Preparation method of silicon-carbon negative electrode material with structure that carbon nanotubes are embedded into soft and hard carbon frames

Abstract

The invention relates to the field of preparation of inorganic materials, and particularly discloses a preparation method of a silicon-carbon negative electrode material with a carbon nanotube embedded soft and hard carbon framework structure, which comprises the following steps: step 1, respectively dissolving cobalt salt, dimethylimidazole and nano silicon powder in ethanol, and stirring to obtain a solution A; uniformly stirring to obtain a cobalt salt solution, a dimethylimidazole solution and a nano silicon dispersion liquid; step 2, pouring the dimethylimidazole solution and the nano silicon dispersion liquid into the cobalt salt solution, fully and uniformly stirring, and standing for a period of time; the novel silicon-carbon negative electrode material is prepared by embedding the carbon nanotubes into a soft and hard carbon frame structure and combining the carbon nanotubes with a silicon material. According to the structural design, the synergistic effect of the carbon nanotubes and the porous carbon can be fully utilized, the conductivity and the structural stability of the material are improved, and the volume change of the silicon material in the charging and discharging process can be effectively buffered, so that the cycling stability and the energy density of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic material preparation, and specifically relates to a method for preparing a silicon-carbon anode material with carbon nanotubes embedded in a hard and soft carbon framework structure. Background Art

[0002] Silicon materials are widely regarded as an ideal choice for the next-generation anode materials of lithium-ion batteries due to their extremely high theoretical specific capacity. However, the huge volume expansion and contraction of silicon during charge and discharge processes will lead to material pulverization and electrode structure damage, thus limiting its practical application. To overcome this challenge, researchers have explored various strategies, one of which is to combine silicon with carbon materials to form silicon-carbon composite materials. This composite material can utilize the high conductivity and good mechanical properties of carbon materials to buffer the volume change of silicon, thereby improving the structural stability and cycle life of the material.

[0003] Among many carbon materials, carbon nanotubes have received special attention due to their unique one-dimensional nanostructure and excellent mechanical and electrical properties. The introduction of carbon nanotubes can further enhance the conductivity of the composite material, provide an efficient electron transport channel, and at the same time, its tubular structure also helps to alleviate the volume expansion of silicon materials during charge and discharge processes. In addition, the introduction of porous carbon materials can increase the specific surface area of the material, provide more active sites, and at the same time improve the permeability of the electrolyte and the ion diffusion rate.

[0004] Chinese Patent CN113860288B uses phenolic resin to wrap nano-silicon powder and cobalt salt, carbonize at high temperature and grow carbon nanotubes simultaneously. However, nano-silicon powder is prone to agglomeration, and it is impossible to ensure the uniform distribution of silicon particles. Moreover, cobalt is used to catalyze phenolic resin to prepare carbon nanotubes in the literature, which will lead to uncontrollable reaction sites and it is difficult to ensure product consistency in production. And the outermost layer is not carbon-coated, which will cause the electrolyte to contact silicon and result in a low initial efficiency during the test.

[0005] Traditional silicon-based anode materials will undergo significant volume expansion and contraction during charge and discharge processes, which will further lead to electrode structure damage and rapid capacity decay. Summary of the Invention

[0006] The present invention aims to provide a method for preparing a silicon-carbon anode material with carbon nanotubes embedded in a hard and soft carbon framework structure. This method uses 2-methylimidazole as the hard carbon framework and PVA as the soft carbon to fill the pores. At high temperature, Co can make the hard carbon generate pores to obtain porous carbon. At the same time, Co can also act as a catalyst to catalyze part of the carbon source gas to generate carbon nanotubes, which is beneficial to improving the migration rate of lithium ions. The other part of the uncatalyzed carbon source gas becomes amorphous carbon and wraps around the surface of the material, which is beneficial to the structural stability of the silicon-carbon material. And there is no need for complicated processes, and the silicon-carbon material with this structure can be obtained by one-step sintering.

