WO2022204979A1

WO2022204979A1 - Silicon-based composite material, preparation method therefor and application thereof

Info

Publication number: WO2022204979A1
Application number: PCT/CN2021/084091
Authority: WO
Inventors: 贾彦龙
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2022-10-06
Also published as: CN114207884B; CN114207884A

Abstract

A silicon-based composite material, a preparation method therefor and an application thereof. The silicon-based composite material comprises a particle composed of a core and a first shell layer present on the surface of the core, and a second shell layer present on the surface of the particle. The core comprises a silicon-oxygen material. The first shell layer comprises a SiMC material containing a silicon element, an M element and a carbon element. The M element comprises at least one of group-IIIA elements, group-VA elements or group-VI elements in the periodic table of elements. The second shell layer comprises a carbon material. The silicon-based composite material has good structural stability and electrical conductivity, facilitates fulfilling functions of the silicon-based composite material as a negative electrode material, and effectively solves the problems of volume expansion, poor circularity and the like in the circulation process of an electrochemical device.

Description

Silicon-based composite material and its preparation method and application

technical field

The invention relates to the field of batteries, in particular to a silicon-based composite material, a preparation method and application thereof, and more particularly, to a negative electrode sheet, an electrochemical device and an electronic device using the silicon-based composite material.

Background technique

Silicon-containing materials have the advantages of higher capacity and lower voltage platform, and have gradually attracted widespread attention. For example, the capacity of currently available silicon-oxygen materials can reach 1400-1800 mAh/g. However, the current silicon-based materials generally have defects such as poor electrical conductivity and poor structural stability, their high-rate charging capacity is insufficient, and the volume change (i.e. volume expansion) of 120% to 300% or even higher is prone to occur during the cycle, resulting in The silicon-based material is pulverized and separated from the current collector, so that the conductivity of the negative electrode is deteriorated (conductivity is less than 1 S/m), thereby reducing the performance of the electrochemical device such as cyclability.

At present, the solution to the problems of volume expansion and poor electrical conductivity of silicon-based materials during the cycle is generally to composite silicon-based materials with graphite or other metal or non-metallic materials. The composite methods mainly include direct physical mixing or chemical vapor deposition. (CVD), solid phase cladding method or liquid phase cladding method to coat silicon-based materials, such as carbon coating, but the existing methods do not improve the conductivity and structural stability of silicon-based materials. Obviously, the electrical conductivity and structural stability of the existing silicon-based materials still need to be improved.

SUMMARY OF THE INVENTION

The present invention provides a silicon-based composite material and a preparation method and application thereof, so as to at least solve the problems of poor electrical conductivity and poor structural stability of the silicon-based composite material existing in the prior art, and the resulting poor cyclability and high volume expansion rate of an electrochemical device. .

In one aspect of the present invention, a silicon-based composite material is provided, comprising: particles consisting of an inner core and a first shell layer existing on the surface of the inner core, and a second shell layer existing on the surface of the particles, the inner core comprising a silicon-oxygen material , the first shell layer contains SiMC material containing silicon element, M element, carbon element, M element includes at least one element in Group IIIA, Group VA or Group VI element in the periodic table, and the second shell layer contains carbon material.

According to the research of the present invention, in some embodiments, the particle size of the silicon-based composite material satisfies 2 μm≤Dv50 ₁ ≤10 μm, Dv99<21 μm, wherein, Dv50 ₁ indicates that in the particle size distribution based on volume, the particles from the small particle size side, The particle size that reaches 50% of the volume accumulation, Dv99 means that in the particle size distribution based on the volume, the particle size reaches 99% of the volume accumulation from the small particle size side; and/or, the specific surface area of the silicon-based composite material is less than 5m ² / g; and/or, the Raman spectrum of the silicon-based composite material shows that the ratio of the peak height I ₁₃₅₀ at 1350 cm ⁻¹ and the peak height I ₁₅₈₀ at 1580 cm ⁻¹ satisfies 0<I ₁₃₅₀ /I ₁₅₈₀ <1.5.

In some embodiments, the silicon-oxygen material includes SiOx material, 0.5<x<1.5; and/or, the particle size of the inner core satisfies 1 μm≤Dv50 ₂ ≤5 μm, wherein Dv50 ₂ represents that in the particle size distribution based on volume, the inner core particle From the small particle size side, the particle size reaches 50% of the volume accumulation; and/or the specific surface area of the inner core is greater than 3 m ² /g. Optionally, in the SiMC material, the atomic ratio of carbon element to silicon element is 0.1 to 6, and the atomic ratio of M element to silicon element is 0.05 to 2.

