Carbon electrode composite material and preparation method thereof, and secondary battery

Abstract

The present application belongs to the field of battery technology, and in particular relates to a carbon electrode composite material and a preparation method thereof, as well as a secondary battery. Among them, the preparation method of the carbon electrode composite material comprises the following steps: mixing a surface-activated carbon material with a solution of a metal catalyst precursor, hydrolyzing and drying to obtain a carbon composite material loaded with metal oxides; under an inert atmosphere, subjecting the carbon composite material to a carbon thermal reaction, and cooling to obtain a carbon electrode composite material comprising a porous carbon material and a metal carbide encapsulated in the pores of the porous carbon material. The preparation method of the present application completes the two steps of pore formation on the surface of the carbon material and in-situ loading of the metal carbide through a single carbon thermal reaction. The preparation efficiency is high, and the active specific surface area of ​​the electrode is effectively increased. At the same time, the catalytic activity and stability of the electrode are improved. Application in secondary batteries is beneficial to improving the power density and cycle life of the battery.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to a carbon electrode composite material and a preparation method thereof, as well as a secondary battery. Background Art

[0002] The extensive use of traditional fossil energy has brought about many problems such as climate warming and environmental pollution. The vigorous development of renewable energy represented by wind and solar energy is an effective way to solve the environmental pollution problem caused by fossil energy. However, renewable energy has the characteristics of volatility and intermittency, which often cause a greater impact on the power grid, becoming a bottleneck restricting its large-scale application. The high-power, high-capacity, low-cost energy storage technology that goes with it is a key technology to promote the adjustment of energy structure and popularize the development of renewable energy. As a new generation of energy storage technology, flow battery has good scalability, good safety, long life, and broad development prospects. The all-vanadium flow battery uses only vanadium (the negative electrode is V 2+ With V 3+ , the positive side is VO 2+ and VO2 + ) As an energy storage medium, there is no problem of cross-contamination between multiple metal ions. It is the most widely studied liquid flow battery and the one closest to commercialization. At present, high construction costs have become the main factor restricting the commercialization of all-vanadium liquid flow batteries. The cost of liquid flow batteries mainly includes the cost of the stack, accessories, and active material costs, of which the proportion of the stack cost is more than 40%, which has become an important reason restricting the commercialization of all-vanadium liquid flow batteries. The most direct and effective way to reduce the cost of liquid flow battery stacks is to increase the operating power density of the battery without sacrificing energy efficiency. Under the same power demand, the increase in operating power density can effectively reduce the active area of ​​the battery, and the number of electrodes, bipolar plates and ion exchange membranes required will also be reduced accordingly.

[0003] Improving the operating power density of flow batteries requires reducing activation polarization loss, ohmic polarization loss, and concentration polarization loss during battery operation, which places higher demands on electrode design, especially the need to significantly increase the catalytic activity and reaction sites of the electrodes. In the past, in order to achieve this goal, the following methods were generally adopted: (1) introducing functional groups, but functional groups are generally not very stable. As the charge and discharge process proceeds, the catalytic effect brought by the functional groups will gradually weaken, and the battery performance will irreversibly decay; (2) surface etching and pore creation, but the continuous high current density operation of the battery will cause the electrode structure to collapse, and the battery performance will also continue to decay. (3) surface attachment of catalysts, but the deposition process of surface attachment of catalysts is generally more complicated, and the catalyst attached to the surface is easily washed away when the flow rate is large. Developing electrodes with high specific surface area, high catalytic activity, and high stability is crucial to improving the power density and cycle life of batteries. This will significantly reduce the cost of battery stack construction and the cost per kilowatt-hour during the battery life cycle, and promote its commercialization process. However, the existing flow battery electrode treatment process can hardly meet the requirements of high power density and long cycle life of the battery by simply introducing functional groups, creating pores on the surface or attaching catalysts. Therefore, it is necessary to improve the existing process. Summary of the Invention

[0004] The purpose of this application is to provide a carbon electrode composite material and a preparation method thereof, as well as a secondary battery, which aims to solve to a certain extent the problem that the existing liquid flow battery electrode processing process is difficult to meet the requirements of high power density and long cycle life of the battery.

[0005] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0006] In a first aspect, the present application provides a method for preparing a carbon electrode composite material, comprising the following steps:

[0007] obtaining a surface-activated carbon material;

[0008] Mixing the surface-activated carbon material with a solution of a metal catalyst precursor, hydrolyzing and drying the mixture to obtain a metal oxide-loaded carbon composite material;

[0009] Under an inert atmosphere, the carbon composite material is subjected to a carbon thermal reaction and cooled to obtain a carbon electrode composite material. The carbon electrode composite material comprises a porous carbon material and metal carbide encapsulated in the pores of the porous carbon material.

[0010] Furthermore, the metal element in the metal catalyst precursor includes at least one of titanium, tungsten, tin, and antimony; and the form of the metal catalyst precursor includes at least one of metal chloride and metal sulfate.

[0011] Furthermore, the solvent in the solution of the metal catalyst precursor is selected from hydrochloric acid with a mass fraction of 20 to 38%.

[0012] Furthermore, the metal catalyst precursor includes at least one of titanium tetrachloride, tungsten chloride, tin chloride, antimony chloride, titanyl sulfate, tungsten sulfate, tin sulfate, and antimony sulfate.

[0013] Furthermore, the conditions of the carbothermal reaction include: heating to 1000-1400° C. at a rate of 2-10° C. / min and keeping the temperature for 1-3 hours under an inert atmosphere.

[0014] Furthermore, in the solution of the metal catalyst precursor, the concentration of the metal catalyst precursor is 0.1 to 0.3 mol / L.

[0015] Furthermore, the mixing treatment step includes: immersing the surface-activated carbon material in a solution of the metal catalyst precursor, drying it in the air and then drying it at a temperature of 50 to 70° C. to obtain the carbon composite material loaded with metal oxide.

[0016] Furthermore, the step of obtaining the surface-activated carbon material includes: performing surface treatment on the carbon material, introducing oxygen-containing functional groups on the surface of the carbon material, and obtaining the surface-activated carbon material.

