Composite current collector base membrane, preparation method thereof, composite current collector, electrode plate and electrochemical device

Abstract

The invention provides a composite current collector base membrane, a preparation method thereof, a composite current collector, an electrode plate and an electrochemical device, relates to the technical field of composite current collector preparation, and is particularly suitable for the technical field of battery preparation. The composite current collector base film comprises an insulating layer and a gradient strengthening structure arranged on at least one surface of the insulating layer; the gradient strengthening structure sequentially comprises an organic hardened layer, a hybrid hardened layer and an inorganic hardened layer from the surface of the insulating layer to the outside; wherein the Young modulus and the hardness of the organic hardened layer, the hybrid hardened layer and the inorganic hardened layer are gradually increased in sequence. According to the composite current collector, the strengthening function layer with the modulus and the hardness gradually increased from inside to outside is stacked on the surface of the insulating layer, an interface transition area with small connection difference is formed, the surface hardness and the overall rigidity of the base film of the composite current collector are effectively enhanced, and the composite current collector is prepared.

Description

Technical Field

[0001] This invention relates to the field of composite current collector preparation technology, and in particular to a composite current collector base film, its preparation method, the composite current collector, electrode sheet, and electrochemical device. Background Technology

[0002] Current collectors are a crucial component of batteries, used to collect the current generated by the battery's active materials to form a larger output current. Their performance directly affects the battery's cycle life, energy density, and safety. Currently, aluminum foil and copper foil are commonly used as current collectors in lithium-ion and sodium-ion batteries, but these types of current collectors are not conducive to controlling battery costs and improving energy density. Composite current collectors have significant advantages over traditional foil current collectors. Composite current collectors typically have a "sandwich" structure, with an inner polymer insulating layer and metal conductive layers on both sides. Because the metal layer on the surface of the composite current collector is thinner and the inner polymer layer is lighter, it can significantly reduce the overall weight of the current collector, thereby increasing the energy density of the lithium-ion battery.

[0003] However, existing composite current collectors, due to significant differences in the rigidity, surface hardness, and other material properties of their polymer insulating layer compared to the metal coating, exhibit substantial differences in interfacial properties. This makes them prone to metal layer detachment after high-pressure compaction rolling. In particular, for composite aluminum foil current collectors, their low overall rigidity results in poor pressure resistance. Under the pressure system required for high-pressure compaction of the positive electrode active material, repeated deformations make them more susceptible to cracking and damage of the polymer insulating layer. Furthermore, lithium-ion batteries are prone to internal short circuits when subjected to abnormal conditions such as squeezing, collision, or puncture, which can cause the battery to catch fire or even explode. Although current composite current collectors contain a polymer insulating layer that can block electron transmission to some extent during puncture, the hardness of the polymer insulating layer material is generally low. When a nail or internal puncture occurs, the metal layer cannot be directly broken or fragmented to form an open circuit. The metal layer still retains a certain conductivity, and the battery temperature continues to rise, posing a risk of thermal runaway. At this time, the short-circuit current is easily conducted to a wide area near the puncture area, expanding the short-circuit area and reducing the pass rate of the nail penetration test and the safety of the battery. Summary of the Invention

[0004] One of the objectives of this invention is to provide a composite current collector base film to at least solve one of the technical problems existing in the prior art.

[0005] The second objective of this invention is to provide a method for preparing a composite current collector base film.

[0006] The third objective of this invention is to provide a composite current collector.

[0007] The fourth objective of this invention is to provide an electrode sheet.

[0008] The fifth objective of this invention is to provide an electrochemical device.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a composite current collector base film, comprising: an insulating layer, and a gradient reinforcement structure disposed on at least one surface of the insulating layer; the gradient reinforcement structure comprises, from the surface of the insulating layer outward, an organic curing layer, a hybrid curing layer and an inorganic curing layer; The Young's modulus and hardness of the organic hardening layer, the hybrid hardening layer, and the inorganic hardening layer increase sequentially.

[0010] Furthermore, the composite current collector base film satisfies at least one of the following conditions: (1) The thickness of the insulating layer is 4μm-8μm; (2) The insulating layer is made of one or more of polyimide, polyethylene, polypropylene and polyethylene terephthalate; (3) The Young's modulus of the insulating layer is 2 GPa-8 GPa, and the hardness is 10 HV-40 HV; (4) The thickness of the organic hardening layer is 100nm-1000nm; (5) The Young's modulus of the organic hardened layer is 5GPa-10GPa, and the hardness is 80HV-150HV; (6) The thickness of the hybrid hardened layer is 100nm-1000nm; (7) The Young's modulus of the hybrid hardened layer is 10 GPa-50 GPa, and the hardness is 200 HV-300 HV; (8) The thickness of the inorganic hardening layer is 10nm-100nm; (9) The Young's modulus of the inorganic hardened layer is 200 GPa-300 GPa and the hardness is 1000 HV-1500 HV.

[0011] In a second aspect, the present invention provides a method for preparing a composite current collector base film, comprising: sequentially stacking an organic curing layer, a hybrid curing layer and an inorganic curing layer on at least one surface of the insulating layer.

[0012] Furthermore, before preparing the organic curing layer on the insulating layer, the method further includes: activating the surface of the insulating layer; The activation process step satisfies at least one of the following conditions: (1) The activation treatment includes one or more of corona treatment and plasma treatment; (2) The power of the corona treatment is 10-50 W·min / m 2 The surface tension of the treated insulation layer is 45 dyn / cm - 50 dyn / cm. (3) The gas used for plasma treatment is a mixture of oxygen and argon, with a vacuum degree of 0.01-0.1 Pa and a radio frequency power of 0.1-10 kW; Preferably, the flow rate ratio of the oxygen to the argon is 1:(1-2).

[0013] Furthermore, the organic curing layer is obtained by coating the insulating layer with a first coating liquid and then curing it. The components of the first coating liquid, by weight percentage, include: 30%-50% high-functionality prepolymer, 20%-40% reactive diluent, 3%-5% interfacial coupling agent, 2%-4% photoinitiator, 0.1%-2% functional additives, and the balance being solvent.

[0014] Furthermore, the hybrid hardening layer is obtained by coating the organic hardening layer with a second coating liquid and then curing it; The second coating liquid comprises, by weight percentage: 20%-40% high-functionality prepolymer, 20%-35% functionalized sol, 10%-25% reactive diluent, 3%-5% interfacial coupling agent, 2%-4% photoinitiator, 0.1%-2% functional additives, with the balance being solvent; Preferably, the functionalized sol includes silica sol; Preferably, the particle size of the functionalized sol is 5nm-50nm.

