Modified carbon nanotube, negative pole piece, preparation method of negative pole piece, battery and electric equipment

Abstract

The invention discloses a modified carbon nanotube and a preparation method thereof, a negative pole piece and a preparation method thereof, a battery and electric equipment. The modified carbon nano tube comprises a carbon nano tube with a modified group on the surface, and the modified group comprises carboxylate. The carboxylate of the modified group is beneficial to improving the uniform dispersion of the carbon nano tube in a solvent, so that the modified carbon nano tube can be relatively uniformly dispersed on the surface of a silicon material in the process of forming the negative electrode slurry by adopting the silicon material and the modified carbon nano tube, and a conductive path of the silicon material is perfected; meanwhile, carboxylate of a modified group on the surface of the carbon nano tube interacts with hydroxyl on the surface of silicon, so that the bonding force between the carbon nano tube and the silicon material is enhanced, a conductive path of the silicon material is further improved, the electrochemical performance of the silicon material is exerted, and the energy density of the battery is further improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to modified carbon nanotubes and a preparation method thereof, a negative electrode sheet and a preparation method thereof, a battery monomer, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in fields such as consumer electronics, energy storage, and power due to their advantages such as high output voltage, high energy density, high power density, long cycle life, and good environmental friendliness.

[0003] With the development of technology, the requirement for the energy density of batteries is getting higher and higher. The capacity of the commonly used graphite negative electrode of lithium-ion batteries is about 360 mAh / g, which is very close to its theoretical specific capacity (372 mAh / g). Therefore, it is difficult for the graphite negative electrode to meet the demand for high energy density of batteries. For silicon materials of the same family, Li 22 Si 5 is formed at high temperature, and the corresponding specific capacity is 4200 mAh / g. At room temperature, Li 15 Si 4 is formed, and the corresponding specific capacity is 3579 mAh / g. Therefore, using silicon as the negative electrode can improve the energy density of the battery.

[0004] However, silicon materials belong to semiconductor materials, with poor electronic conductivity and ionic conductivity, which is not conducive to the exertion of the electrochemical performance of the materials and affects the performance of the battery. Summary of the Invention

[0005] The present application provides a modified carbon nanotube and a preparation method thereof, a negative electrode sheet and a preparation method thereof, a battery monomer, a battery, and an electrical device, which can improve the interaction between the modified carbon nanotubes and the surface of the silicon material, improve the conductive path of the silicon material, and exert the electrochemical performance of the silicon material.

[0006] To solve the above technical problems, a technical solution adopted in the present application is: to provide a modified carbon nanotube, including carbon nanotubes with modified groups on the surface, and the modified groups include carboxylates.

[0007] The carboxylates of the modified groups are beneficial to improving the uniform dispersion of the carbon nanotubes in the solvent, so that during the process of forming a negative electrode slurry with silicon materials and modified carbon nanotubes, the modified carbon nanotubes can be more uniformly dispersed on the surface of the silicon material, improving the conductive path of the silicon material; at the same time, the carboxylates of the modified groups on the surface of the carbon nanotubes interact with the hydroxyl groups on the surface of the silicon, enhancing the adhesion between the carbon nanotubes and the silicon material, further facilitating the improvement of the conductive path of the silicon material, exerting the electrochemical performance of the silicon material, and thus being beneficial to improving the energy density of the battery.

[0008] In one embodiment, the modifying group includes polyhydrocarbyl carboxylate; optionally, the polyhydrocarbyl carboxylate includes any one of lithium polypropylene carboxylate, sodium polypropylene carboxylate, and magnesium polypropylene carboxylate. The polyhydrocarbyl is in a linear chain shape. When the modified carbon nanotubes are used as an additive to the silicon-based material, the linear chains of the modifying groups are anchored on the surface of the silicon particles, restricting the expansion of the silicon particles, reducing the volume expansion rate of silicon during the alloying process with lithium, hindering the pulverization and fragmentation of the silicon particles and the destruction of the SEI film, which is beneficial to improving the cycle life of the battery. While maintaining the high energy density of the silicon negative electrode, its cycle performance is improved and its kinetic advantages are fully exerted.

[0009] In one embodiment, the modifying group includes a cyano group; optionally, the modifying group includes polyacrylonitrile. When the modified carbon nanotubes are used as an additive to the silicon-based active material, the cyano group can interact with the hydroxyl groups on the silicon surface, enhancing the adhesion between the carbon nanotubes and the silicon material, which is beneficial to improving the conductive path of the silicon material and exerting the electrochemical performance of the silicon material, and thus is beneficial to improving the energy density of the battery.

[0010] In one embodiment, the modified carbon nanotubes are modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes, so that the modified carbon nanotubes have a wide range of applicability.

[0011] To solve the above technical problems, another technical solution adopted in this application is: to provide a method for preparing modified carbon nanotubes, which includes dispersing carbon nanotubes in a strongly oxidizing solution to obtain oxidized carbon nanotubes, and a part of the carbon in the oxidized carbon nanotubes is functionalized into oxygen-containing groups; reacting the oxidized carbon nanotubes with a modifier to obtain pre-modified carbon nanotubes, and the modifier includes an acyl group; dispersing the pre-modified carbon nanotubes in an alkaline solution to obtain modified carbon nanotubes, and the surface of the modified carbon nanotubes is provided with a modifying group, and the modifying group includes carboxylate. The preparation method is simple and easy to implement, and the modified carbon nanotubes prepared by this preparation method have at least the same advantages as the above-mentioned modified carbon nanotubes.

[0012] In one embodiment, the reaction of the oxidized carbon nanotubes with the modifier includes: adding a chain initiator to a polymer monomer solution to carry out a polymerization reaction to form a polymerization reaction solution, and the polymer monomer includes an acyl group; adding the dispersion of the oxidized carbon nanotubes to the polymerization reaction solution and continuing the reaction to obtain the pre-modified carbon nanotubes. The pre-modified carbon nanotubes are in a linear chain shape, so that the final modified carbon nanotubes are also in a linear chain shape, and the linear chains are anchored on the surface of the silicon particles, restricting the expansion of the silicon particles.

[0013] In one embodiment, the polymer monomer further includes a cyano group; optionally, adding a chain initiator to the polymer monomer solution to carry out a polymerization reaction to form a polymerization reaction solution includes: adding a chain initiator to a mixed solution of acrylonitrile and acryloyl chloride, and heating and reacting; optionally, the heating temperature is 55°C - 65°C, and the reaction time is 7h - 9h; optionally, adding the dispersion of oxidized carbon nanotubes to the polymerization reaction solution and continuing the reaction includes: dropwise adding the dispersion of oxidized carbon nanotubes to the polymerization reaction solution and continuing to heat and react; optionally, the heating temperature is 75°C - 85°C, and the reaction time is 40h - 50h; optionally, the weight ratio of the oxidized carbon nanotubes: the chain initiator: the acrylonitrile: the acryloyl chloride is (25% - 35%):(5% - 7%):(20% - 30%):(30% - 40%). The cyano group can interact with the hydroxyl groups on the silicon surface, enhancing the adhesion between the carbon nanotubes and the silicon material, which is beneficial to improving the conductive path of the silicon material.

[0014] To solve the above technical problems, another technical solution adopted in this application is: to provide a negative electrode sheet, including a current collector and a negative electrode active layer; the negative electrode active layer is disposed on at least one side of the current collector, and the negative electrode active layer includes a negative electrode active material and a conductive agent, and the conductive agent includes the modified carbon nanotubes described in any one of the above or the modified carbon nanotubes prepared by the preparation method described in any one of the above.

[0015] The lithium ions in the modified carbon nanotubes help to improve the lithium ion migration rate and reduce the concentration polarization; secondly, the carboxyl group and cyano group in the modified carbon nanotubes have relatively large polarities and can react with groups such as hydroxyl groups on the surface of silicon particles, enhancing the adhesion of the carbon nanotubes on the surface of silicon particles, solving the problem that after cyclic charge and discharge, the volume expansion and contraction of silicon particles cause the carbon nanotubes to slip with the silicon particles, and then lose electrical contact, resulting in life attenuation, and maintaining a good long cycle life; finally, the linear long chains of the modified carbon nanotubes are coated on the surface of silicon particles, restricting the expansion of silicon particles, which can reduce the full charge rebound rate of the negative electrode sheet and maintain a relatively high energy density and safety of the battery.

[0016] In one embodiment, the negative electrode active layer includes: a first negative electrode active layer and a second negative electrode active layer; the first negative electrode active layer is disposed on one side of the current collector; the first negative electrode active layer includes a first negative electrode active material and a first conductive agent, and the first negative electrode active material includes graphite; the second negative electrode active layer is disposed on the side of the first negative electrode active layer away from the current collector; the second negative electrode active layer includes a second negative electrode active material and a second conductive agent, the second negative electrode active material includes a silicon-based material, and the second conductive agent includes the modified carbon nanotubes.

