A CoNi-LDH@Co(OH)2@CNFs composite electrode material, its preparation method and application

Abstract

The application discloses a CoNi-LDH@Co(OH)2@CNFs composite electrode material and a preparation method and application thereof, the material has a three-dimensional hierarchical network structure which is interwoven with each other, a carbon nanofiber (CNF) is used as a core, Co(OH)2 nanosheets are used as an intermediate layer, and CoNi-LDH nanoflowers are used as an outer layer; the preparation method comprises the following steps: firstly, performing mixed acid activation treatment on the CNFs under a constant-temperature oil bath, and then adopting a two-step solvothermal method to sequentially grow the intermediate layer Co(OH)2 nanosheets and the outer layer CoNi-LDH nanoflowers in situ on the surface of the CNFs. The CoNi-LDH@Co(OH)2@CNFs composite electrode material can fully exert the synergistic effect between nickel / cobalt hydroxides, has excellent rate performance and cycle stability, can be used as a positive electrode material of a supercapacitor, has good practical application prospect and popularization value, and provides a new idea for the research and development of high-performance electrode materials.

Description

Technical Field

[0001] This invention relates to an electrode material, and more particularly to a CoNi-LDH@Co(OH)2@CNFs composite electrode material, its preparation method, and its application. Background Technology

[0002] Supercapacitors have become one of the most promising energy storage devices due to their remarkable characteristics such as fast charging capability, high power density, and long-term cycle stability. Among them, transition metal cathode materials have attracted widespread attention due to their high specific capacitance.

[0003] Multi-element transition metal matrix composites typically possess advantages such as high electrochemical activity, high energy density, and low cost, making them stand out among numerous electrode materials. For example, nickel-cobalt based hydroxides have high theoretical specific capacitance; nickel-cobalt double hydroxides, with their bimetallic synergistic effect, ability to effectively regulate layered structure, and high redox activity, are considered ideal battery materials. Nevertheless, when these materials are used alone as electrode materials, they suffer from low conductivity, poor dispersibility, and problems such as severe self-aggregation, deformation during charge and discharge, and volume expansion, making it difficult to effectively realize their practical application value. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a CoNi-LDH@Co(OH)2@CNFs composite electrode material with good electrochemical performance and cycle stability, as well as its preparation method and application.

[0005] Technical solution: The CoNi-LDH@Co(OH)2@CNFs composite electrode material uses carbon nanofibers (CNFs) as a conductive substrate, modifies Co(OH)2 nanosheets as an intermediate layer, and grows CoNi-LDH nanoflowers on the surface of the intermediate layer as the outermost layer, forming a hierarchical network nanostructure with carbon nanofibers as the core.

[0006] The CoNi-LDH@Co(OH)2@CNFs composite electrode material uses CNFs as a highly conductive substrate. Co(OH)2 nanosheets and CoNi-LDH nanoflowers are sequentially assembled on the CNFs surface to form an interwoven three-dimensional hierarchical structure. Specifically, the Co(OH)2 nanosheets are grown in situ on the α-CNFs surface and then surface-modified to optimize the material's interfacial properties. The CoNi-LDH nanoflowers are distributed in an interwoven cluster pattern, serving as the main active component to enhance the specific capacity of the composite material. Simultaneously, the CoNi-LDH nanoflowers on the outer layer of the hierarchical structure exhibit a vertically ordered arrangement, forming a porous open network that provides ample active sites for redox reactions, effectively improving the electrochemical reaction efficiency of the electrode material.

[0007] Preferably, the diameter of the carbon nanofibers is 130~170 nm, and the particle size (i.e., lateral size) of the CoNi-LDH nanoflowers is 400~500 nm.

[0008] The preparation method of the CoNi-LDH@Co(OH)2@CNFs composite electrode material includes the following steps:

[0009] (1) Acid activation treatment: CNFs are placed in a mixed acid solution and reacted with potassium permanganate under stirring conditions at a constant temperature to obtain a-CNFs;

[0010] (2) Co(OH)2 nanosheets were modified on the surface of a-CNFs by solvothermal reaction to obtain Co(OH)2@CNFs composite material;

[0011] (3) CoNi-LDH nanoflowers were grown on the surface of Co(OH)2@CNFs by solvothermal reaction to obtain CoNi-LDH@Co(OH)2@CNFs composite electrode material.

