Porous carbon microsphere material, silicon-carbon composite material, and preparation method and application thereof

Abstract

The application discloses a kind of porous carbon microsphere materials, silicon-carbon composite material and its preparation method and application, the preparation method of the porous carbon microsphere includes the following steps: S1: polymer, solvent and conductive carbon black are mixed, and precursor solution is obtained;S2: the precursor solution is prepared into carbon microsphere precursor material using electrostatic spraying method;S3: the carbon microsphere precursor material is sequentially pre-oxidized, heat treated, and spherical carbon material is obtained;S4: the spherical carbon material is supercritical hydrothermal activation, and after processing, porous carbon microsphere material is obtained;The temperature of the activation is 300~600 ℃;The pressure of the activation is 15~30 MPa;The activation time is 0.5~1 h.The porous carbon microsphere prepared by the application has a series of adjustable physical and chemical properties, highly developed pore structure, high mesoporous rate and better mechanical strength, and when further applied to lithium ion battery, it can have low pole piece expansion rate, high initial coulomb efficiency and excellent cycle stability and other characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of porous carbon microsphere material, silicon-carbon composite material and its preparation method and application. BACKGROUND

[0002] Under the background of rapid development of lithium ion battery technology, the performance of negative electrode material becomes the key factor restricting the improvement of battery energy density. Silicon is considered as an ideal negative electrode material due to its extremely high theoretical capacity, however, its significant volume expansion during charge and discharge process will lead to material rupture and poor cycle stability. In order to solve this problem, porous carbon material is considered as an effective way to improve the performance of silicon-based negative electrode due to its excellent electrical conductivity, chemical stability and adjustable pore structure. Porous carbon not only can adapt to the volume change of silicon as a stable buffer framework, but also can provide more active sites and channels, thereby improving the transmission efficiency of electrons and ions. By compounding silicon with porous carbon, the stress concentration of silicon particles can be effectively reduced, the crushing of the material can be inhibited, and the structural stability and cycle life of the composite material can be significantly improved. Therefore, the application of porous carbon in silicon-carbon negative electrode material not only helps to improve the energy density of the battery, but also has important significance for realizing long cycle life of lithium ion battery. Future research will continue to optimize the pore structure and preparation method of porous carbon to further improve the comprehensive performance of silicon-carbon negative electrode and meet the increasing demand for high energy density batteries.

[0003] Chinese patent CN118206115B discloses a high-performance asphalt-based porous carbon material and its preparation method. The precursor is prepared by mixing coal pitch and carbon nanotubes, then pretreated, crushed, added with graphene and dried, pre-oxidized, and carbonized and activated to obtain the final product. Although this method solves the problem of incomplete pre-oxidation of asphalt and improves the carbonization yield, the prepared porous carbon material has a high micropore volume fraction, which is easy to cause pore blockage and is not conducive to the deep deposition of silicon source gas in the chemical vapor deposition process. Chinese patent CN116314734A discloses a preparation method of silicon-carbon composite material, silicon-carbon composite material and its application. The method includes water vapor activation and CO2 activation of graphite paper to prepare modified graphite paper material, then silicon hydride gas and carbon source gas are introduced in the microwave reaction cavity under the action of microwave to obtain silicon-carbon composite material. This preparation method does not use catalyst, which avoids the impurity problem caused by the introduction of catalyst. However, due to the morphology and structure of the activated precursor, the isotropy of the obtained activated material is insufficient, which limits the performance of the material in inhibiting the volume expansion of silicon-based materials during charge and discharge process, and may lead to material pulverization during the cycle process, affecting the cycle stability and service life of the battery. SUMMARY

[0004] The present application aims to solve the problems existing in the above-mentioned scheme, and provides a porous carbon microsphere material, a silicon-carbon composite material, and a preparation method and application thereof. The porous carbon microsphere prepared by the present application has a series of adjustable physical and chemical properties, a highly developed pore structure, a high mesopore rate, and a better mechanical strength, and when further applied to a lithium ion battery, the lithium ion battery has low electrode sheet expansion rate, high initial coulomb efficiency, and excellent cycle stability.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] The present application provides a preparation method of a porous carbon microsphere, which comprises the following steps:

[0007] S1: mixing a polymer, a solvent, and conductive carbon black to obtain a precursor solution;

[0008] S2: preparing the precursor solution into a carbon microsphere precursor material by using an electrostatic spraying method;

[0009] S3: sequentially performing pre-oxidation and heat treatment on the carbon microsphere precursor material to obtain a spherical carbon material;

[0010] S4: performing supercritical hydrothermal activation on the spherical carbon material, and performing post-processing to obtain a porous carbon microsphere material;

[0011] The temperature of the activation is 300-600 DEG C; the pressure of the activation is 15-30 MPa; and the time of the activation is 0.5-1 h.

[0012] In the present application, in step S1, the polymer can include a polymer A and a polymer B; the polymer A and the polymer B are different polymers.

[0013] In some preferred embodiments, in step S1, the polymer A is one of polystyrene, polyacrylonitrile, polydopamine, and poly(aniline-pyrrole) copolymer, for example, polystyrene.

[0014] In the above-mentioned scheme, the weight average molecular weight of the polystyrene is preferably 100000-200000 g / mol, more preferably 130000-170000 g / mol, for example, 150000 g / mol.

[0015] In some preferred embodiments, in step S1, the polymer B is polyvinylpyrrolidone.

[0016] In the above-mentioned scheme, the weight average molecular weight of the polyvinylpyrrolidone is preferably 40000-100000 g / mol, more preferably 40000-70000 g / mol, for example, 60000 g / mol.

[0017] In some preferred embodiments, in step S1, the mass ratio of the polymer A, the polymer B and the conductive carbon black is (4-9):(4-9):(2-5), preferably (5-7):(5-7):(2-4), for example 2:2:1 or 5:5:2.

[0018] In some preferred embodiments, in step S1, the solvent is N,N-dimethylformamide.

