A silicon-carbon composite material and its preparation method, and a battery

Abstract

This application provides a silicon-carbon composite material, its preparation method, and a battery. The silicon-carbon composite material includes: a core comprising silicon-carbon material, the silicon-carbon material comprising porous carbon, with graphene embedded in at least a portion of the porous carbon, and nano-silicon filling at least a portion of the porous carbon; and a coating layer covering at least a portion of the surface of the core, the coating layer comprising amorphous carbon. Graphene can improve the electronic conductivity of the core, and because graphene is doped inside the silicon-carbon material, it can achieve a tight bond with the silicon material, effectively avoiding the problem of silicon grain growth, reducing the expansion degree of the silicon-carbon composite material, and improving the battery cycle performance.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a silicon-carbon composite material and its preparation method, and a battery. Background Technology

[0002] Silicon materials have advantages such as high theoretical specific capacity, low lithium intercalation potential, abundant raw materials, non-toxicity, and environmental friendliness. Silicon-carbon materials, by combining silicon and carbon, have advantages such as high energy density, high initial efficiency, and low full-charge expansion. They are expected to be used as anode materials for next-generation high-performance lithium-ion batteries to improve the energy storage capacity and performance of batteries and meet the needs of electric vehicles, mobile electronic devices, and other applications for high energy density and fast charging.

[0003] However, due to the poor electronic conductivity of the porous carbon in the core of silicon-carbon materials, their rate performance cannot reach an ideal state, thus affecting the fast-charging performance and initial efficiency of the battery. Therefore, how to provide a novel silicon-carbon material with ideal fast-charging performance and initial efficiency is a problem that needs to be solved. Summary of the Invention

[0004] This application provides a silicon-carbon composite material, its preparation method, and a battery, aiming to solve the problem of unsatisfactory electrical performance of batteries prepared from existing silicon-carbon materials.

[0005] The first embodiment of this application provides a silicon-carbon composite material, comprising:

[0006] The core comprises a silicon-carbon material, the silicon-carbon material comprising porous carbon, at least a portion of the porous carbon being embedded in graphene, and at least a portion of the porous carbon being filled with nano-silicon;

[0007] A coating layer covering at least a portion of the surface of the core, the coating layer comprising amorphous carbon.

[0008] In some embodiments, the coating layer further includes an organic lithium salt, which is compounded with the amorphous carbon to form the coating layer.

[0009] In some embodiments, the mass ratio of the kernel to the covering layer is 90-95:5-10.

[0010] In some embodiments, the mass ratio of the porous carbon, the nano-silicon, and the graphene is 40–45:45–49:1–5.

[0011] In some embodiments, the organic lithium salt includes at least one of lithium acetate, lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, and lithium difluorooxalate borate.

[0012] In some embodiments, the silicon grain size of the core is 1 to 2 nm.

[0013] In some embodiments, the thickness of the coating layer is 50–500 nm.

[0014] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 1–5 m². 2 / g.

[0015] In some embodiments, the tap density of the silicon-carbon composite material is 0.9–1.1 g / cm³. 3 .

[0016] The second embodiment of this application provides a method for preparing a silicon-carbon composite material, used to prepare the silicon-carbon composite material in any of the above embodiments, comprising the following steps:

[0017] A carbohydrate compound and graphene oxide are provided, mixed evenly in an inorganic alkaline solution, and subjected to a condensation reaction to obtain graphene-doped porous carbon.

[0018] A silicon source is introduced for the first heat treatment, and a carbon source is introduced for the second heat treatment to obtain silicon-carbon material.

[0019] An organic lithium salt is provided, dissolved in an organic solvent, and then added to the silicon-carbon material and an oxidant. The mixture is heated to carry out an oxidation reaction, thereby obtaining the silicon-carbon composite material.

[0020] In some embodiments, after the polycondensation reaction step, the method further includes:

[0021] Activation is achieved by introducing steam.

[0022] In some embodiments, the flow rate of the water vapor is 100 to 1000 ml / min.

[0023] In some embodiments, the activation temperature is 900–1200°C.

[0024] In some embodiments, the activation time is 30 to 300 minutes.

[0025] In some embodiments, the carbohydrate compound includes at least one of glucose, sucrose, maltose, starch, and cellulose.

[0026] In some embodiments, the inorganic base includes at least one selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide.

[0027] In some embodiments, the silicon source comprises silane and nitrogen, wherein the volume ratio of silane to nitrogen is 1 to 5:10; the silane comprises at least one of methylsilane, diethylsilane, and dichlorodiethylsilane.

[0028] In some embodiments, the carbon source includes alkanes and ammonia, wherein the volume ratio of the alkanes to ammonia is 1 to 5:1; the alkanes include at least one of methane, acetylene, propyne, ethylene, and propylene.

[0029] In some embodiments, the organic lithium salt includes at least one of lithium acetate, lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, and lithium difluorooxalate borate.

[0030] In some embodiments, the organic solvent includes at least one of acrylic acid and acrylonitrile.

