Lithium ion battery negative electrode graphite recovery method and regenerated graphite material
By preparing a deep eutectic solvent using citric acid and urea and combining it with segmented annealing, the problems of high cost and poor performance in the recycling of graphite anodes for lithium-ion batteries were solved, and the preparation of high-purity, high-electrochemical-performance recycled graphite materials was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUBEI WANRUN NEW ENERGY TECH CO LTD
- Filing Date
- 2025-11-28
- Publication Date
- 2026-04-14
AI Technical Summary
Existing methods for recycling graphite from lithium-ion battery anodes are costly and the recycled graphite has a high content of metal impurities and poor electrochemical performance.
Waste graphite material was purified by using a deep eutectic solvent prepared from citric acid and urea. Impurities were removed by segmented annealing, and nitrogen doping was performed to repair the graphite structure.
It effectively reduces the content of metal impurities in recycled graphite and improves its electrochemical performance, making it a battery-grade graphite material.
Smart Images
Figure CN121849938A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery recycling technology, specifically to a method for recycling graphite from the negative electrode of a lithium-ion battery and the recycled graphite material. Background Technology
[0002] Lithium-ion batteries, with their high energy density, high charging efficiency, and excellent cycle performance, are widely used in new energy vehicles, energy storage systems, and other fields. Graphite materials, due to their good conductivity, high crystallinity, low lithium intercalation potential, and small coefficient of expansion, have become the mainstream anode material for commercial lithium-ion batteries. With the expansion of the lithium-ion battery industry, the number of retired lithium-ion batteries is also increasing year by year. A large amount of anode graphite from these waste lithium-ion batteries is not effectively recycled, resulting in resource waste and potential environmental pollution. Therefore, it is necessary to recycle graphite from lithium-ion battery anodes.
[0003] Currently, the main methods for recycling graphite anodes in the market can be divided into two types: wet recycling and pyrometallurgical recycling. Wet recycling yields active materials with high purity and high recovery rates. However, traditional wet recycling often uses strong acids, resulting in high acid consumption and large amounts of wastewater. Compared to wet recycling, pyrometallurgical recycling is simpler, but requires higher energy consumption and has a lower recovery rate.
[0004] The methods described above have limited effectiveness in recycling and regenerating graphite when used alone, and combining multiple methods increases costs. Furthermore, these methods cannot completely remove some metallic impurities (such as copper and aluminum), and high impurity content can affect the electrochemical performance of the material, making the recycled graphite unusable as battery-grade graphite. Summary of the Invention
[0005] In view of the technical problems existing in the background art, this application provides a method for recycling graphite from the negative electrode of lithium-ion batteries and a recycled graphite material, aiming to solve the technical problems of high cost and high content of metal impurities and poor electrochemical performance of existing graphite recycling methods.
[0006] In a first aspect, embodiments of this application provide a method for recycling graphite from the negative electrode of a lithium-ion battery, comprising the following steps: Waste graphite material was separated from lithium-ion batteries; Citric acid and urea were formulated into a deep eutectic solvent; Waste graphite material is mixed with a deep eutectic solvent for purification, and the purified graphite material is collected. The purified graphite material was subjected to segmented annealing to obtain recycled graphite material.
[0007] In the technical solution of this application embodiment, by preparing a deep eutectic solvent from citric acid and urea, and using the deep eutectic solvent to purify waste graphite materials, it is possible to effectively remove impurities such as organic electrolytes, binders, and metals from the waste graphite materials. Then, by segmented annealing treatment, the structure of the graphite materials is repaired and N element is doped, thereby obtaining recycled graphite materials with low impurity content and excellent electrochemical performance at a lower cost.
[0008] In some embodiments, when preparing the deep eutectic solvent, the molar ratio of citric acid to urea is 1:(0.5~4).
[0009] In this embodiment, by adjusting the molar ratio of citric acid and urea, it is beneficial to construct a more dynamic and flexible hydrogen bond network, so as to promote the uniform occurrence of the reaction and thus improve the impurity removal effect of deep eutectic solvent on metals such as aluminum and copper in graphite.
[0010] In some embodiments, the method for preparing the deep eutectic solvent includes: mixing citric acid and urea uniformly at 90~100°C.
[0011] In this embodiment, by controlling the mixing temperature of citric acid and urea, it is beneficial to promote the formation of deep eutectic solvent, so as to effectively purify waste graphite materials using the deep eutectic solvent.
