Flame-retardant composite current collector base film, composite current collector, lithium ion battery and electrochemical device

Abstract

The application provides a fire-retardant composite current collector base film, a composite current collector, a lithium ion battery and an electrochemical device, and relates to the technical field of lithium ion batteries. The fire-retardant composite current collector base film comprises an intermediate core layer, and the intermediate core layer comprises fire-retardant microsphere capsules and a base resin; wherein the fire-retardant microsphere capsules comprise an inner core, a first shell layer and a second shell layer from inside to outside; the inner core comprises a fire retardant, the first shell layer comprises a toughening polymer and a pyrolysis-resistant polymer, and the second shell layer is a porous protective layer. The fire retardant is encapsulated by the multilayer fire-retardant microsphere capsules, so that the fire retardant is effectively prevented from being prematurely decomposed and leaked, and the capsule body can be controlled to be cracked by means of plasma, so that the fire-retardant component is directionally released to the surface layer, and is stably bound by means of anchoring material, thereby preventing the migration and precipitation of the fire retardant.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a flame-retardant composite current collector base film, a composite current collector, a lithium-ion battery, and an electrochemical device. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, higher requirements have been placed on the energy density and safety of lithium-ion batteries. Composite current collectors (such as the "metal-polymer base film-metal" sandwich structure) have become one of the key materials for improving battery energy density and safety due to their advantages such as lightweight and suppression of lithium dendrite perforation. However, the flammable nature of traditional polymer base films (such as polypropylene PP and polyethylene terephthalate PET) makes them a channel for fire spread in the event of battery thermal runaway, posing a serious safety hazard.

[0003] To improve the intrinsic safety of composite current collectors, the industry has widely attempted to add flame retardants to existing polymer base films. Among them, small-molecule phosphorus-based flame retardants, such as triphenyl phosphate (TPP), have been extensively studied due to their highly efficient gas-phase flame-retardant mechanism. However, the traditional method of directly blending small-molecule phosphorus-based flame retardants (such as TPP) with the matrix resin faces two irreconcilable core contradictions in practical industrialization and application: (1) During the film-forming stage, its melting processing temperature partially overlaps with the initial decomposition temperature range of molecular phosphorus flame retardants (such as TPP). High-temperature blending can easily lead to premature decomposition of flame retardants (such as TPP), which not only causes the loss of flame retardant components and affects the flame retardant effect, but also generates by-products that contaminate the base film and affect the processing stability.

[0004] (2) Small molecule phosphorus flame retardants (such as TPP) are small molecules and have poor compatibility with matrices such as PP and PET. During long-term battery use, especially under immersion in electrolyte and temperature cycling, they are prone to migration and precipitation. This will cause the flame retardant performance to decay rapidly over time and may contaminate the electrolyte or degrade the interfacial adhesion between the metal layer and the base film, ultimately damaging the long-term cycle life and safety reliability of the battery.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a base film for a flame-retardant composite current collector, a composite current collector, a lithium-ion battery, and an electrochemical device. It aims to solve the problems of premature decomposition, loss of flame-retardant components, and process instability caused by the overlap of decomposition temperature and processing window of small molecule phosphorus-based flame retardants (such as TPP) during high-temperature melt blending film preparation; poor compatibility and easy migration and precipitation of small molecule flame retardants under electrolyte immersion and thermal cycling, leading to electrolyte contamination, weakening of metal layer / base film interface adhesion, and accelerated cycle decay; and the lack of spatiotemporal controllability in traditional additive flame retardants, making it impossible to achieve functional gradient management of "lock-in during processing, directional release during service life, and efficient surface anchoring."

[0007] 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 flame-retardant composite current collector base film, the flame-retardant composite current collector base film comprising an intermediate core layer, and the intermediate core layer comprising flame-retardant microspheres and a matrix resin; The flame-retardant microsphere comprises, from the inside out, an inner core, a first shell layer, and a second shell layer; the inner core includes a flame retardant, the first shell layer includes a toughening polymer and a pyrolysis-resistant high-temperature polymer, and the second shell layer is a porous protective layer.

[0008] Furthermore, the flame-retardant composite current collector base film shall at least satisfy one of the following conditions: (1) The mass ratio of the flame-retardant microspheres to the matrix resin is (0.02~0.1):1; (2) The matrix resin includes any one or a combination of at least two of polypropylene, chlorinated polypropylene, polyethylene, chlorinated polyethylene, metallocene polyethylene, and polyethylene terephthalate; (3) The flame retardant includes small molecule phosphorus-based flame retardant materials; (4) The toughening polymer includes any one or a combination of at least two of polystyrene, polycarbonate, and polyvinyl chloride; (5) The pyrolysis high-temperature resistant polymer includes octavinyl cage-type silsesquioxane. methyl methacrylate polymers and / or octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymers; (6) The mass ratio of the pyrolytic high-temperature resistant polymer to the toughening polymer is 1:(0.1~2.5); (7) The second shell is a silica shell with a porous nanostructure; (8) The pore size of the second shell is 5~20 nm, and the porosity of the second shell is 30~60%; (9) The particle size of the inner core is 0.1~0.2 μm, the thickness of the first shell layer is 0.05~0.1 μm, and the thickness of the second shell layer is 0.02~0.1 μm.

[0009] Furthermore, a surface layer is provided on both sides of the intermediate core layer, the surface layer comprising a matrix resin and an anchoring material.

[0010] Furthermore, the anchoring material is brominated polyphenylene ether grafted polydimethylsiloxane and / or diphenylmethane bismaleimide grafted polydimethylsiloxane.

[0011] Furthermore, when a surface layer is provided on both sides of the intermediate core layer, the flame-retardant composite current collector base film shall at least satisfy one of the following conditions: (i) The thickness ratio of the surface layer to the thickness of the intermediate core layer is 1:(2~15); (ii) The thickness of the surface layer is 0.4~1 μm, and the thickness of the intermediate core layer is 2~6 μm; (iii) In the surface layer, the mass ratio of the anchoring material to the matrix resin is (0.01~0.05):1; (iv) In the surface layer, the matrix resin comprises any one or a combination of at least two of polypropylene, chlorinated polypropylene, polyethylene, chlorinated polyethylene, metallocene polyethylene, and polyethylene terephthalate.

[0012] Secondly, the present invention provides a method for preparing a flame-retardant composite current collector base film, the method comprising: The pyrolysis high-temperature resistant polymer slurry and the toughening polymer slurry are mixed to obtain a mixed slurry; The mixed slurry was added to the precursor of the porous material and in situ synthesized to obtain the microcapsule preform. After injecting a flame retardant into the core of the microcapsule preform, a semi-curing treatment is performed to obtain an intermediate. The matrix resin and intermediates are mixed to obtain the core layer mixture; The core layer mixture is extruded by co-extrusion to obtain the intermediate core layer of the flame-retardant composite current collector base film.

