Preparation method of regenerated graphite negative electrode material based on molten salt electrochemical repair and regenerated graphite negative electrode material thereof
By employing a four-step method of molten salt electrochemical remediation, the problems of incomplete crystal structure and metal impurities in the recycling of graphite anode materials for lithium-ion batteries were solved, resulting in the preparation of highly efficient and pure recycled graphite anode materials, which improved battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-24
- Publication Date
- 2026-04-14
AI Technical Summary
Existing methods for recycling graphite anode materials for lithium-ion batteries suffer from problems such as incomplete crystal structure, residual SEI film components on the surface, and metal impurities. These issues result in low reversible specific capacity, poor initial coulombic efficiency, and unsatisfactory rate performance, making them unsuitable for direct application in new lithium-ion batteries.
A method based on molten salt electrochemical repair was adopted, which involves four steps: discharge disassembly, pretreatment, molten salt electrochemical repair and posttreatment, to prepare regenerated graphite anode material. Constant voltage electrolysis was performed using CaCl2-based molten salt electrolyte and inert electrodes at a voltage lower than the graphite anion intercalation potential to selectively remove metal impurities and repair the graphite layered structure.
The prepared recycled graphite anode material has high lattice integrity and low metal impurity content. Its initial coulombic efficiency is improved to over 93.3%, and its reversible specific capacity is restored to 343.6~354.2 mAh/g. Its rate performance is significantly improved and approaches the level of commercial graphite.
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Abstract
Description
Technical Field
[0001] This application relates to the field of lithium-ion battery material recycling and regeneration technology, and in particular to a method for preparing regenerated graphite anode material based on molten salt electrochemical repair and the regenerated graphite anode material thereof. Background Technology
[0002] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage, and other fields, the recycling and disposal of used lithium-ion batteries has become an urgent problem to be solved. As the most important negative electrode active material in lithium-ion batteries, the recycling and reuse of graphite is of great significance for reducing battery costs and minimizing resource waste. Effective recycling and reuse of waste graphite negative electrode materials can not only alleviate the shortage of graphite resources to some extent, but also reduce the potential environmental hazards of used batteries, which is of great importance for promoting the sustainable development of the battery industry.
[0003] Currently, the main recycling methods for graphite anode materials are pyrometallurgical and hydrometallurgical processes. Pyrometallurgical recycling primarily involves high-temperature roasting to remove organic matter and the solid electrolyte interphase (SEI) film from the graphite surface, achieving preliminary purification of the graphite. However, it's important to note that if the graphite contains metallic impurities such as Fe, Cu, and Al, improper high-temperature processing can lead to the formation of low-melting-point alloys or compounds, resulting in difficult-to-remove metallic impurities. Furthermore, these substances can penetrate the interlayers or grain boundaries of the graphite, disrupting the orderly arrangement of carbon atoms and hindering grain growth, ultimately leading to numerous grain boundary defects that damage the graphite crystal structure and induce lattice defects. Hydrometallurgical recycling utilizes acid solutions to dissolve impurities in the graphite, thereby purifying it. While this method can dissolve some impurities, it suffers from a long process flow and generates large amounts of acid and alkaline wastewater, causing environmental pollution. Moreover, it cannot repair the already damaged graphite crystal structure.
[0004] In addition, molten salt electrochemical methods are also used to treat lithium-ion batteries, but they still have many drawbacks. The repair mechanism of molten salt electrochemical methods mainly relies on the thermochemical action of high-temperature molten salt. It lacks precise electrochemical control, cannot completely repair the deep structural defects of graphite, and is prone to secondary damage such as anion intercalation due to excessive voltage. At the same time, it is usually carried out at extremely high temperatures, which consumes a lot of energy, and has limited effect on removing trace metal impurities mixed in the negative electrode powder, affecting the purity and electrochemical performance of the regenerated graphite negative electrode material.
[0005] Therefore, the recycled graphite anode materials obtained by these methods generally suffer from problems such as incomplete crystal structure, residual SEI film components on the surface, and metal impurities, resulting in low reversible specific capacity, poor initial coulombic efficiency, and poor rate performance. They cannot be directly applied to new lithium-ion batteries, thus limiting the efficient recycling and reuse of graphite. Summary of the Invention
[0006] To at least overcome one of the problems existing in the prior art, one objective of this application is to provide a method for preparing recycled graphite anode materials based on molten salt electrochemical repair. This method uses spent lithium-ion batteries as raw materials and involves four main steps: discharge disassembly, pretreatment, molten salt electrochemical repair, and post-treatment. This results in a recycled graphite anode material with high lattice integrity, low metal impurity content, and an initial coulombic efficiency exceeding 93.3%. The reversible specific capacity is restored to 343.6~354.2 mAh / g, and the rate performance is significantly improved, comparable to some commercially available graphite. A second objective of this application is to provide the aforementioned recycled graphite anode material.
