Waste graphite repair material, preparation method and application thereof, and lithium secondary battery

Abstract

The application belongs to the field of waste graphite material recycling, and particularly relates to a waste graphite repair material, a preparation method, application and a lithium secondary battery, wherein the preparation method comprises the following steps: waste graphite is separated from waste lithium ion batteries; the waste graphite is pre-modified in a solution of a polyphenol monomer in a first modification process; the polyphenol monomer is an organic compound containing 2-15 phenolic hydroxyl groups and having a carbon number of 6-20; the positive active material in the waste lithium ion battery comprises at least one transition metal element selected from nickel, cobalt, manganese and iron; a primary amine monomer and a phosphorus-containing additive are added to the system of the first modification process to perform phenylamine copolymerization, and a graphite@phenylamine copolymer is prepared; the graphite@phenylamine copolymer is calcined at a temperature of 500-700 DEG C, and then subjected to acid treatment, washing and drying treatment to prepare the waste graphite repair material. The method can improve the rate, low-temperature and long-cycle performance of the waste graphite repair material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling technology, specifically to the field of waste graphite repair and regeneration. Background Technology

[0002] With the increasing popularity of electric vehicles, a large number of retired lithium-ion batteries urgently need to be disposed of. Regenerating graphite anodes from spent batteries is key to reducing battery costs and achieving resource recycling.

[0003] Conventional graphite regeneration methods mainly include high-temperature calcination and acid purification. For example, patent document CN120987314A discloses a method for regenerating waste graphite, a regenerated graphite anode material, and a secondary battery. The method for regenerating waste graphite includes: calcination, oxidizing and calcining waste graphite slag to obtain calcined graphite; shaping, shaping and classifying the calcined graphite to obtain shaped graphite; graphitization, graphitizing the shaped graphite to obtain coarse graphite; and impurity removal, removing impurities from the coarse graphite to obtain impurity-removed graphite. For example, patent document CN117895122A discloses a method for regenerating waste graphite negative electrodes, which includes the following steps: calcining waste graphite powder and then acid washing to remove impurities while retaining lithium in the graphite to obtain pretreated lithium-containing graphite; subjecting the pretreated lithium-containing graphite to high-energy ball milling to obtain pre-lithiated graphite; mixing the pre-lithiated graphite with a reconstructing agent and performing structural reforming by hot isostatic pressing; calcining the graphite, crushing it, and then performing particle size classification to obtain regenerated pre-lithiated graphite. For example, patent document CN115051062A discloses a method for directly regenerating waste graphite using a eutectic solvent, which includes the following steps: (1) discharging, crushing and physically sorting waste lithium-ion batteries to obtain waste graphite material from the waste lithium batteries; (2) preparing a eutectic solvent, using the eutectic solvent to leach the waste graphite material obtained in step (1), and then centrifuging, washing, filtering and drying to obtain regenerated graphite; (3) using the regenerated graphite obtained in step (2) as raw material to prepare graphite electrodes.

[0004] In summary, existing graphite regeneration methods mainly include high-temperature calcination and acid washing, which typically face two major bottlenecks: first, the repair process is energy-intensive and can only restore part of the structure, making it difficult to solve the interface deterioration problem; second, the regenerated graphite suffers from low initial coulombic efficiency, poor rate performance and low-temperature performance due to the reconstruction and residual defects of the surface solid electrolyte interphase (SEI) film, making it difficult to use directly in high-performance batteries. Summary of the Invention

[0005] To address the problems existing in the prior art, the primary objective of this invention is to provide a method for preparing waste graphite repair materials, aiming to obtain regenerated graphite materials with high initial efficiency, fast charging, low temperature resistance, and long cycle stability based on the regeneration of waste graphite.

[0006] The second objective of this invention is to provide a waste graphite repair material prepared by the aforementioned method and its application.

[0007] A third objective of this invention is to provide a lithium secondary battery comprising the aforementioned waste graphite repair material.

[0008] A method for preparing a waste graphite repair material, comprising the following steps:

[0009] Step 1:

[0010] Waste graphite is separated from waste lithium-ion batteries; the waste graphite is pre-modified in a polyphenol monomer solution; the polyphenol monomer is an organic compound containing 2 to 15 phenolic hydroxyl groups and having 6 to 20 carbon atoms; the positive electrode active material in the waste lithium-ion batteries includes at least one transition metal element selected from nickel, cobalt, manganese, and iron.

