METHOD FOR PURIFICATION AND LATTICE RECONSTRUCTION OF GRAPHITE IN POWER BATTERY

Abstract

Disclosed is a method for purification and lattice reconstruction of graphite in a power battery, which includes the following steps: subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially to obtain electrode material powder; mixing the electrode material powder with a metal extractant, standing still, then washing with a purifying agent A, filtering to obtain a filter residue A, mixing the filter residue A with the metal extractant, standing still, then washing with a purifying agent B, and filtering to obtain a crude graphite; subjecting the crude graphite to the de-organic treatment, cooling, ball milling, and ventilation replacement to obtain a primary purified graphite; and introducing a rare gas into a primary purified graphite to repair the graphite lattice.

Claims

1. A method for purification and lattice reconstruction of graphite in a power battery, comprising: (1) subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially to obtain electrode material powder, copper powder, aluminum powder and iron powder, respectively; (2) mixing the electrode material powder with a metal extractant, standing still, then washing with a purifying agent A, filtering to obtain a filter residue A, mixing the filter residue A with the metal extractant, standing still, then washing with a purifying agent B, and filtering to obtain a crude graphite; (3) subjecting the crude graphite to the de-organic treatment, cooling, ball milling, and ventilation replacement to obtain a primary purified graphite; and (4) introducing a rare gas into the primary purified graphite to repair graphite lattice; wherein in step (2), the purifying agent A is a mixed solution of hydrochloric acid, ethanol and acetone, and the purifying agent B is a mixed solution of deionized water, ethanol and acetone.

2. The method for purification and lattice reconstruction of graphite in a power battery of claim 1, wherein the pyrolysis in step (1) is carried out in an oxygen-free environment at a temperature of 350° C.-800° C. for 1-20 h.

3. The method for purification and lattice reconstruction of graphite in a power battery of claim 1, wherein the metal extractant in step (2) is one of a mixed solution of aqua regia and an oxidant, and aqua regia.

4. The method for purification and lattice reconstruction of graphite in a power battery of claim 3, wherein the oxidant is at least one of hydrogen peroxide, sodium peroxide, potassium peroxide, sodium hypochlorite or potassium hypochlorite.

5. The method for purification and lattice reconstruction of graphite in a power battery of claim 1, wherein the de-organic treatment in step (3) comprises placing the crude graphite in a vacuum furnace at a heating rate of 1-5° C./min to be heated to 200° C.-250° C. for the de-organic treatment for 2-4 h.

6. The method for purification and lattice reconstruction of graphite in a power battery of claim 1, wherein the replacement in step (3) comprises introducing a replacement gas at a flow rate of 5-30 mL/min, and then heating to 250° C.-450° C. at a heating rate of 1-5° C./min for replacement for 20-40 min.

7. The method for purification and lattice reconstruction of graphite in a power battery of claim 6, wherein the replacement gas is a gas mixture of H2 and N2.

8. The method for purification and lattice reconstruction of graphite in a power battery of claim 1, wherein the rare gas in step (4) is He with a volumetric purity of 99.999%.

9. The method for purification and lattice reconstruction of graphite in a power battery of claim 1, wherein the repairing graphite lattice in step (4) comprises: introducing a rare gas at a flow rate of 5-30 mL/min within 40-80 min, closing an inlet valve and an outlet valve, and heating to a temperature of 2400° C.-2600° C. at a heating rate of 10-20° C./min, keeping the temperature for 10-30 min, then heating to 2600° C.-3200° C. at a heating rate of 3-10° C./min, and repairing the graphite having damaged lattices within 6-10 h.

