Multilayer composite materials for lithium-ion secondary batteries and their preparation methods and applications

Abstract

A multi-layer composite material for lithium-ion secondary batteries and its preparation method and application are provided. [Solution] The multilayer composite material includes a carbon matrix, a nanosilicon-based composite material, and a carbon shell. The carbon matrix is ​​a matrix material for depositing the nanosilicon-based composite material. The nanosilicon-based composite material is prepared by a vapor phase growth method using silane and one or more gaseous compounds containing any of the elements C, N, B, or P. The particle size of the nanosilicon-based composite material is 0.1 to 200 nm. Carbon atoms in the nanosilicon-based composite material are uniformly embedded on an atomic scale, carbon atoms and silicon atoms are bonded to form amorphous Si-C bonds, nitrogen atoms are bonded to form amorphous Si-N bonds, and defects are generated in the silicon crystals in the nanosilicon-based composite material by boron doping and / or phosphorus doping. The carbon shell is coated on the outer layer of the carbon matrix on which the nanosilicon-based composite material is deposited.

Description

[Technical Field]

[0001] [Cross reference] This application claims priority to a Chinese patent application filed with the China Patent Office on December 10, 2021, bearing application number 202111510520.3 and titled "Multilayer composite material for lithium-ion secondary batteries and its preparation method and application."

[0002] [Technical field] The present invention relates to the technical field of materials, in particular to a multilayer composite material for lithium ion secondary batteries and its preparation method and application. [Background technology]

[0003] In the past few decades, commercialized lithium-ion batteries have achieved great success due to their advantages of long cycle life, high energy density, and environmental friendliness. Conventional secondary lithium-ion batteries mainly consist of a negative electrode (usually a carbonaceous material such as graphite), a positive electrode (e.g., LiCoO2, LiMn2O2, and LiFePO4), and a separator impregnated with an electrolyte solution. Lithium ions shuttle between the two electrodes via the liquid electrolyte, and the charge is transferred via an external circuit.

[0004] However, the theoretical capacity of conventional graphite anode materials is limited to 372 mAh / g, which cannot meet the ever-increasing requirements for high-performance storage capacity.With the increasing demand for portable electronic devices, electric vehicles, and renewable energy, the development of high-capacity anode materials with excellent electrochemical performance has proven to be an important solution for realizing lithium-ion storage and improving overall energy density.

[0005] Silicon is a promising alternative to graphite anodes in lithium-ion batteries due to its natural abundance, environmental friendliness, low discharge potential, and high theoretical capacity (4200 mAh / g). However, the large volume change of silicon (300%-400%) has hindered the practical application of silicon-based anodes.

[0006] Research has shown that combining silicon with carbon materials can effectively improve the shortcomings of silicon anodes. In Patent Document 1, nanosilicon and nanographite sheets are uniformly dispersed in water, then an organic carbon solution is added and spray-dried, and the resulting powder is calcined to obtain a silicon-carbon composite material. This material partially alleviates the poor conductivity and cycle stability of silicon. However, this preparation method involves physically mixing the carbon material with the composite, making it difficult to uniformly disperse the silicon and carbon materials, which affects its electrochemical performance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Chinese Patent No. 108598389 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a multilayer composite material for lithium ion secondary batteries, its preparation method, and applications. The multilayer composite material for lithium ion secondary batteries of the present invention has a stable structure, and compared to conventional silicon-based materials, the interaction between the multilayer structure and the composite material gives the material the advantages of smaller volume expansion, better cycle characteristics, and better rate characteristics. [Means for solving the problem]

[0009] In a first aspect, an embodiment of the present invention provides a multilayer composite material for a lithium ion secondary battery, the multilayer composite material comprising a carbon matrix, a nano silicon-based composite material, and a carbon shell; the carbon matrix is ​​a matrix material for depositing the nano silicon-based composite material; The nanosilicon-based composite material is prepared by vapor deposition of silane and one or more gaseous compounds containing any of C, N, B, and P elements, and the particle size of the nanosilicon-based composite material is 0.1 to 200 nm. Carbon atoms in the nanosilicon-based composite material are uniformly embedded on an atomic scale, carbon atoms and silicon atoms are bonded to form amorphous Si-C bonds, nitrogen atoms and silicon atoms are bonded to form amorphous Si-N bonds, and defects are generated in the silicon crystals in the nanosilicon-based composite material by boron doping and / or phosphorus doping. The carbon shell is coated with an outer layer of a carbon matrix on which a nano silicon based composite material is deposited.

