Silicon-carbon composite negative electrode material prepared by using ALD and CVD technologies, preparation method and lithium battery

Abstract

The invention discloses a silicon-carbon composite negative electrode material prepared by using ALD and CVD technologies, a preparation method and a lithium battery. The preparation method comprises the following steps: growing a first metal oxide on the surface of a carbon substrate material by using an ALD atomic layer deposition method; reducing the first metal oxide on the surface of the carbon substrate material into nanodots containing metal elements in the reaction cavity; heating the carbon substrate material distributed with the nano-dots in a reaction furnace, injecting a gas mixture which comprises silane and inert gas, and growing silicon nanowires on the nano-dots based on a silane CVD (Chemical Vapor Deposition) cracking process; and heating the carbon substrate material on which the silicon nanowire grows in a reaction furnace, injecting hydrocarbon gas, and coating the surface of the silicon nanowire with a carbon layer based on a CVD cracking process to obtain the silicon-carbon composite negative electrode material, so that the method for preparing the silicon-carbon composite negative electrode material can effectively prevent the volume expansion of the silicon nanowire in the charging and discharging process, and the service life of the silicon-carbon composite negative electrode material is prolonged. And the cycle performance of the silicon-carbon composite negative electrode material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of methods for preparing negative electrode materials for lithium-ion batteries, and in particular to a silicon-carbon composite negative electrode material prepared by using ALD and CVD techniques, a preparation method, and a lithium battery. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles and other fields due to their high energy density, long cycle life and environmental friendliness. Among them, the negative electrode material is a key component of lithium-ion batteries, and its performance directly affects the energy density, power density and cycle life of the battery. Currently, the more mature negative electrode material in commercial lithium-ion batteries is graphite, but since the theoretical specific capacity of graphite is only 372mAh / g, it limits the further improvement of the specific energy of lithium-ion batteries.

[0003] In order to solve this problem, researchers began to explore new negative electrode materials, such as silicon. Silicon has the advantages of high capacity (up to 4200mAh / g), low lithium desorption potential and abundant resources, and has received widespread attention. Among them, the US Group14 company announced in US Patent US11495798B1 a method of using silane CVD cracking to deposit nano-silicon particles inside porous carbon channels, which achieved good results. However, there are still some problems with the existing silicon-based negative electrode material preparation technology: First, porous carbon is expensive and the pore-making process is very complicated. Secondly, the pores of porous carbon are generally at the nanometer level, and the pore size distribution is uneven, which makes it difficult for the deposited silicon nanoparticles to enter the pores, or easily clog the pores. These problems limit the performance of silicon-carbon negative electrode materials. For example, Figure 23 of US Patent No. 11495798B1 shows that the volume capacity of carbon-coated silicon-carbon composite materials as negative electrodes remains about 78% after 500 cycles at a rate of C / 2, while Figures 18 and 19 show that the gram capacity of carbon-coated silicon-carbon composite materials as negative electrode materials is reduced by 10% to 50% compared with 5 cycles at 0.5C rate after 5 cycles at 1C and 2C rates. This is mainly because the rate at which lithium ions enter carbon pores is limited, resulting in poor rate performance of existing silicon-carbon negative electrodes and the inability to support fast charging.

[0004] In addition, although silicon nanowires have better cycle performance than silicon nanoparticles, the existing silicon nanowire preparation method disclosed in U.S. Patent US20130220821A1, for example, generates 2nm thick gold in porous alumina and uses gold catalysis to prepare silicon nanowires with a diameter of 40 to 100nm. The pore size of porous carbon and alumina is required to be 40 to 100nm, which is mesoporous. If the pore size of porous carbon and alumina is a microporous structure, the existing silicon nanowire preparation process cannot construct a catalyst in the micropores. The diameter of silane molecules is usually between a few angstroms and tens of angstroms, and it is difficult to enter the micropores to react with the catalyst to form silicon nanowires. Therefore, the existing technology cannot prepare silicon nanowires with a diameter not greater than 5nm. Summary of the invention

[0005] The present invention aims to solve the above-mentioned technical problems. In order to achieve the above-mentioned purpose, the present invention mainly adopts the following technical means:

[0006] A method for preparing a silicon-carbon composite negative electrode material using ALD and CVD technology comprises the following steps:

[0007] Step 1. growing a first metal oxide on the surface of a carbon base material using an ALD atomic layer deposition method;

[0008] Step 2. reducing the first metal oxide on the surface of the carbon base material into nanodots containing metal elements in a reaction chamber;

[0009] Step 3. placing the carbon substrate material with the nanodots distributed thereon in a reaction furnace, heating it and injecting a gas mixture, wherein the gas mixture comprises silane and an inert gas, and growing silicon nanowires on the nanodots based on a chemical vapor deposition process;

[0010] Step 4. Coat a carbon layer on the surface of the silicon nanowires of the carbon base material to obtain a silicon-carbon composite negative electrode material.

[0011] Growing a first metal oxide on the surface of a carbon base material using an ALD atomic layer deposition method includes:

[0012] Step S1: placing the carbon substrate material in a porous container, placing the porous container in an ALD reaction chamber, or placing the carbon substrate material in an ALD reaction chamber, and then repeatedly evacuating and replacing nitrogen at least three times;

[0013] Step S2: Fluidizing the substrate material in the reaction chamber under a nitrogen or argon atmosphere at a fluidizing pressure of 1-1000 torr, or rotating the porous container to achieve a dispersion effect of the substrate material; the fluidizing pressure is preferably 10-100 torr;

[0014] Step S3: According to the type of the first metal oxide to be deposited, a reaction precursor is selected, and the parameters of the ALD reaction chamber are set: the deposition temperature is 100°C-400°C, and the deposition pressure is 0.01torr-500torr; the precursor A is a mixture of one or more of volatile metal alkylamino salts, metal organic compounds, halides, alkoxides, and metal β-diketone complexes, wherein the metal element in the metal alkylamino salts, metal organic compounds, halides, alkoxides, and metal β-diketone complexes is one of copper, tin, indium, gold, titanium, nickel, iron, silver, platinum, tin and gallium, cobalt, aluminum, and silicon;

