MOF material coated carbon fiber porous carbon composite material, preparation method and application

Abstract

The invention provides an MOF material coated carbon fiber porous carbon composite material as well as a preparation method and application thereof, and relates to the technical field of porous carbon materials. The MOF material coated carbon fiber porous carbon composite material is of a fibrous core-shell structure, an inner core is a composite inner core with carbon fibers as a substrate, carbon nanotubes grow on the surface and gaps are filled with porous carbon, and a shell layer is an MOF material coating the inner core. The carbon fibers provide strong mechanical support to inhibit volume expansion, the carbon nanotubes construct a continuous conductive network to reduce impedance, the porous carbon improves electrolyte retention and ion transmission efficiency, the MOF fills the inner core defect and reduces side reaction, and low expansion, high conductivity, high first efficiency and cycle stability of the material are achieved. The preparation method comprises the steps of precursor preparation, carbon nanotube deposition and MOF coating activation, and the material can be applied to a silicon-carbon negative electrode.

Description

Technical Field

[0001] This invention relates to the field of porous carbon materials technology, and in particular to a MOF material-coated carbon fiber porous carbon composite material, its preparation method, and its application. Background Technology

[0002] Porous carbon, as a major component of silicon-carbon materials, plays a crucial role in the specific capacity, power, expansion, and cycling properties of these materials due to its pore volume, pore size, strength, and structure. Currently, porous carbon is mainly prepared from biomass and its resin-based raw materials through processes such as carbonization, activation, and impurity removal. However, the resulting porous carbon often suffers from numerous defects, poor electronic conductivity, low initial efficiency, and small pore size, which hinders the reduction of material expansion and the increase of silicon deposition.

[0003] Therefore, it is necessary to develop a porous carbon with low expansion, low impedance, and high initial efficiency to meet the demand for high-capacity, low-expansion, and high-power silicon-carbon. Summary of the Invention

[0004] To reduce the expansion, power consumption, and initial efficiency of porous carbon materials, this invention improves the electronic conductivity and reduces the expansion of the material by adding high-mechanical-strength carbon fibers to a porous carbon precursor as a carbon matrix and growing carbon nanotubes, and then coating the surface of the precursor with MOF material. Simultaneously, this invention provides a method for preparing MOF-coated porous carbon composite materials and their applications.

[0005] One of the objectives of this invention is to provide a MOF material-coated carbon fiber porous carbon composite material, wherein the composite material has a fibrous core-shell structure; The core-shell structure has a carbon fiber-carbon nanotube-porous carbon composite core. The carbon fiber-carbon nanotube-porous carbon composite core uses carbon fiber as a substrate, carbon nanotubes are grown on the surface of the substrate, and porous carbon is filled in the gap between the substrate and the carbon nanotubes. The shell of the core-shell structure is a MOF material that coats the outer surface of the carbon fiber-carbon nanotube-porous carbon composite core.

[0006] Preferably, the mass ratio of the carbon nanotubes, carbon fibers, porous carbon and MOF materials is (1-5):(30-45):(30-45):(10-20).

[0007] The second objective of this invention is to provide a method for preparing the MOF material-coated carbon fiber porous carbon composite material as described above, comprising the following steps: S1. After uniformly dispersing carbon fibers, catalysts and sugar compounds, the mixture is filtered and vacuum dried to obtain carbon fiber-porous carbon precursor. S2. Deposit carbon nanotubes on the carbon fiber-porous carbon precursor to obtain intermediate material; S3. MOF is coated onto the intermediate material and activated to obtain MOF material coated carbon fiber porous carbon composite material.

[0008] Preferably, the mass ratio of the carbon fiber, catalyst, and sugar compound is 100:(1-5):(50-200).

[0009] Preferably, the metal source of the MOF is nickel acetate tetrahydrate, and the organic ligand is terephthalic acid; The total mass ratio of nickel acetate tetrahydrate, terephthalic acid, and intermediate material is (50-100):100.

[0010] Preferably, the molar ratio of nickel acetate tetrahydrate to terephthalic acid is 1:1.

[0011] Preferably, the carbon fiber in step S1 has a diameter of 150-200 nm and a length of 1-10 μm.

[0012] Preferably, the catalyst in step S1 includes one or more of nickel chloride, ferric chloride, cobalt chloride, nickel nitrate, ferric nitrate, or cobalt nitrate; The glycosyl compound includes one or more of glucose, fructose, galactose, lactose, sucrose, or maltose.

[0013] Preferably, the deposition of carbon nanotubes on the carbon fiber-porous carbon precursor to obtain the intermediate material includes: Carbon nanotubes were grown on the surface of the carbon fiber-porous carbon precursor by vapor deposition at 900-1100℃ and a flow rate of 10-100 ml / min for 30-300 min to obtain the intermediate material.

[0014] Preferably, the intermediate material is coated with MOF, and activated to obtain a MOF-coated carbon fiber porous carbon composite material, comprising: Nickel acetate tetrahydrate and terephthalic acid were added to a mixed solvent consisting of deionized water and N,N-dimethylacetamide to obtain a MOF precursor solution. The intermediate material is added to the MOF precursor solution, mixed evenly, and stirred at 100-200°C for 2-12 hours to obtain the MOF-coated intermediate material. At 800-1000℃, carbon dioxide gas was introduced at a flow rate of 50-200 ml / min to activate the MOF-coated intermediate material for 30-300 min, resulting in MOF-coated carbon fiber porous carbon composite material. The volume ratio of deionized water to N,N-dimethylacetamide is 1:1; the total mass concentration of nickel acetate tetrahydrate and terephthalic acid in the MOF precursor solution is 5-20 wt%.

