Silicon-carbon composite material, method for preparing the same, secondary battery, and electric device

Abstract

This application provides a silicon-carbon composite material and its preparation method, a secondary battery, and an electrical device. The silicon-carbon composite material includes a carbon matrix with a porous structure and silicon-based materials distributed in the porous structure. A coin cell battery is used to charge and discharge the silicon-carbon composite material. A graph is plotted showing the relationship between the differential value dQ / dV obtained by differentiating the voltage V of the coin cell charge / discharge curve with respect to the charge / discharge capacity Q and the voltage V. The maximum value of the differential value dQ / dV between 0.26V and 0.35V is denoted as V. A The maximum value of the differential dQ / dV between 0.42V and 0.52V is denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.40; can significantly improve the cycle performance and first charge / discharge efficiency of silicon-carbon composite materials.

Description

[0001] This application is a divisional application of patent application 202311360972.7 filed on October 20, 2023, entitled "Silicon-carbon composite material and preparation method thereof, secondary battery and electrical device". Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to a silicon-carbon composite material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0003] Rechargeable batteries have a wide range of applications in portable electronic devices, electric vehicles, and other fields. With the continuous development of the new energy industry, users are placing increasingly higher demands on rechargeable batteries, such as high energy density.

[0004] Silicon-based materials are widely used in secondary batteries due to their high capacity. However, due to silicon's high expansion and poor conductivity, while silicon-based materials can improve the energy density of secondary batteries, they also affect the cycle performance, thus limiting the further development of battery technology. Summary of the Invention

[0005] Therefore, it is necessary to provide a silicon-carbon composite material and its preparation method, a secondary battery, and an electrical device to alleviate the expansion of the secondary battery and improve its cycle performance.

[0006] To achieve the above objectives, a first aspect of this application provides a silicon-carbon composite material, comprising: A carbon matrix having a porous structure; and Silicon-based material, distributed within the porous structure of the carbon matrix; The silicon-carbon composite material was charged and discharged using coin cells. A graph was plotted showing the relationship between the differential value dQ / dV (obtained by differentiating the voltage V from the charge / discharge capacity Q) and the voltage V. The maximum value of dQ / dV between 0.26V and 0.35V was denoted as V. A Let the maximum value of the differential dQ / dV between 0.42V and 0.52V be denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.40.

[0007] In this application, at least a portion of the silicon-based material is distributed within the porous structure of the carbon matrix in the silicon-based composite material. The carbon matrix improves the conductivity of the silicon-based material and also acts as a buffer medium for the volume expansion of the silicon-based material during charging and discharging, effectively mitigating the problem of increased secondary battery volume caused by silicon-based material expansion. Furthermore, through process adjustments, the silicon-carbon composite material meets the V... A / V B ≥1.40 can effectively improve the cycle performance and first charge / discharge efficiency of silicon-carbon composite materials.

[0008] In some embodiments, 1.42 ≤ V A / V B ≤1.90.

[0009] In some embodiments, 1.50 ≤ V A / V B ≤1.70.

[0010] In some embodiments, the grain size of the silicon-based material is ≤6nm.

[0011] In some embodiments, the pore size of the pore structure is 0.5 nm to 8 nm.

[0012] In some embodiments, the pore structure includes micropores with a pore size greater than or equal to 0.5 nm and less than 2 nm, and mesopores with a pore size of 2 nm to 8 nm.

[0013] In some embodiments, the number of micropores in the pore structure accounts for 60%-90%.

[0014] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 2 m². 2 / g-10 m 2 / g.

[0015] In some embodiments, the silicon-carbon composite material has at least one of the following characteristics: (1) The silicon-based material includes elemental silicon; (2) The shape of the silicon-based material includes one or more of the following: spherical, near-spherical, sheet-like, and linear. (3) The specific surface area of ​​the carbon matrix is ​​1000 m². 2 / g -2000 m 2 / g; (4) The silicon-based material accounts for 35%-60% of the mass of the silicon-carbon composite material; (5) The volume distribution particle size Dv50 of the silicon-carbon composite material is 3μm-15μm; (6) The volume distribution particle size Dv90 of the silicon-carbon composite material is less than or equal to 50 μm; (7) The silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3; (8) The tap density of the silicon-carbon composite material is 0.8 g / cm³. 3 -1.2g / cm 3 ; (9) The powder resistivity of the silicon-carbon composite material at 16 MPa is less than or equal to 5 Ω·m.

[0016] In some embodiments, at least a portion of the outer surface of the silicon-carbon composite material further includes a carbon coating layer.

[0017] In some embodiments, the carbon coating layer has at least one of the following characteristics: (1) The material of the carbon coating layer includes amorphous carbon; (2) The thickness of the carbon coating layer is 50nm-200nm.

[0018] A second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps: Preparation of carbon substrates; The carbon substrate is subjected to a pore-forming process to obtain a carbon matrix A with a porous structure; The carbon matrix A with a porous structure is subjected to pore size control treatment to obtain a carbon matrix B with a porous structure. The silicon-carbon composite material is prepared by depositing silicon-based material within the porous structure of a porous carbon matrix B. The silicon-carbon composite material is charged and discharged using a coin cell battery. A graph is plotted showing the relationship between the differential value dQ / dV (obtained by differentiating the voltage V from the charge / discharge capacity Q) and the voltage V. The maximum value of dQ / dV between 0.26V and 0.35V is denoted as V. A Let the maximum value of the differential dQ / dV between 0.42V and 0.52V be denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.40.

[0019] In some embodiments, the step of preparing the carbon substrate includes: subjecting a carbon material precursor to a first sintering treatment to prepare the carbon substrate.

[0020] In some embodiments, the preparation of the carbon substrate satisfies at least one of the following conditions: (1) The temperature of the first sintering treatment is 400℃-800℃; (2) The first sintering treatment time is 1h-12h; (3) The atmosphere of the first sintering treatment includes an inert gas; (4) The inert gas includes one or more of nitrogen and argon; (5) The carbon material precursor includes one or more of resin-based carbon materials and biomass carbon materials.

[0021] In some embodiments, the hole-forming process includes: alkaline etching of the carbon substrate using an alkaline substance.

[0022] In some embodiments, the pore-forming process satisfies at least one of the following conditions: (1) The alkaline substance includes one or more of potassium hydroxide and sodium hydroxide; (2) The mass ratio of the alkaline substance to the carbon substrate is (2-6):1.

[0023] In some embodiments, the pore size control process includes: placing the carbon matrix A with the porous structure in a mixed gas containing a first carbon source and an inert gas, and performing a first vapor deposition.

[0024] In some embodiments, the temperature of the first vapor deposition is 800°C-1000°C.

[0025] In some embodiments, the temperature of the first vapor deposition is 850°C-950°C.

[0026] In some embodiments, the time for the first vapor deposition is 1h-4h.

[0027] In some embodiments, the volume ratio of the first carbon source to the inert gas is (2-5):10.

[0028] In some embodiments, the first vapor deposition further includes at least one of the following conditions: (1) The first carbon source includes one or more of methane, ethylene and acetylene; (2) The inert gas includes one or more of nitrogen and argon.

[0029] In some embodiments, the porous carbon matrix B is placed in a mixed gas containing a silicon source and an inert gas for a second vapor deposition.

[0030] In some embodiments, the temperature of the second vapor deposition is 450°C-650°C.

[0031] In some embodiments, the temperature of the second vapor deposition is 500°C-600°C.

[0032] In some embodiments, the second vapor deposition time is 4h-8h.

[0033] In some embodiments, the silicon source accounts for 10%-40% of the volume of the mixed gas; and / or, the inert gas accounts for 60%-90% of the volume of the mixed gas.

