Method for preparing magnesium-doped single crystal nickel-rich ternary positive electrode material by regenerating waste NCM111

Abstract

The invention discloses a method for preparing a magnesium-doped single crystal nickel-rich ternary positive electrode material through regeneration of waste NCM111. According to the method, by utilizing the characteristic that molten lithium carbonate dissolves nickel oxide, nickel elements can be rapidly supplemented and uniformly diffused through a high-temperature solid-phase reaction in a molten environment; the nickel-rich ternary positive electrode material with a relatively good crystal structure and relatively high phase purity can be obtained, component adjustment and particle morphology transformation can be synchronously completed, the nickel-rich ternary positive electrode material stoichiometry and the single crystal particle morphology are met, the cycling stability of the regenerated single crystal nickel-rich ternary positive electrode material is improved through magnesium element doping, and the performance of the regenerated single crystal nickel-rich ternary positive electrode material is improved. And green and efficient recovery and performance upgrading of the waste polycrystalline NCM111 positive electrode material are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling and regeneration of waste NCM cathode materials, and particularly relates to a method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111. Background Art

[0002] To meet the growing demands in fields such as portable devices, electric vehicles, and grid energy storage, the production of lithium-ion batteries has increased rapidly. Among various cathode materials, LiNi x Co y Mn z O2 (NCM) ternary cathode materials have become the mainstream choice for lithium-ion batteries due to their excellent specific capacity, lower cost, and ideal cycle stability, especially showing outstanding performance in the fields of electric vehicles and consumer electronics. Correspondingly, the number of waste NCM lithium batteries has increased rapidly, and a large number of NCM batteries are retired from electric vehicles every year.

[0003] Traditional hydrometallurgical and pyrometallurgical methods have been widely used in the lithium-ion battery recycling industry. The original crystal structure is destroyed by means of strong acids, strong bases, and high temperatures to achieve the recovery of precious metals. However, these processes have obvious disadvantages, such as expensive solvents, highly emissive gases, complex recovery routes, etc. Therefore, we believe that neither pyrometallurgical nor hydrometallurgical methods can achieve a closed-loop economy. In contrast, the direct regeneration method is very attractive because its goal is to restore the waste cathode material to its original performance without the chemical decomposition of secondary particles. The average lifespan of lithium-ion batteries is generally 5 - 10 years, so their recycling usually occurs several years later. Therefore, direct regeneration needs to solve the problem of lagging behind the development of cathode materials due to "only repair without improvement". With the higher energy density requirements for lithium-ion batteries, the nickel content in NCM materials is higher. To avoid material failure caused by anisotropy in polycrystalline materials, the particle morphology is gradually developing towards single crystallization. And LiNi 0.33 Co 0.33 Mn 0.33 O2 (NCM111), as the first-generation ternary cathode material, is gradually being replaced by LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1Replaced by O2 (NCM811), a large amount of waste NCM111 cathode materials are in urgent need of treatment. Facing large-scale scrapping, it is no longer possible to directly restore them to their original electrochemical performance level without changing the composition or particle morphology, which cannot meet the current market demand. Therefore, overcoming the limitations of direct regeneration methods and regenerating waste cathode materials into the next-generation cathode materials is more meaningful.

[0004] To solve the above problems existing in the prior art, we propose a method for regenerating and preparing magnesium-doped single-crystalline nickel-rich ternary cathode materials from waste NCM111. Summary of the Invention

[0005] Aiming at the deficiencies in the existing recycling methods, especially the problems in the direct regeneration method of waste NCM111 cathode materials, the purpose of the present invention is to provide a method for regenerating and preparing magnesium-doped single-crystalline nickel-rich ternary cathode materials from waste NCM111. This method can synchronously complete the composition adjustment and particle morphology transformation, meet the stoichiometry and single-crystalline particle morphology of nickel-rich ternary cathode materials, and improve the cycle stability of the regenerated single-crystalline nickel-rich ternary cathode materials by doping with magnesium element, realizing the green and efficient recycling of waste polycrystalline NCM111 cathode materials.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for regenerating and preparing magnesium-doped single-crystalline nickel-rich ternary cathode materials from waste NCM111, comprising the following steps:

[0007] S1. Perform pretreatment operations such as discharging, disassembling, and separating on waste lithium batteries containing polycrystalline NCM111 to obtain waste polycrystalline NCM111 cathode active material powder.