[0010] Preferably, the carbon shell is prepared by vapor, liquid or solid phase coating.

[0011] Preferably, when the multilayer composite material contains a C element, the solid-state nuclear magnetic resonance NMR spectrum of the multilayer composite material shows that when the silicon peak is at -70 ppm to -130 ppm, a Si-C resonance peak exists between 20 ppm and -20 ppm, and the area ratio of the Si-C resonance peak to the silicon peak is 0.1 to 5.0.

[0012] Preferably, in the multilayer composite material, the mass of the nano silicon-based composite material accounts for 20% to 80% of the total mass, and the mass of any of the C, N, B, and P elements composited with silicon accounts for 0.1% to 50% of the mass of the nano silicon-based composite material; The mass of the carbon matrix accounts for 20% to 70% of the total mass, The mass of the carbon shell accounts for 0 to 10% of the total mass.

[0013] In a second aspect, embodiments of the present invention provide a method for preparing a multilayer composite material for a lithium ion secondary battery according to the first aspect, the method comprising: introducing a protective gas, which is nitrogen gas, argon gas, hydrogen gas, or any mixture thereof, into a reaction vessel filled with a carbon matrix at a flow rate of 1 to 2 L / min; introducing silane and one or more gaseous compounds containing any of C, N, B, and P elements into a reaction vessel and vapor-depositing the compounds on the carbon matrix; applying a carbon coating to the deposited product by at least one of vapor coating, liquid coating, and solid coating to obtain the multilayer composite material for lithium ion secondary batteries; Including, Here, the gas flow rate of silane is 0.5 to 10 L / min, the gas flow rate of the gaseous compound is 0.5 to 10 L / min, the deposition temperature is 500 to 1500° C., and the deposition time is 1 to 20 hours.

[0014] Preferably, the reaction vessel comprises a batch reactor or a continuous reactor, in particular a rotary furnace, a tubular furnace, a bell furnace or a fluidized bed.

[0015] Preferably, the silane comprises one or more of monosilane, disilane, tetrafluorosilane, chlorosilane, hexamethyldisilane, dimethylsiloxane.

[0016] Preferably, the gaseous compound containing a C element comprises one or more of acetylene, methane, propylene, ethylene, propane and gaseous ethanol; The gaseous compound containing an N element includes one or more of nitrogen, ammonia, urea, melamine, and hydrazine, the gaseous compound containing B element includes one or more of diborane, trimethyl borate, tripropyl borate, and boron tribromide; The gaseous compound containing the element P includes phosphine and / or phosphorus oxychloride.

[0017] In a third aspect, embodiments of the present invention provide a negative electrode material for a lithium-ion secondary battery, comprising the multilayer composite material according to the first aspect above.

[0018] In a fourth aspect, an embodiment of the present invention provides a lithium battery comprising the multilayer composite material for a lithium ion secondary battery according to the first aspect above. [Effects of the Invention]

[0019] The multilayer composite material for lithium-ion secondary batteries according to embodiments of the present invention exhibits low volume expansion and excellent cycle and rate characteristics due to the interaction between the three-layer structure of the carbon matrix, nanosilicon-based composite, and carbon shell and the composite. In particular, nanosilicon-based composite materials prepared by vapor deposition of silane and one or more gaseous compounds containing C, N, B, or P have carbon atoms uniformly embedded at the atomic scale, and carbon atoms and silicon atoms bond to form amorphous Si-C bonds, which stabilize the material structure during lithium insertion and deintercalation, reducing volume expansion and providing better cycle characteristics when used in lithium battery anodes. Nitrogen atoms bond to silicon atoms to form amorphous Si-N bonds, which favors lithium ion insertion and deintercalation, improving the rate characteristics of lithium-ion batteries. Boron and / or phosphorus doping creates defects in the silicon crystals within the nanosilicon-based composite, reducing volume expansion during charging and improving battery cycle characteristics. [Brief explanation of the drawings]

[0020] Hereinafter, the technical solutions in the embodiments of the present invention will be described in more detail with reference to the drawings and examples.

