Carbon fiber structure energy storage composite material based on multistage conductive network as well as preparation method and application of carbon fiber structure energy storage composite material

Abstract

The invention 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. A conductive network with high conductivity and good interface bonding force is formed through the synergistic effect of CNTs, graphene and MXene, meanwhile, the uniformity and adhesive force of an electrode coating are remarkably improved by combining an electrostatic spinning or precise spraying technology, the surface energy of the carbon fibers is enhanced through low-temperature plasma treatment, and the conductivity of the electrode coating is improved. The adhesive force and the stability of a conductive network are improved, so that the interface bonding force of the conductive coating is remarkably improved. The high-performance carbon fiber structure energy storage composite material is prepared through construction of a multi-stage conductive network and optimization of a coating process, the mechanical performance and the electrochemical performance of the material are remarkably improved, and a foundation is laid for industrial application of the technology through the optimized coating process and the enhanced interface bonding force.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage materials, and in particular to a carbon fiber structure energy storage composite material based on a multi-level conductive network, and a preparation method and application thereof. Background Art

[0002] As a new type of material that integrates mechanical bearing and electrochemical energy storage functions, carbon fiber structure energy storage composite materials have broad application prospects in the fields of new energy vehicles, aerospace, etc. However, the existing technology still has the following problems in the construction of the conductive network and coating process of the electrode: 1. Imperfect conductive network structure: The electron transmission efficiency of existing carbon fiber composite electrodes is low, which limits the further improvement of energy storage performance. 2. Unstable coating process: The coating process of the electrode material is difficult to ensure the uniformity of the coating over a large area, affecting the overall performance. 3. Insufficient bonding with carbon fiber: In traditional methods, the interface bonding between the conductive material and the carbon fiber matrix is ​​weak, which makes the coating easy to peel off. Summary of the invention

[0003] The purpose of the present invention is to provide a carbon fiber structure energy storage composite material based on a multi-level conductive network, and a preparation method and application thereof. The present invention combines the construction method based on the multi-level conductive network with electrospinning and precision spraying technology to achieve performance optimization of the carbon fiber structure energy storage composite material.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present 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] mixing carbon nanotubes, graphene, MXene and an organic solvent to obtain a suspension;

[0007] mixing the suspension with a binder and a positive electrode active material to obtain a conductive slurry;

[0008] The carbon fiber cloth is subjected to plasma treatment to obtain a modified carbon fiber cloth;

[0009] The conductive slurry is electrostatically spun on the surface of the 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 to 3:1 to 3:1.

[0011] Preferably, the carbon nanotubes have a diameter of 10 to 20 nm, a length of 10 to 30 μm, and a conductivity of more than 10 4S / m; the graphene is a single-layer redox graphene with a thickness of <1nm and a side length of 5 to 10μm; the MXene is Ti3C2T x The thickness of the MXene is <2 nm and the sheet diameter is 1 to 5 μm.

[0012] Preferably, the binder is polyvinylidene fluoride, and the molecular weight of the 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 power of the plasma treatment is 80 to 120 W, and the time is 5 to 10 minutes.

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

[0016] Preferably, when the required surface loading of the positive electrode material is ≥5 mg / cm 2 When the electrospinning is performed, the conductive slurry is sprayed on the conductive coating after the electrospinning; the spraying includes: adjusting the conductive slurry to a viscosity of 500 to 800 mPa·s, and spraying the conductive slurry on the conductive coating in layers; the spraying conditions include: a spraying pressure of 0.2 to 0.5 MPa; a nozzle diameter of 100 μm; and a single layer thickness of 20 to 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] The present invention provides the application of the carbon fiber structure energy storage composite material based on the multi-level conductive network described in the above technical solution in the field of energy storage.

[0019] The present invention uses carbon nanotubes, graphene and MXene to form a conductive slurry, and constructs a high-speed channel for electron transmission through the synergistic effect of CNTs, graphene and MXene, thereby forming a conductive network with high conductivity and good interface bonding force, and combines electrostatic spinning and precision spraying technology to achieve a significant improvement in the uniformity and adhesion of the electrode coating. The surface energy of the carbon fiber is enhanced by low-temperature plasma treatment, and the adhesion and stability of the conductive network are improved, thereby significantly improving the interface bonding force of the conductive coating. The present invention obtains a high-performance carbon fiber structure energy storage composite material through the construction of a multi-level conductive network and the optimization of the coating process, which significantly improves the mechanical properties and electrochemical properties of the material. The optimized coating process and enhanced interface bonding force lay the foundation for the industrial application of this technology.