In order to further optimize the structural stability and conductivity of the silicon-based composite material, in some embodiments, the particle size of the particles satisfies 2 μm≤Dv50 ₃ ≤9 μm, wherein Dv50 ₃ indicates that in the particle size distribution based on the volume, the particles from small From the particle size side, the particle size reaches 50% of the cumulative volume; and/or the specific surface area of the particles is less than 8 m ² /g. Generally, 0.1<(R ₂ -R ₁ )/R ₂ <2/3 can be satisfied, where R ₁ is the radius of the inner core, and R ₂ is the radius of the particle. The thickness of the second shell layer may be 5 nm to 500 nm; and/or, the carbon material may include at least one of amorphous carbon, graphene, or carbon nanotubes.

Another aspect of the present invention provides a method for preparing the above-mentioned silicon-based composite material, comprising: using a mixed solution containing a first carbon source and an organosilane to impregnate the silicon-oxygen material, and subjecting the obtained impregnated product to high-temperature cracking treatment , forming a first shell layer on the surface of the silicon oxide material to obtain particles; mixing the particles with the second carbon source to make a slurry, drying the slurry by spray drying, and carbonizing the obtained dried product. A second shell layer is formed on the surface to obtain a silicon-based composite material. Wherein, the process of high temperature cracking may include a process of cracking at a temperature of 900°C to 1500°C.

In yet another aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, the negative electrode active material layer contains a negative electrode active material, and the negative electrode active material comprises the above-mentioned silicon-based composite material . Optionally, the negative electrode active material further includes graphite. In the negative electrode active material, the mass content of the silicon-based composite material may generally be 0.5% to 80%.

As an extension of the idea of the present invention, an electrochemical device including the above-mentioned negative electrode sheet and an electronic device including the electrochemical device are also provided.

The silicon-based composite material provided by the present invention is designed through a three-layer structure of an inner core (silicon-oxygen material)-first shell layer (SiMC)-second shell layer (carbon material), has good structural stability and electrical conductivity, and can Avoiding the direct contact between the silicon-oxygen material and the electrolyte, reducing the interface corrosion, is beneficial to its function as a negative electrode active material, showing excellent characteristics such as high capacity, long cycle, low expansion, etc., making the negative electrode sheet/electrochemical device both. Good cycle performance, stability, safety and other qualities can effectively solve the problems of volume expansion and poor cyclability during the charge-discharge cycle of electrochemical devices, which are of great significance for practical industrial applications.

Description of drawings

Fig. 1 is the structural representation of the silicon-based composite material of the present invention;

FIG. 2 is a capacity fading curve diagram of a battery during cycling according to an embodiment of the present invention.

Detailed ways

In order for those skilled in the art to better understand the solution of the present invention, the present invention is further described in detail below.

As shown in FIG. 1 , the silicon-based composite material of the present invention includes: a particle consisting of a core and a first shell layer existing on the surface of the core, and a second shell layer existing on the surface of the particle, the core contains a silicon-oxygen material, the first The shell layer includes SiMC material containing silicon element, M element and carbon element, M element includes at least one element from group IIIA, group VA or group VI element in the periodic table, and the second shell layer includes carbon material.

According to the research of the present invention, the particle size of the silicon-based composite material can satisfy 2 μm≤Dv50 ₁ ≤10 μm, Dv99<21 μm, wherein Dv50 ₁ indicates that in the particle size distribution based on volume, the particles start from the small particle size side and reach a volume accumulation of 50 μm. % particle size, Dv99 represents the particle size distribution on the basis of volume, the particle size reaches 99% of the volume accumulation from the small particle size side, Dv50 ₁ For example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm , 10 μm or any two of them, and Dv99 is, for example, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any two of them. By controlling the particle size of the silicon-based composite material within the above range, it is more conducive to its function.

In general, silicon-based composite materials have a porous structure, which is beneficial to improve its defects such as volume expansion during the cycle of electrochemical devices. Usually, the more pores, the material will have a relatively larger specific surface area, but the silicon-based composite material has a relatively large specific surface area. If the specific surface area is too large, it will also affect its function to a certain extent. For example, it is easy to increase its contact area with the electrolyte or other non-ideal components, thereby increasing the degree of corrosion. Therefore, considering these factors comprehensively, the specific surface area of the silicon-based composite material can generally be controlled to be less than 5m ² /g, such as 0.5m ² /g, 1m ² /g , 1.5m ² /g, 2m ² /g, 2.5m ² /g, 3m ² /g, 3.5m ² /g, 4m ² /g, 4.5m ² /g, 5m ² /g or any two of them range of composition.

In addition, the silicon-based composite material with good structural stability and electrical conductivity can also have the following characteristics: its Raman spectrum shows that the ratio of the peak height I ₁₃₅₀ at 1350 cm ^-1 and the peak height I ₁₅₈₀ at 1580 cm ^-1 satisfies 0<1 ₁₃₅₀ /I ₁₅₈₀ <1.5, for example, I ₁₃₅₀ /I ₁₅₈₀ can be in the range of 0.5, 0.8, 1, 1.2, 1.4 or any two of them. The silicon-based composite material is introduced into the negative electrode of the electrochemical device, which can effectively Improve volume expansion, poor cycle performance and other defects.

