Silicon-carbon material, preparation method thereof, negative electrode sheet and battery

Abstract

The application belongs to the technical field of new energy batteries, and particularly relates to a silicon-carbon material, a preparation method thereof, a negative electrode sheet and a battery. The application provides a silicon-carbon material, which comprises a porous diamond substrate and silicon particles dispersed in the inside of a channel of the porous diamond substrate; the porous diamond substrate comprises a diamond crystal structure; the porous diamond substrate comprises a doping element, the doping element is located in the diamond crystal structure, and the doping element comprises at least one of a boron element and a nitrogen element. The battery prepared from the silicon-carbon material has good cycle performance, rate performance and energy density.

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] As people's demand for the driving range and lifespan of electric vehicles continues to increase, higher requirements are also being placed on the energy density, long cycle life and safety of batteries. The theoretical capacity of traditional graphite anodes is low (372mAh / g), while the theoretical specific capacity of silicon-based anodes is 4200Ah / g, and silicon is abundant and environmentally friendly. However, the low conductivity and drastic volume expansion of silicon can significantly damage the integrity of the solid electrolyte interphase (SEI) film on the anode side, leading to increased irreversible lithium consumption and a rapid decline in battery capacity.

[0003] Existing technologies improve the conductivity and cycling performance of silicon-carbon materials and reduce the expansion of silicon alloying by depositing silicon particles on porous carbon matrices. Existing porous carbon matrices mainly include resin-based porous carbon, biomass-based porous carbon, and petroleum coke-based porous carbon. However, these carbon matrices have limited ability to alleviate the expansion of silicon alloying, and silicon-carbon materials are prone to breakage during cycling, resulting in poor cycling performance. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this application is to overcome the defect of poor cycle performance of batteries in the prior art, thereby providing a silicon-carbon material and preparation method, a negative electrode sheet and a battery.

[0005] Therefore, this application provides the following technical solution.

[0006] According to an embodiment of this application, in a first aspect, a silicon-carbon material is provided, the silicon-carbon material comprising a porous diamond substrate and silicon particles dispersed within the pores of the porous diamond substrate. The porous diamond substrate comprises a diamond crystal structure; The porous diamond substrate includes a doping element located within the diamond crystal structure, and the doping element includes at least one of boron and nitrogen.

[0007] In some embodiments, the boron content is 0.05 ppm to 500 ppm based on the mass of the silicon-carbon material.

[0008] In some embodiments, the nitrogen content is 0.1%-5% based on the mass of the silicon-carbon material; further, the nitrogen doping amount is 0.5%-2%.

[0009] In some embodiments, the sphericity of the silicon-carbon material is denoted as F, which satisfies 0.5 ≤ F ≤ 0.95.

[0010] In some embodiments, in the Raman spectrum of the porous diamond substrate, 1.2 ≤ I D / I G ≤1.8, wherein the I D This indicates that the Raman displacement is at 1330 cm. -1 -1380cm -1 The peak intensity of the Raman peak at the location, I G This indicates that the Raman displacement is at 1550 cm. -1 -1620cm -1 The peak intensity of the Raman peak at the location; further, 1.3 ≤ I D / I G ≤1.5.

[0011] In some embodiments, the silicon content is 10%-50% based on the mass of the silicon-carbon material.

[0012] In some embodiments, the median particle size of the silicon-carbon material is 3 μm-15 μm.

[0013] In some embodiments, the particle size distribution span value of the silicon-carbon material is 0.1-10.

[0014] In some embodiments, in the porous diamond substrate, the volume percentage of pores with a diameter not exceeding 2 nm is 75%-95%, the volume percentage of pores with a diameter of 2 nm-5 nm is 5%-20%, and the volume percentage of pores with a diameter of 5 nm-10 nm is 0%-5%.

[0015] In some embodiments, at 25°C, the resistivity of the silicon-carbon material powder is 0.1 Ω·cm-100 Ω·cm, and more specifically 0.1 Ω·cm-50 Ω·cm.

[0016] In some embodiments, the Vickers hardness of the silicon-carbon material is 150-500.

[0017] According to embodiments of this application, in a second aspect, a method for preparing silicon-carbon materials is also provided, comprising any one of method one and method two: Method 1 includes the following steps: boron-doped diamond is sintered in a protective atmosphere and pores are formed in a first gas; the product of the first pore formation is mixed with a pore-forming agent and sintered in a second atmosphere to obtain a porous diamond substrate, and then a first vapor deposition is performed to obtain a silicon-carbon material. Method 2 includes the following steps: sintering boron-doped diamond and / or non-boron-doped diamond under a protective atmosphere, and creating pores under a first gas; mixing the product from the first pore-forming process with a nitrogen source, and performing a first heat treatment to obtain nitrogen-doped carbide diamond; mixing the nitrogen-doped carbide diamond with a pore-forming agent, and performing a second sintering under a protective atmosphere to obtain a porous diamond substrate; and then performing a first vapor deposition to obtain a silicon-carbon material.

[0018] In some embodiments, the first vapor deposition step includes: placing a porous diamond substrate in a vapor deposition furnace, heating it to a first temperature, introducing a second gas, and performing a first calcination.

[0019] In some embodiments, the first vapor deposition is followed by a second vapor deposition, the second vapor deposition step including: a second heating, the introduction of a third gas, and a second calcination.

[0020] In some embodiments, the temperature of the first sintering is 800℃-1200℃; in some embodiments, the time of the first sintering is 1h-5h.

[0021] In some embodiments, the protective atmosphere includes at least one of an inert atmosphere and a nitrogen atmosphere.

[0022] In some embodiments, the first gas comprises water vapor and nitrogen, preferably, the volume ratio of water vapor to nitrogen is 1:(7-11).

[0023] In some embodiments, the first pore-forming step includes: maintaining a temperature of 800℃-1200℃ for 1-5 hours.

[0024] In some embodiments, the temperature of the second sintering is 750℃-1150℃; in some embodiments, the time of the second sintering is 3h-7h.

[0025] In some embodiments, the pore-forming agent includes iron oxide.

[0026] In some embodiments, the first temperature increase includes: increasing the temperature at a rate of 3°C / min to 7°C / min to 300°C-700°C.

[0027] In some embodiments, the second gas includes a silicon-containing gas and a second protective gas, and in some embodiments, the flow rate of the second gas is 2 L / min to 6 L / min.

[0028] Furthermore, in the second gas, the volume ratio of the silicon-containing gas and the second protective gas is 1:(2-6).

[0029] Furthermore, the second protective gas includes at least one of an inert gas and nitrogen.

[0030] In some embodiments, the temperature of the first calcination is 300℃-700℃, and in some embodiments, the time of the first calcination is 1h-5h.

[0031] In some embodiments, the second temperature increase includes increasing the temperature at a rate of 3°C / min to 7°C / min to 350°C-750°C.

[0032] In some embodiments, the third gas includes a carbon-containing gas and a third protective gas, and / or the flow rate of the third gas is 3 L / min to 7 L / min.

[0033] Furthermore, in the third gas, the volume ratio of the carbon-containing gas to the third protective gas is (2-4):(5-9).

[0034] Furthermore, the third protective gas includes at least one of an inert gas and nitrogen.

[0035] In some embodiments, the second calcination temperature is 350℃-750℃, and in some embodiments, the second calcination time is 1h-5h.

[0036] In some embodiments, the preparation steps of the boron-doped diamond include: placing the diamond in a vapor deposition furnace, using hydrogen as the carrier gas, introducing a first boron source, heating to 700℃-1100℃ at a rate of 1℃ / min-5℃ / min under a protective atmosphere, and holding at that temperature for 1h-5h.

