Modified activated carbon, silicon-carbon composite material and preparation method thereof, electrode sheet, application and electrochemical device

Abstract

The application discloses a modified activated carbon, a silicon-carbon composite material and a preparation method, a pole piece, application and an electrochemical device thereof. The preparation method of the modified activated carbon comprises the following steps: subjecting activated carbon and a solvent to microwave reaction to obtain the modified activated carbon; the microwave power is 600-800 W during the microwave reaction; and the microwave reaction time is 10-40 min. The modified activated carbon has a large micropore pore volume and a large micropore ratio. The battery assembled by the silicon-carbon composite material prepared from the modified activated carbon can realize a better capacity performance under the conditions of maintaining a better initial coulomb efficiency and a smaller expansion, and can greatly meet the commercial application level.

Description

TECHNICAL FIELD

[0001] The present application relates to a modified activated carbon, a silicon-carbon composite material and a preparation method thereof, a pole piece, an application and an electrochemical device. BACKGROUND

[0002] Silicon-based anode materials have become one of the most promising anode materials for lithium-ion batteries due to their high theoretical specific capacity (about 10 times that of graphite), low lithium intercalation potential, and abundant natural resources and environmental friendliness. However, the volume expansion and contraction of silicon-based anode materials during lithium-ion charging and discharging can lead to the destruction of the electrode structure, and the low intrinsic electrical conductivity hinders its practical application to some extent. The volume expansion of silicon anode is more than 300% when it is fully lithiated during the silicon-lithium alloying process, which can cause problems such as degranulation and cracking between electrode particles during the cycling process of silicon-based materials, reducing the cycle stability and service life of the battery, and even leading to battery failure. In view of the above problems, many methods have been designed to improve the large expansion. For example, reducing the size of silicon particles to nanoscale, preparing silicon-based anode materials with porous structure, surface modification of silicon particles, wrapping in materials with high elasticity and stability, and compounding silicon with other materials can all alleviate the volume expansion effect of silicon-based anode materials. Non-metals, metals and their oxides, silicon oxides, organic polymers, and various carbon materials have been tried to be compounded with silicon. Among them, carbon material and silicon composite is the most commonly used and effective method, and the mechanical and electrical properties of carbon material can make up for the defects of silicon. The carbon matrix in silicon / carbon composite material has good electrical conductivity, which can effectively promote electron transmission and lithium ion diffusion, and improve the cycle stability during charging and discharging. The addition of carbon material promotes the dispersion of Si particles, and good elasticity and flexibility can adapt to volume changes and effectively buffer the volume expansion effect of silicon particles. However, with the rapid development of electric vehicles and portable electronic devices, its conductivity and cycle stability still need to be improved, and the electrochemical performance still needs to be further optimized. Therefore, it is of great practical application and research value to develop a silicon-carbon anode material with low expansion and high conductivity.

[0003] The patent with publication number CN117317188A discloses a preparation method of an active carbon composite negative electrode material coated with nano-silicon dioxide. Sodium hydride is used as a catalyst to carry out a substitution reaction on octachloromethyl cage silsesquioxane and 2-(2-naphthyl)-1H-benzimidazole to obtain naphthyl benzimidazole cage silsesquioxane. Then, the benzene ring and naphthalene ring structure contained therein undergoes crosslinking polymerization with dimethoxymethane under the catalysis of ferric chloride, and is then calcined in a high-temperature tube furnace to obtain an active carbon negative electrode material coated with nano-silicon dioxide. The nano-silicon dioxide is coated with porous carbon, which alleviates the volume expansion phenomenon of nano-silicon dioxide during charging and discharging, and improves the structural stability of the negative electrode. However, the preparation method is complex and is not conducive to industrial production. Moreover, the specific capacity and cycle performance of the composite material are improved particularly limited, and the capacity and conductivity of silicon dioxide are low, which limits its better application in the electronic market.

[0004] The patent with publication number CN107910540A discloses a preparation method of a silicon-carbon negative electrode material in which silicon material is embedded in the voids of active carbon. Active carbon and silicate are added to water, stirred uniformly, and the particle size of the active carbon is 0.1-30 μm. An acid solution is added, stirred, washed, and dried. Hydrogen is introduced, and after the reaction is complete, the carbon-silicon negative electrode material is obtained after cooling. The silicon material is embedded in the voids of active carbon by methods such as precipitation and reduction, and the carbon-silicon negative electrode material prepared has a stable structure and can be used to prepare lithium ion batteries with good conductivity, high specific capacity, and long cycle life. However, the shape and size of the silicon-carbon composite material prepared by the method are quite different, which may cause differences in electron transport and ion diffusion rate in different parts, and may experience different degrees of volume change and stress effect, thereby significantly affecting the electrochemical performance and cycle stability.

[0005] Therefore, how to provide a new modified active carbon / silicon composite material to improve the conductivity of the electrode material, and composite a layer of conductive, hard, and tough coating layer, and finally prepare a silicon-carbon negative electrode material that can effectively buffer volume expansion, is a key challenge currently faced by the work. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the defect that the small proportion of micropores in the active carbon leads to a small amount of silane adsorption, resulting in poor capacity performance of the battery assembled by the prepared silicon-based composite material, and to provide a modified active carbon, a silicon-carbon composite material, a preparation method thereof, a pole piece, an application, and an electrochemical device. The modified active carbon has a large micropore volume and a large micropore ratio. The battery assembled by the silicon-carbon composite material prepared from the modified active carbon can achieve good capacity performance while maintaining good initial coulombic efficiency and small expansion, which can greatly meet the commercial application level.

[0007] The present application solves the above technical problems by the following technical solutions.

[0008] The present application provides a preparation method of modified activated carbon, which comprises the following steps:

[0009] The activated carbon and the solvent are subjected to microwave reaction to obtain the modified activated carbon; the microwave power in the microwave reaction is 600-800 W; and the microwave reaction time is 10-40 min.

[0010] In the present application, the specific surface area of the activated carbon can be 1100-1150 m 2 / g. The micropore volume of the activated carbon can be 300-360 mm 3 / g. The micropore volume is the volume of micropores (pores with a pore size less than 2 nm) in unit mass of activated carbon.

[0011] In the present application, the activated carbon can be obtained by a conventional preparation method in the art, and is preferably prepared by the following method: pre-oxidation, carbonization and activation of phenolic resin, wherein the pre-oxidation, carbonization and activation are performed at increasing temperatures.

[0012] The phenolic resin can be conventional in the art, for example, a phenolic resin with a model number of 2123 purchased from Shandong Jiaqi Chemical Co., Ltd.

[0013] The pre-oxidation temperature can be 120-140 ℃, for example, 130 ℃. The pre-oxidation time can be 1-3 h, for example, 2 h. The pre-oxidation is preferably performed in an air or oxygen atmosphere.

