Composite negative electrode material, preparation method and application thereof

Abstract

The application relates to a composite negative electrode material and a preparation method and application thereof, and belongs to the technical field of batteries. The composite negative electrode material comprises carbon nanotubes and silicon particles arranged at least on the outer surfaces of two ends of the carbon nanotubes, and the silicon particles are connected with the carbon nanotubes through a covalent bond. The connection mode of the carbon nanotubes and the silicon particles in the composite negative electrode material effectively improves the cycle stability of a negative electrode sheet containing the composite negative electrode material.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite anode material, its preparation method, and its application. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] Secondary batteries possess advantages such as high energy density, long lifespan, wide operating voltage range, low self-discharge, and no memory effect, making them the primary power source for new energy vehicles. With the increasing market demand for high-capacity power batteries, anode materials with high theoretical specific capacity, such as silicon-based materials, have been developed. However, the poor conductivity of traditional silicon-based materials results in poor cycle stability of anode sheets containing silicon-based materials, limiting the further application of silicon-based materials. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite anode material, its preparation method, and its application to improve the cycle stability of anode sheets containing the composite anode material.

[0005] In a first aspect, this application provides a composite anode material comprising carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes, wherein the silicon particles are covalently bonded to the carbon nanotubes.

[0006] The connection method between carbon nanotubes and silicon particles in the above-mentioned composite anode material significantly improves the conductive network between silicon particles. On the other hand, during the expansion and contraction process of silicon particles in charge-discharge cycles, it not only preserves the free expansion space for carbon nanotubes to move with silicon particles, but also improves the problem of free non-conductivity after silicon particles contract, thereby enhancing the cycle stability of the anode sheet containing this composite anode material.

[0007] In some embodiments, the average length of the carbon nanotubes is 0.04 μm to 1 μm.

[0008] In some embodiments, the average diameter of the carbon nanotubes is 0.8 nm to 90 nm.

[0009] In some embodiments, the mass percentage of the carbon nanotubes is 0.1%-20%, optionally 0.1%-10%, based on the mass of the composite anode material.

[0010] In some embodiments, the volume average particle size Dv50 of the silicon particles is 0.2 μm-50 μm, and can be selected as 0.2 μm-12 μm.

[0011] In some embodiments, the silicon particles include one or more of elemental silicon particles, silicon oxide particles, silicon-carbon composite particles, silicon-nitrogen composite particles, and silicon alloy particles.

[0012] In some embodiments, the silicon content in the composite anode material is 35%-70% by mass.

[0013] In some embodiments, the carbon content in the composite anode material is 1%-40% by mass.

[0014] In some embodiments, the silicon particles also contain oxygen, and the mass percentage of oxygen in the composite anode material is 0.02%-60%.

[0015] In some embodiments, the powder resistivity of the composite negative electrode material is 0.1 Ω·m to 200 Ω·m.

[0016] In some embodiments, the specific surface area of ​​the composite negative electrode material is 0.005 m². 2 / g-4m 2 / g.

[0017] A second aspect of this application provides a method for preparing the composite negative electrode material described in the first aspect of this application, comprising the following steps:

[0018] The material to be treated, including metal nanowires and silicon particles, is subjected to heat treatment in a mixed gas containing an organic carbon source.

[0019] The product obtained from the heat treatment is washed with acid to remove the metal nanowires, resulting in the carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes.

[0020] The above preparation method is relatively simple and is conducive to the large-scale production of the above composite anode material.

[0021] In some embodiments, the following steps are included before the step of heat-treating the material to be treated in the mixed gas:

[0022] The metal nanowires, the silicon particles, and the organic solvent are mixed to obtain a mixture.

[0023] The organic solvent in the mixture is removed to obtain the material to be treated.

[0024] In some embodiments, the organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and isopropanol.

[0025] In some embodiments, the acid solution includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0026] In some embodiments, the mass ratio of the metal nanowires to the silicon particles is (0.4-40):1, and optionally (0.4-10):1.

[0027] In some embodiments, the metal nanowires include at least one of copper nanowires and nickel nanowires.

[0028] In some embodiments, the heat treatment process conditions include: a heat treatment temperature of 50℃-3000℃ and a heat treatment time of 30min-180min.

[0029] In some embodiments, the mixed gas contains, in addition to the organic carbon source, a reducing gas and an inert gas.