[0034] In some embodiments, the second vapor deposition further includes at least one of the following conditions: (1) The positive difference between the pressure of the second vapor deposition and atmospheric pressure is 0.2 kPa-0.6 kPa; (2) The silicon source includes one or more of silane, ethane and propane; (3) The inert gas includes one or more of nitrogen and argon.

[0035] In some embodiments, prior to the aperture control process, the method further includes: The alkaline substances remaining on the carbon substrate after pore-forming treatment are removed using acidic substances.

[0036] In some embodiments, the preparation method further includes: The silicon-carbon composite material is placed in a mixed gas containing a second carbon source and an inert gas, and a third vapor phase deposition is performed to form a carbon coating layer on at least a portion of the outer surface of the silicon-carbon composite material.

[0037] In some embodiments, the third vapor deposition satisfies at least one of the following conditions: (1) The second carbon source includes one or more of methane, ethylene and acetylene; (2) The inert gas includes one or more of nitrogen and argon; (3) The volume percentage of the second carbon source in the mixed gas is 5%-20%; (4) The temperature of the third vapor deposition is 500℃-700℃; (5) The time for the third gas phase deposition is 1h-6h.

[0038] A third aspect of this application provides a secondary battery including a negative electrode, said negative electrode comprising a silicon-carbon composite material as described in the first aspect of this application or a silicon-carbon composite material prepared using the method described in the second aspect of this application.

[0039] The fourth aspect of this application provides an electrical device, including the secondary battery of the third aspect of this application. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0041] Figure 2 yes Figure 1An exploded view of a secondary battery according to one embodiment of this application is shown.

[0042] Figure 3 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0043] Figure 4 This is a cross-sectional SEM image of a negative electrode sheet prepared using the silicon-carbon composite material according to an embodiment of this application.

[0044] Figure 5 This is a graph showing the relationship between the differential value dQ / dV of the battery cell prepared using the silicon-carbon composite material in Example 3 and the working electrode potential V.

[0045] Explanation of reference numerals in the attached figures: 1 Secondary battery; 11 Casing; 12 Electrode assembly; 13 Cover plate; 2 Electrical device; 411 Carbon matrix; 412 Carbon coating layer. Detailed Implementation

[0046] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0048] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0049] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0050] In this application, if the unit of a data range is only followed by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 10-1000nm means that the units of the left endpoint "10" and the right endpoint "1000" are both nm (nanometers).

[0051] In this application, terms such as "multiple," "various," and "repeatedly" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "multiple" means two or more. This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0052] The "scope" disclosed in this application is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way may include end values ​​or not.

[0053] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0055] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0056] Silicon-containing materials are widely used in secondary batteries. However, due to the high expansion properties of silicon and its poor conductivity, secondary batteries using silicon-containing materials, while improving energy density, still suffer from problems such as expansion and poor cycle performance.

[0057] To address the aforementioned issues, this application proposes a silicon-carbon composite material, comprising a carbon matrix with a porous structure and silicon-based materials distributed within the porous structure. The porous structure provides space for the expansion of the silicon-based materials, mitigating the problem of increased secondary battery volume due to silicon-based material expansion. Furthermore, to investigate the cycle performance of the silicon-carbon composite material, V... A / VB Silicon-carbon composites with a density of ≥1.4 can significantly improve the cycle performance of silicon-carbon composites.

[0058] The first aspect of this application provides a silicon-carbon composite material, comprising a carbon matrix and a silicon-based material; the carbon matrix has a porous structure, and the silicon-based material is distributed within the porous structure of the carbon matrix; when a coin cell is used for charging and discharging, a graph is plotted showing the relationship between the differential value dQ / dV obtained by differentiating the voltage V of the coin cell charge / discharge curve with respect to the charge / discharge capacity Q and the voltage V, and the maximum value of the differential value dQ / dV between 0.26V and 0.35V is denoted as V. A Let the maximum value of the differential dQ / dV between 0.42V and 0.52V be denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.40.

[0059] The carbon matrix in this application refers to a carbon-based material having a porous structure on its outer surface and / or interior. The carbon matrix may contain one or more porous structures. Silicon-carbon composite materials include silicon-based materials distributed in the porous structure of the carbon matrix, and may also include silicon-based materials distributed on the surface of the support structure of the carbon matrix.

[0060] It should be noted that when plotting the relationship between the differential value dQ / dV obtained by differentiating the working electrode voltage V with respect to the charge / discharge capacity Q and the working electrode voltage V, the curve of voltage V and discharge capacity Q can be obtained according to the coin cell preparation method and testing method, and then the curve can be differentiated and integrated. The coin cell is constructed by using the silicon-carbon composite material of this application as the working electrode, a counter electrode made of lithium metal, and a lithium-ion electrolyte, with a voltage of 0.005V-2.0V and a current of 0.1C.

[0061] Understandably, the silicon-carbon composite material of this application comprises a carbon matrix with a porous structure and silicon-based materials distributed within the porous structure. The carbon matrix can improve the conductivity of the silicon-based materials and also serve as a buffer medium for the volume expansion of the silicon-based materials during charging and discharging, effectively alleviating the problem of increased secondary battery volume caused by the expansion of the silicon-based materials. Furthermore, through process adjustments, the silicon-carbon composite material meets the V... A / V B ≥1.40 can effectively improve the cycle performance and first charge / discharge efficiency of silicon-carbon composite materials.

[0062] In some implementations, 1.40 ≤ V A / V B ≤1.90; for example, V A / V BIt can be, but is not limited to, 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.5, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.6, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.7, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.8, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, 1.88, 1.89, 1.9, or a range between any two of the above values.

[0063] As an example, the ratio V A / V B The possible values ​​are 1.40-1.88, 1.40-1.85, 1.40-1.73, 1.40-1.68, 1.40-1.60, 1.42-1.90, 1.45-1.90, 1.45-1.85, 1.45-1.8, 1.45-1.75, 1.45-1.7, 1.45-1.65, and 1.65-1. .9, 1.65-1.85, 1.65-1.8, 1.5-1.7, 1.51-1.69, 1.52-1.68, 1.53-1.67, 1.54-1.66, 1.55-1.65, 1.56-1.64, 1.57-1.63, 1.58-1.62 or 1.59-1.61, etc., without specific restrictions.

[0064] In some alternative implementations, 1.50 ≤ V A / V B ≤1.70.

[0065] In some embodiments, the grain size of the silicon-based material is ≤6nm. If the grain size of the silicon-based material is larger than this range, the silicon-carbon composite structure may collapse during cycling due to the excessively large grain size. As an example, the grain size of the silicon-based material can be, but is not limited to, 0.01nm, 0.05nm, 0.1nm, 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, or any two of the above values. Optionally, the grain size of the silicon-based material is 1nm-4nm.

[0066] As an example, the grain size of the silicon-based material mentioned above can be calculated using X-ray diffraction patterns or characterized by transmission electron microscopy to obtain the grain size of the silicon-based material.

[0067] In some implementations, the silicon-based material includes elemental silicon.

[0068] In some embodiments, the silicon-based material is shaped as one or more of spherical, near-spherical, sheet-like, and linear.

[0069] In some embodiments, the pore size of the carbon matrix is ​​0.5 nm to 8 nm. When the pore size of the carbon matrix is ​​within this range, the silicon-based material deposited within the pore structure can have a more uniform size, reducing the probability of depositing large-sized silicon-based material. As an example, the pore size of the carbon matrix can be, but is not limited to, 0.5 nm, 1 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, or any two of the above values. Optionally, the pore size of the carbon matrix is ​​0.5 nm to 6 nm.