[0017] Furthermore, the surface-activated carbon material is selected from at least one of carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon mesh.

[0018] Furthermore, the surface-activated carbon material includes at least one of graphite, graphene, carbon nanotubes, carbon black, carbon particles, and carbon fibers.

[0019] In a second aspect, the present application provides a carbon electrode composite material prepared by the above method, comprising a porous carbon material and a metal carbide encapsulated in the pores of the porous carbon material.

[0020] Furthermore, in the carbon electrode composite material, the loading amount of the metal carbide is 0.5 to 10 mg / cm 2 .

[0021] Furthermore, the metal carbide includes at least one of titanium carbide, tungsten carbide, tin carbide, and antimony carbide.

[0022] Furthermore, the porous carbon material has nanopores with a diameter of 20 to 200 nm and a depth of 100 to 500 nm, and the metal carbide is coated in the nanopores.

[0023] Furthermore, the porous carbon material includes carbon fibers with a diameter of 5 to 15 mm.

[0024] Furthermore, the particle size of the metal carbide is 5 to 100 nm.

[0025] Furthermore, the porous carbon material is selected from at least one of carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon mesh.

[0026] In a third aspect, the present application provides a secondary battery, wherein the electrode of the secondary battery contains the carbon electrode composite material prepared by the above method, or the above carbon electrode composite material.

[0027] Furthermore, the secondary battery includes at least one of a flow battery, a lithium-ion battery, a fuel cell, and a hydrogen battery; wherein the flow battery is selected from at least one of an all-vanadium flow battery, an iron-chromium flow battery, and a vanadium-air flow battery.

[0028] Furthermore, the carbon electrode composite material is applied to the negative electrode of the secondary battery.

[0029] In the first aspect of the present application, two steps of pore formation on the surface of the carbon material and in-situ loading of the metal carbide catalyst are completed through a single carbon thermal reaction. The prepared carbon electrode composite material includes a porous carbon material and a metal carbide in-situ coated in the pores of the porous carbon material. On the one hand, the carbon source of the carbon thermal reaction comes from the carbon material body, so that the metal catalyst is in-situ bonded to the pores of the carbon material through chemical bonds, and has good bonding stability with the carbon material. The metal catalyst connected by chemical bonds is very strong and has strong erosion resistance, which avoids the metal catalyst being washed away by the flowing electrolyte during battery operation, thereby improving the cycle stability of the battery; on the other hand, the metal carbide is evenly distributed in the carbon material and has a small particle size, which increases the active specific surface area of ​​the electrode, thereby improving the catalytic activity of the electrode. Its application in secondary batteries is beneficial to improving the power density and cycle life of the battery.

[0030] The carbon electrode composite material provided in the second aspect of the present application is prepared by the above method, including a porous carbon material and a metal catalyst coated in the pores of the porous carbon material, wherein the metal catalyst metal carbide is in situ bonded to the pores of the carbon material through chemical bonds, and has good bonding stability with the carbon material. The metal catalyst connected by chemical bonds is very strong and has strong erosion resistance, which avoids the metal catalyst being washed away by the flowing electrolyte during the operation of the battery, thereby improving the cycle stability of the battery. In addition, the metal catalyst is evenly distributed in the carbon material and has a small particle size, which increases the active specific surface area of ​​the electrode, thereby increasing the catalytic activity of the electrode. Application to secondary batteries is conducive to improving the power density and cycle life of the battery.

[0031] The electrode of the secondary battery provided in the third aspect of the present application uses the above-mentioned carbon electrode composite material with high specific surface area, high catalytic activity, and high stability, thereby improving the power density and cycle life of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] Figure 1 is a morphology diagram of the graphite felt composite material provided in Examples 4 and 5 of the present application and Comparative Example 1;

[0034] Figure 2 This is a scanning electron microscope image of the graphite felt composite material provided in Example 1, Comparative Examples 1 and 3 of the present application;

[0035] Figure 3 1 is an electron microscope image of the graphite felt electrode composite material provided in Example 1 and Comparative Example 4 of the present application;

[0036] Figure 4 This is an X-ray diffraction test diagram of the graphite felt composite material provided in Example 1, Comparative Examples 1 and 3 of the present application;

[0037] Figure 5 The cyclic voltammetry test diagrams of the all-vanadium redox flow battery provided in Example 1 and Comparative Examples 1 to 3 of the present application are as follows;

[0038] Figure 6 The AC impedance test diagram of the all-vanadium redox flow battery provided in Example 1 and Comparative Examples 1 to 3 of the present application is shown;

[0039] Figure 7 The present invention provides a rate performance test diagram of an all-vanadium redox flow battery in Example 1 and Comparative Examples 1 to 3;

[0040] Figure 8 This is a cycle performance test diagram of the all-vanadium redox flow battery provided in Example 1 of the present application. DETAILED DESCRIPTION

[0041] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0042] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0043] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple.

[0044] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0045] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0046] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass in the examples of this application may be μg, mg, g, kg, etc., which are mass units known in the chemical industry.

[0047] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0048] As attached Figure 1As shown, the first aspect of the embodiment of the present application provides a method for preparing a carbon electrode composite material, comprising the following steps:

[0049] S10. Obtaining a surface-activated carbon material;

[0050] S20. The surface-activated carbon material is mixed with a solution of a metal catalyst precursor, hydrolyzed and dried to obtain a carbon composite material loaded with a metal oxide;

[0051] S30. Under an inert atmosphere, subjecting the carbon composite material to a carbon thermal reaction, and cooling the carbon composite material to obtain a carbon electrode composite material. The carbon electrode composite material includes a porous carbon material and a metal carbide (ie, a metal catalyst) encapsulated in the pores of the porous carbon material.

