Separating membrane, secondary battery, battery pack and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly discloses an isolating membrane, a secondary battery, a battery pack and an electric device. The secondary battery comprises a positive pole piece, an isolating membrane and a negative pole piece which are laminated, at least part of the surface of the isolating membrane contains functional groups and any one or more of C1-10 alkyl groups comprising the functional groups; the functional groups comprise a first functional group; the functional groups further comprise any one or more of a second functional group and a third functional group. The surface of the selected isolating membrane contains functional groups, the existence of the functional groups can increase the bonding force between the isolating membrane and the pole piece, the wrinkles of the isolating membrane are reduced to a certain extent, and the probability of displacement between the pole piece and the isolating membrane is reduced, so that the cycle stability and safety of the battery are improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a separator, a secondary battery, a battery pack, and an electrical device. Background Technology

[0002] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect. Among them, lithium-ion batteries have a very wide range of applications in portable electronic devices and electric vehicles.

[0003] As the application of rechargeable batteries becomes more and more widespread, the requirements for battery performance are also becoming higher and higher. Summary of the Invention

[0004] In view of the above problems, this application provides a separator, a secondary battery, a battery pack and an electrical device, which improves the cycle stability and safety of the battery by increasing the adhesion between the separator and the electrode.

[0005] In a first aspect, this application provides a secondary battery, which includes a positive electrode, a separator and a negative electrode stacked together.

[0006] At least a portion of the surface of the separator contains functional groups and C including said functional groups. 1～10 Any one or more of the alkyl groups;

[0007] The functional group includes a first functional group; the first functional group includes any one or more of the following: hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups;

[0008] Functional groups also include any one or more of the second and third functional groups;

[0009] The second functional group includes any one or more of the following: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid group, phosphoric acid group, aminosulfonyl group, halogen atom, hydrazine group, amidine group, guanidinyl group, pyridinyl group, and cyano group;

[0010] The third functional group includes one or more of thiol, nitro, and nitroso.

[0011] In some embodiments of this application, the separator and the positive or negative electrode are treated for 5s to 1000s under hot-pressing conditions of 60℃ to 105℃ and pressure of 0.1MPa to 10MPa; the adhesion force between the separator and the positive or negative electrode is 7N / m to 24N / m.

[0012] In some embodiments of this application, the adhesion force between the separator and the positive electrode sheet is 7 N / m to 10 N / m;

[0013] The adhesion between the aforementioned separator and the aforementioned negative electrode sheet is 10 N / m to 24 N / m.

[0014] In some embodiments of this application, the negative electrode and / or the positive electrode include an adhesive, wherein the molecules contained in the adhesive have one or more of covalent bonds, intermolecular hydrogen bonds, or intermolecular van der Waals forces with the functional groups on the surface of the separator.

[0015] In some embodiments of this application, the negative electrode and / or the aforementioned positive electrode include an adhesive, which includes one or more of polyacrylic acid and its salts, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, cellulose and its salts, and polyvinylidene fluoride.

[0016] In some embodiments of this application, the aforementioned separator membrane comprises a base membrane, the base membrane being made of a polymer material, the polymer material being one or more selected from polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

[0017] In some embodiments of this application, the aforementioned separator membrane comprises a base membrane and a coating located on at least one side surface of the base membrane, the coating comprising one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, carboxymethyl cellulose salt, polyvinyl alcohol, polyimide, and polyamide.

[0018] In some embodiments of this application, along a first direction, the aforementioned separator has a first surface and a second surface facing opposite directions;

[0019] The first surface faces the negative electrode sheet, and the first surface contains the functional groups described above;

[0020] The second surface mentioned above faces the positive electrode sheet, and the second surface does not contain the aforementioned functional groups;

[0021] The first direction refers to the stacking direction of the secondary battery.

[0022] In some embodiments of this application, along a first direction, the aforementioned separator has a first surface and a second surface facing opposite directions;

[0023] The first surface faces the negative electrode plate, and the second surface faces the positive electrode plate;

[0024] The first and second surfaces contain the same type of functional groups;

[0025] The number of the aforementioned functional groups on the first surface is greater than the number of the aforementioned functional groups on the second surface.

[0026] A second aspect of this application is to provide a separator membrane, wherein at least a portion of the surface of the separator membrane contains functional groups and C including the aforementioned functional groups. 1～10 Any one or more of the alkyl groups;

[0027] The aforementioned functional group includes a first functional group; the aforementioned first functional group includes any one or more of the following: hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups;

[0028] The aforementioned functional groups also include any one or more of the second and third functional groups;

[0029] The aforementioned second functional group includes any one or more of the following: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid group, phosphoric acid group, aminosulfonyl group, halogen atom, hydrazine group, amidine group, guanidinyl group, pyridinyl group, and cyano group;

[0030] The aforementioned third functional group includes any one or more of thiol, nitro, and nitroso.

[0031] In some embodiments of this application, the separator includes a base film made of a polymer material, which includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

[0032] In some embodiments of this application, the polymer material includes any one or more of poly(p-phenylene terephthalamide), polyimide, polyamide, polyethylene terephthalate, polytetrafluoroethylene, and polyacrylonitrile.

[0033] At least a portion of the surface of the aforementioned separator contains one or more of a first functional group and a third functional group.

[0034] In some embodiments of this application, the thickness of the separator is 3 μm to 20 μm.

[0035] In some embodiments of this application, the transverse tensile strength of the above-mentioned separator is ≥10MPa, and the longitudinal tensile strength of the above-mentioned separator is ≥10MPa.

[0036] and / or;

[0037] The air permeability of the above-mentioned separator is 100s / 100cc to 300s / 100cc;

[0038] and / or;

[0039] The porosity of the aforementioned separator is 30%–70%;

[0040] and / or;

[0041] The sheet resistance of the aforementioned isolation membrane is ≤1.3Ω, preferably 0.1Ω~1.3Ω.

[0042] A third aspect of this application is to provide a method for preparing a separator membrane, characterized by: providing a separator membrane body, subjecting the separator membrane body to plasma treatment two or more times, to obtain a separator membrane whose surface contains at least a portion of functional groups and C including the functional groups. 1～10 Any one or more of the alkyl groups;

[0043] The aforementioned functional group includes a first functional group; the first functional group includes any one or more of the following: hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups;

[0044] The aforementioned functional groups also include any one or more of the second and third functional groups;

[0045] The aforementioned second functional group includes any one or more of the following: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid group, phosphoric acid group, aminosulfonyl group, halogen atom, hydrazine group, amidine group, guanidinyl group, pyridinyl group, and cyano group;

[0046] The aforementioned third functional group includes any one or more of thiol, nitro, and nitroso.

[0047] In some embodiments of this application, the active substances for plasma treatment include any one or more of the following: nitrogen, oxygen, air, ozone, hydrogen, chlorine, bromine, nitrous oxide, nitrogen monoxide, nitrogen dioxide, carbon dioxide, carbon monoxide, carbon sulfide, carbon disulfide, sulfur dioxide, sulfur trioxide, hydrogen sulfide, hydrogen peroxide, hydrogen chloride, hydrogen bromide, hydrogen cyanide, ammonia, carbonyl dichloride, sulfur hexafluoride, nitrogen trifluoride, haloalkanes, haloolefins, haloalkynes, amino-substituted alkanes, amino-substituted alkenes, amides and imides, cyano-substituted alkanes, and cyano-substituted alkenes.

[0048] In some embodiments of this application, the plasma processing device includes a first electrode and a second electrode, wherein the distance between the first electrode and the second electrode is 0.1 mm to 10 mm;

[0049] and / or;

[0050] The power of the aforementioned plasma treatment equipment ranges from 1W to 1000kW;

[0051] and / or;

[0052] The frequency of the aforementioned plasma processing equipment is 1Hz to 2.5GHz.

[0053] The fourth aspect of this application is to provide a battery pack comprising the secondary battery described in the first aspect, the separator described in the second aspect, or the method for preparing the separator described in the third aspect.

[0054] The fifth aspect of this application is to provide an electrical device that includes the battery pack described in the fourth aspect above.

[0055] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0056] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0057] Figure 1 This is a schematic diagram of the battery structure of some embodiments of this application;

[0058] Figure 2 This is an exploded structural diagram of a battery according to some embodiments of this application;

[0059] Figure 3 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0060] Figure 4 This is a schematic diagram of the battery pack structure according to some embodiments of this application;

[0061] Figure 5 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0062] Figure 6 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0063] The reference numerals in the detailed embodiments are as follows:

[0064] 10000, vehicles;

[0065] 1000, Battery; 2000, Controller; 3000, Motor;

[0066] 100. Battery cell;

[0067] 200. Box body; 210. First part; 220. Second part;

[0068] 10. Secondary batteries;

[0069] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0070] 1. Negative electrode sheet; 11. Current collector; 12. Negative electrode film;

[0071] 2. Positive electrode sheet; 3. Separator membrane; 31. First surface; 32. First surface;

[0072] First direction: the x-axis of the coordinate axis, or it can be the stacking direction or the thickness direction of the separator film;

[0073] The y-axis of the coordinate axis represents the length or width of the isolation membrane. Detailed Implementation

[0074] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the separator, secondary battery, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0075] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0076] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0077] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0078] Unless otherwise specified, all steps in 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.