[0070] It should be noted that when the carbon matrix has only a single pore structure, the pore diameter of the pore structure is the pore diameter of that single pore structure; when the carbon matrix has multiple pore structures, the pore diameter of the pore structure refers to the average pore diameter of the pore structure.

[0071] In some embodiments, the pore structure of the carbon matrix includes micropores with a pore size greater than or equal to 0.5 nm and less than 2 nm and mesopores with a pore size of 2 nm to 8 nm; optionally, the pore structure of the carbon matrix includes micropores with a pore size greater than or equal to 0.5 nm and less than 2 nm and mesopores with a pore size of 2 nm to 6 nm.

[0072] In some embodiments, the proportion of micropores in the pore structure is 60%-90%; for example, it can be, but is not limited to, 60%, 63%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, or any two of the above values. When the proportion of micropores in the pore structure is within the above range, the probability of depositing large-size silicon-based materials can be further reduced, which is more conducive to controlling Vt. A / V B The size of the pores. Optionally, the number of micropores in the pore structure accounts for 70%-80%.

[0073] As one possible implementation, the carbon matrix has a specific surface area of ​​1000 m². 2 / g -2000m 2 / g; When the specific surface area of ​​the carbon matrix is ​​lower than the above range, silicon is easily deposited on the surface of the carbon matrix; when the specific surface area of ​​the carbon matrix is ​​higher than the above range, excessive silicon deposition is easily caused, resulting in excessive silicon volume expansion during cycling and causing the carbon matrix to collapse. As an example, the specific surface area of ​​the carbon matrix can be, but is not limited to, 1000 μm. 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g or a range between any two of the above values. Optionally, the specific surface area of ​​the carbon matrix is ​​1300 m². 2 / g -2000 m 2 / g. In some embodiments, the mass percentage of silicon-based materials in the silicon-carbon composite material is 35%-60%; when the mass percentage of silicon-based materials in the silicon-carbon composite material is lower than the above range, it may result in low capacity and first-efficiency of the silicon-carbon composite material; when the mass percentage of silicon-based materials in the silicon-carbon composite material is higher than the above range, it may result in poor cycle performance of the silicon-carbon composite material. As an example, the mass percentage of silicon-based materials in the silicon-carbon composite material can be, but is not limited to, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60% or any two of the above values. Optionally, the mass percentage of silicon-based materials in the silicon-carbon composite material is 40%-55%.

[0074] As an example, the mass percentage of silicon-based materials in silicon-carbon composites can be determined using ICP emission spectroscopy.

[0075] In some embodiments, the volumetric particle size distribution (Dv50) of the silicon-carbon composite material is 3 μm-15 μm. When the Dv50 is higher than this range, it can easily lead to poorer kinetics in the secondary battery; when the Dv50 is lower than this range, there may be uneven deposition of silicon-based materials in the carbon matrix. As an example, the Dv50 of the silicon-carbon composite material can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any two of the above values. Optionally, the Dv50 of the silicon-carbon composite material is 5 μm-13 μm.

[0076] In some embodiments, the volumetric particle size distribution (Dv90) of the silicon-carbon composite material is less than or equal to 50 μm; if the Dv90 of the silicon-carbon composite material is higher than the above range, it may cause the negative electrode reagent bottle to puncture the diaphragm. As an example, the volumetric particle size distribution (Dv90) of the silicon-carbon composite material can be, but is not limited to, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any two of the above values. Optionally, the volumetric particle size distribution (Dv90) of the silicon-carbon composite material is 20 μm-40 μm.

[0077] In some embodiments, the silicon-carbon composite material satisfies: 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 3; when the silicon-carbon composite material satisfies the above condition, it is beneficial to improve the compaction density of the negative electrode sheet. As an example, (Dv90 - Dv10) / Dv50 can be, but is not limited to, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, or any range between any two of the above values. Optionally, 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 2.

[0078] The Dv10, Dv50, and Dv90 values ​​of the material have well-known meanings in the art and can be tested using methods known in the art. For example, they can be determined using a laser particle size analyzer (such as the Malvern Master Size 3000) in accordance with the standard GB / T 19077-2016.

[0079] The physical definitions of Dv10, Dv50, and Dv90 are as follows: Dv10: The particle size corresponding to a cumulative volume distribution percentage of 10% for the material; Dv50: The particle size corresponding to a cumulative volumetric distribution percentage of 50%; Dv90: The particle size corresponding to a cumulative volume distribution percentage of 90% for the material.

[0080] As one possible implementation method, the silicon-carbon composite material has a specific surface area of ​​2 m². 2 / g -20 m 2 / g; When the specific surface area of ​​the silicon-carbon composite material exceeds the above range, it may lead to a decrease in the initial efficiency of the secondary battery. As an example, the specific surface area of ​​the silicon-carbon composite material can be, but is not limited to, 2m². 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / gg or a range between any two of the above values. Optionally, the specific surface area of ​​the silicon-carbon composite material is 2m². 2 / g -6m 2 / g.

[0081] As an example, the pore size of the carbon matrix and the specific surface area of ​​the silicon-carbon composite material mentioned above are well-known in the art and can be tested using methods known in the art. For example, the nitrogen adsorption specific surface area analysis method can be used with reference to GB / T 19587-2017, and the result can be calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0082] In some possible embodiments, the tap density of the silicon-carbon composite material is 0.8 g / cm³. 3 -1.2g / cm 3 As an example, the tap density of silicon-carbon composite materials can be, but is not limited to, 0.8 g / cm³. 30.83g / cm 3 0.85g / cm 3 0.87g / cm 3 0.9g / cm 3 0.92g / cm 3 0.95g / cm 3 0.98g / cm 3 1g / cm 3 1.02g / cm 3 1.05g / cm 3 1.08g / cm 3 1.1g / cm 3 1.12 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.2g / cm 3 Or a range between any two of the above values. Optionally, the tap density of the silicon-carbon composite material is 0.85 g / cm³. 3 -1g / cm 3 .

[0083] It should be noted that the tap density of the silicon-carbon composite material mentioned above refers to the mass per unit volume of the silicon-carbon composite material powder in the container after tapping under specified conditions.

[0084] The tap density of the negative electrode active material is a well-known concept in the art and can be tested using methods known in the art. For example, it can be determined using a powder tap density tester according to standard GB / T 5162-2006. If using the FZS4-4B tap density tester from the Beijing Iron and Steel Research Institute, the test parameters are as follows: vibration frequency: 250±15 times / minute, amplitude: 3±0.2mm, number of vibrations: 5000 times, measuring cylinder: 25 mL.

[0085] In some embodiments, the silicon-carbon composite material has a powder resistivity of less than or equal to 5 Ω·m at 16 MPa; the silicon-carbon composite material exhibits excellent electrical conductivity, thereby contributing to improved battery kinetic performance. Optionally, the silicon-carbon composite material has a powder resistivity of less than or equal to 2 Ω·m at 16 MPa.

[0086] As an example, the powder resistivity of the aforementioned silicon-carbon composite material at 16 MPa can be determined by the following method: place an appropriate amount of the sample to be tested in the feeding cup of the resistivity tester, apply pressure, manually collect data, and record the powder resistivity test results at different pressure points. The test pressure is 16 MPa.

[0087] In some embodiments, the efficiency of the silicon-carbon composite material in the first charge-discharge cycle is ≥90%; optionally, the efficiency of the silicon-carbon composite material in the first charge-discharge cycle is 92%-95%.