[0014] The carbonization is preferably performed in an inert atmosphere. The inert atmosphere is preferably nitrogen. The gas flow of the inert atmosphere can be 10-30 mL / min, for example, 20 mL / min. The carbonization temperature can be 500-600 ℃, for example, 550 ℃. The carbonization time can be 0.5-1.5 h, for example, 1 h. The rate of increasing the temperature from the pre-oxidation temperature to the carbonization temperature can be 3-5 ℃ / min, for example, 4 ℃ / min.

[0015] After the carbonization and before the activation, the method preferably further comprises the steps of cooling and grinding. The end point of the cooling can be room temperature, generally 20-30 ℃. The particle size of the ground material is 60 mesh-80 mesh.

[0016] The activation is preferably performed under an inert atmosphere. The inert atmosphere is preferably nitrogen. The gas flow of the inert atmosphere can be 10-30 mL / min, for example 20 mL / min. The temperature of the activation can be 600-700℃, for example 650℃. The time of the activation can be 0.5-1.5 h, for example 1 h. The atmosphere of the activation is preferably water vapor. The rate of increasing the temperature from room temperature to the temperature of the activation can be 2-4℃ / min, for example 3℃ / min.

[0017] In the present application, the activated carbon is preferably further subjected to the steps of washing and drying before the microwave reaction.

[0018] The washing operation can be conventional in the art, for example, sequentially using distilled water, inorganic acid and distilled water. The type of inorganic acid can be conventional in the art, for example, nitric acid. The inorganic acid is generally in the form of an inorganic acid aqueous solution during the washing. The mass percentage of inorganic acid in the inorganic acid aqueous solution can be 2%. The end point of the washing is preferably neutral, generally with a pH of 7.0.

[0019] The drying operation can be conventional in the art, for example, drying in an oven. The temperature of the drying can be 110-130℃, for example 120℃.

[0020] In the present application, the type of solvent can be conventional in the art, for example, water or an alcohol solvent. The alcohol solvent is preferably one or more of isopropyl alcohol, ethylene glycol, propylene glycol and n-butanol, for example n-butanol.

[0021] In the present application, the mass-to-volume ratio of the activated carbon to the solvent can be 1 g: (1-5) mL, preferably 1 g: (2-4) mL, for example 1 g: 3 mL.

[0022] In the present application, the microwave power during the microwave reaction is preferably 650-750 W, for example 700 W.

[0023] In the present application, the temperature of the microwave reaction is preferably 60-90℃, for example 80℃.

[0024] In the present application, the time of the microwave reaction is preferably 20-30 min, for example 25 min.

[0025] In the present application, the microwave reaction is preferably further followed by the steps of cooling, washing and drying.

[0026] The cooling operation can be conventional in the art, for example, using natural cooling. The end point temperature of the cooling can be room temperature, generally 20-30℃.

[0027] The washing operation can be conventional in the art, for example, using deionized water for centrifugal washing.

[0028] The drying operation can be conventional in the art, for example, drying in a constant temperature drying oven. The temperature of the drying can be 50-70℃, for example, 60℃. The time of the drying can be 20-30h, for example, 24h.

[0029] In the present application, the microwave reaction is preferably further added with guanidine salt.

[0030] The guanidine salt is a salt compound generated by the reaction of guanidine with acid, and is preferably hydrochloride of guanidine, nitrate of guanidine, sulfate of guanidine or carbonate of guanidine. The hydrochloride of guanidine is preferably aminoguanidine hydrochloride, 1,3-diaminoguanidine hydrochloride or 1-methylguanidine hydrochloride. The sulfate of guanidine is preferably 1,3-diphenylguanidine sulfate or 1-(4-aminobutyl)guanidine sulfate. The carbonate of guanidine is preferably 4-chlorophenylguanidine carbonate or phenylguanidine carbonate.

[0031] The mass ratio of the activated carbon to the guanidine salt is preferably (3-22):1, and more preferably (4-21):1, for example, 10:1, 20:1, 6.67:1 or 5:1.

[0032] In the present application, the microwave reaction is preferably further added with potassium carbonate.

[0033] The mass ratio of the activated carbon to the potassium carbonate is preferably (5-15):1, for example, 10:1.

[0034] In the present application, when the microwave reaction is further added with guanidine salt and potassium carbonate, the guanidine salt, potassium carbonate and solvent are preferably mixed, stirred, cooled and then added with activated carbon. The temperature of the mixing and stirring is 50-70℃, for example, 60℃. The time of the mixing and stirring is 0.5-1.5h, for example, 1h. The endpoint of the cooling can be room temperature, which is generally 20-30℃.

[0035] The present application further provides a modified activated carbon prepared by the preparation method of the modified activated carbon as described above.

[0036] In the present application, the specific surface area of the modified activated carbon can be 1750-2000m 2 / g, for example, 1784.3, 1878.3, 1834.2, 1798.3, 1794.1, 1884.5 or 1939.4m 2 / g.

[0037] In the present application, the micropore volume of the modified activated carbon can be 0.5-0.9cm 3 / g, for example, 0.579, 0.606, 0.583, 0.588, 0.563, 0.598 or 0.637cm 3Micropore pore volume refers to the volume of pores with a pore size of less than 2 nm per unit mass of modified activated carbon.

[0038] In the present application, the micropore ratio of the modified activated carbon can be 78%-86%, such as 79.3%, 81.4%, 78.9%, 79.3%, 79.4%, 81.0% or 84.6%. The micropore ratio represents the volume of pores with a pore size of less than 2 nm per unit mass of modified activated carbon, which accounts for a percentage of the total pore volume of the modified activated carbon.

[0039] In the present application, the mesopore ratio of the modified activated carbon can be 10%-25%, such as 20.38%, 20.25%, 17.25%, 19.10%, 19.38%, 18.5% or 14.9%. The mesopore ratio represents the volume of pores with a pore size of greater than 2.5 nm and less than 50 nm per unit mass of modified activated carbon, which accounts for a percentage of the total pore volume of the modified activated carbon.

[0040] In the present application, the macropore ratio of the modified activated carbon can be 0.2%-2.3%, such as 1.32%, 1.35%, 0.35%, 2.00% or 0.50%. The macropore ratio represents the volume of pores with a pore size of greater than 50 nm per unit mass of modified activated carbon, which accounts for a percentage of the total pore volume of the modified activated carbon.

[0041] In the present application, the guanidine group content of the modified activated carbon can be 0-0.12, such as 0.04, 0.06, 0.09, 0.10, 0.07 or 0.08.

[0042] In the present application, the amino group content of the modified activated carbon can be 0-3.00, such as 1.53, 1.75, 2.08, 2.46, 2.03 or 2.57.

[0043] In the present application, the nitrogen content of the modified activated carbon can be 0.10%-7.00%, such as 0.36%, 4.35%, 5.14%, 5.84%, 6.63%, 4.84% or 5.52%. The nitrogen content represents the mass percentage of nitrogen elements in the mass of the modified activated carbon.

