NiCoC composite nanofiber material for lithium ion battery and preparation method thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a NiCoC composite nanofiber material for a lithium ion battery and a preparation method thereof, which comprises the following steps: dispersing graphene oxide and carbon nanotubes in a functional modification solvent in advance, adding a precursor solution into the composite solution after ultrasonic treatment, preparing a nanofiber membrane through electrospinning under a high-voltage electric field, immersing the nanofiber membrane containing a nickel precursor into a cobalt nitrate methanol solution, and heat-treating the composite nanofiber membrane to obtain the NiCoC composite nanofiber material. Through a three-layer nested modification process, the functional modification solvent is rich in polar functional groups and coordination sites on the surface, can efficiently disperse graphene oxide and carbon nanotubes, solves the industry problems that carbon nanomaterials are prone to agglomeration and have poor interface compatibility, makes graphene oxide and carbon nanotubes uniformly distributed and mutually overlapped in the nanofiber, and forms a continuous three-dimensional conductive network.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a NiCoC composite nanofiber material for lithium-ion batteries and its preparation method. Background Technology

[0002] With the rapid development of new energy technologies, lithium-ion batteries are widely used in portable electronic devices, electric vehicles and energy storage systems due to their advantages such as high energy density, long cycle life and good environmental adaptability. As the core component of lithium-ion batteries, the structural stability, electrochemical activity and conductivity of electrode materials directly determine the overall performance of the battery.

[0003] Currently, graphite is the main anode material for commercial lithium-ion batteries, but its theoretical specific capacity is low and it is prone to capacity decay during high-rate charge-discharge and long-cycle processes, making it difficult to meet the development needs of high-energy-density and high-power-density energy storage devices. Therefore, developing new anode materials with high specific capacity, excellent rate performance and good structural stability has become the focus of current research.

[0004] Transition metals and their compounds have attracted attention due to their high theoretical capacity, but they often suffer from problems such as severe volume expansion, structural pulverization, and insufficient conductivity during charge and discharge, resulting in poor cycle stability. Combining transition metals with carbon materials and utilizing the conductivity and buffering effect of carbon materials is an effective way to improve their electrochemical performance.

[0005] Metal-organic frameworks (MOFs) have advantages such as tunable structure, large specific surface area and uniform composition, and are considered ideal precursors for preparing metal / carbon composite materials. However, most existing MOF-derived materials exist in powder form, which has problems such as easy agglomeration of active materials during electrode preparation, insufficient interfacial contact and insufficient mechanical stability, thus limiting their application in practical electrochemical devices.

[0006] Electrospun nanofibers exhibit significant advantages in the field of electrode materials due to their continuous one-dimensional structure, high porosity, and good electron transport pathways. In-situ growth of MOFs on an electrospun nanofiber framework, followed by heat treatment to obtain a metal / carbon composite nanofiber structure, helps to achieve high dispersion of transition metals and improve structural stability. However, existing related preparation methods still suffer from problems such as complex processes, uneven component distribution, and insufficient material structural stability. Therefore, in response to the problems mentioned above, this invention proposes a NiCoC composite nanofiber material for lithium-ion batteries and its preparation method. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a NiCoC composite nanofiber material for lithium-ion batteries and its preparation method, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing NiCoC composite nanofiber materials for lithium-ion batteries includes the following steps:

[0010] S1. At room temperature, polyacrylonitrile and polyvinylpyrrolidone are dissolved in N,N-dimethylformamide and stirred thoroughly for 10-12 hours to obtain a clear solution. Then, nickel acetate is added to the clear solution and stirring is continued for 3-6 hours to form a precursor solution.

[0011] S2. Graphene oxide and carbon nanotubes are pre-dispersed in a functional modified solvent, and after ultrasonic treatment, they are added to the precursor solution and stirred to obtain a composite solution.

[0012] S3. Nanofiber membranes were prepared by electrospinning the composite solution under a high voltage electric field to obtain nickel-containing precursor nanofiber membranes.

[0013] S4. The nickel-containing precursor nanofiber membrane is immersed in cobalt nitrate methanol solution and reacted at 40-60℃ for 5-6 hours. After full permeation under heating conditions, 2-methylimidazole solution is added and allowed to stand to react, thus obtaining the composite nanofiber membrane.

[0014] S5. The composite nanofiber membrane is subjected to low-temperature air pre-oxidation treatment, high-temperature carbonization treatment under inert atmosphere and secondary heat treatment under air atmosphere in sequence to obtain NiCoC composite nanofiber material.

