Composite separator and its preparation method, secondary battery

Abstract

This application relates to a composite separator and its preparation method, and a secondary battery. The composite separator includes: a base membrane; and a functional layer disposed on at least one side of the surface of the base membrane. The functional layer includes ceramic materials and functional materials, wherein the functional material includes a vinylpyridine-grafted butadiene-styrene copolymer. The composite separator provided by this application utilizes the excellent bonding properties and transition metal ion adsorption properties of the vinylpyridine-grafted butadiene-styrene copolymer. On the one hand, it acts as a binder to achieve good dispersion and adhesion between ceramic materials, improving the peel strength between the base membrane and the functional layer. On the other hand, it can complex transition metal ions, reducing damage to the SEI membrane and improving the cycle performance of the battery. Therefore, this application eliminates the need for additional binders and complexing substances, thereby improving the uniformity of the functional layer, reducing the thickness of the functional layer, and improving the air permeability of the composite separator.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite separator and its preparation method, and a secondary battery. Background Technology

[0002] With the development and expansion of the new energy industry chain, secondary batteries, as an energy storage device, are widely used in electric vehicles, communication equipment, portable electronic devices and other fields.

[0003] In pursuit of higher energy density in batteries, high-voltage cathode materials are currently preferred, such as lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based cathode materials, and manganese-rich materials. In high-voltage battery systems, cathode materials are prone to react with electrolytes, causing the dissolution of transition metal ions such as manganese ions. These transition metal ions migrate to the negative electrode side, are reduced, and deposit on the negative electrode surface, continuously damaging the SEI film on the negative electrode surface and causing the battery cycle performance to deteriorate.

[0004] In traditional technology, complexing materials are usually placed on the diaphragm to complex the transition metal ions dissolved in the positive electrode. However, the complexing materials need to be used in conjunction with the binder. On the one hand, this results in a thicker coating, which affects the permeability of the diaphragm. On the other hand, the compatibility between the current complexing materials and the binder is poor, which affects the uniformity of the coating and the bonding strength with the diaphragm base film. Summary of the Invention

[0005] Therefore, it is necessary to provide a composite separator and its preparation method, as well as a secondary battery, to solve the above-mentioned technical problems.

[0006] The first aspect of this application provides a composite membrane comprising: a base membrane; and a functional layer disposed on at least one side of the surface of the base membrane, the functional layer comprising a ceramic material and a functional material, the functional material comprising a vinylpyridine-grafted butadiene-styrene copolymer.

[0007] In some embodiments, based on the total mass of the vinylpyridine-grafted butadiene-styrene copolymer, the mass percentage of butadiene is 20% to 69.5%, the mass percentage of styrene is 10% to 50%, and the mass percentage of vinylpyridine is 5% to 30%.

[0008] In some embodiments, vinylpyridine includes one or more of 2-vinylpyridine, 3-vinylpyridine, and 4-vinylpyridine.

[0009] In some implementations, the particle size of the functional material is 10 nm to 1000 nm.

[0010] In some implementations, the mass ratio of functional material to ceramic material in the functional layer is (1:99) to (10:90).

[0011] In some implementations, the thickness of the functional layer is 1 μm to 5 μm.

[0012] In some embodiments, the peel strength between the functional layer and the base film is 0.01 kN / m to 0.05 kN / m.

[0013] In some embodiments, the air permeability of the composite diaphragm is 80s / 100ml to 500s / 100ml.

[0014] The second aspect of this application provides a method for preparing the composite membrane provided in the first aspect above. The preparation method includes the following steps: first, dispersing functional materials in deionized water, then adding ceramic materials for dispersion to form a functional layer slurry; wherein, the functional materials include vinylpyridine-grafted butadiene-styrene copolymer; coating the functional layer slurry onto a base membrane, drying it to form a functional layer, and obtaining the composite membrane.

[0015] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and the composite separator provided in the first aspect.

