Hollow nanoflower NiCo-LDH, and preparation method and application thereof

Abstract

The application discloses a hollow nanoflower NiCo-LDH, and uses nickel nitrate, cobalt nitrate, dimethyl imidazole, dimethyl sulfoxide and cetyl trimethyl ammonium bromide as raw materials, uses deionized water and anhydrous ethanol as solvents, and synthesizes the NiCo-LDH through a precipitation method and a hydrothermal method, wherein the NiCo-LDH is a hollow nanoflower structure; the size of the hollow nanoflower NiCo-LDH is 600-700 nm, the wall of the hollow nanoflower structure has a secondary structure, the secondary structure is a layered structure composed of small ball-shaped structures, the size of the small ball-shaped structures is 100 nm, and the primary unit of the small ball-shaped structures is an LDH flake. A preparation method thereof comprises the following steps: 1, preparation of ZIF-67; and 2, preparation of the hollow nanoflower NiCo-LDH. When the hollow nanoflower NiCo-LDH is applied as a supercapacitor electrode material, the specific capacitance of the HNF-NiCo-LDH-6 is 1538-1834 F g ‑1 when a discharge current density is 1 A g ‑1 .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of supercapacitors, and particularly relates to a hollow nanoflower NiCo-LDH and a preparation method and application thereof. BACKGROUND

[0002] Supercapacitors have high power density and can realize fast charge and discharge in a short time. Pseudocapacitance can store electrical energy through fast and reversible Faraday redox reactions on the electrode surface, so theoretically, pseudocapacitance materials have high capacitance. Among them, transition metal hydroxides are a kind of supercapacitor electrode materials with high theoretical capacity, but the currently prepared metal hydroxides tend to form nanosheet structures, and the aggregation of the structure reduces the effective specific surface area of LDHs, further limiting the electrochemical performance. Thus, the actual specific capacitance is far lower than the theoretical specific capacitance, greatly limiting their application effect in the field of supercapacitors.

[0003] There are currently three common solutions:

[0004] 1. Adjusting the morphology by compounding with carbon-based materials. For example, existing document 1 (Chen S, Zhang Y, Zhang, H, et al. The flower-like BSC / NiCo-LDHs composite as a high-performance active material for flexible supercapacitors) uses biomass porous carbon and nickel-cobalt hydroxide to synthesize nanoflower-like BSC / NiCo-LDHs material, and has a specific capacitance of 974 F g -1 under a current density of 1 Ag -1 . Although this technical solution obtains a larger specific surface area than the sheet structure by preparing nanoflowers, the carbon material used has irregular micro-morphology, resulting in uneven size of the obtained nanoflowers, and the nanoflowers with small size have aggregation phenomenon.

[0005] 2. Adjusting the morphology by introducing a carrier. For example, existing document 2 (Xu L, Li Y, Li M, et al. Mo-doped NiCo-LDH nanoflower derived from ZIF-67 nanosheet arrays for high-performance supercapacitors) loads Mo metal ion-doped NiCo-LDH on carbon cloth to synthesize Mo-NiCo-LDH@C nanoflower structure. Under a current density of 1 Ag -1 , it has a specific capacitance of 1368.4 C g -1The technical scheme introduces amorphous phase by doping Mo ions to realize the technical effect of adjusting the electronic structure of NiCo-LDH, thereby improving the charge storage kinetics. However, the interaction force between the NiCo-LDH nanoflower and the carbon cloth is small, which directly leads to the fact that the NiCo-LDH nanoflower cannot be uniformly loaded on the carbon cloth, and the NiCo-LDH nanoflower falls off from the surface of the carbon cloth during the cycle process.

