Composite material for secondary lithium-ion battery, preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a composite material for a secondary lithium-ion battery and a preparation method therefor. The composite material comprises: a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell layer coating the outer surface of the porous matrix. The present invention further relates to a negative electrode sheet including the composite material, and a secondary lithium-ion battery including same. In the present invention, hydrogen-containing silicon is uniformly dispersed in the composite material, thus solving the dispersion problem of silicon and mitigating the volume effect of silicon during charging and discharging; and Si-H bonds in the hydrogen-containing silicon can effectively improve the structural stability of the material during charging and discharging, thereby prolonging the cycle life of a battery. The preparation method for a composite material for a secondary lithium-ion battery in the present invention is simple and easy to operate, and can be used for batch production.

Description

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

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to Chinese patent application number 202311513274.6, filed on November 14, 2023, entitled “A composite material for secondary lithium-ion batteries, its preparation method and application”, and the entire text of the above application is hereby expressly incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of batteries, and in particular to a composite material for secondary lithium-ion batteries, a preparation method thereof, and applications thereof. Background Art

[0004] Lithium-ion batteries are one of the most widely used secondary battery systems. Compared with other rechargeable batteries such as nickel-cadmium batteries and nickel-metal hydride batteries, lithium-ion batteries have the advantages of high energy density, high operating voltage, limited self-discharge, and low maintenance requirements. However, commercial graphite anodes have a capacity of only 372 mAhg -1 The theoretical specific capacity cannot meet the increasing demands of portable electronic devices, electric vehicles and energy storage applications for energy density, operation reliability and system integration.

[0005] 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 gravimetric capacity (4200 mAh g -1 ) and volumetric capacity (9786mAhcm -3 ); (2) The discharge voltage of Si is about 0.4 V on average, which strikes a good balance between maintaining a reasonable open-circuit voltage and avoiding unfavorable lithium plating processes; (3) Silicon reserves are abundant (the second highest content in the earth's crust) and are potentially low-cost, environmentally friendly, and non-toxic.

[0006] However, as silicon undergoes lithium insertion and removal, its volume expands and contracts rapidly (volume change is approximately 360%) and generates enormous stress, which has a series of serious effects on the structure: (1) the integrity of the electrode structure is destroyed during repeated charge and discharge; (2) interfacial stress induces disconnection between the electrode and the current collector; and (3) the solid electrolyte interface (SEI) layer continuously forms, breaks down, and reforms, causing lithium ions to be continuously consumed. These processes will accelerate electrode collapse and capacity decay in a synergistic manner. In addition, the poor intrinsic electronic conductivity of silicon also contributes to the slow electrochemical kinetics.

[0007] Silicon nanomaterials can effectively alleviate the impact of these issues. CN 116454256A discloses a method for preparing a silicon-carbon composite material. Nanosilicon and nanocarbon are directly composited in situ, then coated with a layer of carbon material. A micron-scale silicon-carbon composite material is obtained by spray granulation of a slurry. High-temperature treatment decomposes the binder or other impurities in the slurry, forming pores that provide space for silicon expansion. The conductive carbon enhances the material's electrical conductivity, facilitating electrochemical performance.

[0008] Nanoscaling silicon can effectively mitigate the effects of volume expansion on electrodes, but dispersing nanosilicon particles into carbon materials remains challenging. Agglomeration of nanosilicon can still lead to volume expansion, preventing the full potential of nanosilicon.

[0009] Summary of the Invention

[0010] The present invention provides a composite material for secondary lithium ion batteries, a preparation method thereof and an application thereof, in order to solve the problems faced by nano silicon in secondary lithium ion batteries.

[0011] In one aspect, the present invention relates to a composite material for a secondary lithium ion battery, comprising: a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell layer coated on the outer surface of the porous matrix.

[0012] In one embodiment, in the composite material, the hydrogen content of the hydrogen-containing silicon is 0.01-10 wt %, preferably 0.03-5 wt %, more preferably 0.09-3 wt %, based on the total weight of the composite material.

[0013] On the other hand, the present invention relates to a method for preparing the composite material of the present invention, which comprises 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 layer.

[0014] In another aspect, the present invention relates to a negative electrode sheet comprising the composite material of the present invention.

[0015] In another aspect, the present invention relates to a lithium ion secondary battery comprising the negative electrode sheet of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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.

[0017] Figure 2: XRD spectrum of the composite material sample of Example 1.

[0018] Figure 3: (a) SEM image of the composite material sample of Example 1; (b) TEM image of the composite material sample of Example 1.

[0019] Figure 4: Charge and discharge curves of a button-type half-cell obtained by assembling the negative electrode sheet prepared from the composite material sample of Example 1.

[0020] Figure 5: Cycling curves of button-type full batteries obtained by assembling negative electrode sheets prepared from the composite material samples of Examples 1-7.

[0021] Figure 6: Cycling curve of button-type full battery obtained by assembling negative electrode sheets prepared from the composite material sample of Example 1.

[0022] Figure 7: Thickness expansion curve of a button-type full battery obtained by assembling the negative electrode sheet prepared from the composite material sample of Example 1. DETAILED DESCRIPTION

[0023] General Definitions and Terminology

[0024] Unless otherwise indicated, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0025] 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.

[0026] Unless otherwise indicated, all percentages, parts, ratios, etc. are by weight.

[0027] When providing quantity, concentration or other value or parameter as range, preferred range or preferred upper limit and lower limit or concrete value, it should be understood that specifically disclose all ranges formed from the paired values ​​of any upper limit range or preferred value and any lower limit range or preferred value, no matter whether scope is disclosed individually. Unless otherwise stated, when numerical range is quoted herein, described range refers to and includes its endpoints and integers and fractions within all such ranges. The scope of the present invention is not limited to the specific numerical value quoted when defining the range.

[0028] When values ​​or end-points of a range are described herein, it should be understood that the disclosure includes the specific value or end-point recited.

[0029] The expression "comprising" or its synonyms "including," "containing," and "having" are open-ended and do not exclude additional unrecited elements, steps, or ingredients. The expression "consisting of excludes any elements, steps, or ingredients not specified. The expression "consisting essentially of" means that the scope is limited to the specified elements, steps, or ingredients, plus any optional elements, steps, or ingredients that do not materially affect the basic and novel characteristics of the claimed subject matter. It should be understood that the expression "comprising" encompasses the expressions "consisting essentially of" and "consisting of."

[0030] Unless otherwise stated, the term "combination thereof" means a multi-component mixture of the elements mentioned, for example a mixture of two, three, four and up to the maximum possible multi-component mixture.

[0031] In addition, if the number of parts or components of the present invention is not indicated before, it means that there is no limit to the number of occurrences (or existence) of the parts or components. Therefore, it should be interpreted as including one or at least one, and the singular form of the parts or components also includes the plural form unless the value obviously represents the singular.

[0032] As used herein, the term "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes both occurring and not occurring.

[0033] As used herein, the terms "one or more" or "at least one" refer to one, two, three, four, five, six, seven, eight, nine or more.

[0034] "Carbon" refers to a material or substance consisting essentially of carbon. Examples of carbon materials include, but are not limited to, activated carbon, pyrolytic carbon, hard carbon, graphite, and other allotropes of carbon.

[0035] "Carbonize," "pyrolyze," "carbonization," and "pyrolysis" all refer to the process of heating a carbonaceous material at a pyrolysis soak temperature under an inert atmosphere (e.g., argon or nitrogen) or in a vacuum so that the target material collected at the end of the process is primarily carbon. "Pyrolyzed" refers to a material or substance (e.g., a carbon material) that has undergone a pyrolysis process.

[0036] "Soak temperature" refers to the temperature of the furnace during the portion of the process that is reserved for maintaining a relatively constant temperature (i.e., not increasing or decreasing the temperature). For example, the pyrolysis soak temperature refers to the relatively constant furnace temperature during the pyrolysis process, and the activation soak temperature refers to the relatively constant furnace temperature during the activation process.

[0037] "Pore structure" refers to the surface layout of internal pores within a carbon material (e.g., activated carbon material). The components of the 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.

[0038] "Mesopores" refer to pores with a diameter of 2-50 nm, "micropores" refer to pores with a diameter less than 2 nm, and "macroporous" refers to pores with a diameter greater than 50 nm. In mesoporous carbon materials, mesopores account for at least 50% of the total pore volume. In microporous carbon materials, micropores account for at least 50% of the total pore volume.

[0039] "Surface area" refers to the total specific surface area of ​​a substance that can be measured by the BET technique. Usually, the surface area is expressed in m 2 The BET technique uses an inert gas (such as nitrogen) to measure the amount of gas adsorbed on a material and is commonly used in the art to determine the accessible surface area of ​​a material.