[0007] Therefore, this application adopts the following technical solution: The first aspect of this application provides a method for preparing regenerated graphite anode materials based on molten salt electrochemical repair, comprising the following steps: S1. Discharge and dismantling: Discharge, dismantle, crush and sort the waste lithium-ion batteries to obtain a mixture of negative electrode materials containing graphite. S2. Pretreatment: The graphite-containing negative electrode material mixture is pretreated to obtain pretreated graphite; S3. Molten Salt Electrochemical Remediation: The pretreated graphite is placed in a molten salt electrolyte containing CaCl2 as the cathode, and an inert electrode is used as the anode. Under the protection of inert gas, a voltage lower than the anion intercalation potential of graphite in the molten salt system is applied to the cathode to perform constant voltage electrolysis.
[0008] S4. Post-processing: After electrolysis, the cathode product is removed, washed, and dried to obtain the regenerated graphite anode material.
[0009] In this application, the preparation method of recycled graphite anode material based on molten salt electrochemical repair is divided into four main steps through a step-by-step design: discharge disassembly, pretreatment, molten salt electrochemical repair, and post-treatment. Step S1 eliminates the safety hazards of waste batteries through discharge, followed by disassembly and crushing to separate the anode material from other components. Sorting is used to initially remove coarse impurities and collect graphite components, providing basic raw materials for subsequent preparation processes. Step S2, the pretreatment, helps remove residual electrolyte, binder, and other organic impurities from the graphite, initially improving the purity of the raw materials while maintaining dryness to avoid interfering with the subsequent molten salt electrochemical repair process. Step S... 3. Using pretreated graphite as the cathode and an inert electrode as the anode, in a CaCl2-based molten salt electrolyte, oxidation interference is isolated by inert gas protection, and constant voltage electrolysis is performed by applying a voltage lower than the graphite anion intercalation potential. This selectively extracts lithium ions embedded in the graphite and allows metallic impurities such as iron, copper, and aluminum to dissolve and enter the molten salt through oxidation, thus achieving separation from the graphite matrix. Simultaneously, the electrochemical environment further repairs the layered structure of the graphite, preventing new structural damage. In the post-processing step S4, the electrolyte residue on the graphite is removed by washing, followed by drying to remove moisture, ultimately yielding a high-purity, structurally intact regenerated graphite anode material. Therefore, the synergistic effect between each step ensures that the preparation method of this application achieves significant improvements in safety, purity of the regenerated graphite anode material, and battery performance. The regenerated graphite anode material prepared by the method of molten salt electrochemical repair in this application has high lattice integrity, pure surface, low metal impurity content, and its first coulombic efficiency and reversible specific capacity are effectively improved. This solves the problems of incomplete crystal structure, residual SEI film components and metal impurities that are common in the prior art.
[0010] Preferably, in step S1, the discharge process involves connecting the positive and negative electrodes of the waste lithium-ion battery to the positive and negative terminals of the discharge load box, respectively, and continuing to discharge until the voltage drops to 0~0.05V, at which point the discharge is stopped; the disassembly is performed manually or mechanically, and the negative electrode sheet is removed; the crushing process uses a planetary ball mill for ball milling, controlling the ball-to-material ratio to be (10~15):1, the rotation speed to be 200~300rpm, and the time to be 30~60min, and then screening with an 8~10 mesh sieve to initially separate the large pieces of copper foil that have not been fully crushed; the undersize material is then sorted, and the sorting process involves passing it through a 20~80 mesh sieve and taking the undersize material to obtain a negative electrode material mixture containing graphite.
[0011] Through the processing in step S1, large current collectors such as copper foil and aluminum shell fragments that were not fully crushed were effectively removed, and a negative electrode material mixture containing graphite with relatively uniform particle size was obtained, which provided a good raw material basis for subsequent pretreatment and molten salt electrochemical repair process.
[0012] Preferably, in step S2, the pretreatment includes pyrolysis, stripping, sieving, and drying processes.
