Lithium ion secondary battery, preparation method thereof and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly discloses a lithium ion secondary battery, a preparation method thereof and a power utilization device. The positive pole piece of the lithium ion secondary battery comprises a positive pole film layer, the positive pole film layer comprises a positive pole active material, a carbon nanotube and first hydrogenated butadiene-acrylonitrile rubber, and the weight-average molecular weight of the first hydrogenated butadiene-acrylonitrile rubber is less than or equal to 200,000. According to the design mode provided by the invention, the dispersibility of the carbon nanotubes in the positive electrode film layer is improved, so that the carbon nanotubes exert good conductivity, and the direct-current internal resistance of the battery is reduced by improving the conductivity of the positive electrode plate.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a lithium-ion secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0002] Lithium-ion rechargeable 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. Examples include portable electronic devices and electric vehicles.

[0003] As lithium-ion rechargeable batteries are used more and more widely, the requirements for battery performance are also getting higher and higher. Summary of the Invention

[0004] In view of the above problems, this application provides a lithium-ion secondary battery, a method for preparing the same, and an electrical device thereof, which reduces the DC internal resistance of the battery by improving the conductivity of the positive electrode.

[0005] In a first aspect, this application provides a lithium-ion secondary battery, including a positive electrode, a negative electrode, and a separator.

[0006] The aforementioned positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the aforementioned positive current collector;

[0007] The aforementioned positive electrode film includes a positive electrode active material, carbon nanotubes, and a first hydrogenated nitrile rubber;

[0008] The weight-average molecular weight of the aforementioned first hydrogenated nitrile rubber is less than or equal to 200,000.

[0009] In this application, carbon nanotubes in the positive electrode film serve as a conductive agent. Their excellent conductivity allows them to function effectively with a relatively small amount. However, carbon nanotubes are prone to aggregation, which can affect their conductivity. Therefore, this application selects hydrogenated nitrile butadiene rubber with a weight-average molecular weight ≤200,000 as a dispersant. This hydrogenated nitrile butadiene rubber has a relatively small molecular weight, resulting in stronger molecular polarity compared to hydrogenated nitrile butadiene rubber with a larger molecular weight. This makes it easier to generate intermolecular forces, which weaken the forces between adjacent carbon nanotubes, thereby increasing the dispersion of the carbon nanotubes. The excellent conductivity of the carbon nanotubes effectively reduces the contact resistance between the positive electrode active materials, improves the conductivity of the electrode sheet, and further reduces the DC resistance of the battery.

[0010] In some embodiments, the first hydrogenated nitrile butadiene rubber comprises structural units derived from acrylonitrile monomers; the mass percentage content of acrylonitrile in the first hydrogenated nitrile butadiene rubber is 30% to 40%; and / or,

[0011] The hydrogenation degree of the aforementioned first hydrogenated nitrile rubber is greater than 99% and less than 99.9%.

[0012] This application further selects an acrylonitrile content of 30% to 40% and a hydrogenation degree greater than 99%. Hydrogenated nitrile rubber that meets these performance parameters has better flexibility, which facilitates further dispersion of carbon nanotubes and adhesion to the positive electrode active material.

[0013] In some embodiments, the glass transition temperature of the first hydrogenated nitrile rubber is -33°C to -23°C.

[0014] The first hydrogenated nitrile butadiene rubber of this application, when possessing the aforementioned low molecular weight, also has a low glass transition temperature, as low as -23°C to -33°C. This indicates that the first hydrogenated nitrile butadiene rubber has good chain segment flexibility, which facilitates the dispersion of carbon nanotubes.

[0015] In some embodiments, the weight-average molecular weight of the first hydrogenated nitrile rubber is 30,000 to 200,000.

[0016] In some embodiments, the mass percentage content of the first hydrogenated nitrile rubber in the above-mentioned positive electrode film layer is 0.02% to 2%;

[0017] The mass percentage content of the aforementioned carbon nanotubes in the aforementioned positive electrode film layer is greater than or equal to 0.02%.

[0018] This application selects an appropriate amount of first hydrogenated nitrile butadiene rubber to achieve good dispersion of carbon nanotubes.

[0019] This application selects carbon nanotubes that meet the above-mentioned numerical content and disperses them in the positive electrode film layer. Moreover, these carbon nanotubes are well dispersed in the positive electrode film layer, which is conducive to giving full play to the good conductivity of carbon nanotubes.

[0020] In some embodiments, the mass percentage content of the carbon nanotubes in the positive electrode film is 0.02% to 0.4%.

[0021] In some embodiments, the average diameter of the carbon nanotubes is less than or equal to 10 nm.

[0022] In some embodiments, the average diameter of the carbon nanotubes is 1 nm to 5 nm.

[0023] In some embodiments, the positive electrode film layer includes carbon black;

[0024] The mass percentage content of the carbon black in the above-mentioned positive electrode film layer is 0-2.5%.

[0025] In some embodiments, the compaction density of the above-mentioned positive electrode film is 3.4 g / cm³. 3 ~3.6g / cm 3 ; and / or,

[0026] The film resistance of the above positive electrode is less than 1Ω.

[0027] In some embodiments, the film resistance of the positive electrode is greater than 0.02Ω and less than 1Ω.

[0028] The film resistance of the positive electrode in this application refers to the resistance value of the positive electrode measured using conventional measurement methods in the art, and is mainly used to reflect the conductivity of the positive electrode.

[0029] In some embodiments, the positive electrode film layer includes a second hydrogenated nitrile butadiene rubber, the second hydrogenated nitrile butadiene rubber having a weight-average molecular weight greater than 200,000 and less than 500,000; and / or,

[0030] The degree of hydrogenation of the aforementioned second hydrogenated nitrile rubber is less than 99%.

[0031] In some embodiments of this application, a second hydrogenated nitrile butadiene rubber (NBR) is added to the preparation of the positive electrode slurry. This second NBR, together with the first NBR, is used to better disperse carbon nanotubes while dispersing the positive electrode active material. Specifically, the first NBR has a relatively smaller weight-average molecular weight and a relatively higher degree of hydrogenation. The first NBR has stronger molecular polarity, making it easier to generate intermolecular forces. These forces weaken the forces between adjacent carbon nanotubes, thus increasing the dispersibility of carbon nanotubes. The second NBR has a relatively larger weight-average molecular weight and a relatively lower degree of hydrogenation. This second NBR is mainly used to disperse the positive electrode active material. Since carbon nanotubes in the positive electrode film mainly exist on the surface of the positive electrode active material, the improved dispersibility of the positive electrode active material further enhances the dispersibility of the carbon nanotubes attached to the surface of the positive electrode active material.

[0032] In some embodiments, the positive electrode film layer includes a binder, and the binder accounts for less than or equal to 1.5% by mass in the positive electrode film layer;

[0033] The aforementioned adhesives include any one or more of the following: fluoropolymers, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0034] In some embodiments, the fluoropolymer comprises structural units derived from vinylidene fluoride and structural units derived from acrylic acid monomers, and / or,

[0035] The weight-average molecular weight of the aforementioned fluoropolymers is 1,000,000 to 1,200,000; and / or,

[0036] Based on the total number of moles of structural units in the aforementioned fluoropolymers, the molar content of structural units derived from acrylic monomers is 1.4% to 1.6%.

[0037] In some embodiments, the above-mentioned positive electrode active material includes a nickel-containing layered oxide.

[0038] The chemical formula of the above-mentioned nickel-containing layered oxide is Li x N t (Ni a Co b M c ) 1-d M' d O 2-y A y ;

[0039] N represents a lithium-site doping element, which includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W.

[0040] M includes any one or more of Mn and Al;

[0041] M' includes any one or more of Zr, Sr, B, Ti, Mg, Sn, and Al;

[0042] A represents an oxygen-doped element, which includes any one or more of S, N, B, F, Cl, Br, and I.

[0043] x ranges from 0.2 to 1.2;

[0044] t is 0 to 0.1;

[0045] a ranges from 0.001 to 0.999;

[0046] b is 0.001 to 0.999;

[0047] a+b+c=1,

[0048] 0 ≤ d ≤ 0.1;

[0049] 0 ≤ y < 0.2.

[0050] In some embodiments, the Dv50 of the above-mentioned positive electrode active material is 2μm to 8μm.

[0051] The second aspect of this application is to provide a method for preparing the lithium-ion secondary battery described in the first aspect, comprising the following preparation process:

[0052] Provide the first hydrogenated nitrile butadiene rubber compound;

[0053] Prepare carbon nanotube slurry; take carbon nanotube powder and first hydrogenated nitrile rubber solution and disperse them in first organic solvent;

[0054] Preparation of positive electrode slurry: The above carbon nanotube slurry and positive electrode active material are dispersed in a second organic solvent;

[0055] Preparation of positive electrode sheet: The above positive electrode slurry is coated on at least one side surface of the above positive electrode current collector to form a positive electrode film layer;

[0056] Preparation of lithium-ion batteries: Assemble the above-mentioned positive electrode, negative electrode and separator together.

[0057] In some embodiments, the solid content of the above-mentioned carbon nanotube slurry is greater than 1% and less than or equal to 2%.

[0058] In some embodiments, the viscosity of the above-mentioned carbon nanotube slurry is less than or equal to 1200 mPa·s;

[0059] The above-mentioned carbon nanotube slurry, after standing at 20℃~30℃ for 3 months, has a viscosity of less than or equal to 3500 mpa.s.

[0060] The viscosity of the carbon nanotube slurry changed after being left at room temperature for a certain period of time, but the change was limited. This indicates that the carbon nanotube slurry has good stability, which also means that the first hydrogenated nitrile rubber has good dispersibility of carbon nanotubes.

[0061] In some embodiments, the aspect ratio of the carbon nanotubes is 100 to 100,000;

[0062] The specific surface area of ​​the aforementioned carbon nanotubes is greater than 800 m². 2 / g.

[0063] In some embodiments, the preparation of the positive electrode slurry further includes adding carbon black to the second organic solvent;

[0064] The specific surface area of ​​the above-mentioned carbon black is greater than or equal to 60m². 2 / g; and / or,

[0065] The resistivity of the carbon black powder is less than 0.03 Ω·cm; and / or,

[0066] The median particle size Dv50 of the above carbon black is less than or equal to 30 μm.

[0067] In some embodiments, the first hydrogenated nitrile rubber is dispersed in N-methylpyrrolidone to form a liquid with a mass percentage content of 8% and a viscosity of 300 mPa·s to 1800 mPa·s.

[0068] In some embodiments, the preparation of the positive electrode slurry further includes adding a second hydrogenated nitrile butadiene rubber to the second organic solvent, the second hydrogenated nitrile butadiene rubber having a weight-average molecular weight greater than 200,000 and less than 500,000; and / or,

[0069] The degree of hydrogenation of the aforementioned second hydrogenated nitrile rubber is less than 99%.

[0070] A third aspect of this application is to provide an electrical device comprising the lithium-ion secondary battery described in the first aspect or the lithium-ion battery prepared by the preparation method described in the second aspect.

[0071] 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, specific embodiments of this application are given below. Attached Figure Description

[0072] 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:

[0073] Figure 1 This is a schematic diagram of the battery structure of some embodiments of this application;

[0074] Figure 2 This is an exploded structural diagram of a battery according to some embodiments of this application;

[0075] Figure 3 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0076] Figure 4 This is a schematic diagram of the battery pack structure according to some embodiments of this application;

[0077] Figure 5 This is a structural schematic diagram showing the positional relationship between the positive electrode, the separator, and the negative electrode in some embodiments of this application;

[0078] Figure 6 This is a schematic diagram of the structure of the positive electrode sheet in some embodiments of this application.

[0079] The reference numerals in the detailed embodiments are as follows:

[0080] 10000, vehicles;

[0081] 1000, Battery; 2000, Controller; 3000, Motor;

[0082] 100. Battery cell;

[0083] 200. Box body; 210. First part; 220. Second part;

[0084] 10. Lithium-ion secondary batteries;

[0085] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0086] 1. Negative electrode plate;

[0087] 2. Positive electrode plate; 21. Positive current collector; 22. Positive electrode film;

[0088] 3. Isolation components;

[0089] The x-axis of the coordinate axis represents the stacking direction of the electrode sheets or the thickness direction of the separator.

