Mesoporous silicon-carbon composite material with multi-level structure and preparation method and application thereof

Abstract

The application discloses a kind of mesoporous silicon carbon composite materials with multistage structure and preparation method and application, belong to silicon carbon negative electrode material synthesis technical field.The preparation method of the mesoporous silicon carbon composite materials with multistage structure includes the following steps: after mixing silicon powder and persulfate solution, oxidation treatment is carried out, then the obtained product is dispersed in oleic acid and surface modified, to obtain silicon@oleic acid dispersion liquid;Carbon source, citric acid, surfactant and initiator are pre-assembled in water, then the silicon@oleic acid dispersion liquid is added to carry out polymerization reaction, to obtain silicon@oleic acid@polymer precursor;Under inert atmosphere, the silicon@oleic acid@polymer precursor is carbonized, to obtain the mesoporous silicon carbon composite material with multistage structure.The material as lithium ion battery negative material can significantly improve the rate performance and cycle stability of lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of silicon-carbon anode material synthesis technology, and more specifically relates to a mesoporous silicon-carbon composite material with a multi-level structure, its preparation method and application. Background Technology

[0002] With the rapid development of the new energy industry, the performance requirements for lithium-ion battery anode materials are becoming increasingly stringent. Commercial lithium-ion batteries widely use graphite-based anode materials, but their theoretical specific capacity is relatively low (372 mAh / g), making it difficult to meet the market's demand for high-energy-density batteries. In contrast, silicon (Si) materials offer advantages due to their ultra-high specific capacity (4200 mAh / g) and low lithium intercalation platform (0.2~0.4 V vs. Li / Li). + With its advantages such as abundant resources, Si is considered an ideal anode material for high-energy-density lithium-ion batteries. However, Si undergoes severe volume changes during charging and discharging, with an expansion rate as high as 300%, which can easily lead to electrode structure damage, active material pulverization and shedding. At the same time, the solid electrolyte interphase (SEI) film formed on the Si surface continues to break and reconstruct, causing irreversible consumption of active lithium and electrolyte, resulting in a decrease in coulombic efficiency and rapid capacity decay of the battery.

[0003] To overcome the aforementioned problems, researchers generally employ a strategy of combining Si with carbon materials (such as graphite, amorphous carbon, and graphene). The carbon matrix not only provides a conductive network, improving the overall conductivity of the material, but also effectively buffers the volume changes of Si, inhibits the aggregation of nano-silicon particles, and promotes the formation of a more stable SEI film, thereby significantly enhancing the electrochemical performance of silicon-based anodes. However, existing silicon-carbon composite materials still have limitations in structural design: 1) simple mixing or surface coating is insufficient to adequately cope with the significant stress changes of Si during cycling; 2) single-dimensional carbon structures (such as using only carbon layers or carbon nanotubes) cannot fully meet the multiple requirements of conductivity, buffering, and ion transport. Therefore, constructing silicon-carbon composite materials with multi-level structures and synergistic functions through rational material design has become the key to overcoming its practical application bottleneck. Summary of the Invention

[0004] The purpose of this invention is to provide a mesoporous silicon-carbon composite material with a multi-level structure, its preparation method and application, in order to solve the problems of existing silicon-carbon composite materials such as simple structural design, difficulty in effectively adapting to silicon volume changes, imperfect conductive network, and poor cycle stability and rate performance when used as a negative electrode of lithium-ion batteries.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is to provide a method for preparing a mesoporous silicon-carbon composite material with a multi-level structure, comprising the following steps:

[0007] Silicon powder and persulfate solution were mixed and oxidized. The resulting product was then dispersed in oleic acid for surface modification to obtain a silicon@oleic acid dispersion.

[0008] A carbon source, citric acid, surfactant, and initiator are pre-assembled in water, and then the silicon@oleic acid dispersion is added to it to carry out a polymerization reaction to obtain a silicon@oleic acid@polymer precursor.

[0009] The silicon@oleic acid@polymer precursor was carbonized under an inert atmosphere to obtain the mesoporous silicon-carbon composite material with a multi-level structure.

[0010] Preferably, the persulfate in the persulfate solution includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; the concentration of the persulfate solution is 1-3M; and the ratio of silicon powder to persulfate solution is (5-15mg):1mL.

[0011] Preferably, the oxidation treatment time is 4 to 8 hours.

[0012] Preferably, the concentration of the silicone@oleic acid dispersion is 2.5~7.5 g / L.

[0013] Preferably, the carbon source includes one or more of aniline, pyrrole, and dopamine hydrochloride; the surfactant includes one or more of polyethylene oxide-polypropylene oxide, polyethylene oxide-polybutane, polyethylene oxide-polystyrene, polyethylene oxide-polymethyl methacrylate diblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and polypropylene oxide-polypropylene oxide-polypropylene oxide triblock copolymer.

[0014] Preferably, the initiator includes one or more of ammonium persulfate, hydrogen peroxide, and ferric chloride; the molar ratio of the surfactant, citric acid, carbon source, and initiator is 1:(10~50):(20~100):(20~100); and the volume ratio of the added silicon@oleic acid dispersion to the carbon source is (25~75):1.

