CN115101732A

CN115101732A - Composite silicon-based material and preparation method and application thereof

Info

Publication number: CN115101732A
Application number: CN202210738993.7A
Authority: CN
Inventors: 刘厅; 万远鑫; 孔令涌; 薛山; 朱成奔; 钟泽钦
Original assignee: Shenzhen Dynanonic Co ltd
Current assignee: Shenzhen Dynanonic Co ltd
Priority date: 2022-06-27
Filing date: 2022-06-27
Publication date: 2022-09-23

Abstract

The application discloses a composite silicon-based material and a preparation method and application thereof. The composite silicon-based material comprises a silicon-based body and a conductive carbon layer, wherein the silicon-based body is combined with the conductive carbon layer, and a buffer space is formed between the silicon-based body and the conductive carbon layer. According to the composite silicon-based material, the buffer space arranged between the conductive carbon layer and the surface of the silicon-based body can effectively relieve the deformation effect of the composite silicon-based material in the lithium storage process, so that the cycle performance of the composite silicon-based material is improved, and the capacity attenuation is reduced; and the conductive carbon layer effectively improves the conductivity and rate capability of the composite silicon-based material. In addition, the preparation method of the composite silicon-based material can ensure stable performance of the composite silicon-based material, has high efficiency and saves production cost.

Description

Composite silicon-based material and preparation method and application thereof

Technical Field

The application belongs to the technical field of negative electrode materials, and particularly relates to a composite silicon-based material and a preparation method and application thereof.

Background

Lithium ion batteries are widely used in many fields such as 3C electronic products, power cars and energy storage power stations due to their high energy density, small self-discharge, no memory effect and long cycle life.

With the rapid development of electric vehicles and large-scale energy storage devices, the demand for lithium ion batteries, which play a key role therein, is increasing. High energy density, long cycle life and high safety are the main indicators pursued by the next generation of lithium ion batteries. The current capacity of the current commercial lithium ion battery cathode material, namely graphite, is close to the theoretical capacity (375mAh/g), and is difficult to further improve, and the lithium intercalation potential of the graphite is very close to the deposition potential of lithium, so that the phenomenon of lithium precipitation is very easy to occur under the conditions of quick charging and low temperature environment, and potential safety hazards are caused. Therefore, the search for high-performance negative electrode materials becomes the key to the development of next-generation lithium ion batteries.

The silicon-based negative electrode attracts the attention of numerous researchers due to high theoretical specific capacity, meanwhile, the lithium intercalation potential of silicon is slightly higher than that of graphite, the safety is relatively higher, the silicon is rich in resources in the earth, the cost is low, and the silicon-based negative electrode is suitable for large-scale production. But the silicon-based material also faces a plurality of problems as the negative electrode of the next generation lithium ion battery: the most important problem to be solved is that the electrode material is pulverized or even dropped due to the severe volume expansion effect of silicon in the lithium storage process, so that the cycling stability of the electrode is poor; secondly, silicon belongs to a semiconductor, has poor intrinsic conductivity, and needs to be modified to a certain extent to improve the electrochemical performance; the SEI film on the silicon negative electrode is unstable, and the lower coulombic efficiency of the electrode further aggravates the capacity fading of the electrode.

Disclosure of Invention

The application aims to overcome the defects of the prior art and provide a composite silicon-based material and a preparation method thereof so as to solve the technical problems of serious volume expansion effect, poor conductivity and the like of the conventional silicon-based negative electrode material.

Another object of the present invention is to provide a negative electrode and a secondary battery including the same, which solve the problems of the conventional secondary battery, such as fast capacity degradation and unsatisfactory cycle performance.

To achieve the above object, according to a first aspect of the present application, there is provided a composite silicon-based material. The composite silicon-based material comprises a silicon-based body and a conductive carbon layer, wherein the conductive carbon layer is combined on the surface of the silicon-based body, and a buffer space is formed between the silicon-based body and the conductive carbon layer.

In a second aspect of the present application, a method for preparing a composite silicon-based material of the present application is provided. The preparation method of the composite silicon-based material comprises the following steps:

providing a silicon-based body;

forming a mold layer on the surface of the silicon-based body;

forming a conductive carbon layer on the outer surface of the mold layer;

and removing the mold layer to enable the conductive carbon layer to be combined on the surface of the silicon-based body, and forming a buffer space between the conductive carbon layer and the silicon-based body to obtain the composite silicon-based material.

In a third aspect of the present application, a negative electrode is provided. The cathode of the present application comprises the composite silicon-based material of the present application.

In a fourth aspect of the present application, a secondary battery is provided. This application includes the negative pole, and the negative pole is this application negative pole.

