A dry-wet combined grading method for nano nickel powder for MLCC electrode

Abstract

The application relates to the technical field of metal powder preparation for electronic materials, and discloses a dry-wet combined grading preparation method of nano nickel powder for MLCC electrodes. The method is characterized in that: firstly, the nano nickel powder raw powder is graded under low-oxygen dry conditions to obtain a fine end section, a main body section and a coarse end section; secondly, the main body section is used to prepare main body slurry, and the main body section pre-adsorption mother liquor is obtained from the main body slurry; thirdly, the fine end section and the coarse end section are treated respectively, so that the recyclable powder reenters the system in the liquid phase environment suitable for the main body section; finally, the main body slurry, the fine end recyclable slurry and the coarse end recyclable slurry are wet-reconstructed, and the finished product nickel powder is obtained through common replacement, solid-liquid separation and low-oxygen common drying. The application is favorable for reducing the state difference between the powder of different particle size sections, improving the particle size end distribution, re-dispersion performance and batch stability of the finished product nickel powder.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology for electronic materials, and in particular to a method for dry and wet combined fractionation preparation of nano-nickel powder for MLCC electrodes. Background Technology

[0002] As MLCCs develop towards thinner and higher capacity, the thickness of the internal electrode layer is constantly decreasing, which places higher demands on the average particle size, particle size distribution, ratio of coarse to fine particles, and dispersion stability of nickel powder. In their paper "Fabrication of homogeneous nanosized nickelpowders using a planetary ball mill: Applications to multilayer ceramiccapacitors" published in Powder Technology, Taehyeob Im et al. pointed out that nickel powder with more uniform particle size is beneficial to improving the stability of MLCC electrode layer formation.

[0003] For particle size control of nano-nickel powder used in MLCCs, existing technologies have long proposed grading processes. For example, the metal powder used as an electrode material in multilayer ceramic capacitors and its manufacturing and usage methods disclosed in CN111788650A propose control requirements for particle size indicators such as D50, D90, D99 and coarse particle content, and obtain the target particle size distribution through sieving or gas classification steps.

[0004] However, the quality of nano-nickel powder used in MLCC internal electrodes cannot be judged solely by whether the particle size distribution meets the requirements. Nickel powders of different particle sizes usually differ in specific surface area, surface oxidation degree, redispersion performance, and sintering shrinkage behavior. In their paper "Effect of Passivation on the Sintering Behavior of Submicron Nickel PowderCompacts for MLCC Application" published in the Journal of Korean Powder Metallurgy Institute, Gi-Young Jo et al. pointed out that the passivation state of nickel powder surface affects its sintering behavior and electrode continuity. Even if the particle size distribution of the same batch of nickel powder seems to meet the requirements after grading, if the surface state and redispersion performance of powders of different particle sizes are significantly different, it will still cause batch fluctuations in subsequent pulping, printing, or sintering processes. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing technology usually focuses on removing coarse particles, reducing the average particle size or obtaining the target particle size distribution, but fails to take into account the consistency of powders of different particle size ranges in terms of surface state, redispersibility and subsequent sintering performance. This results in the nickel powder that may meet the particle size index but has insufficient powder state matching. Therefore, a dry and wet combined classification method for preparing nano nickel powder for MLCC electrodes is proposed.

[0006] To achieve the above objectives, this application adopts the following technical solution: a method for preparing nano-nickel powder for MLCC electrodes by a combination of dry and wet fractionation, comprising the following steps: S1: Take nano-nickel powder for MLCC electrodes and fractionate it under low-oxygen dry conditions to obtain fine-end segments, main segments, and coarse-end segments. The fine-end segments account for 3-8 wt% of the mass of the original powder, the main segments account for 86-93 wt% of the mass of the original powder, and the coarse-end segments account for 3-8 wt% of the mass of the original powder. The fine-end segments and coarse-end segments together account for 7-14 wt% of the mass of the original powder; S2: Add the main segments to an alcohol dispersion medium containing a dispersant for dispersion treatment to obtain a main slurry. Separate 30-45 wt% of the slurry from the main slurry for solid-liquid separation, and collect the separated liquid phase as the pre-absorption of the main segments. The mother liquor is added, and the separated solid phase is returned to the unseparated portion of the main slurry. The pre-adsorption mother liquor of the main segment is divided into a first part pre-adsorption mother liquor and a second part pre-adsorption mother liquor; S3: The fine end segment is added to the first part pre-adsorption mother liquor for equalization treatment. After separation and removal of the fine end discharge, the fine end remixed slurry is obtained. The coarse end segment is added to an alcohol dispersion medium for wet release treatment. After separation and removal of the coarse end discharge, the coarse end candidate powder is obtained. The coarse end candidate powder is then added to the second part pre-adsorption mother liquor for equalization treatment to obtain the coarse end remixed slurry; S4: The main slurry is mixed with the fine end remixed slurry and the coarse end remixed slurry for wet reconstruction to obtain the reconstructed slurry; S5: The reconstructed slurry is subjected to co-displacement, solid-liquid separation and low-oxygen co-drying to obtain nano-nickel powder for MLCC electrodes.

[0007] Preferably, in S1, the low-oxygen dry condition is a nitrogen or argon atmosphere, with an oxygen content ≤1000ppm, an atmosphere dew point ≤-20℃, and a powder temperature ≤40℃.

[0008] Preferably, in S1, the grading is performed using an air classifier, with a grading airflow velocity of 3-15 m / s and a grading wheel rotation speed of 2500-9000 r / min.

[0009] Preferably, in S2 and S3, the alcohol dispersion medium is selected from anhydrous ethanol, isopropanol, or a mixture of the two, and the alcohol dispersion medium used when the coarse end segment is subjected to wet release treatment is the same as the alcohol dispersion medium used when the main body segment is prepared into the main slurry.

[0010] Preferably, in S2, the dispersant is selected from one or more of polyvinylpyrrolidone, ammonium polyacrylate, and ammonium citrate. When preparing the main slurry, the solid content of the main segment is 10-18 wt%, and the amount of dispersant is 0.04-0.12 wt% of the mass of the main segment.

[0011] Preferably, in S2, the pre-adsorption mother liquor of the main body section is divided into a first part of pre-adsorption mother liquor and a second part of pre-adsorption mother liquor at a mass ratio of 0.8-1.2:1.

[0012] Preferably, in S3, when the fine end segment is added to the first part of the pre-adsorbed mother liquor for equalization treatment, the solid content of the fine end segment is 2-10 wt%. After equalization treatment, it is separated by short-path centrifugation, and 25-30 vol% of the slurry on the upper liquid surface is removed based on the total volume of the slurry after centrifugation. The remaining slurry is used as the fine end remixing slurry.

