Nanosintered silver paste and preparation method thereof

Abstract

The present disclosure provides a kind of nano sintering silver paste and its preparation method, it is related to electronic paste technical field.The nano sintering silver paste includes the following components by weight parts: nano silver powder 75~90 parts, organic silver salt precursor 5~15 parts, sintering aid 0.1~3 parts, densification aid 1~10 parts;Wherein, densification aid includes small molecule complexing agent, dispersing agent, organic solvent, rheological aid and defoaming agent;Small molecule complexing agent is amine or carboxylic acid ligand.The present disclosure can improve the quality of nano sintering silver paste.

Description

Technical Field

[0001] This disclosure relates to the field of electronic paste technology, and more specifically, to a nano-sintered silver paste and its preparation method. Background Technology

[0002] With the continuous upgrading of power electronic devices, chip packaging, and new energy vehicle electronic systems, the stable operation of devices under high power density, high frequency, and high heat flux environments has become a critical issue. Traditional tin-based solders and conductive silver pastes, due to their limited thermal conductivity, high interface resistance, and thermal stress accumulation, are unable to meet the demands of next-generation packaging technologies for high conductivity, high thermal conductivity, and high reliability interconnect materials. Nano-sintered silver paste, with its excellent conductivity, high temperature resistance, and chemical stability, is considered an important candidate material for achieving efficient packaging and lead-free interconnects.

[0003] However, existing products still have shortcomings in terms of low-temperature sintering and high-temperature service stability, and the quality of nano-sintered silver paste is not good.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this disclosure is to provide a nano-sintered silver paste and its preparation method, thereby overcoming, at least to some extent, the problem of poor quality of nano-sintered silver paste.

[0006] According to a first aspect of this disclosure, a nano-sintered silver paste is provided, comprising the following components by weight: 75-90 parts of nano-silver powder, 5-15 parts of an organic silver salt precursor, 0.1-3 parts of a sintering aid, and 1-10 parts of a densifying aid; wherein the densifying aid includes a small molecule complexing agent, a dispersant, an organic solvent, a rheology modifier, and a defoamer; the small molecule complexing agent is an amine or carboxylic acid ligand.

[0007] Optionally, the nano-silver powder has a particle size of 30~80nm and is prepared by chemical reduction or spray thermal decomposition. The surface of the nano-silver powder is coated with polyvinylpyrrolidone or sodium citrate.

[0008] Alternatively, the organic silver salt precursor includes one or more of silver 2-ethylhexanoate, silver lactate, silver acetate, and their coordination complexes.

[0009] Optionally, the sintering aid includes one or more of the following: low-melting-point inorganic sintering aid, surface-activated sintering aid, and redox synergistic sintering aid; the low-melting-point inorganic sintering aid includes one or more of the following: tin oxide, zinc oxide, bismuth oxide, and borate glass powder; the surface-activated sintering aid includes one or more of the following: organic acid, reducing polyol, and amino alcohol; and the redox synergistic sintering aid includes one or more of the following: stannous salt-hydrogen peroxide, ferrous salt-organic carboxylic acid, and benzoyl peroxide-ascorbic acid.

[0010] Optionally, the dispersant includes one or more of ethylene glycol, polyacrylamide, and fatty alcohol ethers.

[0011] Optionally, the organic solvent includes one or more of isopropanol, butyl propionate, butyl lactate, and ethylene glycol methyl ether.

[0012] Optionally, both the rheology modifier and the defoamer are silicone additives.

[0013] According to a second aspect of this disclosure, a method for preparing nano-sintered silver paste is provided, comprising: adding 5-15 parts by weight of an organic silver salt precursor to an organic solvent, dispersing it evenly, and then adding 0.05-1 parts by weight of a small molecule complexing agent to obtain a first solution; wherein the small molecule complexing agent is an amine or carboxylic acid ligand; adding 75-90 parts by weight of nano-silver powder and 0.1-1.5 parts by weight of a dispersant to the first solution, dispersing it evenly to obtain a second solution; adding 0.1-1 parts by weight of a rheology modifier and 0.1-3 parts by weight of a sintering aid to the second solution, stirring evenly, and then performing three-roll milling to obtain an intermediate slurry; adding 0.1-1 parts by weight of a defoamer to the intermediate slurry, and performing vacuum defoaming treatment to obtain nano-sintered silver paste.

[0014] Optionally, the mixer used for mixing has a revolution speed of 1000~2200 rpm, a rotation speed of 700~1400 rpm, and a mixing time of 10~30 minutes.

[0015] Optionally, the roller gaps of the three-roll mill are 20~30μm, 10~15μm and 3~7μm respectively, and the rotation speed is 300~500 rpm, so as to control the fineness of the intermediate slurry to be less than 5μm.

[0016] In the exemplary embodiments of this disclosure, a composite silver source composed of nano-silver powder and organic silver salt, along with a densifying agent, is used to achieve rapid and dense bonding of silver particles at temperatures below 250°C. This overcomes the technical bottlenecks of low sintering efficiency and insufficient interfacial bonding in traditional low-temperature silver paste, improving the quality of nano-sintered silver paste. Specifically, through the combined action of small-molecule complexing agents, dispersants, and sintering aids, the reactivity, diffusion rate, and interfacial wettability of silver particles are enhanced, enabling the sintered layer to achieve high density, high conductivity, high thermal conductivity, and high bonding strength under low-temperature conditions. Testing shows that the final silver film exhibits a shear strength exceeding 35 MPa and excellent thermal shock resistance. Furthermore, this disclosure introduces an organic silver salt precursor and sintering aid for in-situ generation of nano-silver into the system. Through a chemically driven densification mechanism, it effectively promotes neck growth and interfacial diffusion between silver particles, reduces interfacial resistance, and improves overall sintering density and long-term reliability. Meanwhile, this system is applicable to various substrate materials such as glass, ceramics, and metals, enabling low-temperature interconnection without flux. It effectively reduces the impact of thermal stress on the substrate and simplifies the packaging process, reducing energy consumption. The preparation and sintering process of this system is environmentally friendly and features controllable process parameters, making it suitable for stable, large-scale, and industrial applications.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] Figure 1 A flowchart illustrating the preparation method of nano-sintered silver paste according to an embodiment of the present disclosure is shown.

[0020] Figure 2 The image shown is an SEM (Scanning Electron Microscope) image of the nano-sintered silver paste prepared in Example 1 of this disclosure.

[0021] Figure 3 The cross-sectional SEM image of the nano-sintered silver paste prepared in Example 1 of this disclosure after sintering is shown. Detailed Implementation

[0022] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of these specific details omitted, or other methods, processes, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0023] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. The flowcharts shown in the drawings are merely exemplary illustrations and do not necessarily include all steps. For example, some steps may be broken down, while others may be combined or partially combined; therefore, the actual order of execution may change depending on the actual situation. Additionally, all terms such as "first," "second," etc., used below are for distinction purposes only and should not be construed as limiting the content of this disclosure.

[0024] Nano-sintered silver paste can be composed of nano-sized silver powder, organic binder phase, solvent, and a small amount of additives. Its conductivity, sintering density, and interfacial bonding strength are closely related to the silver powder particle size distribution, surface state, organic system composition, and sintering process. Although high-temperature sintering can achieve high density and conductivity, excessively high process temperatures can easily lead to substrate thermal damage and interfacial stress mismatch. While low-temperature sintering systems can reduce the temperature, they suffer from insufficient densification, weak interfacial bonding, and poor thermal cycling reliability. The root cause is usually poor contact between silver particles and residual organic ligands on the surface, which makes it difficult for sintering necks to form rapidly at low temperatures. High porosity and high solids content systems, due to high viscosity and limited rearrangement, result in insufficient initial packing density, fundamentally weakening the sintering driving force.

[0025] This disclosure provides a low-temperature densified nano-sintered silver paste and its preparation method, aiming to overcome the technical bottlenecks of insufficient densification, weak interfacial bonding, and poor reliability in existing low-temperature sintered silver pastes. This disclosure constructs a composite silver source system, utilizes the synergistic densification mechanism of nano-silver powder and organic silver salts, and designs clearly categorized dispersion, complexation, and sintering aid systems. This enables silver particles to achieve rapid, continuous, and dense sintering connections in the low-temperature region (≤250℃), thereby significantly improving the density, conductivity, interfacial bonding strength, and long-term stability of the sintered layer under power application environments.

[0026] The nano-sintered silver paste of this disclosure comprises the following components by weight: 75-90 parts of nano-silver powder, 5-15 parts of organic silver salt precursor, 0.1-3 parts of sintering aid, and 1-10 parts of densifying aid. The densifying aid may include small molecule complexing agents, dispersants, organic solvents, rheology modifiers, and defoamers. The small molecule complexing agent is an amine or carboxylic acid ligand, such as ethylenediamine, triethanolamine, or citric acid, used to regulate the decomposition rate of the silver source and the diffusion behavior of silver ions, and to inhibit early aggregation.

[0027] In an exemplary embodiment of this disclosure, the nano-silver powder has a particle size of 30-80 nm and a purity of ≥99.9%. This nano-silver powder can be prepared by chemical reduction or spray thermal decomposition. Based on its preparation process, its surface is coated with polyvinylpyrrolidone or sodium citrate. This coating can prevent agglomeration and provide appropriate surface activation energy to promote subsequent densification reactions.

[0028] Organic silver salt precursors may include one or more of silver 2-ethylhexanoate, silver lactate, silver acetate, and their coordination complexes. They can thermally decompose in the range of 160~250℃ to generate silver nanoparticles, which then undergo necking, growth, and grain boundary filling reactions with pre-prepared silver powder during sintering, thereby constructing a continuous and dense silver sintered network.

[0029] Sintering aids may include one or more of the following: low-melting-point inorganic sintering aids, surface-activated sintering aids, and redox synergistic sintering aids.

[0030] The low-melting-point inorganic sintering aids include one or more of tin oxide, zinc oxide, bismuth oxide, and borate glass powder. The particle size of these low-melting-point inorganic sintering aids is 20-200 nm, and they can form a wetting layer at the sintering interface to reduce the particle diffusion activation energy and promote the in-situ metallurgical bonding between the silver and the substrate.

[0031] Surface-activated sintering aids can include one or more of organic acids, reducing polyols, and amino alcohols. Surface-activated sintering aids can remove the oxide layer on the silver surface to activate the sintering process.

[0032] Redox synergistic sintering aids can be micro-redox systems, specifically including one or more of stannous salt-hydrogen peroxide, ferrous salt-organic carboxylic acid, and benzoyl peroxide-ascorbic acid. These redox synergistic sintering aids can be used to induce dislocations on the silver surface, accelerating the formation and growth of sintering necks in silver particles.

[0033] The dispersant in this embodiment may include one or more of ethylene glycol, polyacrylamide, and fatty alcohol ethers. The dispersant can be used to regulate the decomposition rate of the silver source and the diffusion behavior of silver ions, and to inhibit early aggregation.

[0034] Organic solvents may include at least one of low-boiling-point alcohols, esters, and ethers, specifically one or more of isopropanol, butyl propionate, butyl lactate, and ethylene glycol methyl ether. Organic solvents can adjust the viscosity and evaporation rate of the system, ensuring the forming stability of the paste during printing and dispensing processes.

[0035] Both rheology modifiers and defoamers can be silicone additives, such as polyether-modified silicone defoamers, which are used to improve thixotropy and storage stability, so that the slurry has good flowability and resilience after shear force is applied.

[0036] This disclosure also provides a method for preparing the above-mentioned nano-sintered silver paste. Figure 1 A flowchart illustrating a method for preparing nano-sintered silver paste according to an embodiment of this disclosure is shown schematically. (Reference) Figure 1 The preparation method of the nano-sintered silver paste according to the present disclosure may include the following steps:

[0037] S12. By weight, add 5 to 15 parts of the organic silver salt precursor to an organic solvent, disperse evenly, and then add 0.05 to 1 part of a small molecule complexing agent to prepare the first solution.

[0038] As described above, the small molecule complexing agent is an amine or carboxylic acid ligand.

[0039] The uniform dispersion process mentioned in step S12 may include stirring at 500-1200 rpm at 60-90°C to achieve homogeneous dispersion.

[0040] S14. Add 75-90 parts of nano silver powder and 0.1-1.5 parts of dispersant to the first solution and disperse evenly to obtain the second solution.

[0041] According to some embodiments of this disclosure, the silver powder can be uniformly impregnated by ultrasonic or high-speed shearing for 10 to 60 minutes to obtain a stable and homogeneous silver paste precursor system as the second solution.

[0042] S16. Add 0.1 to 1 part of rheology modifier and 0.1 to 3 parts of sintering aid to the second solution, stir evenly, and then perform three-roll milling to obtain intermediate slurry.

[0043] According to some embodiments of this disclosure, the roller gaps of the three-roll mill are 20-30 μm, 10-15 μm, and 3-7 μm respectively, and the rotation speed is 300-500 rpm, so as to control the fineness of the intermediate slurry to be less than 5 μm. For example, the viscosity is controlled to be 10-50 Pa·s to ensure its compatibility in subsequent printing and dispensing processes.

[0044] S18. Add 0.1~1 part of defoamer to the intermediate slurry and perform vacuum defoaming treatment to obtain nano sintered silver paste.

[0045] In addition, the above-mentioned dispersion process can be carried out using a high-speed dispersion vessel with a rotation speed of 1000~5000 rpm and a dispersion temperature controlled at 50~75℃. The stirring and mixing time is 10~30 minutes. The stirring speed of the mixer used is 1000~2200 rpm and the rotation speed is 700~1400 rpm.

[0046] After obtaining the nano-sintered silver paste, subsequent sintering processes can be performed. Specifically, the nano-sintered silver paste prepared according to the embodiments of this disclosure can be applied to the welding of, for example, metal frames, silicon wafers, gallium nitride substrates, or ceramic substrates.

[0047] In this process, the dispensing thickness is controlled at 10~35μm. The pre-drying temperature is 80~150℃, and the time is 10~60 minutes. The temperature is increased to 180~250℃ at a rate of 1~5℃ / min and held for 10~60 minutes to allow the organic silver salt precursor to generate nano-silver and complete the necking growth. After cooling, a dense sintered layer is obtained.

[0048] The sintered layer obtained has a density ≥90%, shear strength ≥35MPa, thermal conductivity ≥180W / m·K, and bulk electrical conductivity ≥5×10⁻⁶. 7 S / m.

[0049] This disclosed scheme introduces reactive precursor ligands to induce the formation of a dense and continuous structure in silver nanoparticles during sintering at a lower temperature, thereby achieving low-temperature sintering, high conductivity, and excellent interfacial bonding performance.

[0050] The scheme of Embodiment 1 of this disclosure will be described below.

[0051] In Example 1, the raw materials, by weight, comprised the following components: 75 parts of nano-silver powder, 15 parts of organic silver salt precursor (silver 2-ethylhexanoate), 1.8 parts of sintering aid (0.6 parts of low-melting-point inorganic sintering aid - Bi2O3, 0.6 parts of surface-activating sintering aid - citric acid, 0.6 parts of redox synergistic sintering aid - benzoyl peroxide-ascorbic acid), and 8.5 parts of densifying aid system (0.6 parts of small molecule complexing agent - ethylenediamine, 0.83 parts of dispersant - polyethylene glycol, 6.57 parts of organic solvent - isopropanol / ethylene glycol methyl ether / butyl propionate, 0.1 parts of rheology modifier BYK-378, and 0.1 parts of defoamer - BYK370). The nano-silver powder had a particle size of 30-80 nm, and the organic solvent consisted of isopropanol / ethylene glycol methyl ether / butyl propionate in a 1:1:1 volume ratio.

[0052] The preparation process includes:

[0053] Step 1: Weigh 15 parts by weight of silver 2-ethylhexanoate and 0.6 parts by weight of ethylenediamine, add them to 6.57 parts by weight of mixed organic solvent, and stir at about 1000 rpm in a high-speed dispersion vessel at 75°C to fully complex and disperse the silver salt in the solvent system to obtain a homogeneous precursor solution.

[0054] Step 2: Slowly add 75 parts of nano silver powder (particle size of about 80 nm) and 0.83 parts of polyethylene glycol to the precursor solution obtained in Step 1. Use an ultrasonic disperser to treat for 30 minutes to make the silver powder uniformly wetted in the solvent and silver source system, so as to obtain a stable and homogeneous silver paste precursor system.

[0055] Step 3: Add 0.6 parts by weight of Bi2O3, 0.6 parts by weight of citric acid, 0.6 parts by weight of benzoyl peroxide-ascorbic acid and 0.1 parts by weight of BYK-378 to the silver paste precursor system obtained in Step 2. After stirring evenly, perform three-roll milling to make the paste fineness ≤5μm.

[0056] Step 4: Add 0.1 parts of BYK370 defoamer and perform vacuum defoaming treatment to obtain stable and uniform nano-sintered silver paste.

[0057] Step 5: Apply the nano-sintered silver paste prepared in Step 4 onto the bare copper lead frame by dispensing, controlling the wet film thickness to be 15~35μm, and let it stand for several minutes to allow the solvent to partially diffuse and spread.

[0058] Step Six: After attaching the silicon wafer to the adhesive layer, place it in an inert atmosphere (nitrogen or argon) sintering furnace and sinter according to the following process: First, pre-dry at 120℃ for 30 minutes to evaporate the solvent; next, heat to 200℃ at 3℃ / min and hold for 30 minutes to allow in-situ thermal decomposition of silver 2-ethylhexanoate to generate nano-silver, completing the necking, growth, and densification of silver particles; then, allow it to cool naturally to room temperature to obtain a continuous and dense silver sintered layer. The sintered sample is used for performance testing, including volume resistivity, shear strength, thermal conductivity, and porosity.

[0059] Figure 2 A SEM image of the nano-sintered silver paste prepared in Example 1 of this disclosure is shown. (Reference) Figure 2 The nano-sintered silver paste prepared in this disclosure has good uniformity.

[0060] Figure 3 A cross-sectional SEM image of the nano-sintered silver paste prepared in Example 1 of this disclosure after sintering is shown. (Reference) Figure 3The silver particles have formed sufficient neck connections, and the particle boundaries gradually disappear, presenting a continuous and dense silver framework structure. The pores are mainly closed pores of sub-200 nm, few in number and uniformly dispersed, with no through-pore structures observed. This structure indicates that the composite silver source system of "nano-silver powder / organic silver salt precursor" disclosed in this paper can achieve a highly dense silver sintered layer at temperatures below 250°C.

[0061] In addition to Example 1, this disclosure also includes the preparation processes of Examples 2 to 6 and Comparative Examples 1 to 3. Specific preparation methods can be found in Example 1 and will not be repeated here. The compositional proportions of the materials involved are shown in Table 1:

[0062] Table 1

[0063]

[0064] The test results for the above embodiments and comparative examples are shown in Table 2:

[0065] Table 2

[0066]

[0067] A performance comparison between the examples and the comparative examples reveals that the low-temperature sintering nano-silver paste prepared according to the technical solution of this disclosure exhibits significant advantages in densification level, electrical conductivity, and mechanical properties. This disclosure employs a composite silver source system of "nano-silver powder + organic silver salt precursor," and promotes interfacial sintering through a ternary synergistic sintering aid, enabling the examples to achieve a densification level far exceeding that of the comparative examples under sintering conditions not exceeding 250°C. The composite silver source system releases ultrafine active silver nuclei early in the sintering process, causing in-situ compensation and interstitial reconstruction on the particle surface. Simultaneously, the ternary synergistic sintering aid generates a synergistic activation effect at the silver particle interface, effectively reducing the initial sintering energy barrier and promoting multi-path diffusion between the solid phase, gas phase, and interface. Thus, a continuous silver grain network can be formed under low-temperature, pressureless conditions, significantly reducing porosity, increasing thermal conductivity, maintaining stable volume resistivity within the range required for high-power devices, and substantially improving shear strength compared to the comparative examples. Meanwhile, the optimized ratio of small-molecule complexing agents and dispersants ensures that the decomposition behavior of the organic silver salt precursor in the system remains consistent with the dispersion state of the nano-silver powder, guaranteeing stable film formation during printing and drying. Comprehensive test results show that the composite silver source system and synergistic sintering technology proposed in this disclosure enable silver films to possess low-temperature sintering properties, high density, high conductivity, excellent mechanical strength, and long-term thermal stability. This makes them fully applicable to power semiconductor device packaging, ceramic substrate interconnects, high-temperature electronic packaging, and flexible high-reliability interconnects, demonstrating significant industrial application potential and promotional value.

[0068] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0069] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this disclosure and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0070] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0071] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing nano-sintered silver paste, characterized in that, include: By weight, 5-15 parts of the organosilver salt precursor are added to an organic solvent and dispersed evenly. Then, 0.05-1 part of a small molecule complexing agent is added to prepare a first solution. The small molecule complexing agent is an amine or carboxylic acid ligand. The organosilver salt precursor includes one or more of silver 2-ethylhexanoate, silver lactate, silver acetate, and their coordination complexes. Add 75-90 parts of nano silver powder and 0.1-1.5 parts of dispersant to the first solution and disperse evenly to obtain a second solution; the surface of the nano silver powder is coated with polyvinylpyrrolidone or sodium citrate. Add 0.1-1 parts of rheology modifier and 0.1-3 parts of sintering aid to the second solution, stir evenly, and then perform three-roll milling to obtain an intermediate slurry; wherein, the sintering aid is composed of three components: a low-melting-point inorganic sintering aid, a surface-activated sintering aid, and a redox synergistic sintering aid; the low-melting-point inorganic sintering aid includes one or more of tin oxide, zinc oxide, bismuth oxide, and borate glass powder; the surface-activated sintering aid includes one or more of organic acids, reducing polyols, and amino alcohols; the redox synergistic sintering aid includes one or more of stannous salt-hydrogen peroxide, ferrous salt-organic carboxylic acid, and benzoyl peroxide-ascorbic acid; Add 0.1 to 1 part of defoamer to the intermediate slurry and perform vacuum defoaming treatment to obtain nano sintered silver paste; The mixer used for mixing has a revolution speed of 1000~2200 rpm, a rotation speed of 700~1400 rpm, and a mixing time of 10~30 minutes.

2. The preparation method according to claim 1, characterized in that, The nano-silver powder has a particle size of 30~80nm and is prepared by chemical reduction or spray thermal decomposition.

3. The preparation method according to claim 1, characterized in that, The dispersant includes one or more of ethylene glycol, polyacrylamide, and fatty alcohol ethers.

4. The preparation method according to claim 1, characterized in that, The organic solvent includes one or more of isopropanol, butyl propionate, butyl lactate, and ethylene glycol methyl ether.

5. The preparation method according to claim 1, characterized in that, Both the rheology modifier and the defoamer are silicone additives.

6. The preparation method according to claim 1, characterized in that, The roller gaps of the three-roll mill are 20~30μm, 10~15μm and 3~7μm respectively, and the rotation speed is 300~500 rpm, so as to control the fineness of the intermediate slurry to be less than 5μm.

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