Silica material has a high gram capacity. By forming the first shell layer and the second shell layer on its surface in turn, the structural stability and conductivity of the overall material (ie, silicon-based composite material) can be improved while ensuring its capacity. Specifically, in some embodiments, the silicon-oxygen material may include a SiOx material, 0.5<x<1.5 (that is, the atomic ratio of silicon to oxygen in the silicon-oxygen material is 1:0.5 to 1:1.5), and x is, for example, 0.6 , 0.8, 1.0, 1.2, 1.4 or the range of any two of them, which is beneficial to further improve the capacity, structural stability and electrical conductivity of the silicon-based composite material.

According to further research of the present invention, the particle size of the inner core satisfies 1 μm≤Dv50 ₂ ≤5 μm, wherein, Dv50 ₂ represents the particle size of the inner core particle from the small particle size side and reaches 50% of the volume accumulation in the particle size distribution based on volume, Dv50 ₂ is, for example, a range of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any two of them. The inner core is a porous structure, which can be formed of a porous silica material with a specific surface area greater than 3m ² /g, such as 4m ² /g, 5m ² /g, 6m ² /g, 7m ² /g, 8m ² /g , 9m ² /g, 10m ² /g or a range of any two of them. Controlling parameters such as the particle size and/or specific surface area of the inner core within the above ranges is beneficial to further ensure the function of the silicon-based composite material.

The first shell layer formed by the SiMC material exists on the surface of the core, which can inhibit the volume expansion of the core material and improve the ion-conducting ability, which has an important impact on the function of the silicon-based composite material. For example, the M element can specifically include At least one of boron, nitrogen, oxygen or aluminum, in some preferred embodiments, the M element includes oxygen element, that is, the SiMC material is a silicon-oxygen-carbon (SiOC) material, in addition, it can also selectively include boron , at least one of nitrogen or aluminum.

Upon further research, in some embodiments, the SiMC material has an atomic ratio of carbon to silicon of 0.1 to 6, such as 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 or the range of any two of them, the atomic ratio of M element to silicon element is 0.05 to 2, such as 0.05, 0.08, 0.1, 03, 0.5, 0.8, 1.0, 1.3, 1.5, 1.8, 2.0 or wherein In the range of any two compositions, the SiMC material is used to further optimize the properties of the silicon-based composite material such as structural stability.

The particles formed by the inner core and the first shell layer existing on the surface of the inner core are the matrix materials of the silicon-based composite material, which determine the properties of the silicon-based composite material such as capacity and structural stability to a large extent. In some embodiments , the particle size of the particles satisfies 2μm≤Dv50 ₃ ≤9μm, where Dv50 ₃ indicates that in the particle size distribution based on volume, the particle size from the small particle size side reaches 50% of the volume accumulation, which is more conducive to ensuring the stability of the silicon-based composite material. function. Further optimization results show that the specific surface area of the particles is less than 8m ² /g, such as 1m ² /g, 2m ² /g, 3m ² /g, 4m ² /g, 5m ² /g, 6m ² /g, 7m ² /g g or a range of any two of them.

As shown in Figure 1, the inner core, the particles and the silicon-based composite material are basically spherical in structure (that is, their cross-section is basically circular), and the thickness of the first shell layer is substantially equal to the difference between the radius of the particle and the radius of the inner core, that is, r =(R ₂ -R ₁ ), r is the thickness of the first shell, R ₁ is the radius of the inner core, and R ₂ is the radius of the particle, generally satisfying 0.1<(R ₂ -R ₁ )/R ₂ <2/3 , (R ₂ -R ₁ )/R ₂ is, for example, a range of 0.2, 0.3, 0.4, 0.5 or any two of these values, which is more conducive to exerting the synergistic effect of structures such as the inner core and the first shell, improving the silicon Structural stability and electrical conductivity of matrix composites. In general, R1 can be ₃ μm to 6 μm, and R2 can be 3 μm to 10 μm.

As the outer layer existing on the surface of the particles, the second shell layer can not only ensure the structural stability of the silicon-based composite material, but also improve its electrical conductivity and other properties. Relatively speaking, the thickness of the second shell layer is too small, and its function It is relatively limited, and the thickness of the second shell layer is too large, although the conductivity can be greatly improved, but at the same time, the depth of lithium insertion (or other ions) during the cycle of the electrochemical device will increase due to the excessive increase in conductivity. To a certain extent, the unfavorable conditions such as cyclic expansion of the electrochemical device can be increased. Therefore, the thickness of the second shell layer can generally be controlled to be 5 nm to 500 nm, such as 5 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm. , 500nm or any two of them in the range, which is beneficial to further improve the performance of the silicon-based composite material.

Further, the carbon material may include at least one of amorphous carbon, graphene or carbon nanotube (CNT), but is not limited thereto, and other carbon materials with conductive functions may also be used.

