Silicon-carbon composite material and preparation method therefor, secondary battery, and electric device

Abstract

A silicon-carbon composite material and a preparation method therefor, a secondary battery, and an electric device. The silicon-carbon composite material comprises a core and a coating coated on the surface of the core; the core comprises a carbon matrix and a silicon-based material located on the surface of the carbon matrix; the silicon-based material comprises a silicon cluster and a silicon carbide cluster; the silicon carbide cluster forms a network structure; and the silicon cluster is located in a gap of the network structure. The silicon-carbon composite material can eliminate the memory effect of silicon and improve the capacity retention rate.

Description

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

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 2023114452677, filed on November 2, 2023, entitled “Silicon-carbon composite material, preparation method thereof, 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 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 significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0006] Silicon-based materials have attracted attention due to their significantly higher capacity than carbon-based materials. This higher capacity translates to higher energy density, leading to the traditional use of a composite of silicon-based and carbon-based materials in negative electrodes. However, silicon is prone to memory effects during cycling, which in turn reduces the battery's capacity retention.

[0007] Summary of the Invention

[0008] The present application provides a silicon-carbon composite material capable of reducing the occurrence of silicon memory effect and improving battery capacity retention rate, a preparation method thereof, and a secondary battery and an electrical device using the silicon-carbon composite material.

[0009] In the first aspect of the present application, a silicon-carbon composite material is provided, comprising an inner core and a coating layer coated on the surface of the inner core; the inner core comprises a carbon matrix and a silicon-based material located on the surface of the carbon matrix, the silicon-based material comprises silicon clusters and silicon carbide clusters, the silicon carbide clusters form a network structure, and the silicon clusters are located in the gaps of the network structure.

[0010] The above-mentioned silicon-carbon composite material arranges the silicon-based material on the surface of the carbon matrix, and compositely adopts silicon and silicon carbide as the silicon-based material. With the help of the conductivity of the carbon matrix, the silicon carbide clusters can form a network structure, and the silicon clusters are located in the gaps of the network structure, which can reduce the memory effect of silicon and improve the capacity retention rate.

[0011] At the same time, the use of silicon and silicon carbide as silicon-based materials can also improve initial efficiency and energy density compared to silicon-oxygen materials. The presence of the coating can reduce the corrosion of the electrolyte on the inner core during cycling, improve the stability of the silicon carbide cluster network structure, and further optimize the capacity retention rate.

[0012] In some embodiments, the grain size of the silicon microcrystals in the silicon cluster is P, P≤5nm. The small grain size of the silicon microcrystals in the silicon cluster can further reduce the long-range migration of Si atoms to form crystalline Li 15 The possibility of Si4 phase can be reduced, thereby reducing the memory effect of silicon and improving the capacity retention rate. Furthermore, 0.2nm≤P<2nm.

[0013] In some embodiments, the carbon matrix includes at least one of graphene oxide, graphene, fluorinated graphene, carbon nanotubes, mesoporous carbon, or carbon nanofibers.

[0014] In some embodiments, the coating layer includes a carbon coating layer. By utilizing the good electrical conductivity of carbon, the electrical conductivity of the entire silicon-carbon composite material can be improved.

[0015] In some embodiments, the silicon-based material has a silicon-to-carbon atomic ratio of 10:(0.1-9). Reasonable control of the silicon-to-carbon atomic ratio in the silicon-based material is conducive to the formation of a silicon carbide cluster network structure and better confines the silicon clusters to the gaps in the network structure.

[0016] In some embodiments, the mass percentage of silicon is 5% to 80% and the mass percentage of carbon is 20% to 95% based on the mass of the silicon-carbon composite material. Reasonable control of the mass percentages of silicon and carbon in the silicon-carbon composite material not only allows the material to have a higher silicon content, thereby achieving a higher specific capacity, but also prevents excessive silicon from increasing the material's expansibility, making the overall structure of the material more stable during charge-discharge cycles and facilitating improved capacity retention.

[0017] In a second aspect of the present application, a method for preparing a silicon-carbon composite material is provided, comprising the following steps:

[0018] Depositing a silicon-based material on the surface of the carbon substrate to prepare an inner core; the silicon-based material includes silicon clusters and silicon carbide clusters, the silicon carbide clusters form a network structure, and the silicon clusters are located in the gaps of the network structure;

[0019] A coating layer is prepared on the surface of the inner core.