[0012] The preparation method involves sequentially growing Co(OH)₂ nanosheets and CoNi-LDH nanoflowers on the surface of α-CNFs. Acid activation treatment increases the active groups on the CNFs surface, providing effective support for subsequent nanomaterial assembly and improving the conductivity and cycling stability of nickel / cobalt hydroxide. The introduction of Co(OH)₂ nanosheets not only regulates the surface electronic structure of CNFs but also facilitates the orderly assembly and dispersion of CoNi-LDH (to some extent suppressing its aggregation tendency), forming CoNi-LDH nanoflowers with high specific surface area.

[0013] Preferably, in step (1), the acid activation treatment method is as follows: carbon nanofibers are added to a mixed acid solution containing concentrated hydrochloric acid and concentrated sulfuric acid, ultrasonically dispersed to form a suspension, and placed in an oil bath; under stirring conditions, potassium permanganate crystals are dissolved in the suspension for a constant temperature reaction; after the reaction is completed, deionized water is added and stirring is continued; hydrogen peroxide solution is added dropwise until no bubbles are generated, and then the product is centrifuged, washed and dried.

[0014] The preferred volume ratio of deionized water, concentrated sulfuric acid, and concentrated nitric acid is 98~102:8~12:8~12, with the most preferred ratio being 10:1:1; the mass ratio of potassium permanganate to α-CNFs is 2.99~3.01:0.49~0.51, with the most preferred ratio being 6:1; the oil bath temperature is 34.2~35.8℃, and the time is 3 h, with the most preferred temperature being 35℃ and 3 h; after adding deionized water, stirring is continued at 34.2~35.8℃, with the most preferred temperature being 3 h.

[0015] Preferably, in step (2), the method for modifying Co(OH)2 nanosheets is as follows: cobalt nitrate hexahydrate is dissolved in a mixed solution of DMF and methanol, a-CNFs are added, the mixture is dissolved by ultrasonication and then subjected to a solvothermal reaction, and the product is centrifuged, washed and dried.

[0016] Preferably, the volume ratio of DMF to methanol in the mixed solution is 3~7:3~7, most preferably 1:1; the mass ratio of cobalt nitrate hexahydrate to α-CNFs powder is 0.24~0.26:0.04~0.06, most preferably 5:1; the solvothermal reaction temperature is 119.2~120.8℃, and the time is 3.92~4.08 h, most preferably 120℃ and 4 h.

[0017] Preferably, in step (3), the method for growing CoNi-LDH nanoflowers is as follows: under ultrasonic conditions, Co(OH)2@CNFs powder is uniformly dispersed in a methanol aqueous solution; then cobalt nitrate hexahydrate, nickel nitrate hexahydrate and activator are added in sequence, and ultrasonically assisted to dissolve to a suspension state and stir; the above solution is placed in an oven for solvothermal reaction, and after the reaction is completed, the supernatant is removed, and the mixture is alternately centrifuged, washed and dried.

[0018] Preferably, the mass ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and Co(OH)2@CNFs powder is 5~10:5~10:1, most preferably 5:5:1; the activator is hexadecyltrimethylammonium bromide; the solvothermal reaction temperature is 179.2~180.8℃, and the time is 23.92~24.08 h, most preferably 180℃ and 24 h.

[0019] The present invention also provides the application of the CoNi-LDH@Co(OH)2@CNFs composite electrode material in the preparation of supercapacitors.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0021] 1. The multiphase hierarchical structure of the CoNi-LDH@Co(OH)2@CNFs composite electrode material can give full play to the synergistic effect between nickel / cobalt hydroxide, effectively increase the specific surface area of ​​the composite material, reduce the ion / electron transport resistance in the electrochemical reaction process, promote the diffusion or transfer of ions / electrons in the electrolyte, and has excellent rate performance and cycle stability.

[0022] 2. The composite electrode material can be used as the positive electrode material of supercapacitors. The hybrid supercapacitor assembled with activated carbon (AC) not only has high energy density and power density, but also exhibits excellent cycle stability. It has good practical application prospects and promotion value, and provides new ideas for the research and development of high-performance electrode materials.

