A plurality of conductive agent composite conductive slurry for lithium battery and a preparation method thereof

Abstract

The present application relates to a kind of multiple conductive agent composite conductive slurry for lithium battery and its preparation method, belong to lithium battery conductive slurry technical field, iron molybdenum catalyst is loaded on expanded graphite, then in situ growth has been vertically oriented carbon nanotube and horizontal graphene blade, increase specific surface area, expanded graphite as layered carrier, its natural pore can be uniformly loaded metal alloy catalyst, keep layered skeleton not collapse at high temperature, provide support for carbon material directional growth, when being prepared into composite conductive slurry, electron can be quickly transported along carbon nanotube, graphene blade then fills the gap between carbon nanotube, forms the conductive network without breakpoint, substantially shorten electron transport path, while abundant pore provides passage for lithium ion diffusion, its abundant specific surface area and subsequent nitrogen, sulfur loading provide sufficient site from structural root source to improve conductive efficiency.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery conductive paste technology, and relates to a composite conductive paste for lithium batteries using multiple conductive agents and its preparation method. Background Technology

[0002] Currently, commonly used conductive agents in the lithium battery field are mainly divided into three categories: carbon-based conductive agents (conductive graphite, conductive carbon black, carbon nanotubes, graphene, carbon fibers, etc.), metal-based conductive agents (metal powder, metal fibers, etc.), and polymer conductive agents. Among them, carbon-based conductive agents have become the mainstream choice for commercial applications due to their advantages such as excellent chemical stability, adjustable conductivity, and controllable cost. However, the microstructure and performance characteristics of a single type of conductive agent have inherent limitations, making it difficult to meet the comprehensive requirements of high energy density and high rate lithium batteries.

[0003] Chinese invention patent application CN114613545B discloses a method for preparing a composite conductive paste with excellent electrical properties. By coating the surface of glass microspheres with graphene oxide, the compatibility between the glass microspheres and graphene is improved, resulting in a more uniform dispersion of graphene and glass microspheres in the system. This reduces the likelihood of agglomeration of glass microspheres and graphene separately, leading to more uniform and stable paste performance. Furthermore, the composite conductive paste for lithium batteries is formed using high-voltage pulse jet technology. The mechanical exfoliation technique can maximize the preservation of the integrity of the graphene and molybdenum disulfide layers, maintaining their high conductivity while effectively preventing the re-accumulation of nanolayers. This significantly improves conductivity, increases the surface area utilization of electrode materials, and solves defects such as agglomeration and low cycle capacity.

[0004] In the above scheme, the glass microspheres only serve as a dispersion support. As an insulating support, the glass microspheres cannot participate in conduction. Graphene and molybdenum disulfide are both sheet-like structures, and the sheets are prone to re-aggregation during long-term storage or coating. There are transmission breaks in the conductive network, which limits the efficiency of electron and ion transport. Summary of the Invention

[0005] The purpose of this invention is to provide a composite conductive slurry for lithium batteries using multiple conductive agents and its preparation method. By mixing active materials, binders, composite carbon nanotubes, conductive carbon black and solvents in a certain proportion, the dispersibility and conductivity of the composite conductive slurry are improved.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a composite conductive slurry of multiple conductive agents for lithium batteries includes the following steps:

[0008] Step 1: Iron salts, aluminum salts, and molybdates are loaded onto expanded graphite, calcined, reduced with hydrogen, and then placed in a plasma reactor to grow vertically oriented carbon nanotubes on the expanded graphite and in situ composite graphene to obtain three-dimensional carbon nanotubes.

[0009] Step 2: Introduce sulfonic acid groups onto three-dimensional carbon nanotubes to obtain sulfonated three-dimensional carbon nanotubes; load nitrogen and sulfur sources onto the sulfonated carbon nanotubes and calcine to obtain composite carbon nanotubes.

[0010] Step 3: Mix the active material, binder, composite carbon nanotubes, conductive carbon black and solvent evenly to obtain a composite conductive slurry for lithium batteries using multiple conductive agents.

