Methods for recovering graphite from carbon residue of spent lithium-ion batteries and regenerated graphite

Abstract

The application discloses a method for recovering graphite from carbon residues of waste lithium ion batteries and regenerated graphite, and relates to the technical field of lithium battery recycling. The carbon residues of waste lithium ion batteries after acid leaching are subjected to heat treatment, in the heat treatment process, the inorganic impurities and organic impurities in the carbon residues can be dissociated into smaller particles, which is convenient for removal in subsequent processes; the pyrolysis carbon residues obtained through heat treatment are subjected to scattering treatment and screening to obtain small particle materials, and the excess large particle impurities are removed; then, through grinding and grading, graphite coarse powder with a particle size Dv50 of 12-15 mu m is obtained, and since the ash impurities are mainly concentrated in the fine powder, the ash can be effectively removed after grading. The heat treatment-scattering, screening-grinding and grading linkage technical means proposed in the application does not need to add additional chemical reagents, but only relies on several physical technical means, which not only can achieve the effect of removing ash impurities, but also can effectively remove amorphous carbon, and the method is simple, easy to operate, safe and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of lithium battery recycling technology, and more specifically, to a method for recovering graphite from carbon residue of waste lithium-ion batteries and the method for regenerating graphite. Background Technology

[0002] The surge in mobile electronics and electric vehicles (EVs) has led to an increased demand for secondary energy storage, primarily a significant increase in the demand for lithium-ion batteries (LIBs). This increased consumption of LIBs has spurred demand and production of battery materials, but natural resources are finite. The recycling of LIBs requires the development of a sustainable closed-loop pathway, particularly focusing on mitigating environmental risks and increasing corporate profits.

[0003] However, current enterprise efforts in processing spent lithium-ion batteries primarily focus on recovering high-value metals. There are no effective, targeted recycling methods for the carbon slag remaining after high-value metal recovery through wet acid leaching and extraction, which is mainly carbon-based and contains small amounts of residual cathode material and electrolyte. Failure to treat and recycle this carbon slag will result in resource waste; furthermore, improper disposal of the carbon slag will have a serious impact on the environment.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for recovering graphite from carbon residue of waste lithium-ion batteries and to regenerate graphite, with the aim of recovering high-purity graphite from carbon residue of waste lithium-ion batteries and effectively improving the electrochemical performance of graphite products.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a method for recovering graphite from carbon residue of spent lithium-ion batteries, comprising:

[0008] The carbon residue from acid leaching of waste lithium-ion batteries is heat-treated to obtain pyrolytic carbon residue. The pyrolytic carbon residue is then broken up and screened to obtain small particles with a particle size of less than 150-300 mesh. The small particles are then ground and graded to obtain coarse graphite powder with a particle size Dv50 of 12μm-15μm.

[0009] In an optional embodiment, the process of obtaining small particulate material includes: dispersing the pyrolysis carbon slag by high-speed mixing, and placing the dispersed material in a vibrating screen with a mesh size of 150-300 mesh to separate the small particulate material.

[0010] Preferably, during the dispersing process, the mixing speed is controlled at 500 rpm to 2000 rpm, and the stirring time is 3 min to 30 min.

[0011] In an optional embodiment, the grinding method is selected from at least one of mechanical impact mill, air jet mill and ball mill, and the particle size Dv50 of the ground material is controlled to be 11μm-15μm.

[0012] Grading involves processing materials by passing them sequentially through a classifier and a cyclone separator.

[0013] In an optional embodiment, when preparing coarse graphite powder using a mechanical impact mill or an air jet mill, the apparatus used is equipped with a classifier and a cyclone separator.

[0014] Preferably, when preparing coarse graphite powder using a mechanical impact mill, the main frequency of the mechanical impact mill is controlled at 20Hz-50Hz, the frequency of the classifier at 25Hz-50Hz, the air pressure of the cyclone separator at 5000Pa-7500Pa, and the air volume of the cyclone separator at 250m³. 3 / min-400m 3 / min;

[0015] Preferably, when preparing coarse graphite powder using an air jet mill, the grinding gas pressure is controlled at 0.15 MPa-0.50 MPa, the main machine frequency at 20 Hz-50 Hz, the classifier frequency at 25 Hz-50 Hz, the cyclone separator air pressure at 5000 Pa-7500 Pa, and the cyclone separator air volume at 250 m³ / h. 3 / min-400m 3 / min.

[0016] In an optional embodiment, when graphite coarse powder is prepared by ball milling, it is processed sequentially by an air classifier and a cyclone separator after ball milling.

[0017] Preferably, during the ball milling process, the ball-to-material ratio is controlled at (3-5):1, and the ball milling time is 3-10 minutes.

[0018] Preferably, after ball milling, the frequency of the air classifier is controlled at 25Hz-50Hz, the air pressure of the cyclone separator is controlled at 5000Pa-7500Pa, and the air volume of the cyclone separator is controlled at 250m³. 3 / min-400m 3 / min.

[0019] In an optional embodiment, the heat treatment method is selected from at least one of electric furnace heat treatment and microwave heat treatment;

[0020] Preferably, the heat treatment is carried out under an inert atmosphere;

[0021] Preferably, during the electric furnace heat treatment process, the heat treatment temperature is controlled at 450℃-1000℃, and the heat treatment time is 2h-5h.

[0022] In an optional embodiment, the carbon slag is first dried and then subjected to microwave heat treatment.

[0023] Preferably, during the microwave heat treatment process, the microwave power is controlled at 400W-1500W and the microwave treatment time is 5min-30min.