Compared with the prior art, the method has the following technical effects:

the composite silicon-based material combines the conductive carbon layer with the surface of the silicon-based body stably; the buffering space is arranged between the conductive carbon layer and the surface of the silicon-based body, and the buffering space can effectively relieve the volume expansion effect of the composite silicon-based material in the lithium storage process, so that the anti-deformation effect capability of the composite silicon-based material is effectively improved, and the cycle performance of the composite silicon-based material is improved; and the existence of the conductive carbon layer can effectively improve the conductivity of the composite silicon-based material. Therefore, the silicon-based body and the conductive carbon layer have the synergistic effect and the special buffer structure, so that the composite silicon-based material has the advantages of good structural stability, high cycle performance and rate capability and low capacity attenuation.

The preparation method of the composite silicon-based material can ensure that the prepared composite silicon-based material has the structural characteristics of the composite silicon-based material, and has high structural stability, deformation effect resistance and cycle performance. In addition, the preparation method of the composite silicon-based material can effectively ensure that the prepared composite silicon-based material has stable electrochemical performance and high efficiency, and saves the production cost.

The cathode contains the composite silicon-based material, so that the cathode has a stable structure, high cycle performance and rate performance and low capacity attenuation in the lithium storage process.

The secondary battery contains the cathode, so that the secondary battery has high specific capacity, high rate performance and excellent cycle performance.

Drawings

In order to more clearly illustrate the detailed description of the present application or the technical solutions in the prior art, the drawings needed to be used in the detailed description of the present application or the prior art description will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic structural diagram of a composite silicon-based material according to an embodiment of the present disclosure;

FIG. 2 is a block flow diagram of a method for preparing a composite silicon-based material according to an embodiment of the present disclosure;

FIG. 3 is a schematic flow chart of a method for preparing a composite silicon-based material according to an embodiment of the present application;

FIG. 4 is a graph of battery rate performance of an example of the present application assembled from composite silicon-based materials;

fig. 5 is a graph of the cycling performance of a cell assembled from composite silicon-based materials according to an example of the present application.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of and not restrictive on the broad application.

In this application, the term "and/or" describes an association relationship of associated objects, which means that there may be three relationships, for example, a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present application may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present application as long as it is scaled up or down according to the description of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In a first aspect, embodiments of the present application provide a composite silicon-based material. The composite silicon-based material comprises a silicon-based body and a conductive carbon layer, wherein the conductive carbon layer is combined on the surface of the silicon-based body, and a buffer space is arranged between the silicon-based body and the conductive carbon layer. Because the buffer space between the conductive carbon layer and the surface of the silicon-based body exists, when the composite silicon-based material in the embodiment of the application is in the lithium storage process, the buffer space provides an expansion space for the volume expansion of the silicon-based body, so that the volume expansion effect of the composite silicon-based material in the embodiment of the application in the lithium storage process is remarkably relieved, the composite silicon-based material in the embodiment of the application is endowed with a high deformation resistance effect, and the cycle performance of the composite silicon-based material is improved. Due to the existence of the conductive carbon layer, the conductivity of the composite silicon-based material is effectively improved, and the composite silicon-based material is endowed with high rate capability. Therefore, the composite silicon-based material provided by the embodiment of the application has the advantages of good structural stability, strong antibody volume deformation capacity, high cycle performance and rate performance and low capacity attenuation due to the synergistic effect of the silicon-based body and the conductive carbon layer and the special buffer structure.

In an embodiment, the conductive carbon layer and the silicon base are bonded by van der waals force and surface tension generated by the two, specifically by van der waals force and surface tension generated by the two opposite surfaces, and due to the bonding between the silicon base and the conductive carbon layer, the buffer space included in the composite silicon-based material according to the embodiment of the present invention is formed by van der waals force and surface tension of the two opposite surfaces of the silicon base and the conductive carbon layer. The conducting carbon layer combined by Van der Waals force and surface tension is stably combined with the silicon substrate, and the buffering space is endowed with elasticity, so that the buffering effect of the conducting carbon layer as the volume expansion of the silicon substrate is enhanced, the volume expansion effect of the composite silicon-based material in the lithium storage process is further relieved, and the high deformation resistance effect of the composite silicon-based material in the embodiment of the application is improved; after the composite silicon-based material stops storing lithium, the silicon-based composite material still keeps a complete sandwich structure without obvious deformation, and the cycle performance of the composite silicon-based material can be further remarkably improved.

