Method for recovering all components of a battery negative electrode and graphite recovered thereby

Abstract

The application provides a method for recovering all components of a battery negative electrode and graphite recovered by the method, and the method comprises the following steps: subjecting a negative electrode sheet to be recovered to ultrasonic alkali leaching to obtain a current collector and slurry; after slurry solid-liquid separation, a lithium-containing solution and graphite residue are obtained, and recovery of the current collector and lithium elements is completed; the graphite residue is subjected to microwave acid leaching to obtain purified graphite; the purified graphite is subjected to surface modification to obtain battery graphite, and recovery of the graphite is completed; the method directly removes powder from the negative electrode sheet, selectively leaches lithium elements, can recover the current collector and metallic lithium, and further removes impurities, so that the content of impurity elements in the graphite is greatly reduced, and finally the microstructure of the graphite is repaired, so that the obtained graphite can return to the negative electrode of a lithium battery, resource maximization utilization is achieved, and the electrochemical performance of the recovered graphite is repaired.

Description

Technical Field

[0001] This invention belongs to the field of battery recycling technology, and relates to a method for recovering all components of a battery negative electrode and the graphite obtained from the recovery. Background Technology

[0002] Current battery recycling typically focuses on extracting and recovering metal elements from the cathode material, while the recovery of graphite anodes from spent batteries is less common. Because graphite has a layered structure and contains various impurities, such as approximately 0.5% Li, 1% P, and 1.8% F, it is difficult to achieve battery-grade graphite standards after recycling. Currently, the industrial-scale treatment of graphite from spent batteries is usually landfilling, which not only wastes resources but also causes serious environmental pollution.

[0003] Currently, existing technologies for graphite recycling are not ideal. The electrochemical performance of recycled graphite is lower than that of commercially available graphite. For example, CN 101710632A discloses a method for recycling and repairing graphite, anode material of waste lithium-ion batteries. The method involves immersing the negative electrode sheet to be recycled in water to separate the copper foil from the graphite. Then, it undergoes room temperature impurity removal with inorganic acid, high temperature treatment, surface modification and curing, and high temperature carbonization of the surface modifier in a nitrogen atmosphere to finally obtain the repaired graphite product for recycling graphite in lithium-ion batteries. However, the impurity removal efficiency of this method is low, and it cannot achieve full recovery of the negative electrode components. The electrochemical performance of the obtained graphite needs to be improved.

[0004] Based on the above research, there is a need to provide a method for the complete recovery of the negative electrode components of a battery. This method can achieve the complete recovery of the negative electrode components without damaging the microstructure of the negative electrode graphite material. It can not only recover graphite and foil, but also recover the lithium contained in the graphite. Furthermore, the recovered graphite has low impurity content and excellent conductivity, and can be returned to the negative electrode of the lithium battery, thus maximizing resource utilization. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the complete recovery of the negative electrode components of a battery and the graphite obtained therefrom. The method directly de-powders the negative electrode sheet, selectively leaches lithium elements, collects fluid and metallic lithium, performs deep impurity removal to reduce the content of impurity elements in the graphite, and finally repairs the microstructure of the graphite so that the graphite can be returned to the negative electrode of the lithium battery. This maximizes resource utilization and results in the recovered graphite having a low impurity content and excellent electrochemical performance.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for the complete recovery of components from a battery negative electrode, the method comprising the following steps:

[0008] (1) The negative electrode sheet to be recycled is subjected to ultrasonic alkaline leaching to obtain a current collector and a slurry. The slurry is separated into solid and liquid components to obtain a lithium-containing solution and graphite slag, thus completing the recycling of the current collector and lithium element.

[0009] (2) Microwave acid leaching is performed on the graphite slag described in step (1) to obtain purified graphite;

[0010] (3) Surface modification step (2) The purified graphite is obtained to obtain graphite for batteries, thus completing the graphite recycling.

[0011] This invention dismantles waste batteries and directly recycles the resulting negative electrode sheets. Specifically, the negative electrode sheets are first subjected to alkaline leaching under ultrasonic conditions, which not only removes powder but also recovers metallic lithium and removes organic impurities. The resulting graphite slag is then further processed to recover the graphite. Specifically, the graphite slag is acid-leached under microwave assistance, achieving deep impurity removal. Simultaneously, microwave acid leaching allows for a more thorough reaction of impurities and the surface SEI layer in the graphite sheets without damaging the graphite microstructure. Therefore, the microwave acid leaching step not only has a good impurity removal effect but also does not damage the graphite structure, resulting in purified graphite with a low impurity content. Finally, this invention also performs surface modification on the purified graphite, repairing the interlayer spacing and achieving surface coating, improving the conductivity of the graphite, thereby enhancing the electrochemical performance of the recycled graphite.