[0020] The above preparation method directly deposits silicon-based materials on the surface of the carbon substrate, and the corresponding network structure can be obtained through one-step deposition, and then the coating layer is prepared. The overall steps are simple and suitable for industrial promotion and application.

[0021] In some embodiments, the method for depositing the silicon-based material on the surface of the carbon substrate is pulse deposition, which can better regulate the formation of the silicon carbide network structure and control the size of silicon.

[0022] In some embodiments, the method of depositing a silicon-based material on a surface of a carbon substrate comprises the following steps:

[0023] preparing a carbon film from the carbon matrix material;

[0024] connecting electrodes at both ends of the carbon film;

[0025] A carbon film with electrodes connected at both ends is placed in a reaction container, a pulse current is applied to the electrodes, a mixed gas of silicon source gas and carbon source gas is introduced, and the silicon-based material is deposited on the surface of the carbon film.

[0026] The above steps utilize the conductivity of the carbon matrix, and after preparing it into a carbon film, it serves as a connecting unit between electrodes. Silicon-based materials can be deposited directly on its surface without introducing additional electrical connecting units, which also simplifies the process flow of silicon-based material deposition.

[0027] Furthermore, by rationally controlling parameters such as the pulse current period, the volume ratio of the silicon source gas to the carbon source gas, and the flow rate of the mixed gas during the deposition of the silicon-based material, the formation of the silicon carbide network structure can be better controlled and the size of silicon can be controlled.

[0028] In some embodiments, the method of depositing a silicon-based material on a surface of a carbon substrate has one or more of the following features:

[0029] (1) The cycle of the pulse current includes: a pulse time of 1ms to 1s and a rest time of 10ms to 10s;

[0030] (2) In the mixed gas, the molar ratio of silicon in the silicon source gas to carbon in the carbon source gas is 10:(0.1-9);

[0031] (3) The flow rate of the mixed gas is 0.01 L / min to 0.5 L / min;

[0032] (4) During the deposition process, the temperature of the carbon film is maintained at ≥450°C.

[0033] In some embodiments, the Dv50 of the inner core is 2 μm to 20 μm. Reasonable control of the particle size of the inner core can, on the one hand, reduce the diffusion distance of ions and provide closer contact between particles, which is beneficial for improving capacity retention. On the other hand, avoiding an excessively small Dv50 increases processing difficulty and facilitates industrial implementation.

[0034] In some embodiments, preparing a coating layer on the surface of the inner core comprises:

[0035] The inner core is mixed with the material of the cladding layer, and the obtained mixture is sintered to form the cladding layer.

[0036] In some embodiments, the mass percentage of the coating material is 1% to 20% based on the mass of the mixed material. This can effectively coat the inner core, reduce electrolyte erosion of the material during cycling, and further improve capacity retention.

[0037] 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 the silicon-carbon composite material described in the first aspect or the silicon-carbon composite material prepared by the preparation method described in the second aspect.

[0038] In some embodiments, the negative electrode active material layer further includes a carbon-based material.

[0039] In some embodiments, the negative electrode active material layer has one or both of the following characteristics:

[0040] (1) In the negative electrode active material layer, the mass percentage of the silicon-carbon composite material is 1% to 80%;

[0041] (2) The carbon-based material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon or mesophase carbon microbeads.

[0042] In a fourth aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet described in the third aspect.

[0043] In a fifth aspect of the present application, an electrical device is provided, comprising the negative electrode sheet described in the third aspect or the secondary battery described in the fourth aspect.

[0044] 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

[0045] 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:

[0046] FIG1 is a schematic structural diagram of a reaction device formed by connecting electrodes at both ends of a carbon film according to an embodiment of the present application;

[0047] FIG2 shows a pulse current cycle during the process of depositing a silicon-based material on the surface of a carbon film according to one embodiment of the present application;

[0048] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0049] FIG4 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG3 ;

[0050] FIG5 is a schematic diagram of a battery module according to an embodiment of the present application;

[0051] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0052] FIG7 is an exploded view of the battery pack shown in FIG6 according to an embodiment of the present application;

[0053] FIG8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

[0054] FIG9 is a TEM electron microscope image of a Si / SiC@graphene composite material prepared according to an embodiment of the present application;

[0055] FIG10 is a second TEM electron microscope image of the Si / SiC@graphene composite material prepared according to an embodiment of the present application;

[0056] FIG11 is a cycling curve of the Si / SiC@graphene composite material prepared in Example 1 of the present application and the commercial Si@C material in Comparative Example 1 between 3.18V and 4.2V;

[0057] 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

[0058] Below, some embodiments of the silicon-carbon composite material and its preparation method, 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.

