Surface modified carbon fiber as well as preparation method and application thereof

Abstract

The invention provides a surface modified carbon fiber as well as a preparation method and application thereof, and belongs to the technical field of battery materials. Physical or chemical treatment on the surface of the carbon fiber is realized by performing one or more of accurate plasma treatment, chemical etching, coupling agent treatment and nano particle deposition on the surface of the carbon fiber, so that functional groups are introduced or a rough nano structure is formed; a functional layer with a specific functional group and a rough structure which are beneficial to attachment of positive electrode material slurry are formed on the surface of the carbon fiber, and then a stable and well-attached surface modified layer is obtained through heat treatment, so that the surface modified carbon fiber is prepared. According to the method disclosed by the invention, the surface roughness and the functional group richness can be improved on the premise that the mechanical property of the fiber is not obviously damaged, so that the adhesiveness and the electrical property of the positive electrode material slurry are enhanced, and a foundation is laid for the preparation of a carbon fiber positive electrode material and a structure-energy storage integrated composite structure.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly to a surface-modified carbon fiber and its preparation method and application. Background Art

[0002] As a high-strength, high-modulus, and low-density reinforcing material, carbon fiber has been widely used in the fields of aerospace, automotive, electronic devices, and energy. With the rise of structure-energy storage integrated composites, directly integrating lithium-ion battery cathode materials onto the surface of carbon fiber to prepare a composite structure that can both bear load and store energy has become a research hotspot. However, the surface of untreated carbon fiber is relatively smooth and chemically inert, resulting in poor adhesion of the cathode material slurry on the fiber surface, which is not conducive to the stable distribution and long-term cycling stability of the cathode coating.

[0003] Currently, the methods for modifying the surface of carbon fiber include plasma treatment, coupling agent treatment, surface oxidation, and nanoparticle coating, etc. However, these methods often lack in-depth optimization of subsequent electrochemical properties after treatment, or the treatment methods are not gentle enough on the mechanical properties of the fiber, and at the same time, they are not specifically optimized for the interfacial bonding with high-energy density (≥200 Wh / kg) cathode slurries. High-energy density cathode materials (such as NCM811, NCA, LiFePO 4 etc.) generally have high electrochemical activity and strong physical and chemical properties (such as high electrical conductivity, chemical activity, and strong requirements for ion and electron conduction). These cathode slurries often need to form a stable interface with the electrode material to ensure the long-term use, good rate performance, and stability of the battery under high-power and high-energy density conditions. Therefore, there is a problem of decreased electrochemical performance due to interfacial chemical mismatch in high-energy density cathode materials. The interfacial bonding of high-energy density materials requires more precise and efficient optimization to ensure the stability and long life of the battery. Summary of the Invention

[0004] The purpose of the present invention is to provide a surface-modified carbon fiber and its preparation method and application, which can improve the adhesion and interfacial bonding between the carbon fiber and the high-energy density cathode material slurry, and obtain a carbon fiber cathode material with higher stability and better electrical conductivity.

[0005] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a surface-modified carbon fiber, comprising the following steps:

[0007] Perform surface treatment on the carbon fiber to obtain treated carbon fiber; the surface treatment method includes one or more of plasma treatment, chemical etching, coupling agent treatment, and nanoparticle deposition;

[0008] The treated carbon fiber is successively dried and heat-treated to obtain surface-modified carbon fiber.

[0009] Preferably, the atmosphere used for the plasma treatment is one or more of oxygen, nitrogen, argon, and hydrogen; the power of the plasma treatment is 10 - 100 W, the treatment time is 30 - 300 s, the gas flow rate is 10 - 50 sccm, the pressure is 0.01 - 0.1 Torr, and the temperature is 50 - 150 °C.

[0010] Preferably, the etching reagent used for the chemical etching is an acid or a base; the acid is hydrofluoric acid, nitric acid, or sulfuric acid; the base is sodium hydroxide solution; the concentration of the etching reagent is 1 - 10 wt%; the chemical etching is carried out by immersing the carbon fiber in the etching reagent; the temperature of the immersion is 20 - 40 °C, and the time is 1 - 30 min.

[0011] Preferably, the coupling agent used for the coupling agent treatment includes an amino-silane coupling agent, an epoxy-silane coupling agent, or a fluoro-silane coupling agent; the coupling agent treatment is carried out by immersing the carbon fiber in the coupling agent solution; the concentration of the coupling agent solution is 0.1 - 5 wt%, the temperature of the coupling agent treatment is 20 - 40 °C, and the time is 0.5 - 2 h.

