Silicon-carbon composite material and preparation method therefor, negative electrode sheet, secondary battery, and electrical device

Abstract

The present application relates to a silicon-carbon composite material and a preparation method therefor, a negative electrode sheet, a secondary battery, and an electrical device. The silicon-carbon composite material comprises a porous carbon matrix and a silicon-based material layer located in pores of the porous carbon matrix, the silicon-based material layer comprises a sub-nano silicon cluster and a sub-nano silicon carbide cluster, and the surface of the sub-nano silicon carbide cluster is in contact with the surface of the sub-nano silicon cluster. The silicon-carbon composite material has small expansibility, good cycle performance and fast charging performance and high energy density.

Description

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

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2023114448084, filed on November 2, 2023, entitled “Silicon-carbon 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-carbon composite material and a preparation method thereof, a negative electrode sheet, a secondary battery and an electrical device. Background Art

[0004] 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 significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0005] Silicon-based materials have attracted attention due to their much higher capacity than carbon-based materials, as higher capacity means higher energy density can be achieved. However, silicon-based materials undergo significant volume changes (>300%) during the charge and discharge process. This change can cause structural damage and particle pulverization, leading to rapid electrode capacity decay and even electrode failure. Therefore, silicon-based materials are often combined with carbon-based materials in the production of electrodes. However, current silicon-carbon composite materials still suffer from high expansion and short cycle life.

[0006] Summary of the Invention

[0007] The present application provides a silicon-carbon composite material with low expansion and long cycle life, a preparation method thereof, and a negative electrode sheet, a secondary battery and an electrical device using the silicon-carbon composite material.

[0008] In a first aspect of the present application, a silicon-carbon composite material is provided, comprising a porous carbon matrix and a silicon-based material layer located in the pores of the porous carbon matrix, wherein the silicon-based material layer comprises sub-nano silicon clusters and sub-nano silicon carbide clusters, and the surfaces of the sub-nano silicon carbide clusters are in contact with the surfaces of the sub-nano silicon clusters.

[0009] By placing a silicon-based material layer within the pores of a porous carbon matrix, the pores reserve space for silicon expansion, thereby reducing the breakage of the silicon-carbon composite particles and improving cycle life. At the same time, the presence of silicon carbide limits the size growth of silicon, promoting the formation of sub-nanometer silicon clusters, ultimately forming surface-contacting sub-nanometer silicon carbide clusters and the sub-nanometer silicon clusters. Compared to traditional nano-silicon, sub-nanometer silicon clusters have less expansion, reducing the material's expansion stress, further reducing the breakage of silicon-carbon composite particles, and improving cycle performance.

[0010] In one embodiment, the radial size of the sub-nanometer silicon cluster is 0.2 nm to 1 nm.

[0011] In one embodiment, the radial size of the sub-nanometer silicon carbide clusters is 0.2 nm to 1 nm.

[0012] In one embodiment, the specific surface area of ​​the porous carbon matrix is ​​≥800 m 2 / g. By using a porous carbon matrix with an ultra-high specific surface area, more silicon-based materials can be deposited, thereby improving the high energy density of the material.

[0013] Optionally, the specific surface area of ​​the porous carbon matrix is ​​800 m 2 / g~2000m 2 / g.

[0014] Further optionally, the specific surface area of ​​the porous carbon matrix is ​​800m 2 / g~1700m 2 / g.

[0015] Further optionally, the specific surface area of ​​the porous carbon matrix is ​​800m 2 / g~1200m 2 / g.

[0016] In one embodiment, the total volume of the silicon-based material layer is less than the total volume of the pores.

[0017] Optionally, the total volume of the silicon-based material layer accounts for 10% to 60% of the total volume of the pores. This can improve high energy density, reduce the breakage of silicon-carbon composite material particles, improve cycle performance, and also optimize fast charging performance to a certain extent.

[0018] Further optionally, the total volume of the silicon-based material layer accounts for 10% to 50% of the total volume of the pores.

[0019] Further optionally, the total volume of the silicon-based material layer accounts for 10% to 30% of the total volume of the pores.

[0020] In one embodiment, the thickness of the silicon-based material layer is less than the pore diameter.

[0021] Optionally, the average pore size is 5 nm to 50 nm. This can improve high energy density, reduce the breakage of silicon-carbon composite material particles, improve cycle performance, and improve fast charging performance to a certain extent.

[0022] Further optionally, the average pore diameter of the pores is 5 nm to 40 nm.

[0023] Further optionally, the average pore diameter of the pores is 5 nm to 25 nm.

[0024] Optionally, the average thickness of the silicon-based material layer is 2 nm to 20 nm.

[0025] Further optionally, the average thickness of the silicon-based material layer is 2 nm to 18 nm.

[0026] Further optionally, the average thickness of the silicon-based material layer is 2 nm to 10 nm.

[0027] In one embodiment, the particle size Dv50 of the silicon-carbon composite material is 3 μm to 30 μm. This can reduce the deterioration of cycle performance caused by side reactions during the cycle, reduce the diffusion distance of ions, improve fast charging performance, and also provide a longer cycle life.