[0013] Furthermore, when a surface layer is provided on both sides of the intermediate core layer, the preparation method of the flame-retardant composite current collector base film includes the following steps: The pyrolysis high-temperature resistant polymer slurry and the toughening polymer slurry are mixed to obtain a mixed slurry; The mixed slurry was added to the precursor of the porous material and in situ synthesized to obtain the microcapsule preform. After injecting a flame retardant into the core of the microcapsule preform, a semi-curing treatment is performed to obtain an intermediate. The matrix resin and intermediates are mixed to obtain the core layer mixture; The base resin and anchoring material are mixed to obtain the surface mixture; The flame-retardant composite current collector base film is obtained by extruding the core layer mixture and the surface layer mixture in a stacked sequence through a three-layer co-extrusion process.

[0014] Thirdly, the present invention provides a flame-retardant composite current collector, the flame-retardant composite current collector comprising an insulating layer and metal layers disposed on both sides of the insulating layer; The insulating layer includes a flame-retardant composite current collector base film as described in the first aspect.

[0015] Fourthly, the present invention provides a method for preparing a flame-retardant composite current collector, the method comprising: The flame-retardant composite current collector base film is placed in a pyrolysis plasma atmosphere, and a metal layer is deposited by magnetron sputtering to obtain the flame-retardant composite current collector.

[0016] Fifthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the flame-retardant composite current collector as described in the third aspect.

[0017] In a sixth aspect, the present invention provides an electrochemical device comprising a lithium-ion battery as described in the fifth aspect.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The flame-retardant microspheres provided by the present invention adopt a layered coating structure of inner core, first shell layer, and second shell layer, which has outstanding advantages over the existing flame-retardant modification methods of single coating or direct blending: the inner core encapsulates the flame retardant, and the synergistic protective effect of the double shell layer effectively avoids the premature decomposition and volatilization failure of the flame retardant by heat, and eliminates the loss of flame-retardant components and the generation of by-products during the processing; at the same time, the first shell layer integrates toughening polymer and pyrolysis high-temperature resistant polymer, which can resist the high temperature of molding and shear force with the high-temperature resistant skeleton structure, and prevent the capsule from being damaged. In the event of material leakage due to body breakage, the toughening components can enhance the flexibility of the shell, avoiding the problem of shell cracking caused by stretching and compression. In addition, the outer layer of porous silica can further enhance physical protection and structural rigidity, locking flame retardant molecules layer by layer and inhibiting the migration and precipitation of flame retardants from the source. Moreover, the composite shell can achieve directional and controllable pyrolysis under subsequent plasma action, releasing flame retardant components, which not only ensures the stability of material processing and long-term use, but also precisely exerts flame retardant performance, and effectively improves the safety and service durability of the composite current collector base film.

[0019] (2) The flame-retardant composite current collector base film provided by the present invention adopts a three-layer composite base film structure of surface layer-intermediate core layer-surface layer. The functional intermediate core layer loaded with flame-retardant microspheres and the surface layer containing anchoring material work together. The flame-retardant microspheres are concentrated in the intermediate core layer. With the help of the multi-level encapsulation structure of microspheres, the flame-retardant components can be stably sealed during the high-temperature processing of the base film, avoiding premature decomposition and leakage of flame retardants, and ensuring the molding and processing performance and structural integrity of the base film. At the same time, the anchoring material introduced on both sides of the surface layer can form intermolecular binding and physical restriction on the flame-retardant molecules that diffuse to the surface layer after the subsequent flame-retardant microspheres are pyrolyzed, effectively inhibiting the migration and precipitation of small flame-retardant molecules under electrolyte immersion and temperature cycling conditions. Therefore, the three-layer structure has a clear division of labor and works together, which not only retains the excellent mechanical properties and processing adaptability of the base film matrix resin itself, but also realizes the controllable release and long-term fixation of flame-retardant components, and simultaneously improves the flame-retardant stability, aging resistance and interfacial bonding strength of the base film. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the flame-retardant microspheres provided by the present invention.

[0022] Figure 2 This is a schematic diagram of the structure of the flame-retardant composite current collector base membrane provided by the present invention.

[0023] Figure 3 This is a schematic diagram of the structure of the flame-retardant composite current collector provided by the present invention.

[0024] Wherein, P is the inner core, A is the toughening polymer, B is the pyrolysis high-temperature resistant polymer, C is the porous protective layer, D is the anchoring material, 10 is the insulation layer, 11 is the intermediate core layer, 12 is the surface layer, and 13 is the metal layer. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] 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.

[0028] In a first aspect, the present invention provides a flame-retardant composite current collector base film, such as... Figure 2 As shown, the flame-retardant composite current collector base film includes an intermediate core layer 11, and the intermediate core layer 11 includes flame-retardant microspheres and a matrix resin; Among them, such as Figure 1 As shown, the flame-retardant microspheres consist of an inner core, a first shell layer, and a second shell layer from the inside out; the inner core includes a flame retardant, the first shell layer includes a toughening polymer A and a pyrolysis-resistant high-temperature polymer B, and the second shell layer is a porous protective layer C.

[0029] It should be noted that the first shell layer is composed of toughening polymer A and pyrolysis-resistant high-temperature polymer B. Polymer B provides a high-temperature resistant framework; its thermal decomposition and heat distortion temperatures are higher than its film-forming temperature, ensuring that the film-forming temperature cannot damage polymer B and guaranteeing the integrity of the inner shell during the film-forming stage. Polymer A improves the toughness of the inner shell, preventing polymer B from cracking during shearing and / or stretching during film formation, further ensuring the integrity of the inner shell and preventing premature leakage and failure of the flame retardant P. The first shell layer forms a continuously cross-linked dense phase with small inter-chain gaps and no inter-difference diffusion channels. Furthermore, both polymers A and B are polar polymers with no affinity for the flame retardant P. In the multi-layer microcapsule structure, the flame retardant P in the inner core is completely locked within the inner shell and cannot diffuse. In addition, the second shell layer provides stronger high-temperature protection and rigid support. Its porous structure facilitates the pyrolysis of the first shell layer while simultaneously promoting the release and diffusion of the flame retardant P.

[0030] As an optional implementation, in the intermediate core layer, the mass ratio of the flame-retardant microspheres to the matrix resin is (0.02~0.1):1, for example, it can be 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, etc.

[0031] It should be noted that within this range, the flame-retardant microspheres exhibit good melt compatibility with the matrix resin, with no obvious agglomeration or phase separation, and are able to release sufficient amounts of flame retardant (such as TPP) to achieve a flame-retardant effect.

[0032] As an optional implementation, in the intermediate core layer, the matrix resin includes any one or a combination of at least two of polypropylene, chlorinated polypropylene, polyethylene, chlorinated polyethylene, metallocene polyethylene, and polyethylene terephthalate.

[0033] As an optional implementation, the flame retardant in the inner core comprises a small molecule phosphorus-based flame retardant material.

[0034] As an optional implementation, the small molecule phosphorus-based flame retardant material includes any one or a combination of at least two of triphenyl phosphate (TPP), trimethyl phosphate (TMP), triethyl phosphate (TEP), and dimethyl methyl phosphate (DMMP).

[0035] In a preferred embodiment, the flame retardant is triphenyl phosphate (TPP).

