Deep impurity removal and recycling method for waste lithium battery graphite negative electrode waste

Abstract

The present invention provides a method for deep impurity removal and recycling of waste graphite negative electrode materials from used lithium batteries, comprising the following steps: heat-treating the waste graphite negative electrode materials to oxidize metal impurities in the waste graphite negative electrode materials, followed by cooling; acid-leaching the heat-treated waste graphite negative electrode materials, stirring for a certain period of time, filtering and separating, washing until neutral, and drying for 2 to 15 hours to obtain impurity-removed graphite I; further removing impurities from the impurity-removed graphite I by low-concentration acid leaching, filtering and separating to obtain impurity-removed graphite II; and fully dispersing the impurity-removed graphite II, electrochemically treating it at a voltage of 0.1 to 30 V for 0.1 to 24 hours, washing, and drying to obtain a high-purity graphite negative electrode. The present invention combines heat treatment, acid leaching, and electrochemical treatment to ensure effective impurity removal while significantly reducing the amount of acid used in the impurity removal process. It also eliminates the use of other reagents such as oxidants, thereby reducing pollution and the burden of subsequent sewage treatment. Furthermore, the impurity-removed graphite particles are uniform, contain low impurities, and have excellent electrochemical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of waste lithium battery recycling, and in particular relates to a method for deep impurity removal and recycling of waste graphite negative electrode waste of waste lithium ion batteries. Background Art

[0002] Since the advent of lithium-ion batteries, they have been widely used in various fields due to their high capacity and excellent electrochemical properties. In recent years, with the increasing use of lithium-ion batteries, the number of retired batteries has also increased year by year. After a period of service, problems may occur in the positive electrode, negative electrode, electrolyte, and current collector inside the battery, leading to an inevitable decline in performance. The industry is currently paying more and more attention to the recycling and treatment of waste lithium-ion batteries. However, due to the high value of positive electrode materials, the focus of recycling is mostly on the recycling and reuse of positive electrode materials. For the relatively low-value negative electrode materials, they are usually treated by methods such as incineration and landfill, which not only pollutes the environment but also wastes resources.

[0003] Currently, graphite is the most commonly used negative electrode material for commercial lithium-ion batteries, with artificial graphite alone accounting for over 80% of the negative electrode material market. As for the negative electrode, as the battery ages, the SEI film on the graphite surface becomes thicker, leading to an increase in the battery's internal resistance, a decrease in performance, and eventual scrapping. However, the structure of the graphite itself is not significantly damaged, and after removing the internal impurities, it can still be reused. Waste graphite negative electrodes contain a high level of impurities, originating from electrolytes, positive electrode materials, positive and negative electrode current collectors, and outer shells. The metal element impurities include Cu, Al, Fe, Ni, Co, Mn, Li, and are relatively complex. Common impurity treatment methods currently include heat treatment, alkaline leaching, and acid leaching. In order to effectively remove metal impurities within the graphite, high concentrations of acid, alkali, oxidants, reducing agents, and other chemical reagents are usually used. If not properly handled, this can cause significant environmental pollution.

[0004] The Chinese Patent Office has published a patent document titled "A Method for Recovering Graphite from a Mixture of Waste Lithium-ion Battery Materials" (Publication No. CN115101842A). This method recovers graphite from mixed positive and negative electrode waste materials through two acid leachings and one alkaline leaching, supplemented by oxidants and surfactants. The process uses highly concentrated acids, alkalis, and other reagents, increasing costs and incurring additional subsequent wastewater treatment expenses. Furthermore, the recovery process introduces new impurities, resulting in lower graphite purity and making further use difficult. Another published patent document, "A Method for Recovering Graphite from Waste Lithium-ion Batteries" (Publication No. CN111072023A), involves subjecting mechanically pulverized lithium-ion battery waste to alkaline and acid leaching to initially separate the positive and negative electrodes. The negative electrode graphite is then screened to remove large copper impurities. A second acid leaching is then performed to remove residual impurities. Finally, a heat treatment in air is performed to remove organic impurities such as binders. Although the negative electrode graphite waste can be removed well, the acid leaching process uses a very high concentration of acid, the subsequent wastewater treatment cost is high, and the environmental protection performance is poor.

[0005] Therefore, it is necessary to solve the defects of the above-mentioned prior art. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for deep impurity removal and recycling of waste graphite negative electrode waste of waste lithium batteries, which can greatly reduce the amount of acid used in the impurity removal process while ensuring the impurity removal effect, does not require alkali or other reagents, and has good environmental protection.