[0015] The functional modified solvent is prepared through the following steps:

[0016] S21. Under nitrogen protection, the pre-modified solution is refluxed with calcium hydride in an azeotropic manner for 2-2.5 hours, and then distilled under reduced pressure to obtain anhydrous modified solution.

[0017] S22. Add dopamine hydrochloride and nickel nitrate hexahydrate to the anhydrous modified solution, adjust the pH to 8.0-8.5 with tris(hydroxymethyl)aminomethane, and stir the reaction at 55-60℃ for 10-12 hours.

[0018] S23. After the reaction is complete, branched polyethyleneimine is added, and the reaction is continued at 45-50℃ for 4-5 hours to obtain the functional modified solvent.

[0019] Furthermore, the pre-modified solution in step S21 is prepared through the following steps:

[0020] S211. Under nitrogen protection at 0-5℃, paraformaldehyde and potassium hydroxide are added to N,N-dimethylformamide, the temperature is raised to 60-70℃, and the reaction is stirred for 4-6 hours. After the reaction is completed, the pH is neutralized to 6.5-7.0 with dilute hydrochloric acid, and hydroxymethylated DMF is obtained after purification.

[0021] S212. Dissolve hydroxymethylated DMF in anhydrous ethanol, add zinc acetate dihydrate ethanol solution dropwise while stirring, reflux at 50-55℃ for 2-3 hours, and after the reaction is completed, remove ethanol and byproduct acetic acid by rotary evaporation to obtain the modified intermediate.

[0022] S213. Dissolve the modified intermediate in diluent N,N-dimethylformamide, add polycondensation catalyst p-toluenesulfonic acid and dehydrating agent triethyl orthoformate, and stir the polymerization reaction at 80-90℃ under nitrogen protection for 8-12 hours. Remove the water generated during the reaction by azeotropic distillation. After the reaction is completed, a pre-modified solution is obtained.

[0023] Furthermore, in step S1, the mass ratio of polyacrylonitrile, polyvinylpyrrolidone, N,N-dimethylformamide to nickel acetate is 1:(0.2-0.6):(15-30):(0.3-0.9), and in step S2, the mass ratio of graphene oxide, carbon nanotubes, and functional modified solvent is 1:1:(400-800).

[0024] Furthermore, in step S3, the electrospinning propulsion rate is 0.5-2.0 mL·h. -1 The distance between the nozzle and the collector plate is 10-20cm, and the applied voltage is 10-20kV.

[0025] Furthermore, in step S4, the mass ratio of the nickel precursor nanofiber membrane, cobalt nitrate methanol solution, and 2-methylimidazole solution is 1:(30-50):(60-80), wherein the cobalt nitrate methanol solution is composed of cobalt nitrate and methanol in a mass ratio of 1:(15-25).

[0026] Furthermore, in step S5, the temperature of the low-temperature air pre-oxidation treatment is set to 200-300℃, the heating rate is 0.5-2℃ / min, and the holding time is 1.5-2h; the carbonization temperature of the high-temperature carbonization treatment is 600-800℃, and the holding time is 1-3h; the temperature of the secondary heat treatment is set to 300-400℃, and the holding time is 1-3h.

[0027] Furthermore, in step S21, the mass ratio of the pre-modified solution to calcium hydride is 1:(0.02-0.06), and in step S22, the mass ratio of the anhydrous modified solution, dopamine hydrochloride, nickel nitrate hexahydrate to the branched polyethyleneimine in step S23 is 1:(0.05-0.15):(0.03-0.1):(0.04-0.1).

[0028] Furthermore, in step S211, the mass ratio of N,N-dimethylformamide, paraformaldehyde, and potassium hydroxide is 1:(0.08-0.15):(0.02-0.06), and in step S212, the mass ratio of hydroxymethylated DMF, anhydrous ethanol, and zinc acetate dihydrate ethanol solution is 1:(6-10):(0.06-0.1), wherein the zinc acetate dihydrate ethanol solution is composed of a mixture of zinc acetate dihydrate and anhydrous ethanol in a mass ratio of 1:(10-15).

[0029] Furthermore, in step S213, the mass ratio of the modified intermediate, N,N-dimethylformamide, p-toluenesulfonic acid, and triethyl orthoformate is 1:(5-12):(0.01-0.04):(0.1-0.3).