[0015] The third objective of this invention is to provide an application of the MOF material-coated carbon fiber porous carbon composite material as described above in silicon-carbon anode materials.

[0016] The beneficial effects of this invention are: This invention constructs a fibrous core-shell structure that synergistically combines the functions of carbon fibers, carbon nanotubes, porous carbon, and MOF materials. Using fibrous carbon fibers as a rigid substrate, their excellent mechanical strength disperses volumetric stress, while the outer MOF material provides physical confinement. This dual effect significantly suppresses material expansion and prevents structural collapse. Carbon nanotubes grow directionally on the carbon fiber surface, forming a continuous conductive network that greatly reduces the material's resistivity. Porous carbon fills the gaps, and its rich pore structure and high specific surface area enhance the electrolyte's adsorption and retention capacity and accelerate ion transport.

[0017] Meanwhile, the dense and uniform MOF coating layer can fill tiny defects on the core surface, reduce side reactions between the electrolyte and carbon materials, and improve initial efficiency and cycle stability. The MOF material-coated carbon fiber porous carbon composite material of this invention achieves a synergistic effect of low expansion, high conductivity, high electrolyte retention, and high mechanical strength, meeting the application requirements of high-capacity, low-expansion, and high-power silicon-carbon materials. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the MOF-coated carbon nanotube-doped carbon porous carbon composite material prepared in Example 1. Detailed Implementation

[0019] The present application will now be described in further detail with reference to embodiments. In the following description, certain specific details are included to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented without employing one or more of these specific details, but using other methods, components, materials, etc. Unless otherwise required by the present invention, the terms "comprising" and "including" should be interpreted in an open-ended, inclusive sense, meaning "including but not limited to". Throughout this specification, "an embodiment," "an embodiment," "a preferred embodiment," or "some embodiments" means that at least one embodiment includes a specific reference element, structure, or feature related to that embodiment. Therefore, the phrases "in an embodiment," "in an embodiment," "in a preferred embodiment," or "in some embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. Furthermore, specific elements, structures, or features may be combined in one or more embodiments in any suitable manner.

[0020] According to a first aspect of the present invention, a MOF material-coated carbon fiber porous carbon composite material is provided, the composite material having a fibrous core-shell structure; The core-shell structure has a carbon fiber-carbon nanotube-porous carbon composite core. The carbon fiber-carbon nanotube-porous carbon composite core uses carbon fiber as a substrate, carbon nanotubes are grown on the surface of the substrate, and porous carbon is filled in the gap between the substrate and the carbon nanotubes. The shell of the core-shell structure is a MOF material that coats the outer surface of the carbon fiber-carbon nanotube-porous carbon composite core.

[0021] In this invention, the fibrous morphology provides mechanical support and an anti-expansion foundation for the material. Traditional porous carbon is mostly in block or granular form, with low mechanical strength, and is prone to breakage due to volume changes during charging, discharging, or fabrication. The fibrous morphology, determined by the carbon fiber substrate, can disperse stress through its slender structure, improving the overall mechanical strength of the material, suppressing volume expansion at its source, and preventing structural collapse. The fibrous morphology also increases the specific surface area of ​​the material and facilitates the uniformity of subsequent carbon nanotube growth and MOF coating, avoiding local component aggregation and ensuring structural integrity.

[0022] In the core-shell structure, the carbon fiber-carbon nanotube-porous carbon composite core functions as support, conductivity, and liquid storage. Carbon fiber serves as a rigid substrate, carbon nanotubes construct a conductive network, and porous carbon provides ion transport channels. These three elements form an integrated system encompassing mechanics, conductivity, and liquid storage, solving the problem of traditional materials where conductivity and liquid storage are mutually exclusive. The shell MOF material is responsible for anti-expansion and defect reduction regulation. MOF itself has a low expansion rate, and when coated on the core surface, it forms a physical constraint layer, directly restricting the volume changes of the core during charging and discharging. Simultaneously, the dense structure of MOF can fill tiny defects on the core surface, reducing side reactions between the electrolyte and carbon materials, improving initial efficiency, and avoiding performance degradation caused by the exposure of core functional components.

[0023] Carbon fiber possesses extremely high mechanical strength and stability. As a core substrate, it not only determines the fibrous morphology of the material but also resists structural deformation during carbon nanotube growth, MOF coating, and activation processes, while mitigating volume expansion during charging and discharging. Traditional porous carbon has numerous inherent defects and obstructed electron transport paths, resulting in high resistivity. Carbon nanotubes, with their excellent electronic conductivity, can form a continuous conductive network after directional growth on the carbon fiber surface, significantly reducing the material's resistivity without occupying excessive pore space or affecting its liquid storage performance. Porous carbon, formed by the carbonization and activation of glycosyl compounds, possesses a rich pore structure that fills the gaps between carbon fibers and carbon nanotubes, greatly enhancing the material's liquid retention capacity while providing ample channels for lithium-ion transport, thus solving the problem of slow ion diffusion caused by the small pore volume and uneven pore size of traditional porous carbon. MOF materials have stable structures and low expansion rates. When coated on the core surface, they can restrict the volume expansion of the core through a combination of physical coating and chemical bonding. Furthermore, the dense structure of MOFs can fill defects on the core surface, reduce side reactions between the electrolyte and carbon materials, thereby improving the initial efficiency of the material and enhancing cycle stability.

