Method for manufacturing artificial graphite negative electrode material through low-temperature graphitization

Abstract

The invention provides a method for preparing an artificial graphite negative electrode material by low-temperature graphitization, which comprises the following steps of: taking iron powder with low carbon content as a cosolvent and a carrying medium of a carbon material, taking graphite precursor fine powder as a main body of the carbon material, and taking asphalt micro powder as a binder for hot press molding; carrying out hot press molding to prepare a microporous biscuit with the thickness of 51-400 mm, and carrying out low-temperature carbonization treatment on a laminated composition of the biscuit and the iron gauze to form a composite material block of a carbon material three-dimensional skeleton with a microporous structure and iron powder, the preparation method comprises the following steps of: performing low-temperature graphitization treatment at the temperature of below 1700 DEG C by adopting a medium-frequency induction heating material self-heating mode, cooling, crushing, pickling to remove iron, filtering, washing, drying, grading by jet milling and demagnetizing to obtain artificial graphite powder, the fixed carbon content of the artificial graphite powder is greater than 98%, the true density is between 2.22 and 2.30 g / cm < 3 >, the d002 is less than 0.3500 nm, the gram volume is greater than 345mAh / g, and the first efficiency is greater than 93%; the method is short in production period, stable and reliable in operation, high in efficiency and low in energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion secondary batteries, and in particular relates to a high-efficiency, low-cost manufacturing method for the artificial graphite anode material used therein. Background Technology

[0002] Graphite, as the negative electrode active material of lithium-ion batteries, has high specific capacity, low reduction potential, good electrochemical reversibility, low volume expansion rate, and high electronic conductivity. It is widely available as a raw material and is currently the mainstream negative electrode material for lithium-ion secondary batteries.

[0003] Commercial graphite anode materials include artificial graphite and natural graphite. The advantages of natural graphite are low cost and high compaction density. The main disadvantages are: (1) The surface of natural graphite powder is rough, with many active sites and a large specific surface area. During the first charge and discharge, the process of forming an SEI film on the surface of the anode active material consumes and wastes a lot of lithium resources, resulting in low first charge and discharge efficiency, which is referred to in the industry as low first efficiency; (2) Natural graphite has obvious polycrystalline anisotropy. The thickness of the SEI after reaction growth on the powder surface is uneven. The thicker SEI film in the middle will be damaged during battery charge and discharge cycles. In the case of cracking or even peeling, the lithium source will be continuously consumed, affecting the cycle life of the battery; (3) The obvious anisotropy of natural graphite powder will also cause the volume expansion of the negative electrode material during charging and discharging to be difficult to cancel each other, the battery is prone to swelling, resulting in large fluctuations in the electrode spacing and a faster decline in battery cycle life; (4) The anisotropy of polycrystalline natural graphite powder will also cause lithium ion insertion or extraction to only be carried out from certain end faces of polycrystalline natural graphite powder, resulting in a small effective area for insertion or extraction, poor charge and discharge rate characteristics of the battery, easy lithium plating during fast charging, and poor battery safety.

[0004] Currently, the mainstream approach in the power battery and energy storage battery industry is to use artificial graphite powder as the negative electrode active material. This involves using mesophase carbon microspheres or calcined needle-shaped coke as raw materials, undergoing high-temperature graphitization treatment in the 2900-3100℃ range, followed by cooling and pulverization to obtain the artificial graphite powder. Compared to the anisotropic crystal orientation of flake-like natural graphite powder, the polycrystalline structure of artificial graphite powder exhibits better isotropic crystal orientation. The powder surface is relatively smooth, with fewer active sites, a smaller specific surface area, higher initial efficiency than natural graphite, longer cycle life, and better rate performance. The main drawback of using artificial graphite powder as a negative electrode material is the necessity of high-temperature graphitization, resulting in a long processing cycle, high energy consumption, and significant burn-off of the resistive material filling the graphite crucible during high-temperature graphitization, leading to high overall costs. Traditional artificial graphite requires high-temperature graphitization temperatures of 2900-3100℃. The main technical principle for improving the degree of graphitization is to utilize the thermal diffusion and recrystallization of carbon atoms at high temperatures to increase the graphitization degree of the graphite precursor and improve specific capacity. High-temperature graphitization equipment typically uses the classic Atchison graphitization furnace. The graphite precursor raw material powder is usually loosely packed in the graphite crucible in an uncompacted state, with a tap density generally less than 1.15 g / cm³. 3 The graphite crucibles are filled with carbon-based resistive granules. 70-80% of the heating heat is used for these auxiliary materials, such as graphite crucibles, resistive materials, and insulation materials. In order to ensure the uniformity of the products, the heating process cannot be too fast. The heating and holding time is nearly 15 days, and the cooling time is nearly 10 days. The processing cycle of one batch is close to one month. The overall energy consumption is high, the energy utilization efficiency is low, the processing cycle is long, and the capital occupation cycle is long, which has become a bottleneck for reducing the cost of artificial graphite.

[0005] As a long-life negative electrode material used in power batteries and energy storage batteries, in order to improve the uniformity of SEI film growth and enhance the battery's initial efficiency and cycle life, some artificial graphite powders adopt a core-shell structured coating product. For example, natural graphite powder or needle-shaped coke powder is coated and modified using carbon precursors such as pitch or furfural resin, followed by medium-temperature carbonization or graphitization, and then pulverized and graded to manufacture coated core-shell structured artificial graphite powder. The aim is to obtain a carbon material surface layer dominated by amorphous carbon with low crystallinity and low graphitization, thereby reducing the thickness of the SEI film formed during the initial contact between the powder surface and the electrolyte. The aforementioned traditional artificial graphite... The coating process has the following disadvantages: (1) The process is complex, the product manufacturing cycle is long, and the overall energy consumption is relatively high; (2) The interface strength between the shell and the core of the coated artificial graphite powder material is limited. When manufacturing the negative electrode sheet, the coating shell is easily crushed during strong rolling, resulting in the battery's first efficiency still not being satisfactory, the cycle life has quality fluctuations, and the battery consistency needs to be improved; (3) It is difficult to control the uniformity of the coated amorphous carbon layer. After coating and high-temperature carbonization, a pulverization process is required. The powder fracture surface formed after pulverization has high reactivity. The coating layer formed after pulverization is micro-uniform, which affects the specific surface area and first efficiency of the powder. The uniformity of the SEI film is poor.