[0011] Step 2:

[0012] Primary amine monomers and phosphorus-containing additives are added to the system of the first stage modification treatment to carry out phenol-amine copolymerization (also referred to as the second stage modification treatment in this invention) to obtain graphite@phenol-amine copolymer (also referred to as the two-stage modified material); during the phenol-amine copolymerization process, the pH of the system is controlled at 7.5~9.0 and the temperature is controlled at 60℃~100℃;

[0013] The primary amine monomer is an organic compound containing 2 to 10 amino groups and having 1 to 10 carbon atoms; the phosphorus-containing auxiliary agent is at least one of elemental phosphorus, phosphoric acid and its water-soluble salts, and organic phosphoric acid and its water-soluble salts.

[0014] Step 3:

[0015] The graphite@phenolamine copolymer is calcined at 500~700℃, followed by acid treatment, washing and drying to obtain the waste graphite repair material.

[0016] Waste graphite from spent lithium-ion batteries contains recycled transition metal elements. This invention innovatively pre-modifies this graphite using polyphenol monomers. Under the induction of the transition metals, the polyphenol monomers are anchored on the surface and between layers of the waste graphite, forming a polyphenol monomer-transition metal composite layer. Further modification with primary amine monomers and phosphorus-containing additives in a second stage allows for the in-situ construction of phenol-amine copolymers on the graphite surface and between layers. Subsequent low-temperature calcination forms a uniform, ultra-thin functional layer between the graphite layers. Research indicates that this preparation method optimizes the physicochemical structure of waste graphite, improving the rate capability, low-temperature stability, and long-cycle performance of waste graphite remediation materials.

[0017] In this invention, as an optional embodiment, the positive electrode active material in the spent lithium-ion batteries includes at least one of NCM and NCA. NCM refers to nickel-cobalt-manganese ternary materials. NCA refers to nickel-cobalt-aluminum ternary materials.

[0018] The graphite content in the waste graphite can be adjusted reasonably as needed. In order to obtain higher recycling efficiency and value, the graphite content can be above 90 wt.%.

[0019] In this invention, the polyphenol monomer includes at least one selected from tea polyphenols, protocatechuic acid, ellagic acid, chlorogenic acid, catechol, hydroquinone, and catechol. Preferably, the polyphenol monomer includes ellagic acid. Studies have shown that the preferred polyphenol monomer, combined with the modification treatment described in this invention, can further enhance the low-temperature and high-rate long-cycle performance of regenerated graphite.

[0020] In this invention, pre-anchoring polyphenol monomers on the surface and between layers of the waste graphite is one of the key factors in synergistically improving the performance of the repair material in conjunction with subsequent processes.

[0021] The weight ratio of waste graphite to polyphenol monomers is 1:0.05~0.15; more preferably, it can be 1:0.08~0.12. Under the preferred ratio, combined with the process described in this invention, it is expected to further synergistically enhance the long-cycle, low-temperature stability and rate capability of the material.

[0022] The pH during the first stage of modification is 4.5~5.5;

[0023] The temperature for the first stage of modification is 50~70℃, and can be further increased to 60~65℃.

[0024] Preferably, the polyphenol monomers further include auxiliary polyphenol monomers, including at least one of tannic acid and quercetin. The preferred combination of polyphenol monomers facilitates further surface modification of waste graphite, and is expected to be combined with other processes to further optimize the phenol-amine reaction behavior, potentially further synergistically enhancing the long-cycle, low-temperature stability, and rate capability of the material.

[0025] In this invention, the content of the auxiliary polyphenol monomer in the polyphenol monomer can be 5~30 wt.%, preferably 15~25 wt.%. Studies have shown that, at the preferred ratio, it is expected to further optimize the phenol-amine reaction behavior and further synergistically enhance the long-cycle, low-temperature stability and rate capability of the material.