[0013] Preferably, in S3, when the coarse end segment undergoes wet release treatment, the solid content of the coarse end segment is 3-15wt%. After wet release treatment, it is separated by short-path centrifugation, and 5-20vol% of the concentrated slurry from the bottom settling side is removed as coarse end discharge based on the total volume of the separated slurry. The remaining slurry is collected as coarse end candidate powder after solid-liquid separation.

[0014] Preferably, in step S3, when the coarse-end candidate powder is added to the second part of the pre-adsorption mother liquor for equalization treatment, the solid content of the coarse-end candidate powder is 3-12wt%, and it is stirred at 10-30℃.

[0015] Preferably, in S4, during wet reconstruction, the powder corresponding to the main segment in the reconstruction slurry accounts for 88-97 wt% of the final product mass, the corresponding powder in the fine end reconstituted slurry accounts for 0.5-5 wt% of the final product mass, and the corresponding powder in the coarse end reconstituted slurry accounts for 1-8 wt% of the final product mass.

[0016] The technical effects and advantages of this invention are as follows:

[0017] In this invention, the nano-nickel powder is first separated into fine-end segments, main segments, and coarse-end segments under low-oxygen dry conditions. Then, the main segment is used to prepare the main slurry and obtain a pre-adsorption mother liquor for the main segment. This ensures that the subsequent remixed powder is not directly treated with fresh dispersion medium or ordinary dispersion liquid, but is adjusted in a liquid phase environment after pre-contact with the main segment. At the same time, the fine-end segments are equilibrated and unsuitable fine-end portions are removed, while the coarse-end segments are wet-released and coarse-end discharges are removed. The resulting fine-end remixed slurry, coarse-end remixed slurry, and main slurry are then reconstructed under wet conditions and subjected to joint displacement, solid-liquid separation, and low-oxygen co-drying. Compared with methods that only use dry classification, liquid-phase classification, or separate treatment followed by dry mixing, this invention can control the influence of coarse and fine-end particles on the particle size distribution of the finished product while reducing the state differences of powders of different particle sizes entering the same product system. This makes the obtained nickel powder more stable in terms of particle size distribution, slurry redispersibility, sampling consistency, and batch stability, thus making it more suitable for the preparation requirements of nano-nickel powder for MLCC internal electrodes. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0019] Figure 1 The figure shows the results of Experimental Example 1 of the present invention;

[0020] Figure 2 The figure shows the results of Experimental Example 2 of the present invention;

[0021] Figure 3 The figure shows the results of Experimental Example 3 of the present invention;

[0022] Figure 4 The figure shows the results of Experimental Example 4 of the present invention. Detailed Implementation

[0023] It is readily understood that, based on the technical solution of the present invention, those skilled in the art can propose various interchangeable structural methods and implementation methods without altering the essential spirit of the present invention. Therefore, the following specific embodiments and accompanying drawings are merely exemplary descriptions of the technical solution of the present invention and should not be regarded as the entirety of the present invention or as a limitation or restriction on the technical solution of the present invention.

[0024] This invention provides a method for preparing nano-nickel powder for MLCC electrodes using a combined dry and wet fractionation process, comprising the following steps:

[0025] S1: Take nano-nickel powder for MLCC electrodes and classify it under low-oxygen dry conditions by adjusting the classifying airflow speed and classifying wheel speed to obtain fine-end segments, main segments, and coarse-end segments; wherein, the fine-end segments account for 3-8 wt% of the raw powder mass, the main segments account for 86-93 wt% of the raw powder mass, and the coarse-end segments account for 3-8 wt% of the raw powder mass, and the fine-end segments and coarse-end segments together account for 7-14 wt% of the raw powder mass;

[0026] S2: The main body segment is added to an alcohol dispersion medium containing a dispersant for dispersion treatment, so that the main body segment and the dispersant are pre-contacted to obtain the main body slurry; 30-45 wt% of the slurry is separated from the main body slurry for solid-liquid separation, and the separated liquid phase is collected as the main body segment pre-adsorption mother liquor, while the separated solid phase is returned to the unseparated portion of the main body slurry; the main body segment pre-adsorption mother liquor is divided into the first part pre-adsorption mother liquor and the second part pre-adsorption mother liquor at a mass ratio of 0.8-1.2:1;

[0027] S3: The fine end segment is added to the first part of the pre-adsorption mother liquor for equalization treatment, and the fine end discharge is removed by separation to obtain fine end remixed slurry; the coarse end segment is added to the alcohol dispersion medium for wet release treatment, and the coarse end discharge is removed by separation to obtain coarse end candidate powder, and then the coarse end candidate powder is added to the second part of the pre-adsorption mother liquor for equalization treatment to obtain coarse end remixed slurry.

[0028] S4: The main slurry is mixed with the fine-end remixed slurry and the coarse-end remixed slurry for wet reconstruction to obtain a reconstructed slurry. The powder corresponding to the main segment in the reconstructed slurry accounts for 88-97 wt% of the final product mass on a dry basis, the corresponding powder in the fine-end remixed slurry accounts for 0.5-5 wt% of the final product mass, and the corresponding powder in the coarse-end remixed slurry accounts for 1-8 wt% of the final product mass.

[0029] S5: The reconstructed slurry is subjected to co-displacement, solid-liquid separation and low-oxygen co-drying to obtain nano-nickel powder for MLCC electrodes.

[0030] In this invention, the nano-nickel powder has a D50 of 80-300 nm, a D90 of 150-600 nm, an oxygen content ≤1.5 wt%, a moisture content ≤0.20 wt%, and a tap density of 1.0-3.5 g / cm³. 3 .

[0031] In S1, the low-oxygen dry state conditions are preferably nitrogen or argon atmosphere, with an oxygen content ≤1000ppm. During the low-oxygen dry state classification process, the atmosphere dew point is ≤-20℃ and the powder temperature is ≤40℃.

[0032] The grading equipment adopts an air classifier, with the grading airflow velocity set at 3-15 m / s and the grading wheel speed at 2500-9000 r / min.

[0033] The fine end segment is the powder portion with a smaller particle size compared to the main body segment, the main body segment is the powder portion with a particle size close to the main particle size range of the target product, and the coarse end segment is the powder portion with a larger particle size compared to the main body segment; the mass ratio of the fine end segment, the main body segment, and the coarse end segment is based on the mass of the dry powder after graded collection.

[0034] In S2, the alcohol dispersion medium is selected from anhydrous ethanol, isopropanol, or a mixture of the two; the dispersant is selected from one or more of polyvinylpyrrolidone, ammonium polyacrylate, and ammonium citrate.

[0035] When preparing the main slurry, the solid content of the main slurry is preferably 10-18 wt%, and the amount of dispersant is 0.04-0.12 wt% of the mass of the main slurry. The slurry is stirred at a speed of 800-2500 r / min at a temperature range of 10-30℃ and dispersed at an ultrasonic power density of 50-200 W / L for 3-10 min.