[0031] In some embodiments, the oxidant includes at least one of hydrogen peroxide, sodium persulfate, and sodium percarbonate.

[0032] In some embodiments, the mass ratio of the carbohydrate compound, the inorganic base, and the graphene oxide is 100:1 to 25:0.5 to 2.

[0033] In some embodiments, the mass ratio of the organolithium, the organic solvent, the silicon-carbon composite material, and the oxidant is 1–5:500:100:0.5–2.

[0034] In some embodiments, the polycondensation reaction is carried out at a temperature of 50–100°C for a time of 0.5–2 hours.

[0035] In some embodiments, the pressure of the first heat treatment is 0.01 to 0.05 MPa.

[0036] In some embodiments, the temperature of the first heat treatment is 400–500°C, and the time is 30–300 min.

[0037] In some embodiments, the flow rate of the silicon source is 100–500 ml / min.

[0038] In some embodiments, the temperature of the second heat treatment is 850–1000°C, and the time is 30–300 min.

[0039] In some embodiments, the flow rate of the carbon source is 10–100 ml / min.

[0040] In some embodiments, the oxidation reaction is carried out at a temperature of 50–100°C for a duration of 2–6 hours.

[0041] The third embodiment of this application provides a battery including a negative electrode sheet, wherein the negative electrode sheet comprises the silicon-carbon composite material in any of the above embodiments or the silicon-carbon composite material prepared by the preparation method in any of the above embodiments.

[0042] This application provides a silicon-carbon composite material, comprising: a core, the core comprising silicon-carbon material, the silicon-carbon material comprising porous carbon, at least a portion of the porous carbon embedding graphene, and at least a portion of the porous carbon being filled with nano-silicon; and a coating layer, the coating layer covering at least a portion of the surface of the core, the coating layer comprising amorphous carbon. Graphene can improve the electronic conductivity of the core, and since graphene is doped inside the silicon-carbon material, it can achieve a tight bond with the silicon material, effectively avoiding the problem of silicon grain growth, reducing the expansion degree of the silicon-carbon composite material, and improving battery cycle performance. Attached Figure Description

[0043] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0044] Figure 1 This is a SEM characterization image of a silicon-carbon composite material provided in Example 1 of this application. Detailed Implementation

[0045] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0046] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection, an indirect connection through an intermediate medium, or an indirect connection through a pipe or conduit; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0047] Silicon-carbon materials are a key material with great potential and research value in the field of batteries, especially lithium-ion batteries. By combining silicon and carbon, carbon materials can provide silicon with a good conductive network, improve electron transport efficiency, and their own structural stability can effectively buffer the volume expansion of silicon during charging and discharging, and inhibit the agglomeration and pulverization of silicon particles. In addition, silicon-carbon materials can combine the advantages of silicon and carbon, maintaining a high specific capacity while taking into account good conductivity, chemical stability and processing performance.

[0048] By coating silicon-carbon materials with a carbon shell, the amorphous carbon coating layer can further provide a good conductive network, improve the electron transport efficiency in the electrode material, and improve the electronic conductivity of the composite material. However, the improvement on the problem of silicon-carbon materials being prone to expansion, leading to unsatisfactory cycle performance, is limited. Therefore, the inventors discovered that depositing graphene before depositing nano-silicon in porous carbon can effectively improve the graphene deposition efficiency and the tightness of the connection between graphene and porous carbon, thereby improving the cycle performance and rate performance of silicon-carbon materials. Based on this, the inventors propose a silicon-carbon composite material, its preparation method, and a battery, aiming to solve the problem of unsatisfactory electrical performance of batteries made from existing silicon-carbon materials.

[0049] The first embodiment of this application provides a silicon-carbon composite material, comprising:

[0050] The core comprises silicon-carbon material, which includes porous carbon, with graphene embedded in at least a portion of the porous carbon and nano-silicon filling at least a portion of the porous carbon.

[0051] A coating layer, which covers at least a portion of the core surface, comprising amorphous carbon.

[0052] Porous carbon possesses a porous structure, including micropores, mesopores, and macropores. Micropores are those with a diameter less than 2 nm, mesopores are those with a diameter between 2 and 50 nm, and macropores are those with a diameter greater than 50 nm. Micropores, mesopores, and macropores can form channels, which can interconnect to facilitate mass transport and charge distribution. Graphene is incorporated into the porous carbon framework in single-layer or multi-layer sheet form, forming graphene-doped porous carbon. Graphene sheets can be uniformly distributed within the porous carbon or oriented using specific methods. The connection between graphene and porous carbon is achieved through covalent bonds, π-π interactions, or electrostatic interactions, enhancing the stability of the graphene-doped porous carbon structure. Graphene can improve the electronic conductivity of the core. Furthermore, because graphene is doped within silicon-carbon materials, it achieves a tight bond with silicon, effectively preventing silicon grain growth, reducing the expansion of silicon-carbon composites, and improving battery cycle performance. The amorphous carbon in the coating layer further improves the electronic conductivity of the silicon-carbon composite, thereby enhancing its overall performance.

