≥390 gf; c) Porosity ≤ 20%; d) Air permeability (Gurley value) ≥ 999 seconds / 100 ml; Multiple nanopores are arbitrarily distributed on the substrate structure, and the channel of any one of the nanopores penetrates both opposite sides of the substrate structure in the thickness direction; and Multiple metal anchor posts are provided, each of which is inserted into any of the nanopores, and each of the metal anchor posts is connected to the first metal layer and the second metal layer at both ends.

14. The composite current collector according to claim 13, characterized in that, It also includes a polymer substrate disposed on one side of the first metal layer relative to the base film layer, or disposed on one side of the second metal layer relative to the base film layer.

15. The composite current collector according to claim 13, characterized in that, The ultra-high molecular weight copolymer includes a first copolymer, a second copolymer, and a third copolymer, wherein the weight-average molecular weight of the first copolymer is greater than that of the second copolymer, and the weight-average molecular weight of the second copolymer is greater than that of the third copolymer.

16. The composite current collector as described in claim 15, characterized in that, The first copolymer has a weight-average molecular weight of not less than 2 million, the second copolymer has a weight-average molecular weight of 1 million to 1.5 million, and the third copolymer has a weight-average molecular weight of 500,000 to 1 million.

17. The composite current collector as described in claim 15, characterized in that, The ultra-high molecular weight copolymer comprises X parts by mass of the first copolymer, Y parts by mass of the second copolymer, and Z parts by mass of the third copolymer, wherein X, Y, and Z are any values ​​greater than 0, and satisfy the relationship: 1.5 ≦ X / (Y+Z) ≦ 4.

0.

18. The composite current collector according to claim 15, characterized in that, The ultra-high molecular weight copolymer satisfies at least one or more of the following: The first copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; The second copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof; The third copolymer includes polyolefins, fluorinated polyolefins, polyethers, acrylic polymers, polyesters, polyols, or any combination thereof.

19. The composite current collector according to claim 13, characterized in that, The pore size of the nanopores is 50 to 500 nanometers, and the areal density of the nanopores on the base film layer is 1 × 10⁻⁶. 4 ~1×10 6 pcs / cm 2 .

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