[0044] The present application provides a preparation method of a silicon-carbon composite material, which comprises the following steps: carrying out gas phase deposition on the modified activated carbon as described above and silane to obtain a silicon-carbon composite material.

[0045] In the present application, the equipment for gas phase deposition can be conventional in the art, such as a fluidized bed.

[0046] In the present application, the temperature for gas phase deposition can be 400-600℃, such as 500℃.

[0047] In the present application, the time for vapor deposition can be 300-400 min, for example 330 min.

[0048] In the present application, the rate for increasing temperature from room temperature to the temperature for vapor deposition can be 2-4℃ / min, for example 3℃ / min.

[0049] In the present application, the mass-volume ratio of the modified activated carbon and the silane can be 1 kg: (3000-12000) L, for example 1 kg: 6000 L or 1 kg: 6600 L.

[0050] In the present application, after the modified activated carbon and the silane are subjected to vapor deposition to obtain a silane composite material A, a step of coating with a MXene material or carbon is preferably further included.

[0051] When the MXene material is used for coating, the mass ratio of the silane composite material A to the MXene material can be 1: (0.2-0.8), for example 1:0.4 or 1:0.6.

[0052] Before the MXene material is coated, the silane composite material A and the MXene material are preferably subjected to ball milling. The rotation speed during the ball milling can be 500-700 rpm, for example 600 rpm. The ball-to-material ratio can be (20-30):1, for example 25:1. The time for ball milling can be 40-56 h, for example 48 h. The ball milling is preferably performed in a ball milling tank. The ball milling generally involves adding ball beads. The material of the ball milling tank and the ball beads is preferably natural agate. The diameter of the ball beads can be 6-8 nm.

[0053] The source of the MXene material can be commercially available or prepared by a method conventional in the art, and is preferably prepared by the following method: etching the aluminum layer in Ti3AlC2.

[0054] The particle size of the Ti3AlC2 can be 300-500 mesh, for example 400 mesh.

[0055] The etching solution for etching is preferably an acid solution of sodium fluoride. The acid solution is preferably an aqueous solution of an inorganic acid, for example an aqueous solution of hydrochloric acid. The molar concentration of the acid solution can be 8-10 M, for example 9 M. In the acid solution of sodium fluoride, the ratio of sodium fluoride to acid can be 1 g: (0.2-0.25) mol, for example 1 g:0.225 mol.

[0056] The mass ratio of the Ti3AlC2 to the sodium fluoride can be 1: (1-3), for example 1:2.

[0057] The etching is preferably performed under water bath conditions. The etching temperature can be 30-60°C, for example, 40 or 60°C. The etching time can be 40-56 hours, for example, 48 hours.

[0058] The etching process preferably includes a centrifugation step. The centrifugation speed can be 3000-4000 rpm, for example, 3500 rpm.

[0059] When using MXene material for coating, the coating method is preferably vapor deposition. The coating is preferably performed under an inert atmosphere, preferably nitrogen.

[0060] When MXene material is used for coating, the coating temperature can be 400-600℃, for example, 500℃. The rate of heating from room temperature to the coating temperature can be 4-6℃ / min, for example, 5℃ / min. The coating time can be 1-3 hours, for example, 2 hours.

[0061] When carbon coating is used, the coating method is preferably gas-phase coating. The carbon source for gas-phase coating can be a conventional gaseous carbon source in the art, preferably acetylene. Preferably, a carrier gas is also introduced into the gaseous carbon source. The carrier gas is preferably nitrogen. The volume ratio of the gaseous carbon source to the carrier gas can be (1-3):1, for example, 2:1. The mass-to-volume ratio of the silicon-carbon composite material to the carbon source can be 1g:(1000-2000)L, for example, 1g:1440L. The carbon coating temperature can be 500-560℃, for example, 560℃. The carbon coating time can be 10-14h, for example, 12h. The rate of heating from room temperature to the carbon coating temperature can be 2-4℃ / min, for example, 3℃ / min.

[0062] This invention provides a silicon-carbon composite material, which is prepared by the silicon-carbon composite material preparation method described above.

[0063] In this invention, the yield of the silane composite material can be 24%-32%, for example 30%, 29%, 28%, 27% or 26%.

[0064] In this invention, the specific surface area of ​​the silane composite material can be 4.0-5.4 m². 2 / g, for example 4.1, 4.2, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1 or 5.3m 2 / g.

[0065] In this invention, the D50 of the silane composite material can be 7.5-8.7 μm, for example 8.6, 8.5, 8.4, 8.3, 8.0, 7.9 or 7.8 μm.

[0066] In the present application, the interlayer spacing of the silane composite material can be 0.2-0.4, for example, 0.301, 0.299, 0.298, 0.296, 0.293, 0.291, 0.287, 0.285, 0.283, 0.279, 0.269 or 0.267.

[0067] In the present application, the micropore volume of the silane composite material can be 0.4-0.8 cm 3 / g, for example, 0.749, 0.747, 0.746, 0.692, 0.672, 0.678, 0.648, 0.618, 0.616, 0.608, 0.593, 0.579, 0.511 or 0.496. The micropore volume refers to the volume of pores with a pore size less than 2 nm per unit mass of the silane composite material.

[0068] The present application also provides a pole piece comprising the silicon-carbon composite material as described above.

[0069] In the present application, preferably, the pole piece is a negative pole piece.

[0070] The present application also provides the use of the pole piece as described above in an electrochemical device.

[0071] The present application also provides an electrochemical device comprising the pole piece as described above.

[0072] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0073] The reagents and raw materials used in the present application are commercially available.

[0074] The positive progress effect of the present application is that:

[0075] The modified porous activated carbon prepared in the present application has a large micropore volume. The battery assembled from the silicon-carbon composite material prepared from the activated carbon can achieve a good capacity performance while maintaining a good initial coulombic efficiency and a small expansion, which can greatly meet the commercial application level. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 Scanning electron microscope image of the silicon-carbon composite material obtained in Example 6.

[0077] Figure 2 First charge-discharge curve of the silicon-carbon composite material obtained in Example 6. DETAILED DESCRIPTION

[0078] The application will be further described in the following by way of examples without thereby limiting the application to the examples described. The experimental methods in the following examples, for which no specific conditions are indicated, are carried out according to conventional methods and conditions, or according to the instructions of the commercial suppliers.