[0026] Preferably, the primary amine monomer includes one or more of urea, melamine, ethylenediamine, hexamethylenediamine, dicyandiamine, amino acids, 4-aminotriphenylamine, diaminoguanidine hydrochloride, and amino-functionalized hexaazatriphenylamine; more preferably, the ratio of melamine to diaminoguanidine hydrochloride is 1-9:1-9, and even more preferably, it is 7-9:1-3. The preferred primary amine monomers, combined with the modification treatment described in this invention, can further enhance the low-temperature and high-rate long-cycle performance of regenerated graphite.

[0027] The phosphorus additives include one or more of sodium hypophosphite, hypophosphite, red phosphorus, ammonium dihydrogen phosphate, phosphoric acid, phytic acid, phenylphosphonic acid, triethyl phosphate, hexachlorocyclotriphosphazene, and ammonium polyphosphate; preferably hexachlorocyclotriphosphazene. The preferred phosphorus additives, combined with the modification treatment described in this invention, can further enhance the low-temperature and high-rate long-cycle performance of regenerated graphite.

[0028] In this invention, the phosphorus auxiliaries, in the phenol-amine copolymerization reaction, can form hydrogen bonds with the hydroxyl groups of phenols or undergo esterification or amidation reactions with the amino groups of amines, participating in and regulating the formation of polymer networks; and are beneficial to forming POC / PNC covalent bonds with subsequent heat treatment, which can improve the carbonization yield, guide the evolution of carbon structure, and help form more ordered carbon with fewer defects.

[0029] In this invention, the weight ratio of the primary amine monomer to the polyphenol monomer is 1:0.1~2; further, 1:0.5~1.5; even further, 1:0.8~1.2; and even further, 1:0.8~1.1.

[0030] The phosphorus additive is 0.5-5% of the weight of waste graphite; further, 0.8-2.5%; and even further, 1-2%.

[0031] The temperature during the phenol-amine copolymerization process is 80~95℃; the copolymerization time is 1~5h, and can be 2~4h.

[0032] The pH during the phenol-amine copolymerization process is 7.9~8.5.

[0033] In this invention, thanks to the aforementioned process, efficient repair and regeneration of graphite can be achieved at ultra-low temperatures.

[0034] The atmosphere during the roasting process is at least one of nitrogen and rare gases.

[0035] The atmosphere during the roasting process also contains 1-5% hydrogen.

[0036] Preferably, the calcination temperature is 580~620℃. At this preferred temperature, it helps to further synergistically enhance the low-temperature and high-rate long-cycle performance of the regenerated graphite.

[0037] Preferably, the roasting time is 1 to 10 hours; more preferably, it can be 4 to 8 hours.

[0038] The present invention demonstrates that the calcination treatment performed under a preferred hydrogen-containing atmosphere can further optimize the physicochemical structure of waste graphite repair materials, and help to further enhance the material's rate capability, low-temperature performance, and long-cycle performance.

[0039] The present invention also provides a waste graphite repair material prepared by the aforementioned preparation method.

[0040] In this invention, thanks to the preparation method described above, the prepared material can be endowed with special physicochemical characteristics, thus giving the material excellent rate capability, low temperature performance, and long cycle performance.

[0041] This invention also provides the application of the aforementioned waste graphite remediation material, using it as a negative electrode active material for the preparation of lithium secondary batteries.

[0042] The present invention also provides a lithium secondary battery, wherein the negative electrode comprises the aforementioned waste graphite repair material.

[0043] The lithium secondary battery of the present invention, apart from containing the waste graphite repair material of the present invention, may have other known components and structural parts.

[0044] Beneficial effects

[0045] (1) Repair-modification integration significantly improves overall electrochemical performance, including high subcoulombic efficiency, excellent fast charging and low temperature performance, and long cycle performance.

[0046] (2) The process is simple and efficient, and is both economical and environmentally friendly.

[0047] (3) The product has high added value. The final product is not simply recycled graphite, but a functionalized graphite composite material with a unique core-shell structure. The "core" is the repaired highly crystalline graphite, which provides stable capacity; the "shell" is a functionalized hybrid conductive interface layer, which gives it advanced characteristics such as fast charging and low temperature. This allows it to directly meet the needs of high-performance power batteries and enhances the value of recycled materials. Attached Figure Description

[0048] Figure 1 Here is a SEM image of the regenerated graphite repair material from Example 1;

[0049] Figure 2 This is a charge-discharge cycle diagram of the regenerated graphite repair material in Example 1. Detailed Implementation

[0050] In this invention, the waste graphite can be obtained by enriching and stripping from waste ternary (such as NCM) batteries; the stripping method is conventional. Furthermore, the graphite content in the waste graphite is above 95%.