[0052] The preparation method of the carbon electrode composite material provided in the first aspect of the embodiment of the present application is to obtain a surface-activated carbon material, mix it with a solution of a metal catalyst precursor, and uniformly adsorb the metal catalyst precursor onto the surface-activated carbon material. During the drying process, the water contacted by the metal precursor loaded in the surface-activated carbon material increases, and it is hydrolyzed and converted into metal oxides to obtain a carbon composite material. Then, the carbon composite material is subjected to a carbon thermal reaction in an inert atmosphere. During the carbon thermal reaction, the oxygen atoms of the metal oxide loaded in the carbon composite material react thermochemically with the carbon atoms in the carbon material to generate gases such as carbon dioxide and carbon monoxide, and the carbon material is subjected to in-situ pore formation, thereby forming pores with uniform distribution and small pore size in the carbon material. At the same time, the metal oxide is reduced to a catalyst of metal carbide, which is in-situ and stably combined with the pore-forming holes of the carbon material. Therefore, the embodiment of the present application completes the two steps of pore formation on the surface of the carbon material and in-situ loading of the metal carbide catalyst through a single carbon thermal reaction. The prepared carbon electrode composite material includes a porous carbon material and a metal carbide in-situ coated in the pores of the porous carbon material. On the one hand, the carbon source of the carbon thermal reaction comes from the carbon material body, so that the metal catalyst is in-situ bonded to the pores of the carbon material through chemical bonds, and has good bonding stability with the carbon material. The metal catalyst connected by chemical bonds is very strong and has strong erosion resistance, which avoids the metal catalyst being washed away by the flowing electrolyte during battery operation, thereby improving the cycle stability of the battery; on the other hand, the metal carbide is evenly distributed in the carbon material and has a small particle size, which increases the active specific surface area of ​​the electrode, thereby improving the catalytic activity of the electrode. Application in secondary batteries is beneficial to improving the power density and cycle life of the battery.

[0053] The carbon electrode composite material prepared in the embodiment of the present application has a high specific surface area, high catalytic activity, and high stability, and is suitable for the negative electrode of secondary batteries such as liquid flow batteries, lithium-ion batteries, fuel cells, and hydrogen batteries, and is particularly suitable for all-vanadium liquid flow batteries, iron-chromium liquid flow batteries, zinc-bromine liquid flow batteries, and new electric fuel energy storage systems, which can effectively improve the power density and cycle life of the battery. For example, when the carbon electrode composite material is used in the negative electrode of the all-vanadium liquid flow battery, due to the V 3+ / V 2+ The limited reaction speed is the main factor restricting the performance improvement of all-vanadium batteries. The application of carbon electrode composite materials to the negative electrode can improve the power density of the battery. Moreover, the carbon electrode composite material is relatively stable on the negative electrode side and has excellent catalytic activity for vanadium ions on the negative electrode side. It can also inhibit hydrogen evolution, thereby increasing the catalytic activity on the negative electrode side and reducing the occurrence of side reactions. However, the oxidizing property of pentavalent vanadium ions on the positive electrode side is too strong, which will reduce the stability of the catalyst in the carbon electrode composite material. After the carbon electrode composite material is applied to the negative electrode of the all-vanadium liquid flow battery, the battery is at 300mAcm -2 The energy efficiency is as high as 80%, and it can run stably for 300 cycles without energy efficiency attenuation, with good cycle stability.

[0054] In some embodiments, in the above step 10, the step of obtaining a surface-activated carbon material includes: performing surface treatment on the carbon material, introducing oxygen-containing functional groups on the surface of the carbon material, and obtaining a surface-activated carbon material. In some embodiments, the methods for surface-treating the carbon material include but are not limited to heat treatment, liquid phase oxidation, plasma treatment, anodic electrolysis or electrodeposition treatment, ozone treatment, gas phase oxidation, etc., and oxygen-containing functional groups such as hydroxyl and carboxyl are introduced on the surface of the carbon material through surface treatment to improve the hydrophilicity of the carbon material, improve the subsequent adsorption and binding efficiency of the metal catalyst precursor and the carbon material, and facilitate the even adsorption and loading of the metal catalyst precursor on the carbon material, thereby improving the distribution uniformity of the metal catalyst in the carbon electrode composite material. In some specific embodiments, the carbon material is heat-treated at a temperature of 400 to 500°C for 4 to 8 hours to introduce oxygen-containing functional groups on the surface of the carbon material to obtain a surface-activated carbon material.

[0055] In certain embodiments, the surface activated carbon material is selected from at least one of carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon net. The surface activated carbon material used in the embodiment of the present application can be the macrostructures such as carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon net. These carbon materials are woven from carbon fibers, and subsequent metal precursor loading, as well as the step of one-step carbon thermal pore making and metal carbide loading, are directly pore-forming on the fiber surface of these surface activated carbon materials and loaded with metal carbide. The obtained carbon electrode composite material can be cut into a size that meets the application requirements according to the size of the battery pole piece to be applied and applied directly as an electrode layer, and is flexible and convenient to apply, has wide adaptability, and is highly efficient. When the surface activated carbon material adopts structures such as carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon net, it is particularly suitable for electrodes of flow batteries.

[0056] In certain embodiments, the surface activated carbon material includes at least one of graphite, graphene, carbon nanotubes, carbon black, carbon particles, and carbon fibers. The surface activated carbon material of the present application embodiment can also adopt the forms such as graphite, graphene, carbon nanotubes, carbon black, carbon particles, and carbon fibers, by carrying out subsequent metal precursor loading to these materials, and the step of one-step carbon thermal pore making and metal catalyst loading, pore making and load metal carbide on these carbon material surfaces, improve the specific surface area of ​​carbon electrode composite material, improve catalytic activity, and stability. In addition, the surface activated carbon material of the present application embodiment adopts materials such as graphite, graphene, carbon nanotubes, carbon black, carbon particles, and carbon fibers, and the obtained carbon electrode material can be made into electrode layers of different specifications and types by pressing, making slurry deposition, etc., and is applied to different battery systems, thereby improving the application flexibility of the obtained carbon electrode composite material.