[0012] In some embodiments, when waste graphite material is mixed with deep eutectic solvent, the mass ratio of waste graphite material to deep eutectic solvent is 1:(5~20).
[0013] In this embodiment, by adjusting the mass ratio of waste graphite material to deep eutectic solvent, it is beneficial to promote the full reaction between deep eutectic solvent and waste graphite material, so as to improve the purification effect of deep eutectic solvent on waste graphite material.
[0014] In some embodiments, the purification process is carried out at a temperature of 80-100°C for 0.5-3 hours.
[0015] In this embodiment, by controlling the temperature and time of the purification process, it is beneficial to promote the purification reaction so that the deep eutectic solvent can effectively remove impurities such as organic electrolyte, binder, and metal from the waste graphite material, thereby improving the purity of the graphite material.
[0016] In some embodiments, the segmented annealing process includes: heating to 450~550°C and holding for 1.5~2.5 hours; thereafter, heating to 800~900°C and holding for 1.5~2.5 hours.
[0017] In this embodiment, by first maintaining the temperature at a lower temperature, the urea in the deep eutectic solvent can be decomposed, thereby achieving N doping of the graphite material; then, by increasing the temperature, the graphite crystal structure can be repaired, thus giving the prepared recycled graphite material better electrochemical performance.
[0018] In some embodiments, the step of separating waste graphite material from a lithium-ion battery includes: Disassembling a lithium-ion battery yields the negative electrode sheet; The negative electrode sheet was immersed in a solvent to obtain a turbid liquid containing graphite. The turbid liquid was subjected to solid-liquid separation, and the collected solid phase was dried to obtain waste graphite material.
[0019] In this embodiment, waste graphite material can be easily and efficiently separated from lithium-ion batteries through processes such as disassembly, soaking, solid-liquid separation, and drying. This step is suitable for industrial-scale processing and has the potential for large-scale application.
[0020] In some embodiments, the step of collecting the purified graphite material includes: Add water to the purified reaction solution, then centrifuge and collect the solids. The solid was dried to obtain purified graphite material.
[0021] In this embodiment, by adding water to the purified reaction solution and then centrifuging it, the viscosity of the reaction solution can be reduced, which is beneficial to promoting the effective separation of graphite materials from impurities such as organic electrolytes, binders, and metals, so as to obtain high-purity graphite materials.
[0022] Secondly, embodiments of this application provide a recycled graphite material obtained from the method for recycling lithium-ion battery negative electrode graphite provided in the first aspect.
[0023] In the technical solution of this application embodiment, the obtained recycled graphite material not only has high purity, but also excellent electrochemical performance.
[0024] In some embodiments, the recycled graphite material is doped with nitrogen (N).
[0025] In this embodiment, the doping with nitrogen element can increase the interlayer spacing of the recycled graphite material, which is beneficial to improving the electrochemical performance of the recycled graphite material.
[0026] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description
[0027] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.
[0028] Figure 1 This is a schematic flowchart of the method for recycling graphite from the negative electrode of a lithium-ion battery provided in the embodiments of this application; Figure 2 XPS comparison images of the recycled graphite material (RG) prepared in Example 4 of this application and the waste graphite material (SG) prepared in Comparative Example 1; Figure 3 Comparison of SEM and HRTEM images of the recycled graphite material (RG) prepared in Example 4 of this application and the waste graphite material (SG) prepared in Comparative Example 1. Figure 4 A comparison of the electrochemical performance of the recycled graphite material (RG) prepared in Example 4 of this application and the waste graphite material (SG) prepared in Comparative Example 1; Figure 5 The image shows the XRD pattern of lithium carbonate prepared in Example 4 of this application; Figure 6 This is a SEM image of the lithium carbonate prepared in Example 4 of this application. Detailed Implementation
[0029] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.
[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0033] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0034] Among existing graphite recycling methods, wet recycling cannot remove metallic impurities such as copper and aluminum from graphite and also generates a significant amount of wastewater; pyrometallurgical recycling has a low recovery rate and requires high temperatures, resulting in high energy consumption and costs. Furthermore, existing methods have limited effectiveness in recycling graphite, and the electrochemical performance of the resulting recycled graphite still needs further improvement.
