Surfactant for recycling lithium iron phosphate negative electrode material and preparation method thereof

Abstract

The invention discloses a surfactant for recycling a lithium iron phosphate negative electrode material and a preparation method of the surfactant, and belongs to the technical field of battery recycling. Comprising the following steps: S1, synthesis of PFPE-CTA: carrying out esterification on PFPE-OH and 4-cyano-4-[(dodecyl thiocarbonyl) sulfenyl] valeric acid under the catalysis of DCC / DMAP, so as to obtain PFPE-CTA; s2, copolymerization is carried out on AA and DOPAM under the initiation of PFPE-CTA; s3, grafting 6-amino-beta CD to the carboxyl of the copolymer under the activation of EDC / NHS; s4, modifying the graphene quantum dots with 1-pyrene butyric acid succinimide ester; and the betaCD copolymer and pyrene-GQDs are compounded through an inclusion effect. The surfactant prepared by the invention can realize high recovery rate of graphite, low impurity residue, low foam, easy separation and excellent regeneration performance.

Description

Technical Field

[0001] This invention belongs to the field of battery recycling technology, specifically relating to a surfactant for recycling lithium iron phosphate anode materials and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, the demand for lithium iron phosphate batteries has increased significantly, leading to the problem of recycling and disposing of a large number of retired lithium iron phosphate batteries. Lithium iron phosphate anode materials contain valuable metal elements and carbon materials, and their effective recycling has significant economic and environmental implications.

[0003] In the recycling process of lithium iron phosphate anode materials, surfactants play a crucial role, helping to separate electrode materials and current collectors, promoting material dissolution and dispersion, and improving recycling efficiency. However, existing surfactants have many problems. Patent application CN117383557A discloses a method for purifying and removing impurities from acid-leached graphite waste residue of waste lithium battery materials. It uses a multi-stage leaching and electrochemical deintercalation process to treat the acid-leached graphite waste residue. Although it avoids the use of strong acids, it requires as many as four processes, including water washing, alkaline leaching, calcination (500-800℃), and electrochemical deintercalation (10-15V), resulting in high energy consumption and a processing cycle of more than 8 hours. Patent application CN116435635A discloses a method for deep impurity removal and recycling of waste lithium battery graphite anode materials, proposing a heat treatment-acid leaching-electrochemical hybrid treatment process. However, it still requires the use of low-concentration acids and does not solve the problem of selective separation between graphite and silicon-carbon components. Patent application CN117701883A discloses an extractant for lithium battery recycling, a method for preparing the extractant, and a method for applying the extractant. It developed an extractant containing perfluoroalkyl phosphate, which can suppress foam, but the cost is as high as 350 yuan / kg and it has no specific binding ability for copper ions.

[0004] Therefore, there is an urgent need to develop a surfactant for recycling lithium iron phosphate anode materials that is highly efficient, environmentally friendly, and cost-effective. Summary of the Invention

[0005] One of the objectives of this invention is to provide a surfactant for recycling lithium iron phosphate anode materials, which has high selectivity, low foaming properties and environmental friendliness, so as to achieve efficient recycling of graphite / silicon-carbon composite materials. The second objective of this invention is to provide a method for preparing a surfactant for recycling lithium iron phosphate anode materials, which is used to prepare the aforementioned surfactant.

[0006] The objective of this invention can be achieved through the following technical solutions: A surfactant for recycling lithium iron phosphate anode materials, the surfactant comprising PFPE-bP(AA-co-DOPAM)-g-βCD / Pyrene block copolymer, wherein the block copolymer comprises perfluoropolyether segments, pH-responsive blocks copolymerized from AA and DOPAM, βCD covalently grafted onto the polymer backbone, and Pyrene-modified graphene quantum dots; thiocarboxylic acid ester bonds are introduced between the blocks.