[0030] Furthermore, a NiCoC composite nanofiber material for lithium-ion batteries is prepared according to the aforementioned preparation method.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention employs a three-layer nested modification process involving hydroxymethylation modification, coordination polycondensation, and dopamine / polyethyleneimine functionalization. This process enriches the surface of the functionalized modified solvent with polar functional groups and coordination sites, enabling efficient dispersion of graphene oxide and carbon nanotubes. This solves the industry problem of easy agglomeration and poor interfacial compatibility of carbon nanomaterials, allowing graphene oxide and carbon nanotubes to be uniformly distributed and interlocked in nanofibers, forming a continuous three-dimensional conductive network.

[0033] 2. This invention achieves highly uniform dispersion of Ni and Co bimetallic ions through functional modification of solvent coordination. Combined with in-situ MOF growth and gradient heat treatment, nitrogen-doped carbon nanofiber materials with uniformly loaded NiCo alloy nanoparticles are obtained. The one-dimensional fiber structure and three-dimensional conductive network can rapidly transport electrons and lithium ions. Nitrogen doping and defect structure further enhance electrochemical activity and interfacial compatibility, giving the material high specific capacity, excellent rate performance and outstanding long-cycle stability. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the preparation process of NiCoC composite nanofiber material in this invention;

[0035] Figure 2 This is a schematic diagram of the preparation process of the functional modified solvent in this invention;

[0036] Figure 3 This is a schematic diagram of the preparation process of the pre-modified solution in this invention;

[0037] Figure 4 The images show SEM images of the NiCoC composite nanofiber material at 10 μm (a) and 5 μm (b) in Example 1 of this invention.

[0038] Figure 5 The images show TEM images of the NiCoC composite nanofiber material in Example 1 of this invention at 200 nm (a) and 100 nm (b), respectively.

[0039] Figure 6 The images show the XRD patterns of the composite nanofiber materials in Example 1, Comparative Example 1, and Comparative Example 2 of this invention.

[0040] Figure 7 The curves showing the change in discharge specific capacity of the composite nanofiber materials with the number of cycles in Examples 1, 1 Comparative Examples, and 2 of this invention are shown.

[0041] Figure 8 The curves show the changes in the long-cycle discharge specific capacity and coulombic efficiency of the composite nanofiber materials in Examples 1, 1 Comparative Examples, and 2 of this invention as a function of the number of cycles. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0043] Please see Figures 1-8 The present invention provides a technical solution:

[0044] Example 1:

[0045] A method for preparing NiCoC composite nanofiber materials for lithium-ion batteries includes the following steps:

[0046] I. Preparation of pre-modified solution:

[0047] Under nitrogen protection at 0℃, 0.8g of paraformaldehyde and 0.2g of potassium hydroxide were added to 10g of N,N-dimethylformamide. The mixture was heated to 60℃ and stirred for 4 hours. The pH was neutralized to 6.5 with dilute hydrochloric acid, and hydroxymethylated DMF was obtained after purification.

[0048] S212. Dissolve 5g of hydroxymethylated DMF in 30g of anhydrous ethanol, and add 0.3g of zinc acetate dihydrate ethanol solution (composed of a 1:10 mixture of zinc acetate dihydrate and anhydrous ethanol) dropwise with stirring. Reflux at 50°C for 2h, and then remove ethanol and acetic acid by rotary evaporation at 50°C and 100rpm for 1h to obtain the modified intermediate.

[0049] S213. Dissolve 4g of the modified intermediate in 20g of N,N-dimethylformamide, add 0.04g of p-toluenesulfonic acid and 0.4g of triethyl orthoformate, and polymerize under nitrogen protection at 80℃ for 8h. Azeotropically remove water to obtain a pre-modified solution.

[0050] II. Preparation of functional modified solvents:

[0051] S21. 10g of pre-modified solution and 0.2g of calcium hydride are azeotropically refluxed under nitrogen for 2h, and then distilled under reduced pressure at -0.1MPa and 50℃ for 2h to obtain anhydrous modified solution.

[0052] S22. Add 0.4g dopamine hydrochloride and 0.24g nickel nitrate hexahydrate to 8g of anhydrous modified solution, adjust the pH to 8.0 with tris(hydroxymethyl)aminomethane, and stir the reaction at 55℃ for 10h.

[0053] S23. Add 0.32g of branched polyethyleneimine and continue stirring at 45℃ for 4h to obtain the functional modified solvent.

[0054] III. Preparation of NiCoC composite nanofiber materials:

[0055] S1. At room temperature, 10g of polyacrylonitrile and 2g of polyvinylpyrrolidone are dissolved in 150g of N,N-dimethylformamide and stirred for 10h until clear. Then, 3g of nickel acetate is added and stirring is continued for 3h to obtain the precursor solution.