[0008] S2. Determine the contents of Li, Ni, Co, and Mn elements in the waste polycrystalline NCM111 cathode active material powder. According to the stoichiometric ratio of the nickel-rich ternary cathode material to be prepared, calculate the masses of nickel oxide and lithium carbonate to be added, and calculate the mass of magnesium oxide to be added according to the doping amount of magnesium element, and weigh the corresponding masses of nickel oxide, lithium carbonate, and magnesium oxide.

[0009] S3. Place the waste polycrystalline NCM111 cathode active material powder, lithium carbonate, nickel oxide, and magnesium oxide in a ball mill jar for ball milling.

[0010] S4. After the ball milling is completed, use a sieve to separate the powder obtained in S3 from the grinding balls to obtain a mixed powder of waste polycrystalline NCM111 cathode active material powder, lithium carbonate, nickel oxide, and magnesium oxide.

[0011] S5. Place the mixed powder obtained in S4 into a corundum porcelain boat, then put the corundum porcelain boat into a box furnace for high-temperature solid-state reaction, and finally cool it to room temperature with the furnace to obtain a regenerated magnesium-doped single-crystal nickel-rich ternary cathode bulk;

[0012] S6. Put the bulk obtained in S5 into a mortar, grind it evenly, and then screen it through a sieve to obtain the required regenerated magnesium-doped single-crystal nickel-rich ternary cathode powder.

[0013] Furthermore, the specific method of pretreatment in S1 is as follows: Discharge the waste lithium battery containing polycrystalline NCM111, then disassemble the battery to obtain the positive electrode sheet. Calcinate the positive electrode sheet in an air atmosphere at 500 - 600 °C for 2 h, and then successively perform vibration separation, grinding, and screening through a sieve with a mesh size of 150 - 400 to obtain the waste polycrystalline NCM111 positive electrode active material powder.

[0014] Furthermore, in S2, the contents of Li, Ni, Co, and Mn elements in the waste polycrystalline NCM111 positive electrode active material powder are determined by an inductively coupled plasma optical emission spectrometer.

[0015] Furthermore, the doping amount of magnesium element in S2 is Mg / Li = 0.01 - 0.05.

[0016] Furthermore, in S3, a planetary ball mill is used. When grinding, the waste polycrystalline NCM111 positive electrode active material powder, lithium carbonate, nickel oxide, and magnesium oxide are divided into two equal parts by mass and placed in two symmetric ball milling jars. Set the ball milling speed to 500 - 600 r / min and the ball milling time to 1 - 3 h.

[0017] Furthermore, the conditions for the high-temperature solid-state reaction in S5 are: Keep the temperature at 800 - 950 °C for 5 - 10 h.

[0018] Another object of the present invention is to provide a magnesium-doped single-crystal nickel-rich ternary cathode material prepared by the above method.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) The present invention uses waste polycrystalline NCM111 as raw material, precisely regulates the addition ratio of Ni and Li, and realizes the low-cost upgrade and regeneration to single-crystal nickel-rich ternary cathode materials; by utilizing the characteristic that molten lithium carbonate can dissolve nickel oxide, in a molten environment, through high-temperature solid-state reaction, rapid replenishment and uniform diffusion of nickel elements can be achieved, which helps to obtain nickel-rich ternary cathode materials with better crystal structures and higher phase purities; compared with direct regeneration, hydrometallurgy and pyrometallurgy, the process flow is simple, energy consumption and greenhouse gas emissions can be significantly reduced, and it has great environmental benefits; upgrading and regenerating obsolete cathode materials into cathode materials suitable for the current market, with an increase in energy density, which is conducive to offsetting the investment in the recycling process and has greater economic benefits.

