Silicon-carbon composite material precursor and preparation method and application thereof

Abstract

The present application relates to the technical field of battery negative electrode materials, and in particular to a silicon-carbon composite material precursor and its preparation method and application. The silicon-carbon composite material precursor includes modified starch particles and a plurality of silicon-based material particles, the silicon-based material particles are at least embedded in the modified starch particles, the modified starch particles include carbon nanomaterials and starch, and the carbon nanomaterials and starch are bonded by oxygen-containing functional groups. The bonding connection of oxygen-containing functional groups limits the free movement of starch molecules and inhibits starch foaming. Therefore, the silicon-carbon composite material precursor of the present application obtains a uniform thickness of carbon walls around silicon particles in the silicon-carbon composite material. The preparation method includes surface modification of the carbon nanomaterial, mixing it with starch, mixing it with silicon-based material particles, and finally granulating it so that the modified carbon nanomaterial forms a bonded connection with the oxygen-containing functional groups in the starch. The precursor is used to prepare silicon-carbon composite materials to improve the comprehensive properties such as conductivity, capacity, and stability.

Description

Technical Field

[0001] The present application relates to the technical field of battery negative electrode materials, and in particular to a silicon-carbon composite material precursor and a preparation method and application thereof. Background Art

[0002] Existing secondary battery negative electrode materials are often based on carbon materials, but the capacity of carbon materials is low. Therefore, further research has been conducted to use high-capacity silicon-based materials as negative electrode materials. However, silicon-based materials have poor conductivity and their volume expands rapidly during the charge and discharge process, which can lead to a series of problems such as poor stability.

[0003] Further research combines silicon-based materials and porous carbon-based materials as silicon-carbon composite materials. The porous carbon material accommodates the volume expansion of the silicon-based material, and a reasonable ratio is designed to obtain a silicon-carbon composite material with good stability, good conductivity, and high capacity. The commonly used method is to prepare a precursor from a carbon-containing raw material and a silicon-containing raw material, and then obtain a silicon-carbon composite material by carbonization. An existing method is to prepare a mixed solution of starch as a carbon-containing raw material and a silicon-containing raw material, and then dry and granulate it to obtain a precursor in which a silicon-based material is embedded in a carbon-based material, and finally the precursor is carbonized to obtain a silicon-carbon composite material. However, when such a precursor is carbonized, the temperature of the carbonization treatment is often higher than 200°C, which will soften the starch. At the same time, bubbles will form under the action of gases such as water vapor and carbon dioxide, that is, the foaming phenomenon of starch. Under the influence of these gases, the starch molecules will move freely. In the porous carbon particle matrix obtained at last, the silicon particles are embedded in the pores, but the carbon layer around each silicon particle is of different thickness and cannot maintain the original morphology. The carbon layer cannot form a good carbon coating on the silicon material if it is too thin, and the carbon layer will be too thick if it is too thick, which will cause the internal silicon material to be unable to exert its capacity. In addition, the free movement of starch molecules will cause the starch to separate from the silicon material, resulting in the starch not being able to accommodate the silicon material, further affecting the effect of porous carbon in adsorbing and accommodating the silicon material.

[0004] Therefore, a technical solution is needed to solve the problem of starch foaming resulting in poor performance of silicon-carbon composite materials made from starch and silicon-based materials. Summary of the invention

[0005] The purpose of the present application is to provide a silicon-carbon composite material precursor and a preparation method and application thereof, aiming to solve the problem in the prior art that starch foaming leads to poor performance of silicon-carbon composite materials prepared with silicon-based materials.

[0006] In order to achieve the above application purpose, the technical solution adopted in this application is as follows:

[0007] In a first aspect, the present application provides a silicon-carbon composite material precursor, which includes modified starch particles and a plurality of silicon-based material particles, wherein the silicon-based material particles are at least embedded in the modified starch particles, and the modified starch particles include carbon nanomaterials and starch, and the carbon nanomaterials and starch are bonded to each other via oxygen-containing functional groups.

[0008] First, the carbon nanomaterial is bonded to the starch through an oxygen-containing functional group, which limits the free movement of the starch molecules. Therefore, when the precursor is subjected to subsequent carbonization treatment, it is beneficial for the starch molecules and the silicon-based material particles to maintain their original relative positions. Secondly, on a microscopic scale, when the starch softens, the carbon nanomaterial separates the softened starch into many small areas, suppressing the bubbling phenomenon. Furthermore, the modified carbon nanotubes further reduce the surface tension of the starch molecules and suppress starch foaming. Therefore, the carbon wall thickness around the silicon particles in the silicon-carbon composite material prepared by the silicon-carbon composite material precursor of the present application is uniform. In summary, the silicon-carbon composite material precursor of the present application solves the technical problem that the starch foaming phenomenon causes the poor performance of the silicon-carbon composite material prepared by the silicon-carbon composite material precursor, and is used to prepare the silicon-carbon composite material to improve the comprehensive performance such as conductivity, capacity, and stability.

[0009] In a second aspect, the present application provides a method for preparing a silicon-carbon composite material precursor, comprising the following steps:

[0010] Performing surface modification on the carbon nanomaterial to obtain a modified carbon nanomaterial;

[0011] Performing a first mixing process on the modified carbon nanomaterial and starch to obtain a starch mixed solution;

[0012] Performing a second mixing process on the starch mixed solution and the silicon-based material particles to obtain a silicon-containing starch mixed solution;

[0013] The silicon-containing starch solution is granulated to form a bond between the modified carbon nanomaterial and the oxygen-containing functional groups in the starch, thereby obtaining a silicon-carbon composite material precursor.

[0014] The preparation method of the present application firstly performs surface treatment on the carbon nanomaterial, and then prepares a starch mixed solution with starch, so that the modified carbon nanomaterial and starch are fully dispersed and pre-combined, and then mixed with silicon-based material particles to prepare a silicon-containing starch mixed solution. When the granulation treatment is finally performed, on the one hand, the modified carbon nanomaterial forms a stable bonding connection with the oxygen-containing functional groups in the starch, inhibiting the free movement of the starch molecules, and on the other hand, the granulation treatment removes the solvent, so that the modified carbon nanomaterial and starch are combined to form modified starch particles, and a number of silicon-based material particles are embedded therein. Therefore, the preparation method can prepare a silicon-carbon composite material precursor, solving the technical problem in the prior art that starch foaming leads to poor performance of silicon-carbon composite materials.

