Silicon composite material and preparation method therefor, negative electrode sheet, secondary battery, and electric device

Abstract

A silicon composite material and a preparation method therefor, a negative electrode sheet, a secondary battery, and an electric device. The silicon composite material comprises a one-dimensional conductive material, an inner core, and a coating layer, the outer surface of the inner core is coated with the coating layer, the one-dimensional conductive material is arranged on the outer surface of the coating layer, and the inner core comprises a silicon-based material. The silicon composite material has good cycle performance and fast charging performance.

Description

Silicon composite material and preparation method thereof, negative electrode sheet, secondary battery and electrical device

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 2023111294347, filed on September 4, 2023, entitled “Silicon composite material and preparation method thereof, negative electrode sheet, secondary battery and electrical device,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the technical field of battery materials, and in particular to a silicon composite material and a preparation method thereof, a negative electrode sheet, a secondary battery and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion batteries have achieved great development, higher requirements have been placed on their energy density and cycle performance.

[0006] Silicon-based materials have attracted attention due to their much higher capacity than carbon-based materials, as higher capacity means higher energy density. However, the cycling performance and fast charging performance of batteries containing silicon-based materials still need to be further improved.

[0007] Summary of the Invention

[0008] The present application provides a silicon composite material with good cycle performance and fast charging performance and a preparation method thereof, as well as a negative electrode plate, a secondary battery and an electrical device using the silicon composite material.

[0009] In a first aspect of the present application, a silicon composite material is provided, comprising a one-dimensional conductive material, an inner core and a coating layer, wherein the coating layer is coated on the outer surface of the inner core, the one-dimensional conductive material is arranged on the outer surface of the coating layer, and the inner core comprises a silicon-based material.

[0010] The above-mentioned silicon composite material arranges the one-dimensional conductive material on the outer surface of the coating layer of the silicon-based material, thereby comprehensively improving the cycle performance and fast charging performance.

[0011] In some embodiments, the one-dimensional conductive material extends outward from an outer surface of the cladding layer.

[0012] In some embodiments, the outer surface of the coating layer further comprises catalyst particles, and the one-dimensional conductive material is disposed on the surface of the catalyst particles;

[0013] Optionally, the catalyst particles include transition metal nanoparticles;

[0014] Further optionally, the transition metal nanoparticles include one or more of iron nanoparticles, cobalt nanoparticles and nickel nanoparticles;

[0015] Optionally, the coating layer comprises a carbon coating layer;

[0016] Further optionally, the carbon coating layer includes amorphous carbon.

[0017] In some embodiments, the mass percentage of the catalyst particles is 0.001% to 0.3% based on the mass of the silicon-based material.

[0018] In some embodiments, the one-dimensional conductive material comprises carbon nanotubes;

[0019] Optionally, the carbon nanotubes have one or more of the following characteristics:

[0020] (1) The average tube length is 0.5 μm to 10 μm; optionally, the average tube length of the carbon nanotubes is 1 μm to 10 μm;

[0021] (2) The average tube diameter is 1 nm to 50 nm; optionally, the average tube diameter of the carbon nanotubes is 20 nm to 30 nm.

[0022] In some embodiments, based on the mass of the silicon-based material, the mass percentage of the one-dimensional conductive material is 0.01% to 5%; optionally, the mass percentage of the one-dimensional conductive material is 0.4% to 5%.

[0023] In some embodiments, the silicon composite material has a Dv50 of 1 μm to 30 μm.

[0024] In some embodiments, the silicon-based material includes one or more of silicon-oxygen compounds, silicon-carbon composites, elemental silicon, or silicon alloys.

[0025] A second aspect of the present application provides a method for preparing a silicon composite material, comprising the following steps:

[0026] preparing a coating layer on the outer surface of an inner core, wherein the inner core comprises a silicon-based material;

[0027] A one-dimensional conductive material is prepared on the outer surface of the coating layer.

[0028] The above preparation method is simple in steps and is easy to promote and apply industrially. In addition, the preparation method prepares a one-dimensional conductive material on the outer surface of the coating layer, which reduces the problem of slurry gelation and agglomeration caused by adding the one-dimensional conductive material to the slurry, making the process of the negative electrode sheet easier to carry out.

