A method for recycling battery negative electrode graphite and its prepared recycled graphite material and application

Abstract

The present invention discloses a method for recycling battery negative electrode graphite, as well as the regenerated graphite material prepared and its application. This method, based on considerations of the conductivity and failure mechanisms of battery negative electrode graphite, employs a combined stripping agent to pre-exfoliate and decompose the waste graphite under specific two-stage process conditions, converting it into highly dispersible graphene / graphene-like materials. The materials are then subjected to autocatalytic thermal polymerization using a mixture of asphalt and a doping modifier, and finally oxidized and carbonized to obtain the regenerated graphite material. The resulting regenerated graphite material exhibits high dispersibility, good conductivity, and excellent structural stability. Its surface possesses abundant ion / electron transport sites and channels, resulting in excellent electrochemical performance when reused in secondary batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery recycling, and in particular to a method for recycling battery negative electrode graphite and a regenerated graphite material prepared therefrom and its application. Background Art

[0002] The metal active materials in the positive electrodes of spent secondary batteries are generally recycled and reused due to their high value, high reactivity, and potential for environmental pollution. In contrast, the active materials in the negative electrodes are generally graphite, which has a lower recycling value. Therefore, in-depth research on the recycling of negative electrode graphite materials has been rare in the prior art. However, with the advancement of secondary battery technology, the high-quality battery-grade graphite used in some high-end secondary batteries has become expensive. Recycling these materials from spent batteries could significantly improve economic benefits.

[0003] Traditional graphite recycling processes typically involve acid washing to remove impurities and calcining to regenerate the graphite. However, these processes fail to consider the conductivity and failure mechanisms of graphite materials in secondary batteries, nor do they consider the repair of graphite materials. Consequently, the regenerated products exhibit poor performance when reused in secondary batteries. Consequently, existing technologies have explored methods for recycling graphite materials, such as gas phase digestion and resin or graphite-like coating and repair. While these processes can repair internal defects in graphite materials to a certain extent, the degree of repair is low, and the electrochemical performance of the resulting regenerated graphite in secondary batteries remains far inferior to that of freshly made graphite. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the aforementioned prior art by providing a method for recycling battery negative electrode graphite. This method, based on considerations of the conductivity and failure mechanisms of battery negative electrode graphite, employs a combined stripping agent to pre-exfoliate and decompose the waste graphite under specific two-stage process conditions, converting it into highly dispersible graphene / graphene-like materials. This is followed by autocatalytic thermal polymerization using a mixture of asphalt and a doping modifier, and finally, oxidative carbonization to yield regenerated graphite. The resulting regenerated graphite material exhibits high dispersibility and excellent conductivity, as well as structural stability. Its surface possesses abundant ion / electron transport sites and channels, resulting in excellent electrochemical performance when reused in secondary batteries.

[0005] To achieve the above objectives, the technical solutions adopted in this paper are:

[0006] A method for recycling battery negative electrode graphite comprises the following steps:

[0007] Separating waste graphite from the negative electrode of waste batteries to obtain graphite powder;

[0008] The graphite powder and the combined stripping agent are mixed, ground, sieved, and then calcined at 400-650° C. to obtain stripped graphite powder; the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, the inorganic stripping agent includes at least one of perchloric acid and its salts, sodium chlorate, potassium permanganate, ammonium pyrosulfate, potassium perchromate, boric acid, and potassium molybdate; the organic stripping agent includes at least one of phenylboric acid and its derivatives, benzenesulfonic acid and its derivatives, and phenylphosphoric acid and its derivatives;

[0009] Grinding the exfoliated graphite powder and dispersing it in a solution containing a dispersant at 80-120° C. to obtain dispersed graphite powder;

[0010] The dispersed graphite powder, asphalt and dopant are uniformly mixed, and then subjected to thermal polymerization reaction at 400-450° C. to obtain mesocarbon microspheres; the dopant contains at least one of nitrogen, sulfur, phosphorus and boron;

[0011] The mesophase carbon microspheres are mixed with an oxidant, and then subjected to secondary calcination at 700-2600° C. to obtain a regenerated graphite material.

