Silicon-carbon composite material, preparation method thereof and lithium ion battery

Abstract

The invention provides a silicon-carbon composite material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion battery negative electrode materials, the silicon-carbon composite material adopts an interlaced network constructed by carbon nanotubes, so that primary silicon-carbon particles are connected into a secondary particle interlaced body; oxygen-containing functional groups on the surfaces of the primary silicon carbon particles form covalent bonds with the carbon nanotubes. According to the invention, the carbon nanotube is used as a'structural rib 'to connect a plurality of independent silicon-carbon particles to construct a complete three-dimensional interwoven body, and an integrated and long-range ordered conductive and buffer network is obtained, so that the silicon-carbon composite material has lower charge transfer resistance and lower volume expansion rate, and the structural integrity of the electrode is remarkably improved.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion battery anode materials, and in particular to a silicon-carbon composite material and its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid growth in demand for high-energy-density lithium-ion batteries from electric vehicles, large-scale energy storage, and portable electronic devices, the development of next-generation high-performance anode materials has become crucial. Silicon (Si) is considered the most promising next-generation anode material due to its extremely high theoretical specific capacity (approximately 4200 mAh / g, more than ten times that of traditional graphite anodes), suitable lithium intercalation potential, and abundant reserves.

[0003] However, silicon materials have long faced two fundamental bottlenecks in practical applications. The first is the huge volume expansion effect. When silicon is fully intercalated with lithium (alloyed), the volume expansion can reach more than 300%. Repeated and violent expansion and contraction will cause the active material particles to break and pulverize, and peel off from the current collector, resulting in the rapid collapse of the electrode structure and a sharp decline in battery cycle life. The second is the poor intrinsic conductivity. As a semiconductor, silicon's low electronic conductivity and ion diffusion rate severely restrict the charge and discharge rate, resulting in poor rate performance of the battery.

[0004] To address the aforementioned issues, existing technologies primarily focus on the nano- and composite design of silicon materials. However, whether it is the existing technology CN113451570A or the various silicon-carbon composite structures reported in academic journals such as Advanced Materials, their improvements are mostly limited to the optimization of the microstructure within individual particles, failing to systematically solve the problems of robustness of the conductive network and synergistic dispersion of volume expansion from the perspective of the overall electrode framework.

[0005] Therefore, developing a novel integrated structure that can macroscopically integrate electrode active materials while providing efficient electronic conduction and mechanical buffering is of great significance for promoting the practical application of silicon-based anodes.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] One of the objectives of this invention is to provide a silicon-carbon composite material with lower charge transport resistance and lower volume expansion rate, which significantly improves the integrity of the electrode structure.

[0008] The second objective of this invention is to provide a method for preparing silicon-carbon composite materials that is suitable for industrial-scale production.

[0009] The third objective of this invention is to provide a lithium-ion battery.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, there is a silicon-carbon composite material, wherein the silicon-carbon composite material employs an interwoven network constructed of carbon nanotubes, which connects primary silicon-carbon particles into a secondary interwoven particle body. The surface of the primary silicon-carbon particles is modified with oxygen-containing functional groups, which form covalent bonds with carbon nanotubes.

[0011] Furthermore, the oxygen-containing functional group includes at least one of hydroxyl, carboxyl, carbonyl, and epoxy groups.

[0012] Furthermore, the total oxygen mass content W1 of the oxygen-containing functional groups satisfies 0.1% ≤ W1 ≤ 1%; Preferably, the total hydrogen mass content W2 of the oxygen-containing functional groups satisfies 0.5% ≤ W2 ≤ 2%.

[0013] Furthermore, the number N1 of the primary silicon-carbon particles satisfies 2≤N1≤50; Preferably, the primary silicon-carbon particles have a particle size of 2μm-20μm; Preferably, the number N2 of interlacing lines between the primary silicon-carbon particles satisfies 1≤N2≤20; Preferably, the interlacing lines are composite carbon nanotubes formed by combining several carbon nanotubes; Preferably, the diameter R1 of the composite carbon nanotube satisfies 0.6nm≤R1≤500nm.