[0006] 3. By adjusting the preparation method, the flaky morphology is adjusted to a core-shell structure. For example, the existing document 3 (Shi Y, Xue J, Yu Y, et al. Facile construction of Mn2O3@NiMn LDH composites electrode with cube core-shell structures for high performance supercapacitors) uses a chemical precipitation method to grow NiMn-LDH on the surface of MnO2S in situ, and synthesizes a core-shell structure Mn2O3@NiMn LDH. At a current density of 0.5 Ag -1 has 1280F g -1 The technical scheme realizes the technical effect of inhibiting the collapse of the electrode structure by constructing a core-shell structure and using Mn2O3 as the core structure to improve the initial specific capacitance of the electrode. However, the size of the core-shell structure obtained by the technical scheme is micron level, thereby leading to a decrease in the electron transmission rate.

[0007] From the above-mentioned existing documents, it can be seen that the micro-morphology of the composite material has a significant influence on the performance, and although the technical schemes adopted by the existing technologies are different, they have successfully adjusted the micro-morphology of the composite material. Further research has found that although the forms of the technical problems existing in the existing technical schemes are different, the common technical problem is that the micro-morphology of the obtained material is not uniform, thereby leading to the phenomenon of falling off after loading the active material, and the problem of the large size of the material being not conducive to electron transmission.

[0008] According to the research of the inventors, since the metal organic framework material MOF has a specific morphology, it can adjust the micro-morphology of the composite material when used as a template, thereby solving the above-mentioned problems. In addition, the MOF also has a rich pore structure, which can improve the transmission and storage of electrons. In addition, according to the research of the inventors, by using solvents with different properties, the technical effect of adjusting the morphology can also be realized, thereby enhancing the interaction between the metal ions and the organic ligands in the MOF material, thereby having better crystallinity.

[0009] Therefore, the inventors combine the above two methods: adding a polar organic solvent DMSO and using ZIF-67 as a template to adjust the micro-morphology of NiCo-LDH, so as to obtain a larger specific surface area and expose more electrochemical sites. SUMMARY

[0010] The purpose of the present application is to provide a hollow nanoflower NiCo-LDH and a preparation method and application thereof.

[0011] By using the polar organic solvent dimethyl sulfoxide DMSO as a solvent to synthesize ZIF-67, the high polarity of DMSO is used to enhance the interaction between metal ions and organic ligands and promote the coordination between them, thereby improving the crystallinity;

[0012] Then, the template ZIF-67 is etched and grown by nitrate, so that the NiCo-LDH is in a hollow nanoflower structure, and the wall of the hollow nanoflower structure has a secondary structure composed of a layered structure of small ball clusters, which is beneficial to expose more active sites, shorten the electron transport path, and effectively improve the electrochemical performance;

[0013] At the same time, the DMSO molecules are embedded in the framework structure of ZIF-67, and then interact with metal ions or reaction intermediates to change the reaction path and energy, so that the material is more likely to have oxygen vacancies during the synthesis process.

[0014] Therefore, the invention principle of the present application is simply summarized as follows: the transition metal elements have rich valence states, which exhibit high Faraday capacitance in the process of electrochemical oxidation-reduction reaction; at the same time, the secondary structure is used to improve the stability of the composite material, expose more active sites, shorten the electron migration path, and improve the conductivity.

[0015] In order to achieve the above-mentioned purpose of the application, the technical scheme adopted by the present application is as follows:

[0016] A hollow nanoflower NiCo-LDH is prepared by using nickel nitrate, cobalt nitrate, dimethyl imidazole, dimethyl sulfoxide, and cetyltrimethylammonium bromide as raw materials, deionized water and anhydrous ethanol as solvents, and by using a precipitation method and a hydrothermal method to synthesize NiCo-LDH, wherein the NiCo-LDH is in a hollow nanoflower structure; the size of the hollow nanoflower NiCo-LDH is 600-700 nm, the wall of the hollow nanoflower structure has a secondary structure composed of a layered structure of small ball clusters, the size of the small ball cluster is 100 nm, and the primary unit of the small ball cluster is an LDH flake.