[0030] In some embodiments, the organic carbon source includes methane.

[0031] In some embodiments, the reducing gas includes hydrogen.

[0032] In some embodiments, the inert gas includes at least one of argon, helium, and neon.

[0033] In some embodiments, the flow rate of the organic carbon source is 15 mL / min to 300 mL / min.

[0034] In some embodiments, the flow rate of the reducing gas is 10 mL / min to 300 mL / min.

[0035] In some embodiments, the flow rate of the inert gas is 50 mL / min to 1200 mL / min.

[0036] A third aspect of this application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises at least one of the composite negative electrode material described in the first aspect of this application and the composite negative electrode material prepared by the preparation method described in the second aspect of this application.

[0037] The negative electrode sheet of this application includes the composite negative electrode material provided in this application, and therefore has at least the same advantages as the composite negative electrode material.

[0038] In some embodiments, the carbon nanotubes have a mass percentage of 0.1%-20% based on the mass of the negative electrode active material layer.

[0039] A fourth aspect of this application provides a secondary battery, including the negative electrode sheet described in the third aspect of this application.

[0040] The secondary battery of this application includes the negative electrode sheet provided in this application, and therefore has at least the same advantages as the composite negative electrode sheet.

[0041] A fifth aspect of this application provides an electrical device including the secondary battery described in the fourth aspect of this application.

[0042] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0043] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0044] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0045] Figure 1 This is a scanning electron microscope image of the composite negative electrode material prepared in Example 1 of this application.

[0046] Figure 2 This is a schematic diagram of the structure of the composite negative electrode material according to one embodiment of this application.

[0047] Figure 3 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0048] Figure 4 for Figure 3 An exploded view of a battery cell according to one embodiment of this application is shown.

[0049] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0050] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0051] Figure 7 for Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0052] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0053] Explanation of reference numerals in the attached figures:

[0054] 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Casing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device; 7 Composite negative electrode material; 71 Silicon particles; 72 Carbon nanotubes. Detailed Implementation

[0055] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments of the composite anode material of this application, its preparation method, and its application. However, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0056] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0057] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0060] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0061] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0062] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0063] Anode materials are one of the key materials for improving the performance of secondary batteries. Among various anode materials, silicon-based materials have attracted much attention due to their high theoretical specific capacity. However, traditional silicon-based materials have poor conductivity, resulting in poor stability of anode sheets containing traditional silicon-based materials. Although carbon nanotubes can be used as conductive agents in conjunction with traditional silicon-based materials to improve the conductivity of the material, the following problems still exist:

[0064] 1. Carbon nanotubes are usually added to traditional silicon-based materials along with other additives. Due to the tendency of carbon nanotubes to agglomerate, traditional silicon-based materials will lose a lot of contact sites regardless of the order of addition. Carbon nanotubes will have ineffective contact with binders and other additives, which greatly reduces the utilization rate of carbon nanotubes.

[0065] 2. Carbon nanotubes typically contain metal particles that adhere to the ends of highly conductive carbon nanotubes. These particles have a strong catalytic effect on the electrode solution, which is detrimental to the stability of the battery.

[0066] 3. The carbon nanotubes added to traditional silicon-based materials result in extremely weak physical connections between different particles, requiring the addition of a large number of carbon nanotubes to effectively form a conductive network.

[0067] 4. In-situ growth of carbon nanotubes on the surface of silicon-based material particles improves the physical contact between the carbon nanotubes and the silicon-based material particles. However, since the carbon nanotubes are only connected to the silicon-based material particles at one end, the contact efficiency between the silicon-based material particles is still not high. A large amount of carbon nanotubes needs to be grown on the surface of the silicon-based material particles to achieve effective electrical contact.

[0068] Based on this, this application provides a composite anode material, which includes carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes. The silicon particles are covalently connected to the carbon nanotubes. The connection between the carbon nanotubes and the silicon particles can significantly improve the conductive network between the silicon particles. On the other hand, during the expansion and contraction of the silicon particles during charge and discharge cycles, it can retain the free expansion space for the carbon nanotubes to move with the silicon particles, and improve the problem of free non-conductivity after the silicon particles contract. This can improve the cycle stability of the anode sheet containing the composite anode material.

[0069] Composite anode materials

[0070] One embodiment of this application provides a composite negative electrode material, including carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes, wherein the silicon particles and the carbon nanotubes are connected by covalent bonds.