[0019] In some preferred embodiments, in step S1, the conductive carbon black is one of Ketjen black, acetylene black and Super P.

[0020] In some preferred embodiments, in step S1, the concentration of the polymer solution is 5-12 wt%, preferably 6-10 wt%, for example 6 wt% or 8 wt%; the concentration of the polymer solution is the percentage of the total mass of the polymer in the mass of the solvent.

[0021] In some preferred embodiments, in step S1, the mixing operation is dissolving the polymers in the solvent, forming a homogeneous polymer solution after magnetic stirring, then adding the conductive carbon black to the polymer solution, and obtaining the precursor solution after ultrasonic dispersion.

[0022] In the above scheme, the speed of the magnetic stirring is preferably 200-350 rpm, for example 300 rpm; the time of the magnetic stirring is preferably 2-6 h, for example 4 h.

[0023] In the above scheme, the time of the ultrasonic dispersion is preferably 1-2 h.

[0024] In some preferred embodiments, in step S1, the mixing operation is dissolving polystyrene and polyvinylpyrrolidone in N,N-dimethylformamide, forming a homogeneous polymer solution after magnetic stirring, then adding conductive carbon black to the polymer solution, and obtaining the precursor solution after ultrasonic dispersion.

[0025] In some preferred embodiments, in step S2, the operation of using the electrostatic spraying method is: injecting the precursor solution prepared in step S1 into a syringe, then fixing the syringe on a microsyringe pump, connecting the positive pole of a high-voltage power supply to the root of the syringe needle, connecting the receiving plate to the ground wire, vertically placing the receiving plate radially and directly below the syringe, adjusting the equipment parameters for electrostatic spraying, and obtaining the carbon microsphere precursor.

[0026] In the above scheme, in step S2, the flow rate of the microsyringe pump is preferably 0.5-1.5 mL / h, for example, 0.6 mL / h or 0.8 mL / h; the voltage of the high-voltage power supply is preferably 15-30 kV, for example, 20 kV or 22 kV; and the receiving distance from the syringe tip to the receiving plate is preferably 12-18 cm, for example, 16 cm.

[0027] In the present application, in step S2, the operating environment temperature of the electrostatic spraying method can be 20-30℃, and the environmental humidity can be 35%-55%.

[0028] In some preferred embodiments, in step S3, the pre-oxidation operation is to dry the carbon microsphere precursor material prepared in step S2 and then transfer it to a muffle furnace for heating in an air atmosphere.

[0029] In the above scheme, in step S3, the drying temperature is preferably 90-160℃, for example, 150℃; and the drying time is preferably 18-36 h, for example, 24 h. The drying is performed to remove the non-volatile solvent in the carbon microsphere precursor material.

[0030] In some preferred embodiments, in step S3, the pre-oxidation temperature is 150-280℃, preferably 170-250℃.

[0031] In some preferred embodiments, in step S3, the pre-oxidation temperature is 150-280℃, preferably 170-250℃.

[0032] In some preferred embodiments, in step S3, the pre-oxidation time is 2-6 h, preferably 2-4 h. The pre-oxidation time is the time for maintaining the temperature after the temperature is raised to the pre-oxidation temperature.

[0033] In the present application, the cross-linking degree of the carbon microsphere precursor material is increased during the pre-oxidation treatment, thereby slowing down the rapid removal of small molecules in the subsequent high-temperature carbonization process and improving the carbon yield of the target product.

[0034] In some preferred embodiments, in step S3, the heat treatment is performed in an inert atmosphere, and the inert atmosphere is at least one or both of nitrogen and argon, for example, nitrogen.

[0035] In some preferred embodiments, in step S3, the heat treatment is performed in a tube-type atmosphere furnace.

[0036] In some preferred embodiments, in step S3, the heat treatment has a temperature rising rate of 5-7℃ / min.

[0037] In some preferred embodiments, in step S3, the temperature of the heat treatment is 500-1200°C, preferably 600-1000°C, for example 900°C.

[0038] In some preferred embodiments, in step S3, the time of the heat treatment is 1-3 h, for example 2 h. The time of the heat treatment is the time of constant temperature preservation after the temperature of the heat treatment is reached.

[0039] In the present application, in step S3, the particle size of the spherical carbon material can be D50<10 μm, D90<20 μm.

[0040] In some preferred embodiments, in step S4, the operation of the supercritical hydrothermal activation is to transfer the spherical carbon material prepared in step S3 into a supercritical water activation reactor, first adjust the preheater to a specified temperature, and then perform hydrothermal activation at a set temperature and pressure in the supercritical water activation reactor to obtain an activated material.

[0041] In some preferred embodiments, in step S4, the water used in the supercritical hydrothermal activation is one of deionized water, ultrapure water and distilled water, preferably deionized water.

[0042] In some preferred embodiments, in step S4, the preheating temperature of the supercritical hydrothermal activation is 100-200°C, for example 150°C.

[0043] In some preferred embodiments, in step S4, the pressure increasing rate of the supercritical hydrothermal activation is 0.8-1.2 MPa / min, for example 1 MPa / min.

[0044] In some preferred embodiments, in step S4, the pressure of the supercritical hydrothermal activation is 15-30 Mpa, for example 20 Mpa or 25 Mpa.

[0045] In some preferred embodiments, in step S4, the temperature increasing rate of the supercritical hydrothermal activation is 25-35°C / min, for example 30°C / min.

[0046] In some preferred embodiments, in step S4, the temperature of the supercritical hydrothermal activation is 300-600°C, for example 500°C.

[0047] In some preferred embodiments, in step S4, the time of the supercritical hydrothermal activation is 30-60 min, for example 45 min. The time of the supercritical hydrothermal activation is the time of constant temperature preservation after the temperature of the supercritical hydrothermal activation is reached.

[0048] In some preferred embodiments, in step S4, the post-treatment operation is to obtain the porous carbon microsphere material by washing and drying the activated material.

