A method for realizing single-crystalization regeneration of waste positive electrode material by vacuum pyrolysis

Abstract

The application discloses a method for realizing single-crystalization and regeneration of waste positive electrode materials by adopting a vacuum cracking method. The method is to mix and melt waste lithium ion battery polycrystal ternary positive electrode materials, nickel stearate and lithium salt, and then calcine under vacuum condition to obtain regenerated single-crystal ternary positive electrode materials. The method can compensate lithium loss of waste single-crystal ternary positive electrode materials, and convert insoluble residual Ni on the surface of single-crystal materials in the nickel stearate cracking process into LiNiO2 which can provide discharge capacity, so that the regenerated positive electrode materials exhibit more excellent electrochemical performance, and the cost is further reduced. The method is simple and easy to operate, and has low requirement on the regeneration reaction temperature, so that the polycrystal cracking into single crystal and lithium compensation processes can be simultaneously performed without long time high-temperature calcination, energy consumption is low, and the method is easy to popularize.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium-ion cathode material recycling technology, specifically involving a method for single-crystal regeneration of waste cathode materials using vacuum pyrolysis. Background Technology

[0002] Lithium-ion batteries are currently the next generation of rechargeable batteries with the highest energy density, widely used in mobile communications and digital technology. In recent years, they have also been widely used in new energy vehicles and energy storage. The future demand for lithium-ion batteries and materials is difficult to estimate. Ternary layered lithium nickel cobalt manganese oxide (NCM) cathode materials combine the advantages of three lithium-ion battery cathode materials: LiCoO2, LiNiO2, and LiMnO2, with a significant synergistic effect among the three transition metals. Due to their high energy density, long cycle life, and good safety, ternary cathode materials have become the cathode material with the largest global market growth in recent years. However, after nearly a thousand cycles, they irreversibly reach the end of their lifespan. Retired lithium-ion batteries contain large amounts of valuable metals such as lithium, nickel, cobalt, and manganese, and can be considered "artificial minerals" from which metals can be extracted. If lithium-ion batteries are not properly recycled, their heavy metal, organic, and fluorine pollution will make them a major source of environmental pollution, which is detrimental to the concept of comprehensive resource utilization and sustainable development. Recycling retired lithium-ion batteries can not only realize the resource utilization of limited resources and promote the development of a circular economy, but also avoid potential threats to human health and the ecological environment. It has multiple benefits in terms of resources, economy, and society. Therefore, the recycling of retired lithium-ion batteries is of great significance and practical value.

[0003] Ternary cathode materials can be classified into single-crystal and polycrystalline types based on their crystal structure. Polycrystalline materials are composed of many single-crystal particles with different orientations, and their entire crystal structure is not permeated by a single lattice. Conventional polycrystalline ternary cathode materials exist as agglomerates of secondary spherical particles. Single-crystal materials refer to crystals that grow evenly from a single nucleus in all directions, with an internal structure that is essentially a complete lattice. Single-crystal technology uses special precursors and sintering processes to achieve a special crystal structure in ternary cathode materials. While maintaining existing capacity and charge / discharge plateaus, it aims to increase the single-crystal grain size of the cathode material, thereby increasing its tap density, improving the volumetric capacity of lithium batteries, and significantly enhancing the safety and quality of lithium batteries. During cycling, the accumulation of lattice strain and defects in polycrystalline ternary cathode materials lead to lattice distortion, inevitably causing grain boundary fracture (intergranular fracture) during cycling. Furthermore, the contact of the electrolyte along grain boundaries and the cracking of secondary particles accelerate the side reactions of the cathode-electrolyte system, leading to the transformation of the layered structure into a spinel structure, ultimately resulting in voltage and capacity decay. Simultaneously, the expansion and contraction of particles can cause the entire secondary sphere to crack and break, drastically altering the battery's electrochemical environment and shortening cycle life. Because the connections between small single-crystal primary particles are relatively fragile, secondary particles are prone to breakage during electrode cold pressing, also easily leading to battery performance degradation. Single-crystal ternary cathode materials are typically composed of one or several large (2~5μm) irregular blocky primary particles. These materials lack grain boundaries, have a smoother microscopic surface, and exhibit better structural stability and high-temperature resistance. Moreover, after compaction and high-temperature cycling, they are less prone to breakage, resulting in superior high-temperature cycling stability. Considering the high cost of resynthesizing ternary cathode materials, regenerating waste polycrystalline cathode materials in single-crystal form not only reduces production costs compared to traditional regeneration methods but also releases a better internal structure and repairs broken morphologies. By exploiting the defects in waste polycrystalline layered cathode materials, they are transformed into single-crystal forms for regeneration, resulting in single-crystal layered cathode materials with excellent structural properties. This technology not only shortens the recycling process but also offers greater economic benefits and broader application prospects.

