Dry multi-layer composite electrode film, method for preparing the same, electrode sheet, and battery

Abstract

The present application relates to the technical field of battery preparation, and more particularly to a dry method multi-layer composite electrode film, a preparation method thereof, an electrode sheet and a battery. The dry method multi-layer composite electrode film comprises an electrolyte induction layer, an active material layer, a structure layer and a buffer layer. The electrolyte induction layer is formed by a polar organic high-molecular cross-linked organic film base material, and the electrolyte is better infiltrated into the electrode interior through the attraction of polar molecules to the electrolyte. The structure layer is supported by a high-strength organic film, which improves the structure and tensile strength of the dry method electrode self-supporting film. The buffer layer is formed by an elastic organic high-molecule film, which sets an elastic buffer layer for the multi-layer electrode sheet structure, plays a buffering role when the active material particles swell and shrink, and prevents the destruction of the PTFE fiber filament structure or the electrode sheet structure caused by the volume change of the particles. The present application solves the problems of low mechanical tensile strength, poor electrolyte infiltration and weak volume change resistance in the prior art.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to dry-process multilayer composite electrode films and their preparation methods, electrode sheets, and batteries. Background Technology

[0002] Electrode manufacturing plays a crucial role in battery production. Traditional electrode preparation employs a wet slurry process, where active materials, conductive carbon, binders, and other materials are mixed in a solvent system to form a slurry, which is then coated onto a current collector to form a complete electrode. The wet slurry process is simple and widely accepted by most battery manufacturers. However, because wet slurries use N-methylpyrrolidone (NMP) solvent to disperse materials, solvent evaporation and recovery are unavoidable, with solvent recovery costs typically accounting for approximately 48-50.2% of the total electrode production cost. Therefore, dry electrode processes have gradually emerged as a new electrode manufacturing technology in recent years.

[0003] Dry electrode technology utilizes binders with special properties (such as heat-fusibility and fiber-forming properties) to mix active materials, conductive carbon, and binders without the use of solvents. Under specific conditions (such as high temperature and high shear force), the binder exerts its bonding effect, enabling the complete electrode production process in small equipment, significantly reducing the equipment footprint. The dry electrode process eliminates solvent recovery and drying steps, saving substantial energy and labor time.

[0004] Taking the manufacturing of lithium iron phosphate (LFP) electrode materials as an example, in wet processes (such as...) Figure 2 In process a), polyvinylidene fluoride (PVDF) is typically used as the binder, and N-methylpyrrolidone (NMP) is typically used as the dispersant. During wet mixing, the role of PVDF particles is non-directional: in the solvent, PVDF particles are uniformly dispersed in the NMP solvent system and tend to adsorb onto the surface of LFP particles. During solvent evaporation, more PVDF particles remain in situ, which may be between two or more LFP particles, thus playing a bonding role; however, it may also be on the surface of a single LFP particle, thus failing to play a bonding role, resulting in low bonding efficiency. Dry processes (such as...) Figure 2 (b) The adhesive is generally polytetrafluoroethylene (PTFE), which undergoes fibrosis under shear force, forming a filamentous structure with a high aspect ratio, similar to a spider web binding water droplets (e.g. Figure 2 c) The LFP particles adhere in the same way; it is worth noting that the shear force is generated by friction between two or more LFP molecules, and the resulting PTFE fibrillation also occurs between these two or more LFP particles. Therefore, in this process, the binder provides higher bonding efficiency. Comparison of scanning electron microscopy (SEM) images of wet and dry electrodes (e.g.) Figure 2 d and Figure 2 (e) In wet-process electrodes, the binder adheres to the entire surface of the LFP particles, resulting in low bonding efficiency; while in dry-process electrodes, the filamentous structure formed by the binder adheres almost entirely between multiple LFP particles, resulting in high bonding efficiency. This high bonding efficiency allows the dry-process electrode process to achieve a higher proportion of active material, resulting in electrodes with high mechanical strength.

[0005] The PTFE dry electrode process involves mixing active materials with conductive additives (such as carbon black) and PTFE, then subjecting the PTFE to shear force to fibrous formation. The protofibrils are only a few nanometers in diameter and tens of micrometers in length, forming a three-dimensional network structure that polymerizes the active material and carbon black together. In subsequent steps, this mixture is pressed between two rolls to form a film hundreds of micrometers thick. This film achieves the desired target thickness and porosity in further rolling. The main challenges currently include: (1) In dry cathodes, due to the non-polar structure of PTFE, the dry electrode sheet has poor wettability to commonly used polar electrolytes. The electrolyte cannot wet the electrode sheet, ion transport is hindered, and the rate performance is poor. By modifying the internal structure of the electrode sheet and the particle and filament structure of PTFE, the wettability of the dry electrode sheet to polar electrolytes can be enhanced, thereby improving its rate performance.

[0006] (2) In order to be processed into a self-supporting film, the dry film must have a certain mechanical tensile strength. If the binder cannot reach this tensile strength, for example due to a very low binder content or defects due to non-uniformity of the mixture, the risk of film cracking is very high, especially for films below 100 μm. The wider the film and the faster the production, the more unstable the corresponding process steps and dry film quality.

