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

Abstract

A silicon-carbon material, a preparation method therefor, a secondary battery, and an electric device. The silicon-carbon material comprises silicon-carbon composite particles; the silicon-carbon composite particles comprise a porous carbon material, nano-silicon grains and a silicon carbide material layer; the porous carbon material is provided with through pores, the nano-silicon grains are located in the through pores, and the silicon carbide material layer is partially located on through pore walls; the grain size of the nano-silicon grains is not smaller than the average pore diameter of the porous carbon material. The silicon-carbon material is used as an active material of a negative electrode sheet, thereby improving the cycle performance of batteries.

Description

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

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410302266.5, filed on March 15, 2024, entitled “Silicon-carbon materials, preparation methods thereof, secondary batteries and electrical devices,” and the entire contents of that application are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of batteries, and in particular to a silicon-carbon material and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0004] Silicon has the highest specific capacity of all known anode materials, reaching 4200 mAh / g. However, the silicon-lithium alloy formed during the charging process of pure silicon in lithium-ion batteries causes the anode material to expand dramatically, with an expansion rate of up to 300%. This causes the anode material to collapse and pulverize, impairing the battery's cycling performance. Silicon-carbon composites can effectively reduce the volume effect of the anode material. Currently, the cycling performance of existing silicon-carbon anode materials has improved somewhat, but further optimization is still needed to meet the needs of power batteries.

[0005] Summary of the Invention

[0006] In view of the above problems, the present application provides a silicon-carbon material and a preparation method thereof, a secondary battery and an electrical device, which are beneficial to improving the cyclability of the battery.

[0007] In a first aspect, the present application provides a silicon-carbon material, including: silicon-carbon composite particles, the silicon-carbon composite particles including:

[0008] Porous carbon material: has through pores;

[0009] Nano-silicon grains: located in the through-holes; the grain size of the nano-silicon grains is not less than the average pore size of the porous carbon material;

[0010] The silicon carbide material layer is at least partially located on the wall of the through hole.

[0011] The silicon-carbon material provided by the present application includes silicon-carbon composite particles, which include porous carbon material. The porous carbon material has through holes, where the through holes include macropores, mesopores and micropores for depositing silicon material. The silicon material is deposited in the through holes of the porous carbon material. On the one hand, the through holes can limit the expansion of the silicon material. On the other hand, because the through holes are connected to the closed holes, they have a certain degree of physical isolation from the electrolyte, which can also reduce the probability of side reactions caused by direct contact between the silicon material and the electrolyte. The present application chooses to form nano-silicon grains with a certain suitable particle size in the through holes. The nano-silicon grains of the suitable particle size are stacked to form nano-silicon particles. The nano-silicon particles are further stacked along the inner wall of the through hole to form a layered or sheet-like film. A silicon carbide material layer is generated where the layered or sheet-like film is in direct contact with the inner wall of the through hole. This arrangement can not only reduce the probability of it reacting with the electrolyte, but also control the expansion rate of the silicon material. This is because the expansion of the silicon material is not only restricted by the through holes, but also by the silicon carbide material layer. Therefore, the silicon-carbon material provided in this application reduces the probability of side reactions between the silicon material and the electrolyte while controlling the expansion degree of the silicon material during the process of lithium ion insertion and extraction, thereby improving the battery's cyclability to a certain extent.

[0012] In some embodiments of the present application, the grain size of the nano-silicon grains is d1, and the average pore size of the porous carbon material is d2, satisfying: d1 / d2=1-15.

[0013] In some embodiments of the present application, the grain size of the nano-silicon grains is d1, and the average pore size of the porous carbon material is d2, satisfying: d1 / d2=2-10.

[0014] In some embodiments of the present application, the grain size of the nano-silicon grains is d1, d1 ≥ 5 nm;

[0015] and / or;

[0016] The average pore diameter of the porous carbon material is d2, and d2 is 1.0 nm to 5.0 nm.

[0017] In some embodiments of the present application, the grain size of the nano-silicon grains is d1, and d1 is 5 nm to 20 nm;

[0018] and / or;

[0019] The average pore diameter of the porous carbon material is d2, and d2 is 1.5 nm to 5.0 nm.

[0020] In some embodiments of the present application, the silicon-carbon composite particles include closed pores, and the pore volume of the closed pores is smaller than the pore volume of the through pores.

[0021] In some embodiments of the present application, the silicon-carbon composite particles include closed pores, the pore volume of the closed pores is V1, and the pore volume of the through pores is V2, satisfying: V2 / V1=5-24.

[0022] In some embodiments of the present application, the silicon-carbon composite particles include closed pores, the pore volume of the closed pores is V1, and the pore volume of the through pores is V2, satisfying: V2 / V1=7-16.

[0023] In some embodiments of the present application, the pore volume of the closed pore is V1, and V1 is 0.04 cm 3 / g~0.16cm 3 / g;

[0024] and / or;

[0025] The pore volume of the through hole is V2, and V2 is 0.3 cm 3 / g~1.5cm 3 / g.

[0026] In some embodiments of the present application, the through pores include micropores, mesopores and macropores, and based on the total volume of the through pores, the volume ratio between the micropores, mesopores and macropores is (40% to 95%): (5% to 50%): (0 to 15%).

[0027] In some embodiments of the present application, the silicon carbide material layer is located between the through hole and the nano-silicon grains, wherein one side of the silicon carbide material layer is connected to the inner wall of the through hole, and the other side is connected to the nano-silicon grains.

[0028] In some embodiments of the present application, the thickness of the silicon carbide material layer is less than 0.7 nm.

[0029] In some embodiments of the present application, the silicon-carbon material further includes a carbon coating layer disposed along the outer surface of the porous carbon material. This carbon coating layer can reduce the probability of the nano-silicon grains being oxidized by contact with the outside air and can also reduce the probability of the nano-silicon grains reacting with the electrolyte.

[0030] In some embodiments of the present application, the porous carbon material comprises porous carbon particles, and the porous carbon particles meet the following conditions:

[0031] (1.1) The volume distribution particle size of the porous carbon particles satisfies the following requirements: Dv50 is 3.0 μm to 6.5 μm; Dv90 is 13.5 μm to 18.5 μm; and Dv10 is 0.9 μm to 2.5 μm.

[0032] (1.2) The specific surface area of ​​porous carbon particles is 900 m 2 / g~1550m 2 / g;

[0033] (1.3) The tap density of porous carbon particles is 0.22 g / cm 3 ~0.48g / cm 3 ;

[0034] (1.4) The compacted density of 5 tons of porous carbon particles is 0.45 g / cm 3 ~0.80g / cm 3 .

[0035] In some embodiments of the present application, the porous carbon material comprises porous carbon particles, and the porous carbon particles satisfy at least one of the following conditions:

[0036] (2.1) The volume distribution particle size of the porous carbon particles satisfies the following requirements: Dv50 is 3.5 μm to 6.0 μm; Dv90 is 14.0 μm to 18.0 μm; and Dv10 is 1.0 μm to 2.0 μm.

[0037] (2.2) The specific surface area of ​​porous carbon particles is 1000m 2 / g~1500m 2 / g;

[0038] (2.3) The tap density of porous carbon particles is 0.25 g / cm 3 ~0.45g / cm 3 ;

[0039] (2.4) The compacted density of 5 tons of porous carbon particles is 0.50 g / cm 3 ~0.75g / cm 3 .

[0040] In some embodiments of the present application, based on the total mass of the silicon-carbon material, the mass percentage content of silicon element in the silicon-carbon material is w 硅 , satisfying: w 硅 It is 38.0% to 48.0%.

[0041] In some embodiments of the present application, the silicon-carbon composite particles meet the following conditions:

[0042] (3.1) The volume distribution particle size of the silicon-carbon composite particles satisfies the following requirements: (Dv90-Dv10) / Dv50 is 1.2 to 2.8;

[0043] (3.2) The specific surface area of ​​the silicon-carbon composite particles is 3.0 m 2 / g~12.0m 2 / g;

[0044] (3.3) The tap density of silicon-carbon composite particles is 0.5 g / cm 3 ~1.0g / cm 3;

[0045] (3.4) The compacted density of 5 tons of silicon-carbon composite particles is 0.80 g / cm 3 ~1.1g / cm 3 .

[0046] In some embodiments of the present application, the silicon-carbon composite particles satisfy at least one of the following:

[0047] (4.1) The volume distribution particle size of the silicon-carbon composite particles satisfies the following requirements: Dv50 is 3.5 μm to 9.0 μm; Dv90 is 14.0 μm to 21.0 μm; and Dv10 is 0.9 μm to 3.0 μm.

[0048] (4.2) The specific surface area of ​​the silicon-carbon composite particles is 5.0 m 2 / g~10.0m 2 / g;

[0049] (4.3) The tap density of the silicon-carbon composite particles is 0.6 g / cm 3 ~0.8g / cm 3 ;

[0050] (4.4) The compacted density of 5 tons of silicon-carbon composite particles is 0.90 g / cm 3 ~1.05g / cm 3 .

[0051] In some embodiments of the present application, the properties of the silicon-carbon composite particles meet the following requirements:

[0052] The powder resistivity of silicon-carbon composite particles at 4 MPa is 1.30 Ω·cm to 3.80 Ω·cm;

[0053] and / or;

[0054] The lithium removal capacity of the silicon-carbon composite particles is 1300mAh / g to 1500mAh / g, and the first coulombic efficiency is 77% to 81%;

[0055] and / or;

[0056] In the dQ / dV curve of the silicon-carbon composite particles, I1 is the peak intensity near 0.3V~0.35V; I2 is the peak intensity near 0.43V~0.50V; it satisfies: I1 / I2=1.4~1.8; the dQ / dV curve of the silicon-carbon composite particles includes silicon-carbon composite particles as the positive electrode active material, metal lithium sheets as the counter electrode, assembled to form a CR2430 button battery, at 25°C, the charge and discharge voltage is 0.005V~2.0V, and the charge and discharge capacity and working electrode potential are obtained by differential processing.

[0057] The second aspect of the present application is to provide a method for preparing the silicon-carbon negative electrode material according to the first aspect, comprising:

[0058] providing a porous carbon substrate;

[0059] introducing a silicon source into the porous carbon substrate to generate a porous carbon material comprising nano-silicon grains and a silicon carbide material layer;

[0060] A carbon source is introduced into the porous carbon material containing nano-silicon grains and a silicon carbide material layer to generate a silicon-carbon material containing a carbon coating layer.

[0061] In some embodiments of the present application, the reaction conditions for generating a porous carbon material comprising nano-silicon grains and a silicon carbide material layer are as follows:

[0062] (5.1) The reaction temperature is 500°C to 700°C, and the silicon source is introduced for 3 hours to 42 hours;

[0063] (5.2) The silicon source comprises a silicon source gas and a diluent gas, wherein the volume fraction of the silicon source gas is 15% to 95%; the silicon source gas comprises either or both of monosilane and disilane;

[0064] (5.3) The ventilation volume of the silicon source is 0.2L / min to 1.5L / min.

[0065] In some embodiments of the present application, the porous carbon substrate comprises carbon, oxygen, and nitrogen, and the mass ratio of carbon to oxygen and nitrogen is (94% to 97%): (2% to 4%): (1% to 2%);

[0066] and / or; the ash content of the porous carbon substrate is ≤0.5%.

[0067] The third aspect of the present application is to provide a secondary battery, which includes a negative electrode plate, and the negative electrode plate includes the silicon-carbon material described in the first aspect or the silicon-carbon material prepared by the preparation method described in the second aspect.

[0068] A fourth aspect of the present application is to provide an electrical device, which includes the secondary battery described in the third aspect.

