Electrochemical impurity removal method for graphite-based materials containing metal element impurities

Abstract

The present application belongs to the field of electrochemical material purification and resource recycling technology, and discloses an electrochemical impurity removal method of graphite material containing metal element impurities. The impurities are removed by using an electrochemical impurity removal device, and the method comprises the following steps: S1: mixing the graphite material containing metal element impurities with an electrolyte solution to prepare a slurry; S2: passing the slurry into an anode chamber and passing a recovered bottom liquid into a cathode chamber; S3: connecting a direct current power supply, under the synergistic action of an electric field and an acidic environment generated in situ by the anode plate, the metal element impurities in the graphite material enter the electrolyte solution in the form of metal ions, and are driven by the electric field force to migrate through the cation exchange membrane to the cathode chamber; and S4: performing solid-liquid separation on the slurry in the anode chamber. The method does not need to rely on high-concentration strong acid to leach the metal element impurities in the graphite material, and uses the water oxidation generated by the anode plate to construct an acidic environment in situ, and under the action of the electric field, the metal element impurities are efficiently removed.

Description

Technical Field

[0001] This invention relates to the field of electrochemical material purification and resource recovery technology, specifically to an electrochemical method for removing impurities from graphite materials containing metallic element impurities. Background Technology

[0002] With the explosive growth of lithium-ion batteries in new energy vehicles, electrochemical energy storage, and consumer electronics, the amount of retired lithium-ion batteries has increased dramatically. Anode materials (mainly graphite) account for approximately 15%-20% of the total battery mass and have extremely high recycling value. However, during battery service and dismantling / crushing, graphite anodes often retain large amounts of lithium salts, "dead lithium" embedded between graphite layers, and metallic element impurities such as copper, iron, and aluminum introduced by current collectors or the outer casing. These metallic element impurities (especially "dead lithium" deeply embedded between graphite lattice layers or formed due to long-term cycling, and trace amounts of transition metal element impurities) are difficult to completely remove using conventional methods, severely restricting the cycling stability and safety of recycled graphite and limiting its application in high-value-added fields.

[0003] Currently, industrial technologies for removing impurities from waste graphite anode materials or graphite slag after hydrometallurgical lithium extraction mainly include high-temperature roasting, chemical acid / alkali leaching, and physical sorting. However, all of these methods have significant limitations. Among them, chemical acid / alkali leaching is currently the most commonly used method. Although strong acids (such as sulfuric acid and hydrochloric acid) can dissolve most of the metallic element impurities on the surface of graphite materials, this process is limited by the liquid-solid phase diffusion mass transfer rate, resulting in low removal efficiency for impurities embedded deep in the graphite lattice or encapsulated within it. Furthermore, this method heavily relies on high concentrations of acid and alkali reagents, which not only leads to the collapse of the graphite layered structure but also generates a large amount of difficult-to-treat waste liquid containing heavy metals, posing a significant environmental burden. High-temperature roasting utilizes high temperatures to remove organic binders and some volatile impurities. However, the high-temperature roasting process is extremely energy-intensive and easily induces carbothermic reduction reactions between metallic element impurities and the carbon matrix, generating even more difficult-to-remove metallic carbides. Simultaneously, high-temperature oxidation etches the graphite surface, reducing the yield and conductivity of the recycled material. Physical separation methods, such as flotation or magnetic separation, can only separate some free impurities with high degree of dissociation. They are almost ineffective for impurities that are tightly bound to graphite or exist in the form of chemical bonds, and are usually only used as a pretreatment method.

[0004] In recent years, electrochemical impurity removal technology has attracted much attention due to its advantages such as environmental friendliness and strong controllability. Some researchers have attempted to use electrochemical impurity removal technology to treat graphite materials. However, most existing electrochemical technologies fall into the category of "assisted leaching," meaning that a large amount of acidic or oxidizing chemical reagents still need to be added to the electrolytic cell beforehand to maintain the dissolution environment, and the dependence on high-concentration acid / base reagents or oxidizing reagents has not been fundamentally eliminated. In addition, existing devices are difficult to achieve targeted enrichment and deep separation of impurities.

[0005] Therefore, there is an urgent need to develop a novel electrochemical impurity removal method that can achieve targeted removal of deep impurities without the need for external high-concentration acid / base reagents and is environmentally friendly. Summary of the Invention

[0006] The present invention aims to at least alleviate or solve at least one of the aforementioned problems to some extent. Therefore, the object of the present invention is to provide an electrochemical impurity removal method that constructs an in-situ impurity removal environment through electrochemical action, thereby achieving efficient purification of graphite materials containing metallic element impurities.

