A regeneration and repair method for recycled graphite

Abstract

The present invention discloses a regeneration and repair method for recycled graphite, wherein the recycled retired batteries are subjected to discharge disassembly, component classification, and mechanical coarse crushing to obtain recycled graphite powder, and the large particles that may exist in the recycled graphite powder are removed by crushing and screening, and then the recovered graphite powder is sequentially subjected to microwave acid leaching, mechanical solid-phase coating with a specific coating agent, ultrasonic cleaning and drying, graphitization, and screening to prepare the obtained repaired graphite. The special coating agent provided by the present invention is used, and after the coating agent is evenly wrapped on the recycled graphite by a multi-layer coating method, the defects of the recycled graphite are filled and repaired by the high-temperature action of graphitization. The method of the present invention is simple in route, and the performance of the graphite after repair is excellent. It can remove impurities in the retired graphite more thoroughly, and is of great help for structural reconstruction. The graphite capacity can be increased to 350mAh / g, and its electrical performance can also be restored to the level before retirement.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to the regeneration of graphite, in particular to a method for regenerating and repairing recycled graphite used in the regeneration and repair of graphite negative electrode materials of retired lithium-ion batteries. Background Art

[0002] The lithium-ion battery industry is gaining popularity year by year due to factors such as the "dual carbon" issue. Batteries contain a large amount of non-renewable resources, and recycling and reusing these resources has become increasingly urgent.

[0003] The common graphite recycling and repair process involves recovery, sorting, screening, pickling, drying, and heat treatment. This process is effective for graphite recovery. Pickling removes copper and aluminum foil debris from the negative electrode, and heat treatment decomposes the binder. Several patents utilize multi-step heat treatments to repair the graphite structure at high temperatures. This process is simple and easy to commercialize. However, the graphite in retired batteries contains a high concentration of impurities, resulting in severe structural damage. The embedded SEI film and solvent molecules alter the graphite's properties. Therefore, low-temperature heat treatment alone is unlikely to restore the negative electrode graphite in retired batteries to battery-grade quality.

[0004] Graphite is widely used as anode material in lithium-ion batteries due to its low price, simple synthesis process, suitable interlayer spacing, and porous structure. However, graphite from retired lithium-ion batteries suffers from numerous defects, such as cracks and shedding, severe structural damage, and a high number of embedded impurities, which affect the performance of recycled graphite. Summary of the Invention

[0005] To address the above issues, the present invention provides a method for regenerating and repairing graphite. This method regenerates and repairs the graphite negative electrode material from retired lithium-ion batteries, using a simple process and resulting in excellent performance. The method can thoroughly remove impurities from retired graphite and significantly aids in structural reconstruction, increasing the graphite capacity to 350 mAh / g while restoring its electrical performance to pre-retirement levels.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a regeneration and repair method for recycled graphite, which comprises the following steps:

[0008] 1) Recycle the battery and perform rough processing to obtain positive electrode sheets, negative electrode sheets, separators, and aluminum shells / aluminum-plastic films;

[0009] 2) immersing the negative electrode sheet obtained in step 1) in a DMC solution, washing multiple times and then drying, mechanically crushing to obtain copper foil and recovered graphite, and sieving to obtain recovered graphite powder;

[0010] 3) subjecting the recovered graphite powder obtained in step 2) to microwave acid leaching in an acid solution to obtain purified graphite;

[0011] 4) preparing a solution containing a coating agent;

[0012] 5) pressing the purified graphite obtained in step 3) into a graphite sheet, uniformly coating the coating agent solution obtained in step 4), laminating another graphite sheet on the coating, and so on, finally pressing to obtain a graphite thin layer;

[0013] 6) ultrasonically cleaning the graphite thin layer obtained in step 5) in deionized water and drying;

[0014] 7) crushing the graphite thin layer treated in step 6), heating and keeping it warm for a period of time under a nitrogen atmosphere, and finally cooling it to room temperature;

[0015] 8) The graphite treated in step 7) is sieved multiple times to obtain a repaired graphite material.

[0016] In this technical solution, graphite materials are widely used as negative electrode materials for lithium-ion batteries due to their low price, simple synthesis process, suitable interlayer spacing, and porous structure. Many defects of retired lithium-ion battery graphite, such as many cracks and shedding, serious structural damage, and many embedded impurities, affect the performance of recycled graphite. The route of the present invention is as follows: first, the recycled retired batteries are discharged and disassembled, the components are classified, and mechanically crushed to obtain recycled graphite powder. The large particles that may exist in the recycled graphite powder are removed by crushing and screening. Then, the recovered graphite powder is sequentially subjected to microwave acid leaching, mechanical solid-phase coating with a specific coating agent, ultrasonic cleaning and drying, graphitization, and screening to prepare the resulting repaired graphite. The special coating agent provided by the present invention is used, and after the coating agent is evenly wrapped on the recycled graphite by a multi-layer coating method, the defects of the recycled graphite are filled and repaired by the high temperature effect of graphitization. The acid solution for microwave acid leaching of graphite can be hydrochloric acid, nitric acid, hydrofluoric acid, or a mixture of multiple acids, with a total concentration of 5-15%. The acid used in the present invention is a commonly used hydrochloric acid solution.