[0023] 3. The preparation method of the composite electrode material optimizes the nickel-cobalt feeding ratio and improves the electrochemical performance of the composite electrode material. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the synthesis route of the CoNi-LDH@Co(OH)2@CNFs composite electrode material of the present invention;

[0025] Figure 2 Scanning electron microscope image of α-CNFs;

[0026] Figure 3 Here is a scanning electron microscope image of Co(OH)2@CNFs;

[0027] Figure 4 The CV curves of Co(OH)2@CNFs in Comparative Example 1 at different rates are shown.

[0028] Figure 5 The GCD curves of Co(OH)2@CNFs in Comparative Example 1 under different current densities are shown.

[0029] Figure 6 This is a scanning electron microscope image of CoNi-LDH@Co(OH)2@CNFs from Example 1;

[0030] Figure 7 The X-ray photoelectron spectrum of CoNi-LDH@Co(OH)2@CNFs in Example 1 is shown below.

[0031] Figure 8 Here is a high-resolution transmission electron microscope image of CoNi-LDH@Co(OH)2@CNFs from Example 1;

[0032] Figure 9 This is the EDS mapping diagram of CoNi-LDH@Co(OH)2@CNFs in Example 1;

[0033] Figure 10 The CV curves of CoNi-LDH@Co(OH)2@CNFs in Example 1 at different rates are shown.

[0034] Figure 11 The GCD curves of CoNi-LDH@Co(OH)2@CNFs in Example 1 under different current densities are shown.

[0035] Figure 12 The CV curves of the hybrid supercapacitor assembled with CoNi-LDH@Co(OH)2@CNFs and AC in Example 1 are shown at different scan rates.

[0036] Figure 13The GCD curves of the hybrid supercapacitor assembled with CoNi-LDH@Co(OH)2@CNFs and AC in Example 1 are shown at different current densities.

[0037] Figure 14 In Example 1, CoNi-LDH@Co(OH)2@CNFs were assembled with AC to form a hybrid supercapacitor at a current density of 10 A g. -1 The charge-discharge curve after 5000 cycles;

[0038] Figure 15 The image shows the illuminated state of a button cell assembled from CoNi-LDH@Co(OH)2@CNFs and AC in Example 1.

[0039] Figure 16 The image shows a scanning electron microscope (SEM) image of CoNi-LDH@CNFs from Comparative Example 2.

[0040] Figure 17 XRD spectra of CoNi-LDH@Co(OH)2@CNFs, Co(OH)2@CNFs, and CoNi-LDH@CNFs;

[0041] Figure 18 The CV curves of CoNi-LDH@CNFs at different scan rates are shown in Comparative Example 2.

[0042] Figure 19 The GCD curves of CoNi-LDH@CNFs under different current densities are shown in Comparative Example 2.

[0043] Figure 20 For Co(OH)2@CNFs, CoNi-LDH@Co(OH)2@CNFs, and CoNi-LDH@CNFs, at a scan rate of 5 mV / s -1 The CV curve below;

[0044] Figure 21 Co(OH)2@CNFs, CoNi-LDH@Co(OH)2@CNFs, and CoNi-LDH@CNFs in 1 A g -1 The GCD curve below;

[0045] Figure 22 The CV curves of CoNi-LDH@Co(OH)2@CNFs-2 at different rates are shown in Example 2.

[0046] Figure 23 The GCD curves of CoNi-LDH@Co(OH)2@CNFs-2 under different current densities are shown in Example 2.

[0047] Figure 24 The CV curves of CoNi-LDH@Co(OH)2@CNFs-3 at different rates are shown in Example 3.

[0048] Figure 25 The GCD curves of CoNi-LDH@Co(OH)2@CNFs-3 under different current densities are shown in Example 3.

