Graphene-modified silicon-carbon negative electrode material and preparation method and application thereof

Abstract

This invention discloses a graphene-modified silicon-carbon anode material, its preparation method, and its application, belonging to the field of secondary battery materials technology. The graphene-modified silicon-carbon anode material has a core-shell structure; the core comprises graphene aerogel and particulate SiO₂ dispersed within the graphene aerogel. x Furthermore, 0 < x < 2; the shell comprises pyrolytic carbon. The graphene-modified silicon-carbon anode material provided by this invention can effectively improve the rate performance and cycle performance of silicon-carbon anodes. This invention also provides a method for preparing the above-mentioned graphene-modified silicon-carbon anode material and its applications.

Description

Technical Field

[0001] This invention relates to the field of secondary battery materials technology, and in particular to a graphene-modified silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] As people pursue a higher standard of living, clean energy is being continuously developed and utilized. To overcome the intermittent and unstable characteristics of clean energy, researchers have introduced energy storage and conversion devices into new energy utilization systems; thus, secondary batteries have come into the researchers' view. Among all secondary batteries, lithium-ion batteries are gradually gaining market share due to their advantages such as high specific energy, high conversion efficiency, and long cycle stability.

[0003] Negative electrode active materials are an important component of lithium-ion secondary batteries. Currently, common negative electrode materials include graphite negative electrodes, lithium-based alloy negative electrodes, and silicon-based negative electrodes. Among them, the reagent capacity of graphite negative electrodes is close to its theoretical capacity (about 370 mAh / g), so it is difficult to achieve further capacity improvement. Lithium-based alloy negative electrodes have high capacity, but their safety needs to be improved, and they suffer from severe pulverization during cycling, resulting in poor cycle performance. Silicon-based negative electrodes have high capacity and slightly better cycle performance than lithium-based alloy negative electrodes, so they are one of the key research areas for lithium-ion secondary batteries.

[0004] However, as mentioned earlier, the cycling performance of silicon-based anodes needs improvement, primarily due to the large volume expansion of silicon-based materials during cycling. To enhance the cycling performance of silicon-based anodes, two main technological directions exist: one is to minimize the particle size of silicon-based materials, and the other is to design materials around the silicon-based materials that can accommodate volume changes. However, the improvement effects of both methods require further refinement. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a graphene-modified silicon-carbon anode material, which can effectively improve the rate performance and cycle performance of silicon-carbon anodes.

[0006] The present invention also provides a method for preparing the above-mentioned graphene-modified silicon-carbon anode material.

[0007] This invention also provides applications of the above-mentioned graphene-modified silicon-carbon anode material.

[0008] According to an embodiment of a first aspect of the present invention, a graphene-modified silicon-carbon anode material is provided, wherein the graphene-modified silicon-carbon anode material has a core-shell structure; wherein:

[0009] The core comprises graphene aerogel and particulate SiO2 dispersed within the graphene aerogel. xAnd 0 < x < 2;

[0010] The shell consists of pyrolytic carbon.

[0011] The graphene-modified silicon-carbon anode material according to embodiments of the present invention has at least the following beneficial effects:

[0012] The graphene used in this invention is a porous and structurally stable graphene, so it remains structurally stable and will not collapse during the cycling process of the negative electrode material.

[0013] The silicon-based material used in this invention is dispersed in graphene aerogel. Therefore, the volume change during the cycling process can be absorbed by the porous structure of graphene. Overall, the volume of the graphene-modified silicon-carbon anode material does not change significantly during cycling, that is, the volume of the battery does not change significantly, thus improving the safety of the battery.

[0014] The graphene-modified silicon-carbon anode material provided by this invention also includes a shell structure. Therefore, even if the silicon-based material is pulverized during cycling, the overall structure of the graphene-modified silicon-carbon anode material will not change, and it will not affect the normal operation of other components of the battery. Moreover, the pulverized silicon-based material can still combine with lithium metal to exert its capacity.

[0015] The graphene-modified silicon-carbon anode material provided by this invention exhibits extremely high conductivity in both the graphene aerogel and pyrolytic carbon, surpassing the conductivity of traditional pyrolytic carbon-supported silicon-based materials. This overcomes the shortcomings of poor conductivity and rate performance inherent in silicon-based materials. Consequently, when using this material as the active material to prepare the anode sheet, no conductive agent needs to be added, thereby further improving the specific energy of the secondary battery.