[0036] It should be noted that the flame-retardant mechanism of TPP is mainly achieved through thermal decomposition. Specifically, at temperatures (typically >150℃), the phosphazene ring of TPP decomposes, releasing phosphorus-containing free radicals (PO·, etc.), which capture H· and OH· free radicals in the flame, while simultaneously promoting char formation. Therefore, during the film-forming and degradation processes, TPP needs to be thoroughly coated and isolated from oxygen to prevent premature thermal decomposition and subsequent flame-retardant failure.

[0037] As an optional implementation, in the first shell layer, the toughening polymer includes any one or a combination of at least two of polystyrene (PS), polycarbonate (PC), and polyvinyl chloride (PVC).

[0038] It should be noted that the toughening polymer improves the toughness of the first shell, preventing polymer A from cracking during film formation due to shear / stretching, and further ensuring the integrity of the first shell.

[0039] As an optional implementation, in the first shell layer, the pyrolysis high-temperature resistant polymer includes an octavinyl cage silsesquioxane-methyl methacrylate polymer and / or an octavinyl cage silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer.

[0040] As an optional embodiment, the raw materials for preparing the octavinyl cage-type silsesquioxane-methyl methacrylate polymer include octavinyl-POSS and methyl methacrylate.

[0041] As an optional implementation, the mass ratio of octavinyl-POSS to methyl methacrylate is (0.01~0.1):1, for example, it can be 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, etc.

[0042] It should be noted that within this mass ratio range, the thermal stability and mechanical strength of the pyrolysis high-temperature resistant polymer B can be significantly improved, meeting the temperature resistance requirements of the three-layer co-extrusion process. This avoids damage to the inner shell and leakage of flame retardants during the film formation process of microcapsules, and also avoids a significant increase in the brittleness of the inner shell. Microcapsules are prone to breakage due to slight stress during processing, which can balance the strength and toughness of the inner shell.

[0043] As an optional implementation, the raw materials for preparing the octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer include octavinyl-POSS, hydrogenated bisphenol A, and epichlorohydrin.

[0044] As an optional implementation, the mass ratio of octavinyl-POSS, hydrogenated bisphenol A, and epichlorohydrin is (0.01~0.1):1:1, for example, it can be 0.01:1:1, 0.02:1:1, 0.03:1:1, 0.04:1:1, 0.05:1:1, 0.06:1:1, 0.07:1:1, 0.08:1:1, 0.09:1:1, 0.1:1:1, etc.

[0045] It should be noted that the addition of the octavinyl cage-like polysilsesquioxane (OvPOSS) backbone in the pyrolytic high-temperature resistant polymer B contributes to its high-temperature resistance. This is attributed to the strong interaction between the cage-like POSS and the polymer matrix, which restricts the movement of polymer chain segments and increases the heat distortion and thermal decomposition temperatures. This increase in thermal temperature ensures that the pyrolytic high-temperature resistant polymer B cannot be destroyed by high temperatures, guaranteeing the integrity of the inner shell during film formation. The toughening polymer A improves the toughness of the inner shell, preventing it from cracking due to shear and tension during film formation, further ensuring the integrity of the inner shell and preventing premature TPP leakage and failure.

[0046] As an optional implementation, in the first shell layer, the mass ratio of the pyrolytic high-temperature resistant polymer to the toughening polymer is 1:(0.1~2.5), for example, it can be 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, etc.

[0047] It should be noted that within this range, toughening polymer A and pyrolysis high-temperature resistant polymer B form a continuously cross-linked dense phase. The molecular chains after cross-linking have small gaps and no gap diffusion channels. Furthermore, both toughening polymer A and pyrolysis high-temperature resistant polymer B are polar polymers and have no affinity for the flame retardant. Under the structure of multilayer microcapsules, the flame retardant is completely locked inside the inner shell and cannot diffuse.

[0048] As an optional implementation, the second shell is a silica shell with a porous nanostructure.

[0049] It should be noted that the porous protective layer C provides stronger high-temperature protection and rigid support.

[0050] As an optional implementation, the pore size of the porous protective layer is 5~20 nm, for example, it can be 5 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, etc.

[0051] As an optional implementation, the porosity of the porous protective layer is 30-60%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.

[0052] It should be noted that within this range of pore size and porosity, the pyrolysis gas is conducive to the pyrolysis of the first shell layer, while also facilitating the release and diffusion of the flame retardant P.

[0053] As an optional implementation, the particle size of the inner core is 0.1~0.2 μm, for example, it can be 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.2 μm, etc.

[0054] As an optional implementation, the thickness of the first shell layer is 0.05~0.1 μm, for example, it can be 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, etc.

[0055] As an optional implementation, the thickness of the second shell layer is 0.02~0.1 μm, for example, it can be 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, etc.

[0056] As an optional implementation, the material of the second shell layer is porous silicon dioxide.

[0057] As an optional implementation method, such as Figure 2As shown, a surface layer 12 is provided on both sides of the intermediate core layer 11, and the surface layer 12 includes a matrix resin and an anchoring material D.

[0058] It should be noted that small molecule phosphorus-based flame retardant materials can move from the middle core layer to the surface layer and be fixed.

[0059] As an optional implementation, the anchoring material is brominated polyphenylene ether grafted polydimethylsiloxane and / or bismaleimide grafted polydimethylsiloxane.

[0060] It should be noted that when the anchoring material is brominated polyphenylene ether grafted polydimethylsiloxane (PPO-g-PDMS), TPP is molecularly anchored by the PPO backbone through π-π conjugation. The PDMS side chains are oleophobic, low surface energy segments, forming oleophobic barrier microdomains within the surface resin. Oil-soluble small TPP molecules are repelled by PDMS, thus preventing TPP from diffusing to the surface, making TPP diffusion behavior effectively controllable. When the anchoring material is BMI, BMI also has conjugated rings for anchoring, and the effect after introducing PDMS side chains is the same as described above.

[0061] As an optional implementation, the thickness ratio of the surface layer to the thickness of the intermediate core layer is 1:(2~15), for example, it can be 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:15, etc.

[0062] It should be noted that this thickness ratio ensures a moderate surface layer thickness, allowing the pyrolysis gas to quickly penetrate along the gaps between the surface molecular chains and reach the flame-retardant microspheres inside the core layer without resistance, thus guaranteeing pyrolysis efficiency and avoiding pyrolysis delays and uneven pyrolysis caused by an excessively thick surface layer.

[0063] As an optional implementation, the thickness of the surface layer is 0.4~1 μm, for example, it can be 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc.

[0064] It should be noted that the surface layer thickness is controlled within this range to prevent the surface layer from being too thick and hindering the pyrolysis gas from reaching the core layer, thus ensuring that the microspheres are fully pyrolyzed and the flame retardant is released smoothly.

[0065] As an optional implementation, the thickness of the intermediate core layer is 2~6 μm, for example, it can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, etc.

[0066] It should be noted that the thickness of the intermediate core layer within this range provides sufficient load space, allowing the flame-retardant microspheres to be uniformly dispersed in the core layer, ensuring the release of sufficient TPP during thermal runaway, and achieving efficient flame retardancy.