[0015] In a third aspect, the present application provides a silicon-carbon composite material, which is obtained by carbonizing the silicon-carbon composite material precursor of the above application or the silicon-carbon composite material precursor prepared by the preparation method of the above application.

[0016] The silicon-carbon composite material of the present application is prepared by carbonization treatment of the silicon-carbon composite material precursor above. Therefore, during the carbonization treatment, the starch molecules are restricted from moving freely, and the foaming phenomenon is suppressed. Even if there is gas overflow, there will be no bubbling, so that the modified starch around the silicon-based material can maintain uniform thickness and stable structure during the carbonization process. Therefore, after the carbonization treatment, the modified starch particles carbonize a porous carbon particle matrix, in which a number of silicon-based materials are contained, and the thickness of the carbon wall around the silicon-based material is uniform. Therefore, the silicon-carbon composite material of the present application has good comprehensive properties such as structural stability, electrical conductivity, and negative electrode capacity.

[0017] In a fourth aspect, the present application provides a secondary battery, the secondary battery comprising a negative electrode, and the negative electrode contains the silicon-carbon composite material of the above-mentioned application.

[0018] The negative electrode of the secondary battery of the present application contains the silicon-carbon composite material of the above-mentioned application, and the silicon-carbon composite material has good structural stability, electrical conductivity and high capacity. Therefore, the secondary battery has good cycle stability and high battery capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is a physical picture of the precursor before carbonization treatment in step S6 of Example A1 of the present application and the silicon-carbon composite material after carbonization treatment;

[0021] in, Figure 1 (a) is a physical picture of the precursor before the carbonization treatment in step S6 of comparative example A1;

[0022] Figure 1 (b) is a physical picture of the silicon-carbon composite material after carbonization treatment in step S6 of comparative example A1;

[0023] Figure 1 (c) is a physical picture of the precursor before carbonization treatment in step S6 of Example A1;

[0024] Figure 1 (d) is a physical picture of the silicon-carbon composite material after carbonization treatment in step S6 of Example A1;

[0025] Figure 2 It is a SEM image of the precursor before carbonization treatment and the silicon-carbon composite material after carbonization treatment in step S6 of Example A1 of the present application and Comparative Example A1;

[0026] in, Figure 2 (a) is a SEM image of the precursor before carbonization treatment in step S6 of comparative example A1;

[0027] Figure 2 (b) is a SEM image of the silicon-carbon composite material after carbonization treatment in step S6 of comparative example A1;

[0028] Figure 2 (c) is a SEM image of the precursor before carbonization treatment in step S6 of Example A1;

[0029] Figure 2 (d) is a SEM image of the silicon-carbon composite material after carbonization treatment in step S6 of Example A1;

[0030] Figure 3 This is a SEM image of the silicon-carbon composite material obtained in step S6 of Example A1 of the present application with adjusted magnification;

[0031] Figure 4 is the XRD diagram of the silicon-carbon composite material obtained in step S6 of Examples A1 to A4 of the present application;

[0032] Figure 5 This is a rate performance diagram of the lithium battery of Example B1 of the present application;

[0033] Figure 6 It is a test chart of the cycle performance of the lithium battery of Example B1 and Comparative Example B1 of the present application. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0035] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0036] In this application, "at least one" means one or more, "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items.

[0037] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0038] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also indicate the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass in the embodiment description of the present application can be a mass unit known in the chemical industry such as µg, mg, g, kg, etc.

[0039] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0040] Explanation of terms in this application:

[0041] Starch softening: When starch granules come into contact with liquids such as water, they absorb water and swell. In this process, the hydrogen bonds between starch molecules are destroyed by water molecules, causing the volume of starch granules to increase and the structure to become loose. After further heating, the movement of starch molecular segments intensifies and the interaction between molecules weakens, making it easier for starch molecules to intertwine and entangle with each other to form a gel network structure, that is, a gelation reaction occurs to form a viscous substance.

[0042] Starch foaming: When starch and water are mixed and heated, the starch molecules will undergo a series of physical changes. When the water evaporates, the starch granules will expand and form starch film bubbles, making the structure unstable.

[0043] Several: that is, "at least one". The "several" in several silicon-based material particles is to facilitate understanding of the spatial position relationship of the silicon-based material particles embedded in the modified starch particles, and to facilitate understanding of the size relationship between the two, rather than referring to the uncertainty of quantity. Therefore, the number of embedded silicon-based material particles is at least one, and there is no need to specify the specific number.

[0044] A first aspect of an embodiment of the present application provides a silicon-carbon composite material precursor, which includes modified starch particles and a plurality of silicon-based material particles. The silicon-based material particles are at least embedded in the modified starch particles (similar to the spatial position relationship of a plurality of watermelon seeds embedded in watermelon pulp). The modified starch particles include carbon nanomaterials and starch, and the carbon nanomaterials and starch are bonded to each other via oxygen-containing functional groups.

[0045] Compared with the existing precursors of silicon-based materials embedded in starch particles, the matrix of the precursor of the silicon-carbon composite material of the present application embodiment is modified starch particles. First, the carbon nanomaterial and starch are bonded by oxygen-containing functional groups, which limits the free movement of starch molecules. Therefore, when the precursor is subjected to subsequent carbonization treatment, it is beneficial for starch molecules and silicon-based material particles to maintain their original relative positions, and the relative positions will not change due to the overflow of gases such as water vapor and carbon dioxide. Secondly, on a microscopic scale, when starch softens, the carbon nanomaterial in the modified starch particles separates the softened starch into many small areas, further suppressing the bubbling phenomenon and starch foaming. Furthermore, the bonding connection between the modified carbon nanotubes and starch further reduces the surface tension between starch molecules, further suppressing starch foaming. Therefore, the carbon wall thickness around the silicon particles in the silicon-carbon composite material obtained by the precursor of the silicon-carbon composite material of the present application embodiment is uniform. Finally, the carbon nanomaterial will also be used as a conductive material in the porous carbon particle matrix after carbonization, further improving the conductivity of the obtained silicon-carbon composite material. In summary, the silicon-carbon composite material precursor in the embodiment of the present application solves the technical problem that the starch foaming phenomenon causes the silicon-carbon composite material precursor to produce a silicon-carbon composite material with poor performance, and can be used to prepare a silicon-carbon composite material to improve comprehensive performance such as conductivity, capacity, and stability.

[0046] The silicon-based material particles are at least embedded in the modified starch particles. In addition to being embedded in the modified starch particles, some of the silicon-based material particles may be adsorbed on the surface of the modified starch particles, or adsorbed in the pores on the surface and partially exposed, etc.

