Multistage carbon composite material, method for manufacturing the same, negative electrode current collector, battery, and electric device

Abstract

The application discloses a multistage carbon composite material and a preparation method thereof, a negative electrode current collector, a battery and an electric device. The multistage carbon composite material comprises: a primary carbon material and a secondary material, the secondary material is attached to the surface of the primary carbon material, and the secondary material is a secondary carbon material or a secondary transition metal oxide material; and a sodium-affinitive metal, which is arranged on the surface and / or inside of the primary carbon material. The multistage structure of the application can provide a fast transmission channel for sodium ions and provide free space to ensure the integrity of the electrode in the cycle process and the good electrical contact between the active material and the current collector. Meanwhile, the specific surface area of the composite material is increased, thereby the local current density on the carbon material can be reduced, and the volume expansion of sodium metal in the continuous charging and discharging process is alleviated, so as to inhibit the growth of sodium dendrites. In addition, the sodium-affinitive metal can reduce the sodium nucleation barrier and provide uniform active positions for the deposition of metal sodium, thereby further inhibiting the formation of sodium dendrites.

Description

Technical Field

[0001] This application belongs to the field of alkali metal battery technology, specifically relating to a multi-level carbon composite material and its preparation method, a negative electrode current collector, a battery, and an electrical device. Background Technology

[0002] With increasing market demand for longer battery discharge times, the development of high-energy-density alkali metal battery technology has attracted significant attention. Lithium / sodium metal batteries consist of a lithium / sodium metal anode, cathode, electrolyte, and separator, while electrodeless batteries are a new type of battery improved upon conventional lithium / sodium metal batteries. An electrodeless battery refers to a battery in which the current collector is used directly as the nominal anode during battery production, along with the cathode and electrolyte. Compared to conventional lithium / sodium-ion batteries, alkali metal batteries use less electrode material, have higher energy density, and offer advantages in raw material cost. Based on these characteristics, alkali metal batteries are expected to be widely used in large-scale energy storage systems, distributed home energy storage, and new energy vehicles in the future.

[0003] In existing technologies, traditional metal foil is generally used as the current collector. However, the specific surface area of ​​traditional metal foil current collectors is limited, which cannot reduce the current density on the electrode surface or alleviate the volume expansion during sodium deposition, leading to the disordered growth of sodium dendrites and the generation of inactive sodium. At the same time, existing alkali metal batteries suffer from problems such as low coulombic efficiency and low cycle stability, hindering their practical application. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art. Therefore, the purpose of this application is to provide a multi-level carbon composite material and its preparation method, a negative electrode current collector, a battery, and an electrical device.

[0005] In one aspect of this application, a multi-level carbon composite material is proposed. According to an embodiment of this application, the multi-level carbon composite material comprises:

[0006] A primary carbon material and a secondary material, wherein the secondary material is attached to at least a portion of the surface of the primary carbon material, and the secondary material is a secondary carbon material or a secondary transition metal oxide material;

[0007] Sodium-loving metal, wherein the sodium-loving metal is disposed on the surface and / or inside the primary carbon material.

[0008] The multi-level carbon composite material according to embodiments of this application includes a primary carbon material and a secondary material. The secondary material is attached to the surface of the primary carbon material, forming a multi-level structure. This structure provides a rapid transport channel for sodium ions and free space to ensure the integrity of the electrode during cycling and good electrical contact between the active material and the current collector. Simultaneously, the secondary material on the surface of the primary carbon material further increases the specific surface area of ​​the material, thereby reducing the local current density on the carbon material and mitigating the volume expansion of sodium metal during continuous charge and discharge, thus suppressing the growth of sodium dendrites. Furthermore, the sodium-loving metal can lower the sodium nucleation barrier and reduce the nucleation overpotential, providing uniform active sites for sodium metal deposition, thereby further suppressing the formation of sodium dendrites. Therefore, the initial coulombic efficiency, cycle stability, and capacity retention of batteries using the aforementioned multi-level carbon composite material as the current collector can be effectively improved.

[0009] In addition, the multi-level carbon composite material according to the above embodiments of this application may also have the following additional technical features:

[0010] In some embodiments of this application, the primary carbon material includes carbon fibers ranging from nanometer to micrometer scale; and / or, the secondary carbon material includes carbon nanotubes.

[0011] In some embodiments of this application, the diameter of the carbon fiber is 100 nm to 600 nm; and / or, the diameter of the carbon nanotube is 5 nm to 30 nm.

[0012] In some embodiments of this application, the secondary transition metal oxide material includes transition metal oxide nanosheets.

[0013] In some embodiments of this application, the particle size of the transition metal oxide nanosheets is 30 nm to 80 nm; and / or, the transition metal oxide nanosheets include at least one of nickel oxide nanosheets, copper oxide nanosheets, iron oxide nanosheets, and tungsten oxide nanosheets.

[0014] In some embodiments of this application, the sodium-loving metal includes at least one of nickel, zinc, iron, cobalt, and manganese.

[0015] In some embodiments of this application, the mass of the primary carbon material accounts for 45% to 82% of the total mass of the multi-level carbon composite material; and / or, the mass of the secondary material accounts for 10% to 42% of the total mass of the multi-level carbon composite material; and / or, the mass of the sodium-loving metal accounts for 2% to 15% of the total mass of the multi-level carbon composite material.

[0016] In some embodiments of this application, oxygen-containing functional groups are also included, which are doped into the primary carbon material.

[0017] In some embodiments of this application, the oxygen-containing functional group accounts for 0.1% to 2% of the total mass of the multi-level carbon composite material; and / or, the oxygen-containing functional group includes at least one of hydroxyl, carboxyl, carbonyl, nitro, phosphate, and sulfonic acid groups.

[0018] In some embodiments of this application, the specific surface area of ​​the multi-level carbon composite material is 13 m². 2 / g~25m 2 / g.

[0019] In some embodiments of this application, the sodium-loving metal is also disposed on at least a portion of the surface of the secondary material.

[0020] In some embodiments of this application, the primary carbon material is a porous carbon framework.

[0021] In a second aspect, this application proposes a method for preparing the aforementioned multi-level carbon composite material. According to an embodiment of this application, the method includes:

[0022] Preparation of precursor framework materials comprising metal-organic framework materials and carbon-containing polymers;

[0023] The precursor skeleton material is treated with a reducing gas containing carbon chains to obtain a multi-level carbon composite material.

[0024] Alternatively, the precursor framework material can be reacted with a transition metal salt solution to obtain an intermediate material; the intermediate material can then be carbonized and grown under a protective atmosphere to obtain a multi-level carbon composite material.

