CN112687864B

CN112687864B - Silica anode material and preparation method thereof

Info

Publication number: CN112687864B
Application number: CN202011565945.XA
Authority: CN
Inventors: 钟泽钦; 万远鑫; 孔令涌; 任望保; 朱成奔; 张於财; 钟文
Original assignee: Foshan Dynanonic Technology Co ltd; Shenzhen Dynanonic Co ltd
Current assignee: Foshan Dynanonic Technology Co ltd; Shenzhen Dynanonic Co ltd
Priority date: 2020-12-25
Filing date: 2020-12-25
Publication date: 2022-03-25
Anticipated expiration: 2040-12-25
Also published as: CN112687864A

Abstract

The application relates to the technical field of battery cathode materials, and provides a silica cathode material and a lithium ion battery. The silicon-oxygen negative electrode material has a core-shell structure and comprises an inner core, a middle layer and an outer shell, wherein the middle layer is coated on the surface of the inner core, and the outer shell is coated on the surface of the middle layer; the material of the inner core comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals increases in a gradient manner along the direction from the center of the inner core to the surface layer of the inner core; the intermediate layer is made of silicon carbide; the outer shell layer includes a carbon layer. The negative electrode core material with the characteristics can guide huge volume expansion stress generated in the lithium embedding process to be released outwards through silicon microcrystals which are distributed in the amorphous silicon oxide main body material and have gradually changed sizes, so that the volume expansion of the silicon-based negative electrode material is inhibited, the irreversible capacity increase caused by the volume expansion is reduced, and the cycle life of the silicon-based negative electrode material is effectively prolonged.

Description

Silica anode material and preparation method thereof

Technical Field

The application belongs to the technical field of battery cathode materials, and particularly relates to a silica cathode material and a preparation method thereof.

Background

The lithium ion secondary battery is the most competitive battery of the new generation, is called as green and environment-friendly energy, and is the first choice technology for solving the current environmental pollution problem and energy problem. In recent years, 10 lithium ion secondary batteries have had great success in the field of high-energy batteries, but consumers still desire batteries with higher overall performance to come out, depending on research and development of new electrode materials and electrolyte systems.

The theoretical reversible capacity of the negative electrode material silicon oxide reaches 2007mAh/g, the cycle performance is excellent, and the negative electrode material is a key negative electrode material for improving the energy density. However, in the process of repeatedly inserting and extracting lithium ions, the crystal structure of the common silicon oxide is easily collapsed along with severe volume expansion and contraction, and irreversible substances are increased after the particles are crushed, so that the reversible capacity is continuously reduced, and the cycle performance of the battery is deteriorated.

Disclosure of Invention

The application aims to provide a silica negative electrode material, a preparation method thereof and a lithium ion battery, and aims to solve the problems that reversible capacity is continuously reduced and the cycle performance of the battery is deteriorated due to volume expansion and contraction of the existing negative electrode material, namely, silicon monoxide, in the process of lithium intercalation and deintercalation.

In order to achieve the purpose of the application, the technical scheme adopted by the application is as follows:

the first aspect of the application provides a silicon-oxygen anode material, which has a core-shell structure and comprises an inner core, a middle layer coated on the surface of the inner core, and an outer shell layer coated on the surface of the middle layer;

the material of the inner core comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals increases in a gradient manner along the direction from the center of the inner core to the surface layer of the inner core;

the intermediate layer is made of silicon carbide;

the outer shell layer includes a carbon layer.

In some embodiments, the grain size of the silicon crystallites of the core skin layer is designated as D_outWill beThe grain size of the silicon crystallite at the depth of 500nm from the surface layer of the inner core is named as D_in，D_outAnd D_inSatisfies the following conditions: d is not less than 0_in/D_out＜1。

In some embodiments, the size of the kernel is: d50 is more than or equal to 0.5 mu m and less than or equal to 20 mu m, D10/D50 is more than or equal to 0.3, and D90/D50 is more than or equal to 2.

In some embodiments, the amorphous silicon oxide is SiO_x，1≤x≤1.3。

In some embodiments, the silicon crystallites are 1-10nm in size.

In some embodiments, the intermediate layer has a thickness of 0.5-3 nm.

In some embodiments, the thickness of the outer shell layer is 1-50 nm.

In some embodiments, the silica anode material has a BET specific surface area of 1 to 10m²/g。

In some embodiments, the carbon layer is prepared from an organic carbon source by chemical vapor carbon deposition or in situ carbonization.

In some embodiments, the carbon layer is prepared by mixing a raw material solid phase or liquid phase comprising an organic carbon source and a silicon-based anode material and then performing in-situ carbonization.

In some embodiments, the material of the carbon layer includes an organic polymer and a conductive agent.

The second aspect of the present application provides a preparation method of a silicon-oxygen negative electrode material, including:

taking silicon monoxide and a carbon source as raw materials, preparing a core-shell structure with an inner core, a middle layer and an outer shell under a dynamic heat preservation condition,

wherein the middle layer is coated on the surface of the inner core, the outer shell layer is coated on the surface of the middle layer,

the material of the inner core comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals increases in a gradient manner along the direction from the center of the inner core to the surface layer of the inner core; the intermediate layer is made of silicon carbide.

In some embodiments, a core-shell structure having an inner core, an intermediate layer, and an outer shell is prepared from silica and a carbon source under a dynamic thermal insulation condition, comprising:

dynamically preserving the temperature of the silicon monoxide at the temperature of 700-1300 ℃ in an inert atmosphere, and introducing a carbon source to prepare the core-shell structure.

dynamically preserving the temperature of the silicon monoxide at the temperature of 700-1300 ℃ in an inert atmosphere to obtain an inner core; and introducing a carbon source to continue reacting, and preparing the intermediate layer and the shell layer on the surface of the inner core to obtain the core-shell structure.

heating the silicon monoxide and a carbon source under the conditions of the temperature of 700-1000 ℃ in an inert atmosphere, and preparing an outer shell layer on the surface of the silicon monoxide; and then raising the temperature to 1000-1300 ℃ for dynamic heat preservation, forming the silica into a core material to obtain a core, and forming a SiC intermediate layer between the core and the shell layer.

In some embodiments, the method of preparing the crust layer on the surface of the silica is:

and placing the silicon monoxide in a non-oxygen atmosphere, and carrying out chemical vapor carbon deposition or in-situ carbonization on an organic carbon source to prepare the shell layer.

mixing an organic carbon source with the solid phase or the liquid phase of the silicon oxide, and then carrying out in-situ carbonization to form on the surface of the silicon oxide to prepare the shell layer.

mixing a solid phase or a liquid phase of a conductive polymer comprising an organic polymer and a conductive agent, and carbonizing the mixture in situ to form the mixture on the surface of the silicon oxide to prepare the shell layer.

