Regenerated graphite and preparation method thereof

Abstract

The invention relates to the field of battery material recovery, and discloses regenerated graphite and a preparation method thereof.The preparation method includes the steps that in protective gas, waste graphite, inorganic fused salt and a fused salt auxiliary are mixed and roasted to obtain the regenerated graphite, the inorganic fused salt comprises sodium chloride and potassium chloride, and the fused salt auxiliary comprises acid phosphate. Binary inorganic fused salt is combined with a fused salt auxiliary agent to form a fused salt system, regeneration treatment including impurity removal and molecular structure reforming can be carried out on waste graphite at a low heat treatment temperature, and doping treatment on a graphite material is completed through the same process. Meanwhile, the method does not need to carry out additional pretreatment on the waste graphite. Therefore, the method provided by the invention has relatively high heat energy utilization rate and relatively low treatment temperature, can be used for directly treating the waste graphite, reduces the requirements on equipment and process in the treatment process of preparing the regenerated graphite, and can be used for preparing the regenerated graphite with relatively high electrochemical performance.

Description

Technical Field

[0001] The present application relates to the field of battery material recycling, and specifically, to recycled graphite and a method for preparing the same. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used in the fields of energy storage and new energy vehicles due to their high energy density, long cycle life, portability, and relative environmental friendliness. In new energy vehicles, the service life of lithium-ion batteries as power batteries is 5 to 8 years. It is estimated that by 2030, more than ten million tons of retired lithium-ion batteries will need to be processed annually. Currently, domestic and foreign research mainly focuses on the recovery of valuable metals in retired lithium-ion batteries, while the anode materials in lithium-ion batteries are usually processed as steelmaking additives or disposed of by burning, stacking, etc., resulting in environmental pollution and resource waste. The anode materials containing a large amount of graphite materials account for 15%-22% of the total weight of lithium-ion batteries, and their cost accounts for about 13%-18% of the total cost. Therefore, the recoverable amount of graphite materials to be recycled will exceed one million tons, and the market scale can reach tens of billions of yuan. Therefore, effectively utilizing the waste graphite recovered from retired lithium-ion batteries is of great significance for realizing the resource utilization of lithium-ion batteries.

[0003] It should be noted that the above statements are only used to provide background technical information related to the present application, and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect of the present application, a method for preparing recycled graphite is proposed, including: mixing and roasting waste graphite with an inorganic molten salt and a molten salt additive in a protective gas to obtain the recycled graphite, wherein the inorganic molten salt includes sodium chloride and potassium chloride, and the molten salt additive includes acid phosphate.

[0005] The method proposed in the present application uses a binary inorganic molten salt composed of sodium chloride and potassium chloride, combined with a molten salt additive to form a molten salt system, which can perform impurity removal, molecular structure reorganization, and regeneration treatment on waste graphite at a lower treatment temperature, and simultaneously complete the doping treatment of graphite materials. Thus, the method proposed in the present application has a high thermal energy utilization rate and a low treatment temperature, can reduce the requirements for equipment and processes in the process of preparing recycled graphite, and can prepare recycled graphite with high electrochemical performance.

[0006] In some embodiments, the molar ratio of the inorganic molten salt to the waste graphite is (0.2-5):1. Thus, when the molar ratio of the inorganic molten salt to the waste graphite is within the foregoing range, it is beneficial to prepare recycled graphite with a regular graphite layer structure, thereby improving the cycle performance of the recycled graphite as an anode material for batteries.

[0007] In some embodiments, the mass ratio of the molten salt additive to the waste graphite is (0.2 - 5):1. Thus, when the mass ratio of the molten salt additive to the waste graphite is within the foregoing range, the interaction between the molten salt additive and the inorganic molten salt can adjust the eutectic point of the two, reducing the temperature of the mixed roasting treatment.

[0008] In some embodiments, the molar ratio of the sodium chloride to the potassium chloride is 1:(1 - 3). Thus, when the molar ratio of the sodium chloride to the potassium chloride is within the foregoing range, it is beneficial to reduce the temperature of the mixed roasting treatment in this method and reduce the energy consumption for preparing the regenerated graphite.