[0079] 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.

[0080] 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).

[0081] Unless otherwise specified, in this application, the terms "first," "second," etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0082] Unless otherwise specified, in this application, the term "multiple" means two or more (including two), similarly, "multiple sets" means two or more (including two sets), and "multiple pieces" means two or more (including two pieces).

[0083] Unless otherwise specified, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0084] Due to their advantages such as high energy density, long cycle life, and safety and reliability, rechargeable batteries have been widely used in various products. In recent years, with the significant increase in demand for rechargeable batteries as an energy source, higher requirements have been placed on their performance, such as cycle life and safety.

[0085] Secondary batteries mainly consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator's primary function is to provide a physical barrier between the electrodes to prevent short circuits, while also providing a transport channel for lithium ions. However, existing separators cannot effectively bond to the positive and negative electrodes, leading to defects at the separator-electrode interface. For example, wrinkles in the separator can cause uneven internal resistance distribution, resulting in localized overcharging or over-discharging during battery cycling, thus affecting cycle stability. Furthermore, displacement of the electrodes and separator during use can cause battery safety issues.

[0086] To address the aforementioned technical problems, this application discloses a secondary battery comprising a positive electrode, a separator, and a negative electrode stacked together; at least a portion of the surface of the separator contains functional groups and C atoms including the functional groups. 1～5 The alkyl group comprises one or more of the following functional groups: the functional group comprises a first functional group; the first functional group comprises one or more of the following functional groups: hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, epoxy; the functional group further comprises one or more of the following functional groups: a second functional group and a third functional group; the second functional group comprises one or more of the following functional groups: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid, phosphate, aminosulfonyl, halogen atom, hydrazine, amidine, guanidine, pyridinyl, cyano; the third functional group comprises one or more of the following functional groups: mercapto, nitro, nitroso.

[0087] The separator selected in this application contains functional groups on its surface. The presence of these functional groups can increase the adhesion between the separator and the electrode, reduce the wrinkles of the separator itself to a certain extent, and reduce the probability of displacement between the electrode and the separator. Therefore, it is beneficial to improve the cycle stability and safety of the battery.

[0088] Therefore, the secondary battery provided in this application improves the cycle stability and safety of the battery without affecting its energy density, thereby enhancing the user experience. The secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte composed of the aforementioned secondary battery. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, including but not limited to polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0089] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 10.

[0090] According to some embodiments of this application, reference is made to Figure 2 The outer packaging may include a housing 101 and a cover plate 103. The housing 101 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 102 by a winding process or a stacking process. The electrode assembly 102 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 102. The secondary battery 10 may contain one or more electrode assemblies 102, which can be selected by those skilled in the art according to specific practical needs.

[0091] The electrode assembly 102 provided in this application is beneficial to improving the performance of a secondary battery when applied in a secondary battery. The secondary battery can be a power source for an electrical device or an energy storage unit for an electrical device. The electrical device is applied in the power field, such as mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited to the above fields.

[0092] For ease of explanation, some embodiments of this application are illustrated using a vehicle as an example of an electrical device.

[0093] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the structure of a vehicle 10000 provided in some embodiments of this application. The vehicle 10000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 1000 is disposed inside the vehicle 10000, and the battery 10000 can be located at the bottom, front, or rear of the vehicle 10000. The battery 10000 can be used to power the vehicle 10000; for example, the battery 10000 can serve as the operating power source for the vehicle 10000. The vehicle 10000 may also include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 10000 to supply power to the motor 3000, for example, to meet the power needs of the vehicle 10000 during startup, navigation, and driving.

[0094] In some embodiments of this application, the battery 1000 can not only serve as the operating power source for the vehicle 10000, but also as the driving power source for the vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 10000.

[0095] Please refer to Figure 4 , Figure 4 This is an exploded view of a battery 1000 provided in some embodiments of this application. The battery 1000 includes a housing 200 and a battery cell 100. A conventional battery cell includes a primary battery or a secondary battery. This application specifically protects a secondary battery 10. The battery cell 100 is housed within the housing 200. The housing 200 provides space for the battery cell 100, and the housing 200 can adopt various structures.

[0096] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220, which overlap each other, and together define a receiving space for accommodating the secondary battery 100. The second portion 220 may be a hollow structure with one open end, and the first portion 210 may be a plate-like structure, with the first portion 210 covering the open side of the second portion 220 so that the first portion 210 and the second portion 220 together define the receiving space; alternatively, the first portion 210 and the second portion 220 may both be hollow structures with one open side, with the open side of the first portion 210 covering the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may be of various shapes, such as a cylinder, a cuboid, etc.

[0097] In battery 1000, there can be multiple battery cells 100, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 100 are connected in both series and parallel configurations. Multiple battery cells 100 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 100 is housed within housing 200. Alternatively, battery 1000 can also be composed of multiple battery cells 100 first connected in series, parallel, or in a mixed manner to form battery modules, and then these modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within housing 200. Battery 1000 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 100.

[0098] Secondary batteries

[0099] This application discloses a secondary battery in some embodiments, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode, separator, and negative electrode are sequentially stacked together to form the secondary battery using a winding or stacking process. Meanwhile, at least a portion of the surface of the separator contains functional groups and C atoms including the aforementioned functional groups. 1～10 The functional group comprises any one or more alkyl groups; the functional group includes a first functional group; the first functional group includes any one or more of hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups; the functional group also includes any one or more of a second and a third functional group; the second functional group includes any one or more of ester, acid anhydride, acyl halide, amide, imide, sulfonic acid, phosphoric acid, aminosulfonyl, halogen atom, hydrazine, amidine, guanidine, pyridinyl, and cyano groups; the third functional group includes any one or more of mercapto, nitro, and nitroso groups.

[0100] The positive electrode, separator, and negative electrode in this application can be formed into a secondary battery using winding or stacking processes. Specifically, this application... Figure 5 The diagram illustrates a secondary battery 10 formed using a stacking method, combined with... Figure 5 It is known that a negative electrode 1 or a positive electrode 2 is placed between two adjacent separators 3, and the negative electrode 1 and the positive electrode 2 are alternately arranged along the stacking direction (coordinate axis x direction). The number and size of the negative electrode 1 and / or the positive electrode 2 can be selected according to the actual situation, and will not be elaborated in this application. Furthermore, this application... Figure 5 The image only illustrates one type of lamination method; other lamination or winding methods are within the scope of protection of this application.

[0101] The functional groups in this application primarily relate to organic compounds. A functional group is an atom or group of atoms that determines the chemical properties of an organic compound. The functional groups listed above in this application include those conventionally defined in the art, and C 1～10 Alkyl groups refer to alkanes, alkenes, or alkynes with 1 to 10 carbon atoms.

[0102] The surface of the separator selected in this application contains a first functional group, as well as a second and / or a third functional group. The presence of these functional groups can increase the adhesion between the separator and the electrode. Specifically, after the battery cell is hot-pressed, the peel strength between the separator and the positive or negative electrode is enhanced, that is, the adhesion is enhanced.

[0103] In some embodiments of this application, the separator and the positive or negative electrode are subjected to hot-pressing at a temperature of 60°C to 105°C and a pressure of 0.1 MPa to 10 MPa for 5 to 1000 seconds; the adhesion between the separator and the positive or negative electrode is 7 N / m to 24 N / m. Specific testing methods are detailed in subsequent performance tests.

[0104] In some embodiments of this application, the adhesion force between the separator and the positive electrode sheet is 7 N / m to 10 N / m;

[0105] The adhesion between the separator and the negative electrode sheet is 10 N / m to 24 N / m. This application discloses in these embodiments that, generally, the adhesion between the separator and the positive electrode sheet is slightly less than the adhesion between the separator and the negative electrode sheet. This design helps reduce the probability of lithium particles precipitated in the negative electrode sheet overflowing, thus improving battery safety.

[0106] In these embodiments, this application discloses that the adhesion force between the separator and the positive electrode sheet is any one of 7 N / m, 7.5 N / m, 8 N / m, 8.5 N / m, 9 N / m, 9.5 N / m, 10 N / m or any one of the above range values.

[0107] In these embodiments, this application discloses that the adhesion strength between the separator and the negative electrode sheet is any one of 10 N / m, 10.5 N / m, 11 N / m, 11.5 N / m, 12 N / m, 12.5 N / m, 13 N / m, 13.5 N / m, 14 N / m, 14.5 N / m, 15 N / m, 15.5 N / m, 16 N / m, 16.5 N / m, 17 N / m, 17.5 N / m, 18 N / m, 18.5 N / m, 19 N / m, 19.5 N / m, 20 N / m, 20.5 N / m, 21 N / m, 21.5 N / m, 22 N / m, 22.5 N / m, 23 N / m, 23.5 N / m, and 24 N / m, or any one of the above range values.

[0108] The test method for the adhesion between the separator and the positive or negative electrode sheet in this application is detailed in the subsequent performance test. In some embodiments of this application, the negative electrode sheet and / or the positive electrode sheet includes an adhesive, wherein the molecules contained in the adhesive have one or more of covalent bonds, intermolecular hydrogen bonds, or intermolecular van der Waals forces with the functional groups on the surface of the separator.

