A method for recovering lithium and copper from waste graphite negative electrode and preparing regenerated graphite

Abstract

The present invention relates to a method for recovering lithium and copper from waste graphite negative electrodes and preparing regenerated graphite. Copper and lithium are recovered by directly subjecting waste graphite negative electrodes with copper current collectors to ultrafast high-temperature thermal shock treatment. The waste graphite separated from the copper current collectors is subjected to high-temperature thermal shock treatment to obtain regenerated graphite that can be directly used as a lithium battery negative electrode. The regenerated graphite ultimately obtained by the present invention has a high degree of graphitization and retains some structural defects such as carbon defects and dislocations. This greatly improves the rate performance of the regenerated graphite, demonstrating rate performance superior to that of other regenerated graphites and commercial graphite. At 2C, its charge capacity can reach 323 mAh / g. The entire process can greatly simplify the waste graphite recovery and processing process, significantly reducing both time and energy costs.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode recovery and preparation of regenerated graphite, and in particular to a method for recovering lithium and copper from waste graphite negative electrodes and preparing regenerated graphite. Background Art

[0002] Graphite is widely used as a negative electrode material for lithium-ion batteries due to its excellent structural stability, high reversible capacity, and high conductivity. In recent years, the use of portable devices such as mobile phones and computers, as well as new energy vehicles, has increased dramatically. The replacement of these electronic products and the scrapping of new energy vehicle batteries have resulted in a large amount of waste lithium-ion batteries. In addition to containing a large amount of graphite negative electrode, these waste batteries also contain a large amount of copper, as well as lithium embedded in the negative electrode material during the charge and discharge process. Recycling this valuable element while recycling waste graphite has great practical application.

[0003] Currently, common recycling methods include wet recycling, pyrometallurgical recycling, and mechanical separation. However, wet recycling requires acid treatment, which poses environmental pollution and equipment corrosion issues. Furthermore, the recycled graphite has high impurity content and poor performance. Conventional pyrometallurgical recycling has low recovery rates, is time-consuming, and consumes a lot of energy. Mechanical separation equipment is complex, and the recycled material has poor reusability. Using these methods individually has limited recovery effectiveness, while combining multiple methods significantly increases recycling costs. Furthermore, the performance of the recycled graphite is suboptimal, and the recycled graphite cannot be directly used as a lithium battery anode. Graphite's unique layered structure results in poor high-rate performance, limiting its application as anode for fast-charging lithium-ion batteries. Preserving some defects in graphite can improve the diffusion kinetics of lithium ions at high rates and the phase transition kinetics of graphite during charge and discharge. However, traditional waste graphite regeneration processes require a long time to reach the regeneration temperature and the subsequent graphitization process. During the regeneration of the waste graphite, existing structural defects such as carbon defects and dislocations are eliminated.

[0004] Therefore, there is an urgent need for a method that has low equipment cost, simple operation process, can recover lithium and copper from waste graphite while retaining some defects in the original waste graphite during recycling, and ultimately obtain regenerated graphite with excellent electrochemical properties. Summary of the Invention

[0005] This invention overcomes the shortcomings of other negative electrode recycling processes, which often involve significant environmental pollution, high energy consumption, complex equipment, cumbersome preparation processes, and poor performance of the recycled graphite. It proposes a method for ultrafast recovery of lithium and copper from spent battery graphite negative electrodes and for producing high-power regenerated graphite. This method can extract lithium and copper from lithium battery negative electrodes and regraphitize the spent graphite to produce defect-rich, high-power regenerated graphite with a high degree of graphitization that can be directly utilized. This method can replace traditional negative electrode recycling methods.

[0006] One of the purposes of the present invention is to recover lithium and copper from the negative electrodes of waste lithium-ion batteries.