[0035] To address the technical problems of high cost, high metal impurity content, and poor electrochemical performance in existing graphite recycling methods, this application provides a method for recycling graphite from lithium-ion battery anodes and a recycled graphite material. By preparing a deep eutectic solvent from citric acid and urea, and using this deep eutectic solvent to purify waste graphite material, impurities such as organic electrolytes, binders, and metals in the waste graphite material can be effectively removed. Then, by segmented annealing treatment, the structure of the graphite material is repaired and nitrogen doping is achieved, thereby obtaining recycled graphite material with low impurity content and excellent electrochemical performance at a lower cost.
[0036] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for recycling graphite from the negative electrode of a lithium-ion battery, comprising the following steps: S1. Separate waste graphite materials from lithium-ion batteries; S2. Prepare a deep eutectic solvent by mixing citric acid and urea. S3. Mix the waste graphite material with a deep eutectic solvent for purification, and collect the purified graphite material. S4. The purified graphite material is subjected to segmented annealing to obtain recycled graphite material.
[0037] In this application, by using environmentally friendly and inexpensive citric acid and urea to prepare a deep eutectic solvent, effective purification of waste graphite materials can be achieved at a relatively low cost. Citric acid, used to prepare the deep eutectic solvent, is a tribasic acid, and urea is a Lewis base. When the two combine, citric acid acts as a hydrogen bond donor, and urea acts as a hydrogen bond acceptor. The resulting deep eutectic solvent is acidic, which is more conducive to the dissolution of metal impurities. Furthermore, compared to other hydrogen bond donors, citric acid can synergistically interact with urea at multiple sites. The citrate ion can also form complexes with metal ions through chelation, resulting in complexes with high stability constants. Therefore, the deep eutectic solvent prepared from citric acid and urea can effectively remove metal impurities such as copper and aluminum from waste graphite materials. Simultaneously, this deep eutectic solvent can also remove organic binders and organic electrolytes from waste graphite materials through the principle of "like dissolves like," thereby obtaining graphite materials with high purity. Subsequently, this application performs segmented annealing on the purified graphite material, which not only repairs the graphite structure but also facilitates the decomposition of urea to achieve N doping of the graphite, thereby effectively improving the electrochemical performance of the regenerated graphite material.
[0038] Furthermore, in some embodiments, when preparing the deep eutectic solvent, the molar ratio of citric acid to urea is 1:(0.5~4).
[0039] In this application, citric acid, used to prepare the deep eutectic solvent, has high polarity and can synergistically interact with urea at multiple sites. By adjusting the molar ratio of citric acid and urea, this application not only adjusts the pH of the prepared deep eutectic solvent to 1.5-2.5 to promote the dissolution of metal impurities, but also facilitates the construction of a more dynamic and flexible hydrogen bond network to promote uniform reaction, thereby improving the removal effect of the deep eutectic solvent on metals such as aluminum and copper in graphite. If the proportion of urea is too low, the acidity of the mixed system will be too high, resulting in a relatively viscous deep eutectic solvent, which is not conducive to uniform reaction and leads to a relatively high content of metal impurities such as aluminum and copper in the purified graphite. If the proportion of urea is too high, it is not conducive to the formation of the deep eutectic solvent, requiring not only an increase in the mixing temperature of citric acid and urea, but also affecting the removal effect on metal impurities such as aluminum and copper. Specifically, the molar ratio of citric acid to urea can be any value in the range of 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1: (0.5~4), preferably 1: (1~3), and more preferably 1:2.
[0040] Furthermore, in some embodiments, the method for preparing the deep eutectic solvent includes: mixing citric acid and urea uniformly at 90~100°C.
[0041] In this application, the mixing temperature of citric acid and urea affects the formation of the deep eutectic solvent. This application promotes the formation of the deep eutectic solvent by uniformly mixing citric acid and urea at 90-100°C, thus enabling effective purification of waste graphite materials. Simultaneously, the mixing temperature of citric acid and urea is also related to their molar ratio. When mixing citric acid and urea, if the proportion of urea is low, the deep eutectic solvent can be formed at a relatively low temperature; if the proportion of urea is high, the mixing temperature needs to be appropriately increased to promote the formation of the deep eutectic solvent. Specifically, when the molar ratio of citric acid to urea is 1:(0.5-2), the preferred mixing temperature is 90-95°C; when the molar ratio of citric acid to urea is 1:(2-4), the preferred mixing temperature is 95-100°C.
[0042] Furthermore, in some embodiments, when the waste graphite material is mixed with the deep eutectic solvent, the mass ratio of the waste graphite material to the deep eutectic solvent is 1:(5~20).