[0069] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0071] FIG1 is a schematic diagram of a battery structure according to some embodiments of the present application;

[0072] FIG2 is a schematic diagram of the exploded structure of batteries according to some embodiments of the present application;

[0073] FIG3 is a schematic diagram of a vehicle structure according to some embodiments of the present application;

[0074] FIG4 is a schematic structural diagram of a battery pack according to some embodiments of the present application;

[0075] FIG5 is an electron microscope image of silicon-carbon materials prepared in some embodiments of the present application;

[0076] FIG6 is a schematic structural diagram of silicon-carbon materials prepared in some embodiments of the present application;

[0077] FIG7 is an X-ray photoelectron spectroscopy analysis graph of silicon-carbon materials prepared in some embodiments of the present application.

[0078] FIG8 is a further magnified electron microscope image of the silicon-carbon material obtained in some embodiments of the present application.

[0079] FIG9 is a transmission electron microscope image of a carbon coating layer of a silicon-carbon material obtained in some embodiments of the present application.

[0080] FIG10 is an X-ray diffraction pattern of silicon-carbon materials obtained in some embodiments of the present application;

[0081] FIG. 11 is a dQ / dV graph of discharge curves of silicon-carbon materials obtained in some embodiments of the present application.

[0082] The figure numbers in the specific implementation manner are as follows: 10000, vehicle; 1000, battery; 2000, controller; 3000, motor; 100, battery cell; 200, casing; 210, first part; 220, second part; 10, secondary battery; 101, casing; 102, electrode assembly; 103, cover plate; 1, silicon-carbon composite particles; 1a, porous carbon material; 1b, nano-silicon grains; 1c, remaining closed pores; 1d, silicon carbide material layer. DETAILED DESCRIPTION

[0083] Below, the silicon-carbon material and its preparation method, the secondary battery and the electric device of the present application are described in detail with appropriate reference to the accompanying 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.

[0084] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive and can be combined arbitrarily, i.e., 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 contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "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 disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0085] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0086] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0087] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0088] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0089] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0090] Unless otherwise specified, in this application, the terms "first", "second", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0091] Unless otherwise specified, in this application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0092] Unless otherwise specified, the orientations or positional relationships indicated by technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", and "circumferential" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limiting the embodiments of the present application.

[0093] The specific capacity of silicon is the highest among all known negative electrode materials, reaching 4200mAh / g. However, the silicon-lithium alloy formed by pure silicon during the charging process in lithium-ion batteries will cause the negative electrode material to undergo huge volume expansion, with an expansion rate of up to 300%, causing the negative electrode material to collapse and pulverize, destroying the safety and cycle performance of the battery. Silicon-carbon composites can effectively reduce the volume effect of negative electrode materials. Specifically, silicon-carbon composites involve mixing nano-silicon with carbon materials. By reducing the particle size of silicon-based materials to the nanometer level, more voids can be obtained to buffer the stress and deformation generated by silicon during the process of lithium ion insertion and extraction. However, as the particle size of silicon-based materials decreases, they are more likely to react with the electrolyte that slowly penetrates into the surface of the silicon-based material, thereby accelerating the cycle attenuation.

[0094] To solve the above problems, the prior art discloses methods including developing new electrolytes or forming physical isolation on the surface of silicon-based materials to reduce the probability of side reactions. However, these improvements are not ideal.

[0095] If the particle size of the silicon-based material can be increased to a certain extent, but not to an unlimited extent, and the probability of side reactions between the silicon-based material and the electrolyte can be reduced while controlling the degree of expansion of the silicon-based material during the deintercalation and extraction of lithium ions, the battery's cyclability can be improved to a certain extent.

[0096] Based on the above considerations, in order to solve the technical problem of accelerated cycle attenuation in batteries due to side reactions between silicon-based materials and electrolytes, a silicon-carbon material and its preparation method, a secondary battery and an electrical device were obtained according to the above design concept and relevant experimental research.

[0097] First, the present application discloses a silicon-carbon material, which includes silicon-carbon composite particles, and the silicon-carbon composite particles include porous carbon material, nano-silicon grains, a silicon carbide material layer and a carbon coating layer. The porous carbon material has through holes, the nano-silicon grains are located in the through holes, and the silicon carbide material layer is located between the through holes and the nano-silicon grains; the grain size of the nano-silicon grains is not less than the average pore size of the porous carbon material; and the carbon coating layer is arranged along the outer surface of the porous carbon material.

[0098] The silicon-carbon material provided by the present application includes silicon-carbon composite particles, which include porous carbon material. The porous carbon material has through-holes, where the through-holes include macropores, mesopores and micropores for depositing silicon material. The silicon material is deposited in the through-holes of the porous carbon material. On the one hand, the through-holes can limit the expansion of the silicon material. On the other hand, due to the physical isolation of the through-holes to a certain extent from the electrolyte, the probability of side reactions caused by direct contact between the silicon material and the electrolyte can be reduced. The present application chooses to form nano-silicon grains with a certain suitable particle size in the through-holes. The nano-silicon grains of the suitable particle size are stacked to form nano-silicon particles. The nano-silicon particles are further stacked along the inner wall of the through-hole to form a layered or sheet-like film. A silicon carbide material layer is generated in the area where the layered or sheet-like film is in direct contact with the inner wall of the through-hole. This arrangement can not only reduce the probability of its reaction with the electrolyte, but also control the expansion rate of the silicon material. This is because the expansion of the silicon material is not only restricted by the through-holes, but also by the silicon carbide material layer. In addition, a carbon coating is formed on the outside of the porous carbon material. This carbon coating can reduce the probability of the nano-silicon grains coming into contact with the outside air and thus being oxidized, and can also reduce the probability of the nano-silicon grains reacting with the electrolyte. Therefore, the silicon-carbon material provided by this application reduces the probability of side reactions between the silicon material and the electrolyte while controlling the expansion degree of the silicon material during the process of lithium ion insertion and extraction, thereby improving the cyclability of the battery to a certain extent.

[0099] The silicon-carbon material provided in this application is used to make negative electrode sheets and is used in batteries, thereby improving the performance of the battery, such as improving the cyclability at a certain capacity, thereby enhancing the user experience. The battery may include an outer packaging. The outer packaging can be used to encapsulate the above-mentioned electrode assembly and electrolyte. The outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic. As plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0100] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 10 with a square structure as an example.

[0101] According to some embodiments of the present application, referring to Figure 2, the outer packaging may include a shell 101 and a cover plate 103. Among them, the shell 101 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 101 has an opening connected to the receiving cavity, and the cover plate 103 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 102 through a winding process or a lamination process. The electrode assembly 102 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 102. The number of electrode assemblies 102 contained in the secondary battery 10 can be one or more, and those skilled in the art can select according to specific actual needs.

[0102] The electrode assembly provided in the present application is applied to batteries to improve battery performance. The battery can be used as a power source for an electrical device or as an energy storage unit for an electrical device. The electrical device is applied to the power field, such as mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but not limited to the above-mentioned fields.

[0103] For the convenience of explanation, some embodiments of the present application are described by taking a vehicle as an example of an electrical device.

[0104] Please refer to Figure 3, which is a structural schematic diagram of the vehicle 10000 provided in some embodiments of the present application. The vehicle 10000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 1000 is provided inside the vehicle 10000, and the battery 1000 can be provided at the bottom, head or tail of the vehicle 10000. The battery 1000 can be used to power the vehicle 10000. For example, the battery 1000 can serve as an operating power source for the vehicle 10000. The vehicle 10000 may also include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 1000 to power the motor 3000, for example, for starting, navigating and driving the vehicle 10000.

[0105] In some embodiments of the present application, the battery 1000 can serve not only as an operating power source for the vehicle 10000, but also as a driving power source for the vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 10000.

[0106] Please refer to Figure 4, which is an exploded view of a battery 1000 provided in some embodiments of the present application. Battery 1000 includes a housing 200 and a battery cell 100. Conventional battery cells include primary or secondary batteries, but this application specifically protects secondary batteries. Battery cell 100 is housed within housing 200. Housing 200 is used to accommodate battery cell 100 and can adopt a variety of structures.

[0107] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220. The first portion 210 and the second portion 220 overlap each other, and together define a storage space for accommodating the secondary battery 100. The second portion 220 may be a hollow structure with one end open, and the first portion 210 may be a plate-like structure. The first portion 210 overlaps the open side of the second portion 220, so that the first portion 210 and the second portion 220 together define the storage space. The first portion 210 and the second portion 220 may also be hollow structures with one end open, with the open side of the first portion 210 overlapping the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0108] In the battery 1000, there may be multiple battery cells 100, and the multiple battery cells 100 may be connected in series, in parallel, or in a hybrid connection. A hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 100. The multiple battery cells 100 may be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery 100 structure may be housed within the housing 200. Of course, the battery 1000 may also be a battery module formed by first connecting multiple battery cells 100 in series, in parallel, or in a hybrid connection, and then the multiple battery modules 1000 are further connected in series, in parallel, or in a hybrid connection to form an entire battery 1000 structure, and then housed within the housing 200. The battery 1000 may also include other structures, for example, the battery 1000 may also include a busbar component for electrically connecting the multiple battery cells 100.

[0109] Silicon-carbon materials

[0110] In some embodiments, the present application discloses a silicon-carbon material, which includes silicon-carbon composite particles, which include porous carbon material, nano-silicon grains, a silicon carbide material layer and a carbon coating layer. The porous carbon material has through holes, the nano-silicon grains are located in the through holes, and the silicon carbide material layer is located on the through hole walls; the grain size of the nano-silicon grains is not less than the average pore size of the porous carbon material.

[0111] The silicon-carbon composite particles in this application include particles mainly composed of silicon and carbon elements. The composite method here includes any conventional composite form in the art.

[0112] The nano-silicon grains in the present application include silicon grains with a particle size of nanometer level, and the formation methods of the nano-silicon grains include but are not limited to chemical vapor deposition, physical vapor deposition or atomic layer deposition.

[0113] The through holes in this application include through holes that are connected to the outside world, such as macropores, mesopores and micropores used to deposit silicon materials. Nano-silicon grains are distributed along the inner wall of the through holes and stacked to form silicon materials with layered or sheet-like films.

[0114] The grain size of the nano-silicon grains in the present application is not less than the average pore size of the porous carbon material. The average pore size of the porous carbon material in the present application includes measurements made by any conventional method in the art. For example, the distribution of each pore is tested using a conventional test instrument in the art and the number of each pore is obtained by statistics, and then the average pore size is calculated by a mathematical function. The pore volume and specific surface area of ​​the porous carbon material can also be obtained by using adsorption and desorption isotherms. According to the model of the relevant pores, the pore volume is divided by the specific surface area and multiplied by the model coefficient to obtain the average pore size; for example, the test instrument used is ASAP2460-physical adsorption analyzer, and the porous carbon material sample after drying and degassing is placed in liquid nitrogen, and different test pressures are adjusted to measure the adsorption amount of nitrogen respectively, and the adsorption and desorption isotherms are drawn. Then, the pore volume and specific surface area of ​​the porous carbon material are obtained according to the adsorption and desorption isotherms, and then the average pore size of the porous carbon material is calculated. The nano-silicon grains in the present application include silicon grains with a particle size of nanometer level, and the crystal form of the nano-level silicon grains includes the conventional crystal structure in the art. The grain size of the nano-silicon grains includes the particle size distribution measured by a testing instrument such as an X-ray diffractometer and then obtained statistically, or the grain size is characterized by a transmission electron microscope and then obtained statistically.

[0115] The grain size of the nano-silicon grains of the present application is not less than the average pore size of the porous carbon material. In some embodiments of the present application, the grain size of the nano-silicon grains is d1, and the average pore size of the porous carbon material is d2, satisfying d1≥d2. This is because the nano-silicon grains are distributed and stacked along the through-holes of the porous carbon material. Therefore, the average pore size of the porous carbon material does not affect the stacking process of the nano-silicon grains, but can limit the result of the stacking of the nano-silicon grains, that is, limit the expansion of the silicon material. The present application selects nano-silicon grains with a certain appropriate particle size to be distributed in the through-holes of the porous carbon material. Under the premise of controlling the expansion degree of the silicon material during the process of lithium ion insertion and extraction, the probability of side reactions between the silicon material and the electrolyte is reduced, and to a certain extent, the cyclability of the battery is also improved.