[0025] According to the method for preparing a multi-level carbon composite material according to embodiments of this application, the multi-level carbon composite material obtained by this method includes a primary carbon material and a secondary material. The secondary material is attached to the surface of the primary carbon material to form a multi-level structure, which can provide a rapid transport channel for sodium ions and provide free space to ensure the integrity of the electrode during cycling and good electrical contact between the active material and the current collector. Simultaneously, the secondary material on the surface of the primary carbon material further increases the specific surface area of ​​the material, thereby reducing the local current density on the carbon material and mitigating the volume expansion of sodium metal during continuous charge and discharge, thus inhibiting the growth of sodium dendrites. Furthermore, the sodium-loving metal can lower the sodium nucleation barrier and reduce the nucleation overpotential, providing uniform active sites for sodium metal deposition, thereby further inhibiting the formation of sodium dendrites. Therefore, the initial coulombic efficiency, cycle stability, and capacity retention of batteries using the above-mentioned multi-level carbon composite material as the current collector can be effectively improved.

[0026] In addition, the method for preparing the above-described multi-level carbon composite material according to the above embodiments of this application may also have the following additional technical features:

[0027] In some embodiments of this application, the preparation of the precursor framework material comprising a metal-organic framework material and a carbon-containing polymer includes: mixing the metal-organic framework material, the carbon-containing polymer, and an organic solvent to obtain a precursor solution; and electrospinning the precursor solution to obtain the precursor framework material.

[0028] In some embodiments of this application, the mass ratio of the carbon-containing polymer to the metal-organic framework material is 8:(1-5); and / or, the carbon-containing polymer includes at least one of polyacrylonitrile, polyvinylpyrrolidone, polyimide, and polyvinylidene fluoride.

[0029] And / or, the inner diameter of the spinneret in the electrospinning is 0.5mm to 0.8mm, the voltage of the electrospinning is 15kV to 25kV, the distance between the spinneret and the receiving device is 12cm to 18cm, and the speed of the electrospinning is 0.5mL H. -1 ~0.9mL H -1 ;

[0030] And / or, the preparation method of the metal-organic framework material includes: mixing an organic ligand solution and a sodium-loving metal salt solution, separating the solid and liquid phases, and drying to obtain the metal-organic framework material.

[0031] In some embodiments of this application, the molar ratio of the organic ligand to the sodium-loving metal salt is (60-80):1; and / or, the organic ligand includes at least one of imidazole compounds, triazole compounds, and terephthalic acid; and / or, the sodium-loving metal salt includes at least one of zinc nitrate, nickel nitrate, iron nitrate, cobalt nitrate, and manganese nitrate.

[0032] In some embodiments of this application, the precursor skeleton material is treated with a reducing gas containing carbon chains at a temperature of 700°C to 1000°C for a time of 10 min to 60 min; and / or, the reducing gas containing carbon chains includes at least one of ethanol, methane, and acetylene.

[0033] And / or, before treating the precursor framework material with the reducing gas containing the carbon chain, the method further includes: subjecting the precursor framework material to a first pre-oxidation;

[0034] And / or, the reaction temperature of the precursor framework material with the transition metal salt solution is 120℃~200℃, and the reaction time is 0.5h~5h; and / or, the transition metal salt includes at least one of nickel nitrate, copper nitrate, iron nitrate and tungsten nitrate; and / or, the concentration of the transition metal salt solution is 0.5mol / L~1mol / L;

[0035] And / or, the intermediate material is carbonized at a temperature of 400℃ to 1200℃ for a reaction time of 0.5h to 2h;

[0036] And / or, prior to carbonization growth of the intermediate material, the process further includes: a second pre-oxidation of the intermediate material.

[0037] In some embodiments of this application, the temperatures of the first pre-oxidation and the second pre-oxidation are 200°C to 250°C, and the times of the first pre-oxidation and the second pre-oxidation are 0.5h to 1.5h, respectively.

[0038] In a third aspect, this application proposes a negative electrode current collector. According to embodiments of this application, the negative electrode current collector comprises the multi-level carbon composite material of the above embodiments or the multi-level carbon composite material prepared by the methods of the above embodiments. That is, the multi-level carbon composite material can be directly used as a negative electrode current collector. Thus, this negative electrode current collector is a three-dimensional current collector. On the one hand, by constructing abundant charge centers to uniformly distribute the electric field and charge on the electrode surface, it reduces the tip curvature of the initial structural protrusions formed during the initial deposition of sodium metal, which is beneficial for planar deposition of sodium metal and the elimination of tip enrichment. On the other hand, the three-dimensional current collector with a high specific surface area can reduce the local current density on the carbon material, alleviate the sodium ion consumption rate per unit area of ​​the three-dimensional negative current collector, reduce concentration polarization, and thus inhibit the growth of sodium dendrites. Simultaneously, this multi-level carbon current collector with sodium-loving sites has a low nucleation overpotential, which can reduce the nucleation barrier and regulate the initial nucleation behavior of sodium. By optimizing the nucleation process of sodium metal, the formation of sodium dendrites can be reduced. Finally, the structural design of the three-dimensional current collector can limit the volume expansion of sodium metal during charging and discharging. By providing sufficient space for the sodium metal, this three-dimensional current collector can reduce internal stress caused by volume expansion, thereby suppressing the growth of lithium dendrites.

[0039] In a fourth aspect, this application proposes a battery. According to an embodiment of this application, the battery includes the negative electrode current collector described in the above embodiments. This effectively improves the battery's initial coulombic efficiency, cycle stability, and capacity retention.

[0040] In a fifth aspect, this application proposes an electrical device. According to an embodiment of this application, the electrical device includes the battery described in the above embodiments. Therefore, the electrical device possesses all the advantages of a battery, which will not be elaborated further here.

[0041] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0042] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0043] Figure 1 XRD patterns of the materials prepared in Example 1 and Comparative Example 1 of this application;

[0044] Figure 2 This is a TEM image of CF@Ni@CNTs in Embodiment 1 of this application;

[0045] Figure 3 This is a display image of the CF@Ni@CNTs prepared in Example 1 after being folded 180°.

[0046] Figure 4 This is a cycle comparison diagram of the button cells of Example 1 and Comparative Example 1. Detailed Implementation

[0047] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0048] In one aspect of this application, a multi-level carbon composite material is proposed. According to an embodiment of this application, the multi-level carbon composite material includes: a primary carbon material and a secondary material, wherein the secondary material is attached to the surface of the primary carbon material, and the secondary material is a secondary carbon material or a secondary transition metal oxide material; a sodium-loving metal, wherein the sodium-loving metal is disposed on the surface of the primary carbon material, or the sodium-loving metal is doped into the interior and surface of the primary carbon material.

