Preparation method of graphite enhanced electrode paste with high voltage resistance and high strength

Abstract

The invention relates to the technical field of electrode paste, in particular to a preparation method of high-pressure-resistant high-strength graphite enhanced electrode paste, which comprises the following steps: sequentially performing oxidation modification and silane modification on crystalline flake graphite powder, preparing silane modified graphite powder, and synchronously preparing a boron-nitrogen source precursor; coating the aminated carbon quantum dots with silicon to obtain silicon-coated carbon quantum dots; preparing a composite adhesive, a tungsten carbide-aluminum nitride composite reinforced phase and carbon-plated silicon powder; the preparation method comprises the following steps: blending and kneading silane modified graphite powder, a boron-nitrogen source precursor and other components, and pressing under gradient pressure to obtain a green body; and performing segmented roasting on the green body, and cooling to obtain the target electrode paste. According to the invention, crystalline flake graphite oxidation-silane modification is adopted to optimize interfacial compatibility, silicon-coated carbon quantum dots are adopted to reinforce a bonding system, a composite reinforcement phase is adopted to construct a mechanical support network, boron-nitrogen source in-situ doping supplemental reinforcement is adopted, and gradient pressure pressing and segmented roasting are combined to ensure that the structure is compact. The normal-temperature compressive strength, high-temperature mechanical stability and compactness of the electrode paste are improved through the synergistic effect of all links, and the electrode paste can stably adapt to the high-temperature and high-load working conditions.

Description

Technical Field

[0001] This application relates to the field of electrode paste technology, specifically to a method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste. Background Technology

[0002] Graphite electrode paste is a key conductive and structural material in high-temperature industries such as metallurgy and chemical engineering. Its pressure resistance and mechanical strength directly determine the stability and safety of industrial production. As industrial equipment develops towards larger scale and higher efficiency, the performance requirements for electrode paste are becoming increasingly stringent. Traditional graphite electrode paste can no longer meet the needs of use under high load and high temperature conditions.

[0003] In existing technologies, to improve the performance of graphite electrode paste, methods such as graphite surface modification, addition of reinforcing phases, and optimization of calcination processes are commonly employed. Regarding graphite modification, conventional methods often involve single oxidation treatment or simple silane coupling agent modification. Oxidation treatment can only introduce a small number of active functional groups onto the graphite surface, and subsequent silane grafting relies mainly on physical adsorption or weak chemical bonding, failing to form a stable interfacial bridging structure. This results in low interfacial bonding strength between graphite and the binder, making it prone to interfacial delamination under stress and leading to poor load transfer efficiency. In terms of reinforcing phase design, existing technologies often employ single-scale or single-type reinforcing phases, lacking multi-scale synergistic design. Micron-scale reinforcing phases are prone to agglomeration and cannot fill micropores, while nano-scale reinforcing phases struggle to form a continuous support network, resulting in limited crack propagation suppression. Regarding calcination processes, traditional processes often involve single-temperature calcination or simple segmented heating, making it difficult to achieve precise synergy between efficient impurity removal, doping modification, and densification. They cannot generate highly dispersed, high-hardness reinforcing phases through in-situ reactions, and the final material porosity is relatively high, further limiting improvements in pressure resistance and mechanical strength.

[0004] Therefore, in response to the current technological bottlenecks, developing a graphite-reinforced electrode paste preparation technology that can construct a stable interface structure and achieve multi-scale synergistic enhancement has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste. This invention utilizes a combination of technologies, including flake graphite oxidation-silane modification to construct a stable interface, aminated carbon quantum dot silicon coating with a synergistic composite binder to optimize bonding performance, multi-scale composite reinforcement phase-synergistic reinforcement, in-situ doping of boron-nitrogen sources and boron carbide generation, and precise control through gradient pressure suppression and two-stage calcination, to improve the pressure resistance and mechanical strength of the electrode paste.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] This application provides a method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste, comprising the following steps:

[0008] Step 1. Add flake graphite powder to a mixed solution of nitric acid and potassium permanganate, mix and react, wash and dry to obtain oxidized graphite powder; disperse the oxidized graphite powder in an ethanol solution, add γ-aminopropyltriethoxysilane and stir to react, filter and dry to obtain silane-modified graphite powder; mix borax and urea, add deionized water and sonicate to dissolve to obtain boron-nitrogen source precursor solution;

[0009] Step 2. Disperse the aminated carbon quantum dots in a mixed solvent of anhydrous ethanol and deionized water, add ammonia to adjust the pH of the system to 9-11, and then slowly add anhydrous ethanol solution of tetraethyl orthosilicate while stirring continuously. After the reaction is completed, centrifuge, wash and dry to obtain silicon-coated carbon quantum dots.