[0040] A "composite material" refers to a composition comprising multiple (2 or more) different chemical species within the same particle, such as a particle comprising a porous carbon material and a silicon material.

[0041] "Allotropes" refer to materials composed of the same single chemical element but that can exist 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-graphitizable carbon materials. At high temperatures (typically 1500-2200°C), hard carbon remains essentially amorphous, while soft carbon undergoes crystallization and becomes graphitized.

[0042] "Coulombic efficiency" refers to the ratio of the discharge capacity to the charge capacity of a lithium-ion energy storage device. Coulombic efficiency is expressed as a percentage or fraction (e.g., 99% = 0.99).

[0043] Composite materials for secondary lithium-ion batteries

[0044] In one aspect, the present invention provides 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 layer coated on the outer surface of the porous matrix.

[0045] porous matrix

[0046] The porous matrix of the present application has a suitable pore structure, which is conducive to the uniform dispersion of silicon particles in the inner pores of the porous matrix to form nano-silicon particles, thereby avoiding the volume expansion effect that may occur due to the agglomeration of silicon particles, thereby giving full play to the advantages of nano-silicon particles and improving the performance of the composite material.

[0047] In the present invention, the porous matrix can be made of various materials, including but not limited to porous carbon, porous polymer materials, porous ceramic materials, porous metal materials, or a combination thereof.

[0048] In a preferred embodiment, the porous matrix material mainly comprises carbon, for example hard carbon. Other allotropes of carbon are also conceivable, for example graphite, amorphous carbon, diamond, C60, carbon nanotubes (for example, single-walled and / or multi-walled), graphene and / or carbon fiber. Porosity can be introduced into the carbon material by various means. For example, the porosity in the carbon material can be achieved by adjusting polymer precursors and / or processing conditions to produce porous carbon material (described in detail in subsequent parts).

[0049] In other embodiments, the porous matrix may comprise a polymer material. 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, water-based polyurethane, polyimide, hydrated aramid nanofiber, polydimethylsiloxane, acrylonitrile-butadiene-styrene, polyethersulfone, and polycarbonate polyacrylonitrile. Polymers also include resin materials such as epoxy resins, polyester resins, acrylic resins, phenolic resins, FEVE fluororesins, ETFE fluororesins, and phthalonitrile resins. Polymers may also include biomass materials such as lignin, coconut shells, bamboo, fructose, sucrose, maltose, glucose, cellulose, and starch.

[0050] The porous matrix material includes porous ceramic materials, including but not limited to porous magnesium oxide, porous aluminum oxide, porous beryllium oxide, porous zirconium oxide, porous tin oxide, porous silica, porous silicon nitride, porous aluminum nitride, porous boron nitride, porous titanium nitride, and porous silicon carbide.

[0051] Porous matrix materials also include porous metals, including but not limited to porous aluminum, porous steel, porous nickel, porous nickel, porous Inconel, porous titanium, porous copper, porous brass, porous gold, porous silver, porous germanium, and the like.

[0052] In the present 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, isostatic compaction and sintering, metallization, metal coating and sintering, metal injection molding and sintering, etc. The preparation method of porous materials may also include other routes to produce porous polymer materials, including the production of porous gels, such as freeze-dried gels, etc.

[0053] The particle size of the silicon particles dispersed in the pores of the porous matrix is ​​affected by the pore size distribution of the porous matrix. A suitable pore size distribution of the porous matrix helps to promote the formation of nano-silicon particles. The porous matrix can contain 20%-90% micropores, 10%-50% mesopores and 0-30% macropores. The total pore volume of the porous matrix can be 0.1-2.5 cm 3 / g, preferably 0.5-1.2cm 3 / g.

[0054] 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 cm 3 In certain embodiments, the total pore volume is 1.0 cm, comprising 25% micropores, 45% mesopores, and 30% macropores. 3 In certain embodiments, the pore volume comprises 30% micropores, 45% mesopores, and 25% macropores, with a total pore volume of 0.9 cm 3 In certain embodiments, the pore volume comprises 35% micropores, 40% mesopores, and 25% macropores, with a total pore volume of 0.8 cm 3 In certain embodiments, the total pore volume is 0.7 cm, comprising 40% micropores, 40% mesopores, and 20% macropores. 3 In certain embodiments, the pore volume comprises 50% micropores, 35% mesopores, and 15% macropores, with a total pore volume of 0.6 cm 3 In certain embodiments, the total pore volume is 0.5 cm, comprising 60% micropores, 30% mesopores, and 10% macropores. 3 In certain embodiments, the total pore volume is 0.4 cm, comprising 70% micropores, 25% mesopores, and 5% macropores. 3 In certain embodiments, the total pore volume is 0.2 cm, comprising 80% micropores, 18% mesopores, and 2% macropores. 3 In certain embodiments, the pore volume is 0.1 cm, which contains 90% micropores, 10% mesopores, and a total pore volume of 0.1 cm 3 / g.

[0055] The appropriate pore volume of the porous matrix is ​​conducive to increasing the silicon content in the composite material, thereby improving the performance of the corresponding product, such as the charge capacity. The specific surface area of ​​the porous matrix can be 1000-2500m 2 / g, for example, 1900-2000m 2 / g, 1000-1200m 2 / g, 1500-1600m 2 / g, 2200-2500m 2 / g, etc.

[0056] An appropriate particle size distribution of the porous matrix is ​​beneficial for increasing the silicon content in the composite material, thereby improving the performance of the corresponding product. The D50 particle size of the porous matrix can be 1-30 μm, preferably 1-20 μm, for example, 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, for example, 10-20 μm, 20-40 μm, 30-50 μm, 40-60 μm, 50-70 μm, 60-80 μm, etc.

[0057] In some embodiments, the porous carbon has a particle size distribution with a D50 of 1-10 μm and a D100 of 5-10 μm. In certain embodiments, the particle size distribution has a D50 of 5-15 μm and a D100 of 10-20 μm. In certain embodiments, the particle size distribution has a D50 of 5-20 μm and a D100 of 20-40 μm. In certain embodiments, the particle size distribution has a D50 of 10-25 μm and a D100 of 30-50 μm. In certain embodiments, the particle size distribution has a D50 of 5-25 μm and a D100 of 40-60 μm. In certain embodiments, the particle size distribution has a D50 of 10-30 μm and a D100 of 50-70 μm. In certain embodiments, the particle size distribution has a D50 of 15-30 μm and a D100 of 60-80 μm.

[0058] An appropriate oxygen content in the porous matrix helps improve the electrochemical performance of the product. Excessive oxygen content in the porous matrix may result in 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, such as 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.

[0059] The tap density of the porous matrix can be 0.2-0.6 g / cm 3 , for example 0.2g / cm 3 , 0.3g / cm 3 , 0.4g / cm 3 、 0.5g / cm 3 , 0.6g / cm 3 In certain embodiments, the composite material for secondary lithium-ion batteries has a tap density of 0.8 g / cm 3 The tap density of the porous matrix is ​​0.4 g / cm 3 In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 1.2 g / cm 3 The tap density of the porous matrix is ​​0.5 g / cm3 In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 1.4 g / cm 3 The tap density of the porous matrix is ​​0.6 g / cm 3 In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 2 g / cm 3 The tap density of the porous matrix is ​​0.6 g / cm 3 .

[0060] Hydrogenated silicon

[0061] In this application, silicon is uniformly dispersed within the pores of the porous matrix to form nanosilicon (i.e., nanosilicon particles), while the outer surface of the porous substrate is substantially free of silicon, which helps the material fully utilize the advantages of nanosilicon. In this application, the silicon dispersed in the porous matrix retains some Si-H bonds, and thus the silicon dispersed in the porous matrix is ​​also referred to as hydrogenated silicon.

[0062] The hydrogenated silicon in this application refers to all nano-silicon particles dispersed in a porous matrix. In the hydrogenated silicon herein, at least a portion of the nano-silicon particles are nano-silicon particles with Si-H bonds.

[0063] The presence of Si-H bonds in hydrogenated silicon can effectively improve the stability of the composite material during charge and discharge, and extend the cycle life of the battery. The Si-H bonds in hydrogenated silicon can be determined by any method in the art, including but not limited to infrared testing. The infrared spectrum of the composite material of the present application is at 625-640 cm -1 The infrared spectrum of the composite material may also have vibration peaks at one or more of the following positions: 845-885cm -1 1990-2010cm -1 .

