Silicon-carbon composite material containing carbon nanotubes, and preparation method therefor and use thereof

Abstract

Disclosed are a silicon-carbon composite material containing carbon nanotubes, and a preparation method therefor and the use thereof. The silicon-carbon composite material comprises a porous composite hard carbon material containing carbon nanotubes, and silicon nanoparticles; the interior of the porous composite hard carbon material is supported by the carbon nanotubes, the silicon-carbon composite material uses the porous composite hard carbon material as a substrate, and silicon nanoparticles are distributed in the pores of the porous composite hard carbon material; the particle size of the silicon-carbon composite material is 1-100 μm; and the pore size of the pores of the porous composite hard carbon material is 1-7 nm. By means of the composite material, the size and uniform dispersion of the silicon nanoparticles is limited, an expansion effect is reduced, and the problem of repeated generation of an SEI film caused by silicon grain pulverization is avoided. The damage to the material from silicon expansion is also reduced, thereby further improving the cycling performance of a battery. The carbon nanotubes can strengthen the compression and tensile resistance of the substrate, keep the structure of the material stable, provide a fast channel for lithium-ion transmission, and ensure the rate performance of the material.

Description

Silicon-carbon composite material containing carbon nanotubes, preparation method thereof, and application thereof

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on July 18, 2023, with application number 202310884957.6 and invention name “A silicon-carbon composite material containing carbon nanotubes, its preparation method and application”. Technical Field

[0002] The present invention relates to the technical field of hard carbon negative electrode materials, and in particular to a silicon-carbon composite material containing carbon nanotubes, a preparation method thereof, and applications thereof. Background Art

[0003] The negative electrode materials widely used in lithium-ion batteries are composed of carbon materials, mainly artificial graphite and natural graphite. Their theoretical capacity is 372mAh / g, which cannot meet the demand for high-capacity batteries. Silicon, as a negative electrode material for lithium-ion batteries, has an extremely high theoretical reversible capacity of up to 4200mAh / g. However, a major problem with silicon is its large volume expansion coefficient. In lithium-ion batteries, the charging and discharging process involves the migration of lithium ions between the positive and negative electrodes of the battery. When lithium ions are embedded in the silicon negative electrode, the silicon crystal undergoes a large volume change.

[0004] During the initial charge and discharge process of lithium-ion batteries, lithium ions will be embedded and de-embedded in the silicon negative electrode, causing the silicon crystal to expand and contract. The volume change will lead to stress concentration and the formation of microcracks in the silicon crystal. With the cycle of charge and discharge, these cracks will gradually expand and eventually lead to the pulverization of the silicon crystal. The silicon particles produced by the pulverization will react with the components in the electrolyte to form a thin film called Solid Electrolyte Interphase (SEI). The SEI film is a thin film formed by the reaction of solvent decomposition products in the electrolyte and electrode materials. It plays a key role in the transmission of lithium ions and the stability of the battery.

[0005] However, since the pulverization of the silicon negative electrode is a repetitive process, each charge and discharge cycle will lead to the formation and pulverization of new silicon grains. These new silicon particles will continue to react with the components in the electrolyte, resulting in the continuous generation and reconstruction of the SEI film. This continuous generation and reconstruction of the SEI film may lead to a reduction in the cycle life of the battery.

[0006] Currently, work on modifying silicon-based materials is ongoing. Research has found that nano-sizing silicon particles can reduce the volume effect and the problem of repeated SEI film formation caused by the pulverization of silicon grains during charging and discharging, thereby improving the cycle performance of silicon-based negative electrode materials and maintaining a high reversible capacity. By further preparing silicon-carbon composite materials and constructing a cage structure, the volume effect of silicon-based negative electrodes can be effectively alleviated. However, the preparation cost of nano-silicon particles is high, and the nanoparticles themselves have poor dispersibility. They are prone to agglomeration during the composite preparation of silicon-carbon negative electrodes, resulting in uneven distribution, affecting the cycle performance of the composite material, and making it difficult to fully utilize the advantages of nano-sizing.

[0007] Summary of the Invention

[0008] The embodiments of the present invention provide a silicon-carbon composite material containing carbon nanotubes, a preparation method and application thereof, which solves the problem that nano-silicon particles have poor dispersion and are easily agglomerated during the composite preparation process of silicon-carbon negative electrodes, resulting in uneven distribution, affecting the cycle performance of the composite material, and making it difficult to fully utilize the advantages of nano-sizing.