In some embodiments, the method when preparing the crust layer on the surface of the silica is: when the shell layer is prepared by chemical vapor deposition or in-situ carbonization in a non-oxygen atmosphere and by adopting an organic carbon source, the organic carbon source is selected from at least one or more of alkanes, alkenes and alkynes with the carbon concentration of C1-C4, and the temperature of the chemical vapor deposition or in-situ carbonization is 700-1300 ℃.

In some embodiments, the method when preparing the crust layer on the surface of the silica is: mixing an organic carbon source with the solid phase or the liquid phase of the silicon oxide, and then carrying out in-situ carbonization on the surface of the silicon oxide to obtain a shell layer, wherein the organic carbon source is selected from one or more of petroleum-based asphalt, coal oil-based asphalt, starch, glucose, polyethylene glycol and polyvinyl alcohol, and the temperature of the in-situ carbonization is 700-1300 ℃.

In some embodiments, the method when preparing the crust layer on the surface of the silica is: mixing a conductive polymer solid phase or liquid phase comprising an organic polymer and a conductive agent, and in-situ carbonizing the mixture to form an outer shell layer on the surface of the silica, wherein the organic polymer is selected from the group consisting of₂-CF₂]_nAn organic substance of the structure containing (C)₆H₇O₆Na)_nOrganic matter of structure [ C ]₆H₇O₂(OH)₂OCH₂COONa]_nHas the structure of [ C ]₃H₄O₂]_nHas the structure of [ C ]₃H₃O₂M]_nHas the structure of (C)₃H₃N)_nThe organic matter, the amide organic matter, the polyimide organic matter containing imide ring-CO-N-CO-on the main chain and one or more polymers in polyvinylpyrrolidone, wherein M is alkali metal, and the organic polymer accounts for 0.1-20 wt% of the total weight of the silicon-oxygen negative electrode material.

In a third aspect, the present application provides a lithium ion battery, including a negative electrode, where the negative electrode includes a negative electrode material, and the lithium ion battery is characterized in that: the negative electrode material is the silicon-oxygen negative electrode material of the first aspect or the silicon-oxygen negative electrode material prepared by the method of the second aspect.

The silicon-oxygen anode material provided by the application has a core-shell structure, wherein the core material of the core-shell structure comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals is increased in a gradient manner along the direction from the center of the core to the surface layer of the core. The negative electrode core material with the characteristics can guide huge volume expansion stress generated in the lithium embedding process to be released outwards through silicon microcrystals which are distributed in the amorphous silicon oxide main body material and have gradually changed sizes, so that the volume expansion of the silicon-based negative electrode material is reduced, the irreversible capacity increase caused by the volume expansion is reduced, and the service life of the silicon-based negative electrode material is effectively prolonged. Simultaneously, the setting improves the bonding strength of shell layer at the kernel surface through the SiC material at the intermediate level between kernel and the shell layer, makes the difficult peeling off of shell carbon layer to make the shell layer have anti spalling, thereby make the shell carbon layer can provide sufficient electric conductivity, and then arouse the capacity performance of silica material, thereby restrain the problem of cycle in-process later stage electric conductivity variation. Therefore, the silicon-oxygen negative electrode material provided by the application can provide enough reversible capacity and can ensure enough cycling stability. When the silicon-oxygen negative electrode material is used as a lithium ion battery negative electrode independently or after being compounded with graphite, particularly as a negative electrode material of a non-aqueous electrolyte secondary lithium ion battery, the silicon-based negative electrode material has the characteristics of high capacity and long cycle.

According to the preparation method of the silicon-oxygen cathode material, the silicon monoxide and the carbon source are used as raw materials, a dynamic heat preservation method is adopted, the middle layer and the outer shell layer which are coated on the surface of the inner core are formed on the surface of the inner core comprising the amorphous silicon oxide and the silicon microcrystal, and the bonding capacity of the outer shell layer on the surface of the inner core is effectively enhanced. Wherein, the size of the silicon microcrystal is increased in a gradient manner along the direction from the center of the inner core to the surface layer of the inner core. The obtained silicon-oxygen negative electrode material can guide huge volume expansion stress generated in the lithium embedding process to be released outwards, so that the negative electrode material is influenced by volume expansion, and the silicon-oxygen negative electrode material is endowed with good cycle performance and conductivity. In addition, the method provided by the application has the advantages that the process conditions are easy to control, and the stable structure and performance of the composite silicon-based negative electrode material can be ensured.

The negative electrode provided by the application contains the silicon-oxygen negative electrode material, so that the formed negative electrode can provide enough reversible capacity and can ensure enough cycling stability. When the silica negative electrode material is used as a lithium ion battery negative electrode alone or after being compounded with graphite, particularly as a negative electrode material of a non-aqueous electrolyte secondary lithium ion battery, the battery has the characteristics of high capacity and long cycle.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

Fig. 1 is a schematic structural diagram of a silicon-oxygen negative electrode material provided in an embodiment of the present application.

Wherein, in the figures, the respective reference numerals:

1-inner core 2-middle layer 3-outer shell.

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 the present application and are not intended to limit the present application.

In this application, the term "and/or" describes an association relationship of associated objects, meaning that there may be three relationships, e.g., 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.

As shown in fig. 1, a first aspect of the embodiments of the present application provides a silicon-oxygen anode material, which is used as a battery anode material, in particular, as a lithium ion battery anode material.

The silicon-oxygen negative electrode material provided by the embodiment of the application has a core-shell structure and comprises an inner core 1, an intermediate layer 2 coated on the surface of the inner core 1 and an outer shell layer 3 coated on the surface of the intermediate layer 2;

wherein, the material of the inner core 1 comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals is increased in a gradient manner along the direction from the center of the inner core 1 to the surface layer of the inner core 1;

the material of the middle layer 2 is silicon carbide;

the envelope layer 3 comprises a carbon layer.

The silicon-oxygen anode material provided by the embodiment of the application has a core-shell structure, wherein the core material of the core-shell structure comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals is increased in a gradient manner along the direction from the center of the core 1 to the surface layer of the core 1. The negative electrode core material with the characteristics can guide huge volume expansion stress generated in the lithium embedding process to be released outwards through silicon microcrystals which are distributed in the amorphous silicon oxide main body material and have gradually changed sizes, so that the volume expansion of the silicon-based negative electrode material is reduced, the irreversible capacity increase caused by the volume expansion is reduced, and the service life of the silicon-based negative electrode material is effectively prolonged. Simultaneously, the intermediate level 2 of setting between kernel 1 and shell 3 improves the bonding strength of shell at the kernel surface through the SiC material, makes the difficult peeling off of shell carbon layer to make the shell have anti spalling, thereby make the shell carbon layer can provide sufficient electric conductivity, and then arouse the capacity performance of silica material, thereby restrain the problem of cycle in-process later stage electric conductivity variation. Therefore, the silicon-oxygen negative electrode material provided by the embodiment of the application can provide enough reversible capacity and ensure enough cycling stability. When the silica negative electrode material is used as a lithium ion battery negative electrode alone or after being compounded with graphite, particularly as a negative electrode material of a non-aqueous electrolyte secondary lithium ion battery, the battery has the characteristics of high capacity and long cycle.