[0014] Furthermore, the diameter R2 of the carbon nanotubes on the surface of the primary silicon-carbon particles satisfies 0.6nm≤R2≤100nm; Preferably, the distribution density K of the carbon nanotubes anchored on the surface of the primary silicon-carbon particles satisfies 0.5 μm. -2 ≤K≤1.8μm -2 .

[0015] Furthermore, in the silicon-carbon composite material, the crystallite size D1 of the nano-silicon on the (111) crystal plane satisfies D1≤3nm; Preferably, the silicon-carbon composite material has a silicon content of 40%-70% by mass, a total carbon content of 25%-60% by mass, an oxygen content of 0.1%-1% by mass, and a hydrogen content of 0.5%-2% by mass.

[0016] Furthermore, the specific surface area of ​​the silicon-carbon composite material is 0.2 m². 2 / g-2m 2 / g, powder resistivity 1Ω cm-15Ω cm, the true density of helium is 1.2 g / cm³. 3 -2.1g / cm 3 .

[0017] Secondly, a method for preparing the silicon-carbon composite material according to any one of the above claims includes the following steps: Silicon carbon, carbon nanotubes, dispersant and surfactant are mixed in the liquid phase and dried to obtain the silicon carbon composite material.

[0018] Furthermore, the silicon-carbon is made of porous carbon-deposited nano-silicon; Preferably, the temperature for depositing porous carbon nanosilicon is 400℃-800℃; Preferably, the silicon-carbon surface is modified with oxygen-containing functional groups; Preferably, the method for modifying the silicon-carbon surface with oxygen-containing functional groups includes plasma treatment. Preferably, the plasma treatment method has a power of 200W-1000W, a treatment time of 10min-100min, and a treatment pressure of 10Pa-100Pa; Preferably, the gas source used in the plasma treatment method includes at least one of oxygen, air, and water vapor.

[0019] Thirdly, a lithium-ion battery, wherein the negative electrode of the lithium-ion battery uses an active material comprising the silicon-carbon composite material described in any of the preceding claims.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: The silicon-carbon composite material provided by this invention has an interwoven structure. Specifically, it utilizes carbon nanotubes to construct an interwoven network, connecting multiple primary silicon-carbon particles into a secondary particle interwoven body. The primary and secondary particles can be spherical, blocky, or amorphous. On one hand, it upgrades from "reinforcing individual particles" (such as carbon coating) to "binding the entire particle cluster." The carbon nanotube network acts like a highly elastic "fishing net," catching and connecting the silicon-carbon particles. When a silicon-carbon particle expands, its stress is absorbed by the surrounding carbon nanotube network and dispersed throughout the electrode, effectively preventing the collapse of the local structure. On the other hand, the carbon nanotubes are connected to the silicon-carbon particles through chemical bonds or tight entanglement, forming a stable "wire," ensuring uninterrupted electron transfer throughout the cycle. In addition, the interwoven body itself forms abundant porous channels, which not only facilitates rapid ion movement but also reserves internal space for the volume expansion of silicon, further reducing the compression on the external electrode structure. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in 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 the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 An electron microscope image and structural schematic diagram of a silicon-carbon composite material provided in one embodiment of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] According to a first aspect of the present invention, a silicon-carbon composite material is provided, see Figure 1 The silicon-carbon composite material uses an interwoven network constructed from carbon nanotubes, which connects primary silicon-carbon particles into a secondary interwoven particle body. The surface of the silicon-carbon particles has oxygen-containing functional groups that form covalent bonds with carbon nanotubes.

[0025] The silicon-carbon composite material of this invention has an interwoven structure, specifically utilizing carbon nanotubes to construct an interwoven network, connecting multiple primary silicon-carbon particles into a secondary particle interwoven body. The primary and secondary particles can be spherical, blocky, or amorphous. On one hand, it upgrades from "reinforcing individual particles" (such as carbon coating) to "binding the entire particle cluster." The carbon nanotube network acts like a highly elastic "fishing net," catching and connecting the silicon-carbon particles. When a silicon-carbon particle expands, its stress is absorbed by the surrounding carbon nanotube network and dispersed throughout the electrode, effectively preventing the collapse of the local structure. On the other hand, the carbon nanotubes are connected to the silicon-carbon particles through chemical bonds or tight entanglement, forming a stable "wire," ensuring uninterrupted electron transfer throughout the cycle. In addition, the interwoven body itself forms abundant porous channels, which not only facilitates rapid ion movement but also reserves internal space for the volume expansion of silicon, further reducing the compression on the external electrode structure.