[0021] (2) Before the solid-state reaction, through a simple ball milling process, the powder of the NCM111 cathode active material of the polycrystal is broken and uniformly mixed with lithium carbonate, nickel oxide and magnesium oxide particles, which helps to shorten the ion diffusion path, reduce the reaction time, increase the uniformity of the solid-state reaction, and rapidly upgrade and regenerate to obtain nickel-rich ternary cathode materials during the subsequent high-temperature solid-state reaction process.

[0022] (3) During the regeneration process, doping magnesium elements into the lattice of the nickel-rich ternary cathode material can reduce cation mixing and inhibit the generation of harmful phase changes and microcracks during the cycling process, thereby improving the cycling stability of the regenerated single-crystal nickel-rich ternary cathode material. Description of the Drawings

[0023] Figure 1 : SEM image of the waste polycrystalline NCM111 of the present invention.

[0024] Figure 2 : SEM images of Comparative Example 1 and Examples 1-3 of the present invention.

[0025] Figure 3 : Surface EDS results of Comparative Example 1 of the present invention.

[0026] Figure 4 : Cross-sectional EDS results of Comparative Example 1 of the present invention.

[0027] Figure 5 : Cross-sectional EDS results of Example 3 of the present invention.

[0028] Figure 6 : Surface EDS results of Comparative Example 2 of the present invention.

[0029] Figure 7 : Charge and discharge cycling performance test diagrams of the waste polycrystalline NCM111, Examples 1-5, Comparative Examples 1-2 and commercial single-crystal NCM622 cathode materials of the present invention assembled into coin cells. Detailed Embodiments

[0030] The present invention will be further described in detail below in conjunction with specific examples and comparative examples. The examples and comparative examples given are only for clarifying the present invention, rather than limiting the scope of the present invention. The experimental methods in the following examples are all conventional methods unless otherwise specified; the materials, reagents, instruments, etc. used can be obtained from commercial sources unless otherwise specified.

[0031] Example 1

[0032] Upgraded recycled NCM622 cathode material:

[0033] First step, discharge the waste lithium battery with polycrystalline NCM111 cathode material, then disassemble it to obtain the cathode plate. Calcinate the cathode plate in an air atmosphere at 500 - 600 °C for 2 h, and then successively carry out shaking separation, grinding, and sieving through a sieve with a mesh size of 150 - 400 meshes to obtain the cathode active material powder.

[0034] Second step, determine the content of each metal element in the waste polycrystalline NCM111 cathode active material powder by inductively coupled plasma mass spectrometry (ICP-MS). According to the NCM622 stoichiometry, weigh the corresponding masses of nickel oxide and lithium carbonate by calculation, and weigh the corresponding mass of magnesium oxide by Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1-x Mg x O2(x = 0.01).

[0035] Third step, divide the cathode active material powder, lithium carbonate, nickel oxide, and magnesium oxide into two equal masses and place them in a ball mill tank. At the same time, put the corresponding masses of grinding balls into the tank according to a ball-to-material ratio of 5:1; then put these two ball mill tanks into a planetary ball mill, close the cover and set the operation mode. Set the ball milling speed to 500 - 600 r / min, the ball milling time to 2 h, reverse and forward rotation alternately every 15 min, and set the interval time of the alternate operation to 15 min. After setting the above operation mode, start the motor for ball milling.

[0036] Fourth step, after ball milling, separate the raw materials obtained in the third step from the grinding balls with a sieve with a mesh size of 100 - 300 meshes to obtain a mixture of waste NCM111 cathode active material powder and lithium carbonate, nickel oxide, and magnesium oxide.