[0007] The present invention provides a method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste, comprising the following steps:

[0008] S1 heat-treats the graphite anode waste to reduce graphite loss and oxidize metal impurities in the graphite anode waste, and then cools it;

[0009] S2: The heat-treated graphite negative electrode waste is stirred under acidic conditions for a period of time, filtered and separated, washed to neutrality, and dried for 2h to 15h to obtain impurity-free graphite I;

[0010] S3 further removing impurities from the impurity-removed graphite I with a low-concentration acid, and filtering and separating to obtain impurity-removed graphite II;

[0011] S4 After the impurity-removed graphite II is fully dispersed, an electrochemical treatment is performed at a voltage of 0.1V to 30V for 0.1h to 24h, and after washing and drying, a recovered high-purity graphite negative electrode material is obtained.

[0012] Optionally, in step S1, the heat treatment temperature is 300° C. to 400° C., and the heat treatment time is 5 h to 15 h.

[0013] Optionally, the acidic condition in step S2 is to add the graphite negative electrode waste into an acid solution, and the acid is at least one of sulfuric acid, hydrochloric acid, nitric acid, citric acid, acetic acid or gluconic acid.

[0014] Optionally, in step S2, the solid-liquid ratio of the graphite negative electrode waste to the acid solution is 0.1 g / L to 300 g / L, the acid concentration is 0.1 mol / L to 1.5 mol / L, the treatment temperature is 20° C. to 100° C., and the treatment time is 0.1 h to 24 h.

[0015] Optionally, in step S3, the solid-liquid ratio of the graphite negative electrode waste to the acid solution is 0.1 g / L to 300 g / L, the acid concentration is 0.01 mol / L to 0.1 mol / L, the treatment temperature is 20° C. to 100° C., and the treatment time is 0.1 h to 24 h.

[0016] Optionally, in the S4 step, the electrochemical treatment is to place the impurity-removing graphite II dispersed in water in an impurity-removing container, and set at least one anode and cathode spaced apart in the impurity-removing container, and the anode and cathode are electrically connected to the positive and negative poles of a DC power supply, respectively; the impurity-removing container is connected to a storage container through a pipeline, and a power pump is provided on the pipeline connecting the storage container and the impurity-removing container, so that a circulation is formed between the storage container and the impurity-removing container.

[0017] Optionally, the distance between the anode and the cathode is ≤2-3 cm.

[0018] Optionally, the anode and the cathode are made of conductive titanium plates, graphite plates or nickel foam plates, and the surfaces of the titanium plates, graphite plates or nickel foam plates are coated with an active material with a large adsorption specific surface area.

[0019] The present invention further comprises a separator, and the separator is connected to the storage container via a pipeline.

[0020] The present invention also includes a control unit, which is used to control the voltage of the DC power supply, the start and stop of the power pump, and the positive and negative connection of the DC power supply with the anode plate and the cathode plate.

[0021] The present invention uses waste graphite cathodes from used lithium-ion batteries as raw material. Through a surface oxidation process in air, the process removes organic impurities from the graphite cathode waste, oxidizes metallic impurities within the graphite cathode waste, and also modifies the graphite surface. A first acid treatment using common organic and inorganic acids separates the majority of oxidized metallic impurities. Remaining trace, difficult-to-separate metallic impurities are then treated again with a lower-concentration acid. Further electrochemical treatment in deionized water further removes impurities, completely removing any remaining impurities from the graphite cathode waste. The treatment process is completed at a relatively low voltage, ultimately yielding pure graphite.

[0022] The method for deep impurity removal and recovery of graphite negative electrode waste provided by the present invention combines pyrolysis and wet processing, uses a small amount of acid in the entire processing flow, can effectively remove metal impurities inside the waste graphite, overcomes the defects caused by the use of strong acids, strong bases, oxidants, high temperatures and high pressures in the existing technology, reduces pollution and the burden of subsequent sewage treatment, has high purity of the product after impurity removal, and the electrochemical properties of the graphite itself are significantly improved due to the removal of impurities, and has good performance in terms of first discharge specific capacity and cycle stability.

[0023] The process of the invention is simple and has a short flow. The treated graphite negative electrode can be used as the negative electrode in a lithium ion battery, thereby avoiding the ineffective waste of negative electrode graphite in waste batteries and reducing the battery material cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the electrochemical treatment device of the present invention.

[0025] Figure 2 The X-ray diffraction comparison diagrams of Examples 1, 2, and 3 of the present invention before and after impurity removal of graphite negative electrode waste are shown.

[0026] Figure 3 The following are scanning electron microscope (SEM) images of Examples 1, 2, and 3 of the present invention before and after impurities removal from graphite negative electrode waste; wherein a) is the SEM image of the graphite negative electrode waste before impurities removal, and b), c), and d) are the SEM images of Examples 1, 2, and 3, respectively.

[0027] FIG4 is a capacity curve of Examples 1, 2, and 3 of the present invention before and after impurity removal of graphite negative electrode waste, cycled 100 times at a rate of 0.1C in a button cell.

