A silicon-carbon material and its preparation method, a negative electrode, and a battery

Abstract

This application belongs to the field of new energy battery technology, specifically relating to a silicon-carbon material and its preparation method, a negative electrode sheet, and a battery. The silicon-carbon material provided in this application includes a core, which comprises porous carbon and silicon-based particles located within the pores of the porous carbon. A plurality of diamond particles are disposed within the porous carbon, with an average particle size D1 nm satisfying 5 ≤ D1 ≤ 500. The elastic modulus a GPa of the silicon-carbon material satisfies 10 ≤ a ≤ 80. The silicon-carbon material contains doping elements, including at least one of nitrogen and phosphorus. This application, by placing diamond particles within porous carbon and controlling the elastic modulus of the silicon-carbon material, can improve the stability of the diamond particles and the surrounding porous carbon, and form a continuous, highly efficient thermally conductive network. The doped nitrogen and / or phosphorus elements can effectively compensate for the decrease in electronic conductivity of the porous carbon caused by the diamond particles, which is beneficial to the cycle performance and thermal safety of the battery.

Description

Technical Field

[0001] This application belongs to the field of new energy battery technology, specifically relating to a silicon-carbon material and its preparation method, a negative electrode sheet, and a battery. Background Technology

[0002] Graphite is currently the most widely used anode material in lithium-ion batteries due to its low cost, stable structure, and excellent electronic conductivity; however, its theoretical specific capacity is relatively low (372 mAh g⁻¹). -1 This makes it difficult to meet the urgent need for high energy density in electric vehicles and energy storage systems; silicon materials, with their extremely high theoretical specific capacity (4200 mAh g⁻¹), are a better choice. -1 Silicon, with its low lithium insertion / extraction potential and isotropic lithium storage mechanism, is considered an ideal choice for the next generation of high-energy-density lithium-ion battery anode materials. However, silicon materials undergo drastic volume expansion (300%) during electrochemical cycling, leading to problems such as silicon particle crushing, repeated rupture and reconstruction of the solid electrolyte interphase (SEI) film, and loss of electrical contact of active materials. This severely deteriorates the cycle stability and thermal safety of the battery. Existing technologies load silicon materials onto porous carbon frameworks using chemical vapor deposition (CVD), enabling the porous carbon framework to serve as both a conductive framework and an expansion buffer layer. However, this technique has limited improvement on the cycle performance and thermal safety of silicon-carbon materials. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this application is to overcome the defects of poor cycle performance and thermal safety of batteries made of silicon-carbon materials in the prior art, thereby providing a silicon-carbon material and preparation method, negative electrode sheet, and battery.

[0004] Therefore, this application provides the following technical solution.

[0005] According to a first aspect of this application, a silicon-carbon material is provided, comprising a core, the core comprising porous carbon and silicon-based particles located within the pores of the porous carbon, wherein a plurality of diamond particles are disposed within the porous carbon. The average particle size of the diamond particles is denoted as D1 nm, which satisfies 5 ≤ ​​D1 ≤ 500; The elastic modulus of the silicon-carbon material is denoted as a GPa, which satisfies 10≤a≤80; The silicon-carbon material contains doping elements, including at least one of nitrogen and phosphorus.

[0006] In some embodiments, the silicon-carbon material also satisfies at least one of the following (1)-(5): (1) 20≤D1≤200; (2) 15≤a≤50; (3) Based on the mass of the porous carbon, the mass content of nitrogen element is denoted as n%, which satisfies 0.2≤n≤3; (4) Based on the mass of the porous carbon, the mass content of the phosphorus element is denoted as p%, which satisfies 0.1≤p≤2; (5) Based on the mass of the porous carbon, the total mass content of the diamond particles is denoted as m%, which satisfies 0.5≤m≤15.

[0007] In some embodiments, the silicon-carbon material also satisfies at least one of the following (1)-(5): (1) 30≤D1≤100; (2) 20 ≤ a ≤ 40; (3) 0.5 ≤ n ≤ 2; (4) 0.2 ≤ p ≤ 1; (5) 2≤m≤8.

[0008] In some embodiments, the porous carbon also satisfies at least one of the following (1)-(5): (1) The porous carbon has micropores, mesopores and macropores. Based on the pore volume of the porous carbon, the volume ratio of micropores is 80%-99%, the volume ratio of mesopores is 1%-20%, and the volume ratio of macropores is 0%-5%. (2) The average pore size of the porous carbon is 1 nm-3 nm; (3) The specific surface area of ​​the porous carbon is 1500 m². 2 / g-2500m 2 / g, preferably 1800m 2 / g-2200m 2 / g; (4) The pore volume of the porous carbon is 0.6 cm³. 3 / g-1cm 3 / g, preferably 0.7cm 3 / g-0.9cm 3 / g; (5) The doping element is nitrogen.

[0009] In some embodiments, the silicon-carbon material further includes a carbon layer that covers at least a portion of the surface of the core, the carbon layer having a thickness of 2 nm to 20 nm.

[0010] Furthermore, in some embodiments, the thickness of the carbon layer is 5nm-10nm; Furthermore, in some embodiments, the carbon layer is located on at least a portion of the surface of the silicon-based particles.

[0011] Furthermore, in some embodiments, the carbon layer is located on at least a portion of the surface of the inner wall of the porous carbon pores.

[0012] In some embodiments, the silicon-carbon material also satisfies at least one of the following (1)-(5): (1) Based on the mass of the silicon-carbon material, the mass content of silicon element is denoted as w%, which satisfies 40≤w≤70; preferably, 45≤w≤60. (2) The volume median particle size of the silicon-carbon material is denoted as D2 μm, which satisfies 3≤D2≤15; preferably, 5≤D2≤12; more preferably, 7≤D2≤9; (3) The particle size distribution Span value of the silicon-carbon material is 0.4-1; (4) The sphericity of the silicon-carbon material is 0.85-1.0; preferably, it is 0.9-0.95; (5) The Raman spectrum of the silicon-carbon material satisfies: 0.7 ≤ I D1 / I G1 ≤1.2, and / or, 0.05≤I G2 / I G1 ≤0.5, where I D1 This indicates that the Raman displacement is between 1340 and 1360 cm. -1 The peak intensity of the Raman peak at the location, I G1 This indicates that the Raman displacement is between 1575 and 1590 cm. -1 The peak intensity of the Raman peak at the location, the I G2 This indicates that the Raman shift is between 1329 and 1335 cm. -1 Peak intensity of the Raman peak at the location.

[0013] According to a second aspect of this application, a method for preparing a silicon-carbon material is also provided, comprising the following steps: (1) Mix porous carbon precursor, organic solvent, diamond particles and additives, dry, sinter, dry and sinter to obtain porous carbon; (2) First vapor deposition is performed on porous carbon to obtain silicon-carbon material; The additive includes at least one of a nitrogen source and a phosphorus source, and the average particle size D1 of the diamond particles is 5nm-500nm.

[0014] In some embodiments, the first vapor deposition includes introducing a silicon source in a rotary kiln, fluidized bed, or tubular furnace at a temperature of 350°C-600°C.

[0015] In some embodiments, after the first vapor deposition, a second vapor deposition is further included, the second vapor deposition satisfying one of the following (A)-(C): (A) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a first carbon source is introduced; (B) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a second carbon source is introduced; (C) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a first carbon source is introduced; then a second carbon source is introduced.

[0016] Furthermore, the first carbon source includes an aromatic ring precursor and an unsaturated hydrocarbon precursor, wherein the unsaturated hydrocarbon precursor includes unsaturated hydrocarbon precursors with 2-10 carbon atoms.

[0017] Furthermore, the aromatic ring-containing precursor includes aromatic hydrocarbon-containing precursors.

[0018] Furthermore, the aromatic hydrocarbon precursor includes toluene.

[0019] Furthermore, the unsaturated hydrocarbon precursor includes at least one of acetylene and ethylene.

[0020] According to a third aspect of this application, a negative electrode sheet is also provided, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising the silicon-carbon material described in the first aspect, or a silicon-carbon material prepared by the method described in the second aspect.

[0021] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 -1.75g / cm 3 .

[0022] In some embodiments, the negative electrode active material further includes a carbon-based material, which includes at least one of graphite, soft carbon, and hard carbon; further, the carbon-based material is graphite; further, the graphite includes primary graphite particles; further, the average particle size of the primary graphite particles is denoted as D3 μm, satisfying 5 ≤ D3 ≤ 11; further, the specific surface area of ​​the primary graphite particles is 0.5 m². 2 / g-3m 2 / g.

[0023] According to a fourth aspect of this application, a battery is also provided, comprising a positive electrode, a separator, an electrolyte, and a negative electrode as described in the third aspect.

[0024] Furthermore, in some embodiments, the electrolyte includes an additive, which includes at least one of triargyl phosphate and fluoroethylene carbonate; Furthermore, based on the mass of the electrolyte, the mass content of the triargyl phosphate is 0.5%-5%.

[0025] Furthermore, based on the mass of the electrolyte, the mass content of the fluoroethylene carbonate is 5%-15%.

[0026] The technical solution of this application has the following advantages: The silicon-carbon material provided in this application includes a core, which comprises porous carbon and silicon-based particles located inside the pores of the porous carbon. The porous carbon contains a plurality of diamond particles, the average particle size of which is denoted as D1 nm and satisfies 5 ≤ ​​D1 ≤ 500. The elastic modulus of the silicon-carbon material is denoted as a GPa and satisfies 10 ≤ a ≤ 80. The silicon-carbon material contains doping elements, which include at least one of nitrogen and phosphorus.