[0015] Step S4: introducing the precursor A vapor into the ALD reaction chamber under the carrier gas of nitrogen or argon, and maintaining the vapor for 10-300 seconds, wherein the flow rate of the carrier gas: nitrogen or argon is 5-8000 sccm;

[0016] Step S5: purge the reaction chamber with nitrogen or argon to take away the remaining precursor A, and the flow rate of the carrying gas: nitrogen or argon is 5-8000 sccm;

[0017] Step S6: Introducing oxygen source vapor into the ALD reaction chamber under the action of a carrier gas for a holding time of 10-300 seconds; the oxygen source is water, hydrogen peroxide, oxygen, ozone, or atomic oxygen, and the carrier gas: nitrogen or argon has a flow rate of 5-8000 sccm;

[0018] Step S7: purging the reaction chamber with nitrogen or argon to remove excess oxygen source vapor and by-products;

[0019] Step S8: Repeat steps S4 to S7 until the metal oxide deposition corresponding to the precursor A reaches a set coating thickness of 0.33-1 nm.

[0020] The step 2 is carried out in the reaction chamber of the hydrogen reduction equipment.

[0021] Furthermore, the nanodots containing metal elements are selected from one or more of copper and / or copper oxide, tin, indium, gold, titanium, nickel, iron, silver, platinum, tin and gallium, cobalt, aluminum, and silicon dioxide.

[0022] Furthermore, the thickness of the first metal oxide is 0.33-1 nm.

[0023] Furthermore, the diameter of the silicon nanowire is no more than 5 nm.

[0024] Furthermore, the coating process is selected from one of chemical vapor deposition, plasma enhanced chemical vapor deposition, electron beam evaporation, vacuum deposition, and atomic layer deposition.

[0025] The step 4 includes introducing hydrocarbon gas, which includes but is not limited to methane, propane, butane, cyclohexane, ethane, propylene and acetylene.

[0026] Furthermore, the coating process is preferably chemical vapor deposition.

[0027] The silicon-carbon composite negative electrode material prepared by the method described herein comprises a carbon base material, the silicon nanowires grown on the surface of the carbon base material, a carbon layer coated on the surface of the silicon nanowires, and nanodots containing metal elements distributed in the silicon nanowires, wherein the nanodots containing metal elements are selected from one or more of copper and / or copper oxide, tin, and indium.

[0028] The carbon-based materials include graphite, hard carbon, soft carbon, carbon fiber, carbon nanofiber, carbon nanotube, mesophase carbon microbeads, carbon black, and Ketjen black.

[0029] A lithium ion battery contains the silicon-carbon composite negative electrode material.

[0030] Furthermore, between step 3 and step 4, the method also includes repeating steps 1 to 2, selecting a reaction precursor according to the type of the deposited second metal oxide, depositing the second metal oxide on the silicon nanowires of the carbon-based material, and then reducing it to second metal particles, so that the silicon nanowires of the carbon-based material and the second metal particles on the silicon nanowires are processed by step 4, a carbon layer is coated on the surface of the silicon nanowires on the carbon-based material, and carbon nanotubes are grown between the second metal particles of the silicon nanowires on the carbon-based material.

[0031] Furthermore, the second metal oxide includes one or more of nickel oxide, iron oxide, cobalt oxide, copper oxide, chromium oxide, manganese oxide, molybdenum oxide, tungsten oxide, platinum oxide, and palladium oxide.

[0032] Furthermore, the metal in the second metal particles is selected from one or more of nickel, iron, cobalt, copper, chromium, manganese, molybdenum, tungsten, platinum and palladium.

[0033] Furthermore, the thickness of the second metal oxide is 0.1-5 nm.

[0034] The silicon-carbon composite negative electrode material prepared by the method described herein comprises a carbon base material, the silicon nanowires grown on the surface of the carbon base material, a carbon layer coated on the surface of the silicon nanowires, carbon nanotubes formed between the silicon nanowires, nanodots containing metal elements distributed in the silicon nanowires, and second metal particles distributed in the carbon nanotubes.

[0035] The carbon-based materials include graphite, hard carbon, soft carbon, carbon fiber, carbon nanofiber, carbon nanotube, mesophase carbon microbeads, carbon black, and Ketjen black.

[0036] A lithium ion battery contains the silicon-carbon composite negative electrode material.

[0037] The coating process uses a carbon source, a reaction precursor of a second metal oxide, and a promoter as raw materials. The raw materials are introduced into a reactor through a carrier gas, and a floating catalyst chemical vapor deposition method is used to coat the surface of the silicon nanowires on the carbon base material to form a carbon layer, and carbon nanotubes are grown between the silicon nanowires on the carbon base material; the promoter is selected from one or both of thiophene and sulfur, the reaction precursor of the second metal oxide is selected from the alkene of the second metal in the second metal oxide, the carbon source includes a gaseous carbon source or a liquid carbon source, and the liquid carbon source is C 1-4 Alcohol and C 6-8 A mixture of hydrocarbons, wherein the gaseous carbon source comprises C 1-3 The carrier gas comprises hydrogen or an inert gas.

[0038] The C 1-4 The alcohol is selected from one or more of n-butanol, methanol and ethanol; the C 6-8 The hydrocarbon is selected from one or more of n-hexane, benzene, toluene and xylene; 1-3 Hydrocarbons include alkanes, alkenes, and alkynes.

[0039] The carbon-based materials include graphite, hard carbon, soft carbon, carbon fiber, carbon nanofiber, carbon nanotube, mesophase carbon microbeads, carbon black, and Ketjen black.

[0040] The metal in the second metal particles is selected from one or more of nickel, iron, cobalt, copper, chromium, manganese, molybdenum, tungsten, platinum and palladium.

[0041] The silicon-carbon composite negative electrode material prepared by the method described herein comprises a carbon base material, the silicon nanowires grown on the surface of the carbon base material, a carbon layer coated on the surface of the silicon nanowires, carbon nanotubes formed between the silicon nanowires, nanodots containing metal elements distributed in the silicon nanowires, and second metal particles distributed in the carbon nanotubes.

[0042] A lithium ion battery contains the silicon-carbon composite negative electrode material.