[0109] The covalent bonds in this application include relatively stable chemical bonds formed by the sharing of electron pairs between some functional groups on the surface of the separator and molecules in the adhesive. The measurement of covalent bonds includes Fourier transform infrared spectroscopy. Because different chemical bonds or functional groups have different absorption frequencies, they will occupy different vibrational peak positions in the infrared spectrum, thus providing information about the types of chemical bonds or functional groups contained in the molecule.

[0110] The intermolecular hydrogen bonds in this application include intermolecular forces formed between hydrogen atoms and atoms with high electronegativity, such as fluorine, oxygen, and nitrogen atoms. The measurement of intermolecular hydrogen bonds includes Fourier transform infrared spectroscopy, because the formation of intermolecular hydrogen bonds typically leads to a shift in the position of the stretching vibration absorption peak or a change in the intensity of the stretching vibration absorption peak.

[0111] The intermolecular van der Waals forces described in this application are also a type of intermolecular force. Generally, nonpolar molecules only experience dispersion forces because they lack permanent dipole moments. When polar molecules approach nonpolar molecules, dispersion and induction forces arise due to the interaction between the dipole moments of the polar molecules and the instantaneous dipole moments of the nonpolar molecules. Induction forces arise because the charge distribution of one molecule is influenced by the dipole moment of another molecule. For polar molecules, in addition to dispersion and induction forces, orientation forces also exist. Orientation forces arise from the interaction of intermolecular dipole moments. All three forces are attractive forces, and intermolecular van der Waals forces encompass all three.

[0112] In this application, the functional groups on the surface of the separator and the molecules in the adhesive have the aforementioned interaction forces. The macroscopic manifestation of these forces is that, compared to not designing the aforementioned functional groups on the surface of the separator, the design method provided in this application enhances the adhesion between the separator and the electrode.

[0113] In some embodiments of this application, the negative electrode and / or positive electrode include an adhesive comprising one or more of polyacrylic acid and its salts, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, cellulose and its salts, and polyvinylidene fluoride.

[0114] The polyacrylic acid in this application is obtained by polymerizing acrylic acid monomers, such as acrylic acid, under certain conditions. The preparation method includes conventional methods in the art, such as emulsion polymerization. Salts of polyacrylic acid include lithium, sodium, or potassium salts. In some embodiments, this application discloses that the weight-average molecular weight of the polyacrylic acid is between 400,000 and 500,000.

[0115] This application discloses, in some embodiments, methods for measuring weight-average molecular weight and number-average molecular weight, including: referring to GB / T 21863-2008 gel permeation chromatography, using an ultra-high performance polymer chromatograph: ACQUITY APC; detector: ACQUITY differential refractive index detector. The test steps are as follows: (1) Preheating: Install the chromatographic column and tubing, turn on the control panel, test the power supply, etc., and open the test software Empower; (2) Parameter settings: Injection volume: 0 μL to 50 μL (depending on the sample concentration); Pump flow rate: 0.2 mL / min; Mobile phase: 30 mol / L LiBr NMP solution; Sealing cleaning solution: isopropanol; Pre-column: PLgel 10 μm MiniMIX-B Guard (size: 50 mm × 4.6 mm × 2); Analytical phase: PL gel 10 μm MiniMIX-B (size: 250 mm × 4.6 mm); Standard: Polystyrene sleeve; Run time: 30 min; Detector: ACQUITY differential refractive index (RI) detector; Column oven temperature: 90 ℃; Detector temperature: 55 ℃. (3) Sample testing: a. Preparation of standard and test samples: Weigh 0.002g to 0.004g of standard / test sample and add 2mL of mobile phase liquid to prepare a 0.1% to 0.5% mixed standard and place it in the refrigerator for >8h; b. Standard / sample testing: Edit the sample group to be tested, select the established sample group method, and after the baseline stabilizes, click the run queue to start testing the sample; (4) Data processing: Based on the relationship between retention time and molecular weight, establish a calibration curve using a chemical workstation, perform integral quantification on the sample spectrum, and the chemical workstation automatically generates molecular weight and molecular weight distribution results.

[0116] The polyacrylamide in this application is obtained by polymerizing acrylamide monomers under certain conditions. In some embodiments, this application discloses that the average relative molecular weight of the polyacrylamide is between 5 million and 18 million. The average relative molecular weight, also known as the average relative molecular mass, is used to reflect the atomic composition of a substance and the number of atoms in its molecules. In other words, once the types and numbers of atoms in a substance are determined, its average relative molecular weight can be calculated.

[0117] The average relative molecular weight of the polyvinyl alcohol in this application is 10,000 to 250,000.

[0118] In this application, polyvinylidene fluoride (PVDF) mainly refers to PVDF homopolymer or copolymer of PVDF with other monomers containing small amounts of fluorinated vinyl groups. In some embodiments, this application discloses that the average relative molecular weight of PVDF is 500,000 to 1,100,000.

[0119] The carboxymethyl cellulose in this application has a weight-average molecular weight of 400,000 to 1,000,000 and a degree of substitution (DS) ranging from 0.5 to 1.5, for example, any one of 0.5, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, or 1.5 satisfies any one of the above range values.

[0120] In some embodiments of this application, the separator includes a base film made of a polymer material, which includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

[0121] The polyethylene and polypropylene used in this application generally do not contain functional groups or have low functional group content. In some embodiments of this application, it is disclosed that the base film made of polyethylene and / or polypropylene is directly processed to make the surface of the base film have the above-mentioned functional groups.

[0122] In some embodiments of this application, the polymer material includes one or more of poly(p-phenylene terephthalamide), polyimide, polyamide, polyethylene terephthalate, polytetrafluoroethylene, and polyacrylonitrile; at least a portion of the surface of the separator membrane contains one or more of a first functional group and a third functional group.

[0123] In this application, the base film made of poly(p-phenylene terephthalamide) and / or polyimide and / or polyamide inherently possesses amide or imide, while the base film made of polyethylene terephthalate inherently possesses ester groups, the base film made of polytetrafluoroethylene inherently possesses fluorine atoms, and the base film made of polyacrylonitrile inherently possesses cyano groups. When processing these materials, this application may cause some of these functional groups to detach from the base film surface. However, since this application may also load new functional groups, the overall result is an increase in the number of functional groups on the base film surface after processing. In these embodiments, this application preferably forms one or more of the first and third functional groups on the base film surface.

[0124] In this application, when the adhesive of the electrode contains hydroxyl groups, the hydroxyl groups readily form ionic bonds with functional groups such as carboxyl groups, acid anhydrides, acyl halides, hydroxyl groups, aldehyde groups, and aminosulfonyl groups. They also generate intermolecular forces with hydroxyl groups, carboxyl groups, aldehyde groups, ketone groups, ether groups, amino groups, imino groups, epoxy groups, esters, acid anhydrides, acyl halides, amides, imides, sulfonic acid groups, phosphate groups, aminosulfonyl groups, hydrazine groups, amidoyl groups, guanidine groups, and pyridinyl groups. Furthermore, they generate intermolecular van der Waals forces with cyano groups, mercapto groups, nitro groups, and nitroso groups.

[0125] In this application, when the adhesive of the electrode contains a carboxyl group, the carboxyl group readily forms ionic bonds with functional groups such as carboxyl, hydroxyl, amino, imino, halogen atom, hydrazine, amidine, guanidine, and pyridyl, and generates intermolecular forces with hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, epoxy, ester, acid anhydride, acyl halide, amide, imide, sulfonic acid, phosphate, aminosulfonyl, hydrazine, amidine, guanidine, and pyridyl, and generates intermolecular van der Waals forces with cyano, mercapto, nitro, and nitroso groups.

[0126] In some embodiments of this application, the separator comprises a base film and a coating on at least one side of the base film, wherein the coating comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, carboxymethyl cellulose salt, polyvinyl alcohol, polyimide, and polyamide.

[0127] The polyvinylidene fluoride in this application can be as described above. The carboxymethyl cellulose salt in this application includes lithium carboxymethyl cellulose or sodium carboxymethyl cellulose. Lithium carboxymethyl cellulose or sodium carboxymethyl cellulose refers to a linear polymer derivative of cellulose containing multiple dehydrated glucose units (β-linked pyranose residues). Each glucose unit has three hydroxyl groups, and the hydrogen in the hydroxyl groups is replaced by carboxymethyl groups. The average number of hydroxyl groups replaced in each dehydrated glucose unit is defined as the degree of substitution (DS). The degree of substitution of the carboxymethyl cellulose compound in this application ranges from 0.7 to 1.2. For example, it can be any one of 0.7, 0.8, 0.9, 1.0, 1.1, or 1.2 that satisfies any of the above range values. The lithium carboxymethyl cellulose selected in this application can be prepared in-house or commercially available. The preparation methods for lithium carboxymethyl cellulose include a one-step direct synthesis method for lithium carboxymethyl cellulose (CMC-Li), specifically using cotton as raw material, activating it with lithium hydroxide solution to produce alkalized cellulose, and then performing an etherification reaction to obtain lithium carboxymethyl cellulose (CMC-Li). Alternatively, a two-step synthesis method can be included, primarily reacting sodium carboxymethyl cellulose (CMC-Na) with an acid to produce carboxymethyl cellulose hydrogen (CMC-H), which then reacts with lithium hydroxide or lithium chloride solution to obtain lithium carboxymethyl cellulose with high purity, essentially free of sodium carboxymethyl cellulose (CMC-Na), and the product exists as a single substance with high purity. Other methods conventional in the field can also be used.

