Modified diaphragm, preparation method thereof, battery and electric device

Abstract

The invention relates to a modified diaphragm, a preparation method thereof, a battery and an electric device. The modified diaphragm comprises a base membrane, and a lithium-phobic layer and a lithium-loving layer which are positioned on the surface of at least one side of the base membrane, wherein the lithium-phobic layer is located between the base film and the lithium-loving layer, the lithium-phobic layer comprises a lithium-phobic material and a binder, and the lithium-loving layer comprises a lithium-loving material. The modified diaphragm disclosed by the invention can continuously play a role in the whole life cycle, and the battery adopting the modified diaphragm has extremely excellent electrochemical properties such as cycle performance and rate capability. The modified diaphragm provided by the invention provides a new technical path for the development of a high-safety and long-cycle lithium metal battery.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a modified diaphragm and a preparation method thereof, a battery and an electrical device. Background Art

[0002] In recent years, with the application of high-nickel materials and silicon-carbon composite materials, the energy density of lithium-ion batteries (LIBs) has reached more than 300Wh / kg. This value is close to the limit energy density threshold of 350Wh / kg for conventional lithium-ion batteries, and there is not much room for further improvement. If we want to achieve the ambitious goal of 400Wh / kg or even higher energy density, we urgently need to explore and develop new system materials. In this context, metallic lithium has excellent theoretical capacity (up to 3860mAh / g), extremely low electrode potential (-3.04Vvs.H / H + ) and low density (0.534g / cm 3 ), becoming an ideal negative electrode material for the next generation of high-energy-density batteries.

[0003] However, the behavior of lithium ions in lithium metal batteries (LMBs) is different from the insertion / extraction behavior of lithium ions in LIBs. During charging of LMBs, lithium ions acquire electrons from the external circuit, and the resulting metallic lithium is deposited on the negative electrode in the form of particles. If the battery system is not improved, it is easy to cause uneven deposition of lithium ions and produce lithium dendrites. The generation of lithium dendrites can cause electrical short circuits, thermal runaway and other problems in severe cases, especially when the current density is uneven in large currents, which makes the uneven deposition of lithium ions more serious, making the safety risks more prominent. Summary of the invention

[0004] In view of this, the present application provides a modified diaphragm and a preparation method thereof, a battery and an electrical device to solve at least one problem existing in the background technology.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] A first aspect of the present invention provides a modified diaphragm, which includes a base film, and a lithium-phobic layer and a lithium-philic layer located on at least one side of the base film; wherein the lithium-phobic layer is located between the base film and the lithium-philic layer, the lithium-phobic layer includes a lithium-phobic material and a binder, and the lithium-philic layer includes a lithium-philic material.

[0007] Preferably, the lithium-phobic material is a three-dimensional skeleton material, preferably at least one selected from carbon nanotubes, carbon black, graphene, carbon fiber, hard carbon and graphite; the binder is selected from at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate and carboxymethyl cellulose;

[0008] Preferably, the mass ratio of the lithium-phobic material to the binder is (80-97): (3-20);

[0009] Preferably, the lithium-phobic layer has a thickness of 1 μm to 10 μm.

[0010] Preferably, the lithium-philic material is selected from at least one of Zn, Al, In, Sn, Au, Ag, Ti, Si, MgF2, LiF2, LiI, MgI2, Li3N and ZnO;

[0011] Preferably, the thickness of the lithium-philic layer is 0.1 μm to 3 μm.

[0012] Preferably, the base film is selected from at least one of a polyethylene base film, a polypropylene base film, a polyvinylidene fluoride based film and a polytetrafluoroethylene based film.

[0013] The second aspect of the present invention provides a method for preparing the modified diaphragm according to the first aspect of the present invention, comprising the following steps:

[0014] S1: adding the lithium-repellent material and the binder to a solvent, mixing them evenly to obtain a slurry, and coating the slurry on at least one side of the base film to form a lithium-repellent layer to obtain an intermediate separator;

[0015] S2: preparing a lithium-philic layer on the lithium-phobic layer of the intermediate separator, so that the lithium-phobic layer is located between the base film and the lithium-philic layer, thereby obtaining the modified separator;

[0016] The lithium-philic layer contains a lithium-philic material.