[0013] Preferably, in step S2, the pyrolysis is carried out under inert gas protection, the pyrolysis temperature is 400~550℃, and the pyrolysis time is 2~5h; the stripping is carried out in a ball mill at a speed of 100~300 rpm for 0.5~1.5h; the sieving collects particles that pass through a 100-mesh sieve and are retained by a 400-mesh sieve; the drying temperature is 100~120℃, and the drying time is 5~8h. More preferably, in step S2, the pyrolysis is carried out under inert gas protection, the pyrolysis temperature is 450~550℃, and the pyrolysis time is 3~5h; the stripping is carried out in a ball mill at a speed of 150~300 rpm for 0.5~1.5h; the sieving collects particles that pass through a 100-mesh sieve and are retained by a 400-mesh sieve; the drying temperature is 100~120℃, and the drying time is 5~8h. More preferably, in step S2, the pyrolysis is carried out under inert gas protection, the pyrolysis temperature is 450~550℃, and the pyrolysis time is 3.5~5h; the stripping is carried out in a ball mill at a speed of 150~300 rpm for 1~1.5h; the sieving collects particles that pass through a 100-mesh sieve and are retained by a 400-mesh sieve; the drying temperature is 110~120℃, and the drying time is 5~8h.
[0014] In step S2, under inert gas protection, pyrolysis is performed at 400~550℃ for 2~5 hours to ensure the full decomposition and volatilization of organic materials such as binders. This also prevents excessively high temperatures from causing oxidation of carbon atoms at the graphite edges, reducing graphite loss. Then, ball milling is performed at 100~300 rpm for 0.5~1.5 hours to further separate the graphite material from current collectors such as copper foil, while also reducing graphite agglomeration. Particles passing through a 100-mesh sieve and retained by a 400-mesh sieve are collected, retaining graphite particles with a diameter of 0.05~0.15 mm. Graphite particles in this size range have a high specific surface area, which is beneficial for the smooth and complete subsequent molten salt electrochemical repair. Drying at 100~120℃ for 5~8 hours completely removes moisture from the surface and pores of the graphite particles, preventing moisture from entering the molten salt electrolyte and causing hydrogen bubbles to form during electrolysis, thus disrupting the stability of the electrolytic interface.
[0015] Preferably, in step S3, the molten salt electrolyte is a CaCl2-based molten salt, which further includes at least one of NaCl, KCl, and LiCl, and the operating temperature of the molten salt electrolyte is 550~920℃. More preferably, in step S3, the molten salt electrolyte is a CaCl2-based molten salt, which further includes at least one of NaCl, KCl, and LiCl, and the operating temperature of the molten salt electrolyte is 650~920℃.
[0016] Preferably, in step S3, 0.8-3 wt% of an oxygen-containing compound is added to the molten salt electrolyte, wherein the oxygen-containing compound is at least one selected from CaO and CaCO3. More preferably, in step S3, 1.5-3 wt% of an oxygen-containing compound is added to the molten salt electrolyte, wherein the oxygen-containing compound is at least one selected from CaO and CaCO3.
[0017] In step S3, the molten salt electrolyte operating temperature of 550~920℃ ensures good fluidity and ion transport capabilities, while avoiding excessively high temperatures that could lead to graphite particle sintering and agglomeration, as well as high energy waste. This temperature also helps maintain graphite dispersion and the contact area at the electrolytic interface. Furthermore, this temperature promotes the oxidation and dissolution of impurity metals. The molten salt electrolyte is based on CaCl2, which has good ionic conductivity and a certain solubility for oxide impurities. The addition of NaCl, KCl, and LiCl to form a eutectic mixture helps lower the melting point of the molten salt system, reducing energy consumption during electrolysis, while simultaneously increasing ionic conductivity and further enhancing the reaction rate of electrochemical repair. Adding 0.8-3 wt% of at least one oxygen-containing compound from CaO and CaCO3 to the molten salt electrolyte allows CaO and CaCO3 to ionize in the high-temperature molten salt to generate O2- ions, which can react with metallic impurities such as iron, copper, and aluminum in the pretreated graphite to form metal oxides. These metal oxides may enter the molten salt, float to the surface as slag, or be reduced to elemental metals under constant voltage electrolysis, depositing on the anode or dissolving in the molten salt, thus achieving deep removal of metallic impurities.
[0018] Preferably, the molten salt electrolyte is a mixture of CaCl2, NaCl, KCl, CaO, and CaCO3 in a weight ratio of (30~60):(10~30):(5~15):(0.5~2):(0.5~2). More preferably, the molten salt electrolyte is a mixture of CaCl2, NaCl, KCl, CaO, and CaCO3 in a weight ratio of (35~60):(12~30):(5~15):(0.5~2):(0.5~2). Even more preferably, the molten salt electrolyte is a mixture of CaCl2, NaCl, KCl, CaO, and CaCO3 in a weight ratio of (35~60):(12~30):(8~15):(1~2):(0.5~2).