[0071] The connection between carbon nanotubes and silicon particles in the aforementioned composite anode material significantly improves the conductive network between silicon particles. Furthermore, during the expansion and contraction of silicon particles during charge-discharge cycles, it preserves the free expansion space for carbon nanotubes to move with the silicon particles while mitigating the problem of non-conductive ionization after silicon particle contraction. This enhances the cycle stability of the anode sheet containing this composite anode material. The aforementioned covalent bonds include, but are not limited to, covalent bonds formed by at least one atom selected from carbon, oxygen, hydrogen, and silicon atoms. Examples include carbon-carbon single bonds, carbon-oxygen single bonds, carbon-hydrogen bonds, and carbon-silicon bonds.

[0072] In the aforementioned composite anode material, the silicon particles at least disposed on the outer surfaces of both ends of the carbon nanotube refer to a single carbon nanotube being connected to at least two silicon particles.

[0073] In general, transmission electron microscopy (TEM) can be used to observe the arrangement and connection of silicon particles and carbon nanotubes.

[0074] In this application, silicon particles include, but are not limited to, at least one of elemental silicon particles, silicon oxide particles, silicon-carbon composite particles, silicon-nitrogen composite particles, and silicon alloy particles.

[0075] In this application, the outer surfaces at both ends of a carbon nanotube refer to the non-internal surfaces at both ends of the carbon nanotube along its length.

[0076] In some implementations, reference Figure 2 The composite negative electrode material 7 includes carbon nanotubes 72 and silicon particles 71 disposed at least on the outer surfaces of both ends of the carbon nanotubes 72. The silicon particles 71 are connected to the carbon nanotubes 72 by covalent bonds.

[0077] In some embodiments, the average length of the carbon nanotubes is 0.04 μm to 1 μm. Controlling the average length of the carbon nanotubes within this range is beneficial for further improving the conductive network between silicon particles, while also allowing sufficient space for the silicon particles to expand freely, thus mitigating the problem of non-conductive ionization after shrinkage. This enhances the conductivity of the composite anode material and further improves the cycle stability of the anode sheet containing this composite anode material. It is understood that the average length of the carbon nanotubes includes, but is not limited to, 0.04 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, and 1 μm.

[0078] In some embodiments, the average diameter of the carbon nanotubes is 0.8 nm to 90 nm. This diameter range provides the composite anode material with a certain degree of rigidity, which is beneficial for further improving the conductive network between silicon particles. It also allows for some free expansion space for the silicon particles, mitigating the problem of non-conductive ionization after shrinkage, thus enhancing the conductivity of the composite anode material and further improving the cycle stability of the anode sheet containing this composite anode material. It is understood that the average diameter of the carbon nanotubes includes, but is not limited to, 0.8 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, and 90 nm.

[0079] Optionally, the average length and average diameter of the carbon nanotubes can be obtained using transmission electron microscopy (TEM). For example, the length and diameter of 100 carbon nanotubes can be observed using TEM, and the average length and average diameter of the carbon nanotubes can be obtained statistically.

[0080] In some embodiments, carbon nanotubes include single-walled carbon nanotubes. Single-walled carbon nanotubes are beneficial for improving the conductivity of composite anode materials and the gravimetric energy density of secondary batteries.

[0081] In some embodiments, the mass percentage of carbon nanotubes is 0.1%-20% based on the mass of the composite anode material. This further improves the cycle stability of the anode sheet containing the composite anode material. The mass percentage of carbon nanotubes includes, but is not limited to: 0.1%, 2%, 5%, 10%, 15%, and 20%. Further, the mass percentage of carbon nanotubes is 0.1%-10% based on the mass of the composite anode material. Controlling the mass percentage of carbon nanotubes within the above range can increase the specific capacity of the composite anode material.

[0082] In some embodiments, the volume average particle size (Dv50) of the silicon particles is 0.2 μm-50 μm. Controlling the volume average particle size (Dv50) of the silicon particles within the above range can improve the contact efficiency between the silicon particles and carbon nanotubes, while also taking into account the cycle stability and rate performance of the composite anode material. It is understood that the volume average particle size (Dv50) of the silicon particles includes, but is not limited to: 0.2 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, and 50 μm. Further, the volume average particle size (Dv50) of the silicon particles is 0.2 μm-12 μm. Even further, the volume average particle size (Dv50) of the silicon particles is 0.4 μm-10 μm.

