Si@SiC@EG ternary composite material and preparation method and application thereof

Abstract

The application discloses a Si@SiC@EG ternary composite material and a preparation method and application thereof, and belongs to the technical field of electrode materials. The Si@SiC@EG ternary composite material is prepared by adopting a coating technology, coating nano Si powder with a high-molecular polymer PEGDA, high-temperature carbonization after coating to obtain a material with a rigid silicon carbide (SiC) outer layer and a Si inner layer (namely Si@SiC), and then tempering the material to precipitate epitaxial graphene (EG), so as to obtain a multilayer composite material with an outermost graphene coating, a SiC intermediate layer and a Si inner layer (namely Si@SiC@EG ternary composite material). The EG can improve the conductivity of the composite material, the SiC intermediate layer can inhibit the volume expansion of the inner core silicon, so that the silicon-based material can have high specific capacity, and can also achieve the effects of enhancing the conductivity and inhibiting the volume expansion when serving as a negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and particularly relates to a Si@SiC@EG ternary composite material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long lifespan, low environmental pollution, and low self-discharge rate, have been widely used in everything from small consumer electronics to large electric vehicles and spacecraft. With the continued development of new energy sources, lithium-ion batteries are expected to find even wider applications in large-scale energy storage and power cell fields. The anode material, as one of the main materials in lithium-ion batteries, accounts for approximately 20% of the total manufacturing cost and has a significant impact on the energy density, safety performance, and lifespan of lithium-ion batteries. Currently, graphite is the primary anode material for lithium-ion batteries. However, the relatively low energy density of graphite anodes (250 Wh / kg) cannot meet the 2025 target of 400 Wh / kg for single-cell batteries.

[0003] Silicon is often used in combination with graphite in the preparation of anode materials for lithium-ion batteries. Since silicon-based materials have a theoretical specific capacity of 4200 mAh / g, more than 10 times that of ordinary graphite, combining silicon and graphite can improve the specific capacity of the anode, potentially leading to a significant increase in the overall battery capacity. Current silicon-based anode material technologies employed by researchers mainly include silicon-carbon composites, carbon-coated silicon, and porous carbon-deposited silicon, to enhance the specific capacity of lithium-ion battery anode materials.

[0004] While silicon-carbon composite technology can greatly improve battery capacity and energy density, the significant volume change and low conductivity of silicon during charging and discharging greatly limit its application in lithium-ion batteries (LIBs). Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a Si@SiC@EG ternary composite material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a Si@SiC@EG ternary composite material, wherein nano-silicon (Si) powder is coated with polyethylene glycol diacrylate (PEGDA), annealed to obtain Si@SiC, and then tempered to obtain the Si@SiC@EG ternary composite material.

[0008] This invention employs a coating technology, utilizing the polymer PEGDA to coat nano-Si powder. After coating, high-temperature carbonization yields a material with an outer rigid silicon carbide (SiC) layer and an inner Si layer (i.e., Si@SiC). This material is then tempered to precipitate epitaxial graphene (EG), resulting in a multilayer composite material with an outermost graphene coating, a middle SiC layer, and an inner Si layer (i.e., a Si@SiC@EG ternary composite material). EG enhances the conductivity of the composite material, while the SiC middle layer suppresses the volume expansion of the core silicon. This allows the silicon-based material, when used as a negative electrode, to achieve both high specific capacity and enhanced conductivity and reduced volume expansion. The coin-type lithium-ion battery assembled from this composite material (Si@SiC@EG ternary composite material) achieves a capacitance of 0.1 A·g. -1 After 150 cycles at a current density, the capacity reaches 1555.6 mAh·g. -1 , in 2 A·g -1 After 2000 cycles at a current density of 887 mAh·g -1 After nano-Si powder generates a rigid SiC layer and precipitates graphene in situ, the overall cycle performance and capacity of the battery are improved. The coating strategy of this invention provides an important method for preparing high-performance silicon-based lithium-ion batteries.