[0064] "Hydrogen content in hydrogenated silicon" refers to the percentage of the total weight of H elements in the retained Si-H bonds in hydrogenated silicon expressed as a percentage of the overall weight of the composite material. The amount of Si-H bonds present in hydrogenated silicon is positively correlated with the hydrogen content. Factors such as the structure of the porous matrix and the dispersion of silicon within the porous matrix can influence the amount of Si-H bonds present and the hydrogen content. An appropriate hydrogen content in hydrogenated silicon can help improve the electrical performance of the product, such as improving the capacity retention of a battery. Based on the total weight of the composite material, the hydrogen content in the hydrogen-containing silicon may 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 may be determined by any method available in the art, for example, the hydrogen content C in the hydrogen-containing silicon H The infrared absorption peak in the swing mode region during infrared testing can be used for fitting calculations.

[0065] 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 impart good electrical properties (such as excellent charge capacity) to the product. It also preserves some pores in the porous matrix, allowing for the subsequent expansion of silicon and preventing the composite material from fracturing or even shattering due to the volume expansion of silicon.

[0066] Based on the total weight of the composite material, the silicon content of the composite material may 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 %, 35 wt %, 40 wt %, 41 wt %, 42 wt %, 43 wt %, 44 wt %, 45 wt %, 46 wt %, 47 wt %, 48 wt %, 49 wt %, 50 wt %, 55 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, etc. It will be understood that when, in the composite material, except for the hydrogenated silicon dispersed in the porous matrix, if the composition of other parts (such as the porous matrix and the shell layer) does not contain Si, the silicon content of the composite material is the content of silicon dispersed in the porous matrix.

[0067] The appropriate particle size of hydrogen-containing silicon is beneficial to improving the performance of the composite material. The particle size of hydrogen-containing silicon ranges from 0.1 to 60 nm, preferably from 0.1 to 20 nm, and more preferably from 1 to 5 nm.

[0068] The hydrogen-containing silicon may be in the form of crystalline silicon or amorphous silicon. In certain embodiments, the hydrogen-containing silicon comprises hydrogen-containing crystalline silicon. In certain embodiments, the hydrogen-containing silicon comprises hydrogen-containing polycrystalline silicon. In certain embodiments, the hydrogen-containing silicon comprises nano-hydrogen-containing polycrystalline silicon. In certain other embodiments, the hydrogen-containing silicon comprises hydrogen-containing amorphous silicon. In certain other embodiments, the hydrogen-containing silicon comprises hydrogen-containing crystalline silicon and hydrogen-containing amorphous silicon.

[0069] The degree of crystallinity of silicon in hydrogenated silicon can be determined by any method known in the art, such as electrochemical curve analysis. For test samples obtained from composite materials, the platform of the charge curve at 0.4-0.5V and the characteristic peak of the corresponding DQ / DV curve at 0.4-0.5V are related to the degree of crystallinity of the hydrogenated silicon. The higher the proportion of crystalline silicon in the hydrogenated silicon, the more pronounced the platform of the charge 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.

[0070] Shell layer coated on the outer surface of the porous substrate

[0071] The porous substrate also contains a dense shell on its outer surface, which acts as the outer layer of the composite. This shell not only protects the highly active hydrogenated silicon nanoparticles within the porous substrate from oxidation and spontaneous combustion in the air, but also prevents the porous substrate and its internal hydrogenated silicon from direct contact with the electrolyte during use, thus facilitating the formation of a stable SEI film.

[0072] The shell layer may be formed by subjecting the porous matrix in which hydrogenated silicon is dispersed to a reaction treatment, or by attaching another material to the surface of the porous matrix.

[0073] The components of the shell layer may include, but are not limited to, amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, silicon oxide (such as silicon dioxide), silicon oxynitride, or combinations thereof. In certain embodiments, the shell layer of the composite material of the present invention is a carbon shell.

[0074] The shell layer can be a single layer or multiple layers. Any layer in the shell layer is not limited to the above-mentioned one component, and can be a combination of several substances.

[0075] The appropriate thickness of the shell helps to fully exert the effect of the shell. The thickness of the shell can be 1-1000nm. In some embodiments, the shell thickness of the composite material of the secondary lithium ion battery is 1-10nm. In certain embodiments, the shell thickness of the composite material of the secondary lithium ion battery is 10-50nm. In certain embodiments, the shell thickness of the composite material of the secondary lithium ion battery is 50-100nm. In certain embodiments, the shell thickness of the composite material of the secondary lithium ion battery is 100-500nm. In certain embodiments, the shell thickness of the composite material of the secondary lithium ion battery is 500-1000nm.

[0076] It should be understood that the term "shell layer coated on the outer surface of the porous substrate" herein does not mean that the shell layer material is located solely on the outer surface of the porous substrate. For example, the shell layer material may be incorporated into pores of the porous substrate near the outer surface. In another example, the shell layer may be formed by reacting the outer portion of the porous substrate in which the nano-silicon is dispersed.

[0077] It should also be understood that there may be a distinct interface between the shell layer and the porous matrix described herein. There may also be no distinct interface between the shell layer and the porous matrix described herein, for example, there may be a boundary region with a certain thickness between the shell layer and the porous matrix.

[0078] It should also be understood that the shell layer described herein may have a uniform thickness at various locations or may have variations in thickness.

[0079] Preparation method

[0080] In another aspect, the present invention provides a method for preparing the composite material for a secondary lithium-ion battery, the method comprising:

[0081] providing a porous matrix;

[0082] forming hydrogen-containing silicon dispersed in a porous matrix by a CVD deposition method and / or a liquid impregnation method;

[0083] The outer surface of the porous matrix in which hydrogen-containing silicon is dispersed is coated to form a shell layer.

[0084] Provision of porous matrix

[0085] Herein, there is no particular limitation on the manner in which the porous matrix is ​​provided. The porous matrix can be obtained commercially or prepared by any method known in the art.

[0086] As an example, for porous carbon, pores can be introduced into the carbon material to form porous carbon in various ways. The pores in the carbon material can be controlled by adjusting the polymer precursor and / or processing conditions during the preparation process to produce the target porous carbon.

[0087] In the present invention, the preparation of porous materials includes but is not limited to the following methods: emulsification, micelle generation, gasification, dissolution followed by solvent removal (e.g., freeze drying), axial compaction and sintering, gravity sintering, powder rolling and sintering, isostatic compaction and sintering, metal spraying, metal coating and sintering, metal injection molding and sintering, etc.

[0088] As an example, for the porous polymer material, the preparation method thereof may include, but is not limited to: preparing a porous gel by freeze-drying.

[0089] Formation of hydrogenated silicon

[0090] Silicon can be dispersed into the pores of the porous matrix by any method known in the art to form hydrogenated silicon dispersed in the porous matrix. The silicon dispersion process (e.g., temperature) can be controlled to retain Si-H bonds, thereby effectively improving the stability of the composite material during charge and discharge, and extending the battery cycle life.

[0091] The silicon dispersion process can be achieved by any method known in the art, including but not limited to CVD deposition and liquid impregnation. Appropriate parameters during the dispersion process help to obtain the desired composite material.

[0092] The process of forming hydrogen-containing silicon dispersed in a porous matrix by CVD deposition includes: placing the porous matrix in a reaction vessel, introducing a protective gas into the reaction vessel; heating the reaction vessel to a reaction temperature; and introducing a silicon-containing gas into the reaction vessel to deposit the silicon in the porous matrix. The heating rate of the reaction vessel can be 1-10°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, etc. The reaction temperature can be 400-600°C, for example, 400°C, 405°C, 420°C, 450°C, 480°C, 500°C, 550°C, 600°C, etc. The flow rate of the shielding 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.

[0093] In the CVD deposition method, silicon-containing gases may include: dichlorosilane, Si n H 2n+2Silane or a combination thereof, wherein n is an integer selected from 1 to 3. The silicon-containing gas may preferably include: dichlorosilane, monosilane, disilane, trisilane or a combination thereof.

[0094] In CVD deposition, the reaction vessel can be designed as a fluidized bed reactor, a tube furnace, a bell furnace, a pit furnace, a lift kiln, a rotary kiln, a box kiln, or other suitable reactor types. In a preferred embodiment, the reaction is carried out under conditions that provide uniform gas phase inflow, such as in a reactor in which the raw materials are fluidized or stirred by other means to provide uniform gas inflow.