[0043] The above method for preparing silicon-carbon composite negative electrode materials can effectively prevent the volume expansion of silicon nanowires during the charge and discharge process, and improve the cycle performance of silicon-carbon composite negative electrode materials. Through the above technical means, the technical solution of the present invention successfully prepares silicon-carbon composite negative electrode materials, solving the problems in the prior art that porous carbon is expensive, the pore-making process is complicated, silicon nanoparticles are difficult to enter the pores, and the diameter of silicon nanowires is limited by the size of metal catalyst particles.

[0044] Compared with the existing technology, the technical solution of the present invention has the following beneficial effects:

[0045] 1. Reduce costs: The present invention uses low-cost graphite or hard carbon as a substrate, grows metal oxides on its surface and in cracks through ALD technology, and then reduces the metal oxides into nano-metal particles as catalysts through H2 reduction process, which greatly reduces the cost of raw materials.

[0046] 2. Optimized structure: The present invention uses a silane CVD cracking process to grow silicon nanowires on a catalyst, and then uses an acetylene CVD cracking process to coat amorphous carbon on the surface of the silicon nanowires or grow carbon nanotubes on the surface of the silicon nanowires, forming a new type of silicon-carbon composite negative electrode material. This structural design enables the silicon nanowires to be better dispersed in the carbon matrix, avoiding the problem of silicon nanoparticles blocking the holes, thereby improving the performance of the material.

[0047] 3. Improve performance: The silicon-carbon composite negative electrode material of the present invention has a reversible specific capacity of more than 2500 mAh / g, a capacity retention rate of more than 90% after 100 cycles, and a capacity retention rate of more than 80% after 500 cycles. Compared with the prior art, it has a higher specific capacity and better cycle performance.

[0048] 4. Achieve the growth of small-sized silicon nanowires: The present invention uses ALD technology and CVD technology to achieve precise control of the growth of silicon nanowires. The thickness of the metal oxide film is controlled by ALD technology to control the diameter of the silicon nanowire, thereby achieving the growth of silicon nanowires with a diameter less than 5 nanometers, which is difficult to achieve with the existing technology. The length of the silicon nanowire is controlled by controlling the concentration and flow rate of silane by CVD.

[0049] 5. The nano-silicon in commercial silicon carbon is grown in the nano-pores of porous carbon, and then the surface is coated with a carbon layer. The rate at which lithium ions enter the pores is limited, resulting in poor rate performance of existing silicon carbon negative electrodes and the inability to support fast charging. The silicon nanowires of the present invention can directly contact the electrolyte after being coated with carbon, and are not restricted by the transmission of nano-pores, so they have better rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a flow chart of preparing silicon-carbon composite negative electrode materials using ALD and CVD techniques in Examples 1, 2 and 4 of the present invention.

[0051] Figure 2 This is a flow chart of preparing silicon-carbon composite negative electrode material using ALD and CVD technology in Example 3 of the present invention.

[0052] Figure 3 is the SEM image of graphite surface;

[0053] Figure 4 This is a SEM image of nano-copper particles formed by hydrogen reduction after copper oxide film is deposited on the graphite surface;

[0054] Figure 5 This is a SEM image of silicon nanowires formed on the graphite surface;

[0055] Figure 6 This is a TEM electron microscope image of 5nm silicon nanowires;

[0056] Figure 7 The gram specific capacity of the silicon-carbon composite negative electrode material of Example 1 of the present invention at a current density of 0.1C;

[0057] Figure 8 This is the cycle life of the silicon-carbon composite negative electrode material of Example 1 of the present invention at a current density of 0.2C. DETAILED DESCRIPTION

[0058] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content in the present application. Various local modifications to the disclosed embodiments are obvious to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments shown, but to the widest scope consistent with the claims.

[0059] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0060] A method for preparing silicon-carbon composite negative electrode material using ALD and CVD technology:

[0061] Step 1: Select graphite, hard carbon, soft carbon, carbon fiber, carbon nanofiber, carbon nanotube, mesophase carbon microsphere, carbon black, Ketjen black as the base material, put it into the atomic layer deposition (ALD) equipment, set the reaction temperature to 100℃-400℃, and the reaction pressure to 0.01torr-500torr. Under this condition, the ALD technology is used to grow the first metal oxide, such as copper oxide, tin oxide, indium oxide, on the surface and cracks of the graphite, and the thickness of the first metal oxide is 0.33-1nm.

[0062] As an example of the present invention, a method for growing a first metal oxide on a surface and in cracks of graphite using an ALD technique includes:

[0063] Step S1: placing the substrate material in a porous container, placing the porous container in an ALD reaction chamber, or placing the substrate material in an ALD reaction chamber, and then repeatedly evacuating and replacing nitrogen at least three times;

[0064] Step S2: Fluidizing the substrate material in the reaction chamber under a nitrogen or argon atmosphere at a fluidizing pressure of 1-1000 torr, or rotating the porous container to achieve a dispersion effect of the substrate material; the fluidizing pressure is preferably 10-100 torr;

[0065] Step S3: According to the type of the first metal oxide to be deposited, a reaction precursor is selected, and the parameters of the ALD reaction chamber are set: the deposition temperature is 100°C-400°C, and the deposition pressure is 0.01torr-500torr; the precursor A is a mixture of one or more of volatile metal alkylamino salts, metal organic compounds, halides, alkoxides, and metal β-diketone complexes, wherein the metal elements in the metal alkylamino salts, metal organic compounds, halides, alkoxides, and metal β-diketone complexes are copper, tin, indium, gold, titanium, nickel, iron, silver, platinum, tin and gallium, cobalt, aluminum, and silicon;

[0066] Step S4: introducing the precursor A vapor into the ALD reaction chamber under the carrier gas of nitrogen or argon, and maintaining the vapor for 10-300 seconds, wherein the flow rate of the carrier gas: nitrogen or argon is 5-8000 sccm;

[0067] Step S5: purge the reaction chamber with nitrogen or argon to take away the remaining precursor A, and the flow rate of the carrying gas: nitrogen or argon is 5-8000 sccm;

[0068] Step S6: Introducing oxygen source vapor into the ALD reaction chamber under the action of a carrier gas for a holding time of 10-300 seconds; the oxygen source is water, hydrogen peroxide, oxygen, ozone, or atomic oxygen, and the carrier gas: nitrogen or argon has a flow rate of 5-8000 sccm;

[0069] Step S7: purging the reaction chamber with nitrogen or argon to remove excess oxygen source vapor and by-products;

[0070] Step S8: Repeat steps S4 to S7 until the metal oxide deposition corresponding to precursor A reaches a set coating thickness of 0.33-1 nm; precursor A is selected from one or more of the precursors in Table 1.