[0015] Furthermore, the first coating liquid and the second coating liquid satisfy at least one of the following conditions: (1) The high-functionality prepolymers in the first coating liquid and the second coating liquid are each independently selected from one or more of epoxy acrylate, polyurethane acrylate, polyester acrylate, amino acrylate and unsaturated polyester. (2) The active diluents in the first coating liquid and the second coating liquid are each independently selected from one or more of the following: tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, ethylene glycol diglycidyl ether diacrylate, propoxylated trihydroxypropane triacrylate, ethoxylated trihydroxypropane triacrylate, pentaerythritol tetraacrylate, ditrihydroxypropane tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate; (3) The interfacial coupling agents in the first coating liquid and the second coating liquid are each independently selected from one or more of γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane and γ-mercaptopropyltrimethoxysilane; (4) The photoinitiators in the first coating liquid and the second coating liquid are each independently selected from one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 1-hydroxy-cyclohexyl benzophenone, benzoin dimethyl ether, isopropylthioxanthone, 4-methylbenzophenone, 4-phenylbenzophenone, and benzyl dimethyl aminoethyl ester. (5) The functional additives in the first coating liquid and the second coating liquid are each independently selected from one or more of leveling agents and antioxidants; Preferably, the leveling agent includes one or more of fluorocarbon compound leveling agents, silicone leveling agents, acrylic leveling agents, and cellulose acetate butyrate leveling agents; Preferably, the antioxidant includes one or more of butylated hydroxytoluene, butylated hydroxyanisole, ethylenediaminetetraacetic acid, and tert-butylhydroquinone; (6) The solvents in the first coating liquid and the second coating liquid are each independently selected from one or more of ethyl acetate, isopropanol, methanol, ethanol, isopropanol, tert-butanol, H2O, n-propyl acetate, n-butyl acetate, acetone, butanone and methyl isobutyl ketone.

[0016] Furthermore, the curing is gradient curing, which includes sequential infrared drying, hot air drying, and ultraviolet irradiation. Preferably, the infrared drying temperature is 40℃-70℃; Preferably, the temperature of the hot air drying is 60℃-100℃; Preferably, the energy of the ultraviolet irradiation is 300 mJ / cm². 2 -1000mj / cm 2 .

[0017] Furthermore, the inorganic hardening layer is formed on the surface of the hybrid hardening layer by vacuum evaporation deposition or magnetron sputtering deposition. Preferably, when vacuum evaporation coating is used, the vacuum degree at the start of the coating process is 1×10⁻⁶. -2 Pa-4×10 -2Pa, oxygen flow rate 1000 sccm-3000 sccm, argon flow rate 500 sccm-1000 sccm, winding speed 200 m / min-800 m / min, wire feeding speed 100 m / min-200 m / min, winding tension 150 N-200 N, unwinding tension 210 N-230 N, ion source voltage 1000 V-2000 V, cold roller temperature 0 ℃-20 ℃.

[0018] Thirdly, the present invention provides a composite current collector, comprising a composite current collector base film and a metal layer located on at least one side of the composite current collector base film; the composite current collector base film is the aforementioned composite current collector base film or a composite current collector base film prepared by the aforementioned preparation method. Fourthly, the present invention provides an electrode sheet comprising the aforementioned composite current collector.

[0019] Fifthly, the present invention provides an electrochemical device comprising the aforementioned electrode sheet.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The composite current collector base film provided by this invention creates a Young's modulus gradient structure on at least one surface of the insulating layer. Within this gradient structure, an organic hardening layer, a hybrid hardening layer, and an inorganic hardening layer are sequentially stacked along the thickness direction, constructing a continuously increasing Young's modulus gradient. This forms stress-relieving channels at the interfaces, effectively dispersing the shear stress at the interlayer interfaces during rolling and significantly suppressing delamination failure between the metal plating layer and the insulating layer. In particular, the continuously increasing Young's modulus stacked structure greatly enhances the overall rigidity of the composite current collector base film, enabling the prepared composite current collector, especially the composite aluminum foil current collector, to exhibit high pressure resistance during battery manufacturing and recycling. Simultaneously, the continuously increasing hardness of the organic hardening layer, the hybrid hardening layer, and the inorganic hardening layer along the thickness direction makes the outermost inorganic hardening layer / metal layer "more brittle and hard." In the needle penetration test, the hard surface layer causes the cracks around the needle tip to localize and expand brittlely, leading to the synchronous and rapid fracture of the metal coating. This cuts off the current path and prevents the large-area diffusion of heat and current, thus fundamentally and significantly improving the pass rate of the battery needle penetration test and the safety of battery use. Detailed Implementation

[0021] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The first aspect of the present invention provides a composite current collector base film, comprising: an insulating layer, and a gradient reinforcement structure disposed on at least one surface of the insulating layer; the gradient reinforcement structure comprises, from the surface of the insulating layer outward, an organic curing layer, a hybrid curing layer and an inorganic curing layer; The Young's modulus and hardness of the organic hardening layer, the hybrid hardening layer, and the inorganic hardening layer increase sequentially.

[0024] The composite current collector base film provided by this invention features a gradient transition of Young's modulus among the functional layers, resulting in a more uniform distribution of interfacial shear stress between the aluminum layer and the base film, reducing the risk of localized delamination. In needle penetration tests, the gradient structure guides the metal layer to crack synchronously, rather than penetrating to the base film, thereby suppressing short-circuit current diffusion. This invention, through the design of the thickness, Young's modulus, and hardness of each functional reinforcement layer, offers significant advantages in interfacial bonding strengthening, modulus gradient control, and synergistic performance of the functional layers. Specifically: 1. In terms of interface bonding strengthening, the bonding between conventional insulating layers and metal plating layers usually relies on physical-mechanical intercalation. However, the overall gradient functional layer design in this invention has different degrees of chemical bonding between layers of different moduli, which can efficiently transfer stress between layers with different moduli and give full play to the characteristics and advantages of each layer.

[0025] 2. Regarding modulus gradient control, conventional composite current collectors are directly composited, resulting in significant abrupt changes in high and low moduli. Under stress, the difference in modulus between layers generates huge shear stress, easily leading to delamination and cracking. In contrast, the overall gradient functional layer design of this invention, by controlling the thickness and modulus parameters of each layer, adopts a continuous gradient distribution of high, medium, and low modulus from the inorganic hardening layer to the organic hardening layer, rather than a direct abrupt change in high / low modulus. This aims to alleviate interlayer stress concentration. This continuous modulus transition design allows stress to be uniformly transmitted along the thickness direction, significantly reducing shear stress and improving the interlayer bonding strength and overall rigidity of the composite material.

[0026] 3. Regarding the synergy of functional layer performance, in conventional composite current collectors, the addition of each functional layer usually interferes with and affects each other, and may even deteriorate the performance of the composite current collector itself. However, this invention adopts interface bonding strengthening, modulus gradient control, and thickness and hardness parameter design of each functional layer to achieve synergy of the performance of each functional layer and overall performance improvement.