[0056] S2. Disperse 0.5g of graphene oxide and 0.5g of carbon nanotubes in 200g of functional modified solvent, sonicate at 200W and 40kHz for 30min, add precursor solution and stir evenly to obtain composite solution.

[0057] S3. Electrospin the composite solution at a feed rate of 0.5 mL / h. -1 With a nozzle-current collector distance of 10cm and a voltage of 10kV, a nickel-containing precursor nanofiber membrane was obtained.

[0058] S4. Take 1g of precursor membrane and immerse it in 30g of cobalt nitrate methanol solution (composed of cobalt nitrate and methanol in a 1:15 ratio). React at 40℃ for 5h. Then add 60g of 2-methylimidazole solution and let it stand to react, thus obtaining the composite nanofiber membrane.

[0059] S5. The composite nanofiber membrane was pre-oxidized in air at 200℃ for 1.5h with a heating rate of 0.5℃ / min; carbonized in nitrogen atmosphere at 600℃ for 1h; and then subjected to secondary heat treatment in air at 300℃ for 1h to obtain NiCoC composite nanofiber material.

[0060] Example 2:

[0061] A method for preparing NiCoC composite nanofiber materials for lithium-ion batteries includes the following steps:

[0062] I. Preparation of pre-modified solution:

[0063] Under nitrogen protection at 3℃, 1.2g of paraformaldehyde and 0.4g of potassium hydroxide were added to 10g of N,N-dimethylformamide. The mixture was heated to 65℃ and stirred for 5h. The pH was neutralized to 6.8 with dilute hydrochloric acid, and hydroxymethylated DMF was obtained after purification.

[0064] S212. Dissolve 5g of hydroxymethylated DMF in 40g of anhydrous ethanol, and add 0.4g of zinc acetate dihydrate ethanol solution (composed of a 1:13 mixture of zinc acetate dihydrate and anhydrous ethanol) dropwise with stirring. Reflux at 53℃ for 2.5h, and then remove ethanol and acetic acid by rotary evaporation at 50℃ and 100rpm for 1h to obtain the modified intermediate.

[0065] S213. Dissolve 4g of the modified intermediate in 32g of N,N-dimethylformamide, add 0.12g of p-toluenesulfonic acid and 0.8g of triethyl orthoformate, and polymerize under nitrogen protection at 85℃ for 10h. Azeotropically remove water to obtain a pre-modified solution.

[0066] III. Preparation of Functional Modified Solvents:

[0067] S21. 10g of pre-modified solution and 0.4g of calcium hydride are azeotropically refluxed under nitrogen for 2.3h, and then distilled under reduced pressure at -0.1MPa and 50℃ for 2h to obtain anhydrous modified solution.

[0068] S22. Add 0.8g dopamine hydrochloride and 0.48g nickel nitrate hexahydrate to 8g of anhydrous modified solution, adjust the pH to 8.3 with tris(hydroxymethyl)aminomethane, and stir the reaction at 58℃ for 11h.

[0069] S23. Add 0.56g of branched polyethyleneimine and continue stirring at 48℃ for 4.5h to obtain the functional modified solvent.

[0070] III. Preparation of NiCoC composite nanofiber materials:

[0071] S1. At room temperature, 10g of polyacrylonitrile and 4g of polyvinylpyrrolidone were dissolved in 230g of N,N-dimethylformamide and stirred for 11h until clear. Then, 6g of nickel acetate was added and stirring was continued for 5h to obtain the precursor solution.

[0072] S2. Disperse 0.5g of graphene oxide and 0.5g of carbon nanotubes in 300g of functional modified solvent, sonicate at 200W and 40kHz for 30min, add precursor solution and stir evenly to obtain composite solution.

[0073] S3. Electrospin the composite solution at a feed rate of 1 mL·h. -1 With a nozzle-current collector distance of 15cm and a voltage of 15kV, a nickel-containing precursor nanofiber membrane was obtained.

[0074] S4. Take 1g of precursor membrane and immerse it in 40g of cobalt nitrate methanol solution (composed of cobalt nitrate and methanol in a 1:20 ratio). React at 50℃ for 5.5h. Then add 70g of 2-methylimidazole solution and let it stand to react, thus obtaining the composite nanofiber membrane.

[0075] S5. The composite nanofiber membrane was pre-oxidized in air at 250℃ for 1.8h with a heating rate of 1.5℃ / min; carbonized in nitrogen atmosphere at 700℃ for 2h; and then subjected to secondary heat treatment in air at 350℃ for 2h to obtain NiCoC composite nanofiber material.