[0007] The second purpose of the present invention is to recover the graphite negative electrode material and retain some defects in the waste graphite, thereby obtaining a regenerated graphite with a high degree of graphitization and high rate performance and cycle performance that are superior to commercial graphite.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for recovering lithium and copper from waste graphite negative electrodes and preparing regenerated graphite is carried out according to the following steps:

[0010] Step 1: dismantle the waste lithium-ion battery to obtain a graphite negative electrode sheet with a copper current collector;

[0011] Step 2: placing the graphite negative electrode sheet with the copper current collector obtained in step 1 on a heated substrate in a heating device, and subjecting the sheet to a rapid high-temperature thermal shock treatment in a protective atmosphere to separate the graphite and the copper foil, thereby obtaining a solid and flue gas;

[0012] Step 3: Screening the solid with a sieve to obtain primary regenerated graphite and copper foil agglomerated into copper balls; collecting the flue gas to obtain lithium;

[0013] Step 4, washing and filtering the once-regenerated graphite in step 3, separating the filtrate and the filter cake, and drying the filter cake to obtain graphite powder;

[0014] Step 5: placing the graphite powder obtained in step 4 on a heated substrate in a heating device in a protective atmosphere for high-temperature heat treatment to obtain high-power secondary regenerated graphite with excellent graphitization degree, wherein the protective atmosphere is argon, helium or nitrogen; and the waste lithium-ion battery includes a hard-pack lithium battery or a soft-pack lithium battery.

[0015] Furthermore, the waste lithium-ion battery in step 1 includes a hard-pack lithium battery or a soft-pack lithium battery. The waste lithium-ion battery is in a fully charged state, a fully discharged state, or any state in between.

[0016] Furthermore, the protective atmosphere in step 2 and step 5 is argon, helium or nitrogen.

[0017] Furthermore, the heating substrate in step 2 and step 5 can be a series of materials with high melting point and good thermal conductivity, such as carbon cloth, carbon paper, carbon felt, graphite sheet, nickel foil, cobalt foil, stainless steel sheet, etc.

[0018] Furthermore, the heating rate in step 2 and step 5 is 103-105°C / s; the heating treatment temperature is 800-3000°C, and the heating treatment time is 30s-120s.

[0019] Preferably, the heating treatment temperature in step 2 and step 5 is 1500° C., and the heating treatment time is 60 seconds.

[0020] Preferably, the cleaning agent in step 4 is N-methylpyrrolidone (NMP).

[0021] Furthermore, the drying treatment temperature in step 4 is 60-120° C., and the drying time is 8-24 hours.

[0022] A method for preparing regenerated graphite comprises the following steps:

[0023] Step 1: dismantle the waste lithium-ion battery to obtain a graphite negative electrode sheet;

[0024] Step 2: washing the graphite negative electrode sheet, filtering, separating the filtrate and the filter cake, and drying the filter cake to obtain graphite powder;

[0025] Step 3: In a protective atmosphere, the graphite powder obtained in step 2 is subjected to a rapid high-temperature thermal shock treatment to obtain regenerated graphite, wherein the protective atmosphere is argon, helium or nitrogen; and the waste lithium-ion battery includes a hard-pack lithium battery or a soft-pack lithium battery.

[0026] Furthermore, the heating rate of the rapid high-temperature thermal shock treatment in step 3 is 103-105°C / s; the heating treatment temperature is 800-3000°C, and the heating treatment time is 30s-120s.

[0027] Furthermore, the heating treatment temperature of the rapid high-temperature thermal shock treatment in step 3 is 1500° C., and the heating treatment time is 60 seconds.

[0028] Furthermore, the drying treatment temperature in step 2 is 60-120° C., and the drying time is 8-24 hours.

[0029] Furthermore, in step 2, N-methylpyrrolidone (NMP) is used as a cleaning agent for washing.

[0030] The beneficial results of the present invention are:

[0031] 1. It can greatly simplify the waste graphite recycling process, and the time cost and energy cost have been greatly reduced.

[0032] 2. Realize the one-step recovery of lithium and copper while recycling graphite.

