Method for stripping attenuation layer of waste lithium ion positive electrode material and recycling method of waste lithium ion positive electrode material

Abstract

The invention discloses a method for stripping an attenuation layer of a waste lithium ion positive electrode material and recycling of the attenuation layer, and belongs to the technical field of lithium ion batteries, and the specific method comprises the following steps: pretreating the waste lithium ion positive electrode material, dispersing the pretreated waste lithium ion positive electrode material into a solvent, and performing ultrasonic dispersion vibration to obtain the attenuation layer of the waste lithium ion positive electrode material; and then putting the material subjected to ultrasonic dispersion vibration into a ball milling tank, adding a ball milling medium, carrying out ball milling, taking out the material subjected to ball milling, carrying out ultrasonic dispersion vibration again, and then filtering, drying and screening to obtain the recycled positive electrode material. The method is simple in process, the adaptability of the waste positive electrode material is high, and the utilization efficiency of the waste positive electrode material is finally improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more specifically, to a method for stripping the attenuation layer of waste lithium-ion cathode materials and its reuse. Background Art

[0002] Due to its advantages such as high energy density, long cycle life, and low self-discharge rate, lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems, especially ternary lithium batteries. The ternary cathode material has a high energy density and is currently the first choice for power batteries of new energy vehicles. However, after long-term cycling, the capacity of ternary lithium batteries will decay. The main reasons are particle microcracks, lithium-ion deficiency, and cation mixing. The ternary cathode material is composed of nanoscale primary particles aggregated into secondary particles. During the charge and discharge process, due to the shrinkage and expansion of the unit cell, microcracks are generated in the secondary particles and even primary particles fall off. The surface microcracks increase the charge and discharge interface and internal resistance, thereby reducing the capacity and efficiency of the battery. At the same time, during long-term charge and discharge, lithium ions in the crystal structure of the surface layer of the ternary cathode material are deficient and cation mixing occurs, changing from the original layered structure to a spinel and rock salt phase structure, making lithium ions unable to enter the crystal structure again, resulting in battery capacity decay. Due to differences in ternary cathode raw materials, battery working conditions, etc., there are huge differences in the number of microcracks, lithium-ion deficiency, cation mixing degree, and residual capacity of the recycled waste ternary cathode materials, making it difficult to achieve batch precision regeneration when recycling waste ternary cathode materials due to poor raw material adaptability.

[0003] Currently, the recycling methods of waste ternary cathode materials mainly adopt wet processes. Usually, acid leaching, alkali leaching, etc. are used to transfer valuable metal elements from the waste cathode materials into the solution, and then methods such as precipitation, extraction, and ion exchange are used to separate and purify the valuable metals. The wet process has high leaching efficiency, and the recovered valuable metal grades and recovery rates are both relatively high, so it has been widely studied. However, the wet process has a cumbersome recycling process, high recycling costs, complex components of the leaching solution obtained, and a large content of impurity metals. In addition, the wet process requires the use of a large amount of acids and alkalis and will generate a large amount of wastewater, which not only has high costs, but also corrodes equipment and damages the environment. The direct regeneration method has the characteristics of simple process and low energy consumption compared with the wet recycling method, but the direct regeneration method is not yet mature at present and has high requirements for waste cathode materials.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a regeneration method for waste ternary cathode materials with simple process, strong adaptability, and environmental friendliness. Summary of the Invention

[0005] In view of this, the present invention provides a method for stripping and reusing the attenuation layer of waste lithium-ion cathode materials. By controlling the ultrasonic vibration and the ball-to-material ratio, ball milling time, and ball milling medium during ball milling, the attenuation layer caused by cation mixing, structural transformation, ion deficiency, microcracks, etc. is removed. The cathode material after screening, filtration, and drying is used to prepare batteries.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] First, the present application provides a method for stripping the attenuation layer of waste lithium-ion cathode materials, which specifically includes the following steps:

[0008] S1, pretreat the waste lithium-ion cathode materials;

[0009] S2, disperse the pretreated waste lithium-ion cathode materials into a solvent and perform ultrasonic dispersion vibration;

[0010] The beneficial effect is that: The ternary cathode material of lithium-ion batteries is composed of nanoscale primary particles aggregated into secondary particles. Through ultrasonic vibration, the loose primary particles and microcracks on the secondary particles are stripped, avoiding the generation of excessive reaction interfaces in the later assembled batteries and reducing the charge and discharge efficiency of the batteries.

[0011] S3, put the material after ultrasonic dispersion vibration in S2 into a ball milling tank, add a ball milling medium, and perform ball milling;

[0012] The beneficial effect is that: Through ball milling, the spinel phase and rock salt phase on the particle surface are removed by ball milling.