[0043] In this application, by controlling the mass ratio of waste graphite material to deep eutectic solvent, it is beneficial to promote the full reaction between the deep eutectic solvent and waste graphite material, thereby improving the purification effect of the deep eutectic solvent on waste graphite material. Specifically, the mass ratio of waste graphite material to deep eutectic solvent can be any value within the range of 1:5, 1:10, 1:15, 1:20, or 1:(5~20).
[0044] Furthermore, in some embodiments, the purification process is carried out at a temperature of 80-100°C for a duration of 0.5-3 hours.
[0045] In this application, by controlling the temperature and time of the purification process, the purification reaction can be accelerated, allowing the deep eutectic solvent to effectively remove impurities such as organic electrolytes, binders, and metals from waste graphite materials, thereby improving the purity of the graphite materials. However, if the purification temperature is too low or the time is too short, the purification effect of the deep eutectic solvent on the waste graphite materials will be affected, resulting in a relatively high content of metal impurities such as aluminum and copper in the purified graphite materials. Conversely, if the purification temperature is too high or the time is too long, the improvement in purification effect is not significant, and it will also lead to increased energy consumption. Specifically, the purification temperature can be any value within the range of 80℃, 85℃, 90℃, 95℃, 100℃, or 80~100℃; the purification time can be any value within the range of 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, or 0.5~3h.
[0046] Furthermore, in some embodiments, the segmented annealing process includes: heating to 450~550°C and holding for 1.5~2.5 hours; thereafter, heating to 800~900°C and holding for 1.5~2.5 hours.
[0047] In this application, by performing segmented annealing under the aforementioned conditions, the graphite crystal structure can be repaired and nitrogen doping can be achieved, thereby effectively improving the rate performance of the recycled graphite material. Specifically, this application first decomposes the urea in the deep eutectic solvent by holding the temperature at 450~550℃ for 1.5~2.5h, so as to utilize the abundant nitrogen element in urea to dope the graphite material with nitrogen; then, the temperature is raised to 800~900℃ and held for 1.5~2.5h to promote the repair of the graphite crystal structure. The segmented annealing temperature in this application is significantly lower than the temperature required for conventional pyrometallurgical recycling, resulting in lower energy consumption, and effectively improving the electrochemical performance of the recycled graphite material by utilizing the repair effect on the graphite crystal structure and the nitrogen doping of graphite.
[0048] Furthermore, in some embodiments, the step of separating waste graphite material from the lithium-ion battery includes: Disassembling a lithium-ion battery yields the negative electrode sheet; The negative electrode sheet was immersed in a solvent to obtain a turbid liquid containing graphite. The turbid liquid was subjected to solid-liquid separation, and the collected solid phase was dried to obtain waste graphite material.
[0049] In this application, waste graphite material can be easily and efficiently separated from lithium-ion batteries through processes such as disassembly, soaking, solid-liquid separation, and drying. This process is suitable for industrial-scale processing and has the potential for large-scale application. Water is the preferred solvent.
[0050] Furthermore, in some embodiments, when separating waste graphite material from lithium-ion batteries using the above method, after solid-liquid separation of the turbid liquid, the following steps are also included: The filtrate obtained from solid-liquid separation is heated to boiling, and then a saturated sodium carbonate solution is added. After the reaction, lithium carbonate precipitate is obtained.
[0051] In this application, the lithium carbonate crystal structure obtained by the above method is complete and can be directly used as a battery-grade raw material, realizing the efficient utilization of waste lithium-ion batteries.
[0052] Furthermore, in some embodiments, the step of collecting the purified graphite material includes: Add water to the purified reaction solution, then centrifuge and collect the solids. The solid was dried to obtain purified graphite material.
[0053] In this application, by adding water to the purified reaction solution and then centrifuging it, the high viscosity of the reaction solution can be diluted with water to facilitate centrifugation and promote the effective separation of graphite material from impurities such as organic electrolyte, binder, and metal, so as to obtain high-purity graphite material.
[0054] Secondly, embodiments of this application provide a recycled graphite material obtained from the method for recycling lithium-ion battery negative electrode graphite provided in the first aspect.
[0055] The recycled graphite material obtained in this application not only has high purity but also excellent electrochemical performance, and can be used as battery-grade graphite, showing good application prospects.
[0056] Furthermore, in some embodiments, the recycled graphite material is doped with nitrogen (N).