[0037] Further, the first boron source includes at least one of a gaseous boron source and a liquid boron source; even further, the gaseous boron source includes at least one of octylborane and diborane; even further, the liquid boron source includes at least one of trimethyl borate and triethyl borate.

[0038] In some embodiments, the preparation steps of the boron-doped diamond include: mixing diamond and a solid boron source, heating to 700℃-1100℃ at 1℃ / min-5℃ / min under a hydrogen atmosphere and / or a protective atmosphere, and holding at that temperature for 1h-5h; further, the solid boron source includes at least one of boron trioxide and elemental boron.

[0039] In some embodiments, the temperature of the first heat treatment is 700℃-1100℃; in some embodiments, the time of the first heat treatment is 1h-5h.

[0040] In some embodiments, the nitrogen source includes at least one of melamine, urea, aniline, and chitosan.

[0041] According to an embodiment of this application, in a third aspect, 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 in the thickness direction, 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 the silicon-carbon material prepared by the method described in the second aspect.

[0042] In some embodiments, the surface of the negative electrode active layer away from the negative electrode current collector is provided with several recesses.

[0043] In some embodiments, the distance between two adjacent recesses is 0.5mm-5mm; in some embodiments, the opening width of the recess is 30μm-500μm; and in some embodiments, the depth of the recess is 5μm-50μm.

[0044] In some embodiments, the negative current collector comprises copper foil.

[0045] In some embodiments, the tensile strength of the copper foil is not less than 400 MPa; in some embodiments, the elongation of the copper foil is 2%-6%.

[0046] According to an embodiment of this application, in a fourth aspect, a battery is also provided, including a positive electrode and a negative electrode as described in the third aspect.

[0047] The technical solution of this application has the following advantages: The silicon-carbon material provided in this application includes a porous diamond substrate and silicon particles dispersed inside the pores of the porous diamond substrate; the porous diamond substrate includes a diamond crystal structure; the porous diamond substrate includes a dopant element located in the diamond crystal structure, and the dopant element includes at least one of boron and nitrogen. When a porous carbon substrate includes a diamond crystal structure, the porous diamond substrate possesses high hardness and strength, maintaining excellent structural integrity over long cycles. This effectively suppresses the volume expansion of silicon particles within its pores, ensuring the stability of the solid electrolyte interphase (SEI) film on the negative electrode side and thus guaranteeing the battery's cycle performance. Simultaneously, the porous diamond substrate also exhibits high compressive strength, making it less prone to breakage during negative electrode fabrication. This allows for increased compaction density of the negative electrode, reducing battery thickness and effectively enhancing energy density. Further research in this application reveals that doping the porous diamond substrate with at least one of boron and nitrogen elements can improve its conductivity and reduce battery impedance, thereby enhancing rate performance while maintaining cycle performance and energy density.

[0048] 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. Detailed Implementation

[0049] 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.

[0050] 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.

[0051] In existing silicon-carbon materials, the porous carbon matrix makes it difficult to mitigate the volume expansion of silicon alloying during cycling, leading to the silicon-carbon material's susceptibility to breakage. This not only degrades the performance of the silicon-carbon material, but the exposed interfaces after breakage react with the electrolyte, causing a sharp increase in the SEI film and excessive electrolyte consumption, severely affecting the battery's cycle performance. To address the aforementioned problems, according to embodiments of this application, in a first aspect, a silicon-carbon material is provided, comprising a porous diamond substrate and silicon particles dispersed within the pores of the porous diamond substrate; The porous diamond substrate comprises a diamond crystal structure; The porous diamond substrate includes a doping element located within the diamond crystal structure, and the doping element includes at least one of boron and nitrogen.

[0052] This application research found that when a porous carbon substrate includes a diamond crystal structure, the porous diamond substrate possesses strong hardness and strength, maintaining excellent structural integrity even under long cycle times. This effectively suppresses the volume expansion of silicon particles within its pores, thereby ensuring the stability of the solid electrolyte interphase (SEI) film on the negative electrode side. It prevents repeated rupture and regeneration of the SEI film due to the drastic volume expansion of silicon-carbon materials, thus avoiding the consumption of active lithium and ensuring the battery's cycle performance. Simultaneously, the porous diamond substrate also exhibits high compressive strength, making it less prone to breakage during negative electrode fabrication. This allows for increased compaction density of the negative electrode, reducing battery thickness and effectively improving energy density. Further research in this application revealed that doping the porous diamond substrate with at least one of boron and nitrogen elements can enhance its conductivity and reduce battery impedance, thereby improving rate performance while maintaining cycle performance and energy density.

[0053] Furthermore, especially when doped with boron, boron atoms with three valence electrons will substitute carbon atoms to become acceptor centers. Moreover, the impurity energy level of boron in diamond is located at 0.37 eV above the top of the valence band, which is a shallow acceptor impurity. This helps to generate several hole carriers in the crystal lattice, making the porous diamond substrate a hole semiconductor. This significantly improves the conductivity of the porous diamond substrate, thereby improving the rate performance of the battery.

[0054] In some embodiments, the boron content is 0.05ppm-500ppm based on the mass of the silicon-carbon material. This allows the boron to effectively reduce the impedance of the silicon-carbon material and improve its conductivity, which is beneficial to the rate performance of the battery. At the same time, it can ensure the crystal phase stability of the porous diamond substrate, avoid distortion or phase transition, and thus ensure the high strength, high hardness and high compressive strength of the porous diamond substrate, thereby ensuring the cycle performance and energy density of the battery.

[0055] In some embodiments, the silicon-carbon material further includes phosphorus. Based on the mass of the silicon-carbon material, the mass content of boron is 0.05ppm-500ppm. The addition of phosphorus can further reduce the interfacial impedance of the silicon-carbon material, improve the rate performance of the battery, and enhance the crystal phase stability of the porous diamond substrate, ensuring the high strength, high hardness, and high compressive strength of the porous diamond substrate, which is also beneficial to the cycle performance and energy density of the battery.

[0056] In some embodiments, the boron and phosphorus elements are present in a mass content of 0.05 ppm to 500 ppm based on the mass of the silicon-carbon material, which can further reduce the impedance of the silicon-carbon material and improve the ion transport rate.

[0057] For example, the mass content of boron and / or phosphorus can be determined using conventional methods in the art. For instance, silicon carbon material is added to a digestion solution (a mixed solution of nitric acid and hydrofluoric acid, with a volume ratio of 1:2) for microwave digestion. After the silicon carbon material is completely dissolved, a small amount of liquid is taken and diluted with the digestion solution to obtain a sample solution. The concentration of silicon carbon material in the sample solution is 100 ppm. The ICP-OES instrument is calibrated using a standard solution. The processed sample solution is then injected into the ICP-OES instrument for analysis to obtain the mass content of boron.

[0058] For example, the mass content (in ppm) of boron or phosphorus can be 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 350, 400, 450, 500, etc., or values ​​within the range of any two of the above values.

[0059] In some embodiments, the nitrogen content is 0.1%-5% based on the mass of the silicon-carbon material; particularly, when it is 0.5%-2%, it can balance good rate performance, cycle performance and energy density. It can ensure the stability of the porous diamond substrate, avoid distortion or phase transition, thereby ensuring the high strength, high hardness and high compressive strength of the porous diamond substrate, and fully utilize the modification effect of nitrogen to reduce impedance, improve conductivity and improve the rate performance of the battery.