[0083] Optionally, the volume average particle size Dv50 of silicon particles can be tested by the following method: taking pictures of the cross-section of the composite anode material using a scanning electron microscope (SEM) (e.g., ZEISS Sigma 300), and obtaining the volume average particle size Dv50 of silicon particles in the composite anode material by measurement and statistical analysis.

[0084] In some embodiments, the mass percentage of silicon in the composite anode material is 35%-70%. It is understood that the mass percentage of silicon in the composite anode material includes, but is not limited to, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70%.

[0085] In some embodiments, the mass percentage of carbon in the composite anode material is 1%-40%. It is understood that the mass percentage of carbon in the composite anode material includes, but is not limited to: 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, and 40%.

[0086] In some embodiments, the silicon particles also contain oxygen, and the mass percentage of oxygen in the composite anode material is 0.02%-60%. It is understood that the mass percentage of oxygen in the composite anode material includes, but is not limited to: 0.02%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, and 60%.

[0087] Optionally, inductively coupled plasma atomic emission spectrometry (ICP) can be used to test the mass percentage content of silicon, carbon and oxygen in the composite anode material.

[0088] In some embodiments, the powder resistivity of the composite anode material is 0.1 Ω·m to 200 Ω·m. It is understood that the powder resistivity of the composite anode material includes, but is not limited to: 0.1 Ω·m, 10 Ω·m, 20 Ω·m, 40 Ω·m, 60 Ω·m, 80 Ω·m, 100 Ω·m, 120 Ω·m, 140 Ω·m, 160 Ω·m, 180 Ω·m, and 200 Ω·m. Further, the powder resistivity of the composite anode material is 0.1 Ω·m to 15 Ω·m. Optionally, a powder resistivity tester can be used to test the powder resistivity of the composite anode material.

[0089] In some embodiments, the specific surface area of ​​the composite negative electrode material is 0.005 m². 2 / g-4m 2 / g. It is understood that the specific surface area of ​​the composite anode material includes, but is not limited to, 0.005m². 2 / g, 0.1m 2 / g, 0.5m 2 / g, 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g.

[0090] The specific surface area of ​​composite anode materials can be tested using nitrogen adsorption-desorption. For example, the BET specific surface area of ​​the material can be measured using a specific surface area analyzer (Tristar II).

[0091] Another embodiment of this application provides a method for preparing the above-mentioned composite negative electrode material, including the following steps:

[0092] The materials to be treated, including metal nanowires and silicon particles, are subjected to heat treatment in a mixed gas containing an organic carbon source.

[0093] The product obtained from heat treatment is washed with acid to remove the metal nanowires, resulting in carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes.

[0094] In the above preparation method, carbon nanotubes grow around the metal nanowires during heat treatment. Because the metal nanowires are in contact with the carbon nanotubes, covalent bonds can be formed between the outer surfaces of the two ends of the carbon nanotubes and silicon particles. During the washing process, the acid solution removes the metal nanowires, thereby obtaining carbon nanotubes and silicon particles at least disposed on the outer surfaces of the two ends of the carbon nanotubes. The above preparation method is relatively simple and is beneficial for the large-scale production of the aforementioned composite anode material.

[0095] In some embodiments, the acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0096] In some embodiments, the following steps are included before the step of heat-treating the material to be treated in the mixed gas:

[0097] Metal nanowires, silicon particles, and organic solvents are mixed to obtain a mixture.

[0098] Remove the organic solvent from the mixture to obtain the material to be treated.

[0099] In the above embodiments, mixing metal nanowires, silicon particles and organic solvents is beneficial to uniformly mixing the metal nanowires and silicon particles, so that carbon nanotubes can be uniformly formed between the silicon particles during the subsequent heat treatment process.

[0100] In some embodiments, the organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and isopropanol.

[0101] In some embodiments, the mass ratio of metal nanowires to silicon particles is (0.4-40):1, optionally (0.4-10):1. It is understood that the mass ratio of metal nanowires to silicon particles includes, but is not limited to: 0.4:1, 1:1, 3:1, 5:1, 8:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, and 40:1.

[0102] In some embodiments, the metal nanowires include at least one of copper nanowires and nickel nanowires.