[0015] Preferably, the pre-assembly time is 1-3 hours; the polymerization reaction time is 4-8 hours.

[0016] Preferably, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere; the flow rates of nitrogen and argon are independently 20~60 mL / min; the carbonization includes: first heating to 350℃ at a heating rate of 1℃ / min and holding for 2~5 h, then heating to 700~1000℃ at a heating rate of 10℃ / min and holding for 2~5 h.

[0017] The second technical solution of the present invention provides a mesoporous silicon-carbon composite material with a multi-level structure prepared by the above preparation method, wherein the multi-level structure is a carbon nanotube structure, a carbon nanosphere structure, and a carbon coating layer structure.

[0018] The third technical solution of the present invention is to provide the application of the above-mentioned mesoporous silicon-carbon composite material with multi-level structure in lithium-ion batteries.

[0019] The present invention discloses the following technical effects:

[0020] 1. The method for preparing a mesoporous silicon-carbon composite material with a multi-level structure provided by this invention involves controlling the oxidation of silicon powder with persulfate to introduce abundant hydroxyl groups onto the silicon surface, followed by grafting oleic acid molecules through esterification to form a stable modified layer. This treatment not only achieves an efficient transformation of silicon particles from hydrophilic to hydrophobic, significantly enhancing their compatibility and binding ability with carbon source monomers and promoting the formation of carbon nanospheres / carbon nanotubes and other structures on their surface; but also generates a continuous and dense thin-layer carbon coating on the silicon surface in situ during high-temperature carbonization, effectively blocking direct contact between the electrolyte and silicon, suppressing side reactions, and significantly improving interfacial stability.

[0021] 2. This invention introduces citric acid as a multifunctional additive. Its multi-carboxyl structure, through hydrogen bonding and synergistic interaction with nonionic surfactants, effectively stabilizes the micelle template, ensuring the formation of mesoporous structures. Simultaneously, citric acid, as a proton acid dopant, participates in the carbon source polymerization process, precisely controlling the arrangement and electronic structure of the carbon source polymer molecular chains. During polymerization, the polymer chains assemble based on the template and crosslink with citric acid, forming a silicon@oleic acid@polymer precursor. After carbonization, the oleic acid layer transforms into a uniform carbon coating layer, and the polymer-citric acid system transforms into a carbon nanosphere / tube composite structure. Simultaneously, the template undergoes thermal decomposition and is removed, naturally forming a mesoporous system with a bimodal distribution (2.6 nm and 32.8 nm), successfully constructing a three-dimensional continuous high-conductivity network throughout the entire material.

[0022] 3. The mesoporous silicon-carbon composite material with a multi-level structure provided by this invention exhibits a multi-level synergistic carbon architecture consisting of a carbon coating layer, carbon nanospheres, and carbon nanotubes. The inner ultrathin carbon coating layer is directly bonded to the silicon surface, effectively mitigating the volume expansion of silicon during lithium insertion / extraction and promoting the formation of a stable, low-impedance SEI film; the carbon nanospheres fill the interparticle gaps, providing excellent mechanical buffering and maintaining the integrity of the macroscopic structure; the carbon nanotubes intertwine to form a highly efficient electron conduction network, significantly improving charge transport dynamics. Through the synergistic design of space and function, these three elements significantly enhance the cycling stability and rate performance of the material. Attached Figure Description

[0023] Figure 1X-ray diffraction patterns of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3;

[0024] Figure 2 X-ray diffraction pattern of the mesoporous silicon-carbon composite material prepared in Comparative Example 1;

[0025] Figure 3 The results show the contact angle test results of silicon powder before and after oleic acid modification, where a is the silicon powder before oleic acid modification and b is the silicon powder after oleic acid modification.

[0026] Figure 4 Scanning electron microscope images of mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3, wherein a is composite material 1 prepared in Example 1, b is composite material 2 prepared in Example 2, and c is composite material 3 prepared in Example 3;

[0027] Figure 5 Scanning electron microscope image of the mesoporous silicon-carbon composite material prepared for Comparative Example 1;

[0028] Figure 6 Transmission electron microscope images of the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1 at different magnifications;

[0029] Figure 7 The energy dispersive spectroscopy (EDS) results are shown for the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1, where a is a high-angle annular dark field image and b~f are elemental surface distribution results.

[0030] Figure 8 The nitrogen adsorption-desorption isotherm (a) and the corresponding pore size distribution curve (b) of the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1.

[0031] Figure 9 The constant current charge-discharge performance curves of the mesoporous silicon-carbon composite materials with multi-level structures prepared in Examples 1-3 are shown in the first, second, third, and fifth cycles, where a is Example 1, b is Example 2, and c is Example 3.

[0032] Figure 10 Rate performance diagrams of mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 and mesoporous silicon-carbon composite materials prepared in Comparative Example 1;

[0033] Figure 11 The cycling performance of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 and the mesoporous silicon-carbon composite material prepared in Comparative Example 1 at a current density of 1.0 A / g is shown in the figure.