[0060] For example, the mass content of nitrogen can be determined using conventional methods in the art, such as energy dispersive X-ray spectroscopy (EDS) or a carbon-sulfur-nitrogen elemental analyzer. The carbon-sulfur-nitrogen elemental analyzer method includes: taking a silicon-carbon material sample, placing it on a ceramic boat in an oxygen environment, and burning it at a high temperature (1100°C). The nitrogen oxides are converted into nitrogen gas, which is then directly introduced into a gas separation system along with the carrier gas for adsorption and detection analysis, thus obtaining the mass content of nitrogen. For example, the mass content of nitrogen can be 0.1, 0.2, 0.3, 0.4, 0.5, or 0. Values ​​of 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, etc., or values ​​within the range of any two of the above values.

[0061] In some embodiments, the sphericity of the silicon-carbon material is denoted as F, satisfying 0.5≤F≤0.95. This results in more uniform stress distribution on the silicon-carbon material, which can improve the compaction density of the electrode, increase the energy density of the battery, and enhance the structural stability of the silicon-carbon material. Furthermore, the consistent ion insertion / extraction and transport properties within the silicon-carbon material reduce stress concentration and the possibility of breakage, thereby reducing the consumption of electrolyte and active lithium, which is beneficial to the battery's cycle performance. At the same time, the silicon-carbon material satisfying 0.5≤F≤0.95 has a low risk of puncturing the separator, which can reduce self-discharge and ensure battery safety.

[0062] For example, the sphericity F of the silicon-carbon material can be measured using conventional methods in the art. For instance, an SEM image (backscattered mode) of the negative electrode active layer at 2500x magnification can be analyzed using image processing software (ImageProPlus) to obtain the perimeter and area of ​​each silicon-based material particle in the image. The equivalent radius r1 of the perimeter and the equivalent radius r2 of the area of ​​each silicon-based material particle can be calculated respectively, and the sphericity S = r2 / r1 can be obtained. Then, the sphericity of each silicon-based material particle can be weighted and averaged to obtain the sphericity of the silicon-based material. For example, the sphericity F of the silicon-carbon material can be 0.5, 0.51, 0.52, or 0. Values ​​of 53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.95, etc., or values ​​within the range of any two of the above values.

[0063] In some embodiments, in the Raman spectrum of the porous diamond substrate, 1.2 ≤ I D / I G ≤1.8, wherein the I D This indicates that the Raman displacement is at 1330 cm. -1 -1380cm -1 The peak intensity of the Raman peak at the location, I G This indicates that the Raman displacement is at 1550 cm. -1 -1620cm -1 The peak intensity of the Raman peak at the location; this application study found that if the defect degree in the porous carbon substrate is low, it is necessary to increase the silicon deposition temperature to catalyze better deposition of silicon particles in the porous carbon substrate, while the I of the porous diamond substrate D / I G The value satisfies 1.2≤I D / IG ≤1.8, especially satisfying 1.3≤I D / I G When the temperature is ≤1.5, while ensuring the high compressive strength, high strength, and high hardness of the porous diamond substrate, the porous diamond substrate has a higher defect degree, which can provide more sites for silicon particle deposition, thereby reducing the temperature. The low temperature environment is conducive to the formation of amorphous silicon and avoids the transformation of amorphous silicon into crystalline silicon at excessively high temperatures. Therefore, in the silicon-carbon material provided in this application, the proportion of amorphous silicon in the silicon particles is higher. Compared with crystalline silicon, amorphous silicon has a smaller volume expansion, which improves the structural stability of the silicon-carbon material and is beneficial to the cycle performance of the battery.

[0064] Exemplarily, the Raman spectrum of the porous diamond substrate can be measured using conventional methods in the art, for example, by adding silicon-carbon material to a Raman spectrometer for testing; Exemplarily, I D (unit: cm) -1 () can be 1330, 1335, 1340, 1345, 1350, 1355, 1360, 1365, 1370, 1375, 1380, etc., or a value within the range of any two of the above values. For example, I G (unit: cm) -1 () can be 1550, 1555, 1560, 1565, 1570, 1575, 1580, 1585, 1590, 1595, 1600, 1605, 1610, 1615, 1620, etc., or a value within the range of any two of the above values. For example, I D / I G It can be 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.4, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.5, 1.55, 1.6, 1.7, 1.75, 1.8, etc., or values ​​within the range of any two of the above values.

[0065] In some embodiments, the silicon content is 10%-50% based on the mass of the silicon-carbon material. This allows the high specific capacity of silicon to be fully utilized, while also ensuring good structural stability of the silicon-carbon material.

[0066] For example, the mass content of silicon can be determined using conventional methods in the art. For instance, a thermogravimetric analyzer can be used. A sample of silicon-carbon material of 10 mg is taken and heated from room temperature (25 °C) to 900 °C at a rate of 10 °C / min under an oxygen atmosphere. The sample is then held at 900 °C for 1 hour to allow the non-silicon components in the sample to volatilize and the silicon to be fully oxidized to silicon dioxide. The mass content of silicon in the silicon-carbon material is calculated based on the mass of silicon dioxide. The calculation formula is: mass percentage of silicon = [(mass of silicon dioxide / mass of test sample) / 60] × 28. For example, the mass content of silicon can be 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 the range of any two of the above values.

[0067] In some embodiments, the median particle size of the silicon-carbon material is 3μm-15μm, especially when it meets the requirement of 5μm-11μm. The silicon-carbon material has a shorter diffusion path inside, good kinetic performance, which is beneficial to the rate performance of the battery. At the same time, the silicon-carbon material has a moderate specific surface area, which will not react too much with the electrolyte, thereby ensuring the cycle performance of the battery.

[0068] For example, the volumetric median particle size of the silicon-carbon material can be measured using conventional methods in the art, such as a Malvern Mastersizer 3000 laser particle size analyzer. For example, the volumetric median particle size (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.

[0069] In some embodiments, the particle size distribution span value of the silicon-carbon material is 0.1-10; the silicon-carbon material exhibits good consistency in ion insertion / extraction and transport, which can improve battery stability, thereby enhancing the battery's rate performance and cycle performance. For example, the particle size distribution span value of the silicon-carbon material can be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a value within any two of the above ranges.

[0070] In some embodiments, the specific surface area of ​​the porous diamond substrate is 500 m². 2 / g-4000m 2 / g, further, for 800m2 / g-2000m 2 / g. In this way, sufficient active sites and effective gas diffusion can be provided for silane deposition, while avoiding excessive growth of silicon particles, reducing the volume expansion of silicon particles, and ensuring the structural stability of silicon-carbon materials.

[0071] Exemplarily, the specific surface area of ​​the porous diamond substrate can be measured using conventional methods in the art, for example, using a TriStar II surface area analyzer. Exemplarily, the specific surface area of ​​the porous diamond substrate (unit: m²) 2 / g) can be 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, etc., or a value within the range of any two of the above values.

[0072] In some embodiments, in the porous diamond substrate, the volume percentage of pores with a diameter not exceeding 2 nm is 75%-95%, the volume percentage of pores with a diameter of 2 nm-5 nm is 5%-20%, and the volume percentage of pores with a diameter of 5 nm-10 nm is 0%-5%. This allows for the preservation of mesopores (2 nm-5 nm in diameter) within the silane material to withstand the volume expansion of silicon particles, which is beneficial to the cycle performance of the battery.