[0016] Compared with traditional technologies, this application has at least the following beneficial effects:

[0017] The composite separator provided in this application utilizes the excellent bonding properties and transition metal ion adsorption properties of vinylpyridine-grafted butadiene-styrene copolymer. On one hand, it acts as a binder, achieving good dispersion and adhesion between ceramic materials and improving the peel strength between the base membrane and the functional layer. On the other hand, it adsorbs transition metal ions, reducing their damage to the SEI membrane and improving the battery's cycle performance. Therefore, by adding vinylpyridine-grafted butadiene-styrene copolymer as a functional material to the functional layer of the composite separator, no additional binder or complexing substance is needed, thereby improving the uniformity of the functional layer, reducing its thickness, and enhancing the air permeability of the composite separator. Detailed Implementation

[0018] Reference will now be made to detailed embodiments of this application, one or more of which are described below. Each example is provided for explanation and not for limitation of this application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0019] Therefore, this application is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of this application are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this application.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0022] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0023] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0024] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0025] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0026] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0027] A first aspect of this application provides a composite membrane comprising a base membrane and a functional layer. The functional layer is disposed on at least one surface of the base membrane, and the functional layer comprises a ceramic material and a functional material, wherein the functional material comprises a vinylpyridine-grafted butadiene-styrene copolymer.

[0028] The composite separator provided in this application utilizes the excellent bonding properties and transition metal ion adsorption properties of vinylpyridine-grafted butadiene-styrene copolymer. On one hand, it acts as a binder, achieving good dispersion and adhesion between ceramic materials and improving the peel strength between the base membrane and the functional layer. On the other hand, it adsorbs transition metal ions, reducing their damage to the SEI membrane and improving the battery's cycle performance. Therefore, by adding vinylpyridine-grafted butadiene-styrene copolymer as a functional material to the functional layer of the composite separator, no additional binder or complexing substance is needed, thereby improving the uniformity of the functional layer, reducing its thickness, and enhancing the air permeability of the composite separator.

[0029] In some embodiments, based on the total mass of the vinylpyridine-grafted butadiene-styrene copolymer, the mass percentage of butadiene is 20%–69.5%, the mass percentage of styrene is 10%–50%, and the mass percentage of vinylpyridine is 5%–30%. Controlling the mass percentages of butadiene, styrene, and vinylpyridine in the vinylpyridine-grafted butadiene-styrene copolymer within a suitable range can effectively improve the liquid absorption and retention capacity of the composite membrane, enabling the composite membrane to simultaneously possess good adhesion and transition metal ion adsorption properties, thereby improving the cycle performance of the battery.

[0030] In some embodiments, the weight-average molecular weight of the vinylpyridine-grafted butadiene-styrene copolymer is 2,000 to 200,000. A weight-average molecular weight range like this is beneficial for the vinylpyridine-grafted butadiene-styrene copolymer to maintain good adhesion and ensure the structural stability of the composite membrane.

[0031] In some embodiments, the particle size of the functional material is 10 nm to 1000 nm, including but not limited to 10 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, and 1000 nm. Within this particle size range, it is beneficial to improve the dispersibility of the functional material in deionized water and to form a uniform functional layer slurry. Further, the particle size of the vinylpyridine-grafted butadiene-styrene copolymer is 100 nm to 500 nm.

[0032] In some embodiments, the mass ratio of functional material to ceramic material in the functional layer is (1:99) to (10:90), including but not limited to 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, 9:91, and 10:90. Within the above mass ratio range, the overall performance of the functional layer is optimized, taking into account the heat resistance, air permeability, mechanical stability, ion transport performance, and transition metal ion adsorption performance of the functional layer. Further, the mass ratio of functional material to ceramic material is (3:97) to (8:92).

[0033] In some embodiments, the thickness of the functional layer is 1 μm to 5 μm, including but not limited to 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm. Within the above thickness range, the composite membrane exhibits good adhesion and good transition metal ion adsorption properties while also possessing high air permeability. Further, the thickness of the functional layer is 2 μm to 4 μm.