In addition, the overall morphology or structural characteristics of the composite silicon-based material are determined based on the morphology, structure and the like of the silicon-based body and the conductive carbon layer contained in the composite silicon-based material in the embodiment of the application. In an embodiment, the silicon substrate has two opposite surfaces, and a conductive carbon layer is bonded to at least one of the two opposite surfaces, and specifically, the conductive carbon layer may be bonded to one of the two opposite surfaces of the silicon substrate by the van der waals force and the surface tension, or the conductive carbon layers may be bonded to the two opposite surfaces by the van der waals force and the surface tension.

In a further embodiment, the composite silicon-based material is structured as shown in fig. 1, wherein the silicon-based body is a silicon substrate 1, and conductive carbon layers 2 are respectively bonded to two opposite surfaces of the silicon substrate 1, and a buffer space 3 is formed between each conductive carbon layer 2 and the surface of the silicon-based body, i.e., the silicon substrate 1, by the combination of the van der waals force and the surface tension force.

The structural feature of the composite silicon-based material shown in fig. 1 is merely an example of one of the structures of the composite silicon-based material according to the embodiment of the present invention, and based on the above-mentioned combination relationship between the silicon-based body and the conductive carbon layer included in the composite silicon-based material according to the embodiment of the present invention, the composite silicon-based material according to the embodiment of the present invention may have other structures besides the structure shown in fig. 1. For example, the silicon substrate may be a pillar, and the conductive carbon layer is coated on the surface of the silicon substrate.

No matter what morphology is, a buffer space is formed between the silicon-based body and the conductive carbon layer in the structure of the composite silicon-based material in each embodiment, and the buffer space can provide a volume expansion space for the expansion of the silicon-based body, so that the structural stability of the composite silicon-based material is improved, the volume expansion deformation capacity of the composite silicon-based material is further improved, and the cycle performance of the composite silicon-based material is improved. Meanwhile, the conductive carbon layer can play a role in conductive modification in the composite silicon-based material, and after the conductive carbon layer forms the electrode active layer, the conductive carbon layer can form a conductive connection effect, so that the conductive performance of the composite silicon-based material is further improved, and the multiplying power performance of the composite silicon-based material is improved.

Based on the structure of the composite silicon-based material in each of the above embodiments, the size of the silicon-based body contained in the composite silicon-based material can be adjusted according to the requirements of practical applications, for example, when the silicon-based body is the silicon substrate 1 shown in fig. 1, the thickness of the silicon substrate 1 can be 5-200 μm.

In an embodiment, the silicon-based body contained in the composite silicon-based material, specifically, the material of the silicon substrate 1 shown in fig. 1, may include at least one of a simple substance and a silicon-based oxide, wherein the silicon-based oxide may be SiO _x SiO and SiO ₂ Etc., SiO _x X in (1) is 0.1 to 2. These silicon-based materials have high capacity.

In one embodiment, the thickness of the conductive carbon layer included in the composite silicon-based material may be 50nm to 5 μm. By controlling the thickness of the conductive carbon layer, the mechanical property of resisting the volume expansion of the silicon-based body can be improved, the conductivity of the conductive carbon layer can be improved, the resistance of the composite silicon-based material can be reduced, and the rate capability of the composite silicon-based material can be improved.

In a specific embodiment, the material of the conductive carbon layer may include at least one of graphene, amorphous carbon, carbon nanotubes, and graphitic carbon. The materials have excellent conductivity, for example, when the materials are graphene, the conductivity of the materials is higher by several orders of magnitude than that of redox graphene, activated carbon and the like, so that the conductivity of the electrode can be greatly improved, and the electrochemical performance of the electrode material is further improved. And the conductive carbon layer formed by the materials has good mechanical property, so that the capacity of resisting the volume expansion of the silicon-based body is improved, and the structural stability and the cycle performance of the composite silicon-based material are improved.

The buffer space contained in the composite silicon-based material is formed between the conductive carbon layer and the silicon-based body, and can be formed by combining Van der Waals force and surface tension. In one embodiment, the thickness of the buffer space along the vertical direction of the conductive carbon layer and the surface of the silicon-based body may be 50nm-5 μm. In addition, the appearance of the buffer space can be designed by the appearance of the combination surface of the conductive carbon layer and the silicon substrate. In one embodiment, the buffer space may be a buffer space layer structure when the surface of the conductive carbon layer and the silicon substrate combined with each other has a certain extended plane or curved surface. Specifically, when the composite silicon-based material is the silicon substrate shown in fig. 1, the buffer space formed between the silicon substrate and the conductive carbon layer is in the form of a buffer space layered structure. At this time, the thickness of the buffer space layer may be 50nm-5 μm. The buffer space in the range fully plays a role in volume expansion buffer of the silicon-based material, and the composite silicon-based material is endowed with high cycle performance due to the structural stability.

