A core-shell structure high-nickel ternary precursor and a preparation method thereof

Abstract

The application relates to the technical field and relates to a core-shell structure high-nickel ternary precursor and a preparation method thereof, which comprises the following steps: preparing a preliminary solution: preparing a mixed solution of Ni, Co and Mn metals, a precipitant solution and a complexing agent solution; preparing a reactor bottom liquid; forming an inner core: keeping the reactor stirring open, continuously adding the mixed solution of the metals, the precipitant and the complexing agent into the reactor bottom liquid at different flow rates, carrying out a co-precipitation reaction, sampling and detecting the slurry particle size every hour, and obtaining an inner core with the highest looseness; forming an intermediate layer: obtaining an intermediate layer with a looseness lower than that of the inner core; forming an outer shell; the precursor structure design of the application is a core-shell structure: a loose inner core-intermediate layer-tight outer shell, there is a loose transition layer with a thickness of about 2 um between the loose inner core and the tight outer shell, the performance play between the inner core and the outer shell is effectively connected, and after subsequent lithium mixing and sintering, the high-nickel ternary positive electrode material has excellent performances of high capacity and long cycle.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a core-shell structured high-nickel ternary precursor and its preparation method. Background Technology

[0002] As the nickel content in ternary materials increases, their specific capacity gradually increases, but at the same time, the cycle stability, thermal stability, and safety performance of the materials significantly decrease, which greatly limits the large-scale commercial application of ultra-high nickel ternary materials. How to ensure high capacity while maintaining excellent cycle stability has always been a key research focus for high-nickel ternary cathode materials. To address the problem of decreased cycle stability caused by increased nickel content in ternary materials, current research mainly focuses on improving the overall performance of ternary materials through doping and coating. Doping modification primarily involves replacing some of the cathode material with other atoms such as Mg, Mn, and W to improve its structural stability. Furthermore, effective surface coating can reduce the reactivity of the ternary material with the electrolyte, minimizing side reactions and thus improving the material's cycle stability.

[0003] Generally, the coating layer is typically an inert material with no electrochemical activity, such as Al₂O₃, ZrO₂, LiF, and TiO₂. If the coating layer is too thick, it will affect Li⁺ transport on the cathode surface, thus limiting the material's capacity and reducing its rate performance. If the coating layer is too thin, it cannot effectively improve the long-term cycle stability of the cathode, because the thin coating layer is prone to dissolution and detachment after long-term erosion by the electrolyte, and the cathode surface will still be attacked by the electrolyte and its decomposition products, resulting in capacity decay. However, coating these "inactive" materials onto lithium-ionized layered transition metal oxides inevitably increases production costs. Therefore, a more cost-effective method is needed to improve the cycle life of nickel-rich materials. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a stable and high-performance core-shell structured high-nickel ternary precursor and its preparation method.

[0005] To solve the above problems, one of the technical solutions of the present invention is achieved through the following method: a method for preparing a core-shell structured high-nickel ternary precursor, comprising the following steps:

[0006] S1, Prepare the initial solution: Prepare a mixed solution of Ni, Co, and Mn metals, a precipitant solution, and a complexing agent solution; prepare the bottom liquid of the reaction vessel;

[0007] S2, Core Formation: Keep the reactor stirring on and continuously purge with nitrogen to ensure the oxygen content in the reactor does not exceed 300 ppm. The reaction temperature is 35~55℃. The metal mixture, precipitant, and complexing agent are continuously added to the bottom liquid of the reactor at different flow rates to carry out a co-precipitation reaction. The slurry particle size is sampled every hour. The slurry particle size at 1h and 2h meets the following requirements: 4um < D50-1 < 4.5um, 3.5um < D50-2 < 4um, to obtain the core with the highest porosity.

[0008] S3, Creating the intermediate layer: After 2 hours of liquid injection, adjust the flow rate of the molten metal and complexing agent in step S2. The particle size of the slurry at 3 hours and 4 hours meets the following requirements: 4.8um < D50-3 < 5.2um, 5.5um < D50-4 < 6um, thus obtaining an intermediate layer with a porosity second only to the core.

