Method for modifying regenerated graphite negative electrode material based on defect repair and surface coating

Abstract

The invention provides a regenerated graphite negative electrode material modification method based on defect repair and surface coating, which comprises the following steps: mixing regenerated graphite with an intercalator according to a solid-to-liquid ratio of 1: 20, stirring for a period of time at 50-100 DEG C, and carrying out centrifugal separation to obtain intercalated graphite; placing the intercalated graphite in an inert atmosphere, and carrying out heat treatment at 300-400 DEG C to obtain repaired graphite; and filling the repaired graphite into a fluidized bed reactor, introducing a mixed gas of C2H2 and NH3, carrying out chemical vapor deposition at 450-550 DEG C, and cooling to obtain the nitrogen-doped and coated regenerated graphite negative electrode material. The invention provides a modification process combining liquid-phase intercalation repair and low-temperature gas-phase coating, and the repair rate and the repair effect of the regenerated graphite can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery recycling, and in particular to a method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating. Background Art

[0002] Currently, the mainstream international lithium-ion battery recycling technology is primarily a "pyrometallurgical + hydrometallurgical" approach, which involves smelting / calcining to decompose organic matter and electrolytes. The remaining materials are then treated with chemical processes such as acid-base precipitation to separate the various valuable components. Domestically, the mainstream lithium battery recycling technology is primarily a "wet process," where the discarded batteries are discharged and then physically disassembled, crushed, and screened to obtain a black powder composed primarily of cathode materials and graphite. This is then followed by gradual acid-base leaching to separate the valuable metals. Compared to the internationally adopted "pyrometallurgical + hydrometallurgical" recycling technology, the mainstream domestic pure "wet process" recycling technology has the advantage of recovering nearly all elemental materials with extremely high regeneration efficiency, reaching over 95% for Co and Ni, over 90% for Al and Cu, and a relatively lower, but still over 75% for Li. However, the recycling of black powder leaching residue, which is mainly graphite, has rarely received sufficient attention in the past. It is generally downgraded and used as boiler fuel or metal reducing agent. In addition, the leaching residue contains a large amount of harmful substances (such as heavy metals, residual electrolyte and organic matter). If it is not effectively treated, it will threaten the ecological environment and human health.

[0003] The regenerated graphite obtained by traditional regeneration process (such as pickling, high temperature annealing) usually has certain defects, such as micro cracks between graphite layers and sp 2 Hybrid defects (Raman ID / IG value>0.25) and so on, result in the first efficiency being less than 85%. In the existing technology, a coating process is used to coat defective regenerated graphite, but the coating process is relatively rough. Direct carbon coating or polymer coating can easily cause uneven coating layers, with thickness deviations>30%, and easy to fall off during the cycle. If coating is done by vapor deposition (CVD), although the performance can be improved, it needs to be heated to above 800°C, which has high energy consumption and high costs (>50,000 yuan / ton), making it difficult to commercialize. Summary of the Invention

[0004] The present invention aims to at least partially address one of the technical problems in the related art. To this end, embodiments of the present invention provide a method for modifying regenerated graphite anode materials based on defect repair and surface coating, which can improve the repair rate and effectiveness of the regenerated graphite and enhance the uniformity of the regenerated graphite surface coating.

[0005] In one embodiment of the present invention, a method for modifying a regenerated graphite negative electrode material based on defect repair and surface coating is provided, comprising the following steps:

[0006] The regenerated graphite is mixed with an intercalating agent at a solid-liquid ratio of 1:20, stirred at 50-100°C for a period of time, and then centrifuged to obtain intercalated graphite; the intercalated graphite is placed in an inert atmosphere and heat-treated at 300-400°C to obtain repaired graphite; the repaired graphite is loaded into a fluidized bed reactor, a mixture of C2H2 and NH3 is introduced, and chemical vapor deposition is carried out at 450-550°C. After cooling, a nitrogen-doped and coated regenerated graphite negative electrode material is obtained.

[0007] In some embodiments, the intercalant comprises lithium nitrate and ethylene glycol, and the molar ratio of lithium nitrate to ethylene glycol is 1:2-4.

[0008] In some embodiments, the regenerated graphite is mixed with the intercalation agent and stirred at 50-100° C. for 6-24 hours.

