Silicon-carbon composite material, preparation method and application thereof

Abstract

The application discloses a silicon-carbon composite material and a preparation method and application thereof, and belongs to the technical field of new energy. The preparation method of the silicon-carbon composite material provided by the application comprises the following steps: S1. mixing pyrolytic carbon, a silicon ester and a metal source in an alcohol solvent; the air humidity of the mixing is greater than or equal to 50%; the mixing time is greater than or equal to 2 hours; the metal source comprises at least one of an iron source and a magnesium source; S2. calcining the product obtained in step S1 in a reducing atmosphere; and S3. acid-treating the product obtained in step S2. The silicon-carbon composite material prepared by the application has excellent electrochemical performances such as capacity, rate and cycle. The application further provides the silicon-carbon composite material prepared by the above preparation method and application thereof.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a silicon-carbon composite material, its preparation method, and its application. Background Technology

[0002] The development of high-performance lithium-ion batteries urgently requires the search for novel anodes with high capacity, long lifespan, and high safety and reliability to replace graphite-based carbon anodes. Silicon-carbon composite materials, with their high capacity and excellent cycle performance, have become one of the most promising next-generation lithium-ion battery anode materials.

[0003] Traditional methods for preparing silicon-carbon composites are mainly divided into top-down and bottom-up methods. The former primarily involves crushing and mixing silicon with a carbon matrix through grinding and other methods. However, this results in a weak bond between carbon and silicon, high interfacial resistance, and a tendency for silicon to detach during use, severely degrading performance in cycling and rate capability. The bottom-up method mainly employs CVD (Chemical Vapor Deposition) to first form carbon material through pyrolysis, then create pores in the carbon material, and finally fill the pores of the porous carbon matrix with elemental silicon using CVD. Because the pore size in the carbon matrix is ​​not uniform, even with a designed porosity, some pores in the CVD-prepared silicon-carbon composite are still filled, leaving no space to accommodate changes in the volume of the silicon matrix. Therefore, the overall performance of the resulting silicon-carbon composite, especially its cycling performance, remains poor.

[0004] Furthermore, in traditional technologies, the capacity of silicon-carbon composite materials mainly comes from silicon-based materials, while the carbon matrix does not contribute, or does not significantly contribute, to the capacity. Therefore, combined with the poor cycle performance of silicon-based materials, the overall cycle performance of the resulting silicon-carbon composite materials is poor, and the specific capacity needs to be further improved.

[0005] In summary, silicon-carbon composite materials prepared by traditional techniques exhibit poor electrochemical properties, such as cycling performance. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for preparing silicon-carbon composite materials, which can effectively improve the cycling and rate performance of silicon-carbon composite materials.

[0007] The present invention also provides a silicon-carbon composite material prepared by the above preparation method.

[0008] The present invention also provides applications of the above-mentioned silicon-carbon composite material.

[0009] According to an embodiment of a first aspect of the present invention, a method for preparing a silicon-carbon composite material is provided, the method comprising the following steps: S1. Pyrolytic carbon, silicate ester, and metal source are mixed in an alcohol solvent; the humidity of the air during mixing is ≥50%; the mixing time is ≥2h; the metal source includes at least one of an iron source and a magnesium source; the metal source is an organometallic salt; S2. The product obtained in step S1 is calcined in a reducing atmosphere; S3. The product obtained from acid treatment step S2.

[0010] The mechanism of the preparation method is as follows: In step S1, silicates are situ generated in situ into silicon dioxide in the pores of pyrolytic carbon; the metal source is hydrolyzed to generate the corresponding metal oxide, or directly physically adsorbed on other solid surfaces.

[0011] In step S2, in a reducing atmosphere, the metal source decomposes into the corresponding metal element, or the metal oxide generated by the metal source is reduced into the corresponding metal element; under the combined action of the metal element and the reducing atmosphere (catalytic action or metal thermal reaction action), silicon dioxide is reduced into silicon element (or silicon suboxide).