[0016] In summary, the graphene-modified silicon-carbon anode material provided by this invention does not exhibit significant volume change during cycling and has good conductivity, thus possessing excellent cycling stability and rate performance.

[0017] According to some embodiments of the present invention, the particle size of the graphene-modified silicon-carbon anode material is 8–14 μm.

[0018] According to some embodiments of the present invention, in the graphene-modified silicon-carbon anode material, SiO x The mass ratio is ≥50%.

[0019] According to an embodiment of a second aspect of the present invention, a method for preparing the graphene-modified silicon-carbon anode material is provided, the method comprising the following steps:

[0020] S1. Graphene is generated by chemical vapor deposition on a porous silica template;

[0021] S2. Porous silica template in the product obtained from partial etching step S1;

[0022] S3. Deposit metallic magnesium in the product obtained in step S2 using chemical vapor deposition;

[0023] S4. The product obtained in step S3 is calcined under conditions of isolation from water and oxygen;

[0024] S5. Pyrolytic carbon is formed on the surface of the product obtained in step S4.

[0025] The mechanism of the preparation method is as follows:

[0026] First, a graphene aerogel is generated using a porous silica template. At this point, the graphene aerogel fills most of the space in the porous silica template.

[0027] Therefore, the porous silica template is partially etched, resulting in a new pore structure in the product obtained in step S2.

[0028] The magnesium generated in step S3 is deposited in the newly formed pores in step S2;

[0029] The calcination in step S4 is actually the in-situ reduction of silicon dioxide by magnesium to form SiO. x The process.

[0030] Step S5 forms an encapsulation of pyrolytic carbon.

[0031] Since the preparation method adopts all the technical solutions of the graphene-modified silicon-carbon anode material in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0032] In addition, the preparation method also has the following beneficial effects:

[0033] Traditional techniques involve mixing solid silicon-based materials and solid porous carbon materials to achieve a uniform distribution of silicon particles within the porous carbon material. However, the particle size of solid silicon-based materials is typically large, and it is difficult to match their particle size well with the pore size of porous carbon. Therefore, the loading capacity, loading uniformity, and stability of the bond between the silicon-based material and porous carbon during use all need to be improved.

[0034] There are also technologies that use CVD to form elemental silicon in porous carbon. However, the silicon formed by this method is mostly in the form of thin films. If the film is too thin, the capacity of the silicon-carbon material is low. If the film is too thick, the internal stress will cause it to crack during use, which will also affect the overall performance of the resulting silicon-carbon material.

[0035] In the preparation method provided by this invention, graphene aerogel is generated using porous silica as a template, and silica is reduced in situ to generate SiO. x Therefore, SiOx It is evenly distributed in graphene aerogel and has high binding stability.

[0036] In the preparation method provided by this invention, although metallic magnesium is deposited using chemical vapor deposition (CVD), the product forms granules rather than a film under the influence of surface energy during the calcination and reduction process. Therefore, the problem of cracking during the use of large-area films is avoided. Furthermore, the magnesium deposited by CVD has high uniformity, resulting in high consistency in the type of silicon-based material (i.e., SiO₂) at different locations in the graphene-modified silicon-carbon anode material. x (The value of x is the same in different positions), and the performance is highly uniform and stable during use.

[0037] According to some embodiments of the present invention, the porous silica template is derived from at least one of the following: homemade or commercially available.

[0038] According to some embodiments of the present invention, when the porous silica template is self-made, the method of obtaining it includes the following steps: mixing and reacting a silicon source, a dispersant, and an acid.

[0039] According to some embodiments of the present invention, the silicon source includes at least one selected from methyl orthosilicate (CAS: 681-84-5), tetraethyl orthosilicate (CAS: 78-10-4), methyltriethoxysilane (CAS: 2031-67-6), and methyltrimethoxysilane (CAS: 1185-55-3). For example, methyltriethoxysilane may be specifically selected.