[0071] Table 1

[0072]

[0073] SnCl4 in Precursor A in Table 1 can also be replaced by other examples of suitable tin-containing precursors, including halogenated tin-containing precursors (e.g., SnBr4) and non-halogenated tin-containing precursors (e.g., organic tin compounds including alkyl-substituted tin amides). Specific examples of alkyl-substituted tin amides suitable for ALD include: tetrakis(dimethylamino)tin, tetrakis(ethylmethylamino)tin, N 2 ,N 3-Di-tert-butyl-butane-2,3-diaminotin(II) (N 2 ,N 3 -di-tert-butyl-butane-2,3-diamino-tin(II)) and (1,3-bis(1,1-dimethylethyl)-4,5-dimethyl-(4R,5R)-1,3,2-diazastannolidin-2-ylidine).

[0074] The Chinese name of In(acac)3 in Table 1 is indium acetylacetonate, which can also be replaced by other liquid compounds of indium: [(CH3CH2)2InN[Si(CH3)3]2, i.e. bis(trimethylsilyl)aminodiethylindium, Et2InN(TMS)2; here, TMS refers to Si(CH3)3, [(CH3)2In(CH2)3N(CH3)2; Me2In(CH2)3NMe2], i.e. dimethyl(3-dimethylaminopropyl)indium.

[0075] Step 2: Place the substrate material with the metal oxide grown on it into the reaction chamber of the hydrogen reduction device. The metal oxide is reduced to a catalyst by a hydrogen reduction process at high temperature. The volume of the catalyst relative to the metal oxide film is reduced to form mutually separated nanodots with a diameter of 0.5 to 1 nm, i.e., catalyst particles, such as copper and cuprous oxide nanoparticles, tin nanoparticles, indium nanoparticles, or the above-mentioned composites. These nanometal particles will be used as catalysts for the subsequent growth of silicon nanowires.

[0076] Step 3: Place the substrate material with the nano-catalyst particles grown in the reaction chamber of the silane chemical vapor deposition (CVD) equipment, use the silane chemical vapor deposition process to crack the silane, and grow silicon nanowires on the nano-metal particles. In this process, the length of the silicon nanowires can be controlled by adjusting the flow rate and reaction time of the silane. The temperature and time of the treatment can vary, for example, the temperature can be between 300 and 400°C, for example, between 400 and 500°C, for example, between 500 and 600°C, for example, between 600 and 700°C, for example, 700-800°C, for example, 800-900°C. The gas mixture can contain 0.1-1% silane and the remaining inert gas. Alternatively, the gas mixture can contain 1% to 10% silane and the remaining inert gas. Alternatively, the gas mixture can contain 10% to 20% silane and the remaining inert gas. Alternatively, the gas mixture can contain 20% to 50% silane and the remaining inert gas. Alternatively, the gas mixture may contain more than 50% silane and the remainder inert gas. Alternatively, the gas may be substantially 100% silane gas. The reactor in which the CVD process is carried out is according to various designs known in the art, for example in a fluidized bed reactor, a static bed reactor, an elevator kiln, a rotary kiln, a box kiln or other suitable reactor type. As known in the art, the reactor material is suitable for the task.

[0077] Step 4: Place the substrate material with silicon nanowires grown in the reaction chamber of a chemical vapor deposition (CVD) device, introduce hydrocarbon gas, and deposit a carbon layer at high temperature. The deposition time can vary, for example, between 0 and 5 minutes, for example, between 5 and 15 minutes, for example, between 15 and 30 minutes, for example, between 30 and 60 minutes, for example, between 60 and 120 minutes, for example, between 120 and 240 minutes. In some embodiments, the deposition time is greater than 240 minutes. The deposition temperature can vary, for example, between 350 and 1050°C, for example, between 350 and 450°C, for example, between 450 and 550°C, for example, between 550 and 650°C. The chemical vapor deposition (CVD) process is used to crack hydrocarbon gas and coat amorphous carbon on the surface of the silicon nanowire. In this process, the thickness of the carbon coating layer can be controlled by adjusting the flow rate and reaction time of the hydrocarbon gas. Hydrocarbon gases include, but are not limited to, methane, propane, butane, cyclohexane, ethane, propylene, and acetylene.

[0078] The method for forming the carbon coating layer in step 4 is not limited to the chemical vapor deposition (CVD) process, but also includes one of plasma enhanced chemical vapor deposition, electron beam evaporation, vacuum deposition, and atomic layer deposition.

[0079] Through the above steps, the present invention successfully prepares a silicon-carbon composite negative electrode material. This material has high capacity, low lithium desorption potential, and good cycle performance. In addition, the present invention uses graphite or hard carbon as the base material. The pore structure and cracks of graphite or hard carbon only play the role of increasing the surface area, and do not serve as a template for the growth of silicon nanowires. The present invention does not use alumina or carbon materials with regular mesoporous structures as templates for the growth of silicon nanowires, thus avoiding the problem of using expensive porous carbon and alumina.

[0080] The existing method for preparing silicon nanowires requires that the pore size of porous carbon and alumina be: mesopore. If the pore size of porous carbon and alumina is a microporous structure, the existing silicon nanowire preparation process cannot construct a catalyst in the micropore. The diameter of silane molecules is usually between a few angstroms and tens of angstroms, and it is difficult for them to enter the micropores and react with the catalyst to form silicon nanowires. Therefore, the existing technology cannot prepare silicon nanowires with a diameter not greater than 5nm; and when silicon nanowires have a high axial diameter ratio, the axial volume expansion of silicon during the cycle can be reduced. The smaller radial size of silicon nanowires can effectively avoid the pulverization of silicon and shorten the diffusion distance of lithium ions, and can fully release the capacity under high rate conditions. Therefore, the pore size of porous carbon and alumina should not be larger than the mesopore size, which leads to the use of complex pore-making processes in the existing technology to prepare porous carbon and alumina.