[0026] In a preferred embodiment, the oxygen-containing functional group can be one or more of hydroxyl (-OH), carboxyl (-COOH), carbonyl (C=O) and epoxy (-CH(O)CH-), which can enhance the anchoring effect of carbon nanotubes on silicon-carbon surfaces.

[0027] In a preferred embodiment, the total oxygen mass content W1 of the oxygen-containing functional groups modified on the surface of the primary silicon-carbon particles can satisfy 0.1%≤W1≤1%; the total hydrogen mass content W2 of the oxygen-containing functional groups modified on the surface of the primary silicon-carbon particles can satisfy 0.5%≤W2≤2%.

[0028] In this invention, the number of primary silicon-carbon particles N1 can satisfy 2≤N1≤50, and the particle size of the primary silicon-carbon particles can be 2μm-20μm.

[0029] There are interlacing lines between adjacent primary silicon-carbon particles, and the number of interlacing lines N2 can satisfy 1≤N2≤20; the interlacing lines can be composite carbon nanotubes formed by combining several carbon nanotubes, and the diameter R1 of the composite carbon nanotubes can satisfy 0.6nm≤R1≤500nm.

[0030] In this invention, the diameter R2 of the carbon nanotubes on the surface of the primary silicon-carbon particles can satisfy 0.6nm≤R2≤100nm.

[0031] In a preferred embodiment, the distribution density K of the carbon nanotubes anchored on the surface of the primary silicon-carbon particles can satisfy 0.5 μm. -2 ≤K≤1.8μm -2 , which refers to the number of carbon nanotubes distributed per unit area on the surface of silicon-carbon composite materials.

[0032] In silicon-carbon composite materials, the crystallite size D1 of nano-silicon on the (111) crystal plane can satisfy D1≤3nm.

[0033] In a preferred embodiment, the silicon mass content in the silicon-carbon composite material can be 40%-70%, with typical but non-limiting mass contents such as 40%, 50%, 60%, and 70%.

[0034] In a preferred embodiment, the total carbon mass content in the silicon-carbon composite material can be 25%-60%, with typical but non-limiting mass contents such as 25%, 30%, 40%, 50%, and 60%.

[0035] In a preferred embodiment, the oxygen content in the silicon-carbon composite material can be 0.1%-1% by mass, with typical but non-limiting mass contents such as 0.1%, 0.5%, and 1%.

[0036] In a preferred embodiment, the hydrogen mass content in the silicon-carbon composite material can be 0.5%-2%, with typical but non-limiting mass contents such as 0.5%, 1%, and 2%.

[0037] In this invention, the specific surface area of ​​the silicon-carbon composite material can be 0.2 m². 2 / g-2m 2 / g, the resistivity of the powder can be 1Ω cm-15Ω The true density of helium is 1.2 g / cm³. 3 -2.1g / cm 3 .

[0038] According to a second aspect of the present invention, a method for preparing the silicon-carbon composite material according to any one of the above claims is provided, comprising the following steps: Silicon-carbon, carbon nanotubes, dispersants, and surfactants are mixed in the liquid phase and then dried to obtain a silicon-carbon composite material.

[0039] The preparation method of this invention is suitable for industrial-scale production.

[0040] A typical preparation method for a silicon-carbon composite material includes the following steps: Step S1: Select commercial porous carbon, introduce silicon source gas under an inert atmosphere, and perform nano-silicon deposition to obtain silicon-carbon; Step S2: Surface treatment of silicon carbon is performed by plasma treatment to modify the surface of silicon carbon with a certain amount of oxygen-containing functional groups to obtain silicon carbon modified with oxygen-containing functional groups. Step S3: Mix oxygen-functionalized silicon-carbon, carbon nanotubes, dispersant and surfactant in liquid phase, and obtain silicon-carbon composite material by flash evaporation, spray drying, filtration or evaporation.

[0041] In a preferred embodiment, the inert atmosphere may be selected from one or more of nitrogen, argon and helium; the silicon source gas may be selected from one or more of silane, silane, propane, silicon tetrachloride and methyltrichlorosilane.

