A carbon fiber structure energy storage composite material based on a multi-stage conductive network and a preparation method and application thereof

Abstract

The application provides a carbon fiber structure energy storage composite material based on a multistage conductive network and a preparation method and application thereof, and belongs to the technical field of energy storage materials. The application forms a conductive network with high conductivity and good interface bonding force through the synergistic effect of CNTs, graphene and MXene, simultaneously combines electrostatic spinning or precision spraying technology, realizes significant improvement of the uniformity and adhesion of the electrode coating, further enhances the surface energy of the carbon fiber through low-temperature plasma treatment, improves the adhesion and stability of the conductive network, and significantly improves the interface bonding force of the conductive coating. The application prepares a high-performance carbon fiber structure energy storage composite material through the construction of the multistage conductive network and the optimization of the coating process, significantly improves the mechanical performance and electrochemical performance of the material, and lays a foundation for the industrial application of the technology through the optimized coating process and the enhanced interface bonding force.

Description

Technical Field

[0001] This invention relates to the field of energy storage materials technology, and in particular to a carbon fiber structure energy storage composite material based on a multi-level conductive network, its preparation method, and its application. Background Technology

[0002] Carbon fiber composite energy storage materials, as a novel material integrating mechanical load-bearing and electrochemical energy storage functions, have broad application prospects in new energy vehicles, aerospace, and other fields. However, existing technologies still have the following problems in the construction of the conductive network of the electrode and the coating process: 1. Imperfect conductive network structure: The electron transport efficiency of existing carbon fiber composite electrodes is low, limiting further improvement in energy storage performance. 2. Unstable coating process: The coating process of electrode materials is difficult to ensure the uniformity of the coating over a large area, affecting the overall performance. 3. Insufficient bonding force with carbon fiber: In traditional methods, the interfacial bonding force between the conductive material and the carbon fiber matrix is ​​weak, leading to easy peeling of the coating. Summary of the Invention

[0003] The purpose of this invention is to provide a carbon fiber structure energy storage composite material based on a multi-level conductive network, its preparation method, and its application. The construction method of the multi-level conductive network combined with electrospinning and precision spraying technology can optimize the performance of the carbon fiber structure energy storage composite material.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a carbon fiber structure energy storage composite material based on a multi-level conductive network, comprising the following steps:

[0006] Carbon nanotubes, graphene, MXene, and organic solvents are mixed to obtain a suspension;

[0007] The suspension is mixed with a binder and a positive electrode active material to obtain a conductive slurry;

[0008] Modified carbon fiber cloth is obtained by plasma treatment of carbon fiber cloth.

[0009] The conductive slurry is electrospun on the surface of modified carbon fiber cloth to form a conductive coating, thereby obtaining a carbon fiber structure energy storage composite material.

[0010] Preferably, the mass ratio of the carbon nanotubes, graphene, and MXene is 1–3:1–3:1.

[0011] Preferably, the carbon nanotubes have a diameter of 10–20 nm, a length of 10–30 μm, and an electrical conductivity >10. 4S / m; the graphene is a single-layer reduced-oxidation graphene with a thickness <1nm and a side length of 5-10μm; the MXene is Ti3C2T x The thickness of the MXene is <2nm, and the flake diameter is 1-5μm.

[0012] Preferably, the adhesive is polyvinylidene fluoride, and the molecular weight of polyvinylidene fluoride is 450,000.

[0013] Preferably, the positive electrode active material includes lithium iron phosphate, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based positive electrode material, phosphate-based positive electrode material, or composite doped positive electrode material.

[0014] Preferably, the plasma treatment power is 80-120W and the time is 5-10min.

[0015] Preferably, the conditions for electrospinning include: voltage 10-15kV; collection distance 10-15cm; slurry flow rate 0.1-0.2mL / min.

