Waste lithium battery positive electrode material green stripping method based on deep eutectic solvent and focused ultrasound cooperation

Abstract

The invention belongs to the technical field of lithium battery recovery, and particularly discloses a waste lithium battery positive electrode material green stripping method based on cooperation of a deep eutectic solvent and focused ultrasound, which comprises the following steps: disassembling a waste lithium battery, separating a positive electrode plate, and cutting the positive electrode plate into positive electrode sheets of 1cm * 1cm or 2cm * 2cm; preparing a deep eutectic solvent; immersing the cut positive electrode sheet into a deep eutectic solvent, and heating; applying high-intensity focused ultrasound; and filtering and separating the aluminum foil and the positive electrode material, and drying the positive electrode material to obtain the high-purity positive electrode material. According to the green stripping method for the waste lithium battery positive electrode material based on the deep eutectic solvent and focused ultrasound cooperation, through the synergistic effect of the eutectic solvent and the high-intensity focused ultrasound, the stripping rate can reach 98.41%, the recovery rate can reach 96.05%, the deep eutectic solvent can be recycled for more than four times, and the method has the advantages of being environmentally friendly, efficient and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery recycling, and specifically relates to a green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound. Background Art

[0002] As energy demand continues to grow, rechargeable lithium-ion batteries are used to meet this demand. However, the accelerated production of these devices will quickly lead to significant waste. Since lithium-ion batteries in small electronic devices have a lifespan of only approximately three years, and those in electric vehicles only five to ten years, significant amounts of lithium-ion waste will be generated in the future. The development of sustainable recycling methods for lithium-ion batteries can minimize adverse impacts and alleviate supply chain constraints for battery manufacturers. For both resource utilization and environmental protection, stripping and recycling the cathode materials from spent lithium-ion batteries is essential.

[0003] However, existing cathode material stripping techniques have the following drawbacks: high-temperature heat treatment (>400°C) releases toxic hydrogen fluoride gas, which damages the material structure; strong acid / base dissolution methods are complex and environmentally polluting; and the use of N-methylpyrrolidone (NMP) solvents is costly and highly biotoxic. Therefore, a green stripping method for spent lithium battery cathode materials, based on the synergy of deep eutectic solvents and focused ultrasound, is needed to effectively address these issues. Summary of the Invention

[0004] The purpose of the present invention is to provide a green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound. This method can achieve a stripping rate of 98.41% and a recovery rate of 96.05% through the synergistic effect of eutectic solvent and high-intensity focused ultrasound. The deep eutectic solvent can be recycled more than 4 times, which has the advantages of environmental protection, high efficiency and low cost.

[0005] To achieve the above objectives, the present invention provides a green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound, comprising the following steps:

[0006] Step S1: dismantle the waste lithium battery, separate the positive electrode sheet and cut it into 1 cm×1 cm or 2 cm×2 cm positive electrode sheets;

[0007] Step S2, preparing a deep eutectic solvent (DES);

[0008] Step S3, immersing the cut positive electrode sheet in a deep eutectic solvent and heating the solvent; and applying high-intensity focused ultrasound (HIFU), wherein the ultrasound focusing area of the HIFU covers the surface of the positive electrode sheet;

[0009] Step S4: filtering and separating the aluminum foil and the positive electrode material, and drying the positive electrode material to obtain a high-purity positive electrode material.

[0010] Preferably, step S2 is specifically as follows:

[0011] Step S21, mixing choline chloride (ChCl) and ethylene glycol (EG) in a molar ratio of 1:2 to obtain a mixture; wherein choline chloride is a hydrogen bond acceptor (HBA) and ethylene glycol is a hydrogen bond donor (HBD); if the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor deviates from 1:2 (such as 1:1.5 or 1:2.5), the solution viscosity is too high or too low, resulting in a 5%-15% decrease in the PVDF dissolution efficiency.

[0012] Step S22: Stir the mixture at 70° C. for 5-6 minutes until it becomes transparent, to obtain a transparent solution with a viscosity of 22-24 mPa·s and a pH of 7.0-7.1, which is the deep eutectic solvent.

[0013] Deep eutectic solvent (DES) destroys the bonding interface between polyvinylidene fluoride (PVDF) and aluminum foil through hydrogen bonding and selectively dissolves polyvinylidene fluoride (PVDF).