[0040] According to some embodiments of the present invention, the dispersant includes at least one selected from polyethylene oxide, polyvinylpyrrolidone, and polyacrylamide. Specifically, polyethylene oxide with a weight-average molecular weight of 5000 may be selected.

[0041] According to some embodiments of the present invention, the acid includes at least one selected from hydrochloric acid, sulfuric acid, nitric acid, and carboxylic acids. Specifically, it may be sulfuric acid.

[0042] According to some embodiments of the present invention, the mass ratio of the silicon source to the acid is 1:1 to 2. For example, it can be approximately 1:1.5.

[0043] According to some embodiments of the present invention, the mass ratio of the silicon source to the dispersant is 1:0.1 to 0.2. For example, it may be approximately 1:0.15.

[0044] According to some embodiments of the present invention, the duration of the mixing reaction is 48–72 hours. This results in a more robust structure for the porous silica template.

[0045] According to some embodiments of the present invention, the duration of the mixing reaction is 55 to 65 hours. For example, it can be approximately 60 hours.

[0046] According to some embodiments of the present invention, the temperature of the mixing reaction is 10–60°C.

[0047] According to some embodiments of the present invention, the temperature of the mixing reaction is 30–50°C. Specifically, it can be about 40°C.

[0048] According to some embodiments of the present invention, the method for obtaining the porous silica template further includes treating the solid product obtained from the mixing reaction with an alkali after the mixing reaction. This results in a more abundant and uniform pore structure in the porous silica template. This step is not mandatory; it can be omitted if the porous silica template obtained from the mixing reaction meets the usage requirements.

[0049] According to some embodiments of the present invention, the alkali used in the alkali treatment includes ammonia.

[0050] According to some embodiments of the present invention, the concentration of the ammonia solution is 0.1 to 1 M. For example, it can be about 0.5 M.

[0051] According to some embodiments of the present invention, the duration of the alkali treatment is 22 to 24 hours. For example, it can be approximately 23 hours.

[0052] According to some embodiments of the present invention, in the alkaline treatment, the solid-liquid ratio is 1g:3-5mL. For example, it can be approximately 1g:4mL.

[0053] According to some embodiments of the present invention, the specific surface area of ​​the porous silica template is ≥500 m². 2 / g. For example, it could be approximately 700m³. 2 / g.

[0054] According to some embodiments of the present invention, the pore size in the porous silica template is between 10 and 100 nm.

[0055] According to some embodiments of the present invention, the preparation method further includes pre-treating the porous silica template between steps S1.

[0056] The pretreatment includes pre-firing. The pre-firing temperature is 600–800°C. This removes water bound to the surface of the porous silica, preventing water and other impurities from affecting the graphene growth process. It also removes the dispersant used in the preparation of the porous silica template, allowing the volume occupied by the dispersant to form new pore structures.

[0057] The preheating temperature is 640–700°C. For example, it could be approximately 650°C.

[0058] According to some embodiments of the present invention, the pre-firing time is 2 to 3 hours. For example, it can be 2.5 hours.

[0059] According to some embodiments of the present invention, in step S1, the atmosphere for chemical vapor deposition is an atmosphere that isolates water and oxygen.

[0060] According to some embodiments of the present invention, in step S1, the carbon source used for chemical vapor deposition includes at least one of methane, ethane, ethylene, acetylene, and toluene. To form high-performance graphene, the carbon source is required to contain only carbon and hydrogen atoms.

[0061] According to some embodiments of the present invention, in step S1, the temperature of the chemical vapor deposition is 1100–1300°C. Chemical vapor deposition within this temperature range first generates silicon carbide, which then acts as a catalyst for graphene formation.

[0062] According to some embodiments of the present invention, in step S1, the temperature of the chemical vapor deposition is 1150–1250°C.

[0063] According to some embodiments of the present invention, in step S1, the duration of the chemical vapor deposition is 1.2 to 1.8 hours. For example, it can be approximately 1.5 hours.

[0064] According to some embodiments of the present invention, in step S2, the etching agent used includes HF or an alkaline solution. This creates pores in the product obtained in step S1, providing space for subsequent deposition of metallic magnesium.

