A composite material for secondary lithium-ion batteries, its preparation method and application

Abstract

This invention discloses a composite material for secondary lithium-ion batteries and its preparation method. The composite material comprises a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell layer covering the outer surface of the porous matrix. This invention also relates to a negative electrode sheet incorporating this composite material and a lithium-ion secondary battery. The hydrogen-containing silicon in this invention is uniformly dispersed in the composite material, solving the silicon dispersion problem and mitigating the volume effect of silicon during charge and discharge. The Si-H bonds contained in the hydrogen-containing silicon can effectively improve the stability of the material structure during charge and discharge, extending the battery cycle life. The preparation method of the composite material for secondary lithium-ion batteries of this invention is simple and easy to operate, and can be applied to mass production.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202311513274.6, filed on November 14, 2023, entitled “A composite material for secondary lithium-ion batteries, preparation method thereof and application thereof”. Technical Field

[0002] This invention relates to the field of battery technology, and in particular to a composite material for secondary lithium-ion batteries, its preparation method, and its application. Background Technology

[0003] Lithium-ion batteries are among the most widely used rechargeable battery systems. Compared to other rechargeable batteries such as nickel-cadmium and nickel-metal hydride batteries, lithium-ion batteries have advantages such as high energy density, high operating voltage, limited self-discharge, and low maintenance requirements. However, commercially available graphite anodes only have a capacity of 372 mAh g / g. -1 The theoretical specific capacity is insufficient to meet the ever-increasing demands for energy density, operational reliability, and system integration from portable electronic devices, electric vehicles, and energy storage applications.

[0004] Among all potential lithium-ion battery anode materials, silicon is one of the most promising candidates to replace graphite for the following reasons: (1) Silicon has the highest specific capacity (4200 mAh g / g) -1 ) and volumetric capacity (9786mAh / cm³) -3 (2) The average discharge voltage of Si is about 0.4V, which achieves a good balance between maintaining a reasonable open circuit voltage and avoiding unfavorable lithium plating process; (3) Silicon is abundant (the second most abundant in the earth's crust), and has the potential to be low-cost, environmentally friendly and non-toxic.

[0005] However, the lithium insertion and extraction processes in silicon involve rapid expansion and contraction (volume change of approximately 360%), generating enormous stress that severely impacts the structure: (1) the integrity of the electrode structure is compromised during repeated charge-discharge cycles; (2) interfacial stress induces the electrode to disconnect from the current collector; and (3) the solid electrolyte interphase (SEI) layer continuously consumes lithium ions during its formation-breakdown-reforming process. These processes synergistically accelerate electrode collapse and capacity decay. Furthermore, the poor intrinsic electronic conductivity of silicon also contributes to the slow electrochemical kinetics.

[0006] The nano-sizing technology of silicon can effectively alleviate the impact of the above-mentioned problems. CN 116454256A discloses a method for preparing silicon-carbon composite materials, in which nano-silicon and nano-carbon are directly composited in situ, and then coated with a layer of carbon material; and micron-sized silicon-carbon composite materials are obtained by spray granulation of slurry; high-temperature treatment pyrolyzes the binder or other impurities in the slurry to form pores, providing expansion space for silicon, and conductive carbon improves the conductivity of the material itself, which is beneficial to the electrochemical performance.

[0007] Nanoscale silicon can effectively mitigate the impact of volume expansion on electrodes, but the dispersion of nanoscale silicon particles with carbon materials still faces significant challenges. Aggregation of nanoscale silicon can still lead to volume expansion, preventing the full realization of its advantages. Summary of the Invention

[0008] This invention provides a composite material for secondary lithium-ion batteries, its preparation method, and its application, in order to solve the problems faced by nano-silicon in secondary lithium-ion batteries.

[0009] In one aspect, the present invention relates to a composite material for a secondary lithium-ion battery, the composite material comprising: a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell covering the outer surface of the porous matrix.

[0010] In one embodiment, the hydrogen content in the hydrogen-containing silicon is 0.01-10 wt%, preferably 0.03-5 wt%, and more preferably 0.09-3 wt%, based on the total weight of the composite material.

[0011] In another aspect, the present invention relates to a method for preparing the composite material of the present invention, comprising the following steps: providing a porous matrix; forming hydrogen-containing silicon dispersed in the porous matrix by CVD deposition and / or liquid impregnation; and coating the outer surface of the porous matrix in which the hydrogen-containing silicon is dispersed to form a shell.

[0012] In another aspect, the present invention relates to a negative electrode sheet comprising the composite material of the present invention.

[0013] In another aspect, the present invention relates to a lithium-ion secondary battery comprising the negative electrode sheet of the present invention. Attached Figure Description

[0014] Figure 1 (a) Infrared spectrum of the composite material sample of Example 1; (b) Infrared spectrum of the composite material sample of Example 2; (c) Infrared spectrum of the composite material sample of Example 3; (d) Infrared spectrum of the composite material sample of Example 4; (e) Infrared spectrum of the composite material sample of Example 5; (f) Infrared spectrum of the composite material sample of Example 6; (g) Infrared spectrum of the composite material sample of Example 7.

[0015] Figure 2 XRD pattern of the composite material sample in Example 1.

[0016] Figure 3 (a) SEM image of the composite material sample of Example 1; (b) TEM image of the composite material sample of Example 1.

[0017] Figure 4 Charge-discharge curves of coin cells obtained by assembling the negative electrode sheet prepared from the composite material sample of Example 1.

[0018] Figure 5 Cyclic curves of coin cells obtained by assembling negative electrode sheets prepared from composite material samples in Examples 1-7.

[0019] Figure 6 Cycling curves of coin cells obtained by assembling the negative electrode sheet prepared from the composite material sample of Example 1.

[0020] Figure 7 Thickness expansion curve of a coin cell obtained by assembling the negative electrode sheet prepared from the composite material sample of Example 1. Detailed Implementation

[0021] General definitions and terms

[0022] Unless otherwise stated, all publications, patent applications, patents and other references mentioned herein are incorporated herein in their entirety by way of citation.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0024] Unless otherwise stated, all percentages, portions, proportions, etc. are based on weight.

[0025] When quantities, concentrations, or other values ​​or parameters are given as ranges, preferred ranges, or preferred upper and lower limits, or specific values, they should be understood as specifically disclosing all ranges formed by pairs of values ​​from any upper or preferred range and any lower or preferred range, regardless of whether the range is disclosed individually. Unless otherwise stated, when a numerical range is referred to herein, the range means including its endpoints and all integers and fractions within that range. The scope of this invention is not limited to the specific numerical values ​​referenced when defining the range.

[0026] When describing numerical or range endpoints in this document, it should be understood that the disclosure includes the specific values ​​or endpoints referenced.

[0027] The expression "comprising," or similar expressions such as "including," "containing," and "having," is open-ended and does not exclude additional unlisted elements, steps, or components. The expression "consisting of," excludes any unspecified elements, steps, or components. The expression "substantially consisting of," limits the scope to the specified elements, steps, or components, plus optional elements, steps, or components that do not materially affect the essential and novel features of the claimed subject matter. It should be understood that the expression "comprising" encompasses both the expressions "substantially consisting of" and "consisting of."

[0028] Unless otherwise stated, the term "combination thereof" refers to a multi-component mixture of the elements, such as two, three, four, and up to the maximum possible multi-component mixture.

[0029] Furthermore, if the number of components or parts of the present invention is not previously specified, it indicates that there is no limitation on the number of times a component or part may appear (or be present). Therefore, it should be interpreted as including one or at least one, and the singular form of a component or part also includes the plural, unless the value clearly indicates a singular number.

[0030] As used herein, the terms “optional” or “optionally” mean that the event or situation subsequently described may or may not occur, including both the occurrence and non-occurrence of the event or situation.

[0031] The term “one or more” or “at least one” as used in this document means one, two, three, four, five, six, seven, eight, nine or more.

[0032] "Carbon" refers to materials or substances that essentially consist of carbon. Examples of carbon materials include, but are not limited to, activated carbon, pyrolytic carbon, hard carbon, graphite, and other allotropes of carbon.

[0033] "Carbonize," "pyrolyze," and "carbonize" all refer to the process of heating a carbon-containing material in an inert atmosphere (e.g., argon or nitrogen) or in a vacuum at a pyrolysis holding temperature so that the target material collected at the end of the process is mainly carbon. "Pyrolytic" refers to a material or substance that has undergone a pyrolysis process (e.g., carbon materials).

[0034] "Holding temperature" refers to the furnace temperature during a portion of the process used to maintain a relatively constant temperature (i.e., without raising or lowering the temperature). For example, pyrolysis holding temperature refers to a relatively constant furnace temperature during pyrolysis, and activation holding temperature refers to a relatively constant furnace temperature during activation.

[0035] "Pore structure" refers to the surface arrangement of internal pores within carbon materials (such as activated carbon). The components of pore structure include pore size, pore volume, surface area, density, pore size distribution, and pore length. Typically, the pore structure of porous carbon materials includes micropores, mesopores, and macropores.

[0036] "Mesopores" refer to pores with a diameter of 2-50 nm, "micropores" refer to pores with a diameter of less than 2 nm, and "macropores" refer to pores with a diameter of more than 50 nm. In mesoporous carbon materials, mesopores account for more than 50% of the total pore volume. In microporous carbon materials, micropores account for more than 50% of the total pore volume.

[0037] "Surface area" refers to the total specific surface area of ​​a substance that can be measured using BET technology. Typically, surface area is expressed in meters (m²). 2 The measurement is expressed in units of / g. BET technology uses an inert gas (such as nitrogen) to measure the amount of gas adsorbed on a material and is commonly used in the field to determine the accessible surface area of ​​a material.

