Coal pitch coated transition metal and nitrogen-doped carbon nanotube composite electrode material, and preparation method and application thereof

Abstract

A coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material, its preparation method, and its application are disclosed, belonging to the technical field of capacitor deionization electrode materials. The method includes: firstly, nitrogen-doping modification of carbon nanotubes to obtain nitrogen-doped carbon nanotubes; then, introducing a transition metal salt precursor and undergoing a first-stage heat treatment to obtain a transition metal-loaded nitrogen-doped carbon nanotube precursor composite material; subsequently, adding coal tar pitch and undergoing a second-stage heat treatment to obtain the coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material. In the obtained material, the nitrogen-doped carbon nanotubes provide a continuous conductive network and mass transfer channels, the transition metal component improves interfacial charge transport performance, and the coal tar pitch-derived carbon layer enhances structural stability and interfacial coupling ability, thereby improving the electroadsorption efficiency, rate performance, and cycle stability during capacitor deionization.

Description

Technical Field

[0001] This invention belongs to the technical field of capacitive deionization electrode materials, specifically relating to a coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material, its preparation method, and its application. Background Technology

[0002] While traditional separation and purification technologies such as thermal distillation, reverse osmosis, and electrodialysis are widely used in water treatment, they still generally suffer from drawbacks such as high energy consumption, high equipment costs, stringent operating conditions, and susceptibility to membrane fouling. Against this backdrop, developing novel electrochemical separation materials and technologies that are structurally stable, renewable, and have low energy consumption is of significant research and application value.

[0003] Capacitive deionization is an electrochemical method based on ion migration driven by an applied electric field and separation and removal achieved by electroadsorption on the electrode surface. It offers advantages such as mild operating conditions, relatively simple device structure, low energy consumption, and reversible electrode regeneration, showing promising application prospects in brackish water treatment, purification of low- to medium-concentration saline wastewater, and other ion separation fields. The core of this technology lies in improving the performance of electrode materials. The conductivity, pore structure characteristics, surface active sites, and interfacial stability of electrode materials directly affect their electroadsorption capacity, mass transfer efficiency, and cycle life. Therefore, constructing electrode materials that combine good conductivity, rapid ion transport capacity, and high structural stability has always been an important research direction in this field.

[0004] Currently, capacitive deionization electrode materials are mostly based on carbon materials, including activated carbon, graphene, porous carbon, and carbon nanotubes. Among them, carbon nanotubes are considered a promising electrode matrix material due to their high conductivity, good chemical stability, and one-dimensional network structure. However, single carbon nanotubes still suffer from problems such as insufficient surface active sites, insufficient pore structure hierarchy, easy entanglement and aggregation, and poor interfacial wettability, thus limiting their overall performance. To improve these shortcomings, existing technologies typically employ nitrogen doping modification, metal component composites, and surface coating to enhance the surface polarity, number of defect sites, interfacial compatibility, and loading capacity of carbon nanotubes with active components.

[0005] Based on carbon nanotube modification, the introduction of transition metal components helps improve the interfacial charge transport performance and overall conductivity of the material. Further coating with coal tar pitch as a carbon source enhances the interfacial bonding between components, inhibits the migration, aggregation, or detachment of active components, and improves the structural stability and cycle durability of the material. Coal tar pitch is widely available, relatively inexpensive, and has good carbonization properties, making it suitable as a coating precursor for composite electrode materials. Therefore, it is still necessary to provide a composite electrode material and its preparation method that uses nitrogen-doped carbon nanotubes as the conductive framework, transition metal components as the functional phase, and achieves stable coating through a coal tar pitch-derived carbon layer, in order to further improve its electroadsorption efficiency, mass transfer performance, and cycle stability during capacitive deionization. Summary of the Invention

[0006] The purpose of this invention is to provide a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material, its preparation method, and its application, aiming to solve the following problems: ① the problem of discontinuous conductive paths and insufficient utilization of active sites in existing capacitive deionization electrode materials; ② the problem of unstable interfacial bonding between the active component and the carbon skeleton in the composite electrode material, which easily leads to migration, aggregation, or desorption during preparation or use; ③ the problem that existing carbon nanotube-based materials still need further improvement in terms of ion transport efficiency, structural stability, and cycling performance; ④ to develop a composite electrode material suitable for capacitive deionization processes that has good conductivity, interfacial stability, and cycling durability.

[0007] This invention provides a coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material, its preparation method, and its application. The composite electrode material uses nitrogen-doped carbon nanotubes as the conductive framework and transition metal components as the functional phase. A carbon coating layer is formed through secondary heat treatment of coal tar pitch, thereby constructing a composite electrode material with a continuous conductive network, stable interface structure, and good mass transfer channels.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material, the method comprising the following steps:

[0010] S1. Nitrogen-doped carbon nanotubes are obtained by modifying carbon nanotubes with nitrogen doping.

[0011] S2. Mix the nitrogen-doped carbon nanotubes obtained in step S1 with the transition metal salt precursor and perform the first heat treatment to obtain a transition metal-supported nitrogen-doped carbon nanotube precursor composite material.

[0012] S3. The precursor composite material obtained in step S2 is mixed with coal tar pitch and subjected to a second heat treatment to obtain a coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material.

[0013] Furthermore, in step S1, the carbon nanotube is one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both.

[0014] Further, in step S1, the nitrogen doping modification treatment is one of the following methods, namely nitrogen atmosphere treatment, nitrogen precursor introduction treatment, or a combination of both, to modify carbon nanotubes to obtain nitrogen-doped carbon nanotubes.

[0015] Further, in step S2, the transition metal salt precursor is one or more of the following: iron salt, cobalt salt, manganese salt, copper salt, zinc salt, molybdenum salt, tungsten salt, and nickel salt.

[0016] Further, in step S2, the transition metal salt precursor and nitrogen-doped carbon nanotubes are dispersed in an organic solvent at a mass ratio of transition metal element to nitrogen-doped carbon nanotubes of (0.01-0.30):1, and subjected to a first heat treatment after sonication for 10-60 min, impregnation for 12-36 h, and drying at 60-100℃ for 6-24 h.

[0017] Furthermore, the organic solvent is one or more mixed solvents selected from ethanol, methanol, isopropanol, and deionized water.

[0018] Furthermore, in step S3, the precursor composite material and coal tar pitch are dispersed, mixed, and dried, and then subjected to a second heat treatment. During the heat treatment process, the coal tar pitch forms a coal tar pitch-derived carbon layer that coats the transition metal components and the surface of the carbon nanotubes.

[0019] Furthermore, both the first and second heat treatments are carried out in an inert or protective atmosphere, with a heat treatment temperature of 500-900℃ and a holding time of 0.5-4 h.