[0012] In step S3, acid treatment can remove the metal or metal oxide generated by the corresponding metal source.

[0013] The preparation method according to embodiments of the present invention has at least the following beneficial effects: (1) In step S1, silicate esters are hydrolyzed in situ in the pores of pyrolytic carbon to form silicon dioxide. The maximum volume of silicon dioxide is the volume of the pores of pyrolytic carbon. When the silicon content is constant, the volume of silicon dioxide is greater than the volume of elemental silicon. Therefore, the calcination in step S2 will improve the pore distribution in situ of elemental silicon.

[0014] Meanwhile, the presence of a certain amount of metal source products within the pores, and the removal of the metal source products in the acidification step of step S3, further enhances the pore distribution in situ.

[0015] For the two reasons mentioned above, the silicon-carbon composite material prepared by this invention has pores near the elemental silicon. These pores provide space for the volume changes in the subsequent lithium silane synthesis process, avoiding structural damage to elemental silicon or pyrolytic carbon, and significantly improving the cycle performance of the obtained silicon-carbon composite material.

[0016] (2) In the preparation method provided by the present invention, the calcination in step S2 not only realizes the transformation of silicon dioxide to elemental silicon, but also improves the bonding strength between elemental silicon and carbon. Specifically, the experiment found that the reduction process includes a metal thermal process. That is, although the reaction is an endothermic reaction, a large amount of heat is still generated during the reaction. This local heat further improves the bonding reaction between elemental silicon and carbon; reduces the interfacial impedance between silicon and carbon, and improves the rate performance and first efficiency of the obtained silicon-carbon composite material as a whole.

[0017] (3) In the preparation method provided by the present invention, by limiting the humidity and time of mixing in step S1, the silicate ester hydrolysis can be ensured to form the corresponding silicon dioxide as much as possible; thus, the silicon content in the product can be predicted to a certain extent by the feed ratio (but not necessarily determined), and the waste of raw materials can be avoided.

[0018] According to some embodiments of the present invention, the method for obtaining pyrolytic carbon includes the following steps: S0. The carbon source, oxidant and pore-forming agent are mixed and reacted, and then pyrolyzed.

[0019] The oxidant can increase the content of oxygen-containing groups such as carboxyl groups in the carbon source, reduce the graphitization orientation of the pyrolytic carbon in the subsequent pyrolysis process, which is equivalent to increasing the width of the lithium-ion shuttle path to a certain extent, and also increasing the lithium storage space. The pore-forming agent provides a porous structure for the pyrolytic carbon, providing a space for the silicon dioxide and metal source (and its preliminary reaction products) in step S1.

[0020] According to some embodiments of the present invention, in step S0, the carbon source includes at least one of polymer, bitumen, and biomass carbon source.

[0021] According to some embodiments of the present invention, in step S0, the carbon source includes at least one of low-temperature asphalt (softening point ≤70℃), medium-temperature asphalt (softening point 70~90℃, excluding 70℃), and high-temperature asphalt (softening point >90℃). During pyrolysis, the asphalt can soften, thereby enhancing the reaction effect with the oxidant and also improving the pore-forming effect.

[0022] According to some embodiments of the present invention, in step S0, the oxidant includes at least one of potassium permanganate, potassium ferrate, sodium hypochlorite, and hydrogen peroxide.

[0023] According to some embodiments of the present invention, in step S0, the mass ratio of the carbon source to the oxidant is 10:0.5~3; for example, it can be about 10:1, 10:1.5, 1:2 or about 10:2.5.

[0024] According to some embodiments of the present invention, in step S0, the pore-forming agent includes at least one of sodium chloride, sodium carbonate, potassium carbonate, and potassium chloride. These substances will melt or partially decompose during the subsequent calcination stage, but will not completely disappear, that is, they act as a placeholder. When washed away later, they leave pores in the corresponding positions, thus achieving the function of pore formation.

