Method for manufacturing battery-grade graphite using a mixed waste of a damaged lithium-ion battery's cathode material and anode material as a raw material

Abstract

The present invention provides a method for efficiently recovering and regenerating battery-grade graphite by using a mixed waste of a damaged lithium-ion battery's positive electrode material and negative electrode material as a raw material. 【Solution means】 Put the mixed waste of the damaged lithium-ion battery's positive electrode material and negative electrode material into a muffle furnace, perform low-temperature roasting surface modification to remove the adhesive and residual electrolyte from the surface of the electrode material, and obtain a powder; introduce the obtained powder into a flotation machine, add clean water, and stir the slurry to improve the subsequent flotation separation effect of the positive electrode material and negative electrode material. Based on the difference in hydrophilicity and hydrophobicity between the positive electrode material and negative electrode material, separate the positive electrode material and negative electrode graphite by flotation to generate a foamed product (material rich in negative electrode graphite) and an ore slurry product (material rich in positive electrode material). Wash the foamed product with weak acid, filter, dry, and then perform repair at high temperature to obtain a graphite product with excellent electrochemical properties. By performing low-temperature roasting surface modification, flotation separation, weak acid washing, and high-temperature graphitization repair, the negative electrode graphite in the mixed waste of the positive electrode material and negative electrode material is regenerated.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing battery-grade graphite, which uses a mixed waste of a positive electrode material and a negative electrode material of a damaged lithium-ion battery as a raw material in the field of recycling of waste lithium-ion battery materials.

Background Art

[0002] Since lithium-ion batteries were developed and used in the 1990s, lithium-ion batteries have many advantages such as high energy density, light weight, long life, no memory effect, and environmental friendliness, and have been widely used in portable electronic devices such as mobile phones, notebook computers, and cameras. In recent years, with the popularization of new energy vehicles, the production volume of lithium-ion batteries has been increasing year by year, and the time for a large amount of waste lithium-ion batteries has arrived. Used lithium-ion batteries contain a large amount of precious metals such as nickel, cobalt, manganese, lithium, copper, and aluminum. Furthermore, organic substances such as residual electrolytes and adhesives contained in used lithium-ion batteries, and heavy metals such as nickel, cobalt, and manganese may severely pollute the environment. Therefore, how to effectively recover and process used lithium-ion batteries has become a serious problem for resource recycling and environmental protection.

[0003] In order to realize the recycling of used lithium-ion batteries, many studies have been conducted. First, after disassembling, discharging, mechanically destroying, and sorting waste lithium-ion batteries, a mixed waste of the positive electrode and the negative electrode is generated (mainly positive electrode materials (such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, etc.), negative electrode materials (graphite), a small amount of copper, aluminum, adhesives, residual electrolytes). Then, the waste is put into an acidic solution to recover high-value metals such as nickel, cobalt, manganese, and lithium contained in the positive electrode material. In the existing methods, the main focus is on the recovery of metal elements contained in the positive electrode material of the waste, and the recycling of graphite contained in the negative electrode material is neglected.

[0004] In fact, graphite is widely used in many fields such as refractory materials, conductive materials, corrosion-resistant materials, high-temperature metallurgical materials, adsorption materials, battery materials, etc., and it is a kind of important strategic mineral resources. A large amount of graphite contained in damaged lithium-ion batteries cannot be recycled, which not only causes waste of resources but also leads to environmental pollution.

[0005] Currently, researchers are gradually beginning to focus on the problem of graphite recycling.

[0006] For example, Cao et al. used the methods of acid leaching and alkali extraction to recover graphite and manufactured it into electrode materials for treating BPA and COD in organic wastewater, and the removal rates are 100% and 87.4% respectively. Zhang et al. used concentrated nitric acid and magnesium nitrate to carry magnesium ions on waste graphite and adsorb precipitated phosphate in aqueous solution, and the phosphate removal rate was 95%.

[0007] Zhao et al. used potassium permanganate and nitric acid to graft-polymerize manganese dioxide onto graphite, and used this modified graphite for heavy metal water treatment. The removal rates of Pb, Cd, and Ag were 99.9%, 79.7%, and 99.8% respectively.

[0008] In the above research, the utilization of graphite resources as materials has been realized. However, even in the case of catalyst materials and adsorption materials, the graphite only functions as a carrier, the market demand is small, and it is difficult to obtain a large amount of graphite from damaged lithium-ion batteries. Recycling graphite using repair means and reusing it in lithium-ion batteries is an ideal solution to the problem of waste graphite.

[0009] Ruan et al. process waste graphite by acid leaching, heat treatment, and coating. The recycled graphite has a small specific surface area, reduced pore defects, a high degree of graphitization, and excellent electrochemical properties. However, this method uses a large amount of acid, resulting in high costs and generating a large amount of waste acid in the recovery process, which is harmful to the environment. Chinese Patent Publication No. 11192483 (CN 111924836 A) reports a method for recovering and recycling the graphite anode of used lithium-ion batteries. The waste lithium-ion battery is discharged and disassembled to obtain the anode plate. After drying the anode plate, it is knocked to separate the waste graphite from the copper foil. Next, the graphite is roasted in two stages to convert the organic components in the graphite into amorphous carbon. Based on the transport characteristics of lithium atoms at various temperatures, prelithiation (preliminary lithiumation) of the graphite is achieved to obtain prelithiated graphite. Furthermore, the prelithiated graphite is uniformly mixed with an organic mixed carbon source and roasted in a rotary furnace to obtain a recycled graphite anode material. This method has a simple process and short working hours and does not use acid or alkaline solutions. However, careful disassembly is required to obtain the anode plate, and the recovery rate of waste graphite is low by knocking the electrode plate. In low-temperature restoration, the amorphous carbon generated by roasting the organic components cannot be converted into a graphite structure with good electrochemical properties, and the electrochemical properties are affected.

