Method for purifying, repairing and regenerating graphite of waste lithium batteries, graphite negative electrode sheet and lithium battery

Abstract

The present application provides a method for purifying, repairing and regenerating graphite of waste lithium batteries, which is to place the negative pole piece of the waste lithium battery in a high-frequency alternating magnetic field and an atmospheric plasma coupling field, quickly heat up the copper collector through the eddy current effect to form a temperature gradient with the graphite coating, simultaneously use air plasma to clean organic matter, and control the temperature to pyrolyze the binder, and after the graphite particles are peeled off, shear homogenization dispersion, reverse flotation, chelation, oxidation purification and coordinated treatment are carried out to remove impurities such as amorphous carbon, metals and oxides, SEI membranes and organic matter, and then through a segmented and integrated screw, the deeply purified graphite is degassed at low pressure in the room temperature section, and the graphite is kneaded and squeezed and filled into the internal pores and surface of the graphite in the medium temperature section. After high-temperature carbonization, the asphalt and graphite are mixed and melted into one, thereby realizing the repair and regeneration of the graphite structure. The present application also provides a graphite negative pole piece and a lithium-ion battery prepared by using the above-mentioned purified, repaired and regenerated graphite as a negative electrode material.

Description

Technical Field

[0001] This application belongs to the technical field of waste lithium battery recycling and regeneration, and specifically relates to a method for purifying, repairing and regenerating graphite from waste lithium batteries, a graphite negative electrode sheet and a lithium ion battery. Background Art

[0002] After a lithium battery is used for 5 to 8 years, its capacity will decay to a certain extent, resulting in a large amount of waste. Among them, waste lithium batteries contain 35-45 wt% of lithium metal oxide, 15-25 wt% of graphite, 10-20 wt% of carbonate electrolyte, 2-5 wt% of polypropylene separator and 15-30 wt% of metal materials.

[0003] The utilization value of waste graphite is lower than that of the metals in the battery. In the industrial recycling process, lithium resources are mainly recovered from waste graphite. After lithium extraction, the carbon slag is generally used as a carburizer or reducing agent in the smelting industry. However, graphite is a non-renewable resource and has an important strategic position. In the production process of negative electrode materials, the energy consumption of graphitization processing is high, accounting for about half of the production cost of negative electrode materials. The recycled waste graphite still maintains an ordered structure and does not require high-temperature treatment again, thus reducing costs. In addition, compared with graphite ore, the graphite content in waste batteries is higher and the types of impurities are fewer, making its recycling and utilization able to shorten the process flow and reduce energy consumption. Therefore, in the resource utilization of waste lithium batteries, it is of great significance to recycle and repair the failed graphite of the negative electrode, which can realize the recycling of resources, contribute to environmental protection and economic development.

[0004] Through constant-potential discharge pretreatment and refined disassembly of waste lithium batteries, failed negative electrode sheets can be recycled. Among them, graphite and conductive carbon black are tightly adhered to the copper foil current collector through a binder to form a negative electrode. The dissociation of the multiphase interface of this structure is the key to the stripping of active materials. Oil-based binders (such as PVDF) have characteristics such as high bonding strength, high chemical stability, and better compatibility with electrolytes, and have been widely used as negative electrode binders in lithium batteries. At present, the methods of stripping negative electrode sheets commonly used at home and abroad are liquid-phase dissolution and high-temperature pyrolysis. Among them, the stripping of graphite and copper foil can be achieved by washing with water and redispersing the water-based binder, or by swelling the oil-based binder with an organic solvent and supplementing with ultrasonic vibration. However, in the large-scale stripping process, the complex binder system limits the application of the above single liquid-phase stripping method. In addition, the electrode sheets obtained after disassembling lithium batteries often remain organic substances such as SEI films and carbonate electrolytes, which will pollute the water body during the liquid-phase stripping process. The high-temperature pyrolysis method is the most direct and effective stripping method. By decomposing and removing conductive additives and organic binders, the internal cohesion of the coating material particles is reduced, and the adhesion between the coating and the current collector is weakened. However, the temperature for the binder to pyrolyze and lose adhesion is high (>500 °C), which is likely to cause partial loss of graphite carbon, high energy consumption, and environmental pollution by fluorine-containing waste gas. In addition, this method requires an inert atmosphere protection to avoid the oxidation and combustion of graphite and the oxidation and embrittlement of copper foil at high temperatures.

[0005] The failed graphite powder obtained by stripping from the copper foil current collector usually remains impurities such as amorphous carbon, SEI film, metal particles, and residual electrolyte organic matter, which seriously affect the electrochemical performance. The methods for purifying graphite and removing impurities include flotation method, screening method, chemical acid leaching and alkali treatment method, and high-temperature calcination method. Among them, the pneumatic flotation method can effectively separate amorphous carbon and graphite, but the accuracy is poor and the efficiency is low; the high-temperature calcination method (>2500 °C) can decompose various impurities, but the energy consumption is high; the gradient calcination method and hydrochloric acid leaching method can leach out metal impurities such as lithium ions, but there are secondary pollutions of harmful gases such as chlorine and equipment corrosion, and there are also problems such as low efficiency of removing organic matter, large pollution in the impurity treatment process, and the impurity content is still difficult to meet the standard of "Graphite Anode Materials for Lithium Ion Batteries" (GB / T 24533-2019) after purification.

[0006] Failed graphite often has microstructural damage, manifested as surface oxidation and internal pores. In addition, the recycled graphite is also prone to microdefects and hard carbon impurities after low-temperature roasting and wet purification. The surface coating method is also a method for repairing and regenerating waste graphite. The coating material can improve the defects on the surface of graphite. The coating layer forms a continuous conductive network on the surface of graphite, which can improve the electron transmission and increase the conductivity. Usually, the waste graphite is pretreated to remove impurities first, and then materials such as glucose, asphalt, phenolic resin, and metal-based are coated on the pretreated graphite, but there are problems such as uneven coating and low tapped and compacted density. Summary of the Invention

[0007] The purpose of this application is to overcome the deficiencies of the above-mentioned prior art, and to provide a method for purifying, repairing and regenerating graphite from waste lithium batteries, as well as a graphite negative electrode sheet and a lithium-ion battery prepared with the regenerated graphite obtained by this method as the active material.

[0008] In the first aspect, this application provides a method for purifying, repairing and regenerating graphite from waste lithium batteries, including the following steps:

[0009] S1 Place the negative electrode sheet of the waste lithium battery in a high-frequency alternating magnetic field, control the electromagnetic induction heating current within the range of 200A - 500A, the frequency of the alternating magnetic field is 20 - 30kHz, the surface temperature of the copper current collector in the negative electrode sheet of the waste lithium battery is 350 - 400°C, and use a plasma generator to process the negative electrode sheet of the waste lithium battery. The pulse power of the plasma generator is 20 - 50kW, so that cracks are formed in the coating between the graphite and the copper current collector in the negative electrode sheet of the waste lithium battery and the interface dislocation between the coating and the copper current collector occurs. Then, the graphite is peeled off from the copper current collector through ultrasonic vibration, and the graphite particles are recovered after sieving;

[0010] S2 Disperse the recovered graphite particles in a dilute acid solution, add a graphite flotation inhibitor, stir, then add an amorphous carbon capture agent, stir again, and then add a foaming agent. After reverse flotation, the amorphous carbon is removed;

[0011] S3 Mix the product obtained in step S2 with a dilute acid solution, then add a chelating agent, stir to form a chelate, and then wash with a dilute acid solution to leach out the metals, oxides and inorganic substances in the SEI film in the product, obtaining a preliminarily purified graphite substrate;

[0012] S4 Adjust the pH value of the preliminarily purified graphite substrate obtained in step S3 to 2 - 3, add ferrous sulfate heptahydrate, stir well, then dropwise add hydrogen peroxide, and then stir and react to oxidize and decompose the organic matter in the SEI film and the residual carbonate electrolyte on the surface of the graphite particles. After filtration, washing and drying, deeply purified graphite is obtained;

[0013] S5 Add high-temperature petroleum pitch to the deeply purified graphite obtained in step S4, knead through a screw kneading device, and then perform high-temperature carbonization to obtain regenerated graphite with structural repair and surface carbon coating.