[0034] In some embodiments, the peel strength between the functional layer and the base film is 0.01 kN / m to 0.05 kN / m, including but not limited to 0.01 kN / m, 0.02 kN / m, 0.03 kN / m, 0.04 kN / m, and 0.05 kN / m. Within this peel strength range, a strong bond between the functional layer and the base film is ensured, reducing the risk of functional layer peeling off during battery use, improving the mechanical stability of the separator, reducing the occurrence of short circuits, and improving the safety and cycle stability of the battery. Further, the peel strength between the functional layer and the base film is 0.3 kN / m to 0.5 kN / m.

[0035] In some embodiments, vinylpyridine includes one or more of 2-vinylpyridine, 3-vinylpyridine, and 4-vinylpyridine. Further, vinylpyridine is 2-vinylpyridine.

[0036] In some embodiments, the ceramic material includes one or more of the following: alumina, silicon oxide, titanium oxide, cerium oxide, calcium carbonate, calcium oxide, zinc oxide, magnesium oxide, cerium titanate, calcium titanate, barium titanate, lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium nitride, lithium lanthanum titanate, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, and lithium lanthanum zirconium tantalum oxide. The ceramic material is used to reduce the thermal shrinkage rate of the composite separator and improve its safety.

[0037] Furthermore, the ceramic materials include one or more of lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, and lithium lanthanum zirconium tantalum oxide. These ceramic materials not only improve the thermal stability of the ceramic material but also enhance the ion transport capability of the composite membrane.

[0038] In some embodiments, the ceramic material has a granular structure, and the particle size D of the ceramic material particles is... V 50 refers to particles ranging from 0.3 μm to 1 μm, including but not limited to 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1 μm. When the particle size of the ceramic particles is within this range, it is beneficial for the ceramic particles to be well dispersed in the functional layer, thereby improving the uniformity of the functional layer.

[0039] In some embodiments, the base membrane comprises a single-layer or multi-layer porous base membrane.

[0040] In some embodiments, the base film is selected from one or more of polyolefins, aramid fibers, polyimide, polyester fibers, acrylic fibers, and polyvinylidene fluoride.

[0041] In some embodiments, the thickness of the base film is 5 μm to 20 μm, including but not limited to 5 μm, 10 μm, 15 μm, and 20 μm.

[0042] In some embodiments, the air permeability of the composite separator ranges from 80 s / 100 ml to 500 s / 100 ml, including but not limited to 80 s / 100 ml, 100 s / 100 ml, 150 s / 100 ml, 200 s / 100 ml, 250 s / 100 ml, 300 s / 100 ml, 350 s / 100 ml, 400 s / 100 ml, 450 s / 100 ml, and 500 s / 100 ml. Within this air permeability range, the composite separator exhibits good air permeability, which facilitates electrolyte penetration, improves the battery's ion conduction performance, reduces internal resistance, and thus enhances the battery's cycle performance and lifespan. Further, the air permeability of the composite separator ranges from 100 s / 100 ml to 300 s / 100 ml.

[0043] The second aspect of this application provides a method for preparing the composite membrane provided in the first aspect above, the method comprising the following steps:

[0044] S1. First, disperse the functional materials in deionized water, then add ceramic materials for dispersion to form a functional layer slurry.

[0045] Among them, the functional materials include vinylpyridine-grafted butadiene-styrene copolymer.

[0046] S2. The functional layer slurry is coated onto the base membrane and dried to form the functional layer, thus obtaining the composite membrane.

[0047] The method for preparing the composite membrane of this application involves first dispersing the functional material and then adding ceramic material for further dispersion. This reduces the agglomeration of the ceramic material and allows the ceramic material to be uniformly dispersed in the vinylpyridine-grafted butadiene-styrene copolymer of the functional material, thereby improving the uniformity of the functional layer.