[0007] The technical solution adopted by the present invention is a preparation method of a silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure, comprising the following steps:

[0008] Step 1: Dissolve cobalt salt, dimethylimidazole, and nano-silicon powder in ethanol respectively. After stirring evenly, obtain a cobalt salt solution, a dimethylimidazole solution, and a nano-silicon dispersion;

[0009] Step 2: Pour the dimethylimidazole solution and the nano-silicon dispersion into the cobalt salt solution. After stirring evenly, let it stand for a period of time to obtain a precursor solution;

[0010] Step 3: Add a soft carbon source to the precursor solution, reflux at 85 °C for 2 hours to form a gel. After freeze-drying, transfer it to a tube furnace under an argon atmosphere and introduce an appropriate amount of carbon source gas for carbonization to obtain a black powder;

[0011] Step 4: Immerse the black powder in 35% hydrochloric acid for 2 h, wash it with deionized water until neutral, and then dry it in vacuum to obtain a silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure.

[0012] Preferably, in Step 1, the cobalt salt is one or more of cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt carbonate, cobalt phosphate, cobalt oxalate, cobalt nitrite, cobalt sulfite, and cobalt fluoride.

[0013] Preferably, in Step 1, the diameter of the nano-silicon powder is 20 - 50 nm.

[0014] Preferably, in Step 2, the standing time of the mixed liquid of the dimethylimidazole solution, the nano-silicon dispersion, and the cobalt salt solution is 8 - 24 h to allow the substances in the mixed liquid to react fully.

[0015] Preferably, in Step 3, the soft carbon source is one or more of polyvinylidene fluoride, polyimide, polypyrrole, polyaniline, polyacrylonitrile, polyvinyl alcohol, polystyrene, and polytetrafluoroethylene.

[0016] Preferably, in Steps 1 - 3, the mass ratio of the cobalt salt, dimethylimidazole, and nano-silicon powder is 1 - 5:2 - 20:1 - 10, and the mass ratio of dimethylimidazole to the soft carbon source is 1 - 10:1.

[0017] Preferably, in Step 3, the sintering temperature of the tube furnace is 600 - 1000 °C, and the heating rate is 1 - 10 °C / min.

[0018] Preferably, in Step 3, the carbon source gas in the tube furnace is one or more of methane, ethane, ethylene, acetylene, and propylene.

[0019] Preferably, in Step 3, the mass ratio of the introduced carbon source gas to the mass of the material obtained after freeze-drying is 0.1 - 1:1.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] By embedding carbon nanotubes into a hard and soft carbon framework structure and combining it with silicon materials, a novel silicon-carbon anode material is prepared. This structural design can not only make full use of the synergistic effect of carbon nanotubes and porous carbon to improve the conductivity and structural stability of the material, but also effectively buffer the volume change of silicon materials during charge and discharge, thereby significantly enhancing the cycle stability and energy density of the battery;

[0022] By precisely controlling the microstructure and chemical composition of the material, the present invention is expected to provide high-performance and long-life anode materials for lithium-ion batteries and other energy storage devices. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the preparation process of the present invention. Detailed Embodiments

[0024] To make the objectives, technical solutions, and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. The embodiments described below are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts in combination with the embodiments of the present invention belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer; for the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0025] In the description of the present invention, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents that the associated objects before and after are in an "or" relationship.

[0026] In the description of the present invention, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or similar expressions thereof refer to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b, or c", or, "at least one (item) of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0027] It should be understood that the weights of the relevant components mentioned in the embodiments of the present invention can not only refer to the specific contents of each component, but also represent the proportional relationship of the weights between the components. Therefore, as long as the contents of the relevant components in the embodiments of the present invention are enlarged or reduced proportionally, they are within the scope disclosed by the present invention. Specifically, the weights described in the embodiments of the present invention can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0028] In addition, unless the context clearly uses otherwise, the singular form of a word should be understood to include the plural form of that word. The terms "comprising" or "having" are intended to specify the presence of features, quantities, steps, operations, elements, parts, or combinations thereof, but are not used to exclude the presence or possible addition of one or more other features, quantities, steps, operations, elements, parts, or combinations thereof.

