Negative electrode powder recovery method

Abstract

The invention discloses a negative electrode powder recovery method which comprises the following steps: S1, carrying out electrified crushing and drying on a waste lithium battery, and then carrying out winnowing to remove a shell and a diaphragm to obtain a mixture; s2, adding the mixture into water for soaking, carrying out solid-liquid separation, drying and screening to obtain negative electrode powder, and then carrying out color sorting separation on a negative electrode current collector and a positive electrode plate; s3, performing heat treatment on the positive plate, stripping the positive powder, and then screening and separating the positive powder and the positive current collector; and S4, the negative electrode powder obtained in S2 is taken and subjected to acid pickling, water washing and calcination in sequence, then graphene and carbon nanotubes are added for ball milling, and modified graphite is obtained. According to the method, the negative electrode powder, the negative electrode current collector, the positive electrode powder and the positive electrode current collector can be effectively separated, the obtained negative electrode powder has few impurities, the impurities can be removed and the layered structure of graphite can be structured only through simple acid pickling and calcination, so that direct ball milling treatment with graphene and carbon nanotubes is facilitated, and the electrochemical performance of the graphite is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery recycling, and in particular to a method for recycling negative electrode powder. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density and good cycle performance, and have been widely used in various fields. With the arrival of the peak of lithium-ion battery retirement, recycling of waste lithium-ion batteries can protect the environment and save resources.

[0003] At present, the mainstream process of battery recycling is to crush the waste lithium-ion batteries, pyrolyze them at low temperature, and burn them at high temperature to finally obtain a mixture of positive and negative electrode powders, and then recycle lithium, iron, phosphorus, graphite, etc. Since there are many kinds of substances in the positive and negative electrode powders, they will interfere with each other during element recycling, which increases the difficulty of recycling and has a low yield; and the performance of graphite recovered from the negative electrode is low, and its electrochemical performance needs to be improved. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a method for recovering negative electrode powder. The present invention can effectively separate negative electrode powder, negative electrode current collector, positive electrode powder, and positive electrode current collector, and the obtained negative electrode powder has fewer impurities. It only needs to be simply pickled and calcined to remove impurities and can regularize the layered structure of graphite, so as to facilitate direct ball milling treatment with graphene and carbon nanotubes to improve the electrochemical properties of graphite. The whole method is simple and easy to realize industrial production.

[0005] The present invention proposes a method for recovering negative electrode powder, comprising the following steps:

[0006] S1. The waste lithium batteries are electrically crushed, dried, and then the shell and the diaphragm are removed by air separation to obtain a mixed material;

[0007] S2, adding the mixture into water for soaking, solid-liquid separation, drying, sieving to obtain negative electrode powder, and then color sorting to separate the negative electrode current collector and the positive electrode sheet;

[0008] S3, heat-treating the positive electrode sheet, peeling the positive electrode powder, and then sieving and separating the positive electrode powder and the positive electrode current collector;

[0009] S4. The negative electrode powder obtained in S2 is sequentially pickled, washed with water, and calcined, and then graphene and carbon nanotubes are added for ball milling to obtain modified graphite.

[0010] In the above waste lithium batteries, the binder of the negative electrode sheet is a water-soluble binder, and the binder of the positive electrode sheet is a non-water-soluble binder.

[0011] In the above waste lithium battery, the negative electrode current collector is copper foil and the positive electrode current collector is aluminum foil.

[0012] Preferably, in S1, the drying temperature is 80-125°C.

[0013] Preferably, in S1, charged crushing is performed to a particle size of 2-4 cm.

[0014] The present invention crushes waste lithium iron phosphate batteries into suitable sizes, selects a suitable drying temperature to remove the electrolyte, and the binder will not decompose at this temperature, and the positive and negative electrode powders can still be bonded to the collector; then, the shell, the diaphragm and other light impurities can be effectively separated by air separation; after this step of processing, 98-100% of the shell and the diaphragm are effectively separated.

[0015] Preferably, in S2, the soaking temperature is room temperature and the soaking time is 10-30 minutes.

[0016] Preferably, in S2, the stirring speed during soaking is 50-100 r / min.

[0017] According to the different water solubilities of the binders in the positive and negative electrode sheets, the present invention separates the negative electrode powder sheets from the negative electrode current collector (copper foil) by soaking in water, and selects a suitable stirring speed to break the negative electrode powder sheets, while the positive electrode sheets are not separated; then, the negative electrode powder can be separated through a simple screening treatment; after this step, more than 95% of the negative electrode powder is effectively separated, this step is simple to operate and takes very little time, the water is pollution-free and can be reused, and the recycling cost is reduced.