[0053] In some embodiments, the coating layer further includes an organic lithium salt, which is formed by combining the organic lithium salt with amorphous carbon.

[0054] It is understandable that the composite form of organic lithium salts and amorphous carbon can be linked by chemical bonds or physically mixed. Organic lithium salts have the characteristic of high lithium-ion transport rate, which can improve the fast charging performance of batteries. When uniformly mixed with amorphous carbon in the coating layer, it can reduce side reactions during discharge and improve the initial efficiency.

[0055] In some embodiments, the mass ratio of the core to the covering layer is 90–95:5–10.

[0056] It is understandable that the mass ratio of the core to the coating layer can be any value or a range between any two of the following: 90:10, 91:9, 92:8, 93:7, 94:6, and 95:5. When the mass ratio of the core to the coating layer meets the above range, the high capacity characteristics of silicon-carbon materials can be fully utilized, improving the energy density of the battery. At the same time, it ensures that the coating layer has sufficient thickness to provide good protection for the core, reduce the adverse effects of silicon volume expansion during charging and discharging, and improve the cycle stability of the material.

[0057] In some embodiments, the mass ratio of porous carbon, nano-silicon, and graphene is 40–45:45–49:1–5.

[0058] When the mass ratio of porous carbon, nano-silicon, and graphene meets the above-mentioned range, it can further ensure that the silicon-carbon material, as the core, possesses both high capacity and high electronic conductivity.

[0059] In some embodiments, the organic lithium salt includes at least one of lithium acetate, lithium trifluoromethanesulfonate, lithium perfluorobutylsulfonate, and lithium difluorooxalateborate.

[0060] In some embodiments, the silicon grain size of the core is 1–2 nm.

[0061] It is understandable that the silicon grain size of the core (in nm) can be any value from 1, 1.2, 1.4, 1.6, 1.8, 2, or any range between two values. Silicon grain size refers to the particle size of silicon crystals formed in silicon-carbon composite materials. Smaller silicon grains can reduce the expansion of silicon-carbon materials, thereby improving the rate performance of the battery.

[0062] In some embodiments, the thickness of the coating layer is 50–500 nm.

[0063] It is understandable that the thickness of the coating layer (in nm) can be any value or a range between any two of the following: 50, 100, 150, 200, 250, 300, 350, 400, 450, and 500. When the thickness of the coating layer meets the above range, the high capacity characteristics of silicon-carbon materials can be fully utilized, improving the energy density of the battery. At the same time, it ensures that the coating layer has sufficient thickness to provide good protection for the core, and that there is sufficient amorphous carbon to improve the electronic conductivity of the silicon-carbon composite material.

[0064] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 1–5 m². 2 / g.

[0065] It is understandable that the specific surface area of ​​silicon-carbon composite materials (unit: m²) 2 The specific surface area ( / g) can be any value from 1, 2, 3, 4, 5, or a range between any two values. When the specific surface area of ​​the silicon-carbon composite material meets the above range, the silicon-carbon composite material has good energy density and reactivity.

[0066] In some embodiments, the tap density of the silicon-carbon composite material is 0.9–1.1 g / cm³. 3 .

[0067] It is understandable that the tap density of silicon-carbon composite materials (unit: g / cm³) 3 The value can be any one of 0.9, 0.95, 1, 1.05, 1.1, or a range between any two values. When the tap density of the silicon-carbon composite material meets the above range, the battery exhibits relatively ideal cycle stability and rate performance.

[0068] The second embodiment of this application provides a method for preparing a silicon-carbon composite material, used to prepare the silicon-carbon composite material in any of the above embodiments, comprising the following steps:

[0069] A carbohydrate compound and graphene oxide are provided, mixed evenly in an inorganic alkaline solution, and subjected to a condensation reaction to obtain graphene-doped porous carbon.

[0070] A silicon source is introduced for the first heat treatment, and a carbon source is introduced for the second heat treatment to obtain silicon-carbon material.

[0071] An organic lithium salt is provided, dissolved in an organic solvent, and then silicon-carbon material and an oxidant are added. The mixture is heated to carry out an oxidation reaction, thereby obtaining a silicon-carbon composite material.

[0072] The preparation method provided in this application first uses carbohydrate compounds as a matrix to prepare porous carbon. Since carbohydrate compounds are granular or powdered materials, they have advantages over porous carbon prepared with resin-based matrices, such as small particle size, spherical shape (which makes the shape of silicon-carbon materials more regular, improving the packing density and structural stability of composite materials), high tap density, and controllable pore-forming process. At the same time, before depositing silicon materials, by controlling the condensation reaction between carbohydrate compounds and graphene oxide in an alkaline environment, the generated graphene can enter the micropores of porous carbon and combine with the porous carbon. Compared with doping graphene on the surface of silicon-carbon materials, this method can better improve the electrical conductivity of silicon-carbon materials and prevent silicon material expansion.