[0009] In some embodiments, in the mixed gas of C2H2 and NH3, the volume ratio of C2H2 to NH3 is 5 to 15:1.

[0010] In some embodiments, the reaction pressure of the chemical vapor deposition process is 5-20 kPa.

[0011] In some embodiments, the intercalated graphite is heated to 300-400° C. at a rate of 5° C. / min in an inert atmosphere and kept at that temperature for 1-3 hours.

[0012] In some embodiments, the inert atmosphere is a nitrogen atmosphere.

[0013] Another embodiment of the present invention provides a regenerated graphite negative electrode material prepared by the above-mentioned modification method, wherein the thickness of the nitrogen-doped coating layer of the regenerated graphite negative electrode material is 3 to 5 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings.

[0015] in:

[0016] Figure 1 Flowchart of a method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating in an embodiment of the present invention;

[0017] Figure 2 This is a comparison curve of the electrochemical cycle performance of regenerated graphite repaired by the method of Example 1 of the present invention and commercial new graphite; DETAILED DESCRIPTION

[0018] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0019] The following describes a method for modifying a regenerated graphite negative electrode material based on defect repair and surface coating according to an embodiment of the present invention with reference to the accompanying drawings.

[0020] like Figure 1 As shown, an embodiment of the present invention provides a method for modifying a regenerated graphite negative electrode material based on defect repair and surface coating, comprising the following steps:

[0021] The regenerated graphite is mixed with an intercalating agent at a solid-liquid ratio of 1:20, stirred at 50-100°C for a period of time, and then centrifuged to obtain intercalated graphite; the intercalated graphite is placed in an inert atmosphere and heat-treated at 300-400°C to obtain repaired graphite; the repaired graphite is loaded into a fluidized bed reactor, a mixture of C2H2 and NH3 is introduced, and chemical vapor deposition is carried out at 450-550°C. After cooling, a nitrogen-doped and coated regenerated graphite negative electrode material is obtained.

[0022] The embodiment of the present invention proposes a modification process that combines liquid-phase intercalation repair with low-temperature gas-phase coating, which can improve the repair rate and repair effect of the regenerated graphite, with a defect repair rate of ≥90%, a Raman ID / IG value reduced to 0.05-0.12, and an improved uniformity of the surface coating of the regenerated graphite, with a carbon layer thickness deviation of <10% (SEM-EDS surface scanning analysis).

[0023] In the defect repair stage, the cracks between graphite layers can be filled and sp 2 Then, through low temperature heat treatment at 300-400℃, the intercalation agent is driven out and a stable interlayer bridge is formed (the XRD interlayer spacing d002 is restored to ).

[0024] In the surface coating stage, acetylene (C2H2) is used as the carbon source to generate a 3-5 nm ultra-thin carbon coating layer by low-temperature chemical vapor deposition (LPCVD, 450-550°C) in a fluidized bed reactor. Nitrogen is simultaneously doped (NH3 is introduced) to form an NC composite coating layer, which improves the lithium ion diffusion rate (DLi+≥1×10 -9 cm 2 / s).

[0025] The method of the embodiment of the present invention is particularly suitable for high-value regeneration of retired graphite from power batteries.

[0026] In some embodiments, the intercalation agent includes lithium nitrate and ethylene glycol, and the molar ratio of lithium nitrate (LiNO3) to ethylene glycol (C2H6O2) is 1:2 to 4, preferably 1:3.

[0027] By using lithium nitrate and ethylene glycol in this ratio for liquid phase intercalation, the filling of cracks between graphite layers and the sp2 The effect of structural repair.

[0028] In some embodiments, the regenerated graphite is mixed with the intercalant and stirred at 50-100° C. for 6-24 hours, preferably at 80° C. for 12 hours.

[0029] In some embodiments, in the mixed gas of C2H2 and NH3, the volume ratio of C2H2 to NH3 is 5 to 15:1, preferably 10:1.

[0030] In some embodiments, the reaction pressure of the chemical vapor deposition process is 5-20 kPa, preferably 10 kPa.

[0031] In some embodiments, the intercalated graphite is heated in an inert atmosphere at a rate of 5°C / min to 300-400°C and kept at that temperature for 1-3 hours. Preferably, the temperature is heated at a rate of 5°C / min to 350°C and kept at that temperature for 2 hours.

[0032] In some embodiments, the inert atmosphere is a nitrogen atmosphere.