[0020] A coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material, the composite electrode material comprising a carbon nanotube conductive framework, a transition metal component loaded on the surface of the carbon nanotube conductive framework, and a coal tar pitch-derived carbon layer coated on the surfaces of both.

[0021] Application of a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material in capacitor deionization.

[0022] The advantages of this invention over the prior art are:

[0023] 1. This invention uses nitrogen-doped carbon nanotubes as the conductive framework of a composite material, which can construct a continuous and stable electron transport network. Compared with the problem of discontinuous conductive paths in traditional carbon materials, this invention can effectively reduce the internal resistance of the electrode and improve the electron transport efficiency. At the same time, nitrogen doping modification is beneficial to improving the polarity, wettability, and defect site distribution of the carbon nanotube surface, promoting electrolyte wetting and ion migration, thereby improving the overall response performance during capacitor deionization.

[0024] 2. This invention introduces transition metal components onto the surface of nitrogen-doped carbon nanotubes, enabling the formation of a relatively stable composite interface structure between the carbon framework and the functional phase. This improves local electron distribution and interfacial charge transport capabilities, and enhances the interfacial response characteristics of the material during adsorption and desorption processes. Compared to single carbon nanotube materials, this invention exhibits significant advantages in conductivity, interfacial control capabilities, and overall performance.

[0025] 3. By introducing coal tar pitch and performing secondary heat treatment, the present invention forms a coal tar pitch-derived carbon coating layer on the surface of transition metal components and carbon nanotubes, which can effectively enhance the interfacial bonding between components and inhibit the migration, agglomeration or desorption of transition metal components during preparation and use, thereby improving the overall structural stability and cycle durability of the composite material.

[0026] 4. The composite material constructed in this invention has a continuous conductive network, a good interfacial coupling structure, and a microenvironment conducive to mass transfer. It can simultaneously improve electron transport efficiency and ion diffusion rate during capacitive deionization, so that the material achieves a good balance between electroadsorption efficiency, rate performance and cycle stability.

[0027] 5. The preparation method of the present invention has relatively clear steps and a relatively reasonable process route. The composite electrode material can be constructed mainly through nitrogen doping modification of carbon nanotubes, loading of transition metal salt precursors and two-stage heat treatment. The conditions are easy to control and the repeatability is good. While ensuring the material performance, the feasibility of experimental operation and application potential are also taken into account.

[0028] In summary, this invention achieves synergistic optimization of conductive network, functional interface, and structural stability by constructing a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite structure. The resulting material can be used for ion adsorption removal in capacitive deionization processes, effectively improving the material's electroadsorption efficiency, rate performance, and cycle stability during capacitive deionization, and has good application prospects. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation process of a coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material.

[0030] Figure 2This is an electron microscope image of the coal tar pitch coated nickel-based nitrogen-doped carbon nanotube composite electrode material prepared in Example 1.

[0031] Figure 3 This is the nitrogen adsorption isotherm diagram of the coal tar pitch coated nickel-based nitrogen-doped carbon nanotube composite electrode material prepared in Example 1.

[0032] Figure 4 This is an electron microscope image of the coal tar pitch coated nickel-based nitrogen-doped carbon nanotube composite electrode material prepared in Example 2.

[0033] Figure 5 This is the nitrogen adsorption isotherm diagram of the coal tar pitch coated nickel-based nitrogen-doped carbon nanotube composite electrode material prepared in Example 2.

[0034] Figure 6 This is an electron microscope image of the coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material prepared in Example 3.

[0035] Figure 7 This is the nitrogen adsorption isotherm diagram of the coal tar pitch coated nickel-based nitrogen-doped carbon nanotube composite electrode material prepared in Example 3.

[0036] Figure 8 This is a cyclic voltammetry curve of the composite electrode material prepared in Example 1.

[0037] Figure 9 This is a charge-discharge curve of the composite electrode material prepared in Example 1. Detailed Implementation

[0038] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific 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.

[0039] Specific Implementation Method 1: This implementation method provides a method for preparing a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material, the method comprising the following steps:

[0040] S1, nitrogen-doped carbon nanotubes

[0041] Nitrogen-doped carbon nanotubes were obtained by nitrogen doping modification of carbon nanotubes.

[0042] Further, in step S1, the carbon nanotube is one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both; the nitrogen doping modification treatment is one of nitrogen-containing atmosphere treatment, nitrogen-containing precursor introduction treatment, or a combination of both to modify the carbon nanotubes to obtain nitrogen-doped carbon nanotubes.

[0043] When using a nitrogen-containing atmosphere for heat treatment, carbon nanotubes are placed in a tube furnace and heated to 800-1000℃ at a heating rate of 5-15℃ / min under a nitrogen-containing atmosphere, held for 60-120 min, and then naturally cooled to room temperature to obtain nitrogen-doped carbon nanotubes.

[0044] When a nitrogen-containing precursor is introduced, carbon nanotubes are dispersed and mixed with the nitrogen-containing precursor, dried at 60-100℃ for 6-24 h, and then placed in a tube furnace. The temperature is increased to 800-1000℃ at a heating rate of 5-15℃ / min under an inert or protective atmosphere, held for 60-120 min, and then naturally cooled to room temperature to obtain nitrogen-doped carbon nanotubes.

[0045] When combining nitrogen-containing atmosphere heat treatment with the introduction of nitrogen-containing precursors, carbon nanotubes and nitrogen-containing precursors are first dispersed and mixed, and then dried at 60-100℃ for 6-24 h. The resulting precursor is then placed in a tube furnace and heated to 800-1000℃ at a heating rate of 5-15℃ / min under a nitrogen atmosphere, held for 60-120 min, and subsequently cooled naturally to room temperature to obtain nitrogen-doped carbon nanotubes.

[0046] S2, Transition metal component loading

[0047] The nitrogen-doped carbon nanotubes obtained in step S1 are mixed with the transition metal salt precursor and dispersed in a solvent. After sonication, impregnation and drying, the first heat treatment is performed to obtain the transition metal-supported nitrogen-doped carbon nanotube precursor composite material.

[0048] Further, in step S2, the transition metal salt precursor is one or more of the following: iron salt, cobalt salt, manganese salt, copper salt, zinc salt, molybdenum salt, tungsten salt, and nickel salt; preferably, it is a chloride, nitrate, acetate, sulfate, or acetylacetone salt of the corresponding metal.

[0049] Furthermore, the transition metal salt precursor and nitrogen-doped carbon nanotubes are added to a solvent at a mass ratio of transition metal element to nitrogen-doped carbon nanotubes of (0.01-0.30):1. After being sonicated for 10-60 min, impregnated for 12-36 h, and dried at 60-100℃ for 6-24 h, the first stage of heat treatment is carried out.

