Silicon-carbon composite material and preparation method and system thereof

Abstract

The invention discloses a silicon-carbon composite material and a preparation method and system thereof. The preparation method comprises the following steps: carrying out solid removal and distillation on petroleum heavy oil to obtain light distillate oil and heavy distillate oil; mixing the light distillate oil with the nano silicon, and adding a dispersing agent to obtain an oil solution of the nano silicon; mixing the heavy distillate oil with an oil solution of nano silicon to obtain mixed pyrolytic oil; carrying out microwave pyrolysis on the mixed pyrolytic oil to obtain pyrolytic carbon containing silicon; and carrying out gas-solid separation, crushing, carbonization and demagnetization on the silicon-containing pyrolytic carbon to obtain the silicon-carbon composite material. The silicon-carbon composite material provided by the invention can provide multi-angle and multi-channel embedding and separating paths of lithium ions, and has relatively high electrochemical performance.

Description

Technical Field

[0001] This invention relates to a silicon-carbon composite material and its preparation method and system, belonging to the field of negative electrode material technology. Background Technology

[0002] Currently, the anode materials used in commercial lithium-ion batteries mainly include carbon materials and non-carbon materials. Carbon materials primarily include disordered carbon materials, hard carbon materials, soft carbon materials, and graphite. Graphite includes two main categories: artificial graphite and natural graphite. Artificial graphite is produced by graphitizing easily graphitizable carbon (such as petroleum coke, needle coke, or pitch coke) at high temperatures of 2800–3000℃ in an N2 atmosphere. Natural graphite includes amorphous graphite and flake graphite. Graphite is a typical example of embedded anode materials, with embedded Li intercalated between layers of graphite, forming different "step" structures. As the amount of Li intercalation increases, a first-order structure is eventually formed, corresponding to a theoretical capacity of 372 mAh / g. However, most current graphite anode materials have capacities of 340–362 mAh / g.

[0003] The lithium storage mechanism of silicon anode materials differs from that of graphite anode materials; it primarily relies on the formation of LiCl with lithium. 12 Si7, Li 13 Si4, Li7Si3, Li 22 Various alloy phases, including Si5, are present, with Li having the highest lithium content. 22 In Si5, silicon and lithium undergo an alloying reaction; one silicon atom can alloy with 4.4 lithium atoms, resulting in a theoretical specific capacity of up to 4200 mAh / g, approximately 10 times that of graphite anode materials. However, the severe volume effect of silicon during lithiation limits its large-scale application. Carbon coating is one of the most commonly used methods for modifying anode materials. During the electrochemical reaction, a uniform and stable solid electrolyte interphase (SEI) film is easily formed on the surface of carbon materials, but it is more difficult to form on the surface of Si. Common carbon coating methods mainly include: chemical vapor deposition (CVD) carbon coating, pyrolysis carbon coating, hydrothermal carbon coating, and polyelectrolyte-modified carbon coating.

[0004] CN118039853A discloses a method for preparing and applying a carbon-coated silicon-based composite material. The method involves dispersing silicon-based material particles and a surfactant in a low-viscosity unsaturated hydrocarbon organic solvent to obtain a monodisperse silicon-based material solution. This solution is then heated to the carbon chain cleavage temperature of olefins, alkynes, and olefin derivatives, and held at this temperature to cause them to decompose into short-chain carbons, which are then deposited on the surface of the silicon-based material particles, resulting in a carbon-coated silicon-based composite material. However, this method uses reagent-grade olefins and alkynes, leading to high manufacturing costs. Furthermore, the high decomposition temperature may cause silicon crystal coalescence, resulting in poor cycle performance and affecting the electrochemical performance of the anode material.

[0005] CN116111093A discloses a liquid-phase preparation method for silicon-carbon anode materials for lithium-ion batteries. This method uses a chemical method to oxidize and purify graphite tailings to prepare micro-expanded graphite. Then, nano-silicon powder, micro-expanded graphite, and pitch are mixed via a simple liquid-phase method, allowing the pitch to composite with silicon and micro-expanded graphite and form a carbon coating during pyrolysis, thus preparing a silicon / micro-expanded graphite / carbon composite material. However, this method requires the use of strong acids and hydrogen peroxide, resulting in poor safety and environmental friendliness. Furthermore, the silicon-carbon material prepared by this method is prone to agglomeration, making it difficult to achieve good cycle performance.

[0006] CN115966669A discloses a graphite anode material and its preparation method. This method uses coal tar pitch as a carbon source to perform secondary carbon coating modification on a prepared silicon / graphite / carbon composite material, and then mixes the secondary carbon-coated silicon / graphite / carbon composite material with artificial graphite to form a silicon-carbon-graphite product. However, this method involves multiple coating processes, which is cumbersome and cannot solve the problem of poor uniformity in pitch coating in existing technologies.

[0007] The existing technologies described above have failed to overcome the problems of poor uniformity and / or stability of silicon-coated carbon, resulting in the need for further improvement in the electrochemical performance of silicon-carbon composites. Furthermore, the gases emitted from the pyrolysis of most polymer-coated carbon are toxic, posing a risk of environmental pollution and poisoning. Summary of the Invention

[0008] To address at least one of the aforementioned technical problems, the present invention aims to provide a silicon-carbon composite material and its preparation method and system. The silicon-carbon composite material of the present invention provides multi-angle and multi-channel pathways for lithium ion insertion and detachment, exhibiting high electrochemical performance.

[0009] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a silicon-carbon composite material, comprising the following steps:

[0010] (1) The heavy petroleum oil is desolidified and distilled to obtain light distillate oil and heavy distillate oil;

[0011] (2) The light distillate oil and nano-silicon are mixed and a dispersant is added to obtain an oil solution of nano-silicon;

[0012] (3) The heavy distillate oil and the oil solution of the nano-silicon are mixed to obtain a mixed pyrolysis oil;

[0013] (4) The mixed pyrolysis oil is microwave pyrolyzed in a fluidized reactor to obtain pyrolysis carbon containing silicon;

[0014] (5) After gas-solid separation, crushing, carbonization and demagnetization of the silicon-containing pyrolytic carbon, the silicon-carbon composite material is obtained.

[0015] According to a specific embodiment of the present invention, preferably, in step (1), based on the total mass of the heavy petroleum oil as 100%, the saturated content is 3-30%, the aromatic content is 45-92%, the gum content is 5-25%, the asphaltenes content is 0-8%, the sulfur content is 0.1-3.2%, the nitrogen content is 0.05-0.85%, and the residual carbon content is 4-17%; and the ash content of the heavy petroleum oil is 100-5000 ppm. Specifically, the heavy petroleum oil includes, but is not limited to, one or more of the following: catalytic cracking slurry oil, coking wax oil, thermal cracking residue oil, hydrotreated tail oil, furfural extract oil, reformed heavy aromatic oil, vacuum distillate oil, ethylene tar, vacuum residue oil, thermal cracking residue oil, and ethylene tar hydrotreated wax oil fraction.

[0016] In this invention, ash content refers to all metallic impurities, generally including one or more of Fe, Ni, V, Al, Cu, Na and Ca.