[0012] In the method for recycling battery negative electrode graphite described in the present invention, the collected graphite powder is first intercalated and stripped with a combined stripping agent. The inorganic stripping agent in the combined stripping agent physically increases the spacing between graphite layers, thereby reducing the theoretical temperature required for one calcination. At the same time, the organic stripping agent can be fully embedded in the spacing and decomposed into gas or macromolecules during calcination to promote the separation of the graphite interlayer structure, and even react with the carbon atoms between the graphite layers to cut off the graphite sheets. The spacing between the graphite sheets is significantly increased and the overall specific surface area is increased. Graphene / graphene-like structures are generated in the graphite powder, and then a dispersant is used for dispersion treatment in liquid phase ultrasound. The interaction force between the solvent and the graphene / graphene-like structures in the graphite powder is used to suppress the agglomeration of the sheets, and the effect of the dispersant forms a barrier on the surface of the sheets, resulting in a high degree of dispersion and stripping. After obtaining highly dispersed graphite powder, the present invention is different In the traditional thermal polymerization process, no catalyst is introduced, which may cause impurity risks. Instead, asphalt is directly used as a template for self-catalytic thermal polymerization to improve the crystallinity of the overall material and the order of the layered structure, control the size of the graphite interlayer structure, and introduce modifiers containing nitrogen, sulfur, phosphorus, and boron atoms for doping modification, which can effectively improve the chemical stability and structural stability of the resulting material; the mesophase carbon microspheres formed by thermal polymerization are further subjected to high-temperature calcination and oxidation with an oxidant, which can be in situ etched on the surface of the microspheres to produce channels and sites for ion / electron transmission. At the same time, the asphalt molecules in the microspheres can be oxidized and condensed to fix the molecular orientation, and some large molecules can form a larger molecular network through connection, further improving the stability of the overall structure, and finally obtaining a recycled graphite material that can be directly used in secondary batteries and has good electrochemical properties.

[0013] In some embodiments, the waste batteries include at least one of waste ternary lithium batteries, waste lithium iron phosphate batteries, waste lithium manganese iron phosphate batteries, waste lithium cobalt oxide batteries, and waste lithium manganese oxide batteries.

[0014] In some embodiments, the perchloric acid and its salts include at least one of perchloric acid, potassium perchlorate, and ammonium perchlorate.

[0015] In some embodiments, the phenylboronic acid and its derivatives include at least one of 1,4-diphenylboronic acid, 4-formylphenylboronic acid, 4,4'-biphenyldiboronic acid, 3,5-dimethoxyphenylboronic acid, triphenyl borate, and 3-aminophenylboronic acid hemisulfate.

[0016] In some embodiments, the benzenesulfonic acid and its derivatives include at least one of 3-aminobenzenesulfonic acid, 4-hydroxybenzenesulfonic acid, and aminobenzenesulfonic acid.

[0017] In some embodiments, the phenylphosphoric acid and its derivatives include at least one of disodium phenyl phosphate, phenyl phosphate, phenyl diaminophosphate, diphenyl aminophosphate, and aniline sulfate.

[0018] Further preferably, the inorganic stripping agent is at least one of ammonium pyrosulfate, boric acid, and potassium molybdate, and the organic stripping agent is at least one of 1,4-diphenylboric acid, 4-formylphenylboric acid, 4,4'-biphenyldiboric acid, 3,5-dimethoxyphenylboric acid, and triphenyl borate.

[0019] Different stripping agents have different stripping effects on graphite powder, and their activity during high-temperature calcination is also different. It has been verified that when the inorganic stripping agent uses boric acid and / or ammonium molybdate, and the organic stripping agent uses phenylboric acid and its derivatives, the former can be more fully inserted into the interlayer of the graphite powder and assist the latter in filling the interior, thereby reacting and expanding and increasing the interlayer spacing.

[0020] In some embodiments, the mass ratio of the combined stripping agent to the graphite powder is (0.2-0.8):1, and the mass ratio of the inorganic stripping agent to the organic stripping agent in the combined stripping agent is (0.3-1.4):1.

[0021] After multiple screenings by the inventors, it was found that the above ratio has a better effect on the preliminary exfoliation of graphite powder and is more effective in constructing graphene / graphene-like structures in the graphite powder.

[0022] In some embodiments, the graphite powder and the combined stripping agent are mixed and ground, and the mesh size of the sieve is 80 to 200 meshes.

[0023] In some embodiments, the primary calcination time is 6 to 12 hours, and the primary calcination atmosphere is an oxygen-containing atmosphere or an inert atmosphere.

