Carbon material for lithium ion battery negative electrode and preparation method, lithium ion battery negative electrode and lithium ion battery

Abstract

The present invention provides a kind of carbon material for lithium ion battery negative electrode and preparation method thereof, lithium ion battery negative electrode and lithium ion battery. The preparation method includes refining, coking and carbonization steps, wherein the sulfur content of raw oil in the refining step is less than 0.5wt%, and the coking step is first heated to 380-460℃, constant temperature 6-20h, and then continued to heat to 480-520℃, after no oil gas is produced, constant temperature 2-10h, and the pressure of the whole coking step is controlled at 0.5-8Mpa. The method does not require a complicated coke pulling process or a hydrogenation process, and only needs to control the sulfur content in the raw oil, and the content of asphaltene, colloid and ash of the raw oil is not limited, and the obtained carbon material can take into account the two performance indicators of capacity and rate when used as a lithium ion battery negative electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon materials, and in particular to a carbon material for a negative electrode of a lithium ion battery and a preparation method thereof, a negative electrode of a lithium ion battery and a lithium ion battery. Background Art

[0002] Lithium-ion batteries use lithium-intercalated carbon materials instead of metallic lithium as the negative electrode material of the battery. They not only retain the main characteristics of lithium batteries such as high voltage and high specific energy, but also have outstanding advantages such as long cycle life, low self-discharge, no memory effect, no environmental pollution and high safety. They are a new generation of batteries after traditional lead-acid batteries, cadmium nickel batteries, and hydrogen nickel batteries, and are widely used in portable electronic devices, electric vehicles, defense industry and other fields.

[0003] The negative electrode material used for energy storage is one of the key materials of lithium-ion batteries. Carbon materials are the earliest developed and most commonly used negative electrode materials. At present, the carbon materials that are studied more are natural graphite, coke, mesophase carbon microspheres, polymer thermal cracking carbon, etc. Studies have shown that different carbon materials have great differences in lithium insertion capacity, cycle life and processing adaptability through different structural treatments. Needle coke has gradually become a high-quality negative electrode material for lithium-ion batteries due to its excellent characteristics such as easy graphitization, high conductivity and low price. According to the properties and generation mechanism of needle coke, the raw materials used to prepare needle coke need to have the characteristics of low sulfur, low asphaltene, low colloid and low ash content (such as catalytic cracking clarified oil, thermal cracking residual oil, etc.), and the processing technology and equipment used in the preparation process have high requirements, such as: the control of coke production and the coke pulling method will increase the difficulty of the process, and the hydrogenation method will increase the production cost.

[0004] For example, Chinese patent document CN103045301A discloses a method for preparing needle coke by a catalytic cracking-delayed coking combined process, specifically a method for preparing needle coke using catalytic cracking oil slurry as raw material, in which all fractions after removing gas and gasoline fractions from coking oil gas are returned to the delayed coking device in the late stage of delayed coking, thereby increasing the coke pulling force. Chinese patent document CN101302434A discloses a method for producing needle coke, in which a programmed variable temperature carbonization process is adopted in the late stage of coking, so that the coke generation rate is controlled at a slower level, and a higher temperature is conducive to increasing the gas yield of the coking system, and promoting the tensile deformation of the unsolidified intermediate phase region, so that needle coke with a developed streamline structure can be obtained. Both of the above methods have a complex gas coke pulling process in the late stage of coking, which increases the process difficulty.

