Lithium ion battery negative electrode material precursor, preparation method thereof and pre-carbonization furnace

Abstract

The application provides a preparation method of a precursor of a lithium ion battery negative electrode material, and pre-carbonization is performed on the core of the precursor. The application also provides a precursor of a lithium ion battery negative electrode material prepared by the preparation method of the precursor. The application also provides a pre-carbonization furnace used in the preparation method of the precursor of the lithium ion battery negative electrode material. By excluding volatile substances in petroleum coke, high-temperature pretreatment to form a graphite-like layer structure, improving the tightness of the coating of pitch and petroleum coke, and gradient heating during the coating process, the coated precursor can reduce the problem of reduced interlayer spacing at high temperature, and reduce the problems of coating layer falling off, pores and bulging at low temperature, thereby improving the performance of the negative electrode material.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery anode material technology, and in particular to a lithium-ion battery anode material precursor and its preparation method. Background Technology

[0002] The negative electrode material is one of the four core materials of lithium-ion batteries. The negative electrode of a lithium battery is mainly made of a mixture of carbon or non-carbon active materials, binders, and additives, coated on both sides of a copper foil, and then processed through drying, rolling, and other processes. During the charging and discharging process of a lithium battery, under the influence of electrode voltage, lithium ions in the positive electrode undergo electrochemical reactions of "intercalation" and "deintercalation," while the negative electrode, as a carrier, is responsible for storing and releasing lithium ions and allowing current to flow through the external circuit.

[0003] Traditional battery anode materials typically involve crushing raw materials to a predetermined particle size during the pretreatment stage before graphitization in a graphitization furnace. To improve the performance of anode materials, current technology first coats carbon materials to prepare a precursor before graphitization. Coating agents are generally asphalt, resin, etc. After high-temperature carbonization, carbon particles adsorb onto the surface of the carbon material, forming a coating layer. Coated anode materials can improve the cycle life, initial coulombic efficiency, and rate performance of uncoated anode materials.

[0004] However, coated carbon materials also have drawbacks. If the coating temperature is too high, the carbon material may undergo structural rearrangement. For hard carbon, this may lead to pore collapse; for soft carbon, it may result in reduced interlayer spacing. This can affect the lithium storage capacity of the anode material. If the coating temperature is too low, many volatile substances in the carbon material cannot be fully released. During the subsequent high-temperature graphitization process, further release of these volatile substances can lead to problems such as coating layer detachment, porosity, and bulging. This, in turn, affects the electrochemical performance of the graphitized anode material. Summary of the Invention

[0005] To address the problems existing in the coating process of current anode materials, this application proposes a lithium-ion battery anode material precursor that can alleviate the problems of high-temperature or low-temperature coating and improve the physical and electrochemical properties of the graphitized anode material.

[0006] This application also proposes a method for preparing a precursor of a lithium-ion battery anode material, which improves the physical and electrochemical properties of the graphitized anode material by pre-carbonizing the carbon material before coating and by processing the carbon material during the coating process.

[0007] This application also proposes a pre-carbonization furnace for preparing precursors, which pre-carbonizes petroleum coke in the precursors.

[0008] A method for preparing a precursor for a lithium-ion battery anode material includes the following steps: Step 1: Raw material processing Petroleum coke is prepared into petroleum coke powder with a particle size of 5-10 μm; Asphalt is prepared into asphalt powder with a particle size of 5-10 μm; Step 2: Pre-carbonization of petroleum coke powder, Gradient heating is performed in a protective gas atmosphere, as follows: At room temperature (120-150℃), heating rate 1-5℃ / min, hold for 1-2 hours; (120~150℃)~(350~400℃), heating rate 2~3℃ / min, holding time 2~3h; (350~400℃)~(600~700℃), heating rate 3~5℃ / min, holding time 2~3h; Step 3: Cooling and reducing the temperature of the petroleum coke powder. (600~700℃)~(400~450℃), a mixture of nitrogen and water vapor is introduced to cool the petroleum coke powder at a rate of 3~4℃ / min. (400~450℃)~room temperature, allow to cool naturally; Step 4: Asphalt coating of petroleum coke powder. Petroleum coke powder and asphalt powder are fed into a rotary kiln at a mass ratio of (85%–90%):(10%–15%) for coating to obtain a precursor. At room temperature (150-200℃), 5-7℃ / min, keep warm for 0.5h; (150~200℃)~(300~350℃), 2~3℃ / min, keep warm for 1h; (300~350℃)~(650~670℃), 1~2℃ / min, keep warm for 1h; Step 5: Cooling down the precursor. The precursor powder coated in step 4 is poured into a cooling reactor for cooling. (650~670℃)~(400~450℃), nitrogen gas is introduced to cool down at a rate of 1~2℃ / min; (400~450℃)~room temperature, open the cooling vessel to allow for natural cooling.

