Carbon fiber positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of battery composite materials, and provides a carbon fiber positive electrode material and a preparation method and application thereof.The preparation method comprises the steps that 1, a positive electrode active material, a conductive agent, a binder and a solvent are mixed to obtain positive electrode slurry; or; mixing the positive electrode active material, a conductive agent, a binder, a dispersant and a solvent to obtain positive electrode slurry; (2) mixing carbon fibers and the positive electrode slurry to obtain intermediate carbon fibers; and (3) carrying out post-treatment on the intermediate carbon fiber to obtain the carbon fiber positive electrode material. The invention provides an innovative technical route, a positive electrode material is directly integrated into a carbon fiber matrix by optimizing a positive electrode active material, a conductive agent and binder system and a slurry coating and curing process, and a multifunctional carbon fiber composite structure capable of simultaneously carrying and storing energy is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of battery composite materials, and particularly to a carbon fiber positive electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of electric vehicles, aerospace vehicles, portable electronic devices, and renewable energy storage systems, people's requirements for lithium-ion batteries in terms of energy density, safety, cycle stability, and environmental friendliness are constantly increasing. At the same time, in order to achieve lightweight and multifunctional integration, the research on structure-energy storage integrated composite materials has become a hot topic. By integrating the functions of the battery positive electrode / negative electrode into the load-bearing structure, it is possible to improve energy storage and load-bearing simultaneously without increasing the overall mass of the system.

[0003] Existing traditional powder electrode materials for positive electrodes (such as LiCoO 2 , NCM, NCA, LiFePO 4 , Li 4 Ti 5 O 12 etc.) face problems such as poor adhesion to the carbon fiber surface, uneven dispersion of the conductive agent, and weak bonding between the binder and the active material, current collector, and fiber when applied to carbon fiber composite structures. In addition, the conductive agent and binder systems used in traditional electrode preparation are not convenient for direct integration onto the carbon fiber surface, and it is difficult to achieve stable structure-energy storage integration without significantly increasing the structural weight.

[0004] Currently, there is still a lack of a mature method to directly and efficiently load the positive electrode functional material uniformly on the surface of high-performance carbon fibers to obtain a composite structure with high energy density, high cycle stability, and mechanical properties. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a carbon fiber positive electrode material, a preparation method thereof, and an application thereof.

[0006] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method for a carbon fiber positive electrode material, comprising the following steps:

[0008] (1) Mixing a positive electrode active material, a conductive agent, a binder, and a solvent to obtain a positive electrode slurry; or;

[0009] Mixing a positive electrode active material, a conductive agent, a binder, a dispersant, and a solvent to obtain a positive electrode slurry;

[0010] (2) Mixing carbon fibers and the positive electrode slurry to obtain intermediate carbon fibers;

[0011] (3) Post-treat the intermediate carbon fiber to obtain the carbon fiber positive electrode material.

[0012] Preferably, the positive electrode active material in step (1) is LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiFePO 4 or Li 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0013] The conductive agent is one or more of carbon nanotubes, graphene, carbon black SuperP, and polyaniline;

[0014] The binder is one or more of PVDF, carboxymethyl cellulose, polyurethane, and polyaniline;

[0015] The solvent is N-methylpyrrolidone;

[0016] The dispersant is nano-silica.

[0017] Preferably, when the positive electrode active material, conductive agent, binder, and solvent are used to obtain the positive electrode slurry, the mass ratio of the positive electrode active material, conductive agent, and binder is 80-100:1-10:1-5; the solid content of the positive electrode slurry is 40-60 wt%, and the viscosity is 1000-2000 mPa·s;

[0018] When the positive electrode active material, conductive agent, binder, dispersant, and solvent are used to obtain the positive electrode slurry, the mass ratio of the positive electrode active material, conductive agent, binder, and dispersant is 80-100:1-10:1-5:0.05-0.15; the solid content of the positive electrode slurry is 40-60 wt%, and the viscosity is 1000-2000 mPa·s.

[0019] Preferably, the rotation speed of the mixing in step (1) is 7000-9000 rpm, and the time is 30-60 min.

[0020] Preferably, the mixing method in step (2) is the impregnation method, spraying method, spin coating method, coating method, or self-assembly method;

[0021] The immersion time of the impregnation method is 5-10 s;

[0022] The spraying pressure of the spraying method is 0.1 - 0.3 MPa, the spraying distance is 10 - 20 cm, and the number of repetitions is 2 - 4 times.