[0027] This application, by incorporating diamond particles (5≤D1≤500) with high thermal conductivity and good mechanical properties into porous carbon, effectively controls the elastic modulus compatibility between diamond particles and porous carbon, giving the silicon-carbon material a better elastic modulus (10≤a≤80). This allows the diamond particles to be fully and uniformly encapsulated by the porous carbon, reducing stress concentration points and thus microcracks. Simultaneously, it ensures the formation of a continuous and efficient thermally conductive network by the diamond particles, and also creates hard constraint points to restrain the volume expansion of silicon-based particles within the pores, thereby improving the structural stability of the silicon-carbon material and benefiting the cycle performance and thermal safety of batteries made from it. Furthermore, by incorporating nitrogen and / or phosphorus elements into the silicon-carbon material, the electronegativity difference between N, P, and carbon atoms is utilized to alter the charge distribution and electronic structure of the silicon-carbon material, particularly the porous carbon surface, creating more conductive active sites and constructing rapid electron transport channels. This effectively compensates for the decrease in electronic conductivity of the silicon-carbon material caused by diamond particles, thereby improving the cycle performance of the battery.

[0028] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1This is a schematic diagram of the structure of the silicon-carbon material of this application; Figure label: 1-Silicon-carbon material; 11-Porous carbon; 12-Silicon-based particles; 13-Carbon layer; 14-Doped element; 111-Diamond particles. Detailed Implementation

[0031] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0032] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0033] To address the shortcomings in thermal safety and cycling performance of existing silicon-carbon materials, according to a first aspect of this application, a silicon-carbon material is provided, comprising a core. The core includes porous carbon and silicon-based particles located within the pores of the porous carbon. The porous carbon contains a plurality of diamond particles. The average particle size of the diamond particles is denoted as D1 nm, which satisfies 5 ≤ ​​D1 ≤ 500; The elastic modulus of the silicon-carbon material is denoted as a GPa, which satisfies 10≤a≤80; The silicon-carbon material contains doping elements, including at least one of nitrogen and phosphorus.

[0034] This study found that diamond particles possess high thermal conductivity and good mechanical properties. When incorporated into porous carbon, they form an efficient heat-conducting network and hard confinement points to restrain the volume expansion of silicon-based particles within the pores. However, experiments have shown that diamond also has a high elastic modulus, significantly different from that of porous carbon. During charging and discharging, the periodic expansion-contraction stress generated by the silicon-based particles during lithium insertion or extraction causes significant stress concentration at the interface between the diamond particles and the surrounding porous carbon due to the difference in elastic modulus. This, in turn, induces the initiation and propagation of microcracks. As the number of cycles increases, these microcracks gradually connect, eventually causing the silicon-carbon material to undergo overall structural fragmentation in the later stages of cycling. This exposes a large amount of fresh surface, triggering violent electrolyte side reactions and causing a sharp drop in battery cycle retention. It also causes diamond particles to detach from porous carbon, cutting off the originally designed heat conduction pathways. The thermal conductivity of diamond cannot be effectively utilized, and heat accumulates inside the cell, making it difficult to dissipate, and significantly deteriorating thermal safety. In addition, diamond itself has poor electrical conductivity, and introducing it into porous carbon will also reduce the overall electronic conductivity of the silicon-carbon material, leading to increased electrode polarization, which also affects the battery's cycle performance.

[0035] Furthermore, this study found that by controlling the average particle size D1 of the diamond particles (5≤D1≤500), the elastic modulus compatibility between the diamond particles and porous carbon can be effectively regulated, resulting in silicon-carbon materials with better elastic modulus (10≤a≤80) and better structural stability during cycling. When 5≤D1≤500, the diamond particles can be fully and uniformly encapsulated by the porous carbon. This full and uniform encapsulation means that the diamond particles are essentially encapsulated by the porous carbon, with as little of the diamond particle surface exposed to the pores of the porous carbon and / or the outer surface of the porous carbon and / or the outer surface of the silicon-carbon material. Such thorough and uniform encapsulation reduces stress concentration points, thereby reducing microcracks and ensuring the continuity of the thermal conductivity network, effectively improving the thermal safety and cycle performance of batteries made from silicon-carbon materials. If D1 is greater than 500, diamond particles are difficult to be effectively encapsulated by porous carbon (effective encapsulation means thorough and uniform encapsulation), resulting in more significant stress concentration points and poor dispersion uniformity, which is detrimental to the cycle performance and thermal safety of the battery. If D1 is less than 5, the specific surface area of ​​diamond particles is too large, making them prone to migration and aggregation due to excessive surface energy, making it difficult to distribute evenly in porous carbon, and also increasing the initiation sites for microcracks, thus deteriorating the cycle performance and thermal safety of the battery. At the same time, the addition of nitrogen and / or phosphorus elements to silicon-carbon materials utilizes the electronegativity difference between N, P and carbon atoms to change the charge distribution and electronic structure of silicon-carbon materials, especially the porous carbon surface, creating more conductive active sites and constructing fast electron transport channels. This effectively compensates for the decrease in electronic conductivity of silicon-carbon materials caused by diamond particles, thereby improving the cycle performance of the battery.

[0036] If a is greater than 80, the silicon-carbon material is brittle. When the silicon-based particles expand in volume, the silicon-carbon material has a weak buffering capacity and is unable to absorb the expansion stress, resulting in cracking, which is detrimental to the cycle performance and thermal safety of the battery. If a is less than 10, the silicon-carbon material has a low elastic modulus and low stiffness. It cannot effectively constrain the volume expansion of the silicon-based particles. It also indicates that the elastic modulus of porous carbon and diamond particles are significantly different, resulting in poor compatibility and easy microcracks, which seriously affect the cycle performance and thermal safety of the battery.

[0037] The average particle size D1 of the diamond particles can be measured using conventional methods in the art. For example, silicon-carbon material is prepared using a cross-sectional ion polishing (CP) instrument, and the diamond particles within are observed using a high-resolution transmission electron microscope (HRTEM). At least 20 diamond particles are randomly selected from the obtained images, and their equivalent circle diameters are measured using image processing software (e.g., ImageJ). The average value is then taken as the average particle size D1 of the diamond particles. Exemplarily, the average particle size D1 (in nm) of the diamond particles can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, or 220 nm. The values ​​can be 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, etc., or values ​​within the range of any two of the above values. It should be noted that the diamond particles used in this application can be obtained using conventional methods in the art, and this application does not impose specific limitations; for example, they can be synthesized using high-temperature high-pressure methods or detonation methods.

[0038] The elastic modulus α of the silicon-carbon material can be measured using conventional methods in the art. For example, the silicon-carbon material can be fixed with epoxy resin, polished to expose the particle cross-section, and at least 10 different silicon-carbon materials can be selected for testing under an inert atmosphere. The cross-section of the silicon-carbon material can be measured using a nanoindentation test in force spectroscopy mode of an atomic force microscope (AFM). The test depth is controlled to be 1 / 10-1 / 5 of the diameter of the silicon-carbon material. Force-displacement curves are obtained, and the elastic modulus is calculated by fitting an Oliver-Pharr model, then the average value is taken. For example, the elastic modulus α (in GPa) of the silicon-carbon material can be 10, 11, 12, 13, 14, or 15. Values ​​of 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 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, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, etc., or values ​​within the range of any two of the above values.

[0039] In some embodiments, the doping element is nitrogen. This can further improve the microscopic electron cloud arrangement, improve the overall conductivity of the material, and enhance the cycle performance of the battery.

[0040] In some implementations, 20≤D1≤200; in particular, satisfying 30≤D1≤100 can further improve the cycle performance and thermal safety of the battery.

[0041] In some implementations, 15≤a≤50; particularly, 20≤a≤40; can further improve the cycle performance and thermal safety of the battery.

[0042] In some embodiments, the mass content of nitrogen element is denoted as n%, based on the mass of the silicon-carbon material, satisfying 0.2≤n≤3; particularly, satisfying 0.5≤n≤2. This can improve the electronic conductivity of the silicon-carbon material and reduce polarization while ensuring its structural stability, thereby further improving the cycle performance of the battery. The mass content of nitrogen element n% can be measured using conventional methods in the art, for example, by using an elemental analyzer or X-ray photoelectron spectroscopy (XPS). When using an elemental analyzer, the sample (silicon-carbon material) is burned at high temperature in pure oxygen, and the content of the generated N oxides is detected. When using XPS testing, the area of ​​the N 1s characteristic peak is analyzed, and the relative content of nitrogen is calculated by combining the sensitivity factor. For example, the mass content of nitrogen n% can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or a value within the range of any two of the above values.

[0043] In some embodiments, the mass content of phosphorus is denoted as p%, based on the mass of the silicon-carbon material, satisfying 0.1≤p≤2; particularly, 0.2≤p≤1. This can improve the electronic conductivity of the silicon-carbon material and reduce polarization while ensuring its structural stability, thereby further improving the cycle performance of the battery. The mass content of phosphorus, p%, can be measured using conventional methods in the art, such as elemental analysis or X-ray photoelectron spectroscopy (XPS). When using an elemental analyzer, the sample (silicon-carbon material) is burned at high temperature in pure oxygen, and the content of the generated P oxides is detected. When using XPS testing, the area of ​​the P 2p characteristic peak is analyzed, and the relative content of phosphorus is calculated by combining the sensitivity factor. For example, the mass content of phosphorus p% can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc., or values ​​within the range of any two of the above values.

[0044] In some embodiments, the total mass content of the diamond particles, based on the mass of the porous carbon, is denoted as m%, satisfying 0.5 ≤ m ≤ 15, and particularly satisfying 2 ≤ m ≤ 8. This effectively leverages the effect of diamond particles constraining the volume expansion of silicon-based particles, and the constructed thermally conductive network exhibits good continuity, further enhancing the battery's cycle performance and thermal safety. If m is greater than 15, the distance between the diamond particles is too close, increasing the difficulty of controlling the elastic modulus. An increase in the elastic modulus may lead to microcracks during cycling and affect the electronic conductivity of the porous carbon, thus impacting the battery's cycle performance and thermal safety. If m is less than 0.5, the improvement effect of the diamond particles is limited. For example, the total mass content of diamond particles, m%, can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a value within any two of the above ranges.