[0009] A precursor for a lithium-ion battery anode material is obtained by the above-described method for preparing a precursor for a lithium-ion battery anode material.

[0010] A precursor precarbonization furnace includes a material boat conveying track and The first heating furnace section, the second heating furnace section, the third heating furnace section, and the cooling section are arranged sequentially and adjacently. The first heating furnace section includes a first heating section and a first heat preservation section; The second heating furnace section includes a second heating section and a second heat preservation section; The third heating furnace section includes a third heating section and a third heat preservation section; The first heating section, the second heating section, and the third heating section use electric heating and airflow heating to control the temperature of the material; the airflow outlet of the cooling section is connected to the airflow inlet of the third heating section through a pipeline; the airflow outlet of the third heating section is connected to the airflow inlet of the second heating section through a pipeline; the airflow outlet of the second heating section is connected to the airflow inlet of the first heating section through a pipeline; and the airflow outlet of the first heating section is connected to the airflow inlet of the cooling section through a pipeline. The first, second, and third insulation sections use electric heating to keep the materials warm.

[0011] The technical advantages of this application are as follows: Before coating the petroleum coke, the application performs a pre-carbonization treatment, gradually releasing the moisture and volatile substances in the petroleum coke through stepped heating, making it less prone to problems such as peeling, porosity, and bulging of the coating layer. After high-temperature pretreatment, the carbon material forms a graphite-like layered structure, and only slight graphitization occurs during subsequent high-temperature coating, mitigating the problem of reduced interlayer spacing caused by excessive ordering.

[0012] Then, water vapor is added during the cooling process, which increases the micropores of the carbon material and roughens the surface. At the same time, -OH, -COOH and other groups are generated on the surface of the carbon material, which increases the affinity with the asphalt and makes the carbon material easier to coat.

[0013] During the coating process, a uniform atmosphere of liquid and gaseous volatiles is formed in the drum furnace through gradient heating, which is uniformly surrounding the surface of graphite particles. During the carbonization process, the liquid and gaseous volatiles are carbonized and deposited, and small particles adhere to the surface of petroleum coke powder, especially adhering and depositing on the surface of particles in uneven areas such as depressions and faults. This increases the sphericity of the precursor, resulting in better wettability of the prepared negative electrode material with the battery electrolyte.

[0014] By eliminating volatile substances from petroleum coke, pre-treating at high temperatures to form a graphite-like layered structure, improving the tightness of the coating of asphalt and petroleum coke, and using gradient heating during the coating process, the problem of reduced interlayer spacing in the coated precursor is mitigated at high temperatures, and the problems of coating layer peeling, porosity, and bulging are mitigated at low temperatures, thereby improving the electrochemical performance of the anode material. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the operation of the precursor pre-carbonization furnace of this application.

[0016] Figure 2 This is a three-dimensional structural diagram of the precursor pre-carbonization furnace of this application.

[0017] Figure 3 This is a cross-sectional view of the precursor pre-carbonization furnace of this application.

[0018] Figure 4 for Figure 3 A partial structural diagram.

[0019] In the diagram: material boat conveyor track 10, first heating furnace section 20, first heating section 201, first heat preservation section 202, second heating furnace section 30, second heating section 301, second heat preservation section 302, third heating furnace section 40, third heating section 401, third heat preservation section 402, cooling section 50, liquid nitrogen tank 60, steam generator 70, heat exchanger 80. Detailed Implementation