[0007] (3) The PTFE fibers are not microscopically strong. When the active material undergoes volume changes, they may be stretched and broken, thus losing their adhesive properties. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a dry-process multilayer composite electrode film and its preparation method, electrode sheet and battery, so as to at least solve the problems of low mechanical tensile strength, poor electrolyte wetting and weak resistance to volume change in the prior art.

[0009] The following is a summary of this disclosure to provide a basic understanding of some aspects. This summary is not intended to identify key or important elements, nor is it intended to limit the implementation or any aspects of the claims. Furthermore, this summary provides a simplified overview of some aspects that can be described in more detail in other parts of this disclosure.

[0010] The present invention solves the above-mentioned technical problems through the following technical means: In a first aspect, embodiments of the present invention provide a dry-processed multilayer composite electrode film, comprising: An electrolyte induction layer is used to induce and promote the penetration of electrolyte into the interior of the electrode. The electrolyte induction layer includes a substrate, a polar monomer, an initiator, and a crosslinking agent. The polar monomer is used to provide polar groups, and the crosslinking agent is used to form a crosslinking network. At least one active material layer is provided to provide battery capacity. The active material layer is formed using a dry electrode process. The active material layer is covered on both opposite sides of the electrolyte induction layer.

[0011] In conjunction with the first aspect, in some embodiments, the electrolyte induction layer comprises: 30-80 wt% substrate, 1-50 wt% polar monomer, 1-10 wt% initiator, 1-10 wt% crosslinking agent, 0-10 wt% conductive carbon, and solvent, wherein the total mass percentage of the substrate, polar monomer, initiator, crosslinking agent, conductive carbon, and solvent is 100%.

[0012] In conjunction with the first aspect, in some embodiments, the substrate is selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polysulfone, polyethersulfone, polyimide, polyamide, cellulose acetate, regenerated cellulose, polyacrylonitrile, polyetheretherketone, polyvinyl chloride, alumina, zirconium dioxide, titanium dioxide, silicon dioxide, silicon carbide, silicon nitride, stainless steel sintered felt, stainless steel sintered mesh, carbon fiber, graphene, graphene oxide, carbon nanotubes, PET nonwoven fabric, glass fiber, titanium, nickel, palladium and their alloys, and carbon-based and composite materials; and / or, The polar monomer is selected from at least one of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, fumaric acid, acrylamide, methacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-hydroxyethylacrylamide, diketoacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, glycidyl methacrylate, polyethylene glycol acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazolium, 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate, ethyl acrylate phosphate, vinyl sulfonic acid, methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and dimethyldiallylammonium chloride; and / or, The initiator is selected from dimethyl azobisisobutyrate, 4,4'-azobis-4-cyanopentanoic acid, azobisisoheptanenitrile, azobisisovalerate, 1,1'-azobiscyclohexanenitrile, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, benzoyl peroxide, dicumyl peroxide, lauroyl peroxide, tert-butyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, methyl ethyl ketone peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, 2-hydroxy-2-methylphenylacetone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl lysylacetone-1, Irgacure 2959, at least one of the following: a mixture of persulfate / sodium bisulfite, a mixture of hydrogen peroxide / ferrous salt, a mixture of benzoyl peroxide / N,N-dimethylaniline, and a mixture of hydrogen peroxide / ascorbic acid; and / or, The crosslinking agent is selected from polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, N,N'-bisacrylamide, N,N'-1,2-ethylenedimethylbisacrylamide, diallyl tartrate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diethylene glycol divinyl ether, allyl glycidyl ether, and glycidyl methacrylate.

[0013] In conjunction with the first aspect, in some embodiments, the dry-process multilayer composite electrode film further includes a structural layer, wherein both opposite sides of the structural layer are covered with an active material layer; and / or, The dry-process multilayer composite electrode film also includes a buffer layer, and both sides of the buffer layer are covered with an active material layer.

[0014] In conjunction with the first aspect, in some embodiments, the dry-process multilayer composite electrode film includes an active material layer, an electrolyte induction layer, an active material layer, a buffer layer, an active material layer, a structural layer, and an active material layer stacked sequentially.

[0015] In conjunction with the first aspect, in some embodiments, the structural layer is a film formed from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, polytrifluoroethylene, polyimide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polypropylene, and polyethylene.

[0016] In conjunction with the first aspect, in some embodiments, the buffer layer is a film formed from at least one of polyethylene oxide, sodium alginate, carboxymethyl cellulose, sodium hyaluronate, carboxymethyl starch, and hydroxypropyl starch.

[0017] Secondly, embodiments of the present invention also disclose a method for preparing the dry-process multilayer composite electrode film described in the first aspect, comprising the following steps: To prepare the active material layer, the electrode active material, conductive agent and binder are mixed and then rolled into a thin sheet at 150-200°C to obtain the active material layer. To prepare the structural layer, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, polytrifluoroethylene, polyimide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polypropylene, and polyethylene is dissolved in an organic solvent, and the film is scraped and dried to obtain a thin film sheet, i.e., the structural layer. To prepare an electrolyte-induced layer, a substrate, polar monomer, initiator, crosslinking agent, and conductive carbon are added to a solvent and subjected to crosslinking polymerization at a temperature of 60–100℃ and a pressure of 0.9–1.2 atm for 2–5 hours. The resulting reaction solution is then coated and steam-induced at a relative humidity of 50–90% to solidify and replace the solvent. After drying, the electrolyte-induced layer is obtained. To prepare a buffer layer, at least one of polyethylene oxide, sodium alginate, carboxymethyl cellulose, sodium hyaluronate, carboxymethyl starch, and hydroxypropyl starch is dissolved in an aqueous solvent, and then cured by coating to form a thin film, i.e., a buffer layer. Multilayer composite is obtained by stacking the layers in the following order: active material layer, electrolyte induction layer, active material layer, buffer layer, active material layer, structural layer, and active material layer, and then rolling the composite at 150–200°C.