[0021] [Figure 1] 1 is a schematic diagram illustrating the configuration of a multilayer composite material for a lithium ion secondary battery according to an embodiment of the present invention. [Figure 2] 1 is a flowchart of a method for preparing a multilayer composite material for a lithium ion secondary battery according to an embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing a solid-state nuclear magnetic resonance (NMR) spectrum of the multilayer composite material according to Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, the present invention will be further described with reference to the drawings and specific examples. However, it should be understood that these examples are merely for the purpose of explaining the present invention in more detail and are not intended to limit the present invention in any way, i.e., they are not intended to limit the protection scope of the present invention.

[0023] The present invention proposes a multilayer composite material for a lithium-ion secondary battery, and Fig. 1 is a schematic structural diagram of a multilayer composite material according to an embodiment of the present invention. As shown in Fig. 1, the multilayer composite material includes a carbon matrix, a nanosilicon-based composite material, and a carbon shell, The carbon matrix is ​​a matrix material for depositing the nano silicon-based composite material, and may specifically include one or more of porous activated carbon, carbon nanotubes, carbon fibers, and mesocarbon microbeads; The nanosilicon-based composite material is prepared by vapor deposition of silane and one or more gaseous compounds containing any of the elements C, N, B, and P, and the particle size of the nanosilicon-based composite material is 0.1 to 200 nm. The carbon atoms in the nanosilicon-based composite material are uniformly embedded on an atomic scale, the carbon atoms and silicon atoms are bonded to form amorphous Si-C bonds, and the nitrogen atoms and silicon atoms are bonded to form amorphous Si-N bonds. Defects are generated in the silicon crystals in the nanosilicon-based composite material by boron doping and / or phosphorus doping. The carbon shell is coated on an outer layer of a carbon matrix on which the nano silicon-based composite material is deposited, and is specifically prepared by vapor, liquid or solid phase coating.

[0024] When the multilayer composite material contains C element, the solid-state nuclear magnetic resonance NMR spectrum of the multilayer composite material shows that the silicon peak is located at -70 ppm to -130 ppm, and the Si-C resonance peak exists between 20 ppm and -20 ppm, and the area ratio of the Si-C resonance peak to the silicon peak is 0.1 to 5.0.

[0025] In the multilayer composite material, the mass of the nano silicon-based composite material accounts for 20% to 80% of the total mass, the mass of any of the C, N, B, and P elements composited with silicon accounts for 0.1% to 50% of the mass of the nano silicon-based composite material, the mass of the carbon matrix accounts for 20% to 70% of the total mass, and the mass of the carbon shell accounts for 0 to 10% of the total mass.

[0026] The material of the present invention is prepared according to the flowchart of the preparation method shown in Figure 2. As shown in Figure 2, it mainly includes the following steps: In step 110, a protective gas is introduced into the reaction vessel filled with the carbon matrix at a flow rate of 1 to 2 L / min; Specifically, the reaction vessel includes a batch reactor or a continuous reactor, specifically a rotary furnace, a tubular furnace, a bell furnace, or a fluidized bed. The protective gas introduced is nitrogen gas, argon gas, hydrogen gas, or a mixture of any two or three of these gases.

[0027] In step 120, silane and one or more gaseous compounds containing any of the elements C, N, B, and P are introduced into the reaction vessel and vapor-deposited onto the carbon matrix; Here, the silane includes one or more of monosilane, disilane, tetrafluorosilane, chlorosilane, hexamethyldisilane, and dimethylsiloxane.

[0028] The gaseous compound containing a C element includes one or more of acetylene, methane, propylene, ethylene, propane, and gaseous ethanol; The gaseous compound containing an N element includes one or more of nitrogen, ammonia, urea, melamine, and hydrazine, the gaseous compound containing B element includes one or more of diborane, trimethyl borate, tripropyl borate, and boron tribromide; The gaseous compound containing the element P includes phosphine and / or phosphorus oxychloride.

[0029] When the compound containing the N, B, or P element is in a liquid or solid state at room temperature and pressure, the gaseous compound is formed by transporting a solution of the element compound using a carrier gas, and is then transported into a reaction vessel.

[0030] The gas flow rate of silane is 0.5-10 L / min, the gas flow rate of the gaseous compound is 0.5-10 L / min, the deposition temperature is 500-1500°C, and the deposition time is 1-20 hours.

[0031] In step 130, the deposited product is coated with carbon by at least one of vapor phase coating, liquid phase coating, and solid phase coating to obtain a multilayer composite material for a lithium ion secondary battery.