[0067] As an optional implementation, in the surface layer, the mass ratio of the anchoring material to the matrix resin is (0.01~0.05):1, for example, it can be 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, etc. This fixes and oleophobically blocks the diffused TPP flame retardant, completely preventing the flame retardant from migrating and precipitating, avoiding contamination of the electrolyte, deterioration of the interfacial bonding between the metal layer and the base film, and ensuring that the anchoring material is uniformly dispersed in the surface layer.

[0068] As an optional implementation, in the surface layer, the matrix resin includes any one or a combination of at least two of polypropylene, chlorinated polypropylene, polyethylene, chlorinated polyethylene, metallocene polyethylene, and polyethylene terephthalate.

[0069] As an optional implementation, the method for preparing the flame-retardant composite current collector base film includes: The pyrolysis high-temperature resistant polymer slurry and the toughening polymer slurry are mixed to obtain a mixed slurry; The mixed slurry was added to the precursor of the porous material and in situ synthesized to obtain the microcapsule preform. After injecting a flame retardant into the core of the microcapsule preform, a semi-curing treatment is performed to obtain an intermediate. The matrix resin and intermediates are mixed to obtain the core layer mixture; The core layer mixture is extruded by co-extrusion to obtain the intermediate core layer of the flame-retardant composite current collector base film.

[0070] As an optional implementation, the flame retardant is injected into the core of the microcapsule preform using a nanoscale injection pump.

[0071] As an optional implementation, when surface layers are also provided on both sides of the intermediate core layer, the preparation method of the flame-retardant composite current collector base film includes the following steps: The pyrolysis high-temperature resistant polymer slurry and the toughening polymer slurry are mixed to obtain a mixed slurry; The mixed slurry was added to the precursor of the porous material and in situ synthesized to obtain the microcapsule preform. After injecting a flame retardant into the core of the microcapsule preform, a semi-curing treatment is performed to obtain an intermediate. The matrix resin and intermediates are mixed to obtain the core layer mixture; The base resin and anchoring material are mixed to obtain the surface mixture; The flame-retardant composite current collector base film is obtained by extruding the core layer mixture and the surface layer mixture in a stacked sequence through a three-layer co-extrusion process.

[0072] As an optional implementation, octavinyl-POSS is prepared by the following steps: Vinyltrimethoxysilane (25% by mass) and acetone (60% by mass) were added separately. Concentrated hydrochloric acid (catalyst, 5%) and deionized water (10%) were added under stirring. The mixture was stirred at 40-60°C for 48 h. After a white solid precipitated, it was washed with anhydrous ethanol and dried under vacuum to obtain octavinyl-POSS.

[0073] As an optional implementation, the high-temperature resistant polymer B (octavinyl cage-type silsesquioxane) is pyrolyzed. The methyl methacrylate polymer is prepared by the following steps: OV-POSS, methyl methacrylate (MMA), and azobisisobutyronitrile (AIBN) were added in a mass ratio of (1-10):100:(0.25-1) using 1,4-dioxane as the solvent to obtain a solution with a solid content of 5-20%. The mixture was stirred at 60-80°C for 7-9 h under a nitrogen atmosphere. After the reaction was complete, cyclohexane and tetrahydrofuran (THF) were alternately precipitated and washed to thoroughly remove unreacted monomers. The solvent was then removed under vacuum to obtain an octavinylcage-type silsesquioxane. Methyl methacrylate polymer.

[0074] As an optional implementation, the pyrolysis high-temperature resistant polymer B (octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer) is prepared by the following steps: Under nitrogen protection, hydrogenated bisphenol A and toluene were added at a mass ratio of 1:(2~5) and mixed, then heated to 120℃ and refluxed for dehydration. The temperature was lowered to 70℃, and anhydrous tin tetrachloride (tin tetrachloride to hydrogenated bisphenol A mass ratio of (0.25~1%):1) and OV-POSS (OV-POSS to hydrogenated bisphenol A mass ratio of (1~10%):1) were added, along with epichlorohydrin (epoxychlorohydrin to hydrogenated bisphenol A mass ratio of 1:1). The mixture was heated to 80℃ and reacted for 6 h. Subsequently, the temperature was lowered to 40℃, and a sodium alkoxide-ethanol solution (anhydrous ethanol to NaOH mass ratio of 1:20, NaOH to hydrogenated bisphenol A mass ratio of 5:100) was added, reacting for 6 h. After the reaction was complete, the organic layer was washed and extracted with toluene and deionized water. The solvent in the organic layer was removed under vacuum to obtain an octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychlorohydrin polymer.

[0075] As an optional implementation, the toughening polymer A slurry is prepared by the following steps: PS / PC / PVC nanosphere powder was ultrasonically dissolved in water to form a suspension: Nanospheres (particle size 30-200 nm), deionized water, and surfactants (sodium dodecyl ether sulfate and / or sodium dodecylbenzene sulfonate) were dispersed by stirring at a mass ratio of (1-5):(93-98.5):(0.5-2) to obtain a suspension. 1-5% PVA (polyvinyl alcohol, stabilizer) was added to the suspension, and the stirring speed and time were 500-2000 rpm for 0.5-2 h.

[0076] As an optional implementation, polymer B slurry is prepared by the following steps: When the high-temperature resistant polymer B is octavinyl cage-type silsesquioxane... When polymerizing methyl methacrylate, octavinyl cage-type silsesquioxane is used. The methyl methacrylate polymer was dissolved by mixing it with a solvent (tetrahydrofuran) at a mass ratio of (20~40):100.

[0077] When the high-temperature resistant polymer B is octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer, the octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer is mixed with acetone at a mass ratio of (20~40):100 for dissolution.

[0078] As an optional implementation, a mixed slurry is obtained by pyrolyzing high-temperature resistant polymer B slurry and toughening polymer A slurry, and the mixed slurry and the precursor of porous material are synthesized in situ at a mass ratio of (0.5~25):1 to obtain a microcapsule preform, namely a microcapsule preform with a silica shell covering the first shell layer.

[0079] It should be noted that the silica shell is prepared by the in-situ sol-gel method, using tetraethyl orthosilicate as the silicon source. A hydrolysis-condensation reaction is carried out in an oil-in-water emulsion system under alkaline conditions and at a low temperature of 40-60°C to form a loosely packed shell of nano-silica particles. No high-temperature calcination or sintering densification treatments are performed during the preparation and post-processing, thus ensuring that the silica shell has a naturally porous structure. The pores allow plasma-active particles to penetrate, providing necessary channels for the pyrolysis of the microcapsule inner shell and the release of the flame retardant.

[0080] As an optional implementation, brominated polyphenylene ether grafted polydimethylsiloxane (PPO-g-PDMS) is specifically prepared by the following steps: Under nitrogen protection, brominated polyphenylene ether (BPPO, Mn = 20000 g / mol) and amino-terminated polydimethylsiloxane (NH2-PDMS, Mn = 5000 g / mol) were added in a 3:7 ratio, along with triethylamine (0.5-2%) as an acid-binding agent and chloroform as a solvent. The reaction was carried out at 60-80℃ for 6-12 h. After the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous methanol, filtered, and dried to obtain brominated polyphenylene ether-grafted polydimethylsiloxane (PPO-g-PDMS).