In the present invention, the preparation method of the silicon-based composite material includes: using a mixed solution containing a first carbon source and an organosilane to impregnate the silicon-oxygen material, subjecting the obtained impregnated product to high-temperature cracking treatment, and forming the first carbon-oxygen material on the surface of the silicon-oxygen material. A shell layer is obtained to obtain particles (the macroscopic appearance of the product is a powder formed by the particles); the particles are mixed with the second carbon source and made into a slurry, the slurry is dried by spray drying, and the obtained dried product is subjected to The carbonization treatment forms a second shell layer on the surface of the particles to obtain a silicon-based composite material.

In the above preparation process, the first carbon source and organosilane are used as raw materials, and SiMC material is generated in situ on the surface of the silicon-oxygen material by high-temperature cracking to form a first shell layer, and the second carbon source is used as a raw material, and is spray-dried on the surface of the particles. To form the second shell layer, in specific implementation, the first carbon source and organosilane can be selected according to the elemental composition of the SiMC material, and the second carbon source can be selected according to the elemental composition of the carbon material. For example, the first carbon source can include glucose and/or sucrose, the organosilane may comprise at least one of siloxane, silazane, polysiloxane, polycarbosilane, polysilazane, polycarborane methylsiloxane, or polysilaborazane The siloxane includes, for example, dimethylsiloxane (C ₂ H ₆ OSi), the silazane includes, for example, hexamethylcyclotrisilazane (C6H21N3Si3), and the second carbon source may include resin, pitch, graphene Or at least one of carbon nanotubes (CNT), etc., wherein, resin and/or pitch is used as the second carbon source, and after the above spray drying, amorphous carbon will be formed by pyrolysis.

In specific implementation, the silica material can be sieved first to obtain the silica material that meets the preset core particle size requirements (eg 1 μm≤Dv50 ₂ ≤5 μm), and then the sieved silica material is added to the The first solution containing the first carbon source is dispersed uniformly to obtain a dispersion liquid; the solution containing the organosilane is added to the above-mentioned dispersion liquid to realize the impregnation of the silicon-oxygen material. During the impregnation process, stirring and other methods can be used It is ensured that the silicon-oxygen material is uniformly dispersed in the system, so that the first carbon source and the organosilane are more fully immersed in the silicon-oxygen material. After the impregnation is completed, the impregnated product is dried to remove the solvent, and then subjected to pyrolysis treatment.

In some embodiments, the high-temperature cracking process includes a process of cracking at a temperature of 900°C to 1500°C, preferably at a temperature of 900°C to 1300°C, and the temperature is too high, which will cause damage to the internal silicon-oxygen material to a certain extent. , affecting the comprehensive performance of the prepared silicon-based composite material, thereby affecting the cyclability and other properties of the electrochemical device. Therefore, it is beneficial to further optimize the comprehensive performance of the silicon-based composite material by controlling the temperature within the above-mentioned range. Optionally, the above-mentioned impregnated product can be first heated to about 500°C at a heating rate of about 1°C/min, and then heated to 900°C to 1500°C at a heating rate of about 3°C/min to perform high-temperature cracking, and the high-temperature cracking time can be for about 3 hours.

In some embodiments, the drying process of the spray drying method includes: entering the slurry from the inlet of the spray drying granulator into the centrifugal turntable nozzle of the spray drying granulator, and controlling the centrifugal rotation speed to be about 2000 r/min, so that the slurry The material forms tiny droplets, which are ejected from the outlet of the spray-drying granulator, and the ejected product (macroscopic appearance is powdery) is collected by cooling to obtain the above-mentioned dried product. The temperature at the inlet of the pellet mill is about 260°C, and the temperature at the outlet is about 105°C.

The carbonization process can further remove the impurity components in the second shell layer. In some embodiments, the carbonization process can be performed in an inert atmosphere such as nitrogen (N ₂ ) or argon (Ar), and the process includes: first The dried product is heated to about 350°C at a heating rate of 1°C/min to 5°C/min, kept for about 2 hours, and then heated to a temperature of 1°C/min to 5°C/min (for example, about 3°C/min). At about 500°C to 800°C, the temperature is kept for about 1 hour to 5 hours, and then the temperature is lowered to room temperature, and the product is collected to obtain the silicon-based composite material.

The negative electrode sheet of the present invention includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, the negative electrode active material layer contains a negative electrode active material, and the negative electrode active material includes the above-mentioned silicon-based composite material.

In addition, the negative electrode active material may further include graphite, and the graphite may include at least one of natural graphite, artificial graphite or mesocarbon microspheres. In some embodiments, the gram capacity of the negative electrode active material obtained by blending the silicon-based composite material with the negative electrode active material such as graphite is 380mAh/g to 1200mAh/g, such as 380mAh/g, 450mAh/g, 500mAh/g, 600mAh/g, 700mAh/g, 800mAh/g, 900mAh/g, 1000mAh/g, 1100mAh/g, 1200mAh/g or the range of any two of them. In specific implementation, it can be compounded according to silicon-based materials and graphite. The gram capacity of the anode active material is controlled by the ratio of .