[0036] After the main slurry is prepared, a slurry accounting for 30-45 wt% of the total mass of the main slurry is separated from the main slurry for solid-liquid separation. The solid-liquid separation can be carried out by centrifugation, membrane filtration or microfiltration.

[0037] When centrifugation is used, the centrifugation acceleration is preferably 1000-3000g and the centrifugation time is preferably 3-10min; when membrane filtration or microfiltration is used, the filter membrane pore size is preferably 0.1-0.5μm.

[0038] The liquid phase obtained after solid-liquid separation is used as the pre-adsorption mother liquor of the main section, and the obtained solid phase is returned to the unseparated portion of the main slurry and mixed evenly.

[0039] In S3, the equalization treatment refers to adding the fine-end segment or coarse-end candidate powder to the pre-adsorption mother liquor of the main segment and dispersing it under stirring and / or ultrasonic conditions.

[0040] When the fine end segment is added to the first part of the pre-adsorbed mother liquor for equalization treatment, the solid content of the fine end segment is preferably 2-10 wt%. Stirring and ultrasonic dispersion are carried out at 10-30℃, wherein the stirring speed is controlled at 500-1500 r / min, the ultrasonic power density is controlled at 30-150 W / L, and the dispersion time is 2-8 min. After equalization treatment, short-path centrifugation is carried out at 300-1000 g for 3-5 min, and 25-30 vol% of the slurry on the upper liquid surface is removed according to the total volume of the slurry after centrifugation. The remaining slurry is used as the fine end segment remixing slurry.

[0041] During the wet release treatment, the alcohol dispersion medium used is consistent with that used in step S2. After adding the coarse end segment to the alcohol dispersion medium at a solid content of 3-15 wt%, it is stirred and ultrasonically dispersed at a temperature not exceeding 35°C. The stirring speed is controlled at 800-2500 r / min, the ultrasonic power density is controlled at 80-300 W / L, and the dispersion time is 3-10 min. After the wet release treatment, it is centrifuged at a centrifugal acceleration of 500-2000 g for 3-6 min. Based on the total volume of the slurry after separation, 5-20 vol% of the concentrated slurry on the bottom sedimentation side is removed as the coarse end discharge. The remaining slurry is collected as the solid phase after solid-liquid separation as the coarse end candidate powder.

[0042] When coarse-end candidate powder is added to the second part of pre-adsorption mother liquor for equalization treatment, the solid content of the coarse-end candidate powder is 3-12wt%; stirring is carried out at 10-30℃, wherein the stirring speed is controlled at 500-1500r / min and the stirring time is 2-8min, and coarse-end remixed slurry is obtained after stirring.

[0043] In S4, during wet reconstruction, the proportion of powder added in each segment is determined on a dry basis. That is, the mass ratio of the powder corresponding to the main segment, the powder corresponding to the fine end remixed slurry, and the powder corresponding to the coarse end remixed slurry in the final product is calculated based on the dry powder mass of nickel powder contained in each slurry. The liquid phase medium in the slurry is not included in the mass of the final product.

[0044] During the wet reconstruction process, the mixture is stirred at 500-1500 r / min for 5-20 min at 10-30℃, and the solid content of the reconstructed slurry is controlled to be 8-22 wt%.

[0045] In S5, when the reconstructed slurry is subjected to co-replacement, the replacement medium is preferably one or more of anhydrous ethanol, isopropanol or ethyl acetate, and the replacement number is preferably 1-3 times.

[0046] Solid-liquid separation can be achieved by filtration or centrifugation; when using filtration, the filtration pressure difference is preferably 0.01-0.08 MPa; when using centrifugation, the centrifugation acceleration is preferably 300-1200 g.

[0047] When drying under low oxygen conditions, the drying atmosphere is preferably nitrogen or argon, with an oxygen content ≤1000ppm, the drying temperature is preferably 45-80℃, the vacuum degree is preferably -0.06 to -0.095MPa, and the drying time is preferably 2-8h.

[0048] The present invention will be further described below with reference to examples and comparative examples. Unless otherwise specified, the alcohol dispersion medium is isopropanol and the dispersant is polyvinylpyrrolidone K30.

[0049] Example 1: This example provides a method for preparing nano-nickel powder for MLCC electrodes using a combination of dry and wet fractionation, including the following steps:

[0050] S1: Take 1000g of nano-nickel powder raw powder and perform low-oxygen dry classification under nitrogen protection. The classification airflow velocity is 8m / s and the classification wheel speed is 6000r / min to obtain fine end segment, main body segment and coarse end segment. Among them, the fine end segment is about 50g, accounting for 5wt% of the raw powder mass; the main body segment is about 900g, accounting for 90wt% of the raw powder mass; and the coarse end segment is about 50g, accounting for 5wt% of the raw powder mass.

[0051] S2: The main component is added to isopropanol to prepare the main slurry. The solid content of the main component is 15wt%, and the amount of polyvinylpyrrolidone K30 added is 0.08wt% of the mass of the main component. The mixture is stirred at 1500r / min at 25℃ and dispersed at 120W / L ultrasonic power density for 6min to pre-contact the main component with polyvinylpyrrolidone K30, thus obtaining the main slurry.

[0052] Take 40wt% of the slurry from the main slurry and centrifuge it at 2000g for 5min. Collect the supernatant after centrifugation as the main segment pre-adsorption mother liquor. Return the solid of the main segment obtained by centrifugation to the unseparated part of the main slurry and mix it evenly. Divide the main segment pre-adsorption mother liquor into the first part pre-adsorption mother liquor and the second part pre-adsorption mother liquor at a mass ratio of 1:1.

[0053] S3: Add the fine end segment to the first part of the pre-adsorption mother liquor for equalization treatment. The solid content of the fine end segment is 5wt%. Stir at 1000r / min at 25℃ and disperse at 80W / L ultrasonic power density for 5min. After equalization treatment, centrifuge at 800g centrifugation acceleration for 3min. Remove 28vol% of the slurry on the upper liquid surface based on the total volume of the slurry after centrifugation. The remaining slurry is used as the fine end remixing slurry.

[0054] The coarse end segment was added to isopropanol for wet release treatment, with a solid content of 8 wt%. It was stirred at 1800 r / min at 25°C and dispersed at an ultrasonic power density of 200 W / L for 6 min. After wet release treatment, it was centrifuged at 1000 g for 3 min. The concentrated slurry at the bottom sedimentation side was removed as the coarse end discharge based on the total volume of the separated slurry. The remaining slurry was collected as the solid phase after solid-liquid separation as the coarse end candidate powder.

