Nano-sized nickel powder for high capacity MLCC electrode and preparation method thereof

Abstract

This invention relates to the field of MLCC electrode materials technology, and discloses a nanoscale nickel powder for high-capacitance MLCC electrodes and its preparation method. The method includes: preparing a complex-type nickel source solution; taking a portion and diluting it to perform a low-concentration nucleation reaction to obtain an FCC seed suspension; simultaneously adding the remaining nickel source and reducing agent to the seed suspension, and carrying out a growth reaction under low reduction flux to control the free Ni. 2+ Concentration and redox potential; after the reaction, crystal phase repair and aging treatment is carried out in a weak complexing and weak reducing environment; after solid-liquid separation, it is washed with weak alkaline water, deionized water and organic solvent in sequence; wet classification is used to remove coarse particles; after mild passivation, it is dried at low temperature. This invention improves the sintering shrinkage consistency of nickel powder by suppressing the metastable HCP nickel phase and stacking faults induced by rapid reduction in wet chemical synthesis, and solves the problem of cracking and reliability failure of the inner electrode layer of MLCC caused by crystal defects.

Description

Technical Field

[0001] This invention relates to the field of MLCC electrode materials technology, and in particular to a nanoscale nickel powder for high-capacitance MLCC electrodes and its preparation method. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are developing towards miniaturization and high capacitance. The continuous thinning of the internal electrode layer places higher demands on the particle size, morphology, and dispersibility of nickel powder. As the core material of the base metal internal electrode, the preparation technology of nickel powder directly determines the performance and reliability of MLCCs. At present, the main preparation methods include physical vapor deposition (PVD), chemical vapor deposition (CVD), and wet chemical method. Among them, the wet chemical method is regarded as a promising route for industrialization due to its advantages such as simple process, controllable cost, and continuous production. It has been widely studied and applied in the field of nickel powder preparation for MLCC internal electrodes.

[0003] For example, Chinese patent CN121467686A discloses a method for preparing highly dispersed ultrafine spherical nickel powder, which involves pre-reaction in a gas-liquid confined micro-region using nickel salt aqueous solution and precipitant micro-nano aerosol, followed by homogeneous hydrothermal reaction and vacuum calcination to prepare highly dispersed ultrafine spherical nickel powder. However, the above-mentioned existing technical solutions all focus on the control of the macroscopic morphology, particle size distribution and dispersibility of nickel powder. Recent academic research has shown that nano-nickel powder prepared by wet chemical methods has crystal defects induced by rapid growth kinetics.

[0004] In their paper "Liquid-Phase Synthesis and Regulatory Mechanisms of Nano-Nickel Powders for MLCC Inner Electrodes" published in *Nanomaterials*, Zhenzong Quan et al. used high-resolution transmission electron microscopy to reveal the crystallographic origin of abnormal protrusions on the surface of nano-nickel particles in a conventional liquid-phase reaction system. The specific crystal plane families in these protrusion regions correspond to the metastable hexagonal close-packed (HCP) nickel phase formed by atomic stacking faults induced by rapid growth kinetics, rather than the conventionally stable face-centered cubic (FCC) structure. The coexistence of FCC / HCP crystal phases will cause the same batch of nickel powder particles to exhibit more inconsistent thermal shrinkage and sintering neck formation behavior during the debinding to co-firing stage, which can easily induce local abnormal shrinkage, pore connectivity or decreased continuity of the inner electrode layer, thereby increasing the risk of electrode cracking, wire breakage and reliability failure. Summary of the Invention

[0005] The technical problem to be solved by this invention is to suppress the metastable HCP nickel phase and stacking faults induced by rapid liquid-phase reduction and improve the sintering shrinkage consistency of nano-nickel powder. To this end, we propose a nano-sized nickel powder for high-capacitance MLCC electrodes and its preparation method.

[0006] To achieve the above objectives, this application adopts the following technical solution: a nano-sized nickel powder for high-capacity MLCC electrodes and its preparation method, comprising the following steps: S1: adding water-soluble nickel salt, complexing agent, and dispersant to deionized water, stirring to dissolve, adjusting the pH, and deoxygenating under an inert atmosphere to obtain a complexed nickel source solution; S2: taking a portion of the complexed nickel source solution obtained in S1, diluting it with deionized water, heating it under an inert atmosphere, adjusting the pH, adding a reducing agent to carry out a nucleation reaction, and obtaining an FCC seed suspension; S3: using the remaining complexed nickel source solution in S1 as a nickel source for growth, and the reducing agent solution as a reducing agent for growth, adding them simultaneously to the FCC seed suspension obtained in S2 to carry out a growth reaction, controlling the free Ni during the reaction. 2+ The concentration was 0.03-2.0 mmol / L, and the nickel ion reduction flux was 0.10-1.50 mmol / (L·min); S4: After the reaction in S3, crystal phase repair aging treatment was carried out in a weak complexing and weak reducing environment. During the aging process, a crystal phase repair auxiliary agent was added and the concentration of the weak reducing agent was maintained. The concentration of the crystal phase repair auxiliary agent in the reaction system was 0.001-0.030 mol / L, and the concentration of the weak reducing agent in the reaction system was 0.001-0.020 mol / L; S5: The nickel powder suspension obtained in S4 was separated into solid and liquid phases to obtain a wet filter cake of nickel powder. It was washed successively with weak alkaline water, deionized water and organic solvent, and then redispersed in a fractionation medium for wet fractionation to remove coarse particles. It was then subjected to mild passivation treatment in an inert atmosphere and then dried at low temperature to obtain nanoscale nickel powder for high-capacity MLCC electrodes. A crystal phase repair aid is added during the aging process, and the concentration of a weak reducing agent is maintained during the aging process. The concentration of the crystal phase repair aid in the reaction system is 0.001-0.030 mol / L, and the concentration of the weak reducing agent in the reaction system is 0.001-0.020 mol / L.