[0095] Preferably, the composite material for secondary lithium-ion batteries provided by the present invention places the porous carbon particles in an inert atmosphere and places them at a high temperature, and fully contacts them with a silicon-containing gas so as to achieve uniform deposition of silicon via chemical vapor deposition, thereby generating hydrogen-containing silicon in the pores of the porous carbon. Specifically, the porous carbon is placed in a reaction vessel, nitrogen or argon is introduced into the reaction vessel as a protective gas at a flow rate of 1-50 L / min, and the reactor is heated to 400-600 ° C at a heating rate of 1-10 ° C / min. The silicon-containing gas is then introduced into the reaction vessel and deposited on the porous carbon. Preferably, the temperature can be 400-450 ° C, or 450-500 ° C, or 500-550 ° C, or 550-600 ° C, or 500-600 ° C. The silicon-containing gas is introduced into the reaction vessel together with the inert gas, wherein the content of the silicon-containing gas 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 having the general formula Si n H 2n+2 (wherein n is an integer selected from 1-3) a gas of one or more silanes in a silane containing silicon. For example, the silicon-containing gas can be monosilane, the silicon-containing gas can also be disilane, and the silicon-containing gas can also be trisilane. The reaction vessel can be designed as: a fluidized bed reactor, a tube furnace, a bell furnace, a pit furnace, a lifting kiln, a rotary kiln, a box kiln or other suitable reactor types. In a preferred embodiment, the porous carbon particles are processed under conditions that provide uniform gas phase entry, such as a reactor in which the porous carbon particles are fluidized, or stirred by other means to provide uniform gas entry.

[0096] The process of forming hydrogenated silicon dispersed in a porous matrix by liquid impregnation includes: uniformly mixing the porous matrix and silane liquid, carbonizing and reducing at high temperature. Silane liquid includes trichlorosilane, Si n H 2n+2silane or a combination thereof, wherein n is an integer selected from 4 to 10. In certain embodiments, the porous substrate to be impregnated or otherwise impregnated with silicon is porous carbon. The porous carbon to be impregnated or otherwise impregnated with silicon may comprise various carbon allotropes. To this end, the porous carbon to be impregnated or otherwise impregnated with silicon may include graphite, nanographite, graphene, nanographene, carbon black, carbon nanowires, carbon nanotubes, etc. and combinations thereof.

[0097] In certain embodiments, a carbon scaffold impregnated or otherwise impregnated with silicon is removed to yield a templated silicon material having desired dimensional characteristics. Removal of the scaffold carbon can be achieved by methods known in the art, such as thermochemical activation under conditions in which 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.

[0098] Shell formation

[0099] The shell layer can be formed by coating the outer surface of a porous substrate in which hydrogenated silicon is dispersed. Coating the shell layer on the surface of the porous substrate in which hydrogenated silicon is dispersed can prevent the highly active hydrogenated silicon from being exposed to air and oxidized. It also reduces direct contact between the porous substrate and the hydrogenated silicon therein and the electrolyte during use of the composite material, helping to form a stable SEI film on the surface.

[0100] There is no special limitation on the coating method in this article. The outer surface of the porous substrate can be coated by reactive coating, adhesive coating, or a combination of reactive coating and adhesive coating. It can also be coated by other methods that can form a shell layer on the surface of the porous substrate dispersed with hydrogen-containing silicon.

[0101] Reactive coating refers to: forming a shell layer by reaction treatment to achieve coating. For example, the shell layer is formed by reacting a porous matrix dispersed with hydrogen-containing silicon. Specifically, the coating can be achieved by reacting the partial oxidation, nitridation, and carbonization of the hydrogen-containing silicon. In certain embodiments, the shell material is silicon dioxide, which can be formed by placing the porous matrix dispersed with hydrogen-containing silicon in an oxidizing atmosphere for heat treatment, that is, by surface oxidation to uniformly generate a layer of silicon dioxide shell on the surface of the porous matrix dispersed with hydrogen-containing silicon. In these embodiments, the oxidizing atmosphere includes but is not limited to one or more of air, oxygen, carbon dioxide, carbon monoxide, water vapor, etc. The heat treatment temperature can be 0-100°C, 100-200°C, 200-300°C, 300-400°C, or 400-500°C.

[0102] Adhesive coating refers to the attachment of materials to the surface of a porous substrate to form a shell.

[0103] The outer surface of the porous substrate can be coated by combining reactive coating and adhesive coating. Specific examples are shown below.

[0104] In some embodiments, the shell material is carbon. A porous matrix (such as porous carbon) dispersed with hydrogen-containing silicon can be brought into contact with a carbon source precursor, and after heat treatment, a carbon shell layer can be uniformly generated 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 of a porous matrix. In the chemical vapor deposition (CVD) method, 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°C, 450-500°C, 500-550°C, or 550-600°C. In the liquid phase coating method, the carbon source precursor includes but is not limited to one or more of asphalt, polyvinyl alcohol, polyethylene glycol, anthracene, aniline, tannic acid, etc. The mixing ratio of the liquid carbon source and the porous carbon dispersed with hydrogenated silicon is in the range of 1:0.5-1:10, and stirring and ultrasonic dispersion are used to mix uniformly. The carbonization temperature can be 400-450°C, 450-500°C, 500-550°C, or 550-600°C. In the solid phase coating method, the carbon source precursor includes but is not limited to one or more combinations of glucose, sucrose, biphenyl, vinyl pyrrolidone, etc. The carbonization temperature can be 400-450°C, 450-500°C, 500-550°C, or 550-600°C. The carbonization time can be 1 hour to 5 hours. The ratio of the solid carbon source to the porous carbon dispersed with hydrogenated silicon can be in the range of 1:0.5-1:10.

[0105] In certain embodiments, the shell material is a metal oxide. A porous carbon layer dispersed with hydrogenated silicon is contacted with a metal oxide precursor and subjected to heat treatment to uniformly form a metal oxide shell layer on the surface of the porous carbon layer dispersed with hydrogenated silicon. 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, aluminum phosphate, etc., and the heat treatment temperature can be 0-100°C, 100-200°C, 200-300°C, 300-400°C, or 400-500°C.

[0106] In one embodiment, the present disclosure provides a method for preparing a composite material for a secondary lithium-ion battery, wherein the matrix is ​​a porous matrix, and silicon is uniformly dispersed in the porous matrix by contacting the porous matrix with a silicon-containing reactant, wherein the silicon is uniformly distributed within the pores of the porous matrix, primarily in the form of hydrogenated silicon. The method may include the following steps:

[0107] 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, thereby producing a porous carbon material in which hydrogen-containing silicon is uniformly dispersed.

[0108] In another embodiment, the present disclosure provides a method for preparing a composite material for a secondary lithium-ion battery, wherein the matrix is ​​a porous matrix, the silicon is uniformly dispersed in the porous matrix by contacting the porous matrix with a silicon-containing reactant, and the final coating is achieved by contacting the composite with a carbon-containing reactant. For example, the method may include the following steps: 1) preparing a porous carbon material as the porous matrix; 2) subjecting the porous matrix to high temperature deposition in the presence of a silicon-containing gas in a reaction vessel to produce a porous carbon material having hydrogen-containing silicon uniformly dispersed therein; and 3) performing carbon coating by any of gas phase coating, liquid phase coating, or solid phase coating.

[0109] In another embodiment, the present disclosure provides a method for preparing a composite material for a secondary lithium-ion battery, wherein the matrix is ​​a porous matrix, the silicon is uniformly dispersed in the porous matrix by contacting the porous matrix with a silicon-containing reactant, the silicon dioxide coating is achieved by contacting the composite with an oxygen-containing atmosphere, and the carbon coating is achieved by contacting the composite with a carbon-containing reactant. 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 deposition in a reaction vessel in the presence of a silicon-containing gas to produce a porous carbon material uniformly dispersed therein with hydrogen-containing silicon; 3) treating the surface of the carbon material uniformly dispersed with hydrogen-containing silicon by oxidative passivation in any one of air, carbon dioxide, and water vapor; and 4) carbon coating by any one of gas phase coating, liquid phase coating, or solid phase coating to obtain a carbon shell.

[0110] Properties of composite materials for secondary lithium-ion batteries

[0111] The composite material of the present 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 conducive to preparing secondary lithium batteries with excellent performance.

[0114] Composite materials for secondary lithium-ion batteries can contain hydrogenated silicon in varying proportions. A suitable element content in the composite material helps improve the composite material's properties, particularly its electrical properties.