[0028] Figure 5 These are the ICP test results of Examples 1, 2, and 3 of the present invention before and after impurities removal from graphite negative electrode waste. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] The present invention provides a method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste, comprising the following steps:

[0031] S1 heat treats the graphite anode waste to oxidize the metal impurities in the graphite anode waste while minimizing graphite loss, and then cools it.

[0032] The graphite anode waste in this step is graphite that has been separated from the positive electrode but not yet cleaned of impurities. It originates from used lithium-ion batteries that have been discharged and disassembled in the factory. The graphite anode waste is placed in a muffle furnace. The temperature is then raised to 300°C to 400°C according to a pre-set heating program. The furnace is then held at this temperature for 5 to 15 hours, then cooled to room temperature. The material is then removed and ready for use.

[0033] Heat treating the graphite anode waste in this step decomposes and volatilizes the organic binder and electrolyte components remaining on the graphite surface. It also oxidizes the metallic impurities within the graphite, making them easier to remove in subsequent processing. Heat treating the graphite anode waste generates new radicals at the irregular interfaces on the recycled graphite particles, helping to reduce interfacial impedance. This allows new lithium-ion batteries made from the recycled graphite particles to form a uniform and stable SEI film during the initial charge and discharge process.

[0034] The heat treatment temperature in this step is between 300°C and 400°C. This temperature range is selected and kept warm for 5h to 15h before natural cooling. This can not only oxidize the metal impurities in the graphite negative electrode waste, but also reduce the oxidation loss of graphite, thereby reducing the material loss caused by high-temperature heating of graphite and improving the material utilization rate after the negative electrode graphite is recovered.

[0035] S2 The heat-treated graphite negative electrode waste is stirred under acidic conditions for a period of time, filtered and separated, washed to neutrality, and dried for 2h to 15h to obtain impurity-removed graphite I.

[0036] The acidic conditions described in this step involve adding the heat-treated graphite anode waste to an acid solution. The acid is selected from sulfuric acid, nitric acid, hydrochloric acid, citric acid, acetic acid, or gluconic acid, with sulfuric acid being preferred. Hydrochloric acid is highly corrosive to equipment, while organic acids such as citric acid, acetic acid, and gluconic acid are relatively expensive. Sulfuric acid is inexpensive and offers relatively stable performance, making it suitable for large-scale recycling of graphite anode waste.

[0037] In this step, the solid-to-liquid ratio of the graphite anode waste to the acid solution is 0.1g / L to 300g / L. Within this range, the graphite is fully exposed to the acid, which facilitates the leaching reaction of metal impurities. The acid concentration is 0.1mol / L to 1.5mol / L, the treatment temperature is 20°C to 100°C, and the leaching reaction is stirred for 0.1h to 24h. Under these conditions, different metal impurities can fully react with the acid and leach into the solution.

[0038] After the leaching reaction is complete, the leachate and graphite are separated by vacuum filtration, and deionized water is added to the graphite for continuous washing until the conductivity of the washed solution reaches zero. Continuous washing with deionized water can elute and separate trace metal ions remaining in the graphite during the filtration process, achieving the purpose of purifying impurities.

[0039] The separated graphite is placed in a forced air drying oven and dried at a temperature of 50°C to 200°C for 2h to 15h to obtain impurity-removed graphite I.

[0040] S3: further removing impurities from the impurity-removed graphite I with a low-concentration acid, and filtering and separating to obtain impurity-removed graphite II.

[0041] The low-concentration acid treatment described in this step is to add the impurity-removed graphite I into the acid solution again. The acid is also sulfuric acid, nitric acid, hydrochloric acid, citric acid, acetic acid or gluconic acid, preferably sulfuric acid.

[0042] In this step, the solid-to-liquid ratio of the impurity-removed graphite I to the acid solution is 0.1 g / L to 300 g / L, the acid concentration is 0.01 mol / L to 0.1 mol / L, the treatment temperature is 20°C to 100°C, and the leaching time is 0.1 hour to 24 hours. Using a low-concentration acid treatment can further remove small amounts of impurities within the impurity-removed graphite I while also reducing the amount of acid used during the treatment process, thereby reducing recycling costs and environmental pollution.

[0043] In this step, the remaining insoluble metal impurities in the impurity-removed graphite I can be leached into soluble metal salts, and a portion of the metal impurities can be removed by filtration to obtain impurity-removed graphite II.

[0044] S4: adding the impurity-removed graphite II obtained in step S3 to deionized water and stirring to uniformly disperse the mixture. Two electrodes are then inserted into the solution and electrochemically treated for 0.1 to 24 hours at an applied voltage of 0.1 to 30 V to separate the impurity ions in the impurity-removed graphite II from the graphite. After the electrochemical treatment, the graphite is slowly extracted using a power pump while maintaining the applied voltage. The extracted graphite is filtered, washed, and dried to obtain a recovered high-purity graphite negative electrode material.