[0010] According to Chinese Patent No. 107887666 (CN 107887666 B), the waste lithium-ion battery anode plate is mixed with a separating agent to obtain the initial product of the anode graphite and copper foil. Furthermore, the initial graphite product is leached by organic acid reduction to obtain high-purity graphite powder, and the graphite powder is graphitized and recycled to produce a graphite material. The separating agent and leaching agent used in this method can be reused by distillation and recovery, which is economical and environmentally friendly. However, the interlayer spacing of the graphite may increase due to organic acid leaching, resulting in a decrease in the degree of graphitization and potentially affecting the electrochemical properties of the recycled graphite.

[0011] Although certain progress has been made in the field of graphite regeneration according to the above research, these methods mainly aim at the recovery of waste negative electrode plates after careful disassembly, and a method for recovering graphite from mixed waste materials of positive and negative electrodes has not yet been developed.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0013] Therefore, an object of the present invention is to provide a graphite regeneration method that performs low-temperature roasting surface modification treatment, flotation separation, weak acid washing, and high-temperature graphitization restoration on mixed waste of positive and negative electrodes, and efficiently recovers and regenerates graphite in the mixed waste of positive and negative electrodes.

[0014] In view of a series of problems in the prior art, such as the difficulty in treating mixed waste of positive and negative electrodes and the insufficient electrochemical properties of the recovered graphite, the present invention provides a method for regenerating graphite from mixed waste of positive and negative electrodes. The regeneration method of the present invention regenerates graphite for a lithium battery negative electrode material with excellent electrochemical properties through steps such as low-temperature roasting surface modification treatment, flotation separation of the positive electrode material and graphite, weak acid washing of graphite, and high-temperature reduction of graphitization. The method of the present invention is simple, efficient, clean, environmentally friendly, low-cost, and is easily suitable for industrial production.

Means for Solving the Problems

[0015] To achieve the above object of the present invention, the present invention provides a method for manufacturing battery-grade graphite using a mixed waste of a damaged positive electrode material and a negative electrode material of a lithium-ion battery as a raw material.

[0016] The method of the present invention comprises the following steps, namely A method for manufacturing battery-grade graphite using a mixed waste of a damaged (deteriorated) positive electrode material and a negative electrode material of a lithium-ion battery as a raw material, (1) A step of placing a mixed waste of a damaged positive electrode material and a negative electrode material of a lithium-ion secondary battery in a muffle furnace and performing low-temperature roasting surface modification in an air atmosphere to obtain a powder; (2) Adding clean water to the powder obtained in step (1) and stirring to form a slurry, introducing the slurry into a flotation machine, adding a collector and a foaming agent to the slurry after stirring, and obtaining a foamed product (a material rich in negative electrode graphite) and an ore slurry product (a material rich in positive electrode material) by flotation separation; (3) After filtering and drying the foamed product obtained in step (2), adding sulfuric acid and hydrogen peroxide at a predetermined concentration to perform weak acid washing, obtaining a leachate and a leach residue by filtration, drying the leach residue, and obtaining negative electrode graphite; (4) After filtering and drying the negative electrode graphite obtained in step (3), putting it into a high-temperature graphitization furnace and performing oxygen-free heating to obtain a regenerated graphite product. It is characterized by including the above steps.

[0017] In the present invention, it is preferable that the above positive electrode waste contains one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, and ternary materials (lithium nickel cobalt manganate).

[0018] In the present invention, for the low-temperature roasting modification treatment in step (1), it is preferable that the heating rate is 5-20 °C / min, the roasting temperature is 400-600 °C, and the heat preservation time is 10-60 minutes.

[0019] In the present invention, in the slurry stirring process of the above step (2), it is preferable that the slurry mass concentration is 20 - 25%, the stirring rotation speed is 1500 - 2000 r / min (rpm, revolutions per minute), and the time is 5 - 20 minutes.

[0020] In the present invention, for the flotation process of the above step (2), it is preferable to use a flotation open circuit with one rough separation and two fine separations (microscopic separations).

[0021] In the present invention, in the flotation process of the above step (2), as the collector, any one or a combination of two or more of n - dodecane, kerosene, light oil, and sodium dodecyl sulfate is used, and as the foaming agent, any one or a combination of two or more of methyl isobutyl carbinol (MIBC), No. 2 oil, and secondary octanol is preferably used.

[0022] In the present invention, as the conditions of the flotation conditions in the above step (2), pH = 7 - 11, the addition amount of the collector for rough separation is 200 - 1000 g / t, the addition amount of the foaming agent for rough separation is 50 - 500 g / t. During fine separation, only the foaming agent is added, and the first addition amount of the foaming agent for fine separation is 50 - 100 g / t, and the second addition amount of the foaming agent for fine separation is 25 - 50 g / t, which is preferable.

[0023] In the present invention, in the weak acid cleaning process of step (3), it is preferable that the liquid - solid ratio is 10 - 30, the sulfuric acid concentration is 0.01 - 0.2 mol / L, the hydrogen peroxide consumption is 3 - 5 times the theoretical value, the temperature is 50 - 100 °C, and the time is 0 - 100 minutes.