[0017] A preparation method of a hollow nanoflower NiCo-LDH, comprising the following steps:

[0018] Step 1, preparation of ZIF-67, first, Co(NO3)·6H2O is dissolved in deionized water to obtain solution A, at the same time, dimethyl imidazole 2-MI, thiourea TU, cetyltrimethylammonium bromide CTAB and dimethyl sulfoxide DMSO are dissolved in deionized water to obtain solution B, then, solution A and solution B are mixed, and the reaction is carried out by stirring first and then standing, after the reaction is completed, the obtained product is centrifuged and dried, and ZIF-67 can be obtained;

[0019] In the step 1, the ratio of Co(NO3)·6H2O, 2-MI, TU, and CTAB and DMSO satisfies 8g:17g:1g:0.02g:14mL;

[0020] In the step 1, the conditions of stirring first and then standing are that the stirring time is 1h and the standing time is 6h;

[0021] Step 2, preparation of hollow nanoflower NiCo-LDH, first, ZIF-67 and Ni(NO3)·6H2O obtained in step 1 are dissolved in anhydrous ethanol under certain conditions to obtain solution C, then, solution C is subjected to hydrothermal reaction under certain conditions, after the reaction is completed, the obtained product is washed and dried, and hollow nanoflower HNF-NiCo-LDH can be obtained;

[0022] In the step 2, the mass ratio of ZIF-67 and Ni(NO3)·6H2O is 1:11;

[0023] In the step 2, the stirring conditions are that the stirring time is 0.5-1h.

[0024] In the step 2, the hydrothermal conditions are that the hydrothermal temperature is 80℃ and the hydrothermal time is 6h.

[0025] When the hollow nanoflower NiCo-LDH is applied as an electrode material of a supercapacitor, the specific capacitance of HNF-NiCo-LDH-6 is 1538-1834F g -1 when the discharge current density is 1Ag -1 .

[0026] The NiCo-LDH material obtained by the application has the beneficial technical effects, and the experimental detection results are as follows:

[0027] It can be known from XRD test that NiCo-LDH has the characteristic peak of NiCo-LDH. The test results show that the composition of NiCo-LDH is NiCo-LDH;

[0028] The XPS test shows that the NiCo-LDH is composed of Ni elements, Co elements, C elements, N elements and O elements, wherein the Ni elements exist in +2 valence, and the Co elements exist in +2 and +3 valences; and oxygen vacancies exist, and the content is 32.7%-41.1%;

[0029] The SEM test shows that the NiCo-LDH is a hollow nanoflower structure, and the size is 600-700nm; the wall of the hollow nanoflower structure has a secondary structure, and the secondary structure is a layered structure composed of multiple small ball-shaped structures; the size of the small ball-shaped structure is 100nm; and the primary unit of the small ball-shaped structure is an LDH flake, which is formed by Ni ion etching and LDH growth;

[0030] The TEM and EDS tests show that the outer layer of the NiCo-LDH is uniformly distributed with Ni elements, Co elements and O elements, and the inner layer is not detected with the three elements. The test result shows that the NiCo-LDH is a hollow structure. In combination with the SEM test and the TEM test result, it can be known that the NiCo-LDH is a hollow nanoflower structure.

[0031] The CV test shows that a group of symmetrical redox peaks exist in the CV curve, which shows that the NiCo-LDH has good charge and discharge reversibility. The CV curve profile remains basically unchanged under different scanning rates, which shows that the NiCo-LDH has good electrochemical stability.

[0032] The three-electrode charge and discharge test shows that when the discharge current density is 1Ag -1 , the specific capacitance of the NiCo-LDH is 1538-1834F g -1 .

[0033] Therefore, compared with the prior art, the hollow nanoflower NiCo-LDH has the following advantages:

[0034] 1. The NiCo-LDH obtained in the application has a hollow nanoflower structure, and the wall of the hollow nanoflower structure has a secondary structure, and the secondary structure is a layered structure composed of small ball-shaped structures.