[0057] In this application, the doping with nitrogen element can increase the interlayer spacing of the recycled graphite material, which is beneficial to improving the electrochemical performance of the recycled graphite material.
[0058] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0059] I. Preparation Method Example 1 This embodiment provides a method for recycling graphite from the negative electrode of a lithium-ion battery, including the following steps: S1. Disassemble the lithium iron phosphate pouch battery to obtain the negative electrode sheet; immerse the negative electrode sheet in water to peel the graphite off the electrode sheet to obtain a mixture containing graphite, and filter the mixture; dry the solid phase obtained after filtration to obtain waste graphite material (SG); heat the filtrate obtained after filtration to a boiling state, and then add a saturated sodium carbonate solution to obtain a white lithium carbonate precipitate.
[0060] S2. Weigh 19.214 g of citric acid and 12 g of urea (molar ratio of citric acid to urea is 1:2), put them into a 250 mL round-bottom flask, then put the round-bottom flask into an oil bath and stir at 400 r / min at 90℃ to obtain a clear and transparent deep eutectic solvent (DES).
[0061] S3. Weigh 3.121 g of SG obtained in step S1 and put it into 31.214 g of DES obtained in step S2 for purification. After reacting at 90℃ for 0.5 h, add 30 mL of water and centrifuge. Collect the solid and put it into an oven to dry at 80℃ for 6 h. Collect the purified graphite material.
[0062] S4. The purified graphite material is placed in a tube furnace for segmented annealing. Under an argon atmosphere, the temperature is first raised to 500°C at a rate of 5°C / min and held for 2 hours. Then, the temperature is raised to 850°C at the same rate and held for 2 hours. The annealed material is collected and ground evenly in a mortar. After passing through a 300-mesh sieve, the recycled graphite material (RG) is obtained.
[0063] Comparative Example 1 This comparative example provides a method for recycling graphite from the negative electrode of a lithium-ion battery. Only step S1 in Example 1 is performed, and steps S2-S4 are omitted. The resulting graphite material is waste graphite material (SG).
[0064] Examples 2-7 Examples 2-7 provide a method for recovering graphite from the negative electrode of a lithium-ion battery. Compared with Example 1, the only difference is that the reaction temperature and reaction time during the purification process in step S3 are changed. The corresponding reaction times in Examples 2-7 are shown in Table 1. The remaining steps are the same as in Example 1 and will not be described again here.
[0065] Table 1. Reaction temperature and reaction time during purification treatment in Examples 2-7 Examples 8-10 Examples 8-10 provide a method for recovering graphite from the negative electrode of a lithium-ion battery. Compared with Example 5, the only difference is that the mass of urea used in step S2 is changed, thereby changing the molar ratio of citric acid to urea. The stirring temperature is also adjusted according to the corresponding molar ratio. The molar ratio and stirring temperature in Examples 8-10 are shown in Table 2. The remaining steps are the same as in Example 5 and will not be repeated here.
[0066] Table 2. Raw material molar ratios and stirring temperatures during DES preparation in Examples 8-10 Examples 11-14 and Comparative Examples 2-3 Examples 11-14 and Comparative Examples 2-3 respectively provide a method for recycling graphite from the negative electrode of a lithium-ion battery. Compared with Example 5, the only difference is that the annealing process and parameters in step S4 are changed. The temperature and holding time of the two annealing processes in Examples 11-14 and Comparative Examples 2-3 are shown in Table 3. The remaining steps are the same as in Example 5 and will not be described again here.
[0067] Table 3. Temperature and holding time of the two-stage annealing treatment in Examples 11-14 and Comparative Examples 2-3 Of these, Comparative Example 2 underwent the second stage of high-temperature annealing, while Comparative Example 3 underwent the first stage of low-temperature annealing.
[0068] Comparative Example 4 This comparative example provides a method for recycling graphite from the negative electrode of a lithium-ion battery. Compared with Example 5, the only difference is that the citric acid used in step S2 is replaced with an equimolar amount of phytic acid, and the urea is replaced with an equimolar amount of choline chloride. The remaining steps are the same as in Example 4, and will not be repeated here.
[0069] II. Testing Methods 1. Property testing of graphite materials (1) Metal impurity content test The Al and Cu contents in the purified graphite materials obtained in each example and comparative example were detected using inductively coupled plasma optical emission spectrometry (ICP-OES).