[0045] In some embodiments, the porous carbon has micropores, mesopores, and macropores. Based on the pore volume of the porous carbon, the volume ratio of micropores is 80%-99%, the volume ratio of mesopores is 1%-20%, and the volume ratio of macropores is 0%-5%. The terms micropores, mesopores, and macropores are conventionally defined in the art, i.e., smaller than 2 nm is micropore, 2-50 nm is mesopore, and larger than 50 nm is macropore. The porous carbon provided in this application, with its micropore-dominated pore structure, provides an extremely high specific surface area, which is beneficial for the uniform anchoring and confined deposition of silicon-based particles within the micropores. The confinement effect of the micropores effectively suppresses the agglomeration and growth of silicon particles during deposition and cycling, thereby effectively constraining the volume expansion of silicon-based particles. A small number of mesopores and macropores serve as transport channels to help the electrolyte enter the micropore region, improving ion diffusion dynamics. Furthermore, the diamond particles set in the porous carbon in this application are encapsulated by the porous carbon and do not occupy the pore space, so their mechanical properties and thermal conductivity are not affected by the pore type.

[0046] For example, the volume percentages of micropores, mesopores, and macropores in porous carbon can be measured using conventional methods in the art, such as a TriStar II surface area analyzer or N2 adsorption-desorption testing combined with t-plot analysis. For example, the volume percentage of micropores can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or values ​​within any two of the above ranges. For example, the volume percentage of mesopores can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or values ​​within any two of the above ranges. For example, the volume percentage of the macropore can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a value within the range of any two of the above values.

[0047] In some embodiments, the average pore size of the porous carbon is 1 nm to 3 nm; this further facilitates the confined deposition of silicon-based particles, improves deposition efficiency, deposition uniformity, and structural stability of silicon-based materials, while reserving appropriate buffer space for the expansion of silicon lithium intercalation, reducing the pulverization of silicon-based particles, and further aiding in the penetration and wetting of the electrolyte, thereby improving the cycle performance and thermal safety of the battery; the average pore size of the porous carbon can be measured using conventional methods in the art, for example, by using N2 adsorption-desorption testing and fitting the pore size distribution curve using an NLDFT model; exemplaryly, the average pore size (unit nm) of the porous carbon can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, etc., or a value within the range of any two of the above values.

[0048] In some embodiments, the porous carbon has a specific surface area of ​​1500 m². 2 / g-2500m 2 / g, especially 1800m 2 / g-2200m 2 / g; It can provide sufficient silicon deposition sites, enabling silicon-carbon materials to fully utilize their high specific capacity characteristics while effectively encapsulating diamond particles. Furthermore, the porous carbon exhibits good mechanical strength, further enhancing the battery's cycle performance and thermal safety. Exemplarily, the specific surface area of ​​the porous carbon can be measured using conventional methods in the art, such as N2 adsorption-desorption testing combined with BET model calculations, or measurement using a TriStar II specific surface area analyzer. Exemplarily, the specific surface area of ​​porous carbon (unit: m²) 2 / g) can be 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500 or a value within the range of any two of the above values.

[0049] In some embodiments, the pore volume of the porous carbon is 0.6 cm³. 3 / g-1cm 3 / g, especially 0.7cm 3 / g-0.9cm 3 / g; This indicates that the porous carbon has a sufficient number of micropores, providing ample deposition space for silicon-based materials, effectively improving the energy density of the battery. Simultaneously, the porous carbon exhibits good mechanical strength and effectively encapsulates diamond particles, thereby effectively leveraging the improving effects of the diamond particles, enhancing the cycle stability of the silicon-carbon material, and further improving the cycle performance and thermal safety of the battery. Exemplarily, the pore volume of the porous carbon can be measured using conventional methods in the art, such as using a TriStar II surface area analyzer or an N2 adsorption-desorption test, calculating the adsorption amount at a relative pressure P / P0≈0.99. Exemplarily, the pore volume of the porous carbon (unit: cm³) 3 / g) can be 0.6, 0.7, 0.8, 0.9, 1, or a value within the range of any two of the above values.

[0050] In some embodiments, the silicon-carbon material further includes a carbon layer covering at least a portion of the surface of the core. The carbon layer has a thickness of 2 nm to 20 nm, particularly 5 nm to 10 nm. This reduces ion diffusion resistance and improves the structural stability of the silicon-carbon material, while further reducing the possibility of contact between silicon-based particles and the electrolyte, reducing side reactions, and further improving the electronic conductivity of the silicon-carbon material. This is beneficial for further improving the cycle performance of the battery. In addition, the carbon layer can further reduce the direct contact between silicon-based particles and water during the negative electrode processing, reducing bubble generation and improving the processing performance of the negative electrode. Exemplarily, the thickness of the carbon layer can be measured using conventional methods in the art, such as high-resolution transmission electron microscopy (HRTEM). The silicon-carbon material is fixed with epoxy resin and ultrathinly sliced. The carbon coating layer at the particle edge is observed under HRTEM, and the coating layer thickness is measured. At least 10 different locations are selected and the average value is taken. For example, the thickness of the carbon layer (in nm) can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., or a value within the range of any two of the above values.

[0051] Furthermore, in some embodiments, the carbon layer is located on at least a portion of the surface of the silicon-based particles. Further, in some embodiments, the carbon layer is located on at least a portion of the surface of the inner wall of the porous carbon pores. The carbon layer helps buffer the volume expansion of the silicon-based particles, improves the structural stability of the porous carbon, and further enhances the cycle performance of the battery. It should be noted that the porous carbon precursor decomposes and shrinks during pyrolysis, and microcracks may form in the carbon layer around the diamond particles. The carbon layer further provided in this application can fill these microcracks, thereby improving the core, especially the structural stability of the porous carbon therein (i.e., the porous carbon has microcracks, and the carbon layer is disposed within the microcracks). It can also further help regulate the elastic modulus of the silicon-carbon material, further improving the cycle performance of the battery.

[0052] like Figure 1 As shown, the silicon-carbon material 1 of this application includes porous carbon 11, silicon-based particles 12, carbon layer 13, and doping element 14, wherein the porous carbon 11 includes diamond particles 111.

[0053] In some embodiments, the mass content of silicon element is denoted as w%, based on the mass of the silicon-carbon material, satisfying 40 ≤ w ≤ 70; particularly 45 ≤ w ≤ 60. This allows for full utilization of silicon's high specific capacity, uniform deposition within micropores and mesopores, and a moderate silicon content in the micropores. This provides sufficient buffer space and reduces surface silicon floating, preventing expansion stress generated during cycling from directly acting on the porous carbon, especially the interface between diamond and surrounding porous carbon, reducing the possibility of microcracks and preventing frequent collisions and pulverization of silicon-based particles, further improving the battery's energy density, cycle performance, and thermal safety. For example, the mass content w% of silicon element in the silicon-carbon material can be obtained through thermogravimetric (TG) testing. A sample (silicon-carbon material) with a mass of m1 is placed in a TG tester, heated to 900°C at a rate of 5°C / min in air, held for 30 min, and the remaining sample mass m2 is obtained. The calculated w% is (m2 / m1 × 28 / 60). For example, the mass content w% of silicon element in silicon-carbon material can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, etc., or values ​​within the range of any two of the above values.

[0054] In some embodiments, the median volumetric particle size of the silicon-carbon material is denoted as D2 μm, satisfying 3≤D2≤15; further, 5≤D2≤12; and even further, 7≤D2≤9. This balances the specific surface area and ion transport distance of the silicon-carbon material, thereby balancing its structural stability and ion transport performance. It provides a suitable contact area with the electrolyte, reducing side reactions, while also having a shorter ion transport distance, improving kinetic performance, further enhancing the battery's cycle performance and thermal safety. Furthermore, it increases the packing density, thereby increasing the battery's energy density. For example, the median volumetric particle size D2 of the silicon-carbon material can be obtained by measuring with a laser particle size analyzer. For instance, the silicon-carbon material can be dispersed in ethanol, ultrasonically dispersed, and then measured using a laser particle size analyzer. For example, the median volumetric particle size D2 (in μm) of the silicon-carbon material can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or a value within any two of the above ranges.

[0055] In some embodiments, the particle size distribution span value of the silicon-carbon material is 0.4-1; the span value is calculated using the formula (Dv90-Dv10) / Dv50, which characterizes the width of the particle size distribution. Here, Dv50 is the volume median particle size D2 of the silicon-carbon material. When the particle size distribution span value is 0.4-1, the silicon-carbon material has a high particle size concentration, which is beneficial for forming a uniform stacking structure in the negative electrode sheet. This avoids uneven coating density and local compaction differences caused by excessively wide particle size distribution, thereby ensuring uniform current density and stress distribution during charging and discharging. It also ensures that the thermal conductivity and mechanical constraint of diamond particles in porous carbon remain consistent at the electrode level, fully leveraging the improvement effect of diamond particles, further reducing the occurrence of local overcharging or stress concentration, and further improving the cycle performance and thermal safety of the battery.

[0056] It should be noted that Dv10 is the particle size corresponding to a cumulative volumetric distribution percentage of 10% for silicon-carbon materials; Dv50 is the particle size corresponding to a cumulative volumetric distribution percentage of 50% for silicon-carbon materials, i.e., D2; and Dv90 is the particle size corresponding to a cumulative volumetric distribution percentage of 90% for silicon-carbon materials. Dv10, Dv50, and Dv90 can be measured using a Malvern Mastersizer 3000 laser particle size analyzer. For example, the particle size distribution Span value of silicon-carbon materials can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value within any two of the above ranges.

[0057] In some embodiments, the sphericity of the silicon-carbon material is 0.85-1.0, particularly 0.9-0.95. This further helps to ensure uniform distribution of the silicon-carbon material, thereby uniformly distributing the stress generated during lithium insertion or extraction within the silicon-carbon material, reducing stress concentration at particle edges, thus reducing microcracks in the silicon-carbon material (especially the porous carbon within it), and improving the interfacial stability between the diamond particles and the surrounding porous carbon. It also improves the uniformity of electrode compaction density and coating surface density, thereby enhancing the cycle performance and energy density of the battery. For example, the sphericity of the silicon-carbon material can be obtained by measuring the ratio of the maximum to the minimum diameter of the particle cross-section using a scanning electron microscope (SEM). Specifically, the silicon-carbon material is fixed with epoxy resin and polished. The lengths of the maximum and minimum diameter points of the same particle cross-section are measured in SEM backscatter mode. The ratio of these two values ​​is the sphericity of the particle. At least 100 particles are randomly measured, and the average value is taken. For example, the sphericity of silicon-carbon materials can be 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.95, 0.96, 0.97, 0.98, 0.9, 1, or a value within the range of any two of the above values.