[0009] S4, Shell Formation: After 4 hours of liquid injection, restore the flow rate of the molten metal and complexing agent to the same flow rate as in step S2. The precipitant also self-adjusts its flow rate to ensure that the pH remains constant. Continue the reaction until the particle size of the slurry in the reactor reaches 9~10 μm and then stop the reaction to obtain a dense shell.

[0010] S5, the co-precipitated product in step S4 is subjected to solid-liquid separation, washing and drying to obtain a core-shell ternary precursor.

[0011] In step S1 above, the total molar concentration of the metal mixed solution is 1~2 mol / L; the precipitant solution is one or more of sodium hydroxide or potassium hydroxide, with a concentration of 6~10 mol / L; the complexing agent is ammonia water, with a concentration of 2~3 mol / L; the bottom liquid of the reaction vessel is a mixture of pure water and complexing agent, with the pH adjusted to 12.00-13.00 by adding precipitant, and the ammonia concentration of the bottom liquid is 0.7~1.5 mol / L.

[0012] In step S2 above, the flow rate of the molten metal and the flow rate of the complexing agent are quantitatively controlled as V1 and V2, respectively. The flow rate of the complexing agent V2 is controlled so that the ammonia concentration of the mother liquor is 0.8~1.2 mol / L during the process. The flow rate of the precipitant is automatically adjusted according to the pH feedback result, and the pH during the process is 12.00~12.50.

[0013] In step S3 above, the flow rates of the molten metal and the complexing agent in step S2 are adjusted to V3 and V4 respectively, V3 / V1=V4 / V2 and the ratio range is between 4 and 6. The precipitant self-adjusts the flow rate to ensure that the pH remains unchanged and is maintained at 12.00~12.50.

[0014] In step S4 above, the flow rates of the molten metal and ammonia are restored to V1 and V2, respectively, and the reaction continues until the target particle size is reached in 10-15 hours. The solid content during the reaction process is 1.15-1.25 g / mL.

[0015] The second technical solution of this invention is achieved through the following method: a core-shell structured high-nickel ternary precursor, obtained according to a preparation method for a core-shell structured high-nickel ternary precursor, wherein the precursor has the chemical formula Ni. x Co y Mn z (OH)2, 0.8 < x < 1, 0 < y < 0.1, x + y + z = 1, D509 ~ 10um, the peak intensity ratio of (001) crystal plane to (101) crystal plane is 1 < I(001) / I(101) < 1.2.

[0016] The aforementioned precursor has a core-shell structure, comprising a loose core, an intermediate layer, and a dense shell, wherein the loose core has a size of 3.5~4 μm, the intermediate layer has a size of 1.5~2.5 μm, and the dense shell has a size of 3.5~4.5 μm.

[0017] The third technical solution of the present invention is achieved by the following method: a high-nickel ternary cathode material, which is formed by mixing a core-shell high-nickel ternary precursor with a lithium source and then sintering at high temperature.

[0018] The present invention features a core-shell structure in the precursor design: a loose core, an intermediate layer, and a dense outer shell. The loose core has a size of 3.5~4 μm, the intermediate layer has a size of 1.5~2.5 μm, and the dense outer shell has a size of 3.5~4.5 μm. There is a loose transition layer of about 2 μm between the loose core and the dense outer shell, which effectively connects the performance of the core and the shell. After subsequent lithium mixing and sintering, a high-nickel ternary cathode material is obtained with excellent performance of high capacity and long cycle life.

[0019] This invention maintains a high pH during the synthesis process, resulting in a large number of OH- particles distributed on the particle surface. The increased surface negative charge can increase the exposure of the (001) crystal plane and improve the peak intensity ratio of the (001) and (101) diffraction peaks. The designed peak intensity ratio of the (001) crystal plane to the (101) crystal plane is between 1 < I(001) / I(101) < 1.2. After subsequent lithium mixing and sintering, a high-nickel ternary cathode material is obtained, which has better capacity and cycle performance.