[0009] In a first aspect, the present invention provides a silicon-carbon composite material containing carbon nanotubes, wherein the silicon-carbon composite material comprises a porous composite hard carbon material containing carbon nanotubes and silicon nanoparticles; wherein the porous composite hard carbon material is supported by the carbon nanotubes;

[0010] The silicon-carbon composite material is based on the porous composite hard carbon material, and the silicon nanoparticles are distributed in the pores of the porous composite hard carbon material;

[0011] The particle size of the silicon-carbon composite material is 1 μm-100 μm;

[0012] The pores of the porous composite hard carbon material have a pore diameter of 1 nm to 7 nm.

[0013] Preferably, the silicon nanoparticles account for 10%-70% of the mass of the silicon-carbon composite material.

[0014] Preferably, the carbon nanotubes have a diameter of ≤1 μm and a length of ≤50 μm.

[0015] In a second aspect, the present invention provides a method for preparing the silicon-carbon composite material as described in the first aspect above, the preparation method comprising:

[0016] The resin, carbon nanotubes and nano water-soluble salt particles are uniformly mixed and heated to obtain a carbonized precursor containing carbon nanotubes;

[0017] The carbonized precursor containing carbon nanotubes is placed in a reaction device for carbonization treatment and crushing, and then washed with water, filtered and dried to obtain a composite hard carbon matrix containing carbon nanotubes with a particle size of 1 μm to 100 μm;

[0018] performing a pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes;

[0019] The porous composite hard carbon material containing carbon nanotubes is used as a substrate, silicon-containing gas is used as a silicon source, and is brought into a reaction furnace through a protective gas to perform vapor deposition to obtain a silicon-carbon composite material containing carbon nanotubes.

[0020] Preferably, the mass ratio of the resin, the carbon nanotubes and the nano water-soluble salt particles is [50%-95%]:[3%-10%]:[2%-40%].

[0021] Preferably, the temperature of the heating and curing treatment is 100°C-300°C, and the time is 1 hour-5 hours;

[0022] The carbonization treatment temperature is 600°C-900°C, and the time is 0.5 hours-15 hours;

[0023] The pore-forming temperature is 800°C-1200°C, and the time is 6 hours-50 hours;

[0024] The temperature of the vapor deposition is 500° C.-1500° C., and the time is 1 hour-20 hours.

[0025] Preferably, the protective gas includes: one or both of nitrogen and argon, with a flow rate of 1-5 L / min.

[0026] Preferably, the silicon-containing gas includes one or more of monosilane, trisilane, dichlorosilane, trichlorosilane, and tetrachlorosilane, with a flow rate of 2-10 L / min.

[0027] In a third aspect, the present invention provides a negative electrode plate, which comprises the silicon-carbon composite material described in the first aspect.

[0028] In a fourth aspect, the present invention provides a lithium battery, comprising the negative electrode sheet described in the third aspect.

[0029] Compared to existing technologies, the nano-silicon particles in the carbon nanotube-containing silicon-carbon composite material are uniformly distributed within the pore structure of the porous composite hard carbon material containing carbon nanotubes through vapor deposition. The porous composite hard carbon material containing carbon nanotubes can, on the one hand, limit the size of the silicon grains formed after the decomposition and deposition of the silicon-containing gas, maintaining them at the nanometer level and evenly dispersing them within the porous composite hard carbon material, thereby reducing the expansion effect and avoiding the problem of repeated SEI film formation caused by the pulverization of the silicon grains during charge and discharge. On the other hand, it can also limit the expansion of silicon, reducing the damage to the silicon-carbon composite material caused by silicon expansion, thereby improving the cycle performance of the battery. At the same time, the porous composite hard carbon material can effectively increase the compaction density of the electrode after coating, thereby improving the energy density of the battery. The pore walls of the porous composite hard carbon material have good compressive resistance, and the addition of carbon nanotubes can improve the tensile strength of the pore wall structure, preventing stress damage during the expansion of the silicon grains. Furthermore, the electrical conductivity of the carbon nanotubes (>100 S / m) is much higher than that of the porous composite hard carbon material (<10 S / m), which can improve the material's rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The technical solutions of the embodiments of the present invention are further described in detail below through the accompanying drawings and examples.