[0020] The technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0021] A method for preparing a precursor for a lithium-ion battery anode material includes the following steps: Step 1: Raw material processing Petroleum coke is prepared into petroleum coke powder with a particle size of 5-10 μm; Asphalt is prepared into asphalt powder with a particle size of 5-10 μm; Step 2: Pre-carbonization of petroleum coke powder, Petroleum coke contains multiple volatile components, such as moisture, low-boiling-point light oil, medium-boiling-point tar, and high-boiling-point asphaltene, with a wide boiling point range. If a single-stage rapid heating method is used, such as directly raising the temperature from room temperature to 700℃, it will lead to: Low-boiling-point components, such as water and light oil, vaporize violently at low temperatures, forming a gas phase impact that causes the collapse of internal pores or surface cracking of the material. High-boiling-point components, such as tar and asphalt, decompose in a concentrated manner at high temperatures, releasing a large amount of gas, resulting in residual pores or pits on the surface of the carbon material before coating. Meanwhile, single-stage heating can lead to a large temperature difference between the inside and outside of the carbon material, resulting in internal stress accumulation and making it prone to microcracks.

[0022] Gradient heating, by segmenting and controlling the heating rate and holding time, can match the removal temperatures of different volatiles, avoid gas phase impact, and promote the homogenization of the internal structure of the carbon material, thus improving the coating effect of petroleum coke. The following is a specific gradient heating scheme for the pre-carbonization of petroleum coke powder in this application: At room temperature (120-150℃), heating rate 1-5℃ / min, hold for 1-2 hours; This section primarily removes free water and light, volatile substances from the petroleum coke powder to prevent the material from cracking due to violent vaporization of moisture.

[0023] (120~150℃)~(350~400℃), heating rate 2~3℃ / min, holding time 2~3h; This section primarily removes light oils, such as benzene, toluene, xylene, and other aromatics, as well as middle oils, such as naphthalene, anthracene, and other polycyclic aromatics from the petroleum coke powder. It also ensures the full decomposition of polycyclic aromatics through heat preservation, reducing tar residue and preventing coking in the subsequent high-temperature section.

[0024] (350~400℃)~(600~700℃), heating rate 3~5℃ / min, holding time 2~3h; This section mainly involves the decomposition and carbonization of high molecular weight substances in petroleum coke powder. At the same time, the carbon structure is rearranged to form a graphite-like layered structure, providing a uniform and structurally stable substrate for subsequent coating.

[0025] The gradient heating process described above is carried out in a protective gas atmosphere. In some preferred embodiments, the protective gas is nitrogen.

[0026] Through the above pre-carbonization process, the structural stability of petroleum coke powder is greatly improved. At the same time, due to the release of gas, the number of micropores on the surface of the carbon material increases and the uniformity of micropores is improved.

[0027] Step 3: Cooling and reducing the temperature of the petroleum coke powder. (600~700℃)~(400~450℃), a mixture of nitrogen and water vapor is introduced to cool the petroleum coke powder at a rate of 3~4℃ / min. Cooling petroleum coke powder with steam improves cooling efficiency and triggers a redox reaction, resulting in increased micropores on the powder surface while absorbing heat. This also increases surface roughness and generates -OH and -COOH groups, allowing for more uniform and compact coating of the asphalt. This facilitates the adhesion of carbon particles to the petroleum coke powder surface after asphalt carbonization. However, excessive -OH and -COOH groups can cause the asphalt to be adhered to numerous core carbon materials, leading to particle agglomeration. Therefore, the amount of steam added needs to be controlled.

[0028] In a preferred embodiment, the temperature of nitrogen and water vapor is 120–150°C, and the volume content of water vapor is 5%. After cooling, the proportion of -OH and -COOH groups is less than 7%.

[0029] (400~450℃)~room temperature, allow to cool naturally; Below 450℃, the reaction between carbon and O2, H2O, etc., is very weak. Especially at low temperatures, it readily absorbs water vapor. Natural cooling can reduce the consumption of nitrogen and water vapor, and also prevent the carbon material from absorbing water vapor.

[0030] Step 4: Asphalt coating of petroleum coke powder. Petroleum coke powder and asphalt powder are added to a rotary kiln at a mass ratio of (85%–90%):(10%–15%), mixed thoroughly, and then coated to obtain a precursor. At room temperature (150-200℃), 5-7℃ / min, keep warm for 0.5h; This process primarily involves softening the asphalt powder, while simultaneously causing some of the lighter volatile components to detach from the asphalt. It should be noted that the rotary drum furnace operates in a sealed, agitated state; although the lighter volatile components have detached from the asphalt, they remain within the furnace. During the agitation process, the softened asphalt gradually coats the surface of the petroleum coke powder.

