A deep eutectic solvent, a method for recycling and regenerating graphite of waste battery negative electrode, and a regenerated graphite material

Abstract

The present invention relates to the technical field of recycling and regenerating waste batteries, and in particular to a deep eutectic solvent, a method for recycling and regenerating graphite of negative electrodes of waste batteries, and a regenerated graphite material. The deep eutectic solvent is composed of a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is phytic acid. The method comprises the following steps: pre-treating waste lithium batteries to obtain waste graphite materials; leaching the waste graphite materials with a deep eutectic solvent, followed by washing and drying to obtain regenerated graphite; the deep eutectic solvent is a combination of choline chloride and phytic acid. The method provided by the present invention has low raw material toxicity, low corrosiveness, and is environmentally friendly; effectively removes metals from waste graphite, and dopes with phosphorus to achieve repair of graphite while improving its lithium storage performance; the regeneration temperature is low, providing a low-energy consumption and low-acid solution for the treatment and regeneration of waste graphite.

Description

Technical Field

[0001] The invention relates to the technical field of recycling and regenerating waste batteries, and in particular to a deep eutectic solvent, a method for recycling and regenerating graphite of negative electrodes of waste batteries, and a regenerated graphite material. Background Art

[0002] As the demand for lithium batteries for energy storage, power and mobile electronic devices continues to increase, waste batteries have also appeared in our field of vision. Researchers and companies attach importance to the metal content and value in them and call them urban mines, but they ignore the negative electrode material graphite in waste batteries. The production process of graphite, especially the graphitization process, requires huge energy and economic costs. If it is directly discarded, the good graphite structure in the graphite and the energy input in the preparation process will be wasted. At present, the main methods for graphite recycling are high-temperature graphitization, wet regeneration and repair, and reuse of graphite derivatives.

[0003] Conventional graphite anode recycling methods include high-temperature graphitization regeneration, such as the existing document 1 (Li Y, Lv W, Zhao H, et al. Regeneration of anode materials from complex graphite residue in spent lithium-ion battery recycling process [J]. Green Chemistry, 2022, 24 (23): 9315-9328.), which expands the crystal structure by continuous alkaline and acid treatment to remove impurities, and then uses high-temperature calcination to graphitize and regenerate the graphite material. The problem with this technical solution is that the graphitization temperature used is as high as 2600 ° C to restore the graphite lattice and thus achieve the purpose of restoring the graphite structure, which directly leads to high energy consumption and higher economic costs than directly purchasing commercial graphite.

[0004] In addition to high-temperature graphitization, there is also wet regeneration and repair, such as the existing document 2 (Yi C, Ge P, Wu X, et al. Tailoring carbon chains for repairing graphite from spent lithium-ion battery toward closed-circuit recycling [J]. Journal of Energy Chemistry, 2022, 72: 97-107.), through heat treatment and water bath carbonization screening, an amorphous carbon coating (glycogen such as sucrose, starch and glucose) is formed on the graphite surface, and the electrochemical performance of the regenerated graphite is comparable to that of industrial graphite. The problem with this technical solution is that acid is used to remove the metal ions embedded in the graphite and repair the carbon layer on the surface, which means that the problem of low graphite capacity cannot be fundamentally solved, and a large amount of acid liquid is generated.

[0005] Therefore, the technical solution for graphite recycling should improve its lithium storage performance while repairing the graphite without polluting the environment, so as to bring valuable prospects and impetus to the graphite recycling industry. Summary of the invention

[0006] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0007] To this end, one of the objects of the present invention is to provide a deep eutectic solvent, wherein the deep eutectic solvent is composed of a hydrogen bond acceptor and a hydrogen bond donor;

[0008] The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is phytic acid.

[0009] In one embodiment, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1:2):(2:1);

[0010] Preferably, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1.

[0011] In one embodiment, the hydrogen bond acceptor and the hydrogen bond donor are mixed at 50-100° C. to form the deep eutectic solvent.

[0012] The second object of the present invention is to provide a method for recycling graphite from the negative electrode of waste batteries, comprising the following steps:

[0013] Pre-treating waste lithium batteries to obtain waste graphite materials;

[0014] Leaching the waste graphite material with a deep eutectic solvent, followed by washing and drying to obtain regenerated graphite;

[0015] The hydrogen bond acceptor of the deep eutectic solvent is a combination of choline chloride and phytic acid.