[0049] In some more preferred embodiments, in step S4, the washing operation is to sequentially perform acid washing, alkali washing and water washing.

[0050] In the above scheme, in step S4, the acid solution used in the acid washing operation is preferably one of hydrochloric acid, sulfuric acid and nitric acid, for example, hydrochloric acid.

[0051] In the above scheme, in step S4, the concentration of the acid solution used in the acid washing operation is preferably 5-30%, more preferably 10-20%. The concentration of the acid solution is the percentage of the mass of the acid substance to the mass of the acid solution.

[0052] In the present application, the acid washing process is mainly to perform deashing treatment on the material after supercritical hydrothermal activation, further to form pores, so as to improve the adsorption performance of the product. However, excessive acid washing will cause the destruction of the pore structure, affecting the mechanical properties and cycle life of the product.

[0053] In the above scheme, in step S4, the alkali solution used in the alkali washing operation is preferably one of sodium hydroxide, potassium hydroxide and potassium carbonate, for example, sodium hydroxide.

[0054] In the above scheme, in step S4, the concentration of the alkali solution used in the alkali washing operation is preferably 3-10%, for example, 5%. The concentration of the alkali solution is the percentage of the mass of the alkali substance to the mass of the alkali solution.

[0055] In the present application, the alkali washing process is mainly to adjust the pH value of the target product.

[0056] In the above scheme, in step S4, the water washing operation is preferably to adjust the pH value of the object to be washed to 6-8.

[0057] In the above scheme, in step S4, the water washing operation is preferably to use pure water.

[0058] In some more preferred embodiments, in step S4, the drying operation is performed under one of air, nitrogen and argon atmosphere, for example, air.

[0059] In some more preferred embodiments, in step S4, the temperature of the drying operation is preferably 100-170°C, more preferably 100-150°C, for example, 130°C.

[0060] In some more preferred embodiments, in step S4, the time of the drying operation is preferably 2-5 h, more preferably 2-4 h.

[0061] In the present application, the carbonization yield of the porous carbon microspheres can be 45% to 60%, preferably 45% to 55%. The carbonization yield is the percentage of the mass of the spherical carbon material obtained in step S3 to the mass of the carbon microsphere precursor material obtained in step S2.

[0062] The present application provides a porous carbon microsphere prepared by the method for preparing a porous carbon microsphere as described above.

[0063] The present application provides a porous carbon microsphere, wherein the average pore size of the porous carbon microsphere is 2 to 6 nm; the mesopore ratio of the porous carbon microsphere is 40% to 80%; the mesopore volume of the porous carbon microsphere is 0.2 to 0.8 cm 3 / g; the micropore volume of the porous carbon microsphere is 0.3 to 0.6 cm 3 / g; and the compressive strength of the porous carbon microsphere is 4.8 to 8.0 Gpa.

[0064] In the present application, the mesopore ratio is the percentage of the mesopore volume of the porous carbon microsphere to the total pore volume; and the total pore volume is the sum of the micropore volume and the mesopore volume.

[0065] In some preferred embodiments, the average pore size of the porous carbon microsphere is 2 to 4 nm; the mesopore ratio of the porous carbon microsphere is 48% to 65%; the mesopore volume of the porous carbon microsphere is 0.3 to 0.6 cm 3 / g; the micropore volume of the porous carbon microsphere is 0.3 to 0.5 cm 3 / g; and the compressive strength of the porous carbon microsphere is 5.2 to 7.0 Gpa.

[0066] In some preferred embodiments, the specific surface area of the porous carbon microsphere is 700 to 1500 m 2 / g, preferably 1000 to 1400 m 2 / g; the total pore volume of the porous carbon microsphere is 0.4 to 1.3 cm 3 / g, preferably 0.7 to 1.0 cm 3 / g.

[0067] In some preferred embodiments, the D50 of the porous carbon microsphere is less than 9 μm, preferably 6.7 to 8.3 μm; and the D90 of the porous carbon microsphere is less than 17 μm, preferably 14.2 to 16.8 μm.

[0068] The present application provides a silicon-carbon composite material, which comprises the above porous carbon microsphere and silicon, and the silicon is enriched inside the pore channels of the porous carbon microsphere.

[0069] In some preferred embodiments, the content of the silicon in the silicon-carbon composite material is 45% to 60%. The content of the silicon is its mass percentage in the silicon-carbon composite material.

[0070] In the present application, the silicon-carbon composite material can be prepared by conventional methods in the art, preferably by chemical vapor deposition to deposit the silicon in the porous carbon microspheres.

[0071] The present application provides a use of the above-mentioned silicon-carbon composite material as an electrode material in a lithium ion battery.

[0072] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining 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] (1) The porous carbon microspheres prepared by the present application have a series of adjustable physical and chemical properties, such as particle size distribution, pore size, pore volume, mesopore rate, and specific surface area, and optimization of these properties further improves the mechanical strength and subsequent electrochemical performance of the material. By precisely controlling the preparation process, the porous carbon microspheres of the present application not only meet the specific needs of high-performance battery materials in diversified applications, but also provide new ideas and solutions for the development of related application fields.

[0076] (2) The present application successfully prepares porous carbon microspheres with high mesopore rate and highly developed pore structure by using supercritical water activation process. This high mesopore rate porous structure not only enhances the electrical conductivity of the material, but also improves the permeability of the electrolyte, providing an effective channel for the rapid transport of lithium ions and providing an efficient carrier for the silicon-carbon negative electrode material of lithium ion batteries. In addition, this porous structure also helps to buffer the volume expansion of silicon during charging and discharging, thereby improving the cycle stability of the battery.

[0077] (3) The porous carbon microspheres prepared by the present application provide the necessary mechanical properties for the material, enabling it to maintain the integrity of the structure during battery charging and discharging. Optimization of this mechanical strength helps to reduce wear and tear of the material, prolongs the service life of the battery, and improves the overall reliability of the battery.

