A method for recycling negative electrode material of waste lithium battery and lithium battery negative electrode material

Abstract

The application relates to a method for recycling waste lithium battery negative electrode material and lithium battery negative electrode material and relates to the field of lithium battery negative electrode material.The method comprises the following steps: placing waste lithium battery negative electrode graphite carbon powder in a water solution containing a complexing agent, applying a bidirectional pulse electric field to perform electrochemical-complexing treatment, obtaining first graphite carbon powder, mixing the first graphite carbon powder and LiNO3-KNO3 eutectic salt to perform molten salt intercalation, obtaining second graphite carbon powder, adding the second graphite carbon powder and a silane coupling agent containing a terminal olefin into a water-ethanol system to perform hydrolysis condensation, obtaining third graphite carbon powder and the like. The various steps are synergistic, the high-temperature charge retention rate of the obtained regenerated graphite carbon powder is significantly improved, and the problem of traditional regenerated graphite high-temperature performance deterioration is solved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery anode materials, and more particularly to a method for recycling and reusing waste lithium battery anode materials, and lithium battery anode materials. Background Technology

[0002] During long-term cycling, the repeated insertion and extraction of lithium ions in the negative electrode material of spent lithium batteries (mainly composed of graphite carbon powder) causes lattice expansion and contraction, resulting in damage to the interlayer structure and loss of active lithium. Traditional recycling methods mainly involve acid washing to remove impurities and high-temperature graphitization regeneration. Although some specific capacity can be restored, the high-temperature charge retention rate (high-temperature storage performance) is significantly degraded, making it difficult to meet the requirements of power batteries for high-temperature safety and long-term stability. Summary of the Invention

[0003] To address the above problems, this invention provides a method for recycling and reusing waste lithium battery anode materials, and lithium battery anode materials.

[0004] This invention provides a method for recycling and reusing waste lithium battery anode materials, and lithium battery anode materials, such as... Figure 1 As shown, it includes the following steps: The graphite carbon powder from the negative electrode of a spent lithium battery was placed in an aqueous solution containing a complexing agent, and an electrochemical-complexing treatment was performed by applying a bidirectional pulsed electric field to obtain the first graphite carbon powder. The first graphite carbon powder and LiNO3-KNO3 eutectic salt are mixed and molten salt intercalated to obtain the second graphite carbon powder. The second graphite carbon powder and a silane coupling agent containing terminal olefins were added to a water-ethanol system for hydrolysis and condensation to obtain the third graphite carbon powder. The third graphite carbon powder was added to an acetonitrile solution of an ionic liquid containing terminal olefins, and an initiator was added to carry out in-situ polymerization to obtain the fourth graphite carbon powder. The fourth graphite carbon powder is subjected to heat treatment and grinding to obtain recycled graphite carbon powder.

[0005] Furthermore, the aqueous solution containing the complexing agent contains citric acid at a concentration of 0.8-1.5 mol / L and disodium ethylenediaminetetraacetate at a concentration of 0.2-0.4 mol / L.

[0006] Furthermore, the operating conditions of the bidirectional pulsed electric field include: using parallel plate electrodes as the device, the electrode spacing is 1-2 cm, the slot voltage is 3-5 V, the frequency is 200-300 Hz, the duty cycle is 40-50%, and the processing time is 1-2 h.

[0007] Furthermore, the molar ratio of LiNO3 to KNO3 in the LiNO3-KNO3 eutectic salt is 1:1.

[0008] Further, the step of mixing the first graphite carbon powder and LiNO3-KNO3 eutectic salt for molten salt intercalation to obtain the second graphite carbon powder includes the following process: The first graphite carbon powder and the LiNO3-KNO3 eutectic salt were mixed at a mass ratio of 1:(3-5), heated to 180-200℃ and kept at that temperature for 2-4 hours, cooled, washed, and dried to obtain the second graphite carbon powder.