[0058] In some embodiments, the Raman spectrum of the silicon-carbon material satisfies: 0.7 ≤ I D1 / I G1 ≤1.2, in some implementations, 0.05≤I G2 / I G1 ≤0.5, where I D1 This indicates that the Raman displacement is between 1340 and 1360 cm. -1 The peak intensity of the Raman peak at the location, I G1 This indicates that the Raman displacement is between 1575 and 1590 cm. -1 The peak intensity of the Raman peak at the location, the I G2 This indicates that the Raman shift is between 1329 and 1335 cm. -1 The peak intensity of the Raman peak at the location. When 0.05 ≤ I G2 / I G1 ≤0.5, I G2 Reflects the characteristic peak intensity of diamond, I G1 The characteristic peak intensity reflects that the diamond particles are uniformly distributed and effectively encapsulated within the porous carbon (effective encapsulation means sufficient and uniform encapsulation). The graphitization structure of the porous carbon remains intact, further enhancing the continuity and sufficiency of the thermally conductive network constructed by the diamond particles, as well as the pinning reinforcement effect. This also reduces the risk of microcracks caused by diamond particle agglomeration, thus further improving the battery's cycle performance and thermal safety. It should be noted that I can be controlled by adjusting the average particle size D1 of the diamond particles and the total mass content m of the diamond particles. G2 / I G1 ;if I G2 / I G1 If I is less than 0.05, the continuity of the thermal conductivity network of the diamond particles is generally poor. G2 / I G1 If the value is greater than 0.5, the diamond particles will have poor uniformity of distribution in porous carbon and may agglomerate.

[0059] When 0.7≤I D1 / I G1 ≤1.2, I D1 I reflects the defect peak intensity of porous carbon. G1 The intensity of the characteristic peaks reflects that porous carbon has an appropriate amount of defect sites and conductive active sites. This means that the doping elements effectively compensate for the conductivity loss caused by diamond particles and control the number of defect sites. This improves both cycle performance and initial coulombic efficiency, preventing excessive consumption of active lithium in the first cycle. It should be noted that Ig can be controlled by adjusting the carbon layer thickness, the mass content of nitrogen (n), and the mass content of phosphorus (p). D1 / I G1 . If ID1 / I G1 A value less than 0.7 may indicate insufficient nitrogen or phosphorus doping, resulting in minimal compensation for conductivity. If I... D1 / I G1 When the value is greater than 1.2, porous carbon has more defect sites and conductive active sites, resulting in more SEI film formation.

[0060] For example, the Raman spectrum of the silicon-carbon composite particles can be obtained by measuring with a Raman spectrometer, using a 532 nm excitation wavelength laser, with a test wavenumber range of 800 cm⁻¹. -1 -2000cm -1 Peak fitting was performed on the spectrum to extract I. G1 I D1 and I G2 Calculate the ratios separately. For example, I D1 / I G1 It can be 0.7, 0.8, 0.9, 1, 1.1, 1.2, etc., or a value within the range of any two of the above values. For example, I... G2 / I G1 It can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, or a value within the range of any two of the above values.

[0061] In some embodiments, the specific surface area of ​​the silicon-carbon material is less than 1 m². 2 / g; further, 0.3m 2 / g-0.8m 2 / g; further, 0.4m 2 / g-0.6m 2 / g; This reduces the contact area between the silicon-carbon material and water, thereby suppressing the generation of hydrogen bubbles and ensuring coating uniformity and electrode processing performance. Simultaneously, a lower specific surface area minimizes side reactions with the electrolyte during electrochemical cycling, improving initial coulombic efficiency and cycle performance. Exemplarily, the specific surface area of ​​the silicon-carbon material can be measured using conventional methods in the art, such as a TriStar II surface area analyzer or by N2 adsorption-desorption detection. Before N2 adsorption-desorption detection, the sample is vacuum degassed at 300°C for 3 hours, and the specific surface area is calculated using the BET model. Exemplarily, the specific surface area of ​​the silicon-carbon material (unit: m²) 2 / g) can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value within the range of any two of the above values.

[0062] In some embodiments, the pore volume of the silicon carbide material is 0.01 cm³. 3 / g-0.1cm 3 / g; especially 0.02cm 3 / g-0.06cm 3 / g; While ensuring energy density, it can provide an appropriate buffer space for silicon-based particles, thereby reducing microcracks in porous carbon caused by the volume expansion of silicon-based particles, and further improving the cycle performance of the battery. Exemplarily, the pore volume of the silicon-carbon material can be measured using conventional methods in the art, such as using a TriStar II surface area analyzer or by N2 adsorption-desorption detection. Before N2 adsorption-desorption detection, the sample is vacuum degassed at 300°C for 3 hours, and the adsorption amount at a relative pressure P / P0≈0.99 is used for calculation. Exemplarily, the pore volume of the silicon-carbon material (unit: cm³) 3 / g) can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc., or a value within the range of any two of the above values.

[0063] In some embodiments, the true density of the silicon-carbon material is 1.7 g / cm³. 3 -2.2g / cm 3 Especially 1.9g / cm 3 -2.1g / cm 3 This design ensures both the specific capacity of the silicon-carbon material and provides ample buffer space for the volume expansion of silicon-based particles, thereby improving the structural stability of the silicon-carbon material. It also enhances the mechanical transfer properties between the diamond particles and the surrounding porous carbon, further improving the structural stability of the silicon-carbon material and reducing microcracks. For example, the true density of the silicon-carbon material can be measured using conventional methods in the art, such as the gas displacement method. For example, the true density of the silicon-carbon material (unit: g / cm³) is... 3 () can be 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, etc., or a value within the range of any two of the above values.

[0064] In some embodiments, the X-ray diffraction pattern of the porous carbon shows diffraction peaks within a 2θ diffraction angle range of 0.8°–4.2°; the half-width at half-maximum (WHM) of these diffraction peaks along the 2θ direction is 0.08°–0.15°. This indicates that the porous carbon possesses an ordered microporous structure, exhibits good structural stability, and facilitates the uniform deposition of silicon-based particles, further enhancing the cycle performance of the battery.

[0065] In some embodiments, the connectivity of the porous carbon is 0.6-1.2; the porous carbon forms a continuous network through micropores, mesopores and macropores, which is beneficial for the uniform deposition of silicon-based particles in the porous carbon channels and improves the wettability of the electrolyte. In addition, the porous carbon has high mechanical strength, which can further improve the thermal conductivity and mechanical improvement effect of diamond particles, and further improve the cycle performance and thermal safety of the battery.

[0066] The connectivity of the porous carbon matrix can be obtained using conventional testing methods in the art, such as small-angle X-ray scattering (SAXS) and fitting, specifically as follows: SAXS curves in the range of 0.015 to 1.1 Å⁻¹ were measured using a Xeuss 2.0 (X enocs) detector under Cu Kα radiation at a power of 30 W, a wavelength of 1.54189 Å, an exposure time of 150 s, a Pilatus 3R 300K detector, and a single pixel size of 172 μm. All acquired SAXS curves were obtained by measuring the volume scattering cross section (I, in cm⁻¹) using standard methods with glassy carbon standard samples. -1 The calibration of the sample attenuation cross section (I', in cm⁻¹) was then normalized to the effective volume density ρ (determined by the sample attenuation method) to convert it into a specific scattering cross section (I', in cm⁻¹). 2 / g). The curve was fitted using the Teubner-Strey model, and the connectivity (fa) of the porous carbon matrix was calculated using the following formula, where c1, c2, and I0 are adjustable parameters: I(Q) = [I0 / (1+c1Q)] 2 +c2Q 4 )],fa=c1 / (2c2 1 / 2 ).

[0067] In some embodiments, the coin cell assembled using the silicon-carbon material exhibits a first characteristic peak in the 0.25-0.3V voltage range and a second characteristic peak in the 0.4-0.45V voltage range in its differential capacity (dQ / dV) curve, with the ratio of the intensity of the first characteristic peak (Q1) to the intensity of the second characteristic peak (Q2) satisfying Q1 / Q2≤1.5. The first characteristic peak corresponds to the lithium-silicon alloy Li... 15 S i4 Li x The delithiation process of the Si phase, while the second characteristic peak corresponds to Li x The delithiation process from Si phase to elemental Si phase. When Q1 / Q2 ≤ 1.5, it indicates that Li is relatively stable during the delithiation process. 15 S i4The efficient conversion to the Si phase significantly suppresses the accumulation of the LixSi intermediate phase, and the highly reversible delithiation behavior of silicon helps reduce the residual volume expansion of silicon during cycling, further mitigating stress accumulation and thus reducing stress impact on porous carbon, especially diamond particles. This, in turn, reduces the initiation and propagation of microcracks, further improving the cycle performance of the battery. Exemplarily, the Q1 / Q2 test method can employ conventional methods in the art. For example, assembling a coin cell half-cell with a lithium electrode as the counter electrode, performing cyclic voltammetry testing at a scan rate of 0.1 mV / s within a voltage range of 0.01-1.5V, or differentiating the constant current charge-discharge data to obtain the dQ / dV curve, extracting the peak intensities of the first characteristic peak (0.25-0.3V) and the second characteristic peak (0.4-0.45V), and calculating the Q1 / Q2 ratio.

[0068] According to a second aspect of this application, a method for preparing a silicon-carbon material is also provided, comprising the following steps: (1) The porous carbon precursor, organic solvent, diamond particles and additives are mixed, dried and sintered to obtain porous carbon; (2) First vapor deposition is performed on porous carbon to obtain silicon-carbon material; The additive includes at least one of a nitrogen source and a phosphorus source, and the average particle size D1 of the diamond particles is 5nm-500nm.

[0069] This application effectively controls the elastic modulus of silicon-carbon materials by adding diamond particles with an average particle size D1 of 5nm-500nm, thereby improving the stability of the diamond particles and the surrounding porous carbon and forming a continuous and efficient thermally conductive network. The doped nitrogen and / or phosphorus elements can effectively compensate for the decrease in electronic conductivity of silicon-carbon materials (especially the porous carbon) caused by diamond particles, which is beneficial to the cycle performance and thermal safety of the battery.