[0017] According to a specific embodiment of the present invention, preferably, in step (1), the distillation range of the deconsolidated heavy petroleum oil is 300–680°C, and the density (at 20°C) is 0.93–1.12 g / cm³. 3 The deconsolidated heavy petroleum oil, based on a total mass of 100%, contains 12-30% saturated fraction, 50-75% aromatic fraction, 10-20% gum content, 0.5-4% asphaltenes content, 0.5-2% sulfur content, 0.1-0.7% nitrogen content, and 5-15% residual carbon content; and the ash content of the deconsolidated heavy petroleum oil is 10-100 ppm. Specifically, the deconsolidation methods include, but are not limited to, one or more of sedimentation deconsolidation, centrifugation deconsolidation, membrane separation deconsolidation, solvent extraction deconsolidation, and electric field deconsolidation. These deconsolidation methods can all be carried out according to existing technologies, and this invention does not impose any special limitations on them, as long as the deconsolidated heavy petroleum oil that meets the above-mentioned indicators of this invention can be obtained.

[0018] According to a specific embodiment of the present invention, preferably, in step (1), the light distillate oil has a distillation range of 300–400°C and a density (20°C) of 0.93–0.98 g / cm³. 3 Based on the total mass of the light distillate oil as 100%, the saturated fraction content is 35-55%, the aromatic fraction content is 40-60%, the gum content is 0.5-6%, the asphaltenes content is 0-0.1%, the sulfur content is 0.3-1%, the nitrogen content is 0.05-0.3%, and the carbon residue content is 3-5%.

[0019] According to a specific embodiment of the present invention, preferably, in step (1), the heavy distillate oil has a boiling range of 350–680°C and a density (20°C) of 0.98–1.15 g / cm³. 3 Based on the total mass of the heavy distillate oil as 100%, the saturated fraction content is 8-15%, the aromatic fraction content is 50-80%, the gum content is 10-30%, the asphaltenes content is 0.7-6%, the sulfur content is 0.6-2.2%, the nitrogen content is 0.1-0.8%, and the carbon residue content is 7-18%.

[0020] In this invention, there are no special restrictions on the distillation method and conditions in step (1). Vacuum distillation or atmospheric distillation can be used, as long as the light distillate oil and heavy distillate oil that meet the above-mentioned indicators of this invention can be obtained.

[0021] According to a specific embodiment of the present invention, preferably, in step (2), the D50 particle size of the nano-silicon is 70-110 nm; the nano-silicon includes one or more of elemental silicon, silicon suboxide, and porous silicon.

[0022] According to a specific embodiment of the present invention, preferably, in step (2), the mixing mass ratio of the nano-silicon and the light distillate oil is (1-3):100.

[0023] According to a specific embodiment of the present invention, preferably, in step (2), the dispersant includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium hexametaphosphate, and sodium alginate; the mass content of the dispersant in the oil solution of nano-silicon is 1-5%.

[0024] According to a specific embodiment of the present invention, preferably, step (2) is performed using a high-speed shearing machine with a shearing speed of 2500-2800 r / min, a temperature of 50-80°C, and a shearing time of 30-60 minutes.

[0025] In this invention, the deconsolidated heavy petroleum oil is distilled to obtain the aforementioned light and heavy distillate oils. The inventors discovered that mixing the heavy distillate oil with nano-silicon makes it difficult to form a uniformly dispersed oil solution; while the light distillate oil, with its lower viscosity and smaller molecular weight, more easily forms a uniformly dispersed oil solution. Therefore, this invention mixes the light distillate oil with nano-silicon and a dispersant, and obtains a uniformly dispersed nano-silicon oil solution through high-speed shearing.

[0026] According to a specific embodiment of the present invention, preferably, in step (3), the mixing of the heavy distillate oil and the nano-silicon oil solution is carried out online, the online mixing temperature is 80-120°C, and the linear velocity is 0.5-0.7 m / s; the mixing mass ratio of the heavy distillate oil and the nano-silicon oil solution is: heavy distillate oil : light distillate oil in the nano-silicon oil solution = 90-100% by mass of the heavy distillate oil obtained in step (1) : light distillate oil obtained in step (1). That is, the mixing mass ratio of the heavy distillate oil and the nano-silicon oil solution is according to the mass ratio of heavy distillate oil to light distillate oil obtained in step (1), or with a reduction of less than 10% by mass of heavy distillate oil. For example, if the mass ratio of heavy distillate oil to light distillate oil obtained in step (1) is 2:1, then when mixing the heavy distillate oil and the nano-silicon oil solution, the heavy distillate oil: the light distillate oil in the nano-silicon oil solution can be mixed according to a mass ratio of 2:1. Alternatively, the heavy distillate oil can be reduced by less than 10% by mass, that is, it can be mixed according to a mass ratio of (1.8~2):1.

[0027] According to a specific embodiment of the present invention, preferably, step (4) includes: introducing the mixed pyrolysis oil into a fluidized bed reactor, the fluidized bed reactor being connected to a microwave generator, and the mixed pyrolysis oil being subjected to microwave pyrolysis by the microwave generator to obtain silicon-containing pyrolysis carbon and oil gas, the silicon-containing pyrolysis carbon being in a fluidized state; wherein, the flow rate of the mixed pyrolysis oil entering the fluidized bed reactor is 1-2 kg / h, the frequency of the microwave generator is controlled at 2350-2550 MHz and the power at 2-5 kW, the residence time of the mixed pyrolysis oil in the fluidized bed reactor is 2-4 seconds, and the temperature in the fluidized bed reactor is controlled at 530-580°C. The fluidized bed reactor connected to the microwave generator can be any existing device, and the present invention does not impose any special limitations on it. Those skilled in the art will understand that the microwave generator includes a control unit and a modulation unit, etc., to regulate the frequency and power of the microwave within the above range. Those skilled in the art will also understand that the fluidized bed reactor can also be referred to as a fluidized bed reactor.

[0028] In this invention, it should be noted that the mixed pyrolysis oil that first enters the fluidized reactor generates silicon-containing pyrolysis carbon and oil gas under the action of microwaves and heat. The mixed pyrolysis oil that enters the fluidized reactor later is in a gaseous state before being pyrolyzed into silicon-containing pyrolysis carbon. Therefore, the fluidized reactor contains the solid silicon-containing pyrolysis carbon and gaseous oil generated by the reaction first. The silicon-containing pyrolysis carbon particles are suspended in the gaseous oil in a fluidized state.

[0029] This invention uses heavy petroleum oil as a carbon source, which contains a large amount of polycyclic aromatic hydrocarbons (PAHs), and different components in the heavy petroleum oil have different pyrolysis rates. After removing metallic impurities through deconsolidation, the heavy petroleum oil is distilled to adjust its composition. By controlling the component content of the light and heavy distillate oils within the range specified in this invention, and by using a fluidized bed reactor for microwave pyrolysis and controlling the pyrolysis conditions within the aforementioned range, the mixed pyrolysis oil can form different reaction networks during the pyrolysis process, thereby forming the silicon-carbon composite material structure of this invention. Specifically, the inventors hypothesize that saturated hydrocarbons in the mixed pyrolysis oil are most prone to pyrolysis, being the first to pyrolyze into small molecule hydrocarbons; and that the side chains of aromatic hydrocarbons in the mixed pyrolysis oil break down, generating small molecule hydrocarbons while polycyclic aromatic hydrocarbons pyrolyze to generate a framework carbon with a larger microcrystalline structure, higher orientation, and more regular shape. Simultaneously, because the small molecule hydrocarbons escape as oil vapor, a three-dimensional porous structure is formed in the framework carbon, i.e., porous carbon. This porous carbon provides a place to accommodate nano-silicon particles. Furthermore, the aromatic ring structures in the polar components such as gums and asphaltenes in the mixed pyrolysis oil are adsorbed onto the nano-silicon particles. This reduces the impact on the regularity and size of carbon microcrystals formed by the pyrolysis of aromatics due to the difference in reactivity between gums and asphaltenes during the pyrolysis process. Additionally, the gums and asphaltenes adsorbed on the nano-silicon particles form a first coating layer on the surface of the silicon particles after pyrolysis. This first coating layer mainly consists of small-sized, low-orientation carbon microcrystals formed after the pyrolysis of gums and asphaltenes. The nano-silicon particles with this first coating layer are embedded in the pores of the porous carbon, resulting in a uniform and stable distribution of the nano-silicon particles on the carbon framework. This overcomes the problem of particle fusion during subsequent carbonization caused by only coating the surface of nano-silicon particles with asphaltenes in existing technologies. Simultaneously, oil and gas are generated during pyrolysis. Some of this oil and gas continues to decompose, leading to carbon chain breakage and causing some carbon to deposit on the surface of the porous carbon containing the nano-silicon particles, forming a second coating layer. This second coating layer mainly consists of amorphous carbon formed by the decomposition of oil and gas. Therefore, the silicon-containing pyrolytic carbon of the present invention has a carbon structure with different layers, which enables the silicon-carbon composite material obtained after subsequent carbonization and other steps to provide multi-angle and multi-channel insertion and detachment pathways for lithium ions, resulting in high electrochemical performance.