[0012] Preferably, the ultrasonic alkaline immersion in step (1) uses an alkaline solution with a mass fraction of 0.5-2wt%, such as 0.5wt%, 0.75wt%, 1wt%, 1.25wt%, 1.5wt%, 1.75wt%, or 2wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] This invention uses dilute alkali with the above-mentioned mass fraction in combination with ultrasonic alkali leaching, which can achieve the goal of powder removal while avoiding damage to the microstructure of graphite caused by excessive alkali concentration. At the same time, it avoids the introduction of too many other ions, reduces the requirements for processing equipment, saves resources, and avoids the generation of a large amount of difficult-to-treat waste liquid.

[0014] Preferably, the alkaline solution comprises sodium hydroxide solution and / or lithium hydroxide solution.

[0015] Preferably, gas is also introduced during the ultrasonic alkaline immersion in step (1).

[0016] This invention introduces gas during ultrasonic alkali leaching, further enhancing the powder removal effect and avoiding the problem of electrode stacking affecting the ultrasonic powder removal effect. It also improves the removal of impurities such as organic matter in the electrolyte. In other words, this invention uses dilute alkali ultrasonic aeration to remove powder from the negative electrode, allowing various conditions to be combined to achieve high powder removal and recovery efficiency.

[0017] Preferably, the gas includes compressed air, and the pressure of the compressed air is 5-50 MPa, for example, it can be 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa or 50 MPa, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0018] Preferably, the solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution in step (1) is 1:(10-30), for example, it can be 1:10, 1:15, 1:20, 1:25 or 1:30, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the ultrasonic frequency of the ultrasonic alkali immersion in step (1) is 10-100KHz, for example, it can be 10KHz, 30KHz, 50KHz, 70KHz, 90KHz or 100KHz, and the time is 10-60min, for example, it can be 10min, 20min, 30min, 40min, 50min or 60min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, in step (1), the lithium-containing solution is used to recover metallic lithium using lithium adsorption resin, and the resulting water is reused in the ultrasonic alkaline leaching step.

[0021] Preferably, the graphite slag in step (1) is further subjected to a cleaning and solid-liquid separation step before microwave acid leaching to obtain crude graphite and filtrate, and the filtrate is reused in the preparation of alkaline solution.

[0022] Preferably, the microwave acid leaching in step (2) is carried out under pressure, heating and stirring.

[0023] The acid leaching described in this invention is carried out under microwave, high pressure, high temperature and stirring conditions. By combining the above conditions, the impurity removal process can be accelerated, the impurity removal time can be shortened, and the impurities in the graphite flakes and the surface SEI layer can be reacted more thoroughly, thereby achieving deep impurity removal.

[0024] The microwave acid leaching described in this invention specifically involves placing graphite slag and acid in a high-temperature, high-pressure reactor, then adding a stirring magnet, and placing the entire device in a microwave reaction chamber.

[0025] Preferably, the microwave acid leaching pressure in step (2) is 0.1-0.5 MPa, for example, it can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa or 0.5 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.2-0.5 MPa.

[0026] Preferably, the temperature of microwave acid leaching in step (2) is 120-200℃, for example, it can be 120℃, 140℃, 160℃, 180℃ or 200℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the microwave pickling speed in step (2) is 100-500 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm, and the time is 20-100 min, for example, 20 min, 40 min, 60 min, 80 min or 100 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the microwave acid leaching in step (2) is performed using an oxidizing and non-volatile acid.

[0029] This invention uses an oxidizing and non-volatile acid for acid leaching, which can accelerate the removal of impurities in graphite slag, improve the impurity removal effect, and avoid the problems of difficult exhaust gas treatment and environmental pollution caused by acid volatilization.

[0030] Preferably, the oxidizing and non-volatile acid includes any one or a combination of at least two of sulfuric acid, permanganic acid, periodic acid, hypochlorous acid, or peracetic acid. Typical but non-limiting combinations include a combination of sulfuric acid and permanganic acid, or a combination of periodic acid and sulfuric acid.