[0004] Patent application CN202110661097.0, entitled "A Method for Single-Crystallization Regeneration of Waste Ternary Cathode Material," describes a process where secondary particles of waste ternary cathode material are split along grain boundaries into primary particles; the split primary particles are then subjected to molten salt calcination to nucleate and grow into single-crystal particles; the molten salt is removed, and the single-crystal particles are annealed to obtain single-crystal ternary cathode material. Patent application CN202210097582.4, entitled "A Method for Single-Crystallization of Polycrystalline Ternary Cathode Material," describes a process where polycrystalline ternary cathode material is uniformly mixed with a milling agent and milled in a plasma ball mill. The milled ternary cathode material is broken into small particles. The plasma milling product is then washed, filtered, and dried. It is then uniformly mixed with lithium salt and subjected to molten salt calcination. The calcined cathode material is removed, washed, dried, and annealed to obtain a single-crystal cathode material with good crystallinity and stable structure. Although the above two methods can regenerate waste polycrystalline ternary cathode materials into single-crystal ternary cathode materials, the method of the former patent application requires long-term high-temperature roasting to crack it into single-crystal particles, while the latter patent application uses ball milling to crack polycrystalline ternary cathode materials into single-crystal cathode materials, but its lithium replenishment process is carried out during subsequent molten salt calcination, and subsequent annealing treatment is also required, which is too cumbersome.

[0005] This invention aims to provide a method for converting waste ternary cathode materials into single-crystal ternary cathode materials through polycrystalline cracking at a low calcination temperature and with a simple procedure. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the single-crystal regeneration of waste cathode materials using vacuum pyrolysis.

[0007] The objective of this invention is achieved by using a vacuum pyrolysis method to regenerate waste cathode materials into single crystals. This method involves thoroughly mixing and melting waste polycrystalline cathode materials from ternary lithium-ion batteries with nickel stearate and lithium salt, and then calcining the mixture under vacuum conditions to obtain regenerated single-crystal ternary cathode materials.

[0008] The lithium salt is a combination of lithium carbonate, lithium nitrate and lithium sulfate, with a molar ratio of lithium carbonate, lithium nitrate and lithium sulfate of 3-5:2-3:1.

[0009] The mass ratio of waste polycrystalline ternary cathode material, nickel stearate, and lithium salt is 1:0.25-2:0.4-1.1.

[0010] The beneficial effects of this invention are as follows:

[0011] 1. The present invention employs a vacuum pyrolysis method to regenerate waste cathode materials into single crystals. This method not only compensates for lithium loss in single-crystal waste ternary cathode materials, but also converts the insoluble residual Ni on the surface of the single crystal material during the "cracking" process of nickel stearate into LiNiO2 that can provide discharge capacity. This results in the regenerated cathode material exhibiting superior electrochemical performance, while further reducing costs.