In general, in the negative electrode active material, the mass content of the silicon-based composite material can be 0.5% to 80%, such as 0.5%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or any two of them, the balance can be graphite or other negative electrode active materials, and controlling the amount of silicon-based composite materials within this range is conducive to improving the energy density of the negative electrode sheet, properties such as cyclability and stability.

The above-mentioned negative electrode active material layer further comprises a conductive agent and a binder. In the negative electrode active material layer, the mass content of the negative electrode active material can be 80% to 95%, the mass content of the conductive agent is 2% to 15%, and the mass content of the binder is 80% to 95%. The mass content is 3% to 15% (that is, the mass ratio of the negative electrode active material, the conductive agent, and the binder is (80-95):2-15:3-15). For example, the conductive agent may include at least one of conductive carbon black (SP), acetylene black, Ketjen black, conductive graphite or graphene, and the binder may include polyacrylic acid (PAA), polyacrylate, polyacryl Imine, polyamide, polyamideimide, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose or at least one of potassium hydroxymethyl cellulose.

The negative electrode sheet of the present invention can be prepared by a coating method, but is not limited thereto. In some embodiments, the preparation process of the negative electrode sheet may include: coating the slurry containing the raw material of the negative electrode active material layer on at least one surface of the negative electrode current collector and forming the negative electrode active material layer to obtain the negative electrode sheet. In specific implementation, the negative electrode active material, conductive agent, and binder can be uniformly mixed in a solvent to form the above slurry, the slurry can be coated on the negative electrode current collector, dried/drying, rolling/cooling After pressing and the like, a negative electrode active material layer is formed, and the above-mentioned negative electrode sheet is obtained. In the specific implementation process, the solid content of the slurry can be controlled to be 60% to 70%. After kneading for a period of time, the viscosity of the slurry can be adjusted to 10000-13000Pa·s with a solvent such as water, and then it is coated on the negative electrode current collector. surface. Wherein, the solvent can be a conventional solvent in the field such as water, and the negative electrode current collector can be a conventional negative electrode current collector such as copper foil. Repeat.

The electrochemical device of the present invention includes the above-mentioned negative electrode sheet, and the electrochemical device may specifically be a battery, such as a lithium ion battery or the like. The electrochemical device further includes a positive electrode sheet and a separator between the negative electrode sheet and the positive electrode sheet. For example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes Positive electrode active material, conductive agent and binder, for example, the positive electrode active material may include lithium cobalt oxide (LiCoO ₂ ), lithium iron phosphate, nickel-cobalt-manganese ternary material (NCM) or nickel-cobalt-aluminum ternary material (NCA). At least one, the positive electrode current collector can be aluminum foil, etc.; the separator is used to separate the positive electrode sheet and the negative electrode sheet, and it can include polyethylene (PE) porous polymer film and the like.

The above electrochemical device also includes an electrolyte, for example, the electrolyte includes an organic solvent, a lithium salt and an additive, and the organic solvent includes fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), At least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate; lithium salts include organic lithium salts or inorganic lithium salts At least one of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium bistrifluoromethanesulfonimide LiN (CF ₃ SO ₂ ) ₂ (LiTFSI), Lithium Bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ )(LiFSI), Lithium Bisoxalate Borate LiB(C ₂ O ₄ ) ₂ (LiBOB) or Lithium Difluorooxalate Borate LiBF At least one of ₂ (C ₂ O ₄ ) (LiDFOB); the additive includes at least one of crown ether compounds, boron-based compounds, inorganic nano oxides, carbonate compounds or amide compounds, for example, may include 12 - crown-4 ether, boron anion acceptor tris (pentafluorophenyl) borane (TFPB), tris (pentafluorophenyl) borate, vinylene carbonate (VC) or acetamide and its derivatives at least one of. In some embodiments, the content of the lithium salt in the electrolyte is 0.5 mol/L to 1.5 mol/L, such as 0.7 mol/L to 1.3 mol/L or 0.9 mol/L to 1.1 mol/L.

The electrochemical device of the present invention can be prepared according to conventional methods in the art. For example, in some embodiments, the electrochemical device is a wound lithium-ion battery, and the preparation process may include: a positive electrode sheet, a separator, a positive electrode sheet After stacking and setting, the bare cells are wound to form the bare cells, and then the bare cells are placed in the outer packaging, and then the electrolyte is injected, and then the battery is obtained after the processes of packaging, chemical formation, degassing, and trimming. The above-mentioned processes such as winding, liquid injection, packaging, chemical formation, degassing, and trimming are all routine operations in the art, and will not be repeated here.

The electronic device of the present invention includes the above-mentioned electrochemical device, and may be the electrochemical device of any of the above-described embodiments, or may be an electrochemical device of other embodiments without departing from the spirit and scope of the present invention.

