Graphitization purification method of waste graphite, graphite crucible and application thereof

Abstract

This invention proposes a method for graphitizing and purifying waste graphite, a graphite crucible, and its applications, relating to the field of lithium-ion battery anode material technology. The graphite crucible includes a crucible body and a cover plate. The crucible body comprises a coaxial hollow outer cylinder and an inner cylinder, the height of which is less than the height of the outer cylinder. The bottom end face of the outer cylinder is horizontally connected to the bottom end face of the inner cylinder, forming an annular cavity. The inner side of the cover plate is provided with a first annular protrusion, which has a first inner hole that penetrates the cover plate and is coaxial with the inner cylinder. The outer diameter of the first annular protrusion is smaller than the inner diameter of the inner cylinder. This graphite crucible can directly pre-carbonize and graphitize waste graphite with high volatile matter and high ash content, significantly reducing costs while improving production efficiency.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a method for graphitizing and purifying waste graphite, a graphite crucible, and its applications. Background Technology

[0002] Graphite's unique layered structure endows it with excellent electrical and thermal conductivity, high-temperature resistance, and corrosion resistance, making it widely used in graphite electrode materials, crucibles for graphitization, lubricants, and insulation materials. Statistics show that global shipments of graphite anode materials exceeded 2 million tons in 2025, compared to only about 163,000 tons in 2017. However, regardless of the application, extremely high purity is required, generally demanding a fixed carbon content greater than 99.9%. With the future retirement and recycling of a large number of lithium-ion batteries, a significant amount of waste graphite will need to be processed.

[0003] The mainstream process for recycling waste batteries involves discharging, crushing, and separating copper and aluminum to obtain battery black powder. This black powder is then acid-leached to extract valuable metals such as nickel, cobalt, manganese, lithium, and ferrophosphorus, resulting in waste graphite. This waste graphite contains a high concentration of organic components from the positive and negative electrodes, including binders, residual electrolyte, and separators, leading to extremely high volatile matter content, typically exceeding 5%. X-ray diffraction tests show that the interlayer van der Waals forces weaken after repeated charging and discharging, and the interlayer spacing d... 002 The nanometer diameter can increase from 0.3354 nm to 0.336-0.348 nm, with a greater degree of disorder. SEM images clearly show numerous structural defects such as cracks and voids. Furthermore, due to the recycling process, waste graphite often contains significant amounts of metallic impurities, resulting in an ash content typically around 10%. Improper handling of this waste graphite can cause substantial environmental pollution. Recycling requires purification to remove volatiles and ash impurities, as well as repair of structural defects. However, existing publicly available methods for impurity removal and regeneration of waste graphite anode materials have the following problems: Flotation: the method with the lowest reagent consumption and lowest cost, but the graphite grade obtained is usually 80-95%, which does not meet the requirements of battery-grade graphite anode materials (carbon content > 99.9%). Acid-base method: Waste graphite is mixed and dispersed with hydrofluoric acid, hydrochloric acid, sulfuric acid or alkaline solution, and then separated by solid-liquid separation, multiple washing and drying. The process is simple and low cost, and the product quality can reach 99.0%. However, it has a great impact on product performance, is difficult to remove some insoluble sulfate impurities, and generates a large amount of fluorine-containing wastewater containing organic solvents during the recycling process, which poses high safety risks and is likely to cause environmental pollution. Chlorination roasting method: Graphite is heat-treated in an oxygen-free atmosphere while chlorine gas is introduced to convert elemental metallic impurities into chlorides, which are then vaporized and discharged at a relatively low temperature (<1800℃). Its advantages are that the process is simple and relatively energy-saving. Its disadvantages are that due to the incomplete gas-solid reaction, the product grade is low (≤98%) and cannot meet the requirements of battery-grade graphite anode materials. In addition, chlorine gas is toxic and poses high risks of safety and environmental pollution. High-temperature graphitization: Waste graphite is loaded into a conventional graphite crucible, which is then placed in an Atchison graphitization furnace and buried with conductive coke. It is then covered with insulating materials such as metallurgical coke, and finally heated to 2000-3000℃ for high-temperature treatment. The high temperature decomposes and vaporizes the impurities and repairs the structural defects of the waste graphite.

[0004] Experiments show that high-temperature graphitization is the most effective process for recycling waste graphite, with a simple process and high-quality graphite products (up to 99.5%). However, its drawbacks include a large amount of volatile matter overflowing during graphitization, leading to a surge in furnace pressure and frequent reports of safety accidents such as furnace blowouts. Using a pre-carbonization followed by graphitization would significantly increase production costs and equipment investment. Metal impurities, after decomposition and gasification, cannot be quickly discharged when they reach the upper layer of the graphite crucible, resulting in substandard impurity content in the material. High-boiling-point impurities, upon reaching the top layer of the furnace, will condense and deposit again due to the lower temperature, causing the top layer insulation material to clump and become unusable. Furthermore, temperature, as a core parameter in the graphitization process, directly affects cost and product quality. However, using conventional graphite crucibles for traditional Atchison graphitization makes it impossible to directly measure the furnace internal temperature; the effectiveness of the graphitization process can only be indirectly ensured by increasing power supply, extending holding time, and checking product indicators, which leads to increased production costs or a lower first-pass yield. In addition, traditional graphite crucibles have a cylindrical, sealed structure, and the cooling cycle after graphitization is long, usually requiring 15-20 days, which greatly affects the production cycle and crucible turnover efficiency. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a graphitization purification method for waste graphite, a graphite crucible and its application. By using a specific graphite crucible, waste graphite with high volatile matter and high ash content can be directly pre-carbonized and graphitized, which significantly reduces costs and improves production efficiency.