[0024] In some embodiments, the dispersant includes at least one of pyrrolidone, polyvinylpyrrolidone, sodium 4-hydroxybenzenesulfonate, sodium 3-carboxylbenzenesulfonate, sodium 3-aminobenzenesulfonate, sodium 4-vinylbenzenesulfonate, sodium benzoylthioethanesulfonate, polyisopropylacrylamide, methylcellulose, sodium dodecylbenzenesulfonate, cetylpyridinium chloride, 3-benzylidenebutamide, benzylsulfonamide, p-carboxylbenzenesulfonamide, phenoxyacetamide, and polystyrene, and the solvent in the solution containing the dispersant is water and / or an organic solvent. Further preferably, the organic solvent includes at least one of pyrrolidone, polyvinylpyrrolidone, sodium 4-hydroxybenzenesulfonate, sodium 3-carboxybenzenesulfonate, sodium 3-aminobenzenesulfonate, sodium 4-vinylbenzenesulfonate, sodium benzoylthioethanesulfonate, polyisopropylacrylamide, methylcellulose, sodium dodecylbenzenesulfonate, cetylpyridinium chloride, 3-benzylidenebutamide, benzylsulfonamide, p-carboxybenzenesulfonamide, phenoxyacetamide, and polystyrene.

[0025] More preferably, the mass concentration of the dispersant-containing solution is 5 to 25 wt %.

[0026] The above-mentioned dispersant has a carbon chain and a π plane, so when mixed with the exfoliated graphite powder, it can form a strong electronic interaction with the surface of the graphene / graphene-like structure in the graphite powder and occupy the spatial position on the surface, thereby avoiding the stacking and agglomeration of these structures and improving the dispersion effect.

[0027] Further preferably, the solid-to-liquid ratio of the exfoliated graphite powder to the solution containing the dispersant is 0.1 to 0.5 g / mL.

[0028] Further preferably, the dispersion treatment is ultrasonic dispersion treatment, and the time of the ultrasonic dispersion treatment is 4 to 8 hours.

[0029] In some embodiments, the mass ratio of the dispersed graphite powder, pitch, and dopant is (0.03-0.15):1:(0.05-0.25).

[0030] Further preferably, the asphalt includes at least one of petroleum asphalt, coal asphalt, and coal tar.

[0031] Further preferably, after the asphalt is subjected to organic solvent separation treatment, the organic solvent is removed at 100-150° C., and the obtained light components and insoluble matter are combined into asphalt raw material in a mass ratio of 1:(0.1-0.4).

[0032] Further preferably, the dopant includes at least one of melamine, pyridine, pyrrole, urea, dicyandiamide, thiourea, phosphorus pentoxide, and boric acid.

[0033] In some embodiments, the thermal polymerization reaction time is 2 to 10 hours, the reaction pressure environment is 0.1 to 3 MPa, and the atmosphere environment is an inert atmosphere.

[0034] Further preferably, the mesocarbon microspheres obtained by the thermal polymerization reaction are further subjected to a washing treatment.

[0035] In some embodiments, the oxidant comprises at least one of air, O2, SO2, NO2, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, sodium hypophosphite, KMnO4, H2O2, and HNO3.

[0036] In some embodiments, the secondary calcination includes carbonization calcination and graphitization calcination, wherein the carbonization calcination is performed at a temperature of 700-900° C. for 10-12 hours; and the graphitization calcination is performed at a temperature of 1900-2600° C. for 10-15 hours.

[0037] Another object of the present invention is to provide a regenerated graphite material prepared by the battery negative electrode graphite recovery method.

[0038] Another object of the present invention is to provide a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the recycled graphite material.

[0039] The regenerated graphite material described in the present invention is recovered and regenerated from the graphite negative electrode in waste batteries through a simple segmented process, with low practical consumption and high yield. In addition, the prepared material has a high degree of defect repair and modification of the graphite material itself, so it can be directly used as an active material on the negative electrode sheet of a new secondary battery without modification. The resulting secondary battery not only has a high reversible capacity but also good cycle stability. After 100 cycles at a 0.1C rate, the capacity retention rate can reach up to 87%, and the electrochemical performance is excellent.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention provides a method for recycling battery negative electrode graphite. Based on considerations of the conductivity and failure mechanisms of battery negative electrode graphite, this method uses a combined stripping agent to pre-exfoliate and decompose the waste graphite under specific two-stage process conditions, converting it into highly dispersible graphene / graphene-like materials. This process is then followed by autocatalytic thermal polymerization using a mixture of pitch and a doping modifier, followed by oxidation and carbonization to produce regenerated graphite. The resulting regenerated graphite material exhibits high dispersibility, excellent conductivity, and structural stability. Its surface possesses abundant ion / electron transport sites and channels, resulting in excellent electrochemical performance when reused in secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The figure is a schematic flow chart of the method for recycling battery negative electrode graphite according to the present invention.