[0013] S4, take out the material after ball milling and perform ultrasonic dispersion vibration again;

[0014] The beneficial effect is that: During ball milling, the primary particles are peeled off under the action of ball milling. Therefore, these particles are removed again by ultrasonic vibration.

[0015] S5, filter, dry, and screen the material after ultrasonic dispersion vibration in S4 to obtain the recycled cathode material.

[0016] The pretreatment in step S1 is to put the used lithium battery into a saturated sodium chloride solution for discharging for 24 h; then disassemble the used lithium-ion battery to separate the positive electrode sheet, separator, and negative electrode sheet; cut the positive electrode sheet into small pieces of 2 cm × 2 cm, calcine at 500 °C to remove the binder and conductive carbon black, and finally obtain the used cathode material powder through screening.

[0017] The solvent in step S2 is any one of anhydrous ethanol, lithium hydroxide aqueous solution, lithium carbonate aqueous solution, and polyethylene glycol;

[0018] Its beneficial effects are as follows: High-concentration lithium salts can prevent lithium loss in the material and supplement lithium in trace amounts, achieving the recovery of lithium in the material while removing the non-layered structure.

[0019] The liquid-solid ratio of the solvent to the pretreated waste lithium-ion cathode material is 2-3:1.

[0020] In step S2, the time of ultrasonic dispersion vibration is 5-300 min, and the ultrasonic frequency is 40 kHz.

[0021] In step S3, the ball-milling medium is any one of zirconia, alumina, and agate;

[0022] The ball-to-material ratio of the ball-milling medium to the material is 10:1-1:20;

[0023] The ball-milling time is 5-600 min, and the ultrasonic frequency is 40 kHz.

[0024] In step S4, the time of ultrasonic dispersion vibration is 5-300 min.

[0025] This application also claims to protect the recycled cathode material prepared by the above method, and the application of the cathode material in the field of lithium-ion battery manufacturing.

[0026] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a method for peeling the attenuation layer of waste lithium-ion cathode material and its reuse. Its beneficial effects are as follows:

[0027] Aiming at the failure reasons of waste ternary cathode materials, ultrasonic vibration and ball milling are used to peel off the failed parts on the outer surface, and the peeled cathode materials are used for battery reconstruction. This method has a simple process and strong adaptability to waste cathode materials, and finally improves the utilization efficiency of waste cathode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0029] Figure 1 SEM image of the ball milling of the present invention.

[0030] Figure 2 SEM image after ball milling by the traditional method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Example 1

[0033] Put the waste ternary cathode material (NCM523) into a saturated sodium chloride solution and discharge it for 24 h; then disassemble the waste lithium-ion battery to separate the cathode plate, separator, and anode plate; cut the cathode plate into small pieces of 2 cm × 2 cm, calcine it at 500 °C to remove the binder and conductive carbon black, and finally obtain the waste cathode material powder through screening.

[0034] Disperse the pretreated waste ternary cathode material (NCM523) into a 1.5 M lithium hydroxide aqueous solution with a liquid-solid ratio of 2:1, and disperse and oscillate it with ultrasonic waves for 60 minutes at an ultrasonic frequency of 40 kHz. Then put the oscillated material into a ball mill tank and add zirconia balls for ball milling, with a ball-to-material ratio of 1:10. Place the ball mill tank into a ball mill and ball mill for 15 minutes. The ball-milled material is ultrasonically oscillated again for 30 minutes at an ultrasonic frequency of 40 kHz. Finally, obtain the recycled cathode material through filtration, drying, and screening. Prepare the recycled cathode material into a coin cell to test its performance. After the first cycle with 0.1C, charge and discharge with 1C. The first-cycle efficiency at 0.1C is 94.5%, the 1C discharge capacity is 146.1 mAh / g, and the capacity retention rate after 100 cycles is 90.3%.

[0035] Example 2

[0036] Put the waste ternary cathode material (NCM523) into a saturated sodium chloride solution and discharge it for 24 h; then disassemble the waste lithium-ion battery to separate the cathode plate, separator, and anode plate; cut the cathode plate into small pieces of 2 cm × 2 cm, calcine it at 500 °C to remove the binder and conductive carbon black, and finally obtain the waste cathode material powder through screening.

