Regenerated graphite, method for preparing the same, graphite negative electrode sheet, and battery

Abstract

This invention relates to the field of waste graphite recycling technology, specifically to recycled graphite and its preparation method, graphite negative electrode sheets, and batteries. The preparation method of recycled graphite includes: sequentially subjecting a dispersion containing waste high-purity graphite powder to precision filtration, spray drying, and microwave heating, wherein the impurity content in the waste high-purity graphite powder is less than 100 ppm. This preparation method can achieve "cost reduction and quality improvement" in the recycling of waste graphite, reducing production costs and improving the performance of the recycled graphite. In particular, it can improve the particle size uniformity, specific surface area, and tap density of the recycled graphite, thereby improving the initial coulombic efficiency and initial discharge specific capacity of the battery formed from it.

Description

Technical Field

[0001] This invention relates to the field of waste graphite recycling technology, and more specifically, to recycled graphite and its preparation method, graphite negative electrode sheets, and batteries. Background Technology

[0002] With in-depth research into graphite, it has been widely applied in various fields, leading to a growing contradiction between the development and protection of graphite and the increasing demand for it from various industries. Therefore, the recycling of existing graphite products is urgently needed.

[0003] For example, graphite is the most commonly used anode material in commercial lithium-ion batteries. Efficiently recovering anode graphite from large quantities of waste lithium-ion batteries can effectively alleviate the graphite resource shortage problem and is also an important way to reduce my country's dependence on limited strategic resources and ensure the supply capacity of key resources. Current waste graphite anode recycling processes are lengthy, costly, and result in unstable graphite performance. The typical lengthy graphite recycling process includes pre-treatment such as coarse crushing and screening of the electrode sheets to obtain graphite powder, extraction and impurity removal from the graphite powder through microwave exfoliation, graphite powder grading, granulation and shaping, and graphite coating, carbonization pre-treatment, and heat treatment. This lengthy process not only increases costs, but the graphite loss at each step leads to a lower final graphite yield. Furthermore, the complex control of each step results in greater instability in graphite properties (such as specific surface area, tap density, particle size uniformity, initial coulombic efficiency, and initial discharge specific capacity). Among these factors, the specific surface area and initial charge-discharge coulombic efficiency of graphite are not only important performance indicators of the material but also closely related to cost. During battery formation, an SEI film forms on the graphite surface, causing irreversible lithium loss. A larger specific surface area of ​​graphite results in a larger SEI film area, meaning more lithium ions are consumed. This manifests as a decrease in initial charge-discharge coulombic efficiency. Increased lithium ion consumption means a larger amount of lithium needs to be matched to the positive electrode in the battery. Since the price of positive electrode materials is much higher than that of graphite negative electrode materials, every 1% improvement in initial efficiency can reduce the consumption of a significant amount of lithium ions, thereby reducing the amount of lithium needed to match the positive electrode and significantly lowering battery costs.

[0004] Therefore, it is necessary to develop a short-process, low-cost waste graphite repair and regeneration technology to improve the electrochemical performance of regenerated graphite, reduce costs and improve quality, and ensure the purity and stability of various performance indicators of regenerated graphite.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide recycled graphite and its preparation method, graphite anode sheets, and batteries. The preparation method provided by the embodiments of this invention can achieve "cost reduction and quality improvement" in the recycling of waste graphite, reduce production costs, and improve the performance of the recycled graphite. In particular, it can improve the particle size uniformity, specific surface area, and tap density of the recycled graphite, thereby improving the initial coulombic efficiency and initial discharge specific capacity of the batteries formed therefrom.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing recycled graphite, comprising: sequentially subjecting a dispersion containing waste high-purity graphite powder to precision filtration, spray drying and microwave heating, wherein the impurity content in the waste high-purity graphite powder is less than 100 ppm.