[0078] (4) The carbon microsphere precursor prepared by the electrostatic spraying technology of the present application has a uniform size distribution, ensuring the consistency and charging and discharging performance of the material in battery applications. In addition, the introduction of conductive carbon black is beneficial to improving the electrical conductivity of the carbon matrix.

[0079] (5) The porous carbon microspheres of the present application are embedded with silicon material by chemical vapor deposition technology, and the prepared silicon-carbon composite material shows low electrode sheet expansion rate and high initial coulomb efficiency, and the improvement of these electrochemical performances directly enhances the cycle stability of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0080] Figure 1 SEM image of the porous carbon microspheres prepared for Example 1 of the present application.

[0081] Figure 2 Nitrogen adsorption-desorption isotherm graph of the porous carbon microspheres prepared for Example 1 and Comparative Example 2 of the present application.

[0082] Figure 3 Pore size distribution graph of the porous carbon microspheres prepared for Example 1 and Comparative Example 2 of the present application.

[0083] Figure 4 Structure diagram of the supercritical water activation reactor in Example 1 of the present application.

[0084] BRIEF DESCRIPTION OF DRAWINGS

[0085] Gas cylinder 1

[0086] Water tower 2

[0087] Gas flow meter 3

[0088] Plunger pump 4

[0089] High-pressure valve 5

[0090] Pressure indicator 6

[0091] Preheater 7

[0092] Reactor 8

[0093] Activation furnace 9

[0094] Heat exchanger 10

[0095] Back pressure regulator 11

[0096] Gas-liquid separator 12. DETAILED DESCRIPTION

[0097] The present application will be further described by way of examples, but the present application is not limited to the scope of the examples. The experimental methods in the following examples, for which no specific conditions are indicated, are selected according to conventional methods and conditions, or according to the instructions of the commercial products.

[0098] The electrostatic spraying environment in the following examples and comparative examples is: temperature 25±5℃, humidity 45%±10%; polystyrene weight average molecular weight is 150000 g / mol, purchased from Shanghai Hongshun Biological Technology Co., Ltd.; polyvinylpyrrolidone weight average molecular weight is 60000 g / mol, purchased from Guangzhou Yuemei Chemical Co., Ltd.

[0099] Example 1

[0100] S1: 0.8 g of polystyrene and 0.8 g of polyvinylpyrrolidone were dissolved in 19 mL of N,N-dimethylformamide (N,N-dimethylformamide density is 0.948 g / cm 3 ) to prepare a solution with a concentration of 8 wt%, and a homogeneous polymer solution was obtained after magnetic stirring at a speed of 300 rpm for 4 h at room temperature. Then 0.4 g of Ketjen black was added and ultrasonic dispersed for 1 h to obtain a uniformly dispersed precursor solution;

[0101] S2: The precursor solution prepared in step S1 was injected into a 20 mL syringe, and then the syringe was fixed on a microsyringe pump. The positive electrode of the high-voltage power supply was connected to the root of the syringe needle, and the receiving plate was connected to the ground. The equipment parameters were adjusted for electrostatic spraying. The push flow rate was set to 0.8 mL / h, the applied voltage was 20 kV, and the receiving distance was 16 cm. The carbon microsphere precursor material was obtained;

[0102] S3: The carbon microsphere precursor material obtained in step S2 was pre-oxidized, i.e. first dried in a constant temperature oven at 150℃ for 24 h, then transferred to a muffle furnace, and heated to 250℃ at a rate of 2℃ / min in air atmosphere and kept constant for 4 h. Then heat treatment was carried out, i.e. in a nitrogen atmosphere tube furnace, heated to 900℃ at a rate of 5℃ / min and kept constant for 2 h, to obtain spherical carbon material;

[0103] S4: The spherical carbon material obtained in step S3 was transferred into a supercritical water activation reactor, the preheater temperature was adjusted to 150℃, and the deionized water was ensured to be in water vapor state when passing through the material. Then the plunger pump was started and the reaction pressure was set to 25 MPa. After increasing the pressure to the set pressure at a rate of 1 MPa / min, the reactor was heated to 500℃ at a rate of 30℃ / min and kept constant for 45 min at constant pressure to obtain the activated material. The obtained activated material was washed with 10% hydrochloric acid, 5% sodium hydroxide and pure water in turn, and then treated in a drying oven at a constant temperature of 130℃ for 2 h to obtain the porous carbon microsphere material.

[0104] Example 2

[0105] S1: 0.55 g polystyrene, 0.55 g polyvinylpyrrolidone was dissolved in 18 mL N,N- dimethylformamide (density of N,N-dimethylformamide is 0.948 g / cm3) to prepare a solution with a concentration of 6 wt%, and a homogeneous polymer solution was obtained after magnetic stirring at a speed of 300 rpm for 4 h at room temperature. Then 0.22 g Ketjen black was added and dispersed by ultrasonic for 1 h to obtain a uniformly dispersed precursor solution. Other conditions were the same as in Example 1. 3 S1: 0.55 g polystyrene, 0.55 g polyvinylpyrrolidone was dissolved in 18 mL N,N- dimethylformamide (density of N,N-dimethylformamide is 0.948 g / cm3) to prepare a solution with a concentration of 6 wt%, and a homogeneous polymer solution was obtained after magnetic stirring at a speed of 300 rpm for 4 h at room temperature. Then 0.22 g Ketjen black was added and dispersed by ultrasonic for 1 h to obtain a uniformly dispersed precursor solution. Other conditions were the same as in Example 1.

[0106] Example 3

[0107] In step S2, the micro-injection pump flow rate was 0.6 mL / h, and the applied voltage was 22 kV. Other conditions were the same as in Example 1.

[0108] Example 4

[0109] In step S4, the activation pressure was set to 20 Mpa. Other conditions were the same as in Example 1.

[0110] Example 5

[0111] In step S4, the activation time was 30 min. Other conditions were the same as in Example 1.