[0018] Thirdly, embodiments of the present invention also provide an electrode sheet, the electrode sheet comprising a current collector and a dry-process multilayer composite electrode film as described in the first or second aspect, wherein the dry-process multilayer composite electrode film is overlapped and attached to the current collector.

[0019] Fourthly, embodiments of the present invention also provide a battery, the battery comprising the electrode sheet described in the third aspect.

[0020] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages: (1) The active material layer in the multilayer composite electrode film of the present invention is produced by solvent-free dry electrode process, which avoids the high energy consumption process of solvent evaporation and recovery, and reduces the manufacturing cost of electrode sheet.

[0021] (2) The electrolyte-inducing layer of the multilayer composite electrode film of the present invention improves the wettability of the electrolyte on the electrode surface, and the contact angle is reduced from about 60° to about 30°, which significantly enhances mass transfer and improves rate performance.

[0022] (3) The multilayer composite electrode film of the present invention improves the tensile strength of the electrode by more than 30% by introducing high-strength polymer materials such as PVDF that take into account elasticity.

[0023] (4) The buffer layer of the multilayer composite electrode film of the present invention provides elastic protection, thereby reducing the volume change of the entire electrode sheet in the direction perpendicular to the electrode sheet by more than 50%.

[0024] (5) The preparation method of the multilayer composite electrode film of the present invention is applicable to large-scale industrial continuous production. Industrially, a self-supporting film can be formed by continuous rolling, and a functional layer film can be formed by continuous photocuring and drying with green solvents such as water. Multiple sets of rolling equipment are used for continuous production, and the resulting multiple film strips are stacked in a stacking machine. Then, they directly enter the final rolling equipment and are formed into the final self-supporting electrode film through continuous high-temperature shearing and rolling. Finally, current collectors such as carbon-coated copper foil / carbon-coated aluminum foil are attached to form a complete electrode. The whole process is applicable to battery workshops and factories with continuous production. Since the commonly used water-absorbing and toxic solvents such as NMP are eliminated, the energy consumption caused by solvent recycling is reduced while being more environmentally friendly, which is more in line with the theme of green production. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the dry-process multilayer composite electrode film of the present invention, wherein the active material layer 100, the electrolyte induction layer 210, the buffer layer 220, and the structural layer 230 are included. Figure 2 This is a comparison diagram of existing wet electrode processes and dry electrode processes. In the diagram, a is a schematic diagram of the preparation principle of the wet electrode process, b is a schematic diagram of the preparation principle of the dry electrode process, c is a visual schematic diagram of the fiber adhesion principle, d is a SEM image of the wet electrode, and e is a SEM image of the dry electrode. Figure 3 This is a SEM image of the active material layer in the positive electrode sheet of Example 6; Figure 4 This is a SEM image of the active material layer behind the positive electrode sheet in Example 6, which was excited by high voltage. Figure 5 This is an EDS image of the active material layer in the positive electrode sheet of Example 6, obtained by scanning the elemental composition of F. Figure 6 This is a high-magnification SEM image of the active material layer in the positive electrode sheet of Example 6, wherein, Figure 6 (a) is a SEM image with a scale bar of 10 μm. Figure 6(b) is a SEM image with a scale bar of 4 μm. Figure 6 (c) is a SEM image with a scale bar of 2 μm. Detailed Implementation

[0026] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0027] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0028] The dry-process multilayer composite electrode film of this application is composed of multiple overlapping structures, specifically including an active material layer 100 and a functional layer. The functional layer further includes an electrolyte-inducing layer 210, a structural layer 220, and a buffer layer 230. Each functional layer has an active material layer on both opposite sides. Specifically, refer to... Figure 1 The dry-process multilayer composite electrode membrane comprises, in sequence, an active material layer 100, an electrolyte induction layer 210, an active material layer 100, a buffer layer 220, an active material layer 100, a structural layer 230, and another active material layer 100. The active material layer and the functional layer are stacked together and then rolled together in a rolling mill to form a dry-process multilayer composite electrode membrane with high strength, good electrolyte wettability, and resistance to volume changes.

[0029] The active material layer 100 is used to provide battery capacity. The active material layer 100 is formed using a dry electrode process and is a thin film formed from electrode active materials, conductive agents, and binders. Specifically, the raw materials for preparing the active material layer include 80–96 wt% electrode active materials, 0.5–10 wt% conductive agents, and 0.5–10 wt% binders. According to existing conventional technology, the powders of electrode active materials, conductive agents, and binders are mixed using a mechanical mixing device to form a uniform dry mixture. The mechanical mixing device can be a high-speed mixer or a ball mill. The dry mixture is then transferred to a rolling mill and rolled into a thin film at 150–200°C to obtain the active material layer. The electrode active materials are used to store and release charge. For the positive electrode, lithium compounds such as lithium iron phosphate and ternary lithium compounds can be used; for the negative electrode, at least one of artificial graphite, natural graphite, silicon suboxide, pre-lithiated silicon suboxide, and silicon-carbon materials can be used. The conductive agent can be at least one of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers, or graphene, used to improve the conductivity of the electrode. The binder is a dry electrode binder used to firmly bond the electrode active material, conductive agent, and other materials together. The binder can include polymeric materials such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). Alternatively, the active material layer of this application can be considered to utilize existing technology, combining an electrolyte induction layer, a structural layer, and a buffer layer on the basis of existing dry electrode films.