[0128] The polyimide of this application refers to a class of polymer materials containing imide functional groups in the molecular backbone, including aromatic polyimides, which are thermoplastic materials, such as those prepared by reacting aromatic dianhydrides and aromatic diamines. In some embodiments, this application discloses that the aromatic polyimide is the product obtained by reacting pyromellitic dianhydride and p-phenylenediamine in a molar ratio of 1:1.2.

[0129] In some embodiments of this application, along a first direction, the separator has a first surface and a second surface facing opposite directions; the first surface faces the negative electrode, and the second surface contains the functional group; the second surface faces the positive electrode, and the second surface does not contain the functional group; the first direction refers to the stacking direction of the secondary battery.

[0130] In conjunction with this application Figure 6 Schematic diagram: Along the first direction (x-axis), the separator 3 has a first surface 31 and a second surface 32 facing opposite directions. The first surface 31 contains the aforementioned functional groups, while the second surface 32 does not contain the aforementioned functional groups. The first surface 31 faces the negative electrode 1, and the second surface 32 faces the positive electrode 2. As described above, since the functional groups on the separator surface and the molecules in the adhesive possess any one or more of covalent bonds, intermolecular hydrogen bonds, or intermolecular van der Waals forces, the macroscopic manifestation of these forces is: enhanced adhesion between the separator and the electrode. Therefore, this application adopts... Figure 6 In the schematic design, the adhesion between the separator 3 and the negative electrode 1 is greater than the adhesion between the separator 3 and the positive electrode 2. This design not only alleviates wrinkles in the separator itself, but also prevents lithium plating or lithium dendrites from easily "leaking" from the separator when they appear on the negative electrode, thus improving battery safety.

[0131] This application also provides other design methods, which can be found in detail in [reference needed]. Figure 6 As shown, along the first direction (coordinate axis x direction), the separator 3 has a first surface 31 and a second surface 32 facing opposite directions; the first surface 31 faces the negative electrode 1, and the second surface 32 faces the positive electrode 2; the first surface 31 and the second surface 32 contain the same type of functional groups; the number of functional groups on the first surface 31 is greater than the number of functional groups on the second surface 32.

[0132] This application discloses in these embodiments a method of distinguishing between a first surface and a second surface using the number of functional groups, wherein the first surface has a greater number of functional groups. The method for measuring the number of functional groups includes chemical titration combined with Fourier transform infrared spectroscopy. First, samples are taken from both the first and second surfaces of the separator. Fourier transform infrared spectroscopy is used to locate the absorption peaks corresponding to the functional groups in the samples. Then, the samples are hydrolyzed. Since hydrolysis generally produces acid radicals or basic groups, the number of functional groups on the surface can be roughly calculated using acid-base titration.

[0133] Separating membrane

[0134] This application provides a separator membrane, at least a portion of the surface of which contains functional groups and C including the functional groups. 1～5The functional group comprises any one or more alkyl groups; the functional group includes a first functional group; the first functional group includes any one or more of hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups; the functional group further includes any one or more of a second and a third functional group; the second functional group includes any one or more of ester, acid anhydride, acyl halide, amide, imide, sulfonic acid, phosphate, aminosulfonyl, halogen atom, hydrazine, amidine, guanidine, pyridinyl, and cyano groups; the third functional group includes any one or more of mercapto, nitro, and nitroso groups.

[0135] The surface of the separator selected in this application contains a first functional group, as well as a second and / or a third functional group. The presence of these functional groups can increase the adhesion between the separator and the electrode. Specifically, after the battery cell is hot-pressed, the peel strength between the separator and the positive or negative electrode is enhanced, that is, the adhesion is enhanced.

[0136] In some embodiments of this application, the separator includes a base film made of a polymer material, which includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

[0137] In some embodiments of this application, the polymer material includes one or more of poly(p-phenylene terephthalamide), polyimide, polyamide, polyethylene terephthalate, polytetrafluoroethylene, and polyacrylonitrile; at least a portion of the surface of the separator membrane contains one or more of a first functional group and a third functional group.

[0138] In some embodiments of this application, the thickness of the separator is 3 μm to 20 μm.

[0139] The thickness of the separator membrane in this application includes the distance between the two end faces along the lamination direction (x-axis). The specific measurement method involves taking different points at different locations on the separator membrane sample and using measuring instruments such as vernier calipers or handheld thickness gauges to measure the distance between the two end faces at each point. The average of these distance values ​​is taken as the thickness of the separator membrane. Testing standards can refer to GB / T 6672-2001 "Mechanical Measurement Method for Determination of Thickness of Plastic Films and Sheets," etc. The thickness parameter of the separator membrane used in this application is mainly used to investigate whether the functional groups on the separator membrane surface affect the membrane thickness before and after their placement.

[0140] In these embodiments, this application discloses that the thickness of the separator membrane includes any one of 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, and 20μm, or satisfies any of the above range values.

[0141] In some embodiments of this application, the transverse tensile strength of the separator is ≥10MPa, and the longitudinal tensile strength of the separator is ≥10MPa.

[0142] The tensile strength of this application is a parameter reflecting the dimensional stability of the release liner under external force during use. The tensile strength parameter used in this application is mainly to investigate whether the presence of functional groups on the release liner surface affects its tensile strength. Specifically, the transverse tensile strength of the release liner refers to the tensile strength along the first direction, and the longitudinal tensile strength refers to the tensile strength along the second direction. Both the first and second directions are perpendicular to the thickness direction of the release liner (x-axis). The method for determining the tensile strength of the release liner includes reference to GB / T 1040.3-2006 "Test of Tensile Properties of Plastics".

[0143] The separator formed by the polyethylene base film in this application has a transverse tensile strength ≥110MPa and a longitudinal tensile strength ≥90MPa.

[0144] The separation membrane formed by the polypropylene base film in this application has a transverse tensile strength ≥110MPa and a longitudinal tensile strength ≥10MPa.

[0145] The separator formed by the base film of poly(p-phenylene terephthalamide) and / or polyethylene terephthalate and / or polyimide and / or polyamide and / or polyacrylonitrile in this application has a transverse tensile strength ≥10MPa and a longitudinal tensile strength ≥10MPa.

[0146] In some embodiments of this application, the air permeability of the separator is 100s / 100cc to 300s / 100cc (per 100 cubic centimeters).

[0147] In this application, the air permeability of the separator membrane is mainly used to characterize its gas permeability and can indirectly reflect its ion permeability. The air permeability parameter is primarily used to investigate whether the presence of functional groups on the separator membrane surface affects its air permeability. The measurement method for the air permeability of the separator membrane involves placing a separator membrane sample in an air permeability meter and measuring the time it takes for a certain volume of air to pass through a specified area of ​​the separator membrane under a certain pressure. The measurement method for the air permeability of the separator membrane includes reference to ASTM D726-94 (2003), "Startdard Test Method for Resistance of Nonporous Paper to Passage of Air".

[0148] In some embodiments of this application, the air permeability of the separator includes any one of 100s / 100cc, 110s / 100cc, 120s / 100cc, 130s / 100cc, 140s / 100cc, 150s / 100cc, 160s / 100cc, 170s / 100cc, 180s / 100cc, 190s / 100cc, 200s / 100cc, 210s / 100cc, 220s / 100cc, 230s / 100cc, 240s / 100cc, 250s / 100cc, 260s / 100cc, 270s / 100cc, 280s / 100cc, 290s / 100cc, and 300s / 100cc, or any one of the above range values.

[0149] In some embodiments of this application, the porosity of the separator is 30% to 70%.

[0150] In this application, the porosity of the separator membrane is related to its air permeability, and refers to the ratio of the volume of micropores in the separator membrane to the total volume of the separator membrane. The porosity parameter used in this application is mainly to investigate whether the functional groups on the separator membrane surface affect its porosity. Porosity measurement methods include the liquid absorption method. For example, the separator membrane sample is cut into square specimens of approximately 20mm × 20mm. The thickness and actual side length are measured using a digital micrometer and vernier calipers, its volume is calculated as V, and its weight M0 is measured. Then, the square specimen is immersed in the electrolyte and soaked for 2 hours at room temperature and in an air atmosphere. After soaking, the electrolyte liquid adsorbed on the surface is absorbed, and its weight M is measured. t The porosity of the separator then satisfies the following mathematical relationship:

[0151] Porosity = (M) t -M0) / ρ×100%;

[0152] In the above mathematical formula, ρ represents the density of the electrolyte, with units of mm. 3 / g, V is the volume of the square sample of the separator, in mm. 3 Weights M0 and M t The unit is g, and the weight measuring instrument is a 0.1 / 1000 balance. The models of the 0.1 / 1000 balance, digital micrometer, and vernier caliper include, but are not limited to, any conventional models in this field.

[0153] In some embodiments of this application, the sheet resistance of the separator is ≤1.3Ω.