[0023] Preferably, the rotation speed of the spin coating method is 1500 - 2500 rpm, and the time is 20 - 40 s;

[0024] The coating thickness of the coating method is 2 - 4 μm;

[0025] The number of self-assembled layers of the self-assembly method is ≥5.

[0026] Preferably, the post-treatment in step (3) is drying and heat treatment carried out sequentially;

[0027] The temperature of the drying is 80 - 130 °C, and the time is 10 - 120 min.

[0028] Preferably, the temperature of the heat treatment is 150 - 250 °C, and the time is 1 - 4 h.

[0029] The present invention also provides a carbon fiber positive electrode material prepared by the preparation method of the carbon fiber positive electrode material.

[0030] The present invention also provides the application of the carbon fiber positive electrode material in a structure-energy storage integrated composite material.

[0031] The present invention provides a preparation method of a carbon fiber positive electrode material, comprising the following steps: (1) mixing a positive electrode active material, a conductive agent, a binder and a solvent to obtain a positive electrode slurry; or; mixing a positive electrode active material, a conductive agent, a binder, a dispersant and a solvent to obtain a positive electrode slurry; (2) mixing carbon fibers and the positive electrode slurry to obtain intermediate carbon fibers; (3) performing post-treatment on the intermediate carbon fibers to obtain the carbon fiber positive electrode material. The present invention provides an innovative technical route. By optimizing the positive electrode active material, conductive agent and binder system, as well as the slurry coating and curing process, the positive electrode material is directly integrated into the carbon fiber matrix to obtain a multifunctional carbon fiber composite structure that can simultaneously bear and store energy.

[0032] The advantages of the present invention are as follows:

[0033] Optimizing the ratio of the positive electrode active substance to the conductive agent: Selecting high-nickel NCM (such as NCM811) or NCA as the main positive electrode active substance, and using a composite conductive agent to multi-dimensionally strengthen the electron conduction path;

[0034] Innovative binder system and solvent system: Using PVDF as the binder, NMP as the solvent, and supplemented with nano-dispersion technology to ensure the uniformity of the slurry and the adhesion to the carbon fiber surface;

[0035] Innovative coating process: According to actual application requirements, the impregnation method, spraying method, spin coating or layer-by-layer self-assembly technology is adopted to achieve uniform coating of carbon fibers, and improve the controllability of the coating thickness and uniformity;

[0036] Improve the heat treatment and curing process: By optimizing the drying rate, heat treatment temperature and time, the binder is fully cured and a strong bonding interface is formed with the fiber surface, ensuring the stability of the electrode material during the electrochemical cycling process;

[0037] Comprehensive performance improvement: Without significantly increasing the thickness or weight of the carbon fiber layer, the capacity retention rate of the prepared positive electrode coating exceeds 90% at a high rate of 2C, and the capacity retention rate reaches more than 80% after 500 cycles, while maintaining the tensile strength of the carbon fiber composite material with a decrease of no more than 10%.

[0038] In the present invention, a stable positive electrode slurry is obtained through specific raw material selection, and then the slurry is uniformly coated on the surface of carbon fibers. After subsequent heat treatment or solvent evaporation, a carbon fiber positive electrode material with high energy density, excellent cycle stability and mechanical bearing capacity is obtained. This composite positive electrode material can be further combined with a resin system or prepreg to prepare a carbon fiber composite material structural part with both structural and energy storage functions. Detailed implementation mode

[0039] The present invention provides a preparation method of a carbon fiber positive electrode material, comprising the following steps:

[0040] (1) Mix the positive electrode active material, conductive agent, binder and solvent to obtain a positive electrode slurry; or;

[0041] Mix the positive electrode active material, conductive agent, binder, dispersant and solvent to obtain a positive electrode slurry;

[0042] (2) Mix the carbon fiber and the positive electrode slurry to obtain an intermediate carbon fiber;

[0043] (3) Post-treat the intermediate carbon fiber to obtain the carbon fiber positive electrode material.

[0044] In the present invention, the positive electrode active material in step (1) is LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiFePO 4 or Li 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0045] The conductive agent is one or more of carbon nanotubes, graphene, carbon black SuperP, and polyaniline;

[0046] The binder is one or more of PVDF, carboxymethyl cellulose, polyurethane, and polyaniline;

[0047] The solvent is N-methylpyrrolidone;

[0048] The dispersant is nano-silica.

