Method for preparing reduction-state black powder by using positive plate of retired lithium battery and application of reduction-state black powder

Abstract

The invention discloses a method for preparing reduced black powder by using a positive plate of a decommissioned lithium battery and application, and belongs to the technical field of resource recycling of decommissioned power batteries. The method comprises the following steps: soaking the retired lithium battery in a sodium chloride solution for chemical discharge, disassembling the battery after the discharge is completed, and separating to obtain a positive plate; cutting the positive plate into flaky fragments, adding the flaky fragments and absolute ethyl alcohol into a closed reaction kettle, and synchronously applying ultrasonic action in a solvothermal reaction process under the protection of nitrogen; after the reaction is finished, washing and drying a solid product to obtain reduced black powder; and carrying out rotary evaporation on the reacted organic liquid phase to recover the ethanol solvent, wherein the recovered ethanol can be circularly used in the subsequent solvothermal reaction process. According to the method, the binder in the positive plate can be efficiently dissociated under the condition of lower temperature, the solvothermal reaction temperature is further reduced, the structural damage of a positive active material is avoided, and the method has the advantages of low energy consumption, small pollution, solvent recycling and the like.

Description

A method for preparing reduced black powder using retired lithium battery cathode sheets and its application Technical Field

[0001] This invention relates to the field of retired lithium battery recycling technology, specifically to a method and application for preparing reduced black powder using the positive electrode sheet of retired lithium batteries. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage equipment, the demand for lithium-ion batteries has increased significantly, leading to a surge in the number of retired lithium batteries. my country's new energy vehicle industry has maintained rapid growth, with sales exceeding 12.87 million units in 2024, accounting for 70.56% of global sales. Driven by the development of new energy vehicles, the installed capacity of power batteries now accounts for the vast majority of lithium battery production. my country's power battery production increased from 569,000 tons in 2018 to 8.486 million tons in 2024. Consequently, the number of retired power batteries has been increasing year by year, reaching 550,000 tons in 2024. It is predicted that by 2030, global waste lithium batteries will exceed 11 million tons, with my country accounting for over 40%. Currently, the commonly used power batteries for new energy vehicles are lithium iron phosphate batteries and ternary lithium batteries. However, with the reduction of national subsidies for new energy vehicles and the rise in cobalt prices, lithium iron phosphate batteries, due to their high safety and relatively low price, occupy the main market share (approximately 80%) in my country's lithium battery market and are more in line with the needs of modern electric vehicles, and have been widely adopted as the preferred power source. Retired lithium batteries contain various valuable metals such as lithium, cobalt, nickel, and manganese. If they are not properly recycled and disposed of, it will not only lead to resource waste but also cause serious environmental pollution.

[0003] Currently, the main methods for recycling cathode materials from retired lithium batteries include pyrometallurgy, hydrometallurgy, and physical sorting. Pyrometallurgy suffers from high energy consumption and the generation of harmful gases; hydrometallurgy requires the use of large amounts of acid and alkali reagents, which can easily cause secondary pollution, and subsequent wastewater treatment costs are high; while physical sorting can achieve material separation to a certain extent, it is difficult to effectively remove tightly bound binders (such as polyvinylidene fluoride) in the cathode material, resulting in low purity of the separated black powder and affecting the efficiency of subsequent recovery of valuable metals.

[0004] Among existing methods for removing adhesives, high-temperature incineration requires relatively high temperatures (typically exceeding 700°C). oThe process under conditions C) is prone to damaging the metal structure in the cathode material, increasing the difficulty of subsequent recycling. Although conventional solvent immersion methods can dissolve some of the binder, the dissolution efficiency is low, the processing time is long, and it is difficult to achieve complete separation of the binder from the inorganic metal oxide. The fundamental reason is that traditional methods have failed to fundamentally solve the problem of strong adhesion between the cathode active material and the aluminum foil current collector at the microscopic scale of the "interface". They can only rely on "violent" methods such as mechanical crushing, strong acid and high temperature to break through, which leads to the modification of the cathode active material, and then the subsequent separation and purification steps are extremely complicated.