[0088] As an example, the efficiency of the aforementioned silicon-carbon composite material during the first charge-discharge cycle can be determined using the following method: The negative electrode sheet prepared from the sample under test was used as the working electrode, and lithium metal was used as the counter electrode. A coin cell was constructed with an electrolyte containing lithium-ion conductive material. After the coin cell was left to stand for 60 minutes, it was tested by constant current discharge at 0.05C to 5mV, discharge at 50μA to 5mV, stand for 10 minutes, and charge at 0.1C to 2.0V. The delithiation capacity of 2.0V represents the capacity of the sample under test, and the corresponding first efficiency = 2.0V delithiation capacity / lithium insertion capacity.

[0089] In some embodiments, at least a portion of the outer surface of the silicon-carbon composite material also includes a carbon coating layer. By providing a carbon coating layer, the contact between the silicon-based material and the electrolyte can be reduced, battery side reactions can be decreased, thereby improving the battery's cycle performance.

[0090] It should be noted that the carbon coating layer can be a continuous and complete coating layer or an incomplete coating layer; "complete" means that the material located inside the carbon coating layer is completely covered by the carbon coating layer, and the carbon coating layer completely isolates the material inside the carbon coating layer from the material outside the carbon coating layer. "Incomplete" means that the material located inside the carbon coating layer is not completely covered by the carbon coating layer, and the material inside the carbon coating layer can at least partially contact the material outside the carbon coating layer. Preferably, the carbon coating layer is a continuous and complete coating layer.

[0091] As an example, a cross-sectional SEM image of the negative electrode sheet prepared using the silicon-carbon composite material of this application is shown below. Figure 4 As shown, the carbon matrix 411 is coated with a uniform carbon coating layer 412, which can prevent the carbon matrix from being exposed, thereby reducing the reaction between the silicon-based material and the electrolyte.

[0092] In some embodiments, the carbon coating material includes amorphous carbon; the amorphous carbon can act as a fast-charging ion ring, improve the kinetic properties of the silicon-carbon composite material, and reduce the contact between the silicon-based material and the electrolyte.

[0093] In some embodiments, the thickness of the carbon coating layer is 50nm-200nm. A thickness less than this range may expose the silicon-based material, affecting processing performance; a thickness greater than this range may reduce the capacity of the secondary battery. As an example, the thickness of the carbon coating layer can be, but is not limited to, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or any two of the above values.

[0094] As an example, the thickness of the aforementioned carbon coating can be measured using a transmission electron microscope.

[0095] The second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps: preparing a carbon substrate; performing a pore-forming treatment on the carbon substrate to obtain a carbon matrix A with a porous structure; performing a pore size control treatment on the carbon matrix A with a porous structure to obtain a carbon matrix B with a porous structure; depositing a silicon-based material within the pore structure of the carbon matrix B with a porous structure to prepare the silicon-carbon composite material; wherein, a coin cell battery is used to charge and discharge the silicon-carbon composite material, and a curve is plotted showing the relationship between the differential value dQ / dV obtained by differentiating the voltage V of the coin cell charge and discharge curve with the charge and discharge capacity Q and the voltage V, and the maximum value of the differential value dQ / dV between 0.26V and 0.35V is denoted as V. A Let the maximum value of the differential dQ / dV between 0.42V and 0.52V be denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.40.

[0096] In some embodiments, the step of preparing the carbon substrate includes: subjecting a carbon material precursor to a first sintering treatment to prepare the carbon substrate.

[0097] In one possible implementation, the temperature of the first sintering treatment is 400℃-800℃, for example, but not limited to 400℃, 430℃, 450℃, 480℃, 500℃, 530℃, 550℃, 570℃, 600℃, 630℃, 650℃, 680℃, 700℃, 730℃, 750℃, 770℃, 800℃, or any range between any two of the above values. The time of the first sintering treatment is 1h-12h; for example, but not limited to 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any range between any two of the above values. The atmosphere of the first sintering treatment includes an inert gas; optionally, the inert gas includes one or more of nitrogen and argon.

[0098] As one possible implementation, the carbon material precursor includes one or more of resin-based carbon materials and biomass carbon materials.

[0099] Optionally, the resin-based carbon material includes one or more of phenolic resin, epoxy resin, urea-formaldehyde resin, and furan resin.

[0100] Alternatively, the biochar material includes one or more of coconut shell, lignin, bamboo powder, and starch.

[0101] It should be noted that bamboo powder refers to powder made from bamboo.

[0102] In some embodiments, the hole-forming process includes: alkaline etching of the carbon substrate using an alkaline substance.

[0103] In some alternative embodiments, the alkaline substance includes one or more of potassium hydroxide and sodium hydroxide.

[0104] In some alternative embodiments, the mass ratio of the alkaline substance to the carbon substrate is (2-6):1; as an example, the mass ratio of the alkaline substance to the carbon substrate can be, but is not limited to, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1 or any two of the above ratios.

[0105] As one possible implementation, prior to the pore size control step, the method further includes: removing residual alkaline substances from the carbon substrate after the pore-forming treatment using an acidic substance. Optionally, the acidic substance includes hydrochloric acid.

[0106] In some embodiments, the pore size control process includes placing a carbon matrix A with a porous structure in a mixed gas containing a first carbon source and an inert gas, and performing a first vapor phase deposition.

[0107] A first carbon source is deposited using vapor deposition to adjust the pore size of the carbon substrate. The volume ratio of the first carbon source to the inert gas during vapor deposition is (2-5):10, which can reduce the large pore size of the carbon substrate and avoid depositing large-sized silicon-based materials.

[0108] In some optional embodiments, the temperature of the first vapor deposition is 800℃-1000℃; for example, it can be, but is not limited to, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, or any range between two of the above values. When the temperature of the first vapor deposition is within the above range, it facilitates the decomposition of the carbon source and is beneficial for pore size control. As an example, the temperature for the first vapor deposition can be 810℃-990℃, 820℃-980℃, 830℃-970℃, 840℃-960℃, 850℃-950℃, 860℃-940℃, 870℃-930℃, or 880℃-920℃, etc., and there is no specific limitation. Optionally, the temperature for the first vapor deposition is 850℃-950℃.

[0109] In some optional embodiments, the first vapor deposition time is 1-4 hours; for example, it can be, but is not limited to, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.3 hours, 2.5 hours, 2.8 hours, 3 hours, 3.3 hours, 3.5 hours, 3.7 hours, 4 hours, or any range between two of the above values. When the first vapor deposition time is within the above range, it is beneficial to adjust the pore size to a suitable size and control the ratio of micropores to mesopores in the pore structure. Optionally, the first vapor deposition time is 1.5 hours to 3 hours.

[0110] In some optional embodiments, the volume ratio of the first carbon source to the inert gas is (2-5):10; when the volume ratio of the first carbon source to the first inert gas is within the above range, it is beneficial to adjust the pore size of the carbon matrix pore structure to be more uniform. As an example, the volume ratio of the first carbon source to the first inert gas can be, but is not limited to, 2:10, 2.3:10, 2.5:10, 2.8:10, 3:10, 3.2:10, 3.5:10, 3.8:10, 4:10, 4.3:10, 4.5:10, 4.8:10, 5:10, or any two of the above ratios. Optionally, the volume ratio of the first carbon source to the inert gas is (2.5-4):10.

[0111] It should be noted that the temperature and time of the first vapor deposition, as well as the volume ratio of the first carbon source to the inert gas, all affect the pore size of the pore structure, and the pore size of the pore structure affects V. A / V B The value of V can be further controlled by adjusting the temperature and time of the first vapor deposition, as well as the volume ratio of the first carbon source to the inert gas. A / V B The value should be within a suitable range; specifically, the temperature of the first vapor phase deposition is too low, VA / V B The value is usually too small; the first vapor deposition time is too short, V A / V B The value is usually too small; the volume ratio of the first carbon source to the inert gas is too small, V A / V B The value is usually too small.