[0031] Preferably, the concentration of the oxidizing and non-volatile acid is 2-8M, for example, it can be 2M, 3M, 4M, 5M, 6M, 7M or 8M, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the solid-liquid ratio of the graphite slag to the oxidizing and non-volatile acid is 1:(3-5), for example, it can be 1:3, 1:4 or 1:5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, after microwave acid leaching in step (2), solid-liquid separation, ultrasonic cleaning, and drying are performed to obtain the purified graphite. The ultrasonic cleaning is performed 3-5 times until the pH of the washing solution is neutral.

[0034] Preferably, the surface modification in step (3) is performed using a modifier and an acidic substance.

[0035] Preferably, the modifier comprises phenolic compounds, particularly m-diphenol and / or phenol.

[0036] Preferably, the acidic substance includes citric acid.

[0037] Since the graphite in waste batteries has undergone cyclic expansion, the interlayer spacing of the graphite has changed. Therefore, this invention modifies the graphite by using a modifier that can undergo a sol-gel reaction and an acidic substance, so that the generated aerogel can enter the graphite layer, thereby repairing the interlayer spacing of the graphite. At the same time, it can also coat the graphite, improving the electrical conductivity and electrochemical performance of the graphite.

[0038] Preferably, the surface modification in step (3) includes: mixing a modifier, an acidic substance and the purified graphite in step (2), and then performing heat treatment in a protective atmosphere.

[0039] Preferably, the solid-liquid ratio of the purified graphite to the modifier in step (2) is (3-5):1, for example, it can be 3:1, 4:1 or 5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the acid in the acidic substance has a mass fraction of 5-10 wt%, for example, it can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the heat treatment is carried out in a rotary tube furnace, the rotation speed of which is 2-10° / min, for example, 2° / min, 4° / min, 6° / min, 8° / min or 10° / min, but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] The heat treatment of this invention is carried out in a rotary tube furnace, which can improve the surface modification effect and enable the modifiers to be evenly dispersed with the purified graphite.

[0043] Preferably, the heat treatment includes a first heating, a second heating, and a third heating in sequence.

[0044] In this invention, surface modification involves a step-by-step heating process. The first heating causes a sol-gel reaction between the modifier and the acidic substance, generating an aerogel precursor that penetrates the graphite layer. A second heating process carbonizes the precursor, repairing the interlayer spacing of the graphite and generating a porous carbon gel for coating. A final heating process increases the graphite surface area after coating with the porous carbon gel. Further high-temperature treatment causes surface shrinkage, reducing the specific surface area of ​​the graphite. Therefore, this invention achieves repair and coating through a three-stage heating process, improving the electrochemical performance of graphite.

[0045] Preferably, the temperature is raised to 100-140°C, for example, 100°C, 120°C or 140°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the heating rate of the first heating is 0.5-1.5℃ / min, for example, it can be 0.5℃ / min, 1℃ / min or 1.5℃ / min, and the holding time is 20-60min, for example, it can be 20min, 30min, 40min, 50min or 60min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the secondary heating to 450-550℃, for example, can be 450℃, 500℃ or 550℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the heating rate of the secondary heating is 4-6℃ / min, for example, 4℃ / min, 5℃ / min or 6℃ / min, and the holding time is 50-70min, for example, 50min, 60min or 70min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the three temperature increases to 800-1000℃, for example, can be 800℃, 900℃ or 1000℃, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the holding time for the three heating cycles is 60-180 min, for example, it can be 60 min, 80 min, 100 min, 120 min, 140 min, 160 min or 180 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] The heat treatment described in this invention is followed by cooling and sieving steps.

[0052] The solid-liquid ratio mentioned in this invention refers to the ratio of the mass of the solid to the mass of the liquid, and the solid-liquid separation method includes pressure filtration or centrifugal separation.

[0053] As a preferred embodiment of the present invention, the method includes the following steps:

[0054] (1) The negative electrode sheet to be recycled is subjected to ultrasonic alkaline leaching with an alkaline solution of 0.5-2wt% by mass. Compressed air with a pressure of 5-50 MPa is blown in during ultrasonic alkaline leaching to obtain a current collector and a slurry. The slurry is separated into solid and liquid to obtain a lithium-containing solution and graphite slag. The lithium-containing solution is used to recover metallic lithium with lithium adsorption resin. The water generated is reused in the ultrasonic alkaline leaching step to complete the recovery of the current collector and lithium element.

[0055] The solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution is 1:(10-30), and the ultrasonic frequency of the ultrasonic alkaline leaching is 10-100KHz, and the time is 10-60min.

[0056] (2) The graphite slag described in step (1) is subjected to microwave acid leaching with an oxidizing and non-volatile acid for 20-100 minutes under pressure, at a temperature of 120-200℃ and a stirring speed of 100-500rpm. After solid-liquid separation, ultrasonic cleaning and drying, purified graphite is obtained.

