Carbon nanotube / graphene composite conductive agent and preparation method thereof

Abstract

The application discloses a carbon nanotube / graphene composite conductive agent and a preparation method thereof, and relates to the technical field of lithium ion battery materials. The application constructs a three-dimensional porous framework by intercalating zinc ions into graphene oxide, provides a highly dispersed catalyst by using iron ammonium citrate, introduces magnesium chloride to establish a magnesium thermal protection mechanism to ensure uniform growth of carbon nanotubes, and uses polyethylene glycol and tartaric acid as a carbon source pore-forming agent. Lithium carbonate is in-situ encapsulated to form a pre-lithiation unit. The application constructs a three-dimensional intercommunication network structure with synergistically enhanced electronic conduction and ion transmission by using a spray-freezing granulation process and a one-step catalytic chemical vapor deposition process. The application has high electrical conductivity, excellent dispersibility and structural stability, high process integration and environmental friendliness, and has significant industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a carbon nanotube / graphene composite conductive agent and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage power stations, higher requirements are being placed on the energy density, rate performance, and cycle life of lithium-ion batteries. Conductive agents, as key auxiliary materials for lithium batteries, play a crucial role in battery performance. Traditional conductive agents such as conductive carbon black, carbon nanotubes, and graphene have achieved some success in improving the electronic conductivity of electrodes, but certain limitations still exist.

[0003] In the prior art, patent CN120600825A discloses an all-solid-state composite dry conductive agent and its preparation method, which improves conductivity through multi-dimensional carbon material combination and surface modification. However, its preparation process is complex, involving multiple organic synthesis steps and using toxic reagents, posing environmental risks and challenges to large-scale production. Patent CN116799214B discloses a carbon nanotube composite conductive agent with high conductivity and its preparation method, which improves heat dissipation performance while introducing phase change materials. However, the long-term compatibility of phase change materials in the battery environment is questionable, and the additive system is complex, making it difficult to control byproducts. Patent CN116314794B discloses a layered porous lithium battery conductive material, preparation method, conductive agent, and battery. It achieves synergistic electron-ion dual-channel conduction through MXene / graphene composite and etching pore-forming strategy, improving conductivity while also meeting ion transport requirements. However, it uses HF / HCl etching process, which poses safety hazards, relies on expensive MXene materials, has harsh process conditions, and insufficient structural stability.

[0004] With the continuous increase in electrode areal density, optimizing ion transport pathways while ensuring electron conduction efficiency has become a crucial research direction in conductive agent design. Existing conductive agent systems are relatively mature in electron conduction, but there is still room for improvement in ion transport optimization and pre-lithiation integration. Particularly in constructing a dual continuous electron-ion transport network, more economical, safe, and easily industrialized technological routes need to be explored. Therefore, based on existing technologies, developing a carbon nanotube / graphene composite conductive agent that can better balance the relationship between electron conduction and ion transport, effectively integrate pre-lithiation functions, and possesses good process feasibility is of great significance for promoting the performance improvement of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon nanotube / graphene composite conductive agent and its preparation method to solve the problems mentioned in the background art.

[0006] In a first aspect, the present invention provides a carbon nanotube / graphene composite conductive agent, comprising the following raw materials in parts by weight:

[0007] 15-35 parts of zinc ion-intercalated graphene oxide;

[0008] 2-6 parts of ferric ammonium citrate;

[0009] 1-3 parts magnesium chloride;

[0010] 12-30 parts of carbon source pore-forming agent;

[0011] 1-4 parts lithium carbonate;

[0012] Sodium dodecylbenzenesulfonate 0.1-1 part;

[0013] 60-180 parts deionized water;

[0014] As a preferred embodiment of the present invention, the preparation steps of the zinc ion intercalated graphene oxide are as follows:

[0015] A1. Disperse graphene oxide powder in deionized water and homogenize it by ultrasonic treatment in an ice-water bath for 40-80 min to obtain a GO dispersion; dissolve zinc acetate dihydrate in deionized water and stir thoroughly to obtain a zinc acetate solution; add the zinc acetate solution dropwise to the GO dispersion while stirring, and stir at room temperature for 10-14 h to obtain a mixed solution.

[0016] In the GO dispersion, the ratio of graphene oxide powder to deionized water is 1g:(500-1000)mL.

[0017] In the zinc acetate solution, the ratio of zinc acetate dihydrate to deionized water is 1g:(100-200)mL;

[0018] The volume ratio of the zinc acetate solution to the GO dispersion is 1:10, wherein the mass ratio of graphene oxide to zinc acetate is maintained at 2:1.

[0019] A2. Centrifuge the mixture obtained in step A1 for 10-20 min, discard the supernatant, add an equal volume of deionized water, and redisperse the precipitate by vortexing. Centrifuge again for 10-20 min. Repeat this process 4-5 times until the pH of the supernatant is 6.8-7.2. Filter to obtain a wet filter cake, disperse the wet filter cake in deionized water, and sonicate for 3-8 min to obtain zinc ion intercalated graphene oxide slurry.