[0007] Preferably, the nickel salt is selected from nickel sulfate, nickel acetate, or nickel nitrate, and the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, ammonium polyacrylate, and polyvinyl alcohol.

[0008] Preferably, the complexing agent includes a first complexing agent and a second complexing agent, wherein the first complexing agent is one or more of sodium citrate, ammonium citrate, and potassium citrate, and the second complexing agent is one or more of sodium tartrate, ammonium tartrate, sodium malate, and sodium lactate.

[0009] Preferably, the pH in step S1 is 8.5-10.2, and the pH in step S2 is 9.2-10.2.

[0010] Preferably, in step S1, the Ni in the complexed nickel source solution... 2+ The concentration is 0.08-0.35 mol / L.

[0011] Preferably, in step S3, the reducing agent reacts with Ni. 2+ The molar ratio is 1.00-1.80:1.

[0012] Preferably, the weak reducing agent in step S4 is one or more of hydrazine hydrate, ascorbic acid, and sulfite, and the crystal phase repair aid is one or more of ammonium citrate, sodium citrate, ammonium tartrate, sodium tartrate, and sodium malate.

[0013] Preferably, in step S2, the nucleation stage Ni 2+ The concentration is 0.015-0.10 mol / L, and the molar amount of Ni in the nickel source used for nucleation accounts for 2-15% of the total molar amount of Ni.

[0014] Preferably, the weakly alkaline washing solution is deionized water with pH adjusted by ammonia, ammonium carbonate or ammonium bicarbonate, and its pH is 7.8-9.2. The organic solvent is one or more of ethanol, isopropanol and n-propanol.

[0015] Preferably, the passivation temperature in step S5 is 25-70℃ and the passivation time is 10-120 min.

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

[0017] This invention constructs an FCC seed template through low-concentration pre-nucleation, providing a stable lattice guide for subsequent growth. Combined with low-reduction flux segmented growth, the nickel atom deposition rate is controlled within the range of crystal plane diffusion and rearrangement capabilities, avoiding atomic stacking faults induced by rapid reduction. Further, phase repair and aging under a weak reduction environment utilizes weak complexation and weak reduction conditions to promote atomic rearrangement or slight dissolution-redeposition of local high-energy stacking structures on the particle surface, transforming them into a stable FCC phase. These steps work together to form a complete crystal phase stability control chain from seed induction and growth regulation to post-treatment repair. Without introducing foreign impurities, it suppresses the metastable HCP nickel phase and stacking faults induced by rapid reduction in wet chemical synthesis, thereby improving the consistency of shrinkage behavior of nickel powder during subsequent sintering and reducing the risk of cracking and reliability failure in the inner electrode layer of MLCCs due to uneven crystal structure. 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 This is a process flow diagram of a method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to the present invention.

[0020] Figure 2 This is an HRTEM image of the edge region of the nanoparticles in Example 1 of the present invention;

[0021] Figure 3 This is a bar graph showing the electrode cracking rate and aging failure rate of each sample in Experiment Example 4.

[0022] Figure 4 This is a bar chart showing the average breakdown voltage of each sample in Experiment Example 4. Detailed Implementation

[0023] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0024] This invention provides a nano-sized nickel powder for high-capacitance MLCC electrodes, wherein the nano-sized nickel powder has a D 50 The wavelength range is 60-220nm, preferably 80-180nm; D 90 / D 10 Not higher than 2.5, preferably not higher than 2.2; D max Not higher than 1000nm, preferably not higher than 800nm; the D 50 D 90 D 10 and D max The particle size distribution can be determined by laser particle size analysis, dynamic light scattering, or scanning electron microscopy. It is preferred to use scanning electron microscopy to count at least 200 particles before determining the particle size.

[0025] The obtained nano-sized nickel powder contains an FCC phase content of not less than 95 wt%, preferably not less than 97 wt%; an HCP phase content of not more than 5 wt%, preferably not more than 3 wt%; an intensity ratio of the HCP characteristic peak to the FCC-Ni(111) peak in XRD not more than 0.06, preferably not more than 0.04; a particle proportion with obvious stacking faults or HCP-related protrusions observed in HRTEM not more than 10%, preferably not more than 8%; the FCC phase content and HCP phase content are determined by X-ray diffraction combined with Rietveld refinement analysis; the particle proportion with obvious stacking faults or HCP-related protrusions is determined by high-resolution transmission electron microscopy observation and counting not less than 100 particles, preferably not less than 200 particles.