[0011] Furthermore, the preparation process of three-dimensional carbon nanotubes is as follows:

[0012] Expanded graphite with a particle size of 6.5 μm, iron salts, aluminum salts, molybdates, and deionized water were mixed and stirred for 2-3 hours. The mixture was then filtered, dried, and placed in a muffle furnace. The temperature was raised to 550-560℃ and heated for 3-4 hours to obtain supported expanded graphite. The graphite was then placed in a tube furnace, and the pressure inside the tube was reduced to 9-13 Pa. Hydrogen gas was injected until the reaction was completed, while the temperature was raised to 700-720℃ at a rate of 22℃ / min. The plasma reactor was started and operated at 300 W for 10-12 minutes. Methane was introduced, and the temperature was maintained at 700-720℃ for 30-40 minutes. The plasma reactor and methane flow rate were then turned off, and the hydrogen flow rate was reduced to 5 sccm. The mixture was cooled to room temperature to obtain three-dimensional carbon nanotubes.

[0013] Furthermore, the ratio of expanded graphite, iron salt, aluminum salt, molybdate and deionized water is 10-20g: 1.0-1.5g: 0.1-0.2g: 0.2-0.3g: 50-60mL.

[0014] Furthermore, the hydrogen flow rate is 20 sccm.

[0015] Furthermore, the methane flow rate is 30 sccm.

[0016] Furthermore, the iron salt is one of ferric acetylacetone and ferric nitrate.

[0017] Furthermore, the aluminum salt is aluminum phosphate.

[0018] Furthermore, molybdate is one of ammonium molybdate and sodium molybdate.

[0019] Furthermore, the preparation process of sulfonated three-dimensional carbon nanotubes is as follows:

[0020] Three-dimensional carbon nanotubes, melamine, and concentrated sulfuric acid were added to a reaction vessel and stirred at 50-55°C for 12-14 hours. The product was then transferred to deionized water, filtered, washed, and dried to obtain sulfonated three-dimensional carbon nanotubes.

[0021] Furthermore, the ratio of three-dimensional carbon nanotubes, melamine, concentrated sulfuric acid, and deionized water is 5-8g: 3-5g: 300-500mL: 1-1.5L.

[0022] Furthermore, the preparation process of composite carbon nanotubes is as follows:

[0023] Sulfonated three-dimensional carbon nanotubes and Tris-HCl buffer solution were added to a reaction vessel and ultrasonically dispersed for 30-40 min. Dopamine hydrochloride was then added, and the mixture was stirred for 12-14 h at 20-25 °C and 500-700 r / min. After centrifugation, filtration, washing, and drying, the mixture was placed in a tube furnace and heated to 850-950 °C at a heating rate of 5 °C / min under argon protection, and heated at 10-12 Pa for 3-4 h. The mixture was then placed in a tube furnace with sublimated sulfur powder and heated to 450-500 °C at a heating rate of 5 °C / min under argon atmosphere, and held at this temperature for 2-3 h to obtain composite carbon nanotubes.

[0024] Furthermore, the ratio of sulfonated three-dimensional carbon nanotubes, Tris-HCl buffer solution, dopamine hydrochloride, and sublimed sulfur powder is 2-5g: 400-600mL: 1-2g: 0.2-0.4g.

[0025] Furthermore, the ratio of active material, binder, composite carbon nanotubes, conductive carbon black and solvent is 9.58-13.58g: 0.3-0.4g: 0.12-0.15g: 0.1-0.3g: 12-18mL.

[0026] Furthermore, the active material is lithium iron phosphate.