[0037] The pretreated waste ternary cathode material (NCM523) was dispersed in absolute ethanol with a liquid-solid ratio of 2:1, and ultrasonic dispersion was carried out for 300 minutes at an ultrasonic frequency of 40 kHz. It was transferred to a ball milling tank, and zirconia balls for ball milling were added with a ball-to-material ratio of 10:1, and ball milling was carried out in a ball mill for 600 minutes. The ball-milled material was ultrasonically vibrated again for 60 minutes at an ultrasonic frequency of 40 kHz. Finally, the recycled cathode material was obtained through filtration, drying, and screening. The recycled cathode material was made into a coin cell to test its performance. After a 0.1C first-cycle activation, 1C charge and discharge were adopted. The 0.1C first-cycle efficiency was 83.2%, the 1C discharge capacity was 102.6 mAh / g, and the capacity retention rate was 30.5% after 100 cycles.

[0038] Example 3

[0039] The waste ternary cathode material (NCM523) was discharged in a saturated sodium chloride solution for 24 h; then the used lithium-ion battery was disassembled to separate the positive electrode sheet, separator, and negative electrode sheet; the positive electrode sheet was cut into small pieces of 2 cm × 2 cm and calcined at 500 °C to remove the binder and conductive carbon black, and finally, the waste cathode material powder was obtained through screening.

[0040] The pretreated waste ternary cathode material (NCM523) was dispersed in an aqueous solution of 1M lithium carbonate with a liquid-solid ratio of 3:1, and ultrasonic dispersion was carried out for 5 minutes at an ultrasonic frequency of 40 kHz. It was transferred to a ball milling tank, and alumina balls for ball milling were added with a ball-to-material ratio of 1:1, and ball milling was carried out in a ball mill for 10 minutes. The ball-milled material was ultrasonically vibrated again for 5 minutes at an ultrasonic frequency of 40 kHz. Finally, the recycled cathode material was obtained through filtration, drying, and screening. The recycled cathode material was made into a coin cell to test its performance. After a 0.1C first-cycle activation, 1C charge and discharge were adopted. The 0.1C first-cycle efficiency was 90.3%, the 1C discharge capacity was 121.5 mAh / g, and the capacity retention rate was 76.8% after 100 cycles.

[0041] Example 4

[0042] The waste ternary cathode material (NCM523) was discharged in a saturated sodium chloride solution for 24 h; then the used lithium-ion battery was disassembled to separate the positive electrode sheet, separator, and negative electrode sheet; the positive electrode sheet was cut into small pieces of 2 cm × 2 cm and calcined at 500 °C to remove the binder and conductive carbon black, and finally, the waste cathode material powder was obtained through screening.

[0043] The pretreated waste ternary cathode material (NCM523) was dispersed in absolute ethanol with a liquid-solid ratio of 2:1, and ultrasonic dispersion was carried out for 100 minutes at an ultrasonic frequency of 40 kHz. It was transferred to a ball-milling tank, and zirconia balls for ball milling were added with a ball-to-material ratio of 1:5, and ball milling was carried out in a ball mill for 6 minutes. The ball-milled material was ultrasonically oscillated again for 300 minutes at an ultrasonic frequency of 40 kHz. Finally, the recycled cathode material was obtained through filtration, drying, and screening. The recycled cathode material was fabricated into a coin cell to test its performance. After a 0.1C first-cycle activation, 1C charge and discharge were adopted. The 0.1C first-cycle efficiency was 93.6%, the 1C capacity was 142.5 mAh / g, and the capacity retention rate was 82.3% after 100 cycles.

[0044] Example 5

[0045] The waste ternary cathode material (NCM523) was discharged in a saturated sodium chloride solution for 24 h; then the used lithium-ion battery was disassembled to separate the positive electrode sheet, separator, and negative electrode sheet; the positive electrode sheet was cut into small pieces of 2 cm × 2 cm and calcined at 500 °C to remove the binder and conductive carbon black, and finally, the waste cathode material powder was obtained through screening.

[0046] The pretreated waste ternary cathode material (NCM523) was dispersed in a 2M lithium carbonate aqueous solution with a liquid-solid ratio of 2:1, and ultrasonic dispersion was carried out for 120 minutes at an ultrasonic frequency of 40 kHz. It was transferred to a ball-milling tank, and agate balls for ball milling were added with a ball-to-material ratio of 5:1, and ball milling was carried out in a ball mill for 30 minutes. The ball-milled material was ultrasonically oscillated again for 60 minutes at an ultrasonic frequency of 40 kHz. Finally, the recycled cathode material was obtained through filtration, drying, and screening. The recycled cathode material was fabricated into a coin cell to test its performance. After a 0.1C first-cycle activation, 1C charge and discharge were adopted. The 0.1C first-cycle efficiency was 93.8%, the 1C capacity was 143.9 mAh / g, and the capacity retention rate was 85.6% after 100 cycles.