[0032] Gas phase coating, liquid phase coating, and solid phase coating are all commonly used coating methods in the industry, and those skilled in the art will already know how to use these methods to achieve carbon coating, so a detailed description thereof will be omitted here.

[0033] The multilayer composite material for lithium ion secondary batteries proposed in the present invention is used as a negative electrode material for lithium ion batteries and is applied to lithium ion batteries.

[0034] The multilayer composite material for lithium-ion secondary batteries according to embodiments of the present invention exhibits low volume expansion and excellent cycle and rate characteristics due to the interaction between the three-layer structure of the carbon matrix, nanosilicon-based composite, and carbon shell and the composite. In particular, nanosilicon-based composite materials prepared by vapor deposition of silane and one or more gaseous compounds containing C, N, B, or P have carbon atoms uniformly embedded at the atomic scale, and carbon atoms and silicon atoms bond to form amorphous Si-C bonds, which stabilize the material structure during lithium insertion and deintercalation, reducing volume expansion and providing better cycle characteristics when used in lithium battery anodes. Nitrogen atoms bond to silicon atoms to form amorphous Si-N bonds, which favors lithium ion insertion and deintercalation, improving the rate characteristics of lithium-ion batteries. Boron and / or phosphorus doping creates defects in the silicon crystals within the nanosilicon-based composite, reducing volume expansion during charging and improving battery cycle characteristics.

[0035] In order to better understand the technical solution of the present invention, several specific examples will be given below to describe the specific process of preparing a multilayer composite material using the method according to the above embodiment of the present invention, as well as the application method and battery characteristics thereof in a lithium ion secondary battery.

[0036] [Example 1] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Nitrogen gas is introduced as a protective gas for silane deposition into a rotary furnace, which is a reaction vessel filled with a carbon matrix, at a flow rate of 1 L / min. (2) Monosilane and methane, a compound containing carbon, are introduced into a reaction vessel in gas form and vapor-phase deposition is performed on a carbon matrix. The gas flow rates of monosilane and methane are 0.5 L / min, the deposition temperature is 500 °C, and the deposition time is 20 hours. (3) The deposited product is coated with carbon by vapor phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0037] [Example 2] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Argon gas is introduced at a flow rate of 1.5 L / min as a protective gas for silane deposition into a tubular furnace, which is a reaction vessel filled with a carbon matrix. (2) Disilane and ammonia, a compound containing N, are introduced into a reaction vessel in gaseous form and vapor-phase deposition is performed on a carbon matrix. The gas flow rates of disilane and ammonia are 0.8 L / min, the deposition temperature is 600 °C, and the deposition time is 12.5 hours. (3) The deposited product is coated with carbon by liquid phase coating to obtain a multilayer composite material for lithium ion secondary batteries.

[0038] [Example 3] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Nitrogen gas is introduced at a flow rate of 2 L / min into a bell-type furnace, which is a reaction vessel filled with a carbon matrix, as a protective gas for silane deposition. (2) Tetrafluorosilane and tripropyl borate, a compound containing B element, are introduced into a reaction vessel in gas form and vapor-phase deposited on a carbon matrix. The gas flow rates of tetrafluorosilane and tripropyl borate are 1 L / min, the deposition temperature is 700 °C, and the deposition time is 10 hours. (3) The deposited product is coated with carbon by solid-phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0039] [Example 4] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Argon gas is introduced at a flow rate of 2 L / min as a protective gas for silane deposition into a fluidized bed, which is a reaction vessel filled with a carbon matrix. (2) Chlorosilanes and phosphorus oxychloride, a compound containing P, are introduced into a reaction vessel in gaseous form and vapor-phase deposited on a carbon matrix. The gas flow rates of the chlorosilanes and phosphorus oxychloride gaseous compounds are 1.25 L / min, the deposition temperature is 800 °C, and the deposition time is 8 hours. (3) The deposited product is coated with carbon by vapor phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0040] [Example 5] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Argon gas is introduced at a flow rate of 1.5 L / min as a protective gas for silane deposition into a tubular furnace, which is a reaction vessel filled with a carbon matrix. (2) Disilane and gaseous compounds containing C, N, B, and P, namely methane, ammonia, trimethyl borate, and phosphorus oxychloride, are introduced into a reaction vessel in gaseous form and vapor-phase deposition is carried out on a carbon matrix. The gas flow rate of disilane is 0.8 L / min, and the gas flow rates of methane, ammonia, trimethyl borate, and phosphorus oxychloride are all 0.2 L / min. The deposition temperature is 600°C, and the deposition time is 12.5 hours. (3) The deposited product is coated with carbon by liquid phase coating to obtain a multilayer composite material for lithium ion secondary batteries.