[0009] In an optional implementation, the impurity content in the waste high-purity graphite powder is less than 50 ppm;

[0010] Preferably, the waste high-purity graphite powder is derived from any one of waste graphite negative electrode sheets, waste graphite crucibles, waste graphite electrodes, and waste graphite slurry;

[0011] Preferably, the waste high-purity graphite powder is formed by a pneumatic airflow separation process;

[0012] Preferably, the waste graphite negative electrode sheet is subjected to pneumatic airflow separation to form the waste high-purity graphite powder;

[0013] Preferably, the conditions for pneumatic airflow separation include a feeding frequency of 10Hz-50Hz, a stripping host frequency of 5Hz-25Hz, and a classifier frequency of 30Hz-45Hz.

[0014] In an optional embodiment, the dispersion further includes a repair agent;

[0015] Preferably, the amount of the repair agent used is less than 10% of the mass of the waste high-purity graphite powder; more preferably, it is 2%-5%.

[0016] Preferably, the repair agent is selected from compounds containing long-chain hydrocarbons and their derivatives and / or polycyclic aromatic hydrocarbons and their derivatives;

[0017] Preferably, the repair agent is selected from petroleum products, and more preferably, it is any one or at least two or more combinations of asphalt, petroleum coke and petroleum resin.

[0018] In an optional embodiment, the diameter of the filter pores in the precision filter is less than 60 micrometers, preferably 40-50 micrometers.

[0019] In an optional embodiment, the spray drying conditions include a temperature of 100-300°C.

[0020] In an optional implementation, the microwave heating conditions include a temperature of 800-1200°C;

[0021] Preferably, the frequency is 300MHz-300GHz; the heating and heat preservation time is 2-8 hours.

[0022] Secondly, the present invention provides a recycled graphite, which is prepared by the method for preparing recycled graphite described in any of the foregoing embodiments.

[0023] Thirdly, the present invention provides a graphite negative electrode sheet, which is prepared by the recycled graphite described in the foregoing embodiments.

[0024] Fourthly, the present invention provides a battery comprising the graphite negative electrode sheet described in the foregoing embodiments.

[0025] In an optional embodiment, the battery is a lithium-ion battery.

[0026] The present invention has the following beneficial effects: In the embodiments of the present invention, waste high-purity graphite powder is precisely filtered, spray-dried and microwave-heated to form high-performance recycled graphite. Specifically, the above operations can improve the particle size uniformity, specific surface area and tap density of the recycled graphite, thereby improving the first coulombic efficiency and first discharge specific capacity of the battery formed by it. Attached Figure Description

[0027] 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.

[0028] Figure 1 A process flow diagram of a method for preparing recycled graphite is provided in this embodiment of the invention;

[0029] Figure 2 The SEM image provided in Example 1 of the present invention;

[0030] Figure 3 This is a particle size diagram provided for Example 1 of the present invention. Detailed Implementation

[0031] 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.

[0032] This invention provides a method for preparing recycled graphite, which involves sequentially subjecting a dispersion containing waste graphite powder of high purity to precision filtration, spray drying, and microwave heating. The precision filtration method provided by this invention removes large particulate impurities such as graphite, which not only improves the particle size of the finished product but also facilitates subsequent spray drying to remove binders before microwave heating to repair the waste graphite, thereby improving the performance of the recycled graphite, such as increasing the initial coulombic efficiency and initial discharge specific capacity of the battery formed from it. If the above order is changed, for example, spray drying and microwave treatment are performed before filtration, then the dried graphite needs to be dispersed in the liquid phase, and then dried again after filtration, increasing the processing steps; or if precision filtration and microwave treatment are performed before spray drying, the pre-decomposition effect of spray drying is not achieved, resulting in a large specific surface area that affects the initial efficiency of the recycled graphite.

[0033] The waste high-purity graphite powder is derived from any one of the following: waste graphite negative electrode sheet, waste graphite crucible, waste graphite electrode, and waste graphite slurry.