[0034] Figure 12The rate performance diagram of pure Si used in Comparative Example 2;

[0035] Figure 13 The graph shows the cycling performance of pure Si used in Comparative Example 2 at a current density of 1.0 A / g. Detailed Implementation

[0036] This invention provides a method for preparing a mesoporous silicon-carbon composite material with a multi-level structure, comprising the following steps:

[0037] Silicon powder and persulfate solution were mixed and oxidized. The resulting product was then dispersed in oleic acid for surface modification to obtain a silicon@oleic acid dispersion.

[0038] A carbon source, citric acid, surfactant, and initiator are pre-assembled in water, and then the silicon@oleic acid dispersion is added to it to carry out a polymerization reaction to obtain a silicon@oleic acid@polymer precursor.

[0039] The silicon@oleic acid@polymer precursor was carbonized under an inert atmosphere to obtain the mesoporous silicon-carbon composite material with a multi-level structure.

[0040] In this invention, the persulfate in the persulfate solution includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; the concentration of the persulfate solution is 1-3M. Using persulfate as an oxidant results in mild reaction conditions, simple operation, and easy removal of byproducts.

[0041] In this invention, the ratio of silicon powder to persulfate solution is 5~15 mg:1 mL.

[0042] In this invention, the oxidation treatment time is 4-8 hours. The oxidation time directly affects the thickness of the oxide layer and the hydroxyl density on the surface of silicon nanoparticles. If the oxidation time is too short, the number of surface hydroxyl groups will be insufficient, which is not conducive to the subsequent reaction with oleic acid and makes it difficult to form a complete coating layer; if the oxidation time is too long, the oxide layer will be too thick, which will hinder the silicon nucleus from participating in the electrochemical reaction and cause a significant decrease in capacity.

[0043] In this invention, the concentration of the silicon@oleic acid dispersion is 2.5~7.5 g / L. Oleic acid undergoes an esterification reaction with the hydroxyl groups on the silicon surface through its carboxyl groups, forming stable siloxane ester bonds, thereby introducing hydrophobic long-chain alkyl groups into the surface of silicon particles, achieving a transformation from hydrophilic to hydrophobic. The dispersion concentration of silicon in oleic acid directly affects the surface modification effect and the final carbon coating quality. When the concentration is below 2.5 g / L, the oleic acid coating layer is too thick, resulting in a thick carbon layer after carbonization, which hinders lithium-ion and electron transport, leading to capacity loss. When the concentration is above 7.5 g / L, the silicon surface modification is incomplete, residual hydroxyl groups cause particle agglomeration, and the volume expansion of silicon during carbonization easily leads to coating layer rupture.

[0044] This invention employs persulfate for controlled oxidation of silicon powder, introducing abundant hydroxyl groups onto the silicon surface. Oleic acid molecules are then grafted via esterification to form a stable modified layer. This treatment not only achieves an efficient transformation of silicon particles from hydrophilic to hydrophobic, significantly enhancing their compatibility and binding ability with carbon source monomers, but also provides the oleic acid modified layer as the foundation for subsequent carbon layer growth. Citric acid, as a key structure-directing agent, readily undergoes intermolecular crosslinking and cyclization during pyrolysis due to its small molecule and multi-carboxyl group characteristics, providing important catalytic sites and carbon sources for the nucleation and growth of carbon nanotubes. Meanwhile, under the constraint of surfactants and the initiation of initiators, the carbon source's own crosslinking polymerization kinetics tend to form a spherical structure, which is inherited and transformed into carbon nanospheres after carbonization. During high-temperature carbonization, the three carbon sources undergo pyrolysis and structural reconstruction: most of the carbon source is transformed into carbon nanospheres, oleic acid forms a continuous carbon coating layer, and citric acid, under catalysis, assists in the generation of carbon nanotubes connecting various parts.

[0045] In this invention, the carbon source includes one or more of aniline, pyrrole, and dopamine hydrochloride; the surfactant includes one or more of polyethylene oxide-polypropylene oxide, polyethylene oxide-polybutane, polyethylene oxide-polystyrene, polyethylene oxide-polymethyl methacrylate diblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and polyethylene oxide-polypropylene oxide-polypropylene oxide triblock copolymer.

[0046] In this invention, the initiator includes one or more of ammonium persulfate, hydrogen peroxide and ferric chloride; the molar ratio of the surfactant, citric acid, carbon source and initiator is 1:(10~50):(20~100):(20~100).

[0047] Initiators are used to initiate the polymerization of carbon source monomers. Citric acid acts as a protonic acid dopant, crosslinking agent, and additional carbon source, and its ratio is crucial to the final carbon structure. Too little initiator leads to low polymerization degree, insufficient molecular weight, discontinuous coating layer after carbonization, and inability to effectively protect the silicon core. Too much initiator results in excessively rapid polymerization, easily forming an over-crosslinked rigid structure, producing defective carbon after carbonization, and reducing conductivity. When the proportion of citric acid is too low, insufficient doping causes polyaniline to be mainly in an insulating form, resulting in poor conductivity after carbonization and limited carbon nanotube formation. When the proportion is too high, it inhibits initiator decomposition, leading to incomplete polymerization and a loose coating layer that is easily detached.

[0048] In this invention, the volume ratio of the added silicon@oleic acid dispersion to the carbon source is (25~75):1.