[0031] FIG1 is a schematic structural diagram of a silicon-carbon composite material containing carbon nanotubes provided in an embodiment of the present invention;

[0032] FIG2 is a flow chart of a method for preparing a silicon-carbon composite material containing carbon nanotubes provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below through the accompanying drawings and specific embodiments, but it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, that is, they are not intended to limit the scope of protection of the present invention.

[0034] The present invention provides a silicon-carbon composite material containing carbon nanotubes, as shown in FIG1 , wherein the silicon-carbon composite material comprises a porous composite hard carbon material containing carbon nanotubes and silicon nanoparticles; wherein the porous composite hard carbon material is supported by carbon nanotubes;

[0035] The silicon-carbon composite material is based on a porous composite hard carbon material, and silicon nanoparticles are distributed in the pores of the porous composite hard carbon material;

[0036] The particle size of the silicon-carbon composite material is 1 μm-100 μm;

[0037] The pores of the porous composite hard carbon material have a pore diameter of 1 nm to 7 nm.

[0038] The silicon nanoparticles account for 10%-70% of the silicon-carbon composite material by mass.

[0039] The diameter of the carbon nanotube is ≤1μm and the length is ≤50μm.

[0040] The present invention also provides a method for preparing the above-mentioned silicon-carbon composite material containing carbon nanotubes. The preparation method is a water-soluble salt template method. During the preparation process, nano water-soluble salt particles are used as a template. The steps are shown in Figure 2 and include the following steps:

[0041] Step 110 : Evenly mix the resin, carbon nanotubes, and nanometer water-soluble salt particles, and heat and solidify them to obtain a carbonized precursor containing carbon nanotubes.

[0042] The resin includes one or more of phenolic resin, epoxy resin and furfural resin; the carbon nanotube has a diameter of ≤1 μm and a length of ≤50 μm; and the particle size of the nano water-soluble salt particles is 20 nm-100 nm.

[0043] The mass ratio of the resin, the carbon nanotubes and the nano water-soluble salt particles is [50%-95%]:[3%-10%]:[2%-40%].

[0044] The temperature of the heat curing treatment is 100° C.-300° C., and the time is 1 hour-5 hours.

[0045] In step 120 , a carbonized precursor containing carbon nanotubes is placed in a reaction device for carbonization treatment and crushing, and then washed, filtered and dried to obtain a composite hard carbon matrix containing carbon nanotubes with a particle size of 1 μm-100 μm.

[0046] The temperature of the carbonization treatment is 600° C.-900° C., and the time is 0.5 hour-15 hours.

[0047] In this step, the nano water-soluble salt particles are removed by washing.

[0048] Step 130 : performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes.

[0049] The composite hard carbon matrix containing carbon nanotubes obtained in step 120 is subjected to pore formation treatment, and the gas source used includes one or two of oxygen, carbon dioxide, and water vapor. The pore formation temperature is 800° C.-1200° C., and the time is 6 hours-50 hours.

[0050] In step 140 , a porous composite hard carbon material containing carbon nanotubes is used as a substrate, and a silicon-containing gas is brought into a reaction furnace through a protective gas to perform vapor deposition to obtain a silicon-carbon composite material containing carbon nanotubes.

[0051] The silicon-containing gas includes one or more of monosilane, trisilane, dichlorosilane, trichlorosilane, and tetrachlorosilane, with a flow rate of 2-10 L / min; the protective gas includes one or both of nitrogen and argon, with a flow rate of 1-5 L / min; the temperature of vapor deposition is 500° C.-1500° C., and the time is 1 hour-20 hours.

[0052] Compared to existing technologies, the nano-silicon particles in the carbon nanotube-containing silicon-carbon composite material are uniformly distributed within the pore structure of the porous composite hard carbon material containing carbon nanotubes through vapor deposition. This porous composite hard carbon material can, on the one hand, limit the size of the silicon grains formed after the decomposition and deposition of the silicon-containing gas, maintaining them at the nanometer level and evenly dispersing them within the porous composite hard carbon material, thereby reducing the expansion effect and avoiding the problem of repeated SEI film formation caused by the pulverization of the silicon grains during charge and discharge. It can also limit the expansion of silicon, reducing the damage to the silicon-carbon composite material caused by silicon expansion, thereby improving the battery's cycling performance. Furthermore, the porous composite hard carbon material can effectively increase the compaction density of the coated electrode, thereby improving the battery's energy density. The pore walls of the porous composite hard carbon material have good compressive strength, while the addition of carbon nanotubes can improve the tensile strength of the pore wall structure, preventing stress damage during the expansion of the silicon grains. Furthermore, the electrical conductivity of carbon nanotubes (>100 S / m) is much higher than that of the porous composite hard carbon material (<10 S / m), which can improve the material's rate performance.

