Method for regenerating graphite negative electrode material of waste battery

Abstract

The invention discloses a waste battery graphite negative electrode material regeneration method, and relates to the technical field of battery recovery. The method comprises the following steps: step A, performing multi-method combined refined impurity precipitation: analyzing the graphite negative electrode material of the waste lithium ion battery by adopting an improved BCR sequential extraction method, and dividing the existence forms of metal elements into a water-soluble state, a weak acid extraction state, a reducible state and a residual state; according to the method, through multi-step precise leaching, metal elements such as copper, lithium, cobalt, manganese and nickel in the waste graphite negative electrode material can be effectively recycled, maximum utilization of resources is achieved, dependence on primary mineral resources is reduced, lattice defects of regenerated graphite are repaired through the steps of deep impurity removal, surface modification, calcination under specific conditions and the like, and the recovery rate of the regenerated graphite is increased. The surface impurities are greatly reduced, the crystal structure is optimized, the specific surface area and the pore structure are more beneficial to intercalation and deintercalation of lithium, and the performance of the regenerated graphite as the battery negative electrode material is remarkably improved.

Description

Technical Field

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

[0002] In today's global trend of vigorously promoting green energy transformation, electric vehicles have become the core direction of the development of the automotive industry with their advantages such as zero emissions and low noise. According to data from the International Energy Agency, the number of electric vehicles in the world has grown exponentially over the past five years, with an average annual growth rate of more than 40%. This explosive growth has directly led to a sharp increase in the market demand for lithium-ion batteries, which in turn has led to a simultaneous increase in the amount of waste lithium-ion batteries.

[0003] Lithium-ion batteries are the "heart" of electric vehicles. The graphite negative electrode materials inside them are not only abundant in reserves, but also account for an important proportion of the battery cost structure. However, the current traditional waste battery treatment model has obvious defects. On the one hand, most treatment processes focus on the recovery of high-value metal elements such as lithium and cobalt, but ignore the effective reuse of graphite negative electrode materials. On the other hand, during the use of batteries, waste graphite negative electrode materials undergo complex electrochemical reactions, and various metal impurities such as copper, lithium, cobalt, manganese, and nickel are attached to the surface, and a large amount of binder and electrolyte remain. These pollutants seriously erode the original regular crystal structure of graphite, causing its conductivity and charge and discharge performance to drop significantly.

[0004] In addition, the existing graphite negative electrode material regeneration technology is full of difficulties in practical application. Some processes use high-temperature smelting, strong acid and strong alkali leaching and other means. Although they can remove impurities to a certain extent, they have problems such as cumbersome processes, huge energy consumption, and serious equipment corrosion, resulting in high production costs. More importantly, the regenerated graphite material is difficult to meet the strict requirements of battery negative electrode materials in key performance indicators such as crystal structure integrity, specific surface area, and porosity, and cannot meet the growing demand for battery performance in high-end application fields such as electric vehicles.

[0005] Therefore, it is urgent to develop an efficient, environmentally friendly and low-cost recycling technology for waste battery graphite negative electrode materials. This is not only an important way to solve resource and environmental problems, but also an inevitable choice to promote the sustainable development of the battery industry. Summary of the invention

[0006] The purpose of the present invention is to provide a method for regenerating graphite negative electrode materials of waste batteries, which solves the problem that the graphite material regeneration technology in the prior art is difficult to meet the strict requirements of battery negative electrode materials in terms of key performance indicators such as crystal structure integrity, specific surface area and porosity, and cannot meet the growing demand for battery performance in high-end application fields of electric vehicles.

[0007] To solve the above technical problems, the present invention is achieved through the following technical solutions.