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

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

[0117] Based on the total weight of the composite material, the carbon content of the composite material can be 10-95wt%, preferably 30-90wt%, more preferably 35-85wt%, for example 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 42.5wt%, 45wt%, 46wt%, 7wt%, 48wt%, 49wt%, 50wt%, 50.8wt%, 51wt%, 51.3wt%, 51.8wt%, 52wt%, 53wt%, 54wt%, 55wt%, 57.3wt%, 60wt%, 60.3wt%, 65wt%, 70wt%, 80wt%, 90wt%, 95wt%, 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 certain embodiments, the composite material has a C content of 51.8 wt%, a Si content of 45.0 wt%, an O content of 0.2 wt%, and a H content of 3.0 wt% in the hydrogenated silicon. In certain embodiments, the composite material has a C content of 51.3 wt%, a Si content of 46.1 wt%, an O content of 0.2 wt%, and a H content of 2.4 wt% in the hydrogenated silicon. In certain embodiments, the composite material has a C content of 50.8 wt%, a Si content of 47.2 wt%, an O content of 0.2 wt%, and a H content of 1.8 wt% in the hydrogenated silicon. In certain embodiments, the composite material has a C content of 58.4 wt%, a Si content of 40.2 wt%, an O content of 0.2 wt%, and a H content of 1.2 wt% in the hydrogenated silicon. In certain embodiments, the composite material has a C content of 60.3 wt%, a Si content of 37.9 wt%, an O content of 0.3 wt%, and a H content of 1.5 wt% in the hydrogenated silicon. In certain embodiments, the composite material has a C content of 57.3 wt %, a Si content of 42.5 wt %, an O content of 0.2 wt %, and a H content of 0.01 wt % in the hydrogenated silicon.

[0120] The specific surface area of ​​the composite material of the secondary lithium ion battery of the present invention can be different. The specific surface area BET of the composite material can be 1-10m 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 certain embodiments, BET is 1m 2 / g, with a total pore volume of less than 0.1 cm 3 / g. In certain embodiments, BET is 2m 2 / g, with a total pore volume of less than 0.1 cm 3 / g. In certain embodiments, BET is 4m 2 / g, with a total pore volume of less than 0.1 cm 3 / g. In certain embodiments, BET is 6m 2 / g, with a total pore volume of less than 0.1 cm 3 / g. In certain embodiments, BET is 8m 2 / g, with a total pore volume of less than 0.1 cm 3 / g. In certain embodiments, BET is 10m 2 / g, with a total pore volume of less than 0.1 cm 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 with a D50 of 1-15 μm and a D100 of 10-30 μm. In certain embodiments, the composite material comprises a size distribution with a D50 of 5-20 μm and a D100 of 20-40 μm. In certain embodiments, the composite material comprises a size distribution with a D50 of 15-25 μm and a D100 of 40-60 μm; in certain embodiments, the composite material comprises a size distribution with a D50 of 20-30 μm and a D100 of 50-70 μm. In certain embodiments, the composite material comprises a size distribution with a D50 of 25-35 μm and a D100 of 60-80 μm. In certain embodiments, the composite material comprises a size distribution with a D50 of 30-40 μm and a D100 of 70-90 μm. In certain embodiments, the composite material consists of the following size distribution: D50 between 40-50 μm and D100 between 80-100 μm.

[0122] In some embodiments, the XRD pattern of the composite material for the secondary lithium ion battery has a peak with amorphous characteristics between 24° and 30°. In some embodiments, there is a sharp characteristic peak with a grain size of 5-30 nm at 28°±0.5°. In certain embodiments, the grain size is 5 nm. In certain embodiments, the grain size is 10 nm. In certain embodiments, the grain size is 15 nm. In certain embodiments, the grain size is 20 nm. In certain 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 / cm 3 In some embodiments, the composite material for secondary lithium-ion batteries has a tap density of 0.5 g / cm 3 The tap density of the porous matrix is ​​0.2 g / cm 3 In certain embodiments, the composite material for a secondary lithium ion battery has a tap density of 0.6 g / cm 3 The tap density of the porous matrix is ​​0.3 g / cm 3In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 0.8 g / cm 3 The tap density of the porous matrix is ​​0.4 g / cm 3 In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 1.2 g / cm 3 The tap density of the porous matrix is ​​0.5 g / cm 3 In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 1.4 g / cm 3 The tap density of the porous matrix is ​​0.6 g / cm 3 In certain embodiments, the composite material for a secondary lithium-ion battery has a tap density of 2 g / cm 3 The tap density of the porous matrix is ​​0.6 g / cm 3 .

[0124] Electrochemical performance

[0125] In certain embodiments, the electrochemical properties of the composite materials disclosed herein are tested in a half-cell. Among them, the preparation of the negative electrode sheet: the composite material of the present application, the conductive additive carbon black, and the adhesive (1:1 sodium carboxymethyl cellulose and styrene-butadiene rubber) are weighed according to a mass ratio of 95:2:3, and a slurry is prepared in a beater at room temperature. The prepared slurry is evenly coated on a copper foil, dried in a blast drying oven at 50°C for 2 hours, and then cut into electrode sheets with a diameter of 8 mm. After the electrode sheet is vacuum-dried in a vacuum drying oven at 100°C for 10 hours, the dried electrode sheet is immediately transferred to a glove box for standby use for battery assembly. Assembling the battery: The assembly of the simulated battery is carried out in a glove box containing a high-purity Ar atmosphere, using metallic lithium as the counter electrode and a solution of 1 mol of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) as the electrolyte to assemble the battery. Testing: A charge-discharge instrument was used in constant current charge-discharge mode, with a discharge cut-off voltage of 0.005V and a charge cut-off voltage of 1.5V. The charge-discharge tests were conducted at a current density of C / 10. The composite material was mixed with commercial graphite in a proportional ratio to produce a 450mAh / g test material. This was then assembled with lithium cobalt oxide into a button-type full cell and cycled at 1C to evaluate its cycling performance.

[0126] In certain embodiments, the electrochemical performance of the composite materials disclosed herein was tested in button-type full cells. The positive electrode sheet was prepared using the following formula parameters: 96.2% positive electrode material + 1.1% binder + 2.7% conductive agent; ingredient parameters: dry mixing, high-speed dispersion (solid content 72%), and viscosity adjusted to approximately 5000 for coating; coating parameters: single-sided surface density 21 mg / cm 2. After being cut into 15cm wide strips, the positive electrode sheets with a size of 73mm×44mm are obtained by die-cutting. Preparation of negative electrode sheets: formula parameters: 95.0wt% negative electrode material (composite material sample of the embodiment) + 3.5wt% binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) + 1.5wt% conductive agent carbon black; ingredient parameters: dry mixing and kneading (solid content 65%), high-speed dispersion (solid content 45%), viscosity adjusted to about 5000 for coating; coating parameters: single-sided surface density 9mg / cm 2 After being cut into 15cm wide strips, the negative electrode sheets with a size of 75mm×46mm are obtained by die-cutting. Assemble the battery: The process is as follows: Lamination: 9 negative electrode sheets and 8 positive electrode sheets are stacked in a Z shape; Welding the tabs: The positive and negative electrodes are welded with tabs (positive electrode: aluminum; Negative electrode: nickel); hot pressing and cold pressing: hot pressing at 80℃ for 1min and cold pressing at room temperature for 1min; aluminum mold punching: the punching depth is 3mm; top sealing and side sealing: the heat sealing temperature is 190℃ and the heat sealing time is 6 seconds; baking: keep warm at 95℃ for 3 days, during which nitrogen replacement is performed to ensure that the sample is in an inert atmosphere; water content test: take about 1g of positive electrode and negative electrode, heat and remove water at 120℃, and the moisture content is less than 200ppm; injection: 1 mol of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) is the electrolyte, injected between the positive electrode and the negative electrode, and the injection coefficient calculated according to the first charge is 3.5; one sealing: heat sealing temperature is 190℃, heat sealing time is 3 seconds, and vacuum degree is -90; soak at 45℃ for 2 days to obtain the assembled battery sample. The cycle conditions for the full battery test were: 1C / 1C; the voltage range was: 2.8-4.25V.

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

[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 a first 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 for a lithium ion battery, the composite material has a charge capacity of 1600 mAh / g or more, for example, 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 certain embodiments, when the composite material of the present invention is used as an electrode of a lithium-ion battery, the capacity retention rate is greater than 40%, or greater than 60%, or greater than 80%, or greater than 85% after 15 cycles at 25°C and a charge / discharge rate of 1C. In certain embodiments, when the composite material of the present invention is used as an electrode of a lithium-ion battery, the capacity retention rate is greater than 60%, or greater than 80%, or greater than 85% after 20 cycles at 25°C and a charge / discharge rate of 1C. In certain embodiments, when the composite material of the present invention is used as an electrode of a lithium-ion battery, the capacity retention rate is greater than 80%, or greater than 85% after 50 cycles at 25°C and a charge / discharge rate of 1C. In certain embodiments, when the composite material of the present invention is used as an electrode of a lithium-ion battery, the capacity retention rate is greater than 80%, or greater than 85% after 1000 cycles at 25°C and a charge / discharge rate of 1C. In one embodiment, when the composite material of the present invention is used as an electrode of a lithium-ion battery, its capacity retention rate is above 80% or above 85% after 1200 cycles at 25°C and 1C charge / discharge rate.

