Process for the production of isotropic coke and the product and graphite obtained thereby

Abstract

The application provides a preparation method of isotropic coke and a product and graphite obtained by the method, and belongs to the technical field of coke material preparation. The preparation method of the isotropic coke comprises the following steps: 1) mixing a water-soluble carbon source, a surfactant and water to obtain an aqueous solution; 2) under physical emulsification conditions, slowly adding an oil phase into the aqueous phase to form an oil-in-water emulsion; and 3) performing a coking reaction on the oil-in-water emulsion obtained in the step 2) to obtain the isotropic coke. The application adopts an oil-in-water emulsion limited coking strategy to control the microtexture of the coke from the source, so that the coke is mainly in the form of small flake isotropic structure, and the defects of poor fast-charging performance and easy cycle attenuation caused by the traditional needle-shaped coke fiber structure are overcome, so that the coke has high capacity, high rate and long cycle life after graphitization.

Description

Technical Field

[0001] This invention belongs to the field of coke material preparation technology, specifically relating to a method for preparing isotropic coke, the resulting product, and graphite. Background Technology

[0002] Traditional needle coke has a highly oriented fibrous structure. Although this structure has a high capacity after graphitization, its large crystallite size and strong anisotropy result in a long diffusion path and high diffusion resistance for lithium ions between graphite layers.

[0003] To improve performance, researchers have attempted to prepare isotropic coke. Isotropic coke is a type of coke material with an optically isotropic structure, possessing excellent high-temperature performance and conductivity, high strength and density, as well as low ash content and low resistivity. Currently, the preparation of isotropic coke mainly falls into two categories: one approach is to improve the isotropicity of the coke, such as patent CN1306070A which prepares isotropic coke through oxidative crosslinking, and patent CN111943184A which improves the isotropicity of the coke by directly coking with heavy raw materials. However, these methods either lead to an increase in the number of difficult-to-graphitize mosaic structures (>30%), reducing the degree of graphitization and reversible capacity; or the process is complex and the effect is limited. The other approach is to add solid nucleating agents to physically block the fusion of intermediate phases, such as patent CN114525153A. However, the poor compatibility between solid particles and oil slurry leads to poor structural uniformity and fails to change the diffusion mode of lithium ions between graphite layers, thus limiting high-rate performance.

[0004] Therefore, there is an urgent need to develop a new type of coke material that can maintain a high degree of graphitization to provide high capacity, and has a microstructure that is more conducive to the rapid diffusion of lithium ions and buffers volume expansion. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for preparing isotropic coke, the resulting product, and graphite. This invention employs a "water-in-oil" emulsion confined coking strategy to control the microstructure of the coke from the source, making it predominantly a small, flake-like isotropic structure. This overcomes the defects of poor fast-charging performance and easy cycle decay caused by the traditional needle-like coke fiber structure, thus achieving high capacity, high rate capability, and long cycle life after graphitization.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing isotropic coke using an oil-in-water emulsion method, comprising the following steps: 1) Mix water-soluble carbon source, surfactant and water to obtain an aqueous solution; 2) Under physical emulsification conditions, the oil phase is added to the aqueous phase to form an oil-in-water emulsion; the mass ratio of the oil phase to the aqueous phase is (3:7)-(7:3); the average droplet size of the formed oil-in-water emulsion is 10-50 μm; 3) The oil-in-water emulsion obtained in step 2) is subjected to a coking reaction to obtain isotropic coke; The water-soluble carbon source is one or more of the following: corn starch, sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylamide, sodium lignosulfonate, dextrin, and cyclodextrin. The surfactant is one or more of the following: hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium cholate, sodium deoxycholate, Tween series and Span series; The oil phase is one or more of the following: catalytic cracking slurry oil, vacuum residue, recycled oil, coking wax oil, ethylene tar, and coal tar pitch.

[0007] Preferably, step 2) further includes pretreatment of the oil phase before adding it to the aqueous phase; the pretreatment method includes one or more of filtration sedimentation, centrifugation, catalytic hydrogenation, vacuum distillation and solvent extraction, wherein the ash content of the oil slurry is controlled to be ≤0.10% by sedimentation filtration or centrifugation, the sulfur content is controlled to be ≤0.3% by catalytic hydrogenation, the initial boiling point of the oil slurry is controlled to be ≥250℃ by vacuum distillation, and the aromatic content of the oil slurry is controlled to be ≥70% by solvent extraction.

[0008] Preferably, the physical emulsification method described in step 2) includes one or more of high-speed shear dispersion, high-pressure homogenization, or ultrasonic emulsification.

[0009] Preferably, the amount of water-soluble carbon source added in step 1) is 0.5-5% of the mass of deionized water.

[0010] Preferably, the amount of surfactant added is 0.1‰-0.5‰ of the mass of deionized water.

[0011] Preferably, the oil phase described in step 2) is added to the aqueous phase at a uniform rate over 30-60 minutes.

[0012] Preferably, the average droplet size of the oil-in-water emulsion formed in step 2) is 10-50 μm.

[0013] Preferably, the coking reaction in step 3) is carried out at a temperature of 420-520°C, a pressure of 0.2-2.0 MPa, and a reaction time of 4-24 h.

[0014] The present invention provides an isotropic focal plane, which is prepared by any one of the methods described above. The polarizing microstructure of the isotropic focal plane is fish-scale shaped, with the proportion of scale-like small structures being ≥90%. The transverse dimension of the small structures is 10-30 μm, and the longitudinal dimension is 10-30 μm.