[0047] About modified starch granules:

[0048] The base material of modified starch granules is starch, which is starch in a broad sense. According to the source, it can be corn starch, potato starch, sweet potato starch, etc. According to the physicochemical properties or chemical treatment, it can be water-soluble starch, oxidized starch, esterified starch, etherified starch, cross-linked starch, grafted starch, etc.

[0049] The oxygen-containing functional groups between the carbon nanomaterial and the starch in the modified starch particles may include at least one of an ester group, an ether bond, a sulfonate group, and an amide group. These groups are conducive to strengthening the bonding connection between the carbon nanomaterial and the starch, further restricting the free movement of the starch molecules, and inhibiting the starch foaming. The distribution state of the carbon nanomaterial in the modified starch particles is random, and it is optional to be evenly dispersed in the modified starch particles to further improve the above-mentioned effect of inhibiting starch foaming. Since starch is a polysaccharide formed by the polymerization of glucose molecules, the carbon nanomaterial is at least partially located between the starch molecules in the modified starch particles or in the three-dimensional structure of a single starch molecule, and can also be partially located between the modified starch particles and the embedded silicon-based material particles, and can also be partially located on the outer surface of the modified starch particles.

[0050] In some embodiments, the carbon nanomaterial includes at least one of carbon nanotubes, graphene, carbon fibers, carbon balls, and nano-hard carbon. Among them, the carbon nanotubes may include single-walled carbon nanotubes, the diameter of which is 0.6 to 2 nm and the length is 1 to 30 μm. The carbon nanotubes may also include multi-walled carbon nanotubes, the diameter of which is 2 to 30 nm and the length is 0.1 to 50 μm, which may be prepared by methods such as arc discharge, laser evaporation, and chemical vapor deposition under the catalytic action of metal catalysts. The number of graphene layers may be 1 to 10 layers, and the lateral size may be 50 nm to 5 μm. The diameter of the carbon fiber may be 50 to 500 nm, and the length may be 3 μm to 20 μm. The diameter of the carbon ball may be 10 to 300 nm. Nano-hard carbon refers to carbon whose structural features are at the nanometer level and is difficult to graphitize. It may be prepared by pyrolysis of polymers, petrochemical products, biomass, etc., and the diameter of the nano-hard carbon may be 10 to 100 nm. These types and parameters of carbon nanomaterials are conducive to bonding with starch, limiting the free movement of starch molecules, and dividing the modified starch particles into many small areas when the starch softens, inhibiting bubbling, reducing the surface tension of starch, and improving the structural stability of the silicon-carbon composite material. In addition, these carbon nanomaterials have good electrical conductivity, which is conducive to the preparation of the electrical conductivity of the silicon-carbon composite material.

[0051] In some embodiments, the particle size of the modified starch particles, that is, the particle size of the silicon-carbon composite precursor, is 3 to 50 μm, which refers to the actual particle size distribution range, and the Dv50 particle size is 10 to 20 μm. The modified starch particles of these particle sizes can accommodate certain silicon-based material particles, so that the silicon-carbon composite prepared by the precursor has a suitable particle size, accommodates enough silicon-based materials, and further improves the capacity, structural stability, conductivity and other comprehensive properties of the prepared silicon-carbon composite.

[0052] About silicon-based material particles:

[0053] A number of silicon-based material particles are embedded in the modified starch particles. The silicon-based material can be pure silicon material or oxidized silicon material. In the prior art, generally speaking, the higher the degree of oxidation of the silicon material, the more the volume expansion phenomenon during charging and discharging is alleviated, but the capacity as a negative electrode material is lower. Therefore, in addition to pure silicon, the prior art can also select silicon materials with a certain degree of oxidation. In the embodiment of the present application, the ratio of oxygen element to silicon element in the silicon-based material particles is (0-2):1.

[0054] In some embodiments, the particle size of the silicon-based material particles is 2 to 80 nm, which refers to the actual particle size distribution range, and may include but is not limited to any value of 2 nm, 10 nm, 30 nm, 50 nm, 80 nm or the range between any two values. The Dv50 particle size can be 30 nm. The silicon-based materials of these particle sizes are nano silicon-based material particles, which have suitable capacity and volume expansion rate as negative electrode materials and can be embedded in modified starch particles of larger volume. The silicon-carbon composite material precursor formed with the modified starch particles is beneficial to further improve the capacity, stability and other comprehensive properties of the prepared silicon-carbon composite material.

[0055] In some embodiments, the mass ratio of modified starch particles and silicon-based material particles can be (1-10):1. In the exemplary examples, it can include but is not limited to any value of 1:1, 3:1, 5:1, 7:1, 10:1 or a range between any two values. These mass ratios enable the modified starch particles in the precursor to accommodate an appropriate number of silicon-based material particles. Thus, the silicon and carbon elements in the silicon-carbon composite material obtained by the precursor are also maintained in an appropriate ratio range, which is beneficial to taking into account the conductivity of the silicon-carbon composite material, the capacity of the negative electrode material and other properties.

[0056] The second aspect of the embodiment of the present application provides a method for preparing the silicon-carbon composite material precursor of the embodiment of the present application, comprising the following steps:

[0057] S10: performing surface modification treatment on the carbon nanomaterial to obtain a modified carbon nanomaterial;

[0058] S20: performing a first mixing process on the modified carbon nanomaterial and starch to obtain a starch mixed solution;

[0059] S30: performing a second mixing process on the starch mixed solution and the silicon-based material particles to obtain a silicon-containing starch mixed solution;

[0060] S40: granulating the silicon-containing starch solution to form a bond between the modified carbon nanomaterial and the oxygen-containing functional groups in the starch to obtain a silicon-carbon composite material precursor.

[0061] The preparation method of the embodiment of the present application first performs surface treatment on the carbon nanomaterial, and then prepares a starch mixed solution with starch, so that the modified carbon nanomaterial and starch are fully dispersed and pre-combined, and then mixed with silicon-based material particles to prepare a silicon-containing starch mixed solution. When the granulation treatment is finally performed, on the one hand, the modified carbon nanomaterial forms a stable bonding connection with the oxygen-containing functional groups in the starch, which inhibits the free movement of the starch molecules. On the other hand, the granulation treatment removes the solvent, so that the modified carbon nanomaterial is combined with the starch to form modified starch particles, and several silicon-based material particles are embedded therein. Therefore, the preparation method can prepare a silicon-carbon composite material precursor. When used for carbonization treatment to prepare silicon-carbon composite materials, the starch molecules in the modified starch particles will not move freely. When the starch softens, the carbon nanomaterial separates the softened starch into many small areas, and also reduces the surface tension of the starch, fully inhibiting the bubbling phenomenon, so that the carbon wall thickness around the silicon-based material particles remains stable. Therefore, the silicon-carbon composite material precursor prepared by the preparation method solves the technical problem that the foaming of starch in the prior art leads to poor performance of silicon-carbon composite materials.