[0029] In some embodiments, preparing a one-dimensional conductive material on the outer surface of the coating layer includes the following steps:

[0030] preparing catalyst particles on the outer surface of the coating layer;

[0031] preparing a one-dimensional conductive material on the surface of the catalyst particles;

[0032] Optionally, the catalyst particles include transition metal nanoparticles;

[0033] Further optionally, the transition metal nanoparticles include one or more of iron nanoparticles, cobalt nanoparticles and nickel nanoparticles.

[0034] In some embodiments, preparing catalyst particles on the outer surface of the coating layer includes the following steps:

[0035] preparing a transition metal oxide and / or a transition metal hydroxide on the surface of the coating layer;

[0036] calcining under a reducing atmosphere to convert the transition metal oxide and / or transition metal hydroxide into transition metal nanoparticles;

[0037] Optionally, the calcination temperature is 600°C to 800°C.

[0038] In some embodiments, the one-dimensional conductive material is in-situ grown on the surface of the catalyst particles.

[0039] In some embodiments, the one-dimensional conductive material comprises carbon nanotubes, and preparing the one-dimensional conductive material on the surface of the catalyst particles comprises the following steps:

[0040] introducing a carbon source gas to in-situ grow the carbon nanotubes on the surface of the catalyst particles;

[0041] Optionally, the carbon source gas includes hydrocarbon gas; further optionally, the carbon source gas includes one or more of CH4, C2H2 and propylene.

[0042] In a 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 one or more of the silicon composite material described in the first aspect or the silicon composite material prepared by the preparation method described in the second aspect.

[0043] In some embodiments, the negative electrode active material layer further comprises a carbon-based material;

[0044] Optionally, the mass ratio of the silicon composite material to the carbon-based material is (10% to 90%): (90% to 10%).

[0045] In a fourth aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet described in the third aspect.

[0046] In a fifth aspect of the present application, an electrical device is provided, comprising one or more of the negative electrode sheet described in the third aspect or the secondary battery described in the fourth aspect.

[0047] 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

[0048] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying 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 currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0049] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0050] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0051] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0052] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0053] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application;

[0054] FIG6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

[0055] FIG7 is a surface electron micrograph of a silicon composite material with in-situ CNT growth prepared in one embodiment of the present application;

[0056] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0057] Below, some embodiments of the silicon composite material and its preparation method, negative electrode plate, secondary battery and electrical device 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 description 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.

[0058] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0059] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0060] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0061] References to "embodiments" herein mean 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 such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0062] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply 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 inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may 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.

[0063] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", 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 that also include 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 includes not only a1, a2, and a3, but also other members". In this 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.

[0064] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0065] Silicon-based materials will produce huge volume changes (>300%) during the charging and discharging process, which is much higher than carbon-based materials. Traditional conductive agents are in point contact with the negative electrode active material particles. After the silicon-based material expands, the gaps between the particles are large, so it is impossible to form an effective conductive network, which in turn significantly reduces its fast charging performance and cycle performance.

[0066] There is a plan to improve this problem by adding carbon nanotubes (CNTs) to the material. However, due to the small number of surface defects and lack of active groups on carbon nanotubes, their solubility in various solvents is very low. In addition, carbon nanotubes are composed of graphite with a lamellar structure. The sp2 hybridization of carbon atoms forms highly delocalized electrons. There is a large van der Waals attraction between carbon nanotubes, and the specific surface area and aspect ratio are relatively large. Therefore, carbon nanotubes generally exist in the form of entangled aggregates. Adding carbon nanotubes at the slurry level will bring a series of problems, such as slurry gelation, agglomeration, and poor dispersion effect. In addition, since carbon nanotubes and carbon-based materials such as graphite are hybridized, after the slurry is coated to form a pole piece, at the pole piece level, carbon nanotubes are more likely to adhere and agglomerate on the surface of the carbon-based material. There are relatively few carbon nanotubes on the surface of the silicon-based material, and it is difficult to improve the conductive network of the silicon-based material and achieve long-range conductivity of the silicon-based material.