[0112] In some alternative embodiments, the first carbon source includes one or more of methane, ethylene, and acetylene.

[0113] In some alternative embodiments, the inert gas includes one or more of nitrogen and argon.

[0114] In some embodiments, a carbon matrix B with a porous structure is placed in a mixed gas containing a silicon source and an inert gas, and a second vapor phase deposition is performed to deposit silicon-based materials within the porous structure of the carbon matrix; using vapor phase deposition to deposit silicon-based materials within the porous structure can increase the proportion of silicon-based materials embedded within the porous structure.

[0115] In some optional embodiments, the temperature of the second vapor deposition is 450℃-650℃; for example, it can be, but is not limited to, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, or any range between two of the above values. When the temperature of the second vapor deposition is within the above range, it is beneficial to control the mass ratio of silicon-based materials in the silicon-carbon composite material to be within a suitable range; if the temperature of the second vapor deposition is too high, the silicon-based materials are prone to crystallization, which will affect the cycle performance of the battery; if the temperature of the second vapor deposition is too low, the silicon source decomposition efficiency will be low. As an example, the temperature for the second vapor deposition can be 460℃-640℃, 470℃-630℃, 480℃-620℃, 490℃-610℃, 500℃-600℃, 510℃-590℃, 520℃-580℃, or 530℃-570℃, etc., and is not specifically limited. Optionally, the temperature for the second vapor deposition is 500℃-600℃; more preferably, the temperature for the second vapor deposition is 520℃-580℃.

[0116] In some optional embodiments, the second vapor deposition time is 4-8 hours; for example, it can be, but is not limited to, 4 hours, 4.2 hours, 4.5 hours, 4.8 hours, 5 hours, 5.2 hours, 5.5 hours, 5.8 hours, 6 hours, 6.3 hours, 6.5 hours, 6.7 hours, 7 hours, 7 hours, 7.3 hours, 7.5 hours, 7.7 hours, 8 hours, or any range between two of the above values. When the second vapor deposition time is within the above range, it is beneficial to control the mass ratio of silicon-based material in silicon-carbon composite materials; if the second vapor deposition time is too long, silicon-based material is easily enriched on the surface of the carbon matrix; if the second vapor deposition time is too short, the amount of silicon-based material deposited is too low, failing to reach the capacity design value. As an example, the time for the second vapor phase deposition can be 4.2h-7.8h, 4.5h-7.5h, 4.8h-7.3h, 5h-7h, 5.2h-6.8h, 5.5h-6.5h, 5.8h-6.3h, etc., and there is no specific limitation. Optionally, the time for the second vapor phase deposition is 4.5h-7h; more preferably, the time for the second vapor phase deposition is 5h-6h.

[0117] In some optional embodiments, the volume percentage of the silicon source in the mixed gas is 10%-40%, and the volume percentage of the fourth inert gas in the mixed gas is 60%-90%. Controlling the volume percentage of the silicon source in the mixed gas within the above range is beneficial for depositing silicon-based materials with more uniform dimensions. For example, the volume percentage of the silicon source in the mixed gas can be, but is not limited to, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any two of the above values; correspondingly, the volume percentage of the fourth inert gas in the mixed gas can be, but is not limited to, 90%, 85%, 80%, 75%, 70%, 65%, 60%, or any two of the above values.

[0118] It should be noted that the temperature and time of the second vapor deposition, as well as the volume ratio of the silicon source to the inert gas, all affect the mass percentage of silicon-based materials in the silicon-carbon composite material. The mass percentage of silicon-based materials in the silicon-carbon composite material affects Va. A / V B The value of V can be further controlled by adjusting the temperature and time of the second vapor deposition and the volume ratio of silicon source to inert gas. A / V B The value of V should be adjusted to a suitable range; specifically, the higher the temperature of the second vapor deposition, the better. A / V B The smaller the value, the longer the second-phase deposition time, the better. A / V B The smaller the value, the greater the volume ratio of silicon source to fourth inert gas, and the higher the V value. A / V B The smaller the value, the better.

[0119] In some alternative embodiments, the positive difference between the pressure of the second vapor deposition and atmospheric pressure is 0.2 kPa to 0.6 kPa, for example, but not limited to 0.2 kPa, 0.25 kPa, 0.3 kPa, 0.35 kPa, 0.4 kPa, 0.45 kPa, 0.5 kPa, 0.55 kPa, 0.6 kPa, or any two of the above values.

[0120] In some alternative embodiments, the silicon source includes one or more of silane, ethane, and propane.

[0121] In some alternative embodiments, the inert gas includes one or more of nitrogen and argon.

[0122] In some embodiments, the preparation method of the silicon-carbon composite material further includes: placing the silicon-carbon composite material in a mixed gas containing a second carbon source and an inert gas, and performing a third vapor phase deposition to form a carbon coating layer on at least a portion of the outer surface of the silicon-carbon composite material. Using vapor phase deposition to prepare the carbon coating layer facilitates the control of the coating amount to improve the surface conductivity of the silicon-carbon composite material, which helps to maximize the material's capacity, while also helping to maintain the stability and safety of the silicon-carbon composite material.

[0123] In some alternative implementations, the second carbon source includes one or more of methane, ethylene, and acetylene.

[0124] In some alternative implementations, the inert gas includes one or more of nitrogen and argon.

[0125] In some optional embodiments, the volume percentage of the second carbon source in the mixed gas is 5%-20%, for example, but not limited to 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any two of the above values. Controlling the volume percentage of the second carbon source in the mixed gas within the above range is beneficial for improving the uniformity of carbon coating.

[0126] In some optional embodiments, the temperature for third vapor deposition is 500°C-700°C, for example, but not limited to 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, or any range between two of the above values. For example, the temperature for third vapor deposition can be 550°C-650°C. The time for third vapor deposition is 1 hour-6 hours, for example, but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any range between two of the above values.

[0127] It should be noted that the terms "first carbon source", "second carbon source", "first inert gas", "fourth inert gas", "fifth inert gas", "first vapor deposition", "second vapor deposition", "third vapor deposition", "first sintering treatment", and "second sintering treatment" mentioned above are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0128] In some embodiments, the preparation method of silicon-carbon composite materials includes the following steps: A carbon material precursor is subjected to a first sintering treatment to prepare a carbon substrate; wherein the temperature of the first sintering treatment is 400℃-800℃, the sintering time is 1h-12h, and the sintering atmosphere includes an inert gas; the carbon material precursor includes one or more of resin-based carbon materials and biomass carbon materials, the resin-based carbon materials include one or more of phenolic resin, epoxy resin, urea-formaldehyde resin and furan resin, and the biomass carbon materials include one or more of coconut shell, lignin, bamboo powder and starch.

[0129] A carbon matrix A with a porous structure is prepared by alkaline etching of a carbon substrate using an alkaline substance; wherein the alkaline substance includes one or more of potassium hydroxide and sodium hydroxide; the mass ratio of the alkaline substance to the carbon substrate is (2-6):1. The residual alkaline substances on the porous carbon substrate 1 are removed by using an acidic substance, followed by heating and drying; the acidic substance includes hydrochloric acid.

[0130] A porous carbon matrix A is placed in a mixed gas containing a first carbon source and an inert gas, and a first vapor phase deposition is performed to prepare a porous carbon matrix B. The first carbon source includes one or more of methane, ethylene, and acetylene. The first inert gas includes one or more of nitrogen and argon. The volume ratio of the first carbon source to the first inert gas is (2-5):10, optionally (2.5-4):10. The temperature of the first vapor phase deposition is 800℃-1000℃, optionally 850℃-950℃. The time of the first vapor phase deposition is 1h-4h, optionally 1.5h-3h.