[0043] Figure 2 The present invention is a schematic diagram of the process of converting graphite powder into dispersed graphite powder in the method for recovering battery negative electrode graphite.

[0044] Figure 3 The present invention is a schematic diagram of the process of converting dispersed graphite powder into mesophase carbon microspheres in the method for recovering battery negative electrode graphite.

[0045] Figure 4 The present invention is a schematic diagram of the process of converting mesophase carbon microspheres into recycled graphite materials in the method for recycling battery negative electrode graphite.

[0046] Figure 5 This is a scanning electron microscope image of the graphite powder after exfoliation described in Example 1 of the present invention.

[0047] Figure 6 This is a scanning electron microscope image of the graphite powder after exfoliation described in Example 2 of the present invention.

[0048] Figure 7 This is a scanning electron microscope image of the graphite powder after exfoliation described in Example 3 of the present invention.

[0049] Figure 8 This is a scanning electron microscope image of the graphite powder after exfoliation described in Comparative Example 1 of the present invention.

[0050] Figure 9 This is a scanning electron microscope image of the graphite powder after exfoliation described in Comparative Example 2 of the present invention.

[0051] Figure 10 This is a scanning electron microscope image of the graphite powder after exfoliation described in Comparative Example 3 of the present invention.

[0052] Figure 11 This is a scanning electron microscope image of the dispersed graphite powder described in Example 1 of the present invention.

[0053] Figure 12 This is a scanning electron microscope image of the dispersed graphite powder described in Example 2 of the present invention.

[0054] Figure 13 This is a scanning electron microscope image of the dispersed graphite powder described in Example 3 of the present invention.

[0055] Figure 14 This is a scanning electron microscope image of the dispersed graphite powder described in Comparative Example 4 of the present invention.

[0056] Figure 15 This is a scanning electron microscope image of the mesocarbon microspheres described in Example 1 of the present invention.

[0057] Figure 16 This is a scanning electron microscope image of the mesocarbon microspheres described in Example 2 of the present invention.

[0058] Figure 17 This is a scanning electron microscope image of the mesocarbon microspheres described in Example 3 of the present invention.

[0059] Figure 18 This is a scanning electron microscope image of the mesocarbon microspheres described in Comparative Example 1 of the present invention.

[0060] Figure 19 This is a scanning electron microscope image of the mesocarbon microspheres described in Comparative Example 2 of the present invention.

[0061] Figure 20 This is a scanning electron microscope image of the mesocarbon microspheres described in Comparative Example 3 of the present invention.

[0062] Figure 21 This is a scanning electron microscope image of the regenerated graphite material described in Example 1 of the present invention.

[0063] Figure 22 This is a scanning electron microscope image of the regenerated graphite material described in Example 2 of the present invention.

[0064] Figure 23 This is a scanning electron microscope image of the regenerated graphite material described in Comparative Example 5 of the present invention.

[0065] Figure 24 This is a scanning electron microscope image of the regenerated graphite material described in Comparative Example 6 of the present invention. DETAILED DESCRIPTION

[0066] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0067] Unless otherwise specified, the materials used in the examples and comparative examples can be obtained through commercial channels.

[0068] Example 1

[0069] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application is provided in the present invention. The battery negative electrode graphite recovery method is as follows: Figure 1 As shown, the following steps are included:

[0070] (1) Dismantling the waste graphite in the negative electrode of the waste ternary lithium battery, separating and pre-treating it to obtain graphite powder;

[0071] (2) mixing the graphite powder and the combined stripping agent, grinding the mixture, passing the mixture through a 200-mesh sieve, and then calcining the mixture once at 650° C. for 6 h in an oxygen-containing atmosphere to obtain stripped graphite powder; the mass ratio of the combined stripping agent to the graphite powder is 0.8:1; the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 1.4:1; the inorganic stripping agent is ammonium pyrosulfate, and the organic stripping agent is 1,4-diphenylboric acid;

[0072] (3) The exfoliated graphite powder is ground and then ultrasonically dispersed at 120° C. for 8 h in a 25 wt% dispersant aqueous solution at a solid-liquid ratio of 0.5 g / mL to obtain dispersed graphite powder; the dispersant is polyvinyl pyrrolidone; the process of converting the graphite powder into dispersed graphite powder is shown in the figure. Figure 2 As shown;