[0024] The fibrous structure provides an ideal carrier for the directional growth of carbon nanotubes, porous carbon filling, and uniform MOF coating, avoiding performance failure caused by component dispersion. The core combination of carbon fiber, carbon nanotube, and porous carbon solves the basic requirements of support, conductivity, and liquid storage, providing a prerequisite for the MOF shell to perform its functions of anti-expansion and defect reduction. The MOF shell compensates for the shortcomings of insufficient control of core expansion and a large number of defects. The synergistic design of structure and composition ultimately achieves multi-dimensional performance optimization of the material, including low expansion, high conductivity, high liquid retention, high initial efficiency, and high cycling stability, meeting the application requirements of high-capacity, low-expansion, and high-power silicon-carbon materials.

[0025] In this invention, the MOF material is a crystalline porous material formed by the self-assembly of metal ions / metal clusters and organic ligands; preferably, the metal ions include Ni. 2+ Zn 2+ Co 2+ Cu2+ or Cr 3+ Organic ligands include terephthalic acid, phthalic acid, or pyromellitic acid. Preferably, the metal ion includes Ni. 2+ or Zn 2+ The organic ligands include terephthalic acid or phthalic acid; preferably, the MOF includes Ni-MOF or Zn-MOF.

[0026] In a preferred embodiment of the present invention, the mass ratio of the carbon nanotubes, carbon fibers, porous carbon and MOF materials is (1-5):(30-45):(30-45):(10-20).

[0027] In this invention, carbon fiber serves as the structural framework. A proportion of 30-45% ensures sufficient mechanical strength and effectively suppresses expansion. If the proportion is below 30%, the framework provides insufficient support, leading to a significant increase in the expansion rate. If it exceeds 45%, it will encroach on the space of porous carbon, resulting in a reduction in pore structure and a decrease in liquid retention and ion transport capabilities. A similar proportion of porous carbon to carbon fiber is intended to match the supporting function of carbon fiber through sufficient pore structure; a proportion of 30-45% creates abundant ion transport channels. If the proportion is too low, the pore volume is insufficient, resulting in poor liquid storage and ion diffusion efficiency. If it is too high, it will reduce the overall mechanical strength of the material and may compress the conductive network space of the carbon nanotubes.

[0028] Carbon nanotubes have extremely high conductivity; a proportion of 1-5% is enough to form a continuous conductive network on the surface of carbon fibers, significantly reducing resistivity. If the proportion is higher than 5%, agglomeration is likely to occur, blocking the pores of porous carbon and affecting liquid retention and ion transport. If the proportion is lower than 1%, the conductive network is discontinuous, which cannot effectively improve the conductivity of the material, and the resistivity will rise, failing to meet the low impedance requirement.

[0029] When used as a coating layer, MOFs with a content of 10-20% can achieve uniform and complete coating, effectively constraining core expansion and filling defects. If the content is less than 10%, the coating is incomplete, and the anti-expansion and defect reduction effects are not good. If it is more than 20%, it will thicken the shell, block the pores of porous carbon, reduce the electrolyte adsorption and ion transport efficiency, and may also increase the material density, affecting electrochemical performance.

[0030] According to a second aspect of the present invention, a method for preparing the MOF material-coated carbon fiber porous carbon composite material as described above is provided, comprising the following steps: S1. After uniformly dispersing carbon fibers, catalysts and sugar compounds, the mixture is filtered and vacuum dried to obtain carbon fiber-porous carbon precursor. S2. Deposit carbon nanotubes on the carbon fiber-porous carbon precursor to obtain intermediate material; S3. MOF is coated onto the intermediate material and activated to obtain MOF material coated carbon fiber porous carbon composite material.

[0031] In this invention, the glycosyl compound is a porous carbon precursor. In step S1, carbon fibers, a catalyst, and the glycosyl compound are uniformly dispersed and dried. This allows the glycosyl compound to bond tightly with the carbon fibers, laying the foundation for subsequent transformation into porous carbon that fills the gaps. It also allows the catalyst to be uniformly loaded onto the carbon fiber surface, providing nucleation sites for the directional growth of carbon nanotubes in step S2, thus achieving the pre-assembly of the substrate, precursor, and catalyst. Step S2 involves growing carbon nanotubes solely through a deposition reaction, allowing for precise control of temperature, carbon source supply, and other conditions, avoiding conflicts with other reaction conditions and ensuring the continuity of the conductive network. Step S3 involves coating the intermediate surface with MOF and activating it. This is because the MOF needs to act as a shell to coat the already formed core, and activation must occur after MOF coating. This protects the core from excessive etching while simultaneously improving the density of the MOF layer, ultimately forming the target core-shell structure.

[0032] In a preferred embodiment of the present invention, the mass ratio of the carbon fiber, the catalyst and the sugar compound is 100:(1-5):(50-200).