[0038] "Composite material" refers to a composition containing multiple (two or more) different chemical substances within the same particle, such as particles containing porous carbon materials and silicon materials.

[0039] Allotropes are materials composed of the same single chemical element but existing in different forms. C60, graphene, diamond, hard carbon, soft carbon, graphite, and carbon nanotubes are all examples of carbon allotropes. "Hard carbon" refers to non-graphitized carbon materials. At high temperatures (typically 1500-2200℃), hard carbon remains essentially amorphous, while soft carbon undergoes crystallization and becomes graphitized.

[0040] "Coulomb efficiency" refers to the ratio of the discharge capacity to the charge capacity of a lithium-ion energy storage device. Coulomb efficiency is expressed as a percentage or fraction (e.g., 99% = 0.99).

[0041] Composite materials for secondary lithium-ion batteries

[0042] On one hand, the present invention provides a composite material for secondary lithium-ion batteries, the composite material comprising: a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell layer covering the outer surface of the porous matrix.

[0043] Porous matrix

[0044] The porous matrix of this application has a suitable pore structure, which is beneficial for silicon particles to be uniformly dispersed in the pores of the porous matrix to form nano-silicon particles. This avoids the volume expansion effect that may occur due to the aggregation of silicon particles, thereby giving full play to the advantages of nano-silicon particles and improving the performance of composite materials.

[0045] In this invention, the porous matrix can accommodate a variety of materials. The porous matrix may include, but is not limited to, porous carbon, porous polymer materials, porous ceramic materials, porous metal materials, or combinations thereof.

[0046] In a preferred embodiment, the porous matrix material primarily comprises carbon, such as hard carbon. Other allotropes of carbon are also contemplated, such as graphite, amorphous carbon, diamond, C60, carbon nanotubes (e.g., single-walled and / or multi-walled), graphene, and / or carbon fibers. Porosity can be introduced into carbon materials in various ways. For example, porosity in carbon materials can be achieved by adjusting the polymer precursor and / or processing conditions to produce porous carbon materials (described in detail later).

[0047] In other embodiments, the porous matrix may comprise polymeric materials. Polymers include, but are not limited to, at least one of polyaniline, polyether, polytetrafluoroethylene, polyethylene oxide, chitosan, polyvinyl alcohol, polyacrylamide, microcrystalline cellulose, polystyrene, 3,4-ethylenedioxythiophene, styrene sulfonate, polyethyleneimine, polyurethane, waterborne polyurethane, polyimide, hydrated aramid nanofibers, polydimethylsiloxane, acrylonitrile-butadiene-styrene, polyethersulfone, and polycarbonate-polyacrylonitrile. Polymers may also include resinic materials such as epoxy resins, polyester resins, acrylic resins, phenolic resins, FEVE fluoropolymers, ETFE fluoropolymers, and phthalonitrile resins. Polymers may also include biomass materials such as lignin, coconut shells, bamboo, fructose, sucrose, maltose, glucose, cellulose, and starch.

[0048] Porous matrix materials include porous ceramic materials, including but not limited to porous magnesium oxide, porous aluminum oxide, porous beryllium oxide, porous zirconium oxide, porous tin oxide, porous silicon dioxide, porous silicon nitride, porous aluminum nitride, porous boron nitride, porous titanium nitride, and porous silicon carbide.

[0049] Porous matrix materials also include porous metals, including but not limited to porous aluminum, porous steel, porous nickel, porous nickel-iron alloy, porous titanium, porous copper, porous brass, porous gold, porous silver, porous germanium, etc.

[0050] In this invention, the preparation of porous materials includes, but is not limited to, the following methods: emulsification, micelle generation, vaporization, dissolution followed by solvent removal (e.g., freeze-drying), axial compaction and sintering, gravity sintering, powder rolling and sintering, isobaric compaction and sintering, metal sputtering, metal coating and sintering, metal injection molding and sintering, etc. The methods for preparing porous materials may also include other pathways for generating porous polymer materials, including the generation of porous gels, such as freeze-dried gels.

[0051] The particle size of silicon particles dispersed within the pores of a porous matrix is ​​influenced by the pore size distribution of the porous matrix. A suitable pore size distribution in the porous matrix helps promote the formation of nano-silicon particles. A porous matrix can contain 20%-90% micropores, 10%-50% mesopores, and 0-30% macropores. The total pore volume of the porous matrix can range from 0.1 to 2.5 cm³. 3 / g, preferably 0.5-1.2cm 3 / g.

[0052] In some embodiments, the porous carbon has a different pore size distribution, comprising 20% ​​micropores, 50% mesopores, and 30% macropores, with a total pore volume of 1.2 cm³. 3 / g. In some embodiments, it comprises 25% micropores, 45% mesopores, and 30% macropores, with a total pore volume of 1.0 cm³. 3 / g. In some embodiments, it comprises 30% micropores, 45% mesopores, and 25% macropores, with a total pore volume of 0.9 cm³. 3 / g. In some embodiments, it comprises 35% micropores, 40% mesopores, and 25% macropores, with a total pore volume of 0.8 cm³. 3 / g. In some embodiments, it comprises 40% micropores, 40% mesopores, and 20% macropores, with a total pore volume of 0.7 cm³. 3 / g. In some embodiments, it comprises 50% micropores, 35% mesopores, and 15% macropores, with a total pore volume of 0.6 cm³. 3 / g. In some embodiments, it comprises 60% micropores, 30% mesopores, and 10% macropores, with a total pore volume of 0.5 cm³. 3 / g. In some embodiments, it comprises 70% micropores, 25% mesopores, and 5% macropores, with a total pore volume of 0.4 cm³. 3 / g. In some embodiments, it comprises 80% micropores, 18% mesopores, and 2% macropores, with a total pore volume of 0.2 cm³. 3 / g. In some embodiments, it comprises 90% micropores and 10% mesopores, with a total pore volume of 0.1 cm³. 3 / g.

[0053] A suitable pore volume in a porous matrix is ​​beneficial for increasing the silicon content in composite materials, thereby improving the performance of the corresponding products, such as charge specific capacity. The specific surface area (BET) of the porous matrix can range from 1000 to 2500 m². 2 / g, for example, 1900-2000m 2 / g, 1000-1200m 2 / g, 1500-1600m 2 / g、2200-2500m 2 / g etc.

[0054] A suitable particle size distribution in a porous matrix is ​​beneficial for increasing the silicon content in composite materials, thereby improving the performance of the corresponding products. The D50 particle size of the porous matrix can be 1-30 μm, preferably 1-20 μm, such as 5-15 μm, 5-20 μm, 10-25 μm, 5-25 μm, 10-30 μm, etc. The D100 particle size of the porous matrix can be 5-80 μm, preferably 5-50 μm, such as 10-20 μm, 20-40 μm, 30-50 μm, 40-60 μm, 50-70 μm, 60-80 μm, etc.

[0055] In some embodiments, the porous carbon has different particle size distributions, with a D50 of 1-10 μm and a D100 of 5-10 μm. In some embodiments, the D50 is 5-15 μm and the D100 is 10-20 μm. In some embodiments, the D50 is 5-20 μm and the D100 is 20-40 μm. In some embodiments, the D50 is 10-25 μm and the D100 is 30-50 μm. In some embodiments, the D50 is 5-25 μm and the D100 is 40-60 μm. In some embodiments, the D50 is 10-30 μm and the D100 is 50-70 μm. In some embodiments, the D50 is 15-30 μm and the D100 is 60-80 μm.

[0056] An appropriate oxygen content in the porous matrix helps improve the electrochemical performance of the product. Excessive oxygen content in the porous matrix may lead to a decrease in the initial coulombic efficiency of the battery. The oxygen content of the porous matrix can be 0.01-0.6 mmol / g, for example, 0.01-0.4 mmol / g, 0.1-0.3 mmol / g, 0.2-0.5 mmol / g, 0.3-0.6 mmol / g, etc.

[0057] The tap density of the porous matrix can be 0.2-0.6 g / cm³. 3 For example, 0.2g / cm 3 0.3g / cm 3 0.4g / cm 3 0.5g / cm 3 0.6g / cm 3 In some embodiments, the tap density of the composite material for the secondary lithium-ion battery is 0.8 g / cm³. 3 The tap density of the porous matrix is ​​0.4 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 1.2 g / cm³. 3 The tap density of the porous matrix is ​​0.5 g / cm³.3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 1.4 g / cm³. 3 The tap density of the porous matrix is ​​0.6 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 2 g / cm³. 3 The tap density of the porous matrix is ​​0.6 g / cm³. 3 .

[0058] Hydrogen-containing silicon

[0059] In this application, silicon is uniformly dispersed within the pores of a porous matrix to form nano-silicon (i.e., nano-silicon particles), while the outer surface of the porous substrate is essentially free of silicon. This allows the material to fully utilize the advantages of nano-silicon. In this application, the silicon dispersed in the porous matrix retains some Si-H bonds, and therefore the silicon dispersed in the porous matrix is ​​also referred to as hydrogen-containing silicon.

[0060] In this application, hydrogen-containing silicon refers to all nano-silicon dispersed in a porous matrix. In the hydrogen-containing silicon described herein, at least a portion of the nano-silicon particles are nano-silicon particles with Si-H bonds.

[0061] The presence of Si-H bonds in hydrogen-containing silicon can effectively improve the stability of the composite material during charge and discharge processes, extending the battery cycle life. Si-H bonds in hydrogen-containing silicon can be determined by any method in the art, including but not limited to infrared spectroscopy. The infrared spectrum of the composite material in this application is in the range of 625-640 cm⁻¹. -1 The infrared spectrum of the composite material also shows vibrational peaks at one or more of the following locations: 845-885 cm⁻¹. -1 1990-2010cm -1 .