[0019] By controlling the weight ratio of CaCl2, NaCl, KCl, CaO, and CaCO3 in the molten salt electrolyte to (30~60):(10~30):(5~15):(0.5~2):(0.5~2), this specific composition and ratio of the molten salt electrolyte compound effectively and significantly lowers the melting point of the molten salt system, improves its fluidity, and thus enhances its ionic conductivity. Simultaneously, CaO and CaCO3 provide sufficient O2- for the conversion and removal of metallic impurities, while avoiding excessive oxidation of the graphite surface due to excessive oxygen-containing compounds. Through the synergistic effect of the components in the molten salt electrolyte compound, metallic impurities in the pretreated graphite are thoroughly and efficiently removed.
[0020] Preferably, in step S3, the voltage below the graphite anion intercalation potential is a voltage relative to the Ca / Ca2+ potential in the molten salt electrolyte, and the voltage is 1.5~2.3 V. More preferably, in step S3, the voltage below the graphite anion intercalation potential is a voltage relative to the Ca / Ca2+ potential in the molten salt electrolyte, and the voltage is 1.8~2.3 V. More preferably, in step S3, the voltage below the graphite anion intercalation potential is a voltage relative to the Ca / Ca2+ potential in the molten salt electrolyte, and the voltage is 2.0~2.3 V.
[0021] Preferably, in step S3, the constant voltage electrolysis time is 1~6 hours. More preferably, in step S3, the constant voltage electrolysis time is 2~6 hours. Even more preferably, in step S3, the constant voltage electrolysis time is 3.5~6 hours.
[0022] In step S3, controlling the voltage within the range of 1.5~2.3V drives lithium ions to be extracted from the graphite. Furthermore, it forces metallic impurities such as aluminum to be oxidized into ions, which then dissolve and are removed into the molten salt electrolyte. This also prevents anions such as Cl- from inserting into the graphite interlayers, thus avoiding the expansion and cracking of the layered structure and further protecting the crystal integrity of the regenerated graphite. Constant voltage electrolysis for 1~6 hours ensures the full progress of the electrochemical reaction, allowing impurities inside the graphite particles to be fully removed and uniformly repaired.
[0023] Preferably, in step S4, the washing includes acid washing and water washing, the drying temperature is 110~120℃, and the drying time is 8~12h. Preferably, in step S4, the acid washing solution is a 0.1~0.15mol / L dilute hydrochloric acid solution, the drying temperature is 115~120℃, and the drying time is 10~11h.
[0024] The second aspect of this application provides a regenerated graphite anode material prepared according to the preparation method of regenerated graphite anode material based on molten salt electrochemical repair as described in the first aspect of this application, wherein the total content of iron, copper and aluminum elements in the regenerated graphite anode material is less than 30 ppm.
[0025] Preferably, the total content of iron, copper, and aluminum in the recycled graphite anode material is less than 28 ppm. More preferably, the total content of iron, copper, and aluminum in the recycled graphite anode material is less than 25 ppm.
[0026] Compared with the prior art, this application has at least the following beneficial effects: 1) In the preparation method of the recycled graphite anode material based on molten salt electrochemical repair in this application, the preparation method uses waste lithium-ion batteries as raw materials and goes through four major steps: discharge disassembly, pretreatment, molten salt electrochemical repair, and post-treatment. The resulting recycled graphite anode material has high lattice integrity, low impurity content, tap density ≥1.05g / cm3, and the first coulombic efficiency is improved to over 93.3%. The reversible specific capacity is restored to 343.6~354.2mAh / g, the rate performance is significantly improved, and the performance is close to and exceeds that of some commercial new graphite.
[0027] 2) The recycled graphite anode material prepared by the method of molten salt electrochemical repair in this application has a low content of metal impurities. The total content of iron, copper and aluminum in the recycled graphite anode materials of Examples 1 to 7 is in the range of 9.9 to 16.8 ppm, which is less than 30 ppm. Detailed Implementation
[0028] The following detailed description of the contents of this application is provided through specific embodiments, comparative examples, and tables, but is not limited to all the arguments and data.
[0029] It is particularly important to emphasize that, unless otherwise specified, the raw materials, reagents or devices used in this application can be obtained from conventional commercial sources.