[0041] [Example 6] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Nitrogen gas is introduced at a flow rate of 2 L / min into a bell-type furnace, which is a reaction vessel filled with a carbon matrix, as a protective gas for silane deposition. (2) Tetrafluorosilane and gaseous compounds containing C, N, B, and P, namely propylene, urea, tripropyl borate, and phosphine, are introduced into a reaction vessel in gaseous form and vapor-phase deposition is performed on a carbon matrix. The gas flow rate of tetrafluorosilane is 1 L / min, and the gas flow rates of propylene, urea, tripropyl borate, and phosphine gaseous compounds are all 0.25 L / min. The deposition temperature is 700 °C, and the deposition time is 10 hours. (3) The deposited product is coated with carbon by solid-phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0042] [Example 7] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Nitrogen gas is introduced as a protective gas for silane deposition into a rotary furnace, which is a reaction vessel filled with a carbon matrix, at a flow rate of 2 L / min. (2) Hexamethyldisilane and compounds containing C, N, B, and P, such as propane, hydrazine, diborane, and phosphine, were introduced into a reaction vessel in gaseous form and vapor-phase deposition was performed on a carbon matrix. The gas flow rate of hexamethyldisilane was 2 L / min, and the gas flow rates of propane, hydrazine, diborane, and phosphine were all 0.5 L / min. The deposition temperature was 900°C, and the deposition time was 5 hours. (3) The deposited product is coated with carbon by liquid phase coating to obtain a multilayer composite material for lithium ion secondary batteries.

[0043] [Example 8] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Argon gas is introduced at a flow rate of 2 L / min as a protective gas for silane deposition into a tubular furnace, which is a reaction vessel filled with a carbon matrix. (2) Monosilane, disilane, ethanol (a compound containing C, N, B, and P elements), nitrogen gas, trimethyl borate, and phosphorus oxychloride were introduced into a reaction vessel in gaseous form and vapor-phase deposited on a carbon matrix. The gas flow rates of monosilane and disilane were both 1.2 L / min, and the gas flow rates of ethanol, nitrogen gas, trimethyl borate, and phosphorus oxychloride gaseous compounds were 0.6 L / min. The deposition temperature was 1000°C, and the deposition time was 4 hours. (3) The deposited product is coated with carbon by solid-phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0044] [Example 9] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Nitrogen gas is introduced at a flow rate of 2 L / min into a bell-type furnace, which is a reaction vessel filled with a carbon matrix, as a protective gas for silane deposition. (2) Monosilane, disilane, tetrafluorosilane, acetylene (a compound containing C, N, B, and P), methane, nitrogen gas, ammonia, diborane, trimethyl borate, phosphine, and phosphorus oxychloride were introduced into a reaction vessel in gaseous form and vapor-phase deposited on a carbon matrix. The gas flow rates of monosilane, disilane, and tetrafluorosilane were 1.3 L / min, and the gas flow rates of acetylene, methane, nitrogen gas, ammonia, diborane, trimethyl borate, phosphine, and phosphorus oxychloride were all 0.5 L / min. The deposition temperature was 1100 °C, and the deposition time was 2.5 hours. (3) The deposited product is coated with carbon by vapor phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0045] [Example 10] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Argon gas is introduced at a flow rate of 2 L / min as a protective gas for silane deposition into a fluidized bed, which is a reaction vessel filled with a carbon matrix. (2) Monosilane, disilane, hexamethyldisilane, and compounds containing C, N, B, and P elements, such as methane, propylene, ammonia, urea, trimethyl borate, boric acid, phosphine, and phosphorus oxychloride, were introduced into a reaction vessel in gaseous form and vapor-phase deposited on a carbon matrix. The gas flow rates of monosilane, disilane, and tetrafluorosilane were 1.7 L / min, and those of methane, propylene, ammonia, urea, trimethyl borate, boric acid, phosphine, and phosphorus oxychloride were all 0.6 L / min. The deposition temperature was 1200°C, and the deposition time was 2 hours. (3) The deposited product is coated with carbon by liquid phase coating to obtain a multilayer composite material for lithium ion secondary batteries.