[0131] A porous carbon matrix B is placed in a mixed gas containing a silicon source and an inert gas for second-phase deposition. The deposition temperature is 450℃-650℃, optionally 500℃-600℃, and more preferably 520℃-580℃. The deposition time is 4h-8h, optionally 4.5h-7h, and more preferably 5h-6h. The pressure difference between the second-phase deposition and atmospheric pressure is 0.2KPa-0.6KPa. The silicon source includes one or more of silane, disilane, and propane. The inert gas includes one or more of nitrogen and argon. The volume percentage of the silicon source in the mixed gas is 10%-40%. The volume percentage of the inert gas in the mixed gas is 60%-90%.

[0132] A silicon-carbon composite material is prepared by placing a carbon matrix in a mixed gas containing a second carbon source and an inert gas, and performing a third vapor phase deposition to form a carbon coating layer on at least a portion of the outer surface of the carbon matrix. The second carbon source includes one or more of methane, ethylene, and acetylene. The inert gas includes one or more of nitrogen and argon. The volume percentage of the second carbon source in the mixed gas is 5%-20%. The temperature for the third vapor phase deposition is 500℃-700℃, optionally 550℃-650℃. The deposition time is 1h-6h.

[0133] A third aspect of this application provides a secondary battery including a negative electrode, wherein the negative electrode comprises a silicon-carbon composite material of the first aspect of this application or a silicon-carbon composite material prepared by the method of the second aspect of this application.

[0134] The secondary battery using the aforementioned silicon-carbon composite material in this application exhibits improved rate performance and cycle performance.

[0135] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0136] Negative electrode sheet The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a silicon-carbon composite material including the first aspect of this application or a silicon-carbon composite material prepared by the method of the second aspect of this application.

[0137] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0138] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0139] In some embodiments, the negative electrode active material may also simultaneously employ negative electrode active materials known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon-nitrogen compounds, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more. The weight percentage of the negative electrode active material in the negative electrode film layer is 70-100% by weight, based on the total weight of the negative electrode film layer.

[0140] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0141] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0142] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0143] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70 wt%, and the viscosity at room temperature is adjusted to 2000-10000 mPa·s; the obtained negative electrode slurry is coated on both sides of the negative electrode current collector, and after a drying process, it is cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coated on one side is 75-220 mg / m². 2 The compaction density of the negative electrode sheet is 1.2-2.0 g / m³. 3 .

[0144] Positive electrode sheet The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0145] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0146] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate includes, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0147] In some embodiments, the lithium-ion cathode active material may comprise cathode active materials known in the art for use in batteries. As an example, the cathode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery cathode active materials may also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode active material accounts for 80-100% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0148] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder accounts for 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0149] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0150] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40-80 wt%, and the viscosity at room temperature is adjusted to 5000-25000 mPa·s. The positive electrode slurry is coated on both sides of the positive current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coated on one side is 15-35 mg / m². 2 The compacted density of the positive electrode sheet is 3.0-3.6 g / cm³. 3 The selectable value is 3.3-3.5 g / cm³. 3 The formula for calculating the compaction density is as follows: Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0151] electrolytes The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0152] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0153] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0154] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0155] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0156] Separating membrane In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0157] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0158] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm.

[0159] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process; the electrode assembly and electrolyte are packaged using the battery cell packaging material of the first aspect of this application.

[0160] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0161] In some embodiments, refer to Figure 2 The outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed on the opening to close the receiving cavity.

[0162] The positive electrode, negative electrode, and separator can be formed into electrode assembly 12 by a winding or stacking process. Electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in electrode assembly 12. The lithium-ion battery 1 can contain one or more electrode assemblies 12, which can be adjusted according to requirements.

[0163] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0164] In a battery module, multiple secondary batteries can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion batteries can be secured using fasteners.

[0165] Optionally, the battery module may also include a housing with a receiving space in which multiple secondary batteries are housed.

[0166] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0167] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0168] Electrical appliances A fourth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in the third aspect of this application. The secondary battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device may be, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; wherein, mobile devices may include, but are not limited to, at least one of mobile phones, laptops, etc.; electric vehicles may include, but are not limited to, at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0169] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0170] Figure 3 This is an example of an electrical device 2. This electrical device 2 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be used.

[0171] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0172] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0173] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0174] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. For example, phenolic resin can be purchased from Jining Huakai Resin Co., Ltd.

[0175] I. Preparation of Silicon-Carbon Composite Materials Example 1 Step 1: Weigh 1 kg of coconut shell (as a carbon material precursor) and place it in a box furnace. Introduce nitrogen (as a second inert gas) and raise the temperature to 600°C at a rate of 5°C / min. Hold the temperature for 2 hours to perform the first sintering treatment. After the furnace has cooled down, remove the carbon substrate. Step 2: Mix potassium hydroxide (as an alkaline substance) and carbon substrate at a mass ratio of 4:1, place in a box furnace, introduce nitrogen (as a third inert gas), raise the temperature to 800℃ at a heating rate of 5℃ / min, hold for 4 hours, and perform pore-forming treatment. Step 3: Mix the carbon substrate after pore-forming treatment with 0.1 mol / L hydrochloric acid solution (as an acidic substance) to remove residual potassium hydroxide from the carbon matrix, and then heat and dry at 80°C for 12 hours. Step 4: Place the carbon substrate after pore-forming treatment in a vapor deposition rotary furnace, mix acetylene (as the first carbon source) and nitrogen (as the first inert gas) at a volume ratio of 2:10, raise the temperature to 950°C at a heating rate of 5°C / min, and perform first vapor deposition for 2 hours to control the pore size and prepare a carbon matrix with a porous structure. Step 5: Place the carbon substrate in a vapor deposition furnace and raise the temperature to 500°C at a rate of 5°C / min. Introduce a mixture of silane (as the silicon source) and nitrogen (as the fourth inert gas), with silane accounting for 20% of the volume and nitrogen accounting for 80% of the volume. The total gas flow rate is 5L / min, and the furnace pressure is controlled to be slightly higher than atmospheric pressure by 200Pa. Perform the second vapor deposition for 6 hours. Step 6: Stop the introduction of silane, continue to heat to 600℃, and introduce a mixture of acetylene (as the second carbon source) and nitrogen (as the fifth inert gas), wherein the volume percentage of acetylene is 20% and the volume percentage of nitrogen is 80%. Perform third gas phase deposition for 1 hour, cool and sieve to obtain silicon-carbon composite material.

[0176] The preparation methods of Examples 2-5 are similar to those of Example 1, and the differences are detailed in Table 1.

[0177] Comparative Example 1 The preparation methods of Comparative Example 1 and Example 1 are similar, except that the first vapor deposition step was not used when preparing the silicon-carbon composite material.

[0178] Comparative Examples 2-4 The preparation methods of Comparative Examples 2-4 and Example 1 are similar, with the differences detailed in Table 1.

[0179] Table 1

[0180] Wherein, n1 represents the mass ratio of alkaline substance to carbon substrate, n2 represents the volume ratio of first carbon source to first inert gas, n3 represents the volume percentage of silicon source in mixed gas during second vapor deposition, n4 represents the volume percentage of second carbon source in mixed gas during third vapor deposition, T1 represents the temperature of first sintering treatment, t1 represents the time of first sintering treatment, T2 represents the sintering temperature and t2 represents the sintering time during pore-forming treatment, T3 represents the temperature and t3 represents the time of first vapor deposition, T4 represents the temperature and t4 represents the time of second vapor deposition, T5 represents the temperature and t5 represents the time of third vapor deposition, and pressure difference represents the difference between the pressure of second vapor deposition and atmospheric pressure.