[0073] (4) The dispersed graphite powder, asphalt and dopant melamine are uniformly mixed in a mass ratio of 0.15:1:0.25, and then thermally polymerized in an inert atmosphere at 1 MPa and 450°C for 10 hours to obtain mesophase carbon microspheres; the asphalt is an asphalt raw material in which the light component and insoluble matter obtained by dispersing petroleum asphalt with quinoline and removing quinoline at 150°C are mixed in a ratio of 1:0.1; the schematic diagram of the process of converting the dispersed graphite powder into mesophase carbon microspheres is shown in FIG. Figure 3 As shown;

[0074] (5) The mesophase carbon microspheres are mixed with the oxidant sodium hypophosphite in a mass ratio of 1:1, and then subjected to secondary calcination to obtain a regenerated graphite material; the secondary calcination includes carbonization calcination and graphitization calcination, the carbonization calcination temperature is 700°C, the time is 12h; the graphitization calcination temperature is 2600°C, the time is 15h; the process diagram of the conversion of the mesophase carbon microspheres into the regenerated graphite material is shown in FIG. Figure 4 shown.

[0075] Example 2

[0076] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention comprises the following steps:

[0077] (1) Dismantling the waste graphite in the negative electrode of the waste ternary lithium battery, separating and pre-treating it to obtain graphite powder;

[0078] (2) mixing the graphite powder and the combined stripping agent, grinding the mixture, passing the mixture through a 200-mesh sieve, and then calcining the mixture once at 550° C. for 9 h in an oxygen-containing atmosphere to obtain stripped graphite powder; the mass ratio of the combined stripping agent to the graphite powder is 0.5:1; the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 0.8:1; the inorganic stripping agent is potassium permanganate, and the organic stripping agent is sodium 3-aminophenylboronic acid hemisulfate;

[0079] (3) grinding the exfoliated graphite powder and then performing ultrasonic dispersion treatment at 100° C. for 6 h in a polyvinyl pyrrolidone solution containing a dispersant having a mass concentration of 15 wt % at a solid-liquid ratio of 0.3 g / mL to obtain dispersed graphite powder; the dispersant is sodium 3-carboxybenzenesulfonate;

[0080] (4) The dispersed graphite powder, asphalt and dopant boric acid are uniformly mixed in a mass ratio of 0.08:1:0.15, and then thermally polymerized in an inert atmosphere at 2 MPa and 420°C for 8 hours to obtain mesophase carbon microspheres; the asphalt is an asphalt raw material in which the light component and insoluble matter obtained by dispersing petroleum asphalt with quinoline and removing quinoline at 150°C are mixed in a ratio of 1:0.25;

[0081] (5) The mesophase carbon microspheres are washed and dried with quinoline, transferred into a calcining furnace, and oxygen is introduced at a flow rate of 45 L / min, followed by secondary calcination to obtain regenerated graphite material; the secondary calcination includes carbonization calcination and graphitization calcination, the carbonization calcination temperature is 800°C, the time is 11 hours, and the graphitization calcination temperature is 2000°C, and the time is 12 hours.

[0082] Example 3

[0083] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention comprises the following steps:

[0084] (1) Dismantling the waste graphite in the negative electrode of the waste ternary lithium battery, separating and pre-treating it to obtain graphite powder;

[0085] (2) mixing the graphite powder and the combined stripping agent, grinding the mixture, passing through a 200-mesh sieve, and then calcining the mixture once at 400° C. for 12 h in an oxygen-containing atmosphere to obtain stripped graphite powder; the mass ratio of the combined stripping agent to the graphite powder is 0.2:1; the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 0.3:1; the inorganic stripping agent is potassium perchlorate, and the organic stripping agent is disodium phenyl phosphate;

[0086] (3) grinding the exfoliated graphite powder and then performing ultrasonic dispersion treatment at 80° C. for 4 h in a polyvinyl pyrrolidone solution containing a dispersant having a mass concentration of 5 wt % at a solid-liquid ratio of 0.1 g / mL to obtain dispersed graphite powder; the dispersant is sodium benzoylthioethane sulfonate;

[0087] (4) The dispersed graphite powder, asphalt and dopant dicyandiamide are uniformly mixed in a mass ratio of 0.03:1:0.05, and then thermally polymerized under an inert atmosphere of 1 MPa and 400°C for 6 hours to obtain mesophase carbon microspheres; the asphalt is an asphalt raw material in which the light component and insoluble matter obtained by dispersing petroleum asphalt in toluene and removing quinoline at 150°C are mixed in a ratio of 1:0.1;

[0088] (5) The mesophase carbon microspheres are mixed with the oxidizing agent nitric acid in a mass ratio of 1:1.1, and then subjected to secondary calcination to obtain a regenerated graphite material; the secondary calcination includes carbonization calcination and graphitization calcination, the carbonization calcination temperature is 900°C, the time is 10 hours, and the graphitization calcination temperature is 1900°C, and the time is 15 hours.