[0055] The coarse-end candidate powder was added to the second part of the pre-adsorption mother liquor for equalization treatment. The solid content of the coarse-end candidate powder was 6wt%. The mixture was stirred at 1000r / min for 5min at 25℃ to obtain the coarse-end remixed slurry.

[0056] S4: Mix the main slurry with the fine-end remixed slurry and the coarse-end remixed slurry for wet reconstruction; wherein, on a dry basis, the mass ratio of the corresponding powder in the main section, the corresponding powder in the fine-end remixed slurry and the corresponding powder in the coarse-end remixed slurry is 92:3:5. During wet reconstruction, the stirring speed is 1000 r / min, the mixing time is 10 min, and the reconstruction temperature is 25℃ to obtain the reconstructed slurry.

[0057] S5: The reconstructed slurry was subjected to co-displacement treatment with isopropanol as the displacement medium. The displacement was performed twice, with a filtration pressure difference of 0.04 MPa. The water content after displacement was 0.32 wt%. Subsequently, the wet powder after displacement was subjected to low-oxygen co-drying under a nitrogen atmosphere, with the oxygen content controlled below 500 ppm. The drying temperature was 60℃, the vacuum degree was -0.08 MPa, and the drying time was 5 h, to obtain nano-nickel powder for MLCC electrodes.

[0058] Example 2: The difference between this example and Example 1 is that after low-oxygen dry grading, the fine end segment accounts for 3 wt% of the original powder mass, the main segment accounts for 93 wt% of the original powder mass, and the coarse end segment accounts for 4 wt% of the original powder mass;

[0059] The solid content of the main section in the main slurry is 16wt%, and the amount of polyvinylpyrrolidone K30 is 0.07wt% of the mass of the main section. A slurry accounting for 30wt% of the total mass of the main slurry is separated from the main slurry for solid-liquid separation. The resulting pre-adsorption mother liquor of the main section is divided into the first part pre-adsorption mother liquor and the second part pre-adsorption mother liquor at a mass ratio of 0.8:1.

[0060] After equalization treatment and short-path centrifugation, 25 vol% of the slurry on the upper liquid surface side is removed from the fine end section based on the total volume of the slurry after centrifugation; after wet release treatment and short-path centrifugation, 8 vol% of the concentrated slurry on the bottom settling side is removed from the coarse end section based on the total volume of the slurry after separation.

[0061] During wet reconstruction, on a dry basis, the mass ratio of the corresponding powder in the main body section, the corresponding powder in the fine end remixed slurry, and the corresponding powder in the coarse end remixed slurry is 96:1:3; except for the above differences, the remaining steps and conditions are the same as in Example 1.

[0062] Example 3: The difference between this example and Example 1 is that after low-oxygen dry grading, the fine end segment accounts for 8 wt% of the original powder mass, the main segment accounts for 86 wt% of the original powder mass, and the coarse end segment accounts for 6 wt% of the original powder mass.

[0063] The solid content of the main section in the main slurry is 14wt%, and the amount of polyvinylpyrrolidone K30 is 0.10wt% of the mass of the main section. A portion of the slurry accounting for 45wt% of the total mass of the main slurry is separated from the main slurry for solid-liquid separation. The resulting pre-adsorption mother liquor of the main section is divided into the first part of the pre-adsorption mother liquor and the second part of the pre-adsorption mother liquor at a mass ratio of 1.2:1.

[0064] After equalization treatment and short-path centrifugation, 30 vol% of the slurry on the upper liquid surface side is removed from the fine end section based on the total volume of the slurry after centrifugation; after wet release treatment and short-path centrifugation, 15 vol% of the concentrated slurry on the bottom settling side is removed from the coarse end section based on the total volume of the slurry after separation.

[0065] During wet reconstruction, on a dry basis, the mass ratio of the corresponding powder in the main body section, the corresponding powder in the fine end remixed slurry, and the corresponding powder in the coarse end remixed slurry is 89:5:6; except for the above differences, the remaining steps and conditions are the same as in Example 1.

[0066] Example 4: The difference between this example and Example 1 is that after low-oxygen dry grading, the fine end segment accounts for 4 wt% of the original powder mass, the main segment accounts for 92 wt% of the original powder mass, and the coarse end segment accounts for 4 wt% of the original powder mass.

[0067] The solid content of the main section in the main slurry is 15wt%, and the amount of polyvinylpyrrolidone K30 is 0.08wt% of the mass of the main section. A slurry accounting for 35wt% of the total mass of the main slurry is separated from the main slurry for solid-liquid separation. The resulting pre-adsorption mother liquor of the main section is divided into the first part pre-adsorption mother liquor and the second part pre-adsorption mother liquor at a mass ratio of 1:1.

[0068] After equalization treatment and short-path centrifugation, 25 vol% of the slurry on the upper liquid surface side is removed from the fine end section based on the total volume of the slurry after centrifugation; after wet release treatment and short-path centrifugation, 10 vol% of the concentrated slurry on the bottom settling side is removed from the coarse end section based on the total volume of the slurry after separation.

[0069] During wet reconstruction, on a dry basis, the mass ratio of the corresponding powder in the main body section, the corresponding powder in the fine end remixed slurry, and the corresponding powder in the coarse end remixed slurry is 94:2:4; except for the above differences, the remaining steps and conditions are the same as in Example 1.

[0070] Example 5: The difference between this example and Example 1 is that after low-oxygen dry grading, the fine end segment accounts for 4 wt% of the original powder mass, the main segment accounts for 88 wt% of the original powder mass, and the coarse end segment accounts for 8 wt% of the original powder mass;

[0071] The solid content of the main section in the main slurry is 15wt%, and the amount of polyvinylpyrrolidone K30 is 0.09wt% of the mass of the main section. A portion of the slurry accounting for 42wt% of the total mass of the main slurry is separated from the main slurry for solid-liquid separation. The resulting pre-adsorption mother liquor of the main section is divided into the first part of the pre-adsorption mother liquor and the second part of the pre-adsorption mother liquor at a mass ratio of 0.8:1.

[0072] After equalization treatment and short-path centrifugation, 25 vol% of the slurry on the upper liquid surface side is removed from the fine end section based on the total volume of the slurry after centrifugation; after wet release treatment and short-path centrifugation, 20 vol% of the concentrated slurry on the bottom settling side is removed from the coarse end section based on the total volume of the slurry after separation.

[0073] During wet reconstruction, on a dry basis, the mass ratio of the corresponding powder in the main body section, the corresponding powder in the fine end remixed slurry, and the corresponding powder in the coarse end remixed slurry is 90:4:6; except for the above differences, the remaining steps and conditions are the same as in Example 1.