[0009] In some embodiments, the acid phosphate includes at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate. Thus, the foregoing acid phosphate as a molten salt additive helps to reduce the process temperature for preparing the regenerated graphite and improves the cycling performance of the regenerated graphite as a battery anode material by introducing doping elements.

[0010] In some embodiments, the temperature of the mixed roasting treatment is 400°C - 700°C. Thus, within the foregoing temperature range, the molten salt system composed of the inorganic molten salt and the molten salt additive used in this application can be a transition molten salt including solid and liquid states. Through the phase change characteristics of the transition molten salt, the interlayer isotropy of the prepared regenerated graphite can be improved, which is beneficial to repairing the surface structure of the regenerated graphite.

[0011] In some embodiments, the temperature of the mixed roasting treatment is 500°C - 600°C, and the roasting treatment time is 3h - 12h. Thus, within the foregoing temperature and time ranges, the molten salt system composed of the inorganic molten salt and the molten salt additive used in this application has a relatively stable heat flux, which is beneficial to the conversion of waste graphite into regenerated graphite with a regular layered structure and doping element doping.

[0012] In some embodiments, the flow rate of the protective gas is 0.01L / min - 0.2L / min. When the flow rate of the protective gas is within the foregoing range, it is beneficial to maintain the temperature stability of the reaction temperature range during the preparation of the regenerated graphite and is beneficial for the protective gas to exert a better oxygen isolation effect. Thus, the influence of other reactions such as oxidation reactions on the performance of the prepared regenerated graphite is reduced.

[0013] In the second aspect of this application, this application proposes a regenerated graphite prepared by using the method for preparing regenerated graphite proposed in this application, and the regenerated graphite includes doping elements.

[0014] The regenerated graphite proposed in this application is obtained by recycling and treating waste graphite through the method proposed in this application, and realizes the co-doping of doping elements on the surface of the regenerated graphite, which is beneficial to improving the cycling performance and rate performance of the regenerated graphite.

[0015] In some embodiments, the doping element includes at least one of fluorine element, phosphorus element, sodium element, and nitrogen element. Co-doping of multiple elements can optimize the electronic structure through a synergistic effect. Thus, the regenerated graphite can have a more uniform charge distribution and better electron transfer ability, and thereby exhibit more excellent activity and performance during the electrochemical reaction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:

[0017] FIG. 1 is a heat flow curve (a) and a thermogravimetric curve (b) of an embodiment of the present application;

[0018] Figure 2 are SEM and EDS diagrams of the regenerated graphite prepared in Example 2 of the present application;

[0019] Figure 3 are XRD diagrams of the regenerated graphite prepared in Example 2 of the present application, waste graphite, and commercially available battery-grade graphite;

[0020] FIG. 4 is a comparison diagram of CV, impedance, rate performance, and 1C long cycle of the regenerated graphite prepared in Example 2 of the present application, waste graphite, and commercially available battery-grade graphite, as well as a schematic diagram of the long cycle of the regenerated graphite for a lithium iron phosphate full battery.

[0021] Figure 5 is a schematic diagram of the optimization of the rate performance of different embodiments of the present application with different mass ratios of waste graphite to ammonium dihydrogen phosphate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the drawings, but there may be cases where unnecessary details are omitted. For example, there may be cases where the detailed description of well-known matters is omitted and the repeated description of actually identical structures is omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0023] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs; the terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application; unless otherwise stated, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0024] The terms "comprising" and "having" and any variations thereof in the description and claims of this application are open-ended expressions, that is, they include the content specified in this application, but do not exclude other aspects.

[0025] In the description of this application, whether or not words such as "about" or "approximately" are used, all the numbers disclosed herein are approximate values. There may be a difference of less than 10% in the value of each number, or a reasonable difference considered by those skilled in the art, such as a difference of 1%, 2%, 3%, 4% or 5%.