[0030] This application describes a method for preparing regenerated graphite anode materials based on molten salt electrochemical remediation, which specifically includes the following steps: S1. Discharge and Disassembly: Connect the positive and negative tabs of a 2800mAh type 18650 waste lithium-ion battery to a DC discharge load box, set the discharge current to 200mA, and continue discharging until the cell voltage drops to 0~0.05V to complete the discharge; manually disassemble in a fume hood and remove the negative electrode sheet; put the negative electrode sheet into a planetary ball mill, add zirconium oxide grinding balls, control the ball-to-material ratio to be (10~15):1, the rotation speed to be 200~300rpm, the time to be 30~60min, and then sieve it with an 8~10 mesh sieve, take the sieve material, and then sort it through a 20~80 mesh sieve, take the sieve material, and obtain a negative electrode material mixture containing graphite; S2. Pretreatment: The above-mentioned graphite-containing negative electrode material mixture is placed in a tube furnace and heated to 400~550℃ at 5℃ / min under inert gas protection, and kept at a constant temperature for 2~5h for pyrolysis. After natural cooling to room temperature, the pyrolyzed material is placed in a planetary ball mill, zirconium oxide grinding balls are added, and the mixture is ball-milled for 0.5~1.5h at a ball-to-material ratio of (10~15):1 and a rotation speed of 100~300 rpm. The particles that pass through a 100-mesh sieve and are retained by a 400-mesh sieve are collected and dried in an oven at 100~120℃ for 5~8h to obtain pretreated graphite. S3. Molten Salt Electrochemical Remediation: Weigh 30-60g, 10-30g, 5-15g, 0.5-2g, and 0.5-2g of CaCl2, NaCl, KCl, CaO, and CaCO3 respectively as molten salt electrolyte mixtures, mix them evenly, and add them to a high-purity graphite crucible. Place the crucible in a muffle furnace and heat it to 550-920℃ under inert gas protection. Take 10g of pretreated graphite and put it into a porous molybdenum basket as the cathode, and use a high-purity graphite rod as the anode. Insert the two electrodes vertically into the molten salt, keeping the distance between them 3cm, and insert a clean molybdenum wire as a quasi-reference electrode. At the same time, continuously introduce inert gas. Using an electrochemical workstation, at a working temperature of 550-920℃, control the voltage of the cathode potential relative to the Ca / Ca2+ potential to be 1.5-2.3 V, and maintain a constant voltage for electrolysis for 1-6 hours. S4. Post-processing: After electrolysis, the cathode product is removed, cooled, and then ultrasonically washed in 0.1 mol / L dilute hydrochloric acid for 30 min. After washing with deionized water until the pH is neutral, it is dried in a vacuum oven at 110~120℃ for 8~12 h to obtain the regenerated graphite anode material.
[0031] Regarding step S2, in some specific implementations, the pyrolysis temperature can be 400℃, 450℃, 500℃ or 550℃, and the pyrolysis time can be 2h, 3h, 4h or 5h; the stripping is carried out in a ball mill with a rotation speed of 100rpm, 200rpm, 250rpm or 300rpm for 0.5h, 1h or 1.5h; the drying temperature can be 100℃, 110℃ or 120℃, and the drying time can be 5h, 6h or 8h.
[0032] Regarding step S3, in some specific implementation schemes, in the molten salt electrolyte compound, the amount of CaCl2 can be 30g, 40g, 45g, 55g, or 60g; the amount of NaCl can be 10g, 15g, 18g, 25g, or 30g; the amount of KCl can be 5g, 8g, 12g, or 15g; the amount of CaO can be 0.5g, 1g, 1.5g, or 2g; and the amount of CaCO3 can be 0.5g, 1g, or 2g. The carbon content of the high-purity graphite crucible is >99.9%; the carbon content of the high-purity graphite rod is >99.9%; the inert gas can be argon; the working temperature of the molten salt electrolyte can be 550℃, 600℃, 700℃, or 920℃; the voltage of the cathode potential relative to the Ca / Ca2+ potential can be 1.5V, 1.8V, 2V, or 2.3V; and the constant voltage electrolysis time can be 1h, 2h, 4h, or 6h.
[0033] Regarding step S4, in some specific implementations, the drying temperature can be 110°C, 115°C, or 120°C, and the drying time can be 8h, 10h, or 12h.