[0006] Traditional methods for manufacturing artificial graphite anode materials using high-temperature graphitization and subsequent carbonization / pulverization / gradation after coating have drawbacks such as high energy consumption, long production cycle, high cost, uneven surface coating, and uneven SEI film growth, and therefore need to be improved.

[0007] The inventors of this invention proposed a method for manufacturing artificial graphite anode materials by cold-pressing graphite precursor powder together with iron powder, followed by medium-temperature graphitization treatment at 1600-2200℃, cooling, crushing, and acid washing to remove iron during the process, due to the lack of effective bonding materials during the cold-pressing process. The resulting graphite precursor powder and iron powder composition blank is difficult to maintain its microporous skeletal structure during the heating process after pressing. This necessitates the use of a graphite crucible to maintain the integrity of the pressed blank. Furthermore, appropriate pressure is required during the medium-temperature graphitization treatment to maintain the porous structure of the blank; otherwise, the product becomes loose and cannot form uniform capillary action, making product consistency difficult to guarantee. Additionally, the graphite crucible is subject to high wear and tear, resulting in unsatisfactory production costs.

[0008] In CN202210281433.3, the inventors proposed a method for pre-pressing a blank from pure graphite precursor powder, then stacking it with an iron plate, and using the molten iron formed by melting the stacked iron plates at 1500-2200℃ for medium-temperature graphitization. After cooling, the block is subjected to electrolytic corrosion or chemical corrosion to remove iron, thus obtaining artificial graphite anode material. This method also requires a graphite crucible or ceramic crucible to maintain the integrity of the blank, and it also has the disadvantages of being dependent on the crucible and having high crucible wear. During the high-temperature treatment, the blank also needs to be subjected to a certain pressure. After melting, the iron plates between the stacks may be squeezed out and dispersed into the interior of the crucible, which cannot guarantee the formation of uniform capillary action in the blank.

[0009] The inventors proposed in CN202210500309.1 a method for manufacturing artificial graphite anode materials by hot pressing graphite precursor powder, iron powder with a carbon content of less than 2%, and asphalt powder into cylindrical preforms with a thickness of 10-50 mm. The preforms are then laminated with steel plates at a thickness ratio of (5:1) to (10:1), followed by molten iron-assisted medium-temperature graphitization at 1700-2200℃. After cooling, the bulk materials are subjected to electrolytic turning or acid leaching to remove iron. This method also requires a complete crucible to protect the preforms and the steel plate laminations, resulting in crucible wear and tear and unsatisfactory production costs. Otherwise, the molten iron between the preforms may flow and damage the equipment. Furthermore, this method produces preforms with a relatively low thickness, leading to slightly lower production efficiency. The medium-temperature graphitization temperature is still as high as 1700-2200℃. At 200℃, the crucible material and the bottom refractory support material are prone to reduction reaction when working at temperatures above 1700℃ for extended periods, resulting in rapid crucible wear. This method has significant room for improvement in terms of production efficiency, equipment operation and maintenance, and manufacturing costs. This method uses high-frequency induction heating for both the carbonization and graphitization processes of the preform. Due to the influence of the asphalt powder as a binder, the preform has insufficient electrical conductivity before carbonization, limiting the use of high-power input during carbonization and resulting in a slower actual carbonization heating rate. Furthermore, the skin effect of high-frequency induction heating leads to uneven heating and can cause rapid thermal decomposition of the asphalt binder in the thermoform during carbonization, resulting in localized rapid gas generation and localized cracking of the preform. This method places stringent requirements on production operation and equipment maintenance.

[0010] In CN202210690493.0, the inventors proposed a method that uses graphite precursor powder, iron powder with a carbon content of less than 4%, and asphalt powder as binder powders, to be hot-pressed together. Then, pulsed current is used for internal heating to achieve iron-assisted medium-temperature graphitization. Finally, the processed block is crushed and chemically etched to remove the iron. The compressive strength of the preform is limited by this method. When applying pressure during pulsed current heating, the preform is easily crushed, resulting in unstable current conduction. Therefore, an external crucible is required for process support. Even a conductive resistive material needs to be placed between the preform and the crucible for external heat generation during low-temperature carbonization. The stability and production efficiency of the low-temperature carbonization process are not satisfactory. This method also suffers from crucible consumption, and the production cost is not satisfactory.

[0011] The above methods, which use iron powder or iron plate as a process medium to assist in the graphitization of graphite precursor powder at medium temperature, have the drawback of generally consuming crucible material, and the manufacturing cost and production efficiency are not satisfactory.

[0012] This invention addresses the numerous drawbacks and shortcomings of traditional high-temperature graphitization methods for manufacturing artificial graphite anode materials, including high energy consumption, long growth cycle, large consumption of auxiliary materials, low material yield, high production cost, and uneven coating layer. Furthermore, it addresses the aforementioned problems and shortcomings of the medium-temperature graphitization method used in powder metallurgy for manufacturing artificial graphite anode materials. Summary of the Invention

[0013] This invention proposes a method for manufacturing artificial graphite anode materials with low energy consumption, fast production cycle, high raw material utilization, stable equipment operation, stable mass production process, and low consumption of process auxiliary materials such as crucibles. The manufactured materials have the characteristics of large specific capacity and high initial efficiency. The technical solution is described below.