[0065] According to some embodiments of the present invention, the concentration of the alkaline solution is 0.5–3 M. The solute in the alkaline solution includes at least one selected from ammonia, sodium hydroxide, and potassium hydroxide. Within this concentration range, the concentration of the alkaline solution is not very high, allowing it to wet the gaps between the graphene and the porous silica template, thus forming a uniform etching.

[0066] According to some embodiments of the present invention, the concentration of the alkaline solution is 1 to 2 M.

[0067] According to some embodiments of the present invention, in step S2, the etching time is not limited, and the etching effect can be determined by testing the silicon content in the etchant.

[0068] According to some embodiments of the present invention, in step S2, the portion accounts for 10-50% of the total mass of the porous silica template. The resulting pore size is sufficient to accommodate subsequently deposited magnesium metal; after the magnesium metal is removed, the remaining space is also sufficient to accommodate SiO. x Volume changes that occur during the cycle.

[0069] According to some embodiments of the present invention, in step S2, the portion accounts for 30-45% of the total mass of the porous silica template.

[0070] According to some embodiments of the present invention, in step S3, the amount of magnesium metal deposited is 20-50% of the mass of the remaining porous silica in the product obtained in step S2. This provides sufficient reducing agent to generate SiO. x .

[0071] According to some embodiments of the present invention, in step S3, the amount of magnesium metal deposited is 25-40% of the mass of the remaining porous silica in the product obtained in step S2.

[0072] According to some embodiments of the present invention, in step S3, the magnesium source used in the chemical vapor deposition method includes at least one of magnesium pyrocene (CAS: 1284-72-6) and magnesium carbonyl (CAS: 10170-69-1).

[0073] According to some embodiments of the present invention, in step S3, the temperature of the chemical vapor deposition method is 400–800°C. During magnesium deposition, a small amount of SiO2 can be formed. x However, the reaction time is insufficient, so the calcination step S4 is required.

[0074] According to some embodiments of the present invention, in step S3, the temperature of the chemical vapor deposition process is 500–700°C. For example, it can be approximately 650°C.

[0075] According to some embodiments of the present invention, in step S4, the calcination temperature is 400–700°C. Within this temperature range, the generated magnesium can undergo a redox reaction with silicon dioxide to generate SiO. x .

[0076] According to some embodiments of the present invention, in step S4, the calcination temperature is 550–650°C.

[0077] According to some embodiments of the present invention, in step S4, the calcination time is 2 to 6 hours. For example, it can be about 4 hours.

[0078] According to some embodiments of the present invention, the preparation method further includes acid washing after step S4.

[0079] This removes magnesium oxide generated in the redox reaction of step S4 and creates a porous structure that can accommodate SiO₂. x The volume change during the cycle can, on the other hand, accommodate the electrolyte, improve the wettability of the graphene-modified silicon-carbon anode material to the electrolyte, and enhance its electrochemical performance.

[0080] According to some embodiments of the present invention, the acid used in the pickling includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0081] According to some embodiments of the present invention, the concentration of the acid used in the pickling is 1 to 5 M. For example, it can be about 2 M.

[0082] According to some embodiments of the present invention, the pickling time is not limited, but is determined by the point at which the concentration of magnesium in the pickling solution no longer increases.

[0083] According to some embodiments of the present invention, in the pickling process, the ratio of the amount of acid used to the amount of magnesium oxide to be removed is ≥2:1.

[0084] According to some embodiments of the present invention, the preparation method further includes washing with water and drying after the pickling. This removes any residual acid from the pickling process.

[0085] According to some embodiments of the present invention, in step S5, the process of forming pyrolytic carbon includes crushing the product of step S4 to 5-12 μm, mixing the resulting crushed product with medium-temperature asphalt, and then pyrolyzing it.

[0086] According to some embodiments of the present invention, the pyrolysis temperature is 500–1100°C. Preliminary pyrolysis of medium-temperature asphalt can be achieved at 500°C. As the temperature increases, impurities with lower vaporization temperatures in the medium-temperature asphalt can be removed, thereby improving the conductivity of the resulting pyrolytic carbon.

[0087] According to some embodiments of the present invention, the pyrolysis duration is 7 to 15 hours.

[0088] According to some embodiments of the present invention, the pyrolysis includes first pyrolyzing at 500-700°C for 5-10 hours, and then raising the temperature to 900-1100°C for 2-5 hours to continue pyrolysis.