[0014] In the second aspect, this application also provides a graphite negative electrode sheet prepared with the regenerated graphite obtained by the above method as the negative electrode active material.

[0015] In the third aspect, this application also provides a lithium-ion battery including the above graphite negative electrode sheet.

[0016] The method for purifying, repairing and recycling graphite from waste lithium batteries provided by this application places the negative electrode sheet of waste lithium batteries in the coupled field of high-frequency alternating magnetic field and atmospheric plasma. Through the eddy current effect of the copper current collector, the temperature is rapidly increased to form a temperature gradient with the graphite coating. At the same time, the organic matter on the electrode sheet is cleaned by the high-energy jet of air plasma, and the binder is pyrolyzed under temperature control. Ultrasonic vibration realizes the efficient peeling of graphite particles. Then, through the synergistic treatment of shear homogenization dispersion, reverse flotation, EDTA chelation, and oxidative purification of the recovered graphite particles, impurities such as amorphous carbon, metals and oxides, SEI film, and organic matter in the graphite particles can be effectively removed, realizing deep purification of graphite; through a segmented and integrated screw, the deeply purified graphite is first degassed at low pressure in the room temperature section, and then the micro-liquid asphalt is kneaded with the deeply purified graphite and extruded and filled in the internal holes and on the surface of the deeply purified graphite in the medium temperature section. Finally, it is carbonized in the high temperature section, so that the carbonized asphalt and graphite are melted into one body, realizing the repair and regeneration of the graphite structure, and meeting the standards of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019) (fixed carbon content > 99.7%, iron < 100 ppm, copper < 5 ppm, aluminum < 5 ppm, magnetic foreign matter < 0.5 ppm, first cycle Coulomb efficiency ≥ 91.0% in electrochemical performance), meeting the application requirements of commercial lithium-ion battery graphite anode materials.

[0017] The method for purifying, repairing and recycling graphite from waste lithium batteries in this application realizes the secondary utilization of the negative electrode graphite of recycled waste lithium-ion batteries, solves the problem of recycling and treatment of recycled waste lithium-ion batteries, realizes the resource conversion of waste lithium-ion batteries, and can ensure the quality of the negative electrode graphite after recycling.

[0018] This application uses the recycled graphite from waste lithium-ion batteries as raw materials, and prepares graphite negative electrode sheets and lithium-ion batteries through purification, repair and regeneration. It can not only recycle resources, but also reduce the manufacturing cost of lithium-ion batteries, realizing the efficient and high-value resource recovery of waste lithium-ion batteries, and having significant industrial application prospects and economic benefits. Brief Description of the Drawings

[0019] Figure 1 is the process flow chart of the method for purifying, repairing and recycling graphite from waste lithium batteries in this application;

[0020] Figure 2 is the XRD pattern of the graphite obtained by the method for purifying, repairing and recycling graphite from waste lithium batteries in Examples 1-3 of this application and the methods in Comparative Examples 1-4;

[0021] Figure 3 is the SEM picture of the graphite obtained by the method in Example 1 of this application;

[0022] Figure 4 is the voltage-specific capacity curve of the first cycle charge and discharge of the graphite obtained by the method in Example 1 of this application;

[0023] Figure 5 SEM images of the graphite obtained by the method of Example 2 of the present application;

[0024] Figure 6 Voltage-specific capacity curves of the first charge-discharge of the graphite obtained by the method of Example 2 of the present application;

[0025] Figure 7 SEM images of the graphite obtained by the method of Example 3 of the present application;

[0026] Figure 8 Voltage-specific capacity curves of the first charge-discharge of the graphite obtained by the method of Example 3 of the present application;

[0027] Figure 9 SEM images of the graphite obtained by the method of Comparative Example 1;

[0028] Figure 10 Voltage-specific capacity curves of the first charge-discharge of the graphite obtained by the method of Comparative Example 1;

[0029] Figure 11 SEM images of the graphite obtained by the method of Comparative Example 2;

[0030] Figure 12 Voltage-specific capacity curves of the first charge-discharge of the graphite obtained by the method of Comparative Example 2;

[0031] Figure 13 SEM images of the graphite obtained by the method of Comparative Example 3;

[0032] Figure 14 Voltage-specific capacity curves of the first charge-discharge of the graphite obtained by the method of Comparative Example 3;

[0033] Figure 15 SEM images of the graphite obtained by the method of Comparative Example 2;

[0034] Figure 16 Voltage-specific capacity curves of the first charge-discharge of the graphite obtained by the method of Comparative Example 2;

[0035] Figure 17 Physicochemical property parameters of the graphite obtained by the methods of Examples 1-3 of the present application;

[0036] Figure 18 Physicochemical property parameters of the graphite obtained by the methods of Comparative Examples 1-4 of the present application. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0038] See Figure 1 , the present application provides a method for purifying, repairing and recycling graphite from waste lithium batteries, including the following steps:

[0039] S1 Place the negative electrode plate of the waste lithium battery in a high-frequency alternating magnetic field, control the electromagnetic induction heating current within the range of 200 A to 500 A, the alternating magnetic field frequency between 20 and 30 kHz, and the surface temperature of the current collector in the negative electrode plate of the waste lithium battery is 350 to 400 °C. At the same time, use a plasma generator to process the negative electrode plate of the waste lithium battery, and control the pulse power of the plasma generator between 20 and 50 kW, so that cracks are formed in the coating (adhesive) between the graphite and the current collector in the negative electrode plate of the waste lithium battery, and the interface dislocation between the coating and the current collector is caused. Then, the graphite is peeled off from the current collector through ultrasonic vibration. After sieving, the material under the sieve is taken to obtain the recovered graphite particles.

[0040] In this step, the air flow rate in the high-frequency alternating magnetic field is controlled at 10 to 20 L / min, the whole step processing time is 30 to 60 s, and the ultrasonic vibration sieve mesh size is 150 to 300 mesh.

[0041] In this step, after the waste lithium battery is discharged at a fixed potential, the negative electrode plate is disassembled, crushed and sorted. Then, the recovered negative electrode plate is placed in a high-frequency alternating magnetic field and a plasma environment for treatment. The working parameters of the electromagnetic induction and the plasma generator are controlled. The surface of the waste negative electrode plate is cleaned by low-temperature atmospheric plasma, and the air flow rate in the high-frequency alternating magnetic field is controlled at 10 to 20 L / min. By using the active oxygen in the air, the surface temperature of the current collector in the negative electrode plate of the waste lithium battery is between 350 and 400 °C. In this way, at a lower temperature (<400 °C), the surface of the negative electrode plate is accelerated to bombard, and the binder and organic matter attached to the graphite coating are partially cracked in a very short time (<60 s). Part of the binder can be retained, reducing the usage amount of the flotation inhibitor required in the subsequent steps. Moreover, large cracks can be formed in the coating between the graphite and the current collector, which helps to improve the subsequent ultrasonic vibration powder removal and peeling rate (>92%), and also solves the problems such as the need for high-purity inert gas protection (>99.99%), high-temperature complete reaction (>550 °C) and long-time sufficient oxidation (>1 h) during the traditional peeling of the negative electrode plate, and can reduce the peeling cost of the negative electrode plate.