[0081] In addition, the diameter of silicon nanowires is limited by the size of metal catalyst particles. The present invention uses atomic layer deposition technology to accurately control the thickness of the copper oxide film on the substrate material, and then reduces the volume of the copper oxide film by reducing the copper oxide film, thereby effectively controlling the size of the metal catalyst particles on the substrate material to 0.5-1nm and spaced apart from each other. Therefore, when using CVD technology to prepare silicon nanowires, the silane gas can contact the metal catalyst particles, avoiding the problem of not being able to enter the micropores of the template.

[0082] As an optimized implementation, between step three and step four, it also includes repeating step one and step two, depositing second metal particles on the silicon nanowires of the base material, the second metal is one of nickel, iron, cobalt, copper, chromium, manganese, molybdenum, tungsten, platinum, and palladium, including the following steps:

[0083] Step I: Place the substrate material with silicon nanowires grown in an atomic layer deposition (ALD) device, set the reaction temperature to 100°C-400°C, and the reaction pressure to 0.01torr-500torr. Under this condition, use ALD technology to grow a second metal oxide on the silicon nanowires, such as nickel oxide, iron oxide, cobalt oxide, copper oxide, chromium oxide, manganese oxide, molybdenum oxide, tungsten oxide, platinum oxide, palladium oxide, and the thickness of the metal oxide is 0.1-5nm. Including:

[0084] Step SI1: placing the substrate material in a porous container, placing the porous container in the ALD reaction chamber, or placing the substrate material in the ALD reaction chamber, and then repeatedly evacuating and replacing nitrogen at least three times;

[0085] Step SI2: Fluidizing the substrate material in the reaction chamber under a nitrogen or argon atmosphere at a fluidizing pressure of 1-1000 torr, or rotating the porous container to achieve a dispersion effect of the substrate material; the fluidizing pressure is preferably 10-100 torr;

[0086] Step SI3: According to the type of the second metal oxide to be deposited, a reaction precursor is selected, and the parameters of the ALD reaction chamber are set: the deposition temperature is 100°C-400°C, and the deposition pressure is 0.01torr-500torr; the precursor B is a mixture of one or more of volatile metal alkylamino salts, metal organic compounds, halides, alkoxides, and metal β-diketone complexes, wherein the metal elements in the metal alkylamino salts, metal organic compounds, halides, alkoxides, and metal β-diketone complexes are nickel, iron, cobalt, copper, chromium, manganese, molybdenum, tungsten, platinum, and palladium;

[0087] Step SI4: introducing the precursor B vapor into the ALD reaction chamber under the carrier gas of nitrogen or argon, holding time 10-300 seconds, the carrier gas: nitrogen or argon flow rate is 5-8000 sccm;

[0088] Step SI5: purge the reaction chamber with nitrogen or argon to take away the remaining precursor B, with the flow rate of nitrogen or argon being 5-8000 sccm;

[0089] Step SI6: Introduce oxygen source vapor into the ALD reaction chamber under the action of a carrier gas for 10-300 seconds; the oxygen source is water, hydrogen peroxide, oxygen, ozone, or atomic oxygen, and the carrier gas: nitrogen or argon has a flow rate of 5-8000 sccm;

[0090] Step SI7: Purge the reaction chamber with nitrogen or argon to remove excess oxygen source vapor and by-products;

[0091] Step SI8: Repeat steps SI4 to SI7 until the second metal oxide deposition corresponding to precursor B reaches a set coating thickness of 0.1-5 nm; precursor B is selected from one or more of Table 2, but is not limited to Table 2.

[0092] Step II: Place the product of step I into a reaction chamber of a hydrogen reduction device and use a hydrogen reduction process at high temperature to reduce the metal oxide into second metal particles.

[0093] By treating the product generated in step II in step IV, a carbon layer can be formed on the surface of the silicon nanowire on the substrate material, and carbon nanotubes can be grown between the second metal particles of the silicon nanowire on the substrate material. The conductivity of the carbon nanotubes is due to the formation of amorphous carbon by the cracking of hydrocarbon gas, and the carbon nanotubes are a network structure, which may connect multiple silicon nanowires. Table 2

[0094] Serial number name Precursor A Oxygen source Reaction temperature 1 <![CDATA[Co3O4]]> <![CDATA[CoCp2]]> <![CDATA[O3]]> 250℃ 2 NiO <![CDATA[Ni(acac)2]]> <![CDATA[O3]]> 250℃ 3 <![CDATA[Fe2O3]]> <![CDATA[Fe(Cp)2]]> <![CDATA[O3]]> 230℃

[0095] As an optimized implementation, the process of step 4 uses a carbon source, a reaction precursor of a second metal oxide, and a promoter as raw materials, the raw materials are introduced into a reactor through a carrier gas, a floating catalyst chemical vapor deposition method is used to coat the surface of the silicon nanowires on the carbon base material to form a carbon layer, and carbon nanotubes are grown between the silicon nanowires on the carbon base material; the promoter is selected from one or both of thiophene and sulfur, the reaction precursor of the second metal oxide is selected from the alkene of the second metal in the second metal oxide, the carbon source includes a gaseous carbon source or a liquid carbon source, and the liquid carbon source is C 1-4 of alcohol and C 6-8 A mixture of hydrocarbons, wherein the gaseous carbon source comprises C 1-3 The carrier gas comprises hydrogen or an inert gas.

[0096] The C 1-4 The alcohol is selected from one or more of n-butanol, methanol and ethanol; the C 6-8 The hydrocarbon is selected from one or more of n-hexane, benzene, toluene and xylene; 1-3 The hydrocarbons include alkanes, alkenes and alkynes, for example, one or two selected from methane, ethylene, acetylene and propylene.