[0034] Specifically, this invention provides a detailed description using waste graphite negative electrode sheets as an example. This invention also provides a method for preparing recycled graphite; see [link to relevant documentation]. Figure 1 ,include:

[0035] S1. Formation of waste high-purity graphite powder;

[0036] The waste high-purity graphite powder is derived from any one of waste graphite negative electrode sheets, waste graphite crucibles, waste graphite electrodes, and waste graphite slurry; the waste high-purity graphite powder can be obtained by processing the above raw materials using existing methods.

[0037] However, existing technologies for forming high-purity waste graphite powder from waste graphite anode sheets are overly complex, requiring pretreatment such as coarse crushing and screening, impurity extraction and microwave stripping, and ultrasonic pulverization. To address this issue, this invention utilizes pneumatic airflow separation to process the aforementioned waste graphite anode sheets. This invention replaces multiple steps—coarse crushing, crushing, extraction, microwave stripping, and ultrasonic pulverization—with a single pneumatic airflow separation step, significantly shortening the raw material processing steps and producing high-purity waste graphite crude product.

[0038] Specifically, the impurity content in the waste high-purity graphite powder formed by pneumatic airflow separation is less than 100 ppm, preferably less than 50 ppm; for example, 25-35 ppm. When the impurity content in the waste high-purity graphite powder is within the above limits, no additional processing is required. Subsequent precision filtration, spray drying, and microwave heating can be carried out directly, which can also ensure the performance of the generated recycled graphite.

[0039] It should be noted that the impurity content mentioned above refers to the content of any single impurity.

[0040] Furthermore, the conditions for pneumatic airflow separation include a feed frequency of 10Hz-50Hz, such as any value or a range between any two values ​​from 10Hz to 50Hz (e.g., 10Hz, 20Hz, 30Hz, 40Hz, and 50Hz). The stripping host frequency is 5Hz-25Hz, such as any value or a range between any two values ​​from 5Hz to 25Hz (e.g., 5Hz, 10Hz, 15Hz, 20Hz, and 25Hz). The classifier frequency is 30Hz-45Hz, such as any value or a range between any two values ​​from 30Hz to 45Hz (e.g., 30Hz, 35Hz, 40Hz, and 45Hz).

[0041] Using the above conditions for pneumatic airflow separation can ensure the effectiveness of pneumatic airflow separation, effectively remove impurities, ensure the purity of the resulting high-purity waste graphite powder, and help improve the performance of the resulting recycled graphite.

[0042] S2, forming a dispersion;

[0043] The aforementioned waste high-purity graphite powder is dispersed in a liquid solvent to form a uniform dispersion. This liquid solvent can be water, an organic solvent, or a mixture of both. Forming this dispersion facilitates subsequent spray drying and promotes the formation of recycled graphite.

[0044] The dispersion provided in this embodiment of the invention may contain only waste high-purity graphite powder and a liquid solvent, and may also include a repair agent. The waste high-purity graphite powder may have cracks or surface defects. During subsequent microwave heating, the repair agent can fill the cracks in the graphite and form a coating layer on the surface, repairing the structure of the recycled graphite and improving its performance.

[0045] Furthermore, the remediating agent is selected from compounds containing long-chain hydrocarbons and their derivatives and / or polycyclic aromatic hydrocarbons and their derivatives; for example, it can be a petroleum product, specifically selected from any one or at least two or more combinations of asphalt, petroleum coke and petroleum resin.

[0046] Using the above-mentioned substances as repair agents can ensure their repair effect on the graphite structure and improve the performance of recycled graphite.

[0047] Furthermore, the amount of the repair agent used is less than 10% of the mass of the waste high-purity graphite powder; for example, it is any value or a range between any two values ​​such as 0.1%, 0.5%, 1%, 2%, 5%, 8%, and 10%, preferably 2%-5%. Using a repair agent within the above range can further ensure its repair effect and improve the performance of the recycled graphite. If the content of the repair agent is too high, some repair agent residue may remain, which may conversely reduce the performance of the recycled graphite.

[0048] Understandably, if the waste high-purity graphite powder has few defects, repair agents are not required, i.e., the amount of repair agent used is 0%.

