A modified silicon-carbon anode material, its preparation method and application

Abstract

This invention discloses a modified silicon-carbon anode material, its preparation method, and its applications, belonging to the field of new energy battery materials technology. The modified silicon-carbon anode material provided by this invention includes: vapor-deposited silicon-carbon, which comprises a carbon skeleton and vapor-phase silicon; the carbon skeleton has a porous structure, and the deposition sites of the vapor-phase silicon include the porous structure; a polymer, which is disposed on the inner and outer surfaces of the carbon skeleton and the surface of the vapor-phase silicon; the monomer of the polymer is a lithium-treated unsaturated monomer. The modified silicon-carbon anode material provided by this invention exhibits good cycle stability, rate performance, and water dispersibility. This invention also discloses the preparation method and applications of the above-mentioned modified silicon-carbon anode material.

Description

Technical Field

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

[0002] Faced with the continued consumption of fossil fuels and the ever-growing demand for sustainable energy, there is an urgent need to develop low-cost, environmentally friendly, and high-performance energy conversion and storage technologies. Lithium-ion batteries, due to their high energy density, superior cycle stability, and lack of environmental pollution or memory effect, have become one of the most promising energy storage technologies. Currently, the growing electric vehicle market and the grid energy storage sector are driving the development of rechargeable batteries towards higher energy and power densities. Silicon anodes, due to their high theoretical capacity (3579 mAh / g) and suitable lithiation potential (0.4V vs Li), are suitable for further development. + Silicon (Si) has attracted widespread attention due to its numerous advantages, including good environmental compatibility and high abundance, and is considered a promising candidate material for next-generation lithium-ion battery anodes. However, the large volume expansion (>300%) of silicon during lithiation has caused a series of problems, severely hindering its application: the huge volume expansion causes silicon particles to pulverize and break down after multiple cycles, resulting in interruption of electron and ion transport; at the same time, the volume expansion of silicon during lithiation promotes the growth of irreversible solid electrolyte, which is continuously shed during repeated lithiation, constantly consuming electrolyte and causing loss of active lithium. In summary, the problems caused by the volume expansion of silicon result in low initial coulombic efficiency (ICE) and poor cycle performance of silicon-based lithium-ion batteries, failing to meet the needs of industrial applications.

[0003] In recent years, composite silicon anodes with a carbon framework deposited on silicon, namely vapor-deposited silicon-carbon (VDC), have attracted attention. VDC involves introducing silane gas into a porous carbon shell at a certain high temperature to induce a chemical decomposition reaction, resulting in a silicon-carbon composite material with silicon nanoparticles dispersed within the porous carbon, exhibiting a micro / nano composite structure. Due to its unique structure, VDC exhibits a high initial discharge specific capacity, reaching up to 2000 mAh / g, and a higher initial coulombic efficiency compared to other silicon-carbon composites, generally exceeding 90%. However, the volume expansion of the nano-silicon particles within the porous carbon during cycling still exists. The stress caused by this significant volume change can easily lead to the breakage of the porous carbon framework, resulting in material failure. Therefore, vapor-deposited silicon-carbon faces the problem of insufficient long-cycle stability in practical applications. At the same time, due to its microstructure characteristics, the rate performance of vapor-deposited silicon-carbon anodes with carbon skeleton deposition has not yet met the requirements of industrial applications. Currently, the most commonly used method in the industry is to use vapor deposition to coat the surface with an inorganic carbon layer in order to stabilize the structural stability of the material during cycling and improve the rate performance. However, this has limited effect on improving the performance of vapor-deposited silicon-carbon anodes.

[0004] In summary, the currently produced vapor-deposited silicon-carbon has problems such as poor long-cycle stability, poor rate performance, and poor water dispersibility. 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 modified silicon-carbon anode material that can effectively improve the cycle stability, rate performance, and water dispersibility of vapor-deposited silicon-carbon.

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

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

[0008] According to an embodiment of a first aspect of the present invention, a modified silicon-carbon anode material is provided, the modified silicon-carbon anode material comprising:

[0009] Vapor-deposited silicon-carbon, wherein the vapor-deposited silicon-carbon comprises a carbon framework and vapor-phase silicon; the carbon framework has a porous structure, and the deposition sites of the vapor-phase silicon include the porous structure;

[0010] The polymer is disposed on the inner and outer surfaces of the carbon skeleton and on the surface of the fumed silicon.

[0011] The monomer of the polymer is a lithium-treated unsaturated monomer;

[0012] The unsaturated monomers include at least one of olefinic monomers and olefinic ester monomers.

[0013] The modified silicon-carbon anode material according to embodiments of the present invention has at least the following beneficial effects:

[0014] The monomer of the polymer is a lithium-treated unsaturated monomer, that is, the polymer is essentially lithium polyacrylate or its derivatives, which has good hydrophilic properties. Since the polymer coats the surface of the vapor-deposited silicon carbon, the resulting modified silicon carbon anode material has good hydrophilicity and water dispersibility, which can ensure the uniformity and storage stability of the aqueous anode slurry prepared later. Moreover, the resulting modified silicon carbon anode material is compatible with novel silicon anode binder systems.