According to the embodiments, the silicon-based body and the conductive carbon layer contained in the composite silicon-based material provided by the embodiment of the application have synergistic interaction, so that the conductive performance of the composite silicon-based material can be improved, meanwhile, the deformation effect of the silicon-based body in the lithium storage process is effectively relieved by the special buffer structure, and the composite silicon-based material provided by the embodiment of the application has good structural stability, high cycle performance and rate capability and low capacity attenuation under the combined action of the silicon-based body and the conductive carbon layer. And the corresponding electrochemical performance of the composite silicon-based material in the embodiment of the application can be improved by controlling and adjusting the structural morphology, the material and the thickness of the silicon-based body and the conductive carbon layer, and forming a buffer space between the silicon-based body and the conductive carbon layer.

In a second aspect, an embodiment of the present application further provides a preparation method of the composite silicon-based material of the embodiment of the present application. The preparation method of the composite silicon-based material in the embodiment of the application has the process flows shown in fig. 2 and 3, and comprises the following steps:

s01: providing a silicon-based body;

s02: forming a mold layer on the surface of the silicon-based body;

s03: forming a conductive carbon layer on the outer surface of the mold layer;

s04: and removing the mold layer to enable the conductive carbon layer to be combined on the surface of the silicon-based body, and forming a buffer space between the conductive carbon layer and the silicon-based body to obtain the composite silicon-based material.

In step S01, the silicon substrate may be, for example, the silicon substrate 1 shown in fig. 1, as the silicon substrate included in the composite silicon-based material according to the embodiment of the present application. Thus, the morphology and material of the silicon base body in step S01 are as described above for the silicon base body comprised in the composite silicon-based material of the example of the present application.

The mold layer formed in step S02 is a mold layer for forming the buffer space contained in the composite silicon-based material according to the embodiment of the above application, specifically, the buffer space 3 shown in fig. 1. Therefore, it needs to be removed in step S04. The material of the mold layer is within the scope of the disclosure of the present specification as long as it can be removed in step S04 without affecting the silicon-based body and the conductive carbon layer. In one embodiment, the material of the mold layer is any one of a metal and a metal oxide, and in another embodiment, the metal material may include any one of aluminum, iron, nickel, copper, zinc, and the like, or an alloy of at least two of the metals, and then the metal oxide may be a corresponding metal oxide of the metals. The metal or metal oxide facilitates the formation of the mold layer, is easily removed, and does not adversely affect the silicon-based body and the conductive carbon layer. Of course, the material may be other materials based on the function of the mold layer.

When the material of the mold layer is a metal material, the mold layer may be formed by deposition, such as magnetron sputtering, plasma spraying, chemical vapor deposition, electrochemical deposition, and the like. When these deposition methods are used, the deposition temperature may be 25 to 1200 ℃ and the deposition time may be 0.1 to 24 hours.

In addition, the thickness of the mold layer may be controlled by controlling the conditions of the formed mold layer, for example, the thickness of the mold layer may be controlled to be 5 to 200 μm.

In step S03, the formed conductive carbon layer is a conductive carbon layer contained in the composite silicon-based material according to the embodiment of the above application, and specifically, may be the conductive carbon layer 2 shown in fig. 1. Therefore, the morphology and material of the conductive carbon layer in step S03 are as described above for the conductive carbon layer included in the composite silicon-based material of the example of the present application.

The method of forming the conductive carbon layer in step S03 may be selected according to the properties of the material of the conductive carbon layer, and in an embodiment, the method of forming the conductive carbon layer on the outer surface of the mold layer includes at least one of chemical vapor deposition and spray pyrolysis.

When the conductive carbon layer is formed by using the chemical vapor deposition method, in an embodiment, the method of forming the conductive carbon layer on the outer surface of the mold layer is a chemical vapor deposition method including the steps of:

and carrying out thermal cracking treatment on the precursor carbon source to generate carbon, and growing in situ on the surfaces of the mold layer and the silicon-based body to form a conductive carbon layer.

The precursor carbon source and the carrier gas can be introduced into the reaction chamber together, wherein the flow rate of the precursor carbon source can be 50-400mm/Hg, and the flow rate ratio of the carrier gas can be 1: 2-1: 10 hydrogen and argon mixture. The temperature for forming the conductive carbon layer such as the graphene carbon layer by in-situ growth can be 700-1200 ℃, and the time can be 0.5-6 h. The distance between the precursor carbon source and the surface of the mold layer at the thermal cracking treatment position can be 15-25cm, so that the temperature of the two temperature zones is well controlled, and the conductive carbon layer grows on the surface of the mold layer in a uniform nucleation mode. In addition, the precursor carbon source can be gaseous or/and powder. In a specific embodiment, the precursor carbon source may include at least one of methane, ethylene, acetylene, ethanol, benzene, toluene, polymethyl methacrylate, polypropylene, polyethylene, polystyrene, polyethylene glycol, and camphor pellets. The thickness of the conductive carbon layer is adjusted by the relevant conditions of the chemical vapor deposition method, such as the flow rate of the precursor carbon source, the deposition interval, the deposition temperature and time, and the like.