[0027] Furthermore, this invention achieves improved surface hardness and overall rigidity by controlling the hardness and modulus parameters of each layer, using a continuous high-medium-low gradient distribution from the alumina coating to the organic hardened layer. Simply increasing the hardness parameters and thickness of the functional layer would easily lead to structural collapse and surface cracking and breakage during processing. Therefore, this invention employs a continuous high-medium-low hardness gradient distribution, reducing the thickness of individual functional layers and simultaneously improving both surface hardness and overall rigidity. For composite current collectors, the metal coating adheres to the surface hardened layer. In battery needle penetration experiments, after the needle penetrates the metal coating, firstly, short radial local microcracks appear at the edge of the puncture hole in the hard surface hardened layer, simultaneously causing cracking of the metal coating and inhibiting the propagation of microcurrents in the local planar direction. Secondly, the puncture hole morphology is stable after penetration, without excessive deformation, and the hole size matches the needle diameter, preventing non-contact adhesion between the current collector and the separator / electrode due to excessive deformation, thus reducing the possibility of short circuits from the source. Third, traditional soft composite current collectors, due to their inherent flexibility, undergo ductile tearing as the needle moves after puncture, leading to further damage and increasing the risk of active material leakage and contact between the positive and negative electrodes. Fourth, high-hardness current collectors have significantly higher puncture resistance (puncture force) than soft current collectors. The needle must overcome greater resistance during puncture, resulting in shallower puncture depth and reduced overall impact on the device's internal structure. This reduces the degree of damage to the internal diaphragm and electrodes, indirectly improving puncture safety.

[0028] In some preferred embodiments, the thickness of the insulating layer is 4μm-8μm, for example, it can be 4μm, 5μm, 6μm, 7μm, 8μm, etc.; Preferably, the insulating layer is made of one or more of polyimide, polyethylene, polypropylene, and polyethylene terephthalate; the Young's modulus of the insulating layer is 2-8 GPa, for example, 2 GPa, 3 GPa, 4 GPa, 5 GPa, 6 GPa, 7 GPa, 8 GPa, etc., and the micro Vickers hardness is 10-40 HV, for example, 10 HV, 20 HV, 30 HV, 40 HV, etc.; wherein, the Young's modulus of PET is 2-6 GPa, and the Young's modulus of the polyimide (PI) base film is 5-8 GPa.

[0029] Preferably, the Young's modulus of the insulating layer is less than that of the organic curing layer.

[0030] Preferably, the thickness of the organic hardening layer is 100nm-1000nm, for example, it can be 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc.; the Young's modulus of the organic hardening layer is 5-10GPa, for example, it can be 5GPa, 6GPa, 7GPa, 8GPa, 9GPa, 10GPa, etc.; and the microVickers hardness is 80-150 HV, for example, it can be 80 HV, 90 HV, 100 HV, 110 HV, 120 HV, 130 HV, 140 HV, 150 HV, etc. Specifically, the greater the thickness of the organic hardening layer, the greater its influence on the overall strength and modulus of the composite current collector. Designing the modulus and hardness of the organic hardening layer within this range can effectively transition between the insulating layer and the hybrid hardening layer.

[0031] Preferably, the thickness of the hybrid hardening layer is 100nm-1000nm, for example, it can be 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc.; the Young's modulus of the hybrid hardening layer is 10-50GPa, for example, it can be 10GPa, 20GPa, 30GPa, 40GPa, 50GPa, etc., more preferably 11-30 GPa; the microVickers hardness is 200-300 HV, for example, it can be 200 HV, 210 HV, 220 HV, 230 HV, 240 HV, 250 HV, 300 HV, etc., more preferably 200-250 HV.

[0032] Preferably, the thickness of the inorganic hardening layer is 10-100 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.; the inorganic hardening layer includes an alumina coating layer; the Young's modulus of the alumina coating layer is 200 GPa-300 GPa, for example, it can be 200 GPa, 220 GPa, 240 GPa, 260 GPa, 280 GPa, 300 GPa, etc., and the micro Vickers hardness is 1000-1500 HV, for example, it can be 1000 HV, 1100 HV, 1200 HV, 1300 HV, 1400 HV, 1500 HV, etc. The modulus of the alumina coating layer is significantly higher than that of the base film and the organic hardened layer. As the outermost rigid protective layer, it is in direct contact with the metal layer and provides excellent resistance to deformation during the needle punching and compaction process, enabling the metal layer and the alumina coating layer to crack synchronously.

[0033] To further explain, Young's modulus is the elastic modulus along the longitudinal direction, describing a material's resistance to elastic deformation. According to Hooke's Law, within the elastic limit of an object, stress and strain are directly proportional; the ratio is called the material's Young's modulus. It is a physical quantity characterizing the material's properties and depends only on the material's inherent physical properties. The magnitude of Young's modulus indicates the material's stiffness; the larger the Young's modulus, the less resistant it is to deformation. The method for measuring the Young's modulus of a material is as follows: Take a material sample and cut it into a rectangle of 15mm × 200mm; measure the sample thickness h using a micrometer, where the unit of sample thickness h is μm; perform a tensile test using a high-speed rail tensile testing machine at room temperature: First, set the initial position and ensure that the sample length clamped between the fixtures of the high-speed rail tensile testing machine is 50mm; stretch the sample at a speed of 50mm / min, and record the load L and the displacement y of the equipment when the sample breaks, where the unit of load L is N and the unit of displacement y is mm. Then, the stress ε = L / (15 h) 1000, strain η=y / 50 100; Plot the stress-strain curve, and take the initial linear region curve as a reference. The slope of this curve is the Young's modulus E of the material.

[0034] By controlling the modulus of each functional layer from the insulating layer (2-8 GPa) to the inorganic hardening layer (200-300 GPa), a smooth transition of modulus is achieved. This effectively disperses the interlayer shear stress, preventing delamination caused by the huge interfacial stress generated under pressure due to abrupt changes in stiffness (such as the insulating layer directly contacting 200-300 GPa alumina); and determines the overall rigidity of the composite base film. The modulus and thickness of each layer material largely determine the overall bending resistance and flattening resistance (pressure resistance) of the composite base film.

[0035] Hardness describes a material's ability to locally resist the indentation of a hard object (its resistance to scratches and abrasions). When a harder object (such as an indenter or needle tip) attempts to penetrate the material's surface, the material's resistance to this intrusion is its hardness. By creating a hardness gradient on the base film surface, the outermost alumina / metal layer becomes more brittle and hard. In a needle penetration test, a hard surface layer causes the cracks around the needle tip to localize and propagate brittlely, leading to the synchronous and rapid fracture of the metal coating, thereby cutting off the current path and preventing large-area heat and current diffusion. If the surface is soft, the needle will penetrate, causing large-area ductile tearing and deformation, leading to an expansion of the short-circuit area. This invention uses micro-Vickers hardness to characterize the hardness properties of materials.

[0036] By designing parameters such as the thickness, modulus, and hardness range of the organic hardening layer, the insulating layer and the hybrid hardening layer can be effectively connected, reducing the difference in interface properties and decreasing the likelihood of interface layer separation.