[0017] As a preferred embodiment of the present invention, in step 2), the negative electrode sheet is immersed in the DMC solution for 0.1-1 h, and the drying temperature is 70-90° C.; the graphite powder is recovered by passing through a 150-200 mesh sieve.

[0018] As a preferred embodiment of the present invention, in step 3), the acid solution is hydrochloric acid, nitric acid, hydrofluoric acid or a mixture of multiple acids, with a total concentration of 5-15%; the solid-liquid ratio is 1:1-5, the stirring speed is 500±200rpm, and the temperature of the acid solution is 80-120°C.

[0019] As a preferred embodiment of the present invention, in step 4), the method for preparing a solution containing a coating agent is as follows: dissolving polymethyl methacrylate in N-methyl-2-pyrrolidone at a solid-to-liquid ratio of 1:2-5, stirring at a speed of 100-200 rpm, stirring for 2 hours until completely dissolved, adding 1-5% by weight of sodium dodecylsulfonate emulsifier and continuing to stir for 1 hour until completely emulsified, the emulsifier includes sodium stearate, calcium dodecylbenzenesulfonate or soap; transferring the emulsion to a water bath, adjusting the temperature to 80-85°C, and gradually adding 1 Mol / L ammonium persulfate solution while stirring continuously for 2 hours to obtain a solution containing a coating agent.

[0020] As a preferred embodiment of the present invention, in step 5), the pressure for pressing the graphite sheet is 1000N, and the thicknesses of the graphite sheet are 10μm, 30μm and 50μm respectively; the pressure for pressing the graphite thin layer is 2000-3000N, and the thickness of the graphite thin layer is 30-150μm.

[0021] As a preferred embodiment of the present invention, in step 5), the coating speed is 0.5-1.5 m / min.

[0022] As a preferred embodiment of the present invention, in step 6), the solid-liquid ratio of the graphite thin layer to deionized water is 1:5-10, ultrasonic cleaning is performed for 0.5-1.5 hours, the ultrasonic frequency is 8-12 kHz; the drying temperature is 75-85°C, and the drying time is 2.5-3.5 hours.

[0023] As a preferred embodiment of the present invention, in step 7), the heating rate is 5-10°C / min, and the temperature is raised to 2750-2850°C and then kept at this temperature for 40-56 hours.

[0024] As a preferred embodiment of the present invention, in step 8), the repaired graphite material is obtained by sequentially passing through two layers of 200-mesh sieves and one layer of 325-mesh sieves.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The coating method of the coating agent of the present invention is simple, which improves the utilization value of the recycled graphite and expands the use scenarios of the recycled graphite.

[0027] 2) The method of the present invention is simple in route, and the performance of the graphite after repair is excellent. It can remove impurities in retired graphite more thoroughly and is of great help in structural reconstruction. The capacity of graphite can be increased to 350mAh / g, and its electrical performance can also be restored to the level before retirement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, purpose and efficacy of the present invention easy to understand, the present invention is further described below in conjunction with specific examples, but the following examples are only preferred embodiments of the present invention, not all. Based on the examples in the embodiments, other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention. The experimental methods in the following examples, unless otherwise specified, are conventional methods, and the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0030] Example 1

[0031] See also Figure 1 This embodiment provides a method for regenerating and repairing recycled graphite, comprising the following steps:

[0032] Step 1: Rough processing of recycled batteries

[0033] The recycled lithium-ion batteries were placed in a 0.1Mol / L NaCl solution for 1 hour and then discharged. After drying, the batteries were disassembled and separated into the positive and negative electrodes, separators, and aluminum shells / aluminum-plastic films.

[0034] Step 2: Crushing and screening

[0035] The negative electrode sheet obtained in step 1 was immersed in DMC solution, washed with deionized water several times after 0.5 h, dried at 80° C., and mechanically crushed to obtain copper foil and recovered graphite powder. The powder was passed through two layers of 150-200 mesh screens to remove large particles.

[0036] Step 3: Microwave Acid Leaching

[0037] The recovered powder obtained in step 2 was transferred to a reactor with a solid-liquid ratio of 1:(1-5), a stirring speed of (500±200) rpm, a suitable temperature of (80-120)°C, and the reactor was placed in a microwave device and stirred for 1 hour to obtain purified graphite.