[0076] Example 3:

[0077] A method for preparing NiCoC composite nanofiber materials for lithium-ion batteries includes the following steps:

[0078] I. Preparation of pre-modified solution:

[0079] Under nitrogen protection at 5℃, 1.5g of paraformaldehyde and 0.6g of potassium hydroxide were added to 10g of N,N-dimethylformamide. The mixture was heated to 70℃ and stirred for 6 hours. The pH was neutralized to 7.0 with dilute hydrochloric acid, and the hydroxymethylated DMF was obtained after purification.

[0080] S212. Dissolve 5g of hydroxymethylated DMF in 50g of anhydrous ethanol, and add 0.5g of zinc acetate dihydrate ethanol solution (composed of a 1:15 mixture of zinc acetate dihydrate and anhydrous ethanol) dropwise with stirring. Reflux at 55℃ for 3h, and then remove ethanol and acetic acid by rotary evaporation at 50℃ and 100rpm for 1h to obtain the modified intermediate.

[0081] S213. Dissolve 4g of the modified intermediate in 48g of N,N-dimethylformamide, add 0.16g of p-toluenesulfonic acid and 1.2g of triethyl orthoformate, and polymerize under nitrogen protection at 90℃ for 12h. Azeotropically remove water to obtain a pre-modified solution.

[0082] III. Preparation of Functional Modified Solvents:

[0083] S21. 10g of pre-modified solution and 0.6g of calcium hydride are azeotropically refluxed under nitrogen for 2.5h, and then distilled under reduced pressure at -0.1MPa and 50℃ for 2h to obtain anhydrous modified solution.

[0084] S22. Add 1.2g dopamine hydrochloride and 0.8g nickel nitrate hexahydrate to 8g of anhydrous modified solution, adjust the pH to 8.5 with tris(hydroxymethyl)aminomethane, and stir the reaction at 60℃ for 12h.

[0085] S23. Add 0.8g of branched polyethyleneimine and continue stirring at 50℃ for 5h to obtain the functional modified solvent.

[0086] III. Preparation of NiCoC composite nanofiber materials:

[0087] S1. At room temperature, 10g of polyacrylonitrile and 6g of polyvinylpyrrolidone were dissolved in 300g of N,N-dimethylformamide and stirred for 12h until clear. Then, 9g of nickel acetate was added and stirring was continued for 6h to obtain the precursor solution.

[0088] S2. Disperse 0.5g of graphene oxide and 0.5g of carbon nanotubes in 400g of functional modified solvent, sonicate at 200W and 40kHz for 30min, add precursor solution and stir evenly to obtain composite solution.

[0089] S3. Electrospin the composite solution at a feed rate of 2 mL·h. -1 With a nozzle-current collector distance of 20cm and a voltage of 20kV, a nickel-containing precursor nanofiber membrane was obtained.

[0090] S4. Take 1g of precursor membrane and immerse it in 50g of cobalt nitrate methanol solution (composed of cobalt nitrate and methanol in a 1:25 ratio). React at 60℃ for 6h. Then add 80g of 2-methylimidazole solution and let it stand to react, thus obtaining the composite nanofiber membrane.

[0091] S5. The composite nanofiber membrane is pre-oxidized in air at 300℃ for 2h with a heating rate of 2℃ / min; carbonized in nitrogen atmosphere at 800℃ for 3h; and then subjected to secondary heat treatment in air at 400℃ for 3h to obtain NiCoC composite nanofiber material.

[0092] Comparative Example 1:

[0093] Compared to Example 1, Comparative Example 1 uses an equal mass of DMF solution instead of a functional modification solvent, removes carbon nanotubes, and adds only graphene oxide. The remaining steps are exactly the same as in Example 1.

[0094] Comparative Example 2:

[0095] Compared to Example 1, Comparative Example 2 uses an equal mass of DMF solution instead of a functional modification solvent, removes graphene oxide, and adds only carbon nanotubes. The remaining steps are exactly the same as in Example 1.

[0096] Comparative Example 3:

[0097] Comparative Example 3 differs from Example 1 in that the functional modification solvent is replaced with an equal mass of DMF solution, while the remaining steps are exactly the same as in Example 1.