[0017] By dividing graphite and silicon-based materials into two active layers, the second conductive agent (i.e., modified carbon nanotubes) acts on the surface of silicon particles, improving the conductive network of the silicon-based material; a first negative electrode active layer is provided between the second negative electrode active layer and the current collector. Graphite is brittle and not very strong, which can act as a buffer layer, well buffering and suppressing the stress changes caused by the volume expansion and contraction during the insertion and extraction of lithium ions in the silicon-based active layer, preventing the active material layer from peeling off from the current collector during continuous charge and discharge. The second conductive agent has good adhesion strength with silicon particles, which can prevent the carbon nanotubes and silicon particles from slipping during repeated cycling, maintaining a good long cycle life. In addition, the grafted modification groups on the carbon nanotubes further restrict the expansion of silicon particles, reducing the full charge rebound rate of the negative electrode sheet and achieving a higher energy density and safety.

[0018] In one embodiment, the first conductive agent includes at least one of carbon black, acetylene black, carbon fiber, carbon nanotubes, and the modified carbon nanotubes, providing diversity in the selection of the first conductive agent.

[0019] To solve the above technical problems, another technical solution adopted in this application is: to provide a battery cell, including the negative electrode sheet described in any one of the above, having at least the same advantages as the negative electrode sheet described above.

[0020] To solve the above technical problems, another technical solution adopted in this application is: to provide a battery, including the battery cell described above or the negative electrode sheet described in any one of the above, having at least the same advantages as the battery cell or negative electrode sheet described above.

[0021] To solve the above technical problems, another technical solution adopted in this application is: to provide an electrical device, including the battery described above, having at least the same advantages as the battery described above.

[0022] To solve the above technical problems, another technical solution adopted in this application is: to provide a method for preparing a negative electrode sheet, including providing a negative electrode slurry, the negative electrode slurry including a negative electrode active material and a conductive agent, the conductive agent including the modified carbon nanotubes described in any one of the above or the modified carbon nanotubes prepared by the preparation method described in any one of the above; coating the negative electrode slurry on a current collector to form a negative electrode active layer. The battery prepared with the negative electrode sheet obtained by using this preparation method has a higher energy density and safety, improving the kinetic performance of the battery.

[0023] In one embodiment, graphite, a binder, a first conductive agent, and a dispersant are mixed to form a graphite slurry; a silicon-based material, a binder, a second conductive agent, and a dispersant are mixed to form a silicon-based slurry, and the second conductive agent includes modified carbon nanotubes; the graphite slurry and the silicon-based slurry are simultaneously coated by a double-layer coating device, wherein the graphite slurry is coated on the surface of the current collector, and the silicon-based slurry is simultaneously coated on the surface of the graphite slurry; drying is performed to obtain a negative electrode sheet.

[0024] The graphite and the silicon-based material are divided into two active layers. The second conductive agent (i.e., modified carbon nanotubes) acts on the surface of silicon particles to improve the conductive network of the silicon-based material; a first negative electrode active layer is provided between the second negative electrode active layer and the current collector. Graphite is brittle and not very strong, and it can act as a buffer layer, which can well buffer and inhibit the stress changes caused by the volume expansion and contraction during the insertion and extraction of lithium ions in the silicon-based active layer, and prevent the active material layer from peeling off from the current collector during continuous charge and discharge. The bonding strength between the second conductive agent and the silicon particles is good, which can prevent the carbon nanotubes from slipping with the silicon particles during repeated cycling, and maintain a good long cycling life. In addition, the grafted modification groups on the carbon nanotubes further restrict the expansion of silicon particles, which can reduce the full charge rebound rate of the negative electrode sheet and achieve a higher energy density and safety.

[0025] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. In order to make the above and other purposes, features, and advantages of the present application more obvious and understandable, the specific embodiments of the present application are specifically described below. Brief Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 is a schematic flowchart of a method for preparing modified carbon nanotubes provided by an embodiment of the present application;

[0028] Figure 2 is a schematic structural diagram of a negative electrode sheet provided by an embodiment of the present application;

[0029] Figure 3 is Figure 2 a schematic structural diagram of an embodiment of a negative electrode active layer shown;

[0030] Figure 4 is a schematic flowchart of a method for preparing a negative electrode sheet provided by an embodiment of the present application;

[0031] Figure 5 Schematic exploded view of the battery cell provided by the embodiment of the present application;

[0032] Figure 6 Schematic exploded view of the battery provided by the embodiment of the present application;

[0033] Figure 7 Schematic view of the structure of the vehicle provided by the embodiment of the present application. Detailed implementation manners

[0034] To make the purpose, technical solutions and effects of the present application clearer and more definite, the following will describe in detail the embodiments of the technical solutions of the present application with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present application more clearly, so they are only examples and cannot be used to limit the protection scope of the present application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0036] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the term "plurality" means two or more (including two). Similarly, "multiple groups" means two or more groups (including two groups), and "multiple pieces" means two or more pieces (including two pieces), unless otherwise specifically defined.

[0037] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0038] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally means that the associated objects before and after are in an "or" relationship.

[0039] In this document, quantities, ratios, and other numerical values are presented in a range format. It should be understood that such range formats are for convenience and brevity, and should be understood flexibly, including not only the numerical values explicitly specified as range limits, but also all individual numerical values or sub-ranges covered within the said range, as if each numerical value and sub-range were explicitly specified.

[0040] If there is no special instruction, all steps of this application can be carried out sequentially, randomly, or in parallel. Preferably, they are carried out sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially, or steps (a) and (b) carried out in parallel simultaneously. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0041] With the development of technology, the requirement for battery energy density is getting higher and higher; for example, to solve the range anxiety problem of electric vehicle users, it is necessary to increase the battery energy density. For anode materials, currently, graphite anodes are widely used in lithium-ion batteries. The capacity of graphite anodes is about 360 mAh / g, which is already very close to its theoretical specific capacity (372 mAh / g). Therefore, it is very difficult for graphite anodes to meet the demand for high battery energy density.

[0042] When using silicon materials in the same group as carbon as the anode material, Li 22 Si 5 is formed at high temperature, and the corresponding specific capacity is 4200 mAh / g; Li 15 Si 4 is formed at room temperature, and the corresponding specific capacity is 3579 mAh / g. In addition, the de-lithiation potential of silicon is relatively low. Therefore, using silicon as the anode material can reduce the amount of material used and increase the battery energy density, which is an important development direction for battery anode materials in the future.

[0043] However, silicon materials belong to semiconductor materials, with poor electronic conductivity and ionic conductivity, which is not conducive to the electrochemical performance of the materials and affects the performance of the battery. In view of this, the embodiments of this application provide a modified carbon nanotube and its preparation method, a negative electrode sheet and its preparation method, a battery monomer, a battery, and an electrical device, to improve the interaction between the modified carbon nanotube and the surface of the silicon material, improve the conductive path of the silicon material, and exert the electrochemical performance of the silicon material, thereby achieving an increase in the energy density of the battery.

[0044] An embodiment of the present application provides a modified carbon nanotube, which includes a carbon nanotube with a modified group on its surface, and the modified group includes carboxylate. When a silicon material is used as a negative electrode active material, the modified carbon nanotube provided by the embodiment of the present application is used as a negative electrode conductive agent. Based on the strong conductivity of the carbon nanotube, the carboxylate of the modified group is beneficial to improving the uniform dispersion of the carbon nanotube in the solvent, so that during the process of forming a negative electrode slurry with the silicon material and the modified carbon nanotube, the modified carbon nanotube can be more uniformly dispersed on the surface of the silicon material, improving the conductive path of the silicon material; at the same time, the carboxylate of the modified group on the surface of the carbon nanotube interacts with the silicon-oxygen bond and hydroxyl group on the surface of the silicon (the silicon material usually exists in the form of SiO x , 0 < x ≤ 1, and hydroxyl and silicon-oxygen bonds are easily formed on its surface), enhancing the adhesion between the carbon nanotube and the silicon material, further facilitating the improvement of the conductive path of the silicon material, exerting the electrochemical performance of the silicon material, and thus being beneficial to improving the energy density of the battery.

[0045] In one embodiment, the modified group includes polyhydrocarbyl carboxylate, and the polyhydrocarbyl is in a linear chain shape, so that the linear chain of the modified group is anchored on the surface of the silicon particles, restricting the expansion of the silicon particles, reducing the volume expansion rate of the silicon during the alloying process with lithium, hindering the pulverization and fragmentation of the silicon particles and the destruction of the SEI film, being beneficial to improving the cycle life of the battery, maintaining the high energy density of the silicon negative electrode, while improving its cycle performance and fully exerting its kinetic advantages.

[0046] Optionally, the polyhydrocarbyl carboxylate includes any one of lithium polyacrylate carboxylate, sodium polyacrylate carboxylate, and magnesium polyacrylate carboxylate. It can be understood that any one of lithium polyacrylate carboxylate, sodium polyacrylate carboxylate, and magnesium polyacrylate carboxylate is grafted on the surface of the carbon nanotube, and the linear chain is anchored on the surface of the silicon particles, restricting the expansion of the silicon particles. When the battery is a lithium battery and the polyhydrocarbyl carboxylate includes lithium polyacrylate carboxylate, the lithium ions in the lithium polyacrylate carboxylate are helpful to improve the migration rate of lithium ions, and thus improve the kinetic performance of the battery.