[0062] "Hydrogen content in hydrogen-containing silicon" refers to the percentage of the total weight of hydrogen elements in the retained Si-H bonds of the composite material. There is a positive correlation between the amount of Si-H bonds present in hydrogen-containing silicon and its hydrogen content. Factors such as the structure of the porous matrix and the dispersion process of silicon within the porous matrix affect the amount of Si-H bonds present in hydrogen-containing silicon and its hydrogen content. An appropriate hydrogen content in hydrogen-containing silicon helps improve the electrical performance of products, such as improving battery capacity retention. Based on the total weight of the composite material, the hydrogen content in the hydrogen-containing silicon can be 0.01-10 wt%, preferably 0.3-5 wt%, more preferably 0.9-3 wt%, for example, 0.01 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, 3.0 wt%, 5.0 wt%, 10.0 wt%, etc. The hydrogen content in the hydrogen-containing silicon can be determined by any method available in the art; for example, the hydrogen content C in the hydrogen-containing silicon... H The infrared absorption peaks in the swing mode region of the infrared test can be used for fitting and calculation.

[0063] The ratio of silicon dispersed in the porous matrix to the porous matrix also affects the performance of the composite material. An appropriate amount of silicon dispersed in the porous matrix can endow the product with better electrical properties (such as excellent charge specific capacity), while also retaining some pores in the porous matrix to provide some space for the expansion of silicon in the later stage, and avoid the composite material from cracking or even shattering due to the volume expansion of silicon.

[0064] Based on the total weight of the composite material, the silicon content of the composite material can be 5-90 wt%, preferably 15-70 wt%, more preferably 30-65 wt%, for example 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%.

[0065] 35wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%,

[0066] 48wt%, 49wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%,

[0067] 85wt%, 90wt%, etc. It can be understood that when the composite material contains no Si except for the hydrogen-containing silicon dispersed in the porous matrix, if the composition of other parts (such as the porous matrix and shell) does not contain Si, the silicon content in the composite material is the content of silicon dispersed in the porous matrix.

[0068] A suitable particle size for hydrogen-containing silicon is beneficial to improving the performance of composite materials. The particle size range of hydrogen-containing silicon is 0.1-60 nm, preferably 0.1-20 nm, and more preferably 1-5 nm.

[0069] The hydrogen-containing silicon can be in the form of crystalline silicon or amorphous silicon. In some embodiments, the hydrogen-containing silicon includes hydrogen-containing crystalline silicon. In some embodiments, the hydrogen-containing silicon includes hydrogen-containing polycrystalline silicon. In some embodiments, the hydrogen-containing silicon includes nano-hydrogen-containing polycrystalline silicon. In some other embodiments, the hydrogen-containing silicon includes hydrogen-containing amorphous silicon. In some other embodiments, the hydrogen-containing silicon includes both hydrogen-containing crystalline silicon and hydrogen-containing amorphous silicon.

[0070] The degree of crystallinity of silicon in hydrogen-containing silicon can be determined by any method in the art, such as by electrochemical curve analysis. For test samples obtained from composite materials, the plateau at 0.4-0.5V on the charging curve and the characteristic peak of the corresponding DQ / DV curve at 0.4-0.5V are related to the degree of crystallinity of the hydrogen-containing silicon. In hydrogen-containing silicon, the higher the proportion of crystalline silicon, the more pronounced the plateau at 0.4-0.5V on the charging curve, and the stronger the intensity of the characteristic peak of the DQ / DV curve at 0.4-0.5V.

[0071] Shell covering the outer surface of a porous matrix

[0072] The outer surface of the porous matrix also contains a dense shell, which serves as the outer layer of the composite material. The shell covering the outer surface of the porous matrix not only prevents the highly active nano-hydrogen-containing silicon inside the porous matrix from oxidizing and spontaneously combusting in the air, but also ensures that the porous matrix and the hydrogen-containing silicon inside it do not come into direct contact with the electrolyte during the use of the composite material, which is conducive to the formation of a stable SEI film.

[0073] A shell can be formed by reacting a porous matrix containing hydrogen-silicon, or by attaching other materials to the surface of the porous matrix.

[0074] The shell composition may include, but is not limited to: amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, alumina, aluminum nitride, silicon carbides, silicon nitrides, silicon oxides (such as silicon dioxide), silicon oxynitrides, or combinations thereof. In some embodiments, the shell of the composite material of the present invention is a carbon shell.

[0075] The shell can be single-layered or multi-layered. Any single layer of the shell is not limited to any one of the components described above; it can be a combination of several substances.

[0076] An appropriate shell thickness helps to fully utilize its function. The shell thickness can range from 1 to 1000 nm. In some embodiments, the shell thickness of the composite material for a rechargeable lithium-ion battery is 1-10 nm. In some embodiments, the shell thickness of the composite material for a rechargeable lithium-ion battery is 10-50 nm. In some embodiments, the shell thickness of the composite material for a rechargeable lithium-ion battery is 50-100 nm. In some embodiments, the shell thickness of the composite material for a rechargeable lithium-ion battery is 100-500 nm. In some embodiments, the shell thickness of the composite material for a rechargeable lithium-ion battery is 500-1000 nm.

[0077] It should be understood that the "shell covering the outer surface of a porous matrix" as described herein does not mean that the shell material is only located on the outside of the porous matrix. For example, the shell material may enter the pores of the porous matrix near the outer surface. As another example, the shell can be formed by reacting the outer portion of a porous matrix in which nano-silicon is dispersed.

[0078] It should also be understood that there may be a clear interface between the shell and the porous matrix described herein. Alternatively, there may be no clear interface between the shell and the porous matrix; for example, there may be a boundary region with a certain thickness between the shell and the porous matrix.

[0079] It should also be understood that the thickness of the shell described in this article may be uniform or may vary at different locations.

[0080] Preparation method

[0081] On the other hand, the present invention provides a method for preparing the above-mentioned composite material for secondary lithium-ion batteries, the method comprising:

[0082] Provide a porous matrix;

[0083] Hydrogen-containing silicon is formed in a porous matrix by CVD deposition and / or liquid impregnation.

[0084] The outer surface of the porous matrix containing hydrogen-containing silicon is coated to form a shell.

[0085] Provision of porous matrix

[0086] In this paper, there are no special restrictions on the way the porous matrix is ​​provided; it can be obtained commercially or prepared by any preparation method in the art.

[0087] As an example, porous carbon can be formed by introducing pores into carbon materials in various ways. The porosity in the carbon material can be controlled by adjusting the polymer precursor and / or processing conditions during the preparation process to produce the desired porous carbon.

[0088] In this invention, the preparation of porous materials includes, but is not limited to, the following methods: emulsification, micelle generation, vaporization, dissolution followed by solvent removal (e.g., freeze drying), axial compaction and sintering, gravity sintering, powder rolling and sintering, isobaric compaction and sintering, metal sputtering, metal coating and sintering, metal injection molding and sintering, etc.

[0089] As an example, the preparation methods for porous polymer materials may include, but are not limited to, preparing porous gels by freeze-drying.

[0090] Formation of hydrogen-containing silicon

[0091] Silicon can be dispersed into the pores of a porous matrix using any method in the art to form hydrogen-containing silicon dispersed in the porous matrix. The retention of Si-H bonds can be achieved by controlling the silicon dispersion process (e.g., temperature), thereby effectively improving the stability of the composite material during charge and discharge processes and extending battery cycle life.

[0092] Silicon dispersion can be achieved in any way possible in the art, including but not limited to CVD deposition and liquid impregnation. Appropriate parameters during dispersion contribute to obtaining the desired composite material.

[0093] The process of forming hydrogen-containing silicon dispersed in a porous matrix by CVD deposition includes: placing the porous matrix in a reaction vessel and introducing a protective gas into the reaction vessel; heating the reaction vessel to the reaction temperature; and introducing silicon-containing gas into the reaction vessel to deposit it in the porous matrix. The heating rate of the reaction vessel can be 1-10℃ / min, for example, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc. The reaction temperature can be 400-600℃, for example, 400℃, 405℃, 420℃, 450℃, 480℃, 500℃, 550℃, 600℃, etc. The flow rate of the protective gas can be 5-30 L / min, for example, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 23 L / min, 25 L / min, 30 L / min, etc. The total flow rate of the silicon-containing gas can be 10-40 L / min, for example, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, etc. The deposition time can be 5-20 hours, for example, 5 hours, 6 hours, 10 hours, 15 hours, 20 hours, etc.

[0094] In CVD deposition, silicon-containing gases may include: dichlorosilane, Si n H 2n+2 Silanes or combinations thereof, where n is an integer selected from 1 to 3. Silicon-containing gases may preferably include: dichlorosilane, methylsilane, diethylsilane, propane, or combinations thereof.

[0095] In CVD deposition, the reaction vessel can be designed as a fluidized bed reactor, tubular furnace, bell furnace, pit furnace, lift-type kiln, rotary kiln, box kiln, or other suitable reactor type. In a preferred embodiment, the reaction is carried out under conditions that provide a uniform gas phase inlet, such as in a reactor in which the feedstock is fluidized, or by other means of agitation to provide a uniform gas inlet.