[0017] Preferably, step S1 satisfies at least one of the following features (1) to (3):

[0018] (1) The solvent is selected from at least one of water, N-methylpyrrolidone, tetrahydrofuran, ethylene glycol dimethyl ether, dioxolane, 1,2-dimethoxyethane, 2-methyltetrahydrofuran and triethylene glycol dimethyl ether;

[0019] (2) The mass ratio of the lithium-phobic material to the binder is (80-97): (3-20);

[0020] (3) The solid content of the slurry is 3% to 10%.

[0021] Preferably, in step S2, the method for preparing the lithium-philic layer is magnetron sputtering.

[0022] Preferably, the RF power of the magnetron sputtering is 30W to 50W; the sputtering temperature of the magnetron sputtering is 20°C to 30°C; the sputtering time of the magnetron sputtering is 1min to 20min; during the magnetron sputtering, the distance between the lithium-philic material and the intermediate separator is 10cm to 30cm.

[0023] A third aspect of the present invention provides a battery, characterized in that the battery comprises the modified diaphragm described in the first aspect of the present invention or the modified diaphragm prepared by the preparation method described in the second aspect of the present invention.

[0024] A fourth aspect of the present invention provides an electrical device, wherein the electrical device comprises the battery described in the third aspect of the present invention.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a modified diaphragm and a preparation method thereof, a battery and an electrical device, wherein the surface of the modified diaphragm constructs a gradient modified composite structure consisting of an inner lithium-phobic layer and an outer lithium-philic layer: the inner layer is a lithium-phobic layer formed by a three-dimensional skeleton material, and the three-dimensional skeleton structure is constructed to effectively reduce the current density of the battery, alleviate the polarization phenomenon of the battery, and inhibit the growth of lithium dendrites; the outer layer is constructed by magnetron sputtering to form a lithium-philic layer on the surface of the lithium-phobic layer by lithium-philic materials, which can effectively promote the uniform deposition of lithium. The modified diaphragm provided by the present invention has stronger adaptability to the processing environment, a wider range of solvent selection, and will not be covered by dead lithium and SEI films generated by lithium metal during the charging and discharging process, and can achieve continuous function throughout the life cycle. The battery using the modified diaphragm has extremely excellent electrochemical properties such as cycle performance and rate performance. The modified diaphragm provided by the present invention provides a new technical path for the development of high-safety, long-cycle lithium metal batteries. DETAILED DESCRIPTION

[0027] In order to make the technical scheme and beneficial effects of the present invention more obvious and easy to understand, the following is described in detail by listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0028] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known in the art are not described; that is, all features of the actual embodiments are not described here, and well-known functions and steps are not described in detail.

[0029] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0030] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below, but in addition to these detailed descriptions, the present application may also have other implementation methods.

[0031] Unless otherwise defined, technical and scientific terms used in this application have the same meanings as those in the technical field to which this application belongs.

[0032] If no specific techniques or conditions are specified in the following examples, the conventional techniques or conditions described in the literature in the art, or the conditions recommended by the product instructions and the manufacturer are generally used. The numerical ranges in the following examples all include the endpoint values.

[0033] Currently, the commonly used methods to inhibit lithium dendrites mainly include: constructing a three-dimensional skeleton, carrying out interface modification engineering and optimizing electrolyte components. Although these methods can alleviate the growth of lithium dendrites to a certain extent, they still have limitations:

[0034] First, although the three-dimensional skeleton can effectively guide the uniform deposition of lithium ions, its introduction significantly reduces the energy density of the negative electrode material, which restricts the overall performance of the battery.

[0035] Secondly, the uniform deposition of lithium can be promoted by performing interface modification on the surface of lithium metal in theory. However, due to the active chemical properties of lithium metal, it is very easy to react with water, so it has strict requirements on the environmental humidity. Moreover, if the metal modification is performed on the surface of lithium metal directly by coating, it is necessary to avoid the reaction between the solvent and lithium metal, and to ensure that the water content of the solvent is extremely low, which is too strict for the selection of the solvent used. In addition, the modified layer directly modified on the surface of lithium metal is very easy to peel off during the charge and discharge process, or covered by dead lithium and the continuously thickening solid electrolyte interface (SEI) film, which leads to the failure of the modified layer, thereby losing the inhibitory effect on the growth of lithium dendrites.

[0036] Finally, the electrolyte components are adjusted by adding specific additives to improve the properties of the electrolyte in order to inhibit lithium dendrites. However, these additives will gradually be consumed during the battery cycle, and their effects are difficult to last due to the limited amount added, and their inhibitory effect on lithium dendrites is relatively limited.