[0049] The principle by which the multi-level carbon composite material proposed in this application achieves the above-mentioned beneficial effects will be explained in detail below:

[0050] This application presents a multi-level carbon composite material comprising a primary carbon material and a secondary material. The primary carbon material is a porous carbon framework, while the secondary material is attached to the surface of the primary carbon material, forming a multi-level structure. This structure provides a rapid transport channel for sodium ions and offers free space to ensure the integrity of the electrode during cycling and good electrical contact between the active material and the current collector. Simultaneously, the secondary material on the surface of the primary carbon material further increases the specific surface area of ​​the material, thereby reducing the local current density on the carbon material and mitigating the volume expansion of sodium metal during continuous charge and discharge, thus inhibiting the growth of sodium dendrites. Furthermore, the sodium-loving metal in the composite material lowers the sodium nucleation barrier and reduces the nucleation overpotential, providing uniform active sites for sodium deposition, further suppressing sodium dendrite formation. Therefore, the initial coulombic efficiency, cycle stability, and capacity retention of batteries using the aforementioned multi-level carbon composite material as the current collector can be effectively improved.

[0051] When the multi-level carbon composite material proposed in this application is used in a three-dimensional current collector, on the one hand, it can reduce the tip curvature of the initial structural protrusions formed by sodium metal deposition by constructing abundant charge centers to uniformly distribute the electric field and charge on the electrode surface, thus facilitating planar deposition of sodium metal and eliminating tip enrichment. On the other hand, the three-dimensional current collector with a high specific surface area can reduce the local current density on the carbon material, alleviate the sodium ion consumption rate per unit area of ​​the three-dimensional negative current collector, reduce concentration polarization, and thus inhibit the growth of sodium dendrites. Simultaneously, this multi-level carbon current collector with sodium-loving sites has a low nucleation overpotential, which can lower the nucleation barrier and regulate the initial nucleation behavior of sodium. By optimizing the nucleation process of sodium metal, the formation of sodium dendrites can be reduced. Finally, the structural design of the three-dimensional current collector can limit the volume expansion of sodium metal during charging and discharging. By providing sufficient space for sodium metal, this three-dimensional current collector can reduce the internal stress caused by volume expansion, thereby inhibiting the growth of sodium dendrites.

[0052] According to some specific embodiments of this application, the secondary material is a secondary carbon material. The secondary carbon material is attached to the surface of the primary carbon material, forming a multi-level carbon structure. This provides a rapid transport channel for sodium ions and provides free space to ensure the integrity of the electrode during cycling and good electrical contact between the active material and the current collector. Simultaneously, the secondary carbon material on the surface of the primary carbon material further increases the specific surface area of ​​the material, thereby reducing the local current density on the carbon material and mitigating the volume expansion of sodium metal during continuous charging and discharging, thus inhibiting the growth of sodium dendrites.

[0053] According to some further embodiments of this application, the primary carbon material includes carbon fibers ranging from nanometer to micrometer scale, and the secondary carbon material includes at least one of carbon nanotubes and nanosheets, thereby forming a multi-level carbon composite material.

[0054] According to some specific embodiments of this application, the diameter of the carbon nanotubes is 10nm to 30nm (examples include 10nm, 15nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, etc.). The resulting hierarchical carbon structure can provide a rapid transport channel for sodium ions, while further increasing the specific surface area of ​​the material. This can further reduce the local current density on the carbon material and alleviate the volume expansion of sodium metal during continuous charging and discharging, thereby inhibiting the growth of sodium dendrites.

[0055] In the embodiments of this application, the diameter of carbon nanotubes can be tested using a scanning electron microscope (SEM).

[0056] As some preferred options, the primary carbon material is carbon nanofibers (CNF), and the secondary material is carbon nanotubes (CNTs). Carbon nanotubes (CNTs) are attached to the surface of carbon nanofibers (CNF), and sodium-loving metals are doped into the interior and surface of the carbon nanofibers (CNF), forming a multi-level carbon composite material. This multi-level carbon composite material, when used for three-dimensional current collectors, has the following advantages: 1) Carbon nanofibers have many pores that can be used for rapid ion and electron transport, serving as stable hosts for sodium metal; 2) The combination of carbon nanofibers (CNF) and carbon nanotubes (CNTs) achieves high conductivity and a multi-level structure, with sufficient space to accommodate the volume expansion of sodium metal; 3) Introducing sodium-loving metal nanoparticles onto carbon nanofibers provides a stable sodium-loving surface, resulting in more uniform sodium metal nucleation and deposition along the carbon nanofiber surface; 4) Carbon nanotubes (CNTs) effectively redistribute the sodium metal ion flux, thereby reducing the local current density on each carbon fiber, further suppressing uneven sodium deposition on the fiber, and delaying the formation of sodium metal dendrites.

[0057] According to some specific embodiments of this application, the diameter of the carbon nanofibers is 100nm to 600nm, for example, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, etc.; further, the diameter of the carbon nanotubes is 5nm to 30nm, for example, 5nm, 10nm, 15nm, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, etc. The resulting multi-level carbon structure can provide a rapid transport channel for sodium ions, while further increasing the specific surface area of ​​the material, thereby further reducing the local current density on the carbon material and alleviating the volume expansion of sodium metal during continuous charging and discharging, thus inhibiting the growth of sodium dendrites.

[0058] In the embodiments of this application, the diameter of carbon nanofibers can be tested using scanning electron microscopy (SEM).

[0059] According to some specific embodiments of this application, the secondary material is a secondary transition metal oxide material, which includes transition metal oxide nanosheets. These nanosheets are attached to the surface of the primary carbon material, forming a multi-level structure. This provides a rapid transport channel for sodium ions and free space to ensure the integrity of the electrode during cycling and good electrical contact between the active material and the current collector. Simultaneously, the transition metal oxide nanosheets on the surface of the primary carbon material further increase the specific surface area of ​​the material, thereby reducing the local current density on the carbon material and mitigating the volume expansion of sodium metal during continuous charging and discharging, thus inhibiting the growth of sodium dendrites.

[0060] According to some specific embodiments of this application, the particle size of the transition metal oxide nanosheets is 30 nm to 80 nm (examples include 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, etc.). The resulting hierarchical structure can provide a rapid transport channel for sodium ions, while further increasing the specific surface area of ​​the material.

[0061] In the embodiments of this application, scanning electron microscopy (SEM) can be used to test the particle size of transition metal oxide nanosheets. Particle size refers to the equivalent diameter of the fan-shaped nanosheets.

[0062] In the embodiments of this application, the specific types of transition metal oxide nanosheets are not particularly limited. As some preferred options, the transition metal oxide nanosheets include at least one of nickel oxide nanosheets, copper oxide nanosheets, iron oxide nanosheets, and tungsten oxide nanosheets.

[0063] In the embodiments of this application, the specific type of the sodium-loving metal is not particularly limited, and those skilled in the art can select it according to actual needs. As some preferred embodiments, the sodium-loving metal includes at least one of nickel, zinc, iron, cobalt, and manganese, which can reduce the sodium nucleation barrier, provide uniform active sites for sodium deposition, and further suppress the formation of sodium dendrites. Meanwhile, the particle size of the sodium-loving metal is at the nanometer level.