[0154] The method for measuring the surface resistance of the separator membrane in this application includes measuring the ion conductivity and resistance value of the separator membrane to obtain an AC impedance spectrum, and then fitting the AC impedance spectrum to obtain the internal resistance of the separator membrane, which is the resistance value of the separator membrane. Alternatively, a resistance measuring instrument can be used for direct measurement. For detailed measurement methods, please refer to the performance test below.

[0155] In addition to a base film, the separator membrane of this application may also include a polymer coating. The polymer material of the polymer coating includes one or more of the following: polyethylene (PE), polypropylene (PP), poly(p-phenylene terephthalamide) (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), polyamide (PA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), carboxymethyl cellulose salt, and polyvinyl alcohol (PVA). The polymer coating may be made of the same or different material as the base film, and the thicknesses of the polymer coating and the base film may be different. Optionally, the thickness of the polymer coating may be less than the thickness of the base film. In these embodiments, this application discloses surface treatment of the polymer coating of the separator membrane to include the aforementioned functional groups on the surface of the polymer coating, and the treatment effect is consistent with the effect of the aforementioned treatment of the base film.

[0156] Preparation method of the isolation membrane

[0157] This application provides a method for preparing a separator membrane, the method comprising: providing a separator membrane body; subjecting the separator membrane body to plasma treatment two or more times to obtain a separator membrane whose surface contains functional groups and C including the aforementioned functional groups. 1～10The alkyl group comprises one or more of the following functional groups: the functional group comprises a first functional group; the first functional group comprises one or more of the following functional groups: hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, epoxy; the functional group further comprises one or more of the following functional groups: a second functional group and a third functional group; the second functional group comprises one or more of the following functional groups: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid, phosphoric acid, aminosulfonyl, halogen atom, hydrazine, amidine, guanidine, pyridinyl, cyano; the third functional group comprises one or more of the following functional groups: mercapto, nitro, nitroso.

[0158] In some embodiments of this application, the active material for plasma treatment includes any one or more of the following: nitrogen, oxygen, air, ozone, hydrogen, chlorine, bromine, nitrous oxide, nitrogen monoxide, nitrogen dioxide, carbon dioxide, carbon monoxide, carbon sulfide, carbon disulfide, sulfur dioxide, sulfur trioxide, hydrogen sulfide, hydrogen peroxide, hydrogen chloride, hydrogen bromide, hydrogen cyanide, ammonia, carbonyl dichloride, sulfur hexafluoride, nitrogen trifluoride, haloalkanes, haloalkenes, haloalkynes, amino-substituted alkanes, amino-substituted alkenes, amide compounds, cyano-substituted alkanes, and cyano-substituted alkenes.

[0159] The haloalkanes in this application include any one or more of the following: monochloromethane, bromomethane, trifluorochloromethane, difluorodichloromethane, monofluorodichloromethane, difluorochloromethane, tetrafluorodichloroethane, difluorobromochloromethane, chloroethane, difluorochloroethane, 1,1,1-trifluoroethane, 1,1-difluoroethane, carbon tetrafluoride, octafluoropropane, octafluorocyclobutane, and trifluoromethane.

[0160] The halogenated olefins of this application include one or more of ethylene bromide, trifluorochloroethylene, hexafluoropropylene, vinylidene fluoride, fluoroethylene, and octafluoroisobutylene.

[0161] The halogenated alkynes in this application include hexafluoro-2-butyne.

[0162] The amino-substituted alkanes in this application include any one or more of ethylenediamine and n-butylamine.

[0163] The amino-substituted olefins in this application include allylamine.

[0164] The amides and imides in this application include any one or more of acrylamide and ethyleneimine.

[0165] The cyano-substituted alkanes in this application include any one or more of n-butadiene nitrile and acetonitrile.

[0166] The cyano-substituted olefins of this application include any one or more of acrylonitrile and methacrylonitrile.

[0167] In some embodiments of this application, plasma treatment is performed in a plasma processing apparatus, which includes a first electrode and a second electrode, with a distance of 0.1 mm to 10 mm between the first electrode and the second electrode.

[0168] In this application, the first electrode and the second electrode refer to two electrodes with opposite polarities. The electrode discharge mode includes one of the following: glow discharge at atmospheric pressure, corona discharge, dielectric barrier discharge, radio frequency discharge, sliding arc discharge, and jet discharge.

[0169] In some embodiments of this application, the power of the plasma processing equipment is 1W to 1000kW;

[0170] In some embodiments of this application, the frequency of the plasma processing device is 1 Hz to 2.5 GHz.

[0171] This application also includes, prior to plasma treatment, placing the separator body in acetone and ultrasonically cleaning for 30 minutes to thoroughly remove any grease and other impurities that may be present on the material surface. Then, it is rinsed with deionized water until clean, and finally dried in an oven at 40℃~50℃.

[0172] This application discloses, in these embodiments, a plasma treatment apparatus for plasma treatment of a separator membrane, including a winding and unwinding device and a plurality of plasma treatment units, wherein each plasma treatment unit includes a gas supply system, each gas supply system is connected to a heating and evaporation device, and each gas supply system is also connected to a flow meter valve to control the content of active material in the plasma treatment.

[0173] The plasma treatment principle in this application includes: ultraviolet radiation and active particles generated by plasma treatment act on the surface of the isolation membrane, causing a large number of active free radicals to be generated on the surface of the isolation membrane. After these free radicals come into contact with the active material of the plasma treatment, the active material replaces the hydrogen atoms in the isolation membrane, initiating a reaction. The active material is grafted onto the surface of the isolation membrane to generate the aforementioned functional groups.

[0174] Negative electrode sheet

[0175] This application provides a negative electrode sheet, which includes a current collector and a negative electrode film layer located on at least one side surface of the current collector. The negative electrode film layer contains an adhesive, which includes one or more of polyacrylic acid and its salts, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, cellulose and its salts, and polyvinylidene fluoride.

[0176] The functional groups in the adhesive of this application can generate covalent bonds, intermolecular hydrogen bonds, or intermolecular van der Waals forces with the functional groups on the surface of the separator. The macroscopic manifestation of these forces is that, compared to a separator surface without these functional groups, the design method provided in this application enhances the adhesion between the separator and the electrode. This reduces wrinkles in the separator itself to a certain extent and decreases the probability of displacement between the electrode and the separator, thus improving the cycle stability and safety of the battery.

[0177] In some embodiments of this application, the adhesive content in the negative electrode film layer is 0.1% to 5% by mass.

[0178] The binder in the negative electrode sheet of this application is mainly used to bond the various substances in the negative electrode sheet. Simultaneously, this binder, especially the binder on the surface of the negative electrode sheet, can also interact with the surface of the separator. The method for determining the binder content in the negative electrode sheet includes TG (thermogravimetric analysis) + Fourier transform infrared spectroscopy + DSC: First, Fourier transform infrared spectroscopy is used to analyze the types of organic matter in the negative electrode sheet, thereby distinguishing crystalline polymer binders such as PVA, and then the content of crystalline polymers is calculated using DSC (differential scanning calorimetry). Furthermore, since the negative electrode active materials such as graphite and conductive agents such as carbon black or carbon nanotubes in the negative electrode sheet are all thermally stable materials, and the binder is a polymer material that is easily decomposed at high temperatures, it is convenient to further calculate the content of other polymers besides crystalline polymers. Specific testing methods are detailed in the performance tests below.

[0179] This application discloses in these embodiments that the mass percentage content of the binder in the negative electrode film layer includes 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, and 2.4%. The percentage is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, or 5.0%, or any of the values ​​within the range mentioned above.

[0180] The negative electrode film layer of this application also includes a negative electrode active material, which comprises a carbonaceous material, including one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Among these, artificial graphite, natural graphite, soft carbon, and hard carbon include any form of material conventional in the art, and include any manufacturer and model conventional in the art. Simultaneously, the negative electrode active material may also include a silicon-based material, which includes one or two of silicon-oxygen materials or silicon-carbon materials. In addition, the negative electrode active material may also include silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloys are used. However, this application is not limited to these materials; other conventional materials that can be used as negative electrode active materials for lithium-ion or sodium-ion batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0181] The negative electrode film layer of this application also contains a conductive agent, which includes any type conventional in the art, such as graphite, superconducting carbon, carbon black (e.g., acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a combination of two or more of these.

[0182] The negative electrode film layer of this application also contains a dispersant, which includes any type conventional in the art, such as cellulose and its salts, specifically including but not limited to methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, sodium carboxymethylcellulose, lithium carboxymethylcellulose, etc. The functional groups on the surface of the separator membrane of this application can also interact with the dispersant under hot-pressing conditions, thereby further enhancing the adhesion.

[0183] The negative electrode current collector of this application includes a metal foil or a composite current collector. The metal foil may be a copper foil, and the composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material, such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy, on a polymer substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE).

[0184] The negative electrode sheet of this application is formed by mixing the above-mentioned raw materials with a solvent (such as deionized water) in a certain mass ratio to form a negative electrode slurry, defoaming the negative electrode slurry, and then uniformly coating the negative electrode slurry onto both sides of the negative electrode current collector; the coating weight on one side is controlled to be 0.13g~0.25g / 1540.25mm. 2Drying and then compacting the material to a certain compaction density using a cold press yields a negative electrode sheet containing a negative electrode film layer.