[0026] The obtained nano-sized nickel powder has an oxygen content of 0.3-2.0 wt%, preferably 0.4-1.5 wt%; a carbon content of no more than 1200 ppm, preferably no more than 800 ppm; and a total Na, K, and Cl content of no more than 150 ppm, preferably no more than 100 ppm. The oxygen content can be determined using an oxygen-nitrogen-hydrogen analyzer, the carbon content can be determined using a carbon-sulfur analyzer, and the total Na, K, and Cl content can be determined using ICP-OES or ion chromatography. When this nano-sized nickel powder is used in the internal electrode slurry of high-capacity MLCCs, it exhibits relatively consistent sintering shrinkage behavior during co-firing, which can reduce the risk of localized abnormal shrinkage, interconnected pores, and electrode discontinuities in the internal electrode layer.

[0027] like Figure 1 As shown, the present invention also provides a method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes, comprising the following steps:

[0028] S1: Add water-soluble nickel salt, complexing agent and dispersant to deionized water, stir to dissolve, adjust pH to 8.5-10.2, and deoxygenate under an inert atmosphere for 15-60 min to obtain complexed nickel source solution.

[0029] S2: Take the complexed nickel source solution obtained in S1 as the nickel source for nucleation and dilute it with deionized water. Under an inert atmosphere, heat the nickel source for nucleation to 65-85℃, adjust the pH to 9.2-10.2, and stir at 300-1000 r / min. Add a reducing agent to carry out the nucleation reaction. The reducing agent is added over a period of 5-30 min. After the addition is complete, continue the reaction for 5-40 min to obtain an FCC seed suspension.

[0030] S3: The nickel source and reducing agent are simultaneously added to the FCC seed suspension obtained in S2 using a metering pump; the reaction temperature in this stage is 75-92℃; the pH is 8.8-10.0; the stirring speed is 250-900 r / min; the redox potential is -580 to -820 mV; the nickel source is added over a period of 60-300 min; after the addition is completed, the reaction is continued at a constant temperature for 10-60 min.

[0031] S4: After the S3 reaction is completed, the obtained nickel powder suspension is subjected to crystal phase repair aging treatment under a weak complexing and weak reducing environment; the temperature of crystal phase repair aging treatment is 88-110℃; the aging time is 20-180min; the pH is 8.4-9.6; the redox potential is -460 to -700mV; a crystal phase repair auxiliary agent is added during the aging process, and the concentration of the weak reducing agent is maintained during the aging process.

[0032] S5: The nickel powder suspension obtained in S4 is cooled to 20-45℃ under an inert atmosphere, and then solid-liquid separation is performed by centrifugation, membrane filtration or pressure filtration to obtain a wet nickel powder filter cake; the wet nickel powder filter cake is washed sequentially with weakly alkaline water, deionized water and organic solvent, wherein the pH of the weakly alkaline water is 7.8-9.2; the number of times the weakly alkaline water is washed is 1-5 times; the number of times the deionized water is washed is 2-6 times; and the number of times the organic solvent is washed is 1-4 times.

[0033] S6: The washed nickel powder obtained in S5 is redispersed in the classification medium and ultrasonically dispersed for 3-30 min. Then, wet classification is performed by centrifugation at an acceleration of 800-5000 g for 2-20 min.

[0034] S7: The nickel powder after S6 classification is subjected to mild passivation treatment in an inert atmosphere with an oxygen volume fraction of 0.1-3.0 vol%, a passivation temperature of 25-70℃, and a passivation time of 10-120 min; then it is dried at low temperature, vacuum dried or inert atmosphere dried at a temperature of 35-80℃, and a drying time of 4-16 h. After drying, it is sealed and packaged under nitrogen or argon protection to obtain nanoscale nickel powder for high-capacity MLCC electrodes.

[0035] Specifically, the nickel salt is selected from nickel sulfate, nickel acetate, or nickel nitrate, preferably nickel sulfate or nickel acetate, and is used to provide the Ni required to form nano-nickel powder. 2+ .

[0036] The complexing agent includes a first complexing agent and a second complexing agent, the complexing agent being used to react with Ni. 2+ Forming a complex system reduces free Ni 2+ Instantaneous concentration slows down the rate of nickel atom formation, preventing rapid reduction from causing non-equilibrium stacking defects.

[0037] The first complexing agent is one or more of sodium citrate, ammonium citrate, and potassium citrate, preferably sodium citrate or ammonium citrate; the second complexing agent is one or more of sodium tartrate, ammonium tartrate, sodium malate, and sodium lactate, preferably sodium tartrate or sodium malate, wherein the carboxylate group in the first complexing agent reacts with Ni. 2+ The molar ratio is 0.10-0.60:1; the carboxylate group in the second complexing agent reacts with Ni. 2+ The molar ratio is 0.03-0.35:1.

[0038] The sodium tartrate may be one or more of L-(+)-disodium tartrate dihydrate, D-disodium tartrate, or DL-disodium tartrate, preferably L-(+)-disodium tartrate dihydrate, whose chemical formula can be represented as Na2C4H4O6·2H2O, and CAS number 6106-24-7; the ammonium tartrate may be one or more of L-(+)-diammonium tartrate or DL-diammonium tartrate, preferably L-(+)-diammonium tartrate, whose chemical formula can be represented as C4H 12 N2O6, CAS number 3164-29-2.

[0039] The sodium malate can be one or more of L-disodium malate, DL-disodium malate, L-monodium malate, or DL-monodium malate, preferably DL-disodium malate, whose chemical formula is Na2C4H4O5 and CAS number is 676-46-0; in other embodiments, monosodium malate can also be used, whose chemical formula is NaC4H5O5 and CAS number is 58214-38-3.