[0015] The present invention provides a graphite obtained by graphitizing the isotropic char described above at 2500-3000℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes a "water-in-oil emulsion confined coking" strategy to prepare isotropic coke. During the coking heating process, the physical boundaries of the droplets restrict the growth space of the mesophase spherulites, preventing them from growing into large-sized domain-like or fibrous structures, and instead forming more small-sized lamellar or mosaic structures. Furthermore, a stable oil-water interface film composed of a water-soluble carbon source and surfactant effectively prevents the contact and fusion of mesophase substances between different droplets, avoiding the continued development of anisotropic structures. The reaction processes within numerous independent microreactors may exhibit slight differences; this asynchronicity further inhibits the formation of large-scale ordered structures across the entire process. Ultimately, the resulting coke exhibits a texture dominated by isotropic flakes. In addition, the evaporation of the aqueous phase during coking may introduce some mesopores, which is beneficial for electrolyte wetting and ion transport.

[0017] 2. This invention provides an isotropic coke with a predominantly flake-like structure (≥90%), fundamentally changing the fibrous texture of traditional needle coke and providing an ideal precursor for fast-charging graphite. The graphite anode based on this isotropic coke possesses abundant rapid lithium-ion diffusion channels and a uniform stress-buffering structure. At 6C rate, it maintains ≥80% capacity retention after 2000 cycles, far superior to traditional needle coke anodes.

[0018] 3. This invention uses biomass waste such as corn starch as a water-soluble carbon source, which is low-cost and environmentally friendly. This type of carbon source can increase the viscosity of the aqueous phase, synergistically stabilize the oil-water interface with surfactants, and form a confined carbon shell and conductive network in situ during coking, thereby effectively inhibiting excessive growth of the mesophase and promoting the formation of isotropic structures. The water-in-oil emulsion method is simple, has mild conditions, is easy to scale up, and has good industrialization prospects. Attached Figure Description

[0019] Figure 1 An optical microscope image of the oil-in-water emulsion prepared in Example 1 of this invention; Figure 2 This is a diagram of the isotropic focal polarization structure prepared in Example 1 of the present invention; Figure 3This is a diagram of the isotropic focal polarization structure prepared in Example 2 of the present invention; Figure 4 This is a diagram of the isotropic focal polarization structure prepared in Example 3 of the present invention; Figure 5 This is a diagram of the isotropic focal polarization structure prepared in Example 4 of the present invention; Figure 6 This is an image of the isotropic focal polarization structure prepared in Example 5 of the present invention; Figure 7 This is a diagram of the isotropic focal polarization structure prepared in Example 6 of the present invention; Figure 8 This is a diagram of the isotropic focal polarization structure prepared in Example 7 of the present invention; Figure 9 This is a diagram of the isotropic focal polarization structure prepared in Example 8 of the present invention; Figure 10 This is a diagram of the conventional needle-shaped focal polarizer structure prepared in Comparative Example 1 of the present invention; Figure 11 This is a polarized structure diagram of the coke prepared in Comparative Example 2 of the present invention; Figure 12 An optical microscope image of the water-in-oil emulsion prepared in Comparative Example 3 of this invention; Figure 13 This is a polarized structure diagram of the coke prepared in Comparative Example 3 of the present invention; Figure 14 This is a polarized structure diagram of the coke prepared in Comparative Example 4 of the present invention; Figure 15 This is a polarized structure diagram of the coke prepared in Comparative Example 5 of the present invention. Detailed Implementation

[0020] The technical solutions in specific embodiments of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are merely some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0021] This invention provides a method for preparing isotropic coke using an oil-in-water emulsion method, comprising the following steps: 1) Mix water-soluble carbon source, surfactant and water to obtain an aqueous solution; 2) Under physical emulsification conditions, the oil phase is added to the aqueous phase to form an oil-in-water emulsion; the mass ratio of the oil phase to the aqueous phase is (3:7)-(7:3). 3) The oil-in-water emulsion obtained in step 2) is subjected to a coking reaction to obtain isotropic coke.

[0022] The coking mechanism for isotropic coke prepared in this invention is based on a "water-in-oil emulsion confined coking" strategy: by dispersing heavy oil into micron-sized independent droplets, a large number of microreactors are formed, utilizing the spatial confinement effect to suppress the growth and directional alignment of mesophase spherulites; a stable oil-water interface film constructed by a water-soluble carbon source and surfactants prevents the coalescence between adjacent droplets; simultaneously, a large number of isolated droplets undergo asynchronous reactions during coking, weakening the synergistic formation of the overall ordered structure. This forces the generation of isotropic coke with a predominantly flake structure.

[0023] This invention involves mixing a water-soluble carbon source, a surfactant, and water to obtain an aqueous solution. In this invention, the water-soluble carbon source is one or more selected from corn starch, sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylamide, sodium lignosulfonate, dextrin, and cyclodextrin; the amount of the water-soluble carbon source added is preferably 0.5-5% of the water mass. The surfactant is one or more selected from hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium cholate, sodium deoxycholate, Tween series, and Span series. In this invention, the amount of surfactant added is preferably 0.1‰-0.5‰ of the deionized water mass.

[0024] In this invention, the amount of water-soluble carbon source added must be strictly controlled within a reasonable range (0.5-5%): if the amount added is too low, the viscosity of the aqueous phase is insufficient, making it difficult to effectively inhibit oil droplet aggregation, and a continuous and dense carbon shell cannot be formed during coking, weakening the confinement effect; if the amount added is too high, the viscosity of the aqueous phase is too high, increasing the mass transfer resistance during emulsification and subsequent coking processes, easily leading to a wider oil droplet size distribution, and even inducing demulsification. The amount of surfactant (0.1‰-0.5‰) also needs to be moderate: if the amount is too low, the oil-water interfacial tension will not be reduced sufficiently, the emulsion stability will be poor, and the oil droplets will easily aggregate rapidly; if the amount is too high, too many impurities may remain after coking, affecting the purity of the coke and increasing costs.