[0026] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4 and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" represents that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] If there is no special indication, all the embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0028] If there is no special indication, all the technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0029] During the service process of lithium-ion batteries, the failure mechanisms related to anode materials mainly include: the formation and deterioration of the SEI film on the surface of the anode material, resulting in an increase in the lithium-ion conduction resistance; the mechanical stress caused by the expansion and contraction of the anode material particles leads to the destruction of the structure and the cracking of the particles; lithium dendrites are formed on the anode material during the lithium-ion insertion process, which further shortens the life of the anode material and deteriorates the battery performance. Based on the above failure mechanisms, it can be known that the layered structure inside the particles of waste graphite in the anode material is less affected. The key issue in the regeneration treatment of waste graphite is to remove the SEI film formed by surface passivation and repair the surface graphite structure. In addition, the waste graphite disassembled from the battery will also be mixed with substances such as binders and electrolytes added during battery assembly, and these substances need to be removed during the treatment of waste graphite.

[0030] Currently, the methods for regenerating waste graphite recovered from lithium-ion batteries mainly include traditional industrial methods such as hydrometallurgy and pyrometallurgy. Among them, hydrometallurgy is to carry out leaching treatment with strong acids or strong bases to remove impurities on the surface of waste graphite. However, the use of a large amount of strong acids / alkalis will cause environmental pollution and reduce the quality of waste graphite, making it difficult for the performance of waste graphite to meet the performance standards for reuse. Pyrometallurgy is to carry out re-graphitization treatment of waste graphite at a high temperature of 2800°C - 3000°C. Pyrometallurgy has huge energy consumption and extremely high equipment requirements. The existing methods for regenerating waste graphite have the disadvantages of complex processes, high energy consumption, and strict equipment requirements, which are not conducive to industrial promotion and make it difficult to reduce the price of regenerated graphite.

[0031] The method for preparing regenerated graphite proposed in this application has a high recovery rate of waste graphite, less waste and pollution emissions during the treatment process, and is characterized by being green, economical, and simple in process. It is conducive to improving the recovery rate of waste graphite in the industry, promoting the development of circular economy, giving full play to the secondary value of waste graphite, reducing the environmental burden and waste of resources.

[0032] In the first aspect of this application, a method for preparing regenerated graphite is proposed, including: mixing and roasting waste graphite with inorganic molten salts and molten salt additives in a protective gas to obtain the regenerated graphite, wherein the inorganic molten salts include sodium chloride and potassium chloride, and the molten salt additives include acid phosphate.

[0033] The method for preparing regenerated graphite proposed in this application adopts a molten salt system composed of binary inorganic molten salts of sodium chloride and potassium chloride and molten salt additives. Due to the ionic radius difference between sodium ions and potassium ions, potassium chloride and sodium chloride absorb heat during the mixing and roasting process to form a solid solution molten salt composed of sodium ions and chloride ions. The solid solution molten salt has a lower free energy of melting, so the eutectic point of this solid solution molten salt is much lower than the melting temperature of solid sodium chloride or solid potassium chloride.

[0034] During the process of forming a solid solution molten salt by mixing molten salt additives and inorganic molten salts, as shown in Figure 1, the molten salt system containing molten salt additives and inorganic molten salts has a wider endothermic range and a lower melting temperature of the solid solution molten salt, which is beneficial to reducing the processing temperature at each stage of the preparation process of recycled graphite and reducing the process difficulty of preparing recycled graphite. The molten salt additives can adjust the ion concentration and permeability in the inorganic molten salts, thereby improving the ion mobility and interaction in the inorganic molten salts. During the process of mixing and roasting waste graphite with inorganic molten salts and molten salt additives, with the assistance of the molten salt additives, the solid solution molten salt of the binary inorganic molten salts can be transformed into a molten molten salt at a lower temperature. This solid solution molten salt has strong polarity and can break the chemical bonds of substances such as residual binders and electrolytes in the waste graphite, promoting their decomposition and dissolution in the molten molten salt, which is beneficial to removing the impurities adhered to or mixed in the waste graphite from the graphite material and reducing the impact on the prepared recycled graphite itself. In addition, referring to Figure 2 , in this method, during the process of recycling waste graphite, elements such as sodium in the inorganic molten salts, fluorine in the binder (containing fluorine), and phosphorus in the molten salt additives can be doped into the graphite material to improve the molecular structure of the recycled graphite. Therefore, referring to Figure 3 Figure 4, using waste graphite to prepare recycled graphite can not only achieve the recycling of waste graphite, but also improve the performance of the graphite material during this process, and prepare recycled graphite with better cycle performance and rate performance.