[0096] Preferably, the composite material for secondary lithium-ion batteries provided by the present invention involves placing porous carbon particles in an inert atmosphere and at a high temperature, allowing them to fully contact with a silicon-containing gas to achieve uniform silicon deposition via chemical vapor deposition, thereby generating hydrogen-containing silicon within the pores of the porous carbon. Specifically, the porous carbon is placed in a reaction vessel, and nitrogen or argon gas is introduced into the reaction vessel as a protective gas at a flow rate of 1-50 L / min. The reactor is heated to 400-600°C at a heating rate of 1-10°C / min. Then, the silicon-containing gas is introduced into the reaction vessel and deposited on the porous carbon. Preferably, the temperature can be 400-450°C, 450-500°C, 500-550°C, 550-600°C, or 500-600°C. A silicon-containing gas is introduced into the reaction vessel along with an inert gas. The silicon-containing gas content can be 0.1-1%, 1%-10%, 10%-20%, 20%-30%, 30%-40%, or 40%-50%. The silicon-containing gas can also be any gas with the general formula Si. n H 2n+2 The gaseous form of one or more silanes selected from the group consisting of silanes (where n is an integer selected from 1 to 3). For example, the silicon-containing gas can be silane, silane, or propane. The reaction vessel can be designed as a fluidized bed reactor, tubular furnace, bell furnace, pit furnace, lift-type kiln, rotary kiln, box kiln, or other suitable reactor type. In a preferred embodiment, the porous carbon particles are processed under conditions that provide a uniform gas phase inlet, such as in a reactor where the porous carbon particles are fluidized, or by other means of agitation to provide a uniform gas inlet.

[0097] The process of forming hydrogen-containing silicon dispersed in a porous matrix via liquid impregnation includes: uniformly mixing the porous matrix and a silane liquid, followed by carbonization and reduction at high temperature. The silane liquid includes: trichlorosilane, Si... n H 2n+2 Silanes or combinations thereof, where n is an integer selected from 4 to 10. In some embodiments, the porous silicon matrix to be impregnated or otherwise impregnated is porous carbon. The porous carbon to be impregnated or otherwise impregnated with silicon can comprise various allotropes of carbon. For this purpose, the porous carbon to be impregnated or otherwise impregnated with silicon can include graphite, nanographite, graphene, carbon black, carbon nanowires, carbon nanotubes, and combinations thereof.

[0098] In some embodiments, the carbon scaffold impregnated or otherwise impregnated with silicon is removed to obtain a templated silicon material with desired dimensional properties. The removal of the scaffold carbon can be achieved in ways known in the art, such as by thermochemical activation under certain conditions, where the silicon does not undergo undesirable changes in its electrochemical properties. Alternatively, if the scaffold is a porous polymer or other material soluble in a suitable solvent, the scaffold can be removed by dissolution.

[0099] Shell formation

[0100] A shell can be formed by coating the outer surface of a porous substrate containing dispersed hydrogen-containing silicon. Coating the surface of the porous substrate containing dispersed hydrogen-containing silicon with a shell can prevent the highly reactive hydrogen-containing silicon from being oxidized by exposure to air. At the same time, during the use of the composite material, it can also reduce the direct contact between the porous substrate and the hydrogen-containing silicon in it and the electrolyte, helping to form a stable SEI film on the surface.

[0101] This article does not impose any special restrictions on the coating method. The outer surface of the porous substrate can be coated by reactive coating, adhesive coating, or a combination of reactive coating and adhesive coating. Other coating methods that can form a shell on the surface of a porous substrate containing hydrogen-containing silicon can also be used.

[0102] Reactive coating refers to forming a shell layer through a reaction process to achieve coating. For example, a shell layer can be formed by reacting a porous substrate containing dispersed hydrogen-silicon. Specifically, coating can be achieved through partial oxidation, nitriding, or carbonization of the hydrogen-silicon. In some embodiments, the shell material is silicon dioxide, which can be formed by heat-treating the porous substrate containing dispersed hydrogen-silicon in an oxidizing atmosphere, i.e., by surface oxidation to uniformly generate a silicon dioxide shell layer on the surface of the porous substrate containing dispersed hydrogen-silicon. In these embodiments, the oxidizing atmosphere includes, but is not limited to, one or more of air, oxygen, carbon dioxide, carbon monoxide, and water vapor. The heat treatment temperature can be 0-100°C, 100-200°C, 200-300°C, 300-400°C, or 400-500°C.

[0103] Adhesive coating refers to the process of attaching materials to the surface of a porous substrate to form a shell.

[0104] The outer surface of a porous substrate can be coated using a combination of reactive and adhesive coating methods, as illustrated in the following examples.

[0105] In some embodiments, the shell material is carbon. A porous matrix dispersed with hydrogen-containing silicon (such as porous carbon) can be contacted with a carbon source precursor, and after heat treatment, a carbon shell layer can be uniformly formed on the surface of the porous matrix dispersed with hydrogen-containing silicon. Coating methods include chemical vapor deposition (CVD), liquid-phase coating, and solid-phase coating. The following describes various coating methods using porous carbon as an example. In chemical vapor deposition (CVD), the carbon source precursor includes, but is not limited to, one or more of methane, propane, butane, cyclohexane, ethane, propylene, and acetylene. The coating temperature can be 400-450℃, 450-500℃, 500-550℃, or 550-600℃. In liquid-phase coating, the carbon source precursor includes, but is not limited to, one or more combinations of asphalt, polyvinyl alcohol, polyethylene glycol, anthracene, aniline, and tannic acid. The mixing ratio of liquid carbon source to dispersed hydrogen-containing porous carbon ranges from 1:0.5 to 1:10. Stirring and ultrasonic dispersion are used for uniform mixing. The carbonization temperature can be 400-450℃, 450-500℃, 500-550℃, or 550-600℃. In the solid-phase coating method, the carbon source precursor includes, but is not limited to, one or more combinations of glucose, sucrose, biphenyl, and vinylpyrrolidone. The carbonization temperature can be 400-450℃, 450-500℃, 500-550℃, or 550-600℃. The carbonization time can be 1 hour to 5 hours. The ratio of solid carbon source to dispersed hydrogen-containing porous carbon can range from 1:0.5 to 1:10.

[0106] In some embodiments, the shell material is a metal oxide. A metal oxide shell is uniformly formed on the surface of the dispersed silicon-containing porous carbon by contacting the metal oxide precursor with porous carbon containing hydrogen silica and then heat-treating it. The coating methods include chemical vapor deposition (CVD), liquid phase coating, and solid phase coating. In these embodiments, the shell material precursor includes, but is not limited to, one or more of titanate esters and aluminum phosphate, and the heat treatment temperature can be 0-100°C, 100-200°C, 200-300°C, 300-400°C, or 400-500°C.

[0107] In one embodiment, this disclosure provides the preparation of a composite material for secondary lithium-ion batteries, wherein the matrix is ​​a porous matrix, and silicon is uniformly dispersed in the porous matrix by contacting the porous matrix with silicon-containing reactants. The silicon is uniformly distributed within the pores of the porous matrix, primarily in the form of hydrogen-containing silicon. The method may include the following steps:

[0108] 1) Prepare porous carbon material as a porous matrix; 2) Deposit the porous matrix at high temperature in a reaction vessel in the presence of silicon-containing gas to produce a porous carbon material in which hydrogen-containing silicon is uniformly dispersed.

[0109] In another embodiment, this disclosure provides a method for preparing a composite material for secondary lithium-ion batteries, wherein the matrix is ​​a porous matrix, silicon is uniformly dispersed in the porous matrix by contacting the porous matrix with silicon-containing reactants, and the final coating layer is achieved by contacting the composite with carbon-containing reactants. For example, the method may include the following steps: 1) preparing a porous carbon material as a porous matrix; 2) subjecting the porous matrix to high temperature in a reaction vessel in the presence of a silicon-containing gas for deposition to produce a porous carbon material in which hydrogen-containing silicon is uniformly dispersed; 3) performing carbon coating by any one of gas-phase coating, liquid-phase coating, or solid-phase coating.

[0110] In another embodiment, this disclosure provides the preparation of a composite material for secondary lithium-ion batteries, wherein the matrix is ​​a porous matrix, silicon is uniformly dispersed in the porous matrix by contacting the porous matrix with silicon-containing reactants, a silica coating layer is obtained by contacting the composite with an oxygen-containing atmosphere, and a carbon coating layer is obtained by contacting the composite with carbon-containing reactants. For example, the method may include the following steps: 1) preparing a porous carbon material as a porous matrix; 2) subjecting the porous matrix to high temperature in a reaction vessel in the presence of a silicon-containing gas for deposition to produce a porous carbon material in which hydrogen-containing silicon is uniformly dispersed; 3) treating the surface of the uniformly dispersed hydrogen-containing silicon carbon material with an oxidizing atmosphere of air, carbon dioxide, or water vapor to obtain a silica shell through oxidation passivation; 4) obtaining a carbon shell layer by carbon coating through any one of gas-phase coating, liquid-phase coating, or solid-phase coating. Properties of composite materials used in secondary lithium-ion batteries able

[0111] The composite material of this invention has various advantageous properties and can be used to prepare secondary lithium-ion batteries with excellent performance.

[0112] Physical properties

[0113] The composite material for secondary lithium-ion batteries of the present invention has suitable physical properties, which is beneficial for producing secondary lithium batteries with excellent performance.

[0114] Composite materials used in secondary lithium-ion batteries can contain varying proportions of hydrogen-containing silicon. Appropriate elemental content in the composite material helps improve its performance, particularly its electrical properties.

[0115] Based on the total weight of the composite material, the hydrogen content in the hydrogen-containing silicon can be 0.01-10 wt%, preferably 0.3-5 wt%, more preferably 0.9-3 wt%, for example 0.01 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, 3.0 wt%, 5.0 wt%, 10.0 wt%, etc.