[0037] Therefore, the advantages of the composite current collector substrate membrane provided by the present invention are as follows: 1. By designing reinforcing functional layers with different moduli and hardnesses layer by layer on the surface of the insulation layer, the problem of aluminum layer delamination under pressure caused by excessive interface differences is alleviated. At the same time, the addition of reinforcing functional layers with different moduli effectively enhances the overall rigidity of the insulation layer, enhances the pressure resistance of the material, and solves the problem of cracking caused by repeated extrusion deformation of the insulation layer.

[0038] 2. Due to the increased hardness of the surface hardened layer of the composite current collector base film, the metal coating is more likely to crack synchronously with the surface hardened layer during the needle penetration test, which inhibits the large-scale propagation of short-circuit current and improves the pass rate of the needle penetration test.

[0039] A second aspect of the present invention provides a method for preparing a composite current collector base film, comprising: sequentially and correspondingly stacking an organic curing layer, a hybrid curing layer and an inorganic curing layer on at least one surface of the insulating layer (for example, one of the main surfaces or two opposing main surfaces).

[0040] This invention employs an overall rigid gradient design combined with a local hardening layer design. Specifically, by designing reinforcing functional layers with different moduli and hardnesses on the upper and lower surfaces of the insulation layer, an interface transition region with small connection differences is formed, which effectively enhances the surface hardness and overall rigidity of the insulation layer.

[0041] Specifically, the process involves: 1. First, introducing active groups such as hydroxyl (-OH) and carboxyl (-COOH) groups onto the surface of the insulating layer through corona or plasma treatment, providing sites for the grafting reaction. 2. Then, applying a UV-curable coating solution online to the surface of the insulating layer (using microgravure coating or slot coating), utilizing the interfacial coupling agent in the coating solution to achieve chemical bonding and improve coating adhesion. 3. Next, using UV light to trigger the in-situ polymerization and cross-linking of multifunctional monomers on the surface of the insulating layer, forming an organic hardened layer. 4. Applying a hybrid coating layer on top of the organic hardened layer, then using UV light curing or thermal curing to form a hybrid hardened layer. 5. Finally, using alumina sputtering or vapor deposition processes on top of the hybrid hardened layer, forming an inorganic hardened layer.

[0042] In summary, this invention employs an overall rigid gradient design combined with a hardening layer design. By designing reinforcing functional layers with different moduli and hardnesses layer by layer on the surface of the insulating layer, it alleviates the problem of aluminum layer detachment under pressure caused by excessive interface differences. At the same time, the addition of reinforcing functional layers with different moduli effectively enhances the overall rigidity of the insulating layer, improves the material's pressure resistance, and solves the problem of cracking caused by repeated extrusion deformation of the insulating layer. Furthermore, due to the increased surface hardness, the metal plating layer is more likely to crack synchronously with the surface hardening layer during the needle penetration test, suppressing the large-scale propagation of short-circuit current and improving the pass rate of the needle penetration test.

[0043] In some preferred embodiments, the present invention achieves layer-by-layer design of different functional reinforcement layers by combining online coating with UV curing and thermosetting processes.

[0044] In some preferred embodiments, prior to preparing the organic curing layer on the insulating layer, the method further includes performing roll-to-roll corona treatment or plasma activation treatment on the surface of the insulating layer.

[0045] Preferably, the power of the corona treatment is 10-50 W·min / m 2 For example, it could be 10 W·min / m 2 30W·min / m 2 50 W·min / m 2 The surface tension of the insulating layer after plasma activation treatment is 45-50 dyn / cm, for example, it can be 45 dyn / cm, 46 dyn / cm, 47 dyn / cm, 48 dyn / cm, 49 dyn / cm, 50 dyn / cm, etc.

[0046] Preferably, the gas used for plasma treatment is a mixture of oxygen and argon with a flow rate ratio of 1:(1-2), more preferably 1, a vacuum degree of 0.01-0.1 Pa, and a radio frequency power of 0.1-10 kW.

[0047] In some preferred embodiments, the organic curing layer is obtained by coating the insulating layer with a first coating liquid (i.e., a UV-curing coating liquid) and then curing it.

[0048] Preferably, the components of the first coating liquid include, by weight percentage: 30%-50% high-functionality prepolymer, 20%-40% reactive diluent, 3%-5% interfacial coupling agent, 2%-4% photoinitiator, 0.1%-2% functional additives, and the balance being solvent, and the sum of the weight percentages of the above components is 100%.

[0049] The amount of high-functionality prepolymer added is 30%-50%, for example, 30%, 35%, 40%, 45%, 50%, etc.; the amount of reactive diluent added is 20%-40%, for example, 20%, 25%, 30%, 35%, 40%, etc.; the amount of interfacial coupling agent added is 3%-5%, for example, 3%, 4%, 5%, etc.; the amount of photoinitiator added is 2%-4%, for example, 2%, 3%, 4%, etc.; and the amount of functional additives added is 0.1%-2%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, etc.

[0050] The high-functionality prepolymer in the first coating liquid is selected from one or more of epoxy acrylate, polyurethane acrylate, polyester acrylate, amino acrylate and unsaturated polyester. The reactive diluent is selected from one or more of the following: tripropylene glycol diacrylate, 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, ethylene glycol diglycidyl ether diacrylate, propoxylated trihydroxypropane triacrylate, ethoxylated trihydroxypropane triacrylate, pentaerythritol tetraacrylate (PETTA), ditrihydroxypropane tetraacrylate (DTEMPTTA), dipentaerythritol pentaacrylate (DPEPA), dipentaerythritol hexaacrylate (DPHA), and trimethylolpropane triacrylate (TMPTA). The interface coupling agent is selected from one or more of γ-methacryloxypropyltrimethoxysilane (KH-570), γ-aminopropyltriethoxysilane (KH-550), γ-glycidyl etheroxypropyltrimethoxysilane (KH-560), and γ-mercaptopropyltrimethoxysilane (KH-590); The photoinitiator is selected from one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), 1-hydroxy-cyclohexyl benzophenone (Irgacure184), benzoin dimethyl ether, isopropylthioxanthone, 4-methylbenzophenone, 4-phenylbenzophenone (4-BPZ), and benzyl dimethylaminoethyl ester. The functional additives are selected from one or more of leveling agents and antioxidants. Preferably, the leveling agent includes one or more of fluorocarbon leveling agents, silicone leveling agents, acrylic leveling agents, and cellulose acetate butyrate leveling agents. Preferably, the antioxidant includes one or more of butylated hydroxytoluene, butylated hydroxyanisole, ethylenediaminetetraacetic acid, and tert-butylhydroquinone.

[0051] Preferably, the solvent in the first coating solution is selected from one or more of ethyl acetate, isopropanol, methanol, ethanol, isopropanol, tert-butanol, H2O, n-propyl acetate, n-butyl acetate, acetone, butanone, and methyl isobutyl ketone.

