Secondary battery, preparation method thereof and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly discloses a secondary battery, a preparation method thereof and a power utilization device, the secondary battery comprises a positive pole piece, the positive pole piece comprises a positive pole current collector and a positive pole film layer located on at least one side surface of the positive pole current collector, the positive electrode film layer comprises a positive electrode active material, a carbon nanotube, a first dispersing agent and a second dispersing agent, the first dispersing agent comprises hydrogenated nitrile rubber and a modified compound thereof, and the second dispersing agent comprises a polyvinylpyrrolidone modified compound; the polyvinylpyrrolidone modified compound comprises a structural unit derived from a vinyl pyrrolidone monomer and a structural unit derived from a solvated chain monomer, and the solvated chain monomer comprises any one or more of ethylene oxide, propylene oxide and C2-9 olefin. The design mode is beneficial to improving the conductivity of the positive pole piece and reducing the direct-current internal resistance of the battery.

Description

Technical Field

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

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

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

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

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

[0006] The aforementioned positive electrode sheet includes a positive current collector and a positive electrode film layer located on at least one side of the surface of the positive current collector. The positive electrode film layer includes a positive active material, carbon nanotubes, a first dispersant, and a second dispersant. The first dispersant includes hydrogenated nitrile rubber and its modified compounds, and the second dispersant includes a polyvinylpyrrolidone modified compound.

[0007] Polyvinylpyrrolidone modified compounds include structural units derived from vinylpyrrolidone monomers and structural units derived from solvated chain monomers, including ethylene oxide, propylene oxide, and C64. 2～9 Any one or more of olefins. The first dispersant in this application can stabilize carbon nanotubes, but because the addition of the first dispersant easily leads to a relatively high viscosity of the carbon nanotube dispersion and problems such as gelation, this application chooses to use the first dispersant in combination with the second dispersant, which helps to reduce the probability of gelation in the carbon nanotube dispersion. At the same time, the second dispersant, by reducing the aggregation between carbon nanotubes and between them and the positive electrode active material, helps to improve the conductivity of the electrode and reduce the DC internal resistance of the battery.

[0008] In some embodiments of this application, the mass ratio between the first dispersant and the second dispersant is (6-23):(7-27).

[0009] Both the first and second dispersants in this application are beneficial for improving the dispersibility of carbon nanotubes. Using them in combination, and controlling the ratio within the aforementioned range, not only helps alleviate the increased dispersion viscosity caused by the first dispersant, but also reduces the probability of agglomeration of the positive electrode active material, thereby improving the conductivity of the electrode and reducing the DC internal resistance of the battery. Simultaneously, the uniform dispersion of all components in the positive electrode further improves the cycle stability of the battery.

[0010] In some embodiments of this application, the mass percentage content of the first dispersant in the above-mentioned positive electrode film layer is A1, which satisfies 0 < A1 ≤ 0.4%.

[0011] The mass percentage content of the first dispersant in the positive electrode film layer of this application is controlled within the above-mentioned range, which is beneficial to improving the dispersibility of carbon nanotubes and reducing the probability of increased dispersion viscosity.

[0012] In some embodiments of this application, the mass percentage content of the second dispersant in the positive electrode film layer is A2, satisfying 0 < A2 ≤ 0.5%.

[0013] The mass percentage content of the second dispersant in the positive electrode film layer of this application is controlled within the above-mentioned range, which is beneficial to improving the dispersibility of carbon nanotubes and also to improving the dispersibility of positive electrode active materials.

[0014] In some embodiments of this application, the weight-average molecular weight of the polyvinylpyrrolidone modified compound is 5,000 to 100,000.

[0015] In some embodiments of this application, the structural units derived from vinylpyrrolidone monomers account for 7% to 55% by mass in the above-mentioned polyvinylpyrrolidone modified compounds;

[0016] In some embodiments of this application, the structural units derived from the solvated chain monomers account for 40% to 75% by mass in the above-mentioned polyvinylpyrrolidone modified compounds.

[0017] In some embodiments of this application, the polyvinylpyrrolidone modified compound further includes structural units derived from crosslinking monomers; the crosslinking monomers include any one or more of trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated glycerol triacrylate, pentaerythritol triacrylate, and pentaerythritol triallyl ether.

[0018] The crosslinking monomer of this application enables the polyvinylpyrrolidone modified compound to have a network structure. This network structure anchors carbon nanotubes and positive electrode active materials through the vinylpyrrolidone monomer, and the carbon nanotubes and positive electrode active materials are fully and effectively dispersed by means of the network structure.

[0019] In some embodiments of this application, the structural units derived from the crosslinking monomer constitute 3% to 25% by mass in the aforementioned polyvinylpyrrolidone modified compound. In some embodiments of this application, the weight-average molecular weight of the hydrogenated nitrile rubber and its modified compound is 50,000 to 200,000.

[0020] In some embodiments of this application, hydrogenated nitrile butadiene rubber and its modified compounds comprise structural units derived from acrylonitrile monomers, wherein the mass percentage content of the structural units derived from acrylonitrile monomers is 20% to 40%.

[0021] In some embodiments of this application, the degree of hydrogenation of hydrogenated nitrile rubber and its modified compounds is ≥99%.

[0022] In some embodiments of this application, the positive electrode film layer also includes carbon black.

[0023] The conductive agent in the positive electrode film layer of this application may contain only carbon nanotubes, or it may contain carbon nanotubes and carbon black. In some embodiments of this application, the conductive agents used in combination are chosen. Compared with a single carbon nanotube conductive agent, this approach is more convenient for controlling the amount of carbon nanotubes used and also helps to bring out the conductivity of the dotted carbon black and linear carbon nanotubes.

[0024] In some embodiments of this application, the mass percentage content of carbon black in the above-mentioned positive electrode film layer is 0 to 2.5%.

[0025] In some embodiments of this application, the specific surface area of ​​the carbon black is BET ≥ 100 m². 2 / g.

[0026] In some embodiments of this application, the mass percentage content of carbon nanotubes in the above-mentioned positive electrode film layer is ≥0.2%.

[0027] In some embodiments of this application, the carbon nanotubes include any one or more of multi-walled carbon nanotubes and single-walled carbon nanotubes. In some embodiments of this application, the specific surface area (BET) of the carbon nanotubes is 200 m². 2 / g~1500m 2 / g.

[0028] In some embodiments of this application, the average diameter of the carbon nanotubes is 1 nm to 15 nm.

[0029] In some embodiments of this application, the mass percentage content of the carbon nanotubes in the positive electrode film layer is 0.2% to 0.8%.

[0030] In some embodiments of this application, the mass percentage content of the positive electrode active material in the above-mentioned positive electrode film layer is ≥96%.

[0031] In some embodiments of this application, the aforementioned positive electrode active material comprises any one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure.

[0032] In some embodiments of this application, the positive electrode film layer further includes a binder, which includes one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0033] In some embodiments of this application, the positive electrode film layer further includes a binder, which includes polyvinylidene fluoride.

[0034] In some embodiments of this application, the polyvinylidene fluoride contains a carboxyl functional group, and the mass percentage content of the carboxyl functional group in the polyvinylidene fluoride is ≤2.0%.

[0035] In some embodiments of this application, the viscosity of the polyvinylidene fluoride liquid with a mass percentage content of 3% is 3000 mPa·s to 5000 mPa·s.

[0036] In some embodiments of this application, the weight-average molecular weight of polyvinylidene fluoride is 2 million to 4 million.

[0037] In some embodiments of this application, the mass percentage content of polyvinylidene fluoride in the above-mentioned positive electrode film layer is ≤1.5%.

[0038] The second aspect of this application is to provide a method for preparing a secondary battery, comprising the following preparation process:

[0039] Preparation of carbon nanotube dispersion: Carbon nanotube powder, a first dispersant and a second dispersant are dispersed in a first solvent to form a carbon nanotube dispersion; the first dispersant includes hydrogenated nitrile rubber and its modified compounds, and the second dispersant includes a polyvinylpyrrolidone modified compound;

[0040] Polyvinylpyrrolidone modified compounds include structural units derived from vinylpyrrolidone monomers and structural units derived from solvated chain monomers, including ethylene oxide, propylene oxide, and C64. 2～9 Any one or more of the olefins;

[0041] Preparation of positive electrode sheet: The positive electrode active material and carbon nanotube dispersion are dispersed in a second solvent to form a positive electrode slurry. The positive electrode slurry is coated on at least one side of the positive electrode current collector and dried to form a positive electrode sheet.

[0042] A secondary battery is formed by stacking positive electrode plates, negative electrode plates, and a separator.

[0043] In some embodiments of this application, the viscosity of the carbon nanotube dispersion is ≤1000 mPa·s.

[0044] This application selects to use the first dispersant and the second dispersant together, which helps to reduce the probability of gelation in the carbon nanotube dispersion.