[0049] When there is too much silicon@oleic acid dispersion, the proportion of silicon in the reaction system is too high, which leads to a decrease in the relative concentration of carbon source that polymerizes on its surface. As a result, there are fewer multi-level carbon components formed after carbonization, causing silicon to be exposed on the material surface and unable to play a protective role. When there is too little silicon@oleic acid dispersion, the silicon content in the obtained material is too low, and the carbon component content on the silicon surface is too high, which makes it easy for silicon to be buried and difficult to participate in the electrochemical reaction.

[0050] In this invention, the pre-assembly time is 1-3 hours; the polymerization reaction time is 4-8 hours.

[0051] In this invention, the inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere; the flow rates of nitrogen and argon are independently 20~60 mL / min; the carbonization includes: first heating to 350℃ at a heating rate of 1℃ / min and holding for 2~5 h, then heating to 700~1000℃ at a heating rate of 10℃ / min and holding for 2~5 h.

[0052] Heating to 350℃ first allows for sufficient pre-carbonization (crosslinking and cyclization) of the precursor, forming a stable primary carbon framework and "fixing" the structure. Then, heating to 700-1000℃ is necessary. If the carbonization temperature is below 700℃, carbonization is incomplete, resulting in extremely poor electronic conductivity of the material. If the carbonization temperature is above 1000℃, the carbon framework will shrink and fuse, causing many mesoporous and macroporous structures to collapse or close. Holding time less than 2 hours may result in insufficient structural evolution (such as graphitization of carbon nanotubes and mesoporous development), while holding time more than 5 hours leads to further loss of heteroatoms and a decrease in specific surface area.

[0053] This invention introduces citric acid as a multifunctional additive. Its multi-carboxyl structure, through hydrogen bonding and synergistic interaction with surfactants, effectively stabilizes the micelle template, ensuring the formation of mesoporous structures. Simultaneously, citric acid, as a protonic acid dopant, participates in the carbon source polymerization process, precisely controlling the arrangement and electronic structure of the carbon source polymer molecular chains. During polymerization, the polymer chains assemble based on the template and crosslink with citric acid, forming a silicon@oleic acid@polymer precursor. After carbonization, the oleic acid layer of this precursor transforms into a uniform carbon coating layer, and the polymer-citric acid system transforms into a carbon nanosphere / tube composite structure. Simultaneously, the template undergoes thermal decomposition and is removed, forming a mesoporous system with a bimodal distribution (2.6 nm and 32.8 nm), successfully constructing a three-dimensional continuous highly conductive network throughout the entire material.

[0054] The present invention also provides a mesoporous silicon-carbon composite material with a multi-level structure prepared by the above preparation method, wherein the multi-level structure is a carbon nanotube structure, a carbon nanosphere structure, and a carbon coating layer structure.

[0055] The mesoporous silicon-carbon composite material with a multi-level structure provided by this invention exhibits a multi-level synergistic carbon architecture consisting of a carbon coating layer, carbon nanospheres, and carbon nanotubes. The ultrathin carbon coating layer formed in the inner layer is directly bonded to the silicon surface, effectively mitigating the volume expansion of silicon during lithium insertion / extraction and promoting the formation of a stable, low-impedance SEI film. Carbon nanospheres fill the interparticle gaps, providing excellent mechanical buffering and maintaining macroscopic structural integrity. Carbon nanotubes intertwine to form a highly efficient electron conduction network, significantly enhancing charge transport dynamics. Through synergistic spatial and functional design, these three components significantly enhance the material's cycling stability and rate performance.

[0056] The present invention also provides the application of the above-mentioned mesoporous silicon-carbon composite material with multi-level structure in lithium-ion batteries. The mesoporous silicon-carbon composite material with multi-level structure, as a negative electrode material of lithium-ion batteries, can significantly improve the rate performance and cycle stability of lithium-ion batteries.

[0057] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0058] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0059] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0060] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0061] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0062] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0063] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of the present invention are commercially available products, and the source of commercially available products does not affect the technical effect of the present invention.

[0064] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0065] Example 1

[0066] This embodiment provides a method for preparing a mesoporous silicon-carbon composite material 1 with a multi-level structure and a lithium-ion battery 1. The specific steps are as follows:

[0067] (1) Preparation of mesoporous silicon-carbon composite material with multi-level structure 1:

[0068] 50 mg of silicon powder was added to 10 mL of 2 M ammonium persulfate (APS) solution and stirred at room temperature for 6 h. After centrifugation and washing with anhydrous ethanol and water, the silicon powder with hydroxyl-rich surface was obtained after drying. Then, it was added to 20 mL of oleic acid (OA) and stirred for 2 h to obtain a silicon@oleic acid dispersion.

[0069] 0.6 g of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (Pluronic F127) was dissolved in 10 mL of deionized water and stirred at room temperature for 5 h to obtain a uniform F127 micelle solution. Separately, 0.4 mL of aniline (ANI) and 0.28 g of citric acid (CA) were stirred in 10 mL of deionized water for 0.5 h. Then, 10 mL of ammonium persulfate solution with a mass concentration of 0.1 g / mL was added, and the reaction was continued for another 0.5 h. Next, the aforementioned F127 micelle solution was added, and the reaction was continued for another 0.5 h. Finally, the above mixed solution was added to a silicone@oleic acid dispersion and stirred for 6 h. After centrifugation, washing, and drying, a silicone@oleic acid@polymer precursor was obtained.