[0089] According to some embodiments of the present invention, the mass ratio between the medium-temperature pitch and the product obtained in step S4 is 0.1 to 1.5:10. This allows the pyrolytic carbon to form a complete encapsulation of the core without significantly affecting the specific capacity of the resulting graphene-modified silicon-carbon anode material.

[0090] According to some embodiments of the present invention, the mass ratio between the medium-temperature asphalt and the product obtained in step S4 is 0.5 to 1:10.

[0091] According to some embodiments of the present invention, the water and oxygen isolation treatment method includes using a protective gas. The protective gas includes at least one of nitrogen and an inert gas.

[0092] According to an embodiment of a third aspect of the present invention, a secondary battery is provided, the secondary battery comprising the graphene-modified silicon-carbon anode material described above.

[0093] Since the secondary battery adopts all the technical solutions of the graphene-modified silicon-carbon anode material of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments. That is, the secondary battery has good cycle performance and rate performance.

[0094] According to some embodiments of the present invention, the secondary battery includes at least one of lithium-ion secondary batteries, sodium-ion secondary batteries, and potassium-ion secondary batteries.

[0095] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0096] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0097] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0098] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0099] Figure 1 This is a TEM image of the graphene-modified silicon-carbon anode material obtained in Example 1 of this invention. Detailed Implementation

[0100] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0101] Material preparation example

[0102] This example demonstrates the preparation of a porous silica template, with the specific steps as follows:

[0103] A1. A silicon source, dispersant, and acid are mixed and reacted; the solid product is then washed with water after the solid-liquid reaction.

[0104] The silicon source is methyltriethoxysilane;

[0105] The dispersant is polyethylene oxide with a weight average molecular weight of 5000;

[0106] The acid is sulfuric acid;

[0107] The mass ratio of silicon source, dispersant and acid is 1:0.15:1.5.

[0108] The temperature of the mixed reaction was approximately 40℃, and the time was 60 hours (0.5 hours of stirring reaction, and the rest of the reaction process was a static reaction).

[0109] The endpoint of washing solid products with water is when the washing solution is nearly neutral, meaning that almost all unreacted products have been reacted.

[0110] A2. The solid product obtained from the alkali treatment step A1, wherein:

[0111] The alkali was 0.5M ammonia water, the solid-liquid ratio of alkali to solid product was 1g:4mL, and the treatment time was 23h.

[0112] A3. Wash the solid product obtained in step A3 to remove water-soluble reaction products and residual alkali.

[0113] The specific surface area and pore size of the porous silica template obtained in this example were tested using the BET method. The pore size mainly fell within the range of 10–100 nm, and the specific surface area was approximately 700 m². 2 / g.

[0114] Unless otherwise specified, the porous silica templates in the specific embodiments are all derived from this example.

[0115] Example 1

[0116] This embodiment prepares a graphene-modified silicon-carbon anode material, and the specific steps are as follows:

[0117] S1. Preparation of graphene aerogel:

[0118] Pretreatment of porous silica template: The porous silica template is calcined at 650°C for 2.5 hours in a dry air atmosphere.

[0119] Deposited graphene:

[0120] Under argon protection, graphene was deposited on a pretreated porous silica template at 1150℃ using toluene as the carbon source. The growth time was 1.5 h.

[0121] S2. Etching the porous silica template in the product obtained in step S1, with an etching ratio of 30% of the mass of the porous silica template obtained in step S1;

[0122] The etching solution used was a 1M sodium hydroxide aqueous solution. During the etching process, stirring was employed to improve the uniformity of etching, and the silicon content in the etching solution was monitored continuously. When the silicon content was approximately 30% of the mass of the porous silica template obtained in step S1, solid-liquid separation was performed, followed by washing with water until the washing solution was nearly neutral, and then drying the washed solid product. This etching process can also break down the continuous porous silica template into small silica particles, facilitating subsequent reduction to generate nanoscale SiO₂. x Provides the foundation.

[0123] S3. Magnesium metal is deposited in the product obtained in step S2 using chemical vapor deposition; wherein...

[0124] The atmosphere is argon.