[0010] Step 3. Phenolic resin is added to polyimide resin and melted, then mixed and stirred with silicon-coated carbon quantum dots and titanate coupling agent to obtain a composite binder; tungsten carbide nanoparticles and aluminum nitride powder are mixed and ball-milled to obtain a composite reinforcing phase; silicon powder is dispersed in formaldehyde solution to adjust pH, and stirred to obtain carbon-coated silicon powder;

[0011] Step 4. After mixing and kneading the silane-modified graphite powder, boron-nitrogen source precursor solution and composite binder, add the composite reinforcing phase and carbon-plated silicon powder, and after aging, add carbon nanotubes and mix and stir to obtain electrode paste. Press the electrode paste under gradient pressure, and demold after molding to obtain electrode paste blank.

[0012] Step 5. The electrode paste blank is placed in an inert atmosphere for segmented calcination treatment, and after cooling, a high-pressure-resistant and high-strength graphite-reinforced electrode paste is obtained.

[0013] Preferably, in step 1, the mass ratio of the flake graphite powder, nitric acid solution, and potassium permanganate solution is 1:(3-5):(0.1-0.3); the concentration of the nitric acid solution is 10wt%-30wt%; the concentration of the potassium permanganate solution is 0.5wt%-2wt%; the mass ratio of the oxidized graphite powder, ethanol solution, and γ-aminopropyltriethoxysilane is 1:(5-15):(0.01-0.05); the concentration of the ethanol solution is 35wt%-55wt%; and the mass ratio of the borax, urea, and deionized water is 1:(1.5-3):(8-45).

[0014] This application employs a nitric acid-potassium permanganate composite oxidation system, with potassium permanganate acting as a strong oxidant to provide MnO4. - Highly active Mn is generated under acidic conditions. 3+In silane modification, the ethoxy group (-OC2H5) of the silane reagent synergistically attacks the C-C bonds at the graphite layer edges. After cleavage, oxygen-containing functional groups such as hydroxyl and carboxyl groups are introduced, ensuring sufficient grafting sites for subsequent silanes without compromising the intrinsic conductivity of graphite. During silane modification, the ethoxy group (-OC2H5) of the silane reagent undergoes hydrolytic condensation with the hydroxyl groups on the graphite surface to form Si-OC covalent bonds. The terminal amino groups then graft onto these bonds to form active sites, effectively preventing the self-aggregation of the silane reagent and improving the interfacial compatibility between graphite and subsequent components. In the preparation of the boron-nitrogen source, hydrogen bonding between the components promotes the dissolution of borax, ensuring that the nitrogen and boron sources form a uniform and stable precursor system, laying the foundation for subsequent uniform doping.

[0015] Preferably, in step 1, the mixing reaction temperature is 15-40℃ and the time is 3-8h; the washing is performed until the pH is 6.5-7.5; the stirring reaction temperature is 40-70℃ and the time is 2-6h; the ultrasonic dissolution ultrasonic power is 100-300W and the time is 60-90min.

[0016] Preferably, in step 2, the pH value is 9-11; the mass ratio of the aminated carbon quantum dots, mixed solvent, ammonia and tetraethyl orthosilicate is 1:(100-200):(1-5):(5-20); the mass ratio of tetraethyl orthosilicate and anhydrous ethanol is 1:(1-2); and the volume ratio of anhydrous ethanol and deionized water in the mixed solvent is (4-9):1.

[0017] This application uses ammonia to regulate the pH of the reaction system, providing a suitable environment for the hydrolysis of tetraethyl orthosilicate, promoting its gradual hydrolysis to generate silanol groups, which then undergo condensation reactions with the amino and hydroxyl groups on the surface of aminated carbon quantum dots, forming a uniform and dense silicon coating layer on the surface of carbon quantum dots.

[0018] Preferably, in step 2, the dispersion temperature is 30-50℃ and the time is 30-60 min; the stirring reaction temperature is 40-70℃ and the time is 2-6 h.

[0019] Preferably, in step 3, the mass ratio of the phenolic resin, polyimide resin, silicon-coated carbon quantum dots, and titanate coupling agent is (6-8):(2-4):(0.1-0.5):(0.1-0.5); the mass ratio of the tungsten carbide nanoparticles to the aluminum nitride powder is (3-7):1; the mass ratio of the silicon powder to the formaldehyde solution is 1:(1-3), and the mass fraction of the formaldehyde solution is 30wt%-40wt%.

[0020] Traditional electrode paste binders often suffer from a trade-off between adhesion and high-temperature resistance, as well as weak interfacial bonding with inorganic components, leading to easy delamination and strength reduction at high temperatures. This application addresses this issue by synergistically melting and mixing two resins, combining their excellent adhesion and high-temperature resistance to form a complementary bonding system. Silicon-coated carbon quantum dots form covalent and hydrogen bonds with resin functional groups through surface silanol groups, and their conjugated structure creates a π-π stacking effect with the resin molecular chains. Simultaneously, a titanate coupling agent acts as an interfacial bridge, with its alkoxy groups reacting with the silanol groups on the silicon-coated carbon quantum dots and binding to the resin functional groups at the other end, further optimizing the interfacial wettability between inorganic particles and the organic binder. These multiple forces synergistically enhance the interfacial bonding and mechanical stability of the bonding system, preventing interfacial delamination caused by binder degradation under high-temperature conditions and ensuring the structural integrity of the electrode paste.