[0064] It should be noted that the aforementioned sodium-loving metal can also be disposed on at least a portion of the surface of the secondary material.

[0065] According to further specific embodiments of this application, the mass of the primary carbon material accounts for 45% to 82% of the total mass of the multi-level carbon composite material (examples include 45%, 50%, 55%, 60%, 65%, 70%, 75%, 82%, etc.); and / or, the mass of the secondary material accounts for 10% to 42% of the total mass of the multi-level carbon composite material (examples include 10%, 15%, 20%, 25%, 30%, 35%, 42%, etc.); and / or, the mass of the sodium-loving metal accounts for 2% to 15% of the total mass of the multi-level carbon composite material (examples include 2%, 4%, 6%, 8%, 10%, 12%, 15%, etc.). This further provides a rapid transport channel for sodium ions, while further increasing the specific surface area of ​​the material, thereby further reducing the local current density on the carbon material and mitigating the volume expansion of sodium metal during continuous charging and discharging, thus inhibiting the growth of sodium dendrites. At the same time, it can further reduce the sodium nucleation barrier, providing uniform active sites for sodium deposition, thereby further inhibiting the formation of sodium dendrites.

[0066] In the embodiments of this application, thermogravimetric analysis (TGA) can be used to test the mass percentage of primary carbon materials in multi-level carbon composite materials, and thermogravimetric analysis (TGA) can be used to test the mass percentage of secondary materials in multi-level carbon composite materials.

[0067] According to some specific embodiments of this application, the above-mentioned multi-level carbon composite material further includes oxygen-containing functional groups, which are doped into the primary carbon material. These oxygen-containing functional groups can effectively ensure the flexibility of the multi-level carbon composite material.

[0068] According to some specific embodiments of this application, the mass of the oxygen-containing functional groups accounts for 0.1% to 2% of the total mass of the multi-level carbon composite material. Examples include 0.1%, 0.3%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 2%, etc., thereby further ensuring the flexibility of the multi-level carbon composite material.

[0069] In the embodiments of this application, potentiometric titration can be used to test the mass percentage of oxygen-containing functional groups in multi-level carbon composite materials.

[0070] In the embodiments of this application, the specific types of oxygen-containing functional groups are not particularly limited. Those skilled in the art can select them according to actual needs. As some preferred embodiments, the oxygen-containing functional groups include at least one of hydroxyl, carboxyl, carbonyl, nitro, phosphate, and sulfonic acid groups, thereby further ensuring the flexibility of the multi-level carbon composite material.

[0071] According to some specific embodiments of this application, the specific surface area of ​​the multi-level carbon composite material is 13 m². 2 / g~25m 2 / g, thus, multi-level carbon composite materials with high specific surface area can reduce the local current density on carbon materials, alleviate the sodium ion consumption rate per unit area of ​​the three-dimensional negative current collector, reduce concentration polarization, and thus inhibit the growth of sodium dendrites.

[0072] In a second aspect, this application proposes a method for preparing the aforementioned multi-level carbon composite material. According to an embodiment of this application, the method includes:

[0073] S100: Preparation of precursor framework materials containing metal-organic framework materials and carbon-containing polymers;

[0074] According to some specific embodiments of this application, step S100 includes the following steps:

[0075] S110: Mix metal-organic framework materials, carbon-containing polymers and organic solvents to obtain a precursor solution;

[0076] In this step, the metal-organic framework material, carbon-containing polymer and organic solvent are mixed and then vigorously stirred at 50℃~70℃ for 1h~3h. Then the precursor solution is stirred at room temperature for 8h~20h until the metal-organic framework material and carbon-containing polymer are completely dissolved to form the precursor solution.

[0077] According to some specific embodiments of this application, the mass ratio of carbon-containing polymer to metal-organic framework material is 8:(1-5), for example, it can be 8:1, 8:2, 8:3, 8:4, 8:5, etc., thereby ensuring that the carbon-containing polymer encapsulates the metal-organic framework material, which is beneficial to the electrospinning of subsequent steps.

[0078] In the embodiments of this application, the specific types of carbon-containing polymers are not particularly limited, and those skilled in the art can select them according to actual needs. As some preferred embodiments, the carbon-containing polymers include at least one of polyacrylonitrile, polyvinylpyrrolidone, polyimide and polyvinylidene fluoride, more preferably polyacrylonitrile.

[0079] S120: Electrospinning the precursor solution to obtain the precursor material;

[0080] In this step, a spinneret (e.g., a syringe) can be used to electrospin the precursor solution onto a receiving device (e.g., an aluminum plate) under a certain voltage. After electrospinning, the thin film on the receiving device is collected to obtain the precursor material. Electrospinning is a processing technology that uses an electric field to stretch a polymer solution into ultrafine fibers. It is simple, efficient, and has adjustable strength.

[0081] According to some specific embodiments of this application, the inner diameter of the spinneret in electrospinning is 0.5mm to 0.8mm, the voltage of electrospinning is 15kV to 25kV, the distance between the spinneret and the receiving device is 12cm to 18cm, and the speed of electrospinning is 0.5mL H. -1 ~0.9mL H -1 The diameter and length of nanofiber materials can be effectively adjusted by regulating the inner diameter of the spinneret, voltage, distance, and spinning speed in electrospinning.

[0082] According to some specific embodiments of this application, the preparation method of the above-mentioned metal-organic framework material includes:

[0083] The organic ligand solution and the sodium-loving metal salt solution were mixed, separated into solid and liquid phases, and dried to obtain the metal-organic framework material.

[0084] In this step, the organic ligand is first dissolved in deionized water to form solution A, while the sodium-loving metal salt is dissolved in deionized water to form solution B. Solution A and solution B are then mixed and stirred for a certain period. The metal ions and organic ligands are linked by coordination bonds to form a porous material. Subsequently, centrifugation and drying yield a metal-organic framework structure. This metal-organic framework structure exhibits high customizability and functionality, as well as tunable pore structure and chemical composition. It should be noted that the organic ligand will form porous carbon fibers in the subsequent step S200; therefore, the addition of the organic ligand can control the pore structure of the carbon fibers.

[0085] According to some specific embodiments of this application, the molar ratio of the organic ligand to the sodium-loving metal salt is (60-80):1, for example, it can be 60:1, 65:1, 70:1, 75:1, 80:1, etc., thereby ensuring that the metal ions and the organic ligand are connected by coordination bonds to form a porous material.

[0086] In the embodiments of this application, the specific types of the organic ligands are not particularly limited, and those skilled in the art can select them according to actual needs. As some preferred embodiments, the organic ligands include at least one of imidazole compounds, triazole compounds, and terephthalic acid. Further, the imidazole compounds include at least one of 2-methylimidazole, 1-methylimidazole, 4-methylimidazole, 1,2-dimethylimidazole, and 1-ethylimidazole.