[0070] It should be noted that the diamond particles used in this application can be obtained by conventional methods in the art, and this application does not make specific limitations. For example, they can be synthesized by high temperature and high pressure method or detonation method. In some embodiments, the diamond particles added in step (1) of this application can be pretreated, such as acid washing (such as HCl and HF mixed acid) or oxidation treatment (such as heat treatment at 300℃-400℃ in air atmosphere) to remove surface impurities and introduce surface functional groups such as -OH and -COOH, so as to further improve the compatibility of diamond particles with porous carbon precursor.

[0071] In some embodiments, the nitrogen source includes at least one of melamine, urea, and dicyandiamide.

[0072] In some embodiments, the phosphorus source includes at least one of phytic acid, phosphoric acid, ammonium phosphate, and ammonium phytate.

[0073] In some embodiments, the drying includes spray drying.

[0074] In some embodiments, the inlet air temperature of the spray dryer is 190°C-210°C.

[0075] In some embodiments, the atomization pressure of the spray dryer is 0.1 MPa-0.5 MPa. More specifically, it is 0.2 MPa-0.3 MPa.

[0076] In some embodiments, the mass ratio of the porous carbon precursor to the diamond particles is (25-35):(0.08-3). Exemplarily, the mass ratio of the porous carbon precursor to the diamond particles can be 25:0.08, 25:0.1, 25:0.2, 25:0.3, 25:0.4, 25:0.5, 25:0.6, 25:0.7, 25:0.8, 25:0.9, 25:1.0, 25:1.1, 25:1.2, 25:1.3, 25:1.4, 25:1.5, 25:1.6, 25:1.7, 25:1.8, 25:1.9, or 25:2.0. 25:2.1, 25:2.2, 25:2.3, 25:2.4, 25:2.5, 25:2.6, 25:2.7, 25:2.8, 25:2.9, 25:3, 30:0.08, 30:0.1, 30:0.2, 30:0.3, 30:0.4, 30:0.5, 30:0.6, 30:0.7, 30:0.8, 30:0.9, 30:1.0, 30:1.1, 30:1.2, 30:1.3, 30:1.4 30:1.5, 30:1.6, 30:1.7, 30:1.8, 30:1.9, 30:2.0, 30:2.1, 30:2.2, 30:2.3, 30:2.4, 30:2.5, 30:2.6, 30:2.7, 30:2.8, 30:2.9, 30:3, 35:0.08, 35:0.1, 35:0.2, 35:0.3, 35:0.4, 35:0.5, 35:0.6, 35:0.7, 35:0.8 Values ​​of 35:0.9, 35:1.0, 35:1.1, 35:1.2, 35:1.3, 35:1.4, 35:1.5, 35:1.6, 35:1.7, 35:1.8, 35:1.9, 35:2.0, 35:2.1, 35:2.2, 35:2.3, 35:2.4, 35:2.5, 35:2.6, 35:2.7, 35:2.8, 35:2.9, 35:3, etc., or values ​​within the range of any two of the above values.

[0077] In some embodiments, the mass ratio of the porous carbon precursor to the nitrogen source is (25-35):(0.25-3). Exemplarily, the mass ratio of the porous carbon precursor to the nitrogen source can be 25:0.25, 25:0.5, 25:0.6, 25:0.7, 25:0.8, 25:0.9, 25:1.0, 25:1.1, 25:1.2, 25:1.3, 25:1.4, 25:1.5, 25:1.6, 25:1.7, 25:1.8, 25:1.9, 25:2.0, 25:2.1, 25... 2.2, 25:2.3, 25:2.4, 25:2.5, 25:2.6, 25:2.7, 25:2.8, 25:2.9, 25:3, 30:0.25, 30:0.5, 30:0.6, 30:0.7, 30:0.8, 30:0.9, 30:1.0, 30:1.1, 30:1.2, 30:1.3, 30:1.4, 30:1.5, 30:1.6, 3 0:1.7, 30:1.8, 30:1.9, 30:2.0, 30:2.1, 30:2.2, 30:2.3, 30:2.4, 30:2.5, 30:2.6, 30:2.7, 30:2.8, 30:2.9, 30:3, 35:0.25, 35:0.5, 35:0.6, 35:0.7, 35:0.8, 35:0.9, 35:1.0, 35:1.1 Values ​​of 35:1.2, 35:1.3, 35:1.4, 35:1.5, 35:1.6, 35:1.7, 35:1.8, 35:1.9, 35:2.0, 35:2.1, 35:2.2, 35:2.3, 35:2.4, 35:2.5, 35:2.6, 35:2.7, 35:2.8, 35:2.9, 35:3, etc., or values ​​within the range of any two of the above values.

[0078] In some embodiments, the mass ratio of the porous carbon precursor to the phosphorus source is (25-35):(0.1-2). For example, the mass ratio of the porous carbon precursor to the phosphorus source can be 25:0.1, 25:0.2, 25:0.3, 25:0.4, 25:0.5, 25:0.6, 25:0.7, 25:0.8, 25:0.9, 25:1.0, 25:1.1, 25:1.2, 25:1.3, 25:1.4, 25:1.5, 25:1.6, 25:1.7, 25:1.8, 25:1.9, 25:2.0, 30:0.1, 30:0.2, 30:0.3, 30:0.4, 30:0.5, 30:0.6, 30:0.7, 30:0.8, 30:0.9, or 30:1.0. Values ​​of 30:1.1, 30:1.2, 30:1.3, 30:1.4, 30:1.5, 30:1.6, 30:1.7, 30:1.8, 30:1.9, 30:2.0, 35:0.1, 35:0.2, 35:0.3, 35:0.4, 35:0.5, 35:0.6, 35:0.7, 35:0.8, 35:0.9, 35:1.0, 35:1.1, 35:1.2, 35:1.3, 35:1.4, 35:1.5, 35:1.6, 35:1.7, 35:1.8, 35:1.9, 35:2.0, etc., or values ​​within the range of any two of the above values.

[0079] In some embodiments, the second mixture further includes the addition of an additive, said additive including at least one selected from polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer and 1,3,5-trimethylbenzene.

[0080] In some embodiments, the mass ratio of the porous carbon precursor to the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer is (25-35):(1-2). Exemplarily, the mass ratio of the porous carbon precursor to the polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer can be 25:1.0, 25:1.1, 25:1.2, 25:1.3, 25:1.4, 25:1.5, 25:1.6, 25:1.7, 25:1.8, 25:1.9, 25:2.0, 30:1.0, 30:1.1, 30:1.2, or 30:1.3. Values ​​such as 30:1.4, 30:1.5, 30:1.6, 30:1.7, 30:1.8, 30:1.9, 30:2.0, 35:1.0, 35:1.1, 35:1.2, 35:1.3, 35:1.4, 35:1.5, 35:1.6, 35:1.7, 35:1.8, 35:1.9, 35:2.0, or values ​​within the range of any two of the above values.

[0081] In some embodiments, the mass ratio of the porous carbon precursor to the 1,3,5-trimethylbenzene is (25-35):(0.2-0.5). Exemplarily, the mass ratio of the porous carbon precursor to the 1,3,5-trimethylbenzene can be 25:0.2, 25:0.3, 25:0.4, 25:0.5, 30:0.2, 30:0.3, 30:0.4, 30:0.5, 35:0.2, 35:0.3, 35:0.4, 35:0.5, or a value within the range of any two of the above values.

[0082] In some embodiments, the ratio of the mass of the porous carbon precursor to the volume of the organic solvent is (25-35):(120-180), the unit of the porous carbon precursor is g, and the unit of the organic solvent is mL.

[0083] In some embodiments, the mixing step includes stirring at 35°C-45°C for 0.5h-1.5h.

[0084] In some embodiments, the sintering includes a first sintering and a second sintering.

[0085] In some embodiments, the first sintering time is 0.5 h to 1 h. In some embodiments, the first sintering temperature is 300 °C to 400 °C. In some embodiments, the heating rate of the first sintering is 1 °C / min to 3 °C / min.

[0086] In some embodiments, the second sintering time is 1-3 hours. In some embodiments, the second sintering temperature is 650°C-800°C. In some embodiments, the heating rate of the second sintering is 3°C / min-7°C / min. After the first and second sintering processes, the porous carbon precursor is converted into a carbon framework, and the diamond particles are fully and uniformly encapsulated within the porous carbon.

[0087] In some embodiments, the second sintering is followed by an activation treatment, which includes: heating to 750°C-900°C at a rate of 5°C / min-15°C / min under an inert atmosphere, switching to a mixed gas of water vapor and inert gas, and holding at that temperature for 0.5-3 hours. Water vapor can etch abundant pore structures into porous carbon, i.e., a structure dominated by micropores, further improving the deposition efficiency and uniformity of silicon-based particles in the first vapor deposition.

[0088] In some embodiments, the volume ratio of the water vapor to the inert gas is (0.1-0.3):1.

[0089] In some embodiments, the activation treatment further includes a third sintering step, which comprises: heating to 800℃-1000℃ at a rate of 5℃ / min-15℃ / min under an inert atmosphere and holding at that temperature for 1h-4h. The third sintering can repair oxygen-containing functional groups and defect sites in porous carbon, reduce side reactions, further improve the mechanical strength of porous carbon, and optimize the distribution of nitrogen or phosphorus elements in porous carbon.

[0090] In some embodiments, the first vapor deposition includes introducing a silicon source in a rotary kiln, fluidized bed, or tubular furnace at a temperature of 350°C-600°C.

[0091] In some embodiments, the time for the first vapor deposition is 2-5 hours. In some embodiments, the heating rate for the first vapor deposition is 5°C / min-15°C / min.

[0092] In some embodiments, the silicon source comprises a silicon-containing gas and a protective gas; in some embodiments, the silicon-containing gas comprises at least one selected from silane, dichlorosilane, trichlorosilane, and tetrachlorosilane. In some embodiments, the protective gas comprises at least one selected from an inert gas and nitrogen.