[0049] Figure 26 The CoNi-LDH@Co(OH)2@CNFs in Examples 1, 2, and 3 were scanned at a rate of 5 mV / s. -1 The CV curve below;

[0050] Figure 27 The CoNi-LDH@Co(OH)2@CNFs in Examples 1, 2, and 3 at 1 A g -1 The GCD curve below. Detailed Implementation

[0051] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0052] Example 1

[0053] This embodiment provides a CoNi-LDH@Co(OH)2@CNFs composite electrode material with a hierarchical network structure. The synthesis route is as follows: Figure 1 The specific preparation method is as follows:

[0054] Step (1): Add 0.5 g CNFs to 20 mL of a mixed solution containing concentrated sulfuric acid and concentrated hydrochloric acid (V 浓硫酸 :V 浓盐酸 The product was ultrasonically dispersed in a 1:1 ratio to form a suspension, which was then placed in an oil bath. While stirring, 3 g of potassium permanganate crystals were slowly added to the suspension, and the mixture was reacted at 35°C for 3 h. Then, 100 mL of deionized water was added, and stirring continued for another 3 h. The resulting solution was purple; hydrogen peroxide solution was added dropwise until no more bubbles were produced. Finally, the product was washed alternately with deionized water and ethanol by centrifugation until the supernatant was colorless. It was then dried in a 60°C oven for 6 h to obtain a black α-CNFs powder. The scanning electron microscope image is shown below. Figure 2 As shown;

[0055] Step (2): Dissolve 0.25 g of cobalt nitrate hexahydrate in 10 mL of a mixed solution containing DMF and methanol (V DMF :V 甲醇=1:1), ultrasonically dissolved to a clear pink solution; then 0.05 g α-CNFs powder was added, ultrasonically dissolved to a suspension, and stirred at room temperature for 30 min. Finally, it was transferred to a 100 mL polytetrafluoroethylene reactor and solvothermal reacted in a 120℃ oven for 4 h. After alternating centrifugation and washing with deionized water and ethanol until the supernatant was colorless and clear, it was dried in a 60℃ oven for 6 h to obtain Co(OH)2@CNFs black powder. Scanning electron microscopy image as shown below. Figure 3 As shown;

[0056] Step (3): In 40 mL of methanol-water mixture (V 甲醇 :V 水 In a 3:1 mixture, 0.25 g of cobalt nitrate hexahydrate, 0.25 g of nickel nitrate hexahydrate, and 0.17 g of activator cetyltrimethylammonium bromide were added sequentially. Then, 0.05 g of pre-prepared Co(OH)₂@CNFs powder was weighed and dissolved into a suspension using ultrasonic assistance. The suspension was stirred at room temperature for 30 min. After uniform dispersion, the mixture was transferred to a 100 mL polytetrafluoroethylene reactor and subjected to a solvothermal reaction at 180 °C for 24 h. After the reaction, the product was centrifuged several times alternately with ethanol and deionized water until the supernatant was colorless. Finally, the product was dried in a 60 °C oven for 6 h to obtain CoNi-LDH@Co(OH)₂@CNFs-1 hazy blue powder.

[0057] The prepared CoNi-LDH@Co(OH)2@CNFs-1 electrode material was scanned and observed, such as... Figure 6 As shown. Elemental valence state analysis of the composite material was performed using XPS technology, such as... Figure 7 As shown. The composition of the composite material was determined by high-resolution TEM analysis, as follows. Figure 8 As shown, the elemental distribution and composition of the composite material were determined through EDS mapping, such as... Figure 9 As shown.

[0058] Electrochemical testing: Electrochemical performance testing was conducted using a CHI660E electrochemical workstation. The electrolyte solution was 2 mkOH solution. Cyclic voltammetry (CV) was performed within the range of 0–0.6 V, with a scan rate range of 5–50 mV s. -1 The test results are shown below. Figure 10 The constant current charge-discharge test (GCD) has a test voltage range of 0~0.5V and a current density range of 1~20 A g. -1 The test results are shown below. Figure 11 The pair of redox peaks in the CV curve confirms that the prepared material is a pseudocapacitive material. Furthermore, the area under the curve can measure the specific capacitance, which can also be determined by the discharge time of the GCD curve according to formula C. s=IΔt / mΔV is calculated, where ΔV is the voltage window, I is the current, m is the mass, and Δt is the discharge time.