[0030] The electrolyte induction layer 210 is used to induce and promote the penetration of electrolyte into the electrode. The electrolyte induction layer 210 comprises: 30-80 wt% substrate, 1-50 wt% polar monomer, 1-10 wt% initiator, 1-10 wt% crosslinking agent, 0-10 wt% conductive carbon, and solvent. The total mass percentage of the substrate, polar monomer, initiator, crosslinking agent, conductive carbon, and solvent is 100%. The substrate, polar monomer, initiator, and crosslinking agent are added to the solvent and subjected to crosslinking polymerization at a temperature of 60-100℃ and a pressure of 0.9-1.2 atm for 2-5 hours. The resulting reaction solution is coated and then subjected to steam induction at a relative humidity of 50-90%. The solvent is then replaced and the mixture is dried to obtain the electrolyte induction layer. The hydrophilic organic material undergoes in-situ crosslinking polymerization at the substrate sites, and the polar groups are fixed on the substrate. After coating, the mixture is induced by 50-90% steam, cured by ultraviolet light or deionized water, and the solvent is replaced. This introduces the polar groups into the micro / nano-structured pores on the surface of the substrate, forming an electrolyte induction layer with both structural and tensile strength properties. Taking liquid batteries as an example, if there are multiple electrolyte induction layers in the composite structure, it can provide a driving force for the electrolyte to continuously penetrate into the electrode sheet, thereby accelerating mass transfer, providing better lithium-ion transport channels, and improving the rate performance of the battery.

[0031] In specific implementation, the solvent used in the preparation of the electrolyte induction layer 210 is used to provide the reaction environment, including at least one of the following: aprotic polar solvents, alcohols and polyols, ethers and cyclic ethers, esters and ketones, nonpolar / weakly polar hydrocarbons, water, acetonitrile, propylene carbonate, and ionic liquids. The aprotic polar solvent is selected from at least one of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), 1,3-dimethyl-2-imidazolinone (DMI), and N-ethylpyrrolidone (NEP); the alcohols and polyols are selected from at least one of ethanol, isopropanol (IPA), ethylene glycol, propylene glycol, and glycerol; the ethers and cyclic ethers are selected from at least one of tetrahydrofuran (THF), 1,4-dioxane, ethylene glycol dimethyl ether (DME), and 2-methyltetrahydrofuran; the esters and ketones are selected from at least one of ethyl acetate, butyl acetate, acetone, butanone, methyl isobutyl ketone, and γ-butyrolactone (GBL); and the nonpolar / weakly polar hydrocarbons are selected from at least one of toluene, xylene, n-hexane, and cyclohexane.

[0032] In specific implementations, the substrate is selected from at least one of the following: polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polysulfone, polyethersulfone, polyimide, polyamide, cellulose acetate, regenerated cellulose, polyacrylonitrile, polyetheretherketone, polyvinyl chloride, alumina, zirconium dioxide, titanium dioxide, silicon dioxide, silicon carbide, silicon nitride, stainless steel sintered felt, stainless steel sintered mesh, carbon fiber, graphene, graphene oxide, carbon nanotubes, PET nonwoven fabric, glass fiber, titanium, nickel, palladium and their alloys, carbon-based and composite materials.

[0033] In practical implementation, taking liquid batteries as an example, polar monomers are used to provide polar groups, enhancing the electrolyte-inducing layer's electrolyte affinity and facilitating electrolyte penetration into the electrode plates. The polar monomers are selected from at least one of the following: acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, fumaric acid, acrylamide, methacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-hydroxyethylacrylamide, diketoacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, glycidyl methacrylate, polyethylene glycol acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate, ethyl acrylate phosphate, vinyl sulfonic acid, methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and dimethyldiallylammonium chloride.

[0034] In practice, the initiator is used to initiate the crosslinking polymerization reaction. The initiator is selected from dimethyl azobisisobutyrate, 4,4'-azobis-4-cyanopentanoic acid, azobisisoheptanenitrile, azobisisovalerate, 1,1'-azobiscyclohexanenitrile, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, benzoyl peroxide, dicumyl peroxide, lauroyl peroxide, tert-butyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, methyl ethyl ketone peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, 2-hydroxy-2-methylphenylacetone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl lysylacetone-1, Irgacure 2959. At least one of the following: a mixture of persulfate / sodium bisulfite, a mixture of hydrogen peroxide / ferrous salt, a mixture of benzoyl peroxide / N,N-dimethylaniline, and a mixture of hydrogen peroxide / ascorbic acid.