[0073] For example, the volume percentage of the pore size can be measured using conventional methods in the art, such as using a TriStar II surface area analyzer. For example, the volume percentage of pores with a diameter not exceeding 2 nm can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or values ​​within any two of the above ranges. For example, the volume percentage of pores with a diameter between 2 nm and 5 nm can be 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 pores with an aperture of 5nm-10nm can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., or a value within the range of any two of the above values.

[0074] In some embodiments, the porous diamond substrate has a pore volume of 0.5 cm³. 3 / g-2.0cm 3 / g. In some embodiments, the pore size of the porous diamond substrate ranges from 0.01nm to 10nm. This further reduces the size of silicon particles, thereby suppressing their volume expansion and improving the structural stability of the silicon-carbon material. Exemplarily, the pore volume of the porous diamond substrate can be measured using conventional methods in the art, for example, using a TriStar II surface area analyzer. Exemplarily, the pore volume of the porous diamond substrate (unit: cm³) 3 / g) can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc., or a value within the range of any two of the above values.

[0075] In some embodiments, at 25°C, the resistivity of the silicon-carbon material powder is 0.1 Ω·cm-100 Ω·cm, and more specifically 0.1 Ω·cm-50 Ω·cm, indicating that the silicon-carbon material has good electrical conductivity, can reduce impedance, and improve the rate performance of the battery. Exemplarily, the resistivity of the silicon-carbon material powder can be measured using conventional methods in the art, for example, using a powder resistivity meter. Exemplarily, the resistivity of the silicon-carbon material powder (in Ω·cm) can be 0.1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a value within any two of the above ranges.

[0076] In some embodiments, the Vickers hardness of the silicon-carbon material is 150-500, indicating good compressive strength, thereby increasing the compaction density of the electrode, improving the energy density of the battery, and effectively mitigating the volume expansion of silicon particles, which is beneficial to the cycle performance of the battery. Exemplarily, the Vickers hardness of the silicon-carbon material can be measured using conventional methods in the art, such as the micro Vickers hardness test, which includes: pressing the silicon-carbon material into a dense block, ensuring a smooth surface, using a micro Vickers hardness tester, applying a test force (typically 1-50 gf), holding for 10-15 seconds, and calculating the hardness value (HV) as 1.8544 × [test force / (average diagonal of the indentation)]. 2For example, the Vickers hardness of silicon-carbon materials can be 150, 160, 170, 180, 190, 200, 210, 220, 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.

[0077] In some embodiments, the specific surface area of ​​the silicon-carbon material is 0.01 m². 2 / g-8m 2 / g, further, is 0.1m 2 / g-4m 2 / g, thus, on the one hand, this specific surface area can effectively prevent excessive electrolyte from entering the interior of silicon-carbon material, avoid the SEI film from being too thick, reduce side reactions, and benefit the rate performance and cycle performance of the battery. On the other hand, it avoids the silicon-carbon material with too small a specific surface area from being too dense, which would affect the movement rate of lithium ions inside, and is also beneficial to the rate performance of the battery.

[0078] Exemplarily, the specific surface area of ​​the silicon-carbon material can be measured using methods conventional in the art, such as the TriStar II surface area analyzer. Exemplarily, the specific surface area of ​​the silicon-carbon material (unit: m²) 2 / g) can be 0.01, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, etc., or a value within the range of any two of the above values.

[0079] According to embodiments of this application, in a second aspect, a method for preparing silicon-carbon materials is also provided, comprising any one of the following methods: Method 1 and Method 2: Method 1 includes the following steps: boron-doped diamond is sintered in a protective atmosphere and pores are formed in a first gas; the product of the first pore formation is mixed with a pore-forming agent and sintered in a second atmosphere to obtain a porous diamond substrate, and then a first vapor deposition is performed to obtain a silicon-carbon material. Method 2 includes the following steps: sintering boron-doped diamond and / or non-boron-doped diamond under a protective atmosphere, and creating pores under a first gas; mixing the product from the first pore-forming process with a nitrogen source, and performing a first heat treatment to obtain nitrogen-doped carbide diamond; mixing the nitrogen-doped carbide diamond with a pore-forming agent, and performing a second sintering under a protective atmosphere to obtain a porous diamond substrate; and then performing a first vapor deposition to obtain a silicon-carbon material.

[0080] In some embodiments, the protective atmosphere includes at least one of an inert atmosphere and a nitrogen atmosphere.

[0081] In some embodiments, the first sintering temperature is 800℃-1200℃; in some embodiments, the first sintering time is 1h-5h. Exemplarily, the first sintering temperature (in °C) can be 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, etc., or a value within the range of any two of the above values. Exemplarily, the first sintering time (in hours) can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values.

[0082] In some embodiments, the first gas comprises water vapor and nitrogen, and further, the volume ratio of the water vapor to nitrogen is 1:(7-11). Exemplarily, the volume ratio of the water vapor to nitrogen may be 1:7, 1:8, 1:9, 1:10, 1:11, or a value within the range of any two of the above values.

[0083] In some embodiments, the first pore-forming step includes: holding at 800℃-1200℃ for 1-5 hours. Performing the first pore-forming under a first gas can preliminarily activate the diamond and increase the number of activation sites.

[0084] In some embodiments, the process before the first sintering includes: increasing the temperature to 800℃-1200℃ at a rate of 1℃ / min-5℃ / min.

[0085] In some embodiments, the pore-forming agent includes iron oxide.

[0086] In some embodiments, the mixing with the pore-forming agent includes cooling to room temperature.

[0087] In some embodiments, the second sintering temperature is 750℃-1150℃; in some embodiments, the second sintering time is 3h-7h. In some embodiments, the second sintering is performed under a protective atmosphere. Exemplarily, the second sintering temperature (in °C) can be 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, etc., or a value within the range of any two of the above values. Exemplarily, the second sintering time (in hours) can be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, etc., or a value within the range of any two of the above values.

[0088] In some embodiments, the process before the second sintering includes: increasing the temperature to 750°C-1150°C at a rate of 3°C / min-7°C / min.

[0089] In some embodiments, the first vapor deposition step includes: placing a porous diamond substrate in a vapor deposition furnace, heating it to a first temperature, introducing a second gas, and performing a first calcination.

[0090] In some embodiments, the first heating is performed under a protective atmosphere.

[0091] In some embodiments, the first temperature increase includes: increasing the temperature at a rate of 3°C / min to 7°C / min to 300°C-700°C.

[0092] In some embodiments, the second gas includes a silicon-containing gas and a second protective gas. In some embodiments, the flow rate of the second gas is 2 L / min to 6 L / min. Exemplarily, the flow rate (in L / min) of the second gas can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or a value within any two of the above values.

[0093] Furthermore, in some embodiments, the volume ratio of the silicon-containing gas and the second protective gas in the second gas is 1:(2-6). Exemplarily, the volume ratio of the silicon-containing gas and the second protective gas can be 1:2, 1:3, 1:4, 1:5, 1:6, or a value within the range of any two of the above values.

[0094] Furthermore, in some embodiments, the second protective gas includes at least one of an inert gas and nitrogen.

[0095] In some embodiments, the temperature of the first calcination is 300℃-700℃, and in some embodiments, the time of the first calcination is 1h-5h. Exemplarily, the temperature of the first calcination (in °C) can be 300, 350, 400, 450, 500, 550, 600, 650, 700, etc., or a value within the range of any two of the above values. Exemplarily, the time of the first calcination (in hours) can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values.

[0096] In some embodiments, the first vapor deposition is followed by a second vapor deposition, the second vapor deposition step including: a second heating, the introduction of a third gas, and a second calcination.

[0097] In some embodiments, the second heating is performed under a protective atmosphere.