[0052] In some preferred embodiments, the hybrid hardening layer is obtained by coating the organic hardening layer with a second coating liquid and then curing it; Preferably, the second coating liquid comprises, by weight percentage: 20%-40% high-functionality prepolymer, 20%-35% functionalized sol, 10%-25% reactive diluent, 3%-5% interfacial coupling agent, 2%-4% photoinitiator, 0.1%-2% functional additives, and the balance being solvent, wherein the sum of the weight percentages of the above components is 100%.

[0053] The amount of high-functionality prepolymer added is 20%-40%, for example, 20%, 25%, 30%, 35%, 40%, etc.; the amount of functionalized sol added is 20%-35%, for example, 20%, 25%, 30%, 35%, etc.; the amount of reactive diluent added is 10%-25%, for example, 10%, 15%, 20%, 25%, etc.; the amount of interfacial coupling agent added is 3%-5%, for example, 3%, 4%, 5%, etc.; the amount of photoinitiator added is 2%-4%, for example, 2%, 3%, 4%, etc.; and the amount of functional additives added is 0.1%-2%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, etc.

[0054] Preferably, the functionalized sol includes silica sol; the preparation process of the silica sol is as follows: one or more of vinyltrimethoxysilane, tetraethyl orthosilicate, and methyltrimethoxysilane are dehydrated and condensed under acidic / alkaline conditions to form a Si-O-Si oligomer sol (silica sol). Preferably, the particle size of the functionalized sol is 5-50nm, for example, it can be 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, etc.

[0055] The high-functionality prepolymer in the second coating liquid is selected from one or more of epoxy acrylate, polyurethane acrylate, polyester acrylate, amino acrylate and unsaturated polyester. The reactive diluent is selected from one or more of the following: tripropylene glycol diacrylate, 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, ethylene glycol diglycidyl ether diacrylate, propoxylated trihydroxypropane triacrylate, ethoxylated trihydroxypropane triacrylate, pentaerythritol tetraacrylate (PETTA), ditrihydroxypropane tetraacrylate (DTEMPTTA), dipentaerythritol pentaacrylate (DPEPA), dipentaerythritol hexaacrylate (DPHA), and trimethylolpropane triacrylate (TMPTA). The interface coupling agent is selected from one or more of γ-methacryloxypropyltrimethoxysilane (KH-570), γ-aminopropyltriethoxysilane (KH-550), γ-glycidyl etheroxypropyltrimethoxysilane (KH-560), and γ-mercaptopropyltrimethoxysilane (KH-590); The photoinitiator is selected from one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), 1-hydroxy-cyclohexyl benzophenone (Irgacure184), benzoin dimethyl ether, isopropylthioxanthone, 4-methylbenzophenone, 4-phenylbenzophenone (4-BPZ), and benzyl dimethylaminoethyl ester. The functional additives are selected from one or more of leveling agents and antioxidants. Preferably, the leveling agent includes one or more of fluorocarbon leveling agents, silicone leveling agents, acrylic leveling agents, and cellulose acetate butyrate leveling agents. Preferably, the antioxidant includes one or more of butylated hydroxytoluene, butylated hydroxyanisole, ethylenediaminetetraacetic acid, and tert-butylhydroquinone.

[0056] The solvent in the second coating solution is selected from one or more of ethyl acetate, isopropanol, methanol, ethanol, isopropanol, tert-butanol, H2O, n-propyl acetate, n-butyl acetate, acetone, butanone, and methyl isobutyl ketone.

[0057] Preferably, the first coating liquid and the second coating liquid are coated using a micro-gravure coating method, the anilox roller has a line count of 100-250 lines, the diameter of the anilox roller is Φ20-50 mm, and the coating speed is 5-20 m / min.

[0058] In some preferred embodiments, the curing process in the preparation of the organic curing layer and the hybrid curing layer is gradient curing, which includes sequential infrared drying, hot air drying and ultraviolet irradiation.

[0059] Preferably, the infrared drying temperature is 40-70℃, for example, 40℃, 50℃, 60℃, 70℃, etc.; preferably, the hot air drying temperature is 60-100℃, for example, 60℃, 70℃, 80℃, 90℃, 100℃, etc.; preferably, the energy of the ultraviolet irradiation is 300mJ / cm². 2 -1000mj / cm 2 For example, it could be 300mj / cm 2 400mj / cm 2 500mj / cm 2 600mj / cm 2 700mj / cm 2 800mj / cm 2 900mj / cm 2 1000mj / cm 2 wait.

[0060] Specifically, the insulating layer coated with UV-curable coating liquid is subjected to the following treatments in sequence: passing through a far-infrared drying oven, a hot air drying oven, a UV back-side irradiation oven, and a UV front-side irradiation oven (or, in sequence, a far-infrared drying oven, a hot air drying oven, a UV front-side irradiation oven, and a UV back-side irradiation oven), with the entire process taking 1.5-3 minutes; the infrared oven temperature is controlled at 40-70℃, the hot air drying temperature is controlled at 60-100℃, and the UV irradiation energy is 300 mJ / cm². 2 -1000mj / cm 2 Between. After the above coating liquid is applied, it first passes through an infrared oven. Because far-infrared rays have strong penetrating power, they can heat the coating from the inside, achieving the effect of drying from the inside. The surface of the hardened coating liquid still has high fluidity, making the hardened coating smoother and more uniform and reducing the internal stress of the coating. After passing through the infrared oven, it passes through a hot air oven to thoroughly evaporate the organic solvents in the coating. Then, ultraviolet light is gradually irradiated from both sides of the insulating layer, causing the prepolymer resin in the coating liquid to crosslink and cure, forming an organic hardened layer.

[0061] To further explain, the present invention adopts a faceted UV curing method. Through gradual curing, each functional layer can fully react and cure, reducing stress concentration and increasing interfacial bonding force. This avoids the problem that simultaneous UV curing on both sides can easily cause thermal stress to be unable to be released, resulting in curling and wrinkles.

[0062] In some preferred embodiments, the inorganic hardening layer is formed on the surface of the hybrid hardening layer by vacuum evaporation or magnetron sputtering. Specifically, based on the organic-inorganic hybrid hardening layer, a 10-100 nm inorganic alumina coating is deposited / sputtered on the surface of the organic-inorganic hybrid hardening layer by vacuum evaporation or sputtering. The alumina coating thickness is set to 10-100 nm, ultimately forming a composite current collector substrate film with an overall rigid gradient design combined with a locally hardened layer design.

[0063] Preferably, when vacuum evaporation coating is used, the vacuum degree at the start of the coating process is 1-4 × 10⁻⁴. -2The oxygen flow rate is 1000-3000 sccm, for example, 1000 sccm, 2000 sccm, 3000 sccm, etc.; the argon flow rate is 500-1000 sccm, for example, 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, 1000 sccm, etc.; the winding speed is 200-800 m / min, for example, 200 m / min, 400 m / min, 600 m / min, 800 m / min, etc.; the wire feeding speed is 100-200 m / min, for example, 100 m / min, 150 m / min, 200 m / min, etc.; the winding tension is 150-200 N, preferably 180 N; the unwinding tension is 210-230 N. N, preferably 220N; ion source voltage 1000-2000V, for example, 1000V, 1500V, 2000V, etc.; cold roller temperature 0-20℃, for example, 0℃, 5℃, 10℃, 15℃, 20℃, etc.