[0037] Fifth step, place the mixed powder obtained in the fourth step in a corundum boat, then put the boat into a box furnace, heat it to 900 °C at a heating rate of 5 °C / min and hold for 8 h, and finally cool it to room temperature with the furnace to obtain a regenerated magnesium-doped single crystal NCM622 cathode block.

[0038] Step 6: Put the bulk obtained in the fifth step into a mortar, grind it evenly, and then pass it through a sieve with a mesh size of 100 - 300 to obtain the required regenerated magnesium-doped single-crystal NCM622 cathode powder.

[0039] Example 2

[0040] Upgraded regenerated magnesium-doped NCM622 cathode material:

[0041] The preparation method is the same as that of Example 1, except that in the second step, according to the stoichiometry of NCM622, the corresponding masses of nickel oxide and lithium carbonate are weighed by calculation, and by Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1-x Mg x O (x = 0.03), the corresponding mass of magnesium oxide is weighed, and finally the required regenerated magnesium-doped single-crystal NCM622 cathode powder is obtained.

[0042] Example 3

[0043] Upgraded regenerated magnesium-doped NCM622 cathode material:

[0044] The preparation method is the same as that of Example 1, except that in the second step, according to the stoichiometry of NCM622, the corresponding masses of nickel oxide and lithium carbonate are weighed by calculation, and by Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1-x Mg x O (x = 0.05), the corresponding mass of magnesium oxide is weighed, and finally the required regenerated magnesium-doped single-crystal NCM622 cathode powder is obtained.

[0045] According to Figure 1-2 , after regeneration, the morphology of the secondary particles formed by the aggregation of primary particles in the original NCM111 has completely disappeared, and the particle morphologies of Examples 1 - 3 have all completely shown a single particle morphology. And with the increase of the Mg content, the single-crystal particle morphology has not changed, indicating that the doping of Mg element has no effect on the particle morphology.

[0046] According to Figure 7 , after regenerating NCM111 into a Ni-rich ternary cathode material NCM622 and doping it with Mg, the regenerated materials all have good discharge specific capacity and are close to the performance of the ternary commercial level NCM622 with the same ratio.

[0047] The present invention utilizes the characteristic of molten lithium carbonate to dissolve nickel oxide, and through high-temperature solid-state reaction, realizes the rapid regeneration of waste low-nickel polycrystalline ternary cathode materials into high-nickel single-crystalline ternary cathode materials. Before the solid-state reaction, the mixed powder is ball-milled, and all material particles are broken and fully mixed, which helps to overcome the problem of uneven high-temperature solid-state reaction. After the high-temperature solid-state reaction, the obtained regenerated magnesium-doped single-crystalline NCM622 presents a single-crystalline particle morphology, and the single-crystalline material has better cycling performance and longer service life.

[0048] Example 4

[0049] Upgraded regenerated magnesium-doped NCM811 cathode material:

[0050] The preparation method is the same as that of Example 1, except that in the second step, according to the stoichiometric ratio of NCM811, the corresponding masses of nickel oxide and lithium carbonate are weighed by calculation, and through Li(Ni 0.8 Co 0.1 Mn 0.1 ) 1-x Mg x O2 (x = 0.01) is calculated and the corresponding mass of magnesium oxide is weighed, and finally the required regenerated magnesium-doped single-crystalline NCM811 cathode powder is obtained.

[0051] Example 5

[0052] Upgraded regenerated magnesium-doped NCM90505 cathode material:

[0053] The preparation method is the same as that of Example 1, except that in the second step, according to the stoichiometric ratio of NCM90505, the corresponding masses of nickel oxide and lithium carbonate are calculated and weighed, and through Li(Ni 0.9 Co 0.05 Mn 0.05 ) 1-x Mg x O2 (x = 0.01) is calculated and the corresponding mass of magnesium oxide is weighed, and finally the required regenerated magnesium-doped single-crystalline NCM90505 cathode powder is obtained.