[0034] Based on the preparation method of the regenerated graphite anode material based on molten salt electrochemical repair of this application, the following examples and comparative examples are listed: Example 1
[0035] A method for preparing regenerated graphite anode materials based on molten salt electrochemical repair specifically includes the following steps: S1. Discharge and Disassembly: Connect the positive and negative tabs of three 18650 type waste lithium-ion batteries with a nominal capacity of 2000mAh to a DC discharge load box. Set the discharge current to 200mA and continue discharging until the cell voltage drops to 0~0.05V to complete the discharge. Manually disassemble in a fume hood and remove the negative electrode sheet. Put the negative electrode sheet into a planetary ball mill, add zirconium oxide grinding balls, control the ball-to-material ratio to be 10:1, the rotation speed to be 250rpm, and the time to be 40min. Then sieve with an 8-mesh sieve and take the sieve material. Separate the sieve material through a 50-mesh sieve and take the sieve material to obtain a negative electrode material mixture containing graphite. S2. Pretreatment: The above-mentioned graphite-containing negative electrode material mixture is placed in a tube furnace and heated to 480°C at 5°C / min under argon protection, and kept at a constant temperature for 3.5h for pyrolysis, and then naturally cooled to room temperature; the pyrolyzed material is placed in a planetary ball mill, zirconium oxide grinding balls are added, and ball milling is carried out for 1h at a ball-to-material ratio of 10:1 and a rotation speed of 200 rpm; the particles that pass through a 100-mesh sieve and are retained by a 400-mesh sieve are collected and dried in an oven at 110°C for 6h to obtain pretreated graphite; S3. Molten Salt Electrochemical Remediation: Weigh 40g, 25g, 10g, 1.2g, and 1g of CaCl2, NaCl, KCl, CaO, and CaCO3 respectively as molten salt electrolyte mixtures, mix them evenly, and add them to a high-purity graphite crucible. Place the crucible in a muffle furnace and heat it to 720℃ under inert gas protection. Take 10g of pretreated graphite and put it into a porous molybdenum basket as the cathode, and use a high-purity graphite rod as the anode. Insert the two electrodes vertically into the molten salt, keeping the distance between them 3cm, and insert a clean molybdenum wire as a quasi-reference electrode. At the same time, continuously introduce inert gas. Using an electrochemical workstation, at a working temperature of 720℃, control the voltage of the cathode potential relative to the Ca / Ca2+ potential to be 2V, and maintain a constant voltage for electrolysis for 5h. S4. Post-processing: After electrolysis, the cathode product is removed, cooled, and then ultrasonically washed in 0.1 mol / L dilute hydrochloric acid for 30 min. After washing with deionized water until the pH is neutral, it is dried in a vacuum oven at 115℃ for 10 h to obtain the regenerated graphite anode material. Example 2
[0036] A method for preparing a regenerated graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that in Example 2, the amounts of CaCl2, NaCl, KCl, CaO, and CaCO3 in the molten salt electrolyte compound in step S3 are 50g, 25g, 10g, 1.2g, and 1g, respectively. Example 3
[0037] The preparation method of a regenerated graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that in Example 3, the amounts of CaCl2, NaCl, KCl, CaO, and CaCO3 in the molten salt electrolyte compound in step S3 are 50g, 20g, 12g, 1g, and 1g, respectively. Example 4
[0038] A method for preparing a recycled graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the working temperature of the molten salt electrolyte in step S3 of Example 4 is 650℃. Example 5
[0039] A method for preparing a recycled graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the working temperature of the molten salt electrolyte in step S3 of Example 5 is 850℃. Example 6
[0040] The preparation method of a recycled graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the voltage of the cathode potential in step S3 of Example 6 is 1.6V relative to the Ca / Ca2+ potential. Example 7
[0041] The preparation method of a regenerated graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the voltage of the cathode potential in step S3 of Example 7 is 2.3V relative to the Ca / Ca2+ potential.
[0042] Comparative Example 1: A method for preparing a regenerated graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the amount of molten salt electrolyte compound in step S3 of Comparative Example 1 is 65g, 25g, 10g, 1.2g, and 1g, respectively, for CaCl2, NaCl, KCl, CaO, and CaCO3.
[0043] Comparative Example 2: A method for preparing a regenerated graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that in step S3 of Comparative Example 2, the amounts of CaCl2, NaCl, and KCl in the molten salt electrolyte complex are 41.2 g, 26 g, and 10 g, respectively.
[0044] Comparative Example 3: A method for preparing a recycled graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the working temperature of the molten salt electrolyte in step S3 of Comparative Example 3 is 500℃.
[0045] Comparative Example 4: A method for preparing a recycled graphite anode material based on molten salt electrochemical repair is the same as in Example 1, except that the voltage of the cathode potential in step S3 of Comparative Example 4 is 2.5V relative to the Ca / Ca2+ potential.