[0070] The precursor obtained above was placed in a corundum boat and transferred into a tube furnace. Argon gas was continuously introduced at a rate of 40 mL / min. The temperature of the tube furnace was increased to 350°C at a rate of 1°C / min and reacted for 2 h. Then, the temperature was increased to 900°C at a rate of 10°C / min and reacted for 2 h. After cooling to room temperature, mesoporous silicon-carbon composite material 1 with a multi-level structure was obtained.

[0071] (2) Preparation of lithium-ion battery 1:

[0072] The obtained mesoporous silica-carbon composite material with a multi-level structure, polyacrylic acid (PAA), and conductive carbon black (SuperP) were thoroughly ground in a mass ratio of 8:1:1. After adding deionized water and continuing to grind and mix evenly, a black paste-like slurry was obtained. The black slurry was uniformly coated on copper foil, dried, and cut into electrode sheets with a diameter of 10 mm as the negative electrode of the lithium-ion battery. A lithium sheet was used as the control electrode, a polypropylene (PP) film was used as the separator, and 1M lithium hexafluorophosphate (LiPF6) was used as the solute. A 1:1 volume ratio of diethyl carbonate (DEC): ethylene carbonate (EC) was used as the base solvent, and a mixed solution of 10% fluoroethylene carbonate (FEC) and 1% vinylene carbonate (VC) was added as the electrolyte. The CR2032 button battery was assembled in a glove box, and its electrochemical performance was tested after standing for 8 hours.

[0073] Example 2

[0074] This embodiment provides a method for preparing a mesoporous silicon-carbon composite material 2 with a multi-level structure and a lithium-ion battery 2. The difference from Embodiment 1 lies in the amount of silicon powder added. The specific steps are as follows:

[0075] (1) Preparation of mesoporous silicon-carbon composite material with multi-level structure 2:

[0076] 150 mg of silicon powder was added to 10 mL of 2 M APS solution and stirred at room temperature for 6 h. After centrifugation and washing with anhydrous ethanol and water, the silicon powder with hydroxyl-rich surface was obtained after drying. Then it was added to 20 mL of OA and stirred for 2 h to obtain a silicon@oleic acid dispersion.

[0077] 0.6 g of Pluronic F127 was dissolved in 10 mL of deionized water and stirred at room temperature for 5 h to obtain a homogeneous F127 micelle solution. Separately, 0.4 mL of LANI and 0.28 g of CA were stirred in 10 mL of deionized water for 0.5 h, then 10 mL of APS solution with a mass concentration of 0.1 g / mL was added, and the reaction was continued for another 0.5 h. Next, the aforementioned F127 micelle solution was added, and the reaction was continued for another 0.5 h. Finally, the above mixed solution was added to a silicone@oleic acid dispersion and stirred for 6 h. After centrifugation, washing, and drying, a silicone@oleic acid@polymer precursor was obtained.

[0078] The precursor obtained above was placed in a corundum boat and transferred into a tube furnace. Argon gas was continuously introduced at a rate of 40 mL / min. The temperature of the tube furnace was increased to 350°C at a rate of 1°C / min and reacted for 2 h. Then, the temperature was increased to 900°C at a rate of 10°C / min and reacted for 2 h. After cooling to room temperature, mesoporous silicon-carbon composite material 2 with a multi-level structure was obtained.

[0079] (2) Preparation of lithium-ion battery 2:

[0080] The mesoporous silicon-carbon composite material 2 with a multi-level structure obtained in Example 2 above, PAA and Super P were thoroughly ground in a mass ratio of 8:1:1. After adding deionized water and continuing to grind and mix evenly, a black paste-like slurry was obtained. The black slurry was uniformly coated on copper foil, dried and cut into electrode sheets with a diameter of 10 mm as the negative electrode of the lithium-ion battery. A lithium sheet was used as the control electrode, a PP film was used as the separator, and 1M LiPF6 was used as the solute. A DEC:EC solution with a volume ratio of 1:1 was used as the base solvent. A mixed solution of 10% FEC and 1% VC was added as the electrolyte. The CR2032 button battery was assembled in a glove box and its electrochemical performance was tested after standing for 8 hours.

[0081] Example 3

[0082] This embodiment provides a method for preparing a mesoporous silicon-carbon composite material with a multi-level structure and a lithium-ion battery 3. The difference from Embodiment 1 lies in the amount of citric acid added. The specific steps are as follows:

[0083] 50 mg of silicon powder was added to 10 mL of 2 M APS solution and stirred at room temperature for 6 h. After centrifugation and washing with anhydrous ethanol and water, the silicon powder with hydroxyl-rich surface was obtained after drying. Then it was added to 20 mL of OA and stirred for 2 h to obtain a silicon@oleic acid dispersion.