[0007] A method for preparing a surfactant for recycling lithium iron phosphate anode materials includes the following steps: S1. PFPE-OH (perfluoropolyether diol) is dispersed with 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid, DCC and DMAP in DCM (dichloromethane) and catalytically reacted for 24-26 hours to obtain PFPE-CTA; S2. Dissolve PFPE-CTA, AA (acrylic acid) and DOPAM (dopamine methacrylamide) in tetrahydrofuran, remove oxygen by purging with nitrogen, add AIBN (azobisisobutyronitrile), polymerize at 55-60℃ for 6-8 hours, and obtain PFPE-bP(AA-co-DOPAM) after precipitation and drying. S3. Dissolve PFPE-bP (AA-co-DOPAM) in DMF, add EDC and NHS, activate, then add 6-amino-βCD DMF solution dropwise. After reacting for 12-14 hours, dialyze and freeze-dry to obtain βCD copolymer. S4. Graphene quantum dots and 1-pyrenebutyrate succinimide ester were reacted in DMF for 6-7 hours to prepare Pyrene-GQDs; βCD copolymer and Pyrene-GQDs were mixed in deionized water, stirred for 24-26 hours, and freeze-dried to obtain PFPE-bP(AA-co-DOPAM)-g-βCD / Pyrene block copolymer (surfactant for recycling lithium iron phosphate anode materials).

[0008] Furthermore, the weight ratio of PFPE-OH, 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid, DCC, DMAP and DCM is (22-28):(1-1.5):(2-3):(0.1-0.2):(100-120).

[0009] Furthermore, the molecular weight of the PFPE-OH is 2000-3000 g / mol.

[0010] Furthermore, the weight ratio of PFPE-CTA, AA, DOPAM, tetrahydrofuran and AIBN is (8-12):(12-18):(7-10):(200-240):(0.1-0.2).

[0011] Furthermore, the weight ratio of PFPE-bP(AA-co-DOPAM), EDC, NHS and 6-amino-βCD is (18-23):(1.5-3):(1-1.5):(6-10).

[0012] Furthermore, the weight ratio of graphene quantum dots, 1-pyrene butyrate succinimide ester and DMF in S4 is (1.5-3):(1.5-2.5):(45-65).

[0013] Furthermore, the weight ratio of βCD copolymer, Pyrene-GQDs and deionized water in S4 is (8-12):(1-2):(350-500).

[0014] Furthermore, the precipitate drying is performed by precipitating with diethyl ether and vacuum drying at 70-80°C for 12-1 hours.

[0015] Furthermore, the dialysis uses a separation membrane with a molecular weight cutoff of ≥3500 Da.

[0016] A method for recovering lithium iron phosphate anode includes the following steps: using the surfactant, selectively peeling graphite from copper foil is achieved under conditions of pH 4.0-4.5 and temperature 40-60℃; after peeling, the graphite is separated by gradient centrifugation; the surfactant is removed from the graphite precipitate under alkaline conditions of pH>10; and then it is electrochemically regenerated.

[0017] Furthermore, the gradient centrifugation speed is 500-5000 rpm.

[0018] The beneficial effects of this invention are: (1) The surfactant PFPE-bP(AA-co-DOPAM)-g-βCD / Pyrene prepared in this invention has a quaternary block structure, forming a multi-functional synergy; the perfluoropolyether (PFPE) chain segment can significantly reduce the surface tension of the system, suppress the foam height, and solve the problem of solid-liquid separation difficulties caused by excessive foam in traditional processes; the pH-responsive block P(AA-co-DOPAM) is protonated under acidic conditions, exposing catechol groups, forming a specific chelation effect with copper foil, and achieving selective peeling of copper foil and graphite; in the βCD / Pyrene chain segment, pyrene-modified graphene quantum dots target and adsorb on the graphite surface through π-π stacking, while the steric hindrance of β-cyclodextrin inhibits the co-adsorption of silicon carbon components and reduces the silicon impurity rate.