[0016] In one embodiment, the waste batteries are selected from any one of waste ternary lithium batteries, waste lithium cobalt oxide batteries, waste lithium manganese oxide batteries, waste lithium iron phosphate batteries and waste lithium nickel oxide batteries, or a combination of at least two thereof.

[0017] In one embodiment, the pretreatment includes soaking the waste battery in a salt solution for discharge, peeling off the outer shell for disassembly after complete discharge, soaking and peeling the negative electrode sheet in a solvent, washing and drying the filter residue to obtain the waste graphite material;

[0018] Preferably, the discharge time is 20-24 hours.

[0019] In one embodiment, the salt solution is selected from any one of sodium chloride, sodium sulfide, sodium sulfate, or a combination of at least two thereof;

[0020] Preferably, the concentration of the salt solution is 8-14 g·L -1 .

[0021] In one embodiment, the solvent is N-methylpyrrolidone solvent or an aqueous solution containing N-methylpyrrolidone.

[0022] In one embodiment, the leaching temperature is 50-100°C, and the leaching time is 10-12h.

[0023] In one embodiment, the mass ratio of the waste graphite material to the deep eutectic solvent is 1:10-1:40; the solid-liquid ratio of the waste graphite material to the deep eutectic solvent is in the range of 35g / L-100g / L.

[0024] A third object of the present invention is to provide a regenerated graphite material obtained by the recycling and regeneration method as described in any one of the above items.

[0025] Based on the above, compared with the prior art, the present invention provides a new solvent, deep eutectic salt, which has the advantages of low toxicity, low corrosiveness, and environmental friendliness; the deep eutectic salt is formed by combining a hydrogen donor and a hydrogen acceptor. The deep eutectic salt provided by the present invention uses phytic acid as a hydrogen donor, which has a high P content and can be used as a P source to dope and modify graphite; choline chloride is used as a hydrogen acceptor, and the strong coordination ability of chloride ions therein can dissolve the embedded transition metals in graphite. In addition, phytic acid and choline chloride are widely present in organisms and have little impact on the environment.

[0026] Therefore, the deep eutectic solvent provided by the present invention has broad application prospects in the field of recycling waste negative electrode graphite in waste batteries.

[0027] Other features and beneficial effects of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other beneficial effects of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A flow chart of a method for recycling graphite from negative electrodes of waste batteries provided by the present invention;

[0030] Figure 2 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 1 of the present invention at a current density of 0.5C;

[0031] Figure 3 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 2 of the present invention at a current density of 0.5C;

[0032] Figure 4 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 3 of the present invention at a current density of 0.5C;

[0033] Figure 5 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 4 of the present invention at a current density of 0.5C;

[0034] Figure 6 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 5 of the present invention at a current density of 0.5C;

[0035] Figure 7 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 6 of the present invention at a current density of 0.5C;

[0036] Figure 8 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 7 of the present invention at a current density of 0.5C;

[0037] Fig. 9 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Example 8 of the present invention at a current density of 0.5C;

[0038] Fig.10This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 1 of the present invention at a current density of 0.5C;

[0039] Fig.11 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 2 of the present invention at a current density of 0.5C;

[0040] Fig.12 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 3 of the present invention at a current density of 0.5C;

[0041] Fig.13 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 4 of the present invention at a current density of 0.5C;

[0042] Fig.14 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 5 of the present invention at a current density of 0.5C;

[0043] Fig.15 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 6 of the present invention at a current density of 0.5C;

[0044] Fig.16 This is a constant current charge-discharge cycle diagram of the regenerated graphite obtained in Comparative Example 7 of the present invention at a current density of 0.5C;

[0045] Fig.17 XRD spectra of waste graphite (SG) and regenerated graphite (DES-G) obtained in Example 1;

[0046] Fig.18 The scanning electron microscope photos of waste graphite and the regenerated graphite obtained in Example 1;

[0047] Fig.19 CV curve diagram of the regenerated graphite obtained in Example 1;

[0048] Fig. 20 Impedance performance diagram of commercial graphite (CG) and regenerated graphite obtained in Example 1;

[0049] Fig.21 The constant current charge-discharge cycle diagram of commercial graphite and the regenerated graphite obtained in Example 1 at a current density of 0.5C. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0051] In the description of the present invention, it should be noted that all terms used in the present invention (including technical terms and scientific terms) have the same meanings as those generally understood by ordinary technicians in the field to which the present invention belongs, and cannot be understood as limiting the present invention; it should be further understood that the terms used in the present invention should be understood to have the same meanings as these terms in the context of this specification and in the relevant fields, and should not be understood in an idealized or overly formal sense, unless explicitly defined in the present invention.