[0090] The y-axis of the coordinate axis represents the length or width of the electrode. Detailed Implementation

[0091] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium-ion secondary battery, its preparation method, and its power application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of 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.

[0092] 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.

[0093] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0094] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0095] 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.

[0096] 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.

[0097] 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).

[0098] 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.

[0099] 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).

[0100] 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.

[0101] Lithium-ion rechargeable batteries have been widely used in various products due to their advantages such as high energy density, long cycle life, and safety and reliability. In recent years, with the significant increase in demand for lithium-ion rechargeable batteries as an energy source, higher requirements have been placed on their performance, such as high conductivity.

[0102] If the conductivity of the conductive additive can be improved without affecting the battery's cycle charge and discharge performance, it will help improve the battery's high conductivity.

[0103] Based on the above considerations, in order to improve the conductivity of the battery, a lithium-ion secondary battery, its preparation method, and its power device were obtained by conducting relevant experimental research according to the above design concept.

[0104] First, this application discloses a lithium-ion secondary battery, which includes a positive electrode, a negative electrode, and a separator; wherein the positive electrode, separator, and negative electrode are sequentially stacked to form a wound cell or a stacked cell. Meanwhile, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material, carbon nanotubes, and a first hydrogenated nitrile butadiene rubber, wherein the weight-average molecular weight of the first hydrogenated nitrile butadiene rubber is ≤200,000.

[0105] In this application, carbon nanotubes in the positive electrode film serve as a conductive agent. Their excellent conductivity allows them to function effectively with a relatively small amount. However, carbon nanotubes are prone to aggregation, which can affect their conductivity. Therefore, this application selects hydrogenated nitrile butadiene rubber (NBR) with a weight-average molecular weight ≤200,000 as a dispersant. The smaller molecular weight of NBR results in stronger molecular polarity compared to NBR with larger molecular weights, making it easier to generate intermolecular forces. Because the NBR is dispersed around the carbon nanotubes, the strong forces between NBRs and between NBR and carbon nanotubes weaken the forces between adjacent carbon nanotubes, thus increasing the dispersion of the carbon nanotubes. This allows the carbon nanotubes to exert their excellent conductivity, effectively reducing the contact resistance between the positive electrode active materials, improving the conductivity of the positive electrode sheet, and ultimately reducing the DC resistance of the battery.

[0106] Therefore, the design method provided in this application is beneficial to improving the conductivity of the entire positive electrode to reduce the DC resistance of the battery.

[0107] Therefore, the lithium-ion secondary battery provided in this application is beneficial to improving the user experience. The lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte composed of the aforementioned lithium-ion secondary battery. The outer packaging of the lithium-ion secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging of the lithium-ion 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.

[0108] This application does not impose any particular limitation on the shape of the lithium-ion secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured lithium-ion secondary battery 10.

[0109] According to some embodiments of this application, reference is made to Figure 2The 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 sheet, negative electrode sheet, and separator can be formed into an electrode assembly 102 through 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 lithium-ion 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.

[0110] The electrode assembly 102 provided in this application is beneficial to improving the performance of lithium-ion batteries when applied in lithium-ion batteries. The lithium-ion battery can be used as a power source for an electrical device or as 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.

[0111] For ease of explanation, some embodiments of this application are illustrated using a vehicle as an example of an electrical device.

[0112] 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.

[0113] 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.

[0114] Please refer to Figure 4 , Figure 4This 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, namely a lithium-ion 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.

[0115] 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 battery cell 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.

[0116] 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.

[0117] Lithium-ion secondary batteries

[0118] This application discloses a lithium-ion secondary battery in some embodiments, comprising a positive electrode, a separator, and a negative electrode. The positive electrode, separator, and negative electrode are sequentially stacked together to form the lithium-ion secondary battery using a winding or stacking process. Simultaneously, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive active material, carbon nanotubes, and a first hydrogenated nitrile butadiene rubber; the weight-average molecular weight of the first hydrogenated nitrile butadiene rubber is ≤200,000.

[0119] The positive electrode, separator, and negative electrode of this application can be formed into a lithium-ion secondary battery using a winding or stacking process. Specifically, this application... Figure 5 The diagram illustrates a lithium-ion secondary battery 10 formed using a winding 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 Only one winding method is shown in the illustration. Other stacking or winding methods are within the scope of protection of this application.

[0120] like Figure 6 The diagram illustrates that the positive electrode 2 includes a positive current collector 21 and a positive electrode film 22 located on at least one side surface of the positive current collector 21. Figure 6 The diagram illustrates the simultaneous formation of a positive electrode film layer 22 on both sides of the positive electrode current collector 21. The positive electrode film layer 22 can be formed on the surface of the positive electrode current collector 21 in any manner conventional in the art, such as coating or deposition.

[0121] The carbon nanotubes in this application refer to carbon allotropes comprising cylindrical layers of one or more carbon atoms, wherein the carbon atoms are covalently bonded to form a hexagonal tile pattern (i.e., graphene sheets), which forms a hollow tube structure with a diameter of up to several hundred nanometers. Here, graphene refers to nanotubes made of sp... 2 A planar sheet, one atom thick, composed of bonded carbon atoms, where the carbon atoms are tightly stacked in a honeycomb lattice.

[0122] The carbon nanotubes of this application have good electron mobility and mainly function as conductive agents in the positive electrode film.

[0123] The carbon nanotubes in this application include any one or more of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0124] The single-walled carbon nanotubes of this application refer to a single cylindrical layer of carbon atoms, while the multi-walled carbon nanotubes of this application refer to two or more layers of carbon atoms connected by intermolecular forces, or a single layer of carbon atoms that is rolled around a hollow cylindrical core several times.

[0125] The carbon nanotubes of this application may be substituted with functional groups or other defects, depending on their production and purification methods, particularly at the ends of the tubes. For example, carbon nanotubes may include oxygen, sulfur, nitrogen, fluorine, or other substituent atoms, and may include, for example, carbonyl, hydroxyl, thiol, amine, and / or amide functional groups. Amorphous carbon and residual catalysts, such as iron or nickel, may also be present, among other impurities. Exemplary carbon nanotube synthesis processes include arc discharge, laser ablation, chemical vapor deposition (CVD), and high-pressure carbon monoxide dismutation (HiPCO). Some common post-synthesis treatments or modifications of carbon nanotubes include ozone treatment, ozone and hydrogen peroxide treatment, hydrochloric acid treatment, sodium hydroxide / potassium hydroxide treatment, and / or thermal treatment.

[0126] The carbon nanotubes of this application can be characterized using various techniques available in the art. For example, X-ray photoelectron spectroscopy (XPS) can be used to measure the content of nitrogen, oxygen, sulfur, or fluorine / halogen, and can indicate the level of impurities and functionalization. Raman spectroscopy can be used to indicate the purity level of the graphene sheets that make up the carbon nanotubes, i.e., their cleanliness. BET measurements can be used to measure the surface area of ​​the carbon nanotubes, and these measurements are affected by the properties of the carbon nanotube structure (e.g., single-walled versus multi-walled nanotubes) and the functionalization and defects of the nanotube structure, which may modify the measured values ​​relative to theoretical values. Finally, scanning electron microscopy can also be used to analyze the surface of the carbon nanotubes, as well as the shape and size of the particles.

[0127] In this application, carbon nanotubes in the positive electrode film serve as a conductive agent. A conductive agent is a substance with electrical conductivity that collects microcurrents between positive electrode active materials and between the positive electrode active materials and the positive electrode current collector, thereby reducing the contact resistance of the electrode and accelerating the electron mobility. This application leverages the excellent conductivity of carbon nanotubes to achieve their conductive function with a relatively small amount. However, carbon nanotubes are prone to aggregation, which affects their conductivity. Therefore, this application selects low-molecular-weight hydrogenated nitrile butadiene rubber (HNBR) as a dispersant. The HNBR has a relatively low molecular weight, and compared to HNBR with a larger molecular weight, its molecules are more polar, making it easier to generate intermolecular forces. These forces weaken the forces between adjacent carbon nanotubes, increasing the dispersion of carbon nanotubes and reducing their aggregation. Through the excellent conductivity of the carbon nanotubes, the contact resistance between the positive electrode active materials is effectively reduced, improving the conductivity of the positive electrode sheet and thus helping to reduce the DC resistance of the battery.

[0128] The hydrogenated nitrile butadiene rubber of this application is a product obtained by hydrogenation saturation of the carbon-carbon double bonds in the molecular chain of nitrile butadiene rubber, which is a polymer formed by the polymerization of acrylonitrile and butadiene monomers. The term "polymer" in this application refers to an aggregate of chemically homogeneous macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass, and chain length. This term also includes derivatives of such macromolecular aggregates formed by polymerization reactions, i.e., compounds that can be obtained through reactions of the functional groups in the aforementioned macromolecules, such as addition or substitution, and can be chemically homogeneous or chemically heterogeneous.

[0129] The weight-average molecular weight in this application refers to the sum of the products of the weight fraction of molecules with different molecular weights in the polymer and their corresponding molecular weights.

[0130] The weight-average molecular weight of hydrogenated nitrile butadiene rubber in this application can be determined using methods known in the art, such as gel permeation chromatography (GPC), specifically a Waters 2695 Isocratic HPLC gel permeation chromatograph (differential refractive index detector 2141). In some embodiments, the test method involves using a polystyrene solution sample of a certain mass fraction as a reference, and selecting a matching chromatographic column (oil-based: Styragel HT5DMF7.8*300mm + Styragel HT4). A hydrogenated nitrile butadiene rubber solution of a certain mass fraction is prepared using purified NMP solvent, and the prepared solution is allowed to stand for one day for later use. During testing, tetrahydrofuran is first drawn into a syringe for rinsing, and this is repeated several times. Then, 5 ml of the experimental solution is drawn, air is expelled from the syringe, and the needle tip is dried. Finally, the sample solution is slowly injected into the injection port. After the reading stabilizes, the data is obtained, and the weight-average molecular weight is read.

[0131] This application selects a first hydrogenated nitrile butadiene rubber with a weight average molecular weight ≤ 200,000 mainly to disperse carbon nanotubes. The relatively small molecular weight of the hydrogenated nitrile butadiene rubber facilitates the generation of strong intermolecular forces with the carbon nanotubes. These intermolecular forces weaken the forces between adjacent carbon nanotubes, thereby ensuring uniform dispersion of the carbon nanotubes and maintaining their good conductivity.

[0132] When the carbon nanotubes of this application contain functional groups of oxygen, sulfur, nitrogen, fluorine or other substituent atoms, the carbon nanotubes are more likely to generate intermolecular forces or hydrogen bonds with the first hydrogenated nitrile rubber, thereby better promoting the dispersion of the carbon nanotubes.

[0133] In some embodiments, the first hydrogenated nitrile butadiene rubber includes structural units derived from acrylonitrile monomers; the mass percentage content of acrylonitrile in the first hydrogenated nitrile butadiene rubber is 30% to 40%.

[0134] The hydrogenation degree of the aforementioned first hydrogenated nitrile rubber is greater than 99% and less than 99.9%.

[0135] The hydrogenated nitrile butadiene rubber of this application is obtained by polymerizing acrylonitrile and butadiene monomers and then further saturating the carbon-carbon double bonds with hydrogen. Therefore, the degree of hydrogenation here refers to the degree of hydrogenation saturation. The determination method includes using an infrared spectrometer to measure the residual double bonds and calculating the double bond content, then the degree of hydrogenation is (100% - double bond content). Alternatively, it can be determined using a proton nuclear magnetic resonance spectrometer.

[0136] The specific values ​​of the weight-average molecular weight, acrylonitrile content, and degree of hydrogenation of the first hydrogenated nitrile rubber in this application refer to the performance parameters of the raw materials during the preparation process, ignoring the changes in the battery.

[0137] This application further selects an acrylonitrile content of 30% to 40% and a hydrogenation degree greater than 99%. Hydrogenated nitrile rubber that meets these performance parameters has better flexibility, which facilitates further dispersion of carbon nanotubes and adhesion to the positive electrode active material.

[0138] In these embodiments, this application discloses that the degree of hydrogenation of hydrogenated nitrile rubber is any one of 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, or any one of the ranges of both above.

[0139] In these embodiments, this application discloses that the mass percentage content of acrylonitrile in the first hydrogenated nitrile butadiene rubber is any one of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any one of the ranges of both of the above.