[0057] In some embodiments, in the above step 20, the step of mixing the surface-activated carbon material with the solution of the metal catalyst precursor includes: immersing the surface-activated carbon material in the solution of the metal catalyst precursor so that the metal catalyst precursor is fully infiltrated into the surface-activated carbon material, drying so that the metal catalyst precursor is evenly loaded into the surface-activated carbon material, and then drying at a temperature of 50 to 70°C. During the drying process, on the one hand, the solvent is evaporated and removed, and on the other hand, during the solvent evaporation process, the concentration of water molecules contacted by the metal catalyst precursor increases, thereby causing the metal catalyst precursor to hydrolyze into metal oxides to obtain a carbon composite material loaded with metal oxides. In some embodiments, the drying temperature is 50 to 70°C. This temperature condition allows the solvent to have a more suitable volatilization rate, which not only ensures the volatilization removal efficiency of the solvent, but also facilitates the hydrolysis of the metal catalyst precursor into metal oxides.

[0058] In some embodiments, the metal element in the metal catalyst precursor includes at least one of titanium, tungsten, tin, and antimony; the form of the metal catalyst precursor includes at least one of metal chloride and metal sulfate. The metal catalyst precursors used in the embodiments of the present application include but are not limited to chlorides or sulfates of metals such as titanium, tungsten, tin, and antimony. These metal salts have good solubility, which is conducive to the metal catalyst precursor being uniformly loaded into the surface-activated carbon material in molecular form, thereby facilitating the improvement of the uniformity of distribution of the metal catalyst in the carbon electrode composite material. Furthermore, these metal salts are easily hydrolyzed with water to form metal oxides, which convert the metal catalyst precursor uniformly distributed in the carbon material into metal oxides. The metal oxide can simultaneously perform in-situ pore formation and reduction to a metal carbide catalyst during the subsequent carbon thermal reaction process, thereby improving the uniformity of distribution of the metal catalyst in the carbon electrode composite material, and the metal catalyst metal carbide is in-situ generated in the pores and cavities of the carbon material, has a small particle size, and has high stability in combination with the carbon material. In addition, the metal catalyst precursors in the embodiments of the present application are primarily in the form of metal chlorides and metal sulfates. After hydrolysis, metal oxides are generated while other elements are converted into hydrogen chloride, sulfur oxide, and other forms. This not only reduces toxic side effects but is also easily removed, preventing elemental residue and improving the purity of the metal catalyst metal carbide in the resulting carbon electrode composite material. If metal nitrates were used as metal catalyst precursors, the hydrolysis of the precursors to metal oxides would generate highly toxic nitrogen oxides.

[0059] In some specific embodiments, the metal catalyst precursor includes at least one of titanium tetrachloride, tungsten chloride, tin chloride, antimony chloride, titanyl sulfate, tungsten sulfate, tin sulfate, and antimony sulfate. In further preferred embodiments, the metal catalyst precursor is a metal chloride, including but not limited to titanium tetrachloride, tungsten chloride, tin chloride, and antimony chloride. These metal chlorides, upon hydrolysis, generate corresponding metal oxides and hydrogen chloride, wherein the hydrogen chloride is easily removed in a gaseous form upon heating.

[0060] In some embodiments, the solvent in the solution of the metal catalyst precursor is selected from hydrochloric acid with a mass fraction of 20 to 38%. The embodiment of the present application uses concentrated hydrochloric acid with a mass fraction of 20 to 38% as the solvent of the metal catalyst precursor. On the one hand, the water content in concentrated hydrochloric acid is low, which can effectively regulate the hydrolysis rate of the metal catalyst precursor and avoid the precursor from hydrolyzing too quickly; on the other hand, hydrochloric acid is easily volatilized and removed when heated, avoiding solvent or element residues, thereby improving the purity of the metal catalyst in the carbon electrode composite material and ensuring the high catalytic activity of the composite material. During the drying process, as the hydrochloric acid evaporates and removes the water contacted by the metal catalyst precursor, the precursor gradually hydrolyzes into metal oxides uniformly distributed in the surface-activated carbon material. In some embodiments, the solvent in the solution of the metal catalyst precursor is selected from hydrochloric acid with a mass fraction of 20 to 38%, 22 to 36%, 25 to 34%, 28 to 30%, etc.

[0061] In some specific embodiments, when the metal catalyst precursor is a metal chloride, the solvent in the solution of the metal catalyst precursor is selected from hydrochloric acid with a mass fraction of 20 to 38%; when the metal catalyst precursor is a metal sulfate, the solvent in the solution of the metal catalyst precursor is selected from sulfuric acid to reduce the introduction of other elemental components.

[0062] In some embodiments, the concentration of the metal catalyst precursor in the solution of the metal catalyst precursor is 0.1 to 0.3 mol / L. This concentration range is conducive to the uniform loading of the metal catalyst precursor into the surface-activated carbon material. If the concentration is too high, the uniformity of the loading of the metal catalyst precursor in the carbon material will be reduced; if the concentration is too low, the metal catalyst precursor will not be fully loaded in the carbon material, reducing the loading amount of the metal catalyst in the prepared carbon electrode composite material, thereby reducing the catalytic activity of the electrode. In some specific embodiments, the concentration of the metal catalyst precursor in the solution of the metal catalyst precursor includes but is not limited to 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, etc.

[0063] In some embodiments, in step 30, the carbon thermal reaction conditions include: heating to 1000-1400°C at a rate of 2-10°C / min and holding for 1-3 hours under an inert atmosphere. During this reaction, the oxygen atoms in the uniformly distributed metal oxides in the carbon composite undergo thermochemical reactions with carbon to produce gases such as carbon dioxide and carbon monoxide, which in situ pore-forming the surface-activated carbon material, thereby forming uniformly distributed and small pores in the carbon material. Simultaneously, the metal oxides are reduced to metal carbide catalysts, which are in situ and stably bound within the pore-forming pores of the surface-activated carbon material. The inert atmosphere can be nitrogen, argon, helium, or other gases to prevent oxidation of the metal elements at high temperatures. Excessively high temperatures, long holding times, or rapid heating rates can lead to pore collapse in the carbon electrode composite. Excessively low temperatures, short holding times, or slow heating rates can hinder the carbon thermal reaction of the metal oxides in the carbon composite, resulting in low efficiency and poor preparation of the desired carbon electrode composite. In some specific embodiments, the heating rate includes but is not limited to 2-10°C / min, 3-9°C / min, 4-8°C / min, 5-7°C / min, 5-6°C / min, etc.; the carbon thermal reaction temperature includes but is not limited to 1000-1400°C, 1000-1300°C, 1000-1200°C, 1000-1100°C, 1200-1400°C, etc.; the holding time includes but is not limited to 1-1.5 hours, 1.5-2 hours, 2-2.5, 2.5-3 hours, etc.