[0064] It should be noted that, in the preparation process of the inorganic hardened layer of the present invention, the thickness of the alumina coating can be precisely controlled by adjusting the kinetic parameters of the deposition process. Specifically, in the vacuum evaporation coating process, those skilled in the art can, according to the target thickness requirements, conventionally adjust the winding speed and wire feeding speed while maintaining the stability of core parameters such as the initial deposition vacuum and the flow rate of the reactive gas, thereby obtaining a dense alumina layer of the required thickness.

[0065] A third aspect of the present invention provides a composite current collector, comprising: a composite current collector base film prepared by the above method, and an aluminum metal layer formed on at least one side surface of the base film.

[0066] Preferably, the metal layer is a copper metal layer with a Young's modulus of 110 GPa-130 GPa and a hardness of 150-200 HV.

[0067] More preferably, the metal layer is an aluminum metal layer with a Young's modulus of 60 GPa-80 GPa and a hardness of 90-120 HV.

[0068] A fourth aspect of the present invention provides an electrode sheet comprising the aforementioned composite current collector.

[0069] A fifth aspect of the present invention provides an electrochemical device comprising the aforementioned electrode sheet.

[0070] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0071] Example 1 This embodiment provides a composite current collector-based membrane, the preparation method of which is as follows: Step 1: Surface activation of PET base film A PET base film with a thickness of 6 μm, a Young's modulus of 4.5 GPa, and a micro-Vickers hardness of 20 HV was subjected to double-sided synchronous corona treatment on a roll-to-roll production line; the corona power was set to 30 W·min / m. 2 The surface tension of the base film after treatment was 47 dyn / cm; Step 2: Apply and cure the organic hardening layer on both sides. Using a micro-gravure coating method (200 lines on the anilox roller, Φ30 mm in diameter), the UV-cured coating liquid (i.e., the first coating liquid) is uniformly coated on the two opposite main surfaces of the PET base film at a coating speed of 12 m / min. The first coating liquid components, by weight percentage, include: 40% epoxy acrylate, 30% tripropylene glycol diacrylate, 4% KH-570, 3% TPO, 0.5% fluorocarbon leveling agent, 0.5% antioxidant butylated hydroxytoluene, and the balance being ethyl acetate solvent. After coating, the following steps are performed sequentially to complete the curing process: (1) Far-infrared drying oven (temperature 55℃, time 1 minute); (2) Hot air drying oven (temperature 80℃, time 1 minute); (3) Irradiate one side of the base film coated with the coating solution with ultraviolet light (energy 600 mJ / cm). 2 (Time is 0.5 minutes). (4) Irradiate the other side of the base film coated with the coating solution with ultraviolet light (energy 600 mJ / cm). 2 (The time is 0.5 minutes).

[0072] The resulting organic hardened layer has a thickness of 500 nm, a Young's modulus of 8 GPa, and a micro Vickers hardness of 120 HV.

[0073] Step 3: Apply and cure the hybrid hardened layer on both sides. On the surface of the cured organic hardened layer, the same microgravure coating process (with the same parameters as in step 2) is used to coat the hybrid coating liquid (i.e., the second coating liquid) at a coating speed of 12 m / min. The second coating solution comprises, by weight percentage: 30% epoxy acrylate, 30% SiO2 sol with a particle size of 20 nm, 20% tripropylene glycol diacrylate, 4% KH-570, 3% Irgacure 184, 0.5% silicone leveling agent, 0.5% antioxidant butylated hydroxytoluene, and the balance is isopropanol.

[0074] The method for preparing SiO2 sol is as follows: vinyltrimethoxysilane is dehydrated and condensed under acidic conditions to form silica sol.

[0075] A hybrid hardened layer was obtained by using the same four-stage curing process as step (2); its thickness was 500 nm, its Young's modulus was 30 GPa, and its micro Vickers hardness was 250 HV.

[0076] Step 4: Double-sided vapor deposition of inorganic alumina hardening layer An alumina layer is deposited on the surface of the hybrid hardened layer using an evaporation deposition process with a deposition vacuum degree of 3×10⁻⁶. -2 The parameters were: Pa, oxygen flow rate 2500 sccm, argon flow rate 800 sccm, winding speed 500 m / min, wire feeding speed 150 m / min, winding tension 180 N, unwinding tension 220 N, ion source voltage 1500 V, and cold roller temperature 10 °C; the resulting alumina layer thickness was 50 nm, Young's modulus was 250 GPa, and micro Vickers hardness was 1200 HV.

[0077] Example 2 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that: In step 2, the first coating liquid components, by weight percentage, include: 30% polyurethane acrylate, 40% 1,6-hexanediol diacrylate, 3% γ-glycidyl etheroxypropyltrimethoxysilane, 2% TPO, 0.05% fluorocarbon leveling agent, 0.05% antioxidant butylated hydroxytoluene, and the balance being ethyl acetate solvent; the obtained organic hardened layer has a Young's modulus of 10 GPa and a micro Vickers hardness of 150 HV; In step 3, the components of the second coating liquid, by weight percentage, include: 20% epoxy acrylate, 35% SiO2 sol with a particle size of 50 nm, 25% tripropylene glycol diacrylate, 3% KH-570, 2% Irgacure 184, 0.05% silicone leveling agent, 0.05% antioxidant butylated hydroxytoluene, and the balance is isopropanol; the resulting hybrid hardened layer has a Young's modulus of 50 GPa and a micro Vickers hardness of 300 HV; In step 4, the vacuum degree for plating is 1x10. -2 Pa, oxygen flow rate of 3000 sccm, the Young's modulus of the inorganic hardened layer is 300 GPa, and the micro Vickers hardness is 1500 HV.

[0078] Example 3 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that: In step 2, the first coating liquid components, by weight percentage, include: 50% polyester acrylate, 20% ethylene glycol diglycidyl ether diacrylate, 5% γ-mercaptopropyltrimethoxysilane, 4% isopropylthioxanthone, 1% organosilicon leveling agent, 1% antioxidant ethylenediaminetetraacetic acid, and the balance being ethanol solvent; the obtained organic hardened layer has a Young's modulus of 5 GPa and a micro Vickers hardness of 80 HV; In step 3, the components of the second coating liquid, by weight percentage, include: 40% polyurethane acrylate, 20% SiO2 sol with a particle size of 5 nm, 10% 1,6-hexanediol diacrylate, 3% KH-570, 2% Irgacure 184, 1% acrylic leveling agent, 1% antioxidant butylated hydroxytoluene, and the balance is isopropanol; the resulting hybrid hardened layer has a Young's modulus of 10 GPa and a micro Vickers hardness of 200 HV; In step 4, the vacuum degree for plating is 1x10. -2 Pa, oxygen flow rate of 2000 sccm, the Young's modulus of the inorganic hardened layer is 200 GPa, and the micro Vickers hardness is 1000 HV.