[0005] Therefore, developing a method for preparing decommissioned lithium battery black powder that is low in energy consumption and pollution, can efficiently remove binders without damaging the metal structure, and simultaneously reduces energy consumption has become an urgent problem to be solved in the industry. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects in the recycling process of retired lithium battery cathode materials, such as low binder removal efficiency, high processing temperature, and easy destruction of the crystal structure of cathode active materials. This invention provides a method and application for preparing reduced black powder using low-temperature solvothermal coupling ultrasound on retired lithium battery cathode sheets.

[0007] This invention introduces an ultrasonic field simultaneously during the ethanol solvothermal reaction, utilizing the microjets, shock waves, and local high-energy interface effects generated by ultrasonic cavitation to continuously disturb and weaken the multiphase interface of "active material-binder-aluminum foil" in the positive electrode. This achieves rapid dissociation of the binder and efficient stripping of the positive electrode active material without relying on increasing the reaction temperature, thereby further reducing the solvothermal reaction temperature and shortening the processing time, resulting in a structurally intact and highly pure reduced black powder.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The present invention provides a method for preparing reduced black powder from the positive electrode sheet of a retired lithium battery, the method comprising the following steps: Step 1: Pretreatment of retired lithium battery. The retired lithium battery is immersed in a sodium chloride solution with a mass fraction of 10-15% for discharge treatment until the battery voltage drops to 0 V to eliminate safety hazards; then the retired lithium battery is disassembled to separate the positive electrode sheet, negative electrode sheet and separator; the positive electrode sheet is cut to obtain fragments with a size of 1 cm × 1 cm to 5 cm × 5 cm for later use; the solid-liquid mass ratio of the retired lithium battery to the sodium chloride solution is 1:80-1:120.

[0009] Step 2: Preparation of the solvothermal reaction system. The positive electrode fragment is placed in the lining of a high-pressure reactor, and ethanol organic solvent is added. The mass ratio of the positive electrode fragment to ethanol is 1:10-1:20.

[0010] Step 3: Solvothermal reaction. The high-pressure reactor is sealed and heated to 80-180℃ under nitrogen protection. Ultrasonic action is applied simultaneously throughout the entire solvothermal reaction process (ultrasound can be achieved through an external ultrasonic transducer or a built-in ultrasonic probe). Under the synergistic effect of solvothermal effect and ultrasonic cavitation effect, the binder swells, dissociates, and weakens the interfacial bonding force between it and the aluminum foil and positive electrode active material, thereby achieving in-situ peeling of the positive electrode active material.

[0011] Furthermore, the power of the ultrasound is 20-200 W, and the frequency is 20-40 kHz.

[0012] Furthermore, the heating rate of the solvothermal reaction is 3-10 °C / min.

[0013] Furthermore, the reaction time is 0-4 h.

[0014] Step 4: Solid-liquid separation and cleaning. After the solvothermal-ultrasonic coupling reaction is completed, cool to room temperature and perform solid-liquid separation on the reaction system. Wash the separated solid product with ethanol 2-3 times to remove residual organic matter.

[0015] Step 5: Drying treatment. The washed solid product is dried to obtain reduced black powder. At the same time, the organic liquid phase after the reaction is recovered by rotary evaporation at a temperature of 50-70 ℃. The recovered ethanol solvent can be recycled for subsequent solvothermal reaction processes.

[0016] The present invention also provides a reduced black powder prepared according to the above method, wherein the purity of the black powder is ≥97.8%.

[0017] The present invention also provides an application of the above method in the separation and recycling of electrode materials from decommissioned lithium batteries.

[0018] Furthermore, the retired lithium battery is one of ternary lithium, lithium iron phosphate, or lithium manganese oxide batteries.

[0019] Through the above technical solution, without relying on simply increasing the solvothermal temperature or extending the processing time, the dissociation of binder and aluminum foil and the preparation of reduced ultrapure black powder during the solvothermal process of retired power batteries can be achieved. This enables the solvothermal process to maintain the original state of the positive electrode active material black powder while possessing extremely high binder and aluminum foil dissociation capabilities.