[0014] Preferably, in step S3, the temperature is raised to 120-130°C. At 120°C, the diffusion coefficient of the deep eutectic solvent (DES) increases by 40%, accelerating the dissolution of polyvinylidene fluoride (PVDF). The high-intensity focused ultrasound power is 30-40W. When the power is below 30W, the stripping time is extended to more than 4 minutes. When the power is above 40W, local deformation of the aluminum foil is caused, affecting the integrity of the material. The high-intensity focused ultrasound duration is 2-3 minutes.

[0015] Preferably, in step S3, the energy density of high-intensity focused ultrasound is 200-300 J / mm 3 , the scanning speed is 50-100 mm / min, the frequency is 1.0-1.1 MHz, and the cavitation effect intensity is 1.8-1.9 MPa.

[0016] Preferably, in step S3, the deep eutectic solvent is used for more than 4 cycles, and after filtration, the deep eutectic solvent (DES) is supplemented with 10% fresh solvent. After 4 cycles, the stripping rate remains at 95.6%; wherein, when recycling the deep eutectic solvent, it needs to be filtered and reheated to 120-130°C.

[0017] Preferably, in step S4, drying the positive electrode material is specifically performed by using a vacuum drying apparatus to dry the positive electrode material in a vacuum environment at 80-120° C. and a vacuum degree of 0.05-0.2 MPa for 20-60 min to obtain a dry black solid, which is the positive electrode material.

[0018] Therefore, the present invention adopts the above-mentioned green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound. This method can achieve a stripping rate of 98.41% and a recovery rate of 96.05% through the synergistic effect of eutectic solvent and high-intensity focused ultrasound. The deep eutectic solvent can be recycled more than 4 times, which has the advantages of environmental protection, high efficiency and low cost.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of an embodiment of the green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention;

[0021] Figure 2 This is a schematic diagram of the ICP results of an embodiment of the green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention;

[0022] Figure 3 This is an XRD diffraction peak image of an embodiment of the green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention;

[0023] Figure 4 This is an XRD data processing diagram of an embodiment of the green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention;

[0024] Figure 5 This is a SEM micrograph (10 μm) of the positive electrode material prepared in an embodiment of the green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention;

[0025] Figure 6 This is a SEM micrograph (50 μm) of the positive electrode material prepared in an embodiment of the green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention;

[0026] Figure 7 The stripping rates of different stripping methods in the embodiment of the green stripping method of waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention are shown;

[0027] Figure 8 The recovery rates of different recycling methods in the embodiment of the green stripping method of waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0030] Example

[0031] like Figure 1 As shown, the green stripping method of waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound includes the following steps:

[0032] Step S1: Dismantle the waste lithium batteries in the laboratory manually, store the positive and negative electrodes separately, and cut the separated metal current collectors into 1 cm × 1 cm or 2 cm × 2 cm square slices.

[0033] Step S2: preparing a deep eutectic solvent.

[0034] Step S21, 30 g of choline chloride and 26.67 g of ethylene glycol were mixed at a molar ratio of 1:2 to obtain a mixture.

[0035] Step S22: Stir the mixture at 70° C. for 5 min until it becomes transparent, to obtain a transparent solution with a viscosity of 22 mPa·s and a pH of 7.0, which is the deep eutectic solvent (DES).

[0036] Step S3: Immerse the cut square slices in a deep eutectic solvent, heat to 120°C, and apply high-intensity focused ultrasound (HIFU). The HIFU focus area covers the surface of the positive electrode slice. The HIFU power is 30-40W and the duration is 2-3 minutes. The energy density of the HIFU is 200-300J / mm 3 , the scanning speed is 50-100 mm / min, the frequency is 1.0 MHz, and the cavitation effect intensity is 1.8 MPa.

[0037] A large number of bubbles can be observed in the solution, and the positive electrode material on the metal current collector (square thin sheet) has obvious shedding phenomenon. The color of the solution gradually deepens, and the white aluminum foil gradually appears. After 3 minutes, it can be observed that the metal current collector has basically turned into white aluminum foil.

[0038] The deep eutectic solvent in this embodiment has the advantage of being recyclable. Experimental results show that the deep eutectic solvent can be recycled more than 4 times. When recycling the deep eutectic solvent, it needs to be filtered and reheated to 120°C.

[0039] Step S4: filter and separate the aluminum foil and the positive electrode material, and dry the positive electrode material in a vacuum drying apparatus at 80-120°C and a vacuum degree of 0.05-0.2 MPa for 20-60 min to obtain a dry black solid, which is a high-purity positive electrode material. Figure 5 、 Figure 6 Shown is the SEM micrograph of the positive electrode material.