[0025] In this invention, corn starch, CMC, and sodium alginate are used as water-soluble carbon sources because they are rich in hydrophilic groups such as hydroxyl and carboxyl groups, which can significantly increase the viscosity of the aqueous phase and inhibit oil droplet collision and aggregation. Their molecular chains adsorb at the oil-water interface, forming a dense composite film with surfactants, enhancing interfacial thermal stability. During coking, these carbon sources carbonize in situ, forming an amorphous carbon shell or mesoporous carbon network around the oil droplets. This provides a conductive framework and, through physical confinement, forces the mesophase to form only fine lamellar structures, avoiding large-sized fibrous structures. CTAB, SDS, Tween / Span, etc., are used as surfactants because their amphiphilic molecules rapidly reduce the interfacial tension between oil and water, causing the oil phase to break into micron-sized droplets under shear. Ionic surfactants (CTAB, SDS, etc.) prevent droplet aggregation through electrostatic repulsion, while non-ionic surfactants (Tween, Span) provide steric stabilization. Together, they ensure small droplet size and narrow distribution, laying the foundation for subsequent confined coking. Water-soluble carbon sources and surfactants form a composite adsorption layer at the interface, which not only stabilizes the oil-in-water emulsion but also maintains the independence of droplets during coking, thus realizing the transformation from continuous phase directional growth to isotropic coking in a confined space.

[0026] After obtaining the aqueous phase, the present invention adds the oil phase to the aqueous phase under physical emulsification conditions to form an oil-in-water emulsion. In this invention, to fully form the oil-in-water emulsion, the oil phase is added to the aqueous phase slowly, preferably at a uniform rate over 30-60 minutes. In this invention, the oil phase is preferably pretreated before being added to the aqueous phase; the pretreatment methods include one or more of filtration and sedimentation, centrifugation, catalytic hydrogenation, vacuum distillation, and solvent extraction. The ash content of the oil slurry is controlled to be ≤0.10% through sedimentation and filtration or centrifugation; the sulfur content is controlled to be ≤0.3% through catalytic hydrogenation; the initial boiling point of the oil slurry is controlled to be ≥250℃ through vacuum distillation; and the aromatic hydrocarbon content of the oil slurry is controlled to be ≥70% through solvent extraction.

[0027] In this invention, pretreatment of the oil phase to control the ash content to ≤0.10% further reduces the damage of impurities such as metals to the negative electrode SEI film, reduces side reactions, and extends battery cycle life. Reducing the sulfur content to below 0.3% minimizes sulfur gas emissions during graphitization, preventing sulfide contamination of the electrolyte and increased interfacial impedance. An initial boiling point ≥250℃ ensures thorough removal of light components, preventing cracks or pores caused by violent escape of light components during coking. An aromatic hydrocarbon content ≥70% ensures the abundance of effective char-forming components in the oil slurry, providing sufficient precursor cores for the formation of highly homogeneous flake structures, while reducing interference from non-char-forming components such as saturated hydrocarbons on mesophase development. Combining these pretreatment parameters significantly improves the structural uniformity, purity, and electrochemical performance of homogeneous coke.

[0028] In this invention, the oil phase is one or more of the following: catalytic cracking slurry, vacuum residue, recycled oil, coking wax oil, ethylene tar, and coal tar pitch. The above technical solution defines the types of slurry in this invention. Catalytic cracking slurry and recycled oil are rich in short-chain polycyclic aromatic hydrocarbons and have high polycondensation activity, making them ideal precursors for forming the coke matrix. Vacuum residue, due to its high content of gums and asphaltenes, can increase the viscosity of the system and physically hinder the excessive growth and fusion of mesophase spheres, which is beneficial for obtaining small-sized lamellar structures. Coking wax oil and ethylene tar have high aromatic hydrocarbon content and few impurities, which can improve the fluidity and stability of the emulsion and promote uniform nucleation of the mesophase. Coal tar pitch has a high aromatic carbon ratio and strong polycondensation activity, providing more carbon structural units, which helps to improve the density and graphitization potential of coke. When multiple slurries are used in combination, their respective advantages can be leveraged to synergistically regulate the nucleation density and growth rate during the coking process.

[0029] This invention does not impose any special limitations on the raw materials used; conventional commercially available products in this field are sufficient.

[0030] In this invention, the physical emulsification method preferably includes one or more of high-speed shear dispersion, high-pressure homogenization, or ultrasonic emulsification. Specifically, when high-speed shear dispersion is used, the shearing speed is preferably 2000-8000 rpm, and the emulsification time is preferably 20-90 minutes; when high-pressure homogenization is used, the homogenization pressure is preferably 20-80 MPa, and the number of cycles is preferably 2-6; when ultrasonic emulsification is used, the ultrasonic power is preferably 100-1000 W, and the processing time is preferably 10-60 minutes.

[0031] In this invention, different emulsification methods are employed, each with its own characteristics: high-speed shear dispersion is suitable for medium viscosity systems. It generates strong shear force through a rotor-stator structure, breaking the oil phase into droplets. A rotation speed of 2000-8000 rpm ensures sufficient emulsification while avoiding excessive heat or over-refinement of the emulsion due to excessive rotation speed. High-pressure homogenization utilizes the cavitation, shearing, and impact effects generated by materials passing through narrow slits under high pressure to achieve a narrower particle size distribution. A pressure range of 20-80 MPa balances homogenization effect with equipment lifespan, and 2-6 cycles are sufficient to achieve a stable particle size. Ultrasonic emulsification relies on the cavitation effect to generate microjets, which is suitable for small batches or high viscosity systems. A power of 100-1000 W can effectively break up oil droplets, but excessive time may introduce impurities or cause temperature rise.