[0007] In one aspect of the invention, an electrochemical method for removing impurities from graphite materials containing metallic element impurities is proposed. The method utilizes an electrochemical impurity removal device, which includes an electrolytic cell body internally divided into an anode chamber and a cathode chamber by a cation exchange membrane. An anode plate is disposed in the anode chamber, and a cathode plate is disposed in the cathode chamber. The method comprises the following steps: S1: Mixing the graphite material containing metallic element impurities with an electrolyte solution to prepare a slurry; S2: Passing the slurry into the anode chamber and passing the recovered bottom solution into the cathode chamber; S3: Connecting the anode plate and cathode plate to the positive and negative terminals of a DC power supply, respectively. Under the synergistic effect of the electric field and the acidic environment generated in situ by the anode plate, the metallic element impurities in the graphite material enter the electrolyte solution in the form of metal ions and migrate through the cation exchange membrane to the cathode chamber under the driving force of the electric field; S4: Performing solid-liquid separation on the slurry in the anode chamber to obtain purified graphite. This method does not rely on high-concentration strong acid leaching to remove metal element impurities from graphite materials. Instead, it utilizes an anode plate to generate water oxidation in situ to create an acidic environment, which efficiently removes metal element impurities under the action of an electric field.

[0008] In some embodiments, in step S1, the electrolyte solution is an acidic solution or a neutral salt solution with pH = 1-6; and / or, in step S2, the recovered bottom solution is an acidic solution or a neutral salt solution with pH = 1-6.

[0009] In some embodiments, in step S3, the applied DC voltage is 1.5-5.0V; and / or, the anode chamber is ultrasonically treated or mechanically stirred during operation.

[0010] In some embodiments, steps S2 and S3 are continuous or intermittent operations; and / or, in step S4, the solid-liquid separation includes at least one of filtration and centrifugation.

[0011] In some embodiments, in step S1, the graphite material is crushed and / or sieved, and then mixed with the electrolyte solution; and / or, in step S1, the graphite material and the electrolyte solution are mixed at a mass ratio of 1:5 to 1:100 to prepare a slurry.

[0012] In some embodiments, in step S2, the slurry is pumped into the anode chamber using a peristaltic pump at a flow rate controlled at 10 mL / min-100 mL / min; and / or, in step S2, the recovered bottom liquid is pumped into the cathode chamber using a peristaltic pump at a flow rate controlled at 10 mL / min-100 mL / min.

[0013] In some embodiments, the method satisfies at least one of the following conditions: the anode plate and the cathode plate are each independently selected from one or more of graphite plates, coated titanium anodes, stainless steel plates, and platinum sheets; the anode chamber is provided with a slurry inlet and a slurry outlet; the cathode chamber is provided with a recovery base liquid inlet and a recovery liquid outlet; the cation exchange membrane includes one or more of perfluorosulfonic acid membranes and heterogeneous cation exchange membranes; the anode plate has a first flow channel; and the cathode plate has a second flow channel.

[0014] In some embodiments, the method satisfies at least one of the following conditions: the first flow channel is a serpentine flow channel, an interdigitated flow channel, a straight flow channel, or a combination thereof; the depth of the first flow channel is 0.5-5.0 mm; one end of the first flow channel is a slurry inlet, and the other end is a slurry outlet; the second flow channel is a serpentine flow channel, an interdigitated flow channel, a straight flow channel, or a combination thereof; the depth of the second flow channel is 0.5-5.0 mm; one end of the second flow channel is a recovery liquid inlet, and the other end is a recovery liquid outlet.

[0015] In some embodiments, the main body of the electrolytic cell is sealed and fixed using insulating plates.

[0016] In some embodiments, the graphite materials include one or more of the following: graphite anode materials from waste lithium-ion batteries, graphite by-products generated during the production or recycling of lithium-ion batteries, graphite bottom slag after lithium extraction by hydrometallurgy, and tailings from natural graphite beneficiation. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 A schematic diagram of an electrochemical impurity removal device according to an embodiment of the present invention is shown; Figure 2 A schematic diagram of an electrochemical impurity removal device according to an embodiment of the present invention is shown. Figure 3 Figures (a) and (b) in the figure are SEM images of the graphite anode before and after impurity removal in Embodiment 1 of the present invention, respectively. Figure 4 The image shows the XRD patterns of the graphite negative electrode before and after impurity removal in Embodiment 1 of the present invention.

[0018] Explanation of reference numerals in the attached figures: 100: Electrolytic cell body; 110: Cation exchange membrane; 120: Anode plate; 121: First flow channel; 121-1: Slurry inlet; 121-2: Slurry outlet; 130: Cathode plate; 131: Second flow channel; 131-1: Recovery liquid inlet; 131-2: Recovery liquid outlet; 210: First plate; 220: Second plate; 140: Gasket; 10: Graphite material; 300: DC power supply. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] In one aspect of this application, an electrochemical method for removing impurities from graphite materials containing metallic elemental impurities is proposed, using an electrochemical impurity removal device. (Reference) Figure 1 The electrochemical impurity removal device includes an electrolytic cell body 100, which is divided into an anode chamber and a cathode chamber by a cation exchange membrane 110. The anode chamber and the cathode chamber are arranged opposite to each other. An anode plate 120 is arranged in the anode chamber and a cathode plate 130 is arranged in the cathode chamber.