[0035] Therefore, the method proposed in this application has a high thermal energy utilization rate and a low processing temperature, can reduce the requirements for equipment and processes in the process of preparing recycled graphite, and complete the doping treatment of the graphite material through the same process, with a relatively high recovery rate of more than 94% (calculated by weighing the mass of waste graphite before regeneration and the prepared recycled graphite), and improve the cycle performance of the prepared recycled graphite.

[0036] In some embodiments, the molar ratio of the inorganic molten salt to the waste graphite is (0.2 - 5):1. The ratio of the inorganic molten salt to the waste graphite material will affect the molecular structure of the prepared recycled graphite. Therefore, when the molar ratio of the inorganic molten salt to the waste graphite is within the foregoing range, it is beneficial to prepare recycled graphite with a regular graphite layer structure, thereby improving the cycle performance of the recycled graphite when used as a battery anode material.

[0037] In some embodiments, the mass ratio of the molten salt additive to the waste graphite is (0.2-5):1. When the mass ratio of the molten salt additive to the waste graphite is within the foregoing range, the interaction between the molten salt additive and the inorganic molten salt can adjust their eutectic point, reducing the temperature of the mixed roasting treatment. At the same time, the phosphorus element in the phosphate radical of the molten salt additive can be doped into the structure of the prepared recycled graphite as a doping element, enhancing the chemical stability and thermal stability of the recycled graphite, thereby improving the cycling performance of the recycled graphite as a battery anode material.

[0038] In some embodiments, the molar ratio of the sodium chloride to the potassium chloride is 1:(1-3). When the molar ratio of the sodium chloride to the potassium chloride is within the foregoing range, the formed solid solution molten salt has a relatively single solid solution phase, so the free energy of its melting decreases significantly, and it can have a eutectic point significantly lower than that of potassium chloride or sodium chloride. Thus, it is beneficial to reduce the temperature of the mixed roasting treatment in this method and reduce the energy consumption for preparing the recycled graphite.

[0039] In some embodiments, the acid phosphate includes at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate. The introduction of poly metaphosphoric acid in the foregoing acid phosphate as a molten salt additive will cause structural changes in the solid solution molten salt formed by sodium chloride and potassium chloride, weakening the strength of the ionic bond in the solid solution molten salt and further reducing the eutectic point of the solid solution molten salt. In addition, the foregoing molten salt additive can also be used as a source of doping elements to introduce doping elements such as phosphorus and nitrogen elements into the recycled graphite. Thus, the foregoing acid phosphate as a molten salt additive helps to reduce the process temperature for preparing the recycled graphite and improve the cycling performance of the recycled graphite as a battery anode material by introducing doping elements.

[0040] In some embodiments, the temperature of the mixed roasting treatment is 400°C-700°C. Within the foregoing temperature range, the molten salt system composed of the inorganic molten salt and the molten salt additive used in this application can be a transition molten salt including solid and liquid states. The phase change characteristics of the transition molten salt can be used to improve the interlayer isotropy of the prepared recycled graphite, which is beneficial to repairing the surface structure of the recycled graphite and retaining the beneficial conductive carbon components in the waste graphite. At the same time, through the action of the transition molten salt and the waste graphite within the foregoing temperature range, co-doping of doping elements on the surface of the recycled graphite is achieved. The doping ions can adjust the growth of the surface SEI film of the recycled graphite as an anode material during charge and discharge cycles in the recycled graphite and enhance the lithium ion migration ability of the recycled graphite, thereby improving the electrochemical performance of the recycled graphite.