[0025] According to some embodiments of the present invention, in step S0, the mass ratio of the carbon source to the pore-forming agent is 1:0.2 to 1.5; for example, it can be about 10:0.5, 10:0.8, 10:1 or about 10:1.2.

[0026] According to some embodiments of the present invention, in step S0, the mixing temperature is 150~250°C. Specifically, it can be about 180°C, 200°C, or about 220°C. Within this temperature range, the asphalt softens, enhancing the interaction between the asphalt, oxidant, and pore-forming agent.

[0027] According to some embodiments of the present invention, in step S0, the mixing time is 10 to 90 minutes. For example, it can be about 30 minutes or about 60 minutes.

[0028] According to some embodiments of the present invention, in step S0, the pyrolysis is carried out in a protective atmosphere. The protective atmosphere includes at least one of nitrogen, argon, and helium.

[0029] According to some embodiments of the present invention, in step S0, the heating rate of the pyrolysis is 1~5°C / min. For example, it can be about 2°C / min or about 3°C / min.

[0030] According to some embodiments of the present invention, in step S0, the isothermal temperature of the pyrolysis is 800~1200°C. For example, it can be about 900°C, 1000°C, or about 1100°C.

[0031] According to some embodiments of the present invention, in step S0, the isothermal duration of the pyrolysis is 1 to 5 hours. For example, it can be about 2 hours, 3 hours, or about 4 hours.

[0032] According to some embodiments of the present invention, step S0 further includes a washing and drying step performed after the pyrolysis. The washing method includes water washing, and the washing endpoint is when the ionic conductivity of the washing solution is ≤30 mS / m.

[0033] According to some embodiments of the present invention, in step S1, the mass ratio of pyrolytic carbon to silicate ester is 100:150 to 250. Specifically, it can be approximately 100:160, 100:170, 100:180, 100:190, 100:200, 100:210, 100:220, 100:230, or approximately 100:240. Within the above range, the capacity of the obtained negative electrode material is significantly improved, and the agglomeration of silicate ester hydrolysis products can be avoided. Furthermore, it ensures that the pyrolytic carbon has sufficient pores to accommodate subsequent changes in the volume of silicon / silicon suboxide particles.

[0034] According to some embodiments of the present invention, the silicate ester includes at least one selected from methyl orthosilicate (CAS: 681-84-5), ethyl orthosilicate (CAS: 78-10-4), methyltrimethoxysilane (CAS: 1185-55-3), phenyltriethoxysilane (CAS: 780-69-8), and tetraethyl orthosilicate (CAS: 78-10-4).

[0035] According to some embodiments of the present invention, the magnesium source includes at least one of magnesium pyrocene, magnesium acetate, and cyclopentadienyl magnesium.

[0036] According to some embodiments of the present invention, the iron source includes at least one of ferrocene, ferric citrate, and ferrous gluconate.

[0037] According to some embodiments of the present invention, in step S1, the mass ratio of the pyrolytic carbon to the metal source is 100:20 to 80. Specifically, it can be approximately 100:30, 100:40, 100:50, 100:60, or approximately 100:70. This ensures sufficient metal source for catalytic or reduction of silicon suboxide, while avoiding excessive metal source and silicon dioxide generated from hydrolysis competing for pore space with the pyrolytic carbon.

[0038] According to some embodiments of the present invention, in step S1, the humidity of the mixture is 60-90%. For example, it can be about 70% or about 80%. Within this humidity range, the hydrolysis of silicates can be achieved, but agglomeration caused by excessively rapid hydrolysis can be avoided.

[0039] The humidity mentioned in this invention is relative humidity, with 100% humidity being the saturation humidity of the air at the corresponding temperature.

[0040] According to some embodiments of the present invention, in step S1, the mixing time is 2 to 5 hours. For example, it can be about 3 hours or about 4 hours.

[0041] According to some embodiments of the present invention, step S1 further includes washing and drying after mixing, wherein the washing method is alcohol washing. The number of alcohol washings is ≥3 times. This avoids the impact of a large amount of water on the components in the mixture.