[0040] The sodium citrate may be anhydrous trisodium citrate or trisodium citrate dihydrate, preferably trisodium citrate dihydrate, with the chemical formula Na3C6H5O7·2H2O and CAS number 6132-04-3; the ammonium citrate may be monoammonium citrate or triammonium citrate, preferably triammonium citrate, with the chemical formula C6H 17 N3O7, CAS number 3458-72-8; the potassium citrate can be anhydrous tripotassium citrate or tripotassium citrate monohydrate, preferably tripotassium citrate monohydrate, whose chemical formula can be represented as K3C6H5O7·H2O, CAS number 6100-05-6.

[0041] The sodium lactate may be one or more of L-sodium lactate, D-sodium lactate or DL-sodium lactate, preferably L-sodium lactate or DL-sodium lactate, and its chemical formula may be represented as NaC3H5O3; wherein, the CAS number of DL-sodium lactate may be 72-17-3, and the CAS number of L-sodium lactate may be 867-56-1.

[0042] The above chemical formulas and CAS numbers are used to describe the specific forms of the chemicals that can be used and do not constitute a limitation on the scope of protection of this invention. 2+ Forming a complex system and reducing free Ni 2+ Provided that the instantaneous concentration is adjusted, the rate of nickel atom formation is regulated, or crystal phase repair and aging are promoted, those skilled in the art may also select other hydrates, acid salts, normal salts, or optical isomers with the same anionic structure.

[0043] The dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, ammonium polyacrylate, and polyvinyl alcohol, preferably PVP-K30 or PEG-400; the amount of the dispersant added is 0.03-0.80 wt% of the mass of the complexed nickel source solution; it is used to reduce the agglomeration tendency between the generated particles and maintain the dispersion state of the seed crystals and growth particles in the liquid phase.

[0044] The reducing agent is one or more of hydrazine hydrate, ascorbic acid, sodium hypophosphite, and sodium borohydride, preferably hydrazine hydrate or a combination of hydrazine hydrate and ascorbic acid. The reducing agent, based on its effective reduction equivalent, generates Ni during the nucleation stage. 2+ The molar ratio is 1.00-1.60:1; used to process Ni 2+ It is reduced to metallic nickel, and the deposition flux of nickel atoms is controlled by adding them in stages.

[0045] The crystal phase repair aid is one or more of ammonium citrate, sodium citrate, ammonium tartrate, sodium tartrate, and sodium malate, preferably ammonium citrate or sodium citrate; the concentration of the crystal phase repair aid in the reaction system is 0.001-0.030 mol / L, and the crystal phase repair aid is used to regulate the complexation-rearrangement process on the particle surface during the aging stage, and promote the transformation of local high-energy structures into stable FCC crystal phases.

[0046] The weak reducing agent is one or more of hydrazine hydrate, ascorbic acid, and sulfite; the concentration of the weak reducing agent in the reaction system is 0.001-0.020 mol / L. The weak reducing agent is used to maintain a weak reducing environment in the aging system and avoid excessive oxidation on the particle surface.

[0047] The weakly alkaline water is deionized water with pH adjusted by ammonia, ammonium carbonate, or ammonium bicarbonate, and its pH is 7.8-9.2. Washing the wet filter cake of nickel powder with weakly alkaline water can remove residual soluble salts, complexing agents, and reducing agents in the reaction system, and avoid uncontrolled oxidation or corrosion of crystal defect areas on the surface of nano-nickel powder caused by strong acid washing.

[0048] The organic solvent is one or more of ethanol, isopropanol, and n-propanol, preferably ethanol or isopropanol. The organic solvent is used to replace the moisture on the surface of the powder and reduce drying agglomeration.

[0049] The classification medium is water, ethanol, isopropanol or a mixture thereof; the volume ratio of ethanol to water is 50:50-95:5; the solid content after redispersement is 2-20wt%; the classification medium is used to redisperse nickel powder and, in conjunction with wet classification, remove coarse particles and soft agglomerates.

[0050] The deionized water has a conductivity of less than 1.0 μS / cm; the nitrogen gas used has a purity of not less than 99.99%; the hydrazine hydrate is an 80% (w / w) aqueous solution of hydrazine hydrate; and the pH is adjusted with ammonia.

[0051] In step S1, the Ni in the complexed nickel source solution 2+ The concentration is 0.08-0.35 mol / L, free Ni 2+ The concentration was determined by ICP-OES; the deoxygenation method was to introduce nitrogen, argon or a mixture of nitrogen and argon, and the dissolved oxygen content in the solution after deoxygenation was not higher than 2.0 mg / L.

[0052] In step S2, the nucleation stage Ni is made 2+ The concentration is 0.015-0.10 mol / L; the molar amount of Ni in the nickel source used for nucleation accounts for 2-15% of the total molar amount of Ni; the average particle size of the FCC seed suspension is 10-60 nm; the crystal phase of the FCC seed suspension can be confirmed by XRD detection after sampling, centrifugation, ethanol washing and low-temperature drying, or by HRTEM lattice fringes and selected area electron diffraction; the FCC seed suspension does not undergo solid-liquid separation and directly enters the subsequent growth stage.