[0033] 3. The high-temperature thermal shock method employed in this invention utilizes ultra-fast heating and cooling rates, along with extremely short holding times, to regraphitize the waste graphite while retaining some of the internal defects generated during long charge-discharge cycles, ultimately yielding defect-rich regenerated graphite. The resulting product exhibits electrochemical properties superior to commercial graphite and can be directly used as a graphite negative electrode for high-power lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 (a) is the copper current collector agglomerated into copper balls recovered after sieve screening in the present invention; Figure 1 (b) is the XRD comparison spectrum of waste graphite and primary recycled graphite before and after recovery;

[0035] Figure 2 is the XRD spectrum of lithium recovered in the present invention;

[0036] Figure 3 This is the electrochemical performance diagram of the primary regenerated graphite prepared in the present invention at 0.5C;

[0037] Figure 4 This is the electrochemical performance diagram of the secondary regenerated graphite prepared in the present invention at 0.5C;

[0038] Figure 5 This is a graph of the electrochemical performance of the secondary regenerated graphite prepared in the present invention at 1C;

[0039] Figure 6 is the XRD spectrum of the regenerated graphite prepared by the present invention;

[0040] Figure 7 (a) (b) are SEM images of waste graphite and regenerated graphite prepared in the present invention;

[0041] Figure 8 Raman images of waste graphite and regenerated graphite prepared by the present invention;

[0042] Figure 9 (a) (b) are TEM images of waste graphite and regenerated graphite prepared in the present invention;

[0043] Figure 10 (a) Comparison of the rate performance of the regenerated graphite prepared in the present invention, waste graphite, and commercial graphite; (b) Comparison of the high-rate cycle performance of the regenerated graphite prepared in the present invention and commercial graphite;

[0044] Figure 11 This is the 0.5C long cycle performance of the regenerated graphite prepared by the present invention. DETAILED DESCRIPTION

[0045] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0046] The technical solution of the present invention is further described below through specific embodiments.

[0047] Example 1

[0048] Step 1: dismantle a fully discharged 18650 hard-pack waste lithium-ion battery to obtain a graphite negative electrode sheet with a copper current collector;

[0049] Step 2: Cut the graphite negative electrode sheet with a copper current collector obtained in step 1 into a size of 2*1.5 cm and place it on heated carbon paper in a heating device. Perform a rapid high-temperature thermal shock treatment in an argon atmosphere to obtain a solid and flue gas. The heating rate is 105°C / s, the heating temperature is 1500°C, and the heating time is 60s.

[0050] Step 3, screening the solid with a 300-mesh sieve to obtain primary regenerated graphite and copper foil agglomerated into copper balls; collecting the flue gas to obtain lithium;

[0051] Step 4: adding N-methylpyrrolidone (NMP) to the primary regenerated graphite in step 3, stirring on a magnetic stirrer for 3 hours to wash it, filtering the obtained mixed solution, separating the filtrate and the filter cake, and drying in a blast oven at 100° C. for 18 hours to obtain graphite powder;

[0052] Step 5: Take the graphite powder obtained in step 4, place it on heated carbon paper in a heating device, and perform high-temperature heat treatment in an argon atmosphere to obtain high-power secondary regenerated graphite with excellent degree of graphitization; wherein the heating and cooling rate is 105°C / s, the heating temperature is 1500°C, and the heating time is 60s.

[0053] Figure 1 (a) is the copper current collector agglomerated into copper balls recovered after sieve screening; Figure 1 (b) The lower and upper curves are XRD comparison diagrams of waste graphite and primary recycled graphite before and after recovery, respectively. It can be clearly seen that the copper peak has dropped significantly after treatment in the manner of the present invention, indicating that copper has been well recovered.

[0054] Figure 2 is the XRD of the recovered lithium.

[0055] Figure 3 The electrochemical properties of the once-regenerated graphite obtained in step 3

[0056] In this embodiment, the protective atmosphere may also be helium or nitrogen; the heating substrate may also be a series of materials with high melting point and good thermal conductivity, such as carbon cloth, carbon felt, graphite sheet, nickel foil, cobalt foil, stainless steel sheet, etc.

[0057] Example 2

[0058] Step 1: dismantle a fully charged 18650 hard-pack waste lithium-ion battery to obtain a graphite negative electrode sheet with a copper current collector;

[0059] Step 2: Cut the graphite negative electrode sheet with copper current collector obtained in step 1 into a size of 2*2 cm and place it on heated carbon paper in a heating device. Perform a rapid high-temperature thermal shock treatment in an argon atmosphere to obtain solid and flue gas. The heating rate is 104°C / s, the heating temperature is 3000°C, and the heating time is 30s.