[0051] Example 1

[0052] Step 1: First stage of modification treatment

[0053] 100g of waste graphite powder was evenly dispersed in 1800g of deionized water to form a suspension. 10g of polyphenol monomer (ellagic acid) was added while continuously stirring. Subsequently, dilute ammonia was slowly added dropwise to precisely adjust the pH of the reaction system to 5.0. The system was heated to 60℃ and stirred at a constant rate for 2 hours.

[0054] Step 2: Second stage modification

[0055] Add a primary amine monomer (melamine in this case; the weight ratio of primary amine monomer to polyphenol monomer is 1:1) to the slurry from step 1, then add a phosphorus auxiliary agent (phytic acid in this case, used at 1% of the weight of waste graphite). Then, add ammonia water dropwise to adjust the pH of the entire reaction system to 8.5. Subsequently, heat the mixture to 85°C and, under an argon atmosphere, continuously stir vigorously and carry out the phenol-amine copolymerization reaction for 3 hours. After the reaction is complete, perform vacuum filtration, and dry the resulting solid under vacuum at 90°C for 8 hours to obtain a dry composite precursor powder.

[0056] Step 3: Heat treatment

[0057] The dried composite precursor powder from step 2 was placed in a quartz boat in a tubular furnace. A reducing atmosphere consisting of 5v% hydrogen and 95v% argon (by volume) was introduced into the furnace. After exhausting the gas, the temperature was programmed to rise to 600°C at a rate of 5°C / min and held at this temperature for 5 hours for calcination. After the heat treatment, the mixture was allowed to cool naturally to room temperature.

[0058] The cooled product was calcined and immersed in a 0.25 mol / L dilute sulfuric acid solution (liquid-to-solid ratio of 5-10 mL / g), and gently stirred and washed at 60°C for 1.5 hours. It was then repeatedly washed with deionized water until the filtrate was neutral. The final product was vacuum dried at 120°C for 12 hours to obtain the regenerated graphite repair material.

[0059] Example 2

[0060] Compared to Example 1, the only difference is that the conditions in step 1 are changed, and the experimental groups are as follows:

[0061] Group A: Except for replacing the polyphenol monomer with tea polyphenol, the other conditions are the same as in Example 1.

[0062] Group B: Except that the polyphenol monomers were replaced with a combination of ellagic acid and tannic acid (the mass ratio of ellagic acid to tannic acid was 4:1), and the total amount added was still 10% of the graphite mass, the other conditions were the same as in Example 1.

[0063] Group C: Except for the first stage of modification treatment, in which the amount of polyphenol monomer (ellagic acid) was adjusted to 5% of the graphite mass, the reaction pH was adjusted to 5.5, the reaction temperature was set to 50°C, and the time was 3 hours, the other conditions were the same as in Example 1.

[0064] Group D: Except for the addition of the auxiliary polyphenol monomer quercetin (ellagic acid at 9.5% of the weight of waste graphite and quercetin at 0.5% of the weight of waste graphite) to the polyphenol monomer, the other conditions were the same as in Example 1.

[0065] Example 3

[0066] Compared to Example 1, the only difference is that the conditions in step 2 are changed, and the experimental groups are as follows:

[0067] Group A: Except for replacing the primary amine monomer with diaminoguanidine hydrochloride, the other conditions were the same as in Example 1.

[0068] Group B: Except for replacing the primary amine monomer with a combination of melamine and diaminoguanidine hydrochloride (mass ratio 8:2), the other conditions were the same as in Example 1.

[0069] Group C: Except for replacing the phosphorus additive with hexachlorocyclotriphosphazene (addition amount is 1% of the mass of waste graphite), the other conditions are the same as in Example 1.