[0021] In some embodiments, the electrochemical impurity removal method for graphite materials containing metallic element impurities includes the following steps: S1: A slurry is prepared by mixing graphite materials containing metallic impurities with an electrolyte solution.

[0022] In some embodiments, graphite materials containing metallic element impurities may include one or more of the following: graphite anode materials from waste lithium-ion batteries, graphite by-products generated during the production or recycling of lithium batteries, graphite bottom slag after hydrometallurgical lithium extraction, and natural graphite beneficiation tailings.

[0023] In some embodiments, in step S1, the electrolyte solution can be an acidic solution or a neutral salt solution with a pH of 1-6, used to assist in the leaching of impurity metal ions and conduction. In some specific embodiments, the electrolyte solution can be a dilute sulfuric acid solution, a dilute hydrochloric acid solution, etc., with a pH of 1-6. In other specific embodiments, the electrolyte solution can be a sulfate (e.g., sodium sulfate) solution, a nitrate (e.g., sodium nitrate) solution, etc. Thus, by using a dilute acid solution or a neutral salt solution as the electrolyte solution, under the action of an electric field, protons are generated in situ through the water oxidation reaction on the surface of the anode plate, creating an acidic environment in situ at the anode. This maintains the acidic leaching environment of the anode chamber without the addition of additional high-concentration acidic reagents.

[0024] In some embodiments, graphite materials containing metallic element impurities can be introduced into the anode chamber in powder, granular, or a combination thereof, or can be subjected to simple physical treatments before introduction, such as sieving, crushing, or dispersion, to increase their contact area with the electrolyte solution.

[0025] In some embodiments, in step S1, the graphite material can be crushed and / or sieved before being mixed with the electrolyte solution. By crushing and / or sieving the graphite material, smaller particle sizes can be obtained, increasing its contact area with the electrolyte solution. This makes it easier for metallic impurities to be removed from the graphite material under the subsequent electric field, thereby facilitating the acquisition of graphite materials with higher purity.

[0026] In some embodiments, the particle size of the graphitic material after crushing and / or sieving can be less than or equal to 200 mesh, for example, the particle size range can be 50-150 mesh.

[0027] In some embodiments, in step S1, graphite materials and electrolyte solutions can be mixed at a mass ratio of 1:5 to 1:100 to prepare a slurry. For example, the mass ratio of graphite materials to electrolyte solutions can be 1:5, 1:10, 1:25, 1:50, 1:75, 1:100, etc. This results in a slurry with good fluidity, and the flow rate is not too fast, allowing it to remain in the impurity removal device for a suitable time, thereby facilitating the removal of metallic element impurities.

[0028] S2: Pass the slurry into the anode chamber and pass the recovered bottom liquid into the cathode chamber.

[0029] In some embodiments, in step S2, the recovered base solution is an acidic solution or a neutral salt solution with a pH of 1-6. In some specific embodiments, the recovered base solution can be a dilute sulfuric acid solution, a dilute hydrochloric acid solution, etc., with a pH of 1-6. In other specific embodiments, the recovered base solution can be a sodium sulfate solution, a nitrate (e.g., sodium nitrate) solution, etc.

[0030] In some embodiments, in step S2, the slurry is pumped into the anode chamber using a peristaltic pump, and the flow rate can be controlled to be 10 mL / min-100 mL / min. For example, the flow rate can be 10 mL / min, 30 mL / min, 50 mL / min, 70 mL / min, 100 mL / min, etc. This prevents the slurry from clogging and allows it to remain in the impurity removal device for an appropriate time, thus facilitating impurity removal.

[0031] In some embodiments, in step S2, the recovered bottom liquid is pumped into the cathode chamber using a peristaltic pump, and the flow rate can be controlled to be 10 mL / min-100 mL / min. For example, the flow rate can be 10 mL / min, 30 mL / min, 50 mL / min, 70 mL / min, 100 mL / min, etc.

[0032] S3: Reference Figure 1 The anode plate 120 and the cathode plate 130 are connected to the positive and negative terminals of the DC power supply 300, respectively. When the DC power supply 300 is turned on, under the synergistic effect of the electric field and the acidic environment generated in situ by the anode plate 120, the metal element impurities in the graphite material enter the electrolyte solution in the form of metal ions. Driven by the electric field force, they overcome the diffusion resistance and migrate through the cation exchange membrane 110 to the cathode chamber.

[0033] In some embodiments, the anode plate 120 and the cathode plate 130 can be conductive inert metal-based electrodes or carbon-based electrodes. The anode plate 120 and the cathode plate 130 should have high electrochemical stability and good conductivity, be able to operate stably for a long time in a wide voltage range, and be suitable for electrochemical impurity removal processes.

[0034] In some embodiments, the anode plate 120 and the cathode plate 130 are each independently selected from one or more of graphite plates, coated titanium anodes (DSA), stainless steel plates, and platinum sheets. These plates possess excellent conductivity and high electrochemical stability, enabling long-term stable operation during electrochemical impurity removal.