[0052] The embodiment of the present invention provides a method for recycling graphite from negative electrodes of waste batteries, comprising the following steps:

[0053] (1) pre-treating waste lithium batteries to obtain waste graphite materials;

[0054] Specifically, the waste batteries are selected from any one of waste ternary lithium batteries, waste lithium cobalt oxide batteries, waste lithium manganese oxide batteries, waste lithium iron phosphate batteries and waste lithium nickel oxide batteries, or a combination of at least two thereof.

[0055] Used batteries usually contain a small amount of electricity and electrolyte. In order to safely and environmentally friendly dispose of these used batteries, they need to be discharged first. The salt solution immersion discharge method is one of the most widely used and effective methods. Its principle is to use the electrolysis reaction to generate current inside the battery and release the electricity in the battery through the electrolysis process. This method can not only effectively reduce the amount of electricity in the battery and reduce safety hazards in the subsequent treatment process, but also reduce the leakage of electrolyte to a certain extent and reduce pollution to the environment.

[0056] Therefore, in some embodiments of the present invention, the pretreatment includes immersing the waste battery in a salt solution for discharge, peeling off the outer shell for disassembly after complete discharge, soaking and peeling the negative electrode sheet in a solvent, washing and drying the filter residue to obtain the waste graphite material;

[0057] In some embodiments, the salt solution is selected from any one of sodium chloride, sodium sulfide, sodium sulfate, or a combination of at least two thereof; preferably, the salt solution is sodium chloride;

[0058] The concentration of the salt solution has a significant effect on the discharge efficiency. Generally speaking, within a certain range, as the concentration of the salt solution increases, the discharge efficiency will also increase accordingly. This is because the increase in concentration can increase the ion concentration in the solution, thereby increasing the speed and efficiency of the electrolytic reaction. However, when the concentration of the salt solution is too high, the discharge efficiency may tend to saturation or even decrease. Therefore, in some preferred embodiments of the present invention, the concentration of the salt solution is 8g·L -1 -14g·L -1 , for example, it can be 8 g·L -1 , 9g·L -1 , 10g·L -1 , 11g·L -1 , 12g·L -1 , 13g·L -1 , 14g·L -1 The present invention can effectively reduce the pressure of waste liquid treatment by controlling the salt solution to be at a lower concentration level while maintaining the speed and efficiency of a strong electrolytic reaction.

[0059] Preferably, the discharge time is 20h-24h, for example, it can be 20h, 20.5h, 21h, 21.5h, 22h, 22.5h, 23h, 23.5h, 24h, 24.5h, 25h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] In some embodiments, the solvent is an N-methylpyrrolidone solvent or an aqueous solution containing N-methylpyrrolidone. The binder used in existing pole pieces is mostly PVDF binder, and the surface of PVDF molecules is covered with fluorine atoms, which makes the PVDF molecules have strong intermolecular forces. When PVDF comes into contact with NMP, electrostatic interactions will occur between the fluorine atoms on the PVDF molecules and the nitrogen atoms in the NMP molecules, thereby forming hydrogen bonds and van der Waals forces. These forces cause PVDF and NMP to be tightly combined. At the same time, PVDF and NMP are both non-polar molecules with similar chemical properties and good compatibility, which enables NMP to effectively dissolve PVDF.

[0061] Therefore, in the embodiment of the present invention, in order to separate the current collector and graphite in the negative electrode sheet, N-methylpyrrolidone or an aqueous solution containing N-methylpyrrolidone is used, which can effectively dissolve the binder in the negative electrode sheet, so that the attachments on the negative electrode sheet are separated from the current collector. Then the obtained coarse graphite powder is washed and dried to obtain the waste graphite material.

[0062] (2) leaching the waste graphite material with a deep eutectic solvent, followed by washing and drying to obtain regenerated graphite;

[0063] The hydrogen bond acceptor of the deep eutectic solvent is a combination of choline chloride and phytic acid.