[0014] A method for manufacturing artificial graphite anode materials by low-temperature graphitization, characterized in that the low-temperature graphitization manufacturing of artificial graphite anode materials includes the following five main steps:

[0015] (1) Hot pressing is used to prepare microporous preforms with a thickness between 51-400 mm. The three raw material powders, graphite precursor powder (G1), iron powder (Fe2), and pitch powder (G3), are mixed and then hot pressed to prepare microporous preforms. The thickness of the microporous preforms is between 51-400 mm. If the thickness of the microporous preforms is too low, the production efficiency will be low. If the thickness of the microporous preforms is too high, it will lead to poor exhaust during low-temperature carbonization after the pyrolysis of pitch powder, and the low-temperature carbonization time will be too long, which will affect the production cycle and efficiency. In addition, if the thickness is too large, the compaction of the middle part of the preform is easy to be uneven during hot pressing. The presence of excessively large micropores or excessively high local porosity in the preform will affect the uniform capillary wetting during subsequent low-temperature graphitization. The porosity of the microporous preforms is between 25%-50%. Too low porosity will also affect the exhaust during low-temperature carbonization, and too high porosity will lead to insufficient strength of the microporous preforms. During negative pressure adsorption handling and assembly, the problem of collapse is prone to occur; in the raw materials, graphite precursor powder (G1) is used as the main carbon material. The graphite precursor raw materials include one or more of needle coke, low-sulfur petroleum coke, natural graphite, coke, anthracite, and microcrystalline graphite. The graphite precursor raw materials are crushed, graded, acid-washed and / or alkali-washed for purification, and dried. The prepared graphite precursor powder (G1) has a particle size D50 between 12-30 micrometers, D90 less than 50 micrometers, fixed carbon content greater than 99.70%, and ash content less than 0.30%; iron powder (Fe2) is used as a co-solvent for carbon elements during low-temperature graphitization. Its initial carbon content is less than 1%, iron content is greater than 99%, and particle size is -250 mesh; asphalt micro powder (G3) is used as a binder functional material for hot pressing. Its softening point is between 130℃ and 280℃, coking value is between 45% and 80%, and ash content is less than 0.10%, particle size D50 between 2-12 micrometers, D90 less than 20 micrometers; mix the three powder raw materials (G1), (Fe2), and (G3) evenly, and control the ratio of the true volume of (Fe2) to the sum of the true volumes of the three raw materials to be between 23% and 32%. If the iron powder content in the raw material ratio is too low, it cannot guarantee that the iron powder will uniformly wet the microporous carbon material after melting, resulting in uneven graphitization and poor product consistency. If the iron powder content in the raw material ratio is too high, it will overflow from the microporous carbon material in a sweating manner after melting, which will cause strength damage to the graphite tray and tooling. Control the (G3) content... The ratio of the true volume to the sum of the true volumes of the three components is between 23% and 32%. If the content of asphalt powder in the raw material ratio is too low, the molding strength of the preform will be insufficient, which is not conducive to handling and assembly. If the content of asphalt powder is too high, it will lead to excessive density of the preform, poor air permeability, and affect exhaust during low-temperature carbonization. It may also cause excessive local exhaust or even local cracking. The remainder of the raw materials is (G1). The mixture of the above three powder raw materials is hot-pressed at a temperature range of 5°C to 50°C above the softening point of (G3) using a pressure of 5-25 MPa to prepare a microporous preform (G1 / Fe2 / G3).

[0016] (2) After stacking the microporous blank with wire mesh, a low-temperature carbonization treatment is performed. The microporous blank (G1 / Fe2 / G3) and 1-3 layers of wire mesh are stacked and placed on a graphite tray fixture and then placed into a vacuum carbonization chamber. In the vacuum carbonization chamber, the microporous blank is subjected to low-temperature carbonization treatment by radiation heating or inert gas convection heating. The wire mesh serves as a low-resistance passage for exhaust during the low-temperature carbonization process of the microporous blank. The thickness of the wire mesh stack placed between adjacent microporous blanks is less than or equal to 3 mm, the mesh size of a single layer of wire mesh is between 50 and 500 meshes, and the carbon content of the wire mesh is less than 0.50%. The low-temperature carbonization process below 700℃ is used to heat the vacuum carbonization chamber to extract the volatile substances and small molecule products formed by thermal decomposition from the microporous blank, transforming the microporous blank into a carbon material with a microporous structure and good electrical conductivity. The composite material block, composed of a three-dimensional skeleton and dispersed low-carbon iron powder, undergoes a total heating time of less than 16 hours for low-temperature carbonization. Radiation heating or inert gas convection heat transfer is used for the microporous preform, making heat input easier to control compared to high-frequency induction heating and reducing the likelihood of microporous preform cracking during heating. By controlling the thickness and porosity of the preform, employing low-resistance channels in the interlayer wire mesh, and controlling the preform heating method, the method of this invention ensures stable and reliable production operation during low-temperature carbonization. After low-temperature carbonization, a carbon material three-dimensional skeleton composite material block with slightly increased porosity and good electrical conductivity is easily obtained, while the iron powder remains dispersed within, providing absorption capacity for high-power input during subsequent medium-frequency induction heating and improving the heating efficiency of the following low-temperature graphitization process.