[0019] (2) The multi-mechanism synergistic effect employed in this invention enables efficient separation of graphite and copper foil under weakly acidic conditions (pH 4.0-4.5), avoiding the use of traditional strong acids or organic solvents and significantly reducing environmental pollution. The PFPE segments and βCD structure in the surfactant also endow it with good foam suppression properties and pH responsiveness, allowing for easy desorption and recovery under alkaline conditions (pH>10), while the graphite structure remains intact and can meet battery-grade application requirements after electrochemical regeneration. The gradient centrifugation process further improves the separation efficiency, achieving high-purity recovery of copper and graphite. This technical solution maintains a high recovery rate while significantly reducing energy consumption and chemical consumption, demonstrating significant environmental and economic advantages. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0021] Example 1

[0022] This embodiment provides a surfactant for recycling lithium iron phosphate anode materials, which is prepared through the following steps: S1. Add 25 parts of PFPE-OH (Mn=2500) and 1.2 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; S2. Dissolve 10 parts of PFPE-CTA, 15 parts of acrylic acid, and 8.2 parts of dopamine methacrylamide in 200 mL of tetrahydrofuran, add 0.15 parts of AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain PFPE-bP(AA-co-DOPAM). S3. Dissolve 20 parts of PFPE-bP (AA-co-DOPAM) in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 8.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze-dry to obtain the βCD modified copolymer; S4. Pyrene-GQDs were prepared by reacting 2 parts of graphene quantum dots with 1.8 parts of 1-pyrenebutyrate succinimide ester in 50 parts of DMF for 6 hours. Pyrene-GQDs were prepared by mixing 10 parts of βCD copolymer with 1.5 parts of Pyrene-GQDs in water, stirring at 25°C for 24 hours, and freeze-drying.

[0023] Example 2

[0024] The difference between this embodiment and Example 1 is that the proportion of 4-cyano-4-[(dodecylthiocarbonyl)thio]pentanoic acid is increased. The specific implementation steps of S1 are as follows: S1. Add 23 parts of PFPE-OH (Mn=2500) and 1.5 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; The remaining raw materials and preparation process are the same as in Example 1.

[0025] Example 3

[0026] The difference between this embodiment and Example 1 is that the proportion of 4-cyano-4-[(dodecylthiocarbonyl)thio]pentanoic acid is reduced. The specific implementation steps of S1 are as follows: S1. Add 28 parts of PFPE-OH (Mn=2500) and 1 part of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; The remaining raw materials and preparation process are the same as in Example 1.

[0027] Example 4

[0028] The difference between this embodiment and Example 1 is that the ratio of AA (acrylic acid) and DOPAM (dopamine methacrylamide) is adjusted. The specific implementation steps of S2 are as follows: S2. Dissolve 9 parts of PFPE-CTA, 18 parts of acrylic acid, and 9.5 parts of dopamine methacrylamide in 200 mL of tetrahydrofuran, add 0.15 parts of AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain PFPE-bP(AA-co-DOPAM). The remaining raw materials and preparation process are the same as in Example 1.

[0029] Example 5

[0030] The difference between this embodiment and Example 1 is that the ratio of AA (acrylic acid) and DOPAM (dopamine methacrylamide) is adjusted. The specific implementation steps of S2 are as follows: S2. Dissolve 11 parts PFPE-CTA, 12 parts acrylic acid, and 7.5 parts dopamine methacrylamide in 200 mL tetrahydrofuran, add 0.15 parts AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain PFPE-bP(AA-co-DOPAM). The remaining raw materials and preparation process are the same as in Example 1.

[0031] Example 6

[0032] The difference between this embodiment and Example 1 is that the proportion of 6-amino-βCD is increased. The specific implementation steps of S3 are as follows: S3. Dissolve 18 parts of PFPE-bP (AA-co-DOPAM) in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 9.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze-dry to obtain the βCD modified copolymer; The remaining raw materials and preparation process are the same as in Example 1.

[0033] Example 7

[0034] The difference between this embodiment and Example 1 is that the proportion of 6-amino-βCD is reduced. The specific implementation steps of S3 are as follows: S3. Dissolve 22 parts of PFPE-bP (AA-co-DOPAM) in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 7.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze-dry to obtain the βCD modified copolymer; The remaining raw materials and preparation process are the same as in Example 1.