[0079] Example 1

[0080] (1) Phenolic resin (phenolic resin type 2123, purchased from Shandong Jiaqi Chemical Co., Ltd.) was pre-oxidized at 130℃ for 2h in air atmosphere, carbonized at 550℃ for 1h in nitrogen atmosphere (gas flow rate was 20mL / min), the rate of temperature rise from pre-oxidation temperature to carbonization temperature was 4℃ / min, after cooling to room temperature, the particles were ground and sieved to obtain the particles below 60 mesh and above 80 mesh, then the particles were activated by steam at 650℃ (the rate of temperature rise from room temperature to activation temperature was 3℃ / min) for 1h in nitrogen atmosphere (gas flow rate was 20mL / min), to obtain activated carbon. The specific surface area of the activated carbon obtained was 1100-1150m 2 / g, and the micropore volume was 300-360mm 3 / g.

[0081] (2) The activated carbon was washed with distilled water to remove inorganic impurities on the surface, then washed with 2% nitric acid aqueous solution to remove organic impurities on the surface, and then washed with distilled water until neutral, and dried in an oven at 120℃. 5g of 1,3-diamino guanidine hydrochloride, 10g of potassium carbonate and 300mL of n-butanol were added into a three-necked flask, heated to 60℃, and stirred electromagnetically for 1h. After cooling to room temperature, 100g of activated carbon was added and stirred uniformly, and then transferred into a microwave reactor, the microwave frequency was fixed at 700W, and the reaction was carried out at 80℃ for 20min. After natural cooling to room temperature, the precipitate was collected and washed by centrifugation with deionized water, and dried in a constant temperature drying box at 60℃ for 24h to obtain modified activated carbon.

[0082] (3) 1kg of modified activated carbon was placed in a fluidized bed, heated from room temperature to 500℃ at a rate of 3℃ / min, and then silane was introduced, the flow rate of silane was 20L / min, and the introduction time was 330min, so that silicon was deposited into the modified activated carbon, and the silicon-carbon composite material was obtained after natural cooling to room temperature. The mass-volume ratio of the modified activated carbon and the silane was 1kg:6600L.

[0083] The yield of the silicon-carbon composite material was 29%, the specific surface area was 5.1m 2 / g, and the D50 was 8.5μm; the capacity of the assembled battery was 1900.8mAh / g at a current density of 0.1C, and the coulombic efficiency was 89.8%.

[0084] Example 2

[0085] The difference from Example 1 is only that the mass of 1,3-diaminoguanidine hydrochloride in step (2) is 10 g.

[0086] Example 3

[0087] The difference from Example 1 is only that the mass of 1,3-diaminoguanidine hydrochloride in step (2) is 15 g.

[0088] Example 4

[0089] The difference from Example 1 is only that the mass of 1,3-diaminoguanidine hydrochloride in step (2) is 20 g.

[0090] Example 5

[0091] The difference from Example 2 is only that after step (3), the following step is further included:

[0092] (4) Ti3AlC2 Mxene material is prepared by in-situ etching method. 20 g of NaF is uniformly mixed with 500 mL of 9M hydrochloric acid aqueous solution and stirred for 20 min. 10 g of Ti3AlC2 powder (400 mesh) is added and stirred at 60°C water bath for 48 h to etch off the aluminum layer, and washed repeatedly by centrifugation with deionized water at 3500 rpm. Add appropriate amount of deionized water to re-disperse the bottom precipitate, shake for 5 min to separate the Mxene, then vacuum filter to obtain single-layer Ti3C2 Mxene nanosheet, and dry in a freeze-drying box to obtain Mxene material.

[0093] (5) 10 g of silicon-carbon composite material prepared in step (3) and 2 g of Mxene material obtained in step (4) are placed into a ball mill tank, and mechanical grinding is performed for 48 hours, the running speed of the ball mill is 600 rpm / min, the ball-to-material ratio is 25:1, and the ball and the tank are made of natural agate, the diameter of the agate ball is 6-8 nm. Finally, the obtained powder is placed into a CVD, coated for 2 h at 500°C under nitrogen atmosphere at a heating rate of 5°C / min, to obtain a silicon-carbon composite material.

[0094] The yield of the silicon-carbon composite material is 29%, the specific surface area is 4.0 m 2 / g, and the D50 is 8.4 μm; the assembled battery has a capacity of 2116.6 mAh / g at a current density of 0.1C and a coulombic efficiency of 91.2%.

[0095] Example 6

[0096] The difference from Example 5 is only that the mass of 1,3-diaminoguanidine hydrochloride in step (2) is 10 g; and the mass of Mxene material in step (5) is 4 g.

[0097] Example 7

[0098] The difference from Example 5 is only that the mass of 1,3-diaminoguanidine hydrochloride in step (2) is 10 g; the mass of Mxene material in step (5) is 6 g.

[0099] Example 8

[0100] The difference from Example 7 is only that the mass of Mxene material in step (5) is 8 g.

[0101] Example 9

[0102] The difference from Example 7 is only that the mass of Mxene material in step (5) is 4 g, and the coating temperature is 400℃.

[0103] Example 10

[0104] The difference from Example 6 is only that the mass of Mxene material in step (5) is 4 g, and the coating temperature is 600℃.

[0105] Example 11

[0106] The difference from Example 6 is only that step (4) and step (5) are replaced by the following steps: the silicon-carbon composite material (10 g) prepared in step (3) is placed in a rotary furnace, acetylene and nitrogen gas (the gas flow rates of acetylene and nitrogen are 20 L / min and 10 L / min, respectively) are introduced, the temperature is raised to 530℃ at a heating rate of 3℃ / min, and the carbon layer is deposited to the surface by coating for 12 h to obtain a silicon-carbon composite material.

[0107] The yield of the silicon-carbon composite material is 27%, the specific surface area is 4.6 m 2 / g, and the D50 is 8.3 μm; the capacity of the assembled battery is 2015 mAh / g at a current density of 0.1C, and the coulombic efficiency is 90.3%.

[0108] Example 12

[0109] The difference from Example 6 is only that the time for introducing silane in step (3) is 300 min.

[0110] Example 13

[0111] The difference from Example 6 is only that the microwave reaction time in step (2) is 10 min.

[0112] Example 14

[0113] The difference from Example 6 is only that the microwave reaction temperature in step (2) is 40 min.

[0114] Example 15

[0115] (1) The phenolic resin (phenolic resin type 2123, purchased from Shandong Jiaqi Chemical Co., Ltd.) was pre-oxidized at 130°C for 2h in an air atmosphere, carbonized at 550°C for 1h under a nitrogen atmosphere (gas flow rate was 20mL / min), the rate of temperature rise from the pre-oxidation temperature to the carbonization temperature was 4°C / min, after cooling to room temperature, the particles were ground and sieved to obtain particles below 60 mesh and above 80 mesh, then the particles were activated by steam at 650°C (the rate of temperature rise from room temperature to the activation temperature was 3°C / min) for 1h under a nitrogen atmosphere (gas flow rate was 20mL / min) to obtain activated carbon. The specific surface area of the activated carbon obtained was 1100-1150m 2 / g, the micropore volume was 300-360mm 3 / g.