[0059] 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.

[0060] 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.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0062] 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.

[0063] Those skilled in the art will appreciate 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 internal logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, for example, in some of the examples, they are performed 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.

[0064] 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.

[0065] 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.

[0066] Some examples of the present application provide a silicon-carbon composite material, comprising an inner core and a coating layer coated on the surface of the inner core; the inner core comprises a carbon matrix and a silicon-based material located on the surface of the carbon matrix, the silicon-based material comprises silicon clusters and silicon carbide clusters, the silicon carbide clusters form a network structure, and the silicon clusters are located in the gaps of the network structure.

[0067] The memory effect of silicon refers to the fact that when a battery cell containing a silicon negative electrode is charged to a high SOC (≥90%) state, if the discharge process cannot discharge all the electricity, then during the next charge and discharge process, this residual capacity will be stored in the negative electrode and cannot be released. As the number of charge and discharge cycles increases, the capacity that cannot be released accumulates rapidly, causing the available capacity of the battery cell to decay rapidly. Studies have found that the main reason for the memory effect of silicon is that silicon usually undergoes long-range migration during the charging process. At the same time, when the amount of lithium embedded is large (such as x≥3.75 in LixSi), silicon will gradually transform from a partially amorphous lithium-silicon alloy to a crystalline lithium-silicon alloy (Li) along with the long-range migration. 15 Si4), and due to the poor diffusion dynamics of crystalline lithium-silicon alloy, it needs to be discharged to a lower voltage (that is, the charge is completely discharged) before it can be transformed into an amorphous lithium-silicon alloy. In actual use, since the discharge process cannot completely discharge the charge, some crystalline lithium-silicon alloy will remain in the silicon phase, resulting in a large unusable capacity. As the number of charge and discharge cycles increases, the unusable capacity gradually accumulates, which leads to a rapid decay of the available capacity.

[0068] The above-mentioned silicon-carbon composite material arranges the silicon-based material on the surface of the carbon matrix, and compositely adopts silicon and silicon carbide as the silicon-based material. With the help of the conductivity of the carbon matrix, the silicon carbide clusters can form a network structure, and the silicon clusters are located in the gaps of the network structure. During charging, due to the existence of the silicon carbide cluster network structure, the long-range migration of silicon atoms can be limited. When the amount of lithium embedded is large, the amorphous lithium-silicon alloy is difficult to be transformed into a crystalline lithium-silicon alloy, so that during discharge, the residual amount of crystalline lithium-silicon alloy in the silicon bulk phase is greatly reduced, thereby reducing the memory effect of silicon and improving the capacity retention rate.

[0069] At the same time, using silicon and silicon carbide as silicon-based materials can also improve initial efficiency and energy density compared to silicon-oxygen materials. The presence of the coating can reduce the corrosion of the electrolyte on the inner core during the cycle, improve the stability of the silicon carbide cluster network structure, and thus improve the structural stability of the silicon-based material, further optimizing the capacity retention rate.

[0070] In some examples, the grain size of the silicon microcrystals in the silicon cluster is P, and P≤5 nanometers (nm). The grain size of the silicon microcrystals in the silicon cluster is smaller, which can further reduce the possibility of long-range migration of silicon atoms to form crystalline lithium-silicon alloys, thereby reducing the memory effect of silicon and improving the capacity retention rate. At the same time, the use of a smaller grain size can also reduce the volume expansion of the pole piece and the consumption rate of active lithium during the cycle, thereby improving the cycle life. Furthermore, 0.2nm≤P≤5nm. Further, 0.2nm≤P<3.6nm. Further, 0.2nm≤P<2nm. Without limitation, the grain size of the silicon microcrystals in the silicon cluster can be characterized by measuring the diameter of the range of the lattice fringes under a TEM electron microscope photograph. It can be understood that after the silicon-carbon composite material is applied to a secondary battery for charging and discharging, the silicon microcrystals in the silicon cluster will be converted into amorphous particles accordingly.

[0071] In some examples, the carbon matrix includes at least one of graphene oxide, graphene, graphene fluoride, carbon nanotubes, mesoporous carbon, or carbon nanofibers. It is understood that when the carbon matrix is ​​graphene oxide, it may be partially or completely reduced to graphene during processing. Furthermore, without limitation, the mesoporous carbon has a pore diameter of 2 nm to 20 nm.