[0062] [Step S10]

[0063] This step is to perform surface modification on the carbon nanomaterial so that functional groups are bound to the surface of the carbon nanomaterial, which is beneficial for subsequent binding with starch.

[0064] The types and parameters of the carbon nanomaterials can refer to the content of the carbon nanomaterials in the silicon-carbon composite material precursor. In the exemplary embodiment, the carbon nanomaterials can include at least one of carbon nanotubes, graphene, carbon fibers, carbon balls, and nano hard carbon.

[0065] In some embodiments, the surface modification treatment may include at least one of aqua regia oxidation, ultrasound in hydrogen peroxide solution, plasma treatment in oxygen atmosphere, and plasma treatment in ammonia atmosphere. Aqua regia oxidation causes carboxylation and nitration of the carbon nanomaterial surface, ultrasound in hydrogen peroxide solution causes hydroxylation of the carbon nanomaterial surface, plasma treatment in oxygen atmosphere causes hydroxylation and carbonylation of the carbon nanomaterial surface, and plasma treatment in ammonia atmosphere causes amination of the carbon nanomaterial surface. Therefore, the surface of the modified carbon nanomaterial contains at least one of carboxyl, hydroxyl, nitro, sulfonic acid, amine, and carbonyl groups.

[0066] [Step S20]

[0067] This step is to prepare the modified carbon nanomaterial and starch into a starch mixed solution. The type of starch can refer to the content of the carbon nanomaterial in the silicon-carbon composite material precursor, such as corn starch, potato starch, sweet potato starch, etc. Optionally, the starch also includes a step of pre-treating the starch before the first mixing treatment with the modified carbon nanomaterial. The pre-treatment may include gelatinization treatment, which may be dissolving starch in hot water, boiling starch with water, and gelatinization treatment at high pressure and high temperature in a hydrothermal kettle. These pre-treatment methods are conducive to improving the solubility of starch, and are more conducive to the subsequent preparation of a uniformly dispersed starch mixed solution with the modified carbon nanomaterial.

[0068] The solvent used in the first mixing treatment may include one of deionized water, ultrapure water, ethanol, and propanol, and deionized water may be selected. During the first mixing treatment, the mass ratio of the modified carbon nanomaterial and the starch may be 1: (20-300), and may include but is not limited to any value of 1:20, 1:50, 1:100, 1:300 or a range between any two values. These mass ratios allow the modified carbon nanomaterial to be fully dispersed in the starch. When the modified starch particles are subsequently formed, the modified carbon nanomaterial and the starch have a suitable mass ratio, which is conducive to the formation of a bonded connection between the modified carbon nanomaterial and the starch, and restricts the free movement of the starch molecules.

[0069] Before the first mixing treatment, the modified carbon nanomaterial can be uniformly dispersed in the solvent to reduce agglomeration and the like, and can be dispersed by a high-pressure homogenizer. The first mixing treatment can be carried out by stirring the modified carbon nanomaterial and starch in the solvent at high speed, or by ultrasonic dispersion to obtain a starch mixed solution.

[0070] In the mixed solution, some of the modified carbon nanomaterials have formed preliminary bonding interactions with starch according to the types of their surface functional groups, mainly intermolecular forces such as hydrogen bonds, such as hydrogen bonds between hydroxyl groups and hydroxyl groups in starch, and hydrogen bonds between nitro groups and hydroxyl groups.

[0071] [Step S30]

[0072] This step is the step of preparing a silicon-containing starch mixed solution. Optionally, the silicon-based material particles are directly added to the starch mixed solution and then dispersed, but this may be difficult to achieve uniform dispersion. Therefore, in some embodiments, the silicon-based material particles are subjected to a second mixing treatment with the starch mixed solution in the form of a dispersion. The silicon-based material particle dispersion can add the silicon-based material particles to a solvent and fully mix them. The solvent of the dispersion can include at least one of deionized water, ultrapure water, ethanol, and propanol. The mass ratio of silicon-based material particles to solvent can be 1: (10-100), and the dispersion can be prepared by dispersion with a homogenizer or the like.

[0073] In addition, when the silicon-based material particles are prepared into a dispersion, a protective agent can be added to the dispersion. The protective agent can include at least one of polyacrylamide, hydroxymethyl cellulose, gelatin, chitosan, gel red alginic acid, and water-soluble vitamin E. These protective agents can be combined with the surface of the silicon-based material particles to improve the properties of the surface of the silicon-based material particles and stabilize the interface between the surface of the silicon-based material particles and the solvent. For example, after adding hydroxymethyl cellulose, the hydroxymethyl cellulose will be adsorbed on the surface of the silicon-based material particles, so that the surface of the silicon-based nanoparticles carries a negative charge. In this way, in the solvent, the surface of the silicon-based material particles carries a negative charge and generates a mutual repulsive force, so that the silicon-based material particles can maintain a uniform dispersion in the dispersion without agglomeration and sedimentation, which is also conducive to the final uniform dispersion with the starch mixed solution. At the same time, the addition of these protective agents is also conducive to the silicon-based material particles maintaining stable chemical properties in the dispersion so that they are not fully oxidized. In the exemplary embodiment, the mass ratio of the silicon-based material particles to the protective agent can be (5-20):1.

[0074] The second mixing treatment for preparing the silicon-containing starch mixed solution may be a stirring treatment, such as stirring for 5 to 300 minutes. In the prepared silicon-containing starch mixed solution, the mass ratio of silicon-based material particles to starch combined with carbon nanomaterials may be 1: (1 to 10), or in steps S10 to S30, the mass ratio of the raw materials such as modified carbon nanomaterials, starch, and silicon-based material particles may be 1: (20 to 300): (2 to 30). These mass ratios allow the silicon-based material particles to be evenly dispersed between the starch molecules in the mixed solution, and a small amount of carbon nanomaterials are combined with starch molecules, which is conducive to the subsequent preparation of a precursor in which silicon-based material particles are embedded in modified starch particles.