[0067] There is also a proposal to provide a composite material, which uses carbon material to jointly coat physically mixed carbon nanotubes and silicon-based materials. Although this allows the carbon nanotubes to be dispersed inside the carbon coating layer to reduce their agglomeration, the carbon nanotubes are dispersed inside the carbon coating layer at this time and can only play the role of connecting the silicon-based materials inside the negative electrode active material particles. They have little effect on constructing a conductive network between multiple negative electrode active material particles. In particular, during the charging and discharging process, after the negative electrode active material particles expand, it is difficult to achieve good electrical contact between the multiple negative electrode active material particles to form an effective conductive network. Therefore, this solution has little effect on improving the cycle performance and fast charging performance of the secondary battery.

[0068] Based on this, some examples of the present application provide a silicon composite material, including a one-dimensional conductive material, an inner core and a coating layer, wherein the coating layer is coated on the outer surface of the inner core, the one-dimensional conductive material is arranged on the outer surface of the coating layer, and the inner core contains a silicon-based material.

[0069] The above-mentioned silicon composite material arranges the one-dimensional conductive material on the outer surface of the coating layer of the silicon-based material. This can, on the one hand, reduce the entanglement and agglomeration between the one-dimensional conductive materials, thereby reducing the problems of slurry gelation, agglomeration, and poor dispersion effect during the preparation of the negative electrode plate; on the other hand, the one-dimensional conductive material arranged on the outer surface of the coating layer can improve the electrical contact between multiple negative electrode active material particles. Even if the negative electrode active material particles at the plate level expand during the charging and discharging process, an effective conductive network can still be constructed between the particles, thereby comprehensively improving the cycle performance and fast charging performance.

[0070] It can be understood that the coating layer preferably continuously and completely coats the outer surface of the inner core containing the silicon-based material, while discontinuous or partial coating on the outer surface of the inner core is not excluded.

[0071] It can be understood that the material composition of the one-dimensional conductive material and the coating layer may be the same, different or partially the same. Preferably, the material composition of the one-dimensional conductive material and the coating layer is the same.

[0072] It is understood that "the one-dimensional conductive material is disposed on the outer surface of the coating layer" can mean that the one-dimensional conductive material is directly disposed on the outer surface of the coating layer without an intermediate connecting unit, or it can mean that the one-dimensional conductive material is disposed on the outer surface of the coating layer via an intermediate connecting unit. In some examples of the present application, the intermediate connecting unit can be a catalyst particle.

[0073] In some examples, the one-dimensional conductive material extends outward from the outer surface of the coating. The one-dimensional conductive material is formed on the surface of the coating and can fully extend and disperse outward, facilitating the formation of a conductive network between particles, thereby improving cycling performance and fast charging performance.

[0074] It can be understood that the coating layer may include a single-layer coating layer or a multi-layer coating layer.

[0075] In some examples, the outer surface of the coating layer further comprises catalyst particles, and the one-dimensional conductive material is disposed on the surface of the catalyst particles. Without limitation, the presence of catalyst characteristic elements can be characterized by methods such as ICP.

[0076] Furthermore, the catalyst particles include transition metal nanoparticles.

[0077] In some examples, the transition metal nanoparticles include one or more of iron nanoparticles, cobalt nanoparticles, and nickel nanoparticles. Selecting appropriate transition metal nanoparticles helps improve structural stability and thus cycle life. It is understandable that the iron nanoparticles, cobalt nanoparticles, and nickel nanoparticles are all elemental metal particles. Furthermore, the transition metal nanoparticles include one or more of cobalt nanoparticles and nickel nanoparticles.

[0078] In some examples, the coating layer includes a carbon coating layer. Coating the inner core with the carbon coating layer is beneficial to further improve the conductivity between the particles. Without limitation, the carbon coating layer includes amorphous carbon.

[0079] In some examples, the mass percentage of the catalyst particles is 0.001% to 0.3% based on the mass of the silicon-based material. Reasonable control of the mass percentage of the catalyst particles can regulate the content and distribution of the one-dimensional conductive material, so that it can be more fully stretched and dispersed, which is beneficial to improving the cycle performance and fast charging performance. Specifically, the mass percentage of the catalyst particles includes but is not limited to: 0.001%, 0.005%, 0.01%, 0.015%, 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or a range between any two of the foregoing. Furthermore, the mass percentage of the catalyst particles is 0.05% to 0.3%.