[0047] In one embodiment, the modified group includes a cyano group, which can interact with the hydroxyl group on the surface of the silicon, enhancing the adhesion between the carbon nanotube and the silicon material, being beneficial to improving the conductive path of the silicon material, exerting the electrochemical performance of the silicon material, and thus being beneficial to improving the energy density of the battery.

[0048] Optionally, the modified group includes polyacrylonitrile. It can be understood that polyacrylonitrile is grafted on the surface of the carbon nanotube, and the polypropylene group is in a linear chain shape, so that the linear chain of the modified group is anchored on the surface of the silicon particles, restricting the expansion of the silicon particles.

[0049] In one embodiment, the modifying group includes polyhydrocarbyl carboxylate and cyano group, and has the technical effects of both polyhydrocarbyl carboxylate and cyano group. For the relevant descriptions, please refer to the above and will not be elaborated here. Optionally, the modifying group includes lithium polyacrylate and polyacrylonitrile. Lithium polyacrylate and polyacrylonitrile can be grafted onto the surface of carbon nanotubes separately, or lithium polyacrylate and polyacrylonitrile can be copolymerized and grafted onto the surface of carbon nanotubes.

[0050] In one embodiment, the modified carbon nanotubes are modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes, which have wide applicability.

[0051] The embodiment of the present application also provides a preparation method of modified carbon nanotubes, which can be used to prepare the modified carbon nanotubes introduced in the above embodiments. Please refer to Figure 1 , Figure 1 which is a schematic flow chart of the preparation method of the modified carbon nanotubes provided by the embodiment of the present application.

[0052] The preparation method of the modified carbon nanotubes specifically includes:

[0053] Step S01: Dispersing carbon nanotubes in a strongly oxidizing solution to obtain oxidized carbon nanotubes, and a part of the carbon in the oxidized carbon nanotubes is functionalized into oxygen-containing groups.

[0054] In one embodiment, the strongly oxidizing solution includes at least one of concentrated sulfuric acid, concentrated nitric acid, and hydrogen peroxide. The strongly oxidizing solution has strong oxidizing property, attacks the defect positions on the surface and end caps of carbon nanotubes, and a part of the carbon in the carbon nanotubes is functionalized into oxygen-containing groups, such as hydroxyl group, carboxyl group, etc. In other words, polar groups such as hydroxyl group and carboxyl group are introduced on the surface and end caps of carbon nanotubes as the active sites for the reaction in Step S02. It should be noted that the selection of the type of the strongly oxidizing solution and the proportional relationship between the strongly oxidizing solution and the carbon nanotubes can be designed according to needs, and the same effects can be achieved, but the difference is the length of the oxidation time.

[0055] Optionally, the strongly oxidizing solution includes concentrated sulfuric acid and concentrated nitric acid, which is a mixed acid solution; the concentrated nitric acid is 68% nitric acid; the concentrated sulfuric acid is 98% sulfuric acid; the volume ratio of the concentrated sulfuric acid to the concentrated nitric acid is 2:1 to 4:1, which has strong oxidizing property and a short oxidation time.

[0056] In one embodiment, the carbon nanotubes are multi-walled carbon nanotubes or single-walled carbon nanotubes. Exemplarily, when the carbon nanotubes are multi-walled carbon nanotubes, the multi-walled carbon nanotubes are acid-treated. The aspect ratio of the initial multi-walled carbon nanotubes (i.e., the multi-walled carbon nanotubes without acid treatment) is characterized by a scanning electron microscope (SEM) to be 3000 - 6000, and the aspect ratio of the multi-walled carbon nanotubes after acid treatment is 2000 - 5000. When the initial multi-walled carbon nanotubes are analyzed by X-ray photoelectron spectroscopy (XPS), it is found that the initial multi-walled carbon nanotubes only have a 1s C peak. After acid treatment, the multi-walled carbon nanotubes have a 1s C peak and a 1s O peak, and the relative contents of C element and O element are 70%:30% (molar ratio), indicating that 30% of the C in the carbon nanotubes is functionalized into oxygen-containing groups such as hydroxyl groups and carboxyl groups.

[0057] In one embodiment, treating the carbon nanotubes in a strongly oxidizing solution to obtain oxidized carbon nanotubes specifically includes: dispersing the carbon nanotubes in a strongly oxidizing solution for reaction, after ultrasonic oscillation for a first preset time, refluxing and reacting at a first preset temperature for a second preset time, taking out the reactant, repeatedly washing it with deionized water and filtering it until the pH of the filtrate is neutral, and finally drying the solid in a vacuum oven at a second preset temperature to obtain oxidized carbon nanotubes. Among them, ultrasonic oscillation and heating reflux promote the acidification reaction, making the reaction more complete. Since the negative electrode paste is neutral, acidic additives will cause some adverse side reactions. Repeatedly washing and filtering the reactant until the filtrate is neutral enables the prepared modified carbon nanotubes to be suitable for preparing the negative electrode paste. The solid after filtration is further dried to remove moisture in a vacuum oven.

[0058] Optionally, the strongly oxidizing solution is a mixed acid of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 2:1 to 4:1; the first preset time is 2h - 4h; the first preset temperature is 110°C - 130°C; the second preset time is 0.5h - 1.5h; the second preset temperature is 30°C - 50°C.

[0059] Step S02: React the oxidized carbon nanotubes with a modifier to obtain pre-modified carbon nanotubes, and the modifier includes an acyl group.

[0060] In one embodiment, the acyl group includes at least one of acyl chloride and carboxylic acid ester. By making the modifier include an acyl group, the pre-modified carbon nanotubes obtained by reacting the oxidized carbon nanotubes with the modifier include an acyl group. When the pre-modified carbon nanotubes proceed to the subsequent step S03, the acyl group of the pre-modified carbon nanotubes reacts with the alkaline solution to generate carboxylate, and the carboxylate is beneficial to improving the uniform dispersion of the carbon nanotubes in the solvent. At the same time, the carboxylate interacts with the hydroxyl groups on the silicon surface, enhancing the adhesion between the carbon nanotubes and the silicon material. Exemplarily, the acyl group includes acyl chloride.

[0061] In one embodiment, the modifier is a hydrocarbon polymer including an acyl group, so that the modification group of the obtained pre-modified carbon nanotubes is in a long-chain shape. Furthermore, the modification group of the modified carbon nanotubes obtained by performing the subsequent step S03 on the pre-modified carbon nanotubes is in a long-chain shape, and can linearly anchor on the silicon particles to restrict the expansion of the silicon particles.

[0062] In one embodiment, on the basis that the modifier includes an acyl group, the modifier further includes a cyano group, so that the pre-modified carbon nanotubes obtained by the reaction of the oxidized carbon nanotubes and the modifier include a cyano group, which can interact with the hydroxyl groups and silicon-oxygen bonds on the silicon surface, and enhance the adhesion between the carbon nanotubes and the silicon material.

[0063] In one embodiment, the reaction of the oxidized carbon nanotubes and the modifier includes: adding a chain initiator to a polymer monomer solution to perform a polymerization reaction to form a polymerization reaction solution, and the polymer monomer includes an acyl group; adding a dispersion of the oxidized carbon nanotubes to the polymerization reaction solution and continuing the reaction to obtain pre-modified carbon nanotubes. Herein, the monomer of the polymer refers to a small molecule for synthesizing the polymer; the chain initiator decomposes to generate free radicals at a certain temperature for initiating the polymerization of the polymer monomer, and the polymer monomer forms a polymer under the action of the chain initiator.

[0064] Optionally, the dispersion of the oxidized carbon nanotubes specifically includes: adding the oxidized carbon nanotubes prepared in step S01 to a first solvent, and performing ultrasonic oscillation to promote more uniform dispersion to obtain a dispersion of the oxidized carbon nanotubes. Herein, the first solvent can be at least one of dioxane, acetone, and N-methylpyrrolidone. It should be noted that when the first solvent is dioxane, dioxane can well disperse the carbon nanotubes. At the same time, the decomposition temperature of dioxane is relatively low, and dioxane is easily decomposed during subsequent processing, and the content of dioxane in the final modified carbon nanotubes is less or even none.

[0065] Optionally, the polymer monomer further includes a cyano group. At this time, adding a chain initiator to the polymer monomer solution to perform a polymerization reaction to form a polymerization reaction solution specifically includes: adding a chain initiator to a mixed solution of acrylonitrile and acryloyl chloride (in other words, the polymer monomer includes acrylonitrile and acryloyl chloride), and performing a heating reaction, wherein the heating temperature is 55°C - 65°C and the reaction time is 7h - 9h to form polyacrylonitrile, polyacryloyl chloride, and a copolymer of polyacrylonitrile and polyacryloyl chloride. The heating temperature and reaction time can be determined according to the half-life of the selected chain initiator to set the heating temperature and reaction time for smooth reaction. Further, when adding a chain initiator to the mixed solution of acrylonitrile and acryloyl chloride, stirring is performed during the heating reaction to promote the reaction. It should be noted that the solvent of the mixed solution of acrylonitrile and acryloyl chloride can be dioxane, which reduces the types of substances introduced during the preparation of the modified carbon nanotubes and reduces the difficulty of treating and removing the solvent.