[0020] The synthesis process of the ternary precursor of this invention maintains a pH value above 12.00. The high concentration of OH- and the matching high ammonia ratio can effectively control the supersaturation of the system. The ammonia concentration of the mother liquor is controlled at 0.8~1.2 mol / L during the synthesis process. If the ammonia concentration is below this range, the complexation effect is poor, resulting in the particle size not meeting the requirements in the process stage. If it is above this range, the complexation effect will reach its maximum value, resulting in waste of raw materials.

[0021] The present invention has simple process control, convenient production operation, and can realize large-scale preparation. Attached Figure Description

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0023] Figure 1 The image shows a SEM image of the core-shell structured high-nickel ternary precursor prepared in Example 4.

[0024] Figure 2 This is an internal cross-sectional view of the core-shell structured high-nickel ternary precursor prepared in Example 4.

[0025] Figure 3 The image shows the SEM diffraction pattern of the core-shell structured high-nickel ternary precursor prepared in Example 5.

[0026] Figure 4 This is an internal cross-sectional view of the core-shell structured high-nickel ternary precursor prepared in Example 5. Detailed Implementation

[0027] The present invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of the present invention.

[0028] Example 1: This embodiment of the invention discloses a method for preparing a core-shell structured high-nickel ternary precursor, comprising the following steps:

[0029] S1, Prepare the initial solution: Prepare a mixed solution of Ni, Co, and Mn metals, a precipitant solution, and a complexing agent solution; prepare the bottom liquid of the reaction vessel;

[0030] S2, Core Formation: Keep the reactor stirring on and continuously purge with nitrogen to ensure the oxygen content in the reactor does not exceed 300 ppm. The reaction temperature is 35~55℃. The metal mixture, precipitant, and complexing agent are continuously added to the bottom liquid of the reactor at different flow rates to carry out a co-precipitation reaction. The slurry particle size is sampled every hour. The slurry particle size at 1h and 2h meets the following requirements: 4um < D50-1 < 4.5um, 3.5um < D50-2 < 4um, to obtain the core with the highest porosity.

[0031] S3, Creating the intermediate layer: After 2 hours of liquid injection, adjust the flow rate of the molten metal and complexing agent in step S2. The particle size of the slurry at 3 hours and 4 hours meets the following requirements: 4.8um < D50-3 < 5.2um, 5.5um < D50-4 < 6um, thus obtaining an intermediate layer with a porosity second only to the core.

[0032] S4, Shell Formation: After 4 hours of liquid injection, restore the flow rate of the molten metal and complexing agent to the same flow rate as in step S2. The precipitant also self-adjusts its flow rate to ensure that the pH remains constant. Continue the reaction until the particle size of the slurry in the reactor reaches 9~10 μm and then stop the reaction to obtain a dense shell.

[0033] S5, the co-precipitated product in step S4 is subjected to solid-liquid separation, washing and drying to obtain a core-shell ternary precursor.

[0034] In step S1, the total molar concentration of the metal mixed solution is 1-2 mol / L; the precipitant solution is one or more of sodium hydroxide or potassium hydroxide, with a concentration of 6-10 mol / L; the complexing agent is ammonia water with a concentration of 2-3 mol / L; the bottom liquid of the reaction vessel is a mixture of pure water and complexing agent, with the pH adjusted to 12.00-13.00 by adding precipitant, and the ammonia concentration of the bottom liquid is 0.7-1.5 mol / L.

[0035] In step S2, the flow rates of the molten metal and the complexing agent are quantitatively controlled as V1 and V2, respectively. The flow rate of the complexing agent V2 is controlled so that the ammonia concentration of the mother liquor is between 0.8 and 1.2 mol / L. The flow rate of the precipitant is automatically adjusted according to the pH feedback result, and the pH of the process is between 12.00 and 12.50.

[0036] In step S3, the flow rates of the molten metal and the complexing agent in step S2 are adjusted to V3 and V4, respectively, with V3 / V1=V4 / V2 and the ratio ranging from 4 to 6. The precipitant self-adjusts its flow rate to ensure that the pH remains constant, and the pH is maintained at 12.00 to 12.50.