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

[0021] The present invention utilizes electrostatic spinning technology to achieve precise control of nano-scale coatings. When large-area preparation is required, combined with spraying technology, the preparation of carbon fiber structure energy storage composite materials can be achieved. DETAILED DESCRIPTION

[0022] In the present invention, unless otherwise specified, the raw materials or reagents used are commercially available products well known in the art.

[0023] The present 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] mixing carbon nanotubes, graphene, MXene and an organic solvent to obtain a suspension;

[0025] mixing the suspension with a binder and a positive electrode active material to obtain a conductive slurry;

[0026] The carbon fiber cloth is subjected to plasma treatment to obtain a modified carbon fiber cloth;

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

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

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

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

[0031] In the present invention, the organic solvent is preferably N-methylpyrrolidone (NMP); the present invention has no special limitation on the amount of the organic solvent, and the amount can be adjusted according to the dosage known in the art to ensure sufficient mixing of the materials.

[0032] In the present invention, the carbon nanotubes, graphene and MXene are preferably added to an organic solvent and dispersed for 30 minutes using an ultrasonic disperser 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 the present invention, the binder is preferably polyvinylidene fluoride (PVDF), and the molecular weight of the polyvinylidene fluoride is preferably 450,000; the mass proportion of the binder in the conductive paste is preferably 5-10%, and more preferably 5-8%.

[0035] The present invention preferably dissolves PVDF in NMP to form a binder solution with a concentration of 10 wt%, adds the binder solution to the suspension, stirs evenly, adds the positive electrode active material to the suspension, stirs at high speed for 5 minutes, and obtains a conductive slurry.

[0036] In the present invention, the positive electrode active material preferably includes lithium iron phosphate, lithium iron phosphate, lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel cobalt manganese oxide (LiNixCoyMnO2, NCM / NMC), lithium nickel cobalt aluminum oxide (LiNi x Co yAlO2, NCA), lithium-rich manganese-based positive electrode materials (Li-rich Mn-based oxide), phosphate-based positive electrode materials (LiMnPO4, LiCoPO4) or composite doped positive electrode materials (Li2FeSiO4, LiVPO4F); the mass of the positive electrode active material is preferably 75-85wt% of the mass of the suspension, more preferably 80wt%. The present invention has no special limitation on the source of the positive electrode active material, and any corresponding positive electrode active material known in the art can be used.

[0037] The present invention performs plasma treatment on carbon fiber cloth to obtain modified carbon fiber cloth; the conductive slurry is electrostatically spun on the surface of the modified carbon fiber cloth to form a conductive coating to obtain a carbon fiber structure energy storage composite material.

[0038] The present invention has no particular limitation on the specification and source of the carbon fiber cloth, and any commercially available product known in the art may be used.

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

[0040] The present invention has no special limitation on the equipment and other conditions of the plasma treatment, and the treatment may be carried out according to the process well known in the art.

[0041] In an embodiment of the present invention, the plasma equipment is a low-temperature vacuum plasma processor; the main gas used is oxygen, and the oxygen flow rate is 50 to 100 mL / min; the auxiliary gas (optional) is argon, which is used to stabilize the discharge and reduce fiber damage; the auxiliary gas flow rate (such as argon) is 20 to 50 mL / min; the cavity pressure is 10 to 30 Pa. The present invention preferably cuts the carbon fiber cloth to the required size, wipes the surface with a dust-free cloth and anhydrous ethanol, starts the vacuum pump, and reduces the pressure in the cavity to 10 to 30 Pa; injects oxygen and (optional) argon at a set flow rate; starts the plasma generator, and sets the power to 100 W; places the carbon fiber cloth on a rotating sample table to ensure that all parts are evenly exposed to the plasma. The treatment time is set to 5 minutes. After the treatment is completed, turn off the gas supply, restore the atmospheric pressure, and clean the cavity; place the treated carbon fiber cloth in a dry and clean environment to avoid re-contamination.