In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Example. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Unless otherwise specified, in the following examples and comparative examples, the spectral analysis and performance testing of materials are conventional methods in the art, and the relevant testing process is briefly described as follows:

(1) Scanning Electron Microscope (SEM) test: Detect the surface and/or side of the sample under the conditions of 10kV and 10mA to determine the thickness of the carbon layer;

(2) Material conductivity test: use a resistivity tester (Suzhou Lattice Electronics ST-2255A) to test: take a 5g powder sample, use an electronic press to constant pressure to 5000kg ± 2kg, and maintain for 15-25s; place the sample on the Between the electrodes of the tester, the height of the sample is h (cm), the voltage at both ends is U, the current is I, and the area of the resistance R (KΩ) after the powder is pressed is S=3.14cm ² , according to the formula δ=h/(S*R )/1000 to calculate the electronic conductivity of the powder, the unit is S/m;

(3) Specific surface area test: At a constant temperature of 77K (liquid nitrogen temperature), after measuring the adsorption amount of gas on the solid surface at different relative pressures, based on the Brown Noel-Etter-Taylor adsorption theory and its formula (BET calculation formula ) to obtain the adsorption capacity of the sample monolayer, thereby calculating the specific surface area of the solid;

(4) Particle size test: use an ultrasonic particle size analyzer to test the particle size distribution (Dv50, Dv99, etc.) of the material;

(5) Raman test: use a Raman spectrometer with a light source wavelength of 532nm, select a test range of 0cm ^-1 to _4000cm ^-1 , count and calculate the ratio of I ₁₃₅₀ /I ₁₅₈₀ (ID / _IG );

(6) Negative sheet resistivity test: The four-point probe method is used to test the negative electrode sheet resistance. The instrument used for the four-point probe method is a precision DC voltage and current source (type SB118), four copper plates with a length of 1.5cm*width of 1cm* and a thickness of 2mm It is fixed on a line at equal distances, the distance between the two copper plates in the middle is L (1-2cm), and the base material for fixing the copper plates is an insulating material; during the test, press the lower end face of the four copper plates on the negative electrode to be measured (the pressure is 3000Kg), the maintenance time is 60s, the copper plates at both ends are connected to the DC current I, the voltage V is measured on the two copper plates in the middle, the values of I and V are read three times, and the average values of I and V are taken respectively Ia and Va, Va/Ia The value is the membrane resistance at the test place, and the ratio of the resistance value to the thickness of the negative plate is the membrane resistivity; each negative plate is tested at 12 points, and the average value is the final negative plate resistivity result;

(7) Battery cycle performance test

At a test temperature of 25°C, the battery was charged to 4.45V with a constant current of 0.7C, charged to 0.025C with a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes. The capacity obtained in this step is the initial capacity; Then carry out 0.7C charge/0.5C discharge for cycle test, take the ratio of the capacity of each step to the initial capacity, which is the capacity retention rate, and then obtain the capacity decay curve (that is, the relationship between the cycle capacity retention rate and the number of cycles);

(8) Expansion rate test when the battery is cycled for 500 cycles: use a screw micrometer to measure the thickness d ₀ of the battery _at the beginning and the thickness d _x of the battery when it is cycled to 500 times. _x ;

Example 1

(1) Preparation of silicon matrix composites

(11) classifying and sieving the porous SiOx raw material to obtain a porous SiOx material with a Dv50 of 3 μm;

(12) 10g glucose is dissolved in 200mL xylene, after being completely dissolved, add 10g above-mentioned SiO material wherein, stir 3h, make SiO material disperse uniformly in the system, obtain dispersion;

20 g of C ₂ H ₆ OSi was added to xylene, stirred for 3 hours, and the C ₂ H ₆ OSi was completely dissolved to obtain a C ₂ H ₆ OSi solution; the C ₂ H ₆ OSi solution was added to the above dispersion, stirred for 4 hours, In order to ensure that the SiOx material is fully impregnated with C ₂ H ₆ OSi and glucose, the system is then heated and stirred at 80°C to remove the solvent, and then placed in an oven at 80°C for drying for 24 hours to obtain an impregnated product;

Put the impregnated product into a tube furnace, with _N2 as a protective atmosphere, first heat the impregnated product to 500 °C at a heating rate of 1 °C/min, keep it for 30 min, and then heat up to 1000 °C at a heating rate of 3 °C/min Perform high-temperature cracking, generate SiOC material on the surface of SiOx material, form a first shell layer, and obtain a powdery particulate product (referred to as SiOx@SiMC); wherein, the high-temperature cracking time is 3h (that is, kept at 1000 ° C for 3h);

(13) 10g of SiOx@SiMC and 1.01g of resin slurry with a solid content of 10% were added to the MSK-SFM-10 vacuum mixer, stirred for 180min, then added 100mL of deionized water, and continued to stir for 120min to obtain Mixing slurry; wherein, during the stirring process, the revolution speed is 10-40r/min, and the rotation speed is 1000-1500r/min;