[0037] In view of this, the present invention provides the following technical solutions:

[0038] [Modified diaphragm]

[0039] A first aspect of the present invention provides a modified diaphragm, which includes a base film, and a lithium-phobic layer and a lithium-philic layer located on at least one side of the base film; wherein the lithium-phobic layer is located between the base film and the lithium-philic layer, the lithium-phobic layer includes a lithium-phobic material and a binder, and the lithium-philic layer includes a lithium-philic material.

[0040] In some embodiments, the lithium-phobic layer and the lithium-philic layer are located on only one surface of the base film.

[0041] In certain embodiments, the lithium-phobic material is a three-dimensional framework material.

[0042] In certain embodiments, the lithium-phobic material is selected from at least one of carbon nanotubes, carbon black, graphene, carbon fiber, hard carbon and graphite.

[0043] In certain embodiments, the binder is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate and carboxymethyl cellulose.

[0044] In the present invention, the inner layer of the modified diaphragm adopts a lithium-phobic layer formed by a three-dimensional skeleton material, which effectively reduces the current density of the battery by constructing a three-dimensional skeleton structure, alleviates the polarization phenomenon of the battery, and can inhibit the growth of lithium dendrites; the outer lithium-philic layer can effectively promote the uniform deposition of lithium. In addition, the modified diaphragm of the present invention has stronger adaptability to the processing environment, a wider range of solvent selection, and will not be covered by the dead lithium and SEI film generated by lithium metal during the charging and discharging process, and can achieve continuous function throughout the life cycle. The battery using the modified diaphragm has extremely excellent electrochemical properties such as cycle performance and rate performance.

[0045] In some embodiments, the mass ratio of the lithium-phobic material to the binder is (80-97):(3-20), for example 80:3, 80:5, 80:10, 80:15, 80:20, 85:3, 85:10, 85:15, 85:20, 90:3, 90:5, 90:10, 90:15, 90:20, 95:3, 95:5, 95:10, 95:15, 95:20, 97:3, 97:5, 97:10, 97:15 or 97:20, but is not limited to the ratios listed, and other ratios not listed within the ratio range are also applicable.

[0046] In some embodiments, the thickness of the lithium-phobic layer is 1 μm to 10 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In certain embodiments, the lithium-philic material is selected from at least one of Zn, Al, In, Sn, Au, Ag, Ti, Si, MgF2, LiF2, LiI, MgI2, Li3N and ZnO.

[0048] In some embodiments, the thickness of the lithium-philic layer is 0.1 μm to 3 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3 μm, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0049] In certain embodiments, the base film is selected from at least one of a polyethylene-based film, a polypropylene-based film, a polyvinylidene fluoride-based film, and a polytetrafluoroethylene-based film.

[0050] [Method for preparing modified diaphragm]

[0051] The second aspect of the present invention provides a method for preparing the modified diaphragm according to the first aspect of the present invention, comprising the following steps:

[0052] S1: adding the lithium-repellent material and the binder to a solvent, mixing them evenly to obtain a slurry, and coating the slurry on at least one side of the base film to form a lithium-repellent layer to obtain an intermediate separator;

[0053] S2: preparing a lithium-philic layer on the lithium-phobic layer of the intermediate separator, so that the lithium-phobic layer is located between the base film and the lithium-philic layer, thereby obtaining the modified separator;

[0054] The lithium-philic layer contains a lithium-philic material.

[0055] In the present invention, the lithium-philic layer prepared by magnetron sputtering has compactness and uniformity, and has excellent bonding with the intermediate separator, which can significantly promote the uniformity of lithium deposition, thereby improving the performance of the battery.

[0056] In certain embodiments, in step S1, the solvent is selected from at least one of water, N-methylpyrrolidone, tetrahydrofuran, ethylene glycol dimethyl ether, dioxolane, 1,2-dimethoxyethane, 2-methyltetrahydrofuran and triethylene glycol dimethyl ether.

[0057] In some embodiments, in step S1, the mass ratio of the lithium-phobic material to the binder is (80-97):(3-20), for example 80:3, 80:5, 80:10, 80:15, 80:20, 85:3, 85:10, 85:15, 85:20, 90:3, 90:5, 90:10, 90:15, 90:20, 95:3, 95:5, 95:10, 95:15, 95:20, 97:3, 97:5, 97:10, 97:15 or 97:20, but is not limited to the ratios listed, and other ratios not listed within the ratio range are also applicable.