In the embodiment of this applicationThe material of the core 1 is a silicon oxide material, i.e., a material containing silicon or an oxide of silicon. Specifically, the material of the core 1 includes amorphous silicon oxide and silicon crystallites. Amorphous silicon oxide in the negative electrode material has a high theoretical reversible capacity. In some embodiments, the amorphous silicon oxide is SiO_xWherein, the value of x satisfies: x is more than or equal to 1 and less than or equal to 1.3.

In the embodiment of the application, the silicon microcrystal is dispersed in the silicon oxide, and the size of the silicon microcrystal is increased in a gradient manner along the direction from the center of the inner core 1 to the surface layer of the inner core 1, so that huge volume expansion stress generated in the lithium embedding process is guided to be released outwards, particle breakage is inhibited, the phenomenon of irreversible capacity increase caused by the stress is reduced, and the cycle life of the battery is effectively prolonged.

In some embodiments, the grain size of the silicon crystallites of the surface layer of the core 1 is designated as D_outThe particle size of the silicon crystallite at a depth of 500nm from the surface layer of the core 1 was designated as D_in，D_outAnd D_inSatisfies the following conditions: d is not less than 0_in/D_outIs less than 1. The silicon microcrystal with gradually changed size in the inner core 1 is controlled to meet the gradually changing requirement, so that huge volume expansion stress generated in the lithium embedding process can be more effectively guided to be released outwards, particle breakage is inhibited, the phenomenon of irreversible capacity increase caused by the particle breakage is reduced, and the cycle life of the battery is effectively prolonged. D provided by the embodiment of the application_outAnd D_inThe Focused Ion Beam (FIB) was cut and measured by High Resolution Transmission Electron Microscopy (HRTEM).

In some embodiments, the silicon crystallites are 1-10nm in size. That is, the size of the silicon crystallites distributed in the core 1 is in the range of 1 to 10nm, and the silicon crystallites having a size of 1 to 10nm increase in size in a gradient in the direction from the center of the core 1 to the surface layer of the core 1. By controlling the size of the silicon microcrystal, the agglomeration of silicon microcrystal particles can be effectively reduced, and the silicon microcrystal has a monodisperse distribution state, so that the volume expansion is effectively inhibited. The size of the silicon microcrystal is within the range of 1-10nm, so that the high first coulombic efficiency of the silicon-based negative electrode material can be effectively guaranteed, the overall stress of particles after lithium embedding can be guided outwards, the particle crushing is relieved, and the volume effect is reduced. If the silicon crystallite size is small, the amorphous silicon oxide accounts for a large amount, and at the moment, excessive active lithium ions are consumed, so that the first efficiency is low; the silicon crystallite size is too large, the disproportionation degree is increased, and the reversible capacity of the particles is lower. The size of the silicon microcrystal provided by the embodiment of the application is obtained by utilizing X-ray diffraction analysis, through Si (111) diffraction peak and half-height peak width in an XRD (X-ray diffraction) spectrum and through calculation of a Scherrer formula.

In some embodiments, the silicon crystallite content is 2-30 wt% of the total weight of the silicon-oxygen anode material, so that the above properties are better exerted. If the content of the silicon microcrystals is too small, the purpose of disproportionation cannot be achieved, namely, if the content of the amorphous silicon oxide is too large, excessive active lithium ions can be consumed, and the first coulombic effect is reduced; if the content of the silicon microcrystal is too high, the disproportionation is excessive, and the reversible capacity of the battery is low.

In some embodiments, the size of core 1 is: d50 is more than or equal to 0.5 mu m and less than or equal to 20 mu m, D10/D50 is more than or equal to 0.3, and D90/D50 is more than or equal to 2. Under the condition, the silicon-oxygen cathode material has better capacity, and the first coulombic efficiency is improved. If the size of the inner core 1 is too small, the specific surface area is too large, and in the lithium ion battery, the contact area between the surface of the negative electrode and the electrolyte is large, so that an SEI (solid electrolyte interface) film is easily formed by reaction, and excessive lithium ions are consumed; if the size of the core 1 is too large, the lithium ion migration path becomes long, and the resistance is large, which is not favorable for diffusion and transport of lithium ions. In conclusion, if the size of the core 1 is not within this range, the capacity of the silicon-based negative electrode material is easily reduced, and the first coulombic efficiency is low.

The silicon oxygen anode material provided by the embodiment of the application comprises a shell layer 3, and the shell layer 3 comprises a carbon layer. The outer shell 3, which includes a carbon layer, serves to provide sufficient conductivity to excite the capacity exertion of the silicon oxygen material in the core 1. In addition, the outer shell layer 3 has a certain peel strength, and can suppress the problem of poor conductivity caused by the peeling of the carbon layer after severe volume expansion and contraction.

In some embodiments, the envelope layer 3 is a single layer film, in particular, the envelope layer 3 is a carbon layer. In some embodiments, the outer shell layer 3 is a multilayer film and includes at least a carbon layer. The multilayer film can be all carbon layers, and can also be composed of carbon layers and other material layers.

In the present embodiment, the outer shell layer 3 can be prepared by various methods. Illustratively, the outer shell 3 may be prepared by solid phase mixing, liquid phase mixing, or gas phase mixing, among others.

In some embodiments, the carbon layer is prepared from an organic carbon source by chemical vapor carbon deposition or in situ carbonization. Wherein, the organic carbon source can be one or more of alkanes, alkenes and alkynes of C1-C4. Wherein C1-C4 means that the number of carbon atoms is 1-4.

In some embodiments, the carbon layer is prepared by mixing a raw material solid phase or liquid phase comprising an organic carbon source and a silicon-based anode material and then performing in-situ carbonization. Wherein, the organic carbon source can be one or more of petroleum-based asphalt, coal oil-based asphalt, starch, glucose, polyethylene glycol and polyvinyl alcohol. In some embodiments, the material of the carbon layer includes an organic polymer and a conductive agent. The pure high molecular organic polymer has insufficient conductivity and is easy to cause the increase of polarization impedance, and the influence of the polarization impedance caused by the pure organic polymer can be prevented by introducing a certain amount of conductive agent. In some embodiments, the material of the carbon layer is composed of an organic polymer and a conductive agent.