[0093] Furthermore, in some embodiments, the volume ratio of silicon-containing gas to protective gas in the silicon source is (3-5):(15-17).

[0094] In some embodiments, the flow rate of the silicon source is 40 sccm-80 sccm.

[0095] In some embodiments, before the silicon source undergoes the first vapor deposition, the process further includes: heating the silicon source to 400°C-550°C at a rate of 5°C / min-15°C / min under an inert atmosphere, and then introducing it into a rotary kiln, fluidized bed, or tubular furnace.

[0096] In some embodiments, the protective gas includes, for example, at least one of nitrogen, argon, and helium.

[0097] During the sintering process, the dopants inside the porous carbon diffuse outward and may appear on the outside of the porous carbon, such as in the channels of the porous carbon or on the outer surface of the porous carbon.

[0098] In some embodiments, after the first vapor deposition, a second vapor deposition is further included, the second vapor deposition satisfying one of the following (A)-(C): (A) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a first carbon source is introduced; (B) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a second carbon source is introduced; (C) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a first carbon source is introduced; then a second carbon source is introduced.

[0099] In some embodiments, the first carbon source includes an aromatic ring precursor and an unsaturated hydrocarbon precursor, wherein the unsaturated hydrocarbon precursor includes an unsaturated hydrocarbon precursor with 2-10 carbon atoms.

[0100] In some embodiments, the aromatic ring-containing precursor includes an aromatic hydrocarbon-containing precursor.

[0101] In some embodiments, the aromatic hydrocarbon precursor includes toluene.

[0102] In some embodiments, the unsaturated hydrocarbon precursor includes at least one of acetylene and ethylene.

[0103] Furthermore, this study found that by controlling the type and proportion (e.g., mass ratio) of aromatic ring precursors and unsaturated hydrocarbon precursors in the first carbon source, the elastic modulus of silicon-carbon materials can be further controlled, and a buffer layer can be formed between porous carbon and silicon-based particles, reducing the occurrence of microcracks. For example, increasing the amount of aromatic ring precursors can improve the elastic modulus of silicon-carbon materials and the density of the carbon layer; increasing the amount of unsaturated hydrocarbon precursors can reduce the elastic modulus of silicon-carbon materials and increase the flexibility of the carbon layer. Simultaneously, the first carbon source can also form a protective passivation layer on the surface of silicon-based particles, reducing side reactions and preventing ignition upon contact with air. In addition, if cracks appear in the porous carbon during sintering, the first carbon source can also form carbon layers within these cracks, thereby improving the structural stability of the porous carbon. Furthermore, the temperature at which the first carbon source is introduced can also indirectly affect the elastic modulus of silicon-carbon materials. Introducing the first carbon source at temperatures between 350℃ and 600℃, higher temperatures can increase the orderliness of the formed carbon layer, thereby further improving the elastic modulus of the silicon-carbon material.

[0104] In some embodiments, the flow rate of the aromatic hydrocarbon precursor is 5 sccm-50 sccm.

[0105] In some embodiments, the flow rate of the unsaturated hydrocarbon precursor is 5 sccm-50 sccm.

[0106] In some implementations, the first carbon source is introduced for 1-3 hours.

[0107] In some embodiments, the second carbon source includes at least one of methane, acetylene, propylene, cyclopropane, n-butane, and isobutane.

[0108] In some embodiments, the second vapor deposition is performed under an inert atmosphere.

[0109] In some embodiments, the flow rate of the second carbon source is 80 sccm-120 sccm.

[0110] In some implementations, the second carbon source is introduced for 1-3 hours.

[0111] Introducing a second carbon source can further reduce the micropore inlets and defects on the surface of silicon-carbon materials, regulate the specific surface area of ​​silicon-carbon materials, thereby reducing the generation of hydrogen bubbles when silicon-carbon materials come into contact with water, and facilitating processing.

[0112] According to a third aspect of this application, a negative electrode sheet is also provided, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising the silicon-carbon material described in the first aspect, or a silicon-carbon material prepared by the method described in the second aspect.

[0113] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 -1.75g / cm 3 At this point, the electrode retains an appropriate amount of porosity to allow for electrolyte wetting and buffering of the volume expansion of silicon-carbon particles, providing sufficient space for the expansion stress of the silicon-carbon material to be released. This results in low contact resistance between the silicon-carbon materials and good conductivity, further improving the battery's cycle performance. For example, the compaction density of the negative electrode can be measured using conventional methods in the art. For instance, taking single-sided coating as an example, first, the weight gain of the electrode is measured, and the areal density of the coating is calculated, i.e., weight gain / total coating area. After rolling, the thickness is measured. Compaction density = coating areal density / (thickness after rolling - copper foil thickness). The weight gain of the electrode can be obtained by calculating the weight difference between the coated area and the empty foil area. For example, the compaction density of the negative electrode (unit: g / cm³) is... 3 () can be 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, etc., or a value within the range of any two of the above values.

[0114] In some embodiments, the negative electrode active material further includes a carbon-based material, which includes at least one of graphite, soft carbon, and hard carbon; further, the carbon-based material is graphite; further, the graphite includes primary graphite particles. As the skeleton material of the negative electrode active layer, primary graphite particles have higher mechanical stability than secondary graphite particles. They are less prone to breakage under high compaction density and cyclic expansion stress, and can persistently maintain the conductive network and stable pore structure of the electrode, providing a uniform stress environment for the silicon-carbon material. Based on the elastic modulus regulation of porous carbon containing diamond particles, primary graphite particles can further uniformly disperse the expansion stress generated by the silicon-carbon material to the entire electrode layer, avoiding electrode deformation and active material shedding caused by local stress concentration, thereby further improving the cycle performance of the battery. Further, the average particle size of the primary graphite particles is denoted as D3 μm, satisfying 5≤D3≤11; further, the specific surface area of ​​the primary graphite particles is 0.5m². 2 / g-3m 2 / g. This can further improve the structural stability and kinetic performance of primary graphite particles, thereby improving the cycle performance and first-time efficiency of the battery.

[0115] For example, the average particle size D3 of the primary graphite particles can be measured using conventional methods in the art. For instance, under a scanning electron microscope (5000x magnification), 50 primary graphite particles can be randomly selected, processed using image processing software (e.g., Image J), ​​and the arithmetic mean can be taken as D3. Alternatively, it can be measured using a particle size analyzer. For example, the average particle size D3 (in μm) of the primary graphite particles can be 5, 6, 7, 8, 9, 10, 11, etc., or a value within any two of the above values. For example, the specific surface area of ​​the primary graphite particles can be measured using conventional methods in the art, for example, using a TriStar II specific surface area analyzer. For example, the specific surface area of ​​the primary graphite particles (in m²) can be measured using conventional methods in the art. 2 / g) can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, etc., or values ​​within the range of any two of the above values.

[0116] In some embodiments, the negative electrode active layer further includes at least one of a conductive agent and a binder.

[0117] In some embodiments, the silicon-carbon material content is 5%-40% based on the mass of the negative electrode active layer. In some embodiments, the primary graphite particles content is 55%-94% based on the mass of the negative electrode active layer. This approach balances good energy density and structural stability, further improving the battery's cycle performance and thermal safety.

[0118] In some embodiments, the mass content of the conductive agent is 0.5%-3% based on the mass of the negative electrode active layer.

[0119] In some embodiments, the binder content is 0.5%-3% based on the mass of the negative electrode active layer.

[0120] In some embodiments, the conductive agent includes carbon nanotubes with a diameter of 5 nm to 50 nm, and in some embodiments, the aspect ratio of the carbon nanotubes is 500 to 2000. In this way, the carbon nanotubes can form a long-range bridging conductive network between the silicon-carbon material and the primary graphite particles, effectively improving conductivity. At the same time, the flexible fiber structure of the carbon nanotubes can provide elastic buffering when the silicon-carbon material expands in volume, maintaining electrical contact between active materials, reducing impedance, and further improving the cycle performance of the battery.

[0121] For example, the aspect ratio and diameter of the carbon nanotubes can be measured using conventional methods in the art, such as transmission electron microscopy. The specific testing steps are as follows: Take an appropriate amount of carbon nanotube sample, disperse it in anhydrous ethanol, and ultrasonically disperse it for 20 minutes to form a uniform low-concentration suspension; use a pipette to draw up the suspension and drop it onto a copper grid for transmission electron microscopy. After the ethanol evaporates and dries, observe it under a transmission electron microscope (accelerating voltage 120kV) at a magnification of 200,000 times; randomly collect microscopic images of no less than 100 carbon nanotubes in a clear field of view, and use ImageJ image analysis software to measure the length L and diameter d of each carbon nanotube (measurement direction perpendicular to the tube axis). Calculate the aspect ratio L / d of each single tube and take the arithmetic mean, which is the aspect ratio of the carbon nanotube. Take the arithmetic mean of the diameters d, which is the diameter of the carbon nanotube. For example, the aspect ratio of the carbon nanotube can be 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, or a value within any two of the above values. For example, the diameter (in nm) of the carbon nanotube can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or a value within any two of the above values.

[0122] In some embodiments, the conductive agent also includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, and carbon fiber.

[0123] In some embodiments, the binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, and polyimide; preferably, the binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; preferably, the binder includes polyacrylic acid, or a combination of sodium carboxymethyl cellulose and styrene-butadiene rubber; the combination of sodium carboxymethyl cellulose and styrene-butadiene rubber can provide good slurry dispersibility and electrode flexibility, while the carboxyl groups of polyacrylic acid can form hydrogen bonds with the silicon surface, enhancing the bonding strength between the silicon-carbon material and the current collector, and further improving the structural stability of the battery.

[0124] In some embodiments, the negative current collector comprises a copper foil with a thickness of 4 μm-10 μm.

[0125] According to a fourth aspect of this application, a battery is also provided, comprising a positive electrode, a separator, an electrolyte, and a negative electrode as described in the third aspect.