[0009] Further, the step of adding the second graphite carbon powder and a silane coupling agent containing carbon-carbon double bonds to a solvent for in-situ hydrolysis and condensation to obtain the third graphite carbon powder includes the following processes: Deionized water and ethanol were mixed in a volume ratio of 1:1, and then glacial acetic acid was added to adjust the pH of the system to 5.0-5.5 to obtain the hydrolysis precursor solution. The second graphite carbon powder is added to the hydrolysis precursor solution and ultrasonically dispersed for 15-30 min at an ultrasonic power of 200-300 W. Then, it is mechanically stirred for 30-45 min and a silane coupling agent containing carbon-carbon double bonds is added dropwise under continuous stirring at a dropping rate of 0.5-1 mL / min. The mass ratio of the second graphite carbon powder to the silane coupling agent containing carbon-carbon double bonds is controlled to be 1:0.05-0.1. After the addition is complete, the mixture is continuously stirred in a constant temperature water bath at 50-65℃ for 5-8 hours, then filtered, washed, and dried to obtain the third graphite carbon powder. The silane coupling agent containing terminal olefins includes 3-methacryloyloxypropyltrimethoxysilane.

[0010] Further, the mass ratio of the third graphite carbon powder, the carbon-carbon double bond-containing ionic liquid, and the initiator is 1:(1-2):0.005-0.01, the carbon-carbon double bond-containing ionic liquid includes 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt, and the initiator includes azobisisobutyronitrile.

[0011] Furthermore, the working conditions for the in-situ polymerization include: being carried out in an inert gas atmosphere, at a temperature of 70-80℃, and for a time of 2-3 hours.

[0012] Furthermore, the heat treatment includes the following processes: First stage: Increase the temperature to 260-300℃ at a rate of 2-5℃ / min and hold for 1.5-2 hours; Second stage: Increase the temperature to 450-500℃ at a rate of 5-10℃ / min and hold for 2-4 hours; The working conditions for the grinding process include: a grinding speed of 100-200 rpm and a grinding time of 1-2 hours.

[0013] In a second aspect, the present invention provides a lithium battery anode material, including recycled graphite carbon powder obtained by the method of recycling and reusing waste lithium battery anode materials described in the first aspect.

[0014] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art: This invention provides a method for recycling and reusing waste lithium battery anode materials, and the resulting lithium battery anode material. The various steps of this invention work synergistically to significantly improve the high-temperature charge retention rate of the obtained recycled graphite carbon powder, solving the problem of high-temperature performance degradation in traditional recycled graphite. Specifically: 1. Electrochemical-complexation treatment Compared to traditional acid washing or high-temperature roasting methods for impurity removal, this invention employs a bidirectional pulsed electric field treatment in an aqueous solution containing a complexing agent. By utilizing the coupling mechanism of electrochemical oxidation-reduction and complexation dissolution, it achieves non-destructive deep removal of impurities on the surface of waste graphite negative electrodes and regeneration of active sites. This creates an ideal reaction interface for subsequent molten salt ion intercalation and surface chemical modification, significantly improving the processing efficiency and uniformity of subsequent steps.

[0015] 2. LiNO3-KNO3 eutectic salt intercalation This invention utilizes the liquid ionic environment of the LiNO3-KNO3 eutectic salt to enter the interlayer of graphite, rearranging the collapsed and disordered layered structure during long-term cycling, promoting the reorientation of graphite microcrystals, and repairing edge structural defects. Furthermore, this step replenishes the waste graphite with an active lithium source, compensating for lithium loss during cycling, thereby restoring the bulk lithium storage capacity of the graphite anode and laying the structural foundation for improving capacity retention at high temperatures.

[0016] 3. Hydrolysis and condensation of silane coupling agents containing terminal olefins This invention utilizes a hydrolysis-condensation reaction containing a terminal olefin silane coupling agent to not only form a high-density Si-OC covalent anchoring layer on the graphite surface, but also introduce highly reactive terminal olefin groups onto the carbon matrix surface. These olefin groups serve as chemical bridging nodes, laying the foundation for the subsequent introduction of ionic liquid polymers.

[0017] 4. In-situ polymerization and heat treatment of ionic liquids containing terminal olefins This invention uses ionic liquids containing terminal olefins as raw materials and performs in-situ free radical polymerization on the surface of carbon powder under the action of an initiator. Through the copolymerization reaction of olefin groups, chemically cross-linked ionic liquid polymers are formed, and controllable carbonization occurs during subsequent staged heat treatment. This results in a uniform, dense, and intrinsically ionicly conductive high-temperature stable heteroatom-doped film layer, thereby significantly improving the high-temperature charge retention rate of recycled graphite carbon powder and solving the problem of high-temperature performance degradation of traditional recycled graphite. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic flowchart illustrating a method for recycling and reusing waste lithium battery negative electrode materials according to an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Furthermore, unless otherwise specified, the process steps and parameters involved in this invention can be carried out according to processes disclosed in the prior art or implemented using existing equipment and conventional operating methods.