[0031] (150~200℃)~(300~350℃), 2~3℃ / min, keep warm for 1h; During this process, asphalt has already coated the surface of the petroleum coke powder. Then, as the temperature continues to rise, the non-volatile components of the asphalt begin to detach from the asphalt. As stirring continues, the asphalt coating gradually becomes uniform.

[0032] (300~350℃)~(650~670℃), 1~2℃ / min, keep warm for 1h; During this process, the asphalt gradually carbonizes, and numerous micropores appear on its surface. Simultaneously, the volatiles inside the drum furnace also carbonize. With the stirring action of the drum furnace, the carbonized volatiles gradually and evenly adhere to the micropores on the asphalt surface, gradually increasing the sphericity of the particles.

[0033] Step 5: Cooling down the precursor. The precursor powder coated in step 4 is poured into a cooling reactor for cooling. (650~670℃)~(400~450℃), nitrogen gas is introduced to cool down at a rate of 1~2℃ / min; the introduction of nitrogen gas can prevent the precursor from being over-oxidized, which would lead to excessive porosity on the surface of the precursor.

[0034] (400-450℃) to room temperature, open the cooling vessel for natural cooling. During this stage, oxygen in the air also reacts with the precursor surface for oxidation, generating -OH and -COOH groups with a content of less than 4%. A small amount of -OH and -COOH groups can cover the highly active sites on the carbon surface, reducing their direct reaction with the electrolyte and improving the initial coulombic efficiency. If the -OH and -COOH groups are excessive, they will significantly deteriorate the electrochemical performance of the lithium-ion battery and even affect the processability and thermal stability of the material.

[0035] The precursor of this application adopts a gradient cooling method, which will not cause a sudden drop in temperature, and the coating layer of the precursor is not prone to cracking or peeling.

[0036] The precursor obtained by the above-mentioned method for preparing the precursor of lithium-ion battery anode material uses asphalt as the coating intermediate. During the coating process, the asphalt gradually carbonizes and is eventually coated on the petroleum coke powder in the form of carbon.

[0037] The solution of this application will be described below with reference to the embodiments.

[0038] Example 1: Precarbonization of petroleum coke powder Petroleum coke processing Oil-based petroleum coke blocks with an ash content of less than 0.05% and a volatile matter content of less than 0.5% are selected to ensure thermal stability after graphitization. The coke is crushed in two stages using a crusher and an air jet mill to produce a fine powder smaller than 5μm. A 300-mesh sieve is used for sieving to remove large particles and prevent localized agglomeration during mixing. Subsequently, an electromagnetic separator with a magnetic field strength of 1.5T is used to remove metallic impurities such as Fe and Ni, ensuring an ash content of less than 0.03% to prevent battery self-discharge.

[0039] Petroleum coke powder precarbonization Petroleum coke powder is loaded into a feed boat and subjected to gradient heating in a continuous furnace. Nitrogen gas is introduced into the continuous furnace to maintain a slightly positive pressure and prevent outside air from entering.

[0040] In the first heating section 20 of the continuous furnace, the heating rate of the petroleum coke powder is adjusted by controlling the electric heating power or the flow rate of high-temperature gas. This allows the temperature to range from room temperature to 120℃, with a heating rate of 1℃ / min. When the temperature of the petroleum coke powder reaches 120℃, the furnace temperature in the first heating section 20 of the continuous furnace is stabilized at 120℃ and held for 1 hour. In the second heating section 30 of the continuous furnace, the heating rate of the petroleum coke powder is adjusted by controlling the electric heating power or the air flow rate of high temperature gas, so that the temperature ranges from 120℃ to 350℃ and the heating rate is 2℃ / min. When the temperature of the petroleum coke powder reaches 350℃, the furnace temperature in the second heating section 30 of the continuous furnace is controlled to be stabilized at 350℃ and kept at that temperature for 2 hours. In the third heating section 40 of the continuous furnace, the heating rate of the petroleum coke powder is adjusted by controlling the electric heating power or the gas flow rate of high temperature gas, so that the temperature ranges from 350℃ to 600℃ and the heating rate is 3℃ / min. When the temperature of the petroleum coke powder reaches 600℃, the furnace temperature in the third heating section 40 of the continuous furnace is controlled to be stabilized at 600℃ and kept at that temperature for 2 hours. Petroleum coke powder cooling In the fourth section of the continuous furnace, the cooling rate of the petroleum coke powder is adjusted by controlling the flow rate of the mixed gas of nitrogen and water vapor, so that the temperature drops from 600℃ to 400℃ and the cooling rate is 3 to 4℃ / min. When the material boat cools down to 400°C, it is removed from the continuous furnace and allowed to cool down naturally.