[0035] In practice, the crosslinking agent is used to form a crosslinked network, preventing hydrophilic groups from entering the deionized water system during solvent replacement processes such as immersion in deionized water. The crosslinking agent is selected from polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, N,N'-bisacryloylcysteine, N,N'-1,2-ethylenedimethylbisacrylamide, diallyl tartaramide, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diethylene glycol divinyl ether, allyl glycidyl ether, and glycidyl methacrylate.

[0036] The structural layer 220 is supported by a high-strength organic film (such as PVDF), providing a supporting structure for the dry-process multilayer composite electrode film and improving mechanical properties such as tensile strength. Specifically, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, polytrifluoroethylene, polyimide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polypropylene, and polyethylene is dissolved in an organic solvent, and the film is dried to obtain a thin film sheet, i.e., the structural layer. The organic solvent is one of N-methylpyrrolidone and dimethylacetamide.

[0037] The buffer layer 230 is a thin film formed from elastic organic polymers, providing an elastic buffer layer for the dry-process multilayer composite electrode film. It buffers the expansion and contraction of active material particles (such as silicon carbon), preventing damage to the PTFE fiber filament structure or electrode structure caused by particle volume changes. Specifically, at least one of polyethylene oxide, sodium alginate, carboxymethyl cellulose, sodium hyaluronate, carboxymethyl starch, and hydroxypropyl starch is dissolved in an aqueous solvent, and then cured by coating to form a thin film, i.e., the buffer layer.

[0038] Taking liquid lithium-ion batteries as an example, the dry-process multilayer composite electrode film and its preparation method of the present invention are described in detail below: Example 1

[0039] In this embodiment, the dry-process multilayer composite electrode film is used as the positive electrode, and its preparation method is as follows: (1) To prepare the active material layer, 90 wt% lithium iron phosphate, 3 wt% conductive carbon black and 7 wt% polytetrafluoroethylene were mixed in a high-speed mixer and then rolled into thin sheets at 180°C by differential speed to obtain the active material layer.

[0040] (2) To prepare the structural layer, polyvinylidene fluoride is dissolved in dimethylacetamide, and the film is dried to obtain a thin film sheet, i.e., the structural layer.

[0041] (3) To prepare the electrolyte-induced layer, 75 wt% polyethylene, 10 wt% acrylic acid, 6 wt% dimethyl azobisisobutyrate, 6 wt% polyethylene glycol diacrylate and 3 wt% conductive carbon were added to N,N-dimethylformamide solvent and crosslinked polymerized at 80℃ and 1.0 atm for 3 h. The resulting reaction solution was coated and steam-induced at 60% relative humidity. The solution was cured with deionized water and the solvent was replaced. After drying, the electrolyte-induced layer was obtained.

[0042] (4) Prepare a buffer layer by dissolving polyethylene oxide in deionized water and curing it into a thin film, i.e., a buffer layer.

[0043] (5) Multilayer composite: The layers are stacked in the order of active material layer, electrolyte induction layer, active material layer, buffer layer, active material layer, structural layer, and active material layer, and then differentially rolled at 180°C to obtain a dry multilayer composite electrode film.

[0044] Tensile strength tests were conducted on the dry-process multilayer composite electrode film of this embodiment. The experimental group consisted of the dry-process multilayer composite electrode film of this embodiment, while the control group consisted of a traditional PTFE single-layer dry-process electrode film without a structural layer. The active material loading and thickness of both groups of samples remained consistent. The tensile strength test results showed that the average tensile strength of the control group was 8.8 MPa, while the tensile strength of the dry-process multilayer composite electrode film of this embodiment reached 11.9 MPa. These data indicate that the introduction of the structural layer improved the tensile performance of the electrode by approximately 35.2%. In addition, the experimental group also exhibited better toughness in terms of elongation at break, which can meet the belt conveying requirements of high-speed coating roll forming production lines under high tension conditions, effectively reducing the film breakage rate during the production process. Example 2

[0045] In this embodiment, the dry-process multilayer composite electrode film is used as the positive electrode, and its preparation method is as follows: (1) To prepare the active material layer, 91wt% ternary lithium compound, 3wt% conductive carbon black and 6wt% polytetrafluoroethylene were mixed in a high-speed mixer and then rolled into thin sheets at 180℃ to obtain the active material layer.

[0046] (2) To prepare the structural layer, polytetrafluoroethylene is dissolved in dimethylacetamide, and the film is dried to obtain a thin film sheet, i.e., the structural layer.

[0047] (3) To prepare the electrolyte-induced layer, 80 wt% polypropylene, 8 wt% methacrylic acid, 4 wt% sodium persulfate, 4 wt% ethylene glycol dimethacrylate and 4 wt% conductive carbon were added to DMPU solvent and crosslinked polymerized at 60℃ and 0.9 atm for 5 h. The resulting reaction solution was coated and steam-induced at 50% relative humidity. The solution was cured with deionized water and the solvent was replaced. The solution was then dried to obtain the electrolyte-induced layer.

[0048] (4) Prepare a buffer layer by dissolving carboxymethyl cellulose in deionized water and curing it into a thin film, i.e., a buffer layer.

[0049] (5) Multilayer composite: The layers are stacked in the order of active material layer, electrolyte induction layer, active material layer, buffer layer, active material layer, structural layer, and active material layer, and then differentially rolled at 150°C to obtain a dry multilayer composite electrode film. Example 3

[0050] In this embodiment, the dry-process multilayer composite electrode film is used as the negative electrode, and its preparation method is as follows: (1) To prepare the active material layer, 85wt% silicon carbon material, 8wt% conductive carbon black and 7wt% polytetrafluoroethylene were mixed in a high-speed mixer and then rolled into thin sheets at 200℃ to obtain the active material layer.