[0042] In this invention, the temperature for depositing porous carbon nano-silicon can be 400°C-800°C, with typical but non-limiting temperatures such as 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, and 800°C.

[0043] In this invention, the power of the reaction chamber device in plasma treatment can be 200W-1000W, the reaction chamber treatment time can be 10min-100min, the reaction gas source can be selected from oxygen, air or water vapor, and the gas pressure inside the chamber is kept stable between 10Pa-100Pa.

[0044] In a preferred embodiment, the carbon nanotubes may be selected from one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and double-walled carbon nanotubes.

[0045] In a preferred embodiment, the dispersant may be selected from one or more of sodium carboxymethyl cellulose, sodium alginate, polyacrylic acid, and polyvinylpyrrolidone.

[0046] In a preferred embodiment, the surfactant may be selected from one or more of sodium alkylbenzene sulfonate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether phosphate, and nonylphenol polyoxyethylene ether phosphate.

[0047] According to a third aspect of the present invention, a lithium-ion battery is provided, wherein the negative electrode of the lithium-ion battery uses an active material comprising the silicon-carbon composite material described in any of the preceding claims.

[0048] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0049] Example 1 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, vacuumed, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 600 W, and a reaction time of 600 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium carboxymethyl cellulose, and sodium dodecylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.012:0.004:0.003, with a solid content of 30%. The mixture was stirred for 2 hours and then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 38% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0050] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray diffraction, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.23 m. 2 / g、9Ω cm, 1.97g / cm 3 1.1nm and 0.8μm -2 .

[0051] Example 2 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 3 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, vacuumed, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 600 W, and a reaction time of 600 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium carboxymethyl cellulose, and sodium dodecylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.015:0.004:0.003, with a solid content of 30%. The mixture was stirred for 2 hours and then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 65% silicon by mass, 33% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0052] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray derivatization, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.02 m. 2 / g, 13Ω cm, 2.0g / cm 3 1.7nm and 0.9μm -2 .

[0053] Example 3 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 7 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, vacuumed, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 600 W, and a reaction time of 600 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium alginate and sodium alkylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.018:0.004:0.003, with a solid content of 30%. The mixture was stirred for 2 hours and then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 70% silicon by mass, 28% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0054] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray derivatization, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 0.89 m. 2 / g, 15Ω cm, 2.05g / cm 32.4nm and 1.1μm -2 .

[0055] Example 4 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, a vacuum was drawn, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 800 W, and a reaction time of 660 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium carboxymethyl cellulose and sodium dodecylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.012:0.004:0.003, with a solid content of 30%, and stirred for 2 hours. The mixture was then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 37% carbon by mass, 1% oxygen by mass, and 2% hydrogen by mass.

[0056] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray diffraction, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.33 m. 2 / g, 7Ω cm, 1.92g / cm 3 1.2nm and 1.0μm -2 .

[0057] Example 5 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, vacuumed, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 600 W, and a reaction time of 600 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium carboxymethyl cellulose and sodium dodecylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.021:0.004:0.003, with a solid content of 30%, and stirred for 2 hours. The mixture was then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 38% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0058] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray diffraction, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.26 m. 2 / g, 4Ω cm, 1.93g / cm 3 1.1nm and 1.5μm -2 .

[0059] Example 6 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 450℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, vacuumed, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 600 W, and a reaction time of 600 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium carboxymethyl cellulose and sodium alkylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.012:0.004:0.003, with a solid content of 30%. The mixture was stirred for 2 hours and then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 40% silicon by mass, 58% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0060] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray derivatization, surface area analyzer, powder resistivity meter, and gas displacement true density meter. The results showed that the specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K were 2m. 2 / g, 10Ω cm, 1.81g / cm 3 0.7nm and 0.8μm -2 .

[0061] Example 7 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon was placed in the reaction chamber, a vacuum was drawn, and a reaction gas source was introduced to maintain a pressure of 50 Pa, an equipment power of 600 W, and a reaction time of 10 seconds to obtain silicon carbon modified with oxygen-containing functional groups. Finally, oxygen-functionalized silicon-carbon, carbon nanotubes, sodium alginate and sodium dodecylbenzenesulfonate were dispersed in water at a volume ratio of 1:0.012:0.004:0.003, with a solid content of 20%, and stirred for 2 hours. The mixture was then flash-dried to obtain the silicon-carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 39.4% carbon by mass, 0.1% oxygen by mass, and 0.5% hydrogen by mass.