[0073] Secondly, the preparation method provided in this application, after obtaining silicon-carbon material, uses an oxidation reaction to polymerize organic solvent under the action of an oxidant to form amorphous carbon, without the need for high-temperature sintering. Furthermore, since the reaction is carried out in solution, it can ensure that the amorphous carbon and organic lithium salt are fully and uniformly mixed, thereby improving the mechanical strength and conductivity of the final coating layer.

[0074] In some embodiments, the pressure of the first heat treatment is 0.01 to 0.05 MPa.

[0075] Understandably, the pressure (in MPa) of the first heat treatment can be any value or a range between any two of 0.01, 0.02, 0.03, 0.04, and 0.05. Under negative pressure, the deposition of nano-silicon in graphene-doped porous carbon results in high deposition efficiency and a low silane decomposition temperature, effectively preventing silicon grain growth, reducing silicon expansion, and thus improving the cycle performance of the subsequent battery.

[0076] In some embodiments, after the polycondensation reaction step, the method further includes:

[0077] Activation is achieved by introducing steam.

[0078] At high temperatures, water vapor can vaporize porous carbon materials formed by carbohydrate compounds, opening previously closed pores, expanding existing micropores, burning away pore walls, and creating new pores to form a well-developed pore structure, increasing the specific surface area. This, in turn, increases the doping amount of graphene in porous carbon and the reaction efficiency. In addition, water vapor activation can introduce oxygen-containing functional groups, such as hydroxyl and carboxyl groups, onto the surface of carbon materials, giving them better chemical reactivity and improving the reaction efficiency of subsequent deposition and oxidation reactions.

[0079] In some embodiments, the flow rate of water vapor is 100 to 1000 ml / min.

[0080] It is understandable that the flow rate of water vapor (unit: ml / min) can be any value or a range between any two of 100, 200, 400, 600, 800, and 1000. When the flow rate of water vapor meets the above range, it can ensure proper activation of the porous carbon material and the formation of ideal pores.

[0081] In some embodiments, the activation temperature is 900–1200°C.

[0082] It is understandable that the activation temperature (unit: °C) can be any value or a range between any two of the following: 900, 950, 1000, 1050, 1100, 1150, and 1200.

[0083] In some embodiments, the activation time is 30 to 300 minutes.

[0084] It is understandable that the activation time (in minutes) can be any value or a range between any two of the following: 30, 50, 100, 150, 200, 250, and 300.

[0085] When the temperature and time for steam activation meet the above-mentioned range, the activation results of porous carbon materials can be further optimized to form ideal pores while avoiding the generation of by-products.

[0086] In some embodiments, the carbohydrate compound includes at least one selected from glucose, sucrose, maltose, starch, and cellulose; more preferably, it is a monosaccharide or disaccharide molecule such as glucose, sucrose, or maltose. When the carbohydrate compound is selected from monosaccharides or disaccharides such as glucose, sucrose, or maltose, since the reactants are small molecule compounds, it can ensure that the prepared porous carbon particles have a smaller size, are more spherical, and have good uniformity and tap density.

[0087] Specifically, the method for preparing the silicon-carbon composite material provided in this application embodiment can be achieved through the following steps:

[0088] S1. Add carbohydrate compounds to an inorganic alkaline solution and mix thoroughly. Then add graphene oxide solution, disperse evenly, heat to carry out condensation reaction, filter, and vacuum dry. Then heat the obtained material, introduce water vapor, and activate it to obtain graphene-doped porous carbon.

[0089] S2. Transfer graphene-doped porous carbon to a fluidized bed, evacuate to ≤-0.1 MPa, heat and introduce a silicon source, and maintain a negative pressure environment inside the chamber for the first heat treatment, so that graphene is deposited in the micropores of the porous carbon; heat again, introduce a carbon source at normal pressure, and perform a second heat treatment to complete passivation and obtain silicon-carbon material.

[0090] S3. Dissolve the organic lithium salt in an organic solvent to prepare a solution, then add silicon carbon material and mix evenly. Add oxidant dropwise to carry out an oxidative polymerization reaction, filter, and dry the resulting filter residue in a vacuum overnight to obtain a silicon carbon composite material.

[0091] In some embodiments, the inorganic base includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide.

[0092] In some embodiments, the silicon source includes silane and nitrogen, with a volume ratio of silane to nitrogen of 1 to 5:10; the silane includes at least one of methylsilane, diethylsilane, and dichlorodiethylsilane.

[0093] It is understandable that the volume ratio of silane to nitrogen can be any value from 1:10, 1:5, 3:10, 2:5, 1:2, or any two values ​​in between. When the volume ratio of silane to nitrogen meets the above range, the silane can be fully decomposed to generate nano-silicon that is deposited in porous carbon.

[0094] In some embodiments, the carbon source includes alkanes and ammonia, with a volume ratio of alkane to ammonia of 1 to 5:1; the alkanes include at least one of methane, acetylene, propyne, ethylene, and propylene.