[0140] In some embodiments, the glass transition temperature of the first hydrogenated nitrile rubber is -23°C to -33°C.

[0141] The glass transition temperature (Tg) of this application is an important physical property of amorphous polymers. It refers to the temperature at which a material transitions from a glassy state to a rubbery state. Below the glass transition temperature, the polymer is in the glassy state, where the molecular chains and segments cannot move; only the atoms (or groups) constituting the molecules vibrate in their equilibrium positions.

[0142] The glass transition temperature (Tg) measurement method of this application includes any method conventional in the art, and this application selects differential scanning calorimetry (DSC).

[0143] The first hydrogenated nitrile butadiene rubber of this application, when possessing the aforementioned low molecular weight, also has a low glass transition temperature, as low as -23°C to -33°C. This indicates that the first hydrogenated nitrile butadiene rubber has good chain segment flexibility, which facilitates the dispersion of carbon nanotubes.

[0144] In these embodiments, this application provides that the glass transition temperature of the first hydrogenated nitrile rubber is any one of -23°C, -24°C, -25°C, -26°C, -27°C, -28°C, -29°C, -30°C, -31°C, -32°C, or -33°C, or any one of the ranges of both above.

[0145] In some embodiments, the weight-average molecular weight of hydrogenated nitrile rubber is 30,000 to 200,000.

[0146] The weight-average molecular weight of the hydrogenated nitrile butadiene rubber in this application is as described above. In these embodiments, the weight-average molecular weight of the hydrogenated nitrile butadiene rubber is selected to be between 30,000 and 200,000, which is beneficial for further dispersing carbon nanotubes.

[0147] In these embodiments, this application discloses that the weight-average molecular weight of hydrogenated nitrile rubber is any one of 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, 170,000, 180,000, 190,000, or 200,000, or any one of the above ranges.

[0148] In some embodiments, the mass percentage content of the first hydrogenated nitrile rubber in the above-mentioned positive electrode film layer is 0.02% to 2%.

[0149] This application selects an appropriate amount of first hydrogenated nitrile butadiene rubber to achieve good dispersion of carbon nanotubes.

[0150] In these embodiments, the first hydrogenated nitrile rubber is provided to have a mass percentage content of 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or 2.0% in the above-mentioned positive electrode film layer, or any of the above-mentioned range values.

[0151] In some embodiments, the mass percentage content of carbon nanotubes in the above-mentioned positive electrode film layer is ≥0.02%.

[0152] The carbon nanotubes in this application can be observed by scanning electron microscopy of the positive electrode film. The mass percentage content here refers to the amount added during the preparation of lithium-ion batteries. Since the properties of carbon nanotubes are stable, their mass percentage content in the positive electrode film remains basically unchanged.

[0153] In some embodiments, the mass percentage content of carbon nanotubes in the above-mentioned positive electrode film layer is greater than or equal to 0.02% and less than or equal to 0.4%.

[0154] This application selects carbon nanotubes that meet the above-mentioned numerical content and disperses them in the positive electrode film layer. Moreover, these carbon nanotubes are well dispersed in the positive electrode film layer, which is conducive to giving full play to the good conductivity of carbon nanotubes.

[0155] In some embodiments, this application discloses that the positive electrode film layer contains only carbon nanotubes as conductive agents.

[0156] In these embodiments, this application discloses that the mass percentage content of carbon nanotubes in the above-mentioned positive electrode film layer is any one of 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.25%, 0.3%, 0.35%, and 0.4%, or any one of the above ranges.

[0157] In some embodiments, the average diameter of the carbon nanotubes is ≤10 nm.

[0158] In some embodiments, the average diameter of the carbon nanotubes is 1 nm to 10 nm.

[0159] In some embodiments, the average diameter of the carbon nanotubes is 1 nm to 5 nm.

[0160] In some embodiments, the average diameter of the carbon nanotubes is 1 nm to 3 nm.

[0161] The average diameter of the carbon nanotubes in this application refers to the average outer diameter of the carbon nanotubes.

[0162] The method for determining the average diameter of carbon nanotubes in this application includes any conventional method in the art, such as using a high-power electron microscope. Specifically, the average diameter testing method is as follows: 1) Instrument model: TEM transmission electron microscope; 2) Adjust the magnification of the equipment: 100K; 3) Select 100 carbon nanotubes in the field of view for statistical analysis and take the average value L1 (nm).

[0163] In these embodiments, this application discloses that the average diameter of the carbon nanotubes is any one of 10nm, 9nm, 8.5nm, 8nm, 7nm, 6nm, 5.4nm, 5nm, 4nm, 2.9nm, 3nm, 2nm, 1.5nm, 1nm or any one of the above ranges.

[0164] The carbon nanotubes in this application are further selected as single-walled carbon nanotubes, which have better electron mobility compared to other types of carbon nanotubes, and the first hydrogenated nitrile rubber provided in this application can effectively disperse the single-walled carbon nanotubes.

[0165] In these embodiments, the average diameter of the carbon nanotubes is provided as any one of 1 nm, 2 nm, 3 nm, or any one of the ranges of both above.

[0166] In some embodiments, the positive electrode film layer includes carbon black;

[0167] The carbon black content in the positive electrode film layer is 0-2.5% by mass.

[0168] As described above, carbon nanotubes serve as a conductive agent in the positive electrode film layer. The carbon nanotubes are one-dimensional tubular structures. To further increase the conductivity of the conductive agent, this application also chooses to use dotted conductive agent carbon black.

[0169] The carbon black content disclosed in these embodiments refers to the actual amount added during the preparation process, ignoring any changes in content. To reduce the impact of carbon black usage on the amount of positive electrode active material, this application selects a carbon black usage amount that meets the above-mentioned range.

[0170] In these embodiments, this application discloses that the mass percentage content of carbon black in the above-mentioned positive electrode film layer is any one of 0, 0.1%, 0.5%, 1%, 2%, 2.5%, or any one of the numerical ranges between any two of the above.

[0171] The carbon black in this application is an industrial product, whose main component is elemental carbon, and contains small amounts of oxygen, hydrogen and sulfur.

[0172] In some embodiments, the compaction density of the above-mentioned positive electrode film is 3.4 g / cm³. 3 ~3.6g / cm 3 ;

[0173] The film resistance of the above positive electrode is <1Ω.

[0174] The compaction density of the positive electrode film layer in this application can be used to characterize the energy density of the material. The compaction density of the positive electrode film layer = the areal density of the positive electrode film layer / the thickness of the positive electrode film layer. The thickness of the positive electrode film layer includes the distance between the two end faces of the positive electrode film layer along the thickness direction. The areal density of the positive electrode film layer = the weight of a single-sided positive electrode film layer / the area of ​​a single-sided positive electrode film layer. The weight of a single-sided positive electrode film layer can be obtained by weighing, and the area of ​​a single-sided positive electrode film layer can be obtained by using the area calculation formula according to the shape of the film layer. The test method for the compaction density of the positive electrode film layer is given in the test method of the following specific embodiments of this application, and will not be repeated here.

[0175] The compaction density of the positive electrode film layer in this application is 3.4 g / cm³. 3 ~3.6g / cm 3When the film resistance of the positive electrode is less than 1Ω, it indicates that the design method provided in this application can also achieve its conductivity function with less conductive agent, thereby increasing the compaction density of the electrode to improve the energy density of the battery.

[0176] In these embodiments, the compaction density of the positive electrode film is given as 3.4 g / cm³. 3 3.5g / cm 3 3.6g / cm 3 It can be any one of the above or any one of the numerical ranges between any two of the above.

[0177] The film resistance of the positive electrode in this application refers to the resistance value of the positive electrode measured using conventional methods in the art, and is mainly used to reflect the conductivity of the positive electrode. The methods for measuring the film resistance of the positive electrode in this application include conventional methods in the art, such as the four-probe method, which are described in detail in the following specific embodiments.

[0178] The film resistance of the positive electrode in this application is <1Ω, which indicates that the positive electrode has good conductivity.

[0179] In some embodiments of this application, the film resistance of the positive electrode is provided to be greater than 0.02Ω and 1Ω.

[0180] In some embodiments, the positive electrode film layer includes a second hydrogenated nitrile butadiene rubber, the second hydrogenated nitrile butadiene rubber having a weight-average molecular weight greater than 200,000 and less than 500,000.

[0181] The degree of hydrogenation of this second hydrogenated nitrile rubber is <99%.

[0182] In some embodiments, the second hydrogenated nitrile butadiene rubber comprises structural units derived from acrylonitrile monomers; the mass percentage content of acrylonitrile in the second hydrogenated nitrile butadiene rubber is 30% to 40%.

[0183] In these embodiments, this application selects to add a second hydrogenated nitrile butadiene rubber to the positive electrode film layer. The molecular weight and degree of hydrogenation of the second hydrogenated nitrile butadiene rubber are lower than those of the second hydrogenated nitrile butadiene rubber described above. The meaning and measurement method of the weight-average molecular weight and degree of hydrogenation are the same as those described above.

[0184] In some embodiments of this application, a second hydrogenated nitrile butadiene rubber (NBR) is added to the preparation of the positive electrode slurry. This second NBR, together with the first NBR, is used to better disperse carbon nanotubes while dispersing the positive electrode active material. Specifically, the first NBR has a relatively smaller weight-average molecular weight and a relatively higher degree of hydrogenation. The first NBR has stronger molecular polarity, making it easier to generate intermolecular forces. These forces weaken the forces between adjacent carbon nanotubes, thus increasing the dispersibility of carbon nanotubes. The second NBR has a relatively larger weight-average molecular weight and a relatively lower degree of hydrogenation. This second NBR is mainly used to disperse the positive electrode active material. Since carbon nanotubes in the positive electrode film mainly exist on the surface of the positive electrode active material, the improved dispersibility of the positive electrode active material further enhances the dispersibility of the carbon nanotubes attached to the surface of the positive electrode active material.

[0185] In these embodiments, this application discloses that the weight-average molecular weight of the second hydrogenated nitrile rubber is any one of 216,000, 230,000, 240,000, 250,000, 260,000, 270,000, 280,000, 290,000, 300,000, 310,000, 320,000, 330,000, 340,000, 350,000, 360,000, 370,000, 380,000, 390,000, 400,000, 410,000, or 420,000, or any one of the numerical ranges between any two of the above.

[0186] In these embodiments, this application discloses that the degree of hydrogenation of the second hydrogenated nitrile rubber is any one of 97.5, 97.6, 97.7, 97.8, 97.9, 98.0, 98.1, 98.2, 98.3, 98.4, 98.5, 98.6, 98.7, 98.8, 98.9, or any value within a range between any two of the above.

[0187] In some embodiments, the second hydrogenated nitrile rubber has a mass percentage content of ≥0.01% in the positive electrode film layer.

[0188] In some embodiments, the positive electrode film layer includes a binder, wherein the binder comprises ≤1.5% by mass in the positive electrode film layer;

[0189] The adhesive includes any one or more of the following: fluoropolymers, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0190] In addition to their functions of dispersing carbon nanotubes and positive electrode active materials, the first and second hydrogenated nitrile butadiene rubbers described above also possess a certain degree of adhesion. Therefore, the amount of binder in the positive electrode film layer of this application is ≤1.5%. A binder refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium. The types of binders used in this application are any conventional types in the art; only a few are exemplarily listed herein.

[0191] In some embodiments, the adhesive comprises a fluoropolymer; the fluoropolymer comprises structural units derived from vinylidene fluoride and structural units derived from acrylic monomers.

[0192] The weight-average molecular weight of this fluoropolymer is 1 million to 1.2 million.

[0193] Based on the total number of moles of structural units in the aforementioned fluoropolymers, the molar content of structural units derived from acrylic monomers is 1.4% to 1.6%.

[0194] The meaning of "polymer" in this application remains consistent with that described above. In this application, a fluoropolymer refers to a polymer in which at least one hydrogen atom is replaced by a fluorine atom. The fluoropolymers in this application are primarily used as binders in the positive electrode film layer.

[0195] In some embodiments, the fluoropolymer includes vinylidene fluoride monomer and acrylic acid monomer, wherein the molar mass percentage content of the acrylic acid monomer in the fluoropolymer is 1.4% to 1.6%.