[0015] The polymer is present on the inner and outer surfaces of the carbon skeleton and the surface of the fumed silicon. This improves the contact between the carbon skeleton and the nano-fumed silicon particles, reduces the stress caused by the expansion of the fumed silicon particles during cycling, thereby reducing the stress on the carbon skeleton. From a mechanical perspective, this ensures the structural integrity of the carbon skeleton and prevents it from breaking, thus improving the cycling stability of the resulting modified silicon-carbon anode material. Secondly, the polymer also acts as an artificial SEI film to some extent, thereby further modifying the performance of the SEI film formed during cycling. The combination of these two factors prevents the vicious cycle of repeated breakage of the SEI film during charging and discharging, and promotes the formation of a stable surface. In other words, it improves the cycling stability of the modified silicon-carbon anode material from a chemical perspective.

[0016] The polymer used in this invention effectively lowers the energy barrier for lithium-ion conduction, reducing impedance; thereby improving the rate performance of the resulting modified silicon-carbon anode material to a certain extent.

[0017] In summary, due to the synergistic effect between vapor-deposited silicon-carbon and polymers, this invention significantly improves the water dispersibility, cycle stability, and rate performance of modified silicon-carbon anode materials.

[0018] According to some embodiments of the present invention, the particle size of the fumed silicon is 1 to 100 nm.

[0019] According to some embodiments of the present invention, the carbon content of the vapor-deposited silicon-carbon is 30% to 60%. Specifically, it can be about 40%, 45%, 50%, or about 55%.

[0020] According to some embodiments of the present invention, the pore structure of the carbon framework includes macropores (pore size > 50 nm), mesopores (pore size 2–50 nm), and micropores (pore size < 2 nm). The micropores account for 80–90% of the total pore volume of the pore structure. The macropores account for ≤5% of the total pore volume of the pore structure.

[0021] According to some embodiments of the present invention, the acrylic monomers include acrylic acid and its derivatives (referred to as acrylic monomers).

[0022] According to some embodiments of the present invention, the acrylate monomers include acrylates and their derivatives (referred to as acrylate monomers).

[0023] According to some embodiments of the present invention, the D50 of the vapor-deposited silicon-carbon is 4–10 μm. Specifically, it can be about 5 μm, 6 μm, 7 μm, 8 μm, or about 9 μm.

[0024] According to some embodiments of the present invention, the specific surface area of ​​the vapor-deposited silicon-carbon is 1–15 m². 2 / g. For example, it could be approximately 2m. 2 / g、3m 2 / g、4m 2 / g、5m 2 / g, 10m 2 / g or approximately 12m 2 / g.

[0025] According to some embodiments of the present invention, the tap density of the vapor-deposited silicon carbide is 0.6–1.4 g / cm³. 3 For example, it could be approximately 0.8 g / cm³. 3 0.9g / cm 3 or approximately 1.0 g / cm³ 3 .

[0026] According to some embodiments of the present invention, the vapor-deposited silicon-carbon has a first-cycle discharge specific capacity of 1600–2000 mAh / g at 0.1C and 1.5V. Specifically, it can be approximately 1700 mAh / g, 1800 mAh / g, or approximately 1900 mAh / g.

[0027] According to some embodiments of the present invention, the first-cycle coulombic efficiency of the vapor-deposited silicon-carbon at 0.1C and 0.8V is 90-95%. Specifically, it can be approximately 91%, 92%, 93%, or approximately 94%.

[0028] According to some embodiments of the present invention, the vapor-deposited silicon-carbon has a first-cycle discharge specific capacity of 1400–1600 mAh / g at 0.1C and 0.8V. For example, it can be approximately 1500 mAh / g or approximately 1550 mAh / g.

[0029] According to some embodiments of the present invention, the first-cycle coulombic efficiency of the vapor-deposited silicon-carbon at 0.1C and 0.8V is 80% to 85%. Specifically, it can be about 81%, 82%, 83%, or about 84%.

[0030] According to some embodiments of the present invention, the mass ratio of the polymer to the vapor-deposited silicon carbon is 0.5 to 3.5:10. Specifically, it can be about 0.8:10, 1:10, 1.2:10, 1.5:10, 1.8:10, 2:10, 2.2:10, 2.5:10, or about 3:10.

[0031] According to an embodiment of a second aspect of the present invention, a method for preparing the modified silicon-carbon anode material is provided, the method comprising the following steps:

[0032] S1. Lithate the unsaturated monomer to obtain the modified monomer;

[0033] The modified monomer, vapor-deposited silicon carbon, and surfactant were mixed.

[0034] S2. Mix the mixture obtained in step S1 with the initiator and react.

[0035] The mechanism of the preparation method is as follows:

[0036] In step S1, the modified monomer is adsorbed onto the surface of vapor-deposited silicon carbon by the adsorption of surfactant, including the inner and outer surfaces of the carbon skeleton and the surface of the vapor-deposited silicon particles; the surfactant increases the water dispersibility of vapor-deposited silicon carbon, thereby increasing the uniformity of the distribution of modified monomer on vapor-deposited silicon carbon.