[0049] S3, Precision filtration;

[0050] The above dispersion is subjected to precision filtration to remove large particles such as graphite and repair agents. Precision filtration replaces multiple steps of sieving or filtration, ensuring the uniformity of particle size in the final product and improving the performance of recycled graphite.

[0051] Furthermore, in precision filtration, the pore diameter is below 60 micrometers, preferably 40-50 micrometers. Limiting the pore size of the filter is beneficial for removing large particles and further improving the particle size uniformity of the recycled graphite.

[0052] S4, spray drying;

[0053] The filtrate after the above precision filtration is spray-dried. During spray drying, the binder in the filtered waste high-purity graphite powder is decomposed in the medium temperature range, but the repair agent does not change. It simply dries and forms spherical shapes with the graphite.

[0054] The spray drying conditions include a temperature of 100-300℃. For example, any value within the 100-300℃ range, or any range between two values, such as 100℃, 150℃, 200℃, 250℃, and 300℃. Limiting the temperature to this range ensures that the binder is decomposed while the repair agent remains unchanged, and also allows for drying and shaping to form the graphite precursor material, thus guaranteeing the performance of the resulting recycled graphite.

[0055] S5. Microwave heating;

[0056] Then, microwave heating is performed. In this embodiment of the invention, microwave heating utilizes the internal friction and heat generated by the polarized molecular motion and forced oscillations to carbonize and decompose the repair agent, filling the cracks in the waste graphite and forming a coating layer on the surface. At the same time, microwave heating carbonization reduces the energy consumption of the heat treatment for repair and regeneration.

[0057] The microwave heating conditions include: a temperature of 800-1200℃; for example, any value or range between 800℃, 900℃, 1000℃, 1100℃, and 1200℃. A frequency of 300MHz-300GHz; for example, any value or range between 300MHz, 500MHz, 1GHz, 10GHz, 100GHz, and 300GHz. A heating and holding time of 2-8 hours; for example, any value or range between 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.

[0058] The above conditions effectively enable the repair agent to repair and restore waste graphite. Furthermore, this embodiment of the invention utilizes the energy conversion generated by the coupling of the material to be heated with microwaves for high-temperature heating, resulting in high energy utilization.

[0059] It should be noted that materials heated by microwave can be used directly, or they can be further processed by crushing, sieving, or other post-processing to obtain graphite materials that meet the requirements for use.

[0060] Secondly, the present invention provides a recycled graphite, which is prepared by the recycled graphite preparation method described in any of the foregoing embodiments. The recycled graphite provided by the embodiments of the present invention has good particle size uniformity, specific surface area and tap density, which can improve the initial coulombic efficiency and initial discharge specific capacity of the battery formed therefrom.

[0061] Thirdly, the present invention provides a graphite negative electrode sheet, which is prepared by the recycled graphite described in the foregoing embodiments.

[0062] Fourthly, the present invention provides a battery comprising the graphite negative electrode sheet described in the foregoing embodiments, for example, a lithium-ion battery.

[0063] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0064] Example 1

[0065] This embodiment provides a method for preparing recycled graphite, including:

[0066] (1) Waste graphite negative electrode sheets (obtained from recycled unfilled battery cells by Hunan Bangpu Recycling Technology Co., Ltd.) were subjected to pneumatic airflow separation to obtain waste high-purity graphite powder. The pneumatic airflow separation conditions were: feed frequency 25Hz, stripping host frequency 15Hz, and classifier frequency 40Hz. The impurity content in the waste high-purity graphite powder was 30ppm.

[0067] (2) Mix the waste high-purity graphite powder obtained in step 1 with asphalt in an aqueous solution at a mass ratio of 100:2.

[0068] (3) Pass the aqueous dispersion from step 2 through a 40μm precision filter to remove excessively large graphite and asphalt particles.

[0069] (4) Pump the aqueous solution mixture filtered in step 3 into a spray dryer and dry it at 300°C to form a graphite precursor.