[0131] In some embodiments, in tests of lithium-ion half-cells prepared from the composite materials of secondary lithium-ion batteries of the present invention, the charging curve has no obvious platform at 0.4-0.5V, and the characteristic peak intensity at 0.4-0.5V of the DQ / DV curve is relatively low. In certain embodiments, in tests of lithium-ion half-cells prepared from the composite materials of secondary lithium-ion batteries, the charging curve has a platform at 0.4-0.5V, and the characteristic peak intensity at 0.4-0.5V of the DQ / DV curve is relatively high.

[0132] The platform of the charge curve at 0.4-0.5V and the characteristic peak of the corresponding DQ / DV curve at 0.4-0.5V are related to the degree of crystallinity of the hydrogenated silicon. The higher the crystalline silicon content, the more pronounced the platform of the charge curve at 0.4-0.5V and the stronger the characteristic peak of the DQ / DV curve at 0.4-0.5V.

[0133] The composite materials for secondary lithium-ion batteries disclosed herein can improve the properties of electrical storage devices. For example, they have been shown to reduce the expansion rate of electrodes in lithium-based batteries. Thickness expansion rate testing can be performed as follows: Initial thickness calibration: 1. Place the battery in a fixture after capacity separation and fully charge and discharge it at 0.2C to calibrate the capacity and determine its actual initial discharge capacity. 2. Charge at 0.2C for 2.5 hours at the initial discharge capacity, adjusting the SOC to 50%. 3. Remove the fixture and measure the initial thickness of the battery at 50% SOC. 4. Measure the thickness of the soft pack using a caliper. Measure the thickness in the middle of the battery until a relatively stable thickness is reached, which is recorded as T0. Full-charge thickness expansion test: 1. During the cycling process, the full-charge thickness of the battery is measured every 50cl for the first 200cl and every 100cl thereafter until the capacity decays to 80%. 2. Full charge is performed using a 0.2C CC 4.25V, 4.25V CV 0.04C process. 3. The soft pack thickness is tested using a caliper to measure the thickness in the middle of the battery until a relatively stable thickness is obtained, recorded as Tn. 4. The thickness expansion after 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, it operates for 1200 cycles at 25°C and a 1C charge and discharge rate, and its 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. Beneficial effects

[0135] Existing silicon nanomaterials still have certain shortcomings. First, nanosilicon is difficult to disperse evenly and easily agglomerates, preventing its full potential. Second, nanosilicon is highly reactive, consuming significant amounts of lithium ions during the formation of the solid electrolyte interface (SEI) film, reducing coulombic efficiency. Furthermore, during use, the nanosilicon surface reacts with the electrolyte, leading to gassing, which degrades battery capacity, reduces cycle performance, and can even lead to safety issues. Therefore, the application of nanosilicon in secondary lithium-ion batteries still faces significant challenges.

[0136] The present invention provides a method for preparing and applying a composite material for secondary lithium-ion batteries. Compared to existing technologies, the composite material of the present invention features a porous matrix with a rich pore structure, and the nano-silicon is hydrogen-containing silicon, which is uniformly dispersed within the pores of the porous matrix. The porous matrix is ​​silicon-free on the outer surface, and the outermost layer of the material also includes a dense carbon shell. Using a variety of silicon-containing precursors and a porous matrix as raw materials, the present invention uniformly disperses silicon within the porous matrix. By controlling the temperature, the silicon retains a portion of Si-H bonds, forming hydrogen-containing silicon. Finally, the entire material is carbon-coated to prevent spontaneous combustion of the highly active nano-hydrogen-containing silicon in air. This also ensures that the material does not come into direct contact with the electrolyte during use, facilitating the formation of a stable SEI film. The present invention uniformly disperses hydrogen-containing silicon within the composite material, solving the silicon dispersion problem and preventing the volume effect caused by silicon agglomeration during charge and discharge. Furthermore, the Si-H bonds contained in the hydrogen-containing silicon effectively improve the stability of the material structure during charge and discharge, extending the battery cycle life.

[0137] The preparation method of the composite material for secondary lithium ion batteries provided by the present invention is simple and easy to operate and can be applied to batch production.

[0138] Example

[0139] Below by specific embodiment, the present invention is further described in detail, but it should be understood that these embodiments are only for the purpose of describing in more detail, and should not be interpreted as limiting the present invention in any form, that is, not intended to limit the scope of protection of the present invention. Unless otherwise indicated, the instrument equipment and reagent materials used herein are all commercially available. The porous carbon used in the embodiment of the present application is prepared according to the conventional method of this area.

[0140] Sample preparation

[0141] Example 1: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.8-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 405°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 405°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 1.

[0142] Example 2: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.8-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 420°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 420°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by vapor coating to obtain the composite material sample of Example 2.

[0143] Example 3: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.8-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by vapor coating to obtain the composite material sample of Example 3.

[0144] Example 4: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.8-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 480°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 480°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 4.

[0145] Example 5: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.8-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 500°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 500°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by vapor coating to obtain the composite material sample of Example 5.

[0146] Example 6: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g, and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 550°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 550°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 6.

[0147] Example 7: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 600 ° C at a heating rate of 5 ° C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 600 ° C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 7.

[0148] Example 8 uses porous carbon with the following parameters as the porous matrix: oxygen content of 0.01-0.4 mmol / g, and BET of 1000-1100 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.4-0.6 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 405°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 405°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 8.

[0149] Example 9 uses porous carbon with the following parameters as the porous matrix: oxygen content of 0.01-0.4 mmol / g, and BET of 1500-1600 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.6-0.8 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 9.

[0150] Example 10: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g, and a BET of 2200-2500 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 1.0-1.2 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 27 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 50 L / min and the deposition time was 4 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by gas phase coating to obtain the composite material sample of Example 10.

[0151] Example 11: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 1-5 μm, D100 is 10-20 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tube furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The material was carbon-coated by vapor coating to obtain the composite material sample of Example 11.

[0152] Example 12: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g, and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 10-12 μm, D100 is 15-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The above-mentioned composite material was carbon-coated by gas phase coating to obtain the composite material sample of Example 12.

[0153] Example 13: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 12-15 μm, D100 is 20-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The above-mentioned composite material was carbon-coated by gas phase coating to obtain the composite material sample of Example 13.

[0154] Example 14: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.01-0.4 mmol / g, and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 15-20 μm, D100 is 25-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The above-mentioned composite material was carbon-coated by gas phase coating to obtain the composite material sample of Example 14.

[0155] Example 15: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.1-0.3 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min, and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The above-mentioned composite material was carbon-coated by gas phase coating to obtain the composite material sample of Example 15.

[0156] Example 16: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.2-0.5 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The above-mentioned composite material was carbon-coated by gas phase coating to obtain the composite material sample of Example 16.

[0157] Example 17: A porous carbon having the following parameters is used as the porous matrix: an oxygen content of 0.3-0.6 mmol / g and a BET of 1900-2000 m 2 / g, particle size distribution D50 is 5-10 μm, D100 is 20-50 μm, and the total pore volume is 0.9-1.0 cm 3 / g. 12 kg of porous carbon was placed in a fluidized bed, and nitrogen was introduced as a protective gas at a nitrogen flow rate of 23 L / min. The tubular furnace was heated to 450°C at a heating rate of 5°C / min. Silicon-containing gas monosilane was then introduced into the fluidized bed and deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours. After the deposition was completed, the reaction temperature was maintained at 450°C, and acetylene gas was introduced at a flow rate of 15 L / min for 2 hours. The above-mentioned composite material was carbon-coated by gas phase coating to obtain the composite material sample of Example 17.

[0158] Performance Testing

[0159] Infrared: After mixing the composite material sample powder and potassium bromide powder evenly, the mixture was pressed into tablets at a pressure of 8-10 MPa for 1 minute. The prepared tablet samples were placed in a Fourier transform infrared spectrometer for testing. The infrared absorption characteristics corresponding to the silicon-hydrogen bonding mode generally have three regions in the infrared absorption spectrum: (I) 500-800 cm -1 Rocking mode region, (II) 800-1000 cm -1 Bending mode region, (III) 1850-2250cm -1 The stretching mode area; the characteristic peak I signal is stronger, and the latter two characteristic absorption peaks are related to the preparation conditions. The hydrogen content can be calculated by the rocking mode calculation method. -1 The absorption peak at the position is Gaussian fitted, and the hydrogen content C in the hydrogenated silicon in the composite material is determined by the integral area of ​​the fitting function. H , the specific data are shown in Table 1 below.