[0035] In some embodiments, the cation exchange membrane 110 may include one or more of a perfluorosulfonic acid membrane (perfluorosulfonic acid proton exchange membrane) and a heterogeneous cation exchange membrane. This exchange membrane allows cations to pass through and migrate directionally under the influence of an electric field, enabling metal cations (e.g., Figure 1 Cu shown 2+ Fe 3+ Li + The metal element impurities enter the cathode chamber, thereby separating them from the graphite-based materials. The exchange membrane hinders the passage of anions, especially blocking the reflux of hydroxide ions generated at the cathode, thus maintaining an acidic environment in the anode chamber.

[0036] In some embodiments, reference Figure 2 The anode chamber is equipped with a slurry inlet 121-1 and a slurry outlet 121-2 for circulating a slurry formed by mixing graphite materials containing metal element impurities with an electrolyte solution. The slurry can enter the anode chamber through the slurry inlet 121-1, and the treated slurry can be removed from the anode chamber through the slurry outlet 121-2 for filtration and / or centrifugation to obtain purified graphite.

[0037] In some embodiments, reference Figure 2 The anode plate 120 has a first flow channel 121, which can guide the slurry flow and enhance the mass transfer effect. In some embodiments, the first flow channel 121 can be a serpentine flow channel (e.g., Figure 2 (As shown), interdigitated flow channels, straight flow channels, or combinations thereof. The first flow channel 121 can also be other structural forms that can increase the fluid residence time, as long as it can achieve effective flow of the slurry on the electrode surface or in the anode chamber.

[0038] In some embodiments, the depth of the first flow channel 121 can be 0.5-5.0 mm, for example, the depth of the first flow channel 121 can be 0.5 mm, 1 mm, 1.5 mm, 3 mm, 4.5 mm, 5.0 mm, etc. Therefore, the first flow channel 121 can accommodate an appropriate amount of slurry, and is beneficial for the uniform distribution of the electric field and the removal of metal element impurity ions. It should be noted that the depth of the first flow channel 121 and the depth of the second flow channel 131 mentioned later refer to the dimension of the flow channel along the direction perpendicular to the paper surface.

[0039] In some embodiments, reference Figure 2 One end of the first flow channel 121 can be a slurry inlet 121-1, and the other end can be a slurry outlet 121-2.

[0040] In some embodiments, reference Figure 2 The cathode chamber is equipped with a recovery liquid inlet 131-1 and a recovery liquid outlet 131-2. The recovery liquid can enter the cathode chamber through the recovery liquid inlet 131-1, and after the treatment is completed, the recovery liquid can be removed from the cathode chamber through the recovery liquid outlet 131-2.

[0041] In some embodiments, reference Figure 2 The cathode plate 130 may have a second flow channel 131, which can be used to form a flow electrode.

[0042] In some embodiments, the second flow channel 131 may be a serpentine flow channel (e.g., Figure 2 (As shown), the second flow channel 131 can be an interdigitated flow channel, a straight flow channel, or a combination thereof. The second flow channel 131 can also be any other structural form that can increase the fluid residence time, as long as it can achieve effective flow of the solution on the electrode surface or in the cathode chamber.

[0043] In some embodiments, the depth of the second flow channel 131 can be 0.5-5.0 mm, for example, the depth of the second flow channel 131 can be 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5.0 mm, etc.

[0044] In some embodiments, reference Figure 2 One end of the second flow channel 131 can be the recovery liquid inlet 131-1, and the other end can be the recovery liquid outlet 131-2.

[0045] In some embodiments, the electrolytic cell body 100 may be sealed and fixed using an insulating plate. Specifically, refer to... Figure 1 and Figure 2 The electrochemical impurity removal device may further include a first plate 210 and a second plate 220, which are insulating plates used to seal and fix the electrolytic cell body 100. In some specific embodiments, the first plate 210 and the second plate 220 may each be independently made of acrylic sheet, engineering plastic sheet or other corrosion-resistant material, and the overall device can be assembled by bolts or clamping structures.

[0046] In some embodiments, reference Figure 2 The electrochemical impurity removal device may further include a gasket 140, located between the anode plate 120 and the cathode plate 130, with a hollow structure in the middle to ensure a tighter fit between the various components of the device and prevent leakage. The specific material of the gasket 140 is not particularly limited in this invention; those skilled in the art can choose according to actual needs. For example, a gasket made of insulating polymer material can be used. In some specific embodiments, the electrolytic cell body 100 may include the anode plate 120, gasket 140, cation exchange membrane 110, and cathode plate 130 stacked sequentially. In other specific embodiments, the electrolytic cell body 100 may include the anode plate 120, cation exchange membrane 110, gasket 140, and cathode plate 130 stacked sequentially.