[0023] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0024] The graphite carbon powder used in the following embodiments and comparative examples of waste lithium-ion battery negative electrodes was obtained using the following method: Waste lithium batteries are soaked in a battery cell for 100 minutes and then dried. The packaged waste lithium batteries are disassembled using a combination of manual and machine methods. The rolled negative electrode material of the lithium batteries is disassembled and unfolded into strips of carbon-coated copper foil. The carbon-coated copper foil is placed in a temperature-controlled water washing tank with a stirring device. Clean water is poured into the tank until all the copper foil is submerged. The water temperature in the tank is heated to 70°C. After the carbon powder is completely washed off the copper foil, the stirring is stopped. The copper foil without carbon powder after wet separation is taken out of the water washing tank, dried and packaged to complete the recovery of metallic copper. The remaining material in the temperature-controlled water washing tank is then filtered and dried to obtain graphite carbon powder from the waste lithium battery negative electrode.

[0025] Example 1 This example provides a method for recycling and reusing waste lithium battery negative electrode materials, including the following steps: Step (1), Electrochemical-complexation treatment: The graphite carbon powder of the waste lithium battery negative electrode is placed in an aqueous solution containing 1.0 mol / L citric acid and 0.3 mol / L disodium ethylenediaminetetraacetate. A bidirectional pulsed electric field is applied for electrochemical-complexation treatment. Parallel plate electrodes are used as the device, with an electrode spacing of 2 cm, a cell voltage of 4 V, a frequency of 240 Hz, a duty cycle of 45%, and a treatment time of 1.5 h. After filtration, washing, and drying, the first graphite carbon powder is obtained. Step (2), LiNO3-KNO3 eutectic salt intercalation treatment: The first graphite carbon powder obtained in step (1) and LiNO3-KNO3 eutectic salt (the molar ratio of LiNO3 to KNO3 is 1:1) are mixed at a mass ratio of 1:4, heated to 190℃ and kept at that temperature for 3 hours, cooled, washed and dried to obtain the second graphite carbon powder; Step (3) Hydrolysis and condensation treatment of silane coupling agent containing carbon-carbon double bonds: Deionized water and ethanol with a volume ratio of 1:1 were mixed, and then glacial acetic acid was added to adjust the pH of the system to 5.2 to obtain a hydrolysis precursor solution; the second graphite carbon powder was added to the hydrolysis precursor solution and ultrasonically dispersed for 20 min at an ultrasonic power of 260 W, and then mechanically stirred for 30 min. Under continuous stirring, a silane coupling agent containing carbon-carbon double bonds (specifically 3-methacryloyloxypropyltrimethoxysilane) was added dropwise at a dropping rate of 0.8 mL / min, and the mass ratio of the second graphite carbon powder and the silane coupling agent containing carbon-carbon double bonds was controlled to be 1:0.08; after the dropwise addition was completed, the mixture was continuously stirred in a 60℃ constant temperature water bath for 6 h, filtered, washed, and dried to obtain the third graphite carbon powder; Step (4) In-situ polymerization of ionic liquid containing terminal olefins: Under an inert gas atmosphere (specifically nitrogen), the third graphite carbon powder obtained in step (3) is added to an acetonitrile solution of an ionic liquid containing terminal olefins (specifically 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt), and an initiator (specifically azobisisobutyronitrile) is added for in-situ polymerization at a temperature of 75°C for 2.5 h. The mass ratio of the third graphite carbon powder, the ionic liquid containing carbon-carbon double bonds, and the initiator is 1:1.5:0.005. After filtration, washing, and drying, the fourth graphite carbon powder is obtained. Step (5): The fourth graphite carbon powder obtained in step (4) is subjected to heat treatment and grinding treatment. The heat treatment includes the following processes: First stage: heating to 280℃ at 3℃ / min and holding for 2h; Second stage: heating to 490℃ at 6℃ / min and holding for 3h; The working conditions of the grinding treatment include: grinding speed of 160rpm and time of 1.5h, to obtain regenerated graphite carbon powder.