[0053] In step S3, the remaining complexed nickel source solution from S1 is used as the nickel source for growth, and the reducing agent solution is used as the reducing agent for growth; during the reaction, free Ni... 2+ The concentration was controlled at 0.03-2.0 mmol / L, and the nickel ion reduction flux was 0.10-1.50 mmol / (L·min); the reducing agent and Ni 2+ The molar ratio is 1.00-1.80:1; the final reaction solution contains free Ni. 2+ Concentrations below 0.10 mmol / L; rate-limited release of Ni via complexing agents. 2+ The segmented supply of reducing agent, pH control, and redox potential control are used to match the nickel atom generation rate with the diffusion and rearrangement rate on the FCC seed surface, thereby reducing atomic stacking faults and metastable HCP nickel phases induced by rapid deposition.

[0054] The formula for nickel ion reduction flux is shown below: ;

[0055] Where Φ is the nickel ion reduction flux, in mmol·L. -1 ·min -1 ; Δn is the Ni reduced within the time interval Δt. 2+ Mole number, unit: mmol; V is the volume of the reaction system, unit: L; Δt is the time interval, unit: min.

[0056] Δn can be calculated by subtracting the molar amount of Ni in the nickel source added to the reaction system per unit time from the residual soluble Ni in the filtrate of the reaction solution during the same time interval. 2+ Calculated after changes in molar quantity; under continuous and stable feeding conditions, it can also be calculated based on the Ni content in the nickel source solution. 2+ The concentration is approximated by the product of the nickel source flow rate and the concentration.

[0057] As an optional method in step S4, the crystal phase repair aging treatment can also be carried out in a closed reactor at a temperature of 105-135℃ for 20-120 minutes. Nitrogen or argon is used to replace the gas in the closed reactor to avoid air oxidation. In this invention, the weak complexing environment refers to the presence of 0.001-0.030 mol / L of crystal phase repair auxiliary agent in the reaction system; the weak reducing environment refers to the redox potential of the reaction system being maintained at -460mV to -700mV, and the concentration of the weak reducing agent being 0.001-0.020 mol / L. This step is used to cause surface atomic rearrangement or slight dissolution-redeposition in the local high-energy protrusions on the surface of nickel powder particles, reduce the proportion of HCP metastable phase and stacking fault, and further transform the nickel powder crystal structure into the stable FCC phase.

[0058] In step S5, the washing endpoint is that the conductivity of the filtrate is not higher than 50 μS / cm; the total content of Na, K, and Cl in the nickel powder after washing is not higher than 150 ppm; and the carbon content is not higher than 1200 ppm.

[0059] In step S6, the dispersion method is selected from one or more of mechanical stirring, ultrasonic dispersion, and high-shear dispersion, with a high-shear dispersion speed of 1000-6000 r / min; the wet classification method is one or more of centrifugal classification, membrane classification, sedimentation classification, or wet sieving; after wet classification, coarse particles with a particle size greater than 500-1000 nm are removed; the classified nickel powder D 90 / D 10 Not higher than 2.5.

[0060] In step S7, the mild passivation atmosphere is an oxygen-containing inert gas, which is nitrogen, argon, or a nitrogen-argon mixture; the low-temperature drying method is one of vacuum drying, freeze drying, inert atmosphere drying, or inert atmosphere spray drying.

[0061] The core working principle of this invention lies in: reducing free Ni through a complexing agent. 2+ Instantaneous concentration, FCC seed crystals are pre-formed through low-concentration nucleation, nickel atom deposition flux is controlled by synchronously adding nickel source and reducing agent in segments, and the rearrangement or slight dissolution-redeposition of high-energy structure on particle surface is promoted by weak reduction crystal phase repair and aging. The above steps work together to make nickel powder particles preferentially grow along stable FCC lattice template during formation, reducing the proportion of metastable HCP phase and stacking fault.

[0062] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art should understand that various modifications and changes can be made to the present invention without departing from the technical principles of the present invention, and these modifications and changes should also fall within the scope of protection of the present invention.

[0063] Example 1: S1: Weigh 52.6g of nickel sulfate hexahydrate, add it to 800mL of deionized water and stir to dissolve. Then add 17.6g of sodium citrate, 4.6g of sodium tartrate and 2.0g of PVP-K30, and continue stirring for 30min to form a homogeneous complexed nickel source solution. Adjust the pH of the solution to 9.3 with ammonia water, and then add deionized water to make the total volume 1000mL. Purge the solution with nitrogen gas for 30min.

[0064] S2: Take 50 mL of the complexed nickel source solution obtained in S1, dilute it with deionized water to 200 mL, and place the solution in a reactor equipped with a stirrer, temperature control, and nitrogen protection device. Under nitrogen protection, heat to 75 °C, control the stirring speed at 600 r / min, and maintain the pH at 9.6. Dilute the hydrazine hydrate solution and add it to the reaction system within 10 min, allowing the hydrazine hydrate to react with Ni in the nucleation stage. 2+ The molar ratio was 1.20:1. After the addition was completed, the reaction continued for 15 minutes to obtain a seed suspension containing FCC nickel seeds.

[0065] S3: The seed crystal suspension was heated to 84℃, the pH was maintained at 9.3-9.6, and the redox potential of the system was controlled between -660mV and -730mV. The remaining 950mL of complexed nickel source solution and hydrazine hydrate solution were simultaneously added dropwise to the seed crystal suspension using two metering pumps over a period of 150min. During the addition process, the nickel ion reduction flux was controlled at 0.65mmol / (L·min), and samples were taken every 30min. After filtration through a 0.22μm filter membrane, the free Ni in the filtrate was measured. 2+ Concentration, causing free Ni 2+ The concentration was maintained in the range of 0.1-0.8 mmol / L, and during the growth stage, hydrazine hydrate and the remaining Ni...2+ The molar ratio was 1.30:1; after the addition was completed, the reaction was continued at a constant temperature for 20 minutes until free Ni was found in the filtrate. 2+ The concentration is below 0.05 mmol / L.