[0029] The technical solution adopted by the present invention is a preparation method of a silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure. The preparation process is as follows:

[0030] Step 1: Dissolve cobalt salt, dimethylimidazole, and nano-silicon powder in ethanol respectively. After stirring evenly, obtain a cobalt salt solution, a dimethylimidazole solution, and a nano-silicon dispersion.

[0031] Step 2: Pour the dimethylimidazole solution and the nano-silicon dispersion into the cobalt salt solution. After stirring evenly, let it stand for a period of time to obtain a precursor solution.

[0032] Step 3: Add the soft carbon source to the precursor solution, reflux at 85 °C for 2 hours to form a gel. After freeze-drying, transfer it to a tubular furnace under an argon atmosphere and introduce an appropriate amount of carbon source gas for carbonization to obtain a black powder.

[0033] Step 4: Immerse the black powder in 35% hydrochloric acid for 2 h, wash it with deionized water until neutral, and then vacuum dry it to obtain a silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure.

[0034] By embedding carbon nanotubes in a hard and soft carbon framework structure and combining them with silicon materials, the present invention prepares a novel silicon-carbon anode material. This structural design can not only make full use of the synergistic effect of carbon nanotubes and porous carbon to improve the conductivity and structural stability of the material, but also effectively buffer the volume change of silicon materials during charge and discharge, thereby significantly improving the cycle stability and energy density of the battery. By precisely controlling the microstructure and chemical composition of the material, the present invention is expected to provide high-performance and long-life anode materials for lithium-ion batteries and other energy storage devices.

[0035] Among the finally prepared silicon carbide, the mass ratio of silicon to carbon (including amorphous carbon and CNT) is 1-1.5:2. Porous hard carbon is prepared by compounding Co with the material. At the same time, Co catalyzes the carbon source gas to generate carbon nanotubes. The carbon nanotubes and silicon are embedded in the porous carbon. The soft carbon fills the excess pores, and the amorphous carbon wraps around the outermost layer of the material to prevent the electrolyte from penetrating into the interior.

[0036] Specifically, the size of the nano-silicon powder is 20 nm;

[0037] Specifically, the mass ratio of cobalt salt, dimethylimidazole, and nano-silicon powder is 1-2:5-10:3-6;

[0038] Specifically, the mass ratio of dimethylimidazole to the soft carbon source is 8-10:1;

[0039] Specifically, the size of the generated CNT is 7-15 nm in tube diameter and 5-10 μm in tube length;

[0040] Specifically, the heating rate of the tube furnace is 3 °C / min until it is heated to 800-1000 °C;

[0041] To enable those skilled in the art to clearly understand the above implementation details and operations of the present invention, and to significantly demonstrate the progressive performance of the embodiments of the present invention, the following technical solutions will be illustrated by multiple examples.

[0042] Example 1

[0043] A method for preparing a silicon-carbon negative electrode material with carbon nanotubes embedded in a hard and soft carbon framework structure, which includes the following steps:

[0044] Dissolve 1 g of Co(NO3)2·6H2O and 2 g of dimethylimidazole in 50 ml of ethanol respectively;

[0045] After mixing the above two solutions, stir evenly and let stand for 8 h to obtain a precursor solution;

[0046] Add 1 g of PVA to the precursor solution, stir evenly, and reflux at 85 °C for 2 hours to form a gel;

[0047] After freeze-drying, place the product in a tube furnace, heat it to 600 °C at a rate of 1 °C / min under an argon atmosphere, and start to introduce propylene gas at a rate of 150 ml / min. After maintaining for 30 min, stop introducing propylene, and take it out after cooling to room temperature in an Ar atmosphere to obtain a black powder;

[0048] Soak the black powder in 35% hydrochloric acid for 2 h, wash it with deionized water until neutral, and then dry it in vacuum to obtain the silicon-carbon negative electrode material of the present invention.