[0084] 0.6 g of Pluronic F127 was dissolved in 10 mL of deionized water and stirred at room temperature for 5 h to obtain a homogeneous F127 micelle solution. Separately, 0.4 mL of LANI and 0.14 g of CA were stirred in 10 mL of deionized water for 0.5 h, then 10 mL of APS solution with a mass concentration of 0.1 g / mL was added, and the reaction was continued for another 0.5 h. Next, the aforementioned F127 micelle solution was added, and the reaction was continued for another 0.5 h. Finally, the above mixed solution was added to a silicone@oleic acid dispersion and stirred for 6 h. After centrifugation, washing, and drying, a silicone@oleic acid@polymer precursor was obtained.

[0085] The precursor obtained above was placed in a corundum boat and transferred into a tube furnace. Argon gas was continuously introduced at a rate of 40 mL / min. The temperature of the tube furnace was increased to 350°C at a rate of 1°C / min and reacted for 2 h. Then, the temperature was increased to 900°C at a rate of 10°C / min and reacted for 2 h. After cooling to room temperature, mesoporous silicon-carbon composite material 3 with a multi-level structure was obtained.

[0086] (2) Preparation of lithium-ion batteries 3:

[0087] The mesoporous silicon-carbon composite material 3 with a multi-level structure obtained in Example 3 above, PAA and Super P were thoroughly ground in a mass ratio of 8:1:1. After adding deionized water and continuing to grind and mix evenly, a black paste was obtained. The black paste was uniformly coated on copper foil, dried and cut into electrode sheets with a diameter of 10 mm as the negative electrode of the lithium-ion battery. A lithium sheet was used as the control electrode, a PP film was used as the separator, 1M LiPF6 was used as the solute, DEC:EC was used as the base solvent with a volume ratio of 1:1, and a mixed solution of 10% FEC and 1% VC was added as the electrolyte. The CR2032 button battery was assembled in a glove box and its electrochemical performance was tested after standing for 8 hours.

[0088] Comparative Example 1

[0089] This comparative example provides a method for preparing a mesoporous silicon-carbon composite material and a lithium-ion battery 4. The difference from Example 1 is that citric acid is not added. The specific steps are as follows:

[0090] (1) Preparation of mesoporous silicon-carbon composite materials:

[0091] 50 mg of silicon powder was added to 10 mL of 2 M APS solution and stirred at room temperature for 6 h. After centrifugation and washing with anhydrous ethanol and water, the silicon powder with hydroxyl-rich surface was obtained after drying. Then it was added to 20 mL of OA and stirred for 2 h to obtain a silicon@oleic acid dispersion.

[0092] 0.6 g of Pluronic F127 was dissolved in 10 mL of deionized water and stirred at room temperature for 5 h to obtain a homogeneous F127 micelle solution. Separately, 0.4 mL of LANI was stirred in 10 mL of deionized water for 0.5 h, then 10 mL of APS solution with a mass concentration of 0.1 g / mL was added, and the reaction was continued for another 0.5 h. Next, the aforementioned F127 micelle solution was added, and the reaction was continued for another 0.5 h. Finally, the above mixed solution was added to a silicone@oleic acid dispersion and stirred for 6 h. After centrifugation, washing, and drying, a silicone@oleic acid@polymer precursor was obtained.

[0093] The precursor obtained above was placed in a corundum boat and transferred into a tube furnace. Argon gas was continuously introduced at a rate of 40 mL / min. The temperature of the tube furnace was increased to 350°C at a rate of 1°C / min and reacted for 2 h. Then, the temperature was increased to 900°C at a rate of 10°C / min and reacted for 2 h. After cooling to room temperature, mesoporous silicon-carbon composite material was obtained.

[0094] (2) Preparation of lithium-ion batteries 4:

[0095] The mesoporous silicon-carbon composite material, PAA, and Super P obtained in Comparative Example 1 were thoroughly ground in a mass ratio of 8:1:1. After adding deionized water and continuing to grind and mix evenly, a black paste-like slurry was obtained. The black slurry was uniformly coated on copper foil, dried, and cut into electrode sheets with a diameter of 10 mm as the negative electrode of the lithium-ion battery. A lithium sheet was used as the control electrode, a PP film was used as the separator, and 1M LiPF6 was used as the solute. A DEC:EC solution with a volume ratio of 1:1 was used as the base solvent. A mixed solution of 10% FEC and 1% VC was added as the electrolyte. A CR2032 button battery was assembled in a glove box, and its electrochemical performance was tested after standing for 8 hours.

[0096] Comparative Example 2

[0097] (1) This comparative example uses the same pure Si as Examples 1, 2 and 3 for the experiment, without any treatment.

[0098] (2) The comparative example provides a method for preparing lithium-ion battery 5, the specific steps of which are as follows:

[0099] Pure silicon powder, PAA, and Super P were thoroughly ground in a mass ratio of 6:2:2. After adding deionized water and continuing to grind and mix evenly, a brown paste-like slurry was obtained. The brown slurry was evenly coated onto copper foil, dried, and cut into electrode sheets with a diameter of 10 mm as the negative electrode of the lithium-ion battery. A lithium sheet was used as the control electrode, a PP film was used as the separator, and 1 M LiPF6 was used as the solute. A DEC:EC solution with a volume ratio of 1:1 was used as the base solvent. A mixed solution of 10% FEC and 1% VC was added as the electrolyte. CR2032 button batteries were assembled in a glove box, and their electrochemical performance was tested after standing for 8 hours.