[0098] In some embodiments, the second temperature increase includes increasing the temperature at a rate of 3°C / min to 7°C / min to 350°C-750°C.

[0099] In some embodiments, the third gas includes a carbon-containing gas and a third protective gas, and in some embodiments, the flow rate of the third gas is 3 L / min to 7 L / min. Exemplarily, the flow rate (in L / min) of the third gas can be 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, or a value within any two of the above values.

[0100] Furthermore, in some embodiments, the volume ratio of the carbon-containing gas to the third protective gas in the third gas is (2-4):(5-9). Exemplarily, the volume ratio of the carbon-containing gas to the third protective gas can be 2:5, 2:6, 2:7, 2:8, 2:9, 3:5, 3:6, 3:7, 3:8, 4:5, 4:6, 4:7, 4:9, or a value within the range of any two of the above values.

[0101] Furthermore, in some embodiments, the protective gas includes at least one of an inert gas and nitrogen.

[0102] In some embodiments, the second calcination temperature is 350℃-750℃, and in some embodiments, the second calcination time is 1h-5h. Exemplarily, the second calcination temperature (in °C) can be 350, 400, 450, 500, 550, 600, 650, 700, 750, etc., or a value within the range of any two of the above values. Exemplarily, the second calcination time (in hours) can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values.

[0103] In some embodiments, the boron-doped diamond also includes phosphorus.

[0104] In some embodiments, the undoped diamond also includes phosphorus.

[0105] In some embodiments, the preparation steps of the boron-doped diamond include: placing the diamond in a vapor deposition furnace, using hydrogen as a carrier gas, introducing a first boron source, and heating to 700℃-1100℃ at a rate of 1℃ / min-5℃ / min under a protective atmosphere, and holding at this temperature for 1h-5h. The hydrogen gas carries the first boron source and provides a reducing atmosphere, maintaining surface hydrogen termination, thereby helping boron atoms to be effectively doped into the diamond and diffuse, improving the uniformity of doping.

[0106] In some embodiments, the preparation steps of the boron-doped diamond include: mixing diamond and a solid boron source, heating to 700℃-1100℃ at a rate of 1℃ / min-5℃ / min under a hydrogen atmosphere and / or a protective atmosphere, and holding at that temperature for 1h-5h.

[0107] In some embodiments, the first boron source includes at least one of a gaseous boron source and a liquid boron source.

[0108] Furthermore, in some embodiments, the gaseous boron source includes at least one of octylborane and diborane.

[0109] Furthermore, in some embodiments, the liquid boron source includes at least one of trimethyl borate and triethyl borate.

[0110] Furthermore, in some embodiments, the solid boron source includes at least one of boron trioxide and elemental boron.

[0111] The phosphorus-doped diamond and boron-doped phosphorus diamond can be prepared using conventional methods in the art, and this application does not impose any specific limitations. For example, they can be prepared using chemical vapor deposition. The phosphorus source can be any conventionally selected method in the art, such as phosphine.

[0112] In some embodiments, the temperature of the first heat treatment is 700℃-1100℃; the time of the first heat treatment is 1h-5h; for example, the temperature of the first heat treatment (in °C) can be 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, etc., or a value within the range of any two of the above values. For example, the time of the first heat treatment (in hours) can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values.

[0113] Before the first heat treatment, the temperature is increased to the temperature of the first heat treatment by 1℃ / min-5℃ / min.

[0114] In some embodiments, the nitrogen source includes at least one of melamine, urea, aniline, and chitosan.

[0115] According to an embodiment of this application, in a third aspect, 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 in the thickness direction, 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 the silicon-carbon material prepared by the method described in the second aspect.

[0116] It is understood that the negative electrode provided in this application has better cycle performance, energy density and rate performance because it is made of silicon-carbon material prepared by the method described in the first aspect or the method described in the second aspect.

[0117] In some embodiments, the surface of the negative electrode active layer away from the negative electrode current collector is provided with several recesses. Due to the high strength and high hardness of the porous diamond substrate, the silicon-carbon material is not easily damaged during the preparation of the recesses. While ensuring the stability of the silicon-carbon material, it can further improve the wettability of the electrolyte to the negative electrode active layer and the liquid retention capacity of the negative electrode active layer, thereby further improving the cycle performance of the battery.

[0118] In some embodiments, the spacing between two adjacent recesses is 0.5mm-5mm; in some embodiments, the opening width of the recess is 30μm-500μm; and in some embodiments, the depth of the recess is 5μm-50μm. This further improves wettability and liquid retention, thereby enhancing the battery's cycle performance. For example, the spacing (in mm) between two adjacent recesses can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a value within any two of the above values. For example, the opening width (in μm) of the recess can be 30, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, or a value within any two of the above values. For example, the depth of the recess (in μm) can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc., or a value within the range of any two of the above values.

[0119] In this invention, there are no particular limitations on the manufacturing method of the recess, as long as the purpose of this invention can be achieved. For example, the manufacturing method of the recess may include at least one of laser etching, machining, and pore-forming agent processing. In particular, when using laser etching, the high strength and high hardness of the porous diamond substrate can maintain good stability of the silicon-carbon material. In this application, the spacing between two adjacent recesses, the opening width of the recess, and the depth of the recess can be obtained by scanning electron microscopy.

[0120] In some embodiments, the negative electrode current collector comprises copper foil. In some embodiments, the tensile strength of the copper foil is not less than 400 MPa; in some embodiments, the elongation of the copper foil is 2%-6%. Thus, the negative electrode current collector can better withstand the mechanical stress during the production process and the volume changes of the active material during charging and discharging, preventing the electrode from wrinkling or breaking, and ensuring the structural stability of the negative electrode during long cycles. It also avoids the loss of active material or increased internal resistance due to excessive elongation, which would affect the cycle performance of the battery.

[0121] For example, the tensile strength of the copper foil can be measured using conventional methods in the art, such as a universal testing machine. For example, the tensile strength (in MPa) of the copper foil can be 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, or a value within the range of any two of the above values.

[0122] Exemplarily, the elongation of the copper foil can be measured using conventional methods in the art, such as a universal testing machine. Exemplarily, the elongation of the copper foil can be 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, or a value within the range of any two of the above values.

[0123] According to an embodiment of this application, in a fourth aspect, a battery is also provided, including a positive electrode and a negative electrode as described in the third aspect.

[0124] It is understood that the battery provided in this application has better cycle performance, energy density and rate performance because it has the negative electrode sheet described in the third aspect.

[0125] 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.