[0006] According to a first aspect of the present invention, a graphite crucible is provided, comprising a crucible body and a cover plate; The crucible body includes a coaxial hollow outer cylinder and an inner cylinder, the height of which is less than the height of the outer cylinder; The bottom end face of the outer cylinder is horizontally connected to the bottom end face of the inner cylinder, forming an annular cavity; The cover plate has a first annular protrusion on its inner side. The first annular protrusion has a first inner hole that passes through the cover plate and is coaxial with the inner cylinder. The outer diameter of the first annular protrusion is smaller than the inner diameter of the inner cylinder.

[0007] After the crucible body is covered with a cover plate, the cover plate fits onto the upper end face of the outer cylinder, leaving a gap between it and the upper end face of the inner cylinder. The size of the gap should be such that impurities can be discharged smoothly, for example, 1~10mm. The first annular protrusion on the inner side of the cover plate fits with the hollow inner cylinder with a clearance fit. Volatile gases or impurities generated during pre-carbonization or graphitization can be discharged through the channel in the center of the inner cylinder and the first inner hole of the first annular protrusion, preventing furnace spray. At the same time, the first annular protrusion of the cover plate forms a special flow channel with the outer and inner cylinders, which can prevent small particles of raw material from being carried out. The inner cylinder also increases the heat dissipation area, which helps to shorten the cooling cycle. Traditional graphite crucibles are shown in the appendix of this invention. Figure 1 It is generally a cylindrical hollow structure containing the material to be processed. The top is a cover plate. The height-to-diameter ratio (the ratio of height to inner diameter) is usually 3-5. It is a closed structure during graphitization. If the graphitization raw material contains a lot of volatiles and cannot be discharged in time, it is easy to cause a furnace accident. In addition, the cooling cycle after graphitization is also relatively long.

[0008] In some embodiments, the graphite crucible satisfies at least one of the following conditions: a. The ratio of the height to the inner diameter of the outer cylinder is 1-3; b. The ratio of the inner diameter of the inner cylinder to the inner diameter of the outer cylinder is 0.1-0.5; c. The difference between the inner diameter of the inner cylinder and the outer diameter of the first annular boss is 5-10 mm; d. The sum of the height of the inner cylinder and the height of the first annular boss is greater than the height of the outer cylinder.

[0009] It should be noted that the height mentioned in this invention is measured from the inner side of the bottom surface. The ratio of the height H1 of the outer cylinder to the inner diameter d1 is denoted as λ, i.e., λ = H1 / d1. When λ is between 1 and 3, the ash content of the product after graphitization treatment is lower and the purity is higher. The ratio of the inner diameter d2 of the inner cylinder to the inner diameter d1 of the outer cylinder is denoted as κ, i.e., κ = d2 / d1, preferably 0.1-0.5. If the κ value is too small, it is not conducive to the discharge of ash and volatile matter, the channel in the center of the inner cylinder is easily blocked, and the small heat dissipation area results in a longer cooling time; while if the κ value is too large, the feeding amount decreases significantly, which is not conducive to production. The gap distance between the outer diameter of the first annular boss and the inner diameter of the inner cylinder is denoted as ε, and it is optimal when controlled at 5-10 mm. The sum of the height H2 of the inner cylinder and the height H3 of the first annular boss is greater than the height H1 of the outer cylinder, i.e., H2+H3>H1. This sealing structure can ensure that impurities or volatiles are smoothly discharged into the internal channels during the heating process, while foreign objects (such as insulation material or conductive coke) will not enter the graphite crucible and cause material contamination.

[0010] In some embodiments, a second annular protrusion is further provided on the outer side of the cover plate. The second annular protrusion has a second inner hole, which is coaxially connected to the first inner hole. When the graphite crucible is located at the top layer, a second annular protrusion with a certain height can be provided on the outer side of the cover plate. The second annular protrusion can extend outward to cover the conductive coke and insulation layer on the surface of the graphite crucible, preventing the insulation material or conductive coke from entering the inner cylindrical channel and causing blockage. Of course, a second annular protrusion can also be provided on the outer side of the cover plate of the graphite crucible located in the middle or bottom layer, which is clearance-fitted with the inner cylindrical channel of the graphite crucible in the upper layer.