[0042] Meanwhile, in this step, the negative electrode sheet is heated by high-frequency alternating magnetic field induction, and the eddy current effect of the current collector is used to rapidly increase the temperature (>200 °C / s), so that the instantaneous differential temperature (temperature gradient) of the current collector (active temperature increase by eddy current) and the graphite coating (passive temperature increase by heat conduction) forms a thermal stress. Through the interfacial shear force of the differential thermal expansion volume change of the metal (current collector) and graphite, dislocations are formed at the interface between the current collector and the graphite coating, which can further improve the subsequent ultrasonic vibration powder removal and peeling rate (>96%), and solve the problem of low efficiency (<10 °C / s) in the heating-up stage of the existing technology by resistance wire heat conduction or heat radiation.

[0043] In this step, high-frequency alternating magnetic field and atmospheric plasma are coupled and used in cooperation. While partially cracking the binder and organic matter attached to the graphite, dislocations are formed at the interface between its coating and the current collector, providing conditions for the subsequent ultrasonic vibration of the graphite powder to peel off the current collector, and a higher peeling rate (>99%) can be obtained. Moreover, in this process, only part of the organic impurities in the negative electrode sheet are oxidized, and the removal of the remaining organic matter is centrally disposed during subsequent liquid-phase purification, improving the environmental protection of the treatment process. Further, by using the rapid heating of metal eddy current and the high-pressure acceleration of the plasma gas flow, its energy consumption is about 1 / 10 of that of other physical methods of heating, and the time is about 1 / 60 of that of other high-temperature pyrolysis, greatly reducing the energy consumption, saving energy, and solving the problem of incompatibility of a single method for complex systems of different binders (such as water-based CMC, SBR, PAA, and oil-based PVDF).

[0044] This step does not require treatment in an inert atmosphere, and has a short treatment time and low energy consumption.

[0045] S2 Disperse the recovered graphite particles in a dilute acid solution, then add a graphite flotation inhibitor, stir, add an amorphous carbon capturer, stir again, add a foaming agent, and after reverse flotation for 10 - 15 min, remove the amorphous carbon.

[0046] In the preferred implementation of this step, when the graphite particles are dispersed in the dilute acid solution, the solid-liquid ratio of the graphite particles to the dilute acid solution is 10 - 50 g / L. The dilute acid can preferably be sulfuric acid, and the concentration of the sulfuric acid solution is 0.05 - 0.10 mol / L; the graphite flotation inhibitor is selected from at least one of sodium carboxymethyl cellulose or water glass, and the solid-liquid ratio of the graphite particles to the graphite flotation inhibitor is 0.3 - 1 g / L. After adding the graphite flotation inhibitor, stir for 10 - 20 min; the amorphous carbon capturer is selected from at least one of sodium dodecylbenzenesulfonate or oleic acid, and the solid-liquid ratio of the graphite particles to the amorphous carbon capturer is 0.1 - 0.2 g / L. After adding the amorphous carbon capturer, stir for 10 - 20 min; the foaming agent is selected from at least one of methyl isobutyl carbinol or 2-ethylhexanol, and the solid-liquid ratio of the graphite particles to the foaming agent is 0.05 - 0.15 g / L.

[0047] In a preferred embodiment of the present application, the recycled graphite particles are dispersed in a dilute acid solution by a stator-rotor high-shear homogenizer, with a shear speed of 9000 - 12000 rpm and a time of 60 - 120 min.

[0048] The negative electrode material obtained by stator-rotor high-shear homogenization and dispersion in this step utilizes a relatively high linear velocity and a small gap between the stator and the rotor. Through strong turbulent flow, amorphous carbon impurities (including conductive carbon black and pyrolytic amorphous carbon, etc.) and graphite are sheared and separated, which helps to strengthen the dispersion of graphite in the aqueous phase and the leaching of water-soluble impurities, solving the problems of difficult wetting of the powder particle surface and difficult dispersion of agglomerated particles in traditional dispersion methods, and can improve the recovery rate and recovery quality of graphite.

[0049] In the field of recycling and separation of waste ion battery materials, flotation methods are usually used to change the hydrophilicity and hydrophobicity of the positive electrode active material and the negative electrode graphite, and a large amount of reagents need to be added to achieve separation. The present application uses reverse flotation to separate graphite and amorphous carbon. Under the action of a foaming agent, using a graphite flotation inhibitor, the graphite is kept hydrophilic, so that it is dispersed in the solution or sinks to form a substrate, while using an amorphous carbon capturer to make the amorphous carbon float, so as to improve the sorting accuracy. Since the content of amorphous carbon is low (<5 wt%), the usage amounts of the capturer and the foaming agent are lower than those of traditional methods. In addition, the residual CMC and its derivatives in the recycled exfoliated graphite can still promote the dispersion of graphite in water, so the usage amount of the flotation inhibitor is low. In this way, the use of externally added reagents can be reduced, and the recovery quality of graphite can be improved.

[0050] S3 Mix the product obtained in step S2 with a dilute acid solution, then add a chelating agent, stir to form a chelate, and then wash with a dilute acid solution to leach out metals, oxides and inorganic substances in the SEI film in the product, and obtain a preliminarily purified graphite substrate.

[0051] The dilute acid in this step is also preferably sulfuric acid, the concentration of the sulfuric acid solution is 0.05 - 0.10 mol / L, and the solid-liquid ratio of the product obtained in step S2 to the sulfuric acid solution is 10 - 50 g / L; the chelating agent is selected as ethylenediaminetetraacetic acid (EDTA), and the mass ratio of the graphite particles to ethylenediaminetetraacetic acid is 1:0.01 - 0.05, and the stirring time after adding the chelating agent ethylenediaminetetraacetic acid is 10 - 20 min.

[0052] In this step, the metal oxides in the recycled graphite particles undergo a double decomposition reaction under the action of an acid to form soluble metal salts. The double decomposition reaction precipitates metal impurity elements, which are further treated by EDTA chelation. By forming chelates between EDTA and metal ions, and then through centrifugal sedimentation, the metal impurity components in the graphite particles can be removed. Then, it is washed with a dilute acid solution to elute and separate the trace metal ions remaining in the graphite, further purifying the impurities. In this way, the leaching efficiency of metal ions in the graphite particles can be >99% at room temperature (~25°C), and the oxides and inorganic substances in the SEI film are removed, solving the high energy consumption problem of traditional wet leaching of graphite that requires heating (>80°C).

[0053] S4 Adjust the pH value of the preliminarily purified graphite substrate obtained in step S3 to 2 - 3, add ferrous sulfate heptahydrate, fully stir, then dropwise add hydrogen peroxide, and then carry out a stirring reaction to further purify the preliminarily purified graphite substrate, so as to oxidize and decompose the organic matter in the SEI film and the residual carbonate electrolyte on the surface of the graphite particles. After filtration, washing with deionized water, and heating and drying, highly purified graphite is obtained.

[0054] In this step, add ferrous sulfate heptahydrate at 140 - 560 mg / L, stir for 10 - 20 min, and then dropwise add hydrogen peroxide in batches at 85 - 340 mg / L, with a dropping rate of 2 - 5 mL / min·m 3 , and further stir for 30 - 60 min. The molar ratio between hydrogen peroxide and ferrous ions is 1:1 - 5:1.

[0055] This step is a process of oxidative purification of the preliminarily purified graphite substrate. By combining ferrous sulfate heptahydrate with hydrogen peroxide, in an acidic environment (pH value 2 - 3), highly reactive hydroxyl radicals are generated. At room temperature, it can completely oxidize the residual carbonate organic matter, organic impurities in the SEI film, residual amorphous carbon, other added organic agents, etc., so as to remove the organic matter generated during the purification of graphite. The above process is a centralized disposal of organic impurities, removing the organic impurities in the graphite, improving the purification degree of graphite, and can fully accommodate the differential disposal of different recycled pole piece materials.