[0081] As an optional implementation, diphenylmethane bismaleimide-grafted polydimethylsiloxane (BMI-g-PDMS) is specifically prepared by the following steps: Under nitrogen protection, diphenylmethane bismaleimide and aminopropyl-terminated polydimethylsiloxane (NH2-PDMS, Mn = 5000 g / mol) were added in a 1:4 ratio, and NMP solvent was added. The reaction was carried out at 120-150℃ for 7-9 h. After the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous methanol, filtered, and dried to obtain diphenylmethane bismaleimide-grafted polydimethylsiloxane (BMI-g-PDMS).

[0082] As an optional implementation, the three-layer co-extrusion includes an extrusion process, a casting process, a longitudinal stretching process, and a transverse stretching process performed sequentially.

[0083] As an optional implementation, the process parameters of the extrusion process include: the pressure of each extruder die head is independently 15~35 MPa, for example, 15 MPa, 16 MPa, 18 MPa, 20 MPa, 22 MPa, 24 MPa, 25 MPa, 26 MPa, 28 MPa, 30 MPa, 32 MPa, 34 MPa, 36 MPa, etc.; the temperature of the composite die head is 240~260℃, for example, 240℃, 245℃, 250℃, 255℃, 260℃, etc.; and the pressure of the composite die head is 10~25 MPa, for example, 10 MPa, 12 MPa, 14 MPa, 15 MPa, 16 MPa, 18 MPa, 20 MPa, 22 MPa, 24 MPa, 25 MPa, etc.

[0084] As an optional implementation, the process parameters of the casting process include: the surface temperature of the chilling roller is 80~120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, etc.; the gas temperature of the air knife and the edge blowing nozzle is 80~120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, etc.

[0085] As an optional implementation, the process parameters of the longitudinal stretching process include: a longitudinal stretching preheating temperature of 100~160℃, such as 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, etc.; a longitudinal stretching temperature of 150~170℃, such as 150℃, 155℃, 160℃, 165℃, 170℃, etc.; and a longitudinal stretching setting temperature of 140~145℃, such as 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, etc.

[0086] As an optional implementation, the process parameters of the transverse stretching process include: a transverse stretching preheating temperature of 150~180℃, such as 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, etc.; a transverse stretching temperature of 160~170℃, such as 160℃, 162℃, 164℃, 165℃, 166℃, 168℃, 170℃, etc.; and a transverse stretching setting temperature of 165~175℃, such as 165℃, 166℃, 168℃, 170℃, 172℃, 174℃, 175℃, etc.

[0087] As an optional implementation, the longitudinal stretching ratio of the flame-retardant composite current collector base film is 4 to 6 times, for example, 4 times, 4.5 times, 5 times, 5.5 times, 6 times, etc., and the transverse stretching ratio of the flame-retardant composite current collector base film is 8 to 10 times, for example, 8 times, 8.5 times, 9 times, 9.5 times, 10 times, etc.

[0088] Thirdly, this invention provides a flame-retardant composite current collector, such as... Figure 3 As shown, the flame-retardant composite current collector includes an insulating layer 10 and metal layers 13 disposed on both sides of the insulating layer 10; The insulating layer includes a flame-retardant composite current collector base film as described in the first aspect.

[0089] Fourthly, the present invention provides a method for preparing a flame-retardant composite current collector, the method comprising: The flame-retardant composite current collector base film is placed in a pyrolysis plasma atmosphere, and a metal layer is deposited by magnetron sputtering to obtain the flame-retardant composite current collector.

[0090] It should be noted that during the magnetron sputtering process, in a mixed reaction atmosphere of argon (Ar) and a special gas (such as CH4), the high-energy particles (ions, electrons, free radicals, etc.) generated by plasma treatment interact with the surface and pores of the polymer material, causing the polymer chains of the microsphere wall material (shell) to break (A-fracture), thus enabling the TPP molecules to diffuse further. Alternatively, as another implementation method, the base film can be subjected to plasma treatment separately in a mixed reaction atmosphere of argon (Ar) and a special gas (such as CH4) before magnetron sputtering to ensure sufficient fracture of the flame-retardant microspheres within the base film for flame-retardant composite current collectors.

[0091] The active ions and free radicals generated by Ar+CH4 plasma have a particle size of <1 nm, which is much smaller than the free volume gaps between polymer molecular chains. The total thickness of the composite current collector base film is only 6~12 μm, and the surface layer thickness is only 1~2 μm. The effective plasma depth completely covers the core layer region. Active particles can freely diffuse along the molecular chain gaps of the surface polymer (including anchoring material D), penetrate the surface layer into the core layer, and then reach the first shell layer through the microcapsule porous SiO2 shell, achieving precise cleavage of the first shell layer. The penetration process is unimpeded by any structural obstacles, resulting in high efficiency and good uniformity.

[0092] Meanwhile, the Ar+CH4 plasma possesses only a fixed range of bond-breaking energies, capable of breaking only strongly polar chemical bonds, while weakly polar chemical bonds remain unbroken. The first shell contains polar groups and has densely packed electron cloud sites, making it a CH3+ pyrolysis polymer B. / H The free radical is the only priority target. It breaks, cracks, and collapses upon contact. Other substances have stable chemical bonds and no active sites, so they do not react with it. Moreover, the high-temperature resistant polymer B and the toughening polymer A are blended and have weak molecular chain entanglement. As long as the plasma breaks a small number of main chains, the entire inner shell will break and collapse, forming discontinuous pores.

[0093] In addition, the first shell of the microcapsule is broken down and collapsed by plasma particles, and TPP is released from the core layer. The TPP molecules undergo free volume diffusion migration between molecular chains inside the polymer matrix. Since the TPP concentration in the core layer is much higher than that in the surface layer, TPP spontaneously diffuses from the core layer to the surface layer under the drive of the concentration gradient. The core layer and the surface layer of the three-layer co-extruded base film are continuously connected, and the total thickness of the base film is relatively thin, so TPP can diffuse from the core layer into the surface region.

[0094] Specifically, when the anchoring material is PPO-g-PDMS, it is molecularly anchored by the PPO backbone through π-π conjugation. The PDMS side chains are oleophobic, low surface energy segments, forming oleophobic barrier microregions within the surface resin. Oil-soluble small molecule TPP is repelled by PDMS, thus preventing TPP from diffusing to the surface, making TPP diffusion behavior effectively controllable. When the anchoring material is BMI, BMI also has conjugated rings, and the effect after introducing PDMS side chains is the same as described above.

[0095] As an optional implementation, the conductive layer includes copper foil.

[0096] Fifthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the flame-retardant composite current collector as described in the third aspect.

[0097] In a sixth aspect, the present invention provides an electrochemical device comprising a lithium-ion battery as described in the fifth aspect.

[0098] 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.