[0100] To verify the performance of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3, the mesoporous silicon-carbon composite material prepared in Comparative Example 1, and pure Si in Comparative Example 2, as well as the performance of the lithium-ion batteries prepared using the above materials, performance tests were conducted on the above materials and the prepared lithium-ion batteries. The test results are as follows: Figures 1-13 As shown.

[0101] Figure 1 The X-ray diffraction patterns of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 are shown. Figure 1It can be seen that the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 showed obvious diffraction peaks at 28°, 47°, 56°, 69° and 76°, which correspond to the (111), (220), (311), (331) and (400) crystal planes of crystalline silicon, respectively; at the same time, the characteristic diffraction peak of the (002) crystal plane of carbon appeared at ~26°, indicating that the carbon component in the material has undergone local graphitization, and silicon-carbon composite materials have been successfully formed.

[0102] Figure 2 The X-ray diffraction pattern is shown for the mesoporous silicon-carbon composite material prepared in Comparative Example 1. According to... Figure 2 It can be seen that the mesoporous silicon-carbon composite material prepared in Comparative Example 1 (without citric acid) has a similar XRD pattern to that of Examples 1-3, all showing characteristic diffraction peaks of silicon and carbon components. This indicates that even without the participation of citric acid, the carbon source monomer can still be converted into a carbon skeleton after polymerization and has a certain graphitization structure.

[0103] Figure 3 The figures show the contact angle test results of silicon powder before and after oleic acid modification, where a represents silicon powder before oleic acid modification and b represents silicon powder after oleic acid modification. Based on... Figure 3 It can be seen that the contact angle between silicon powder treated with ammonium persulfate and water is 18.0°, indicating that abundant hydroxyl groups have been successfully introduced into its surface, giving it strong hydrophilicity. After further modification with oleate, the contact angle increases to 38.4°, proving that the silicon powder has successfully changed from hydrophilic to hydrophobic, which is beneficial for its composite with hydrophobic carbon source monomers.

[0104] Figure 4 Scanning electron microscope images of mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3, wherein a is composite material 1 prepared in Example 1, b is composite material 2 prepared in Example 2, and c is composite material 3 prepared in Example 3. Figure 4 It can be seen that in the mesoporous silicon-carbon composite materials 1-3 prepared in Examples 1-3, carbon nanospheres and carbon nanotubes intertwine to form a three-dimensional network structure, with silicon nanoparticles embedded within it. For example... Figure 4 As shown in Figure a, in the silicon-carbon composite material, the carbon layer directly and uniformly coats the surface of the silicon nanoparticles, carbon nanospheres are dispersed between the silicon particles, and carbon nanotubes intertwine throughout the composite material to form a three-dimensional, continuous conductive network that penetrates and connects all silicon particles and carbon spheres; as shown in Figure a. Figure 4 As shown in b, when the amount of silicon powder used increases, silicon particles appear outside the multi-level carbon structure; as... Figure 4 As shown in Figure c, the number of carbon nanotubes formed decreases when the amount of citric acid used is reduced, which directly indicates that the amount of citric acid used affects the number of carbon nanotubes formed.

[0105] Figure 5Scanning electron microscope image of the mesoporous silicon-carbon composite material prepared for Comparative Example 1. According to... Figure 5 It can be seen that the mesoporous silica-carbon composite material prepared in Comparative Example 1 did not form a carbon nanotube structure because no citric acid was added for the reaction, indicating that citric acid plays a key role in guiding the formation of carbon nanotubes.

[0106] Figure 6 Transmission electron microscope images of the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1 at different magnifications. According to... Figure 6 As can be seen, in the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1, silicon nanoparticles are coated with carbon layers and interwoven between carbon nanospheres and carbon nanotubes to form an interwoven multi-level structure, wherein the particle size of the carbon nanospheres is about 100 nm and the width of the carbon nanotubes is about 60 nm.

[0107] Figure 7 The energy dispersive spectroscopy (EDS) results are shown for the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1, where a is a high-angle annular dark-field image, and b~f are elemental surface distribution results. Figure 7 It can be seen that the silicon nanoparticles in the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1 have a particle size of about 60 nm and are uniformly coated with a carbon layer with a thickness of about 2 nm. At the same time, N and O elements are uniformly doped in the carbon skeleton.

[0108] Figure 8 The nitrogen adsorption-desorption isotherm (a) and corresponding pore size distribution curve (b) of the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1 are shown. Figure 8 It can be seen that the nitrogen adsorption-desorption isotherm curve of the mesoporous silicon-carbon composite material 1 with a multi-level structure prepared in Example 1 is a typical type IV isotherm curve, indicating that there are a large number of mesopores in the material, and its specific surface area is 119 m². 2 / g, from the corresponding pore size distribution curve, it can be seen that the most probable pore sizes are 2.6nm and 32.8nm.

[0109] Figure 9 The constant current charge-discharge performance curves of the mesoporous silicon-carbon composite materials with multi-level structures prepared in Examples 1-3 are shown for the first, second, third, and fifth cycles, where a represents Example 1, b represents Example 2, and c represents Example 3. According to... Figure 9 It can be seen that the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 have high first-cycle discharge specific capacities of 1230.1, 1869.7, and 1391.7 mAh / g at a current density of 0.1 A / g, respectively, which correspond to 29.3%, 44.5%, and 33.1% of the theoretical specific capacity of pure Si (4200 mAh / g). The curves of each cycle in Examples 1-3 basically overlap during subsequent cycles, indicating that the battery has good cycle performance.