[0005] Chinese patent document CN111892952A discloses a method for producing carbon materials, which specifically uses ethylene tar, thermal cracking residue, petroleum heavy oil, catalytic cracking oil slurry or coal tar pitch as raw material oil, and controls the mass ratio of raw material oil to vacuum residue oil to be 1:0.2-2.0, mixes the raw material oil with vacuum residue oil, and separates light distillate oil, middle distillate oil and bottom oil through a vacuum distillation device, the bottom oil exits the device, the middle distillate oil enters a hydrotreating device, and the hydrogenation treatment The liquid product obtained after treatment is separated into at least hydrogenated light fraction oil and hydrogenated heavy fraction oil through a fractionation device, the hydrogenated heavy fraction oil is mixed with the vacuum distillation light fraction oil as the intermediate phase material, heated by heating furnace a and then enters the coke tower, the coking gas generated by the coke tower is passed through a coking fractionation tower to obtain coking wax oil, the coking wax oil is mixed with the hydrogenated light fraction oil as the coke pulling material, heated by heating furnace b and then enters the coke tower, and the coke tower sequentially completes the intermediate phase formation stage and the coke pulling stage to obtain needle coke. This method requires the use of a hydrogenation process, which increases the cost of the entire method and is less economical.

[0006] Because the properties of the raw oil are strictly limited during the preparation of needle coke, and the preparation process is difficult or costly, it cannot be produced on a large scale industrially, and thus cannot meet the supply demand for negative electrode materials for lithium-ion batteries. Summary of the invention

[0007] The purpose of the present invention is to solve the problems in the prior art of preparing needle coke, that is, the characteristics of the raw oil are relatively strict, the preparation process is difficult or the cost is high, so as to provide a carbon material for a lithium ion battery negative electrode and a preparation method, a lithium ion battery negative electrode and a lithium ion battery.

[0008] To achieve the above object, the present invention provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, comprising the following steps:

[0009] A method for preparing a carbon material for a negative electrode of a lithium ion battery, characterized in that it comprises the following steps:

[0010] Refining: removing solids from the crude oil with a sulfur content of less than 0.5wt% to obtain refined crude oil;

[0011] Coking: In an inert gas atmosphere, the refined crude oil is heated to 380-460°C, kept at this temperature for 6-20 hours, and then continued to be heated to 480-520°C. After no oil gas is generated, the temperature is continued to be kept at this temperature for 2-10 hours to obtain a coke-like product;

[0012] Carbonization: the charred material is carbonized in an inert gas atmosphere to obtain the carbon material for the negative electrode of the lithium ion battery;

[0013] The pressure of the entire coking step is controlled at 0.5-8Mpa.

[0014] Optionally, the oil and gas displacement during the heating process in the coking step is 5-25L / h to control the heating rate of the heating process so that the coking reaction process is in a relatively stable process, that is, the exhaust volume is relatively stable. The specific emission rate unit is L / h, ml / h or other units, which is determined by the capacity of the equipment used in the actual preparation process. It is only necessary to maintain a relatively stable exhaust volume to ensure a stable coking reaction.

[0015] Optionally, the feedstock oil with a sulfur content of less than 0.5 wt% is obtained by mixing feedstock oils of different types and different sulfur contents; or is a single feedstock oil.

[0016] The feedstock oil can be selected from at least one of catalytic cracking slurry, ethylene tar, coker wax oil, thermal cracking residue oil, hydrogenation tail oil, furfural extracted oil, reformed heavy aromatic oil, ester refined solvent extracted lubricating oil and deasphalted oil of vacuum residue oil.

[0017] Optionally, the inert gas is nitrogen, argon or helium.

[0018] Optionally, the solid content of the refined raw oil is less than 150ppm, the aromatic content is 30wt%-80wt%, and the density is 0.9-1.1g / cm 3 .

[0019] Optionally, in the carbonization step, the carbonization temperature is 1000-1500° C., the pressure is 1-2 MPa, and the time is 2-10 h.

[0020] Optionally, in the carbonization step, the heating rate is 50-400°C / h. The specific heating rate can be determined according to the heating capacity of the equipment, such as 50-200°C / h, 250-400°C / h, etc.

[0021] Optionally, the method of removing solids includes physical desolidification and / or solvent extraction.