[0099] Example 1 This embodiment provides a flame-retardant microsphere, a base membrane, and a composite current collector, which are prepared by the following steps: S1. Preparation of flame-retardant microspheres: (a) Pyrolysis of high-temperature resistant polymers (octavinyl cage-type silsesquioxanes) Preparation of methyl methacrylate polymer: Vinyltrimethoxysilane (25% by mass) and acetone (60% by mass) were added separately. Concentrated hydrochloric acid (catalyst, 5%) and deionized water (10%) were added under stirring. The mixture was stirred at 50°C for 48 h. After a white solid precipitated, it was washed with anhydrous ethanol and dried under vacuum to obtain octavinyl-POSS (OV-POSS). OV-POSS, methyl methacrylate (MMA), azobisisobutyronitrile (AIBN), and 1,4-dioxane were added in a mass ratio of 6:100:0.65 to obtain a solution with a solid content of 12 wt%. The mixture was stirred at 70 °C for 8 h under a nitrogen atmosphere. After the reaction was complete, unreacted monomers were thoroughly removed by alternating precipitation and washing with cyclohexane and tetrahydrofuran (THF), and the solvent was removed under vacuum to obtain an octavinylcage-type silsesquioxane. Methyl methacrylate polymer.

[0100] (b) Preparation of flame-retardant microspheres: Prepare octavinyl cage-like silsesquioxanes with a mass ratio of 1:1.2. methyl methacrylate polymers and polystyrene; 50 nm polystyrene nanospheres, deionized water, and sodium dodecyl ether sulfate were dispersed by stirring at a mass ratio of 3:96:1 to obtain a suspension; 3% PVA (polyvinyl alcohol, stabilizer) was added to the above suspension, and the stirring speed and time were 1000 rpm and 1 h to obtain a polystyrene suspension. Octavinyl cage silsesquioxane Methyl methacrylate polymer and solvent tetrahydrofuran were stirred and dissolved at a mass ratio of 30:100 to obtain octavinyl cage-like silsesquioxane. methyl methacrylate polymer solution; Octavinyl cage silsesquioxane A stable O / W emulsion was formed by stirring a methyl methacrylate solution and a polystyrene suspension. The O / W emulsion was then added dropwise to a tetraethyl orthosilicate (TEOS) diluent at a mass ratio of 10:1. The TEOS was diluted with anhydrous ethanol at a mass ratio of 1:8. After the addition was complete, the pH of the system was adjusted to 9-10 with ammonia, and the reaction temperature was maintained at 50°C for 3 hours. After the reaction, the product was centrifuged and washed several times with deionized water and anhydrous ethanol to remove unreacted TEOS, yielding the microcapsule preform. Flame retardant TPP was injected into the core of the microcapsule preform using a nanoscale injection pump to obtain an intermediate with a core particle size of 0.15 μm. The intermediate was spray-dried (inlet air temperature 80℃, outlet air temperature 60℃) and then semi-cured at 180℃ for 30 min in an inert environment to obtain flame-retardant microspheres. The thickness of the first shell layer was 0.07 μm, and the thickness of the second shell layer (silica) was 0.06 μm. The pore size of the second shell layer was 12 nm, and the porosity of the second shell layer was 45%. S2. Preparation of the base film: (a) Preparation of anchoring material (brominated polyphenylene ether grafted polydimethylsiloxane (PPO-g-PDMS)): Under nitrogen protection, brominated polyphenylene ether (BPPO, Mn = 20000 g / mol): amino-terminated polydimethylsiloxane (NH2-PDMS, Mn = 5000 g / mol) were added in a ratio of 3:7. Triethylamine (1.2%) as an acid-binding agent and chloroform as a solvent were added, and the reaction was carried out at 70°C for 9 h. After the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous methanol, filtered, and dried to obtain brominated polyphenylene ether grafted polydimethylsiloxane (PPO-g-PDMS).

[0101] (b) Preparation of the base film: Polypropylene resin at a mass ratio of 1:0.06 was mixed with the prepared flame-retardant microspheres to obtain the core layer mixture. Polypropylene resin with a mass ratio of 1:0.03 was mixed with the prepared polyphenylene ether-grafted polydimethylsiloxane (PPO-g-PDMS) to obtain a surface mixture. A flame-retardant composite current collector base film is obtained by extruding the core layer mixture and the surface layer mixture in a stacked sequence through a three-layer co-extrusion process. The three-layer co-extrusion process includes extrusion, casting, longitudinal stretching, and transverse stretching processes performed sequentially. In the extrusion process, the die head pressure of each extruder is set to 25 MPa, the composite die head temperature is set to 250℃, and the composite die head pressure is set to 20 MPa. In the casting process, the surface temperature of the chiller roller is set to 90℃, and the gas temperature of the air knife and the edge blowing nozzle is set to 90℃. In the longitudinal stretching process, the longitudinal stretching preheating temperature is 130℃, the longitudinal stretching temperature is 160℃, and the longitudinal stretching setting temperature is 142℃. In the transverse stretching process, the transverse stretching preheating temperature is 165℃, the transverse stretching temperature is 165℃, and the transverse stretching setting temperature is 168℃. The longitudinal stretching ratio is 5, and the transverse stretching ratio is 9. A core layer with a thickness of 4 μm and a surface layer with a thickness of 0.5 μm are prepared.

[0102] S3. Preparation of composite current collectors: (a) Preparation of the magnetron sputtering substrate: A roll-to-roll double-sided magnetron sputtering apparatus was used to sequentially deposit copper seed layers on both sides of the flame-retardant composite current collector substrate film prepared above. High-purity copper targets (99.99% purity) were used as sputtering targets, with a total of 20 target sets configured, 10 sets corresponding to each side of the substrate film. After loading the flame-retardant composite current collector substrate film into the apparatus, one side was deposited onto the target first. The process parameters were set as follows: working vacuum degree of 0.3 Pa, total gas flow rate of 150 sccm, of which CH4 gas flow rate was 15 sccm, target power of 7 kW, main roller temperature maintained at -20℃, substrate film conveyor belt speed of 10 m / min, and winding and unwinding tension controlled at 100 N. Finally, 30 nm copper seed layers were sputtered on both sides of the substrate film. (b) Preparation of the electroplated thickening layer: After the copper seed layer was prepared, the base film was placed in a water plating device, and the metal layer was thickened by water electroplating process. The current was 5A, the line speed was 5m / min, and the total thickness of the metal layer was controlled to be 1μm, thus preparing a flame-retardant composite current collector.

[0103] Example 2 The only difference between Example 2 and Example 1 is that octavinyl cage-type silsesquioxane is used. The methyl methacrylate polymer was replaced with an equal mass of octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer; In this embodiment, the preparation of the pyrolysis high-temperature resistant polymer in S1 is replaced by the preparation of the octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymer, and the preparation method is as follows: Hydrogenated bisphenol A and toluene were mixed at a mass ratio of 1:3, refluxed at 120°C for dehydration, and then cooled to 70°C. Anhydrous tin tetrachloride (tannin tetrachloride to hydrogenated bisphenol A mass ratio of 0.65:100) and OV-POSS (OV-POSS to hydrogenated bisphenol A mass ratio of 5:100) were added, along with epichlorohydrin (epicochlorohydrin to hydrogenated bisphenol A mass ratio of 1:1). The mixture was then heated to 80°C and reacted for 6 hours. Subsequently, the mixture was cooled to 40°C, and a sodium alkoxide-ethanol solution (anhydrous ethanol to NaOH mass ratio of 1:20, NaOH to hydrogenated bisphenol A mass ratio of 5:100) was added, followed by a reaction for 6 hours. After the reaction was complete, the organic layer was washed and extracted with toluene and deionized water. The solvent in the organic layer was removed under vacuum to obtain an octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epicochlorohydrin polymer.