[0018] The remaining copper foil and positive electrode sheet have different colors and can be separated using a color sorter. After this step, more than 95% of the negative electrode current collector is effectively separated.

[0019] Preferably, in S3, the heat treatment temperature is 400-450°C, and the heat treatment time is 1.5-2h.

[0020] Preferably, in S3 , heat treatment is performed in an inert gas atmosphere.

[0021] Preferably, in S3, after the heat treatment, friction is performed to peel the positive electrode powder from the positive electrode current collector.

[0022] The present invention performs heat treatment on the separated positive electrode sheets to decompose the binder in the positive electrode sheets, and then peels the positive electrode powder from the positive electrode current collector (aluminum foil) through friction, and then effectively separates the positive electrode powder and the aluminum foil through screening. After this treatment, more than 95% of the positive electrode powder and the positive electrode current collector are effectively separated.

[0023] Preferably, the negative electrode powder is washed with a sulfuric acid aqueous solution having a mass fraction of 1-3 wt % for 20-40 min.

[0024] Preferably, calcination is carried out in an inert gas atmosphere.

[0025] Preferably, the calcination is carried out at 700-800°C for 8-10 hours.

[0026] Preferably, the weight ratio of the negative electrode powder, graphene and carbon nanotubes is 10:0.4-0.6:0.7-0.9.

[0027] Preferably, ball milling is carried out in an inert gas atmosphere.

[0028] Preferably, the ball milling time is 2.5-3 h, and the ball milling speed is 250-300 r / min.

[0029] The present invention sequentially performs acid washing and water washing on the separated negative electrode powder to remove a small amount of impurity elements such as Li, Fe, and P contained in the negative electrode powder, thereby improving the purity of graphite, and then performs calcination treatment on the graphite to remove the attachments on the surface of the graphite, and makes the layered structure of the graphite regular, and then performs ball milling treatment with an appropriate amount of graphene and carbon nanotubes, so that the layered graphite, the flaky graphene and the tubular carbon nanotubes form a multidimensional conductive network, thereby greatly improving the conductivity of the graphite, and the multidimensional conductive network can provide more space for contact with the electrolyte, increase more ion paths, and improve Li + The insertion and extraction speed of graphite can be increased, thereby improving the electrochemical performance of graphite.

[0030] The negative electrode powder recovered by the method of the present invention has less impurities introduced, and only needs to be simply pickled and calcined to remove the impurities and regularize the layered structure of graphite, so as to facilitate direct ball milling with graphene and carbon nanotubes and improve the electrochemical performance of graphite; the whole method is simple and easy to realize industrial production.

[0031] The method of the present invention is simple to operate, pollution-free, has a short separation cycle, low recovery cost, high separation efficiency, and can effectively separate negative electrode powder, negative electrode current collector, positive electrode powder, and positive electrode current collector, thereby avoiding the problem of mutual interference between the positive and negative electrode powder mixtures obtained in the existing process during element recovery, thereby increasing the difficulty of recovery and leading to a low element recovery rate. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described in detail below through specific embodiments.

[0033] Example 1

[0034] A method for recycling negative electrode powder comprises the following steps:

[0035] S1. The waste lithium batteries are charged and crushed to a particle size of 2 cm, and then transferred to a low-temperature volatilization furnace, dried at 80°C, and the shell, diaphragm, and tape are removed by air separation to obtain a mixed material; 99.5% of the shell, diaphragm, and tape are removed;

[0036] S2. Add the mixture into the hydrodynamic sorting equipment, soak it in water for 10 minutes at room temperature, and keep the stirring speed at 50r / min during soaking, filter, dry, and sieve to obtain negative electrode powder, and then use a color sorter to separate the positive electrode sheet and the yellow copper foil; 98% of the negative electrode powder is separated, and 97% of the copper foil is separated;

[0037] S3, taking the positive electrode sheet and heat treating it at 450°C for 1.5h under nitrogen protection, then rubbing the positive electrode powder to peel it off from the positive electrode current collector, and then sieving and separating the positive electrode powder and aluminum foil; 96% of the positive electrode powder and aluminum foil were separated;

[0038] S4. Take the negative electrode powder obtained in S2 and add a 3wt% sulfuric acid aqueous solution to wash the negative electrode powder for 20 minutes. After filtering, wash it with water twice, and then calcine it at 800°C for 8 hours in a nitrogen atmosphere. Then add graphene and carbon nanotubes, and adjust the ball mill speed to 300r / min and the ball-to-material ratio to 10:1 in a nitrogen atmosphere. Ball mill for 2.5 hours to obtain modified graphite, wherein the weight ratio of the negative electrode powder, graphene, and carbon nanotubes is 10:0.6:0.7.