[0058] In certain embodiments, in step S1, the solid content of the slurry is 3% to 10%, for example 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0059] In certain embodiments, in step S1, after the coating is completed, a drying step is also included.

[0060] In certain embodiments, the drying temperature is 60°C to 100°C, for example 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] In certain embodiments, the drying time is 18 h to 30 h, for example 18 h, 20 h, 22 h, 24 h, 26 h, 28 h or 30 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] In certain embodiments, in step S2, the method for preparing the lithium-philic layer is magnetron sputtering.

[0063] In certain embodiments, the magnetron sputtering is performed using a high vacuum multifunctional magnetron sputtering device.

[0064] In some embodiments, the vacuum degree of the magnetron sputtering is 10 -5 Pa~10 -3 Pa, for example 10 -5 Pa, 10 -4 Pa or 10 -3 Pa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] In certain embodiments, the magnetron sputtering is performed in an inert gas atmosphere, and the inert gas is selected from one or more of helium, neon, argon, and nitrogen.

[0066] In certain embodiments, the RF power of the magnetron sputtering is 30W to 50W, such as 30W, 35W, 40W, 45W or 50W, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0067] In some embodiments, the sputtering temperature of the magnetron sputtering is 20°C to 30°C, for example 20°C, 22°C, 24°C, 25°C, 26°C, 28°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] In certain embodiments, the sputtering time of the magnetron sputtering is 1 min to 20 min, such as 1 min, 5 min, 10 min, 15 min or 20 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0069] In certain embodiments, during the magnetron sputtering, the distance between the lithium-philic material and the intermediate separator is 10 cm to 30 cm, for example, 10 cm, 15 cm, 20 cm, 25 cm or 30 cm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0070] In some embodiments, the pressure of the magnetron sputtering is 0.5Pa to 1.5Pa, for example 0.5Pa, 0.6Pa, 0.7Pa, 0.8Pa, 0.9Pa, 1Pa, 1.1Pa, 1.2Pa, 1.3Pa, 1.4Pa or 1.5Pa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0071] In certain embodiments, the lithium-philic material is selected from at least one of Zn, Al, In, Sn, Au, Ag, Ti, Si, MgF2, LiF2, LiI, MgI2, Li3N and ZnO.

[0072] In certain embodiments, the purity of the lithiophilic material is ≥ 99.9%.

[0073] [Battery]

[0074] A third aspect of the present invention provides a battery, comprising the modified diaphragm according to the first aspect of the present invention or the modified diaphragm prepared by the preparation method according to the second aspect of the present invention.

[0075] In some embodiments, the battery may be a secondary battery or a primary battery, preferably a secondary battery. For example, the battery may be a lithium metal battery, but is not limited thereto. The battery structure of the present application includes but is not limited to a soft-pack lithium metal battery, a square hard-shell lithium metal battery, or a cylindrical hard-shell lithium metal battery.

[0076] In some embodiments, the battery further comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. Typically, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a diaphragm, and the diaphragm is disposed between the positive electrode sheet and the negative electrode sheet. During the battery charge and discharge process, active ions migrate back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The diaphragm is disposed between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive / negative electrode from short-circuiting, while allowing ions to pass through. In the present invention, the active ions are lithium ions.

[0077] In some embodiments, the negative electrode plate is a lithium plate.

[0078] As for the modified separator described in the first aspect of the present invention, when the lithium-phobic layer and the lithium-philic layer are only located on one side surface of the base film, the side surface is the surface of the base film facing the negative electrode plate.

[0079] In certain embodiments, when the lithium-phobic layer and the lithium-philic layer are located on only one side of the base film, the lithium-philic layer is in contact with the negative electrode plate.

[0080] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode current collector may be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material suitable for the present invention may be various known positive electrode active materials that can be used for lithium metal batteries. The positive electrode active material may be selected from a composite oxide containing lithium and at least one selected from cobalt, manganese, nickel and iron, preferably a composite oxide containing lithium. The lithium-containing composite oxide is preferably LiM x O y and LiM x PO4, wherein M is a combination of one or more transition metals, 0<x≤3, 0<y≤4. Examples of positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate (LiFePO4), etc.

[0081] In certain embodiments, the positive electrode active material includes NCM (613).