[0047] In some embodiments, the applied DC voltage in step S3 can be 1.5-5.0V, for example, the DC voltage can be 1.5V, 2.5V, 3.5V, 4.5V, 5.0V, etc. Therefore, under the action of the electric field, an acidic environment can be generated in situ on the surface of the anode plate, which is conducive to the metal element impurities in the graphite material entering the electrolyte solution in ionic form and migrating to the cathode chamber under the action of the electric field, thereby achieving impurity removal. The above voltage helps to reduce operating costs and can achieve a better impurity removal effect.

[0048] In some embodiments, the anode chamber can be ultrasonically treated or mechanically stirred during operation to prevent graphite particles from settling. This is more conducive to the uniform dispersion of the slurry and the removal of impurities.

[0049] The electrochemical impurity removal device of the present invention can be operated in either an intermittent or continuous manner, that is, steps S2 and S3 can be operated in either an intermittent or continuous manner.

[0050] In intermittent operation, graphite-based materials containing metallic impurities and an electrolyte solution are added to the anode chamber of the device at once. After the voltage is applied and the device is run for a predetermined time, the operation is stopped and the solution in the cathode chamber is collected.

[0051] In continuous operation, graphite-based materials containing metal element impurities can be continuously replenished to the anode chamber (i.e., slurry is continuously supplied to the anode chamber), while a solution rich in impurity metal ions is continuously or periodically discharged from the cathode chamber, establishing a circulating flow system to achieve continuous impurity removal.

[0052] Continuous operation is beneficial for achieving large-scale impurity removal; intermittent operation is beneficial for obtaining graphite materials with higher purity.

[0053] S4: Perform solid-liquid separation on the slurry in the anode chamber to obtain purified graphite.

[0054] After separation, the slurry in the anode chamber can be removed and subjected to solid-liquid separation to obtain purified graphite. In some embodiments, at least one of the following methods can be used for solid-liquid separation: filtration, centrifugation, etc. In some specific embodiments, the slurry in the anode chamber can be filtered, washed, and dried to obtain purified graphite.

[0055] In some embodiments, a lithium-ion-rich recovery solution can be continuously or intermittently discharged from the cathode chamber, and lithium can be extracted from it. The above method enables the effective migration and extraction of lithium from graphite materials containing metallic element impurities. Under conditions without introducing high temperatures and large concentrations of acid / alkali chemical reagents, the concentration of impurity metal ions in the cathode chamber gradually increases with operating time, indicating that the method of the present invention can stably achieve electrochemical impurity removal from graphite materials containing metallic element impurities.

[0056] In some specific embodiments, reference is made to Figure 1 Graphite materials can be mixed with an electrolyte solution (0.1M HCl solution) to obtain a slurry. This slurry is then pumped into the anode chamber using a peristaltic pump. A 0.1M HCl solution is used as the recovery base solution, which is then pumped into the cathode chamber using a peristaltic pump. The graphite materials contain lithium iron phosphate (Fe2+). 2+In the acidic environment of the anode chamber, it will be oxidized to Fe. 3+ Impurities such as copper oxide and elemental lithium are introduced into the anode plate 120 under an applied electric field, creating an acidic environment that causes the metallic element impurities in the graphite material 10 to exist in ionic form (Cu). 2+ Fe 3+ Li + The graphite material enters the electrolyte solution and, under the influence of an electric field, passes through the cation exchange membrane 110 into the cathode chamber, while the graphite material remains in the anode chamber, thus achieving the separation of the graphite material 10 from the metallic element impurities; at least a portion of the Cu... 2+ Fe 3+ The metals are reduced in the cathode chamber to form elemental copper and elemental iron. The elemental metals attached to the cathode plate can then be removed by ultrasonic treatment.

[0057] In other specific embodiments, the graphite material contains impurities such as aluminum oxide, calcium oxide, and iron oxide. Under the condition of applying an electric field, an acidic environment is generated in situ on the anode plate, which causes the metal elements in the above impurities to enter the electrolyte solution in ionic form and pass through the cation exchange membrane into the cathode chamber under the action of the electric field.

[0058] Compared with the prior art, the beneficial effects of the electrochemical impurity removal method of the present invention are reflected in the following aspects: (1) This invention does not rely on strong acid (high concentration of acid solution) to leach out metal element impurities in graphite materials. Instead, it uses dilute acid solution or neutral salt solution as electrolyte for dissolution and utilizes the anode plate to generate water oxidation in situ to create an acidic environment, which efficiently removes metal element impurities under the action of an electric field.

[0059] (2) This invention has good applicability to graphite materials containing metal element impurities from different sources. It can be used to treat graphite anode materials in waste lithium-ion batteries, graphite by-products generated during the production or recycling of lithium batteries, graphite bottom slag after lithium extraction by hydrometallurgy, and graphite tailings from natural graphite beneficiation, etc., which can release metal ions under electrochemical conditions. The operating conditions are mild, which can effectively reduce the impurity content in graphite materials, and can completely preserve the layered crystal structure of graphite.