[0125] The magnesium source used is carbonyl magnesium, and the deposition temperature is about 650℃; the magnesium content obtained by deposition is 40% of the mass of the porous silica template remaining in step S2 (calculated based on the amount of material fed);

[0126] S4. Calcination: The product obtained in step S3 is calcined in an argon atmosphere; wherein the calcination temperature is 650℃ and the calcination time is 4h.

[0127] Pickling: The calcined product is immersed in a 2M sulfuric acid aqueous solution, wherein the ratio of the amount of sulfuric acid in the sulfuric acid aqueous solution to the amount of magnesium deposited in step S3 is 2:1; the pickling endpoint is when the magnesium ion content in the sulfuric acid aqueous solution no longer increases.

[0128] Washing: Wash the solid product after acid washing with water until the washing solution is nearly neutral, and then dry.

[0129] S5. Crushing: Grind and crush the product obtained in step S4, and then classify it to obtain crushed products with a particle size between 5 and 12 μm.

[0130] Mixing: Mix the crushed products and medium-temperature asphalt at a mass ratio of 0.5:10; the mixing temperature is higher than the softening point of the medium-temperature asphalt, approximately 100°C.

[0131] Pyrolysis: The mixed products were pyrolyzed at 600℃ for 7 hours in a nitrogen atmosphere, and then the temperature was raised to 900℃ and held for 3 hours.

[0132] Sieving: The pyrolysis product is passed through two 300-mesh sieves. The sieving step removes large particles and also acts as a crushing agent.

[0133] Example 2

[0134] This embodiment prepares a graphene-modified silicon-carbon anode material. The specific steps differ from those in Example 1 in that:

[0135] In step S2, the etching ratio is 45% of the mass of the porous silica template obtained in step S1.

[0136] Example 3

[0137] This embodiment prepares a graphene-modified silicon-carbon anode material. The specific steps differ from those in Example 1 in that:

[0138] In step S3, the amount of magnesium deposited is 25% of the mass of the remaining silica template from step S2.

[0139] Comparative Example 1

[0140] This comparative example prepared a graphene-modified silicon-carbon anode material. The specific steps differ from those in Example 1 in that:

[0141] Steps S3 to S4 are not included.

[0142] In step S2, all porous silica templates were completely removed, and elemental silicon was deposited in the resulting graphene aerogel using MOCVD. The selected silicon source was SiH4. The deposition amount was similar to that of SiO2 in Example 1. x The quality is comparable.

[0143] Comparative Example 2

[0144] This comparative example prepared a graphene-modified silicon-carbon anode material. The specific steps differ from those in Example 1 in that:

[0145] Steps S3 to S4 are not included.

[0146] In step S2, all the porous silica templates are completely removed, and the resulting graphene aerogel and SiO2 are... x Ball milling was performed for 3 hours according to the proportions of the product obtained in Example 1. The SiO₂ used... x Purchased from Beijing Yijin New Energy Technology Co., Ltd., D50≤100nm.

[0147] Comparative Example 3

[0148] This comparative example prepared a graphene-modified silicon-carbon anode material. The specific steps differ from those in Example 1 in that:

[0149] Excluding the mixing, pyrolysis, and sieving steps in S5, the product after crushing is the final product.

[0150] Test case

[0151] The first aspect of this test example tested the particle size of the graphene-modified silicon-carbon anode materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as the morphology of the graphene-modified silicon-carbon anode material obtained in Example 1. The particle size was directly measured using a particle size analyzer; the morphology was measured using transmission electron microscopy (TEM).

[0152] The second aspect of this test example tested the content of silicon-based materials in the graphene-modified silicon-carbon anode materials obtained in Examples 1-3 and Comparative Examples 1-3. The specific test method was as follows: the obtained products were soaked in an excess of 5M sodium hydroxide aqueous solution for 3 days (or the silicon content in the aqueous solution was not increased), then washed with water, dried, and the weight loss was tested.