[0072] In some examples, the coating layer includes a carbon coating layer. Utilizing the excellent electrical conductivity of carbon, the electrical conductivity of the entire silicon-carbon composite material can be improved. Furthermore, the carbon coating layer includes amorphous carbon.

[0073] In some examples, the atomic ratio of silicon atoms to carbon atoms in the silicon-based material is 10:(0.1-9). Reasonable control of the atomic ratio of silicon atoms to carbon atoms in the silicon-based material is conducive to the formation of a network structure of silicon carbide clusters and better confines the silicon clusters to the gaps in the network structure. Specifically, the atomic ratio of silicon atoms to carbon atoms includes but is not limited to: 10:0.1, 10:1, 10:2, 10:3, 10:4, 10:5, 10:6, 10:7, 10:8, 10:9 or a range between any two of the foregoing.

[0074] In some examples, the mass percentage of silicon is 5% to 80%, and the mass percentage of carbon is 20% to 95%, based on the mass of the silicon-carbon composite material. Reasonable control of the mass percentages of silicon and carbon in the silicon-carbon composite material can, on the one hand, allow the material to have a higher content of silicon, thereby obtaining a higher gram capacity, and on the other hand, avoid excessive silicon content that increases the expansibility of the material, making the overall structure of the material more stable during the charge and discharge cycle, which is conducive to improving the capacity retention rate. Furthermore, the mass percentage of silicon is 5% to 45%, and the mass percentage of carbon is 55% to 95%. Without limitation, the mass percentages of silicon and carbon can be characterized by observing the internal cross-section of the material through SEM, and by using EDS to semi-quantitatively characterize the mass ratio of Si and C.

[0075] Some other examples of the present application provide a method for preparing a silicon-carbon composite material, comprising the following steps:

[0076] Depositing a silicon-based material on the surface of the carbon substrate to prepare an inner core; the silicon-based material includes silicon clusters and silicon carbide clusters, the silicon carbide clusters form a network structure, and the silicon clusters are located in the gaps of the network structure;

[0077] A coating layer is prepared on the surface of the inner core.

[0078] The above preparation method directly deposits silicon-based materials on the surface of the carbon substrate, and the corresponding network structure can be obtained through one-step deposition, and then the coating layer is prepared. The overall steps are simple and suitable for industrial promotion and application.

[0079] 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.

[0080] In some examples, the method for depositing the silicon-based material on the surface of the carbon substrate is pulse deposition, which can better control the formation of the silicon carbide network structure and the size of the silicon.

[0081] In some examples, a method for depositing a silicon-based material on a surface of a carbon substrate includes the following steps:

[0082] preparing a carbon film from the carbon matrix material;

[0083] connecting electrodes at both ends of the carbon film;

[0084] A carbon film with electrodes connected at both ends is placed in a reaction container, a pulse current is applied to the electrodes, a mixed gas of silicon source gas and carbon source gas is introduced, and the silicon-based material is deposited on the surface of the carbon film.

[0085] The above steps utilize the conductivity of the carbon matrix, and after preparing it into a carbon film, it serves as a connecting unit between electrodes. Silicon-based materials can be deposited directly on its surface without introducing additional electrical connecting units, which also simplifies the process flow of silicon-based material deposition.

[0086] In some examples, forming the carbon film from the carbon matrix material includes:

[0087] preparing the carbon matrix material into a slurry;

[0088] The slurry is coated on a smooth substrate and dried. Without limitation, the drying temperature can be 80 degrees Celsius (° C.) to 130° C.

[0089] It can be understood that after connecting electrodes at both ends of the carbon film, the electrodes are electrically connected via the carbon film. As an example, a reaction device is formed as shown in Figure 1, wherein a carbon film 100 is formed on a substrate, and electrodes 200 are connected to both ends of the carbon film 100 to form the reaction device. Q1 represents a silicon source gas, and Q2 represents a carbon source gas. Both gases are deposited on the surface of the carbon film 100 to form the silicon-based material.

[0090] Furthermore, by rationally controlling parameters such as the pulse current period, the volume ratio of the silicon source gas to the carbon source gas, and the flow rate of the mixed gas during the deposition of the silicon-based material, the formation of the silicon carbide network structure can be better controlled and the size of silicon can be controlled.