[0045] The electrochemical treatment in this step is to set at least one anode and cathode in the impurity removal container. Multiple anodes and cathodes can be arranged alternately and spaced apart and electrically connected to the positive and negative poles of a DC power supply, respectively. Deionized water is then added to the impurity removal container, and the impurity removal graphite II is fully dispersed in the deionized water so that the soluble metal salts in the impurity removal graphite II are dissolved in the water. However, if it is directly filtered at this time, some metal ions will remain between the layers of graphite and cannot be removed. In this step, a certain voltage is applied to the electrode. Through the electrochemical process, a double layer is formed on the electrode surface, and the metal ions inside the graphite are adsorbed to the electrode, thereby achieving the separation of the impurity ions in the impurity removal graphite II from the graphite. After the electrochemical treatment is completed, the electrode is kept energized and the graphite in the solution is sucked out at a lower flow rate to complete the deep removal of impurities in the graphite. The above-mentioned treatment process can avoid the use of reagents such as acids and alkalis, reduce environmental pollution, and the treatment process is simple. The electrode can be regenerated and reused by disconnecting the power or reversing the power after use. The impurities inside the obtained graphite are completely removed without damaging the original structure.

[0046] The electrodes used in this step are all inert electrodes. A conductive titanium plate, graphite plate, or nickel foam plate is used as the substrate. A porous carbon active material with a large specific surface area, such as activated carbon, graphene, or carbon fiber, is mixed with a conductive agent and a binder in a ratio of 8:1:1. The mixture is stirred into a slurry and coated on the substrate surface. After drying, the electrode is produced to enhance the electrode's adsorption performance and accelerate the adsorption process of impurity ions in water. A low proportion of active material in the slurry will result in a reduction in the effective pores of the electrode, while a high proportion of active material will prevent the slurry from firmly bonding to the substrate surface.

[0047] The electrochemical treatment parameters mentioned above include an applied DC voltage of 0.1V to 30V and a treatment time of 0.1h to 24h. If the applied voltage is too high, strong side reactions will occur, reducing the treatment effect. If the treatment time is too short, the ions in the solution will not be fully adsorbed onto the electrodes, reducing the impurity removal effect.

[0048] See Figure 1This electrochemical treatment step includes a decontamination container 2 and a storage container 5. Decontamination container 2 contains decontamination-free graphite II (a negative electrode graphite solution) dispersed in deionized water, with a solid-to-liquid ratio of 0.1 g / L to 100 g / L. Within decontamination container 2, at least one anode plate 21 and cathode plate 22 are spaced apart. Multiple anode plates 21 and cathode plates 22 are arranged in a staggered arrangement. The lower ends of the anode plates 21 and cathode plates 22 are each inserted into the liquid within decontamination container 2, while the upper ends are electrically connected to the positive and negative electrodes of a DC power supply 1, respectively. The storage container 5 is connected to the impurity removal container 2 through a pipeline. There are two connecting pipelines between the storage container 5 and the impurity removal container 2, and a first power pump 6 and a second power pump 7 are respectively provided on the pipelines. The liquid inlet end of the first power pump 6 is connected to the interface B2 of the storage container 5, and the liquid outlet end is connected to the interface A2 of the impurity removal container 2. The liquid inlet end of the second power pump 7 is connected to the interface A1 of the impurity removal container 2, and the liquid outlet end is connected to the interface B3 of the storage container 5, so that the liquid in the storage container 5 and the impurity removal container 2 circulates under the action of the first power pump 6 and the second power pump 7. In this way, for the waste negative electrode graphite from which most of the impurities have been removed, this step adopts an electrochemical treatment method. Without using reagents such as acids and alkalis, the water in which the waste negative electrode graphite is dispersed is circulated between the storage container 5 and the impurity removal container 2, and the impurity ions dissolved in the water are adsorbed onto the anode plate 21 and the cathode plate 22, so that the impurities inside the waste lithium battery negative electrode graphite are completely removed. The purified negative electrode graphite solution is circulated back to the storage container 5, completing the deep impurity removal process of the waste lithium battery negative electrode graphite.

[0049] In the electrochemical treatment step, the distance between each anode plate 21 and cathode plate 22 is ≤ 2-3 cm. The electric field formed between the anode plate 21 and cathode plate 22 adsorbs impurity ions in the water.

[0050] During the electrochemical treatment step, a conductivity meter 51 may be installed in the storage container 5 to monitor the conductivity of the negative electrode graphite solution in real time. The lower probe of the conductivity meter 51 is inserted into the liquid, while the upper probe is located outside the storage container 5 for easy reading. The liquid conductivity can be used to determine the removal of impurities from the liquid in the storage container 5. When the set value is reached, subsequent treatment is initiated.