[0196] The vinylidene fluoride monomer of this application has the following structural formula (1), and the acrylic acid monomer has the following structural formula (2):

[0197]

[0198] In formula (1) above, substituents R1 and R2 are each independently selected from hydrogen, fluorine, chlorine, and trifluoromethyl; in formula (2) above, substituents R3, R4, and R5 are each independently selected from hydrogen, C 1～3 Any one of them.

[0199] In some embodiments, the substituents R1 and R2 in formula (1) above are each independently selected from hydrogen, and the substituents R3, R4, and R5 in formula (2) above are each independently selected from hydrogen.

[0200] In these embodiments, this application discloses that the molar content of the structural units derived from acrylic monomers is any one of 1.4%, 1.5%, 1.6%, or any one of the above ranges.

[0201] In these embodiments, this application discloses fluoropolymers with a weight-average molecular weight of 1 million, 1.1 million, or 1.2 million, or any value within a range between any two of the above.

[0202] This application selects a fluoropolymer that meets the above parameters as an adhesive. This fluoropolymer is beneficial for generating intermolecular forces or hydrogen bonds with hydrogenated nitrile rubber to enhance the adhesion performance to the positive electrode active material.

[0203] In some embodiments, the mass percentage content of the fluoropolymer in the above-mentioned positive electrode film layer is less than or equal to 1.5%.

[0204] The content mentioned here refers to the amount added during the preparation of lithium-ion secondary batteries. Since fluoropolymers are stable in batteries, their content does not change much.

[0205] In these embodiments, this application discloses that the fluoropolymer content is any one of 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1.0% by mass or any one of the above ranges.

[0206] In some embodiments, the above-mentioned positive electrode active material includes a nickel-containing layered oxide.

[0207] The chemical formula of the above-mentioned nickel-containing layered oxide is Li x N t (Ni a Co b M c ) 1-d M' d O 2-y A y ;

[0208] N represents a lithium-site doping element, which includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W.

[0209] M includes any one or more of Mn and Al;

[0210] M' includes any one or more of Zr, Sr, B, Ti, Mg, Sn, and Al;

[0211] A represents an oxygen-doped element, which includes any one or more of S, N, B, F, Cl, Br, and I.

[0212] x ranges from 0.2 to 1.2;

[0213] t is 0 to 0.1;

[0214] a ranges from 0.001 to 0.999;

[0215] b is 0.001 to 0.999;

[0216] a+b+c=1,

[0217] 0 ≤ d ≤ 0.1;

[0218] 0 ≤ y < 0.2.

[0219] The lithium-site doping element in this application refers to an external element that is introduced into the lattice of nickel-containing layered oxides to occupy lithium-ion sites, which is beneficial to improving the structural stability of nickel-containing layered oxides.

[0220] The oxygen-doped element in this application refers to an external element that is introduced into the lattice of nickel-containing layered oxides to occupy oxygen ion sites, which is also beneficial to improving the structural stability of nickel-containing layered oxides.

[0221] In these embodiments, this application discloses that x is any one of 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 or any one of the ranges of both above.

[0222] In these embodiments, this application discloses that t is any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any one of the ranges of both above.

[0223] This application discloses in these embodiments that 'a' is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0 0.6, 0.7, 0.8, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 0.999, or any one of the above ranges.

[0224] This application discloses in these embodiments that b is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0 0.6, 0.7, 0.8, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 0.999, or any one of the above ranges.

[0225] In these embodiments, this application discloses that d is any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any one of the ranges of both above.

[0226] In these embodiments, this application discloses that y is any one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19 or any one of the ranges of both above.

[0227] All of the aforementioned positive electrode active materials described in this application can be purchased through commercial channels, and the elemental composition of the purchased products is already indicated. Furthermore, the components of the positive electrode active materials of this application can also be detected by commonly used chemical analysis methods in the art, including but not limited to: complexation titration, precipitation gravimetric method, redox method, differential method, inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry. Among these, ICP-AES and atomic absorption spectrometry are convenient and efficient, and their mechanisms are as follows:

[0228] Plasma emission spectroscopy is an analytical method that uses a high-temperature excitation source generated by plasma as the excitation source for atomic emission spectra. Different elements produce different characteristic spectra. These characteristic spectra are projected onto a grating in a spectrometer through a lens. By controlling a motor to rotate the grating, a transmission mechanism accurately positions the intensity of the characteristic spectral lines of the element to be measured at the exit slit after spectral dispersion. A photomultiplier tube converts this spectral intensity into an electric current. After further circuit processing and conversion, the data is processed by a computer to obtain the analytical results.

[0229] Atomic absorption spectrometry (AAS), also known as atomic absorption spectrophotometry, is an analytical method based on the absorption of characteristic radiation (spectral lines) emitted by atomic vapors of the same type of atom. The analytical process involves irradiating the sample solution with atomized and atomized atomic vapors of the sample solution using characteristic radiation emitted by the same type of atom. The gaseous ground-state atoms of the analyte in the vapor absorb the characteristic radiation lines emitted from the light source. Different elements exhibit selective absorption of these characteristic radiation lines, and the concentration of the analyte in the sample is determined by the degree of radiation attenuation.

[0230] In some embodiments, the Dv50 of the above-mentioned positive electrode active material is 2μm to 8μm.

[0231] The Dv50 of this application includes a particle size distribution where 50% of the volume is larger than the particle size and 50% of the volume is smaller than the particle size; it is also known as the median diameter and is commonly used to represent the average particle size. In these embodiments, this application selects to determine the particle size distribution using laser diffraction particle size analysis, specifically referring to standard GB / T19077-2016 to obtain the particle size distribution map, and then calculating the result.

[0232] This application selects positive electrode active materials that meet the above-mentioned range values, which facilitates the dispersion of carbon nanotubes and hydrogenated nitrile rubber on the surface of each positive electrode active material.

[0233] In these embodiments, this application discloses that the Dv50 of the positive electrode active material is any one of 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or any one of the numerical ranges between any two of the above.

[0234] [Positive electrode plate]

[0235] 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 a positive electrode active material, a conductive agent, a binder, etc., and each component is as described above.

[0236] The positive 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 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).

[0237] [Preparation method of positive electrode sheet]

[0238] According to some embodiments of this application, this application provides a method for preparing a positive electrode sheet, comprising the following preparation process:

[0239] Provide the first hydrogenated nitrile butadiene rubber compound;

[0240] Preparation of carbon nanotube slurry: Carbon nanotube powder and first hydrogenated nitrile rubber are dispersed in a first solvent to form carbon nanotube slurry;

[0241] Preparation of positive electrode slurry: The above-mentioned carbon nanotube slurry and positive electrode active material are dispersed in a second solvent to form a positive electrode slurry;

[0242] Preparation of positive electrode sheet: The positive electrode slurry is coated on at least one side of the positive electrode current collector, the coating weight on one side is controlled, and after drying, it is compacted to a certain compaction density using a cold press to form a positive electrode sheet.

[0243] In some embodiments, the mass ratio of carbon nanotubes to the first hydrogenated nitrile rubber in the carbon nanotube slurry is 100:(20-200).

[0244] In this application, the first hydrogenated nitrile butadiene rubber is mainly used to disperse carbon nanotubes, and a certain amount of the first hydrogenated nitrile butadiene rubber can effectively disperse the carbon nanotube slurry. Therefore, it is convenient to control the amount of the first hydrogenated nitrile butadiene rubber used in the carbon nanotube slurry, thereby increasing the carbon nanotube content in the carbon nanotube slurry.

[0245] In some embodiments of this application, the mass ratio of carbon nanotubes to the first hydrogenated nitrile rubber in the carbon nanotube slurry is any one of 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, 100:100, 100:110, 100:120, 100:130, 100:140, 100:150, 100:160, 100:170, 100:180, 100:190, or 100:200, or any one of the above range values.

[0246] In some embodiments, the solid content of the carbon nanotube slurry is greater than 1% and less than or equal to 2%.

[0247] The solid content of this application refers to the mass ratio of the slurry after drying in a certain way to that before drying. The measurement method includes methods known in the art, such as: weighing 1 to 4 g of slurry, recorded as m1, placing it in an oven to dry the slurry (120℃ / 4h), weighing the solid residue, recorded as m2, and the solid content = m2 / m1*100%.

[0248] The solid content of the carbon nanotube slurry in this application is increased compared to the previous version, which increases the content of carbon nanotubes in the slurry and makes the carbon nanotubes uniformly dispersed, which is beneficial to improving the conductivity of the electrode.

[0249] In these embodiments, this application discloses that the solid content of the carbon nanotube slurry is any one of 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any one of the above range values.

[0250] In some embodiments, the viscosity of the above-mentioned carbon nanotube slurry is ≤1200 mPa·s;

[0251] The viscosity of the above-mentioned carbon nanotube slurry is ≤3500 mpa.s after standing at 20℃~30℃ for 3 months.

[0252] The viscosity of the carbon nanotube slurry in this application is ≤1200 mPa·s, which indicates that the carbon nanotube slurry has good fluidity.

[0253] The viscosity of the carbon nanotube slurry changed after being left at room temperature for a certain period of time, but the change was limited. This indicates that the carbon nanotube slurry has good stability, which also means that the first hydrogenated nitrile rubber has good dispersibility of carbon nanotubes.

[0254] The method for determining the viscosity of carbon nanotube slurry in this application includes any conventional method in the art, such as using a Brook DV2T viscometer. At 25°C, 200 ml of the above-mentioned stirred slurry is placed in a 250 ml beaker, a 64# rotor is inserted into the slurry, the rotation speed of the device is 100 r / min, the start test button is clicked, and the viscosity data is recorded after 5 minutes.

[0255] In this application, the viscosity of the carbon nanotube slurry was measured by the above-mentioned method after being left to stand at 20℃~30℃ for 3 months.

[0256] In some embodiments, the aspect ratio of the carbon nanotubes is 100 to 100,000.

[0257] The carbon nanotubes of this application are considered to be almost one-dimensional, thus possessing a high aspect ratio. The carbon nanotubes of this application have a one-dimensional tubular structure, therefore possessing a certain length and diameter. The length includes the length of the tubular structure corresponding to the longer dimension (the third dimension) compared to the other two dimensions, and the distance between one end of the tubular structure. This one-dimensional tubular length can be obtained by photographing, for example, using a scanning electron microscope or a scanning transmission electron microscope to photograph the carbon nanotubes. Similarly, the diameter of the carbon nanotube includes the dimension of one of the two smaller dimensions. The diameter of the one-dimensional tubular structure can be obtained by photographing the cross-section of the one-dimensional tubular structure and calculating the distance between one end of the cross-section. This application describes the average length and average diameter, and the specific measurement method includes: Average diameter testing method: 1) Instrument model: TEM transmission electron microscope; 2) Adjust the equipment magnification: 100K; 3) Select 100 carbon nanotubes within the field of view to measure the diameter and statistically analyze them, taking the average value L1 (nm). Average tube length testing method: 1) Instrument model: SEM scanning electron microscope; 2) Adjust the magnification of the equipment: 30K / 40K; 4) Select 100 carbon nanotubes and measure their lengths for statistical analysis, taking the average value L2 (um). Then the aspect ratio is L2 / L1. The aspect ratio of the carbon nanotubes in this application is 100 to 100,000.

[0258] The aspect ratio of the carbon nanotubes in this application is any one of 100, 500, 800, 1000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000 or any one of the above range values.

[0259] In some embodiments, the specific surface area of ​​carbon nanotubes is >800 m². 2 / g.

[0260] The specific surface area of ​​the carbon nanotubes in this application is >800 m². 2 / g, which is related to the one-dimensional tubular structure of carbon nanotubes and their aspect ratio. Under this performance parameter, carbon nanotubes can contact the positive electrode active material to exert good conductivity.

[0261] The specific surface area (BET) of carbon nanotubes in this application refers to the specific surface area determined by nitrogen adsorption according to ASTM D 366378 based on the Brunauer Emmett Teller method described in The Journal of the American Chemical Society, 60, 309 (1938). The method for determining the specific surface area (BET) in this application includes methods conventionally known in the art.

[0262] For example, the testing instrument used is the ASAP2460 physical adsorption analyzer. According to GB / T19587-2017, the dried and degassed carbon nanotube sample is placed in liquid nitrogen, and different test pressures are adjusted to measure the amount of nitrogen adsorbed. Adsorption and desorption isotherms are plotted, and the specific surface area BET of the carbon nanotube is calculated based on the adsorption and desorption isotherms.