[0042] According to some embodiments of the present invention, in step S2, the reducing atmosphere is a mixture of hydrogen and an inert atmosphere; wherein the volume percentage of hydrogen is 5-10%. For example, it can be about 8%.

[0043] According to some embodiments of the present invention, in step S2, the calcination temperature is 500~900°C. Specifically, it can be about 600°C, 700°C, or about 800°C. Within this temperature range, the metal oxide generated by the metal source can be reduced to the elemental metal, thereby allowing the elemental metal to function.

[0044] According to some embodiments of the present invention, in step S2, the calcination time is 2 to 5 hours. For example, it can be about 3 hours or about 4 hours.

[0045] According to some embodiments of the present invention, in step S3, the acid used for the acid treatment is selected from hydrochloric acid solution. The concentration of the hydrochloric acid solution is 0.5~3 mol / L. Specifically, it can be about 1 mol / L, 1.5 mol / L, 2 mol / L, or about 2.5 mol / L. Thus, the acid treatment can sufficiently remove the product from the metal source, but does not affect the product of potassium permanganate.

[0046] According to some embodiments of the present invention, in step S3, the solid-liquid ratio of the acid treatment is 1g:8~15mL. Specifically, it can be about 1g:10mL or about 1g:12mL. Within the above range, combined with the concentration of the acid solution used, it can be ensured that the products from the metal source are sufficiently removed.

[0047] According to some embodiments of the present invention, in step S3, the duration of the acid treatment is 20-60 minutes. For example, it can be about 30 minutes, 40 minutes, or about 50 minutes.

[0048] According to some embodiments of the present invention, step S3 further includes washing and drying after the acid treatment. The washing method is water washing, with the endpoint being an ionic conductivity of the washing solution ≤30 mS / m; this washing removes excess acid, as well as reaction products of acid and other substances.

[0049] According to some embodiments of the present invention, the preparation method further includes the following steps after step S3: S4. A carbon coating layer is deposited on the surface of the product obtained in step S3 using the CVD method.

[0050] In actual production, parameters such as the thickness of the carbon coating layer can be determined as needed. This invention does not impose strict limitations. Limiting the presence of the carbon coating layer is also to prevent the silicon-carbon composite material from being eroded by the electrolyte to a certain extent, thereby improving the cycle performance to a certain degree.

[0051] According to an embodiment of a second aspect of the present invention, a silicon-carbon composite material prepared by the preparation method provided in the first aspect of the present invention is provided; the silicon-carbon composite material comprises: Pyrolytic carbon, wherein pores are distributed in the pyrolytic carbon; A silicon-based material, comprising at least one of elemental silicon and silicon suboxide; the silicon-based material fills the pore, and a gap exists between the silicon-based material and at least one side wall of the pore.

[0052] Since the silicon-carbon composite material adopts all the technical solutions of the preparation method of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0053] According to some embodiments of the present invention, the silicon-carbon composite material exhibits a capacity retention of ≥82% after 800 cycles at a current density of 1 A / g. Specifically, this retention can be approximately 83%, 84%, 85%, 86%, 87%, 88%, or approximately 89%.

[0054] According to some embodiments of the present invention, the specific capacity of the silicon-carbon composite material is ≥1000 mAh / g. For example, it can be about 1200 mAh / g, 1300 mAh / g, 1400 mAh / g, 1500 mAh / g, 1600 mAh / g, or about 1700 mAh / g.

[0055] According to some embodiments of the present invention, the silicon-carbon composite material further includes a carbon coating layer that encapsulates the core composed of pyrolytic carbon and silicon-based material.

[0056] According to some embodiments of the present invention, the silicon content in the silicon-carbon composite material is 15-40 wt%. For example, it can be about 20%, 25%, 30%, or about 35%.