[0070] Group D: Except for adjusting the phenol-amine copolymerization conditions to reduce the mass ratio of primary amine to polyphenol to 1:0.8 and adjusting the reaction pH to 8.0, the other conditions were the same as in Example 1.

[0071] Group E: Except that the primary amine monomer is ethylenediamine, the phosphorus auxiliaries are a combination of sodium hypophosphite and ammonium dihydrogen phosphate (mass ratio 1:1, total addition amount is 2% of graphite mass), the reaction temperature is set at 82℃, and the treatment time is 4h, the other conditions are the same as in Example 1.

[0072] Example 4

[0073] Compared to Example 1, the only difference is that the conditions in step 3 are changed, and the experimental groups are as follows:

[0074] Group A: Except for the heat treatment atmosphere in step 3 being changed to pure argon (without hydrogen), the other conditions are the same as in Example 1.

[0075] Group B: Except for changing the heat treatment temperature in step 3 to 550℃ and the holding time to 2 hours, the other conditions are the same as in Example 1.

[0076] Group C: Except for step 3, which uses optimized heat treatment conditions: the heat treatment atmosphere is a hydrogen / argon mixture (hydrogen volume percentage 8%), the heat treatment temperature is 600℃, and the holding time is extended to 7 hours, the other conditions are the same as in Example 1.

[0077] Comparative Example 1

[0078] Compared with Example 1, the only difference is that the first modification treatment in step 1 is not performed in advance. Instead, the waste graphite is dispersed in water to obtain a slurry, and polyphenol monomers, primary amine monomers and phosphorus additives are added to the slurry. Step 2 and subsequent treatments are then performed together. All other operations and parameters are the same as in Example 1.

[0079] Comparative Example 2

[0080] Compared with Example 1, the only difference is that the treatment in step 1 was not performed in advance. Instead, the raw materials of waste graphite, polyphenol monomer, primary amine monomer from step 2 and phosphorus additive were physically mixed and directly used as precursor raw materials for the treatment in step 3. The components did not undergo surface phenol-amine copolymerization. All other operations and parameters were the same as in Example 1.

[0081] Comparative Example 3

[0082] Compared with Example 1, the only difference is that in step 1, phenol is used to replace the polyphenol monomer, while other operations and parameters are the same as in Example 1.

[0083] Comparative Example 4

[0084] Compared with Example 1, the only difference is that in step 2, choline hydrochloride is used to replace the primary amine monomer, while other operations and parameters are the same as in Example 1.

[0085] Comparative Example 5

[0086] Compared with Example 1, the only difference is that in step 2, no phosphorus auxiliaries are added. Instead, the phosphorus auxiliaries and the composite precursor of step 2 are physically mixed and then processed together in step 3. That is, the phosphorus auxiliaries of step 2 are added in step 3. All other operations and parameters are the same as in Example 1.

[0087] Comparative Example 6

[0088] Compared with Example 1, the only difference is that in step 3, the heat treatment temperature is 900°C, and all other operations and parameters are the same as in Example 1.

[0089] Tests and Results

[0090] Electrode Preparation: First, the negative electrode was prepared. The recycled graphite sample to be tested was used as the active material and mixed with a conductive agent (Super P) and a binder (sodium carboxymethyl cellulose CMC and styrene-butadiene rubber SBR) at a mass ratio of 96:2:2. Using deionized water as the dispersion medium, the mixture was stirred at high speed in a planetary mixer for 4 hours to form a uniform and stable slurry. Subsequently, the slurry was uniformly coated onto a 10-micron thick copper foil current collector using a coating machine. By controlling the coating thickness, the areal density of the active material in the electrode was approximately 11.5 mg / cm² (corresponding to a total areal density of approximately 12 mg / cm²). The coated electrode was first pre-dried in an 85°C forced-air drying oven for 30 minutes, and then transferred to a 120°C vacuum drying oven for 12 hours to ensure complete removal of moisture. Finally, the dried electrode was cut into 14 mm diameter discs and accurately weighed using a precision balance. The net weight of each electrode was recorded to accurately calculate the mass of its active material.