[0056] S5 Add high-temperature petroleum pitch to the highly purified graphite obtained in step S4, knead it through a screw kneading device, and then carry out high-temperature carbonization to obtain regenerated graphite with structural repair and surface carbon coating.

[0057] This step is divided into three stages:

[0058] The first stage: First, put the highly purified graphite into the screw kneading device, control the screw extrusion pressure between 0.01 - 0.05 MPa, and degas at room temperature for 2 - 5 min to discharge the gas on the surface and in the pores of the highly purified graphite using the low-pressure section.

[0059] The second stage: Add asphalt with a mass ratio of 2.5 - 8 wt% to the deeply purified graphite, and knead the deeply purified graphite and asphalt at a temperature higher than the softening point of solid asphalt. The softening point temperature of solid asphalt is 220 - 280 °C, heat for 15 - 25 min to make the solid asphalt in a slightly liquefied state. The screw extrusion pressure of the screw kneading equipment is 0.20 - 0.30 MPa, and the kneading time is 5 - 10 min. Use the high-pressure end of the screw kneading equipment to extrude and fill the slightly liquefied asphalt mixed in the deeply purified graphite into the internal pores and on the surface of the deeply purified graphite, so that after carbonization, it is melted and integrated with the graphite to reduce micro-defects and improve the graphitization degree (>97.0%). Moreover, this high-pressure extrusion also improves the tap density (>1.1 g / cm 3 3) and the compaction density (>1.9 g / cm 3 3) as well as the uniformity and efficiency of graphite coating, and can make the carbon material completely embedded in the internal pores of the graphite, solving the problems of difficult wetting and difficult penetration of internal pores in traditional asphalt-coated graphite.

[0060] In addition, in this step, a screw kneading equipment is used. Its segmented and integrated screw can efficiently mix and achieve continuous feeding by continuously mixing materials - filling the internal pores with slightly liquefied flowing pressure infiltration asphalt and coating the graphite, solving the problems of pre-burning in a rotary kiln and segmented programmed temperature rise carbonization in traditional asphalt coating, and simplifying the process flow.

[0061] The third stage: Place the kneaded graphite-asphalt mixture in a high-temperature furnace for carbonization treatment to carbonize the asphalt. The carbonization temperature is 1100 - 1250 °C, and the carbonization holding time is 1 - 2 h to remove the volatile components in the asphalt, convert it into a more stable carbonaceous material, and at the same time enhance the structural stability of the carbonaceous material penetrating into the graphite pores and on the surface, repair the performance of the recycled graphite, so that the regenerated graphite anode material has battery-grade performance, thereby improving the capacity and energy density of the lithium battery prepared as the anode material subsequently.

[0062] The graphite prepared by the above method has good structural integrity, good stability, the content of impurity elements is below 10 ppm, the initial lithium insertion specific capacity is above 380 mAh / g, and the initial lithium deinsertion specific capacity is above 350 mAh / g, meeting the commercial battery-grade graphite material standard.

[0063] The following further details the method for purifying, repairing and regenerating graphite from waste lithium batteries of the present application in combination with specific embodiments.

[0064] Example 1:

[0065] This Example 1 adopts the following steps:

[0066] S1 After discharging the waste lithium battery at a constant potential of 0.50 V, the disassembled and sorted negative electrode sheets are placed in a high-frequency alternating magnetic field and plasma for treatment. Adjust the electromagnetic induction heating current to 200 A, the alternating magnetic field frequency to 20 kHz, control the surface temperature of the metal copper current collector to 350 °C, and at the same time adjust the pulse power of the plasma generator to 20 kW and the air flow rate to 10 L / min. Control the treatment time to 30 s. Finally, the product is treated by ultrasonic vibration, passed through a 300-mesh sieve, and the material under the sieve is taken to obtain the recovered graphite particles.

[0067] S2 1 kg of the recovered graphite particles obtained in step S1 are dispersed in a 0.05 mol / L sulfuric acid solution by a high-shear rotor-stator homogenizer with a rotation speed of 9000 rpm. Control the solid-liquid ratio to 10 g / L and the leaching time to 60 min. Then add sodium carboxymethyl cellulose, a graphite flotation inhibitor, with a solid-liquid ratio of 0.3 g / L, stir for 10 min, then add sodium dodecylbenzenesulfonate, an amorphous carbon capture agent, with a solid-liquid ratio of 0.1 g / L, and further stir for 10 min. Then add methyl isobutyl carbinol, a foaming agent, with a solid-liquid ratio of 0.05 g / L, and perform reverse flotation for 10 min to remove amorphous carbon.

[0068] S3 The product obtained in step S2 is mixed with a 0.05 mol / L sulfuric acid solution with a solid-liquid ratio of 10 g / L, and then ethylenediaminetetraacetic acid is added. For every 1 kg of graphite treated, 0.01 kg of ethylenediaminetetraacetic acid is added, and stir for 10 min to form an EDTA chelate. Then, it is pickled with a 0.10 mol / L sulfuric acid solution to further leach out impurities such as metals, their oxides, and inorganic non-metals in the SEI film, and a preliminarily purified graphite substrate is obtained.

[0069] S4 Adjust the pH of the preliminarily purified graphite substrate in step S3 to 2, add ferrous sulfate heptahydrate at 140 mg / L, and further stir for 10 min. Then, hydrogen peroxide is added dropwise in batches at 85 mg / L, control the dropping rate to 2 mL / min·m 3 , and further stir and react for 30 min to fully oxidize and decompose the organic matter in the SEI film and the residual carbonate electrolyte on the surface of the recovered graphite. After filtration, washing with deionized water, and vacuum heating and drying, deeply purified graphite is obtained.

[0070] Put the deeply purified graphite obtained in step S4 into a screw kneading device. Through segmented screw kneading, control the extrusion pressure of the screw kneading device at 0.01 MPa in the first stage and degas at room temperature for 2 minutes; in the second stage, add asphalt according to a mass ratio of 2.5 wt%, knead and mix it with the deeply purified graphite put in the first stage, and extrude and fill the flowing asphalt at 0.20 MPa at 220 °C for 15 minutes; then place the graphite-asphalt mixture kneaded and extruded from the screw kneading device into a high-temperature furnace and carbonize it at 1100 °C for 1 hour to obtain regenerated graphite with structure repair and surface carbon coating.

[0071] The structure and performance of Example 1 are characterized as follows:

[0072] Figure 2 The XRD pattern results show that the purified, repaired and regenerated graphite in Example 1 is a pure phase without any impurity phases.

[0073] Figure 3 The SEM image results show that the surface of the purified, repaired and regenerated graphite in Example 1 has no impurities, cracks or pores.

[0074] Figure 4 The charge-discharge results show that in the 0.1C charge-discharge of the purified, repaired and regenerated graphite in Example 1, the first-cycle discharge specific capacity is 384.5 mAh / g, the first-cycle charge specific capacity is 355.3 mAh / g, and the first-cycle Coulombic efficiency is 92.41%. Its electrochemical performance has recovered to the average level of commercial graphite.