[0011] Preferably, the height of the first annular boss on the cover plate of the top graphite crucible is the same as the height of the first annular boss on the cover plate of the middle or bottom graphite crucible.

[0012] In some embodiments, the bottom of the inner cylinder is closed. When the graphite crucible is at the bottom, the closed bottom of the inner cylinder can be used to collect the condensed ash, preventing the ash from entering the insulation material or conductive coke and causing contamination, thus affecting secondary utilization. Of course, the bottom of the inner cylinder of the graphite crucible at the bottom can remain open to facilitate ventilation for purging or accelerated cooling.

[0013] In some embodiments, the graphite crucibles are arranged in at least two coaxially stacked layers. The graphite crucibles of the present invention are arranged in a coaxially stacked manner so that, during the pre-carbonization or graphitization process, volatile gases or impurities are discharged outside the graphite crucible through the inner cylindrical channels of each layer, the first inner hole of the first annular boss, etc. The number of stacked layers depends on the height of the crucible and the size of the graphitization furnace, for example, from two to ten layers.

[0014] According to a second aspect of the present invention, a method for graphitizing and purifying waste graphite is provided, comprising the following steps: S1: Load waste graphite into a graphite crucible, and then load the graphite crucible into a graphitization furnace; S2: Proceed to a heating stage until the center temperature of the graphitization furnace reaches 600-1200℃, and hold for 2-12 hours; S3: Continue the second stage of heating until the center temperature of the graphitization furnace reaches 2000-3000℃, and hold for 12-48 hours; The graphite crucible is selected from the graphite crucible described in the first aspect of the present invention.

[0015] In some embodiments, the waste graphite is loaded into the graphite crucible to a height of 80%-95%. This loading height is slightly lower than the internal height of the graphite crucible, allowing space for the evaporation of volatiles and impurities. If the loading height is too low, there will be more air inside, which can easily cause product oxidation and increase the specific surface area.

[0016] In some embodiments, the waste graphite is obtained by discharging, crushing, and sieving waste lithium-ion batteries to obtain battery black powder. The battery black powder is then acid-leached, washed, and subjected to solid-liquid separation to obtain a leachate containing a large amount of valuable metal salts and wet graphite slag. The leachate is used to extract nickel, cobalt, manganese, lithium, etc. The wet graphite slag is washed with water until neutral and then dried to obtain the waste graphite. During the drying process, the water in the wet graphite slag is evaporated and discharged, while the residual MSO4 precipitates and remains in the graphite slag. Here, M represents metal salt ions such as Fe, Ca, Cu, Al, Ni, Co, Mn, and Li. If waste lithium iron phosphate batteries are mixed in, the waste graphite slag will also contain phosphate impurities.

[0017] In some embodiments, the volatile matter content of the waste graphite is 5% to 30%; and / or, the ash content of the waste graphite is 5% to 20%. For waste graphite, the volatile matter mainly comes from organic impurities such as binders, residual membranes, and electrolytes, while the ash content mainly consists of inorganic salt impurities.

[0018] In some embodiments, step S1, before loading the waste graphite into the graphite crucible, further includes treating the waste graphite using an air classifier. This allows for control of the particle size distribution of the graphitized product.

[0019] In some embodiments, step S1, the process of loading the graphite crucible into the graphitization furnace, includes: The graphite crucibles are stacked coaxially in at least two layers, and a second annular protrusion is provided on the outer side of the cover plate of the graphite crucible located on the top layer; after the graphite crucibles are filled with conductive coke, the conductive cokes are covered with insulating material to form an insulating layer; wherein the insulating layer is lower than the top of the second annular protrusion.

[0020] This invention employs the traditional Atchison graphite charging method, where graphite crucibles are individually buried with conductive coke, and the outermost layer is covered with an insulating material (such as metallurgical coke). The graphite crucibles are stacked coaxially, ensuring that the inner cylindrical channels between the graphite crucibles and the inner holes of the first annular protrusions are interconnected. Finally, volatile matter and ash impurities are discharged through the inner hole of the second annular protrusion of the top graphite crucible extending out of the insulating layer.

[0021] In some embodiments, step S2 further includes: setting an infrared thermometer aligned with the center of the inner cylinder of the graphite crucible located at the center of the graphitization furnace.

[0022] In some preferred embodiments, step S2 further includes: pre-embedding thermocouples in the furnace bottom and sides of the graphitization furnace. Since the accuracy of infrared thermometers is easily affected in the low-temperature range (<800℃), thermocouple data can be used to calibrate and ensure accurate temperature control during the low-temperature carbonization stage, serving as a verification and supplement to the infrared thermometer.