[0012] Preferably, the nanoparticles used for the nanoparticle deposition include SiO 2 、TiO 2 、aluminum oxide, or carbon nanotubes; the nanoparticle deposition is carried out by immersing the carbon fiber in the nanoparticle dispersion; the concentration of the nanoparticle dispersion is 0.1 - 10 wt%; the temperature of the nanoparticle deposition is 20 - 40 °C, and the time is 30 - 60 s.

[0013] Preferably, the temperature of the heat treatment is 50 - 200 °C, the time is 0.5 - 2 h, and the atmosphere is nitrogen or argon.

[0014] The present invention provides the surface-modified carbon fiber prepared by the preparation method described in the above technical solution.

[0015] The present invention provides the application of the surface-modified carbon fiber described in the above technical solution in a carbon fiber positive electrode material.

[0016] Preferably, the preparation method of the carbon fiber positive electrode material includes: compounding a positive electrode paste with the surface-modified carbon fiber, and successively drying and heat-treating to obtain the carbon fiber positive electrode material; the positive electrode paste includes a positive electrode active material, a conductive agent, a binder, and a solvent, and the energy density of the positive electrode active material is ≥200 Wh / kg.

[0017] Preferably, the positive electrode active material includes NCM811, NCA or LiFePO 4 .

[0018] The present invention provides a method for preparing surface-modified carbon fibers. By performing one or several treatments on the carbon fiber surface, such as precise plasma treatment, chemical etching, coupling agent treatment, and nanoparticle deposition, physical or chemical treatment of the carbon fiber surface is achieved, introducing functional groups or forming a rough nanostructure on the carbon fiber surface, so that a functionalized layer with specific functional groups and a rough structure conducive to the adhesion of the positive electrode material slurry are formed on the carbon fiber surface. Then, a stable and well-adhered surface modification layer is obtained through heat treatment, thereby preparing surface-modified carbon fibers. The method of the present invention can improve the surface roughness and the richness of functional groups without significantly damaging the mechanical properties of the fibers, so as to enhance the adhesion and electrical properties of the positive electrode material slurry, and lay a foundation for the preparation of carbon fiber positive electrode materials and structure-energy storage integrated composite structures.

[0019] The method of the present invention can design surface treatment conditions based on the electrochemical properties of the positive electrode coating, and precisely control the density of free radicals and functional groups on the carbon fiber surface by controlling the plasma treatment conditions and solution chemical modification parameters.

[0020] The present invention adopts a nanoparticle-assisted surface modification technology to endow the fiber surface with a high specific surface area and nanoscale roughness, enhancing the construction of the conductive agent network while improving the slurry adhesion.

[0021] Matching the surface-modified carbon fibers prepared by the present invention with a specific high-energy density positive electrode slurry (such as the NCM811 / CNT / graphene / PVDF system) can establish a more stable bonding between the fiber surface and the positive electrode particles and the binder, thereby improving the cycle life and rate performance of the electrode material. The surface modification method of the present invention can be widely applied to the field of manufacturing structural battery composite materials, which is conducive to the large-scale production of high-performance energy storage structural components.

[0022] The interfacial bonding principle between the surface modification method provided by the present invention and the high-energy density positive electrode slurry:

[0023] 1. Plasma treatment

[0024] The present invention excites the carbon fiber surface through plasma treatment to generate a large number of free radicals and functional groups (such as carboxyl groups, amino groups, hydroxyl groups, etc.). For high-energy density positive electrode slurries, the type and density of surface functional groups directly affect the interaction force between the positive electrode slurry and the carbon fiber:

[0025] Enhanced adhesion: Plasma treatment can improve the surface polarity and activity of fibers, increasing the affinity between the fiber surface and the positive electrode slurry, especially for the adhesion of binders such as PVDF. This is particularly important for high-energy density slurries because such slurries usually contain various conductive materials (such as CNT, graphene, etc.) and require strong interfacial bonding to ensure stability during high-rate discharge.

[0026] Precise control of interfacial bonding: By adjusting the power and time of plasma treatment, the distribution of active sites on the fiber surface can be precisely regulated, optimizing the distribution of conductive agents in the slurry and the effectiveness of electrochemical reactions.

