Low-concentration acid selective leaching-electrochemical reduction synergistic negative electrode graphite regeneration method

Abstract

The invention provides a low-concentration acid selective leaching-electrochemical reduction synergistic negative electrode graphite regeneration method which comprises the following steps: immersing crushed graphite into a mixed solution of citric acid and an SDS (sodium dodecyl sulfate) solution according to a solid-to-liquid ratio of 1: 20, heating and stirring for a period of time, filtering, and washing with water until the pH is neutral to obtain graphite without amorphous carbon. The graphite without the amorphous carbon is placed in electrolyte composed of Li2SO4 and H2O2, the concentration ratio of Li2SO4 to H2O4 is 2: 1, the graphite without the amorphous carbon serves as a cathode, a Pt net serves as an anode, voltage is applied to the graphite without the amorphous carbon, constant-voltage treatment is conducted for a period of time, and wet graphite is obtained. And taking out the wet graphite, filtering, cleaning and drying to obtain regenerated graphite. According to the method, the regeneration efficiency of the graphite can be improved and the graphite is prevented from being corroded in a synergistic mode of low-concentration acid selective leaching and electrochemical reduction.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery recycling technology, and in particular to a method for regenerating negative electrode graphite through a combination of low-concentration acid selective leaching and electrochemical reduction. Background Technology

[0002] Currently, the mainstream international lithium-ion battery recycling technology mainly follows the "pyrometallurgical + hydrometallurgical" approach. This involves smelting / calcining to decompose organic matter and electrolyte, and then using chemical treatments such as acid-base precipitation to separate various valuable components from the remaining materials. In China, the mainstream lithium battery recycling technology primarily uses the "hydrometallurgical" approach. This involves first discharging the spent batteries, then physically dismantling, crushing, and screening them to obtain black powder, mainly composed of cathode materials and graphite. Valuable metals are then gradually separated through acid-base leaching. Compared to the internationally used "pyrometallurgical + hydrometallurgical" recycling technology, the advantage of the mainstream pure "hydrometallurgical" recycling technology in China is that almost all elements can be recycled with extremely high regeneration efficiency. Co and Ni can reach over 95%, Al and Cu over 90%, and Li is relatively lower but still over 75%. However, the recycling of black powder leaching residue, which is mainly composed of graphite, has not received enough attention in the past and is generally used as boiler fuel or metal reducing agent for downgrading. In addition, the leaching residue contains a large number of harmful substances (such as heavy metals, residual electrolyte and organic matter), which will threaten the ecological environment and human health if not effectively treated.

[0003] In graphite recycling, acid leaching, electrochemical methods, or a combination of both are commonly used, but the results are not ideal. Acid leaching primarily uses high-concentration acids (such as 5M H₂SO₄) to dissolve LiF / Li₂CO₃ in the SEI film; this process is relatively crude and easily corrodes graphite, resulting in a graphite mass loss exceeding 15%. Electrochemical methods are less efficient; electrochemical reduction alone is insufficient to repair interlaminar cracks in graphite (Raman ID / IG value > 0.25), with an initial efficiency below 85%. If acid leaching and electrochemical treatment are performed separately, the process is lengthy, with a processing time exceeding 10 hours and high energy consumption (> 5 kWh / kg). Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a method for regenerating negative electrode graphite using a low-concentration acid selective leaching-electrochemical reduction synergy, which can improve graphite regeneration efficiency and avoid graphite corrosion.

[0005] This invention proposes a method for regenerating negative electrode graphite through a synergistic process of low-concentration acid selective leaching and electrochemical reduction, comprising the following steps:

[0006] The crushed graphite was immersed in a mixed solution of citric acid and SDS, with a solid-liquid ratio of 1:20. The mixture was heated and stirred for a period of time, filtered, and washed with water until the pH was neutral to obtain graphite free of amorphous carbon.

[0007] Amorphous carbon-removed graphite was placed in an electrolyte composed of Li2SO4 and H2O2 with a concentration ratio of 2:1. The amorphous carbon-removed graphite was used as the cathode and a Pt mesh as the anode. A voltage was applied to the amorphous carbon-removed graphite, and it was treated under constant voltage for a period of time to obtain wet graphite.

[0008] The wet graphite is removed, filtered, washed, and dried to obtain recycled graphite.

[0009] In some embodiments, the concentration of citric acid is 0.5–1 M, and the mass concentration of the SDS solution is 0.05%–0.2%.

[0010] In some embodiments, crushed graphite is immersed in a mixed solution, heated to 50–70°C, and stirred for 1–3 hours.

[0011] In some embodiments, the concentration of Li2SO4 in the electrolyte is 0.1M and the concentration of H2O2 is 0.05M.