[0098] Using the NiCoC composite nanofiber materials prepared in Examples 1-3 and Comparative Examples 1-3 as the active materials for the negative electrode, the negative electrode material, conductive carbon black, and polyvinylidene fluoride binder were mixed in a mass ratio of 8:1:1 and thoroughly ground in N-methylpyrrolidone solvent to form a uniform slurry. The resulting slurry was then coated onto an area of ​​1.539 cm². 2 The negative electrode is a copper foil coated with carbon; the positive electrode is a lithium metal sheet; the electrolyte is 1.0M LiPF6 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1; the separator is a porous polypropylene separator; the lithium-ion battery is assembled in a glove box under the protection of high-purity argon gas, wherein the oxygen and moisture content are not higher than 0.1ppm.

[0099] Performance testing:

[0100] I. Constant Current Charge-Discharge Test (Specific Capacity, Initial Coulombic Efficiency, Cycle Stability):

[0101] Between 0.01 and 3.0 V (vs. Li / Li) + Tests were conducted within the specified voltage range, with the first charge / discharge cycle at 0.1Ag. -1 First discharge specific capacity (mAhg) tested at current density -1 ), first charge specific capacity (mAhg) -1 ), first-time Coulomb efficiency (%).

[0102] Long-term cycling performance: at 0.5Ag -1 The discharge specific capacity (mAhg) was recorded for each of the 200 continuous cycles at the current density. -1 ) and capacity retention rate (%).

[0103] II. Ratio Performance Test:

[0104] Sequentially at 0.1Ag -1 0.2Ag -1 0.5Ag -1 1.0Ag -1 2.0Ag -1Charge and discharge were performed at various current densities, with each current density cycling for 5 consecutive cycles. The discharge specific capacity at the 5th cycle was taken as the stable capacity (mAh / g) at that rate. -1 After the test is completed, it returns to 0.1Ag. -1 The capacity recovery rate (%) was tested, and the specific test results are shown in Tables 1 and 2 below:

[0105] Table 1: Constant Current Charge-Discharge Test Table

[0106]

[0107] Table 2: Ratio Performance Test Table

[0108]

[0109] As can be seen from the data in Tables 1 and 2, the NiCoC composite nanofiber materials prepared in Examples 1-3 exhibit superior rate discharge specific capacity and capacity recovery rate at different current densities, with overall electrochemical performance significantly better than the comparative examples. Example 2 shows the best rate performance and capacity recovery rate, slightly higher than Examples 1 and 3, indicating that the functional modified solvent has the best dispersion effect on graphene oxide and carbon nanotubes under this ratio, resulting in the strongest electron transport and lithium-ion diffusion capabilities. Comparative Examples 1 and 2, due to the absence of a functional modified solvent and the use of graphene oxide or carbon nanotubes alone, are prone to agglomeration of individual graphene oxide or carbon nanotubes, leading to poor conductive network integrity and consequently lower discharge specific capacity at various current densities. With a significant decrease in capacity recovery, graphene oxide or carbon nanotubes alone cannot form a synergistic conductivity enhancement effect. The rate performance and capacity recovery ability are also significantly inferior to those of the embodiments of the present invention. Although the electrochemical performance of Comparative Example 3 is better than that of Comparative Example 1 and Comparative Example 2 which use only a single carbon material, it is still significantly lower than that of Examples 1-3. This shows that even if graphene oxide and carbon nanotubes are introduced at the same time, without the use of functional modified solvents for pre-dispersion treatment, carbon nanomaterials are still difficult to be uniformly dispersed in nanofibers and form a continuous three-dimensional conductive network, thereby limiting the specific capacity, rate performance and cycle stability of the material. This further proves that the three-layer nested functional modified solvent and GO / CNTs complex system can significantly improve the rate performance and structural stability of the material.

[0110] Figure 4 The image shows a surface SEM image of the NiCoC composite nanofiber material in Example 1 of this invention. The NiCoC composite nanofiber material exhibits a continuous nanofiber network structure. In local areas, a layered structure can be observed distributed on the fiber surface or at fiber intersections, corresponding to the introduced graphene oxide component. Graphene oxide and carbon nanotubes are synergistically distributed in the nanofiber framework to form a multi-level composite structure.

[0111] Figure 5The image shows a TEM image of the NiCoC composite nanofiber material in Example 1 of this invention. The image reveals that the material exhibits a continuous fibrous structure. Various morphological components exist within and on the surface of the fibers. In some areas, lamellar structures are visible distributed on the fiber surface or in interwoven areas, corresponding to the introduced graphene oxide component. Simultaneously, linear or tubular structures, corresponding to carbon nanotube components, can be observed on the fiber surface and adjacent areas. High-magnification images show that carbon nanotubes and lamellar structures are distributed around the nanofiber framework. Different carbon-based components contact each other and form a composite structure with the nanofibers, indicating that graphene oxide and carbon nanotubes are synergistically introduced into the material.