[0048] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and the composite separator provided in the first aspect.

[0049] In some embodiments, the positive electrode includes a positive electrode active material, which includes at least one transition metal element.

[0050] In some of these implementations, the transition metal element refers to one of nickel, cobalt, or manganese.

[0051] positive electrode:

[0052] In some embodiments of the present invention, the secondary battery provided by the present invention includes a positive electrode, which includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer includes a positive electrode active material. The positive electrode active material includes a compound that reversibly inserts and extracts lithium ions. In the present invention, the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based positive electrode material, and lithium nickel cobalt manganese oxide. They can be used individually or in any combination of two or more.

[0053] In some embodiments of the present invention, the positive electrode material layer further includes a binder. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode material layer and the positive electrode current collector.

[0054] In some embodiments of the present invention, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0055] In some embodiments of the invention, the positive electrode material layer includes a conductive agent, thereby imparting conductivity to the electrode. The conductive agent may include any conductive material, as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0056] In some embodiments of the present invention, the positive electrode includes a positive current collector, which, by way of example, may be aluminum (Al), but is not limited thereto.

[0057] In some embodiments of the present invention, the positive electrode sheet provided by the present invention further includes a second solid electrolyte powder for improving the ionic conductivity of the composite positive electrode. The present invention does not limit the type of the second solid electrolyte powder, which can be an oxide solid electrolyte powder, a sulfide solid electrolyte powder, or a halide solid electrolyte powder. Optionally, the mass of the second solid electrolyte powder accounts for 1%-20% of the mass of the positive electrode sheet; preferably 5%-20%.

[0058] In some embodiments of the present invention, the thickness of the positive electrode material layer in the positive electrode sheet provided by the present invention is 30-400 μm, for example 30 μm, 40 μm, 50 μm, 80 μm, 110 μm, 200 μm, 300 μm, 400 μm, preferably 50-110 μm.

[0059] Negative electrode plate:

[0060] In some embodiments of the present invention, the negative electrode sheet includes a current collector and a layer of negative electrode active material disposed on the current collector.

[0061] In this invention, the specific type of negative electrode active material is not specifically limited and can be selected according to requirements. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 One or more of Li-Al alloys. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, small flake-shaped, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, etc.

[0062] In some embodiments of the present invention, elemental metals and metal compounds may also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0063] In some embodiments of the present invention, the mass percentage of the negative electrode active material contained in the negative electrode active material layer can be 80%-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95%-97%.

[0064] In some embodiments of the present invention, the negative electrode material layer may include a binder; the binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0065] In some embodiments of the present invention, non-limiting examples of adhesives include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0066] In some embodiments of the present invention, the negative electrode active material layer can be obtained by coating a negative electrode slurry onto a negative electrode current collector and then performing operations such as drying. The negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as the liquid medium for forming the negative electrode slurry, it is preferable to use a thickener for slurry formation. The thickener is typically used to adjust the viscosity of the slurry.

[0067] In some embodiments of the present invention, the aforementioned thickener may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and their salts, etc.

[0068] In some embodiments of the present invention, the mass percentage of the thickener in the negative electrode slurry can be 0.1%-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5%-3%, and more preferably 0.6%-2%.

[0069] In some embodiments of the invention, the negative electrode active material layer includes a conductive material, thereby making the electrode conductive. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0070] In some embodiments of the present invention, the negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0071] Electrolyte:

[0072] The lithium battery and electrochemical device involved in this invention also include an electrolyte.

[0073] In some embodiments of the present invention, the electrolyte includes a lithium salt and a solvent.

[0074] In some embodiments of the present invention, the lithium salt includes at least one of organic lithium salts or inorganic lithium salts. In some embodiments of the present invention, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalateborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0075] In some embodiments of the present invention, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0076] In some embodiments of the present invention, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0077] In some embodiments of the present invention, the aforementioned additives include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propylene-1,3-sulfonyl lactone, vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, saturated phosphate compounds and unsaturated phosphate compounds, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, tris(triethylsilane) borate, succinic acid nitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptacyanide, octanoic acid nitrile, azelaic acid nitrile, and sebacate.