[0028] Optionally, the particle size Dv50 of the silicon-carbon composite material is 10 μm to 30 μm.

[0029] Further optionally, the particle size Dv50 of the silicon-carbon composite material is 10 μm to 20 μm.

[0030] In one embodiment, the surface of the porous carbon matrix is ​​further covered with a coating layer.

[0031] Optionally, the coating layer includes a carbon coating layer; further optionally, the material of the carbon coating layer includes amorphous carbon; optionally, the average thickness of the coating layer is 5 nm to 60 nm.

[0032] In one embodiment, in the silicon-carbon composite material, the mass percentage of silicon is 20% to 40%, and the mass percentage of carbon is 60% to 80%.

[0033] In one embodiment, the silicon-carbon composite material includes one or both of the following features:

[0034] (1) Tap density is 0.7g / cm 3 ~1.3g / cm 3 ;

[0035] (2) Specific surface area is 0.8m 2 / g~1.5m 2 / g.

[0036] In a second aspect of the present application, a method for preparing a silicon-carbon composite material is provided, comprising the following steps:

[0037] A silicon-based material layer is deposited in the pores of the porous carbon matrix. The silicon-based material layer includes sub-nanometer silicon clusters and silicon carbide clusters. The surfaces of the silicon carbide clusters are in contact with the surfaces of the sub-nanometer silicon clusters.

[0038] The preparation method has simple steps and is suitable for industrial promotion and application.

[0039] In one embodiment, depositing a silicon-based material layer in the pores of the porous carbon matrix includes:

[0040] The porous carbon substrate is placed in a reaction container, and a mixed gas of silicon source gas and carbon source gas is introduced to perform vapor deposition.

[0041] In one embodiment, the vapor deposition by introducing a mixture of silicon source gas and carbon source gas includes one or more of the following features:

[0042] (1) In the mixed gas, the volume ratio of the silicon source gas to the carbon source gas is 10:(1-5);

[0043] (2) The silicon source gas includes SiH4;

[0044] (3) The carbon source gas includes C2H4;

[0045] (4) The flow rate of the mixed gas is 0.05 L / min to 0.2 L / min;

[0046] (5) The deposition temperature is 400℃~600℃;

[0047] (6) The deposition time is 30 minutes to 2 hours.

[0048] In one embodiment, after depositing the silicon-based material layer, the method further comprises the step of preparing a coating layer on the surface of the porous carbon substrate;

[0049] Optionally, the method for preparing the coating layer on the surface of the porous carbon substrate includes a vapor deposition method.

[0050] In one embodiment, the preparation method of the porous carbon matrix includes a template method, an acid-base activation method or a pyrolysis method; optionally, the preparation method of the porous carbon matrix includes an acid-base activation method.

[0051] In one embodiment, the method for preparing the porous carbon substrate comprises:

[0052] mixing a template, a carbon source, and a solvent to prepare a carbon solution;

[0053] The carbon solution is subjected to a first heat treatment and then dried to prepare an expanded carbon precursor;

[0054] subjecting the expanded carbon precursor to a second heat treatment to prepare a carbonized intermediate;

[0055] The template in the carbonized intermediate is removed to prepare the porous carbon matrix.

[0056] In one embodiment, the method for preparing the porous carbon substrate has one or more of the following characteristics:

[0057] (1) The mass ratio of the template to the carbon source is (1-10):1;

[0058] (2) The temperature of the first heat treatment is 70℃~90℃ and the time is 6h~10h;

[0059] (3) The drying temperature is 120°C to 140°C and the drying time is 1h to 4h;

[0060] (4) The second heat treatment includes: heating to 400°C to 600°C at a heating rate of 3°C / min to 10°C / min, and maintaining for 2h to 6h.

[0061] 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-carbon composite material described in the first aspect and the silicon-carbon composite material prepared by the preparation method described in the second aspect.

[0062] The negative electrode plate of the present application includes the silicon-carbon composite material provided in the present application, and thus has at least the same advantages as the silicon-carbon composite material.

[0063] In a fourth aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet described in the third aspect.

[0064] 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 negative electrode sheet.

[0065] 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 and the secondary battery described in the fourth aspect.

[0066] The electric device of the present application includes the negative electrode sheet or secondary battery provided in the present application, and thus has at least the same advantages as the negative electrode sheet or secondary battery.

[0067] Details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objectives, and advantages of the present application will become apparent from the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] 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:

[0069] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0070] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0071] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0072] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0073] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application;

[0074] 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;

[0075] FIG7 is an electron microscope image of a porous carbon substrate according to an embodiment of the present application;

[0076] FIG8 is an electron microscope image of a silicon-based material layer according to an embodiment of the present application;

[0077] FIG9 is an electron microscope image of a silicon-carbon composite material according to an embodiment of the present application;

[0078] FIG10 is an electron microscope image of a silicon-based material layer according to another embodiment of the present application;

[0079] 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

[0080] Below, some embodiments of the silicon-carbon composite material and its preparation method, negative electrode sheet, 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.