[0075] [Step S40]

[0076] This step is the final step of granulation to obtain the precursor, and the solvent in the silicon-containing starch mixed solution is removed to obtain the precursor particles. In addition, the granulation process can also create suitable reaction conditions, such as temperature, pressure, etc., so that the functional groups on the surface of the modified carbon nanomaterial react chemically with the oxygen-containing functional groups (mainly hydroxyl groups) in the starch molecules to form a bond connection, thereby obtaining modified starch particles, in which a number of silicon-based material particles are embedded to obtain a silicon-carbon composite material precursor.

[0077] In the exemplary embodiment, the granulation process may include at least one of air flow spray drying granulation, pressure spray drying granulation, centrifugal spray drying granulation, spray freezing granulation, boiling granulation and fluidized bed granulation, wherein the granulation temperature used in the air flow spray drying granulation, pressure spray drying granulation and centrifugal spray drying granulation is 150-300°C; the air flow in the air flow spray drying granulation method may be at least one of air, nitrogen, argon, helium and argon hydrogen; the granulation temperature used in the spray freezing granulation method may be -210°C to -196°C. Through these granulation treatment methods, the solvent in the silicon-containing starch mixed solution is removed, and at the same time, the groups on the surface of the modified carbon nanomaterial react with the oxygen-containing groups (mainly hydroxyl groups) in the starch molecules to form a bond connection, or form hydrogen bonds and other intermolecular forces to form a bond connection, such as carboxyl groups reacting with hydroxyl groups to form ester groups, hydroxyl groups mainly form hydrogen bonds with hydroxyl groups, and some will be dehydrated to form ether bonds, nitro groups and hydroxyl groups form hydrogen bonds, sulfonic acid groups and hydroxyl groups react to form sulfonate groups, and amine groups and hydroxyl groups react to form amide groups. Through the above series of chemical reactions or intermolecular forces, the modified carbon nanomaterial and starch are bonded through oxygen-containing functional groups to obtain modified starch particles.

[0078] During the granulation process, solvent evaporation, especially instantaneous evaporation, is conducive to pre-forming pores in the silicon-carbon composite material precursor. The modified starch particles contain uniformly dispersed silicon-based material particles therein to obtain a silicon-carbon composite material precursor. When the precursor is carbonized, the foaming phenomenon of starch can be suppressed, which is conducive to obtaining a silicon-carbon composite material with uniform carbon wall thickness around the silicon material.

[0079] A third aspect of the embodiments of the present application provides a silicon-carbon composite material, which is obtained by carbonizing the silicon-carbon composite material precursor of the above embodiments of the present application or the silicon-carbon composite material precursor prepared by the preparation method of the above embodiments of the present application.

[0080] The silicon-carbon composite material of the embodiment of the present application is prepared by carbonization treatment of the silicon-carbon composite material precursor mentioned above. Therefore, during the carbonization treatment, the starch molecules are restricted from moving freely, and the foaming phenomenon is suppressed. Even if there is gas overflow, there will be no bubbling, so that the modified starch around the silicon-based material can maintain uniform thickness and stable structure during the carbonization process. Therefore, after the carbonization treatment, the modified starch particles are carbonized into a porous carbon particle matrix, in which a number of silicon-based materials are contained (similar to the spatial position relationship of melon seeds embedded in the melon pulp), and the thickness of the carbon wall around the silicon-based material is uniform. Therefore, the silicon-carbon composite material of the embodiment of the present application has good comprehensive properties such as structural stability, conductivity, and negative electrode capacity.

[0081] In addition, similar to the positional relationship in the silicon-carbon composite material precursor, in the silicon-carbon composite material after carbonization treatment, some silicon-based materials may be adsorbed on the surface of the porous carbon particle matrix, adsorbed in the pores on the surface, and other spatial positional relationships.

[0082] In some embodiments, the carbonization treatment includes heating and carbonization in a protective atmosphere, and the protective atmosphere may include at least one of nitrogen, helium, argon, hydrogen, and argon. The carbonization treatment may be staged, and the precursor particles may be pre-carbonized first, and the pre-carbonization temperature may be 50 to 400°C, and the time may be 0.5 to 10 h. After the pre-carbonization treatment, the particles are further heated to 500 to 1400°C and carbonized for 1 to 10 h to carbonize the modified starch particles into a porous carbon particle matrix. After the above carbonization treatment, the silicon-carbon composite material of the embodiment of the present application may be obtained.

[0083] The specific surface area of ​​the silicon-carbon composite material is between 100 and 250 m 2 / g, and the average pore size is 5 to 10 nm.

[0084] In some embodiments, carbon coating can be performed on the surface of the silicon-carbon composite material to further improve the conductivity, structural stability, capacity and other properties of the silicon-carbon composite material. In a demonstration example, the carbon coating can include chemical vapor deposition coating, asphalt, biomass coating carbonization and other methods.

[0085] A fourth aspect of an embodiment of the present application provides a secondary battery, the secondary battery comprising a negative electrode, the negative electrode containing the silicon-carbon composite material of the embodiment of the present application.

[0086] The negative electrode of the secondary battery of the embodiment of the present application contains the silicon-carbon composite material of the embodiment of the present application. The silicon-carbon composite material has good structural stability, electrical conductivity and high capacity. Therefore, the secondary battery has good cycle stability and high battery capacity.

[0087] In some embodiments, the negative electrode may contain a binder and a conductive agent in addition to the silicon-carbon composite material as the negative electrode active material. In the embodiments, the conductive agent may be a commonly used conductive agent, such as at least one of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes. Of course, the negative electrode may also contain other negative electrode active materials, such as graphite.

[0088] The following describes the invention in conjunction with specific embodiments.

