Preparation method and application of oxygen vacancy-rich-NiFe-LDH-coated CoNi-LDH composite material

Abstract

The invention provides a preparation method of an oxygen vacancy-NiFe-LDH coated CoNi-LDH composite material. The preparation method comprises the following steps: firstly, preparing NiFe-LDH by taking nickel sulfate, ferrous sulfate, sodium borohydride and sodium hydroxide as raw materials; then, cobalt nitrate, methanol and 2-methylimidazole are used as raw materials to be subjected to an aging reaction, and ZIF-67 is prepared. NiFe-LDH and ZIF-67 react with a nickel source and absolute ethyl alcohol to prepare NiFe-LDH (at) CoNi-LDH, and the NiFe-LDH (at) CoNi-LDH is immersed into a sodium borohydride aqueous solution containing sodium hydroxide to prepare oxygen vacancy-NiFe-LDH (at) CoNi-LDH. Applications are also provided for use in the positive electrode of a supercapacitor. According to the alkali etching method selected by the invention, LDH with unique morphology is formed by using an anchoring strategy, the self-aggregation effect of LDH nanoparticles is reduced, the LDH nanoparticles are not easy to collapse or agglomerate and are more stable in the charge-discharge cycle process, oxygen vacancies are introduced by sodium borohydride assisted reduction, the oxygen vacancies improve the exposure of active sites of the material, charge transfer is promoted, and the performance of the material is improved. The efficient oxidation-reduction reaction is realized. Therefore, the material has the electrochemical properties of high specific capacitance, high rate capability and good cycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercapacitor electrode positive electrode materials, and specifically relates to a preparation method and application of an oxygen vacancy-rich NiFe-LDH@CoNi-LDH composite material. Background Art

[0002] Supercapacitors have good performance indicators, such as good charge and discharge capabilities, strong power density and long cycle life, and have received widespread attention in many fields. However, the energy density significantly lower than that of lithium batteries limits the widespread use of supercapacitors. Improving energy density without sacrificing power density is the main topic of current supercapacitor research and development.

[0003] Layered double hydroxide (LDH) is an ideal supercapacitor electrode material due to its high specific surface area, easily exposed metal sites and inherent ion migration channels. However, the narrow interlayer spacing and poor conductivity hinder the mass transfer rate of electrolyte ions and electrons, limit the depth of redox reactions, and further affect the supercapacitor performance of the material.

[0004] Zeolitic imidazolate framework material (ZIF) is a metal-organic framework compound containing a combination of metal sources and organic ligands. Due to its strong ordered extended network, high specific surface area and unique electronic structure, it can become a self-sacrificing template for the synthesis of LDH. The resulting composite material will have more active sites and transmission channels, accelerate the rapid diffusion of ions / electrons in electrochemical reactions, and effectively improve the kinetic performance and cycle stability of the material.

[0005] The generation of vacancies means defects in materials, among which oxygen vacancies are a representative type. When there are defects in the surface structure of electrode materials, the mass transfer process of ions can be promoted. The formation of defects not only expands the interlayer distance and enhances the ion intercalation pseudocapacitance, but also acts as a shallow donor to store a small amount of electrolyte, shortening the transfer time of electrolyte ions and thus enhancing the electrochemical behavior of the material. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material and its application in view of the deficiencies of the above-mentioned prior art. The method adopts a clever etching method to anchor NiFe-LDH nanoparticles on CoNi-LDH with a dodecahedral morphology, and a subsequent sodium borohydride-assisted reduction strategy successfully prepares an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material rich in oxygen defects. The prepared electrode material has high specific capacitance, good rate performance, and stable cycle performance, which has practical guiding significance for the preparation of positive electrode materials for supercapacitors.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material, the method comprising:

[0008] S1. Mix nickel sulfate, ferrous sulfate and deionized water and stir them magnetically, then add sodium hydroxide solution, adjust the pH to 6.5, then add sodium borohydride, and continue stirring magnetically to obtain solution A;

[0009] S2, after centrifuging the solution A obtained in S1, washing and drying the obtained solid matter, the obtained black powder is named NiFe-LDH;

[0010] S3, mixing cobalt nitrate and methanol, and performing magnetic stirring to obtain solution B;

[0011] S4, mixing 2-methylimidazole and methanol, and stirring magnetically to obtain solution C, transferring the solution C to solution B obtained in S3, and stirring magnetically to obtain solution D;

[0012] S5, aging the solution D obtained in S4, and then centrifuging it, washing and drying the obtained solid matter to obtain a purple powder, named ZIF-67;

[0013] S6, dispersing the NiFe-LDH obtained in S2 in anhydrous ethanol, then adding nickel nitrate, and stirring to obtain a solution E;

[0014] S7, dispersing the ZIF-67 obtained in S5 in anhydrous ethanol to obtain a solution F, transferring the solution F to the solution E obtained in S6, reacting by magnetic stirring, and then centrifuging, washing and drying the obtained solid to obtain a green powder, named NiFe-LDH@CoNi-LDH;

[0015] S8. Immerse the NiFe-LDH@CoNi-LDH obtained in S7 into an aqueous solution of sodium borohydride containing sodium hydroxide and stir. After the reaction is completed, centrifuge the mixture. Wash and dry the solid to obtain a dark green powder, which is an oxygen vacancy-rich NiFe-LDH@CoNi-LDH composite material (Ov-NiFe-LDH@CoNi-LDH composite material).