[0024] In the present invention, it is preferable that in the foaming product after flotation separation in the above step (2), the graphite grade > 95%, the graphite recovery rate > 65%, and the recovery rate of the positive electrode material in the ore slurry product > 97%.

[0025] In the present invention, in the graphitization repair process of step (4), it is preferable that the heating rate is 5 - 20 °C / min, the repair temperature is 1300 - 2800 °C, the heat - preservation time is 2 - 10 hours, and the graphitization degree of the repaired product is 90 - 99%.

Brief Description of the Drawings

[0026] To more clearly explain the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly described below. It goes without saying that the drawings in the following description are only some embodiments of the present invention.

Figure 1

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Figure 11

Embodiments for Carrying Out the Invention

[0027] According to the present invention, a method for recycling / reusing waste graphite negative electrode materials using the positive and negative electrode mixed waste of damaged lithium-ion batteries is obtained.

[0028] By means of low-temperature roasting surface modification of the mixed waste of the positive electrode material and the negative electrode material of the present invention, the adhesive and residual electrolyte are removed from the surface of the electrode material, and the difference in hydrophilicity and hydrophobicity between the waste of the positive electrode material and the negative electrode material becomes larger, forming favorable conditions for subsequent flotation separation. By stirring the slurry, the positive electrode material and the negative electrode material are dissociated from each other, the adhesion effect between particles is reduced, and the subsequent flotation separation effect is improved. By adding a flotation agent, the slurry flotation environment is improved, and the difference in hydrophilicity and hydrophobicity between graphite, the positive electrode material, and impurities becomes even larger, and the positive electrode material and the negative electrode material are effectively separated and recovered. By weak acid washing treatment, the impurities remaining in the graphite are further purified. By subjecting the recovered graphite to high-temperature graphitization, the fine morphology and layered structure on the graphite surface are restored, and the performance of the graphite product is improved.

[0029] Compared with the prior art, the present invention has the following advantages. (1) The present invention effectively and cleanly separates the positive and negative electrodes of used lithium-ion batteries through low-temperature roasting modification and flotation separation, providing a good basis for the recovery and regeneration of graphite in the mixed waste of used lithium-ion batteries. (2) Throughout the entire recovery and regeneration process, the consumption of acid is extremely low, not only low-cost, clean, and environmentally friendly, but also preventing strong acids and strong alkalis from damaging the graphite structure, so the recovered and regenerated graphite has excellent electrochemical properties. (3) Through high-temperature graphitization treatment, the fine morphology and layered structure on the graphite surface are restored, and the electrochemical properties of the graphite are recovered.

[0030] The battery-grade graphite produced using the mixed waste of the damaged positive and negative electrode materials of the lithium-ion battery of the present invention as raw materials can be used in button batteries, and its composition includes a lithium-ion positive electrode material, a suitable electrolyte, a separator, and the regenerated battery-grade graphite material of the present invention.

[0031] The battery-grade graphite produced using the mixed waste of the damaged positive and negative electrode materials of the lithium-ion battery of the present invention as raw materials is suitable for the manufacture of the power sources of lithium-ion batteries, energy storage devices of electronic products, industrial battery energy storage devices, electric vehicles, or electric bicycles. Electronic products include mobile phones, cameras, laptops, tablets, portable (portable) power tools, etc. Industrial batteries are wind energy, solar energy storage devices, and standby power sources.

Example

[0032] To clarify the problems, solutions, and advantages (effects of the invention) of the present invention, the present invention will be described in more detail below with reference to the drawings through specific embodiments and comparative examples.

[0033] [Example 1] The present invention provides a method for manufacturing battery-grade graphite using the mixed waste of damaged cathode and anode materials of lithium-ion batteries as raw materials. The raw materials are purchased on the market and are the mixed waste of the cathode and anode of damaged ternary lithium-ion batteries represented by BM-NT, and this method includes the following steps. (1) The mixed waste of the cathode material and anode material of the damaged lithium-ion secondary battery is subjected to low-temperature roasting at 400 °C for 20 minutes in an air atmosphere to obtain a powder designated as BM-T. (2) Clean water is added to the above powder and mixed to form a 21% by mass slurry, and the slurry is introduced into an XFD IV 1.5L flotation machine for laboratory use. (3) The specific flotation treatment parameters are as follows. Ore slurry pH = 10.68, Air filling amount: 0.4m 3 / hour, Initial rough separation and slurry stirring operation: 10 minutes, Subsequently added collector n-dodecane addition amount: 500 g / t, Foaming agent MIBC addition amount: 300 g / t, Scraping foam: 3 minutes, Initial cleaning and stirring operation: 5 minutes, Subsequent addition amount of foaming agent MIBC: 75 g / t, Scraping foam: 2 minutes. Through an open-circuit flotation operation of one rough separation operation and two cleaning separation operations, a foaming product and an ore slurry product are obtained. The graphite grade in the foaming product is 95.13%, the graphite recovery rate is 69.60%, the cathode material grade in the ore slurry product is 87.5%, and the cathode material recovery rate is 97.31%. (4) After the foaming product is filtered and dried, it is put into a high-temperature graphitization furnace and heated to 2800 °C at a heating rate of 12 °C / min for 4 hours in an oxygen-free environment. The graphite product obtained after recovery and repair is 2800-TF-K.