[0032] In this invention, excessively small particle size (<5μm) leads to insufficient precursor within individual oil droplets, resulting in excessively thick or loosely structured carbon shells after coking, and a significant increase in emulsification energy consumption. Conversely, excessively large particle size (>50μm) weakens the confinement effect, leaving sufficient space within the oil droplet for the mesophase to grow into a fibrous structure, thus reducing isotropy. A particle size range of 10-50μm ensures both effective spatial confinement within the droplets and balances emulsion stability and production efficiency, making it a key control parameter for achieving a high proportion of lamellar structures.

[0033] In this invention, the mass ratio of the oil phase to the water phase is (3:7) to (7:3), preferably 5:5. In this invention, when the oil phase ratio is too low (<30%), the single-reactor yield is low and the economic efficiency is poor; when the oil phase ratio is too high (>70%), the emulsion is prone to phase transformation or excessively dense oil droplets agglomerate, destroying the confined structure. A preferred oil-water ratio of 3:7 to 5:3 can obtain a sufficient number of independent oil droplet microreactors while ensuring emulsion stability, thereby fully realizing the synergistic effect of spatial confinement, interfacial barrier, and asynchronous reaction, ultimately obtaining a high-performance isotropic coke with a high proportion of flake structure and very little fiber structure.

[0034] After obtaining the oil-in-water emulsion, the present invention subjectes the oil-in-water emulsion to a coking reaction to obtain isotropic coke. In the present invention, the preferred reaction temperature for the coking reaction is 420-520℃, the preferred reaction pressure is 0.2-2.0 MPa, and the preferred reaction time is 4-24 h.

[0035] Reaction temperature is crucial for controlling the rate of polycondensation and the evolution of the mesophase: Too low a temperature (<420℃) results in insufficient cracking and polycondensation, leading to high volatile matter content and poor mechanical strength in the raw coke, and hindering the formation or development of mesophase spherulites, thus preventing the formation of regular small flake / mosaic structures; too high a temperature (>520℃) results in an overly vigorous reaction, easily generating large anisotropic fibers or domain structures, and potentially producing excessive gas, increasing coke porosity. This invention controls the reaction temperature within a window of 420-520℃, ensuring sufficient polycondensation into coke while utilizing the confinement effect of the oil-in-water emulsion to suppress excessive mesophase growth. Controlling the reaction pressure at 0.2-2.0 MPa maintains a liquid-phase reaction environment by suppressing the rapid volatilization of light components, promoting orderly mesophase growth without excessive orientation. Too low a pressure causes rapid escape of light components, easily disrupting droplet integrity; too high a pressure may excessively suppress the release of volatile components, resulting in a lower coke softening point. The reaction time (4-24 hours) needs to be controlled in conjunction with the temperature: too short a time results in incomplete reaction and low coking degree; too long a time may lead to excessive condensation, increasing energy consumption and not being conducive to isotropic structure optimization. This invention optimizes the matching of these three factors to ensure that the emulsion droplets complete sufficient condensation and solidification in an independent microreactor, ultimately obtaining isotropic coke with a high proportion of sheet-like structures and a uniform structure.

[0036] After the coking reaction is completed, the reaction product is preferably dried. In this invention, the drying temperature is preferably 80-120℃, and the drying time is preferably 10-15 hours.

[0037] The present invention provides an isotropic focal plane, which is prepared by any one of the methods described above. The polarizing microstructure of the isotropic focal plane is fish-scale shaped, with the proportion of scale-like small structures being ≥90%. The transverse dimension of the small structures is 10-30 μm, and the longitudinal dimension is 10-30 μm.

[0038] It should be noted that the polarization structure of traditional isotropic focal planes is mainly a mosaic structure, accounting for ≥50%, with a structure size ≤10μm. At the same time, there is also a considerable proportion of streamlined fiber structures in the system, accounting for ≥20%. Among them, the mosaic structure is difficult to graphitize, which will lead to a decrease in reversible capacity; while the fiber structure is prone to volume expansion during charge and discharge, which will cause damage to the electrode structure.

[0039] The isotropic coke provided by this invention, as a graphite anode precursor, has two advantages. Firstly, the high proportion of 10-30μm flake structures provides lithium ions with more and more uniform "highway entrances and exits," enabling faster response and less polarization during high-rate charging and discharging (such as fast charging), thus giving the graphite anode superior rate and capacity performance. Secondly, due to its high isotropy and minimal fiber structure, its expansion behavior is "partially distributed." Therefore, it can significantly reduce the electrode expansion rate and improve battery cycle life and safety.

[0040] In another aspect, the present invention provides a graphite obtained by graphitizing the isotropic foil described above at 2500-3000°C.

[0041] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] In the following examples and comparative examples, the ash content, sulfur content, etc. of the oil slurry used are as follows: Catalytic cracking slurry: ash content 0.2%, sulfur content 0.7%, initial boiling point 205℃, total aromatics 60%; vacuum residue: ash content 0.3%, sulfur content 0.6%, initial boiling point 270℃, total aromatics 76%; ethylene tar: ash content 0.05%, sulfur content 0.2%, initial boiling point 180℃, total aromatics 72%; coking wax oil: ash content 0.1%, sulfur content 0.5%, initial boiling point 265℃, total aromatics 80%; coal tar pitch: ash content 0.4%, sulfur content 0.1%, initial boiling point 258℃, total aromatics 73%.