[0017] (3) Low-temperature graphitization treatment by medium-frequency induction heating: The composite material block and the wire mesh laminate formed after low-temperature carbonization are kept at a temperature above 550°C and transferred to a vacuum graphitization chamber while hot. Then, low-temperature graphitization treatment is carried out by medium-frequency induction heating mode with material self-heating. The graphite crucible has a magnetic groove. The alternating magnetic field generated by the water-cooled induction coil can pass through the composite material block and the wire mesh laminate, generating an induced current in it. The material generates heat itself to achieve low-temperature graphitization heating treatment. The working frequency of medium-frequency induction heating is between 100-1200 Hz. The low-temperature graphitization treatment includes at least two consecutive processes: the high-temperature micro-dissolution process of carbon elements by low-carbon molten steel and the precipitation and deposition process of supersaturated carbon elements in molten iron during the cooling process. The composite material block and the wire mesh laminate are induction heated together to a temperature range of 1550-1700°C (TH). The iron powder dispersed in the composite material block or the wire mesh between the block laminates after melting above their melting point all have a carbon content of less than 1%.Molten steel with 0% carbon content has a contact angle of less than 70 degrees with the three-dimensional carbon material skeleton with a microporous structure formed after low-temperature carbonization, exhibiting good wetting properties and capillary action. Combined with the electromagnetic stirring effect generated by the electromagnetic force during medium-frequency induction heating, when the material is in the (TH) temperature range, the molten steel with low carbon content can rapidly spread and form capillary flow in the micropores of the three-dimensional carbon material skeleton. The molten steel with low carbon content produces a micro-dissolution reaction on the highly active carbon elements in the three-dimensional carbon material skeleton it contacts. As the carbon element dissolves more, the molten steel with low carbon content gradually transforms into carbon-saturated molten iron. The molten steel with low carbon content also produces wetting and micro-dissolution reactions on the amorphous carbon at the grain boundaries of the polycrystalline three-dimensional carbon material skeleton. The high-temperature micro-dissolution time in the (TH) temperature range is between 30-120 minutes. Then, in a vacuum graphitization chamber, the composite material block material is cooled from the (TH) temperature range to 1500-1200℃ (TL) temperature. During the cooling process, supersaturated carbon elements in the molten iron gradually precipitate out. Some carbon elements deposit on the surface of the micropores in the three-dimensional framework of the carbon material, or recrystallize at the grain boundaries of the polycrystalline three-dimensional framework of the carbon material after precipitation. The time for carbon element precipitation and deposition treatment in the (TL) temperature range is between 1 and 4 hours. The total treatment time of the above low-temperature graphitization treatment, including heating and cooling, is less than 16 hours. The low-carbon iron powder turns into molten steel at high temperature. This invention essentially acts as a flux and transport medium for carbon elements. Through the capillary action, electromagnetic stirring, high-temperature micro-dissolution, and supersaturated carbon element precipitation and deposition mechanism formed by the above technical measures, the graphitization degree of carbon materials can still be improved at low temperatures below 1700℃, and a carbon material-encapsulated core-shell structure is naturally formed. The material after low-temperature graphitization treatment is transferred into the cooling chamber, and the space freed up in the vacuum graphitization chamber is used to place the next piece of material after low-temperature carbonization, forming a cycle-type continuous production.

[0018] (4) Forced cooling: The material after the above low-temperature graphitization treatment is transferred from the vacuum graphitization chamber into the cooling chamber, and forced air cooling heat exchange is carried out under the protection atmosphere of inert gas. The material is cooled to below 300°C or cooled to room temperature before being taken out of the furnace.

[0019] (5) Acid washing to remove iron: After cooling to room temperature, the material is pulverized to -60 mesh. Iron is then removed by chemical dissolution using an aqueous solution of dilute nitric acid, dilute sulfuric acid, or dilute hydrochloric acid in slightly excess of the iron in the material. The remaining carbon powder after iron removal is filtered, washed with water, dried at 126-160℃, cooled, and then classified by an air jet mill. After demagnetization, artificial graphite powder is obtained, with a fixed carbon content greater than 98% and a true density between 2.22-2.30 g / cm³. 3 d002 is less than 0.3500 nm, specific capacity is greater than 345 mAh / g, and initial efficiency is greater than 93%.

[0020] To achieve high-efficiency, low-energy consumption, and continuous production of low-temperature graphitized artificial graphite anode materials, the present invention adopts the following integrated system device corresponding to the above manufacturing method. The device mainly includes: (1) a vacuum carbonization chamber with a radiant heating mode and a hot fireplace structure, which has a multi-temperature zone heating function, for example, four heating zones of 200℃, 350℃, 500℃, and 650℃. The graphite tray can carry the combination material of microporous blank and wire mesh and enter the above four temperature zones in the vacuum carbonization chamber in a time-phased manner for controllable heating and carbonization treatment; the vacuum carbonization chamber's vacuum pipeline system is equipped with a cold trap to absorb and buffer the tar-like products formed after thermal decomposition; (2) a vacuum graphitization chamber with a cold fireplace structure using medium-frequency induction heating for low-temperature graphitization treatment; (3) the material that has completed the low-temperature graphitization treatment is transferred into a cooling chamber and forced air cooling with inert gas is adopted.

[0021] The technical solution and its technical benefits of the present invention will be further described below.

[0022] This invention achieves the following beneficial effects through the above technical solutions and steps: Using asphalt micropowder as a binder and low-carbon iron powder as a flux for carbon, a microporous blank with suitable handling strength is manufactured through hot-pressing powder metallurgy. By controlling the appropriate thickness and porosity, and by setting low-air-resistance wire mesh between the blanks, the efficiency of low-temperature carbonization is improved. The three-dimensional skeleton of the carbon blank with controllable porosity and pore size distribution formed after low-temperature carbonization is rapidly spread and wetted by the low-carbon molten steel formed in situ after the iron powder melts during subsequent low-temperature graphitization, under the capillary action of the microporous carbon blank. This achieves the effect of wetting the microporous surface of the carbon blank. The invention utilizes the micro-dissolution of highly active carbon elements and the micro-dissolution of amorphous carbon in polycrystalline materials. During the cooling process, it leverages the characteristic of carbon supersaturation in molten iron to precipitate out, thereby increasing the graphitization degree of carbon materials and naturally forming core-shell structured coated carbon materials. The ferric nitrate or ferrous sulfate formed after chemical dissolution to remove iron has high purity and can be used as raw materials for producing positive electrode materials for lithium iron phosphate or sodium-ion batteries. Through the coordination of equipment and processes, and the modular functional integration, this invention achieves highly efficient, cycle-based production. The method of manufacturing artificial graphite powder negative electrode materials using this invention has comprehensive advantages, including low material and auxiliary material consumption, high production efficiency, and low energy consumption. Attached Figure Description