[0081] 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.

[0082] 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.

[0083] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0084] 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.

[0085] Those skilled in the art will appreciate that, in the methods of each embodiment or example, 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 internal logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0086] 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.

[0087] 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.

[0088] Traditional silicon-carbon composite materials are prepared by directly mixing silicon-based materials with carbon-based materials, or coating the surface of silicon-based materials with a layer of carbon-based materials, or granulating silicon-based materials and carbon-based materials. These materials have large restrictions on the silicon content. When the silicon content is too high, the expansion is still large, making the electrode structure easily damaged, thereby shortening the cycle life.

[0089] Based on the above problems, some examples of the present application provide a silicon-carbon composite material, which includes a porous carbon matrix and a silicon-based material layer located in the pores of the porous carbon matrix, the silicon-based material layer includes sub-nano silicon clusters and sub-nano silicon carbide clusters, and the surfaces of the sub-nano silicon carbide clusters are in contact with the surfaces of the sub-nano silicon clusters.

[0090] The silicon-carbon composite material is constructed by placing a silicon-based material layer within the pores of a porous carbon matrix. The pores can reserve space for the expansion of silicon, thereby reducing the breakage of the silicon-carbon composite material particles and improving the cycle life. At the same time, the presence of silicon carbide in the silicon-based material layer limits the size growth of silicon, promotes the formation of sub-nanometer silicon clusters, and ultimately forms sub-nanometer silicon carbide clusters and sub-nanometer silicon clusters in contact with each other on the surface. Compared with traditional nano-silicon, the sub-nanometer silicon clusters have smaller expansion, reduce the expansion stress of the material, further reduce the breakage of the silicon-carbon composite material particles, improve the cycle performance, and the sub-nanometer silicon clusters have smaller radial dimensions, which can reduce the diffusion distance of ions, improve solid-phase diffusion, and improve fast charging performance.

[0091] In addition, the above-mentioned silicon-carbon composite material can also take into account the high energy density characteristics of silicon-based materials.

[0092] In some examples, the contact between the surfaces of the sub-nanometer silicon carbide clusters and the surfaces of the sub-nanometer silicon clusters means that the sub-nanometer silicon clusters and the sub-nanometer silicon carbide clusters are in an interlaced structure. As an example, the interlaced structure can be a mosaic-like arrangement structure.

[0093] It can be understood that the silicon-based material can form a layer structure within the pores of the porous carbon matrix through methods such as deposition.

[0094] Furthermore, the radial size of the sub-nanometer silicon cluster is 0.2 nanometers (nm) to 1 nm.

[0095] Furthermore, the radial size of the sub-nanometer silicon carbide cluster is 0.2 nm to 1 nm.

[0096] In some examples, the specific surface area of ​​the porous carbon matrix is ​​≥800 m2 / g (m 2 / g). By using a porous carbon matrix with an ultra-high specific surface area, more silicon-based materials can be deposited, thereby improving the high energy density of the material. Furthermore, the specific surface area of ​​the porous carbon matrix is ​​800m2 / g~2000m 2 / g. This can improve the cycle performance under high energy density. Specifically, the specific surface area of ​​the porous carbon matrix includes but is not limited to: 800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g or a range between any two of the above. Further, the specific surface area of ​​the porous carbon matrix is ​​800m 2 / g~1700m 2 / g. Furthermore, the specific surface area of ​​the porous carbon matrix is ​​800m 2 / g~1200m 2 Without limitation, the specific surface area of ​​the porous carbon substrate can be measured by a nitrogen isothermal adsorption-desorption method.

[0097] In some examples, the total volume of the silicon-based material layer is less than the total volume of the pores. Furthermore, the total volume of the silicon-based material layer accounts for 10% to 60% of the total volume of the pores. In this way, on the one hand, the content of silicon-based materials is larger, which improves high energy density. On the other hand, it provides more expansion space for silicon-based materials, reduces the breakage of silicon-carbon composite material particles, improves cycle performance, and also optimizes fast charging performance to a certain extent. Specifically, the total volume of the silicon-based material layer accounts for the total volume of the pores, including but not limited to: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or a range between any two of the foregoing. Furthermore, the total volume of the silicon-based material layer accounts for 10% to 50% of the total volume of the pores. Still further, the total volume of the silicon-based material layer accounts for 10% to 30% of the total volume of the pores. Without limitation, the total volume of the silicon-based material layer can be obtained by calculating the pore volume of the porous carbon matrix before and after the deposition of the silicon-based material layer, wherein the "pore volume" can be measured by a nitrogen isothermal adsorption-desorption method.

[0098] In some examples, the thickness of the silicon-based material layer is less than the pore diameter of the pore.