[0070] (5) The graphite precursor material from step 4 is placed in a sagger and placed in a microwave orbital kiln. Under a nitrogen atmosphere, it is heated to 900°C. The microwave heating frequency is 2.45 GHz, and the temperature is maintained for 4 hours.

[0071] (6) The material after microwave carbonization in step 5 is broken up and sieved to obtain high-performance recycled graphite.

[0072] Example 2

[0073] This embodiment provides a method for preparing recycled graphite, including:

[0074] (1) Waste graphite negative electrode sheets were subjected to pneumatic airflow separation to obtain waste high-purity graphite powder. The pneumatic airflow separation conditions were: feed frequency 50Hz, stripping host frequency 25Hz, and classifier frequency 45Hz. The impurity content in the waste high-purity graphite powder was 35ppm.

[0075] (2) Mix the waste high-purity graphite powder obtained in step 1 with asphalt in an aqueous solution at a mass ratio of 100:5.

[0076] (3) Pass the aqueous dispersion from step 2 through a 50μm precision filter to remove excessively large graphite and asphalt particles.

[0077] (4) Pump the aqueous solution mixture filtered in step 3 into a spray dryer and dry it at 100°C to form a graphite precursor.

[0078] (5) The graphite precursor material from step 4 is placed in a sagger and placed in a microwave orbital kiln. Under a nitrogen atmosphere, it is heated to 1200°C. The microwave heating frequency is 2.45 GHz, and the temperature is maintained for 2 hours.

[0079] (6) The material after microwave carbonization in step 5 is broken up and sieved to obtain high-performance recycled graphite.

[0080] Example 3

[0081] This embodiment provides a method for preparing recycled graphite, including:

[0082] (1) Waste graphite negative electrode sheets were subjected to pneumatic airflow separation to obtain waste high-purity graphite powder. The conditions for pneumatic airflow separation were: feed frequency 10Hz, stripping host frequency 5Hz, and classifier frequency 30Hz. The impurity content in the waste high-purity graphite powder was 25ppm.

[0083] (2) The waste high-purity graphite powder obtained in step 1 is mixed with petroleum resin in an aqueous solution at a mass ratio of 100:2.

[0084] (3) Pass the aqueous dispersion from step 2 through a 45μm precision filter to remove excessively large graphite and petroleum resin particles.

[0085] (4) Pump the aqueous solution mixture filtered in step 3 into a spray dryer and dry it at 250°C to form a graphite precursor.

[0086] (5) The graphite precursor material from step 4 is placed in a sagger and placed in a microwave orbital kiln. Under a nitrogen atmosphere, it is heated to 800°C. The microwave heating frequency is 2.45 GHz, and the temperature is maintained for 8 hours.

[0087] (6) The material after microwave carbonization in step 5 is broken up and sieved to obtain high-performance recycled graphite.

[0088] Example 4

[0089] This embodiment provides a method for preparing recycled graphite, including:

[0090] (1) Waste graphite negative electrode sheets were subjected to pneumatic airflow separation to obtain waste high-purity graphite powder. The pneumatic airflow separation conditions were: feed frequency 40Hz, stripping host frequency 10Hz, and classifier frequency 35Hz. The impurity content in the waste high-purity graphite powder was 28ppm.

[0091] (2) The waste high-purity graphite powder obtained in step 1 and coke are mixed in an aqueous solution at a mass ratio of 100:4.

[0092] (3) Pass the aqueous dispersion from step 2 through a 50μm precision filter to remove excessively large graphite and coke particles.

[0093] (4) Pump the aqueous solution mixture filtered in step 3 into a spray dryer and dry it at 300°C to form a graphite precursor.

[0094] (5) The graphite precursor material from step 4 is placed in a sagger and placed in a microwave orbital kiln. Under a nitrogen atmosphere, it is heated to 1200°C. The microwave heating frequency is 2.45 GHz, and the temperature is maintained for 2 hours.

[0095] (6) The material after microwave carbonization in step 5 is broken up and sieved to obtain high-performance recycled graphite.