[0087] In the embodiments of this application, the specific types of the sodium-loving metal salts are not particularly limited, and those skilled in the art can select them according to actual needs. As some preferred embodiments, the sodium-loving metal salts include at least one of zinc nitrate, nickel nitrate, iron nitrate, cobalt nitrate, and manganese nitrate.

[0088] S200: The precursor skeleton material is treated with a reducing gas containing carbon chains to obtain a multi-level carbon composite material.

[0089] In this step, a reducing gas containing carbon chains is used to treat the precursor framework material, resulting in a multi-level carbon composite material with secondary carbon materials attached to the surface of primary carbon materials. Specifically, the reducing gas containing carbon chains is used as both a reducing agent and a carbon source. This reducing gas first reduces the metal salts in the metal-organic framework structure to elemental metals, and then the nano-metal particles catalyze the growth of carbon nanotubes from the reducing gas containing carbon chains, a process belonging to vapor deposition. Simultaneously, organic ligands and carbon-containing polymers form porous carbon nanofibers, with carbon nanotubes attached to the surface of these porous carbon nanofibers. Sodium-loving metals are doped into the interior and surface of the carbon nanofibers, ultimately forming a multi-level carbon nanofiber composite material. Specifically, the precursor framework material can be placed in a sealed tube furnace, and the intermediate material can be catalytically grown in an atmosphere of reducing gas containing carbon chains.

[0090] According to some specific embodiments of this application, the temperature for catalytic growth of the precursor framework material using a carbon-chain-containing reducing gas is 700℃~1000℃ (e.g., 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc.), and the time is 10min~60min (e.g., 10min, 20min, 30min, 40min, 50min, 60min, etc.). This further ensures that the reducing gas first reduces the metal salt in the metal-organic framework structure to elemental metal, and then the nano-metal particles catalyze the growth of the carbon-chain-containing reducing gas into carbon nanotubes. Simultaneously, it avoids poor flexibility caused by excessively high catalytic growth temperatures. The inventors have discovered that controlling the growth temperature during catalytic growth can regulate the toughness of multi-level carbon materials; the lower the catalytic temperature, the stronger the toughness, i.e., the better the flexibility; conversely, the higher the catalytic temperature, the lower the toughness and the weaker the flexibility.

[0091] In the embodiments of this application, the specific types of carbon-chain-containing reducing gases are not particularly limited. Those skilled in the art can select them according to actual needs. As some preferred embodiments, carbon-chain-containing reducing gases include at least one of ethanol, methane, and acetylene.

[0092] Before treating the precursor framework material with the reducing gas containing the carbon chain, the following steps are also included:

[0093] The precursor material undergoes a first pre-oxidation;

[0094] In this step, the precursor material can be placed in a muffle furnace to perform a first pre-oxidation on the precursor material to oxidize the organic groups in the precursor material, thereby obtaining nanofibers with exposed metal nanoparticles. Then, in step S200, the material is treated with a reducing gas containing carbon chains to obtain a multi-level carbon composite material.

[0095] According to some specific embodiments of this application, the temperature of the first pre-oxidation is 200°C to 250°C (examples include 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, etc.), and the time of the first pre-oxidation is 0.5h to 1.5h (examples include 0.5h, 0.7h, 0.9h, 1h, 1.1h, 1.3h, 1.5h, etc.), thereby further ensuring the oxidation of organic groups in the precursor material.

[0096] The method for preparing hierarchical carbon composite materials according to embodiments of this application combines electrospinning and vapor deposition methods. By changing the type and content of metal ions in the solution, a three-dimensional hierarchical carbon composite material with high specific surface area and strong sodium affinity is obtained. Compared with traditional chemical synthesis methods, this method has the advantage of precisely controlling the length and diameter of carbon nanowires, which is beneficial for studying the influence of certain specific factors on the deposition / dissolution of sodium metal ions. When used as a current collector, the hierarchical carbon composite material prepared by this method has adjustable thickness and light weight, making it suitable for dendrite-free sodium metal batteries to increase their mass and volumetric energy density. This method can also obtain nanofibers filled with different metal particles by changing the metal ions in the electrospinning solution. Combined with the surface nucleation and diffusion model mechanism, the nucleation and growth of sodium metal dendrites can be suppressed, further improving the initial coulombic efficiency, cycle stability, and capacity retention of sodium metal batteries.

[0097] Alternatively, S200': react the precursor framework material with a transition metal salt solution to obtain an intermediate material;

[0098] In this step, the precursor framework material is reacted with a transition metal salt solution to form a transition metal hydroxide on the precursor framework material, thus obtaining an intermediate material.

[0099] As some specific embodiments, the precursor framework material is immersed in a reaction vessel containing a transition metal salt solution and reacted to obtain an intermediate material.

[0100] According to some specific embodiments of this application, the reaction temperature of the precursor framework material and the transition metal salt solution is 120℃~200℃ (e.g., 120℃, 150℃, 170℃, 200℃, etc.), and the reaction time is 0.5h~5h (e.g., 0.5h, 1h, 2h, 3h, 4h, 5h, etc.), which can further ensure that the precursor framework material and the transition metal salt react fully.

[0101] According to some specific embodiments of this application, the concentration of the transition metal salt solution is 0.5 mol / L to 1 mol / L (for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc.), which can further ensure that the precursor framework material reacts fully with the transition metal salt.

[0102] In the embodiments of this application, the specific types of transition metal salts are not particularly limited, and those skilled in the art can select them according to actual needs. As some preferred embodiments, the transition metal salts include at least one of nickel nitrate, copper nitrate, iron nitrate, and tungsten nitrate.

[0103] S300': The intermediate material is carbonized and grown under a protective atmosphere to obtain a multi-level carbon composite material;

[0104] In this step, the intermediate material is carbonized and grown under a protective atmosphere to obtain a multi-level carbon composite material in which secondary transition metal oxide material is attached to the surface of primary carbon material. As some specific embodiments, the intermediate material is placed in a sealed tube furnace and carbonized and grown under a protective atmosphere to obtain the multi-level carbon composite material.

[0105] According to some specific embodiments of this application, the intermediate material undergoes carbonization growth at a temperature of 400℃ to 1200℃ (e.g., 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, etc.), and the reaction time is 0.5h to 2h (e.g., 0.5h, 1h, 1.5h, 2h, etc.). This further ensures that the intermediate material undergoes sufficient carbonization growth.

[0106] According to further specific embodiments of this application, before carbonizing and growing the intermediate material, the method further includes:

[0107] The intermediate material is subjected to a second pre-oxidation in order to oxidize the organic groups in the intermediate material.

[0108] According to some specific embodiments of this application, the temperature of the second pre-oxidation is 200°C to 250°C (examples include 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, etc.), and the time of the second pre-oxidation is 0.5h to 1.5h (examples include 0.5h, 0.7h, 0.9h, 1h, 1.1h, 1.3h, 1.5h, etc.), thereby further ensuring the oxidation of organic groups in the intermediate material.