[0008] The present invention relates to a method for regenerating graphite anode materials from waste batteries, comprising the following steps: Step A: Multi-method combined analysis of impurities: The improved BCR sequential extraction method is used to analyze the graphite anode materials of waste lithium-ion batteries, and the existing forms of metal elements are divided into water-soluble state, weak acid extraction state, reducible state and residual state. The water-soluble state is leached by diluted acid solution, the weak acid extraction state is extracted by acetic acid-sodium acetate buffer solution, the reducible state is extracted by hydroxylamine hydrochloride-acetic acid buffer solution, and the residual state is extracted by aqua regia; Step B: EDTA-assisted hydrothermal efficient leaching of copper impurities: For the Cu impurities in the weak acid extraction state, the hydrothermal leaching method is adopted, and DESs is selected as the reagent. Ethylenediaminetetraacetic acid chelating agent accounting for 5%-10% of its mass is added to the DESs reagent. Waste graphite, DESs and deionized water are added to the reaction kettle with a stirring device, and the stirring speed is controlled at 150-250 r / min. Leaching is carried out under the conditions of a temperature of 120 °C, a time of 10 min, a solid-liquid ratio of 1:40 g / mL, and a mass ratio of DESs to waste graphite of 0.4 g / g. During the leaching process, the concentration of Cu ions in the solution is detected in real time by an online ion selective electrode. When the concentration of Cu ions reaches equilibrium, the reaction is stopped; Step C: TiO 2 Catalytic dynamic hydrothermal extraction of lithium element: After removing the Cu impurities, for the Li impurities, waste graphite and deionized water are added to the reactor to form a hydrothermal reaction system. Nanoscale titanium dioxide particles accounting for 0.5%-1.0% of the mass of the waste graphite are added to the system as a catalyst. Leaching is carried out under the conditions of a temperature of 200 °C, a time of 3 h, and a solid-liquid ratio of 1:30 g / mL. The dynamic hydrothermal leaching method is adopted, and deionized water is continuously supplemented into the reactor at a flow rate of 0.5-1.0 mL / min through a peristaltic pump, and the reaction solution after the reaction is discharged at the same flow rate; Step D: SDS-enhanced microwave-assisted leaching of cobalt, manganese and nickel with sulfide: After the Li leaching, for the Co, Mn, Ni impurities, waste graphite and DESs are added to the reactor to form a sulfide leaching system. Sodium dodecyl sulfate surfactant with a concentration of 0.05-0.1 mol / L is added to the system, and microwave-assisted leaching technology is adopted. The microwave frequency is set to 2450 MHz, and the power is 200-300 W. Leaching is carried out under the conditions of a temperature of 80 °C, a time of 50 min, a solid-liquid ratio of 1:30 g / mL, and a DESs concentration of 0.4 mol / L; Step E: Low-temperature calcination for repairing graphite lattice and performance regeneration: Evenly spread the leached graphite material in the crucible of the resistance furnace. Start the power supply and set the heating program. Gradually increase the furnace temperature from room temperature to 500 °C at a heating rate of 5 - 10 °C / min. When the temperature approaches 500 °C, appropriately reduce the heating rate to 1 - 2 °C / min to enable the temperature to reach and stabilize at 500 °C more precisely. After the furnace temperature stabilizes at 500 °C, start timing and maintain this temperature for continuous calcination for 2 hours. Then, let it cool naturally. When the furnace temperature drops below 100 °C, the furnace door can be opened, and the crucible can be taken out. The regenerated graphite sample needs to be placed in a dry and clean environment to further cool to room temperature; Step F: RO preconcentration combined with seeded precipitation for efficient lithium recovery: Before adjusting the pH of the Li-containing leaching solution to 12, first use reverse osmosis technology to concentrate the solution volume to 1 / 3 - 1 / 2 of the original using the RO membrane. After adjusting the pH to 12, evaporate and concentrate, and then add saturated sodium carbonate solution to precipitate Li ions. During the precipitation process, slowly add sodium carbonate solution at a dropping rate of 1 - 2 mL / min and continuously stir at a stirring speed of 100 - 150 r / min to make Li ions fully react with carbonate ions to form lithium carbonate precipitate; Step G: Ultrasonic-nitric acid synergistic deep impurity removal and CVD surface modification: Place the graphite regenerated in Step E in a nitric acid solution with a concentration of 0.5 - 1.0 mol / L and perform ultrasonic treatment for 30 - 60 min under the conditions of a temperature of 60 - 80 °C and an ultrasonic frequency of 40 - 60 kHz. Utilize the cavitation effect of ultrasound to make nitric acid react with trace impurities remaining on the graphite surface to further remove metal impurities. Subsequently, adopt chemical vapor deposition technology, use methane as the carbon source and hydrogen as the carrier gas, and process in a high-temperature tube furnace at a temperature of 800 - 1000 °C for 1 - 2 h to grow a uniform nanoscale carbon coating on the graphite surface; Step H: Multi-dimensional performance detection to ensure the quality of regenerated graphite meets the standards: After completing all regeneration steps, conduct a comprehensive performance detection on the regenerated graphite. Perform constant current charge-discharge tests. Under the conditions of a voltage range of 0.01 - 3.0 V and a current density of 100 - 200 mA / g, conduct multiple charge-discharge cycles on the regenerated graphite to detect its performance indicators of the first charge-discharge efficiency and cycle stability. Observe the surface morphology of the regenerated graphite using a scanning electron microscope to detect its particle size, shape, and surface flatness. Measure the specific surface area and pore structure parameters of the regenerated graphite through a specific surface area analyzer.

[0009] The present invention is further configured such that in step A, X-ray photoelectron spectroscopy analysis technology is introduced to analyze the valence state and chemical environment of metal elements to determine the existing form of metal elements. When performing BCR sequential extraction, inductively coupled plasma mass spectrometry analysis is carried out on the solution after each extraction step.

[0010] The present invention is further configured such that in step B, subsequent treatment is performed on the simultaneously leached Li, Co, Mn, and Ni impurities, including precisely measuring and analyzing their leaching amounts, adjusting the treatment parameters of subsequent steps according to their contents, and quantitatively analyzing the ICP-AES measurement results using the standard curve method, with the correlation coefficient R² of the standard curve ≥ 0.999.

[0011] The present invention is further configured such that in step C, subsequent treatment is performed on the simultaneously leached Co, Mn, and Ni impurities, and their leaching conditions are recorded. When measuring Co, Mn, and Ni, corresponding hollow cathode lamps are used, with the lamp current being 3 - 5 mA, the spectral bandwidth being 0.2 - 0.5 nm, the hollow cathode lamps being the hollow cathode lamps corresponding to cobalt, manganese, and nickel elements respectively, and the preheating time being 30 - 60 min.

[0012] The present invention is further configured such that in step A, during each extraction with the improved BCR sequential extraction method, the solid-liquid ratio of the solution to the sample is controlled at 1:10 - 1:20 g / mL, the oscillation frequency is 150 - 200 times / min, and the oscillation time is 1 - 2 h for the water-soluble state extraction, 4 - 6 h for the weak acid extraction state extraction, 6 - 8 h for the reducible state extraction, and 12 - 16 h for the residual state extraction respectively in different extraction stages. When performing XPS analysis, a monochromatic AlKα X-ray source is used, with a power of 150 - 200 W, and the vacuum degree in the analysis chamber is maintained at 10⁻ 9 -10⁻ 8 Pa. When performing ICP-MS analysis, the nebulizer gas flow rate is 0.8 - 1.2 L / min, the auxiliary gas flow rate is 0.5 - 1.0 L / min, and the RF power is 1100 - 1500 W.

[0013] The present invention is further configured such that in step B, the reaction kettle is made of stainless steel with a polytetrafluoroethylene lining, with a volume of 500 - 1000 mL. The EDTA chelating agent uses disodium ethylenediaminetetraacetate, with a purity ≥ 99%. The on-line ion selective electrode uses a copper ion specific electrode, with a response time ≤ 10 s and a measurement accuracy of ±0.1 mg / L.