[0040] (I) The peeling rate and recovery rate of this embodiment were measured, as shown in Table 1 and Table 2. It can be seen that the peeling rate and recovery rate are both greater than 96%. Figure 7 As shown in the figure, the stripping rate comparison of different stripping methods shows that the stripping rate of the method of this embodiment is higher than that of traditional high-temperature heat treatment, DMF solvent method and other processes, and efficient stripping can be achieved at 120°C, highlighting the energy-saving advantage. Figure 8 The results show that the recovery rate of this example far exceeds that of traditional mechanical separation methods, demonstrating that this separation method can effectively retain the active components of the positive electrode material. The separation method used in this example can separate positive electrode materials from discarded lithium batteries, and the stripping rate and recovery rate both meet the experimental requirements, making it environmentally friendly and reliable.

[0041] Table 1 Recovery

[0042]

[0043] Table 2 Peeling rate

[0044]

[0045] (2) IPC data analysis was performed on the high-purity positive electrode material prepared in this example.

[0046] like Figure 2 As shown, the average lithium content in the obtained positive electrode material is 5.59%, and the average aluminum content is 1.325%, while the lithium content in a normal new lithium battery is about 6%, thus meeting the experimental requirements, that is, the positive electrode material obtained in this embodiment can be used for lithium battery repair.

[0047] (3) XRD data analysis of the high-purity positive electrode material prepared in this embodiment.

[0048] like Figure 3-Figure 4 As shown, the green stripping technology of this embodiment does not damage the content and structure of lithium cobalt oxide. This experimental analysis effectively realizes the green stripping of the positive electrode material.

[0049] Comparative Example 1

[0050] The green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound includes the following steps:

[0051] Step S1: Dismantle the waste lithium batteries in the laboratory manually, store the positive and negative electrodes separately, and cut the separated metal current collectors into 1 cm × 1 cm or 2 cm × 2 cm square slices.

[0052] Step S2: preparing a deep eutectic solvent.

[0053] Step S21, 30 g of choline chloride and 26.67 g of ethylene glycol were mixed at a molar ratio of 1:2 to obtain a mixture.

[0054] Step S22: Stir the mixture at 70° C. for 5 min until it becomes transparent, to obtain a transparent solution with a viscosity of 22 mPa·s and a pH of 7.0, which is the deep eutectic solvent (DES).

[0055] Step S3: Immerse the cut square slices in a deep eutectic solvent, raise the temperature to 100°C, and apply high-intensity focused ultrasound (HIFU). The HIFU focus area covers the surface of the positive electrode slice. The HIFU power is 30-40W and the duration is 2-3 minutes. The energy density of the HIFU is 200-300J / mm 3 , the scanning speed is 50-100 mm / min, the frequency is 1.0 MHz, and the cavitation effect intensity is 1.8 MPa.

[0056] A large number of bubbles can be observed in the solution, and the positive electrode material on the metal current collector (square thin sheet) has obvious shedding phenomenon. The color of the solution gradually deepens, and the white aluminum foil gradually appears. After 2-3 minutes, it can be observed that the metal current collector basically turns into white aluminum foil.

[0057] The deep eutectic solvent in this embodiment has the advantage of being recyclable. Experimental results show that the recyclable number of times is 4.

[0058] Step S4: filter and separate the aluminum foil and the positive electrode material, and pass the positive electrode material through a vacuum drying apparatus, and dry it for 20-60 minutes under a vacuum environment of 80-120° C. and a vacuum degree of 0.05-0.2 MPa to obtain a dry black solid, which is a high-purity positive electrode material.

[0059] (1) The stripping rate and recovery rate of comparative example 1 were measured.

[0060] As shown in Tables 3 and 4, it can be seen that the average stripping rate and recovery rate are slightly less than 96%. The separation method used can separate the positive electrode material from the waste lithium battery. The experimental effect is good, but the overall recovery rate and stripping rate are lower than those in the embodiment.

[0061] Table 3 Recovery

[0062]

[0063] Table 4 Peeling rate

[0064]

[0065] Comparative Example 2

[0066] The method for stripping cathode materials of waste lithium batteries based on a deep eutectic solvent comprises the following steps:

[0067] Step S1: disassemble the waste lithium batteries in the laboratory through manual procedures, store the positive and negative electrodes separately, and cut the metal current collector into square sheets of 1 cm×1 cm or 2 cm×2 cm.

[0068] Step S2: preparing a deep eutectic solvent.

[0069] Step S21, 30 g of choline chloride and 26.67 g of ethylene glycol were mixed in a molar ratio of 1:2 to obtain a mixture.