[0045] In some embodiments of this application, the carbon nanotube dispersion is left to stand at 20°C to 30°C for 3 months, and the viscosity is ≤3600 mPa·s.

[0046] This application selects to use the first dispersant and the second dispersant together, and the resulting carbon nanotube dispersion has relatively stable properties. Even if it is left at room temperature for a period of time, there will be no significant change in viscosity.

[0047] In some embodiments of this application, the solid content of the carbon nanotube dispersion is ≥50%.

[0048] In some embodiments of this application, the solid content of the above-mentioned carbon nanotube dispersion is 50% to 80%.

[0049] In some embodiments of this application, the mass percentage content of carbon nanotubes in the carbon nanotube dispersion is ≥50%.

[0050] In some embodiments of this application, the average length of the carbon nanotubes in the carbon nanotube dispersion is <15 μm.

[0051] In some embodiments of this application, the aspect ratio of the carbon nanotubes in the carbon nanotube dispersion is >150.

[0052] In some embodiments of this application, the mass percentage content of hydrogenated nitrile rubber and its modified compounds in the carbon nanotube dispersion is ≥15%.

[0053] In some embodiments of this application, the mass percentage content of the polyvinylpyrrolidone modified compound in the carbon nanotube dispersion is ≥18%.

[0054] In some embodiments of this application, the mass percentage content of carbon nanotubes in the above-mentioned carbon nanotube dispersion is 50% to 65%.

[0055] In some embodiments of this application, the mass percentage content of hydrogenated nitrile rubber and its modified compounds in the above-mentioned carbon nanotube dispersion is 15% to 30%.

[0056] In some embodiments of this application, the mass percentage content of the polyvinylpyrrolidone modified compound in the above-mentioned carbon nanotube dispersion is 18% to 25%. In some embodiments of this application, the carbon nanotube powder satisfies: DV 50 The range is 10nm to 60nm, DV 90 The wavelength range is 40nm to 120nm.

[0057] In some embodiments of this application, the volume resistivity of the carbon nanotube powder is 20 Ω·cm to 100 Ω·cm.

[0058] In some embodiments of this application, the average length of the carbon nanotube powder is >20 μm.

[0059] In some embodiments of this application, the aspect ratio of the carbon nanotube powder is >1000. In some embodiments of this application, the first solvent and the second solvent each independently include one or more of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, acetone, dimethyl carbonate, and polycarbonate.

[0060] A third aspect of this application is to provide an electrical device comprising a secondary battery of the first aspect or a secondary battery prepared by the method of the second aspect.

[0061] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0062] 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:

[0063] Figure 1 This is a schematic diagram of the battery structure of some embodiments of this application;

[0064] Figure 2This is an exploded structural diagram of a battery according to some embodiments of this application;

[0065] Figure 3 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0066] Figure 4 This is a schematic diagram of the battery pack structure according to some embodiments of this application;

[0067] Figure 5 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0068] Figure 6A This is a schematic diagram of the structure of a negative electrode sheet in some embodiments of this application;

[0069] Figure 6B This is a schematic diagram of another structure of the negative electrode sheet in some embodiments of this application.

[0070] The reference numerals in the detailed embodiments are as follows:

[0071] 10000, vehicles;

[0072] 1000, Battery; 2000, Controller; 3000, Motor;

[0073] 100. Battery cell;

[0074] 200. Box body; 210. First part; 220. Second part;

[0075] 10. Secondary batteries;

[0076] 101. Housing; 102. Electrode assembly; 103. Cover plate;

[0077] 1. Negative electrode plate;

[0078] 2. Positive electrode plate; 21. Positive current collector; 22. Positive electrode film;

[0079] 3. Separating membrane;

[0080] x-axis: The stacking direction or thickness direction of the electrodes;

[0081] The y-axis of the coordinate axis represents the length or width of the electrode. Detailed Implementation

[0082] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, and its power-consuming device according to this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0083] 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" and "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.

[0084] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0085] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0086] 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.

[0087] 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.

[0088] 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).

[0089] 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.

[0090] 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).

[0091] 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.

[0092] Due to their advantages such as high energy density, long cycle life, and safety and reliability, rechargeable batteries have been widely used in various products. In recent years, with the significant increase in demand for rechargeable batteries as an energy source, higher requirements have been placed on their performance, such as high energy density and high conductivity.

[0093] The energy density of a battery refers to the amount of energy stored in a certain space or mass of material. Generally speaking, the energy density of a battery mainly depends on the proportion of active materials. However, to ensure that the battery can cycle through charging and discharging, many inactive materials, such as conductive additives, are also needed to play a role.

[0094] If the conductivity of the conductive additive can be improved and the proportion of active material can be increased without affecting the battery's cycle charge and discharge performance, it will help improve the battery's conductivity, thereby increasing the battery's energy density and reducing electrode polarization, thus further improving the battery's cycle stability.

[0095] Based on the above considerations, in order to improve the conductivity of the electrode and reduce the DC resistance of the battery, a secondary battery and power-consuming device were obtained by conducting relevant experimental research based on the above design concept.

[0096] First, this application discloses a secondary battery, which includes a positive electrode, a separator, and a negative electrode. The positive electrode, separator, and negative electrode are sequentially stacked to form a wound cell or a stacked cell. Simultaneously, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, carbon nanotubes, a first dispersant, and a second dispersant. The first dispersant includes hydrogenated nitrile rubber and its modified compounds, and the second dispersant includes a polyvinylpyrrolidone modified compound. The polyvinylpyrrolidone modified compound includes structural units derived from vinylpyrrolidone monomers and structural units derived from solvated chain monomers. The solvated chain monomers include ethylene oxide, propylene oxide, and C... 2～9 Any one or more of the olefins.

[0097] In this application, carbon nanotubes in the positive electrode film serve as a conductive agent. Due to their excellent conductivity, they can exert their conductive function with a relatively small amount. However, carbon nanotubes are prone to aggregation, which affects their conductivity. This application employs a first dispersant and a second dispersant working synergistically to further improve the dispersion of carbon nanotubes. This allows the carbon nanotubes to exhibit excellent conductivity with relatively controlled usage, thereby improving the conductivity of the electrode and reducing the DC internal resistance of the battery.

[0098] Therefore, the secondary battery provided in this application helps reduce electrode polarization, thereby improving battery cycle stability and enhancing user experience. The secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte composed of the aforementioned secondary battery. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, including but not limited to polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0099] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 10.

[0100] According to some embodiments of this application, reference is made to Figure 2 The outer packaging may include a housing 101 and a cover plate 103. The housing 101 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 102 by a winding process or a stacking process. The electrode assembly 102 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 102. The secondary battery 10 may contain one or more electrode assemblies 102, which can be selected by those skilled in the art according to specific practical needs.

[0101] The electrode assembly 102 provided in this application is beneficial to improving the performance of a secondary battery when applied in a secondary battery. The secondary battery can be a power source for an electrical device or an energy storage unit for an electrical device. The electrical device is applied in the power field, such as mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited to the above fields.

[0102] For ease of explanation, some embodiments of this application are illustrated using a vehicle as an example of an electrical device.

[0103] 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.

[0104] 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.

[0105] 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 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.

[0106] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220, which overlap each other, and together define a receiving space for accommodating the secondary battery 100. The second portion 220 may be a hollow structure with one open end, and the first portion 210 may be a plate-like structure, with the first portion 210 covering the open side of the second portion 220 so that the first portion 210 and the second portion 220 together define the receiving space; alternatively, the first portion 210 and the second portion 220 may both be hollow structures with one open side, with the open side of the first portion 210 covering the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may be of various shapes, such as a cylinder, a cuboid, etc.

[0107] 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.

[0108] Secondary batteries

[0109] This application discloses a secondary battery in some embodiments, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode, separator, and negative electrode are sequentially stacked together to form the secondary battery using a winding or stacking process. Meanwhile, 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 electrode active material, carbon nanotubes, a first dispersant, and a second dispersant. The first dispersant includes hydrogenated nitrile rubber and its modified compounds, and the second dispersant includes a polyvinylpyrrolidone modified compound. The polyvinylpyrrolidone modified compound includes structural units derived from vinylpyrrolidone monomers and structural units derived from solvated chain monomers, wherein the solvated chain monomers include ethylene oxide, propylene oxide, and C... 2～9 Any one or more of the olefins.

[0110] The positive electrode, separator, and negative electrode of this application can be formed into a secondary battery using winding or stacking processes. Specifically, this application... Figure 5 The diagram illustrates a secondary battery 10 formed using a stacking method, combined with... Figure 5 It is known that a negative electrode 1 or a positive electrode 2 is placed between two adjacent separators 3, and the negative electrode 1 and the positive electrode 2 are alternately arranged along the stacking direction (coordinate axis x direction). The number and size of the negative electrode 1 and / or the positive electrode 2 can be selected according to the actual situation, and will not be elaborated in this application. Furthermore, this application... Figure 5 The image only illustrates one type of lamination method; other lamination or winding methods are within the scope of protection of this application.