[0024] Figure 1This is a schematic diagram of a system for manufacturing artificial graphite anode materials using the manufacturing method of the present invention. The device includes interconnected vacuum carbonization chamber, vacuum graphitization chamber, and cooling chamber. 1 is an infrared thermometer used to test the real-time temperature of the bulk material during low-temperature graphitization; 2 is the top cover of the vacuum graphitization chamber; 3 is a gate valve 1; 4 is a vacuum valve 1; 5 is an air inlet valve 1; 6 is a carbon / carbon composite material lifting rod fixture; 7 is the vacuum carbonization chamber; 8 is a microporous preform; 9 is the wire mesh between the layers; 10 is a thermocouple 1; 11 is a graphite tray fixture; 12... 13 is a material handling trolley; 14 is an insulation cover for the vacuum graphitization chamber; 15 is an insulation felt; 16 is a graphite crucible with magnetic grooves; 17 is the furnace body of the vacuum graphitization chamber; 18 is a refractory brick support; 19 is an external support mechanism for the vacuum graphitization chamber; 20 is a medium-frequency induction water-cooled coil; 21 is a vacuum valve; 22 is an air inlet valve; 23 is a supporting steel frame; 24 is a cooling chamber; 25 is a thermocouple; 26 is a slide gate valve; 27 is a vacuum valve; 28 is an air inlet valve; 29 is a dynamic seal between the lifting rod and the top cover.

[0025] Figure 2 This is an assembly diagram showing a microporous blank and wire mesh stacked together and placed on a graphite tray. In the diagram, 1 is a carbon / carbon composite material hanger tooling; 2 is a microporous blank with a thickness of 248 mm; 3 is a three-layer composite wire mesh, with the middle layer of the wire mesh using 150 mesh and the two sides using 300 mesh, with a total thickness of about 2 mm; 4 is a graphite tray tooling.

[0026] Figure 3 To facilitate the self-heating of the graphite crucible with uniformly opened magnetic grooves by generating induced current in the laminated composition of microporous blank and wire mesh after low-temperature carbonization.

[0027] Figure 4For comparison, this diagram illustrates the assembly of a monolithic microporous preform undergoing vacuum carbonization and low-temperature graphitization without the use of wire mesh. In the diagram, 1 represents an infrared thermometer used to measure the real-time temperature of the bulk material during low-temperature graphitization; 2 represents the top cover of the vacuum graphitization chamber; 3 represents a slide valve 1; 4 represents a vacuum valve 1; 5 represents an air inlet valve 1; 6 represents a carbon / carbon composite material lifting rod fixture; 7 represents the vacuum carbonization chamber; 8 represents the powder skeleton within the monolithic microporous preform; 9 represents the micropores within the monolithic microporous preform; 10 represents a thermocouple 1; and 11 represents a graphite tray fixture. 2 is a material handling trolley; 13 is the insulation cover of the vacuum graphitization chamber; 14 is the insulation felt; 15 is a graphite crucible with magnetic grooves; 16 is the furnace body of the vacuum graphitization chamber; 17 is the refractory brick support; 18 is the external support mechanism of the vacuum graphitization chamber; 19 is the medium-frequency induction water-cooled coil; 20 is the vacuum valve 2; 21 is the air inlet valve 2; 22 is the supporting steel frame; 23 is the cooling chamber; 24 is the thermocouple 2; 25 is the slide valve 2; 26 is the vacuum valve 3; 27 is the air inlet valve 3; 28 is the dynamic seal between the lifting rod and the top cover; 29 is the lifting rod.

[0028] Figure 5 This is an assembly diagram of a thin microporous blank and wire mesh. In the diagram, 1 is a carbon / carbon composite material hanger tooling; 2 is a microporous blank with a thickness of 123 mm; 3 is a three-layer composite wire mesh, with the middle layer of the wire mesh using 150 mesh and the two sides using 300 mesh, with a total thickness of about 2 mm; 4 is a graphite tray tooling.

[0029] Figure 6 This is an assembly diagram of a concentric cylindrical microporous preform. Three different sizes of concentric cylindrical microporous preforms were prepared by hot pressing. During assembly, a venting gap was left between the cylindrical microporous preform and the central hanger, and a venting gap was also reserved between the cylindrical microporous preforms. In the figure, 1 is a carbon / carbon composite material hanger fixture; 2 is a large cylindrical microporous preform; 3 is a medium-sized cylindrical microporous preform; 4 is a small cylindrical microporous preform; and 5 is a graphite tray fixture. Detailed Implementation

[0030] The following embodiments are implemented based on the technical solution and spirit of the present invention, and provide detailed implementation methods and specific processes, but do not limit the scope of protection of the present invention. All technical solutions obtained by substitution or equivalent transformation should be understood to fall within the protection scope of the present invention.