[0046] [Example 11] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Nitrogen gas is introduced as a protective gas for silane deposition into a rotary furnace, which is a reaction vessel filled with a carbon matrix, at a flow rate of 2 L / min. (2) Monosilane, disilane, dimethylsiloxane, and compounds containing C, N, B, and P elements, such as ethylene, propane, urea, melamine, tripropyl borate, boron tribromide, phosphine, and phosphorus oxychloride, were introduced into a reaction vessel in gaseous form and vapor-phase deposited onto a carbon matrix. The gas flow rates for monosilane, disilane, and dimethylsiloxane were all 2.7 L / min, and the gas flow rates for ethylene, propane, urea, melamine, tripropyl borate, boron tribromide, phosphine, and phosphorus oxychloride were all 1 L / min. The deposition temperature was 1400 °C, and the deposition time was 1.25 hours. (3) The deposited product is coated with carbon by solid-phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0047] [Example 12] This example provides a method for preparing a multilayer composite material for a lithium-ion secondary battery, which includes the following steps: (1) Argon gas is introduced at a flow rate of 2 L / min as a protective gas for silane deposition into a tubular furnace, which is a reaction vessel filled with a carbon matrix. (2) Monosilane, disilane, tetrafluorosilane, hexamethyldisilane, and compounds containing C, N, B, and P elements, such as acetylene, propane, ammonia, hydrazine, tripropyl borate, boron tribromide, phosphine, and phosphorus oxychloride, were introduced into a reaction vessel in gaseous form and vapor-phase deposited onto a carbon matrix. The gas flow rates for monosilane, disilane, tetrafluorosilane, and hexamethyldisilane were all 2.5 L / min, and the gas flow rates for acetylene, propane, ammonia, hydrazine, tripropyl borate, boron tribromide, phosphine, and phosphorus oxychloride were all 1 L / min. The deposition temperature was 1500 °C, and the deposition time was 1 hour. (3) The deposited product is coated with carbon by vapor phase coating to obtain a multilayer composite material for lithium-ion secondary batteries.

[0048] [Comparative Example 1] This comparative example provides a method for preparing a silicon-carbon composite material based on the prior art, which includes the following steps: (1) Silicon particles, polyvinylpyrrolidone as a precursor of the carbon source, graphite, and citric acid as an antioxidant are added to an ethanol system, and ground in a mass ratio of 1:1:1:0.1 to obtain a dispersion. (2) The dispersion is spray-dried to obtain silicon-carbon powder. (3) The powder is then vapor-coated to finally obtain a silicon-carbon composite material.

[0049] The composite materials obtained in each of the above examples and comparative examples were combined with commercially available graphite in proportion to form a 450 mAh / g composite, which was then assembled with lithium cobalt oxide into a button-type all-solid-state battery. The battery was cycled at a 1C rate to evaluate its cycle characteristics. The data are shown in Table 1.

[0050] [Table 1]

[0051] As can be seen from the results in Table 1, in the comparative example, the silicon-carbon composite material prepared by mechanical mixing has a high coulombic efficiency in the first cycle but poor cycle performance, while the multilayer composite material of the present invention has better cycle performance.

[0052] The present invention further improves the first-cycle coulombic efficiency and cycle performance of the material by adjusting the deposition time, temperature, and gas flow rate. If the gas flow rate and temperature are too high, the silane decomposes too quickly and deposits directly on the surface of the carbon matrix, resulting in uneven bonding between the deposited silicon and the elements C, N, B, and P, which affects battery performance. If the temperature is too low, the silane decomposes incompletely and fails to bond well with the elements C, N, B, and P, which affects cycle performance.

[0053] The multilayer composite material for lithium-ion secondary batteries according to embodiments of the present invention exhibits low volume expansion and excellent cycle and rate characteristics due to the interaction between the three-layer structure of the carbon matrix, nanosilicon-based composite, and carbon shell and the composite. In particular, nanosilicon-based composite materials prepared by vapor deposition of silane and one or more gaseous compounds containing C, N, B, or P have carbon atoms uniformly embedded at the atomic scale, and carbon atoms and silicon atoms bond to form amorphous Si-C bonds, which stabilize the material structure during lithium insertion and deintercalation, reducing volume expansion and providing better cycle characteristics when used in lithium battery anodes. Nitrogen atoms bond to silicon atoms to form amorphous Si-N bonds, which favors lithium ion insertion and deintercalation, improving the rate characteristics of lithium-ion batteries. Boron and / or phosphorus doping creates defects in the silicon crystals within the nanosilicon-based composite, reducing volume expansion during charging and improving battery cycle characteristics.