[0030] According to a specific embodiment of the present invention, preferably, step (4) further includes: distilling the oil and gas at least to obtain gasoline, diesel, and wax oil, etc. Specifically, after the oil and gas flows out from the top of the fluidized reactor, it can be cooled first to collect non-condensable gases; then the remaining part is distilled. The distillation can be carried out using a distillation column. The present invention does not impose special restrictions on the specific operating conditions of the distillation column, and conventional conditions in the art can be used. The gasoline, diesel, and wax oil obtained after distillation can be used as fuel oil.

[0031] According to a specific embodiment of the present invention, preferably, in step (5), the temperature of the gas-solid separation is 470–500°C. Because the pyrolysis time is relatively short, the porous structure of the silicon-containing pyrolysis carbon formed may adsorb some oil and gas, and the silicon-containing pyrolysis carbon may also carry some unreacted components (especially aromatics). The present invention performs gas-solid separation on the silicon-containing pyrolysis carbon discharged from the fluidized reactor, separating the adsorbed and entrained oil and gas, as well as the unreacted components, from the silicon-containing pyrolysis carbon. The separated oil and gas and unreacted components can be returned to the fluidized reactor for further pyrolysis and / or oil and gas recovery. Specifically, the gas-solid separation can be carried out in a gas-solid separator.

[0032] According to a specific embodiment of the present invention, preferably, in step (5), the D10 particle size of the pulverized silicon-containing pyrolytic carbon is 2-3 μm, the D50 particle size is 7-9 μm, and the D90 particle size is 15-17 μm. Specifically, the pulverization can be carried out using an air jet mill and / or a mechanical grinder, etc., which should have pulverization and classification functions to obtain the pyrolytic carbon with the above-mentioned particle size range of the present invention. After pulverization, the present invention obtains silicon-containing pyrolytic carbon with suitable particle morphology and particle size distribution.

[0033] According to a specific embodiment of the present invention, preferably, in step (5), the carbonization temperature is 800–900°C, and the time is 3–4 hours. Furthermore, the carbonization is carried out in a protective atmosphere, such as, but not limited to, nitrogen. After carbonization, the microcrystals in the different layers of the carbon structure will further transform, thereby forming the silicon-carbon composite material structure of the present invention.

[0034] According to a specific embodiment of the present invention, preferably, in step (5), the demagnetization method includes electromagnetic demagnetization, with a magnetic field strength of 1.5-2T.

[0035] A second aspect of the present invention provides a silicon-carbon composite material, which is prepared by the above-described method for preparing silicon-carbon composite materials.

[0036] According to a specific embodiment of the present invention, preferably, based on the total mass of the silicon-carbon composite material as 100%, the silicon content is 10-30%, the carbon content is 65-86%, the hydrogen content is 3-5%, the sulfur content is 0.1-0.7%, and the nitrogen content is 0.1-0.3%.

[0037] According to a specific embodiment of the present invention, preferably, the silicon-carbon composite material comprises: a porous carbon framework, nano-silicon with a first coating layer distributed on the porous carbon framework, and a second coating layer coating the surface of the porous carbon framework, wherein the first coating layer and the second coating layer each contain carbon. Specifically, the first coating layer contains carbon microcrystals with small crystallite size and low orientation, and the second coating layer contains amorphous carbon. Preferably, the interlayer spacing of the carbon microcrystals in the first coating layer is 0.365–0.375 nm, and the interlayer spacing of the carbon microcrystals in the second coating layer is 0.385–0.395 nm.

[0038] The third aspect of the present invention provides a preparation system for silicon-carbon composite materials, which is used to realize the above-mentioned preparation method of silicon-carbon composite materials. The preparation system includes: a desolidification device, a distillation column, a high-speed shear machine, a nano-silicon feeder, an online mixer, a fluidized reactor, a microwave generator, a gas-solid separator, a pulverizing device, a carbonization furnace, and a demagnetizer.

[0039] The desolidification device is connected to the inlet of the distillation column, which has a light distillate oil outlet and a heavy distillate oil outlet. The light distillate oil outlet is connected to the light distillate oil inlet of the high-speed shear machine, which is connected to the nano-silicon feeder and also has a dispersant inlet. The nano-silicon oil solution outlet of the high-speed shear machine is connected to the inlet of the online mixer, the heavy distillate oil outlet is connected to the inlet of the online mixer, and the outlet of the online mixer is connected to the inlet of the fluidized bed reactor.

[0040] The fluidized reactor is connected to the microwave generator for providing microwave heating to the fluidized reactor;

[0041] The silicon-containing pyrolytic carbon outlet of the fluidized reactor is connected to the inlet of the gas-solid separator, and the silicon-containing pyrolytic carbon outlet of the gas-solid separator is sequentially connected to the pulverizing device, the carbonization furnace, and the demagnetizer.

[0042] According to a specific embodiment of the present invention, preferably, the desolidification device includes one or more of the following: sedimentation desolidification device, centrifugal desolidification device, membrane separation desolidification device, solvent extraction desolidification device, and electric field desolidification device. These devices can all be existing devices in the prior art, and the present invention does not impose any special limitations on them.

[0043] According to a specific embodiment of the present invention, preferably, the preparation system further includes a heavy distillate oil buffer tank, and the heavy distillate oil outlet of the distillation column is connected to the inlet of the online mixer through the heavy distillate oil buffer tank.

[0044] According to a specific embodiment of the present invention, preferably, the microwave generator includes at least a control unit and a modulation unit for regulating the frequency and power of the microwaves.

[0045] According to a specific embodiment of the present invention, preferably, the preparation system further includes a distillation column, the fluidized reactor is also provided with an oil and gas outlet, the oil and gas outlet is connected to the inlet of the distillation column, and the distillation column is provided with at least a gasoline outlet, a diesel outlet and a wax oil outlet.

[0046] According to a specific embodiment of the present invention, preferably, the gas-solid separator is further provided with an oil-gas and unreacted component outlet, which is connected to the fluidized reactor for returning the oil-gas and unreacted components separated from the silicon-containing pyrolytic carbon to the fluidized reactor for further pyrolysis and / or oil-gas recovery.

[0047] According to a specific embodiment of the present invention, preferably, the pulverizing device includes one or two of an air jet mill and a mechanical grinder.

[0048] According to a specific embodiment of the present invention, preferably, the demagnetizer includes an electromagnetic demagnetizer, etc.