[0079] Example 4 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that: the thickness of the organic curing layer is 100 nm, the thickness of the hybrid curing layer is 100 nm, and the thickness of the alumina layer is 10 nm.

[0080] Example 5 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that: the thickness of the organic hardening layer is 1000 nm, the thickness of the hybrid hardening layer is 1000 nm, and the thickness of the alumina layer is 100 nm.

[0081] Example 6 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that: the thickness of the organic curing layer is 300 nm, the thickness of the hybrid curing layer is 300 nm, and the thickness of the alumina layer is 30 nm.

[0082] Example 7 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that: the thickness of the organic curing layer is 800 nm, the thickness of the hybrid curing layer is 800 nm, and the thickness of the alumina layer is 80 nm.

[0083] Example 8 This embodiment provides a composite current collector base film, which differs from Embodiment 1 in that it uses polyimide with a thickness of 6 μm, a Young's modulus of 7.2 GPa, and a micro Vickers hardness of 30 HV as the insulating layer.

[0084] Comparative Example 1 This comparative example provides a composite current collector-based membrane, which differs from Example 1 in that: The hybrid hardening layer is directly disposed on the surface of the insulating layer, while the organic hardening layer is disposed on the surface of the hybrid hardening layer away from the insulating layer.

[0085] Comparative Example 2 This comparative example provides a composite current collector base film, which differs from Example 1 in that: no organic curing layer is prepared, and the thickness of the hybrid curing layer is 1 μm. That is, the structure of the composite current collector base film is PET base film + hybrid curing layer + alumina inorganic curing layer.

[0086] Comparative Example 3 This comparative example provides a composite current collector base film, which differs from Example 1 in that: no hybrid curing layer is prepared, and the thickness of the organic curing layer is 1 μm. That is, the structure of the composite current collector base film is PET base film + organic curing layer + alumina inorganic curing layer.

[0087] Comparative Example 4 This comparative example provides a composite current collector base film, which differs from Example 1 in that: no aluminum oxide inorganic hardening layer is prepared, and the thickness of the organic hardening layer is 550 nm. That is, the structure of the composite current collector base film is PET base film + organic hardening layer + hybrid hardening layer.

[0088] Comparative Example 5 This comparative example provides a composite current collector base film, which differs from Example 1 in that: the structure of the composite current collector base film is a PET base film + an organic curing layer, and the thickness of the organic curing layer is 1.05 μm.

[0089] Comparative Example 6 This comparative example provides a composite current collector base film, which differs from Example 1 in that: the structure of the composite current collector base film is a PET base film + a hybrid hardening layer, and the thickness of the hybrid hardening layer is 1.05 μm.

[0090] Comparative Example 7 This comparative example provides a composite current collector base film, which differs from Example 1 in that it does not have any reinforcing layer.

[0091] Test Example 1 The composite current collector substrates prepared in Examples 1-8 and Comparative Examples 1-7 were tested for Young's modulus and micro Vickers hardness. The test results are shown in Table 1.

[0092] Micro Vickers hardness test: embedding → mirror polishing → light load (preferably 0.001-0.01 kgf) → hold load for 15 seconds → measure diagonal → average at multiple points.

[0093] Test Example 2 The composite aluminum foil current collectors prepared using the composite current collector base films obtained in Examples 1-8 and Comparative Examples 1-7 were used for performance testing. The test results are shown in Table 2.

[0094] The composite aluminum foil current collector is prepared as follows: Aluminum layers were prepared on the composite current collector substrates obtained in Examples 1-8 and Comparative Examples 1-7, respectively. The aluminum layers were prepared using a vapor deposition process, as follows: Step 1: Using 72 evaporation boats and 2 mm diameter aluminum wires, the aluminum wires are vacuum-deposited onto the opposite surfaces of the composite current collector base film. A first metal layer and a second metal layer are then sequentially stacked, each with a thickness of 1 μm, to obtain the composite aluminum foil current collector. The vacuum deposition process parameters include: aluminum wire feed speed of 450 mm / min, deposition rate of 15 m / min, deposition main roller temperature of -10℃, deposition winding tension of 200 N, and a distance of 300 mm between the evaporation boats and the polymer composite film.

[0095] Step 2: After the vapor deposition is completed, the winding and slitting process is completed to obtain the composite aluminum foil current collector.

[0096] Battery assembly: The positive electrode current collector uses the composite aluminum foil current collector prepared in this invention (i.e., the metal element in the metal layer is aluminum), and the positive electrode material uses LiNi. 0.6 Mn 0.2 Co 0.2 O2 (NCM622), compacted density is 4.3 g / cm³ 3 For the negative electrode: the negative electrode current collector uses traditional copper foil (6 micrometers thick), and the negative electrode material uses artificial graphite with a compaction density of 1.55 g / cm³. 3 For the separator, an alumina ceramic-coated polyethylene separator (25 micrometers thick) is used; for the electrolyte, a 1 mol / L LiPF6 carbonate solution is used, wherein the carbonate is propylene carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1; using the above materials, lithium-ion batteries are assembled according to the relevant process.

[0097] Safety performance testing: The safety performance of the battery was verified using a needle penetration test, as follows: The prepared battery was placed in a needle penetration test apparatus with a needle diameter of 3 mm, a penetration speed of 10 mm / s, a sampling interval of 100 ms, and a sampling time of 15 min. The highest temperature of the battery after the needle penetration process and the battery voltage after the needle penetration were recorded to characterize the battery's safety performance. A lower highest temperature and a higher battery voltage after the needle penetration indicate better battery safety performance.

[0098] Table 1

[0099] The Young's modulus improvement rates in Table 1 are all calculated based on Comparative Example 7 (i.e., a pure PET insulation layer without any reinforcement treatment, with a measured Young's modulus of 4.5 GPa). The micro Vickers hardness of the composite current collector base film in Table 1 is the surface hardness, and the measured value is the hardness of the outermost layer of the composite current collector base film.

[0100] As shown in Table 1, in Examples 1-8, a complete three-layer gradient structure of organic hardening layer + hybrid hardening layer + inorganic hardening layer was constructed. Examples 1, 6, and 8 showed no delamination and no structural damage. Examples 2-5 and 7 showed slight delamination or slight structural damage, but were still superior to all comparative examples. The embodiments of the present invention did not show the failure modes such as obvious delamination or structural damage that are common in the comparative examples. This indicates that the composite current collector base film structure of the present invention has good structural stability within a reasonable range of process parameter fluctuations.