[0064] In some embodiments, in order to prevent the nano-titanium carbide particles from being oxidized by air due to excessive temperature, the product after the carbothermal reaction is cooled and placed in a nitrogen, argon or vacuum environment for protection until it cools down.

[0065] A second aspect of an embodiment of the present application provides a carbon electrode composite material prepared by the above method, comprising a porous carbon material and a metal carbide, i.e., a metal catalyst, encapsulated in the pores of the porous carbon material.

[0066] The carbon electrode composite material provided in the second aspect of the embodiment of the present application is prepared by the above method, including a porous carbon material and a metal catalyst coated in the pores of the porous carbon material, wherein the metal catalyst metal carbide is in situ bonded to the pores of the carbon material through chemical bonds, and has good bonding stability with the carbon material. The metal catalyst connected by chemical bonds is very strong and has strong erosion resistance, which prevents the metal catalyst from being washed away by the flowing electrolyte during the operation of the battery, thereby improving the cycle stability of the battery. In addition, the metal catalyst is evenly distributed in the carbon material and has a small particle size, which increases the active specific surface area of ​​the electrode, thereby increasing the catalytic activity of the electrode. Application in secondary batteries is beneficial to improving the power density and cycle life of the battery.

[0067] In some embodiments, the metal carbide includes at least one of titanium carbide, tungsten carbide, tin carbide, antimony carbide, bismuth carbide, and copper carbide; these metal carbides are highly active, and the carbon atoms therein come from porous carbon materials, which improves the bonding stability between the metal catalyst and the porous carbon material substrate, prevents the metal catalyst from being washed away by the flowing electrolyte during battery operation, and improves the cycle stability of the battery.

[0068] In some embodiments, the loading amount of metal carbide in the carbon electrode composite material is 0.5 to 10 mg / cm 2 The loading amount of the metal catalyst metal carbide fully ensures the high catalytic activity of the carbon electrode composite material. If the loading amount of the metal carbide is too low, the catalytic effect of the carbon electrode composite material is reduced. If the loading amount of the metal carbide is too high, it will cause the metal catalyst in the composite material to agglomerate, resulting in a larger catalyst particle size, reducing the active specific surface area of ​​the catalyst and also reducing the catalytic effect of the carbon electrode composite material. In some specific embodiments, the loading amount of the metal carbide in the carbon electrode composite material includes but is not limited to 0.5 to 1 mg / cm 2 , 1~2mg / cm 2 2~4mg / cm 2 4~6mg / cm 2 , 6~8mg / cm 2 , 8~10mg / cm 2 wait.

[0069] In some embodiments, the porous carbon material includes carbon fibers with a diameter of 5 to 15 mm, and the porous carbon material of this diameter has the best active specific surface area. If the diameter of the carbon fibers in the porous carbon material is less than 5 mm, the porosity of the carbon electrode composite material will become smaller, and the channels formed by the overlap between the fibers, the space and path for fluid transmission will become smaller, thereby hindering the transmission of active substances. On the one hand, concentration polarization will occur, reducing the power density and energy efficiency of the battery. On the other hand, the capacity of the battery will be reduced, and the effective utilization rate of the active substance will be reduced. If the diameter of the carbon fibers in the porous carbon material is higher than 15 mm, not only will the process be difficult, but the specific surface area and reaction active sites of the carbon electrode composite material will also be reduced. In some embodiments, the diameter of the carbon fibers in the porous carbon material includes but is not limited to 5 to 15 mm, 6 to 14 mm, 7 to 13 mm, 8 to 12 mm, 9 to 11 mm, etc.

[0070] In some embodiments, the surface of the carbon fibers in the porous carbon material has nanopores with a diameter of 20 to 200 nm and a depth of 100 to 500 nm, so that a worm-like pore structure with a small pore size and a high depth is uniformly distributed in the porous carbon material. If the pore size of the nanopores is too large, the mechanical properties of the carbon electrode composite material will be damaged, which may easily lead to electrode damage. If the pore size of the nanopores is too small or the depth is too high, the ions will diffuse into the pores and react with the metal catalyst metal carbide, and their discharge will be affected, thereby affecting the catalytic effect. If the pore depth of the nanopores is too shallow, the coating effect on the metal catalyst is poor, which reduces the stability of the metal catalyst. In some embodiments, the diameter of the nanopores on the surface of the carbon fibers in the porous carbon material includes but is not limited to 20-200 nm, 30-180 nm, 50-150 nm, 80-120 nm, 100-110 nm, etc.; the depth includes but is not limited to 100-500 nm, 150-450 nm, 200-400 nm, 250-350 nm, 300-500 nm, etc.

[0071] In some embodiments, the porous carbon material is selected from at least one of carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon mesh. Pores are directly formed on the fiber surface of these carbon materials and metal catalyst metal carbides are loaded. The obtained carbon electrode composite material can be cut into a size that meets the application requirements according to the size of the battery electrode to be used and directly used as an electrode layer. It is flexible and convenient to use, has wide adaptability, and high efficiency.

[0072] In some embodiments, the carbon electrode composite material is used in flow battery electrodes, where the porous carbon material has an electrode thickness of 0.5 to 2.5 mm. Electrodes thicker than 2.5 mm are generally used in flow-through batteries, i.e., traditional flow batteries without a flow field. This type of battery generally has a lower power density because excessively thick electrodes lead to excessive battery resistance and ohmic losses, which reduces battery performance. Electrode thicknesses below 0.5 mm result in poor mechanical properties and a smaller surface area, so even with surface modification, battery performance is limited.

[0073] A third aspect of an embodiment of the present application provides a secondary battery, wherein the electrode of the secondary battery comprises the carbon electrode composite material prepared by the above method, or the above carbon electrode composite material.