[0054] According to Figure 7 , comparing Examples 1, 4, and 5, the discharge specific capacities of the regenerated magnesium-doped single-crystalline NCM622, NCM811, and NCM90505 gradually increase, that is, with the increase of the nickel supplementation amount, it helps to improve the electrochemical performance of the regenerated material.

[0055] Using lithium carbonate and nickel oxide as the lithium source and nickel source respectively, it can successfully realize the upgrade and regeneration of waste low-nickel ternary cathode materials into high-nickel ternary cathode materials. At the same time, doping with Mg element can further increase the cycling performance of the regenerated material.

[0056] Comparative Example 1

[0057] Upgraded recycled NCM622 cathode material:

[0058] The preparation method is the same as that of Example 1, except that in the second step, according to the stoichiometric ratio of NCM622, the corresponding masses of nickel oxide and lithium carbonate are calculated and weighed, and finally the recycled single-crystal NCM622 cathode powder without Mg element doping is obtained.

[0059] According to Figure 3-4 , for Comparative Example 1 (undoped with Mg), the element distribution on the surface and cross-section is uniform. It can be seen that using lithium carbonate and nickel oxide as the lithium source and nickel source respectively can successfully achieve composition adjustment. According to Figure 5 , after Mg doping, the distribution of each element inside the recycled NCM622 particles is uniform, indicating that the Mg element has been successfully and uniformly doped into the bulk phase of the recycled NCM622.

[0060] According to Figure 7 , the discharge specific capacity and the capacity retention rate after 100 cycles of Comparative Example 1 are both close to the level of commercial single-crystal NCM622, indicating that this method can successfully adjust the composition of the waste polycrystalline NCM111 cathode to rich-nickel single-crystal NCM622. At the same time, due to the doping of Mg element, the cycling performance of Examples 1-3 is better than that of Comparative Example 1, but it is not that the more Mg element is doped, the better the cycling performance of the cathode material. The doping amount needs to be maintained within a certain range. It can be seen from the figure that the cycling performance of Example 2 is the best.

[0061] Table 1 Comparison of structural parameters of X-ray diffraction results

[0062]

[0063] Please refer to Table 1. Table 1 is a comparison of the structural parameters obtained after Rietveld refinement of the X-ray diffraction results of Comparative Example 1 and Examples 1-3. In Examples 1-3, with the doping of Mg element, the capacity retention rate after 100 cycles is higher than that of Comparative Example 1 and commercial single-crystal NCM622 (the capacity retention rate is the slope of the straight line in the figure. The larger the slope, the faster the capacity drops, that is, the worse the cycling performance), indicating that the doping of magnesium element helps to stabilize the crystal structure of the recycled NCM622 and improve the cycling performance. This is because the Mg element is partially doped at the 3a site of the lithium layer and mostly doped at the 3b site, reducing the Ni 2+ content and reducing the degree of cation mixing.

[0064] Comparative Example 2

[0065] Upgraded recycled NCM622 cathode material:

[0066] The preparation method is the same as that of Example 1, except that in the second step, according to the stoichiometric ratio of NCM622, the corresponding masses of nickel oxide and lithium hydroxide are calculated and weighed to finally obtain the required regenerated single-crystal NCM622 cathode powder.

[0067] According to Figure 6 , in the regenerated single-crystal NCM622 cathode material of Comparative Example 2, lithium hydroxide is selected as the lithium source for the regenerated single-crystal NCM622 cathode material, and the nickel element distribution is uneven. It shows that the present invention uses lithium carbonate and nickel oxide as the lithium source and nickel source respectively, and can adjust the waste low-nickel ternary cathode material to a nickel-rich ternary cathode material. This is because in the high-temperature solid-phase reaction stage, molten lithium carbonate can dissolve nickel oxide, and the nickel element exists in the molten lithium carbonate in the form of ions, so it is easier to enter the waste NCM111 to achieve composition adjustment.