In some embodiments, the mass ratio of the organic polymer to the conductive agent in the carbon layer is 2:1 to 1: 2. The organic polymer is equivalent to an artificial SEI film, and can prevent loss of the SEI film caused by direct contact of the silicon-based material of the core 1 with the electrolyte. However, organic polymers have poor conductivity, so that a conductive agent can be added to realize better conductivity, and the excellent electrical property of the material is ensured by the synergistic effect of the conductive agent and the conductive agent.

In some embodiments, the organic polymer is selected from the group consisting of polymers containing- [ CH ]₂-CF₂]_nAn organic substance of the structure containing (C)₆H₇O₆Na)_nOrganic matter of structure [ C ]₆H₇O₂(OH)₂OCH₂COONa]_nHas the structure of [ C ]₃H₄O₂]_nHas the structure of [ C ]₃H₃O₂M]_nHas the structure of (C)₃H₃N)_nThe organic matter, the amide organic matter, the polyimide organic matter containing imide ring-CO-N-CO-on the main chain, and one or more polymers in polyvinylpyrrolidone PVP, wherein M is alkali metal. The high molecular polymers have good stability in a conventional electrochemical window, and are not easy to generate oxidation-reduction reaction; in addition, the high molecular polymer has certain adhesiveness, can strengthen a structure on the outer layer of the inner core 1 formed by the silicon-based composite, relieves the problem of fragmentation caused by expansion and contraction of materials in the process of lithium extraction and insertion, and ensures the integrity of the whole structure of the materials.

In some embodiments, the organic polymer accounts for 0.1-20 wt% of the total weight of the silicon-oxygen negative electrode material, which can effectively improve the conductivity, thereby activating the capacity exertion of the silicon-oxygen material in the inner core 1.

Preferably, the organic polymer layer is a conductive polymer, such as polyvinylidene fluoride, sodium alginate, carboxymethyl cellulose, polypropylene and salts thereof, PVP, and the like.

In some embodiments, the conductive agent may be one or more of conductive carbon black, conductive graphite, interlayer carbon nanospheres, carbon nanofibers, carbon nanotubes, graphene. In some embodiments, the conductive agent comprises 0.5-5 wt% of the total weight of the silicon-oxygen anode material, thereby effectively preventing the polarization impedance from being affected by a simple organic polymer.

In some embodiments, the outer shell layer is a double-layer structure including a first carbon layer near the intermediate layer and a second carbon layer far from the intermediate layer, and the first carbon layer is a pure carbon layer and the second carbon layer is a mixed material layer of an organic polymer and a conductive agent.

In some embodiments, the thickness of the shell layer 3 is 1-50 nm. When the envelope layer 3 is a carbon layer, the carbon layer has a thickness of 1-50 nm. If the thickness of the carbon layer is too thick, the transmission resistance of lithium ions is increased, and the diffusion transmission of the lithium ions is not facilitated; if the carbon layer is too thin, the contact between the electrolyte and the core body cannot be effectively blocked, an SEI (solid electrolyte interface) film is easily generated, the electric conduction effect is not obvious, and the first coulombic efficiency and capacity are reduced.

In some embodiments, the outer shell 3 includes a carbon layer, and the weight of the carbon layer is 0.5% to 10% of the total weight of the silicon-oxygen negative electrode material, and the carbon layer has a better function of exciting the capacity of the silicon-oxygen material in the inner core 1, thereby endowing the negative electrode with excellent cycle performance and conductivity. If the carbon layer content is too low, the conductivity decreases, thereby reducing the ability to excite the capacity of the silica material in the core 1; if the content of the carbon layer is too high, the negative active material content in the core 1 decreases, and the battery capacity tends to decrease.

In the embodiment of the application, because the outer shell 3 including the carbon layer is directly combined on the surface of the inner core 1, the combination strength is not high, and the carbon layer is easy to fall off after severe volume expansion and contraction generated in the charging and discharging process of the battery. In view of this, the embodiment of the present application provides the intermediate layer 2 between the core 1 and the outer shell layer 3, the intermediate layer 2 is coated on the surface of the core 1, and the outer shell layer 3 is coated on the surface of the intermediate layer 2. Specifically, the material of the intermediate layer 2 is silicon carbide. The embodiment of the application forms the carbon layer on the intermediate layer 2, namely the silicon carbide layer, by coating the silicon carbide on the surface of the core 1, so that the bonding strength of the carbon layer on the core can be effectively improved, severe volume expansion and contraction of the battery in the charging and discharging process can be effectively resisted, and the risk of falling off of the carbon layer is reduced.

In the present embodiment, the thickness of the intermediate layer 3 is as uniform and dense as possible, so as to better improve the bonding strength of the outer shell layer 3 containing the carbon layer on the outer surface of the core 1. In some embodiments, the thickness of the intermediate layer 3 is 0.5-3 nm. The thickness of the intermediate layer 3 within this range can effectively improve the bonding strength of the outer shell layer 3 and improve the fixing effect of the carbon layer. If the thickness of the envelope layer 3, i.e. the silicon carbide layer, is too thick, the silicon carbide layer may lead to Li⁺Transport impediments, which in turn reduce the electrochemical performance of the cell; if the thickness of the shell layer 3, i.e. the silicon carbide layer, is too thin, it does not function well for fixing the carbon layer.

In some embodiments, the BET specific surface area of the silicon oxygen anode material is 1-10m²(ii) in terms of/g. Namely, the specific surface area of the silicon-oxygen anode material provided by the embodiment of the application is 1-10m measured by a BET specific surface area test method²(ii) in terms of/g. If the BET specific surface area of the silicon-oxygen anode material is too large, the anode is in a later stageLarge contact area of electrolyte and easy to cause excessive irreversible Li⁺Loss, reducing cell electrochemical performance; if the BET specific surface area of the silicon-oxygen anode material is too small, the particles become too large and kinetic Li is also not favored⁺And (5) transmitting.

The silicon-oxygen anode material provided by the first aspect of the embodiment of the application can be prepared by the following method.

In a second aspect, an embodiment of the present application provides a method for preparing a silicon-oxygen negative electrode material, including:

the material of the inner core comprises amorphous silicon oxide and silicon microcrystals, and the size of the silicon microcrystals is increased in a gradient manner along the direction from the center of the inner core to the surface layer of the inner core; the material of the intermediate layer is silicon carbide.

In the embodiment of the application, the inner core is a main component of a silicon-oxygen negative electrode material for providing electrochemical performance, namely an active component of a negative electrode. According to the preparation method provided by the embodiment of the application, the inner core is formed by disproportionating the silicon monoxide. Specifically, the embodiment of the application is implemented by carrying out high-temperature heat treatment on the silicon monoxideThe disproportionation produces amorphous silicon oxide and silicon crystallites, forming an inner core. Wherein the amorphous silicon oxide is SiO_xAnd the value of x satisfies: x is more than or equal to 1 and less than or equal to 1.3.