[0026] Example 2 This example provides a method for recycling and reusing waste lithium battery negative electrode materials, including the following steps: Step (1): Place the waste lithium battery negative electrode graphite carbon powder in an aqueous solution containing 0.8 mol / L citric acid and 0.2 mol / L disodium ethylenediaminetetraacetate, and apply a bidirectional pulsed electric field for electrochemical-complexation treatment. Use parallel plate electrodes as the device, with an electrode spacing of 2 cm, a cell voltage of 3 V, a frequency of 300 Hz, a duty cycle of 50%, and a treatment time of 1.5 h. Filter, wash, and dry to obtain the first graphite carbon powder. Step (2): The first graphite carbon powder obtained in step (1) and the LiNO3-KNO3 eutectic salt (the molar ratio of LiNO3 and KNO3 is 1:1) are mixed at a mass ratio of 1:4, heated to 200℃ and kept at that temperature for 2.5h, cooled, washed and dried to obtain the second graphite carbon powder. Step (3): Mix deionized water and ethanol in a volume ratio of 1:1, then add glacial acetic acid to adjust the pH of the system to 5.2 to obtain a hydrolysis precursor solution; add the second graphite carbon powder to the hydrolysis precursor solution and ultrasonically disperse for 20 min at an ultrasonic power of 300 W, then mechanically stir for 20 min and dropwise add a silane coupling agent containing carbon-carbon double bonds (specifically 3-methacryloyloxypropyltrimethoxysilane) under continuous stirring, with a dropping rate of 0.8 mL / min, and control the mass ratio of the second graphite carbon powder and the silane coupling agent containing carbon-carbon double bonds to be 1:0.08; after the dropwise addition is completed, continuously stir in a 60℃ constant temperature water bath for 6 h, filter, wash, and dry to obtain the third graphite carbon powder; Step (4): Under an inert gas atmosphere (specifically nitrogen), the third graphite carbon powder obtained in step (3) is added to an acetonitrile solution of an ionic liquid containing terminal olefins (specifically 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt), and an initiator (specifically azobisisobutyronitrile) is added for in-situ polymerization at a temperature of 75°C for 2.5 h. The mass ratio of the third graphite carbon powder, the ionic liquid containing carbon-carbon double bonds, and the initiator is 1:2:0.008. The mixture is then filtered, washed, and dried to obtain the fourth graphite carbon powder. Step (5): The fourth graphite carbon powder obtained in step (4) is subjected to heat treatment and grinding treatment. The heat treatment includes the following processes: First stage: heating to 260℃ at 3℃ / min and holding for 2h; Second stage: heating to 480℃ at 5℃ / min and holding for 4h; The working conditions of the grinding treatment include: grinding speed of 160rpm and time of 1.5h, to obtain regenerated graphite carbon powder.

[0027] Comparative Example 1 This example provides a method for recycling and reusing waste lithium battery negative electrode materials, which differs from Example 1 only in that: (1) The LiNO3-KNO3 eutectic salt intercalation treatment in step (2) was not performed.

[0028] Comparative Example 2 This example provides a method for recycling and reusing waste lithium battery negative electrode materials, which differs from Example 1 only in that: (1) The silane coupling agent containing carbon-carbon double bonds in step (3) was not subjected to hydrolysis and condensation treatment.

[0029] Comparative Example 3 This example provides a method for recycling and reusing waste lithium battery negative electrode materials, which differs from Example 1 only in that: (1) The in-situ polymerization of ionic liquids containing terminal olefins in step (4) was not carried out.

[0030] Test case In this example, referring to the GB / T 43092-2023 standard, the recycled graphite carbon powder obtained from the above examples and comparative examples was used as the negative electrode material for lithium batteries and made into negative electrode sheets. High-temperature storage performance tests were then conducted. The test conditions included: being placed at 50°C for 30 days; after the high-temperature placement ended and the temperature returned to room temperature, a capacity test was performed. The high-temperature charge retention rate was calculated according to the formula: η = C1 / C0 × 100%, where η (%) is the high-temperature charge retention rate, C1 is the first standard discharge capacity after high-temperature placement, and C0 is the initial standard discharge capacity. The waste lithium battery negative electrode graphite carbon powder (i.e., raw material) in Example 1 was used as the basic control.

[0031] The test results are shown in Table 1.

[0032] Table 1 As shown in Table 1, compared with the comparative example and the graphite carbon powder of the negative electrode of waste lithium battery, the recycled graphite carbon powder obtained by the method provided in this embodiment of the invention has excellent high-temperature storage performance, and its high-temperature charge retention rate is maintained at more than 90%, which solves the problem of high-temperature performance degradation of traditional recycled graphite.