[0099] Furthermore, the average pore size of the pores is 5nm to 50nm. In this way, on the one hand, the content of silicon-based materials is larger, and the high energy density is improved. On the other hand, more expansion space is provided for silicon-based materials, which reduces the breakage of silicon-carbon composite material particles and improves the cycle performance. In addition, the fast charging performance can be improved to a certain extent. Specifically, the average pore size of the pores includes but is not limited to: 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm or a range between any two of the foregoing. Furthermore, the average pore size of the pores is 5nm to 40nm. Furthermore, the average pore size of the pores is 5nm to 25nm. Without limitation, the average pore size of the pores can be determined by a nitrogen isothermal adsorption-desorption method.

[0100] Furthermore, the average thickness of the silicon-based material layer is 2nm to 20nm. In this way, on the one hand, the content of silicon-based materials is larger, and the high energy density is improved. On the other hand, more expansion space is provided to the silicon-based material, which reduces the breakage of silicon-carbon composite material particles and improves the cycle performance. In addition, it can also improve the fast charging performance to a certain extent. Specifically, the average thickness of the silicon-based material layer includes but is not limited to: 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm or a range between any two of the foregoing. Furthermore, the average thickness of the silicon-based material layer is 2nm to 18nm. Furthermore, the average thickness of the silicon-based material layer is 2nm to 10nm. Without limitation, it can be measured by an indirect method. Specifically: the average pore size of the porous carbon matrix before depositing the silicon-based material layer is recorded as R1, and after depositing silicon, the average pore size is recorded as R2. The average thickness of the silicon-based material layer is (R1-R2) / 2, wherein the "average pore size" can be measured by the nitrogen isothermal adsorption-desorption method.

[0101] In some examples, the particle size Dv50 of the silicon-carbon composite material is 3 microns (μm) to 30μm. In this way, on the one hand, the deterioration of the cycle performance caused by side reactions during the cycle can be reduced, and on the other hand, the diffusion distance of ions can be reduced, the fast charging performance can be improved, and it also has a good cycle life. Specifically, the particle size Dv50 of the silicon-carbon composite material includes but is not limited to: 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 20μm, 25μm, and 30μm. Further, the particle size Dv50 of the silicon-carbon composite material is 10μm to 30μm. Furthermore, without limitation, the particle size Dv50 of the silicon-carbon composite material is 10μm to 20μm. The particle size Dv50 of the silicon-carbon composite material can be tested by laser particle size test.

[0102] In some of the examples, the surface of the porous carbon substrate is further covered with a coating layer.

[0103] In some examples, the coating layer includes a carbon coating layer. Without limitation, the carbon coating layer is made of amorphous carbon.

[0104] In some examples, the average thickness of the coating layer is 5 nm to 60 nm. This effectively isolates the material from electrolyte corrosion during cycling and improves the material's conductivity. Without limitation, the average thickness of the carbon coating layer can be measured using transmission electron microscopy or sputtering XPS.

[0105] In some examples, the silicon-carbon composite material comprises 20% to 40% silicon by weight and 60% to 80% carbon by weight. This allows the material to have both high specific capacity and low expansion. Without limitation, the silicon and carbon content can be determined using an ICP test.

[0106] In some examples, the tap density of the silicon-carbon composite material is 0.7 g / cm3 (g / cm 3 )~1.3g / cm 3 .

[0107] In some examples, the specific surface area of ​​the silicon-carbon composite material is 0.8 m 2 / g~1.5m 2 / g.

[0108] Some other examples of the present application provide a method for preparing a silicon-carbon composite material, comprising the following steps:

[0109] A silicon-based material layer is deposited in the pores of the porous carbon matrix. The silicon-based material layer includes sub-nanometer silicon clusters and silicon carbide clusters. The surfaces of the silicon carbide clusters are in contact with the surfaces of the sub-nanometer silicon clusters.

[0110] The preparation method has simple steps and is suitable for industrial promotion and application.

[0111] In addition, it can be understood that the silicon-carbon composite material involved in the above preparation method has the same characteristics and advantages as the silicon-carbon composite material in the above examples, which will not be described in detail here.

[0112] Furthermore, subnano-scaling silicon-based materials can reduce expansion stress, thereby reducing the breakage of material particles. It can also reduce the ion diffusion distance, improve solid-phase diffusion, and enhance fast-charging performance. In combination with a porous carbon matrix, it can greatly reduce expansion by reserving space for silicon-based materials to expand. Therefore, a further purpose of this application is to prepare subnano-scale silicon-based materials.

[0113] Some examples of depositing a layer of silicon-based material within the pores of a porous carbon matrix include:

[0114] The porous carbon substrate is placed in a reaction container, and a mixed gas of silicon source gas and carbon source gas is introduced to perform vapor deposition.

[0115] Furthermore, in the mixed gas, the volume ratio of the silicon source gas to the carbon source gas is 10:(1-5). Specifically, the volume ratio of the silicon source gas to the carbon source gas includes but is not limited to: 10:1, 10:2, 10:3, 10:4, 10:5, or a range between any two of the foregoing.

[0116] Without limitation, the silicon source gas includes SiH 4 .

[0117] Without limitation, the carbon source gas includes C2H4.