[0066] S4: After the growth reaction is completed, the system temperature is raised to 98℃, and ammonium citrate is added to make its concentration in the system 0.010 mol / L. At the same time, a small amount of hydrazine hydrate is added to maintain the concentration of hydrazine hydrate in the system at about 0.006 mol / L. During the aging process, the pH is controlled at 8.9-9.2, the redox potential is controlled at -560mV to -640mV, nitrogen is continuously protected, and the aging time is 60 min.

[0067] S5: The reaction solution obtained in S4 was cooled to 35°C under nitrogen protection and then separated into solid and liquid by centrifugation. The resulting wet powder was washed sequentially with weakly alkaline deionized water (pH 8.5), deionized water, and ethanol. The weakly alkaline deionized water was washed 3 times, the deionized water was washed 3 times, and the ethanol was washed 2 times. The washing endpoint was when the conductivity of the filtrate was less than 30 μS / cm.

[0068] S6: The washed nickel powder was redispersed in a mixed medium of ethanol / water with a volume ratio of 80:20, and the solid content was controlled at 8wt%. After ultrasonic dispersion for 10 min, it was centrifuged and classified at 2500g for 8 min.

[0069] S7: The graded nickel powder is placed in a nitrogen atmosphere and a nitrogen-oxygen mixture with an oxygen content of 0.8 vol% is slowly introduced at 45°C for gentle passivation for 45 min. After passivation, it is dried under vacuum at 55°C for 8 h to obtain nanoscale nickel powder for high-capacity MLCC electrodes.

[0070] Example 2: This example provides a method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes. The difference from Example 1 is that Ni in S1... 2+ The concentration was adjusted to 0.16 mol / L, with citrate and Ni 2+ The molar ratio was adjusted to 0.25:1, with tartrate and Ni... 2+ The molar ratio was adjusted to 0.08:1; the synchronous addition time of the remaining complexed nickel source solution and hydrazine hydrate solution in S3 was extended to 210 min, and the nickel ion reduction flux was controlled to 0.38 mmol / (L·min); the crystal phase repair aging temperature in S4 was 96℃, the aging time was 90 min, and the remaining steps were the same as in Example 1.

[0071] Example 3: This example provides a method for preparing nano-sized nickel powder for high-capacity MLCC electrodes. The difference from Example 1 is that S4 adopts a closed weak reducing hydrothermal crystalline phase repair aging treatment. Specifically, the reaction solution obtained in S3 is transferred to a closed reaction vessel, nitrogen is introduced for purging, and then the vessel is sealed. The vessel is aged at 120°C for 60 minutes. No strong reducing agent is added to the aging system. Only the residual weak reducing environment in the reaction system is retained. The pH is controlled at 8.8-9.1. The remaining steps are the same as in Example 1.

[0072] Example 4: This example provides a method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes. The difference from Example 1 is that nickel acetate is used instead of nickel sulfate in S1. 2+ The concentration was 0.18 mol / L; the complexing agent was a compound system of sodium citrate and sodium malate, with citrate ions and Ni 2+ The molar ratio of malate to Ni is 0.28:1. 2+ The molar ratio is 0.12:1; the nucleation temperature in S2 is 72℃ and the nucleation time is 20min; the growth temperature in S3 is 82℃ and the feeding time is 180min, and the remaining steps are the same as in Example 1.

[0073] Comparative Example 1: This comparative example provides a method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes. The difference from Example 1 is that 52.6 g of nickel sulfate hexahydrate is weighed and added to deionized water to prepare Ni 2+ A 0.20 mol / L nickel salt solution was prepared, with 2.0 g of PVP-K30 added as a dispersant. The pH was adjusted to 9.5 using ammonia, and the solution was heated to 84 °C under nitrogen protection. Hydrazine hydrate was then added to the reaction system in one step, allowing the hydrazine hydrate to react with Ni... 2+ The molar ratio was 1.30:1. After reacting for 90 minutes, solid-liquid separation, washing, passivation and drying were performed. The remaining steps were the same as in Example 1.

[0074] Comparative Example 2: This comparative example provides a method for preparing nanoscale nickel powder for high-capacity MLCC electrodes. The difference from Example 1 is that the low-concentration nucleation step S2 is omitted. Instead, the entire complexed nickel source solution is directly heated to 84°C and then simultaneously added dropwise with hydrazine hydrate solution. The remaining steps are the same as in Example 1.

[0075] Comparative Example 3: This comparative example provides a method for preparing nanoscale nickel powder for high-capacity MLCC electrodes. The difference from Example 1 is that the low-concentration nucleation step S2 and the low-reduction flux segmented growth step S3 are retained, but the weak reduction crystal phase repair and aging step S4 is omitted. After the S3 reaction is completed, solid-liquid separation, washing, classification, passivation and drying are performed directly. The remaining steps are the same as in Example 1.