[0075] From Figure 17 it can be seen that the D50 of the purified, repaired and regenerated graphite in Example 1 is 14.39 μm and the D90 is 29.05 μm; the graphitization degree is 97.87%, indicating that the graphite lattice damage has been repaired and the amorphous carbon has been removed; the iron, copper, aluminum and magnetic foreign matters are all less than 5 ppm, indicating that the graphite has been purified and the metal impurities have been removed; the fixed carbon content is 99.962% and the ash content is 0.038%, indicating that the graphite has been purified and the inorganic and organic impurities in the SEI film have been removed; the specific surface area is 2.155 m 2 / g, the 5T compaction density is 1.91 g / cm 3 and the tapped density is 1.15 g / cm 3 , indicating that the pore defects in the graphite have been repaired.

[0076] The above results show that the physical and chemical indexes of the purified, repaired and regenerated graphite in Example 1 meet the standards of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0077] Example 2:

[0078] This Example 2 adopts the following steps:

[0079] S1 After discharging the waste lithium battery at a fixed potential of 0.50 V, place the disassembled and sorted negative electrode sheets in a high-frequency alternating magnetic field and plasma for treatment. Adjust the magnitude of the electromagnetic induction heating current to 500 A, the frequency of the alternating magnetic field to 30 kHz, control the surface temperature of the metal copper current collector to 400 °C, and at the same time adjust the pulse power of the plasma generator to 50 kW and the air flow rate to 20 L / min. Control the treatment time to 60 s. Finally, subject the product to ultrasonic vibration treatment, pass it through a 200-mesh sieve, and take the material under the sieve to obtain the recovered graphite particles.

[0080] S2 Disperse 1 kg of the recovered graphite particles obtained in step S1 in a 0.10 mol / L sulfuric acid solution using a high-shear rotor-stator homogenizer with a rotation speed of 12,000 rpm. Control the solid-liquid ratio to 50 g / L and the leaching time to 120 min. Then add the graphite flotation inhibitor - sodium silicate with a solid-liquid ratio of 1 g / L, stir for 20 min, add the amorphous carbon capture agent - oleic acid with a solid-liquid ratio of 0.2 g / L, further stir for 20 min, and then add the foaming agent - 2-ethylhexanol with a solid-liquid ratio of 0.15 g / L. After reverse flotation for 15 min, remove the amorphous carbon.

[0081] S3 Mix the product obtained in step S2 with a 0.1 mol / L sulfuric acid solution with a solid-liquid ratio of 50 g / L, and then add ethylenediaminetetraacetic acid. Add 0.05 kg of ethylenediaminetetraacetic acid for every 1 kg of graphite treated, stir for 20 min to form an EDTA chelate, and then pickle with a 0.10 mol / L sulfuric acid solution to further leach out impurities such as metals, their oxides, and inorganic non-metals in the SEI film to obtain a preliminarily purified graphite substrate.

[0082] S4 Adjust the pH of the preliminarily purified graphite substrate in step S3 to 3, add ferrous sulfate heptahydrate at 560 mg / L, further stir for 20 min, and then dropwise add hydrogen peroxide in batches at 340 mg / L, controlling the dropping rate to 5 mL / min·m 3 , further stir and react for 60 min to fully oxidize and decompose the organic matter in the SEI film and the residual carbonate electrolyte on the surface of the recovered graphite. After filtration, washing with deionized water, and vacuum heating and drying, obtain the deeply purified graphite.

[0083] Put the deeply purified graphite obtained in step S4 into a screw kneading device, and through segmented screw kneading, control the extrusion pressure of the screw kneading device at 0.05 MPa in the first stage and degas at room temperature for 5 minutes. In the second stage, add asphalt according to a mass ratio of 8 wt%, knead and mix it with the deeply purified graphite input in the first stage, and extrude and fill the flowing asphalt at 0.30 MPa at 280 °C for 25 minutes. Then, place the graphite-asphalt mixture kneaded and extruded from the screw kneading device into a high-temperature furnace and carbonize it at 1250 °C for 2 hours to obtain regenerated graphite with structural repair and surface carbon coating.

[0084] The structure and performance of Example 2 are characterized as follows:

[0085] Figure 2 The results of the XRD pattern show that the purified, repaired and regenerated graphite in Example 2 is a pure phase without any impurity phases.

[0086] Figure 5 The results of the SEM image show that the surface of the purified, repaired and regenerated graphite in Example 2 has no impurities, cracks or holes.

[0087] Figure 6 The charge-discharge results show that in the 0.1C charge-discharge of the purified, repaired and regenerated graphite in Example 2, the initial discharge specific capacity is 384.2 mAh / g, the initial charge specific capacity is 353.2 mAh / g, and the initial Coulomb efficiency is 91.93%. Its electrochemical performance has recovered to the average level of commercialized graphite.

[0088] From Figure 17 it can be seen that for the purified, repaired and regenerated graphite in Example 1, D50 is 16.78 μm and D90 is 33.46 μm; the graphitization degree is 97.82%, indicating that the graphite lattice damage has been repaired and the amorphous carbon has been removed; the contents of iron, copper, aluminum and magnetic foreign matters are all less than 5 ppm, indicating that the graphite has been purified and the metal impurities have been removed; the fixed carbon content is 99.958% and the ash content is 0.042%, indicating that the graphite has been purified and the inorganic and organic impurities in the SEI film have been removed; the specific surface area is 2.132 m 2 / g, the 5T compaction density is 1.92 g / cm 3 and the tapped density is 1.14 g / cm 3 , indicating that the pore defects in the graphite have been repaired.

[0089] The above results show that the physical and chemical indexes of the purified, repaired and regenerated graphite in Example 2 meet the standards of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0090] Example 3:

[0091] This Example 3 adopts the following steps:

[0092] S1 After discharging the waste lithium battery at a fixed potential of 0.50 V, the disassembled and sorted negative electrode sheets are placed in a high-frequency alternating magnetic field and plasma for treatment. Adjust the magnitude of the electromagnetic induction heating current to 300 A, the alternating magnetic field frequency to 25 kHz, control the surface temperature of the metal copper current collector to 400 °C, and at the same time adjust the pulse power of the plasma generator to 25 kW and the air flow rate to 15 L / min. Control the treatment time to 40 s. Finally, the product is treated by ultrasonic vibration, passed through a 150-mesh sieve, and the material under the sieve is taken to obtain the recovered graphite particles.

[0093] S2 1 kg of the recovered graphite particles obtained in step S1 are dispersed in a 0.1 mol / L sulfuric acid solution by a high-shear rotor-stator homogenizer with a rotation speed of 10,000 rpm. Control the solid-liquid ratio to 30 g / L and the leaching time to 90 min. Then, add the graphite flotation inhibitor - sodium carboxymethylcellulose with a solid-liquid ratio of 0.6 g / L, stir for 15 min, add the amorphous carbon capture agent - oleic acid with a solid-liquid ratio of 0.15 g / L, and further stir for 15 min. Then, add the foaming agent - 2-ethylhexanol with a solid-liquid ratio of 0.10 g / L, and perform reverse flotation for 15 min to remove amorphous carbon.

[0094] S3 The product obtained in step S2 is mixed with a 0.1 mol / L sulfuric acid solution with a solid-liquid ratio of 30 g / L. Then, add ethylenediaminetetraacetic acid, with 0.03 kg of ethylenediaminetetraacetic acid added for every 1 kg of graphite treated. Stir for 15 min to form an EDTA chelate, and then pickle with a 0.10 mol / L sulfuric acid solution to further leach out impurities such as metals, their oxides, and inorganic non-metals in the SEI film, obtaining a preliminarily purified graphite substrate.

[0095] S4 Adjust the pH of the preliminarily purified graphite substrate in step S3 to 3, add ferrous sulfate heptahydrate at 560 mg / L, and further stir for 20 min. Then, dropwise add hydrogen peroxide in batches at 340 mg / L, control the dropping rate to 3 mL / min·m 3 , and further stir and react for 40 min to fully oxidize and decompose the organic matter in the SEI film and the residual carbonate electrolyte on the surface of the recovered graphite. After filtration, washing with deionized water, and vacuum heating and drying, deeply purified graphite is obtained.