In step S04, after the mold layer is removed, the conductive carbon layer is bonded to the surface of the base body while a gap is formed between the silicon base body and the conductive carbon layer to form a buffer space contained in the composite silicon-based material. In particular a buffer space 3 as shown in fig. 1. In the embodiment, due to the characteristics of the silicon substrate and the conductive carbon layer, the silicon substrate and the conductive carbon layer are combined by van der waals force and surface tension of the two opposite surfaces, and the buffer space is formed between the silicon substrate and the conductive carbon layer. When the mold layer is a metal layer, the method for removing the mold layer comprises an acid etching method. The buffer space is formed, for example, by immersing the composite material deposited with the conductive carbon layer in an acid solution so that the metal reacts with the acid to remove the metal mold layer. In an embodiment, the acid solution may include at least one of nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid. It should be understood, however, that the acid solution is only used to remove the mold layer and should not adversely damage the conductive carbon layer and the silicon-based body.

The preparation method of the composite silicon-based material in the embodiment of the application can ensure that the prepared composite silicon-based material has the structural characteristics of the composite silicon-based material in the embodiment of the application, and has high structural stability and cycle performance. In addition, the preparation method of the composite silicon-based material can effectively ensure that the prepared composite silicon-based material has stable electrochemical performance and high efficiency, and saves the production cost.

In a third aspect, an embodiment of the present application further provides a negative electrode. The negative electrode of the embodiment of the application contains the composite silicon-based material of the embodiment of the application. The composite silicon-based material can be directly used as a negative electrode. Thus, the negative electrode of the embodiment of the application has a stable structure, high cycle performance and rate performance and low capacity attenuation in the lithium storage process.

In a fourth aspect, embodiments of the present application further provide a secondary battery. The secondary battery of the embodiment of the present application includes necessary components such as a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and of course, includes other necessary or auxiliary components. The negative electrode plate is the negative electrode in the embodiment of the present application, that is, the negative electrode plate contains the composite silicon-based material in the embodiment of the present application. Because the secondary battery in the embodiment of the application contains the composite silicon-based material in the embodiment of the application, the secondary battery in the embodiment of the application has high specific capacity, high rate performance and excellent cycle performance.

The composite silicon-based material and the preparation method thereof according to the embodiments of the present application will be illustrated by a plurality of specific examples.

1. The embodiment of the composite silicon-based material and the preparation method thereof comprises the following steps:

example A1

The embodiment provides a composite silicon-based material and a preparation method thereof. The composite silicon-based material comprises a silicon wafer and graphene layers combined on two surfaces of the silicon wafer, a sandwich structure of the graphene layer/the silicon wafer/the graphene layer is formed, the graphene layers are combined with the surface of the silicon wafer, and a buffer space is formed between the graphene layers and the surface of the silicon wafer.

The preparation method of the composite silicon-based material comprises the following steps:

s1, preparing a copper/silicon/copper precursor: selecting a silicon wafer with the thickness of 8 mu m as a raw material, and performing metal pre-deposition on two sides of the silicon wafer in a cathode magnetron sputtering mode: selecting a copper sheet with the size of phi 60mm as a target material, wherein the target base distance is 90mm, and the vacuum degree is 3 multiplied by 10 ^-4 Pa, the working air pressure (Ar) is 2Pa, the direct-current power supply sputtering power is 20W, the sputtering time is 100s, and the thickness of the pre-deposited copper layer is 50 mu m;

s2, preparing a graphene/copper/silicon/copper/graphene intermediate: uniformly growing a graphene layer on the surface of the precursor metal substrate prepared in the step S1 by adopting a chemical vapor deposition method, wherein the pyrolytic carbon source of graphene is methane, and the flow velocity ratio is 1: 2, introducing the hydrogen-argon mixed gas, introducing methane gas with the flow rate of 20mm/Hg simultaneously, placing the precursor in the middle of a tubular furnace chamber, and reacting for 5 hours at 800 ℃; the thickness of the conductive carbon layer on the surface of the copper layer was 50 nm.