[0035] Example 8

[0036] The difference between this embodiment and embodiment 1 is that the proportion of Pyrene-GQDs is increased. The specific implementation steps of S4 are as follows: S4. Pyrene-GQDs were prepared by reacting 2 parts of graphene quantum dots with 1.8 parts of 1-pyrenebutyrate succinimide ester in 50 parts of DMF for 6 hours. Pyrene-GQDs were prepared by mixing 8 parts of βCD copolymer with 1.8 parts of Pyrene-GQDs in water, stirring at 25°C for 24 hours, and freeze-drying to obtain PFPE-bP(AA-co-DOPAM)-g-βCD / Pyrene block copolymer.

[0037] The remaining raw materials and preparation process are the same as in Example 1.

[0038] Example 9

[0039] The difference between this embodiment and embodiment 1 is that the proportion of Pyrene-GQDs is reduced. The specific implementation steps of S4 are as follows: S4. Pyrene-GQDs were prepared by reacting 2 parts of graphene quantum dots with 1.8 parts of 1-pyrenebutyrate succinimide ester in 50 parts of DMF for 6 hours. Pyrene-GQDs were prepared by mixing 12 parts of βCD copolymer with 1.2 parts of Pyrene-GQDs in water, stirring at 25°C for 24 hours, and freeze-drying to obtain PFPE-bP(AA-co-DOPAM)-g-βCD / Pyrene block copolymer.

[0040] The remaining raw materials and preparation process are the same as in Example 1.

[0041] Comparative Example 1

[0042] The difference between this comparative example and Example 1 is that DOPAM (dopamine methacrylamide) is not added. The specific implementation steps are as follows: S1. Add 25 parts of PFPE-OH (Mn=2500) and 1.2 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; S2. Dissolve 10 parts of PFPE-CTA and 15 parts of acrylic acid in 210 mL of tetrahydrofuran, add 0.15 parts of AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain an amphiphilic copolymer. S3. Dissolve 20 parts of the amphiphilic copolymer in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 8.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze-dry to obtain the βCD modified copolymer; S4. Pyrene-GQDs were prepared by reacting 2 parts of graphene quantum dots with 1.8 parts of 1-pyrenebutyrate succinimide ester in 50 parts of DMF for 6 hours; Pyrene-GQDs were prepared by mixing 10 parts of βCD copolymer with 1.5 parts of Pyrene-GQDs in water, stirring at 25°C for 24 hours, and freeze-drying.

[0043] The remaining raw materials and preparation process are the same as in Example 1.

[0044] Comparative Example 2

[0045] The difference between this comparative example and Example 1 is that 6-amino-βCD is not added. The specific implementation steps are as follows: S1. Add 25 parts of PFPE-OH (Mn=2500) and 1.2 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; S2. Dissolve 10 parts PFPE-CTA, 15 parts acrylic acid, and 8.2 parts dopamine methacrylamide in 200 mL tetrahydrofuran, add 0.15 parts AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain an amphiphilic copolymer. S3. Pyrene-GQDs were prepared by reacting 2 parts of graphene quantum dots with 1.8 parts of 1-pyrenebutyrate succinimide ester in 50 parts of DMF for 6 hours. Pyrene-GQDs were prepared by mixing 10 parts of amphiphilic copolymer with 1.5 parts of Pyrene-GQDs in water, stirring at 25°C for 24 hours, and freeze-drying.

[0046] The remaining raw materials and preparation process are the same as in Example 1.