[0027] Furthermore, the adhesive is one of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0028] Furthermore, the solvent is one or a mixture of ethylene glycol dimethyl ether and N-methylpyrrolidone in any ratio.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention loads an iron-molybdenum catalyst onto expanded graphite, and then grows vertically oriented carbon nanotubes and horizontally oriented graphene blades in situ, increasing the specific surface area. Expanded graphite, as a layered support, has natural pores that can uniformly load the metal alloy catalyst, maintaining the layered framework without collapse at high temperatures, providing support for the directional growth of carbon materials. When preparing a composite conductive slurry, electrons can be rapidly transported along the carbon nanotubes, while the graphene blades fill the gaps between the carbon nanotubes, forming a seamless conductive network that significantly shortens the electron transport path. At the same time, the abundant pores provide channels for lithium-ion diffusion, improving conductivity from the structural root. Its abundant specific surface area and subsequent loading of nitrogen and sulfur provide sufficient sites. Nitrogen and sulfur atoms synergistically optimize the electronic structure of the composite carbon nanotubes, improving lithium-ion adsorption and embedding at active sites, reducing charge transfer resistance, and enhancing lithium storage activity.

[0031] 2. The layered pores of the expanded graphite in this invention provide physical adsorption sites for metal salts. Aluminum phosphate decomposes into alumina during drying and muffle furnace calcination. Its high dispersibility can prevent the agglomeration of Fe-Mo alloy oxide nanoparticles generated by the reaction of Fe2O3 and MoO3, so that the catalyst particles are uniformly anchored between the layers and on the surface of the expanded graphite, ensuring the balance between the axial growth rate of carbon nanotubes and the lateral growth rate of graphene blades. Concentrated sulfuric acid is used as a sulfonating agent to introduce sulfonic acid groups, and melamine is introduced into the sulfonation process simultaneously, providing hydrogen bond sites for the subsequent adsorption of dopamine hydrochloride, improving the dispersibility of composite carbon nanotubes in composite conductive slurry, and playing a self-dispersing role.

[0032] 3. The sulfonic acid groups and nitrogen-sulfur doped groups on the surface of the composite carbon nanotubes of this invention form multiple interactions with the hydroxyl groups on the surface of lithium iron phosphate and the fluorocarbon chains of polyvinylidene fluoride, which enhances the interfacial bonding force, prevents the active material lithium iron phosphate from falling off during cycling, improves cycling stability, and balances conductivity and mechanical strength. The mixed solvent of ethylene glycol dimethyl ether and N-methylpyrrolidone synergistically adjusts the viscosity, so that the slurry has both good coating smoothness and dispersion stability, making the composite conductive slurry have high conductivity, high stability and high energy density. Detailed Implementation

[0033] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0034] Example 1: This example provides a composite conductive slurry for lithium batteries using multiple conductive agents, prepared through the following steps:

[0035] S1: Mix 15g of expanded graphite (95% purity, purchased from Qingdao Tianheda Graphite Co., Ltd.) with a particle size of 6.5μm, 1.25g of ferric nitrate (purchased from Tianjin Damao Chemical Reagent Factory), 0.15g of aluminum phosphate (analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.25g of ammonium molybdate (purchased from Xilong Scientific Co., Ltd.), and 55mL of deionized water. Stir at 40r / min and 22℃ for 2.5h, filter, dry at 75℃ for 7h, and then place in a muffle furnace (purchased from Anhui Beiyike Equipment Technology Co., Ltd.), heat to 555℃, and add... After heating for 3.5 hours, catalyst-supported expanded graphite was obtained and then placed in an RF-PECVD tube furnace (purchased from Hefei Kejing Materials Technology Co., Ltd.). The pressure inside the tube was reduced to 11 Pa using a vacuum pump, and hydrogen gas (20 sccm) was injected until the reaction was completed. At the same time, the temperature was increased to 710 °C at a rate of 22 °C / min. The plasma reactor was started and operated at 300 W for 11 minutes. Methane was introduced at 30 sccm, and the temperature was maintained at 710 °C for 35 minutes. The plasma reactor and methane flow rate were turned off, the hydrogen flow rate was reduced to 5 sccm, and the mixture was cooled to room temperature to obtain three-dimensional carbon nanotubes.