[0037] In step S2, the mixing reaction involves the initiator initiating the in-situ polymerization of the modified monomers after adsorption and localization.

[0038] Since the preparation method adopts all the technical solutions of the 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.

[0039] Furthermore, the preparation method employs in-situ polymerization to form the polymer, allowing the modified monomer to easily diffuse into the internal porous structure of the carbon skeleton and the surface of the fumed silicon particles. Thus, the polymer is positioned on both the inner and outer surfaces of the carbon skeleton and the surface of the fumed silicon. The polymer on the surface of the fumed silicon effectively alleviates the stress caused by the volume expansion of the fumed silicon, while the polymer on the surface of the carbon skeleton alleviates the expansion stress of the vapor-deposited silicon-carbon, protecting the carbon skeleton from breakage and electrode failure during cycling. Therefore, the modified silicon-carbon anode material obtained by coating and modifying the vapor-deposited silicon-carbon effectively improves the contact interface between the carbon skeleton and the fumed silicon particles, and also improves the contact interface between the overall particles and the electrolyte. During cycling, it not only reduces unnecessary side reactions between the electrolyte and the modified silicon-carbon anode material but also alleviates the stress on the carbon skeleton caused by the expansion of the fumed silicon particles, comprehensively improving the cycling stability of the modified silicon-carbon anode material from both mechanical and chemical stability perspectives.

[0040] Furthermore, the present invention uses in-situ polymerization to form the polymer, thereby the polymer is distributed in a uniform and dense coating layer; compared with traditional dot-like coating, it is more conducive to relieving stress and acting as an artificial SEI.

[0041] The preparation method used in this invention is simple, the reaction conditions are mild, and the operation process is straightforward.

[0042] According to some embodiments of the present invention, in step S1, the lithiation treatment method includes reacting the unsaturated monomer and the lithium source in a solvent.

[0043] According to some embodiments of the present invention, the molar ratio of the unsaturated monomer to the lithium source is 1:0.8 to 1.2. For example, it can be about 1:0.9, 1:0.95, 1:1.05 or about 1:1.1.

[0044] According to some embodiments of the present invention, the pH of the mixture obtained by the lithiation treatment is 6.5 to 8.5. Specifically, it can be about 7.0, 7.5, or about 8.0. Generally, a specific ratio of unsaturated monomer and lithium source will necessarily result in a specific pH. If it is not within the above range, a trace amount of lithium source can be added as a pH adjuster. The amount added as a pH adjuster is very small and can be ignored when calculating the molar ratio of the materials.

[0045] According to some embodiments of the present invention, in step S1, the unsaturated monomer includes at least one selected from methacrylic acid (CAS: 79-41-4), acrylic acid (CAS: 79-10-7), butenedioic acid (CAS: 110-17-8), methyl acrylate (CAS: 96-33-3), butyl acrylate (CAS: 141-32-2), ethyl acrylate (CAS: 140-88-5), methyl 2-methacrylate (CAS: 80-62-6), ethyl 2-methacrylate (CAS: 97-63-2), and vinyl acetate (CAS: 108-05-4). Further specifically:

[0046] The olefinic monomers include at least one of methacrylic acid, acrylic acid, and butenedioic acid;

[0047] The acrylate monomers include at least one of methyl acrylate, butyl acrylate, ethyl acrylate, methyl 2-methacrylate, ethyl 2-methacrylate, and vinyl acetate.

[0048] According to some embodiments of the present invention, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate.

[0049] According to some embodiments of the present invention, in step S1, the mass ratio of the unsaturated monomer to the vapor-deposited silicon-carbon is 0.5 to 3.5:10. For example, it can be about 0.8:10, 1:10, 1.2:10, 1.5:10, 1.8:10, 2:10, 2.2:10, 2.5:10 or about 3:10.

[0050] According to some embodiments of the present invention, in step S1, the source of the vapor-deposited silicon-carbon is commercially purchased.

[0051] According to some embodiments of the present invention, in step S1, the method for preparing the vapor-deposited silicon-carbon includes the following steps:

[0052] D1. Pyrolysis of polymer materials to obtain the carbon skeleton;

[0053] D2. Silane gas is introduced into the carbon skeleton, and the silane gas is converted into gaseous silicon by hydrothermal decomposition.

[0054] Because the raw material used is fumed silane, it can be fully distributed within the porous structure of the carbon framework. Consequently, the generated fumed silicon is also uniformly distributed within the porous structure of the carbon framework; the resulting fumed silicon-carbon exhibits a micron / nano structure. During the electrochemical reaction, the fumed silicon particles undergo lithiation / delithiation within the porous structure of the carbon framework. The carbon framework, acting as a carrier for the fumed silicon particles, withstands the stress caused by the volume expansion of the fumed silicon particles during cycling. This method enables molecular-scale control of the prepared nanomaterials, resulting in good particle morphology. Furthermore, the deposited fumed silicon-carbon exhibits a uniform composition and a relatively dense structure.