[0118] Furthermore, the flow rate of the mixed gas is 0.05 liters / minute (L / min) to 0.2 L / min. Specifically, the flow rate of the mixed gas includes but is not limited to: 0.05 L / min, 0.08 L / min, 0.1 L / min, 0.12 L / min, 0.15 L / min, 0.2 L / min, or a range between any two of the foregoing.

[0119] Furthermore, the deposition temperature is 400 degrees Celsius (° C.) to 600° C. Specifically, the deposition temperature includes but is not limited to: 400° C., 450° C., 500° C., 550° C., 600° C. or a range between any two of the foregoing.

[0120] Furthermore, the deposition time is 30 minutes (min) to 2 hours (h). Specifically, the deposition time includes but is not limited to: 30 minutes, 1 hour, 1.5 hours, 2 hours or a range between any two of the foregoing.

[0121] By adopting the vapor deposition method to prepare the silicon-based material layer and rationally controlling the gas ratio, flow rate, temperature and time during the preparation process, the generated silicon carbide can be made to surround the silicon after nucleation, limiting its size growth, and ultimately forming a silicon-based material layer including sub-nanometer silicon clusters and silicon carbide clusters, and the surface of the silicon carbide clusters is in contact with the surface of the sub-nanometer silicon clusters.

[0122] In some examples, after depositing the silicon-based material layer, a step of preparing a coating layer on the surface of the porous carbon substrate is also included. Furthermore, the method for preparing the coating layer on the surface of the porous carbon substrate includes a vapor deposition method. Without limitation, the coating layer is a carbon coating layer, the carbon source gas used can be one or both of CH4 and C2H2, the deposition temperature can be 600°C to 900°C, and the deposition time can be controlled according to the preset thickness, for example, 15 minutes to 30 minutes.

[0123] In some examples, the preparation method of the porous carbon matrix includes a template method, an acid-base activation method, or a thermal decomposition method.

[0124] As an example, the template method can use SiO2 nanospheres as templates, immerse them in a carbon source solution, and obtain the porous carbon matrix through centrifugation, drying, annealing, and acid etching.

[0125] For example, the acid-base activation method can mix activators such as potassium hydroxide and phosphoric acid with a carbon source, and remove organic matter and natural templates within the carbon source through physical and chemical sparking to obtain the porous carbon matrix. Potassium hydroxide, as a chemical activator, can generate potassium carbonate, potassium oxide, and even metallic potassium, which are then removed during subsequent pyrolysis and washing. Phosphoric acid can generate phosphorus-containing functional groups in the carbon matrix, promoting micropore formation.

[0126] As an example, the pyrolysis method refers to obtaining the porous carbon matrix by pyrolysis without adding any template or activator, relying on the gas generated by pyrolysis and the properties of the material itself.

[0127] Furthermore, the preparation method of the porous carbon matrix includes an acid-base activation method.

[0128] In some examples, the method for preparing the porous carbon substrate includes:

[0129] mixing a template, a carbon source, and a solvent to prepare a carbon solution;

[0130] The carbon solution is subjected to a first heat treatment and then dried to prepare an expanded carbon precursor;

[0131] subjecting the expanded carbon precursor to a second heat treatment to prepare a carbonized intermediate;

[0132] The template in the carbonized intermediate is removed to prepare the porous carbon matrix.

[0133] Furthermore, the mass ratio of the template to the carbon source is (1-10): 1. Specifically, the mass ratio of the template to the carbon source includes but is not limited to: 1:1, 2:1, 2.7:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or a range between any two of the foregoing.

[0134] Furthermore, the temperature of the first heat treatment is 70°C to 90°C, and the time is 6 hours to 10 hours. Specifically, the temperature of the first heat treatment includes, but is not limited to, 70°C, 75°C, 80°C, 85°C, 90°C, or a range between any two of the foregoing. The time of the first heat treatment includes, but is not limited to, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or a range between any two of the foregoing.

[0135] Furthermore, the drying temperature is 120° C. to 140° C., and the drying time is 1 hour to 4 hours.

[0136] Furthermore, the second heat treatment includes: heating to 400°C to 600°C at a heating rate of 3 degrees Celsius / minute (°C / min) to 10°C / min, and maintaining for 2h to 6h. Specifically, the heating rate of the second heat treatment includes but is not limited to: 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min or a range between any two of the foregoing. The temperature of the second heat treatment includes but is not limited to: 400°C, 450°C, 500°C, 550°C, 600°C or a range between any two of the foregoing. The time of the second heat treatment includes but is not limited to: 2h, 3h, 4h, 5h, 6h or a range between any two of the foregoing.

[0137] In addition, without limitation, the method for removing the template in the carbonized intermediate may include acid treatment, for example, mixing the carbonized intermediate with an acid solution and performing a third heat treatment, followed by washing and drying.

[0138] 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, the negative electrode active material layer including one or more of the silicon-carbon composite material as described above and the silicon-carbon composite material prepared by the preparation method as described above.

[0139] Some other examples of the present application provide a secondary battery including the negative electrode sheet as described above.