[0043] Example 1 (1) Preparation of aqueous phase: Dissolve water-soluble carbon source (corn starch, added at 5% of the mass of deionized water) and surfactant (hexadecyltrimethylammonium bromide, added at 0.5‰ of the mass of deionized water) in deionized water and stir for 1 hour until completely dissolved to obtain aqueous phase.

[0044] (2) Preparation of the oil phase: The catalytic cracking slurry is pretreated by filtration and sedimentation, catalytic hydrogenation, vacuum distillation, and solvent extraction to obtain the oil phase. The specific steps are as follows: First, the catalytic cracking slurry is left to settle in a storage tank (the temperature inside the tank is maintained at 120℃ to reduce the viscosity of the raw material) for 48 hours, so that most of the particles are naturally separated under gravity. Then, it is filtered to ensure that the ash content of the finished slurry is ≤0.10%.

[0045] The filtered and settled oil slurry was subjected to catalytic hydrogenation, with the reaction temperature controlled at 330℃ and the system pressure at 10MPa (high pressure). A Co-Mo catalyst (Co to Mo mass ratio of 3:7) was used, with the catalyst addition amount being 0.1% of the oil slurry mass. A high hydrogen-to-oil ratio (800 Nm³) was maintained throughout the process. 3 / m 3 To ensure reaction efficiency and heat transfer, and by controlling a low volumetric space velocity (1 h⁻¹). -1 This ensures sufficient reaction contact time, ultimately stabilizing the sulfur content of the oil slurry at ≤0.3%.

[0046] After catalytic hydrogenation, the oil slurry is subjected to vacuum fractionation. During vacuum fractionation, a high vacuum (3 kPa absolute pressure) is maintained at the top of the column, while the bottom temperature is controlled at 310°C to prevent cracking and coking. By adjusting the side stream extraction and the reflux ratio within the column, the fractions are precisely cut to ensure that the initial boiling point of the target product oil slurry is ≥250°C.

[0047] After obtaining an oil slurry with an initial boiling point ≥250℃, the oil slurry is subjected to solvent extraction using furfural as the extractant, with a solvent-to-oil ratio (volume ratio) of 2:1, an extraction temperature of 70℃, and two-stage countercurrent extraction. The solvent is recovered by vacuum distillation of the extract phase to obtain an aromatic oil with an aromatic content ≥70%.

[0048] (3) Preparation of the emulsion: The oil phase and the aqueous phase were mixed at a mass ratio of 5:5. Under high-speed shearing conditions of 5000 rpm, the oil phase was slowly added to the aqueous phase. After the addition was complete, shearing was continued for 30 minutes to obtain a homogeneous and stable oil-in-water emulsion. An optical microscope image of this oil-in-water emulsion is shown below. Figure 1 As shown, the oil-in-water emulsion consists of uniformly dispersed oil droplets with an average particle size of approximately 20 μm.

[0049] (4) Coking reaction: The emulsion was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 480°C, and maintained at a pressure of 0.6 MPa for 12 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80°C for 12 hours to obtain isotropic coke. The polarized structure diagram of this isotropic coke is shown below. Figure 2 As shown, the coke has a "fish scale"-like shape, with scale structure accounting for ≥90%, and the scale structure has a lateral dimension of 10-30μm and a longitudinal dimension of 10-30μm.

[0050] Example 2 (1) Preparation of aqueous phase: Dissolve water-soluble carbon source (sodium carboxymethyl cellulose, added at 1% of the mass of deionized water) and surfactant (sodium dodecyl sulfate, added at 0.2‰ of the mass of deionized water) in deionized water and stir for 1 hour until completely dissolved to obtain aqueous phase.

[0051] (2) Preparation of the oil phase: The vacuum residue is pretreated by filtration, sedimentation and catalytic hydrogenation to form the oil phase. The specific reaction conditions for filtration, sedimentation and catalytic hydrogenation are the same as in Example 1.

[0052] (3) Preparation of emulsion: The oil phase and the water phase were mixed at a mass ratio of 4:6 and homogenized under high pressure at 50 MPa for 3 cycles. The average particle size of the oil droplets was observed to be about 15 μm under an optical microscope.

[0053] (4) Coking reaction: The emulsion was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 450°C, and maintained at a pressure of 1.0 MPa for 18 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80°C for 12 hours to obtain isotropic coke. The polarized structure diagram of the isotropic coke is shown below. Figure 3 As shown, the charcoal has a "fish scale"-like appearance.

[0054] Example 3 (1) Preparation of aqueous phase: Dissolve water-soluble carbon source (hydroxyethyl cellulose, added at 2% of the mass of deionized water) and surfactant (sodium cholate, added at 0.3‰ of the mass of deionized water) in deionized water and stir for 1 hour until completely dissolved to obtain aqueous phase.

[0055] (2) Preparation of oil phase: Ethylene tar is pretreated by vacuum fractionation and used as oil phase.

[0056] The vacuum fractionation process is basically the same as in Example 1, except that the bottom temperature is controlled at 280°C to avoid cracking and coking, and to ensure that the initial boiling point of the target product oil slurry is ≥250°C.

[0057] (3) Preparation of emulsion: The oil phase and the water phase were mixed at a mass ratio of 3:7, and the ultrasonic power was controlled at 800 W for 40 minutes. The average particle size of the oil droplets was observed to be about 10 μm under an optical microscope.

[0058] (4) Coking reaction: The emulsion was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 500℃, and maintained at a pressure of 1.2 MPa for 10 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80℃ for 12 hours to obtain isotropic coke. The polarized structure diagram of the isotropic coke is shown below. Figure 4 As shown, the charcoal has a "fish scale"-like appearance.