[0097] Example 1

[0098] by Figure 3 The graphite shown is used as a substrate material, and a method for preparing a silicon-carbon composite negative electrode material using ALD and CVD technology is as follows:

[0099] Step 1: Select graphite as the substrate material, put it into an atomic layer deposition (ALD) reactor, and evacuate the reactor through an exhaust pump, use argon to fluidize the substrate material, keep the temperature of the substrate material at 120°C, raise the temperature of the container containing Cu(dmamb)2 to 70°C, adjust the pressure in the reactor to 5Torr, introduce Cu(dmamb)2 vapor into the ALD reactor under argon, keep it for 10-300 seconds, and the flow rate of argon is 100sccm. Purge the reactor with argon, purge it for 10 seconds, introduce O3 into the ALD reactor under argon, keep it for 10-300 seconds, and the flow rate of argon is 100sccm. Purge the reactor with argon, purge it for 10 seconds, and form a copper oxide film with a thickness of 1nm after 30 ALD cycles by atomic layer deposition.

[0100] Step 2: Place the substrate material with the copper oxide film in a hydrogen reduction reaction chamber, heat it to a reaction temperature of 500°C in a hydrogen atmosphere, and react for 10 minutes. Use the hydrogen reduction process to reduce the copper oxide into copper and cuprous oxide nanoparticles, such as Figure 4 The diameters of the copper and cuprous oxide nanoparticles are in the nanometer range, with gaps between the copper and cuprous oxide nanoparticles. These copper and cuprous oxide nanoparticles act as catalysts for the subsequent growth of silicon nanowires.

[0101] Step 3: Place the substrate material with copper and cuprous oxide nanoparticles in a silane chemical vapor deposition (CVD) reaction chamber, evacuate the reaction chamber through an exhaust pump, and introduce silane gas under the protection of an inert atmosphere of Ar for 4 hours at 600°C. The reaction pressure is 1 Torr. Silicon nanowires are grown on nanometal particles using a silane CVD cracking process. Figure 5 and Figure 6 The silicon nanowires shown have a diameter of 5 nm.

[0102] In this process, copper and cuprous oxide nanoparticles react with silane as follows to obtain a Cu3Si alloy catalyst for the growth of silicon nanowires: SiH4+Cu→Cu3Si+H2

[0103] SiH4+Cu2O→Cu3Si+H2+H2O.

[0104] Copper and cuprous oxide nanoparticles catalyze the growth of silicon nanowires by VSS mechanism. Dispersed copper and cuprous oxide nanoparticles catalyze the growth to obtain dispersed silicon nanowires with a diameter of 5 nm.

[0105] Step 4: Place the substrate material with silicon nanowires grown in a CVD reaction chamber, bring acetylene into the reaction chamber through nitrogen, adjust the reaction temperature in the reaction chamber to 700°C, and the reaction time to 6 hours. Use the acetylene CVD cracking process to coat amorphous carbon on the surface of the silicon nanowires. In this process, the temperature at which acetylene forms a carbon coating on the surface of the silicon nanowires is lower than the temperature at which methane forms a carbon coating on the surface of the silicon nanowires, which can prevent carbon from reacting with silicon to form a silicon carbide coating. In this step, the thickness of the amorphous carbon coating is 50nm or less.

[0106] The prepared silicon-carbon negative electrode material and metallic lithium were combined into a half-cell for electrochemical performance testing. The charge and discharge test was carried out at a current density of C / 10 (first time) + C / 2 (cycle), and the 5C / 0.5C rate discharge performance was tested. The charge and discharge voltage range was 0.005 to 2.0 V. The test results are detailed in Table 3.

[0107] Example 2

[0108] Method for preparing silicon-carbon composite negative electrode material using ALD and CVD technology using hard carbon as the base material:

[0109] Step 1: Select hard carbon as the substrate material, put it into an atomic layer deposition (ALD) reactor, and evacuate the reactor through an exhaust pump, fluidize the substrate material with argon, maintain the temperature of the substrate material at 120°C, raise the temperature of the container containing Cu(dmamb)2 to 70°C, adjust the pressure in the reactor to 5Torr, introduce Cu(dmamb)2 vapor into the ALD reactor under argon, keep it for 10-300 seconds, and the flow rate of argon is 100sccm. Purge the reactor with argon, purge it for 10 seconds, introduce O3 into the ALD reactor under argon, keep it for 10-300 seconds, and the flow rate of argon is 100sccm. Purge the reactor with argon, purge it for 10 seconds, and form a copper oxide film with a thickness of 1nm after 30 ALD cycles by atomic layer deposition.

[0110] Step 2: Place the substrate material with the copper oxide film in a hydrogen reduction reaction chamber, heat it to a reaction temperature of 500°C in a hydrogen atmosphere, and react for 30 minutes. The copper oxide is reduced to copper and cuprous oxide nanoparticles using a hydrogen reduction process. The diameters of the copper and cuprous oxide nanoparticles are nanometers, and there are gaps between the copper and cuprous oxide nanoparticles. These copper and cuprous oxide nanoparticles serve as catalysts for the subsequent growth of silicon nanowires.

[0111] Step 3: Place the substrate material with copper and cuprous oxide nanoparticles in a silane chemical vapor deposition (CVD) reaction chamber, evacuate the reaction chamber through an exhaust pump, and introduce silane gas under the protection of an inert atmosphere of Ar for 4 hours at 600°C. The reaction pressure is 1 Torr. Silicon nanowires are grown on nanometal particles using a silane CVD cracking process. The diameter of the silicon nanowire is 5nm.

[0112] Step 4: Place the substrate material with silicon nanowires grown in a CVD reaction chamber, bring acetylene into the reaction chamber through nitrogen, adjust the reaction temperature in the reaction chamber to 700°C, and the reaction time to 6 hours. Use the acetylene CVD cracking process to coat amorphous carbon on the surface of the silicon nanowires. The thickness of the amorphous carbon coating layer is 50nm or less.

[0113] The prepared silicon-carbon negative electrode material and metallic lithium were combined into a half-cell for electrochemical performance testing. The charge and discharge test was carried out at a current density of C / 10 (first time) + C / 2 (cycle), and the 5C / 0.5C rate discharge performance was tested. The charge and discharge voltage range was 0.005 to 2.0 V. The test results are detailed in Table 3.