[0016] Preferably, when the required areal loading of the positive electrode material is ≥5 mg / cm³ 2 After electrospinning, the process further includes spraying a conductive slurry onto a conductive coating; the spraying includes: adjusting the viscosity of the conductive slurry to 500-800 mPa·s and spraying it in layers onto the conductive coating; the spraying conditions include: a spraying pressure of 0.2-0.5 MPa; a nozzle diameter of 100 μm; and a single layer thickness of 20-25 μm.

[0017] The present invention provides a carbon fiber structure energy storage composite material based on a multi-level conductive network prepared by the preparation method described in the above technical solution.

[0018] This invention provides the application of the carbon fiber structure energy storage composite material based on a multi-level conductive network described above in the field of energy storage.

[0019] This invention employs carbon nanotubes (CNTs), graphene, and MXene to form a conductive paste. Through the synergistic effect of CNTs, graphene, and MXene, high-speed electron transport channels are constructed, resulting in a conductive network with high conductivity and excellent interfacial adhesion. Simultaneously, electrospinning and precision spraying technologies significantly improve the uniformity and adhesion of the electrode coating. Furthermore, low-temperature plasma treatment enhances the surface energy of the carbon fibers, improving the adhesion and stability of the conductive network, thereby significantly enhancing the interfacial adhesion of the conductive coating. This invention, through the construction of a multi-level conductive network and optimization of the coating process, yields a high-performance carbon fiber structure energy storage composite material, significantly improving the material's mechanical and electrochemical properties. The optimized coating process and enhanced interfacial adhesion lay the foundation for the industrial application of this technology.

[0020] This invention significantly reduces the electron transport resistance of the electrode through a multi-level conductive network, thereby improving conductivity. The optimized coating process achieves microscopic and macroscopic consistency of the electrode coating, improving coating uniformity. The conductive coating bonds more firmly with the carbon fiber matrix, improving the durability and mechanical stability of the composite material, thus achieving high energy storage density, good cycle stability and rate performance, and improving electrochemical performance.

[0021] This invention utilizes electrospinning technology to achieve precise control of nanoscale coatings. When large-area preparation is required, it can be combined with spraying technology to realize the preparation of carbon fiber structure energy storage composite materials. Detailed Implementation

[0022] Unless otherwise specified, all raw materials or reagents used in this invention are commercially available products well known in the art.

[0023] This invention provides a method for preparing a carbon fiber structure energy storage composite material based on a multi-level conductive network, comprising the following steps:

[0024] Carbon nanotubes, graphene, MXene, and organic solvents are mixed to obtain a suspension;

[0025] The suspension is mixed with a binder and a positive electrode active material to obtain a conductive slurry;

[0026] Modified carbon fiber cloth is obtained by plasma treatment of carbon fiber cloth.

[0027] The conductive slurry is electrospun on the surface of modified carbon fiber cloth to form a conductive coating, thereby obtaining a carbon fiber structure energy storage composite material.

[0028] This invention mixes carbon nanotubes, graphene, MXene, and an organic solvent to obtain a suspension.

[0029] In this invention, the diameter of the carbon nanotubes is preferably 10–20 nm, the length is preferably 10–30 μm, and the conductivity is preferably >10. 4 S / m; the graphene is preferably a single-layer reduced redox graphene, with a thickness preferably <1nm and a side length preferably 5-10μm; the MXene is preferably Ti3C2T x The thickness of the MXene is preferably <2nm, and the flake diameter is preferably 1-5μm.

[0030] In this invention, the mass ratio of carbon nanotubes, graphene and MXene is preferably 1 to 3:1 to 3:1, and more preferably 2:2:1.

[0031] In this invention, the organic solvent is preferably N-methylpyrrolidone (NMP); the amount of the organic solvent used is not particularly limited in this invention, and can be adjusted according to the amount known in the art to ensure sufficient mixing of the materials.

[0032] In this invention, carbon nanotubes, graphene, and MXene are preferably added to an organic solvent and dispersed using an ultrasonic disperser for 30 minutes to form a uniform suspension.

[0033] After obtaining the suspension, the present invention mixes the suspension with a binder and a positive electrode active material to obtain a conductive slurry.