[0012] 2. The method of the present invention is simple, safe and easy to operate. It does not require ball milling, has a short cycle, and does not have high requirements for the regeneration reaction temperature (the maximum roasting temperature is only 650℃). It can carry out the two processes of polycrystalline fission single crystal and lithium replenishment simultaneously without long-term high-temperature roasting. The residual nickel is also reasonably converted and its value is brought into play. It has low energy consumption and no pollution, and is suitable for promotion. Attached Figure Description

[0013] Figure 1 SEM image of waste polycrystalline ternary cathode material SNCM;

[0014] Figure 2 Here is a SEM image of the waste single-crystal ternary cathode material SNCM-S from Example 1;

[0015] Figure 3 SEM image of the regenerated polycrystalline ternary cathode material RNCM in Comparative Example 1;

[0016] Figure 4 SEM image of waste single-crystal ternary cathode material SNCM-S1 in Comparative Example 2;

[0017] Figure 5 SEM image of waste single-crystal ternary cathode material SNCM-S2 in Comparative Example 3;

[0018] Figure 6 Here is a SEM image of the regenerated single-crystal ternary cathode material RSNCM from Example 1;

[0019] Figure 7 Here is a SEM image of RSNCM-1, the regenerated single-crystal ternary cathode material of Comparative Example 2.

[0020] Figure 8 SEM image of RSNCM-2, the regenerated single-crystal ternary cathode material of Comparative Example 3;

[0021] Figure 9 Here is a SEM image of RSNCM-4, the regenerated single-crystal ternary cathode material from Example 5;

[0022] Figure 10 The XRD patterns are of the recycled single-crystal cathode material (RSNCM) and the waste (SNCM) prepared in Example 1.

[0023] Figure 11The diagram shows the electrochemical cycling performance of the regenerated single-crystal cathode material (RNCM) prepared in Example 1 and Comparative Example 1, the regenerated cathode material (RSNCM-1) prepared in Comparative Example 2, and the waste (SNCM). Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0025] The present invention discloses a method for the single-crystal regeneration of waste cathode materials using a vacuum pyrolysis method. The method involves thoroughly mixing and melting waste polycrystalline ternary cathode materials from lithium-ion batteries with nickel stearate and lithium salt, and then calcining the mixture under vacuum conditions to obtain regenerated single-crystal ternary cathode materials.

[0026] The lithium salt is a combination of lithium carbonate, lithium nitrate and lithium sulfate, with a molar ratio of lithium carbonate, lithium nitrate and lithium sulfate of 3-5:2-3:1.

[0027] The mass ratio of waste polycrystalline ternary cathode material, nickel stearate, and lithium salt is 1:0.25-2:0.4-1.1.

[0028] This method is implemented in the following steps:

[0029] 1) Mix waste polycrystalline ternary cathode material, nickel stearate and lithium salt, and stir and heat at 90-120℃ for 8-12 hours to obtain waste polycrystalline ternary cathode material with partial nickel stearate infiltration;

[0030] 2) The polycrystalline waste ternary cathode material infiltrated with nickel stearate is placed in a vacuum atmosphere and sintered at 360-420℃ for 5-8 h at a heating rate of 2-10℃ / min to obtain waste single crystal ternary cathode material.

[0031] 3) After uniformly mixing the waste single-crystal ternary cathode material in a mortar, calcine it at 400-450℃ for 3-6 hours in an oxygen atmosphere, then raise the temperature to 650-700℃ and calcine for 6-12 hours. After cooling in the furnace, wash with water, filter, dry at 80℃, and calcine at 650-700℃ in an oxygen atmosphere for 2-6 hours. After cooling in the furnace, the recycled single-crystal ternary cathode material is obtained.

[0032] Example 1

[0033] 2g of waste lithium-ion battery polycrystalline ternary cathode material SNCM was uniformly mixed with 2g of nickel stearate and 0.738g of Li2CO3, 0.517g of LiNO3 and 0.275g of Li2SO4 (molar ratio of 4:3:1), stirred at 100℃ for 10h in an electric thermostatic oil bath, and then heated at 400℃ for 6h in a tube furnace under vacuum to obtain waste single crystal ternary cathode material.