[0049] The present invention has at least the following beneficial effects:

[0050] This invention uses heavy petroleum oil as a carbon source, improving the utilization rate and product diversity of heavy oil. It fully utilizes heavy oil, a byproduct of refining, and by adjusting the composition of the heavy oil, constructs a three-dimensional structure for silicon-carbon composite materials. Furthermore, it can also produce fuel oil as a byproduct, reducing the preparation cost of silicon-carbon composite materials while improving their performance. Therefore, this invention has the advantages of simple process and low cost, making it suitable for large-scale industrial applications. The silicon-carbon composite material of this invention can provide multi-angle and multi-channel pathways for lithium ion insertion and extraction, exhibiting high electrochemical performance, and can be used as a negative electrode material for lithium-ion batteries. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the silicon-carbon composite material preparation system in an embodiment of the present invention.

[0052] Explanation of icon numbers:

[0053] 1-Desolidification device; 2-Distillation column; 3-High-speed shear machine; 4-Nano silicon feeder; 5-Heavy distillate oil buffer tank; 6-Online mixer; 7-Fluorescent reactor; 8-Microwave generator; 801-Control unit; 802-Modulation unit; 9-Distillation column; 10-Gas-solid separator; 11-Pulverizing device; 12-Carbonization furnace; 13-Demagnetizer. Detailed Implementation

[0054] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0055] Test method:

[0056] The saturated content, aromatic content, resin content and asphaltene content of the oil were obtained according to the test results in SH / T 0509-2010 "Determination of Four Components of Petroleum Asphalt".

[0057] The sulfur content of the oil was determined according to the specifications in GB / T 17040-2019 "Determination of Sulfur Content in Petroleum and Petroleum Products by Energy Dispersive X-ray Fluorescence Spectrometry".

[0058] Nitrogen content of oil: Tested according to the description in SH / T 0657-2007 "Determination of trace nitrogen in liquid petroleum hydrocarbons by oxidative combustion and chemiluminescence method".

[0059] The carbon residue content of the oil was determined according to the specifications in GB / T 17144-2021 "Determination of Carbon Residue in Petroleum Products (Trace Method)".

[0060] Ash content of oil: Tested according to the method for determination of ash content in petroleum products in GB / T 508-1985.

[0061] The carbon, hydrogen, sulfur, and nitrogen content of the silicon-carbon composite material was obtained by testing according to the records in GB / T 214-2007 "Determination of Total Sulfur in Coal" and GB / T 30733-2014 "Determination of Carbon, Hydrogen, and Nitrogen in Coal". The silicon content of the silicon-carbon composite material was calculated by subtracting the total content of carbon, hydrogen, sulfur, and nitrogen by 100%.

[0062] The structure and carbon microcrystal spacing of the silicon-carbon composite material were observed using a high-resolution transmission microscope.

[0063] Electrochemical performance of silicon-carbon composite material: Silicon-carbon material, binder LA133, and conductive agent Super-p (mass ratio 91:6:3) were added to an appropriate amount of deionized water and thoroughly mixed to obtain a negative electrode slurry. This slurry was coated onto copper foil and then dried in a vacuum drying oven for 12 hours to obtain the negative electrode. The electrolyte was a 1 mol / L LiPF6 electrolyte, with the solvent being a 1:1:1 mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). The separator was a PP-PE-PP composite membrane, and the counter electrode was a lithium sheet. Using the above-mentioned negative electrode, electrolyte, separator, and counter electrode, a lithium-ion button half-cell was assembled in a glove box. The cell size was Φ20.0×1.6mm. Constant current charge-discharge experiments were conducted in the Xinwei battery testing system, with a charge-discharge voltage of 0.005-2V and a charge-discharge current of 0.1C.

[0064] It should be noted that in the following examples and comparative examples, if the sum of the contents of the four components is not equal to 100%, it is due to testing errors, which is a common occurrence in the art.

[0065] Example 1

[0066] This embodiment provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0067] (1) A catalytic cracking slurry and an ethylene tar hydrogenated wax oil fraction are mixed at a mass ratio of 2:1 to obtain a mixed heavy petroleum oil; wherein, based on the total mass of the catalytic cracking slurry as 100%, the saturated fraction content is 21%, the aromatic fraction content is 56%, the gum content is 21%, the asphaltenes content is 2%, the sulfur content is 1.2%, the nitrogen content is 0.4%, and the residual carbon content is 10%; and the ash content of the catalytic cracking slurry is 3600 ppm; the ethylene tar hydrogenated wax oil fraction is... The total mass of the ethylene tar is 100%, comprising 3% saturated fraction, 89% aromatic fraction, 6% gum content, 2% asphaltenes content, 0.1% sulfur content, 0.06% nitrogen content, and 18% residual carbon content; the ash content of the ethylene tar is 200 ppm. The mixed heavy petroleum oil is then subjected to electric field deconsolidation to obtain deconsolidated heavy petroleum oil. The distillation range of the deconsolidated heavy petroleum oil is 330–650℃, and its density (20℃) is 1.12 g / cm³. 3 Based on the total mass of the deconsolidated heavy petroleum oil as 100%, the saturated content is 15%, the aromatic content is 66%, the gum content is 17%, the asphaltenes content is 2%, the sulfur content is 0.8%, the nitrogen content is 0.3%, and the residual carbon content is 13%; and the ash content of the deconsolidated mixed heavy petroleum oil is 20 ppm.

[0068] The solidified mixed heavy petroleum oil was then distilled to obtain light and heavy distillate oils; the light distillate oil had a distillation range of 330–380℃ and a density (20℃) of 0.94 g / cm³. 3 Based on the total mass of the light distillate oil (100%), the saturated fraction content is 47%, the aromatic fraction content is 51%, the gum content is 3%, the asphaltenes content is 0%, the sulfur content is 0.5%, the nitrogen content is 0.2%, and the carbon residue content is 4%. The heavy distillate oil has a distillation range of 370–650℃ and a density (20℃) of 1.15 g / cm³. 3 Based on the total mass of the heavy distillate oil as 100%, the saturated fraction content is 8%, the aromatic fraction content is 70%, the gum content is 20%, the asphaltenes content is 2%, the sulfur content is 0.89%, the nitrogen content is 0.35%, and the carbon residue content is 16%.

[0069] (2) Light distillate oil and elemental silicon with a D50 particle size of 100 nm were mixed in a high-speed shearing machine. The mass ratio of elemental silicon to light distillate oil was 1:100. Sodium carboxymethyl cellulose was added during the high-speed shearing process to obtain an oil solution of nano-silicon. The mass content of sodium carboxymethyl cellulose in the oil solution of nano-silicon was 2%. The speed of the high-speed shearing machine was 2800 r / min, the temperature was 80℃, and the shearing time was 60 minutes.

[0070] (3) The heavy distillate oil and the nano-silicon oil solution are mixed online. The mixing mass ratio of the heavy distillate oil and the nano-silicon oil solution is heavy distillate oil: light distillate oil in the nano-silicon oil solution = heavy distillate oil obtained in step (1) : light distillate oil obtained in step (1). The online mixing temperature is 80℃ and the linear velocity is 0.7m / s to obtain mixed pyrolysis oil.

[0071] (4) The mixed pyrolysis oil is continuously fed into a fluidized reactor, which is connected to a microwave generator. The mixed pyrolysis oil is subjected to microwave pyrolysis by the microwave generator to obtain silicon-containing pyrolysis carbon and oil gas. The silicon-containing pyrolysis carbon is in a fluidized state. The flow rate of the mixed pyrolysis oil into the fluidized reactor is 2 kg / h, the frequency of the microwave generator is controlled at 2450 MHz and the power is controlled at 3 KW, the residence time of the mixed pyrolysis oil in the fluidized reactor is 3 seconds, and the temperature in the fluidized reactor is controlled at 570℃.