[0014] The present invention is further configured such that in step C, the reactor is a glass reaction kettle with a jacket, and the temperature is controlled by circulating water. The peristaltic pump uses a multi-channel peristaltic pump, with a material of corrosion-resistant silica gel and the inner diameter of the pump tube being 1 - 2 mm.

[0015] The present invention is further configured that in step D, the SDS surfactant is of analytical purity. When in use, it is first formulated into a stock solution of 1 - 2 mol / L and then added to the reaction system as needed.

[0016] The present invention is further configured that in step E, the calcination equipment is a box - type resistance furnace, the heating element is a silicon carbide rod, the temperature control accuracy is ±5°C, the graphite material is placed in a corundum crucible, and the crucible size is selected according to the amount of graphite material to ensure that the material thickness is 2 - 5 cm.

[0017] The present invention is further configured that in step F, the reverse osmosis device uses a spiral - wound RO membrane module, the membrane material is a polyamide composite membrane, the operating pressure is 1 - 2 MPa, evaporation and concentration use a rotary evaporator, the water - bath temperature is controlled at 60 - 80°C, and the sodium carbonate solution is of analytical purity.

[0018] The present invention has the following beneficial effects.

[0019] 1. Through precise leaching in multiple steps, the present invention can effectively recover metal elements such as copper, lithium, cobalt, manganese, and nickel in waste graphite anode materials, achieving the maximum utilization of resources, reducing the dependence on primary mineral resources. Through steps such as deep impurity removal, surface modification, and calcination under specific conditions, the lattice defects of the regenerated graphite are repaired, the surface impurities are significantly reduced, the crystal structure is optimized, and the specific surface area and pore structure are more conducive to the insertion and extraction of lithium, significantly improving the performance of the regenerated graphite as a battery anode material, which can be comparable to or even exceed some primary graphite materials. Compared with traditional regeneration processes, this method adopts efficient catalytic, dynamic leaching, and microwave - assisted technologies in some steps, reducing energy consumption, shortening the processing time, and improving production efficiency, with significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments will be briefly introduced below.

[0021] Figure 1 It is a flow chart of a method for regenerating waste battery graphite anode materials. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The technical solutions in the embodiments of the present invention will be described below with reference to the drawings in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0023] Example 1 Step A: Analyze impurities by combining multiple methods: The improved BCR sequential extraction method is used to analyze the graphite anode material of waste lithium-ion batteries. The existing forms of metal elements are divided into water-soluble state, weak acid extraction state, reducible state and residual state. The water-soluble state is leached by diluted acid solution, the weak acid extraction state is extracted by acetic acid-sodium acetate buffer solution, the reducible state is extracted by hydroxylamine hydrochloride-acetic acid buffer solution, and the residual state is extracted by aqua regia; Step B: EDTA-assisted hydrothermal efficient leaching of copper impurities: For the Cu impurities in the weak acid extraction state, the hydrothermal leaching method is adopted. DESs is selected as the reagent, and ethylenediaminetetraacetic acid chelating agent accounting for 5%-10% of its mass is added to the DESs reagent. Waste graphite, DESs and deionized water are added to the reaction kettle with a stirring device, and the stirring speed is controlled at 150-250 r / min. Leaching is carried out under the conditions of a temperature of 120 °C, a time of 10 min, a solid-liquid ratio of 1:40 g / mL, and a mass ratio of DESs to waste graphite of 0.4 g / g. During the leaching process, the concentration of Cu ions in the solution is detected in real time by an on-line ion selective electrode. When the concentration of Cu ions reaches equilibrium, the reaction is stopped; Step C: TiO 2 Catalytic dynamic hydrothermal extraction of lithium element: After removing Cu impurities, for Li impurities, waste graphite and deionized water are added to the reactor to form a hydrothermal reaction system. Nanoscale titanium dioxide particles accounting for 0.5%-1.0% of the mass of waste graphite are added to the system as a catalyst. Leaching is carried out under the conditions of a temperature of 200 °C, a time of 3 h, and a solid-liquid ratio of 1:30 g / mL. The dynamic hydrothermal leaching method is adopted, and deionized water is continuously supplemented into the reactor at a flow rate of 0.5-1.0 mL / min through a peristaltic pump, and the reacted solution is discharged at the same flow rate; Step D: SDS-enhanced microwave-assisted leaching of cobalt, manganese and nickel with sulfide: After Li leaching, for Co, Mn, Ni impurities, waste graphite and DESs are added to the reactor to form a sulfide leaching system. A sodium dodecyl sulfate surfactant with a concentration of 0.05-0.1 mol / L is added to the system, and microwave-assisted leaching technology is adopted. The microwave frequency is set at 2450 MHz and the power is 200-300 W. Leaching is carried out under the conditions of a temperature of 80 °C, a time of 50 min, a solid-liquid ratio of 1:30 g / mL, and a DESs concentration of 0.4 mol / L; Step E: Low-temperature calcination to repair graphite lattice and regenerate performance: Evenly spread the leached graphite material in the crucible of the resistance furnace. Start the power supply and set the heating program. Gradually increase the furnace temperature from room temperature to 500°C at a heating rate of 5 - 10°C / min. When the temperature approaches 500°C, appropriately reduce the heating rate to 1 - 2°C / min to enable the temperature to reach and stabilize at 500°C more precisely. After the furnace temperature stabilizes at 500°C, start timing and maintain this temperature for continuous calcination for 2 hours. Then, let it cool naturally. When the furnace temperature drops below 100°C, the furnace door can be opened, and the crucible can be taken out. The regenerated graphite sample needs to be placed in a dry and clean environment to further cool to room temperature; Step F: High - efficient recovery of lithium by RO pre - concentration combined with seeded precipitation: Before adjusting the pH of the Li - containing leaching solution to 12, first use the reverse osmosis technology to concentrate the solution volume to 1 / 3 - 1 / 2 of the original with the RO membrane. After adjusting the pH to 12, perform evaporation concentration, and then add saturated sodium carbonate solution to precipitate Li ions. During the precipitation process, slowly drip the sodium carbonate solution at a dripping rate of 1 - 2 mL / min and continuously stir at a stirring speed of 100 - 150 r / min to make Li ions fully react with carbonate ions to form lithium carbonate precipitate; Step G: Ultrasonic - nitric acid synergistic deep impurity removal and CVD surface modification: Place the regenerated graphite from step E in a nitric acid solution with a concentration of 0.5 - 1.0 mol / L, and perform ultrasonic treatment for 30 - 60 min under the conditions of a temperature of 60 - 80°C and an ultrasonic frequency of 40 - 60 kHz. Utilize the cavitation effect of ultrasound to make nitric acid react with trace impurities remaining on the graphite surface to further remove metal impurities. Subsequently, adopt chemical vapor deposition technology, using methane as the carbon source and hydrogen as the carrier gas, and treat it in a high - temperature tube furnace at a temperature of 800 - 1000°C for 1 - 2 h to grow a uniform nanoscale carbon coating on the graphite surface; Step H: Multi - dimensional performance detection to ensure the quality of regenerated graphite meets the standards: After completing all the regeneration steps, conduct a comprehensive performance detection on the regenerated graphite. Adopt constant - current charge - discharge testing. Under the conditions of a voltage range of 0.01 - 3.0 V and a current density of 100 - 200 mA / g, perform multiple charge - discharge cycles on the regenerated graphite to detect its performance indicators of the first charge - discharge efficiency and cycle stability. Observe the surface morphology of the regenerated graphite using a scanning electron microscope to detect its particle size, shape, and surface flatness. Measure the specific surface area and pore structure parameters of the regenerated graphite through a specific surface area analyzer.