[0041] Example 2 Similar to Example 1, the difference is that the upper limit of each threshold is used to pre-carbonize the petroleum coke powder.

[0042] Because the feed boats in each section of the continuous furnace start and stop synchronously, but the heating time, holding time, and cooling time of the petroleum coke powder are different, existing continuous furnace technologies cannot adjust the heating and holding times while starting and stopping synchronously. For example, after the petroleum coke powder has been held at the first heating section 20 of the continuous furnace for 1 hour, it needs to be moved to the second heating section 30 for heating. However, the feed boat in the second heating section 30 is still being held at the same temperature. After the feed boat in the first heating section 20 moves to the second heating section 30, the feed boat in the second heating section 30 will also be moved out, causing the holding time to be interrupted.

[0043] In order to enable continuous operation in a continuous furnace, this application also proposes a pre-carbonization furnace for gradient heating and cooling of the anode material precursor.

[0044] Please refer to Figures 1 to 4 A precursor precarbonization furnace includes a material boat conveying track 10 and The first heating furnace section 20, the second heating furnace section 30, the third heating furnace section 40, and the cooling section 50 are arranged sequentially and adjacently. The first heating furnace section 20 includes a first heating section 201 and a first heat preservation section 202; The second heating furnace section 30 includes a second heating section 301 and a second heat preservation section 302; The third heating furnace section 40 includes a third heating section 401 and a third heat preservation section 402; The first heating section 201, the second heating section 301, and the third heating section 401 use electric heating and airflow heating to control the temperature of the material; the airflow outlet of the cooling section 50 is connected to the airflow inlet of the third heating section 401 through a pipe; the airflow outlet of the third heating section 401 is connected to the airflow inlet of the second heating section 301 through a pipe; the airflow outlet of the second heating section 301 is connected to the airflow inlet of the first heating section 201 through a pipe; and the airflow outlet of the first heating section 201 is connected to the airflow inlet of the cooling section 50 through a pipe. The first insulation section 202, the second insulation section 302, and the third insulation section 402 use electric heating to keep the material warm.

[0045] Adjacent sections are separated by insulation partitions, with only the inlet or outlet remaining.

[0046] The material boat first enters the first heating section 201 along the material boat conveyor track 10, where it is heated from room temperature to 120°C. The temperature is controlled by airflow and electric heating, so that when the material boat enters the first heat preservation section 202, the temperature reaches 120°C. The first heat preservation section 202 maintains the temperature at 120°C through electric heating. When the material boat enters the second heating section 301, the heat preservation time reaches 1 hour. This process continues until the material boat exits the cooling section 50.

[0047] When the heating rate and holding time of each section change, the heating rate and holding time are controlled by adjusting the air volume and the material boat's movement speed. For example, if holding at 120℃ for 2 hours, the material boat's movement speed is reduced to half of the holding time for 1 hour. It should be noted that once the material's operating parameters are set, they are rarely adjusted. For example, if the first holding section (202) holds for 1 hour, subsequent adjustments are generally unnecessary after the equipment stabilizes. Even if adjustments are made, the magnitude is very small to ensure product quality stability. Therefore, the equipment can operate stably without adjusting the length of each section. The precursor precarbonization furnace of this application utilizes the heat from the airflow in the cooling section 50 to regulate the heating rate of the petroleum coke in the feed boat, which has the following advantages.

[0048] First, it can make full use of the heat from the cooling section 50 to heat the materials, thus reducing energy consumption.

[0049] Secondly, electric heating is slow in regulating the temperature of materials and has a delayed feedback. However, regulating the temperature through airflow allows for a wider range of temperature and flow rate variations, resulting in more timely temperature control.

[0050] In addition, the airflow can also disturb the thermal field, reduce temperature dead zones, and make the temperature of the thermal field more uniform; the protective gas in the airflow can maintain a slightly positive pressure state and reduce the entry of air; the airflow exiting the first heating section 201 carries a small amount of water vapor, which can oxidize the petroleum coke in the cooling section 50, causing the petroleum coke to produce -OH and -COOH groups.