[0020] Compared with existing technologies, the beneficial effects of this invention are as follows: 1. By simultaneously coupling ultrasound during the ethanol solvothermal reaction, this invention enables the ultrasonic cavitation effect and the solvothermal effect to work synergistically. The transient high-energy micro-regions generated by ultrasonic cavitation can weaken the physical adsorption force between the binder molecular chains and the aluminum foil surface at the interface scale, thereby shifting the effective dissociation temperature range of the binder towards lower temperatures and significantly enhancing the swelling and dissociation process of the binder; 2. Compared with traditional solvothermal or high-temperature incineration processes, this invention can further reduce the processing temperature of the positive electrode sheet to 80-180℃, effectively avoiding the destruction of the crystal structure of the positive electrode active material and improving the structural integrity and recycling value of the reduced black powder; 3. The ultrasound-solvothermal coupled reaction process can maintain the homogeneous state of the reaction system, shorten the processing time, and improve the binder removal efficiency, with a binder removal rate of over 98%; 4. The ethanol solvent can be recovered and recycled through low-temperature rotary evaporation, reducing the consumption of organic solvents, lowering environmental pollution and processing costs, and conforming to the concept of green and low-carbon recycling. Attached Figure Description

[0021] Figure 1 is a schematic diagram of the overall process of the method for preparing reduced black powder using retired lithium battery positive electrode sheets of the present invention, which is used to illustrate the logical relationship between electrode sheet acquisition, solvent thermal treatment, acoustic cavitation intervention and solvent recovery.

[0022] Figure 2 is a schematic diagram of the swelling and defluorination of polyvinylidene fluoride binder and the dissociation of aluminum foil during the solvothermal process in an embodiment of the present invention. It is used to illustrate the promoting effect of ethanol solvothermal on the migration of fluorine and the physical intervention of acoustic cavitation on the stripping of black powder.

[0023] Figure 3 is a schematic diagram of the enhanced dissociation of polyvinylidene fluoride binder during solvothermal coupled ultrasonic intervention in an embodiment of the present invention, which is used to illustrate the principle of how the transient high-energy micro-regions generated by ultrasonic cavitation weaken the physical adsorption force of the binder at the interface scale.

[0024] Figure 4 shows the characterization results of the structural stability and surface fluorine removal effect of the cathode material before and after the solvent thermal coupling ultrasonic treatment of the ternary lithium battery in Example 1. It is used to illustrate the structure and elemental comparison of the cathode sheet of the ternary lithium battery after treatment by the method of the present invention. (a) is the XRD pattern of the cathode material before and after the solvent thermal coupling ultrasonic treatment of the ternary lithium battery; (b) is the XRD magnified pattern of the cathode material before ultrasonic treatment; (c) is the XRD magnified pattern of the cathode material after ultrasonic treatment; and (d) is the XPS F1s characterization spectrum of the surface fluorine removal effect of the cathode material.

[0025] Figure 5 shows the characterization results of the structural stability and surface fluorine removal effect of the cathode material before and after the solvent thermal coupling ultrasonic treatment of lithium iron phosphate battery in Example 2. It is used to illustrate the structure and elemental comparison of the cathode sheet of lithium iron phosphate battery after treatment by the method of the present invention. (a) is the XRD pattern of the cathode material before and after the solvent thermal coupling ultrasonic treatment of lithium iron phosphate battery; (b) is the XRD magnified pattern of the cathode material before ultrasonic treatment; (c) is the XRD magnified pattern of the cathode material after ultrasonic treatment; and (d) is the XPS F1s characterization spectrum of the surface fluorine removal effect of the cathode material. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical and methodological essence of the present invention shall still fall within the scope of the technical and methodological solutions of the present invention.