[0070] (2) XPS test The recycled graphite material prepared in Example 4 and the waste graphite material prepared in Comparative Example 1 were tested using X-ray photoelectron spectroscopy (XPS).
[0071] (3) Morphological test The recycled graphite material prepared in Example 4 and the waste graphite material prepared in Comparative Example 1 were tested using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), respectively.
[0072] (4) Electrochemical performance testing The recycled graphite materials prepared in each embodiment and comparative example were used to prepare negative electrode materials and assembled into coin cells. The electrochemical performance of each coin cell was then tested.
[0073] 2. Properties of Lithium Carbonate (1) XRD test The lithium carbonate obtained in Example 4 was tested using an X-ray diffractometer (XRD).
[0074] (2) SEM test The lithium carbonate obtained in Example 4 was tested using a scanning electron microscope (SEM).
[0075] III. Analysis of Test Results for Each Embodiment and Comparative Example Figure 2 XPS comparison images of RG prepared in Example 4 and SG prepared in Comparative Example 1 are shown, where (2a) is a comparison image of the total XPS spectrum of RG prepared in Example 4 and SG prepared in Comparative Example 1, (2b) is the N1s fine spectrum of RG prepared in Example 4, and (2c) is the F1s fine spectrum of SG prepared in Comparative Example 1. Figure 2 As can be seen from (2a) and (2c) in Comparative Example 1, the SG prepared in Comparative Example 1 contains obvious impurity F, mainly derived from LiPF6 and PVDF, indicating that the SG still contains impurities such as electrolyte and binder; combined with Figure 2 As can be seen from (2a) and (2b) in Example 4, the impurity F has been removed from the RG prepared in Example 4, and the N element has been doped by segmented annealing, and the N element exists in the form of graphitic nitrogen and pyrrole nitrogen.
[0076] Figure 3 The images show a comparison of SEM and HRTEM images of the RG prepared in Example 4 and the waste graphite material SG prepared in Comparative Example 1. (3a) and (3b) are SEM images of the SG prepared in Comparative Example 1 at scale bars of 50 μm and 10 μm, respectively; (3c) is an HRTEM image of the SG prepared in Comparative Example 1; (3d) and (3e) are SEM images of the RG prepared in Example 4 at scale bars of 50 μm and 10 μm, respectively; and (3f) is an HRTEM image of the RG prepared in Example 4. Figure 3 As can be seen from (3a) and (3b) in Comparative Example 1, the SG prepared in Comparative Example 1 was not purified and annealed, resulting in rough particle surfaces, numerous impurities, and severe agglomeration; Figure 3 As can be seen from (3d) and (3e), the RG particles prepared in Example 4 are uniformly dispersed, of uniform size, and have smooth and clean surfaces. Figure 3 As can be seen in Figure (3c), the SG particles prepared in Comparative Example 1 have a SEI film on their surface, and their crystal structure is damaged; Figure 3 As can be seen from Figure (3f), the RG particles prepared in Example 4 are coated with a layer of carbon, have a complete crystal structure, and the interlayer spacing of the crystals increases due to the doping of nitrogen.
[0077] Figure 4 This is a comparison of the electrochemical performance of RG prepared in Example 4 and SG prepared in Comparative Example 1. Figure 4It can be seen that the initial discharge specific capacities of SG and RG are 168.7 mAh / g and 270.1 mAh / g, respectively. As cycling progresses, the specific capacity of RG gradually increases and stabilizes at 315.4 mAh / g. After 500 cycles, the capacity retention rate is almost unchanged, while that of SG begins to decay after 200 cycles. This indicates that the electrochemical performance of the prepared RG can be significantly improved after purification and segmented annealing treatment in Example 4.
[0078] Figure 5 and Figure 6 The images show the XRD and SEM images of lithium carbonate prepared in Example 4, respectively. Figure 5 It can be seen that the lithium carbonate obtained by precipitation in Example 4 has a complete crystal structure, and is composed of... Figure 6 It can be seen that the lithium carbonate has a uniform morphology, combined with Figure 5 and Figure 6 It can be concluded that the lithium carbonate prepared in Example 4 can be directly used as a battery-grade raw material.
[0079] Table 4 shows the metal impurity content of the purified graphite materials prepared in Examples 1-14 and Comparative Examples 1-4 and the electrochemical performance data of the regenerated graphite materials.