[0034] Waste single-crystal ternary cathode material is uniformly mixed in a mortar and calcined at 450°C for 5 hours in an oxygen atmosphere. Then, the temperature is raised to 650°C and calcined for 12 hours. After washing with water, filtration, and drying at 80°C, it is calcined at 650°C for 4 hours in an oxygen atmosphere. The resulting solid is the regenerated single-crystal ternary cathode material.

[0035] Example 2

[0036] 2g of waste lithium-ion battery polycrystalline ternary cathode material SNCM was uniformly mixed with 0.5g of nickel stearate and 0.738g of Li2CO3, 0.738g of LiNO3 and 0.550g of Li2SO4 (molar ratio of 2:2:1), stirred at 120℃ for 8h in an electric thermostatic oil bath, and then heated at 360℃ for 8h in a tube furnace vacuum environment at a heating rate of 2℃ / min to obtain waste single crystal ternary cathode material.

[0037] Waste single-crystal ternary cathode material was uniformly mixed in a mortar and calcined at 400°C for 4 hours in an oxygen atmosphere. Then, the temperature was raised to 700°C and calcined for 10 hours. After washing with water, filtration, and drying at 80°C, it was calcined at 700°C for 2 hours in an oxygen atmosphere to obtain regenerated single-crystal ternary cathode material.

[0038] Example 3

[0039] 2g of waste lithium-ion battery polycrystalline ternary cathode material SNCM was uniformly mixed with 1g of nickel stearate and 0.246g of Li2CO3, 0.460g of LiNO3 and 0.366g of Li2SO4 (molar ratio of 3:2:1), stirred at 110℃ for 10h in an electric thermostatic oil bath, and then heated at 380℃ for 7h in a tube furnace vacuum environment at a heating rate of 2℃ / min to obtain waste single crystal ternary cathode material.

[0040] Waste single-crystal ternary cathode material was uniformly mixed in a mortar and calcined at 425°C for 6 hours in an oxygen atmosphere. Then, the temperature was raised to 650°C and calcined for 8 hours. After washing with water, filtration, and drying at 80°C, it was calcined at 650°C for 6 hours in an oxygen atmosphere to obtain regenerated single-crystal ternary cathode material.

[0041] Example 4

[0042] 2g of waste lithium-ion battery polycrystalline ternary cathode material SNCM was uniformly mixed with 4g of nickel stearate and 0.739g of Li2CO3, 0.414g of LiNO3 and 0.220g of Li2SO4 (molar ratio of 5:3:1), stirred at 90℃ for 12h in an electric thermostatic oil bath, and then heated at 420℃ for 5h in a tube furnace vacuum environment at a heating rate of 2℃ / min to obtain waste single crystal ternary cathode material.

[0043] Waste single-crystal ternary cathode material was uniformly mixed in a mortar and calcined at 450°C for 5 hours in an oxygen atmosphere. Then, the temperature was raised to 650°C and calcined for 12 hours. After washing with water, filtration, and drying at 80°C, it was calcined at 700°C for 6 hours in an oxygen atmosphere to obtain pretreated regenerated single-crystal cathode material. The pretreated regenerated single-crystal cathode material was washed with water, dried, and calcined at 700°C for 4 hours in an oxygen atmosphere to obtain regenerated single-crystal ternary cathode material.

[0044] Example 5

[0045] The method in this embodiment is basically the same as that in Example 1, and the lithium salt is 0.8g of lithium carbonate (Li2CO3).

[0046] Example 6

[0047] The method in this embodiment is basically the same as that in Example 1, and the lithium salt is 0.6g of lithium nitrate (LiNO3).

[0048] Comparative Example 1

[0049] Nickel stearate was not added in this comparative example, and the other steps were the same as in Example 1.

[0050] Comparative Example 2

[0051] In this comparative example, the heating rate under vacuum is 5°C / min, and the other steps are the same as in Example 1.