[0031] Example 1. A method for manufacturing artificial graphite anode materials using low-temperature graphitization, employing... Figure 2 or Figure 5 The stacking and assembly of the microporous blank and wire mesh shown mainly includes the following five processes:

[0032] (1) Hot pressing is used to prepare microporous blanks with a thickness between 120-300 mm. The microporous blanks are prepared by hot pressing after mixing three raw material powders: graphite precursor powder (G1), iron powder (Fe2), and pitch powder (G3). The thickness of the microporous blanks is between 120-300 mm, and the porosity is between 30%-45%. Graphite precursor powder (G1) is the main carbon material. Its particle size D50 is between 15-25 micrometers, D90 is less than 40 micrometers, its true density is between 2.05-2.13 g / cm³, its fixed carbon content is greater than 99.80%, and its ash content is less than 0.20%. Iron powder (Fe2) is used as a flux for carbon elements during low-temperature graphitization. Its initial carbon content is less than 0.35%, its iron content is greater than 99.2%, and its particle size is -325 mesh. Pitch powder (G3)... As a functional binder material for hot pressing, its softening point is between 170℃ and 220℃, coking value is between 50% and 60%, ash content is less than 0.10%, true density is between 1.35 and 1.55 g / cm³, particle size D50 is between 2 and 8 micrometers, and D90 is less than 15 micrometers. Three powder raw materials (G1), (Fe2), and (G3) are mixed evenly. The ratio of the true volume of (Fe2) to the sum of the true volumes of the three raw materials is controlled to be between 25% and 30%, the ratio of the true volume of (G3) to the sum of the true volumes of the three raw materials is controlled to be between 25% and 30%, and the remainder is (G1). The mixture of the above three powder raw materials is hot-pressed at a temperature range 10℃ to 30℃ above the softening point of (G3) using a pressure of 12-20 MPa to prepare a microporous preform (G1 / Fe2 / G3).

[0033] (2) After stacking the microporous blank with wire mesh, a low-temperature carbonization treatment is carried out. The microporous blank (G1 / Fe2 / G3) and three layers of wire mesh are stacked and placed on a graphite tray tooling and put into a vacuum carbonization chamber. The microporous blank is subjected to low-temperature carbonization treatment by radiation heating in the vacuum carbonization chamber. The wire mesh serves as a low-resistance passage for exhaust during the low-temperature carbonization process of the microporous blank. The mesh size of the middle layer of the wire mesh is between 100-150 mesh, and the mesh size of the wire mesh on both sides is between 300-500 mesh. The carbon content of the wire mesh is less than 0.30%. The low-temperature carbonization process below 700℃ is used to heat the vacuum carbonization chamber to extract the volatile substances and small molecule products formed by thermal decomposition in the microporous blank. The microporous blank is transformed into a composite material block composed of a three-dimensional skeleton of carbon material with good conductivity microporous structure and low carbon content iron powder dispersed in it. The total heating time of the low-temperature carbonization treatment is less than 12 hours.

[0034] (3) Low-temperature graphitization treatment using medium-frequency induction heating: The composite material block formed after low-temperature carbonization treatment and the laminated composition with the wire mesh are maintained at above 600°C and transferred to a vacuum graphitization chamber. Low-temperature graphitization treatment is carried out using a medium-frequency induction heating mode with material self-heating. The working frequency of the medium-frequency induction heating is between 150-600 Hz. The low-temperature graphitization treatment includes at least two consecutive processes: the high-temperature micro-dissolution process of carbon elements by molten steel with low carbon content and the precipitation and deposition process of supersaturated carbon elements in molten iron during the cooling process. The above-mentioned composite material block and the wire mesh are then... The laminated composition is induction heated together to a temperature range of 1580-1699℃ (TH), and the high-temperature micro-dissolution time in the (TH) temperature range is between 60-90 minutes; then, in a vacuum graphitization chamber, the composite material block material is cooled from the (TH) temperature range to a temperature range of 1400-1500℃ and held for 1-2 hours, and then further cooled to a temperature range of 1250-1400℃ and held for 1-2 hours; the total processing time of the low-temperature graphitization treatment in the vacuum graphitization chamber, including heating and cooling, is less than 12 hours.

[0035] (4) Forced cooling: The material after the above low-temperature graphitization treatment is cooled to below 1150°C in the vacuum graphitization chamber and transferred into the cooling chamber. Forced air cooling heat exchange is carried out under the protection atmosphere of inert gas, and the material is cooled to below 200°C before being taken out of the furnace.

[0036] (5) Acid washing to remove iron: After cooling to room temperature, the material is pulverized to -100 mesh. Iron is removed by chemical dissolution using an aqueous solution of dilute nitric acid in slightly excess of the iron in the material. The remaining carbon powder after iron removal is filtered, washed with water, dried at 135-160℃, cooled, and then classified by an air jet mill. After demagnetization, artificial graphite powder is obtained, with a fixed carbon content greater than 98.5% and a true density between 2.23-2.29 g / cm³. 3 d002 is less than 0.3500 nm, specific capacity is greater than 355 mAh / g, and initial efficiency is greater than 94%.