[0034] In this invention, the binder is preferably polyvinylidene fluoride (PVDF), and the molecular weight of the polyvinylidene fluoride is preferably 450,000; the mass percentage of the binder in the conductive paste is preferably 5-10%, more preferably 5-8%.

[0035] In this invention, PVDF is preferably dissolved in NMP to form a 10wt% binder solution, which is then added to a suspension and stirred until homogeneous. The positive electrode active material is then added to the suspension and stirred at high speed for 5 minutes to obtain a conductive slurry.

[0036] In this invention, the positive electrode active material preferably includes lithium iron phosphate, lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel cobalt manganese oxide (LiNixCoyMnO2, NCM / NMC), and lithium nickel cobalt aluminum oxide (LiNi). x Co yThe cathode active material can be an AlO2, NCA, lithium-rich manganese-based cathode material (Li-rich Mn-based oxide), a phosphate-based cathode material (LiMnPO4, LiCoPO4), or a composite-doped cathode material (Li2FeSiO4, LiVPO4F); the mass of the cathode active material is preferably 75-85 wt% of the suspension mass, more preferably 80 wt%. The present invention does not have a specific limitation on the source of the cathode active material; any corresponding cathode active material well known in the art can be used.

[0037] The present invention involves plasma treatment of carbon fiber cloth to obtain modified carbon fiber cloth; electrospinning of the conductive slurry on the surface of the modified carbon fiber cloth to form a conductive coating, thereby obtaining a carbon fiber structure energy storage composite material.

[0038] The present invention does not impose any special limitations on the specifications and source of the carbon fiber cloth; commercially available products well known in the art are acceptable.

[0039] In this invention, the power of the plasma treatment is preferably 80-120W, more preferably 90-100W, and the time is preferably 5-10min, more preferably 5-8min.

[0040] The present invention does not impose any special limitations on the equipment and other conditions for plasma treatment; the process can be carried out according to procedures well known in the art.

[0041] In embodiments of this invention, the plasma device is a low-temperature vacuum plasma treatment machine; the main gas used is oxygen, with an oxygen flow rate of 50–100 mL / min; the auxiliary gas (optional) is argon, used to stabilize the discharge and reduce fiber damage; the auxiliary gas flow rate (e.g., argon) is 20–50 mL / min; the chamber pressure is 10–30 Pa. Preferably, the carbon fiber cloth is cut to the required size, the surface is wiped with a lint-free cloth and anhydrous ethanol, the vacuum pump is started, and the chamber pressure is reduced to 10–30 Pa; oxygen and (optionally) argon are injected at the set flow rate; the plasma generator is started, and the power is set to 100 W; the carbon fiber cloth is placed on a rotating sample stage, ensuring that all parts are uniformly exposed to the plasma. The treatment time is set to 5 minutes. After treatment, the gas supply is turned off, atmospheric pressure is restored, and the chamber is cleaned; the treated carbon fiber cloth is placed in a dry, clean environment to avoid recontamination.

[0042] This invention involves plasma treatment of carbon fiber cloth to enhance its surface energy, thereby strengthening the interfacial bonding between the carbon fiber cloth and the conductive coating. Simultaneously, it removes surface contaminants, cleans the carbon fiber surface, and removes grease, dust, and residual additives. Furthermore, it introduces polar functional groups such as hydroxyl and carboxyl groups into the carbon fiber surface, promoting chemical bonding with the conductive coating. This invention enhances the interfacial bonding performance between carbon fiber and the matrix through plasma treatment, optimizing both energy storage and mechanical properties. The interfacial shear strength of the composite material after treatment can be increased by more than 30%.

[0043] In this invention, the electrospinning conditions preferably include: voltage 10-15 kV; collection distance 10-15 cm; slurry flow rate 0.1-0.2 mL / min; more preferably, the voltage is 12-15 kV; more preferably, the collection distance is 12 cm; and more preferably, the slurry flow rate is 0.1-0.15 mL / min.