[0078] Secondary batteries:

[0079] In some embodiments of the present invention, the secondary battery involved in the present invention includes the above-mentioned positive electrode, negative electrode, separator, electrolyte, etc., but is not limited thereto.

[0080] In some embodiments of the present invention, the secondary battery involved in the present invention is made by stacking the above-mentioned positive and negative electrode sheets.

[0081] In some embodiments of the present invention, the secondary battery involved in the present invention may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0082] In some embodiments of the present invention, a battery module is also provided. This battery module includes the aforementioned secondary battery. The battery module of the present invention can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0083] In some embodiments of the present invention, a battery pack comprising the aforementioned battery modules is also provided. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0084] Device:

[0085] The present invention also provides an apparatus comprising at least one of the above-described secondary battery, battery module, or battery pack.

[0086] In some embodiments of the present invention, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. To meet the device's requirements for high power and high energy density of lithium batteries, battery packs or battery modules can be used.

[0087] In other embodiments of the invention, the device may be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a thin and light design and may use a lithium battery as its power source.

[0088] The present invention will be further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0089] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all chemical reagents used in the embodiments of the present invention were obtained through conventional commercial means. Unless otherwise specified, all contents mentioned below are mass contents. Unless otherwise specified, it is understood that the process was carried out at room temperature.

[0090] The present application will be further described below with reference to specific embodiments and comparative examples.

[0091] Examples 1-11

[0092] Preparation of functional materials:

[0093] Step 1: Preparation of aqueous pre-emulsion: An aqueous pre-emulsion is prepared using deionized water, rosin soap solution, fatty acid soap solution, sodium dodecylbenzene sulfonate, alkylphenol polyoxyethylene ether, sodium methylene dinaphthalene sulfonate, and potassium chloride.

[0094] Step 2, Preparation of oil phase solution: Prepare an oil phase solution using tert-dodecyl mercaptan, 2-vinylpyridine, styrene, and butadiene for later use.

[0095] Step 3, latex synthesis: The aqueous pre-emulsion and oil phase solution are placed in a reaction vessel, and the initiator azobisisoheptanenitrile is added to promote the reaction. After reacting for 15-20 hours, the functional material vinylpyridine-grafted butadiene styrene copolymer can be obtained.

[0096] Preparation of composite membrane:

[0097] S1. First, the above-mentioned functional material vinylpyridine-grafted butadiene styrene copolymer is dispersed in deionized water, and then ceramic material alumina is added for dispersion to form a functional layer slurry.

[0098] The ceramic material is granular with a particle size D. v 50 represents 0.5μm.

[0099] S2. The functional layer slurry is coated onto the base membrane and dried to form the functional layer, thus obtaining the composite membrane.

[0100] The base membrane is a single-layer porous polyethylene base membrane with a thickness of 29 μm.

[0101] Preparation of secondary batteries:

[0102] A secondary battery is prepared by stacking the positive electrode, the above-mentioned composite separator, and the negative electrode, primary encapsulation, liquid injection (EC:DMC = 1:1 vol%), and secondary encapsulation.

[0103] The positive electrode includes a positive electrode active material, which includes lithium manganese oxide; the negative electrode includes a negative electrode active material, which includes graphite.

[0104] In the examples prepared according to the above method, the specific parameters are shown in Table 1 below.

[0105] Table 1

[0106]

[0107]

[0108] Comparative Example 1

[0109] Preparation of composite membrane:

[0110] S1. First, the functional material poly(4-vinylpyridine) and the binder PVDF are dispersed in N-methylpyrrolidone, and then the ceramic material alumina is added for dispersion to form a functional layer slurry.