[0052] Comparative Example 3

[0053] In this comparative example, the heating rate under vacuum was 10°C / min, and the other steps were the same as in Example 1.

[0054] Detection Example 1

[0055] The waste single-crystal cathode materials prepared in Examples 1 and 5, and Comparative Examples 1, 2, and 3, were compared with the recycled cathode materials by SEM. The results are as follows: Figure 1-9 As shown.

[0056] from Figure 1-9 It can be seen that the waste polycrystalline ternary cathode material SNCM ( Figure 1The polycrystalline waste ternary cathode material consists of spherical secondary particles formed by the accumulation of primary particles, with a particle size of 8-10 nm. The surface shows cracks and is covered with white flocculent material, which may be residual PVDF and conductive carbon. In contrast, the waste single-crystal cathode material obtained in Example 1 (…) Figure 2 The "explosion" consists of large areas of independent primary particles, as shown in Comparative Example 1 ( Figure 3 The material obtained in Comparative Example 2 and Comparative Example 3 still consists of secondary particles and has not "exploded" into single-crystal particles, and the surface microcracks have not been completely repaired. In contrast, the "exploded" waste single-crystal cathode material particles obtained in Comparative Example 3 still retain relatively large spherical secondary particles. Figure 4-5 This indicates that an excessively high heating rate cannot fully guarantee that the polycrystalline particles will "explode" into primary particles. Example 1: Regenerated single-crystal cathode material obtained through regeneration ( Figure 6 The first example exhibits primary particles, with a smooth surface free of cracks and impurities. It also contains single-crystal LiNiO2, which appears as elongated primary particles, significantly different from the primary particles of the ternary material, but still smooth and free of impurities and cracks. Comparative Examples 2 and 3, however, did not exhibit good "cracking" during the single-crystallization process, resulting in primary particles. Figure 7-8 Therefore, the recycled materials agglomerate over a large area. At the same time, the synthesized LiNiO2 agglomerates together with the single-crystal ternary cathode material and adheres to the surface of the polycrystalline material that has not been broken. This is not conducive to the insertion and extraction of lithium ions and will greatly affect the electrochemical performance of the recycled materials, failing to meet the material requirements.

[0057] Example 5 uses lithium carbonate (Li2CO3) as a single lithium source to obtain the regenerated cathode material. Figure 9 There are no microcracks, the crystal surface is relatively clear but there is still a small-scale agglomeration phenomenon, and a small amount of lithium salt is attached. Therefore, the lithium-ion transport resistance is increased, and the degree of repair on the cathode material is not as good as in Example 1.

[0058] Detection Example 2

[0059] XRD analysis was performed on the spent lithium-ion battery ternary cathode material (SNCM) and the recycled single-crystal cathode material (RSNCM) prepared in Example 1. The results are as follows. Figure 10 As shown.

[0060] from Figure 10It can be seen that the diffraction peaks of SNCM and RSNCM are similar, and their spectra are basically consistent with the standard LiNiO2 spectrum PDF#09-0063, which is a typical hexagonal layered LiNiO2 structure with R-3m space group. Compared with RSNCM, the diffraction peaks of SNCM material are flatter, and (006) and (012) are merged, (108) and (110) are merged, and the splitting is not obvious. These phenomena indicate that the crystallinity of the waste polycrystalline cathode (SNCM) material has been reduced and the crystal structure has been damaged to a certain extent. This may be due to the irreversible phase transition during the charge and discharge process. The XRD pattern of the regenerated RSNCM material shows sharper diffraction peaks. The splitting of the (006) / (012) and (108) / (110) diffraction characteristic peaks is more obvious, indicating that the material has a better layered structure. The sharper diffraction peaks also indicate that the crystallinity of the material has been greatly restored. Furthermore, no other impurity peaks were found in the XRD pattern of the SRNCM material, indicating that the method of the present invention does not introduce new impurity phases, and effectively converts the residual Ni compound on the surface into LiNiO2 that can provide capacity, which is consistent with the above. Figure 5 The results are consistent with the SEM analysis.