S3, constructing a graphene-silicon-graphene hollow structure: and (4) carrying out acid etching treatment on the intermediate prepared in the step S2 by using 1mol/L sulfuric acid, soaking the intermediate in the sulfuric acid for 6 hours, removing the copper layer of the interlayer, and then carrying out centrifugal treatment to obtain the composite silicon-based material of the embodiment. The thickness of the buffer space between the graphene layer and the silicon substrate body was measured to be 500 nm.

Example A2

The embodiment provides a composite silicon-based material and a preparation method thereof. The composite silicon-based material comprises a silicon chip and a carbon nano tube layer combined on two surfaces of the silicon chip, a sandwich structure of the carbon nano tube layer/the silicon chip/the carbon nano tube layer is formed, the carbon nano tube layer is combined with the surface of the silicon chip, and a buffer space is formed between the carbon nano tube layer and the surface of the silicon chip.

s1, preparing a nickel/silicon/nickel precursor: selecting a silicon wafer with the thickness of 20 mu m as a raw material, and performing metal pre-deposition on two sides of the silicon wafer in a chemical vapor deposition mode: selecting a nickel sheet with the size of phi 40mm as a target electrode and the vacuum degree of 5 multiplied by 10 ^-3 Pa, the working pressure (Ar) is 44Pa, the current of the microwave filament is 0.2A, the regulation is started from the initial voltage of 60V until the glow turns blue gradually, which indicates that nickel ions enter the plasma, and the voltage is maintained to be deposited for 2h in a steady state at 900V. The thickness of the nickel layer pre-deposited was 80 μm.

S2, preparing a carbon nanotube/nickel/silicon/nickel/carbon nanotube intermediate: uniformly growing a carbon nanotube layer on the surface of the precursor metal substrate prepared in the step S1 by adopting a chemical vapor deposition method, wherein the pyrolytic carbon source of the carbon nanotubes is ethanol, the ethanol and the precursor are respectively placed in an upper heating furnace chamber and a middle heating furnace chamber, and the flow velocity ratio is 1: 5, reacting for 12 hours at 600 ℃ in the process of introducing hydrogen and argon mixed gas; the thickness of the conductive carbon layer on the surface of the nickel layer is 3 μm.

S3, constructing a carbon nanotube-silicon-carbon nanotube hollow structure: and (4) carrying out acid etching treatment on the intermediate prepared in the step S2 by using 1mol/L sulfuric acid and 2mol/L hydrochloric acid mixed acid solution, soaking the intermediate in the mixed acid solution for 9 hours, removing a nickel layer of the intermediate layer, and then carrying out centrifugal treatment to obtain the composite silicon-based material of the embodiment. The thickness of the buffer space between the carbon nanotube layer and the silicon substrate body is 4 μm.

Example A3

The embodiment provides a composite silicon-based material and a preparation method thereof. The composite silicon-based material comprises a silicon chip and graphene layers combined on two surfaces of the silicon chip, a sandwich structure of amorphous carbon/silicon chip/amorphous carbon is formed, the amorphous carbon layers are combined with the surface of the silicon chip, and a buffer space is formed between the amorphous carbon layers and the surface of the silicon chip.

s1, preparing a zinc oxide/silicon/zinc oxide precursor: selecting a silicon wafer with the thickness of 150 mu m as a raw material, and performing metal pre-deposition on two sides of the silicon wafer in an electrochemical deposition mode: firstly, preparing zinc nitrate solution with the solubility of 3mol/L, taking a silicon wafer as a working electrode, and carrying out a three-electrode system at the temperature of 6mA cm ^-1 Constant current deposition for 600s at the current of (2);

s2, preparing an amorphous carbon/zinc oxide/silicon/zinc oxide/amorphous carbon intermediate: and (2) uniformly growing an amorphous carbon layer on the surface of the precursor metal substrate prepared in the step (S1) by adopting a chemical vapor deposition method, wherein a pyrolytic carbon source of the amorphous carbon is camphor balls, the camphor balls and the precursor are respectively placed in an upper heating furnace chamber and a middle heating furnace chamber, and the flow velocity ratio is 1: 8, reacting for 16 hours at 1000 ℃ in the process of introducing hydrogen-argon mixed gas; the thickness of the conductive carbon layer on the surface of the zinc oxide layer was set to 800 nm.

S3, constructing an amorphous carbon-silicon-amorphous carbon hollow structure: and (4) carrying out acid etching treatment on the intermediate prepared in the step S2 by using 5mol/L nitric acid solution, soaking the intermediate in the nitric acid solution for 12 hours, removing the zinc oxide layer of the intermediate layer, and then carrying out centrifugal treatment to obtain the composite silicon-based material of the embodiment. The buffer spacing between the amorphous carbon layer and the silicon based body was found to be 1.2 μm.