[0066] Optionally, adding the dispersion of carbon nanotubes into the polymerization reaction solution and continuing the reaction specifically includes: dropping the dispersion of carbon nanotubes into the polymerization reaction solution drop by drop and continuing the heating reaction; wherein, the heating temperature is 75°C - 85°C and the reaction time is 40h - 50h, so that polyacryloyl chloride is grafted onto the surface of carbon nanotubes, polyacrylonitrile is grafted onto the surface of carbon nanotubes, or a copolymer of polyacryloyl chloride and polyacrylonitrile is grafted onto the surface of carbon nanotubes. The heating temperature and reaction time can be determined according to the grafting situation of carbon nanotubes and the dispersibility of carbon nanotubes after grafting, so that the dispersibility of the modified carbon nanotubes prepared under this reaction condition is good. Further, during the process of dropping the dispersion of carbon nanotubes into the polymerization reaction solution drop by drop and continuing the heating reaction, stirring is carried out to promote the reaction. Further, when dropping the dispersion of carbon nanotubes into the polymerization reaction solution drop by drop, a catalyst is added simultaneously to promote the reaction; the catalyst can be triethylamine, etc.

[0067] Optionally, the weight part ratio of carbon nanotubes: chain initiator: acrylonitrile: acryloyl chloride is (25% - 35%): (5% - 7%): (20% - 30%): (30% - 40%), and the prepared modified carbon nanotubes have good conductivity and good dispersibility. Exemplarily, the weight part ratio of carbon nanotubes: chain initiator: acrylonitrile: acryloyl chloride is 30%: 6.5%: 25%: 38.5%.

[0068] Optionally, the chain initiator includes one or more of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, ammonium sulfate, potassium persulfate, hydrogen peroxide, sodium persulfate.

[0069] In one embodiment, after reacting the carbon nanotubes with the modifier, it further includes: filtering out the reactants after reacting the carbon nanotubes with the modifier, and then repeatedly rinsing with deionized water until the filtrate is clear.

[0070] Step S03: Dispersing the pre-modified carbon nanotubes in an alkaline solution to obtain modified carbon nanotubes, and the surface of the modified carbon nanotubes has a modified group, and the modified group includes carboxylate.

[0071] In one embodiment, the alkaline solution includes at least one of lithium hydroxide, sodium hydroxide, and magnesium hydroxide.

[0072] It can be understood that the reaction of the pre-modified carbon nanotubes with the alkaline solution is specifically that the polyacryloyl chloride grafted onto the surface of the carbon nanotubes reacts with the alkaline solution to form polyacrylate. The ratio of the alkaline solution to polyacryloyl chloride is greater than 1:1 to be fully converted into carboxylate. When the battery is a lithium battery and the alkaline solution is lithium hydroxide, lithium polyacrylate is generated, and the lithium ions in lithium polyacrylate help to improve the lithium ion migration rate, thereby improving the kinetic performance.

[0073] In one embodiment, the pre-modified carbon nanotubes are dispersed in an alkaline solution and subjected to ultrasonic oscillation to promote the reaction.

[0074] In one embodiment, after the pre-modified carbon nanotubes react with the alkaline solution, suction filtration is carried out and the solid is repeatedly washed with deionized water until the filtrate is neutral. The solid is dried in a vacuum oven to remove moisture and dried to a constant weight to obtain modified carbon nanotube powder.

[0075] In a specific embodiment, 5 g of multi-walled carbon nanotubes are placed in a 500 mL flask, and added to a mixed solution of 200 mL of concentrated sulfuric acid / concentrated nitric acid (the volume ratio of concentrated sulfuric acid to concentrated nitric acid v1 / v2 = 3:1) for reaction. After ultrasonic oscillation for 3 h, the reaction mixture is refluxed at 120 °C for 1 h. The reactant is taken out and repeatedly washed with deionized water and suction filtered until the pH of the filtrate is neutral. Finally, the solid is dried at 40 °C in a vacuum oven to obtain oxidized carbon nanotubes.

[0076] The oxidized carbon nanotubes are placed in a dry flask filled with nitrogen (nitrogen can be replaced by an inert gas), and 500 mL of dioxane is added. After ultrasonic oscillation for 4 h, a dispersion of oxidized carbon nanotubes is obtained. A chain initiator (including one or more of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, ammonium sulfate, potassium persulfate, hydrogen peroxide, sodium persulfate) is placed in a dry flask filled with nitrogen (nitrogen can be replaced by an inert gas), 60 mL of dioxane, monomer acrylonitrile and acryloyl chloride are added. After magnetic stirring for 5 min, the mixture is stirred at a constant temperature of 60 °C for 8 h to form a polymerization reaction solution. The polymerization reaction solution is poured into a flask containing 50 mL of freshly distilled dioxane, and the dispersion of oxidized carbon nanotubes is slowly added drop by drop and 0.1 mL of triethylamine is added. The mixture is stirred at a constant temperature of 80 °C for 48 h. The reactant is suction filtered in a nitrogen (nitrogen can be replaced by an inert gas) glove box, and then repeatedly rinsed until the filtrate is clear to form pre-modified carbon nanotubes. In this step, the weight ratio of oxidized carbon nanotubes: chain initiator: acrylonitrile: acryloyl chloride is 30%: 6.5%: 25%: 38.5%. In this step, polyacryloyl chloride-polyacrylonitrile is covalently grafted onto the surface of the carbon nanotubes to form pre-modified carbon nanotubes.

[0077] The pre-modified carbon nanotubes are dispersed in 200 mL of 2 mo / L lithium hydroxide aqueous solution. After ultrasonic oscillation for 1 h, the mixture is allowed to stand for 24 h, suction filtered and repeatedly washed with deionized water until the filtrate is neutral. The solid is dried in a vacuum oven to a constant weight to obtain poly(lithium acrylate)-polyacrylonitrile grafted carbon nanotube powder, that is, modified carbon nanotube powder.

[0078] It should be noted that the modified carbon nanotubes obtained after steps S01 to S03 on the carbon nanotubes, through infrared characterization, 1560 cm -1A strong absorption peak at the wavenumber, which is caused by the stretching vibration of the C=O bond of the carboxyl group in the surface graft copolymer. At 2242 cm -1 A strong absorption peak at the wavenumber, which is caused by the stretching vibration of the C≡N bond. This is consistent with the characteristic peak in the pure polymer, indicating that the modified matrix grafted on the surface of the modified carbon nanotubes includes carboxylate and cyano groups.

[0079] The modified carbon nanotubes prepared by the preparation method of the modified carbon nanotubes provided in the embodiments of the present application include carboxylate and cyano groups. The carboxylate is beneficial to the uniform dispersion of the carbon nanotubes in the solvent, and the modified carbon nanotubes can be relatively uniformly dispersed on the surface of the silicon material. At the same time, the carboxylate and cyano groups interact with the hydroxyl groups on the silicon surface, enhancing the adhesion between the carbon nanotubes and the silicon material, facilitating the improvement of the conductive path of the silicon material, and exerting the electrochemical performance of the silicon material, thereby facilitating the improvement of the energy density of the battery.

[0080] The embodiments of the present application also provide a negative electrode plate. Please refer to Figure 2 , Figure 2 which is a schematic structural diagram of the negative electrode plate provided in the embodiments of the present application.

[0081] The negative electrode plate includes a current collector 31 and a negative electrode active layer 32. The negative electrode active layer 32 is provided on at least one side of the current collector 31; that is, the negative electrode active layer 32 is provided on one side of the current collector 31, or the negative electrode active layers 32 are respectively provided on both sides of the current collector 31. The negative electrode active layer 32 includes a negative electrode active material and a conductive agent. The conductive agent includes the modified carbon nanotubes introduced in the above embodiments or the modified carbon nanotubes prepared by the preparation method of the modified carbon nanotubes introduced in the above embodiments.

[0082] The lithium ions in the modified carbon nanotubes help to improve the lithium ion migration rate and reduce the concentration polarization. Secondly, the carboxyl and cyano groups in the modified carbon nanotubes have relatively large polarities and can react with groups such as hydroxyl groups on the surface of the silicon particles, enhancing the adhesion of the carbon nanotubes on the surface of the silicon particles, solving the problem that after cyclic charge and discharge, the volume expansion and contraction of the silicon particles cause the carbon nanotubes to slip with the silicon particles, and then lose electrical contact, resulting in life attenuation, and maintaining a good long cycle life. Finally, the linear long chains of the modified carbon nanotubes are coated on the surface of the silicon particles, restricting the expansion of the silicon particles, and can reduce the full charge rebound rate of the negative electrode plate, maintaining a high energy density and safety of the battery.

[0083] Please refer to Figure 3 , Figure 3 which is Figure 2 a schematic structural diagram of an embodiment of the negative electrode active layer shown.