[0116] Based on the total weight of the composite material, the silicon content of the composite material can be 5-90 wt%, preferably 15-70 wt%, more preferably 30-65 wt%, such as 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 37.9 wt%, 40 wt%, 40.2 wt%, 42.5 wt%, 45 wt%, 46 wt%, 46.1 wt%, 47 wt%, 47.2 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 80 wt%, 85 wt%, 90 wt%, etc.

[0117] Based on the total weight of the composite material, the carbon content of the composite material can be 10-95 wt%, preferably 30-90 wt%, more preferably 35-85 wt%, such as 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 42.5 wt%, 45 wt%, 46 wt%, 7 wt%, 48 wt%, 49 wt%, 50 wt%, 50.8 wt%, 51 wt%, 51.3 wt%, 51.8 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 57.3 wt%, 60 wt%, 60.3 wt%, 65 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, etc.

[0118] Based on the total weight of the composite material, the oxygen content of the composite material can be 0-3wt%, for example, 0wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, etc.

[0119] In some embodiments, the composite material contains 51.8 wt% C, 45.0 wt% Si, 0.2 wt% O, and 3.0 wt% H in the hydrogen-containing silicon. In some embodiments, the composite material contains 51.3 wt% C, 46.1 wt% Si, 0.2 wt% O, and 2.4 wt% H in the hydrogen-containing silicon. In some embodiments, the composite material contains 50.8 wt% C, 47.2 wt% Si, 0.2 wt% O, and 1.8 wt% H in the hydrogen-containing silicon. In some embodiments, the composite material contains 58.4 wt% C, 40.2 wt% Si, 0.2 wt% O, and 1.2 wt% H in the hydrogen-containing silicon. In some embodiments, the composite material contains 60.3 wt% C, 37.9 wt% Si, 0.3 wt% O, and 1.5 wt% H in the hydrogen-containing silicon. In some embodiments, the composite material contains 57.3 wt% C, 42.5 wt% Si, 0.2 wt% O, and 0.01 wt% H in the hydrogen-containing silicon.

[0120] The specific surface area of ​​the composite material in the secondary lithium-ion battery of the present invention can vary. The specific surface area (BET) of the composite material can be 1-10 m². 2 / g, for example, 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、。The total pore volume of the composite material can be 0.1cm. 3 / g or less. In some implementations, BET is 1m. 2 / g, total pore volume less than 0.1cm³ 3 / g. In some implementations, BET is 2m. 2 / g, total pore volume less than 0.1cm³ 3 / g. In some implementations, BET is 4m. 2 / g, total pore volume less than 0.1cm³ 3 / g. In some implementations, BET is 6m. 2 / g, total pore volume less than 0.1cm³ 3 / g. In some implementations, BET is 8m. 2 / g, total pore volume less than 0.1cm³ 3 / g. In some implementations, BET is 10m. 2 / g, total pore volume less than 0.1cm³ 3 / g.

[0121] In preferred embodiments, the composite material has a relatively uniform size distribution, with upper and lower limits within a preferred range, for example, a particle size distribution of D50 of 1-15 μm and D100 of 10-30 μm. In some embodiments, the composite material has a size distribution of D50 of 5-20 μm and D100 of 20-40 μm. In some embodiments, the composite material has a size distribution of D50 of 15-25 μm and D100 of 40-60 μm; in some embodiments, the composite material has a size distribution of D50 of 20-30 μm and D100 of 50-70 μm. In some embodiments, the composite material has a size distribution of D50 of 25-35 μm and D100 of 60-80 μm. In some embodiments, the composite material has a size distribution of D50 of 30-40 μm and D100 of 70-90 μm. In some embodiments, the composite material has the following size distribution: D50 in the range of 40-50 μm and D100 in the range of 80-100 μm.

[0122] In some embodiments, the XRD pattern of the composite material for the secondary lithium-ion battery exhibits amorphous characteristic peaks between 24-30°. In some embodiments, it has sharp characteristic peaks with a grain size of 5-30 nm at 28° ± 0.5°. In some embodiments, the grain size is 5 nm. In some embodiments, the grain size is 10 nm. In some embodiments, the grain size is 15 nm. In some embodiments, the grain size is 20 nm. In some embodiments, the grain size is 30 nm.

[0123] The tap density of the composite material for secondary lithium batteries of the present invention can be 0.5-2 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 0.5 g / cm³. 3 The tap density of the porous matrix is ​​0.2 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 0.6 g / cm³. 3 The tap density of the porous matrix is ​​0.3 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 0.8 g / cm³. 3 The tap density of the porous matrix is ​​0.4 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 1.2 g / cm³.3 The tap density of the porous matrix is ​​0.5 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 1.4 g / cm³. 3 The tap density of the porous matrix is ​​0.6 g / cm³. 3 In some implementations, the tap density of the composite material for the secondary lithium-ion battery is 2 g / cm³. 3 The tap density of the porous matrix is ​​0.6 g / cm³. 3 .

[0124] Electrochemical performance

[0125] In some embodiments, the electrochemical performance of the composite material disclosed herein is tested in a half-cell. Specifically, the negative electrode is prepared as follows: the composite material of this application, conductive additive carbon black, and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) are weighed at a ratio of 95:2:3 and prepared as a slurry in a pulping machine at room temperature. The prepared slurry is uniformly coated onto copper foil and dried in a forced-air drying oven at 50°C for 2 hours, then cut into electrode sheets with a diameter of 8 mm. The electrode sheets are then vacuum-dried in a vacuum drying oven at 100°C for 10 hours, and the dried electrode sheets are immediately transferred to a glove box for use in battery assembly. Battery assembly: A simulated battery is assembled in a glove box containing a high-purity Ar atmosphere, using lithium metal as the counter electrode and a solution of 1 mole of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1) as the electrolyte. Testing: Constant current charge-discharge mode tests were conducted using a charge-discharge apparatus. The discharge cutoff voltage was 0.005V, and the charge cutoff voltage was 1.5V. The charge-discharge tests were performed at a current density of C / 10. The composite material was compounded with commercial graphite in a specific ratio to form a test material of 450mAh / g, which was then assembled with lithium cobalt oxide into coin cells. The cells were cycled at 1C to evaluate their cycle performance.

[0126] In some embodiments, the electrochemical performance of the composite materials disclosed herein is tested in coin cells. Specifically, the preparation of the positive electrode sheet includes: formulation parameters: 96.2% positive electrode material + 1.1% binder + 2.7% conductive agent; mixing parameters: dry mixing, high-speed dispersion (72% solid content), adjusting viscosity to approximately 5000 for coating; coating parameters: single-sided areal density 21 mg / cm³. 2After being cut into 15cm wide strips, positive electrode sheets with dimensions of 73mm × 44mm are obtained by die-cutting. Preparation of the negative electrode sheet: Formula parameters: 95.0wt% negative electrode material (composite material sample of the example) + 3.5wt% binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) + 1.5wt% conductive agent carbon black; Batching parameters: dry mixing and kneading (solid content 65%), high-speed dispersion (solid content 45%), adjusting the viscosity to approximately 5000 before coating; Coating parameters: single-sided surface density 9mg / cm². 2 After being cut into 15cm wide strips, negative electrode sheets with dimensions of 75mm × 46mm are obtained by die-cutting. Battery assembly: The following process is performed: Stacking: 9 negative electrode sheets and 8 positive electrode sheets are stacked in a Z-shape; Welding tabs: Tabs are welded onto the positive and negative electrodes respectively (positive electrode: aluminum; negative electrode: nickel); Hot pressing and cold pressing: Hot pressing at 80℃ for 1 minute, and cold pressing at room temperature for 1 minute; Aluminum molding and punching: Punching depth is 3mm; Top sealing and side sealing: Heat sealing temperature is 190℃, and heat sealing time is 6 seconds; Baking: Incubation at 95℃ for 3 days, during which nitrogen purging is performed to ensure that the sample is in an inert atmosphere; Water content test: Take... Approximately 1g each of the positive and negative electrode sheets are heated at 120℃ to remove water, reducing the moisture content to below 200ppm. Electrolyte injection: A solution of 1 mole of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1) is injected between the positive and negative electrode sheets. The injection coefficient calculated based on the initial charge is 3.5. Sealing: Heat-sealing temperature 190℃, heat-sealing time 3 seconds, vacuum degree -90. The assembled battery sample is obtained by immersion at 45℃ for 2 days. Cycling conditions for full cell testing: 1C / 1C; voltage range: 2.8-4.25V.

[0127] The composite materials disclosed herein for use in secondary lithium-ion batteries can improve the properties of electrical storage devices, for example, improvements in the initial coulombic efficiency, specific charge capacity, and capacity retention of lithium-based batteries have been shown.

[0128] In one embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, the composite material has an initial coulombic efficiency of 75% or more, or 80% or more, or 82% or more, or 85% or more, or 88% or more, or 90% or more, or 92% or more, or 93% or more, or 95% or more, or 98% or more, or 99% or more.

[0129] In one embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, the composite material has a charge specific capacity of 1600 mAh / g or higher, such as 1600 mAh / g, 1650 mAh / g, 1680 mAh / g, 1700 mAh / g, 1750 mAh / g, 1800 mAh / g, 1850 mAh / g, 1900 mAh / g, 1950 mAh / g, 2000 mAh / g, 2100 mAh / g, 2200 mAh / g, etc.