[0111] The ceramic material is granular with a particle size D. v 50 represents 0.5 μm; the mass ratio of poly(4-vinylpyridine), PVDF, and ceramic materials is 3:2:95.

[0112] S2. The functional layer slurry is coated onto the base membrane and dried to form the functional layer, thus obtaining the composite membrane.

[0113] The base membrane is a single-layer porous polyethylene base membrane with a thickness of 29 μm; the functional layer has a thickness of 2 μm.

[0114] Preparation of secondary batteries:

[0115] A secondary battery is prepared by stacking the positive electrode, the above-mentioned composite separator, and the negative electrode, primary encapsulation, liquid injection (EC:DMC = 1:1 vol%), and secondary encapsulation.

[0116] The positive electrode includes a positive electrode active material, which includes lithium manganese oxide; the negative electrode includes a negative electrode active material, which includes graphite.

[0117] Comparative Example 2

[0118] Preparation of composite membrane:

[0119] S1. Add ceramic material alumina and binder CMC to deionized water for dispersion to form functional layer slurry.

[0120] The ceramic material is granular with a particle size D. v 50 represents 0.5μm.

[0121] S2. The functional layer slurry is coated onto the base membrane and dried to form the functional layer, thus obtaining the composite membrane.

[0122] The base membrane is a single-layer porous polyethylene base membrane with a thickness of 29 μm; the functional layer has a thickness of 2 μm.

[0123] Preparation of secondary batteries:

[0124] A secondary battery is prepared by stacking the positive electrode, the above-mentioned composite separator, and the negative electrode, primary encapsulation, liquid injection (EC:DMC = 1:1 vol%), and secondary encapsulation.

[0125] The positive electrode includes a positive electrode active material, which includes lithium manganese oxide; the negative electrode includes a negative electrode active material, which includes graphite.

[0126] Comparative Example 3

[0127] Preparation of composite membrane:

[0128] S1. First, the functional material styrene-butadiene is dispersed in deionized water, and then the ceramic material alumina is added for dispersion to form a functional layer slurry.

[0129] The ceramic material is granular with a particle size D. v 50 represents 0.5 μm; the mass ratio of styrene-butadiene to ceramic material is 5:95.

[0130] S2. The functional layer slurry is coated onto the base membrane and dried to form the functional layer, thus obtaining the composite membrane.

[0131] The base membrane is a single-layer porous polyethylene base membrane with a thickness of 29 μm; the functional layer has a thickness of 2 μm.

[0132] Preparation of secondary batteries:

[0133] A secondary battery is prepared by stacking the positive electrode, the above-mentioned composite separator, and the negative electrode, primary encapsulation, liquid injection (EC:DMC = 1:1 vol%), and secondary encapsulation.

[0134] The positive electrode includes a positive electrode active material, which includes lithium manganese oxide; the negative electrode includes a negative electrode active material, which includes graphite.

[0135] Performance testing

[0136] (1) Peel strength test

[0137] Take a square diaphragm with a width of 20 mm, stretch the sample and tape at a speed of 2 mm / min, and judge the peel strength of the diaphragm based on the magnitude of the peel force.

[0138] (2) Breathability test

[0139] Place a 50mm×50mm diaphragm in an air permeability tester and record the time required for 100ml of air to pass through; this is the air permeability value.

[0140] (3) Heat shrinkage rate test

[0141] First, cut the diaphragm into 20mm diameter circular pieces using a stamping machine and calculate its initial area S0. Then, raise the oven temperature to the test temperature of 130℃, place the diaphragm circular sample in the oven for 1 hour, and remove it. Measure the diameter of the diaphragm after heat treatment and calculate the corresponding area S1. Calculate the heat shrinkage rate using the following formula:

[0142]