[0072] After the oil and gas flow out from the top of the fluidized reactor, they are first cooled to collect the non-condensable gas; then the remaining part is distilled to obtain gasoline, diesel and wax oil.

[0073] (5) The silicon-containing pyrolysis carbon is fed into a gas-solid separator for gas-solid separation. The temperature in the gas-solid separator is controlled at 480°C. The adsorbed and entrained oil and gas, as well as unreacted components, are separated from the silicon-containing pyrolysis carbon to obtain silicon-containing pyrolysis carbon after gas-solid separation. The separated oil and gas and unreacted components can be returned to the fluidized reactor for further pyrolysis and / or oil and gas recovery.

[0074] Subsequently, the silicon-containing pyrolytic carbon after gas-solid separation was pulverized using an air jet mill to obtain pulverized silicon-containing pyrolytic carbon with a D10 particle size of 2.5 μm, a D50 particle size of 8.3 μm, and a D90 particle size of 16.5 μm.

[0075] Then, the pulverized silicon-containing pyrolytic carbon was added to the carbonization furnace and carbonized for 3 hours at 900°C in a nitrogen atmosphere. After that, it was demagnetized by electromagnetic demagnetization with a magnetic field strength of 2T to obtain silicon-carbon composite material.

[0076] Tests conducted according to the methods described above revealed that, based on the total mass of the silicon-carbon composite material of this embodiment (100%), the silicon content was 10%, the carbon content was 85%, the hydrogen content was 4.3%, the sulfur content was 0.5%, and the nitrogen content was 0.2%. High-resolution transmission microscopy observation showed that the silicon-carbon composite material comprises: a porous carbon skeleton, elemental silicon with a first coating layer distributed on the porous carbon skeleton, and a second coating layer covering the surface of the porous carbon skeleton. Both the first and second coating layers contain carbon, and the D50 particle size of the elemental silicon is maintained at approximately 100 nm. The interlayer spacing of the carbon microcrystals in the first coating layer is approximately 0.367 nm, and the interlayer spacing of the carbon microcrystals in the second coating layer is approximately 0.385 nm.

[0077] After assembling the silicon-carbon composite material of this embodiment into a lithium-ion button half-cell according to the method described above, a constant current charge-discharge experiment was conducted. The results showed that the initial delithiation capacity (also known as the initial reversible specific capacity) was 450 mAh / g, the initial coulombic efficiency was 95%, and the capacity retention rate after 200 cycles was 98%.

[0078] Example 2

[0079] This embodiment provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0080] (1) Furfural extract oil and vacuum residue oil are mixed at a mass ratio of 1:3 to obtain mixed heavy petroleum oil; wherein, based on the total mass of the furfural extract oil as 100%, the saturated content is 16%, the aromatic content is 73%, the gum content is 9%, the asphaltenes content is 2%, the sulfur content is 0.2%, the nitrogen content is 0.2%, and the carbon residue content is 4%; and the ash content of the furfural extract oil is 300 ppm; based on the total mass of the vacuum residue oil as 100%, the saturated content is 28%, the aromatic content is 56%, the gum content is 14%, the asphaltenes content is 2%, the sulfur content is 0.5%, the nitrogen content is 0.1%, and the carbon residue content is 7%; and the ash content of the vacuum residue oil is 2400 ppm.

[0081] Then, the mixed heavy petroleum oil is subjected to electric field desolidification to obtain desolidified heavy petroleum oil; the distillation range of the desolidified heavy petroleum oil is 300–620℃, and the density (20℃) is 1.105 g / cm³. 3 Based on the total mass of the deconsolidated heavy petroleum oil as 100%, the saturated content is 25%, the aromatic content is 60%, the gum content is 13%, the asphaltenes content is 2%, the sulfur content is 0.4%, the nitrogen content is 0.1%, and the residual carbon content is 6%; and the ash content of the deconsolidated mixed heavy petroleum oil is 25 ppm.

[0082] The solidified mixed heavy petroleum oil was then distilled to obtain light and heavy distillate oils; the light distillate oil had a boiling range of 300–380℃ and a density (20℃) of 0.94 g / cm³. 3 Based on the total mass of the light distillate oil (100%), the saturated fraction content is 51%, the aromatic fraction content is 47%, the gum content is 2%, the asphaltenes content is 0%, the sulfur content is 0.3%, the nitrogen content is 0.08%, and the carbon residue content is 3%. The heavy distillate oil has a distillation range of 370–620℃ and a density (20℃) of 1.15 g / cm³. 3 Based on the total mass of the heavy distillate oil as 100%, the saturated fraction content is 14%, the aromatic fraction content is 65%, the gum content is 18%, the asphaltenes content is 3%, the sulfur content is 0.45%, the nitrogen content is 0.12%, and the carbon residue content is 8%.

[0083] (2) Light distillate oil and silicon suboxide with a D50 particle size of 100 nm were mixed in a high-speed shearing machine. The mass ratio of silicon suboxide to light distillate oil was 2:100. Sodium alginate was added during the high-speed shearing process to obtain an oil solution of nano-silicon. The mass content of sodium alginate in the oil solution of nano-silicon was 3%. The speed of the high-speed shearing machine was 2500 r / min, the temperature was 60℃, and the shearing time was 50 minutes.

[0084] (3) The heavy distillate oil and the nano-silicon oil solution are mixed online. The mixing mass ratio of the heavy distillate oil and the nano-silicon oil solution is heavy distillate oil: light distillate oil in the nano-silicon oil solution = 90% by mass of the heavy distillate oil obtained in step (1) : light distillate oil obtained in step (1). The online mixing temperature is 120℃ and the linear velocity is 0.7m / s to obtain mixed pyrolysis oil.

[0085] (4) The mixed pyrolysis oil is continuously fed into a fluidized reactor, which is connected to a microwave generator. The mixed pyrolysis oil is subjected to microwave pyrolysis by the microwave generator to obtain silicon-containing pyrolysis carbon and oil gas. The silicon-containing pyrolysis carbon is in a fluidized state. The flow rate of the mixed pyrolysis oil into the fluidized reactor is 1 kg / h, the frequency of the microwave generator is controlled at 2350 MHz and the power is controlled at 4 KW, the residence time of the mixed pyrolysis oil in the fluidized reactor is 2 seconds, and the temperature in the fluidized reactor is controlled at 560℃.

[0086] After the oil and gas flow out from the top of the fluidized reactor, they are first cooled to collect the non-condensable gas; then the remaining part is distilled to obtain gasoline, diesel and wax oil.

[0087] (5) The silicon-containing pyrolysis carbon is fed into a gas-solid separator for gas-solid separation. The temperature in the gas-solid separator is controlled at 500°C. The adsorbed and entrained oil and gas, as well as unreacted components, are separated from the silicon-containing pyrolysis carbon to obtain silicon-containing pyrolysis carbon after gas-solid separation. The separated oil and gas and unreacted components can be returned to the fluidized reactor for further pyrolysis and / or oil and gas recovery.

[0088] Subsequently, the silicon-containing pyrolytic carbon after gas-solid separation was pulverized by an air jet mill to obtain pulverized silicon-containing pyrolytic carbon with a D10 particle size of 2.6 μm, a D50 particle size of 8.5 μm, and a D90 particle size of 16.8 μm.

[0089] Then, the pulverized silicon-containing pyrolytic carbon was added to the carbonization furnace and carbonized for 3 hours at 900°C in a nitrogen atmosphere. After that, it was demagnetized by electromagnetic demagnetization with a magnetic field strength of 1.5T to obtain silicon-carbon composite material.