[0021] In this application, the composite reinforcing phase constructs a hard and tough reinforcing phase framework through the synergistic combination of two reinforcing phases. The hard reinforcing phase provides excellent compressive strength, while the tough reinforcing phase inhibits brittle fracture through crack deflection, avoiding performance defects caused by a single reinforcing phase. Simultaneously, the carbon-plated silicon powder undergoes a carbon source condensation reaction catalyzed under acidic conditions, forming a uniform and complete carbon layer on the silicon powder surface. This carbon layer not only fills the micropores between graphite and the binder, improving the system's densification, but also provides isolation and protection, preventing excessive reaction between the silicon powder and the graphite matrix under high-temperature conditions that could lead to volume expansion. The synergistic effect of the components simultaneously improves the compressive strength and density of the electrode paste, making it suitable for high-temperature, high-load smelting conditions.

[0022] Preferably, in step 3, the melting temperature is 120-160℃ and the time is 30-90 min; the mixing temperature is 180-220℃ and the time is 20-60 min; the ball-to-material ratio of the ball milling is (5-10):1, the rotation speed is 200-400 rpm, and the time is 2-6 h; the pH is 3.0-4.0.

[0023] Preferably, in step 4, the mass ratio of the silane-modified graphite powder, boron-nitrogen source precursor solution, composite binder, composite reinforcing phase, carbon-plated silicon powder, and carbon nanotubes is 1:(0.1-0.3):(0.2-0.4):(0.05-0.15):(0.03-0.08):(0.01-0.05).

[0024] Preferably, in step 4, the gradient pressure includes a first gradient pre-pressure exhaust pressure and a second gradient main pressure compaction pressure; the first gradient pre-pressure exhaust pressure is 10-30 MPa and the holding time is 1-3 min, and the second gradient main pressure compaction pressure is 50-100 MPa and the holding time is 3-8 min.

[0025] Preferably, in step 5, the segmented roasting process includes a first-stage roasting and a second-stage roasting. The temperature of the first-stage roasting is 100-800℃, and the holding time is 4-8h. The temperature of the second-stage roasting is 900-1200℃, and the holding time is 4-8h.

[0026] This application employs a segmented firing process. The first stage of firing gradually removes residual moisture and low-molecular-weight volatiles from the binder, preventing rapid heating that could cause the volatiles to boil over and crack. Simultaneously, it completes the initial carbonization of the binder and the pyrolysis of the boron-nitrogen source, generating boron nitride and boron carbide crystal nuclei. The second stage of firing promotes the growth and uniform dispersion of boron carbide crystal nuclei, achieving partial graphitization of amorphous carbon to improve conductivity. Furthermore, it strengthens the bonding between components through interfacial diffusion, further enhancing the density of the green body. The slow cooling process releases the thermal stress generated during the high-temperature stage, preventing cracking caused by excessive internal and external temperature differences.

[0027] Compared with the prior art, the beneficial effects of this application are as follows:

[0028] This application provides a method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste. First, flake graphite is oxidized to introduce active functional groups such as hydroxyl and carboxyl groups. Then, silane modification is used to construct a Si-OC covalent bond interface bridging structure. Simultaneously, amino groups at the molecular ends are grafted to form active sites, improving the interfacial compatibility between graphite and subsequent components. After silicon coating, the silanol groups on the surface of the aminated carbon quantum dots form hydrogen and covalent bonds with the hydroxyl and amino groups of the composite binder (phenolic resin / polyimide). Simultaneously, the conjugated structure of the carbon quantum dots forms π-π stacks with the resin molecules. Furthermore, the titanate coupling agent acts as an interfacial bridging medium, and its alkoxy groups react with the silanol groups on the surface of the silicon-coated carbon quantum dots, while also binding with the functional groups of the phenolic resin / polyimide, improving interfacial wettability and thus enhancing interfacial adhesion. In the composite reinforcing phase, tungsten carbide nanoparticles and aluminum nitride powder construct a hard supporting framework, suppressing mechanical damage through a crack deflection mechanism. Carbon-plated silicon powder fills the micropores between graphite and binder, enhancing densification. Carbon nanotubes bridge the components to form continuous conductive pathways, improving strength and conductivity. The boron-nitrogen source precursor undergoes in-situ pyrolysis and reaction during a two-stage calcination process. Urea pyrolysis produces NH3, and borax pyrolysis produces B2O3. The two react first to form BN, and then B2O3 further reacts with the carbon matrix to generate a highly dispersed B4C reinforcing phase in situ, forming a strong interfacial bond with the graphite matrix, further improving the material's hardness and pressure resistance. Gradient pressure pressing, through pre-pressure venting and main pressure densification control, ensures uniform densification of the green body. Two-stage calcination controls the carbonization of the binder, in-situ doping of BN, and the formation of boron carbide, while slow cooling releases residual stress to prevent crack formation. The synergistic effect of each component and process parameters improves the pressure resistance and mechanical stability of the electrode paste. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a process for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste;

[0030] Figure 2 This is a photograph of the high-pressure-resistant and high-strength graphite-reinforced electrode paste obtained in Example 3. Detailed Implementation

[0031] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0032] In this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0033] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0034] The following describes in detail, with reference to different embodiments, a method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste provided by this application.