[0036] Expanded graphite, ferric nitrate, aluminum phosphate, and ammonium molybdate are mixed, allowing the iron, aluminum, and molybdenum salts to be uniformly dispersed in the layered pores of the expanded graphite through physical adsorption. Subsequently, the mixture is heated to 550-560℃ in a muffle furnace. Ferric nitrate decomposes into Fe2O3, ammonium molybdate decomposes into MoO3, and aluminum phosphate decomposes into Al2O3. At the same time, Fe2O3 and MoO3 react at high temperature to form Fe-Mo alloy oxide nanoparticles. The expanded graphite expands slightly at high temperature but maintains its layered structure, providing a support framework for the subsequent directional growth of carbon nanomaterials. In a tube furnace, hydrogen reduces the Fe-Mo alloy oxides into active particles. The plasma reactor is then activated, and high-energy particles dissociate the introduced methane to generate active carbon. The carbon material is deposited on the surface of the Fe-Mo particles and grows axially to form vertically oriented carbon nanotubes. Plasma bombardment creates defects in the walls of the carbon nanotubes, and the active carbon material grows laterally at the defects to form graphene blades. The two are then in situ composited into a 3D structure through van der Waals forces.

[0037] S2: 6.5g of three-dimensional carbon nanotubes, 4g of melamine (purity 99.8%, purchased from Wujiang Huaxu Chemical Technology Co., Ltd.) and 400mL of concentrated sulfuric acid (concentration 98%, purchased from Sinopharm Chemical Reagent Co., Ltd.) were added to a reaction vessel and stirred at 52℃ for 13h. The product was transferred to 1.2L of deionized water, filtered, and the filter cake was washed with deionized water until neutral. It was then dried at 65℃ for 13h to obtain sulfonated three-dimensional carbon nanotubes.

[0038] S3: 3.5g of sulfonated three-dimensional carbon nanotubes and 500mL of Tris-HCl buffer solution (purchased from Beijing Solarbio Science & Technology Co., Ltd.) were added to a reaction vessel and ultrasonically dispersed for 35min. Then, 1.5g of dopamine hydrochloride (analytical grade, purchased from Maclean's Reagent) was added. The mixture was stirred at 22℃ and 600r / min for 13h, centrifuged, filtered, and the filter cake was washed three times with deionized water. It was then dried at 85℃ for 13h and placed in a tube furnace. Under argon protection, the temperature was increased to 900℃ at a rate of 5℃ / min and heated at 11Pa for 3.5h. Then, it was placed in a tube furnace with 0.3g of sublimed sulfur powder (analytical grade, purchased from Aladdin Reagent Co., Ltd.) and heated to 475℃ at a rate of 5℃ / min under argon atmosphere. The temperature was held for 2.5h to obtain composite carbon nanotubes.

[0039] S4: Mix 11.58g of active material lithium iron phosphate (battery grade, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 0.35g of binder polyvinylidene fluoride (model HSV900, purchased from Aladdin Chemical Reagent Co., Ltd.), 0.135g of composite carbon nanotubes, 0.2g of conductive carbon black (purity 98.9%, purchased from Tianjin Baochi Chemical Technology Co., Ltd.), 2.5mL of ethylene glycol dimethyl ether (analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), and 12.5mL of N-methylpyrrolidone (purchased from Sinopharm Chemical Reagent Co., Ltd.) evenly to obtain a composite conductive slurry for lithium batteries using multiple conductive agents.

[0040] Example 2: This example provides a composite conductive slurry for lithium batteries using multiple conductive agents, prepared through the following steps:

[0041] S1: Mix 10g of expanded graphite (95% purity, purchased from Qingdao Tianheda Graphite Co., Ltd.) with a particle size of 6.5μm, 1.0g of ferric nitrate (purchased from Tianjin Damao Chemical Reagent Factory), 0.1g of aluminum phosphate (analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.2g of ammonium molybdate (purchased from Xilong Scientific Co., Ltd.), and 50mL of deionized water. Stir at 30r / min and 20℃ for 2h, filter, dry at 70℃ for 6h, and then place in a muffle furnace (purchased from Anhui Beiyike Equipment Technology Co., Ltd.) and heat to 550℃. After 3 hours, catalyst-supported expanded graphite was obtained and placed in an RF-PECVD tube furnace (purchased from Hefei Kejing Materials Technology Co., Ltd.). The pressure inside the tube was reduced to 9 Pa using a vacuum pump, and hydrogen gas (20 sccm) was injected until the reaction was completed. At the same time, the temperature was increased to 700℃ at a rate of 22℃ / min. The plasma reactor was started and operated at 300W for 10 minutes. Methane was introduced at 30 sccm, and the temperature was maintained at 700℃ for 30 minutes. The plasma reactor and methane flow rate were turned off, the hydrogen flow rate was reduced to 5 sccm, and the mixture was cooled to room temperature to obtain three-dimensional carbon nanotubes.

[0042] S2: Add 5g of three-dimensional carbon nanotubes, 3g of melamine (purity 99.8%, purchased from Wujiang Huaxu Chemical Technology Co., Ltd.) and 300mL of concentrated sulfuric acid (concentration 98%, purchased from Sinopharm Chemical Reagent Co., Ltd.) to a reaction vessel, stir at 50℃ for 12h, transfer the product to 1L of deionized water, filter, wash the filter cake with deionized water until neutral, and dry at 60℃ for 12h to obtain sulfonated three-dimensional carbon nanotubes.

[0043] S3: 2g of sulfonated three-dimensional carbon nanotubes and 400mL of Tris-HCl buffer solution (purchased from Beijing Solarbio Science & Technology Co., Ltd.) were added to a reaction vessel and ultrasonically dispersed for 30min. Then, 1g of dopamine hydrochloride (analytical grade, purchased from Maclean's Reagent) was added. The mixture was stirred at 20℃ and 500r / min for 12h, centrifuged, filtered, and the filter cake was washed twice with deionized water and dried at 80℃ for 12h. The mixture was then placed in a tube furnace and heated to 850℃ at a heating rate of 5℃ / min under argon protection, and heated at 10Pa for 3h. The mixture was then placed in a tube furnace with 0.2g of sublimed sulfur powder (analytical grade, purchased from Aladdin Reagent Co., Ltd.) and heated to 450℃ at a heating rate of 5℃ / min under argon atmosphere, and held for 2h to obtain composite carbon nanotubes.

[0044] S4: Mix 9.58g of active material lithium iron phosphate (battery grade, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 0.3g of binder polyvinylidene fluoride (model HSV900, purchased from Aladdin Chemical Reagent Co., Ltd.), 0.12g of composite carbon nanotubes, 0.1g of conductive carbon black (purity 98.9%, purchased from Tianjin Baochi Chemical Technology Co., Ltd.), 2mL of ethylene glycol dimethyl ether (analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), and 10mL of N-methylpyrrolidone (purchased from Sinopharm Chemical Reagent Co., Ltd.) evenly to obtain a composite conductive slurry for lithium batteries using multiple conductive agents.

[0045] Example 3: This example provides a composite conductive slurry of multiple conductive agents for lithium batteries, prepared through the following steps:

[0046] S1: Mix 20g of expanded graphite (95% purity, purchased from Qingdao Tianheda Graphite Co., Ltd.) with a particle size of 6.5μm, 1.5g of ferric nitrate (purchased from Tianjin Damao Chemical Reagent Factory), 0.2g of aluminum phosphate (analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 0.3g of ammonium molybdate (purchased from Xilong Scientific Co., Ltd.), and 60mL of deionized water. Stir at 50r / min and 25℃ for 3h, filter, dry at 80℃ for 8h, and then place in a muffle furnace (purchased from Anhui Beiyike Equipment Technology Co., Ltd.) and heat to 560℃. After 4 hours, catalyst-supported expanded graphite was obtained and placed in an RF-PECVD tube furnace (purchased from Hefei Kejing Materials Technology Co., Ltd.). The pressure inside the tube was reduced to 13 Pa using a vacuum pump, and hydrogen gas (20 sccm) was injected until the reaction was completed. At the same time, the temperature was increased to 720°C at a rate of 22°C / min. The plasma reactor was started and operated at 300 W for 12 minutes. Methane was introduced at 30 sccm, and the temperature was maintained at 720°C for 40 minutes. The plasma reactor and methane flow rate were turned off, the hydrogen flow rate was reduced to 5 sccm, and the mixture was cooled to room temperature to obtain three-dimensional carbon nanotubes.