[0130] In one embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, after 15 cycles at 25°C and a 1C charge / discharge rate, its capacity retention rate is 40% or more, or 60% or more, or 80% or more, or 85% or more. In another embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, after 20 cycles at 25°C and a 1C charge / discharge rate, its capacity retention rate is 60% or more, or 80% or more, or 85% or more. In another embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, after 50 cycles at 25°C and a 1C charge / discharge rate, its capacity retention rate is 80% or more, or 85% or more. In yet another embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, after 1000 cycles at 25°C and a 1C charge / discharge rate, its capacity retention rate is 80% or more, or 85% or more. In one embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, it maintains a capacity retention of more than 80% or more than 85% after 1200 cycles under operating conditions of 25°C and 1C charge / discharge rate.

[0131] In some embodiments, the lithium-ion half-cell prepared from the composite material of the secondary lithium-ion battery of the present invention exhibits a charging curve without a significant plateau at 0.4-0.5V and a low characteristic peak intensity at 0.4-0.5V on the DQ / DV curve. In other embodiments, the lithium-ion half-cell prepared from the composite material of the secondary lithium-ion battery exhibits a charging curve with a plateau at 0.4-0.5V and a high characteristic peak intensity at 0.4-0.5V on the DQ / DV curve.

[0132] The plateau in the charging curve at 0.4-0.5V, and the corresponding characteristic peak of the DQ / DV curve at 0.4-0.5V, are related to the degree of crystallinity of the hydrogen-containing silicon. The higher the crystalline silicon content, the more pronounced the plateau in the charging curve at 0.4-0.5V, and the stronger the intensity of the characteristic peak of the DQ / DV curve at 0.4-0.5V.

[0133] The composite materials disclosed herein for use in secondary lithium-ion batteries can improve the properties of electrical storage devices, for example, they have been shown to reduce the electrode expansion rate of lithium-based batteries. Thickness expansion rate testing can be performed as follows: Initial thickness calibration: 1. After capacity grading, clamp the battery and perform a full charge-discharge cycle at 0.2C to determine its actual initial discharge capacity; 2. Charge at 0.2C for 2.5 hours according to the initial discharge capacity, adjusting the SOC to 50%; 3. Remove the clamp and test the initial thickness of the battery at 50% SOC; 4. For pouch thickness testing, use calipers to measure the thickness at the center of the battery until a relatively stable thickness is observed, recorded as T0. Full charge thickness expansion test: 1. During the cycle, test the full charge thickness every 50C for the first 200C cycles, and every 100C after that until the capacity decays to 80%; 2. Full charge is performed according to the process of 0.2C CC 4.25V, 4.25V CV 0.04C; 3. The thickness of the soft pack is tested with calipers, measuring the thickness at the middle position of the battery until a relatively stable thickness is reached, which is recorded as Tn; 4. The thickness expansion at a specific number of cycles can be calculated using the formula Tn / T0-1.

[0134] In one embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, after 1200 cycles of operation at 25°C and a 1C charge / discharge rate, the electrode expansion rate is less than 15%, or less than 10%, or less than 8%, for example, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, etc.

[0135] Beneficial effects

[0136] Current silicon nanotechnology still has certain shortcomings: Firstly, nano-silicon is difficult to disperse uniformly and tends to agglomerate, failing to fully utilize its advantages. Secondly, nano-silicon exhibits high activity, consuming a large amount of lithium ions during the formation of the solid electrolyte interphase (SEI) film, thus reducing coulombic efficiency. Furthermore, during use, the surface of nano-silicon reacts with the electrolyte, leading to gas generation, which causes battery capacity decay, reduced cycle performance, and even safety issues. Therefore, the application of nano-silicon in rechargeable lithium-ion batteries still faces significant challenges.

[0137] This invention provides a method for preparing a composite material for secondary lithium-ion batteries and its application. Compared with existing technologies, the composite material of this invention features a porous matrix with abundant pore structure, hydrogen-containing nano-silicon uniformly dispersed within the pores of the porous matrix, and a silicon-free outer layer on the porous matrix. The outermost layer of the material also includes a dense carbon shell. This invention uses various silicon-containing precursors and a porous matrix as raw materials, uniformly dispersing silicon within the porous matrix. By controlling the temperature, some Si-H bonds are retained in the silicon, forming hydrogen-containing silicon. Finally, the entire material is carbon-coated to prevent the highly active nano-hydrogen-containing silicon from spontaneously combusting in air, while also ensuring that the material does not directly contact the electrolyte during use, facilitating the formation of a stable SEI film. This invention solves the silicon dispersion problem by uniformly dispersing hydrogen-containing silicon in the composite material, avoiding the volume effect caused by silicon agglomeration during charging and discharging. Furthermore, the Si-H bonds in the hydrogen-containing silicon effectively improve the stability of the material structure during charging and discharging, extending the battery cycle life.

[0138] The method for preparing composite materials for secondary lithium-ion batteries provided by this invention is simple and easy to operate, and can be applied to mass production.

[0139] Example

[0140] The present invention will be further described in detail below through specific embodiments. However, it should be understood that these embodiments are merely for the purpose of further elaboration and should not be construed as limiting the present invention in any way, i.e., they are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the instruments, equipment, and reagents used herein are commercially available. The porous carbon used in the embodiments of this application was prepared according to conventional methods in the art.

[0141] Sample preparation

[0142] Example 1 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.8-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 405 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 405 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 1.

[0143] Example 2 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.8-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 420°C at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 420°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 2.

[0144] Example 3 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.8-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 450 °C at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 3.

[0145] Example 4 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.8-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 480°C at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 480°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 4.

[0146] Example 5 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.8-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 500 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 500 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 5.

[0147] Example 6 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 550 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 550 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 6.

[0148] Example 7 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 600 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 600 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 7.

[0149] Example 8 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1000-1100 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.4-0.6cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 405 °C at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 405 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to carbonize the material through gas-phase coating, obtaining the composite material sample of Example 8.

[0150] Example 9 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1500-1600 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.6-0.8cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 450 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 9.

[0151] Example 10 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 2200-2500 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 1.0-1.2cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 27 L / min. The temperature of the tube furnace was increased to 450 °C at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 50 L / min for 4 hours. After deposition, the reaction temperature was maintained at 450 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 10.

[0152] Example 11 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 1-5μm, D100 is 10-20μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 450°C at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours to achieve carbon coating of the material through gas-phase coating, obtaining the composite material sample of Example 11.

[0153] Example 12 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 10-12μm, D100 is 15-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 450°C in a tube furnace at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. Carbon coating was then performed on the composite material through gas-phase coating to obtain the composite material sample of Example 12.

[0154] Example 13 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 12-15μm, D100 is 20-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 450°C at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. Carbon coating of the composite material was then achieved through gas-phase coating, yielding the composite material sample of Example 13.

[0155] Example 14 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.01-0.4 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 15-20μm, D100 is 25-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 450 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. Carbon coating was then performed on the composite material through gas-phase coating to obtain the composite material sample of Example 14.

[0156] Example 15 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.1-0.3 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature was raised to 450 °C in a tube furnace at a heating rate of 5 °C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited onto the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450 °C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. Carbon coating was then performed on the composite material through gas-phase coating to obtain the composite material sample of Example 15.

[0157] Example 16 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.2-0.5 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 450°C at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. Carbon coating of the composite material was then achieved through gas-phase coating, yielding the composite material sample of Example 16.

[0158] Example 17 uses porous carbon with the following parameters as a porous matrix: oxygen content of 0.3-0.6 mmol / g and BET of 1900-2000 m. 2 / g, particle size distribution D50 is 5-10μm, D100 is 20-50μm, and total pore volume is 0.9-1.0cm³. 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen gas was introduced as a protective gas at a flow rate of 23 L / min. The temperature of the tube furnace was increased to 450°C at a heating rate of 5°C / min. Then, silicon-containing gas silane was introduced into the fluidized bed and deposited on the porous carbon at a flow rate of 35 L / min for 6 hours. After deposition, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. Carbon coating of the composite material was then achieved through gas-phase coating, yielding the composite material sample of Example 17.

[0159] Performance testing

[0160] Infrared: The composite material sample powder from the example was mixed evenly with potassium bromide powder and then compressed into tablets at a pressure of 8-10 MPa for 1 minute. The prepared tablets were then tested using a Fourier transform infrared spectrometer. The infrared absorption characteristics corresponding to the silane-hydrogen bonding mode generally fall into three regions in the infrared absorption spectrum: (I) 500-800 cm⁻¹ -1 The swing pattern zone, (II) 800-1000cm -1 The bending mode region, (III) 1850-2250cm -1 The stretching mode region; the characteristic peak I signal is strong, and the latter two characteristic absorption peaks are related to the preparation conditions. The hydrogen content can be obtained by the rocking mode calculation method, for 630 cm⁻¹ -1 The hydrogen content C in the hydrogen-containing silicon of the composite material is determined by Gaussian fitting of the absorption peaks at the location and the integral area of ​​the fitted function. H The specific data is shown in Table 1 below.

[0161] Figure 1 (a)-(g) show the infrared spectra of the composite material samples from Examples 1-7, respectively. Figure 1 As shown in (a), in the infrared spectrum of the sample from Example 1, at 630 cm⁻¹ -1 The nearby absorption peak is attributed to the rocking vibration absorption of silicon-hydrogen bonds, 1050 cm⁻¹. -1 The nearby absorption peak is attributed to the stretching vibration absorption of the carbon-oxygen bond, 1384 cm⁻¹. -1 The nearby absorption peak is attributed to the stretching vibration absorption of carbon-hydrogen bonds, 1630 cm⁻¹. -1 The nearby absorption peak is attributed to the stretching vibration absorption of carbon-carbon bonds, 2370 cm⁻¹. -1 The nearby absorption peaks are attributed to the absorption of asymmetric stretching vibrations of carbon-oxygen bonds.