[0034] The CR2016 type button lithium-ion battery was assembled as follows. That is, the recovered and repaired graphite material 2800-TF-K described above was electrochemically tested. The recovered and repaired graphite material, acetylene black, and carboxymethyl cellulose solution were uniformly mixed at a mass ratio of 8:1:1, applied to a copper foil, pressed into a circular thin plate with a diameter of 6-8 mm, and dried in a vacuum drying box to obtain an electrode. A solution prepared by mixing LiPF6 at 1 mol / L in EC and DMC (volume ratio 1:1) was used as the electrolyte, glass fiber was used as the separator, and a metal lithium plate was used as the counter electrode. A CR2016 type button lithium-ion battery was fabricated in a glove box filled with argon gas.

[0035] After the battery was assembled, a constant current charge-discharge test was performed using a Land battery test device at a temperature of 25°C and a test voltage range of 0.01-2.0 V. The test contents included the cycle performance at a 0.2C rate for 100 cycles, the cycle performance at a 1C rate for 350 cycles, and the rate capability (0.1C, 0.2C, 0.5C, 1C, 2C, 5C).

[0036] Figure 1 is a scanning electron microscope photograph of the graphite product 2800-TF-K. From A1-A2 in Figure 1, it can be seen that the graphite in the flotation concentrate TFK contains a small amount of ternary substances. Also, from B1-B2 in Figure 1, it can be seen that the surface impurities of the graphite after graphitization treatment at 2800°C are significantly reduced, and the layered structure of the graphite is clear.

[0037] Figure 7 shows the X-ray diffraction (X-rd) spectrum of the recovered and repaired graphite obtained by the method of the present invention. The graphite peak of the graphite product 2800-TF-K is clearly shown, and basically no other impurity peaks exist. Further, as described in Table 1, the half-value width of 2800-TF-K decreases, and the graphite unit cell crystal spacing becomes smaller. The graphitization degree is 99.02%, indicating that the crystal structure of graphite was well repaired during the recovery process. Table 2 shows the elemental composition analysis of the recovered graphite according to the present invention. Since the purity of 2800-TF-K reaches 99.92% and it contains almost no metal impurities, it can be seen that the purity of graphite is good in the recovery process.

[0038] Figure 11 shows the test charts of 100 cycles and 350 cycles respectively under the constant current charge and discharge conditions of 0.2C and 1C, and the rate test chart of the button battery manufactured from the recovered and repaired graphite obtained in the present invention. Under the condition of 0.2C, the discharge capacity of the graphite product 2800-TF-K reaches 371 mAh / g, the capacity retention rate exceeds 99.99%, under the condition of 1C, the discharge capacity reaches 354 mAh / g, the capacity retention rate exceeds 99.99%, and the initial Coulomb efficiency is 93.38%.

[0039] [Example 2] The waste used in this example is the same as that in Example 1, and the method of this example includes the following steps. (1) 10 g of the froth product after flotation in Example 1 was taken and put into 300 ml of a sulfuric acid solution with a concentration of 0.1 mol / L, hydrogen peroxide four times the theoretical amount was added, and after leaching at 80 °C for 90 minutes, filtration was carried out to obtain a leachate and a leach residue. The leaching rates of lithium, nickel, cobalt, and manganese in the leachate are all close to 100%. (2) After drying the leach residue, it was put into a high-temperature graphitization furnace and heated in an oxygen-free environment to 2800 °C at a heating rate of 12 °C / min for 4 hours. The graphite product obtained after recovery and repair is 2800-LTFK.

[0040] Perform electrochemical tests on the recovered and repaired graphite material 2800-LNT. The method for assembling the button-type lithium-ion battery and the method for electrochemical tests used in this example are the same as those in Example 1.

[0041] Figure 2 is a scanning electron microscope photograph of the graphite product 2800-LTFK. From A1 - A2 in Figure 2, it can be seen that there are almost no metal impurities in LTFK after flotation and leaching, and a small amount of amorphous carbon exists on the graphite surface. Furthermore, from B1 - B2 in Figure 2, it can be seen that the impurities on the surface of 2800-LTFK after graphitization treatment at 2800 °C are significantly reduced, the content of amorphous carbon decreases, and the layered structure of graphite is clear.

[0042] Figure 7 is the X-ray diffraction (X-rd) spectrum of the recovered and repaired graphite obtained by the method of the present invention. The graphite peak of the graphite product 2800-LTFK is clearly shown, and other impurity peaks basically do not exist. From Table 1, the change in the interlayer spacing of graphite after weak acid washing is not large, and the graphitization degree of 2800-LTFK is 98.65%. That is, it can be seen that the damage to the graphite structure by weak acid washing is almost negligible.

[0043] Table 2 is the elemental composition analysis of the recovered graphite provided by the present invention. The purity of 2800-LTFK reaches 99.97%, and almost no metal impurities are contained, indicating that good purity of graphite is obtained by the recovery treatment.

[0044] Figure 11 shows the test charts of 100 cycles and 350 cycles respectively under the constant current charge and discharge conditions of 0.2C and 1C, and the rate test chart of the button battery manufactured from the recovered and repaired graphite obtained in the present invention. Under the condition of 0.2C, the discharge capacity of the graphite product 2800-LTFK reached 343.3 mAh / g, and the capacity retention rate exceeded 99.99%. Under the condition of 1C, the discharge capacity reached 270.2 mAh / g, the capacity retention rate exceeded 99.99%, and the initial Coulomb efficiency was 92.24%.

[0045] In this example, through flotation - weak acid washing, impurities in the recovered graphite are further removed, and valuable metals such as Ni, Co, Mn, and Li in the cathode material are completely recovered. At the same time, the use of weak acid washing prevents damage to the graphite structure by acid, and the repaired and regenerated graphite products have good electrochemical properties.