[0074] Example 6: The difference between this example and Example 1 is that after low-oxygen dry grading, the fine end segment accounts for 8 wt% of the original powder mass, the main segment accounts for 88 wt% of the original powder mass, and the coarse end segment accounts for 4 wt% of the original powder mass;

[0075] The solid content of the main section in the main slurry is 13wt%, and the amount of polyvinylpyrrolidone K30 is 0.10wt% of the mass of the main section. A portion of the slurry accounting for 42wt% of the total mass of the main slurry is separated from the main slurry for solid-liquid separation. The resulting pre-adsorption mother liquor of the main section is divided into the first part of the pre-adsorption mother liquor and the second part of the pre-adsorption mother liquor at a mass ratio of 1.2:1.

[0076] After equalization treatment and short-path centrifugation, 30 vol% of the slurry on the upper liquid surface side is removed from the fine end section based on the total volume of the slurry after centrifugation; after wet release treatment and short-path centrifugation, 8 vol% of the concentrated slurry on the bottom settling side is removed from the coarse end section based on the total volume of the slurry after separation.

[0077] During wet reconstruction, on a dry basis, the mass ratio of the corresponding powder in the main body section, the corresponding powder in the fine end remixed slurry, and the corresponding powder in the coarse end remixed slurry is 92:4:4; except for the above differences, the remaining steps and conditions are the same as in Example 1.

[0078] Comparative Example 1: This comparative example provides a method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that low-oxygen dry-state fractionation is not performed, and no pre-adsorption mother liquor is prepared for the main segment.

[0079] Specifically, 1000g of nano-nickel powder was directly added to isopropanol to prepare a slurry with a solid content of 15wt% and polyvinylpyrrolidone K30 added at 0.08wt% of the powder mass. The slurry was stirred at 1500r / min at 25℃ and dispersed at 120W / L ultrasonic power density for 6min to obtain the slurry to be treated.

[0080] Subsequently, the slurry to be treated was processed under the common displacement conditions and low-oxygen common drying conditions in Example 1 to obtain nickel powder.

[0081] Comparative Example 2: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that after low-oxygen dry fractionation, the fine end segment accounts for 1 wt% of the original powder mass, the main segment accounts for 94 wt% of the original powder mass, and the coarse end segment accounts for 5 wt% of the original powder mass; the remaining steps and conditions are the same as in Example 1.

[0082] Comparative Example 3: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that after low-oxygen dry fractionation, the fine end segment accounts for 12 wt% of the original powder mass, the main segment accounts for 83 wt% of the original powder mass, and the coarse end segment accounts for 5 wt% of the original powder mass; the remaining steps and conditions are the same as in Example 1.

[0083] Comparative Example 4: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that after low-oxygen dry fractionation, the fine end segment accounts for 5 wt% of the original powder mass, the main segment accounts for 94 wt% of the original powder mass, and the coarse end segment accounts for 1 wt% of the original powder mass; the remaining steps and conditions are the same as in Example 1.

[0084] Comparative Example 5: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that after low-oxygen dry fractionation, the fine end segment accounts for 5 wt% of the original powder mass, the main segment accounts for 82 wt% of the original powder mass, and the coarse end segment accounts for 13 wt% of the original powder mass; the remaining steps and conditions are the same as in Example 1.

[0085] Comparative Example 6: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that fresh dispersion is used instead of the pre-adsorption mother liquor of the main body to treat the fine end segment and the coarse end candidate powder.

[0086] Specifically, the low-oxygen dry state fractionation was carried out according to the method of Example 1 to obtain a fine end segment, a main body segment and a coarse end segment, wherein the fine end segment accounts for 5 wt% of the original powder mass, the main body segment accounts for 90 wt% of the original powder mass, and the coarse end segment accounts for 5 wt% of the original powder mass.

[0087] The main segment was prepared as a main slurry according to the method of Example 1, but the main segment pre-adsorption mother liquor was not separated from the main slurry. A fresh dispersion with the same liquid phase composition as the main slurry was prepared separately, and the fresh dispersion was divided into a first part of fresh dispersion and a second part of fresh dispersion at a mass ratio of 1:1.

[0088] The fine end segment was added to the first part of the fresh dispersion for equalization treatment, and the fine end segment was separated according to the method in Example 1 to obtain the fine end remixed slurry; the coarse end segment was subjected to wet release treatment according to the method in Example 1 to obtain coarse end candidate powder, and the coarse end candidate powder was added to the second part of the fresh dispersion for treatment to obtain the coarse end remixed slurry; then wet reconstruction, co-displacement, solid-liquid separation and low oxygen co-drying were performed according to the method in Example 1 to obtain nickel powder.

[0089] Comparative Example 7: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that the amount of pre-adsorption mother liquor prepared in the main body segment is different.

[0090] Specifically, the low-oxygen dry-state classification and main slurry preparation were carried out according to the method of Example 1, except that 15 wt% of the slurry was separated from the main slurry for solid-liquid separation, and the supernatant after centrifugation was collected as the main segment pre-adsorption mother liquor. The main segment solid obtained by centrifugation was returned to the unseparated part of the main slurry and mixed evenly. The obtained main segment pre-adsorption mother liquor was divided into a first part pre-adsorption mother liquor and a second part pre-adsorption mother liquor at a mass ratio of 1:1, and used for subsequent processing of fine end segment and coarse end candidate powder, respectively. The remaining steps and conditions were the same as in Example 1.

[0091] Comparative Example 8: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that the amount of pre-adsorption mother liquor prepared in the main body segment is different.

[0092] Specifically, the low-oxygen dry-state classification and main slurry preparation were carried out according to the method of Example 1, except that 60 wt% of the slurry was separated from the main slurry for solid-liquid separation, and the supernatant after centrifugation was collected as the main segment pre-adsorption mother liquor. The main segment solid obtained by centrifugation was returned to the unseparated part of the main slurry and mixed evenly. The obtained main segment pre-adsorption mother liquor was divided into a first part pre-adsorption mother liquor and a second part pre-adsorption mother liquor at a mass ratio of 1:1, and used for subsequent processing of fine end segment and coarse end candidate powder, respectively. The remaining steps and conditions were the same as in Example 1.

[0093] Comparative Example 9: This comparative example provides a dry and wet combined fractionation method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that the fine end segment and the coarse end candidate powder were not subjected to equalization treatment using the pre-adsorption mother liquor of the main segment.

[0094] Specifically, the low-oxygen dry grading and main slurry preparation were carried out according to the method of Example 1 to obtain the fine end segment, the main segment, the coarse end segment, and the main slurry.

[0095] For the fine end segment, instead of adding it to the first pre-adsorption mother liquor for equalization treatment, the fine end segment is directly added to isopropanol for dispersion and separated according to the short-range centrifugation conditions for the fine end segment in Example 1 to obtain the fine end slurry.