[0009] Further, the step of coating the nano-Si powder with the PEGDA and annealing it to obtain Si@SiC is as follows:

[0010] The PEGDA and azobisisobutyronitrile were added to acetone and stirred until homogeneous to obtain the first solution.

[0011] The nano-Si powder was added to acetone and ultrasonically treated to obtain a second solution.

[0012] The first solution and the second solution were mixed and reacted under heating conditions to obtain an intermediate.

[0013] The intermediate was annealed to obtain Si@SiC.

[0014] Furthermore, the mass ratio of PEGDA to azobisisobutyronitrile (AIBN) is 1:0.021.

[0015] Furthermore, the mass ratio of the PEGDA to the nano-Si powder is 2:0.45.

[0016] Furthermore, the particle size of the nano-silicon powder is 30 nm.

[0017] Furthermore, the heating temperature is 70 °C, and the heating time is 12 hours;

[0018] And / or, the annealing temperature is 1450 °C and the holding time is 2 h.

[0019] Furthermore, the tempering treatment temperature is 1500℃, and the holding time is 15min.

[0020] The present invention also provides a Si@SiC@EG ternary composite material prepared according to the above preparation method.

[0021] In existing methods, SiC@EG lithium-ion battery anode materials can be prepared by calcining nano-silicon carbide particles at 1500℃ under an argon atmosphere. However, the material prepared by this method only contains SiC@EG and lacks a silicon core, resulting in a lower battery capacity than that assembled from the Si@SiC@EG ternary composite material synthesized by the method of this invention, thus failing to maximize the material's performance. In existing methods, Zn2SiO4 / C nanowires are prepared as sacrificial templates using a one-step hydrothermal method, and Si / SiC / C composite microspindle structures are prepared via a magnesothermic reduction reaction. Compared to the Si@SiC@EG ternary composite material prepared by the method of this invention, the conductivity of C in the Si@SiC@C composite anode material prepared by this method is far inferior to that of epitaxial graphene (EG). Therefore, the material performance is not as good as that of batteries assembled from the Si@SiC@EG ternary composite material prepared by this invention.

[0022] The present invention also provides a lithium-ion battery, wherein the negative electrode material is the above-mentioned Si@SiC@EG ternary composite material.

[0023] The present invention also provides an application of the above-mentioned Si@SiC@EG ternary composite material in the preparation of lithium-ion batteries, wherein the Si@SiC@EG ternary composite material is used as the negative electrode material of lithium-ion batteries.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] Silicon (Si) possesses an extremely high specific capacity, ten times that of graphite, making it a promising candidate for lithium-ion battery anode materials. However, its poor conductivity and significant volume expansion during charge and discharge lead to short cycle life and low charge transfer efficiency. Therefore, designing different composite structures with silicon and carbon materials is a key method for improving the performance of silicon-carbon lithium-ion battery materials. This invention, in addition to considering material morphology modification strategies (such as altering the material surface shape) to suppress volume expansion, also employs a tempering method to precipitate epitaxial graphene (EG) to enhance charge transfer conductivity, further improving and enhancing the performance of lithium-ion batteries. The specific approach is as follows: First, select oligomers (PEGDA) to polymerize and coat Si, making the coating on the Si material surface more uniform. Second, use high-temperature annealing to form a rigid SiC structure on the Si material surface, suppressing the volume expansion effect of Si material during cycling. Third, temper the Si@SiC composite material with SiC coating on the surface to precipitate epitaxial graphene (EG) on the SiC surface, improving its ion migration performance (lithium ion) and charge transfer performance, thereby enhancing lithium storage performance and conductivity, and ultimately improving the overall performance of lithium-ion batteries. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 This is a flowchart illustrating the preparation process of the Si@SiC@EG ternary composite material in Example 1 of the present invention.

[0028] Figure 2 This is a schematic diagram of the formation process of the Si@SiC@EG ternary composite material in Embodiment 1 of the present invention;

[0029] Figure 3 The images show the overall XRD pattern and the magnified XRD pattern at 17~27.5° of the Si@SiC and Si@SiC@EG ternary composite materials in Example 1, where (a) is the overall XRD pattern and (b) is the magnified XRD pattern at 17~27.5°.