[0042] The present invention performs plasma treatment on carbon fiber cloth to enhance the surface energy of carbon fiber cloth, thereby enhancing the interface bonding force between carbon fiber cloth and conductive coating; at the same time, surface pollutants can be removed, the surface of carbon fiber can be cleaned, grease, dust and residual additives can be removed; polar functional groups such as hydroxyl and carboxyl groups are introduced on the surface of carbon fiber to promote chemical bonding with conductive coating. The present invention enhances the interface bonding performance between carbon fiber and matrix through plasma treatment, optimizes the comprehensive performance of energy storage and mechanics, and the interface shear strength of the composite material after treatment can be increased by more than 30%.

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

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

[0045] The present invention has no special limitation on the thickness of the conductive coating, which can be adjusted according to actual needs; in the embodiment of the present invention, it is specifically 20 μm.

[0046] In the present invention, when the required surface loading of the positive electrode material is ≥5 mg / cm 2 When the electrospinning is performed, the conductive slurry is sprayed on the conductive coating after the electrospinning; the spraying includes: adjusting the conductive slurry to a viscosity of 500-800mPa·s, more preferably 600-700mPa·s, and spraying it on the conductive coating in layers; the spraying conditions include: a spraying pressure of 0.2-0.5MPa, more preferably 0.2-0.3MPa; a nozzle diameter of 100μm; and a single layer thickness of 20-25μm. The present invention has no special limitation on the number of conductive layers formed by the spraying, and it can be adjusted according to actual needs.

[0047] Electrospinning is suitable for uniform coating at the microscopic scale (nano / micrometer level), and can ensure the refinement of the conductive network during small-scale or sample-level preparation; when expanded to higher loads or larger areas, relying solely on electrospinning will result in low efficiency; the present invention first forms a "skeleton" or a high-adhesion nanofiber layer through electrospinning, and then sprays an additional conductive coating on its surface to achieve high capacity requirements.

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

[0049] After the spraying is completed, the present invention is preferably cured in an oven at 120° C. after natural leveling.

[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] The present invention provides the application of the carbon fiber structure energy storage composite material based on the multi-level conductive network described in the above technical solution in the field of energy storage. The present invention has no special limitation on the application method, and the application can be carried out according to the method known in the art.

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

[0053] In the following examples, carbon fiber cloth: T700 grade carbon fiber, fiber diameter 7 μm, density 1.8 g / cm 3 , produced by Toray Industries.

[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 10-20nm, length 10-30μm, conductivity>10 4 S / m, Qianrenhe Material Technology Co., Ltd.

[0056] Graphene: Single-layer redox graphene, 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, with high conductivity and excellent ionic conductivity.

[0058] Binder: 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 in a mass ratio of 2:2:1, and dispersed for 30 minutes using an ultrasonic disperser to form a uniform suspension. PVDF was dissolved in NMP to form a binder solution with a concentration of 10wt%, and the binder solution was added to the suspension at a mass ratio of 5% in the conductive slurry, and stirred evenly. Lithium iron phosphate (LiFePO4), a positive electrode active material, was added to the suspension at a ratio of 80wt%, and stirred at high speed for 5 minutes to obtain a conductive slurry.

[0062] The carbon fiber cloth was treated with low-temperature plasma using a low-temperature vacuum plasma treatment machine, the carbon fiber cloth was cut into the required size, the surface was wiped with a dust-free cloth and anhydrous ethanol, the vacuum pump was started, and the pressure in the cavity was reduced to 150Pa; oxygen was injected at a set flow rate of 60mL / min; the plasma generator was started and the power was set to 100W; the carbon fiber cloth was placed on a rotating sample table to ensure that all parts were evenly exposed to the plasma, and the treatment time was set to 5min. After the treatment was completed, the gas supply was turned off, the atmospheric pressure was restored, and the cavity was cleaned to obtain a 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: 15 kV; collection distance: 12 cm; slurry flow rate: 0.1 mL / min, and electrospinning was performed to form a conductive coating on the surface of the carbon fiber cloth. The coating thickness was 20 μm, and the carbon fiber cloth was dried in a vacuum drying oven at 80° C. for 6 h to obtain a carbon fiber structure energy storage composite material.

[0064] Example 2

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

[0066] The conductive slurry was adjusted to a viscosity of 600 mPa·s and sprayed on the modified carbon fiber cloth in layers with a spraying pressure of 0.2 MPa; the nozzle diameter was 100 μm; the number of spray layers was 3, and the thickness of a single layer was 20 μm. After natural leveling, the slurry was cured in an oven at 120°C 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 using a scanning electron microscope (SEM); the results showed that the nanofibers had a uniform diameter ranging from 200 to 500 nm; an interlaced multi-level network was formed between the fibers, with a coverage rate of nearly 95%; there was no obvious breakage or aggregation, indicating that the coating had good uniformity.