[0049] Example 2

[0050] Preparation method of silicon-carbon anode material with carbon nanotubes embedded in hard and soft carbon framework structure, which comprises the following steps:

[0051] Dissolve 5 g of Co(NO3)2·6H2O and 20 g of dimethylimidazole in 50 ml of ethanol respectively;

[0052] After mixing the above two solutions, stir evenly and let stand for 24 h to obtain a precursor solution;

[0053] Add 1 g of PVA to the precursor solution, stir evenly, and reflux at 85 °C for 2 hours to form a gel;

[0054] After freeze-drying, place the product in a tube furnace, heat it to 1000 °C at a rate of 10 °C / min under an argon atmosphere, and start to introduce propylene gas at a rate of 150 ml / min. After maintaining for 30 min, stop introducing propylene, cool it to room temperature under an Ar atmosphere, and then take it out to obtain a black powder;

[0055] Soak the black powder in 35% hydrochloric acid for 2 h, wash it with deionized water until neutral, and then dry it under vacuum to obtain the silicon-carbon anode material of the present invention.

[0056] Example 3

[0057] Preparation method of silicon-carbon anode material with carbon nanotubes embedded in hard and soft carbon framework structure, which comprises the following steps:

[0058] Dissolve 1 g of Co(NO3)2·6H2O and 9 g of dimethylimidazole in 50 ml of ethanol respectively;

[0059] After mixing the above two solutions, stir evenly and let stand for 16 h to obtain a precursor solution;

[0060] Add 1 g of PVA to the precursor solution, stir evenly, and reflux at 85 °C for 2 hours to form a gel;

[0061] After freeze-drying, place the product in a tube furnace, heat it to 800 °C at a rate of 3 °C / min under an argon atmosphere, and start to introduce propylene gas at a rate of 150 ml / min. After maintaining for 30 min, stop introducing propylene, cool it to room temperature under an Ar atmosphere, and then take it out to obtain a black powder;

[0062] Soak the black powder in 35% hydrochloric acid for 2 h, wash it with deionized water until neutral, and then dry it under vacuum to obtain the silicon-carbon anode material of the present invention.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 3 is that PVA is not added.

[0065] Comparative Example 2

[0066] Dissolve 1 g of Co(NO3)2·6H2O and 9 g of dimethylimidazole in 50 ml of ethanol respectively;

[0067] Mix the above two solutions, add 5 g of nano-silica powder, stir evenly, and let stand for 16 h to obtain a precursor solution;

[0068] Add 1 g of PVA to the precursor solution, stir evenly, and reflux at 85 °C to form a gel;

[0069] After freeze-drying, place the product in a tubular furnace, heat it to 800 °C at a rate of 3 °C / min under an argon atmosphere, and cool it to room temperature in an Ar atmosphere and then take it out to obtain a black powder;

[0070] Immerse the black powder in 35% hydrochloric acid for 2 h, wash it with deionized water until neutral, and then dry it in vacuum to obtain the silicon-carbon anode material of the present invention.

[0071] Performance Test

[0072] Based on the silicon-carbon composite anode materials provided in the above Example 3, Comparative Example 1 and Comparative Example 2, button cells were fabricated and electrochemical performance tests were conducted.

[0073] The preparation steps of the button cell include: stirring and mixing the negative electrode silicon-carbon material, binder LA133, conductive carbon black and deionized water to obtain a negative electrode slurry; wherein, the mass-volume ratio of the silicon-carbon composite anode material, conductive carbon black, binder LA132, SBR and deionized water is 3 g: 0.03148 g: 0.04722 g: 0.21 g: 5.5 g; coat the negative electrode slurry on the copper foil, and after drying and rolling, a negative electrode sheet is prepared; the electrolyte is a solution with LiPF6 and 10% FEC as electrolytes, with a concentration of 1 mol / L, wherein the solvent is a mixed solution of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1; a metal lithium sheet is used as the counter electrode, and the separator is a polypropylene membrane.