[0185] [Positive electrode plate]

[0186] According to some embodiments of this application, as described above, the positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector. The positive electrode film layer includes an adhesive, which includes one or more of polyacrylic acid and its salts, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, cellulose and its salts, and polyvinylidene fluoride.

[0187] The functional groups in the adhesive of this application can generate covalent bonds, intermolecular hydrogen bonds, or intermolecular van der Waals forces with the functional groups on the surface of the separator. The macroscopic manifestation of these forces is that, compared to a separator surface without these functional groups, the design method provided in this application enhances the adhesion between the separator and the electrode. This reduces wrinkles in the separator itself to a certain extent and decreases the probability of displacement between the electrode and the separator, thus improving the cycle stability and safety of the battery.

[0188] In some embodiments of this application, the adhesive content in the positive electrode film layer is 0.1% to 5% by mass.

[0189] The binder in the negative electrode sheet of this application is mainly used to bond the various materials in the positive electrode sheet. Simultaneously, this binder, especially the binder on the surface of the positive electrode sheet, can also interact with the surface of the separator membrane. The method for determining the binder content in the positive electrode sheet is the same as the method for determining the binder content in the negative electrode sheet described above. In these embodiments, this application discloses that the mass percentage content of the binder in the positive electrode film layer includes 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, and 2.4%. The percentage is 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, or 5.0%, or any of the values ​​within the range mentioned above.

[0190] The positive electrode film layer of this application also contains a positive electrode active material. According to some embodiments of this application, when the positive electrode sheet is applied to a lithium-ion battery, the positive electrode active material includes, but is not limited to, one or more combinations of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphate with an olivine structure; wherein, the structural formula of the lithium phosphate with an olivine structure is: LiFe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y<1, 0≤x+y≤1, M contains one or more transition metal elements or non-transition metal elements other than Fe and Mn, and M preferably contains one or more of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr. This application specifically includes, but is not limited to, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 CO 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 CO 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 CO 0.15 Al 0.05 One or more of O2, LiFePO4 (LFP) and LiMnPO4.

[0191] According to some embodiments of this application, when the positive electrode sheet is applied to a sodium-ion battery, the positive electrode active material includes, but is not limited to, at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. Specifically, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and the sodium transition metal oxide is, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1. Polyanionic compounds include sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, and one or more of these. Prussian blue compounds are Na... xM1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0 < x ≤ 2.

[0192] According to some embodiments of this application, the positive electrode film layer also includes conductive agents, binders, etc. Conductive agents include, but are not limited to, one or more combinations of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Binders include, but are not limited to, one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc. The positive electrode current collector in this application can be a metal foil or a composite current collector. The metal foil can be an aluminum foil, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. Composite current collectors can be formed by forming metallic materials, such as aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, on polymer substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0193] The method for forming the positive electrode film in this application includes mixing the above-mentioned raw materials with a solvent (such as N-methylpyrrolidone) in a certain mass ratio to form a positive electrode slurry, and uniformly coating the positive electrode slurry onto both sides of the positive electrode current collector; controlling the coating weight on one side to be 0.25g~0.50g / 1540.25mm. 2 After drying, the material is then compacted to a certain compaction density using a cold press to obtain a positive electrode sheet containing a positive electrode film layer.

[0194] Electrolyte

[0195] Electrolytes are disclosed in some embodiments of this application. The electrolyte in this application can be liquid, solid, or gel-like. Solid state refers to a solid electrolyte, liquid state to a liquid electrolyte, and gel-like state to a gel electrolyte. The secondary battery in this application uses a liquid electrolyte, i.e., an electrolyte solution. This electrolyte solution contains an electrolyte salt and an organic solvent. The electrolyte salt can be any type conventional in the art, such as, but not limited to, inorganic metal salts, such as RClO4, RAsF6, RPF6, RBF4, RSbF6, RSO3F, RN(FSO2)2, etc.; fluorinated organometallic salts, such as RCF3SO3, RN(FSO2)(CF3SO2), RN(CF3SO2)2, RN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonylimide lithium / sodium, cyclic 1,2-tetrafluoroethanedisulfonylimide lithium / sodium, RN(CF3SO2)(C4F9SO2). Examples of lithium salts containing dicarboxylic acid complexes include: RC(CF3SO2)3, RPF4(CF3)2, RPF4(C2F5)2, RPF4(CF3SO2)2, RPF4(C2F5SO2)2, RBF2(CF3)2, RBF2(C2F5)2, RBF2(CF3SO2)2, RBF2(C2F5SO2)2, etc.; and metal salts containing dicarboxylic acid complexes, such as lithium / sodium bis(oxalate)borate, lithium / sodium difluorooxalate borate, lithium / sodium tri(oxalate)phosphate, lithium / sodium difluorobis(oxalate)phosphate, lithium / sodium tetrafluoro(oxalate)phosphate, etc. Here, both the metal and R contain one or a combination of lithium ions and sodium ions.

[0196] According to some embodiments of this application, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L. In these embodiments, this application discloses that the concentration of the electrolyte salt is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, and 4 mol / L, or any one of the above ranges.

[0197] As described above, the organic solvent comprises one or more of carboxylic acid esters, carbonates, and ethers. Specifically, the carboxylic acid esters comprise one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL); the carbonates comprise one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), and fluoroethylene carbonate (FEC). The ethers comprise at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvents of this application further include one or two of nitrile solvents and sulfone solvents. The nitrile solvents include one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvents include at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0198] According to some embodiments of this application, the electrolyte further comprises a film-forming stabilizer, which includes a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer includes carbonate additives and / or sulfate additives. The carbonate additives include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additives include cyclic sulfonate additives and / or alkyl sulfate additives; further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro1,3-propanesulfonate lactone (FPS); the alkyl sulfate additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS). The negative electrode film-forming stabilizer includes one or more of boron lithium salts, phosphorus-containing lithium salts, and sulfur-containing lithium salts; the boron-containing lithium salts include lithium tetrafluoroborate (LiBF4) and lithium bis(oxalato)borate.

[0199] One or more of lithium (LiBOB) and lithium difluorooxalate borate (LiDFOB); phosphorus-containing lithium salts include one or more of lithium difluorophosphate (LiPO2F2), lithium fluorophosphate (Li2PO3F), and lithium phosphate (Li3PO4). Sulfur-containing lithium salts include one or more of lithium fluorosulfonate (LiFSO3), lithium sulfate (Li2SO4), and lithium aminosulfonate (LiSO3NH2).

[0200] The secondary battery of this application will be described in detail below with reference to specific embodiments.

[0201] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0202] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0203] This application may employ conventional inorganic chemistry techniques within the art. In the following examples, efforts have been made to ensure the accuracy of the figures used (including quantities, temperatures, reaction times, etc.), but some experimental errors and biases should be considered. Temperatures (in degrees Celsius) used in the following examples are expressed in °C, and pressures are at or near atmospheric pressure. All reagents were purchased from AR-grade suppliers, and all reactions were carried out under argon protection. Unless otherwise stated, all reagents were obtained commercially.

[0204] Experimental materials:

[0205] 1. Adhesives: Sodium carboxymethyl cellulose (supplier: DAICL Japan, degree of substitution: 0.8-1.0, average relative molecular weight: 650,000, viscosity of 1% aqueous solution: 1500 mPa·s-2500 mPa·s), PVDF (supplier: Arkema France, average relative molecular weight: 1 million).

[0206] 2. Separator: Contains only the base film, and the base film material is polyethylene (supplier is Xingyuan Material, thickness is 5μm~10μm), polypropylene (supplier is Xingyuan Material, thickness is 12μm~16μm), or polytetrafluoroethylene (supplier is Enjie, thickness is 12μm~20μm).

[0207] Example 1

[0208] A secondary battery is provided, comprising a positive electrode, a separator and a negative electrode stacked in sequence, and an electrolyte.

[0209] Preparation of the separating membrane:

[0210] A 9μm thick polyethylene separator film is placed on a winding and unwinding device and clamped. Oxygen is introduced into the first plasma treatment unit, ammonia + oxygen (volume ratio of 2:1) is introduced into the second plasma treatment unit, and carbon tetrafluoride is introduced into the third plasma treatment unit. The distance between the first electrode and the second electrode in each plasma treatment unit is 6.5mm.

[0211] The polyethylene separator is subjected to plasma treatment on both sides of its thickness direction. The first plasma treatment unit has a power of 50kW and a frequency of 10GHz, the second plasma treatment unit has a power of 100kW and a frequency of 10GHz, and the third plasma treatment unit has a power of 250kW and a frequency of 10GHz.

[0212] Preparation of negative electrode sheet:

[0213] Artificial graphite, conductive carbon black, and carboxymethyl cellulose (CMC) binder were added to a mixer in a weight ratio of 96:1:3. Deionized water was then added, and the mixture was stirred under vacuum until homogeneous, yielding a negative electrode slurry with a solid content of 60 wt%. The negative electrode slurry was then uniformly coated onto both sides of the copper foil used as the negative electrode current collector, with a coating width of 75 mm and a coating surface density of 11 mg / cm³. 2 The film was dried using a nine-section drying oven with sequential temperature settings of 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃, followed by compaction using a cold press to achieve a single-sided coating weight of 0.15g / 1540.25mm for the negative electrode film. 2 .