[0037] In step S4, the flow rates of the molten metal and ammonia are restored to V1 and V2, respectively, and the reaction continues until the target particle size is reached in 10-15 hours. The solid content during the reaction process is 1.15-1.25 g / mL.

[0038] In this embodiment of the invention, the initial reaction solution of the ternary precursor is pure water, and the system has a high degree of supersaturation, which dominates the nucleation rate. After the solution is introduced, the particle size gradually decreases with the progress of the reaction time. This invention strictly controls the nucleation time and the corresponding nucleation particle size. These two dimensions determine the number of crystal nuclei. The nucleation time is 2 hours, and the nucleation particle size is 3.5 μm < D50-2 < 4 μm. To meet the initial nucleation quantity, the particle size in 1 hour needs to meet 4 μm < D50-1 < 4.5 μm. If it is below this range, the particle size in 2 hours will be lower than 3.5 μm, resulting in too many nuclei. If it is higher than this range, the particle size in 2 hours will be higher than 4.5 μm, resulting in too few nuclei. At this stage, the nuclei with the highest porosity are obtained.

[0039] Furthermore, by controlling the number of crystal nuclei, the crystal growth stage is entered. By significantly increasing the flow rate of the molten metal, on the one hand, the large amount of solute generated instantaneously under high flow rate can effectively achieve primary particle refinement; on the other hand, the crystal growth rate is positively correlated with the increase in the flow rate of the molten metal, resulting in a 4-6 times increase in crystal growth rate. At 3 hours, the particle size undergoes a sudden change, with a particle size increase of 1-1.5 μm, and at 4 hours, the particle size increase is between 0.7-1 μm, further forming a 2 μm loose layer, whose looseness is second only to the loose core.

[0040] Finally, after the particle size mutation ends, the flow rate of the molten metal is restored to the original flow rate to achieve slow growth and obtain a dense shell.

[0041] In summary, this invention maintains a high pH during the synthesis process, resulting in a large number of OH- particles distributed on the particle surface. The increased surface negative charge can increase the exposure of the (001) crystal plane and improve the peak intensity ratio of the (001) and (101) diffraction peaks. The designed peak intensity ratio of the (001) crystal plane to the (101) crystal plane is between 1 < I(001) / I(101) < 1.2. After subsequent lithium mixing and sintering, a high-nickel ternary cathode material is obtained, which has better capacity and cycle performance.

[0042] Meanwhile, the ternary precursor synthesis process of this invention maintains a pH value above 12.00. The high concentration of OH- and the matching high ammonia ratio can effectively control the supersaturation of the system. The ammonia concentration of the mother liquor is controlled at 0.8~1.2 mol / L during the synthesis process. If the ammonia concentration is below this range, the complexation effect is poor, resulting in the particle size not meeting the requirements in the process stage. If it is above this range, the complexation effect will reach its maximum, resulting in raw material waste. This invention has simple process control, convenient production operation, and can realize large-scale preparation.

[0043] Example 2: This embodiment of the invention discloses a core-shell structured high-nickel ternary precursor, obtained according to the preparation method of the core-shell structured high-nickel ternary precursor, whose chemical formula is Ni. x Co y Mn z (OH)2, 0.8 < x < 1, 0 < y < 0.1, x + y + z = 1, D509 ~ 10um, the peak intensity ratio of (001) crystal plane to (101) crystal plane is 1 < I(001) / I(101) < 1.2.

[0044] The precursor has a core-shell structure, consisting of a loose core, an intermediate layer, and a dense shell. The loose core has a size of 3.5~4 μm, the intermediate layer has a size of 1.5~2.5 μm, and the dense shell has a size of 3.5~4.5 μm.

[0045] In this embodiment of the invention, the precursor structure is designed as a core-shell structure: a loose core, an intermediate layer, and a dense outer shell. The loose core has a size of 3.5~4 μm, the intermediate layer has a size of 1.5~2.5 μm, and the dense outer shell has a size of 3.5~4.5 μm. There is a loose transition layer of about 2 μm between the loose core and the dense outer shell, which effectively connects the performance of the core and the shell. After subsequent lithium mixing and sintering, the resulting high-nickel ternary cathode material has excellent performance of high capacity and long cycle life.