[0012] In some embodiments, the voltage applied to the graphite after removing amorphous carbon is a cathode voltage of -1.2 to -1.5V.

[0013] In some embodiments, wet graphite is dried using a supercritical CO2 drying device.

[0014] In some embodiments, when wet graphite is dried using supercritical CO2, the pressure is 8–12 MPa and the temperature is 40–60 °C.

[0015] In some embodiments, the wet graphite is removed and then filtered and washed. The liquid obtained from the washing is used to recover the electrolyte by distillation, and the electrolyte obtained by filtration and distillation is recycled.

[0016] In some embodiments, the Li in the electrolyte obtained by distillation is maintained by adding LiOH. + concentration. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0018] in:

[0019] Figure 1This is a flowchart of the negative electrode graphite regeneration method using low-concentration acid selective leaching-electrochemical reduction synergistic in an embodiment of the present invention. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] The following describes, with reference to the accompanying drawings, a method for regenerating negative electrode graphite using a low-concentration acid selective leaching-electrochemical reduction synergistic method according to embodiments of the present invention.

[0022] like Figure 1 As shown in the figure, this invention proposes a method for regenerating negative electrode graphite through a synergistic process of low-concentration acid selective leaching and electrochemical reduction, comprising the following steps:

[0023] S1. Acid leaching treatment: The crushed graphite is immersed in a mixed solution of citric acid (C6H8O7) and sodium dodecyl sulfonate (SDS). The solid-liquid ratio of the crushed graphite to the mixed solution is 1:20. The solution is heated and stirred for a period of time, filtered, and washed with water until the pH is neutral to obtain graphite with amorphous carbon removed.

[0024] S2. Electrochemical reduction: The graphite with amorphous carbon removed is placed in an electrolyte composed of Li2SO4 and H2O2 with a concentration ratio of 2:1. The graphite with amorphous carbon removed is used as the cathode and the Pt mesh is used as the anode. A voltage is applied to the graphite with amorphous carbon removed and it is treated under constant voltage for a period of time to obtain wet graphite.

[0025] S3. Post-processing: Remove the wet graphite, filter, wash, and dry it to obtain recycled graphite.

[0026] The embodiments of the present invention can improve the graphite regeneration efficiency and avoid graphite corrosion by using a synergistic approach of selective leaching with low-concentration acid and electrochemical reduction.

[0027] Specifically, in the selective acid leaching stage: the chelating effect of citric acid (C6H8O7) is used to selectively dissolve LiF / Li2CO3 in the SEI film (reaction formula: LiF + C6H8O7 → LiC6H5O7 + HF↑), avoiding graphite corrosion and reducing mass loss to less than 3%. Adding sodium dodecyl sulfate (SDS) enhances wettability and allows penetration into microcracks, resulting in a LiF solubility greater than or equal to 90%.

[0028] In the electrochemical reduction and remediation stage: In the electrolytic cell, graphite is used as the cathode, a voltage is applied, and the electrolyte is Li₂SO₄ + H₂O₂, Li + Embedded graphite interlayer repair sp 2The structure, while H2O2 decomposes to produce reactive oxygen species (·O2). - Oxidize residual organic matter.

[0029] The combination of selective acid leaching and electrochemical reduction repair produces a synergistic effect, exposing microcracks on the graphite surface after acid leaching, thereby increasing the electrochemical reduction efficiency by 50%.

[0030] The embodiments of the present invention are applicable to the efficient recycling and performance restoration of graphite from retired power batteries, which is both environmentally friendly and economical.

[0031] In some embodiments, the concentration of citric acid is 0.5–1 M, preferably 0.8 M, and the mass concentration of the SDS solution is 0.05%–0.2%, preferably 0.1%.

[0032] In some embodiments, crushed graphite is immersed in a mixed solution, heated to 50–70°C, preferably 50°C, and stirred for 1–3 hours, preferably 2 hours.

[0033] In some embodiments, the concentration of Li2SO4 in the electrolyte is 0.1M and the concentration of H2O2 is 0.05M.

[0034] In some embodiments, the voltage applied to the graphite after removing amorphous carbon is a cathode voltage of -1.2 to -1.5V, preferably -1.3V.

[0035] In some embodiments, wet graphite is dried using a supercritical CO2 drying device.

[0036] In some embodiments, when wet graphite is dried by supercritical CO2, the pressure is 8-12 MPa, preferably 10 MPa, and the temperature is 40-60°C, preferably 50°C.

[0037] In some embodiments, the wet graphite is removed and then filtered and washed. The liquid obtained from the washing is used to recover the electrolyte by distillation, and the electrolyte obtained by filtration and distillation is recycled.

[0038] In some embodiments, the Li in the electrolyte obtained by distillation is maintained by adding LiOH. + Concentration. This can reduce costs by 40%.