[0214] Preparation of electrolyte:

[0215] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate, diethyl carbonate, and dimethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain a solvent. Lithium hexafluorophosphate is added to the solvent to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0216] Preparation of positive electrode sheet:

[0217] Lithium nickel cobalt manganese (NCM811, chemical formula Li) 1.1 Ni 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, and PVDF were added to a mixer in a ratio of 97:1:2. Then, N-methylpyrrolidone was added and stirred until a homogeneous positive electrode slurry with a solid content of 60% was formed. This slurry was then coated onto both surfaces of the positive electrode current collector aluminum foil, with a coating width of 70 mm and a coating surface density of 19 mg / cm³. 2The material is heated and dried using a multi-section oven with temperatures set sequentially at 120℃, 100℃, and 90℃. Then, it is compacted using a cold press to obtain a positive electrode sheet with a compacted density of 2.7 g / cm³. 3 The positive electrode sheet has a single-sided coating weight of 0.34g / 1540.25mm. 2 .

[0218] Preparation of secondary batteries:

[0219] The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Three copper wires are added for the electrodes, and the tabs are welded together to form a stacked battery cell. The stacked battery cell is then hot-pressed at 90°C and 7 MPa for 300 seconds. The stacked battery cell is then placed in an outer packaging shell, dried, and injected with the electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0220] Example 2

[0221] The difference from Example 1 is that the separator contains a polyethylene base film (9 μm) + a PVDF coating (2 μm thick). Everything else is the same as in Example 1. The preparation method of the separator includes coating both sides of the polyethylene base film with PVDF NMP slurry and then drying it to obtain a coating with a thickness of 2 μm.

[0222] Example 3

[0223] The difference from Example 1 is that the separator contains a polyethylene base film (9 μm) + a PI coating (2 μm thick). Everything else is the same as in Example 1. The preparation method of the separator includes coating the two sides of the polyethylene base film with NMP slurry of PI, and then drying it to obtain a coating with a thickness of 2 μm.

[0224] Example 4

[0225] The difference from Example 1 is that the separator is a polytetrafluoroethylene (PTFE) vinyl membrane (15 μm), while all other aspects remain the same as in Example 1.

[0226] Example 5

[0227] The difference from Example 1 is that a polyethylene separator with a thickness of 9 μm is placed on a winding and unwinding device and clamped, oxygen is introduced into the first plasma treatment unit, acrylonitrile is introduced into the second plasma treatment unit, and carbon tetrafluoride is introduced into the third plasma treatment unit; the distance between the first electrode and the second electrode in each plasma treatment unit is 6.5 mm.

[0228] The polyethylene separator is subjected to plasma treatment on both sides of its thickness direction. The first plasma treatment unit has a power of 50kW and a frequency of 10GHz, the second plasma treatment unit has a power of 50kW and a frequency of 10GHz, and the third plasma treatment unit has a power of 250kW and a frequency of 10GHz.

[0229] Example 6

[0230] The difference from Example 1 is that only one side of the separator is plasma treated, and this side is positioned in the battery facing the negative electrode.

[0231] Example 7

[0232] The difference from Example 1 is that the processing time for the first surface of the separator is longer than that for the second surface. For example, for a separator with a length of 1 meter, the processing time for the first surface is 10 seconds and the processing time for the second surface is 4 seconds, while all other aspects remain the same.

[0233] The first surface of the separator is positioned facing the negative electrode in the battery, and the second surface of the separator is positioned facing the positive electrode in the battery.

[0234] Comparative Example 1

[0235] A secondary battery is provided, which differs from Example 1 in that it uses the original separator provided, which is untreated, but otherwise remains the same as Example 1.

[0236] Comparative Example 2

[0237] A secondary battery is provided, which differs from Embodiment 1 in that a polyethylene separator with a thickness of 9 μm is placed on a winding and unwinding device and clamped, and carbon tetrafluoride is introduced into a third plasma treatment unit; the distance between the first electrode and the second electrode in the plasma treatment unit is 6.5 mm.

[0238] The polyethylene separator is subjected to plasma treatment on both sides of its thickness direction. The third plasma treatment unit has a power of 250kW and a frequency of 10GHz.

[0239] Comparative Example 3

[0240] A secondary battery is provided, which differs from Embodiment 1 in that a polyethylene separator with a thickness of 9 μm is placed on a winding and unwinding device and clamped, and oxygen is introduced into a first plasma treatment unit, wherein the distance between the first electrode and the second electrode in the plasma treatment unit is 6.5 mm.

[0241] The polyethylene separator is subjected to plasma treatment on both sides of its thickness direction. The first plasma treatment unit has a power of 50kW and a frequency of 10GHz.

[0242] [Performance Testing]

[0243] ① Test the adhesion between the separator and the electrode after the battery is cycled 800 times at 25℃ and 1C / 1C:

[0244] Place the battery in a 25°C environment and let it stand for 2 hours. After the battery temperature reaches 25°C, charge the battery at a constant current of 1C and constant voltage to 3.65V, charge at constant voltage to the cutoff current of 0.05C, let it rest for 5 minutes, and then discharge it at 1C to 2.5V. The above process is one cycle, and the cycle is repeated 800 times.

[0245] The battery was disassembled, and the adhesion between the separator and the electrode was measured. Specifically, the separator and positive and negative electrode samples were cut into 15mm × 54.2mm strips to obtain test strips for testing the adhesion between the separator and the electrode. A 15mm × 55mm double-sided adhesive tape (NITTO.NO5000NS) was attached to a steel plate, and the test strip was then attached to the tape with the test side facing down. A 15mm × 70mm paper strip was connected to one end of the test strip via the double-sided adhesive tape. A 2kg roller was manually pushed across the test strip 8 times to obtain the test sample. A tensile testing machine was used: the test sample was fixed on the test table, the paper strip was folded 180° upwards and secured with clamps, and then the tensile testing machine was used to pull the paper strip at a speed of 50mm / min until the separator and electrode separated from the double-sided adhesive surface. The test data was then saved. The bonding force F between the separator and the electrode under test is calculated based on the tensile force and the displacement during separation. The unit is N / m.

[0246] ② Test the tensile strength of the separator:

[0247] Referring to GB / T 1040.3-2006 "Test of Tensile Properties of Plastics", the specific procedure involves cutting a test sample of release film with a fixed thickness of T into 100mm × 15mm sheets along the MD (length) and TD (width) directions using a die. The sheets are then held perpendicular to the clamps of a high-speed rail tensile testing machine with an initial vertical clamping height of 5cm. A tensile rate of 50mm / min is set, and the maximum tensile force is measured as F. Tensile strength = F / 9.8 / (15mm × T). In this application, the transverse tensile strength is mainly represented in the table below.

[0248] ③ Test the air permeability of the separator membrane:

[0249] Refer to ASTM D726-94(2003) "Startdard Test Method for Resistance of Nonporous Paper to Passage of Air". In an environment with a temperature of 15℃~28℃ and humidity less than 80%, prepare a 4cm×4cm test sample of the separator membrane and measure it using the Gurley test (100cc) method with the Air-permeability-tester to directly obtain the air permeability value.

[0250] ④ Test the porosity of the isolation membrane:

[0251] The separator sample was cut into square specimens of approximately 20mm × 20mm. The thickness and actual side length were measured using a digital micrometer and vernier calipers, and its volume (V) was calculated. Its weight (M0) was then measured. The square specimens were then immersed in the electrolyte solution and soaked for 2 hours at room temperature and in air. After soaking, the electrolyte adsorbed on the surface was removed, and the weight (M0) was measured. t The porosity of the separator then satisfies the following mathematical relationship:

[0252] Porosity = (M) t -M0) / ρ×100%;

[0253] In the above mathematical formula, ρ represents the density of the electrolyte, with units of mm. 3 / g, V is the volume of the square sample of the separator, in mm. 3 Weights M0 and M t The unit is g, and the weight measuring instrument is a 0.1 / 1000 balance. The models of the 0.1 / 1000 balance, digital micrometer, and vernier caliper include, but are not limited to, any conventional models in this field.

[0254] ⑤ Test the surface resistivity of the diaphragm:

[0255] Referring to the People's Republic of China Electronic Industry Standard SJ / T10171.5-91, five 1.6cm diameter samples of the separator membrane were cut and immersed in the prepared electrolyte solution. The power supply of the resistance measuring instrument was turned on, and its wiring to the resistance test cell was connected. The total resistance R2 of the sample and the resistance R1 of the solution were measured respectively. The formula for the surface resistance R of the separator membrane is as follows:

[0256] R = (R2 - R1) × S;

[0257] R - Surface resistance of the diaphragm (Ω / cm) 2 )

[0258] R2 - Total resistance of the membrane and solution (Ω);

[0259] R1 - Solution resistance (Ω);

[0260] S-diaphragm test area (cm²) 2 );

[0261] The arithmetic mean of the five measurements was taken as the test result.

[0262] ⑥ Infrared spectroscopy analysis:

[0263] The surface sample of the separator was scanned using an infrared spectrometer (Nicolet AVATAR 360FT-IR, USA) at a constant temperature of 20℃ and humidity of 55%. The number of scans was 64, and the resolution was 4 cm⁻¹. -1 .