[0090] Tests conducted according to the methods described above revealed that, based on the total mass of the silicon-carbon composite material of this embodiment (100%), the silicon content was 30%, the carbon content was 66%, the hydrogen content was 3.7%, the sulfur content was 0.2%, and the nitrogen content was 0.1%. High-resolution transmission microscopy observation showed that the silicon-carbon composite material comprises: a porous carbon skeleton, silicon suboxide with a first coating layer distributed on the porous carbon skeleton, and a second coating layer covering the surface of the porous carbon skeleton. Both the first and second coating layers contain carbon, and the D50 particle size of the silicon suboxide is maintained at approximately 100 nm. The interlayer spacing of the carbon microcrystals in the first coating layer is approximately 0.365 nm, and the interlayer spacing of the carbon microcrystals in the second coating layer is approximately 0.387 nm.

[0091] After assembling the silicon-carbon composite material of this embodiment into a lithium-ion button half-cell according to the method described above, a constant current charge-discharge experiment was conducted, and the initial delithiation capacity was 480 mAh / g, the initial coulombic efficiency was 94%, and the capacity retention rate after 200 cycles was 98%.

[0092] Example 3

[0093] This embodiment provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0094] (1) The catalytic cracking slurry (same as in Example 1) was subjected to membrane separation to remove the solidified petroleum heavy oil; the distillation range of the removed petroleum heavy oil was 320–610 °C, and the density (20 °C) was 1.11 g / cm³. 3 Based on the total mass of the deconsolidated heavy petroleum oil as 100%, the saturated content is 18%, the aromatic content is 70%, the gum content is 10%, the asphaltenes content is 2%, the sulfur content is 0.6%, the nitrogen content is 0.2%, and the residual carbon content is 12%; and the ash content of the deconsolidated heavy petroleum oil is 40 ppm.

[0095] The deconsolidated heavy petroleum oil was then distilled to obtain light and heavy distillate oils; the light distillate oil had a boiling range of 320–380℃ and a density (20℃) of 0.96 g / cm³. 3 Based on the total mass of the light distillate oil (100%), the saturated fraction content is 36%, the aromatic fraction content is 58%, the gum content is 6%, the asphaltenes content is 0%, the sulfur content is 0.3%, the nitrogen content is 0.08%, and the carbon residue content is 5%. The heavy distillate oil has a distillation range of 370–610℃ and a density (20℃) of 1.15 g / cm³. 3 Based on the total mass of the heavy distillate oil as 100%, the saturated fraction content is 10%, the aromatic fraction content is 74%, the gum content is 13%, the asphaltenes content is 3%, the sulfur content is 0.45%, the nitrogen content is 0.12%, and the carbon residue content is 15%.

[0096] (2) Light distillate oil and porous silicon with a D50 particle size of 100 nm were mixed in a high-speed shearing machine. The mass ratio of porous silicon to light distillate oil was 3:100. Sodium hexametaphosphate was added during the high-speed shearing process to obtain an oil solution of nano-silicon. The mass content of sodium hexametaphosphate in the oil solution of nano-silicon was 4%. The speed of the high-speed shearing machine was 2700 r / min, the temperature was 70℃, and the shearing time was 30 minutes.

[0097] (3) The heavy distillate oil and the nano-silicon oil solution are mixed online. The mixing mass ratio of the heavy distillate oil and the nano-silicon oil solution is heavy distillate oil: light distillate oil in the nano-silicon oil solution = 95% by mass of the heavy distillate oil obtained in step (1) : light distillate oil obtained in step (1). The online mixing temperature is 100℃ and the linear velocity is 0.5m / s to obtain mixed pyrolysis oil.

[0098] (4) The mixed pyrolysis oil is continuously fed into a fluidized reactor, which is connected to a microwave generator. The mixed pyrolysis oil is subjected to microwave pyrolysis by the microwave generator to obtain silicon-containing pyrolysis carbon and oil gas. The silicon-containing pyrolysis carbon is in a fluidized state. The flow rate of the mixed pyrolysis oil into the fluidized reactor is 1.5 kg / h, the frequency of the microwave generator is controlled at 2550 MHz and the power is controlled at 5 KW, the residence time of the mixed pyrolysis oil in the fluidized reactor is 4 seconds, and the temperature in the fluidized reactor is controlled at 530℃.

[0099] After the oil and gas flow out from the top of the fluidized reactor, they are first cooled to collect the non-condensable gas; then the remaining part is distilled to obtain gasoline, diesel and wax oil.

[0100] (5) The silicon-containing pyrolysis carbon is fed into a gas-solid separator for gas-solid separation. The temperature in the gas-solid separator is controlled at 470°C. The adsorbed and entrained oil and gas, as well as unreacted components, are separated from the silicon-containing pyrolysis carbon to obtain silicon-containing pyrolysis carbon after gas-solid separation. The separated oil and gas and unreacted components can be returned to the fluidized reactor for further pyrolysis and / or oil and gas recovery.

[0101] Subsequently, the silicon-containing pyrolytic carbon after gas-solid separation was pulverized by an air jet mill to obtain pulverized silicon-containing pyrolytic carbon with a D10 particle size of 2.2 μm, a D50 particle size of 7.5 μm, and a D90 particle size of 15.8 μm.

[0102] Then, the pulverized silicon-containing pyrolytic carbon was added to the carbonization furnace and carbonized at 800°C for 4 hours in a nitrogen atmosphere. After that, it was demagnetized by electromagnetic demagnetization with a magnetic field strength of 1.8T to obtain silicon-carbon composite material.

[0103] Tests conducted according to the methods described above revealed that, based on the total mass of the silicon-carbon composite material of this embodiment (100%), the silicon content was 20%, the carbon content was 75%, the hydrogen content was 4.5%, the sulfur content was 0.4%, and the nitrogen content was 0.1%. High-resolution transmission microscopy observation showed that the silicon-carbon composite material comprises: a porous carbon skeleton, porous silicon with a first coating layer distributed on the porous carbon skeleton, and a second coating layer covering the surface of the porous carbon skeleton. Both the first and second coating layers contain carbon, and the D50 particle size of the porous silicon is maintained at approximately 100 nm. The interlayer spacing of the carbon microcrystals in the first coating layer is approximately 0.372 nm, and the interlayer spacing of the carbon microcrystals in the second coating layer is approximately 0.393 nm.

[0104] After assembling the silicon-carbon composite material of this embodiment into a lithium-ion button half-cell according to the method described above, a constant current charge-discharge experiment was conducted, and the initial delithiation capacity was 510 mAh / g, the initial coulombic efficiency was 94%, and the capacity retention rate after 200 cycles was 98%.

[0105] Example 4

[0106] This embodiment provides a silicon-carbon composite material preparation system, which is used to implement the silicon-carbon composite material preparation methods of Examples 1-3, such as... Figure 1 As shown, the preparation system includes: a desolidification device 1, a distillation column 2, a high-speed shear machine 3, a nano-silicon feeder 4, a heavy distillate oil buffer tank 5, an online mixer 6, a fluidized bed reactor 7, a microwave generator 8, a distillation column 9, a gas-solid separator 10, a pulverizing device 11, a carbonization furnace 12, and a demagnetizer 13.

[0107] The solidification device 1 is connected to the inlet of the distillation column 2, which has a light distillate oil outlet and a heavy distillate oil outlet. The light distillate oil outlet of the distillation column 2 is connected to the light distillate oil inlet of the high-speed shear machine 3, which is connected to the nano-silicon feeder 4 and also has a dispersant inlet. The nano-silicon oil solution outlet of the high-speed shear machine 3 is connected to the inlet of the online mixer 6. The heavy distillate oil outlet of the distillation column 2 is connected to the inlet of the online mixer 6 via the heavy distillate oil buffer tank 5, and the outlet of the online mixer 6 is connected to the inlet of the fluidized reactor 7.