[0116] (2) The activated carbon was washed with distilled water to remove inorganic impurities on the surface, then washed with a 2% nitric acid aqueous solution to remove organic impurities on the surface, and then washed with distilled water until neutral, and dried in an oven at 120°C. 100g of activated carbon and 300mL of n-butanol were added to a three-necked flask, heated to 60°C, and stirred electromagnetically for 1 hour. After cooling to room temperature, 100g of activated carbon was added and stirred uniformly, then transferred to a microwave reactor, the microwave frequency was fixed at 700W, and the reaction was carried out at 80°C for 20min. After natural cooling to room temperature, centrifugal washing with deionized water was performed, and the precipitate was collected and dried in a constant temperature drying box at 60°C for 24h to obtain modified activated carbon.

[0117] Comparative Example 1

[0118] The difference from Example 1 is only that step (2) is omitted, and the yield of the silicon-carbon composite material is 29%, the specific surface area is 4.4m 2 / g, D50 is 8.5μm; the capacity of the assembled battery is 1818.2mAh / g at a current density of 0.1C, and the coulombic efficiency is 88.6%.

[0119] Effect Example 1

[0120] The modified activated carbon prepared in the examples and comparative examples was tested for specific surface area, micropore volume, micropore, mesopore and macropore ratio, guanidine group content, amino group content and nitrogen content.

[0121] The test method for specific surface area is as follows: 0.1g of the modified activated carbon prepared in the above examples and comparative examples was weighed using weighing paper, and nitrogen adsorption-desorption test was performed in an ASAP2460 adsorption-desorption instrument of Micromeritics, wherein the degassing temperature was 300°C, the degassing time was 4h, and the adsorption atmosphere was nitrogen.

[0122] The test method of the micropore volume is as follows: a specific surface area and pore size micropore analyzer is used for testing, a nitrogen adsorption method is adopted, nitrogen molecules are physically adsorbed on the surface of the modified activated carbon under low-temperature conditions, the nitrogen adsorption amount under different pressures is measured, a nitrogen adsorption isotherm is drawn, and the pore volume of the modified activated carbon in the micropore filling process can be obtained by combining a theoretical model (BET model, BJH model).

[0123] The test method of the micropore, mesopore and macropore ratio is as follows: a nitrogen adsorption method is adopted, and the adsorption layer formed by nitrogen on the surface of a solid is used to judge the pore size and pore volume. The modified activated carbon is placed in a nitrogen adsorption instrument, nitrogen is introduced at 300 DEG C to be adsorbed on the surface of the sample, the nitrogen pressure change before and after adsorption can obtain the adsorption amount and adsorption isotherm, and the pore size distribution is analyzed.

[0124] The test method of the guanidine group content is as follows: a mass spectrometry method is adopted to measure the mass-to-charge ratio of the modified activated carbon. The modified activated carbon prepared in the examples and the comparative examples is washed with deionized water for 10 minutes, after removing the surface floating and soluble impurities, grinding and drying are performed to obtain a modified activated carbon form suitable for mass spectrometry analysis, and then the modified activated carbon is injected into a mass spectrometer for analysis. After the modified activated carbon is ionized into ions, the ions are deflected or separated in an electric field or a magnetic field, the mass-to-charge ratio and abundance information of the modified activated carbon are determined according to a mass spectrum, and the guanidine group content is calculated by comparing a standard spectrum or a database.

[0125] The test method of the amino group content is as follows: the modified activated carbon prepared in the examples and the comparative examples is dissolved in deionized water, and titration is performed using a potentiometric titrator. The potential change in the titration process is measured and recorded by the potentiometric titrator, and the amino group content is calculated according to the titration curve.

[0126] The test method of the nitrogen content is as follows: an elemental analyzer is used to measure the nitrogen element content in the modified activated carbon.

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130] Effect Example 2

[0131] Figure 1 The SEM image of the silicon-carbon composite material obtained in Example 6 is shown in FIG. 1. Figure 1 As can be seen, the modified activated carbon is obtained by modifying the phenolic resin with 1,3-diamino guanidine hydrochloride, the modified activated carbon is adsorbed with silane to form block-shaped particles, and then the Mxene material is coated to form a lamellar structure on the surface. The finally obtained silicon-carbon composite material is a block-shaped particle with a lamellar structure on the surface.

[0132] The yield of the silicon-carbon composite material obtained in the above examples and comparative examples was tested, and the yield was the percentage of the mass of the obtained silicon-carbon composite material divided by the mass of the phenolic resin in step (1).

[0133] The specific surface area of the silicon-carbon composite material obtained in the above examples and comparative examples was tested by using an ASAP2460 adsorption and desorption instrument of Micromeritics. The test method was as follows: 0.1 g of the silicon-carbon composite material obtained in the above examples and comparative examples was weighed by using a weighing paper for nitrogen adsorption and desorption test, wherein the degassing temperature was 300°C, the degassing time was 4 h, and the adsorption atmosphere was nitrogen.

[0134] The D50 particle size of the silicon-carbon composite material obtained in the above examples and comparative examples was tested by using a Malvern 3000 laser particle size instrument.

[0135] The test method for obtaining the interlayer spacing by using XRD test was as follows: first, the silicon-carbon composite material obtained in the above examples and comparative examples was laid flat on the surface of a glass slide, and another glass slide was used for flattening treatment, and then a D8DISCOVER instrument of Bruker was used for powder XRD test, the test range was 10-70°, and the scanning speed was 5° / min. The angle corresponding to the 002 peak in the XRD spectrum was 2θ, and then the Bragg equation 2dsinθ = λ was used to calculate the interlayer spacing d of the sample; wherein λ represented the wavelength of incident X-ray, and θ was the included angle between the incident line and the reflected line and the reflected crystal face.

[0136] The test method for micropore volume was as follows: a specific surface area and pore size micropore analyzer was used for testing, nitrogen adsorption method was used, nitrogen molecules were physically adsorbed on the surface of the silicon-carbon composite material under low temperature conditions, the nitrogen adsorption amount under different pressures was measured, the nitrogen adsorption isotherm was drawn, and the pore volume of the silicon-carbon composite material in the micropore filling process could be obtained by combining the theoretical model (BET model, BJH model).

[0137] The above test results are shown in Table 2.

[0138] Table 2

[0139]

[0140] The silicon-carbon composite material prepared in the above examples and comparative examples was tested for nitrogen content, oxygen content, silicon content, carbon content and silicon nanoparticle particle size.

[0141] The test results are shown in Table 3.

[0142] Table 3

[0143]

[0144] Example 3

[0145] The silicon-carbon composite materials prepared in the above examples and comparative examples were assembled into half-cells as anode materials and lithium metal pieces, respectively, and tested. The electrolyte was a 1 M NaFP6 solution (solvent: Diglyme), and the separator was a glass fiber (GF / A). The assembled half-cells were tested for charge-discharge cycling at a temperature of 25°C and a current density of 0.1C using a blue electric tester to obtain data for reversible specific capacity and initial coulombic efficiency.