[0095] It is understandable that the volume ratio of alkanes to ammonia can be any value from 1:1, 2:1, 3:1, 4:1, 5:1, or any two values ​​in between. When the volume ratio of alkanes to ammonia meets the above range, nitrogen atoms can be doped into amorphous carbon to improve the electronic conductivity and tap density of the material.

[0096] In some embodiments, the organic lithium salt includes at least one of lithium acetate, lithium trifluoromethanesulfonate, lithium perfluorobutylsulfonate, and lithium difluorooxalateborate.

[0097] In some embodiments, the organic solvent includes at least one of acrylic acid and acrylonitrile.

[0098] In some embodiments, the oxidant includes at least one of hydrogen peroxide, sodium persulfate, and sodium percarbonate.

[0099] In some embodiments, the mass ratio of carbohydrate compound, inorganic base and graphene oxide is 100:1 to 25:0.5 to 2.

[0100] In some embodiments, the mass ratio of organolithium, organic solvent, silicon-carbon composite material and oxidant is 1-5:500:100:0.5-2.

[0101] In some embodiments, the polycondensation reaction is carried out at a temperature of 50–100°C for a time of 0.5–2 hours.

[0102] It is understandable that the temperature of the polycondensation reaction (unit: °C) can be any value or any range between two of the following: 50, 60, 70, 80, 90, 100, and the time of the polycondensation reaction (unit: h) can be any value or any range between two of the following: 0.5, 1, 1.5, 2.

[0103] In some embodiments, the temperature of the first heat treatment is 400–500°C, and the time is 30–300 min.

[0104] Understandably, the temperature of the first heat treatment (unit: °C) can be any value or a range between any two of 400, 420, 440, 460, 480, and 500, and the time of the first heat treatment (unit: min) can be any value or a range between any two of 30, 50, 100, 150, 200, 250, and 300.

[0105] In some embodiments, the flow rate of the silicon source is 100–500 ml / min.

[0106] It is understandable that the flow rate of the silicon source (unit: ml / min) can be any value or a range between any two of 100, 200, 300, 400, and 500.

[0107] In some embodiments, the temperature of the second heat treatment is 850–1000°C, and the time is 30–300 min.

[0108] It is understandable that the temperature of the second heat treatment (unit: °C) can be any value or a range between any two of 850, 900, 950, and 1000, and the time of the second heat treatment (unit: min) can be any value or a range between any two of 30, 50, 100, 150, 200, 250, and 300.

[0109] In some embodiments, the flow rate of the carbon source is 10–100 ml / min.

[0110] It is understandable that the flow rate of the carbon source (unit: ml / min) can be any value of 10, 20, 40, 60, 80, 100 or a range between any two values.

[0111] In some embodiments, the oxidation reaction is carried out at a temperature of 50–100°C for a duration of 2–6 hours.

[0112] It is understandable that the temperature of the oxidation reaction (unit: °C) can be any value or any two values ​​between 50, 60, 71, 80, 90, and 100, and the time of the oxidation reaction (unit: h) can be any value or any two values ​​between 2, 3, 4, 5, and 6.

[0113] The third embodiment of this application provides a battery including a negative electrode sheet, which includes a silicon-carbon composite material as described in any of the above embodiments or a silicon-carbon composite material prepared by the preparation method described in any of the above embodiments.

[0114] The following description, in conjunction with specific embodiments, illustrates a silicon-carbon composite material, its preparation method, and the battery provided in this application:

[0115] Example 1

[0116] This embodiment provides a silicon-carbon composite material, which is prepared through the following steps:

[0117] S1. Add 100g of glucose to sodium hydroxide solution (300g, 3wt%) and mix well. Then add graphene oxide solution (100g, 1wt%) and disperse evenly. Perform polycondensation reaction at 80℃ for 1h, filter, and vacuum dry at 80℃ for 24h. Then heat the obtained material to 1100℃, introduce water vapor at a flow rate of 500ml / min, and activate for 150min to obtain graphene-doped porous carbon.

[0118] S2. Transfer graphene-doped porous carbon to a fluidized bed, evacuate to ≤-0.1 MPa, heat to 450°C, and introduce a silane-nitrogen mixture (volume ratio of silane:nitrogen = 3:10) at a flow rate of 300 ml / min, maintaining the chamber pressure at 0.03 MPa for 150 min. Then, raise the temperature to 950°C, and under normal pressure, introduce an ethylene-ammonia mixture (volume ratio of ethylene:ammonia = 3:1) at a flow rate of 50 ml / min for 150 min to obtain silicon-carbon material.

[0119] S3. Dissolve 3g of lithium acetate in 500g of acrylic acid solvent (concentration of 20wt%) to prepare a solution. Then add 100g of silicon-carbon material and mix evenly. Add 1g of hydrogen peroxide oxidant dropwise and oxidize and polymerize at 80℃ for 4h. Filter and dry the filter residue under vacuum at 80℃ for 24h to obtain silicon-carbon composite material.