[0050] Furthermore, the solvent is one or more mixed solvents selected from ethanol, methanol, isopropanol, and deionized water.

[0051] When the above two solvents are used to form a mixed solvent, the volume ratio of the two solvent components is (1-10):(1-10).

[0052] When the above three solvents are used to form a mixed solvent, the volume ratio of the three solvent components is (1-10):(1-10):(1-10).

[0053] When the above four solvents are used to form a mixed solvent, the volume ratio of the four solvent components is (1-10):(1-10):(1-10):(1-10).

[0054] Equal volume mixing is preferred.

[0055] S3, coal tar pitch composite and second-stage heat treatment

[0056] The transition metal-loaded nitrogen-doped carbon nanotube precursor composite material obtained in step S2 is dispersed, mixed and dried with coal tar pitch, followed by a second heat treatment to obtain a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material.

[0057] Further, in step S3, the precursor composite material and coal tar pitch are dispersed, mixed and then dried at a temperature of 50-80℃ for 6-24 h. During the second heat treatment, the coal tar pitch undergoes pyrolysis and carbonization, forming a coal tar pitch-derived carbon layer that coats the transition metal components and the surface of carbon nanotubes.

[0058] Furthermore, both the first and second heat treatments are carried out in an inert or protective atmosphere, with a heat treatment temperature of 500-900℃ and a holding time of 0.5-4 h.

[0059] In this embodiment, nitrogen-doped carbon nanotubes serve as the conductive framework of the composite material, which is beneficial for constructing a continuous electron transport network and ion transport channels. The transition metal component is loaded on the surface of the nitrogen-doped carbon nanotubes, which is beneficial for improving the interfacial charge transport performance of the composite material. The coal tar-derived carbon layer is coated on the surface of the transition metal component and the carbon nanotubes, which is beneficial for enhancing the composite interface bonding and inhibiting the migration, aggregation or detachment of the transition metal component, thereby improving the electroadsorption efficiency, rate performance and cycle stability of the composite electrode material in the capacitor deionization process.

[0060] Specific Implementation Method 2: This implementation method provides a coal tar pitch coated with transition metal nitrogen-doped carbon nanotube composite electrode material prepared by the method described in Specific Implementation Method 1. The composite electrode material includes a carbon nanotube conductive framework, a transition metal component loaded on the surface of the carbon nanotube conductive framework, and a coal tar pitch-derived carbon layer coated on the surfaces of both.

[0061] Specific Implementation Method 3: This implementation method provides an application of the coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material described in Specific Implementation Method 2 in capacitor deionization.

[0062] Specific Implementation Method Four: This implementation method provides a method for preparing a coal tar pitch-coated cobalt-based nitrogen-doped carbon nanotube composite electrode material, the method comprising the following steps:

[0063] S1, nitrogen-doped modification of single-walled carbon nanotubes

[0064] Weigh out single-walled carbon nanotubes and place them in a tube furnace for heat treatment in a nitrogen atmosphere. Heat the tubes to 850°C at a heating rate of 10°C / min, hold for 90 min, and then allow them to cool naturally to room temperature to obtain nitrogen-doped single-walled carbon nanotubes.

[0065] The nitrogen doping modification process described above can introduce nitrogen-containing functional groups and defect sites onto the surface of single-walled carbon nanotubes, improving their surface polarity and wettability, and providing sites for the adsorption and anchoring of subsequent cobalt salt precursors.

[0066] S2, cobalt-based component loading

[0067] The nitrogen-doped single-walled carbon nanotubes obtained in step S1 are mixed with the cobalt salt precursor and dispersed in a mixed solvent composed of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 1:1.

[0068] Further, the cobalt salt precursor is one or a combination of cobalt nitrate, cobalt chloride, cobalt acetate, cobalt sulfate, and cobalt acetylacetonate. The amount of cobalt salt precursor added is controlled according to a mass ratio of cobalt to nitrogen-doped single-walled carbon nanotubes of 0.05:1; after mixing, it is ultrasonically dispersed for 30 min and impregnated at room temperature for 24 h to allow the cobalt salt precursor to be fully adsorbed on the surface of nitrogen-doped single-walled carbon nanotubes.

[0069] After impregnation, the resulting mixture was dried at 80°C for 12 h to obtain a cobalt salt-supported nitrogen-doped single-walled carbon nanotube precursor. The precursor was then placed in a tube furnace and subjected to the first stage of heat treatment under argon atmosphere protection. The heat treatment temperature was 700°C and the holding time was 2 h. After cooling, a cobalt-based nitrogen-doped single-walled carbon nanotube precursor composite material was obtained.

[0070] S3, coal tar coating and second-stage heat treatment

[0071] The cobalt-based nitrogen-doped single-walled carbon nanotube precursor composite material obtained in step S2 was mixed with coal tar pitch dispersion and subjected to ultrasonic or stirring treatment to ensure that the coal tar pitch was uniformly attached to the surface of the precursor composite material. Then, solid-liquid separation was performed and the mixture was dried at 60°C for 12 h to obtain the coal tar pitch / cobalt-based nitrogen-doped single-walled carbon nanotube composite precursor.

[0072] The composite precursor was placed in a tube furnace and subjected to a second heat treatment under an argon atmosphere. The heat treatment temperature was 700℃ and the holding time was 2 h. The material was then naturally cooled to room temperature to obtain a cobalt-based nitrogen-doped carbon nanotube composite electrode material coated with coal tar pitch.

[0073] In this embodiment, single-walled carbon nanotubes possess a high aspect ratio and good electrical conductivity. Nitrogen doping improves their surface activity and interfacial wettability. The introduction of cobalt-based components helps to regulate the local electronic structure and interfacial charge transport behavior of the material. The coal tar-derived carbon layer enhances the bonding stability between the cobalt-based components and the nitrogen-doped single-walled carbon nanotubes. The resulting composite electrode material is suitable for ion adsorption removal in capacitive deionization processes.

[0074] Specific Implementation Method 5: This implementation method provides a method for preparing a coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material, which is prepared using a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes. The method includes the following steps:

[0075] S1, nitrogen-doped modification of composite carbon nanotubes

[0076] Single-walled carbon nanotubes and multi-walled carbon nanotubes are mixed to obtain a composite carbon nanotube matrix; the composite carbon nanotube matrix is ​​then subjected to heat treatment in a nitrogen-containing atmosphere to achieve nitrogen doping modification.

[0077] Preferably, single-walled carbon nanotubes and multi-walled carbon nanotubes are mixed and placed in a tube furnace, heated to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere, held at that temperature for 120 min, and then naturally cooled to room temperature to obtain nitrogen-doped composite carbon nanotubes.