[0162] XRD: The composite material sample powder from the example was placed in an XRD diffractometer at 10-65° and 5° / min to compare the differences between crystalline and amorphous silicon peaks. At the same time, the grain size could be fitted. A copper target was used for X-rays at a wavelength of 0.154 nm.

[0163] SEM: Used to characterize the surface morphology of composite materials, observe the surface roughness, and help determine the deposition of silicon on the surface.

[0164] TEM: An electron beam emitted from an electron gun travels along the optical axis of the microscope in a vacuum channel, passing through a condenser lens. The condenser lens converges the electron beam into a sharp, bright, and uniform spot, illuminating the sample in the sample chamber. The electron beam carrying the internal structural information of the sample transmits fewer electrons to denser areas and more electrons to sparser areas. After focusing and primary magnification by the objective lens, the electron beam enters the intermediate lens and the first and second projection lenses for comprehensive magnification and imaging. Finally, the magnified electron image is projected onto a fluorescent screen in the observation chamber. The composite material powder is uniformly dispersed in ethanol, and a small amount is dropped onto a copper grid, allowed to dry, and then injected. TEM allows observation of the silicon domain size in the composite material.

[0165] The XRD pattern of the composite material sample in Example 1 is shown below. Figure 2 As shown. According to Figure 2 It can be seen that the hydrogen-containing silicon deposited at this temperature is in an amorphous state, with a relatively wide peak between 20-30° diffraction angles, and no sharp diffraction response peak belonging to the (111) plane of crystalline silicon was found near 28.4°.

[0166] Figure 3 (a) shows a SEM image of the composite material sample of Example 1. Figure 3 (b) shows a TEM image of the composite material sample from Example 1. Figure 3 As can be seen, the surface of the composite material obtained under these preparation conditions is not significantly different from the surface of the porous carbon substrate without silicon deposition, exhibiting a uniform rough structure, and no granular nano-silicon deposition was found. TEM characterization of the near-surface region of the material revealed no obvious diffraction fringes belonging to crystalline Si, proving that the hydrogen-containing silicon deposited at this temperature is in an amorphous state.

[0167] According to the XRD, SEM, and TEM test results, the deposited hydrogen-containing silicon in all the samples of the embodiments was in an amorphous state.

[0168] Elemental analysis: For the composite material samples in the examples, the C content was determined using a carbon-sulfur analyzer, the O content was determined using a nitrogen-oxygen analyzer, and the hydrogen content in the hydrogen-containing silicon was determined using a nitrogen-oxygen analyzer. H The Si content in the composite material sample was calculated by fitting the infrared absorption peaks in the swing mode region, with the content of components other than C, O, and H as the basis. Specific data are shown in Table 1 below.

[0169] Electrical performance testing

[0170] Half battery:

[0171] The negative electrode sheet was prepared using the composite material sample from the example, and a coin cell was assembled for testing, as detailed below:

[0172] Preparation of the negative electrode sheet: The composite material sample, conductive additive carbon black, and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) from the example were weighed according to a mass ratio of 95:2:3 and prepared into a slurry in a pulping machine at room temperature. The prepared slurry was uniformly coated onto copper foil and dried in a forced-air drying oven at 50°C for 2 hours. After drying, it was cut into electrode sheets with a diameter of 8 mm and vacuum-dried in a vacuum drying oven at 100°C for 10 hours. The dried electrode sheets were then transferred to a glove box for use in battery assembly.

[0173] Battery Assembly: Simulated battery assembly was performed in a glove box containing a high-purity Ar atmosphere. Lithium metal was used as the counter electrode, and a solution of 1 mole of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1) was used as the electrolyte to assemble the battery.

[0174] Half-cell test: Constant current charge and discharge mode test was performed using a charge and discharge instrument. The discharge cutoff voltage was 0.005V and the charge cutoff voltage was 1.5V. The charge and discharge test was performed at a current density of C / 10. The relevant test data (charge specific capacity, initial coulombic efficiency, etc.) are detailed in Table 1.

[0175] The charge-discharge curves of the coin half-cells assembled from the negative electrode sheets prepared from the composite material sample of Example 1 are as follows: Figure 4 As shown, the initial discharge (lithium intercalation) curve exhibits three plateaus at 0.3-0.5V, 0.1-0.3V, and 0-0.1V, corresponding to the three lithium intercalation peaks in the DQ / DV curve. The lithium intercalation peak at 0.3-0.5V is related to the microporous structure and oxygen content of the porous carbon substrate, while the lithium intercalation peak at 0.1-0.3V corresponds to Si→Li. 2.0 Si alloy phase transition; the lithium intercalation peak at 0-0.1V corresponds to Li 2.0 Si→Li 3.5 The Si alloy undergoes a phase transition; the initial charge (delithiation) curve exhibits three plateaus at 0.2-0.4V, 0.4-0.6V, and 0.6-0.8V, corresponding to the three delithiation peaks in the DQ / DV curve. The delithiation peak at 0.2-0.4V corresponds to the Li-phase phase transition. 3.5 Si→Li 2.0 The alloying phase transition of Si, with the delithiation peak at 0.4-0.6V corresponding to Li 2.0 The Si→Si alloy phase transition, with a delithiation peak at 0.6-0.8V, is related to the microporous structure and oxygen content of the porous carbon substrate. In some other embodiments, the DQ / DV curves also show a sharp delithiation peak between 0.4-0.5V, the intensity of which is related to the content of crystalline silicon; the higher the content of crystalline silicon, the stronger the peak.

[0176] Full battery:

[0177] Referring to the preparation and testing process of the half-cell described above, the composite material sample from the example was used as the negative electrode material to prepare a sheet negative electrode, and a full cell was assembled and tested, as detailed below:

[0178] Preparation of the positive electrode: Formulation parameters: 96.2wt% LiNi 0.6 Co 0.2 Mn 0.2 O2 (622 cathode material) + 1.1wt% PVDF (binder) + 2.7wt% Super P (conductive agent); Ingredient parameters: dry mixing, high-speed dispersion (solid content 72%), adjust viscosity to approximately 5000 cP before coating; Coating parameters: single-sided areal density 21 mg / cm³ 2 After being cut into 15cm wide strips, positive electrode sheets with dimensions of 73mm×44mm are obtained by die-cutting.

[0179] Preparation of the negative electrode sheet: Formulation parameters: 95.0 wt% negative electrode material (composite sample of the example) + 3.5 wt% binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) + 1.5 wt% conductive agent carbon black; Batching parameters: dry mixing and kneading (solid content 65%), high-speed dispersion (solid content 45%), adjusting the viscosity to about 5000 before coating; Coating parameters: single-sided surface density 9 mg / cm³ 2 After being cut into 15cm wide strips, the negative electrode sheet with a size of 75mm×46mm is obtained by die cutting.

[0180] Battery Assembly: The process is as follows: Stacking: Stack 9 negative electrode sheets and 8 positive electrode sheets in a Z-shape; Welding tabs: Weld tabs onto the positive and negative electrodes respectively (positive electrode: aluminum; negative electrode: nickel); Hot pressing and cold pressing: Hot press at 80℃ for 1 minute, then cold press at room temperature for 1 minute; Aluminum molding and punching: Punch depth is 3mm; Top sealing and side sealing: Heat seal temperature is 190℃, heat seal time is 6 seconds; Baking: Keep at 95℃ for 3 days, during which nitrogen purging is performed to ensure the sample is in an inert atmosphere; Water content test: Take... Approximately 1g each of the positive and negative electrode sheets are heated at 120℃ to remove water, reducing the moisture content to below 200ppm. Electrolyte injection: A solution of 1 mole of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1) is injected between the positive and negative electrode sheets, with an injection coefficient of 3.5 calculated based on the initial charge. Sealing: Heat sealing temperature 190℃, heat sealing time 3 seconds, vacuum degree -90. After immersion at 45℃ for 2 days, the assembled battery sample is obtained.

[0181] Full battery test: Cycling conditions: 1C / 1C; Voltage range: 2.8-4.25V.

[0182] Figure 5 Cycle curves of the button cells in Examples 1-7 are shown (number of cycles: 50). Figure 6 The cycling curve of the button cell of Example 1 is shown (number of cycles: 1200).

[0183] Thickness expansion rate test:

[0184] Initial thickness calibration: 1. After the battery has been calibrated, clamp it and fully charge and discharge it once at 0.2C to determine its actual initial discharge capacity; 2. Charge it at 0.2C for 2.5 hours according to the initial discharge capacity, and adjust the SOC to 50%; 3. Remove the clamp and test the initial thickness of the battery at 50% SOC; 4. Measure the thickness of the soft pack with calipers, clamping the thickness at the middle position of the battery until a relatively stable thickness is obtained, and record it as T0.

[0185] Full charge thickness expansion test: 1. During the cycle, test the full charge thickness every 50C for the first 200C cycles, and every 100C after that until the capacity decays to 80%; 2. Full charge is performed according to the process of 0.2C CC 4.25V, 4.25V CV 0.04C; 3. The thickness of the soft pack is tested with calipers, measuring the thickness at the middle position of the battery until a relatively stable thickness is reached, which is recorded as Tn; 4. The thickness expansion at a specific number of cycles can be calculated using the formula Tn / T0-1.

[0186] Figure 7 The thickness expansion curve of the button cell of Example 1 is shown.

[0187] Table 1

[0188]

[0189] H content*: Hydrogen content in hydrogen-containing silicon (C) H .