[0027] 2. Deposition of nanoparticles (such as nano-SiO 2 , TiO 2 )

[0028] Nanoparticles can be used to increase the specific surface area and roughness of the carbon fiber surface, which is very important for improving the adhesion and stability of the slurry:

[0029] Enhancing the construction of the conductive network: The addition of nanoparticles such as nano-SiO 2 and TiO 2 can form a nano-scale rough structure on the fiber surface, providing more attachment points, thereby enhancing the conductive connection between the conductive agents (such as graphene, CNT) in the slurry and the carbon fiber. In high-energy density positive electrode slurries, this structural optimization is crucial for maintaining low contact impedance and good current conduction.

[0030] Improving the dispersibility of the slurry: Nanoparticles can not only enhance surface roughness but also improve the dispersibility of each component in the slurry, reducing the agglomeration between positive electrode particles, thereby improving the stability and uniformity of the slurry. This is particularly important for high-energy density slurries because they usually require a very uniform distribution to ensure stable electrochemical performance during high-rate and long-term cycling.

[0031] Matching the surface-modified carbon fibers prepared by the present invention with a positive electrode slurry (such as the NCM811 / CNT / graphene / PVDF system), the interfacial bonding of components such as NCM811, CNT, graphene, and PVDF in the positive electrode material requires higher chemical compatibility and stability; the present invention can improve the compatibility and bonding force between the carbon fiber and each component (such as NCM811, CNT, graphene, etc.) in the positive electrode material through surface chemical modification, reduce the occurrence of interfacial electrochemical reactions, enhance the interfacial strength and stability, and ensure the long-term reliability of the battery in high-energy density applications.

[0032] Due to the complexity of high-energy density slurries and the high requirements for interfacial bonding, the surface modification method provided by the present invention can significantly improve the interfacial stability and electrochemical performance between carbon fibers and high-energy density cathode material slurries by optimizing the distribution of surface functional groups, increasing surface roughness, and enhancing chemical compatibility, thereby significantly improving the energy density, cycle life, and rate performance of carbon fiber cathode materials. These surface modification methods ensure that carbon fibers can exhibit optimal performance when used as carriers for battery cathode materials, meeting the application requirements of high power, long cycle life, and high energy density, thus achieving high-performance applications of structure-energy storage integrated composites. Detailed implementation manners

[0033] In the present invention, unless otherwise specified, the raw materials or reagents used are well-known commercially available products in the art.

[0034] The present invention provides a method for preparing surface-modified carbon fibers, comprising the following steps:

[0035] Perform surface treatment on the carbon fibers to obtain treated carbon fibers; the methods of the surface treatment include one or more of plasma treatment, chemical etching, coupling agent treatment, and nanoparticle deposition;

[0036] Successively dry and heat-treat the treated carbon fibers to obtain surface-modified carbon fibers.

[0037] The present invention has no special limitation on the specific specifications and sources of the carbon fibers, and commercially available carbon fibers well-known in the art can be used; in the examples of the present invention, specifically T700 carbon fibers or M55J high-modulus carbon fibers.

[0038] In the present invention, the atmosphere used for the plasma treatment is preferably one or more of oxygen, nitrogen, argon, and hydrogen; the power of the plasma treatment is preferably 10 - 100 W, more preferably 30 - 80 W, further preferably 50 W, the treatment time is preferably 30 - 300 s, more preferably 50 - 200 s, further preferably 60 - 90 s, the gas flow rate is preferably 10 - 50 sccm, more preferably 15 - 20 sccm, the pressure is preferably 0.01 - 0.1 Torr, more preferably 0.02 - 0.08 Torr, further preferably 0.05 - 0.06 Torr, and the temperature is preferably 50 - 150 °C, more preferably 100 °C.

[0039] The present invention uses plasma treatment for surface modification, which can enhance the surface energy without significantly damaging the mechanical properties of carbon fibers. Hydroxyl, carboxyl, amino and other functional groups are generated on the surface of carbon fibers by the excitation of plasma, improving the hydrophilicity and chemical activity of the fiber surface for subsequent attachment of the cathode slurry.

[0040] In the present invention, the etching reagent used for chemical etching is preferably an acid or a base; the acid is preferably hydrofluoric acid, nitric acid or sulfuric acid; the base is preferably a sodium hydroxide solution; the concentration of the etching reagent is preferably 1-10 wt%, more preferably 2-8 wt%, and further preferably 5-6 wt%, and the solvent used is preferably water; the chemical etching is preferably carried out by immersing the carbon fiber in the etching reagent; the temperature of the immersion is preferably 20-40 °C, more preferably 25 °C, and the time is preferably 1-30 min, more preferably 10-30 min.