[0060] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the materials and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0061] Example 1 In this embodiment, the graphite material containing metallic impurities is graphite anode waste obtained from dismantling waste lithium iron phosphate batteries, wherein the carbon content is 92.5%, the lithium content is 1000 ppm, the copper content is 1500 ppm, and the iron content is 800 ppm. The electrochemical impurity removal device includes an anode chamber and a cathode chamber. The anode plate is coated with titanium (DSA), and the cathode plate is made of 304 stainless steel. A perfluorosulfonic acid proton exchange membrane (Nafion 117) is installed between the anode chamber and the cathode chamber. Both the anode plate and the cathode plate are engraved with a serpentine flow channel structure (e.g., Figure 2 (As shown), the depth is 2.0 mm. Graphite material containing metallic impurities was mixed with 0.1 M Na₂SO₄ solution at a mass ratio of 1:10 and pumped into the anode chamber of the electrolytic cell at a peristaltic pump flow rate of 10 mL / min. The 0.1 M Na₂SO₄ solution was then pumped into the cathode chamber at a peristaltic pump flow rate of 10 mL / min. A voltage of 4.0 V was applied between the two electrodes. After 6.0 h of operation, the final product graphite purity increased from 92.5% to over 99.5%, indicating that the metallic impurities in the graphite material were removed, and impurity removal was successfully achieved.

[0062] Figure 3 In the figure, (a) and (b) are SEM images of the graphite anode material before and after impurity removal in Example 1, respectively. It can be seen that the graphite anode material has a layered crystal structure before and after impurity removal. Therefore, it can be seen that the layered crystal structure of the graphite anode material can be completely preserved by using the method of the present invention to process the graphite anode material.

[0063] Figure 4 The XRD patterns of the graphite anode material before and after impurity removal in Example 1 are shown. It can be seen that the XRD pattern of the graphite anode material before impurity removal contains some diffraction peaks of impurities, while the XRD pattern of the graphite anode material after impurity removal basically does not contain diffraction peaks corresponding to these impurities.

[0064] Example 2 Without altering the graphite anode material and device structure of Example 1, the electrode plates in both the anode and cathode chambers were configured as conductive inert metal-based electrodes (platinum electrodes). The graphite anode material containing metal element impurities was mixed with a dilute sulfuric acid solution at pH 4.0 at a mass ratio of 1:5 and pumped into the anode chamber of the electrolytic cell at a peristaltic pump flow rate of 30 mL / min. The dilute sulfuric acid solution at pH 4.0 was pumped into the cathode chamber at a peristaltic pump flow rate of 30 mL / min. A voltage of 4.0 V was applied between the two electrodes. After 6.0 hours of operation, the impurity removal rate of the final product was >99%, indicating successful impurity removal.

[0065] Example 3 Under the premise that the graphite anode material and device structure of Example 1 remain unchanged, the graphite anode material containing metal element impurities is mixed with a dilute sulfuric acid solution with pH=4.0 at a mass ratio of 1:5 and then pumped into the anode chamber of the electrolytic cell. The flow rate of the peristaltic pump is 50 mL / min. The dilute sulfuric acid solution with pH=4.0 is pumped into the cathode chamber. The flow rate of the peristaltic pump is 50 mL / min. After running for 6.0 h with a voltage of 5.0 V between the two electrodes, the impurity removal rate of the final product is >99%, indicating that the impurity removal has been successfully achieved.

[0066] Example 4 Based on the apparatus of Example 1, electrochemical impurity removal and lithium extraction were performed in a continuous operation mode.

[0067] Graphite-based material containing metallic impurities was continuously added to the anode chamber, while a lithium-ion-rich solution was continuously discharged from the cathode chamber. During continuous operation, the device voltage remained at 3.0V, the operating condition was stable, and no significant performance degradation was observed.

[0068] This embodiment demonstrates that the apparatus and method used in this invention are suitable for continuous, large-scale operation scenarios.

[0069] Example 5 Example 5 followed the same steps as Example 2 for electrochemical impurity removal, except that the pH of the dilute sulfuric acid solution in Example 5 was 6.0.

[0070] The results show that lithium ion migration and extraction, as well as electrochemical impurity removal from graphite materials, can be achieved using dilute acid solutions of different concentrations.

[0071] Example 6 Based on the device described in Example 1, the flow channel structure in the anode chamber is adjusted, and the anode chamber and cathode chamber adopt a straight flow channel and a serpentine flow channel structure, respectively.

[0072] Electrochemical impurity removal and lithium extraction experiments were conducted under the same operating conditions. The results showed that different flow channel structures could all achieve effective lithium ion migration, and the flow channel structure helped to enhance the contact between the solution and the electrode surface, thereby improving the stability of the device operation.

[0073] Example 7 Based on the apparatus described in Example 1, lithium extraction is performed in an intermittent operation mode, that is, the slurry is introduced into the anode chamber in an intermittent mode.