[0041] As an example, the temperature of the mixed roasting treatment is 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C.

[0042] In some embodiments, the temperature of the mixed calcination treatment is 500°C - 600°C, and the time of the calcination treatment is 3h - 12h. Thus, within the foregoing temperature and time ranges, the molten salt system composed of the inorganic molten salt and the molten salt auxiliary agent adopted in the present application has a relatively stable heat flux, which is beneficial to the conversion of waste graphite into regenerated graphite with a regular layered structure and doped with doped elements.

[0043] In some embodiments, the flow rate of the protective gas is 0.01L / min - 0.2L / min. The protective gas includes inert gases, nitrogen and other gases with stable chemical properties. When the flow rate of the protective gas is within the foregoing range, it is beneficial to maintain the temperature stability of the reaction temperature range during the preparation of regenerated graphite and is beneficial to the protective gas to exert a better oxygen isolation effect. Thus, the influence of other reactions such as oxidation reaction on the performance of the prepared regenerated graphite is reduced.

[0044] In the second aspect of the present application, the present application proposes a regenerated graphite, which is prepared by the method for preparing regenerated graphite proposed by the present application, and the regenerated graphite includes doped elements.

[0045] The regenerated graphite proposed by the present application is composed of Figure 3 It can be seen that it has a good layered structure, is obtained by recycling waste graphite through the method proposed by the present application, and realizes the co-doping of doped elements on the surface of the regenerated graphite, which is beneficial to improving the cycle performance and rate performance of the regenerated graphite.

[0046] In some embodiments, the doped elements include at least one of fluorine element, phosphorus element, sodium element, and nitrogen element. Among the foregoing doped elements, N has a relatively high electronegativity (3.04), which can introduce local polarization phenomena, increase the electron density, and improve the conductivity of the regenerated graphite. P has a relatively low electronegativity (2.19), and doping in the regenerated graphite can cause local enrichment of electrons and form additional active sites. F has an extremely high electronegativity (3.98), which can cause strong charge rearrangement and adjust the Fermi level to improve the electron transfer rate. Sodium element can effectively regulate the layer spacing of the regenerated graphite and improve the ion diffusion rate, thereby enhancing the capacity and rate performance of the regenerated graphite. From Figure 2 It can be seen that the regenerated graphite of the present application has a clean surface, contains conductive carbon components, and can realize the co-doping of multiple elements. When more than one of the foregoing doped elements are co-doped in the regenerated graphite, the doped elements can have a synergistic effect to optimize the electronic structure, making the regenerated graphite have a more uniform charge distribution and better electron transfer ability, and thus showing more excellent activity and performance during the electrochemical reaction process.

[0047] The solution of the present application will be described below through specific embodiments. It should be noted that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those without specific technologies or conditions noted in the embodiments, the technologies or conditions described in the literature in the field or according to the product specifications are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchases.

[0048] Example 1

[0049] (1) Immerse the NCM111 waste lithium-ion battery in a sodium chloride solution for 24 hours for discharging, and perform disassembly and separation treatment to obtain the negative electrode current collector.

[0050] (2) Immerse the negative electrode current collector in deionized water for 2 hours to separate the waste graphite from the copper foil, and then perform suction filtration to obtain water-containing waste graphite; dry the water-containing waste graphite for 12 hours and perform grinding treatment to obtain waste graphite.

[0051] (3) Mix 0.5 g of waste graphite with NaCl and KCl with a molar ratio of waste graphite of 1:1:1 and ammonium dihydrogen phosphate with a mass ratio of waste graphite to ammonium dihydrogen phosphate of 1:4, grind them evenly and place them in a crucible, and calcine them at 500 °C for 5 hours under an argon atmosphere.

[0052] (4) Ultrasonically disperse the calcined material in 250 ml of deionized water, then perform suction filtration and washing, and then dry it at 80 °C for 12 hours to obtain regenerated graphite.