[0041] In the present invention, functional groups such as carboxyl, carbonyl, hydroxyl or amino are introduced onto the fiber surface by chemical etching.

[0042] In the present invention, the coupling agent used for the coupling agent treatment preferably includes an amino-silane coupling agent, an epoxy-silane coupling agent or a fluoro-silane coupling agent; the coupling agent treatment is preferably carried out in the form of immersing the carbon fiber in a coupling agent solution; the concentration of the coupling agent solution is preferably 0.1-5 wt%, more preferably 0.5-2 wt%, the solvent used is preferably ethanol, the temperature of the coupling agent treatment is preferably 20-40 °C, more preferably 25 °C, and the time is preferably 0.5-2 h, more preferably 0.5-1 h.

[0043] In the present invention, the amino-silane coupling agent is preferably KH550 (3-aminopropyltriethoxysilane), APTES (aminopropyltriethoxysilane) or GPTMS (3-aminopropyltrimethoxysilane); the epoxy-silane coupling agent is preferably GPTES (3-glycidoxypropyltriethoxysilane) or EP-PTES (glycidoxypropyltriethoxysilane); the fluoro-silane coupling agent is preferably FS-100 (fluorinated silane) or Z-6020 (3,3,3-trifluoropropyltriethoxysilane).

[0044] In the present invention, through the coupling agent treatment, the chemical activity of the carbon fiber surface is further improved, especially providing more reaction sites for PVDF and the conductive agent in the positive electrode slurry, thereby enhancing the binding force between the carbon fiber and the positive electrode slurry.

[0045] In the present invention, the nanoparticles used for nanoparticle deposition preferably include SiO 2 , TiO 2 , alumina or carbon nanotubes; the nanoparticle deposition is preferably carried out in the form of immersing the carbon fiber in a nanoparticle dispersion; the concentration of the nanoparticle dispersion is preferably 0.1-10 wt%, more preferably 0.1-1 wt%, the dispersant used is preferably water; the temperature of the nanoparticle deposition is preferably 20-40 °C, more preferably 25 °C, and the time is preferably 30-60 s, more preferably 30-50 s.

[0046] The present invention has no special limitation on the drying conditions, and the drying process well-known in the art can be followed.

[0047] In the present invention, the temperature of the heat treatment is preferably 50 - 200 °C, more preferably 100 - 150 °C, the time is preferably 0.5 - 2 h, more preferably 1 h, and the atmosphere is preferably nitrogen or argon.

[0048] After the surface modification is completed, in the present invention, the heat treatment is carried out to 1) promote the stabilization of functional groups: the functional groups generated by the surface modification (such as carboxyl groups, hydroxyl groups, etc.) need to be stabilized by heat treatment to prevent decomposition or loss during subsequent use. The heat treatment helps to enhance the binding force of these functional groups and form a more stable interface with the binder and conductive agent in the positive electrode slurry; 2) improve the coating adhesion and conductivity: through heat treatment, the binder in the slurry is fully cured, enabling the positive electrode material layer to firmly adhere to the surface of the carbon fiber, enhancing the adhesion between the positive electrode material layer and the carbon fiber, ensuring a stable combination between the coating and the fiber, and effectively improving the conductivity and electrochemical performance of the electrode.

[0049] The present invention provides a surface-modified carbon fiber prepared by the preparation method described in the above technical solution. The surface-modified carbon fiber prepared by the present invention has enhanced interfacial adhesion and conductive channels on its surface.

[0050] The present invention provides the application of the surface-modified carbon fiber described in the above technical solution in a carbon fiber positive electrode material.

[0051] In the present invention, the preparation method of the carbon fiber positive electrode material includes: compounding a positive electrode slurry with a surface-modified carbon fiber, and sequentially performing drying and heat treatment to obtain a carbon fiber positive electrode material; the positive electrode slurry includes a positive electrode active material, a conductive agent, a binder, and a solvent, and the energy density of the positive electrode active material is ≥200 Wh / kg.

[0052] In the present invention, the preferred way to compound the positive electrode slurry with the surface-modified carbon fiber is coating or impregnation; in the present invention, the thickness of the coating formed by the positive electrode slurry is preferably 1 - 20 μm, more preferably 10 μm; the present invention has no special limitation on the specific conditions of the impregnation or coating, and the above thickness can be achieved according to the process well-known in the art.