[0020] A3. The zinc ion intercalated graphene oxide slurry obtained in step A2 is pre-frozen in an ultra-low temperature freezer at -80℃ for 4 hours, and then transferred to a freeze dryer for 48 hours to obtain zinc ion intercalated graphene oxide.

[0021] As a preferred technical solution of the present invention, in step A3, the conditions of the freeze dryer are: cold trap temperature ≤ -50℃ and vacuum degree ≤ 10Pa.

[0022] It should be noted that the preparation of zinc ion intercalated graphene oxide is based on ion exchange and coordination. In a liquid environment, zinc ions interact with oxygen-containing functional groups such as carboxyl and epoxy groups on the surface of graphene oxide sheets. Some zinc ions further intercalate into the interlayer region of graphene oxide, effectively expanding the interlayer spacing. During subsequent heat treatment, the intercalated zinc ions are reduced to metallic zinc in a reducing atmosphere. Since the melting point of zinc is significantly lower than the system reaction temperature, the formed metallic zinc exists in the form of liquid particles. These liquid zinc particles have high surface energy and migration ability at high temperatures, and can migrate within a carbon matrix. Surface migration and aggregation occur, leaving initial channels and voids between graphene layers and on the surface. In the acid washing step after catalytic pyrolysis, these zinc components, existing in the form of metallic elements or oxides, react with dilute hydrochloric acid to generate soluble zinc salts, which are then selectively removed from the material system. The spaces left after their removal, together with the channels formed during the high-temperature process and the graphene oxide sheets, constitute a three-dimensional conductive framework with macro-meta-micro multi-level channels. This framework not only provides efficient channels for electrolyte wetting and lithium-ion transport, but its surface defect sites also contribute to the subsequent nucleation and growth of carbon nanotubes.

[0023] As a preferred embodiment of the present invention, the carbon source pore-forming agent is composed of polyethylene glycol and tartaric acid, wherein the mass ratio of polyethylene glycol to tartaric acid is (1-3):1, and the molecular weight of polyethylene glycol is 500-2000.

[0024] It should be noted that the carbon source pore-forming agent undergoes decomposition and carbonization during heat treatment, playing multiple synergistic roles. Upon heating, polyethylene glycol and tartaric acid first undergo esterification and cross-linking to form a polymer network. Simultaneously, the thermal motion of polyethylene glycol segments and the gas generated from their decomposition jointly construct the initial pore structure. During carbonization, the mixture transforms into an amorphous carbon matrix, and the escape pathways of the gas generated from its decomposition further form abundant mesopores and micropores. Tartaric acid can also form a mixed coordination structure with the already complexed iron centers in the iron ammonium citrate molecule, which serves as a catalyst precursor, further inhibiting the migration and aggregation of iron species in the early stages of heat treatment. Meanwhile, polyethylene glycol facilitates the dispersion and coating of lithium carbonate particles. This combination enables the spontaneous construction of a continuous hierarchical pore system while forming a conductive carbon matrix, providing a highly dispersed catalyst support for subsequent carbon nanotube growth.

[0025] It should be reiterated that the carbon shell formed by polyethylene glycol and tartaric acid can preferentially and selectively coat the surface of lithium carbonate particles for the following reasons:

[0026] Firstly, lithium carbonate possesses hydrophilicity and high surface energy. Its ionic crystal structure readily forms polar interactions and hydrogen bonds with the ether-oxygen bonds of polyethylene glycol (PEG) and the hydroxyl / carboxyl groups of tartaric acid. This makes PEG / tartaric acid molecules more likely to spontaneously adsorb and accumulate on the surface of lithium carbonate particles in the slurry system, forming a molecular pre-coating layer. Zinc-intercalated graphene oxide, after zinc ion intercalation and subsequent partial reduction, exhibits enhanced surface hydrophobicity and a two-dimensional sheet structure. Its polar interaction with PEG / tartaric acid is far weaker than that with lithium carbonate. Other components, such as ferric ammonium citrate and magnesium chloride, are water-soluble small molecules dispersed in the slurry in molecular or ionic states, lacking the conditions to provide large-size solid surfaces. Therefore, in the mixed slurry, PEG and tartaric acid preferentially wet and adsorb onto the hydrophilic lithium carbonate particle surface based on the principle of minimizing interfacial energy, laying the foundation for selectivity.