[0096] Example 5

[0097] This embodiment provides a method for preparing recycled graphite, including:

[0098] (1) Waste graphite negative electrode sheets (negative electrode scraps from Guangdong Bangpu Recycling) were subjected to pneumatic airflow separation to obtain waste high-purity graphite powder. The pneumatic airflow separation conditions were: feed frequency 25Hz, stripping host frequency 15Hz, and classifier frequency 40Hz. The impurity content in the waste high-purity graphite powder was 30ppm.

[0099] (2) Disperse the waste high-purity graphite powder obtained in step 1 in an aqueous solution.

[0100] (3) Pass the aqueous dispersion from step 2 through a 40μm precision filter to remove graphite particles that are too large.

[0101] (4) Pump the aqueous solution mixture filtered in step 3 into a spray dryer and dry it at 300°C to form a graphite precursor.

[0102] (5) The graphite precursor material from step 4 is placed in a sagger and placed in a microwave orbital kiln. Under a nitrogen atmosphere, it is heated to 900°C. The microwave heating frequency is 2.45 GHz, and the temperature is maintained for 4 hours.

[0103] (6) The material after microwave carbonization in step 5 is broken up and sieved to obtain high-performance recycled graphite.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1. The only difference is that precision filtration is not performed. That is, the aqueous mixture in step 2 is pumped into a spray dryer for spray drying without precision filtration. All other operations and conditions are the same as in Example 1.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1, except that spray drying is replaced with oven drying, the drying temperature is still 300℃, and other operations and conditions are the same as in Example 1.

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1, except that microwave heating is replaced by conventional electric heating, the heating temperature is still 900℃, the holding time is still 4h, and other operations and conditions are the same as in Example 1.

[0110] Comparative Example 4

[0111] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1, except that the microwave heating temperature is changed to 600℃, microwave heating is still used, the heat preservation time is still 4h, and other operations and conditions are the same as in Example 1.

[0112] Comparative Example 5

[0113] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1, except that microwave heating is replaced with conventional electric heating and the heating temperature is changed to 1200℃. Other operations and conditions are also the same as in Example 1.

[0114] Comparative Example 6

[0115] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1, except that the ratio of high-purity graphite powder to pitch is changed to 100:15, and other operations and conditions are the same as in Example 1.

[0116] Comparative Example 7

[0117] This comparative example provides a method for preparing recycled graphite, which is basically the same as the method for preparing recycled graphite provided in Example 1, except that the conditions for pneumatic airflow separation are changed to a feed frequency of 60Hz, a stripping host frequency of 40Hz, and a classifier frequency of 60Hz.

[0118] Comparative Example 8

[0119] (1) Waste graphite negative electrode sheets were subjected to pneumatic airflow separation to obtain waste high-purity graphite powder. The conditions for pneumatic airflow separation were: feed frequency 25Hz, stripping host frequency 15Hz, and classifier frequency 40Hz. The impurity content in the waste high-purity graphite powder was 33ppm.

[0120] (2) Mix the waste high-purity graphite powder obtained in step 1 with asphalt in an aqueous solution at a mass ratio of 100:2.

[0121] (3) The aqueous dispersion from step 2 is filtered through a plate and frame filter to obtain wet waste graphite.

[0122] (4) Dry the waste graphite wet material from step 3 in an oven at 100°C.

[0123] (5) The waste graphite material from step 4 is loaded into a sagger and placed in a microwave track kiln. Under a nitrogen atmosphere, it is heated to 900°C. The microwave heating frequency is 2.45 GHz, and the temperature is maintained for 4 hours.

[0124] (6) The material after microwave carbonization in step 5 is broken up and sieved to obtain recycled graphite.