Make the above-mentioned mixed slurry enter into the centrifugal turntable nozzle of the spray drying granulator from the inlet of the spray drying granulator (temperature is 260 ℃), and make the mixed slurry form tiny mist droplets under the condition that the centrifugal speed is 2000 r/min, And spray from the outlet of the spray drying granulator (temperature is 105 ° C), cool and collect the sprayed product (the macroscopic appearance is powder), that is, the dried product (referred to as SiOx@SiOC@precursor); SiOx@ The SiOC@precursor was placed in an atmosphere furnace with N ₂ as the protective atmosphere, first heated to 350°C at 5°C/min, held for 2h, and then heated to 800°C at 3°C/min for 2h. The carbon material is formed into a second shell layer, cooled to room temperature, and the material is collected to obtain a silicon-based composite material (referred to as SiOx@SiMC@C).

(2) Preparation of negative electrode sheet

Mix SiOx@SiMC@C and graphite in a mass ratio of 70:22 to obtain a mixed powder with a gram capacity of 500mAh/g, and place the mixed powder, acetylene black, and PAA in deionized water in a weight ratio of 95:1.2:3.8, After stirring evenly, a negative electrode slurry is prepared, and the negative electrode slurry is coated on the positive and negative surfaces of the copper foil. After drying and cold pressing, a negative electrode active material layer is formed on the positive and negative surfaces of the copper foil to obtain a negative electrode. piece.

(3) Preparation of positive electrode sheet

LiCoO ₂ , conductive carbon black and PVDF were fully stirred and mixed in N-methylpyrrolidone at a weight ratio of 96.7:1.7:1.6, and then coated on the front and back surfaces of the aluminum foil. After drying and cold pressing, forming a positive electrode active material layer on the positive electrode current collector to obtain a positive electrode sheet;

(4) Preparation of batteries

With the PE porous polymer film as the separator, the positive electrode sheet, separator film and negative electrode sheet are stacked in sequence, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to isolate the film, and then rolled to form a bare cell, the bare battery The core is placed in the outer package, the electrolyte is injected into it and packaged, and then processed by chemical formation, degassing, trimming, etc., to obtain a lithium ion battery; wherein, the electrolyte is composed of LiPF ₆ , an organic solvent and an additive, and the organic solvent is composed of It is composed of EC, DMC, DEC and FEC, wherein the volume ratio of EC, DMC and DEC in the organic solvent is EC:DMC:DEC=1:1:1, the mass content of FEC in the electrolyte is 10%, and the LiPF in the electrolyte The concentration of ₆ is 1mol/L, the additives include TFPB, 12-crown-4 ether, VC, the concentration of TFPB in the electrolyte is 0.1mol/L, the concentration of 12-crown-4 ether in the electrolyte is 0.05mol/L, The concentration of VC in the electrolyte was 0.1 mol/L.

Referring to the process of Example 1, the silicon-based composite material, negative electrode sheet and battery of Example 2 to Example 12 were obtained. The second carbon source used to generate the second shell layer and the carbon material in the second shell layer are shown in Table 1; the x value in the SiOx material, the particle size of the SiOx material (Dv50 ₂ ), the specific surface area of the SiOx material (BET ₂ ) , Type of M element in SiMC material, atomic ratio of carbon element to silicon element in SiMC material (C:Si), atomic ratio of M element to silicon element in SiMC material (M:Si), particle size (SiOx@SiMC) Particle size (Dv50 ₃ ), specific surface area of particles (BET ₃ ), particle radius R ₂ , inner core radius R ₁ , (R ₂ -R ₁ )/R ₂ , thickness of second shell (carbon layer), silicon base The particle size (Dv50 ₁ , Dv99) of the composite material, the specific surface area (BET ₁ ) of the silicon-based composite material, and the I ₁₃₅₀ /I ₁₅₈₀ of the Raman spectrum test result of the silicon-based composite material are shown in Table 2; except for the differences shown in Table 1 In addition, the remaining conditions of each embodiment are basically the same.

Comparative Example 1

The difference between this comparative example 1 and Example 1 is that the silicon-based composite material (SiOx@C) consists of SiOx material and a carbon layer existing on the surface of the SiOx material (that is, there is no SiMC material between the SiOx material and the carbon layer), SiOx The relevant parameters of @C are shown in Table 2; the preparation process of this Comparative Example 1 is the same as that of Example 1 except that step (12) in Example 1 is not included.

Comparative Example 2

The difference between this comparative example 2 and Example 1 is that the silicon-based composite material (SiOC@C) consists of a SiOC material and a carbon layer existing on the surface of the SiOC material (ie, no SiOx material). The relevant parameters of SiOC@C are shown in Table 2. ; Except that the preparation process of this comparative example 2 does not include the step (11) in embodiment 1, other preparation conditions are identical with embodiment 1.