[0047] Comparative Example 3

[0048] The difference between this comparative example and Example 1 is that graphene quantum dots are not added. The specific implementation steps are as follows: S1. Add 25 parts of PFPE-OH (Mn=2500) and 1.2 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; S2. Dissolve 10 parts PFPE-CTA, 15 parts acrylic acid, and 8.2 parts dopamine methacrylamide in 200 mL tetrahydrofuran, add 0.15 parts AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain an amphiphilic copolymer. S3. Dissolve 20 parts of the amphiphilic copolymer in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 8.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze-dry to obtain the βCD modified copolymer; S4. Mix 10 parts of βCD copolymer with 1.5 parts of 1-pyrenebutyrate succinimide ester in water, stir at 25°C for 24 hours, and freeze dry to obtain a surfactant for recycling lithium iron phosphate anode materials.

[0049] The remaining raw materials and preparation process are the same as in Example 1.

[0050] Comparative Example 4

[0051] The difference between this comparative example and Example 1 is that 1-pyrenebutyrate succinimide ester is not added. The specific implementation steps are as follows: S1. Add 25 parts of PFPE-OH (Mn=2500) and 1.2 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; S2. Dissolve 10 parts PFPE-CTA, 15 parts acrylic acid, and 8.2 parts dopamine methacrylamide in 200 mL tetrahydrofuran, add 0.15 parts AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain an amphiphilic copolymer. S3. Dissolve 20 parts of the amphiphilic copolymer in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 8.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze-dry to obtain the βCD modified copolymer; S4. Mix 10 parts of βCD copolymer with 1.5 parts of graphene quantum dots in water, stir at 25°C for 24 hours, and freeze dry to obtain a surfactant for recycling lithium iron phosphate anode materials.

[0052] The remaining raw materials and preparation process are the same as in Example 1.

[0053] Comparative Example 5

[0054] The difference between this comparative example and Example 1 is that graphene quantum dots and 1-pyrenebutyrate succinimide are not added. The specific implementation steps are as follows: S1. Add 25 parts of PFPE-OH (Mn=2500) and 1.2 parts of 4-cyano-4-[(dodecylthiocarbonyl)thio]valeric acid to a reaction vessel and dissolve it in 100 parts of anhydrous dichloromethane; add 2.5 parts of DCC and 0.15 parts of DMAP, and react at 25°C under nitrogen protection for 24 hours; filter to remove DCC, and rotary evaporate to obtain PFPE-CTA; S2. Dissolve 10 parts PFPE-CTA, 15 parts acrylic acid, and 8.2 parts dopamine methacrylamide in 200 mL tetrahydrofuran, add 0.15 parts AIBN, polymerize at 60℃ for 6 hours, precipitate with diethyl ether, and dry under vacuum to obtain an amphiphilic copolymer. S3. Dissolve 20 parts of the amphiphilic copolymer in 150 parts of DMF, add 2.0 parts of EDC and 1.2 parts of NHS, and activate the carboxyl groups for 30 minutes; add 8.5 parts of 6-amino-βCD in 50 parts of DMF solution, and react at 25°C for 12 hours; dialyze (MWCO 3500) to remove unreacted substances, and freeze dry to obtain a surfactant for recycling lithium iron phosphate anode materials.

[0055] The remaining raw materials and preparation process are the same as in Example 1.

[0056] A method for recovering lithium iron phosphate anode materials involves testing the recovery of lithium iron phosphate anode materials from surfactants prepared in Examples 1-9 and Comparative Examples 1-5. The specific steps are as follows: (1) Crush the waste LFP negative electrode sheet (containing 95.2% graphite, 3.1% silicon carbon, and 1.7% copper foil) into 2×2cm sheets; prepare a 0.5% w / v surfactant solution (the solution is a pH=4.2 acetate buffer). (2) Take 10g of negative electrode sheet and immerse it in 100mL of surfactant solution. Sonicate at 50℃ (150W) for 15 minutes. Then perform gradient centrifugation: collect copper foil precipitate at 500rpm×10min; collect silicon carbon component at 2000rpm×10min; collect graphite precipitate at 5000rpm×10min. (3) The graphite precipitate was treated with NaOH at pH=10.5, stirred at 60℃ for 30 minutes to decompose the surfactant, and electrolyzed with 0.5M Li2SO4 solution at a constant voltage of 1.5V for 30 minutes to achieve electrochemical regeneration.