[0112] Figure 6 The figures show the XRD patterns of the composite nanofiber materials in Examples 1, 1, and 2 of this invention. As can be seen from the figures, different samples exhibit broad diffraction peaks in the 2θ range of approximately 20°-30°, indicating the presence of an amorphous or low-crystallinity carbon phase structure in the material. Compared with the samples in Comparative Example 2 (which introduced carbon nanotubes) and Comparative Example 1 (which introduced graphene oxide), the diffraction characteristics of the sample in Example 1 (which simultaneously introduced graphene oxide and carbon nanotubes) changed in the corresponding angular range, reflecting the influence of different carbon-based component combinations on the material structure. In addition, multiple sets of diffraction peaks can be observed in the 2θ range of approximately 30°-70°, corresponding to the diffraction characteristics of the metal-related phase in the composite material, indicating that the metal component exists in the composite nanofiber material in the form of a crystalline phase.

[0113] Figure 7 The curves show the discharge specific capacity of the composite nanofiber materials in Examples 1, Comparative Examples 1 and 2 of this invention as a function of the number of cycles under the same test conditions. Different samples all showed high discharge specific capacity in the initial cycling stage. Subsequently, as the number of cycles increased, the specific capacity gradually decreased and tended to be relatively stable. In the middle and later cycling stages, the change in discharge specific capacity of each sample decreased, showing relatively stable cycling characteristics. Compared with the samples in Comparative Examples 1 and 2, the NiCoC composite nanofiber material in Example 1, which simultaneously introduced graphene oxide and carbon nanotubes, maintained a high discharge specific capacity level throughout the cycling process and maintained stable output in the long cycling stage, showing the influence of different combinations of conductive carbon components on electrochemical performance.

[0114] Figure 8The graph shows the curves of the long-cycle discharge specific capacity and coulombic efficiency of the composite nanofiber materials in Examples 1, Comparative Examples 1 and 2 of this invention under the same test conditions, as well as the curves of discharge specific capacity variation with the number of cycles. From the discharge specific capacity variation curve at the bottom of the graph, it can be seen that the discharge specific capacity of each sample fluctuates to some extent in the initial cycling stage. Subsequently, as the number of cycles increases, the discharge specific capacity gradually stabilizes. During the long cycling process, different samples can maintain a relatively stable capacity output, indicating that the prepared materials have good cycling stability. Comparing different samples, it can be found that the NiCoC composite nanofiber material in Example 1, which simultaneously introduces graphene oxide and carbon nanotubes, maintains a high discharge specific capacity level during long cycling, with a small capacity change amplitude, reflecting the influence of the composite conductive carbon component on the electrochemical behavior of the material. From the coulombic efficiency variation curve at the top of the graph, it can be observed that the coulombic efficiency of each sample rapidly increases and stabilizes at a high level after the initial cycling, and then remains relatively stable during long cycling, indicating that the electrochemical reaction process has good reversibility.