[0022] The physical desolidification is selected from at least one of sedimentation separation desolidification, filtration desolidification, electrostatic separation desolidification and centrifugal separation desolidification;

[0023] In the solvent extraction process, the solvent used can be selected from at least one of furfural, dimethyl sulfoxide, N,N-dimethylformamide and C3-C6 straight or linear alkanes, wherein the C3-C6 straight or linear alkanes can be selected from propane, butane, etc.

[0024] The present invention also provides a carbon material for a negative electrode of a lithium ion battery prepared by the above-mentioned method for preparing the carbon material for a negative electrode of a lithium ion battery.

[0025] The present invention also provides a lithium ion battery negative electrode, which contains the carbon material for lithium ion battery negative electrode prepared by the above-mentioned method for preparing the carbon material for lithium ion battery negative electrode.

[0026] The present invention also provides a lithium ion battery, which contains the above-mentioned lithium ion battery negative electrode.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The inventors have found through in-depth research that by limiting the specific two-stage heating temperature, holding time and pressure in the coking step, the parameters are coordinated with each other, and combined with the refining and carbonization steps, the obtained carbon material has both isotropic and anisotropic optical properties. When used as the negative electrode of a lithium-ion battery, it can take into account both capacity and rate performance indicators. The coordination between the specific parameters in the coking step is conducive to conformational adjustment during the coking process. The main reason is that during the thermal cracking process, the small molecules in the crude oil or the light components escaping during the cracking process are dissolved in the bulk phase under a high-pressure environment, reducing the viscosity of the system. The two-stage heating process is conducive to the nucleation and growth of the intermediate phase spheres. Due to the low viscosity of the system, the generated intermediate phase spheres are highly mobile and are easily melted into a bulk intermediate phase under the surging of the airflow. The formation of the intermediate phase is conducive to the full development of the fibrous optical texture, thereby effectively changing the optical structure of the high-performance carbon material.

[0029] 2. The method for preparing the carbon material for the negative electrode of a lithium-ion battery provided by the present invention does not require a complicated coke pulling process of needle coke or a hydrogenation process in the entire preparation process. It only needs to control the sulfur content in the raw oil, and has no restrictions on the asphaltene, colloid and ash contents of the raw oil. Not only is the process simple, easy to operate and low in cost, but it also greatly reduces the cost of raw oil pretreatment and is easy for industrial large-scale production.

[0030] 3. The carbon material for lithium ion battery negative electrode prepared by the method for preparing the carbon material for lithium ion battery negative electrode provided by the present invention is comparable to needle coke and has high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention provides a system for preparing a carbon material for a negative electrode of a lithium ion battery according to embodiment 1;

[0032] 10. Online regulating unit; 11. Mixing device; 20. Pretreatment unit; 21. Physical desolidification device; 22. Solvent extraction device; 30. Coking unit; 40. Carbonization unit; 50. Oil-gas separation tank. DETAILED DESCRIPTION

[0033] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0034] The technical solution of the present invention does not limit the asphaltene, ash and gum content of the raw oil. Regardless of whether it is a single raw oil or a mixed raw oil composed of several raw oils, as long as the sulfur content of the single raw oil or the mixed raw oil is less than 0.5wt%, it can meet the implementation of the technical solution of this application.

[0035] Example 1

[0036] This embodiment provides a preparation system of a carbon material for a lithium ion battery negative electrode, comprising an online adjustment unit 10, a pretreatment unit 20, a coking unit 30 and a carbonization unit 40 which are sequentially connected by pipelines;

[0037] The online regulating unit 10 comprises a mixing device 11, and a raw oil inlet, a raw oil outlet and a detection sampling port are arranged on the side wall of the mixing device 11;

[0038] The pretreatment unit 20 includes a pretreatment device, the pretreatment device is provided with an inlet and an outlet, the inlet is connected to the feedstock oil outlet of the mixing device; the pretreatment device is a physical desolidification device 21, a solvent extraction device 22, or a physical desolidification device 21 and a solvent extraction device 22 connected in series;