[0120] The silicon-carbon composite material prepared in this embodiment was subjected to SEM scanning, and the scanning characterization image is shown below. Figure 1 As shown, the material exhibits a granular structure with a reasonable particle size distribution, ranging from 5 to 10 μm in size.

[0121] Example 2

[0122] This embodiment provides a silicon-carbon composite material, which is prepared through the following steps:

[0123] S1. Add 100g of sucrose to potassium hydroxide solution (100g, 5wt%) and mix well. Then add graphene oxide solution (50g, 1wt%) and disperse evenly. Perform polycondensation reaction at 50℃ for 2h, filter, and vacuum dry at 80℃ for 24h. Then heat the obtained material to 900℃, pass water vapor through it at a flow rate of 100ml / min, and activate for 300min to obtain graphene-doped porous carbon.

[0124] S2. Transfer graphene-doped porous carbon to a fluidized bed, evacuate to ≤-0.1 MPa, heat to 400℃, and introduce a silane mixture (volume ratio of silane:nitrogen = 1:10) at a flow rate of 100 ml / min, maintaining the chamber pressure at 0.01 MPa for 300 min; then raise the temperature to 850℃, and at atmospheric pressure, introduce an acetylene mixture (volume ratio of acetylene:ammonia = 1:1) at a flow rate of 10 ml / min for 300 min to obtain silicon-carbon material;

[0125] S3. Dissolve 1g of lithium trifluoromethanesulfonate in 500g of acrylonitrile solvent (concentration of 20wt%) to prepare a solution. Then add 100g of silicon-carbon material and mix evenly. Add 0.5g of sodium persulfate oxidant dropwise and oxidize and polymerize at 50℃ for 6h. Filter and dry the filter residue under vacuum at 80℃ for 24h to obtain silicon-carbon composite material.

[0126] Example 3

[0127] This embodiment provides a silicon-carbon composite material, which is prepared through the following steps:

[0128] S1. Add 100g of maltose to calcium hydroxide solution (500g, 1wt%) and mix evenly. Then add graphene oxide solution (200g, 1wt%) and disperse evenly. Perform polycondensation reaction at 100℃ for 0.5h, filter, and vacuum dry at 80℃ for 24h. Then heat the obtained material to 1200℃, introduce water vapor at a flow rate of 1000ml / min, and activate for 30min to obtain graphene-doped porous carbon.

[0129] S2. Transfer graphene-doped porous carbon to a fluidized bed, evacuate to ≤-0.1 MPa, heat to 500℃, and introduce a mixed gas of dichlorodiethylsilane (volume ratio of dichlorodiethylsilane:nitrogen = 1:2) at a flow rate of 500 ml / min, while maintaining the pressure of the chamber at 0.05 MPa for 30 min. Then, raise the temperature to 1000℃, and under normal pressure, introduce a mixed gas of methane (volume ratio of methane:ammonia = 5:1) at a flow rate of 100 ml / min for 30 min to obtain silicon-carbon material.

[0130] S3. Dissolve 5g of lithium perfluorobutyl sulfonate in 500g of acrylic acid solvent (concentration of 20wt%) to prepare a solution. Then add 100g of silicon-carbon material and mix evenly. Add 2g of sodium percarbonate oxidant dropwise and oxidize and polymerize at 100℃ for 2h. Filter and dry the filter residue under vacuum at 80℃ for 24h to obtain silicon-carbon composite material.

[0131] Example 4

[0132] The preparation method of silicon-carbon composite material provided in Example 4 is the same as that in Example 1, except that the amount of sodium hydroxide solution used in step S1 is 50g (3wt%), and the amount of graphene oxide solution added afterward is 1000g (1wt%). The rest is the same as in Example 1.

[0133] Example 5

[0134] The preparation method of silicon-carbon composite material provided in Example 5 is the same as that in Example 1, except that in step S2, graphene-doped porous carbon is transferred to a fluidized bed, evacuated to ≤-0.1 MPa, heated to 600°C, and a mixture of silane gas (volume ratio of silane:nitrogen = 3:10) is introduced at a flow rate of 300 ml / min, while maintaining the pressure of the chamber at 0.03 MPa for 150 min. Then, the temperature is raised to 1200°C, and at atmospheric pressure, a mixture of ethylene gas (volume ratio of ethylene:ammonia = 3:1) is introduced at a flow rate of 50 ml / min for 150 min to obtain silicon-carbon material. The rest is the same as in Example 1.

[0135] Example 6

[0136] The preparation method of silicon-carbon composite material provided in Example 6 is the same as that in Example 1, except that in step S3, 10g of lithium trifluoromethanesulfonate is dissolved in 500g of acrylonitrile solvent (concentration of 20wt%) to prepare a solution, then 100g of silicon-carbon material is added and mixed evenly, and 0.5g of sodium persulfate oxidant is added dropwise and oxidized and polymerized at a temperature of 50°C for 6h. After filtration, the obtained filter residue is vacuum dried at 80°C for 24h to obtain silicon-carbon composite material.