[0047] S2: Add 8g of three-dimensional carbon nanotubes, 5g of melamine (purity 99.8%, purchased from Wujiang Huaxu Chemical Technology Co., Ltd.) and 500mL of concentrated sulfuric acid (concentration 98%, purchased from Sinopharm Chemical Reagent Co., Ltd.) to a reaction vessel, stir at 55℃ for 14h, transfer the product to 1.5L of deionized water, filter, wash the filter cake with deionized water until neutral, and dry at 70℃ for 14h to obtain sulfonated three-dimensional carbon nanotubes.

[0048] S3: Add 5g of sulfonated three-dimensional carbon nanotubes and 600mL of Tris-HCl buffer solution (purchased from Beijing Solarbio Science & Technology Co., Ltd.) to a reaction vessel, sonicate for 40min, then add 2g of dopamine hydrochloride (analytical grade, purchased from Maclean's Reagent), stir for 14h at 25℃ and 700r / min, centrifuge, filter, wash the filter cake 4 times with deionized water, dry at 90℃ for 14h, place it in a tube furnace, heat to 950℃ at a heating rate of 5℃ / min under argon protection, and heat at 12Pa for 4h. Then place it and 0.4g of sublimed sulfur powder (analytical grade, purchased from Aladdin Reagent Co., Ltd.) in a tube furnace, heat to 500℃ at a heating rate of 5℃ / min under argon atmosphere, and hold for 3h to obtain composite carbon nanotubes.

[0049] S4: Mix 13.58g of active material lithium iron phosphate (battery grade, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.), 0.4g of binder polyvinylidene fluoride (model HSV900, purchased from Aladdin Chemical Reagent Co., Ltd.), 0.15g of composite carbon nanotubes, 0.3g of conductive carbon black (purity 98.9%, purchased from Tianjin Baochi Chemical Technology Co., Ltd.), 3mL of ethylene glycol dimethyl ether (analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), and 15mL of N-methylpyrrolidone (purchased from Sinopharm Chemical Reagent Co., Ltd.) evenly to obtain a composite conductive slurry for lithium batteries using multiple conductive agents.

[0050] Example 4: This example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that in step S1, ferric acetylacetone is used instead of ferric nitrate, and sodium molybdate is used instead of ammonium molybdate.

[0051] Example 5: This example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that in step S4, polyvinylidene fluoride-hexafluoropropylene copolymer is used instead of polyvinylidene fluoride.

[0052] Example 6: This example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that ethylene glycol dimethyl ether is removed in step S4.

[0053] Comparative Example 1: This comparative example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that commercially available carbon nanotubes are used instead of three-dimensional carbon nanotubes in step S2.

[0054] Comparative Example 2: This comparative example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that in step S3, the three-dimensional carbon nanotubes prepared in step S1 are used instead of the sulfonated three-dimensional carbon nanotubes.

[0055] Comparative Example 3: This comparative example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that in step S4, the three-dimensional carbon nanotubes prepared in step S1 are used instead of the composite carbon nanotubes.

[0056] Comparative Example 4: This comparative example provides a composite conductive slurry for lithium batteries using multiple conductive agents. The difference from Example 1 is that in step S4, the sulfonated three-dimensional carbon nanotubes prepared in step S2 are used instead of the composite carbon nanotubes.