[0023] Step S2 is the low-temperature carbonization process, which refers to the process of starting power supply and heating after the furnace is loaded. When the temperature reaches 600-1200℃, it is held for a certain period of time to release volatiles. Considering the temperature difference between the inside and outside of the graphitization furnace, and the pyrolysis temperature of volatiles in waste graphite being 500-600℃, the low-temperature carbonization temperature of waste graphite is set at 600℃. For materials such as petroleum coke, a higher temperature is required for low-temperature pre-carbonization. The holding time is preferably 2-12 hours. The holding time can be shortened when the temperature is higher, but if the temperature is too high, a large amount of gas will be discharged rapidly, which can easily carry out the material and cause blockage of the inner pores. The volatile gases generated during the low-temperature carbonization process are promptly extracted by the exhaust gas device and discharged after incineration and purification. During this process, the system will automatically adjust the power supply according to the target temperature and the actual temperature to ensure temperature stability. At the same time, it is necessary to observe whether there is any furnace spraying phenomenon during this process.

[0024] In some implementations, step S2 includes the following heating process: After heating to 450-550℃, hold the temperature for 1-3 hours, then heat to 600-1200℃ and hold for 1-9 hours; the heating rate in this first stage is <50℃ / h.

[0025] The low-temperature carbonization process in step S2 can be divided into a low-temperature decomposition stage and an impurity volatilization stage. The low-temperature decomposition stage is the main decomposition temperature range for organic materials such as binders and electrolytes. It employs a "slow heating + long-term holding" method, controlling the heating rate to <50℃ / h to ensure slow and stable precipitation of volatiles and prevent "furnace spraying" and material clogging of the channels. In the impurity volatilization stage, the temperature is raised to the target temperature (600-1200℃) and then held. The specific temperature and time can be dynamically adjusted according to the impurity content and type of the waste graphite. Based on online gas detection (such as CO, CO2, CH4 concentrations), the system determines the end of this stage and proceeds to the next step when the concentration of combustible components in the exhaust gas falls below a set threshold.

[0026] In some embodiments, the graphitization purification method further includes introducing a protective gas into the bottom of the graphite crucible located at the bottom. When the inner cylinder of the bottom graphite crucible remains open, a slightly positive pressure protective gas (such as nitrogen) purging port can be set at the bottom of the furnace and connected to the inner cylinder of the bottommost crucible. Introducing a small amount of nitrogen at the initial stage of heating can help purge the volatile gases upwards and reduce the risk of them remaining in the crucible and undergoing secondary cracking and carbon deposition. In the later stage of the high-temperature holding phase (such as the last 2-4 hours), a small amount of high-purity nitrogen, argon, or helium is introduced to create a slightly positive pressure in the furnace. This effectively prevents outside air (which may still penetrate despite the insulation material covering) from entering the furnace, avoiding graphite oxidation at high temperatures, reducing the product specific surface area (BET), and improving the initial efficiency.

[0027] In some implementations, in step S3, the rate of the two-stage heating is 50-100℃ / h.

[0028] Step S3 is the graphitization process, which can employ a "platform-style" power supply curve. In the heating phase below 2000℃, maximum power is used to shorten the time. Once the temperature exceeds 2000℃ and the graphitization stage begins, the power is appropriately reduced to maintain the temperature between 2800-3000℃ for "platform-style" heat preservation. This is more energy-efficient than continuous high power and avoids surface vaporization of the product or shortened crucible life due to overheating. After low-temperature carbonization, heating continues. The target temperature can be selected based on the physicochemical properties of the impurity components in the waste graphite, achieving structural defect repair while removing impurities. During this process, the system automatically adjusts the power supply based on the target and actual temperatures to ensure temperature stability. The high-temperature gas generated in this stage can be used to preheat the drying process during waste graphite pretreatment or other stages requiring heat energy, achieving energy cascade utilization.

[0029] In some embodiments, after step S3, the graphitization purification method further includes cooling. After the center temperature drops to 200°C, the insulating material and conductive coke are removed, and the graphite crucible is taken out and allowed to cool naturally to room temperature. Optionally, an "enhanced heat exchange" measure can be introduced. Under the premise of ensuring safety, preheated protective gas or clean air is introduced from channels designed at the bottom or side of the furnace to accelerate cooling and shorten the cooling time.

[0030] In some embodiments, the graphitization purification method further includes using a vacuum suction system to remove the material.

[0031] According to a third aspect of the present invention, the application of the graphite crucible described in the first aspect or the graphitization purification method described in the second aspect in the preparation of graphite anode materials is proposed.

[0032] According to one embodiment of the present invention, at least the following beneficial effects are achieved: 1. The unique crucible structure of this invention facilitates the rapid discharge of volatile and ash impurities from the inner pores during graphitization, which are then carried away by the waste system. This results in graphitized products with an ash content as low as 0.05%, a charging specific capacity exceeding 345 mAh / g, an initial coulombic efficiency greater than 92%, and a specific surface area of ​​less than 2.5 m². 2 / g, the performance of recycled graphite reaches the level of commercially available battery-grade artificial graphite anode materials; 2. The pressure generated during the discharge of volatiles will not accumulate inside the graphite crucible, thus preventing furnace blowouts and ensuring higher safety. 3. It is suitable for the direct graphitization treatment of high volatile materials, reducing the pre-carbonization steps and helping to reduce the overall process cost; 5. The graphite crucible structure of the present invention has a larger heat dissipation area, and the cooling time of graphitized products can be shortened by more than 50% compared with the traditional method, which can greatly shorten the graphitization production cycle.