[0146] The expansion test method was as follows: 7.5 g of conductive graphite (SFG-6), 2.5 g of conductive carbon black (SP), and 33.3 g of aqueous binder (LA132) were added to 120 g of water, and the stirring speed of the disperser was set to 2000 rpm / min. The mixture was stirred for 0.5 h, and then 35 g of the silicon-carbon composite material was added and stirring was continued for 2.5 h to obtain a slurry. The prepared slurry was uniformly coated on a metal foil (aluminum foil for the positive electrode and copper foil for the negative electrode) to form a thin film. After coating, the surface was allowed to stand until no obvious solvent was present, and then the coated foil was placed in a vacuum drying oven for drying. To ensure that the electrode sheet coating reached a certain thickness, a special coating thickness adjusting roller and a reverse roller were used to ensure the uniformity and thickness of the coating. The dried electrode sheet was cut into a specified size using a roll cutter to obtain an electrode sheet, and the thickness of the electrode sheet was tested to be H1. A 1 M LiPF6 solution (solvent: EC (ethylene carbonate): EMC (ethyl methyl carbonate) volume ratio = 3:7 and 10% FEC (fluoroethylene carbonate)) was used as the electrolyte, a Celgard 2400 film was used as the separator, and a lithium sheet was used as the counter electrode. In a vacuum glove box [w(H2O) < 0.1 x 10 -4 % and w(O2) < 0.1 x 10 -4 %], a CR2025 button-type half-cell was assembled, and was subjected to discharge-charge-discharge. Discharge: 0.1C to 0.01V, rest for 10 min, charge: 0.1C to 1.5V. The cell was disassembled, and the thickness of the electrode sheet H2 was tested. The expansion rate = (H2-H1) / H1 x 100%.

[0147] The results are shown in Table 4 and Figure 2 .

[0148] Table 4

[0149]

[0150] Based on the above examples and comparative examples, it can be seen that examples 1 to 4 are 1,3-diamine guanidine hydrochloride modified silicon-carbon composite materials, examples 5 to 10 are 1,3-diamine guanidine hydrochloride modified silicon-carbon composite materials coated with Mxene. Comparative example 1 is a silicon-carbon composite material without 1,3-diamine guanidine hydrochloride modification, and example 11 is a 1,3-diamine guanidine hydrochloride modified silicon-carbon composite material coated with a carbon layer by CVD method.

[0151] From table 2 and table 4, first of all, the specific surface area of the activated carbon after modification by 1,3-diamine guanidine hydrochloride will increase, and the micropore volume will also increase, and the mass of 1,3-diamine guanidine hydrochloride added should not be too low or too high, when the mass of 1,3-diamine guanidine hydrochloride added is 10g, the specific surface area and micropore volume increase more, and the electrochemical performance is the best. If the mass of 1,3-diamine guanidine hydrochloride is too low, the degree of modification of the surface functional groups of the activated carbon is low, and the influence of the micropore ratio is small. If the mass of 1,3-diamine guanidine hydrochloride is too high, the modification process is more intense, and the porosity is greatly reduced. Secondly, the present application uses a microwave method to modify activated carbon, and under the action of microwaves, activated carbon can produce a large number of micropores, which is beneficial to the production of activated carbon with rich micropores. In addition, the microwave reaction time is rapid and uniform, which can quickly and uniformly modify 1,3-diamine guanidine hydrochloride on the surface of activated carbon. The fluidized bed process provides good gas-solid mass transfer conditions, allowing silane to quickly and uniformly deposit on porous carbon, thereby effectively improving the capacity of the silicon-carbon negative electrode. Finally, in order to further buffer the volume expansion of the silicon-carbon negative electrode and improve the conductivity, the technical scheme uses a ball milling assembly process to wrap Mxene material on the surface of the silicon-carbon negative electrode, which effectively buffers the volume expansion and yield of the silicon-carbon negative electrode material during the cyclic charging and discharging process, and also greatly improves the electronic conductivity of the material, allowing electrons and lithium ions to be transmitted more quickly, thereby improving the capacity of the electrode material. As can be seen, the activated carbon modification method provided by the present application can well improve the surface functional groups, pore structure and later adsorption of silane of activated carbon, and the Mxene material coating process improves the conductivity of the material, buffers the volume expansion of the electrode material, and can well improve the electrochemical lithium storage performance of the silicon-carbon material.

[0152] Figure 2 The first charge-discharge curve of the battery assembled with the silicon-carbon composite material prepared in example 6 under 0.1C condition. From the figure, it can be seen that the initial discharge capacity of the battery is 1430mAh / g, and the initial charge capacity is 1370mAh / g, which is a good result. Figure 2It can be seen that the voltage slope of the battery assembled by the silicon-carbon composite material appears at about 0.7 V in the first discharge, which corresponds to the process of forming a solid electrolyte interface film (SEI) on the surface of the electrode by first lithium intercalation; a long voltage platform appears at about 0.1 V, which corresponds to the process of generating lithium-silicon alloy (LixSi) by the reaction of lithium and silicon; the charging voltage platform at about 0.4 V corresponds to the process of delithiation of LixSi alloy. The first discharge and charge capacities of the battery assembled by the silicon-carbon composite material are 2239.6 mAh / g and 2431.7 mAh / g, respectively, and the coulombic efficiency is 92.1%. The irreversible capacity loss in the first cycle is mainly due to the consumption of the lithium content in the electrolyte by the generation of SEI film on the surface of the electrode material. The long platform area further indicates that the silicon-carbon composite material has stronger intercalation and deintercalation capacity.

Claims

1. A method for preparing modified activated carbon, characterized in that, It includes the following steps: Modified activated carbon is obtained by microwave reaction of activated carbon and solvent; the microwave power during the microwave reaction is 600-800W; the microwave reaction time is 10-40min. Guanidine salt is also added during the microwave reaction; the mass ratio of activated carbon to guanidine salt is (3-22):1; Potassium carbonate is also added during the microwave reaction; the mass ratio of activated carbon to potassium carbonate is (5-15):

1. The modified activated carbon has a specific surface area of ​​1750-2000 m². 2 / g, wherein the mesoporous content of the modified activated carbon is 10%-25%.

2. The method for preparing modified activated carbon as described in claim 1, characterized in that, The method for preparing the modified activated carbon satisfies one or more of the following conditions: (1) The specific surface area of ​​the activated carbon is 1100-1150 m². 2 / g; (2) The micropore volume of the activated carbon is 300-360 mm. 3 / g; (3) The activated carbon is prepared by the following method: pre-oxidizing, carbonizing and activating phenolic resin, wherein the temperature of the pre-oxidation, carbonization and activation is increased sequentially; (4) The solvent is water or an alcohol solvent; (5) The mass-to-volume ratio of the activated carbon to the solvent is 1 g: (1-5) mL; (6) The microwave power during the microwave reaction is 650-750W; (7) The temperature of the microwave reaction is 60-90℃; and, (8) The microwave reaction time is 20-30 min.