[0068] According to Figure 7 , when lithium hydroxide is used as the lithium source, the performance of the regenerated NCM622 is poor, far lower than the level of commercial single-crystal NCM622. This is because the diffusion of nickel elements is uneven and there are many internal structure defects in the regenerated NCM622. However, when lithium carbonate and nickel oxide are used as the lithium source and nickel source respectively, the regenerated NCM622 reaches the commercial level, indicating that the present method has excellent applicability in realizing the regeneration of low-nickel ternary cathode materials into high-nickel ternary cathode materials.

[0069] The composition adjustment is carried out by the high-temperature solid-phase method, and the problem of uneven reaction is likely to occur in this process. The present invention overcomes this problem by the characteristics of pre-ball milling and mixing and the dissolution of nickel oxide by molten lithium carbonate, and successfully realizes the rapid regeneration of waste low-nickel polycrystalline ternary cathode materials into high-nickel single-crystal ternary cathode materials.

[0070] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111, characterized in that, It includes the following steps: S1. Perform pretreatment operations such as discharging, disassembling, and separating the waste lithium battery containing polycrystalline NCM111 to obtain the waste polycrystalline NCM111 cathode active material powder. S2. Determine the contents of Li, Ni, Co, and Mn elements in the waste polycrystalline NCM111 cathode active material powder. According to the stoichiometric ratio of the nickel-rich ternary cathode material to be prepared, calculate the masses of nickel oxide and lithium carbonate to be added, and calculate the mass of magnesium oxide to be added according to the magnesium element doping amount. Weigh the corresponding masses of nickel oxide, lithium carbonate, and magnesium oxide. S3. Place the waste polycrystalline NCM111 cathode active material powder, lithium carbonate, nickel oxide, and magnesium oxide in a ball mill jar for ball milling. S4. After the ball milling is completed, use a sieve to separate the powder obtained in S3 from the grinding balls to obtain a mixed powder of the waste polycrystalline NCM111 cathode active material powder, lithium carbonate, nickel oxide, and magnesium oxide. S5. Place the mixed powder obtained in S4 in a corundum boat, then put the corundum boat into a box furnace for high-temperature solid-phase reaction, and finally cool it to room temperature with the furnace to obtain the regenerated magnesium-doped single-crystal nickel-rich ternary cathode block. S6. Put the block obtained in S5 into a mortar, grind it evenly, and then pass it through a sieve to obtain the required regenerated magnesium-doped single-crystal nickel-rich ternary cathode powder.

2. The method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111 according to claim 1, wherein The specific method of pretreatment in S1 is: discharge the waste lithium battery containing polycrystalline NCM111, then disassemble the battery to obtain the cathode plate, calcine the cathode plate in an air atmosphere at 500 - 600 °C for 2 h, and successively perform vibration separation, grinding, and sieving through a 150 - 400 mesh sieve to obtain the waste polycrystalline NCM111 cathode active material powder.

3. The method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111 according to claim 1, characterized in that In S2, the contents of Li, Ni, Co, and Mn elements in the waste polycrystalline NCM111 cathode active material powder are determined by an inductively coupled plasma emission mass spectrometer.

4. The method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111 according to claim 1, characterized in that, In S2, the magnesium element doping amount is Mg / Li = 0.01 - 0.

05.

5. The method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111 according to claim 1, characterized in that, In S3, a planetary ball mill is used. During grinding, the waste polycrystalline NCM111 cathode active material powder, lithium carbonate, nickel oxide, and magnesium oxide are divided into two equal masses and placed in two symmetric ball mill jars. Set the ball milling speed to 500 - 600 r / min and the ball milling time to 1 - 3 h.

6. The method for regenerating and preparing a magnesium-doped single-crystal nickel-rich ternary cathode material from waste NCM111 according to claim 1, wherein The conditions for the high-temperature solid-phase reaction in S5 are: keep the temperature at 800 - 950 °C for 5 - 10 h.

7. The magnesium-doped single-crystal nickel-rich ternary cathode material prepared by the method according to any one of claims 1 - 6.

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