[0084] In one embodiment, the negative electrode active layer 32 includes a first negative electrode active layer 321 and a second negative electrode active layer 322. The first negative electrode active layer 321 is disposed on one side of the current collector 31. The first negative electrode active layer 321 includes a first negative electrode active material and a first conductive agent, and the first negative electrode active material includes graphite. The second negative electrode active layer 322 is disposed on the side of the first negative electrode active layer 321 away from the current collector. The second negative electrode active layer 322 includes a second negative electrode active material and a second conductive agent, the second negative electrode active material includes a silicon-based material, and the second conductive agent includes modified carbon nanotubes.

[0085] In the prior art, usually graphite and silicon are first blended, and then a stabilizer, a conductive agent, and a binder are added to prepare a uniform anode slurry. However, since the graphite component in the system is greater than silicon, after the conductive agent is uniformly dispersed, more of it acts on the graphite particles, and less conductive agent is on the surface of the silicon particles with poor conductivity, resulting in an imperfect conductive path for the silicon material and a slow lithium intercalation rate. In the embodiment of the present application, by separating the graphite and the silicon-based material into two active layers, the second conductive agent (i.e., modified carbon nanotubes) acts on the surface of the silicon particles, improving the conductive network of the silicon-based material, fully exerting the conductivity of the silicon-based material, enhancing the kinetic performance of the battery, increasing the lithium intercalation rate, and preventing the silicon particles from cracking and electrical isolation caused by expansion during lithium intercalation, which is beneficial to improving the cycle performance of the battery.

[0086] A first negative electrode active layer 321 (i.e., a graphite active layer) is provided between the second negative electrode active layer 322 (i.e., a silicon-based active layer) and the current collector 31. Graphite is brittle and not very strong in strength, which can act as a buffer layer, well buffering and suppressing the stress changes caused by the volume expansion and contraction during the lithium deintercalation and intercalation of the silicon-based active layer, and preventing the active material layer from peeling off from the current collector 31 during continuous charge and discharge. The second conductive agent (i.e., modified carbon nanotubes) has good adhesion strength with the silicon particles, can prevent the carbon nanotubes and the silicon particles from slipping during repeated cycling, maintaining a good long cycle life. In addition, the grafted modification groups on the carbon nanotubes further restrict the expansion of the silicon particles, reducing the full charge rebound rate of the negative electrode sheet, and achieving a higher energy density and safety.

[0087] Optionally, the first conductive agent includes at least one of carbon black, acetylene black, carbon fiber, carbon nanotubes, and modified carbon nanotubes. It should be noted that since the conductivity of graphite is stronger than that of the silicon-based material, the conductivity of the second conductive agent can be greater than that of the first conductive agent.

[0088] Optionally, the second conductive agent further includes carbon black, that is, the second conductive agent is a mixture of modified carbon nanotubes and carbon black, having stronger conductivity.

[0089] In one embodiment, the sum of the thickness of the first negative electrode active layer 321 and the thickness of the second negative electrode active layer 322 is less than or equal to 200 μm; and / or, the ratio of the thickness of the first negative electrode active layer 321 to the thickness of the second negative electrode active layer 322 is 3:1 - 19:1, and the battery has a relatively high energy density and good installation performance. Exemplarily, the ratio of the thickness of the first negative electrode active layer 321 to the thickness of the second negative electrode active layer 322 can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, etc., or a range composed of any two of the above values. Optionally, the thickness of the first negative electrode active layer 321 is 75 μm - 95 μm; and / or, the thickness of the second negative electrode active layer 322 is 5 μm - 25 μm. Under the same area, the capacity of the first negative electrode active layer 321 (i.e., the graphite layer) is less than the capacity of the second negative electrode active layer 322 (i.e., the silicon-based layer), so the thickness of the first negative electrode active layer 321 needs to be greater than the thickness of the second negative electrode active layer 322.

[0090] The embodiment of the present application also provides a method for preparing a negative electrode plate, which can be used to prepare the negative electrode plate introduced in the above embodiment. Please refer to Figure 4 , Figure 4 FIG. is a schematic flow chart of the method for preparing a negative electrode plate provided by the embodiment of the present application.

[0091] The method for preparing a negative electrode plate provided by the embodiment of the present application specifically includes:

[0092] Step S11: Provide a negative electrode slurry, the negative electrode slurry includes a negative electrode active material and a conductive agent, and the conductive agent includes modified carbon nanotubes.

[0093] Specifically, the modified carbon nanotubes are the modified carbon nanotubes introduced in the above embodiment or the modified carbon nanotubes prepared by the method for preparing the modified carbon nanotubes introduced in the above embodiment.

[0094] In one embodiment, providing the negative electrode slurry includes providing a first negative electrode slurry and a second negative electrode slurry. The first negative electrode slurry includes a first negative electrode active material and a first conductive agent, and the first negative electrode active material includes graphite. The second negative electrode slurry includes a second negative electrode active material and a second conductive agent, the second negative electrode active material includes a silicon-based material, and the second conductive agent includes modified carbon nanotubes.

[0095] Optionally, the first negative electrode slurry further includes a binder and a dispersant, that is, graphite, the first conductive agent, the binder, the dispersant, etc. are mixed to form a graphite slurry. Among them, the dispersant includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyacrylic acid; the binder includes at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, polyvinyl alcohol, and polyacrylic acid.

[0096] The preparation method of the first negative electrode slurry includes:

[0097] ① Dry mixing of powders: At room temperature, graphite, the first conductive agent, and part of the dispersant sodium carboxymethylcellulose are simultaneously added to a stirring tank, and under a certain stirring speed condition, they are stirred and mixed evenly to obtain a uniformly mixed powder;

[0098] ② Add part of the deionized water to the stirring tank and carry out kneading under a certain stirring speed condition to obtain a wetted material;

[0099] ③ Then add the remaining dispersant sodium carboxymethylcellulose and deionized water to the stirring tank and prepare a uniform slurry under a certain stirring speed condition;

[0100] ④ Add the binder to the stirring tank and obtain a uniform slurry under a certain stirring speed condition;

[0101] ⑤ Viscosity adjustment: If the viscosity of the slurry obtained in step ④ is too high, a small amount of deionized water needs to be added to the slurry for viscosity adjustment, and the deionized water is added in small amounts and multiple times;

[0102] ⑥ Vacuum degassing: Seal the mixer, start vacuum degassing until the vacuum degree in the mixer reaches above -50 KPa, and stir for a certain time to obtain a uniform first negative electrode slurry.

[0103] Optionally, the second negative electrode slurry further includes a binder and a dispersant. That is to say, a silicon-based material, a second conductive agent, a binder, a dispersant, etc. are mixed to form a silicon-based slurry. Among them, the dispersant includes at least one of sodium carboxymethylcellulose, lithium carboxymethylcellulose, and polyacrylic acid; the binder includes at least one of styrene-butadiene rubber, sodium carboxymethylcellulose, polyvinyl alcohol, and polyacrylic acid.

[0104] The preparation method of the second negative electrode slurry includes:

[0105] ① Dry mixing of powders: At room temperature, the silicon-based material, the second conductive agent, and part of the dispersant sodium carboxymethylcellulose are simultaneously added to a stirring tank, and under a certain stirring speed condition, they are stirred and mixed evenly to obtain a uniformly mixed powder;

[0106] ② Add part of the deionized water to the stirring tank and carry out kneading under a certain stirring speed condition to obtain a wetted material;

[0107] ③ Then add the remaining dispersant sodium carboxymethylcellulose and deionized water to the stirring tank and prepare a uniform slurry under a certain stirring speed condition;

[0108] ④ Add the binder to the stirring tank and obtain a uniform slurry under a certain stirring speed condition;

[0109] ⑤Viscosity adjustment: If the viscosity of the slurry obtained in step ④ is too high, a small amount of deionized water needs to be added to the slurry for viscosity adjustment. The deionized water is added in small amounts and multiple times.

[0110] ⑥Vacuum degassing: Seal the blender, turn on the vacuum degassing until the vacuum degree in the blender reaches more than -50 KPa, and stir for a certain time to obtain a uniform second negative electrode slurry.

[0111] Step S12: Coat the negative electrode slurry on the current collector to form a negative electrode active layer.

[0112] In one embodiment, the negative electrode slurry includes a first negative electrode slurry and a second negative electrode slurry. The first negative electrode slurry and the second negative electrode slurry are simultaneously coated through a double-layer coating device. The first negative electrode slurry and the second negative electrode slurry are uniformly coated on the current collector at a certain speed and weight. The first negative electrode slurry is coated on the surface of the current collector, and the second negative electrode slurry is coated on the surface of the first negative electrode slurry, and then dried to form a negative electrode active layer, that is, the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer.

[0113] It should be noted that after the negative electrode active layer is formed, a cold press can be used to compact the negative electrode plate to a certain density at a certain pressure and speed to obtain a negative electrode plate with a certain thickness; during the cold pressing process, collect the weight of the powder scraped off from the surface of the cold pressing roller by the scraping knife, and test the adhesion of the negative electrode plate after cold pressing.