[0062] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray derivatization, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.21 m. 2 / g, 15Ω cm, 1.99g / cm 3 1.2nm and 0.5μm -2 .

[0063] Comparative Example 1 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, using plasma treatment, silicon carbon is placed in the reaction chamber, vacuum is drawn and a reaction gas source is introduced, maintaining a pressure of 50 Pa, equipment power of 600 W, and reaction time of 600 seconds to obtain silicon carbon modified with oxygen-containing functional groups, which is a silicon carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 38% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0064] The specific surface area, powder resistivity, helium true density, and silicon crystal size of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray diffraction, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.06 μm. 2 / g, 78Ω cm, 1.90g / cm 3 And 1.1nm.

[0065] Comparative Example 2 A method for preparing a silicon-carbon composite material includes the following steps: First, porous carbon with a Dv50 of 6.5 μm was selected. Under N2 atmosphere, the furnace temperature was kept constant at 550℃, silane gas was introduced, and deposition was carried out for 2 hours to obtain silicon-carbon. Then, silicon carbon, carbon nanotubes, sodium carboxymethyl cellulose and sodium dodecylbenzene sulfonate were dispersed in water at a volume ratio of 1:0.012:0.004:0.003, with a solid content of 30%, and stirred for 2 hours. The mixture was then flash-dried to obtain the silicon carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 39.95% carbon by mass, 0.02% oxygen by mass, and 0.03% hydrogen by mass.

[0066] The specific surface area, powder resistivity, helium true density, silicon crystal size, and carbon nanotube distribution density K of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray derivatization, surface resistivity analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.17 m. 2 / g, 25Ω cm, 1.92g / cm 3 1.1nm and 0.1μm -2 .

[0067] Comparative Example 3 A method for preparing a silicon-carbon composite material includes the following steps: Porous carbon with a Dv50 of 6.5 μm was selected, and under N2 atmosphere, the furnace temperature was kept constant at 550℃. Silane gas was introduced and deposited for 2 hours to obtain silicon-carbon composite material. The resulting silicon-carbon composite material contains 60% silicon by mass, 38% carbon by mass, 0.5% oxygen by mass, and 1.5% hydrogen by mass.

[0068] The specific surface area, powder resistivity, helium true density, and silicon crystal size of the silicon-carbon composite material were measured using scanning electron microscopy, X-ray diffraction, surface area analyzer, powder resistivity meter, and gas displacement true density meter, respectively, and were found to be 1.23 μm. 2 / g, 65Ω cm, 1.97g / cm 3 And 1.1nm.

[0069] Test case The parameters of N1, N2, R1, and R2 of the silicon-carbon composite material are shown in Table 1.

[0070] A negative electrode sheet was prepared using silicon-carbon composite material as the negative electrode active material; The negative electrode sheet is composed of: 95% active material, 2% SBR binder, 2.8% conductive agent SP, and 0.2% SWCNT. The negative electrode sheet is prepared into a CR2032 coin cell using conventional methods, and the battery's electrical performance is tested. The specific testing method is as follows: (1) Half-cell assembly: Assemble CR2032 button cells in a glove box, with lithium metal sheet as counter electrode, polypropylene microporous membrane as separator, and LiPF6 dissolved in a mixture of ethyl carbonate (EC) and diethyl carbonate (DEC) (the volume ratio of EC to DEC is 1:1), wherein the concentration of LiPF6 is 1 mol / L. The battery was charged and discharged using the LAND battery testing system; (2) Charge transfer resistance test: After the CR2032 button battery was left to stand for 6 hours, it was discharged at 0.1C to 0.005V, and then discharged at a constant voltage of 0.005V until the current was cut off at 0.01C. After standing for 5 minutes, it was charged at a constant current of 0.1C for 5 hours. After standing for 5 minutes, the charge transfer resistance Rct was tested using an electrochemical workstation. (3) Electrode expansion rate: After the CR2032 type button cell was left to stand for 6 hours, it was discharged to 0.005V at 0.05C, and then discharged to 0.005V at 0.01C; the button cell was disassembled in the glove box, the electrode was cleaned with DMC and the thickness of the electrode was measured; the expansion rate was calculated as: (thickness of electrode in the first fully charged state - thickness of fresh electrode) / thickness of fresh electrode × 100%; The test results are shown in Table 1.