[0112] Comparative Example 1

[0113] In step S3, no pre-oxidation treatment was performed, and the specific implementation process was as follows:

[0114] The carbon microsphere precursor material obtained in step S2 of Example 1 was dried in a constant temperature drying box at 150°C for 24 h, then transferred to a tube-type gas furnace in a nitrogen atmosphere, and heated to 900°C at a heating rate of 5°C / min and kept constant for 2 h to obtain spherical carbon material. Other conditions were the same as in Example 1.

[0115] Comparative Example 2

[0116] In step S4, no supercritical hydrothermal activation was performed, and the specific implementation process was as follows:

[0117] The spherical carbon material obtained in step S3 of Example 1 was transferred into the reactor, the preheater temperature was adjusted to 150°C to ensure that the deionized water passed through the material in the form of water vapor, and the plunger pump was adjusted to stabilize the water vapor flow at 2 L / min. The reactor was heated to 800°C at a heating rate of 10°C / min and kept constant for 45 min. Other conditions were the same as in Example 1.

[0118] Comparative Example 3

[0119] In step S4, the activation temperature was set to 700°C. Other conditions were the same as in Example 1.

[0120] Effect Example 1

[0121] Property characterization of the porous carbon microsphere material

[0122] (1) Test method

[0123] A. The specific surface area, total pore volume, average pore size, mesopore ratio, mesopore volume, micropore volume, and nitrogen adsorption-desorption isotherm of the porous carbon microsphere material prepared in the above examples and comparative examples were characterized by using an Autosorb iQ-3 full-automatic specific surface area and pore size analyzer.

[0124] Before testing, the sample needs to be degassed to remove water and other low-volatility substances. The degassing temperature is 250°C, and the degassing time is 720 min. Then the sample tube is installed on the analysis station and placed in a cold trap Dewar bottle at liquid nitrogen temperature (77 K) to determine its nitrogen adsorption-desorption isotherm. The test pressure range is 10 -7 -1 bar. The specific surface area of the sample is determined by the BET (Brunauer-Emmett-Teller) method, and the selected point range (P / P0) is 0.004-0.3. The micropore specific surface area and micropore volume of the sample are determined by the t-plot method, and the selected point range is 0.2-0.4. The value corresponding to the relative pressure point 0.99 is its total pore volume. The pore size distribution of the sample is analyzed by the non-localized density functional theory (NLDFT).

[0125] B. Carbonization yield

[0126] Carbonization yield = mass (g) of the spherical carbon material obtained in step S3 / mass (g) of the carbon microsphere precursor material obtained in step S2.

[0127] C. Compressive strength

[0128] (a) Test standard: GB / T 43091-2023

[0129] (b) Test instrument: FT-2000A

[0130] (c) Test steps:

[0131] The porous carbon microsphere material prepared in each example and comparative example was tested for compressive strength. According to the requirements in the test standard, the test environment temperature was 25±3°C, the relative humidity was not greater than 60%, and there was no vibration and convection air influence during the test process.

[0132] The sample to be tested was placed on the test platform, and a single particle within the field of view range of the flat indenter was found by using a microscope. The particle was subjected to pressure by using the flat indenter, and the powder particle was deformed until it was crushed with the increase of pressure. The test force when the powder was crushed was the crushing force F ykThe force area of the particles is calculated according to the particle size d of the powder particles, and then the compressive strength pcs of the powder particles is calculated. The number of test particles is not less than 5, and the number of test particles can also be selected according to actual needs.

[0133] Calculation of powder compressive strength:

[0134]

[0135] In the formula, p cs is the compressive strength, the unit is MPa; alpha is the calculation coefficient, which is 2.48; F yk is the crushing force, the unit is mN; d is the particle size, the unit is mu m.

[0136] D, surface morphology

[0137] The surface morphology of the prepared porous carbon microsphere material is tested by using a German Zeiss Sigma 300 type field emission scanning electron microscope.

[0138] Test steps: take a small amount of sample and attach it to the sample stage with conductive glue, spray gold on the sample for 45s, and then put it into the scanning electron microscope vacuum chamber for surface morphology observation.

[0139] Test conditions: accelerating voltage 5.0 kV, electron imaging resolution: 1.6 nm (1 kV), 1.0 nm (15 kV)

[0140] (2) Test results

[0141] Table 1

[0142]

[0143] Figure 1 SEM image of the porous carbon microspheres prepared in Example 1 of the present application; Figure 2 Nitrogen adsorption-desorption isotherm graph of the porous carbon microspheres prepared in Example 1 and Comparative Example 2 of the present application; Figure 3 Pore size distribution graph of the porous carbon microspheres prepared in Example 1 and Comparative Example 2 of the present application. According to the IUPAC classification standard, Figure 2 The adsorption isotherm of Example 1 and Comparative Example 2 shows a typical IV curve and has a clear H3 hysteresis loop, that is, there are both microporous and mesoporous structures, and the difference between the two is that the total adsorption amount of Comparative Example 2 is greater than that of Example 1, indicating that the specific surface area of Comparative Example 2 is larger. From Figure 3It can be seen that the difference of the pore structure in Example 1 and Comparative Example 2 is further revealed by the pore size distribution calculated by the NLDFT method, the pore size distribution in Example 1 is wider, and the pores are mainly mesopores between 2-3 nm and 3.5-4.5 nm, while the pores in Comparative Example 2 are mainly micropores <2 nm and part of mesopores between 4.5-5 nm, Figure 2 This is also confirmed by the hysteresis loop of the adsorption-desorption curve.

[0144] In combination with the data in Table 1, it can be seen that the porous carbon microsphere material prepared by the technical scheme of the present application has the characteristics of uniform size, high mesopore rate and high particle strength. By comparing Example 1-5 and Comparative Example 2, it can be found that the material prepared by the supercritical water activation technology has higher particle strength and mesopore rate. In combination with Comparative Example 3, it can be seen that the porous carbon microsphere after supercritical water over-activation has a high mesopore rate, but the carbon matrix inside for supporting has been over-activated, resulting in a low compressive strength. At the same time, the average pore diameter of the porous carbon microsphere material obtained in Example 1-5 is higher than that of Comparative Example 2 and lower than that of Comparative Example 3.