[0076] Comparative Example 4: This comparative example provides a method for preparing nanoscale nickel powder for high-capacity MLCC electrodes. The difference from Example 1 is that the synchronous addition time of the remaining nickel source and reducing agent in S3 is shortened to 45 min, and the nickel ion reduction flux is increased to about 2.15 mmol / (L·min). The remaining steps are the same as in Example 1.

[0077] In order to systematically evaluate the advantages of the method provided by the present invention in terms of crystal structure control, sintering shrinkage consistency and MLCC internal electrode application performance, the nickel powders obtained in Examples 1-4 and Comparative Examples 1-4 were compared and tested.

[0078] Experimental Example 1: The nickel powders obtained in Examples 1-4 and Comparative Examples 1-4 were tested using an X-ray diffractometer. The X-ray diffractometer used Cu and Kα rays as radiation sources, with a tube voltage of 40 kV, a tube current of 40 mA, a test angle range of 20°-90°, and a scanning speed of 5° / min. The content of FCC and HCP phases was analyzed using Rietveld refinement. High-resolution transmission electron microscopy (HRTEM) was used to observe the particle edge regions, and the proportion of particles with stacking faults or HCP-related protrusions was statistically analyzed. At least 200 nickel powder particles were randomly selected from each sample group for HRTEM statistical analysis. Particles with obvious lattice misalignment, local HCP stacking fringes, or abnormal protrusions at the particle edges were considered abnormal structure particles. The test results are shown in Table 1 below. Figure 2 As shown: Table 1. Test results of nickel powder particle size and crystal phase structure

[0079] As shown in Table 1, the nickel powders obtained in Examples 1-4 have a particle size in the nanometer range and a lower HCP phase content than the comparative example. This indicates that the present invention effectively suppresses the metastable HCP phase and stacking faults induced by rapid growth through a combination of low-concentration nucleation, low-reduction-flux segmented growth and weak-reduction crystal phase repair aging.

[0080] Experimental Example 2: The nickel powders obtained in Examples 1-4 and Comparative Examples 1-4 were pressed into test blanks with a diameter of 5 mm and a height of approximately 5 mm. Thermomechanical analysis was performed under a nitrogen-hydrogen mixed atmosphere. The N2 / H2 volume ratio in the nitrogen-hydrogen mixed atmosphere was 95 / 5, and the gas flow rate was 100 mL / min. The heating rate was 5 °C / min, and the test temperature range was from room temperature to 1000 °C. The shrinkage initiation temperature, the peak temperature of the maximum shrinkage rate, and the intra-batch deviation of the peak temperature of the maximum shrinkage rate were recorded. The test results are shown in Table 2. Table 2 Results of Nickel Powder Sintering Shrinkage Test

[0081] As can be seen from Table 2, the shrinkage initiation temperature of the nickel powder obtained in Examples 1-4 is relatively higher, and the batch deviation of the peak temperature of the maximum shrinkage rate is reduced. This indicates that the nickel powder obtained by the present invention has more consistent sintering shrinkage behavior. The reason is that the present invention reduces the degree of mixing of FCC phase and HCP metastable phase in the same batch of powder, and reduces the shrinkage difference of different crystal structure regions in the degreasing and co-firing stages.

[0082] Experimental Example 3: The nickel powder obtained from Examples 1-4 and Comparative Examples 1-4 were respectively formulated into MLCC internal electrode slurries. The slurries included nickel powder, barium titanate powder, organic carrier, dispersant, and solvent, wherein the mass fraction of nickel powder was 55 wt%, the mass fraction of barium titanate powder was 3 wt%, and the remainder was organic carrier and solvent. The slurries were milled by three rollers and then coated onto the surface of ceramic green sheets. After drying, they were laminated and pressed together. Then, in a nitrogen atmosphere, the temperature was raised to 350℃ at a heating rate of 1℃ / min and held for 2 hours for degreasing treatment. After degreasing, co-firing was carried out in a reducing atmosphere with a N2 / H2 volume ratio of 95 / 5. The co-firing heating rate was 3℃ / min, the maximum sintering temperature was 1180℃, and the holding time was 2 hours. Subsequently, the furnace was cooled to room temperature. After sintering, the internal electrode layer was observed using cross-sectional SEM, the electrode continuity was statistically analyzed, and the sheet resistance was measured. The test results are shown in Table 3. Table 3 Results of Internal Electrode Continuity and Sheet Resistance Tests

[0083] As can be seen from Table 3, after the nickel powder obtained in Examples 1-4 was used in the inner electrode film of MLCC, the electrode continuity was higher and the sheet resistance was lower after sintering. No continuous cracks or large-scale discontinuous areas appeared in the inner electrode layer. This result shows that the present invention not only improves the particle size and dispersibility of nickel powder, but also improves the shrinkage consistency of nickel powder during co-firing by controlling the crystal phase stability, thereby improving the structural integrity of the inner electrode layer of high-capacity MLCC.

[0084] Experimental Example 4: To further evaluate the reliability improvement effect of the nano-sized nickel powder prepared in this invention in the internal electrode of high-capacity MLCC, the nickel powder obtained in Examples 1-4 and Comparative Examples 1-4 were used to prepare MLCC internal electrode slurries according to the method described in Experimental Example 3. MLCC samples were prepared using the same ceramic green body, stacking, pressing, degreasing and co-firing process. 1000 sintered MLCCs were randomly selected from each group of samples for reliability testing.