[0038] Step 4: Prepare the coating agent

[0039] Dissolve an appropriate amount of polymethyl methacrylate in N-methyl-2-pyrrolidone at a solid-to-liquid ratio of 1:(2-5) at a stirring speed of (100-200) rpm. Stir for 2 hours until completely dissolved. Add (1-5)% by weight of sodium dodecylsulfonate emulsifier (e.g., sodium stearate, calcium dodecylbenzenesulfonate, soap, etc.) and continue stirring for 1 hour until completely emulsified. Transfer the emulsion to a water bath, adjust the temperature to (80-85)°C, and gradually add 1 mol / L ammonium persulfate solution while stirring continuously for 2 hours to obtain a mixed solution.

[0040] Step 5: Solid Phase Coating

[0041] Take the graphite powder obtained in step 3 and two pieces of flat glass, set a pressure of 1000N, press the graphite powder into a graphite sheet, and also use this method to prepare multiple pieces for standby use. The thickness of the graphite sheets is 10μm, 30μm, and 50μm, respectively, with 3 sheets of each thickness. After taking a 10μm thick sheet and placing it on an automatic coating machine, take the mixed solution obtained in step 4 and evenly apply it on the graphite sheet at a speed of 1m / min. The solution coating thickness is about 10μm. Take another 10μm thick graphite sheet and fit it on top of the solution coating. Continue to apply an equal amount of solution on the surface at the same speed. Then take another 10μm thick graphite sheet and place it on top of the solution coating. At this time, remove the resulting mixed coating sheet, place it between the flat glass, set a pressure of (2000-3000)N, and press it into a graphite thin layer with a thickness of about 30μm.

[0042] Step 6: Ultrasonic cleaning and drying

[0043] Place the thin layer obtained in step 5 in a beaker and add deionized water at a solid-to-liquid ratio of 1:(5-10). Ultrasonic cleaning is performed for 1 hour at a frequency of 10 kHz. After cleaning, remove the thin layer, place it in a drying dish, seal it, and place it in an oven at 80°C for 3 hours.

[0044] Step 7: Graphitization

[0045] Place the graphite layer obtained in step 6 in a mortar and grind at low speed until it is pulverized to obtain graphite layer powder. The powder is placed in an Acheson furnace, filled with nitrogen, and heated at a rate of (5-10)°C / min to 2800°C and maintained for 48 hours. Then cool to room temperature in air.

[0046] Step 8: Sieving

[0047] The graphite obtained in step 7 is sequentially passed through two layers of 200-mesh sieves and one layer of 325-mesh sieve to obtain the final repaired graphite material.

[0048] Example 2

[0049] The difference from Example 1 is that in step 5, the thickness of the first, third and fifth graphite sheets is 10 μm, the thickness of the solution coating is increased to 20 μm, the pressure remains unchanged, and the thickness of the final pressed mixed graphite layer is about 40 μm.

[0050] Example 3

[0051] The difference from Example 1 is that in step 5, the thickness of the first, third and fifth graphite sheets is 30 μm, the thickness of the solution coating remains unchanged, and the thickness of the final pressed mixed graphite layer is about 100 μm.

[0052] Example 4

[0053] The difference from Example 1 is that in step 5, the thickness of the first, third and fifth graphite sheets is 50 μm, the thickness of the solution coating remains unchanged, and the thickness of the final pressed mixed graphite layer is about 150 μm.

[0054] Comparative Example 1

[0055] Steps 1-3 are the same as in Example 1.

[0056] Step 4: Carbon Coating

[0057] The acid-washed graphite obtained in step 3 was placed in a beaker, and 1% by weight of petroleum asphalt was added into the same beaker and mixed evenly.

[0058] The graphitization screening process is the same as steps 7-8 of Example 1.

[0059] Comparative Example 2

[0060] Steps 1-4 are the same as in Example 1.

[0061] Step 5: Solid Phase Coating

[0062] Take the graphite powder obtained in step 3 and two pieces of flat glass, set a pressure of 1000N, and press the graphite powder into a graphite sheet with a thickness of 10μm3. After taking one piece and placing it on an automatic coating machine, take the mixed solution obtained in step 4 and evenly apply it on the graphite sheet at a speed of 1m / min. The solution coating thickness is about 10μm. Take another 10μm thick graphite sheet and stick it on top of the solution coating. Repeat the coating and graphite sheet operation twice in the same way. At this time, remove the obtained mixed coating sheet, place it between the flat glass, set a pressure of (2000-3000)N, and press it into a thin graphite layer with a thickness of about 50μm.