[0089] Example 4

[0090] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 1.2:1.

[0091] Example 5

[0092] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 1:1.

[0093] Example 6

[0094] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 0.8:1.

[0095] Example 7

[0096] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 0.5:1.

[0097] Example 8

[0098] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the combined stripping agent includes an inorganic stripping agent and an organic stripping agent, and the mass ratio of the two is 0.3:1.

[0099] Example 9

[0100] An embodiment of the method for recycling battery negative electrode graphite and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the inorganic stripping agent is boric acid and the organic stripping agent is 4-formylphenylboric acid.

[0101] Example 10

[0102] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from embodiment 1 only in that the inorganic stripping agent is ammonium molybdate and the organic stripping agent is 4,4'-biphenyldiboric acid.

[0103] Example 11

[0104] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the inorganic stripping agent is sodium chlorate and the organic stripping agent is 3-aminobenzenesulfonic acid.

[0105] Example 12

[0106] An embodiment of the battery negative electrode graphite recovery method and the regenerated graphite material prepared therefrom and its application according to the present invention differs from Example 1 only in that the inorganic stripping agent is potassium perchromate and the organic stripping agent is phenyl phosphate.

[0107] Comparative Example 1

[0108] A method for recycling battery negative electrode graphite, a regenerated graphite material prepared therefrom, and its application, differing from Example 1 only in that, in step (2), the graphite powder is directly ground and then passed through a 200-mesh sieve, followed by a single calcination at 650° C. for 6 h in an oxygen-containing atmosphere to obtain exfoliated graphite powder. No combined exfoliating agent is added in this step.

[0109] Comparative Example 2

[0110] A method for recycling battery negative electrode graphite and the regenerated graphite material prepared therefrom and its application, the difference from Example 1 being that the combined stripping agent is replaced with an equal mass of pure inorganic stripping agent ammonium pyrosulfate, and no organic stripping agent is added.

[0111] Comparative Example 3

[0112] A method for recycling battery negative electrode graphite and the recycled graphite material prepared therefrom and its application, the only difference from Example 1 being that the combined stripping agent is replaced with an equal mass of pure organic stripping agent 1,4-diphenylboric acid, and no inorganic stripping agent is added.

[0113] Comparative Example 4

[0114] A method for recycling battery negative electrode graphite and a regenerated graphite material prepared therefrom and its application, the difference from Example 1 being that the step (3) is: grinding the exfoliated graphite powder and then ultrasonically dispersing it in water at 120° C. for 8 h at a solid-liquid ratio of 0.5 g / mL to obtain dispersed graphite powder.

[0115] Comparative Example 5

[0116] A method for recycling battery negative electrode graphite, and a regenerated graphite material prepared therefrom and its application, the difference from Example 1 being that the step (4) comprises: uniformly mixing the dispersed graphite powder and asphalt in a mass ratio of 0.15:1, and then performing a thermal polymerization reaction under an inert atmosphere of 1 MPa and 450°C for 10 hours to obtain mesophase carbon microspheres; the asphalt is an asphalt raw material obtained by dispersing petroleum asphalt with quinoline and removing quinoline at 150°C, and mixing the light components and insoluble matter in a ratio of 1:0.1.

[0117] Comparative Example 6

[0118] A method for recycling battery negative electrode graphite and a regenerated graphite material prepared therefrom and its application, the difference from Example 1 being that in step (5), the mesophase carbon microspheres are not mixed with an oxidant and are directly subjected to secondary calcination to obtain the regenerated graphite material.