[0033] In this invention, carbon fiber serves as the skeletal carrier of the entire material, with a fixed proportion as a baseline, forming the basis for subsequent catalyst loading and glycosylation compound bonding. The catalyst provides nucleation sites for the growth of S2 carbon nanotubes, and a proportion of 1-5 parts is just right for uniform loading on the surface of 100 parts of carbon fiber. If it is less than 1 part, there are insufficient nucleation sites, resulting in sparse carbon nanotube growth and an inability to form a continuous conductive network; if it is more than 5 parts, the catalyst particles are prone to agglomeration, which not only reduces catalytic efficiency but may also block the pores of subsequent porous carbon or affect the bonding between glycosylation compounds and carbon fiber. The low proportion design satisfies the catalytic requirements while avoiding the process and performance problems caused by catalyst redundancy. The glycosylation compound is a precursor to porous carbon, and a proportion of 50-200 parts ensures that after subsequent carbonization and activation, sufficient porous carbon is generated to fill the gaps between carbon fiber and carbon nanotube. If the amount is less than 50 parts, the converted porous carbon is insufficient, and the pore volume and specific surface area do not meet the requirements for liquid storage and ion transport. If the amount is more than 200 parts, the excessive sugar compounds will cover the carbon fiber surface, hindering catalyst loading and carbon nanotube growth, and may also lead to excessive accumulation of porous carbon, reducing the overall mechanical strength of the material. This range can ensure the core function of porous carbon while matching its supporting-liquid storage function with the carbon fiber substrate.

[0034] In a preferred embodiment of the present invention, the total mass ratio of nickel acetate tetrahydrate, terephthalic acid, and intermediate material is (50-100):100; In a preferred embodiment of the present invention, the molar ratio of nickel acetate tetrahydrate to terephthalic acid is 1:1.

[0035] In this invention, nickel acetate tetrahydrate and terephthalic acid are used as metal sources (Ni) for the MOF. 2+ The molar ratio of metal ions to organic ligands is close to 1:1. This equiproportion allows the metal ions and ligands to fully coordinate, generating a structurally complete and dense MOF material without excess metal source or ligand residue, thus avoiding impurities affecting the material's electrochemical performance. If the proportion of any component deviates, it will lead to poor crystallinity, abnormal porosity, or residual unreacted components in the MOF, reducing the coating's anti-expansion and defect reduction effects.

[0036] The ratio of the total mass of nickel acetate tetrahydrate and terephthalic acid to the intermediate material is (50-100):100, which allows the MOF to form a thin and complete coating layer on the surface of the intermediate. If the total proportion of nickel acetate tetrahydrate and terephthalic acid is less than 50%, the amount of MOF generated is insufficient and cannot completely cover the surface of the intermediate, resulting in discontinuous coating and making it difficult for the MOF to play its core role of constraining expansion and filling defects. If the total proportion of nickel acetate tetrahydrate and terephthalic acid is greater than 100%, the MOF coating layer is too thick, which will block the pore structure of the intermediate material, hinder electrolyte adsorption and ion transport, and may also increase the material impedance, offsetting the conductivity and liquid storage advantages of the core.

[0037] In a preferred embodiment of the present invention, the carbon fiber in step S1 has a diameter of 150-200 nm and a length of 1-10 μm.

[0038] In this invention, if the diameter is less than 150 nm, the carbon fiber itself lacks sufficient mechanical strength and cannot withstand the stress during subsequent vapor deposition, MOF coating, and activation processes, making it prone to breakage and collapse, thus losing its core role as a structural framework. Simultaneously, the small surface area results in insufficient catalyst loading sites and carbon nanotube growth space, making it difficult to form a continuous conductive network. If the diameter is greater than 200 nm, the specific surface area of ​​the carbon fiber will significantly decrease, leading to insufficient binding of glycosyl compounds, making it difficult for the subsequently converted porous carbon to uniformly fill the gaps. Furthermore, an excessively large diameter will crowd out the internal pore space of the material, reducing ion transport channels and lowering liquid retention and electrochemical kinetics performance.

[0039] A diameter of 150-200nm ensures that the carbon fiber has sufficient rigidity to support the overall structure and suppress expansion, while also providing sufficient surface sites to ensure uniform catalyst loading and directional growth of carbon nanotubes.

[0040] If the length is less than 1 μm, the carbon fibers are short and fibrous, making it difficult for them to interweave and form a continuous skeletal network. This results in weak stress dispersion and a decrease in the overall mechanical strength and anti-expansion properties of the material. Furthermore, short fibers are prone to agglomeration, leading to uneven dispersion of the catalyst and glycosyl compounds in S1, and causing localized defects in subsequent carbon nanotube growth and MOF coating. If the length is greater than 10 μm, the carbon fibers are easily entangled and knotted, making uniform dispersion difficult during ultrasonic dispersion. This results in uneven catalyst loading and locally dense or sparse carbon nanotube growth. Simultaneously, excessively long fibers affect the uniformity of subsequent slurry coating, reducing application compatibility. A length of 1-10 μm allows the carbon fibers to form a continuous interwoven skeleton, dispersing volumetric stress, while also ensuring uniform dispersion during the process.