[0057] According to some embodiments of the present invention, the specific surface area of ​​the silicon-carbon composite material is 3~4.5 m². 2 / g. For example, it could be approximately 3.5m. 2 / g or approximately 4m 2 / g.

[0058] According to some embodiments of the present invention, the silicon-carbon composite material is doped with manganese. The manganese content is 1-2% by mass, specifically about 1.5%.

[0059] According to an embodiment of a third aspect of the present invention, a lithium-ion battery is provided, wherein the raw materials for preparing the lithium-ion battery include the silicon-carbon composite material provided in the second aspect of the present invention.

[0060] Since the lithium-ion battery adopts all the technical solutions of the silicon-carbon composite material of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0061] According to some embodiments of the present invention, the lithium-ion battery includes at least one of button cells, pouch cells, prismatic cells, and cylindrical cells.

[0062] According to some embodiments of the present invention, the lithium-ion battery includes at least one of a half-cell and a full-cell.

[0063] According to some embodiments of the present invention, when the lithium-ion battery comprises a full cell, the silicon-carbon composite material serves as the negative electrode active material; The positive electrode active material can be lithium cobalt oxide, binary positive electrode material, ternary positive electrode material, etc.; the present invention does not strictly limit the above-mentioned positive electrode active material, and it can be determined based on commercially available materials or actual performance requirements.

[0064] According to an embodiment of the fourth aspect of the present invention, an application of the lithium-ion battery provided in the third aspect of the present invention is provided in the fields of energy storage technology, power battery technology, and electronic information technology.

[0065] Since the application adopts all the technical solutions of the lithium-ion battery in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0066] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0067] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0068] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0069] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0070] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0071] Example 1 This example demonstrates the preparation of a silicon-carbon composite material, whose specific structure comprises the following components: Pyrolytic carbon, which contains pores; pyrolytic carbon is doped with Mn; Silicon-based materials, including elemental silicon and silicon suboxide; the silicon-based materials fill pores, and there is a gap between the silicon-based materials and at least one side of the pore wall.

[0072] The carbon coating layer encapsulates a core composed of pyrolytic carbon and silicon-based materials.

[0073] The weight percentage of each component in the silicon-carbon composite material and parameters such as porosity are shown in Table 1.

[0074] The preparation method used in this example includes the following steps: S0. Asphalt (carbon source, softening point 110℃), potassium permanganate (oxidant), and sodium chloride (pore-forming agent) are mixed in a mass ratio of 10:1:1 and then pyrolyzed. The reaction temperature is 220℃, and the reaction time is 1 hour. Pyrolysis is carried out under nitrogen protection, with a heating rate of 3℃ / min; the isothermal temperature is 1100℃, and the isothermal time is 3 hours; after the isothermal period, the mixture is allowed to cool naturally. After cooling to room temperature, the product is repeatedly washed with water until the ionic conductivity of the washing solution is ≤30mS / m; then the solid product is dried to obtain pyrolytic carbon.

[0075] S1. Pyrolytic carbon, tetraethyl orthosilicate (silicate ester), and ferrocene (metal source) are mixed in an alcohol solvent (ethanol); the air humidity during mixing is 70%; the mixing time is 4 hours; wherein, The mass ratio of pyrolytic carbon, tetraethyl orthosilicate, and ferrocene is 100:200:60; the volume ratio of tetraethyl orthosilicate to alcohol solvent is 1:20.

[0076] After mixing, solid-liquid separation, washing with ethanol three times, and drying were performed in sequence.

[0077] S2. The product obtained in step S1 is calcined in a reducing atmosphere; wherein, The reducing atmosphere is a mixture of argon and hydrogen in a volume ratio of 90:10. The calcination temperature was 750℃ and the duration was 4 hours.

[0078] After calcination, allow it to cool naturally to room temperature.

[0079] S3. The product obtained from acid treatment step S2. Wherein...