[0027] Example 1 A method for preparing reduced black powder by low temperature solvothermal coupling ultrasound of retired ternary lithium battery positive electrode sheet In this example, the retired ternary lithium-ion battery positive electrode sheet is used as raw material, and the reduced black powder is prepared by synchronous coupling ultrasound during solvothermal process. The specific steps are as follows: (1) Pretreatment of retired ternary lithium battery Select a retired ternary lithium-ion battery (model 18650), immerse it in a sodium chloride solution with a mass fraction of 12% at a solid-liquid mass ratio of 1:100 for chemical discharge until the battery voltage drops to 0 V; then disassemble the battery, separate the positive electrode sheet, and cut the positive electrode sheet into sheet-like fragments with a size of 3 cm × 3 cm for later use.

[0028] (2) Construction of solvothermal reaction system: Weigh 10 g of the above positive electrode fragment and place it in the lining of a 500 mL high-pressure reactor. Add 150 mL of anhydrous ethanol to it so that the mass ratio of the positive electrode to ethanol is about 1:15.

[0029] (3) Solvent-ultrasound coupled reaction: After sealing the high-pressure reactor, nitrogen gas was introduced to purge the air inside the reactor for 5 min to remove the air. The reactor was heated to 150 °C under nitrogen protection, and ultrasonic action was applied simultaneously during the heating and isothermal stages. The ultrasonic power was 100 W and the frequency was 20 kHz. The solvothermal reaction time was 1 h. Under the synergistic effect of ethanol solvothermal effect and ultrasonic cavitation effect, the polyvinylidene fluoride binder in the positive electrode sheet swelled and dissociated. The positive electrode active material was gradually peeled off from the aluminum foil surface in situ. The binder swelling and aluminum foil dissociation process is shown in Figure 2. The interface action process of ultrasonic cavitation enhanced dissociation is shown in Figure 3.

[0030] (4) After the solid-liquid separation and washing reaction is completed, the reaction system is naturally cooled to room temperature and the solid-liquid separation is carried out. The solid product obtained by separation is washed three times with ethanol solvent. After each washing, it is filtered to remove residual organic matter. At the same time, the organic liquid phase obtained during the solid-liquid separation and washing process is collected and used for subsequent solvent recovery treatment.

[0031] (5) Drying treatment: The cleaned solid product was placed in a vacuum drying oven and dried at 70 °C and a vacuum of −0.09 MPa for 6 h. After cooling, reduced black powder was obtained. At the same time, the organic liquid phase obtained after solid-liquid separation was used to recover the ethanol solvent by rotary evaporation. The rotary evaporation temperature was controlled at 50 °C. The recovered ethanol was used for subsequent solvothermal reactions.

[0032] The reduced black powder obtained in Example 1 was subjected to structural and compositional analysis. X-ray diffraction (XRD) was used to characterize the crystal structure of the ternary cathode material before and after solvothermal coupled ultrasonic treatment, and the results are shown in Figure 4. As can be seen from Figure 4, the characteristic diffraction peak positions of the material before and after treatment remained basically consistent, and the crystal lattice showed almost no significant shift, indicating that the damage to the crystal structure of the ternary cathode active material caused by the solvothermal coupled ultrasonic treatment process was negligible. Simultaneously, X-ray photoelectron spectroscopy (XPS) was used to detect and analyze the fluorine content in the black powder, and its F 1s spectrum is also shown in Figure 4. The results show that the proportion of fluorine in the black powder was significantly reduced after solvothermal coupled ultrasonic treatment, with an F removal rate of 99.19%, indicating that the fluorine-containing components related to the polyvinylidene fluoride binder were efficiently removed. Combined with the results of the black powder purity test, the purity of the reduced black powder obtained in this example was 99.2%.

[0033] Example 2 A method for preparing reduced black powder by low temperature solvothermal coupling ultrasound of retired lithium iron phosphate battery positive electrode sheet In this example, retired lithium iron phosphate battery positive electrode sheet is used as raw material, and the preparation method is as follows: (1) Pretreatment of retired lithium iron phosphate battery The retired lithium iron phosphate power battery is immersed in a sodium chloride solution with a mass fraction of 10% at a solid-liquid mass ratio of 1:100 for discharge treatment until the battery voltage is 0 V; the battery is disassembled and the positive electrode sheet is separated, and the positive electrode sheet is cut into 2 cm × 2 cm sheet fragments for later use.