[0057] Test Standards and Methods

[0058] 1. Foam performance

[0059] Standard: GB / T 7462-1994 "Determination of Foaming Power of Surfactants"

[0060] Methods: The initial foam height and 5-minute decay rate of a 0.5% surfactant solution were measured and compared with those of a traditional surfactant (SDS / Triton X-100).

[0061] 2. Metal residue

[0062] Standard: GB / T 38823-2020 Silicon-Carbon

[0063] Methods: ICP-OES (PerkinElmer Optima 8000) was used to analyze the Cu, Fe, and Li contents in recycled graphite.

[0064] 3. Graphite recovery rate and purity

[0065] Standard: YS / T 1178-2024 X-ray Diffraction Method for Phase Analysis of Aluminum Ash Slag

[0066] Methods: The mass of recovered graphite was weighed, and the structural integrity was assessed by Raman spectroscopy (ID / IG value).

[0067] 4. Electrochemical performance

[0068] Standard: GB / T 30836-2014 "Lithium titanate and its carbon composite anode materials for lithium-ion batteries"

[0069] Method: Half-cell test (0.1C first effect, 1C cycle 100 times).

[0070] The results are shown in Table 1: Table 1

[0071] As can be seen from Table 1, the quaternary block structure surfactant of the present invention has significant performance advantages. The graphite recovery rate (93.7%~96.2%), copper residue (480-680ppm), silicon contamination rate (4.3%~7.2%), foam height (2-6mm), and regeneration first efficiency (86.6%~90.5%) of Examples 1-9 are all far superior to the comparative examples lacking key components.

[0072] In Comparative Example 1, without the addition of DOPAM, the copper residue level surged to 5300 ppm, and the graphite recovery rate dropped to 87.6%. This is because DOPAM is protonated under pH 4.0-4.5 conditions, and the exposed catechol groups form stable coordination bonds with the hydroxylation sites on the copper foil surface, accelerating the interfacial separation between graphite and copper foil.

[0073] The silicon impurity rate of Comparative Example 2 (without βCD) was as high as 92.10%, while the silicon impurity rate of Examples 1-9 was only 4.3% to 7.2%. This data directly confirms that the cyclic structure of βCD repels silicon-carbon particles (silicon-carbon surfaces lack π-bond sites) through steric hindrance, preventing them from co-precipitating with graphite. The silicon impurity rate of Example 6 (increased βCD ratio) (5.2%) was lower than that of Example 7 (reduced βCD ratio, 5.35%), further illustrating that a βCD grafting ratio of 30% to 50% can optimally utilize the steric hindrance effect, solving the industry pain point that traditional surfactants cannot separate silicon-carbon and graphite.

[0074] The foam height of Examples 1-9 was only 2-6 mm, while the foam height of Comparative Example 1 (without DOPAM) and Comparative Example 2 (without βCD) reached 80-85 mm. This is because the PFPE segments (low surface energy, γ<30mN / m) reduce the interfacial tension of the system, and the hydrophobic ends of pyrene-modified graphene quantum dots (Pyrene-GQDs) synergistically disrupt the stability of the foam film. The two together achieve a "low foaming-rapid defoaming" effect, solving the problem of solid-liquid separation interruption caused by foam in traditional processes.

[0075] The initial efficiency of the recycled graphite in Examples 1-9 (86.6%–90.5%) was significantly higher than that in the comparative examples (78.3%–82.2%), indicating that the surfactant of the present invention can exfoliate graphite under weakly acidic conditions (pH 4.0–4.5) and is easily desorbed under alkaline conditions (pH > 10), with minimal damage to the layered structure of graphite.

[0076] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A surfactant for recovering a lithium iron phosphate negative electrode material, characterized by, The surface active agent comprises PFPE-b-P(AA-co-DOPAM)-g-βCD / Pyrene block copolymer, which comprises a perfluoropolyether chain segment, a pH-responsive block copolymerized from AA and DOPAM, βCD covalently grafted on the polymer skeleton, and Pyrene-modified graphene quantum dots; a thioester bond is introduced between the blocks.

