Composite negative electrode material and preparation method and application thereof

Abstract

The invention 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 a carbon nano tube and silicon particles at least arranged on the outer surfaces of the two ends of the carbon nano tube, and the silicon particles are connected with the carbon nano tube through covalent bonds. The connection mode of the carbon nanotubes and the silicon particles in the composite negative electrode material effectively improves the cycling stability of a negative electrode plate containing the composite negative electrode material.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a composite negative electrode material and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Secondary batteries have the advantages of high energy density, long service life, wide operating voltage range, low self-discharge, and no memory effect. They are currently the main power source for new energy vehicles. As the market demand for high-capacity power batteries grows, negative electrode materials with high theoretical specific capacity, such as silicon-based materials, have been developed. However, the poor conductivity of traditional silicon-based materials makes the cycle stability of negative electrode sheets containing silicon-based materials poor, which limits the further application of silicon-based materials. Summary of the invention

[0004] Based on this, it is necessary to provide a composite negative electrode material and a preparation method and application thereof to improve the cycle stability of the negative electrode sheet containing the composite negative electrode material.

[0005] In a first aspect of the present application, a composite negative electrode material is provided, which includes carbon nanotubes and silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes, wherein the silicon particles are connected to the carbon nanotubes via covalent bonds.

[0006] The connection method between carbon nanotubes and silicon particles in the above-mentioned composite negative electrode material, on the one hand, significantly improves the conductive network between silicon particles, and on the other hand, during the expansion and contraction of silicon particles during the charge and discharge cycle, it not only retains the free expansion space for carbon nanotubes to move with silicon particles, but also improves the free non-conductivity problem of silicon particles after shrinkage, thereby improving the cycle stability of the negative electrode sheet containing the composite negative electrode material.

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

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

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

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

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

[0012] In some embodiments, the mass percentage of silicon in the composite negative electrode material is 35%-70%.

[0013] In some embodiments, the mass percentage of carbon element in the composite negative electrode material is 1%-40%.

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

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

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

[0017] The second aspect of the present application provides a method for preparing the composite negative electrode material according to the first aspect of the present application, comprising the following steps:

[0018] thermally treating a material to be treated in a mixed gas containing an organic carbon source, wherein the material to be treated includes metal nanowires and the silicon particles;

[0019] The product obtained by the heat treatment is washed with an acid solution to remove the metal nanowires, thereby obtaining the carbon nanotubes and the silicon particles at least arranged 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 negative electrode material.

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

[0022] Mixing the metal nanowires, the silicon particles and an organic solvent to obtain a mixed material;

[0023] The organic solvent in the mixed material 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 isopropyl alcohol.

[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 can be 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 process conditions of the heat treatment include: the heat treatment temperature is 50°C-3000°C, and the heat treatment time is 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 comprises methane.

[0031] In some embodiments, the reducing gas comprises 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-300 mL / min.

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

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

[0036] In the third aspect of the present application, a negative electrode plate is provided, comprising a negative electrode current collector and a negative electrode active material layer arranged 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 the present application and the composite negative electrode material prepared by the preparation method described in the second aspect of the present application.

[0037] The negative electrode plate of the present application includes the composite negative electrode material provided in the present application, and thus has at least the same advantages as the composite negative electrode material.

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

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

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

[0041] In a fifth aspect of the present application, there is provided an electrical device comprising the secondary battery described in the fourth aspect of the present application.

[0042] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0043] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

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

[0046] Figure 2 Schematic diagram of the structure of a composite negative electrode material according to one embodiment of the present application.

[0047] Figure 3 It is a schematic diagram of a battery cell according to an embodiment of the present application.

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

[0049] Figure 5 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0050] Figure 6 A schematic diagram of a battery pack according to an embodiment of the present application.

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

[0052] Figure 8 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0053] Description of reference numerals:

[0054] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 power-consuming device; 7 composite negative electrode material; 71 silicon particles; 72 carbon nanotubes. DETAILED DESCRIPTION

[0055] Below, some embodiments of the composite negative electrode material, preparation method and application thereof of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0056] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed 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 the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0058] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0059] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0060] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating 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.

