Nickel powder manufacturing method and its use

Abstract

To provide nickel powder excellent in sintering resistance.SOLUTION: A manufacturing method of nickel powder contains preparation step S10 for preparing Ni slurry with which Ni particles are dispersed in organic solvent, sulfuration Ni layer formation step S20 for forming a sulfuration Ni layer on a surface of the Ni particle by adding a thiourea compound with non-water solubility to the Ni slurry and then heating the same and amine adhesion step S40 for adhering an amine-based compound on the surface of the Ni particle by dispersing the Ni particle in the amine-based compound and then heating the same. Thereby, since the sulfuration Ni layer including an excellent sinter inhibitory effect and the amine-based compound can be present on the surface of the Ni particle, sintering resistance of the nickel powder after manufacturing can be significantly improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to a method for producing nickel powder and its use. [Background technology]

[0002] Electrodes for electronic components such as multilayer ceramic capacitors (MLCCs) are formed, for example, by firing an electrode paste containing nickel powder. The nickel powder in the paste sinters easily at relatively low temperatures. Therefore, structural defects such as cracks may occur in the fired electrode due to differences in sintering temperature with other components (dielectrics, substrates, etc.) that are fired simultaneously. For this reason, nickel powder used to form electrodes is sometimes surface-treated with a sulfur compound (sulfurization treatment). This increases the sintering temperature of the nickel particles during firing, thereby suppressing structural defects after firing.

[0003] Examples of techniques related to this sulfurization treatment are disclosed in Patent Documents 1 and 2. For example, in the manufacturing method described in Patent Document 1, nickel powder is treated with a sulfur-containing compound. Patent Document 1 describes that this sulfurization treatment produces a coating of sulfur compounds on the surface of the nickel particles, or forms a compound layer of nickel and sulfur (Ni sulfide layer), thereby improving sintering behavior. Meanwhile, in the examples of Patent Document 2, a sulfur compound (dodecanethiol) is added to a metallic nickel particle slurry containing nickel powder and laurylamine. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2005 / 123307 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-231230 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, attempts have been made to miniaturize nickel powder for electrode formation. This reduces the film thickness of the electrode after firing, which can greatly contribute to the miniaturization of electronic components. However, the sintering temperature of nickel particles tends to decrease as the particle size decreases. For this reason, there is a growing demand for sulfurization treatment that can further improve the sintering resistance of nickel powder. The technology disclosed herein was developed in light of these circumstances and aims to realize nickel powder with excellent sintering resistance. [Means for solving the problem]

[0006] In order to solve the above problems, the technology disclosed herein provides a method for producing nickel powder (hereinafter also simply referred to as "production method") having the following configuration.

[0007] The manufacturing method disclosed herein includes a preparation step of preparing a Ni slurry in which Ni particles are dispersed in an organic solvent; a Ni sulfide layer formation step of adding a water-insoluble thiourea compound to the Ni slurry and then heating the mixture to form a Ni sulfide layer on the surfaces of the Ni particles; and an amine attachment step of dispersing the Ni particles in an amine compound and then heating the mixture to attach the amine compound to the surfaces of the Ni particles.

[0008] After extensive experiments, the present inventors discovered a surprising phenomenon: the use of a specific sulfur source (sulfur compound) in the sulfurization treatment significantly improves the sintering resistance of the produced nickel powder. Further investigation into this point revealed that, among various sulfur compounds, thiourea compounds are particularly susceptible to decomposition and can adequately supply sulfur elements to the surface of Ni particles. As described above, sulfurization of nickel powder can result in either a sulfur compound coating on the particle surface or a Ni sulfide layer on the particle surface. Comparing these, the Ni sulfide layer has a more effective sintering-inhibiting effect than the sulfur compound coating. In other words, the manufacturing method described above uses a thiourea compound to form a suitable Ni sulfide layer on the surface of Ni particles, thereby significantly improving the sintering resistance of the nickel powder. In addition, the manufacturing method disclosed herein includes an amine deposition step in which an amine compound is deposited on the surface of the Ni particles on which the Ni sulfide layer has been formed. This amine compound functions as a protective agent for the Ni particles, further significantly improving the sintering resistance of the nickel powder. As described above, the manufacturing method disclosed herein can produce nickel powder with superior sintering resistance compared to conventional methods.

[0009] In one embodiment of the manufacturing method disclosed herein, a separation step of separating Ni particles from the Ni slurry is carried out between the Ni sulfide layer formation step and the amine adhesion step, which makes it easier for the amine compound to adhere to the surface of the Ni particles, thereby further improving the sintering resistance of the manufactured nickel powder.

[0010] In one embodiment of the manufacturing method disclosed herein, the thiourea compound includes a thiourea compound represented by R1-HNCSNH-R2 (wherein R1 and R2 in the formula are linear or cyclic alkyl groups having 6 or more carbon atoms). Examples of such thiourea compounds include N,N'-diphenylthiourea, N,N'-dihexylthiourea, and 1,3-dicyclohexylthiourea. These thiourea compounds can more effectively promote the formation of a Ni sulfide layer.

[0011] In one embodiment of the production method disclosed herein, the amine compound includes an aliphatic monoamine having 8 to 18 carbon atoms. Examples of such amine compounds include n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine. These amine compounds can better protect Ni particles during firing and further improve sintering resistance.

[0012] In one embodiment of the manufacturing method disclosed herein, the average particle size of Ni particles based on FE-SEM observation is 100 nm or less. While such small Ni particles can contribute to thinner electrode layers, they are prone to sintering during firing. However, the manufacturing method disclosed herein can produce nickel powder with excellent sintering resistance even when such small Ni particles are used.

[0013] In one embodiment of the manufacturing method disclosed herein, the Ni particles are core-shell particles having a core particle and a shell covering at least a portion of the surface of the core particle, and the shell contains nickel, which allows for the production of a large amount of particles while maintaining a small particle size.

[0014] In one embodiment of the manufacturing method disclosed herein, in the Ni sulfide layer formation step, the heat treatment is carried out while bubbling an inert gas through the Ni slurry, which prevents cross-linking between thiourea compounds during heating, thereby enabling the Ni sulfide layer to be formed more efficiently.

[0015] Another aspect of the technology disclosed herein provides a nickel powder primarily composed of Ni particles. The Ni particles of the nickel powder include a Ni sulfide layer primarily composed of nickel sulfide and an amine compound attached to the surface of the Ni sulfide layer. In a photoelectron spectrum of the Ni particles measured by X-ray photoelectron spectroscopy, the ratio of the peak area of ​​the peak derived from nickel sulfide to the total peak area in the region showing the S2p orbital is 80% or more.