[0145] In addition, by comparing Example 1-5 and Comparative Example 1, it can be found that the carbonization yield and compressive strength of the carbon material after pre-oxidation treatment are obviously higher than those of the carbon material without pre-oxidation treatment. This is because the oxygen introduced in the air atmosphere during the pre-oxidation process can enhance the cross-linking between the resin molecules and inhibit the conversion of carbon in the molecules into small-molecule carbon-containing gas. The increase of carbon yield helps to build a more continuous and efficient conductive network, thereby improving the structural stability.

[0146] Effect Example 2

[0147] Property characterization of silicon-carbon composite material

[0148] (1) Test method

[0149] Silane gas phase chemical deposition

[0150] The porous carbon microspheres prepared in each example and comparative example were subjected to silicon source gas phase deposition to prepare silicon-carbon composite materials, and the specific steps were as follows:

[0151] A mixture of silane and nitrogen gas was introduced into a 120 kPa positive pressure fluidized bed reactor, the silane gas flow rate was 10 L / min, the nitrogen gas flow rate was 25 L / min, the silane in the mixed gas was deposited on the porous carbon microspheres at 650℃, and the deposition reaction time was 1.5 h. After the completion of the deposition reaction, the silane was stopped and only nitrogen was introduced to complete the gas replacement in the reactor, then air was introduced and heated at 100℃ for 0.5 h for surface passivation treatment, to obtain a silicon-carbon composite material.

[0152] The calculation method of the silicon content in the silicon-carbon composite material prepared above is as follows:

[0153] Silicon content = (mass m1 after passivation treatment - mass m0 before deposition reaction) / mass m1 after passivation treatment.

[0154] (2) Test results

[0155] The test results are shown in Table 2.

[0156] Table 2

[0157]

[0158] From the above Table 2, it can be found that the silicon deposition content of the product prepared by using the supercritical water activation technology in Comparative Examples 1-5 is higher than that of Comparative Example 2, which is because the average pore diameter of the product without using the supercritical water activation technology is smaller, and the pore channel is easily blocked after deposition, so that the internal space cannot continue to be deposited, resulting in a lower silicon content, and the corresponding electrochemical performance is also weakened. It can be found from Comparative Examples 1-5 and Comparative Example 3 that when the average pore diameter of the product prepared by using the supercritical water activation technology at the temperature defined in the application is larger and the specific surface area is smaller, the silicon content that can be deposited is less, which will also have an adverse effect on the corresponding electrochemical performance.

[0159] As for Comparative Example 1, the carbon material without pre-oxidation forms a certain degree of closed pores (the internal pores have no channels connected to the outer surface, forming independent pore structures) after carbonization, resulting in a decrease in carbonization yield, and part of the closed pores are opened after activation, which contributes to the increase in specific surface area and pore volume. However, the formation of closed pores is not conducive to the mechanical properties of the carbon material, and it is more prone to crushing under the same pressure. In addition, due to the limitation of lithium ions embedded in the nano space in the internal opened closed pores during the charging and discharging process, the lithium ions are not timely removed, forming "dead lithium", so the subsequent electrochemical performance is also poor.

[0160] Effect Example 3

[0161] Electrochemical performance test

[0162] (1) Test method

[0163] The silicon-carbon composite material prepared by silane deposition of each example and comparative example was mixed with SFG-6 and LA132 to prepare a slurry at a mixing ratio of 75:15:10. The mixed slurry was coated on a copper foil, dried, rolled, and then cut into a circular sheet with a diameter of 13.5 mm as a negative electrode sheet. The negative electrode sheet was assembled with a lithium sheet, an electrolyte, a polypropylene separator, a positive electrode shell, and a negative electrode shell to form a CR2430 button cell. The electrolyte was prepared by using lithium hexafluorophosphate as a solute and ethylene carbonate and diethyl carbonate as solvents, wherein the volume ratio of ethylene carbonate to diethyl carbonate was 1:1, and the concentration of lithium hexafluorophosphate was 0.8 mol / L. The button cell was subjected to constant current charge and discharge test at 0.1 C by using a blue cell test system, and the capacity, initial efficiency, and capacity retention rate after 100 and 500 cycles were tested.

[0164] (2) Test results

[0165] The test results are shown in Table 3.

[0166] Table 3

[0167]

[0168] As shown in Table 3, the silicon-carbon composite material prepared by the present application has excellent reversible specific capacity, initial coulombic efficiency, capacity retention rate after 100 cycles, and capacity retention rate after 500 cycles. The reversible specific capacity and capacity retention rate after 500 cycles of Examples 1-5 are higher than those of Comparative Examples 1-3. In combination with the mechanical properties of the material, the capacity retention rates after 100 cycles of Comparative Example 1 and Comparative Example 2 are relatively close, but the capacity retention rate of the silicon-carbon composite material prepared by water vapor activation in Comparative Example 2 is greatly attenuated after 500 cycles, which indicates that the silicon-carbon composite material prepared by the present application has excellent mechanical properties and electrochemical properties.