[0041] In a preferred embodiment of the present invention, the catalyst in step S1 includes one or more of nickel chloride, ferric chloride, cobalt chloride, nickel nitrate, ferric nitrate, or cobalt nitrate. The glycosyl compound includes one or more of glucose, fructose, galactose, lactose, sucrose, or maltose.

[0042] In this invention, the catalyst described in step S1 is, for example, nickel chloride, ferric chloride, cobalt chloride, nickel nitrate, ferric nitrate, cobalt nitrate, nickel chloride and ferric chloride, nickel chloride and cobalt chloride, ferric chloride and cobalt chloride, nickel nitrate and ferric nitrate, nickel nitrate and cobalt nitrate, ferric nitrate and cobalt nitrate, nickel chloride and nickel nitrate, ferric chloride and ferric nitrate, cobalt chloride and cobalt nitrate, nickel chloride, ferric chloride and cobalt chloride, nickel nitrate, ferric nitrate and cobalt nitrate, nickel chloride, ferric chloride and nickel nitrate, nickel chloride, cobalt chloride and cobalt nitrate, ferric chloride, cobalt chloride and ferric nitrate, nickel chloride, ferric nitrate and nickel nitrate, or cobalt chloride, ferric nitrate and cobalt nitrate.

[0043] Sugar compounds include, for example, glucose, fructose, galactose, lactose, sucrose, maltose, glucose and fructose, glucose and sucrose, glucose and maltose, fructose and galactose, sucrose and maltose, lactose and maltose, glucose, fructose and galactose, glucose, sucrose and maltose, fructose, galactose and sucrose, glucose, maltose and lactose, or fructose, sucrose and maltose.

[0044] In a preferred embodiment of the present invention, carbon nanotubes are deposited on the carbon fiber-porous carbon precursor to obtain an intermediate material comprising: Carbon nanotubes were grown on the surface of the carbon fiber-porous carbon precursor by vapor deposition at 900-1100℃ and a flow rate of 10-100 ml / min for 30-300 min to obtain the intermediate material.

[0045] In a preferred embodiment of the present invention, the carbon source gas includes any one or a combination of at least two of methane, ethylene, acetylene, or propyne.

[0046] In a preferred embodiment of the present invention, the metal source of the MOF is nickel acetate tetrahydrate, and the organic ligand is terephthalic acid.

[0047] In a preferred embodiment of the present invention, MOF is coated onto the intermediate material, and the resulting MOF-coated carbon fiber porous carbon composite material is activated, comprising: Nickel acetate tetrahydrate and terephthalic acid were added to a mixed solvent consisting of deionized water and N,N-dimethylacetamide to obtain a MOF precursor solution. The intermediate material is added to the MOF precursor solution, mixed evenly, and stirred at 100-200°C for 2-12 hours to obtain the MOF-coated intermediate material. At 800-1000℃, carbon dioxide gas was introduced at a flow rate of 50-200 ml / min to activate the MOF-coated intermediate material for 30-300 min, resulting in MOF-coated carbon fiber porous carbon composite material. The volume ratio of deionized water to N,N-dimethylacetamide is 1:1; the total mass concentration of nickel acetate tetrahydrate and terephthalic acid in the MOF precursor solution is 5-20 wt%.

[0048] In this invention, CO2 reacts with residual impurities in the MOF shell and some carbon on the surface of the porous carbon core at high temperatures. On the one hand, it can form a more uniform microporous / mesoporous structure in the MOF shell, remove defects, and improve its coating density and resistance to expansion. On the other hand, it can widen the pore channels of the porous carbon core, increase the specific surface area, and enhance the electrolyte adsorption and ion transport efficiency. Moreover, CO2 has mild reactivity and will not excessively etch the carbon fiber skeleton and carbon nanotube conductive network, thus balancing the material's mechanical strength and conductivity, ultimately ensuring the synergistic performance of low expansion, high conductivity, and high liquid retention.

[0049] According to a third aspect of the present invention, an application of the MOF material-coated carbon fiber porous carbon composite material as described above in silicon-carbon anode materials is provided.

[0050] Example 1 A method for preparing MOF-coated carbon fiber porous carbon composite material includes the following steps: S1. Soak 100g of carbon fiber and 100g of glucose in 100g of a 3wt% nickel chloride aqueous solution, disperse evenly by ultrasonication, filter, and vacuum dry at 80℃ for 24h to obtain carbon fiber-porous carbon precursor; the diameter of the carbon fiber is 150-200nm and the length is 1-10μm. S2. The carbon fiber-porous carbon precursor is transferred to a tube furnace and heated to 1000℃ by vapor deposition. Methane gas is introduced at a flow rate of 50 ml / min for 150 min to grow carbon nanotubes on the carbon fiber surface to obtain the intermediate material. S3. Add 48g of nickel acetate tetrahydrate and 32g of terephthalic acid to 800g of a solution with a mass concentration of 10wt% prepared by mixing deionized water and N,N-dimethylacetamide solvent (volume ratio 1:1). Then add 100g of intermediate material, stir and mix evenly, and then stir and react at 150℃ for 6h. After the reaction is completed, cool to room temperature, separate the solid and liquid, wash, vacuum dry at 80℃ for 24h, and heat to 900℃. Then, introduce carbon dioxide gas and activate for 150min at a flow rate of 100ml / min to obtain Ni-MOF coated carbon nanotube doped carbon fiber porous carbon composite material.