[0080] The acid is 1.5 mol / L hydrochloric acid; the mass-to-volume ratio of the product obtained in step S2 to the acid is 1 g: 10 mL; the acid treatment is carried out under ultrasonic conditions for 30 min; after acid washing, the product is washed multiple times with ultrapure water until the ionic conductivity of the washing solution is ≤30 mS / m; finally, the product is dried to obtain the final product.

[0081] S4. The product obtained in step S3 is carbon-coated using CVD with acetylene as the carbon source, wherein the gas flow rate is 4 L / min, the temperature is 550 °C, and the deposition time is 2 h.

[0082] Unless otherwise specified, the operating environment for the steps in this example is an air environment, at room temperature (approximately 25°C) and at normal pressure.

[0083] Example 2 This example prepares a silicon-carbon composite material, which differs from Example 1 in that: In step S1, the mass ratio of pyrolytic carbon, tetraethyl orthosilicate, and ferrocene is 100:200:25.

[0084] Example 3 This example prepares a silicon-carbon composite material, which differs from Example 1 in that: In step S0, an equal amount of hydrogen peroxide is used as the oxidant.

[0085] Comparative Example 1 This example demonstrates a method for preparing a silicon-carbon composite material, which differs from Example 1 in that: Replace steps S1-S3 with the following steps: Silicon was deposited in the porous structure of the pyrolytic carbon obtained in step S0 using CVD with silane as a precursor. The silicon deposition ratio was similar to that in Example 1. Specifically, SiH4 was used as the silicon source, N2 was used as the carrier gas, the volume percentage of SiH4 in the mixed gas was 35%, and the chemical vapor deposition of silicon was carried out at 600°C.

[0086] Comparative Example 2 This example prepares a silicon-carbon composite material, which differs from Example 1 in that: Step S1 does not include a metal source.

[0087] Comparative Example 3 This example prepares a silicon-carbon composite material, which differs from Example 1 in that: Replace step S1 with the following steps: S1a. Mix pyrolytic carbon and silicate in an alcohol solvent; S1b. Mix the solid product obtained in step S1a in an alcohol solution of a metal source.

[0088] In this example, the proportions of the raw materials used and the concentrations of each component are the same as in Example 1; the mixing conditions for each mixing are the same as those in Example 1.

[0089] Application Example 1 This example provides a coin cell lithium-ion battery, wherein the test electrode consists of a negative electrode current collector copper foil and a negative electrode coating attached to the surface of the negative electrode current collector; the negative electrode coating consists of active material, binder PVDF, and conductive agent SP in a mass ratio of 9:0.6:0.4, and the active material is a silicon-carbon composite material prepared in the example or comparative example; the counter electrode is a lithium metal sheet; the separator is a common PP separator; the electrolyte is a 1M lithium hexafluorophosphate carbonate solution containing 15% FEC + 1-2% VCI; the electrolyte wets the working electrode, the counter electrode, and the separator.

[0090] Application Example 2 This example provides a pouch cell, wherein the positive electrode consists of a positive current collector aluminum foil and a positive electrode coating attached to the positive current collector; the positive electrode coating consists of active material NCM811, binder PVDF and conductive agent SP in a mass ratio of 8:1:1; the composition of the negative electrode is the same as the test electrode of Application Example 1, and the composition of the separator and electrolyte is the same as in Application Example 1; the designed capacity is 5Ah; the designed N / P value is 1.05; and the electrolyte filling volume is sufficient.

[0091] Test Example 1 This example tested the physicochemical properties of the silicon-carbon composite materials obtained in the examples and comparative examples. Specifically, the Si content was calculated by testing the silicon content in the alkaline leaching solution; the Mn and metal source products were calculated using the content of the corresponding metal elements in the acid leaching solution. The acid used for leaching was a mixture of nitric acid, phosphoric acid, hydrochloric acid, and hydrogen peroxide. The specific surface area was obtained using the BET method. The test results are shown in Table 1.