[0053] The carbon nanotube-containing silicon-carbon composite material provided by the present invention can be used for negative electrode plates, and further used in liquid, semi-solid, quasi-solid, and all-solid electrolyte lithium-ion batteries.

[0054] To better understand the technical solution provided by the present invention, the following uses multiple specific examples to illustrate the specific process of preparing carbon nanotube-containing silicon-carbon composite materials using the method provided in the above embodiments of the present invention, as well as the characteristics of the prepared carbon nanotube-containing silicon-carbon composite materials.

[0055] Example 1

[0056] Step 1: mixing phenolic resin, carbon nanotubes and nano water-soluble salt particles in a ratio of 50%:10%:40%, and heating at 100° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0057] Step 2: placing a carbonized precursor containing carbon nanotubes into a reaction device, heating it to 600°C, and keeping it warm for 15 hours to carbonize the carbonized precursor containing carbon nanotubes, crush it, and then wash, filter, and dry it to obtain a 12 μm composite hard carbon matrix containing carbon nanotubes;

[0058] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes, wherein the gas source used is oxygen with a flow rate of 10 L / min; the pore-forming temperature is 900° C. and the time is 6 hours;

[0059] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and dichlorosilane gas as the silicon source at a flow rate of 2 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 2 L / min, the vapor deposition temperature is 500°C, and the vapor deposition time is 2 hours.

[0060] The resulting silicon-carbon composite material containing carbon nanotubes was used as the negative electrode material. The negative electrode material, conductive additive carbon black, and binder (a 1:1 ratio of sodium carboxymethyl cellulose and styrene-butadiene rubber) were weighed in a mass ratio of 96%:2%:2%, and a slurry was prepared using a beater at room temperature. The prepared slurry was evenly applied to copper foil and dried in a forced-air drying oven at 80°C for 2 hours. The electrode pieces were cut into circular pieces with a diameter of 16 mm and dried in a vacuum drying oven at 90°C for 5 hours. The dried electrode pieces were then transferred to a glove box for future battery assembly.

[0061] The simulated battery was assembled in a glove box containing a high-purity Ar atmosphere, using metallic lithium as the counter electrode and a 1M LiPF6 solution in ethylene carbonate (EC) / diethyl carbonate (DEC) as the electrolyte. Constant current charge and discharge tests were performed using a charge-discharge instrument, with a discharge cut-off voltage of 0.005V and a charge cut-off voltage of 1.5V. The charge and discharge tests were conducted at a current density of C / 10. The test results are reported in Table 1.

[0062] Comparative Example 1

[0063] Step 1: Evenly mix phenolic resin and nano-silicon particles at a ratio of 70%:30%, and heat at 100° C. for 5 hours for curing to obtain a silicon-carbon material precursor;

[0064] Step 2: Place the silicon-carbon material precursor into a reaction device, heat it to 900° C., keep it warm for 6 hours, perform carbonization treatment, and crush it to obtain a 12 μm silicon-carbon composite material.

[0065] Comparative Example 2

[0066] Step 1: Phenolic resin and nanometer water-soluble salt particles are mixed uniformly at a ratio of 50%:50%, and then heated at 100° C. for 5 hours for curing to obtain a carbonized precursor;

[0067] Step 2: Place the carbonized precursor into a reaction device, heat it to 900°C, and keep it warm for 6 hours to carbonize the carbonized precursor, crush it, and then wash, filter, and dry it to obtain a 12 μm composite hard carbon matrix;

[0068] Step 3: Performing pore-forming treatment on the composite hard carbon matrix to obtain a porous composite hard carbon material; the gas source used is oxygen, the air flow rate is 10 L / min; the pore-forming temperature is 800° C., and the time is 8 hours;

[0069] Step 4: Use the porous composite hard carbon material as the substrate and dichlorosilane gas as the silicon source at a flow rate of 2 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 2 L / min, the vapor deposition temperature is 500°C, and the vapor deposition time is 2 hours.