[0059] CoNi-LDH@Co(OH)2@CNFs-1 was assembled with AC to form a hybrid supercapacitor, and CV testing was performed. The test range was 0~1.6 V, and the scan rates were 5, 10, 20, 30, 50, 80, and 100 mV s. -1 The test results are shown below. Figure 12 GCD tests (two-electrode system) were performed on CoNi-LDH@Co(OH)2@CNFs-1. The test voltage window was 0~1.6 V, and the current density was 1, 2, 5, 10, and 20 A g. -1 The test results are shown below. Figure 13 At a current density of 10 A g -1 The composite material underwent 5000 charge-discharge cycles. The test results are shown below. Figure 14 Cyclic charging and discharging is an important indicator of the stability of a two-electrode system, which affects the performance of the assembled device or finished product. Higher cyclic stability indicates less internal loss during each charge and discharge cycle and a greater number of uses.

[0060] Battery Assembly: CoNi-LDH@Co(OH)2@CNFs-1 was assembled with AC to form a button cell, and further practical applications were implemented. A light board composed of 32 LEDs was used for the button cell lighting experiment. The light board operated at a power of over 2.5V. A schematic diagram showing the LEDs lighting up and off is shown below. Figure 15 This indicates that the prepared material has the potential for practical applications, such as assembling with AC to form button batteries.

[0061] Example 2

[0062] This embodiment provides a CoNi-LDH@Co(OH)2@CNFs composite electrode material with a hierarchical network structure. The difference from Example 1 lies in the nickel-cobalt feeding ratio in step (3) of the preparation method. The preparation method is as follows:

[0063] Step (1): Same as step (1) in Example 1;

[0064] Step (2): Same as step (2) in Example 1;

[0065] Step (3): In 40 mL of methanol-water mixture (V 甲醇 :V 水Add 0.5 g of cobalt nitrate hexahydrate, 0.25 g of nickel nitrate hexahydrate, and 0.17 g of activator cetyltrimethylammonium bromide sequentially to a mixture of 3:1. Then weigh 0.05 g of the pre-prepared Co(OH)2@CNFs powder, dissolve it into a suspension with ultrasonic assistance, and stir at room temperature for 30 min. The remaining operations are the same as step (3) in Example 1. CoNi-LDH@Co(OH)2@CNFs-2 hazy blue powder is obtained.

[0066] Electrochemical testing: The three-electrode testing procedure is the same as in Example 1. The CV curve is shown below. Figure 22 GCD curve as Figure 23 .

[0067] Example 3

[0068] This embodiment provides a CoNi-LDH@Co(OH)2@CNFs composite electrode material with a hierarchical network structure. The difference from Example 1 lies in the nickel-cobalt feeding ratio in step (3) of the preparation method. The preparation method is as follows:

[0069] Step (1): Same as step (1) in Example 1;

[0070] Step (2): Same as step (2) in Example 1;

[0071] Step (3): In 40 mL of methanol-water mixture (V 甲醇 :V 水 Add 0.25 g of cobalt nitrate hexahydrate, 0.5 g of nickel nitrate hexahydrate, and 0.17 g of activator cetyltrimethylammonium bromide sequentially to a mixture of 3:1. Then weigh 0.05 g of pre-prepared Co(OH)2@CNFs powder, dissolve it into a suspension with ultrasonic assistance, and stir at room temperature for 30 min. The remaining operations are the same as step (3) in Example 1. CoNi-LDH@Co(OH)2@CNFs-3 hazy blue powder is obtained.

[0072] Electrochemical testing: The three-electrode testing procedure is the same as in Example 1. The CV curve is shown below. Figure 24 GCD curve as Figure 25 .

[0073] Comparison of CV curves and GCD curves in Examples 1-3 Figure 26 , 27 As shown, the electrochemical performance of the obtained material is optimal under the nickel-cobalt feed ratio of Example 1.