[0061] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means 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", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0063] Negative electrode material is one of the key materials for improving the performance of secondary batteries. Among many negative electrode materials, silicon-based materials have attracted much attention due to their high theoretical specific capacity. However, the conductivity of traditional silicon-based materials is poor, which makes the stability of negative electrode sheets containing traditional silicon-based materials poor. Although carbon nanotubes can be used as conductive agents together with traditional silicon-based materials to improve the conductivity of materials, the following problems still exist:

[0064] 1. Carbon nanotubes are usually added to traditional silicon-based materials together with other auxiliary materials. Since carbon nanotubes are easy to agglomerate, traditional silicon-based materials will lose a lot of contact sites regardless of the order of adding materials. Carbon nanotubes have ineffective contact with auxiliary materials such as binders, which greatly reduces the utilization rate of carbon nanotubes.

[0065] 2. Carbon nanotubes usually contain metal particles, which are attached to the ends of highly conductive carbon nanotubes and have strong catalytic properties on the electrode liquid, which is not conducive to the stability of the battery;

[0066] 3. The carbon nanotubes added to traditional silicon-based materials make the physical connection between different particles extremely weak, and more carbon nanotubes need to be added to effectively form a conductive network;

[0067] 4. Although the in-situ growth of carbon nanotubes on the surface of silicon-based material particles makes the physical contact between the carbon nanotubes and the silicon-based material particles better, since only one end of the carbon nanotubes is connected to the silicon-based material particles, the contact efficiency between the silicon-based material particles is still not high. It is necessary to grow a large amount of carbon nanotubes on the surface of the silicon-based material particles to achieve effective electrical contact.

[0068] Based on this, the present application provides a composite negative electrode material, which includes carbon nanotubes and silicon particles arranged on the outer surfaces of at least two ends of the carbon nanotubes, and the silicon particles are connected to the carbon nanotubes by covalent bonds; the connection method between the above-mentioned carbon nanotubes and silicon particles can, on the one hand, significantly improve the conductive network between the silicon particles, and on the other hand, during the expansion and contraction of the silicon particles during the charge and discharge cycle, it can not only retain the free expansion space for the carbon nanotubes to move with the silicon particles, but also improve the free non-conductivity problem of the silicon particles after shrinkage, thereby improving the cycle stability of the negative electrode sheet containing the composite negative electrode material.

[0069] Composite negative electrode materials

[0070] An embodiment of the present 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 mode between carbon nanotubes and silicon particles in the above-mentioned composite negative electrode material, on the one hand, significantly improves the conductive network between silicon particles, and on the other hand, during the expansion and contraction of silicon particles during the charge and discharge cycle, it not only retains the free expansion space for carbon nanotubes to move with silicon particles, but also improves the problem of free non-conductivity after the silicon particles shrink, thereby improving the cycle stability of the negative electrode sheet containing the composite negative electrode material. The above-mentioned covalent bonds include but are not limited to covalent bonds formed by at least one of carbon atoms, oxygen atoms, hydrogen atoms and silicon atoms, and examples include: carbon-carbon single bonds, carbon-oxygen single bonds, carbon-hydrogen bonds, carbon-silicon bonds, etc.

[0072] In the composite negative electrode material, the silicon particles disposed at least on the outer surfaces of both ends of the carbon nanotubes refer to a single carbon nanotube connecting at least two silicon particles.

[0073] Generally, the arrangement and connection between silicon particles and carbon nanotubes can be observed using a transmission electron microscope (TEM).

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

[0075] In the present application, the outer surfaces at both ends of the carbon nanotube refer to the non-tube inner surfaces at both ends of the carbon nanotube along the length direction.

[0076] In some embodiments, 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 , and the silicon particles 71 are connected to the carbon nanotubes 72 through covalent bonds.