[0111] like Figure 6A and 6B 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 6B This diagram illustrates the placement of a positive electrode film layer 22 on either side of the surface of the positive electrode current collector 21. Figure 6A 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.

[0112] The hydrogenated nitrile butadiene rubber (NBR) in this application refers to the product obtained by hydrogenating and saturating the carbon-carbon double bonds in the molecular chain of NBR. NBR is a polymer synthesized from acrylonitrile and butadiene monomers. The polymer in this application refers to an aggregate of chemically homogeneous macromolecules prepared through polymerization reactions, but differing in degree of polymerization, molar mass, and chain length. The modified compounds of hydrogenated NBR in this application generally refer to mixtures obtained through chemical modification, such as functional group modification of hydrogenated NBR, where functional groups include, but are not limited to, carboxyl, ester, and amide groups. Hydrogenated NBR, as a primary dispersant for carbon nanotubes, is beneficial for increasing the carbon nanotube content in the carbon nanotube dispersion, i.e., improving the carbon nanotube content in the carbon nanotube dispersion.

[0113] The polyvinylpyrrolidone modified compounds of this application comprise polymers formed by polymerizing vinylpyrrolidone monomers and solvated chain monomers. The solvated chain monomers include any one or more of ethylene oxide, propylene oxide, ethylene, propylene, butene, pentene, hexene, heptene, octene, and nonene.

[0114] The hydrogenated nitrile butadiene rubber (HNBR) in this application can stabilize carbon nanotubes. However, the addition of HNBR and its modified compounds results in a relatively high viscosity of the carbon nanotube dispersion and a tendency for gelation. Therefore, this application further selects a polyvinylpyrrolidone (PVP) modified compound. The PPVP modified compound not only acts as a dispersant to further improve the dispersibility of carbon nanotubes, but also, when used in combination with HNBR and its modified compounds, alleviates the increased viscosity of the dispersion caused by HNBR, thus promoting the conductivity of the carbon nanotubes. Furthermore, when the second dispersant is a PPVP modified compound, the PPVP in this compound acts as an anchoring group, firmly anchoring to the surface of the carbon nanotubes and the positive electrode active material, while providing electrostatic repulsion. The solvated polymer chains formed by the solvated monomers provide steric hindrance, reducing agglomeration between carbon nanotubes and between the carbon nanotubes and the positive electrode active material. Therefore, the design method provided in this application is beneficial for improving the conductivity of the electrode and reducing the DC internal resistance of the battery.

[0115] The solvated chain monomers in this application include one or more of ethylene oxide, propylene oxide, ethylene, propylene, butene, pentene, hexene, heptene, octene, and nonene. Among them, this application lists solvated chain monomers containing specific types of functional groups. These specific types of functional groups can reduce the probability of the solvated chain monomers themselves becoming coiled or entangled, which is beneficial for providing certain steric hindrance. Compared with single polyvinylpyrrolidone compounds, introducing solvated polymer segments containing specific types of solvated chain monomers into polyvinylpyrrolidone modified compounds is beneficial for reducing the aggregation phenomenon between carbon nanotubes and between carbon nanotubes and positive electrode active materials.

[0116] This application also discloses a method for preparing polyvinylpyrrolidone modified compounds in these embodiments. Specifically, vinylpyrrolidone monomer and solvated chain monomer are dispersed in an organic solvent such as N-methylpyrrolidone in a certain amount, and a polymerization reaction is carried out under the action of a conventional initiator such as azobisisobutyronitrile and a catalyst to obtain polyvinylpyrrolidone modified compounds.

[0117] The qualitative method for identifying the first and second dispersants in the electrode sheet of this application includes separating such substances from the electrode sheet and then determining them using infrared spectroscopy and X-ray photoelectron spectroscopy or in combination with conventional methods in the art.

[0118] In some embodiments of this application, the compaction density of the above-mentioned positive electrode film layer is 3.2 g / cm³. 2 ~3.7g / cm 2 .

[0119] The compaction density of the positive electrode film in this application can be used to characterize the energy density of the material. The compaction density of the positive electrode film = areal density of the positive electrode film / thickness of the positive electrode film. The thickness of the positive electrode film includes the distance between the two end faces of the positive electrode film along the thickness direction. The areal density of the positive electrode film = weight of a single-sided positive electrode film / area of ​​a single-sided positive electrode film. The weight of a single-sided positive electrode film can be obtained by weighing, and the area of ​​a single-sided positive electrode film can be obtained using an area calculation formula based on the film shape. The calculation method for the compaction density of the positive electrode film is given in subsequent specific embodiments of this application.

[0120] In these embodiments, this application discloses that the compaction density of the positive electrode film is 3.2 g / cm³. 2 3.3g / cm 2 3.4g / cm 2 3.5g / cm 2 3.6g / cm 2 3.7g / cm 2 Any one of the above values ​​or any one of the above range values.

[0121] In some embodiments of this application, the mass ratio between the first dispersant and the second dispersant is (6-23):(7-27).

[0122] Both the first and second dispersants in this application are beneficial for improving the dispersibility of carbon nanotubes. Using them in combination, and controlling the ratio within the aforementioned range, not only helps alleviate the increased dispersion viscosity caused by the first dispersant, but also reduces the probability of agglomeration of the positive electrode active material, thereby improving the conductivity of the electrode and reducing the DC internal resistance of the battery. Simultaneously, the uniform dispersion of all components in the positive electrode further improves the cycle stability of the battery.

[0123] In these embodiments, the present application provides that the mass ratio between the first dispersant and the second dispersant is any one of 6:7, 14:17, 15:19, 18:16, 23:17, 22:27 or any one of the above range values.

[0124] In some embodiments of this application, the mass percentage content of the first dispersant in the positive electrode film layer is A1, satisfying 0 < A1 ≤ 0.4%, and further selected as 0 < A1 ≤ 0.2%. In some embodiments of this application, the mass percentage content of the second dispersant in the positive electrode film layer is A2, satisfying 0 < A2 ≤ 0.5%, and further selected as 0.02% ≤ A1 ≤ 0.4%.

[0125] The contents of the first and second dispersants in this application refer to the amount added during the preparation of the secondary battery. Since they are relatively stable in the positive electrode, their contents change little. Meanwhile, after determining the specific types of the first and second dispersants using the qualitative method described above, their contents can be further calculated using inductively coupled plasma mass spectrometry (ICP-MS).

[0126] The mass percentage content of the first dispersant in the positive electrode film layer of this application is controlled within the above-mentioned range, which is beneficial to improving the dispersibility of carbon nanotubes and reducing the probability of increased dispersion viscosity.

[0127] The mass percentage content of the second dispersant in the positive electrode film layer of this application is controlled within the above-mentioned range, which is beneficial to improving the dispersibility of carbon nanotubes and also to improving the dispersibility of positive electrode active materials.

[0128] In these embodiments, this application discloses that the mass percentage content of the first dispersant in the positive electrode film layer includes 0.001%, 0.005%, 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%, and 0. Any one of the following: 18%, 0.19%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.4%, or any one of the values ​​within the above range.

[0129] In these embodiments, this application discloses that the mass percentage content of the second dispersant in the positive electrode film layer includes 0.001%, 0.005%, 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%, and 0. Any one of the following: 18%, 0.19%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.4%, or any one of the values ​​within the above range.

[0130] In some embodiments of this application, the weight-average molecular weight of the polyvinylpyrrolidone modified compound is 5,000 to 100,000, and more preferably 10,000 to 100,000.

[0131] 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.

[0132] The method for testing the weight-average molecular weight of the polyvinylpyrrolidone modified compound in this application includes: as described above, after qualitative and quantitative testing of the polyvinylpyrrolidone modified compound in the electrode, further testing is performed using gel chromatography to obtain the weight-average molecular weight.

[0133] This application discloses in these embodiments that the weight-average molecular weights of the polyvinylpyrrolidone modified compounds include 5000, 6000, 7000, 8000, 9000, 10,000, 12,000, 14,000, 16,000, 18,000, 20,000, 22,000, 24,000, 26,000, 28,000, 30,000, 32,000, 34,000, 36,000, 38,000, 40,000, 42,000, 44,000, and 46,000. The value is any one of the following: 10,000, 48,000, 50,000, 52,000, 54,000, 56,000, 58,000, 60,000, 62,000, 64,000, 66,000, 68,000, 70,000, 72,000, 74,000, 76,000, 78,000, 80,000, 82,000, 84,000, 86,000, 88,000, 90,000, 92,000, 94,000, 96,000, 98,000, 100,000, or any one of the values ​​within the above range.