[0054] The above-mentioned specific embodiments further describe the objectives, technical solutions and beneficial effects of the present invention, and the above are only specific embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0055] (Addendum) (Appendix 1) A multilayer composite material for a lithium ion secondary battery, comprising: The multilayer composite material includes a carbon matrix, a nano silicon-based composite material, and a carbon shell; the carbon matrix is ​​a matrix material for depositing the nano silicon-based composite material; The nanosilicon-based composite material is prepared by vapor deposition of silane and one or more gaseous compounds containing any of C, N, B, and P elements, and the particle size of the nanosilicon-based composite material is 0.1 to 200 nm. Carbon atoms in the nanosilicon-based composite material are uniformly embedded on an atomic scale, carbon atoms and silicon atoms are bonded to form amorphous Si-C bonds, nitrogen atoms and silicon atoms are bonded to form amorphous Si-N bonds, and defects are generated in the silicon crystals in the nanosilicon-based composite material by boron doping and / or phosphorus doping. The carbon shell is coated with an outer layer of a carbon matrix on which a nano silicon based composite material is deposited. A multilayer composite material for a lithium ion secondary battery, characterized in that:

[0056] (Appendix 2) The carbon shell is prepared by vapor coating, liquid coating, or solid coating. 2. The multilayer composite material for a lithium ion secondary battery according to claim 1,

[0057] (Appendix 3) When the multilayer composite material contains C element, the NMR spectrum of the multilayer composite material shows that when the silicon peak is at -70 ppm to -130 ppm, the Si-C resonance peak is present between 20 ppm and -20 ppm, and the area ratio of the Si-C resonance peak to the silicon peak is 0.1 to 5.0; 2. The multilayer composite material for a lithium ion secondary battery according to claim 1,

[0058] (Appendix 4) In the multilayer composite material, the mass of the nano silicon-based composite material accounts for 20% to 80% of the total mass, and the mass of any of the C, N, B, and P elements composited with silicon accounts for 0.1% to 50% of the mass of the nano silicon-based composite material; The mass of the carbon matrix accounts for 20% to 70% of the total mass, The mass of the carbon shell accounts for 0 to 10% of the total mass. 2. The multilayer composite material for a lithium ion secondary battery according to claim 1,

[0059] (Appendix 5) A method for preparing the multilayer composite material for a lithium ion secondary battery according to any one of Supplementary Notes 1 to 4, comprising: introducing a protective gas, which is nitrogen gas, argon gas, hydrogen gas, or any mixture thereof, into a reaction vessel filled with a carbon matrix at a flow rate of 1 to 2 L / min; introducing silane and one or more gaseous compounds containing any of C, N, B, and P elements into a reaction vessel and performing vapor deposition on the carbon matrix; applying a carbon coating to the deposited product by at least one of vapor phase coating, liquid phase coating, and solid phase coating to obtain the multilayer composite material for lithium ion secondary batteries; Including, wherein the gas flow rate of silane is 0.5-10 L / min, the gas flow rate of the gaseous compound is 0.5-10 L / min, the deposition temperature is 500-1500°C, and the deposition time is 1-20 hours; A preparation method characterized by:

[0060] (Appendix 6) The reaction vessel may be a batch reactor or a continuous reactor, specifically a rotary furnace, a tubular furnace, a bell furnace, or a fluidized bed. 6. The method of claim 5,

[0061] (Appendix 7) The silane includes one or more of monosilane, disilane, tetrafluorosilane, chlorosilane, hexamethyldisilane, and dimethylsiloxane. 6. The method of claim 5,

[0062] (Appendix 8) The gaseous compound containing a C element includes one or more of acetylene, methane, propylene, ethylene, propane, and gaseous ethanol; The gaseous compound containing an N element includes one or more of nitrogen, ammonia, urea, melamine, and hydrazine, the gaseous compound containing B element includes one or more of diborane, trimethyl borate, tripropyl borate, and boron tribromide; The gaseous compound containing the P element includes phosphine and / or phosphorus oxychloride. 6. The method of claim 5,