[0074] Comparative Example 1

[0075] This comparative example provides a Co(OH)2@CNFs electrode material, and the preparation method is as follows:

[0076] (1) Add 0.5 g CNFs to 20 mL of a mixed solution containing concentrated sulfuric acid and concentrated hydrochloric acid (V 浓硫酸 :V 浓盐酸 =1:1), sonicate to form a suspension, and place in an oil bath; under stirring, take 3 g of potassium permanganate crystals and slowly add to the above suspension, react at 35℃ for 3 h; then add 100 mL of deionized water and continue stirring for 3 h; the mixed solution after the reaction is purple, add hydrogen peroxide solution dropwise until no bubbles are generated; finally, wash the product with deionized water and ethanol alternately by centrifugation until the supernatant is colorless, place in a 60℃ oven and dry for 6 h to obtain α-CNFs black powder;

[0077] (2) Dissolve 0.25 g of cobalt nitrate hexahydrate in 10 mL of a mixed solution containing DMF and methanol (V DMF :V 甲醇 The solution was dissolved in a 1:1 ratio using ultrasonication until a clear pink solution was obtained. Then, 0.05 g of α-CNFs powder was added and dissolved in ultrasonication until a suspension was formed. The suspension was then stirred at room temperature for 30 min, and finally transferred to a 100 mL polytetrafluoroethylene reactor. The mixture was then solvothermal reacted in a 120°C oven for 4 h. After alternating centrifugation and washing with deionized water and ethanol until the supernatant was colorless and clear, the solution was dried in a 60°C oven for 6 h to obtain a black Co(OH)2@CNFs powder.

[0078] The electrochemical testing method is the same as in Example 1. The electrochemical performance of Co(OH)2@CNFs is shown in [reference needed]. Figure 4 and Figure 5 .

[0079] Comparative Example 2

[0080] This comparative example provides a CoNi-LDH@CNFs electrode material, and the preparation method is as follows:

[0081] (1) Add 0.5 g CNFs to 20 mL of a mixed solution containing concentrated sulfuric acid and concentrated hydrochloric acid (V 浓硫酸 :V 浓盐酸 =1:1), sonicate to form a suspension, and place in an oil bath; while stirring, take 3 g of potassium permanganate crystals and slowly add them to the above suspension, and react at 35℃ for 3 h; then add 100 mL of deionized water and continue stirring for 3 h; the mixed solution after the reaction is dark purple, add hydrogen peroxide solution dropwise until no more bubbles are generated; finally, wash the product with deionized water and ethanol alternately by centrifugation until the supernatant is colorless, and dry it in a 60℃ oven for 6 h to obtain α-CNFs black powder;

[0082] (2) In 40 mL of methanol-water mixture (V 甲醇 :V 水 In a 3:1 ratio, 0.25 g of cobalt nitrate hexahydrate, 0.25 g of nickel nitrate hexahydrate, and 0.17 g of activator cetyltrimethylammonium bromide were added sequentially. Then, 0.05 g of pre-prepared α-CNFs powder was weighed and dissolved into a suspension using ultrasonic assistance. The suspension was stirred at room temperature for 30 min. After uniform dispersion, the mixture was transferred to a 100 mL polytetrafluoroethylene reactor and subjected to a solvothermal reaction at 180 °C for 24 h. After the reaction, the product was centrifuged several times alternately with ethanol and deionized water until the supernatant was colorless. Finally, it was dried in a 60 °C oven for 6 h to obtain CoNi-LDH@CNFs hazy blue powder. Its microstructure is as follows: Figure 16 As shown.

[0083] The electrochemical testing method is the same as in Example 1. The electrochemical performance of Co(OH)2@CNFs is shown in [reference needed]. Figure 18 and Figure 19 .

[0084] The electrode materials of Example 1, Comparative Example 1, and Comparative Example 2 were compared:

[0085] 1. Based on the morphology of the three materials Figure 3 , 6 As can be clearly seen from Figures 1 and 16, the material in Example 1 has a large specific surface area and is well-ordered; the crystal structure analysis results are shown in Figure 1. Figure 17 ;

[0086] 2. Through Figure 20 A comparison of the specific electrochemical performance graphs shows that the material in Example 1 has a larger CV curve area and a longer GCD charge-discharge time.