[0153] The third aspect of this test example tested the electrochemical performance of the graphene-modified silicon-carbon anode materials obtained in Examples 1-3 and Comparative Examples 1-3. Specifically, lithium-ion secondary batteries were prepared according to the following parameters, and then tested:

[0154] Cyclic performance test battery type: pouch battery;

[0155] Design capacity: 5Ah;

[0156] Positive electrode active material: lithium cobalt oxide, from Shanshan New Energy, designed voltage 4.4V;

[0157] Negative electrode active materials: derived from Examples 1-3 and Comparative Examples 1-3;

[0158] Negative electrode composition: Negative electrode active material: binder SBR: thickener CMC = 97:2:1 (mass ratio).

[0159] N / P value: 1.1.

[0160] Test method: After the pouch cells were fabricated and formed using conventional methods, they were charged and discharged at 0.05C / 0.05C for 3 weeks within a voltage range of 2.8–4.3V. Then, they were cycled at 1C / 1C for 1000 cycles. The charging capacity at the 1st, 800th, and 1000th cycles was recorded. The capacity retention rate at 800 and 1000 cycles was calculated.

[0161] Other electrochemical performance tests were conducted using a 2025 coin cell.

[0162] Working electrode: Same as the negative electrode of a pouch cell;

[0163] Counter electrode: Lithium metal sheet.

[0164] Test method: After assembly, within a voltage range of 0–2.5V, perform a 5-week charge / discharge cycle at 0.05C / 0.05C, followed by 5-week charge / discharge cycles at 0.5C / 0.5C, 1C / 1C, 2C / 2C, and 5C / 5C. Record the charge specific capacity and discharge specific capacity for the first week, and calculate the initial efficiency = charge specific capacity / discharge specific capacity; and the ratio of the average charge specific capacity at other rates to the average charge specific capacity at 0.05C / 0.05C.

[0165] In electrochemical testing, at least three parallel tests are performed on each group of samples. After removing significant outliers, the average value of the results is calculated.

[0166] The test results are all recorded in Table 1.

[0167] Table 1. Performance of the graphene-modified silicon-carbon anode materials obtained in Examples 1-3 and Comparative Examples 1-3

[0168]

[0169] The results in Table 1 are rounded down, therefore there are actual differences between particle sizes, etc.

[0170] Morphology tests show that the graphene-modified silicon-carbon anode material obtained in this invention does indeed possess a core-shell structure, with faintly visible dot-like distributions within the core (presumably dot-like silicon-based particles). Specific test results are as follows: Figure 1 As shown, Figure 1 Due to the limitations of the TEM instrument used in this invention and the clarity of the accompanying drawings, the internal structure of the core cannot be clearly shown, but a distinct core-shell structure is revealed.

[0171] The test results show that the graphene-modified silicon-carbon anode material provided by this invention, due to the crushing and particle size screening in step S5, has a relatively uniform particle size under the same screening conditions. However, if the preparation method in Comparative Example 2 is used, ball milling will affect the particle size, and small silica particles that are not fully embedded in the pores of the graphene aerogel will agglomerate to form small-sized products. Therefore, although step S5 screens out intermediate products between 5 and 12 μm, the proportion of small-sized intermediate products is relatively high, resulting in a decrease in the overall particle size of the final graphene-modified silicon-carbon anode material. In Comparative Example 3, the lack of a shell made of pyrolytic carbon inevitably leads to a decrease in the particle size of the product.

[0172] The test results also demonstrate that the present invention can control the amount of SiO2 in the obtained graphene-modified silicon-carbon anode material by controlling the amount of silicon dioxide etched in step S3 and the amount of pyrolytic carbon precursor (medium-temperature pitch) used in step S5. xThe mass content; however, due to the low apparent density of both graphene and pyrolytic carbon, SiO2... x The adjustable range of its mass content is relatively small.

[0173] The test results also show that the graphene-modified silicon-carbon anode material provided by this invention has excellent electrochemical performance. Specifically, its capacity is about 4 times or more that of graphite; its initial efficiency is between 89% and 91%, reaching a level comparable to graphite; its capacity retention rate after 800 cycles is ≥80%, meeting the commercial requirements for the cycle performance of power batteries; and its rate performance is comparable to that of graphite.

[0174] A comparison of Examples 1 and 2 shows that if the SiO content in the graphene-modified silicon-carbon anode material is reduced... x The content of SiO2 decreases the specific capacity of the corresponding negative electrode active material, but at the same time, it retains more porous structures to accommodate SiO2. x The volume change and electrolyte change improve the cycle performance and rate performance of the resulting secondary battery.