[0035] Example 1

[0036] like Figure 1 As shown, this embodiment provides a method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste, including the following steps:

[0037] Step 1. Add flake graphite powder to a mixed solution of nitric acid and potassium permanganate, and react at 15°C for 3 hours. The mass ratio of flake graphite powder, nitric acid solution, and potassium permanganate solution is 1:3:0.1, the concentration of nitric acid solution is 10 wt%, and the concentration of potassium permanganate solution is 0.5 wt%. Wash until pH 6.5 and then dry to obtain oxidized graphite powder. Disperse the oxidized graphite powder in a 35 wt% ethanol solution, add γ-aminopropyltriethoxysilane, and stir at 40°C for 2 hours. The mass ratio of oxidized graphite powder, ethanol solution, and γ-aminopropyltriethoxysilane is 1:5:0.01. Filter and dry to obtain silane-modified graphite powder. Mix borax and urea, add deionized water, and sonicate at 100W for 60 minutes to obtain a boron-nitrogen source precursor solution. The mass ratio of borax, urea, and deionized water is 1:1.5:8.

[0038] Step 2. At 30°C, aminated carbon quantum dots were dispersed in a mixed solvent of anhydrous ethanol and deionized water and stirred for 30 min. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent was 4:1. Ammonia was added dropwise to adjust the pH of the system to 9. Then, an anhydrous ethanol solution of tetraethyl orthosilicate was slowly added dropwise, and the reaction was continued at 40°C with stirring for 2 h. The mass ratio of tetraethyl orthosilicate to anhydrous ethanol was 1:1. The mass ratio of the aminated carbon quantum dots, the mixed solvent, ammonia, and tetraethyl orthosilicate was 1:100:1:5. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain silicon-coated carbon quantum dots.

[0039] Step 3. Phenolic resin is added to polyimide resin and melted at 120°C for 30 min, then mixed and stirred with the silicon-coated carbon quantum dots and titanate coupling agent at 180°C for 20 min to obtain a composite binder, wherein the mass ratio of phenolic resin, polyimide resin, silicon-coated carbon quantum dots and titanate coupling agent is 6:2:0.1:0.1; Tungsten carbide nanoparticles are mixed with aluminum nitride powder and ball-milled for 2 h at a ball-to-particle ratio of 5:1 and a rotation speed of 200 rpm to obtain a composite reinforcing phase, wherein the mass ratio of tungsten carbide nanoparticles to aluminum nitride powder is 3:1; Silicon powder is dispersed in formaldehyde solution and the pH is adjusted to 3, and the reaction is stirred to obtain carbon-coated silicon powder, wherein the mass ratio of silicon powder to formaldehyde solution is 1:1, and the mass fraction of formaldehyde solution is 30 wt%.

[0040] Step 4. After mixing and kneading the silane-modified graphite powder, boron-nitrogen source precursor solution, and composite binder, add the composite reinforcing phase and carbon-plated silicon powder. After aging, add carbon nanotubes and mix to obtain an electrode paste. The mass ratio of the silane-modified graphite powder, boron-nitrogen source precursor solution, composite binder, composite reinforcing phase, carbon-plated silicon powder, and carbon nanotubes is 1:0.1:0.2:0.05:0.03:0.01. Press the electrode paste under gradient pressure. First, perform a first gradient pre-pressure venting treatment at a pressure of 10 MPa and hold for 1 min. Then, perform a second gradient main pressure densification treatment at a pressure of 50 MPa and hold for 3 min. After molding, demold to obtain an electrode paste blank.

[0041] Step 5. The electrode paste blank is placed in an inert atmosphere for segmented calcination treatment, wherein the segmented calcination treatment includes a first stage calcination and a second stage calcination. The first stage calcination is carried out at 100°C for 4 hours, and the second stage calcination is carried out at 900°C for 4 hours. After cooling, a high pressure-resistant and high-strength graphite-reinforced electrode paste is obtained.