[0134] In some embodiments of this application, the structural units derived from vinylpyrrolidone monomers account for 7% to 55% by mass in the polyvinylpyrrolidone modified compound.

[0135] As described above, after performing qualitative and quantitative tests on the polyvinylpyrrolidone modified compound in the electrode, the mass percentage content of the structural units derived from the vinylpyrrolidone monomer in the polyvinylpyrrolidone modified compound can be further calculated.

[0136] This application discloses in these embodiments that the mass percentage content of structural units derived from vinylpyrrolidone monomers in polyvinylpyrrolidone modified compounds includes 7%, 7.2%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 25.2%, 26%, and 27%. Any one of the following: %, 28%, 29%, 30%, 30.6%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 53.4%, 54%, 55%, or any one of the values ​​within the above range.

[0137] In some embodiments of this application, the structural units derived from solvated chain monomers account for 40% to 75% by mass in the polyvinylpyrrolidone modified compound.

[0138] As described above, after performing qualitative and quantitative tests on the polyvinylpyrrolidone modified compound in the electrode, the mass percentage content of the structural unit derived from the solvated chain monomer in the polyvinylpyrrolidone modified compound can be further calculated. This application discloses in these embodiments that the mass percentage content of the solvated chain monomer in the polyvinylpyrrolidone modified compound comprises any one of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 46.6%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 68.6%, 69%, 69.4%, 70%, 71%, 72%, 73%, 74%, 74.8%, 75% or satisfies any of the above ranges.

[0139] In some embodiments of this application, the polyvinylpyrrolidone modified compound further includes structural units derived from crosslinking monomers; the crosslinking monomers include any one or more of trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated glycerol triacrylate, pentaerythritol triacrylate, and pentaerythritol triallyl ether.

[0140] This application further incorporates structural units derived from crosslinking monomers into the polyvinylpyrrolidone modified compound. These structural units possess multifunctional branched structures, thereby giving the polyvinylpyrrolidone modified compound a network structure. This network structure anchors carbon nanotubes and positive electrode active materials through vinylpyrrolidone monomers, and the carbon nanotubes and positive electrode active materials are fully and effectively dispersed through the network structure.

[0141] In some embodiments of this application, the crosslinking monomer content in the polyvinylpyrrolidone modified compound is 3% to 25% by mass.

[0142] As described above, after performing qualitative and quantitative tests on the polyvinylpyrrolidone modified compound in the electrode, the mass percentage content of the structural units derived from the crosslinking monomer in the polyvinylpyrrolidone modified compound can be further calculated. In these embodiments, this application discloses that the mass percentage content of the crosslinking monomer in the polyvinylpyrrolidone modified compound includes any one of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 24.2%, and 25%, or any value within the above range.

[0143] This application also discloses a method for preparing polyvinylpyrrolidone modified compounds in these embodiments. Specifically, vinylpyrrolidone monomer, solvated chain monomer, and crosslinking monomer are dispersed in an organic solvent such as N-methylpyrrolidone in a certain amount, and a polymerization reaction is carried out under the action of a conventional initiator such as azobisisobutyronitrile and a catalyst to obtain polyvinylpyrrolidone modified compounds.

[0144] In some embodiments of this application, the weight-average molecular weight of hydrogenated nitrile rubber and its modified compounds is 50,000 to 200,000, and more preferably 50,000 to 150,000.

[0145] The method for testing the weight-average molecular weight of hydrogenated nitrile butadiene rubber and its modified compounds in this application includes, as described above, qualitative and quantitative tests of hydrogenated nitrile butadiene rubber and its modified compounds in an electrode, followed by further testing using gel chromatography to obtain the weight-average molecular weight.

[0146] This application discloses in these embodiments that the weight average molecular weight of hydrogenated nitrile butadiene rubber and its modified compounds includes any one or more of the following: 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 105,000, 110,000, 112,000, 115,000, 120,000, 125,000, 130,000, 135,000, 140,000, 145,000, and 150,000.

[0147] In some embodiments of this application, hydrogenated nitrile butadiene rubber and its modified compounds contain structural units derived from acrylonitrile monomers, with the mass percentage content of the structural units derived from acrylonitrile monomers being 20% ​​to 40%.

[0148] The hydrogenated nitrile butadiene rubber of this application is a product obtained by further hydrogenating the carbon-carbon double bond of a polymer synthesized from acrylonitrile and butadiene monomers. The modified compounds of hydrogenated nitrile butadiene rubber generally refer to mixtures obtained through chemical modification, such as functional group modification of hydrogenated nitrile butadiene rubber, where the functional groups include, but are not limited to, carboxyl, ester, and amide groups. As described above, after qualitative and quantitative testing of the hydrogenated nitrile butadiene rubber and its modified compounds in the electrode, the mass percentage content of acrylonitrile can be easily calculated.

[0149] In these embodiments, this application discloses that the mass percentage content of structural units derived from acrylonitrile monomers in hydrogenated nitrile butadiene rubber and its modified compounds comprises any one or more of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%.

[0150] In some embodiments of this application, the degree of hydrogenation of hydrogenated nitrile rubber and its modified compounds is ≥99%.

[0151] The degree of hydrogenation in this application 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. The degree of hydrogenation is then (100% - double bond content).

[0152] In some embodiments of this application, the positive electrode film layer also includes carbon black.

[0153] The conductive agent in the positive electrode film layer of this application may contain only carbon nanotubes, or it may contain carbon nanotubes and carbon black. In some embodiments of this application, the conductive agents used in combination are chosen. Compared with a single carbon nanotube conductive agent, this approach is more convenient for controlling the amount of carbon nanotubes used and also helps to bring out the conductivity of the dotted carbon black and linear carbon nanotubes.

[0154] In some embodiments of this application, the mass percentage content of carbon black in the positive electrode film layer is 0-2.5%. In some embodiments of this application, the mass percentage content of carbon black in the positive electrode film layer is further selected to be 0-1.2%.

[0155] The carbon black content in this application refers to the amount added during the preparation of secondary batteries. Since it is relatively stable in the positive electrode, the content changes little.

[0156] This application can also scan the carbon black and carbon nanotubes in the electrode using a high-magnification electron microscope, and then separate the carbon black and carbon nanotubes by means of dissolution and separation.

[0157] In these embodiments, this application discloses that the mass percentage content of carbon black in the positive electrode film layer includes any one of 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, and 2.5%, or any one of the above ranges.

[0158] In some embodiments of this application, the specific surface area of ​​the carbon black is BET ≥ 100 m². 2 / g.

[0159] As described above, after successfully separating carbon black and carbon nanotubes, the specific surface area (BET) of carbon black is measured, and the measurement method is similar to that of carbon nanotubes.

[0160] In some embodiments of this application, the specific surface area (BET) of the carbon black is 100 m². 2 / g~1000m 2 / g. In these embodiments, the specific surface area (BET) of carbon black is given as 100 m². 2 / g~150m 2 / g, 120m 2 / g~180m 2 / g, 150m 2 / g~250m 2 / g、180m 2 / g~300m 2 / g、250m 2 / g~400m 2 / g、300m 2 / g~450m 2 / g、400m 2 / g~500m 2 / g、450m 2 / g~550m 2 / g、500m 2 / g~600m 2 / g、550m 2 / g~700m 2 / g、600m 2 / g~800m 2 / g、650m 2 / g~1000m 2 / g or any of the values ​​in the above range. In some embodiments of this application, the mass percentage content of carbon nanotubes in the positive electrode film is ≥0.2%.

[0161] In some embodiments of this application, the mass percentage content of carbon nanotubes in the positive electrode film layer is 0.2% to 0.8%.

[0162] The carbon nanotube content in this application refers to the amount added during the preparation of secondary batteries. Since it is relatively stable in the positive electrode, the content changes little.

[0163] As described above, after successfully separating carbon black and carbon nanotubes, the mass percentage content of carbon nanotubes in the positive electrode film layer is calculated. In these embodiments, this application discloses that the mass percentage content of carbon nanotubes in the positive electrode film layer includes any one of 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, and 0.85%, or multiple values ​​within the above range.

[0164] In some embodiments of this application, carbon nanotubes include any one or more of multi-walled carbon nanotubes and single-walled carbon nanotubes.

[0165] 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.

[0166] In some embodiments of this application, the specific surface area (BET) of the carbon nanotubes is 200 m². 2 / g~1500m 2 / g.