[0263] In some embodiments, the specific surface area of ​​carbon nanotubes is greater than 800 m². 2 / g, but less than 2000m 2 / g.

[0264] The conductive agent in the positive electrode film layer of this application may contain only carbon nanotubes, or it may contain carbon nanotubes + carbon black, or it may contain carbon nanotubes + carbon black + other conventional conductive agents known in the art. Compared with one-dimensional carbon nanotubes, the addition of carbon black is beneficial to exerting the conductivity of dot-shaped carbon black + linear carbon nanotubes.

[0265] This application discloses in these embodiments that the specific surface area of ​​carbon nanotubes is 287 m². 2 / g、810m 2 / g、834m 2 / g、1041m 2 / g、1234m 2 / g, 1500m 2 / g、1800m 2 Any one of / g or any one of the ranges of the above two.

[0266] The carbon black described in this application is an industrial product, primarily composed of elemental carbon, with trace amounts of oxygen, hydrogen, and sulfur. Due to different preparation processes, various types of carbon black exhibit differences in specific surface area, powder resistivity, and other properties.

[0267] In some embodiments, the specific surface area of ​​carbon black is greater than or equal to 60 m². 2 / g.

[0268] The definition and measurement method of specific surface area in this application remain the same as those described above. In some embodiments, this application discloses that the specific surface area of ​​carbon black is greater than or equal to 60 m². 2 / g, and less than 500m 2 / g. This application discloses in these embodiments that the specific surface area of ​​the carbon black is 60m². 2 / g、70m 2 / g、80m 2 / g、90m 2 / g, 100m 2 / g、200m 2 / g、300m 2 / g、312m 2 / g、400m 2 / g、500m 2 Any one of / g or any one of the above range values.

[0269] In these embodiments, this application discloses that the specific surface area of ​​the carbon black is 60 m². 2 / g, 150m 2 / g、200m 2 / g、300m 2 Any one of / g or any one of the ranges of the above two.

[0270] In some embodiments, the resistivity of the carbon black powder is <0.03 Ω·cm.

[0271] The powder resistivity in this application is also the volume resistivity, which refers to the resistance of a powder material per unit length and per unit area at room temperature (10℃~30℃). The method for measuring the powder resistivity is any conventional method in the art. This application selects: using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analysis Technology Co., Ltd.: Lorester GP Powder Resistivity Measuring System MCP-PD-51), with a sample mass of 1.2g, a powder probe unit (four-probe probe unit) using a ring electrode, an electrode spacing of 5.0mm, an electrode radius of 1.0mm, a sample radius of 12.5mm, and measuring the volume resistivity [Ω·cm] of the conductive powder under a certain pressure (3t) with a 90V voltage limiter applied.

[0272] In some embodiments, the resistivity of the carbon black powder is 0.001 Ω·cm to 0.02 Ω·cm.

[0273] In these embodiments, this application discloses that the powder resistivity of carbon black is any one of 0.001 Ω·cm, 0.014 Ω·cm, 0.0171 Ω·cm, 0.02 Ω·cm, or any one of the ranges of both of the above.

[0274] In some embodiments, the carbon black has a Dv50 ≤ 30 μm.

[0275] The Dv50 of this application includes a particle size distribution where 50% of the volume is larger than the particle size and 50% of the volume is smaller than the particle size; it is also known as the median diameter and is commonly used to represent the average particle size. In these embodiments, this application selects to determine the particle size distribution using laser diffraction particle size analysis, specifically referring to standard GB / T19077-2016 to obtain the particle size distribution map, and then calculating the result.

[0276] In some embodiments, the Dv50 of the carbon black is 2 μm to 30 μm. Carbon black that meets this range is easily dispersed in the positive electrode film and forms a good conductive network together with other conductive agents.

[0277] In these embodiments, this application discloses that the carbon black has a Dv50 of any one of 2 μm, 3 μm, 25 μm, 30 μm or any one of the above two ranges.

[0278] In some embodiments, the first organic solvent and the second organic solvent each independently include one or more of N,N-dimethylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, acetone, dimethyl carbonate, and polycarbonate.

[0279] In some embodiments, the first hydrogenated nitrile rubber is dispersed in N-methylpyrrolidone to form a liquid with a mass percentage content of 8%, and the viscosity of the liquid is 300 mPa·s to 1800 mPa·s.

[0280] This application selects a first hydrogenated nitrile rubber liquid with a certain viscosity, which is used to disperse carbon nanotubes to form a carbon nanotube slurry. On the other hand, the carbon nanotube slurry has little effect on the viscosity of the electrode slurry.

[0281] The viscosity determination method of this application includes any conventional method in the art, such as a rotational viscometer. Specifically, the adhesive solution is first dispersed by stirring with a high-speed grinder at 800 rpm for 120 minutes, followed by ultrasonic agitation for 30 minutes to remove air bubbles. Then, a Brook DV2T viscometer is used. At 25°C, 200 ml of the stirred adhesive solution is placed in a 250 ml beaker. A 64# rotor is inserted into the slurry, and the device rotates at 100 rpm. The start test button is pressed, and the viscosity data is recorded after 5 minutes.

[0282] In some embodiments, the preparation process of the first hydrogenated nitrile rubber is as follows:

[0283] Preparation of nitrile butadiene rubber (NBR): The reactor was evacuated / purged with nitrogen three times. The emulsifier (dodecyl ether sulfate), monomer AN (acrylonitrile), relative molecular mass regulator n-dodecyl tert-thiol, and initiator potassium persulfate were added sequentially to a 10L polymerization reactor under negative pressure. Then, monomer Bd (butadiene) was added. The temperature was raised to 25°C under stirring for polymerization. When the polymerization conversion rate reached more than 98.0%, the material was cooled and discharged. After coagulation, washing, and drying, nitrile butadiene rubber was obtained.

[0284] Hydrogenation of nitrile butadiene rubber (NBR): This process is carried out in a high-pressure autoclave reactor. First, a certain amount of NBR is dissolved in monochlorobenzene, then a palladium-rhodium catalyst (Rh) is added. 3+ x Pd 2+ 10-x The NBR solution was added. Subsequently, H2 was introduced into the reactor via a hydrogen adapter, and the pressure was maintained at 5.5 MPa after the NBR mixture was degassed three times with H2. The hydrogenation temperature was 100°C, the stirring speed was 600 rpm, and the reaction time was 7 h. After the given reaction time, the system was cooled. HNBR (hydrogenated nitrile butadiene rubber) was obtained by discharging the crude product, adding ethanol for flocculation, and drying and filtering the resulting rubber. The organic solution was evaporated, and the catalyst (Rh) was recovered. 3+ x Pd 2+ 10-x ).

[0285] In some embodiments, the preparation process of the above-mentioned carbon nanotube slurry is as follows:

[0286] Kneading: The first hydrogenated nitrile rubber prepared above is dispersed in an organic solvent to form a certain mass fraction of adhesive solution. Carbon nanotube powder is added to the adhesive solution and kneaded thoroughly to obtain blend 1.

[0287] Pre-mixing: Continue adding the organic solvent and the above-mentioned first hydrogenated nitrile rubber solution to blend 1, and mix until the entire system becomes homogeneous. The organic solvent here includes any one or more of N,N-dimethylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, acetone, dimethyl carbonate, and polycarbonate.

[0288] High-pressure homogenization: Dispersion is performed using a high-pressure homogenizer. The high-pressure homogenizer mentioned here includes any model conventionally available in this field.

[0289] [Negative electrode plate]

[0290] The negative electrode sheet of this application includes a negative current collector and a negative electrode film layer located on one or both surfaces of the negative current collector. Generally, the negative electrode film layer is located on both surfaces of the negative current collector, and is formed by methods such as coating or deposition. In this application, both sides will be used as examples.

[0291] In some embodiments, this application discloses that the compaction density of the negative electrode film layer is ≥1.65 g / cm³. 3 .

[0292] In this application, the compaction density of the negative electrode film can be used to characterize the energy density of the material; however, the compaction density of the negative electrode film is used to evaluate the overall compaction density of the negative electrode sheet. The compaction density of the negative electrode film = areal density of the negative electrode film / thickness of the negative electrode film. The thickness of the negative electrode film includes the distance between the two end faces of the negative electrode film along the thickness direction. The areal density of the negative electrode film = weight of a single positive electrode layer / area of ​​a single positive electrode layer. The weight of a single positive electrode layer can be obtained by weighing, and the area of ​​a single negative electrode layer can be obtained using the area calculation formula based on the shape of the film. In these embodiments, this application lists a compaction density of the negative electrode film ≥ 1.65 g / cm³. 3 .

[0293] This application discloses in some embodiments that the negative electrode film layer includes a negative electrode active material, and the active material includes one or more of carbonaceous materials, silicon-based materials, silicon-carbon composite materials, tin-based materials and their alloys. The carbonaceous materials in this application include one or more combinations of artificial graphite, natural graphite, soft carbon, and hard carbon. Among them, artificial graphite, natural graphite, soft carbon, hard carbon, etc., include any form of material conventional in the art, and include any manufacturer and model conventional in the art. The silicon-based materials in this application include one or two of silicon-oxygen materials or silicon-carbon materials, or silicon-carbon composites. The tin-based materials and their alloys in this application include, but are not limited to, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, etc. Furthermore, this application is not limited to these materials; other conventional materials that can be used as negative electrode active materials for lithium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0294] In some embodiments, this application discloses that the conductive agent includes one or more of dot-shaped conductive agents, linear conductive agents, and planar conductive agents. The dot-shaped conductive agent includes one or more of conductive carbon black (Super P or Super S), acetylene black, conductive graphite (KS-6 or KS-15 or SFG-6 or SFG-15), and Ketjen black. The linear conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon nanofibers. The planar conductive agent includes, but is not limited to, graphene.

[0295] In some embodiments, this application discloses the use of the same type of conductive agent in the negative electrode as in the positive electrode to further reduce the DC internal resistance of the battery.

[0296] This application discloses in some embodiments that the negative electrode film layer includes a binder and a dispersant. The binder includes, but is not limited to, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc. The dispersant also includes any type conventional in the art, such as cellulose and its salts, specifically including, but not limited to, methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0297] The method of forming the negative electrode film layer in this application includes 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, uniformly coating the negative electrode slurry on both sides of the negative electrode current collector; controlling the coating weight on one side; drying, and compacting it to a certain compaction density using a cold press to obtain a negative electrode sheet containing a negative electrode film layer.

[0298] [Isolation membrane]

[0299] Some embodiments of this application disclose a separator membrane. This application does not have any particular limitation on the type of separator membrane, and any well-known porous structure separator membrane with good chemical and mechanical stability can be selected.

[0300] In some embodiments, the separator includes a substrate material layer and a coating disposed on the surface of the substrate material layer; the substrate material of the substrate material layer includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide; the coating includes a ceramic coating and / or a polymer coating. The substrate material layer has good lithium ion permeability, which is beneficial to lithium ion migration; the coating disposed on the surface of the substrate material layer can further improve the mechanical properties of the separator. Optionally, the ceramic particles in the ceramic coating include one or more of SiO2, Al2O3, AlOOH, CaO, TiO2, MgO, ZnO, ZrO2, Mg(OH)2, and BaSO4. Optionally, the polymer material of the polymer coating includes one or more of polyethylene (PE), polypropylene (PP), poly(p-phenylene terephthalamide) (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and polyamide (PA). The polymer coating can be made of the same or different material as the substrate material layer, and the thicknesses of the polymer coating and the substrate material layer can be different. Optionally, the thickness of the polymer coating is less than the thickness of the substrate material layer.

[0301] In other embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0302] Electrolyte

[0303] Some embodiments of this application disclose an electrolyte, which 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 lithium-ion battery of this application uses a liquid electrolyte, i.e., an electrolyte. This electrolyte contains an electrolyte salt and an organic solvent. The electrolyte salt can be any type conventional in the art, including, 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-hexafluoropropane disulfonylimide lithium, cyclic 1,2-tetrafluoroethane disulfonylimide lithium, RN(CF3SO2)(C4F9S O2), 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 bis(oxalate)borate, lithium difluorooxalate borate, lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, lithium tetrafluoro(oxalate)phosphate, etc. Here, both the metal and R contain lithium ions.