[0085] The cracking rate of the inner electrode layer was statistically analyzed using a combination of cross-sectional grinding and scanning electron microscopy. A breakdown withstand voltage tester was used, with a voltage ramp rate of 50V / s, and the voltage at which the sample broke down was recorded. An insulation resistance tester was used to test the initial insulation resistance of the samples at a rated voltage of 16V or 10V. The samples were then placed in a constant temperature and humidity environment of 85℃ and 85% relative humidity and aged at a rated voltage of 16V or 10V for 1000 hours. The insulation resistance retention rate and failure rate after aging were tested, and the results are shown in Table 4. Figure 3 As shown: Table 4 MLCC Reliability Test Results

[0086] As shown in Table 4, compared with Comparative Examples 1-4, the MLCC samples prepared from nickel powder obtained in Examples 1-4 have lower internal electrode cracking rate, higher average breakdown voltage, higher initial insulation resistance, and better damp heat aging stability. Specifically, the internal electrode cracking rates of the MLCC samples obtained in Examples 1 and 2 are 0.8% and 0.6%, respectively, which are lower than 6.5% of Comparative Example 1 and 5.4% of Comparative Example 4. After aging at 85°C and 85%RH for 1000 hours, the insulation resistance retention rates of Examples 1 and 2 still reach 91.5% and 92.8%, respectively, and the failure rates after aging are only 0.6% and 0.4%, respectively.

[0087] 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 nanoscale nickel powder for high-capacitance MLCC electrodes, characterized in that, Includes the following steps: S1: Add water-soluble nickel salt, complexing agent and dispersant to deionized water, stir to dissolve, adjust pH, and deoxygenate under an inert atmosphere to obtain complexed nickel source solution; S2: Take part of the complexed nickel source solution obtained in S1, dilute it with deionized water, raise the temperature under an inert atmosphere, adjust the pH, add a reducing agent to carry out the nucleation reaction, and obtain FCC seed suspension; S3: The remaining complexed nickel source solution from S1 is used as the nickel source for growth, and the reducing agent solution is used as the reducing agent for growth. These are added simultaneously to the FCC seed suspension obtained in S2 to carry out the growth reaction. During the reaction, the free Ni is controlled. 2+ The concentration was 0.03-2.0 mmol / L, and the nickel ion reduction flux was 0.10-1.50 mmol / (L·min); S4: After the S3 reaction is completed, crystal phase repair aging treatment is carried out in a weak complexing and weak reducing environment. During the aging process, a crystal phase repair auxiliary agent is added and the concentration of the weak reducing agent is maintained. The concentration of the crystal phase repair auxiliary agent in the reaction system is 0.001-0.030 mol / L, and the concentration of the weak reducing agent in the reaction system is 0.001-0.020 mol / L. S5: The nickel powder suspension obtained in S4 is separated into solid and liquid phases to obtain a wet filter cake of nickel powder. The cake is washed sequentially with weakly alkaline water, deionized water and organic solvent, and then redispersed in a classification medium for wet classification to remove coarse particles. It is then subjected to mild passivation treatment in an inert atmosphere and dried at low temperature to obtain nanoscale nickel powder for high-capacity MLCC electrodes.

2. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: The nickel salt is selected from nickel sulfate, nickel acetate, or nickel nitrate, and the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, ammonium polyacrylate, and polyvinyl alcohol.

3. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: The complexing agent includes a first complexing agent and a second complexing agent, wherein the first complexing agent is one or more of sodium citrate, ammonium citrate, and potassium citrate, and the second complexing agent is one or more of sodium tartrate, ammonium tartrate, sodium malate, and sodium lactate.

4. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: In step S1, the pH is 8.5-10.2, and in step S2, the pH is 9.2-10.

2.

5. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: In step S1, the Ni in the complexed nickel source solution 2+ The concentration is 0.08-0.35 mol / L.

6. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: In step S3, the reducing agent and Ni 2+ The molar ratio is 1.00-1.80:

1.

7. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: In step S4, the weak reducing agent is one or more of hydrazine hydrate, ascorbic acid, and sulfite, and the crystal phase repair aid is one or more of ammonium citrate, sodium citrate, ammonium tartrate, sodium tartrate, and sodium malate.

8. The method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: In step S2, the nucleation stage Ni is made 2+ The concentration is 0.015-0.10 mol / L, and the molar amount of Ni in the nickel source used for nucleation accounts for 2-15% of the total molar amount of Ni.

9. A method for preparing nanoscale nickel powder for high-capacitance MLCC electrodes according to claim 1, characterized in that: The weakly alkaline water in step S5 is deionized water with pH adjusted by ammonia, ammonium carbonate or ammonium bicarbonate, and its pH is 7.8-9.

2. The organic solvent is one or more of ethanol, isopropanol and n-propanol. The passivation treatment temperature is 25-70℃ and the passivation time is 10-120min.

10. A nanoscale nickel powder for high-capacitance MLCC electrodes prepared by the preparation method according to any one of claims 1-9, characterized in that, Based on the total mass of the nano-grade nickel powder, the oxygen content is 0.3-2.0 wt%, the carbon content is not higher than 1200 ppm, the total content of Na, K, and Cl is not higher than 150 ppm, and the balance is nickel. The nano-grade nickel powder contains not less than 95 wt% FCC phase and not more than 5 wt% HCP phase. The nano-grade nickel powder has a D... 50 The wavelength range is 60-220nm.

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