[0057] The concentration of the oxidizing and non-volatile acid is 2-8M, and the solid-liquid ratio of the graphite slag to the oxidizing and non-volatile acid is 1:(3-5).

[0058] (3) Mix the modifier, acidic substance and the purified graphite described in step (2), and then in a protective atmosphere and in a rotary tube furnace with a rotation speed of 2-10° / min, heat the graphite to 100-140°C at a heating rate of 0.5-1.5°C / min, hold it for 20-60 min, then heat it to 450-550°C at a heating rate of 4-6°C / min, hold it for 50-70 min, and then heat it to 800-1000°C, hold it for 60-180 min to complete the surface modification and obtain graphite for batteries, thus completing the graphite recycling.

[0059] The solid-liquid ratio of the purified graphite to the modifier is (3-5):1, and the mass fraction of the acid in the acidic substance is 5-10 wt%.

[0060] In a second aspect, the present invention provides a recycled graphite, wherein the recycled graphite is obtained by means of the method described in the first aspect.

[0061] Preferably, the surface of the recycled graphite is coated with porous nano-carbon gel particles.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] First, this invention, through ultrasonic alkaline leaching, not only achieves powder removal but also recovers metallic lithium and removes organic impurities from the negative electrode sheet, reducing the impurity content in graphite and improving the graphite recovery rate. Second, microwave acid leaching allows for a more thorough reaction of impurities in the graphite sheets and the surface SEI layer without damaging the graphite microstructure, achieving deep impurity removal. Furthermore, since the graphite in waste batteries has undergone cyclic expansion, this invention, through surface modification, repairs the interlayer spacing of the cyclically expanded waste graphite and can coat porous carbon gel particles, thereby improving the electrochemical performance of graphite. Attached Figure Description

[0064] Figure 1 This is a flowchart of the method described in Embodiment 1 of the present invention;

[0065] Figure 2 This is a SEM image of the coarse graphite described in step (2) of Embodiment 1 of the present invention;

[0066] Figure 3 This is a SEM image of the purified graphite described in step (2) of Embodiment 1 of the present invention;

[0067] Figure 4 This is a SEM image of the graphite for batteries described in step (3) of Embodiment 1 of the present invention;

[0068] Figure 5 The graphs show the charge-discharge curves of the coarse graphite and battery graphite described in Example 1 of the present invention, as well as the graphite in Comparative Examples 1 and 2, after being prepared into batteries.

[0069] Figure 6 The graphs show the discharge capacity of the coarse graphite and battery graphite described in Example 1 of the present invention, as well as the discharge capacity of the batteries prepared from the graphite described in Comparative Examples 1 and 2 at different rates. Detailed Implementation

[0070] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0071] Example 1

[0072] This embodiment provides a method for the complete component recovery of a battery negative electrode, the flowchart of which is shown below. Figure 1 As shown, it includes the following steps:

[0073] (1) 1 kg of negative electrode sheet to be recycled (of which the graphite content is 0.44 kg) is placed in 10 kg of 1 wt% alkaline solution for ultrasonic alkaline leaching. At the same time, compressed air with a pressure of 20 MPa is blown in during ultrasonic alkaline leaching to obtain current collector copper foil and slurry. After centrifugation, lithium-containing solution and graphite residue are obtained. The concentration of lithium-containing solution is 0.35 g / L. Lithium metal is recovered by using lithium adsorption resin. The water generated is reused in the ultrasonic alkaline leaching step to complete the recovery of current collector copper foil and lithium element.

[0074] The solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution is 1:10, the alkaline solution is sodium hydroxide solution, and the ultrasonic frequency of the ultrasonic alkaline leaching is 20KHz and the time is 20min.

[0075] (2) The graphite slag described in step (1) is washed with pure water and centrifuged to obtain crude graphite (0.66 kg, water content 43%) and filtrate. The filtrate is reused in the preparation of alkaline solution. Then, the crude graphite is subjected to microwave acid leaching with sulfuric acid for 30 min under a pressure of 0.2 MPa, a temperature of 120°C and a stirring speed of 200 rpm. Then, the filter cake is obtained by centrifugation. The filter cake is ultrasonically washed with pure water 4 times until the pH of the pure water is neutral. After drying, purified graphite (0.396 kg) is obtained.

[0076] The concentration of the sulfuric acid is 4M, and the solid-liquid ratio of the graphite slag to the sulfuric acid is 1:3.5.