[0091] In some examples, during the process of depositing the silicon-based material on the surface of the carbon film, the period of the pulse current is as shown in Figure 2, including: a pulse time of 1 millisecond (ms) to 1 second (s), and a standing time of 10ms to 10s. Under the period of this pulse current, the deposition of silicon and carbon elements can be regulated, and the deposited silicon microcrystals have a smaller grain size. Specifically, the pulse time includes but is not limited to: 10ms, 20ms, 50ms, 70ms, 100ms, 150ms, 200ms, 250ms, 300ms, 350ms, 400ms, 450ms, 500ms, 550ms, 600ms, 650ms, 700ms, 750ms, 800ms, 850ms, 900ms, 950ms, 1s, 2s, 3s, 4s, 5s, 6s, 7s, 8s, 9s, 10s or a range between any two of the foregoing. The standby time includes but is not limited to: 10ms, 50ms, 0.1ms, 0.3ms, 0.5s, 0.7s, 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, 5s, 5.5s, 6s, 6.5s, 7s, 7.5s, 8s, 8.5s, 9s, 9.5s, 10s or a range between any two of the foregoing.

[0092] In some examples, during the deposition of the silicon-based material on the surface of the carbon film, the molar ratio of silicon in the silicon source gas to carbon in the carbon source gas in the mixed gas is 10:(0.1-9). Specifically, the molar ratio of silicon in the silicon source gas to carbon in the carbon source gas includes, but is not limited to, 10:0.1, 10:0.5, 10:1, 10:2, 10:3, 10:4, 10:5, 10:6, 10:7, 10:8, 10:9, or a range between any two of the foregoing.

[0093] Without limitation, the silicon source gas includes one or more of monosilane, dichlorosilane and silicon tetrachloride.

[0094] Without limitation, the carbon source gas includes at least one of ethylene, propylene, butene, butadiene, acetylene or propyne.

[0095] In some examples, during the deposition of the silicon-based material on the surface of the carbon film, the flow rate of the mixed gas is 0.01 liter / minute (L / min) to 0.5 L / min. Specifically, the flow rate of the mixed gas is 0.01 L / min, 0.1 L / min, 0.2 L / min, 0.3 L / min, 0.4 L / min, 0.5 L / min, or any range therebetween.

[0096] In some examples, during the process of depositing the silicon-based material on the surface of the carbon film, the temperature of the carbon film is set to be ≥450° C. during the deposition process.

[0097] In some examples, the Dv50 of the inner core is 2 microns (μm) to 20μm. Reasonable control of the particle size of the inner core, on the one hand, a smaller particle size can reduce the diffusion distance of ions, and the contact between particles is closer, which is beneficial to improving the capacity retention rate. On the other hand, avoiding too small Dv50 increases the difficulty of processing and is more convenient for industrial implementation. Specifically, the Dv50 of the inner core includes but is not limited to: 2μm, 5μm, 8μm, 10μm, 12μm, 15μm, 17μm, 20μm or a range between any two of the foregoing. Further, the Dv50 of the inner core is 8μm to 20μm. Further, the Dv50 of the inner core is 8μm to 12μm. Without limitation, the Dv50 of the inner core can be measured by a laser particle size analyzer.

[0098] In some examples, after depositing the silicon-based material on the surface of the carbon film, the carbon film with the silicon-based material deposited thereon is further crushed and granulated to prepare the inner core. The crushing and granulation are performed to obtain the desired inner core size.

[0099] In some examples, the method of preparing the coating layer on the surface of the inner core includes:

[0100] The inner core is mixed with the material of the cladding layer, and the obtained mixture is sintered to form the cladding layer.

[0101] It is understood that the coating material needs to be well coated on the surface of the inner core during the mixing process. If the coating material is liquid, it can well coat the inner core during the mixing process and can be used directly; if the coating material is solid, it can be made into a slurry before mixing.

[0102] Without limitation, the material of the coating layer is a carbon source material, for example, one or more of glucose, polyvinyl alcohol, phenolic resin, polystyrene, polytetrafluoroethylene, polyacrylonitrile, polypropylene, polyacrylonitrile, coke, coal tar, petroleum asphalt, liquid asphalt, and emulsified asphalt.