[0053] In the present invention, the positive electrode active material is preferably NCM811, NCA or LiFePO 4 ; the conductive agent is preferably one or more of carbon nanotubes, graphene, carbon black SuperP, and polyaniline; the binder is preferably one or more of PVDF, carboxymethyl cellulose, polyurethane, and polyaniline; the solvent is preferably N-methylpyrrolidone (NMP).

[0054] In the present invention, the theoretical energy density of the NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) is 900 - 1000 Wh / kg, and the actual energy density is 250 - 300 Wh / kg; the theoretical energy density of the NCA (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) is 950 - 1050 Wh / kg, and the actual energy density is 260 - 320 Wh / kg; the theoretical energy density of the LiFePO 4 (lithium iron phosphate) is 580 - 600 Wh / kg, and the actual energy density is 160 - 200 Wh / kg.

[0055] The present invention has no special limitation on the source of the positive electrode active material, and it can be obtained as a commercially available product or self-made in a manner well-known in the art.

[0056] The present invention has no special limitation on the ratio of each component in the positive electrode slurry, and a positive electrode slurry with a ratio well-known in the art can be used.

[0057] After the positive electrode slurry is compounded with the surface-modified carbon fiber, the temperature of the heat treatment is preferably 150 - 250 °C, more preferably 180 - 200 °C, and the time is preferably 1 - 3 h, more preferably 1.5 - 2 h.

[0058] The present invention enables the binder in the positive electrode slurry to be fully cured through heat treatment and enhances its binding force with the surface of the carbon fiber, so as to ensure that the adhesion and conductivity of the slurry layer are improved.

[0059] The carbon fiber positive electrode material prepared by the present invention has a capacity retention rate of not less than 85% at a 1C rate and a capacity retention rate of not less than 80% after 100 cycles.

[0060] In the present invention, the carbon fiber positive electrode material can be used in structure - energy storage integrated composites, aerospace lightweight energy storage structures, electric vehicle body integrated batteries, or household energy storage systems.

[0061] The following is a detailed description of the specific embodiments of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0062] The following experimental methods and detection methods are all conventional methods unless otherwise specified; the following reagents and raw materials are all commercially available unless otherwise specified.

[0063] Example 1

[0064] Put the T700 carbon fiber tow into a low-pressure oxygen plasma treatment system (radio frequency power 50 W, gas flow rate O 2 is 20 sccm, treatment time 60 s, pressure 0.05 Torr, temperature 100 °C) for plasma treatment, and heat-treat the treated carbon fiber in a nitrogen atmosphere at 100 °C for 1 h to obtain surface-modified carbon fiber;

[0065] Coat the surface-modified carbon fiber with NCM811 / CNT / graphene / PVDF slurry (NCM811 45 wt%, CNT 2 wt%, graphene 2 wt%, PVDF 1 wt%, NMP 50 wt%), and the formed coating thickness is 10 μm. Place the coated sample at 80 °C and dry for 1 h, and heat-treat it in a nitrogen atmosphere at 200 °C for 2 h to obtain a carbon fiber positive electrode material.

[0066] Perform performance testing on the prepared carbon fiber positive electrode material. The results show that the initial capacity at a 0.5C rate can be increased by 10% compared to the untreated fiber, and at the same time, the capacity retention rate after 100 cycles is increased by 8%.

[0067] Example 2

[0068] Immerse the M55J high-modulus carbon fiber in 5 wt% HNO 3 aqueous solution for 30 min, then wash with deionized water and dry at 80 °C, and then heat-treat it in a nitrogen atmosphere at 100 °C for 1 h to obtain surface-modified carbon fiber;

[0069] Coat the surface-modified carbon fiber with NCA positive electrode slurry (NCA 45 wt%, CNT 2 wt%, graphene 2 wt%, PVDF 1 wt%, NMP 50 wt%), and the formed coating thickness is 10 μm. Then dry at 120 °C for 30 min and heat-treat it under argon protection at 200 °C for 2 h to obtain a carbon fiber positive electrode material.

[0070] The chemical oxidation method is used to introduce carboxyl and carbonyl groups on the fiber surface, so that stronger interfacial interactions occur between them and PVDF and graphene sheets in the slurry. The electrochemical test results after coating the positive electrode slurry show that the carbon fiber positive electrode material prepared in Example 2 has an 8% increase in capacity at a 1C rate, and the capacity retention rate after 200 cycles is increased by 5% compared to the untreated fiber.