[0049] In the present invention, when the positive electrode active material, conductive agent, binder, and solvent are used to obtain the positive electrode paste, the mass ratio of the positive electrode active material, conductive agent, and binder is preferably 80-100:1-10:1-5, more preferably 85-95:2-8:1.5-4.5, and even more preferably 88-92:4-6:2-3; the solid content of the positive electrode paste is preferably 40-60 wt%, more preferably 45-55 wt%, and even more preferably 48-52 wt%; the viscosity is preferably 1000-2000 mPa·s, more preferably 1200-1800 mPa·s, and even more preferably 1400-1600 mPa·s.

[0050] In the present invention, when the positive electrode active material, conductive agent, binder, dispersant, and solvent are used to obtain the positive electrode paste, the mass ratio of the positive electrode active material, conductive agent, binder, and dispersant is preferably 80-100:1-10:1-5:0.05-0.15, more preferably 85-95:2-8:1.5-4.5:0.06-0.14, and even more preferably 88-92:4-6:2-3:0.08-0.12; the solid content of the positive electrode paste is preferably 40-60 wt%, more preferably 45-55 wt%, and even more preferably 48-52 wt%; the viscosity is preferably 1000-2000 mPa·s, more preferably 1200-1800 mPa·s, and even more preferably 1400-1600 mPa·s.

[0051] In the present invention, the rotation speed of the mixing in step (1) is preferably 7000-9000 rpm, more preferably 7500-8500 rpm, and even more preferably 7800-8200 rpm; the time is preferably 30-60 min, more preferably 35-55 min, and even more preferably 40-50 min.

[0052] In the present invention, the mixing method in step (2) is the dipping method, spraying method, spin coating method, coating method, or self-assembly method.

[0053] In the present invention, the immersion time of the dipping method is preferably 5-10 s, more preferably 6-9 s, and even more preferably 7-8 s.

[0054] In the present invention, the spraying pressure of the spraying method is preferably 0.1 - 0.3 MPa, more preferably 0.15 - 0.25 MPa, and even more preferably 0.18 - 0.22 MPa; the spraying distance is preferably 10 - 20 cm, more preferably 12 - 18 cm, and even more preferably 14 - 16 cm; the number of repetitions is preferably 2 - 4 times, and more preferably 3 times.

[0055] In the present invention, the rotation speed of the spin coating method is preferably 1500 - 2500 rpm, more preferably 1600 - 2400 rpm, and even more preferably 1800 - 2200 rpm; the time is preferably 20 - 40 s, more preferably 25 - 35 s, and even more preferably 28 - 32 s.

[0056] In the present invention, the coating thickness of the coating method is preferably 2 - 4 μm, more preferably 2.5 - 3.5 μm, and even more preferably 2.8 - 3.2 μm.

[0057] In the present invention, the number of assembly layers of the self-assembly method is preferably ≥5, more preferably ≥8, and even more preferably ≥10.

[0058] In the present invention, the post-treatment in step (3) is drying and heat treatment carried out sequentially.

[0059] In the present invention, pre-drying is carried out before drying. The temperature of the pre-drying is preferably 20 - 30 °C, more preferably 22 - 28 °C, and even more preferably 24 - 26 °C; the time is preferably 20 - 40 min, more preferably 25 - 35 min, and even more preferably 28 - 32 min.

[0060] In the present invention, the temperature of the drying is preferably 80 - 130 °C, more preferably 90 - 120 °C, and even more preferably 100 - 110 °C; the time is preferably 10 - 120 min, more preferably 30 - 90 min, and even more preferably 40 - 60 min.

[0061] In the present invention, the heat treatment is carried out in a protective atmosphere; the protective atmosphere is preferably nitrogen or argon.

[0062] In the present invention, the temperature of the heat treatment is preferably 150 - 250 °C, more preferably 160 - 240 °C, and even more preferably 180 - 220 °C; the time is preferably 1 - 4 h, more preferably 1.5 - 3.5 h, and even more preferably 2 - 3 h.

[0063] The present invention also provides a carbon fiber positive electrode material prepared by the preparation method of the carbon fiber positive electrode material.

[0064] The present invention also provides an application of the carbon fiber cathode material in a structure-energy storage integrated composite material.

[0065] 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 protection scope of the present invention.

[0066] Example 1

[0067] Configure according to the following ratio:

[0068] LiNi 0.8 Co 0.1 Mn 0.1 O 2 : carbon nanotubes: graphene: carbon black SuperP: PVDF = 90:3:2:2:3;

[0069] Among them, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (particle size D50 is 10 μm), carbon nanotubes (diameter 10 - 20 nm, length 5 - 20 μm); the sheet diameter of graphene < 5 μm;

[0070] Disperse the above raw materials in N-methylpyrrolidone, stir at 8000 rpm for 30 min to obtain a cathode slurry with a viscosity of 1500 mPa·s and a solid content of 50 wt%; immerse the T700 grade carbon fiber monofilament bundle in the slurry for 5 s and take it out, pre-dry at 25 °C for 30 min, then dry at 120 °C for 1 h, and finally heat-treat at 200 °C in an argon atmosphere for 2 h to obtain the carbon fiber cathode material.