[0039] Example 2

[0040] A method for recycling negative electrode powder comprises the following steps:

[0041] S1. The waste lithium batteries are charged and crushed to a particle size of 4 cm, and then transferred to a low-temperature volatilization furnace, dried at 125°C, and the shell, diaphragm, and tape are removed by air separation to obtain a mixed material; 99.8% of the shell, diaphragm, and tape are removed;

[0042] S2. Add the mixture into the hydrodynamic sorting equipment, soak it in water for 30 minutes at room temperature, and keep the stirring speed at 100r / min during soaking, filter, dry, and sieve to obtain negative electrode powder, and then use a color sorter to separate the positive electrode sheet and the yellow copper foil; 98.5% of the negative electrode powder is separated, and 97.4% of the copper foil is separated;

[0043] S3, taking the positive electrode sheet and heat treating it at 400°C for 2h under nitrogen protection, then rubbing the positive electrode powder to peel it off from the positive electrode current collector, and then sieving and separating the positive electrode powder and aluminum foil; 96.3% of the positive electrode powder and aluminum foil were separated;

[0044] S4. Take the negative electrode powder obtained in S2 and add a 1wt% sulfuric acid aqueous solution to wash the negative electrode powder for 40 minutes. After filtering, wash it with water twice, and then calcine it at 700°C for 10 hours in a nitrogen atmosphere. Then add graphene and carbon nanotubes, and adjust the ball mill speed to 250r / min and the ball-to-material ratio to 10:1 in a nitrogen atmosphere. Ball mill for 3 hours to obtain modified graphite, wherein the weight ratio of the negative electrode powder, graphene, and carbon nanotubes is 10:0.4:0.9.

[0045] Example 3

[0046] A method for recycling negative electrode powder comprises the following steps:

[0047] S1. The waste lithium batteries are charged and crushed to a particle size of 3 cm, and then transferred to a low-temperature volatilization furnace, dried at 90°C, and the shell, diaphragm, and tape are removed by air separation to obtain a mixed material; 99.8% of the shell, diaphragm, and tape are removed;

[0048] S2. Add the mixture into the hydrodynamic sorting equipment, soak it in water for 20 minutes at room temperature, and keep the stirring speed at 80r / min during soaking, filter, dry, and sieve to obtain negative electrode powder, and then use a color sorter to separate the positive electrode sheet and the yellow copper foil; 99.1% of the negative electrode powder is separated, and 97.8% of the copper foil is separated;

[0049] S3, taking the positive electrode sheet and heat treating it at 430°C for 1.7h under nitrogen protection, then rubbing the positive electrode powder to peel it off from the positive electrode current collector, and then sieving and separating the positive electrode powder and aluminum foil; 97.2% of the positive electrode powder and aluminum foil were separated;

[0050] S4. Take the negative electrode powder obtained in S2, add a 2wt% sulfuric acid aqueous solution to wash the negative electrode powder for 30 minutes, filter, wash with water twice, and then calcine at 750°C for 9 hours in a nitrogen atmosphere, then add graphene and carbon nanotubes, and adjust the ball mill speed to 280r / min and the ball-to-material ratio to 10:1 in a nitrogen atmosphere, and ball mill for 2.8 hours to obtain modified graphite, wherein the weight ratio of the negative electrode powder, graphene, and carbon nanotubes is 10:0.5:0.8.

[0051] Comparative Example 1

[0052] In S1, the waste lithium batteries are electrically crushed to a particle size of 10 cm, and the rest is the same as in Example 3, except that only 90.2% of the shell, the diaphragm, and the tape are removed.

[0053] Comparative Example 2

[0054] The stirring speed during immersion in S2 is 150 r / min, and the other parts are the same as those in Example 3. The obtained negative electrode powder contains part of positive electrode powder, and the aluminum foil shed from the positive electrode powder will cause interference in the color sorting and separation of copper foil.