[0030] Figure 4 (a) is the CV curve of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1; (b) is the b-value of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1; (c) is the pseudocapacitive contribution rate of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1 at different scan rates; and (d) is the value of 1 mV·s. -1The pseudocapacitive contribution rate of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1 below;

[0031] Figure 5 The graphs show the electrochemical performance of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1 at different current densities, where (a) shows a current density of 0.1 A·g. -1 (b) represents the current density during testing, starting from 0.1 A g. -1 Increase to 0.2, 0.5, 0.8, 1.0, 3.0, 5.0 A·g -1 The average reversible capacitance at time (c) is 2 A·g. -1 . Detailed Implementation

[0032] 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.

[0033] 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. Every smaller range between any stated value or intermediate value within a stated range, and 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The present invention provides a method for preparing a Si@SiC@EG ternary composite material, wherein nano-silicon (Si) powder is coated with polyethylene glycol diacrylate (PEGDA), and after annealing, Si@SiC (which is a core-shell material, with SiC as the outer shell and Si as the core) is obtained, and then tempered to obtain the Si@SiC@EG ternary composite material.

[0038] This invention selects nano-sized Si powder (preferably with a particle size of 30 nm) primarily to maintain a nanoscale particle size and prevent the silicon particles from becoming too large (e.g., micrometer-sized) and fragmenting due to expansion during electrochemical cycling. Nanoscale sizes are easier to control and have a lower impact on the battery's electrochemical cycling performance. PEGDA is an oligomer (average molecular weight 575). This oligomer was chosen because it can undergo thermal polymerization with azobisisobutyronitrile (AIBN) as an initiator to obtain high-molecular-weight polyethylene oxide (PEO). This forms polymer chains that encapsulate the nano-sized Si powder, resulting in a carbon-coated silicon material. Calcination at 1450°C yields a SiC-coated silicon (Si@SiC) material, protecting the silicon while preventing expansion. Further calcination at 1500°C causes the SiC to decompose, yielding a ternary structure with a graphene outer layer (Si@SiC@EG ternary composite material), further preventing Si expansion and fragmentation.

[0039] In an embodiment of the present invention, the steps of coating nano-Si powder with PEGDA and obtaining Si@SiC after annealing are as follows:

[0040] PEGDA and azobisisobutyronitrile were added to acetone and stirred until homogeneous to obtain the first solution;

[0041] Nano-Si powder was added to acetone and ultrasonically treated to obtain a second solution.

[0042] The first and second solutions were mixed and reacted under heating conditions to obtain an intermediate.

[0043] The intermediate was annealed to obtain Si@SiC.

[0044] In an embodiment of the present invention, the mass ratio of PEGDA to azobisisobutyronitrile (AIBN) is 1:0.021.

[0045] In an embodiment of the present invention, the mass ratio of PEGDA to nano-Si powder is 2:0.45. After PEGDA and nano-Si powder (Si nanoparticles) are mixed uniformly, a thermal polymerization reaction occurs on the outer layer of the Si nanoparticles under the action of an AIBN initiator to obtain polymer PEO, which then encapsulates the Si nanoparticles more densely through polymer chains. After PEGDA polymerizes into PEO, carbon transformation occurs at high temperatures (above 500°C, derivatized carbon begins to form). Further at high temperatures, this carbon is deposited on the surface of the Si nanoparticles for carbon small molecule coating (Si@C). Upon continued high-temperature treatment, silicon and carbon react to generate SiC, that is, the carbon on the surface of the Si nanoparticles is converted into SiC, forming a structure where Si nanoparticles are coated with SiC (Si@SiC). Then, after treatment at 1500°C for 15 minutes, some of the SiC undergoes thermal decomposition, and the resulting graphene is deposited on the surface of the SiC to obtain a ternary structure of silicon / silicon carbide / graphene (Si@SiC@EG). In this invention, PEGDA is both a source of carbon and one of the sources of SiC, as well as a precursor to graphene.