[0071] Assemble and test the obtained cathode carbon fiber sample in a button cell (the counter electrode is metallic lithium). The initial discharge capacity is about 195 mAh / g (0.1C), the capacity retention rate reaches 92% at a 2C rate, and the capacity retention rate is about 90% after 100 cycles.

[0072] Example 2

[0073] On the basis of Example 1, use LiNi 0.8 Co 0.15 Al 0.05 O 2 (particle size D50 is 8 μm) to replace LiNi 0.8 Co 0.1 Mn 0.1 O 2As the positive electrode active material, other components and ratios remain unchanged. The slurry viscosity is controlled at 1200 mPa·s. The spraying method is used to reciprocally spray 3 times on the carbon fiber surface with a spray gun pressure of 0.2 MPa and a spraying distance of 15 cm. The drying and heat treatment processes are the same as those in Example 1. After testing, the initial discharge capacity is about 200 mAh / g (0.1 C), the capacity retention rate at the 2C rate reaches 90%, the capacity retention rate after 100 cycles is 85%, and the coating uniformity is good.

[0074] Example 3

[0075] On the basis of Example 1, the positive electrode material is changed to LiFePO 4 (with a particle size D50 of 200 nm), the conductive agent combination is CNT:SuperP = 1:1 (mass ratio), and graphene is not used. The slurry viscosity is controlled at 1800 mPa·s. The spin coating method (rotation speed 2000 rpm, spin coating time 30 s) is used to form a film on the carbon fiber monofilament. The obtained coated positive electrode has a capacity of about 160 mAh / g at the 1C rate, and the capacity retention rate after 500 cycles is 82%, with excellent safety performance and thermal stability.

[0076] Example 4

[0077] In the basic formulation of Example 1, polyaniline (PANI) is added as an auxiliary conductive polymer, and the mass ratio is as follows: LiNi 0.8 Co 0.1 Mn 0.1 O 2 : carbon nanotubes: graphene: carbon black Super P: polyaniline: PVDF = 90:3:2:2:1:3, aiming to further improve the conductive network. The brush coating method is used to manually coat the carbon fiber surface to obtain a relatively thick coating (coating thickness about 3 μm). After testing, the capacity at the 1C rate is about 193 mAh / g, and the capacity retention rate after 200 cycles is increased to 93%, indicating that the introduction of PANI improves the conductivity and coating binding stability.

[0078] Example 5

[0079] On the basis of Example 1, carboxymethyl cellulose (CMC) is added to the slurry to replace part of the PVDF, enabling the slurry to be partially dispersed in an aqueous system. The mass ratio is LiNi 0.8 Co 0.1 Mn 0.1 O 2:Carbon nanotubes: graphene: carbon black SuperP: carboxymethyl cellulose: PVDF=90:3:2:2:0.5:2.5;Then a layer-by-layer self-assembly process is performed (each layer is dried at 80℃ for 10 minutes after self-assembly, and a total of 5 layers are assembled). The final coating has a capacity of 185mAh / g at 0.5C, a retention rate of 90% after 300 cycles, and improved performance stability in a high humidity environment, showing the environmental friendliness and ease of processing of the water-based process.

[0080] Example 6

[0081] Based on Example 1, PVDF mixed with a small amount of polyurethane (PU) (PVDF: PU = 4: 1 mass ratio) was used as a binder. The carbon fiber was coated by the impregnation method and heat treated at 150°C under argon for 3 hours. The resulting coating was more flexible and could resist bending stress. In the tensile test after structural composite, the tensile strength of the unidirectional carbon fiber composite sheet only decreased by about 8%, and the capacity retention rate was still 88% after 200 cycles of 1C, showing excellent structural and electrochemical performance characteristics.

[0082] Example 7

[0083] In the formulation of Example 1, the raw materials were changed as follows: Li 1.2 Ni 0.2 Mn 0.6 O 2 :Carbon nanotubes: graphene: carbon black SuperP: PVDF=90:2:3:2:2; at the same time, the drying temperature is increased to 130℃ and the heat treatment time is extended to 3 hours. The test results show that the initial discharge capacity at 0.1C can reach 230mAh / g, and the capacity remains above 85% after 300 cycles.