[0071] As shown in Table 1, compared with the silicon-carbon composite materials of Comparative Examples 1-3, Examples 1-7 of the present invention modify oxygen-containing functional groups and then interweave carbon nanotubes with silicon-carbon to construct a complete three-dimensional interwoven body, thereby obtaining an integrated, long-range ordered conductive and buffering network. This results in the silicon-carbon composite material having lower charge transport resistance and lower volume expansion rate, significantly improving the integrity of the electrode structure.

[0072] Table 1

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material uses an interwoven network constructed from carbon nanotubes, which connects primary silicon-carbon particles into a secondary interwoven particle body. The surface of the primary silicon-carbon particles has oxygen-containing functional groups that form covalent bonds with carbon nanotubes.

2. The silicon-carbon composite material according to claim 1, characterized in that, The oxygen-containing functional group includes at least one of hydroxyl, carboxyl, carbonyl and epoxy groups.

3. The silicon-carbon composite material according to claim 2, characterized in that, The total oxygen mass content W1 of the oxygen-containing functional groups satisfies 0.1% ≤ W1 ≤ 1%; Preferably, the total hydrogen mass content W2 of the oxygen-containing functional groups satisfies 0.5% ≤ W2 ≤ 2%.

4. The silicon-carbon composite material according to any one of claims 1-3, characterized in that, The number of silicon-carbon particles N1 in a single step satisfies 2≤N1≤50; Preferably, the primary silicon-carbon particles have a particle size of 2μm-20μm; Preferably, the number N2 of interlacing lines between the primary silicon-carbon particles satisfies 1≤N2≤20; Preferably, the interlacing lines are composite carbon nanotubes formed by combining several carbon nanotubes; Preferably, the diameter R1 of the composite carbon nanotube satisfies 0.6nm≤R1≤500nm.

5. The silicon-carbon composite material according to any one of claims 1-3, characterized in that, The diameter R2 of the carbon nanotubes on the surface of the primary silicon-carbon particles satisfies 0.6nm≤R2≤100nm; Preferably, the distribution density K of the carbon nanotubes anchored on the surface of the primary silicon-carbon particles satisfies 0.5 μm. -2 ≤K≤1.8μm -2 .

6. The silicon-carbon composite material according to claim 1, characterized in that, In the silicon-carbon composite material, the crystallite size D1 of nano-silicon on the (111) crystal plane satisfies D1≤3nm; Preferably, the silicon-carbon composite material has a silicon content of 40%-70% by mass, a total carbon content of 25%-60% by mass, an oxygen content of 0.1%-1% by mass, and a hydrogen content of 0.5%-2% by mass.

7. The silicon-carbon composite material according to claim 6, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 0.2 m². 2 / g-2m 2 / g, powder resistivity 1Ω cm-15Ω cm, the true density of helium is 1.2 g / cm³. 3 -2.1g / cm 3 .

8. A method for preparing the silicon-carbon composite material according to any one of claims 1-7, characterized in that, Includes the following steps: Silicon carbon, carbon nanotubes, dispersant and surfactant are mixed in the liquid phase and dried to obtain the silicon carbon composite material.

9. The preparation method according to claim 8, characterized in that, The silicon-carbon is made of porous carbon-deposited nano-silicon; Preferably, the temperature for depositing porous carbon nanosilicon is 400℃-800℃; Preferably, the silicon-carbon surface is modified with oxygen-containing functional groups; Preferably, the method for modifying the silicon-carbon surface with oxygen-containing functional groups includes plasma treatment. Preferably, the plasma treatment method has a power of 200W-1000W, a treatment time of 10min-100min, and a treatment pressure of 10Pa-100Pa; Preferably, the gas source used in the plasma treatment method includes at least one of oxygen, air, and water vapor.

10. A lithium-ion battery, characterized in that, The active material used in the negative electrode of the lithium-ion battery includes the silicon-carbon composite material as described in any one of claims 1-7.

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