[0046] Example 3: This embodiment of the invention discloses a high-nickel ternary cathode material, which is formed by mixing a core-shell high-nickel ternary precursor with a lithium source and then sintering at high temperature.

[0047] Example 4: This embodiment of the invention discloses a method for preparing a core-shell structured high-nickel ternary precursor, comprising the following steps:

[0048] Step 1: Prepare a mixed solution of Ni, Co, and Mn metals, an 8 mol / L sodium hydroxide solution, and a 2 mol / L ammonia solution, wherein the elemental ratio of Ni, Co, and Mn is 94:05:01, and the total molar concentration of Ni, Co, and Mn is 2.5 mol / L.

[0049] Step 2: Preparation of the reaction base solution: In a 300L reactor, first add 150L of cold pure water, heat the reactor to 45℃, add ammonia solution and sodium hydroxide solution, maintain the ammonia concentration of the reaction base solution mother liquor at 1mol / L and the pH value at 12.40-12.60, keep the reactor sealed, and continuously introduce nitrogen gas at a flow rate of 0.3L / min.

[0050] Step 3: Turn on the stirrer in the reactor at 400 rpm. Continuously add the molten metal and ammonia water into the reactor at 300 ml / min and 250 ml / min respectively through their respective pipelines and react for 2 hours. The temperature inside the reactor is 45℃, and the pH is controlled at 12.20-12.40. Take samples every hour to monitor the particle size of the slurry in the reactor. The D50 of the slurry after 1 hour is 4.2 μm, and the D50 of the slurry after 2 hours is 3.65 μm.

[0051] Step 4: After 2 hours of liquid injection, adjust the flow rate distribution of molten metal and ammonia to 1500 ml / min and 1000 ml / min respectively. Take samples every hour to monitor the particle size of the slurry in the reactor. The D50 of the slurry after 3 hours is 4.95 μm, and the D50 of the slurry after 4 hours is 5.68 μm. Maintain the pH at 12.20-12.40.

[0052] Step 5: After 4 hours of liquid injection, restore the flow rates of the molten metal and ammonia to 300 ml / min and 250 ml / min respectively, and maintain the pH at 12.20-12.40. Continue the reaction for 13 hours until the particle size reaches 9.7 μm, at which point the reaction is complete.

[0053] Step 6: The co-precipitated product from Step 5 is subjected to solid-liquid separation, washing, and drying to obtain the core-shell ternary precursor. The relevant data for the precursor obtained after washing and drying are shown in Table 1.

[0054] Example 5: The difference from Example 4 is that in step three, the pH of the reaction substrate was 11.40-11.60, and the ammonia concentration of the mother liquor in the reactor was 0.5 mol / L. In subsequent steps three, four, and five, the synthesis process maintained the reaction pH at 11.40-11.60 and the ammonia concentration of the mother liquor in the reactor at 0.5 mol / L. The precursor obtained after washing and drying is shown in Table 1.

[0055] As can be seen from the data in Table 1, the sample prepared in Example 5 has low tap and large specific surface area, and I(001) / (101) < 1. The first discharge capacity of the cathode material after lithium mixing and sintering is slightly higher than that of the Example, with a capacity difference within 1 mAh / g. However, the cycling performance of Example 5 at room temperature and high temperature is severely poor. The cathode material prepared in Example 4 has excellent cycling performance after lithium mixing and sintering, taking into account the advantages of high capacity and long cycle.

[0056] From the comparative cross-sectional views ( Figure 2 and Figure 4 Examples 4 and 5 have a loose core, but Example 4 features a loose core and a dense shell, while Example 5's shell maintains the looseness of the core. Figure 1 and Figure 3 SEM images show that the shell morphology of Example 4 is dense, and the high-nickel ternary precursor prepared by this core-shell structure design of the present invention has excellent performance in terms of capacity and cycling.