[0024] Preferably, during the drying process, the drying temperature is controlled at 80℃-200℃ and the drying time is 10h-30h.

[0025] In an optional embodiment, coarse graphite powder is mixed with a carbon source, and the resulting mixture is graphitized.

[0026] Preferably, the carbon source is selected from at least one of pitch, petroleum coke and needle coke;

[0027] Preferably, the total amount of carbon source to the mass ratio of graphite powder is (2-10):100; more preferably, it is (3-5):100.

[0028] Preferably, the carbon source includes at least bitumen;

[0029] When the carbon source is a mixture of pitch and petroleum coke, the mass ratio of pitch to petroleum coke should be controlled at 1:(0.1-1.0).

[0030] When the carbon source is a mixture of pitch and needle coke, the mass ratio of pitch to needle coke is controlled to be 1:(0.1-1.0).

[0031] When the carbon source is a mixture of pitch, petroleum coke and needle coke, the mass ratio of pitch to the total amount of petroleum coke and needle coke is controlled to be 1:(0.1-1.0).

[0032] Preferably, the particle size Dv50 of the carbon source is 3μm-6μm, more preferably 3μm-4μm;

[0033] Preferably, the coarse graphite powder and the carbon source are mixed at high speed, with the stirring speed controlled at 500 rpm-2000 rpm and the mixing time at 5 min-30 min.

[0034] In an optional embodiment, the graphitization treatment temperature is 2400℃-3100℃, and the holding time is 1h-72h;

[0035] More preferably, the graphitization treatment temperature is 2500℃-2800℃, and the holding time is 2h-4h.

[0036] Secondly, the present invention provides a recycled graphite prepared by any of the methods described in the foregoing embodiments.

[0037] This invention offers the following advantages: The carbon slag from acid leaching of waste lithium-ion batteries undergoes heat treatment. During this process, inorganic and organic impurities in the slag are dissociated into smaller particles, facilitating removal in subsequent processes. The pyrolytic carbon slag obtained after heat treatment is then dispersed and sieved to obtain small particles, removing excess large impurities. Subsequently, grinding and grading yield coarse graphite powder with a particle size Dv50 of 12μm-15μm. Since ash impurities are mainly concentrated in the fine powder, ash can be effectively removed after grading. The heat treatment-dispersion, sieving-grinding, and grading linkage technology proposed in this invention does not require the addition of additional chemical reagents. Relying solely on a few physical steps, it not only removes ash impurities but also effectively removes amorphous carbon. The method is simple, safe, environmentally friendly, and highly operable. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart for recovering graphite from carbon residue of waste lithium-ion batteries provided by the present invention;

[0040] Figure 2 This is a SEM image of the recycled graphite prepared in Example 1 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] This invention provides a method for recovering graphite from carbon residue of spent lithium-ion batteries. Please refer to [the relevant documentation]. Figure 1 This includes the following steps:

[0043] S1, Heat Treatment

[0044] Pyrolytic carbon slag is obtained by heat treatment of carbon slag after acid leaching of waste lithium-ion batteries. Through heat treatment, inorganic and organic impurities in the carbon slag can be dissociated into smaller particles, which are easier to remove in subsequent processes.

[0045] Specifically, acid leaching of waste lithium-ion batteries is a conventional battery recycling process, and the residue obtained after acid leaching is called "carbon slag".

[0046] In some embodiments, the heat treatment method is selected from at least one of electric furnace heat treatment and microwave heat treatment, and can be any one or both of the above. Microwave heat treatment is preferred, as it is easier to form smaller particles and also helps to reduce energy consumption. Heat treatment can be carried out in an inert atmosphere, and the type of inert atmosphere is not limited, such as nitrogen, argon, etc. Since nitrogen is readily available and inexpensive, it is preferred.

[0047] It should be noted that the main effects of heat treatment on carbon slag are as follows: (1) Heat treatment can decompose the interfacial continuous phase resistance layer in graphite carbon slag, forming inorganic particles with finer particle size. In particular, microwave pyrolysis treatment makes it easier to form particles with finer particle size; (2) Heat treatment can completely decompose the binder in the carbon slag to produce amorphous carbon, which is convenient for subsequent removal.

[0048] For graphite, both fine particles and amorphous carbon produced by the complete pyrolysis of the binder are impurities that can affect the properties of graphite and need to be removed through subsequent processes.

[0049] In some embodiments, during the electric furnace heat treatment process, the heat treatment temperature is controlled at 450℃-1000℃ and the heat treatment time is 2h-5h. When the temperature is below 450℃, the binder in the graphite cannot be completely decomposed and will adhere to the graphite surface, making it difficult to remove through subsequent grinding-grading-cyclone separation. When the temperature is above 1000℃, excessive energy consumption will be generated.

[0050] Specifically, during electric furnace heat treatment, the temperature can be controlled at 450℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, etc., and the heat treatment time can be 2h, 3h, 4h, 5h, etc. When using electric furnace heat treatment, drying can be performed before heat treatment, or it can be omitted.

[0051] In some embodiments, the carbon slag is first dried before microwave heat treatment. Drying removes surface moisture from the carbon slag, preventing interference with the microwave heat treatment. During microwave heat treatment, the microwave power is controlled between 400W and 1500W, and the treatment time is 5-30 minutes. When the microwave pyrolysis power is below 400W, the binder in the graphite cannot be completely decomposed and will adhere to the graphite surface, making it difficult to remove through subsequent grinding, grading, and cyclone separation. When the microwave power is above 1500W, excessive energy consumption occurs.