[0033] 6. This invention provides a systematic solution that not only achieves the goal of "turning waste into treasure" but also solves the problem of environmental pollution and resource waste caused by treating waste graphite slag as solid waste. 7. In this invention, the center temperature of the graphitization furnace can be directly measured. The measurement signal is linked with the graphitization power supply system to effectively control the power supply and the quality of the graphitized products, and to establish a scientific power supply curve. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of a conventional graphite crucible structure; Figure 2 This is a schematic diagram of the structure of the first type of graphite crucible according to an embodiment of the present invention; Figure 3This is a schematic diagram of the structure of the second type of graphite crucible according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of a graphite crucible according to a third embodiment of the present invention; Figure 5 This is a process flow diagram of the graphitization and purification method of the present invention; Figure 6 This is a top view of the furnace after loading in an embodiment of the present invention; Figure 7 This is a schematic diagram of the stacking and temperature measurement of the graphite crucible located at the center in an embodiment of the present invention; Figure 8 Scanning electron microscope image of waste graphite; Figure 9 This is a scanning electron microscope image of the recycled graphite obtained in Example 1; Figure 10 A photograph of the shell-like material in Comparative Example 1; Figure 11 This is a photograph of the graphitized product of Example 3.

[0035] Figure label: 101. Outer cylinder; 102. Inner cylinder; 103. Inner cylindrical channel; 104. Graphitized raw material; 201. Cover plate; 202. First annular boss; 203. First inner hole; 204. Second annular boss; 205. Second inner hole; 301. Furnace head electrode; 302. Temperature measuring point; 303. Conductive coke; 304. Insulation material; 305. Furnace wall; 401. Temperature control system; 402. Infrared thermometer; 403. Insulation layer; 500. Top layer graphite crucible; 600. Middle layer graphite crucible; 700. Bottom layer graphite crucible. Detailed Implementation

[0036] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention, but the present invention is not limited to the scope of the embodiments described.

[0037] Unless otherwise specified, experimental methods in the following examples were performed according to conventional methods and conditions. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following examples or comparative examples can be obtained from conventional commercial sources or by existing known methods. Waste graphite was obtained as follows: waste lithium-ion batteries were discharged, crushed, and sieved to obtain battery black powder. The battery black powder was then acid-leached, washed, and subjected to solid-liquid separation. The solid phase was wet graphite slag. The wet graphite slag was washed with water until neutral and then dried to obtain waste graphite. The test data are shown in Table 1. Waste graphite observed under a scanning electron microscope is shown below. Figure 8As shown, the surface of waste graphite has a large number of structural defects such as voids and cracks, and the small amount of particles smaller than 5μm are mainly non-graphite carbon such as binders and conductive agents.

[0038] Table 1

[0039] This invention proposes a graphite crucible, comprising a crucible body and a cover plate 201. The crucible body includes a coaxial hollow outer cylinder 101 and an inner cylinder 102. The height H2 of the inner cylinder is less than the height H1 of the outer cylinder. The interior of the inner cylinder is an inner cylinder channel 103. The bottom ends of the outer and inner cylinders are horizontally connected to form an annular cavity for holding graphitization raw material 104 (waste graphite). The cover plate has a first annular boss 202 coaxial with the inner cylinder on the side facing the inner cylinder. The first annular boss has a first inner hole 203 that communicates with the inner cylinder channel. The outer diameter of the first annular boss is smaller than the inner diameter of the inner cylinder. When the cover plate is closed, the two are fitted with a clearance fit.

[0040] In some specific embodiments, the bottom of the inner cylinder of the bottom graphite crucible 700 has a closed structure, such as... Figure 3 As shown; on the other side of the cover plate of the top graphite crucible 500, there is a second annular boss 204, and the second inner hole 205 of the second annular boss is coaxially connected with the channel of the first annular boss, as shown. Figure 4 As shown.

[0041] In some other specific embodiments, the bottom of the inner cylinder of the bottom graphite crucible 700 remains open, such as... Figure 2 As shown.

[0042] In the following embodiments, the furnace is loaded in the following manner: The graphite crucibles containing waste graphite are loaded into the furnace according to the traditional Atchison crucible furnace loading method. The outermost layer is insulation material 304, forming an insulation layer 403. The gaps between the graphitization furnace and the graphite crucibles are filled with conductive coke 303. Graphite crucibles with closed inner cylindrical bottoms are placed at the bottom of the furnace, while those with a second annular protrusion are placed at the top layer, with the second annular protrusion extending beyond the insulation layer. The remaining crucibles are placed in the middle layers of the graphitization furnace, ensuring that the vertical axes of the graphite crucibles coincide and that the internal channels are unobstructed. After loading, an infrared thermometer 402 is aligned with the inner cylindrical channel of the graphite crucible at the center of the graphitization furnace, i.e., the temperature measuring point 302. The infrared thermometer is connected to the power supply system (temperature control system 401). A top view of the loading diagram is shown below. Figure 6 As shown in the diagram, the setup of the graphite crucible and the infrared temperature measurement are as follows: Figure 7 As shown.