[0046] Material performance testing: The recycled graphite anode materials obtained in Examples 1-7 and Comparative Examples 1-4 were subjected to various performance tests, and the test methods are as follows: 1. Total content of iron, copper and aluminum: The content of metallic impurities iron, copper and aluminum in the recycled graphite anode material was detected by ICP-OES inductively coupled plasma spectroscopy, and the total content of iron, copper and aluminum was calculated by adding them together.
[0047] 2. Particle size D90: Tested using laser diffraction.
[0048] 3. Tap density: Tested using an automatic tap density meter.
[0049] 4. Electrical Performance Testing: Regenerated graphite anode material, Super P, CMC, and SBR were mixed in a mass ratio of 95:1.5:1.5:2 to form a slurry. This slurry was then uniformly coated onto copper foil, dried, and punched into circular electrode sheets with a diameter of 12mm. Using lithium metal sheets as the counter electrode, CR2032 coin cell half-cells were assembled in an argon-protected glove box. The initial discharge capacity, initial charge capacity, and initial coulombic efficiency were tested using a Blue Electric testing system at a voltage window of 0.005~2.0V and a temperature of 25℃. The initial coulombic efficiency was calculated as: Initial charge capacity / Initial discharge capacity. The capacity is calculated as follows: 100% × 100%; At the same 0.1C rate, the battery is continuously charged and discharged, and the discharge capacity of the second charge is taken as the reversible specific capacity of the regenerated graphite anode material; Charge and discharge cycles are performed sequentially at 0.1C, 0.5C, and 1C rates, with 10 cycles at each rate. The charging capacity of the last cycle at each rate is recorded, and then the capacity retention rate at that rate is calculated: Capacity retention rate at a certain rate = Charging capacity at that rate / Initial charging capacity at 0.1C rate × 100%.
[0050] The test results are shown in Table 1: The test performance of the recycled graphite anode materials of Examples 1-7 and Comparative Examples 1-4 is shown in Table 1 below:
[0051] The preparation methods of recycled graphite anode materials based on molten salt electrochemical repair in Examples 1-7 use waste lithium-ion batteries as raw materials. Through four major steps—discharge dismantling, pretreatment, molten salt electrochemical repair, and post-treatment—the total content of iron, copper, and aluminum in the prepared recycled graphite anode materials is in the range of 9.9-16.8 ppm, with low impurity content, tap density ≥1.05 g / cm3, initial coulombic efficiency of 93.3%-94.3%, reversible specific capacity of 343.6-354.2 mAh / g, significantly improved rate performance, and 1C capacity retention rate of 88%-94%. This indicates that the recycled graphite anode materials prepared by the method of this application have achieved significant repair and activation in terms of performance.
[0052] Compared with Example 1, Comparative Example 1 differs in that the amount of CaCl2 used in the molten salt electrolyte complex in step S3 of Comparative Example 1 is not within the scope of this application. The results show that the various properties of the recycled graphite anode material in Comparative Example 1 are reduced, and the total content of iron, copper, and aluminum even reaches 28.1 ppm. This may be because the amount of CaCl2 used in the molten salt electrolyte complex in step S3 is too high, which breaks the eutectic equilibrium of the molten salt system, resulting in a decrease in the fluidity of the molten salt, which in turn leads to insufficient uniform dispersion of O2- and insufficient reaction of metal impurities. At the same time, the local sintering of graphite particles increases their particle size, ultimately increasing the content of metals such as iron, copper, and aluminum in the prepared recycled graphite anode material, reducing the tap density, and consequently reducing the electrochemical performance.
[0053] Compared to Example 1, Comparative Example 2 differs in that no oxygen-containing compounds were added to the molten salt electrolyte complex in step S3. The results show that Comparative Example 2 has an extremely high impurity content of 35.9 ppm, resulting in a significant decrease in initial coulombic efficiency, reversible specific capacity, and rate performance. This may be because the molten salt system lacks oxygen-containing compounds, thus hindering effective metal impurity conversion and leading to a high metal impurity content. Furthermore, the presence of numerous residual metal impurities may trigger other side reactions, and the uneven uniformity of the melt also results in insufficient repair of the graphite lattice, further degrading initial coulombic efficiency, reversible specific capacity, and rate performance.