[0096] For the coarse end segment, wet release treatment was performed according to the method of Example 1 to obtain coarse end candidate powder; the coarse end candidate powder was not added to the second part of the pre-adsorption mother liquor for equalization treatment, but was directly added to isopropanol for dispersion to obtain coarse end slurry.

[0097] Subsequently, the main slurry, fine-end slurry, and coarse-end slurry were mixed for wet reconstruction; wherein, on a dry basis, the mass ratio of the corresponding powder in the main segment, the corresponding powder in the fine-end slurry, and the corresponding powder in the coarse-end slurry was 92:3:5; the remaining common replacement, solid-liquid separation, and low-oxygen common drying conditions were the same as in Example 1, and nickel powder was obtained.

[0098] Comparative Example 10: This comparative example provides a method for preparing nano-nickel powder for MLCC electrodes. The difference between this method and Example 1 is that the main body segment, the fine end remixed slurry, and the coarse end remixed slurry are not reconstructed in a wet state, but are dried separately and then mixed in a dry state.

[0099] Specifically, the following steps were performed according to Example 1: low-oxygen dry classification, preparation of main slurry, preparation of pre-adsorption mother liquor for main segment, equalization treatment of fine end segment, and equalization treatment of coarse end candidate powder, to obtain main slurry, fine end recycled slurry, and coarse end recycled slurry, respectively.

[0100] Subsequently, the main slurry, the fine-end recycled slurry, and the coarse-end recycled slurry were subjected to displacement, solid-liquid separation, and low-oxygen drying, respectively, to obtain dry powder of the main section, dry powder of the fine-end recycled slurry, and dry powder of the coarse-end recycled slurry; then, they were dry-mixed at a dry powder mass ratio of 92:3:5 to obtain nickel powder.

[0101] The nickel powder obtained in the examples and comparative examples was tested and evaluated to verify the effect of the method of the present invention on improving the particle size window and powder stability of nano-nickel powder for MLCC electrodes.

[0102] Experimental Example 1: This experimental example aims to evaluate the particle size distribution and finished powder recovery rate of the nickel powder obtained in the examples and comparative examples.

[0103] Nickel powder obtained in Examples 1-6 and Comparative Examples 1-5 was used as the test object. During the test, each sample was dispersed in isopropanol at a solid content of 15 wt%, and 0.08 wt% polyvinylpyrrolidone K30 was added. The mixture was stirred at 1500 r / min for 5 min and dispersed at an ultrasonic power density of 120 W / L for 3 min. Subsequently, D10, D50, D90 and D99 were measured using a laser particle size analyzer, and D10 / D50 and D99 / D50 were calculated. D10 / D50 was used to evaluate the relative distribution of fine-end powder in the finished product, and D99 / D50 was used to evaluate the relative distribution of coarse-end powder in the finished product.

[0104] Simultaneously, each sample was observed using a scanning electron microscope. Before testing, the samples were dispersed in the same manner and dropped onto the conductive adhesive surface. After drying, five fields of view were randomly selected at 20,000x magnification for statistical analysis. Particles with a diameter ≥500nm were counted as abnormal coarse-end particles, and a total of 500 particles were counted. The number of abnormal coarse-end particles in each 500 particles was used as an auxiliary evaluation index for coarse-end residue. The recovery rate of the finished powder was calculated as the ratio of the mass of the final dried nickel powder to the mass of the original powder. The test results are shown in Table 1 and 2. Figure 1 As shown: Table 1. Particle size distribution and finished powder recovery rate of nickel powder

[0105] From Table 1 and Figure 1 As can be seen, the nickel powder obtained in Examples 1-6 has a D99 / D50 of 2.22-2.45, a D10 / D50 of 0.39-0.43, an abnormal coarse-end particle count of 3-10 per 500 particles, and a finished powder recovery rate of 86.8-93.0%, indicating that the nickel powder obtained in the examples can maintain a good balance between coarse-end particle residue, fine-end distribution, and finished product recovery rate.

[0106] The D99 / D50 ratio of the sample in Comparative Example 1 increased, and the number of abnormal coarse-end particles was relatively large, indicating that it is difficult to control the coarse-end residue and fine-end fluctuations simultaneously by only performing full dispersion treatment on the raw powder; the D10 / D50 ratio of the sample in Comparative Example 2 was lower than that in Examples 1-6, indicating that when the fine-end powder is not fully separated, it will still affect the fine-end distribution of the finished product; the powder recovery rate of Comparative Example 3 decreased, indicating that excessive separation of the fine-end segment will increase powder loss and reduce the overall recovery level.

[0107] The D99 / D50 ratio of Comparative Example 4 increased, and the number of abnormal coarse-end particles increased, indicating that when the separation of the coarse-end segment is insufficient, some coarse particles will still remain in the main powder. Although Comparative Example 5 underwent wet release treatment, the powder recovery rate decreased and the D99 / D50 was still higher than that of Examples 1-6, indicating that excessive separation of the coarse-end segment will increase the load of subsequent coarse-end treatment, which is not conducive to balancing particle size stability and powder recovery rate.

[0108] Experimental Example 2: This experimental example is used to evaluate the effects of pre-adsorption mother liquor and equalization treatment on the state of the recycled slurry and the redispersion performance of the finished product.

[0109] Example 1, Example 4 and Comparative Examples 6-9 were selected as experimental subjects. During the test, the viscosity of the finished slurry, redispersion stability and dispersant residue of the dried nickel powder obtained from each sample were tested.

[0110] The viscosity of the 15wt% slurry was determined as follows: the dried nickel powder was dispersed in isopropanol at a solid content of 15wt%, and 0.08wt% of polyvinylpyrrolidone K30 was added. The mixture was stirred at 1500r / min for 5min and the viscosity of the slurry was then measured.

[0111] The increase in D99 after redispersion is used to characterize the degree of coarse-end particle size enlargement after redispersion of the dried product. It is calculated based on the D99 of the reconstituted slurry and according to the increase ratio of the redispersion D99 to the D99 of the reconstituted slurry. The redispersion conditions of the dried product are consistent with the dispersion conditions in the viscosity test of 15wt% slurry. The residual amount of dispersant is determined by thermogravimetric analysis.

[0112] To evaluate the disturbance caused by the addition of fine-end and coarse-end remixed slurries to the bulk slurry, the viscosity increase after the addition of the fine-end remixed slurry and the D99 / D50 increase after the addition of the coarse-end remixed slurry were recorded during the wet reconstruction process. The viscosity increase after the addition of the fine-end remixed slurry refers to the increase in the viscosity of the bulk slurry after adding the fine-end remixed slurry, measured at 15 wt% solids content, relative to the viscosity of the bulk slurry before addition. The D99 / D50 increase after the addition of the coarse-end remixed slurry refers to the increase in D99 / D50 relative to the value before the addition of the coarse-end remixed slurry after adding coarse-end remixed slurry to a slurry already containing fine-end remixed slurry. The test results are shown in Table 2 and [Table data missing]. Figure 2 As shown: Table 2. Effects of pre-adsorption mother liquor and equalization treatment on powder state in the main body section.