[0108] The fluidized reactor 7 is connected to a microwave generator 8, which is used to provide microwave heating to the fluidized reactor 7;

[0109] The oil and gas outlet of the fluidized reactor 7 is connected to the inlet of the distillation column 9, which is equipped with at least a gasoline outlet, a diesel outlet, and a wax oil outlet.

[0110] The outlet of the silicon-containing pyrolytic carbon in the fluidized reactor 7 is connected to the inlet of the gas-solid separator 10; the gas-solid separator 10 is also provided with an oil and gas outlet and an outlet for unreacted components, which are connected to the fluidized reactor 7 to return the oil and gas and unreacted components separated from the silicon-containing pyrolytic carbon to the fluidized reactor 7 for further pyrolysis and / or recovery of oil and gas.

[0111] The silicon-containing pyrolytic carbon outlet of the gas-solid separator 10 is sequentially connected to the crushing device 11, the carbonization furnace 12, and the demagnetizer 13, and the demagnetizer 13 produces silicon-carbon composite material.

[0112] In this embodiment, the desolidification device 1 includes one or more of the following: sedimentation desolidification device, centrifugal desolidification device, membrane separation desolidification device, solvent extraction desolidification device, and electric field desolidification device. The microwave generator 8 includes at least a control unit 801 and a modulation unit 802 for controlling the frequency and power of the microwaves. The pulverizing device 11 includes one or two of the following: an air jet mill and a mechanical grinder. The demagnetizer 13 includes an electromagnetic demagnetizer.

[0113] Comparative Example 1

[0114] This comparative example provides a silicon-carbon composite material, the preparation method of which includes the following steps:

[0115] The deconsolidated heavy petroleum oil from Example 3 (the distillation range of the deconsolidated heavy petroleum oil is 320–610°C, and the density (at 20°C) is 1.11 g / cm³) 3 The total mass of the deconsolidated heavy petroleum oil is 100%, and its saturated content is 18%, aromatic content is 70%, gum content is 10%, asphaltenes content is 2%, sulfur content is 0.6%, nitrogen content is 0.2%, and residual carbon content is 12%; and the ash content of the deconsolidated heavy petroleum oil is 40 ppm. The oil is added to an electrically heated reactor for pyrolysis. The temperature in the electrically heated reactor is controlled at 530℃ and the pressure at 0.3 MPa. Pyrolysis is carried out for 10 hours to obtain pyrolytic carbon.

[0116] Then, the pyrolytic char is pulverized by an air jet mill to obtain pulverized pyrolytic char with a D10 particle size of 2.4 μm, a D50 particle size of 8.2 μm, and a D90 particle size of 16.3 μm.

[0117] Subsequently, the pulverized pyrolytic carbon and porous silicon with a D50 particle size of 100 nm were mixed. The mass ratio of porous silicon to pulverized pyrolytic carbon was 3:100 to obtain a silicon-carbon mixture.

[0118] Then, the silicon-carbon mixture and epoxy resin were added to a kneader for solid-phase coating. The amount of epoxy resin added was 10% of the mass of the silicon-carbon mixture. The temperature in the kneader was controlled at 500℃, the rotation speed was 700r / min, and the coating time was 5 hours to obtain a silicon-carbon mixture with a coating layer.

[0119] Then, the silicon-carbon mixture with the coating layer is added to the carbonization furnace and carbonized at 800°C for 4 hours in a nitrogen atmosphere to obtain the silicon-carbon composite material.

[0120] Tests conducted according to the methods described above revealed that, based on a total mass of 100% for the silicon-carbon composite material in this comparative example, the silicon content was 4%, the carbon content was 89%, the hydrogen content was 6.4%, the sulfur content was 0.4%, and the nitrogen content was 0.2%. High-resolution transmission microscopy observation showed that the porous silicon particles in the composite material agglomerated, with particle sizes ranging from 100 to 300 nm. Furthermore, the epoxy resin coating layer failed to completely cover the porous silicon particles, and the interlayer spacing of the carbon microcrystals in the coating layer was approximately 0.368 nm.

[0121] After assembling the silicon-carbon composite material of this comparative example into a lithium-ion button half-cell according to the method described above, a constant current charge-discharge experiment was conducted. The results showed that the initial delithiation capacity was 389 mAh / g, the initial coulombic efficiency was 82%, and the capacity retention rate after 200 cycles was 70%.

[0122] Comparative Example 2

[0123] This comparative example provides a silicon-carbon composite material, the preparation method of which is basically the same as that of Example 3, except that: the mixed pyrolysis oil in Example 3 is added to an electrically heated reactor for pyrolysis reaction, the temperature in the electrically heated reactor is controlled at 530°C and the pressure at 0.3 MPa, and pyrolysis is carried out for 10 hours to obtain silicon-containing pyrolysis carbon; there is no need for gas-solid separation afterward, and silicon-containing pyrolysis carbon is obtained after cooling in the reactor. Then, the crushing, carbonization and demagnetization conditions are the same as in Example 3 to obtain the silicon-carbon composite material.

[0124] Following the methods described above, the uneven distribution of porous silicon in the electrically heated reactor resulted in silicon content ranging from 2% to 8%, carbon content from 85% to 91%, hydrogen content from 4% to 6.4%, sulfur content of 0.4%, and nitrogen content of 0.2% (based on a total mass of 100% for the silicon-carbon composite material). High-resolution transmission microscopy revealed agglomeration of porous silicon particles in the composite material, with particle sizes ranging from 500 to 1000 nm. The interlayer spacing of carbon microcrystals in this composite material was approximately 0.363 nm.

[0125] Following the method described above, silicon-carbon composite materials from different locations in this comparative example were assembled into lithium-ion button half-cells. Constant current charge-discharge experiments were then conducted, revealing that the initial delithiation capacity was 200–320 mAh / g, the initial coulombic efficiency was 60–70%, and the capacity retention rate after 200 cycles was 20–30%.

[0126] Comparative Example 3

[0127] This comparative example provides a silicon-carbon composite material, the preparation method of which is basically the same as that of Example 3, except that: the deconsolidated heavy petroleum oil and porous silicon with a D50 particle size of 100 nm from Example 3 are mixed in a high-speed shear mill, the mixing mass ratio of porous silicon to deconsolidated heavy petroleum oil is 3:100, sodium hexametaphosphate is added during the high-speed shearing process to obtain mixed pyrolysis oil; wherein, the mass content of sodium hexametaphosphate in the mixed pyrolysis oil is 4%, the speed of the high-speed shear mill is 2700 r / min, the temperature is 70℃, and the shearing time is 30 minutes; the conditions for microwave pyrolysis, gas-solid separation, pulverization, carbonization and demagnetization in the subsequent fluidized reactor are the same as those in Example 3, to obtain the silicon-carbon composite material.

[0128] Following the methods described above, tests were conducted. Due to the low dispersibility of porous silicon in the deconsolidated heavy petroleum oil, the silicon content of the comparative silicon-carbon composite material collected at different times ranged from 0.5% to 6%, the carbon content from 87% to 92.5%, the hydrogen content from 4% to 6.4%, the sulfur content from 0.4%, and the nitrogen content from 0.2% (based on the total mass of the silicon-carbon composite material as 100%). High-resolution transmission microscopy revealed that the porous silicon particles in the silicon-carbon composite material agglomerated, with particle sizes ranging from 500 to 1000 nm. The interlayer spacing of the carbon microcrystals in this silicon-carbon composite material was approximately 0.363 nm.