[0078] In this step, single-walled carbon nanotubes are beneficial for improving electrical conductivity, while multi-walled carbon nanotubes are beneficial for constructing a stable one-dimensional framework structure. The combination of the two can form a relatively continuous conductive network and mass transfer channels. Nitrogen doping modification can further improve the surface polarity and defect site distribution of the composite carbon nanotubes.

[0079] S2, composite transition metal component support

[0080] The nitrogen-doped composite carbon nanotubes obtained in step S1 are mixed with a transition metal salt precursor and dispersed in a mixed solvent of methanol and isopropanol. The volume ratio of methanol to isopropanol is 1:1.

[0081] Further, the transition metal salt precursor is one or more of iron salts, manganese salts, copper salts, zinc salts, molybdenum salts, and tungsten salts, preferably chlorides, nitrates, acetates, sulfates, or acetylacetone salts of the corresponding metals. The amount of the transition metal salt precursor added is controlled according to a mass ratio of transition metal element to nitrogen-doped composite carbon nanotubes of 0.10:1; after mixing, it is ultrasonically dispersed for 60 min and impregnated at room temperature for 36 h to ensure that the transition metal salt precursor is fully adsorbed and dispersed on the surface of nitrogen-doped composite carbon nanotubes.

[0082] After impregnation, the resulting mixture was dried at 100℃ for 6 h to obtain a transition metal salt-supported nitrogen-doped composite carbon nanotube precursor. Subsequently, the precursor was placed in a tube furnace and subjected to the first stage of heat treatment under nitrogen atmosphere protection. The heat treatment temperature was 800℃ and the holding time was 1 h. After cooling, the transition metal-supported nitrogen-doped composite carbon nanotube precursor composite material was obtained.

[0083] S3, coal tar pitch composite and carbon coating formation

[0084] The transition metal-supported nitrogen-doped composite carbon nanotube precursor obtained in step S2 was mixed with a coal tar pitch dispersion and subjected to ultrasonic and stirring treatment to ensure that the coal tar pitch was uniformly adhered to the transition metal component and the surface of the nitrogen-doped composite carbon nanotubes. Subsequently, the mixture was subjected to solid-liquid separation and dried at 70°C for 10 h to obtain the coal tar pitch / transition metal-supported nitrogen-doped composite carbon nanotube composite precursor.

[0085] The aforementioned composite precursor was placed in a tube furnace and subjected to a second stage of heat treatment under a nitrogen atmosphere at a temperature of 800℃ for 1 hour. During the heat treatment, the coal tar pitch underwent pyrolysis and carbonization, forming a coal tar pitch-derived carbon layer coating the transition metal components and the surface of the carbon nanotubes. After the heat treatment, the material was naturally cooled to room temperature to obtain a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material.

[0086] In this embodiment, the composite carbon nanotube framework can improve the overall conductivity and structural stability of the material; the transition metal component can form a dispersed functional phase on the surface of nitrogen-doped carbon nanotubes, which is beneficial to improving the interfacial charge transport capability; the coal tar pitch-derived carbon layer can further fix the transition metal component and improve the interfacial bonding strength. The resulting composite electrode material can be used as a capacitor deionization electrode material.

[0087] Specific implementation method six: such as Figure 1 As shown, this embodiment discloses a method for preparing a coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material, the method comprising the following steps:

[0088] S1. Nitrogen-doped modification of carbon nanotubes (preparation of nitrogen-doped carbon nanotubes)

[0089] Nitrogen-doped carbon nanotubes were obtained by nitrogen-doping modification of carbon nanotubes.

[0090] Furthermore, in step S1, the carbon nanotube is a single-walled carbon nanotube, a multi-walled carbon nanotube, or a combination of both; the nitrogen doping modification treatment can be carried out by nitrogen-containing atmosphere heat treatment, nitrogen-containing precursor introduction treatment, or other methods that can achieve nitrogen doping modification.

[0091] Preferably, carbon nanotubes are placed in a tube furnace and heat-treated in a nitrogen-containing atmosphere. The heat treatment temperature range is 800-1000℃, the holding time is 60-120 min, and the heating rate is 5-15℃ / min. Then, the carbon nanotubes are cooled to room temperature to obtain nitrogen-doped carbon nanotubes.

[0092] S2, nickel-based component loading

[0093] The nitrogen-doped carbon nanotubes obtained in step S1 are mixed with the nickel salt precursor and dispersed in an organic solvent. After sonication, impregnation and drying, the first heat treatment is performed to obtain a nickel-based nitrogen-doped carbon nanotube precursor composite material.

[0094] Further, in step S2, the nickel salt precursor is one or more of nickel chloride, nickel nitrate, nickel acetate, and nickel sulfate; the organic solvent is one or more of ethanol, methanol, isopropanol, and deionized water.

[0095] When the above two solvents are used to form a mixed solvent, the volume ratio of the two solvent components is (1-10):(1-10).

[0096] When the above three solvents are used to form a mixed solvent, the volume ratio of the three solvent components is (1-10):(1-10):(1-10).

[0097] When the above four solvents are used to form a mixed solvent, the volume ratio of the four solvent components is (1-10):(1-10):(1-10):(1-10).

[0098] Equal volume mixing is preferred.

[0099] Further, in step S2, the impregnation time is 12-36 h, the drying temperature is 60-100℃, and the drying time is 6-24 h; the temperature range of the first heat treatment is 500-900℃, and the holding time is 60-180 min.

[0100] S3, coal tar composite

[0101] The nickel-based nitrogen-doped carbon nanotube precursor composite material obtained in step S2 is mixed with coal tar pitch dispersion and subjected to ultrasonic and / or stirring treatment to ensure that the coal tar pitch is uniformly attached to the surface of the precursor composite material. After separation and drying, the coal tar pitch / nickel-based nitrogen-doped carbon nanotube composite precursor is obtained.

[0102] Further, in step S3, the precursor composite material and coal tar pitch are subjected to solid-liquid separation and drying after ultrasonic and / or stirring treatment. The drying temperature is 50-80℃ and the drying time is 6-24 h.

[0103] S4, Secondary Heat Treatment

[0104] The composite precursor obtained in step S3 is placed in a tube furnace and subjected to a second heat treatment under an inert or protective atmosphere, followed by cooling to room temperature to obtain a coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material. The resulting material can be used for ion adsorption removal in capacitor deionization processes.

[0105] Furthermore, in step S4, the second heat treatment temperature range is 500-900℃, and the holding time is 60-180 min; during the second heat treatment, coal tar pitch undergoes pyrolysis and forms a carbon coating layer on the surface of the nickel-based component and / or the carbon nanotube surface.