[0137] Comparative Example 1

[0138] Comparative Example 1 uses commercially available porous carbon (Kuraray Co., Ltd., Japan, model YP-80F) to replace the graphene-doped porous carbon prepared in step S1, and the rest is the same as in Example 1.

[0139] Comparative Example 2

[0140] The preparation method of silicon-carbon composite material provided in Comparative Example 2 is basically the same as that in Example 1, except that step S3 is omitted, and the rest is the same as in Example 1.

[0141] Performance testing of silicon-carbon composite materials:

[0142] The silicon-carbon composite materials in the above embodiments and comparative examples were tested for particle size, tap density, specific surface area, silicon grain size, powder resistivity, gas generation, specific capacity, and initial efficiency.

[0143] Test method: The resistivity of the powder was tested using a four-probe tester; m1g of powder material was added to a 10% sodium hydroxide aqueous solution and soaked at 45℃ for 48h, and then the gas production V1 was tested. The gas production was then calculated as V1 / m1*100%. Other test items were tested according to GB / T38823-2020 "Silicon Carbon". The test results are shown in Table 1.

[0144] Table 1

[0145]

[0146] Fabrication of button cells:

[0147] A binder, conductive agent, and solvent were added to the corresponding silicon-carbon composite materials, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain a negative electrode sheet. The binder used was LA132, the conductive agent was SP (conductive carbon black), and the solvent was NMP. The ratio of silicon-carbon composite material, SP, LA132, and NMP was 95g:1g:4g:220mL. The electrolyte was a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent was a mixture of EC and DEC with a volume ratio of 1:1. The lithium metal sheet was used as the counter electrode, and the separator was a polypropylene (PP) membrane.

[0148] Each button cell was assembled in an argon-filled glove box, and then its electrochemical performance was tested. Specifically, the electrochemical performance was tested on a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The test results are shown in Table 2 below.

[0149] The negative electrode of the above coin cell was also subjected to full-charge expansion. The specific test process was as follows: the thickness D1 of the negative electrode of the rolled coin cell was measured, and then the full-charge thickness D2 of the negative electrode was dissected at 100% SOC of the coin cell. The full-charge expansion rate was then calculated (full-charge expansion rate = (D2-D1) / D1*100%). The test results are shown in Table 2 below.

[0150] Table 2

[0151]

[0152] As can be seen from the data in Table 2 above, the silicon-carbon composite material prepared in this application embodiment performs significantly better than the comparative example in terms of initial efficiency and full charge expansion. The reason is that the graphene doping in the material improves the electronic conductivity of the material and the outer layer of organic lithium improves the diffusion rate of lithium ions, thereby improving the initial efficiency and reducing expansion.

[0153] Soft package performance test:

[0154] The silicon-carbon composite material corresponding to the above embodiments and comparative examples, doped with 90% artificial graphite, was used as the negative electrode material (i.e., the negative electrode sheet), and the positive electrode ternary material (LiNi) was used. 1 / 3 Co 1 / 3 Mn 1 / 3 The battery was assembled with O2, electrolyte, and separator to form a 5Ah soft-pack battery. The separator was Celegard 2400, and the electrolyte was a LiPF6 solution (the solvent was a 1:1 volume ratio of EC and DEC mixed solution, and the concentration of LiPF6 was 1.3mol / L).

[0155] The following performance tests were performed on each pouch battery:

[0156] a. Liquid absorption capacity test: Use a 1mL burette, draw 1mL of electrolyte, add one drop to the surface of each negative electrode, and time the process until the electrolyte is completely absorbed. Record the time t, which is the liquid absorption rate. The test results are shown in Table 2 below.

[0157] b. Ratio test: The constant current ratio of the above embodiments and comparative examples under 2C conditions is tested simultaneously. Constant current ratio = 2C constant current capacity / (2C constant current capacity + 0.1C constant voltage capacity).

[0158] c. Cyclic performance test: Cyclic performance tests were conducted on each of the prepared pouch cells. The test conditions for the cycle performance test were as follows: charge and discharge voltage range of 2.5 to 4.2V, temperature of 25±3.0℃, charge and discharge rate of 1.0C / 1.0C, and number of cycles of 500. The test results are shown in Table 3 below.

[0159] Table 3

[0160] Example Liquid aspiration rate (s) 2C constant current ratio Cyclic performance Example 1 78 91.3％ 92.1％ Example 2 84 90.2％ 93.3％ Example 3 63 92.6％ 91.2％ Example 4 51 93.2％ 91.7％ Example 5 96 93.7％ 89.7％ Example 6 84 89.4％ 92.2％ Comparative Example 1 112 86.8％ 84.6％ Comparative Example 2 132 83.3％ 85.2％

[0161] As can be seen from Table 3 above, the rate performance, cycle performance, and liquid absorption capacity of the soft-pack lithium-ion batteries prepared using the silicon-carbon composite materials provided in Examples 1-6 are significantly better than those of Comparative Examples 1-2. This is because the materials in these examples have a high specific surface area, which enhances the liquid absorption capacity of the materials; and high powder conductivity, which enhances the constant current ratio of the materials; and low expansion, which enhances the cycle performance. As can be seen from Examples 4-6, when the proportion of inorganic alkali or oxidant used exceeds the range specified in the scheme provided in this application, it will have a certain impact on the tap density, silicon grain size, and coating thickness, resulting in a slightly higher full-charge expansion rate and a slightly lower cycle performance, but its overall performance is still better than that of Comparative Examples 1-2.