[0054] Compared with Example 1, Comparative Example 3 differs in that the molten salt electrolyte operating temperature in step S3 of Comparative Example 3 is 500°C. The results show that the total content of metallic impurities (iron, copper, and aluminum) in Comparative Example 3 is as high as 42.4 ppm, and the reversible specific capacity is as low as 300.2 mAh / g. The operating temperature of the molten salt electrolyte in Comparative Example 3 is lower than the range defined in this application, which may have resulted in incomplete melting of the molten salt, stagnation of ion transport performance, extremely low removal efficiency of metallic impurities, and insufficient graphite lattice repair power. Therefore, among Comparative Examples 1-4, Comparative Example 3 has the highest total content of iron, copper, and aluminum and the lowest reversible specific capacity.
[0055] Compared with Example 1, Comparative Example 4 differs in that the voltage of the cathode potential in step S3 of Comparative Example 4 relative to the Ca / Ca2+ potential is 2.5V, which exceeds the range defined in this application. The results show that the tap density of the recycled graphite anode material drops to 0.99 g / cm3, the reversible specific capacity decreases, especially the rate performance, and the 1C capacity retention rate is only 60%. This may be because the voltage of the cathode potential relative to the Ca / Ca2+ potential is 2.5V, which causes chloride ions in the molten salt to be embedded in the interlayer of graphite, triggering irreversible structural expansion and damage. This structural damage is directly manifested in the fact that although the higher voltage enhances the ability to oxidize and remove metal impurities, resulting in a relatively low total content of iron, copper, and aluminum, the lithium storage structure of the graphite body has been damaged to a certain extent, thus exhibiting a reversible specific capacity decrease, especially a significant decrease in rate performance.
[0056] Obviously, the above embodiments of this application are merely examples for clearly illustrating this application, and are not intended to limit the implementation of this application. For those skilled in the art, other variations or modifications can be made based on the above description. Any obvious variations or modifications derived from the technical solutions of this application are still within the protection scope of this application.
Claims
1. A method for preparing regenerated graphite anode material based on molten salt electrochemical remediation, characterized in that, Includes the following steps: S1. Discharge and dismantling: Discharge, dismantle, crush and sort the waste lithium-ion batteries to obtain a mixture of negative electrode materials containing graphite. S2. Pretreatment: The graphite-containing negative electrode material mixture is pretreated to obtain pretreated graphite; S3, Molten Salt Electrochemical Remediation: The pretreated graphite is placed in a molten salt electrolyte containing CaCl2 as the cathode, and an inert electrode is used as the anode. Under the protection of inert gas, a voltage lower than the anion intercalation potential of graphite in the molten salt system is applied to the cathode to perform constant voltage electrolysis. S4. Post-processing: After electrolysis, the cathode product is removed, washed, and dried to obtain the regenerated graphite anode material.
2. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 1, characterized in that, In step S1, the sorting process involves passing the material through a 20-80 mesh sieve and collecting the material that passes through the sieve.
3. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 1, characterized in that, In step S2, the pretreatment includes pyrolysis, stripping, sieving, and drying processes.
4. The preparation method of regenerated graphite anode material based on molten salt electrochemical repair according to claim 3, characterized in that, In step S2, the pyrolysis is carried out under inert gas protection at a temperature of 400-550°C for 2-5 hours; the stripping is performed in a ball mill at a speed of 100-300 rpm for 0.5-1.5 hours; the sieving process collects particles that pass through a 100-mesh sieve and are retained by a 400-mesh sieve; and the drying process is carried out at a temperature of 100-120°C for 5-8 hours.
5. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 1, characterized in that, In step S3, the molten salt electrolyte is a CaCl2-based molten salt, which further includes at least one of NaCl, KCl, and LiCl, and the working temperature of the molten salt electrolyte is 550~920℃.
6. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 1 or 5, characterized in that, In step S3, 0.8-3 wt% of an oxygen-containing compound is added to the molten salt electrolyte, wherein the oxygen-containing compound is at least one of CaO and CaCO3.
7. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 6, characterized in that, The molten salt electrolyte is a compound of CaCl2, NaCl, KCl, CaO, and CaCO3 in a weight ratio of (30~60):(10~30):(5~15):(0.5~2):(0.5~2).
8. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 1, characterized in that, In step S3, the voltage below the graphite anion intercalation potential is the voltage relative to the Ca / Ca2+ potential in the molten salt electrolyte, and the voltage is 1.5~2.3 V.
9. The method for preparing regenerated graphite anode material based on molten salt electrochemical repair according to claim 1, characterized in that, In step S3, the constant voltage electrolysis time is 1~6 hours.
10. A recycled graphite anode material, characterized in that, The material is prepared by the method described in any one of claims 1 to 9, and the total content of iron, copper and aluminum elements in the recycled graphite anode material is less than 30 ppm.