[0167] In these embodiments, the specific surface area (BET) of carbon nanotubes is given as 200 m². 2 / g~300m 2 / g、250m 2 / g~400m 2 / g、300m 2 / g~450m 2 / g、400m 2 / g~500m 2 / g、450m 2 / g~550m 2 / g、500m 2 / g~600m 2 / g、550m 2 / g~700m 2 / g、600m2 / g~800m 2 / g、650m 2 / g~1000m 2 / g、700m 2 / g~1100m 2 / g、800m 2 / g~1200m 2 / g、900m 2 / g~1200m 2 / g, 1000m 2 / g~1500m 2 / g, or any one of the values ​​in the above range.

[0168] 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.

[0169] 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 the adsorption amount of nitrogen is measured by adjusting different test pressures. 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.

[0170] As described above, this application measures the specific surface area (BET) of carbon nanotubes. The measurement method includes obtaining adsorption and desorption isotherms of the carbon nanotubes. For example, an ASAP2460 physical adsorption analyzer is used. 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 nanotubes is calculated based on these adsorption and desorption isotherms.

[0171] In some embodiments of this application, the average diameter of the carbon nanotubes is 1 nm to 15 nm.

[0172] The average diameter of the carbon nanotubes in this application refers to the average outer diameter of the carbon nanotubes.

[0173] This application discloses in some embodiments that the average diameter of carbon nanotubes includes any one of 1nm, 2nm, 3nm, 3.2nm, 3.4nm, 3.6nm, 3.8nm, 4nm, 4.2nm, 4.4nm, 4.6nm, 4.8nm, 5nm, 5.2nm, 5.4nm, 5.5nm, 5.6nm, 5.8nm, 6nm, 6.2nm, 6.4nm, 6.6nm, 6.8nm, 7nm, 8nm, 8.5nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, and 15nm, or multiple values ​​within the above range.

[0174] This application uses high-magnification electron microscopy to identify carbon nanotubes in the electrode and uses high-magnification electron microscopy to calculate the average diameter, average length and aspect ratio of the carbon nanotubes.

[0175] In some embodiments of this application, the mass percentage content of the positive electrode active material in the positive electrode film layer is ≥96%.

[0176] The content of the positive electrode active material in this application refers to the amount added during the preparation of the secondary battery. In this application, the positive electrode active material is separated from the positive electrode sheet and its content is calculated. In these embodiments, this application discloses that the mass percentage content of the positive electrode active material in the positive electrode film layer includes 97%, 97.5%, etc.

[0177] In some embodiments of this application, the above-mentioned positive electrode active material includes any one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure.

[0178] In some embodiments of this application, the positive electrode film layer further includes a binder, which includes one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0179] In some embodiments of this application, the positive electrode film layer further includes a binder, which includes polyvinylidene fluoride (PVDF). The PVDF contains carboxyl functional groups, and the mass percentage content of the carboxyl functional groups in the PVDF is ≤2.0%.

[0180] In some embodiments of this application, the carboxyl functional group has a mass percentage content of 0.5% to 1.5% in the polyvinylidene fluoride.

[0181] In some embodiments of this application, the viscosity of the polyvinylidene fluoride liquid with a mass percentage content of 3% is 3000 mPa·s to 5000 mPa·s.

[0182] The polyvinylidene fluoride adhesive of this application refers to a dispersion formed by dispersing polyvinylidene fluoride in N-methylpyrrolidone.

[0183] In these embodiments, this application provides a 3% by mass polyvinylidene fluoride adhesive with a viscosity of any one of 3000 mPa·s, 4000 mPa·s, or 5000 mPa·s, or any one of the above ranges.

[0184] The viscosity determination method in this application includes measurement using a rotational viscometer.

[0185] In some embodiments of this application, the weight-average molecular weight of polyvinylidene fluoride is 2 million to 4 million.

[0186] In this application, polyvinylidene fluoride is first separated from the electrode, and then it is characterized by infrared spectroscopy and X-ray photoelectron spectroscopy.

[0187] In these embodiments, this application discloses that the weight-average molecular weight of polyvinylidene fluoride includes any one of 2,000,000, 2,100,000, 2,200,000, 2,300,000, 2,400,000, 2,500,000, 2,600,000, 2,700,000, 2,800,000, 2,900,000, 3,000,000, 3,100,000, 3,200,000, 3,300,000, 3,400,000, 3,500,000, 3,600,000, 3,700,000, 3,800,000, 3,900,000, and 4,000,000, or any one of the above ranges.

[0188] The method for testing the weight-average molecular weight of polyvinylidene fluoride in this application includes, as described above, qualitative testing of polyvinylidene fluoride in an electrode, followed by further testing using gel permeation chromatography to obtain the weight-average molecular weight.

[0189] In some embodiments of this application, the mass percentage content of polyvinylidene fluoride in the positive electrode film layer is ≤1.5%. In this application, the mass percentage content of polyvinylidene fluoride in the positive electrode film layer is greater than zero.

[0190] The content of polyvinylidene fluoride in the positive electrode film layer in this application refers to the amount added during the preparation of the secondary battery. Since polyvinylidene fluoride is stable in secondary batteries, its content changes little.

[0191] After determining the specific type of polyvinylidene fluoride using the qualitative method described above, this application can further calculate the content using inductively coupled plasma mass spectrometry (ICP-MS) and other methods.

[0192] In these embodiments, this application discloses that the mass percentage content of polyvinylidene fluoride includes 1.5%, 1.0%, etc.

[0193] [Positive electrode plate]

[0194] 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 contains a positive electrode active material.

[0195] According to some embodiments of this application, when the positive electrode sheet is applied to a lithium-ion battery, the positive electrode active material includes, but is not limited to, any one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphate with an olivine structure; wherein, the structural formula of the lithium phosphate with an olivine structure is: LiFe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y<1, 0≤x+y≤1, M contains one or more transition metal elements or non-transition metal elements other than Fe and Mn, and M preferably contains one or more of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr. This application specifically includes, but is not limited to, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 CO 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 CO 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 CO 0.15 Al 0.05 One or more of O2, LiFePO4 (LFP) and LiMnPO4.

[0196] According to some embodiments of this application, when the positive electrode sheet is applied to a sodium-ion battery, the positive electrode active material includes, but is not limited to, at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. Specifically, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and the sodium transition metal oxide is, for example, Na. xMO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 < x ≤ 1. Polyanionic compounds include sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, and one or more of these. Prussian blue compounds are Na... x M1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0 < x ≤ 2.

[0197] 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).

[0198] [Preparation method of positive electrode sheet]

[0199] According to some embodiments of this application, this application provides a method for preparing a positive electrode sheet, comprising the following preparation process:

[0200] S1. Preparation of carbon nanotube dispersion: Carbon nanotube powder, a first dispersant, and a second dispersant are dispersed in a first solvent to form a carbon nanotube dispersion; the first dispersant includes hydrogenated nitrile butadiene rubber and its modified compounds, and the second dispersant includes a polyvinylpyrrolidone modified compound; the polyvinylpyrrolidone modified compound includes structural units derived from vinylpyrrolidone monomers and structural units derived from solvated chain monomers, and the structural units derived from solvated chain monomers include ethylene oxide, propylene oxide, and C... 2～9 Any one or more of the olefins.

[0201] S2. Preparation of positive electrode slurry: The positive electrode active material, carbon nanotube dispersion and binder are dispersed in the second solvent and mixed thoroughly to form a positive electrode slurry.

[0202] S3. 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 prepare the positive electrode sheet.

[0203] In some embodiments of this application, the viscosity of the carbon nanotube dispersion is ≤1000 mPa·s.

[0204] In some embodiments of this application, the carbon nanotube dispersion was left to stand at 20°C to 30°C for 3 months, and the viscosity was ≤3600 mPa·s.

[0205] The viscosity measurement method in this application is the same as that described above, and is measured using a rotational viscometer.

[0206] In some embodiments of this application, the solid content of the carbon nanotube dispersion is ≥50%.

[0207] In some embodiments of this application, the solid content of the above-mentioned carbon nanotube dispersion is 50% to 80%.

[0208] The method for determining the solid content of the carbon nanotube dispersion in this application includes: weighing the carbon nanotube dispersion slurry by 3-4g, denoted as m1, drying the slurry in an oven (150℃ / 4h), weighing the solid residue, denoted as m2, and calculating the solid content as m2 / m1*100%.

[0209] In some embodiments of this application, the mass percentage content of carbon nanotubes in the carbon nanotube dispersion is ≥50%, for example, 50% to 65%;

[0210] In some embodiments of this application, the average length of the carbon nanotubes in the carbon nanotube dispersion is <15 μm.

[0211] In some embodiments of this application, the aspect ratio of the carbon nanotubes in the carbon nanotube dispersion is >150.

[0212] The average length and aspect ratio of the carbon nanotubes in the carbon nanotube dispersion of this application are both lower than those of the undispersed powder. The average length of the carbon nanotubes in the dispersion is determined by scanning electron microscopy. This application does not provide a lower limit for the average length of the carbon nanotubes in the dispersion or an upper limit for the aspect ratio; these can be determined based on the raw materials and dispersion conditions, and will not be elaborated upon here.