[0039] The coking unit 30 includes a coking reactor, a refined crude oil inlet is provided on the side wall of the coking reactor, a gas outlet is provided on the top, and a coke outlet is provided on the bottom; the refined crude oil inlet is connected to the outlet of the pretreatment device, and the gas outlet on the top of the coking reactor is connected to the oil-gas separation tank;

[0040] The carbonization unit 40 includes a carbonization reactor, which has an air outlet at the top, a char feed inlet on the side wall, and a carbon material outlet at the bottom; the air outlet at the top of the carbonization reactor is connected to the oil-gas separation tank 50; the char feed inlet on the side wall of the carbonization reactor is connected to the char outlet of the charring reactor.

[0041] Specifically, a high-pressure water inlet is also provided on the top of the coking reactor for hydraulic decoking.

[0042] Specifically, the mixing device is provided with a metering device at the inlet of the raw oil, and the mixing device can be any conventional commercially available device in the art, such as a metering mixer, etc.;

[0043] Specifically, the physical desolidification device 21 can be a conventional sedimentation separator, filter, electrostatic separator, centrifugal separator, etc. in the art, and the solvent extraction device can be a conventional solvent extractor, etc. in the art.

[0044] Example 2

[0045] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0046] Refining: Catalytic cracking oil slurry, furfural extracted oil and vacuum residue oil are mixed online by a metering mixer to obtain a mixed stock oil with a sulfur content of 0.38wt% (the specific amount of each stock oil is based on controlling the sulfur content in the mixed stock oil to be less than 0.5wt%); then the mixed stock oil is transported to a pretreatment unit for desolidification treatment through a membrane filter. The refined stock oil obtained after the treatment has a solid content of 106ppm, an aromatic content of 65wt%, and a density of 0.910g / cm 3 ;

[0047] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 420°C (the heating rate is based on the oil and gas discharge rate of 10L / h), the pressure is controlled to 3Mpa, and the temperature is maintained for 10 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 490°C (the heating rate is based on the oil and gas discharge rate of 10L / h), the pressure is controlled to 3Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is maintained for 6 hours to obtain a coke-like material;

[0048] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1200°C at a rate of 300°C / h, and after reacting at 1Mpa for 6 hours, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.08wt% and a sulfur content of 0.4wt%.

[0049] Example 3

[0050] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0051] Refining: Ethylene tar, coker wax oil, thermal cracking residue oil and reforming heavy aromatic oil are mixed online by a metering mixer to obtain a mixed raw material oil with a sulfur content of 0.45wt% (the specific amount of each raw material oil is based on controlling the sulfur content in the mixed raw material oil to be less than 0.5wt%); then the mixed raw material oil is transported to a pretreatment unit for desolidification treatment through a membrane filter. The refined raw material oil obtained after treatment has a solid content of 78ppm, an aromatic content of 50wt%, and a density of 0.921g / cm 3 ;

[0052] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 410°C (the heating rate is based on the oil and gas discharge rate of 20L / h), the pressure is controlled to 4Mpa, and the constant temperature is maintained for 6 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 520°C (the heating rate is based on the oil and gas discharge rate of 20L / h), the pressure is controlled to 8Mpa, and the generated oil and gas continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is continued to be maintained for 2 hours to obtain a coke-like material;

[0053] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged into the carbonization reactor through the char outlet at the bottom; in a nitrogen atmosphere, the temperature is raised to 1500°C at a rate of 400°C / h, and after reacting at 1Mpa for 4 hours, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.05wt% and a sulfur content of 0.3wt%.