[0070] Example 2

[0071] Step 1: Phenolic resin, carbon nanotubes, and nano water-soluble salt particles are uniformly mixed in a ratio of 50%:9%:41%, and then heated at 120° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0072] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 900° C., and keeping it warm for 0.5 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 16 μm composite hard carbon matrix containing carbon nanotubes;

[0073] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is water vapor with a flow rate of 0.5 L / min; the pore-forming temperature is 1200° C. and the duration is 6 hours;

[0074] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and monosilane gas as the silicon source at a flow rate of 0.5 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 1 L / min, the vapor deposition temperature is 1500°C, and the vapor deposition time is 1 hour.

[0075] Example 3

[0076] Step 1: Evenly mix phenolic resin, carbon nanotubes, and nanometer water-soluble salt particles in a ratio of 50%:7%:33%, and heat at 100° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0077] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 600° C., and keeping it warm for 15 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain an 85 μm composite hard carbon matrix containing carbon nanotubes;

[0078] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is carbon dioxide, the air flow rate is 20 L / min; the pore-forming temperature is 950° C., and the time is 48 hours;

[0079] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate, and use monosilane and trichlorosilane gas as the silicon source at a flow rate of 5 L / min; pass nitrogen as a protective gas into the reactor at a flow rate of 3 L / min, the vapor deposition temperature is 500°C, and the vapor deposition time is 18 hours.

[0080] Example 4

[0081] Step 1: Evenly mix phenolic resin, carbon nanotubes, and nanometer water-soluble salt particles in a ratio of 60%:10%:30%, and heat at 100° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0082] Step 2: placing a carbonized precursor containing carbon nanotubes into a reaction device, heating it to 700° C., and keeping it warm for 15 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 1 μm composite hard carbon matrix containing carbon nanotubes;

[0083] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is carbon dioxide, the air flow rate is 9 L / min; the pore-forming temperature is 880° C., and the time is 22 hours;

[0084] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate, and use trisilane and dichlorosilane gases as silicon sources at a flow rate of 10 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 4.5 L / min, the vapor deposition temperature is 1350°C, and the vapor deposition time is 10 hours.

[0085] Example 5

[0086] Step 1: Evenly mix epoxy resin, carbon nanotubes, and nanometer water-soluble salt particles in a ratio of 70%:5%:25%, and heat at 300° C. for 1 hour for curing to obtain a carbonized precursor containing carbon nanotubes;

[0087] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 1250° C., and keeping it at that temperature for 10 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 38 μm composite hard carbon matrix containing carbon nanotubes;

[0088] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is water vapor with a flow rate of 7.5 L / min; the pore-forming temperature is 1050° C. and the time is 29 hours;

[0089] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and trisilane gas as the silicon source at a flow rate of 3.5 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 4.5 L / min, the vapor deposition temperature is 1450°C, and the vapor deposition time is 12 hours.

[0090] Example 6

[0091] Step 1: Evenly mix epoxy resin, carbon nanotubes, and nanometer water-soluble salt particles in a ratio of 95%:3%:2%, and heat at 100° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0092] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 850° C., and keeping it at that temperature for 15 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 72 μm composite hard carbon matrix containing carbon nanotubes;

[0093] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is carbon dioxide, the air flow rate is 12 L / min; the pore-forming temperature is 1350° C., and the time is 7 hours;

[0094] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and tetrachlorosilane gas as the silicon source at a flow rate of 3.5 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 2 L / min, the vapor deposition temperature is 600°C, and the vapor deposition time is 20 hours.

[0095] Example 7

[0096] Step 1: Evenly mix epoxy resin, carbon nanotubes, and nanometer water-soluble salt particles in a ratio of 75%:10%:15%, and heat at 100° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0097] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 900° C., and keeping it warm for 8 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 15 μm composite hard carbon matrix containing carbon nanotubes;

[0098] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is carbon dioxide, the air flow rate is 9 L / min; the pore-forming temperature is 800° C., and the time is 25 hours;

[0099] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and monosilane gas as the silicon source at a flow rate of 1.5 L / min; pass nitrogen gas into the reactor as a protective gas at a flow rate of 1 L / min, the vapor deposition temperature is 800°C, and the vapor deposition time is 10 hours.