[0140] Some other examples of the present application provide an electrical device including one or more of the negative electrode sheet and the secondary battery as described above.

[0141] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0142] 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.

[0143] Positive electrode

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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 Mn0.2 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.

[0150] 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.

[0151] 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.

[0152] 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·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 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0153] Negative electrode

[0154] The negative electrode plate is as described above.

[0155] 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.

[0156] 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.

[0157] In some embodiments, the above-mentioned silicon-carbon composite material can be used alone in the negative electrode active material layer, or the silicon-carbon composite material can be mixed with other negative electrode active materials for batteries known in the art in any proportion. As non-limiting examples, other negative electrode active materials for batteries 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials 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.

[0158] In some embodiments, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0159] 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).

[0160] 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.

[0161] 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)).

[0162] 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 on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s to 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 can be 1.0g / cm 3 ~1.8g / cm 3 .

[0163] electrolytes

[0164] 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.

[0165] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0166] 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).

[0167] 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), butylene 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.

[0168] 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.

[0169] 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.

[0170] Isolation film

[0171] 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.

[0172] 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.

[0173] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may optionally be 12 to 20 μm.

[0174] 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.

[0175] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0176] 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.

[0177] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] The secondary battery may be a battery module 4 or a battery pack 1 .

[0182] 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.

[0183] 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, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0189] 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.

[0190] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0191] 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.

[0192] Example 1

[0193] 1) Preparation of positive electrode sheet

[0194] 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 .

[0195] 2) Preparation of negative electrode sheet

[0196] 2.1 Preparation of negative electrode active materials

[0197] Preparation of the porous carbon matrix: 11g of glucose monohydrate and 30g of zinc chloride were placed in a 200mL beaker. 30mL of deionized water was added and stirred with a glass rod to form a clear, transparent solution. The solution was transferred to a thermostatically heated magnetic stirrer and heated to 80°C. Slow mechanical stirring with a stirring paddle was performed for 8 hours to evaporate most of the water, leaving a uniform, brown-black, viscous liquid. A forced-air drying oven was preheated to 130°C. While still hot, the brown-black viscous liquid was immediately placed into the oven and held for 2 hours to obtain a loose, porous, expanded carbon precursor. After the carbon precursor cooled to room temperature, it was loaded into a magnetic boat and transferred to a tubular resistance furnace. The temperature was raised at a controlled rate of 6°C / min to 500°C and held for 4 hours. N2 was used throughout the carbonization process.

[0198] Prepare 250mL of 1mol / L dilute hydrochloric acid and grind the carbonized product, cooled to room temperature, into powder using an agate mortar. Mix 50mL of 1mol / L dilute hydrochloric acid and all the powder in a conical flask. Heat to boiling on a constant-temperature magnetic stirrer and maintain for 20 minutes. Repeat four times to wash away the template in the carbon material. After filtering out the washing liquid, wash the carbon material with a large amount of deionized water until neutral and dry it in a forced air drying oven at 110°C for 20 hours to prepare a porous carbon matrix. An electron microscope image of the porous carbon matrix is ​​shown in Figure 7, showing that the prepared carbon matrix has a porous structure.

[0199] Preparation of the silicon-based material layer: The porous carbon substrate is placed in a tube furnace, and a mixture of SiH4 and C2H4 (volume ratio between 10:3) is introduced at a temperature of 500°C and a ventilation rate of 0.1L / min for 1 hour to deposit the silicon-based material layer in the pores of the porous carbon substrate. An electron microscope image of the silicon-based material layer is shown in Figure 8. It can be seen that the silicon-based material layer includes sub-nanometer silicon clusters and silicon carbide clusters, and the two are in contact with each other, or the silicon carbide clusters are located around the sub-nanometer silicon clusters. The radial size of the sub-nanometer silicon clusters is about 0.2nm to 1nm, and the radial size of the sub-nanometer silicon carbide clusters is about 0.2nm to 1nm.

[0200] Preparation of the carbon coating: The gas introduced was then replaced with CH4 and the temperature was set to 700°C for 25 minutes. This allowed an amorphous carbon coating to form on the surface of the porous carbon substrate. The substrate was then cooled to room temperature to obtain a silicon-carbon composite material. The amorphous carbon coating had a thickness of 30 nm. An electron micrograph of the silicon-carbon composite material is shown in Figure 9.

[0201] 2.2. The silicon-carbon composite material prepared in step 2.1 was used as the negative electrode active material, mixed with a thickener of sodium carboxymethyl cellulose, a binder of styrene-butadiene rubber, and a conductive agent of acetylene black in a mass ratio of 97:1:1:1, 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 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 was 0.17 g / 1540.25 mm 2 .

[0202] 3) Isolation film

[0203] A 12μm thick polypropylene isolation film was selected.

[0204] 4) Preparation of electrolyte

[0205] 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.

[0206] 5) Preparation of batteries

[0207] 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.