[0059] Example 4 (1) Preparation of aqueous phase: Dissolve water-soluble carbon source (sodium alginate, added at 0.5% of the mass of deionized water) and surfactant (sodium dodecylbenzenesulfonate, added at 0.1‰ of the mass of deionized water) in deionized water and stir for 1 hour until completely dissolved to obtain aqueous phase.

[0060] (2) Preparation of oil phase: Ethylene tar is pretreated by vacuum fractionation and used as oil phase.

[0061] The vacuum fractionation process is basically the same as in Example 1, except that the bottom temperature is controlled at 280°C to avoid cracking and coking, and to ensure that the initial boiling point of the target product oil slurry is ≥250°C.

[0062] (3) Preparation of emulsion: The oil phase and the water phase were mixed at a mass ratio of 3:7, and the mixing process was the same as in Example 1. The average particle size of the oil droplets was observed to be about 10 μm under an optical microscope.

[0063] (4) Coking reaction: The emulsion was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 500℃, and maintained at a pressure of 1.2 MPa for 10 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80℃ for 12 hours to obtain isotropic coke. The polarized structure diagram of the isotropic coke is shown below. Figure 5 As shown, the charcoal has a "fish scale"-like appearance.

[0064] Example 5 (1) Preparation of aqueous phase: Dissolve water-soluble carbon source (sodium lignosulfonate, added at 5% of the mass of deionized water) and surfactant (Tween 20, added at 0.2‰ of the mass of deionized water) in deionized water and stir for 1 hour until completely dissolved to obtain aqueous phase.

[0065] (2) Preparation of oil phase: Coking wax oil is pretreated by catalytic hydrogenation and used as oil phase.

[0066] The catalytic hydrogenation process is basically the same as in Example 1, except that the reaction temperature is controlled at 300°C and the system pressure at 8 MPa, and the sulfur content of the oil slurry is finally stabilized at ≤0.3%.

[0067] (3) Preparation of emulsion: The oil phase and the water phase were mixed at a mass ratio of 7:3, and the mixing method was the same as in Example 1. The average particle size of the oil droplets was observed to be about 35 μm under an optical microscope.

[0068] (4) Coking reaction: The emulsion was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 420°C, and maintained at 2 MPa for 24 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80°C for 12 hours to obtain isotropic coke. The polarized structure diagram of the isotropic coke is shown below. Figure 6 As shown, the charcoal has a "fish scale"-like appearance.

[0069] Example 6 (1) Preparation of aqueous phase: Dissolve water-soluble carbon source (cyclodextrin, added at 5% of the mass of deionized water) and surfactant (Tween 20, added at 0.5‰ of the mass of deionized water) in deionized water and stir for 1 hour until completely dissolved to obtain aqueous phase.

[0070] (2) Preparation of the oil phase: Coal tar pitch is pretreated by sedimentation and filtration to serve as the oil phase. The sedimentation and filtration process conditions are the same as in Example 1.

[0071] (3) The emulsion preparation conditions are the same as in Example 1.

[0072] (4) The coking reaction conditions are the same as in Example 1. The obtained isotropic polarized structure diagram is shown below. Figure 7 As shown, the charcoal has a "fish scale"-like appearance.

[0073] Example 7 The difference between this embodiment and Embodiment 1 is that: The catalytic cracking slurry oil was untreated, with an ash content of 0.2%, a sulfur content of 0.7%, an initial boiling point of 205°C, and a total aromatic hydrocarbon content of 60%. All other operations were identical to those in Example 1. The resulting isotropic structure was obtained using a polarized coke oven. Figure 8 As shown, the charcoal has a "fish scale"-like appearance.

[0074] Example 8 (1) Preparation of aqueous phase: Same as in Example 1 (2) Preparation of oil phase: catalytic cracking oil slurry and recycled oil are mixed in a 1:1 ratio, and then pretreated by filtration sedimentation, catalytic hydrogenation, vacuum fractionation and solvent extraction to form the oil phase.

[0075] First, the catalytic cracking slurry and recycled oil are transferred into a storage tank at a mass ratio of 1:1. The tank is then left to stand and settle for 48 hours (the temperature inside the tank is maintained at 120°C to reduce the viscosity of the raw materials), allowing most of the particles to separate naturally under gravity. The mixture is then filtered to ensure that the ash content of the finished slurry is ≤0.10%.

[0076] The filtered and settled oil slurry was subjected to catalytic hydrogenation, with the reaction temperature controlled at 330℃ and the system pressure at 10MPa (high pressure). A Co-Mo catalyst (Co to Mo mass ratio of 3:7) was used, with the catalyst addition amount being 0.1% of the oil slurry mass. A high hydrogen-to-oil ratio (800 Nm³) was maintained throughout the process. 3 / m 3 To ensure reaction efficiency and heat transfer, and by controlling a low volumetric space velocity (1 h⁻¹). -1 This ensures sufficient reaction contact time, ultimately stabilizing the sulfur content of the oil slurry at ≤0.3%.

[0077] After catalytic hydrogenation, the oil slurry is subjected to vacuum fractionation. During vacuum fractionation, a high vacuum (3 kPa absolute pressure) is maintained at the top of the column, while the bottom temperature is controlled at 310°C to prevent cracking and coking. By adjusting the side stream extraction and the reflux ratio within the column, the fractions are precisely cut to ensure that the initial boiling point of the target product oil slurry is ≥250°C.

[0078] After obtaining an oil slurry with an initial boiling point ≥250℃, the oil slurry is subjected to solvent extraction using furfural as the extractant, with a solvent-to-oil ratio (volume ratio) of 2:1, an extraction temperature of 70℃, and two-stage countercurrent extraction. The solvent is recovered by vacuum distillation of the extract phase to obtain an aromatic oil with an aromatic content ≥70%.