[0046] In an embodiment of the present invention, the particle size of the nano-Si powder is 30 nm.

[0047] In an embodiment of the present invention, the heating temperature is 70 ℃ and the time is 12 h; the annealing temperature is 1450 ℃ and the holding time is 2 h.

[0048] In an embodiment of the present invention, annealing is carried out in a tube furnace. Before annealing, nitrogen gas at 150 sccm is introduced for 90 to 100 minutes to purify the furnace environment.

[0049] In an embodiment of the present invention, the tempering treatment is carried out in a tubular furnace. Before the tempering treatment, nitrogen gas at 150 sccm is introduced for 90 to 100 minutes to purify the furnace environment.

[0050] In an embodiment of the present invention, the tempering temperature is 1500℃ and the holding time is 15 min. The present invention first anneals at 1450℃ for 2 hours to form a Si@SiC core-shell structure; then, it undergoes a short tempering treatment at 1500℃ for 15 minutes to induce epitaxial graphene (EG) growth. This better protects the Si nanoparticles, preventing fragmentation due to expansion during electrochemical cycling and avoiding the instability of the electrochemical performance of lithium-ion batteries.

[0051] An embodiment of the present invention also provides a Si@SiC@EG ternary composite material prepared according to the above preparation method.

[0052] An embodiment of the present invention also provides a lithium-ion battery, wherein the negative electrode material is the above-mentioned Si@SiC@EG ternary composite material.

[0053] The embodiments of the present invention also provide an application of the above-mentioned Si@SiC@EG ternary composite material in the preparation of lithium-ion batteries, wherein the Si@SiC@EG ternary composite material is used as the negative electrode material of lithium-ion batteries.

[0054] In this invention, oligomer PEGDA undergoes thermal polymerization under the initiator of AIBN to obtain a polymer (i.e., PEO), resulting in a uniformly encapsulated Si nanoparticle structure (Si@PEO). Then, through high-temperature calcination, the polymer PEO is converted into derived carbon, which further tightly encapsulates the outer surface of the Si nanoparticles. Simultaneously, at 1450°C, Si and C react to generate a SiC outer layer, transforming Si@PEO into a SiC-encapsulated Si nanoparticle structure (i.e., Si@SiC). Further, at 1500°C, partial thermal decomposition of the SiC outer layer yields graphene, forming a ternary structure (i.e., Si@SiC@EG ternary composite material). This better protects the Si nanoparticles, preventing fragmentation due to expansion during electrochemical cycling and avoiding the instability of the electrochemical performance of lithium-ion batteries. Furthermore, this invention strictly controls the calcination gas flow (i.e., introduces nitrogen gas at 150 sccm for 90-100 min to purify the furnace environment) to avoid the formation of impurities such as SiO2 in the ternary structure, which would affect the electrochemical performance of the ternary structure. It also avoids the problem of reduced capacity and rate capability caused by the reduction in Si content.

[0055] In the embodiments of the present invention, the performance test is performed in accordance with the national standard GB / T 31486-2015 for lithium-ion batteries.

[0056] In the following embodiments of the present invention, the meanings of proper nouns and English abbreviations are shown in Table 1.

[0057] Table 1. Meanings of proper nouns and English abbreviations

[0058]

[0059] The pseudocapacitive contribution rate is an indicator of the dominance of pseudocapacitance in energy storage. Its value reflects the proportion of the pseudocapacitive mechanism's contribution to charge storage; a high contribution rate usually indicates higher energy density, power density, and cycle stability. Peak current values ​​were obtained through CV testing at different voltage scan rates (e.g., 0.1-10 mV / s). The value of b was calculated using the formula logi = blogv + logk (where i is the current (A), v is the scan rate (V / s), b is the slope value obtained by linearly fitting the relationship between logi and logv, k is a constant (related to the intrinsic electrochemical activity of the electrode material), and logk is the intercept term of the linear fit):

[0060] b = 0.5: The electrode material exhibits battery properties (dominated by diffusion control), and charge storage mainly depends on the bulk diffusion process (such as lithium-ion insertion / extraction).