[0074] The electrode of the secondary battery provided in the third aspect of the embodiment of the present application uses the above-mentioned carbon electrode composite material with high specific surface area, high catalytic activity, and high stability, thereby improving the power density and cycle life of the secondary battery.

[0075] In some embodiments, the secondary battery includes at least one of a flow battery, a lithium-ion battery, a fuel cell, and a hydrogen battery; wherein the flow battery is selected from at least one of an all-vanadium flow battery, an iron-chromium flow battery, and a vanadium-air flow battery.

[0076] In some embodiments, the carbon electrode composite material is applied to the negative electrode of a secondary battery. In some specific embodiments, the carbon electrode composite material is applied to the negative electrode of an all-vanadium liquid flow battery. Since the reaction rate on the negative electrode side of the all-vanadium liquid flow battery is limited, it is the main factor restricting the performance improvement of the all-vanadium battery. The application of the carbon electrode composite material to the negative electrode can increase the power density of the battery, and the carbon electrode composite material is relatively stable on the negative electrode side, has excellent catalytic activity for the vanadium ions on the negative electrode side, and can inhibit hydrogen evolution, thereby increasing the catalytic activity on the negative electrode side and reducing the occurrence of side reactions. The pentavalent vanadium ions on the positive electrode side are too oxidizing, which will reduce the stability of the catalyst in the carbon electrode composite material. After the carbon electrode composite material is applied to the negative electrode of the all-vanadium liquid flow battery, the battery is at 300mAcm -2 The energy efficiency is as high as 80%, and it can run stably for 300 cycles without energy efficiency attenuation, with good cycle stability.

[0077] In order to make the above implementation details and operations of this application clearly understood by those skilled in the art, as well as to significantly demonstrate the improved performance of the carbon electrode composite material and its preparation method and the secondary battery in the embodiments of this application, the above technical solutions are illustrated by multiple embodiments below.

[0078] Example 1

[0079] A graphite felt electrode composite material, the preparation of which comprises the following steps:

[0080] ① Place the graphite felt in a muffle furnace for heat treatment at 500°C for 6 hours, and cool it to obtain surface-activated graphite felt;

[0081] ② Dissolve 1 volume of titanium tetrachloride solution in 99 volumes of concentrated hydrochloric acid to form a titanium tetrachloride solution with a concentration of approximately 0.1M. Then, impregnate the surface-activated graphite felt twice and perform ultrasonic treatment for 1 minute. The treated graphite felt is air-dried and then dried in an oven at 60°C to obtain a titanium oxide-loaded graphite felt composite material. The chemical reaction formula is: TiCl4+2H2O→TiO2+4HCl.

[0082] ③ In an argon atmosphere, the graphite felt composite material loaded with titanium oxide was subjected to carbon thermal treatment at a heating rate of 5°C / min and a heat treatment temperature of 1200°C. After reaching the heat treatment temperature, the carbon thermal reaction was carried out for one hour. The chemical reaction formula is: The reaction product was cooled and placed in a nitrogen environment for protection until cooled to obtain a graphite felt electrode composite material.

[0083] A graphite felt electrode is obtained by directly cutting the graphite felt electrode composite material prepared in Example 1 into an electrode size.

[0084] An all-vanadium redox flow battery, wherein the negative electrode adopts the graphite felt electrode of Example 1, the end plate is an aluminum plate, the flow field plate is a graphite bipolar plate, the diaphragm is DuPont's 212 series, and the electrolyte is commercial 1.7M vanadium ion + 3M sulfuric acid

[0085] Examples 2 to 5

[0086] A graphite felt composite material, which differs from Example 1 in that:

[0087] 0.25, 0.5, 2, and 4 volumes of titanium tetrachloride solution were dissolved in 99.75, 99.5, 98, and 96 volumes of concentrated hydrochloric acid, respectively, to form titanium tetrachloride solutions with concentrations of approximately 0.025, 0.05, 0.2, and 0.4 M, respectively. Specifically, Example 2 used a 0.025 M titanium tetrachloride solution, Example 3 used a 0.05 M titanium tetrachloride solution, Example 4 used a 0.2 M titanium tetrachloride solution, and Example 5 used a 0.4 M titanium tetrachloride solution.

[0088] A graphite felt electrode. The difference between Examples 2 to 5 and Example 1 is that the graphite felt electrodes are made of the graphite felt electrode composite materials prepared in Examples 2 to 5 respectively.

[0089] An all-vanadium redox flow battery, wherein the difference between Examples 2 to 5 and Example 1 is that the negative electrodes respectively use the graphite felt electrodes prepared in Examples 2 to 5.

[0090] Comparative Example 1

[0091] Take the original graphite felt as comparative example 1

[0092] An all-vanadium liquid flow battery, which differs from Example 1 in that: the negative electrode uses original graphite felt.

[0093] Comparative Example 2

[0094] A graphite felt electrode material, which differs from Example 1 in that:

[0095] Only the graphite felt is heat-treated, that is, the graphite felt is placed in a muffle furnace for heat treatment at a temperature of 500° C. for 6 hours, and then cooled to obtain a surface graphite felt electrode material.

[0096] An all-vanadium liquid flow battery, which differs from Example 1 in that the negative electrode adopts the graphite felt electrode material prepared in Comparative Example 2.

[0097] Comparative Example 3

[0098] A graphite felt electrode material, which differs from Example 1 in that:

[0099] No carbon heat treatment was performed, that is, ① the graphite felt was placed in a muffle furnace for heat treatment at a temperature of 500°C for 6 hours, and then cooled to obtain surface-activated graphite felt;

[0100] ② Dissolve 4 volumes of titanium tetrachloride solution in 96 volumes of concentrated hydrochloric acid to form a titanium tetrachloride solution with a concentration of approximately 0.2M. Then, immerse the surface-activated graphite felt twice and perform ultrasonic treatment for 1 minute. Place the treated graphite felt in the air to dry, and then place the dried graphite felt in an oven at 60°C to dry to obtain a graphite felt electrode material loaded with titanium oxide.

[0101] An all-vanadium redox flow battery is different from Example 1 in that the negative electrode adopts the titanium oxide-loaded graphite felt electrode material prepared in Comparative Example 3.