[0162] The foregoing has provided a detailed description of a silicon-carbon composite material, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: A carbohydrate compound and graphene oxide are provided, mixed evenly in an inorganic alkaline solution, and subjected to a condensation reaction to obtain graphene-doped porous carbon. A silicon source is introduced for the first heat treatment, and a carbon source is introduced for the second heat treatment to obtain silicon-carbon material. An organic lithium salt is provided, dissolved in an organic solvent, and then added to the silicon-carbon material and an oxidant. The mixture is heated to carry out an oxidation reaction, thereby obtaining the silicon-carbon composite material. The carbohydrate compound includes at least one of glucose, sucrose, maltose, starch, and cellulose; the inorganic base includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide. The organic solvent includes at least one of acrylic acid and acrylonitrile; The oxidant includes at least one of hydrogen peroxide, sodium persulfate, and sodium percarbonate. The polycondensation reaction is carried out at a temperature of 50~100℃ for a time of 0.5~2h. The pressure of the first heat treatment is 0.01~0.05 MPa; The temperature of the first heat treatment is 400~500℃.

2. The method for preparing a silicon-carbon composite material according to claim 1, characterized in that, After the polycondensation reaction step, the process also includes: Activation is performed by introducing steam. At least one of the following conditions must be met: a) The flow rate of the water vapor is 100~1000 ml / min; b) The activation temperature is 900~1200℃; c) The activation time is 30~300 min.

3. The method for preparing a silicon-carbon composite material according to claim 1, characterized in that, The silicon source comprises silane and nitrogen gas, wherein the volume ratio of silane to nitrogen gas is 1~5:10; the silane comprises at least one selected from methylene silane, ethyl silane, and dichlorodiethyl silane; and / or, The carbon source includes alkanes and ammonia, wherein the volume ratio of alkanes to ammonia is 1 to 5:1; the alkanes include at least one selected from methane, acetylene, propyne, ethylene, and propylene; and / or, The organic lithium salt includes at least one of lithium acetate, lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, and lithium difluorooxalate borate.

4. The method for preparing a silicon-carbon composite material according to claim 1, characterized in that, The mass ratio of the carbohydrate compound, the inorganic base, and the graphene oxide is 100:1~25:0.5~2; and / or, The mass ratio of the organolithium, the organic solvent, the silicon-carbon composite material, and the oxidant is 1~5:500:100:0.5~2; and / or, The first heat treatment time is 30~300 min; and / or, The flow rate of the silicon source is 100~500 ml / min; and / or, The second heat treatment is performed at a temperature of 850~1000℃ for a time of 30~300 min; and / or, The flow rate of the carbon source is 10~100 ml / min; and / or, The oxidation reaction is carried out at a temperature of 50-100℃ for 2-6 hours.

5. A silicon-carbon composite material prepared by the method according to any one of claims 1 to 4, characterized in that, include: The core comprises a silicon-carbon material, the silicon-carbon material comprising porous carbon, at least a portion of the porous carbon having graphene embedded therein, and at least a portion of the porous carbon having nano-silicon filled therein; A coating layer covering at least a portion of the surface of the core, the coating layer comprising amorphous carbon.

6. A silicon-carbon composite material according to claim 5, characterized in that, The coating layer also includes an organic lithium salt, which is formed by combining the organic lithium salt with the amorphous carbon.

7. A silicon-carbon composite material according to claim 5, characterized in that, The mass ratio of the core to the covering layer is 90~95:5~10; and / or, The mass ratio of the porous carbon, the nano-silicon, and the graphene is 40~45:45~49:1~5.

8. A silicon-carbon composite material according to claim 5, characterized in that, The organic lithium salt includes at least one of lithium acetate, lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, and lithium difluorooxalate borate.

9. A silicon-carbon composite material according to claim 5, characterized in that, The silicon grain size of the core is 1~2nm; and / or, The thickness of the coating layer is 50~500 nm; and / or, The specific surface area of ​​the silicon-carbon composite material is 1~5m². 2 / g; and / or, The tap density of the silicon-carbon composite material is 0.9~1.1 g / cm³. 3 .

10. A battery, comprising a negative electrode, characterized in that, The negative electrode sheet comprises a silicon-carbon composite material prepared by any one of claims 1 to 4 or a silicon-carbon composite material prepared by any one of claims 5 to 9.

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