[0074] In an argon glove box, assemble the button cell on a Neware CT-4008Tn type battery tester for electrochemical cycling performance testing, with the charge-discharge voltage range of 0.01 V to 2.0 V and the charge-discharge rate of 1 C. The test results are shown in the following table:

[0075]

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to protect the present invention

[0077] Limitations of the scope. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited only to those listed in the embodiments. Those of ordinary skill in the art should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solution of the present invention.

Claims

1. Preparation method of silicon-carbon anode material with carbon nanotubes embedded in hard and soft carbon framework structure, characterized in that, It includes the following steps: Step 1: Dissolve cobalt salts, dimethylimidazole, and nano-silicon powder in ethanol respectively. After stirring evenly, cobalt salt solution, dimethylimidazole solution, and nano-silicon dispersion are obtained; Step 2: Pour the dimethylimidazole solution and nano-silicon dispersion into the cobalt salt solution. After stirring evenly, let it stand for a period of time to obtain a precursor solution; Step 3: Add a soft carbon source to the precursor solution, reflux at 85 °C for 2 hours to form a gel. After freeze-drying, transfer it to a tube furnace under an argon atmosphere and introduce an appropriate amount of carbon source gas for carbonization to obtain black powder; Step 4: Immerse the black powder in 35% hydrochloric acid for 2 h. After washing with deionized water until neutral, vacuum dry to obtain a silicon-carbon anode material with carbon nanotubes embedded in a hard and soft carbon framework structure.

2. The preparation method of the silicon-carbon negative electrode material with a carbon nanotube embedded in a hard and soft carbon framework structure as claimed in claim 1, wherein In Step 1, the cobalt salt is one or more of cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt carbonate, cobalt phosphate, cobalt oxalate, cobalt nitrite, cobalt sulfite, and cobalt fluoride.

3. The preparation method of the silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure according to claim 1, wherein, In Step 1, the diameter of the nano-silicon powder is 20 - 50 nm.

4. The preparation method of the silicon-carbon anode material with a carbon nanotube-embedded hard and soft carbon framework structure as described in claim 1, characterized in that, In Step 2, the standing time of the mixed liquid of dimethylimidazole solution, nano-silicon dispersion, and cobalt salt solution is 8 - 24 h to allow the substances in the mixed liquid to react fully.

5. The preparation method of the silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure as described in claim 1, wherein, In Step 3, the soft carbon source is one or more of polyvinylidene fluoride, polyimide, polypyrrole, polyaniline, polyacrylonitrile, polyvinyl alcohol, polystyrene, and polytetrafluoroethylene.

6. The preparation method of the silicon-carbon anode material with a carbon nanotube-embedded hard and soft carbon framework structure as described in claim 1, characterized in that, In Steps 1 - 3, the mass ratio of the cobalt salt, dimethylimidazole, and nano-silicon powder is 1 - 5:2 - 20:1 - 10, and the mass ratio of dimethylimidazole to the soft carbon source is 1 - 10:

1.

7. The preparation method of the silicon-carbon negative electrode material with a carbon nanotube embedded in a hard and soft carbon framework structure according to claim 1, wherein In Step 3, the sintering temperature of the tube furnace is 600 - 1000 °C, and the heating rate is 1 - 10 °C / min.

8. The preparation method of the silicon-carbon anode material with a carbon nanotube-embedded hard and soft carbon framework structure as claimed in claim 1, wherein In Step 3, the carbon source gas in the tube furnace is one or more of methane, ethane, ethylene, acetylene, and propylene.

9. The preparation method of the silicon-carbon anode material with a carbon nanotube embedded in a hard and soft carbon framework structure as claimed in claim 1, wherein, In Step 3, the mass ratio of the introduced carbon source gas to the mass of the material obtained after freeze-drying is 0.1 - 1:

1.

10. Silicon-carbon anode material with carbon nanotubes embedded in a hard and soft carbon framework structure, characterized in that, The silicon-carbon anode material is prepared by the method described in any one of Claims 1 - 9; In the silicon-carbon anode material, the carbon nanotube has a diameter of 7 - 15 nm and a length of 5 - 10 μm.

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