[0024] Measure the specific surface area and pore structure parameters of the regenerated graphite using a specific surface area analyzer: Operating steps for measuring the regenerated graphite: Sample Pretreatment: First, take an appropriate amount of regenerated graphite sample, usually 0.1 - 1 g, and place it in a vacuum oven for degassing at a temperature of 150 - 200 °C for 2 - 4 hours. The purpose of this step is to remove the adsorbed water, air, and other impurities on the sample surface to ensure the accuracy of the measurement results. For example, if there is residual water on the sample surface, the water will occupy some adsorption sites during the measurement, resulting in deviations in the measured specific surface area and pore structure parameters.

[0025] Instrument Preparation and Calibration: Turn on the specific surface area analyzer to make the instrument reach a stable working state. Check the vacuum system of the instrument. At the same time, use a standard sample (such as high-purity silica gel with a known specific surface area) to calibrate the instrument to ensure the accuracy of the measurement results. During the calibration process, according to the requirements of the instrument operation manual, put the standard sample into the sample tube of the instrument for adsorption measurement, compare the measured result of the instrument with the known specific surface area of the standard sample, and if there is a deviation, make corresponding parameter adjustments to the instrument.

[0026] Sample Measurement: Carefully place the pretreated regenerated graphite sample into the sample tube of the instrument, install the sample tube and connect it to the measurement system of the instrument. Add sufficient liquid nitrogen to the Dewar flask of the instrument to provide a low-temperature environment for the adsorption process. Start the measurement program of the instrument. The instrument will automatically control the pressure of nitrogen, gradually change the value of the relative pressure P / P0 (usually select multiple measurement points within the range of 0.05 - 0.35), and measure the adsorption amount of nitrogen on the surface of the regenerated graphite sample at each relative pressure. As the relative pressure increases, nitrogen molecules gradually adsorb on the sample surface and in the pores. When the relative pressure reaches a certain value, the adsorption amount tends to saturate. After the adsorption process is completed, the instrument will automatically switch to the desorption mode to measure the desorption amount of nitrogen and obtain a complete adsorption - desorption isotherm.

[0027] Meaning of the Obtained Pore Structure Parameters Specific Surface Area: The specific surface area calculated by the BET equation reflects the total surface area per unit mass of the regenerated graphite sample. The larger the specific surface area, the larger the contact area between the regenerated graphite and the electrolyte. During the charge and discharge process of the battery, it can provide more active sites for the insertion and extraction of lithium ions, which is beneficial to improving the charge and discharge performance of the battery. For example, if the specific surface area of the regenerated graphite increases from 50 m² / g by the traditional regeneration method to 80 m² / g by the technology of the present invention, theoretically its reaction activity with the electrolyte will be significantly enhanced.

[0028] Pore size distribution: The pore size distribution data calculated through models such as BJH or DFT shows the proportion of pores with different pore sizes in the recycled graphite. For the anode material of the battery, a suitable pore size distribution is crucial. Micropores (pore size less than 2 nm) are beneficial to increasing the specific surface area of the material and enhancing the adsorption capacity for lithium ions; mesopores (pore size between 2 - 50 nm) help the rapid transport of lithium ions inside the material. For example, if there are a large number of mesopores with a pore size of 5 - 10 nm in the recycled graphite, it can effectively shorten the diffusion path of lithium ions inside the material and improve the charge and discharge rate of the battery.

[0029] Pore volume: The pore volume refers to the total volume of all pores in a unit mass of the recycled graphite sample. A higher pore volume can accommodate more lithium ions, thereby increasing the specific capacity of the battery. For example, during the charge and discharge process of the battery, the recycled graphite with a larger pore volume can store more lithium ions, enabling the battery to release more electrical energy under the same mass and enhancing the energy density of the battery.