[0213] In some embodiments of this application, the mass percentage content of hydrogenated nitrile rubber and its modified compounds in the carbon nanotube dispersion is ≥15%, for example, 15% to 30%.

[0214] In some embodiments of this application, the mass percentage content of the polyvinylpyrrolidone modified compound in the carbon nanotube dispersion is ≥18%, for example, 18% to 25%.

[0215] In some embodiments of this application, the volumetric particle size distribution of the carbon nanotube powder satisfies: DV 50 The range is 10nm to 60nm, DV 90The wavelength range is 40nm to 120nm.

[0216] In this application, the volumetric particle size distribution Dv50 of the carbon nanotube powder includes particles larger than its diameter accounting for 50% of the volume, and particles smaller than its diameter also accounting for 50% of the volume; this is also known as the median diameter and is typically used to represent the average particle size. Dv90 includes particles smaller than its diameter accounting for 90% of the volume. The volumetric particle size distribution of this application can be measured using conventional methods in the art, such as using a particle size analyzer to determine the particle size distribution and then obtaining it statistically. In these embodiments, this application selects to use laser diffraction particle size analysis, specifically referring to standard GB / T19077-2016 to obtain the particle size distribution map, and then calculating it.

[0217] In some embodiments of this application, the volume resistivity of the carbon nanotube powder is 20 Ω·cm to 100 Ω·cm.

[0218] In this application, the volume resistivity of carbon nanotube powder refers to the resistance value of the powder material per unit length and unit area. The method for measuring this volume resistivity includes: 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 1.2 g, a powder probe unit (four-probe probe unit) using ring electrodes, an electrode spacing of 5.0 mm, an electrode radius of 1.0 mm, and a sample radius of 12.5 mm, measuring the volume resistivity [Ω·cm] of the conductive powder under various pressures with a 90 V voltage limiter applied.

[0219] In some embodiments of this application, the average length of the carbon nanotube powder is >20 μm.

[0220] In some embodiments of this application, the average length of the carbon nanotube powder is 25 μm to 100 μm.

[0221] In some embodiments, this application discloses that the average tube length of the carbon nanotube powder includes 20.5 μm, 21.5 μm, 22 μm, 25 μm, 28 μm, 35 μm, 55 μm, etc.

[0222] In some embodiments of this application, the aspect ratio of the carbon nanotube powder is >1000.

[0223] In some embodiments of this application, the aspect ratio of the carbon nanotube powder is >4000.

[0224] In some embodiments of this application, the aspect ratio of the carbon nanotube powder is >7000.

[0225] The aspect ratio of the carbon nanotube powder in this application refers to the ratio between the average length of the carbon nanotube powder and the average diameter of the carbon nanotube powder. This application does not give an upper limit value for the aspect ratio, but the upper limit value can be derived from the specific values ​​of the average length and average diameter of the carbon nanotube powder mentioned above. This application will not elaborate on it here.

[0226] The carbon nanotube powder of this application is considered to be almost one-dimensional, and therefore has a high aspect ratio.

[0227] This application discloses in some embodiments that the aspect ratio of the carbon nanotube powder includes 1005, 1012, 1020, etc. In some embodiments of this application, the first solvent and the second solvent each independently include N-methylpyrrolidone. The first solvent and the second solvent in this application are non-aqueous organic solvents, and may also include one or more of dimethylacetamide, N,N-dimethylformamide, acetone, dimethyl carbonate, polycarbonate, etc.

[0228] [Negative electrode plate]

[0229] 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.

[0230] In some embodiments, this application discloses that the compaction density of the negative electrode film layer is ≥1.65 g / cm³. 3 .

[0231] 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-sided positive electrode film / area of ​​a single-sided positive electrode film. The weight of a single-sided positive electrode film can be obtained by weighing, and the area of ​​a single-sided negative electrode film can be obtained using the area calculation formula based on the film shape. In these embodiments, this application lists a compaction density of the negative electrode film > 1.65 g / cm³. 3 .

[0232] 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, and hard carbon 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 or sodium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0233] In some embodiments, this application discloses that the negative electrode film layer contains a conductive agent, and the mass percentage of the conductive agent in the negative electrode film layer is 0% to 2.5%.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] [Isolation membrane]

[0238] 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.

[0239] 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.

[0240] 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.

[0241] Electrolyte

[0242] Electrolytes are disclosed in some embodiments of this application. The electrolyte in this application can be liquid, solid, or gel-like. Solid state refers to a solid electrolyte, liquid state to a liquid electrolyte, and gel-like state to a gel electrolyte. The secondary battery in this application uses a liquid electrolyte, i.e., an electrolyte solution. This electrolyte solution contains an electrolyte salt and an organic solvent. The electrolyte salt can be any type conventional in the art, such as, but not limited to, inorganic metal salts, such as RClO4, RAsF6, RPF6, RBF4, RSbF6, RSO3F, RN(FSO2)2, etc.; fluorinated organometallic salts, such as RCF3SO3, RN(FSO2)(CF3SO2), RN(CF3SO2)2, RN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonylimide lithium / sodium, cyclic 1,2-tetrafluoroethanedisulfonylimide lithium / sodium, RN(CF3SO2)(C4F9SO2). Examples of lithium salts containing dicarboxylic acid complexes include: RC(CF3SO2)3, RPF4(CF3)2, RPF4(C2F5)2, RPF4(CF3SO2)2, RPF4(C2F5SO2)2, RBF2(CF3)2, RBF2(C2F5)2, RBF2(CF3SO2)2, RBF2(C2F5SO2)2, etc.; and metal salts containing dicarboxylic acid complexes, such as lithium / sodium bis(oxalate)borate, lithium / sodium difluorooxalate borate, lithium / sodium tri(oxalate)phosphate, lithium / sodium difluorobis(oxalate)phosphate, lithium / sodium tetrafluoro(oxalate)phosphate, etc. Here, both the metal and R contain one or a combination of lithium ions and sodium ions.

[0243] 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.

[0244] 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).

[0245] 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).

[0246] The secondary battery of this application will be described in detail below with reference to specific embodiments.

[0247] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0248] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0249] 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.

[0250] Experimental materials:

[0251] 1. Graphite: Commercially available;

[0252] 2. NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 02) or lithium iron phosphate (LiFeO4): commercially available;

[0253] 3. Carbon nanotubes: Commercially available;

[0254] 4. First dispersant—hydrogenated nitrile butadiene rubber and its modified compounds: Zeon Corporation;

[0255] 5. Second dispersant—polyvinylpyrrolidone modified compound: prepared by Shanghai Sanrui Polymer Materials Co., Ltd. or in-house;

[0256] 6. Carbon black: Commercially available;

[0257] 7. PVDF: Commercially available.

[0258] Preparation Example 2-1:

[0259] Preparation of polyvinylpyrrolidone modified compound 2-1:

[0260] In this preparation example 2-1, vinylpyrrolidone monomer and ethylene oxide monomer were dispersed in N-methylpyrrolidone at a mass ratio of 1:2.3. A small amount of hydrogen peroxide (mass fraction of 30%) was used as a catalyst, and azobisisobutyronitrile (ANOVA) of about 120% of the mass of vinylpyrrolidone monomer was added. The polymerization reaction was initiated at about 15°C to obtain the polymer.

[0261] The polymers listed in Tables 1-2 below in this application are prepared using the same or similar preparation methods as those in this preparation example, or commercially available finished products can be used directly.

[0262] The specific raw material parameters used in each embodiment and comparative example are shown in the following list:

[0263] Raw Material Table 1-1 (Carbon Nanotube Powder)

[0264]

[0265] Raw materials table 1-2 (polyvinylpyrrolidone modified compounds)

[0266]

[0267] Raw Material Table 1-3 (Hydrogenated Nitrile Butadiene Rubber)

[0268]

[0269]

[0270] Raw Material Table 1-4 (Carbon Black)

[0271] Serial Number <![CDATA[Specific surface area BET / m 2 / g]]> 4-1 255

[0272] Raw materials list 1-5 (polyvinylidene fluoride)

[0273] Serial Number Carboxyl functional group / wt% 3wt% viscosity / mPa·s Weight-average molecular weight 5-1 0.74 3891 2.26 million

[0274] Example 1

[0275] A secondary battery is provided, comprising a positive electrode, a separator and a negative electrode stacked in sequence, and an electrolyte.

[0276] The preparation of the positive electrode sheet includes the following steps:

[0277] (1) Preparation of carbon nanotube dispersion: Carbon nanotube powder 1-1, second dispersant 2-1 and first dispersant 3-1 are dispersed in N-methylpyrrolidone to form carbon nanotube dispersion; The composition and physicochemical characteristics of the carbon nanotube dispersion are shown in Table 2.