Since the silicon oxide is sensitive to temperature, the static state is easy to cause the disproportionation degree of samples in different areas to be different. In view of this, the embodiments of the present application perform dynamic high temperature processing. In the process of dynamic heat preservation of the silicon oxide, as heat is transferred inwards from the surface of the silicon oxide (silicon-based material), the heat gradually decreases in the direction from the surface layer of the silicon-based material to the center of the core of the silicon-based material, the disproportionation reaction degree of the silicon oxide gradually decreases, the silicon oxide on the surface of the core of the silicon-based material is heated uniformly and fully to react to form silicon microcrystals with larger grain sizes under certain time and temperature conditions, and the size of the generated silicon microcrystals from the center of the core of the silicon-based material to the surface of the core gradually increases.

The core-shell structure having an inner core, an intermediate layer and an outer shell may be formed simultaneously by a one-step reaction or may be prepared by a step-by-step reaction. In the embodiment of the application, the silica is subjected to dynamic high-temperature treatment to prepare the inner core, and then the middle layer and the outer shell layer are prepared on the inner core; alternatively, the dynamic heat preservation treatment may be performed on the silicon monoxide and the carbon source at the same time, so that the silicon monoxide is disproportionated to generate amorphous silicon oxide and silicon microcrystals to form a core, a carbon outer shell layer is formed on the surface of the core, and a silicon carbide intermediate layer is formed between the core and the carbon outer shell layer.

In a first embodiment, a core-shell structure having an inner core, an intermediate layer and an outer shell is prepared from a silicon oxide and a carbon source under a dynamic thermal insulation condition, and comprises: dynamically preserving the temperature of the silicon monoxide at the temperature of 700-1300 ℃ in an inert atmosphere, and introducing a carbon source to prepare the core-shell structure.

In this embodiment, during the dynamic incubation, the silicon monoxide disproportionates to form an inner core, the carbon source forms a carbon material, reacts with the material on the surface of the inner core to form a silicon carbide intermediate layer, and then continues to grow on the surface of the intermediate layer to form an outer shell of the carbon material. During the disproportionation, the higher the degree of disproportionation with the increase of temperature. While the higher the disproportionation, the more kernelThe higher the coulombic efficiency exhibited by the silicon-based composite. However, excessive disproportionation leads to large size of silicon crystallites, more amorphous silicon oxide is associated with the vicinity of the silicon crystallites, and the silicon oxide compound accompanying the increase is disadvantageous for Li⁺Transport, thereby reducing reversible capacity exertion. In some embodiments, the temperature of the dynamic heat-preservation treatment is 700-1300 ℃, and the dynamic heat preservation is carried out for 0.5-3 hours. Thus, the silicon monoxide forms a core comprising amorphous silicon oxide and silicon microcrystals through dynamic high-temperature treatment, and the size of the silicon microcrystals increases in a gradient manner along the direction from the center of the core to the surface layer of the core. The amorphous silicon oxide and the silicon crystallites are as above, and are not described herein for brevity. If the temperature is too low, the disproportionation degree is low, the first coulombic efficiency is reduced, and the intermediate layer SiC cannot be formed at the low temperature.

In a second embodiment, a core-shell structure having an inner core, an intermediate layer and an outer shell is prepared from a silicon oxide and a carbon source under a dynamic thermal insulation condition, and comprises:

dynamically preserving the temperature of the silicon monoxide at the temperature of 700-1300 ℃ in an inert atmosphere to obtain an inner core; and introducing a carbon source to continue reacting, and preparing a middle layer and an outer shell layer on the surface of the inner core to obtain the core-shell structure.

In the embodiment, in the dynamic heat preservation process, the silicon monoxide is subjected to disproportionation reaction to form an inner core; after the carbon source is added, the carbon source forms a carbon material, reacts with the material on the surface of the inner core to form a silicon carbide intermediate layer, and then continues to grow on the surface of the intermediate layer to form an outer shell layer of the carbon material. During the disproportionation, the higher the degree of disproportionation with the increase of temperature. While the higher the disproportionation, the higher the coulombic efficiency exhibited by the silica-based composite of the core. However, excessive disproportionation leads to large size of silicon crystallites, more amorphous silicon oxide is associated with the vicinity of the silicon crystallites, and the silicon oxide compound accompanying the increase is disadvantageous for Li⁺Transport, thereby reducing reversible capacity exertion. In some embodiments, the temperature of the dynamic heat-preservation treatment is 700-1300 ℃, and the dynamic heat preservation is carried out for 0.5-3 hours. Thus, the silicon oxide is dynamically processed at high temperature to form a core comprising amorphous silicon oxide and silicon microcrystals, and the silicon microcrystals are formed along the direction from the center of the core to the surface layer of the coreThe size of the crystals increases in a gradient. The amorphous silicon oxide and the silicon crystallites are as above, and are not described herein for brevity. The temperature is too low, the disproportionation degree is low, the first coulombic efficiency is reduced, and the intermediate layer SiC can not be formed at the low temperature.

In a third embodiment, a core-shell structure having an inner core, an intermediate layer, and an outer shell is prepared from a silica and a carbon source under a dynamic thermal insulation condition, comprising:

heating the silicon monoxide and a carbon source under the conditions of 700-1000 ℃ in an inert atmosphere to prepare an outer shell layer on the surface of the silicon monoxide; and then raising the temperature to 1000-1300 ℃ for dynamic heat preservation, forming the silica into a core material to obtain a core, and forming a SiC intermediate layer between the core and the shell.

In this embodiment, a carbon source is bonded to the surface of the silica to form an outer shell of carbon material at a temperature of 700-; in the dynamic heat preservation process, the silicon monoxide is subjected to disproportionation reaction to form an inner core, meanwhile, the carbon of the outer shell layer and the silicon of the inner core move in a mutual molecular mode, the molecules move in an accelerated mode at high temperature, and the carbon and the silicon penetrate in the interface of the inner core and the outer shell layer to form a silicon carbide middle layer. During the disproportionation, the higher the degree of disproportionation with the increase of temperature. While the higher the disproportionation, the higher the coulombic efficiency exhibited by the silica-based composite of the core. However, excessive disproportionation leads to large size of silicon crystallites, more amorphous silicon oxide is associated with the vicinity of the silicon crystallites, and the silicon oxide compound accompanying the increase is disadvantageous for Li⁺Transport, thereby reducing reversible capacity exertion. In some embodiments, the temperature of the dynamic heat-preservation treatment is 1000-1300 ℃, and the dynamic heat-preservation is carried out for 0.5-3 hours. Thus, the silicon monoxide forms a core comprising amorphous silicon oxide and silicon microcrystals through dynamic high-temperature treatment, and the size of the silicon microcrystals increases in a gradient manner along the direction from the center of the core to the surface layer of the core. The amorphous silicon oxide and the silicon crystallites are as above, and are not described herein for brevity. The temperature is too low, the disproportionation degree is low, the first coulombic efficiency is reduced, and the intermediate layer SiC can not be formed at the low temperature.