[0129] Following the method described above, the silicon-carbon composite materials collected at different times in this comparative example were assembled into lithium-ion button half-cells. Constant current charge-discharge experiments were then conducted, and the initial delithiation capacity was 200–320 mAh / g, the initial coulombic efficiency was 60–70%, and the capacity retention rate after 200 cycles was 20–30%.

Claims

1. A method for preparing a silicon-carbon composite material, comprising the following steps: (1) The heavy petroleum oil is desolidified and distilled to obtain light distillate oil and heavy distillate oil; (2) The light distillate oil and nano-silicon are mixed and a dispersant is added to obtain an oil solution of nano-silicon; (3) The heavy distillate oil and the oil solution of the nano-silicon are mixed to obtain a mixed pyrolysis oil; (4) The mixed pyrolysis oil is microwave pyrolyzed in a fluidized reactor to obtain pyrolysis carbon containing silicon; (5) After gas-solid separation, crushing, carbonization and demagnetization of the silicon-containing pyrolytic carbon, the silicon-carbon composite material is obtained.

2. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (1), the distillation range of the deconsolidated heavy petroleum oil is 300–680℃, and the density is 0.93–1.12 g / cm³. 3 The total mass of the deconsolidated heavy petroleum oil is 100%, and its saturated content is 12-30%, aromatic content is 50-75%, gum content is 10-20%, asphaltenes content is 0.5-4%, sulfur content is 0.5-2%, nitrogen content is 0.1-0.7%, and residual carbon content is 5-15%; and the ash content of the deconsolidated heavy petroleum oil is 10-100 ppm.

3. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (1), the light distillate oil has a boiling range of 300–400°C and a density of 0.93–0.98 g / cm³. 3 Based on the total mass of the light distillate oil as 100%, the saturated fraction content is 35-55%, the aromatic fraction content is 40-60%, the gum content is 0.5-6%, the asphaltenes content is 0-0.1%, the sulfur content is 0.3-1%, the nitrogen content is 0.05-0.3%, and the carbon residue content is 3-5%.

4. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (1), the heavy distillate oil has a boiling range of 350–680°C and a density of 0.98–1.15 g / cm³. 3 Based on the total mass of the heavy distillate oil as 100%, the saturated fraction content is 8-15%, the aromatic fraction content is 50-80%, the gum content is 10-30%, the asphaltenes content is 0.7-6%, the sulfur content is 0.6-2.2%, the nitrogen content is 0.1-0.8%, and the carbon residue content is 7-18%.

5. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (2), the D50 particle size of the nano-silicon is 70-110 nm; the nano-silicon includes one or more of elemental silicon, silicon suboxide and porous silicon.

6. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (2), the mass ratio of the nano-silicon to the light distillate oil is (1-3):

100.

7. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (2), the dispersant includes one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium hexametaphosphate, and sodium alginate; the mass content of the dispersant in the oil solution of nano-silicon is 1-5%.

8. The method for preparing the silicon-carbon composite material according to claim 1, wherein, Step (2) is performed using a high-speed shearing machine with a shearing speed of 2500-2800 r / min, a temperature of 50-80℃, and a shearing time of 30-60 minutes.

9. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (3), the heavy distillate oil and the nano-silicon oil solution are mixed online. The online mixing temperature is 80-120°C and the linear velocity is 0.5-0.7 m / s. The mixing mass ratio of the heavy distillate oil and the nano-silicon oil solution is: heavy distillate oil: light distillate oil in the nano-silicon oil solution = 90-100% by mass of the heavy distillate oil obtained in step (1): light distillate oil obtained in step (1).

10. The method for preparing the silicon-carbon composite material according to claim 1, wherein, Step (4) includes: introducing the mixed pyrolysis oil into a fluidized bed reactor, the fluidized bed reactor being connected to a microwave generator, and the mixed pyrolysis oil being subjected to microwave pyrolysis by the microwave generator to obtain silicon-containing pyrolysis carbon and oil gas, the silicon-containing pyrolysis carbon being in a fluidized state; wherein, the flow rate of the mixed pyrolysis oil entering the fluidized bed reactor is 1-2 kg / h, the frequency of the microwave generator is controlled at 2350-2550 MHz and the power is controlled at 2-5 KW, the residence time of the mixed pyrolysis oil in the fluidized bed reactor is 2-4 seconds, and the temperature in the fluidized bed reactor is controlled at 530-580℃.

11. The method for preparing the silicon-carbon composite material according to claim 10, wherein, Step (4) further includes: distilling the oil and gas at least to obtain gasoline, diesel and wax oil.

12. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (5), the temperature of the gas-solid separation is 470-500℃.

13. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (5), the particle size of the pulverized silicon-containing pyrolytic carbon is 2-3 μm for D10, 7-9 μm for D50, and 15-17 μm for D90.

14. The method for preparing the silicon-carbon composite material according to claim 1, wherein, In step (5), the carbonization temperature is 800-900°C and the time is 3-4 hours.

15. A silicon-carbon composite material, which is prepared by the method of any one of claims 1-14.

16. The silicon-carbon composite material according to claim 15, wherein, Based on the total mass of the silicon-carbon composite material as 100%, the silicon content is 10-30%, the carbon content is 65-86%, the hydrogen content is 3-5%, the sulfur content is 0.1-0.7%, and the nitrogen content is 0.1-0.3%.

17. A system for preparing a silicon-carbon composite material, used to implement the method for preparing the silicon-carbon composite material according to any one of claims 1-14, the system comprising: Desolidification device, distillation column, high-speed shear machine, nano-silicon feeder, online mixer, fluidized reactor, microwave generator, gas-solid separator, pulverizing device, carbonization furnace and demagnetizer; The desolidification device is connected to the inlet of the distillation column, which has a light distillate oil outlet and a heavy distillate oil outlet. The light distillate oil outlet is connected to the light distillate oil inlet of the high-speed shear machine, which is connected to the nano-silicon feeder and also has a dispersant inlet. The nano-silicon oil solution outlet of the high-speed shear machine is connected to the inlet of the online mixer, the heavy distillate oil outlet is connected to the inlet of the online mixer, and the outlet of the online mixer is connected to the inlet of the fluidized bed reactor. The fluidized reactor is connected to the microwave generator for providing microwave heating to the fluidized reactor; The silicon-containing pyrolytic carbon outlet of the fluidized reactor is connected to the inlet of the gas-solid separator, and the silicon-containing pyrolytic carbon outlet of the gas-solid separator is sequentially connected to the pulverizing device, the carbonization furnace, and the demagnetizer.

18. The silicon-carbon composite material preparation system according to claim 17, wherein, The desolidification device includes one or more of the following: sedimentation desolidification device, centrifugal desolidification device, membrane separation desolidification device, solvent extraction desolidification device, and electric field desolidification device.

19. The silicon-carbon composite material preparation system according to claim 17, wherein, The preparation system further includes a distillation column, and the fluidized reactor is also provided with an oil and gas outlet, which is connected to the inlet of the distillation column. The distillation column is provided with at least a gasoline outlet, a diesel outlet, and a wax oil outlet.

20. The silicon-carbon composite material preparation system according to claim 17, wherein, The gas-solid separator is also provided with oil and gas outlets and unreacted component outlets, which are connected to the fluidized reactor to return the oil and gas and unreacted components separated from the silicon-containing pyrolytic carbon to the fluidized reactor for further pyrolysis and / or oil and gas recovery.

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