[0304] 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.

[0305] 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).

[0306] 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 comprises 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 sulfated hydrocarbon ester additives; further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro-1,3-propanesulfonate lactone (FPS); the sulfated hydrocarbon ester 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; boron-containing lithium salts include one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (LiBOB), and lithium bis(oxalate)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).

[0307] The lithium-ion secondary battery of this application will be described in detail below with reference to specific embodiments.

[0308] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0309] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0310] 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.

[0311] Experimental materials:

[0312] Lithium nickel cobalt manganese oxide (LiNi) 0.5 CO 0.2 Mn 0.3 O2): Commercially available, with a median particle size Dv50 of 6.5 μm.

[0313] Carbon black: Commercially available, including Sample 1 and Sample 2, with the following performance parameters for each sample: Sample 1: Powder resistivity 0.0171 Ω·cm, median particle size Dv50 3 μm, specific surface area 150 m² / cm². 2 / g; Sample 2: Powder resistivity is 0.014 Ω·cm, median particle size Dv50 is 25 μm, and specific surface area is 60 m² / g. 2 / g.

[0314] Carbon nanotubes: Commercially available, including Sample 1, Sample 2, Sample 3, and Sample 4. The performance parameters of each sample are as follows: Sample 1: average tube diameter 1.5 nm, aspect ratio 20000, specific surface area 1234 m². 2 / g; Sample 2: Average tube diameter 2.9nm, aspect ratio 10000, specific surface area 1041m² 2 / g; Sample 3: Average tube diameter 5.4nm, aspect ratio 800, specific surface area 834m² 2 / g; Sample 4: Average tube diameter 8.5nm, aspect ratio 500, specific surface area 287m² 2 / g.

[0315] First hydrogenated nitrile butadiene rubber: Preparation.

[0316] Second hydrogenated nitrile butadiene rubber: commercially available, with a weight-average molecular weight of 216,000, acrylonitrile content of 38% by mass in the above-mentioned second hydrogenated nitrile butadiene rubber, and a degree of hydrogenation of 98.0%.

[0317] Fluoropolymer: Commercially available, with a weight-average molecular weight of 1.1 million and a molar content of 1.5% of structural units derived from acrylic acid monomers.

[0318] Preparation Example 1

[0319] A method for preparing a first hydrogenated nitrile butadiene rubber (weight-average molecular weight of 5W) is provided, comprising the following preparation process:

[0320] Preparation of nitrile butadiene rubber (NBR): The reactor was evacuated / purged with nitrogen three times. The emulsifier (3.5 parts of dodecyl ether sulfate), monomer AN (40 parts of acrylonitrile), relative molecular mass regulator n-dodecyl tert-thiol (6 parts), and initiator potassium persulfate (1.8 parts) were added sequentially to a 10L polymerization reactor under negative pressure. Then, monomer Bd (60 parts of butadiene) was added. The temperature was raised to 25°C under stirring for polymerization. When the polymerization conversion rate reached more than 98.0%, the material was cooled and discharged. After coagulation, washing, and drying, nitrile butadiene rubber was obtained.

[0321] Hydrogenation of nitrile butadiene rubber (NBR): This was carried out in a high-pressure autoclave reactor. First, a certain amount of NBR (0.9 g) was dissolved in monochlorobenzene (35 mL), then the catalyst (Rh...) was added... 3+ x Pd 2+ 10-x (Catalyst / NBR = 0.020–0.022 wt%) was added to the NBR solution. Subsequently, H2 was introduced into the reactor via a hydrogen adapter, and the pressure was maintained at 5.5 MPa after the NBR mixture was degassed three times with H2. The hydrogenation temperature was 100 °C, the stirring speed was 600 rpm, and the reaction time was 7 h. After the given reaction time, the system was cooled. HNBR (hydrogenated nitrile butadiene rubber) was obtained by discharging the crude product, adding ethanol for flocculation, and drying and filtering the resulting rubber. The organic solution was evaporated, and the catalyst (Rh) was recovered. 3+ x Pd 2+ 10-x ).

[0322] [Physical Characterization of First Hydrogenated Nitrile Butadiene Rubber]

[0323] ①Test weight-average molecular weight:

[0324] A Waters 2695 Isocratic HPLC gel electrophoresis system (differential refractive index detector 2141) was used. A 3.0% (w / w) polystyrene solution was used as a reference, and a matched column (oil-based: Styragel HT5DMF7.8*300mm + Styragel HT4) was selected. An 8.0% first-hydrogenated nitrile butadiene rubber (NMP) solution was prepared using purified NMP solvent and allowed to stand for one day. For testing, tetrahydrofuran was first drawn into the syringe and used to flush the solution, repeated several times. Then, 5 ml of the experimental solution was drawn, air was expelled from the syringe, and the needle tip was dried. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the data was acquired, and the weight-average molecular weight was read.

[0325] ② Test the degree of hydrogenation:

[0326] In the preparation example 1 above, when nitrile rubber was hydrogenated, the carbon-carbon double bond content of the reactant sample was tested using a Bruker AV400 nuclear magnetic resonance spectrometer, yielding [C=C]0. At hydrogenation reaction time t, the carbon-carbon double bond content of the product sample was [C=C]t. Therefore, the degree of hydrogenation HD satisfies:

[0327]

[0328] All the above samples were dissolved in tritium-substituted chloroform to complete the test.

[0329] ③ Test the glass transition temperature:

[0330] Includes the following steps:

[0331] 1. Sample preparation: Select an appropriate amount of sample (usually 5mg ± 1mg), ensuring the sample is homogeneous and free of moisture. Place the sample into the DSC sample crucible, typically made of aluminum or other inert materials.

[0332] 2. Instrument settings: Start the DSC instrument, set the temperature program, including the heating rate (usually 10-20℃ / min, this application uses 12℃ / min), and select an appropriate atmosphere (such as nitrogen or air) to prevent sample oxidation.

[0333] 3. Baseline calibration: Before testing, run an empty crucible (reference material) to calibrate the baseline and ensure the accuracy of the instrument.

[0334] 4. Heating test: Start heating and record the relationship between the heat flow difference between the sample and the reference as a function of temperature. Observe the DSC curve. The glass transition usually shows a step-like change in the baseline.

[0335] 5. Data analysis: Take the inflection point (the point of maximum slope) when the curve changes as Tg.

[0336] To ensure the reliability of the results, the same sample can be tested three times and the average value can be taken.

[0337] ④ Test the viscosity of the adhesive:

[0338] First, use a high-speed grinder to disperse the 8% adhesive solution by stirring at 800 rpm for 120 minutes, followed by ultrasonic vibration for 30 minutes to remove air bubbles. Then, using a Brook DV2T viscometer, at 25°C, place 200 ml of the stirred adhesive solution in a 250 ml beaker, insert a 64# rotor into the adhesive solution, rotate the device at 100 rpm, click the start test button, and record the viscosity data after 5 minutes.

[0339] The performance parameters of the first hydrogenated nitrile rubber prepared in Example 1 were obtained according to the above test methods, as shown in Table 1-1 below:

[0340] Table 1-1 List of performance parameters of the first fluoropolymer

[0341]

[0342] Example 1

[0343] A method for preparing a lithium-ion secondary battery is provided, comprising the following steps:

[0344] Preparation of positive electrode sheet:

[0345] Preparation of carbon nanotube slurry: 10 parts by mass of 8% of the first hydrogenated nitrile butadiene rubber solution were added to a solvent, and 1.0 part by mass of carbon nanotube powder sample 1 (average tube diameter 1.5 nm, aspect ratio 20000, specific surface area 1234 m²) was added. 2 / g), set the rotation speed to 25 rpm, the revolution speed to 800 rpm, and the stirring time to 30 minutes, knead to obtain blend 1; add N-methylpyrrolidone to blend 1 for dilution, and add the remaining 2.5 parts of the first hydrogenated nitrile rubber liquid while stirring, at a stirring speed of 1000 rpm for 60 minutes, and turn on the cooling water circulation until the whole mixture becomes uniform. Then, disperse using a high-pressure homogenizer to obtain carbon nanotube slurry, wherein the performance parameters of the carbon nanotube slurry are shown in Table 1-2;

[0346] Preparation of positive electrode slurry: The positive electrode active material LiNi... 0.5 Co 0.2 Mn 0.3 O2 (median particle size Dv50 of 6.5 μm) and the above carbon nanotube slurry were dispersed in N-methylpyrrolidone, and then conductive agent carbon black sample 1 (powder resistivity of 0.0171 Ω·cm, median particle size Dv50 of 3 μm, specific surface area of ​​150 m²) was added.2 / g) and binder polyvinylidene fluoride (including structural units derived from vinylidene fluoride and structural units derived from acrylic monomers, wherein, based on the total number of moles of structural units in the fluoropolymer, the molar content of structural units derived from acrylic monomers is 1.5%, and the weight-average molecular weight of the fluoropolymer is 1.1 million), are thoroughly mixed to form a positive electrode slurry.

[0347] Preparation of the positive electrode sheet: The positive electrode slurry is coated on both sides of the above-mentioned positive electrode current collector to form a positive electrode film layer; after drying and cold pressing, the compaction density of the positive electrode film layer is 3.4 g / cm³. 3 The positive electrode sheet.

[0348] The types and contents of each component in the positive electrode film are shown in Table 1-3.

[0349] Preparation of negative electrode sheet:

[0350] Graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 96.2:1.8:0.8:1.2. The mixture was stirred under vacuum until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both sides of the copper foil of the negative electrode current collector. The foil was dried in a nine-section oven with the following temperatures set sequentially: 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃. The resulting material was then compacted using a cold press to obtain the negative electrode sheet.

[0351] Preparation of electrolyte:

[0352] 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.

[0353] Provide isolation membrane

[0354] A porous polyethylene (PE) membrane with a thickness of 13 μm was used as the separator.

[0355] Preparation of lithium-ion secondary batteries

[0356] The positive electrode, separator, and negative electrode are wound in sequence, with the separator acting as a separator between the positive and negative electrodes, and the corresponding components are assembled to form a wound bare cell. The wound bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion secondary battery is obtained.

[0357] Comparative Example 1

[0358] A method for preparing a lithium-ion secondary battery is provided. This method differs from Example 1 in that a commercially available second hydrogenated nitrile butadiene rubber is used in the carbon nanotube slurry. This second hydrogenated nitrile butadiene rubber has a weight-average molecular weight of 216,000, a degree of hydrogenation of 98.0%, and an acrylonitrile content of 38% by mass. All other aspects remain the same as in Examples 1-1.

[0359] [Testing the performance of carbon nanotube slurry]

[0360] ⑤ Test solid content:

[0361] For details, please refer to DB13_T 5025.1-2019:

[0362] Weigh 2g of slurry sample into an empty weighing dish with constant mass, spread it evenly, and let its mass before drying be m1. Place the weighing dish containing the sample in an electric thermostatic drying oven at 120℃±2℃ for 3 hours. After cooling, obtain the total mass of the weighing dish and the sample after drying, m20. Place it again in an electric thermostatic drying oven at 120℃±2℃ for 30 minutes. After taking it out, weigh it, m21. Repeat this operation until the difference between the last two weighings is no more than 0.0003g. When calculating, take the average of the last two weighings as m2. Then, the solid content = m2 / m1*100%.

[0363] ⑥ Test viscosity:

[0364] First, the carbon nanotube slurry was dispersed using a high-speed grinder at 800 rpm for 120 minutes, followed by ultrasonic agitation for 30 minutes to remove air bubbles. Then, using a Brook DV2T viscometer, at 25°C, 200 ml of the above-dispersed slurry was placed in a 250 ml beaker. A 64# rotor was inserted into the slurry, the device was rotated at 100 rpm, and the start test button was pressed. The viscosity data was recorded after 5 minutes.

[0365] 480g of carbon nanotube slurry was placed in a 500ml fluorinated bottle. The bottle was marked with 3M (month). The sample bottle was placed in a room temperature, light-proof area and stored for 3 months. The viscosity was measured using the above method.