[0016] The nickel powder produced by the above-described manufacturing method has a sufficient nickel sulfide layer formed on the surface of the nickel particles, and an amine compound adhered to the surface of the particles. Such nickel powder has excellent sintering resistance, which can prevent structural defects such as cracks from occurring in the electrode after firing.

[0017] In one embodiment of the nickel powder disclosed herein, the average particle size of the Ni particles based on FE-SEM observation is 100 nm or less. As described above, the technology disclosed herein can ensure sufficient sintering resistance of the nickel powder even when fine Ni particles are used, which can contribute to thinner electrodes.

[0018] In one embodiment of the nickel powder disclosed herein, the Ni particles have a carbon content of 2% or more and 4% or less based on elemental analysis by combustion-infrared absorption spectroscopy. In the nickel powder disclosed herein, an amine compound adheres to the surface of the Ni particles, and a large amount of carbon element derived from the amine compound is detected. This allows the Ni particles to be adequately protected during sintering, further improving the sintering resistance of the nickel powder.

[0019] In one embodiment of the nickel powder disclosed herein, the Ni particles have an oxygen content of 2.5% or more and 4% or less, based on elemental analysis by inert gas fusion-non-dispersive infrared absorption spectroscopy, which can further improve the sintering resistance of the nickel powder.

[0020] In one embodiment of the nickel powder disclosed herein, the amine-based compound includes an aliphatic monoamine having 8 to 18 carbon atoms. Examples of such amine-based compounds include n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine. As described above, these amine-based compounds can better protect Ni particles during sintering and further improve sintering resistance.

[0021] Another aspect of the technology disclosed herein is an electrode paste. The electrode paste disclosed herein includes the nickel powder having the above-described configuration and a dispersion medium for dispersing the nickel powder. Because the electrode paste includes the nickel powder with excellent sintering resistance, it is possible to suppress the occurrence of structural defects such as cracks in the electrode after firing. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a flow diagram showing a method for producing nickel particles according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Preferred embodiments of the technology disclosed herein are described below. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the technical common sense in the relevant field. The following explanation is not intended to limit the technology disclosed herein to specific embodiments. In this specification and claims, when a specific numerical range is expressed as A to B (A and B are arbitrary numerical values), this means "greater than A and less than B." Therefore, "greater than A but less than B" is also included.

[0024] 1. Nickel particle manufacturing method The method for producing nickel particles according to this embodiment will be described below. FIG. 1 is a flow diagram showing the method for producing nickel particles according to this embodiment. As shown in FIG. 1, the production method according to this embodiment includes a preparation step S10, a Ni sulfide layer formation step S20, and an amine attachment step S40. Furthermore, in the production method according to this embodiment, a separation step S30 is carried out between the Ni sulfide layer formation step S20 and the amine attachment step S40. Each step will be described below.

[0025] (1) Preparation process S10 In the preparation step S10, a Ni slurry in which Ni particles are dispersed in an organic solvent is prepared. For example, the Ni slurry can be prepared by adding Ni particles to an organic solvent and performing a dispersion process. Alternatively, the Ni particles can be generated by, for example, a thermal decomposition method in which a Ni salt is added to an organic solvent to generate a Ni complex, followed by a heat treatment to precipitate the Ni particles. This thermal decomposition method results in Ni particles dispersed in the organic solvent, which can then be used as a Ni slurry as is. Note that the preparation step S10 in the technology disclosed herein does not necessarily require the Ni slurry to be prepared by hand; a commercially available Ni slurry may be purchased, for example. In other words, the detailed procedure of the preparation step S10 does not limit the technology disclosed herein, and conventionally known means can be used without particular limitation.

[0026] Next, raw materials for the Ni slurry that can be used in the manufacturing method according to this embodiment will be described.

[0027] (a)Ni particles Nickel particles (Ni particles) are a material that constitutes the main component of electrodes after firing. By firing these Ni particles, high-performance (low-resistance) conductive materials can be formed inexpensively. For this reason, Ni particles are suitable as an electrode material for electronic components such as MLCCs. In this specification, "Ni particles" refers to particles in which the main element of the particle surface layer is Ni. That is, "Ni particles" in this specification encompasses not only particles composed entirely of Ni (single Ni particles) but also Ni alloy particles, core-shell particles, and the like. The above-mentioned "the main element of the particle surface layer is Ni" means that Ni is the most abundant metal element identified in the particle surface layer (a region 10 nm thick from the particle surface) in elemental analysis using XPS. Specifically, "Ni particles" in this specification refer to particles in which Ni accounts for 50 mol % or more (preferably 60 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, and particularly preferably 90 mol % or more) of the total number of metal elements constituting the particle surface layer, taken as 100 mol %. Metal elements other than Ni that may be contained in Ni particles include gold (Au), platinum (Pt), silver (Ag), palladium (pd), copper (Cu), aluminum (Al), zinc (Zn), lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and barium (Ba).

[0028] The "core-shell particles" mentioned above are multilayer particles comprising a core particle and a shell covering the surface of the core particle. When core-shell particles are used as Ni particles, a shell containing Ni element is formed. On the other hand, examples of core particles include Cu particles, Au particles, Pt particles, Ag particles, and Pd particles. Forming a Ni shell on the surface of these core particles stabilizes particle size control during Ni particle production. Therefore, in producing this type of core-shell particle, a large amount of particles can be produced while maintaining a small particle size, thereby improving productivity. Among the above core particles, Cu particles are preferred from the perspective of obtaining Ni particles at low material cost while suppressing a decrease in conductivity. The shell need not completely cover the entire core particle as long as it covers at least a portion of the surface of the core particle. For example, core-shell particles (Ni particles) with sufficient conductivity can be obtained when the average coverage of the Ni shell based on SEM observation is 50% or more (more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more). The upper limit of the average coverage rate of the Ni shell may be 100% or less, 99% or less, or 95% or less.

[0029] Furthermore, the average particle size of the Ni particles, as determined by FE-SEM observation, is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 100 nm or less, and particularly preferably 60 nm or less. The use of such fine Ni particles reduces the film thickness of the electrode after firing, contributing to the miniaturization of electronic components. On the other hand, miniaturized Ni particles have reduced sintering resistance, which can cause structural defects in the electrode after firing. However, the manufacturing method according to this embodiment can effectively improve the sintering resistance of the Ni particles, thereby effectively suppressing structural defects caused by the use of miniaturized Ni particles. In other words, the manufacturing method according to this embodiment is particularly suitable for use when using fine Ni particles. The lower limit of the average particle size of the Ni particles is not particularly limited and may be 1 nm or more, 5 nm or more, or 10 nm or more. In this specification, the term "average particle size based on FE-SEM observation" refers to the cumulative 50% particle size (D) based on the number of particles in the particle size distribution of 1,000 Ni particles extracted from an image of nickel powder taken using a field emission scanning electron microscope (FE-SEM). 50 )

[0030] The shape of the Ni particles is not particularly limited and may be spherical or non-spherical. Examples of non-spherical Ni particles include plate-like, scale-like, flake-like, and irregularly shaped particles. When spherical Ni particles are used, the aspect ratio of the Ni particles is preferably 1.2 or less, more preferably 1.15 or less, and particularly preferably 1.1 or less. This facilitates improving the packing density of the Ni particles in the electrode paste. The lower limit of the aspect ratio of such spherical Ni particles is 1 or more. On the other hand, when non-spherical Ni particles are used, the aspect ratio of the Ni particles is preferably 1.3 or more, more preferably 1.5 or more, even more preferably 1.7 or more, and particularly preferably 2 or more. When Ni particles with such a high aspect ratio are used, the Ni particles are oriented along a predetermined direction in the electrode paste, which facilitates the formation of a suitable conductive path in the fired electrode. On the other hand, considering the ease of particle generation, the upper limit of the aspect ratio of non-spherical Ni particles is preferably 5 or less, more preferably 4 or less, and particularly preferably 3 or less. The nickel powder in this embodiment may be a mixed powder of spherical particles and non-spherical particles.

[0031] Furthermore, when generating Ni particles by thermal decomposition in this process, a nickel salt is used as the Ni supply source. Examples of such nickel salts include nickel formate, nickel nitrate, nickel sulfate, nickel carbonate, nickel carboxylate, nickel hydroxide, and nickel chloride. Adding these nickel salts to an organic solvent generates a nickel complex. Heating this nickel complex produces Ni particles. When generating core-shell particles having a Ni shell by thermal decomposition, a salt of the metal element that will form the core particles can be added to the organic solvent along with the nickel salt. If the standard potential of the added metal element is higher than that of Ni, the metal element will precipitate preferentially. This allows for the formation of a Ni shell on the surface of the core particles after the core particles containing the desired metal element are generated. Examples of salts of metal elements that can generate such core particles include copper formate, copper acetate, copper chloride, copper sulfate, copper nitrate, silver acetate, silver nitrate, silver chloride, silver oxalate, palladium chloride, chloroplatinic acid, and chloroauric acid.

[0032] (b) Organic solvent The organic solvent is not particularly limited as long as it can disperse Ni particles and dissolve the thiourea compound described below. Examples of such organic solvents include low-polarity solvents such as ethylene glycol, alcohols, amine compounds, N,N-dimethylformamide, dimethyl sulfoxide, and acetone. When generating Ni particles by a thermal decomposition method, it is preferable to use an organic solvent that generates a nickel complex when dissolving a nickel salt. Examples of such organic solvents include amine compounds such as n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

[0033] In addition, the Ni slurry in this embodiment preferably has a Ni particle content relative to the organic solvent adjusted to a predetermined range. Specifically, by dispersing a certain amount or more of Ni particles in the organic solvent, the Ni sulfide layer forming step S20, which will be described later, can be carried out efficiently. From this perspective, the Ni particle content, when the weight (g) of the organic solvent is taken as 100%, is preferably 0.5% or more, more preferably 1% or more, and particularly preferably 5% or more. On the other hand, if the Ni particle content is too high, the Ni particles may not be properly dispersed in the organic solvent, which may result in a non-uniform reaction in the Ni sulfide layer forming step S20. From this perspective, the upper limit of the Ni particle content is preferably 30% or less, more preferably 25% or less, and particularly preferably 20% or less.

[0034] (2)Ni sulfide layer formation step S20 In this process, a water-insoluble thiourea compound is added to the Ni slurry and then heated. This thiourea compound is easily decomposed by heat treatment. Therefore, in the Ni sulfide layer formation step S20 of this embodiment, a sulfur coating, in which undecomposed sulfur compounds cover the surface of the Ni particles, is hardly formed, and instead a Ni sulfide layer, primarily composed of a Ni and S compound (nickel sulfide), is formed on the surface of the Ni particles. This Ni sulfide layer has a stronger sintering suppression effect than a sulfur compound coating because Ni atoms and S atoms are strongly bonded. Therefore, in the manufacturing method according to this embodiment, the Ni sulfide layer formation step S20 using a thiourea compound is performed, and the sintering resistance of the manufactured nickel powder can be significantly improved. Specifically, experiments conducted by the present inventors have confirmed a significant effect in that Ni particles with a Ni sulfide layer formed thereon have a sintering temperature that is 100°C or more higher than Ni particles with a sulfur coating.

[0035] The thiourea compound used in this embodiment is a water-insoluble thiourea compound. This allows the thiourea compound to be suitably dissolved in an organic solvent, thereby enabling a Ni sulfide layer to be appropriately formed on the surface of Ni particles. An example of such a water-insoluble thiourea compound is a compound represented by the following formula (1). It has been confirmed that the thiourea compound represented by formula (1) can suitably promote the formation of a Ni sulfide layer. In formula (1), R1 and R2 are chain alkyl groups or cyclic alkyl groups having 6 or more carbon atoms. The chain alkyl group here may have a linear or branched chain structure. R1-HNCSNH-R2(1)

[0036] Examples of the thiourea compound represented by the formula (1) include N,N'-diphenylthiourea, N,N'-dihexylthiourea, and 1,3-dicyclohexylthiourea. These thiourea compounds are easily dissolved in organic solvents and easily decomposed by heat treatment. Therefore, the use of the above-mentioned thiourea compounds can further promote the formation of a Ni sulfide layer. Furthermore, these thiourea compounds have lower reactivity with oxygen than other sulfur compounds (e.g., alkylthiols), and therefore can suppress gelation of the Ni slurry. Therefore, the above-mentioned thiourea compounds can suppress non-uniform reaction due to gelation of the Ni slurry.

[0037] The amount of the thiourea compound added is preferably set so that the Ni weight and S weight in the Ni slurry satisfy a predetermined ratio. For example, the amount of the thiourea compound added is preferably set so that the ratio of S weight to Ni weight (100%) in the Ni slurry is 0.01% or more (more preferably 0.05% or more, even more preferably 0.1% or more, and particularly preferably 0.5% or more). This allows sufficient S element to be supplied to the surface of the Ni particles, allowing a Ni sulfide layer to be suitably formed. On the other hand, if the amount of the thiourea compound added exceeds a certain level, not only will the sintering suppression effect saturate, but sulfur contamination of the heating furnace may occur, resulting in increased equipment costs. From this perspective, the amount of the thiourea compound added is preferably set so that the ratio of S element content to Ni element content is 3.0% or less (more preferably 2.5% or less, even more preferably 2.0% or less, and particularly preferably 1.5% or less).

[0038] The heating temperature in this step is preferably 50°C or higher, more preferably 80°C or higher, and particularly preferably 100°C or higher. This allows the thiourea compound to decompose quickly, allowing a Ni sulfide layer to be formed more efficiently on the surface of the Ni particles. On the other hand, the heating temperature in this step is preferably 200°C or lower, more preferably 180°C or lower, and particularly preferably 150°C or lower. This prevents the organic solvent from thermally decomposing and producing nickel carbide. The heating time is preferably 5 minutes or longer, more preferably 10 minutes or longer, and particularly preferably 15 minutes or longer. This allows the thiourea compound to be sufficiently decomposed. On the other hand, the heating time is preferably 90 minutes or shorter, more preferably 60 minutes or shorter, and particularly preferably 30 minutes or shorter. This prevents the organic solvent from decomposing.

[0039] In this step, it is preferable to perform the heat treatment while bubbling an inert gas into the Ni slurry. This can prevent crosslinking between thiourea compounds during heating. As a result, most of the thiourea compound added to the Ni slurry can contribute to the formation of the Ni sulfide layer. Examples of inert gases include Ni gas and Ar gas. The gas supply rate during bubbling is 100 cm per 1 L of Ni slurry. 3 / min or more is preferable, and 200cm 3 / min or more is preferable, and 300cm 3 / min or more is particularly preferred. This makes it possible to more appropriately suppress the crosslinking between the thiourea compounds. On the other hand, the upper limit of the supply amount of the inert gas is not particularly limited, and is preferably 7000 cm3 / L of Ni slurry. 3 / min or less is also acceptable, and 5000 cm 3 / min or less is also acceptable, and 2000cm 3 / min or less is also acceptable.

[0040] (3) Separation process S30 As shown in FIG. 1 , in the manufacturing method according to this embodiment, a separation step S30 is performed between the Ni sulfide layer formation step S20 and the amine attachment step S40. In this separation step S30, Ni particles are separated from the Ni slurry. This prevents the organic solvent used in the Ni sulfide layer formation step S20 from diluting the amine compound used in the amine attachment step S40 (described later). As a result, the amine compound adheres more easily to the surface of the Ni particles, further improving the sintering resistance of the manufactured nickel powder. This step can be performed using any conventional separation method known for separating powder from a slurry. Examples of such separation methods include settling separation, centrifugation, and filtration. This separation step is not essential to the manufacturing method disclosed herein. For example, the Ni slurry after the Ni sulfide layer formation step may be subjected to the amine attachment step (described later). Even in this case, the amine compound can be sufficiently attached to the surface of the Ni particles.

[0041] (4) Amine attachment step S40 In this process, Ni particles are dispersed in an amine compound and then heated. This causes the amine compound to adhere to the surfaces of the Ni particles. The amine compound attached to the particle surfaces prevents the surfaces of the Ni particles from coming into direct contact with each other. This further effectively prevents necking (sintering) between Ni particles during firing. In other words, the amine compound attached to the Ni particle surfaces functions as a protective agent for the Ni particles. This further improves the sintering resistance of the produced nickel powder. Specifically, experiments conducted by the present inventors have confirmed that Ni particles to which an amine compound is attached after forming a Ni sulfide layer exhibit a significant effect of increasing the sintering temperature by 100°C or more compared to Ni particles to which only a Ni sulfide layer is formed.

[0042] An example of the amine compound used in this step is an aliphatic monoamine having 8 to 18 carbon atoms. The alkyl group in the aliphatic monoamine may be a chain alkyl group, a saturated hydrocarbon, or an unsaturated hydrocarbon. The chain alkyl group may have a linear or branched chain structure. An aliphatic monoamine having such a structure has excellent adhesion to the Ni particle surface and can more effectively function as the protective agent. Examples of such aliphatic monoamines include n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

[0043] Furthermore, it is preferable that the amine compound be added at a certain ratio or more relative to the weight of the Ni particles to be treated. For example, the amount of the amine compound added relative to the weight (100%) of the Ni particles is preferably 100% or more (more preferably 120% or more, even more preferably 140% or more, and particularly preferably 150% or more). This allows a sufficient amount of the amine compound to adhere to the surface of the Ni particles. On the other hand, if the amount of the amine compound added is too large, the sintering suppression effect will saturate, resulting in an unnecessarily high increase in material costs. From this perspective, it is preferable that the amount of the amine compound added relative to the weight of the Ni particles is 200% or less (more preferably 190% or less, even more preferably 180% or less, and particularly preferably 170% or less).

[0044] Furthermore, the heating temperature in the amine adhering step S40 is preferably 50°C or higher, more preferably 80°C or higher, and particularly preferably 100°C or higher. Heat treatment at a temperature above the melting point of the amine compound facilitates adhesion of the amine compound to the surface of the Ni particles. Meanwhile, the heating temperature in this step is preferably 200°C or lower, more preferably 180°C or lower, and particularly preferably 150°C or lower. This prevents decomposition and vaporization of the amine compound. Furthermore, the heating time is preferably 30 minutes or longer, more preferably 60 minutes or longer, and particularly preferably 90 minutes or longer. This ensures sufficient time for the amine compound to adhere. Meanwhile, the heating time is preferably 210 minutes or shorter, more preferably 180 minutes or shorter, and particularly preferably 150 minutes or shorter. This prevents a decrease in production efficiency due to a prolonged amine adhering step S40.

[0045] Furthermore, the heat treatment in the amine attachment step S40 is preferably carried out in an oxidizing atmosphere (e.g., in air). This allows nickel oxide (NiO) to be present on the surface of the Ni particles. Specifically, when the amine attachment step S40 is carried out in an oxidizing atmosphere, a portion of the Ni particles is oxidized. For example, if there is a region on the surface of the Ni particles where Ni is exposed without the formation of a Ni sulfide layer, the exposed Ni can be oxidized. This can further improve the sintering suppression effect.

[0046] (4) Summary As described above, the manufacturing method according to this embodiment includes the Ni sulfide layer formation step S20 using a thiourea compound. This allows a Ni sulfide layer to be properly formed on the surface of the Ni particles. This Ni sulfide layer has an excellent sintering-inhibiting effect, thereby significantly improving the sintering resistance of the manufactured nickel powder. Furthermore, this embodiment includes the amine attachment step S40, in which an amine compound is attached to the surface of the Ni particles on which the Ni sulfide layer has been formed. This amine compound functions as a protective agent for the Ni particles, further significantly improving the sintering resistance of the nickel powder. As described above, the manufacturing method according to this embodiment allows the manufacture of nickel powder with significantly improved sintering resistance due to the Ni sulfide layer and amine compound.

[0047] 2. Nickel powder Next, the nickel powder produced by the manufacturing method described above will be described. The Ni particles contained in the nickel powder according to this embodiment have a Ni sulfide layer formed on the particle surface, and an amine compound attached to the particle surface. The nickel powder having such a configuration will be specifically described below.

[0048] First, the term "nickel powder" in this specification refers to a powder material (a group of fine particles) primarily composed of Ni particles. Here, "primarily composed of Ni particles" means that, among the inorganic fine particles contained in the powder material, the inorganic fine particles that are present in the largest amount by weight are Ni particles having a Ni sulfide layer and an amine-based compound. More specifically, the term "nickel powder" in this specification refers to a powder material containing 50 wt % or more (preferably 60 wt % or more, more preferably 70 wt % or more, even more preferably 80 wt % or more, and particularly preferably 90 wt % or more) of Ni particles having the above-described structure. In other words, the nickel powder disclosed herein may contain inorganic fine particles other than Ni particles having the above-described structure, as long as the sintering-inhibiting effect of the technology disclosed herein is not significantly impaired. Examples of such minor components include Ni particles that do not have a Ni sulfide layer and / or an amine-based compound, and inorganic fine particles whose main component is another metal element (e.g., Cu particles, Au particles, Ag particles, Pd particles, Pt particles).

[0049] The Ni sulfide layer of the Ni particles according to this embodiment is a layer containing nickel sulfide as its main component. As described above, this Ni sulfide layer is formed by heat treatment in the presence of a thiourea compound around the Ni particles. Here, "containing nickel sulfide as its main component" means that when the surface of the Ni particles is analyzed using X-ray photoelectron spectroscopy (XPS), the majority of the constituent components are nickel sulfide. Specifically, when the photoelectron spectrum of the Ni particles is obtained using XPS, peaks originating from the components that constitute the surface of the Ni particles are observed in the 158 to 170 eV region, which indicates the S2p orbital. Among these, the peak originating from Ni sulfide is observed in the 162±0.5 eV region. Therefore, the total area PA of the peaks observed in the region indicating the S2p orbital is 158~170 The area of ​​the peak due to Ni sulfide, PA NiS Percentage of PA NiS / PA 158~170 ) can be used to analyze the proportion of Ni sulfide present on the surface of the Ni particles. Since the Ni particles in this embodiment have a Ni sulfide layer containing nickel sulfide as the main component, the ratio of the peak areas (PA NiS / PA 158~170 ) is 80% or more. NiS / PA 158~170 ) is preferably 85% or more, more preferably 90% or more, and particularly preferably 95% or more. This makes it possible to obtain nickel powder with better sintering resistance. NiS / PA 158~170 The upper limit of ) is not particularly limited, and may be 100% or less, or 99% or less.

[0050] The sulfur content of the Ni particles is 0.1% or more (more preferably 0.2% or more, even more preferably 0.3% or more, and particularly preferably 0.4% or more). This sulfur is believed to originate from the Ni sulfide layer on the particle surface. For this reason, Ni particles containing a large amount of sulfur tend to have excellent sintering resistance. On the other hand, the upper limit of the sulfur content is not particularly limited, and may be 1.5% or less, 1.2% or less, 1% or less, or 0.9% or less. In this specification, the "sulfur content" refers to the weight ratio, where the weight of all metal elements constituting the Ni particles is 100%, and is measured based on elemental analysis using combustion-infrared absorption spectroscopy.

[0051] Next, in this embodiment, the Ni particles have an amine-based compound attached to their particle surfaces. As described above, this amine-based compound functions as a protective agent for the Ni particles, thereby significantly improving the sintering resistance of the nickel powder. The detailed structure of the amine-based compound has already been described, so a repeated description will be omitted. The Ni particles to which the amine-based compound is attached have a carbon content of 2% or more (more preferably 2.2% or more, even more preferably 2.4% or more, and particularly preferably 2.5% or more). This carbon content is considered to be derived from the amine-based compound attached to the particle surface. In other words, as the carbon content increases, the sintering resistance of the nickel powder tends to improve. Meanwhile, the upper limit of the carbon content is not particularly limited and may be 4% or less, 3.5% or less, or 3% or less. As with the sulfur content described above, the "carbon content" in this specification is measured based on elemental analysis using a combustion-infrared absorption method.

[0052] The amine compound contains nitrogen element in addition to the carbon element. Therefore, the amount of nitrogen element present on the surface of Ni particles to which the amine compound is attached also increases. Specifically, the amount of nitrogen element present on the surface of Ni particles to which the amine compound is attached increases. 0.08% or more (More preferably 0.081% or more , and more preferably 0.082% or more) In other words, the nickel powder in which the contents of both the carbon element and the nitrogen element are increased has more favorably improved sintering resistance. On the other hand, the upper limit of the nitrogen element content is not particularly limited, Less than 1% But often, 0.5% or less But often, 0.1% or less The nitrogen element is measured based on the inert gas fusion-thermal conductivity method (TCD).

[0053] Furthermore, when the Ni slurry is heated in an oxidizing atmosphere in the amine attachment step S40, nickel oxide is generated on the surface of the Ni particles. In this case, the oxygen content in the Ni particles is 2.5% or more (more preferably 2.7% or more, even more preferably 3.0% or more, and particularly preferably 3.2% or more). This further improves the sintering suppression effect. The oxygen content in the Ni particles may be 4% or less, 3.8% or less, or 3.4% or less. In this specification, the "oxygen content" refers to the weight ratio, where the weight of all metal elements constituting the Ni particles is 100%, and is measured based on elemental analysis using inert gas fusion-non-dispersive infrared absorption spectroscopy.

[0054] 3. Electrode paste The nickel powder according to this embodiment can be dispersed in an appropriate dispersion medium to prepare a paste for forming an electrode (electrode paste). Because this electrode paste contains nickel powder with excellent sintering resistance, it can effectively suppress structural defects in the electrode after firing.

[0055] The dispersion medium may be any one that can disperse nickel powder well, and any conventionally known dispersion medium that can be used for electrode pastes can be used without particular limitation. Examples of such dispersion mediums include petroleum hydrocarbons (especially aliphatic hydrocarbons) such as mineral spirits, ethylene glycol and diethylene glycol derivatives, and high-boiling organic solvents such as toluene, xylene, butyl carbitol (BC), isobornyl acetate, and terpineol.

[0056] Furthermore, although not intended to limit the technology disclosed herein, the content of nickel particles relative to the total weight of the electrode paste is preferably approximately 30% to 70% (e.g., 40% to 60%). Furthermore, the viscosity of the electrode paste is preferably approximately 10 mPa·s to 100 mPa·s (e.g., approximately 20 mPa·s to 50 mPa·s). This makes it easy to obtain an electrode paste that facilitates the formation of precise electrode patterns. The viscosity of the electrode paste can be measured using an E-type viscometer.

[0057] The electrode paste may contain additives other than nickel particles. Examples of such additives include binders, conductive materials, dispersants, viscosity adjusters, etc. As these additives, any conventionally known additives that can be added to electrode pastes can be used without particular limitation, as long as they do not significantly impair the effects of the technology disclosed herein.

[0058] An embodiment of the technology disclosed herein has been described above. However, the above-described embodiment is not intended to limit the technology disclosed herein. In other words, the technology disclosed herein may include various modifications of the above-described embodiment.

[0059] [Test example] Test examples relating to the technology disclosed herein will be described below, but the technology disclosed herein is not limited to the following test examples.

[0060] 1. Sample Preparation In this test example, six types of nickel powder (samples 1 to 6) were prepared using different manufacturing methods. The manufacturing procedures for each sample are described below.

[0061] (1) Sample 1 For Sample 1, a Ni slurry containing Ni particles (Cu / Ni core-shell particles) dispersed in an organic solvent (oleylamine) was prepared according to the following procedure. Specifically, 5.1 g of nickel formate dihydrate (Ni content: 1.62 g) was added to 957.7 g of oleylamine. The mixture was then heated at 120 °C for 120 minutes. This resulted in the formation of a nickel formate-oleylamine complex in the solution. Next, 0.69 g of copper formate tetrahydrate (Cu content: 0.19 g) was added to the solution. This mixture was then heated at 60 °C for 30 minutes. This resulted in the formation of a copper formate-oleylamine complex in the solution. The solution containing these two complexes was heated at 190 °C under a nitrogen atmosphere for 10 minutes. When the solution containing these two complexes was heated, Cu, which has a higher standard potential, preferentially precipitated, resulting in the formation of Cu core particles. Further heating resulted in the formation of a Ni shell on the surface of the Cu core particles. This process produced Cu / Ni core-shell particles. Furthermore, in this experiment, the generated Cu / Ni core-shell particles were used as seed particles to further grow the Ni shells on the seed particle surfaces. Specifically, 341.9 g of nickel acetate tetrahydrate (Ni content: 74.27 g) was added to the seed particle slurry containing the seed particles. This was then heated at 135°C for 120 minutes. This produced a nickel acetate-oleylamine complex in the slurry. The seed particle slurry containing this complex was then heated at 200°C for 30 minutes in a nitrogen atmosphere. This resulted in the precipitation of Ni, which adhered to the seed particle surfaces. As a result, a Ni slurry was prepared in which Cu / Ni core-shell particles with sufficiently thick Ni shells were dispersed in oleylamine.

[0062] Next, for Sample 1 of this test, a sulfurization treatment (Ni sulfide layer formation step) was carried out to form a Ni sulfide layer on the surface of the Ni particles (Cu / Ni core-shell particles). Specifically, for Sample 1, 5.85 g of diphenylthiourea (S amount: 0.82 g) was added to the Ni slurry as a sulfur source. Then, a heat treatment was carried out at 100°C for 5 minutes while bubbling nitrogen gas into the slurry. This decomposed the diphenylthiourea, and a Ni sulfide layer was formed on the surface of the Ni shell of the Cu / Ni core-shell particles.

[0063] Next, in Sample 1, Ni particles were separated from the Ni slurry. Specifically, the Ni particles were allowed to settle in the Ni slurry by static settling, and the supernatant was removed to separate the Ni particles.

[0064] In Sample 1, an amine compound was attached to the surface of Ni particles (Cu / Ni core-shell particles). Specifically, the separated Ni particles were dispersed in 120 g of oleylamine. This dispersion was then heated at 100°C for 30 minutes. This allowed the oleylamine to be adsorbed onto the surface of the Cu / Ni core-shell particles.

[0065] Next, for Sample 1, the oleylamine in the slurry was replaced with hexane, followed by a drying treatment. Specifically, the Ni particles after the adsorption treatment were first allowed to settle, and the supernatant liquid was removed. Next, hexane was added to the settled Ni particles, and the mixture was stirred while irradiated with ultrasound, thereby dispersing the Ni particles in hexane. This procedure of settling the Ni particles, removing the supernatant liquid, and then dispersing the Ni particles in hexane was repeated three times. A drying treatment was then performed at 120°C, yielding a dry nickel powder (Sample 1) composed primarily of Cu / Ni core-shell particles.

[0066] (2) Sample 2 For this sample, nickel powder was produced following the same procedure as for Sample 1, except that the amount of diphenylthiourea added in the sulfurization treatment was changed to 1.17 g (amount of S: 0.16 g).

[0067] (3) Sample 3 For this sample, nickel powder was produced following the same procedure as for Sample 1, except that the amount of diphenylthiourea added in the sulfurization treatment was changed to 2.93 g (amount of S: 0.41 g).

[0068] (4) Sample 4 For Sample 4, nickel powder was produced without sulfurization treatment and oleylamine adhesion treatment. Specifically, for this sample, Ni slurry containing Cu / Ni core-shell particles was prepared according to the same procedure as for Sample 1. Then, this Ni slurry was subjected to a drying treatment at 120°C to obtain a dry nickel powder.

[0069] (5) Sample 5 For Sample 5, nickel powder was produced according to the same procedure as for Sample 1, except that 1.04 g of 1-dodecanethiol (amount of S: 0.16 g) was added instead of diphenylthiourea as the sulfur source in the sulfurization treatment.

[0070] (6) Sample 6 For Sample 6, nickel powder was produced without carrying out the oleylamine adhesion treatment. Specifically, for this sample, a sulfurization treatment was carried out in the same procedure as for Sample 1, followed by a drying treatment to obtain a dry nickel powder.

[0071] 2.Evaluation Test (1) Analysis of particle size distribution The nickel powder of each sample was observed using FE-SEM (Hitachi High-Tech Corporation, Model: SU8230). 1000 particles whose entire periphery could be seen from the SEM image were randomly selected, and the Heywood diameter was measured to determine the particle size distribution. Based on the particle size distribution, the average particle diameter (D 50 The particle size and coefficient of variation (CV value) were measured. The measurement results are shown in Table 1.

[0072] (2) Element content measurement The carbon and sulfur contents of nickel powder samples 1 to 6 were measured. These measurements were performed using a Horiba carbon / sulfur analyzer (model: EMIA-321V) based on the combustion-infrared absorption method. The sample weight was set to 0.2 g for carbon measurement and 0.1 g for sulfur measurement. Next, the oxygen content was measured using a Horiba oxygen / nitrogen analyzer (model: EMGA-930) based on the inert gas fusion-nondispersive infrared absorption method (NDIR). The nitrogen content was also measured using the same analyzer based on the inert gas fusion-thermal conductivity method (TCD). The sample weight was set to 0.01 g for oxygen measurement and 0.075 g for nitrogen measurement. The results of the elemental content measurements are shown in Table 1.

[0073] (3) Surface analysis of Ni particles First, an indium wire was pressed onto aluminum foil, and nickel powder from each sample was sprinkled onto the indium and pressed again to prepare samples for XPS analysis. Then, a photoelectron spectrum was obtained from each sample in a narrow scan range of 158 to 170 eV using a photoelectron spectrometer (ULVAC-PHI, Model: XPS PHI5000 VersaProbe). The measurement conditions are as follows:

[0074] X-ray source: Monochromatic Al-Kα Tube voltage: 15kV Output: 200W Neutralization gun: Not used Pass energy: 23.5 eV Step: 0.1 eV Capture time: 200ms Accumulation count: 15 times

[0075] From this photoelectron spectrum, the region of photoelectron energy (158-170 eV) originating from the S2p orbital was separated. The total area of ​​the peaks identified in this separated region, PA 158~170Next, the area PA of the peak at 162±0.5 eV due to Ni sulfide was measured. NiS Then, the total area PA 158~170 Peak area PA of Ni sulfide versus NiS Ratio of PA NiS / PA 158~170 The measurement results are shown in Table 1.

[0076] (4) Evaluation of sintering resistance In this test, the sintering resistance of each sample was evaluated according to the following procedure. First, 0.5 g of nickel powder was placed in an 8 mm diameter mold and uniaxially pressed. This resulted in a disk-shaped pellet approximately 2 mm thick. These pellets were then subjected to six firing processes, each with a different maximum firing temperature. Specifically, the first firing process was performed at 200 °C for 10 minutes in a nitrogen atmosphere. The second through sixth firing processes were then performed, each with a firing temperature increase of 100 °C. The firing temperature for the sixth firing process was set to 600 °C. After each firing process, the pellet surface was observed using a field emission scanning electron microscope (FE-SEM) to determine whether sintering of the Ni particles had occurred. The temperature at which 10% or more of the Ni particles were sintered was considered the sintering temperature. The measurement results are shown in Table 1.

[0077] [Table 1]

[0078] As shown in Table 1 above, the amount of sulfur added in the sulfurization treatment was almost the same for Samples 2 and 5 (0.16 g). Therefore, the abundance ratio of sulfur element in Samples 2 and 5 was also about the same (0.2%) in the element amount measurement after production. However, Sample 2 had a peak area ratio (PA) based on XPS analysis. NiS / PA 158~170 ) was a very high value of 97.8. This shows that a large amount of Ni sulfide was generated on the surface of the Ni particles in Sample 2. On the other hand, in Sample 5, the peak area ratio (PA NiS / PA 158~170) was a low value of 36.8. In addition, a peak at 63 eV due to mercapto groups was confirmed in the photoelectron spectrum of XPS analysis of Sample 5. From these points, it is understood that the thiol compound (dodecanethiol) used in Sample 5 is hardly decomposed during the sulfurization treatment and coats the Ni particles in its compound state. Furthermore, in the sintering resistance evaluation, the Ni particles of Sample 5 sintered when the firing temperature reached 500 °C. On the other hand, the Ni particles of Sample 2 hardly sintered even when the firing temperature exceeded 600 °C. In other words, the sintering temperature of Sample 2 is more than 100 °C higher than that of Sample 5. From these points, it was found that sulfurization treatment using a thiourea compound such as diphenylthiourea appropriately forms a Ni sulfide layer on the surface of Ni particles, significantly improving sintering resistance.

[0079] Next, in Samples 1 to 3 and 6, the Ni sulfide layer was properly formed using a thiourea compound. However, the sintering temperatures of Samples 1 to 3 were more than 100°C higher than that of Sample 6. This indicates that amine adhesion treatment to the Ni particle surface significantly improves sintering resistance. This is believed to be because the amine compound attached to the particle surface prevents direct contact between the surfaces of the Ni particles, thereby inhibiting necking (sintering) between the Ni particles during sintering.

[0080] The technology disclosed herein has been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. In other words, the technology disclosed herein encompasses the aspects described in items 1 to 12 below.

[0081] <Item 1> A preparation step of preparing a Ni slurry in which Ni particles are dispersed in an organic solvent; a Ni sulfide layer forming step of adding a water-insoluble thiourea compound to the Ni slurry and then heating the slurry to form a Ni sulfide layer on the surface of the Ni particles; an amine adhering step of dispersing the Ni particles in an amine compound and then heating the dispersed Ni particles to cause the amine compound to adhere to the surfaces of the Ni particles; A method for producing nickel powder, comprising:

[0082] <Item 2> Item 2. The method for producing nickel powder according to item 1, wherein a separation step of separating the Ni particles from the Ni slurry is carried out between the Ni sulfide layer formation step and the amine attachment step.

[0083] <Item 3> 3. The method for producing a nickel powder according to item 1 or 2, wherein the thiourea compound contains an organic sulfur compound represented by R1-HNCSNH-R2 (wherein R1 and R2 in the formula are linear alkyl groups or cyclic alkyl groups having 6 or more carbon atoms).

[0084] <Item 4> 4. The method for producing a nickel powder according to item 3, wherein the thiourea compound includes at least one selected from the group consisting of N,N'-diphenylthiourea, N,N'-dihexylthiourea, and 1,3-dicyclohexylthiourea.

[0085] <Item 5> 5. The method for producing a nickel powder according to any one of items 1 to 4, wherein the amine compound contains an aliphatic monoamine having 8 to 18 carbon atoms.

[0086] <Item 6> 6. The method for producing a nickel powder according to Item 5, wherein the amine compound includes at least one selected from the group consisting of n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

[0087] <Item 7> 7. The method for producing a nickel powder according to any one of items 1 to 6, wherein the Ni particles have an average particle size of 100 nm or less based on FE-SEM observation.

[0088] <Item 8> 8. The method for producing a nickel powder according to any one of items 1 to 7, wherein the Ni particles are core-shell particles having a core particle and a shell covering at least a part of the surface of the core particle, and the shell contains nickel element.

[0089] <Item 9> 9. The method for producing a nickel powder according to any one of items 1 to 8, wherein in the Ni sulfide layer forming step, the heat treatment is carried out while bubbling an inert gas through the Ni slurry.

[0090] <Item 10> A nickel powder mainly composed of Ni particles, The Ni particles are A Ni sulfide layer mainly composed of nickel sulfide, an amine compound attached to the surface of the Ni sulfide layer; It is equipped with A nickel powder in which, in a photoelectron spectrum of the Ni particles measured by X-ray photoelectron spectroscopy, the ratio of the peak area of ​​the peak derived from the nickel sulfide to the total peak area in a region showing the S2p orbital is 80% or more.

[0091] <Item 11> Item 11. The nickel powder according to item 10, wherein the Ni particles have an average particle size of 100 nm or less based on FE-SEM observation.

[0092] <Item 12> Item 12. The nickel powder according to item 10 or 11, wherein the Ni particles have a carbon element content of 2% or more and 4% or less based on elemental analysis by combustion-infrared absorption spectroscopy.

[0093] <Item 13> 13. The nickel powder according to any one of items 10 to 12, wherein the Ni particles have an oxygen element content of 2.5% or more and 4% or less based on elemental analysis by inert gas fusion-non-dispersive infrared absorption method.

[0094] <Item 14> 14. The nickel powder according to any one of items 10 to 13, wherein the amine compound contains an aliphatic monoamine having 8 to 18 carbon atoms.

[0095] <Item 15> Item 15. The nickel powder according to item 14, wherein the amine compound includes at least one selected from the group consisting of n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

[0096] <Item 16> The nickel powder according to any one of items 10 to 15, a dispersion medium for dispersing the nickel powder; Electrode paste comprising:

Claims

1. A method for producing nickel powder containing 50 mass% or more of surface-treated Ni particles, the surface of which has a Ni sulfide layer containing nickel sulfide formed on it and an amine compound attached to the surface of the particle, comprising: a preparation step of preparing a Ni slurry in which Ni particles are dispersed in an organic solvent; a Ni sulfide layer forming step of adding a water-insoluble thiourea compound to the Ni slurry and then heating the slurry to form a Ni sulfide layer on the surface of the Ni particles; an amine adhering step of adhering the amine compound to the surface of the Ni particles by dispersing the Ni particles in an amine compound and then heating the dispersed Ni particles after the Ni sulfide layer forming step is performed; Including, The thiourea compound includes a thiourea compound represented by R 1 -HNCSNH-R 2 (wherein R 1 and R 2 in the formula are linear alkyl groups or cyclic alkyl groups having 6 or more carbon atoms), the amine compound includes an aliphatic monoamine having 8 to 18 carbon atoms, In the surface-treated Ni particles, in a photoelectron spectrum obtained by X-ray photoelectron spectroscopy, the ratio (PA NiS / PA NiS ) of the total area PA of peaks observed in the 158 to 170 eV region representing S2p orbitals to the area PA NiS of the peak observed in the 162±0.5 eV region derived from Ni sulfide is 80% or more.

2. 2. The method for producing nickel powder according to claim 1, further comprising the step of separating the Ni particles from the Ni slurry between the Ni sulfide layer forming step and the amine adhering step.

3. 2. The method for producing nickel powder according to claim 1, wherein the thiourea compound includes at least one selected from the group consisting of N,N'-diphenylthiourea, N,N'-dihexylthiourea, and 1,3-dicyclohexylthiourea.

4. 2. The method for producing nickel powder according to claim 1, wherein the amine-based compound includes at least one selected from the group consisting of n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

5. The method for producing nickel powder according to claim 1 or 2, wherein the average particle size of the Ni particles based on FE-SEM observation is 100 nm or less.

6. 3. The method for producing nickel powder according to claim 1, wherein the Ni particles are core-shell particles having a core particle and a shell covering at least a portion of the surface of the core particle, and the shell contains nickel element.

7. The method for producing nickel powder according to claim 1 or 2, wherein the Ni sulfide layer forming step is performed by heating the Ni slurry while bubbling an inert gas through the Ni slurry.

8. A nickel powder containing 50 mass% or more of surface-treated Ni particles, The surface-treated Ni particles are a Ni sulfide layer containing nickel sulfide; an amine compound attached to the surface of the Ni sulfide layer; It is equipped with In a photoelectron spectrum of the Ni particles measured by X-ray photoelectron spectroscopy, the ratio of the peak area of ​​the peak derived from the nickel sulfide to the total peak area in a region showing an S2p orbital is 80% or more, the amine compound includes an aliphatic monoamine having 8 to 18 carbon atoms, The surface-treated Ni particles are nickel powders in which the ratio (PA NiS / PA 158-170 ) of the total area of ​​peaks observed in the 158-170 eV region representing S2p orbitals to the area of ​​peaks observed in the 162±0.5 eV region derived from Ni sulfide in a photoelectron spectrum obtained by X-ray photoelectron spectroscopy is 80% or more.

9. The nickel powder according to claim 8, wherein the average particle size of the surface-treated Ni particles based on FE-SEM observation is 100 nm or less.

10. The nickel powder according to claim 8 or 9, wherein the surface-treated Ni particles have a carbon element content of 2% or more and 4% or less based on elemental analysis by combustion-infrared absorption method.

11. The nickel powder according to claim 8 or 9, wherein the surface-treated Ni particles have an oxygen element content of 2.5% or more and 4% or less based on elemental analysis by inert gas fusion-non-dispersive infrared absorption method.

12. 9. The nickel powder according to claim 8, wherein the amine-based compound includes at least one selected from the group consisting of n-octylamine, 2-ethylhexylamine, n-decylamine, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, stearylamine, and oleylamine.

13. The nickel powder according to claim 8 or 9, a dispersion medium for dispersing the nickel powder; Electrode paste comprising:

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