[0035] 2. The DMSO has extremely high polarity, which can enhance the interaction between cobalt ions and organic ligands dimethyl imidazole, promote the coordination between them, improve the crystallinity and regularity, and at the same time, the DMSO molecules are embedded into the framework structure of ZIF-67, and then interact with metal ions or reaction intermediates to change the path and energy of the reaction, so that the material is more likely to have oxygen vacancies in the synthesis process.

[0036] 3. The electrode material prepared by the application has low temperature requirement, short preparation time, economy and simple method, excellent product performance, and reduces the energy consumption and equipment requirement of the process. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 XRD patterns of ZIF-67, HNF-NiCo-LDH-6, HNF-NiCo-LDH-3 and HNF-NiCo-LDH-9 materials prepared in Example 1, Comparative Example 2 and Comparative Example 3;

[0038] Figure 2 XPS image of the HNF-NiCo-LDH-6 material prepared in Example 1;

[0039] Figure 3 SEM image of the HNF-NiCo-LDH-6 material prepared in Example 1;

[0040] Figure 4 TEM image of the HNF-NiCo-LDH-6 material prepared in Example 1;

[0041] Figure 5 EDS image of the HNF-NiCo-LDH-6 material prepared in Example 1;

[0042] Figure 6 Cyclic voltammetry curves of the HNF-NiCo-LDH-6 material prepared in Example 1 at scan rates of 1mV, 2mV, 5mV, 8mV, and 10mV;

[0043] Figure 7 The HNF-NiCo-LDH-6 material prepared in Example 1 was tested at 1 Ag. -1 Constant current charge-discharge curves at current density;

[0044] Figure 8 SEM image of the HNF-NiCo-LDH-FS material prepared in Comparative Example 1;

[0045] Figure 9 ZIF-67, HNF-NiCo-LDH-6, HNF-NiCo-LDH-3, and HNF-NiCo-LDH-9 materials from Examples 1, 2, and 3 were tested at 1 Ag. -1 Constant current charge-discharge curves at current density;

[0046] Figure 10 SEM image of the HNF-NiCo-LDH-3 material prepared in Comparative Example 2;

[0047] Figure 11 The image shows the SEM image of the HNF-NiCo-LDH-9 material prepared in Comparative Example 3. Detailed Implementation

[0048] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0049] Example 1

[0050] A method for preparing hollow nanoflower NiCo-LDH includes the following steps:

[0051] Step 1, Preparation of ZIF-67: First, dissolve 2.6g Co(NO3)·6H2O in 10mL of deionized water to obtain solution A. Simultaneously, dissolve 5.2g dimethylimidazole 2-MI, 0.3g thiourea TU, 0.006g hexadecyltrimethylammonium bromide CTAB, and 8mL dimethyl sulfoxide DMSO in 102mL of deionized water to obtain solution B. Then, mix solutions A and B and react by stirring and then allowing to stand. After the reaction is complete, centrifuge and dry the resulting product to obtain ZIF-67.

[0052] The conditions for stirring before settling are: stirring time is 1 hour and settling time is 6 hours.

[0053] Step 2, Preparation of Hollow Nanoflower NiCo-LDH: First, 0.1g of ZIF-67 obtained in Step 1 and 1.16g of Ni(NO3)·6H2O were dissolved in 50mL of anhydrous ethanol and stirred for 1h to obtain solution C. Then, solution C was subjected to hydrothermal reaction at a hydrothermal temperature of 80℃ for 6h. After the reaction was completed, the obtained product was washed and dried to obtain hollow nanoflower Hollow-Nano-Flowers-NiCo-LDH, abbreviated as HNF-NiCo-LDH. Specifically, the HNF-NiCo-LDH obtained in Example 1 is abbreviated as HNF-NiCo-LDH-6.

[0054] To verify the composition and structure of HNF-NiCo-LDH-6, XRD tests were performed. The test results are as follows: Figure 1 As shown, HNF-NiCo-LDH-6 exhibits characteristic peaks of NiCo-LDH. The test results indicate that HNF-NiCo-LDH-6 is composed of NiCo-LDH.