In the above embodiments, the inert atmosphere includes, but is not limited to, an argon atmosphere, and a nitrogen atmosphere.

In some embodiments, the temperature increase rate for dynamic holding of the silicon oxide or for dynamic high temperature treatment of the silicon oxide and the carbon source simultaneously is 2-10 ℃/min.

The outer shell layer may be prepared in a variety of ways. Illustratively, the outer shell layer can be prepared by solid phase mixing, liquid phase mixing, or gas phase mixing, among others.

In one possible embodiment, the method for producing the outer shell layer on the surface of the silicon oxide comprises: and (3) putting the silicon monoxide in a non-oxygen atmosphere, and carrying out chemical vapor carbon deposition or in-situ carbonization on an organic carbon source to prepare the shell layer.

In some embodiments, the organic carbon source may be one or more of a C1-C4 alkane, alkene, alkyne. In some embodiments, the temperature of the chemical vapor carbon deposition or in situ carbonization is 700-. The above materials are carbonized at high temperature to form a carbon layer and bonded to the surface of the intermediate layer.

In one possible embodiment, the method for producing the outer shell layer on the surface of the silicon oxide comprises: mixing an organic carbon source with a solid phase or a liquid phase of the silicon oxide, and then carrying out in-situ carbonization to form the mixture on the surface of the silicon oxide to prepare the shell layer.

In some embodiments, the outer shell layer is a carbon layer prepared by mixing a raw material solid phase or liquid phase comprising an organic carbon source and a silicon-based anode material and then performing in-situ carbonization. Wherein, the organic carbon source can be one or more of petroleum-based asphalt, coal oil-based asphalt, starch, glucose, polyethylene glycol and polyvinyl alcohol, and the temperature of in-situ carbonization is 700-1300 ℃. The above materials are carbonized at high temperature to form a carbon layer and bonded to the surface of the intermediate layer.

In some embodiments, the in-situ carbonization apparatus may be selected from roller kilns, pushed slab kilns, rotary furnaces, fluidized beds, and other high temperature calcination apparatuses.

In one possible embodiment, the method for producing the outer shell layer on the surface of the silicon oxide comprises: mixing a solid phase or a liquid phase of a conductive polymer comprising an organic polymer and a conductive agent, and carbonizing the mixture in situ to form the mixture on the surface of the silicon oxide to prepare the shell layer.

In some embodiments, the outer shell layer is a carbon layer, the material of the carbon layer further comprising a second layer of an organic polymer and a conductive agent. In some embodiments, the material of the carbon layer is composed of an organic polymer and a conductive agent. The pure high molecular organic polymer has insufficient conductivity and is easy to cause the increase of polarization impedance, and the influence of the polarization impedance caused by the pure organic polymer can be prevented by introducing a certain amount of conductive agent.

In some embodiments, the outer shell layer has a double-layer structure including a first carbon layer near the intermediate layer and a second carbon layer far from the intermediate layer, the first carbon layer is a carbon layer formed by carbonizing a carbon source, and the second carbon layer is a mixed material layer of an organic polymer and a conductive agent.

In some embodiments, the mass ratio of the organic polymer to the conductive agent in the carbon layer is 2:1 to 1: 2. The specific effect is that the organic polymer is equivalent to an artificial SEI film, which can prevent the loss of the SEI film caused by the direct contact of the silicon-based material of the core 1 with the electrolyte. However, organic polymers have poor conductivity, so that a conductive agent can be added to realize better conductivity, and the excellent electrical property of the material is ensured by the synergistic effect of the conductive agent and the conductive agent.

In some embodiments, the organic polymer is selected from the group consisting of polymers containing- [ CH ]₂-CF₂]_nAn organic substance of the structure containing (C)₆H₇O₆Na)_nOrganic matter of structure [ C ]₆H₇O₂(OH)₂OCH₂COONa]_nHas the structure of [ C ]₃H₄O₂]_nHas the structure of [ C ]₃H₃O₂M]_nHas the structure of (C)₃H₃N)_nThe organic matter, the amide organic matter, the polyimide organic matter containing imide ring-CO-N-CO-on the main chain, and one or more polymers in polyvinylpyrrolidone PVP, wherein M is alkali metal. The high molecular polymers have good stability in a conventional electrochemical window, and are not easy to generate oxidation-reduction reaction; further, the polymer isThe polymer has certain adhesiveness, can strengthen the structure on the outer layer of the inner core 1 formed by the silicon-based composite, relieves the problem of fragmentation caused by expansion and contraction of the material in the process of lithium release and intercalation, and ensures the integrity of the whole structure of the material.

In some embodiments, the organic polymer accounts for 0.1-20 wt% of the total weight of the silicon-oxygen anode material, which can effectively improve the conductivity, thereby exciting the capacity exertion of the silicon-oxygen material in the inner core.

In some embodiments, the conductive agent may be one or more of conductive carbon black, conductive graphite, mesocarbon nanospheres, carbon nanofibers, carbon nanotubes, graphene. In some embodiments, the conductive agent comprises 0.5-5 wt% of the total weight of the silicon-oxygen anode material, thereby effectively preventing the effects of the planned impedance from the simple organic polymer.

In some embodiments, a mixed solution of an organic polymer and a conductive agent is sufficiently mixed and dispersed, and then formed on the surface of the intermediate layer, and a carbon layer is prepared through drying treatment, so that the silicon-oxygen negative electrode material is obtained.

In some embodiments, the organic polymer content of the mixed liquor active is 2-20 wt%, thereby achieving better processability. If the organic polymer content of the organic substance is large, the viscosity of the liquid slurry is too high, and the liquid slurry is not easy to disperse uniformly; if the organic polymer content of the organic substance is too small, the consumption of the solvent is large, the energy consumption is high, and the cost is increased.

A third aspect of the embodiments of the present application provides a lithium ion battery, including a negative electrode, where the negative electrode includes a negative electrode material, and is characterized in that: the negative electrode material is the silicon-oxygen negative electrode material of the first aspect or the silicon-oxygen negative electrode material prepared by the method of the second aspect.

The negative electrode provided by the embodiment of the application contains the silicon-oxygen negative electrode material, so that the formed negative electrode can provide enough reversible capacity and can ensure enough cycling stability. When the silica negative electrode material is used as a lithium ion battery negative electrode alone or after being compounded with graphite, particularly as a negative electrode material of a non-aqueous electrolyte secondary lithium ion battery, the battery has the characteristics of high capacity and long cycle.