[0054] Example 4

[0055] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0056] Refining: Ethylene tar, vacuum residue and catalytic cracking oil slurry are mixed online by a metering mixer to obtain a mixed stock oil with a sulfur content of 0.38wt% (the specific amount of each stock oil is based on controlling the sulfur content in the mixed stock oil to be less than 0.5wt%); then the mixed stock oil is transported to a pretreatment unit and desolidified by a membrane filter. The refined stock oil obtained after the treatment has a solid content of 92ppm, an aromatic content of 59wt%, and a density of 0.923g / cm 3 ;

[0057] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 385°C (the heating rate is based on the oil and gas discharge rate of 15L / h), the pressure is controlled to 6Mpa, and the temperature is maintained for 20 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 500°C (the heating rate is based on the oil and gas discharge rate of 15L / h), the pressure is controlled to 2Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is maintained for 10 hours to obtain a coke-like substance;

[0058] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1100°C at a rate of 300°C / h, and after reacting at 2Mpa for 10h, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for a negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.04wt% and a sulfur content of 0.28wt%.

[0059] Example 5

[0060] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0061] Refining: The hydrogenation tail oil, furfural extraction oil and reforming heavy aromatic oil are mixed online by a metering mixer to obtain a mixed stock oil with a sulfur content of 0.48wt% (the specific amount of each stock oil is based on controlling the sulfur content in the mixed stock oil to be less than 0.5wt%); then the mixed stock oil is transported to the pretreatment unit for desolidification treatment through a membrane filter. The refined stock oil obtained after the treatment has a solid content of 92ppm, an aromatic content of 68wt%, and a density of 0.940g / cm 3 ;

[0062] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 460°C (the heating rate is based on the oil and gas discharge rate of 5L / h), the pressure is controlled to 6Mpa, and the temperature is maintained for 16 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 510°C (the heating rate is based on the oil and gas discharge rate of 5L / h), the pressure is controlled to 2Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is continued to be maintained for 8 hours to obtain a coke-like material;

[0063] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1200°C at a rate of 350°C / h, and after reacting at 1Mpa for 4h, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.03wt% and a sulfur content of 0.43wt%.

[0064] Example 6

[0065] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0066] Refining: Catalytic cracking oil slurry, ethylene tar, coker wax oil, thermal cracking residue oil, hydrogenation tail oil and furfural extracted oil are mixed online by a metering mixer to obtain a mixed raw material oil with a sulfur content of 0.46wt% (the specific amount of each raw material oil is based on controlling the sulfur content in the mixed raw material oil to be less than 0.5wt%); then the mixed raw material oil is transported to a pretreatment unit and desolidified through a membrane filter. The refined raw material oil obtained after the treatment has a solid content of 87ppm, an aromatic content of 50wt%, and a density of 0.954g / cm 3 ;

[0067] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 410°C (the heating rate is based on the oil and gas discharge rate of 25L / h), the pressure is controlled to 1Mpa, and the temperature is maintained for 20 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 490°C (the heating rate is based on the oil and gas discharge rate of 25L / h), the pressure is controlled to 2Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is maintained for 4 hours to obtain a coke-like material;

[0068] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1300°C at a rate of 250°C / h, and after reacting at 2Mpa for 3h, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.031wt% and a sulfur content of 0.32wt%.

[0069] Example 7

[0070] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0071] Refining: Catalytic cracking oil slurry and ethylene tar are mixed online by a metering mixer to obtain a mixed stock oil with a sulfur content of 0.36wt% (the specific amount of each stock oil is based on controlling the sulfur content in the mixed stock oil to be less than 0.5wt%); then the mixed stock oil is transported to a pretreatment unit for desolidification treatment through a membrane filter. The refined stock oil obtained after treatment has a solid content of 75ppm, an aromatic content of 80wt%, and a density of 0.924g / cm 3 ;

[0072] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 460°C (the heating rate is based on the oil and gas discharge rate of 25L / h), the pressure is controlled to 1Mpa, and the temperature is maintained for 20 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 520°C (the heating rate is based on the oil and gas discharge rate of 25L / h), the pressure is controlled to 2Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is maintained for 4 hours to obtain a coke-like material;

[0073] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1300°C at a rate of 250°C / h, and after reacting at 2Mpa for 3h, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.031wt% and a sulfur content of 0.32wt%.