[0069] 2) Transmission electron microscopy (TEM) was used to observe the distribution of graphene, CNTs, and MXene in the nanoscale coating: samples were taken from the coating, suspended in an ethanol solution by ultrasonic exfoliation, dropped onto a copper mesh, and then dried.

[0070] The results show that CNTs and graphene are distributed in the nanofibers to form a conductive channel that runs through them; MXene sheets are evenly embedded in the fiber matrix with a stable interlayer spacing, further improving the conductive properties.

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

[0072] Test conditions: Scanning 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; the coating thickness is evenly distributed, with a thickness of 1.5 μm.

[0074] Performance Testing

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

[0076] 2. Performance test of the carbon fiber structure energy storage composite material prepared in Example 1:

[0077] 1) Electrochemical performance

[0078] Test method: Use CR2032 button battery for testing.

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

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

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

[0082] 2) Mechanical properties

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

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

[0085] Tensile bonding test: The pull-off method is used to test the bonding strength between the coating and the carbon fiber substrate. A gradually increasing vertical peeling force is applied and the maximum load is recorded.

[0086] Results: The coating bonding strength 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 volume conductivity of the coating was measured using the four-probe method. The results showed that the surface resistance of the coating was 0.4Ω / m and the conductivity of the electrospun coating reached 2.5×10 5 S / m, compared with the traditional spray coating (1.8×10 5 S / m), the conductivity increased by about 38%.

[0089] 4) The thermal stability of the coating was tested using thermogravimetric analysis (TGA). The results showed that the mass retention rate of the coating at 400°C was 95%, showing good high temperature stability.

[0090] 5) The thermal conductivity of the coating was measured by 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 show that the present invention uses electrospinning technology to achieve precise control of nanoscale fiber coatings; the coating fibers have uniform diameters, close distribution, high coverage, and exhibit excellent nanoscale morphological characteristics; the conductivity of the coating is significantly improved to meet the needs of efficient electron transmission; the bonding between the coating and the carbon fiber matrix is ​​significantly enhanced to ensure the interface stability of the composite material; the thermal conductivity and thermal stability are improved to adapt to high-temperature energy storage environments. The nanoscale coating design optimized by electrospinning technology in the present invention provides key support for the construction of multi-level conductive networks, showing excellent performance and broad application potential.

[0092] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as 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: The following steps are involved: mixing carbon nanotubes, graphene, MXene and an organic solvent to obtain a suspension; mixing the suspension with a binder and a positive electrode active material to obtain a conductive slurry; The carbon fiber cloth is subjected to plasma treatment to obtain a modified carbon fiber cloth; The conductive slurry is electrostatically spun on the surface of the modified carbon fiber cloth to form a conductive coating, thereby obtaining a carbon fiber structure energy storage composite material.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the carbon nanotubes, graphene and MXene is 1 to 3:1 to 3:

1.

3. The preparation method according to claim 1, characterized in that: The carbon nanotubes have a diameter of 10 to 20 nm, a length of 10 to 30 μm, and an electrical conductivity of more than 10 4 S / m; the graphene is a single-layer redox graphene with a thickness of <1nm and a side length of 5 to 10μm; the MXene is Ti3C2T x The thickness of the MXene is <2 nm and the sheet diameter is 1 to 5 μm.

4. The preparation method according to claim 1, characterized in that: The binder is polyvinylidene fluoride, and the molecular weight of the polyvinylidene fluoride is 450,000.

5. 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.

6. The preparation method according to claim 1, characterized in that: The power of the plasma treatment is 80-120 W, and the time is 5-10 minutes.

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

8. The preparation method according to claim 1, characterized in that: When the required surface loading of the positive electrode material is ≥5 mg / cm 2 When the electrospinning is performed, the conductive slurry is sprayed on the conductive coating after the electrospinning; the spraying includes: adjusting the conductive slurry to a viscosity of 500 to 800 mPa·s, and spraying the conductive slurry on the conductive coating in layers; the spraying conditions include: a spraying pressure of 0.2 to 0.5 MPa; a nozzle diameter of 100 μm; and a single layer thickness of 20 to 25 μm.

9. A 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 8.

10. Application of the carbon fiber structure energy storage composite material based on multi-level conductive network as claimed in claim 9 in the field of energy storage.