[0208] The secondary batteries of Examples 2 to 19 are prepared in a similar manner to that of Example 1, with the main differences being the specific surface area of ​​the porous carbon matrix, the total volume of the silicon-based material layer to the total volume of the porous carbon matrix pores, the average pore size of the porous carbon matrix pores, and the thickness of the silicon-based material layer.

[0209] Among them, the electron microscope image of the silicon-based material layer prepared in Example 7 is shown in Figure 10. It can be seen that through the co-deposition of silicon source (SiH4) gas and carbon source (C2H4) gas, sub-nanometer silicon carbide clusters are deposited and formed at the same time as sub-nanometer silicon clusters are deposited, and the two grow in an interlaced manner, and finally form sub-nanometer silicon clusters and sub-nanometer silicon carbide clusters that are in contact with each other in the silicon-based material layer. The contact between the sub-nanometer silicon clusters and the sub-nanometer silicon carbide clusters is characterized by an interlaced, mosaic-like structure.

[0210] 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 C2H4 is not introduced during the preparation of the silicon-based material layer, that is, the silicon-based material layer is a Si layer.

[0211] Table 1

[0212] Test Case

[0213] Test method:

[0214] (1) Anode full charge rebound:

[0215] The original thickness of the negative electrode sheet is measured and recorded as W0. The assembled battery is then disassembled after full charge, and the thickness of the negative electrode sheet after full charge is measured and recorded as W1.

[0216] Anode full charge rebound α = (W1-W0) / W0.

[0217] (2) Fast charging performance:

[0218] At 25°C, a battery with pre-embedded copper wire was charged at a constant current of 0.33C to 4.25V. Constant voltage charging continued until the current reached 0.05C, at which point the battery was fully charged. The charge capacity at this point was recorded as the first cycle charge capacity. After the battery rested for 30 minutes, it was discharged at a constant current of 0.33C to 2.5V. This constituted a single charge-discharge cycle, and the discharge capacity at this point was recorded as the first cycle discharge capacity. Lithium plating then began. A charging device was connected to the copper wire and the positive electrode, charging at a constant current of 20uA for 2 hours. Then, the charging device was connected to the copper wire and the negative electrode, charging at a constant current of 20uA for 2 hours. The copper wire after lithium plating served as the reference electrode, and the reference electrode potential was set to 0mV by default. After lithium plating, the battery was charged at a constant current of 2C, and the potential difference between the negative electrode and the reference electrode was recorded. When the potential difference reached 0mV, the ratio of the charged capacity to the first cycle charge capacity was recorded. This ratio represents the fast charging performance of the secondary battery.

[0219] (3) Cycle life:

[0220] At 25°C, the prepared battery was charged at a constant current of 0.5C to 4.25V. The battery was then charged at a constant voltage until the current reached 0.05C, at which point the battery was fully charged. The charge capacity at this point was recorded as the first cycle charge capacity. The battery was allowed to rest for 30 minutes and then discharged at a constant current of 1C to 2.5V. This constituted one cycle of charge and discharge. The discharge capacity at this point was recorded as the first cycle discharge capacity. The battery was then subjected to cyclic charge and discharge testing as described above, with the discharge capacity after each cycle recorded until the discharge capacity decayed to 80% of the first cycle discharge capacity. The number of cycles at this point was used to characterize the cycle life of the secondary battery.

[0221] (4) Energy density:

[0222] The battery was placed in a constant temperature environment at 25°C for 2 hours, then charged at 0.33C to 4.25V at 2.5V~4.25V, then charged at a constant voltage at 4.25V to a current ≤0.05C, placed in a constant temperature environment for 10 minutes, and then discharged at 0.33C to 2.5V, and the capacity C0 of the battery was recorded. VED is the ratio of C0 to the volume of the battery shell, which is the volume energy density (VED) of the secondary battery.

[0223] The test results are shown in Table 2 below:

[0224] Table 2

[0225] It can be seen that by arranging sub-nano silicon clusters and sub-nano silicon carbide clusters in the silicon-based material layer, the present application can make the prepared material less expansive, have better cycle performance and fast charging performance, and also have a higher energy density.

[0226] 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.

[0227] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A silicon-carbon composite material, comprising a porous carbon matrix and a silicon-based material layer located in the pores of the porous carbon matrix, wherein the silicon-based material layer comprises sub-nano silicon clusters and sub-nano silicon carbide clusters, and the surfaces of the sub-nano silicon carbide clusters are in contact with the surfaces of the sub-nano silicon clusters.

2. The silicon-carbon composite material according to claim 1, wherein: The silicon-carbon composite material includes one or two of the following features: (1) The radial size of the sub-nanometer silicon cluster is 0.2 nm to 1 nm; (2) The radial size of the sub-nanometer silicon carbide cluster is 0.2 nm to 1 nm.

3. The silicon-carbon composite material according to claim 1 or 2, wherein: The specific surface area of ​​the porous carbon matrix is ​​≥800m 2 / g.

4. The silicon-carbon composite material according to claim 3, wherein: The specific surface area of ​​the porous carbon matrix is ​​800 m 2 / g~2000m 2 / g.