[0074] During each operation, graphite-based material containing metallic impurities and an electrolyte solution are added to the anode chamber of the device, while the electrolyte solution is added to the cathode chamber. After applying voltage and operating for a predetermined time of 4 hours, operation is stopped, and the lithium-ion-rich solution in the cathode chamber is collected. This process is repeated, and the device performance remains stable, allowing for multiple repetitions to achieve electrochemical extraction of lithium.

[0075] Comparative Example 1 The difference between this comparative example and Example 1 is that the Nafion 117 cation exchange membrane in Example 1 was replaced with a PP / PE composite microporous membrane (pore size 0.1 μm). All other processes were the same as in Example 1. In Comparative Example 1, the pH of the anolyte was consistently maintained between 5 and 6, making it impossible to create a strongly acidic environment. The impurity removal results are shown in Table 1; the removal rate of metallic elemental impurities (Li, Cu, Fe) was approximately 80%.

[0076] Comparative Example 2 The difference between this comparative example and Example 2 is that the voltage between the two electrodes was set to 0V in this comparative example, while all other processes were the same as in Example 2. The impurity removal results are shown in Table 1. The removal effect of metallic elemental impurities (Li, Cu, Fe) was generally good, with a removal rate of approximately 60%.

[0077] Example 8 The difference between this embodiment and Example 1 is that the reaction time in this embodiment is 4 hours. Other parameters are the same as in Example 1. The impurity removal results are shown in Table 1, indicating that the removal effect of metallic element impurities (Li, Cu, Fe) is relatively good.

[0078] Graphite anode waste obtained from the dismantling of a waste lithium iron phosphate battery was used as the target for lithium extraction. After being mixed with an electrolyte solution, it was pumped into the anode chamber, and the apparatus was operated according to the methods described in Examples 1-8 and Comparative Examples 1-2. The impurity removal rate was tested by digesting the graphite materials before and after impurity removal, and then using an ICP spectrometer to test the content of metal element impurities in the graphite materials. The removal efficiency of metal element impurities was calculated based on the content of metal element impurities in the graphite materials before and after impurity removal. The metal element impurity removal effects of each example and comparative example are shown in Table 1.

[0079] Table 1. Removal efficiency of metallic element impurities in Examples 1-8 and Comparative Examples 1-2

[0080] As shown in Table 1, the graphite purity in the electrochemical impurity removal devices described in Examples 1-8 can all reach over 99.6%, which is significantly better than that of the comparative examples. This indicates that the electrochemical impurity removal method of the present invention can stably and efficiently remove metal element impurities from the graphite negative electrode waste obtained from the dismantling of old lithium iron phosphate batteries.

[0081] Graphite materials containing metallic element impurities from different sources were selected to simulate the complexity of the composition of materials containing metallic element impurities in practical applications. The initial content of impurity metals in the various graphite materials differed, but all could achieve efficient impurity removal under the operating conditions of this device.

[0082] Example 9 The same apparatus and method as in Example 1 were used for impurity removal. The difference from Example 1 is that the graphite material in Example 9 was made from natural graphite beneficiation tailings.

[0083] Example 10 The same apparatus and method as in Example 2 were used for impurity removal. The difference from Example 2 is that the graphite material in Example 10 was made from natural graphite beneficiation tailings.

[0084] Example 11 The same apparatus and method as in Example 3 were used for impurity removal. The difference from Example 3 is that the graphite material in Example 11 was made from natural graphite beneficiation tailings.

[0085] Example 12 The same apparatus and method as in Example 4 were used for impurity removal. The difference from Example 4 is that the graphite material in Example 12 was made from natural graphite ore tailings.

[0086] Example 13 The same apparatus and method as in Example 5 were used for impurity removal. The difference from Example 5 is that the graphite material in Example 13 was made from natural graphite beneficiation tailings.

[0087] Example 14 The same apparatus and method as in Example 6 were used for impurity removal. The difference from Example 6 is that the graphite material in Example 14 was made from natural graphite beneficiation tailings.

[0088] Example 15 The same apparatus and method as in Example 7 were used for impurity removal. The difference from Example 7 is that the graphite material in Example 15 was made from natural graphite ore tailings.

[0089] Example 16 The same apparatus and method as in Example 8 were used for impurity removal, except that in Example 16, the graphite material used was natural graphite beneficiation tailings.

[0090] Comparative Example 3 The same apparatus and method as Comparative Example 1 were used for impurity removal. The difference from Comparative Example 1 is that the graphite material in Comparative Example 3 was made from natural graphite beneficiation tailings.

[0091] Comparative Example 4 The same apparatus and method as Comparative Example 2 were used for impurity removal. The difference from Comparative Example 2 is that the graphite material in Comparative Example 4 was made from natural graphite beneficiation tailings.

[0092] The graphite materials from Examples 9-16 and Comparative Examples 3-4, before and after impurity removal, were digested. The content of metallic element impurities in the graphite materials was then measured using an ICP spectrometer. The removal efficiency of metallic element impurities was calculated based on the content of metallic element impurities in the graphite materials before and after impurity removal. The results of the impurity removal efficiency and graphite purity tests are shown in Table 2.