[0278] (2) Preparation of positive electrode sheet:

[0279] Take LiNi 0.8 Co 0.1 Mn 0.1O2, carbon nanotube dispersion, and PVDF (weight-average molecular weight 2.26 million, parameters detailed in Table 1-5) are mixed together, and N-methylpyrrolidone solvent is added and stirred to form a positive electrode slurry with a solid content of 60%. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain the positive electrode film layer. In the positive electrode film layer, LiNi... 0.8 Co 0.1 Mn 0.1 The mass percentage contents of O2, carbon nanotubes, first dispersant, second dispersant, and PVDF are shown in Table 3. The positive electrode film coating width is 70 mm, and the coating surface density is 19 mg / cm³. 2 The material is then heated and dried using a multi-section drying oven with temperatures set sequentially at 120℃, 100℃, and 90℃. Finally, it is compacted using a cold press to achieve a compacted density of 3.4 g / cm³. 3 The positive electrode sheet contains a first dispersant with a mass percentage content of 0.14% and a second dispersant with a mass percentage content of 0.17%.

[0280] Preparation of negative electrode sheet:

[0281] 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, yielding a negative electrode slurry with a solid content of 60 wt%. The negative electrode slurry was then uniformly coated onto both sides of the copper foil used as the negative electrode current collector, with a coating width of 75 mm and a coating surface density of 11 mg / cm³. 2 The negative electrode sheet is prepared by drying in a nine-section oven with temperature settings of 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃, and then compacted using a cold press.

[0282] Preparation of electrolyte:

[0283] 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 then added to the solvent to prepare an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0284] Provide a separating membrane:

[0285] A porous polyethylene (PE) membrane with a thickness of 13 μm was used as the separator.

[0286] Preparation of secondary batteries:

[0287] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Three copper wires are added for the electrodes, and the tabs are welded together to form a stacked bare cell. The stacked 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 battery is obtained.

[0288] Example 2-1

[0289] A secondary battery is provided, differing from Example 1 in that the second dispersant 2-1 is replaced with 2-2, wherein the mass percentage content of the first dispersant in the positive electrode film is 0.15%, the mass percentage content of the second dispersant is 0.19%, and the remaining components, such as LiNi... 0.8 Co 0.1 Mn 0.1 O2, carbon nanotubes and PVDF (weight-average molecular weight of 2.26 million, parameters are detailed in Tables 1-5) were used in the proportions shown in Table 3, and other parameters were kept the same as in Example 1.

[0290] Example 2-2

[0291] A secondary battery is provided, differing from Example 1 in that the second dispersant 2-1 is replaced with 2-3. The mass percentage content of the first dispersant in the positive electrode film is 0.18%, and the mass percentage content of the second dispersant is 0.16%. Meanwhile, the remaining components, such as LiNi... 0.8 Co 0.1 Mn 0.1 O2, carbon nanotubes, and PVDF (weight-average molecular weight of 2.26 million, parameters detailed in Tables 1-5) were used in the proportions shown in Table 3, and other parameters remained the same as in Example 1.

[0292] Example 2-3

[0293] A secondary battery is provided, differing from Example 1 in that the second dispersant 2-1 is replaced with 2-4. The mass percentage content of the first dispersant in the positive electrode is 0.23%, and the mass percentage content of the second dispersant is 0.17%. Meanwhile, the remaining components, such as LiNi... 0.8 Co 0.1 Mn 0.1 O2, carbon nanotubes, and PVDF (weight-average molecular weight of 2.26 million, parameters detailed in Tables 1-5) were used in the proportions shown in Table 3, and other parameters remained the same as in Example 1.

[0294] Example 3-1

[0295] A secondary battery is provided, which differs from Example 1 in that carbon nanotube powder 1-1 is replaced with 1-2, while the rest remains the same as in Example 1.

[0296] Example 3-2

[0297] A secondary battery is provided, which differs from Example 1 in that carbon nanotube powder 1-1 is replaced with 1-3, while the rest remains the same as in Example 1.

[0298] Example 4-1

[0299] A secondary battery is provided, which differs from Example 1 in that carbon black is added as a conductive agent. The performance parameters of the carbon black are shown in Tables 1-4, and the others are the same as in Example 1. The amount of each component in the positive electrode is shown in Table 3.

[0300] Example 5-1

[0301] A secondary battery is provided, which uses the carbon nanotube dispersion in Example 1. The difference from Example 1 is that the amount of carbon nanotube dispersion added is different, which reduces the carbon nanotube content, the content of the first dispersant, and the mass ratio of the second dispersant in the positive electrode film. Other aspects are the same as in Example 1, as shown in Table 3.

[0302] Example 5-2

[0303] A secondary battery is provided, which uses the carbon nanotube dispersion in Example 1. The difference from Example 1 is that the amount of carbon nanotube dispersion added is different, which increases the carbon nanotube content, the content of the first dispersant and the mass ratio of the second dispersant in the positive electrode film layer. Other aspects are the same as in Example 1, as shown in Table 3.

[0304] Comparative Example 1

[0305] A secondary battery is provided, which differs from Example 1 in that the conductive agent carbon nanotubes are completely replaced with carbon black, and LiNi is used. 0.8 Co 0.1 Mn 0.1 O2, carbon black (see raw material table 1-4): PVDF (see raw material table 1-5) are mixed together in a ratio of 96:2.5:1.5.

[0306] Comparative Example 2

[0307] A secondary battery is provided, which differs from Example 1 in that no second dispersant is added to the carbon nanotube dispersion, while the rest remains the same as in Example 1, and the amounts of each component in the positive electrode film are shown in Table 3.

[0308] The specific testing methods for the relevant parameters of the carbon nanotube dispersion in Table 2 are as follows:

[0309] ① Method for determining solid content: Weigh 3-4g of carbon nanotube dispersion slurry, and record it as m1; dry the slurry in an oven (150℃ / 4h), weigh the solid residue, and record it as m2. Solid content = m2 / m1×100%.

[0310] ② Viscosity determination method: Using a Brook DV2T viscometer, at a temperature of 25℃, 200ml of carbon nanotube dispersion slurry was placed in a 250ml beaker. A 64# rotor was inserted into the slurry, and the rotation speed of the device was 100r / min. The start test button was clicked, and the viscosity data was recorded after 5 minutes.

[0311] 480g of carbon nanotube dispersion 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.

[0312] ③ Method for determining viscosity stability: 480g of carbon nanotube dispersion slurry was placed in a 500ml fluorinated bottle. The bottles were labeled with dates of 7D (days), 1M (months), 2M (months), and 3M (months). The sample bottles were then placed in a cool, dark place and allowed to stand. At 7 days, 1M (months), 2M (months), and 3M (months), the slurry was observed to determine if it had gelled. The gel determination method included using a steel ruler to lift the slurry from the beaker and judging whether it had gelled based on its flow pattern. If the slurry did not gel, it was recorded as "No"; if the slurry gelled, it was recorded as "Yes".

[0313] Gel formation: The slurry clumps together or fails to flow naturally and continues to flow.

[0314] No gel: The slurry flows naturally and continuously, and flows horizontally on the surface of the steel ruler without clumping.

[0315] ④ Methods for determining the average tube length and aspect ratio of carbon nanotubes: Average tube diameter test method: 1) Instrument model: TEM transmission electron microscope; 2) CNT slurry dilution: 10000 times, equipment magnification adjusted to 100K; 3) Select 100 carbon nanotubes and measure their diameters for statistical analysis, taking the average value L1 (nm). Average tube length test method: 1) Instrument model: SEM scanning electron microscope; 2) CNT slurry dilution: 1000 times, sample dried at 60℃ for 4h; 3) Equipment magnification adjusted to 30K / 40K; 4) Select 100 carbon nanotubes and measure their lengths for statistical analysis, taking the average value L2 (um); Aspect ratio = L2*1000 / L1.

[0316] ⑤ Method for determining the compaction density of the positive electrode film:

[0317] The thickness H of the positive electrode film is obtained using a thickness gauge or a micrometer.

[0318] 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.

[0319] 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.

[0320] Table 2 Carbon Nanotube Dispersions

[0321]

[0322] Table 3 Positive electrode sheet

[0323]

[0324] [Battery Performance Test]

[0325] ⑥ Detailed testing methods for cell DCR:

[0326] (1) DCR1 corresponding to 100% SOC: At 25°C, the batteries corresponding to the examples and comparative examples were charged to 4.3V with a constant current of 1 / 3*C, and then charged to a current of 0.05C with a constant voltage of 4.3V. After resting for 5 minutes, the voltage V1 was recorded. Then, the batteries were discharged at 1 / 3C for 30 seconds, and the voltage V2 was recorded. The DC resistance DCR1 of the battery was obtained by calculating 3*(V2-V1) / C.