[0103] In some examples, the mass percentage of the material of the coating layer is 1% to 20% based on the mass of the mixture. This can better coat the inner core, reduce the erosion of the electrolyte on the internal material during the cycle, and further improve the capacity retention rate. Specifically, the mass percentage of the coating layer includes but is not limited to: 1%, 8%, 10%, 12%, 15%, 17%, 20% or a range between any two of the foregoing. Furthermore, the mass percentage of the coating layer is 8% to 20%.

[0104] Without limitation, the sintering treatment conditions include: a temperature of 850° C. to 950° C., and a time of 1 hour to 5 hours.

[0105] 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 the silicon-carbon composite material as described above or the silicon-carbon composite material prepared by the preparation method as described above.

[0106] In some examples, the negative electrode active material layer further includes a carbon-based material.

[0107] In some examples, the mass percentage of the silicon-carbon composite material in the negative electrode active material layer is 1% to 80%. Specifically, the mass percentage of the silicon-carbon composite material includes, but is not limited to, 1%, 5%, 10%, 15%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range between any two of the foregoing.

[0108] In some examples, the carbon-based material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, or mesocarbon microbeads (MCMB).

[0109] Some other examples of the present application provide a secondary battery including the negative electrode sheet as described above.

[0110] Some other examples of the present application provide an electrical device including the negative electrode sheet as described above or the secondary battery as described above.

[0111] Without limitation, the secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0112] 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.

[0113] Positive electrode

[0114] 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.

[0115] 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.

[0116] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0117] 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.

[0118] 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.

[0119] 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 Co0.25 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.

[0120] 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.

[0121] 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.

[0122] 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 is 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 a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40% by weight (wt%) to 80% by weight. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascals·seconds (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 / cm3 )~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0123] Negative electrode

[0124] The negative electrode plate is as described above.

[0125] 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.

[0126] 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.

[0127] 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, mesophase carbon microbeads, 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.

[0128] 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).

[0129] 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.

[0130] 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)).

[0131] 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 .

[0132] electrolytes

[0133] 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.

[0134] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0135] 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 difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0136] 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.

[0137] 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.

[0138] 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.

[0139] Isolation film

[0140] 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.

[0141] 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.

[0142] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may optionally be 12 μm to 20 μm.

[0143] 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.

[0144] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0145] 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.

[0146] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0147] 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.

[0148] 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, FIG3 shows a battery cell 5 with a square structure as an example.

[0149] In some embodiments, referring to FIG4 , 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.

[0150] The secondary battery may be a battery module 4 or a battery pack 1 .

[0151] 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.

[0152] FIG5 shows an example battery module 4. Referring to FIG5 , in 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.

[0153] 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.

[0154] 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.

[0155] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , 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 positioned 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.

[0156] 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.

[0157] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0158] FIG8 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.

[0159] 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.

[0160] 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.

[0161] Example 1

[0162] 1) Preparation of positive electrode sheet

[0163] The positive electrode active material ternary material lithium nickel cobalt manganese oxide (the molar ratio of nickel, cobalt and manganese is 95:2:3), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 97:2:1 and added to the solvent NMP to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at 85°C and then cold pressed, and then die-cut and slit to make the lithium-ion battery positive electrode sheet.

[0164] 2) Preparation of negative electrode sheet

[0165] 2.1 Preparation of negative electrode active materials

[0166] a) Graphene oxide (carbon matrix) was dispersed in water to prepare a slurry, which was then coated on a smooth non-conductive substrate (mica) and dried at 110°C to form a film with an area density of 3 mg / cm 2 , two graphite electrodes are set at both ends of the substrate, and the electrodes are connected by graphene oxide;

[0167] b) placing the entire apparatus of step a) in a reaction chamber, introducing monosilane (silicon source) and ethylene (carbon source) gas at a gas flow rate of 0.05 L / min, with a volume ratio of monosilane to ethylene gas of 10:1.5 (i.e., a molar ratio of monosilane to ethylene gas of 10:1.5, and a molar ratio of silicon in monosilane to carbon in ethylene of 10:3);

[0168] c) applying a pulse current to the electrode with a pulse period of 50 ms and a rest time of 0.5 s, so that the temperature on the graphene oxide reaches 480° C. After 20 pulses, a Si / SiC@graphene composite material is obtained; the Si / SiC@graphene composite material is tested by TEM electron microscopy. As shown in Figures 9 and 10, the grain size of the silicon microcrystals is distributed in the range of 0.2 nm to 2 nm, and the silicon microcrystal clusters are distributed in the network gaps formed by the silicon carbide microcrystal clusters;