[0102] Comparative Example 4

[0103] A composite electrode, the preparation of which comprises the following steps:

[0104] ① The original porous carbon felt was placed in a muffle furnace and maintained at a high temperature of 500°C for 5 hours in an air atmosphere to obtain a heat-treated porous carbon felt.

[0105] ② Dissolve 200 mg of bismuth nitrate in 20 mL of ethylene glycol to obtain a bismuth nitrate solution. Then, immerse the heat-treated porous carbon felt in the bismuth nitrate solution, stir in an ultrasonic bath for 1 hour, and then dry at 80°C for 2 hours to obtain a carbon felt with a Bi(NO3)3 coating.

[0106] ③ The carbon felt coated with Bi(NO3)3 was transferred to a tube furnace and calcined at 200°C in an argon atmosphere at a heating rate of 10°C / min for 1 hour to completely decompose the Bi(NO3)3, resulting in a carbon felt coated with Bi2O3. The bismuth oxide generated by the thermal decomposition of the bismuth salt and the carbon on the electrode surface were then subjected to a carbothermal reduction reaction under argon. The reaction was maintained at 700°C for 1.5 hours at a heating rate of 5°C / min. Finally, the sample was washed with ultrapure water to obtain a carbon electrode composite material with bismuth particles adsorbed on its surface, i.e., a composite electrode.

[0107] An all-vanadium redox flow battery is different from Example 1 in that: the negative electrode adopts the carbon electrode composite material prepared in Comparative Example 4 and having bismuth elemental particles adsorbed on the surface.

[0108] Furthermore, in order to verify the progress of the embodiments of the present application, the carbon electrode composite materials, electrodes, secondary batteries, etc. in Examples 1 to 5 and Comparative Example 1 were subjected to the following performance tests:

[0109] 1. The morphology of the graphite felt composite materials prepared in Example 1 and Comparative Example 1 was observed respectively. Figures 1 to 3 As shown. Figure 1 (1-1) is a macroscopic morphology of the original graphite felt of Comparative Example 1, (1-2) is a morphology of the graphite felt electrode composite material prepared in Example 4, and (1-3) is a macroscopic morphology of the graphite felt electrode composite material prepared in Example 5. As can be seen from the accompanying drawings, when the solution concentration of the titanium tetrachloride solution is too high, reaching 0.4M, the surface of the graphite felt electrode composite material obtained is damaged to a certain extent. From the accompanying drawings (1-3), it can be seen that when the 0.4M titanium tetrachloride solution is used for immersion and burning and then subjected to carbon thermal reaction, the surface of the graphite felt electrode composite material obtained is obviously damaged to the naked eye, indicating that the titanium tetrachloride solution with too high a concentration is not suitable for immersion and will destroy the graphite felt structure. When the concentration of the titanium tetrachloride solution is 0.2M, the graphite felt electrode composite material can basically maintain the original porous structure characteristics of the graphite felt on a macroscopic basis, and a slight silk falling phenomenon occurs. When the concentration of the titanium tetrachloride solution was 0.1M, the graphite felt electrode composite material was able to maintain the original porous structure of the graphite felt on a macroscopic scale, and the graphite felt structure did not collapse. Because the nature of the carbothermal reaction is to corrode the porous electrode surface, it will reduce the electrode's mechanical properties. Tests have found that when the TiCl4 concentration is 0.2M, the carbon electrode body will fall off. At a concentration of 0.8M, the electrode will suffer severe burns, and it is difficult to maintain mechanical properties.

[0110] In addition, Figure 2 (2-1 and 2-11) are microscopic electron micrographs of the original graphite felt fibers of Comparative Example 1, (2-2 and 2-22) are microscopic electron micrographs of the graphite felt composite material after loading titanium oxide in Comparative Example 3, and (2-3 and 2-33) are microscopic morphology images of the graphite felt electrode composite material prepared in Example 1. The electron micrographs reveal that titanium oxide is uniformly loaded on the carbon fiber surface in the graphite felt composite material after impregnation with a 0.1M titanium tetrachloride solution, and that after carbon heat treatment, uniform worm-like nanopores are distributed on the surface of the graphite felt carbon fibers. The worm-like nanopores have a diameter of approximately 20-200 nanometers and a pore depth of approximately 100-500 nanometers.

[0111] In addition, Figure 3 Figure (3-1) is a transmission electron micrograph of the graphite felt electrode composite material of Example 1. It can be seen that the titanium carbide particles in the composite material of Example 1 are small and evenly coated within the pores of the graphite felt. Figure (3-2) is a scanning electron micrograph of a carbon electrode composite material prepared in Comparative Example 4 with bismuth elemental particles adsorbed on the surface. It can be seen that in the composite electrode material prepared in Comparative Example 4, no nanopores are formed on the carbon fiber surface, and the bismuth metal is directly attached to the carbon fiber surface in the form of independent elemental particles, rather than being embedded and coated within the carbon fiber through pores. In addition, the bismuth metal particles are relatively large in size.

[0112] 2. X-ray diffraction tests were performed on the original graphite felt of Comparative Example 1, the titanium oxide loaded graphite felt electrode material of Comparative Example 3, and the graphite felt electrode composite material prepared in Example 1. Figure 4 The test results show that before the carbothermal reaction, the titanium oxide-loaded graphite felt composite material only had a strong TiO2 signal peak, indicating that the TiO2 seeds had successfully attached to the porous graphite felt surface. After the carbothermal reaction, the TiO2 signal peak in the graphite felt electrode composite material completely disappeared, and a strong TiC peak appeared, indicating that the TiO2 seeds adsorbed on the graphite felt surface had completely transformed into TiC nanoparticles through the carbothermal reaction.