[0366] Table 1-2 Performance List of Carbon Nanotube Slurry

[0367]

[0368] As can be seen from Table 1-2, the first hydrogenated nitrile rubber provided in this application has good dispersibility for carbon nanotubes, which increases the solid content of the carbon nanotube slurry. At the same time, the carbon nanotube slurry of this application has low viscosity, which facilitates the preparation of electrode slurry, and the carbon nanotube slurry has good stability.

[0369] The mass percentage of each component added to the positive electrode film layer is calculated based on the amount of each component added, as shown in Table 1-3.

[0370] Table 1-3 Mass percentage content of each component in the positive electrode film

[0371]

[0372] The film resistance and compaction density of the positive electrode sheets prepared in each embodiment were measured according to the following measurement methods, as shown in Tables 1-4.

[0373] ⑦ Test the film resistance of the positive electrode:

[0374] Cut 3*3mm small circles from the left, center, and right sides of the positive electrode. Turn on the indicator light of the Yuaneng Technology electrode resistance meter, place the probe at the appropriate position on the meter, and click the "Start" button. Once the reading stabilizes, take the reading. Test two positions for each small circle, and finally calculate the average of the six measurements, which is the film resistance of that electrode.

[0375] ⑧ Method for determining the compaction density of the positive electrode film:

[0376] The thickness H of the positive electrode film was obtained using a micrometer.

[0377] Take a positive electrode sheet that has been coated on one side and cold-pressed (if it is a double-sided coated electrode sheet, the electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S0, weigh it, and record its weight as M1; then wipe off the electrode film layer of the positive electrode sheet after weighing it, weigh the current collector, and record it as M0. The surface density of the positive electrode film layer is D = (M1 - M0) / S0.

[0378] Then the compaction density of the positive electrode film is equal to the surface density D of the positive electrode film / the thickness H of the positive electrode film.

[0379] The performance parameters of the positive electrode sheet prepared in Example 1 were obtained according to the above testing method, as shown in Tables 1-4 below:

[0380] Table 1-4 Performance List of Positive Electrode Films

[0381] Serial Number diaphragm resistance / Ω <![CDATA[Compaction density / g / cm 3 > Example 1 0.222 3.4 Comparative Example 1 0.821 3.4

[0382] As can be seen from Tables 1-4, the first hydrogenated nitrile rubber provided in this application has good dispersibility for carbon nanotubes, which enables the carbon nanotubes to exhibit good conductivity, thereby increasing the conductivity of the positive electrode sheet.

[0383] Examples 2-1 to 2-3

[0384] A method for preparing a lithium-ion secondary battery is provided. This method differs from Example 1 in that different first hydrogenated nitrile rubbers are obtained by adjusting the process parameters and dosages.

[0385] In Example 2-1, the weight-average molecular weight of the first hydrogenated nitrile butadiene rubber was 3W; in Example 2-2, it was 10W; and in Example 2-3, it was 20W. The preparation processes for the first hydrogenated nitrile butadiene rubbers with different weight-average molecular weights are as follows:

[0386] (1) The preparation process of the first hydrogenated nitrile butadiene rubber with a weight average molecular weight of 3W is as follows:

[0387] Preparation of nitrile butadiene rubber (NBR): The reactor was evacuated / purged with nitrogen three times. The emulsifier (2.0 parts of dodecyl ether sulfate), monomer AN (25 parts of acrylonitrile), relative molecular mass regulator n-dodecyl tert-thiol (3.5 parts), and initiator potassium persulfate (1.0 part) were added sequentially to a 10L polymerization reactor under negative pressure. Then, monomer Bd (36 parts of butadiene) was added. The temperature was raised to 25°C under stirring for polymerization. When the polymerization conversion rate reached more than 98.0%, the material was cooled and discharged. After coagulation, washing, and drying, nitrile butadiene rubber was obtained.

[0388] Hydrogenation of nitrile butadiene rubber (NBR): This was carried out in a high-pressure autoclave reactor. First, a certain amount of NBR (0.9 g) was dissolved in monochlorobenzene (35 mL), then the catalyst (Rh...) was added... 3+ x Pd 2+ 10-x (Catalyst / NBR = 0.020–0.022 wt%) was added to the NBR solution. Subsequently, H2 was introduced into the reactor via a hydrogen adapter, and the pressure was maintained at 5.5 MPa after the NBR mixture was degassed three times with H2. The hydrogenation temperature was 100 °C, the stirring speed was 600 rpm, and the reaction time was 7 h. After the given reaction time, the system was cooled. HNBR (hydrogenated nitrile butadiene rubber) was obtained by discharging the crude product, adding ethanol for flocculation, and drying and filtering the resulting rubber. The organic solution was evaporated, and the catalyst (Rh) was recovered. 3+ x Pd 2+ 10-x ).

[0389] (2) The preparation process of the first hydrogenated nitrile butadiene rubber with a weight average molecular weight of 10W is as follows:

[0390] Preparation of nitrile butadiene rubber (NBR): The reactor was evacuated / purged with nitrogen three times. The emulsifier (7.5 parts of dodecyl ether sulfate), monomer AN (85 parts of acrylonitrile), relative molecular mass regulator n-dodecyl tert-thiol (13.5 parts), and initiator potassium persulfate (3.8 parts) were added sequentially to a 20L polymerization reactor under negative pressure. Then, monomer Bd (125 parts of butadiene) was added. The temperature was raised to 25℃ under stirring for polymerization. When the polymerization conversion rate reached more than 98.0%, the material was cooled and discharged. After coagulation, washing, and drying, nitrile butadiene rubber was obtained.

[0391] Hydrogenation of nitrile butadiene rubber (NBR): This was carried out in a high-pressure autoclave reactor. First, a certain amount of NBR (0.9 g) was dissolved in monochlorobenzene (35 mL), then the catalyst (Rh...) was added... 3+ x Pd 2+ 10-x (Catalyst / NBR = 0.020–0.022 wt%) was added to the NBR solution. Subsequently, H2 was introduced into the reactor via a hydrogen adapter, and the pressure was maintained at 5.5 MPa after the NBR mixture was degassed three times with H2. The hydrogenation temperature was 105 °C, the stirring speed was 600 rpm, and the reaction time was 7 h. After the given reaction time, the system was cooled. HNBR (hydrogenated nitrile butadiene rubber) was obtained by discharging the crude product, adding ethanol for flocculation, and drying and filtering the resulting rubber. The organic solution was evaporated, and the catalyst (Rh) was recovered. 3+ x Pd 2+ 10-x ).

[0392] (3) The preparation process of the first hydrogenated nitrile butadiene rubber with a weight average molecular weight of 20W is as follows:

[0393] Preparation of nitrile butadiene rubber (NBR): The reactor was evacuated / purged with nitrogen four times. The emulsifier (16 parts of dodecyl ether sulfate), monomer AN (200 parts of acrylonitrile), relative molecular mass regulator n-dodecyl tert-thiol (25 parts), and initiator potassium persulfate (8 parts) were added sequentially to a 10L polymerization reactor under negative pressure. Then, monomer Bd (250 parts of butadiene) was added. The temperature was raised to 25°C under stirring for polymerization. When the polymerization conversion rate reached more than 98.0%, the material was cooled and discharged. After coagulation, washing, and drying, nitrile butadiene rubber was obtained.

[0394] Hydrogenation of nitrile butadiene rubber (NBR): This was carried out in a high-pressure autoclave reactor. First, a certain amount of NBR (0.9 g) was dissolved in monochlorobenzene (35 mL), then the catalyst (Rh...) was added... 3+ x Pd 2+ 10-x(Catalyst / NBR = 0.020–0.022 wt%) was added to the NBR solution. Subsequently, H2 was introduced into the reactor via a hydrogen adapter, and the pressure was maintained at 5.5 MPa after the NBR mixture was degassed three times with H2. The hydrogenation temperature was 105 °C, the stirring speed was 600 rpm, and the reaction time was 7 h. After the given reaction time, the system was cooled. HNBR (hydrogenated nitrile butadiene rubber) was obtained by discharging the crude product, adding ethanol for flocculation, and drying and filtering the resulting rubber. The organic solution was evaporated, and the catalyst (Rh) was recovered. 3+ x Pd 2+ 10-x ).

[0395] The performance parameters of the first hydrogenated nitrile rubber in each embodiment are shown in Table 2-1 below.

[0396] Table 2-1 Performance Parameters of First Hydrogenated Nitrile Rubber

[0397]

[0398] As shown in Table 2-1, each hydrogenated nitrile rubber with a different molecular weight also has a different degree of hydrogenation, glass transition temperature, and viscosity.

[0399] The performance of the carbon nanotube slurry in each embodiment is illustrated in Table 2-2.

[0400] Table 2-2 Performance List of Carbon Nanotube Slurry

[0401]

[0402] As can be seen from Table 2-2, the first hydrogenated nitrile rubber provided in Examples 1 and 2-2 of this application has a significant impact on the solid content of the carbon nanotube slurry.

[0403] In the above embodiments, the positive electrode film layer contains 0.1% carbon nanotubes, 0.1% first hydrogenated nitrile rubber, 1.2% polyvinylidene fluoride, 1.0% carbon black, and 97.6% positive electrode active material and other essential components, as detailed in Tables 2-3 below.

[0404] Table 2-3 Mass percentage content of each component in the positive electrode film

[0405]

[0406] The performance of the prepared lithium-ion secondary batteries is shown in Table 6 below.

[0407] Examples 3-1 to 3-2

[0408] A method for preparing a lithium-ion battery is provided. This method differs from Example 1 in that, during the preparation of the positive electrode slurry, a second hydrogenated nitrile butadiene rubber (with a weight-average molecular weight of 216,000, an acrylonitrile content of 38% by mass in the second hydrogenated nitrile butadiene rubber, and a degree of hydrogenation of 98.0%) is added to N-methylpyrrolidone. In Example 3-1, the mass percentage content of the second hydrogenated nitrile butadiene rubber is 0.05%, and in Example 3-2, the mass percentage content of the second hydrogenated nitrile butadiene rubber is 0.2%.

[0409] Furthermore, the composition and content of each positive electrode film layer in each embodiment are shown in Table 3-1.

[0410] Table 3-1 Mass percentage content of each component in the positive electrode film

[0411]

[0412] The performance parameters of the positive electrode sheets of each embodiment were obtained according to the above testing method, as shown in Table 3-2 below:

[0413] Table 3-2 Performance List of Positive Electrode Films

[0414]

[0415] As shown in Table 3-1, the addition of a second hydrogenated nitrile rubber, which is different from the first hydrogenated nitrile rubber, to the positive electrode film layer in this application does not have a significant effect on the film resistance of the electrode, but it does reduce the film resistance of the positive electrode to a certain extent.

[0416] Examples 4-1 to 4-4

[0417] A method for preparing a lithium-ion battery is provided, which differs from Example 1 in that the type of carbon nanotubes and the mass percentage content of carbon nanotubes in the positive electrode film are different.

[0418] In Example 4-1, the carbon nanotubes of Example 1 were used, and the mass percentage content of the carbon nanotubes in the positive electrode film layer was 0.02%.

[0419] In Example 4-2, the carbon nanotubes illustrated in Sample 2 were used. These carbon nanotubes had an average diameter of 2.9 nm, an aspect ratio of 10000, and a specific surface area of ​​1041 m². 2 / g, the mass percentage content of the carbon nanotubes in the positive electrode film is 0.2%.

[0420] Examples 4-3 use carbon nanotubes illustrated in Sample 3. These carbon nanotubes have an average diameter of 5.4 nm, an aspect ratio of 800, and a specific surface area of ​​834 m². 2 / g, the mass percentage content of the carbon nanotubes in the positive electrode film is 0.3%.

[0421] Examples 4-4 use carbon nanotubes illustrated in Sample 4, which have an average diameter of 8.5 nm, an aspect ratio of 500, and a specific surface area of ​​287 m². 2 / g, the mass percentage content of the carbon nanotubes in the positive electrode film is 0.4%.

[0422] All other aspects of Example 4 are the same as those of Example 1, and the composition and content of each positive electrode film layer in each example are shown in Table 4-1.