[0055] According to some embodiments of the present invention, in step S1, the surfactant includes at least one of hexadecyltrimethylammonium chloride (CAS: 112-02-7), dodecyl dimethyl benzyl ammonium chloride (CAS: 139-07-1), octadecyltrimethylammonium chloride (CAS: 112-03-8), sodium dodecyl sulfonate (CAS: 2386-53-0), dodecyl trimethylammonium bromide (CAS: 1119-94-4), and polydiallyl dimethylammonium chloride (CAS: 26062-79-3).

[0056] According to some embodiments of the present invention, in step S1, when the surfactant is selected from polydiallyldimethylammonium chloride, the molecular weight of the surfactant is 400,000 to 500,000. For example, it can be about 450,000.

[0057] According to some embodiments of the present invention, in step S1, the surfactant accounts for 100-200% of the mass percentage of the vapor-deposited silicon-carbon. Specifically, it can be about 120%, 140%, 150%, or about 160%.

[0058] In actual production, the surfactant is used in the form of an aqueous solution. Specifically, the mass concentration of the aqueous solution is 30-40%, for example, approximately 35%.

[0059] According to some embodiments of the present invention, step S1 includes the following steps:

[0060] S1a. React the unsaturated monomer and lithium source in a solvent to obtain a mixture A including the modified monomer;

[0061] The vapor-deposited silicon carbon and the surfactant are initially mixed to obtain mixture B;

[0062] S1b. Mix the mixture A and the mixture B.

[0063] According to some embodiments of the present invention, in step S1a, the solvent includes water.

[0064] According to some embodiments of the present invention, the mass-to-volume ratio of the vapor-deposited silicon-carbon to the solvent is 1 g: 10 to 30 mL. For example, it can be about 1 g: 15 mL, 1 g: 20 mL, or about 1 g: 25 mL.

[0065] According to some embodiments of the present invention, in step S1b, the mixing further includes adding ethanol. The amount of ethanol added is 0.5% to 1.5% of the solvent volume in step S1a. Specifically, it can be about 1%. This can further improve the mutual dispersibility between mixture A and mixture B.

[0066] According to some embodiments of the present invention, in step S1b, the mixing temperature is 30–50°C. For example, it can be approximately 40°C.

[0067] According to some embodiments of the present invention, in step S1b, the mixing time is 20 to 60 minutes. For example, it can be about 30 minutes, 40 minutes, or about 50 minutes.

[0068] Unlike traditional silicon-based materials, such as silicon-oxygen materials or traditional silicon-carbon materials, the vapor-deposited silicon-carbon used in this invention is more difficult to disperse in water, and therefore more difficult to uniformly adsorb the modified monomers in the water solvent. The preparation method provided by this invention increases the mixing temperature to some extent, promoting the uniform adsorption of the modified monomers on the surface of the vapor-deposited silicon-carbon.

[0069] According to some embodiments of the present invention, in step S1, the pH of the resulting mixture is 6 to 9. Specifically, it can be about 6.5, 7, 7.5 or about 8.

[0070] According to some embodiments of the present invention, in step S2, the initiator includes at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate.

[0071] According to some embodiments of the present invention, the initiator accounts for 0.1% to 5% of the mass percentage of the unsaturated monomer. Specifically, it may be about 0.5%, 1%, 2%, 3%, or about 4%.

[0072] According to some embodiments of the present invention, in step S2, the temperature of the mixing reaction is 40–100°C. For example, it can be about 50°C or about 80°C.

[0073] According to some embodiments of the present invention, in step S2, the duration of the mixing reaction is 1 to 6 hours. For example, it can be about 2 hours or about 4 hours.

[0074] Since the adsorption between the vapor-deposited silicon carbon and the modified monomer is difficult, and it is even more difficult to form a uniform and continuous coating in aqueous solvents, organic solvents are often used in traditional technologies. In the preparation method provided by the present invention, in order to avoid the problem of uneven distribution of the polymer, in addition to adding a small amount of surfactant, the temperature and duration of the mixing reaction in step S2 are appropriately increased, which promotes the smooth progress of the in-situ polymerization reaction.

[0075] According to some embodiments of the present invention, step S2 includes the following steps:

[0076] S2a. Prepare an aqueous solution of the initiator;

[0077] S2b adds the aqueous solution of the initiator to the mixture obtained in step S1.

[0078] According to some embodiments of the present invention, in step S2a, the mass-to-volume ratio of the initiator to the solvent water in the aqueous solution is 1 mg: 0.5 to 5 mL. For example, it can be approximately 1 mg: 0.8 mL, 1 mg: 1 mL, 1 mg: 2 mL, 1 mg: 3 mL, or approximately 1 mg: 4 mL.

[0079] According to some embodiments of the present invention, the preparation method further includes solid-liquid separation, washing, and drying after step S2.

[0080] The solid-liquid separation method includes centrifugation.

[0081] The washing method includes washing with water.