2. A method for preparing a surfactant for recovering a lithium iron phosphate negative electrode material, characterized by, The surface active agent of claim 1 is prepared by the following steps: S1, dispersing PFPE-OH, 4-cyano-4-[(dodecylthiothiocarbonyl)thio]valeric acid, DCC and DMAP in DCM, catalyzing the reaction for 24-26 hours to obtain PFPE-CTA; S2, dissolving PFPE-CTA, AA and DOPAM in tetrahydrofuran, adding AIBN after removing oxygen by nitrogen, and polymerizing at 55-60°C for 6-8 hours, then precipitating and drying to obtain PFPE-b-P(AA-co-DOPAM); S3, dissolving PFPE-b-P(AA-co-DOPAM) in DMF, adding EDC and NHS, adding dropwise 6-amino-βCD DMF solution after activation, dialyzing after reacting for 12-14 hours, and freeze-drying to obtain the βCD copolymer; S4, separately reacting graphene quantum dots and 1-pyrene butyric acid succinimidyl ester in DMF for 6-7 hours to prepare Pyrene-GQDs; mixing the βCD copolymer and Pyrene-GQDs in deionized water, stirring for 24-26 hours, and freeze-drying to obtain the PFPE-b-P(AA-co-DOPAM)-g-βCD / Pyrene block copolymer.

3. The method for preparing a surfactant for recycling lithium iron phosphate anode materials according to claim 2, characterized in that, The weight ratio of PFPE-OH, 4-cyano-4-[(dodecylthiothiocarbonyl)thio]valeric acid, DCC, DMAP and DCM is (22-28):(1-1.5):(2-3):(0.1-0.2):(100-120); the molecular weight of PFPE-OH is 2000-3000 g / moL.

4. The method for preparing a surfactant for recycling lithium iron phosphate negative materials according to claim 2, characterized in that, The weight ratio of PFPE-CTA, AA, DOPAM, tetrahydrofuran and AIBN is (8-12):(12-18):(7-10):(200-240):(0.1-0.2).

5. The method for preparing a surfactant for recovering lithium iron phosphate negative materials according to claim 2, characterized in that, The weight ratio of PFPE-b-P(AA-co-DOPAM), EDC, NHS and 6-amino-βCD is (18-23):(1.5-3):(1-1.5):(6-10).

6. The method for preparing a surfactant for recycling lithium iron phosphate negative materials according to claim 2, characterized in that, The weight ratio of graphene quantum dots, 1-pyrene butyric acid succinimidyl ester and DMF in S4 is (1.5-3):(1.5-2.5):(45-65).

7. The method for preparing a surfactant for recycling lithium iron phosphate anode materials according to claim 2, characterized in that, The weight ratio of βCD copolymer, Pyrene-GQDs and deionized water in S4 is (8-12):(1-2):(350-500).

8. The method for preparing a surfactant for recycling lithium iron phosphate anode materials according to claim 2, characterized in that, The precipitation and drying is carried out by precipitating with diethyl ether and vacuum drying at 70-80°C for 12-1 hours.

9. The method for preparing a surfactant for recycling lithium iron phosphate anode materials according to claim 2, characterized in that, The dialysis adopts a separation membrane with a molecular weight cut-off ≥3500 Da.

10. A lithium iron phosphate negative electrode recovery method, characterized by, The use of the surfactant of claim 1 comprises the following steps: The selective exfoliation of graphite and copper foil is realized under the conditions of pH 4.0-4.5 and temperature 40-60 DEG C, and after the exfoliation, the graphite is separated by gradient centrifugation, the surfactant is removed from the surface of the graphite under the alkaline condition of pH>10, and then the graphite is electrochemically regenerated; The rotating speed of the gradient centrifugation is 500-5000 rpm.

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