[0052] Specifically, during microwave heat treatment, the microwave power can be controlled at 400W, 600W, 800W, 1000W, 1200W, 1500W, etc., and the microwave treatment time can be 5min, 10min, 15min, 20min, 25min, 30min, etc.

[0053] In some embodiments, during the drying process, the drying temperature is controlled at 80℃-200℃, and the drying time is 10h-30h, so as to fully remove the moisture from the surface of the carbon slag after acid leaching. Specifically, the drying temperature can be 80℃, 100℃, 120℃, 150℃, 180℃, 200℃, etc., and the drying time can be 10h, 15h, 20h, 25h, 30h, etc.

[0054] S2. Dispersing and sieving

[0055] The pyrolysis carbon slag obtained in step S1 is broken up and screened to remove small particles with a particle size of less than 150-300 mesh, and excess large particles are removed.

[0056] In actual operation, the process of obtaining small particulate materials includes: dispersing the pyrolysis carbon slag by high-speed mixing, and then sieving the dispersed material in a vibrating screen with a mesh size of 150-300 to remove excess large particulate impurities.

[0057] In some embodiments, high-speed mixing can be carried out in a high-speed mixer, where the high-speed agitator blades of the mixer disperse the carbon slag. The rotation speed of the high-speed mixer is 500 rpm-2000 rpm, and the mixing time is 3 min-30 min. Specifically, the rotation speed of the high-speed mixer can be 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, etc., and the mixing time can be 3 min, 5 min, 10 min, 20 min, 30 min, etc.

[0058] In some embodiments, the mesh size of the vibrating screen is 150-300 mesh, such as 150 mesh, 200 mesh, 250 mesh, 300 mesh, etc., with 200 mesh being preferred.

[0059] S3, Grinding, Grading

[0060] The small particles obtained in step S2 are ground and classified to obtain coarse graphite powder with a particle size Dv50 of 12μm-15μm (e.g., particle size Dv50 can be 12μm, 13μm, 14μm, 15μm, etc.). Grinding the small particles can effectively de-agglomerate them, and classifying them can remove fine powder impurities, resulting in coarse graphite powder with a low impurity content.

[0061] In some embodiments, the method for preparing coarse graphite powder using small particulate materials is selected from at least one of mechanical impact milling, air jet milling and ball milling. It can be any one of the above methods, or a combination of two or three methods, as long as it can be graded to obtain coarse graphite powder with a particle size Dv50 of 12μm-15μm.

[0062] In some embodiments, coarse graphite powder is prepared using a mechanical impact mill or an air jet mill. The apparatus used is required to be equipped with a classifier and a cyclone separator. The particle size Dv50 of the material is controlled to be 11 μm-15 μm after mechanical impact milling and before classification. Similarly, when coarse graphite powder is prepared using a ball mill, it is processed sequentially through an air jet classifier and a cyclone separator after ball milling. The particle size requirement for the ground graphite powder is a Dv50 of 11 μm-15 μm, and the particle size requirement for the classified and cyclone-separated coarse graphite powder is a Dv50 of 12 μm-15 μm. Further deagglomeration of the heat-treated carbon slag is performed, and coarse and fine powders are separated by cyclone separation technology. The coarse powder obtained after processing according to the embodiments of the present invention has a very low ash impurity content.

[0063] It should be noted that the ash impurities are mainly concentrated in the fine powder, and the amorphous carbon produced by the cracking of the binder is also concentrated in the fine powder after being separated by cyclone separation. The method provided by the embodiments of the present invention can achieve the purpose of removing inorganic impurities and amorphous carbon impurities, and can further improve the electrochemical performance of graphite products.

[0064] Furthermore, in order to obtain coarse graphite powder with the required particle size, the inventors optimized the operating parameters of different grinding methods:

[0065] When preparing coarse graphite powder using a mechanical impact mill, the main frequency of the mechanical impact mill is controlled at 20Hz-50Hz, the frequency of the classifier at 25Hz-50Hz, the air pressure of the cyclone separator at 5000Pa-7500Pa, and the air volume of the cyclone separator at 250m³ / h. 3 / min-400m 3 / min. Specifically, the main frequency of the mechanical impact mill can be 20Hz, 30Hz, 40Hz, 50Hz, etc., the frequency of the classifier can be 25Hz, 30Hz, 40Hz, 50Hz, etc., the air pressure of the cyclone separator can be 5000Pa, 5500Pa, 6000Pa, 6500Pa, 7000Pa, 7500Pa, etc., and the air volume of the cyclone separator can be 250m³ / min. 3 / min, 300m 3 / min, 350m 3 / min, 400m 3 / min etc.

[0066] When preparing coarse graphite powder using an air jet mill, the grinding gas pressure is controlled at 0.15 MPa-0.50 MPa, the main mill frequency at 20 Hz-50 Hz, the classifier frequency at 25 Hz-50 Hz, the cyclone separator air pressure at 5000 Pa-7500 Pa, and the cyclone separator air volume at 250 m³ / h. 3 / min-400m 3 / min. Specifically, the grinding gas pressure can be controlled at 0.15MPa, 0.20MPa, 0.305MPa, 0.40MPa, 0.50MPa, etc., the main unit frequency can be 20Hz, 30Hz, 40Hz, 50Hz, etc., the classifier frequency can be 25Hz, 30Hz, 40Hz, 50Hz, etc., the cyclone separator air pressure can be 5000Pa, 5500Pa, 6000Pa, 6500Pa, 7000Pa, 7500Pa, etc., and the cyclone separator air volume can be 250m³ / min. 3 / min, 300m 3 / min, 350m 3 / min, 400m 3 / min etc.