[0116] The formation of the silicon carbide material layer of the present application is affected by the preparation conditions. For example, during the growth of silicon grains, the silicon grains close to the inner wall of the through hole are easy to contact the wall and react to form a silicon carbide material layer. The hardness of the silicon carbide material layer is greater than that of the silicon material, and it can limit the degree of outward expansion when the silicon material expands. Therefore, the silicon-carbon material provided by the present application reduces the probability of side reactions between the silicon material and the electrolyte while controlling the expansion degree of the silicon material during the deintercalation and extraction of lithium ions, thereby improving the cyclability of the battery to a certain extent.

[0117] In some embodiments of the present application, the grain size d1 of the nano-silicon grains and the average pore size d2 of the porous carbon material satisfy the following relationship: d1 / d2=1-15.

[0118] In some embodiments of the present application, the grain size d1 of the nano-silicon grains and the average pore size d2 of the porous carbon material satisfy the following relationship: d1 / d2=2-10.

[0119] The grain size d1 of the nano-silicon grains provided in this application cannot be indefinitely larger than the average pore size d2 of the porous carbon material. Otherwise, it will not only hinder the formation of the nano-silicon grains, but may also affect the performance of the battery. For example, lithium ions need to complete the deintercalation process from the relatively large silicon material, thereby affecting the battery's rate capability. This application chooses to control d1 / d2 = 1 to 15. On the one hand, this facilitates the efficient formation of nano-silicon grains within the through-pores of the porous carbon material, and on the other hand, it does not affect the overall performance of the battery, such as cyclability and rate capability. In these embodiments, the present application provides that the relationship between the grain size d1 of the nano-silicon grains and the average pore size d2 of the porous carbon material satisfies, including but not limited to, d1 / d2=1, d1 / d2=2, d1 / d2=3, d1 / d2=4, d1 / d2=5, d1 / d2=6, d1 / d2=7, d1 / d2=8, d1 / d2=9, d1 / d2=10, d1 / d2=11, d1 / d2=12, d1 / d2=13, d1 / d2=14, d1 / d2=15.

[0120] In some embodiments of the present application, the grain size d1 of the nano-silicon grains is ≥5 nm.

[0121] In some embodiments of the present application, the grain size d1 of the nano-silicon grains is 5 nm to 20 nm.

[0122] In some embodiments of the present application, the grain size d1 of the nano-silicon grains is 5 nm to 15 nm.

[0123] The nano-silicon grains herein include silicon grains having a size of nanometers, and the crystal form of the nano-silicon grains includes a conventional crystal structure in the art. The grain size of the nano-silicon grains includes the grain size calculated using the Scherrer formula using an X-ray diffraction pattern known in the art, and the silicon grain size is a statistical size.

[0124] The present application selects a grain size of nano-silicon grains ≥ 5nm, because the grain size of the silicon grains cannot be too small, otherwise it will easily increase the probability of side reactions. Silicon grains with this size are convenient and efficient to form in the through-holes, while also reducing the probability of them reacting with the electrolyte. At the same time, the grain size of the nano-silicon grains cannot be increased indefinitely. On the one hand, it is limited by the preparation process. On the other hand, nano-silicon grains with larger grain sizes not only increase the degree and probability of expansion of the silicon material during the process of lithium ion insertion and extraction, but are also not conducive to the diffusion of lithium ions during the process of lithium ion insertion and extraction. Therefore, the present application selects a grain size d1 of the nano-silicon grains of 5nm to 20nm. The present application discloses in these embodiments that the grain size d1 of the nano-silicon grains includes but is not limited to any one of 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm or any one of the values ​​in the above range.

[0125] In some embodiments of the present application, the average pore diameter d2 of the porous carbon material is 1.0 nm to 5.0 nm.

[0126] In some embodiments of the present application, the average pore diameter d2 of the porous carbon material is 1.5 nm to 5.0 nm.

[0127] The present application selects a porous carbon material with an average pore size of 1.0 nm to 5.0 nm, which facilitates the efficient formation of the silicon material in the through-holes and also facilitates the subsequent restriction of the expansion of the silicon material.

[0128] The present application discloses in these embodiments that the average pore diameter of the porous carbon material is any one of 1.0 nm, 1.5 nm, 2.0 nm, 3.0 nm, 4.0 nm, 4.5 nm, and 5.0 nm, or any one of the values ​​within the above ranges.

[0129] In some embodiments of the present application, the silicon-carbon composite particles include closed pores, and the pore volume of the closed pores is smaller than the pore volume of the through pores.

[0130] The closed pores of the present application include pores in the silicon-carbon composite particles that are not connected to the outside world. The closed pores include the closed pores possessed by the porous carbon material itself, and also include a certain number of closed pores formed in the through holes after the nano-silicon grains are formed in the through holes. These closed pores can further provide a slow-release space for the expansion of the silicon material on the basis of the above-mentioned through holes and the silicon carbide material layer to limit the expansion of the silicon material, thereby alleviating the expansion of the silicon-carbon material.

[0131] In some embodiments of the present application, the pore volume of the closed pores is V1, and the pore volume of the through pores is V2, satisfying V1<V2.

[0132] The pore volume of this application is also called pore volume, wherein the pore volume V1 of the closed pores can be calculated using formula (I) and combined with relevant test results to obtain: V1 = 1 / ρ 真 -1 / (w 硅 ×ρ 硅 +w 碳 ×ρ 碳 ); Formula (I).

[0133] In formula (I), ρ 真 is the test true density of silicon carbon material, w 硅 is the mass percentage of silicon in silicon-carbon material, w 碳 is the mass percentage of carbon in silicon-carbon material, ρ 硅 is the theoretical true density of silicon, ρ 碳 is the theoretical true density of carbon. 硅 It includes the total mass of silicon-carbon material, the mass percentage of silicon element, and w 碳 Contains the mass percentage of carbon element based on the total mass of silicon-carbon material. 硅 is the theoretical true density of silicon, and its specific value is 2.34g / cm 3 , ρ 碳 is the theoretical true density of carbon, and its specific value is 2.26g / cm 3 ρ 真is the test true density of the silicon-carbon material, which can be obtained by testing with reference to GB / T24586-2009. The pore volume of the through-pores of the porous carbon material of the present application can also be the pore volume of the porous carbon material, that is, the pore volume of the porous carbon material, which can be measured using instruments and methods well known in the art, for example, it can be tested with reference to GB / T21650.2-2008. The testing instrument can be the TRISTAR II 3020 specific surface area and porosity analyzer of Micromeritics, USA. The through-pores of the present application are mainly used to deposit silicon materials, while the closed pores are used to provide a slow-release space when the silicon material expands, so that the closed pores occupy a certain pore volume to reduce the amount of nano-silicon grains formed inside the porous carbon material, but not to the extent of affecting the amount of nano-silicon grains used as negative electrode active materials. Therefore, the pore volume V1 of the closed pores is selected to be smaller than the pore volume V2 of the through-pores in the present application.

[0134] In some embodiments of the present application, the pore volume V1 of the closed pores and the pore volume V2 of the through pores satisfy: V2 / V1=5-24.

[0135] This application explores obtaining nano-silicon particles with suitable size and formation amount by selecting V2 / V1=5-24, and improving the battery's cyclability by reducing the reaction between the nano-silicon particles and the electrolyte without affecting the battery capacity.

[0136] In some embodiments of the present application, the pore volume V1 of the closed pores and the pore volume V2 of the through pores satisfy: V2 / V1=7-16.

[0137] The present application further improves the cyclability of the battery by selecting V2 / V1=7-16.

[0138] In some embodiments, the present application also specifically defines any one of V2 / V1=5, V2 / V1=6, V2 / V1=7, V2 / V1=8, V2 / V1=9, V2 / V1=10, V2 / V1=11, V2 / V1=12, V2 / V1=13, V2 / V1=14, V2 / V1=15, V2 / V1=16, V2 / V1=17, V2 / V1=18, V2 / V1=19, V2 / V1=20, V2 / V1=21, V2 / V1=22, V2 / V1=23, and V2 / V1=24, or any one of the values ​​satisfying the above range.

[0139] In some examples, the present application provides specific values ​​of the closed pore volume, V1 is 0.04 cm 3 / g~0.16cm 3 / g.

[0140] In some examples, the present application further provides specific values ​​of the closed pore volume, V1 is 0.05 cm3 / g~0.15cm 3 / g.

[0141] This application selects the closed pore volume V1 as 0.04cm 3 / g~0.16cm 3 / g, which can occupy a certain pore volume, thereby limiting the amount of silicon material formed inside the porous carbon material, and can also buffer part of the expansion deterioration of the silicon material caused by the expansion of the silicon material during the process of lithium insertion and extraction.

[0142] In these examples, the closed pore volume V1 includes but is not limited to 0.04 cm 3 / g, 0.05cm 3 / g, 0.06cm 3 / g, 0.07cm 3 / g, 0.08cm 3 / g, 0.09cm 3 / g, 0.1cm 3 / g, 0.11cm 3 / g, 0.12cm 3 / g, 0.13cm 3 / g, 0.14cm 3 / g, 0.15cm 3 / g, 0.16cm 3 / g or any of the values ​​satisfying the above ranges.

[0143] In some embodiments of the present application, the pore volume V2 of the through hole is 0.3 cm 3 / g~1.5cm 3 / g.

[0144] The pore volume of the through hole in this application affects the compressive strength of the silicon-carbon material, and also affects the amount of silicon material formed and the size of silicon grains. Therefore, the pore volume V2 of the through hole is selected as 0.3 cm in this application. 3 / g~1.5cm 3 / g.

[0145] In some embodiments of the present application, the pore volume V2 of the through hole is further 0.6 cm 3 / g~1.2cm 3 / g.

[0146] In these embodiments, the pore volume V2 of the through-hole selected by the present application includes but is not limited to 0.3 cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g or any of the values ​​satisfying the above ranges.

[0147] In some embodiments of the present application, the through pores include micropores, mesopores and macropores. Based on the total volume of the through pores, the volume ratio between the micropores, mesopores and macropores is (40% to 95%): (5% to 50%): (0 to 15%), preferably (45% to 95%): (5% to 45%): (0 to 10%).

[0148] The micropores, mesopores and macropores in this application include the conventional meanings in this field, such as the pore size of micropores is less than 2nm, mesopores are also called mesopores, and their pore size is 2nm to 50nm, and the pore size of macropores is greater than 50nm. This application includes the use of conventional testing instruments in this field to test the distribution of each pore, such as the use of ASAP2460-physical adsorption analyzer as the testing instrument, placing the porous carbon material sample (porous carbon substrate) after drying and degassing in liquid nitrogen, adjusting different test pressures, measuring the adsorption amount of nitrogen respectively, and drawing adsorption and desorption isotherms. The shape of the pore is determined according to the shape of the hysteresis loop, the pore distribution is calculated according to different pore models, the BJH model is used to fit the pore size distribution curves of the mesopores and macropores, and the DFT model is used to fit the pore size distribution curve of the micropores.

[0149] In this application, since the pore size affects the particle size and formation amount of the silicon material formed, the volume ratio of micropores, mesopores and macropores is selected as (40% to 95%): (5% to 50%): (0 to 15%). In these embodiments, the volume percentage of macropores includes but is not limited to any one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15% or any one of the above range values. In some embodiments, the present application also discloses that no macropores are included. The volume percentage of micropores includes but is not limited to any one of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or any one of the above range values. The volume percentage of mesopores includes but is not limited to any one of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any one of the values ​​satisfying the above range.

[0150] In some embodiments of the present application, the silicon-carbon material further includes a silicon carbide layer, which is formed on at least a portion of the inner wall of the through-hole. One side of the silicon carbide layer is connected to the inner wall of the through-hole, and the other side is connected to the nano-silicon grains. In these embodiments, the thickness of the silicon carbide layer is less than 0.7 nm, and more preferably less than 0.4 nm.