[0126] In some embodiments, the electrolyte includes an additive, which includes at least one of triargyl phosphate and fluoroethylene carbonate; Furthermore, in some embodiments, the mass content of triargyl phosphate is 0.5%-5% based on the mass of the electrolyte. Triargyl phosphate decomposes at high temperatures (>200°C) to generate phosphorus-containing free radicals, which catalyze the formation of a dense and stable carbonized protective layer between the electrolyte and the polymer matrix, blocking the continued occurrence of the combustion chain reaction. Therefore, this application uses diamond particles in porous carbon to quickly disperse local heat and delay thermal runaway, while triargyl phosphate uses its chemical properties for flame retardancy and expands its application range. The two form a dual protection of "physical thermal conduction and flame suppression + chemical carbonization and flame retardancy", which can further improve the thermal safety of the battery. If the mass content of triargyl phosphate is less than 0.5%, the improvement effect of triargyl phosphate is limited. If the mass content of triargyl phosphate is greater than 5%, the electrolyte viscosity increases, the ionic conductivity decreases, and ion transport is hindered, affecting the cycle performance and first efficiency of the battery. For example, the mass content of the triargyl phosphate can be determined using conventional methods in the art, such as GC (gas chromatography) or GC-MS (gas chromatography-mass spectrometry). For example, the mass content of triargyl phosphate can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, etc., or a value within any two of the above ranges.

[0127] Further, in some embodiments, the mass content of the fluoroethylene carbonate is 5%-15% based on the mass of the electrolyte. Fluoroethylene carbonate can form a LiF-rich SEI film on the negative electrode surface. This SEI film has good stability and effectively passivates the surface of the silicon-carbon material, reducing side reactions and further improving the cycle performance and first-efficiency of the battery. Exemplarily, the mass content of the fluoroethylene carbonate can be measured using conventional methods in the art, such as GC (gas chromatography) or GC-MS (gas chromatography-mass spectrometry). Exemplarily, the mass content of the fluoroethylene carbonate can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., or values ​​within any two of the above ranges.

[0128] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector. The positive active layer includes a positive active material, which includes at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, nickel-cobalt-manganese-aluminum quaternary material, lithium iron phosphate, and lithium manganese iron phosphate.

[0129] In some embodiments, the positive current collector comprises an aluminum foil with a thickness of 8 μm-15 μm.

[0130] In some embodiments, the diaphragm includes at least one of polyethylene (PE) and polypropylene (PP); it is understood that the diaphragm may also be a PE / PP composite diaphragm.

[0131] In some embodiments, the thickness of the diaphragm is 5 μm-10 μm.

[0132] It should be noted that the diaphragm may include a ceramic coating and / or an adhesive layer to improve the thermal stability of the diaphragm or its adhesion to the electrode, but this application does not make any specific limitations.

[0133] In some embodiments, the electrolyte further includes a lithium salt, including lithium hexafluorophosphate.

[0134] In some embodiments, the concentration of lithium hexafluorophosphate in the electrolyte is 0.8 mol / L to 1.5 mol / L.

[0135] In some embodiments, the electrolyte further includes a solvent, which includes a carbonate solvent.

[0136] In some embodiments, the carbonate solvent includes at least one of cyclic carbonate solvents and chain carbonate solvents.

[0137] In some embodiments, the cyclic carbonate solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0138] In some embodiments, the chain carbonate solvent includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0139] In some embodiments, the volume ratio of the cyclic carbonate solvent to the chain carbonate solvent is (2-4):(6-8).

[0140] In some embodiments, the electrolyte further includes at least one of vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (PS), and succinate (SN). Vinylene carbonate can further improve the stability of the SEI film; vinyl sulfate can reduce the impedance of the SEI film and improve ion transport efficiency; 1,3-propanesulfonate lactone can improve the high-temperature stability of the electrolyte, thereby improving the thermal safety of the battery; and succinate can complex transition metal ions dissolved from the positive electrode, reducing side reactions and further improving the cycle performance and thermal safety of the battery.

[0141] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products. In all embodiments and comparative examples of this application, the unit % represents mass percentage.

[0142] Example A1 This embodiment provides a method for preparing silicon-carbon materials, including the following steps: (1) Add 30g of phenolic resin to 150mL of ethanol and stir magnetically at 40℃ for 1h to obtain a homogeneous solution. Take 0.75g of diamond particles (average particle size D1 is 50nm), 1.2g of melamine (nitrogen source), 0.6g of phytic acid (phosphorus source), 1.5g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (F127) and 0.3g of 1,3,5-trimethylbenzene (TMB) and add them to the above solution. Disperse ultrasonically for 2h to obtain a precursor suspension. Spray dry (inlet air temperature 200℃, atomization pressure 0.25MPa, feed rate 5mL / min) to obtain a porous carbon precursor.

[0143] (2) The porous carbon precursor was placed in a muffle furnace and heated to 350°C at 2°C / min in a nitrogen atmosphere for the first sintering, and held for 1 h. Then, it was heated to 700°C at 6°C / min for the second sintering, and held for 2 h. The precursor was then placed in a tube furnace and heated to 800°C under an inert atmosphere. A mixture of water vapor and inert gas (water vapor volume fraction of 20%) was introduced and held for 1.5 h for activation treatment. Then, the inert atmosphere was switched back and the temperature was raised to 900°C and held for 2 h for the third sintering to obtain porous carbon.

[0144] (3) The porous carbon was placed in a tube furnace. The silicon source area was heated to 500°C at 10°C / min under an inert atmosphere, and the deposition area was heated to 440°C at 10°C / min. A mixed gas (SiH4 and nitrogen in a volume ratio of 1:4) was introduced (the mixed gas flow rate was 60 sccm), and deposition was maintained for 4 h.

[0145] (4) Under an inert atmosphere, the first carbon source (toluene flow rate of 30 sccm and acetylene flow rate of 20 sccm) was introduced, and deposition was maintained at 500℃ for 2 h.

[0146] (2) Under an inert atmosphere, the temperature is raised to 500°C, acetylene gas (flow rate 100 sccm) is introduced, and the temperature is maintained for 2 hours to carry out the second carbon coating to obtain silicon-carbon material. The parameters of the silicon-carbon material are detailed in Table 2.

[0147] The average pore size of the porous carbon obtained in step (2) is 1.7 nm; based on the pore volume of the porous carbon, the volume ratio of micropores is 93%, the volume ratio of mesopores is 5%, and the volume ratio of macropores is 2%; the specific surface area of ​​the porous carbon is 1920 m². 2 / g, the pore volume of porous carbon is 0.76cm³. 3 / g, the connectivity (fa) of porous carbon is 0.93.

[0148] The silicon-carbon material prepared in this embodiment has a specific surface area of ​​0.48 m². 2 / g, based on the mass of silicon-carbon material, the silicon content (w%) is 49%; the pore volume of the silicon-carbon material is 0.04 cm³. 3 / g; the true density of silicon-carbon material is 1.98 g / cm³. 3 .

[0149] In the X-ray diffraction pattern of the porous carbon, the porous carbon has diffraction peaks in the range of 0.8°-4.2° of 2θ diffraction angle; the half-peak width of the diffraction peaks along the 2θ direction is 0.12°.

[0150] The coin cell assembled using the silicon-carbon material exhibits a first characteristic peak in the voltage range of 0.25-0.3V and a second characteristic peak in the voltage range of 0.4-0.45V, and the ratio of the intensity of the first characteristic peak (Q1) to the intensity of the second characteristic peak (Q2) satisfies Q1 / Q2 equal to 1.3.

[0151] The preparation methods for Examples A2-A25 and Comparative Examples A1-A2 are basically the same as those for Example A1. The differences are shown in Tables 1-2. In the tables, " / " indicates that the item does not exist. The symbol indicates that it is the same as in Example A1, but there may be reasonable deviations due to the testing process.

[0152] Table 1. Preparation process variables of the examples and comparative examples 1

[0153] Table 2 Variables for Examples and Comparative Examples 2

[0154] Comparative Example A3 This comparative example provides a method for preparing silicon-carbon material. The only difference from Example A1 is that diamond particles are not added in step (1).

[0155] Comparative Example A4 This comparative example provides a method for preparing silicon-carbon materials. The only difference from Example A1 is that melamine and phytic acid are not added in step (1).

[0156] Example B1 This embodiment provides a method for preparing a battery, including the following steps: (1) Preparation of positive electrode Lithium cobalt oxide, polyvinylidene fluoride, acetylene black, and carbon nanotubes were mixed in a mass ratio of 96.5:2:1.2:0.3. N-methylpyrrolidone was added, and the mixture was stirred under vacuum until homogeneous. The positive electrode slurry was then uniformly coated onto both sides of an aluminum foil with a thickness of 9 μm. The coated positive electrode sheet was baked in an oven, then dried in an oven at 150°C for 12 hours. Finally, it was rolled and slit to obtain the positive electrode sheet.

[0157] (2) Preparation of negative electrode sheet The silicon-carbon material, primary graphite particles, hydroxymethyl cellulose, styrene-butadiene rubber, lithium polyacrylate, conductive carbon black (Super P), and carbon nanotubes (25 nm in diameter, with an aspect ratio of 1000 in some embodiments) prepared in Example A1 were mixed in a ratio of 20:76.5:0.8:0.6:1.1:0.8:0.2. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated on both sides of an 8 μm thick copper foil current collector. The negative electrode sheet coated with the negative electrode slurry was transferred to an 80°C oven and dried for 12 hours. Then, it was rolled, laser-cut, and slit to obtain a negative electrode sheet with a compaction density of 1.68 g / cm³. 3 The specific surface area of ​​primary graphite particles is 1.3 m². 2 / g, with an average particle size D3 of 8μm.

[0158] (3) Electrolyte preparation Lithium hexafluorophosphate was dissolved in a solvent consisting of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 2:4:4. Based on the mass of the electrolyte, 2.5 wt% of triargyl phosphate and 10 wt% of fluoroethylene carbonate (FEC) were added to obtain an electrolyte with a lithium hexafluorophosphate concentration of 1.2 mol / L.