[0067] When preparing coarse graphite powder using ball milling, the particle size Dv50 of the material after ball milling should be controlled to be 11μm-15μm. During the ball milling process, the ball-to-material ratio should be controlled to be (3-5):1, the milling time to be 3-10 minutes, and the loading volume of the ball milling jar should be 1 / 3 to 2 / 3 full. After ball milling, the frequency of the air classifier should be controlled to be 25Hz-50Hz, the air pressure of the cyclone separator should be controlled to be 5000Pa-7500Pa, and the air volume of the cyclone separator should be 250m³. 3 / min-400m 3 / min. Specifically, the ball-to-material ratio can be controlled at 3:1, 4:1, 5:1, etc., and the ball milling time can be 3 min, 5 min, 8 min, 10 min, etc.; the frequency of the air classifier can be controlled at 25Hz, 30Hz, 40Hz, 50Hz, etc., the air pressure of the cyclone separator can be 5000Pa, 5500Pa, 6000Pa, 6500Pa, 7000Pa, 7500Pa, etc., and the air volume of the cyclone separator can be 250m³ / min. 3 / min, 300m 3 / min, 350m 3 / min, 400m 3 / min etc.

[0068] The heat treatment-dispersion, sieving-grinding, grading, and cyclone separation linkage technology proposed in this invention does not require the addition of additional chemical reagents. It only relies on a few physical technology steps to not only remove ash impurities, but also effectively remove amorphous carbon (including SP in carbon slag and amorphous carbon generated by the cracking of binders). The method is simple, safe, environmentally friendly, and highly operable, and has great industrial application value.

[0069] S4, carbon coating

[0070] Mixing coarse graphite powder with a carbon source and coating the coarse graphite powder before graphitization fills the defects formed on the surface of the coarse graphite powder. Under high temperature, the asphalt softens and melts and bonds with other materials, which can effectively repair the surface defects of graphite, effectively reduce the BET (specific surface area) of graphite, and improve the reversible capacity of negative electrode graphite, thereby improving the first efficiency.

[0071] In some embodiments, the carbon source is selected from at least one of pitch, petroleum coke, and needle coke, and can be any one or more of the above. The total amount of carbon source to graphite powder is in a mass ratio of (2-10):100, preferably (3-5):100. The amount of carbon source is preferably within the above range to better repair graphite surface defects, reduce the BET of graphite, and improve the reversible capacity of graphite.

[0072] Specifically, the total amount of carbon source used can be in a mass ratio of 2:100, 3:100, 4:100, 5:100, 8:100, 10:100, etc.

[0073] In a preferred embodiment, the carbon source includes at least bitumen, which can be bitumen alone or a mixture of bitumen and other raw materials. The specific types of carbon sources fall into the following four categories:

[0074] Case 1: If the carbon source is asphalt alone, the mass ratio of asphalt addition to graphite powder should be controlled to be (2-10):100, preferably (3-5):100.

[0075] Scenario 2: If the carbon source is a mixture of asphalt and petroleum coke, then the amount of mixture used should be controlled to meet the above requirements, and the mass ratio of asphalt to petroleum coke should be controlled to be 1:(0.1-1.0), such as 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1.0, etc.

[0076] Scenario 3: If the carbon source is a mixture of pitch and needle coke, then the amount of the mixture should be controlled to meet the above requirements, and the mass ratio of pitch to needle coke should be controlled to be 1:(0.1-1.0), such as 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1.0, etc.

[0077] Scenario 4: When the carbon source is a mixture of pitch, petroleum coke and needle coke, the amount of the mixture should be controlled to meet the above requirements. At the same time, the mass ratio of pitch to the total amount of petroleum coke and needle coke should be controlled to be 1:(0.1-1.0), such as 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1.0, etc. The ratio of petroleum coke to needle coke is not limited and can be any ratio.

[0078] In some embodiments, the particle size Dv50 of the carbon source material is 3μm-6μm, preferably 3μm-4μm, to better form carbon coating on the coarse graphite powder. Specifically, the particle size Dv50 of the carbon source material can be 3μm, 4μm, 5μm, 6μm, etc.

[0079] In some embodiments, coarse graphite powder and a carbon source can be mixed at high speed, with the stirring speed controlled at 500 rpm-2000 rpm and the mixing time at 5 min-30 min, to form a uniform carbon coating. Specifically, the high-speed mixing can be carried out in a high-speed mixer, with stirring speeds of 500 rpm, 800 rpm, 1000 rpm, 1500 rpm, 2000 rpm, etc., and mixing times of 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc.

[0080] S5, graphitization treatment

[0081] The graphite mixture formed by graphite coarse powder and carbon source is graphitized. In this embodiment of the invention, the process route of heat treatment-dispersion, sieving-grinding, grading and cyclone separation is used to reduce the ash impurity content and amorphous carbon impurity content in graphite. Graphite coarse powder with low ash content is used for graphitization. After graphitization, the ash impurity content is extremely low, meeting the standard for battery-grade negative electrode graphite.

[0082] It should be noted that carbon slag that has not undergone S1-S4 treatment still has a high ash content, making it difficult to meet the standards for battery-grade negative electrode graphite even after graphitization. This invention creatively proposes removing amorphous carbon before graphitization, which can effectively improve the electrochemical performance of the finished graphite product, especially its lithium removal specific capacity.

[0083] In some embodiments, the graphitization temperature is 2400℃-3100℃ and the holding time is 1h-72h; preferably, the graphitization temperature is 2500℃-2800℃ and the holding time is 2h-4h. By optimizing the temperature and time of the graphitization treatment, a battery-grade negative electrode graphite product can be obtained after graphitization treatment.