[0063] The remaining steps are the same as in Example 1.

[0064] The graphites obtained from the above four examples and two comparative examples were assembled into button cells and then subjected to gram capacity testing. The capacity data are shown in Table 1.

[0065] Table 1. Capacity data

[0066] Sample number Gram capacity (mAh / g) First effect (%) Example 1 355 92 Example 2 355 91 Example 3 352 90 Example 4 352 90 Comparative Example 1 342 89 Comparative Example 2 350 91

[0067] As can be seen from Table 1, the use of a specific coating agent solid-phase coating method in Examples 1-4 improves both the capacity and initial efficiency of the repaired graphite. When the thickness of the graphite sheet and the coating layer is 1:1 during the mixed coating, the initial efficiency is at a high level. Increasing the coating thickness or the thickness of the graphite sheet has no effect on improving the capacity of the final product. Comparison of Example 1 with Comparative Example 2 reveals that the number of coating layers during solid-phase coating is controlled within an appropriate range. More layers are not necessarily better. Adjusting the relationship between the number of layers and coating thickness is necessary to achieve a more optimal solution.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for regenerating and repairing recycled graphite, characterized in that: The regeneration and repair method comprises the following steps: 1) Recycle the battery and perform rough processing to obtain positive electrode sheets, negative electrode sheets, separators, and aluminum shells / aluminum-plastic films; 2) immersing the negative electrode sheet obtained in step 1) in a DMC solution, washing multiple times and then drying, mechanically crushing to obtain copper foil and recovered graphite, and sieving to obtain recovered graphite powder; 3) subjecting the recovered graphite powder obtained in step 2) to microwave acid leaching in an acid solution to obtain purified graphite; the acid solution is hydrochloric acid, nitric acid, hydrofluoric acid, or a mixture of multiple acids, with a total concentration of 5-15%; the solid-liquid ratio is 1:1-5, the stirring speed is 500±200 rpm, and the temperature of the acid solution is 80-120°C; 4) Preparing a solution containing a coating agent; the method for preparing the solution containing the coating agent is as follows: dissolving polymethyl methacrylate in N-methyl-2-pyrrolidone at a solid-to-liquid ratio of 1:2-5, stirring at a speed of 100-200 rpm, stirring for 2 hours until completely dissolved, adding 1-5% by weight of sodium dodecylsulfonate emulsifier and continuing to stir for 1 hour until completely emulsified; the emulsifier includes sodium stearate, calcium dodecylbenzenesulfonate, or soap; transferring the emulsion to a water bath, adjusting the temperature to 80-85°C, and gradually adding 1 mol / L ammonium persulfate solution while stirring continuously for 2 hours to obtain a solution containing the coating agent; 5) pressing the purified graphite obtained in step 3) into a graphite sheet, uniformly coating the coating agent solution obtained in step 4), laminating another graphite sheet on the coating, and so on, finally pressing to obtain a graphite thin layer; 6) ultrasonically cleaning the graphite thin layer obtained in step 5) in deionized water and drying; 7) crushing the graphite thin layer treated in step 6), heating the mixture to 2750-2850°C at a rate of 5-10°C / min under a nitrogen atmosphere, holding the temperature for 40-56 hours, and finally cooling the mixture to room temperature; 8) The graphite treated in step 7) is sieved multiple times to obtain a repaired graphite material.

2. A method for regenerating and repairing recycled graphite according to claim 1, characterized in that: In step 2), the negative electrode sheet is immersed in the DMC solution for 0.1-1 h, and the drying temperature is 70-90° C.; the recovered graphite powder is passed through a 150-200 mesh sieve.

3. The method for regenerating and repairing recycled graphite according to claim 1, wherein: In step 5), the pressure for pressing the graphite sheets is 1000N, and the thicknesses of the graphite sheets are 10μm, 30μm and 50μm respectively; the pressure for pressing the graphite thin layer is 2000-3000N, and the thickness of the graphite thin layer is 30-150μm.

4. The method for regenerating and repairing recycled graphite according to claim 1, wherein: In step 5), the coating speed is 0.5-1.5 m / min.

5. The method for regenerating and repairing recycled graphite according to claim 1, wherein: In step 6), the solid-liquid ratio of the graphite thin layer to deionized water is 1:5-10, ultrasonic cleaning is performed for 0.5-1.5 hours, the ultrasonic frequency is 8-12 kHz; the drying temperature is 75-85° C., and the drying time is 2.5-3.5 hours.

6. The method for regenerating and repairing recycled graphite according to claim 1, characterized in that: In step 8), the repaired graphite material is obtained by sequentially passing through two layers of 200-mesh sieves and one layer of 325-mesh sieves.

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