[0091] Battery Assembly: Electrochemical testing was conducted using CR2032 coin cell half-cells. All assembly steps were performed in a glove box filled with high-purity argon gas, with water and oxygen content below 0.1 ppm. The battery assembly used lithium metal sheets as the counter and reference electrodes, a Celgard 2400 polypropylene membrane as the separator, and a 1.0 mol / L lithium hexafluorophosphate (LiPF6) solution as the electrolyte. The solvent was a 1:1:1 mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) by volume, with 2% fluoroethylene carbonate (FEC) added as a film-forming additive. The negative electrode shell, prepared graphite negative electrode sheet, separator with sufficient electrolyte added, lithium sheet, stainless steel gasket, and spring sheet were stacked sequentially. Finally, the positive electrode shell was placed on top, and a manual hydraulic sealer was used to apply a pressure of approximately 5.5 MPa to seal the battery. The sealed battery was left to stand at room temperature for 12 hours to allow the electrolyte to fully wet the electrodes.

[0092] Performance Testing: All electrochemical tests were conducted in a constant temperature environment of 25±2℃ (except for low temperature tests). The initial coulombic efficiency and reversible specific capacity test procedure was as follows: first, charge at a constant current rate of 0.1C to 0.01V, then switch to constant voltage charging until the current drops to 0.01C, let stand for 5 minutes, and then discharge at a constant current rate of 0.1C to 1.5V. This constitutes one cycle. Subsequently, the above charge and discharge steps were repeated once at a rate of 0.2C, and the data were recorded.

[0093] The rate performance test involved activating the device by cycling it three times at 0.2C, followed by cycling it at 2C. The capacity retention rate was obtained by calculating the ratio of the discharge capacity at each high rate to the initial 0.2C discharge capacity.

[0094] After activation twice at 0.2C, long-cycle stability testing was performed by continuous constant current charge-discharge cycles at 1C. The capacity retention rate was calculated by the ratio of the discharge capacity of the 2000th cycle (cycle temperature 25℃) to the discharge capacity of the 3rd cycle (first stable cycle).

[0095] The low-temperature performance test involves placing the battery in a -20°C constant temperature chamber for 4 hours, and then conducting a charge-discharge test at a 0.2C rate under the same conditions. The ratio of its discharge capacity to the 0.2C discharge capacity at 25°C is the low-temperature capacity retention rate.

[0096] The test results for each case are shown in Table 1:

[0097]

[0098] As shown in Table 1, the innovative first-stage modification treatment of graphite using polyphenol monomers, under the induction of transition metals, promotes the anchoring of polyphenol monomers on the surface and interlayer of waste graphite, forming a polyphenol monomer-transition metal composite layer. Further combined with a second-stage modification treatment using primary amine monomers and phosphorus-containing additives, this allows for the in-situ construction of phenol-amine copolymers on the graphite surface and interlayer. Subsequent low-temperature calcination results in the formation of a uniform, ultra-thin functional layer within the graphite interlayer. This invention demonstrates that the described preparation method optimizes the physicochemical structure of waste graphite, improving the rate capability, low-temperature stability, and long-cycle performance of waste graphite remediation materials.

[0099] Furthermore, as can be seen from Examples 1 and 2, the use of a composite polyphenol monomer of ellagic acid and tannic acid can further synergistically enhance the low-temperature and high-rate long-cycle performance of the material.

[0100] As demonstrated in Examples 1 and 3, the use of a composite primary amine monomer of melamine and diaminoguanidine hydrochloride can further synergistically enhance the low-temperature and high-rate long-cycle performance of the material. Furthermore, the use of hexachlorocyclotriphosphazene in the phenolamine copolymerization can further enhance the low-temperature and high-rate long-cycle performance of the material.

[0101] As can be seen from Examples 1 and 4, using a hydrogen-containing atmosphere for calcination and further controlling the temperature can unexpectedly achieve synergy, further enhancing the low-temperature and high-rate long-cycle performance of the material.

[0102] As can be seen from Example 1 and Comparative Example 1, pre-modifying waste graphite with polyphenol monomers can be combined and synergistically with other processes to enhance the low-temperature and high-rate long-cycle performance of the material.

[0103] As can be seen from Example 1 and Comparative Example 2, subjecting the monomer to the two-stage surface reaction described above can be combined and synergistically with other processes to enhance the low-temperature and high-rate long-cycle performance of the material.