[0043] In this context, the ratio of the height H1 of the outer cylinder to its inner diameter d1 is denoted as λ, the ratio of the inner diameter d2 of the inner cylinder to the inner diameter d1 of the outer cylinder is denoted as κ, and the gap between the outer wall of the first annular boss and the inner wall of the inner cylinder is denoted as ε. Figure 3 As shown. Meanwhile, the inner diameter of the outer cylinder of the graphite crucible used in this embodiment and the inner diameter of the conventional graphite crucible used in the comparative example are both 300 mm.

[0044] Example 1 This embodiment provides a method for graphitizing and purifying waste graphite, including the following steps: S1: Load the waste graphite into the graphite crucible described above, such as... Figure 2 , Figure 3 , Figure 4 As shown, λ takes the value 1, κ takes the value 0.1, and ε takes the value 5mm; S2: Load the furnace as described above; S3: Power is supplied to raise the temperature to 450℃ and hold for 1 hour, then raise the temperature to 600℃ and hold for 7 hours. The heating rate is controlled within 50℃ / h. During the holding process, a large amount of gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the pyrolysis of organic components such as binder, electrolyte, and diaphragm. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon was observed during the low-temperature carbonization process. S4: After the above heat preservation is completed, continue to supply power to raise the temperature to 2800℃ and then keep it for 12 hours. The heating rate is controlled at 100℃ / h. During this process, a large amount of flue gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the decomposition and gasification of inorganic salts and other metal impurities. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon was observed during the high-temperature graphitization process. S5: After the graphitization insulation is completed, the power is cut off and the furnace is cooled. When the temperature at the center measuring point is below 200℃, the insulation material and conductive coke are removed. The graphite crucible is then taken out and cooled to below 50℃ to ensure that the material is not oxidized. The cooling time T is approximately 10 days. S6: A vacuum feeder was used to remove the material from the graphite crucible. Cleaning the internal channels revealed a small amount of deposits, primarily high-melting-boiling-point impurities that condensed upon reaching the internal channels due to temperature reduction. A mixed sample after high-temperature graphitization was taken and tested for ash content, volatile matter, specific surface area, specific capacity, and initial efficiency. The SEM image is shown below. Figure 9 As shown.

[0045] Example 2 This embodiment provides a method for graphitizing and purifying waste graphite, including the following steps: S1: Load the waste graphite into the graphite crucible described above, such as... Figure 2 , Figure 3 , Figure 4As shown, λ takes the value 2, κ takes the value 0.3, and ε takes the value 8 mm; S2: Load the furnace as described above.

[0046] S3: Power is supplied to raise the temperature to 500℃ and hold for 1 hour, then raise the temperature to 800℃ and hold for 5 hours. The heating rate is controlled within 50℃ / h. During the holding process, a large amount of gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the pyrolysis of organic components such as binder, electrolyte, and diaphragm. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon was observed during the low-temperature carbonization process. S4: After the above heat preservation is completed, continue to supply power to raise the temperature to 2600℃ and then keep it for 16 hours. The heating rate is controlled at 100℃ / h. During this process, a large amount of flue gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the decomposition and gasification of inorganic salts and other metal impurities. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon was observed during the high-temperature graphitization process. S5: After the graphitization insulation is completed, the power is cut off and the furnace is cooled. When the temperature at the central temperature measuring point is below 200℃, the insulation material and conductive coke are removed. The graphite crucible is then taken out and cooled to below 50℃ to ensure that the material is not oxidized. The cooling time T is approximately 8.5 days. S6: A vacuum feeder was used to remove the material from the inside of the graphite crucible. Cleaning the internal channels of the crucible revealed a small amount of deposits, mainly high-melting-boiling-point impurities that condensed upon reaching the internal channels due to temperature reduction. A mixed sample after high-temperature graphitization was taken for testing of ash content, volatile matter, specific surface area, specific capacity, and initial efficiency.

[0047] Example 3 This embodiment provides a method for graphitizing and purifying waste graphite, including the following steps: S1: Load the waste graphite into the graphite crucible described above, such as... Figure 2 , Figure 3 , Figure 4 As shown, λ takes the value 3, κ takes the value 0.5, and ε takes the value 10mm; S2: Load the furnace as described above.