[0057] The lithium batteries prepared in Examples 1-6 and Comparative Examples 1-3 were coated onto copper foil current collectors using a multi-conductive conductive slurry coated with various conductive agents, and then transferred to a vacuum drying oven for drying. The dried electrode sheets were cut into 12mm diameter pieces using a pressing machine, and their mass was recorded as m1. Five to ten clean copper foil pieces (12mm) were cut and weighed, and their average mass was calculated and recorded as m2. The mass m of the active material on the electrode sheets was calculated using the formula m = (m1 – m2) × 0.7. During assembly, the battery device used CR2025 button-type half-cells. The operation was conducted in a glove box filled with high-purity argon, where the water and oxygen content were both below 0.1ppm. The electrolyte (LB-001) used was a 1.0M LiPF6 in EC:DMC 1:1 (Vol%). Lithium foil was used as the counter electrode, and a Celgard membrane was used as the separator. The half-cells were then assembled.

[0058] The assembled battery was then subjected to electrochemical performance testing.

[0059] Constant current charge-discharge test: Using the Blue Electric testing system, the operating voltage within the system is set to 0.01-3.0V, and the current is set to 0.1-5.0A•g. -1 The charge-discharge cycle performance and rate performance of lithium-ion battery anode materials were tested using constant current.

[0060] Cyclic Voltmeter-Ampere Test:

[0061] Cyclic voltammetry (CV) tests were performed using an electrochemical workstation (CHI670E) to analyze redox peak values. The voltage range was set to 0.01–3.0 V, and the scan rate range was set to 0.1 mV•s. -1 -1.5mV•s -1 .

[0062] The test results are shown in the table below:

[0063] Table 1 Performance Test Overview

[0064] Test Project Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 <![CDATA[Reversible specific capacity (mAh•g -1 )]]> 1085.6 1088.2 1075.5 1081.2 1078.9 1073.4 825.5 798.7 811.3 886.4 First-time Coulomb efficiency (%) 81.6 79.2 80.5 80.1 79.8 81.0 68.4 65.9 67.2 72.5 Capacity retention rate after 100 cycles (%) 92.8 90.3 91.7 91.2 90.6 91.0 75.5 72.8 74.1 78.9

[0065] As shown in Table 1, the reversible specific capacity, initial coulombic efficiency, and capacity retention after 100 cycles of Examples 1-6 are all higher than those of Comparative Examples 1-4, indicating that Examples 1-6 have better electrochemical performance. This may be because the 3D structure of the carbon nanotubes and graphene blades in the three-dimensional carbon nanotubes constructs a continuous conductive network, reducing electron transport breakpoints. The sulfonation introduces sulfonic acid groups, which improves the dispersibility of the material and avoids agglomeration. Nitrogen-sulfur co-doping increases the surface defect density and active sites of the composite carbon nanotubes, while optimizing the electronic structure and reducing the ion migration barrier. The synergistic effect of these three factors significantly improves the lithium storage capacity and reaction kinetics.