[0051] Example 2 A method for preparing MOF-coated carbon fiber porous carbon composite material includes the following steps: S1. Soak 100g of carbon fiber and 50g of sucrose in 100g of 1wt% ferric chloride solution, disperse evenly by ultrasonication, filter, and vacuum dry at 80℃ for 24h to obtain carbon fiber-porous carbon precursor; the diameter of carbon fiber is 150-200nm and the length is 1-10μm. S2. The carbon fiber-porous carbon precursor is transferred to a tube furnace and heated to 900°C by vapor deposition. Methane gas is introduced at a flow rate of 10 ml / min for 300 min to grow carbon nanotubes on the carbon fiber surface to obtain the intermediate material. S3. 30g of nickel acetate tetrahydrate and 20g of terephthalic acid were added to 1000g of deionized water and N,N-dimethylacetamide solvent (volume ratio 1:1) to prepare a solution with a mass concentration of 5wt%. Then, 100g of intermediate material was added and stirred until homogeneous. The mixture was then stirred at 100℃ for 12h. After the reaction was completed, the mixture was cooled to room temperature, and after solid-liquid separation, it was washed, vacuum dried at 80℃ for 24h, and then heated to 800℃. Carbon dioxide gas was introduced and activated at a flow rate of 50ml / min for 30min to obtain Ni-MOF coated carbon nanotube-doped carbon fiber porous carbon composite material. Example 3 A method for preparing MOF-coated carbon fiber porous carbon composite material includes the following steps: S1. Soak 100g of carbon fiber and 200g of lactose in 50g of cobalt chloride solution with a mass concentration of 10wt%, disperse evenly by ultrasonication, filter, and vacuum dry at 80℃ for 24h to obtain carbon fiber-porous carbon precursor; the diameter of carbon fiber is 150-200nm and the length is 1-10μm. S2. The carbon fiber-porous carbon precursor is transferred to a tube furnace and heated to 1100℃ by vapor deposition. Methane gas is introduced at a flow rate of 100 ml / min for 300 min to grow carbon nanotubes on the carbon fiber surface to obtain the intermediate material. S3. Add 60g of nickel acetate tetrahydrate and 40g of terephthalic acid to 500g of a solution with a mass concentration of 20wt% prepared by mixing deionized water and N,N-dimethylacetamide solvent (volume ratio 1:1). Then add 100g of intermediate material, stir and mix evenly, and then stir and react at 200℃ for 2h. After the reaction is completed, cool to room temperature, separate the solid and liquid, wash, vacuum dry at 80℃ for 24h, and heat to 1000℃. Then, introduce carbon dioxide gas and activate for 30min at a flow rate of 200ml / min to obtain Ni-MOF coated carbon nanotube doped carbon fiber porous carbon composite material.

[0052] Example 4 Unlike Example 1, ethylene gas is introduced in step S2, but otherwise it is the same as Example 1.

[0053] Example 5 Unlike Example 1, the metal source of MOF in step S3 is zinc acetate tetrahydrate, while the rest is the same as in Example 1.

[0054] Example 6 Unlike Example 1, carbon dioxide is not introduced during the activation process in step S3; otherwise, it is the same as Example 1.

[0055] Example 7 Unlike Example 1, the organic ligand of MOF in step S3 is phthalic acid, while the rest is the same as in Example 1.

[0056] Comparative Example 1: Unlike Example 1, no nickel chloride catalyst was added in step S1, and there was no step S2, i.e. no carbon nanotubes were deposited. Otherwise, it was the same as Example 1.

[0057] Comparative Example 2: Unlike Example 1, step S3 is omitted, i.e., MOF is not covered; otherwise, it is the same as Example 1.

[0058] Comparative Example 3 Unlike Example 1, 100g of phenolic resin was added in step S1, but glucose was not added; otherwise, it was the same as Example 1.

[0059] Comparative Example 4 Unlike Example 1, no activation is performed in step S3; otherwise, it is the same as Example 1.

[0060] Performance testing 1) XRD test: XRD analysis of the Ni-MOF-coated carbon nanotube-doped carbon fiber porous carbon composite material prepared in Example 1, by... Figure 1 It can be seen that the (002) crystal plane peak of carbon is relatively broad at 2θ=23.81°, indicating that the material has a high degree of disorder. There is a very weak diffraction peak at 2θ=43.54°, which corresponds to the graphitization peak of carbon material, indicating that the material has a high degree of order.

[0061] 2) Physicochemical and button cell testing: 2.1) Physicochemical property testing: The pore volume and pore size of the porous carbon materials obtained in Examples 1-3 and Comparative Examples 1-2 were tested according to the national standard GB / T-38949-2020 "Determination of Pore Size of Porous Membranes - Standard Particle Method". Their specific surface area and tap density were tested according to the national standard GB / T38823-2020 "Silicon Carbon". The powder resistivity of each porous carbon material was measured using a four-probe tester. The test results are shown in Table 1.

[0062] Table 1 Performance Tests of Examples and Comparative Examples

[0063] As can be seen from Table 1, the materials in the examples have low powder resistivity and high pore volume. This is because the doping of carbon fibers and carbon nanotubes in the materials reduces the powder resistivity of the materials, and the high pore volume of MOF increases the pore volume of the composite material.