[0061] 0.5 < b < 1: The electrode material exhibits hybrid properties of battery and pseudocapacitance (coexistence of pseudocapacitance and battery behavior), and surface redox reaction and bulk diffusion jointly contribute to charge storage.

[0062] b ≥ 1: The electrode material exhibits pseudocapacitance properties (dominated by capacitance control), and charge storage is mainly achieved through rapid redox reactions on the surface or near the surface.

[0063] Unless otherwise specified, the room temperature in this invention is calculated as 25 ± 2 °C.

[0064] All raw materials used in the embodiments of this invention are obtained by purchasing commercially.

[0065] The technical solutions of this invention are further described below through embodiments.

[0066] Example 1

[0067] A preparation method of a Si@SiC@EG ternary composite material, the preparation flow chart is as Figure 1 shown, and the schematic diagram of the formation process of the Si@SiC@EG ternary composite material is as Figure 2 shown. The steps are as follows:

[0068] (1) Weigh 2.000 ± 0.001 g of polyethylene glycol diacrylate (PEGDA) and add it to 15 ± 1 mL of acetone, then add 0.042 ± 0.001 g of azobisisobutyronitrile (AIBN), and stir for 30 min to obtain a uniformly stirred first solution; weigh 0.450 ± 0.001 g of nano-silicon (Si) powder (particle size of 30 nm), put it into a beaker containing 15 ± 1 mL of acetone, and perform ultrasonic blending for 30 min to obtain a second solution.

[0069] (2) After pouring the second solution into the uniformly stirred first solution, continue ultrasonic treatment for 30 min to obtain a mixture.

[0070] (3) Heat the above mixture at 70 °C for 12 h, then evaporate all the solvents, take out the dried product inside after cooling and grind it until there is no obvious particle feeling to obtain the ground powder (i.e., the intermediate).

[0071] (4) Transfer the ground powder to a ceramic boat and place it in a tube furnace. Pour 150 sccm of nitrogen (N2) into the furnace for 90 min to purify the furnace environment. Raise the temperature from room temperature to 1450 ℃ and calcine for 2 h (i.e., annealing temperature is 1450 ℃ and holding time is 2 h). After cooling to room temperature, take out the calcined sample and grind it for 15 min to obtain silicon carbide-coated Si nanoparticles (Si@SiC) powder.

[0072] (5) Place the Si@SiC powder in a ceramic boat, transfer it to a tube furnace, and purge the furnace with 150 sccm of nitrogen for 90 min to purify the furnace environment. Raise the temperature from room temperature to 1500 ℃ and calcine for 15 min (i.e., the tempering temperature is 1500 ℃ and the holding time is 15 min). After the temperature drops to room temperature, take out the calcined sample and grind it until there is no obvious particle feel to obtain the silicon / silicon carbide / epi-epi-graphene (Si@SiC@EG) ternary composite material.

[0073] Figure 3 The images show the overall XRD pattern and magnified XRD patterns at 17–27.5° for Si@SiC and Si@SiC@EG in Example 1, where (a) is the overall XRD pattern and (b) is the magnified XRD pattern at 17–27.5°. Figure 3 As shown in (a), all the peaks correspond well to Si (ICDD PDF no. 27-1402) and SiC (ICDD PDF no. 29-1129). The peaks of Si@SiC and Si@SiC@EG particles at approximately 28.4°, 47.3°, 56.1°, 69.1°, and 76.3° correspond to the peaks on the Si PDF card; additionally, to determine the presence of EG, a magnified XRD pattern from 17° to 27.5° is provided. Figure 3 In (b), a small peak of graphene appears at about 22°, indicating that EG, Si and SiC can coexist after tempering.