[0113] From Table 2 and Figure 2 It can be seen that the 15wt% slurry viscosities of the nickel powder obtained in Examples 1 and 4 are 52.1 mPa·s and 49.6 mPa·s, respectively, and the D99 increase after redispersibility is 6.8% and 5.9%, respectively. Meanwhile, the viscosity increase after adding the fine end does not exceed 8.6%, and the D99 / D50 increase after adding the coarse end does not exceed 0.06, indicating that the fine end remixed slurry and the coarse end remixed slurry have little disturbance to the viscosity of the main slurry and the coarse end particle size distribution.

[0114] The viscosity of the 15wt% nickel powder slurry obtained in Comparative Example 6 increased to 74.3 mPa·s, and the D99 increase after redispersibility increased to 14.5%. The viscosity of the 15wt% nickel powder slurry obtained in Comparative Example 9 increased to 82.5 mPa·s, and the D99 increase after redispersibility increased to 19.2%. Furthermore, the viscosity increase after adding the fine end and the D99 / D50 increase after adding the coarse end both increased, indicating that when the pre-adsorption mother liquor in the main section is used in conjunction with the equalization treatment, the state difference of the recycled slurry after entering the main slurry can be reduced.

[0115] Compared with Examples 1 and 4, the viscosity of 15wt% slurry, the increase in D99 after redispersibility, the increase in viscosity after adding the fine end, and the increase in D99 / D50 after adding the coarse end of Comparative Examples 7 and 8 were all increased, indicating that the amount of pre-adsorbed mother liquor prepared in the main body section affects the processing stability of the fine end section and the coarse end candidate powder.

[0116] Experimental Example 3: This experimental example is used to evaluate the effects of wet reconstruction, co-displacement and low-oxygen co-drying on the sampling consistency and redispersion performance of finished nickel powder.

[0117] Nickel powder obtained from Examples 1, 4, and Comparative Example 10 was used as the test object. After each sample was dried, it was placed in a clean sample tray and spread out. Samples were taken from the upper, middle, lower, left, and right regions of the sample tray. D50, D90, and D99 were measured at each sampling point, and D99 / D50 was calculated. The average value of D99 / D50 is the average value of D99 / D50 at the five sampling points. The range of D99 / D50 is the difference between the maximum and minimum values ​​of D99 / D50 at the five sampling points. The fluctuation rate of D99 / D50 is calculated according to the relative standard deviation of the D99 / D50 test values ​​at the five sampling points.

[0118] Meanwhile, each sample was dispersed in isopropanol at a solid content of 15 wt%, and polyvinylpyrrolidone K30 (0.08 wt% of nickel powder) was added. The mixture was stirred at 1500 r / min for 5 min and then dispersed at an ultrasonic power density of 120 W / L for 3 min. The viscosity of the 15 wt% slurry was measured. For Examples 1 and 4, the reconstituted slurry D99 after wet reconstruction and before co-displacement was used as the baseline. For Comparative Example 10, the wet mixed slurry D99 formed by mixing the main slurry, fine-end reconstituted slurry, and coarse-end reconstituted slurry in the corresponding dry basis ratio was used as the baseline. The increase in D99 after redispersibility was calculated according to the increase ratio of the redispersible D99 relative to the reconstituted slurry D99. The residual amount of dispersant was determined by thermogravimetric analysis, and the residual amount fluctuation rate was calculated according to the relative standard deviation of the dispersant residual amount detection values ​​at five sampling points. The test results are shown in Table 3 and... Figure 3 : Table 3. Effects of wet remodeling and co-drying on product consistency

[0119] From Table 3 and Figure 3 As can be seen, the D99 / D50 volatility of the nickel powder obtained in Examples 1 and 4 is 1.1% and 0.8%, respectively, and the D99 / D50 range is 0.06 and 0.04, respectively; the D99 / D50 volatility of Comparative Example 10 increases to 5.3%, and the D99 / D50 range increases to 0.31, indicating that the present invention can reduce the coarse end distribution difference between different sampling locations, so that the finished nickel powder has better sampling consistency.

[0120] The 15wt% slurry viscosities of Examples 1 and 4 were 52.1 mPa·s and 49.6 mPa·s, respectively, and the D99 increases after redispersibility were 6.8% and 5.9%, respectively. The 15wt% slurry viscosity of Comparative Example 10 increased to 69.5 mPa·s, and the D99 increase after redispersibility increased to 17.6%. This indicates that reconstructing the main slurry, fine-end remixed slurry, and coarse-end remixed slurry in a wet state and then displacing and drying them together can reduce the coarse-end enlargement phenomenon that occurs when powders of different particle sizes are redispersed after drying. However, when they are dried separately and then mixed in a dry state, the state differences between powders of different particle sizes are more difficult to eliminate, and the resulting nickel powder is more likely to exhibit coarse-end particle size enlargement and increased slurry viscosity after redispersibility.

[0121] Furthermore, the residual fluctuation rates of Examples 1 and 4 were 3.2% and 2.8%, respectively, while the residual fluctuation rate of Comparative Example 10 was 12.5%. This indicates that the main slurry, fine-end reconstituted slurry, and coarse-end reconstituted slurry in the examples were jointly replaced and dried after wet reconstruction, which is beneficial to reducing the residual differences between different sampling locations.

[0122] Experimental Example 4: This experimental example is used to verify the adaptability of the method of the present invention under different grading ratios and process parameters.

[0123] During testing, D10 / D50, D99 / D50, and the recovery rate of the finished powder were determined according to the testing method described in Experimental Example 1. The viscosity of the 15wt% slurry was determined according to the method described in Experimental Example 2, that is, the dried nickel powder was dispersed in isopropanol at a solid content of 15wt%, and 0.08wt% of polyvinylpyrrolidone K30 was added. After stirring at 1500 r / min for 5 min, the viscosity of the slurry was measured. The increase in D99 after redispersibility was calculated based on the D99 of the reconstituted slurry, according to the increase ratio of the D99 after redispersibility to the D99 of the reconstituted slurry. The increase in oxygen content was the difference between the oxygen content of the finished nickel powder and the oxygen content of the corresponding original powder. The test results are shown in Table 4 and [Table data missing]. Figure 4 As shown: Table 4 Finished Product Indicators

[0124] From Table 4 and Figure 4 It can be seen that the finished products obtained in each embodiment can maintain relatively stable results in terms of particle size distribution, slurry viscosity, redispersion performance and powder recovery rate.