[0084] Specifically, graphitization can be carried out in a graphitization furnace at temperatures of 2400℃, 2500℃, 2600℃, 2800℃, 3000℃, and 3100℃, with holding times of 1h, 2h, 3h, 4h, 10h, 30h, 50h, and 70h. After graphitization, the graphite is cooled and removed from the furnace. The removed graphite then undergoes conventional crushing, demagnetization, and sieving to obtain the final high-performance lithium-ion battery anode graphite material.

[0085] This invention also provides a recycled graphite, prepared by the method provided in this invention, which has the advantages of low preparation cost and excellent electrochemical performance, with an initial delithiation specific capacity greater than 350 mAh g. -1 The Coulomb efficiency is greater than 93.9%.

[0086] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0087] It should be noted that the following examples and comparative examples are all carbon slag produced by using sulfuric acid as a leaching agent in the production of waste lithium-ion batteries. It inevitably contains complex components such as calcium sulfate, nickel and cobalt metal oxides, conductive carbon black, and residues after membrane carbonization, and may even contain silicon dust. Specifically, the composition of the carbon slag is shown in Table 1.

[0088] Table 1 Composition of carbon slag

[0089]

[0090] Example 1

[0091] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0092] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0093] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0094] (3) The sieved carbon slag is ground in a mechanical impact mill. The main frequency of the mechanical impact mill is 40Hz, the frequency of the classifier is 45Hz, the air pressure of the cyclone separator is 7000Pa, and the air volume is 350m³. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the coarse graphite powder after mechanical impact, classification, and cyclone separation is Dv50 = 12~15μm.

[0095] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm (i.e., the mass ratio of carbon source to graphite coarse powder is 3:100), the high-speed mixer speed is 1500rpm, and the mixing time is 10min.

[0096] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0097] The SEM image of the high-performance lithium-ion battery anode graphite material prepared in this embodiment is shown below. Figure 2 As shown, the graphite particles have a uniform particle size, a smooth surface without obvious textures or bumps, and a relatively regular morphology. No other obvious impurity phases were observed.

[0098] Example 2

[0099] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0100] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0101] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0102] (3) The sieved carbon slag is ground in a mechanical impact mill. The main frequency of the mechanical impact mill is 40 Hz, the frequency of the classifier in the impact mill is 45 Hz, the air pressure of the cyclone separator is 7000 Pa, and the air volume is 350 m³ / h. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the coarse graphite powder after mechanical grinding, classification, and cyclone separation is Dv50 = 12~15μm.

[0103] (4) The graphite coarse powder obtained above is put into a high-speed mixer, and 3% of asphalt with a particle size of Dv50=4μm is added (i.e., the mass ratio of carbon source to graphite coarse powder is 3:100). The high-speed mixer speed is 1500rpm and the mixing time is 10min.

[0104] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0105] Example 3

[0106] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0107] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0108] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0109] (3) The sieved carbon slag is ground in a mechanical impact mill. The main frequency of the mechanical impact mill is 40Hz, the frequency of the classifier is 45Hz, the air pressure of the cyclone separator is 7000Pa, and the air volume is 350m³. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the coarse graphite powder after mechanical grinding, classification, and cyclone separation is Dv50 = 12~15μm.

[0110] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% of a mixture of asphalt and petroleum coke with a particle size of Dv50=4μm, wherein the mass ratio of asphalt to petroleum coke is 2:1; the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0111] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0112] Example 4

[0113] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0114] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0115] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0116] (3) The sieved carbon slag is ground in a mechanical impact mill. The main frequency of the mechanical impact mill is 40Hz, the frequency of the classifier is 45Hz, the air pressure of the cyclone separator is 7000Pa, and the air volume is 350m³. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the coarse graphite powder after mechanical grinding, classification, and cyclone separation is Dv50 = 12~15μm.

[0117] (4) The coarse powder obtained above is put into a high-speed mixer, and 3% of a mixture of asphalt and needle coke with a particle size of Dv50 = 4μm is added, wherein the mass ratio of asphalt to needle coke is 2:1, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0118] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0119] Example 5

[0120] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0121] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0122] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0123] (3) The sieved carbon slag was ground in an air jet mill. The grinding gas pressure of the air jet mill was 0.2 MPa, the main frequency was 40 Hz, the classifier frequency was 45 Hz, the cyclone separator pressure was 7000 Pa, and the air volume was 350 m³ / h. 3 / min, after grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the graphite coarse powder after air jet milling, classification and cyclone separation is Dv50 = 12~15μm.

[0124] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0125] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0126] Example 6

[0127] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0128] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0129] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0130] (3) The sieved carbon slag was ground in an air jet mill. The grinding gas pressure of the air jet mill was 0.2 MPa, the main frequency was 40 Hz, the classifier frequency was 45 Hz, the cyclone separator pressure was 7000 Pa, and the air volume was 350 m³ / h. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for graphite powder after air jet milling is Dv50 = 11~15μm, and the particle size requirement for coarse graphite powder after classification and cyclone separation is Dv50 = 12~15μm.

[0131] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0132] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0133] Example 7

[0134] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0135] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0136] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0137] (3) The sieved carbon slag was ground in an air jet mill. The grinding gas pressure of the air jet mill was 0.2 MPa, the main frequency was 40 Hz, the classifier frequency was 45 Hz, the cyclone separator pressure was 7000 Pa, and the air volume was 350 m³ / h. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the coarse graphite powder after air jet milling, classification, and cyclone separation is Dv50 = 12~15μm.