[0051] (2) To prepare the structural layer, polyimide is dissolved in N-methylpyrrolidone, and the film is scraped and dried to obtain a thin film sheet, i.e., the structural layer.

[0052] (3) To prepare the electrolyte-induced layer, 70 wt% polyacrylonitrile, 15 wt% N-vinylpyrrolidone, 6 wt% tert-butyl peroxide, 6 wt% divinylbenzene and 3 wt% conductive carbon were added to isopropanol solvent and crosslinked polymerized at 100℃ and 1.2 atm for 2 h. The resulting reaction solution was coated and steam-induced at 90% relative humidity. The solution was cured with deionized water and the solvent was replaced. The solution was then dried to obtain the electrolyte-induced layer.

[0053] (4) Prepare a buffer layer by dissolving hydroxypropyl starch in deionized water and curing it into a thin film, i.e., a buffer layer.

[0054] (5) Multilayer composite: The layers are stacked in the order of active material layer, electrolyte induction layer, active material layer, buffer layer, active material layer, structural layer, and active material layer, and then differentially rolled at 200°C to obtain a dry multilayer composite electrode film. Example 4

[0055] In this embodiment, the dry-process multilayer composite electrode film is used as the negative electrode, and its preparation method is as follows: (1) To prepare the active material layer, 85wt% silicon carbon material, 7wt% conductive carbon black and 8wt% polytetrafluoroethylene were mixed in a high-speed mixer and then rolled into thin sheets at 150℃ to obtain the active material layer.

[0056] (2) To prepare the structural layer, polyimide is dissolved in N-methylpyrrolidone, and the film is scraped and dried to obtain a thin film sheet, i.e., the structural layer.

[0057] (3) To prepare the electrolyte-induced layer, 70 wt% polyacrylonitrile, 15 wt% N-vinylpyrrolidone, 6 wt% tert-butyl peroxide, 6 wt% divinylbenzene and 3 wt% conductive carbon were added to isopropanol solvent and crosslinked polymerized at 80 °C and 1.1 atm for 3 h. The resulting reaction solution was coated and steam-induced at 60% relative humidity. The solution was cured with deionized water and the solvent was replaced. The solution was then dried to obtain the electrolyte-induced layer.

[0058] (4) Prepare a buffer layer by dissolving sodium alginate in deionized water and curing it into a thin film, i.e., a buffer layer.

[0059] (5) Multilayer composite: The layers are stacked in the order of active material layer, electrolyte induction layer, active material layer, buffer layer, active material layer, structural layer, and active material layer, and then differentially rolled at 200°C to obtain a dry multilayer composite electrode film. Example 5

[0060] The positive electrode sheet in this embodiment uses the dry-process multilayer composite electrode film of Example 1. Specifically, the dry-process multilayer composite electrode film of Example 1 and the aluminum foil current collector are stacked together and rolled at a temperature of 100°C and a pressure of 2MPa to obtain the positive electrode sheet.

[0061] The dry-process multilayer composite electrode film in the positive electrode sheet of this embodiment exhibits excellent electrolyte wetting performance, reducing the wetting contact angle from 62° in the original dry process to 28°, and improving the capacity retention rate at 3C rate by more than 15% compared to the traditional dry electrode. The dry-process multilayer composite electrode film in the positive electrode sheet of this embodiment achieves a tensile strength of 12 MPa, which is 35% higher than that of the film without structural layers, enabling it to withstand higher industrial production tensions without breaking, thus effectively improving its mechanical properties.

[0062] In the dry-process multilayer composite electrode film of the positive electrode sheet in this embodiment, the electrolyte-inducing layer provides abundant electrolyte-loving groups through in-situ cross-linked polar monomers. These polar sites form a chemical pump that guides the electrolyte to permeate into the electrode sheet, thereby overcoming the hydrophobic problem caused by the non-polarity of PTFE. At the same time, the PVDF structural layer, as the core framework, uses the strong cohesive force of its polymer chains to compensate for the strength defects of PTFE fibers at extremely low content, achieving a balance between mechanical strength and electrochemical activity. Example 6

[0063] The positive electrode sheet in this embodiment uses the dry-process multilayer composite electrode film of Example 2. Specifically, the dry-process multilayer composite electrode film of Example 2 and the aluminum foil current collector are stacked together and rolled at a temperature of 80°C and a pressure of 3MPa to obtain the positive electrode sheet.

[0064] SEM image (scale bar is 20 μm) of the active material layer in the positive electrode sheet of this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that PTFE has undergone good fibrosis. Since the filamentous structure forms a protective film on the electrode surface, preventing electron penetration, a higher voltage (15 kV vs. 3 kV) is used to excite electrons with higher penetration ability, resulting in the SEM image shown below. Figure 4 As shown, the ternary lithium compound particles remain intact and are uniformly distributed. The EDS image obtained by scanning the F element using energy dispersive spectroscopy (EDS) is shown below. Figure 5 As shown in the image, the PTFE fiber structure is uniformly distributed in the electrode sheet, providing excellent adhesion. A high-magnification SEM image of the active material layer in the positive electrode sheet of this embodiment is shown below. Figure 6 As shown, where, Figure 6 (a) is a SEM image with a scale bar of 10 μm. Figure 6 (b) is a SEM image with a scale bar of 4 μm. Figure 6 (c) is a SEM image with a scale bar of 2 μm. It can be seen that the conductive carbon is uniformly distributed in the PTFE network and forms a bonding-conductive composite network system.