[0060] Step 3, screening the solid with a 300-mesh sieve to obtain primary regenerated graphite and copper foil agglomerated into copper balls; collecting the flue gas to obtain lithium;

[0061] Step 4: adding N-methylpyrrolidone (NMP) to the primary regenerated graphite in step 3, stirring on a magnetic stirrer for 3 hours to wash it, filtering the obtained mixed solution, separating the filtrate and the filter cake, and drying in a blast oven at 120° C. for 8 hours to obtain graphite powder;

[0062] Step 5: Take the graphite powder obtained in step 4, place it on heated carbon paper in a heating device, and perform high-temperature heat treatment in an argon atmosphere to obtain high-power secondary regenerated graphite with excellent degree of graphitization; wherein the heating and cooling rate is 104°C / s, the heating temperature is 3000°C, and the heating time is 30s.

[0063] Figure 4 This is the 0.5C cycle performance of the secondary regenerated graphite prepared in step 5 of this embodiment.

[0064] In this embodiment, the protective atmosphere may also be helium or nitrogen; the heating substrate may also be a series of materials with high melting point and good thermal conductivity, such as carbon cloth, carbon felt, graphite sheet, nickel foil, cobalt foil, stainless steel sheet, etc.

[0065] Example 3

[0066] Step 1: dismantle a half-discharged 18650 hard-pack waste lithium-ion battery to obtain a graphite negative electrode sheet with a copper current collector;

[0067] Step 2: Cut the graphite negative electrode sheet with a copper current collector obtained in step 1 into a size of 2*1.5 cm and place it on heated carbon paper in a heating device. Perform a rapid high-temperature thermal shock treatment in an argon atmosphere to obtain a solid and flue gas. The heating rate is 103°C / s, the heating temperature is 800°C, and the heating time is 120s.

[0068] Step 3, screening the solid with a 300-mesh sieve to obtain primary regenerated graphite and copper foil agglomerated into copper balls; collecting the flue gas to obtain lithium;

[0069] Step 4: adding N-methylpyrrolidone (NMP) to the primary regenerated graphite, stirring on a magnetic stirrer for 3 h to wash it, filtering the obtained mixed solution, separating the filtrate and the filter cake, and drying in a blast oven at 60° C. for 24 h to obtain graphite powder;

[0070] Step 5: Take the graphite powder obtained in step 4, place it on heated carbon paper in a heating device, and perform high-temperature heat treatment in an argon atmosphere to obtain high-power secondary regenerated graphite with excellent degree of graphitization; wherein the heating and cooling rate is 105°C / s, the heating temperature is 800°C, and the heating time is 120s.

[0071] In this embodiment, the protective atmosphere may also be helium or nitrogen; the heating substrate may also be a series of materials with high melting point and good thermal conductivity, such as carbon cloth, carbon felt, graphite sheet, nickel foil, cobalt foil, stainless steel sheet, etc.

[0072] Figure 5 1C cycle performance of the secondary regenerated graphite prepared in step 5 of this embodiment.

[0073] Example 4

[0074] Step 1: dismantling a completely discharged waste lithium-ion battery to obtain a graphite negative electrode sheet;

[0075] Step 2: adding N-methylpyrrolidone (NMP) to the graphite negative electrode sheet obtained in step 1, stirring on a magnetic stirrer for 3 hours to wash it, filtering the obtained mixed solution, separating the filtrate and the filter cake, and drying in a 90° C. forced air oven for 24 hours to obtain graphite powder;

[0076] Step 3: In a protective atmosphere, take the graphite powder obtained in step 2, place it on heated carbon paper in a heating device, and perform high-temperature heat treatment in an argon atmosphere to obtain high-power regenerated graphite with excellent degree of graphitization; wherein the heating and cooling rate is 105°C / s, the heating temperature is 1500°C, and the heating time is 60s.

[0077] In this embodiment, the protective atmosphere may also be helium or nitrogen; the heating substrate may also be a series of materials with high melting point and good thermal conductivity, such as carbon cloth, carbon felt, graphite sheet, nickel foil, cobalt foil, stainless steel sheet, etc.

[0078] Figure 6 This is the XRD pattern of the regenerated graphite obtained in step 3. As shown in the figure, the strongest characteristic peak is located near 26.5°, corresponding to the (002) plane of graphite. This indicates that the regenerated graphite has a good crystal structure.