[0051] To facilitate the adjustment of gas volume and gas temperature, this application also includes a liquid nitrogen tank 60 and a steam generator 70. The exhaust pipes of the liquid nitrogen tank 60 and the steam generator 70 are connected to the gas flow outlet of the first heating section 201. A heat exchanger 80 is provided on the exhaust pipe of the nitrogen tank. The heat exchanger 80 is located at the outlet of the cooling section 50 and is used to heat the nitrogen and cool the material in the material boat. In a preferred embodiment, an auxiliary heating wire is installed on the airflow duct to heat the airflow for easier temperature adjustment.

[0052] Example 3: Pitch coating and cooling of petroleum coke powder Asphalt treatment Medium-temperature coal tar pitch is selected, with a softening point of 80–100℃ and quinoline insoluble content less than 5%. The medium-temperature coal tar pitch is fed into a crusher via a hopper for crushing and fine crushing, then piped into an air jet mill for air jet milling to a particle size of 5μm, matching the particle size of petroleum coke to avoid stratification during mixing. After air jet milling, a cyclone dust collector collects the material of the required particle size, with a dust collection rate of approximately 80%. The exhaust gas is filtered by a cartridge filter before being discharged. The filter material is filter cloth with pores smaller than 0.2 micrometers, which can intercept all dust particles larger than 0.2 micrometers. The fan controls the entire system to operate under negative pressure.

[0053] Coated asphalt The petroleum coke powder prepared in Example 1 and the asphalt powder were fed into a vertical drum furnace at a mass ratio of 85%:15% for coating to obtain a precursor. The temperature was maintained at 5℃ / min for 0.5h from room temperature to 150℃; at 2℃ / min for 1h from 150℃ to 300℃; and at 1℃ / min for 1h from 300℃ to 650℃. The vertical drum furnace was electrically heated.

[0054] Precursor cooling The coated precursor powder was poured into a cooling vessel to cool to 650–400°C. Nitrogen gas was introduced to cool the powder at a rate of 1°C / min. The temperature was then reduced to 400°C to room temperature, and the cooling vessel was opened to allow for natural cooling.

[0055] Example 4 Similar to Example 3, the difference is that Example 4 uses the upper limit of the parameters. That is... The precursor powder coated in step 4 is poured into a cooling reactor for cooling. Cooling is carried out by introducing nitrogen gas at a temperature of 670℃~450℃ at a rate of 2℃ / min. 450℃~room temperature, open the cooling vessel to allow for natural cooling.

[0056] This application also includes comparative examples to compare with the embodiments of this application, in order to verify the implementation effect of this application.

[0057] Comparative Example 1 Similar to Example 1, the difference lies in the continuous heating of the petroleum coke and the processing of the resulting petroleum coke powder in accordance with the method of Example 3.

[0058] Comparative Example 2 Similar to Example 1, the difference is that only nitrogen gas is introduced to cool the petroleum coke, and the resulting petroleum coke powder is processed in accordance with the method of Example 3.

[0059] Comparative Example 3 Similar to Example 3, the difference lies in the continuous heating during the coating process, which involves low-temperature coating. Specifically, the room-temperature petroleum coke pre-carbonized in Example 1 is heated to 550°C at a heating rate of 5°C / min, and then held at that temperature for 5 hours.

[0060] Comparative Example 4 Similar to Example 3, the difference lies in the continuous heating during the coating process, resulting in high-temperature coating. Specifically, the pre-carbonized room-temperature petroleum coke from Example 1 is heated to 900°C at a heating rate of 5°C / min, and then held at that temperature for 4 hours.

[0061] Comparative Example 5 The difference from Example 3 is that the petroleum coke powder was not pre-carbonized.

[0062] After graphitizing the precursors prepared in the above examples and comparative examples, the sphericity and interlayer spacing of the negative electrode material were measured. Then, electrodes were fabricated, and 100 electrodes were randomly selected for charge-discharge testing. The average physical and electrochemical properties of the negative electrode material were detected, and the results are shown in Table 1.

[0063] Table 1: Physical and Electrochemical Properties of Various Anode Materials As can be seen from Table 1, the sphericity, initial discharge specific capacity, initial coulombic efficiency, and peel strength of Example 3 are basically the same as those of Example 4.