[0160] Figures 1(a)-(g) show the infrared spectra of the composite material samples of Examples 1-7, respectively. As shown in Figure 1(a), in the infrared spectrum of the sample of Example 1, 630 cm -1 The absorption peak near 1050cm is attributed to the swing vibration absorption of Si-H bond. -1 The absorption peak near 1384 cm is attributed to the stretching vibration absorption of carbon-oxygen bond. -1 The absorption peak near 1630cm is attributed to the stretching vibration absorption of carbon-hydrogen bonds. -1 The absorption peak near 2370cm is attributed to the stretching vibration absorption of carbon-carbon bonds. -1 The nearby absorption peak is attributed to the asymmetric stretching vibration absorption of the carbon-oxygen bond.

[0161] XRD: The composite material sample powder of the embodiment was placed in an XRD diffractometer at 10-65° and 5° / min. The difference between the crystalline and amorphous silicon peaks was compared and the grain size was fitted. The X-ray used a copper target with a wavelength of 0.154 nm.

[0162] SEM: used to characterize the surface morphology of composite materials, observe the surface roughness, and assist in determining the deposition of surface silicon.

[0163] TEM: An electron beam emitted from an electron gun travels through a vacuum channel along the optical axis of the microscope, passing through a condenser lens. The condenser lens focuses the electron beam into a sharp, bright, and uniform spot, which then illuminates the sample within the chamber. The electron beam, after passing through the sample, carries information about the sample's internal structure, with less electrons passing through dense areas and more electrons passing through sparse areas. After convergence and focusing by the objective lens and initial magnification, 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 within the observation chamber. Composite material powder is evenly dispersed in ethanol, and a small amount is dripped onto a copper grid. After drying, the sample is then loaded. TEM allows observation of the size of silicon crystal domains within the composite material.

[0164] The XRD spectrum of the composite material sample of Example 1 is shown in Figure 2. As shown in Figure 2, the hydrogenated silicon deposited at this temperature is in an amorphous state, with a broad peak between diffraction angles of 20-30°, and no sharp diffraction response peak attributable to the (111) plane of crystalline silicon is found near 28.4°.

[0165] FIG3(a) shows an SEM image of the composite material sample of Example 1. FIG3(b) shows a TEM image of the composite material sample of Example 1. As can be seen from FIG3, the surface of the composite material obtained under these preparation conditions is not significantly different from the surface of the porous carbon substrate on which silicon is not deposited, and exhibits a uniform rough structure, with no granular nano-silicon deposition found. TEM characterization of the near-surface region of the material revealed no obvious diffraction fringes attributable to crystalline Si, proving that the hydrogenated silicon deposited at this temperature is in an amorphous state.

[0166] According to the test results of XRD, SEM and TEM, in the samples of all the embodiments, the deposited hydrogen-containing silicon was in an amorphous state.

[0167] Elemental analysis: For the composite material samples of the embodiment, the C content was determined by a carbon-sulfur analyzer, the O content was determined by a nitrogen-oxygen analyzer, and the hydrogen content C in hydrogenated silicon was determined by a nitrogen-oxygen analyzer. H The Si content in the composite material sample was calculated by fitting the infrared absorption peak in the rocking mode region, and the content of components other than C, O, and H was used. The specific data are shown in Table 1 below.

[0168] Electrical performance test

[0169] Half-cell:

[0170] The composite material sample of the embodiment was used to prepare the negative electrode sheet, and button-type half-cells were assembled for testing, as follows:

[0171] Preparation of the negative electrode: The composite material sample from the example, the conductive additive carbon black, and the binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) were weighed to a mass ratio of 95:2:3 and slurried in a beater at room temperature. The prepared slurry was evenly coated on copper foil and dried in a forced-air drying oven at 50°C for 2 hours. The slurry was then cut into 8mm diameter electrode pieces and dried in a vacuum drying oven at 100°C for 10 hours. The dried electrode pieces were then transferred to a glove box for use in battery assembly.

[0172] Battery Assembly: A simulated battery was assembled in a glove box containing a high-purity Ar atmosphere. Metallic lithium was used as the counter electrode, and a solution of 1 mol LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1) was used as the electrolyte.

[0173] Half-cell test: A constant current charge-discharge mode test was performed using a charge-discharge instrument. The discharge cut-off voltage was 0.005 V, and the charge cut-off voltage was 1.5 V. The charge-discharge test was performed at a current density of C / 10. The relevant test data obtained (charge specific capacity, first coulombic efficiency, etc.) are detailed in Table 1.

[0174] The charge and discharge curves of the button half-cell obtained by assembling the negative electrode sheet prepared from the composite material sample of Example 1 are shown in FIG4 . The first discharge (lithium insertion) curve has three platforms at 0.3-0.5V, 0.1-0.3V and 0-0.1V, corresponding to the three lithium insertion peaks in the DQ / DV curve. The lithium insertion peak at 0.3-0.5V is related to the microporous structure and oxygen content of the porous carbon substrate, and the lithium insertion peak at 0.1-0.3V corresponds to Si→Li 2.0 Si alloy phase transition; the lithium insertion peak at 0-0.1V corresponds to Li 2.0 Si→Li 3.5 Si alloy phase transition; the first charge (delithiation) curve has three platforms 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, of which the 0.2-0.4V delithiation peak corresponds to Li 3.5 Si→Li 2.0 The alloy phase transition of Si, the delithiation peak at 0.4-0.6V corresponds to Li 2.0 The Si→Si alloy phase transition and the delithiation peak at 0.6-0.8V are related to the microporous structure and oxygen content of the porous carbon substrate. In the DQ / DV curves of some other examples, a sharp delithiation peak between 0.4-0.5V is also present. The intensity of this peak is related to the crystalline silicon content; higher crystalline silicon content indicates a greater peak intensity.

[0175] Full Battery:

[0176] Referring to the preparation and testing process of the above half-cell, the composite material sample of the embodiment was used as the negative electrode material to prepare a negative electrode sheet, and a full cell was assembled and tested as follows:

[0177] Preparation of positive electrode: Formula 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 the viscosity to about 5000cP before coating; coating parameters: single-sided density 21mg / cm 2 After being cut into 15 cm wide strips, the positive electrode sheets with a size of 73 mm × 44 mm were obtained by die cutting.

[0178] Preparation of negative electrode sheet: formula parameters: 95.0wt% negative electrode material (composite material sample of the embodiment) + 3.5wt% binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) + 1.5wt% conductive agent carbon black; ingredient parameters: dry mixing and kneading (solid content 65%), high-speed dispersion (solid content 45%), and viscosity adjustment to about 5000 for coating; coating parameters: single-side surface density 9mg / cm 2 After being cut into 15 cm wide strips, negative electrode sheets with a size of 75 mm × 46 mm were obtained by die cutting.

[0179] Assemble the battery: proceed as follows: stacking: 9 negative electrode sheets and 8 positive electrode sheets are stacked in a Z shape; welding the tabs: the positive and negative electrodes are welded with tabs (positive electrode: aluminum; negative electrode: nickel); hot pressing and cold pressing: hot pressing at 80°C for 1 minute and cold pressing at room temperature for 1 minute; aluminum mold punching: the punching depth is 3mm; top sealing and side sealing: the heat sealing temperature is 190°C and the heat sealing time is 6 seconds; baking: keep warm at 95°C for 3 days, during which nitrogen replacement is performed to ensure that the sample is in an inert atmosphere; water content test: take About 1g of each positive electrode and negative electrode are heated at 120℃ to remove water to reduce the moisture content to less than 200ppm; liquid injection: a solution of 1 mol of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) is injected as the electrolyte between the positive electrode and the negative electrode, and the liquid injection coefficient calculated according to the first charge is 3.5; sealing: heat sealing temperature 190℃, heat sealing time 3 seconds, vacuum degree -90; soak at 45℃ for 2 days to obtain the assembled battery sample.

[0180] Full battery test: Cycle conditions: 1C / 1C; Voltage range: 2.8-4.25V.

[0181] Figure 5 shows the cycle curves of the coin-type full cells of Examples 1 to 7 (cycle number: 50 cycles). Figure 6 shows the cycle curve of the coin-type full cell of Example 1 (cycle number: 1200 cycles).

[0182] Thickness expansion rate test:

[0183] Initial thickness calibration: 1. Place the battery on the fixture after capacity separation, and calibrate the capacity by fully charging and discharging at 0.2C to determine its actual initial discharge capacity. 2. Charge for 2.5 hours at the initial discharge capacity of 0.2C and adjust the SOC to 50%. 3. Remove the fixture and measure the initial thickness of the battery at 50% SOC. 4. Use a caliper to test the thickness of the soft pack. Measure the thickness in the middle of the battery until a relatively stable thickness appears, which is recorded as T0.