[0096] S5 Feed the deeply purified graphite obtained in step S4 into a screw kneading device, and through segmented screw kneading, control the extrusion pressure of the screw kneading device at 0.03 MPa in the first stage and degas at room temperature for 5 min. In the second stage, add asphalt at a mass ratio of 5 wt%, knead and mix it with the deeply purified graphite fed in the first stage, and extrude and fill the flowing asphalt at 0.25 MPa at 260 °C for 20 min. Then place the graphite-asphalt mixture kneaded and extruded from the screw kneading device into a high-temperature furnace and carbonize it at 1150 °C for 2 h to obtain regenerated graphite with structural repair and surface carbon coating.

[0097] The structure and performance of Example 3 are characterized as follows:

[0098] Figure 2 The results of the XRD pattern show that the purified, repaired and regenerated graphite in Example 3 is a pure phase without any impurity phases.

[0099] Figure 7 The results of the SEM image show that the surface of the purified, repaired and regenerated graphite in Example 3 has no impurities, cracks or pores.

[0100] Figure 8 The charge-discharge results show that in the 0.1C charge-discharge of the purified, repaired and regenerated graphite in Example 3, the initial discharge specific capacity is 384.9 mAh / g, the initial charge specific capacity is 352.1 mAh / g, and the initial Coulomb efficiency is 91.48%. Its electrochemical performance has recovered to the average level of commercial graphite.

[0101] From Figure 17 it can be seen that the D50 of the purified, repaired and regenerated graphite in Example 3 is 18.63 μm and the D90 is 35.22 μm; the graphitization degree is 97.83%, indicating that the graphite lattice damage has been repaired and the amorphous carbon has been removed; the iron, copper, aluminum and magnetic foreign matters are all less than 5 ppm, indicating that the graphite has been purified and the metal impurities have been removed; the fixed carbon content is 99.953% and the ash content is 0.047%, indicating that the graphite has been purified and the inorganic and organic impurities in the SEI film have been removed; the specific surface area is 2.129 m 2 / g, the 5T compaction density is 1.92 g / cm 3 and the tap density is 1.18 g / cm 3 , indicating that the pore defects in the graphite have been repaired.

[0102] The above results show that the physical and chemical indexes of the purified, repaired and regenerated graphite in Example 3 meet the standards of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0103] Comparative Example 1:

[0104] This Comparative Example 1 adopts the following steps:

[0105] S1 After discharging the waste lithium battery at a fixed potential of 0.50 V, it is heated to 500 °C under a nitrogen atmosphere and kept at a constant temperature for 3 h to fully pyrolyze and carbonize the binder, obtaining a preliminarily treated negative electrode sheet. Then, it is placed in water and treated under an ultrasonic power of 400 W for 20 min to separate the coating on the negative electrode sheet from the copper current collector. After passing through a 200-mesh sieve, the material under the sieve is taken to obtain preliminarily separated graphite particles.

[0106] S2 The preliminarily separated graphite particles in step S1 are placed in an H2SO4 solution with a concentration of 1.2 mol / L, and under the condition of a solid-liquid ratio of 10 g / L, they are heated in a water bath at 45 °C and leached for 2 h under the stirring of a paddle at 3000 rpm to obtain preliminarily purified graphite.

[0107] The remaining steps S3 - S5 are the same as those in Example 1.

[0108] The structure and performance of this Comparative Example 1 are characterized as follows:

[0109] Figure 2 The results of the XRD pattern show that the graphite obtained in this Comparative Example 1 exhibits a broad diffraction peak bulge at approximately 20 - 26° (2 Theta), without other impurity phases, and the obtained graphite contains a small amount of amorphous carbon.

[0110] Figure 9 The results of the SEM image show that the surface of the graphite obtained in this Comparative Example 1 contains a large number of aggregates of carbon black spherical small particles and amorphous carbon particles (there are obvious impurities on the graphite surface), but there are no cracks or holes on the surface. Therefore, comparing the results of Examples 1 - 3, it shows that in this application, the synergistic use of high-frequency alternating magnetic field and atmospheric plasma, combined with the combined use of a stator-rotor high-shear homogenization dispersion and reverse flotation method, can effectively remove the amorphous carbon generated by the high-temperature pyrolysis of the organic binder on the graphite surface, especially can efficiently remove the aggregates of carbon black conductive agents.

[0111] Figure 10 The charge-discharge results show that in the 0.1C charge-discharge of the graphite obtained in this Comparative Example 1, the initial discharge specific capacity is 391.0 mAh / g, the initial charge specific capacity is 341.7 mAh / g, and the initial Coulombic efficiency is 87.41%. It can be seen that due to the residual amorphous carbon in the graphite of this Comparative Example 1, the initial charge specific capacity and Coulombic efficiency are relatively low.

[0112] From Figure 18It can be seen that the D50 of the graphite obtained in Comparative Example 1 is 15.24 μm, and the D90 is 31.26 μm; the graphitization degree is 96.23%, indicating that there is a residual part of amorphous carbon in the graphite; the contents of iron, copper, aluminum and magnetic foreign matters are all less than 5 ppm, but the copper content is 0.873 ppm, which is higher than that in Examples 1 to 3. This is mainly because the copper current collector becomes brittle and difficult to separate due to high-temperature carbonization and pyrolysis stripping at 500 °C; the fixed carbon content is 99.879% and the ash content is 0.121%, which is much higher than the ash content in Examples 1 to 3. This is mainly caused by the residual trace copper. At the same time, there is no lamellar residue structure on the surface, indicating that both inorganic and organic impurities in the SEI film have been removed; the specific surface area is 3.152 m 2 / g, the 5T compaction density is 1.87 g / cm 3 , and the tap density is 1.09 g / cm 3 , which is lower than the compaction and tap densities in Examples 1 to 3. This is mainly due to the incomplete removal of amorphous carbon in the graphite; in addition, the pore defects in the graphite have been repaired.

[0113] The above results show that the first-cycle Coulombic efficiency in the electrochemical performance of Comparative Example 1 < 91%, which does not meet the standard of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0114] Comparative Example 2:

[0115] This Comparative Example 2 adopts the following steps:

[0116] S1 is the same as that in Comparative Example 1.

[0117] S2 Stir and disperse 1 kg of the recovered graphite particles obtained in step S1 in a 0.1 mol / L sulfuric acid solution, control the solid-liquid ratio to be 30 g / L, control the leaching time to be 90 min, then add the graphite flotation inhibitor - sodium carboxymethylcellulose, with a solid-liquid ratio of 0.6 g / L, stir for 15 min, then add the amorphous carbon capturer - oleic acid, with a solid-liquid ratio of 0.15 g / L, further stir for 15 min, then add the foaming agent - 2-ethylhexanol, with a solid-liquid ratio of 0.10 g / L, and perform reverse flotation for 15 min to remove amorphous carbon.

[0118] S3 Adjust the pH value of the product after reverse flotation and removal of amorphous carbon to 3, add ferrous sulfate heptahydrate at 560 mg / L, further stir for 20 min, then dropwise add hydrogen peroxide in batches at 340 mg / L, control the dropping rate to be 3 mL / min·m 3 , further stir and react for 40 min to fully oxidize and decompose the organic matter in the SEI film and the residual carbonate electrolyte on the surface of the recovered graphite, and obtain deeply purified graphite after filtration, washing and drying.

[0119] The S4 step is the same as the S5 step in Example 1.