[0125] Figure 4 The normalized comparison was performed using D99 / D50≤2.5, 15wt% slurry viscosity≤80mPa·s, and D99 increase ≤15% after redispersibility as relative control limits. The normalized value is the ratio of the measured value to the corresponding control limit. The results show that the normalized values ​​of the above three items in Examples 1-6 are all less than 1, indicating that the finished products obtained in each example did not show significant enlargement of coarse-end particle size, abnormal increase of slurry viscosity, or significant increase of redispersible particle size after drying.

[0126] To further investigate the stability of repeated preparations, batch-to-batch fluctuation statistics were performed on the D99 / D50, 15wt% slurry viscosity, and D99 increase after redispersion of the products obtained in Examples 1-6. The results are shown in Table 5. Table 5 Batch volatility of finished products

[0127] As shown in Table 5, the batch fluctuation rate of D99 / D50 of the finished products obtained in Examples 1-6 was 1.5-3.2%, the batch fluctuation rate of 15wt% slurry viscosity was 2.0-4.1%, and the batch fluctuation rate of D99 increase after redispersibility was 2.5-4.8%. This indicates that the nickel powder prepared in multiple batches in each example has good repeatability in terms of particle size distribution, slurry viscosity, and redispersibility. This demonstrates that the method of the present invention has good adaptability to different classification states and process parameter combinations, and can stably obtain nano-nickel powder suitable for MLCC electrodes.

[0128] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for preparing nano-nickel powder for MLCC electrodes using a combined dry and wet fractionation process, characterized in that, Includes the following steps: S1: Take MLCC electrode nano-nickel powder raw material and classify it under low oxygen dry conditions to obtain fine end segment, main body segment and coarse end segment. The fine end segment accounts for 3-8 wt% of the raw powder mass, the main body segment accounts for 86-93 wt% of the raw powder mass, and the coarse end segment accounts for 3-8 wt% of the raw powder mass. The fine end segment and coarse end segment together account for 7-14 wt% of the raw powder mass. S2: The main body segment is added to an alcohol dispersion medium containing a dispersant for dispersion treatment to obtain a main body slurry. A slurry accounting for 30-45 wt% of the total mass of the main body slurry is separated for solid-liquid separation. The separated liquid phase is collected as the main body segment pre-adsorption mother liquor, and the separated solid phase is returned to the unseparated part of the main body slurry. The main body segment pre-adsorption mother liquor is divided into a first part pre-adsorption mother liquor and a second part pre-adsorption mother liquor. S3: The fine end segment is added to the first part of the pre-adsorption mother liquor for equalization treatment. After separation and removal of the fine end discharge, fine end remixed slurry is obtained. The coarse end segment is added to the alcohol dispersion medium for wet release treatment. After separation and removal of the coarse end discharge, coarse end candidate powder is obtained. The coarse end candidate powder is then added to the second part of the pre-adsorption mother liquor for equalization treatment to obtain coarse end remixed slurry. S4: Mix the main slurry with the fine-end remixed slurry and the coarse-end remixed slurry for wet reconstruction to obtain the reconstructed slurry; S5: The reconstructed slurry is subjected to co-displacement, solid-liquid separation and low-oxygen co-drying to obtain nano-nickel powder for MLCC electrodes.

2. The method for preparing MLCC electrode nano-nickel powder using a combined dry and wet fractionation method according to claim 1, characterized in that: In S1, the low-oxygen dry conditions are nitrogen or argon atmosphere, with an oxygen content ≤1000ppm, an atmosphere dew point ≤-20℃, and a powder temperature ≤40℃.

3. The method for preparing MLCC electrode nano-nickel powder using a combined dry and wet fractionation method according to claim 1, characterized in that: In S1, the grading is carried out using an air classifier, with a grading airflow velocity of 3-15 m / s and a grading wheel rotation speed of 2500-9000 r / min.

4. The method for preparing MLCC electrode nano-nickel powder using a combined dry and wet fractionation method according to claim 1, characterized in that: In S2 and S3, the alcohol dispersion medium is selected from anhydrous ethanol, isopropanol, or a mixture of the two, and the alcohol dispersion medium used when the coarse end segment is subjected to wet release treatment is the same as the alcohol dispersion medium used when the main body segment is prepared into the main slurry.

5. The method for preparing MLCC electrode nano-nickel powder using a combined dry and wet fractionation method according to claim 1, characterized in that: In S2, the dispersant is selected from one or more of polyvinylpyrrolidone, ammonium polyacrylate, and ammonium citrate. When preparing the main slurry, the solid content of the main segment is 10-18 wt%, and the amount of the dispersant is 0.04-0.12 wt% of the mass of the main segment.

6. The method for preparing MLCC electrode nano-nickel powder using a combined dry and wet fractionation method according to claim 1, characterized in that: In S2, the pre-adsorption mother liquor of the main section is divided into a first part of pre-adsorption mother liquor and a second part of pre-adsorption mother liquor at a mass ratio of 0.8-1.2:

1.

7. The method for preparing MLCC electrode nano-nickel powder by combined dry and wet fractionation according to claim 1, characterized in that: In S3, when the fine end segment is added to the first part of the pre-adsorption mother liquor for equalization treatment, the solid content of the fine end segment is 2-10wt%. After equalization treatment, it is separated by short-path centrifugation, and 25-30 vol% of the slurry on the upper liquid surface is removed according to the total volume of the slurry after centrifugation. The remaining slurry is used as the fine end remixing slurry.

8. The method for preparing MLCC electrode nano-nickel powder by combined dry and wet fractionation according to claim 1, characterized in that: In S3, when the coarse end segment is subjected to wet release treatment, the solid content of the coarse end segment is 3-15wt%. After wet release treatment, it is separated by short-path centrifugation, and 5-20vol% of the concentrated slurry from the bottom settling side is removed as coarse end discharge based on the total volume of the separated slurry. The remaining slurry is collected as coarse end candidate powder after solid-liquid separation.

9. The method for preparing MLCC electrode nano-nickel powder using a combined dry and wet fractionation method according to claim 1, characterized in that: In S3, when the coarse-end candidate powder is added to the second part of the pre-adsorption mother liquor for equalization treatment, the solid content of the coarse-end candidate powder is 3-12wt%, and it is stirred at 10-30℃.

10. The method for preparing MLCC electrode nano-nickel powder by combined dry and wet fractionation according to claim 1, characterized in that: In S4, during wet reconstruction, the powder corresponding to the main segment in the reconstruction slurry accounts for 88-97 wt% of the final product mass, the corresponding powder in the fine end reconstituted slurry accounts for 0.5-5 wt% of the final product mass, and the corresponding powder in the coarse end reconstituted slurry accounts for 1-8 wt% of the final product mass.

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