[0106] Example 1:

[0107] This embodiment discloses a method for preparing a coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material, specifically involving a method for preparing a coal tar pitch-coated Ni / Ni3C-loaded nitrogen-doped carbon nanotube composite electrode material, comprising the following steps:

[0108] I. Preparation of Nitrogen-Doped Carbon Nanotubes

[0109] 100 mg of multi-walled carbon nanotubes were weighed and placed in a tube furnace. The furnace was subjected to high-temperature treatment under an ammonia atmosphere, with the temperature increased to 900 °C at a rate of 10 °C / min and held for 90 min. The furnace was then allowed to cool naturally to room temperature to obtain nitrogen-doped multi-walled carbon nanotubes.

[0110] II. Preparation of Nickel Salt Precursor Dispersion

[0111] Weigh 30 mg of nickel chloride hexahydrate, add it to 40 mL of anhydrous ethanol, then add the nitrogen-doped multi-walled carbon nanotubes mentioned above, and sonicate for 20 min to obtain a uniform nickel salt / nitrogen-doped carbon nanotube mixed dispersion.

[0112] III. Impregnation Preparation of Ni / Ni3C Precursor Composites

[0113] The above mixed dispersion was impregnated at room temperature for 24 h to allow the nickel salt precursor to be fully adsorbed onto the surface of nitrogen-doped multi-walled carbon nanotubes. Then it was dried at 80 °C for 12 h to obtain the Ni / Ni3C precursor composite material precursor.

[0114] IV. Heat Treatment Preparation of Ni / Ni3C Precursor Composites

[0115] The dried precursor was placed in a tube furnace and heat-treated at 650 °C for 120 min under N2 atmosphere protection, and then naturally cooled to room temperature to obtain Ni / Ni3C supported nitrogen-doped multi-walled carbon nanotube precursor composite material.

[0116] V. Preparation of Coal Tar Pitch Dispersion

[0117] Weigh 30 mg of coal tar pitch and add it to 40 mL of ethanol. Disperse the mixture under ultrasonic conditions for 20 min to obtain a coal tar pitch dispersion.

[0118] VI. Mixing and Composite Materials of Coal Tar Pitch and Precursor Composites

[0119] The above coal tar pitch dispersion was added to the Ni / Ni3C supported nitrogen-doped multi-walled carbon nanotube precursor composite material suspension system, and ultrasonication was continued for 20 min. The mixture was then stirred at room temperature for 12 h to ensure that the coal tar pitch was uniformly attached to the surface of the precursor composite material, thus obtaining a composite suspension.

[0120] VII. Drying and Preparation of Composite Precursors

[0121] The above composite suspension was separated by vacuum filtration, the resulting solid product was collected, and dried in a vacuum drying oven at 60℃ for 12 h to obtain a coal tar pitch / Ni / Ni3C supported nitrogen-doped multi-walled carbon nanotube composite precursor.

[0122] VIII. Secondary Heat Treatment of Composite Materials

[0123] The composite precursor was placed in a tube furnace and subjected to a second heat treatment at 650°C under N2 atmosphere protection for 120 min, and then naturally cooled to room temperature to obtain a coal tar pitch coated nickel-based nitrogen-doped carbon nanotube composite electrode material.

[0124] As shown in Figure 2, the composite electrode material prepared in Example 1 maintains the one-dimensional conductive network structure formed by the interwoven carbon nanotubes. Granular or coated structures can be observed on the surface of the carbon nanotubes, indicating that the nickel-based component and the coal tar pitch-derived carbon layer can bond with the nitrogen-doped carbon nanotube framework. This structure facilitates the formation of continuous electron transport channels and provides pathways for electrolyte wetting and ion migration.

[0125] As shown in Figure 3, the composite electrode material prepared in Example 1 exhibits significant nitrogen adsorption behavior, with a marked increase in adsorption amount in the higher relative pressure region. This indicates the presence of a certain porous structure and open mass transfer space in the material, which is beneficial for the diffusion and electroadsorption of salt ions during the capacitor deionization process.

[0126] As shown in Figure 8, the cyclic voltammetry curve of the composite electrode material prepared in Example 1 exhibits a relatively obvious capacitance response characteristic and the curve morphology is relatively stable, indicating that the material has good electrochemical reversibility and interfacial charge response capability.

[0127] As shown in Figure 9, the charge-discharge curve of the composite electrode material prepared in Example 1 exhibits good linear charge-discharge characteristics, indicating that the material has good capacitive behavior and reversible energy storage capacity during charge-discharge, which is beneficial for its use as a capacitor deionization electrode material.

[0128] Example 2:

[0129] This embodiment discloses a method for preparing a coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material. Specifically, it relates to a method for preparing a coal tar pitch-coated Ni / Ni3C-loaded nitrogen-doped carbon nanotube composite electrode material using single-walled carbon nanotubes and a nickel nitrate precursor, comprising the following steps:

[0130] I. Preparation of Nitrogen-Doped Carbon Nanotubes

[0131] 100 mg of single-walled carbon nanotubes were weighed and placed in a tube furnace. The furnace was subjected to high-temperature treatment under an ammonia atmosphere, with the temperature increased to 900°C at a rate of 10°C / min and held for 90 min. The furnace was then allowed to cool naturally to room temperature to obtain nitrogen-doped single-walled carbon nanotubes.

[0132] II. Preparation of Nickel Salt Precursor Dispersion

[0133] Weigh 20 mg of nickel nitrate hexahydrate and add it to a mixed solvent of 40 mL of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 1:1. Then add the nitrogen-doped single-walled carbon nanotubes and disperse them under ultrasonic conditions for 20 min to obtain a uniform nickel salt / nitrogen-doped carbon nanotube mixed dispersion.

[0134] III. Impregnation Preparation of Ni / Ni3C Precursor Composites

[0135] The above mixed dispersion was impregnated at room temperature for 24 h to allow the nickel nitrate precursor to be fully adsorbed onto the surface of nitrogen-doped single-walled carbon nanotubes. Then it was dried at 80 °C for 12 h to obtain the Ni / Ni3C precursor composite material precursor.

[0136] IV. Heat Treatment Preparation of Ni / Ni3C Precursor Composites

[0137] The dried precursor was placed in a tube furnace and heat-treated at 650°C for 120 min under an argon atmosphere, and then naturally cooled to room temperature to obtain a Ni / Ni3C supported nitrogen-doped single-walled carbon nanotube precursor composite material.

[0138] V. Preparation of Coal Tar Pitch Dispersion

[0139] Weigh 20 mg of coal tar pitch and add it to 40 mL of ethanol. Disperse the mixture under ultrasonic conditions for 20 min to obtain a coal tar pitch dispersion.