[0074] Example 8

[0075] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Embodiment 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0076] Refining: The thermal cracking residue oil is mixed online by a metering mixer to obtain a mixed stock oil with a sulfur content of 0.49wt% (the specific amount of each stock oil is based on controlling the sulfur content in the mixed stock oil to be less than 0.5wt%); then the mixed stock oil is transported to the pretreatment unit for desolidification treatment through a membrane filter. The refined stock oil obtained after treatment has a solid content of 87ppm, an aromatic content of 30wt%, and a density of 1.03g / cm 3 ;

[0077] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 380°C (the heating rate is based on the oil and gas discharge rate of 25L / h), the pressure is controlled to 1Mpa, and the temperature is maintained for 20 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 480°C (the heating rate is based on the oil and gas discharge rate of 25L / h), the pressure is controlled to 2Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is continued to be maintained for 4 hours to obtain a coke-like material;

[0078] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1300°C at a rate of 250°C / h, and after reacting at 2Mpa for 3h, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.031wt% and a sulfur content of 0.32wt%.

[0079] Example 9

[0080] This embodiment provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the same preparation system as in Example 1 (a separate membrane filter is used in the pretreatment unit), and the specific steps are as follows:

[0081] Refining: Catalytic cracking oil slurry, coking wax oil and thermal cracking residue oil are mixed by a metering mixer to obtain a mixed raw oil. The sulfur content in the mixed raw oil is 0.69wt% after testing. Then, low-sulfur ethylene tar is added to adjust the sulfur content of the mixed raw oil to 0.38wt%, and then it is transported to the pretreatment unit for desolidification treatment through a membrane filter. The refined raw oil obtained after treatment has a solid content of 78ppm, an aromatic content of 65wt%, and a density of 0.923g / cm 3 ;

[0082] Coking: The refined crude oil is transported to the coking reactor and heated in two stages under nitrogen conditions. In the first stage, the temperature is raised to 410°C (the heating rate is based on the oil and gas discharge rate of 15L / h), the pressure is controlled to 4Mpa, and the constant temperature is maintained for 12 hours. The oil and gas generated in the process will enter the oil and gas separation tank for separation to obtain oil and gas by-products; in the second stage, the temperature is continued to be raised to 500°C (the heating rate is based on the oil and gas discharge rate of 15L / h), the pressure is controlled to 4Mpa, and the oil and gas generated continue to enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is continued to be maintained for 6 hours to obtain a coke-like material;

[0083] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1300°C at a rate of 320°C / h, and after reacting at 1Mpa for 6 hours, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for the negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.04wt% and a sulfur content of 0.45wt%.

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing a carbon material for a negative electrode of a lithium ion battery, using the preparation system in Example 1 (the pretreatment unit uses a separate membrane filter), and the specific steps are as follows:

[0086] Refining: Ethylene tar, vacuum residue and catalytic cracking oil slurry are mixed online by a metering mixer to obtain a mixed stock oil with a sulfur content of 0.38wt% (the specific amount of each stock oil is based on controlling the sulfur content in the mixed stock oil to be less than 0.5wt%); then the mixed stock oil is transported to a pretreatment unit and desolidified by a membrane filter. The refined stock oil obtained after the treatment has a solid content of 92ppm, an aromatic content of 59wt%, and a density of 0.923g / cm 3 ;

[0087] Coking: The refined crude oil is transported to the coking reactor, and the temperature is raised to 500°C under nitrogen conditions (the heating rate is based on controlling the oil and gas discharge rate to be 15L / h), and the pressure is controlled to be 4Mpa. The generated oil and gas enter the oil and gas separation tank for separation to obtain oil and gas by-products. After no oil and gas are generated, the temperature is maintained for 6 hours to obtain a coke-like product;

[0088] Carbonization: The char in the coking reactor is hydraulically decoked with high-pressure water and then discharged from the char outlet at the bottom into the carbonization reactor; in a nitrogen atmosphere, the temperature is raised to 1100°C at a rate of 300°C / h, and after reacting at 2Mpa for 10h, it is discharged from the carbon material outlet at the bottom to obtain a carbon material for a negative electrode of a lithium-ion battery. The carbon material is tested to have an ash content of 0.04wt% and a sulfur content of 0.28wt%.