[0044] After the electrospinning is completed, the present invention preferably dries the product in a vacuum drying oven at 80°C for 6 hours to remove the solvent.

[0045] The present invention does not impose a specific limitation on the thickness of the conductive coating, which can be adjusted according to actual needs; in the embodiments of the present invention, it is specifically 20 μm.

[0046] In this invention, when the areal loading of the desired positive electrode material is ≥5 mg / cm³ 2 After electrospinning, the process further includes spraying a conductive slurry onto the conductive coating. The spraying process includes: adjusting the viscosity of the conductive slurry to 500–800 mPa·s, more preferably 600–700 mPa·s, and spraying it in layers onto the conductive coating. The spraying conditions include: a spraying pressure of 0.2–0.5 MPa, more preferably 0.2–0.3 MPa; a nozzle diameter of 100 μm; and a single-layer thickness of 20–25 μm. This invention does not impose a specific limitation on the number of conductive layers formed by the spraying process; adjustments can be made according to actual needs.

[0047] Electrospinning is suitable for uniform coating at the microscale (nano / micron level), ensuring the fineness of the conductive network during pilot or sample preparation. However, when expanding to higher loading or larger area preparation, relying solely on electrospinning leads to lower efficiency. This invention first forms a "skeleton" or a highly adhesive nanofiber layer through electrospinning, and then uses spraying to superimpose an additional conductive coating on its surface to achieve high capacity requirements.

[0048] In this invention, the equipment used for spraying is preferably a Nordson EFD Optimum spraying device.

[0049] After the spraying is completed, the present invention preferably allows the coating to level naturally and then cures it in an oven at 120°C.

[0050] The present invention provides a carbon fiber structure energy storage composite material based on a multi-level conductive network prepared by the preparation method described in the above technical solution.

[0051] This invention provides the application of the carbon fiber structure energy storage composite material based on a multi-level conductive network described above in the field of energy storage. This invention does not impose any particular limitation on the method of application; any method well-known in the art can be used.

[0052] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0053] In the following examples, the carbon fiber cloth is made of T700 grade carbon fiber with a fiber diameter of 7 μm and a density of 1.8 g / cm³. 3 Produced by Toray Industries, Inc.

[0054] Positive electrode active material: Lithium iron phosphate (LiFePO4), particle size 300nm, specific capacity 170mAh / g, provided by Xiamen Junshi Energy Technology Co., Ltd.

[0055] Carbon nanotubes (MWCNTs): diameter 10-20 nm, length 10-30 μm, electrical conductivity >10 4 S / m, Qianrenhe Materials Technology Co., Ltd.

[0056] Graphene: Single-layer reduced graphene oxide, thickness <1nm, side length 5-10μm, Sixth Element Materials Technology Co., Ltd.

[0057] MXene (Ti3C2Tx): Thickness <2nm, flake diameter 1-5μm, synthesized by Ningbo Institute of Materials Technology and Engineering, exhibiting high electrical conductivity and excellent ionic conductivity.

[0058] Adhesive: Polyvinylidene fluoride (PVDF), molecular weight 450,000, Arkema.

[0059] Solvent: N-methylpyrrolidone (NMP), analytical grade.

[0060] Example 1

[0061] CNTs, graphene, and MXene were added to NMP at a mass ratio of 2:2:1 and dispersed using an ultrasonic disperser for 30 minutes to form a uniform suspension. PVDF was dissolved in NMP to form a 10wt% binder solution, which was added to the suspension at a mass ratio of 5% of the binder in the conductive slurry and stirred until homogeneous. The positive electrode active material, lithium iron phosphate (LiFePO4), was added to the suspension at a ratio of 80wt% and stirred at high speed for 5 minutes to obtain the conductive slurry.