[0140] VI. Mixing and Composite Materials of Coal Tar Pitch and Precursor Composites

[0141] The above coal tar pitch dispersion was added to the Ni / Ni3C supported nitrogen-doped single-walled carbon nanotube precursor composite material suspension system, and ultrasonication was continued for 20 min. The mixture was then stirred at room temperature for 12 h to ensure that the coal tar pitch was uniformly attached to the surface of the precursor composite material, thus obtaining a composite suspension.

[0142] VII. Drying and Preparation of Composite Precursors

[0143] The above composite suspension was separated by vacuum filtration, and the resulting solid product was collected and dried in a vacuum drying oven at 60℃ for 12 h to obtain a coal tar pitch / Ni / Ni3C supported nitrogen-doped single-walled carbon nanotube composite precursor.

[0144] VIII. Secondary Heat Treatment of Composite Materials

[0145] The composite precursor was placed in a tube furnace and subjected to a second heat treatment at 650°C under an argon atmosphere for 120 min. It was then naturally cooled to room temperature to obtain a coal tar pitch-coated Ni / Ni3C-loaded nitrogen-doped carbon nanotube composite electrode material.

[0146] As shown in Figure 4, in the composite electrode material prepared in Example 2, the carbon nanotubes are entangled and interwoven, maintaining a good tubular structure, and granular structures formed by loading or coating can be observed on the surface. This morphology demonstrates that a composite structure with nickel-based component loading and coal tar-derived carbon layer coating can still be formed using single-walled carbon nanotubes and nickel nitrate precursor.

[0147] As shown in Figure 5, the composite electrode material prepared in Example 2 exhibits obvious nitrogen adsorption-desorption characteristics. The adsorption amount gradually increases with increasing relative pressure, with a more significant increase observed in the high relative pressure region, indicating that the material possesses a porous structure suitable for gas adsorption and ion transport. This structure is beneficial for improving the electrolyte contact area and mass transfer efficiency during the capacitor deionization process.

[0148] Example 3:

[0149] This embodiment describes a method for preparing a coal tar pitch-coated nickel-based nitrogen-doped carbon nanotube composite electrode material. Specifically, it involves a method for preparing a coal tar pitch-coated Ni / Ni3C-loaded nitrogen-doped carbon nanotube composite electrode material using a combination of single-walled and multi-walled carbon nanotubes and a composite nickel salt precursor. The method includes the following steps:

[0150] I. Preparation of Nitrogen-Doped Carbon Nanotubes

[0151] 100 mg of single-walled carbon nanotubes and multi-walled carbon nanotubes were weighed out, with a mass ratio of 1:1. The mixture was placed in a tube furnace and subjected to high-temperature treatment under an ammonia atmosphere. The temperature was increased to 900°C at a heating rate of 10°C / min and held for 90 min. The mixture was then allowed to cool naturally to room temperature to obtain nitrogen-doped composite carbon nanotubes.

[0152] II. Preparation of Nickel Salt Precursor Dispersion

[0153] Weigh out 40 mg of nickel acetate and nickel sulfate in a mass ratio of 1:1, add them to a mixed solvent of 40 mL of methanol and isopropanol in a volume ratio of 1:1, then add the nitrogen-doped composite carbon nanotubes, and disperse under ultrasonic conditions for 20 min to obtain a uniform nickel salt / nitrogen-doped carbon nanotube mixed dispersion.

[0154] III. Impregnation Preparation of Ni / Ni3C Precursor Composites

[0155] The above mixed dispersion was impregnated at room temperature for 24 h to allow the composite nickel salt precursor to be fully adsorbed onto the surface of nitrogen-doped composite carbon nanotubes. Then it was dried at 80 °C for 12 h to obtain the Ni / Ni3C precursor composite material precursor.

[0156] IV. Heat Treatment Preparation of Ni / Ni3C Precursor Composites

[0157] The dried precursor was placed in a tube furnace and heat-treated at 650°C for 120 min under a helium atmosphere, and then naturally cooled to room temperature to obtain a Ni / Ni3C supported nitrogen-doped composite carbon nanotube precursor composite material.

[0158] V. Preparation of Coal Tar Pitch Dispersion

[0159] Weigh 40 mg of coal tar pitch and add it to 40 mL of ethanol. Disperse the mixture under ultrasonic conditions for 20 min to obtain a coal tar pitch dispersion.

[0160] VI. Mixing and Composite Materials of Coal Tar Pitch and Precursor Composites

[0161] The above coal tar pitch dispersion was added to the Ni / Ni3C supported nitrogen-doped composite carbon nanotube precursor composite material suspension system, and ultrasonication was continued for 20 min. The mixture was then stirred at room temperature for 12 h to ensure that the coal tar pitch was uniformly attached to the surface of the precursor composite material, thus obtaining the composite suspension.

[0162] VII. Drying and Preparation of Composite Precursors

[0163] The above composite suspension was separated by vacuum filtration, and the resulting solid product was collected and dried in a vacuum drying oven at 60°C for 12 h to obtain a coal tar pitch / Ni / Ni3C supported nitrogen-doped carbon nanotube composite precursor.

[0164] VIII. Secondary Heat Treatment of Composite Materials

[0165] The composite precursor was placed in a tube furnace and subjected to a second heat treatment at 650°C under helium atmosphere protection for 120 min, and then naturally cooled to room temperature to obtain a coal tar pitch coated Ni / Ni3C supported nitrogen-doped carbon nanotube composite electrode material.

[0166] As shown in Figure 6, the composite electrode material prepared in Example 3 exhibits a network structure formed by interwoven carbon nanotubes, with granular or coated components distributed on the surface. This indicates that the composite nickel salt precursor, after heat treatment, can be loaded onto the surface of nitrogen-doped composite carbon nanotubes and together with the coal tar pitch-derived carbon layer to form a composite structure. The combination of single-walled and multi-walled carbon nanotubes is beneficial for improving the connectivity and structural stability of the conductive network.

[0167] As shown in Figure 7, the composite electrode material prepared in Example 3 exhibits significant nitrogen adsorption characteristics, with a rapid increase in adsorption capacity in the high relative pressure region, indicating that the material possesses a relatively abundant pore structure and mass transfer space. This pore structure facilitates the entry of electrolyte into the electrode interior and promotes the diffusion and adsorption of salt ions during the capacitor deionization process.

[0168] Comparative Example 1:

[0169] A method for preparing Ni / Ni3C supported nitrogen-doped carbon nanotube materials includes the following steps:

[0170] I. Preparation of Nitrogen-Doped Carbon Nanotubes

[0171] 100 mg of multi-walled carbon nanotubes were weighed and placed in a tube furnace. The furnace was subjected to high-temperature treatment under an ammonia atmosphere, with the temperature increased to 900 °C at a rate of 10 °C / min and held for 90 min. The furnace was then allowed to cool naturally to room temperature to obtain nitrogen-doped carbon nanotubes.