[0030] Example 2 Based on Example 1, in step A, X-ray photoelectron spectroscopy analysis technology is introduced to analyze the valence state and chemical environment of metal elements, determine the existence form of metal elements, and during the BCR sequential extraction, inductively coupled plasma mass spectrometry analysis is performed on the solution after each extraction step.

[0031] The XPS instrument mainly consists of parts such as an X-ray source, a sample chamber, an energy analyzer, a detector, and a vacuum system. The X-ray source usually uses monochromatic AlKα or MgKα rays to provide an X-ray beam with stable and single energy. The sample chamber is used to place the sample to be analyzed, and it is necessary to ensure that the sample is in a high-vacuum environment to avoid contamination of the sample surface and affect the analysis results. The function of the energy analyzer is to accurately analyze the kinetic energy of photoelectrons. A common energy analyzer is a hemispherical energy analyzer, which can separate and focus photoelectrons with different kinetic energies onto the detector according to the motion trajectory of photoelectrons in the electric and magnetic fields. The detector is responsible for detecting the number of photoelectrons, converting them into electrical signals and amplifying and recording them. The vacuum system runs through the entire instrument to ensure that each component is in a high-vacuum state to prevent air molecules from colliding with photoelectrons and interfering with the detection signal.

[0032] When analyzing the graphite anode material of waste lithium-ion batteries, XPS can sensitively detect various elements on the material surface, such as C, O, Li, Cu, Co, Mn, Ni, etc. By measuring the intensities of the photoelectron peaks of different elements and combining the sensitivity factors of the instrument and the corresponding correction methods, the relative contents of various elements on the material surface can be semi-quantitatively determined. For example, by accurately measuring the intensity of the Li element photoelectron peak and comparing it with a standard sample of known content, the approximate content of the Li element on the surface of the waste graphite anode material can be estimated, providing an important reference for the subsequent lithium element recovery process.

[0033] In step B, the simultaneously leached Li, Co, Mn, and Ni impurities are subjected to subsequent treatment, including accurately measuring and analyzing their leaching amounts, adjusting the processing parameters of the subsequent steps according to their contents, and quantitatively analyzing the ICP-AES measurement results using the standard curve method, with the correlation coefficient R² of the standard curve ≥ 0.999.

[0034] Application of the standard curve method in the analysis of waste battery graphite anode materials: Preparation of standard solutions: When analyzing metal elements in the graphite anode material of waste lithium-ion batteries, a series of metal standard solutions with different concentration gradients need to be prepared first. For example, when detecting copper elements, high-purity copper salts (such as copper sulfate) need to be prepared and dissolved in a suitable solvent (such as dilute nitric acid) to form multiple solutions with different concentrations, and the concentration range should cover the concentration range of copper elements in the expected samples to be measured. Suppose the concentrations of the prepared copper standard solutions are 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, 2.0 mg / L, and 5.0 mg / L respectively.

[0035] Instrument measurement and standard curve drawing: The prepared standard solutions are sequentially introduced into the instrument for detection, such as an inductively coupled plasma atomic emission spectrometer (ICP-AES). ICP-AES emits light of specific wavelengths. When the metal elements in the standard solution absorb this light, characteristic spectral lines will be emitted, and the instrument detects the intensity of the characteristic spectral lines and converts it into an absorbance value. Record the absorbances corresponding to different concentration standard solutions, use the copper element concentration as the abscissa and the absorbance as the ordinate, and draw a standard curve using data analysis software. Under ideal conditions, these data points should show a linear relationship, and the equation of the standard curve is obtained through linear fitting , with the correlation coefficient R2 ≥ 0.999, indicating that the standard curve has good linear correlation and can be used for accurate quantitative analysis.

[0036] Sample determination and concentration calculation: The waste graphite anode material sample to be measured is pretreated to convert it into a solution state. The treated sample solution is measured under the same instrument conditions as the standard solution to obtain the absorbance value of the sample solution. Assuming that the absorbance of the measured sample solution is 0.8, substituting it into the standard curve equation 0.8 = 0.2c + 0.05, the concentration c of copper element in the sample solution can be calculated by solving the equation as c = 3.75 mg / L. Combining with information such as the dilution factor during the sample pretreatment process, the content of copper element in the original waste graphite anode material can be accurately calculated.

[0037] In step C, the simultaneously leached Co, Mn, and Ni impurities are subjected to subsequent treatment, and their leaching conditions are recorded. When measuring Co, Mn, and Ni, the corresponding hollow cathode lamps are used, the lamp current is 3 - 5 mA, the spectral bandwidth is 0.2 - 0.5 nm, the hollow cathode lamps are the hollow cathode lamps corresponding to cobalt, manganese, and nickel elements respectively, and the preheating time is 30 - 60 min.

[0038] In step A, during each extraction with the improved BCR sequential extraction method, the solid-liquid ratio of the solution to the sample is controlled at 1:10 - 1:20 g / mL, the oscillation frequency is 150 - 200 times / min, and the oscillation time is 1 - 2 h for the water-soluble state extraction, 4 - 6 h for the weak acid extraction state, 6 - 8 h for the reducible state extraction, and 12 - 16 h for the residual state extraction according to different extraction stages. When performing XPS analysis, a monochromatic AlKα X-ray source is used with a power of 150 - 200 W, and the vacuum degree in the analysis chamber is maintained at 10⁻ 9 -10⁻ 8 Pa. When performing ICP-MS analysis, the nebulizer gas flow rate is 0.8 - 1.2 L / min, the auxiliary gas flow rate is 0.5 - 1.0 L / min, and the RF power is 1100 - 1500 W.

[0039] In step B, the reaction kettle is made of stainless steel with a polytetrafluoroethylene lining, the volume is 500 - 1000 mL, the EDTA chelating agent uses disodium ethylenediaminetetraacetate with a purity ≥ 99%, the on-line ion selective electrode uses a copper ion specific electrode with a response time ≤ 10 s and a measurement accuracy of ±0.1 mg / L.