[0046] [Comparative Example 1] The waste used in this example (Comparative Example 1) is the same as that in Example 1, and this method includes the following steps. (1) Add clean water to the mixed waste BM - NT of the damaged cathode material and anode material of the lithium - ion secondary battery, mix to form a slurry of 50 - 70% by mass, put this slurry into a ball mill for ball - milling treatment for 5 minutes, and set the rotation speed to 65 - 75% of the critical rotation speed of the ball mill. (2) Add clean water to the raw material treated by the ball mill and mix to form a slurry of 21% by mass, and introduce the slurry into an XFD IV 1.5L laboratory flotation machine. (3) The specific flotation process parameters are as follows. Ore slurry pH = 10.68, Air filling volume: 0.4m 3 / hour, Dosage of dispersant sodium hexametaphosphate after stirring the slurry for 10 minutes: 1500g / t, Dosage of collector n - dodecane: 300g / t, Dosage of foaming agent MIBC: 50g / t, Skimming of foam: 0.4m 3 / hour: 300g / t, Dosage of foaming agent MIBC: 50g / t, Skimming of foam: 3 minutes, Generation of foaming products and ore slurry products, Graphite grade in the foaming product: 33.54%, Graphite recovery rate: 88.46%, Cathode material grade in the ore slurry product: 86.25%, Positive electrode material recovery rate: 33.63%.

[0047] From FIGS. 8(b), (c), (e), and (f), it can be seen that the contact angle of the froth product after flotation separation is significantly higher than that of the ore slurry product. The larger the contact angle, the stronger the hydrophobicity and the higher the buoyancy. As can be seen from the contact angles (a) and (d) shown in FIG. 7, the contact angle of the positive and negative electrode mixed waste of the damaged lithium-ion battery is 82.56°, the hydrophobicity is very strong, the buoyancy of the material is very high, and the contact angle of the waste (d) is close to that of the flotation froth product (e), indicating that the hydrophobicity and hydrophilicity of the concentrate and the raw ore are similar. Although the yield of the concentrate is very high, the flotation separation effect is not good. Through surface modification by low-temperature roasting, the contact angle of the waste decreases to 33.83°, the hydrophobicity decreases, and as a result, the buoyancy decreases. The roasted product undergoes flotation separation, and the difference in the contact angles of the raw ore, concentrate, and tailings is obvious, indicating that roasting effectively improves the flotation separation effect. Compared with Example 1, the graphite concentrate grade of 33.54% and the positive electrode material recovery rate of 33.63% after directly flotation separating the positive and negative electrode mixed waste of the damaged lithium-ion secondary battery without surface modification by low-temperature roasting are significantly lower than 95.13% and 97.31% of Example 1, and the separation effect is not good either.

[0048] [Comparative Example 2] (1) The mixed waste of the positive electrode material and negative electrode material of the damaged lithium-ion secondary battery is subjected to low-temperature roasting at 400°C for 20 minutes in an air atmosphere to obtain a powder designated as BM-T. (2) Clean water is added to the powder and mixed to form a 21% by mass slurry, and the slurry is placed in an XFD IV 1.5L laboratory flotation machine. (3) The specific flotation process parameters are as follows. Ore slurry pH = 10.68, Air filling amount: 0.4m 3 / hour, Dosage of collector n-dodecane after stirring the slurry for 10 minutes: 200 g / t, Dosage of foaming agent MIBC: 200 g / t, Skimming of foam: 3 minutes, Production of foamed product and ore slurry product Graphite grade of foamed product: 77.68% Graphite recovery rate: 48.62% Positive electrode material grade in ore slurry product: 78.83% Positive electrode material recovery rate: 91.17%

[0049] Compared with Example 1, the usage amounts of the current collector and the foaming agent are small, the recovery rates of both the positive electrode material and the negative electrode material are low, and the separation effect is not good enough

[0050] [Comparative Example 3] (1) Mixing waste of the positive electrode material and the negative electrode material of a damaged lithium-ion secondary battery is subjected to low-temperature roasting at 400 °C for 20 minutes in an air atmosphere to obtain a powder called BM-T (2) Add clean water to the powder and mix to form a 30% by mass slurry, and put the slurry into an XFD IV 1.5 L laboratory flotation machine (3) The specific flotation process parameters are as follows pH of ore slurry = 10.68 Air filling amount: 0.4 m 3 / h Dosage of collector n-dodecane after stirring the slurry for 10 minutes: 500 g / t Dosage of foaming agent MIBC: 300 g / t: 300 g / t Skimming of foam: 3 minutes Produce foamed product and ore slurry product Graphite grade of foamed product: 54.56% Graphite recovery rate: 93.23% Positive electrode material grade in ore slurry product: 96.33% Positive electrode material recovery rate: 76.12%

[0051] Compared with Example 1, since the flotation concentration is increased, a large amount of the positive electrode material is incorporated into the foamed product. As a result, the recovery rate of the positive electrode material is significantly lower than that of Example 1

[0052] [Comparative Example 4] (1) The mixed waste of the positive electrode material and the negative electrode material of the damaged lithium-ion secondary battery is subjected to low-temperature roasting at 400 °C for 20 minutes in an air atmosphere to obtain a powder called BM-T. (2) Add clean water to the powder and mix to form a 21% by mass slurry. The slurry is put into an XFD IV 1.5 L flotation machine for laboratory use, and sulfuric acid is added to adjust the pH of the ore slurry to 5, 7, and 9, respectively. (3) Other flotation process parameters are as follows. Air filling amount: 0.4 m 3 / hour, Dosage of collector n-dodecane after stirring the slurry for 10 minutes: 500 g / t, Dosage of foaming agent MIBC: 300 g / t, Skimming of foam: 3 minutes, Generation of foaming products and ore slurry products, The flotation indexes under different pH conditions are as shown in the following table. At natural pH, the separation effect between NCM and graphite is the most obvious, and the recovery rate of NCM is the highest.