[0110] Figure 10 Rate performance diagrams of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 and the mesoporous silicon-carbon composite material prepared in Comparative Example 1 are shown. Figure 10 As can be seen, the specific capacities of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 and the mesoporous silicon-carbon composite material prepared in Comparative Example 1 at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g are shown in Table 1. Examples 1-3 all have good rate performance, while the rate performance of Comparative Example 1 is worse than that of Example 3. This is because the formation of carbon nanotubes is lacking, and an efficient and continuous conductive network cannot be constructed, further demonstrating the performance advantages of multi-level carbon nanostructures.

[0111] Table 1. Specific capacities (unit: mAh / g) of the mesoporous silicon-carbon composite materials with multi-level structures prepared in Examples 1-3 and the mesoporous silicon-carbon composite material prepared in Comparative Example 1 at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g.

[0112]

[0113] Figure 11 The graphs show the cycling performance of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 and the mesoporous silicon-carbon composite material prepared in Comparative Example 1 at a current density of 1.0 A / g. According to... Figure 11 It can be seen that the capacity retention rates of the mesoporous silicon-carbon composite materials 1-3 with multi-level structures prepared in Examples 1-3 and the mesoporous silicon-carbon composite material prepared in Comparative Example 1 after stable cycling for 300 cycles at a current density of 1.0 A / g were 30.2%, 40.8%, 38.7% and 31.2%, respectively, which proves that the appropriate amount of citric acid added can improve the cycling stability of silicon-carbon composite materials.

[0114] Figure 12 This is a rate performance diagram of pure Si used in Comparative Example 2. According to... Figure 12 It can be seen that the specific capacities of Comparative Example 2 at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 A / g are 3368.7, 3024.1, 2581.8, 2118.2, 1643.4, and 1080.7 mAh / g, respectively, indicating that the rate performance of pure Si is generally poor.

[0115] Figure 13 The graph shows the cycling performance of pure Si used in Comparative Example 2 at a current density of 1.0 A / g. Based on... Figure 13It can be seen that the capacity retention rate of Comparative Example 2 after 300 stable cycles at a current density of 1.0 A / g is only 28.2%, which is lower than that of the mesoporous silicon-carbon materials in Examples 1-3, indicating that the cycling stability of pure Si is very poor.

[0116] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0117] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a mesoporous silicon-carbon composite material with a multi-level structure, characterized in that, Includes the following steps: Silicon powder and persulfate solution were mixed and oxidized. The resulting product was then dispersed in oleic acid for surface modification to obtain a silicon@oleic acid dispersion. A carbon source, citric acid, surfactant, and initiator are pre-assembled in water, and then the silicon@oleic acid dispersion is added to it to carry out a polymerization reaction to obtain a silicon@oleic acid@polymer precursor. The silicon@oleic acid@polymer precursor was carbonized under an inert atmosphere to obtain the mesoporous silicon-carbon composite material with a multi-level structure. The carbon source includes one or more of aniline, pyrrole, and dopamine hydrochloride; the surfactant includes one or more of polyethylene oxide-polypropylene oxide, polyethylene oxide-polybutane, polyethylene oxide-polystyrene, polyethylene oxide-polymethyl methacrylate diblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and polyethylene oxide-polypropylene oxide-polypropylene oxide triblock copolymer.

2. The preparation method according to claim 1, characterized in that, The persulfate in the persulfate solution includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; the concentration of the persulfate solution is 1~3M; and the ratio of silicon powder to persulfate solution is (5~15mg):1mL.

3. The preparation method according to claim 1, characterized in that, The oxidation treatment time is 4-8 hours.

4. The preparation method according to claim 1, characterized in that, The concentration of the silicone@oleic acid dispersion is 2.5~7.5 g / L.

5. The preparation method according to claim 1, characterized in that, The initiator includes one or more of ammonium persulfate, hydrogen peroxide, and ferric chloride; the molar ratio of the surfactant, citric acid, carbon source, and initiator is 1:(10~50):(20~100):(20~100); the volume ratio of the added silica@oleic acid dispersion and carbon source is (25~75):

1.

6. The preparation method according to claim 1, characterized in that, The pre-assembly time is 1-3 hours; the polymerization reaction time is 4-8 hours.

7. The preparation method according to claim 1, characterized in that, The inert atmosphere includes a nitrogen atmosphere and / or an argon atmosphere; the flow rates of nitrogen and argon are independently 20~60 mL / min; the carbonization includes: first heating to 350℃ at a heating rate of 1℃ / min and holding for 2~5 h, then heating to 700~1000℃ at a heating rate of 10℃ / min and holding for 2~5 h.

8. The mesoporous silicon-carbon composite material with a multi-level structure prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The multi-level structure comprises carbon nanotube structure, carbon nanosphere structure, and carbon coating layer structure.

9. The application of the mesoporous silicon-carbon composite material with a multi-level structure as described in claim 8 in lithium-ion batteries.

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