[0077] (3) Mix m-diphenol, citric acid solution and the purified graphite described in step (2), and then in an argon atmosphere and in a rotary tube furnace with a rotation speed of 5° / min, heat to 120°C at a heating rate of 1°C / min, hold for 30 min, then heat to 500°C at a heating rate of 5°C / min, hold for 60 min, then heat to 800°C, hold for 180 min, then cool to room temperature, and obtain battery graphite after passing through a 200-mesh sieve, thus completing the graphite recycling;

[0078] The solid-liquid ratio of the purified graphite to resorcinol is 3:1, and the mass fraction of the citric acid solution is 8 wt%.

[0079] In this embodiment, the SEM image of the coarse graphite in step (2) is as follows: Figure 2 As shown, the SEM image of the purified graphite in step (2) is as follows. Figure 3 As shown, the SEM image of the graphite for the battery described in step (3) is as follows. Figure 4 As shown, the charge-discharge curves of the coarse graphite and the battery after being made into a battery using graphite are as follows. Figure 5 As shown, the discharge capacity diagrams at different rates are as follows: Figure 6 As shown.

[0080] Example 2

[0081] This embodiment provides a method for the complete recovery of components from a battery negative electrode, the method comprising the following steps:

[0082] (1) The negative electrode sheet to be recycled is subjected to ultrasonic alkaline leaching with an alkaline solution of 2wt% by mass. At the same time, compressed air with a pressure of 50Mpa is blown in during ultrasonic alkaline leaching to obtain a current collector and a slurry. The slurry is centrifuged to obtain a lithium-containing solution and graphite residue. The lithium-containing solution is used to recover metallic lithium with lithium adsorption resin. The water generated is reused in the ultrasonic alkaline leaching step to complete the recovery of the current collector and lithium element.

[0083] The solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution is 1:20, the alkaline solution is sodium hydroxide solution, and the ultrasonic frequency of the ultrasonic alkaline leaching is 10KHz and the time is 10min.

[0084] (2) The graphite slag described in step (1) is washed and centrifuged with pure water to obtain crude graphite and filtrate. The filtrate is reused in the preparation of alkaline solution. Then, the crude graphite is acid-leached with sulfuric acid for 20 minutes at a pressure of 0.2 MPa, a temperature of 200°C, and a stirring speed of 100 rpm. Then, the filter cake is obtained by centrifugation. The filter cake is ultrasonically washed with pure water 5 times until the pH of the pure water is neutral. After drying, purified graphite is obtained.

[0085] The concentration of the sulfuric acid is 8M, and the solid-liquid ratio of the graphite slag to the sulfuric acid is 1:5.

[0086] (3) Mix m-diphenol, citric acid solution and the purified graphite described in step (2), and then in an argon atmosphere and in a rotary tube furnace with a rotation speed of 10° / min, heat to 140°C at a heating rate of 1.5°C / min, hold for 20 min, then heat to 450°C at a heating rate of 4°C / min, hold for 70 min, then heat to 1000°C, hold for 60 min, then cool to room temperature, and obtain battery graphite after passing through a 200-mesh sieve, thus completing the graphite recycling;

[0087] The solid-liquid ratio of the purified graphite to resorcinol is 5:1, and the mass fraction of the citric acid solution is 10 wt%.

[0088] Example 3

[0089] This embodiment provides a method for the complete recovery of components from a battery negative electrode, the method comprising the following steps:

[0090] (1) The negative electrode sheet to be recycled is subjected to ultrasonic alkaline leaching with an alkaline solution of 0.5 wt% by mass. At the same time, compressed air with a pressure of 5 MPa is blown in during ultrasonic alkaline leaching to obtain a current collector and a slurry. The slurry is separated by pressure filtration to obtain a lithium-containing solution and graphite slag. The lithium-containing solution is used to recover metallic lithium with lithium adsorption resin. The water generated is reused in the ultrasonic alkaline leaching step to complete the recovery of the current collector and lithium element.

[0091] The solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution is 1:30, the alkaline solution is a lithium hydroxide solution, and the ultrasonic leaching is performed at a frequency of 100 kHz for 60 minutes.

[0092] (2) The graphite slag described in step (1) is washed and centrifuged with pure water to obtain crude graphite and filtrate. The filtrate is reused in the preparation of alkaline solution. Then, the crude graphite is microwave-treated with permanganate solution for 100 minutes under a pressure of 0.5 MPa, a temperature of 120°C, and a stirring speed of 500 rpm. Then, the filter cake is obtained by centrifugation. The filter cake is ultrasonically washed three times with pure water until the pH of the pure water is neutral. After drying, purified graphite is obtained.