[0125] Detection Example 1

[0126] The recycled graphite prepared in Example 1, Comparative Examples 1 and 8 was subjected to SEM analysis and particle size analysis. The results are shown in [reference needed]. Figure 2 and Figure 3 .in, Figure 2 SEM image of recycled graphite. Figure 2 In the image, 'a' represents the SEM image of the recycled graphite from Example 1. Figure 2 In the image, b represents the SEM image of the recycled graphite in Comparative Example 1. Figure 2 In the image, c represents the SEM image of the recycled graphite in Comparative Example 8. Figure 3 This is a particle size distribution diagram of recycled graphite. Figure 3 In the diagram, 'a' represents the particle size distribution of the recycled graphite from Example 1. Figure 3 In the diagram, b represents the particle size distribution of the recycled graphite in Comparative Example 1. Figure 3 In the diagram, c represents the particle size distribution of the recycled graphite in Comparative Example 8.

[0127] according to Figure 2 It can be seen that, Figure 2 The middle a is significantly higher than Figure 2 The particles in samples b and c are more uniform, indicating that precision filtration can improve the particle size uniformity of recycled graphite. Furthermore, according to... Figure 3 As shown in a, recycled graphite has a more uniform particle size distribution, compared to... Figure 3 Compared to b and c, there is no peak on the side of large particles.

[0128] Detection Example 2

[0129] The recycled graphite of Example 1 and Comparative Examples 1-8 were subjected to ICP, TD, BET and electrical performance tests. The test results are shown in Table 1.

[0130] Table 1 Test Results

[0131] index ICP-Cu Tap density Specific surface area First effect First discharge specific capacity Example 1 30ppm <![CDATA[1.22g / m 3 ]]> <![CDATA[1.1m 2 / g]]> 94.2％ 354.5mAh / g Comparative Example 1 35ppm <![CDATA[1.15g / m 3 ]]> <![CDATA[1.3m 2 / g]]> 93.6％ 349.8mAh / g Comparative Example 2 32ppm <![CDATA[1.13g / m 3 ]]> <![CDATA[2.2m 2 / g]]> 90.7％ 349.5mAh / g Comparative Example 3 30ppm <![CDATA[0.88g / m 3 ]]> <![CDATA[2.6m 2 / g]]> 89.5％ 348.9mAh / g Comparative Example 4 30ppm <![CDATA[1.05g / m 3 ]]> <![CDATA[2.1m 2 / g]]> 90.8％ 350.6mAh / g Comparative Example 5 32ppm <![CDATA[0.99g / m 3 ]]> <![CDATA[1.6m 2 / g]]> 92.0％ 350.2mAh / g Comparative Example 6 32ppm <![CDATA[1.10g / m 3 ]]> <![CDATA[1.2m 2 / g]]> 93.5％ 340.6mAh / g Comparative Example 7 540ppm <![CDATA[1.18g / m 3 ]]> <![CDATA[1.5m 2 / g]]> 93.2％ 346.8mAh / g Comparative Example 8 33ppm <![CDATA[1.12g / m 3 ]]> <![CDATA[2.3m 2 / g]]> 90.6％ 349.2mAh / g

[0132] According to Table 1 above, (1) comparing Example 1 and Comparative Example 2, spray drying of the pre-pyrolyzed binder reduces the amount of pores caused by binder pyrolysis during subsequent heat treatment, thus reducing the specific surface area of ​​the final product (1.1 m²).2 / g vs2.2m 2 / g), effectively improving the coulombic efficiency of the first charge and discharge (94.2% vs 90.7%).

[0133] (2) Comparing Example 1 and Comparative Example 3, it can be seen that under the same heat treatment temperature of 900℃, the graphite product heated by microwave has a higher tap density (1.22 g / m³) than that heated by ordinary electric heating. 3 vs 0.88g / m 3 Smaller specific surface area (1.1m²) 2 / g vs2.6m 2 It exhibits superior electrochemical performance (94.2% vs 89.5%).

[0134] (3) Comparing Example 1 and Comparative Examples 4-5, it can be seen that the microwave heating temperature of 600℃ does not reach the temperature point for coating carbonization, resulting in poor performance across the board. Microwave heating carbonization at 900℃ surpasses ordinary electric heating carbonization at 1200℃. Microwave carbonization can effectively improve energy utilization efficiency and reduce processing temperature. It also improves various indicators of recycled graphite, reduces specific surface area, increases tap density, and improves initial charge-discharge efficiency.