[0082] The positive electrode active material layer may also include one or two selected from a conductive agent and a binder. The conductive agent is used to improve the conductivity of the electrode. Examples of the conductive agent of the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, Ketjen black, graphene and carbon nanotubes. The binder of the positive electrode improves the bonding performance between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder of the positive electrode include at least one of a fluorine-containing resin, a polypropylene resin, a fiber-type binder, a rubber-type binder and a polyimide-type binder. In some embodiments, the conductive agent in the positive electrode active material layer is conductive carbon black and single-walled carbon nanotubes, and the binder is polyvinylidene fluoride. The mass ratio of each component in the positive electrode active material layer can be conventional.

[0083] The positive electrode active material layer is obtained by coating a positive electrode slurry containing various components of the positive electrode active material layer and a solvent onto a positive electrode current collector, and then rolling and slitting. The solvent of the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0084] The electrolyte solution includes an organic solvent and an electrolyte salt.

[0085] Organic solvents suitable for the electrolyte of the present invention may include carbonate solvents, carboxylate solvents, ether solvents or other aprotic solvents. In some embodiments, the electrolyte includes carbonate solvents. In the electrolyte of the present invention, the mass of carbonate solvents can be 80% to 100% of the total mass of the organic solvent, such as 85%, 90%, 95%. Examples of carbonate solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate, etc. In some embodiments, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate. In some embodiments, the organic solvent comprises at least one cyclic carbonate and at least one linear carbonate. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, etc. Examples of linear carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.

[0086] The electrolyte salt may include or be selected from a lithium salt. The lithium salt may be selected from one or more of an organic lithium salt and an inorganic lithium salt. In some embodiments, the electrolyte salt is selected from at least one of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFB, and LiPO2F2. In some embodiments, the concentration of the electrolyte salt in the electrolyte is 0.5 mol / L to 2 mol / L, for example 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L.

[0087] The battery of the present application also includes a packaging shell for accommodating a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in a lithium metal battery, and the present application does not limit the above other components. The present application does not specifically limit the packaging shell, and it can be a packaging shell known in the art, as long as it can achieve the purpose of the present application.

[0088] The present invention has no special limitation on the method for preparing the battery, and the technical scheme for preparing the separator into a battery such as a secondary battery, which is well known to those skilled in the art, can be adopted.

[0089] It should be understood that since the battery provided in the present application includes the modified diaphragm provided by the first aspect of the present invention or the composite diaphragm prepared by the preparation method provided by the second aspect of the present invention, the beneficial effects of the modified diaphragm or its preparation method described in any of the above embodiments are applicable to the battery.

[0090] [Electrical devices]

[0091] A fourth aspect of the present invention provides an electrical device, wherein the electrical device comprises the battery described in the third aspect of the present invention.

[0092] The use of the battery of the present application is not particularly limited, and it can be used for any electrical device known in the prior art. In some embodiments, the battery of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, drones, and capacitors, etc.

[0093] It should be understood that, since the electrical device provided in the present application includes the battery described in the third aspect of the present invention, the beneficial effects of the modified diaphragm or its preparation method described in any of the above embodiments are applicable to the electrical device.

[0094] The method of the present invention is described below by means of specific examples. It should be understood that these examples are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following examples; the implementation conditions adopted in the examples can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in routine experiments.

[0095] Example 1

[0096] Step S101: Place carbon nanotubes and polyvinylidene fluoride into N-methylpyrrolidone in a mass ratio of 9:1 and mix them evenly to obtain a slurry to be coated (the solid content of the obtained slurry is 6%), and use a 50μm scraper to coat the obtained slurry on one side of the PE diaphragm, and then dry it in an oven at 80°C for 24 hours to obtain a diaphragm containing an inner layer modification (i.e., the intermediate diaphragm); wherein the thickness of the lithium-repellent layer is about 3μm.

[0097] Step S102: further modifying the intermediate membrane obtained in step S101 by using a high vacuum multifunctional magnetron sputtering device, specifically: -4High-purity argon gas was introduced into a Pa vacuum chamber, the sputtering pressure was 0.8 Pa, the sputtering temperature was 25°C, the sputtering distance between the Au target and the intermediate diaphragm placed on the sample stage was 20 cm, the sputtering time was 10 min, and the Au target sputtered the intermediate diaphragm at a radio frequency power of 40 W. The Au sputtered layer was deposited on the surface of one side of the diaphragm (i.e., the lithium-philic layer) to obtain a diaphragm containing an outer layer modification (i.e., the modified diaphragm); wherein the lithium-phobic layer was located between the base film and the lithium-philic layer; wherein the thickness of the lithium-philic layer was 1 μm.