[0064] The deep eutectic salt provided by the present invention uses phytic acid as a hydrogen donor, which has a high P content and can be used as a P source to dope and modify graphite; choline chloride is used as a hydrogen acceptor, and the strong coordination ability of chloride ions therein can dissolve the transition metal embedded in the graphite. In addition, phytic acid and choline chloride are widely present in organisms and have little impact on the environment.

[0065] In some embodiments of the present invention, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1:2):(2:1). The molar ratio can be, for example, 1:2, 1:1, 2:1, etc., but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0066] Preferably, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1.

[0067] Deep eutectic solvent (DES) is a low eutectic mixture formed by mixing hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) in a certain proportion. Its properties are affected by the chemical properties and molar ratio of the components. As the proportion of hydrogen bond donor phytic acid increases, the viscosity of DES will increase to a certain extent, because the formation of hydrogen bonds will increase the interaction between molecules. The viscosity directly affects the fluidity of DES during the leaching process, and then affects the leaching efficiency and the quality of regenerated graphite.

[0068] In some embodiments of the present invention, since the deep eutectic solvent used in the present invention is a combination of choline chloride and phytic acid, mixing can be achieved at a relatively low temperature until a uniform transparent liquid, i.e., a eutectic solvent, is formed. That is, the hydrogen bond acceptor and the hydrogen bond donor are mixed at 50-100°C to form the deep eutectic solvent. The temperature may be, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0069] In one embodiment, the leaching temperature is 50°C-100°C, for example, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable; the leaching time is 10h-12h, for example, it can be 10h, 10.5h, 11h, 11.5h, 12h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0070] In one embodiment, the mass ratio of the waste graphite material to the deep eutectic solvent is 1:10-1:40; the solid-liquid ratio of the waste graphite material to the deep eutectic solvent is in the range of 35g / L-100g / L.

[0071] The present invention provides a regenerated graphite material obtained by any of the above recycling methods.

[0072] The following examples and comparative examples are used to illustrate the present invention in more detail but are not intended to limit the present invention in any way.

[0073] Unless otherwise specified, the raw materials used in the embodiments of the present invention may be conventional commercial products in the art, or may be prepared by conventional methods in the art.

[0074] Example 1

[0075] refer to Figure 1 The present invention provides a method for recycling graphite from the negative electrode of waste batteries, comprising the following steps:

[0076] Step 1: Disassembly of used batteries:

[0077] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0078] Step 2: Preparation of deep eutectic solvent:

[0079] The deep eutectic solvent is composed of choline chloride and phytic acid in a molar ratio of 1:1. 0.01 mol of choline chloride and 0.01 mol of phytic acid are added to a 30 ml glass bottle and heated at 80° C. until transparent to form a deep eutectic solvent;

[0080] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0081] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0082] Example 2

[0083] Step 1: Disassembly of used batteries:

[0084] The used batteries were first discharged at 10 g·L -1The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0085] Step 2: Preparation of deep eutectic solvent:

[0086] The deep eutectic solvent is composed of choline chloride and phytic acid in a molar ratio of 1:2. 0.01 mol of choline chloride and 0.02 mol of phytic acid are added to a 30 ml glass bottle and heated at 80° C. until transparent to form a deep eutectic solvent;

[0087] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0088] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0089] Example 3

[0090] Step 1: Disassembly of used batteries:

[0091] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0092] Step 2: Preparation of deep eutectic solvent:

[0093] The deep eutectic solvent is composed of choline chloride and phytic acid in a molar ratio of 1:1. 0.02 mol of choline chloride and 0.02 mol of phytic acid are added to a 30 ml glass bottle and heated at 80° C. until transparent to form a deep eutectic solvent;

[0094] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0095] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0096] Example 4

[0097] The difference between this embodiment and embodiment 1 is that the molar ratio of choline chloride to phytic acid is 2:1.

[0098] Example 5

[0099] The only difference between this embodiment and embodiment 1 is that the heating temperature in step 2 is 50°C.

[0100] Example 6

[0101] The difference between this embodiment and embodiment 1 is that the heating temperature in step 2 is 100°C.

[0102] Example 7

[0103] The only difference between this embodiment and embodiment 1 is that the leaching temperature in step 3 is 50°C.

[0104] Example 8

[0105] The only difference between this embodiment and embodiment 1 is that the leaching temperature in step 3 is 100°C.