3. The method for preparing modified activated carbon as described in claim 2, characterized in that, The method for preparing the modified activated carbon satisfies one or more of the following conditions: (1) The alcohol solvent is one or more of isopropanol, ethylene glycol, propylene glycol and n-butanol; (2) The mass-to-volume ratio of the activated carbon to the solvent is 1 g: (2-4) mL; (3) The microwave power during the microwave reaction is 700W; (4) The temperature of the microwave reaction is 80℃; and, (5) The microwave reaction time is 25 min.

4. The method for preparing modified activated carbon as described in claim 3, characterized in that, The method for preparing the modified activated carbon satisfies one or two of the following conditions: (1) The alcohol solvent is n-butanol; and, (2) The mass-volume ratio of the activated carbon to the solvent is 1g:3mL.

5. The method for preparing modified activated carbon as described in claim 2, characterized in that, The pre-oxidation temperature is 120-140℃.

6. The method for preparing modified activated carbon as described in claim 5, characterized in that, The pre-oxidation temperature is 130°C.

7. The method for preparing modified activated carbon as described in claim 2, characterized in that, The pre-oxidation time is 1-3 hours.

8. The method for preparing modified activated carbon as described in claim 7, characterized in that, The pre-oxidation time is 2 hours.

9. The method for preparing modified activated carbon as described in claim 2, characterized in that, The pre-oxidation is carried out in an air or oxygen atmosphere.

10. The method for preparing modified activated carbon as described in claim 2, characterized in that, The carbonization is carried out under an inert atmosphere.

11. The method for preparing modified activated carbon as described in claim 10, characterized in that, The inert atmosphere is nitrogen.

12. The method for preparing modified activated carbon as described in claim 10, characterized in that, The inert atmosphere has a gas flow rate of 10-30 mL / min.

13. The method for preparing modified activated carbon as described in claim 12, characterized in that, The inert atmosphere has a gas flow rate of 20 mL / min.

14. The method for preparing modified activated carbon as described in claim 2, characterized in that, The carbonization temperature is 500-600℃.

15. The method for preparing modified activated carbon as described in claim 14, characterized in that, The carbonization temperature is 550°C.

16. The method for preparing modified activated carbon as described in claim 2, characterized in that, The carbonization time is 0.5-1.5 hours.

17. The method for preparing modified activated carbon as described in claim 16, characterized in that, The carbonization time is 1 hour.

18. The method for preparing modified activated carbon as described in claim 2, characterized in that, The rate of heating from the pre-oxidation temperature to the carbonization temperature is 3-5 °C / min.

19. The method for preparing modified activated carbon as described in claim 18, characterized in that, The rate of heating from the pre-oxidation temperature to the carbonization temperature is 4 °C / min.

20. The method for preparing modified activated carbon as described in claim 2, characterized in that, The activation is carried out under an inert atmosphere.

21. The method for preparing modified activated carbon as described in claim 20, characterized in that, The inert atmosphere is nitrogen.

22. The method for preparing modified activated carbon as described in claim 20, characterized in that, The inert atmosphere has a gas flow rate of 10-30 mL / min.

23. The method for preparing modified activated carbon as described in claim 22, characterized in that, The inert atmosphere has a gas flow rate of 20 mL / min.

24. The method for preparing modified activated carbon as described in claim 2, characterized in that, The activation temperature is 600-700℃.

25. The method for preparing modified activated carbon as described in claim 24, characterized in that, The activation temperature is 650°C.

26. The method for preparing modified activated carbon as described in claim 2, characterized in that, The activation time is 0.5-1.5 hours.

27. The method for preparing modified activated carbon as described in claim 26, characterized in that, The activation time is 1 hour.

28. The method for preparing modified activated carbon as described in claim 2, characterized in that, The rate of heating from room temperature to the activation temperature is 2-4 °C / min.

29. The method for preparing modified activated carbon as described in claim 28, characterized in that, The rate of heating from room temperature to the activation temperature is 3 °C / min.

30. The method for preparing modified activated carbon as described in claim 2, characterized in that, The activating atmosphere is water vapor.

31. The method for preparing modified activated carbon as described in claim 1, characterized in that, The guanidine salt is a guanidine hydrochloride, a guanidine nitrate, a guanidine sulfate, or a guanidine carbonate.

32. The method for preparing modified activated carbon as described in claim 31, characterized in that, The guanidine hydrochloride is aminoguanidine hydrochloride, 1,3-diaminoguanidine hydrochloride, or 1-methylguanidine hydrochloride.

33. The method for preparing modified activated carbon as described in claim 31, characterized in that, The sulfate of the guanidine is 1,3-diphenylguanidine sulfate or 1-(4-aminobutyl)guanidine sulfate.

34. The method for preparing modified activated carbon as described in claim 31, characterized in that, The guanidine carbonate is 4-chlorophenylguanidine carbonate or phenylguanidine carbonate.

35. The method for preparing modified activated carbon as described in claim 1, characterized in that, The mass ratio of the activated carbon to the guanidine salt is (4-21):

1.

36. The method for preparing modified activated carbon as described in claim 35, characterized in that, The mass ratio of the activated carbon to the guanidine salt is 10:1, 20:1, 6.67:1, or 5:

1.

37. The method for preparing modified activated carbon according to claim 1, characterized in that, The mass ratio of the activated carbon to the potassium carbonate is 10:

1.

38. A modified activated carbon, characterized in that, It is prepared by the method of any one of claims 1-37 for the preparation of modified activated carbon.

39. The modified activated carbon according to claim 38, characterized in that, The modified activated carbon has a specific surface area of ​​1784.3 m². 2 / g、1878.3 m 2 / g, 1834.2 m 2 / g, 1798.3 m 2 / g, 1794.1 m 2 / g, 1884.5 m 2 / g or 1939.4m 2 / g.

40. The modified activated carbon according to claim 38, characterized in that, The modified activated carbon has a micropore volume of 0.5-0.9 cm³. 3 / g.

41. The modified activated carbon according to claim 40, characterized in that, The modified activated carbon has a micropore volume of 0.579 cm³. 3 / g, 0.606 cm 3 / g, 0.583 cm 3 / g, 0.588 cm 3 / g, 0.563 cm 3 / g, 0.598 cm 3 / g or 0.637cm 3 / g.

42. The modified activated carbon according to claim 38, characterized in that, The modified activated carbon has a micropore content of 78%-86%.

43. The modified activated carbon according to claim 42, characterized in that, The modified activated carbon has a micropore content of 79.3%, 81.4%, 78.9%, 79.3%, 79.4%, 81.0%, or 84.6%.