[0051] This step also includes a separator 3, which is connected to the port B1 of the storage container 5 via a pipeline. The separator 3 is equipped with a filter membrane and a vacuum filter. After the impurities are removed, the negative electrode graphite solution enters the separator 3 from the storage container 5, is filtered through the filter membrane, and further passes through the vacuum filter to achieve solid-liquid separation and recover the negative electrode graphite.

[0052] This step also includes a control unit 11, which can control the opening and closing of the first power pump 6 and the second power pump 7, the opening and closing of each interface such as the storage container 5, the impurity removal container 2, and the separator 3, the voltage of the DC power supply 1, and the positive and negative connection of the DC power supply 1 with the anode plate 21 and the cathode plate 22. After the impurity removal is completed, the first power pump 6 can be turned off, and the graphite and water in the impurity removal container 2 are transported to the storage container 5 by the second power pump 7, and then sent to the separator 3 for separation and recovery of the negative electrode graphite. Afterwards, water is added to the impurity removal container 2, and the positive and negative poles of the DC regulated power supply 1 are controlled by the control unit 11 so that they are opposite to the previous polarity, completing the regeneration process of the anode plate 21 and the cathode plate 22. After the regeneration process is completed, the interface A3 of the impurity removal container 2 is opened, and the sewage generated during the regeneration process of the anode plate 21 and the cathode plate 22 in the impurity removal container 2 is discharged into the sewage collector 4 through the interface A3. By adopting the control unit 11, the anode plate 21 and the cathode plate 22 can be repeatedly recycled, thereby saving the cost of recycling the negative electrode graphite of waste lithium batteries.

[0053] The above-mentioned method for deep impurity removal and recovery of graphite negative electrode waste is further described in detail below with reference to specific embodiments. Example 1:

[0054] The method for deep impurity removal and recycling of graphite negative electrode waste in this embodiment 1 includes the following specific steps:

[0055] S1: 50 g of graphite negative electrode waste separated from the factory was placed in a crucible, heated to 400 °C at a rate of 5 °C / min in a muffle furnace and kept warm for 10 h. It was then cooled to room temperature with the furnace and taken out for use.

[0056] S2: 30g of heat-treated graphite anode waste was slowly added to 3L of 1mol / L sulfuric acid solution. The mixture was heated to 70°C in a water bath and magnetically stirred for 4 hours. The mixture was then cooled to room temperature and filtered using a vacuum filter. The mixture was then washed with deionized water until the conductivity reached zero. The resulting graphite was then dried in a forced-air drying oven at 100°C for 12 hours to obtain a black-gray powder, impurity-free graphite I.

[0057] S3: Take 20g of impurity-removed graphite I and slowly add it to 2L of 0.1mol / L sulfuric acid solution. Heat it to 70℃ in a water bath and stir it magnetically for 2h. Then stop heating and stirring, cool it to room temperature, and separate it by vacuum filtration to obtain impurity-removed graphite II.

[0058] S4 Add 2L of deionized water into the impurity removal container 2, and immerse the lower ends of the anode plate 21 and the cathode plate 22 (graphite plate, the surface of which is coated with activated carbon material) in the deionized water, and electrically connect the upper ends to the positive and negative poles of the DC power supply 1 respectively. The interval between the anode plate 21 and the cathode plate 22 is 2cm. The impurity removal container 2 is connected to the storage container 5. The impurity removal container 2 has three interfaces A1, A2, and A3, and the storage container 5 has three interfaces B1, B2, and B3. The storage container 5 and the impurity removal container 2 are connected by two pipelines, and the connecting pipelines are respectively provided with a first power pump 6 and a second power pump 7. The liquid inlet end of the first power pump 6 is connected to the interface B2 of the storage container 5, and the liquid outlet end is connected to the interface A2 of the impurity removal container 2. The liquid inlet end of the second power pump 7 is connected to the interface A1 of the impurity removal container 2, and the liquid outlet end is connected to the interface B3 of the storage container 5. At the same time, the interface A3 of the impurity removal container 2 is connected to the sewage collector 4, and the interface B1 of the storage container 5 is connected to the separator 3. The storage container 5 is provided with a conductivity tester 51. The DC power supply 1 has a voltage of 1V and is electrically connected to the control unit 11. The control unit 11 is used to control the opening and closing of the first power pump 6 and the second power pump 7, the opening and closing of the interfaces of the storage container 5 and the impurity removal container 2, and the positive and negative connection of the DC power supply 1 with the anode plate 21 and the cathode plate 22.