[0080] It is understandable that the one-dimensional conductive material refers to a one-dimensional material with electrical conductivity. A one-dimensional material refers to a linear material. For example, a whisker has atoms arranged regularly in one direction on the order of micrometers to centimeters, and only a few atoms are arranged in the other two directions, which are on the nanometer scale. Accordingly, electrons basically only move in a straight line in one nanometer-scale direction. One-dimensional materials include nanobelts, nanotubes, quantum wire materials, etc. Without limitation, the one-dimensional conductive material can be exemplified by carbon nanotubes, metal nanofibers, one-dimensional conductive polymer nanomaterials, etc.

[0081] In some examples, the one-dimensional conductive material includes carbon nanotubes.

[0082] Furthermore, the average tube length of the carbon nanotubes is 0.5 microns (μm) to 10 μm. Reasonable control of the tube length of the carbon nanotubes is beneficial to the construction of a conductive network between the particles of the negative electrode active material on the one hand, and on the other hand reduces the possibility of entanglement and agglomeration between the carbon nanotubes, thereby improving the fast charging performance and cycle performance. Specifically, the average tube length of the carbon nanotubes includes but is not limited to: 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm or a range between any two of the foregoing. Furthermore, the average tube length of the carbon nanotubes is 1 μm to 10 μm.

[0083] Furthermore, the average diameter of the carbon nanotubes is 1 nanometer (nm) to 50 nm. Reasonable control of the diameter of the carbon nanotubes is conducive to improving the cycle performance. Specifically, the average diameter of the carbon nanotubes includes but is not limited to: 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or a range between any two of the foregoing. Furthermore, the average diameter of the carbon nanotubes is 20 nm to 30 nm.

[0084] In some examples, the mass percentage of the one-dimensional conductive material is 0.01% to 5% based on the mass of the silicon-based material. Reasonable control of the mass percentage of the one-dimensional conductive material is beneficial to the construction of a conductive network between the particles of the negative electrode active material, and on the other hand, it reduces the possibility of entanglement and agglomeration between the one-dimensional conductive materials. Specifically, the mass percentage of the one-dimensional conductive material includes but is not limited to: 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the foregoing. Furthermore, the mass percentage of the one-dimensional conductive material is 0.4% to 5%.

[0085] In some examples, the Dv50 of the silicon composite material is 1μm to 30μm. The silicon composite material has a good size and good dimensional uniformity. The Dv50 of the silicon composite material is within the above range. On the one hand, it is beneficial to improve ion conductivity, reduce internal resistance during discharge, and increase material life; on the other hand, it enables the material to have a suitable specific surface area, reduce particle agglomeration during processing and improve storage performance. Specifically, the Dv50 of the silicon composite material includes but is not limited to: 1μm, 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm or a range between any two of the foregoing.

[0086] In addition, without limitation, the silicon-based material includes one or more of silicon oxides (SiOx, 0<x<2), silicon-carbon composites, elemental silicon, or silicon alloys.

[0087] It can be understood that the structure of the silicon oxide compound (SiOx, 0<x<2) and the silicon carbon composite is a coating structure, a supporting structure or a dispersed structure.

[0088] In some examples of the present application, the silicon-based material includes a silicon-oxygen compound with a supported structure, and the silicon-oxygen compound is specifically a composite material formed by nano-silicon particles supported on a silicon dioxide matrix.

[0089] In some examples of the present application, the silicon-based material includes a silicon oxide compound with a coating structure, and the silicon oxide compound is specifically an outer layer of silicon monoxide coated with a layer of carbon-based material as a protective layer.

[0090] In some examples of the present application, the silicon-based material includes a silicon-carbon composite with a coating structure, and the silicon-carbon compound is specifically an outer layer of elemental silicon and / or silicon alloy coated with a carbon-based material layer as a protective layer.

[0091] In some examples of the present application, the silicon-based material includes a dispersed silicon-carbon composite, wherein the silicon-carbon composite is specifically a composite system in which a single silicon and / or silicon alloy inner core and a carbon-based inner core form physical contact and uniformity.