[0082] The drying temperature is 50–80°C; specifically, it can be about 60°C or about 70°C.

[0083] The drying time is 6 to 18 hours; for example, it can be about 8 hours, 10 hours, 12 hours, 14 hours or about 16 hours.

[0084] The drying method includes vacuum drying.

[0085] According to an embodiment of a third aspect of the present invention, a lithium-ion battery is provided, wherein the raw materials for preparing the lithium-ion battery include the modified silicon-carbon anode material described above.

[0086] Since the lithium-ion battery adopts all the technical solutions of the 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.

[0087] According to some embodiments of the present invention, the lithium-ion battery includes at least one of pouch cells, prismatic cells, cylindrical cells, button cells, and irregular cells.

[0088] According to some embodiments of the present invention, the lithium-ion battery includes at least one of liquid battery, semi-solid battery and all-solid battery.

[0089] According to some embodiments of the present invention, the lithium-ion battery includes at least one of aqueous battery and organic battery, based on the type of solvent in the electrolyte.

[0090] According to some embodiments of the present invention, the lithium-ion battery includes a positive electrode and a negative electrode; the raw material for preparing the negative electrode includes the modified silicon-carbon negative electrode material.

[0091] The raw materials for preparing the positive electrode include positive electrode active materials.

[0092] The type of positive electrode active material is not strictly limited, and can be selected based on commercial availability or compatibility in actual production; it should be noted that the modified silicon-carbon negative electrode material provided by this invention is compatible with all commonly used lithium-ion battery positive electrode active materials currently on the market.

[0093] According to an embodiment of the fourth aspect of the present invention, an application of the lithium-ion battery described herein is provided in the fields of power batteries, energy storage batteries, and 3C small household appliances.

[0094] Since the application adopts all the technical solutions of the lithium-ion battery in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0095] According to some embodiments of the present invention, the field of power batteries includes at least one of electric vehicles and electric motorcycles.

[0096] 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.

[0097] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0098] 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

[0099] 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:

[0100] Figure 1 This is a schematic diagram of the structure of the modified silicon-carbon anode material prepared according to an embodiment of the present invention.

[0101] Figure 2 This is the infrared spectrum of the modified silicon-carbon anode material obtained in Example 1 of this invention.

[0102] Figure 3 This is the infrared spectrum of vapor-deposited silicon-carbon A.

[0103] Figure 4 This is a comparison chart of the cycle performance of the modified silicon-carbon anode materials obtained in Examples 1-3 of this invention and vapor-deposited silicon-carbon A at 0.8 A / g;

[0104] Figure 5 This is a comparison chart of the cycle performance of the modified silicon-carbon anode material obtained in Examples 4-5 of the present invention and the vapor-deposited silicon-carbon A at 0.8 A / g;

[0105] Figure 6 This is a comparison chart of the cycle performance of the modified silicon-carbon anode material obtained in Examples 6-7 of the present invention and the vapor-deposited silicon-carbon B at 0.8 A / g.

[0106] Figure 7 Comparison of the cycling performance of the modified silicon-carbon anode materials obtained in Examples 6-7 of this invention and vapor-deposited silicon-carbon B at 1.2 A / g;

[0107] Figure 8 Electrochemical impedance spectroscopy diagrams of the modified silicon-carbon anode materials obtained in Examples 6-7 of this invention and the vapor-deposited silicon-carbon B.

[0108] Figure label:

[0109] Carbon skeleton 110, fumed silicon 120, polymer 200, lithium ion 300. Detailed Implementation

[0110] 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.

[0111] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0112] Example 1

[0113] This example demonstrates the preparation of a modified silicon-carbon anode material. The specific steps are as follows:

[0114] S1. Synthesis of modified monomers:

[0115] Acrylic acid and lithium source (Li2CO3) were uniformly mixed in 200 mL of aqueous solution at a molar ratio of 1:1.1, and the pH was controlled at 7.2 to obtain mixture A including the modified monomer; wherein the mass of acrylic acid was 0.5 g.

[0116] Preparation of mixture B:

[0117] 10g of vapor-deposited silicon carbon (parameters are shown in Table 1 for vapor-deposited silicon carbon A) was mixed with 15g (by solid mass) of polydiallyldimethylammonium chloride (molecular weight 450,000, purity = 35wt%).

[0118] Mixed adsorption:

[0119] Mixture B was added to mixture A, and 2 mL of anhydrous ethanol was added. The mixture was stirred at 40°C for 0.5 h to obtain a uniformly dispersed mixture. The pH of the resulting mixture was approximately 7.5.

[0120] S2. Dissolve 0.005g of ammonium persulfate in 20mL of deionized water, and add the resulting ammonium persulfate aqueous solution to the mixture obtained in step S1 in 4 portions, adding about 5mL every half hour.

[0121] After the addition was complete, the mixture was reacted at 40°C for 2 hours.

[0122] S3. The mixture obtained in step S2 is centrifuged, and the resulting solid is washed three times with deionized water and then dried in a vacuum drying oven at 50°C for 12 hours to obtain the modified silicon-carbon anode material.