[0059] The impurity-removed graphite II obtained in step S3 is added to the deionized water in the impurity-removing container 2, the DC power supply 1 is connected, and the first power pump 6 is turned on, so that the liquid in the storage container 5 and the impurity-removing container 2 circulates under the action of the first power pump 6 and the second power pump 7. At this time, the impurities in the impurity-removed graphite II gradually dissolve in the water and are adsorbed on the anode plate 21 and the cathode plate 22, so that the impurity ions are separated from the graphite. The above-mentioned treatment time is 1 hour. After the treatment is completed, the first power pump 6 is turned off, the voltage is kept unchanged, and the solution in the impurity removal container 2 is transported to the storage container 5 through the second power pump 7. The interface B1 connecting the separator 3 and the storage container 5 is opened, and the graphite in the solution of the storage container 5 is slowly sucked out by the power pump. During the whole process, the anode plate 21 and the cathode plate 22 are kept submerged in the liquid. After that, the sucked-out graphite is separated by vacuum filtration in the separator 3 and washed with deionized water until the conductivity is zero. The graphite is heated to 100°C in a blast drying oven and dried for 12 hours to obtain high-purity graphite negative electrode recovery material.

[0060] After the impurity removal is completed, water is added to the impurity removal container 2, and the control unit 11 is used to make the positive and negative poles of the DC regulated power supply 1 opposite to the previously connected anode plate 21 and cathode plate 22, completing the regeneration process of the anode plate 21 and the cathode plate 22 (10 minutes), and then open the interface A3 to discharge the water in the regeneration process into the sewage collector 4.

[0061] The structure and performance of this embodiment 1 are as follows:

[0062] from Figure 2 As can be seen, the untreated graphite negative electrode powder still has strong graphite diffraction peaks, along with impurity peaks of copper (CuO) and aluminum oxide (Al2O3), originating from the copper foil, the negative electrode current collector, and the aluminum foil, the positive electrode current collector, within the battery. After treatment, only the graphite diffraction peak remains, with no other impurity peaks present, demonstrating that the treatment with this invention effectively removes impurities from the graphite.

[0063] contrast Figure 3 From the morphology images a) and b) in the figure, we can see that the graphite particles are larger before impurity removal, and a large amount of impurities are covered on the surface of the graphite particles. After impurity removal, the graphite particles are reduced in size, and the impurities on the surface basically disappear.

[0064] from Figure 4a As can be seen, the capacity of the button cell directly prepared from the raw materials is poor, with a first-week coulombic efficiency of 66.59%, an initial specific capacity of 290.4 mAh / g, and a capacity retention rate of only 63.84% after 100 cycles. In Example 1, the first-week coulombic efficiency was 87.23%, the initial specific capacity was 358.7 mAh / g, and the capacity retention rate after 100 cycles was 99.69%, showing a significant improvement in electrochemical performance.

[0065] Figure 5 The ICP test results of the graphite negative electrode waste after impurities removal in Example 1 are shown. Figure 5 It can be seen that the content of metal impurities in the treated graphite negative electrode powder is extremely low and can meet the use requirements. Example 2:

[0066] S1: 100 g of graphite anode waste separated from the factory was placed in a crucible, heated to 300 °C at a rate of 5 °C / min in a muffle furnace and kept warm for 15 h. It was then cooled to room temperature with the furnace and taken out for use.

[0067] S2: 70 g of heat-treated graphite anode waste was slowly added to 1.4 L of a mixed solution of 1.5 mol / L nitric acid and acetic acid. The mixture was heated to 100°C in a water bath and magnetically stirred for 12 hours. After that, heating and stirring were stopped, the mixture was cooled to room temperature, filtered and separated using a vacuum filter, and washed with deionized water until the conductivity reached zero. The resulting graphite was dried in a forced air drying oven at 100°C for 12 hours to obtain a black-gray powder, impurity-free graphite I.

[0068] S3: 70 g of impurity-removed graphite I was slowly added to 1.4 L of 0.01 mol / L sulfuric acid solution, heated to 90°C in a water bath, and magnetically stirred for 1 h. Then, heating and stirring were stopped, the mixture was cooled to room temperature, and filtered and separated using a vacuum filter to obtain impurity-removed graphite II.

[0069] S4: Add 1.4 L of deionized water into the impurity removal container 2, and immerse the lower ends of the anode plate 21 and the cathode plate 22 (titanium plate, with graphene material coated on the surface) in the deionized water, and electrically connect the upper ends to the positive and negative poles of the DC power supply 1 respectively. The interval between the anode plate 21 and the cathode plate 22 is 3 cm.