[0064] Example 3: 200g of lactose was used as a porous carbon precursor. After sufficient carbonization, it formed a richer pore structure with a pore volume of 0.94cm³. 3 / g; Cobalt chloride exhibits high catalytic activity, resulting in uniform carbon nanotube growth, a denser porous carbon structure with interstitial filling, and an increased specific surface area of ​​1887.6 m². 2 / g.

[0065] The resistivity of the powder in Example 3 is lower than that in Example 1 and Example 2 because the carbon nanotubes generated by cobalt chloride catalysis are denser and the conductive network is more continuous; the catalytic effect of ferric chloride is slightly weaker, the carbon nanotubes grow sparsely, and the conductivity is slightly reduced.

[0066] The physicochemical properties of Example 4 (using ethylene instead of methane as the carbon source), Example 5 (using zinc acetate instead of nickel acetate), and Example 7 (using phthalic acid instead of terephthalic acid) were similar to, but slightly lower than, those of Example 1. This indicates that both methane and ethylene can meet the growth requirements of carbon nanotubes; the porous structure and coating density of Ni-MOF are superior to Zn-MOF; the MOF structure formed by terephthalic acid as a ligand is more suitable for the material's pore structure requirements, while phthalic acid is slightly inferior.

[0067] Comparative Example 1 shows that carbon nanotubes cannot grow without a catalyst, resulting in a lack of a continuous conductive network and a surge in resistivity. Without the interstitial filling of carbon nanotubes, the porous carbon structure is loose, with insufficient pore volume and specific surface area.

[0068] Comparative Example 2, without MOF coating, exhibits the largest pore size, smallest pore volume, and lowest specific surface area. Without MOF filling the core defects, the porous carbon channels are prone to collapse, and the lack of MOF's own porous structure contribution leads to a decrease in pore volume and specific surface area, and a disordered increase in pore size.

[0069] In Comparative Example 3, phenolic resin replaced sugar compounds. After carbonization, sugar compounds formed a richer porous structure, while non-sugar compounds had a poorer porous carbon structure.

[0070] Comparative Example 4, which had no activation step, demonstrates that CO2 activation can broaden the porous carbon channels and remove impurities from the MOF shell. Without activation, the channels become blocked, and the specific surface area and pore volume are significantly reduced.

[0071] 2.2) Button cell battery performance test: The porous carbon materials corresponding to Examples 1-3 and Comparative Examples 1-2 were used as negative electrode materials for lithium-ion batteries to prepare coin cells according to the following method: A binder, conductive agent, and solvent are added to the corresponding porous carbon materials, stirred to form a slurry, coated onto copper foil, and dried and rolled to obtain a negative electrode sheet. The binder used is LA132, the conductive agent is SP (conductive carbon black), and the solvent is NMP. The ratio of porous carbon material: SP: LA132: NMP is 80g: 15g: 15g: 300mL. The electrolyte is a solution with LiPF6 as the electrolyte and a concentration of 1mol / L. The solvent is a mixture of EC and DEC with a volume ratio of 1:1. The lithium metal sheet is used as the counter electrode, and the separator is a polypropylene (PP) membrane.

[0072] Each button cell was assembled in an argon-filled glove box, and then the following performance tests were performed: Electrochemical performance testing: Electrochemical performance was specifically performed on the Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was 0.005V to 2.0V, and the charge / discharge rate was 0.1C. The discharge specific capacity and initial efficiency of the corresponding coin cell were tested. At the same time, the room temperature charge DCR and cycle performance (0.1C / 0.1C, 100 cycles) of the corresponding coin cell were tested. The diffusion coefficient of the material and the full charge expansion of the negative electrode were also tested by GITT.

[0073] The test results are shown in Table 2.

[0074] Table 2. Performance testing of coin cells in the examples and comparative examples.

[0075] As can be seen from Table 2, Examples 1-3 have high specific capacity and high diffusion coefficient. This is because Examples 1-3 contain carbon nanotubes to reduce the resistivity of the material and rely on the mechanical strength of the carbon nanotubes to reduce expansion. At the same time, the MOF material coating on the surface reduces the defects of the material and restricts the expansion of the core, thereby improving the initial efficiency and expansion, and improving the cycling performance.

[0076] Comparative Examples 1 and 2 show that the absence of carbon nanotubes leads to poor conductivity, hindered ion transport, and low diffusion coefficient; the lack of MOF coating results in severe core expansion, pore collapse, and decreased specific capacity and cycling stability.

[0077] The fully charged expansion of Comparative Examples 1 and 2 was 1.7-2 times that of Example 3, and the initial efficiency was also 2-8 percentage points lower. This is because the dual anti-expansion properties of carbon fiber and MOF failed, and the core volume change was unrestrained; the absence of MOF led to the exposure of core defects, an increase in electrolyte side reactions, and a decrease in initial efficiency.

[0078] Example 3 exhibited the highest diffusion coefficient, lowest full-charge expansion, and highest initial efficiency. This was because the carbon nanotube conductive network generated by cobalt chloride catalysis was optimal, the porous carbon channels converted from 200g of lactose were the most abundant, and the MOF shell after CO2 activation was dense with unobstructed porous carbon channels, resulting in fast ion transport and strong resistance to expansion.