[0080] Table 4 Performance data for Examples 1-14 and Comparative Examples 1-4 As can be seen from Table 4, compared with the waste graphite material obtained in Comparative Example 1, the waste graphite material purified by preparing a deep eutectic solvent and subjected to segmented annealing in each embodiment of this application can effectively reduce the content of metal impurities in the graphite material and improve its electrochemical performance.
[0081] Specifically, comparing Examples 1-7 shows that appropriately increasing the reaction temperature and extending the reaction time is more beneficial for reducing the metal impurity content in the prepared recycled graphite material, and for giving the battery prepared based on the recycled graphite material a higher initial discharge specific capacity and capacity retention rate. When the reaction temperature reaches 90°C and the reaction time is 2 hours, further increasing the reaction temperature or extending the reaction time does not significantly reduce the metal impurity content in the recycled graphite material or improve its electrochemical performance.
[0082] Comparing Examples 5 and 8-10, it can be seen that when the molar ratio of citric acid to urea is controlled, the content of metal impurities in the prepared recycled graphite material first decreases and then increases as the proportion of urea increases. The corresponding initial release capacity first increases and then decreases. When the molar ratio of citric acid to urea is 1:2, it exhibits the lowest content of metal impurities and the highest initial release capacity. On this basis, reducing or increasing the proportion of uric acid is not conducive to improving the performance of the recycled graphite material, and excessively high uric acid content will lead to an increase in the required stirring temperature.
[0083] Comparing Examples 5, 11-14, and 2-3, it can be seen that changes in annealing conditions mainly affect the electrochemical performance of the recycled graphite material, with little impact on its metal impurity content. If only one annealing process is performed as in Comparative Examples 2-3, whether high-temperature or low-temperature annealing, the initial discharge specific capacity of the battery prepared from the recycled graphite material will be significantly reduced. Examples 5 and 11-14 both underwent segmented annealing, first heating to 450-550℃ and holding for 1.5-2.5 hours, followed by heating to 800-900℃ and holding for 1.5-2.5 hours. This process effectively improved the electrochemical performance of the prepared recycled graphite material by simultaneously achieving nitrogen doping of the graphite and promoting the repair of the graphite crystal structure.
[0084] By comparing Example 5 and Comparative Example 4, it can be seen that, compared with the deep eutectic solvent prepared using phytic acid and choline chloride, the deep eutectic solvent prepared using citric acid and uric acid in Example 5 has a better impurity removal effect and can achieve nitrogen doping of graphite materials, thereby significantly reducing the content of metal impurities in recycled graphite materials and improving their electrochemical performance.
[0085] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.
Claims
1. A method for recycling graphite from the negative electrode of a lithium-ion battery, characterized in that, Includes the following steps: Waste graphite materials were separated from lithium-ion batteries; Citric acid and urea were formulated into a deep eutectic solvent; The waste graphite material is mixed with the deep eutectic solvent for purification, and the purified graphite material is collected. The purified graphite material is subjected to segmented annealing to obtain regenerated graphite material.
2. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, When preparing the deep eutectic solvent, the molar ratio of citric acid to urea is 1:(0.5~4).
3. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The method for preparing the deep eutectic solvent includes: mixing citric acid and urea evenly at 90~100℃.
4. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, When the waste graphite material is mixed with the deep eutectic solvent, the mass ratio of the waste graphite material to the deep eutectic solvent is 1:(5~20).
5. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The purification process is carried out at a temperature of 80-100℃ for 0.5-3 hours.
6. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The segmented annealing process includes: heating to 450~550℃ and holding for 1.5~2.5h; then heating to 800~900℃ and holding for 1.5~2.5h.
7. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The step of separating waste graphite material from lithium-ion batteries includes: Disassembling a lithium-ion battery yields the negative electrode sheet; The negative electrode sheet was immersed in a solvent to obtain a turbid liquid containing graphite. The turbid liquid was subjected to solid-liquid separation, and the collected solid phase was dried to obtain waste graphite material.
8. The method for recycling graphite from the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The steps for collecting and purifying the graphite material include: Add water to the reaction solution obtained from the purification process, then centrifuge and collect the solids. The solid was dried to obtain purified graphite material.
9. A recycled graphite material, characterized in that, Obtained by the method for recycling graphite from the negative electrode of a lithium-ion battery according to any one of claims 1-8.
10. The recycled graphite material according to claim 9, characterized in that, The recycled graphite material is doped with nitrogen (N).