Example A4

The embodiment provides a composite silicon-based material and a preparation method thereof. The composite silicon-based material comprises a silicon chip and graphene layers combined on two surfaces of the silicon chip, a sandwich structure of a graphitized carbon layer/silicon chip/graphitized carbon layer is formed, the graphitized carbon layer is combined with the surface of the silicon chip, and a buffer space is formed between the graphitized carbon layer and the silicon chip.

s1, preparing an iron/silicon/iron precursor: selecting a silicon wafer with the thickness of 80 mu m as a raw material, and collectingPerforming metal pre-deposition on two sides of a silicon wafer in a cathode magnetron sputtering mode: selecting an iron sheet with the size of phi 50mm as a target material, wherein the target base distance is 90mm, and the vacuum degree is 5 multiplied by 10 ^-4 Pa, working air pressure (Ar) of 4.5Pa, direct current power supply sputtering power of 30W, sputtering time of 300s and thickness of the iron layer to be deposited of 100 mu m.

S2, preparing a graphitized carbon/iron/silicon/iron/graphitized carbon intermediate: and (3) uniformly growing a graphitized carbon layer on the surface of the precursor metal matrix prepared in the step S1 by adopting a spray pyrolysis method, wherein a pyrolysis carbon source of the graphitized carbon is polystyrene, and the flow velocity ratio is 1: 6, introducing the hydrogen-argon mixed gas, introducing acetylene gas with the flow rate of 50mm/Hg simultaneously, putting the precursor into the middle of a tubular furnace chamber, and reacting for 15 hours at 1200 ℃; the thickness of the conductive carbon layer on the surface of the iron layer was set to 500 nm.

S3, constructing a graphitized carbon-silicon-graphitized carbon hollow structure: and (4) carrying out acid etching treatment on the intermediate prepared in the step S2 by using 4mol/L phosphoric acid, soaking the intermediate in sulfuric acid for 16h, removing an iron thin layer in an intermediate layer, and then carrying out centrifugal treatment to obtain the composite silicon-based material of the embodiment. The thickness of the buffer space between the graphitized carbon layer and the silicon substrate body was measured to be 1 μm.

Comparative example A1

This comparative example provides a composite silicon-based material and a method of making the same. The composite silicon-based material comprises a silicon wafer and graphene layers combined on two surfaces of the silicon wafer to form a sandwich structure of graphene layer/silicon wafer/graphene layer, and compared with the composite silicon-based material in the embodiment A1, the graphene layers are tightly combined on the surfaces of the silicon wafers, namely, no buffer space exists between the graphene layers and the silicon wafers.

Comparative example A2

This comparative example provides a silicon carbon composite electrode material. The carbon composite electrode material comprises silicon particles and a carbon coating layer coated on the surfaces of the silicon particles. The silicon-carbon composite electrode material is prepared by the following method:

silicon-based powder and glucose powder are mixed according to a molar ratio of 20: 1, transferring the mixture to a hydrothermal reaction kettle for hydrothermal reaction at 200 ℃ for 12 hours, and centrifuging and cleaning to obtain the silicon-carbon composite electrode material. However, since there is no obvious buffer layer between the silicon and the carbon, the volume expansion effect of the silicon can make the silicon expand the carbon layer and completely separate from the carbon layer in the recharging and discharging process, the composite effect of the silicon completely fails, and the capacity of the electrode can be rapidly attenuated.

2. The lithium ion battery comprises the following embodiments:

the present examples B1 to B4 and comparative examples B1 to B2 respectively provide a lithium ion battery. The lithium ion batteries are assembled into the lithium ion batteries according to the following methods:

1) positive plate:

according to NMP: LiFePO ₄ : super P: PVDF is mixed according to the mass ratio of 100:93:2:3, the mixing mode is ball milling, and the ball milling time is 60 min; the rotation speed is set to be 30 Hz; the anode plate is prepared by the operations of homogenizing, coating, drying and cutting, and is baked in a vacuum oven at 100 ℃ to remove trace water.

2) And (3) negative plate: negative plates were cut from the composite silicon-based materials provided in examples a1 through a6 and comparative examples a1 through a2, respectively.

3) A diaphragm: a Polyethylene (PE) separator was used.

4) Electrolyte: LiPF with electrolyte of 1mol/L ₆ The solvent consists of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1: 1.

5) Assembling the secondary battery:

and assembling the positive plate, the negative plate, the electrolyte and the diaphragm into the lithium ion soft package battery according to the lithium ion battery assembly requirement.