5. The silicon-carbon composite material according to claim 4, wherein: The specific surface area of ​​the porous carbon matrix is ​​800 m 2 / g~1200m 2 / g.

6. The silicon-carbon composite material according to any one of claims 1 to 5, wherein: The total volume of the silicon-based material layer is less than the total volume of the pores.

7. The silicon-carbon composite material according to claim 6, wherein: The total volume of the silicon-based material layer accounts for 10% to 60% of the total volume of the pores.

8. The silicon-carbon composite material according to claim 7, wherein: The total volume of the silicon-based material layer accounts for 10% to 30% of the total volume of the pores.

9. The silicon-carbon composite material according to any one of claims 1 to 8, wherein: The thickness of the silicon-based material layer is less than the pore diameter.

10. The silicon-carbon composite material according to claim 9, wherein: The average pore diameter of the pores is 5 nm to 50 nm.

11. The silicon-carbon composite material according to claim 9 or 10, wherein: The average thickness of the silicon-based material layer is 2nm-20nm.

12. The silicon-carbon composite material according to any one of claims 1 to 11, wherein: The particle size Dv50 of the silicon-carbon composite material is 3 μm to 30 μm.

13. The silicon-carbon composite material according to claim 12, wherein: The particle size Dv50 of the silicon-carbon composite material is 10 μm to 20 μm.

14. The silicon-carbon composite material according to any one of claims 1 to 13, wherein: The surface of the porous carbon matrix is ​​also coated with a coating layer; the coating layer includes a carbon coating layer.

15. The silicon-carbon composite material according to any one of claims 1 to 14, wherein: In the silicon-carbon composite material, the mass percentage of silicon element is 20% to 40%, and the mass percentage of carbon element is 60% to 80%.

16. The silicon-carbon composite material according to any one of claims 1 to 15, wherein: The silicon-carbon composite material includes one or two of the following features: (1) Tap density is 0.7g / cm 3 ~1.3g / cm 3 ; (2) Specific surface area is 0.8m 2 / g~1.5m 2 / g.

17. A method for preparing a silicon-carbon composite material, comprising the following steps: A silicon-based material layer is deposited in the pores of the porous carbon matrix, wherein the silicon-based material layer includes sub-nanometer silicon clusters and silicon carbide clusters, and the surface of the silicon carbide clusters is in contact with the surface of the sub-nanometer silicon clusters.

18. The method for preparing the silicon-carbon composite material according to claim 17, wherein: Depositing a silicon-based material layer in the pores of a porous carbon matrix includes: The porous carbon substrate is placed in a reaction container, and a mixed gas of a silicon source gas and a carbon source gas is introduced to perform vapor deposition.

19. The method for preparing the silicon-carbon composite material according to claim 18, wherein: The method of introducing a mixed gas of silicon source gas and carbon source gas for vapor deposition includes one or more of the following features: (1) In the mixed gas, the volume ratio of the silicon source gas to the carbon source gas is 10:(1-5); (2) The silicon source gas includes SiH4; (3) The carbon source gas includes C2H4; (4) The flow rate of the mixed gas is 0.05 L / min to 0.2 L / min; (5) The deposition temperature is 400°C to 600°C; (6) The deposition time is 30 minutes to 2 hours.

20. The method for preparing the silicon-carbon composite material according to any one of claims 17 to 19, wherein: After depositing the silicon-based material layer, the method further includes preparing a coating layer on the surface of the porous carbon matrix.

21. The method for preparing the silicon-carbon composite material according to any one of claims 17 to 20, wherein: The preparation method of the porous carbon matrix includes a template method, an acid-base activation method or a pyrolysis method.

22. The method for preparing the silicon-carbon composite material according to any one of claims 17 to 21, wherein: The preparation method of the porous carbon substrate comprises: mixing a template, a carbon source and a solvent to prepare a carbon solution; The carbon solution is subjected to a first heat treatment and then dried to prepare an expanded carbon precursor; subjecting the expanded carbon precursor to a second heat treatment to prepare a carbonized intermediate; The template in the carbonized intermediate is removed to prepare the porous carbon matrix.

23. The method for preparing the silicon-carbon composite material according to claim 22, wherein: The method for preparing the porous carbon substrate has one or more of the following characteristics: (1) The mass ratio of the template to the carbon source is (1-10):1; (2) The temperature of the first heat treatment is 70°C to 90°C and the time is 6h to 10h; (3) The drying temperature is 120°C to 140°C and the drying time is 1h to 4h; (4) The second heat treatment includes: heating to 400°C to 600°C at a heating rate of 3°C / min to 10°C / min, and maintaining for 2h to 6h.

24. 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, the negative electrode active material layer comprising one or more of the silicon-carbon composite material according to any one of claims 1 to 16 and the silicon-carbon composite material prepared by the preparation method according to any one of claims 17 to 23.

25. A secondary battery comprising the negative electrode sheet according to claim 24.

26. An electrical device comprising one or more of the negative electrode sheet according to claim 24 and the secondary battery according to claim 25.

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