[0092] In some other examples of the present application, a method for preparing a silicon composite material is provided, comprising the following steps:

[0093] preparing a coating layer on the outer surface of an inner core, wherein the inner core comprises a silicon-based material;

[0094] A one-dimensional conductive material is prepared on the outer surface of the coating layer.

[0095] The above preparation method is simple in steps and is easy to promote and apply industrially. In addition, the preparation method prepares a one-dimensional conductive material on the outer surface of the coating layer, which reduces the problem of slurry gelation and agglomeration caused by adding the one-dimensional conductive material to the slurry, making the process of the negative electrode sheet easier to carry out.

[0096] It can be understood that the silicon composite material in the preparation method has the same or similar technical solutions and effects as the aforementioned silicon composite material, and will not be described in detail here.

[0097] In some examples, preparing a one-dimensional conductive material on the outer surface of the coating layer includes the following steps:

[0098] preparing catalyst particles on the outer surface of the coating layer;

[0099] A one-dimensional conductive material is prepared on the surface of the catalyst particles.

[0100] In some examples, preparing catalyst particles on the outer surface of the coating layer includes the following steps:

[0101] preparing a transition metal oxide and / or a transition metal hydroxide on the surface of the coating layer;

[0102] The transition metal oxide and / or transition metal hydroxide is calcined in a reducing atmosphere to generate transition metal nanoparticles.

[0103] In some examples, the calcination temperature is 600 degrees Celsius (°C) to 800°C.

[0104] In some examples, preparing transition metal oxide and / or transition metal hydroxide on the surface of the sub-coating layer includes: mixing the inner core of the sub-coating layer with a solution of a transition metal salt to generate transition metal oxide and / or transition metal hydroxide on the surface of the sub-coating layer.

[0105] In some examples, the one-dimensional conductive material is in-situ grown on the surface of the catalyst particles. Through in-situ growth, the one-dimensional conductive material is distributed more uniformly and can even be aligned.

[0106] In some examples, the one-dimensional conductive material includes carbon nanotubes, and preparing the one-dimensional conductive material on the surface of the catalyst particles includes the following steps:

[0107] A carbon source gas is introduced to in-situ grow the carbon nanotubes on the surface of the catalyst particles.

[0108] Without limitation, the carbon source gas includes hydrocarbon gas. Further, the carbon source gas includes one or more of CH4, C2H2 and propylene.

[0109] Without limitation, the temperature condition for preparing the one-dimensional conductive material on the surface of the catalyst particles is 500° C. to 800° C.

[0110] Without limitation, the flow rate of the carbon source gas is 0.5 liters / minute (L / min) to 1.5 L / min, and the reaction time is 0.5 hours (h) to 5 hours.

[0111] Some other examples of the present application provide 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, wherein the negative electrode active material layer includes one or more of the silicon composite materials as described above or the silicon composite materials prepared by the preparation method as described above.

[0112] In some examples, the negative electrode active material layer further includes a carbon-based material.

[0113] Without limitation, the mass ratio of the silicon composite material to the carbon-based material is (10% to 90%): (90% to 10%). Specifically, the mass ratio includes but is not limited to: 10%:90%, 20%:80%, 30%:70%, 40%:60%, 50%:50%, 60%:40%, 70%:30%, 80%:20%, 90%:10%, or a range between any two of the foregoing. Furthermore, the mass ratio of the silicon composite material to the carbon-based material is (10% to 50%): (90% to 50%).

[0114] Some other examples of the present application provide a secondary battery including the negative electrode sheet as described above.

[0115] Some other examples of the present application provide an electrical device including one or more of the negative electrode sheet described above or the secondary battery described above.

[0116] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0117] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0118] Positive electrode

[0119] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content 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 new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0120] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0121] 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.

[0122] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0123] 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.

[0124] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, 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 battery positive electrode active materials 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 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 olivine-structured lithium-containing phosphates 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 0.80 Co 0.15 Al 0.05 O2.

[0125] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0126] In some embodiments, the positive electrode active material layer may further 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.

[0127] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode 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 current 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 of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascals per second (mPa·s) to 25000 mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15 mg / cm2 (mg / cm 2 )~35mg / cm 2 The compacted density of the positive electrode can be 3.0 g / cm3 (g / cm 3 )~3.6g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0128] Negative electrode

[0129] The negative electrode plate is as described above.