[0106] Comparative Example 1

[0107] Step 1: Disassembly of used batteries:

[0108] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0109] Step 2: Preparation of deep eutectic solvent:

[0110] The deep eutectic solvent is composed of choline chloride and oxalic acid in a molar ratio of 1:1. 0.01 mol of choline chloride and 0.01 mol of oxalic acid are added to a 30 ml glass bottle and heated at 80° C. until transparent to form a deep eutectic solvent;

[0111] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0112] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0113] Comparative Example 2

[0114] Step 1: Disassembly of used batteries:

[0115] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0116] Step 2: Preparation of deep eutectic solvent:

[0117] The deep eutectic solvent is composed of choline chloride and salicylic acid in a molar ratio of 1:1. 0.01 mol of choline chloride and 0.01 mol of salicylic acid are added to a 30 ml glass bottle and heated at 80° C. until transparent to form a deep eutectic solvent;

[0118] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0119] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0120] Comparative Example 3

[0121] Step 1: Disassembly of used batteries:

[0122] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0123] Step 2: Preparation of deep eutectic solvent:

[0124] The deep eutectic solvent is composed of choline chloride and ethylene glycol in a molar ratio of 1:1. 0.01 mol of choline chloride and 0.01 mol of ethylene glycol are added to a 30 ml glass bottle and heated at 80° C. until transparent to form a deep eutectic solvent;

[0125] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0126] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0127] Comparative Example 4

[0128] Step 1: Disassembly of used batteries:

[0129] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0130] Step 2: Preparation of deep eutectic solvent:

[0131] The deep eutectic solvent is composed of choline chloride and citric acid in a molar ratio of 1:1. 0.01 mol of choline chloride and 0.01 mol of citric acid are added to a 30 ml glass bottle and heated at 80°C until transparent to form a deep eutectic solvent;

[0132] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0133] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0134] Comparative Example 5

[0135] Step 1: Disassembly of used batteries:

[0136] The used batteries were first discharged at 10 g·L -1 The discharge time is 24 hours in a sodium chloride solution, and then the graphite is disassembled into a metal shell, a positive electrode and a current collector, a separator, a negative electrode and a current collector, wherein the negative electrode is stripped by NMP, washed, and dried to obtain waste graphite;

[0137] Step 2: Preparation of deep eutectic solvent:

[0138] The deep eutectic solvent is composed of choline chloride and ammonium tartrate in a molar ratio of 1:1. 0.01 mol of choline chloride and 0.01 mol of tartaric acid are added to a 30 ml glass bottle and heated at 80°C until transparent to form a deep eutectic solvent;

[0139] Step 3: Regeneration of deep eutectic solvent to recover graphite:

[0140] Take 0.5 g of the waste graphite obtained in step 1 and add it to the deep eutectic solvent in step 2 for leaching, soak it at 80° C. for 10 hours, and then filter, wash and dry to obtain regenerated graphite.

[0141] Comparative Example 6

[0142] The difference between this comparative example and Example 1 is that the hydrogen bond acceptor is betaine and the hydrogen bond donor is phytic acid.

[0143] Comparative Example 7

[0144] The difference between this comparative example and Example 1 is that the hydrogen bond acceptor is tetrabutylammonium bromide and the hydrogen bond donor is phytic acid.

[0145] In order to compare the performance of the regenerated graphite obtained by the method for recycling and regenerating the negative electrode graphite of waste batteries of the present invention as the negative electrode material of lithium ion batteries, the regenerated graphites obtained in Examples 1-10 and Comparative Examples 1-7 were assembled into lithium ion batteries as negative electrode materials for electrochemical performance testing. The experimental data of each sample are shown in Table 1, and the charge and discharge cycle diagram is shown in Table 1. Figure 2-Figure 16 shown.

[0146] The obtained button battery was left to stand for 12 hours, then discharged at 27°C with a constant current of 0.1C to 0.01V, left to stand for 5 minutes, charged to 2.5V with a constant current of 0.1C, left to stand for 5 minutes, and activated for three cycles; then discharged to 0.01V with a constant current of 0.5C, left to stand for 5 minutes, charged to 2.5V with a constant current of 0.5C, left to stand for 5 minutes, and cycled for 500 cycles, and the charge and discharge specific capacity was recorded.