[0089] Experimental example

[0090] The carbon materials for lithium-ion battery negative electrodes prepared in each embodiment and comparative example were crushed and sieved to obtain carbon materials with a particle size range of 10-30 μm. After graphitization at 2800°C for 36 hours, they were fully mixed with a binder and carbon black in a mass ratio of 90:6:4, and N-methylpyrrolidone (NMP) was added to prepare a negative electrode slurry. After that, the slurry was evenly coated on a copper foil, dried, and rolled into a circular electrode sheet with a diameter of 12 mm. The electrode sheet was vacuum dried at 110°C for 24 hours, and then the battery was assembled in a vacuum glove box, with metallic lithium as the counter electrode. At 0.5 mA / cm 2 The constant current charge and discharge experiment was carried out at a current density of 0.2C, and the charge and discharge voltage was limited to 0.005-2.0V. The first discharge specific capacity, first efficiency, 0.5C reversible capacity and 10C reversible capacity retention rate of the carbon material were tested. The specific test results are shown in the table below.

[0091] Table 1 Test results

[0092]

[0093]

[0094] It can be seen from the experimental data in the above table that the carbon material prepared by the preparation method provided by the present invention is used as the negative electrode material of the lithium ion battery, and the obtained lithium ion battery has a higher charge and discharge capacity and a more stable charge and discharge platform.

[0095] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a carbon material for a negative electrode of a lithium ion battery, characterized in that: The steps include: Refining: removing solids from the crude oil with a sulfur content of less than 0.5wt% to obtain refined crude oil; Coking: In an inert gas atmosphere, the refined crude oil is heated to 380-460°C, kept at this temperature for 6-20 hours, and then continued to be heated to 480-520°C. After no oil gas is generated, the temperature is kept at this temperature for 2-10 hours to obtain a coke-like product; Carbonization: carbonizing the charred material in an inert gas atmosphere to obtain the carbon material for the negative electrode of a lithium ion battery; The pressure of the entire coking step is controlled at 0.5-8Mpa.

2. The method for preparing a carbon material for a negative electrode of a lithium ion battery according to claim 1, characterized in that: The oil and gas emission rate during the temperature increase process in the coking step is 5-25 L / h.

3. The method for preparing a carbon material for a negative electrode of a lithium ion battery according to claim 1, characterized in that: The solid content of the refined raw oil is less than 150ppm, the aromatic content is 30wt%-80wt%, and the density is 0.9-1.1g / cm 3 .

4. The method for preparing a carbon material for a negative electrode of a lithium ion battery according to claim 1, characterized in that: The stock oil with a sulfur content of less than 0.5 wt% is obtained by mixing stock oils of different types and different sulfur contents.

5. The method for preparing a carbon material for a negative electrode of a lithium ion battery according to claim 1, characterized in that: In the carbonization step, the carbonization temperature is 1000-1500° C., the pressure is 1-2 MPa, and the time is 2-10 h.

6. The method for preparing a carbon material for a negative electrode of a lithium ion battery according to claim 1, characterized in that: In the carbonization step, the heating rate is 50-400° C. / h.

7. The method for preparing a carbon material for a negative electrode of a lithium ion battery according to any one of claims 1 to 6, characterized in that: The solid removal method includes physical solid removal and / or solvent extraction.

8. The carbon material for negative electrode of lithium ion battery obtained by the method for preparing the carbon material for negative electrode of lithium ion battery according to any one of claims 1 to 7.

9. A negative electrode for a lithium ion battery, characterized in that: Contains the carbon material for lithium ion battery negative electrode according to claim 8.

10. A lithium ion battery, characterized in that: A lithium ion battery negative electrode comprising the negative electrode of claim 9.

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