Claims

1. A method for manufacturing artificial graphite anode materials by low-temperature graphitization, characterized in that... The low-temperature graphitization process for manufacturing artificial graphite anode materials includes the following five main steps: (1) Hot pressing is used to prepare microporous preforms with a thickness between 51-400 mm. The preforms are prepared by hot pressing a mixture of three raw material powders: graphite precursor powder (G1), iron powder (Fe2), and pitch powder (G3). The thickness of the preforms is between 51-400 mm, and the porosity is between 25%-50%. Graphite precursor powder (G1) serves as the main carbon material in the raw materials. The graphite precursor raw materials include needle-shaped... The graphite precursor raw materials are crushed, graded, acid-washed and / or alkali-washed for purification, and dried to prepare graphite precursor powder (G1) with a particle size D50 between 12-30 micrometers, D90 less than 50 micrometers, fixed carbon content greater than 99.70%, and ash content less than 0.30%. Iron powder (Fe2) is used as a flux for carbon elements during low-temperature graphitization. Its initial carbon content is less than 1%, iron content is greater than 99%, and particle size is -250 mesh; asphalt powder (G3), as a binder functional material for hot pressing, has a softening point between 130℃ and 280℃, a coking value between 45% and 80%, an ash content of less than 0.10%, a particle size D50 between 2 and 12 micrometers, and a D90 of less than 20 micrometers; the three powder raw materials (G1), (Fe2), and (G3) are mixed evenly, and the raw material ratio is as follows: The ratio of the true volume of (Fe2) to the sum of the true volumes of the three components is controlled to be between 23% and 32%, and the ratio of the true volume of (G3) to the sum of the true volumes of the three components is controlled to be between 23% and 32%, with the remainder being (G1). The mixture of the above three powder raw materials is hot-pressed at a temperature range of 5°C to 50°C above the softening point of (G3) to prepare a microporous preform (G1 / Fe2 / G3). (2) After stacking the microporous blank with wire mesh, a low-temperature carbonization treatment is performed. The microporous blank (G1 / Fe2 / G3) and 1-3 layers of wire mesh are stacked and placed on a graphite tray fixture before entering the vacuum carbonization chamber. In the vacuum carbonization chamber, the microporous blank is subjected to low-temperature carbonization treatment by radiation heating or inert gas convection heating. The wire mesh serves as a low-resistance passage for exhaust during the low-temperature carbonization process of the microporous blank. The thickness of the wire mesh stack placed between adjacent microporous blank layers is less than or equal to 3 mm. The mesh size is between 50 and 500 meshes, the carbon content of the wire mesh is less than 0.50%, and the iron content is greater than 99.2%. The low-temperature carbonization process below 700℃ is used to heat the microporous blank in a vacuum carbonization chamber, extracting the volatile substances and small molecule products formed by thermal decomposition from the microporous blank. The microporous blank is transformed into a composite material block composed of a three-dimensional framework of carbon material with good conductivity and low carbon content iron powder dispersed in it. The total heating time of the low-temperature carbonization treatment is less than 16 hours. (3) Low-temperature graphitization treatment by medium-frequency induction heating: The composite material block and the wire mesh laminate formed after low-temperature carbonization are kept at a temperature above 550°C and transferred to a vacuum graphitization chamber. Low-temperature graphitization is carried out using a medium-frequency induction heating mode that uses the material to generate its own heat. The graphite crucible has a magnetic groove, and the alternating magnetic field generated by the water-cooled induction coil can pass through the composite material block and the wire mesh laminate, generating an induced current in it. The material generates its own heat, thus achieving low-temperature graphitization heating treatment. The working frequency of the medium-frequency induction heating is between 100-1200 Hz. The low-temperature graphitization treatment includes at least two consecutive processes: the high-temperature micro-dissolution process of carbon elements in low-carbon molten steel and the precipitation and deposition process of supersaturated carbon elements in molten iron during the cooling process. The composite material block and the wire mesh laminate were induction heated together to a temperature range of 1550-1700℃ (TH). The iron powder dispersed in the composite material block, or the wire mesh between the blocks, melted after exceeding its melting point to form molten steel with a carbon content of less than 1.0%. The low-carbon molten steel and the three-dimensional carbon material skeleton with a microporous structure formed after low-temperature carbonization have a contact angle of less than 70 degrees, exhibiting good wetting properties and capillary action. Combined with the electromagnetic stirring effect generated by the electromagnetic force during medium-frequency induction heating, the low-carbon molten steel can quickly spread and form capillary flow in the micropores of the three-dimensional carbon material skeleton. The low-carbon molten steel has a high activity level in the three-dimensional carbon material skeleton it contacts. The carbon elements undergo a micro-dissolution reaction, and the low-carbon steel gradually transforms into carbon-saturated molten iron as more carbon is dissolved. The low-carbon steel also wets and micro-dissolves the amorphous carbon at the grain boundaries of the three-dimensional polycrystalline framework of the carbon material. The high-temperature micro-dissolution time in the (TH) temperature range is between 30-120 minutes. Then, in a vacuum graphitization chamber, the composite material block is cooled from the (TH) temperature range to the (TL) temperature range of 1500-1200℃. During the cooling process, the supersaturated carbon elements in the molten iron gradually precipitate out, with some carbon elements depositing on the surface of the micropores in the three-dimensional framework of the carbon material, or recrystallizing at the grain boundaries of the polycrystalline framework. At the (TL) temperature... The time for carbon precipitation deposition treatment in the temperature range is between 1 and 4 hours; the total treatment time for low-temperature graphitization treatment in the vacuum graphitization chamber, including heating and cooling, is less than 16 hours. Low-carbon iron powder is turned into molten steel at high temperature, which serves as a flux and transport medium for carbon elements in carbon materials. Through the above technical measures, a mechanism of supersaturated precipitation deposition of carbon elements in molten iron is formed through capillary action, electromagnetic stirring, high-temperature micro-dissolution, and cooling, achieving the function of increasing the graphitization degree of carbon materials at low temperatures below 1700℃, and naturally forming a core-shell structure of carbon materials. The material after low-temperature graphitization treatment is transferred into a cooling chamber, and the space freed up in the vacuum graphitization chamber is used to place the next piece of material after low-temperature carbonization, forming a cycle-type continuous production. (4) Forced cooling: After the material undergoes the above-mentioned low-temperature graphitization treatment, it enters the cooling chamber and is subjected to forced air cooling heat exchange under an inert gas protective atmosphere. It is cooled to below 300°C or cooled to room temperature before being taken out of the furnace. (5) Acid washing to remove iron: After cooling to room temperature, the material is pulverized to -60 mesh. Iron is then removed by chemical dissolution using an aqueous solution of dilute nitric acid, dilute sulfuric acid, or dilute hydrochloric acid in slightly excess of the iron in the material. The remaining carbon powder after iron removal is filtered, washed with water, dried at 126-160℃, cooled, and then classified by an air jet mill. After demagnetization, artificial graphite powder is obtained, with a fixed carbon content greater than 98.0% and a true density between 2.22-2.30 g / cm³. 3 d002 is less than 0.3500 nm, specific capacity is greater than 345 mAh / g, and initial efficiency is greater than 93%.