[0123] The structural schematic of the obtained modified silicon-carbon anode material is shown below. Figure 1 As shown, it specifically includes:

[0124] Vapor-deposited silicon-carbon includes a carbon framework 110 and vapor-phase silicon 120. The carbon framework 110 contains a porous structure, and the vapor-phase silicon 120 is located inside the porous structure.

[0125] The polymer 200 is disposed on the inner and outer surfaces of the carbon skeleton 110 and the surface of the fumed silicon 120.

[0126] In the process of using the modified silicon-carbon anode material obtained in this example, lithium ions 300 pass through the carbon skeleton 110 and polymer 200, and finally react with fumed silicon 120.

[0127] Example 2

[0128] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0129] In step S1, the mass of acrylic acid is 1g. The molar ratio of acrylic acid to lithium source remains 1:1.1 (if the molar ratio remains constant, the corresponding pH remains constant; the same applies to other embodiments).

[0130] Example 3

[0131] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0132] In step S1, the mass of acrylic acid is 2g. The molar ratio of acrylic acid to lithium source is maintained at 1:1.1.

[0133] Example 4

[0134] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0135] In step S1, while keeping the mass of acrylic acid constant, the amount of lithium source is adjusted so that the molar ratio of acrylic acid to lithium source is 1:0.8.

[0136] Correspondingly, the pH of mixture A obtained in step S1 is 6.5.

[0137] In step S1, the pH of the mixture system after mixing mixture A and mixture B is 6.9.

[0138] Example 5

[0139] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0140] In step S1, the mass of acrylic acid is 1g, and the amount of lithium source is adjusted so that the molar ratio of acrylic acid to lithium source is 1:0.8.

[0141] Correspondingly, the pH of mixture A obtained in step S1 is 6.5.

[0142] In step S1, the pH of the mixture system after mixing mixture A and mixture B is 6.9.

[0143] Example 6

[0144] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0145] (1) In step S1, while keeping the mass of acrylic acid constant, the amount of lithium source is adjusted so that the molar ratio of acrylic acid to lithium source is 1:0.8. Correspondingly, the pH of mixture A obtained in step S1 is 6.5.

[0146] In step S1, the pH of the mixture system after mixing mixture A and mixture B is 6.9.

[0147] (2) In step S1, different types of vapor-deposited silicon carbon are used. For details of the parameters, please refer to Vapor-deposited Silicon Carbon B in Table 1.

[0148] (3) In step S1, the temperature for mixed adsorption is 60℃.

[0149] (4) In step S2, the mass of the initiator is 0.025g.

[0150] (5) In step S2, the reaction temperature is 60℃.

[0151] Example 7

[0152] This example prepares a modified silicon-carbon anode material, which differs from Example 6 in that:

[0153] In step S1, lithium hydroxide is used as the lithium source. The molar ratio of acrylic acid to lithium source is kept constant, and the amount of acrylic acid is adjusted to 1.5g.

[0154] Correspondingly, the pH of mixture A obtained in step S1 is 7.2;

[0155] In step S1, the pH of the mixture system after mixing mixture A and mixture B is 7.5.

[0156] Table 1. Parameters of vapor-deposited silicon-carbon used in the examples.

[0157]

[0158] In Table 1, vapor-deposited silicon-carbon A was purchased from Shida Shenghua New Materials Group Co., Ltd., with the product number SH-S01; vapor-deposited silicon-carbon B was purchased from Shida Shenghua New Materials Group Co., Ltd., with the product number SH-S02.

[0159] According to information provided by the vendor, the carbon framework used in vapor-deposited silicon-carbon A and vapor-deposited silicon-carbon B has a BET size of approximately 1633 μm.2 / g; micropore volume is approximately 0.66cm³. 3 / g, accounting for 89%; mesoporous pore volume is approximately 0.07cm³. 3 / g, accounting for 9.8%; macropore volume is approximately 0.005cm³. 3 / g, accounting for 0.7%. Since the pore structure of the carbon skeleton has a certain limiting effect on the particle size of the gaseous silicon particles, it can be seen that in the modified silicon-carbon anode material provided by the invention, the particle size of the gaseous silicon particles is mainly ≤2nm, and a portion is distributed between 2 and 50nm.

[0160] Comparative Example 1

[0161] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0162] In step S1, acrylic acid is replaced with an equal amount of a mixture of acrylic acid, acrylamide, and hexafluorobutyl methacrylate, wherein the mass ratio of acrylic acid:acrylamide:hexafluorobutyl methacrylate is 6:3:1.

[0163] Comparative Example 2

[0164] This example prepares a modified silicon-carbon anode material, which differs from Example 1 in that:

[0165] Step S1 does not include the preparation step of mixture B, nor does it include the mixing and adsorption step;

[0166] In step S2, mixture A and an aqueous solution of ammonium persulfate are directly mixed and reacted, and the resulting reactants are mixed with mixture B and subjected to mixed adsorption.

[0167] In this example, the amount of raw materials used is the same as in Example 1.