[0190] like Figure 5 As shown, the coin cells prepared using the composite materials described in Examples 1-7 of this application exhibit excellent long-cycle retention. After 15 cycles at 25°C and a 1C charge / discharge rate, their capacity retention is consistently above 40%. Figure 5 It is evident that the capacity retention rate is positively correlated with the hydrogen content in the hydrogen-containing silicon of the composite material. In Example 6, the hydrogen content in the hydrogen-containing silicon of the composite material sample increased to 0.03 wt%. The coin cell prepared from the sample of Example 6, after 20 cycles at 25°C and a 1C charge / discharge rate, still retained a capacity retention rate of over 60%. For the composite material samples of Examples 1-5, where the hydrogen content in the hydrogen-containing silicon was above 0.09%, the coin cells prepared exhibited significantly better long-cycle retention rates, retaining a capacity retention rate of over 80% after 50 cycles at 25°C and a 1C charge / discharge rate.

[0191] The full cell prepared using the composite material of Example 1 exhibits excellent long-cycle retention. After 1200 cycles at 25°C and a 1C charge / discharge rate, its capacity retention reaches 87%, far exceeding the 80% capacity retention requirement for power batteries after 1000 cycles. Regarding electrode expansion, the coin cell of Example 1 only expands by 8% after 1000 cycles.

[0192] In the composite material samples of Examples 3 and 8-10, the contents of other elements, BET, and particle size distribution are very similar, except for the silicon content. Table 2 shows that the specific charge capacity of the composite material samples increases with the increase of silicon content.

[0193] As can be seen from the preparation processes of Examples 8-10, the silicon content of the composite material samples is positively correlated with the pore volume of the porous carbon matrix (e.g., BET test results). As can be seen from the preparation processes of Examples 11-14, the silicon content of the composite material samples is negatively correlated with the particle size of the porous carbon matrix (e.g., D50 particle size).

[0194] In the samples of Examples 1 and 15-17, the contents of other elements, BET, and particle size distribution were very similar, except for the oxygen content. Table 2 shows that as the oxygen content of the composite material samples increased, the initial coulombic efficiency of the samples exhibited a slow decreasing trend.

[0195] Through Table 1 and Figure 5 The test data shows that the composite material assembled for secondary lithium-ion batteries in this embodiment of the invention has a higher charge specific capacity and first coulombic efficiency than the negative electrode on the market, while the cycle performance is also significantly improved.

[0196] In the composite material of this invention, the porous matrix has a rich pore structure, and the nano-silicon is hydrogen-containing silicon, which is uniformly dispersed in the pores of the porous matrix. The outermost layer of the porous matrix is ​​silicon-free, and the outermost layer of the material also includes a dense shell. This invention uses various silicon-containing precursors and a porous matrix as raw materials, uniformly dispersing silicon in the porous matrix. By controlling the temperature, some Si-H bonds are retained in the silicon, forming hydrogen-containing silicon. Finally, the entire material is coated to prevent the highly reactive nano-hydrogen-containing silicon from spontaneously combusting in air, and also to ensure that the material does not directly contact the electrolyte during use, easily forming a stable SEI film.

[0197] On the one hand, this invention uniformly disperses hydrogen-containing silicon in a porous matrix, solving the problem of silicon dispersion and avoiding the volume effect caused by silicon agglomeration during charging and discharging; on the other hand, the Si-H bonds contained in the hydrogen-containing silicon can effectively improve the stability of the material structure during charging and discharging, and extend the battery cycle life.

[0198] Those skilled in the art will recognize that many modifications and variations can be made to this invention without departing from its spirit and scope. The specific embodiments described herein are provided by way of example only and are not intended to limit the scope in any way. The true scope and spirit of the invention are shown in the appended claims, and the description and embodiments are merely exemplary.

Claims

1. A composite material for secondary lithium-ion batteries, characterized in that, The composite material comprises: a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell layer covering the outer surface of the porous matrix, wherein: In the composite material, based on the total weight of the composite material, the hydrogen content in the hydrogen-containing silicon is 0.3-5 wt%; The hydrogen-containing silicon consists of all the nano-silicon particles dispersed in the porous matrix, and at least a portion of the nano-silicon particles have Si-H bonds; and the particle size of the hydrogen-containing silicon ranges from 0.1 to 60 nm. The porous matrix is ​​porous carbon; the porous matrix comprises 20%-90% micropores, 10%-50% mesopores, and 0-30% macropores; and the total pore volume of the porous matrix is ​​0.1-2.5 cm³. 3 / g; The oxygen content of the porous matrix is ​​0.01-0.6 mmol / g.

2. The composite material according to claim 1, characterized in that, In the composite material, based on the total weight of the composite material, the hydrogen content in the hydrogen-containing silicon is 0.9-3 wt%.

3. The composite material according to claim 1, characterized in that, Based on the total weight of the composite material, the silicon content of the composite material is 5-90 wt%; and / or Based on the total weight of the composite material, the carbon content of the composite material is 10-95 wt%; and / or Based on the total weight of the composite material, the oxygen content of the composite material is 0.1-3 wt%.

4. The composite material according to claim 1, characterized in that, Based on the total weight of the composite material, the silicon content of the composite material is 15-70 wt%; and / or Based on the total weight of the composite material, the carbon content of the composite material is 30-90 wt%.

5. The composite material according to claim 1, characterized in that, Based on the total weight of the composite material, the silicon content of the composite material is 30-65 wt%; and / or Based on the total weight of the composite material, the carbon content of the composite material is 35-85 wt%.

6. The composite material according to claim 1, characterized in that, The tap density of the composite material is 0.5-2 g / cm³. 3 ; and / or The tap density of the porous matrix is ​​0.2-0.6 g / cm³. 3 .

7. The composite material according to claim 1, characterized in that, The infrared spectrum of the composite material is in the range of 625-640 cm⁻¹. -1 It has a vibration peak.

8. The composite material according to claim 7, characterized in that, The infrared spectrum of the composite material also exhibits vibrational peaks at one or more of the following locations: 845-885 cm⁻¹ -1 1990-2010 cm -1 .

9. The composite material according to claim 1, characterized in that, The particle size range of the hydrogen-containing silicon is 0.1-20 nm.

10. The composite material according to claim 1, characterized in that, The particle size range of the hydrogen-containing silicon is 1-5 nm.

11. The composite material according to claim 1, characterized in that, The composite material has one or more of the following characteristics: The specific surface area (BET) of the composite material is 10 m². 2 / g or less; The total pore volume of the composite material is 0.1 cm³. 3 / g or less; The particle size D50 of the composite material is 1-50 μm; The composite material has a D100 particle size of 10-100 μm.

12. The composite material according to claim 1, characterized in that, The porous matrix has one or more of the following characteristics: The specific surface area (BET) of the porous matrix is ​​1000-2500 m². 2 / g; The D50 particle size of the porous matrix is ​​1-30 μm; The D100 particle size of the porous matrix is ​​5-80 μm.

13. The composite material according to claim 12, characterized in that, The porous matrix has one or more of the following characteristics: The total pore volume of the porous matrix is ​​0.5-1.2 cm³. 3 / g; The D50 particle size of the porous matrix is ​​1-20 μm; The D100 particle size of the porous matrix is ​​5-50 μm.

14. The composite material according to claim 1, characterized in that, The shell components include: amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, aluminum oxide, aluminum nitride, silicon carbides, silicon nitrides, silicon oxides, silicon oxynitrides, or combinations thereof.

15. The composite material according to claim 1, characterized in that, The thickness of the shell is 1-1000 nm.

16. The composite material according to claim 1, characterized in that, The electrochemical charging curve of the half-cell prepared by the composite material has a plateau at 0.4-0.5 V, and / or The DQ / DV curve of the half-cell prepared by the composite material has a characteristic peak at 0.4-0.5 V.

17. A method for preparing the composite material according to any one of claims 1-16, comprising the following steps: Provide a porous matrix; Hydrogen-containing silicon is formed in a porous matrix by CVD deposition and / or liquid impregnation. The outer surface of the porous matrix containing hydrogen-containing silicon is coated to form a shell.

18. The method of claim 17, characterized in that, The process of forming hydrogen-containing silicon dispersed in a porous matrix by CVD deposition includes: The porous matrix is ​​placed in a reaction vessel, and a protective gas is introduced into the reaction vessel; Heat the reaction vessel to the reaction temperature; Silicon-containing gas is introduced into the reaction vessel to deposit it in a porous matrix.

19. The method of claim 18, wherein: The reaction vessel is heated at a rate of 1-10 °C / min; The reaction temperature is 400-600 ℃; The flow rate of the protective gas is 5-30 L / min; The total flow rate of silicon-containing gas is 10-40 L / min; The deposition time is 5-20 hours.

20. The method according to claim 18 or 19, characterized in that, The silicon-containing gas includes: dichlorosilane, Si n H 2n+2 Silanes or combinations thereof, where n is an integer selected from 1 to 3.

21. The method according to claim 18 or 19, characterized in that, The silicon-containing gas includes: dichlorosilane, methylsilane, diethylsilane, propane, or combinations thereof.

22. The method of claim 17, characterized in that, The process of forming hydrogen-containing silicon dispersed in a porous matrix by liquid impregnation includes: The porous matrix and silane liquid are uniformly mixed. Carbonization and reduction are carried out at high temperatures.

23. The method of claim 22, characterized in that, The silane liquid includes: trichlorosilane, Si n H 2n+2 Silanes or combinations thereof, where n is an integer selected from 4 to 10.

24. The method of claim 17, characterized in that, A shell is formed by coating the outer surface of a porous matrix in which hydrogen-containing silicon is dispersed by reactive coating, adhesive coating, or a combination thereof.

25. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the composite material according to any one of claims 1-16.

26. A lithium-ion secondary battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 25.

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