[0169] d) crushing and granulating the Si / SiC@graphene composite material prepared in step c) to produce particles (inner core) with a Dv50 of 10 μm;

[0170] e) mixing the particles prepared in step d) with liquid asphalt (material for the coating layer) at a mass percentage of 10% by mass of the liquid asphalt, based on the total mass of the particles and the liquid asphalt, so that the particle surfaces are fully covered, and sintering in an air atmosphere at 900° C. for 2 h to obtain an amorphous carbon-coated Si / SiC@graphene composite material powder (hereinafter referred to as silicon-carbon composite material);

[0171] Artificial graphite is mixed with silicon-carbon composite material (the mass ratio of artificial graphite to silicon-carbon composite material is 3:1), and then added with conductive agent acetylene black, thickener sodium hydroxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) in a mass ratio of 96:2:1:1 into solvent water and mixed evenly to form a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried at 85°C and then cold pressed to form a lithium-ion battery negative electrode sheet.

[0172] 3) Isolation film

[0173] A polyethylene microporous film is used as the substrate of the porous isolation membrane. Inorganic alumina powder, polyvinylpyrrolidone, and acetone solvent are evenly mixed in a weight ratio of 3:1.5:5.5 to form a slurry, which is coated on one side of the substrate and dried. The thickness of the substrate is 7 μm and the thickness of the coating is 3 μm to obtain an isolation membrane.

[0174] 4) Preparation of electrolyte

[0175] Lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1:2:1) to obtain a lithium ion battery electrolyte, wherein the concentration of lithium hexafluorophosphate is 1 mol / L.

[0176] 5) Battery Preparation

[0177] The positive electrode sheet, negative electrode sheet and separator are wound to obtain a bare cell, which is then packaged, injected, formed, vented and other processes to produce a lithium-ion battery.

[0178] The secondary batteries of Examples 2 to 20 were prepared in a similar manner to the secondary battery of Example 1, with the main differences being shown in Tables 1 and 2.

[0179] 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 prepared silicon-carbon composite material is replaced by a commercial Si@C material, the carbon matrix of which is porous carbon obtained by processing hard carbon, which includes silicon microcrystals with a grain size of 6nm to 8nm (measured by electron microscopy), the Dv50 of the overall Si@C material is 12μm, the mass percentage of silicon element is 45%, and the mass percentage of carbon element is 55%.

[0180] The preparation method of the secondary battery of Comparative Example 2 is similar to that of the secondary battery of Example 1, the main difference being that ethylene gas is not introduced in step b, i.e., silicon carbide clusters are not generated. At the same time, the amount of monosilane introduced is adjusted so that the mass percentage of silicon and carbon in the silicon-carbon composite material remains the same as in Example 1.

[0181] Table 1

[0182] Table 2

[0183] Note: In Examples 15 to 18, the coating amount of graphene oxide was changed while the mass percentage of the material of the coating layer was changed, while the mass percentage of the silicon and carbon elements in the entire material remained unchanged; in Examples 19 to 20, the coating amount of graphene oxide was changed to change the mass percentage of the silicon and carbon elements in the entire material.

[0184] Performance testing:

[0185] (1) Cycle test

[0186] The test temperature is 25℃, the charge rate is 0.33C, the discharge rate is 0.33C, and the cycle voltage range is 3.18~4.2V. The specific process is as follows: starting voltage is 3.18V, 0.33C constant current and constant voltage charging to 4.2V, standing for 10 minutes, then 0.33C constant current discharge to 3.18V, standing for 10 minutes, and so on.

[0187] Cycle capacity retention rate = discharge capacity at the nth cycle / discharge capacity at the first cycle.

[0188] (2) Memory effect

[0189] The significance of the memory effect can be determined by the cyclic decay trend over the first 50 cycles. Taking Example 1 (Si-A) and Comparative Example 1 (Si-B) as examples, the cycling curves for Example 1 (Si-A) and Comparative Example 1 (Si-B) are shown in Figure 11 when cycling between 3.18V and 4.2V. The cyclic decay trend for Comparative Example 1 (Si-B) decreases rapidly over the first 50 cycles, indicating a significant memory effect for Comparative Example 1. The overall cyclic decay trend for Example 1 is gentle, with no significant drop in the first 50 cycles, indicating an insignificant memory effect for Example 1 (Si-A).

[0190] The test results are shown in Table 3 below.