[0074] Example 2

[0075] A method for preparing a Si@SiC@EG ternary composite material, comprising the following steps:

[0076] (1) Weigh 2.000±0.001g of PEGDA and add it to 15±1mL of acetone, then add 0.042±0.001g of AIBN and stir for 30min to obtain a uniform first solution; weigh 0.450±0.001g of nano Si powder (particle size of 30nm), put it into a beaker containing 15±1mL of acetone, and sonicate for 40min to obtain a second solution;

[0077] (2) After pouring the second solution into the first solution after stirring evenly, continue sonicating for 40 minutes to obtain a mixture;

[0078] (3) Heat the above mixture at 80 °C for 12 h, then evaporate all the solvent, cool and take out the dried product inside and grind it until there is no obvious particle feel, and obtain the ground powder.

[0079] (4) Transfer the ground powder to a ceramic boat and place it in a tube furnace. Pour 150 sccm of nitrogen gas for 100 min to purify the furnace environment. Raise the temperature from room temperature to 1450 ℃ and calcine for 2 h. After cooling to room temperature, take out the calcined sample and grind it for 15 min to obtain Si@SiC powder.

[0080] (5) Place the Si@SiC powder in a ceramic boat, transfer it to a tube furnace, and purge the furnace with 150 sccm of nitrogen for 100 min to purify the furnace environment. Raise the temperature from room temperature to 1500 ℃ and calcine for 15 min. After the temperature drops to room temperature, take out the calcined sample and grind it until there is no obvious particle feel to obtain the Si@SiC@EG ternary composite material.

[0081] The performance of the Si@SiC@EG ternary composite material prepared in Example 1 is described below:

[0082] To further investigate the electrochemical kinetics of Si@SiC@EG, cyclic voltammetry (CV) was used to analyze a half-cell assembled with Si@SiC@EG as the negative electrode from 0.1 mV·s. -1 up to 1 mV·s -1 The scanning test was conducted as follows: CR2032 coin cells were used and assembled in an argon-protected glove box, where both moisture and oxygen content were below 1 ppm. The working electrode was prepared by mixing Si@SiC@EG, Ketjen Black (conductive agent), and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, using N-methylpyrrolidone as a solvent. After thorough mixing, the mixture was coated onto a copper foil current collector and vacuum-dried overnight at 80 °C to obtain the working electrode. The average active material loading of the resulting working electrode was 1.9 mg, and the electrode diameter was 12 mm. In the test battery, a lithium metal sheet served as both the counter and reference electrode. A polypropylene membrane impregnated with electrolyte (1 mol·L⁻¹) was used between the positive and negative electrodes. -1A solution of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1). The CV curves are shown in Figure 4(a). It can be seen that with increasing potential scan rate, all CV curves show reversibility in the lithium insertion and delithiation processes, and their polarization is relatively small. The b-value of the half-cell assembled from Si@SiC@EG ternary composite materials is shown in Figure 4(a). Figure 4 As shown in (b), it can be seen that at 0.1 mV·s -1 Up to 1 mV·s -1 At different scan rates, the real-time k value (slope) is always between 0.5 and 1.0, which confirms that pseudocapacitance contributes capacitance at each scan rate. Figure 4 (c) represents the pseudocapacitive contribution rate of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1 at different scan rates, and (d) represents the contribution rate of 1 mV·s. -1 The contribution rate of pseudocapacitance is shown below. It can be seen that as the scan speed increases from 0.1 mV·s... -1 Increased to 1 mV·s -1 The contribution rate of pseudocapacitance gradually increases, reaching 1 mV·s when the scan rate reaches this level. -1 At this point, the pseudocapacitive contribution rate can reach 93%, indicating that the capacitance contribution brought by the pseudocapacitive can significantly improve the electrochemical performance of the material.