[0033] Another embodiment of the present invention provides a regenerated graphite negative electrode material prepared by the above-mentioned modification method, wherein the thickness of the nitrogen-doped coating layer of the regenerated graphite negative electrode material is 3 to 5 nm.

[0034] The present invention is further described below through specific examples.

[0035] Example 1

[0036] A method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating comprises the following steps:

[0037] S1, the graphite (particle size D50 = 15 μm, specific surface area 4.5m 2 / g) was mixed with lithium nitrate / ethylene glycol intercalation agent at a solid-liquid ratio of 1:20, stirred at 80°C for 12h, and then centrifuged to obtain intercalated graphite.

[0038] S2, placing the intercalated graphite in a nitrogen atmosphere, heating it to 350°C at a rate of 5°C / min, and keeping it at that temperature for 2 hours to repair the interlayer defects and obtain repaired graphite.

[0039] S3, the repaired graphite is loaded into a fluidized bed reactor, and a mixed gas of C2H2 and NH3 is introduced, with a volume ratio of C2H2 to NH3 of 10:1. The reaction is carried out at 500°C and a pressure of 10kPa for 30 minutes. After natural cooling, a nitrogen-doped and coated regenerated graphite negative electrode material is obtained, and the thickness of the coating layer is 4.2±0.3nm.

[0040] Table 1 compares the performance of the regenerated graphite repaired by the method of this embodiment with the regenerated graphite after conventional pickling. Raman analysis shows that the ID / IG value and interlayer spacing d002 of the regenerated graphite repaired by the method of this embodiment are lower than those of the regenerated graphite after conventional pickling, indicating that the defects of the regenerated graphite obtained by the method of Example 1 have been repaired.

[0041] Table 1

[0042]

[0043] Table 2 compares the electrochemical properties of the regenerated graphite repaired by the method of this embodiment with those of commercial new graphite. The test shows that the various properties of the regenerated graphite repaired by the method of this embodiment are close to those of commercial new graphite, and therefore it is conducive to recycling.

[0044] Table 2

[0045] index Commercial New Graphite Example 1 Repaired Regenerated Graphite First Coulombic efficiency 92.5％ 91.8％ Initial capacity (mAh / g) 340 335 0.5C cycle 500 times capacity retention rate (such as Figure 2 shown) 88％ 93％ 1C cycle 500 times capacity retention 88％ 90％ Low temperature performance (-20℃) 210mAh / g 235mAh / g

[0046] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0047] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating, characterized in that: The steps include: The regenerated graphite is mixed with the intercalation agent at a solid-liquid ratio of 1:20, stirred at 50-100°C for a period of time, and then centrifuged to obtain intercalated graphite; The intercalated graphite is placed in an inert atmosphere and heat treated at 300-400°C to obtain repaired graphite; The repaired graphite is loaded into a fluidized bed reactor, a mixture of C2H2 and NH3 is introduced, and chemical vapor deposition is carried out at 450-550°C. After cooling, a nitrogen-doped and coated regenerated graphite negative electrode material is obtained.

2. The method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating according to claim 1, characterized in that: The intercalation agent comprises lithium nitrate and ethylene glycol, and the molar ratio of lithium nitrate to ethylene glycol is 1:2-4.

3. The method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating according to claim 1, characterized in that: The regenerated graphite is mixed with the intercalation agent and stirred at 50-100°C for 6-24 hours.

4. The method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating according to claim 1, characterized in that: In the mixed gas of C2H2 and NH3, the volume ratio of C2H2 to NH3 is 5 to 15:

1.

5. The method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating according to claim 1, characterized in that: The reaction pressure of the chemical vapor deposition process is 5 to 20 kPa.

6. The method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating according to claim 1, characterized in that: The intercalated graphite is heated to 300-400°C at a rate of 5°C / min in an inert atmosphere and kept warm for 1-3 hours.

7. The method for modifying regenerated graphite negative electrode materials based on defect repair and surface coating according to claim 1, characterized in that: The inert atmosphere was a nitrogen atmosphere.

8. A regenerated graphite negative electrode material prepared by the modification method according to any one of claims 1 to 7, characterized in that: The thickness of the nitrogen-doped coating layer of the regenerated graphite negative electrode material is 3 to 5 nm.

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