[0103] In some embodiments, the heat treatment process conditions include: a heat treatment temperature of 50℃-3000℃ and a heat treatment time of 30min-180min. It is understood that the heat treatment temperature includes, but is not limited to: 50℃, 200℃, 500℃, 800℃, 1000℃, 1300℃, 1500℃, 1800℃, 2000℃, 2200℃, 2500℃, 2800℃, and 3000℃.

[0104] In some embodiments, the mixture contains, in addition to an organic carbon source, a reducing gas and an inert gas.

[0105] In some specific implementations, the organic carbon source includes methane.

[0106] In some specific implementations, the organic carbon source includes methane and other commonly used organic carbon sources.

[0107] In some specific implementations, the reducing gas includes hydrogen.

[0108] In some specific implementations, the reducing gas includes hydrogen and other commonly used reducing gases.

[0109] In some specific embodiments, the inert gas includes at least one of argon, helium, and neon.

[0110] In some specific implementations, the flow rate of the organic carbon source is 15 mL / min to 300 mL / min.

[0111] In some specific implementations, the flow rate of the reducing gas is 10 mL / min to 300 mL / min.

[0112] In some specific implementations, the flow rate of the inert gas is 50 mL / min to 1200 mL / min.

[0113] Another embodiment of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes at least one of the above-described composite negative electrode material and the composite negative electrode material prepared by the above-described preparation method.

[0114] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0115] In some embodiments, based on the mass of the negative electrode active material layer, the mass percentage of carbon nanotubes is 0.1%-20%, optionally 0.1%-10%. It is understood that, based on the mass of the negative electrode active material layer, the mass percentage of carbon nanotubes includes, but is not limited to: 0.1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, and 20%.

[0116] In some embodiments, the negative electrode active material layer may include, in addition to the aforementioned composite negative electrode material, a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0117] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0118] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0119] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0121] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, or other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s-10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75 g / m². 2 -220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 -1.8g / cm 3 .

[0122] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0123] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0124] Positive electrode sheet

[0125] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0126] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0127] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0128] Given that the Li content in the positive electrode active material can change, how should the subscript of Li be defined in the general formula?

[0129] For ternary materials:

[0130] Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y x is between 0.2 and 1.2;

[0131] Li x A a (Ni a Co b Mn c ) 1-d M d O 2-y A y x+a is 0.2-1.2;

[0132] For lithium manganese iron phosphate materials:

[0133] 1)Li a Mn 1-y B y P 1-z C z O 4-n Dn a is 0-1.1;

[0134] 2)Li a A x Mn 1-y B y P 1-z C z O 4-n D n a+x is 0-1.1;

[0135] The above limitation on x includes the molar content of Li under different charge and discharge states of the battery (typically the battery voltage is between 2V and 5V).

[0136] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the examples of positive electrode active materials listed in this application, unless otherwise specified, the Li content refers to the initial state of the material. When positive electrode active materials are applied to the positive electrode in a battery system, the Li content in the positive electrode active material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0137] In the examples of positive electrode active materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0138] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.85 Co 0.15 Al 0.05 O2.

[0139] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0140] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s-25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area, based on dry weight (excluding solvent), can be 15 mg / cm³. 2 -35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 -3.6g / cm 3 3.3g / cm³ is an option. 3 -3.5g / cm 3 .

[0142] Negative electrode sheet

[0143] The negative electrode sheet described in this application is used.

[0144] electrolytes

[0145] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0146] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0147] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0148] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate ( One or more of the following: fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0149] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0150] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0151] Separating membrane

[0152] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0153] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0154] In some embodiments, the thickness of the isolation membrane is 6μm-40μm, and optionally 12μm-20μm.

[0155] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0156] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0157] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0158] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0159] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0160] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 The example shown is a square-structured battery cell 5.

[0161] In some implementations, refer to Figure 4The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0162] The secondary battery can be either battery module 4 or battery pack 1.

[0163] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0164] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0165] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0166] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the battery pack may contain one or more battery modules. Those skilled in the art can select an appropriate number based on the application and capacity of the battery pack.

[0167] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0168] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0169] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0170] Figure 8 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0171] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0172] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0173] Example 1

[0174] The silicon particles used in this embodiment are carbon-coated silicon suboxide (SiO).

[0175] The preparation method of composite anode materials includes the following steps:

[0176] (1) 0.3g of copper nanowires (average length of 0.6μm and average tube diameter of 70nm) and 1g of silicon particles were dispersed in 1LDMC and stirred. After stirring for 2h, the mixture was filtered and the filter residue was dried in a vacuum oven for 12h.