[0100] Example 8

[0101] Step 1: Evenly mix epoxy resin, carbon nanotubes, and nanometer water-soluble salt particles in a ratio of 70%:5%:25%, and heat at 150° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0102] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 750° C., and keeping it at that temperature for 3 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 44 μm composite hard carbon matrix containing carbon nanotubes;

[0103] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is oxygen, the air flow rate is 3 L / min; the pore-forming temperature is 850° C., and the time is 15 hours;

[0104] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and monosilane gas as the silicon source at a flow rate of 8 L / min; pass argon gas as the protective gas into the reactor at a flow rate of 5 L / min, the vapor deposition temperature is 800°C, and the vapor deposition time is 10 hours.

[0105] Example 9

[0106] Step 1: Furfural resin, carbon nanotubes, and nano water-soluble salt particles are mixed uniformly at a ratio of 90%:5%:5%, and then heated at 200° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0107] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 900° C., and keeping it warm for 2 hours to carbonize the carbonized precursor containing carbon nanotubes and crush it to obtain a 56 μm composite hard carbon matrix containing carbon nanotubes;

[0108] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is water vapor, the air flow rate is 13 L / min, the pore-forming temperature is 1050° C., and the duration is 27 hours;

[0109] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate and trisilane gas as the silicon source at a flow rate of 5 L / min; pass argon gas as the protective gas into the reactor at a flow rate of 2.5 L / min, the vapor deposition temperature is 1200°C, and the vapor deposition time is 4 hours.

[0110] Example 10

[0111] Step 1: Furfural resin, carbon nanotubes, and nano water-soluble salt particles are mixed uniformly in a ratio of 60%:5%:35%, and then heated at 100° C. for 5 hours for curing to obtain a carbonized precursor containing carbon nanotubes;

[0112] Step 2: placing the carbonized precursor containing carbon nanotubes into a reaction device, heating it to 750° C., and keeping it warm for 8 hours to carbonize the composite carbonized precursor containing carbon nanotubes and crush it to obtain a 12 μm composite hard carbon matrix containing carbon nanotubes;

[0113] Step 3: Performing pore-forming treatment on the composite hard carbon matrix containing carbon nanotubes to obtain a porous composite hard carbon material containing carbon nanotubes; the gas source used is oxygen, the air flow rate is 3 L / min; the pore-forming temperature is 1150° C., and the time is 18 hours;

[0114] Step 4: Use the porous composite hard carbon material containing carbon nanotubes as the substrate, and use trisilane and dichlorosilane gases as silicon sources at a flow rate of 6 L / min; pass argon gas into the reactor as a protective gas at a flow rate of 2.5 L / min, the vapor deposition temperature is 1350°C, and the vapor deposition time is 2.5 hours.

[0115] Under the same conditions, button cells were assembled according to the method of Example 1 for the materials obtained in Comparative Examples 1-2 and Examples 2-10, and their electrochemical properties were evaluated by testing. The test results are recorded in Table 1.

[0116] Table 1

[0117] It can be seen from the data in Table 1 that under the condition that the charge specific capacity and first cycle efficiency between Examples 1-10 and Comparative Examples 1-2 are not much different, the rate performance of Example 1-10 is significantly better than that of Comparative Examples 1-2, and the electrode expansion at full charge is significantly lower than that of Comparative Examples 1-2. Comparative Example 1 is an ordinary silicon-carbon structure, which is fired after mixing nano-silicon and carbon matrix. Its nanoparticles are unevenly dispersed and have a large expansion effect. Its electrode expands by 46.25% in the fully charged state. Comparative Example 2 is a deposited silicon-carbon composite structure. In comparison, the addition of carbon nanotubes to the silicon-carbon composite material provided in Example 1 can not only inhibit the stress damage during the expansion of silicon particles, but also reduce the expansion of the full electrode sheet from 15.93% to 8.35%, further improve the structural stability of the particles during the charge and discharge process, prevent the problem of repeated generation of SEI film caused by the pulverization of silicon grains during the charge and discharge process, enhance the cycle performance of the battery, and effectively improve the conductivity of the material, thereby improving the rate performance of the material.