Claims

1. A method for preparing porous carbon microspheres, characterized by, It comprises the following steps: S1: mixing a polymer, a solvent and conductive carbon black to obtain a precursor solution; S2: preparing the precursor solution into a carbon microsphere precursor material by using an electrostatic spraying method; S3: sequentially pre-oxidizing and heat-treating the carbon microsphere precursor material to obtain a spherical carbon material; S4: supercritical hydrothermal activation of the spherical carbon material, post-processing to obtain a porous carbon microsphere material; The polymer comprises a polymer A and a polymer B; the polymer A and the polymer B are different polymers; The polymer A is one of polystyrene, polyacrylonitrile, polydopamine and poly (aniline-pyrrole) copolymer; the polymer B is polyvinylpyrrolidone; in step S2, the operation of using an electrostatic spraying method is: injecting the precursor solution prepared in step S1 into a syringe, then fixing the syringe on a micro-injection pump, connecting the root of the syringe needle to the positive pole of a high-voltage power supply, connecting the receiving plate to the ground wire, vertically arranging the receiving plate in the radial direction of the syringe and placing it directly below the syringe, adjusting the equipment parameters for electrostatic spraying to obtain a carbon microsphere precursor; In step S2, the flow rate of the micro-injection pump is 0.5-1.5 mL / h, and the voltage of the high-voltage power supply is 15-30 kV; the receiving distance from the tip of the syringe to the receiving plate is 12-18 cm; In step S3, the pre-oxidation temperature is 150-280℃, and the pre-oxidation time is 2-6 h; The activation temperature is 300-500℃, the activation pressure is 15-30 MPa, and the activation time is 0.5-1 h.

2. The method of claim 1, wherein the porous carbon microspheres are prepared by the steps of: It satisfies one or more of the following conditions: (1) In step S1, the polymer A is polystyrene; (2) In step S1, the solvent is N,N-dimethylformamide; (3) In step S1, the conductive carbon black is one of Ketjen black, acetylene black and Super P; (4) In step S1, the polymer solution concentration is 5-12 wt%; (5) In step S1, the mixing operation is dissolving the polymer in the solvent, forming a homogeneous polymer solution after magnetic stirring, then adding the conductive carbon black to the polymer solution, and obtaining a precursor solution after ultrasonic dispersion; (6) In step S1, the mixing operation is dissolving polystyrene and polyvinylpyrrolidone in N,N-dimethylformamide, forming a homogeneous polymer solution after magnetic stirring, then adding conductive carbon black to the polymer solution, and obtaining a precursor solution after ultrasonic dispersion.

3. The method for preparing porous carbon microspheres as described in claim 2, characterized in that, It satisfies one or more of the following conditions: (1) The weight average molecular weight of the polystyrene is 100000-200000 g / mol; (2) The weight average molecular weight of the polyvinylpyrrolidone is 40000-100000 g / mol; (3) In step S1, the mass ratio of the polymer A, the polymer B and the conductive carbon black is (4-9):(4-9):(2-5); (4) In step S1, the polymer solution concentration is 6-10 wt%; (5) In step S1, the rotating speed of the magnetic stirring is 200-350 rpm; (6) In step S1, the time of the magnetic stirring is 2-6 h; (7) In step S1, the time of the ultrasonic dispersion is 1-2 h.

4. The method for preparing porous carbon microspheres as described in claim 3, characterized in that, It meets one or more of the following conditions: (1) The weight average molecular weight of the polystyrene is 130000-170000 g / mol; (2) The weight average molecular weight of the polyvinylpyrrolidone is 40000-70000 g / mol; (3) In step S1, the mass ratio of the polymer A, the polymer B and the conductive carbon black is (5-7):(5-7):(2-4) or 2:2:1; (4) In step S1, the concentration of the polymer solution is 6 wt% or 8 wt%; (5) In step S1, the rotating speed of the magnetic stirring is 300 rpm; (6) In step S1, the time of the magnetic stirring is 4 h.

5. The method for preparing porous carbon microspheres as described in claim 4, characterized in that, It meets one or more of the following conditions: (1) The weight average molecular weight of the polystyrene is 150000 g / mol; (2) The weight average molecular weight of the polyvinylpyrrolidone is 60000 g / mol; (3) In step S1, the mass ratio of the polymer A, the polymer B and the conductive carbon black is 5:5:

2.

6. The method for preparing porous carbon microspheres as described in claim 1, characterized in that, It meets one or more of the following conditions: (1) In step S2, the push flow rate of the micro-injection pump is 0.6 mL / h or 0.8 mL / h; the voltage of the high-voltage power supply is 20 kV or 22 kV; the receiving distance from the tip of the syringe to the receiving plate is 16 cm; (2) In step S2, the operation environment temperature of the electrostatic spraying method is 20-30℃, and the environmental humidity is 35%-55%.

7. The method for preparing porous carbon microspheres as described in claim 1, characterized in that, It meets one or more of the following conditions: (1) In step S3, the operation of the pre-oxidation is that the carbon microsphere precursor material prepared in step S2 is dried and then transferred to a muffle furnace for heating in an air atmosphere; (2) In step S3, the heating rate of the pre-oxidation is 1-4℃ / min; (3) In step S3, the temperature of the pre-oxidation is 170-250℃; (4) In step S3, the time of the pre-oxidation is 2-4 h; (5) In step S3, the heat treatment is carried out in an inert atmosphere, and the inert atmosphere is at least one of nitrogen and argon or both; (6) In step S3, the heat treatment is carried out in a tube atmosphere furnace; (7) In step S3, the heating rate of the heat treatment is 5-7℃ / min; (8) In step S3, the temperature of the heat treatment is 500-1200℃; (9) In step S3, the time of the heat treatment is 1-3 h; (10) The particle size of the spherical carbon material is D50<10 μm and D90<20 μm.

8. The method for preparing porous carbon microspheres as described in claim 7, characterized in that, It meets one or more of the following conditions: (1) In step S3, the temperature of the drying is 90-160℃; (2) In step S3, the time of the drying is 18-36 h; (3) In step S3, the temperature increasing rate of the pre-oxidation is 2 ℃ / min; (4) In step S3, the inert atmosphere is nitrogen; (5) In step S3, the temperature of the heat treatment is 600-1000 ℃; (6) In step S3, the time of the heat treatment is 2 h.

9. The method for preparing porous carbon microspheres as described in claim 8, characterized in that, It satisfies one or more of the following conditions: (1) In step S3, the temperature of the drying is 150 ℃; (2) In step S3, the time of the drying is 24 h; (3) In step S3, the temperature of the heat treatment is 900 ℃.