[0151] The formation of the silicon carbide material layer of the present application is affected by the preparation conditions. For example, during the growth of silicon grains, the silicon grains near the inner wall of the through hole are prone to contact with the wall and react to form a silicon carbide material layer. The hardness of the silicon carbide material layer is greater than that of the silicon material, which can limit the degree of outward expansion when the silicon material expands. The thickness of the silicon carbide material layer is not easy to be too thick. This is because the thickness of the silicon carbide material layer affects the conductivity of the silicon-carbon material. The thickness of the silicon carbide material layer in the present application is mainly obtained with the help of the relevant X-ray related maps.

[0152] The present application discloses in these embodiments that a silicon carbide material layer is formed on the interface of the inner wall of the through hole where the nano-silicon grains are in contact with the porous carbon material. The silicon carbide material layer is located between the through hole and the nano-silicon grains. One side of the silicon carbide material layer is connected to the inner wall of the through hole of the porous carbon material, and the other side is connected to the nano-silicon to form a silicon carbide interface layer. The silicon carbide interface layer is arranged adjacent to the nano-silicon grains to limit the degree of outward expansion of the nano-silicon grains during lithium insertion and extraction.

[0153] The present application discloses in these embodiments that the silicon-carbon material further includes a carbon coating layer, and the carbon coating layer is disposed along the outer surface of the porous carbon material.

[0154] In addition, the carbon coating layer in the present application includes a carbon material layer arranged along the outer surface of the porous carbon material to form an outer shell layer that wraps the porous carbon material. On the one hand, the outer shell layer can reduce the probability of nano-silicon contacting with the outside air and thus being oxidized, and on the other hand, it can reduce the probability of nano-silicon grains contacting and reacting with the electrolyte.

[0155] In some embodiments of the present application, the carbon coating layer is amorphous carbon, such as soft carbon or hard carbon obtained by cracking during the preparation process. In these embodiments, the present application discloses that the thickness of the carbon coating layer is 5nm to 50nm, preferably 10nm to 30nm. The carbon coating layer of suitable thickness will not affect the insertion of lithium ions and the capacity of the silicon-carbon material, but can also effectively protect the internal silicon particles to reduce the probability of side reactions. The thickness of the carbon coating layer in the present application can also be obtained by means of the relevant X-ray correlation spectrum.

[0156] In some embodiments of the present application, the silicon-carbon material contains silicon element, and the mass percentage content of silicon element is w based on the total mass of the silicon-carbon material. 硅 , satisfying: w 硅 It is 38.0% to 48.0%.

[0157] In some embodiments of the present application, w 硅 It is 40.0% to 45.0%.

[0158] In some embodiments of the present application, the silicon-carbon material contains carbon element, and the mass percentage content of the carbon element is w based on the total mass of the silicon-carbon material. 碳 , satisfying: w 碳 It is 50.0% to 55.0%.

[0159] In this application, the amount of silicon material formed in the through-hole affects the probability of its reaction with the electrolyte. Generally speaking, the more silicon material is formed, the greater its expansion during the lithium insertion and extraction cycle, and the greater the probability of its reaction with the electrolyte. The content of silicon material also affects the capacity of the battery. Limited by the pore volume of the through-hole and the pore volume of the closed pore, this application chooses to control w 硅 In these embodiments, w 硅 Including but not limited to any one of 38.0%, 40.0%, 42.0%, 43.0%, 44.0%, 45.0%, 48.0% or any one of the above range values. The silicon-carbon material in this application mainly contains silicon and carbon. In addition, it also contains other elements that are not necessary for the porous carbon material. The silicon content and the carbon content can be measured with the help of relevant standards. For example, the silicon content can refer to GB / T 20975.5-2020, and the carbon content can refer to GB / T 20123-2006 / ISO 15350:2000.

[0160] In some embodiments of the present application, the porous carbon material comprises porous carbon material particles, and the particle size of the porous carbon material particles meets the following requirements: Dv50 is 3.0 μm to 6.5 μm; Dv90 is 13.5 μm to 18.5 μm; and Dv10 is 0.9 μm to 2.5 μm.

[0161] In some embodiments, the present application discloses that the particle size of the porous carbon material particles meets the following requirements: Dv50 is 3.5 μm to 6.0 μm; Dv90 is 14.0 μm to 18.0 μm; and Dv10 is 1.0 μm to 2.0 μm.

[0162] In this application, Dv90 includes 90% of the volume of particles with a diameter smaller than it, Dv10 includes 10% of the volume of particles with a diameter smaller than it, and Dv50 includes 50% of the volume of particles with a diameter larger than it, and 50% of the volume of particles smaller than it. It is also called the median diameter and is usually used to represent the average particle size of the particles. Whether it is Dv90, Dv10 or Dv50, conventional measurement methods in the art can be used, such as using a particle size analyzer to measure the particle size distribution and then obtain it statistically. In these embodiments, this application chooses to refer to the laser diffraction particle size analysis method for determination, specifically referring to the standard GB / T19077-2016 to obtain a particle size distribution diagram, and then obtains it by calculation.

[0163] The present application controls the particle size of the porous carbon material particles to meet the following requirements: Dv50 is 3.0μm to 6.5μm; Dv90 is 13.5μm to 18.5μm; and Dv10 is 0.9μm to 2.5μm. This allows the efficient formation of nano-silicon grains within the through-pores of the porous carbon material. In these embodiments, the present application discloses that Dv50 is any one of 3.0μm, 3.3μm, 3.5μm, 3.8μm, 4.0μm, 4.2μm, 4.5μm, 4.8μm, 5.0μm, 5.2μm, 5.5μm, 5.8μm, 6.0μm, and 6.5μm, or any value within this range. Dv90 includes but is not limited to any one of 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, 18.0 μm, 18.5 μm, or any one of the above ranges. Dv10 includes but is not limited to any one of 0.9 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, or any one of the above ranges.

[0164] The present application discloses in some embodiments that the specific surface area of ​​the porous carbon material particles is 900 m 2 / g~1550m 2 / g.

[0165] In some embodiments, the present application discloses that the specific surface area of ​​the porous carbon material particles is 1000 m 2 / g~1500m 2 / g.

[0166] The specific surface area in this application includes any conventional concept in the art, which can be obtained by testing using instruments or methods known in the art, such as using a gas adsorption method to test the specific surface area, specifically referring to the standard test of GB / T19587-2017.

[0167] In these examples, the specific surface area of ​​the porous carbon material particles is controlled to be 900 m 2 / g~1550m 2 / g, so as to facilitate the efficient formation of nano-silicon particles in the through-pores of the porous carbon material. The present application also discloses in these embodiments that the specific surface area of ​​the porous carbon material particles includes but is not limited to 900m 2 / g、990m 2 / g、1000m 2 / g、1050m 2 / g、1100m 2 / g、1150m 2 / g、1200m 2 / g、1250m 2 / g、1300m 2 / g、1350m 2 / g、1400m 2 / g、1450m 2 / g、1500m 2 / g、1550m 2 / g or any of the values ​​satisfying the above ranges.

[0168] The present application discloses in some embodiments that the tap density of the porous carbon material particles is 0.22 g / cm 3 ~0.48g / cm 3 .

[0169] The present application discloses in some embodiments that the tap density of the porous carbon material particles is 0.25 g / cm 3 ~0.45g / cm 3 .

[0170] The tap density in this application includes any conventional concept in the art, which can be measured using instruments or methods known in the art, such as those measured in accordance with standard GB / T5162-2006. In these examples, the tap density of the porous carbon material particles is controlled to be 0.22 g / cm 3 ~0.48g / cm 3 Under the premise of ensuring that the porous carbon material has the above-mentioned particle size and specific surface area, nano-silicon grains are effectively formed.

[0171] The present application discloses in these embodiments that the tap density of the porous carbon material particles includes but is not limited to 0.22 g / cm 3 , 0.25g / cm 3 , 0.30g / cm 3 , 0.35g / cm 3 , 0.40g / cm 3, 0.45g / cm 3 , 0.48g / cm 3 Any one of or any one of the above range values.

[0172] The present application discloses in some embodiments that the compacted density of 5 tons of porous carbon material particles is 0.45 g / cm 3 ~0.80g / cm 3 .

[0173] In some embodiments, the present application discloses that the compacted density of 5 tons of porous carbon material particles is 0.50 g / cm 3 ~0.75g / cm 3 .

[0174] The compaction density in this application includes any conventional concept in the field, which can be obtained by testing using instruments or methods known in the field, such as limiting the cold pressing pressure to 5 tons and referring to the calculation method of GB / T 24533-2009. For example, it is measured using an electronic pressure tester (such as UTM7305). Specifically, a specific amount M of the powder sample to be tested is placed on a special pressing die (with a bottom area of ​​S0) and different pressures are set. Each pressure is maintained for 30 seconds and then released. After 10 seconds, the thickness H0 of the powder pressed under the pressure is read on the device. The compaction density under the pressure is obtained by calculation, and the compaction density of the negative plate material under the pressure is equal to M / (H0×S0).

[0175] The present invention selects to control the compaction density of the porous carbon material particles to be 0.50 g / cm when the cold pressing pressure is 5 tons. 3 ~0.75g / cm 3 , so as to effectively form nano-silicon grains while ensuring that the porous carbon material has the above-mentioned particle size, specific surface area and tap density.

[0176] The present application discloses in these examples that the compacted density of the porous carbon material particles at 5 tons includes but is not limited to 0.45 g / cm 3 , 0.50g / cm 3 , 0.55g / cm 3 、0.60g / cm 3 , 0.65g / cm 3 , 0.70g / cm 3 , 0.75g / cm 3 、0.80g / cm 3 Any one of or any one of the above range values.

[0177] In some embodiments of the present application, the particle size of the silicon-carbon composite particles satisfies the following relationship: (Dv90-Dv10) / Dv50 is 1.2-2.8.

[0178] In some embodiments of the present application, the particle size of the silicon-carbon composite particles satisfies the following relationship: (Dv90-Dv10) / Dv50 is 1.3-2.5.

[0179] In this application, Dv90 includes 90% of the volume of particles with a diameter smaller than it, Dv10 includes 10% of the volume of particles with a diameter smaller than it, and Dv50 includes 50% of the volume of particles with a diameter larger than it, and 50% of the volume of particles smaller than it. It is also called the median diameter and is usually used to represent the average particle size of the particles. Whether it is Dv90, Dv10 or Dv50, conventional measurement methods in the art can be used, such as using a particle size analyzer to measure the particle size distribution and then obtain it statistically. In these embodiments, this application chooses to refer to the laser diffraction particle size analysis method for determination, specifically referring to the standard GB / T19077-2016 to obtain a particle size distribution diagram, and then obtains it by calculation.

[0180] The particle size of the silicon-carbon composite particles selected in this application satisfies the following conditions: (Dv90-Dv10) / Dv50 is 1.2 to 2.8, so that the silicon-carbon composite particles of different sizes are properly matched to improve the volume energy density of the battery while minimizing the expansion of the silicon-carbon material during the lithium insertion and extraction process.

[0181] In these embodiments, the present application provides (Dv90-Dv10) / Dv50 including but not limited to 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8 or any one of the values ​​satisfying the range.

[0182] Some embodiments of the present application set specific numerical limits on the particle sizes of the silicon-carbon composite particles, such as Dv50 of 3.5 μm to 9.0 μm, Dv90 of 14.0 μm to 21.0 μm, and Dv10 of 0.9 μm to 3.0 μm.

[0183] In some embodiments of the present application, Dv50 is given as 4.0 μm to 6.5 μm; Dv90 is given as 15.0 μm to 20.0 μm; and Dv10 is given as 1.0 μm to 2.5 μm.