The following description will be given with reference to specific examples.

Example 1

A preparation method of a silicon-oxygen anode material comprises the following steps:

1kg of SiO_xPlacing the negative electrode material in a rotary furnace, introducing Ar to replace gas in the rotary furnace and ensuring complete evacuation; starting heating, heating to 750 ℃ at a speed of 5 ℃/min, switching to acetylene/Ar mixed gas, and then dynamically preserving heat for 1.5h, and uniformly coating a carbon layer on the surface layer of the material; and switching gas to Ar, further heating to 1200 ℃ at the speed of 5 ℃/min, preserving the temperature for 20min, cooling to room temperature under the protection of non-oxidizing gas, taking out the material to obtain the conductive silicon-oxygen compound with the silicon microcrystal gradient distribution structure, and analyzing by using a carbon-sulfur analyzer to obtain the carbon coating amount of 3.0 wt%.

Example 2

1kg of SiO_xUniformly mixing the material with 80g of petroleum-based asphalt by a high-temperature coating machine, placing the material in a rotary furnace, introducing Ar for replacement to ensure complete emptying, starting heating to raise the temperature to 1150 ℃ at a speed of 5 ℃/min, dynamically preserving the temperature for 2h, completely carbonizing the surface layer of the material, cooling to room temperature under the protection of non-oxidizing gas, taking out the material to obtain a conductive silica-oxygen compound with a silicon microcrystal gradient distribution structure, and analyzing by a carbon-sulfur analyzer to obtain 5.1 wt% of carbon coating amount.

Example 3

1kg of SiO_xPlacing the negative electrode material in a rotary furnace, introducing Ar to replace gas in the rotary furnace and ensuring complete evacuation; starting heating, raising the temperature to 1000 ℃ at a speed of 5 ℃/min, switching to methane/Ar mixed gas, and then dynamically preserving the temperature for 1.5h, and uniformly coating a carbon layer on the surface layer of the material; and (3) cooling to room temperature under the protection of non-oxidizing gas, taking out the material, placing the powder in a vacuum high-temperature furnace, further heating to 1200 ℃ at the rate of 5 ℃/min, keeping the temperature for 20min, taking out the material after cooling to room temperature under the protection of non-oxidizing gas, and analyzing by using a carbon-sulfur analyzer to obtain the carbon coating amount of 4.0 wt%.

The above 100g of carbon-coated SiO_x300g of a solid content of2 wt% of water-soluble conductive liquid (m)_{Conductive carbon black}:m_Graphene:m_{Carbon nanotube}：m_PAA：m_PVP0.7:0.1:0.2:0.7:0.3) and drying to finally obtain the conductive silicon-oxygen composite with the silicon microcrystal gradient distribution structure. The carbon coating amount of 7.5 wt% was obtained by analysis using a carbon sulfur analyzer.

Comparative example 1

1kg of SiO_xPlacing the negative electrode material in a rotary furnace, introducing Ar for replacement to ensure complete evacuation, starting heating to raise the temperature to 750 ℃ at the speed of 5 ℃/min, switching to acetylene/Ar mixed gas, dynamically preserving the temperature for 1.5h, uniformly coating a carbon layer on the surface layer of the material, taking out the material after the temperature is reduced to room temperature under the protection of non-oxidizing gas to obtain a conductive silica-oxygen compound with a silicon microcrystal gradient distribution structure, and analyzing by using a carbon-sulfur analyzer to obtain the carbon coating amount of 3.0 wt%.

Comparative example 2

1kg of SiO_xThe material is uniformly mixed with 80g of petroleum-based asphalt through a high-temperature coating machine and then placed in a rotary furnace, Ar replacement is conducted to ensure complete emptying, heating is started to raise the temperature to 1000 ℃ at 5 ℃/min, dynamic heat preservation is carried out for 2h, the surface layer of the material is completely carbonized, the material is taken out after the temperature is reduced to room temperature under the protection of non-oxidizing gas, a conductive silica-oxygen compound with a silicon microcrystal gradient distribution structure is obtained, and a carbon-sulfur analyzer is utilized to analyze the conductive silica-oxygen compound to obtain 5.1 wt% of carbon coating amount.

Comparative example 3

1kg of SiO_xPlacing the negative electrode material in a rotary furnace, introducing Ar for replacement to ensure complete evacuation, starting heating to raise the temperature to 1000 ℃ at the speed of 5 ℃/min, switching to methane/Ar mixed gas, dynamically preserving the temperature for 1.5h, uniformly coating a carbon layer on the surface layer of the material, taking out the material after the temperature is reduced to room temperature under the protection of non-oxidizing gas, and analyzing by using a carbon-sulfur analyzer to obtain the carbon coating amount of 4.0 wt%.

Comparative example 4

The above 100g of carbon-coated SiO_xAdding into 300g of water-soluble conductive liquid with the solid content of 2 wt.% (m)_{Conductive carbon black}:m_Graphene:m_{Carbon nanotube}：m_PAA：m_PVP0.7:0.1:0.2:0.7:0.3) and drying to finally obtain the conductive silicon-oxygen composite with the silicon microcrystal gradient distribution structure. The carbon coating amount of 7.5 wt% was obtained by analysis using a carbon sulfur analyzer.

The silica negative electrode materials obtained in the above examples and comparative examples are also applied as negative electrode materials and the preparation of lithium ion batteries, and the preparation method of the lithium ion batteries comprises the following steps:

according to the anode material: conductive agent: LA133 80: 10: 10, stirring and mixing 40% of aqueous solvent to form slurry, uniformly coating the slurry on the surface of copper foil, rolling the slurry to a certain thickness, and performing vacuum drying overnight at 110 ℃ to prepare the negative pole piece.

Assembling a negative pole piece, a polypropylene microporous diaphragm PP and a lithium piece into a button battery of a factory, wherein the electrolyte is ethylene carbonate EC/methyl ethyl carbonate with the ratio of 3:7(V/V), wherein LiPF₆The concentration was 1M. Placing the assembled battery at room temperature for 12h, performing charge-discharge test, discharging at constant current of 0.1C to 0.01V, changing to constant current of 0.01C to 0.01V, and recording the first discharge capacity as Q_PutThen charged to a constant voltage of 1.5V at 0.1C, and the corresponding reversible charge capacity is recorded as Q_{Charging device}. First effect

The silicon-oxygen anode materials obtained in the above examples and comparative examples were subjected to physical and chemical property tests and calculations, and the test results are shown in table 1 below.

TABLE 1 physicochemical Properties of silica materials treated under different conditions

By comparing example 1 with comparative example 1 in combination with table 1, it can be seen that: in the embodiment 1, after high-temperature heat treatment, the silicon-based core is disproportionated to form a structural layer with the size of microcrystalline Si gradually reduced from the outer layer to the core, the first coulombic efficiency is higher, and new-phase SiC is formed between Si and a carbon layer aggravated by the high-temperature heat treatment, so that huge volume expansion is realized in the cyclic charge-discharge process, the carbon layer is not easy to fall off, and good conductivity is ensured.