[0138] (4) The coarse powder obtained above is put into a high-speed mixer, and 3% of a mixture of asphalt and petroleum coke with a particle size of Dv50 = 4μm is added, wherein the mass ratio of asphalt to petroleum coke is 2:1, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0139] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0140] Example 8

[0141] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0142] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0143] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0144] (3) The sieved carbon slag was ground in an air jet mill. The grinding gas pressure of the air jet mill was 0.2 MPa, the main motor frequency was 40 Hz, the classifier frequency was 45 Hz, the cyclone separator pressure was 7000 Pa, and the air volume was 350 m³ / h. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the coarse graphite powder after air jet milling, classification, and cyclone separation is Dv50 = 12~15μm.

[0145] (4) The coarse powder obtained above is put into a high-speed mixer, and 3% of a mixture of asphalt and needle coke with a particle size of Dv50=4μm is added, wherein the mass ratio of asphalt to needle coke is 2:1, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0146] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0147] Example 9

[0148] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0149] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0150] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0151] (3) The sieved carbon slag is ball-milled in a ball mill at a ball-to-material ratio of 4:1, with the ball mill jar filled to 2 / 3 capacity, and the milling time is 5 minutes. After ball milling, the carbon slag is placed in an air classifier for classification. The air classifier operates at a frequency of 45 Hz, with a cyclone separator pressure of 7000 Pa and an air volume of 350 m³ / h. 3 / min. After grinding, collect the required coarse powder at the discharge point, and collect the fine powder at the cyclone separator discharge point. The particle size requirement for graphite after ball milling is Dv50 = 11~15μm; the particle size requirement for coarse graphite powder after classification and cyclone separation is Dv50 = 12~15μm.

[0152] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0153] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0154] Example 10

[0155] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0156] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0157] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0158] (3) The sieved carbon slag was ball-milled in a ball mill at a ball-to-material ratio of 4:1, with the ball mill jar filled to 2 / 3 capacity, for 5 minutes. After ball milling, the carbon slag was placed in an air classifier for classification. The air classifier frequency was 45Hz, the cyclone separator pressure was 7000Pa, and the air volume was 350m³. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for graphite after ball milling is Dv50 = 11~15μm; the particle size requirement for coarse graphite powder after classification and cyclone separation is Dv50 = 12~15μm.

[0159] (4) The coarse powder obtained above is put into a high-speed mixer, and 3% of a mixture of asphalt and petroleum coke with a particle size of Dv50 = 4μm is added, wherein the mass ratio of asphalt to petroleum coke is 2:1, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0160] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0161] Example 11

[0162] This embodiment provides a method for recovering graphite from carbon residue of waste lithium-ion batteries, including the following specific steps:

[0163] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in a microwave pyrolysis furnace and microwave pyrolysis is performed under a nitrogen atmosphere. The microwave power is 1200W and the microwave treatment time is 15min to obtain pyrolytic carbon slag.

[0164] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0165] (3) The sieved carbon slag was ball-milled in a ball mill at a ball-to-material ratio of 4:1, with the ball mill jar filled to 2 / 3 capacity, for 5 minutes. After ball milling, the carbon slag was placed in an air classifier for classification. The air classifier frequency was 45Hz, the cyclone separator pressure was 7000Pa, and the air volume was 350m³. 3The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for graphite after ball milling is Dv50 = 11~15μm; the particle size requirement for coarse graphite powder after classification and cyclone separation is Dv50 = 12~15μm.

[0166] (4) The coarse powder obtained above is put into a high-speed mixer, and 3% of a mixture of asphalt and petroleum coke with a particle size of Dv50 = 4μm is added, wherein the mass ratio of asphalt to petroleum coke is 2:1; the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0167] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0168] Comparative Example 1

[0169] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0170] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0171] (3) Put the sieved carbon slag obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the high-speed mixer speed is 1500rpm, and the mixing time is 10min;

[0172] (4) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and removed from the furnace. After being removed from the furnace, it is crushed, demagnetized and screened to obtain recycled graphite material.

[0173] It should be noted that the difference between Comparative Example 1 and Example 1 is only that step (3) is omitted and carbon coating is performed directly after step (2).

[0174] Comparative Example 2

[0175] The only difference from Example 2 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0176] Comparative Example 3

[0177] The only difference from Example 3 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0178] Comparative Example 4

[0179] The only difference from Example 4 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0180] Comparative Example 5

[0181] The only difference from Example 5 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0182] Comparative Example 6

[0183] The only difference from Example 6 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0184] Comparative Example 7

[0185] The only difference from Example 7 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0186] Comparative Example 8

[0187] The only difference from Example 8 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0188] Comparative Example 9

[0189] The only difference from Example 9 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0190] Comparative Example 10

[0191] The only difference from Example 10 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0192] Comparative Example 11

[0193] The only difference from Example 11 is that step (3) is omitted, and carbon coating is performed directly after step (2).

[0194] Comparative Example 12

[0195] The difference from Example 1 is that the pyrolysis temperature is different. The specific steps are as follows:

[0196] (1) The carbon slag produced during the production of waste lithium-ion batteries is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 350°C for 2 hours to obtain pyrolytic carbon slag.

[0197] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0198] (3) The sieved carbon slag was ground in a mechanical impact mill. In this comparative example, the main unit frequency was 40 Hz, the classifier frequency was 45 Hz, the cyclone separator pressure was 7000 Pa, and the air volume was 350 m³ / h. 3 The grinding process is carried out at a rate of / min. After grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator. The particle size requirement for the graphite powder after ball milling is Dv50 = 11~15μm, and the particle size requirement for the coarse graphite powder after classification and cyclone separation is Dv50 = 12~15μm.