[0135] (4) Comparing Example 1 and Comparative Example 6, it can be seen that the addition of excessive repair agent asphalt will lead to a decrease in the first discharge specific capacity (354.5mAh / g vs 340.6mAh / g).

[0136] (5) Comparing Example 1 and Comparative Example 7, it can be seen that the parameters of pneumatic airflow separation have an important impact on the purity of graphite. Inappropriate feeding, stripping host and classifier frequency will lead to excessive impurity content in the stripped waste graphite powder.

[0137] (6) Comparing Example 1 and Comparative Example 8, it can be seen that during precision filtration, the waste graphite is in the liquid phase, while during ordinary plate and frame filtration, the waste graphite is in the solid phase. If spray drying is required, the wet material must be dispersed again into the aqueous solution, which is meaningless and does not remove large particulate impurities. When the solid wet material is directly subjected to subsequent drying and microwave carbonization treatment, the specific surface area is large and the initial efficiency is low because the pre-decomposition of spray drying is not performed.

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 preparing recycled graphite, characterized in that, include: The dispersion containing waste high-purity graphite powder is subjected to precision filtration, spray drying and microwave heating in sequence, wherein the impurity content in the waste high-purity graphite powder is less than 100 ppm. The waste high-purity graphite powder is formed by a pneumatic airflow separation process; the conditions for pneumatic airflow separation include a feeding frequency of 10Hz-50Hz, a stripping host frequency of 5Hz-25Hz, and a classifier frequency of 30Hz-45Hz. The conditions for microwave heating include a temperature of 800-1200℃; In precision filtration, the pore diameter is less than 60 micrometers.

2. The method for preparing recycled graphite according to claim 1, characterized in that, The impurity content in the waste high-purity graphite powder is less than 50 ppm.

3. The method for preparing recycled graphite according to claim 1, characterized in that, The waste high-purity graphite powder is derived from any one of the following: waste graphite negative electrode sheet, waste graphite crucible, waste graphite electrode, and waste graphite slurry.

4. The method for preparing recycled graphite according to claim 3, characterized in that, The waste graphite negative electrode sheet is subjected to pneumatic airflow separation to form the waste high-purity graphite powder.

5. The method for preparing recycled graphite according to claim 1, characterized in that, The dispersion also includes a repair agent.

6. The method for preparing recycled graphite according to claim 5, characterized in that, The amount of the repair agent used is less than 10% of the mass of the waste high-purity graphite powder.

7. The method for preparing recycled graphite according to claim 5, characterized in that, The amount of the repair agent used is 2%-5% of the mass of the waste high-purity graphite powder.

8. The method for preparing recycled graphite according to claim 5, characterized in that, The repair agent is selected from compounds containing long-chain hydrocarbons and their derivatives and / or polycyclic aromatic hydrocarbons and their derivatives.

9. The method for preparing recycled graphite according to claim 5, characterized in that, The repair agent is selected from petroleum products.

10. The method for preparing recycled graphite according to claim 5, characterized in that, The repair agent is any one or a combination of at least two of asphalt, petroleum coke, and petroleum resin.

11. The method for preparing recycled graphite according to claim 1, characterized in that, In precision filtration, the pore diameter is 40-50 micrometers.

12. The method for preparing recycled graphite according to claim 1, characterized in that, The conditions for spray drying include a temperature of 100-300℃.

13. The method for preparing recycled graphite according to any one of claims 1-12, characterized in that, The conditions for microwave heating include: a frequency of 300MHz-300GHz; and a heating and holding time of 2-8 hours.

14. A type of recycled graphite, characterized in that, It is prepared by the method for preparing recycled graphite as described in any one of claims 1-13.

15. A graphite negative electrode sheet, characterized in that, It is prepared by the recycled graphite as described in claim 14.

16. A battery, characterized in that, It includes the graphite negative electrode sheet as described in claim 15.

17. The battery according to claim 16, characterized in that, The battery is a lithium-ion battery.

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