[0040] In step C, the reactor is a glass reaction kettle with a jacket, the temperature is controlled by circulating water, the peristaltic pump uses a multi-channel peristaltic pump made of corrosion-resistant silica gel, and the inner diameter of the pump tube is 1 - 2 mm.

[0041] In step D, the SDS surfactant is of analytical purity. When using it, it is first prepared into a stock solution of 1 - 2 mol / L and then added to the reaction system as needed.

[0042] In step E, the calcination equipment is a box-type resistance furnace, the heating element is a silicon carbide rod, the temperature control accuracy is ±5°C, the graphite material is placed in a corundum crucible, and the crucible size is selected according to the amount of graphite material to ensure that the material thickness is 2 - 5 cm.

[0043] In step F, the reverse osmosis device uses a spiral wound RO membrane module, the membrane material is a polyamide composite membrane, the operating pressure is 1 - 2 MPa, evaporation and concentration use a rotary evaporator, the water bath temperature is controlled at 60 - 80°C, and the sodium carbonate solution is of analytical purity.

[0044] Example 3 Multi-method combined precise analysis of impurities: Take 100 g of waste graphite anode materials of lithium-ion batteries, and use the improved BCR sequential extraction method. When extracting in the water-soluble state, use 1000 mL of deionized water, oscillate at 150 times / min for 1.5 h, and separate the water-soluble metal element solution; when extracting in the weak acid extraction state, use 1000 mL of acetic acid-sodium acetate buffer solution (pH = 4.5), oscillate at 180 times / min for 5 h to obtain the weak acid-extractable metal element solution; when extracting in the reducible state, use 1000 mL of hydroxylamine hydrochloride-acetic acid buffer solution, oscillate at 160 times / min for 7 h; when extracting in the residual state, digest and extract with aqua regia. At the same time, perform ICP-MS analysis on the solutions after extraction in each step and XPS analysis on the material to determine the existing forms and contents of metal elements.

[0045] EDTA-assisted hydrothermal efficient leaching of copper impurities: Put the above-treated material into a 500 mL stainless steel reaction kettle lined with polytetrafluoroethylene, add 40 g of DESs reagent, add 2 g of disodium ethylenediaminetetraacetate (purity 99%), add 1600 mL of deionized water, stir at a speed of 200 r / min, and react at 120°C for 10 min. Use an on-line ion selective electrode to monitor the Cu ion concentration in real time, stop the reaction when the expected leaching rate is reached, and analyze the contents of other metal impurities leached simultaneously.

[0046] TiO 2 Catalytic dynamic hydrothermal extraction of lithium element: In the system after removing Cu impurities, add 0.5 g of nano-scale titanium dioxide particles, at 200°C, with a solid-liquid ratio of 1:30 g / mL, use a peristaltic pump to continuously supplement and discharge the solution at a flow rate of 0.8 mL / min, react for 3 h, and record the situations of Co, Mn, and Ni impurities leached simultaneously.

[0047] SDS-assisted microwave-assisted sulfide leaching of cobalt, manganese, and nickel: Add a sodium dodecyl sulfate surfactant solution with a concentration of 0.08 mol / L to the system after leaching Li, use a modified microwave device, react at 80°C for 50 min at a power of 2450 MHz and 250 W.

[0048] Low-temperature calcination for repairing graphite lattice and regenerating properties: The leached graphite was placed in a corundum crucible in a box-type resistance furnace and calcined at 500 °C for 2 h.

[0049] Efficient lithium recovery by RO preconcentration combined with seeded precipitation: The Li-containing leachate was first concentrated to 1 / 2 of the original volume using an RO device (operating pressure 1.5 MPa). After adjusting the pH to 12, it was evaporated and concentrated in a rotary evaporator (water bath temperature 70 °C). A saturated sodium carbonate solution was slowly added dropwise (dropwise rate 1.5 mL / min), the stirring speed was 120 r / min, and lithium carbonate seeds accounting for 0.8% of the expected precipitation amount were added. Lithium was recovered by precipitation, washing, and drying.

[0050] Ultrasound-nitric acid synergistic deep impurity removal and CVD surface modification: The regenerated graphite was placed in a 0.8 mol / L nitric acid solution and ultrasonically treated at 65 °C and an ultrasonic frequency of 50 kHz for 45 min. Then, in a high-temperature tube furnace, with a volume ratio of methane to hydrogen of 1:8 and a total flow rate of 80 mL / min, CVD treatment was carried out at 900 °C for 1.5 h.

[0051] Multi-dimensional performance detection to ensure the quality of regenerated graphite meets the standard: The regenerated graphite was subjected to constant current charge-discharge testing, SEM observation, and BET measurement, and all performance indicators reached the high-quality standards of battery anode materials.

[0052] Example 4: Multi-method combined analysis of impurities: 200 g of waste lithium-ion battery graphite anode material was selected and the improved BCR sequential extraction method was used. When extracting in the water-soluble state, 2000 mL of deionized water was used and oscillated at 180 times / min for 2 h; when extracting in the weak acid extraction state, 2000 mL of acetic acid-sodium acetate buffer solution with pH = 4.8 was used, the oscillation frequency was 200 times / min, and the duration was 6 h; when extracting in the reducible state, 1500 mL of hydroxylamine hydrochloride-acetic acid buffer solution was used, the oscillation speed was 180 times / min, and it lasted for 8 h; the residual state was extracted by aqua regia digestion. Similarly, ICP-MS analysis was carried out on the extraction solutions at each stage, and the material was analyzed by XPS to clarify the occurrence state and content of metal elements.