44. The modified activated carbon as described in claim 38, characterized in that, The modified activated carbon has a mesoporous content of 20.38%, 20.25%, 17.25%, 19.10%, 19.38%, 18.5%, or 14.9%.

45. The modified activated carbon as described in claim 38, characterized in that, The modified activated carbon has a macroporous content of 0.2%-2.3%.

46. ​​The modified activated carbon according to claim 45, characterized in that, The modified activated carbon has a macroporous content of 1.32%, 1.35%, 0.35%, 2.00%, or 0.50%.

47. A method for preparing a silicon-carbon composite material, characterized in that, It includes the following steps: performing vapor deposition on the modified activated carbon and silane as described in any one of claims 38-46 to obtain a silicon-carbon composite material.

48. The method for preparing the silicon-carbon composite material as described in claim 47, characterized in that, The preparation method of the silicon-carbon composite material satisfies one or more of the following conditions: (1) The temperature of the vapor deposition is 400-600℃; (2) The vapor deposition time is 300-400 min; (3) The rate of heating from room temperature to the temperature of the vapor deposition is 2-4 °C / min; (4) The mass-to-volume ratio of the modified activated carbon and the silane is 1 kg : (3000-12000) L; and, (5) After obtaining silane composite material A by vapor deposition of the modified activated carbon and silane, the process further includes the step of coating with MXene material or carbon.

49. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, The preparation method of the silicon-carbon composite material satisfies one or more of the following conditions: (1) The temperature of the vapor deposition is 500℃; (2) The vapor deposition time is 330 min; (3) The rate of heating from room temperature to the temperature at which the vapor phase is deposited is 3 °C / min; and, (4) The mass-volume ratio of the modified activated carbon and the silane is 1 kg: 6000 L or 1 kg: 6600 L.

50. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When MXene material is used for coating, the mass ratio of the silane composite material A to the MXene material is 1:(0.2-0.8).

51. The method for preparing the silicon-carbon composite material as described in claim 50, characterized in that, The mass ratio of the silane composite material A to the MXene material is 1:0.4 or 1:0.

6.

52. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When using MXene material for coating, the coating method is vapor deposition.

53. The method for preparing the silicon-carbon composite material as described in claim 52, characterized in that, The coating process is carried out under an inert atmosphere.

54. The method for preparing the silicon-carbon composite material as described in claim 53, characterized in that, The inert atmosphere is nitrogen.

55. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When using MXene material for coating, the coating temperature is 400-600℃.

56. The method for preparing the silicon-carbon composite material as described in claim 55, characterized in that, The temperature during the coating process is 500℃.

57. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When using MXene material for coating, the rate of heating from room temperature to the coating temperature is 4-6 °C / min.

58. The method for preparing the silicon-carbon composite material as described in claim 57, characterized in that, The rate of temperature increase from room temperature to the temperature of the coating is 5°C / min.

59. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When using MXene material for coating, the coating time is 1-3 hours.

60. The method for preparing the silicon-carbon composite material as described in claim 59, characterized in that, The coating time is 2 hours.

61. The method for preparing the silicon-carbon composite material as described in claim 60, characterized in that, When carbon coating is used, the coating method is gas phase coating.

62. The method for preparing the silicon-carbon composite material as described in claim 61, characterized in that, The carbon source for the gas-phase coating is acetylene.

63. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When carbon coating is used, a carrier gas is also introduced when the carbon source is introduced.

64. The method for preparing the silicon-carbon composite material as described in claim 63, characterized in that, The carrier gas is nitrogen.

65. The method for preparing the silicon-carbon composite material as described in claim 64, characterized in that, The volume ratio of the carbon source to the carrier gas is (1-3):

1.

66. The method for preparing the silicon-carbon composite material as described in claim 65, characterized in that, The volume ratio of the carbon source to the carrier gas is 2:

1.

67. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When carbon coating is used, the mass-to-volume ratio of the silicon-carbon composite material to the carbon source used for carbon coating is 1g:(1000-2000)L.

68. The method for preparing the silicon-carbon composite material as described in claim 67, characterized in that, The mass-to-volume ratio of the silicon-carbon composite material to the carbon source is 1g:1440L.

69. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When carbon coating is used, the carbon coating temperature is 500-560℃.

70. The method for preparing the silicon-carbon composite material as described in claim 69, characterized in that, The carbon coating temperature is 560°C.

71. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When carbon coating is used, the carbon coating time is 10-14 hours.

72. The method for preparing the silicon-carbon composite material as described in claim 71, characterized in that, The carbon coating time is 12 hours.

73. The method for preparing the silicon-carbon composite material as described in claim 48, characterized in that, When carbon coating is used, the rate of heating from room temperature to the carbon coating temperature is 2-4℃ / min.

74. The method for preparing the silicon-carbon composite material as described in claim 73, characterized in that, The rate of heating from room temperature to the carbon coating temperature is 3℃ / min.

75. A silicon-carbon composite material, characterized in that, It is prepared by the method for preparing silicon-carbon composite materials as described in any one of claims 47-74.

76. The silicon-carbon composite material as described in claim 75, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 4.0-5.4 m². 2 / g.

77. The silicon-carbon composite material as described in claim 76, characterized in that, The specific surface area of ​​the silicon-carbon composite material is 4.1 m². 2 / g、4.2 m 2 / g、4.6 m 2 / g, 4.7 m 2 / g、4.8 m 2 / g、4.9 m 2 / g, 5.0 m 2 / g, 5.1 m 2 / g or 5.3m 2 / g.

78. The silicon-carbon composite material as described in claim 75, characterized in that, The D50 of the silicon-carbon composite material is 7.5-8.7 μm.

79. The silicon-carbon composite material as described in claim 78, characterized in that, The D50 of the silicon-carbon composite material is 8.6μm, 8.5μm, 8.4μm, 8.3μm, 8.0μm, 7.9μm or 7.8μm.

80. The silicon-carbon composite material as described in claim 75, characterized in that, The micropore volume of the silicon-carbon composite material is 0.4-0.8 cm³. 3 / g.

81. The silicon-carbon composite material as described in claim 80, characterized in that, The micropore volume of the silicon-carbon composite material is 0.749 cm³. 3 / g, 0.747 cm 3 / g, 0.746 cm 3 / g, 0.692 cm 3 / g, 0.672 cm 3 / g, 0.678 cm 3 / g, 0.648cm 3 / g, 0.618 cm 3 / g, 0.616 cm 3 / g, 0.608 cm 3 / g, 0.593 cm 3 / g, 0.579 cm 3 / g, 0.511 cm 3 / g or 0.496 cm 3 / g.

82. An electrode sheet, characterized in that, It includes silicon-carbon composite materials as described in any one of claims 75-81.

83. The application of the electrode as described in claim 82 in an electrochemical device.

84. An electrochemical device, characterized in that, It includes the electrode as described in claim 83.

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