[0109] In a third aspect, this application proposes a negative electrode current collector. According to embodiments of this application, the negative electrode current collector comprises the multi-level carbon composite material of the above embodiments or the multi-level carbon composite material prepared by the methods of the above embodiments. That is, the multi-level carbon composite material can be directly used as a negative electrode current collector. Thus, this negative electrode current collector is a three-dimensional current collector. On the one hand, by constructing abundant charge centers to uniformly distribute the electric field and charge on the electrode surface, it reduces the tip curvature of the initial structural protrusions formed during the initial deposition of sodium metal, which is beneficial for planar deposition of sodium metal and the elimination of tip enrichment. On the other hand, the three-dimensional current collector with a high specific surface area can reduce the local current density on the carbon material, alleviate the sodium ion consumption rate per unit area of ​​the three-dimensional negative current collector, reduce concentration polarization, and thus inhibit the growth of sodium dendrites. Simultaneously, this multi-level carbon current collector with sodium-loving sites has a low nucleation overpotential, which can reduce the nucleation barrier and regulate the initial nucleation behavior of sodium. By optimizing the nucleation process of sodium metal, the formation of sodium dendrites can be reduced. Finally, the structural design of the three-dimensional current collector can limit the volume expansion of sodium metal during charging and discharging. By providing sufficient space for the sodium metal, this three-dimensional current collector can reduce internal stress caused by volume expansion, thereby suppressing the growth of lithium dendrites. This effectively improves the initial coulombic efficiency, cycle stability, and capacity retention of batteries with the aforementioned current collector.

[0110] In a fourth aspect, this application proposes a battery. According to an embodiment of this application, the battery includes the negative electrode current collector described in the above embodiments. This effectively improves the battery's initial coulombic efficiency, cycle stability, and capacity retention.

[0111] The aforementioned battery can be a lithium metal battery or a sodium metal battery.

[0112] Specifically, the battery includes a positive electrode, a separator, a negative electrode current collector, and an electrolyte, with the separator disposed between the positive electrode and the negative electrode current collector. The specific material of the separator is not particularly limited; as some specific examples, the separator includes at least one of PP separator, PE separator, single-sided ceramic separator, double-sided ceramic separator, non-woven fabric separator, and glass fiber separator.

[0113] The positive electrode sheet includes a positive current collector and a positive electrode material layer formed on the positive current collector. The positive electrode material layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0114] For sodium metal batteries, the positive electrode active material can be one or more of the following, including but not limited to transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue-based materials. In sodium transition metal oxides, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, Na is a sodium transition metal oxide. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 < x ≤ 1, for example Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0115] The aforementioned polyanionic compounds possess sodium ion, transition metal ion, and tetrahedral (YO4) structures. n- A class of compounds with an anionic unit, wherein the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state, for example, Na3V2(PO4)3.

[0116] The aforementioned Prussian blue compounds contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds whose general chemical formula can be represented as Na x M1[M2(CN)6], where 0 < x ≤ 2, and M1 and M2 are at least one of Ni, Cu, Fe, Mn, Co and Zn, respectively.

[0117] The specific materials of the above-mentioned positive electrode binder are not particularly limited. As some specific examples, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), and polyacrylic acid (PAA).

[0118] The specific materials of the aforementioned positive electrode conductive agent are not particularly limited. As some specific examples, the positive electrode conductive agent may include, but is not limited to, one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, etc.

[0119] In the embodiments of this application, the specific material of the positive current collector is not particularly limited. As some specific examples, the positive current collector may include, but is not limited to, at least one of aluminum foil, carbon-coated aluminum foil, and stainless steel foil.

[0120] In the embodiments of this application, the electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and the organic solvent are conventional choices in the battery field and can be selected according to actual needs.

[0121] In some embodiments, the electrolyte salt may include, but is not limited to, at least one of: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium bis(trifluoromethanesulfonyl)imide (NaN(CF3SO2)2), sodium bis(fluorosulfonyl)imide (NaN(SO2F)2), sodium bis(oxalateborate)borate (NaB(C2O4)2), and sodium difluorooxalateborate (NaBF2C2O4).

[0122] In some embodiments, the organic solvent may include, but is not limited to, at least one of: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), diethylene glycol dimethyl ether (DEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), and tetraethylene glycol dimethyl ether (TEGDME).

[0123] The battery of this application may be in the form of a battery cell, a battery module, or a battery pack. In some embodiments, battery cells may be assembled into a battery module, and the number of battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, and the number of battery modules contained in a battery pack may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0124] In a fifth aspect, this application proposes an electrical device. According to an embodiment of this application, the electrical device includes the battery described in the above embodiments. Therefore, the electrical device possesses all the advantages of a battery, which will not be elaborated further here.

[0125] Specifically, the aforementioned electrical equipment can include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0126] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0127] Example 1

[0128] This embodiment provides a method for preparing a multi-level carbon composite material, the process of which includes:

[0129] 1) 2-Methylimidazole was dissolved in deionized water to form solution A, and nickel nitrate was dissolved in deionized water to form solution B. Solutions A and B were mixed and stirred, then centrifuged and dried to obtain the metal-organic framework structure. During the synthesis, the molar ratio of 2-methylimidazole to nickel nitrate was 70:1.

[0130] 2) Polyacrylonitrile (PAN) powder and metal-organic framework structure were dissolved in N,N-dimethylformamide (DMF) at a mass ratio of 8:3. The mixture was then vigorously stirred at 60°C for 2 hours to form solution C. Solution C was then stirred at room temperature for 12 hours to obtain the precursor solution.

[0131] 3) The precursor solution was electrospun at 20kV, with the distance between the spinneret and the aluminum plate being 15cm and the spinning speed being 0.7ml H. -1 Electrospinning was performed using an 8mL medical syringe with a 0.6mm inner diameter stainless steel needle as the spinneret. The precursor material (i.e., nanofiber material) was collected from an aluminum plate and cut into rectangular slices (3cm × 4cm).

[0132] 4) Then, the nanofiber material was placed in a muffle furnace and pre-oxidized in air at 220°C for 1 hour, with a heating rate of 3°C / min. -1 (This intermediate product is denoted as CF).

[0133] 5) The intermediate material was placed in a sealed tube furnace and catalytically grown in an ethanol atmosphere at a temperature of 850℃ for 30 minutes. Ethanol was used as a reducing agent and carbon source. The reducing gas first reduced the transition metal oxides in the metal-organic framework structure to elemental Ni. Then, the Ni nanoparticles catalyzed the growth of carbon nanotubes into carbon nanotubes, ultimately forming a multi-level carbon nanofiber composite material (CF@Ni@CNTs).

[0134] Example 2

[0135] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0136] 1) In the synthesis of the metal-organic framework, the molar ratio of 2-methylimidazole to nickel nitrate is 60:1.