[0327] (2) DCR2 corresponding to 20% SOC: At 25°C, the batteries corresponding to the examples and comparative examples were charged to 4.3V with a constant current of 1 / 3C, and then charged to a current of 0.05C with a constant voltage of 4.3V. After resting for 5 minutes, they were discharged at 1C for 2880s. After resting for 5 minutes, the voltage V3 was recorded. Then, they were discharged at 1 / 3C for 30s, and the voltage V4 was recorded. The DC resistance DCR2 of the battery was obtained according to 3×(V4-V3) / C.

[0328] ⑦ Cyclic stability, detailed test method for capacity retention after 1000 cycles:

[0329] At 25℃, the secondary battery was charged at a constant current of 1C to 4.3V, 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 1000 cycles at 25℃ = discharge capacity after 1000 cycles / discharge capacity of the first cycle × 100%.

[0330] Table 4 Performance List of Secondary Batteries

[0331]

[0332] As can be seen from the above embodiments and comparative examples, the design provided in this application is beneficial to improving the conductivity of the battery. At the same time, since the conductivity is improved due to the uniform dispersion of the conductive agent, the amount of positive electrode active material is also increased accordingly. In addition, the DC internal resistance of the battery is reduced and polarization is reduced, which is also beneficial to enable the battery to still exhibit good capacity after 1000 cycles.

[0333] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized by: The positive electrode sheet, the separator, and the negative electrode sheet are provided. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer on at least one side surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, carbon nanotubes, a first dispersant, and a second dispersant, the first dispersant comprises hydrogenated nitrile rubber and a modified compound thereof, and the second dispersant comprises a polyvinylpyrrolidone modified compound. The polyvinylpyrrolidone-modified compound includes structural units derived from a vinylpyrrolidone monomer and structural units derived from a solvent chain monomer including an ethylene oxide, a propylene oxide, a C 2～9 any one or more of the olefins.

2. The secondary battery according to claim 1, characterized by: The mass ratio of the first dispersant to the second dispersant is (6-23):(7-27).

3. The secondary battery according to any one of claims 1 to 2, characterized by: The mass percentage content of the first dispersant in the positive electrode film layer is A1, and 0 And / or The mass percentage content of the second dispersant in the positive electrode film layer is A2, and 0 4. The secondary battery according to any one of claims 1 to 3, characterized by: The weight average molecular weight of the polyvinylpyrrolidone modified compound is 5,000-1,000,000.

5. The secondary battery according to any one of claims 1 to 4, characterized by: The mass percentage content of the structural unit derived from the vinylpyrrolidone monomer in the polyvinylpyrrolidone modified compound is 7%-55%; And / or The mass percentage content of the structural unit derived from the solvent chain monomer in the polyvinylpyrrolidone modified compound is 40%-75%.

6. The secondary battery according to any one of claims 1 to 5, characterized by: The polyvinylpyrrolidone modified compound further comprises a structural unit derived from a crosslinking monomer. The crosslinking monomer comprises any one or more of trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glycerol triacrylate, ethoxylated glycerol triacrylate, pentaerythritol triacrylate, and pentaerythritol triallyl ether. And / or The mass percentage content of the structural unit derived from the crosslinking monomer in the polyvinylpyrrolidone modified compound is 3%-25%.

7. The secondary battery according to any one of claims 1 to 6, characterized by: The weight average molecular weight of the hydrogenated nitrile rubber and the modified compound thereof is 50,000-200,000. And / or The hydrogenated nitrile rubber and the modified compound thereof comprise a structural unit derived from an acrylonitrile monomer, and the mass percentage content of the structural unit derived from the acrylonitrile monomer in the hydrogenated nitrile rubber and the modified compound thereof is 20%-40%. And / or The hydrogenation degree of the hydrogenated nitrile rubber and the modified compound thereof is ≥99%.

8. The secondary battery according to any one of claims 1 to 7, characterized by: The positive electrode film layer further comprises carbon black. The mass percentage content of the carbon black in the positive electrode film layer is 0-2.5%. And / or The specific surface area BET of the carbon black is > 100 m2 / g. 2 / g.

9. The secondary battery according to any one of claims 1 to 8, characterized by: The mass percentage content of the carbon nanotubes in the positive electrode film layer is ≥0.2%. And / or The carbon nanotubes comprise any one or more of multi-walled carbon nanotubes and single-walled carbon nanotubes. And / or The specific surface area BET of the carbon nanotubes is 200 m 2 / g to 1500 m 2 / g; The average tube diameter of the carbon nanotubes is 1-15 nm. The mass percentage content of the carbon nanotubes in the positive electrode film layer is 0.2%-0.8%.

10. The secondary battery according to any one of claims 1 to 9, characterized by: The mass percentage content of the positive electrode active material in the positive electrode film layer is ≥96%.

11. The secondary battery according to any one of claims 1 to 10, characterized by: And / or The positive electrode active material comprises any one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-containing phosphate with an olivine structure. ​ 12. The secondary battery according to any one of claims 1 to 11, characterized by: The positive electrode film layer further comprises a binder, and the binder comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a fluorine-containing acrylate resin, a styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

13. The secondary battery according to any one of claims 1 to 12, characterized by: The positive electrode film layer further comprises a binder, and the binder comprises polyvinylidene fluoride; The polyvinylidene fluoride contains carboxyl functional groups, and the mass percentage content of the carboxyl functional groups in the polyvinylidene fluoride is ≤2.0%; And / or The viscosity of the polyvinylidene fluoride glue solution with a mass percentage content of 3% is 3000-5000 mpa.s; And / or The weight average molecular weight of the polyvinylidene fluoride is 2-4 million; And / or The mass percentage content of the polyvinylidene fluoride in the positive electrode film layer is ≤1.5%.

14. A method of producing a secondary battery, characterized by: The preparation process comprises: Preparation of a carbon nanotube dispersion liquid: dispersing carbon nanotube powder, a first dispersant and a second dispersant into a first solvent to form a carbon nanotube dispersion liquid; the first dispersant comprises hydrogenated butyl nitrile rubber and its modified compounds, and the second dispersant comprises a polyvinylpyrrolidone modified compound; The polyvinylpyrrolidone-modified compound includes structural units derived from a vinylpyrrolidone monomer and structural units derived from a solvent chain monomer, the structural units derived from the solvent chain monomer including an oxirane, an oxetane, a C 2～9 any one or more of an olefin; Preparation of a positive electrode sheet: dispersing a positive electrode active material and the carbon nanotube dispersion liquid into a second solvent to form a positive electrode slurry, coating the positive electrode slurry on at least one side surface of a positive electrode current collector, and drying to form a positive electrode sheet; Stacking the positive electrode sheet, a negative electrode sheet and a separator to form a secondary battery.

15. The method of claim 14, wherein: The viscosity of the carbon nanotube dispersion liquid is ≤1000 mpa.s; and / or The carbon nanotube dispersion liquid is left to stand at 20-30°C for 3 months, and the viscosity is ≤3600 mpa.s; And / or The solid content of the carbon nanotube dispersion liquid is ≥50%.

16. The method of any one of claims 14-15, wherein: The solid content of the carbon nanotube dispersion liquid is 50-80%.

17. The method of any one of claims 14-16, wherein: The mass percentage content of the carbon nanotubes in the carbon nanotube dispersion liquid is ≥50%; And / or The average tube length of the carbon nanotubes in the carbon nanotube dispersion liquid is <15 μm; And / or The aspect ratio of the carbon nanotubes in the carbon nanotube dispersion liquid is >150.

18. The method of any one of claims 14-17, wherein: The mass percentage content of the hydrogenated butyl nitrile rubber and its modified compounds in the carbon nanotube dispersion liquid is ≥15%; And / or The mass percentage content of the polyvinylpyrrolidone modified compound in the carbon nanotube dispersion liquid is ≥18%.

19. The method of any one of claims 14-18, wherein: The mass percentage content of the carbon nanotubes in the carbon nanotube dispersion liquid is 50-65%; And / or The mass percentage content of the hydrogenated butyl nitrile rubber and its modified compounds in the carbon nanotube dispersion liquid is 15-30%; And / or The mass percentage content of the polyvinylpyrrolidone modified compound in the carbon nanotube dispersion liquid is 18-25%.

20. The method of any one of claims 14-19, wherein: The carbon nanotube powder satisfies: DV 50 is 10 nm to 60 nm, DV 90 is 40 nm to 120 nm; And / or The volume resistivity of the carbon nanotube powder is 20-100 Ω·cm; And / or The average tube length of the carbon nanotube powder is >20 μm; And / or The aspect ratio of the carbon nanotube powder is >1000.

21. An electrical device, comprising: The secondary battery according to any one of claims 1 to 13 or the secondary battery produced by the production method according to any one of claims 14 to 20.

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