[0126] Example A1 This embodiment provides a method for preparing silicon-carbon materials, including the following steps: (1) Place 100g of diamond in a vapor deposition furnace, use hydrogen as the carrier gas, introduce trimethyl borate, heat to 900℃ at 2℃ / min under a nitrogen atmosphere, and hold at 900℃ for 2h to obtain boron-doped diamond. (2) In a vapor deposition furnace, under a nitrogen atmosphere, the temperature is increased to 1000℃ at 2℃ / min, held at 1000℃ for 2h, the nitrogen atmosphere is switched to the first gas (the first gas is water vapor and nitrogen with a volume ratio of 1:9), held at 1000℃ for 2h, and cooled to room temperature under a nitrogen atmosphere to obtain carbide diamond. (4) Mix diamond carbide and melamine at a mass ratio of 10:1, place them in a tube furnace, heat them to 900°C at 5°C / min under a nitrogen atmosphere, keep them at 900°C for 3 hours, and cool them to room temperature to obtain nitrogen-doped diamond carbide. (5) Nitrogen-doped carbide diamond and iron oxide were mixed at a mass ratio of 1:5, placed in a tube furnace, heated to 950°C at a rate of 5°C / min under a nitrogen atmosphere, held for 5 hours, cooled to room temperature, washed in aqua regia, filtered, washed with deionized water until neutral, and then transferred to a vacuum oven at 120°C for drying to obtain a porous diamond substrate with a specific surface area of ​​1800 m². 2 / g, the pore volume of the porous diamond substrate is 0.81cm³. 3 / g, the pore size of the porous diamond substrate ranges from 0.05nm to 8.5nm; (6) Place the porous diamond substrate in a vapor deposition furnace, and heat it to 500°C at 5°C / min under a nitrogen atmosphere. Then, introduce a second gas at 4L / min (the second gas is silane gas and nitrogen gas with a volume ratio of 1:4). Keep it at 500°C for 3 hours and then stop introducing the second gas. (7) Under a nitrogen atmosphere, the temperature is increased to 550°C at 5°C / min, and a third gas (a mixture of acetylene and nitrogen with a volume ratio of 3:7) is introduced at 5L / min. The temperature is maintained at 550°C for 3 hours, the third gas is stopped, and the temperature is cooled to room temperature under a nitrogen atmosphere to obtain silicon-carbon material.

[0127] The parameters of the silicon-carbon material prepared in this embodiment are detailed in Table 1-2. The powder resistivity of the silicon-carbon material is 1.35 Ω·cm, and the specific surface area of ​​the silicon-carbon material is 0.98 m². 2 / g, the particle size distribution Span value of the silicon-carbon material is 0.95, and the I in the Raman spectrum D This indicates that the Raman displacement is at 1350 cm. -1 The peak intensity of the Raman peak at the location, I G This indicates that the Raman displacement is at 1580 cm. -1 Peak intensity of the Raman peak at the location.

[0128] The preparation methods of Examples A2-A22 and Comparative Example A1 are basically the same as those of Example A1. The differences are shown in Tables 1-2. In the table, " / " indicates that the item does not exist.

[0129] Example A23 This embodiment provides a method for preparing silicon-carbon materials, including the following steps: (1) Place 100g of diamond in a vapor deposition furnace, use hydrogen as the carrier gas, introduce octylborane, and heat to 850℃ at 2℃ / min under a nitrogen atmosphere. Hold at 850℃ for 1h to obtain boron-doped diamond. (2) In a vapor deposition furnace, under a nitrogen atmosphere, the temperature is increased to 950℃ at 2℃ / min, held at 950℃ for 2.5h, the nitrogen atmosphere is switched to the first gas (the first gas is water vapor and nitrogen with a volume ratio of 1.5:8.5), held at 950℃ for 2.5h, and cooled to room temperature under a nitrogen atmosphere to obtain carbide diamond. (4) Mix diamond carbide and urea at a mass ratio of 8:1, place them in a tube furnace, heat them to 900°C at 4°C / min under a nitrogen atmosphere, keep them at 900°C for 4 hours, and cool them to room temperature to obtain nitrogen-doped diamond carbide. (5) Nitrogen-doped carbide diamond and iron oxide are mixed at a mass ratio of 1:6, placed in a tube furnace, heated to 900°C at 4°C / min under a nitrogen atmosphere, kept at the temperature for 5.5h, cooled to room temperature, washed in aqua regia, filtered, washed with deionized water until neutral, and transferred to a vacuum oven at 120°C for drying to obtain a porous diamond substrate. (6) Place the porous diamond substrate in a vapor deposition furnace, and heat it to 450°C at 5°C / min under a nitrogen atmosphere. Then, introduce a second gas at 5L / min (the second gas is silane gas and nitrogen gas with a volume ratio of 1:5). Keep it at 450°C for 4 hours and then stop introducing the second gas. (7) Under a nitrogen atmosphere, the temperature is increased to 550°C at 5°C / min, and a third gas (acetylene and nitrogen in a volume ratio of 3:8) is introduced at 4L / min. The temperature is maintained at 550°C for 3.5h, the third gas is stopped, and the temperature is cooled to room temperature under a nitrogen atmosphere to obtain silicon-carbon material.

[0130] The parameters of the silicon-carbon material prepared in this embodiment are detailed in Table 1-2.

[0131] Example A24 This embodiment provides a method for preparing silicon-carbon materials, including the following steps: (1) Mix 100g of diamond and 1g of boron trioxide solid phase, heat to 950℃ at 2℃ / min under nitrogen atmosphere, and keep at 950℃ for 2.5h to obtain boron-doped diamond; (2) In a vapor deposition furnace, under a nitrogen atmosphere, the temperature is increased to 1050℃ at 2℃ / min, held at 1050℃ for 2h, the nitrogen atmosphere is switched to the first gas (the first gas is water vapor and nitrogen with a volume ratio of 1:9), held at 1050℃ for 2.5h, and cooled to room temperature under a nitrogen atmosphere to obtain carbide diamond. (4) Mix diamond carbide and aniline at a mass ratio of 9:1, place them in a tube furnace, heat them to 950°C at 5°C / min under a nitrogen atmosphere, hold them at that temperature for 3 hours, and cool them to room temperature to obtain nitrogen-doped diamond carbide. (5) Mix nitrogen-doped carbide diamond and iron oxide at a mass ratio of 1:4, place them in a tube furnace, heat them to 1000℃ at 5℃ / min under a nitrogen atmosphere, keep them at the temperature for 4h, cool them to room temperature, wash them in aqua regia, filter them, wash them with deionized water until they are neutral, transfer them to a vacuum oven at 120℃ for drying, and obtain a porous diamond substrate. (6) Place the porous diamond substrate in a vapor deposition furnace, and heat it to 550°C at 5°C / min under a nitrogen atmosphere. Then, introduce a second gas at 5L / min (the second gas is silane gas and nitrogen gas with a volume ratio of 1:4). Keep it at 550°C for 3 hours and then stop introducing the second gas. (7) Under a nitrogen atmosphere, the temperature is increased to 600°C at 5°C / min, and a third gas (a mixture of acetylene and nitrogen with a volume ratio of 3:7) is introduced at 6L / min. The temperature is maintained at 600°C for 3 hours, the third gas is stopped, and the temperature is cooled to room temperature under a nitrogen atmosphere to obtain silicon-carbon material.

[0132] The parameters of the silicon-carbon material prepared in this embodiment are detailed in Table 1-2.

[0133] Example A25 This embodiment provides a method for preparing silicon-carbon materials, including the following steps: (1) Place 100g of diamond in a vapor deposition furnace, use hydrogen as the carrier gas, introduce triethyl borate, heat to 900℃ at 2℃ / min under a nitrogen atmosphere, and hold at 900℃ for 2h to obtain boron-doped diamond. (2) In a vapor deposition furnace, under a nitrogen atmosphere, the temperature is increased to 1000℃ at 2℃ / min, held at 1000℃ for 2h, the nitrogen atmosphere is switched to the first gas (the first gas is water vapor and nitrogen with a volume ratio of 1:9), held at 1000℃ for 2h, and cooled to room temperature under a nitrogen atmosphere to obtain carbide diamond. (4) Mix carbonized diamond and chitosan at a mass ratio of 10:1, place them in a tube furnace, heat them to 900°C at 5°C / min under a nitrogen atmosphere, keep them at 900°C for 3 hours, and cool them to room temperature to obtain nitrogen-doped carbonized diamond. (5) Nitrogen-doped carbide diamond and iron oxide are mixed at a mass ratio of 1:5, placed in a tube furnace, heated to 950°C at 5°C / min under a nitrogen atmosphere, kept at the temperature for 5 hours, cooled to room temperature, washed in aqua regia, filtered, washed with deionized water until neutral, and transferred to a vacuum oven at 120°C for drying to obtain a porous diamond substrate. (6) Place the porous diamond substrate in a vapor deposition furnace, and heat it to 500°C at 5°C / min under a nitrogen atmosphere. Then, introduce a second gas at 4L / min (the second gas is silane gas and nitrogen gas with a volume ratio of 1:4). Keep it at 500°C for 3 hours and then stop introducing the second gas. (7) Under a nitrogen atmosphere, the temperature is increased to 600°C at 5°C / min, and a third gas (a mixture of acetylene and nitrogen with a volume ratio of 3:7) is introduced at 5L / min. The temperature is maintained at 600°C for 2.5h, the third gas is stopped, and the temperature is cooled to room temperature under a nitrogen atmosphere to obtain silicon-carbon material.