[0057]

Claims

1. A method for preparing a core-shell structured high-nickel ternary precursor, characterized in that, Includes the following steps: S1, Prepare the initial solution: Prepare a mixed solution of Ni, Co, and Mn metals, a precipitant solution, and a complexing agent solution; prepare the bottom liquid of the reaction vessel; S2, Core Formation: Keep the reactor stirred and continuously purge with nitrogen to ensure the oxygen content in the reactor does not exceed 300 ppm. The reaction temperature is 35~55℃. The metal mixed solution, precipitant, and complexing agent are continuously added to the bottom liquid of the reactor at different flow rates to carry out a co-precipitation reaction. The slurry particle size is sampled every hour. The slurry particle size at 1h and 2h meets the following requirements: 4um < D50-1 < 4.5um, 3.5um < D50-2 < 4um, to obtain the core with the highest porosity. S3, Creating the intermediate layer: After 2 hours of liquid injection, adjust the flow rate of the metal mixture solution and complexing agent in step S2. The particle size of the slurry at 3 hours and 4 hours meets the following requirements: 4.8um < D50-3 < 5.2um, 5.5um < D50-4 < 6um, thus obtaining an intermediate layer with a porosity second only to the core. S4, Shell Formation: After 4 hours of liquid injection, restore the flow rate of the metal mixture and complexing agent to the same flow rate as in step S2. The precipitant also self-adjusts its flow rate to ensure that the pH remains constant. Continue the reaction until the particle size of the slurry in the reactor reaches 9~10 μm and then stop the reaction to obtain a dense shell. S5, the coprecipitated product in step S4 is subjected to solid-liquid separation, washing and drying to obtain a core-shell structured ternary precursor; In step S2, the flow rates of the metal mixed solution and the complexing agent are quantitatively controlled as V1 and V2, respectively. The flow rate of the complexing agent V2 is controlled so that the ammonia concentration of the mother liquor is between 0.8 and 1.2 mol / L during the process. The flow rate of the precipitant is automatically adjusted according to the pH feedback result, and the pH during the process is between 12.00 and 12.

50. In step S3, the flow rates of the metal mixed solution and the complexing agent in step S2 are adjusted to V3 and V4 respectively, V3 / V1=V4 / V2 and the ratio range is between 4 and 6. The precipitant self-adjusts the flow rate to ensure that the pH remains unchanged and is maintained at 12.00~12.

50. In step S4, the flow rates of the metal mixed solution and ammonia water are restored to V1 and V2, respectively, and the reaction continues until the target particle size is reached in 10-15 hours. The solid content during the reaction process is 1.15-1.25 g / mL.

2. The method for preparing the core-shell structured high-nickel ternary precursor according to claim 1, characterized in that, In step S1, the total molar concentration of the metal mixed solution is 1-2 mol / L; the precipitant solution is one or more of sodium hydroxide or potassium hydroxide, with a concentration of 6-10 mol / L; the complexing agent is ammonia water with a concentration of 2-3 mol / L; the bottom liquid of the reaction vessel is a mixture of pure water and complexing agent, with the pH adjusted to 12.00-13.00 by adding precipitant, and the ammonia concentration of the bottom liquid is 0.7-1.5 mol / L.

3. A core-shell structured high-nickel ternary precursor, characterized in that, The precursor is obtained by the preparation method of the core-shell structured high-nickel ternary precursor according to any one of claims 1-2, wherein the precursor has the chemical formula Ni. x Co y Mn z (OH)2, 0.8 < x < 1, 0 < y < 0.1, x + y + z = 1, D509 ~ 10 μm, peak intensity ratio of (001) crystal plane to (101) crystal plane 1 < I(001) / I(101) < 1.2; the precursor is a core-shell structure, including a loose core, an intermediate layer and a dense shell, wherein the loose core size is 3.5 ~ 4 μm, the intermediate layer size is 1.5 ~ 2.5 μm and the dense shell size is 3.5 ~ 4.5 μm.

4. A high-nickel ternary cathode material, characterized in that, This material is formed by high-temperature sintering of a core-shell structured high-nickel ternary precursor as described in claim 3 with a lithium source.

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