[0042] Example 2

[0043] like Figure 1 As shown, this embodiment provides a method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste, including the following steps:

[0044] Step 1. Add flake graphite powder to a mixed solution of nitric acid and potassium permanganate, and react at 25°C for 5 hours. The mass ratio of flake graphite powder, nitric acid solution, and potassium permanganate solution is 1:4:0.2, the concentration of nitric acid solution is 20 wt%, and the concentration of potassium permanganate solution is 1.5 wt%. Wash until pH 7 and then dry to obtain oxidized graphite powder. Disperse the oxidized graphite powder in a 40 wt% ethanol solution, add γ-aminopropyltriethoxysilane, and stir at 55°C for 4 hours. The mass ratio of oxidized graphite powder, ethanol solution, and γ-aminopropyltriethoxysilane is 1:10:0.03. Filter and dry to obtain silane-modified graphite powder. Mix borax and urea, add deionized water, and sonicate at 200W for 70 minutes to obtain a boron-nitrogen source precursor solution. The mass ratio of borax, urea, and deionized water is 1:2:22.

[0045] Step 2. Aminated carbon quantum dots were dispersed in a mixed solvent of anhydrous ethanol and deionized water at 40°C and stirred for 45 min. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent was 6:1. Ammonia was added dropwise to adjust the pH of the system to 10. Then, an anhydrous ethanol solution of tetraethyl orthosilicate was slowly added dropwise and the reaction was continued at 55°C with stirring for 4 h. The mass ratio of tetraethyl orthosilicate to anhydrous ethanol was 1:1.5. The mass ratio of the aminated carbon quantum dots, the mixed solvent, ammonia, and tetraethyl orthosilicate was 1:150:2:12. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain silicon-coated carbon quantum dots.

[0046] Step 3. Phenolic resin is added to polyimide resin and melted at 140°C for 60 min, then mixed and stirred with the silicon-coated carbon quantum dots and titanate coupling agent at 200°C for 40 min to obtain a composite binder, wherein the mass ratio of phenolic resin, polyimide resin, silicon-coated carbon quantum dots and titanate coupling agent is 7:3:0.3:0.3; Tungsten carbide nanoparticles are mixed with aluminum nitride powder and ball-milled for 4 h at a ball-to-particle ratio of 7:1 and a rotation speed of 300 rpm to obtain a composite reinforcing phase, wherein the mass ratio of tungsten carbide nanoparticles to aluminum nitride powder is 5:1; Silicon powder is dispersed in formaldehyde solution and the pH is adjusted to 3.5, and the reaction is stirred to obtain carbon-coated silicon powder, wherein the mass ratio of silicon powder to formaldehyde solution is 1:2, and the mass fraction of formaldehyde solution is 35 wt%.

[0047] Step 4. After mixing and kneading the silane-modified graphite powder, boron-nitrogen source precursor solution, and composite binder, add the composite reinforcing phase and carbon-plated silicon powder. After aging, add carbon nanotubes and mix to obtain an electrode paste. The mass ratio of the silane-modified graphite powder, boron-nitrogen source precursor solution, composite binder, composite reinforcing phase, carbon-plated silicon powder, and carbon nanotubes is 1:0.2:0.3:0.1:0.05:0.03. Press the electrode paste under gradient pressure. First, perform a first gradient pre-pressure venting treatment at a pressure of 20 MPa and hold for 2 minutes. Then, perform a second gradient main pressure densification treatment at a pressure of 70 MPa and hold for 5 minutes. After molding, demold to obtain an electrode paste blank.

[0048] Step 5. The electrode paste blank is placed in an inert atmosphere for segmented calcination treatment, wherein the segmented calcination treatment includes a first stage calcination and a second stage calcination. The first stage calcination is carried out at 500°C for 6 hours, and the second stage calcination is carried out at 1000°C for 6 hours. After cooling, a high pressure-resistant and high-strength graphite-reinforced electrode paste is obtained.

[0049] Example 3

[0050] like Figure 1 As shown, this embodiment provides a method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste, including the following steps:

[0051] Step 1. Flake graphite powder is added to a mixed solution of nitric acid and potassium permanganate and reacted at 40°C for 8 hours. The mass ratio of flake graphite powder, nitric acid solution, and potassium permanganate solution is 1:5:0.3, the concentration of nitric acid solution is 30wt%, and the concentration of potassium permanganate solution is 2wt%. After washing to pH 7.5, the mixture is dried to obtain oxidized graphite powder. The oxidized graphite powder is dispersed in a 55wt% ethanol solution, and γ-aminopropyltriethoxysilane is added and stirred at 70°C for 6 hours. The mass ratio of oxidized graphite powder, ethanol solution, and γ-aminopropyltriethoxysilane is 1:15:0.05. The mixture is filtered and dried to obtain silane-modified graphite powder. Borax and urea are mixed, and deionized water is added and ultrasonically dissolved at 300W for 90 minutes to obtain a boron-nitrogen source precursor solution. The mass ratio of borax, urea, and deionized water is 1:3:45.