Comparative Example 3

The difference between Comparative Example 3 and Example 1 is that the silicon-based composite material (SiOx@SiOC) is composed of SiOx material and SiCO material existing on the surface of the SiOx material (that is, there is no second shell layer). For the relevant parameters of SiOx@SiOC, see Table 2; the preparation process of this comparative example 3 is the same as that of example 1 except that step (13) in example 1 is not included.

Comparative Example 4

The difference between Comparative Example 4 and Example 1 is that the silicon-based composite material is a SiOx material (ie, without the first shell layer and the second shell layer). The relevant parameters of the SiOx material are shown in Table 2.

The electrical conductivity, negative electrode sheet resistivity, first coulombic efficiency of the battery, capacity retention rate when the battery is cycled 500 cycles, and expansion rate when the battery is cycled 500 cycles are measured in Table 3. In addition, the measured capacity decay curves of the batteries in Example 6 and Comparative Example 4 during cycling are shown in FIG. 2 .

Table 1

table 3

The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

A silicon-based composite material, characterized in that it comprises: particles consisting of an inner core and a first shell layer existing on the surface of the inner core, and a second shell layer existing on the surface of the particles, the inner core comprising silicon oxygen material, the first shell layer comprises SiMC material containing silicon element, M element, carbon element, and the M element comprises at least one element in Group IIIA, Group VA or Group VI in the periodic table, The second shell layer includes a carbon material.
The silicon-based composite material according to claim 1, wherein:

The particle size of the silicon-based composite material satisfies 2 μm≤Dv50 1 ≤10 μm, and Dv99<21 μm, wherein Dv50 1 represents the particle size from the small particle size side to reach 50% of the volume accumulation in the particle size distribution based on volume, Dv99 indicates that in the particle size distribution based on volume, the particle size reaches 99% of the cumulative volume from the small particle size side;

and / or,

The specific surface area of the silicon-based composite material is less than 5 m 2 /g.
The silicon-based composite material according to claim 1 or 2, wherein the Raman spectrum of the silicon-based composite material shows that the ratio of the peak height I 1350 at 1350 cm -1 and the peak height I 1580 at 1580 cm -1 satisfies 0<I 1350 /I 1580 <1.5.
The silicon-based composite material according to claim 1, wherein the silicon-oxygen material comprises a SiOx material, and 0.5<x<1.5.
The silicon-based composite material according to claim 1 or 4, characterized in that,

The particle size of the inner core satisfies 1 μm≤Dv50 2 ≤5 μm, wherein, Dv50 2 represents the particle size of the inner core particle from the small particle size side to reach 50% of the volume accumulation in the particle size distribution based on the volume;

and / or,

The inner core has a specific surface area greater than 3 m 2 /g.
The silicon-based composite material according to claim 1, wherein, in the SiMC material, the atomic ratio of carbon element to silicon element is 0.1 to 6, and the atomic ratio of M element to silicon element is 0.05 to 2.
The silicon-based composite material according to claim 1 or 6, wherein the particle size of the particles satisfies 2 μm≦Dv50 3 ≦9 μm, wherein Dv50 3 indicates that in the particle size distribution based on volume, the particles from the small particle size side up to 50% of the particle size accumulated by volume;

and / or,

The specific surface area of the microparticles is less than 8 m 2 /g.
The silicon-based composite material according to claim 1 or 6, wherein 0.1<(R 2 -R 1 )/R 2 <2/3 is satisfied, wherein R 1 is the radius of the inner core, and R 2 is The radius of the particle.
The silicon-based composite material according to claim 1, wherein the thickness of the second shell layer is 5 nm to 500 nm.
The silicon-based composite material according to claim 1 or 9, wherein the carbon material comprises at least one of amorphous carbon, graphene or carbon nanotubes.
The preparation method of the silicon-based composite material according to any one of claims 1-10, characterized in that, comprising:

The silicon oxide material is impregnated with a mixed solution containing a first carbon source and organosilane, and the obtained impregnated product is subjected to high temperature cracking treatment to form the first shell layer on the surface of the silicon oxide material to obtain the particle;

mixing the microparticles with the second carbon source to prepare a slurry, drying the slurry by a spray drying method, carbonizing the obtained dried product, and forming the second shell layer on the surface of the microparticles, The silicon-based composite material is obtained.
The preparation method according to claim 11, wherein the process of pyrolysis comprises a process of cracking at a temperature of 900°C to 1500°C.
A negative electrode sheet, characterized in that it comprises a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, the negative electrode active material layer contains a negative electrode active material, and the negative electrode active material comprises claim 1 - The silicon-based composite material of any one of 10.
The negative electrode sheet according to claim 13, wherein the negative electrode active material further comprises graphite.
The negative electrode sheet according to claim 13 or 14, wherein, in the negative electrode active material, the mass content of the silicon-based composite material is 0.5% to 80%.
An electrochemical device, characterized by comprising the negative electrode sheet according to any one of claims 13-15.
An electronic device, characterized by comprising the electrochemical device of claim 16 .