[0114] The negative electrode active layer formed by using the modified carbon nanotubes and the silicon-based material enables the battery to have a higher energy density and safety, and improves the kinetic performance of the battery.

[0115] In a specific embodiment, graphite, a binder, a first conductive agent, and a dispersant are mixed to form a graphite slurry; a silicon-based material, a binder, a second conductive agent, and a dispersant are mixed to form a silicon-based slurry, and the second conductive agent includes modified carbon nanotubes; the graphite slurry and the silicon-based slurry are simultaneously coated through a double-layer coating device, wherein the graphite slurry is coated on the surface of the current collector, and the silicon-based slurry is simultaneously coated on the surface of the graphite slurry; then dried to obtain a negative electrode plate.

[0116] Please refer to Figure 5 , Figure 5 which is a schematic exploded view of the battery cell provided by the embodiment of the present application.

[0117] The battery cell 20 refers to the smallest unit that makes up the battery 100. As Figure 5 shown, the battery cell 20 includes an end cap 21, a housing 22, a battery core assembly 23, and other functional components.

[0118] The end cap 21 refers to a component that covers the opening of the housing 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the housing 22 to fit the housing 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy). In this way, the end cap 21 is not easily deformed when subjected to extrusion and collision, enabling the battery cell 20 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on the end cap 21. The electrode terminal 21a can be used for electrical connection with the battery core assembly 23 to output or input the electrical energy of the battery cell 20. In some embodiments, a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold can also be provided on the end cap 21. The material of the end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special restrictions on this. In some embodiments, an insulating member can also be provided on the inner side of the end cap 21. The insulating member can be used to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. Exemplarily, the insulating member can be plastic, rubber, etc.

[0119] The housing 22 is a component for cooperating with the end cap 21 to form the internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the battery core assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 is covered at the opening to form the internal environment of the battery cell 20. Without limitation, the end cap 21 and the housing 22 can also be integrated. Specifically, the end cap 21 and the housing 22 can first form a common connection surface before other components are inserted into the housing, and when it is necessary to encapsulate the inside of the housing 22, the end cap 21 is then covered on the housing 22. The housing 22 can be of various shapes and sizes, such as rectangular parallelepiped, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the battery core assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special restrictions on this.

[0120] The battery cell assembly 23 is the component in the battery cell 100 where the electrochemical reaction occurs. The housing 22 may contain one or more battery cell assemblies 23. The battery cell assembly 23 is mainly formed by winding or laminating a positive electrode plate and a negative electrode plate, and a separator is usually provided between the positive electrode plate and the negative electrode plate. The portions of the positive electrode plate and the negative electrode plate having active materials constitute the main body of the battery cell assembly, and the portions of the positive electrode plate and the negative electrode plate without active materials respectively constitute the electrode tabs 23a. The positive electrode tab and the negative electrode tab may be located together at one end of the main body or respectively at both ends of the main body. During the charging and discharging process of the battery, the positive active material and the negative active material react with the electrolyte, and the electrode tabs 23a are connected to the electrode terminals to form a current loop.

[0121] Please refer to Figure 6 , Figure 6 which is a schematic exploded view of the battery provided by the embodiment of the present application.

[0122] The battery 100 includes a box body 10 and battery cells 20, and the battery cells 20 are accommodated in the box body 10. Among them, the box body 10 is used to provide an accommodation space for the battery cells 20, and the box body 10 can adopt various structures. In some embodiments, the box body 10 may include a first part 11 and a second part 12, the first part 11 and the second part 12 are covered with each other, and the first part 11 and the second part 12 jointly define an accommodation space for accommodating the battery cells 20. The second part 12 may be a hollow structure with one end open, and the first part 11 may be a plate-like structure. The first part 11 is covered on the opening side of the second part 12 so that the first part 11 and the second part 12 jointly define an accommodation space; the first part 11 and the second part 12 may also both be hollow structures with one side open, and the opening side of the first part 11 is covered on the opening side of the second part 12. Of course, the box body 10 formed by the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0123] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a combined series-parallel connection. A combined series-parallel connection means that there are both series and parallel connections among the multiple battery cells 20. The multiple battery cells 20 may be directly connected in series, in parallel, or in a combined series-parallel connection together, and then the whole formed by the multiple battery cells 20 is accommodated in the box body 10; of course, the battery 100 may also be that multiple battery cells 20 are first connected in series, in parallel, or in a combined series-parallel connection to form a battery module form, and then multiple battery modules are connected in series, in parallel, or in a combined series-parallel connection to form a whole and are accommodated in the box body 10. The battery 100 may further include other structures. For example, the battery 100 may further include a busbar component for realizing the electrical connection between the multiple battery cells 20.

[0124] Among them, each battery cell 20 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes, etc.

[0125] The battery disclosed in the embodiments of the present application can be used in electrical devices that use the battery as a power source or various energy storage systems that use the battery as an energy storage element. The electrical device can be, but is not limited to, a mobile phone, a tablet computer, a laptop computer, an electric toy, an electric tool, a battery car, an electric vehicle, a ship, a spacecraft, and so on. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, and an electric aircraft toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, and a spaceship, etc.

[0126] For the convenience of description in the following embodiments, a vehicle 1000, which is an electrical device in an embodiment of the present application, is taken as an example for description. Please refer to Figure 7 , Figure 7 which is a schematic structural diagram of the vehicle provided by the embodiments of the present application.

[0127] The vehicle 1000 can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. A battery 100 is disposed inside the vehicle 1000. The battery 100 can be disposed at the bottom, the head, or the tail of the vehicle 1000. The battery 100 can be used for power supply of the vehicle 1000. For example, the battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300. For example, it is used for the working power requirements during the start, navigation, and driving of the vehicle 1000.

[0128] In some embodiments of the present application, the battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0129] The present application also studied the battery performance obtained by using the modified carbon nanotubes provided by the embodiments of the present application.

[0130] The preparation process of Example 1 is as follows:

[0131] (1) Preparation of the first negative electrode paste:

[0132] ① At room temperature, graphite, the first conductive agent, and a dispersant are added to a blender simultaneously at a weight ratio of 96.2%:0.8%:0.5% and dry-mixed and stirred for 15 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 800 rpm to obtain a uniform dry powder mixture;

[0133] ② Add part of the deionized water to the dry powder mixture obtained in ① and stir for 60 min. The proportion of deionized water is 54% of the negative electrode active material (i.e., graphite). Knead with a stirring revolution speed of 15 rpm to obtain a moistened material;

[0134] ③ Add the remaining 0.5% dispersant sodium carboxymethyl cellulose and the remaining deionized water to the mixture obtained in step ② and stir for 65 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 1800 rpm to obtain a high-viscosity slurry with a viscosity of 8000 - 30000 Pa·s and a solid content of 50 - 60%;

[0135] ④ Add 2.0% of the binder to the high-viscosity slurry obtained in step ③ and stir for 30 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 1200 rpm to obtain a uniformly mixed slurry;

[0136] ⑤ Viscosity adjustment: If the viscosity of the slurry prepared in step ④ is too high, a small amount of deionized water needs to be added to the slurry for viscosity adjustment. The deionized water is added in small amounts and multiple times, and stirred for 20 min, with a stirring revolution speed of 10 rpm and a stirring rotation speed of 900 rpm. Finally, a first negative electrode slurry with a viscosity of 3000 - 15000 Pa·s, that is, a graphite slurry, is obtained.

[0137] It should be noted that in the preparation of the graphite slurry, the weight ratio of graphite, the first conductive agent, the dispersant, and the binder is 96.2%:0.8%:1.0%:2.0%.

[0138] (2) Preparation of the second negative electrode slurry:

[0139] ① At room temperature, a silicon-based material, a second conductive agent, and part of the dispersant sodium carboxymethyl cellulose are added to a blender simultaneously at a ratio of 96.7%:0.3%:0.5% and dry-mixed and stirred for 15 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 800 rpm to obtain a uniform dry powder mixture;

[0140] ② Add part of the deionized water to the dry powder mixture obtained in ① and stir for 60 min. The proportion of deionized water is 54% of the negative electrode active material (i.e., the silicon-based material). Knead with a stirring revolution speed of 15 rpm to obtain a moistened material;

[0141] ③ Add the remaining 0.5% dispersant sodium carboxymethyl cellulose and the remaining deionized water to the mixture obtained in step ② and stir for 65 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 1800 rpm to prepare a high-viscosity slurry with a viscosity of 8000 - 30000 Pa·s and a solid content of 50 - 60%;

[0142] ④ Add 2% binder to the high-viscosity slurry obtained in step ③ and stir for 30 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 1200 rpm to obtain a uniformly mixed slurry;

[0143] ⑤ Viscosity adjustment: If the viscosity of the slurry prepared in step ④ is too high, a small amount of deionized water needs to be added to the slurry for viscosity adjustment. The deionized water is added in small amounts and multiple times, and stirred for 20 min, with a stirring revolution speed of 10 rpm and a stirring rotation speed of 900 rpm. Finally, a second active slurry with a viscosity of 3000 - 15000 Pa·s, namely the silicon-based slurry, is prepared.