[0093] The concentration of the permanganate solution is 2M, and the solid-liquid ratio of the graphite slag to the permanganate solution is 1:3.

[0094] (3) Mix phenol, citric acid solution and the purified graphite described in step (2), and then in an argon atmosphere in a rotary tube furnace with a rotation speed of 2° / min, heat to 100°C at a heating rate of 0.5°C / min, hold for 40 min, then heat to 550°C at a heating rate of 6°C / min, hold for 50 min, then heat to 800°C, hold for 180 min, then cool to room temperature, and obtain battery graphite after passing through a 200-mesh sieve, thus completing the graphite recycling.

[0095] The solid-liquid ratio of the purified graphite to phenol is 3:1, and the mass fraction of the citric acid solution is 5 wt%.

[0096] Example 4

[0097] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for step (1) where gas is not introduced during ultrasonic alkaline leaching, the method is the same as that in Embodiment 1.

[0098] Example 5

[0099] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for the fact that the mass fraction of the alkaline solution in step (1) is 0.1 wt%, the method is the same as that in Example 1.

[0100] Example 6

[0101] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for the fact that the mass fraction of the alkaline solution in step (1) is 3 wt%, the method is the same as that in Example 1.

[0102] Example 7

[0103] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for the microwave acid leaching in step (2) which is carried out at normal pressure (0.1 MPa), the method is the same as that in embodiment 1.

[0104] Example 8

[0105] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for step (2), where the microwave acid leaching is carried out at room temperature of 25°C, the method is the same as that in Example 1.

[0106] Example 9

[0107] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for step (3), which does not involve three heating steps but only one heating step and two heating steps, the method is the same as that in embodiment 1.

[0108] Example 10

[0109] This embodiment provides a method for the complete recovery of the negative electrode components of a battery. Except for step (3), which does not involve a first heating and a second heating, but directly heats to 800°C, the method is the same as in embodiment 1.

[0110] Comparative Example 1

[0111] This comparative example provides a method for graphite recycling, the method comprising the following steps:

[0112] 1 kg of waste lithium battery negative electrode sheet (graphite content 0.44 kg) was placed in 10 kg of pure water for ultrasonic de-powdering, followed by centrifugal separation and drying to achieve graphite recycling.

[0113] The charge-discharge curve of the battery made from the recycled graphite in this comparative example is shown below. Figure 5 As shown, the discharge capacity diagrams at different rates are as follows: Figure 6 As shown.

[0114] Comparative Example 2

[0115] This comparative example provides a type of graphite, which is commercially available graphite (commercially available BTR graphite);

[0116] The charge-discharge curve of the graphite battery described in this comparative example is shown below. Figure 5 As shown, the discharge capacity diagrams at different rates are as follows: Figure 6 As shown.

[0117] Comparative Example 3

[0118] This comparative example provides a method for the complete recovery of the negative electrode components of a battery. Except for step (3), which does not involve adding m-diphenol and citric acid solution for surface modification, but instead directly regenerating and repairing the purified graphite described in step (2) at 800°C for 180 minutes, the method is the same as in Example 1.

[0119] Comparative Example 4

[0120] This comparative example provides a method for the complete recovery of the negative electrode components of a battery. Except for step (2), where the acid leaching is not performed under microwave, the method is the same as that in Example 1.

[0121] The content of impurity elements in the graphite obtained by the methods described in the above embodiments and comparative examples, as well as the content of impurity elements in the crude graphite in Example 1, are shown in Table 1. The graphite recovery rate and the first efficiency and discharge capacity of the coin cell made from the recovered graphite are shown in Table 2. In Table 1, the impurity content of Examples 1-10 and Comparative Examples 3-4 refers to the impurity content in the purified graphite in step (2). The graphite recovery rate of Examples 1-10 and Comparative Examples 3-4 in Table 3 refers to the recovery rate obtained by removing moisture from the crude graphite in step (1) and comparing it with the original graphite mass. The coin cell is made from the recovered graphite, lithium sheet, electrolyte (DMC:EC = 1:1, 1.1 mol LiPF6), and Celgard 2500 separator.