[0184] In this application, since the size of silicon grains affects the lithium ion diffusion path, this application controls the silicon-carbon composite particles to have a suitable particle size under the premise that the average particle size of the above-mentioned silicon grains is ≥5nm to balance the overall performance of the silicon-carbon material. In these embodiments, this application discloses that the Dv50 of the silicon-carbon composite particles is any one of 3.5μm, 3.8μm, 4.0μm, 4.2μm, 4.5μm, 5.0μm, 5.5μm, 5.8μm, 6.0μm, 6.2μm, 6.5μm, 6.7μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm or any one of the above ranges. In these embodiments, the present application further discloses that the Dv90 of the silicon-carbon composite particles is any one of 14.0 μm, 14.5 μm, 15.0 μm, 15.2 μm, 15.5 μm, 15.8 μm, 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, 18.0 μm, 18.5 μm, 19.0 μm, 19.5 μm, 20.0 μm, 20.5 μm, and 21 μm, or any one of the above ranges. In these embodiments, the present application further discloses that the Dv10 is any one of 0.9 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, and 3.0 μm, or any one of the above ranges.

[0185] In some embodiments of the present application, the specific surface area of ​​the silicon-carbon composite particles is 3.0 m 2 / g~12.0m 2 / g.

[0186] In some embodiments of the present application, the specific surface area of ​​the silicon-carbon composite particles is 5.0 m 2 / g~10.0m 2 / g.

[0187] The specific surface area in this application includes any conventional concept in the art, which can be obtained by testing using instruments or methods known in the art, such as using a gas adsorption method to test the specific surface area, specifically referring to the standard test of GB / T19587-2017.

[0188] The specific surface area of ​​the silicon-carbon composite particles is selected to be 3.0 m 2 / g~12.0m 2 / g, so that the silicon-carbon material has suitable lithium insertion and extraction sites to improve the capacity and cyclability of the battery.

[0189] In some embodiments of the present application, the tap density of the silicon-carbon composite particles is 0.5 g / cm 3 ~1.0g / cm 3 .

[0190] In some embodiments of the present application, the tap density of the silicon-carbon composite particles is 0.6 g / cm 3 ~0.8g / cm 3 .

[0191] The tap density in this application includes any conventional concept in the art, which can be obtained by testing using instruments or methods known in the art, such as by testing with reference to standard GB / T5162-2006.

[0192] The tap density of the silicon-carbon composite particles selected in this application is 0.5 g / cm 3 ~1.0g / cm 3 , while ensuring that the silicon-carbon composite particles have the above-mentioned particle size and specific surface area, the volume energy density of the battery can be effectively improved.

[0193] The present application discloses in these embodiments that the tap density of the silicon-carbon composite particles includes but is not limited to 0.5 g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 Any one of or any one of the above range values.

[0194] In some embodiments of the present application, the compacted density of 5 tons of silicon-carbon composite particles is 0.80 g / cm 3 ~1.1g / cm 3 .

[0195] In some embodiments of the present application, the compacted density of 5 tons of silicon-carbon composite particles is 0.90 g / cm 3 ~1.05g / cm 3 .

[0196] The compaction density in this application includes any conventional concept in the field, which can be obtained by testing using instruments or methods known in the field, such as limiting the cold pressing pressure to 5 tons and referring to the calculation method of GB / T 24533-2009. For example, it is measured using an electronic pressure tester (such as UTM7305). Specifically, a specific amount M of the powder sample to be tested is placed on a special pressing die (with a bottom area of ​​S0) and different pressures are set. Each pressure is maintained for 30 seconds and then released. After 10 seconds, the thickness H0 of the powder pressed under the pressure is read on the device. The compaction density under the pressure is obtained by calculation, and the compaction density of the negative plate material under the pressure is equal to M / (H0×S0).

[0197] The compaction density of 5 tons of silicon-carbon composite particles selected in this application is 0.80 g / cm 3 ~1.1g / cm 3 To effectively improve the capacity of the battery and enhance its practicality.

[0198] The present application discloses in these examples that the compacted density of the silicon-carbon composite particles at 5 tons is 0.80 g / cm 3 , 0.90g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 Any one of or any one of the above range values.

[0199] In some embodiments of the present application, the powder resistivity of the silicon-carbon composite particles at 4 MPa is 1.30 Ω·cm to 3.80 Ω·cm.

[0200] The powder resistivity of the silicon-carbon composite particles in this application is different from the resistivity of the electrode. It is used to characterize the conductivity of the silicon-carbon material itself. The powder resistivity in this application includes any conventional concept in the field, such as placing an appropriate amount of silicon-carbon material in the feeding cup of a resistivity tester, applying pressure, manually collecting data, recording the powder resistivity test results at different pressure points, and then taking the average value. The test pressure is 4 MPa.

[0201] The powder resistivity of the silicon-carbon composite particles of the present application at 4 MPa is 1.30 Ω·cm to 3.80 Ω·cm. This indicates that the amount of silicon crystals formed in the silicon material particles of the present application is appropriate and effective. This is because, among the silicon-carbon materials, the porous carbon material has good conductivity, while the silicon material has weak conductivity. The powder resistivity of the carbon composite particles selected in the present application at 4 MPa is 1.30 Ω·cm to 3.80 Ω·cm, which is beneficial for improving the capacity and cyclability of the battery.

[0202] In some embodiments of the present application, the lithium-free capacity of the silicon-carbon composite particles is 1300mAh / g to 1500mAh / g, and the first coulombic efficiency is 77% to 81%. In these embodiments, the silicon-carbon composite particles are used as the positive electrode active material, the metal lithium sheet is used as the counter electrode, and a CR2430 button battery is assembled. At 25°C, the charge and discharge voltage is 0.005 to 2.0V, and the measured lithium-free capacity is 1300mAh / g to 1500mAh / g, and the first coulombic efficiency is 77% to 81%. The lithium-free capacity obtained in the test of this application is 1300mAh / g to 1500mAh / g, which matches the silicon content in the silicon-carbon material and the positional relationship of the silicon material.

[0203] In some embodiments of the present application, in the dQ / dV curve of the silicon-carbon composite particles, I1 is the peak intensity near 0.3V~0.35V; I2 is the peak intensity near 0.43V~0.50V; and satisfies: I1 / I2=1.4~1.8; the dQ / dV curve of the silicon-carbon composite particles includes silicon-carbon composite particles as the positive electrode active material, a metal lithium sheet as the counter electrode, and a CR2430 button battery assembled. At 25°C, the charge and discharge voltage is 0.005V~2.0V, and the charge and discharge capacity and the working electrode potential are obtained by differential processing.

[0204] The differential capacity / voltage curve of the charge and discharge curve of the silicon-carbon material provided in this application under certain conditions gives peaks with certain intensities at a certain voltage. The ratio between the peaks is used to indicate that the amount of silicon material particles formed in the through-holes is appropriate, and the appropriate formation amount is conducive to improving the cyclability of the battery.

[0205] In summary, the present application provides a silicon-carbon material, which comprises silicon-carbon composite particles with a certain particle size, specific surface area, tap density and compacted density, the silicon-carbon composite particles comprise a porous carbon material with a certain pore size, the porous carbon material comprises a certain number of through holes with a certain pore volume, the silicon-carbon composite particles further comprise a certain number of closed pores with a certain pore volume, nano-silicon grains are distributed along the inner wall of the through hole of the porous carbon material and form a suitable particle size, the nano-silicon grains with a suitable particle size are further stacked along the inner wall of the through hole to form a layered or sheet-like film, and the layered or sheet-like film forms a silicon carbide material layer in the area in direct contact with the inner wall of the through hole. This arrangement can not only reduce the probability of its reaction with the electrolyte, but also control the expansion rate of the silicon material, because the expansion of the silicon material is not only restricted by the through hole, but also by the silicon carbide material layer. In addition, a carbon coating is formed on the outside of the porous carbon material. This carbon coating can reduce the probability of the nano-silicon grains coming into contact with the outside air and thus being oxidized, and can also reduce the probability of the nano-silicon grains reacting with the electrolyte. Therefore, the silicon-carbon material provided by this application reduces the probability of side reactions between the silicon material and the electrolyte while controlling the expansion degree of the silicon material during the process of lithium ion insertion and extraction, thereby improving the cyclability of the battery to a certain extent.

[0206] In order to better explain the structure and properties of the above silicon-carbon material, the preparation method thereof is described in detail below.

[0207] Preparation method of silicon-carbon material

[0208] In some embodiments, the present application provides a method for preparing a silicon-carbon material, including the following preparation process:

[0209] providing a porous carbon substrate;

[0210] introducing a silicon source into the porous carbon substrate to generate a porous carbon material comprising nano-silicon grains and a silicon carbide material layer;

[0211] A carbon source is introduced into a porous carbon material comprising nano-silicon grains and a silicon carbide material layer to generate a silicon-carbon negative electrode material comprising a carbon coating layer.

[0212] In some embodiments of the present application, the porous carbon substrate comprises carbon, oxygen, and nitrogen, and the mass ratio of carbon to oxygen and nitrogen is (94% to 97%): (2% to 4%): (1% to 2%).

[0213] Preferably, the ash content of the porous carbon substrate is ≤0.5%.

[0214] The porous carbon substrate of the present application is made from conventional carbon material precursors in the art. The types of carbon material precursors are not particularly limited and may include, but are not limited to, asphalt-based carbon material precursors, asphaltene-based carbon material precursors, coal-based carbon material precursors, coke-based carbon material precursors, biochar-based carbon material precursors, carbon black-based carbon material precursors, oil product-based carbon material precursors, tar-based carbon material precursors, polymer-based carbon material precursors, protein-based carbon material precursors, carbohydrate-based carbon material precursors, cotton-based carbon material precursors, fat-based carbon material precursors, waste-based carbon material precursors, graphite-based carbon material precursors, melamine-based carbon material precursors, wood-based carbon material precursors, porous graphene, porous graphene oxide, activated carbon and combinations thereof. Carbon material precursors of this type are easy to prepare porous carbon materials that meet the above-mentioned particle size, specific surface area, tap density and compacted density. The present application discloses a method for preparing a porous carbon substrate in these embodiments, such as high-temperature sintering of the carbon material precursor to remove impurities, and then forming pores to obtain a porous carbon material. The pore forming in this application includes chemical methods such as strong alkali corrosion. The measurement method of the carbon element, oxygen element and nitrogen element in the porous carbon substrate of the present application includes any conventional method in the art, such as measurement according to relevant test standards. The present application discloses in these embodiments that the mass percentage of the carbon element in the porous carbon substrate includes any one of 94%, 95%, 96%, 97% or any one of the above-mentioned range values. The mass percentage of the oxygen element in the porous carbon substrate includes any one of 2%, 3%, 4% or any one of the above-mentioned range values. The mass percentage of the nitrogen element in the porous carbon substrate includes any one of 1% and 2% or any one of the above-mentioned range values.

[0215] The ash content in this application includes inorganic matter remaining after the porous carbon substrate is calcined at high temperature. The ash content measurement method can refer to GB / T 1429-2009.

[0216] In some embodiments of the present application, the reaction conditions for generating a porous carbon material comprising nano-silicon grains and a silicon carbide material layer include one or more of the following:

[0217] (5.1) The reaction temperature is 500°C to 700°C, and the silicon source is introduced for 3 hours to 42 hours; preferably, the reaction temperature is 650°C to 700°C; and the silicon source is introduced for 5 hours to 40 hours;

[0218] (5.2) The silicon source comprises a silicon source gas and a diluent gas, wherein the volume percentage of the silicon source gas is 15% to 95%; preferably, the volume percentage of the silicon source gas is 20% to 50%; preferably, the silicon source gas comprises either or both of monosilane and disilane;

[0219] (5.3) The ventilation volume of the silicon source is 0.3L / min to 1.4L / min.