[0065] The positive electrode sheet in this embodiment exhibits significant structural stability during cycle testing. After 500 deep charge-discharge cycles, the electrode sheet maintains good integrity with no obvious cracks. The electrolyte-induced efficiency in the dry-process multilayer composite electrode film reduces the ion diffusion resistance inside the electrode by approximately 22%, ensuring that the battery temperature rise is controlled within a reasonable range under high current density.

[0066] In this embodiment, the dry-process multilayer composite electrode film in the positive electrode sheet effectively locks in polar groups through a cross-linked network structure, preventing their loss during long-term immersion in the electrolyte and ensuring the persistence of the induction effect. By adding an appropriate amount of conductive carbon to the electrolyte induction layer, wettability is improved while an electron transport network penetrating each layer is constructed, reducing interfacial contact resistance and thus synergistically enhancing the high-rate discharge capability of the ternary material. Example 7

[0067] The negative electrode sheet in this embodiment uses the dry-process multilayer composite electrode film of Example 3. Specifically, the dry-process multilayer composite electrode film of Example 3 and the copper foil current collector are stacked together and hot-pressed at a temperature of 100°C and a pressure of 2MPa to obtain the negative electrode sheet.

[0068] In this embodiment, the vertical volume expansion rate of the negative electrode sheet during the charging and discharging process is only 18%, which successfully suppresses the electrode pulverization caused by the expansion of silicon-based materials. Moreover, after 300 long cycles, the battery capacity retention rate remains stable at over 82%, proving the effective confinement of active material particles by the multilayer composite structure. Example 8

[0069] The negative electrode sheet in this embodiment uses the dry-process multilayer composite electrode film of Example 4. Specifically, the dry-process multilayer composite electrode film of Example 4 and the copper foil current collector are stacked together and hot-pressed at a temperature of 150°C and a pressure of 1MPa to obtain the negative electrode sheet.

[0070] The dry-process multilayer composite electrode film in the negative electrode sheet of this embodiment achieves excellent mechanical toughness through the combination of a sodium alginate buffer layer and a polyimide structural layer. No active material detachment occurred during the 180° folding test. In the low-temperature negative electrode kinetic test, its charge transfer impedance remained stable, indicating that the multilayer structure can still maintain a highly efficient ion conduction channel under extreme conditions.

[0071] In this embodiment, the polyimide film, as a structural layer, provides extremely high thermal stability and tear resistance in the dry-process multilayer composite electrode film of the negative electrode sheet, providing stable support for the self-supporting film during high-temperature rolling. The buffer layer formed by sodium alginate utilizes its abundant hydroxyl groups to form hydrogen bonds with the surface of the active material, providing elasticity while enhancing interlayer bonding and effectively preventing interlayer delamination caused by volume changes.

[0072] Using the negative electrode sheets of Examples 7 and 8 as experimental samples and the traditional dry-process negative electrode as the control group, the thickness change of the electrode sheets was quantitatively analyzed using an in-situ displacement monitoring system. The experimental results showed that the traditional dry-process electrode without a buffer layer exhibited a vertical volume expansion rate as high as 42.6% under full charge (100% SOC); while the vertical volume expansion rates of the negative electrode sheets of Examples 7 and 8 under the same charge-discharge conditions were 17.8% and 17.5%, respectively. These data demonstrate that the introduction of the buffer layer reduced the overall vertical volume change of the electrode sheet by approximately 58.2%. Furthermore, after 500 deep cycles, the surfaces of the negative electrode sheets of Examples 7 and 8 remained smooth, and no PTFE fiber breakage or active material pulverization and shedding phenomena commonly observed in traditional dry-process electrodes were observed.

[0073] The dry-process multilayer composite electrode film of this invention can be applied to lithium-ion batteries, sodium-ion batteries, or zinc batteries to improve battery performance. Furthermore, the dry-process multilayer composite electrode film of this invention is applicable not only to liquid batteries using electrolytes but also to all-solid-state batteries. By using a solid electrolyte film as a functional layer film to form a multilayer structure, the performance of solid-state batteries can be improved.

[0074] The foregoing description includes examples from this specification. Of course, for the purposes of describing this specification, it is impossible to describe every conceivable combination of components or methods; however, those skilled in the art will understand that many other combinations and arrangements are possible. Therefore, this specification is intended to cover all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, with regard to the use of the term "comprising" in the detailed description or claims, the term is intended to be inclusive in a manner similar to the term "including," as interpreted when "comprising" is used as a transitional word in the claims.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dry-process multilayer composite electrode film, characterized in that, include: An electrolyte induction layer is used to induce and promote the penetration of electrolyte into the interior of the electrode. The electrolyte induction layer includes a substrate, a polar monomer, an initiator, and a crosslinking agent. The polar monomer is used to provide polar groups, and the crosslinking agent is used to form a crosslinking network. At least one active material layer is provided to provide battery capacity. The active material layer is formed using a dry electrode process. The active material layer is covered on both opposite sides of the electrolyte induction layer.