[0264] XPS photoelectron spectroscopy analysis:

[0265] An X-ray photoelectron spectrometer (Kratos XSAM800 multi-functional electron spectrometer, UK) was used in an environment with a constant temperature of 20℃ and a humidity of 55%, with an AlKα target (1486.6 eV) as the excitation source, operating at a power of 12 kV × 15 mA, achieving a flux of 35.75 eV. The vacuum level at the bottom of the analysis chamber was 6 × 10⁻⁶. -7 Pa. The analyzer was used in high-magnification, fixed-reduction-ratio, high-resolution mode. All binding energies were corrected to carbon C1s (Eb = 284.8 eV), and the photoelectron acceptance angle was 45°. The spectra were processed using the XPSPEAK program.

[0266] ⑦ Test the capacity retention of the battery after 800 cycles at 25°C:

[0267] Place the battery in a 25℃ environment and let it stand for 2 hours. After the battery temperature reaches 25℃, charge the battery at a constant current of 1C and constant voltage to 3.65V, charge at constant voltage to the cutoff current of 0.05C, let it rest for 5 minutes, and then discharge it at 1C to 2.5V. Record the initial capacity Q0, record the capacity after each cycle, and use the capacity of the previous discharge as the battery capacity Q2. Calculate the capacity retention rate (%) (the calculation formula used is as follows: cycle capacity retention rate = Q2 / Q0 × 100%), and record the capacity retention rate of the cell after 800 cycles.

[0268] ⑧ This application also includes checking whether the battery cells are qualified:

[0269] Test method: The cells of Example 1 and Comparative Example 1 were hot-pressed at 70°C for 60s, then charged at a constant current of 0.5C to voltage U1, charged at a constant voltage of U1 to 0.05C, and left to stand for 10min; then discharged at a constant current of 0.5C to voltage U2 and left to stand for 10min.

[0270] Repeat the above steps 100 times, then disassemble the battery cells;

[0271] Cells that have not reached 100 revolutions are also marked;

[0272] After separating the positive and negative electrode plates, observe whether there is obvious lithium powder leakage at the overhang between the negative electrode plate and the separator. Here, overhang refers to the portion of the separator that extends beyond the negative electrode plate.

[0273] Judgment criteria:

[0274] Qualified: No short circuit or overcharge occurs during battery cycling, and the separator structure remains intact after disassembly.

[0275] Failure: If the battery is overcharged and short-circuited in advance or after disassembly, the structure of the separator is incomplete or has pores, or there is obvious overflow and migration of lithium powder, or lithium powder can be clearly observed on the positive electrode sheet, etc. In addition, if the battery contains 100 layers of separator, and there is one wrinkle or lithium powder, the failure rate is 1%.

[0276] Table 1

[0277]

[0278]

[0279] As can be seen from the list, the design method provided in this application increases the types and content of functional groups on the surface of the separator. The presence of these functional groups can increase the adhesion between the separator and the electrode, reduce the wrinkles of the separator itself to a certain extent, and reduce the probability of displacement between the electrode and the separator, thus improving the cycle stability and safety of the battery.

[0280] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode, a separator, and a negative electrode stacked together; At least a portion of the surface of the separator contains functional groups and C including the functional groups. 1～10 Any one or more of the alkyl groups; The functional group includes a first functional group; the first functional group includes any one or more of hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups; The functional group also includes any one or more of the second functional group and the third functional group; The second functional group includes any one or more of the following: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid group, phosphoric acid group, aminosulfonyl group, halogen atom, hydrazine group, amidine group, guanidinyl group, pyridinyl group, and cyano group; The third functional group includes one or more of thiol, nitro, and nitroso.

2. The secondary battery according to claim 1, characterized in that, The separator and the positive or negative electrode are subjected to hot pressing at a temperature of 60℃ to 105℃ and a pressure of 0.1MPa to 10MPa for 5s to 1000s; the adhesion between the separator and the positive or negative electrode is 7N / m to 24N / m.

3. The secondary battery according to claim 2, characterized in that, The adhesion force between the separator and the positive electrode sheet is 7 N / m to 10 N / m; The adhesion between the separator and the negative electrode sheet is 10 N / m to 24 N / m.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The negative electrode and / or the positive electrode include an adhesive, wherein the molecules contained in the adhesive have one or more of the following relationships with the functional groups on the surface of the separator: covalent bonds, intermolecular hydrogen bonds, or intermolecular van der Waals forces.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The negative electrode and / or the positive electrode include an adhesive, which includes one or more of polyacrylic acid and its salts, polyacrylamide, polyvinyl alcohol, sodium alginate, carboxymethyl chitosan, cellulose and its salts, and polyvinylidene fluoride.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The separator membrane includes a base membrane, the base membrane being made of a polymer material, the polymer material including one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The separator membrane comprises a base membrane and a coating located on at least one side of the base membrane, the coating comprising one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, carboxymethyl cellulose salt, polyvinyl alcohol, polyimide, and polyamide.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, Along a first direction, the separator has a first surface and a second surface facing opposite directions; The first surface faces the negative electrode sheet, and the first surface contains the functional groups; The second surface faces the positive electrode sheet, and the second surface does not contain the functional group; The first direction refers to the stacking direction of the secondary battery.

9. The secondary battery according to any one of claims 1 to 7, characterized in that, Along a first direction, the separator has a first surface and a second surface facing opposite directions; The first surface faces the negative electrode plate, and the second surface faces the positive electrode plate; The first surface and the second surface contain the same type of functional groups; The number of functional groups on the first surface is greater than the number of functional groups on the second surface.

10. A separating membrane, characterized in that: At least a portion of the surface of the separator contains functional groups and C including the functional groups. 1～10 Any one or more of the alkyl groups; The functional group includes a first functional group; the first functional group includes any one or more of hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups; The functional group also includes any one or more of the second functional group and the third functional group; The second functional group includes any one or more of the following: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid group, phosphoric acid group, aminosulfonyl group, halogen atom, hydrazine group, amidine group, guanidinyl group, pyridinyl group, and cyano group; The third functional group includes one or more of thiol, nitro, and nitroso.

11. The separator membrane according to claim 10, characterized in that: The separator membrane includes a base membrane, the base membrane being made of a polymer material, the polymer material including one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

12. The separator membrane according to claim 11, characterized in that: The polymer material includes any one or more of poly(p-phenylene terephthalamide), polyimide, polyamide, polyethylene terephthalate, polytetrafluoroethylene, and polyacrylonitrile. At least a portion of the surface of the isolation membrane contains one or more of a first functional group and a third functional group.

13. The separator membrane according to any one of claims 10 to 12, characterized in that: The thickness of the isolation membrane is 3μm to 20μm.

14. The separator membrane according to any one of claims 10 to 13, characterized in that, The transverse tensile strength of the separator is ≥10MPa, and the longitudinal tensile strength of the separator is ≥10MPa. and / or; The air permeability of the isolation membrane is 100s / 100cc to 300s / 100cc; and / or; The porosity of the isolation membrane is 30% to 70%; and / or; The sheet resistance of the isolation membrane is ≤1.3Ω, preferably 0.1Ω~1.3Ω.

15. A method for preparing a separating membrane, characterized in that: This includes providing an isolation membrane body, subjecting the isolation membrane body to two or more plasma treatments, resulting in an isolation membrane whose surface contains functional groups and C including the functional groups. 1～10 Any one or more of the alkyl groups; The functional group includes a first functional group; the first functional group includes any one or more of hydroxyl, carboxyl, aldehyde, ketone, ether, amino, imino, and epoxy groups; The functional group also includes any one or more of the second functional group and the third functional group; The second functional group includes any one or more of the following: ester, acid anhydride, acyl halide, amide, imide, sulfonic acid group, phosphoric acid group, aminosulfonyl group, halogen atom, hydrazine group, amidine group, guanidinyl group, pyridinyl group, and cyano group; The third functional group includes one or more of thiol, nitro, and nitroso.

16. The preparation method according to claim 15, characterized in that: The active substances for plasma treatment include any one or more of the following: nitrogen, oxygen, air, ozone, hydrogen, chlorine, bromine, nitrous oxide, nitrogen monoxide, nitrogen dioxide, carbon dioxide, carbon monoxide, carbon sulfide, carbon disulfide, sulfur dioxide, sulfur trioxide, hydrogen sulfide, hydrogen peroxide, hydrogen chloride, hydrogen bromide, hydrogen cyanide, ammonia, carbonyl dichloride, sulfur hexafluoride, nitrogen trifluoride, haloalkanes, haloalkenes, haloalkynes, amino-substituted alkanes, amino-substituted alkenes, amides and imides, cyano-substituted alkanes, and cyano-substituted alkenes.

17. The preparation method according to any one of claims 15 to 16, characterized in that: The plasma treatment is performed in a plasma treatment device, which includes a first electrode and a second electrode, with a distance of 0.1 mm to 10 mm between the first electrode and the second electrode. and / or; The power of the plasma treatment equipment is 1W to 1000kW; and / or; The frequency of the plasma processing equipment is 1Hz to 2.5GHz.

18. A battery pack, characterized in that, The method for preparing the secondary battery according to any one of claims 1 to 9, the separator according to any one of claims 10 to 14, or the separator according to any one of claims 15 to 17.

19. An electrical appliance, characterized in that, Includes the battery pack as described in claim 18.

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