[0062] The carbon fiber cloth was subjected to low-temperature plasma treatment using a low-temperature vacuum plasma treatment machine. The carbon fiber cloth was cut to the required size, and the surface was wiped with a lint-free cloth and anhydrous ethanol. The vacuum pump was started to reduce the pressure in the chamber to 150 Pa. Oxygen was injected at a set flow rate of 60 mL / min. The plasma generator was started and the power was set to 100 W. The carbon fiber cloth was placed on a rotating sample stage to ensure that all parts were evenly exposed to the plasma. The treatment time was set to 5 min. After the treatment was completed, the gas supply was turned off, atmospheric pressure was restored, and the chamber was cleaned to obtain the modified carbon fiber cloth.

[0063] The conductive slurry was placed in an electrospinning machine (NaBond FS-100), and the parameters were adjusted as follows: voltage: 15kV; collection distance: 12cm; slurry flow rate: 0.1mL / min. Electrospinning was performed to form a conductive coating on the surface of the carbon fiber cloth with a coating thickness of 20μm. The coating was then dried in a vacuum drying oven at 80℃ for 6h to obtain a carbon fiber structure energy storage composite material.

[0064] Example 2

[0065] The only difference from Example 1 is that the required areal loading of the positive electrode material is 10 mg / cm³. 2 After electrospinning is completed, the conductive slurry is sprayed onto the conductive coating surface using a Nordson EFD Optimum spraying machine. The specific steps are as follows:

[0066] The conductive slurry was adjusted to a viscosity of 600 mPa·s and sprayed in layers onto the modified carbon fiber cloth. The spraying pressure was 0.2 MPa, the nozzle diameter was 100 μm, and the number of sprayed layers was 3, with a single layer thickness of 20 μm. After natural leveling, it was cured in an oven at 120℃ to obtain a carbon fiber structure energy storage composite material.

[0067] Characterization test

[0068] 1) The morphology and fiber distribution of the coating prepared in Example 1 were observed by scanning electron microscopy (SEM). The results showed that the nanofibers had uniform diameters ranging from 200 to 500 nm. The fibers formed an interlaced multi-level network with a coverage of nearly 95%. There were no obvious breaks or aggregations, indicating that the coating had good uniformity.

[0069] 2) The distribution of graphene, CNTs and MXene in the nanoscale coating was observed using transmission electron microscopy (TEM): Samples were taken from the coating, suspended in an ethanol solution by ultrasonic exfoliation, dropped onto a copper mesh and dried.

[0070] The results show that CNTs and graphene are distributed in the nanofibers, forming through conductive channels; MXene sheets are uniformly embedded in the fiber matrix with stable interlayer spacing, further improving conductivity.

[0071] 3) The surface roughness and uniformity of the coating were analyzed using atomic force microscopy (AFM):

[0072] Test conditions: Scan range: 10μm×10μm; Mode: Contact mode.

[0073] The results show that the coating surface is uniform with an average roughness (Ra) of 10–20 nm and the coating thickness is uniform with a thickness of 1.5 μm.

[0074] Performance testing

[0075] 1. The surface of the plasma-treated carbon fiber cloth was measured using the water contact angle measurement method. The results showed that the water contact angle was >90° before treatment and <30° after treatment. This indicates that the surface energy of the carbon fiber cloth is significantly improved after treatment, which can enhance the interfacial bonding force between the carbon fiber and the conductive coating.

[0076] 2. Performance testing was performed on the carbon fiber structure energy storage composite material prepared in Example 1:

[0077] 1) Electrochemical performance

[0078] Test method: Tested using CR2032 button cell batteries.

[0079] Initial specific capacity: At a 0.1C rate, the specific capacity of the positive electrode is 165 mAh / g.

[0080] Rate performance: At 1C rate, the specific capacity is 140mAh / g.

[0081] Cycling performance: After 200 cycles at 1C rate, capacity retention is 98%.

[0082] 2) Mechanical properties

[0083] Peel strength: The peel strength between the conductive coating and the carbon fiber cloth is 5.5 N / cm.

[0084] Tensile strength: The overall tensile strength of the composite material is 600 MPa.