[0199] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0200] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0201] Comparative Example 13

[0202] The only difference between this comparative example and Example 1 is the change in the frequency of the classifier. The specific steps are as follows:

[0203] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0204] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0205] (3) The sieved carbon slag is ground in a mechanical impact mill. The main frequency of the mechanical impact mill is 40Hz, the frequency of the classifier is 60Hz, the air pressure of the cyclone separator is 7000Pa, and the air volume is 350m³. 3 / min, after grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator; after processing, the particle size of the coarse powder after cyclone separation is Dv50=7~10μm.

[0206] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0207] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain lithium-ion battery negative electrode graphite material.

[0208] Comparative Example 14

[0209] The only difference between this comparative example and Example 5 is the pressure of the air jet mill and the frequency of the classifier. The specific steps are as follows:

[0210] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0211] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0212] (3) The sieved carbon slag was ground in an air jet mill. In this comparative example, the air jet mill had a gas pressure of 0.7 MPa, a main unit frequency of 40 Hz, a classifier frequency of 55 Hz, a cyclone separator pressure of 7000 Pa, and an air volume of 350 m³ / h.3 The grinding process was carried out at a speed of [speed] min. After grinding, the required coarse powder was collected at the discharge point, and the fine powder was collected at the fine powder discharge point of the cyclone separator. By changing the gas pressure of the air jet mill and the frequency of the classifier, the Dv50 of the graphite coarse powder after cyclone separation was measured to be 7-10 μm.

[0213] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0214] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain lithium-ion battery negative electrode graphite material.

[0215] Comparative Example 15

[0216] The only difference between this comparative example and Example 9 is the ball-to-material ratio and the ball-milling time. The specific steps are as follows:

[0217] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag; the dried carbon slag is placed in an electric furnace and heat-treated under a nitrogen atmosphere at a temperature of 800°C for 1.5 hours to obtain pyrolytic carbon slag.

[0218] (2) The above-mentioned pyrolysis carbon slag is placed in a high-speed mixer for mixing. The high-speed mixing blades of the high-speed mixer are used to break up the carbon slag. The rotation speed of the high-speed mixer is 1500 rpm and the mixing time is 10 min. The carbon slag after being broken up by the high-speed mixer is placed in a 200-mesh vibrating screen for sieving to remove excess large particulate impurities.

[0219] (3) The sieved carbon slag was ball-milled in a ball mill. In this comparative example, the ball-to-material ratio was 6:1, the ball mill loading was 2 / 3 full, and the milling time was 25 minutes. After ball milling, the carbon slag was placed in an air classifier for classification. The air classifier frequency was 45 Hz, the cyclone separator pressure was 7000 Pa, and the air volume was 350 m³ / h. 3 / min, after grinding, the required coarse powder is collected at the discharge point, and the fine powder is collected at the fine powder discharge point of the cyclone separator; the particle size of the coarse powder collected after cyclone separation is tested as Dv50=7~10μm.

[0220] (4) Put the coarse powder obtained above into a high-speed mixer, add 3% asphalt with a particle size of Dv50=4μm, the speed of the high-speed mixer is 1500rpm, and the mixing time is 10min.

[0221] (5) The above mixture is put into a graphitization furnace for graphitization treatment. The graphitization temperature is 2600℃ and the graphitization holding time is 3h. After the graphitization treatment is completed, the mixture is cooled down and taken out of the furnace. After taking out of the furnace, it is crushed, demagnetized and screened to obtain high-performance lithium-ion battery negative electrode graphite material.

[0222] Comparative Example 16

[0223] The only difference from Example 1 is that the carbon slag is only dried and not pyrolyzed.

[0224] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag.

[0225] (2) The dried carbon slag is placed in a high-speed mixer for mixing. The specific steps are as described in step (2) of Example 1.

[0226] (3) Refer to step (3) of Example 1.

[0227] (4) Refer to step (4) of Example 1.

[0228] (5) Refer to step (5) of Example 1.

[0229] Comparative Example 17

[0230] The only difference from Example 5 is that the carbon slag is only dried and not pyrolyzed.

[0231] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag.

[0232] (2) The dried carbon slag is placed in a high-speed mixer for mixing. The specific steps are as described in step (2) of Example 5.

[0233] (3) Refer to step (3) of Example 5.

[0234] (4) See step (4) in Example 5.

[0235] (5) Refer to step (5) of Example 5.

[0236] Comparative Example 18

[0237] The only difference from Example 9 is that the carbon slag is only dried and not pyrolyzed.

[0238] (1) The carbon slag produced during the production of waste lithium-ion batteries after acid leaching is dried in a drying oven at 120°C for 12 hours to obtain dried carbon slag.

[0239] (2) The dried carbon slag is placed in a high-speed mixer for mixing. The specific steps are as described in step (2) of Example 9.

[0240] (3) Refer to step (3) of Example 9.

[0241] (4) See step (4) of Example 9.

[0242] (5) See step (5) of Example 9.

[0243] Experimental Example 1

[0244] The physicochemical properties of the products at each stage of the preparation of recycled graphite in the test examples and comparative examples are shown in Tables 1-3.

[0245] Table 1 compares the impurity element content of Examples 1-11 and Comparative Examples 1-15; Table 2 shows the tap density, ash content, and specific surface area of ​​graphite before graphitization of Examples 1-11 and Comparative Examples 1-15; Table 3 shows the tap density, ash content, and specific surface area of ​​graphite after graphitization (regeneration) of Examples 1-11 and Comparative Examples 1-15.