[0191] Table 3

[0192] From the comparison between the embodiment and the comparative example, it can be seen that the present application can effectively improve the memory effect of silicon and increase the capacity retention rate by introducing a silicon carbide cluster network structure so that the silicon clusters are located in the gaps of the network structure.

[0193] 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.

[0194] 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-carbon composite material, comprising an inner core and a coating layer coated on the surface of the inner core; the inner core comprises a carbon matrix and a silicon-based material located on the surface of the carbon matrix, the silicon-based material comprises silicon clusters and silicon carbide clusters, the silicon carbide clusters form a network structure, and the silicon clusters are located in the gaps of the network structure.

2. The silicon-carbon composite material according to claim 1, wherein: The grain size of silicon microcrystals in the silicon cluster is P, and P≤5nm.

3. The silicon-carbon composite material according to claim 2, wherein: 0.2nm≤P<2nm.

4. The silicon-carbon composite material according to any one of claims 1 to 3, wherein: The carbon matrix includes at least one of graphene oxide, graphene, fluorinated graphene, carbon nanotubes, mesoporous carbon or carbon nanofibers.

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

6. The silicon-carbon composite material according to any one of claims 1 to 5, wherein: In the silicon-based material, the atomic ratio of silicon atoms to carbon atoms is 10:(0.1-9).

7. The silicon-carbon composite material according to any one of claims 1 to 6, wherein: Calculated by the mass of the silicon-carbon composite material, the mass percentage of silicon element is 5-80%, and the mass percentage of carbon element is 20-95%.

8. A method for preparing a silicon-carbon composite material, comprising the following steps: Depositing a silicon-based material on the surface of the carbon matrix to prepare an inner core; the silicon-based material includes silicon clusters and silicon carbide clusters, the silicon carbide clusters form a network structure, and the silicon clusters are located in the gaps of the network structure; A coating layer is prepared on the surface of the inner core.

9. The method for preparing the silicon-carbon composite material according to claim 8, wherein: The method for depositing the silicon-based material on the surface of the carbon substrate is a pulse deposition method.

10. The method for preparing the silicon-carbon composite material according to claim 9, wherein: The method for depositing a silicon-based material on the surface of a carbon substrate comprises the following steps: Making the carbon matrix material into a carbon film; Connecting electrodes at both ends of the carbon film; A carbon film with electrodes connected at both ends is placed in a reaction container, a pulse current is applied to the electrodes, a mixed gas of silicon source gas and carbon source gas is introduced, and the silicon-based material is deposited on the surface of the carbon film.

11. The method for preparing the silicon-carbon composite material according to claim 10, wherein: The method of depositing a silicon-based material on the surface of a carbon substrate has one or more of the following characteristics: (1) The cycle of the pulse current includes: the pulse time is 1ms to 1s, and the rest time is 10ms to 10s; (2) In the mixed gas, the molar ratio of silicon element in the silicon source gas to carbon element in the carbon source gas is 10:(0.1-9); (3) The flow rate of the mixed gas is 0.01L / min to 0.5L / min; (4) During the deposition process, the temperature of the carbon film is maintained at ≥450°C.

12. The method for preparing the silicon-carbon composite material according to any one of claims 8 to 11, wherein: The Dv50 of the inner core is 2 μm to 20 μm.

13. The method for preparing the silicon-carbon composite material according to any one of claims 8 to 12, wherein: Preparing a coating layer on the surface of the inner core comprises: The inner core is mixed with the material of the cladding layer, and the obtained mixed material is sintered to form the cladding layer.

14. The method for preparing the silicon-carbon composite material according to claim 13, wherein: Based on the mass of the mixed material, the mass percentage of the material of the coating layer is 1% to 20%.

15. 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 the silicon-carbon composite material according to any one of claims 1 to 7 or the silicon-carbon composite material prepared by the preparation method according to any one of claims 8 to 14.

16. The negative electrode sheet according to claim 15, wherein: The negative electrode active material layer further includes a carbon-based material.

17. The negative electrode sheet according to claim 16, wherein: The negative electrode active material layer has one or both of the following characteristics: (1) In the negative electrode active material layer, the mass percentage of the silicon-carbon composite material is 1% to 80%; (2) The carbon-based material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon or mesophase carbon microbeads.

18. A secondary battery comprising the negative electrode sheet according to any one of claims 15 to 17.

19. An electrical device comprising the negative electrode sheet according to any one of claims 15 to 17 or the secondary battery according to claim 18.

Images