[0048] S3: Power is supplied to raise the temperature to 550℃ and hold for 1 hour, then raise the temperature to 1000℃ and hold for 3 hours. The heating rate is controlled within 50℃ / h. During the holding process, a large amount of gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the pyrolysis of organic components such as binder, electrolyte, and diaphragm. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon was observed during the low-temperature carbonization process. S4: After the above heat preservation is completed, continue to supply power to raise the temperature to 2400℃ and then keep it for 20 hours. The heating rate is controlled at 100℃ / h. During this process, a large amount of flue gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the decomposition and gasification of inorganic salts and other metal impurities. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon was observed during the high-temperature graphitization process. S5: After graphitization and heat preservation, power is cut off and the furnace is cooled. When the temperature at the central temperature measuring point is below 200℃, the insulating material and conductive coke are removed. The graphite crucible is then removed and cooled to below 50℃ to ensure the material is not oxidized. The cooling time T is approximately 7 days. The state of the material after cooling is as follows: Figure 11 As shown; S6: A vacuum feeder was used to remove the material from the inside of the graphite crucible. Cleaning the internal channels of the crucible revealed a small amount of deposits, mainly high-melting-boiling-point impurities that condensed upon reaching the internal channels due to temperature reduction. A mixed sample after high-temperature graphitization was taken for testing of ash content, volatile matter, specific surface area, specific capacity, and initial efficiency.

[0049] Example 4 The difference from Example 1 is that the κ value is 0.3.

[0050] Example 5 The difference from Example 1 is that the κ value is 0.5.

[0051] Example 6 The difference from Example 3 is that the value of λ is 3.

[0052] Comparative Example 1 This embodiment provides a method for graphitizing and purifying waste graphite, including the following steps: S1: Load waste graphite into a conventional graphite crucible, which includes a lid and a cylindrical hollow crucible body with a closed bottom, having a height-to-diameter ratio of 3. Figure 1 As shown; S2: The graphite crucible containing the waste is loaded into the furnace according to the traditional Atchison crucible furnace loading method. The outermost layer is placed with insulating material, and the gap between the graphitization furnace and the crucible is filled with conductive coke. The axes of the graphite crucibles in the vertical direction coincide. The difference from the embodiment is that the graphite crucible does not have internal channels and is a sealed structure.

[0053] S3: Power is supplied to raise the temperature to 1000℃ and hold for 4 hours. During the heating process, a large amount of gas is discharged from the top layer of insulation material. This gas is mainly generated by the pyrolysis of organic components such as binder, electrolyte, and diaphragm. It can be centrally treated by introducing it into the tail gas treatment device. Occasionally, there will be a furnace spray phenomenon ("flame tongues spraying out") during the low-temperature carbonization process. S4: After the above heat preservation is completed, continue to supply power to raise the temperature to 2800℃ and then keep it for 12 hours. During this process, a large amount of flue gas is discharged from the internal channels of the graphite crucible. It is mainly generated by the decomposition and gasification of inorganic salt and other metal impurities. It can be introduced into the tail gas treatment device for centralized treatment. No furnace spraying phenomenon ("flame tongue spraying") was observed during the high temperature graphitization process. S5: After the graphitization insulation is completed, the power is cut off and the furnace is cooled. When the temperature at the central temperature measuring point is below 200℃, the insulation material and conductive coke are removed. It is found that the insulation material has caking. The graphite crucible is removed and then cooled to below 50℃ to ensure that the material is not oxidized. The cooling time T is approximately 16 days. S6: Using a vacuum feeder to remove the material from inside the graphite crucible, a layer of "shell-like material" was found on the surface of the upper layer of material in the graphite crucible. Figure 10 As shown, the ash content of the "shell-like material" was as high as 6.58%, mainly due to the condensation of high-melting-boiling-point impurities as they reached the upper surface and cooled. Ash content, volatile matter, specific surface area, specific capacity, and initial efficiency were tested on the mixed sample after high-temperature graphitization.

[0054] Comparative Example 2 The difference from Comparative Example 1 is that the graphitization temperature was 2400℃ and the holding time was 20 hours. The ash content of the "shell-like material" was 7.60%.

[0055] Comparative Example 3 The difference from Example 2 is that the value of λ is 4.

[0056] Comparative Example 4 The difference from Example 2 is that the value of λ is 5.

[0057] Test case According to the national standard GB / T 3521-2023 "Methods for Chemical Analysis of Graphite", the volatile matter and ash content of graphitized products were tested using a tube furnace, and the specific surface area of ​​graphitized products was tested using the nitrogen adsorption method. The data are shown in Table 2.

[0058] To test the electrochemical performance of recycled graphite, the recycled graphite materials obtained in this example and comparative example were sieved through a 200-mesh sieve and assembled into button cells for testing. The positive electrode of the cell was a lithium sheet, and the active material of the negative electrode was recycled graphite. The ratio of the negative electrode material was graphite active material (90% wt), acetylene black (5% wt), and polyvinylidene fluoride (PVDF) (5% wt), with PVDF:NMP (N-methylpyrrolidone) = 1:10. The solvent used was a three-system mixture of EC (ethylene carbonate), DMC (dimethyl ethylene carbonate), and EMC (methyl ethyl carbonate). The electrolyte was a 1 mol / L LiPF6 solution (with a volume ratio of EC, DMC, and EMC of 1:1:1). The button cells were prepared in an argon-filled glove box. The charge-discharge tests of the cells were conducted on a LAND battery system, with a charge-discharge voltage range of 0–2V, a rate of 0.1C, and a temperature of 25°C. The ratio of the initial charge specific capacity to the initial discharge specific capacity is the initial coulombic efficiency, and the data are shown in Table 2.