[0055] To further confirm the elemental chemical valence state of HNF-NiCo-LDH-6, XPS analysis was performed. The test results are as follows: Figure 2 As shown, HNF-NiCo-LDH-6 is composed of Ni, Co, C, N and O elements. Ni exists in the +2 oxidation state, Co exists in both the +2 and +3 oxidation states, and HNF-NiCo-LDH-6 also contains oxygen vacancies, with a content of 41.1%.

[0056] To verify the microstructure of HNF-NiCo-LDH-6, SEM measurements were performed. The test results are as follows: Figure 3 As shown, the microstructure of HNF-NiCo-LDH-6 is a hollow nanoflower structure with a size of 600-700 nm. The walls of the hollow nanoflower structure have a secondary structure, which is a layered structure composed of multiple small hydrangeas with a size of 100 nm. The primary unit of the small hydrangeas is an LDH sheet, which is formed by Ni ion etching and LDH growth.

[0057] To further verify the microstructure of HNF-NiCo-LDH-6, TEM and EDS tests were performed. The test results are as follows: Figure 4 and Figure 5 As shown, Ni, Co, and O elements are uniformly distributed in the outer layer of HNF-NiCo-LDH-6, while these three elements were not detected in the inner layer. The test results indicate that HNF-NiCo-LDH-6 has a hollow structure. Combined with SEM and TEM results, it is clear that HNF-NiCo-LDH-6 has a hollow nanoflower structure.

[0058] To demonstrate the electrochemical performance of HNF-NiCo-LDH-6, HNF-NiCo-LDH-6 was prepared as an electrode. Taking HNF-NiCo-LDH-6 as an example, the specific preparation method of the HNF-NiCo-LDH electrode is as follows: First, 0.008g of HNF-NiCo-LDH-6, 0.001g of acetylene black, 0.001g of polytetrafluoroethylene micro powder, and 0.5mL of ethanol were mixed and ground to obtain a mixed material; then, the mixed material was pressed onto a 2mm thick nickel foam current collector under a pressure of 10kPa to obtain the electrode; finally, it was dried under air and room temperature conditions to obtain the supercapacitor electrode based on HNF-NiCo-LDH-6. Since there is no need to distinguish it, the obtained electrode is also simply referred to as HNF-NiCo-LDH-6.

[0059] The CV test results of HNF-NiCo-LDH-6 are as follows: Figure 6 As shown, a set of symmetrical redox peaks exists in the CV curve. The test results indicate that NiCo-LDH-6 is a Faraday capacitor, and the symmetry of the redox peaks indicates that HNF-NiCo-LDH-6 has good charge-discharge reversibility.

[0060] The CV test results of HNF-NiCo-LDH-6 at different scan rates are as follows: Figure 6As shown, within a potential window of 0 to 0.6 V, the CV curve profiles of HNF-NiCo-LDH-6 remained essentially unchanged at different scan rates. The test results indicate that HNF-NiCo-LDH-6 possesses good electrochemical stability.

[0061] The three-electrode charge-discharge test results of HNF-NiCo-LDH-6 are as follows: Figure 7 As shown, at a discharge current density of 1Ag -1 At that time, the specific capacitance of HNF-NiCo-LDH-6 was 1834 F g. -1 .

[0062] To demonstrate the effect of DMSO on NiCo-LDH, Comparative Example 1 is provided, showing NiCo-LDH prepared without the addition of DMSO.

[0063] Comparative Example 1

[0064] A method for preparing NiCo-LDH without adding DMSO. Unless otherwise specified, step 1 is the same as in Example 1, except that DMSO is not added in step 1. The resulting NiCo-LDH Flaky structure is referred to as NiCo-LDH-FS.

[0065] To demonstrate the composition and structure of NiCo-LDH-FS, XRD tests were performed, and the results are as follows. Figure 1 As shown, the diffraction peaks of NiCo-LDH-FS are the same as those of HNF-NiCo-LDH-6, indicating the presence of characteristic peaks of NiCo-LDH. The test results demonstrate that NiCo-LDH-FS and HNF-NiCo-LDH-6 have the same composition and structure.