[0093] Table 2. Removal efficiency of metallic element impurities from graphite materials under the apparatus and operating conditions described in Examples 9-16 and Comparative Examples 3-4.

[0094] As shown in Tables 1 and 2, the devices described in Examples 1-16 all exhibited high impurity metal removal rates for graphite materials containing metal element impurities from different sources, indicating that the impurity removal method of the present invention has good applicability to graphite materials containing metal element impurities.

[0095] In summary, the electrochemical impurity removal methods described in Examples 1-16 all exhibit high removal efficiency, good operational stability, and strong applicability in the removal of metal element impurities from graphite materials containing metal element impurities. Their overall performance is significantly better than that of the comparative examples, proving that the impurity removal method of the present invention can efficiently remove metal element impurities from graphite materials containing metal element impurities under mild conditions.

[0096] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An electrochemical method for removing impurities from graphite materials containing metallic elements, characterized in that, An electrochemical impurity removal device is used for impurity removal. The electrochemical impurity removal device includes an electrolytic cell body, which is internally divided into an anode chamber and a cathode chamber by a cation exchange membrane. The cation exchange membrane is located between the anode chamber and the cathode chamber. An anode plate is disposed in the anode chamber, and a cathode plate is disposed in the cathode chamber. The method includes the following steps: S1: A slurry is prepared by mixing graphite materials containing metallic impurities with an electrolyte solution; S2: The slurry is introduced into the anode chamber, and the recovered bottom liquid is introduced into the cathode chamber; S3: Connect the anode plate and cathode plate to the positive and negative terminals of a DC power supply, respectively. When the DC power supply is turned on, under the synergistic effect of the electric field and the acidic environment generated in situ by the anode plate, the metal element impurities in the graphite material enter the electrolyte solution in the form of metal ions and migrate through the cation exchange membrane to the cathode chamber under the driving force of the electric field. S4: Perform solid-liquid separation on the slurry in the anode chamber to obtain purified graphite.

2. The method according to claim 1, characterized in that, In step S1, the electrolyte solution is an acidic solution or a neutral salt solution with a pH of 1-6; And / or, in step S2, the recovered bottom solution is an acidic solution or a neutral salt solution with a pH of 1-6.

3. The method according to claim 1, characterized in that, In step S3, the applied DC voltage is 1.5-5.0V; and / or, the anode chamber is subjected to ultrasonic treatment or mechanical stirring during operation.

4. The method according to claim 1, characterized in that, Steps S2 and S3 are continuous or intermittent operations; and / or, in step S4, the solid-liquid separation includes at least one of filtration and centrifugation.

5. The method according to claim 1, characterized in that, In step S1, the graphite material is crushed and / or sieved, and then mixed with the electrolyte solution. And / or, in step S1, the graphite material is mixed with the electrolyte solution at a mass ratio of 1:5 to 1:100 to prepare a slurry.

6. The method according to claim 1, characterized in that, In step S2, the slurry is pumped into the anode chamber using a peristaltic pump, with the flow rate controlled at 10 mL / min-100 mL / min; And / or, in step S2, the recovered bottom liquid is pumped into the cathode chamber using a peristaltic pump, with the flow rate controlled at 10 mL / min-100 mL / min.

7. The method according to claim 1, characterized in that, At least one of the following conditions must be met: The anode plate and the cathode plate are each independently selected from one or more of the following: graphite plate, coated titanium anode, stainless steel plate, and platinum sheet; The anode chamber is provided with a slurry inlet and a slurry outlet; The cathode chamber is equipped with a recovery liquid inlet and a recovery liquid outlet; The cation exchange membrane includes one or more of perfluorosulfonic acid membranes and heterogeneous cation exchange membranes. The anode plate has a first flow channel; The cathode plate has a second flow channel.

8. The method according to claim 7, characterized in that, At least one of the following conditions must be met: The first flow channel is a serpentine flow channel, a forked flow channel, a straight flow channel, or a combination thereof; The depth of the first flow channel is 0.5-5.0 mm; One end of the first flow channel is the slurry inlet, and the other end is the slurry outlet; The second flow channel is a serpentine flow channel, a forked flow channel, a straight flow channel, or a combination thereof; The depth of the second flow channel is 0.5-5.0 mm; One end of the second flow channel is the inlet for the recovered bottom liquid, and the other end is the outlet for the recovered liquid.

9. The method according to claim 1, characterized in that, The main body of the electrolytic cell is sealed and fixed using insulating plates.

10. The method according to any one of claims 1-9, characterized in that, The graphite materials include one or more of the following: graphite anode materials from waste lithium-ion batteries, graphite by-products generated during the production or recycling of lithium-ion batteries, graphite bottom slag after lithium extraction by hydrometallurgy, and natural graphite beneficiation tailings.

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