[0220] The present application discloses in some embodiments that the reaction temperature for generating a porous carbon material comprising nano-silicon grains and a silicon carbide material layer comprises any one of 500°C, 600°C, 650°C, 680°C, and 700°C or satisfies any one of the above-mentioned ranges. The present application discloses in these embodiments that the time for introducing a silicon source comprises any one of 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h, 30h, 31h, 32h, 33h, 34h, 35h, 36h, 37h, 38h, 39h, 40h, 41h, and 42h or satisfies any one of the above-mentioned ranges. In these embodiments, the present application selects a reaction temperature of 500°C to 700°C and a silicon source introduction time of 3h to 42h; this facilitates the growth of silicon grains with a grain size d1 ≥ 5nm in the through-holes, and the silicon grains are stacked along the inner wall of the through-holes to form a layered or sheet-like film. During the continuous growth process, the layered or sheet-like film is also prone to generate a silicon carbide material layer in the area that is in direct contact with the inner wall of the through-hole within the above-mentioned reaction temperature, and the silicon carbide material layer and the through-holes of the porous carbon material restrict the growth of the silicon grains, and finally generate nano-silicon grains with a certain suitable particle size.

[0221] In some embodiments, the present application discloses that a silicon source for forming silicon grains includes a silicon source gas and a dilution gas, wherein the silicon source gas includes, but is not limited to, monosilane, disilane, etc., and the dilution gas includes an inert gas, which includes conventional inert gases in the art, including, but not limited to, rare gases corresponding to Group 0 of the periodic table. In these embodiments, the present application discloses that the volume fraction of the silicon source gas in the silicon source includes any one of 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 95%, or any value within the aforementioned ranges.

[0222] The present application discloses in some embodiments that in the process of generating a porous carbon material comprising nano-silicon grains and a silicon carbide material layer, it is also necessary to control the ventilation volume of the silicon source. The ventilation volume of the silicon source can be measured using conventional measurement methods in the art, such as by setting a flow valve in the reaction equipment. The present application discloses in these embodiments that the ventilation volume of the silicon source includes any one of 0.3L / min, 0.4L / min, 0.5L / min, 0.6L / min, 0.7L / min, 0.8L / min, 0.9L / min, 1.0L / min, 1.1L / min, 1.2L / min, 1.3L / min, 1.4L / min or any one of the above range values. The present application controls the volume percentage and ventilation volume of each component in the silicon source to control the growth rate of the silicon grains, thereby affecting the grain size of the silicon grains and the formation and thickness of the silicon carbide material layer.

[0223] In some embodiments of the present application, the reaction conditions for generating a silicon-carbon negative electrode material including a carbon coating layer include the following:

[0224] (6.1) The reaction temperature is 600°C to 750°C, and the time for introducing the carbon source is 0.5h to 5h. The preferred reaction temperature is 650°C to 700°C; the preferred time for introducing the carbon source is 1h to 4h.

[0225] (6.2) The carbon source comprises a carbon source gas and a diluent gas, wherein the volume fraction of the carbon source gas is 15% to 95%; preferably, the volume fraction of the carbon source gas is 20% to 40%; preferably, the carbon source gas comprises any one of methane, ethylene, acetylene, and propylene, or a combination of two or more thereof;

[0226] (6.3) The aeration rate of the carbon source is 1.0 L / min to 3.0 L / min, preferably 1.5 L / min to 2.5 L / min.

[0227] The reaction temperature of the carbon coating layer of the present application includes any one of 600°C, 650°C, 700°C, 750°C or any one of the above range values. The time for introducing the carbon source in the present application includes any one of 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or any one of the above range values. At the reaction temperature of the present application and the time for introducing the carbon source, the carbon coating layer is formed along the outer surface of the porous carbon material and has a certain thickness. And under the reaction conditions, the silicon material with a layered or sheet-like film stacked along the inner wall of the through hole may continue to generate a silicon carbide material layer in the area directly in contact with the inner wall of the through hole.

[0228] The present application discloses in some embodiments that the carbon source for forming the carbon coating layer includes a carbon source gas and a dilution gas. As mentioned above, the dilution gas includes an inert gas, and the inert gas includes an inert gas conventional in the art, including but not limited to the noble gases corresponding to Group 0 of the periodic table. The carbon source gas includes but is not limited to methane, ethylene, acetylene, propylene, etc. The present application also discloses in these embodiments that the volume percentage of the carbon source gas includes but is not limited to any one of 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or any one of the above range values. The ventilation rate of the carbon source includes but is not limited to any one of 1.0 L / min, 2.0 L / min, 3.0 L / min or any one of the above range values. The present application generates a carbon coating layer with a thickness of 5 nm to 50 nm and a silicon carbide material layer with a thickness of less than 0.7 nm under the reaction conditions of controlling the volume percentage of the carbon source gas and the ventilation rate of the carbon source.

[0229] Negative electrode

[0230] Some embodiments of the present application disclose a negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. The negative electrode film layer comprises a silicon-carbon material as a negative electrode active material, and further comprises other negative electrode active materials, such as carbonaceous materials, specifically including but not limited to one or a combination of two or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Artificial graphite, natural graphite, soft carbon, hard carbon, etc., include any form of material conventional in the art and include any manufacturer and model conventional in the art.

[0231] In some embodiments of the present application, it is disclosed that the negative electrode film layer also includes a conductive agent, a thickener, a binder, etc., wherein the conductive agent includes but is not limited to one or a combination of two of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers; the thickener includes cellulose and its sodium salt, cellulose includes methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, etc.; the binder includes but is not limited to polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc.

[0232] The negative electrode current collector of the present application may be a metal foil or a composite current collector. The metal foil may be a copper 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 formed by forming a metal material, such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, on a polymer material substrate, such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0233] In some embodiments, the present application discloses the mass ratios of silicon-carbon materials, carbonaceous materials, conductive agents, thickeners and binders in the negative electrode film layer: (10% to 50%): (45% to 95%): (0.2% to 2.0%): (0.2% to 2.0%): (1.2% to 2.2%).

[0234] Positive electrode

[0235] In some embodiments of the present application, a positive electrode sheet is disclosed, which includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer in the present application includes positive electrode active particles, a positive electrode conductive agent, a positive electrode binder, etc. The present application does not specifically limit the specific types of positive electrode active particles. For example, when the positive electrode sheet is used in a lithium-ion battery, the positive electrode active particles include but are not limited to LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 CO 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 CO 0.1 Mn 0.1 O2(NCM811), LiNi0.85 CO 0.15 Al 0.05 One or more of O2, LiFePO4 (LFP) and LiMnPO4.

[0236] For example, when the positive electrode is used in a sodium ion battery, the positive electrode active particles include but are not limited to at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. Among them, the transition metal in the sodium transition metal oxide can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1. Polyanionic compounds include sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, one or more of the following. Prussian blue compounds are Na x M1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0<x≤2.

[0237] Positive electrode conductive agents include, but are not limited to, one or a combination of two or more of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Positive electrode binders include, but are not limited to, one or a combination of two or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0238] The positive electrode current collector in the present application may be a metal foil or a composite current collector, wherein the metal foil may be an aluminum foil, and the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0239] electrolyte

[0240] In some embodiments of the present application, an electrolyte is disclosed, which includes a sodium salt or a lithium salt and an organic solvent, and the organic solvent can be an organic solvent commonly used in the art for electrolytes. As an example, the organic solvent can be selected from at least one or a combination of two of 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 (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE). The sodium salt or lithium salt may be a sodium salt or lithium salt commonly used in the art for electrolyte, such as sodium hexafluorophosphate, lithium hexafluorophosphate, etc.

[0241] Isolation film

[0242] According to some embodiments of the present application, the battery not only includes a negative electrode sheet, a positive electrode sheet and an electrolyte, but also includes a separator stacked together. The stacking method includes but is not limited to conventional winding or lamination in the art. The material, size, etc. of the separator include but are not limited to any conventional form in the art. Similarly, the material, size, etc. of the positive electrode sheet include but are not limited to any conventional form in the art. For example, the separator is arranged between the positive electrode sheet and the negative electrode sheet to play an isolating role. The separator includes a substrate and also includes a functional coating provided on at least one surface of the substrate. The functional coating can be used to improve the heat resistance, mechanical strength, etc. of the separator. For example, the functional coating may also include other functional materials (such as ceramic particles, other polymers, etc.). Ceramic particles include, but are not limited to, boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, and the like. The present application does not particularly limit the type of separator substrate; any known substrate suitable for secondary battery separators may be selected. In some embodiments, the separator substrate includes, but is not limited to, a single-layer film or a multi-layer composite film of one or more of glass fiber, non-woven fabric, polyethylene, and polypropylene.

[0243] [Preparation of silicon-carbon materials]

[0244] This application discloses, in some embodiments, a method for preparing a silicon-carbon material, comprising the following preparation steps:

[0245] S1. Providing a porous carbon substrate, wherein the porous carbon substrate comprises carbon, oxygen, and nitrogen, wherein the mass ratio of carbon to oxygen and nitrogen is (94% to 97%):(2% to 4%):(1% to 2%), and the ash content of the porous carbon substrate is ≤0.5%;

[0246] At the same time, the porous carbon substrate comprises porous carbon material particles, and the pore volume, average pore diameter, number and distribution of through pores, particle size, specific surface area and tap density of the porous carbon material particles meet the following requirements:

[0247] a. Average pore diameter is 1.0nm~5.0nm;

[0248] b. The volume percentage of macropores is ≤15%, and the volume ratio of micropores to hollows is (40-95%):(5-50%);

[0249] c. Dv50 is 3.0μm to 6.5μm; Dv90 is 13.5μm to 18.5μm; Dv10 is 0.9μm to 2.5μm;

[0250] d. Specific surface area is 900m 2 / g~1550m 2 / g;

[0251] e. Tap density is 0.22g / cm 3 ~0.48g / cm 3 ;

[0252] f. Compacted density is 0.45g / cm 3 ~0.80g / cm 3 ;

[0253] S2. Placing the porous carbon substrate of S1 in a CVI device, introducing a silicon source for 3 h to 42 h, and performing a chemical vapor deposition reaction at 500° C. to 700° C. to generate a porous carbon material containing nano-silicon grains, wherein the CVI device comprises a fluidized bed and any one of a rotary kiln, a pusher furnace, or a tubular furnace; the silicon source has a ventilation rate of 0.2 L / min to 1.5 L / min, and the silicon source comprises a silicon source gas and a dilution gas, and the volume fraction of the silicon source gas is 15% to 95%; the silicon source gas comprises any one or both of monosilane and disilane;

[0254] S3. A carbon source is introduced into the porous carbon material containing nano-silicon grains in S2 for 0.5h to 5h, and the reaction is carried out at 600℃ to 750℃ to obtain a silicon-carbon negative electrode material containing a carbon coating layer. The carbon source has a ventilation rate of 1.0L / min to 3.0L / min, and the carbon source contains carbon source gas and dilution gas. The volume fraction of the carbon source gas is 15% to 95%; the carbon source gas contains any one of methane, ethylene, acetylene, and propylene, or a combination of two or more.

[0255] Among them, Examples 1 to 16 are silicon-carbon materials obtained according to the raw materials listed in Tables 1, 2, and 3 and the process parameters listed in Table 4, and the particle size, specific surface area, etc. of the silicon-carbon materials are shown in Table 5.

[0256] Figure 5 is an electron micrograph of the silicon-carbon material obtained in Example 8, which was tested using a field emission scanning electron microscope (Zeiss Gemini 360) in accordance with the JY / T010-1996 standard. As shown in Figure 5 , the silicon-carbon material is composed of irregularly shaped particles of varying sizes.