[0084] Example 8

[0085] Based on Example 1, the carbon fiber is replaced with high modulus M55J carbon fiber, and the formula is changed to: LiNi 0.8 Co 0.1 Mn 0.1 O 2 :Carbon nanotubes: graphene: carbon black SuperP: PVDF: nano-silica = 90: 3: 2: 2: 3: 0.1; the nano-silica added to the slurry can improve the dispersibility and adhesion of the slurry. The spraying method (0.1MPa, distance 10cm) was adopted, sprayed twice and rotated 90° and sprayed again twice. After the coating was dried and cured, SEM showed that the coating was dense and uniform, with a discharge capacity of 190mAh / g at 0.5C, a capacity retention rate of 92% after 100 cycles, and the strength of the composite material decreased by less than 5% in the tensile test.

[0086] As can be seen from the above embodiments, the present invention can effectively improve the electrochemical performance and mechanical stability of carbon fiber positive electrode materials by changing the types of positive electrode materials, the proportion of conductive agents, the binder system, and the coating process parameters. This method shows significant advantages in the structure-energy storage integrated carbon fiber composite material, providing a feasible approach for the practical application of lightweight energy storage structural components.

[0087] The above are only the preferred embodiments of the present invention. It should be noted 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 a carbon fiber positive electrode material, characterized in that: It includes the following steps: (1) mixing a positive electrode active material, a conductive agent, a binder and a solvent to obtain a positive electrode slurry; or; Mixing a positive electrode active material, a conductive agent, a binder, a dispersant and a solvent to obtain a positive electrode slurry; (2) mixing carbon fiber and positive electrode slurry to obtain intermediate carbon fiber; (3) The intermediate carbon fiber is post-processed to obtain the carbon fiber positive electrode material.

2. The method for preparing a carbon fiber positive electrode material according to claim 1, characterized in that: The positive electrode active material in step (1) is LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.8 Co 0.15 Al 0.05 O2, LiFePO4 or Li 1.2 Ni 0.2 Mn 0.6 O2; The conductive agent is one or more of carbon nanotubes, graphene, carbon black SuperP and polyaniline; The binder is one or more of PVDF, carboxymethyl cellulose, polyurethane and polyaniline; The solvent is N-methylpyrrolidone; The dispersant is nano silicon dioxide.

3. The method for preparing a carbon fiber positive electrode material according to claim 1 or 2, characterized in that: When the positive electrode active material, the conductive agent, the binder and the solvent are used to obtain a positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent and the binder is 80-100:1-10:1-5; the solid content of the positive electrode slurry is 40-60wt%, and the viscosity is 1000-2000mPa·s; When the positive electrode active material, the conductive agent, the binder, the dispersant and the solvent obtain the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent, the binder and the dispersant is 80-100: 1-10: 1-5: 0.05-0.15; the solid content of the positive electrode slurry is 40-60wt%, and the viscosity is 1000-2000mPa·s.

4. The method for preparing a carbon fiber positive electrode material according to claim 3, characterized in that: The mixing speed in step (1) is 7000-9000 rpm and the mixing time is 30-60 min.

5. The method for preparing a carbon fiber positive electrode material according to claim 4, characterized in that: The mixing method in step (2) is a dipping method, a spraying method, a spin coating method, a coating method or a self-assembly method; The immersion time of the immersion method is 5 to 10 seconds; The spraying pressure of the spraying method is 0.1-0.3 MPa, the spraying distance is 10-20 cm, and the number of repetitions is 2-4 times.

6. The method for preparing the carbon fiber positive electrode material according to claim 5, characterized in that: The spin coating method has a rotation speed of 1500 to 2500 rpm and a time of 20 to 40 s; The coating thickness of the coating method is 2 to 4 μm; The number of assembly layers of the self-assembly method is ≥5.

7. The method for preparing a carbon fiber positive electrode material according to claim 6, characterized in that: The post-treatment in step (3) is drying and heat treatment performed sequentially; The drying temperature is 80-130° C. and the drying time is 10-120 min.

8. The method for preparing a carbon fiber positive electrode material according to claim 7, characterized in that: The heat treatment temperature is 150-250° C. and the time is 1-4 hours.

9. The carbon fiber positive electrode material prepared by the method for preparing the carbon fiber positive electrode material according to any one of claims 1 to 8.

10. Use of the carbon fiber positive electrode material according to claim 9 in a structure-energy storage integrated composite material.