[0092] Table 1. Partial physicochemical parameters of silicon-carbon composite materials in the examples and comparative examples. As shown in Table 1, using different types of oxidants, adjusting the amount of metal source, including or excluding the metal source, using CVD, or adjusting the step sequence do not significantly affect the silicon content in the obtained silicon-carbon composite material. The differences in the results in Table 1 may be due to testing errors or batch errors. Furthermore, as acid leaching proceeds in step S3, the metal source product is washed away, but the manganese-based product of potassium permanganate is not completely removed.

[0093] However, if the amount of metal source is reduced or even excluded, the occupancy of the metal source product decreases, the vacancies left after acid etching decrease, or the reduction ratio of silica is insufficient, resulting in a reduction in the porosity released by silica itself. In short, the overall specific surface area of ​​the resulting silicon-carbon composite material decreases. In the preparation of pyrolytic carbon, potassium permanganate is used as an oxidant. On the one hand, it generates a large number of oxygen-containing groups; on the other hand, manganese ions themselves participate in the formation of chemical bonds. The combination of these two aspects can significantly improve the anisotropy of the obtained pyrolytic carbon (hard carbon), thereby increasing its specific surface area. Therefore, if other types of oxidants are used, the specific surface area of ​​the obtained pyrolytic carbon and the final silicon-carbon composite material decreases. Using the CVD method, although the proportion of silicon in the obtained silicon-carbon composite material is the same, during the pore filling process, some pores are completely filled, leaving larger empty spaces. That is, with the same pore volume, the pore size is larger, thus also reducing the specific surface area to some extent. If the steps of the preparation method in this invention are adjusted so that the silicate ester is hydrolyzed first and then the metal source is impregnated, a problem similar to that in Comparative Example 1 will occur. Furthermore, it cannot be determined whether the metal source and silicon dioxide will come into contact, and therefore it is uncertain whether the silicon dioxide can be reduced.

[0094] Test Example 2 This example tests the first-cycle reversible capacity and coulombic efficiency of the coin cell lithium-ion battery obtained in Application Example 1. The test rate is 0.1C, and the test voltage is 0.005~2V. This example also tests the ratio of the reversible capacity of the coin cell lithium-ion battery obtained in Application Example 1 at 0.2C, 0.5C, 1.0C, and 1.5C rates to the reversible capacity at 0.1C. In this example, the current density at 1C is set at 1400mAh / g. The above test results are shown in Table 2.

[0095] The second aspect of this example tested the cycle performance of the pouch lithium-ion battery obtained in Example 2. Specifically, it was first cycled at 0.1C for 3 weeks, followed by a cycle test at a current density of 1A / g (approximately 0.7C), with a test voltage of 2.5~4.3V. The ratio of the reversible capacity of the 800th test at 1A / g to the reversible capacity of the first test at 1A / g was recorded. The test results are shown in Table 2.

[0096] Table 2. Electrochemical performance test results of silicon-carbon composite materials obtained in the examples and comparative examples. Table 2 shows that the silicon-carbon composite material provided in this invention exhibits superior electrochemical performance, with a significantly better specific capacity than commonly used graphite anodes. Furthermore, its initial efficiency, rate capability, and cycle performance are comparable to those of graphite anodes. Due to these advantages, the silicon-carbon composite material prepared in this invention holds promise for replacing existing commercial graphite to some extent, enabling the fabrication of lithium-ion batteries with higher energy density. The resulting lithium-ion batteries are expected to find wide application in energy storage, power battery, and electronic information technology fields.