[0070] Same as Example 1, the impurity-removed graphite II obtained in step S3 is added to the deionized water in the impurity removal container 2, the DC power supply 1 is connected, the voltage is 2V, the first power pump 6 is turned on, and the liquid in the storage container 5 and the impurity removal container 2 is circulated under the action of the first power pump 6 and the second power pump 7. After 4 hours, the voltage is kept unchanged, the first power pump 6 is turned off, and the solution in the impurity removal container 2 is transported to the storage container 5 by the second power pump 7. The interface B1 connecting the separator 3 and the storage container 5 is opened, and the graphite in the solution of the storage container 5 is slowly sucked out by the peristaltic pump. During the whole process, the anode plate 21 and the cathode plate 22 are kept submerged in the liquid. After that, the sucked-out graphite is separated by suction filtration in the vacuum filter in the separator 3 and washed with deionized water until the conductivity is zero. The graphite is heated to 100° C. and dried for 12 h in a blast drying oven to obtain a high-purity graphite negative electrode recovery material.

[0071] After the impurity removal is completed, the regeneration process of the anode plate 21 and the cathode plate 22 is the same as that in Example 1.

[0072] The structure and performance of Example 2 are as follows:

[0073] from Figure 2 As can be seen, the untreated graphite negative electrode powder still has strong graphite diffraction peaks, along with impurity peaks of copper (CuO) and aluminum oxide (Al2O3), originating from the copper foil, the negative electrode current collector, and the aluminum foil, the positive electrode current collector, within the battery. After treatment, only the graphite diffraction peak remains, with no other impurity peaks present, demonstrating that the treatment with this invention effectively removes impurities from the graphite.

[0074] contrast Figure 3 From the morphology images a) and c) in the figure, we can see that the graphite particles are larger before impurity removal, and a large amount of impurities are covered on the surface of the graphite particles. After impurity removal, the graphite particles are reduced in size, and the impurities on the surface basically disappear.

[0075] from Figure 4b As can be seen, the capacity of the button cell directly prepared from the raw materials is poor, with a first-week coulombic efficiency of 66.59%, an initial specific capacity of 290.4 mAh / g, and a capacity retention rate of only 63.84% after 100 cycles. In Example 2, the first-week coulombic efficiency was 87.91%, the initial specific capacity was 350.5 mAh / g, and the capacity retention rate after 100 cycles was 99.71%, showing a significant improvement in electrochemical performance.

[0076] from Figure 5 It can be seen that the content of metal impurities in the graphite negative electrode powder after being treated in Example 2 is extremely low and can meet the use requirements. Example 3:

[0077] S1: Place 20 g of graphite anode waste separated from the factory in a crucible, heat it to 350 °C at a rate of 5 °C / min in a muffle furnace and keep it warm for 12 h. Then cool it to room temperature with the furnace and take it out for use.

[0078] S2: 15g of heat-treated graphite anode waste was slowly added to 750mL of a 0.5mol / L sulfuric acid solution. The mixture was heated to 60°C in a water bath and magnetically stirred for 6 hours. After that, heating and stirring were stopped, the mixture was cooled to room temperature, filtered and separated using a vacuum filter, and washed with deionized water until the conductivity reached zero. The resulting graphite was heated to 100°C in a forced air drying oven and dried for 12 hours to obtain a black-gray powder, impurity-free graphite I.

[0079] S3: 7 g of impurity-removed graphite I was slowly added to 750 mL of 0.05 mol / L sulfuric acid solution, heated to 60°C in a water bath, and magnetically stirred for 2 h. Then, heating and stirring were stopped, the mixture was cooled to room temperature, and filtered and separated using a vacuum filter to obtain impurity-removed graphite II.

[0080] S4: Add 700 mL of deionized water into the impurity removal container 2, and immerse the lower ends of the anode plate 21 and the cathode plate 22 (foam nickel plate, the surface of which is coated with graphene material) in the deionized water, and electrically connect the upper ends to the positive and negative poles of the DC power supply 1 respectively. The interval between the anode plate 21 and the cathode plate 22 is 2 cm.

[0081] Same as Example 1, the impurity-removed graphite II obtained in step S3 is added to the deionized water in the impurity removal container 2, the DC power supply 1 is connected, the voltage is 0.8V, the first power pump 6 is turned on, and the liquid in the storage container 5 and the impurity removal container 2 is circulated under the action of the first power pump 6 and the second power pump 7. After 0.5 hours, the voltage is kept constant, the first power pump 6 is turned off, and the solution in the impurity removal container 2 is transported to the storage container 5 by the second power pump 7. The interface B1 connecting the separator 3 and the storage container 5 is opened, and the graphite in the solution of the storage container 5 is slowly sucked out by the peristaltic pump. During the whole process, the anode plate 21 and the cathode plate 22 are kept submerged in the liquid. After that, the sucked-out graphite is separated by suction filtration in the vacuum filter in the separator 3 and washed with deionized water until the conductivity is zero. The graphite is heated to 100° C. and dried for 12 h in a blast drying oven to obtain a high-purity graphite negative electrode recovery material.