[0137] Example 3

[0138] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0139] 1) In the synthesis of the metal-organic framework, the molar ratio of 2-methylimidazole to nickel nitrate is 80:1.

[0140] Example 4

[0141] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0142] 1) Replace 2-methylimidazole with triazole.

[0143] Example 5

[0144] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0145] 1) Replace 2-methylimidazole with terephthalic acid.

[0146] Example 6

[0147] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0148] 1) Replace nickel nitrate with zinc nitrate in a molar ratio.

[0149] Example 7

[0150] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0151] 1) Replace nickel nitrate with ferric nitrate, nickel nitrate and cobalt nitrate in a molar ratio of 1:1:1.

[0152] Example 8

[0153] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0154] 2) The mass ratio of polyacrylonitrile (PAN) powder to metal-organic framework structure is 8:1.

[0155] Example 9

[0156] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0157] 2) The mass ratio of polyacrylonitrile (PAN) powder to metal-organic framework structure is 8:5.

[0158] Example 10

[0159] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0160] 2) Replace polyacrylonitrile (PAN) with polyvinylpyrrolidone.

[0161] Example 11

[0162] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0163] 2) Replace polyacrylonitrile (PAN) with polyimide.

[0164] Example 12

[0165] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0166] 3) The precursor solution was electrospun at 15kV, with the distance between the spinneret and the aluminum plate being 12cm and the spinning speed being 0.5ml H. -1 The electrospinning process was performed using an 8mL medical syringe, with a stainless steel needle with an inner diameter of 0.5mm serving as the spinneret.

[0167] Example 13

[0168] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0169] 3) The precursor solution was electrospun at 25 kV, with the distance between the spinneret and the aluminum plate being 18 cm and the spinning speed being 0.9 ml / h. -1 The electrospinning operation was performed in an 8mL medical syringe, using a stainless steel needle with an inner diameter of 0.7mm as the spinneret.

[0170] Example 14

[0171] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0172] 5) The catalytic growth temperature is 700℃ and the time is 60min.

[0173] Example 15

[0174] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0175] 5) The catalytic growth temperature is 1000℃ and the time is 10min.

[0176] Example 16

[0177] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0178] 5) Replace ethanol gas with methane gas.

[0179] Example 17

[0180] The preparation method in this embodiment is basically the same as that in Example 1, except that:

[0181] 5) Replace ethanol gas with acetylene gas.

[0182] Example 18

[0183] Steps 1) to 3) in this embodiment are the same as steps 1) to 3) in embodiment 1, the difference being:

[0184] 4) The nanofiber material was then immersed in a reaction vessel containing a 0.8 mol / L nickel nitrate aqueous solution and reacted at 160°C for 2 hours. After the reaction was completed, the nanofiber material was placed in a muffle furnace and pre-oxidized in air at 220°C for 1 hour at a heating rate of 3°C / min. -1 .

[0185] 5) The intermediate material is placed in a sealed tube furnace and carbonized in a nitrogen atmosphere. The carbonization temperature is 850℃ and the time is 30min, eventually forming a composite material of one-dimensional carbon nanofibers and two-dimensional nickel oxide nanosheets.

[0186] Example 19

[0187] The preparation method of this embodiment is basically the same as that of Example 18, except that:

[0188] 4) Replace the nickel nitrate aqueous solution with the copper nitrate aqueous solution.

[0189] Example 20

[0190] The preparation method of this embodiment is basically the same as that of Example 18, except that:

[0191] 4) Replace the nickel nitrate aqueous solution with the ferric nitrate aqueous solution.

[0192] Comparative Example 1

[0193] The preparation method of this comparative example is basically the same as that of Example 1, except that:

[0194] Comparative Example 1 includes only steps 1) to 4), but not step 5), that is, the intermediate material CF is not catalytically grown.

[0195] The CF@Ni@CNTs prepared in Example 1 were subjected to XRD tests, such as... Figure 1 As shown, the peak around 26° corresponds to the diffraction peaks of carbon materials CF and CNTs, while the diffraction peaks around 45° and 52° are diffraction peaks of Ni metal particles. This was determined by transmission electron microscopy (TEM). Figure 2It can be seen that a large number of metal particles are on the fiber surface and catalyze the generation of a large number of carbon nanotubes, forming a multi-level carbon nanocomposite structure.

[0196] Appendix Figure 3 The image shows the CF@Ni@CNTs prepared in Example 1 after being folded 180°. It can be seen that the composite material has excellent flexibility and can be used as a self-supporting negative electrode.

[0197] The mass percentages of carbon nanofibers (CNFs), secondary materials, sodium-loving metals, oxygen functional groups, the diameter of carbon nanofibers (CNFs), and the diameter or particle size of secondary materials in the multi-level carbon composite materials prepared in Examples 1-20 and Comparative Example 1 were measured, and the results are shown in Table 1. The specific surface area of ​​the multi-level carbon composite materials prepared in Examples 1-20 and Comparative Example 1 was also measured, and the results are shown in Table 1.

[0198] The mass percentages of nanofibers (CNF), carbon nanotubes (CNT), and sodium-loving metals were tested using thermogravimetric analysis (TGA). First, an appropriate weight of sample was weighed into a crucible, the program was set, the working conditions were initialized, and the measurement was started. After the experiment, the raw data were analyzed using the professional software OriginLab.

[0199] Mass percentage test of oxygen functional groups: The mass percentage of oxygen-containing functional groups in multi-level carbon composite materials can be tested by potentiometric titration.

[0200] The diameter of carbon nanofibers (CNF) and the diameter or particle size of secondary materials were measured by statistical analysis of SEM images at different magnifications using Smile-view software.

[0201] Specific surface area test: The specific surface area of ​​the multi-stage carbon composite material was tested using the nitrogen adsorption-desorption method.

[0202] Table 1

[0203]

[0204]

[0205] The multi-level carbon composite materials prepared in Examples 1-20 and Comparative Example 1 were used directly as current collectors, with the current collector serving as the working electrode and sodium metal as the counter electrode, to assemble coin cells. The initial coulombic efficiency and capacity retention after 800 cycles of the coin cells from Examples 1-20 and Comparative Example 1 were tested, and the results are shown in Table 2. After 800 cycles, the coin cells from Examples 1-20 and Comparative Example 1 were disassembled, and the sodium dendrites on the current collector were observed; the results are shown in Table 2.

[0206] Table 2

[0207]

[0208]

[0209] As shown in Table 2, compared with Comparative Example 1, the initial coulombic efficiency and capacity retention after 800 cycles of Examples 1-20 were significantly improved, and the sodium dendrites on the current collector of Examples 1-20 were significantly reduced. This is because the secondary material on the surface of the carbon nanofibers (CNF) in Examples 1-20 further increased the specific surface area of ​​the material, thereby reducing the local current density on the carbon material and alleviating the volume expansion of sodium metal during continuous charge and discharge, thus inhibiting the growth of sodium dendrites and effectively improving the initial coulombic efficiency and capacity retention of the battery.