[0159] (4) Battery preparation The prepared negative electrode sheet, separator (polyethylene film with a thickness of 7μm) and prepared positive electrode sheet are stacked in sequence and then wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film shell and the electrolyte is injected into the dried bare cell. After vacuum sealing, standing, formation and sorting, a lithium-ion battery is obtained.

[0160] The preparation methods for Examples B2-B25 and Comparative Examples B1-B4 are basically the same as those for Example B1, except that the silicon-carbon materials used in Examples A2-A25 and Comparative Examples A1-A4, respectively, are used to prepare lithium-ion batteries. The preparation methods for Examples B26-B34 are basically the same as those for Example B1. The differences are shown in Table 3. In the table, " / " indicates that the item does not exist. The symbols indicate that the results are the same as in Example B1, but there may be reasonable deviations due to the testing process. Example B28 refers to replacing the primary graphite particles of Example B1 with secondary graphite particles of equal mass, and the average particle size of the secondary graphite particles is 8 μm.

[0161] Table 3 Variable 3 of the Example

[0162] Test case The lithium-ion batteries of Examples B1-B34 and Comparative Examples B1-B4 were tested as follows: (1) Cyclic performance test: The battery is charged at a constant current density of 1.2C to 4.53V, then charged at a constant voltage of 4.53V with a cutoff current of 0.05C, and then left to stand for 10 minutes. Then it is discharged at a current density of 0.7C to 2.5V, and then left to stand for 10 minutes. The discharge capacity of the battery at this time is recorded as the initial capacity. The above charging and discharging process is repeated until the 1000th cycle of constant current discharge to 2.5V, left to stand for 10 minutes, and the discharge capacity of the battery at this time is recorded as the capacity after the cycle. The cycle capacity retention rate is calculated as the capacity after the cycle / the initial capacity × 100%, and the integer part is the cycle performance.

[0163] (2) Thermal safety test: First, the lithium-ion battery was fully charged using a constant current and constant voltage at 0.5C, and then placed in a constant temperature chamber at 25±5℃. Subsequently, the temperature was increased to 130℃ at a rate of 5℃ / min and held at that temperature for 60min. If the battery did not catch fire or explode within 60min, it was considered to have passed the thermal chamber test. The temperature of the air chamber was adjusted to A+1℃ and held for 60min before the test was ended. The temperature was then increased until the battery sample exploded and / or caught fire. The temperature at which no explosion or fire occurred was recorded as the passing temperature.

[0164] (3) First Coulomb efficiency test: The battery is charged at a constant current density of 0.5C to 4.53V, and then charged at a constant voltage of 4.53V to 0.05C to obtain the charging capacity. After standing for 10 minutes, it is discharged at 0.2C to 3.0V to obtain the discharging capacity. The first Coulomb efficiency = discharging capacity / charging capacity × 100%.

[0165] The specific results are shown in Table 4-5.

[0166] Table 4 Test Results of Examples and Comparative Examples 1

[0167] Table 5 Test Results of Example 2

[0168] As can be seen from Tables 1-5, compared to Comparative Examples B1 (D1 is too large) and B2 (D1 is too small), the cycle performance and thermal safety of Examples B1-B34 were improved to varying degrees. However, the cycle performance and thermal safety of Comparative Examples 3 (without diamond particles) and 4 (without nitrogen and / or phosphorus doping) significantly decreased. This indicates that the full and uniform encapsulation of diamond particles by porous carbon effectively regulates the elastic modulus compatibility between diamond particles and porous carbon, giving the silicon-carbon material a better elastic modulus, reducing stress concentration points, and thus reducing microcracks. It also ensures the connectivity of the thermal conductivity network, effectively improving the thermal safety and cycle performance of batteries made from silicon-carbon materials. The addition of nitrogen and / or phosphorus elements to the silicon-carbon material creates more conductive active sites and constructs rapid electron transport channels, effectively compensating for the decrease in electronic conductivity of porous carbon caused by diamond particles, thereby improving the battery's cycle performance.

[0169] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A silicon-carbon material, characterized in that, The core comprises porous carbon and silicon-based particles located within the pores of the porous carbon, wherein a plurality of diamond particles are disposed within the porous carbon. The average particle size of the diamond particles is denoted as D1 nm, which satisfies 5 ≤ ​​D1 ≤ 500; The elastic modulus of the silicon-carbon material is denoted as a GPa, which satisfies 10≤a≤80; The silicon-carbon material contains doping elements, including at least one of nitrogen and phosphorus.

2. The silicon-carbon material according to claim 1, characterized in that, The silicon-carbon material also satisfies at least one of the following (1)-(5): （1）20≤D1≤200； （2）15≤a≤50； (3) Based on the mass of the porous carbon, the mass content of nitrogen element is denoted as n%, which satisfies 0.2≤n≤3; (4) Based on the mass of the porous carbon, the mass content of the phosphorus element is denoted as p%, which satisfies 0.1≤p≤2; (5) Based on the mass of the porous carbon, the total mass content of the diamond particles is denoted as m%, which satisfies 0.5≤m≤15.

3. The silicon-carbon material according to claim 2, characterized in that, The silicon-carbon material also satisfies at least one of the following (1)-(5): （1）30≤D1≤100； （2）20≤a≤40； （3）0.5≤n≤2； （4）0.2≤p≤1； （5）2≤m≤8。 4. The silicon-carbon material according to any one of claims 1-3, characterized in that, The porous carbon also satisfies at least one of the following (1)-(5): (1) The porous carbon has micropores, mesopores and macropores. Based on the pore volume of the porous carbon, the volume ratio of micropores is 80%-99%, the volume ratio of mesopores is 1%-20%, and the volume ratio of macropores is 0%-5%. (2) The average pore size of the porous carbon is 1 nm-3 nm; (3) The specific surface area of ​​the porous carbon is 1500 m². 2 / g-2500m 2 / g, preferably 1800m 2 / g-2200m 2 / g; (4) The pore volume of the porous carbon is 0.6 cm³. 3 / g-1cm 3 / g, preferably 0.7cm 3 / g-0.9cm 3 / g; (5) The doping element is nitrogen.

5. The silicon-carbon material according to any one of claims 1-3, characterized in that, The silicon-carbon material further includes a carbon layer that covers at least a portion of the surface of the core, and the thickness of the carbon layer is 2nm-20nm. Preferably, the thickness of the carbon layer is 5nm-10nm; Preferably, the carbon layer is located on at least a portion of the surface of the silicon-based particles; Preferably, the carbon layer is located on at least a portion of the surface of the inner wall of the porous carbon pores.

6. The silicon-carbon material according to any one of claims 1-3, characterized in that, The silicon-carbon material also satisfies at least one of the following (1)-(5): (1) Based on the mass of the silicon-carbon material, the mass content of silicon element is denoted as w%, which satisfies 40≤w≤70; preferably, 45≤w≤60. (2) The volume median particle size of the silicon-carbon material is denoted as D2 μm, which satisfies 3≤D2≤15; preferably, 5≤D2≤12; more preferably, 7≤D2≤9; (3) The particle size distribution Span value of the silicon-carbon material is 0.4-1; (4) The sphericity of the silicon-carbon material is 0.85-1.0; preferably, it is 0.9-0.95; (5) The Raman spectrum of the silicon-carbon material satisfies: 0.7 ≤ I D1 / I G1 ≤1.2, and / or, 0.05≤I G2 / I G1 ≤0.5, where I D1 This indicates that the Raman displacement is between 1340 and 1360 cm. -1 The peak intensity of the Raman peak at the location, I G1 This indicates that the Raman shift is between 1575 and 1590 cm. -1 The peak intensity of the Raman peak at the location, the I G2 This indicates that the Raman shift is between 1329 and 1335 cm. -1 Peak intensity of the Raman peak at the location.

7. A method for preparing a silicon-carbon material, characterized in that, Includes the following steps: (1) The porous carbon precursor, organic solvent, diamond particles and additives are mixed, dried and sintered to obtain porous carbon; (2) First vapor deposition is performed on porous carbon to obtain silicon-carbon material; The additive includes at least one of a nitrogen source and a phosphorus source, and the average particle size D1 of the diamond particles is 5nm-500nm. Preferably, the first vapor deposition includes: introducing a silicon source in a rotary kiln, fluidized bed, or tubular furnace at a temperature of 350°C-600°C; Preferably, after the first vapor phase deposition, a second vapor phase deposition is further included, wherein the second vapor phase deposition satisfies one of the following (A)-(C): (A) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a first carbon source is introduced; (B) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a second carbon source is introduced; (C) In a rotary kiln, fluidized bed or tubular furnace, at 400℃-600℃, a first carbon source is introduced, followed by a second carbon source; Preferably, the first carbon source includes an aromatic ring precursor and an unsaturated hydrocarbon precursor, wherein the unsaturated hydrocarbon precursor includes an unsaturated hydrocarbon precursor with 2-10 carbon atoms; Preferably, the aromatic ring-containing precursor includes an aromatic hydrocarbon-containing precursor; Preferably, the aromatic hydrocarbon precursor includes toluene; Preferably, the unsaturated hydrocarbon precursor includes at least one of acetylene and ethylene.

8. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, which includes the silicon-carbon material according to any one of claims 1-6, or the silicon-carbon material prepared by the method of preparing the silicon-carbon material according to claim 7.

9. The negative electrode sheet according to claim 8, characterized in that, The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 -1.75g / cm 3 ; And / or, the negative electrode active material further includes a carbon-based material, wherein the carbon-based material includes at least one selected from graphite, soft carbon, and hard carbon; preferably, the carbon-based material is graphite; preferably, the graphite comprises primary graphite particles; preferably, the average particle size of the primary graphite particles is denoted as D3 μm, satisfying 5 ≤ D3 ≤ 11; preferably, the specific surface area of ​​the primary graphite particles is 0.5 m². 2 / g-3m 2 / g.

10. A battery, characterized in that, Includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in any one of claims 8-9; Preferably, the electrolyte includes an additive, which includes at least one of triargyl phosphate and fluoroethylene carbonate; More preferably, based on the mass of the electrolyte, the mass content of the triargyl phosphate is 0.5%-5%; More preferably, the mass content of the fluoroethylene carbonate is 5%-15% based on the mass of the electrolyte.

Images