[0083] The electrochemical performance of the half-cell assembled from the Si@SiC@EG ternary composite material in Example 1 was tested under different current densities. The specific process was as follows: CR2032 coin cells were used and assembled in an argon-protected glove box, where the moisture and oxygen content were both below 1 ppm. The working electrode was prepared by mixing Si@SiC@EG, Ketjen black (conductive agent), and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, using N-methylpyrrolidone as a solvent, stirring until homogeneous, and then coating the mixture onto the surface of a copper foil current collector. The mixture was then vacuum-dried overnight at 80 °C. The resulting electrode had an average active material loading of approximately 1.9 mg and an electrode diameter of 12 mm. In the test cell, a lithium metal sheet served as both the counter and reference electrode, and a polypropylene membrane impregnated with electrolyte was used between the positive and negative electrodes. The electrolyte was 1 mol·L⁻¹. -1 A solution of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1). Results are as follows. Figure 5 As shown. Figure 5 Electrochemical performance tests in (a) show that when the Si@SiC@EG ternary composite material is used as a lithium-ion anode, it exhibits excellent performance at 0.1 A·g⁻¹. -1 The capacity after 100 cycles at the current density is 1550 mA·h·g -1It is significantly higher than the capacity of pure graphite (~370 mA·h·g). -1 Furthermore, the half-cell assembled from Si@SiC@EG ternary composite materials exhibits a capacity of up to 1555.6 mAh·g after 150 cycles. -1 Its coulombic efficiency remains at 100%, which indicates that the Si@SiC@EG ternary composite material is comparable to conventional graphite anodes (370 mAh·g). -1 Compared to graphite anodes, it has a higher specific capacity, approximately four times that of graphite anodes. Figure 5 As can be seen in (b), when the tested current density increases from 0.1 A·g -1 Increase to 0.2, 0.5, 0.8, 1.0, 3.0, 5.0 A·g -1 At that time, the average reversible capacitance also increased from 1631 mA·h·g -1 The values ​​changed to 1416, 1092, 932, 855, 664, and 465 mA·h·g. -1 And when the current density drops back to 0.1 A·g -1 At that time, the capacitance value remained at 1651 mA·h·g -1 This fully demonstrates that using Si@SiC@EG ternary composite materials as the negative electrode of lithium-ion batteries exhibits excellent reversibility in lithium-ion storage. For example... Figure 5 As shown in (c), at 2 A·g -1 At a current density of 887 mA·h·g, the half-cell assembled from Si@SiC@EG ternary composite materials maintained a capacity of approximately 887 mA·h·g after 2000 cycles. -1 As can be seen, its capacity remains stable even at such a high number of cycles, demonstrating its excellent electrochemical performance even at high current densities.

[0084] It should be noted that the Si@SiC@EG ternary composite material prepared in Example 2 has no significant difference in performance from the Si@SiC@EG ternary composite material in Example 1.

[0085] The above performance analysis fully demonstrates that the design of the Si@SiC@EG ternary composite material has greatly improved the lithium-ion storage performance and charge transfer efficiency of the lithium-ion battery prepared using it, thereby optimizing the electrochemical performance of the lithium-ion battery.

[0086] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a Si@SiC@EG ternary composite material, characterized in that, Nano-silicon powder was coated with polyethylene glycol diacrylate and annealed to obtain Si@SiC. Then, it was tempered to obtain the Si@SiC@EG ternary composite material. The tempering temperature was 1500℃ and the holding time was 15min. The steps for obtaining Si@SiC by coating the nano-silicon powder with the aforementioned polyethylene glycol diacrylate and then annealing are as follows: The polyethylene glycol diacrylate and azobisisobutyronitrile were added to acetone and stirred until homogeneous to obtain a first solution. The mass ratio of the polyethylene glycol diacrylate to azobisisobutyronitrile was 1:0.

021. The nano-silicon powder is added to acetone and ultrasonically treated to obtain a second solution. The mass ratio of polyethylene glycol diacrylate to the nano-silicon powder is 2:0.45, and the particle size of the nano-silicon powder is 30 nm. The first solution and the second solution were mixed and reacted under heating conditions to obtain an intermediate. The heating temperature was 70°C and the time was 12 hours. The intermediate was annealed to obtain Si@SiC. The annealing temperature was 1450℃ and the holding time was 2h. The coin cell lithium-ion battery assembled using the Si@SiC@EG ternary composite material achieved a performance of 0.1 A·g -1 After 150 cycles at a current density, the capacity reaches 1555.6 mAh·g. -1 , in 2 A·g -1 After 2000 cycles at a current density of 887 mAh·g -1 .

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