[0120] The structure and performance of Comparative Example 2 are characterized as follows:

[0121] Figure 2 The XRD pattern results show that the graphite obtained in Comparative Example 2 exhibits a broad diffraction peak bulge at approximately 20 - 26° (2 Theta), with no other impurity phases. The resulting graphite contains only trace amounts of amorphous metal or its compounds.

[0122] Figure 11 The SEM image results show that since the stator-rotor high-shear homogenizer was not used for dispersion in Step 1 of Comparative Example 2, the surface of the obtained graphite contains aggregates of a small amount of carbon black spherical particles, but there are no cracks or holes on the surface. It can be seen that the stator-rotor high-shear homogenization used in the present application can efficiently remove the aggregates of carbon black conductive agents.

[0123] Figure 12 The charge-discharge results show that in the 0.1C charge-discharge of the graphite obtained in Comparative Example 2, the initial discharge specific capacity is 349.7 mAh / g, the initial charge specific capacity is 297.1 mAh / g, and the initial Coulombic efficiency is 84.96%. Since chelation treatment was not performed in Comparative Example 2, there are still trace amounts of amorphous metal or its compounds remaining in the graphite, resulting in a decrease in the initial charge-discharge specific capacity and Coulombic efficiency.

[0124] From Figure 18 it can be seen that the D50 of the graphite obtained in Comparative Example 2 is 17.16 μm, and the D90 is 34.94 μm; the graphitization degree is 97.68%, indicating that the damage to the graphite lattice has been repaired and most of the amorphous carbon has been removed; the contents of iron, copper, aluminum, and magnetic foreign substances are all greater than 5 ppm, where iron is 136.329 ppm, copper is 912.184 ppm, aluminum is 79.256, and magnetic foreign substances are 25.584, which are greatly increased compared to the metal contents in Examples 1 - 3, mainly due to the lack of EDTA chelation to remove metal impurity ions or amorphous metal or its compounds in the graphite; the fixed carbon content is 99.627% and the ash content is 0.273%, which is higher than the ash content in Comparative Example 1, mainly due to the lack of EDTA chelation to remove metal impurity ions or amorphous metal or its compounds in the graphite, and at the same time, the surface graphite has been purified, and both inorganic and organic impurities in the SEI film have been removed; the specific surface area is 2.273 m 2 / g, the 5T compaction density is 1.90 g / cm 3 , and the tapped density is 1.13 g / cm 3 , and the pore defects in the surface graphite have been repaired.

[0125] The above results show that in Comparative Example 2, the iron content of trace metal elements > 100 ppm, the copper and aluminum content > 5 ppm, the magnetic foreign matter > 0.5 ppm, the fixed carbon content < 99.70%, and the Coulombic efficiency of the first cycle in the electrochemical performance < 91%, which does not meet the standard of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0126] Comparative Example 3:

[0127] This Comparative Example 3 adopts the following steps:

[0128] S1 to S3 are the same as those in Example 1.

[0129] S4 puts the preliminarily purified graphite obtained in step S3 into a screw kneading device, and through segmented screw kneading, the extrusion pressure of the screw kneading device in the first stage is controlled at 0.03 MPa, and degassing is carried out at room temperature for 5 min. In the second stage, asphalt is added according to a mass ratio of 5 wt%, and kneaded and mixed with the deeply purified graphite input in the first stage, and extruded and filled with flowing asphalt at 0.25 MPa at 260 °C for 20 min. Then, the graphite-asphalt mixture kneaded and extruded from the screw kneading device is placed in a high-temperature furnace and carbonized at 1150 °C for 2 h to obtain regenerated graphite with structure repair and surface carbon coating.

[0130] The structure and performance of this Comparative Example 3 are characterized as follows:

[0131] Figure 2 The XRD pattern results show that the graphite obtained in this Comparative Example 3 is a pure phase without any impurity phase.

[0132] Figure 13 The SEM image results show that the surface of the graphite obtained in this Comparative Example 3 has no cracks or holes. Since the oxidation purification step is not adopted, there are local lamellar residual carbonate electrolyte residue derivatives on the graphite surface. Comparing the results of the above Examples 1 to 3, it shows that the oxidation purification step adopted in this application can effectively remove inorganic and organic impurities in the SEI film.

[0133] Figure 14 The charge-discharge results show that in this Comparative Example 2, the first-cycle discharge specific capacity of the obtained graphite at 0.1C is 380.3 mAh / g, the first-cycle charge specific capacity is 343.2 mAh / g, and the first-cycle Coulombic efficiency is 90.24%. Comparing the results of the above Examples 1 to 3, it shows that the residual inorganic and organic impurities in the SEI film in the graphite will lead to a decrease in the first-cycle charge specific capacity, specific capacity, and Coulombic efficiency.

[0134] From Figure 18It can be seen that the D50 of the graphite obtained in Comparative Example 3 is 18.40 μm, and the D90 is 34.46 μm; the graphitization degree is 97.84%, indicating that the damage to the graphite lattice has been repaired; the contents of iron, copper, aluminum and magnetic foreign matters are all less than 5 ppm, indicating that the graphite has been purified and the metal impurities have been removed; the fixed carbon content is 99.889% and the ash content is 0.111%, which is much higher than the ash content in Examples 1 to 3, mainly caused by inorganic and organic impurities in the SEI film; the specific surface area is 2.161 m 2 / g, the 5T compaction density is 1.92 g / cm 3 , and the tapped density is 1.14 g / cm 3 , and the pore defects in the surface graphite have been repaired.

[0135] The above results show that the first-cycle Coulomb efficiency in the electrochemical performance of Comparative Example 3 is <91%, which does not meet the standard of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0136] Comparative Example 4:

[0137] This Comparative Example 4 adopts the following steps:

[0138] S1 to S4 are the same as those in Example 1.

[0139] In S5, pitch is added to the deeply purified graphite obtained in step S4 at a mass ratio of 5 wt%, and after mixing, it is placed in a roller hearth furnace. Under a high-purity nitrogen atmosphere, it is heated to 260 °C at a rate of 5 °C / min, held for 1 h, and then heated to 1150 °C at the same rate and held for 2 hours to obtain carbon-coated regenerated graphite.

[0140] The structure and performance of this Comparative Example 4 are characterized as follows:

[0141] Figure 2 The XRD pattern results show that the graphite obtained in this Comparative Example 4 is a pure phase without any impurity phases.

[0142] Figure 15 The SEM image results show that although there are no impurities on the surface of the graphite obtained in this Comparative Example 4, there are cracks and holes. Comparing the results of Examples 1 to 3, it shows that the segmented screw pressure infiltration coating adopted in this application can effectively fill the surface defects and internal holes of the graphite with pitch.

[0143] Figure 16 The charge and discharge results show that the first-cycle discharge specific capacity of the graphite obtained in this Comparative Example 4 during 0.1C charge and discharge is 392.1 mAh / g, the first-cycle charge specific capacity is 351.7 mAh / g, and the first-cycle Coulomb efficiency is 89.70%. It can be seen that when there are cracks on the graphite surface and internal holes, the first-cycle Coulomb efficiency will be reduced.

[0144] FromFigure 18 It can be seen that the D50 of the graphite obtained in Comparative Example 4 is 18.34 μm, and the D90 is 35.65 μm; the graphitization degree is 97.70%, indicating that the damage to the graphite lattice has been partially repaired; the contents of iron, copper, aluminum and magnetic foreign matters are all less than 5 ppm, indicating that the metal impurities have been removed; the fixed carbon content is 99.942% and the ash content is 0.058%, indicating that the graphite has been purified and the inorganic and organic impurities in the SEI film have been removed; the specific surface area is 4.867 m 2 / g, and the 5T tap density is 1.73 g / cm 3 , and the vibration density is 0.98 g / cm 3 . The pore defects in the surface graphite are not completely repaired.