[0066] The core reason for the poor performance of Comparative Examples 1-4 is that Comparative Example 1 uses commercially available carbon nanotubes instead of self-made three-dimensional carbon nanotubes, lacking the planar connection structure of graphene blades, resulting in insufficient continuity of the conductive network. Comparative Example 2 did not introduce sulfonic acid groups, resulting in strong inertness on the surface of the composite carbon nanotubes, poor dispersibility, and no active sites introduced. Comparative Example 3 directly uses unmodified three-dimensional carbon nanotubes, lacking the engineering optimization for defects caused by nitrogen and sulfur doping. Comparative Example 4 only underwent sulfonation without nitrogen and sulfur doping, resulting in a limited number of active sites. None of them can achieve a synergistic improvement in conductivity, dispersion, and active sites.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a composite conductive slurry of multiple conductive agents for lithium batteries, characterized in that, Includes the following steps: Step 1: Iron salts, aluminum salts and molybdates are loaded onto expanded graphite, calcined and reduced with hydrogen, and then placed in a plasma reactor to grow vertically oriented carbon nanotubes on the expanded graphite and composite graphene in situ to obtain three-dimensional carbon nanotubes. Step 2: Add three-dimensional carbon nanotubes, melamine and concentrated sulfuric acid to a reaction vessel, stir at 50-55℃ for 12-14 hours, transfer the product to deionized water, filter, wash and dry to obtain sulfonated three-dimensional carbon nanotubes. Sulfonated three-dimensional carbon nanotubes and Tris-HCl buffer solution were added to a reaction vessel and ultrasonically dispersed for 30-40 min. Dopamine hydrochloride was then added, and the mixture was stirred for 12-14 h at 20-25 °C and 500-700 r / min. The mixture was then centrifuged, filtered, washed, dried, and placed in a tube furnace. Under argon protection, the temperature was increased to 850-950 °C at a heating rate of 5 °C / min and heated at 10-12 Pa for 3-4 h. The mixture was then placed in a tube furnace with sublimated sulfur powder and heated to 450-500 °C at a heating rate of 5 °C / min under argon atmosphere. The temperature was maintained for 2-3 h to obtain composite carbon nanotubes. Step 3: Mix the active material, binder, composite carbon nanotubes, conductive carbon black and solvent evenly to obtain a composite conductive slurry for lithium batteries using multiple conductive agents.

2. The method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents according to claim 1, characterized in that, The preparation process of the three-dimensional carbon nanotubes described in step one is as follows: Expanded graphite with a particle size of 6.5 μm, iron salts, aluminum salts, molybdates, and deionized water were mixed and stirred for 2-3 hours. The mixture was then filtered, dried, and placed in a muffle furnace. The temperature was raised to 550-560℃ and heated for 3-4 hours to obtain supported expanded graphite. The graphite was then placed in a tube furnace, and the pressure inside the tube was reduced to 9-13 Pa. Hydrogen gas was injected until the reaction was completed, while the temperature was raised to 700-720℃ at a rate of 22℃ / min. The plasma reactor was started and operated at 300 W for 10-12 minutes. Methane was introduced, and the temperature was maintained at 700-720℃ for 30-40 minutes. The plasma reactor and methane flow rate were then turned off, and the hydrogen flow rate was reduced to 5 sccm. The mixture was cooled to room temperature to obtain three-dimensional carbon nanotubes.

3. The method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents according to claim 2, characterized in that, The ratio of expanded graphite, iron salt, aluminum salt, molybdate, and deionized water is 10-20g: 1.0-1.5g: 0.1-0.2g: 0.2-0.3g: 50-60mL; The hydrogen flow rate is 20 sccm; the methane flow rate is 30 sccm.

4. The method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents according to claim 3, characterized in that, The iron salt is one of ferric acetylacetone and ferric nitrate; The aluminum salt is aluminum phosphate; the molybdate is either ammonium molybdate or sodium molybdate.

5. The method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents according to claim 1, characterized in that, The ratio of the three-dimensional carbon nanotubes, melamine, concentrated sulfuric acid and deionized water is 5-8g: 3-5g: 300-500mL: 1-1.5L.

6. The method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents according to claim 1, characterized in that, The ratio of the sulfonated three-dimensional carbon nanotubes, Tris-HCl buffer solution, dopamine hydrochloride, and sublimed sulfur powder is 2-5g: 400-600mL: 1-2g: 0.2-0.4g.

7. The method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents according to claim 1, characterized in that, In step three, the ratio of the active material, binder, composite carbon nanotubes, conductive carbon black, and solvent is 9.58-13.58 g : 0.3-0.4 g : 0.12-0.15 g : 0.1-0.3 g : 12-18 mL. The active material is lithium iron phosphate; the binder is one of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer; the solvent is one of ethylene glycol dimethyl ether and N-methylpyrrolidone or a mixture of the two in any ratio.

8. A composite conductive slurry for lithium batteries using multiple conductive agents, characterized in that, It is prepared by the method for preparing a composite conductive slurry for lithium batteries using multiple conductive agents as described in any one of claims 1-7.