10. The method for preparing porous carbon microspheres as described in claim 1, characterized in that, It satisfies one or more of the following conditions: (1) In step S4, the operation of the supercritical hydrothermal activation is that the spherical carbon material prepared in step S3 is transferred into a supercritical water activation reactor, a preheater is first adjusted to a specified temperature, and then the hydrothermal activation is carried out at a specified temperature and pressure in the supercritical water activation reactor to obtain an activated material; (2) In step S4, the water used in the supercritical hydrothermal activation is one of deionized water, ultrapure water and distilled water; (3) In step S4, the preheating temperature of the supercritical hydrothermal activation is 100-200 ℃; (4) In step S4, the pressure increasing rate of the supercritical hydrothermal activation is 0.8-1.2 MPa / min; (5) In step S4, the pressure of the supercritical hydrothermal activation is 20 Mpa or 25 Mpa; (6) In step S4, the temperature increasing rate of the supercritical hydrothermal activation is 25-35 ℃ / min; (7) In step S4, the time of the supercritical hydrothermal activation is 45 min; (8) In step S4, the operation of the post-treatment is that the activated material is washed and dried to obtain a porous carbon microsphere material; (9) The carbonization yield of the porous carbon microsphere is 45%-60%.

11. The method for preparing porous carbon microspheres as described in claim 10, characterized in that, It satisfies one or more of the following conditions: (1) In step S4, the water used in the supercritical hydrothermal activation is deionized water; (2) In step S4, the preheating temperature of the supercritical hydrothermal activation is 150 ℃; (3) In step S4, the pressure increasing rate of the supercritical hydrothermal activation is 1 MPa / min; (4) In step S4, the temperature increasing rate of the supercritical hydrothermal activation is 30 ℃ / min; (5) In step S4, the operation of the washing is that acid washing, alkali washing and water washing are sequentially carried out.

12. The method for preparing porous carbon microspheres as described in claim 11, characterized in that, It satisfies one or more of the following conditions: (1) In step S4, the acid solution used in the operation of the acid washing is one of hydrochloric acid, sulfuric acid and nitric acid; (2) In step S4, the concentration of the acid solution used in the operation of the acid washing is 5-30%; (3) In step S4, the alkali solution used in the operation of the alkali washing is one of sodium hydroxide, potassium hydroxide and potassium carbonate; (4) In step S4, the concentration of the alkali solution used in the operation of the alkali washing is 3-10%; (5) In step S4, the operation of the water washing is that the pH value of the object to be washed is adjusted to 6-8; (6) In step S4, the operation of the water washing is that pure water is used; (7) In step S4, the operation of the drying is carried out under one of air, nitrogen and argon atmosphere; (8) In step S4, the drying temperature is 100-170℃; (9) In step S4, the drying time is 2-5 h; (10) In step S4, the carbonization yield of the porous carbon microspheres is 45%-55%.

13. The method for preparing porous carbon microspheres as described in claim 12, characterized in that, It satisfies one or more of the following conditions: (1) In step S4, the acid solution used in the acid washing operation is hydrochloric acid; (2) In step S4, the concentration of the acid solution used in the acid washing operation is 10-20%; (3) In step S4, the base solution used in the base washing operation is sodium hydroxide; (4) In step S4, the concentration of the base solution used in the base washing operation is 5%; (5) In step S4, the drying operation is carried out in air; (6) In step S4, the drying temperature is 100-150℃; (7) In step S4, the drying time is 2-4 h.

14. The method of claim 13, wherein the porous carbon microspheres are prepared by the process of claim 13. In step S4, the drying temperature is 130℃.

15. Porous carbon microspheres prepared by the method of any one of claims 1-14.

16. The porous carbon microspheres of claim 15, wherein, The average pore size of the porous carbon microspheres is 2-6 nm; the mesoporous rate of the porous carbon microspheres is 40%-80%; the mesoporous pore volume of the porous carbon microspheres is 0.2-0.8 cm 3 / g; the microporous pore volume of the porous carbon microspheres is 0.3-0.6 cm 3 / g; and the compressive strength of the porous carbon microspheres is 4.8-8.0 Gpa.

17. The porous carbon microspheres of claim 16, wherein, The average pore size of the porous carbon microspheres is 2-4 nm; the mesoporous rate of the porous carbon microspheres is 48%-65%; the mesoporous pore volume of the porous carbon microspheres is 0.3-0.6 cm 3 / g; the microporous pore volume of the porous carbon microspheres is 0.3-0.5 cm 3 / g; and the compressive strength of the porous carbon microspheres is 5.2-7.0 Gpa. And / or, the specific surface area of the porous carbon microspheres is 700~1500 m 2 / g; the total pore volume of the porous carbon microspheres is 0.4~1.3 cm 3 / g; And / or, the D50 of the porous carbon microspheres is <9 μm; the D90 of the porous carbon microspheres is <17 μm.

18. The porous carbon microspheres of claim 17, wherein, The specific surface area of the porous carbon microspheres is 1000-1400 m 2 / g; the total pore volume of the porous carbon microspheres is 0.7-1.0 cm 3 / g; and / or, the D50 of the porous carbon microspheres is 6.7-8.3 μm; the D90 of the porous carbon microspheres is 14.2-16.8 μm.

19. A silicon-carbon composite material, characterized by, It comprises the porous carbon microspheres of any one of claims 15-18 and silicon, and the silicon is enriched inside the pores of the porous carbon microspheres.

20. The silicon-carbon composite of claim 19, wherein, The content of the silicon in the silicon-carbon composite material is 45%-60%.

21. The silicon-carbon composite of claim 19, wherein, The silicon-carbon composite material uses chemical vapor deposition to deposit the silicon in the porous carbon microspheres.

22. Use of the silicon-carbon composite material of any one of claims 19-21 as an electrode material in a lithium ion battery.

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