[0177] (2) Grind and crush the material obtained in step (1), put it into a quartz tube, and feed the mixture of H2, CH4 and Ar into the reactor at flow rates of X (150 mL / min), Y (170 mL / min) and Z (800 mL / min), respectively, and heat treat it at 1200℃ for 60 min.

[0178] (3) Take 50g of the product obtained in step (2) and soak it in 1L of concentrated hydrochloric acid (16M) and heat it to 80℃. After 30min, stir and filter it. Then wash it repeatedly with 3L of deionized water 3 times and dry it to obtain the composite negative electrode material.

[0179] Preparation of lithium-ion batteries

[0180] (1) Preparation of positive electrode sheet

[0181] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black SP, and binder PVDF are dispersed in NMP solvent at a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated on both sides of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet is obtained, with a coating weight of 0.27 g / 1540.25 mm². 2 .

[0182] (2) Preparation of negative electrode sheet

[0183] Graphite and composite negative electrode materials prepared in each embodiment or comparative example were used as negative electrode active materials. The negative electrode active material, thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agents (acetylene black and conductive agent) were mixed in a mass ratio of 80:5:5:10. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated on both sides of a copper foil. After the copper foil was dried at room temperature, it was transferred to a 120°C oven for 1 hour, then cold-pressed and slit to obtain the negative electrode sheet, with a coating weight of 0.14 g / 1540.25 mm². 2 The composite anode material accounts for 40% of the mass percentage of the anode active material layer.

[0184] (3) Separating membrane

[0185] A 12μm thick polypropylene separator membrane was selected.

[0186] (4) Preparation of electrolyte

[0187] The organic solvent was a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC:20:20:60. Thoroughly dried lithium salt LiPF6 was dissolved in the organic solvent and mixed thoroughly in an argon-atmosphere glove box with a water content of <10 ppm to obtain the electrolyte. The concentration of the lithium salt was 1 mol / L.

[0188] (5) Battery manufacturing

[0189] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, and then 10g of the corresponding electrolyte is injected and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a finished battery with a capacity of 4000mAh is obtained.

[0190] Example 2-14

[0191] The basic structure is the same as in Example 1, except that the parameters described in Tables 1-2 are different.

[0192] Comparative Example 1

[0193] The process is basically the same as in Example 1, except that the silicon particles in step (1) of Example 1 are used as the composite negative electrode material, and conductive carbon nanotubes are added when preparing the negative electrode slurry, so that the content of carbon nanotubes added to the negative electrode active material layer is the same as the content of carbon nanotubes in the negative electrode active material layer of Example 1.

[0194] Cyclic performance test

[0195] At 25°C, the battery is charged to 4.3V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.3V, and then discharged to 2.5V with a constant current of 1C. The discharge specific capacity of the first cycle (Cd1) is obtained. This charging and discharging is repeated until the 400th cycle, and the discharge specific capacity after 400 cycles is denoted as Cdn.

[0196] Capacity retention rate = discharge specific capacity after 400 cycles (Cdn) / discharge specific capacity in the first cycle (Cd1).

[0197] Table 1 Product parameters of composite anode materials

[0198]

[0199] Table 2 Preparation parameters of composite anode materials

[0200]

[0201] Table 3 Performance test results of composite anode materials and batteries

[0202]

[0203] Depend on Figure 1 It can be seen that silicon particles are connected to both ends of the carbon nanotubes on the outer surface of the composite anode material prepared in Example 1.

[0204] As can be seen from Tables 1-3, when the carbon nanotube content in the negative electrode sheets of Examples 1-14 and Comparative Example 1 is the same, the capacity retention rate of the batteries in Examples 1-14 after 400 cycles is significantly higher than that in Comparative Example 1. This indicates that the carbon nanotubes and silicon particles contained in the composite negative electrode materials of Examples 1-14 effectively improve the cycle stability of the negative electrode sheets.

[0205] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0206] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite negative electrode material, characterized in that, It includes carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes, wherein the outer surfaces of both ends of the carbon nanotubes are the non-inner surfaces of the carbon nanotubes at both ends along the length direction, and the silicon particles are connected to the carbon nanotubes by covalent bonds.