[0122] Table 1

[0123]

[0124]

[0125] Table 2

[0126]

[0127]

[0128] As can be seen from the table above:

[0129] (1) The method described in this invention can achieve full component recovery, and the recovered graphite exhibits excellent electrochemical performance; Figures 2-4 It can be seen that graphite obtained by direct descaling is like... Figure 2 As shown, the surface is covered with byproduct impurities generated during the recycling process. Some particles have cracks on their surface and are rough. After deep impurity removal in step (2) of this invention, as shown... Figure 3As shown, it can remove impurities from the graphite surface and obtain graphite with a clean and impurity-free surface. However, the graphite is still relatively rough and has cracks. After surface modification in step (3) of the present invention, graphite with a smooth surface and uniformly distributed nano carbon gel particles can be obtained. Specifically, as can be seen from Example 1 and Comparative Examples 1-2, the graphite recovered by the present invention has a low impurity content, meets the national standard requirements, and has excellent electrochemical performance. Its first efficiency and rate capability can reach those of the commercially available graphite in Comparative Example 2. Therefore, the graphite recovered by the present invention is battery-grade graphite that can be directly reused. Moreover, compared with the method of Comparative Example 1, the recovery method of the present invention can significantly reduce impurities in graphite and significantly improve electrochemical performance.

[0130] (2) As shown in Example 1 and Comparative Example 3, compared with high-temperature regeneration repair, the surface modification described in this invention can not only repair the interlayer spacing of graphite, but also coat the graphite surface with nano-carbon gel particles, thereby improving the electrochemical performance of the recovered graphite (first-time efficiency increased from 88% to 93%); As shown in Example 1 and Comparative Example 4, the acid leaching of this invention under microwave can significantly improve the impurity removal effect, and can be combined with other conditions to achieve a synergistic effect and achieve deep impurity removal; As shown in Example 1 and Example 4, the lack of gas blowing during ultrasonic alkaline leaching reduced the powder removal efficiency, thus affecting the graphite recovery rate; As shown in Example 1 and Examples 5-6, during alkaline leaching, the alkaline solution... The mass fraction affects the powder removal effect. If the alkali concentration is too high, it will not only affect the recovery rate but also waste resources, thus affecting the subsequent graphite purification and cleaning. As shown in Examples 1 and 7-8, the combination of pressure and heating during acid leaching can further improve the impurity removal effect, exert a synergistic effect, and achieve deep impurity removal. As shown in Examples 1 and 9, since the graphite surface area will increase after being coated with nano-carbon gel, the third heating can further reduce the graphite specific surface area, thereby further improving the performance. As shown in Examples 1 and 10, directly modifying the surface with modifiers and acidic substances at high temperatures cannot achieve the purpose of repairing the graphite interlayer spacing and coating of the present invention.

[0131] In summary, this invention provides a method for the complete recovery of components from a battery negative electrode and the graphite obtained from the recovery. The method can recover the collected fluid and metallic lithium, while reducing the content of impurity elements in the graphite and repairing the microstructure of the graphite, enabling the graphite to be returned to the negative electrode of the lithium battery, thereby maximizing resource utilization.

[0132] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for the complete recovery of components from a battery negative electrode, characterized in that, The method includes the following steps: (1) The negative electrode sheet to be recycled is subjected to ultrasonic alkaline leaching to obtain current collector and slurry. The slurry is separated into solid and liquid to obtain lithium-containing solution and graphite slag, thus completing the recycling of current collector and lithium element. (2) Microwave acid leaching is performed on the graphite slag described in step (1) to obtain purified graphite; (3) Surface modification step (2) The purified graphite is obtained to obtain graphite for batteries, thus completing the recycling of graphite; The surface modification in step (3) is performed using a modifier and an acidic substance, wherein the modifier includes diphenol and / or phenol, and the acidic substance includes citric acid; The surface modification in step (3) includes: mixing a modifier, an acidic substance and the purified graphite described in step (2), followed by heat treatment in a protective atmosphere; The heat treatment includes a first heating, a second heating, and a third heating in sequence, wherein the first heating is to 100-140°C, the second heating is to 450-550°C, and the third heating is to 800-1000°C.

2. The method according to claim 1, characterized in that, The ultrasonic alkaline leaching in step (1) uses an alkaline solution with a mass fraction of 0.5-2wt%.

3. The method according to claim 2, characterized in that, The alkaline solution includes sodium hydroxide solution and / or lithium hydroxide solution.

4. The method according to claim 1, characterized in that, During the ultrasonic alkaline immersion in step (1), gas was also introduced.

5. The method according to claim 4, characterized in that, The gas includes compressed air, and the pressure of the compressed air is 5-50 MPa.

6. The method according to claim 2, characterized in that, In step (1), the solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution is 1:(10-30).