[0077] In some embodiments, the average length of the carbon nanotubes is 0.04 μm-1 μm. Controlling the average length of the carbon nanotubes to the above range is conducive to further improving the conductive network between the silicon particles, while retaining a certain amount of free expansion space for the silicon particles to improve the problem of free non-conductivity after shrinkage, thereby improving the conductivity of the composite negative electrode material, and further improving the cycle stability of the negative electrode sheet containing the composite negative electrode material. It can be 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, 1 μm.

[0078] In some embodiments, the average diameter of the carbon nanotubes is 0.8nm-90nm. The diameter of the carbon nanotubes is within the above range, so that the composite negative electrode material has a certain rigidity, and is conducive to further improving the conductive network between the silicon particles. At the same time, it can also reserve a certain amount of free expansion space for the silicon particles to improve the problem of free non-conductivity after shrinkage, thereby improving the conductivity of the composite negative electrode material and further improving the cycle stability of the negative electrode sheet containing the composite negative electrode material. It can be understood that the average diameter of the carbon nanotubes includes but is not limited to: 0.8nm, 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm.

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

[0080] In some embodiments, the carbon nanotubes include single-walled carbon nanotubes, which are beneficial for improving the conductivity of the composite negative electrode material and the mass energy density of the secondary battery.

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

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

[0083] Optionally, the volume average particle size Dv50 of silicon particles can be tested by the following method: use a scanning electron microscope (SEM) (such as ZEISS Sigma 300) to take pictures of the cross-section of the composite negative electrode material, and obtain the volume average particle size Dv50 of the silicon particles in the composite negative electrode material through measurement and statistics.

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

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

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

[0087] Optionally, the mass percentage of silicon, carbon and oxygen in the composite negative electrode material can be tested by inductively coupled plasma emission spectroscopy (ICP method).

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

[0089] In some embodiments, the specific surface area of ​​the composite negative electrode material is 0.005 m 2 / g-4m 2 / g. It can be understood that the specific surface area of ​​the composite negative electrode material includes but is not limited to: 0.005m 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 ​​the composite negative electrode material can be tested by nitrogen adsorption and desorption. For example, a specific surface area analyzer (Tri star II) can be used to measure the BET specific surface area of ​​the material.

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

[0092] thermally treating a material to be treated in a mixed gas containing an organic carbon source, wherein the material to be treated includes metal nanowires and silicon particles;

[0093] The product obtained by the heat treatment is washed with an acid solution to remove the metal nanowires, thereby obtaining carbon nanotubes and silicon particles at least arranged 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 the heat treatment process. Since the metal nanowires are in contact with the carbon nanotubes, the outer surfaces of both ends of the carbon nanotubes can form covalent bonds with the silicon particles. During the washing process, the acid solution can remove the metal nanowires, thereby obtaining the carbon nanotubes and at least the silicon particles arranged on the outer surfaces of both ends of the carbon nanotubes. The above preparation method is relatively simple and is conducive to the large-scale production of the above composite negative electrode material.

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

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

[0097] mixing metal nanowires, silicon particles and an organic solvent to obtain a mixed material;

[0098] The organic solvent in the mixed material is removed to obtain the material to be treated.

[0099] In the above embodiment, the metal nanowires, silicon particles and organic solvent are mixed, which is conducive 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 isopropyl alcohol.

[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, 40: 1.

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

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

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

[0105] In some specific embodiments, the organic carbon source comprises methane.

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

[0107] In some specific embodiments, the reducing gas comprises hydrogen.

[0108] In some specific embodiments, 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 embodiments, the flow rate of the organic carbon source is 15 mL / min-300 mL / min.

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

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

[0113] Another embodiment of the present application provides a negative electrode plate, including a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer includes at least one of the above-mentioned composite negative electrode material and the composite negative electrode material prepared by the above-mentioned preparation method.

[0114] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one 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 the 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 the carbon nanotubes includes but is not limited to: 0.1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%.