[0066] To verify the microstructure of NiCo-LDH-FS, SEM testing was performed, and the results are as follows. Figure 8 As shown, the microstructure of NiCo-LDH-FS is a sheet-like structure with a size of 700-800 nm, which is formed by the growth and stacking of many irregular nanosheets. Compared with Example 1, it can be seen that the addition of DMSO can transform NiCo-LDH from a two-dimensional sheet-like structure into a hollow nanoflower structure.

[0067] The charge-discharge test results of NiCo-LDH-FS are as follows: Figure 9 As shown, at a discharge current density of 1Ag -1 At that time, the specific capacitance of NiCo-LDH-W was 1326 F g. -1 Compared with Example 1, it can be seen that adding DMSO can significantly improve the specific capacitance, with an increase of 38.3%.

[0068] As shown in Example 1 and Comparative Example 1, the addition of DMSO transforms NiCo-LDH from a two-dimensional sheet structure into a hollow nanoflower structure, which can significantly increase the number of electrochemical sites. At the same time, the addition of DMSO embedded in the framework structure of ZIF-67 can change the reaction pathway and energy through interaction with metal ions. Specifically, the addition of DMSO can form oxygen vacancies.

[0069] To demonstrate the effect of hydrothermal time on NiCo-LDH, Comparative Example 2 and Comparative Example 3 are provided, with NiCo-LDH prepared by hydrothermal times of 3 h and 9 h, respectively.

[0070] Comparative Example 2

[0071] A method for preparing NiCo-LDH material with a hydrothermal time of 3 hours is described. Step 1, unless otherwise specified, is the same as in Example 1. The difference is that in step 2, the hydrothermal time is 3 hours, and the resulting material is named HNF-NiCo-LD-3.

[0072] To verify the composition and structure of the HNF-NiCo-LDH-3 material, XRD tests were performed. The test results are as follows: Figure 1 As shown, the HNF-NiCo-LDH-3 material exhibits characteristic peaks of NiCo-LDH. Test results indicate that the HNF-NiCo-LDH-3 material has the same composition and structure as the product HNF-NiCo-LDH-6 from Example 1.

[0073] To verify the microstructure of HNF-NiCo-LDH-3, SEM measurements were performed. The test results are as follows: Figure 10 As shown, the microstructure of HNF-NiCo-LDH is a hollow nanoflower structure with a size of 600-700 nm, and the surface contains irregular nanosheets, meaning that the small hydrangea structure was not etched. Compared with Example 1, it can be seen that increasing the hydrothermal time can promote the etching of Ni ions and the growth of LDH, further generating a hollow nanoflower structure with secondary structure, thereby increasing the electrochemical sites.

[0074] To demonstrate the electrochemical performance of HNF-NiCo-LDH-3, a three-electrode charge-discharge test was conducted. The test results are as follows: Figure 9 As shown, at a discharge current density of 1Ag -1 At that time, the specific capacitance of HNF-NiCo-LDH-3 was 1538 F g. -1 Compared with Example 1, it can be seen that increasing the hydrothermal time can improve the specific capacitance by 19.2%.

[0075] Comparative Example 3

[0076] A method for preparing NiCo-LDH material with a hydrothermal time of 9 hours is described. Step 1, unless otherwise specified, is the same as in Example 1. The difference is that in step 2, the hydrothermal time is 9 hours, and the resulting material is named HNF-NiCo-LD-9.

[0077] To verify the composition and structure of the HNF-NiCo-LDH-9 material, XRD tests were performed. The test results are as follows: Figure 1 As shown, the HNF-NiCo-LDH-9 material exhibits characteristic peaks of NiCo-LDH. Test results indicate that the HNF-NiCo-LDH-9 material has the same composition and structure as the product HNF-NiCo-LDH-6 from Example 1.