10. A graphite produced by: (1) subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially to obtain electrode material powder, copper powder, aluminum powder and iron powder, respectively; (2) mixing the electrode material powder with a metal extractant, standing still, then washing with a purifying agent A, filtering to obtain a filter residue A, mixing the filter residue A with the metal extractant, standing still, then washing with a purifying agent B, and filtering to obtain a crude graphite; (3) subjecting the crude graphite to the de-organic treatment, cooling, ball milling, and ventilation replacement to obtain a primary purified graphite; and (4) introducing a rare gas into the primary purified graphite to repair graphite lattice; wherein in step (2), the purifying agent A is a mixed solution of hydrochloric acid, ethanol and acetone, and the purifying agent B is a mixed solution of deionized water, ethanol and acetone.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:

[0032] FIG. 1 is an SEM image of graphite prepared in Embodiment 1;

[0033] FIG. 2 is a flow chart of a method for purification and lattice reconstruction of graphite in a power battery according to Embodiments 1-3 of the disclosure;

[0034] FIG. 3 is an XRD pattern of graphite prepared in Embodiment 1; and

[0035] FIG. 4 is a graph showing the cycle performance of graphite prepared in Embodiment 1 and Comparative Embodiment 1.

DETAILED DESCRIPTION OF THE INVENTION

[0036] In order to make those skilled in the art more clearly understand the technical solutions of the disclosure, the following embodiments are set forth for description. It should be noted that the following embodiments do not constitute a limitation on the protection scope of the disclosure.

[0037] Unless particularly stated, the raw materials, reagents or devices used in the following embodiments can all be obtained from conventional commercial sources, or can be obtained by existing known methods.

Embodiment 1

[0038] A method for purification and lattice reconstruction of graphite in a power battery of this embodiment includes the following specific steps: [0039] a) subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially to obtain electrode material powder, copper foil, aluminum foil and iron powder, respectively; [0040] b) mixing the electrode material powder with aqua regia having a concentration of 20% and hydrogen peroxide having a concentration of 0.1 mol/L at a solid-liquid ratio of 1:1 in a metal extraction tank and standing still for 4 hours to extract metal elements in the graphite anode, then washing with hydrochloric acid having a concentration of 2%, ethanol, and acetone at a ratio of 1:1:1, filtering to obtain a filter residue A and mixing the filter residue A with aqua regia having a concentration of 10% and hydrogen peroxide having a concentration of 0.05 mol/L at a solid-liquid ratio of 1:1 in a metal extraction tank, and standing still for 4 hours, extracting the metal elements in the graphite anode again, washing the same with deionized water, ethanol and acetone at a ratio of 1:1:1, and filtering to obtain a crude graphite; [0041] c) subjecting the crude graphite to de-organic treatment in a vacuum furnace at 200° C. (with a heating rate of 1° C./min) for 2 h, ball-milling the same at 100 r/min for 20 min after natural cooling, and then placing the de-organized crude graphite in a high-temperature furnace, and introducing a replacement gas (H.sub.2 with a concentration of 2%) at a flow rate of 5 mL/min, then performing replacement at a temperature of 250° C. (with a heating rate of 1° C./min) for 20 min to remove surface adsorbed species; and [0042] d) after the replacement is completed, introducing He with a volumetric purity of 99.999% at a flow rate of 5 mL/min at 250° C. within 40 min, closing an inlet valve and an outlet valve, and heating to a temperature of 2400° C. at a heating rate of 10° C./min, keeping the temperature for 10 min, then heating to 2600° C. at a heating rate of 3° C./min, and repairing the graphite having damaged lattices within 6 h to obtain a battery-grade graphite.

Embodiment 2

[0043] A method for purification and lattice reconstruction of graphite in a power battery of this embodiment includes the following specific steps: [0044] e) subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially to obtain electrode material powder, copper foil, aluminum foil and iron powder, respectively; [0045] f) mixing the electrode material powder with aqua regia having a concentration of 35% and sodium hypochlorite having a concentration of 0.5 mol/L at a solid-liquid ratio of 1:3 in a metal extraction tank and standing still for 8 hours at 25° C. to extract metal elements in the graphite anode, then washing with hydrochloric acid having a concentration of 15%, ethanol, and acetone at a ratio of 1:3:3, filtering to obtain a filter residue A and mixing the filter residue A with aqua regia having a concentration of 20% and sodium hypochlorite having a concentration of 0.15 mol/L at a solid-liquid ratio of 1:3 in the metal extraction tank, and standing still for 8 hours, extracting the metal elements in the graphite anode again, washing the same with deionized water, ethanol and acetone at a ratio of 1:3:3, and filtering to obtain a crude graphite; [0046] g) subjecting the crude graphite to de-organic treatment in a vacuum furnace at 230° C. (with a heating rate of 3° C./min) for 3 h, ball-milling the same at 2000 r/min for 40 min after natural cooling, and then placing the de-organized crude graphite in a high-temperature furnace, and introducing a replacement gas (H.sub.2 with a concentration of 15%) at a flow rate of 5 mL/min, then performing replacement at a temperature of 300° C. (with a heating rate of 3° C./min) for 30 min to remove surface adsorbed species; and [0047] h) after the replacement is completed, introducing He with a purity of 99.999% at a flow rate of 20 mL/min at 300° C. within 60 min, closing an inlet valve and an outlet valve, and heating to a temperature of 2500° C. at a heating rate of 15° C./min, keeping the temperature for 20 min, then heating to 3000° C. at a heating rate of 7° C./min, and repairing the graphite having damaged lattices within 8 h to obtain a battery-grade graphite.