[0089] Example A1

[0090] This embodiment provides a silicon-carbon composite material precursor, a silicon-carbon composite material, and a preparation method. The preparation method includes the following steps S1 to S7:

[0091] S1: Add hydroxymethyl cellulose to deionized water and stir for 120 min, wherein the mass ratio of hydroxymethyl cellulose to deionized water is 1:200, then add silicon particles with a Dv50 particle size of 50 nm to the hydroxymethyl cellulose solution, and ultrasonicate for 20 min, wherein the ratio of silicon particles to hydroxymethyl cellulose is 10:1, and the ultrasonic power is 100 W, to obtain a silicon particle dispersion;

[0092] S2: adding potato starch into deionized water at 60°C, stirring for 30 min, wherein the ratio of potato starch to deionized water is 2:98, filtering, washing and drying to obtain pretreated potato starch;

[0093] S3: adding single-walled carbon nanotubes to aqua regia, wherein the mass ratio of single-walled carbon nanotubes to aqua regia is 1:199, stirring for 120 min, centrifuging and washing to obtain functionalized single-walled carbon nanotubes, using a high-pressure homogenizer to evenly disperse the functionalized single-walled carbon nanotubes in water, wherein the ratio of functionalized single-walled carbon nanotubes to water is 1:200, then adding pretreated potato starch and stirring at high speed for 30 min, and then ultrasonicating for 60 min to obtain a starch mixed solution, wherein the mass ratio of single-walled carbon nanotubes to pretreated potato starch is 1:10;

[0094] S4: mixing the starch mixed solution with the silicon particle dispersion and adjusting the mass ratio of nano-silicon to modified potato starch in the dispersion to 1:9, and stirring for 60 min to obtain a silicon-containing starch mixed dispersion;

[0095] S5: spray freeze granulation of the mixed dispersion using a spray freeze granulator, spray the mixed dispersion into liquid nitrogen to obtain freeze-dried particles, wherein the liquid nitrogen temperature is -196°C to -210°C, and the feed rate is 1000 mL / h; then put the frozen particles into a freeze dryer for freeze drying, wherein the freeze drying time is 12 to 32 h, to obtain a silicon-carbon composite material precursor;

[0096] S6: heat-treating the silicon-carbon composite material precursor in a nitrogen atmosphere, first preheating at 200°C for 2 h, and then carbonizing at 1000°C for 2 h to obtain a preliminary silicon-carbon composite material;

[0097] S7: The silicon-carbon composite material was coated with sucrose and heat-treated in an argon atmosphere, preheated at 200°C for 3 h, and then heat-treated at 1000°C for 2 h to obtain a carbon-coated silicon-carbon composite material.

[0098] Example A2

[0099] This embodiment provides a silicon-carbon composite material precursor, a silicon-carbon composite material, and a preparation method. The preparation method includes the following steps S1 to S7:

[0100] S1: Add polyacrylamide to deionized water and stir for 30 min, wherein the mass ratio of polyacrylamide to deionized water is 1:1000, then add silicon particles with a particle size of 100 nm to the polyacrylamide solution, ultrasonicate for 20 min, wherein the ratio of silicon particles to polyacrylamide is 20:1, and the ultrasonic power is 100 W, to obtain a silicon particle dispersion;

[0101] S2: adding corn starch into 80° C. deionized water, stirring for 30 min, wherein the ratio of corn starch to deionized water is 6:100, and then filtering, washing and drying to obtain pretreated corn starch;

[0102] S3: Add multi-walled carbon nanotubes to 30% concentration of hydrogen peroxide, wherein the mass ratio of multi-walled carbon nanotubes to hydrogen peroxide is 1:99, ultrasonicate for 30 minutes, centrifuge and wash to obtain functionalized multi-walled carbon nanotubes, use a high-pressure homogenizer to evenly disperse the functionalized multi-walled carbon nanotubes in water, wherein the ratio of multi-walled carbon nanotubes to water is 1:150, then add pretreated corn starch to water and stir at high speed for 20 minutes, ultrasonicate for 30 minutes to obtain a starch mixed solution, wherein the mass ratio of multi-walled carbon nanotubes to pretreated corn starch is 1:10;

[0103] S4: mixing the starch mixed solution with the silicon particle dispersion and adjusting the mass ratio of nano-silicon to modified corn starch in the dispersion to 1:9, and stirring for 60 min to obtain a silicon-containing starch mixed dispersion;

[0104] S5: spray drying and granulating the mixed dispersion using a centrifugal spray dryer, adjusting the inlet and outlet temperatures to 170°C and 60°C, respectively, and the feed rate to 2000 mL / h to obtain a silicon-carbon composite material precursor;

[0105] S6: heat-treating the silicon-carbon composite material precursor in an argon atmosphere, first preheating at 400°C for 3 h, and then carbonizing at 700°C for 4 h to obtain a preliminary silicon-carbon composite material;

[0106] S7: The silicon-carbon composite material is coated with water-soluble starch and heat-treated in an argon atmosphere, preheated at 400°C for 3 h, and then heat-treated at 700°C for 4 h to obtain a carbon-coated silicon-carbon composite material.

[0107] Example A3

[0108] This embodiment provides a silicon-carbon composite material precursor, a silicon-carbon composite material, and a preparation method. The preparation method includes the following steps S1 to S7:

[0109] S1: adding gel alkali acid to deionized water and stirring for 30 min, wherein the mass ratio of gel alkali acid to deionized water is 1:400, then adding silicon particles with a particle size of 30 nm to the gel alkali acid solution and stirring for 60 min, wherein the mass ratio of silicon particles to gel alkali acid is 5:1, to obtain a silicon particle dispersion;

[0110] S2: adding cross-linked starch into pure water and heating to boiling, stirring for 30 min, wherein the mass ratio of cross-linked starch to deionized water is 3:97, then filtering, washing and drying to obtain pretreated cross-linked starch;

[0111] S3: Multi-walled carbon nanotubes were plasma treated in an oxygen atmosphere to obtain functionalized multi-walled carbon nanotubes, and the functionalized multi-walled carbon nanotubes were uniformly dispersed in water using a high-pressure homogenizer, wherein the ratio of multi-walled carbon nanotubes to water was 1:100, and then pretreated cross-linked starch was added to the water and stirred at high speed for 60 min, and ultrasonicated for 30 min to obtain a starch mixed solution, wherein the mass ratio of multi-walled carbon nanotubes to pretreated cross-linked starch was 1:20;

[0112] S4: mixing the conductive starch solution with the silicon particle dispersion and adjusting the mass ratio of nano-silicon to modified cross-linked starch in the dispersion to 1:6, and stirring for 60 min to obtain a silicon-containing starch mixed dispersion;

[0113] S5: performing boiling granulation on the mixed dispersion using a boiling granulation kettle, wherein the inlet air temperature is 40°C to 120°C, the outlet air temperature is 30°C to 80°C, and the feed rate is 1500 mL / h to obtain a silicon-carbon composite material precursor;

[0114] S6: heat-treating the silicon-carbon composite material precursor in an argon-hydrogen atmosphere, first preheating at 300°C for 3 h, and then carbonizing at 1200°C for 3 h to obtain a preliminary silicon-carbon composite material;

[0115] S7: The silicon-carbon composite material is coated by chemical vapor deposition to obtain a carbon-coated silicon-carbon composite material.