[0144] It should be noted that in the preparation of the silicon-based slurry, the weight ratio of silicon-based, the second conductive agent, the dispersant, and the binder is 96.7%:0.3%:1.0%:2.0%.

[0145] (3) Preparation of the negative electrode sheet:

[0146] Uniformly coat the graphite slurry in step (1) on the copper foil current collector with a thickness of 90 μm, and coat the silicon-based slurry on the graphite slurry with a thickness of 10 μm. The coating speed is 20 m / min, and the oven temperature is set at 80°C; use a cold press to compact the negative electrode sheet to a certain density. The cold press pressure is set at 30 tons, and the cold press speed is 15 m / min. During the cold pressing process, collect the mass of the powder scraped off the surface of the cold press roller by the collecting scraper, and test the adhesion and cohesion of the negative electrode sheet after cold pressing.

[0147] (4) Preparation of the positive electrode sheet:

[0148] The preparation of the positive electrode sheet includes: uniformly stirring and dispersing the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 , the conductive agent Super-P, and the binder polyvinylidene fluoride in a mass ratio of 96:2:2 in N-methylpyrrolidone to make a positive electrode slurry, coat it on the positive electrode current collector aluminum foil, and after compaction by a cold press, obtain the positive electrode sheet.

[0149] (5) Preparation of the electrolyte:

[0150] In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with a mass ratio of 35:65, add the lithium salt LiPF 6, mix evenly to obtain an electrolyte, where the molar concentration of LiPF in the electrolyte is 1 mol / L. 6

[0151] (6) Separator:

[0152] Select a 12-μm-thick polyethylene porous membrane as the separator.

[0153] It should be noted that the prepared negative electrode sheet, separator, and positive electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets to play a role in isolation, and then wound to obtain a bare battery cell. After that, it is inserted into the battery case and processed through baking, liquid injection, standing, encapsulation, formation, grading, etc. to obtain a lithium-ion battery.

[0154] The preparation processes of Examples 1 to 15 are the same. Specifically, by modifying the slurry formulation ratio and coating thickness, the batteries of Examples 2 to 15 can be prepared. The specific formulation ratios and coating thicknesses of Examples 1 to 15 are different, as shown in Table 1.

[0155] The difference between Example 16 and Example 1 is that the materials of the first negative electrode active layer and the second negative electrode active layer are the same. That is to say, the two negative electrode active layers in Example 16 can be understood as one negative electrode active layer. The preparation process of Example 16 is as follows:

[0156] ① Dry mixing of powders: Add graphite, silicon-based material, the first conductive agent (carbon black), the second conductive agent (modified carbon nanotubes), and the dispersant sodium carboxymethyl cellulose into a blender according to the ratio of 86.31%:9.59%:0.8%:0.3%:0.5% and conduct dry mixing and stirring for 15 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 800 rpm to obtain a uniform dry powder mixture;

[0157] ② Add part of deionized water to the dry powder mixture obtained in ① and stir for 60 min, where the proportion of deionized water is 54% of the negative electrode active material, and the stirring revolution speed is 15 rpm;

[0158] ③ Add the remaining 0.5% of the dispersant sodium carboxymethyl cellulose and the remaining deionized water to the mixture obtained in step ② and stir for 65 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 1800 rpm to obtain a high-viscosity slurry with a viscosity of 8000 - 30000 Pa·s and a solid content of 50 - 60%;

[0159] ④ Add a binder with a weight ratio of 2.0% to the high-viscosity slurry obtained in step ③ and stir for 30 min, with a stirring revolution speed of 25 rpm and a stirring rotation speed of 1200 rpm to obtain a uniformly mixed negative electrode slurry;

[0160] ⑤Viscosity adjustment: If the viscosity of the slurry prepared in step ④ is too high, a small amount of deionized water needs to be added to the slurry for viscosity adjustment. The deionized water is added in small amounts and multiple times, and stirred for 20 min, with the revolution speed of stirring being 10 rpm and the rotation speed of stirring being 900 rpm. Finally, a negative electrode slurry with a viscosity of 3000 - 15000 Pa·s is prepared.

[0161] ⑥Vacuum defoaming: Seal the mixer, turn on the vacuum degassing until the vacuum degree in the mixer reaches above -50 KPa, and stir for 20 min, with the revolution speed of stirring being 10 rpm and the rotation speed of stirring being 0 rpm. Finally, a mixed negative electrode slurry with a solid content of 40 - 60% is prepared.

[0162] The difference between Comparative Example 1 and Example 1 is that the second conductive agent used is carbon nanotubes, that is, unmodified carbon nanotubes, and the preparation process and other parameters are the same as those in Example 1.

[0163] The difference between Comparative Example 2 and Example 15 is that the conductive agent used is carbon nanotubes, that is, unmodified carbon nanotubes, and the preparation process and other parameters are the same as those in Example 15.

[0164] It should be noted that in Table 1 and Table 2, T2 represents the second negative electrode active layer, T1 represents the first negative electrode active layer, modified CNT represents modified carbon nanotubes, CNT represents carbon nanotubes (i.e., unmodified carbon nanotubes), SBR is styrene-butadiene rubber, and CMC is sodium carboxymethyl cellulose.

[0165] Table 1 Formulation ratios and coating thicknesses of each example

[0166]

[0167]

[0168] Table 2 Formulation ratios and coating thicknesses of each comparative example

[0169]

[0170] The relevant parameters of the above-mentioned examples and comparative examples are tested as follows:

[0171] 1. Process of testing the adhesion of the negative electrode plate

[0172] Equipment model: Zhongzhi testing tensile machine (model LXG2-LLCS-0009), specific testing process:

[0173] ①Take the electrode plate to be tested, use a blade to cut a specimen with a width of 30 mm and a length of 90 - 150 mm, stick the double-sided tape on the steel plate, with the tape width of 20 mm and the length of 90 - 150 mm.

[0174] ③ Stick the pole piece specimen cut in the first step on the double-sided tape with the test surface facing up. The width is 20 mm, and roll it three times in the same direction with a roller.

[0175] ④ Turn on the power of the Sansi tensile testing machine. Fix one end of the steel plate without the pole piece attached with the lower clamp, ensuring that the steel plate is placed perpendicular to the base table and the bottom end of the steel plate is flush with the base. Fold up the pole piece stuck on the steel plate and fix it with the upper clamp.

[0176] ⑤ First pre-stretch about 5 mm, then "zero" the "force" and "displacement" parameters. After making the above two parameters zero, click the start button to start the test, and then record the test results. Then do three groups in parallel, calculate the average value N1, and the final bonding force size = N1 * 50.

[0177] 2. Testing process of the cohesive force of the negative pole piece

[0178] Equipment model: Zhongzhi Testing Tensile Testing Machine (model LXG2-LLCS-0009), specific testing process:

[0179] ① Take the pole piece to be tested, cut a specimen with a width of 30 mm and a length of 90 - 150 mm with a blade, stick the double-sided tape on the steel plate, and the tape width is 20 mm * length 90 - 150 mm.

[0180] ② Stick the pole piece specimen cut in the first step on the double-sided tape with the test surface facing up. Stick a low-tack green tape with a width of 20 mm and a length 80 - 200 mm longer than the specimen length flat on the surface of the test surface, and roll it three times in the same direction with a roller.

[0181] ③ Turn on the power of the Sansi tensile testing machine. Fix one end of the steel plate without the pole piece attached with the lower clamp, ensuring that the steel plate is placed perpendicular to the base table and the bottom end of the steel plate is flush with the base. Fold up the green glue with the hard paper stuck on it and fix it with the upper clamp.

[0182] ④ First pre-stretch about 5 mm, then "zero" the "force" and "displacement" parameters. After making the above two parameters zero, click the start button to start the test, and then record the test results. Then do three groups in parallel, calculate the average value N1, and the final cohesive force size = N1 * 50.

[0183] 3. Testing process of the physical rebound of the negative pole piece

[0184] Equipment model: Mitutoyo Micrometer (model 293-100-20), specific testing process:

[0185] ① After adjusting the process parameters of the cold pressing, use a micrometer to measure the thickness of the pole piece just after passing through the roller. Take this measured thickness as the initial thickness (initial thickness = designed thickness ± 2 μm), and mark the test points and the test time on the pole piece, and place it in an environment of 25 °C and humidity < 40%.

[0186] ②At intervals of 1H, 2H, 24H, and 48H, test the test points of the electrode sheet, record the thickness, and calculate the physical rebound rate.

[0187] ③Then disassemble the lithium-ion battery cells in the formation, formation and full charge stages, measure the thickness with a micrometer, record the thickness, and calculate the chemical rebound.

[0188] 4. Battery cycle performance test

[0189] Taking Example 1 as an example, the cycle performance test process of the lithium-ion battery is as follows: Charge the lithium-ion battery at 0.5C and discharge it at 1C at 25°C and 45°C respectively, and record the capacity retention rate of the lithium-ion battery after 500 cycles. The test processes of the comparative example and other examples are the same as above. The data in Table 3 are the data measured after the battery has been cycled 500 times under the above test conditions.