[0070] Step S22: Stir the mixture at 70° C. for 5 min until it becomes transparent, to obtain a transparent solution with a viscosity of 22 mPa·s and a pH of 7.0, which is the deep eutectic solvent (DES).

[0071] Step S3: Immerse the cut square wafer in a deep eutectic solvent and heat it only to 120°C without applying high-intensity focused ultrasound. Bubble generation in the solution was significantly reduced, the cathode material from the metal current collector fell slowly, and the solution color did not change significantly. Even after the aluminum foil exposure process was extended to 10-15 minutes, a small amount of cathode material remained.

[0072] The deep eutectic solvent in Comparative Example 2 was recycled 3 times (filtered and reheated to 120° C. before use).

[0073] Step S4: filter and separate the aluminum foil and the positive electrode material, and dry the positive electrode material in a vacuum drying apparatus at 80-120° C. and a vacuum degree of 0.05-0.2 MPa for 20-60 min to obtain a dry black solid, which is the positive electrode material.

[0074] (1) The peeling rate and recovery rate of comparative example 2 were measured, as shown in Tables 5 and 6.

[0075] Table 5 Recovery

[0076]

[0077] Table 6 Peeling rate

[0078]

[0079] Comparison of Example 1 with Comparative Example 2 reveals that when using only the deep eutectic solvent for stripping, the average stripping rate drops to 92.32% and the average recovery rate drops to 89.45%, significantly lower than the effects achieved with ultrasound synergy. This demonstrates that high-intensity focused ultrasound enhances the stripping effect of DES on the cathode material through the cavitation effect. The synergy of high-intensity focused ultrasound significantly improves stripping efficiency and material recovery, validating the key role of ultrasound synergy in the present invention.

[0080] Therefore, the present invention adopts the above-mentioned green stripping method for waste lithium battery positive electrode materials based on the synergy of deep eutectic solvent and focused ultrasound. This method can achieve a stripping rate of 98.41% and a recovery rate of 96.05% through the synergistic effect of eutectic solvent and high-intensity focused ultrasound. The deep eutectic solvent can be recycled more than 4 times, which has the advantages of environmental protection, high efficiency and low cost.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A green stripping method for waste lithium battery cathode materials based on deep eutectic solvent and focused ultrasound, characterized in that: The following steps are involved: Step S1: dismantle the waste lithium battery, separate the positive electrode sheet and cut it into 1 cm×1 cm or 2 cm×2 cm positive electrode sheets; Step S2, preparing a deep eutectic solvent; Step S3, immersing the cut positive electrode sheet in a deep eutectic solvent and heating the solution; applying high-intensity focused ultrasound, wherein the ultrasound focusing area of the high-intensity focused ultrasound covers the surface of the positive electrode sheet; Step S4: filtering and separating the aluminum foil and the positive electrode material, and drying the positive electrode material to obtain a high-purity positive electrode material.

2. The green stripping method for waste lithium battery cathode materials based on deep eutectic solvent and focused ultrasound according to claim 1, characterized in that: Step S2 is specifically as follows: Step S21, mixing choline chloride and ethylene glycol in a molar ratio of 1:2 to obtain a mixture; Step S22: Stir the mixture at 70° C. for 5-6 minutes until it becomes transparent, to obtain a transparent solution with a viscosity of 22-24 mPa·s and a pH of 7.0-7.1, which is the deep eutectic solvent.

3. The green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound according to claim 1, characterized in that: In step S3, the temperature is raised to 120-130° C.; the power of the high-intensity focused ultrasound is 30-40 W; and the duration of the high-intensity focused ultrasound is 2-3 minutes.

4. The green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound according to claim 3, characterized in that: In step S3, the energy density of high-intensity focused ultrasound is 200-300 J / mm 3 , the scanning speed is 50-100 mm / min, the frequency is 1.0-1.1 MHz, and the cavitation effect intensity is 1.8-1.9 MPa.

5. The green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound according to claim 1, characterized in that: In step S3, the deep eutectic solvent is used for more than four cycles; wherein, when the deep eutectic solvent is recycled, it needs to be filtered and reheated to 120-130°C.

6. The green stripping method for waste lithium battery cathode materials based on the synergy of deep eutectic solvent and focused ultrasound according to claim 1, characterized in that: In step S4, drying the positive electrode material is specifically performed by using a vacuum drying apparatus in a vacuum environment at 80-120° C. and a vacuum degree of 0.05-0.2 MPa for 20-60 min to obtain a dry black solid, which is a high-purity positive electrode material.

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