[0079] Figure 7 The morphology of the waste graphite and the regenerated graphite obtained in step 3 is compared. Figure 7 As shown in (a), the waste graphite has undergone a long-term charge and discharge cycle, and its original large particles have peeled off into small separated particles and aggregated together. Figure 7 As shown in (b), after the regeneration treatment by the method of the present invention, the particle surface of the secondary regenerated graphite becomes smooth and flat without agglomeration.

[0080] Figure 8 The figure shows a comparison of Raman spectra of waste graphite (lower curve) and regenerated graphite (upper curve) obtained in step 3. It can be seen that the ID / IG of the regenerated graphite is smaller than that of the waste graphite, which indicates that the waste graphite is well re-graphitized in the present invention.

[0081] Figure 9 TEM comparison of waste graphite and regenerated graphite obtained in step 3. Figure 9 As shown in (a), waste graphite has many carbon defects and dislocations and other structural defects. Figure 9 As shown in (b), after the regeneration treatment by the method of the present invention, the graphite layer structure becomes better and the number of defects in the regenerated graphite is reduced but still partially retained.

[0082] Figure 10 The electrochemical properties of the regenerated graphite prepared by the present invention are as follows. Figure 10 As shown in (a), the rate performance of the regenerated graphite ("○") is greatly improved compared to that of the waste graphite ("△"), and it shows better electrochemical performance than commercial graphite ("□") at high rates (commercial graphite purchased from CLUDE), especially at 2C. Figure 10 As shown in (b), the recycled graphite still has a capacity retention rate of 100% after 500 cycles and can reach a specific capacity of 323 mAh / g, while the commercial graphite shows a significant performance degradation around 130 cycles and has a specific capacity of only 120 mAh / g after 500 cycles.

[0083] Figure 11 The long cycle performance of the regenerated graphite prepared in the present invention at 0.5C shows that the regenerated graphite prepared in the present invention has very excellent structural stability.

[0084] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

[0085] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for recovering lithium and copper from waste graphite negative electrodes and preparing regenerated graphite, characterized in that: The following steps are involved: Step 1: dismantle the waste lithium-ion battery to obtain a graphite negative electrode sheet with a copper current collector; Step 2: subjecting the graphite negative electrode sheet with the copper current collector obtained in step 1 to a rapid high-temperature thermal shock treatment in a protective atmosphere to separate the graphite and the copper foil to obtain a solid and flue gas, wherein the protective atmosphere is argon, helium or nitrogen; Step 3: Screening the solid to obtain primary regenerated graphite and copper foil agglomerated into copper balls; collecting the flue gas to obtain lithium; Step 4, washing the primary regenerated graphite in step 3, filtering, separating the filtrate and the filter cake, and drying the filter cake to obtain graphite powder; Step 5: In a protective atmosphere, the graphite powder obtained in step 4 is subjected to a rapid high-temperature thermal shock treatment to obtain secondary regenerated graphite, wherein the protective atmosphere is argon, helium or nitrogen; and the waste lithium-ion battery includes a hard-pack lithium battery or a soft-pack lithium battery.

2. The method for recovering lithium and copper from waste graphite negative electrode and preparing regenerated graphite according to claim 1, characterized in that: The heating rate of the rapid high temperature thermal shock treatment in step 2 and step 5 is 10 3 -10 5 ℃ / s; the heating treatment temperature is 800-3000℃, and the heating treatment time is 30s-120s.

3. The method for recovering lithium and copper from waste graphite negative electrode and preparing regenerated graphite according to claim 1, characterized in that: The heating treatment temperature of the rapid high-temperature thermal shock treatment in step 2 and step 5 is 1500° C., and the heating treatment time is 60 seconds.

4. The method for recovering lithium and copper from waste graphite negative electrode and preparing regenerated graphite according to claim 1, characterized in that: The drying temperature in step 4 is 60-120° C., and the drying time is 8-24 hours.

5. The method for recovering lithium and copper from waste graphite negative electrode and preparing regenerated graphite according to claim 1, characterized in that: In step 4, N-methylpyrrolidone (NMP) is used as a cleaning agent for washing.

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