[0257] Figure 6 is a schematic structural diagram of the silicon-carbon composite particles of the present application. In conjunction with Figure 6, it can be seen that the silicon-carbon composite particles 1 include a porous carbon material 1a, which has through holes, and nano-silicon grains 1b are distributed along the inner wall of the through holes of the porous carbon material 1a, while leaving some remaining closed holes 1c; a silicon carbide material layer 1d is formed inside the through holes, and one side of the silicon carbide material layer 1d is connected to the inner wall of the through hole, and the other side is connected to the nano-silicon grains 1b. The remaining closed holes 1c formed on the inner wall of the through hole of the present application can be used to alleviate the partial expansion of the nano-silicon material when lithium is inserted, thereby alleviating the expansion of the silicon-carbon composite particles. The silicon carbide material layer can be used to limit the degree of outward expansion of the nano-silicon particles during the process of lithium insertion and removal to reduce the effect of the reaction between the nano-silicon particles and the electrolyte.

[0258] Further reference to Figure 7 shows that a certain amount of silicon carbide material layer has indeed formed within the silicon-carbon material. Figure 7 shows an X-ray photoelectron spectroscopy analysis of the silicon-carbon material obtained in Example 8. The thickness of the silicon carbide material layer was calculated to be less than 0.7 nm.

[0259] FIG8 is an electron microscope image of nano-silicon grains 1b obtained by magnifying the silicon-carbon material obtained in Example 8. As shown in FIG8 , the nano-silicon grains are stacked along the inner wall of the through hole to form a layered or sheet-like film.

[0260] FIG9 is a transmission electron microscope image of the silicon-carbon material obtained in Example 8. It can be seen from FIG9 that a carbon coating layer is formed on the outer surface of the porous carbon material, and the thickness of the carbon coating layer is 18.4 nm.

[0261] FIG10 is an X-ray diffraction pattern of the silicon-carbon material obtained in Example 8. This pattern can be obtained using an X-ray diffractometer using methods known in the art. For example, reference is made to the general rules for XRD testing, JIS K 0131-1996, which include the following requirements: (1) sample dryness; (2) sample particle size <10 μm. For electrode scraping powder or bulk samples, the sample must be ground and passed through a 200-mesh sieve. FIG10 shows that the silicon-carbon material has a strong silicon crystallization peak. The silicon grain size of the silicon-carbon material calculated using the Scherrer formula is 7.2 nm.

[0262] Figure 11 shows the dQ / dV curve of the discharge curve of the silicon-carbon material prepared in Example 8. As shown in Figure 11, the I1 / I2 ratio of the silicon-carbon material is 1.45, indicating that the amount of silicon material particles formed in the through-pores is appropriate, which is beneficial for improving the cyclability of the battery. I1 represents the peak intensity near 0.3V to 0.35V, and I2 represents the peak intensity near 0.43V to 0.50V.

[0263] Comparative Example 1

[0264] A silicon-carbon material is provided. The carbon substrate used to generate the silicon-carbon material is different from that of the present application. The silicon grains are generated at a low temperature of 450°C. The average particle size of the obtained nano-silicon grains is smaller than the average pore size of the porous carbon material and no silicon carbide material layer is generated. See Tables 1 to 5 for details.

[0265] Comparative Example 2

[0266] A silicon-carbon material is provided. The carbon substrate for generating the silicon-carbon material remains the same as that of the present application. A low temperature of 450°C is used in the process of generating silicon grains, and a reaction temperature of 500°C is used in the carbon coating process, resulting in no generation of a silicon carbide material layer. See Tables 1 to 5 for details.

[0267] Among them, transmission electron microscope images and X-ray photoelectron spectroscopy analysis patterns of the silicon-carbon materials prepared in Comparative Examples 1 and 2 were obtained, and it was analyzed that no silicon carbide material layer was actually generated.

[0268] [Performance test of silicon carbon materials]

[0269] ①Particle size test:

[0270] Refer to standard GB / T19077-2016: Obtain a volume particle size distribution curve for porous carbon particles or silicon-carbon composite particles. Take the particle size corresponding to 50% of the cumulative volume distribution percentage as the average particle size Dv50, the particle size corresponding to 90% of the cumulative volume distribution percentage as the average particle size Dv90, and the particle size corresponding to 10% of the cumulative volume distribution percentage as the average particle size Dv10. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0271] ②Specific surface area test:

[0272] According to the standard GB / T19587-2017, the porous carbon particles or silicon-carbon composite particles are tested using nitrogen adsorption specific surface area analysis, and the specific surface area is calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a TRISTAR II 3020 Specific Surface Area and Porosity Analyzer from Micromeritics, USA.

[0273] ③Through hole pore volume test:

[0274] The porous carbon particles were tested according to the GB / T21650.2-2008 test method. The test instrument can be a TRISTAR II 3020 surface area and porosity analyzer from Micromeritics, USA.

[0275] ④Pore volume test of closed pores:

[0276] Refer to GB / T24586-2009 to obtain the tested true density of silicon-carbon materials, refer to GB / T 20975.5-2020 to obtain the silicon content in silicon-carbon materials, and refer to GB / T 20123-2006 / ISO 15350:2000 to obtain the carbon content in silicon-carbon materials. Theoretical true density of silicon ρ 硅 2.34g / cm 3 , the theoretical true density of carbon ρ 碳 2.26g / cm 3 According to the calculation formula: V1=1 / ρ 真 -1 / (w 硅 ×ρ 硅 +w 碳 ×ρ 碳 ) to calculate the pore volume V1 of the closed pores.

[0277] ⑤Porous structure quantity test:

[0278] Using the ASAP2460 physical adsorption analyzer, the dried and degassed carbon particle samples were placed in liquid nitrogen. The nitrogen adsorption was measured at various test pressures, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the hysteresis loop, and the pore distribution was calculated using different pore models. The pore size distribution curves for mesopores were fitted using the BJH model, and the pore size distribution curves for micropores were fitted using the DFT model. Statistical calculations were then performed to obtain the pore size distribution curves.

[0279] ⑥ Pore size test of porous structure:

[0280] In the above ⑤ test on the number of porous structures, the pore size distribution curve of each pore is obtained, the specific surface area is obtained in ②, and the pore volume is obtained in ③. Based on the model of the relevant pores in ⑤, the average pore size is obtained by dividing the pore volume by the specific surface area and multiplying by the model coefficient.

[0281] ⑦ Silicon grain size test:

[0282] Obtain the X-ray diffraction pattern of silicon-carbon material and calculate it using the Scherrer formula.

[0283] ⑧Tap density test:

[0284] Reference standard GB / T5162-2006.

[0285] ⑨Compaction density test under 5 tons:

[0286] Refer to standard GB / T 24533-2009: Measured using an electronic pressure tester (e.g., UTM7305). Specifically, a specific amount M of powder sample to be tested is placed on a dedicated compression mold (with a base area of ​​S0) and set to different pressures. Each pressure is maintained for 30 seconds, then released. After 10 seconds, the thickness H0 of the powder pressed at that pressure (5 tons) is read on the instrument. The compacted density at that pressure is calculated as M / (H0 × S0).

[0287] ⑩Powder resistivity test under 4Mpa:

[0288] Place an appropriate amount of silicon-carbon material in the feeding cup of the resistivity tester, apply pressure, manually collect data, record the powder resistivity test results at different pressure points and then take the average value. The test pressure is 4 MPa.

[0289] Table 1 Properties of porous carbon substrates (I)

[0290] Table 2 Properties of porous carbon substrates (II)

[0291] Table 3 Ratios of the grain size d1 of nano-silicon grains to the average pore size d2 of porous carbon materials (III)

[0292] Table 4 Process parameter list (IV)

[0293] Table 5 List of silicon-carbon materials in Examples and Comparative Examples

[0294] [Preparation of button cells]

[0295] 1. Negative electrode:

[0296] The silicon-carbon composite material, conductive carbon black, and binder polyacrylic acid prepared above were mixed in a mass ratio of 8:1:1, and deionized water was added and stirred thoroughly to form a negative electrode slurry; the negative electrode slurry was evenly coated on one surface of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet was obtained.

[0297] 2. Electrolyte:

[0298] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 20:20:60, and LiPF6 was evenly dissolved in the above solution. Fluorinated ethylene carbonate (FEC) was added as an additive to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass proportion of FEC in the electrolyte was 5%.

[0299] 3. Isolation film

[0300] Polyethylene film is used as the isolation film.

[0301] 4. Preparation of Button Cells

[0302] The above-mentioned negative electrode sheet is used as the working electrode and the metallic lithium is used as the counter electrode; the negative electrode sheet, the isolation membrane and the metallic lithium are stacked in order so that the isolation membrane is between the working electrode and the counter electrode, the above-mentioned electrolyte is injected, and a CR2430 button battery is assembled.

[0303] (1) Test of the first delithiation specific capacity and first coulombic efficiency:

[0304] The CR2430 button cell was subjected to the first charge and discharge test. At 25°C, the cell was discharged to 5 mV using a constant current of 0.05C, allowed to stand for 10 minutes, and then charged to 2.0 V using 0.1C to obtain the first discharge capacity and the first charge capacity.

[0305] First delithiation specific capacity = first delithiation capacity / mass of active material; wherein, the first delithiation capacity is also the first discharge capacity.

[0306] First coulombic efficiency = first discharge capacity / first charge capacity × 100%.

[0307] (2) Charge and discharge curve test:

[0308] A charge and discharge curve test of the above-mentioned CR2430 button battery was plotted. At 25°C, the charge and discharge voltage was 0.005~2.0V, and the charge and discharge capacity and the working electrode potential were differentiated to obtain a dQ / dV curve. Specifically, a constant current of 0.05C was used to discharge to 5mV, a constant current of 50μA was used to discharge to 5mV, and the battery was allowed to stand for 10 minutes. The battery was then charged to 2.0V at 0.1C. A curve graph showing the relationship between the differential value dQ / dV obtained by differentiating the charge and discharge capacity Q with the working electrode potential V and the working electrode potential V was plotted.

[0309] In this dQ / dV curve, I1 is the peak intensity near 0.3V to 0.35V; I2 is the peak intensity near 0.43V to 0.50V;

[0310] Satisfies: Calculate R=I1 / I2.

[0311] The performance test results of the negative electrode are shown in Table 6.

[0312] Table 6 Performance list of negative electrode

[0313] [Preparation of negative electrode sheet]

[0314] The silicon-carbon materials prepared in Examples 1 to 16, and Comparative Examples 1 and 2 were mixed with artificial graphite, binder styrene-butadiene rubber (SBR), binder polyacrylic acid (PAA), dispersant (CMC-Na), conductive carbon black (Super-P, SP), and carbon nanotubes (CNT) in a mass ratio of 20%: 75%: 2%: 1%: 1%: 0.7%: 0.3% with deionized water to form a uniformly stirred slurry. The slurry was defoamed and then evenly coated on the negative electrode current collector copper foil at a coating speed of 50 m / min and a coating mass of 130 mg / 1540.25 mm 2 The temperature settings of the nine-section oven are 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃ respectively; a cold press is used to compact the negative electrode sheet to a certain density to obtain a negative electrode sheet.

[0315] [Preparation of positive electrode sheet]

[0316] Taking lithium-ion batteries as an example, the positive electrode active material LiNi 0.8Co 0.1 Mn 0.1 O2 (NCM811), binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are stirred and dispersed in N-methylpyrrolidone in a mass ratio of 97%:1.5%:1.5% to prepare a positive electrode slurry, which is then coated on the positive electrode current collector aluminum foil and compacted by a cold press to obtain a positive electrode sheet.

[0317] [Select a release film]

[0318] A polyethylene porous membrane with a thickness of 12 μm was selected.

[0319] [Select electrolyte]

[0320] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte solution. The concentration of LiPF6 in the electrolyte solution was 1 mol / L.

[0321] [Forming a battery]

[0322] According to some embodiments of the present application, the prepared negative electrode sheet, the isolation membrane, and the positive electrode sheet are stacked in order, so that the isolation membrane is placed between the positive and negative electrode sheets to play an isolation role, and are wound to obtain a bare battery cell, which is then inserted into a battery casing. After baking, liquid injection, standing, packaging, formation, and capacity division, a lithium-ion secondary battery is obtained.