[0181] II. Preparation of Button Cells 1. Negative electrode plate The silicon-carbon composite material, conductive carbon black, and binder polyacrylic acid prepared above are mixed in a mass ratio of 8:1:1. Deionized water is added and the mixture is stirred thoroughly to form a negative electrode slurry. The negative electrode slurry is uniformly coated on one surface of the negative electrode current collector copper foil. After drying and cold pressing, a negative electrode sheet is obtained.

[0182] 2. Electrolyte Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 20:20:60. LiPF6 was then uniformly dissolved in this solution, and fluoroethylene carbonate (FEC) was added as an additive to obtain the electrolyte. In this electrolyte, the concentration of LiPF6 was 1 mol / L, and the mass percentage of FEC was 5%.

[0183] 3. Separating membrane Polyethylene film is used as the separator.

[0184] 4. Preparation of button cells Using the aforementioned negative electrode as the working electrode and lithium metal as the counter electrode, the negative electrode, separator, and lithium metal are stacked in sequence, with the separator positioned between the working electrode and the counter electrode. The aforementioned electrolyte is then injected to assemble a coin cell.

[0185] III. Preparation of Secondary Batteries (Full Cells) 1. Negative electrode plate The silicon-carbon composite material, conductive carbon nanotubes and SP mixture, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 95.5:1:2:1.5 to form a negative electrode slurry. The negative electrode slurry was coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet was obtained.

[0186] 2. Positive electrode sheet The positive electrode active material LiNi0.8Co0.1Mn0.1O2 (NCM811) was mixed with conductive carbon black and polyvinylidene fluoride at a weight ratio of 97.5:1.2:1.3. An appropriate amount of solvent NMP was added, and the mixture was stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.

[0187] 3. Electrolyte: A mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) was used as the organic solvent, with a volume ratio of EC:20%:20%:60%. Thoroughly dried lithium salt (LiPF6) was dissolved in the above organic solvent in an argon-atmosphere glove box with a water content of <10 ppm, and fluoroethylene carbonate (FEC) was added as an additive to obtain the electrolyte. In this electrolyte, the concentration of LiPF6 was 1 mol / L, and the mass percentage of FEC in the electrolyte was 5%.

[0188] 4. Separating membrane Polyethylene film is used as the separator.

[0189] 5. Preparation of secondary batteries The separator is placed sequentially with the prepared positive and negative electrode sheets, with the separator positioned between them to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with the prepared electrolyte. After vacuum sealing, settling, formation, and capacity testing, a soft-pack secondary battery is obtained. The secondary battery measures 135mm × 72mm × 60mm and has a capacity of 4.65Ah.

[0190] III. Battery Performance Testing 1. Initial charge / discharge efficiency After the prepared coin cells were left to stand for 60 minutes, they were discharged to 5mV using a constant current of 0.05C, discharged to 5mV using 50μA, left to stand for 10 minutes, and then charged to 1.5V using 0.1C. The delithiation capacity at 1.5V represents the capacity of the sample under test. The initial charge-discharge efficiency = delithiation capacity at 1.5V / lithium insertion capacity × 100%. The results are shown in Table 2.

[0191] 2. V A / V B After the prepared coin cells were left to stand for 60 minutes, they were discharged to 5mV using a constant current of 0.05C, then discharged to 5mV using 50μA, left to stand for 10 minutes, and then charged to 1.5V using 0.1C. A graph showing the relationship between the differential value dQ / dV obtained by differentiating the working electrode potential V from the charge / discharge capacity Q and the working electrode potential V was plotted. The maximum value of the differential value dQ / dV between 0.26V and 0.33V when applying current in the delithiation direction of the negative electrode material was denoted as V. A The maximum value of the differential dQ / dV between 0.42V and 0.52V is denoted as V. B Calculate V A / V B The values ​​are shown in Table 2.

[0192] Figure 5 This is a graph showing the relationship between the differential value dQ / dV of the battery cell prepared using the silicon-carbon composite material in Example 3 and the working electrode potential V. Figure 5 It can be seen that the V of this battery cell A / V B It is 1.62.

[0193] 3. Cyclic performance test At 25°C, the prepared secondary battery (full cell) was charged to 4.25V at 0.5C, and then discharged to 2.5V at 1C. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as the initial discharge capacity. The secondary battery was then subjected to the same charge-discharge cycle test, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decreased to 80% of the initial discharge capacity. The number of cycles at this point was recorded.

[0194] Table 2

[0195] As can be seen from the comparison of the results of the embodiments and comparative examples in Table 2, the silicon-carbon composite material of this application includes a carbon matrix with a porous structure and silicon-based materials distributed in the porous structure of the carbon matrix, and the V of the material is controlled simultaneously. A / V B ≥1.4 can significantly improve the initial charge-discharge efficiency and cycle performance of silicon-carbon composite materials.

[0196] In Comparative Example 1, the silicon-carbon composite material was prepared without a first vapor deposition process, and the pore size was not controlled. The large pore size resulted in silicon-based material depositing on the surface of the carbon matrix, leading to a large grain size of the silicon-based material and consequently, a low Vt in the final silicon-carbon composite material. A / V B <1.4, which cannot significantly improve the initial charge-discharge efficiency and cycle performance of silicon-carbon composite materials.

[0197] In Comparative Example 2, the temperature of the first vapor deposition in the preparation of the silicon-carbon composite material was low, the pretreatment of the pore structure was insufficient, the proportion of micropores was low, some silicon-based material was deposited on the surface of the carbon matrix, and the grain size of the silicon-based material was large, which resulted in the Va of the silicon-carbon composite material being low. A / V B <1.4.

[0198] In Comparative Example 3, the first vapor deposition temperature was low during the preparation of the silicon-carbon composite material, resulting in insufficient pretreatment of the pore structure, a low proportion of micropores, and the deposition of some silicon-based material on the carbon matrix surface, leading to large silicon-based material grain size. Furthermore, the high third vapor deposition temperature caused further growth of silicon grains, resulting in a lower Vt of the final silicon-carbon composite material. A / V B <1.4.

[0199] In Comparative Example 4, the first vapor deposition temperature was low during the preparation of the silicon-carbon composite material, resulting in insufficient pretreatment of the pore structure and a low proportion of micropores. Furthermore, the second vapor deposition temperature was too high, accelerating the decomposition of the silicon-based material, with most of it deposited on the surface of the carbon matrix. This silicon grain aggregation promoted rapid grain growth, reducing the Va of the silicon-carbon composite material. A / V B <1.4. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered to be within the scope of this specification.

[0200] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A silicon-carbon composite material, characterized in that, include: A carbon matrix having a porous structure; and Silicon-based material, distributed within the porous structure of the carbon matrix; The grain size of the silicon-based material is ≤6nm; The pore size of the pore structure is 0.5 nm-8 nm; The silicon-based material accounts for 35%-60% of the mass of the silicon-carbon composite material.

2. The silicon-carbon composite material as described in claim 1, characterized in that, The silicon-carbon composite material was charged and discharged using coin cells. A graph was plotted showing the relationship between the differential value dQ / dV (obtained by differentiating the charge / discharge capacity Q from the voltage V) and the voltage V. The maximum value of dQ / dV between 0.26V and 0.35V was denoted as V. A Let the maximum value of the differential dQ / dV between 0.42V and 0.52V be denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.

40.