[0134] The parameters of the silicon-carbon material prepared in this embodiment are detailed in Table 1-2.

[0135] The preparation methods of Examples A26-A29 are basically the same as those of Example A1, with the differences shown in Tables 1-2. " / " indicates that the item does not exist.

[0136] Table 1. Preparation process variables of the examples

[0137] Table 2 Variables for Example and Comparative Example 2

[0138] Comparative Example A2 This comparative example provides a method for preparing silicon-carbon materials, including the following steps: (1) Place 100g of phenolic resin in a vapor deposition furnace, and heat it to 900℃ at 2℃ / min under a nitrogen atmosphere. Hold it at 900℃ for 2h, then heat it to 1000℃ at 2℃ / min and hold it at 1000℃ for 2h. Switch the nitrogen atmosphere to the first gas (the first gas is water vapor and nitrogen in a volume ratio of 1:9), hold it at 1000℃ for 3h, and cool it to room temperature under a nitrogen atmosphere to obtain resin-based porous carbon. (2) Place the resin-based porous carbon in a vapor deposition furnace, and under a nitrogen atmosphere, heat it to 500°C at 5°C / min. Then, introduce a second gas at 4L / min (the second gas is silane and nitrogen in a volume ratio of 1:4). Keep it at 500°C for 3 hours and then stop introducing the second gas. (3) Under a nitrogen atmosphere, the temperature is increased to 550°C at 5°C / min, and a third gas (acetylene and nitrogen in a volume ratio of 3:7) is introduced at 5L / min. The temperature is maintained at 550°C for 3 hours, the third gas is stopped, and the temperature is cooled to room temperature under a nitrogen atmosphere to obtain silicon-carbon material.

[0139] Comparative Example A3 This comparative example provides a method for preparing silicon-carbon materials, including the following steps: (1) Place 100g of phenolic resin in a vapor deposition furnace, and heat it to 900℃ at 2℃ / min under a nitrogen atmosphere. Hold it at 900℃ for 2h, then heat it to 1000℃ at 2℃ / min and hold it at 1000℃ for 2h. Switch the nitrogen atmosphere to the first gas (the first gas is water vapor and nitrogen in a volume ratio of 1:9), hold it at 1000℃ for 3h, and cool it to room temperature under a nitrogen atmosphere to obtain resin-based porous carbon. (2) Place the resin-based porous carbon in a vapor deposition furnace, and under a nitrogen atmosphere, heat it to 580°C at 5°C / min. Then, introduce a second gas at 4L / min (the second gas is silane and nitrogen in a volume ratio of 1:4). Keep it at 580°C for 3 hours and then stop introducing the second gas. (3) Under a nitrogen atmosphere, maintain 580°C and introduce a third gas at a rate of 5 L / min (the third gas is acetylene and nitrogen in a volume ratio of 3:7). Keep at 580°C for 3 hours, stop introducing the third gas, and cool to room temperature under a nitrogen atmosphere to obtain silicon-carbon material.

[0140] 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.

[0141] (2) Preparation of negative electrode The silicon-carbon material, artificial graphite, hydroxymethyl cellulose, styrene-butadiene rubber, lithium polyacrylate, conductive carbon black (Super P), and carbon nanotubes prepared in Example A1 were mixed in a ratio of 10:86.5:0.8:0.6:1.1:0.8:0.2. 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 for negative electrode current collector (parameters are detailed in Table 3). 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 the negative electrode sheet. The parameters of the concave part on the negative electrode sheet are detailed in Table 3.

[0142] (3) Electrolyte preparation Lithium hexafluorophosphate was dissolved in a solvent with a volume ratio of ethylene carbonate / dimethyl carbonate of 1:1. Based on the mass of the electrolyte, 10 wt% of fluoroethylene carbonate (FEC) was added, and the concentration of lithium hexafluorophosphate was 1.2 mol / L to obtain the electrolyte.

[0143] (4) Preparation of lithium-ion batteries The prepared negative electrode sheet, separator (polyethylene film with a thickness of 9μm) and prepared positive electrode sheet are stacked in sequence, and then the bare cell is obtained by winding. 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.

[0144] The preparation methods of Examples B2-B29 and Comparative Examples B1-B3 are basically the same as those of Example B1, with the differences shown in Table 3. In the table, " / " indicates that the item does not exist.

[0145] Table 3 Variables for Examples and Comparative Examples

[0146] Test case The lithium-ion batteries of Examples B1-B29 and Comparative Examples B1-B3 were tested as follows: (1) Cyclic performance test: The lithium-ion battery is charged to 4.5V at a constant current density of 1.5C, then charged at a constant voltage of 4.5V with a cutoff current of 0.05C, and then left to stand for 10 minutes. Then it is discharged to 3.0V at a current density of 1C, 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 3.0V, 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%.

[0147] (2) Volumetric energy density test: The lithium-ion battery was charged to 4.5V with a constant current density of 0.2C, and then charged at a constant voltage of 4.5V. The current was cut off at 0.02C. After standing for 10 minutes, the battery was discharged to 3.0V with a constant current density of 0.2C and then stood for 10 minutes. The first charge capacity, discharge capacity and first discharge energy of the battery were recorded. Then the battery was charged with a constant current density of 0.2C. The cutoff condition was that the charging capacity reached half of the first discharge capacity. After the cutoff, the battery was removed and the thickness, length and width of the battery were measured. The volumetric energy density of the battery = first discharge energy / (length × width × thickness).

[0148] (3) Rate performance test: At 25℃, charge to 4.5V at 0.2C, cut off current at 0.05C, discharge to cut off voltage at 0.2C to 3.0V to obtain the initial capacity C0. Then charge to 4.5V at 0.2C, cut off current at 0.05C, discharge to cut off voltage at 1C to 3.0V, and record the discharge capacity as C1. That is, rate performance = C1 / C0×100%.

[0149] (4) K-value pass rate test: The batteries prepared in each example and comparative example were placed in an ambient temperature of (25±2)℃. After the batteries were formed, they were first placed at 60℃ for 24 hours, and the open circuit voltage OCV1 of the battery was tested at time t1. Then, they were placed at 25℃ for 48 hours, and the open circuit voltage OCV2 of the battery was tested at time t2. K value = ((OCV1-OCV2) / (t1-t2)). A K value less than or equal to 0.02mv / h was considered to have passed the K-value test. 50 batteries were tested and the pass rate was calculated. The specific results are shown in Table 4.