[0079] (3) The emulsion preparation conditions are the same as in Example 1.

[0080] (4) The emulsion was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 520°C, and maintained at a pressure of 0.2 MPa for 4 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80°C for 12 hours to obtain isotropic coke. The polarization structure of the obtained isotropic coke is shown in the figure below. Figure 9 As shown, the charcoal has a "fish scale"-like appearance.

[0081] Comparative Example 1 The difference between this comparative example and Example 1 is that the aqueous phase preparation and emulsion preparation process were omitted. The specific preparation steps are as follows: The catalytic cracking slurry was pretreated by filtration and sedimentation, catalytic hydrogenation, vacuum distillation, and solvent extraction to obtain a pretreated slurry. The above pretreatment process is exactly the same as that in Example 1.

[0082] The pretreated oil slurry was transferred to a high-pressure reactor, purged with nitrogen three times, heated to 480°C, and maintained at a pressure of 0.6 MPa for 12 hours. After natural cooling to room temperature, the reactor was opened, the product was removed, and dried at 80°C for 12 hours to obtain needle coke. A polarized light micrograph of the needle coke is shown below. Figure 10 As shown, Figure 10 It can be seen that it exhibits a distinct fibrous structure.

[0083] Comparative Example 2 The difference between this comparative example and Example 1 is that no aqueous phase was included in the process. The specific preparation steps are as follows: The catalytic cracking slurry was pretreated (the pretreatment method is the same as in Example 1) to serve as the oil phase; the oil phase and the water phase were mixed at a mass ratio of 5:5, and the mixing method was the same as in Example 1.

[0084] The coking reaction was the same as in Example 1. The resulting isotropic polarized optical structure is shown in the figure below. Figure 11 As shown, the charcoal has a "fish scale"-like appearance.

[0085] Comparative Example 3 The difference between this comparative example and Example 1 is that it forms a water-in-oil structure. The specific preparation steps are as follows: The oil phase and water phase were mixed at a mass ratio of 9:1, with the water phase added to the oil phase, following the same mixing method as in Example 1. An optical microscope image of the resulting water-in-oil emulsion is shown below. Figure 12 As shown.

[0086] The coking reaction was the same as in Example 1. The resulting isotropic polarized optical structure is shown in the figure below. Figure 13 As shown, the charcoal has a "fish scale"-like appearance.

[0087] Comparative Example 4 The difference between this comparative example and Example 1 is that there is no emulsion preparation process, i.e., no emulsification.

[0088] The specific preparation steps are as follows: The oil phase and water phase were mixed at a mass ratio of 5:5 and stirred at 100 r / min. The resulting mixture was then subjected to a coking reaction, as described in Example 1. The resulting isotropic polarized optical structure is shown in the figure. Figure 14 As shown, the charcoal has a "fish scale"-like appearance.

[0089] Comparative Example 5 The difference between this comparative example and Example 1 is as follows: The coking temperature was 400℃. The resulting isotropic polarized optical structure diagram is shown below. Figure 15 As shown, the charcoal has a "fish scale"-like appearance.

[0090] Performance testing The coke obtained in Examples 1-8 and Comparative Examples 1-5 was graphitized, and the resulting graphite was used as the negative electrode to prepare batteries. The graphitization reaction parameters were controlled as follows: graphitization temperature was 3000°C, and time was 1 hour.

[0091] Half-battery test: Graphitized samples were used as the negative electrode active material and mixed with conductive carbon black (Super P), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) at a mass ratio of 94:2:2:2. Deionized water was added to prepare a homogeneous slurry. The slurry was coated onto a copper foil current collector, dried, rolled, and cut into negative electrode sheets with a diameter of 12 mm. CR2032 coin cell half-cells were assembled in an argon-filled glove box: a lithium metal sheet was used as the counter electrode, a polypropylene microporous membrane was used as the separator, and the electrolyte was 1 M LiPF6 dissolved in ethylene carbonate / dimethyl carbonate / diethyl carbonate (volume ratio 1:1:1). After assembly, constant current charge-discharge tests were performed with a voltage window of 0.005-2.0V and a test temperature of 30℃. The cells were first activated at 0.1 C for two cycles, and then cycled at 1 C; the initial reversible capacity and initial coulombic efficiency were recorded.

[0092] Full battery test: The graphitized negative electrode was matched with a commercial NCM622 positive electrode to assemble a full cell. The capacity ratio (N / P) of the negative electrode to the positive electrode was controlled at 1.1:1. The negative electrode was prepared using the same method as the half-cell, while the positive electrode was prepared by coating an aluminum foil with a mixture of active material, conductive carbon black, and PVDF in a 90:5:5 ratio. The electrolyte and separator were the same as those for the half-cell. Before assembly, the negative electrode underwent electrochemical pre-lithiation to compensate for the initial irreversible capacity loss. The full cell was tested in the voltage range of 2.5-4.1 V, activated at 0.1 C for three cycles, and then cycled at 10 C. Cycle retention was recorded.

[0093] Polarization test operation procedure: The coke particles in the test examples and comparative samples were crushed and ground to a particle size of 0.2-1 mm, then mixed with thermally mounted resin, and polished to obtain smooth samples with a flat surface. The prepared samples were then observed under a polarizing microscope. The microscope was adjusted to crossed polarization mode, and a 50x objective lens was selected. Under these conditions, the samples exhibited bright and vivid interference colors (such as blue, yellow, or red), and their microstructural features, such as "sheet-like" or "fibrous" structures, were clearly discernible. Identification was based on the size, shape, and degree of protrusion of the isochromatic regions. A random point counting method was used, with a total of 500 points counted, to calculate the volume percentage of various optical structures. Specific judgment criteria are shown in Table 1. Specific test results are shown in Table 2.