[0130] In addition, as a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0131] 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.

[0132] In some embodiments, the negative electrode active material layer may also include other negative electrode active materials for batteries that are well known in the art. As non-limiting examples, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, 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.

[0133] 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).

[0134] 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.

[0135] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0136] 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 negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. 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 two 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 to 10000 mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 to 220 g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0137] electrolytes

[0138] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0139] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0140] 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).

[0141] 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0142] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0143] 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.

[0144] Isolation film

[0145] 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 and mechanical stability can be selected.

[0146] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven 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.

[0147] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may optionally be 12 to 20 μm.

[0148] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0149] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0150] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0151] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0152] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0153] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0154] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates 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 be formed into 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 impregnated 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.

[0155] The secondary battery may be a battery module 4 or a battery pack 1 .

[0156] A battery module includes at least one battery cell. The number of battery cells contained 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.

[0157] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, the arrangement may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0158] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0159] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0160] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0161] In addition, the present application also provides an electrical device, which includes the secondary battery provided in 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 can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can 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 these.

[0162] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0163] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0164] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0165] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0166] Example 1

[0167] 1) Preparation of positive electrode sheet

[0168] The positive electrode active material NCM811, conductive carbon black SP and binder PVDF were dispersed in the solvent NMP in a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained. The coating amount per unit area on both sides was 0.27g / 1540.25mm 2 .

[0169] 2) Preparation of negative electrode sheet

[0170] 2.1 Preparation of negative electrode active materials

[0171] Amorphous carbon-coated pure silicon (commercially available, with a pure silicon content of 95%) was used as the raw material and ultrasonically dispersed in an aqueous FeCl3 solution in ethanol (volume ratio 1:1). Iron oxide was generated on the surface of the amorphous carbon-coated pure silicon. The product was then calcined at 700°C in a reducing atmosphere (argon:hydrogen = 95:5, volume ratio) to produce iron nanoparticles (the mass percentage of the iron nanoparticles was 0.15% based on the mass of the pure silicon). Using the iron nanoparticles as a catalyst, carbon source gas C2H2 was introduced at a flow rate of 1 L / min. The reaction was maintained at 700°C for 3 hours, followed by natural cooling. This yielded a silicon composite material with in-situ carbon nanotubes (CNTs) with a particle size Dv50 of 8 μm, an average CNT length of 5 μm, an average tube diameter of 25 nm, and a CNT content of 2% by mass based on the mass of the pure silicon. Meanwhile, the surface electron microscopy image of the silicon composite material with in-situ CNT growth is shown in FIG7 , showing that the CNTs extend outward from the outer surface of the amorphous carbon coating layer, rather than being closely attached to the surface of the carbon coating layer or fused with the carbon coating layer.

[0172] 2.2. The negative electrode active material (the silicon material (silicon composite material) for in-situ growth of CNTs prepared in step 2.1 and graphite (carbon-based material) are mixed in a mass ratio of 20%:80%), a thickener, sodium carboxymethyl cellulose, an adhesive, styrene butadiene rubber, and a conductive agent, acetylene black, are mixed in a mass ratio of 97:1:1:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on both sides of the copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then super-cold pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides is 0.17 g / 1540.25 mm 2 .

[0173] 3) Isolation film

[0174] A 12μm thick polypropylene isolation film was selected.

[0175] 4) Preparation of electrolyte

[0176] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution. The concentration of the lithium salt is 1 mol / L.

[0177] 5) Battery Preparation

[0178] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, with the isolation film placed between the positive and negative electrode sheets to serve as an isolation. After winding into a square bare battery cell, an aluminum-plastic film is placed in it. After baking at 80°C to remove water, 10g of the corresponding non-aqueous 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.

[0179] The secondary batteries of Examples 2 to 23 are prepared in a similar manner to the secondary battery of Example 1, with the main difference being the types and proportions of materials, as shown in Table 1 below. The average length and average diameter of the carbon nanotubes can be controlled by adjusting parameters such as temperature, flow rate of the carbon source gas, and time.