[0116] Example A4

[0117] This embodiment provides a silicon-carbon composite material precursor, a silicon-carbon composite material, and a preparation method. The preparation method includes the following steps S1 to S7:

[0118] S1: chitosan was added to deionized water and stirred for 30 min, wherein the mass ratio of chitosan to deionized water was 1:1200, and then silicon particles with a particle size of 30 nm were added to the chitosan solution and stirred for 60 min, wherein the mass ratio of silicon particles to chitosan was 15:1, to obtain a silicon particle dispersion;

[0119] S2: adding water-soluble starch to deionized water, stirring for 30 min, and then boiling for 60 min, wherein the mass ratio of water-soluble starch to deionized water is 1:99, and then filtering, washing and drying to obtain pretreated water-soluble starch;

[0120] S3: multi-walled carbon nanotubes were plasma treated in an ammonia atmosphere to obtain functionalized multi-walled carbon nanotubes, and the functionalized multi-walled carbon nanotubes were uniformly dispersed in water using a high-pressure homogenizer, wherein the ratio of multi-walled carbon nanotubes to water was 1:200, and then pretreated water-soluble starch was added to the water and stirred at high speed for 10 min, and ultrasonicated for 60 min to obtain a starch mixed solution, wherein the mass ratio of multi-walled carbon nanotubes to pretreated water-soluble starch was 1:30;

[0121] S4: mixing the starch mixed solution with the silicon particle dispersion and adjusting the mass ratio of nano-silicon to modified water-soluble starch in the dispersion to 1:6, and stirring for 60 min to obtain a silicon-containing starch mixed dispersion;

[0122] S5: drying and granulating the mixed dispersion by a fluidized bed granulation method, wherein the fluidized bed spray rate is 700 mL / h, the atomization pressure is 0.01-0.02 MPa, the air inlet temperature is 50-60°C, and drying is performed for 60-120 min to obtain a silicon-carbon composite material precursor;

[0123] S6: heat-treating the silicon-carbon composite material precursor in a nitrogen atmosphere, first preheating at 350°C for 2 h, and then carbonizing at 800°C for 1.5 h to obtain a preliminary silicon-carbon composite material;

[0124] S7: The silicon-carbon composite material was coated with sucrose and then heat-treated in an argon atmosphere, first preheated at 350°C for 2 h, and then heat-treated at 800°C for 1.5 h to obtain a carbon-coated silicon-carbon composite material.

[0125] Comparative Example A1

[0126] This comparative example provides a silicon-carbon composite material precursor, a silicon-carbon composite material, and a preparation method. The only difference from Example 1 is that no modified carbon nanotubes are used in step S3, and the pretreated potato starch in step S3 is directly used in step S4. The rest is the same as Example A1.

[0127] Comparative Example A2

[0128] This comparative example provides a silicon-carbon composite material precursor, a silicon-carbon composite material, and a preparation method. The only difference from Example 1 is that the carbon nanotubes in step S3 are not modified, but the single-walled carbon nanotubes and pretreated potato starch are directly subjected to high-speed stirring treatment in step S3. The rest is the same as Example A1.

[0129] Lithium-ion battery example:

[0130] The final silicon-carbon composite materials provided in the above-mentioned Examples A1 to A4 and Comparative Examples A1 to A2 are respectively assembled into lithium batteries according to the following methods:

[0131] The silicon-carbon composite material, carbon nanotubes CNTs, and polyacrylic acid were mixed uniformly in water at a mass ratio of 8:1:1 to obtain a uniformly mixed slurry. The slurry was then evenly applied to the copper current collector, dried in a vacuum oven at 100°C for 5 h, and cut into a circular electrode with a diameter of 16 mm. The metal lithium sheet was used as the positive electrode, the polyolefin microporous membrane was used as the diaphragm, the mixed organic solution was used as the electrolyte, and the solvent was EC:EMC:DMC with a mass ratio of 1:1:1. The button battery was assembled in an argon-protected glove box.

[0132] Among them, the silicon-carbon composite material of Example A1 is used to make the lithium battery of Example B1, the silicon-carbon composite material of Example A2 is used to make the lithium battery of Example B2, and so on, until the silicon-carbon composite material of Comparative Example A2 is used to make the lithium battery of Comparative Example B2.

[0133] Related performance tests and result analysis

[0134] 1. Appearance analysis

[0135] The actual pictures of the precursor before carbonization treatment and the silicon-carbon composite material after carbonization treatment in step S6 of Example A1 and Comparative Example A1 are as follows: Figure 1 As shown. Among them, Figure 1 (a) is a physical picture of the precursor before the carbonization treatment in step S6 of comparative example A1; Figure 1 (b) is a physical picture of the silicon-carbon composite material after carbonization treatment in step S6 of comparative example A1; Figure 1 (c) is a physical picture of the precursor before carbonization treatment in step S6 of Example A1; Figure 1 (d) is a physical picture of the silicon-carbon composite material after carbonization treatment in step S6 of Example A1. By comparison, it can be seen that the preparation method of Comparative Example A1 does not add modified carbon nanotubes, and the final precursor has serious starch foaming during the carbonization process, and the carbonized product has serious bubbling, while the carbonization treatment of the preparation method of Example A1 does not have bubbling phenomenon, and the obtained silicon-carbon composite material has no bubbling problem.

[0136] 2. Morphological analysis

[0137] The precursor before the carbonization treatment in step S6 of Example A1 and Comparative Example A1 and the silicon-carbon composite material after the carbonization treatment were subjected to electron microscope scanning to obtain SEM images, as shown in FIG. Figure 2 As shown, Figure 2 (a) is a SEM image of the precursor before carbonization treatment in step S6 of comparative example A1; Figure 2(b) is a SEM image of the silicon-carbon composite material after carbonization treatment in step S6 of comparative example A1; Figure 2 (c) is a SEM image of the precursor before carbonization treatment in step S6 of Example A1; Figure 2 (d) is a SEM image of the silicon-carbon composite material after the carbonization treatment in step S6 of Example A1. Figure 3 This is a SEM image of the silicon-carbon composite material obtained in step S6 of Example A1, and the magnification is different from the above. Figure 2 It can be seen that Figure 2 (a) and Figure 2 The precursors in (c) are spherical before carbonization. After carbonization, Figure 2 (b) shows that comparative example A1 has obvious foaming phenomenon, nano-silicon is adsorbed on the starch carbon wall, the carbon wall is in an exploded state, the carbon wall has poor uniformity, and the coating effect on nano-silicon is poor; Figure 2 (d) shows that Example A1 still maintains spherical particles after carbonization. Figure 3 It can be seen that the silicon-carbon composite material includes a porous carbon particle matrix, in which silicon-based material particles are embedded. The silicon-based material is contained in the porous carbon particle matrix and is used in batteries. The porous carbon particle matrix can well accommodate the volume expansion of the silicon-based material and improve the structural stability and other properties.