[0098] Step S103: Assembly of Li / NCM613 full battery

[0099] The NCM613 positive electrode sheet, modified diaphragm, lithium sheet (negative electrode sheet) and gasket are placed in a CR2016 button battery shell in sequence (where the lithium-philic and lithium-phobic modification layers on the diaphragm are facing the lithium sheet side), an appropriate amount of electrolyte is added (DME and TTE are mixed in a volume ratio of 1:1 as a solvent, and LiFSI is added to prepare an electrolyte, and the concentration of LiFSI in the electrolyte is 1.0 M), and compacted to obtain a Li / NCM613 full battery.

[0100] Example 2

[0101] The only difference between Example 2 and Example 1 is that the carbon nanotubes in step S101 of Example 1 are replaced by carbon black.

[0102] Example 3

[0103] The only difference between Example 3 and Example 1 is that Au in step S102 of Example 1 is replaced by Ti.

[0104] Example 4

[0105] The only difference between Example 4 and Example 1 is that the PE diaphragm in step S101 of Example 1 is replaced by a PP diaphragm.

[0106] Comparative Example 1

[0107] The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include step S102 in Example 1, and the intermediate membrane prepared in step S101 is used as a modified membrane, and then the battery is assembled according to the method of step S103.

[0108] Comparative Example 2

[0109] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not include step S101 in Example 1, that is, a lithium-philic layer is directly prepared on the PE separator according to the method of step S102 in Example 1, and then the battery is assembled according to the method of step S103.

[0110] Comparative Example 3

[0111] The only difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, no modification is made to the PE separator, and the battery is assembled directly according to the method in step S103.

[0112] Comparative Example 4

[0113] The only difference between Comparative Example 4 and Example 1 is that: Comparative Example 4 changes the modified object in Example 1 from a diaphragm to a lithium sheet, replaces the solvent in step S101 of Example 1 from N-methylpyrrolidone to tetrahydrofuran, replaces the coating method from doctor blade coating to spin coating, and replaces the diaphragm in step S103 with an unmodified PE diaphragm.

[0114] Performance Testing

[0115] The electrochemical performance tests of the batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were conducted, specifically:

[0116] (1) Capacity retention rate test: At 25°C, charge to 4.3V at a current density of 0.2C, and record the charge capacity at this time as the first charge capacity; then discharge to 3.0V at a current density of 0.5C, and record the discharge capacity at this time as the first discharge capacity; repeat the above charge and discharge cycle for 100 cycles, and record the discharge capacity at the 100th cycle. The capacity retention rate of 100 cycles can be calculated by the following formula: Capacity retention rate of the 100th cycle = discharge capacity at the 100th cycle / first discharge capacity * 100%. The test results are shown in Table 1.

[0117] (2) Rate performance test: At 25°C, charge to 4.3V at 0.2C rate, continue to discharge to 3.0V at 0.2C rate, cycle 5 times to obtain a stable capacity, record the discharge capacity at this time as 0.2C discharge capacity; then charge to 4.3V at 0.2C rate, continue to discharge to 3.0V at XC (X = 0.5, 1, 2, 3) high rate, cycle 5 times to obtain a stable capacity, record the discharge capacity at this time as XC (X = 0.5, 1, 2, 3) discharge capacity, then XC rate performance = XC discharge capacity / 0.2C discharge capacity*100%. The test results are shown in Table 2.

[0118] Table 1

[0119]

[0120] Table 2

[0121]

[0122] As can be seen from the results in Table 1, by comparing Examples 1 to 4 and Comparative Examples 1 to 3, it can be found that the modified diaphragms prepared in Examples 1 to 4 with lithium-phobic and lithium-philic gradient modifications show excellent performance in terms of battery capacity retention, and their values ​​are all maintained at a level above 89.5%, which fully demonstrates the superiority of such modified diaphragms in cycle performance; while the battery capacity retention rate of the unmodified or only partially modified diaphragms in Comparative Examples 1 to 3 is significantly reduced (72.32% to 81.36%). In addition, by comparing Examples 1 to 4 and Comparative Example 4, it can be found that after lithium-phobic and lithium-philic gradient modifications are performed on the lithium sheet, the capacity retention rate of the battery is significantly reduced compared to the modification on the diaphragm.