[0027] Secondly, the reaction during the programmed temperature rise process is sequential. The low-temperature stage (300-400℃) is the window for the esterification and cross-linking reaction of polyethylene glycol and tartaric acid. Pre-enriched polyethylene glycol and tartaric acid molecules on the lithium carbonate surface undergo localized and rapid in-situ cross-linking, forming a stable, insoluble polymer network shell on the lithium carbonate particle surface. This cross-linking reaction is preferential over most other carbonization processes. In the medium-to-high temperature stage (above 450℃), the lithium carbonate particles, physically isolated by the polymer shell, are protected, and other carbon sources in the system (such as the decomposition of oxygen-containing functional groups in graphene oxide itself and small amounts of carbon sources adsorbed at other locations) begin to undergo significant decomposition and carbonization. Because the lithium carbonate surface is already occupied by the cross-linked polymer, new carbon layers are difficult to nucleate and grow directly on its surface.

[0028] Third, the two-dimensional sheet structure of graphene oxide forms a three-dimensional network in the slurry, which has a certain spatial confinement effect on the lithium carbonate particles dispersed therein. This helps to maintain the dispersion of lithium carbonate particles and prevent them from agglomerating, thereby ensuring that polyethylene glycol / tartaric acid can be uniformly coated on each particle.

[0029] A second aspect of the present invention provides a method for preparing a carbon nanotube / graphene composite conductive agent, comprising the following steps:

[0030] S1. Sodium dodecylbenzenesulfonate was dissolved in deionized water and homogenized to obtain a micelle solution. The solution was added to a high-speed shear disperser and stirred at 10,000-15,000 rpm. Zinc ion intercalated graphene oxide, ferric ammonium citrate, magnesium chloride, carbon source pore-forming agent and lithium carbonate were added sequentially to the micelle solution. The solution was dispersed at 10,000-15,000 rpm for 90-150 min to obtain the initial slurry.

[0031] S2. The initial slurry obtained in S1 is atomized by a sprayer and sprayed into a receiving device cooled by liquid nitrogen. The resulting frozen particles are transferred to a freeze dryer and dried for 36-60 hours to obtain composite precursor powder.

[0032] As a preferred technical solution of the present invention, in step S2, the conditions of the freeze dryer are: cold trap temperature ≤ -50℃ and vacuum degree ≤ 5Pa;

[0033] S3. Spread the composite precursor powder obtained in S2 on a quartz boat and place it in a tube furnace. Under the protection of argon atmosphere, the temperature is programmed to rise to 450-550℃ at a rate of 3-5℃ / min and held for 60-90min. Ethanol vapor carried by argon is introduced into the furnace and catalytic cracking reaction is carried out at 750-850℃ for 80-150min. After that, the mixture is naturally cooled to room temperature under argon atmosphere to obtain crude conductive agent powder.

[0034] As a preferred embodiment of the present invention, the operation and parameters for introducing ethanol vapor in step S3 are as follows:

[0035] Argon gas is used as a carrier gas and is introduced into a bubbler placed in a constant temperature water bath at 75-85℃ at a flow rate of 50-100 sccm. The bubbler contains a sufficient amount of anhydrous ethanol. When the carrier gas flows through the bubbler, it carries the saturated vapor generated by the constant temperature ethanol and together they are introduced into the reaction zone of the tubular furnace.

[0036] It should be noted that during the catalytic cracking reaction stage, the system undergoes a precisely controlled multiphase transformation process. During the catalyst activation and protection stage, ferric ammonium citrate decomposes under heat in a reducing atmosphere, initially releasing gaseous products. Subsequently, iron ions are reduced to nanoscale metallic iron particles, which are uniformly distributed on the carbon matrix surface. Simultaneously, the metallic magnesium produced by the decomposition of magnesium chloride, due to its excellent oxygen affinity, preferentially undergoes redox reactions with free oxygen in the system and the amorphous carbon layer coating the iron catalyst surface. This magnesium thermal protection mechanism effectively removes the amorphous carbon covering the catalyst's active sites, maintaining the catalyst surface cleanliness and reactivity, and preventing early catalyst deactivation. Simultaneously, the polymer network formed by the esterification crosslinking of polyethylene glycol and tartaric acid undergoes a carbonization transformation, forming a protective carbon shell with ion conductivity on the surface of lithium carbonate particles, achieving in-situ encapsulation and stabilization of the pre-lithiated functional unit; the oxygen-containing functional groups in zinc ion intercalated graphene oxide begin to undergo thermal decomposition reactions such as thermal decarboxylation / dehydration at this heat treatment temperature, being removed in the form of CO, CO2, and H2O, etc. The removal of oxygen-containing functional groups reduces sp 3 The proportion of hybrid carbon makes sp 2The conjugated network is partially reconstructed, the electron delocalization ability is enhanced, the conductivity is significantly improved, and due to the removal of oxygen-containing functional groups and the release of surface tension, the lamellar wrinkles are reduced, and the lamellar structure is repaired and smoothed to a certain extent.