[0052] Step 2. At 50°C, aminated carbon quantum dots were dispersed in a mixed solvent of anhydrous ethanol and deionized water and stirred for 60 min. The volume ratio of anhydrous ethanol to deionized water in the mixed solvent was 9:1. Ammonia was added dropwise to adjust the pH of the system to 11. Then, an anhydrous ethanol solution of tetraethyl orthosilicate was slowly added dropwise, and the reaction was continued at 70°C with stirring for 6 h. The mass ratio of tetraethyl orthosilicate to anhydrous ethanol was 1:2. The mass ratio of the aminated carbon quantum dots, the mixed solvent, ammonia, and tetraethyl orthosilicate was 1:200:5:20. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain silicon-coated carbon quantum dots.

[0053] Step 3. Phenolic resin is added to polyimide resin and melted at 160°C for 90 min. Then, it is mixed and stirred with the silicon-coated carbon quantum dots and titanate coupling agent at 220°C for 60 min to obtain a composite binder. The mass ratio of phenolic resin, polyimide resin, silicon-coated carbon quantum dots, and titanate coupling agent is 8:4:0.5:0.5. Tungsten carbide nanoparticles are mixed with aluminum nitride powder and ball-milled for 6 h at a ball-to-particle ratio of 10:1 and a rotation speed of 400 rpm to obtain a composite reinforcing phase. The mass ratio of tungsten carbide nanoparticles to aluminum nitride powder is 7:1. Silicon powder is dispersed in formaldehyde solution and the pH is adjusted to 4. The reaction is stirred to obtain carbon-coated silicon powder. The mass ratio of silicon powder to formaldehyde solution is 1:3, and the mass fraction of formaldehyde solution is 40 wt%.

[0054] Step 4. After mixing and kneading the silane-modified graphite powder, boron-nitrogen source precursor solution, and composite binder, add the composite reinforcing phase and carbon-plated silicon powder. After aging, add carbon nanotubes and mix to obtain an electrode paste. The mass ratio of the silane-modified graphite powder, boron-nitrogen source precursor solution, composite binder, composite reinforcing phase, carbon-plated silicon powder, and carbon nanotubes is 1:0.3:0.4:0.15:0.08:0.05. Press the electrode paste under gradient pressure. First, perform a first gradient pre-pressure venting treatment at a pressure of 30 MPa and hold for 3 minutes. Then, perform a second gradient main pressure densification treatment at a pressure of 100 MPa and hold for 8 minutes. After molding, demold to obtain an electrode paste blank.

[0055] Step 5. The electrode paste preform is placed in an inert atmosphere for segmented calcination treatment, wherein the segmented calcination treatment includes a first stage calcination and a second stage calcination. The first stage calcination is carried out at 800°C for 8 hours, and the second stage calcination is carried out at 1200°C for 8 hours. After cooling, a high-pressure-resistant and high-strength graphite-reinforced electrode paste is obtained. Figure 2 As shown.

[0056] Comparative Example 1

[0057] A method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste differs from Example 3 in that, except for step 1, where the flake graphite powder is not modified by oxidative silane and is used directly, the remaining steps and parameters are completely consistent with Example 3.

[0058] Comparative Example 2

[0059] A method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste, which differs from Example 3 in that step 2 does not involve the preparation of silicon-coated carbon quantum dots, while the remaining steps and parameters are completely consistent with Example 3.

[0060] Comparative Example 3

[0061] A method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste differs from Example 3 in that step 3 uses only tungsten carbide nanoparticles as a single reinforcing phase, without aluminum nitride powder or carbon-plated silicon powder, and step 4 does not add carbon-plated silicon powder and carbon nanotubes. All other steps and parameters are completely consistent with Example 3.

[0062] Comparative Example 4

[0063] A method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste differs from Example 3 in that step 1 does not prepare a boron-nitrogen source precursor solution and step 4 does not add a boron-nitrogen source precursor solution; the remaining steps and parameters are completely consistent with Example 3.

[0064] Comparative Example 5

[0065] A method for preparing a high-pressure-resistant and high-strength graphite-reinforced electrode paste, which differs from Example 3 in that step 4 uses single pressure pressing instead of gradient pressure pressing. The specific parameters are as follows: the pressure is 60 MPa and the holding time is 11 min. The remaining steps and parameters are completely consistent with Example 3.

[0066] The high-pressure-resistant and high-strength graphite-reinforced electrode pastes prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance testing, and the testing methods are as follows:

[0067] 1. Room temperature compressive strength test: The Φ50mm×50mm electrode paste sample was tested for room temperature compressive strength using a microcomputer-controlled electronic universal testing machine at a loading rate of 2mm / min.

[0068] 2. High-temperature mechanical strength retention rate test: Place the Φ50mm×50mm electrode paste sample in an inert atmosphere furnace and keep it at 1000℃ for 2 hours. After cooling to room temperature, test the strength according to the above-mentioned room temperature compressive strength test method. The ratio of the strength after high-temperature treatment to the strength at room temperature is the strength retention rate.

[0069] 3. Density test: The Archimedes displacement method was used to measure the mass of the electrode paste sample in air and the mass immersed in deionized water using an electronic balance. The bulk density of the sample was calculated by combining the density of water, and thus the density was obtained.