[0034] (2) Construction of solvothermal reaction system: Weigh 8 g of positive electrode fragment and add it to the lining of a 300 mL high-pressure reactor. Add 80 mL of anhydrous ethanol to make the mass ratio of positive electrode to ethanol about 1:10.

[0035] (3) Solvothermal-ultrasound coupling reaction: After sealing the reactor, nitrogen gas is introduced to purge the air inside the reactor. The reactor is heated to 180 °C under nitrogen protection and ultrasonic action is applied simultaneously throughout the solvothermal reaction process. The ultrasonic power is 80 W, the frequency is 25 kHz, and the isothermal reaction time is 0.5 h. Under the ultrasonic-solvothermal coupling conditions, the binder in the positive electrode sheet is rapidly dissociated, and the lithium iron phosphate positive electrode active material is efficiently peeled off from the aluminum foil.

[0036] (4) After the solid-liquid separation and washing reaction is completed, the reaction system is cooled to room temperature and the solid-liquid separation is carried out. The obtained solid product is washed twice with 40 mL of ethanol and filtered to remove residual organic matter. At the same time, the organic liquid phase obtained during the solid-liquid separation and washing process is collected and used for subsequent solvent recovery treatment.

[0037] (5) Drying treatment: The cleaned solid product was placed in a vacuum drying oven and dried for 8 h at 60 °C and a vacuum of −0.08 MPa to obtain reduced black powder. At the same time, the organic liquid phase obtained after solid-liquid separation was used to recover the ethanol solvent by rotary evaporation. The rotary evaporation temperature was controlled at 60 °C. The recovered ethanol was used for subsequent solvothermal reactions.

[0038] The reduced black powder obtained in Example 2 was subjected to structural and valence state analysis. XRD was used to characterize the crystal structure of the lithium iron phosphate cathode material before and after solvothermal coupled ultrasonic treatment, and the results are shown in Figure 5. As can be seen from Figure 5, the characteristic diffraction peak positions of the material before and after treatment remain basically consistent, and the lattice shows almost no significant shift, indicating that the damage to the lithium iron phosphate crystal structure caused by this treatment process is negligible. Furthermore, combined with the valence state characterization results shown in Figure 5, it can be seen that the solvothermal coupled ultrasonic treatment of this invention can reduce the oxidized trivalent iron (Fe3+) in the decommissioned black powder. 3+ It is reduced to divalent iron (Fe). 2+ This process, which involves solvothermal coupling with ultrasonic treatment, results in a reduced-state black powder. Simultaneously, XPS analysis was used to detect and analyze the fluorine content in the black powder, and its F 1s spectrum is shown in Figure 5. The results indicate that the proportion of fluorine in the black powder significantly decreased after solvothermal coupling ultrasonic treatment, with an F removal rate of 98.2%, indicating that the fluorine-containing components related to the binder were effectively removed. The purity of the prepared reduced black powder was 97.8%, and the crystal structure of lithium iron phosphate remained stable.

[0039] Example 3 A method for preparing reduced black powder by low temperature solvothermal coupling ultrasound of retired lithium manganese oxide battery positive electrode sheet In this example, the positive electrode sheet of retired lithium manganese oxide battery is used as raw material, and the preparation process is as follows: (1) Pretreatment of retired lithium manganese oxide battery The retired lithium manganese oxide battery is immersed in a sodium chloride solution with a mass fraction of 10% at a solid-liquid mass ratio of 1:100 for discharge treatment until the battery voltage is 0 V; the battery is disassembled and the positive electrode sheet is obtained. The positive electrode sheet is cut into 5cm × 5cm sheet fragments for later use.

[0040] (2) Construction of solvothermal reaction system: Weigh 12 g of positive electrode fragment and add it to the lining of a 500 mL high-pressure reactor. Add 240 mL of ethanol solvent to make the mass ratio of positive electrode to ethanol about 1:20.