[0172] II. Preparation of Nickel Salt Precursor Dispersion

[0173] Weigh 30 mg of nickel chloride hexahydrate, add it to 40 mL of anhydrous ethanol, then add the nitrogen-doped carbon nanotubes mentioned above, and disperse under ultrasonic conditions for 20 min to obtain a uniform nickel salt / nitrogen-doped carbon nanotube mixed dispersion.

[0174] III. Impregnation Preparation of Ni / Ni3C Precursor Composites

[0175] The above mixed dispersion was impregnated at room temperature for 24 h to allow the nickel salt precursor to be fully adsorbed onto the surface of nitrogen-doped carbon nanotubes. Then it was dried at 80 °C to obtain the Ni / Ni3C precursor composite material precursor.

[0176] IV. Heat Treatment Preparation of Ni / Ni3C Precursor Composites

[0177] The dried precursor was placed in a tube furnace and heat-treated at 650°C for 120 min under N2 atmosphere protection, and then naturally cooled to room temperature to obtain Ni / Ni3C supported nitrogen-doped carbon nanotube material.

[0178] Compared with Comparative Example 1, Example 1 further introduces coal tar pitch and performs a second heat treatment on the Ni / Ni3C supported nitrogen-doped carbon nanotube precursor composite material. During the heat treatment, the coal tar pitch is transformed into a derived carbon layer coating the nickel-based component and the surface of the nitrogen-doped carbon nanotubes. This coal tar pitch-derived carbon layer enhances the interfacial bonding between the nickel-based component and the nitrogen-doped carbon nanotube framework, inhibits the migration, aggregation, or detachment of the nickel-based component during electrode fabrication and capacitor deionization, and also improves the overall conductivity continuity and structural stability of the composite material.

[0179] Comparative Example 1 did not involve coating with coal tar pitch or a second heat treatment process with coal tar pitch. The resulting material was primarily Ni / Ni3C-loaded nitrogen-doped carbon nanotubes. Due to the lack of interfacial fixation and protection from the coal tar pitch-derived carbon layer, the bonding stability between the nickel-based components and the carbon nanotube framework was relatively weak. This made the active components more prone to exposure, migration, aggregation, or desorption during subsequent electrode use, which was detrimental to the material's cycle stability and capacitive deionization performance.

[0180] Comparative Example 2

[0181] A method for preparing a coal tar pitch-coated Ni / Ni3C supported undoped carbon nanotube composite electrode material includes the following steps:

[0182] I. Pretreatment of Undoped Carbon Nanotubes

[0183] Weigh 100 mg of multi-walled carbon nanotubes and set aside directly without ammonia atmosphere treatment.

[0184] II. Preparation of Nickel Salt Precursor Dispersion

[0185] Weigh 30 mg of nickel chloride hexahydrate, add it to 40 mL of anhydrous ethanol, then add the above-mentioned undoped carbon nanotubes, and disperse under ultrasonic conditions for 20 min to obtain a uniform nickel salt / carbon nanotube mixed dispersion.

[0186] III. Impregnation Preparation of Ni / Ni3C Precursor Composites

[0187] The above mixed dispersion was impregnated at room temperature for 24 h to allow the nickel salt precursor to be adsorbed onto the surface of carbon nanotubes, and then dried at 80 °C to obtain the Ni / Ni3C precursor composite material precursor.

[0188] IV. Heat Treatment Preparation of Ni / Ni3C Precursor Composites

[0189] The dried precursor was placed in a tube furnace and heat-treated at 650°C for 120 min under N2 atmosphere protection, and then naturally cooled to room temperature to obtain Ni / Ni3C supported undoped carbon nanotube precursor composite material.

[0190] V. Preparation of Coal Tar Pitch Dispersion

[0191] Weigh 30 mg of coal tar pitch and add it to 40 mL of ethanol. Disperse the mixture under ultrasonic conditions for 20 min to obtain a coal tar pitch dispersion.

[0192] VI. Mixing and Composite Materials of Coal Tar Pitch and Precursor Composites

[0193] The above coal tar pitch dispersion was added to the Ni / Ni3C supported undoped carbon nanotube precursor composite material suspension system, and ultrasonication was continued for 20 min. The mixture was then stirred at room temperature for 12 h to ensure that the coal tar pitch was uniformly attached to the surface of the precursor composite material, thus obtaining a composite suspension.

[0194] VII. Drying and Preparation of Composite Precursors

[0195] The above composite suspension was separated by vacuum filtration, and the resulting solid product was collected and dried in a vacuum drying oven at 60°C for 12 h to obtain a coal tar pitch / Ni / Ni3C supported undoped carbon nanotube composite precursor.

[0196] VIII. Secondary Heat Treatment of Composite Materials

[0197] The composite precursor was placed in a tube furnace and subjected to a second heat treatment at 650°C under N2 atmosphere protection for 120 min, and then naturally cooled to room temperature to obtain a coal tar pitch coated Ni / Ni3C supported undoped carbon nanotube composite electrode material.

[0198] Compared with Comparative Example 2, Example 2 uses nitrogen-doped single-walled carbon nanotubes as the conductive framework and nickel nitrate as the nickel salt precursor. A mixed solvent of ethanol and deionized water is used for dispersion treatment. Nitrogen doping introduces nitrogen-containing active sites and defect structures onto the carbon nanotube surface, improving the surface polarity, wettability, and adsorption and anchoring ability of the nickel salt precursor. Single-walled carbon nanotubes have good conductive connectivity, which is beneficial for forming effective electron transport channels. The mixed solvent system helps improve the dispersion contact between the nickel salt precursor and the carbon nanotubes. Therefore, the composite electrode material obtained in Example 2 has better overall performance in terms of interfacial bonding, electron transport, and ion mass transfer.

[0199] Comparative Example 2 did not involve nitrogen doping modification of the carbon nanotubes. The undoped carbon nanotubes used had relatively insufficient surface polarity and defect sites, resulting in weak adsorption and anchoring ability for nickel salt precursors. This could easily lead to uneven loading of nickel-based components or unstable interfacial bonding. Furthermore, the surface wettability of the undoped carbon nanotubes was relatively poor, which was not conducive to sufficient electrolyte wetting and rapid migration of salt ions, thus limiting the electroadsorption efficiency, rate performance, and cycle stability of the composite electrode material during capacitive deionization.