[0037] It needs to be reiterated that after entering the carbon nanotube growth phase, ethanol vapor undergoes catalytic cracking on the surface of the iron catalyst activated by the magnesium thermoprotection mechanism, following a gas-liquid-solid growth mechanism. The carbon atoms produced by the cracking dissolve and become supersaturated in the quasi-liquid iron catalyst particles, then precipitate from the catalyst surface to form graphene sheets, which subsequently curl and grow into carbon nanotubes. These newly formed carbon nanotubes and the three-dimensional graphene framework share carbon-carbon splines. 2 The carbon network (forming a continuous carbon structure) is firmly bonded, forming a robust conductive network. This process, synergistic with the melting, migration, and removal of zinc ions, not only creates additional mesoporous and microporous structures within the framework but also promotes further reduction and defect repair of the graphene sheets. In the final three-dimensional interconnected network structure, the carbon nanotube-graphene framework provides an efficient electronic conduction pathway, the hierarchical pore system ensures excellent ion transport capabilities, and the well-encapsulated pre-lithiation units endow the system with controllable lithium compensation. The synergistic integration of these three functions achieves integrated optimization of electronic conduction, ion transport, and electrochemical compensation.

[0038] S4. Soak the crude conductive agent powder obtained in S3 in dilute hydrochloric acid for 15-30 minutes, wash it with deionized water until neutral, and vacuum dry it at 100-120℃ for 8-12 hours. Then, use an air jet mill to micronize it to obtain the carbon nanotube / graphene composite conductive agent.

[0039] As a preferred embodiment of the present invention, in step S4, the concentration of the dilute hydrochloric acid is 0.05-0.2 mol / L.

[0040] As a preferred technical solution of the present invention, in step S4, the parameters for micronization by the air jet mill are: classifier wheel frequency 35-45 Hz, air pressure 0.7-0.9MPa; the milling endpoint requirements are powder particle size D50=2.5±1.0μm, D90≤15μm, and moisture content≤1.0%.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) A three-dimensional interconnected network structure for dual continuous electron-ion transport was constructed. Through the synergistic effect of thermal migration pore formation by zinc ion intercalation graphene oxide and decomposition pore formation by carbon source pore-forming agent, a multi-level pore system was formed inside the material. At the same time, a carbon nanotube-graphene covalently bonded electron conduction network was constructed on the three-dimensional framework through in-situ catalytic growth technology. This structure makes the electron conduction pathway and ion transport channel continuous and nested in three-dimensional space, which improves the problems of poor rate performance and severe polarization caused by ion transport bottleneck in high energy density batteries.

[0043] (2) A magnesium thermal protection catalytic mechanism is adopted to ensure uniform growth of carbon nanotubes. By introducing magnesium chloride as a catalyst protectant, the strong reducing property of magnesium at high temperature is utilized to effectively remove the amorphous carbon layer wrapped on the surface of the iron catalyst, prevent catalyst deactivation, and ensure that the nano-iron catalyst can maintain high catalytic activity in complex multi-component systems. This achieves uniform and controllable growth of carbon nanotubes on a three-dimensional porous framework, and improves the problem of easy agglomeration and uneven distribution of carbon nanotubes when directly added in the preparation method of traditional carbon nanotube conductive agents.

[0044] (3) In-situ integration and secure encapsulation of pre-lithiation function and conductive network were achieved. By utilizing the preferential wettability of polyethylene glycol and tartaric acid on lithium carbonate particles and the in-situ cross-linking and carbonization effect on the surface, a protective carbon shell was successfully formed on the surface of lithium carbonate particles, constructing carbon-coated lithium carbonate nanocapsules. This ensured the stability of the pre-lithiation agent during high-temperature synthesis and post-processing, and also achieved controlled lithium release during battery operation. Integrating the pre-lithiation functional unit into a key position of the ion transport network optimized the interfacial ion transport kinetics while compensating for irreversible capacity, achieving functional synergy between pre-lithiation and conductivity.

[0045] (4) High process integration and environmentally friendly. The process integrates multiple steps such as three-dimensional structure construction, conductive network growth, channel engineering and pre-lithiation agent encapsulation into a continuous process flow with water as the solvent. This avoids the use of toxic organic solvents, dangerous fluoride etchants or highly active lithium metal in traditional processes. It has the advantages of simple process flow, high production safety and environmental friendliness, and has significant potential for industrial application. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Preparation Example 1

[0048] The preparation steps of zinc ion intercalated graphene oxide are as follows:

[0049] A1. Disperse 1g of graphene oxide powder in 1000mL of deionized water and homogenize by ultrasonic treatment in an ice-water bath at 0℃ for 60min to obtain a GO dispersion; dissolve 0.5g of zinc acetate dihydrate in 100mL of deionized water and stir thoroughly to obtain a zinc acetate solution; add 100mL of zinc acetate solution dropwise to 1000mL of GO dispersion while stirring, and stir at room temperature for 12h to obtain a mixed solution;

[0050] A2. Centrifuge the mixture obtained in step A1 for 15 minutes, discard the supernatant, add an equal volume of deionized water, and redisperse the precipitate by vortexing. Centrifuge again for 15 minutes. Repeat this process 4 times until the pH of the supernatant is 7. Filter to obtain a wet filter cake, disperse the wet filter cake in deionized water, and sonicate for 5 minutes to obtain zinc ion intercalated graphene oxide slurry.