[0118] Compared to the prior art, the carbon nanotube-containing silicon-carbon composite material provided by the present invention features nano-silicon particles uniformly distributed within the pore structure of a porous composite hard carbon material containing carbon nanotubes via vapor deposition. The porous composite hard carbon material containing carbon nanotubes, on the one hand, limits the size of silicon grains formed after the decomposition and deposition of silicon-containing gases, maintaining them at the nanometer level and uniformly dispersing them within the porous composite hard carbon material containing carbon nanotubes, thereby reducing the expansion effect and avoiding the problem of repeated SEI film formation caused by the pulverization of silicon grains during charge and discharge. On the other hand, it limits silicon expansion, reducing the damage to the silicon-carbon composite material caused by silicon expansion, thereby improving the battery's cycle performance. Furthermore, the porous composite hard carbon material can effectively increase the compaction density of the electrode after coating, thereby improving the battery's energy density. The pore walls of the porous composite hard carbon material have good compressive strength, while the addition of carbon nanotubes can, on the one hand, increase the tensile strength of the pore wall structure, preventing stress damage during silicon grain expansion. Furthermore, the electrical conductivity of carbon nanotubes (>100 S / m) is much higher than that of the porous composite hard carbon material (<10 S / m), thereby improving the material's rate performance.

[0119] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A silicon-carbon composite material containing carbon nanotubes, characterized in that: The silicon-carbon composite material comprises a porous composite hard carbon material containing carbon nanotubes and silicon nanoparticles; wherein the porous composite hard carbon material is supported by the carbon nanotubes; The silicon-carbon composite material is based on the porous composite hard carbon material, and the silicon nanoparticles are distributed in the pores of the porous composite hard carbon material; The particle size of the silicon-carbon composite material is 1 μm-100 μm; The pores of the porous composite hard carbon material have a pore diameter of 1 nm to 7 nm.

2. The silicon-carbon composite material according to claim 1, characterized in that: The silicon nanoparticles account for 10%-70% of the silicon-carbon composite material by mass.

3. The silicon-carbon composite material according to claim 1, characterized in that: The carbon nanotube has a diameter of ≤1 μm and a length of ≤50 μm.

4. A method for preparing a silicon-carbon composite material containing carbon nanotubes as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises: The resin, carbon nanotubes and nano water-soluble salt particles are uniformly mixed and heated to obtain a carbonized precursor containing carbon nanotubes; The carbonized precursor containing carbon nanotubes is placed in a reaction device for carbonization treatment, crushed, washed, filtered and dried to obtain a composite hard carbon matrix containing carbon nanotubes with a particle size of 1 μm-100 μm; The composite hard carbon matrix containing carbon nanotubes is subjected to pore formation treatment to obtain a porous composite hard carbon material containing carbon nanotubes; The porous composite hard carbon material containing carbon nanotubes is used as a substrate, and silicon-containing gas is used as a silicon source, which is brought into a reaction furnace through a protective gas for vapor deposition to obtain a silicon-carbon composite material containing carbon nanotubes.

5. The preparation method according to claim 4, characterized in that: The mass ratio of the resin, the carbon nanotubes and the nano water-soluble salt particles is [50%-95%]: [3%-10%]: [2%-40%].

6. The preparation method according to claim 4, characterized in that: The temperature of the heating and curing treatment is 100°C-300°C, and the time is 1 hour-5 hours; The carbonization treatment temperature is 600°C-900°C, and the time is 0.5 hour-15 hours; The pore-making temperature is 800°C-1200°C and the time is 6 hours-50 hours; The temperature of the vapor deposition is 500° C.-1500° C., and the time is 1 hour-20 hours.

7. The preparation method according to claim 4, characterized in that: The protective gas includes: one or both of nitrogen and argon, with a flow rate of 1-5 L / min.

8. The preparation method according to claim 7, characterized in that: The silicon-containing gas includes: one or more of monosilane, trisilane, dichlorosilane, trichlorosilane, and tetrachlorosilane; and the flow rate is 2-10 L / min.

9. A negative electrode plate, characterized in that: The negative electrode plate comprises the silicon-carbon composite material as described in any one of claims 1 to 3 above.

10. A lithium battery, characterized in that: The lithium battery comprises the negative electrode sheet as described in claim 9 above.

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