[0323] [Performance test of secondary batteries]

[0324] (3) Cyclic performance test at 45°C:

[0325] The prepared secondary battery was charged at a constant current rate of 1C to a voltage of 4.25V at a constant temperature of 45°C. Then, it was charged at a constant voltage at 4.25V to a current of less than or equal to 0.05mA. After that, it was allowed to rest for 5 minutes. Then, it was discharged at a constant current rate of 1C to a voltage of 2.5V and allowed to rest for 5 minutes. This constituted one cycle of charge and discharge. The discharge capacity of this cycle was recorded as the discharge capacity of the secondary battery in the first cycle. The secondary battery was subjected to cyclic charge and discharge tests according to the above method until the cycle capacity retention rate reached 80%, which was recorded as the cycle life CL (45°C).

[0326] The 45° C. cycle capacity retention rate of the secondary battery at the nth cycle (%) = discharge capacity at the nth cycle / discharge capacity at the 1st cycle × 100%. Specific test results are shown in Table 6.

[0327] (4) Electrode cyclic expansion performance test at 45°C:

[0328] The thickness of the negative electrode sheet of the secondary battery after the cold pressing process is recorded as h0. According to the battery cycling performance test method described above at 45°C, the secondary battery is cycled 300 times. The battery is charged at a constant current rate of 1C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of less than or equal to 0.05mA, and then allowed to rest for 5 minutes. The cycled battery cell is disassembled in a dry room. The thickness of the negative electrode sheet after 300 cycles is recorded as h300. The expansion rate of the secondary battery sheet after 300 cycles at 45°C is Δh300.

[0329] Δh300(%)=(h300-h0) / h0×100%. Specific test results are shown in Table 7.

[0330] Table 7 Battery performance list

[0331] Combined with the above list, it can be seen that, in combination with Examples 1 to 16, the battery cycle performance of each embodiment that meets the scope of the list of this application has been improved to a certain extent. This may be due to the fact that the silicon-carbon material provided by this application is improved from multiple levels, such as forming nano-silicon grains with a certain suitable particle size, physical isolation, physical restriction, etc., while controlling the degree of expansion of the silicon material during the deintercalation and extraction of lithium ions. The probability of side reactions between the silicon material and the electrolyte is reduced, thereby improving the cyclability of the battery to a certain extent.

[0332] Combined with Comparative Example 1, it can be seen that the size of the nano-silicon grains has a great influence on the battery. If the size of the nano-silicon grains cannot be reasonably matched with the aperture of the through-hole, it is easy to cause the side reaction to increase and the material expansion to worsen.

[0333] It can be seen from Comparative Example 1, Comparative Example 2 and the embodiment that the presence of the silicon carbide material layer can significantly limit the expansion of the silicon material.

[0334] Therefore, on the one hand, this application controls the size of nano-silicon grains to an appropriate level and reasonably matches them with the through holes, and on the other hand, limits the expansion size of silicon grains (such as setting closed holes, such as designing a silicon carbide material layer) to improve the cycle performance of the battery.

[0335] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A silicon-carbon material, characterized in that: include: Silicon-carbon composite particles, comprising: Porous carbon material: has through pores; Nano-silicon grains: located in the through holes; the grain size of the nano-silicon grains is not less than the average pore size of the porous carbon material; The silicon carbide material layer is at least partially located on the wall of the through hole.

2. The silicon-carbon material according to claim 1, wherein: The grain size of the nano-silicon grains is d1, and the average pore size of the porous carbon material is d2, satisfying: d1 / d2=1-15.

3. The silicon-carbon material according to any one of claims 1 to 2, characterized in that: The grain size of the nano-silicon grains is d1, and the average pore size of the porous carbon material is d2, satisfying: d1 / d2=2-10.

4. The silicon-carbon material according to any one of claims 1 to 3, characterized in that: The grain size of the nano-silicon grains is d1, d1≥5nm; and / or; The average pore diameter of the porous carbon material is d2, and d2 is 1.0 nm to 5.0 nm.

5. The silicon-carbon material according to any one of claims 1 to 4, characterized in that: The grain size of the nano-silicon grains is d1, and d1 is 5nm to 20nm; and / or; The average pore diameter of the porous carbon material is d2, and d2 is 1.5 nm to 5.0 nm.

6. The silicon-carbon material according to any one of claims 1 to 5, characterized in that: The silicon-carbon composite particles include closed pores, and the pore volume of the closed pores is smaller than the pore volume of the through pores.

7. The silicon-carbon material according to any one of claims 1 to 6, characterized in that: The silicon-carbon composite particles contain closed pores, the pore volume of the closed pores is V1, and the pore volume of the through pores is V2. Satisfies: V2 / V1=5~24.

8. The silicon-carbon material according to any one of claims 1 to 7, characterized in that: The silicon-carbon composite particles include closed pores, the pore volume of the closed pores is V1, and the pore volume of the through pores is V2, satisfying: V2 / V1=7-16.

9. The silicon-carbon material according to any one of claims 1 to 8, characterized in that: The pore volume of the closed pore is V1, which is 0.04 cm 3 / g~0.16cm 3 / g; and / or; The pore volume of the through hole is V2, and V2 is 0.3 cm 3 / g~1.5cm 3 / g.

10. The silicon-carbon material according to any one of claims 1 to 9, characterized in that: The through pores include micropores, mesopores and macropores, and based on the total volume of the through pores, the volume ratio of the micropores, the mesopores and the macropores is (40% to 95%): (5% to 50%): (0 to 15%).

11. The silicon-carbon material according to any one of claims 1 to 10, characterized in that: The silicon carbide material layer is located between the through hole and the nano-silicon grains, wherein one side of the silicon carbide material layer is connected to the inner wall of the through hole, and the other side is connected to the nano-silicon grains.

12. The silicon-carbon material according to any one of claims 1 to 11, characterized in that: The thickness of the silicon carbide material layer is less than 0.7 nm.

13. The silicon-carbon material according to any one of claims 1 to 12, characterized in that: The silicon-carbon material further includes a carbon coating layer, which is arranged along the outer surface of the porous carbon material.

14. The silicon-carbon material according to any one of claims 1 to 13, characterized in that: The porous carbon material comprises porous carbon particles, and the porous carbon particles meet the following conditions: (1.1) The volume distribution particle size of the porous carbon particles satisfies the following requirements: Dv50 is 3.0 μm to 6.5 μm; Dv90 is 13.5 μm to 18.5 μm; and Dv10 is 0.9 μm to 2.5 μm; (1.2) The specific surface area of ​​the porous carbon particles is 900 m 2 / g~1550m 2 / g; (1.3) The tap density of the porous carbon particles is 0.22 g / cm 3 ~0.48g / cm 3 ; (1.4) The compacted density of 5 tons of porous carbon particles is 0.45 g / cm 3 ~0.80g / cm 3 .

15. The silicon-carbon material according to any one of claims 1 to 14, characterized in that: The porous carbon material comprises porous carbon particles, and the porous carbon particles satisfy at least one of the following requirements: (2.1) The volume distribution particle size of the porous carbon particles satisfies the following requirements: Dv50 is 3.5 μm to 6.0 μm; Dv90 is 14.0 μm to 18.0 μm; and Dv10 is 1.0 μm to 2.0 μm. (2.2) The specific surface area of ​​the porous carbon particles is 1000 m 2 / g~1500m 2 / g; (2.3) The tap density of the porous carbon particles is 0.25 g / cm 3 ~0.45g / cm 3 ; (2.4) The compacted density of 5 tons of porous carbon particles is 0.50 g / cm 3 ~0.75g / cm 3 .

16. The silicon-carbon material according to any one of claims 1 to 15, characterized in that: Based on the total mass of the silicon-carbon material, the mass percentage content of silicon element in the silicon-carbon material is w 硅 , satisfying: w 硅 It is 38.0% to 48.0%.

17. The silicon-carbon material according to any one of claims 1 to 16, characterized in that: The silicon-carbon composite particles meet the following conditions: (3.1) The volume distribution particle size of the silicon-carbon composite particles satisfies the following requirements: (Dv90-Dv10) / Dv50 is 1.2 to 2.8; (3.2) The specific surface area of ​​the silicon-carbon composite particles is 3.0 m 2 / g~12.0m 2 / g; (3.3) The tap density of the silicon-carbon composite particles is 0.5 g / cm 3 ~1.0g / cm 3 ; (3.4) The compacted density of 5 tons of the silicon-carbon composite particles is 0.80 g / cm 3 ~1.1g / cm 3 .

18. The silicon-carbon material according to any one of claims 1 to 17, characterized in that: The silicon-carbon composite particles meet at least one of the following requirements: (4.1) The volume distribution particle size of the silicon-carbon composite particles satisfies the following requirements: Dv50 is 3.5 μm to 9.0 μm; Dv90 is 14.0 μm to 21.0 μm; and Dv10 is 0.9 μm to 3.0 μm. (4.2) The specific surface area of ​​the silicon-carbon composite particles is 5.0 m 2 / g~10.0m 2 / g; (4.3) The tap density of the silicon-carbon composite particles is 0.6 g / cm 3 ~0.8g / cm 3 ; (4.4) The compacted density of 5 tons of the silicon-carbon composite particles is 0.90 g / cm 3 ~1.05g / cm 3 .

19. The silicon-carbon material according to any one of claims 1 to 18, characterized in that: The properties of the silicon-carbon composite particles are as follows: The powder resistivity of the silicon-carbon composite particles at 4 MPa is 1.30 Ω·cm to 3.80 Ω·cm; and / or; The silicon-carbon composite particles have a lithium removal capacity of 1300 mAh / g to 1500 mAh / g and a first coulombic efficiency of 77% to 81%. and / or; In the dQ / dV curve of the silicon-carbon composite particles, I1 is the peak intensity near 0.3V~0.35V; I2 is the peak intensity near 0.43V~0.50V; and satisfies: I1 / I2=1.4~1.8; the dQ / dV curve of the silicon-carbon composite particles includes the silicon-carbon composite particles as the positive electrode active material, the metal lithium sheet as the counter electrode, and the CR2430 button battery assembled. At 25°C, the charge and discharge voltage is 0.005V~2.0V, and the charge and discharge capacity and the working electrode potential are obtained by differential processing.

20. A method for preparing the silicon-carbon material according to any one of claims 1 to 19, characterized in that: include: providing a porous carbon substrate; introducing a silicon source into the porous carbon substrate to generate a porous carbon material comprising nano-silicon grains and a silicon carbide material layer; A carbon source is introduced into the porous carbon material comprising the nano-silicon grains and the silicon carbide material layer to generate a silicon-carbon material comprising a carbon coating layer.

21. The method for preparing a silicon-carbon material according to claim 20, wherein: The reaction conditions for generating the porous carbon material comprising nano-silicon grains and a silicon carbide material layer are as follows: (5.1) The reaction temperature is 500°C to 700°C, and the silicon source is introduced for 3 hours to 42 hours; (5.2) The silicon source comprises a silicon source gas and a dilution gas, wherein the volume percentage of the silicon source gas is 15% to 95%; the silicon source gas comprises either or both of monosilane and disilane; (5.3) The ventilation volume of the silicon source is 0.2L / min to 1.5L / min.

22. The method for preparing a silicon-carbon negative electrode material according to any one of claims 20 to 21, characterized in that: The porous carbon substrate comprises carbon, oxygen and nitrogen, and the mass ratio of the carbon to the oxygen and nitrogen is (94% to 97%): (2% to 4%): (1% to 2%). And / or; the ash content of the porous carbon substrate is ≤0.5%.

23. A secondary battery comprising a negative electrode plate, characterized in that: The negative electrode plate comprises the silicon-carbon negative electrode material according to any one of claims 1 to 19 or the silicon-carbon material prepared by the preparation method according to any one of claims 20 to 22.

24. An electrical device, characterized in that: A secondary battery according to claim 23 is included.

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