7. The method according to claim 1, characterized in that, The ultrasonic alkali immersion in step (1) has an ultrasonic frequency of 10-100KHz and a duration of 10-60min.

8. The method according to claim 1, characterized in that, In step (1), the lithium-containing solution is used to recover metallic lithium using lithium adsorption resin, and the resulting water is reused in the ultrasonic alkaline leaching step.

9. The method according to claim 1, characterized in that, The microwave acid leaching in step (2) is carried out under pressure, heating and stirring.

10. The method according to claim 1, characterized in that, The microwave acid leaching pressure in step (2) is 0.1-0.5 MPa, and the temperature is 120-200℃.

11. The method according to claim 1, characterized in that, In step (2), the microwave pickling speed is 100-500 rpm and the time is 20-100 min.

12. The method according to claim 1, characterized in that, Step (2) involves microwave acid leaching using an oxidizing and non-volatile acid.

13. The method according to claim 12, characterized in that, The oxidizing and non-volatile acid includes any one or a combination of at least two of sulfuric acid, permanganic acid, periodic acid, hypochlorous acid, or peracetic acid.

14. The method according to claim 12, characterized in that, The concentration of the oxidizing and non-volatile acid is 2-8 M.

15. The method according to claim 12, characterized in that, The solid-liquid ratio of the graphite slag to the oxidizing and non-volatile acid is 1:(3-5).

16. The method according to claim 1, characterized in that, Step (2) involves microwave acid leaching followed by solid-liquid separation, ultrasonic cleaning, and drying to obtain the purified graphite.

17. The method according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the purified graphite to the modifier is (3-5):

1.

18. The method according to claim 1, characterized in that, The acid in the acidic substance has a mass fraction of 5-10 wt%.

19. The method according to claim 1, characterized in that, The heat treatment is carried out in a rotary tube furnace, the rotary tube furnace rotating at a speed of 2-10° / min.

20. The method according to claim 1, characterized in that, The heating rate for each heating cycle is 0.5-1.5℃ / min, and the holding time is 20-60min.

21. The method according to claim 1, characterized in that, The heating rate for the secondary heating is 4-6℃ / min, and the holding time is 50-70min.

22. The method according to claim 1, characterized in that, The holding time for the three heating cycles is 60-180 minutes.

23. The method according to claim 1, characterized in that, The method includes the following steps: (1) The negative electrode sheet to be recycled is subjected to ultrasonic alkaline leaching with an alkaline solution of 0.5-2wt% by mass. Compressed air with a pressure of 5-50 MPa is blown in during ultrasonic alkaline leaching to obtain a current collector and a slurry. The slurry is separated into solid and liquid to obtain a lithium-containing solution and graphite slag. The lithium-containing solution is used to recover metallic lithium with lithium adsorption resin. The water generated is reused in the ultrasonic alkaline leaching step to complete the recovery of the current collector and lithium element. The solid-liquid ratio of the negative electrode sheet to be recycled to the alkaline solution is 1:(10-30), and the ultrasonic frequency of the ultrasonic alkaline leaching is 10-100KHz, and the time is 10-60min. (2) The graphite slag described in step (1) is subjected to microwave acid leaching with an oxidizing and non-volatile acid for 20-100 minutes under a pressure of 0.1-0.5 MPa, a temperature of 120-200℃, and a stirring speed of 100-500 rpm. After solid-liquid separation, ultrasonic cleaning, and drying, purified graphite is obtained. The concentration of the oxidizing and non-volatile acid is 2-8M, and the solid-liquid ratio of the graphite slag to the oxidizing and non-volatile acid is 1:(3-5). (3) Mix the modifier, acidic substance and the purified graphite described in step (2), and then in a protective atmosphere and in a rotary tube furnace with a rotation speed of 2-10° / min, heat the graphite to 100-140°C at a heating rate of 0.5-1.5°C / min, hold it for 20-60 min, then heat it to 450-550°C at a heating rate of 4-6°C / min, hold it for 50-70 min, and then heat it to 800-1000°C, hold it for 60-180 min to complete the surface modification and obtain graphite for batteries, thus completing the graphite recycling. The solid-liquid ratio of the purified graphite to the modifier is (3-5):1, and the mass fraction of the acid in the acidic substance is 5-10 wt%.

24. A type of recycled graphite, characterized in that, The recovered graphite is obtained by means of any one of claims 1-23.

25. The recycled graphite according to claim 24, characterized in that, The recovered graphite surface is coated with porous nano-carbon gel particles.

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