[0104] Example 3 The only difference between Example 3 and Example 1 is that the polystyrene nanospheres are replaced with polycarbonate nanospheres of equal mass and particle size.

[0105] Example 4 The only difference between Example 4 and Example 1 is that the polystyrene nanospheres are replaced with polyvinyl chloride nanospheres of equal mass and particle size.

[0106] Example 5 The only difference between Example 5 and Example 1 is that triphenyl phosphate is replaced with an equal mass of dimethyl methyl phosphate.

[0107] Example 6 The only difference between Example 6 and Example 1 is that polyphenylene ether grafted polydimethylsiloxane (PPO-g-PDMS) is replaced with an equal mass of diphenylmethane bismaleimide grafted polydimethylsiloxane (BMI-g-PDMS). In this example, the preparation of the anchoring material in S2 of Example 1 is replaced by the preparation of diphenylmethane bismaleimide-grafted polydimethylsiloxane (BMI-g-PDMS), and the specific steps are as follows: Diphenylmethane bismaleimide and aminopropyl-terminated polydimethylsiloxane (NH2-PDMS, Mn = 5000 g / mol) were added at a mass ratio of 1:4, and NMP solvent was added. The reaction was carried out at 130°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous methanol, filtered, and dried to obtain diphenylmethane bismaleimide-grafted polydimethylsiloxane (BMI-g-PDMS).

[0108] Example 7 The only difference between Example 7 and Example 1 is that the octavinyl cage-like silsesquioxane prepared in S1 is used instead. The mass ratio of methyl methacrylate polymer to polystyrene was adjusted to 1:0.1.

[0109] Example 8 The only difference between Example 8 and Example 1 is that the octavinyl cage-like silsesquioxane prepared in S1 is used instead. The mass ratio of methyl methacrylate polymer to polystyrene was adjusted to 1:2.5.

[0110] Comparative Example 1 The only difference between this comparative example and Example 1 is that the preparation of S1 flame-retardant microspheres is not performed. Instead, when preparing the base film, the flame-retardant microspheres are directly replaced with an equal mass of flame retardant TPP. The other steps are the same as in Example 1.

[0111] Comparative Example 2 The only difference between this comparative example and Example 1 is that tetraethyl orthosilicate is no longer added during the preparation of the S1 flame-retardant microspheres, meaning that the final flame-retardant microspheres do not have a silica shell: the other steps are the same as in Example 1.

[0112] Comparative Example 3 The only difference between this comparative example and Example 1 is that toughening polymer A is no longer added during the preparation of the S1 flame-retardant microspheres; the other steps are the same as in Example 1.

[0113] Comparative Example 4 The only difference between this comparative example and Example 1 is that the pyrolytic high-temperature resistant polymer B is no longer added during the preparation of the S1 flame-retardant microspheres; the other steps are the same as in Example 1.

[0114] Comparative Example 5 The only difference between this comparative example and Example 1 is that polyphenylene ether grafted polydimethylsiloxane (PPO-g-PDMS) is no longer added during the preparation of the S2 base film; the other steps are the same as in Example 1.

[0115] Comparative Example 6 This comparative example provides a conventional composite current collector, which is prepared by the following steps: S1. Preparation of the base film: Polypropylene resin is used as the core layer material; at the same time, polypropylene resin is also used as the surface layer compound; and the core layer compound and the surface layer compound are extruded in a stacked order by three-layer co-extrusion according to the process parameters of Example 1 to obtain a composite current collector base film.

[0116] S2. Preparation of composite current collectors: (a) Preparation of the magnetron sputtering substrate: A roll-up double-sided magnetron sputtering device was used, and copper seed layers were deposited sequentially on both sides of the composite current collector substrate film prepared above, according to the process parameters of Example 1. (b) Preparation of the electroplated thickening layer: After the copper seed layer was prepared, the base film was placed in a water plating device, and the metal layer was thickened by water electroplating according to the process parameters of Example 1. The total thickness of the metal layer was controlled to be 1 μm, and a composite current collector was prepared.

[0117] Test case The composite current collectors prepared in the above embodiments and comparative examples were used as samples for testing.

[0118] Test sample: The composite current collectors obtained in the above embodiments and comparative examples are assembled into batteries. The preparation method includes: the preparation step of the positive electrode sheet: adding the positive electrode active material LiNi to N-methylpyrrolidone. 0.6 Mn 0.2 Co 0.2 O2 (NCM622), conductive carbon black, and binder are mixed evenly and coated onto the surface of conventional aluminum foil. After drying, the foil is cut to obtain the positive electrode sheet. The negative electrode sheet is prepared by adding artificial graphite, conductive carbon black, thickener, and binder to N-methylpyrrolidone, mixing evenly, coating onto the composite current collector obtained in the above examples and comparative examples, drying, and cutting to obtain the negative electrode sheet. The separator is a zirconia-coated polypropylene film (20 μm thick). The electrolyte is a 1 mol / L lithium hexafluorophosphate carbonate solution (where EMC:EC:PC = 1:1:1). The positive electrode sheet, separator, and negative electrode sheet are stacked in a Z-shape, placed in the casing, injected with electrolyte, and sealed to obtain a stacked battery. The battery is placed for 24 h before testing to ensure that the electrode materials are fully wetted by the electrolyte.

[0119] Battery stability and durability testing: (1) Internal resistance test: The initial internal resistance of the battery and the internal resistance after 500 charge-discharge cycles were tested using an AC impedance meter; (2) After the battery is fully charged at 0.5C at room temperature, it is left to stand for more than 3 hours. Then, a needle penetration test is performed in accordance with GB / T31485-2015, and the pass rate of the needle penetration test is calculated. The maximum surface temperature is tested by a real-time temperature tester. The thermocouple induction probe of the temperature tester is placed on the surface of the battery and the real-time temperature is detected. The highest temperature of the battery surface during the needle penetration test is calculated.

[0120] The specific test results are shown in Table 1: Table 1

[0121] As shown in Table 1, the batteries assembled from the composite current collectors prepared in Examples 1 to 8 have an initial internal resistance range of 21.9 to 23.9 mΩ, an internal resistance range of 23.2 to 25.6 mΩ after 500 cycles, an internal resistance change rate between 5.94% and 7.11%, a maximum needle penetration test temperature controlled between 160.4 and 172.2℃, a needle penetration test pass rate of 100%, and stable overall internal resistance stability and flame retardant safety performance.