[0145] The above results show that the specific surface area of Comparative Example 4 > 4.5 m 2 / g, the vibration density < 1.00 g / cm 3 , and the Coulombic efficiency of the first cycle in the electrochemical performance < 91%, which does not meet the standard of "Graphite Anode Materials for Lithium-Ion Batteries" (GB / T 24533-2019).

[0146] The present application also provides a graphite negative electrode sheet, which is prepared by using the regenerated graphite obtained by the above-mentioned structure repair and surface carbon coating of recycled waste lithium battery graphite as the negative electrode active material. When it is used to prepare a lithium-ion battery, the Coulombic efficiency of the first cycle > 91.4%, which reliably guarantees the electrochemical performance of the lithium-ion battery and can meet the requirements of commercial energy storage lithium batteries.

[0147] The present application also provides a lithium-ion battery, the preparation of which includes the above-mentioned graphite negative electrode sheet, which solves the problem of recycling the negative electrode materials of waste lithium batteries and reduces the manufacturing cost of lithium-ion batteries.

[0148] The above embodiments shown in the present application are only part of the preferred embodiments of the present application, and the present application cannot be limited by this. Without departing from the essence of the present application, any modifications, equivalent substitutions and improvements made by those skilled in the art all fall within the protection scope of the present application.

Claims

1. A method for purifying, repairing and regenerating graphite from waste lithium batteries, characterized in that: The steps include: S1. Placing the negative electrode of the waste lithium battery in a high-frequency alternating magnetic field, controlling the electromagnetic induction heating current to be within the range of 200A to 500A, the alternating magnetic field frequency to be 20 to 30kHz, the surface temperature of the copper current collector in the negative electrode of the waste lithium battery to be 350 to 400°C, and treating the negative electrode of the waste lithium battery with a plasma generator, the pulse power of the plasma generator to be 20 to 50kW, so that cracks are formed in the coating between the graphite in the negative electrode of the waste lithium battery and the copper current collector and the interface between the coating and the copper current collector is dislocated, and then the graphite is peeled off from the copper current collector by ultrasonic vibration, and the graphite particles are recovered after sieving; S2. dispersing the recovered graphite particles in a dilute acid solution, adding a graphite flotation inhibitor, stirring, adding an amorphous carbon capture agent, stirring, and then adding a frother, and after reverse flotation, removing the amorphous carbon; The graphite flotation depressant is selected from at least one of sodium carboxymethyl cellulose or water glass; The amorphous carbon capture agent is selected from at least one of sodium dodecylbenzene sulfonate or oleic acid; The foaming agent is selected from at least one of methyl isobutyl carbinol and 2-ethylhexanol; S3: mixing the product obtained in step S2 with a dilute acid solution, then adding a chelating agent, stirring to form a chelate, and then washing with a dilute acid solution to leach out metals, oxides and inorganic substances in the SEI film in the product, thereby obtaining a preliminarily impurity-removed graphite substrate; S4: adjusting the pH value of the preliminarily impurity-removed graphite substrate obtained in step S3 to 2-3, adding ferrous sulfate heptahydrate, adding hydrogen peroxide dropwise after sufficient stirring, and then stirring to react to oxidize and decompose organic matter in the SEI film and the carbonate electrolyte remaining on the surface of the graphite particles, and filtering, washing, and drying to obtain deeply purified graphite; S5: adding petroleum asphalt to the deeply purified graphite obtained in step S4, and then kneading the deeply purified graphite and the petroleum asphalt at a temperature higher than the softening point of solid asphalt through a screw kneading device, and then carbonizing the kneaded graphite-petroleum asphalt mixture to obtain regenerated graphite with repaired structure and surface carbon coating.

2. The method for purifying, repairing and regenerating graphite from waste lithium batteries according to claim 1, characterized in that: In the step S1, the air flow rate in the high-frequency alternating magnetic field is controlled at 10 to 20 L / min, and the processing time is 30 to 60 s.

3. The method for purifying, repairing and regenerating graphite from waste lithium batteries according to claim 1, characterized in that: In the step S2, when the graphite particles are dispersed in the dilute acid solution, the solid-liquid ratio of the graphite particles to the dilute acid solution is 10 to 50 g / L, and the graphite particles are dispersed in the dilute acid solution by a stator-rotor high shear homogenizer, the shear speed is 9000 to 12000 rpm, and the time is 60 to 120 min.

4. The method for purifying, repairing and regenerating graphite from waste lithium batteries according to claim 1, characterized in that: In the step S2 and the step S3, the dilute acid is sulfuric acid, and the concentration of the sulfuric acid solution is 0.05-0.10 mol / L.

5. The method for purifying, repairing and regenerating graphite from waste lithium batteries according to any one of claims 1, 3 or 4, characterized in that: In the step S2, the solid-liquid ratio of the graphite particles to the graphite flotation inhibitor is 0.3-1 g / L, and the graphite flotation inhibitor is added and stirred for 10-20 minutes; the solid-liquid ratio of the graphite particles to the amorphous carbon capture agent is 0.1-0.2 g / L, and the amorphous carbon capture agent is added and stirred for 10-20 minutes; the solid-liquid ratio of the graphite particles to the frother is 0.05-0.15 g / L; and the reverse flotation time is 10-15 minutes.

6. The method for purifying, repairing and regenerating graphite from waste lithium batteries as claimed in claim 4, characterized in that: In the step S3, the solid-liquid ratio of the product obtained in the step S2 to the sulfuric acid solution is 10 to 50 g / L; the chelating agent is ethylenediaminetetraacetic acid, the mass ratio of the graphite particles to the ethylenediaminetetraacetic acid is 1:0.01 to 0.05, and the stirring time after adding the ethylenediaminetetraacetic acid is 10 to 20 minutes.

7. The method for purifying, repairing and regenerating graphite from waste lithium batteries according to claim 1, characterized in that: In the step S4, 140-560 mg / L of ferrous sulfate heptahydrate is added, stirred for 10-20 min, and then 85-340 mg / L of hydrogen peroxide is added dropwise in batches at a rate of 2-5 mL / min·m 3 , and further stir for 30 to 60 minutes.

8. The method for purifying, repairing and regenerating graphite from waste lithium batteries as claimed in claim 1, characterized in that: The S5 step is divided into three stages. In the first stage, the deeply purified graphite is put into a screw kneading device, the screw extrusion pressure is controlled, and degassing is performed at room temperature. In the second stage, asphalt with a mass ratio of 2.5 to 8 wt% is added to the deeply purified graphite, and the deeply purified graphite and the asphalt are kneaded at a temperature higher than the softening point of solid asphalt. In the third stage, the kneaded graphite-asphalt mixture is carbonized.

9. The method for purifying, repairing and regenerating graphite from waste lithium batteries as claimed in claim 8, characterized in that: In the S5 step, the screw extrusion pressure of the screw kneading equipment in the first section is 0.01-0.05MPa, and the room temperature degassing time is 2-5min. The screw extrusion pressure of the screw kneading equipment in the second section is 0.20-0.30MPa, the solid asphalt softening point temperature is 220-280°C, and the kneading time is 5-10min. The third section is to place the kneaded graphite-asphalt mixture in a high-temperature furnace to carbonize the asphalt, the carbonization temperature is 1100-1250°C, and the carbonization insulation time is 1-2h.

10. A graphite negative electrode plate, characterized in that: The regenerated graphite obtained by the method according to any one of claims 1 to 9 is used as the negative electrode active material for preparation.

11. A lithium ion battery, characterized in that: Comprising the graphite negative electrode sheet as claimed in claim 10.

Images