[0064] Compared to Comparative Example 1, Example 3 showed a sphericity improvement of 0.5. Generally, the more uniform the coating, the fewer problems such as coating layer detachment and bulging, resulting in higher sphericity. This indicates that gradient heating of petroleum coke can improve coating uniformity and significantly reduce problems such as coating layer detachment and bulging. Simultaneously, compared to Comparative Example 1, Example 3 showed a significant improvement in initial discharge specific capacity and initial coulombic efficiency. When the coating layer is exposed, an unstable SEI film forms, affecting the battery's initial discharge specific capacity and initial coulombic efficiency. This indicates that gradient heating of petroleum coke results in less coating layer exposure and more uniform coating. Compared to Comparative Example 1, Example 3 showed a 0.2 N / m increase in peel strength. After gradient heating, the core uniformity is better, making it easier to bond with asphalt, thus improving the coating tightness.

[0065] Compared with Comparative Example 2, Example 3 showed a significant improvement in peel strength. The oxidation effect of water vapor significantly increased the number of -OH and -COOH groups on the core surface, thereby enhancing the bonding strength between the core and the coating layer.

[0066] Compared with Comparative Example 3, Example 3 exhibits better sphericity and improved initial discharge specific capacity and initial coulombic efficiency. Through gradient heating coating, the volatiles in the asphalt are fully released, forming a uniform atmosphere of liquid and gaseous volatiles that evenly surrounds the surface of the graphite particles. During carbonization, the liquid and gaseous volatiles carbonize and deposit, with small particles adhering to the surface of the petroleum coke powder, especially adhering and depositing on uneven areas such as depressions and faults on the particle surface. This maintains good sphericity of the precursor, and the coating layer is tightly bonded to the core. Compared with Comparative Example 4, Example 3 showed improved initial discharge specific capacity and initial coulombic efficiency. While high-temperature coating can improve the tightness of the coating layer, the asphalt carbonization process easily forms pores, exposing the core and thus affecting the battery's initial discharge specific capacity and initial coulombic efficiency.

[0067] Compared with Comparative Example 5, Example 3 showed significant improvements in sphericity, initial discharge specific capacity, initial coulombic efficiency, and peel strength. This demonstrates that the pre-carbonization of the core in this application can significantly improve the performance of the anode material.

[0068] The initial discharge specific capacity and initial coulombic efficiency of the above-mentioned anode materials are based on the standard "Graphite Anode Materials for Lithium-ion Batteries" (GB / T 24533—2019). Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a precursor for a lithium-ion battery anode material, characterized in that: Includes the following steps: Step 1: Raw material processing Petroleum coke is prepared into petroleum coke powder with a particle size of 5-10 μm; Asphalt is prepared into asphalt powder with a particle size of 5–10 μm; Step 2: Pre-carbonization of petroleum coke powder, Gradient heating is performed in a protective gas atmosphere, as follows: At room temperature to 120℃, the heating rate is 1 to 5℃ / min, and the holding time is 1 to 2 hours. 120~350℃, heating rate 2~3℃ / min, holding time 2~3h; 350~600℃, heating rate 3~5℃ / min, holding time 2~3h; Step 3: A mixture of nitrogen and water vapor is introduced to cool the petroleum coke powder. The temperature ranges from 600 to 400℃, with a cooling rate of 3 to 4℃ / min. 400℃~room temperature, allow to cool naturally; Step 4: Asphalt coating of petroleum coke powder. Petroleum coke powder and asphalt powder are fed into a rotary kiln at a mass ratio of (85%–90%):(10%–15%) for coating to obtain a precursor. At room temperature to 150℃, at a rate of 5 to 7℃ / min, for 0.5 hours; 150~300℃, 2~3℃ / min, keep warm for 1 hour; 300~650℃, 1~2℃ / min, keep warm for 1h.

2. The method for preparing the precursor of the lithium-ion battery anode material as described in claim 1, characterized in that: It also includes step 5: cooling the precursor. The precursor powder coated in step 4 is poured into a cooling reactor for cooling. At 650–450℃, nitrogen gas is introduced to cool the temperature at a rate of 1–2℃ / min. 450℃~room temperature, open the cooling vessel to allow for natural cooling.

3. A precursor for a lithium-ion battery anode material, characterized in that: It is obtained by the precursor preparation method of lithium-ion battery anode material according to any one of claims 1 to 2.

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