[0114] Example 3

[0115] Method for preparing silicon-carbon composite negative electrode material using ALD and CVD technology with graphite as base material:

[0116] Step 1: Select graphite as the substrate material, put it into an atomic layer deposition (ALD) reactor, and evacuate the reactor through an exhaust pump, use argon to fluidize the substrate material, keep the temperature of the substrate material at 120°C, raise the temperature of the container containing Cu(dmamb)2 to 70°C, adjust the pressure in the reactor to 5Torr, introduce Cu(dmamb)2 vapor into the ALD reactor under argon, keep it for 10-300 seconds, and the flow rate of argon is 100sccm. Purge the reactor with argon, purge it for 10 seconds, introduce O3 into the ALD reactor under argon, keep it for 10-300 seconds, and the flow rate of argon is 100sccm. Purge the reactor with argon, purge it for 10 seconds, and form a copper oxide film with a thickness of 0.5nm after 15 ALD cycles by atomic layer deposition.

[0117] Step 2: Place the substrate material with the copper oxide film in a hydrogen reduction reaction chamber, heat it to a reaction temperature of 500°C in a hydrogen atmosphere, and react for 10 minutes. The copper oxide is reduced to copper and cuprous oxide nanoparticles using a hydrogen reduction process. The diameters of the copper and cuprous oxide nanoparticles are nanometers, and there are gaps between the copper and cuprous oxide nanoparticles. These copper and cuprous oxide nanoparticles serve as catalysts for the subsequent growth of silicon nanowires.

[0118] Step 3: Place the substrate material with copper and cuprous oxide nanoparticles in a silane chemical vapor deposition (CVD) reaction chamber, evacuate the reaction chamber through an exhaust pump, and introduce silane gas under the protection of an inert atmosphere of Ar for 4 hours at 600°C. The reaction pressure is 1 Torr. Silicon nanowires are grown on nanometal particles using a silane CVD cracking process. The diameter of the silicon nanowire is less than 5nm.

[0119] Step 4: Place the substrate material with silicon nanowires grown in a CVD reaction chamber, bring acetylene into the reaction chamber through nitrogen, adjust the reaction temperature in the reaction chamber to 650°C, and the reaction time to 6 hours. Use the acetylene CVD cracking process to coat amorphous carbon on the surface of the silicon nanowires. The thickness of the amorphous carbon coating layer is 50nm or less.

[0120] The prepared silicon-carbon negative electrode material and metallic lithium were combined into a half-cell for electrochemical performance testing. The charge and discharge test was carried out at a current density of C / 10 (first time) + C / 2 (cycle), and the 5C / 0.5C rate discharge performance was tested. The charge and discharge voltage range was 0.005 to 2.0 V. The test results are detailed in Table 3.

[0121] Example 4

[0122] The method of preparing a silicon-carbon composite negative electrode material using ALD and CVD technology using graphite as a base material is the same as that of Example 1 in that a method similar to steps one to four is adopted, except that: between steps three and four, steps one and two are repeated to deposit second metal particles on the silicon nanowires of the base material, and the second metal is one of nickel oxide, iron oxide, cobalt oxide, platinum oxide, and palladium oxide.

[0123] Example 5

[0124] The method for preparing a silicon-carbon composite negative electrode material using graphite as a base material and using ALD and CVD technology is the same as that of Example 1 in that a method similar to steps 1 to 4 is used, except that: the process of step 4 uses a carbon source, a reaction precursor of a second metal oxide, and a co-catalyst as raw materials, the raw materials are introduced into the reactor through a carrier gas, and a floating catalyst chemical vapor deposition method is used to coat the surface of the silicon nanowires on the carbon base material to form a carbon layer, and carbon nanotubes are grown between the silicon nanowires on the carbon base material; the co-catalyst is selected from thiophene, the reaction precursor of the second metal oxide is selected from ferrocene, nickelocene and cobaltocene, the carbon source is ethylene, and the carrier gas is hydrogen.

[0125] Comparative Example 1

[0126] The method for preparing a silicon-carbon composite negative electrode material using graphite as a base material and ALD and CVD technology is the same as that of Example 1 in that a method similar to steps 1 to 4 is used, except that:

[0127] The copper oxide film formed by 60 ALD cycles in step 1 has a thickness of 2 nm;

[0128] In step three, the diameter of silicon nanowires grown on nano-metal particles by using a silane CVD cracking process is 20 to 50 nm.

[0129] The prepared silicon-carbon negative electrode material and metallic lithium were combined into a half-cell for electrochemical performance testing. The charge and discharge test was carried out at a current density of C / 10 (first time) + C / 2 (cycle), and the 5C / 0.5C rate discharge performance was tested. The charge and discharge voltage range was 0.005 to 2.0 V. The test results are detailed in Table 3.

[0130] Comparative Example 2

[0131] The method for preparing a silicon-carbon composite negative electrode material using graphite as a base material and ALD and CVD technology is the same as that of Example 1 in that a method similar to steps 1 to 4 is used, except that:

[0132] The copper oxide film formed by atomic layer deposition in step 1 with 165 ALD cycles has a thickness of 5.5 nm;

[0133] In step three, silicon nanoparticles with a diameter of 50 to 100 nm are grown on the nanometal particles using a silane CVD cracking process.

[0134] The prepared silicon-carbon negative electrode material and metallic lithium were combined into a half-cell for electrochemical performance testing. The charge and discharge test was carried out at a current density of C / 10 (first time) + C / 2 (cycle), and the 5C / 0.5C rate discharge performance was tested. The charge and discharge voltage range was 0.005 to 2.0 V. The test results are detailed in Table 3.

[0135] C / 10 (first charge): means that when charging for the first time, the battery is charged with a current of one tenth of its nominal capacity (10% charging rate). This charging method is usually gentle and helps the initial stability and long life of the battery.

[0136] C / 2 (Cyclic Charge): Indicates that in the subsequent 1 to 500 cycles, the battery is charged with a current of half its nominal capacity (50% charging rate). This charging method is relatively fast and can fully charge the battery in a shorter time.

[0137] 5C / 0.5C discharge performance: Under this condition, the battery will be rapidly discharged at a current 5 times the capacity, while charging at a rate of 0.5C. This high-rate discharge test can evaluate the performance of the battery under extreme usage conditions.