[0053]

Table 1

[0054] [Comparative Example 5] (1) The mixed waste of the positive electrode material and the negative electrode material of the damaged lithium-ion secondary battery is subjected to low-temperature roasting at 400 °C for 20 minutes in an air atmosphere to obtain a powder called BM-T. (2) Add clean water to the powder and mix to form a 21% by mass slurry. The slurry is put into an XFD IV 1.5 L flotation machine for laboratory use. (3) Other flotation treatment parameters: pH = 10.78 (natural pH), Air filling amount: 0.4 m 3 / hour, After stirring the slurry for 10 minutes, add ethylenediaminetetraacetic acid (EDTA), Dosage of collector n-dodecane: 500 g / t, Dosage of foaming agent MIBC: 300 g / t, Skimming of foam: 3 minutes,

[0055] Generation of foamed products and ore slurry products, The flotation indices under various dosages of EDTA are as shown in the following table.

[0056] After adding EDTA, the graphite recovery rate does not change significantly, while the NCM recovery rate decreases significantly. Therefore, EDTA is not beneficial for the separation and recovery of graphite and NCM. In the present invention, in addition to EDTA, the effects of commonly used inhibitors of graphite ore such as tartaric acid, citric acid, and sodium hexametaphosphate on the separation of graphite and NCM are investigated.

[0057] As a result of the study, it was found that this series of compounds do not have a positive effect on the separation of the positive and negative electrode mixed waste of damaged lithium-ion batteries.

[0058] [Table 2]

[0059] [Comparative Example 6] The waste used in this example is the same as that in Example 1, and the method of the present invention includes the following steps. (1) Take 10 g of waste BM-NT and put it into 100 ml of sulfuric acid aqueous solution with a concentration of 4 mol / L, add hydrogen peroxide four times the theoretical amount, leach at 80 °C for 60 minutes, and then filter to obtain a leachate and a leach residue, so that the leaching rates of lithium, nickel, cobalt, and manganese in the leachate are all close to 100%. (2) After drying the leach residue, put it into a high-temperature graphitization furnace, heat it in an oxygen-free environment to 2800 °C at a heating rate of 12 °C / min for 4 hours. The graphite product obtained after recovery and repair is 2800-LNT.

[0060] An electrochemical test of the recovered and repaired graphite material 2800-LNT is carried out. The method for assembling the button-type lithium-ion battery and the electrochemical test method used in this example are the same as those in Example 1.

[0061] Figure 3 is a scanning electron microscope photograph of the graphite product 2800-LNT. From A1-2 in Figure 3, it can be seen that the interlayer opening phenomenon occurs in the acid-leached graphite material, and it also contains a lot of amorphous carbon. Also, from B1-2 in Figure 3, although the surface impurities of the graphite after graphitization treatment at 2800 °C are significantly reduced, amorphous carbon and acetylene black remain in 2800-LNT, which may have an adverse effect on its subsequent electrochemical properties.

[0062] Figure 7 is the X-ray diffraction (X-rd) spectrum of the recovered and repaired graphite according to the present invention. The graphite peak of the graphite product 2800-LNT is clearly shown, and other impurity peaks basically do not exist. From Table 1, it can be seen that the interlayer spacing of the graphite after acid leaching expands, and it is also difficult to completely repair by high-temperature graphitization. The graphitization degree of 2800-LNT is 98.06%, which is lower than 99.02% in Example 1. Figure 11 is the test chart of 100 cycles and 350 cycles under the constant current charge and discharge conditions of 0.2 °C and 1 °C, and the rate test chart of the button battery made from the recovered and repaired graphite obtained in the present invention. Under the condition of 0.2C, the discharge capacity of the graphite product 2800-LNT reaches 357 mAh / g, the capacity retention rate exceeds 99.99%, under the condition of 1C, the discharge capacity reaches 233.9 mAh / g, the capacity retention rate exceeds 99.99%, and the initial Coulomb efficiency is 86.56%.

[0063] Compared with Example 1, the graphitization degree of 2800-LNT decreased by 0.96%, the discharge capacity decreased by 14 mAh / g under the condition of 0.2C, the discharge capacity decreased by 120.1 mAh / g under the condition of 1C, and the initial Coulomb efficiency decreased by 6.82%.

[0064] [Comparative Example 7] The waste used in this example is the same as that in Example 1, and the method of the present invention includes the following steps. (1) The mixed waste of the positive electrode material and the negative electrode material of the damaged lithium-ion secondary battery is low-temperature roasted at 400 °C for 20 minutes in an air atmosphere to obtain a powder called BM-T. (2) 10 g of the powder raw material BM-T is collected and put into 100 ml of a sulfuric acid solution with a concentration of 4 mol / L, hydrogen peroxide three times the theoretical amount is added, and after leaching at 50 °C for 1 hour, filtration is carried out to obtain a leachate and a leach residue, and the leaching rates of lithium, nickel, cobalt, and manganese in the leachate are all close to 100%. (3) After drying the leach residue, it is put into a high-temperature graphitization furnace, and non-oxygen heating is carried out at a heating rate of 12 °C / min to 2800 °C for 4 hours. The graphite product obtained after recovery and repair is 2800-LT.