[0119] Effect Example 1

[0120] In order to verify the use effect of the recycled graphite materials obtained by the recycling methods described in the present invention, each product was used to prepare lithium-ion half-cells for electrochemical performance testing:

[0121] (1) The regenerated graphite material obtained in each embodiment / comparative example was mixed with polyacrylic acid and conductive carbon black in water at a mass ratio of 8:1:1, and then ball milled at 180 rpm for 4 h to obtain a negative electrode slurry;

[0122] (2) The negative electrode slurry was coated on copper foil and vacuum dried at 100°C for 12 hours, and then cut into circular negative electrode sheets with a diameter of 12 mm. The active material weight of the sheet was 1.2 to 1.5 mg. Subsequently, a metal lithium sheet was used as the counter electrode sheet, a commercial polypropylene diaphragm was used as the diaphragm, and a mixed solution of dimethyl carbonate and ethylene carbonate containing 1M lithium hexafluorophosphate (LiFP6) was used as the electrolyte (the volume ratio of dimethyl carbonate to ethylene carbonate was 1:1). The cells were assembled into button-type lithium-ion half-cells in a vacuum glove box and allowed to stand.

[0123] (3) Carry out 100 charge and discharge tests at a rate of 0.1C within the voltage range of 0.01 to 3 V, record the first discharge specific capacity and the discharge specific capacity at the 100th charge and discharge test, and calculate the cycle capacity retention rate.

[0124] At the same time, the same test was performed using commercially available conductive graphite powder as a control material.

[0125] The test results are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] It can be seen from the results that the recycled graphite material obtained by the recycling method described in each embodiment has ideal electrochemical properties when directly used in lithium-ion secondary batteries. It not only has a high discharge capacity but also has good cycle stability. This is mainly due to the repair and regeneration of waste graphite by the recycling method described in the present invention. Figures 5-7 Scanning electron microscopy of the exfoliated graphite powder prepared in Examples 1 to 3 shows that after effective exfoliation by the combined exfoliating agent, graphene / graphene-like sheet structures appear in the graphite powder with larger interlayer spacing, while the exfoliated graphite powder prepared by the method of Comparative Examples 1 to 3 without using the combined exfoliating agent or using only one exfoliating agent is as shown in FIG. Figures 8-10 As shown, the product has no obvious lamellar structure or the degree of lamellar structure peeling is low; then Figures 11-13 As shown in FIG. 1 , the interparticle spacing of the dispersed graphite powder obtained in Examples 1 to 3 after the dispersion treatment using a dispersant is further increased, and an obvious highly dispersed lamellar structure can be observed. However, the dispersed graphite powder prepared by the method described in Comparative Example 4 using only water as the dispersion liquid is as shown in FIG. Figure 14 As shown, the flakes of the product are not dispersible due to reagglomeration; the graphite powders dispersed in Examples 1 to 3 are further subjected to thermal polymerization to form mesophase carbon microspheres as shown in FIG. Figures 15-17 As shown in FIG, these products have distinct particles and uniform size, while the mesophase microspheres prepared in Comparative Examples 1 to 3 are as follows. Figures 18-20 As shown in FIG, the morphology is not clear, and even no obvious spherical structure is observed in Comparative Example 1; Finally, after the second calcination, the regenerated graphite materials prepared in Examples 1 and 2 are as follows Figures 21-22 As shown in FIG, it can be seen that all materials exhibit obvious particle dispersion, among which Example 1 has the best quality, while Comparative Examples 5 and 6 do not introduce dopants and oxidants during the preparation process, and the particle sphericity of the products is relatively low. Figure 23 and 24As shown in the results, the electrochemical performance of these comparative products is also poor.

[0130] The performance results of the products in Examples 1 and 4-12 demonstrate that the type and ratio of inorganic and organic strippers used in combined stripping have a certain impact on the morphology of the prepared products. This is because the stripping mechanisms of the two strippers are different, yet they act together on the graphite powder. These morphological differences can also lead to differences in the rate and efficiency of lithium deintercalation in the prepared regenerated graphite materials, resulting in different electrochemical properties.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of this article may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of this article.

Claims

1. A method for recycling battery negative electrode graphite, characterized in that: The following steps are involved: Separating waste graphite from the negative electrode of waste batteries to obtain graphite powder; The graphite powder and the combined stripping agent are mixed, ground, sieved, and then calcined once at 400-650° C. to obtain stripped graphite powder; the combined stripping agent comprises an inorganic stripping agent and an organic stripping agent, the inorganic stripping agent comprises at least one of perchloric acid and its salts, sodium chlorate, potassium permanganate, ammonium pyrosulfate, potassium perchromate, boric acid, and potassium molybdate; the organic stripping agent comprises at least one of phenylboric acid and its derivatives, benzenesulfonic acid and its derivatives, and phenylphosphoric acid and its derivatives; Grinding the exfoliated graphite powder and dispersing it in a solution containing a dispersant at 80-120° C. to obtain dispersed graphite powder; The dispersed graphite powder, asphalt and dopant are uniformly mixed, and then subjected to thermal polymerization at 400-450° C. to obtain mesocarbon microspheres; The dopant contains at least one of nitrogen, sulfur, phosphorus and boron; The mesocarbon microspheres are mixed with an oxidant, and then subjected to secondary calcination at 700-2600° C. to obtain a regenerated graphite material.