[0115] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing NiCoC composite nanofiber materials for lithium-ion batteries, characterized in that, Includes the following steps: S1. Under room temperature conditions, polyacrylonitrile and polyvinylpyrrolidone are dissolved in N,N-dimethylformamide and stirred thoroughly for 10-12 hours to obtain a clear solution. Then, nickel acetate is added to the clear solution and stirring is continued for 3-6 hours to form a precursor solution. S2. Graphene oxide and carbon nanotubes are pre-dispersed in a functional modified solvent, and after ultrasonic treatment, they are added to the precursor solution and stirred to obtain a composite solution. S3. Nanofiber membranes were prepared by electrospinning the composite solution under a high voltage electric field to obtain nickel-containing precursor nanofiber membranes. S4. The nickel-containing precursor nanofiber membrane is immersed in cobalt nitrate methanol solution and reacted at 40-60℃ for 5-6 hours. After full permeation under heating conditions, 2-methylimidazole solution is added and allowed to stand to react, thus obtaining the composite nanofiber membrane. S5. The composite nanofiber membrane is subjected to low-temperature air pre-oxidation treatment, high-temperature carbonization treatment under inert atmosphere and secondary heat treatment under air atmosphere in sequence to obtain NiCoC composite nanofiber material. The functional modified solvent is prepared through the following steps: S21. Under nitrogen protection, the pre-modified solution is refluxed with calcium hydride in an azeotropic manner for 2-2.5 hours, and then distilled under reduced pressure to obtain anhydrous modified solution. S22. Add dopamine hydrochloride and nickel nitrate hexahydrate to the anhydrous modified solution, adjust the pH to 8.0-8.5 with tris(hydroxymethyl)aminomethane, and stir the reaction at 55-60℃ for 10-12 hours. S23. After the reaction is complete, branched polyethyleneimine is added, and the reaction is continued at 45-50℃ for 4-5 hours to obtain the functional modified solvent. The pre-modified solution in step S21 is prepared through the following steps: S211. Under nitrogen protection at 0-5℃, paraformaldehyde and potassium hydroxide are added to N,N-dimethylformamide, the temperature is raised to 60-70℃, and the reaction is stirred for 4-6 hours. After the reaction is completed, the pH is neutralized to 6.5-7.0 with dilute hydrochloric acid, and hydroxymethylated DMF is obtained after purification. S212. Dissolve hydroxymethylated DMF in anhydrous ethanol, add zinc acetate dihydrate ethanol solution dropwise while stirring, reflux at 50-55℃ for 2-3 hours, and after the reaction is completed, remove ethanol and byproduct acetic acid by rotary evaporation to obtain the modified intermediate. S213. Dissolve the modified intermediate in diluent N,N-dimethylformamide, add polycondensation catalyst p-toluenesulfonic acid and dehydrating agent triethyl orthoformate, and stir the polymerization reaction at 80-90℃ under nitrogen protection for 8-12 hours. Remove the water generated during the reaction by azeotropic distillation. After the reaction is completed, a pre-modified solution is obtained. In step S211, the mass ratio of N,N-dimethylformamide, paraformaldehyde, and potassium hydroxide is 1:(0.08-0.15):(0.02-0.06). In step S212, the mass ratio of hydroxymethylated DMF, anhydrous ethanol, and zinc acetate dihydrate ethanol solution is 1:(6-10):(0.06-0.1), wherein the zinc acetate dihydrate ethanol solution is composed of zinc acetate dihydrate and anhydrous ethanol in a mass ratio of 1:(10-15). In step S213, the mass ratio of the modified intermediate, N,N-dimethylformamide, p-toluenesulfonic acid, and triethyl orthoformate is 1:(5-12):(0.01-0.04):(0.1-0.3).

2. The method for preparing NiCoC composite nanofiber material for lithium-ion batteries according to claim 1, characterized in that, In step S1, the mass ratio of polyacrylonitrile, polyvinylpyrrolidone, N,N-dimethylformamide and nickel acetate is 1:(0.2-0.6):(15-30):(0.3-0.9), and in step S2, the mass ratio of graphene oxide, carbon nanotubes and functional modified solvent is 1:1:(400-800).

3. The method for preparing NiCoC composite nanofiber material for lithium-ion batteries according to claim 1, characterized in that, In step S3, the electrospinning feed rate is 0.5-2.0 mL·h. -1 The distance between the nozzle and the collector plate is 10-20cm, and the applied voltage is 10-20kV.

4. The method for preparing NiCoC composite nanofiber material for lithium-ion batteries according to claim 1, characterized in that, In step S4, the mass ratio of the nickel precursor nanofiber membrane, cobalt nitrate methanol solution, and 2-methylimidazole solution is 1:(30-50):(60-80), wherein the cobalt nitrate methanol solution is composed of cobalt nitrate and methanol in a mass ratio of 1:(15-25).

5. The method for preparing NiCoC composite nanofiber material for lithium-ion batteries according to claim 1, characterized in that, In step S5, the temperature of the low-temperature air pre-oxidation treatment is set to 200-300℃, the heating rate is 0.5-2℃ / min, and the holding time is 1.5-2h; the carbonization temperature of the high-temperature carbonization treatment is 600-800℃, and the holding time is 1-3h; the temperature of the secondary heat treatment is set to 300-400℃, and the holding time is 1-3h.

6. The method for preparing NiCoC composite nanofiber material for lithium-ion batteries according to claim 1, characterized in that, In step S21, the mass ratio of the pre-modified solution to calcium hydride is 1:(0.02-0.06), and in step S22, the mass ratio of the anhydrous modified solution, dopamine hydrochloride, nickel nitrate hexahydrate to the branched polyethyleneimine in step S23 is 1:(0.05-0.15):(0.03-0.1):(0.04-0.1).

7. A NiCoC composite nanofiber material for lithium-ion batteries, characterized in that, It is prepared according to the preparation method according to any one of claims 1-6 above.

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