[0078] To verify the microstructure of HNF-NiCo-LDH-9, SEM measurements were performed. The test results are as follows: Figure 11 As shown, the microstructure of HNF-NiCo-LDH-9 is a nanoflower structure with a size of 700-800 nm. Compared with Example 1, it can be seen that further increasing the hydrothermal time directly leads to the self-assembly of NiCo-LDH from a hollow nanoflower structure into a nanoflower structure, with an increased size, while the nanoflower structure has fewer electrochemical sites than the hollow nanoflower structure.

[0079] To demonstrate the electrochemical performance of HNF-NiCo-LDH-9, a three-electrode charge-discharge test was conducted. The test results are as follows: Figure 9 As shown, at a discharge current density of 1Ag -1 At that time, the specific capacitance of HNF-NiCo-LDH-9 was 1630 F g. -1 Compared with Example 1, it can be seen that further increasing the hydrothermal time will reduce the specific capacitance by 12.5%.

[0080] By comparing and analyzing Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that the hydrothermal reaction time directly determines the microstructure of the composite material, specifically as follows:

[0081] 1. When the hydrothermal reaction time is short, due to insufficient etching, the secondary structure of small hydrangeas cannot be formed on the surface of the hollow nanoflower structure, and only irregular nanosheets exist.

[0082] 2. When the hydrothermal reaction time is too long, NiCo-LDH will undergo re-self-assembly.

Claims

1. A method for preparing hollow nanoflower NiCo-LDH, characterized in that... Includes the following steps: Step 1, Preparation of ZIF-67: First, Co(NO3)·6H2O is dissolved in deionized water to obtain solution A. At the same time, dimethylimidazolium 2-MI, thiourea TU, hexadecyltrimethylammonium bromide CTAB, and dimethyl sulfoxide DMSO are dissolved in deionized water to obtain solution B. Then, solutions A and B are mixed and reacted by stirring and then allowing to stand. After the reaction is complete, the resulting product is centrifuged and dried to obtain ZIF-67. Step 2, Preparation of hollow nanoflowers NiCo-LDH: First, under certain conditions, ZIF-67 and Ni(NO3)·6H2O obtained in step 1 are dissolved in anhydrous ethanol and stirred to obtain solution C. Then, under certain conditions, solution C is subjected to a hydrothermal reaction. After the reaction is completed, the obtained product is washed and dried to obtain hollow nanoflowers HNF-NiCo-LDH. In step 2, the stirring conditions are: stirring time is 0.5-1 h; in step 2, the hydrothermal conditions are: hydrothermal temperature is 80℃, and hydrothermal time is 6 h. The obtained hollow nanoflower NiCo-LDH was synthesized from nickel nitrate, cobalt nitrate, dimethyl imidazole, dimethyl sulfoxide, and hexadecyltrimethylammonium bromide as raw materials, and deionized water and anhydrous ethanol as solvents, through precipitation and hydrothermal methods. The NiCo-LDH has a hollow nanoflower structure. The hollow nanoflower NiCo-LDH has a size of 600-700 nm. The wall of the hollow nanoflower structure has a secondary structure, which is a layered structure composed of small hydrangeas. The size of the small hydrangeas is 100 nm, and the primary unit of the small hydrangeas is an LDH sheet.

2. The preparation method according to claim 1, characterized in that: In step 1, the ratio of Co(NO3)·6H2O, 2-MI, TU, CTAB, and DMSO satisfies 8 g: 17 g: 1 g: 0.02 g: 14 mL; In step 2, the mass ratio of ZIF-67 to Ni(NO3)·6H2O is 1:

11.

3. The preparation method according to claim 1, characterized in that: In step 1, the conditions for stirring first and then letting it stand are: stirring time is 1 hour and standing time is 6 hours.

4. The preparation method according to claim 1, characterized in that: The obtained hollow nanoflower NiCo-LDH was used as an electrode material for supercapacitors, and its application was demonstrated at a discharge current density of 1 A g. -1 At that time, the specific capacitance of HNF-NiCo-LDH-6 was 1538-1834 F g. -1 .

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