[0087] In summary, compared with Co(OH)2@CNFs and CoNi-LDH@CNFs electrode materials, the hierarchical network structure of CoNi-LDH@Co(OH)2@CNFs composite electrode material has a larger specific surface area and more reaction sites, resulting in superior specific capacitance and electrochemical performance. This is because the introduction of α-CNFs and Co(OH)2 can effectively alleviate the defect of LDH agglomeration, promote ion diffusion and electron transfer between the electrolyte and the electrode material, and effectively improve its cycle stability.

Claims

1. A CoNi-LDH@Co(OH)2@CNFs composite electrode material, characterized in that, Using carbon nanofibers as a conductive substrate, Co(OH)2 nanosheets are modified on it as an intermediate layer, and CoNi-LDH nanoflowers are grown on the surface of the intermediate layer as the outermost layer, forming a hierarchical network nanostructure with carbon nanofibers as the core.

2. The composite electrode material according to claim 1, characterized in that, The carbon nanofibers have a diameter of 130-170 nm, and the CoNi-LDH nanoflowers have a particle size of 400-500 nm.

3. A method for preparing the CoNi-LDH@Co(OH)2@CNFs composite electrode material according to claim 1, characterized in that, Includes the following steps: (1) Acid activation treatment: CNFs are placed in a mixed acid solution and reacted with potassium permanganate under stirring conditions at a constant temperature to obtain a-CNFs; (2) Co(OH)2 nanosheets were modified on the surface of a-CNFs by solvothermal reaction to obtain Co(OH)2@CNFs composite material; (3) CoNi-LDH nanoflowers were grown on the surface of Co(OH)2@CNFs by solvothermal reaction to obtain CoNi-LDH@Co(OH)2@CNFs composite electrode material.

4. The preparation method according to claim 3, characterized in that, In step (1), the acid activation treatment method is as follows: carbon nanofibers are added to a mixed acid solution containing concentrated hydrochloric acid and concentrated sulfuric acid, ultrasonically dispersed to form a suspension, and placed in an oil bath; under stirring conditions, potassium permanganate crystals are dissolved in the suspension for a constant temperature reaction; after the reaction is completed, deionized water is added and stirring is continued; hydrogen peroxide solution is added dropwise until no bubbles are generated, and then the product is centrifuged, washed and dried.

5. The preparation method according to claim 4, characterized in that, The volume ratio of deionized water, concentrated sulfuric acid, and concentrated nitric acid was 98~102:8~12:8~12; the mass ratio of potassium permanganate to α-CNFs was 2.99~3.01:0.49~0.51; the oil bath temperature was 34.2~35.8℃, and the time was 2.92~3.08 h; after adding deionized water, stirring was continued for 2.92~3.08 h.

6. The preparation method according to claim 3, characterized in that, In step (2), the method for modifying Co(OH)2 nanosheets is as follows: Cobalt nitrate hexahydrate is dissolved in a mixed solution of DMF and methanol, a-CNFs are added, and after ultrasonic dissolution, a solvothermal reaction is carried out. The product is then centrifuged, washed, and dried.

7. The preparation method according to claim 6, characterized in that, The volume ratio of DMF to methanol in the mixed solution was 3~7:3~7; the mass ratio of cobalt nitrate hexahydrate to α-CNFs powder was 0.24~0.26:0.04~0.06; the solvothermal reaction temperature was 119.2~120.8℃, and the time was 3.92~4.08 h.

8. The preparation method according to claim 3, characterized in that, In step (3), the method for growing CoNi-LDH nanoflowers is as follows: under ultrasonic conditions, Co(OH)2@CNFs powder is uniformly dispersed in methanol aqueous solution; then cobalt nitrate hexahydrate, nickel nitrate hexahydrate and activator are added in sequence, and ultrasonically assisted dissolution is carried out to a suspension state and stirred; the above solution is placed in an oven for solvothermal reaction, and after the reaction is completed, the supernatant is removed, and the solution is washed by alternating centrifugation and dried.

9. The preparation method according to claim 8, characterized in that, The mass ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and Co(OH)2@CNFs powder was 5~10:5~10:1; the activator was hexadecyltrimethylammonium bromide; the solvothermal reaction temperature was 179.2~180.8℃, and the time was 23.92~24.08 h.

10. The application of the CoNi-LDH@Co(OH)2@CNFs composite electrode material of claim 1 in the preparation of supercapacitors.

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