[0113] 3. Cyclic voltammetry tests were performed on the all-vanadium redox flow batteries prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1. Figure 5 The test results show that the battery made of original graphite felt in Comparative Example 1 has only hydrogen evolution peaks, but no redox peaks of vanadium ions, which means that the original graphite felt electrode not only has poor catalytic activity for vanadium ions, but also easily triggers hydrogen evolution reaction. Comparative Example 2 uses only heat-treated graphite felt to make batteries, Comparative Example 3 uses a battery made of materials that are impregnated with TiO2 after heat treatment but not subjected to carbon heat treatment, and the battery made of the graphite felt electrode composite material in Example 1, the catalytic activity for vanadium ions gradually increases, especially in Example 1, where a very obvious redox peak appears. This shows that the graphite felt electrode composite material with worm-like nanopores embedded in the catalyst in Example 1 has extremely strong catalytic activity for vanadium ions. In addition, during the reduction process, the titanium carbide deposition clearly does not show the appearance of hydrogen evolution peaks, which means that the TiC metal carbide catalyst can effectively inhibit the hydrogen evolution reaction.

[0114] 4. AC impedance test was performed on the graphite felt electrodes prepared in Example 1 and Comparative Examples 1 to 3. The test results are shown in the attached figure. Figure 6 As shown, the charge transfer impedance of the graphite felt electrode of the original graphite felt (P-GF) in comparative example 1, the graphite felt electrode of only heat treatment (T-GF) in comparative example 2, the graphite felt electrode of TiO2 impregnation (TiO2-GF) in comparative example 3, and the graphite felt electrode after carbon thermal reaction (TiC-WN-GF) in example 1 gradually decreases, which is consistent with the results of cyclic voltammetry test.

[0115] 5. The rate performance test of the all-vanadium redox flow batteries prepared in Example 1 and Comparative Examples 1 to 3 was carried out. The test results are shown in the attached figure. Figure 7 As shown, the battery of Example 1, when the current density is 300mAcm -2Under these conditions, energy efficiency remained as high as 80%, and electrolyte utilization reached 73%. Battery disassembly revealed that the graphite felt electrode in Example 1 had blocked flow channels. Battery disassembly revealed that the worm-like nanopore-embedded catalyst electrode prepared at a TiCl4 concentration of 0.2M in Example 4 had blocked flow channels. This suggests that as TiCl4 concentration increases, the number of nanopores and catalysts gradually increases, leading to improved battery performance.

[0116] 6. The cycle stability of Example 1 was tested, and the test results are shown in the attached figure. Figure 8 As shown, after 300 cycles of long-term cycle testing, the battery energy efficiency can always be maintained above 95%, and the coulombic efficiency and voltage efficiency can be maintained above 80%, with no obvious attenuation and good cycle stability.

[0117] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a carbon electrode composite material, characterized in that: The following steps are involved: obtaining a surface-activated carbon material; The surface-activated carbon material is mixed with a solution of a metal catalyst precursor, hydrolyzed, and dried to obtain a carbon composite material loaded with metal oxides; the metal element in the metal catalyst precursor includes at least one of titanium, tungsten, tin, and antimony; and the concentration of the metal catalyst precursor in the solution is 0.1 to 0.3 mol / L; Under an inert atmosphere, the carbon composite material is subjected to a carbon thermal reaction and cooled to obtain a carbon electrode composite material. The carbon electrode composite material comprises a porous carbon material and metal carbide encapsulated in the pores of the porous carbon material.

2. The method for preparing the carbon electrode composite material according to claim 1, wherein: The metal catalyst precursor is in the form of at least one of metal chloride and metal sulfate.

3. The method for preparing the carbon electrode composite material according to claim 2, wherein: The solvent in the solution of the metal catalyst precursor is selected from hydrochloric acid with a mass fraction of 20 to 38%; And / or, the metal catalyst precursor includes at least one of titanium tetrachloride, tungsten chloride, tin chloride, antimony chloride, titanyl sulfate, tungsten sulfate, tin sulfate, and antimony sulfate.

4. The method for preparing the carbon electrode composite material according to any one of claims 1 to 3, wherein: The conditions of the carbon thermal reaction include: heating to 1000-1400° C. at a rate of 2-10° C. / min and keeping the temperature for 1-3 hours under an inert atmosphere.

5. The method for preparing the carbon electrode composite material according to claim 4, wherein: The mixing treatment step includes: soaking the surface-activated carbon material in the solution of the metal catalyst precursor, drying it in the air and then drying it at a temperature of 50 to 70° C. to obtain the carbon composite material loaded with metal oxide.

6. The method for preparing the carbon electrode composite material according to claim 1 or 5, wherein: The step of obtaining the surface-activated carbon material comprises: performing surface treatment on the carbon material, introducing oxygen-containing functional groups on the surface of the carbon material, and obtaining the surface-activated carbon material; And / or, the surface activated carbon material is selected from at least one of carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon mesh; And / or, the surface-activated carbon material includes at least one of graphite, graphene, carbon nanotubes, carbon black, carbon particles, and carbon fibers.

7. A carbon electrode composite material prepared by the method according to any one of claims 1 to 6, characterized in that: The invention comprises a porous carbon material and metal carbide encapsulated in the pores of the porous carbon material.

8. The carbon electrode composite material according to claim 7, wherein In the carbon electrode composite material, the loading amount of the metal carbide is 0.5 to 10 mg / cm 2 ; And / or, the metal carbide includes at least one of titanium carbide, tungsten carbide, tin carbide, and antimony carbide; And / or, the porous carbon material has nanopores with a diameter of 20 to 200 nm and a depth of 100 to 500 nm, and the metal carbide is coated in the nanopores; And / or, the porous carbon material includes carbon fibers having a diameter of 5 to 15 mm; And / or, the particle size of the metal carbide is 5 to 100 nm; And / or, the porous carbon material is selected from at least one of carbon paper, carbon cloth, carbon felt, graphite felt, and electrospun carbon mesh.

9. A secondary battery, characterized in that: The electrode of the secondary battery comprises the carbon electrode composite material prepared by the method according to any one of claims 1 to 6, or the carbon electrode composite material according to any one of claims 7 to 8.

10. The secondary battery according to claim 9, wherein The secondary battery includes at least one of a flow battery, a lithium-ion battery, a fuel cell, and a hydrogen battery; wherein the flow battery is selected from at least one of an all-vanadium flow battery, an iron-chromium flow battery, and a vanadium-air flow battery; And / or, the carbon electrode composite material is applied to the negative electrode of the secondary battery.

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