[0070] The performance test data analysis is shown in Table 1.

[0071] Table 1. Performance test data of high-pressure-resistant and high-strength graphite-reinforced electrode pastes prepared in Examples 1-3 and Comparative Examples 1-5

[0072]

[0073] As shown in Table 1, the performance of Examples 1-3, through the technical solutions of flake graphite oxidation-silane modification, silicon-coated carbon quantum dot strengthening bonding, multi-scale reinforcing phase synergy, boron-nitrogen source in-situ doping, gradient pressure, and two-stage calcination, showed an increasing trend. Example 3 performed best, with a room temperature pressure resistance of up to 183 MPa, a high temperature mechanical strength retention rate of 90.5%, and a density of 95.8%, demonstrating excellent pressure resistance, high temperature stability, and structural compactness. This was due to the Si-OC covalent bonds constructed by silane modification strengthening the interfacial bonding force, the multiple effects of silicon-coated carbon quantum dots and titanate coupling agent improving the stability of the bonding system, the multi-scale reinforcing phase forming a "hard support-tough buffer-pore filling-conductive bridging" network, the boron carbide generated in-situ by the boron-nitrogen source further improving the hardness, and the gradient pressure and segmented calcination ensuring the compactness and defect-free nature of the blank. The synergistic effect of each step improved the performance of the electrode paste.

[0074] Compared with Example 3, Comparative Example 1 used unmodified flake graphite powder, which lacked the oxygen-containing functional groups introduced by oxidation, the Si-OC covalent bonds grafted with silane, and the amino active sites. The interfacial bonding force between graphite and the binder and reinforcing phase was greatly weakened, and interfacial peeling was prone to occur under stress. As a result, the room temperature compressive strength dropped to 118 MPa, and the interfacial defects further expanded at high temperature. The strength retention rate was only 72.3%, and the density dropped to 87.5% due to the increase in interfacial porosity. The compressive strength and high temperature stability were greatly reduced.

[0075] Compared with Example 3, Comparative Example 2 lacks the preparation step of silicon-coated carbon quantum dots. The composite binder loses the π-π stacking effect of the conjugated structure of carbon quantum dots and the covalent bond of silanol groups. It relies only on the adhesive force of the resin itself, resulting in insufficient interfacial bonding strength. The compressive strength at room temperature drops to 125 MPa. At high temperatures, the adhesive system is easily degraded, leading to a strength retention rate of 75.8% and a density of 89.2%, with significantly weakened mechanical stability.

[0076] Compared with Example 3, Comparative Example 3 only used tungsten carbide nanoparticles as a single reinforcing phase, lacking the toughness buffering effect of aluminum nitride, the pore filling effect of silicon carbide powder, and the bridging and reinforcing effect of carbon nanotubes. The single hard reinforcing phase is prone to stress concentration and cannot fill the micropores of the matrix, resulting in a decrease in room temperature compressive strength to 106 MPa, the lowest value among all groups. The risk of brittle fracture at high temperature is increased, the strength retention rate is only 70.1%, and the density drops to 85.3%, with a comprehensive decline in compressive strength, toughness, and density.

[0077] Compared with Example 3, Comparative Example 4 lacked the preparation and addition of boron-nitrogen source precursors, and could not generate highly dispersed boron carbide reinforcing phase in situ through calcination. The material hardness and interfacial bonding strength lost their key support, the room temperature compressive strength dropped to 132 MPa, and there was no reinforcing effect of boron carbide at high temperature, and the strength retention rate dropped to 78.5%. However, due to the retention of gradient pressure pressing process, the density was still maintained at 93.1%, which shows that the boron-nitrogen source mainly plays a role in improving strength.

[0078] Compared with Example 3, Comparative Example 5 uses single pressure pressing instead of gradient pressure pressing. It is impossible to fully remove free gas in the slurry through pre-pressurization and venting. The green body has residual closed-cell defects, and the density drops to 88.7%. The pores become stress concentration points when under stress, which leads to a drop in room temperature compressive strength to 129 MPa. At high temperature, pore expansion further damages the structural integrity, and the strength retention rate drops to 76.4%. This highlights the key influence of gradient pressure pressing on the compactness and mechanical properties of the green body.

[0079] In summary, Examples 1-3 achieved high compressive strength, excellent high-temperature stability, and high density of graphite-reinforced electrode paste through the synergistic effects of flake graphite interface modification, silicon-coated carbon quantum dot bonding strengthening, composite reinforcement synergy, boron-nitrogen source in-situ reinforcement, and gradient pressure-segmented calcination process control. This allows the paste to stably meet the application requirements of high-temperature and high-load conditions in metallurgy, chemical industry, and other fields, providing a reliable technical solution for the preparation of high-performance electrode paste.