[0138] Table 3 Gram ratio, first effect, rate and cycle test results of the embodiments and comparative examples

[0139]

[0140] Through the above steps, the present invention successfully prepares a silicon-carbon composite negative electrode material. This material has high capacity, low lithium desorption potential, good cycle performance, and avoids the problems of high price of porous carbon, complex pore-making process, difficulty for silicon nanoparticles to enter the pores, and the diameter of silicon nanowires being limited by the size of metal catalyst particles. Example 4 improves the conductivity of the negative electrode material by coating carbon on silicon nanowires and growing carbon nanotubes between silicon nanowires, and improves the cycle capacity retention rate of the negative electrode material. Comparative Examples 1 and 2 have larger silicon nanoparticles and larger volume changes during lithium ion embedding, causing the carbon coating layer to crack and peel off, reducing the capacity retention rate. Commercial silicon-carbon negative electrode materials were purchased from Shanghai Yuling New Energy Technology Co., Ltd., and the manufacturing method was referred to CN114079045B.

[0141] The nano-silicon in the existing commercial silicon-carbon negative electrode materials is grown inside the nano-pores of porous carbon, and then a carbon layer is coated on the surface of the nano-silicon. The rate at which lithium ions enter the nano-pores is limited, resulting in poor rate performance of the existing silicon-carbon negative electrode and the inability to support fast charging. The silicon nanowires of the present invention can directly contact the electrolyte after being coated with carbon, and are not restricted by the transmission of nano-pores, so they have better rate performance.

[0142] Due to the advanced nature of the technical solution of the present invention, it can be widely used in application fields such as lithium-ion battery manufacturing, new energy electric vehicles, and portable electronic devices. With the development of science and technology, the demand for batteries in electronic products and electric vehicles is increasing, and lithium-ion batteries have become the first choice due to their high energy density, long cycle life, and environmental friendliness. However, there are still some problems with the existing silicon-based negative electrode material preparation technology, such as the high price of porous carbon, the complex pore-making process, and the uneven distribution of silicon nanoparticles in the pores. The present invention proposes a new method for preparing silicon-based negative electrode materials, which can effectively solve these problems, improve the performance of silicon-carbon negative electrode materials, and thus improve the energy density and cycle life of lithium-ion batteries. Therefore, the present invention has broad market demand and good application prospects.

Claims

1. A method for preparing a silicon-carbon composite negative electrode material using ALD and CVD technology, characterized in that: The following steps are involved: Step 1. growing a first metal oxide on the surface of a carbon base material using an ALD atomic layer deposition method; Step 2. reducing the first metal oxide on the surface of the carbon base material into nanodots containing metal elements in a reaction chamber; Step 3. placing the carbon substrate material with the nanodots distributed thereon in a reaction furnace, heating it and injecting a gas mixture, wherein the gas mixture comprises silane and an inert gas, and growing silicon nanowires on the nanodots based on a chemical vapor deposition process; Step 4. Coat a carbon layer on the surface of the silicon nanowires of the carbon base material to obtain a silicon-carbon composite negative electrode material.

2. The method according to claim 1, characterized in that The nanodots containing metal elements are selected from one or more of copper and / or copper oxide, tin, indium, gold, titanium, nickel, iron, silver, platinum, tin and gallium, cobalt, aluminum, and silicon dioxide.

3. The method according to claim 1, characterized in that The thickness of the first metal oxide is 0.33-1 nm.

4. The method according to claim 1, characterized in that The diameter of the silicon nanowire is no greater than 5 nm.

5. The method according to claim 1, characterized in that The coating process is selected from one of chemical vapor deposition, plasma enhanced chemical vapor deposition, electron beam evaporation, vacuum deposition, and atomic layer deposition.

6. The method according to claim 1, characterized in that The method between step 3 and step 4 also includes repeating steps 1 to 2, selecting a reaction precursor according to the type of the deposited second metal oxide, depositing the second metal oxide on the silicon nanowires of the carbon-based material, and then reducing it to second metal particles, so that the silicon nanowires of the carbon-based material and the second metal particles on the silicon nanowires are processed by step 4, a carbon layer is coated on the surface of the silicon nanowires on the carbon-based material, and carbon nanotubes are grown between the second metal particles of the silicon nanowires on the carbon-based material.

7. The method according to claim 1, characterized in that The coating process uses a carbon source, a reaction precursor of a second metal oxide, and a promoter as raw materials. The raw materials are introduced into a reactor through a carrier gas, and a floating catalyst chemical vapor deposition method is used to coat the surface of the silicon nanowires on the carbon base material to form a carbon layer, and carbon nanotubes are grown between the silicon nanowires on the carbon base material; the promoter is selected from one or both of thiophene and sulfur, the reaction precursor of the second metal oxide is selected from the alkene of the second metal in the second metal oxide, the carbon source includes a gaseous carbon source or a liquid carbon source, and the liquid carbon source is C 1-4 Alcohol and C 6-8 A mixture of hydrocarbons, wherein the gaseous carbon source comprises C 1-3 The carrier gas comprises hydrogen or an inert gas.

8. The method according to any one of claims 6 to 7, characterized in that: The metal in the second metal particles and the second metal oxide is selected from one or more of nickel, iron, cobalt, copper, chromium, manganese, molybdenum, tungsten, platinum and palladium.

9. The method according to claim 6, characterized in that The thickness of the second metal oxide is 0.1-5 nm.

10. The silicon-carbon composite negative electrode material prepared by the method according to any one of claims 3 to 5, characterized in that: It includes a carbon base material, the silicon nanowires grown on the surface of the carbon base material, a carbon layer coated on the surface of the silicon nanowires, and nanodots containing metal elements distributed in the silicon nanowires, wherein the nanodots containing metal elements are selected from one or more of copper and / or copper oxide, tin, and indium.

11. The silicon-carbon composite negative electrode material prepared by the method according to any one of claims 6 to 7, characterized in that: It includes a carbon base material, the silicon nanowires grown on the surface of the carbon base material, a carbon layer coated on the surface of the silicon nanowires, carbon nanotubes formed between the silicon nanowires, nanodots containing metal elements distributed in the silicon nanowires, and second metal particles distributed in the carbon nanotubes.

12. A lithium ion battery comprising the silicon-carbon composite negative electrode material according to claim 10 or claim 11.

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