[0423] Table 4-1 Mass percentage content of each component in the positive electrode film

[0424]

[0425] The performance parameters of the positive electrode sheet prepared in Example 4 were obtained according to the above testing method, as shown in Table 4-2 below:

[0426] Table 4-2 Performance List of Positive Electrode Films

[0427] Serial Number Carbon nanotube content / % diaphragm resistance / Ω <![CDATA[Compaction density / g / cm 3 > Example 1-1 0.1 0.222 3.4 Example 4-1 0.02 0.457 3.4 Example 4-2 0.2 0.231 3.4 Example 4-3 0.3 0.503 3.4 Example 4-4 0.4 0.489 3.4

[0428] As shown in Table 4-1, the first hydrogenated nitrile rubber provided in this application has the ability to disperse carbon nanotubes with different diameters. Furthermore, under the premise of good dispersion, for carbon nanotubes of the same diameter, the conductivity of the positive electrode is enhanced as the carbon nanotube content increases within a certain range.

[0429] Examples 5-1 to 5-2

[0430] A method for preparing a lithium-ion battery is provided, which differs from Example 1 in that the type and content of carbon black are different.

[0431] In Example 5-1, the carbon black powder resistivity was 0.014 Ω·cm, the median particle size Dv50 was 25 μm, and the specific surface area was 60 m². 2 / g, otherwise the same as in Example 1.

[0432] Example 5-2 differs from Example 1 in that no carbon black is added.

[0433] Furthermore, the composition and content of each positive electrode film layer in each embodiment are shown in Table 5-1.

[0434] Table 5-1 Mass percentage content of each component in the positive electrode film

[0435]

[0436] The performance parameters of the positive electrode sheet prepared in Example 5 were obtained according to the above testing method, as shown in Table 5-2 below:

[0437] Table 5-2 Performance List of Positive Electrode Films

[0438] Serial Number Carbon black content / % diaphragm resistance / Ω <![CDATA[Compaction density / g / cm 3 > Example 1-1 1.0 0.222 3.4 Example 5-1 2.0 0.251 3.4 Example 5-2 0 0.442 3.4

[0439] As shown in Table 5-1, the type and content of carbon black have a certain impact on the film resistance of the positive electrode sheet, and carbon nanotubes together with carbon black are beneficial to improving the conductivity of the positive electrode sheet.

[0440] [Battery Performance Test]

[0441] ⑨ Cyclic stability, test method for capacity retention after 500 cycles:

[0442] At 25℃, the lithium-ion secondary battery was charged at a constant current of 1C to 4.25V, then charged at a constant voltage to a current of 0.05C (corresponding to 100% SOC). After resting for 5 minutes, the secondary battery was discharged at a constant current of 1C to the lower limit of 2.8V (corresponding to 0% SOC), and the discharge capacity at this point was recorded, which is the discharge capacity of the first cycle. The secondary battery was subjected to a cyclic charge-discharge test according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 500 cycles at 25℃ = discharge capacity after 500 cycles / discharge capacity of the first cycle × 100%.

[0443] ⑩ Test method for DC resistance (DCR) growth rate after 500 cycles:

[0444] Testing the initial resistance (DCR1) of the battery: At room temperature (25℃), the lithium-ion secondary battery was discharged to 50% SOC using a 1 / 3C1 current, followed by a 4C1 current for 10 seconds. The open-circuit voltage before discharge was recorded as U1, and the voltage at the end of discharge was recorded as U2. U2-U1 was recorded as ΔU1. ΔU1 is related to the current I. 4C1 The ratio is the initial internal resistance of the battery, DCR1, i.e., DCR1 = ΔU1 / I. 4C1 C1 represents the initial capacity of the battery. The testing method includes: at 25°C, charging the individual battery cells to 4.25V with a constant current of 0.33C; further charging with a constant voltage of 4.25V to a current of 0.05C; letting it rest for 30 minutes; and then discharging the lithium-ion battery to 2.8V with a constant current of 0.33C. The discharge capacity is recorded as C1. The specific process for discharging to 50% SOC is as follows: at 25°C, charging the battery to 4.25V with a constant current of 0.33C1; further charging with a constant voltage of 4.25V to a current of 0.05C1; letting it rest for 30 minutes; and then discharging with a constant current of 0.33C1 to 0.5C1 (cutoff).

[0445] Following the above cycle method, charge to 100% SOC after 500 cycles.

[0446] Test of resistance DCR2 after 500 battery cycles: At room temperature (25℃), the lithium-ion secondary battery was discharged to 50% SOC, followed by a 4C2 discharge for 10 seconds. The open-circuit voltage before discharge was recorded as U3, and the final voltage after discharge was recorded as U4. U4-U2 was recorded as ΔU2. ΔU2 is related to the current I. 4C2 The ratio is the internal resistance DCR2, i.e., DCR2 = ΔU2 / I4C2. Where C2 is the capacity of the battery after 500 cycles. The test method includes: at 25℃, first charging the lithium-ion battery to 4.25V with a constant current of 0.33C, then further charging it to 0.05C with a constant voltage of 4.25V, letting it rest for 30 minutes, and then discharging it to 2.8V with a constant current of 0.33C. The discharge capacity is recorded as C2. The specific process for discharging to 50% SOC is as follows: at 25℃, first charging the battery to 4.25V with a constant current of 0.33C2, then further charging it to 0.05C2 with a constant voltage of 4.25V, letting it rest for 30 minutes, and then discharging it to 0.5C2 with a constant current of 0.33C2 until it is cut off.

[0447] The DCR growth rate after 500 cycles = (DCR2-DCR1) / DCR1, which can represent the DCR growth during the cycle. The larger the DCR growth, the more the battery DCR deteriorates under the influence of current density gradient, conductive network, battery polarization and other factors during the cycle, affecting the battery dynamic performance and cycle life.

[0448] Table 6 Battery Performance List

[0449]

[0450]

[0451] In summary, the design method provided in this application is beneficial to improving the dispersion of carbon nanotubes in the positive electrode film, enabling the carbon nanotubes to exert good conductivity, thereby reducing the DC internal resistance of the battery by improving the conductivity of the positive electrode sheet, and ultimately improving the cycle stability of the battery.

[0452] 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 lithium-ion secondary battery, characterized by: Includes positive electrode plate, negative electrode plate and separator; The positive electrode includes a positive current collector and a positive film layer located on at least one side surface of the positive current collector; The positive electrode film layer includes a positive electrode active material, carbon nanotubes, and a first hydrogenated nitrile rubber; The weight-average molecular weight of the first hydrogenated nitrile rubber is less than or equal to 200,000.

2. The lithium-ion secondary battery according to claim 1, characterized by: The first hydrogenated nitrile butadiene rubber comprises structural units derived from acrylonitrile monomers; the acrylonitrile content in the first hydrogenated nitrile butadiene rubber is 30% to 40% by mass; and / or, The degree of hydrogenation of the first hydrogenated nitrile rubber is greater than 99% and less than 99.9%.

3. The lithium-ion secondary battery according to any one of claims 1 to 2, characterized by: The glass transition temperature of the first hydrogenated nitrile rubber is -33°C to -23°C.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized by: The weight-average molecular weight of the first hydrogenated nitrile rubber is 30,000 to 200,000.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, characterized by: The first hydrogenated nitrile rubber has a mass percentage content of 0.02% to 2% in the positive electrode film layer; and / or, The carbon nanotubes in the positive electrode film have a mass percentage content of greater than or equal to 0.02%.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized by: The carbon nanotubes in the positive electrode film have a mass percentage content of 0.02% to 0.4%.

7. The lithium-ion secondary battery according to any one of claims 1 to 6, characterized by: The average diameter of the carbon nanotubes is less than or equal to 10 nm.

8. The lithium-ion secondary battery according to claim 7, characterized by: The average diameter of the carbon nanotubes is 1 nm to 5 nm.

9. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized by: The positive electrode film layer includes carbon black; The carbon black content in the positive electrode film layer is 0-2.5% by mass.

10. The lithium-ion secondary battery according to any one of claims 1 to 9, characterized by: The compacted density of the positive electrode film layer is 3.4 g / cm 3 ~ 3.6 g / cm 3 ; and / or, The film resistance of the positive electrode is less than 1Ω.

11. The lithium-ion secondary battery according to claim 10, characterized by: The film resistance of the positive electrode is greater than 0.02Ω and less than 1Ω.

12. The lithium-ion secondary battery according to any one of claims 1 to 11, characterized by: The positive electrode film layer includes a second hydrogenated nitrile butadiene rubber, the second hydrogenated nitrile butadiene rubber having a weight-average molecular weight greater than 200,000 and less than 500,000; and / or, The degree of hydrogenation of the second hydrogenated nitrile rubber is less than 99%.

13. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized by: The positive electrode film layer includes a binder, and the binder contains a mass percentage of less than or equal to 1.5% in the positive electrode film layer; The adhesive includes any one or more of the following: fluoropolymer, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

14. The lithium-ion secondary battery according to claim 13, characterized by: The fluoropolymer comprises structural units derived from vinylidene fluoride and structural units derived from acrylic acid monomers, and / or, The weight-average molecular weight of the fluoropolymer is 1,000,000 to 1,200,000; and / or, Based on the total number of moles of structural units in the fluoropolymer, the molar content of structural units derived from acrylic monomers is 1.4% to 1.6%.

15. The lithium-ion secondary battery according to any one of claims 1 to 14, characterized by: The positive electrode active material includes a nickel-containing layered oxide. The chemical formula of the nickel-containing layered oxide is Li x N t (Ni a Co b M c ) 1-d M’ d O 2-y A y ; N represents a lithium-site doping element, which includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; M includes any one or more of Mn and Al; M' includes any one or more of Zr, Sr, B, Ti, Mg, Sn, and Al; A represents an oxygen-doped element, which includes any one or more of S, N, B, F, Cl, Br, and I; x ranges from 0.2 to 1.2; t is 0 to 0.1; a ranges from 0.001 to 0.999; b is 0.001 to 0.999; a+b+c=1, 0≤d≤0.1； 0≤y＜0.2。 16. The lithium-ion secondary battery according to any one of claims 1 to 15, characterized by: The Dv50 of the positive electrode active material is 2μm to 8μm.

17. A method of producing the lithium-ion secondary battery according to claim 1, characterized by: The preparation process includes the following: Provide the first hydrogenated nitrile butadiene rubber compound; Prepare carbon nanotube slurry; take carbon nanotube powder and first hydrogenated nitrile rubber solution and disperse them in first organic solvent; Preparation of positive electrode slurry: The carbon nanotube slurry and the positive electrode active material are dispersed in a second organic solvent; Preparation of positive electrode sheet: The positive electrode slurry is coated on at least one side surface of the positive electrode current collector to form a positive electrode film layer; Preparation of lithium-ion secondary battery: Assemble the positive electrode, negative electrode and separator together.

18. The preparation method according to claim 17, characterized in that: The solid content of the carbon nanotube slurry is greater than 1% and less than or equal to 2%.

19. The preparation method according to any one of claims 17 to 18, characterized in that: The viscosity of the carbon nanotube slurry is ≤1200 mPa·s; The carbon nanotube slurry, after being left to stand at 20℃~30℃ for 3 months, has a viscosity ≤3500mpa.s.

20. The preparation method according to any one of claims 17 to 19, characterized in that: The aspect ratio of the carbon nanotubes is 100 to 100,000; The specific surface area of the carbon nanotubes is > 800 m 2 / g.

21. The preparation method according to any one of claims 17 to 20, characterized in that: The preparation of the positive electrode slurry also includes adding carbon black to the second organic solvent; The carbon black has a specific surface area of 60 m 2 / g; and / or, The resistivity of the carbon black powder is less than 0.03 Ω·cm; and / or, The median particle size Dv50 of the carbon black is less than or equal to 30 μm.

22. The preparation method according to any one of claims 17 to 21, characterized in that: The first hydrogenated nitrile rubber is dispersed in N-methylpyrrolidone to form a liquid with a mass percentage content of 8%, and the viscosity of the liquid is 300 mPa·s to 1800 mPa·s.

23. The preparation method according to any one of claims 17 to 22, characterized in that: The preparation of the positive electrode slurry further includes adding a second hydrogenated nitrile butadiene rubber to the second organic solvent, wherein the weight-average molecular weight of the second hydrogenated nitrile butadiene rubber is greater than 200,000 and less than 500,000; and / or, The degree of hydrogenation of the second hydrogenated nitrile rubber is less than 99%.

24. An electrical device, characterized in that: The lithium-ion secondary battery includes any one of claims 1 to 16 or any one of claims 17 to 23 prepared by the method thereof.

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