[0175] A comparison of Examples 1 and 3 shows that if the amount of magnesium deposited is reduced, the SiO2 after reduction will increase. x The value of x is closer to 2. Since silicon dioxide has virtually no electrochemical activity, it significantly reduces the capacity of the graphene-modified silicon-carbon anode material. However, this capacity is still significantly higher than the specific capacity of commercial graphite. Furthermore, the rate performance and cycle performance of the resulting secondary battery are slightly lower than those of Example 1.

[0176] A comparison of Example 1 and Comparative Example 1 shows that if elemental silicon is deposited directly using chemical vapor deposition, the capacity of the resulting graphene-modified silicon-carbon anode material is significantly improved because silicon has a significantly higher specific capacity than silicon suboxide. However, since silicon in the graphene-modified silicon-carbon anode material is loaded in a film-like form within the graphene aerogel, its volume change is still significant during cycling and high-rate charge-discharge processes, resulting in an overall decrease in electrochemical performance.

[0177] A comparison of Example 1 and Comparative Example 2 shows that if the silica suboxide and graphene aerogel are combined using ball milling, the spatial structure of the aerogel may be disrupted. Furthermore, the silica suboxide cannot be uniformly filled into the pores of the graphene aerogel, and the bond between the two is not tight enough. Therefore, the overall electrochemical performance decreases.

[0178] A comparison of Example 1 and Comparative Example 3 shows that if the pyrolytic carbon shell is not included, the electrolyte wets the graphene-modified silicon-carbon anode material faster, thus improving the first efficiency and rate performance to a certain extent. However, without the shell protection, various side reactions are significantly enhanced, resulting in a significant decrease in cycle performance.

[0179] In summary, the graphene-modified silicon-carbon anode material provided by this invention has excellent physical and chemical stability as well as electrochemical performance, and is expected to be widely used in energy storage batteries, power batteries and other fields.

[0180] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A graphene-modified silicon-carbon negative electrode material, characterized in that, The graphene-modified silicon-carbon anode material has a core-shell structure; wherein: The core comprises graphene aerogel and particulate SiO dispersed in the graphene aerogel x and 0 < x < 2. The shell includes pyrolytic carbon; The graphene-modified silicon-carbon anode material is prepared by a method comprising the following steps: S1. Graphene is generated by chemical vapor deposition on a porous silica template; S2. Porous silica template in the product obtained from partial etching step S1; S3. Deposit metallic magnesium in the product obtained in step S2 using chemical vapor deposition; S4. The product obtained in step S3 is calcined under conditions of isolation from water and oxygen; S5. Pyrolytic carbon is formed on the surface of the product obtained in step S4.

2. The graphene-modified silicon-carbon anode material according to claim 1, characterized in that, The particle size of the graphene-modified silicon-carbon anode material is 8~14μm.

3. The graphene-modified silicon-carbon anode material according to claim 1, characterized in that, The mass ratio of SiO x in the graphene-modified silicon-carbon negative electrode material is ≥ 50%.

4. The graphene-modified silicon-carbon anode material according to claim 1, characterized in that, In step S2, the etching agent used includes HF or alkaline solution.

5. The graphene-modified silicon-carbon anode material according to claim 1, characterized in that, In step S2, the portion accounts for 10-50% of the total mass of the porous silica template.

6. The graphene-modified silicon-carbon anode material according to claim 1, characterized in that, In step S3, the amount of magnesium metal deposited is 20-50% of the mass of the remaining porous silica in the product obtained in step S2.

7. The graphene-modified silicon-carbon anode material according to claim 1, characterized in that, In step S4, the calcination temperature is 400~700℃.

8. The graphene-modified silicon-carbon anode material according to claim 7, characterized in that, In step S4, the calcination time is 2 to 6 hours.

9. The graphene-modified silicon-carbon anode material according to any one of claims 1 to 8, characterized in that, The preparation method further includes acid washing after step S4.

10. A secondary battery, characterized in that, The secondary battery includes the graphene-modified silicon-carbon anode material as described in any one of claims 1 to 9.

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