[0071] Example 3

[0072] The T700 carbon fiber was first ultrasonically cleaned in acetone, dried, and then immersed in a 0.5 wt% KH550 ethanol solution for 60 min. After taking it out, it was dried at 120 °C for 2 h, and then heat-treated in a nitrogen atmosphere at 100 °C for 1 h to obtain surface-modified carbon fiber;

[0073] The positive electrode slurry (LiFePO 4 45 wt%, SuperP 3 wt%, carbon nanotubes 1 wt%, PVDF 1 wt%, NMP 50 wt%) was coated on the surface-modified carbon fiber, and the formed coating thickness was 10 μm. Subsequently, it was dried at 100 °C for 1 h, heated to 180 °C in a nitrogen atmosphere, and maintained for 1.5 h to obtain the carbon fiber positive electrode material.

[0074] After the carbon fiber positive electrode material prepared in Example 3 was formed into a film and subjected to battery testing, the capacity retention rate increased by 10% at a 2C rate, and good structural stability could still be maintained after 300 cycles, indicating that introducing amino groups and siloxane bonds on the carbon fiber surface by using a coupling agent is beneficial to generating strong interactions with CNT and PVDF, thereby improving the electrochemical performance.

[0075] Example 4

[0076] T700 carbon fiber was impregnated in an aqueous dispersion of nano-SiO 2 (0.1 wt%) for 30 s, dried at room temperature, and then heat-treated at 150 °C for 1 h to attach nano-SiO 2 nanoparticles to the fiber surface, forming a micro-nano hierarchical structure to obtain surface-modified carbon fiber;

[0077] The positive electrode slurry (NCM811 45 wt%, CNT 2 wt%, graphene 2 wt%, PVDF 1 wt%, NMP 50 wt%)) was coated on the surface-modified carbon fiber, and the formed coating thickness was 10 μm. The coated sample was placed at 80 °C and dried for 1 h, and heat-treated in a nitrogen atmosphere at 200 °C for 2 h to obtain the carbon fiber positive electrode material.

[0078] The results show that the carbon fiber positive electrode material prepared in Example 4 can stably maintain a capacity of about 185 mAh / g at a 1C rate, and the capacity retention rate exceeds 85% after 500 cycles.

[0079] Example 5

[0080] The T700 carbon fiber was treated with nitrogen plasma (power 30 W, gas flow rate N 2 is 15 sccm, treatment time 90 s, pressure 0.06 Torr, temperature 100 °C), and then heat-treated in a nitrogen atmosphere at 100 °C for 1 h to obtain surface-modified carbon fiber;

[0081] Coat LiFePO on the surface - modified carbon fiber 4 / Super P / PVDF slurry (LiFePO 4 45 wt%, SuperP 3 wt%, carbon nanotubes 1 wt%, PVDF 1 wt%, NMP 50 wt%), the formed coating thickness is 10 μm. Place the coated sample in an 80 °C oven for drying for 1 h, and then heat - treat it in a nitrogen atmosphere at 200 °C for 2 h to obtain the carbon - fiber positive electrode material.

[0082] The results show that the rate performance of the carbon - fiber positive electrode material prepared in Example 5 has a 12% increase in capacity under the 5C condition compared to the untreated one, and the long - cycle life is also significantly extended. This indicates that introducing pyridine - nitrogen and pyrrole - nitrogen structures on the fiber surface in this example can improve the electron - transfer ability.

[0083] Example 6

[0084] Put the T700 carbon - fiber tow into a low - pressure plasma treatment system for plasma treatment. The radio - frequency power is 50 W, the pure oxygen flow rate is 20 sccm, the treatment time is 60 s, the pressure is 0.06 Torr, and the temperature is 100 °C;

[0085] Immerse the plasma - treated carbon - fiber tow in an ethanol solution containing 0.5 wt% amino - silane (KH550) for 30 min. After taking it out, dry it at 120 °C for 2 h, and then perform heat - treatment in a nitrogen atmosphere at 100 °C for 1 h to obtain the surface - modified carbon fiber.