[0063] (Appendix 9) The multilayer composite material for a lithium ion secondary battery according to any one of Supplementary Notes 1 to 5 is included. A negative electrode material characterized by:

[0064] (Appendix 10) The multilayer composite material for a lithium ion secondary battery according to any one of Supplementary Notes 1 to 5 is included. A lithium-ion battery characterized by:

Claims

1. A multilayer composite material for a lithium ion secondary battery, comprising: The multilayer composite material includes a carbon matrix, a nano silicon-based composite material, and a carbon shell; the carbon matrix is ​​a matrix material for depositing the nano silicon-based composite material; The nanosilicon-based composite material is prepared by vapor deposition of silane and gaseous compounds containing C, N, B, and P elements, and the particle size of the nanosilicon-based composite material is 0.1 to 200 nm. The carbon atoms in the nanosilicon-based composite material are uniformly embedded on an atomic scale, the carbon atoms and silicon atoms are bonded to form amorphous Si-C bonds, and the nitrogen atoms and silicon atoms are bonded to form amorphous Si-N bonds. The boron doping and phosphorus doping cause defects in the silicon crystals in the nanosilicon-based composite material. The carbon shell is coated with an outer layer of a carbon matrix on which a nano silicon based composite material is deposited. A multilayer composite material for a lithium ion secondary battery, characterized in that:

2. The carbon shell is prepared by vapor coating, liquid coating, or solid coating. The multilayer composite material for a lithium ion secondary battery according to claim 1 .

3. When the multilayer composite material contains a C element, the NMR spectrum of the solid-state nuclear magnetic resonance of the multilayer composite material shows that when the silicon peak is located between -70 ppm and -130 ppm, a Si-C resonance peak is present between 20 ppm and -20 ppm, and the area ratio of the Si-C resonance peak to the silicon peak is 0.1 to 5.0; The multilayer composite material for a lithium ion secondary battery according to claim 1 .

4. In the multilayer composite material, the mass of the nano silicon-based composite material accounts for 20% to 80% of the total mass, and the mass of the C, N, B, and P elements combined with silicon accounts for 0.1% to 50% of the mass of the nano silicon-based composite material; The mass of the carbon matrix accounts for 20% to 70% of the total mass; The mass of the carbon shell accounts for 0 to 10% of the total mass. The multilayer composite material for a lithium ion secondary battery according to claim 1 .

5. A method for preparing the multilayer composite material for a lithium ion secondary battery according to any one of claims 1 to 4, comprising: introducing a protective gas, which is nitrogen gas, argon gas, hydrogen gas, or any mixture thereof, into a reaction vessel filled with a carbon matrix at a flow rate of 1 to 2 L / min; introducing silane and a gaseous compound containing each of the elements C, N, B, and P into a reaction vessel and vapor-depositing the compound on the carbon matrix; applying a carbon coating to the deposited product by at least one of vapor phase coating, liquid phase coating, and solid phase coating to obtain the multilayer composite material for a lithium ion secondary battery; Including, wherein the gas flow rate of silane is 0.5-10 L / min, the gas flow rate of the gaseous compound is 0.5-10 L / min, the deposition temperature is 500-1500°C, and the deposition time is 1-20 hours; A preparation method characterized by:

6. The reaction vessel may be a batch reactor or a continuous reactor, specifically a rotary furnace, a tubular furnace, a bell furnace, or a fluidized bed.

6. The method of claim 5.

7. The silane includes one or more of monosilane, disilane, tetrafluorosilane, chlorosilane, hexamethyldisilane, and dimethylsiloxane; 6. The method of claim 5.

8. The gaseous compound containing a C element includes one or more of acetylene, methane, propylene, ethylene, propane, and gaseous ethanol; the gaseous compound containing an N element includes one or more of nitrogen, ammonia, urea, melamine, and hydrazine; the gaseous compound containing B element includes one or more of diborane, trimethyl borate, tripropyl borate, and boron tribromide; The gaseous compound containing the P element includes phosphine and / or phosphorus oxychloride.

6. The method of claim 5.

9. The multilayer composite material for a lithium ion secondary battery according to any one of claims 1 to 4, A negative electrode material characterized by:

10. The multilayer composite material for a lithium ion secondary battery according to any one of claims 1 to 4, A lithium-ion battery characterized by:

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