[0053] Example 2

[0054] Example 2 is the same as Example 1, except that the mass ratio of waste graphite to ammonium dihydrogen phosphate is 1:2.5.

[0055] Grind them evenly and place them in a crucible, and calcine them at 550 °C for 5 hours under an argon atmosphere.

[0056] Testing method:

[0057] 1. Testing method for melting point and heat flow

[0058] TGA-DSC analysis is performed using a PerkinElmer STA8000 system, and XRD testing is performed using a Rigaku D / Max X-ray diffractometer (Cu Kα radiation source).

[0059] 2. Electrochemical testing

[0060] To prepare the anode material, recycled graphite, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder (weight ratio 85:10:5) were thoroughly mixed in N-methylpyrrolidone (NMP). The mixed slurry was coated on a copper current collector and vacuum dried overnight at 70 °C to form the working anode (graphite loading: 2.5 - 3.5 mg / cm 2 ). The commercial lithium iron phosphate cathode material was purchased from Kelude Co., Ltd., and the preparation method was the same. The electrolyte used was the commercially available lithium-ion battery electrolyte LB-037, with 1 M LiPF6 dissolved in DEC:EC:EMC (volume ratio 1:1:1). CR 2025 coin cells were assembled in a glove box. The charge-discharge tests were completed by a CT-2001A battery test system (LAND).

[0061] Test results:

[0062] As can be seen from Figure 4, the recycled graphite of this application has better cycling performance and rate performance compared to commercially available commercial battery-grade graphite or recycled untreated waste graphite. Even after 250 cycles at a rate of 1C, Example 2 still has a specific capacity of 371.4 mAh g -1 , while commercial graphite only has 144.1 mAh g -1 . The lithium iron phosphate full cell assembled in Example 2 has a specific capacity as high as 135.4 mAh g -1 at a rate of 0.5C, as well as excellent cycling stability with a capacity retention rate of 92.2% after 500 cycles. Example 2 has a specific capacity of 219.9 mAh g -1 at a rate of 2C and 144.6 mAh g -1 at a rate of 3C, showing rate performance far exceeding that of commercial graphite.

[0063] As Figure 5 shows, when the addition amount of the molten salt additive is within the range proposed in this application, the prepared recycled graphite has better cycling performance.

[0064] In this application, the writing order of each step does not mean a strict execution order that constitutes any limitation to the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Without special instructions, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0065] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various deformations that can be thought of by those skilled in the art are imposed on the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for preparing regenerated graphite, characterized in that: include: In a protective gas, waste graphite is mixed with an inorganic molten salt and a molten salt additive and calcined to obtain the regenerated graphite, wherein the inorganic molten salt includes sodium chloride and potassium chloride, and the molten salt additive includes acid phosphate.

2. The method according to claim 1, characterized in that The molar ratio of the inorganic molten salt to the waste graphite is (0.2-5):

1.

3. The method according to claim 1, characterized in that The mass ratio of the molten salt additive to the waste graphite is (0.2-5):

1.

4. The method according to claim 1, characterized in that: The molar ratio of the sodium chloride to the potassium chloride is 1:(1-3).

5. The method according to claim 1, characterized in that The acid phosphate includes at least one of ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate.

6. The method according to any one of claims 1 to 5, characterized in that: The temperature of the mixed calcination treatment is 400°C-700°C.

7. The method according to claim 6, characterized in that The temperature of the mixed calcination treatment is 500° C.-600° C., and the time of the calcination treatment is 3 h-12 h.

8. The method according to any one of claims 1 to 5, characterized in that: The flow rate of the protective gas is 0.01L / min-0.2L / min.

9. A regenerated graphite, characterized in that: Prepared by the method according to any one of claims 1 to 8, the regenerated graphite includes doping elements.

10. The regenerated graphite according to claim 9, characterized in that: The doping element includes at least one of fluorine, phosphorus, sodium and nitrogen.

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