[0033] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0034] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for recycling and reusing waste lithium battery negative electrode materials, characterized in that, Includes the following steps: The graphite carbon powder from the negative electrode of a spent lithium battery was placed in an aqueous solution containing a complexing agent, and an electrochemical-complexing treatment was performed by applying a bidirectional pulsed electric field to obtain the first graphite carbon powder. The first graphite carbon powder and LiNO3-KNO3 eutectic salt are mixed and molten salt intercalated to obtain the second graphite carbon powder. The second graphite carbon powder and a silane coupling agent containing terminal olefins were added to a water-ethanol system for hydrolysis and condensation to obtain the third graphite carbon powder. The third graphite carbon powder was added to an acetonitrile solution of an ionic liquid containing terminal olefins, and an initiator was added to carry out in-situ polymerization to obtain the fourth graphite carbon powder. The fourth graphite carbon powder is subjected to heat treatment and grinding to obtain recycled graphite carbon powder.

2. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 1, characterized in that, The aqueous solution containing the complexing agent contains citric acid at a concentration of 0.8-1.5 mol / L and disodium ethylenediaminetetraacetate at a concentration of 0.2-0.4 mol / L.

3. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 2, characterized in that, The operating conditions of the bidirectional pulsed electric field include: using parallel plate electrodes as the device, the electrode spacing is 1-2 cm, the slot voltage is 3-5 V, the frequency is 200-300 Hz, the duty cycle is 40-50%, and the processing time is 1-2 h.

4. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 1, characterized in that, The molar ratio of LiNO3 to KNO3 in the LiNO3-KNO3 eutectic salt is 1:

1.

5. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 4, characterized in that, The step of mixing the first graphite carbon powder and the LiNO3-KNO3 eutectic salt for molten salt intercalation to obtain the second graphite carbon powder includes the following process: The first graphite carbon powder and the LiNO3-KNO3 eutectic salt were mixed at a mass ratio of 1:(3-5), heated to 180-200℃ and kept at that temperature for 2-4 hours, cooled, washed, and dried to obtain the second graphite carbon powder.

6. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 1, characterized in that, The step of adding the second graphite carbon powder and a silane coupling agent containing carbon-carbon double bonds to a solvent for in-situ hydrolysis and condensation to obtain the third graphite carbon powder includes the following processes: Deionized water and ethanol were mixed in a volume ratio of 1:1, and then glacial acetic acid was added to adjust the pH of the system to 5.0-5.5 to obtain the hydrolysis precursor solution. The second graphite carbon powder is added to the hydrolysis precursor solution and ultrasonically dispersed for 15-30 min at an ultrasonic power of 200-300 W. Then, it is mechanically stirred for 30-45 min and a silane coupling agent containing carbon-carbon double bonds is added dropwise under continuous stirring at a dropping rate of 0.5-1 mL / min. The mass ratio of the second graphite carbon powder to the silane coupling agent containing carbon-carbon double bonds is controlled to be 1:0.05-0.

1. After the addition is complete, the mixture is continuously stirred in a constant temperature water bath at 50-65℃ for 5-8 hours, then filtered, washed, and dried to obtain the third graphite carbon powder. The silane coupling agent containing terminal olefins includes 3-methacryloyloxypropyltrimethoxysilane.

7. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 1, characterized in that, The mass ratio of the third graphite carbon powder, the carbon-carbon double bond-containing ionic liquid, and the initiator is 1:(1-2):0.005-0.

01. The carbon-carbon double bond-containing ionic liquid includes 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt, and the initiator includes azobisisobutyronitrile.

8. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 7, characterized in that, The working conditions for the in-situ polymerization include: being carried out in an inert gas atmosphere, at a temperature of 70-80℃, and for a time of 2-3 hours.

9. The method for recycling and reusing waste lithium battery negative electrode materials according to claim 1, characterized in that, The heat treatment includes the following processes: First stage: Increase the temperature to 260-300℃ at a rate of 2-5℃ / min and hold for 1.5-2 hours; Second stage: Increase the temperature to 450-500℃ at a rate of 5-10℃ / min and hold for 2-4 hours; The working conditions for the grinding process include: a grinding speed of 100-200 rpm and a grinding time of 1-2 hours.

10. A lithium battery anode material, characterized in that, This includes recycled graphite carbon powder prepared by the method for recycling and reusing waste lithium battery anode materials as described in any one of claims 1-9.

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