[0150] Table 4 Test results of the examples and comparative examples

[0151] As can be seen from Tables 1-4, compared to Comparative Example B1 (porous diamond substrate without dopant elements) and Comparative Examples B2-B3 (resin-based porous carbon as porous carbon substrate), Examples B1-B29 showed varying degrees of improvement in cycle performance, rate performance, and energy density. This indicates that the porous diamond substrate possesses strong hardness and strength, maintaining excellent structural integrity even after long cycles, thereby improving battery stability. Furthermore, the dopant elements enhance the conductivity of the porous diamond substrate and reduce battery impedance, thus simultaneously improving the battery's cycle performance, rate performance, and energy density.

[0152] 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 silicon-carbon material includes a porous diamond substrate and silicon particles dispersed inside the pores of the porous diamond substrate. The porous diamond substrate comprises a diamond crystal structure; The porous diamond substrate includes a doping element located within the diamond crystal structure, and the doping element includes at least one of boron and nitrogen.

2. The silicon-carbon material according to claim 1, characterized in that, Based on the mass of the silicon-carbon material, the mass content of the boron element is 0.05ppm-500ppm; And / or, based on the mass of the silicon-carbon material, the mass content of nitrogen is 0.1%-5%; preferably, the doping amount of nitrogen is 0.5%-2%.

3. The silicon-carbon material according to claim 1 or 2, characterized in that, The sphericity of the silicon-carbon material is denoted by F, and satisfies 0.5 ≤ F ≤ 0.95; And / or, in the Raman spectrum of the porous diamond substrate, 1.2 ≤ I D / I G ≤1.8, wherein the I D This indicates that the Raman displacement is at 1330 cm. -1 -1380cm -1 The peak intensity of the Raman peak at the location, I G This indicates that the Raman displacement is at 1550 cm. -1 -1620cm -1 The peak intensity of the Raman peak at the location; preferably, 1.3 ≤ I D / I G ≤1.

5.

4. The silicon-carbon material according to claim 1 or 2, characterized in that, Based on the mass of the silicon-carbon material, the silicon content is 10%-50% by mass; And / or, the median particle size of the silicon-carbon material is 3 μm-15 μm; And / or, the particle size distribution Span value of the silicon-carbon material is 0.1-10; And / or, in the porous diamond substrate, the volume percentage of pores with a diameter not exceeding 2 nm is 75%-95%, the volume percentage of pores with a diameter of 2 nm-5 nm is 5%-20%, and the volume percentage of pores with a diameter of 5 nm-10 nm is 0%-5%; And / or, at 25°C, the resistivity of the silicon carbide powder is 0.1 Ω·cm-100 Ω·cm, preferably 0.1 Ω·cm-50 Ω·cm; And / or, the Vickers hardness of the silicon-carbon material is 150-500.

5. A method for preparing a silicon-carbon material, characterized in that, Includes either Method 1 or Method 2 as follows: Method 1 includes the following steps: boron-doped diamond is sintered in a protective atmosphere and pores are formed in a first gas; the product of the first pore formation is mixed with a pore-forming agent and sintered in a second atmosphere to obtain a porous diamond substrate, and then a first vapor deposition is performed to obtain a silicon-carbon material. Method 2 includes the following steps: sintering boron-doped diamond and / or non-boron-doped diamond under a protective atmosphere, and creating pores under a first gas; mixing the product from the first pore-forming process with a nitrogen source, and performing a first heat treatment to obtain nitrogen-doped carbide diamond; mixing the nitrogen-doped carbide diamond with a pore-forming agent, and performing a second sintering under a protective atmosphere to obtain a porous diamond substrate; and then performing a first vapor deposition to obtain a silicon-carbon material. Preferably, the first vapor deposition step includes: placing a porous diamond substrate in a vapor deposition furnace, heating it to a first temperature, introducing a second gas, and performing a first calcination. Preferably, the first vapor deposition is followed by a second vapor deposition, the second vapor deposition step including: a second heating, the introduction of a third gas, and a second calcination.

6. The method for preparing silicon-carbon material according to claim 5, characterized in that, The first sintering temperature is 800℃-1200℃; and / or the first sintering time is 1h-5h; And / or, the protective atmosphere includes at least one of an inert atmosphere and a nitrogen atmosphere; And / or, the first gas comprises water vapor and nitrogen, preferably, the volume ratio of water vapor to nitrogen is 1:(7-11); And / or, the first pore-forming step includes: maintaining a temperature of 800℃-1200℃ for 1h-5h; And / or, the second sintering temperature is 750℃-1150℃; and / or, the second sintering time is 3h-7h; And / or, the pore-forming agent includes iron oxide; And / or, the first temperature increase includes: increasing the temperature to 300°C-700°C at a rate of 3°C / min-7°C / min; And / or, the second gas includes a silicon-containing gas and a second protective gas, and / or, the flow rate of the second gas is 2 L / min to 6 L / min; preferably, the volume ratio of the silicon-containing gas and the second protective gas in the second gas is 1:(2-6); preferably, the second protective gas includes at least one of an inert gas and nitrogen. And / or, the temperature of the first calcination is 300℃-700℃, and / or, the time of the first calcination is 1h-5h; And / or, the second temperature increase includes: increasing the temperature at a rate of 3°C / min to 7°C / min to 350°C to 750°C; And / or, the third gas includes a carbon-containing gas and a third protective gas, and / or, the flow rate of the third gas is 3 L / min-7 L / min; preferably, the volume ratio of the carbon-containing gas to the third protective gas in the third gas is (2-4):(5-9); preferably, the third protective gas includes at least one of an inert gas and nitrogen. And / or, the temperature of the second calcination is 350℃-750℃, and / or, the time of the second calcination is 1h-5h; And / or, the preparation steps of the boron-doped diamond include: placing diamond in a vapor deposition furnace, using hydrogen as the carrier gas, introducing a first boron source, and heating to 700℃-1100℃ at a rate of 1℃ / min-5℃ / min under a protective atmosphere, and holding at that temperature for 1h-5h; preferably, the first boron source includes at least one of a gaseous boron source and a liquid boron source; more preferably, the gaseous boron source includes at least one of octylborane and diborane; more preferably, the liquid boron source includes at least one of trimethyl borate and triethyl borate; And / or, the preparation steps of the boron-doped diamond include: mixing diamond and a solid boron source, heating to 700℃-1100℃ at 1℃ / min-5℃ / min under a hydrogen atmosphere and / or a protective atmosphere, and holding at that temperature for 1h-5h; preferably, the solid boron source includes at least one of boron trioxide and elemental boron. And / or, the temperature of the first heat treatment is 700℃-1100℃; and / or, the time of the first heat treatment is 1h-5h; And / or, the nitrogen source includes at least one of melamine, urea, aniline, and chitosan.

7. 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 in the thickness direction, the negative electrode active layer comprising a negative electrode active material; the negative electrode active material comprising the silicon-carbon material of any one of claims 1-4 or the silicon-carbon material prepared by the method of preparing the silicon-carbon material of claims 5 or 6.

8. The negative electrode sheet according to claim 7, characterized in that, The surface of the negative electrode active layer away from the negative electrode current collector is provided with several recesses; The distance between two adjacent recesses is 0.5mm-5mm, and / or the opening width of the recess is 30μm-500μm, and / or the depth of the recess is 5μm-50μm.

9. The negative electrode sheet according to claim 7 or 8, characterized in that, The negative electrode current collector includes copper foil. The copper foil has a tensile strength of not less than 400 MPa; and / or, the copper foil has an elongation of 2%-6%.

10. A battery, characterized in that, It includes a positive electrode and a negative electrode as described in any one of claims 7-9.

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