[0200] Comparative Example 3:

[0201] A method for preparing a coal tar pitch / Ni / Ni3C supported nitrogen-doped carbon nanotube composite precursor includes the following steps:

[0202] I. Preparation of Nitrogen-Doped Carbon Nanotubes

[0203] 100 mg of multi-walled carbon nanotubes were weighed and placed in a tube furnace. The furnace was subjected to high-temperature treatment under an ammonia atmosphere, with the temperature increased to 900 °C at a rate of 10 °C / min and held for 90 min. The furnace was then allowed to cool naturally to room temperature to obtain nitrogen-doped carbon nanotubes.

[0204] II. Preparation of Nickel Salt Precursor Dispersion

[0205] Weigh 30 mg of nickel chloride hexahydrate, add it to 40 mL of anhydrous ethanol, then add the nitrogen-doped carbon nanotubes mentioned above, and disperse under ultrasonic conditions for 20 min to obtain a uniform nickel salt / nitrogen-doped carbon nanotube mixed dispersion.

[0206] III. Impregnation Preparation of Ni / Ni3C Precursor Composites

[0207] The above mixed dispersion was impregnated at room temperature for 24 h to allow the nickel salt precursor to be fully adsorbed onto the surface of nitrogen-doped carbon nanotubes. Then it was dried at 80 °C to obtain the Ni / Ni3C precursor composite material precursor.

[0208] IV. Heat Treatment Preparation of Ni / Ni3C Precursor Composites

[0209] The dried precursor was placed in a tube furnace and heat-treated at 650°C for 120 min under N2 atmosphere protection, and then naturally cooled to room temperature to obtain Ni / Ni3C supported nitrogen-doped carbon nanotube precursor composite material.

[0210] V. Preparation of Coal Tar Pitch Dispersion

[0211] Weigh 30 mg of coal tar pitch and add it to 40 mL of ethanol. Disperse the mixture under ultrasonic conditions for 20 min to obtain a coal tar pitch dispersion.

[0212] VI. Mixing and Composite Materials of Coal Tar Pitch and Precursor Composites

[0213] The above coal tar pitch dispersion was added to the Ni / Ni3C supported nitrogen-doped carbon nanotube precursor composite material suspension system, and ultrasonication was continued for 20 min. The mixture was then stirred at room temperature for 12 h to ensure that the coal tar pitch was uniformly attached to the surface of the precursor composite material, thus obtaining a composite suspension.

[0214] VII. Drying and Preparation of Composite Precursors

[0215] The above composite suspension was separated by vacuum filtration, and the resulting solid product was collected and dried in a vacuum drying oven at 60°C for 12 h to obtain a coal tar pitch / Ni / Ni3C supported nitrogen-doped carbon nanotube composite precursor.

[0216] Compared with Comparative Example 3, Example 3 further incorporated a second heat treatment on the coal tar pitch / Ni / Ni3C-supported nitrogen-doped carbon nanotube composite precursor. This second heat treatment caused the coal tar pitch to undergo pyrolysis and carbonization, forming a coal tar pitch-derived carbon layer coating the nickel-based component and the surface of the nitrogen-doped composite carbon nanotubes. This second heat treatment not only improved the bonding between the coal tar pitch and the carbon nanotube framework but also transformed the coating layer into a carbon layer with a certain degree of conductivity, thereby improving the electron transport capability, interfacial stability, and structural durability of the composite material.

[0217] Comparative Example 3 only yielded a coal tar pitch / Ni / Ni3C-supported nitrogen-doped carbon nanotube composite precursor, without undergoing a second-stage heat treatment. Due to the incomplete pyrolysis and carbonization of the coal tar pitch, a stable coal tar pitch-derived carbon coating layer was difficult to form. The components in the precursor primarily relied on physical mixing or weak interactions for bonding, resulting in relatively insufficient interfacial stability and conductive continuity. During capacitor deionization, the uncarbonized coal tar pitch and nickel-based components were more prone to structural loosening, interfacial desorption, or transport obstruction, thus hindering the stable performance of the composite electrode material.

Claims

1. A method for preparing a coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material, characterized in that: The method includes the following steps: S1. Nitrogen-doped carbon nanotubes are obtained by modifying carbon nanotubes with nitrogen doping. S2. Mix the nitrogen-doped carbon nanotubes obtained in step S1 with the transition metal salt precursor and perform the first heat treatment to obtain a transition metal-supported nitrogen-doped carbon nanotube precursor composite material. S3. The precursor composite material obtained in step S2 is mixed with coal tar pitch and subjected to a second heat treatment to obtain a coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material.

2. The preparation method according to claim 1, characterized in that: In step S1, the carbon nanotube is one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination of both.

3. The preparation method according to claim 1, characterized in that: In step S1, the nitrogen doping modification treatment is one of the following methods, namely nitrogen atmosphere treatment, nitrogen precursor introduction treatment, or a combination of both, to modify carbon nanotubes to obtain nitrogen-doped carbon nanotubes.

4. The preparation method according to claim 1, characterized in that: In step S2, the transition metal salt precursor is one or more of the following: iron salt, cobalt salt, manganese salt, copper salt, zinc salt, molybdenum salt, tungsten salt, and nickel salt.

5. The preparation method according to claim 1, characterized in that: In step S2, the transition metal salt precursor and nitrogen-doped carbon nanotubes are dispersed in an organic solvent at a mass ratio of transition metal element to nitrogen-doped carbon nanotubes of (0.01-0.30):

1. After being sonicated for 10-60 min, impregnated for 12-36 h, and dried at 60-100℃ for 6-24 h, the first heat treatment is carried out.

6. The preparation method according to claim 5, characterized in that: The organic solvent is one or more of the following: ethanol, methanol, isopropanol, and deionized water.

7. The preparation method according to claim 5, characterized in that: In step S3, the precursor composite material and coal tar pitch are dispersed, mixed and dried and then subjected to a second heat treatment. During the heat treatment, the coal tar pitch forms a coal tar pitch-derived carbon layer that coats the transition metal components and the surface of carbon nanotubes.

8. The preparation method according to claim 7, characterized in that: Both the first and second heat treatments are carried out in an inert or protective atmosphere, with a heat treatment temperature of 500-900℃ and a holding time of 0.5-4 h.

9. A coal tar pitch-coated transition metal nitrogen-doped carbon nanotube composite electrode material prepared by the method according to any one of claims 1 to 8, characterized in that: The composite electrode material includes a carbon nanotube conductive framework, a transition metal component loaded on the surface of the carbon nanotube conductive framework, and a coal tar pitch-derived carbon layer coating the surfaces of both.

10. The application of the coal tar pitch coated transition metal nitrogen-doped carbon nanotube composite electrode material as described in claim 9 in capacitor deionization.

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