[0065] An electrochemical test of the recovered and repaired graphite material 2800-LT is carried out. The method for assembling the button-type lithium-ion battery and the electrochemical test method used in this example are the same as those in Example 1.

[0066] Figure 4 is a scanning electron microscope photograph of the graphite product 2800-LNT. From A1-2 in Figure 4, it can be seen that an interlayer opening phenomenon occurs in the acid-leached graphite material LT, and it also contains a lot of amorphous carbon. From B1-2 in Figure 4, it can be seen that the impurities on the surface of the graphite after graphitization treatment at 2800 °C are significantly reduced, but amorphous carbon and acetylene black remain in 2800-LT, which may have an adverse effect on the subsequent electrochemical properties.

[0067] Figure 7 is an X-ray diffraction (X-rd) spectrum of the recovered and repaired graphite according to the present invention. The graphite peak of the graphite product 2800-LT is clearly shown, and basically no other impurity peaks exist. From Table 1, the interlayer spacing of the graphite after acid leaching is enlarged, and it is also difficult to completely repair at high temperature. Through graphitization, the graphitization degree of 2800-LT is 98.61%, which is lower than 99.02% in Example 1.

[0068] Figure 9 shows the Raman spectra of the recovered graphite and the repaired and recycled graphite according to the present invention. The value I(D) / I(G) is used to indicate the proportion of amorphous carbon in the sample. From the figure, it can be seen that the directly leached and recovered graphite LT has a higher amorphous carbon content than the graphite TFK recovered by the flotation method. Although the amorphous carbon content of the graphite product 2800-LT after high-temperature graphitization repair has decreased, it is still significantly higher than that of the graphite product 2800-TFK, and it can be understood that amorphous carbon may have an adverse effect on subsequent electrochemical properties.

[0069] Figure 10 shows the TG-DTA analysis results of the recovered graphite according to the present invention. The thermogravimetric behavior of LT and TFK before 800 °C is mainly divided into three stages. The first stage is the thermogravimetric loss of a small amount of adhesive that was not removed by low-temperature roasting, and the second and third stages are mainly the thermogravimetric loss of the carbon material. When comparing the second stage of LT and TFK, the mass loss of LT is 12.57%, which is higher than 7.18% of TFK.

[0070] Amorphous carbon is structurally unstable, and its combustion temperature is lower than that of structurally stable graphite.

[0071] Figure 11 shows the test charts of 100 cycles and 350 cycles respectively under the constant current charge and discharge conditions of 0.2C and 1C, and the rate test chart of the button battery manufactured from the recovered and repaired graphite obtained in the present invention; under the condition of 0.2C, the discharge capacity of the graphite product 2800-LNT reaches 380.2 mAh / g, and the capacity retention rate is 99.61%. Under the condition of 1C, the discharge capacity reaches 285.6 mAh / g, the capacity retention rate exceeds 99.99%, and the initial Coulomb efficiency is 88.65%.

[0072] Compared with Example 1, the graphitization degree of 2800-LT decreased by 0.41%, the discharge capacity decreased by 68.4 mAh / g under the condition of 1C, and the initial Coulomb efficiency decreased by 4.73%.

[0073] [Comparative Example 8] The waste used in this example is the same as that in Example 1, and the method of the present invention includes the following steps. (1) The foamed product after flotation in Example 1 is filtered and dried to obtain a powder. (2) After drying the leaching residue, it is placed in a tubular furnace and heated in an oxygen-free atmosphere to 1400 °C at a heating rate of 10 °C / min for 4 hours. The graphite product obtained after recovery and repair is 1400-TF-K.

[0074] Electrochemical tests are performed on the recovered and repaired graphite material 1400-TF-K. The method for assembling the button-type lithium-ion battery and the electrochemical test method used in this example are the same as those in Example 1.

[0075] Figure 5 is a scanning electron microscope photograph of the graphite product 1400-TF-K. From Figure 5, it can be seen that the graphite in the flotation concentrate TFK contains a small amount of ternary substances and is reduced at high temperature to obtain metal spheres. At a high temperature of 1400 °C, the metal spheres cannot be removed, which may cause problems in the subsequent electrochemical properties.

[0076] Figure 7 is an X-ray diffraction (X-rd) spectrum of the recovered and repaired graphite according to the present invention. From the XRD graph, it can be seen that the graphite in the flotation concentrate TFK contains a small amount of ternary substances. After heat treatment at 1400 °C, the ternary substances are reduced to ternary metal alloys, but still act as impurities present in the graphite. The heat treatment at 1400 °C cannot effectively remove the impurities in the graphite. From Table 1, it can be seen that the graphitization degree of 1400-TF-K is 99.10%.

[0077] Table 2 is an elemental composition analysis of the recovered graphite according to the present invention. The purity of 1400-TFK is only 91.97%, and the residual metal impurities are mainly nickel at 2.88% and manganese at 3.47%. It can be seen that the heat treatment at 1400 °C cannot effectively remove the impurities in the graphite.

[0078] Figure 11 includes the test charts of 100 cycles and 350 cycles under the constant current charge and discharge conditions of 0.2C and 1C, and the rate test chart of the button battery manufactured from the recovered and repaired graphite obtained in the present invention.

[0079] Under the condition of 0.2C, the discharge capacity of the graphite product 1400-TF-K reaches 351.5 mAh / g, the capacity retention rate exceeds 99.99%, under the condition of 1C, the discharge capacity reaches 228.7 mAh / g, the capacity retention rate is 72.28%, and the initial Coulomb efficiency is 83.77%.