[0246] Table 1. Graphite impurity element content (ppm)

[0247]

[0248]

[0249] Table 2. Tap density, ash content, and specific surface area of ​​graphite before graphitization

[0250]

[0251]

[0252] Table 3. Tap density, ash content, and specific surface area of ​​graphite after regeneration (after graphitization).

[0253]

[0254]

[0255] The results show that the impurity elements in the examples and comparative examples are much lower. Compared with the ungraphitated examples, the examples have lower ash content, higher tap density, and lower specific surface area. After graphitization, the examples have even lower ash content, higher tap density, and lower specific surface area. Furthermore, after reducing impurities and removing amorphous carbon, the ash content of the examples reaches that of battery-grade graphite, and they exhibit excellent electrical performance.

[0256] Experimental Example 2

[0257] The electrochemical performance of the recycled graphite prepared in the test examples and comparative examples is shown in Table 4.

[0258] Table 4. Initial discharge specific capacity and coulombic efficiency test data of graphite samples.

[0259]

[0260]

[0261] Table 4 compares the initial delithiation specific capacity and coulombic efficiency of the samples prepared in Examples 1-11 and Comparative Examples 1-18. It can be seen that the initial delithiation specific capacity and coulombic efficiency of the recycled graphite prepared in the examples of the present invention are significantly higher.

[0262] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering graphite from carbon residue of spent lithium-ion batteries, characterized in that, include: The carbon residue after acid leaching of waste lithium-ion batteries is heat-treated to obtain pyrolytic carbon residue. The pyrolytic carbon residue is then dispersed by high-speed mixing and sieved in a vibrating screen with a mesh size of 150-300 to remove excess large particulate impurities. The sieved carbon residue is then ground and graded to obtain coarse graphite powder with a particle size Dv50 of 12μm-15μm. The heat treatment method is selected from at least one of electric furnace heat treatment and microwave heat treatment; during the electric furnace heat treatment, the heat treatment temperature is controlled at 450℃-1000℃; during the microwave heat treatment, the microwave power is controlled at 400W-1500W. The grinding method is selected from at least one of mechanical impact mill, air jet mill and ball mill, and the particle size Dv50 of the ground material is controlled to be 11μm-15μm; the classification is to process the material sequentially through a classifier and a cyclone separator. When the coarse graphite powder is prepared by mechanical impact milling, the main frequency of the mechanical impact mill is controlled to be 20Hz-50Hz. When the graphite coarse powder is prepared by air jet milling, the grinding gas pressure is controlled at 0.15MPa-0.50MPa and the host frequency is 20Hz-50Hz. When preparing the coarse graphite powder by ball milling, the ball-to-material ratio is controlled to be (3-5):1, and the ball milling time is 3-10 min.

2. The method according to claim 1, characterized in that, During the dispersing process, the mixing speed is controlled at 500 rpm-2000 rpm, and the stirring time is 3 min-30 min.

3. The method according to claim 1, characterized in that, The classifier operates at a frequency of 25Hz-50Hz, the cyclone separator operates at a pressure of 5000Pa-7500Pa, and the cyclone separator operates at a flow rate of 250m³ / h. 3 / min-400m 3 / min.

4. The method according to claim 1, characterized in that, Heat treatment is performed under an inert atmosphere.

5. The method according to claim 1, characterized in that, During the electric furnace heat treatment process, the heat treatment time is 2h-5h.

6. The method according to claim 1, characterized in that, The carbon slag is first dried, and then subjected to microwave heat treatment.

7. The method according to claim 6, characterized in that, During the microwave heat treatment process, the microwave treatment time is controlled to be 5 min-30 min.

8. The method according to claim 6, characterized in that, During the drying process, the drying temperature is controlled at 80℃-200℃ and the drying time is 10h-30h.

9. The method according to claim 1, characterized in that, The coarse graphite powder is mixed with a carbon source, and the resulting mixture is then graphitized.

10. The method according to claim 9, characterized in that, The carbon source is selected from at least one of pitch, petroleum coke and needle coke.

11. The method according to claim 9, characterized in that, The total amount of carbon source used is in a mass ratio of (2-10):100 to the amount of graphite powder.

12. The method according to claim 11, characterized in that, The total amount of carbon source used is in a mass ratio of (3-5):100 to the mass of the coarse graphite powder.

13. The method according to claim 9, characterized in that, The carbon source includes at least bitumen; When the carbon source is a mixture of pitch and petroleum coke, the mass ratio of pitch to petroleum coke is controlled to be 1:(0.1-1.0). When the carbon source is a mixture of pitch and needle coke, the mass ratio of pitch to needle coke is controlled to be 1:(0.1-1.0). When the carbon source is a mixture of pitch, petroleum coke and needle coke, the mass ratio of pitch to the total mass of petroleum coke and needle coke is controlled to be 1:(0.1-1.0).

14. The method according to claim 9, characterized in that, The particle size Dv50 of the carbon source is 3μm-6μm.

15. The method according to claim 14, characterized in that, The particle size Dv50 of the carbon source is 3μm-4μm.

16. The method according to claim 9, characterized in that, The coarse graphite powder and the carbon source are mixed at high speed, with the stirring speed controlled at 500 rpm-2000 rpm and the mixing time at 5 min-30 min.

17. The method according to claim 9, characterized in that, The graphitization treatment temperature is 2400℃-3100℃, and the holding time is 1h-72h.

18. The method according to claim 17, characterized in that, The graphitization treatment temperature is 2500℃-2800℃, and the holding time is 2h-4h.

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