3. The silicon-carbon composite material as described in claim 1, characterized in that, 1.42≤V A / V B ≤1.90。 4. The silicon-carbon composite material as described in claim 1, characterized in that, 1.50≤V A / V B ≤1.70。 5. The silicon-carbon composite material as described in claim 1, characterized in that, The pore structure includes micropores with a pore size greater than or equal to 0.5 nm and less than 2 nm, and mesopores with a pore size of 2 nm to 8 nm.

6. The silicon-carbon composite material as described in claim 5, characterized in that, The number of micropores in the pore structure accounts for 60%-90%.

7. The silicon-carbon composite material as described in claim 1, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 2m². 2 / g -10 m 2 / g.

8. The silicon-carbon composite material according to any one of claims 1 to 7, characterized in that, The silicon-carbon composite material has at least one of the following characteristics: (1) The silicon-based material includes elemental silicon; (2) The shape of the silicon-based material includes one or more of the following: spherical, near-spherical, sheet-like, and linear. (3) The specific surface area of ​​the carbon matrix is ​​1000 m². 2 / g -2000 m 2 / g; (4) The volume distribution particle size Dv50 of the silicon-carbon composite material is 3μm-15μm; (5) The volume distribution particle size Dv90 of the silicon-carbon composite material is less than or equal to 50 μm; (6) The silicon-carbon composite material satisfies: 1≤(Dv90-Dv10) / Dv50≤3; (7) The tap density of the silicon-carbon composite material is 0.8 g / cm³. 3 -1.2g / cm 3 ; (8) The powder resistivity of the silicon-carbon composite material at 16 MPa is less than or equal to 5 Ω·m.

9. The silicon-carbon composite material as described in claim 8, characterized in that, At least a portion of the outer surface of the silicon-carbon composite material also includes a carbon coating layer.

10. The silicon-carbon composite material as described in claim 9, characterized in that, The carbon coating layer has at least one of the following characteristics: (1) The material of the carbon coating layer includes amorphous carbon; (2) The thickness of the carbon coating layer is 30nm-200nm.

11. A method for preparing a silicon-carbon composite material as described in any one of claims 1 to 10, characterized in that, Includes the following steps: Preparation of carbon substrates; The carbon substrate is subjected to a pore-forming process to obtain a carbon matrix A with a porous structure; The carbon matrix A with a porous structure is subjected to pore size control treatment to obtain a carbon matrix B with a porous structure. The silicon-carbon composite material is prepared by depositing silicon-based materials within the pore structure of a carbon matrix B with a porous structure.

12. The method for preparing the silicon-carbon composite material as described in claim 11, characterized in that, The silicon-carbon composite material was charged and discharged using coin cells. A graph was plotted showing the relationship between the differential value dQ / dV (obtained by differentiating the charge / discharge capacity Q from the voltage V) and the voltage V. The maximum value of dQ / dV between 0.26V and 0.35V was denoted as V. A Let the maximum value of the differential dQ / dV between 0.42V and 0.52V be denoted as V. B Then the silicon-carbon composite material satisfies: V A / V B ≥1.

40.

13. The method for preparing the silicon-carbon composite material as described in claim 12, characterized in that, The step of preparing the carbon substrate includes: subjecting the carbon material precursor to a first sintering treatment to prepare the carbon substrate.

14. The method for preparing the silicon-carbon composite material as described in claim 13, characterized in that, The method for preparing the carbon substrate satisfies at least one of the following conditions: (1) The temperature of the first sintering treatment is 400℃-800℃; (2) The first sintering treatment time is 1h-12h; (3) The atmosphere of the first sintering treatment includes an inert gas; (4) The inert gas includes one or more of nitrogen and argon; (5) The carbon material precursor includes one or more of resin-based carbon materials and biomass carbon materials.

15. The method for preparing the silicon-carbon composite material as described in claim 12, characterized in that, The hole-forming process includes: alkaline etching of the carbon substrate using an alkaline substance.

16. The method for preparing the silicon-carbon composite material as described in claim 15, characterized in that, The pore-forming process satisfies at least one of the following conditions: (1) The alkaline substance includes one or more of potassium hydroxide and sodium hydroxide; (2) The mass ratio of the alkaline substance to the carbon substrate is (2-6):

1.

17. The method for preparing the silicon-carbon composite material as described in claim 11, characterized in that, The steps of the pore size control process include: placing the carbon matrix A with the porous structure in a mixed gas containing a first carbon source and an inert gas, and performing a first vapor phase deposition.

18. The method for preparing the silicon-carbon composite material as described in claim 17, characterized in that, The temperature for the first vapor deposition is 800℃-1000℃.

19. The method for preparing the silicon-carbon composite material as described in claim 18, characterized in that, The temperature for the first vapor deposition is 850℃-950℃.

20. The method for preparing the silicon-carbon composite material as described in claim 17, characterized in that, The first vapor deposition time is 1h-4h.

21. The method for preparing the silicon-carbon composite material as described in claim 17, characterized in that, The volume ratio of the first carbon source to the inert gas is (2-5):

10.

22. The method for preparing the silicon-carbon composite material according to any one of claims 17 to 21, characterized in that, The first vapor deposition also includes at least one of the following conditions: (1) The first carbon source includes one or more of methane, ethylene and acetylene; (2) The inert gas includes one or more of nitrogen and argon.

23. The method for preparing the silicon-carbon composite material as described in claim 12, characterized in that, The porous carbon matrix B is placed in a mixed gas containing a silicon source and an inert gas for a second vapor phase deposition.

24. The method for preparing the silicon-carbon composite material as described in claim 23, characterized in that, The temperature of the second vapor deposition is 450℃-650℃.

25. The method for preparing the silicon-carbon composite material as described in claim 24, characterized in that, The temperature of the second vapor deposition is 500℃-600℃.

26. The method for preparing the silicon-carbon composite material as described in claim 23, characterized in that, The second vapor deposition time is 4h-8h.

27. The method for preparing the silicon-carbon composite material as described in claim 23, characterized in that, The silicon source accounts for 10%-40% of the volume of the mixed gas; and / or, the inert gas accounts for 60%-90% of the volume of the mixed gas.

28. The method for preparing the silicon-carbon composite material according to any one of claims 23 to 27, characterized in that, The second vapor deposition also includes at least one of the following conditions: (1) The positive difference between the pressure of the second vapor deposition and atmospheric pressure is 0.2 kPa-0.6 kPa; (2) The silicon source includes one or more of silane, ethane and propane; (3) The inert gas includes one or more of nitrogen and argon.

29. The method for preparing the silicon-carbon composite material according to any one of claims 15 to 16, characterized in that, Prior to the pore size control step, the method further includes: removing the alkaline substances remaining on the carbon substrate after the pore-forming treatment using an acidic substance.

30. The method for preparing the silicon-carbon composite material as described in claim 12, characterized in that, The preparation method further includes: placing the silicon-carbon composite material in a mixed gas containing a second carbon source and an inert gas, and performing a third vapor phase deposition to form a carbon coating layer on at least a portion of the outer surface of the silicon-carbon composite material.

31. The method for preparing the silicon-carbon composite material as described in claim 30, characterized in that, The third vapor deposition satisfies at least one of the following conditions: (1) The second carbon source includes one or more of methane, ethylene and acetylene; (2) The inert gas includes one or more of nitrogen and argon; (3) The volume percentage of the second carbon source in the mixed gas is 5%-20%; (4) The temperature of the third vapor deposition is 500℃-700℃; (5) The time for the third gas phase deposition is 1h-6h.

32. A secondary battery, characterized in that, Includes a negative electrode sheet, said negative electrode sheet comprising a silicon-carbon composite material as described in any one of claims 1 to 11 or a silicon-carbon composite material prepared by the method described in any one of claims 12 to 31.

33. An electrical device, characterized in that, Includes the secondary battery as described in claim 32.

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