[0180] The secondary batteries of Examples 24 to 27 are prepared in a similar manner to that of Example 1, with the main difference being that the mass ratios of the silicon composite material to the carbon-based material are 10%:90%, 90%:10%, 50%:50%, and 65%:35%, respectively.

[0181] The preparation method of the secondary battery of Comparative Example 1 is similar to that of the secondary battery of Example 1, the main difference being that the preparation of the silicon composite material for in-situ growth of CNTs in step 2.1 is not performed. Instead, in step 2.2, amorphous carbon-coated pure silicon material and graphite are directly mixed in a ratio of 20%:80% as the negative electrode active material, and CNTs accounting for 2% by mass of pure silicon are additionally added to the negative electrode slurry.

[0182] Table 1

[0183] Test example:

[0184] Test method:

[0185] (1) Fast charging performance:

[0186] At 25°C, take the battery with the pre-embedded copper wire and charge it at a constant current of 0.33C to 4.2V. Continue to charge it at a constant voltage until the current reaches 0.05C. At this point, the battery is fully charged. The charge capacity at this point is recorded, which is the charge capacity of the first cycle. After the battery is left to rest for 30 minutes, it is discharged at a constant current of 0.33C to 2.8V. This is a cycle of charge and discharge. The discharge capacity at this point is recorded, which is the discharge capacity of the first cycle. Then, lithium plating begins. Connect the charging device to the copper wire and the positive electrode and charge it at a constant current of 20uA for 2 hours. Then connect the charging device to the copper wire and the negative electrode and charge it at a constant current of 20uA for 2 hours. The copper wire after lithium plating serves as the reference electrode, and the reference electrode potential defaults to 0mV. After lithium plating, charge the battery at a constant current of 2C and record the potential difference between the anode and reference electrode. When the potential difference reaches 0mV, record the ratio of the charged capacity to the charge capacity of the first cycle. This ratio represents the fast charging performance of the battery cell.

[0187] (2) Cycle performance:

[0188] At 25°C, charge the battery at a constant current of 0.5C to 4.2V. Continue charging at a constant voltage until the current reaches 0.05C. At this point, the battery is fully charged. Record the charge capacity at this point, which is the charge capacity of the first cycle. After the battery is allowed to rest for 30 minutes, discharge it at a constant current of 1C to 2.8V. This is a cycle of charge and discharge. Record the discharge capacity at this point, which is the discharge capacity of the first cycle. Perform a cyclic charge and discharge test on the battery according to the above method, recording the discharge capacity after each cycle until the battery's discharge capacity decays to 80% of the discharge capacity of the first cycle. The number of cycles at this point is used to represent the cycle life of the battery.

[0189] (3) Slurry dispersion: The processed slurry is allowed to stand for 24 hours, and the slurry is picked up by a stirring rod to observe the slurry flow characteristics. If there is no obvious aggregation or gelation, it is judged as "good".

[0190] The test results are shown in Table 2 below:

[0191] Table 2

[0192] Comparisons between Examples 1-23 and Comparative Example 1 demonstrate that the present invention effectively improves the fast-charging and cycling performance of the silicon composite material by placing a one-dimensional conductive material on the outer surface of the coating layer. Furthermore, the good dispersion of the materials facilitates the fabrication of the negative electrode sheet.

[0193] From the comparison between Examples 1 to 7, it can be seen that reasonable control of the mass percentage of carbon nanotubes is beneficial to further improve the cycle performance and fast charging performance.

[0194] From the comparison between Example 1 and Examples 8 to 9, it can be seen that selecting appropriate transition metal nanoparticles is beneficial to improving the stability of the structure and thus improving the cycle life.

[0195] From the comparison between Example 1 and Examples 10 to 18, it can be seen that reasonable control of the tube length of carbon nanotubes is conducive to further improving the cycle performance and fast charging performance.

[0196] From the comparison between Example 1 and Examples 19 to 23, it can be seen that reasonable control of the diameter of carbon nanotubes is beneficial to improving the cycle performance.

[0197] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0198] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A silicon composite material, comprising a one-dimensional conductive material, an inner core and a coating layer, wherein the coating layer is coated on the outer surface of the inner core, the one-dimensional conductive material is arranged on the outer surface of the coating layer, and the inner core comprises a silicon-based material.