[0147] Table 1 Electrochemical performance of negative electrode graphite of each sample

[0148]

[0149]

[0150] It can be seen from Table 1 that the deep eutectic solvent provided by the present invention has an excellent initial specific capacity for the negative electrode graphite of waste batteries treated compared with other deep eutectic solvents, and after 500 cycles of charge and discharge, the capacity retention rate can also be maintained at a relatively high level.

[0151] For further reference, Fig.17 It can be seen from the XRD spectrum that the waste graphite material has obvious characteristic peaks of Fe2O3 and Li2CO3, while the raw graphite (DES-G) treated by the regeneration method provided by the present invention does not contain other impurities, and only has three characteristic peaks of graphite: (002)(101)(004). It can be seen that the regeneration method of the present invention can completely remove other impurities.

[0152] refer to Fig.18 In a and b, the SEM images show that the surface of the waste graphite material is rough, with cavities in some serious places and severe cracks in some places. Fig.18 In Figures c and d, the surface of the raw graphite (DES-G) treated by the regeneration method provided by the present invention is smooth, which can prove that the graphite is perfectly regenerated.

[0153] refer to Fig.19 The raw graphite (DES-G) treated by the regeneration method provided by the present invention has a simple and obvious SEI film formation peak at 0.7V, and the 2-5 circles of the oxidation peak and the reduction peak of DES-G are highly overlapped, proving that it has a high degree of reversibility.

[0154] refer to Fig. 20 The impedance of the raw graphite (DES-G) treated by the regeneration method provided by the present invention is smaller than that of commercial graphite;

[0155] refer to Fig.21 The raw graphite (DES-G) treated by the regeneration method provided by the present invention still has 427 mAh / g after 500 cycles, and the capacity retention rate is 94.9%. However, the capacity of commercial graphite (CG) after 500 cycles is only 298 mAh / g, and the capacity retention rate is 85.1%.

[0156] 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 it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling graphite from the negative electrode of waste batteries, characterized in that: The following steps are involved: Pre-treating waste lithium batteries to obtain waste graphite materials; Leaching the waste graphite material with a deep eutectic solvent, followed by washing and drying to obtain regenerated graphite; The deep eutectic solvent is a combination of choline chloride and phytic acid; The deep eutectic solvent consists of a hydrogen bond acceptor and a hydrogen bond donor; The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is phytic acid.

2. The method for recycling graphite from the negative electrode of waste batteries according to claim 1, characterized in that: The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is (1:2):(2:1).

3. The method for recycling graphite from the negative electrode of waste batteries according to claim 2, characterized in that: The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:

1.

4. The method for recycling graphite from the negative electrode of waste batteries according to claim 1, characterized in that: The hydrogen bond acceptor and the hydrogen bond donor are mixed at 50-100° C. to form the deep eutectic solvent.

5. The method for recycling graphite from the negative electrode of waste batteries according to claim 1, characterized in that: The pretreatment comprises soaking the waste battery in a salt solution for discharge, peeling off the outer shell for disassembly after the battery is completely discharged, soaking and peeling the negative electrode sheet in a solvent, washing and drying the filter residue, and obtaining the waste graphite material; 6. The method for recycling graphite from the negative electrode of waste batteries according to claim 5, characterized in that: The discharge time is 20-24h.

7. The method for recycling graphite from the negative electrode of waste batteries according to claim 1, characterized in that: The salt solution is selected from any one of sodium chloride, sodium sulfide, and sodium sulfate, or a combination of at least two thereof; 8. The method for recycling graphite from the negative electrode of waste batteries according to claim 7, characterized in that: The concentration of the salt solution is 8-14 g·L -1 .

9. The method for recycling graphite from the negative electrode of waste batteries according to claim 1, characterized in that: The solvent is N-methylpyrrolidone solvent or an aqueous solution containing N-methylpyrrolidone.

10. The method for recycling graphite from the negative electrode of waste batteries according to claim 1, characterized in that: The leaching temperature is 50-100°C, and the leaching time is 10-12h.

11. The method for recycling graphite from negative electrodes of waste batteries according to claim 1, characterized in that: The mass ratio of the waste graphite material to the deep eutectic solvent is 1:10-1:40; the solid-liquid ratio of the waste graphite material to the deep eutectic solvent is 35g / L-100g / L.

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