Comparing example 2 with comparative example 2, it can be seen that: after the high-temperature heat treatment is carried out on the embodiment 2 and the comparative example 2, the silicon-based core is disproportionated to form a structural layer with the size of microcrystalline Si gradually reduced from the outer layer to the inner core, the first coulombic efficiency is high, however, the sample of the embodiment 2 is subjected to heat treatment at a higher temperature to intensify the formation of new-phase SiC between Si and the carbon layer, so that the huge volume expansion is caused in the cyclic charge-discharge process, the carbon layer is not easy to fall off, and the good conductivity is ensured.

Comparing example 3 with comparative example 4, it can be seen that: after the high-temperature heat treatment is carried out on the samples in the embodiment 3 and the comparative example 3, the silicon-based core is disproportionated to form a structural layer with the size of microcrystalline Si gradually reduced from the outer layer to the core, the first coulombic efficiency is high, however, after the samples in the embodiment 3 are subjected to the vacuum high-temperature heat treatment, the formation of new-phase SiC between Si and a carbon layer is aggravated, so that the huge volume expansion is caused in the cyclic charge-discharge process, the carbon layer is not easy to fall off, and the good conductivity is ensured.

Comparing comparative example 3 with comparative example 4, it can be seen that: in both the embodiment 3 and the comparative example 3, after high-temperature heat treatment, the silicon-based core is disproportionated to form a structural layer with the gradually reduced microcrystalline Si size from the outer layer to the inner core, the first coulombic efficiency is higher, however, after the surface layer is coated by the conductive polymer, a natural SEI film is formed on the surface, and the comparative example 4 has more excellent cycling stability.

The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.

Claims

1. The silicon-oxygen negative electrode material is characterized by having a core-shell structure and comprising an inner core, a middle layer and an outer shell, wherein the middle layer is coated on the surface of the inner core, and the outer shell is coated on the surface of the middle layer;

the intermediate layer is made of silicon carbide;

the outer shell layer includes a carbon layer.

2. The silicon-oxygen anode material as claimed in claim 1, wherein the grain size of the silicon crystallites of the inner core surface layer is designated as D_outThe grain size of the silicon crystallites of the core at a depth of 500nm from the surface layer is designated as D_in，D_outAnd D_inSatisfies the following conditions: 0<D_in/D_out＜1。

3. The silicon oxygen anode material of claim 1, wherein the size of the inner core is: d50 is more than or equal to 0.5 mu m and less than or equal to 20 mu m, D10/D50 is more than or equal to 0.3, and D90/D50 is more than or equal to 2; and/or

The size of the silicon microcrystal is 1-10 nm; and/or

The amorphous silicon oxide is SiO_xAnd x is more than or equal to 1 and less than or equal to 1.3.

4. The silicon-oxygen anode material of claim 1, wherein the thickness of the intermediate layer is 0.5-3 nm; and/or

The thickness of the outer shell layer is 1-50 nm.

5. Silicon as claimed in any of claims 1 to 4The oxygen anode material is characterized in that the BET specific surface area of the silicon-oxygen anode material is 1-10m²/g。

6. A preparation method of a silicon-oxygen anode material is characterized by comprising the following steps:

7. The preparation method of the silicon-oxygen anode material of claim 6, wherein the core-shell structure with the inner core, the middle layer and the outer shell is prepared by taking the silicon monoxide and the carbon source as raw materials under the condition of dynamic heat preservation, and comprises the following steps:

dynamically preserving the temperature of the silicon monoxide at the temperature of 700-1300 ℃ in an inert atmosphere, and introducing a carbon source to prepare the core-shell structure;

or

Dynamically preserving the temperature of the silicon monoxide at the temperature of 700-1300 ℃ in an inert atmosphere to obtain an inner core; introducing a carbon source to continue reacting, and preparing the middle layer and the outer shell layer on the surface of the inner core to obtain the core-shell structure;

or

8. The method for preparing a silicon-oxygen anode material according to claim 7, wherein the method for preparing the outer shell layer on the surface of the silicon monoxide comprises the following steps:

placing the silicon monoxide in a non-oxygen atmosphere, and carrying out chemical vapor carbon deposition or in-situ carbonization on an organic carbon source to prepare a shell layer; or

Mixing an organic carbon source with the solid phase or the liquid phase of the silicon monoxide, and then carrying out in-situ carbonization on the surface of the silicon monoxide to prepare a shell layer; or

9. The method of preparing a silicon oxygen anode material of claim 8, wherein when preparing the crust layer on the surface of the silicon monoxide: placing the shell in a non-oxygen atmosphere, and adopting an organic carbon source to prepare the shell layer through chemical vapor carbon deposition or in-situ carbonization, wherein the organic carbon source is selected from at least one or more of C1-C4 alkane, alkene and alkyne, and the temperature of the chemical vapor carbon deposition or in-situ carbonization is 700-1000 ℃;

the method for preparing the outer shell layer on the surface of the silicon oxide comprises the following steps: mixing an organic carbon source with the solid phase or the liquid phase of the silicon oxide, and then carrying out in-situ carbonization on the surface of the silicon oxide to obtain a shell layer, wherein the organic carbon source is selected from one or more of petroleum-based asphalt, kerosene-based asphalt, starch, glucose, polyethylene glycol and polyvinyl alcohol, and the temperature of the in-situ carbonization is 700-1000 ℃;

the method for preparing the outer shell layer on the surface of the silicon oxide comprises the following steps: mixing a conductive polymer solid phase or liquid phase comprising an organic polymer and a conductive agent, and in-situ carbonizing the mixture to form an outer shell layer on the surface of the silica, wherein the organic polymer is selected from the group consisting of₂-CF₂]_nAn organic substance of the structure containing (C)₆H₇O₆Na)_nOrganic matter of structure [ C ]₆H₇O₂(OH)₂OCH₂COONa]_nHas the structure of [ C ]₃H₄O₂]_nHas the structure of [ C ]₃H₃O₂M]_nHas the structure of (C)₃H₃N)_nThe organic matter, the amide organic matter, the polyimide organic matter containing imide ring-CO-N-CO-on the main chain and one or more polymers in polyvinylpyrrolidone, wherein M is alkali metal, and the organic polymer accounts for 0.1-20 wt% of the total weight of the silicon-oxygen negative electrode material.

10. A battery anode comprising an anode material, characterized in that: the silicon-oxygen negative electrode material of any one of claims 1 to 5 or the silicon-oxygen negative electrode material prepared by the method of any one of claims 6 to 9.