[0168] Application Example 1

[0169] This example provides a coin cell lithium-ion battery. Specifically, the coin cell battery includes a negative electrode (working electrode), a lithium metal sheet (counter electrode), a separator disposed between the working electrode and the counter electrode; an electrolyte impregnating the working electrode, the counter electrode, and the separator; and a CR2032 type coin cell battery casing that encloses and houses all the above components.

[0170] The preparation process of the working electrode is as follows: Active material (modified silicon-carbon anode material provided in the examples, and vapor-deposited silicon-carbon A-B), conductive carbon black, single-walled carbon nanotube slurry, binder (CMC), and binder (SBR) are mixed and stirred for 8 hours at a mass ratio of 91:4.85:0.15:1.5:2.5 to obtain a slurry; the above slurry is coated onto copper foil, with an active material loading of 1.5-2 mg / cm³. 2(Within this range), after vacuum drying at 60℃ for 12 hours, the material is cut into round pieces with a diameter of 12mm using a cutting machine to obtain the negative electrode.

[0171] The electrolyte is composed of lithium salt, solvent and additives; the lithium salt is LiPF6 with a concentration of 1M; the solvent is ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 (w) ratio; the additives are 6 wt% (per electrolyte) of fluoroethylene carbonate (FEC) and 2 wt% (per electrolyte) of ethylene carbonate (VC).

[0172] The assembly of button cells is carried out in a glove box that is isolated from water and oxygen.

[0173] Test Case

[0174] The first aspect of this example involves testing the infrared spectra of the modified silicon-carbon anode material obtained in Example 1 and the vapor-deposited silicon-carbon A. The results show that after coating with lithium polyacrylate, the surface of Example 1 exhibits characteristic peaks of lithium polyacrylate. In the standard spectrum, the carboxyl group COOH is at 1700 cm⁻¹. -1 There is a characteristic infrared peak at this location, which is caused by the stretching vibration of C1 / 4O in the carboxyl group; when Li + Replace H + When (COOLi), due to the homogenization of C1 / 4O and CO in the carboxyl group, 1700cm -1 The peak at 1560 cm⁻¹ will disappear, while the dipole moment will change with salt formation, and the peak at 1560 cm⁻¹ will disappear. -1 A new peak appears at 1563 cm⁻¹. The modified silicon-carbon anode material provided by this invention exhibits a peak at 1563 cm⁻¹. -1 A peak was observed at 1700 cm⁻¹. -1 No peak was observed at Li; this indicates that + It has completely replaced the H in the carboxyl group. + Furthermore, the modified silicon-carbon anode material obtained in Example 1 was tested at 842 cm⁻¹. -1 The nearby peak is caused by the absorption of carbon-carbon chains in the polymer compound, 1438 cm⁻¹ -1 The peak at this point is caused by the bending vibration of the CH2 alkyl group, indicating that lithium polyacrylate successfully bonds with vapor-deposited silicon-carbon; detailed results are as follows. Figure 2 As shown. For comparison, vapor-deposited silicon-carbon A does not include characteristic peaks such as COOLi; the results are as follows. Figure 3 As shown.

[0175] The second aspect of this example tested the long-cycle performance of the modified silicon-carbon anode material obtained in the previous examples, along with vapor-deposited silicon-carbon A and vapor-deposited silicon-carbon B. The test conditions were:

[0176] The charge-discharge current density in the first week was 200 mA / g, and the initial coulombic efficiency of the modified silicon-carbon anode materials obtained in the examples was all >90%.

[0177] The charge / discharge current density in the later cycle is 800 mA / g.

[0178] The test voltage range for first-efficiency, capacity, and cycle testing is 0.005V-1.5V.

[0179] The results show:

[0180] The modified silicon-carbon anode material obtained in Example 2 showed almost no capacity decay after 150 cycles, while Example 1 was slightly worse than Example 2 but better than Example 3; and Examples 1-3 all outperformed the long-cycle results of vapor-deposited silicon-carbon A. This indicates that when the polymer dosage is high, it will hinder lithium-ion conduction to a certain extent; when the polymer dosage is low, its encapsulation effect cannot be fully utilized. An appropriate polymer dosage can alleviate the volume expansion of vapor-phase silicon particles while enhancing conductivity, significantly improving the cycling stability of vapor-deposited silicon-carbon at high current densities. The comparison results of Examples 1-3 and vapor-deposited silicon-carbon A are as follows: Figure 4 As shown.

[0181] Examples 4-5 controlled the composition of the polymer by controlling the pH (ratio of acrylic acid to lithium source). A lower pH resulted in a higher proportion of polyacrylic acid in the coating layer. Compared with vapor-deposited silicon-carbon A, the modified silicon-carbon anode materials obtained in Examples 4-5 had a capacity retention rate of over 95% after 100 cycles at 800 mA / g, indicating that enhanced cycling performance can be obtained by reasonably controlling the polymer layer composition by pH.

[0182] The cycling results of the modified silicon-carbon anode materials obtained in Examples 4-5 and vapor-deposited silicon-carbon A are compared to those in Examples 5. Figure 5 As shown.