[0143] (4) Liquid absorption and retention test

[0144] Cut a 50mm×50mm sample strip and weigh it to obtain its initial weight. Completely immerse the sample strip in a beaker containing a certain amount of electrolyte, seal the beaker with plastic wrap, and after 1 hour, remove the sample strip with tweezers, wipe the electrolyte off the surface with filter paper, weigh and record the weight of the diaphragm after absorbing the electrolyte; place the sample strip in a clean beaker, place it in a fume hood for another 1 hour, weigh and record the weight of the diaphragm after standing. Calculate the liquid absorption rate of the diaphragm using the following formula (1), and calculate the liquid retention rate of the diaphragm using the following formula (2):

[0145]

[0146] (5) Transition metal ion test on the negative electrode side

[0147] Weigh approximately 0.1 g of the negative electrode powder (accurate to ±0.0003 g) from each of the examples and comparative examples, place them in 100 mL beakers, add a small amount of distilled water to moisten the bottom of the beaker, then add 5 mL of 12 mol / L aqua regia to dissolve it. Heat on an electric heating plate for 20 min, remove and cool, dilute and then test. Introduce the prepared series of standard solutions into an iCAP7000 inductively coupled plasma optical transilluminator (ICP). Measure the intensity of each element in the standard solution at the wavelength of the element to be measured (lithium, nickel, cobalt, and manganese). When the linear correlation coefficient r of the working curve is ≥0.9995, the measurement can be performed. The test results are shown in Table 2.

[0148] (6) Battery cycle performance test

[0149] The secondary batteries from each embodiment and comparative example were cycled for 800 cycles at room temperature under 1C / 1C charge / discharge conditions, with a voltage range of 3.0V to 4.5V. The average value of the ratio of the discharge capacity in the 800th cycle to the discharge capacity in the 1st cycle was calculated. The test results are shown in Table 2.

[0150] Table 2

[0151]

[0152]

[0153] As shown in Table 2, comparing Examples 1-11 and Comparative Examples 1-3, it can be seen that the separator and secondary battery provided in this application improve the peel strength between the base film and the functional layer, can adsorb transition metal ions, reduce the damage of transition metal ions to the SEI film, improve the cycle performance of the battery, and improve the air permeability of the composite separator.

[0154] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A secondary battery characterized by comprising: The positive electrode, the negative electrode, and the composite separator are included. The positive electrode includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium nickel manganate, a lithium-rich manganese-based positive electrode material, and lithium nickel cobalt manganate. The composite separator includes: a base film; and a functional layer disposed on at least one surface of the base film, the functional layer including a ceramic material and a functional material, and the functional material including a vinylpyridine grafted butadiene styrene copolymer. The mass percentage of butadiene in the total mass of the vinylpyridine grafted butadiene styrene copolymer is 20% to 69.5%, the mass percentage of styrene is 10% to 50%, and the mass percentage of vinylpyridine is 5% to 30%.

2. The secondary battery according to claim 1, characterized by The vinylpyridine includes one or more of 2-vinylpyridine, 3-vinylpyridine, and 4-vinylpyridine.

3. The secondary battery according to claim 1, characterized by The particle size of the functional material is 10 nm to 1000 nm.

4. The secondary battery according to claim 1, characterized by In the functional layer, the mass ratio of the functional material to the ceramic material is (1:99) to (10:90).

5. The secondary battery according to claim 1, characterized by The peeling strength of the functional layer to the base film is 0.01 kN / m to 0.05 kN / m.

6. The secondary battery according to claim 1, characterized by The thickness of the functional layer is 1 μm to 5 μm.

7. The secondary battery according to any one of claims 1 to 6, characterized by The air permeability of the composite separator is 80 s / 100 ml to 500 s / 100 ml.

8. A method of producing a secondary battery as claimed in any one of claims 1 to 7, characterized by, The method includes the following steps: The functional material is first dispersed in deionized water, and then the ceramic material is added for dispersion to form a functional layer slurry. The functional material includes a vinylpyridine grafted butadiene styrene copolymer. The functional layer slurry is coated on the base film, and a functional layer is formed after drying to obtain a composite separator.

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