[0122] As can be seen from the data of Examples 1-8 and Comparative Example 1, the maximum temperature in Comparative Example 1 increased significantly during the needle penetration test, indicating that the flame retardant failed prematurely during the film-forming stage, resulting in a poorer flame retardant effect.

[0123] As can be seen from the data of Examples 1-8 and Comparative Examples 1-2, when the flame-retardant microspheres do not have a silica shell, they cannot provide rigid protection. Some flame-retardant microspheres rupture during the preparation process, causing the flame retardant to fail and the temperature to rise during the needle penetration test.

[0124] As can be seen from the data of Examples 1-8 and Comparative Example 3, when the flame-retardant microspheres do not have toughening polymer, the maximum temperature increases, indicating that the lack of toughening polymer reduces the toughness of the first shell. During film formation or the preparation of the second shell, the microspheres may rupture due to shearing / stretching, leading to the release and leakage of flame retardant, reducing the flame retardant effect, and decreasing the needle penetration rate.

[0125] Data from Examples 1-8 and Comparative Examples 4 and 6 show that the highest temperature during the needle penetration test is similar to that of Comparative Example 6, indicating that the flame retardant cannot be released and function due to the lack of pyrolysis material, resulting in a sharp decrease in the needle penetration pass rate. Specifically, Examples 1-8 of this invention provide a synergistic structure employing a mid-core layer loaded with flame-retardant microspheres and a surface layer composite anchoring material. This allows for efficient release and effective function of the flame retardant upon needle penetration triggering, significantly suppressing temperature rise and greatly improving battery safety performance. In contrast, Comparative Example 6, lacking both flame-retardant microspheres and anchoring material, exhibits a sharp increase in needle penetration temperature, further confirming the crucial and effective role of this composite structure in improving safety performance.

[0126] The data from Examples 1-8 and Comparative Example 5 show that the battery internal resistance increases and the temperature rises during the nail penetration test. This indicates that the flame retardant without anchoring material is released during battery cycling, resulting in poor adhesion of the metal layer, increased internal resistance, and failure of the flame retardant release, thereby reducing the flame retardant effect.

[0127] 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 flame-retardant composite current collector base membrane, characterized in that, The flame-retardant composite current collector base film includes an intermediate core layer, and the intermediate core layer includes flame-retardant microspheres and a matrix resin; The flame-retardant microsphere comprises, from the inside out, an inner core, a first shell layer, and a second shell layer; the inner core includes a flame retardant, the first shell layer includes a toughening polymer and a pyrolysis-resistant high-temperature polymer, and the second shell layer is a porous protective layer.

2. The flame-retardant composite current collector base film according to claim 1, characterized in that, The intermediate core layer must satisfy at least one of the following conditions: (1) The mass ratio of the flame-retardant microspheres to the matrix resin is (0.02~0.1):1; (2) The matrix resin includes any one or a combination of at least two of polypropylene, chlorinated polypropylene, polyethylene, chlorinated polyethylene, metallocene polyethylene, and polyethylene terephthalate; (3) The flame retardant includes small molecule phosphorus-based flame retardant materials; (4) The toughening polymer includes any one or a combination of at least two of polystyrene, polycarbonate, and polyvinyl chloride; (5) The pyrolysis high-temperature resistant polymer includes octavinyl cage-type silsesquioxane. methyl methacrylate polymers and / or octavinyl cage-type silsesquioxane-hydrogenated bisphenol A-epoxychloropropane polymers; (6) The mass ratio of the pyrolytic high-temperature resistant polymer to the toughening polymer is 1:(0.1~2.5); (7) The second shell is a silica shell with a porous nanostructure; (8) The pore size of the second shell is 5~20 nm, and the porosity of the second shell is 30~60%; (9) The particle size of the inner core is 0.1~0.2 μm, the thickness of the first shell layer is 0.05~0.1 μm, and the thickness of the second shell layer is 0.02~0.1 μm.

3. The flame-retardant composite current collector base film according to claim 1, characterized in that, The intermediate core layer is further provided with a surface layer on both sides, and the surface layer includes a matrix resin and an anchoring material. Preferably, the anchoring material is brominated polyphenylene ether grafted polydimethylsiloxane and / or diphenylmethane bismaleimide grafted polydimethylsiloxane.

4. The flame-retardant composite current collector base film according to claim 1 or 3, characterized in that, When a surface layer is provided on both sides of the intermediate core layer, the surface layer and the core layer must also meet at least one of the following conditions: (i) The thickness ratio of the surface layer to the thickness of the intermediate core layer is 1:(2~15); (ii) The thickness of the surface layer is 0.4~1 μm, and the thickness of the intermediate core layer is 2~6 μm; (iii) In the surface layer, the mass ratio of the anchoring material to the matrix resin is (0.01~0.05):1; (iv) In the surface layer, the matrix resin comprises any one or a combination of at least two of polypropylene, chlorinated polypropylene, polyethylene, chlorinated polyethylene, metallocene polyethylene, and polyethylene terephthalate.

5. A method for preparing a flame-retardant composite current collector base film according to any one of claims 1 to 4, characterized in that, The preparation method of the flame-retardant composite current collector base film includes: The pyrolysis high-temperature resistant polymer slurry and the toughening polymer slurry are mixed to obtain a mixed slurry; The mixed slurry was added to the precursor of the porous material and in situ synthesized to obtain the microcapsule preform. After injecting a flame retardant into the core of the microcapsule preform, a semi-curing treatment is performed to obtain an intermediate. The matrix resin and intermediates are mixed to obtain the core layer mixture; The core layer mixture is extruded by co-extrusion to obtain the intermediate core layer of the flame-retardant composite current collector base film.

6. The method for preparing the flame-retardant composite current collector base film according to claim 5, characterized in that, When a surface layer is provided on both sides of the intermediate core layer, the preparation method of the flame-retardant composite current collector base film includes the following steps: The pyrolysis high-temperature resistant polymer slurry and the toughening polymer slurry are mixed to obtain a mixed slurry; The mixed slurry was added to the precursor of the porous material and in situ synthesized to obtain the microcapsule preform. After injecting a flame retardant into the core of the microcapsule preform, a semi-curing treatment is performed to obtain an intermediate. The matrix resin and intermediates are mixed to obtain the core layer mixture; The base resin and anchoring material are mixed to obtain the surface mixture; The flame-retardant composite current collector base film is obtained by extruding the core layer mixture and the surface layer mixture in a stacked sequence through a three-layer co-extrusion process.

7. A flame-retardant composite current collector, characterized in that, The flame-retardant composite current collector includes an insulating layer and metal layers disposed on both sides of the insulating layer; The insulating layer includes a flame-retardant composite current collector base film as described in any one of claims 1 to 4.

8. The method for preparing the flame-retardant composite current collector according to claim 7, characterized in that, The preparation method of the flame-retardant composite current collector includes: The flame-retardant composite current collector is obtained by placing the base film of the flame-retardant composite current collector in a pyrolysis plasma atmosphere and depositing a metal layer by magnetron sputtering.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the flame-retardant composite current collector as described in claim 7.

10. An electrochemical device, characterized in that, The electrochemical device includes the lithium-ion battery as described in claim 9.

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