[0183] A comparison of the long-cycle results of the modified silicon-carbon anode materials obtained in Examples 6 and 7 and vapor-deposited silicon-carbon B shows that the capacity of Example 6 hardly decreased after 150 cycles. However, the thicker coating of lithium polyacrylate (Example 7) somewhat hindered lithium-ion transport, so the capacity of Example 7 was slightly lower than that of Example 6. Specific test results are as follows: Figure 6 As shown.

[0184] The third aspect of this example tested the electrochemical performance of the modified silicon-carbon anode material obtained in Example 6 and the vapor-deposited silicon-carbon B at high current densities. The test conditions were:

[0185] The initial charge / discharge current density is 150 mA / g;

[0186] Subsequent cycles were performed using a long-cycle charge-discharge test at a current density of 1200 mA / g (approximately 1C); the test voltage range was 0.005V-1.5V.

[0187] The results showed that after 280 cycles, Example 6 exhibited a capacity retention of 76.3% and a specific capacity of 706 mAh / g, while the vapor-deposited silicon-carbon capacity was only 162 mAh / g. Specific test results are as follows... Figure 7 As shown.

[0188] The fourth aspect of this example tested the electrochemical impedance of the silicon-carbon anode materials obtained in Examples 6 and 7 and the vapor-deposited silicon-carbon B. The test conditions were 1.5V, 0.01Hz to 100000Hz. The results showed that the impedance of the modified silicon-carbon anode materials obtained in the examples was lower than that of the vapor-deposited silicon-carbon B, indicating that the coating layer formed by lithium polyacrylate effectively lowered the energy barrier for lithium-ion conduction. Specific test results are as follows... Figure 8 As shown.

[0189] The test results for the above electrochemical performance are summarized in Table 2.

[0190] Table 2 shows the electrochemical performance results of the modified silicon-carbon anode materials obtained in the examples and the vapor-deposited silicon-carbon materials A to B used.

[0191]

[0192] In summary, this invention utilizes a simple and efficient liquid-phase reaction to deposit a polymer layer on and within vapor-deposited silicon-carbon. The polymer material includes lithium polyacrylate. An appropriate amount of polymer significantly improves the electrochemical performance of the resulting modified silicon-carbon anode material, especially its cycling performance at high current densities. This invention provides a simple and effective method for improving the electrochemical performance of vapor-deposited silicon-carbon.

[0193] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art 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 modified silicon-carbon anode material, characterized in that, The modified silicon-carbon anode material includes: Vapor-deposited silicon-carbon, wherein the vapor-deposited silicon-carbon comprises a carbon framework and vapor-phase silicon; the carbon framework has a porous structure, and the deposition sites of the vapor-phase silicon include the porous structure; The polymer is disposed on the inner and outer surfaces of the carbon skeleton and on the surface of the fumed silicon. The monomer of the polymer is a lithium-treated unsaturated monomer; The unsaturated monomers include at least one of olefinic monomers and olefinic ester monomers.

2. The modified silicon-carbon anode material according to claim 1, characterized in that, The mass ratio of the polymer to the vapor-deposited silicon-carbon is 0.5~3.5:

10.

3. A method for preparing the modified silicon-carbon anode material as described in claim 1, characterized in that, The preparation method includes the following steps: S1. Lithate the unsaturated monomer to obtain the modified monomer; The modified monomer, vapor-deposited silicon carbon, and surfactant were mixed. S2. Mix the mixture obtained in step S1 with the initiator and react.

4. The preparation method according to claim 3, characterized in that, In step S1, the mass ratio of the unsaturated monomer to the vapor-deposited silicon carbon is 0.5~3.5:10; and / or, the unsaturated monomer includes at least one of methacrylic acid, acrylic acid, butenedioic acid, methyl acrylate, butyl acrylate, ethyl acrylate, methyl 2-methacrylate, ethyl 2-methacrylate, and vinyl acetate.

5. The preparation method according to claim 3, characterized in that, In step S1, the lithiation process includes mixing the unsaturated monomer and the lithium source in water.

6. The preparation method according to claim 5, characterized in that, The molar ratio of the unsaturated monomer to the lithium source is 1:0.8~1.2; and / or the pH of the mixture obtained by the lithiation treatment is 6.5~8.

5.

7. The preparation method according to claim 5, characterized in that, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium nitrate.

8. The preparation method according to claim 3, characterized in that, The initiator accounts for 0.1-5% of the mass of the unsaturated monomer.

9. The preparation method according to claim 3, characterized in that, In step S2, the temperature of the mixing reaction is 40~100℃.

10. The preparation method according to claim 3, characterized in that, In step S2, the duration of the mixing reaction is 1 to 6 hours.

11. A lithium-ion battery, characterized in that, The raw materials for preparing the lithium-ion battery include the modified silicon-carbon anode material as described in claim 1 or 2.

12. An application of the lithium-ion battery as described in claim 11 in the fields of power batteries, energy storage batteries, and 3C small household appliances.

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