[0101] Table 2

[0102] As shown in Table 2, the batteries prepared in Examples 1-8 all exhibited excellent safety performance in the nail penetration test. The maximum temperature rise after nail penetration was controlled within 15°C, and the voltage retention rate after 300s was higher than 4.00 V. In contrast, the temperature rise of the comparative battery increased significantly, and the voltage decay was aggravated. This indicates that the composite current collector base film structure of the present invention effectively suppressed the thermo-electric positive feedback caused by nail penetration and improved the battery safety performance.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite current collector-based membrane, characterized in that, include: An insulating layer, and a gradient reinforcement structure disposed on at least one surface of the insulating layer; the gradient reinforcement structure comprises, from the surface of the insulating layer outward, an organic hardening layer, a hybrid hardening layer and an inorganic hardening layer; The Young's modulus and hardness of the organic hardening layer, the hybrid hardening layer, and the inorganic hardening layer increase sequentially.

2. The composite current collector-based membrane according to claim 1, characterized in that, The composite current collector base film satisfies at least one of the following conditions: (1) The thickness of the insulating layer is 4μm-8μm; (2) The insulating layer is made of one or more of polyimide, polyethylene, polypropylene and polyethylene terephthalate; (3) The Young's modulus of the insulating layer is 2 GPa-8 GPa, and the hardness is 10 HV-40 HV; (4) The thickness of the organic hardening layer is 100nm-1000nm; (5) The Young's modulus of the organic hardened layer is 5GPa-10GPa, and the hardness is 80HV-150HV; (6) The thickness of the hybrid hardened layer is 100nm-1000nm; (7) The Young's modulus of the hybrid hardened layer is 10 GPa-50 GPa, and the hardness is 200 HV-300 HV; (8) The thickness of the inorganic hardening layer is 10nm-100nm; (9) The Young's modulus of the inorganic hardened layer is 200 GPa-300 GPa and the hardness is 1000 HV-1500 HV.

3. The method for preparing the composite current collector-based membrane as described in claim 1 or 2, characterized in that, include: An organic curing layer, a hybrid curing layer, and an inorganic curing layer are sequentially stacked on at least one surface of the insulating layer.

4. The preparation method according to claim 3, characterized in that, Before preparing the organic curing layer on the insulating layer, the method further includes: activating the surface of the insulating layer; The activation process step satisfies at least one of the following conditions: (1) The activation treatment includes one or more of corona treatment and plasma treatment; (2) The power of the corona treatment is 10-50 W·min / m 2 The surface tension of the treated insulation layer is 45 dyn / cm-50 dyn / cm. (3) The gas used for plasma treatment is a mixture of oxygen and argon, with a vacuum degree of 0.01-0.1 Pa and a radio frequency power of 0.1-10 kW; Preferably, the flow rate ratio of the oxygen to the argon is 1:(1-2).

5. The preparation method according to claim 3, characterized in that, The organic hardening layer is obtained by coating the insulating layer with a first coating liquid and then curing it. The components of the first coating liquid, by weight percentage, include: 30%-50% high-functionality prepolymer, 20%-40% reactive diluent, 3%-5% interfacial coupling agent, 2%-4% photoinitiator, 0.1%-2% functional additives, and the balance being solvent.

6. The preparation method according to claim 5, characterized in that, The hybrid hardening layer is obtained by coating the organic hardening layer with a second coating liquid and then curing it. The second coating liquid comprises, by weight percentage: 20%-40% high-functionality prepolymer, 20%-35% functionalized sol, 10%-25% reactive diluent, 3%-5% interfacial coupling agent, 2%-4% photoinitiator, 0.1%-2% functional additives, with the balance being solvent; Preferably, the functionalized sol includes silica sol; Preferably, the particle size of the functionalized sol is 5nm-50nm.

7. The preparation method according to claim 6, characterized in that, The first coating liquid and the second coating liquid satisfy at least one of the following conditions: (1) The high-functionality prepolymers in the first coating liquid and the second coating liquid are each independently selected from one or more of epoxy acrylate, polyurethane acrylate, polyester acrylate, amino acrylate and unsaturated polyester. (2) The active diluents in the first coating liquid and the second coating liquid are each independently selected from one or more of the following: tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, ethylene glycol diglycidyl ether diacrylate, propoxylated trihydroxypropane triacrylate, ethoxylated trihydroxypropane triacrylate, pentaerythritol tetraacrylate, ditrihydroxypropane tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate; (3) The interfacial coupling agents in the first coating liquid and the second coating liquid are each independently selected from one or more of γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane and γ-mercaptopropyltrimethoxysilane; (4) The photoinitiators in the first coating liquid and the second coating liquid are each independently selected from one or more of 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 1-hydroxy-cyclohexyl benzophenone, benzoin dimethyl ether, isopropylthioxanthone, 4-methylbenzophenone, 4-phenylbenzophenone, and benzyl dimethyl aminoethyl ester. (5) The functional additives in the first coating liquid and the second coating liquid are each independently selected from one or more of leveling agents and antioxidants; Preferably, the leveling agent includes one or more of fluorocarbon compound leveling agents, silicone leveling agents, acrylic leveling agents, and cellulose acetate butyrate leveling agents; Preferably, the antioxidant includes one or more of butylated hydroxytoluene, butylated hydroxyanisole, ethylenediaminetetraacetic acid, and tert-butylhydroquinone; (6) The solvents in the first coating liquid and the second coating liquid are each independently selected from one or more of ethyl acetate, isopropanol, methanol, ethanol, isopropanol, tert-butanol, H2O, n-propyl acetate, n-butyl acetate, acetone, butanone and methyl isobutyl ketone.

8. The preparation method according to claim 5 or 6, characterized in that, The curing is gradient curing, which includes sequential infrared drying, hot air drying, and ultraviolet irradiation. Preferably, the infrared drying temperature is 40℃-70℃; Preferably, the temperature of the hot air drying is 60℃-100℃; Preferably, the energy of the ultraviolet irradiation is 300 mJ / cm². 2 -1000mj / cm 2 .

9. The preparation method according to claim 3, characterized in that, The inorganic hardening layer is formed on the surface of the hybrid hardening layer by vacuum evaporation coating or magnetron sputtering coating. Preferably, when vacuum evaporation coating is used, the vacuum degree at the start of the coating process is 1×10⁻⁶. -2 Pa-4×10 -2 Pa, oxygen flow rate 1000 sccm-3000 sccm, argon flow rate 500 sccm-1000 sccm, winding speed 200 m / min-800 m / min, wire feeding speed 100 m / min-200 m / min, winding tension 150 N-200 N, unwinding tension 210 N-230 N, ion source voltage 1000 V-2000 V, cold roller temperature 0 ℃-20 ℃.

10. A composite current collector, characterized in that, It includes a composite current collector base film and a metal layer located on at least one side of the composite current collector base film; the composite current collector base film is the composite current collector base film according to claim 1 or 2 or the composite current collector base film prepared by the preparation method according to any one of claims 3-9.

11. An electrode sheet, characterized in that, Includes the composite current collector as described in claim 10.

12. An electrochemical device, characterized in that, Includes the electrode sheet as described in claim 11.

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