[0080] Compared with Example 1, the discharge capacity of 1400-TF-K under the 0.2C condition decreased by 19.5 mAh / g, the discharge capacity under the 1C condition decreased by 125.3%, and the initial Coulomb efficiency decreased by 9.61%.

[0081] The above embodiments are illustrative and do not mean that the present invention is limited to these embodiments. The present invention can also combine the technical features of different embodiments that can be appropriately changed within the scope not departing from the gist of the present invention, and the steps can be implemented in any order. In addition, there are many other variations of the different embodiments of the present invention as described above, but detailed descriptions are omitted for the purpose of simplification.

[0082] The embodiments of the present invention are intended to include all substitutions, changes, and variations included within the scope of the claims. Therefore, omissions, modifications, equivalent substitutions, or improvements made within the scope of the spirit and principles of the present invention shall be included in its protection scope.

[0083]

Table 3

[0084]

Table 4

[0085]

Table 5

[0086]

Table 6

Claims

1. A method for manufacturing battery-grade graphite using a mixed waste of a damaged lithium-ion battery's positive electrode material and negative electrode material as a raw material, comprising: (1) A step of putting the mixed waste of the positive electrode material and negative electrode material of a damaged lithium-ion secondary battery into a muffle furnace, performing low-temperature roasting surface modification in an air atmosphere, and obtaining powder; (2) Adding clean water to the powder obtained in step (1), stirring to form a slurry, introducing the slurry into a flotation machine, adding a collector and a foaming agent to the slurry after stirring, and obtaining a foamed product (material rich in negative electrode graphite) and an ore slurry product (material rich in positive electrode material) by flotation separation; (3) After filtering and drying the foamed product obtained in step (2), adding sulfuric acid and hydrogen peroxide at a predetermined concentration for weak acid washing, obtaining a leachate and a leach residue by filtration, drying the leach residue, and obtaining negative electrode graphite; (4) After filtering and drying the negative electrode graphite obtained in step (3), putting the negative electrode graphite into a high-temperature graphitization furnace for oxygen-free heating to obtain a regenerated graphite product. A method for manufacturing battery-grade graphite, characterized by comprising the above steps.

2. The method for manufacturing battery-grade graphite according to Claim 1, wherein the positive electrode waste of the damaged lithium-ion battery contains one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, and ternary materials (lithium nickel cobalt manganese oxide).

3. The method for manufacturing battery-grade graphite according to Claim 1 or 2, wherein in the low-temperature roasting surface modification treatment, the heating rate is 5-20 °C / min, the roasting temperature is 400-600 °C, and the heat preservation time is 10-60 minutes.

4. The method for manufacturing battery-grade graphite according to Claim 1 or 2, wherein in the slurry stirring treatment, the slurry mass concentration is 20-25%, the stirring rotation speed is 1500-2000 revolutions / min, and the time is 5-20 minutes.

5. The method for manufacturing battery-grade graphite according to Claim 1 or 2, wherein the flotation separation treatment uses a flotation open circuit with one rough separation and two fine separations.

6. In the flotation separation process, any one or a combination of two or more of n-dodecane, kerosene, light oil, and sodium dodecyl sulfate is used as a collector, and any one or a combination of two or more of methyl isobutyl carbinol (MIBC), No. 2 oil, and secondary octanol is used as a foaming agent. The method for manufacturing battery-grade graphite according to claim 1 or 2, characterized in that.

7. The flotation conditions are the following conditions, that is, pH = 7 to 11, the addition amount of the collector for rough separation is 200 to 1000 g / t, the addition amount of the foaming agent for rough separation is 50 to 500 g / t. During fine separation, only the foaming agent is added. The first addition amount of the foaming agent for fine separation is 50 to 100 g / t, and the second addition amount of the foaming agent for fine separation is 25 to 50 g / t. The method for manufacturing battery-grade graphite according to claim 1 or 2, characterized in that.

8. In the weak acid washing treatment, the liquid-solid ratio is 10 to 30, the sulfuric acid concentration is 0.01 to 0.2 mol / L, the hydrogen peroxide consumption is 3 to 5 times the theoretical value, the temperature is 50 to 100 °C, and the time is 0 to 100 minutes. The method for manufacturing battery-grade graphite according to claim 1 or 2, characterized in that.

9. In the foaming product after flotation separation, the graphite grade > 95%, the graphite recovery rate > 65%, and the positive electrode material recovery rate in the ore slurry product > 97%. The method for manufacturing battery-grade graphite according to claim 1 or 2, characterized in that.

10. In the graphitization repair treatment, the heating rate is 5 to 20 °C / min, the repair temperature is 1300 to 2800 °C, and the heat preservation time is 2 to 10 hours. The method for manufacturing battery-grade graphite according to claim 1 or 2, characterized in that.

11. After high-temperature graphitization, the graphitization degree of the graphite product is 90 to 99%. The method for manufacturing battery-grade graphite according to claim 1 or 2, characterized in that.

12. A battery-grade graphite product manufactured by the method according to claim 1 or 2.

13. A method of using battery-grade graphite produced by the method according to claim 1 or 2 in the manufacture of a power source for a lithium-ion battery, an energy storage device for an electronic product, an industrial battery energy storage device, an electric vehicle or an electric bicycle, wherein the electronic product is a mobile phone, a camera, a laptop, a tablet and other portable power tools, and the industrial battery storage device is a storage device for wind energy or solar energy and a standby power source.

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