[0059] Using Best Instruments – Static Volumetric Method, with nitrogen as the adsorbate, fully automated in-situ aspiration and degassing was performed to test the pore size distribution of the waste graphite and the graphitized product of Example 1. The data are shown in Table 3.

[0060] Table 2

[0061] Table 3

[0062] As shown in Tables 1 and 2, the graphite crucible described in this invention features a unique internal channel structure design. Compared to the traditional Atchison crucible furnace graphitization method, it solves safety issues such as furnace spraying, increases the material heat dissipation area, and significantly shortens the cooling cycle of graphitization, thereby greatly improving the efficiency of the graphitization furnace. It can also be seen that for conventional graphite crucibles, the longer the graphitization time, the higher the volatile matter content and the more ash content in the graphitized product. Increasing the height-to-diameter ratio λ is not conducive to ash discharge, and the ash content of the product will increase. Increasing the inner diameter ratio κ will significantly shorten the cooling cycle, but an excessively high κ value will significantly reduce the loading capacity, affecting production capacity.

[0063] Comparison of scanning electron microscopy and the electrochemical performance of the product shows that the surface impurities of the graphite particles are significantly reduced after high-temperature treatment, as evidenced by a significant reduction in ash content and volatile matter.

[0064] Comparing the data in Table 3, it can be seen that the overall pore volume of graphite particles decreased significantly after graphitization, resulting in a significant reduction in specific surface area. Among them, the proportion of mesopores with micropores below 50nm decreased, while the proportion of macropores increased. This is mainly because the high-temperature treatment process can cause structural defects such as mesopores and micropores to fuse and shrink, significantly improving electrochemical performance such as specific capacity and first-efficiency, reaching the level of commercial battery-grade graphite anode materials.

[0065] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A graphite crucible, characterized in that, Includes the crucible body and lid; The crucible body includes a coaxial hollow outer cylinder and an inner cylinder, the height of which is less than the height of the outer cylinder; The bottom end face of the outer cylinder is horizontally connected to the bottom end face of the inner cylinder, forming an annular cavity; The cover plate has a first annular protrusion on its inner side. The first annular protrusion has a first inner hole that passes through the cover plate and is coaxial with the inner cylinder. The outer diameter of the first annular protrusion is smaller than the inner diameter of the inner cylinder.

2. The graphite crucible according to claim 1, characterized in that, At least one of the following conditions must be met: a. The ratio of the height to the inner diameter of the outer cylinder is 1-3; b. The ratio of the inner diameter of the inner cylinder to the inner diameter of the outer cylinder is 0.1-0.5; c. The difference between the inner diameter of the inner cylinder and the outer diameter of the first annular boss is 5-10 mm; d. The sum of the height of the inner cylinder and the height of the first annular boss is greater than the height of the outer cylinder.

3. The graphite crucible according to claim 1, characterized in that, The outer side of the cover plate is also provided with a second annular protrusion, the second annular protrusion is provided with a second inner hole, and the second inner hole is coaxially connected with the first inner hole.

4. The graphite crucible according to claim 1, characterized in that, The bottom of the inner cylinder is closed.

5. The graphite crucible according to claim 1, characterized in that, The graphite crucibles are arranged in at least two layers coaxially stacked.

6. A method for graphitizing and purifying waste graphite, characterized in that, Includes the following steps: S1: Load waste graphite into a graphite crucible, and then load the graphite crucible into a graphitization furnace; S2: Proceed to a heating stage until the center temperature of the graphitization furnace reaches 600-1200℃, and hold for 2-12 hours; S3: Continue the second stage of heating until the center temperature of the graphitization furnace reaches 2000-3000℃, and hold for 12-48 hours; The graphite crucible is selected from the graphite crucible described in any one of claims 1-5.

7. The graphitization and purification method according to claim 6, characterized in that, Step S1, the process of loading the graphite crucible into the graphitization furnace includes: The graphite crucibles are stacked coaxially in at least two layers, and a second annular protrusion is provided on the outer side of the cover plate of the graphite crucible located on the top layer; after the graphite crucibles are filled with conductive coke, the conductive cokes are covered with insulating material to form an insulating layer; wherein the insulating layer is lower than the top of the second annular protrusion.

8. The graphitization and purification method according to claim 6, characterized in that, In step S2, the heating process includes: After heating to 450-550℃, hold the temperature for 1-3 hours, then heat to 600-1200℃ and hold for 1-9 hours. The heating rate of the aforementioned section is <50℃ / h.

9. The graphitization and purification method according to claim 7, characterized in that, It also includes introducing a protective gas into the bottom of the graphite crucible located at the bottom layer.

10. The application of the graphite crucible according to any one of claims 1-5 or the graphitization purification method according to any one of claims 6-9 in the preparation of graphite anode materials.

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