[0055] Comparative Example 3

[0056] No graphene is added to S4, and the rest is the same as in Example 3.

[0057] Comparative Example 4

[0058] No carbon nanotubes are added to S4, and the rest is the same as in Example 3.

[0059] Comparative Example 5

[0060] S4 is not subjected to calcination treatment, and the rest is the same as in Example 3.

[0061] Comparative Example 6

[0062] In S4, the negative electrode powder obtained in S2 is added with a 2 wt % sulfuric acid aqueous solution to wash the negative electrode powder for 30 min, filtered, washed twice with water, and then calcined at 750° C. for 9 h in a nitrogen atmosphere to obtain modified graphite. The rest is the same as in Example 3.

[0063] The modified graphites obtained in Examples 1-3 and Comparative Examples 3-6 were used to make lithium-ion batteries in the same manner, and their electrochemical properties were tested. The results are shown in Table 1.

[0064] The manufacturing method of the lithium-ion battery is as follows: modified graphite, conductive carbon black SuperP, and PVDF are mixed in a weight ratio of 90:2:8, and prepared into a slurry with N-methylpyrrolidone; then coated on the surface of the copper foil, dried, roll-dried, and cut to obtain a circular negative electrode sheet with a diameter of 16 mm, a metal lithium sheet is used as the positive electrode, and a 1 mol / L LiPF6 solution is selected as the electrolyte, and assembled into a CR2025 button battery.

[0065] Table 1 Test results

[0066] Test items First discharge capacity (mAh / g) 0.1C cycle 100 times capacity retention rate (%) Example 1 400 94.2 Example 2 405 95.1 Example 3 409 95.7 Comparative Example 3 381 89.8 Comparative Example 4 375 89.0 Comparative Example 5 370 85.6 Comparative Example 6 364 85.8

[0067] It can be seen from Table 1 that the modified graphite prepared by the method of the present invention has good electrochemical properties.

[0068] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for recovering negative electrode powder, characterized in that: The steps include: S1. The waste lithium batteries are electrically crushed, dried, and then the shell and the diaphragm are removed by air separation to obtain a mixed material; S2, adding the mixture into water for soaking, solid-liquid separation, drying, sieving to obtain negative electrode powder, and then color sorting to separate the negative electrode current collector and the positive electrode sheet; S3, heat-treating the positive electrode sheet, peeling the positive electrode powder, and then sieving and separating the positive electrode powder and the positive electrode current collector; S4. The negative electrode powder obtained in S2 is sequentially pickled, washed with water, and calcined, and then graphene and carbon nanotubes are added for ball milling to obtain modified graphite.

2. The negative electrode powder recovery method according to claim 1, characterized in that: In S1, the drying temperature is 80-125°C; preferably, in S1, charged crushing is performed to a particle size of 2-4 cm.

3. The negative electrode powder recovery method according to claim 1 or 2, characterized in that: In S2, the soaking temperature is room temperature, and the soaking time is 10-30 min; preferably, in S2, the stirring speed during soaking is 50-100 r / min.

4. The negative electrode powder recovery method according to any one of claims 1 to 3, characterized in that: In S3, the heat treatment temperature is 400-450°C, and the heat treatment time is 1.5-2h; preferably, in S3, the heat treatment is performed in an inert gas atmosphere.

5. The negative electrode powder recovery method according to any one of claims 1 to 4, characterized in that: In S3, after the heat treatment, friction is performed to peel the positive electrode powder from the positive electrode current collector.

6. The negative electrode powder recovery method according to any one of claims 1 to 5, characterized in that: The negative electrode powder is washed with a sulfuric acid aqueous solution with a mass fraction of 1-3wt% for 20-40min.

7. The negative electrode powder recovery method according to any one of claims 1 to 6, characterized in that: Calcination is carried out in an inert gas atmosphere; preferably, calcination is carried out at 700-800° C. for 8-10 h.

8. The negative electrode powder recovery method according to any one of claims 1 to 7, characterized in that: The weight ratio of negative electrode powder, graphene and carbon nanotubes is 10:0.4-0.6:0.7-0.

9.

9. The negative electrode powder recovery method according to any one of claims 1 to 8, characterized in that: Ball milling was performed under an inert gas atmosphere.

10. The negative electrode powder recovery method according to any one of claims 1 to 9, characterized in that: The ball milling time is 2.5-3h, and the ball milling speed is 250-300r / min.