[0210] Appendix Figure 4 This is a comparison chart of the cycles of Example 1 and Comparative Example 1. It can be seen that the multi-level carbon nanocomposite material in Example 1 has better cycle stability. This is because the material has a larger specific surface area, a stronger affinity for sodium metal, and is better able to alleviate the volume expansion during the sodium metal deposition process.

[0211] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. 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. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0212] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A multi-level carbon composite material, characterized in that, include: A primary carbon material and a secondary material, wherein the secondary material is attached to at least a portion of the surface of the primary carbon material, and the secondary material is a secondary carbon material or a secondary transition metal oxide material; Sodium-loving metal, wherein the sodium-loving metal is disposed on the surface and / or inside the primary carbon material.

2. The multi-level carbon composite material according to claim 1, characterized in that, The primary carbon material includes carbon fibers with diameters ranging from nanometers to micrometers; And / or, the secondary carbon material includes carbon nanotubes.

3. The multi-level carbon composite material according to claim 2, characterized in that, The diameter of the carbon fiber is 100nm to 600nm; And / or, the diameter of the carbon nanotubes is 5 nm to 30 nm.

4. The multi-level carbon composite material according to claim 1, characterized in that, The secondary transition metal oxide material includes transition metal oxide nanosheets.

5. The multi-level carbon composite material according to claim 4, characterized in that, The particle size of the transition metal oxide nanosheets is 30 nm to 80 nm; And / or, the transition metal oxide nanosheets include at least one of nickel oxide nanosheets, copper oxide nanosheets, iron oxide nanosheets, and tungsten oxide nanosheets.

6. The multi-level carbon composite material according to claim 1, characterized in that, The sodium-loving metal includes at least one of nickel, zinc, iron, cobalt, and manganese.

7. The multi-level carbon composite material according to claim 1, characterized in that, The mass of the primary carbon material accounts for 45% to 82% of the total mass of the multi-level carbon composite material; And / or, the mass of the secondary material accounts for 10% to 42% of the total mass of the multi-stage carbon composite material; And / or, the mass of the sodium-loving metal accounts for 2% to 15% of the total mass of the multi-level carbon composite material.

8. The multi-stage carbon composite material according to any one of claims 1 to 7, characterized in that, It also includes oxygen-containing functional groups, which are doped into the primary carbon material.

9. The multi-level carbon composite material according to claim 8, characterized in that, The oxygen-containing functional groups account for 0.1% to 2% of the total mass of the multi-level carbon composite material; And / or, the oxygen-containing functional group includes at least one of hydroxyl, carboxyl, carbonyl, nitro, phosphate, and sulfonic acid groups.

10. The multi-level carbon composite material according to any one of claims 1 to 7, characterized in that, The specific surface area of ​​the multi-level carbon composite material is 13 m². 2 / g~25m 2 / g.

11. The multi-level carbon composite material according to any one of claims 1 to 7, characterized in that, The sodium-loving metal is also disposed on at least a portion of the surface of the secondary material.

12. The multi-level carbon composite material according to any one of claims 1 to 7, characterized in that, The primary carbon material is a porous carbon framework.

13. A method for preparing a multi-level carbon composite material according to any one of claims 1 to 12, characterized in that, include: Preparation of precursor framework materials comprising metal-organic framework materials and carbon-containing polymers; The precursor framework material is treated with a reducing gas containing carbon chains to obtain a multi-level carbon composite material; or, the precursor framework material is reacted with a transition metal salt solution to obtain an intermediate material; the intermediate material is then carbonized and grown under a protective atmosphere to obtain a multi-level carbon composite material.

14. The method according to claim 13, characterized in that, The preparation of the precursor framework material comprising a metal-organic framework material and a carbon-containing polymer includes: The metal-organic framework material, the carbon-containing polymer, and the organic solvent are mixed to obtain a precursor solution; The precursor solution is electrospun to obtain the precursor skeleton material.

15. The method according to claim 14, characterized in that, The mass ratio of the carbon-containing polymer to the metal-organic framework material is 8:(1-5); And / or, the carbon-containing polymer includes at least one of polyacrylonitrile, polyvinylpyrrolidone, polyimide and polyvinylidene fluoride; And / or, the inner diameter of the spinneret in the electrospinning is 0.5mm to 0.8mm, the voltage of the electrospinning is 15kV to 25kV, the distance between the spinneret and the receiving device is 12cm to 18cm, and the speed of the electrospinning is 0.5mL H. -1 ~0.9mL H -1 ; And / or, the preparation method of the metal-organic framework material includes: mixing an organic ligand solution and a sodium-loving metal salt solution, separating the solid and liquid phases, and drying to obtain the metal-organic framework material.

16. The method according to claim 15, characterized in that, The molar ratio of the organic ligand to the sodium-loving metal salt is (60-80):1; And / or, the organic ligand includes at least one of imidazole compounds, triazole compounds, and terephthalic acid; And / or, the sodium-loving metal salt includes at least one of zinc nitrate, nickel nitrate, iron nitrate, cobalt nitrate, and manganese nitrate.

17. The method according to any one of claims 13 to 16, characterized in that, The precursor skeleton material is treated with a reducing gas containing carbon chains at a temperature of 700℃~1000℃ for a time of 10min~60min. And / or, the carbon-chain-containing reducing gas includes at least one of ethanol, methane, and acetylene; And / or, prior to treating the precursor framework material with the reducing gas containing the carbon chain, the method further includes: The precursor skeleton material is subjected to a first pre-oxidation. And / or, the reaction temperature of the precursor skeleton material with the transition metal salt solution is 120℃~200℃, and the reaction time is 0.5h~5h; And / or, the transition metal salt includes at least one of nickel nitrate, copper nitrate, ferric nitrate, and tungsten nitrate; And / or, the concentration of the transition metal salt solution is 0.5 mol / L to 1 mol / L; And / or, the intermediate material is carbonized at a temperature of 400℃ to 1200℃ for a reaction time of 0.5h to 2h; And / or, prior to carbonization growth of the intermediate material, the process further includes: a second pre-oxidation of the intermediate material.

18. The method according to claim 17, characterized in that, The temperatures of the first pre-oxidation and the second pre-oxidation are 200℃~250℃, and the times of the first pre-oxidation and the second pre-oxidation are 0.5h~1.5h, respectively.

19. A negative electrode current collector, characterized in that, The multi-level carbon composite material includes any one of claims 1 to 12, or the multi-level carbon composite material prepared by the method described in any one of claims 13 to 18.

20. A battery, characterized in that, Includes the negative electrode current collector as described in claim 19.

21. An electrical appliance, characterized in that, It has the battery as described in claim 20.

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