[0051] A3. The zinc ion intercalated graphene oxide slurry obtained in step A2 is pre-frozen in an ultra-low temperature freezer at -80℃ for 4 hours, then transferred to a freeze dryer and dried for 48 hours at a cold trap temperature of -50℃ and a vacuum degree of 8Pa to obtain zinc ion intercalated graphene oxide.

[0052] Preparation Example 2

[0053] The preparation steps of the carbon source pore-forming agent are as follows:

[0054] Polyethylene glycol is compounded with tartaric acid; the mass ratio of polyethylene glycol to tartaric acid is 2:1, and the molecular weight of polyethylene glycol is 1000.

[0055] Example 1

[0056] A method for preparing a carbon nanotube / graphene composite conductive agent includes the following steps:

[0057] S1. Dissolve 0.5 parts of sodium dodecylbenzenesulfonate in 120 parts of deionized water, homogenize to obtain a micelle solution, add it to a high-speed shear disperser, and under stirring at 12000 rpm, add 25 parts of zinc ion intercalated graphene oxide, 4 parts of ferric ammonium citrate, 2 parts of magnesium chloride, 21 parts of carbon source pore-forming agent and 2.5 parts of lithium carbonate in sequence, and continue to disperse at 12000 rpm for 120 min to obtain the initial slurry;

[0058] S2. The initial slurry obtained in S1 is atomized by a sprayer and sprayed into a receiving device cooled by liquid nitrogen. The resulting frozen particles are transferred to a freeze dryer and dried for 48 hours at a cold trap temperature of -50°C and a vacuum degree of 5Pa to obtain composite precursor powder.

[0059] S3. Spread the composite precursor powder obtained in S2 on a quartz boat and place it in a tube furnace. Under the protection of argon atmosphere, the temperature is programmed to rise to 500℃ at a rate of 4℃ / min and held for 90min. Argon is used as the carrier gas and is introduced into a bubbler placed in an 80℃ constant temperature water bath at a flow rate of 80sccm. The bubbler contains sufficient anhydrous ethanol. When the carrier gas flows through the bubbler, it carries the saturated vapor generated by the constant temperature ethanol and is introduced into the reaction zone of the tube furnace. After catalytic cracking reaction at 800℃ for 120min, it is naturally cooled to room temperature under argon atmosphere to obtain crude conductive agent powder.

[0060] S4. The crude conductive agent powder obtained in S3 is soaked in 0.1 mol / L dilute hydrochloric acid for 20 min, washed with deionized water until neutral, and vacuum dried at 110℃ for 10 h. It is then micronized using an air jet mill with a classifying wheel frequency of 40 Hz and an air pressure of 0.8 MPa to obtain the carbon nanotube / graphene composite conductive agent.

[0061] In this embodiment, some of the raw materials used are the same as those obtained in Preparation Examples 1-2, and the other examples are the same.

[0062] Example 2

[0063] A method for preparing a carbon nanotube / graphene composite conductive agent includes the following steps:

[0064] S1. Dissolve 0.8 parts of sodium dodecylbenzenesulfonate in 140 parts of deionized water, homogenize to obtain a micelle solution, add it to a high-speed shear disperser, and add 30 parts of zinc ion intercalated graphene oxide, 5 parts of ferric ammonium citrate, 3 parts of magnesium chloride, 27 parts of carbon source pore-forming agent and 3 parts of lithium carbonate to the micelle solution in sequence under stirring at 12000 rpm, and continue to disperse at stirring at 12000 rpm for 120 min to obtain the initial slurry;

[0065] S2. The initial slurry obtained in S1 is atomized by a sprayer and sprayed into a receiving device cooled by liquid nitrogen. The resulting frozen particles are transferred to a freeze dryer and dried for 48 hours at a cold trap temperature of -50°C and a vacuum degree of 5Pa to obtain composite precursor powder.

[0066] S3. Spread the composite precursor powder obtained in S2 on a quartz boat and place it in a tube furnace. Under the protection of argon atmosphere, the temperature is programmed to rise to 500℃ at a rate of 4℃ / min and held for 90min. Argon is used as the carrier gas and is introduced into a bubbler placed in an 80℃ constant temperature water bath at a flow rate of 80sccm. The bubbler contains sufficient anhydrous ethanol. When the carrier gas flows through the bubbler, it carries the saturated vapor generated by the constant temperature ethanol and is introduced into the reaction zone of the tube furnace. After catalytic cracking reaction at 800℃ for 120min, it is naturally cooled to room temperature under argon atmosphere to obtain crude conductive agent powder.