[0104] As can be seen from Example 1 and Comparative Examples 3 and 4, the combination of polyphenol monomers and primary amines described in this invention can improve the low-temperature and high-rate long-cycle performance of materials based on surface polymerization.

[0105] As can be seen from Example 1 and Comparative Example 5, the in-situ participation of phosphorus additives in the phenolamine reaction can enhance the low-temperature and high-rate long-cycle performance of the material.

[0106] As can be seen from Example 1 and Comparative Example 6, the special low-temperature calcination described in this invention can synergistically optimize the physicochemical structure of the material and enhance its low-temperature and high-rate long-cycle performance.

Claims

1. A method for preparing a waste graphite repair material, characterized in that the steps include... include: Step 1: Waste graphite was obtained from waste lithium-ion batteries; the waste graphite was pre-treated in a polyphenol monomer solution for the first stage of modification. The positive electrode active material in the waste lithium-ion battery includes at least one transition metal element selected from nickel, cobalt, manganese, and iron; the polyphenol monomer includes at least one selected from tea polyphenols, protocatechuic acid, ellagic acid, chlorogenic acid, catechol, and hydroquinone. The weight ratio of waste graphite to polyphenol monomers is 1:0.05~0.15; Step 2: Primary amine monomers and phosphorus-containing additives were added to the system after the first stage of modification to carry out phenol-amine copolymerization and obtain graphite@phenol-amine copolymer; during the phenol-amine copolymerization process, the pH of the system was controlled at 7.5~9.0 and the temperature at 60℃~100℃. The primary amine monomers include one or more of urea, melamine, ethylenediamine, hexamethylenediamine, dicyandiamine, amino acids, 4-aminotriphenylamine, diaminoguanidine hydrochloride, and amino-functionalized hexaazatriphenylamine; The phosphorus-containing additives include one or more of sodium hypophosphite, hypophosphite, red phosphorus, ammonium dihydrogen phosphate, phosphoric acid, phytic acid, phenylphosphonic acid, triethyl phosphate, hexachlorocyclotriphosphazene, and ammonium polyphosphate. The weight ratio of the primary amine monomer to the polyphenol monomer is 1:0.1~2; The phosphorus additive is 0.5-5% of the weight of waste graphite; Step 3: The graphite@phenolamine copolymer is calcined at 500~700℃, followed by acid treatment, washing and drying to obtain the waste graphite repair material.

2. The preparation method of the waste graphite repair material as described in claim 1, characterized in that, The positive electrode active material in spent lithium-ion batteries includes at least one of NCM and NCA; The waste graphite contains more than 90 wt.% graphite.

3. The preparation method of the waste graphite repair material as described in claim 1, characterized in that, The pH during the first stage of modification is 4.5~5.5; The temperature for the first stage of modification is 50~70℃.

4. The preparation method of the waste graphite repair material as described in claim 3, characterized in that, The polyphenol monomers also include auxiliary polyphenol monomers, including at least one of tannic acid and quercetin. The content of auxiliary polyphenol monomers in the polyphenol monomers is 5-30%.

5. The method for preparing waste graphite repair material as described in claim 1, characterized in that, The primary amine monomers include melamine and diaminoguanidine hydrochloride in a ratio of 1 to 9:1 to 9; The phosphorus additive mentioned is hexachlorocyclotriphosphazene.

6. The method for preparing waste graphite repair material as described in claim 1, characterized in that, The weight ratio of the primary amine monomer to the polyphenol monomer is 1:0.5~1.5; The phosphorus additive is 0.8-2.5% of the weight of waste graphite; The temperature during the phenol-amine copolymerization process is 80~95℃; the copolymerization time is 1~5h.

7. The method for preparing waste graphite repair material as described in claim 1, characterized in that, In step 3, the atmosphere during the roasting process is at least one of nitrogen and rare gases; The atmosphere during the roasting process also contains 1-5% hydrogen.

8. A waste graphite repair material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the waste graphite repair material according to claim 8, characterized in that, It is used as a negative electrode active material in the preparation of lithium secondary batteries.

10. A lithium secondary battery, characterized in that, Its negative electrode comprises the waste graphite repair material as described in claim 8.

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