2. The method according to claim 1, characterized in that, The integrated system device for manufacturing low-temperature graphitized artificial graphite anode materials mainly includes: (1) a vacuum carbonization chamber with a radiant heating mode hot fireplace structure, which has a multi-temperature zone heating function, and the vacuum pipeline is equipped with a cold trap for absorbing and buffering thermal cracking tar products; (2) a vacuum graphitization chamber with a medium-frequency induction heating cold fireplace structure; and (3) a cooling chamber with inert gas forced air cooling.

3. The method according to claim 1, characterized in that, The low-temperature graphitization process for manufacturing artificial graphite anode materials includes the following five steps: (1) Hot pressing is used to prepare microporous blanks with a thickness between 120-300 mm. The microporous blanks are prepared by hot pressing after mixing three raw material powders: graphite precursor powder (G1), iron powder (Fe2), and pitch powder (G3). The thickness of the microporous blanks is between 120-300 mm, and the porosity is between 30%-45%. Graphite precursor powder (G1) is the main carbon material. Its particle size D50 is between 15-25 micrometers, D90 is less than 40 micrometers, its true density is between 2.05-2.13 g / cm³, its fixed carbon content is greater than 99.80%, and its ash content is less than 0.20%. Iron powder (Fe2) is used as a flux for carbon elements during low-temperature graphitization. Its initial carbon content is less than 0.35%, its iron content is greater than 99.2%, and its particle size is -325 mesh. Pitch powder (G3)... As a functional binder material for hot pressing, its softening point is between 170℃ and 220℃, coking value is between 50% and 60%, ash content is less than 0.10%, true density is between 1.35 and 1.55 g / cm³, particle size D50 is between 2 and 8 micrometers, and D90 is less than 15 micrometers. Three powder raw materials (G1), (Fe2), and (G3) are mixed evenly. The ratio of the true volume of (Fe2) to the sum of the true volumes of the three raw materials is controlled to be between 25% and 30%, the ratio of the true volume of (G3) to the sum of the true volumes of the three raw materials is controlled to be between 25% and 30%, and the remainder is (G1). The mixture of the above three powder raw materials is hot-pressed at a temperature range 10℃ to 30℃ above the softening point of (G3) using a pressure of 12-20 MPa to prepare a microporous preform (G1 / Fe2 / G3). (2) After stacking the microporous blank with wire mesh, a low-temperature carbonization treatment is carried out. The microporous blank (G1 / Fe2 / G3) and three layers of wire mesh are stacked and placed on a graphite tray tooling and put into a vacuum carbonization chamber. The microporous blank is subjected to low-temperature carbonization treatment by radiation heating in the vacuum carbonization chamber. The wire mesh serves as a low-resistance passage for exhaust during the low-temperature carbonization process of the microporous blank. The mesh size of the middle layer of the wire mesh is between 100-150 mesh, and the mesh size of the wire mesh on both sides is between 300-500 mesh. The carbon content of the wire mesh is less than 0.30%. The low-temperature carbonization process below 700℃ is used to heat the vacuum carbonization chamber to extract the volatile substances and small molecule products formed by thermal decomposition in the microporous blank. The microporous blank is transformed into a composite material block composed of a three-dimensional skeleton of carbon material with good conductivity microporous structure and low carbon content iron powder dispersed in it. The total heating time of the low-temperature carbonization treatment is less than 12 hours. (3) Low-temperature graphitization treatment using medium-frequency induction heating: The composite material block formed after low-temperature carbonization treatment and the laminated composition with the wire mesh are maintained at above 600°C and transferred to a vacuum graphitization chamber. Low-temperature graphitization treatment is carried out using a medium-frequency induction heating mode with material self-heating. The working frequency of the medium-frequency induction heating is between 150-600 Hz. The low-temperature graphitization treatment includes at least two consecutive processes: the high-temperature micro-dissolution process of carbon elements by molten steel with low carbon content and the precipitation and deposition process of supersaturated carbon elements in molten iron during the cooling process. The above-mentioned composite material block and the wire mesh are then... The laminated composition is induction heated together to a temperature range of 1580-1699℃ (TH), and the high-temperature micro-dissolution time in the (TH) temperature range is between 60-90 minutes; then, in a vacuum graphitization chamber, the composite material block material is cooled from the (TH) temperature range to a temperature range of 1400-1500℃ and held for 1-2 hours, and then further cooled to a temperature range of 1250-1400℃ and held for 1-2 hours; the total processing time of the low-temperature graphitization treatment in the vacuum graphitization chamber, including heating and cooling, is less than 12 hours. (4) Forced cooling: The material after the above low-temperature graphitization treatment is cooled to below 1150°C in the vacuum graphitization chamber and transferred into the cooling chamber. Forced air cooling heat exchange is carried out under the protection atmosphere of inert gas, and the material is cooled to below 200°C before being taken out of the furnace. (5) Acid washing to remove iron: After cooling to room temperature, the material is pulverized to -100 mesh. Iron is removed by chemical dissolution using an aqueous solution of dilute nitric acid in slightly excess of the iron in the material. The remaining carbon powder after iron removal is filtered, washed with water, dried at 135-160℃, cooled, and then classified by an air jet mill. After demagnetization, artificial graphite powder is obtained, with a fixed carbon content greater than 98.5% and a true density between 2.23-2.29 g / cm³. 3 d002 is less than 0.3500 nm, specific capacity is greater than 355 mAh / g, and initial efficiency is greater than 94%.

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