[0190] 5. Storage performance test of lithium-ion battery

[0191] Taking the example as an example, the storage performance test process of the lithium-ion battery: Fully charge the lithium-ion battery at 1C, and then store it at storage temperatures of 25°C and 60°C for 60 days, and record the capacity retention rate of the lithium-ion battery after 60 days of storage. The test processes of Comparative Example 1 and other examples are the same as above. The data in Table 3 are the data measured after 60 days of storage under the above test conditions.

[0192] 6. DCR test

[0193] Taking the example as an example, the test process of the 25°C DCR of the lithium-ion battery: Place the lithium-ion battery cell in a constant temperature environment of 25°C for 30 min, and then fully charge it at 0.33C under this constant temperature condition. Then, adjust it to 90% SOC, 50% SOC, and 10% SOC respectively, and then discharge it at a rate of 4C for 30 s first, and then charge it for 30 s. Obtain the DCR data according to the voltage drop and current change values.

[0194] Taking the example as an example, the test process of the -25°C DCR of the lithium-ion battery: Place the lithium-ion battery cell in a constant temperature environment of 25°C for 30 min, and then fully charge it at 0.33C under this constant temperature condition. Then, adjust it to 90% SOC, 50% SOC, and 10% SOC respectively, and then place the lithium-ion battery cell in a constant temperature environment of -25°C for 2 h. Then, discharge it at a rate of 0.36C for 30 s first and then charge it for 30 s in the constant temperature environment of -25°C. Obtain the DCR data according to the voltage drop and current change values.

[0195] Table 3 Cohesive force and cohesion of each comparative example and example

[0196] Adhesion force N / m Cohesion force N / m Pole piece width Example 1 20.2 115.5 30mm Example 2 20.4 121.8 30mm Example 3 20.9 129.2 30mm Example 4 19.7 133.1 30mm Example 5 21.9 138.6 30mm Example 6 20.5 143.0 30mm Example 7 20.1 147.9 30mm Example 8 21.8 125.0 30mm Example 9 24.5 122.9 30mm Example 10 26.3 120.4 30mm Example 11 25.7 121.7 30mm Example 12 25.2 124.1 30mm Example 13 24.9 123.9 30mm Example 14 24.9 122.0 30mm Example 15 25.0 123.8 30mm Example 16 17.1 116.7 30mm Comparative Example 1 15.7 95.4 30mm Comparative Example 2 15.4 93.8 30mm

[0197] Table 4 Rebound Rates of Negative Electrodes of Each Comparative Example and Example

[0198]

[0199]

[0200] Table 5 Test Results of DC Impedance, Cycling Performance and Storage Performance of Each Comparative Example and Example

[0201]

[0202] It can be seen from Table 3 that the adhesion and cohesion of the negative electrode sheets made of modified carbon nanotubes (Examples 1-16) are both higher than those of the negative electrode sheets made of carbon nanotubes (Comparative Examples 1-2). Comparing Examples 1 to 7, as the content of modified carbon nanotubes increases, the cohesion of the negative electrode sheet increases.

[0203] It can be seen from Table 4 that the physical and chemical rebound rates of the negative electrode sheets made of modified carbon nanotubes (Examples 1-16) are both lower than those of the negative electrode sheets made of carbon nanotubes (Comparative Examples 1-2). Comparing Examples 1 to 7, as the content of modified carbon nanotubes increases, the physical rebound rate of the negative electrode sheet decreases.

[0204] It can be seen from Table 5 that the cycling performance, storage performance and DC impedance of the batteries made of modified carbon nanotubes (Examples 1-16) are significantly improved compared with the batteries made of carbon nanotubes (Comparative Examples 1-2).

[0205] The above description is only the implementation mode of this application, and does not limit the patent scope of this application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of this application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of this application.

Claims

1. A modified carbon nanotube, characterized in that: include: The carbon nanotube has a modified group on the surface, wherein the modified group includes carboxylate.

2. The modified carbon nanotube according to claim 1, characterized in that: The modifying group includes a polyalkyl carboxylate; Optionally, the polyalkyl carboxylate includes any one of lithium polypropylene carboxylate, sodium polypropylene carboxylate and magnesium polypropylene carboxylate.

3. The modified carbon nanotube according to claim 1 or 2, characterized in that: The modifying group includes a cyano group; Optionally, the modifying group comprises polyacrylonitrile.

4. The modified carbon nanotube according to any one of claims 1 to 3, characterized in that: The modified carbon nanotubes are modified single-walled carbon nanotubes or modified multi-walled carbon nanotubes.

5. A method for preparing modified carbon nanotubes, characterized in that: include: Dispersing carbon nanotubes in a strong oxidizing solution and treating them to obtain oxidized carbon nanotubes, wherein a portion of carbon in the oxidized carbon nanotubes is functionalized into oxygen-containing groups; reacting the oxidized carbon nanotubes with a modifier to obtain pre-modified carbon nanotubes, wherein the modifier includes an acyl group; The pre-modified carbon nanotubes are dispersed in an alkaline solution and treated to obtain modified carbon nanotubes, wherein the surface of the modified carbon nanotubes has a modified group, and the modified group includes a carboxylate.

6. The method for preparing modified carbon nanotubes according to claim 5, characterized in that: The step of reacting the oxidized carbon nanotubes with a modifier comprises: Adding a chain initiator to a polymer monomer solution to perform a polymerization reaction to form a polymerization reaction solution, wherein the polymer monomer includes an acyl group; The dispersion of the oxidized carbon nanotubes is added to the polymerization reaction solution, and the reaction is continued to obtain the pre-modified carbon nanotubes.

7. The method for preparing modified carbon nanotubes according to claim 6, characterized in that: The polymer monomer also includes a cyano group; Optionally, the step of adding a chain initiator to the polymer monomer solution to perform a polymerization reaction to form a polymerization reaction solution comprises: Adding a chain initiator to a mixed solution of acrylonitrile and acryloyl chloride, and heating for reaction; optionally, the heating temperature is 55° C.-65° C., and the reaction time is 7 h-9 h; Optionally, the step of adding the dispersion of the oxidized carbon nanotubes into the polymerization reaction solution and continuing the reaction comprises: Add the dispersion of oxidized carbon nanotubes dropwise into the polymerization reaction solution, and continue heating the reaction; optionally, the heating temperature is 75° C.-85° C., and the reaction time is 40 h-50 h; Optionally, the weight ratio of the oxidized carbon nanotubes: the chain initiator: the acrylonitrile: the acryloyl chloride is (25%-35%): (5%-7%): (20%-30%): (30%-40%).

8. A negative electrode plate, characterized in that: include: current collector; A negative electrode active layer is provided on at least one side of the current collector, wherein the negative electrode active layer comprises a negative electrode active material and a conductive agent, wherein the conductive agent comprises the modified carbon nanotubes according to any one of claims 1 to 4 or the modified carbon nanotubes prepared by the preparation method according to any one of claims 5 to 7.

9. The negative electrode sheet according to claim 8, characterized in that: The negative electrode active layer comprises: A first negative electrode active layer is disposed on one side of the current collector; the first negative electrode active layer comprises a first negative electrode active material and a first conductive agent, and the first negative electrode active material comprises graphite; The second negative electrode active layer is arranged on a side of the first negative electrode active layer away from the current collector; the second negative electrode active layer comprises a second negative electrode active material and a second conductive agent, the second negative electrode active material comprises a silicon-based material, and the second conductive agent comprises the modified carbon nanotubes.

10. The negative electrode sheet according to claim 8 or 9, characterized in that: The first conductive agent includes at least one of carbon black, acetylene black, carbon fiber, carbon nanotube, and the modified carbon nanotube.

11. A battery cell, characterized in that: include: The negative electrode sheet according to any one of claims 8 to 10.

12. A battery, characterized in that: include: The battery cell according to claim 11 or the negative electrode sheet according to any one of claims 8 to 10.

13. An electrical equipment, characterized in that: Comprising the battery as claimed in claim 12.

14. A method for preparing a negative electrode sheet, characterized in that: include: Providing a negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material and a conductive agent, wherein the conductive agent comprises the modified carbon nanotube according to any one of claims 1 to 4 or the modified carbon nanotube prepared by the preparation method according to any one of claims 5 to 7; The negative electrode slurry is coated on a current collector to form a negative electrode active layer.

15. The method for preparing a negative electrode sheet according to claim 14, characterized in that: Mixing graphite, an adhesive, a first conductive agent, and a dispersant to form a graphite slurry; mixing a silicon-based material, an adhesive, a second conductive agent, and a dispersant to form a silicon-based slurry, wherein the second conductive agent includes modified carbon nanotubes; The graphite slurry and the silicon-based slurry are simultaneously coated by a double-layer coating device, wherein the graphite slurry is coated on the surface of the current collector, and the silicon-based slurry is simultaneously coated on the surface of the graphite slurry; Drying to obtain the negative electrode sheet.

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