[0041] (3) Solvent-ultrasound coupled reaction: The reactor was sealed and purged with nitrogen. Under nitrogen protection, it was heated to 140 °C. Ultrasound was applied simultaneously during the heating and isothermal stages. The ultrasonic power was 120 W, the frequency was 30 kHz, and the reaction time was 1 h. Under the synergistic effect of ultrasonic cavitation and solvothermal action, the binder in the lithium manganese oxide positive electrode was fully dissociated, and the positive electrode active material was uniformly peeled off from the aluminum foil surface.

[0042] (4) After the solid-liquid separation and washing reaction is completed, the reaction system is cooled to room temperature and the solid-liquid separation is carried out. The obtained solid product is washed with ethanol three times to remove residual organic matter. At the same time, the organic liquid phase obtained during the solid-liquid separation and washing process is collected and used for subsequent solvent recovery treatment.

[0043] (5) Drying treatment: The cleaned solid product was dried at 80 °C and vacuum degree of −0.1 MPa for 4 h to obtain reduced black powder.

[0044] By implementing the same detection method described in 1, the reduced black powder prepared in Example 3 was tested. The test results showed that the binder removal rate in this example was 99.1%, the purity of the reduced black powder was 98.5%, and the structure of the lithium manganese oxide cathode material did not change significantly.

[0045] The results show that this invention can effectively achieve efficient separation of aluminum foil, binder, and cathode material. The aluminum content in the black powder is almost zero, ensuring the purity of the cathode material. Simultaneously, the method provided by this invention is energy-saving and environmentally friendly, reducing energy consumption and the use of chemical reagents, lowering wastewater treatment costs and environmental impact. The method also helps improve the quality of material regeneration, avoiding damage to the material structure from repeated operations and preserving the original activity and performance of the material. Furthermore, the method can improve economic efficiency, reduce resource waste, and achieve efficient recycling of materials.

[0046] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing reduced black powder using retired lithium battery positive electrode sheets, characterized in that, Includes the following steps: S1. The retired lithium battery is immersed in a 10-15% sodium chloride solution for discharge treatment until the voltage reaches 0V. The battery is then disassembled, and the positive electrode sheet is obtained. S2. The positive electrode sheet is cut into sheet-like fragments and added to a sealed high-pressure reactor along with ethanol organic solvent. Under nitrogen protection, ultrasonic treatment is performed simultaneously during the solvothermal reaction. The reaction temperature is 80-180℃, and the reaction time is 0-4 h. S3. After the reaction, solid-liquid separation, washing, and drying are performed to obtain reduced black powder. At the same time, the organic liquid phase after the reaction is recycled as solvent.

2. The method for preparing reduced black powder according to claim 1, characterized in that, In step S1, the solid-liquid mass ratio of the retired lithium battery to the sodium chloride solution is 1:80-1:

120.

3. The method for preparing reduced black powder according to claim 1, characterized in that, In step S2, the size of the sheet-like fragment is from 1 cm × 1 cm to 5 cm × 5 cm.

4. The method for preparing reduced black powder according to claim 1, characterized in that, In step S2, the mass ratio of the positive electrode sheet to the ethanol organic solvent is 1:10-1:

20.

5. The method for preparing reduced black powder according to claim 1, characterized in that, In step S2, the power of the ultrasound is 20-200 W and the frequency is 20-40 kHz.

6. The method for preparing reduced black powder according to claim 1, characterized in that, In step S2, the heating rate of the solvothermal reaction is 3-10 °C / min.

7. The method for preparing reduced black powder according to claim 1, characterized in that, In step S3, the ethanol solvent is recovered by rotary evaporation of the organic liquid phase after the reaction at a temperature of 50-70 °C. The recovered ethanol is used for subsequent solvothermal reactions.

8. A reduced black powder prepared by the method according to any one of claims 1-7, characterized in that, The purity of the reduced black powder is ≥97.8%.

9. The application of the method according to any one of claims 1-7 in the separation and recycling of electrode materials from decommissioned lithium batteries.

10. The application according to claim 9, characterized in that, The retired lithium battery mentioned is one of the following: ternary lithium, lithium iron phosphate, and lithium manganese oxide batteries.

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