[0094] Note: Structures with lateral and longitudinal dimensions in the range of 10-30 μm are defined as small-piece structures.

[0095] Table 1. Optical Structure Identification Criteria

[0096] Table 2 Battery Performance

[0097] As can be seen, in the isotropic structure coke prepared in Example 1, the optical microscopy results of the emulsion oil droplets are as follows: Figure 1 As shown, the particles are uniform in size, with an average particle size of approximately 20 μm, and the polarization structure is as follows. Figure 1 As shown, the electrodes exhibit a "scale-like" distribution, with small flakes accounting for 92%. After being fabricated as the negative electrode, the first-cycle reversible capacity reaches 362 mAh / g at a 1C current, achieving an initial efficiency of 96.8%. After 2000 cycles at a 10C rate, the capacity retention rate is 84%. In Example 7, the catalytic cracking slurry was not pretreated, resulting in high levels of coke sulfur and ash, which affected the initial efficiency of the graphitized product, resulting in an initial efficiency of only 94.8%. The isotropic focal polarization structures prepared in Examples 2-8 are shown in the photographs. Figure 3-9 Comparative Example 1 is a traditional needle-shaped focal plane, with a polarizing structure as follows: Figure 10 As shown, the structure is mainly fiber-based, with fibers accounting for 55%. After 2000 cycles at 10C, the capacity retention rate is only 69%, indicating poor stability during fast charging and long-cycle operation. Comparative Example 2, without surfactants or water-soluble carbon sources, showed stratification of the water-oil two-phase mixture after standing. The resulting coked polarizer exhibited poor structural uniformity, as shown in the polarization results. Figure 11 As shown, the cycling capacity retention rate at 10C was only 72%; Comparative Example 3 shows the formation of a water-in-oil structure, and the optical microscopic results of the emulsion oil droplets are as follows. Figure 12 As shown, the oil is a continuous phase with no confinement effect, and the coke is mainly composed of fibrous structures. The polarization results are as follows. Figure 13 As shown, the fiber content was 48%, the first-cycle reversible capacity at 1C was only 357mAh / g, and the cycle capacity retention rate at 10C was only 72%; Comparative Example 4 was an unemulsified process, with severe water-oil phase separation, and the product structure after coking was uneven, as shown in the polarization results. Figure 14 As shown, some areas are plate-like, while others contain a large amount of amorphous carbon. The cycle capacity retention rate at 10C is only 65%. Comparative Example 5, with its lower coking temperature and incomplete coking, has volatile matter ≥10%, making it impossible to observe the polarized structure. The polarization results are as follows: Figure 15 As shown, the 1C reversible capacity is only 355mAh / g.

[0098] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing isotropic coke, characterized in that, The oil-in-water emulsion method is used for preparation, including the following steps: 1) Mix water-soluble carbon source, surfactant and water to obtain an aqueous solution; 2) Under physical emulsification conditions, the oil phase is added to the aqueous phase to form an oil-in-water emulsion; the mass ratio of the oil phase to the aqueous phase is (3:7)-(7:3). 3) The oil-in-water emulsion obtained in step 2) is subjected to a coking reaction to obtain isotropic coke; The water-soluble carbon source is one or more of the following: corn starch, sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylamide, sodium lignosulfonate, dextrin, and cyclodextrin. The surfactant is one or more of the following: hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium cholate, sodium deoxycholate, Tween series and Span series; The oil phase is one or more of the following: catalytic cracking slurry oil, vacuum residue, recycled oil, coking wax oil, ethylene tar, and coal tar pitch.

2. The preparation method according to claim 1, characterized in that, Step 2) includes pretreatment of the oil phase before adding it to the aqueous phase. The pretreatment methods include one or more of filtration and sedimentation, centrifugation, catalytic hydrogenation, vacuum distillation and solvent extraction. The ash content of the oil slurry is controlled to be ≤0.10% by sedimentation and filtration or centrifugation, the sulfur content is controlled to be ≤0.3% by catalytic hydrogenation, the initial boiling point of the oil slurry is controlled to be ≥250℃ by vacuum distillation, and the aromatic content of the oil slurry is controlled to be ≥70% by solvent extraction.

3. The preparation method according to claim 1, characterized in that, The physical emulsification method described in step 2) includes one or more of high-speed shear dispersion, high-pressure homogenization, or ultrasonic emulsification.

4. The preparation method according to claim 1, characterized in that, The amount of water-soluble carbon source added in step 1) is 0.5-5% of the mass of deionized water.

5. The preparation method according to claim 1, characterized in that, The amount of surfactant added in step 1) is 0.1‰-0.5‰ of the mass of deionized water.

6. The preparation method according to claim 1, characterized in that, In step 2), the oil phase is added to the aqueous phase at a uniform rate over 30-60 minutes.

7. The preparation method according to claim 1, characterized in that, The average droplet size of the oil-in-water emulsion formed in step 2) is 10-50 μm.

8. The preparation method according to claim 1, characterized in that, The coking reaction in step 3) has a reaction temperature of 420-520℃, a reaction pressure of 0.2-2.0 MPa, and a reaction time of 4-24h.

9. An isotropic focal plane, characterized in that, The isotropic structure focal plane is prepared by the method described in any one of claims 1-7. The polarizing microstructure of the focal plane is fish-scale shaped, with the proportion of scale-like small structures being ≥90%. The transverse dimension of the small structures is 10-30 μm, and the longitudinal dimension is 10-30 μm.

10. A type of graphite, characterized in that, It is obtained by graphitization treatment at 2500-3000℃ from the isotropic foil described in claim 9.

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