[0067] S4. The crude conductive agent powder obtained in S3 is soaked in 0.1 mol / L dilute hydrochloric acid for 20 min, washed with deionized water until neutral, and vacuum dried at 110℃ for 10 h. It is then micronized using an air jet mill with a classifying wheel frequency of 40 Hz and an air pressure of 0.8 MPa to obtain the carbon nanotube / graphene composite conductive agent.

[0068] Example 3

[0069] A method for preparing a carbon nanotube / graphene composite conductive agent includes the following steps:

[0070] S1. Dissolve 0.3 parts of sodium dodecylbenzenesulfonate in 100 parts of deionized water, homogenize to obtain a micelle solution, add it to a high-speed shear disperser, and under stirring at 12000 rpm, add 20 parts of zinc ion intercalated graphene oxide, 3 parts of ferric ammonium citrate, 1 part of magnesium chloride, 15 parts of carbon source pore-forming agent and 2 parts of lithium carbonate in sequence, and continue to disperse at 12000 rpm for 120 min to obtain the initial slurry;

[0071] S2. The initial slurry obtained in S1 is atomized by a sprayer and sprayed into a receiving device cooled by liquid nitrogen. The resulting frozen particles are transferred to a freeze dryer and dried for 48 hours at a cold trap temperature of -50°C and a vacuum degree of 5Pa to obtain composite precursor powder.

[0072] S3. Spread the composite precursor powder obtained in S2 on a quartz boat and place it in a tube furnace. Under the protection of argon atmosphere, the temperature is programmed to rise to 500℃ at a rate of 4℃ / min and held for 90min. Argon is used as the carrier gas and is introduced into a bubbler placed in an 80℃ constant temperature water bath at a flow rate of 80sccm. The bubbler contains sufficient anhydrous ethanol. When the carrier gas flows through the bubbler, it carries the saturated vapor generated by the constant temperature ethanol and is introduced into the reaction zone of the tube furnace. After catalytic cracking reaction at 800℃ for 120min, it is naturally cooled to room temperature under argon atmosphere to obtain crude conductive agent powder.

[0073] S4. The crude conductive agent powder obtained in S3 is soaked in 0.1 mol / L dilute hydrochloric acid for 20 min, washed with deionized water until neutral, and vacuum dried at 110℃ for 10 h. It is then micronized using an air jet mill with a classifying wheel frequency of 40 Hz and an air pressure of 0.8 MPa to obtain the carbon nanotube / graphene composite conductive agent.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is that zinc ion intercalated graphene oxide was not added; instead, untreated graphene oxide was added. Otherwise, it is the same as Example 1.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that magnesium chloride was not added; otherwise, they are the same as in Example 1.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 1 is that ferric ammonium citrate is replaced with ferric nitrate in an equal molar amount of iron, otherwise it is the same as Example 1.

[0080] Comparative Example 4

[0081] The difference between this comparative example and Example 1 is that ferric ammonium citrate was not added; otherwise, they are the same as in Example 1.

[0082] Comparative Example 5

[0083] The difference between this comparative example and Example 1 is that the carbon source pore-forming agent is replaced with an equal mass of polyethylene glycol with a molecular weight of 1000; otherwise, it is the same as Example 1.

[0084] Comparative Example 6

[0085] The difference between this comparative example and Example 1 is that the carbon source pore-forming agent is replaced with an equal mass of tartaric acid, otherwise it is the same as Example 1.

[0086] Comparative Example 7

[0087] The difference between this comparative example and Example 1 is that no carbon source pore-forming agent was added; otherwise, they are the same as in Example 1.

[0088] The carbon nanotube / graphene composite conductive agents prepared in Examples 1-3 and Comparative Examples 1-7 were tested:

[0089] 1. Conductivity test: The conductive agent and polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 95:5, pressed into a disc with a diameter of 10 mm, and the conductivity is measured using the four-probe method.

[0090] II. Specific surface area and pore size analysis: The nitrogen adsorption-desorption method was used to calculate the specific surface area using the BET model and the pore size distribution was analyzed using the BJH model.

[0091] III. Lithium-ion Battery Performance Testing: Electrodes were prepared by mixing conductive agent with lithium iron phosphate cathode material and PVDF binder at a mass ratio of 4:93:3, and then assembled into CR2032 button batteries. The rate performance and cycle life of the batteries were tested within a voltage range of 2.5-3.6V.

[0092] IV. Pre-lithiation effect evaluation: Electrodes were prepared by mixing conductive agent with lithium iron phosphate cathode material and PVDF binder at a mass ratio of 4:93:3, and then assembled into CR2032 button batteries. The pre-lithiation effect was evaluated by the first-week charge-discharge efficiency. First-week efficiency (%) = (first-week discharge specific capacity / first-week charge specific capacity) × 100%.