[0086] Immerse the surface - modified carbon fiber into the NCM811 / CNT / graphene / PVDF positive - electrode slurry (NCM811 45 wt%, CNT 2 wt%, graphene 2 wt%, PVDF 1 wt%, NMP 50 wt%) at a pulling rate of 0.5 cm / s and an impregnation time of 10 s. The formed coating thickness is 10 μm. The coated carbon - fiber sample is naturally dried at room temperature for 1 h, then dried at 80 °C for 1 h, and heat - treated at 200 °C for 2 h in a nitrogen - protection atmosphere to obtain the carbon - fiber positive - electrode material.

[0087] Prepare the treated carbon - fiber positive - electrode material into a battery and conduct electrochemical performance tests. The test results show that at the 0.5C rate, the initial capacity is increased by about 12% compared to the untreated fiber, and the capacity retention rate is increased by about 10% after 100 cycles. In addition, the rate performance and long - cycle stability of the battery are significantly improved.

[0088] Through the combined treatment of plasma treatment and amino-silane coupling agent treatment, the carbon fiber surface has richer functional groups and higher chemical activity, which provides more binding sites for the positive electrode slurry and ensures the stability and electrochemical performance of the coating. The surface modification method combining plasma treatment with amino-silane coupling agent treatment can significantly improve the chemical activity of the carbon fiber surface, enhance the interfacial binding force between the positive electrode slurry and the carbon fiber, and the prepared carbon fiber positive electrode material shows higher stability during long-term cycling, and during high-rate discharge, the material can still maintain good capacity output. This method not only improves the electrochemical performance of the positive electrode material but also provides a feasible technical path for large-scale production.

[0089] The results of the above embodiments show that the carbon fiber surface treatment method of the present invention can effectively improve the interfacial bonding degree and electrochemical performance between the carbon fiber and the positive electrode material slurry, making the carbon fiber positive electrode material perform more excellently in the integrated application of structure-energy storage.

[0090] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing surface-modified carbon fiber, characterized in that: The following steps are involved: Performing surface treatment on the carbon fiber to obtain treated carbon fiber; the surface treatment method includes one or more of plasma treatment, chemical etching, coupling agent treatment and nanoparticle deposition; The treated carbon fibers are sequentially dried and heat treated to obtain surface-modified carbon fibers.

2. The preparation method according to claim 1, characterized in that: The atmosphere used for the plasma treatment is one or more of oxygen, nitrogen, argon and hydrogen; the power of the plasma treatment is 10-100W, the treatment time is 30-300s, the gas flow rate is 10-50sccm, the pressure is 0.01-0.1Torr, and the temperature is 50-150°C.

3. The preparation method according to claim 1, characterized in that: The etching reagent used for the chemical etching is an acid or an alkali; the acid is hydrofluoric acid, nitric acid or sulfuric acid; the alkali is a sodium hydroxide solution; the concentration of the etching reagent is 1 to 10 wt%; the chemical etching is performed by immersing the carbon fiber in the etching reagent; the immersion temperature is 20 to 40°C and the time is 1 to 30 minutes.

4. The preparation method according to claim 1, characterized in that: The coupling agent used in the coupling agent treatment includes an aminosilane coupling agent, an epoxysilane coupling agent or a fluorosilane coupling agent; the coupling agent treatment is carried out in the form of immersing the carbon fiber in a coupling agent solution; the concentration of the coupling agent solution is 0.1 to 5wt%, the temperature of the coupling agent treatment is 20 to 40°C, and the time is 0.5 to 2h.

5. The preparation method according to claim 1, characterized in that: The nanoparticles used for the nanoparticle deposition include SiO2, TiO2, aluminum oxide or carbon nanotubes; The nanoparticle deposition is carried out in the form of immersing the carbon fiber in a nanoparticle dispersion liquid; the concentration of the nanoparticle dispersion liquid is 0.1-10wt%; the temperature of the nanoparticle deposition is 20-40°C, and the time is 30-60s.

6. The preparation method according to claim 1, characterized in that: The heat treatment temperature is 50-200° C., the time is 0.5-2 hours, and the atmosphere is nitrogen or argon.

7. The surface-modified carbon fiber prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the surface modified carbon fiber according to claim 7 in carbon fiber positive electrode materials.

9. The use according to claim 8, characterized in that: The preparation method of the carbon fiber positive electrode material comprises: compounding a positive electrode slurry with surface modified carbon fiber, and sequentially performing drying and heat treatment to obtain the carbon fiber positive electrode material; the positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder and a solvent, and the energy density of the positive electrode active material is ≥200Wh / kg.

10. The use according to claim 8 or 9, characterized in that: The positive electrode active material includes NCM811, NCA or LiFePO4.