[0061] Detection Example 3

[0062] The battery cycle performance of the recycled lithium-ion battery ternary cathode material (SNCM), the recycled single-crystal cathode material (RSNCM) prepared in Example 1, the recycled cathode material (RNCM) prepared in Comparative Example 1, and the recycled single-crystal cathode material (RSNCM-1) prepared in Comparative Example 2 were tested. The battery cycle results are shown in Table 1 and... Figure 11 As shown.

[0063] The results showed that the regenerated single-crystal ternary cathode material (RSNCM) in Example 1 achieved a first-cycle discharge specific capacity of 206.198 mAh g⁻¹. -1 This is significantly higher than the 162.687 mAh g of the recycled cathode material (RNCM) prepared in Comparative Example 1. -1 And the 192.772 mAh g of the recycled single-crystal cathode material RSNCM-1 in Comparative Example 2. -1 This is attributed to the partial capacity provided by LiNiO2 converted from residual Ni, while the capacity of the original waste single-crystal cathode material was recovered after sufficient lithium compensation. After 100 cycles, the capacity retention rate of the RSNCM material was 86.7%, significantly higher than that of the regenerated cathode material (RNCM) prepared in Comparative Example 1 and the regenerated single-crystal cathode material (RSNCM-1) prepared in Comparative Example 2, indicating that the electrochemical performance of the material was recovered and can meet the application requirements.

[0064] Table 1. Battery charge-discharge test results of the recycled cathode materials prepared in Example 1 and Comparative Examples 1 and 2

[0065] sample <![CDATA[Discharge specific capacity in the first cycle (mAh g -1 ).]]> <![CDATA[Discharge specific capacity at the 100th cycle (mAh g -1 )]]> Retention rate after 100 cycles (%) SNCM (Spent Polycrystalline Ternary Cathode Material) 92.467 30.861 33.3% Example 1 RSNCM 206.020 176.585 86.7% Comparative Example 1 RNCM 162.687 139.646 85.8% Comparative Example 2 RSNCM-1 192.772 145.282 75.4%

Claims

1. A method for single-crystal regeneration of waste cathode materials using vacuum pyrolysis, characterized in that, Waste single-crystal ternary cathode material is obtained by fully mixing and melting waste polycrystalline cathode material of ternary lithium-ion batteries with nickel stearate and lithium salt, and then calcining it under vacuum conditions. The lithium salt is a combination of lithium carbonate, lithium nitrate and lithium sulfate, with a molar ratio of lithium carbonate, lithium nitrate and lithium sulfate of 3-5:2-3:

1. The mass ratio of polycrystalline waste ternary cathode material, nickel stearate, and lithium salt is 1:0.25-2:0.4-1.

1.

2. The method for single-crystal regeneration of waste cathode materials using vacuum pyrolysis as described in claim 1, characterized in that, To achieve this, follow these steps: 1) Mix waste polycrystalline ternary cathode material, nickel stearate and lithium salt, and stir and heat at 90-120℃ for 8-12 hours to obtain waste polycrystalline ternary cathode material with partial nickel stearate infiltration; 2) The waste polycrystalline ternary cathode material with partially infiltrated nickel stearate is placed in a vacuum atmosphere and sintered at 360-420℃ for 5-8 h at a heating rate of 2-10℃ / min to obtain waste single crystal ternary cathode material. 3) After uniformly mixing the waste single-crystal ternary cathode material in a mortar, calcine it at 400-450℃ for 3-6 hours in an oxygen atmosphere, then raise the temperature to 650-700℃ and calcine for 6-12 hours. After cooling in the furnace, wash with water, filter, dry at 80℃, and calcine at 650-700℃ in an oxygen atmosphere for 2-6 hours. After cooling in the furnace, the recycled single-crystal ternary cathode material is obtained.

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