[0093] The test results are shown in Table 1.

[0094] V. Summary of Results

[0095] Table 1

[0096]

[0097] VI. Conclusion and Discussion

[0098] As shown in Table 1, the carbon nanotube / graphene composite conductive agents prepared in Examples 1-3 of this invention exhibit significant advantages in all performance indicators.

[0099] Comparative Example 1 exhibited poorer pore structure parameters and rate performance, with its specific surface area and mesopore volume significantly lower than Examples 1-3, demonstrating the crucial role of zinc ion intercalation in constructing hierarchical porous structures. The volatilization of zinc ions during heat treatment not only created abundant mesoporous structures but also provided favorable nucleation sites for carbon nanotube growth.

[0100] Comparative Example 2 exhibited the second lowest conductivity and a comprehensive decline in electrochemical performance, demonstrating the importance of the magnesium thermal protection mechanism for obtaining high-quality carbon nanotubes. Without magnesium thermal protection, the catalyst surface is easily deactivated by amorphous carbon encapsulation, leading to poor carbon nanotube growth and the inability to form a complete conductive network.

[0101] Comparative Example 3 showed slightly better performance than the other comparative examples, but significantly lower than Examples 1-3. This indicates that although tartaric acid has a certain complexing ability and can partially replace the complexing function of ferric ammonium citrate, the role of ferric ammonium citrate in this system is not limited to this. In Examples 1-3, ferric ammonium citrate, as a complete functional unit, exhibited good kinetic matching with other components in the system due to its thermal decomposition characteristics. During heating, it underwent a progressive decomposition process from the complex to metallic iron. This process synergized with the reduction of graphene oxide, the decomposition of the carbon source pore-forming agent, and the activation of the magnesium thermal protection mechanism in terms of temperature and time, ensuring that the catalyst exists in a suitable size and distribution state when carbon nanotubes begin to grow. In contrast, although the combination of ferric nitrate and tartaric acid provided the same elemental composition, their decomposition pathways and reaction kinetics differed, resulting in a catalyst with inferior particle size distribution and activity compared to the ferric ammonium citrate system, thus affecting the growth quality of carbon nanotubes and the perfection of the conductive network. This demonstrates that ferric ammonium citrate, as a catalyst precursor in this invention, plays a role that is difficult to replace compared to other simple mixtures.

[0102] Comparative Example 4 exhibits the lowest conductivity, consisting solely of a two-dimensional conductive network formed by reduced graphene oxide (rGO), resulting in a single conductive pathway and high contact resistance between the layers. In contrast, in Examples 1-3, carbon nanotubes (CNTs) grown in situ under the action of a catalyst intersect between the rGO layers, forming a stable, multi-dimensional conductive pathway and improving electron transport efficiency. Simultaneously, due to the lack of CNT support and bridging, the electrode structure of Comparative Example 4 also suffers from poor stability, leading to the worst rate performance and cycle life among all samples. Without a catalyst, CNTs cannot be grown, making it impossible to construct the efficient three-dimensional conductive network upon which this invention relies, ultimately resulting in a comprehensive decline in electrochemical performance.

[0103] The electrochemical performance of Comparative Examples 5 and 6 falls between that of Examples 1 and 7, but neither reaches the electrochemical performance level of Example 1. The decomposition of the long-chain polymer polyethylene glycol (PEG) can form a carbon skeleton and larger pores; while the small-molecule organic acid tartaric acid not only catalyzes the decomposition of PEG and promotes the formation of finer channels, but also complexes with metal ions in the system, improving the uniformity of the precursor, thereby optimizing the pore size distribution and conductive network quality of the final carbon material. Comparative Example 5 has high conductivity but insufficient specific surface area and pore volume, while Comparative Example 6 has a decent specific surface area but poor conductivity and electrochemical performance, indirectly confirming the complementary nature of their functions.

[0104] The electrochemical performance of Comparative Example 7 was significantly inferior to that of Example 1, indicating the crucial role of the carbon source pore-forming agent in constructing a high specific area and rich mesoporous structure.

[0105] In summary, this invention, through reasonable material design and optimized preparation process, especially the synergistic application of zinc ion intercalated graphene oxide, magnesium thermal protection, iron ammonium citrate, and carbon source pore-forming agent, has successfully prepared a carbon nanotube / graphene composite conductive agent with excellent comprehensive performance, showing good application prospects in the field of lithium-ion batteries.

[0106] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0107] The above content is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the scope defined by the invention, they should all fall within the protection scope of the present invention.