2. The silicon composite material according to claim 1, wherein: The one-dimensional conductive material extends outward from the outer surface of the cladding layer.

3. The silicon composite material according to claim 1 or 2, wherein: The outer surface of the coating layer also has catalyst particles, and the one-dimensional conductive material is arranged on the surface of the catalyst particles; the catalyst particles include transition metal nanoparticles.

4. The silicon composite material according to claim 3, wherein: The transition metal nanoparticles include one or more of iron nanoparticles, cobalt nanoparticles and nickel nanoparticles.

5. The silicon composite material according to any one of claims 1 to 4, wherein: The coating layer includes a carbon coating layer, and the carbon coating layer includes amorphous carbon.

6. The silicon composite material according to any one of claims 3 to 5, wherein: Based on the mass of the silicon-based material, the mass percentage of the catalyst particles is 0.001% to 0.3%.

7. The silicon composite material according to any one of claims 1 to 6, wherein: The one-dimensional conductive material includes carbon nanotubes.

8. The silicon composite material according to claim 7, wherein: The carbon nanotubes have one or more of the following characteristics: (1) The average tube length is 0.5 μm to 10 μm; (2) The average tube diameter is 1nm~50nm.

9. The silicon composite material according to claim 8, wherein: The carbon nanotubes have one or more of the following characteristics: (1) The average tube length is 1 μm to 10 μm; (2) The average tube diameter is 20nm~30nm.

10. The silicon composite material according to any one of claims 1 to 9, wherein: Based on the mass of the silicon-based material, the mass percentage of the one-dimensional conductive material is 0.01% to 5%.

11. The silicon composite material according to claim 10, wherein: Based on the mass of the silicon-based material, the mass percentage of the one-dimensional conductive material is 0.4% to 5%.

12. The silicon composite material according to any one of claims 1 to 11, wherein: The Dv50 of the silicon composite material is 1 μm to 30 μm.

13. The silicon composite material according to any one of claims 1 to 12, wherein: The silicon-based material includes one or more of silicon-oxygen compounds, silicon-carbon composites, elemental silicon or silicon alloys.

14. A method for preparing a silicon composite material, comprising the following steps: preparing a coating layer on the outer surface of an inner core, wherein the inner core comprises a silicon-based material; A one-dimensional conductive material is prepared on the outer surface of the coating layer.

15. The method for preparing the silicon composite material according to claim 14, wherein: Preparing a one-dimensional conductive material on the outer surface of the coating layer comprises the following steps: preparing catalyst particles on the outer surface of the coating layer; A one-dimensional conductive material is prepared on the surface of the catalyst particles.

16. The method for preparing the silicon composite material according to claim 15, wherein: The preparation of catalyst particles on the outer surface of the coating layer comprises the following steps: Preparing transition metal oxide and / or transition metal hydroxide on the surface of the coating layer; The transition metal oxide and / or transition metal hydroxide is calcined in a reducing atmosphere to generate transition metal nanoparticles.

17. The method for preparing the silicon composite material according to claim 16, wherein: The calcination temperature is 600°C to 800°C.

18. The method for preparing the silicon composite material according to any one of claims 15 to 17, wherein: The one-dimensional conductive material is in-situ grown on the surface of the catalyst particles.

19. The method for preparing the silicon composite material according to any one of claims 15 to 18, wherein: The one-dimensional conductive material includes carbon nanotubes, and preparing the one-dimensional conductive material on the surface of the catalyst particles includes the following steps: A carbon source gas is introduced to in-situ grow the carbon nanotubes on the surface of the catalyst particles.

20. A negative electrode plate, 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 one or more of the silicon composite material according to any one of claims 1 to 13 or the silicon composite material prepared by the preparation method according to any one of claims 14 to 19.

21. The negative electrode sheet according to claim 20, wherein: The negative electrode active material layer also includes a carbon-based material, and the mass ratio of the silicon composite material to the carbon-based material is (10% to 90%): (90% to 10%).

22. A secondary battery comprising the negative electrode sheet according to claim 20 or 21.

23. An electrical device comprising one or more of the negative electrode sheet according to claim 20 or 21 or the secondary battery according to claim 22.

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