[0080] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste, characterized in that, Includes the following steps: Step 1. Add flake graphite powder to a mixed solution of nitric acid and potassium permanganate, mix and react, wash and dry to obtain oxidized graphite powder; disperse the oxidized graphite powder in an ethanol solution, add γ-aminopropyltriethoxysilane and stir to react, filter and dry to obtain silane-modified graphite powder; mix borax and urea, add deionized water and sonicate to dissolve to obtain boron-nitrogen source precursor solution; Step 2. Disperse the aminated carbon quantum dots in a mixed solvent of anhydrous ethanol and deionized water, add ammonia to adjust the pH of the system, and then slowly add anhydrous ethanol solution of tetraethyl orthosilicate while stirring continuously. After the reaction is completed, centrifuge, wash and dry to obtain silicon-coated carbon quantum dots. Step 3. Phenolic resin is added to polyimide resin and melted, then mixed and stirred with silicon-coated carbon quantum dots and titanate coupling agent to obtain a composite binder; tungsten carbide nanoparticles and aluminum nitride powder are mixed and ball-milled to obtain a composite reinforcing phase; silicon powder is dispersed in formaldehyde solution to adjust pH, and stirred to obtain carbon-coated silicon powder; Step 4. After mixing and kneading the silane-modified graphite powder, boron-nitrogen source precursor solution and composite binder, add the composite reinforcing phase and carbon-plated silicon powder, and after aging, add carbon nanotubes and mix and stir to obtain electrode paste. Press the electrode paste under gradient pressure, and demold after molding to obtain electrode paste blank. Step 5. The electrode paste blank is placed in an inert atmosphere for segmented calcination treatment, and after cooling, a high-pressure-resistant and high-strength graphite-reinforced electrode paste is obtained.

2. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 1, the mass ratio of the flake graphite powder, nitric acid solution, and potassium permanganate solution is 1:(3-5):(0.1-0.3); the concentration of the nitric acid solution is 10wt%-30wt%; the concentration of the potassium permanganate solution is 0.5wt%-2wt%; the mass ratio of the oxidized graphite powder, ethanol solution, and γ-aminopropyltriethoxysilane is 1:(5-15):(0.01-0.05); the concentration of the ethanol solution is 35wt%-55wt%; and the mass ratio of the borax, urea, and deionized water is 1:(1.5-3):(8-45).

3. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 1, the mixing reaction is carried out at a temperature of 15-40℃ for 3-8 hours; the washing is carried out until the pH reaches 6.5-7.5; the stirring reaction is carried out at a temperature of 40-70℃ for 2-6 hours; and the ultrasonic dissolution is carried out at an ultrasonic power of 100-300W for 60-90 minutes.

4. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 2, the pH value is 9-11; the mass ratio of the aminated carbon quantum dots, mixed solvent, ammonia and tetraethyl orthosilicate is 1:(100-200):(1-5):(5-20); the mass ratio of tetraethyl orthosilicate and anhydrous ethanol is 1:(1-2); and the volume ratio of anhydrous ethanol and deionized water in the mixed solvent is (4-9):

1.

5. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 2, the dispersion temperature is 30-50℃ and the time is 30-60 min; the stirring reaction temperature is 40-70℃ and the time is 2-6 h.

6. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 3, the mass ratio of the phenolic resin, polyimide resin, silicon-coated carbon quantum dots and titanate coupling agent is (6-8):(2-4):(0.1-0.5):(0.1-0.5); the mass ratio of the tungsten carbide nanoparticles and aluminum nitride powder is (3-7):1; the mass ratio of the silicon powder and formaldehyde solution is 1:(1-3), and the mass fraction of the formaldehyde solution is 30wt%-40wt%.

7. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 3, the melting temperature is 120-160℃ and the time is 30-90 min; the mixing temperature is 180-220℃ and the time is 20-60 min; the ball-to-material ratio of the ball milling is (5-10):1, the rotation speed is 200-400 rpm, and the time is 2-6 h; the pH is 3.0-4.

0.

8. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 4, the mass ratio of the silane-modified graphite powder, boron-nitrogen source precursor solution, composite binder, composite reinforcing phase, carbon-plated silicon powder and carbon nanotubes is 1:(0.1-0.3):(0.2-0.4):(0.05-0.15):(0.03-0.08):(0.01-0.05).

9. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 4, the gradient pressure includes a first gradient pre-pressure exhaust pressure and a second gradient main pressure compaction pressure; the first gradient pre-pressure exhaust pressure is 10-30 MPa and the holding time is 1-3 min, and the second gradient main pressure compaction pressure is 50-100 MPa and the holding time is 3-8 min.

10. The method for preparing a high-pressure-resistant, high-strength graphite-reinforced electrode paste according to claim 1, characterized in that, In step 5, the segmented roasting process includes a first-stage roasting and a second-stage roasting. The temperature of the first-stage roasting is 100-800℃, and the holding time is 4-8h. The temperature of the second-stage roasting is 900-1200℃, and the holding time is 4-8h.

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