[0085] Tensile bond strength test: The bond strength between the coating and the carbon fiber matrix was tested using the pull-out method. Gradually increasing vertical peel forces were applied, and the maximum load was recorded.

[0086] Results: The coating adhesion was 18 MPa, which was 50% higher than that of the untreated sample (12 MPa), indicating that the electrospinning process made the interface between the coating and the carbon fiber more stable.

[0087] 3) Conductivity test

[0088] The volumetric conductivity of the coating was measured using the four-probe method. The results showed that the surface resistivity of the coating was 0.4 Ω / m, and the conductivity of the electrospun coating reached 2.5 × 10⁻⁶. 5 S / m, compared to traditional spray coatings (1.8×10 5 The conductivity (S / m) is increased by approximately 38%.

[0089] 4) Thermogravimetric analysis (TGA) was used to test the thermal stability of the coating. The results showed that the coating retained 95% of its mass at 400℃, demonstrating good high-temperature stability.

[0090] 5) The thermal conductivity of the coating was measured using the laser flash method. The results showed that the thermal conductivity was 3.2 W / m·K, which was 45% higher than that of the uncoated sample.

[0091] The above results demonstrate that the electrospinning process employed in this invention achieves precise control over the nanoscale fiber coating; the coated fibers exhibit uniform diameter, dense distribution, and high coverage, displaying excellent nanoscale morphological characteristics; the coating's electrical conductivity is significantly improved, meeting the requirements for efficient electron transport; the bonding force between the coating and the carbon fiber matrix is ​​significantly enhanced, ensuring the interfacial stability of the composite material; and the improved thermal conductivity and thermal stability make it suitable for high-temperature energy storage environments. This invention, through its optimized nanoscale coating design using electrospinning technology, provides crucial support for the construction of multi-level conductive networks, demonstrating excellent performance and broad application potential.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon fiber structure energy storage composite material based on a multi-level conductive network, characterized in that, Includes the following steps: Carbon nanotubes, graphene, MXene, and organic solvents are mixed to obtain a suspension; The suspension is mixed with a binder and a positive electrode active material to obtain a conductive slurry; Modified carbon fiber cloth is obtained by plasma treatment of carbon fiber cloth. The conductive slurry is electrospun on the surface of the modified carbon fiber cloth to form a conductive coating, thereby obtaining a carbon fiber structure energy storage composite material. The mass ratio of the carbon nanotubes, graphene, and MXene is 1~3:1~3:1; The plasma treatment power is 80~120W, and the time is 5~10min; When the required surface loading of the positive electrode active material is ≥5 mg / cm³ 2 After electrospinning, the process further includes spraying a conductive slurry onto a conductive coating; the spraying includes: adjusting the viscosity of the conductive slurry to 500~800 mPa·s, and spraying it in layers onto the conductive coating; the spraying conditions include: spraying pressure of 0.2~0.5 MPa; nozzle diameter of 100 µm; and single-layer thickness of 20~25 µm; The carbon nanotubes have a diameter of 10–20 nm, a length of 10–30 µm, and an electrical conductivity >10. 4 S / m; the graphene is a single-layer reduced-oxidation graphene with a thickness <1 nm; the MXene is Ti3C2T x The thickness of the MXene is <2 nm, and the sheet diameter is 1~5 µm; The adhesive is polyvinylidene fluoride, and the molecular weight of polyvinylidene fluoride is 450,000.

2. The preparation method according to claim 1, characterized in that, The positive electrode active material includes lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based positive electrode material, phosphate-based positive electrode material, or composite doped positive electrode material.

3. The preparation method according to claim 1, characterized in that, The conditions for electrospinning include: voltage 10~15kV; collection distance 10~15 cm; slurry flow rate 0.1~0.2 mL / min.

4. The carbon fiber structure energy storage composite material based on a multi-level conductive network prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the carbon fiber structure energy storage composite material based on a multi-level conductive network as described in claim 4 in the field of energy storage.