[0097] Comparing Examples 1, 2, and 2, it is evident that the amount of elemental metal obtained from the decomposition and reduction of the metal source is related to the amount of silicon-based materials such as silicon / silicon suboxide that can contribute to the capacity, thus affecting the capacity of the silicon-carbon composite material. Based on this, it is speculated that the reaction mechanism between the elemental metal and silicon dioxide may be one of the following two: one is a catalytic reaction based on contact; if the amount of catalyst is insufficient, it cannot fully contact with silicon dioxide, thus failing to react completely; the other is a metallothermic reaction based on contact, where the elemental metal acts as a reducing agent, and therefore the amount of reducing agent determines the final extent of the reaction. However, this invention actually extends the calcination time without significantly improving the overall performance of the obtained silicon-carbon composite material. Furthermore, at the corresponding calcination temperature, hydrogen can continuously act as a reducing agent; therefore, the actual reaction process may be dominated by the first speculation. In Comparative Example 2, the actual capacity comes from hard carbon, represented by pyrolytic carbon, resulting in better cycle life and rate capability. In Example 2, part of the capacity comes from silicon-based materials, so silicon and silicon dioxide are interspersed, which also hinders the shuttle of lithium ions, resulting in a slight decrease in rate capability and cycle life compared to Example 1.

[0098] Comparing Examples 1 and 3, it can be seen that because the pyrolytic carbon has fewer pores, some silicon material cannot be embedded in the pores, but instead covers the surface and agglomerates. Therefore, the silicon will pulverize and fall off during charging and discharging, resulting in a decrease in cycle life and rate capability. Furthermore, due to the lack of manganese, the capacity of the pyrolytic carbon formed from asphalt also decreases to some extent. Therefore, the overall capacity of the obtained silicon-carbon composite material also decreases significantly.

[0099] As can be seen from the comparison of Example 1 and Comparative Example 1, the silicon-carbon composite material prepared by the present invention provides a space for the volume change of each silicon / silicon suboxide particle, thus significantly improving its high-rate and long-cycle performance.

[0100] Comparing Example 1 and Comparative Example 3, it can be seen that if silicon dioxide and a metal source are distributed and loaded, the silicon dioxide may not come into contact with the metal source, affecting the subsequent reduction of silicon dioxide and thus affecting the overall performance.

[0101] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for producing a silicon-carbon composite material, characterized by, The preparation method includes the following steps: S0. Pyrolytic carbon is obtained by mixing and reacting carbon source, oxidant and pore-forming agent and then pyrolyzing the mixture. The pore-forming agent is at least one of sodium chloride and potassium chloride; the oxidizing agent includes potassium permanganate. S1. Pyrolytic carbon, silicate ester, and metal source are mixed in an alcohol solvent; the humidity of the air during mixing is ≥50%; the mixing time is ≥2h; the metal source includes at least one of iron and magnesium sources; the metal source is an organometallic salt; the mass ratio of pyrolytic carbon, silicate ester, and metal source is 100:150~250:40~80; S2. Calcination of the product obtained in step S1 in a reducing atmosphere; the calcination temperature is 500~900℃; the calcination time is 2~5h; S3. The product obtained from acid treatment step S2.

2. The production method according to claim 1, characterized by, In step S0, the carbon source includes at least one of polymer, bitumen, and biomass carbon source.

3. The production method according to claim 1 or 2, characterized by, In step S2, the reducing atmosphere is a mixture of hydrogen and an inert atmosphere; wherein the volume percentage of hydrogen is 5-10%.

4. The silicon-carbon composite material produced by the production method according to any one of claims 1 to 3, characterized by The silicon-carbon composite material includes: Pyrolytic carbon, wherein pores are distributed in the pyrolytic carbon; A silicon-based material, comprising at least one of elemental silicon and silicon suboxide; the silicon-based material fills the pore, and a gap exists between the silicon-based material and at least one side wall of the pore.

5. The silicon-carbon composite of claim 4, wherein, The silicon-carbon composite material exhibits a capacity retention of ≥82% after 800 cycles at a current density of 1 A / g. And / or, the specific capacity of the silicon-carbon composite material is ≥1000mAh / g.

6. A lithium-ion battery, characterized by The raw materials for preparing the lithium-ion battery include the silicon-carbon composite material as described in claim 4 or 5.

7. An application of the lithium-ion battery as described in claim 6 in the fields of energy storage technology, power battery technology, and electronic information technology.

Images