[0116] In some embodiments, the negative electrode active material layer may contain negative electrode active materials for batteries known in the art in addition to the above-mentioned composite negative electrode material. 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, lithium titanate, etc. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries 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 polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0118] In some embodiments, the negative electrode active material layer may further 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 further include a conductive agent, which 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 further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0121] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode 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 2000mPa·s-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 -220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 -1.8g / cm 3 .

[0122] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0123] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0124] Positive electrode

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

[0126] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode 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 base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0128] As the Li content in the positive electrode active material changes, how to define the subscript of Li 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 0.2-1.2;

[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 definition of x includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2V-5V).

[0136] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode active material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that the new material obtained by appropriate modification on the basis of the listed positive electrode active materials is also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode active material, and non-limiting examples include coating modification.

[0137] In the list of positive electrode active materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0138] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. 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 referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O2.

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

[0140] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As non-limiting examples, 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 in the following manner: the components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode 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 5000mPa·s-25000mPa·s. When applying the positive electrode slurry, the coating unit surface density based on dry weight (excluding solvent) can be 15 mg / cm 2 -35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 -3.6g / cm 3 , optional 3.3g / cm 3 -3.5g / cm 3 .

[0142] Negative electrode

[0143] The negative electrode sheet mentioned above in this application is adopted.

[0144] Electrolytes

[0145] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0146] In some embodiments, the electrolyte is an electrolyte solution, which 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 bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0148] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl 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 fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0149] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high 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), trifluoromethylethylene carbonate (TFPC), and the like.

[0151] Isolation film

[0152] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0153] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane 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 isolation film has a thickness of 6 μm-40 μm, and optionally 12 μm-20 μm.

[0155] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0156] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

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

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

[0159] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0160] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 5 is a square structure as an example.

[0161] In some embodiments, reference Figure 4, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0162] The secondary battery may be a battery module 4 or a battery pack 1 .

[0163] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0164] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0165] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0166] In some embodiments, the battery modules described above may also be assembled into a battery pack. The number of battery modules contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0167] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0168] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0169] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0170] Figure 8 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0171] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0172] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0173] Example 1

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

[0175] The preparation method of the composite negative electrode material comprises the following steps:

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

[0177] (2) grinding the material obtained in step (1) and placing it in a quartz tube, feeding a 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 treating at 1200°C for 60 min;

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

[0179] Preparation of lithium-ion batteries

[0180] (1) Preparation of positive electrode sheet

[0181] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black SP and binder PVDF were dispersed in solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain positive electrode slurry; the positive electrode slurry was evenly coated on the double-side surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained, and the coating amount per unit area was 0.27g / 1540.25mm 2 .

[0182] (2) Preparation of negative electrode sheet

[0183] Graphite and the composite negative electrode materials prepared in each embodiment or comparative example were used as negative electrode active materials, the negative electrode active material, the thickener sodium carboxymethyl cellulose, the binder styrene butadiene rubber, and the conductive agent (acetylene black and the conductive agent) were mixed in a mass ratio of 80:5:5:10, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of the copper foil; the copper foil was dried at room temperature and then transferred to a 120°C oven for drying for 1h, and then supercooled and cut to obtain a negative electrode sheet, and the coating amount per unit area was 0.14g / 1540.25mm 2 The mass percentage of the composite negative electrode material in the negative electrode active material layer is 40%.

[0184] (3) Isolation film

[0185] A 12μm thick polypropylene isolation film was selected.

[0186] (4) Preparation of electrolyte

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

[0188] (5) Preparation of batteries

[0189] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role. Then, they are wound into a square bare battery cell, loaded with aluminum-plastic film, and then baked at 80°C to remove water, and 10g of the corresponding electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0190] Example 2-14

[0191] The method is basically the same as Example 1, except that the parameters described in Table 1-2 are different.