3, electrochemical performance of the lithium ion battery:

the electrochemical performance of the lithium secondary batteries comprising examples B1 to B4 and comparative examples B1 to B2 was tested under the following test conditions:

the results of the relevant electrochemical performance test of the lithium secondary battery are shown in table 1 below.

TABLE 1

Among them, the battery rate curves and cycle curves provided in example B1 and comparative example B1 are shown in fig. 4 and 5, respectively. As can be seen from Table 1 and FIGS. 4 and 5, the composite silicon-based material of the present application can effectively improve the electrochemical performance of the silicon electrode, and can be stabilized at about 80% after 500 cycles. In contrast to the

documents

1 and 2, only simple carbon coating is performed, so that the cycling stability and coulombic efficiency of the electrode can be improved to a certain extent in the early stage, and the capacity attenuation is still serious in long cycle, which is mainly because tight coating does not provide a buffer space between silicon and carbon, and the carbon layer is broken due to the serious silicon volume expansion effect in long cycle, so that the composite effect cannot be achieved.

The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not to be construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, and these are all within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A composite silicon-based material, characterized by: the conductive carbon layer is combined on the surface of the silicon substrate, and a buffer space is formed between the silicon substrate and the conductive carbon layer.

2. The composite silicon-based material of claim 1, wherein: the silicon-based body is provided with two opposite surfaces, and the conductive carbon layer is combined on at least one surface; and/or

The thickness of the buffer space is 50nm-5 μm along the vertical direction of the conductive carbon layer and the surface of the silicon substrate body.

3. A composite silicon-based material according to any one of claims 1 to 2, characterised in that: the silicon substrate body is a silicon substrate, and the two opposite surfaces of the silicon substrate are respectively combined with the conductive carbon layers; and/or

The silicon-based body and the conductive carbon layer are combined through van der waals force and surface tension of the two opposite surfaces.

4. A composite silicon-based material according to claim 3, wherein: the thickness of the silicon substrate is 5-200 μm.

5. Composite silicon-based material according to any one of claims 1 to 2 or 4, characterized in that: the material of the silicon-based body comprises at least one of a silicon simple substance and a silicon-based oxide; and/or

The material of the conductive carbon layer comprises at least one of graphene, amorphous carbon, carbon nanotubes and graphitic carbon; and/or

The thickness of the conductive carbon layer is 50nm-5 μm.

6. The preparation method of the composite silicon-based material is characterized by comprising the following steps of:

providing a silicon-based body;

forming a mold layer on the surface of the silicon-based body;

forming a conductive carbon layer on the outer surface of the mold layer;

7. The method of manufacturing according to claim 6, characterized in that: the material of the mold layer comprises any one of metal and metal oxide; and/or

The thickness of the mould layer is 5-200 μm; and/or

The silicon-based body is provided with two opposite surfaces, and the mold layer is formed on at least one surface;

the method for forming the conductive carbon layer on the outer surface of the mold layer includes at least one of chemical vapor deposition and pyrolysis spraying.

8. The method for preparing a mold according to claim 7, wherein the method for forming the conductive carbon layer on the outer surface of the mold layer is a chemical vapor deposition method comprising the steps of:

and carrying out thermal cracking treatment on the precursor carbon source to generate carbon, and growing in situ on the outer surface of the mold layer to form the conductive carbon layer.

9. The method of claim 8, wherein:

the precursor carbon source comprises at least one of methane, ethylene, acetylene, ethanol, benzene, toluene, polymethyl methacrylate, polypropylene, polyethylene, polystyrene and polyethylene glycol; and/or

The precursor carbon source and carrier gas are introduced into the thermal cracking environment together, and the flow rate of the precursor carbon source is 50-400 mm/Hg; and/or

The distance between the precursor carbon source and the surface of the mold layer at the thermal cracking treatment is 15-25 cm; and/or

The temperature for forming the conductive carbon layer by in-situ growth is 700-1200 ℃, and the time is 0.5-6 h.

10. The production method according to any one of claims 7 to 9, characterized in that:

the mold layer is a metal or metal oxide layer, and the method for forming the mold layer on the surface of the silicon-based body comprises at least one of cathode magnetron sputtering, plasma spraying, chemical vapor deposition and electrochemical deposition; and/or

The mold layer is a metal or metal oxide layer, and the method for removing the mold layer comprises an acid etching method.

11. A negative electrode, characterized by: comprising the composite silicon-based material according to any one of claims 1 to 5 or produced by the production method according to any one of claims 6 to 10.

12. A secondary battery comprising a negative electrode, characterized in that: the negative electrode is the negative electrode according to claim 11.