[0184] Full-charge thickness expansion test: 1. During the cycling process, the full-charge thickness of the battery is measured every 50cl for the first 200cl and every 100cl thereafter until the capacity decays to 80%. 2. Full charge is performed using a 0.2C CC 4.25V, 4.25V CV 0.04C process. 3. The soft pack thickness is tested using a caliper to measure the thickness in the middle of the battery until a relatively stable thickness is obtained, recorded as Tn. 4. The thickness expansion after a specific number of cycles can be calculated using the formula Tn / T0-1.

[0185] FIG7 shows the thickness expansion curve of the button-type full battery of Example 1.

[0186] Table 1

[0187] H content*: hydrogen content C in hydrogenated silicon H .

[0188] As shown in Figure 5, the button-type full battery prepared using the composite materials of Examples 1-7 of the present application has an excellent long cycle retention rate. Under the working conditions of 25°C and 1C charge and discharge rate, the capacity retention rate is above 40% after 15 cycles. As can be seen from Figure 5, the capacity retention rate is positively correlated with the hydrogen content in the hydrogenated silicon in the composite material. The hydrogen content in the hydrogenated silicon in the composite material sample of Example 6 is increased to 0.03wt%. The button-type full battery prepared from the sample of Example 6 is still above 60% after 20 cycles under the working conditions of 25°C and 1C charge and discharge rate. For the composite material samples of Examples 1-5, the hydrogen content in the hydrogenated silicon in the samples is above 0.09%, and the long cycle retention rate of the button-type full battery prepared is significantly better. Under the working conditions of 25°C and 1C charge and discharge rate, the capacity retention rate is above 80% after 50 cycles.

[0189] A full battery prepared using the composite material of Example 1 exhibited exceptional long-cycle retention. After 1200 cycles at 25°C and a 1C charge / discharge rate, its capacity retention reached 87%, significantly exceeding the 80% capacity retention requirement for power batteries after 1000 cycles. Regarding electrode expansion, the button-type full battery of Example 1 exhibited only 8% expansion after 1000 cycles.

[0190] In the composite materials of Example 3 and Examples 8-10, except for the silicon content, the other element contents, BET and particle size distributions are very similar. As shown in Table 2, as the silicon content of the composite materials increases, the charge capacity of the samples increases.

[0191] From the preparation processes of Examples 8-10, it can be seen that the silicon content of the composite material samples is positively correlated with the pore volume of the porous carbon matrix (such as the BET test results). From the preparation processes of Examples 11-14, it can be seen that the silicon content of the composite material samples is negatively correlated with the particle size of the porous carbon matrix (such as the D50 particle size).

[0192] In the samples of Example 1 and Examples 15-17, except for the oxygen content, the other element contents, BET and particle size distributions are very similar. As shown in Table 2, as the oxygen content of the composite material samples increases, the first coulombic efficiency of the samples shows a slow downward trend.

[0193] It can be seen from the test data in Table 1 and FIG5 that the battery assembled with the composite material for secondary lithium-ion batteries according to the embodiment of the present invention has higher charge capacity and first coulombic efficiency than the negative electrode on the market, and the cycle performance is also significantly improved.

[0194] In the composite material of the present invention, the porous matrix has a rich pore structure, and the nano-silicon is hydrogen-containing silicon, which is evenly dispersed in the inner pores of the porous matrix. The outer surface of the porous matrix is ​​silicon-free, and the outermost layer of the material also includes a dense shell. The present invention uses a variety of silicon-containing precursors and a porous matrix as raw materials, uniformly dispersing silicon in the porous matrix. By controlling the temperature, the silicon retains a portion of Si-H bonds, forming hydrogen-containing silicon. Finally, the entire material is coated to prevent the highly active nano-hydrogen-containing silicon from spontaneous combustion in air. It also ensures that the material does not come into direct contact with the electrolyte during use, easily forming a stable SEI film.

[0195] On the one hand, the present invention evenly disperses hydrogen-containing silicon in a porous matrix, solving the silicon dispersion problem and avoiding the volume effect caused by silicon agglomeration during the charging and discharging process; on the other hand, the Si-H bonds contained in hydrogen-containing silicon can effectively improve the stability of the material structure during the charging and discharging process and extend the battery cycle life.

[0196] It will be apparent to those skilled in the art that many modifications and variations of the present invention may be made without departing from its spirit and scope. The specific embodiments described herein are provided by way of example only and are not intended to be limiting in any way. The true scope and spirit of the present invention are shown by the appended claims, and the description and examples are merely exemplary.

Claims

1. A composite material for a secondary lithium-ion battery, characterized in that: The composite material comprises: a porous matrix, hydrogen-containing silicon dispersed in the porous matrix, and a shell layer coated on the outer surface of the porous matrix.

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 0.01-10 wt %, preferably 0.3-5 wt %, and more preferably 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 5-90wt%, preferably 15-70wt%, more preferably 30-65wt%; and / or Based on the total weight of the composite material, the carbon content of the composite material is 10-95wt%, preferably 30-90wt%, more preferably 35-85wt%; and / or The oxygen content of the composite material is 0-3 wt % based on the total weight of the composite material.

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

5. The composite material according to claim 1, characterized in that The infrared spectrum of the composite material is at 625-640 cm -1 There is a vibration peak.

6. The composite material according to claim 5, characterized in that The infrared spectrum of the composite material also has vibration peaks at one or more of the following positions: 845-885cm -1 1990-2010cm -1 .

7. The composite material according to claim 1, characterized in that The particle size of the hydrogen-containing silicon is in the range of 0.1-60 nm, preferably 0.1-20 nm, and more preferably 1-5 nm.

8. 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 of ​​the composite material is 10 m 2 / g or less; The total pore volume of the composite material is 0.1 cm 3 / g or less; The particle size D50 of the composite material is 1-50 μm; The D100 particle size of the composite material is 10-100 μm.

9. The composite material according to claim 1, characterized in that: The porous matrix has one or more of the following characteristics: The oxygen content of the porous matrix is ​​0.01-0.6 mmol / g; The porous matrix comprises 20%-90% micropores, 10%-50% mesopores and 0-30% macropores; The specific surface area of ​​the porous matrix is ​​1000-2500 m 2 / g; The total pore volume of the porous matrix is ​​0.1-2.5 cm 3 / g, preferably 0.5-1.2cm 3 / g; The D50 particle size of the porous matrix is ​​1-30 μm, preferably 1-20 μm; The D100 particle size of the porous matrix is ​​5-80 μm, preferably 5-50 μm.

10. The composite material according to claim 1, characterized in that The porous matrix includes porous carbon, porous polymer material, porous ceramic material, porous metal material or a combination thereof.

11. The composite material according to claim 1, characterized in that The components of the shell layer include: amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, silicon oxide, silicon oxynitride or a combination thereof.

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

13. 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 platform at 0.4-0.5V, and / or The DQ / DV curve of the half-cell prepared from the composite material has a characteristic peak at 0.4-0.5V.

14. A method for preparing the composite material according to any one of claims 1 to 13, comprising the following steps: providing a porous matrix; forming hydrogen-containing silicon dispersed in a porous matrix by a CVD deposition method and / or a liquid impregnation method; The outer surface of the porous matrix in which the hydrogen-containing silicon is dispersed is coated to form a shell layer.

15. The method according to claim 14, characterized in that The process of forming hydrogenated silicon dispersed in a porous matrix by CVD deposition includes: Placing the porous matrix in a reaction container, and introducing protective gas into the reaction container; heating the reaction vessel to a reaction temperature; Passing a silicon-containing gas into a reaction vessel to deposit in the porous substrate; Preferably, The heating rate of the reaction vessel is 1-10°C / min; The reaction temperature is 400-600°C; The flow rate of protective gas is 5-30L / min; The total flow rate of silicon-containing gas is 10-40L / min; The deposition time is 5-20 hours.

16. The method of claim 15, characterized in that The silicon-containing gas includes: dichlorosilane, Si n H 2n+2 Silane or a combination thereof, wherein n is an integer selected from 1-3; Preferably, The silicon-containing gas includes: dichlorosilane, monosilane, disilane, trisilane or a combination thereof.

17. The method of claim 14, wherein: The process of forming hydrogenated silicon dispersed in a porous matrix by liquid impregnation includes: The porous matrix and the silane liquid are uniformly mixed. Carbonization and reduction are carried out by high temperature.

18. The method of claim 17, characterized in that The silane liquid includes: trichlorosilane, Si n H 2n+2 Silane or a combination thereof, wherein n is an integer selected from 4-10.

19. The method of claim 14, wherein: The outer surface of the porous matrix in which hydrogen-containing silicon is dispersed is coated by reactive coating, adhesive coating or a combination thereof to form a shell layer.

20. A negative electrode plate, characterized in that: The negative electrode plate comprises the composite material according to any one of claims 1-13.

21. A lithium ion secondary battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 20.

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