[0047] Example 6

[0048] The waste ternary cathode material (NCM523) was discharged in a saturated sodium chloride solution for 24 h; then the used lithium-ion battery was disassembled to separate the positive electrode sheet, separator, and negative electrode sheet; the positive electrode sheet was cut into small pieces of 2 cm × 2 cm and calcined at 500 °C to remove the binder and conductive carbon black, and finally, the waste cathode material powder was obtained through screening.

[0049] The pretreated waste ternary cathode material (NCM523) was dispersed into an aqueous solution of 1 M lithium hydroxide with a liquid-solid ratio of 3:1, and ultrasonic dispersion was carried out for 120 minutes at an ultrasonic frequency of 40 kHz. It was transferred to a ball-milling tank, and alumina balls for ball-milling were added with a ball-to-material ratio of 1:20, and ball-milling was carried out in a ball mill for 120 minutes. The ball-milled material was ultrasonically vibrated again for 240 minutes at an ultrasonic frequency of 40 kHz. Finally, the recycled cathode material was obtained through filtration, drying, and sieving. The recycled cathode material was fabricated into a coin cell to test its performance. After a 0.1C first-cycle activation, 1C charge-discharge was adopted. The 0.1C first-cycle efficiency was 94.6%, the 1C capacity was 144.3 mAh / g, and the capacity retention rate was 89.2% after 100 cycles.

[0050] SEM characterization

[0051] The recycled cathode material prepared in Example 1 and the cathode material prepared in Example 2 were subjected to SEM characterization, and the results are shown in Figure 1 and Figure 2 , where Example 2 is close to the ball-milling process of traditional cathode materials. It can be seen from the comparison in the figure that the ball-milling time has a greater impact on the particle size. Using the attenuation layer peeling method of the present method can reduce the damage of particles. Although the fine particles are sieved out in the subsequent process, the product yield is reduced. However, by adding lithium salts during the ball-milling process, the loss of lithium in the cathode material is reduced, and even the lack of lithium in the waste cathode material is supplemented, which is reflected in the electrochemical detection data in the implementation cases.

[0052] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for stripping the attenuation layer of waste lithium ion positive electrode materials, characterized in that: The specific steps include: S1, pre-treating the waste lithium-ion positive electrode material; S2, dispersing the pretreated waste lithium ion positive electrode material powder into a solvent and performing ultrasonic dispersion vibration; S3, placing the material after ultrasonic dispersion and vibration in S2 into a ball mill, adding ball milling media, and ball milling; S4, taking out the ball-milled material and subjecting it to ultrasonic dispersion vibration again; S5, filtering, drying and screening the material after ultrasonic dispersion vibration in S4 to obtain recovered positive electrode material.

2. The method for stripping the attenuation layer of waste lithium ion positive electrode material according to claim 1, characterized in that: The pretreatment in step S1 is to place the waste lithium battery in a saturated sodium chloride solution for discharge for 24 hours; then disassemble the waste lithium-ion battery to separate the positive electrode sheet, the separator, and the negative electrode sheet; cut the positive electrode sheet into small pieces of 2 cm×2 cm, calcine at 500°C to remove the binder and conductive carbon black, and finally obtain the waste positive electrode material powder by screening.

3. The method for stripping the attenuation layer of waste lithium ion positive electrode material according to claim 1, characterized in that: The solvent described in step S2 is any one of anhydrous ethanol, lithium hydroxide aqueous solution, lithium carbonate aqueous solution, and polyethylene glycol; The liquid-to-solid ratio of the solvent to the pretreated waste lithium ion positive electrode material is 2 to 3:

1.

4. The method for stripping the attenuation layer of waste lithium ion positive electrode material according to claim 1, characterized in that: The ultrasonic dispersion vibration time in step S2 is 5 to 300 minutes, and the ultrasonic frequency is 40 kHz.

5. The method for stripping the attenuation layer of waste lithium ion positive electrode material according to claim 1, characterized in that: The ball milling medium in step S3 is any one of zirconium oxide, aluminum oxide, and agate; The ball-to-material ratio of the ball-milling medium to the material is 10:1 to 1:20; The ball milling time is 5 to 600 minutes.

6. The method for stripping the attenuation layer of waste lithium ion positive electrode material according to claim 1, characterized in that: The ultrasonic dispersion vibration time in step S4 is 5 to 300 minutes, and the ultrasonic frequency is 40 kHz.

7. A recycled positive electrode material prepared by the method for stripping the attenuation layer of waste lithium ion positive electrode material as claimed in claim 1.

8. Use of the recycled positive electrode material prepared by the method according to claims 1 to 6 or the recycled positive electrode material according to claim 7 in the field of lithium ion battery manufacturing.

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