[0053] EDTA synergistic hydrothermal efficient leaching of copper impurities: The treated material was put into a 1000 mL stainless steel reaction kettle lined with polytetrafluoroethylene, 80 g of DESs reagent was added, 4 g of disodium ethylenediaminetetraacetate with a purity of 99% was added, 3200 mL of deionized water was injected, the stirring speed was set at 220 r / min, and the reaction was carried out at 125 °C for 12 min. The concentration of Cu ions was monitored in real time using an online ion-selective electrode. After reaching the expected leaching rate, the reaction was terminated, and the content of other metal impurities accompanying the leaching was analyzed.

[0054] TiO2 Catalytic dynamic hydrothermal leaching of lithium: In the system for removing Cu impurities, add 1 g of nanoscale titanium dioxide particles, maintain a solid-liquid ratio of 1:30 g / mL at 210 °C, continuously supplement and discharge the solution with a peristaltic pump at a flow rate of 1 mL / min, and react for 3.5 h. Record in detail the situation of Co, Mn, and Ni impurities leached simultaneously.

[0055] SDS-enhanced microwave-assisted leaching of cobalt, manganese, and nickel from sulfides: Add a sodium dodecyl sulfate surfactant solution with a concentration of 0.1 mol / L to the system after leaching Li. Use a modified microwave device to react at 85 °C for 55 min at a power of 300 W and a frequency of 2450 MHz.

[0056] Low-temperature calcination for repairing graphite lattice and property regeneration: Place the leached graphite in a corundum crucible in a box-type resistance furnace and calcine at 520 °C for 2.2 h.

[0057] Efficient recovery of lithium by RO preconcentration combined with seeded precipitation: First, concentrate the Li-containing leachate to 1 / 3 of its original volume through an RO device (operating pressure 1.8 MPa). After adjusting the pH to 12.5, evaporate and concentrate it in a rotary evaporator (water bath temperature 75 °C). Slowly drip a saturated sodium carbonate solution at a rate of 2 mL / min, with a stirring speed of 130 r / min. Add lithium carbonate seeds accounting for 1% of the expected precipitation amount, and precipitate, wash, and dry to recover Li.

[0058] Ultrasound-nitric acid synergistic deep impurity removal and CVD surface modification: Put the regenerated graphite into a 1 mol / L nitric acid solution and ultrasonically treat it at 70 °C and an ultrasonic frequency of 55 kHz for 50 min. Subsequently, in a high-temperature tube furnace, perform CVD treatment at 950 °C for 1.8 h with a volume ratio of methane to hydrogen of 1:9 and a total flow rate of 90 mL / min.

[0059] Multi-dimensional performance testing to ensure the quality of regenerated graphite meets the standard: Conduct constant current charge-discharge tests, SEM observations, and BET measurements on the regenerated graphite. All performance indicators meet the high-quality standards of battery anode materials, further verifying the stability and universality of the invention under different parameter conditions.

[0060] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. The present specification selects and specifically describes these embodiments to better explain the principles and practical applications of the present invention, so that those skilled in the relevant technical fields can understand and utilize the present invention well.

Claims

1. A method for regenerating graphite negative electrode materials from waste batteries, characterized in that: Includes the following Steps: Step A: Multiple methods combined to analyze impurities: The improved BCR sequential extraction method was used to analyze the graphite negative electrode materials of waste lithium-ion batteries. The existence forms of metal elements were divided into water-soluble state, weak acid extraction state, reducible state and residual state. The water-soluble state was leached by dilute acid solution, the weak acid extraction state was extracted by acetic acid-sodium acetate buffer solution, the reducible state was extracted by hydroxylamine hydrochloride-acetic acid buffer solution, and the residual state was extracted by aqua regia. Step B: EDTA synergistic hydrothermal leaching of copper impurities: For Cu impurities in a weak acid extraction state, a hydrothermal leaching method is used, DESs is selected as a reagent, and an ethylenediaminetetraacetic acid chelating agent accounting for 5%-10% of the mass of the DESs reagent is added, and waste graphite, DESs and deionized water are added to a reactor with a stirring device, and the stirring speed is controlled at 150-250r / min. Leaching is carried out under the conditions of a temperature of 120°C, a time of 10min, a solid-liquid ratio of 1:40g / mL, and a mass ratio of DESs to waste graphite of 0.4g / g. During the leaching process, an online ion selective electrode is used to detect the concentration of Cu ions in the solution in real time. When the Cu ion concentration reaches equilibrium, the reaction is stopped; Step C: TiO2 catalyzed dynamic hydrothermal leaching of lithium: After removing the Cu impurities, for the Li impurities, waste graphite and deionized water are added to the reactor to form a hydrothermal reaction system, and nano-scale titanium dioxide particles accounting for 0.5%-1.0% of the mass of the waste graphite are added to the system as a catalyst, and leaching is carried out under the conditions of a temperature of 200°C, a time of 3h, and a solid-liquid ratio of 1:30g / mL. A dynamic hydrothermal leaching method is adopted, and deionized water is continuously added to the reactor at a flow rate of 0.5-1.0mL / min through a peristaltic pump, and the reacted solution is discharged at the same flow rate; Step D: SDS enhanced microwave assisted sulfide leaching of cobalt, manganese and nickel: After Li leaching, for Co, Mn, and Ni impurities, waste graphite and DESs were added to the reactor to form a sulfide leaching system, a sodium dodecyl sulfate surfactant with a concentration of 0.05-0.1 mol / L was added to the system, and microwave-assisted leaching technology was used, with the microwave frequency set to 2450 MHz, the power to 200-300 W, and the leaching was carried out at a temperature of 80°C, a time of 50 min, a solid-liquid ratio of 1:30 g / mL, and a DESs concentration of 0.4 mol / L; Step E: Low temperature calcination to repair graphite lattice and regenerate performance: The graphite material after leaching treatment is evenly spread in the crucible of the resistance furnace, the power is turned on, the heating program is set, and the temperature in the furnace is gradually increased from room temperature to 500°C at a heating rate of 5-10°C / min. When the temperature is close to 500°C, the heating rate is appropriately reduced to 1-2°C / min, so that the temperature can reach and stabilize at 500°C more accurately. When the temperature in the furnace is stabilized at 500°C, the timing is started, and the temperature is maintained for continuous calcination for 2 hours, and the temperature is naturally cooled. When the temperature in the furnace drops below 100°C, the furnace door can be opened and the crucible can be taken out. The regenerated graphite sample needs to be placed in a dry and clean environment to further cool to room temperature; Step F: RO pre-concentration combined with seed precipitation to efficiently recover lithium: Before adjusting the pH of the Li-containing leachate to 12, first use reverse osmosis technology to concentrate the solution volume to 1 / 3-1 / 2 of the original volume using an RO membrane. After adjusting the pH to 12, evaporate and concentrate, and then add a saturated sodium carbonate solution to precipitate Li ions. During the precipitation process, slowly add the sodium carbonate solution dropwise at a rate of 1-2 mL / min, and continue stirring at a rate of 100-150 r / min, so that the Li ions and carbonate ions fully react to form lithium carbonate precipitates. Step G: Ultrasonic-nitric acid synergistic deep impurity removal and CVD surface modification: The graphite regenerated in step E is placed in a nitric acid solution with a concentration of 0.5-1.0 mol / L, and ultrasonically treated for 30-60 min at a temperature of 60-80° C. and an ultrasonic frequency of 40-60 kHz, and the nitric acid is reacted with the trace impurities remaining on the surface of the graphite by using the ultrasonic cavitation effect to further remove the metal impurities, and then, chemical vapor deposition technology is used, with methane as the carbon source and hydrogen as the carrier gas, in a high temperature tube furnace, at a temperature of 800-1000° C. for 1-2 h to grow a uniform nanoscale carbon coating on the surface of the graphite; Step H: Multi-dimensional performance testing to ensure that the quality of recycled graphite meets the standards: After completing all the regeneration steps, the regenerated graphite is subjected to a comprehensive performance test. A constant current charge and discharge test is used. Under the conditions of a voltage range of 0.01-3.0V and a current density of 100-200mA / g, the regenerated graphite is subjected to multiple charge and discharge cycles to detect the performance indicators of the initial charge and discharge efficiency and cycle stability. The surface morphology of the regenerated graphite is observed using a scanning electron microscope, and its particle size, shape and surface flatness are detected. The specific surface area and pore structure parameters of the regenerated graphite are measured using a specific surface area analyzer.

2. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In step A, X-ray photoelectron spectroscopy analysis technology is introduced to analyze the valence state and chemical environment of the metal elements to determine the existence form of the metal elements. When performing BCR sequential extraction, the solution after each step of extraction is subjected to inductively coupled plasma mass spectrometry analysis.

3. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step B, the simultaneously leached Li, Co, Mn and Ni impurities are subsequently treated, including accurately measuring and analyzing their leaching amounts, adjusting the treatment parameters of the subsequent steps according to their contents, and quantitatively analyzing the ICP-AES measurement results using a standard curve method, wherein the correlation coefficient of the standard curve is R²≥0.

999.

4. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step C, the simultaneously leached Co, Mn and Ni impurities are subsequently treated, and their leaching conditions are recorded. When measuring Co, Mn and Ni, corresponding hollow cathode lamps are used, the lamp current is 3-5 mA, the spectral passband width is 0.2-0.5 nm, the hollow cathode lamps are hollow cathode lamps corresponding to the cobalt, manganese and nickel elements respectively, and the preheating time is 30-60 min.

5. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step A, the improved BCR sequential extraction method controls the solid-liquid ratio of the solution to the sample at 1:10-1:20 g / mL during each extraction, the oscillation frequency is 150-200 times / min, and the oscillation time is 1-2 hours for water-soluble state extraction, 4-6 hours for weak acid extraction, 6-8 hours for reducible state extraction, and 12-16 hours for residual state extraction according to different extraction stages. During XPS analysis, a monochromatic AlKα X-ray source is used with a power of 150-200 W, and the vacuum degree of the analysis chamber is maintained at 10⁻ 9 -10⁻ 8 Pa, during ICP-MS analysis, the nebulizer gas flow rate was 0.8-1.2 L / min, the auxiliary gas flow rate was 0.5-1.0 L / min, and the RF power was 1100-1500 W.

6. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step B, the reaction kettle is made of stainless steel, lined with polytetrafluoroethylene, and has a volume of 500-1000 mL. The EDTA chelating agent uses disodium ethylenediaminetetraacetic acid with a purity of ≥99%. The online ion selective electrode uses a copper ion specific electrode with a response time of ≤10s and a measurement accuracy of ±0.1 mg / L.

7. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step C, the reactor is a glass reactor with a jacket, the temperature is controlled by circulating water, the peristaltic pump is a multi-channel peristaltic pump made of corrosion-resistant silicone, and the inner diameter of the pump tube is 1-2 mm.

8. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step D, the SDS surfactant is analytically pure and is first prepared into a 1-2 mol / L stock solution before use, and then added into the reaction system as needed.

9. A method for regenerating graphite negative electrode materials from waste batteries according to claim 1, characterized in that: In the step E, the calcination equipment is a box-type resistance furnace, the heating element is a silicon carbon rod, the temperature control accuracy is ±5°C, the graphite material is placed in a corundum crucible, and the crucible size is selected according to the amount of graphite material to ensure that the material thickness is 2-5cm.

10. The method for regenerating graphite negative electrode materials of waste batteries according to claim 1, characterized in that: In the step F, the reverse osmosis device uses a rolled RO membrane assembly, the membrane material is a polyamide composite membrane, the operating pressure is 1-2 MPa, the evaporation concentration uses a rotary evaporator, the water bath temperature is controlled at 60-80°C, and the sodium carbonate solution is analytical grade.

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