2. The composite negative electrode material according to claim 1, characterized in that, The composite anode material possesses at least one of the following characteristics: (1a) The average length of the carbon nanotubes is 0.04 μm-1 μm; (1b) The average diameter of the carbon nanotubes is 0.8 nm to 90 nm.

3. The composite negative electrode material according to claim 1 or 2, characterized in that, Based on the mass of the composite anode material, the mass percentage of the carbon nanotubes is 0.1%-20%.

4. The composite negative electrode material according to claim 3, characterized in that, Based on the mass of the composite anode material, the mass percentage of the carbon nanotubes is 0.1%-10%.

5. The composite negative electrode material according to claim 1 or 2, characterized in that, The volume average particle size Dv50 of the silicon particles is 0.2μm-50μm.

6. The composite negative electrode material according to claim 5, characterized in that, The volume average particle size Dv50 of the silicon particles is 0.2μm-12μm.

7. The composite negative electrode material according to claim 1 or 2, characterized in that, The silicon particles include one or more of elemental silicon particles, silicon oxide particles, silicon-carbon composite particles, silicon-nitrogen composite particles, and silicon alloy particles.

8. The composite negative electrode material according to claim 1 or 2, characterized in that, The composite anode material possesses at least one of the following characteristics: (2a) The mass percentage of silicon in the composite anode material is 35%-70%; (2b) The carbon content in the composite anode material is 1%-40% by mass; (2c) The silicon particles also contain oxygen, and the mass percentage of oxygen in the composite anode material is 0.02%-60%.

9. The composite negative electrode material according to claim 1 or 2, characterized in that, The composite anode material possesses at least one of the following characteristics: (3a) The powder resistivity of the composite negative electrode material is 0.1 Ω·m-200 Ω·m; (3b) The specific surface area of ​​the composite negative electrode material is 0.005 m². 2 / g-4m 2 / g.

10. The method for preparing the composite negative electrode material according to any one of claims 1-9, characterized in that, Includes the following steps: The material to be treated, including metal nanowires and silicon particles, is subjected to heat treatment in a mixed gas containing an organic carbon source. The product obtained from the heat treatment is washed with acid to remove the metal nanowires, resulting in the carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes.

11. The preparation method according to claim 10, characterized in that, Before the step of heat-treating the material to be treated in the mixed gas, the following steps are also included: The metal nanowires, the silicon particles, and the organic solvent are mixed to obtain a mixture. The organic solvent in the mixture is removed to obtain the material to be treated.

12. The preparation method according to claim 11, characterized in that, The organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, and isopropanol.

13. The preparation method according to claim 10, characterized in that, The acid solution includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

14. The preparation method according to claim 11, characterized in that, The mass ratio of the metal nanowires to the silicon particles is (0.4-40):

1.

15. The preparation method according to claim 14, characterized in that, The mass ratio of the metal nanowires to the silicon particles is (0.4-10):

1.

16. The preparation method according to claim 11, characterized in that, The metal nanowires include at least one of copper nanowires and nickel nanowires.

17. The preparation method according to any one of claims 10-16, characterized in that, The heat treatment process conditions include: a heat treatment temperature of 50℃-3000℃ and a heat treatment time of 30min-180min.

18. The preparation method according to any one of claims 10-16, characterized in that, In addition to the organic carbon source, the mixed gas also contains reducing gases and inert gases.

19. The preparation method according to claim 18, characterized in that, The organic carbon source includes methane.

20. The preparation method according to claim 18, characterized in that, The reducing gas includes hydrogen.

21. The preparation method according to claim 18, characterized in that, The inert gas includes at least one of argon, helium, and neon.

22. The preparation method according to claim 18, characterized in that, The flow rate of the organic carbon source is 15 mL / min to 300 mL / min.

23. The preparation method according to claim 18, characterized in that, The flow rate of the reducing gas is 10 mL / min to 300 mL / min.

24. The preparation method according to claim 18, characterized in that, The flow rate of the inert gas is 50 mL / min to 1200 mL / min.

25. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes at least one of the composite negative electrode material according to any one of claims 1-9 and the composite negative electrode material prepared by the preparation method according to any one of claims 10-24.

26. The negative electrode sheet according to claim 25, characterized in that, Based on the mass of the negative electrode active material layer, the mass percentage of the carbon nanotubes is 0.1%-20%.

27. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 25-26.

28. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 27.

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