Embodiment 3

[0048] A method for purification and lattice reconstruction of graphite in a power battery of this embodiment includes the following specific steps:

[0049] (1) subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially to obtain electrode material powder, copper foil, aluminum foil and iron powder, respectively;

[0050] (2) mixing the electrode material powder with aqua regia having a concentration of 50% and potassium hypochlorite having a concentration of 1 mol/L at a solid-liquid ratio of 1:5 in a metal extraction tank and standing still for 12 hours to extract metal elements in the graphite anode, then washing with hydrochloric acid having a concentration of 30%, ethanol, and acetone at a mass ratio of 1:5:5, filtering to obtain a filter residue A and mixing the filter residue A with aqua regia having a concentration of 30% and potassium hypochlorite having a concentration of 0.3 mol/L at a solid-liquid ratio of 1:5 in the metal extraction tank, and standing still for 12 hours, extracting the metal elements in the graphite anode again, washing the same with deionized water, ethanol and acetone at a mass ratio of 1:5:5, and filtering to obtain a crude graphite;

[0051] (3) subjecting the crude graphite to de-organic treatment in a vacuum furnace at 250° C. (with a heating rate of 5° C./min) for 4 h, ball-milling the same at 3000 r/min for 60 min after natural cooling, and then placing the de-organized crude graphite in a high-temperature furnace, and introducing a replacement gas (H.sub.2 with a concentration of 30%) at a flow rate of 30 mL/min, then performing replacement at a temperature of 450° C. (with a heating rate of 5° C./min) for 40 min to remove surface adsorbed species; and

[0052] (4) after the replacement is completed, introducing He with a volumetric purity of 99.999% at a flow rate of 20 mL/min at 450° C. within 40 min, closing an inlet valve and an outlet valve, and heating to a temperature of 2600° C. at a heating rate of 15° C./min, keeping the temperature for 30 min, then heating to 3200° C. at a heating rate of 10° C./min, and repairing the graphite having damaged lattices within 10 h to obtain a battery-grade graphite.

Comparative Embodiment 1

[0053] A method for preparing artificial graphite anode material includes the following steps: [0054] i) subjecting a waste power battery to discharging, coarse breaking, pyrolysis, fine breaking and sorting sequentially, taking and leaching an electrode material powder and 0.1 mol/L of sulfuric acid at a solid-liquid volume ratio of 1:5 for 6 hours, then washing with 2% of hydrochloric acid, and filtering to obtain graphite.

[0055] Performance Test:

[0056] The graphite obtained respectively in the above Embodiments 1-3 and Comparative Embodiment 1 was used as the anode, and a lithium sheet was used as the cathode. The graphite and the lithium sheet were assembled into a button battery, and the initial discharge test was carried out at a rate of 1 C. The results are shown in Table 2 and Table 3. It can be seen from Table 1 that the regenerated graphite in Embodiment 2 has low impurity content, and the degree of graphitization reaches 96%, while the degree of graphitization in Comparative Embodiment 1 is only 92%. It can be seen according to Table 2 that, at a rate of 1 C, the initial discharge specific capacity of the regenerated graphite anode material of the disclosure is higher than that of graphite recovered by an ordinary method, and the initial discharge specific capacity of Embodiment 2 is 362.3 mAh/g, while the initial discharge specific capacity of Comparative Embodiment is only 333.1 mAh/g. It can be seen according to Table 3 that, at a rate of 1 C, the cycle life of the regenerated graphite anode material of the disclosure is higher than that of graphite recovered by an ordinary method, and the capacity retention rate of Embodiment 2 after 1600 cycles at 1 C is 96.6%, while the capacity retention rate of Comparative Embodiment 1 is only 92.8%. Table 4 shows the concentration and ash content of the impurity elements obtained in Embodiment 2 and Comparative Embodiment 2 after extracting the metal elements by the acid solution. It can be seen from Table 4 that after two acid extractions in Embodiment 2, the content of metal impurities in graphite is significantly lower than that of metal impurities in Comparative Embodiment 2 after one acid extraction.

[0057] The results are as shown in Table 1:

TABLE-US-00001 TABLE 1 Composition Analysis and Physical Properties of Graphite Embodi- Embodi- Embodi- Comparative Item ment 1 ment 2 ment 3 Embodiment 1 Ash content % 0.046 0.043 0.041 0.088 Moisture % 0.0331 0.0335 0.0329 0.0656 Volatile % 0.0193 0.0198 0.0211 0.0466 D50 μm 18.59 18.61 18.56 18.63 Degree of 95 96 94 92 graphiti- zation % Fixed carbon 99.96 99.98 99.95 99.70 content %

TABLE-US-00002 TABLE 2 Performance of button battery of graphite Embodi- Embodi- Embodi- Comparative Item ment 1 ment 2 ment 3 Embodiment 1 Initial discharge 361.9 362.3 362.1 333.1 specific capacity mAh/g Initial charge- 93.8 93.9 93.9 91.2 discharge efficiency %

TABLE-US-00003 TABLE 3 Full battery cycle performance of graphite Embodi- Embodi- Embodi- Comparative Item ment 1 ment 2 ment 3 Embodiment 1 Discharge capacity 95.9 96.6 96.3 92.8 retention rate % after 1600 cycles at 1 C

TABLE-US-00004 TABLE 4 Impurity content of graphite after metal extraction Impurities Ni Co Mn Li Fe Al Cu Total Ash (%) (%) (%) (%) (%) (%) (%) (%) (%) Embodiment 2 0.001 0.003 0.001 0.001 0.002 0.001 0.001 0.01 0.019 Comparative 0.01 0.008 0.005 0.02 0.05 0.01 0.004 0.107 0.183 Embodiment 2

[0058] From the XRD pattern of the graphite prepared in Embodiment 1 (FIG. 3), it is found that in comparison with PDF #65-6212, the peak at around 26.5° corresponds to the crystal plane (002) of the regenerated graphite in Embodiment 1, which shows that the crystal form of the regenerated graphite sample of Embodiment 1 is better. From the graphs of the cycle performance of the graphite prepared in Embodiment 1 and Comparative Embodiment 1 (FIG. 4), it is found that the capacity and cycle stability of the regenerated graphite of Embodiment 1 are better than those of Comparative Embodiment 1.

[0059] A detailed introduction to a method for purification and lattice reconstruction of graphite in a power battery according to the disclosure is provided above. The principles and implementations of the disclosure are explained by way of specific embodiments herein. The above embodiments are only provided to facilitate the understanding of the method of the disclosure and core concepts thereof, including the best mode, and also enables any person skilled in the art to practice the disclosure, including manufacturing and using any device or system, and implementing any combined method. It should be noted that several improvements and modifications may be made by an ordinary person skilled in the art without departing from the principles of the present disclosure, and that such improvements and modifications also fall within the protection scope of the appended claims of the present disclosure. The scope of patent protection of the disclosure is defined by the claims, and other embodiments conceivable by those skilled in the art may be included. If these other embodiments have structural elements that are not different from the literal expressions of the claims, or if they include equivalent structural elements that are not substantially different from the literal expressions of the claims, these other embodiments should also be included within the scope of the claims.

[0060] Of note, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes”, and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0061] As well, the corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

[0062] Having thus described the invention of the present application in detail and by reference to embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims as follows: