Composite additive for improving overburning resistance of electrode paste and preparation method and application thereof

Abstract

The invention discloses a composite additive for improving the overburning resistance of electrode paste as well as a preparation method and application of the composite additive, and belongs to the technical field of electrode paste preparation. Graphene compounded aluminum nitride particles serve as a core, a uniform silicon carbide layer is constructed on the surface of the core through a fluidized bed chemical vapor deposition method, a shell layer with cardanol-based phenolic resin, carbon black and a silane coupling agent as main components is constructed on the surface of the silicon carbide layer, and the composite additive of a complete core-shell structure is formed. The shell layer of the additive keeps a complete structure when the temperature is lower than 600 DEG C, erosion of volatile components in electrode paste to core silicon carbide particles is reduced, when the temperature is increased to be higher than 600 DEG C, the shell layer is gradually decomposed, the inner core silicon carbide particles are released, the heat conduction and shunting effects are achieved, and electrode paste overburning caused by current gathering and local overheating is avoided; the composite additive disclosed by the invention is added in an electrode paste mixing stage, so that the overburning resistance of the electrode paste can be improved.

Description

Technical Field

[0001] This invention relates to the field of electrode paste preparation technology, specifically to a composite additive for improving the overheat resistance of electrode paste, its preparation method, and its application. Background Technology

[0002] Electrode paste, a core conductive consumable in high-temperature metallurgical equipment such as calcium carbide furnaces and ferroalloy furnaces, is mainly made by mixing carbon aggregates such as anthracite, metallurgical coke, and graphite powder with coal tar pitch binder, followed by high-temperature calcination. It possesses key properties including conductivity, high-temperature resistance, and thermal shock resistance, directly determining the smelting efficiency, electrode consumption rate, and production safety of the submerged arc furnace. During submerged arc furnace operation, the electrode paste needs to be exposed to a high-temperature environment above 1000℃ for extended periods. Due to factors such as arc discharge and uneven material reaction, localized heat concentration can easily occur, leading to overheating of the electrode paste. This manifests as localized softening, melting, and cracking of the electrode paste, and may even result in electrode breakage and furnace leakage, significantly increasing the consumption cost of the electrode paste and severely restricting the continuous and stable operation of the submerged arc furnace. Therefore, improving the overheating resistance of electrode paste has become one of the core research directions in the field of carbon materials. Summary of the Invention

[0003] The purpose of this invention is to provide a composite additive for improving the overheating resistance of electrode paste, its preparation method, and its application. The composite additive has a core-shell structure, with graphene-composite aluminum nitride particles as the core. A silicon carbide layer is constructed on the surface of the core using fluidized bed chemical vapor deposition. Subsequently, a shell layer is constructed outside the silicon carbide layer, which is composed of cashew phenolic resin, carbon black, and a silane coupling agent. The shell layer of this core-shell structure detaches at a high temperature of 800°C, releasing the internal core@silicon carbide particles. The graphene in the core begins to divert uneven current in the electrode paste, and the aluminum nitride and silicon carbide layers in the core conduct heat together, reducing local heat accumulation and alleviating overheating and softening in the later stages of electrode self-baking.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a composite additive for improving the overheat resistance of electrode paste, the composite additive comprising a core and a coating layer formed on the surface of the core; the core being graphene-composite aluminum nitride particles; the coating layer comprising a silicon carbide layer and a shell layer, the silicon carbide layer being prepared by fluidized bed chemical vapor deposition using methyltrichlorosilane as a precursor and hydrogen as a carrier gas; the shell layer comprising cashew phenolic resin, carbon black, and a silane coupling agent.

[0005] Further, the core has a particle size of 2-4µm, the coating layer has a thickness of 1-3µm, the silicon carbide layer in the coating layer has a thickness of 0.5-0.8µm, and the shell layer has a thickness of 0.5-2.2µm; in the fluidized bed chemical vapor deposition method, the molar ratio of methyltrichlorosilane to hydrogen is (3-4):1; in the shell layer, the mass ratio of cashew phenolic resin, carbon black, and silane coupling agent is 15:(1.5-3):2.

[0006] The graphene-composite aluminum nitride core helps improve the uniformity of thermal and electrical conductivity of the matrix, thereby mitigating localized overheating. The silicon carbide interlayer, generated through fluidized bed chemical vapor deposition, acts as a highly heat-resistant barrier, effectively preventing high-temperature oxidation and erosion of the core. The outer resin composite shell decomposes at specific temperatures, releasing the internal core@silicon carbide particles, which helps provide some protection under abnormal operating conditions. Due to the thermal conductivity of the silicon carbide layer and core particles, the oxidation rate and softening tendency of the electrode paste in the high-temperature region of the arc are reduced, the retention rate of high-temperature flexural strength is improved, and oxidation weight loss is reduced. Simultaneously, the graphene composite in the core promotes a more uniform current distribution, reducing the thermoelectric effect exacerbated by localized current concentration. These improved properties work together to enhance the electrode paste's resistance to overheating.

[0007] Secondly, the present invention provides a method for preparing a composite additive to improve the overheating resistance of electrode paste, comprising the following steps:

[0008] Step S1: Aluminum nitride and yttrium oxide are ground in isopropanol with zirconium dioxide balls to obtain an aluminum nitride suspension; graphene nanosheets are dispersed in an aqueous isopropanol solution to obtain a graphene dispersion; the aluminum nitride suspension and the graphene dispersion are mixed, spray-dried, and sintered under nitrogen at atmospheric pressure to obtain graphene-composite aluminum nitride particles.

[0009] Step S2: Add the graphene-composite aluminum nitride particles to the modification solution, react, centrifuge, wash the precipitate with anhydrous ethanol, and dry to obtain the silanized core.

[0010] Step S3: Add the silanized core to the nickel salt solution, stir, centrifuge, wash the precipitate with anhydrous ethanol, vacuum dry, and pre-reduce in hydrogen / argon to obtain the surface-modified core.

[0011] Step S4: Place the surface-modified core in a fluidized bed reactor, introduce hydrogen gas, perform chemical vapor deposition using methyltrichlorosilane as a precursor, and anneal in nitrogen to obtain core@silicon carbide particles.

[0012] Step S5: Add the core@silicon carbide particles to the shell solution, stir, rotary evaporate, collect the particles, and solidify to obtain a composite additive that improves the overburn resistance of the electrode paste.

[0013] Further, in step S1, the mass-to-volume ratio of aluminum nitride, yttrium oxide, isopropanol, and zirconium dioxide spheres is 100g:(2.7-3.2)g:100mL:20g; the average diameter of the aluminum nitride is 3-5µm, and the diameter of the zirconium dioxide spheres is 1.5-3mm; the grinding time is 60-120min; the thickness of the graphene nanosheets is 5-10nm, and the mass-to-volume ratio of the graphene nanosheets to the isopropanol aqueous solution is 1g:(30-50)mL; in the isopropanol aqueous solution, the mass-to-volume ratio of isopropanol to water is (1-3)g:1L; and the dispersion time is 45-75min.

[0014] Further, in step S1, the volume ratio of the aluminum nitride suspension to the graphene dispersion is 100:(5-8); the mixing method is ultrasonic, the ultrasonic power is 300-400W, and the ultrasonic time is 100-150min; the inlet temperature of the spray drying is 190-210℃, the outlet temperature is 75-85℃, the atomization speed is 14000-16000rpm, and the spray pressure is 1.5-2.5bar; the sintering temperature is 1450-1500℃, and the sintering time is 4-6h.

[0015] Further, in step S2, the mass-to-volume ratio of the graphene-composite aluminum nitride particles to the modification solution is 1g:(10-12)mL; the modification solution is a KH560 ethanol aqueous solution, the mass-to-volume ratio of KH560 to the ethanol aqueous solution is 1g:(80-120)mL, and the volume fraction of the ethanol aqueous solution is 90%-98%; the stirring speed of the reaction is 200-400rpm, the reaction time is 40-60min; the drying temperature is 110-120℃, and the drying time is 1-2h.

[0016] Further, in step S3, the mass-to-volume ratio of the silanized core to the nickel salt solution is 1 g : (3-5) mL; the nickel salt solution comprises nickel nitrate, citric acid, and deionized water, and the mass-to-volume ratio of nickel nitrate, citric acid, and deionized water is (3-5) g : (0.3-0.5) g : 100 mL; the stirring speed is 150-300 rpm, and the stirring time is 2-4 h; the vacuum drying temperature is 75-85℃, and the vacuum drying time is 45-75 min; the pre-reduction temperature is 300-400℃, and the pre-reduction time is 20-40 min; the volume ratio of hydrogen to argon is (10-20) : (80-90).

[0017] Further, in step S4, the mass ratio of the surface-modified core to methyltrichlorosilane is 1:(5-10); the hydrogen flow rate is 85-90 sccm; the methyltrichlorosilane is introduced by heating it at 25-35°C and then carrying it into the fluidized bed reactor with hydrogen; the chemical vapor deposition temperature is 1200-1300°C, the heating rate is 8-12°C / min, the chemical vapor deposition time is 2-3 h, and the pressure is 5-10 kPa; the annealing temperature is 1150-1250°C, and the annealing time is 20-40 min.

[0018] Further, in step S5, the mass-to-volume ratio of the core@silicon carbide particles to the shell solution is 1g:(10-20)mL; the shell solution comprises cashew nut shell resin, carbon black, silane coupling agent, dispersant, and solvent, with a mass ratio of cashew nut shell resin, carbon black, silane coupling agent, dispersant, and solvent of 15:(1.5-3):2:0.2:(200-250); the solvent is an aqueous ethanol solution, with a volume ratio of ethanol to water of (80-90):(10-20); the dispersant is polyvinylpyrrolidone K30; the silane coupling agent is KH560; the stirring speed is 300-500rpm, and the stirring time is 1-2h; the rotary evaporation temperature is 50-60℃; the curing temperature is 170-190℃, and the curing time is 4-6h.

[0019] Thirdly, the present invention provides an application of a composite additive to improve the overheat resistance of electrode paste. The composite additive described in the first aspect is added during the electrode paste mixing stage. The electrode paste includes dry material and binder. The mass ratio of the composite additive, dry material and binder is (2-5):100:(11.1-17.6).

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0021] This invention provides a composite additive that, when added during the electrode paste mixing stage, enhances the electrode paste's resistance to overheating and alleviates softening caused by overheating in the later stages of electrode self-baking. The composite additive has a core-shell structure, with its core consisting of graphene-composite aluminum nitride particles, which helps improve the uniformity of thermal and electrical conductivity of the electrode paste, mitigating localized heat accumulation and uneven current distribution from within. Secondly, a silicon carbide layer is coated around the core using fluidized bed chemical vapor deposition technology. This silicon carbide layer further assists in heat conduction, reduces high-temperature oxidation and erosion of the core, and provides a foundation for the stable adhesion of the subsequent shell solution. A shell layer composed of cashew phenolic resin, carbon black, and a silane coupling agent is then coated around the silicon carbide layer. This shell layer remains stable below 600°C, reducing the erosion of the internal structure by volatile components. When the temperature rises above 600°C, the shell structure gradually decomposes, releasing the internal core@silicon carbide particles, thus avoiding over-protection. This multi-level core-shell structure can slow down the oxidation and softening process of the electrode paste at high temperatures from multiple levels, thereby improving its resistance to overheating and its service life. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a preparation method for a composite additive that improves the overheating resistance of electrode paste. Detailed Implementation

[0023] The technical solution of the present invention will be described in detail below through specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0024] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0025] The cashew nut phenol-based phenolic resin used in this invention is prepared by the following method: Cashew nut phenol and zinc acetate catalyst are magnetically stirred in a three-necked flask for 30 minutes at a stirring temperature of 50°C. The amount of zinc acetate used is 3% of the mass of cashew nut phenol. Then, formaldehyde solution is added dropwise over 1-2 hours; n(cashew nut phenol):n(formaldehyde) = 1:0.75. Subsequently, the temperature is raised to 90°C, and after reacting for 4 hours, the solvent is removed to obtain the cashew nut phenol-based phenolic resin.

[0026] Example 1

[0027] like Figure 1 As shown, a composite additive for improving the overheating resistance of electrode paste is prepared by means of:

[0028] Step S1: Aluminum nitride and yttrium oxide were milled in isopropanol using zirconium dioxide balls to obtain an aluminum nitride suspension. The mass-to-volume ratio of aluminum nitride, yttrium oxide, isopropanol, and zirconium dioxide balls was 100g:2.9g:100mL:20g. The average diameter of the aluminum nitride was 4µm, and the diameter of the zirconium dioxide balls was 2mm. The milling time was 90min. 8nm thick graphene nanosheets were dispersed in an aqueous isopropanol solution to obtain a graphene dispersion. The mass-to-volume ratio of graphene nanosheets to the aqueous isopropanol solution was 1g:40mL. The mass-to-volume ratio of isopropanol to water in the aqueous isopropanol solution was 2g:1L. The dispersion time was 60min. Aluminum nitride suspension and graphene dispersion were ultrasonically mixed at 360W for 120 min, with a volume ratio of 100:7. Spray drying was performed at an inlet temperature of 200℃, an outlet temperature of 80℃, an atomization speed of 15000 rpm, and a spray pressure of 2.0 bar. The spray-dried particles were then sintered under nitrogen at atmospheric pressure for 5 h at a sintering temperature of 1475℃ to obtain graphene-composite aluminum nitride particles.

[0029] Step S2: Add graphene-composite aluminum nitride particles to the modification solution. The mass-to-volume ratio of graphene-composite aluminum nitride particles to the modification solution is 1 g: 11 mL. The modification solution is prepared as follows: Disperse 1 g of KH560 in 100 mL of 94% (v / v) ethanol aqueous solution. Stir the reaction at 300 rpm for 50 min. After the reaction is complete, centrifuge, wash the precipitate 6 times with anhydrous ethanol, and dry it at 115 °C for 1.5 h to obtain the silanized core.

[0030] Step S3: Add the silanized core to the nickel salt solution. The mass-to-volume ratio of the silanized core to the nickel salt solution is 1 g:4 mL. The nickel salt solution is prepared as follows: Dissolve 4 g of nickel nitrate in 100 mL of deionized water, then add 0.4 g of citric acid, and sonicate in a water bath for 5 min to obtain a clear nickel salt solution. Stir at 220 rpm for 3 h, centrifuge after stirring, wash the precipitate twice with anhydrous ethanol, dry under vacuum at 80 °C for 60 min, and then pre-reduce in hydrogen / argon gas at a volume ratio of 15:85. The pre-reduction temperature is 350 °C, and the pre-reduction time is 30 min to obtain the surface-modified core.

[0031] Step S4: Place the surface-modified core in a fluidized bed reactor, introduce hydrogen gas at a flow rate of 87.5 sccm, and perform chemical vapor deposition (CVD) at 1250℃ using methyltrichlorosilane as a precursor. The heating rate is 10℃ / min, the CVD time is 2.5 h, and the pressure is 7.5 kPa. The mass ratio of the surface-modified core to methyltrichlorosilane is 1:7.5. The methyltrichlorosilane is introduced as follows: after being heated to 30℃ in a water bath, it is carried into the fluidized bed reactor by bubbling hydrogen gas. The molar ratio of methyltrichlorosilane to hydrogen is 3.4:1. After fluidized bed CVD treatment, the particles are annealed in nitrogen at 1200℃ for 30 min to obtain core@silicon carbide particles.

[0032] Step S5: Add core@silicon carbide particles to the shell solution at a mass-to-volume ratio of 1g:15mL. Stir at 400rpm for 1.5h. After stirring, evaporate at 55℃ to remove the solvent, collect the particles, and solidify them at 180℃ for 5h to obtain a composite additive that improves the overheating resistance of electrode paste. The composite additive has a core-shell structure with a core particle size of 3µm and a coating thickness of 2µm, wherein the silicon carbide layer has a thickness of 0.7µm and the shell layer has a thickness of 1.3µm.

[0033] The shell solution was prepared as follows: 0.2 g of polyvinylpyrrolidone K30 was dissolved in 100 mL of 85% ethanol aqueous solution to obtain solution A; 2 g of KH560 was added to 120 mL of 85% ethanol aqueous solution and stirred at 200 rpm for 30 min, then 2 g of carbon black was added and ultrasonically treated at 200 W for 10 min to obtain solution B; solution A was added to solution B and stirred at 200 rpm for 10 min, then 15 g of cashew phenolic resin was added and stirred at 400 rpm for 30 min to obtain the shell solution.

[0034] Example 2

[0035] like Figure 1 As shown, a composite additive for improving the overheating resistance of electrode paste is prepared by means of:

[0036] Step S1: Aluminum nitride and yttrium oxide were milled in isopropanol using zirconium dioxide balls to obtain an aluminum nitride suspension; the mass-to-volume ratio of aluminum nitride, yttrium oxide, isopropanol, and zirconium dioxide balls was 100g:2.7g:100mL:20g; the average diameter of aluminum nitride was 3µm; the diameter of zirconium dioxide balls was 1.5mm; and the milling time was 120min. Graphene nanosheets with a thickness of 5nm were dispersed in an isopropanol aqueous solution to obtain a graphene dispersion; the mass-to-volume ratio of graphene nanosheets to the isopropanol aqueous solution was 1g:30mL; the mass-to-volume ratio of isopropanol to water in the isopropanol aqueous solution was 1g:1L; and the dispersion time was 45min. Aluminum nitride suspension and graphene dispersion were ultrasonically mixed at 300W for 150 min, with a volume ratio of 100:8. Spray drying was performed at an inlet temperature of 190℃, an outlet temperature of 75℃, an atomization speed of 14000 rpm, and a spray pressure of 1.5 bar. The spray-dried particles were then sintered under nitrogen at atmospheric pressure for 6 h at a sintering temperature of 1450℃ to obtain graphene-composite aluminum nitride particles.

[0037] Step S2: Add graphene-composite aluminum nitride particles to the modification solution. The mass-to-volume ratio of graphene-composite aluminum nitride particles to the modification solution is 1 g: 12 mL. The modification solution is prepared as follows: Disperse 1 g of KH560 in 120 mL of 90% (v / v) ethanol aqueous solution. Stir the reaction at 200 rpm for 60 min. After the reaction is complete, centrifuge, wash the precipitate 6 times with anhydrous ethanol, and dry it at 110 °C for 2 h to obtain the silanized core.

[0038] Step S3: Add the silanized core to the nickel salt solution. The mass-to-volume ratio of the silanized core to the nickel salt solution is 1 g:3 mL. The nickel salt solution is prepared as follows: Dissolve 5 g of nickel nitrate in 100 mL of deionized water, then add 0.5 g of citric acid, and sonicate in a water bath for 5 min to obtain a clear nickel salt solution. Stir at 150 rpm for 4 h, centrifuge after stirring, wash the precipitate twice with anhydrous ethanol, dry under vacuum at 75 °C for 75 min, and then pre-reduce in hydrogen / argon gas at a volume ratio of 10:90, a temperature of 400 °C, and a time of 20 min to obtain the surface-modified core.

[0039] Step S4: Place the surface-modified core in a fluidized bed reactor, introduce hydrogen gas at a flow rate of 85 sccm, and perform chemical vapor deposition (CVD) at 1200℃ using methyltrichlorosilane as a precursor. The heating rate is 8℃ / min, the CVD time is 3 h, and the pressure is 5 kPa. The mass ratio of the surface-modified core to methyltrichlorosilane is 1:5. The methyltrichlorosilane is introduced as follows: after being heated to 25℃ in a water bath, it is carried into the fluidized bed reactor by bubbling hydrogen gas. The molar ratio of methyltrichlorosilane to hydrogen is 3:1. After fluidized bed CVD treatment, the particles are annealed in nitrogen at 1150℃ for 40 min to obtain core@silicon carbide particles.

[0040] Step S5: Add core@silicon carbide particles to the shell solution at a mass-to-volume ratio of 1g:20mL. Stir at 300rpm for 2 hours. After stirring, evaporate by rotary evaporation at 50℃ to remove the solvent, collect the particles, and solidify the particles at 170℃ for 6 hours to obtain a composite additive that improves the overheating resistance of electrode paste. The composite additive has a core-shell structure with a core particle size of 2µm and a coating thickness of 1µm, wherein the silicon carbide layer has a thickness of 0.5µm and the shell layer has a thickness of 0.5µm.

[0041] The shell solution was prepared as follows: 0.2 g of polyvinylpyrrolidone K30 was dissolved in 80 mL of 90% ethanol aqueous solution to obtain solution A; 2 g of KH560 was added to 120 mL of 90% ethanol aqueous solution and stirred at 200 rpm for 30 min, then 1.5 g of carbon black was added and ultrasonically treated at 200 W for 10 min to obtain solution B; solution A was added to solution B and stirred at 200 rpm for 10 min, then 15 g of cashew phenolic resin was added and stirred at 400 rpm for 30 min to obtain the shell solution.

[0042] Example 3

[0043] like Figure 1 As shown, a composite additive for improving the overheating resistance of electrode paste is prepared by means of:

[0044] Step S1: Aluminum nitride and yttrium oxide were milled in isopropanol using zirconium dioxide balls to obtain an aluminum nitride suspension. The mass-to-volume ratio of aluminum nitride, yttrium oxide, isopropanol, and zirconium dioxide balls was 100g:3.2g:100mL:20g. The average diameter of the aluminum nitride was 5µm, and the diameter of the zirconium dioxide balls was 3mm. The milling time was 60min. Graphene nanosheets with a thickness of 10nm were dispersed in an aqueous isopropanol solution to obtain a graphene dispersion. The mass-to-volume ratio of graphene nanosheets to the aqueous isopropanol solution was 1g:50mL. The mass-to-volume ratio of isopropanol to water in the aqueous isopropanol solution was 3g:1L. The dispersion time was 75min. Aluminum nitride suspension and graphene dispersion were ultrasonically mixed at 400W for 100 min, with a volume ratio of 100:5. Spray drying was performed at an inlet temperature of 210℃, an outlet temperature of 85℃, an atomization speed of 16000 rpm, and a spray pressure of 2.5 bar. The spray-dried particles were then sintered under nitrogen at atmospheric pressure for 4 h at a sintering temperature of 1500℃ to obtain graphene-composite aluminum nitride particles.

[0045] Step S2: Add graphene-composite aluminum nitride particles to the modification solution. The mass-to-volume ratio of graphene-composite aluminum nitride particles to the modification solution is 1g:10mL. The modification solution is prepared as follows: Disperse 1g of KH560 in 180mL of 98% (v / v) ethanol aqueous solution. Stir the mixture at 400rpm for 40min. After the reaction is complete, centrifuge the mixture, wash the precipitate 6 times with anhydrous ethanol, and dry it at 120℃ for 1h to obtain the silanized core.

[0046] Step S3: Add the silanized core to the nickel salt solution. The mass-to-volume ratio of the silanized core to the nickel salt solution is 1 g: 5 mL. The nickel salt solution is prepared as follows: Dissolve 3 g of nickel nitrate in 100 mL of deionized water, then add 0.3 g of citric acid, and sonicate in a water bath for 5 min to obtain a clear nickel salt solution. Stir at 300 rpm for 2 h, centrifuge after stirring, wash the precipitate twice with anhydrous ethanol, and vacuum dry at 85 °C for 45 min. Then, pre-reduce it in hydrogen / argon gas at a volume ratio of 20:80, a temperature of 300 °C, and a time of 40 min to obtain the surface-modified core.

[0047] Step S4: Place the surface-modified core in a fluidized bed reactor, introduce hydrogen gas at a flow rate of 90 sccm, and perform chemical vapor deposition (CVD) at 1300℃ using methyltrichlorosilane as a precursor. The heating rate is 12℃ / min, the CVD time is 2 h, and the pressure is 10 kPa. The mass ratio of the surface-modified core to methyltrichlorosilane is 1:10. The methyltrichlorosilane is introduced as follows: after being heated to 35℃ in a water bath, it is carried into the fluidized bed reactor by bubbling hydrogen gas. The molar ratio of methyltrichlorosilane to hydrogen is 4:1. After fluidized bed CVD treatment, the particles are annealed in nitrogen at 1250℃ for 20 min to obtain core@silicon carbide particles.

[0048] Step S5: Add core@silicon carbide particles to the shell solution at a mass-to-volume ratio of 1g:10mL. Stir at 500rpm for 1 hour. After stirring, evaporate by rotary evaporation at 50°C to remove the solvent, collect the particles, and solidify the particles at 190°C for 4 hours to obtain a composite additive that improves the overheating resistance of electrode paste. The composite additive has a core-shell structure with a core particle size of 4µm and a coating layer thickness of 3µm, wherein the silicon carbide layer has a thickness of 0.8µm and the shell layer has a thickness of 2.2µm.

[0049] The shell solution was prepared as follows: 0.2 g of polyvinylpyrrolidone K30 was dissolved in 100 mL of 80% ethanol aqueous solution to obtain solution A; 2 g of KH560 was added to 150 mL of 80% ethanol aqueous solution and stirred at 200 rpm for 30 min, then 3 g of carbon black was added and ultrasonically treated at 200 W for 10 min to obtain solution B; solution A was added to solution B and stirred at 200 rpm for 10 min, then 15 g of cashew phenolic resin was added and stirred at 400 rpm for 30 min to obtain the shell solution.

[0050] Example 4

[0051] An electrode paste with added composite additives is prepared as follows:

[0052] The dry electrode paste was mixed with the composite additive prepared in Example 1, and the mixture was dry-mixed at 120 rpm for 20 min at room temperature to ensure initial uniformity. Subsequently, the binder was heated to 130°C to melt and poured into the above mixture. The mixture was stirred at 150 rpm for 15 min until the paste was uniformly mixed. After uniform mixing, the paste was pressed and shaped according to conventional processes to obtain an electrode paste with added composite additive, wherein the mass ratio of composite additive, dry paste and binder was 3.5:100:14.4.

[0053] Example 5

[0054] An electrode paste with added composite additives is prepared as follows:

[0055] The dry electrode paste was mixed with the composite additive prepared in Example 2, and the mixture was dry-mixed at 120 rpm for 20 min at room temperature to make the two initially uniform. Then, the binder was heated to 130°C to melt and poured into the above mixture. The mixture was stirred at 150 rpm for 15 min until the paste was uniformly mixed. After uniform mixing, the paste was pressed and shaped according to conventional process to obtain an electrode paste with composite additive, wherein the mass ratio of composite additive, dry paste and binder is 5:100:17.6.

[0056] Example 6

[0057] An electrode paste with added composite additives is prepared as follows:

[0058] The dry electrode paste was mixed with the composite additive prepared in Example 3, and the mixture was dry-mixed at 120 rpm for 20 min at room temperature to make the two initially uniform. Then, the binder was heated to 130°C to melt and poured into the above mixture. The mixture was stirred at 150 rpm for 15 min until the paste was uniformly mixed. After uniform mixing, the paste was pressed and shaped according to conventional process to obtain an electrode paste with composite additive, wherein the mass ratio of composite additive, dry paste and binder is 2:100:11.1.

[0059] Comparative Example 1

[0060] An electrode paste, which differs from Example 4 in that the composite additive prepared in Example 1 is not added, but the other operating steps and process parameters are exactly the same as those in Example 4.

[0061] Comparative Example 2

[0062] An electrode paste, which differs from Example 4 in that the core of the added composite additive is silicon carbide, while the rest is exactly the same as in Example 1. The preparation process and process parameters of the electrode paste with added composite additive are exactly the same as in Example 4.

[0063] Comparative Example 3

[0064] An electrode paste differs from Example 4 in that the added composite additive lacks a silicon carbide layer, the coating layer on the core surface is a shell layer, and the rest is exactly the same as Example 1. The preparation process and process parameters of the electrode paste with added composite additive are exactly the same as those of Example 4.

[0065] Comparative Example 4

[0066] An electrode paste differs from Example 4 in that the added composite additive lacks a shell layer, the coating layer on the core surface is a silicon carbide layer, and the rest is exactly the same as Example 1. The preparation process and process parameters of the electrode paste with added composite additive are exactly the same as those of Example 4.

[0067] Electrode paste performance testing:

[0068] The electrode pastes prepared in Examples 4-6 and Comparative Examples 1-4 were subjected to performance tests. The electrode pastes underwent the following treatment before testing to simulate the calcination process during electrode paste production.

[0069] Step A1: Take 6 kg of sample and crush it to below 25 mm without damaging the particle size distribution. Divide it into two portions using the quartering method. One portion is kept as a reserve sample. The other portion is heated to no more than 150°C while stirring carefully until the paste is completely melted. Then, pound it into a sheet metal cylinder in three batches, filling it to a height of 250 mm. Stand the cylinder vertically on a cylinder stand and cool it to room temperature before placing it into a calcining crucible.

[0070] Step A2: Place a 50mm thick layer of filler material at the bottom of the crucible. Place the iron cylinder filled with the paste upright inside the crucible, with a 20mm distance between the cylinder and the crucible wall, and a 15mm distance between the cylinders. Place the thermocouple in the center of the crucible, with its hot end parallel to the bottom of the sample. After filling all the gaps in the crucible with the filler material, place the crucible in the constant temperature zone of the calcining furnace for calcination.

[0071] Step A3: Turn on the power to heat at a rate of 100℃ / h. After gradually heating up, the sample inside the iron cylinder melts. When the temperature reaches 900℃, hold it at this temperature for 3 hours and then stop heating. Allow it to cool naturally in the furnace to below 100℃ and remove the crucible.

[0072] Step A4: Remove the sample from the sheet metal, remove the filler adhering to the bottom, cut off the bottom 10mm, and then process it into a cylindrical sample with a diameter × length of 45mm × 40mm for testing the resistivity and compressive strength of the electrode paste. The resistivity and compressive strength tests of the electrode paste were conducted in accordance with the YB / T4448-2014 standard, and the test results are shown in Table 1.

[0073] Table 1. Electrode paste performance test results for Examples 4-6 and Comparative Examples 1-4

[0074] Electrode paste resistivity (µΩ∙m) Electrode paste compressive strength (MPa) Example 4 46.3 41.3 Example 5 48.7 39.6 Example 6 49.5 40.7 Comparative Example 1 68.7 20.3 Comparative Example 2 107.8 19.5 Comparative Example 3 76.2 20.5 Comparative Example 4 70.3 27.6

[0075] As shown in Table 1, the resistivity of the electrode pastes prepared in Examples 4-6 was significantly reduced, and the compressive strength of the electrode pastes was significantly improved, about twice that of Comparative Example 1.

[0076] Comparative Example 1, without any composite additives, exhibited electrode paste resistivity and compressive strength within national standards, classifying it as a qualified conventional product. Comparative Example 2, however, included electrode paste with composite additives. The addition of silicon carbide as the core material replaced the original graphene-composite aluminum nitride particles, weakening the conductivity of the composite additives and causing an increase in electrode paste resistivity, far exceeding that of Examples 4-6, Comparative Example 1, and Comparative Examples 3-4. This increased resistivity further led to current accumulation and excessively high localized heat. The thermal conductivity of silicon carbide was insufficient to dissipate all the heat, resulting in partial overheating of the electrode paste and a decrease in compressive strength, making it the lowest among all tested samples. The electrode paste of Comparative Example 3, with the addition of a composite additive lacking a silicon carbide layer, exhibited a compressive strength similar to Comparative Example 1. However, its resistivity increased compared to Comparative Example 1. This may be due to the lack of the protective effect of the silicon carbide layer at high temperatures, leading to the slight oxidation of some aluminum nitride and graphene under sustained high temperatures. This resulted in the partial failure of the conductive network within the core, thus significantly increasing the resistivity compared to Comparative Example 1, but still lower than Comparative Example 2. The electrode paste of Comparative Example 4, with the addition of a composite additive lacking a shell layer, caused premature exposure of the functional particles. Volatile components in the electrode paste eroded the core through the gaps in the silicon carbide layer, leading to core failure and an increase in resistivity compared to Comparative Example 1. However, the composite additive lacking a shell layer still maintained the simple core-shell structure of the core@silicon carbide, allowing the functional particles to exert localized thermal conductivity and preventing heat accumulation leading to localized overheating. Therefore, the compressive strength of the electrode paste of Comparative Example 4 was still higher than that of Comparative Examples 1-3, but lower than that of Examples 4-6.

[0077] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A composite additive for improving the overheat resistance of electrode paste, characterized in that, The composite additive comprises a core and a coating layer formed on the surface of the core; the core is graphene-composite aluminum nitride particles; the coating layer comprises a silicon carbide layer and a shell layer, the silicon carbide layer is prepared by fluidized bed chemical vapor deposition method with methyltrichlorosilane as a precursor and hydrogen as a carrier gas; and the shell layer comprises cashew phenol-based phenolic resin, carbon black and silane coupling agent.

2. A composite additive to enhance the overburning resistance of the electrode paste according to claim 1, characterized in that, The particle size of the core is 2-4 µm, the thickness of the coating layer is 1-3 µm, in the coating layer, the thickness of the silicon carbide layer is 0.5-0.8 µm, and the thickness of the shell layer is 0.5-2.2 µm; in the fluidized bed chemical vapor deposition method, the molar ratio of methyltrichlorosilane to hydrogen is (3-4):1; in the shell layer, the mass ratio of cashew phenol-based phenolic resin, carbon black and silane coupling agent is 15:(1.5-3):

2.

3. A method of preparing a composite additive for improving the overburning resistance of an electrode paste according to claim 1 or 2, characterized in that, The method comprises the following steps: Step S1, grinding aluminum nitride and yttrium trioxide in isopropyl alcohol with zirconium dioxide balls to obtain an aluminum nitride suspension; Dispersing graphene nanosheets in isopropyl alcohol aqueous solution to obtain a graphene dispersion; mixing the aluminum nitride suspension and the graphene dispersion, spray drying, and sintering under normal pressure in nitrogen to obtain graphene-composite aluminum nitride particles; Step S2, adding the graphene-composite aluminum nitride particles into a modification liquid, reacting, centrifuging, washing the precipitate with anhydrous ethanol, and drying to obtain a silanized core; Step S3, adding the silanized core into a nickel salt solution, stirring, centrifuging, washing the precipitate with anhydrous ethanol, vacuum drying, and pre-reducing in hydrogen / argon to obtain a surface-modified core; Step S4, placing the surface-modified core in a fluidized bed reactor, passing in hydrogen, and performing chemical vapor deposition with methyltrichlorosilane as a precursor, and annealing in nitrogen to obtain core@silicon carbide particles; Step S5, adding the core@silicon carbide particles into a shell layer solution, stirring, rotary evaporation, collecting particles, and solidifying to obtain a composite additive for improving the overfiring resistance of electrode paste.

4. The method of claim 3, wherein the composite additive is prepared by mixing the first additive and the second additive in a weight ratio of 1 : 1 to 1 :

3. In the step S1, the mass-volume ratio of the aluminum nitride, yttrium trioxide, isopropyl alcohol and zirconium dioxide balls is 100g:(2.7-3.2)g:100mL:20g; the average diameter of the aluminum nitride is 3-5 µm, and the diameter of the zirconium dioxide balls is 1.5-3 mm; the grinding time is 60-120 min; the thickness of the graphene nanosheets is 5-10 nm, and the mass-volume ratio of the graphene nanosheets and isopropyl alcohol aqueous solution is 1g:(30-50)mL; in the isopropyl alcohol aqueous solution, the mass-volume ratio of isopropyl alcohol to water is (1-3)g:1L; and the dispersion time is 45-75 min.

5. The method of claim 3, wherein the composite additive is prepared by mixing the first additive and the second additive in a weight ratio of 1 : 1 to 1 :

3. The volume ratio of the aluminum nitride suspension and the graphene dispersion liquid in the step S1 is 100: (5-8); the mixing mode is ultrasonic, the power of the ultrasonic is 300-400 W, the ultrasonic time is 100-150 min; the inlet temperature of the spray drying is 190-210 ℃, the outlet temperature is 75-85 ℃, the atomization rotating speed is 14000-16000 rpm, the spray pressure is 1.5-2.5 bar; the sintering temperature is 1450-1500 ℃, the sintering time is 4-6 h.

6. The method of claim 3, wherein the composite additive is prepared by mixing the first additive and the second additive in a weight ratio of 1 : 1 to 1 :

3. The mass volume ratio of the graphene-composite aluminum nitride particles and the modification liquid in the step S2 is 1 g: (10-12) mL; the modification liquid is a KH560 ethanol aqueous solution, the mass volume ratio of the KH560 and the ethanol aqueous solution is 1 g: (80-120) mL, the volume fraction of the anhydrous ethanol in the ethanol aqueous solution is 90%-98%; the stirring speed of the reaction is 200-400 rpm, the reaction time is 40-60 min; the drying temperature is 110-120 ℃, the drying time is 1-2 h.

7. The method of claim 3, wherein the composite additive is prepared by mixing the first additive and the second additive in a weight ratio of 1 : 1 to 1 :

3. The mass volume ratio of the silanization core and the nickel salt solution in the step S3 is 1 g: (3-5) mL; the nickel salt solution includes nickel nitrate, citric acid and deionized water, the mass volume ratio of the nickel nitrate, the citric acid and the deionized water is (3-5) g: (0.3-0.5) g: 100 mL; the stirring speed is 150-300 rpm, the stirring time is 2-4 h; the vacuum drying temperature is 75-85 ℃, the vacuum drying time is 45-75 min; the pre-reduction temperature is 300-400 ℃, the pre-reduction time is 20-40 min; the volume ratio of the hydrogen and the argon is (10-20): (80-90).

8. The method of claim 3, wherein the composite additive is prepared by mixing the first additive and the second additive in a weight ratio of 1 : 1 to 1 :

3. The mass ratio of the surface-modified core and the methyltrichlorosilane in the step S4 is 1: (5-10); the flow rate of the hydrogen is 85-90 sccm; the feeding mode of the methyltrichlorosilane is that the methyltrichlorosilane is heated at 25-35 ℃ and carried into the fluidized bed reactor by the hydrogen; the chemical vapor deposition temperature is 1200-1300 ℃, the heating rate is 8-12 ℃ / min, the chemical vapor deposition time is 2-3 h, and the pressure is 5-10 kPa; the annealing temperature is 1150-1250 ℃, and the annealing time is 20-40 min.

9. The method of claim 3, wherein the composite additive is prepared by mixing the first additive and the second additive in a weight ratio of 1 : 1 to 1 :

3. In the step S5, the mass-volume ratio of the core silicon carbide particles and the shell layer solution is 1g:(10-20)mL; the shell layer solution comprises cashew phenolic phenolic resin, carbon black, silane coupling agent, dispersant and solvent, the mass ratio of the cashew phenolic phenolic resin, carbon black, silane coupling agent, dispersant and solvent is 15:(1.5-3):2:0.2:(200-250), the solvent is ethanol aqueous solution, the volume ratio of ethanol and water in the ethanol aqueous solution is (80-90):(10-20); the dispersant is polyvinylpyrrolidone K30; the silane coupling agent is KH560; the stirring speed is 300-500rpm, and the stirring time is 1-2h; the rotary evaporation temperature is 50-60℃; the solidification temperature is 170-190℃, and the solidification time is 4-6h.

10. Use of a composite additive to improve the overburning resistance of an electrode paste according to claim 1, characterized in that, The composite additive of claim 1 is added in the electrode paste mixing stage, the electrode paste comprises dry materials and binder, and the mass ratio of the composite additive, dry materials and binder is (2-5):100:(11.1-17.6).

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