Claims

1. A carbon nanotube / graphene composite conductive agent, characterized by: The following ingredients are included by weight: 15-35 parts of zinc ion-intercalated graphene oxide; 2-6 parts of ferric ammonium citrate; 1-3 parts magnesium chloride; 12-30 parts of carbon source pore-forming agent; 1-4 parts lithium carbonate; Sodium dodecylbenzenesulfonate 0.1-1 part; 60-180 parts deionized water; The preparation steps of the zinc ion intercalated graphene oxide are as follows: A1. Disperse graphene oxide powder in deionized water and homogenize it by ultrasonic treatment in an ice-water bath for 40-80 min to obtain a GO dispersion; dissolve zinc acetate dihydrate in deionized water and stir thoroughly to obtain a zinc acetate solution; add the zinc acetate solution dropwise to the GO dispersion while stirring, and stir at room temperature for 10-14 h to obtain a mixed solution. A2. Centrifuge the mixture obtained in step A1 for 10-20 min, discard the supernatant, add an equal volume of deionized water, and redisperse the precipitate by vortexing. Centrifuge again for 10-20 min. Repeat this process 4-5 times until the pH of the supernatant is 6.8-7.

2. Filter to obtain a wet filter cake, disperse the wet filter cake in deionized water, and sonicate for 3-8 min to obtain zinc ion intercalated graphene oxide slurry. A3. The zinc ion intercalated graphene oxide slurry obtained in step A2 is pre-frozen in an ultra-low temperature freezer at -80℃ for 4 hours, then transferred to a freeze dryer and dried for 48 hours. The cold trap temperature is ≤-50℃ and the vacuum degree is ≤10Pa to obtain zinc ion intercalated graphene oxide. The carbon source pore-forming agent is composed of polyethylene glycol and tartaric acid, and the mass ratio of polyethylene glycol to tartaric acid is (1-3):

1. The preparation method of the carbon nanotube / graphene composite conductive agent is as follows: S1. Sodium dodecylbenzenesulfonate was dissolved in deionized water and homogenized to obtain a micelle solution. The solution was added to a high-speed shear disperser and stirred at 10,000-15,000 rpm. Zinc ion intercalated graphene oxide, ferric ammonium citrate, magnesium chloride, carbon source pore-forming agent and lithium carbonate were added sequentially to the micelle solution. The solution was dispersed for 90-150 minutes under stirring at 10,000-15,000 rpm to obtain the initial slurry. S2. The initial slurry obtained in S1 is atomized by a sprayer and sprayed into a receiving device cooled by liquid nitrogen. The resulting frozen particles are transferred to a freeze dryer and dried for 36-60 hours to obtain composite precursor powder. S3. Spread the composite precursor powder obtained in S2 on a quartz boat and place it in a tube furnace. Under the protection of argon atmosphere, the temperature is programmed to rise to 450-550℃ at a rate of 3-5℃ / min and held for 60-90min. Ethanol vapor carried by argon is introduced into the furnace and catalytic cracking reaction is carried out at 750-850℃ for 80-150min. After that, the mixture is naturally cooled to room temperature under argon atmosphere to obtain crude conductive agent powder. S4. Soak the crude conductive agent powder obtained in S3 in dilute hydrochloric acid for 15-30 minutes, wash it with deionized water until neutral, and vacuum dry it at 100-120℃ for 8-12 hours. Then, use an air jet mill to micronize it to obtain the carbon nanotube / graphene composite conductive agent.

2. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized in that: In step A1, the ratio of graphene oxide powder to deionized water in the GO dispersion is 1g:(500-1000)mL.

3. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized in that: In step A1, the ratio of zinc acetate dihydrate to deionized water in the zinc acetate solution is 1 g:(100-200) mL; the volume ratio of the zinc acetate solution to the GO dispersion is 1:10, wherein the mass ratio of graphene oxide to zinc acetate is maintained at 2:

1.

4. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized by: The molecular weight of the polyethylene glycol is 500-2000.

5. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized by: In step S2, the conditions for the freeze dryer are: cold trap temperature ≤ -50℃ and vacuum degree ≤ 5Pa.

6. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized in that: In step S3, the operation and parameters for introducing ethanol vapor carried by argon gas into the furnace are as follows: Argon gas is used as a carrier gas and is introduced into a bubbler placed in a constant temperature water bath at 75-85℃ at a flow rate of 50-100 sccm. The bubbler contains a sufficient amount of anhydrous ethanol. When the carrier gas flows through the bubbler, it carries the saturated vapor generated by the anhydrous ethanol and together they are introduced into the reaction zone of the tubular furnace.

7. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized in that: In step S4, the concentration of the dilute hydrochloric acid is 0.05-0.2 mol / L.

8. The carbon nanotube / graphene composite conductive agent according to claim 1, characterized in that: In step S4, the parameters for micronization by the air jet mill are: classifier wheel frequency 35-45 Hz, air pressure 0.7-0.9MPa; the milling endpoint requirements are powder particle size D50=2.5±1.0μm, D90≤15μm, and moisture content≤1.0%.

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