[0192] Comparative Example 1

[0193] The method is basically the same as 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 was charged to 4.3V at a constant current of 1C, then charged at a constant voltage of 4.3V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the first-cycle discharge capacity (Cd1); this charging and discharging was repeated until the 400th cycle, and the discharge capacity after 400 cycles was recorded as Cdn.

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

[0197] Table 1 Product parameters of composite negative electrode materials

[0198]

[0199] Table 2 Preparation parameters of composite negative electrode materials

[0200]

[0201] Table 3 Performance test results of composite negative electrode materials and battery performance

[0202]

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

[0204] It can be seen from Tables 1-3 that when the carbon nanotube contents in the negative electrode sheets of Examples 1-14 and Comparative Example 1 are the same, the capacity retention rate of the battery of Examples 1-14 after 400 cycles is significantly higher than that of Comparative Example 1, indicating 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 above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0206] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A composite negative electrode material, characterized in that: It comprises carbon nanotubes and silicon particles at least arranged on the outer surfaces of two ends of the carbon nanotubes, wherein the silicon particles are connected to the carbon nanotubes through covalent bonds.

2. The composite negative electrode material according to claim 1, characterized in that: The composite negative electrode material has 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-90 nm.

3. The composite negative electrode material according to claim 1 or 2, characterized in that: Based on the mass of the composite negative electrode material, the mass percentage of the carbon nanotubes is 0.1%-20%, and can be optionally 0.1%-10%.

4. 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 0.2 μm-50 μm, and can be optionally 0.2 μm-12 μm; Optionally, the silicon particles include one or more of elemental silicon particles, silicon-oxygen compound particles, silicon-carbon composite particles, silicon-nitrogen composite particles and silicon alloy particles.

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

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

7. The method for preparing the composite negative electrode material according to any one of claims 1 to 6, characterized in that: The steps include: thermally treating a material to be treated in a mixed gas containing an organic carbon source, wherein the material to be treated includes metal nanowires and the silicon particles; The product obtained by the heat treatment is washed with an acid solution to remove the metal nanowires, thereby obtaining the carbon nanotubes and the silicon particles at least arranged on the outer surfaces of both ends of the carbon nanotubes.

8. The preparation method according to claim 7, characterized in that: Before the step of heat treating the material to be treated in the mixed gas, the following steps are also included: Mixing the metal nanowires, the silicon particles and an organic solvent to obtain a mixed material; Removing the organic solvent from the mixed material to obtain the material to be treated; Optionally, the organic solvent includes at least one of dimethyl carbonate, diethyl carbonate and isopropyl alcohol; Optionally, the acid solution includes at least one of hydrochloric acid, sulfuric acid and nitric acid.

9. The preparation method according to claim 8, characterized in that: The mass ratio of the metal nanowires to the silicon particles is (0.4-40):1, and can be optionally (0.4-10):1; Optionally, the metal nanowires include at least one of copper nanowires and nickel nanowires.

10. The preparation method according to any one of claims 7 to 9, characterized in that: The process conditions of the heat treatment include: the heat treatment temperature is 50°C-3000°C, and the heat treatment time is 30min-180min.

11. The preparation method according to any one of claims 7 to 9, characterized in that: The mixed gas contains, in addition to the organic carbon source, a reducing gas and an inert gas; Optionally, the organic carbon source comprises methane; Optionally, the reducing gas includes hydrogen; Optionally, the inert gas includes at least one of argon, helium and neon; Optionally, the flow rate of the organic carbon source is 15 mL / min-300 mL / min; Optionally, the flow rate of the reducing gas is 10 mL / min-300 mL / min; Optionally, the flow rate of the inert gas is 50 mL / min-1200 mL / min.

12. A negative electrode plate, characterized in that: 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 according to any one of claims 1 to 6 and the composite negative electrode material prepared by the preparation method according to any one of claims 7 to 11; Optionally, based on the mass of the negative electrode active material layer, the mass percentage of the carbon nanotubes is 0.1%-20%.

13. A secondary battery, characterized in that: Including the negative electrode sheet as described in claim 12.

14. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 13.

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