[0082] After the impurity removal is completed, the regeneration process of the anode plate 21 and the cathode plate 22 is the same as that in Example 1.

[0083] The structure and performance of Example 3 are as follows:

[0084] from Figure 2 As can be seen, the untreated graphite negative electrode powder still has strong graphite diffraction peaks, along with impurity peaks of copper (CuO) and aluminum oxide (Al2O3), originating from the copper foil, the negative electrode current collector, and the aluminum foil, the positive electrode current collector, within the battery. After treatment, only the graphite diffraction peak remains, with no other impurity peaks present, demonstrating that the treatment with this invention effectively removes impurities from the graphite.

[0085] contrast Figure 3 From the morphology images a) and d) in the figure, we can see that the graphite particles are larger before impurity removal, and a large amount of impurities are covered on the surface of the graphite particles. After impurity removal, the graphite particles are reduced in size, and the impurities on the surface basically disappear.

[0086] from Figure 4c As can be seen, the capacity of the button cell directly prepared from the raw materials is poor, with a first-week coulombic efficiency of 66.59%, an initial specific capacity of 290.4 mAh / g, and a capacity retention rate of only 63.84% after 100 cycles. In Example 3, the first-week coulombic efficiency was 87.77%, the initial specific capacity was 350.4 mAh / g, and the capacity retention rate after 100 cycles was 99.88%, showing a significant improvement in electrochemical performance.

Claims

1. A method for deep impurity removal and recycling of waste graphite negative electrode waste from waste lithium batteries, characterized in that: The steps include: S1. The graphite anode waste is heat treated to reduce graphite loss while oxidizing metal impurities in the graphite anode waste, and then cooled; S2. The heat-treated graphite anode waste is stirred under acidic conditions for a period of time, filtered and separated, washed to neutrality, and dried for 2h to 15h to obtain impurity-free graphite I; S3. The graphite Ⅰ was further impurity-removed with a low concentration of acid, and the impurity-removed graphite Ⅱ was separated by filtration; S4. After the impurity-removing graphite II is fully dispersed, electrochemical treatment is performed at a voltage of 0.1V to 30V for 0.1h to 24h, and after washing and drying, a high-purity graphite negative electrode material is recovered; The electrochemical treatment comprises placing the impurity-removing graphite II dispersed in water in an impurity-removing container, arranging at least one anode and cathode with a spacing of ≤2 to 3 cm in the impurity-removing container, and electrically connecting the anode and cathode to the positive and negative electrodes of a DC power supply, respectively; the impurity-removing container is connected to a storage container via a pipeline, and a power pump is provided on the pipeline connecting the storage container and the impurity-removing container to form a circulation between the storage container and the impurity-removing container.

2. The method for deep impurity removal and recycling of graphite negative electrode waste according to claim 1, wherein: In the step S1, the heat treatment temperature is 300° C. to 400° C., and the heat treatment time is 5 h to 15 h.

3. The method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste as claimed in claim 1, wherein: The acidic condition in step S2 is to add the graphite negative electrode waste into an acid solution, wherein the acid is at least one of sulfuric acid, hydrochloric acid, nitric acid, citric acid, acetic acid or gluconic acid.

4. The method for deep impurity removal and recovery of waste lithium battery graphite negative electrode waste as claimed in claim 3, wherein: In the step S2, the solid-liquid ratio of the graphite negative electrode waste to the acid solution is 0.1 g / L to 300 g / L, the acid concentration is 0.1 mol / L to 1.5 mol / L, the treatment temperature is 20° C. to 100° C., and the treatment time is 0.1 h to 24 h.

5. The method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste as claimed in claim 1, wherein: In the step S3, the solid-liquid ratio of the graphite negative electrode waste to the acid solution is 0.1 g / L to 300 g / L, the acid concentration is 0.01 mol / L to 0.1 mol / L, the treatment temperature is 20° C. to 100° C., and the treatment time is 0.1 h to 24 h.

6. The method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste as claimed in claim 1, wherein: The anode and the cathode are made of conductive titanium plates, graphite plates or nickel foam plates, and the surfaces of the titanium plates, graphite plates or nickel foam plates are coated with active materials with large adsorption specific surface area.

7. The method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste as claimed in claim 1, wherein: It also includes a separator, which is connected to the storage container through a pipeline.

8. The method for deep impurity removal and recycling of waste lithium battery graphite negative electrode waste as claimed in claim 1, wherein: It also includes a control unit, which is used to control the voltage of the DC power supply, the start and stop of the power pump, and the positive and negative connection of the DC power supply with the anode plate and the cathode plate.

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