2. The method for recycling battery negative electrode graphite according to claim 1, wherein: The waste batteries include at least one of waste ternary lithium batteries, waste lithium iron phosphate batteries, waste lithium manganese iron phosphate batteries, waste lithium cobalt oxide batteries, and waste lithium manganese oxide batteries.

3. The method for recycling battery negative electrode graphite according to claim 1, wherein: The perchloric acid and its salts include at least one of perchloric acid, potassium perchlorate, and ammonium perchlorate; And / or, the phenylboronic acid and its derivatives include at least one of 1,4-diphenylboronic acid, 4-formylphenylboronic acid, 4,4'-biphenyldiboronic acid, 3,5-dimethoxyphenylboronic acid, triphenyl borate, and 3-aminophenylboronic acid hemisulfate; And / or, the benzenesulfonic acid and its derivatives include at least one of 3-aminobenzenesulfonic acid, 4-hydroxybenzenesulfonic acid, and aminobenzenesulfonic acid; And / or, the phenylphosphoric acid and its derivatives include at least one of disodium phenyl phosphate, phenyl phosphate, phenyl diaminophosphate, diphenyl aminophosphate, and aniline sulfate.

4. The method for recovering battery negative electrode graphite according to claim 1 or 3, wherein: The inorganic stripping agent is at least one of ammonium pyrosulfate, boric acid, and potassium molybdate, and the organic stripping agent is at least one of 1,4-diphenylboric acid, 4-formylphenylboric acid, 4,4'-biphenyldiboric acid, 3,5-dimethoxyphenylboric acid, and triphenyl borate.

5. The method for recycling battery negative electrode graphite according to claim 1, wherein: The mass ratio of the combined stripping agent to the graphite powder is (0.2-0.8):

1. In the combined stripping agent, the mass ratio of the inorganic stripping agent to the organic stripping agent is (0.3-1.4):

1.

6. The method for recycling battery negative electrode graphite according to claim 1, wherein: The dispersant includes at least one of pyrrolidone, polyvinylpyrrolidone, sodium 4-hydroxybenzenesulfonate, sodium 3-carboxylbenzenesulfonate, sodium 3-aminobenzenesulfonate, sodium 4-vinylbenzenesulfonate, sodium benzoylthioethanesulfonate, polyisopropylacrylamide, methylcellulose, sodium dodecylbenzenesulfonate, cetylpyridinium chloride, 3-benzylidenebutamide, benzylsulfonamide, p-carboxylbenzenesulfonamide, phenoxyacetamide, and polystyrene, and the solvent in the solution containing the dispersant is water and / or an organic solvent.

7. The method for recycling battery negative electrode graphite according to claim 1, wherein: The mass ratio of the dispersed graphite powder, asphalt and dopant is (0.03-0.15):1:(0.05-0.25); the asphalt includes at least one of petroleum asphalt, coal asphalt and coal tar; the dopant includes at least one of melamine, pyridine, pyrrole, urea, dicyandiamide, thiourea, phosphorus pentoxide and boric acid.

8. The method for recycling battery negative electrode graphite according to claim 1, wherein: The oxidant includes at least one of air, O2, SO2, NO2, sodium dihydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, sodium hypophosphite, KMnO4, H2O2, and HNO3; the secondary calcination includes carbonization calcination and graphitization calcination, the carbonization calcination temperature is 700-900°C, and the time is 10-12h; the graphitization calcination temperature is 1900-2600°C, and the time is 10-15h.

9. The regenerated graphite material prepared by the method for recycling battery negative electrode graphite according to any one of claims 1 to 8.

10. A secondary battery, characterized in that: The negative electrode comprises a negative electrode plate, wherein the negative electrode plate comprises a regenerated graphite material prepared by the method for recycling battery negative electrode graphite according to any one of claims 1 to 8 or the regenerated graphite material according to claim 9.

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