[0123] As can be seen from the results in Table 2, the differences between Examples 1 to 4 and Comparative Examples 1 to 4 under different rate conditions are also significant. Specifically, compared with the unmodified separators, only partially modified separators, or the cases where the separators are modified on the lithium sheet in Comparative Examples 1 to 4, the batteries of Examples 1 to 4 with modified separators with gradient modification of lithium phobia and lithium affinity all exhibited the best capacity retention and cycle performance under the rate conditions of 0.5C, 1C, 2C and 3C.

[0124] This shows that the lithium-phobic and lithium-philic gradient modification technology implemented in the present invention significantly promotes the uniform deposition of lithium ions and effectively inhibits the growth of lithium dendrites. In addition, the three-dimensional structure of the lithium-phobic material provides a channel for the transfer of ions, reduces the current density of the battery, alleviates the battery polarization phenomenon, and effectively controls the volume expansion of lithium, greatly improving the cycle stability of the battery.

[0125] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations included in the claims. Various modifications and changes may be made on the basis of the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A modified diaphragm, characterized in that: The modified diaphragm includes a base film, and a lithium-phobic layer and a lithium-philic layer located on at least one side of the base film; wherein the lithium-phobic layer is located between the base film and the lithium-philic layer, the lithium-phobic layer includes a lithium-phobic material and a binder, and the lithium-philic layer includes a lithium-philic material.

2. The modified diaphragm according to claim 1, characterized in that: The lithium-phobic material is a three-dimensional skeleton material, preferably at least one selected from carbon nanotubes, carbon black, graphene, carbon fiber, hard carbon and graphite; the binder is selected from at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate and carboxymethyl cellulose; The mass ratio of the lithium-phobic material to the binder is (80-97): (3-20); and / or, The thickness of the lithium-phobic layer is 1 μm to 10 μm.

3. The modified diaphragm according to claim 1, characterized in that: The lithium-philic material is selected from at least one of Zn, Al, In, Sn, Au, Ag, Ti, Si, MgF2, LiF2, LiI, MgI2, Li3N and ZnO; and / or, The thickness of the lithium-philic layer is 0.1 μm to 3 μm.

4. The modified diaphragm according to any one of claims 1 to 3, characterized in that: The base film is selected from at least one of a polyethylene base film, a polypropylene base film, a polyvinylidene fluoride based film and a polytetrafluoroethylene based film.

5. A method for preparing the modified diaphragm according to any one of claims 1 to 4, characterized in that: The steps include: S1: adding the lithium-repellent material and the binder to a solvent, mixing them evenly to obtain a slurry, and coating the slurry on at least one side of the base film to form a lithium-repellent layer to obtain an intermediate separator; S2: preparing a lithium-philic layer on the lithium-phobic layer of the intermediate separator, so that the lithium-phobic layer is located between the base film and the lithium-philic layer, thereby obtaining the modified separator; The lithium-philic layer contains a lithium-philic material.

6. The preparation method according to claim 5, characterized in that: Step S1 satisfies at least one of the following characteristics (1) to (3): (1) The solvent is selected from at least one of water, N-methylpyrrolidone, tetrahydrofuran, ethylene glycol dimethyl ether, dioxolane, 1,2-dimethoxyethane, 2-methyltetrahydrofuran and triethylene glycol dimethyl ether; (2) The mass ratio of the lithium-phobic material to the binder is (80-97): (3-20); (3) The solid content of the slurry is 3% to 10%.

7. The preparation method according to claim 5, characterized in that: In step S2, the method for preparing the lithium-philic layer is magnetron sputtering.

8. The preparation method according to claim 7, characterized in that: The RF power of the magnetron sputtering is 30W to 50W; the sputtering temperature of the magnetron sputtering is 20°C to 30°C; the sputtering time of the magnetron sputtering is 1min to 20min; during the magnetron sputtering, the distance between the lithium-philic material and the intermediate separator is 10cm to 30cm.

9. A battery, characterized in that: The battery comprises the modified diaphragm according to any one of claims 1 to 4 or the modified diaphragm prepared by the preparation method according to any one of claims 5 to 8.

10. An electrical device, characterized in that: The electrical device comprises the battery according to claim 9.

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