[0039] The present invention will be further illustrated by specific embodiments below.

[0040] Example 1

[0041] A method for regenerating negative electrode graphite through a synergistic combination of low-concentration acid selective leaching and electrochemical reduction includes the following steps:

[0042] S1. Acid leaching treatment: Pulverize crushed graphite with a particle size of 0.5-1 mm into a mixed solution of 0.8 M citric acid (C6H8O7) and 0.1% sodium dodecyl sulfonate (SDS) solution. The solid-liquid ratio of crushed graphite to the mixed solution is 1:20. Stir at 50 °C for 2 h, filter, and wash with water until the pH is neutral to obtain graphite with amorphous carbon removed and LiF residue of less than 5%.

[0043] S2, Electrochemical Reduction: The graphite with amorphous carbon removed was placed in an electrolyte composed of 0.1M Li2SO4 and 0.05M H2O2, with a concentration ratio of Li2SO4 to H2O2 of 2:1. The graphite with amorphous carbon removed was used as the cathode and the Pt mesh as the anode. A voltage of -1.3V was applied to the graphite with amorphous carbon removed and the constant voltage treatment was carried out for 1 hour to obtain wet graphite.

[0044] S3. Post-processing: The wet graphite is removed, filtered, washed, and dried in a supercritical CO2 dryer at 50°C and 10MPa to obtain regenerated graphite. The liquid obtained from washing is used to recover the electrolyte by distillation, and the electrolyte obtained from filtration and distillation is recycled.

[0045] Table 1 compares the structural repair effects of recycled graphite recovered using the method of this embodiment with those recovered using traditional acid washing. Tests show that the ID / IG value of the recycled graphite obtained using the method of this embodiment is significantly higher than the interlayer spacing d. 002 Both the ID / IG value and interlayer spacing d of the recycled graphite obtained by traditional acid washing methods are lower than those obtained by traditional acid washing methods. 002 This demonstrates that the recycled graphite obtained using the method in this embodiment exhibits less fracture and is more conducive to recycling.

[0046] Table 1

[0047]

[0048] Table 2 compares the electrochemical performance (0.1C charge / discharge) of the recycled graphite obtained using the method of this embodiment with that of commercial virgin graphite. Tests show that the initial discharge capacity and coulombic efficiency of the recycled graphite obtained in this embodiment are close to those of commercial virgin graphite, facilitating its recycling.

[0049] Table 2

[0050] sample Initial discharge capacity (mAh / g) Coulomb efficiency Commercial New Graphite 355 92.5％ Regenerated graphite obtained in Example 1 345 91.2％

[0051] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0052] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for regenerating negative electrode graphite through a synergistic process of low-concentration acid selective leaching and electrochemical reduction, characterized in that, Includes the following steps: The crushed graphite was immersed in a mixed solution of citric acid and SDS, with a solid-liquid ratio of 1:20 between the crushed graphite and the mixed solution. The mixture was heated and stirred for a period of time, filtered, and washed with water until the pH was neutral to obtain graphite with amorphous carbon removed. The graphite with amorphous carbon removed was placed in an electrolyte composed of Li2SO4 and H2O2, with a concentration ratio of Li2SO4 to H2O2 of 2:

1. The graphite with amorphous carbon removed was used as the cathode and a Pt mesh was used as the anode. A voltage was applied to the graphite with amorphous carbon removed and it was treated under constant voltage for a period of time to obtain wet graphite. The wet graphite is removed, filtered, washed, and dried to obtain recycled graphite.

2. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 1, characterized in that, The concentration of citric acid is 0.5–1 M, and the mass concentration of the SDS solution is 0.05%–0.2%.

3. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 1, characterized in that, The crushed graphite is immersed in the mixed solution, heated to 50-70°C, and stirred for 1-3 hours.

4. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 1, characterized in that, The electrolyte contains 0.1 M Li2SO4 and 0.05 M H2O2.

5. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 1, characterized in that, The voltage applied to the graphite after removing amorphous carbon is a cathode voltage of -1.2 to -1.5V.

6. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 1, characterized in that, The wet graphite was dried using a supercritical CO2 drying device.

7. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 6, characterized in that, When the wet graphite is dried by supercritical CO2, the pressure is 8-12 MPa and the temperature is 40-60℃.

8. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 1, characterized in that, After the wet graphite is removed, it is filtered and washed. The liquid obtained from the washing is recycled as electrolyte by distillation. The electrolyte obtained by filtration and distillation is recycled.

9. The method for regenerating negative electrode graphite by low-concentration acid selective leaching-electrochemical reduction synergy according to claim 8, characterized in that, In the electrolyte obtained by distillation, the Li content in the electrolyte is maintained by adding LiOH. + concentration.

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