[0138] 3. XRD test

[0139] The silicon-carbon composite material obtained in step S6 of Example A1 to Example A4 was subjected to an X-ray diffraction test, and the results were as follows: Figure 4 As shown, Figure 4 A1, A2, A3, A4 in the embodiment correspond to embodiments A1 to A4, from Figure 4 It can be seen that there is a peak representing nano-silicon near 28° and a peak of amorphous carbon near 20°, indicating that the preparation method successfully produced a silicon-carbon composite material.

[0140] 4. Electrochemical characterization:

[0141] The lithium batteries of Examples B1 to B4 and Comparative Examples B1 to B2 were subjected to constant current charge and discharge tests. The charge and discharge rates of the first and second cycles were 0.05 C, and the charge and discharge rates from the third cycle onwards were 0.5 C, and the charge and discharge voltage range was 0.1 to 1.5 V. The test results are shown in Table 1, and the rate performance of the lithium battery of Example B1 is shown in the figure below. Figure 5 As shown, the cycle performance test diagram of the lithium battery of Example B1 and Comparative Example B1 is as follows Figure 6 shown.

[0142] Table 1

[0143]

[0144] Combining Table 1 and Figure 5 , Figure 6 It can be seen that compared with comparative examples B1 and B2, embodiments B1 to B4 of the present application have better rate performance and charge-discharge cycle performance. The silicon-carbon composite material used in comparative example B1 does not add carbon nanotubes at all. Starch and silicon particles are directly used to prepare the precursor and then the silicon-carbon composite material is prepared. The capacity retention rate of the lithium battery finally prepared is very low. Although carbon nanotubes are added to the silicon-carbon composite material used in comparative example B1, they are only ordinary unmodified carbon nanotubes. Although the performance is improved compared with comparative example B1, it is still far lower than that of each embodiment. Combined with the characterization in point 1 above, it can be further seen that the preparation method of the present application solves the technical problem of starch foaming during the carbonization process, and the obtained silicon-carbon composite material has excellent performance when used in batteries.

[0145] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A silicon-carbon composite material precursor, characterized in that: It comprises modified starch particles and a plurality of silicon-based material particles, wherein the silicon-based material particles are at least embedded in the modified starch particles, the modified starch particles comprise carbon nanomaterials and starch, and the carbon nanomaterials are bonded to the starch via oxygen-containing functional groups, and the carbon nanomaterials are dispersed in the modified starch particles.

2. The silicon-carbon composite material precursor according to claim 1, characterized in that: The oxygen-containing functional group includes at least one of an ester group, an ether bond, a sulfonate group, and an amide group; And / or, the carbon nanomaterial includes at least one of carbon nanotubes, graphene, carbon fibers, carbon spheres, and nano-hard carbon.

3. The silicon-carbon composite material precursor according to claim 2, characterized in that: The carbon nanotubes include single-walled carbon nanotubes, wherein the diameter of the single-walled carbon nanotubes is 0.6 to 2 nm and the length is 1 to 30 μm; And / or, the carbon nanotubes include multi-walled carbon nanotubes, the multi-walled carbon nanotubes have a diameter of 2 to 30 nm and a length of 0.1 to 50 μm; And / or, the number of layers of the graphene is 1 to 10, and the lateral size is 50 nm to 5 μm; And / or, the carbon fiber has a diameter of 50 to 500 nm and a length of 3 μm to 20 μm; And / or, the diameter of the carbon sphere is 10 to 300 nm; And / or, the diameter of the nano hard carbon is 10-100 nm.

4. The silicon-carbon composite material precursor according to any one of claims 1 to 3, characterized in that: The mass ratio of the modified starch particles to the silicon-based material particles is (1-10):1; And / or, the particle size of the silicon-based material particles is 2 to 80 nm; And / or, the particle size of the silicon-carbon composite material precursor is 3 to 50 μm.

5. A method for preparing a silicon-carbon composite material precursor, characterized in that: The steps include: Performing surface modification on the carbon nanomaterial to obtain a modified carbon nanomaterial; Performing a first mixing process on the modified carbon nanomaterial and starch to obtain a starch mixed solution; Performing a second mixing process on the starch mixed solution and silicon-based material particles to obtain a silicon-containing starch mixed solution; The silicon-containing starch mixed solution is granulated to form a bonding connection between the modified carbon nanomaterial and the oxygen-containing functional groups in the starch, thereby obtaining a silicon-carbon composite material precursor.

6. The preparation method according to claim 5, characterized in that: The surface of the modified carbon nanomaterial contains at least one of a carboxyl group, a hydroxyl group, a nitro group, a sulfonic acid group, an amine group, and a carbonyl group; And / or, the surface modification treatment comprises at least one of aqua regia oxidation, ultrasound in a hydrogen peroxide solution, plasma treatment in an oxygen atmosphere, and plasma treatment in an ammonia atmosphere; And / or, the mass ratio of the modified carbon nanomaterial, the starch, and the silicon-based material particles is 1:(20-300):(2-30).

7. The preparation method according to claim 5 or 6, characterized in that: The starch also includes a step of gelatinizing the starch before the first mixing treatment; And / or, the silicon-based material particles are in the form of a dispersion and are subjected to the second mixing treatment with the starch mixed solution.

8. The preparation method according to claim 7, characterized in that: The solvent of the dispersion includes at least one of deionized water, ultrapure water, ethanol and propanol; And / or, a protective agent is further added to the dispersion, and the protective agent includes at least one of polyacrylamide, hydroxymethyl cellulose, gelatin, chitosan, gel kelp, and water-soluble vitamin E.

9. A silicon-carbon composite material, characterized in that: The silicon-carbon composite material is prepared by carbonizing the silicon-carbon composite material precursor as claimed in any one of claims 1 to 4 or the silicon-carbon composite material precursor prepared by the preparation method as claimed in any one of claims 5 to 8.

10. A secondary battery, characterized in that: It comprises a negative electrode, wherein the negative electrode contains the silicon-carbon composite material as claimed in claim 9.

Images