[0079] Example 6, without CO2 activation, showed lower specific capacity and cycling performance than Example 1. The unactivated MOF shell contained more residual impurities and defects, the porous carbon channels were not widened, ion diffusion was hindered, and structural stability decreased during cycling. Example 5, using zinc acetate instead of nickel, showed a 14.4% expansion under full charge; Example 7, using phthalic acid instead of terephthalic acid, showed a cycling performance of 85.1%, both slightly inferior to Example 1. This indicates that Ni-MOF has better resistance to expansion and defect filling ability than Zn-MOF; the MOF formed by terephthalic acid has a tighter bond with the core, resulting in better cycling stability. Example 4, using ethylene instead of methane, showed performance close to Example 1, indicating that both methane and ethylene can meet the growth requirements of carbon nanotubes, demonstrating strong process compatibility.

[0080] In this invention, carbon nanotubes reduce resistivity and increase diffusion coefficient, while MOFs inhibit expansion and improve initial efficiency; both are core functional components and none can be omitted. CO2 activation, sufficient supply of glycosides, and appropriate catalysts are key processes for optimizing performance. Ethylene carbon source, Zn-MOF, and phthalic acid ligands can be used as alternatives, with slightly lower performance but still better than the comparative example, demonstrating process flexibility.

[0081] The preferred catalyst is cobalt chloride, the preferred glycosyl compound is 200g of lactose, the preferred carbon source is methane, the preferred MOF is the Ni-terephthalic acid system, and with CO2 activation, it can achieve synergistic performance of high pore volume, high conductivity, low expansion and excellent cycle performance.

[0082] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A MOF material-coated carbon fiber porous carbon composite material, characterized in that, The composite material has a fibrous core-shell structure; The core-shell structure has a carbon fiber-carbon nanotube-porous carbon composite core. The carbon fiber-carbon nanotube-porous carbon composite core uses carbon fiber as a substrate, carbon nanotubes are grown on the surface of the substrate, and porous carbon is filled in the gap between the substrate and the carbon nanotubes. The shell of the core-shell structure is a MOF material that coats the outer surface of the carbon fiber-carbon nanotube-porous carbon composite core.

2. The MOF material-coated carbon fiber porous carbon composite material as described in claim 1, characterized in that, The mass ratio of carbon nanotubes, carbon fibers, porous carbon and MOF materials is (1-5):(30-45):(30-45):(10-20).

3. A method for preparing a MOF material-coated carbon fiber porous carbon composite material as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. After uniformly dispersing carbon fibers, catalysts and sugar compounds, the mixture is filtered and vacuum dried to obtain carbon fiber-porous carbon precursor. S2. Deposit carbon nanotubes on the carbon fiber-porous carbon precursor to obtain intermediate material; S3. MOF is coated onto the intermediate material and activated to obtain MOF material coated carbon fiber porous carbon composite material.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the carbon fiber, catalyst and glycosyl compound is 100:(1-5):(50-200).

5. The preparation method according to claim 3, characterized in that, The metal source of the MOF is nickel acetate tetrahydrate, and the organic ligand is terephthalic acid. The total mass ratio of nickel acetate tetrahydrate, terephthalic acid and intermediate material is (50-100):100; The molar ratio of nickel acetate tetrahydrate to terephthalic acid is 1:

1.

6. The preparation method according to claim 3, characterized in that, The carbon fiber described in step S1 has a diameter of 150-200 nm and a length of 1-10 μm.

7. The preparation method according to claim 3, characterized in that, The catalyst mentioned in step S1 includes one or more of nickel chloride, ferric chloride, cobalt chloride, nickel nitrate, ferric nitrate, or cobalt nitrate; The glycosyl compound includes one or more of glucose, fructose, galactose, lactose, sucrose, or maltose.

8. The preparation method according to claim 3, characterized in that, The intermediate material obtained by depositing carbon nanotubes on the carbon fiber-porous carbon precursor includes: Carbon nanotubes were grown on the surface of the carbon fiber-porous carbon precursor by vapor deposition at 900-1100℃ and a flow rate of 10-100 ml / min for 30-300 min to obtain the intermediate material.

9. The preparation method according to claim 5, characterized in that, MOF is coated onto the intermediate material, and activated to obtain MOF-coated carbon fiber porous carbon composite material, including: Nickel acetate tetrahydrate and terephthalic acid were added to a mixed solvent consisting of deionized water and N,N-dimethylacetamide to obtain a MOF precursor solution. The intermediate material is added to the MOF precursor solution, mixed evenly, and stirred at 100-200°C for 2-12 hours to obtain the MOF-coated intermediate material. At 800-1000℃, carbon dioxide gas was introduced at a flow rate of 50-200 ml / min to activate the MOF-coated intermediate material for 30-300 min, resulting in MOF-coated carbon fiber porous carbon composite material. The volume ratio of deionized water to N,N-dimethylacetamide is 1:1; the total mass concentration of nickel acetate tetrahydrate and terephthalic acid in the MOF precursor solution is 5-20 wt%.

10. The application of a MOF material-coated carbon fiber porous carbon composite material as described in any one of claims 1-2 in silicon-carbon anode materials.

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