2. The dry-process multilayer composite electrode film according to claim 1, characterized in that, The electrolyte induction layer comprises: 30-80 wt% substrate, 1-50 wt% polar monomer, 1-10 wt% initiator, 1-10 wt% crosslinking agent, 0-10 wt% conductive carbon, and solvent, wherein the total mass percentage of the substrate, polar monomer, initiator, crosslinking agent, conductive carbon, and solvent is 100%.

3. The dry-process multilayer composite electrode film according to claim 2, characterized in that, The substrate is selected from at least one of the following: polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polysulfone, polyethersulfone, polyimide, polyamide, cellulose acetate, regenerated cellulose, polyacrylonitrile, polyetheretherketone, polyvinyl chloride, alumina, zirconium dioxide, titanium dioxide, silicon dioxide, silicon carbide, silicon nitride, stainless steel sintered felt, stainless steel sintered mesh, carbon fiber, graphene, graphene oxide, carbon nanotubes, PET nonwoven fabric, glass fiber, titanium, nickel, palladium and their alloys, and carbon-based and composite materials; and / or, The polar monomer is selected from at least one of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, fumaric acid, acrylamide, methacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-hydroxyethylacrylamide, diketoacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, glycidyl methacrylate, polyethylene glycol acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazolium, 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate, ethyl acrylate phosphate, vinyl sulfonic acid, methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and dimethyldiallylammonium chloride; and / or, The initiator is selected from dimethyl azobisisobutyrate, 4,4'-azobis-4-cyanopentanoic acid, azobisisoheptanenitrile, azobisisovalerate, 1,1'-azobiscyclohexanenitrile, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, benzoyl peroxide, dicumyl peroxide, lauroyl peroxide, tert-butyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, methyl ethyl ketone peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, 2-hydroxy-2-methylphenylacetone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl lysylacetone-1, Irgacure 2959, at least one of the following: a mixture of persulfate / sodium bisulfite, a mixture of hydrogen peroxide / ferrous salt, a mixture of benzoyl peroxide / N,N-dimethylaniline, and a mixture of hydrogen peroxide / ascorbic acid; and / or, The crosslinking agent is selected from polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, N,N'-bisacrylamide, N,N'-1,2-ethylenedimethylbisacrylamide, diallyl tartrate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diethylene glycol divinyl ether, allyl glycidyl ether, and glycidyl methacrylate.

4. The dry-process multilayer composite electrode film according to any one of claims 1-3, characterized in that, The dry-process multilayer composite electrode film further includes a structural layer, wherein both opposite sides of the structural layer are covered with an active material layer; and / or, The dry-process multilayer composite electrode film also includes a buffer layer, and both sides of the buffer layer are covered with an active material layer.

5. The dry-process multilayer composite electrode film according to claim 4, characterized in that, The dry-process multilayer composite electrode film comprises, in sequence, an active material layer, an electrolyte induction layer, an active material layer, a buffer layer, an active material layer, a structural layer, and another active material layer.

6. The dry-process multilayer composite electrode film according to claim 5, characterized in that, The structural layer is a film formed from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, polytrifluoroethylene, polyimide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polypropylene, and polyethylene.

7. The dry-process multilayer composite electrode film according to claim 5, characterized in that, The buffer layer is a film formed from at least one of polyethylene oxide, sodium alginate, carboxymethyl cellulose, sodium hyaluronate, carboxymethyl starch, and hydroxypropyl starch.

8. The method for preparing a dry-process multilayer composite electrode film according to any one of claims 1-7, characterized in that, Includes the following steps: To prepare the active material layer, the electrode active material, conductive agent and binder are mixed and then rolled into a thin sheet at 150-200°C to obtain the active material layer. To prepare the structural layer, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, ethylene-tetrafluoroethylene copolymer, polytrifluoroethylene, polyimide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polypropylene, and polyethylene is dissolved in an organic solvent, and the film is scraped and dried to obtain a thin film sheet, i.e., the structural layer. To prepare an electrolyte-induced layer, a substrate, polar monomer, initiator, crosslinking agent, and conductive carbon are added to a solvent and subjected to crosslinking polymerization at a temperature of 60–100℃ and a pressure of 0.9–1.2 atm for 2–5 hours. The resulting reaction solution is then coated and steam-induced at a relative humidity of 50–90% to solidify and replace the solvent. After drying, the electrolyte-induced layer is obtained. To prepare a buffer layer, at least one of polyethylene oxide, sodium alginate, carboxymethyl cellulose, sodium hyaluronate, carboxymethyl starch, and hydroxypropyl starch is dissolved in an aqueous solvent, and then cured by coating to form a thin film, i.e., a buffer layer. Multilayer composite is obtained by stacking the layers in the following order: active material layer, electrolyte induction layer, active material layer, buffer layer, active material layer, structural layer, and active material layer, and then rolling the composite at 150–200°C.

9. An electrode sheet, characterized in that, The electrode sheet includes a current collector and a dry-process multilayer composite electrode film as described in any one of claims 1-8, wherein the dry-process multilayer composite electrode film is overlapped and attached to the current collector.

10. A battery, characterized in that, Includes the electrode sheet as described in claim 9.

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