[0016] Preferably, the usage ratio of nickel sulfate, ferrous sulfate, sodium borohydride and deionized water in S1 is 297.5 mg: 314.7 mg: 1200 mg: 20 mL; the magnetic stirring time is 10 min to 60 min, and the rotation speed is 400 r / min to 600 r / min.

[0017] Preferably, the centrifugal speed in S2 is 5000r / min~8000r / min, and the centrifugal time is 2min~5min; the washing method is: washing with deionized water for 3~4 times, and then washing with anhydrous ethanol for 3~4 times; the drying temperature is 60℃~70℃, and the drying time is 12h~24h.

[0018] Preferably, the usage ratio of cobalt nitrate and methanol in S3 is 2.91 g:250 mL; the magnetic stirring time is 10 min to 30 min, and the rotation speed is 400 r / min to 600 r / min.

[0019] Preferably, the usage ratio of 2-methylimidazole and methanol in S4 is 3.28 g:250 mL; the magnetic stirring time is 10 min to 30 min, and the rotation speed is 400 r / min to 600 r / min.

[0020] Preferably, the aging time in S5 is 12h to 36h, the centrifugal speed is 5000r / min to 8000r / min, and the centrifugal time is 2min to 5min; the washing method is: washing with methanol for 3 to 4 times, and then washing with anhydrous ethanol for 3 to 4 times; the drying temperature is 60°C to 70°C, and the drying time is 12h to 24h.

[0021] Preferably, the dosage ratio of NiFe-LDH, nickel nitrate and anhydrous ethanol in S6 is 10 mg:900 mg:25 mL; the stirring time is 10 min to 30 min, and the rotation speed is 400 r / min to 600 r / min.

[0022] Preferably, the dosage ratio of ZIF-67 and anhydrous ethanol in S7 is 200 mg:100 mL; the stirring time is 1 h to 3 h, the centrifugal speed is 5000 r / min to 8000 r / min, and the centrifugal time is 2 min to 5 min; the washing method is: washing with anhydrous ethanol 6 to 7 times; the drying temperature is 60°C to 70°C, and the drying time is 12 h to 24 h.

[0023] Preferably, the amount ratio of sodium borohydride, sodium hydroxide and deionized water in the sodium borohydride aqueous solution containing sodium hydroxide in S8 is 378.3 mg: 200 mg: 20 mL; the stirring time is 0.5 h to 1.5 h, and the rotation speed is 400 r / min to 600 r / min; the centrifugal speed is 5000 r / min to 8000 r / min, and the centrifugal time is 2 min to 5 min; the washing method is: after washing with methanol for 3 to 4 times, washing with anhydrous ethanol for 3 to 4 times; the drying temperature is 60°C to 70°C, and the drying time is 12 h to 24 h.

[0024] The present invention also provides an application of the oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material prepared by the above method, wherein the oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material is applied in a supercapacitor positive electrode; at 1A·g -1 The specific capacitance is 1307.2F·g at a current density of -1 ~1417.6F·g -1 , after 5000 cycles, the capacitance retention rate is 70.5% to 82.7%.

[0025] The present invention uses ZIF-67 as a template, converts it into CoNi-LDH at a specific point, and anchors NiFe-LDH on its surface to reduce the stacking of LDH sheets during the charge and discharge process. The subsequent sodium borohydride-assisted reduction strategy successfully introduces oxygen defects, thereby effectively improving the conductivity and cycle performance of the material.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention uses ZIF-67 as a precursor, and uses a clever etching technique to anchor NiFe-LDH nanoparticles on CoNi-LDH with a dodecahedral morphology. The subsequent sodium borohydride-assisted reduction strategy successfully prepares an oxygen-defect-rich Ov-NiFe-LDH@CoNi-LDH composite material, wherein oxygen defects can increase electrochemical active sites and reduce the resistance of the material itself, thereby improving the electrochemical reaction kinetics. The electrode material prepared by this method of precisely constructing surface defects has high specific capacitance, good rate performance, and stable cycle performance, which has practical guiding significance for the preparation of positive electrode materials for supercapacitors. The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the XRD pattern of Ov-NiFe-LDH@CoNi-LDH prepared in Example 1 of the present invention and the corresponding standard card.

[0029] Figure 2 This is the SEM image of Ov-NiFe-LDH@CoNi-LDH prepared in Example 1 of the present invention.

[0030] Figure 3 Cyclic voltammograms of Ov-NiFe-LDH@CoNi-LDH prepared in Example 1 of the present invention at different scan rates.

[0031] Figure 4 This is a constant current charge and discharge diagram of Ov-NiFe-LDH@CoNi-LDH prepared in Example 1 of the present invention at different current densities.

[0032] Figure 5 This is a cycle performance diagram of Ov-NiFe-LDH@CoNi-LDH prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] Example 1

[0034] The preparation method of the oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material of this embodiment is as follows:

[0035] S1. Mix 297.5 mg of nickel sulfate, 314.7 mg of ferrous sulfate and 20 mL of deionized water, stir magnetically at a speed of 400 r / min for 60 min, slowly add 1200 mg of sodium hydroxide solution, adjust the pH to 6.5, then quickly add 1200 mg of sodium borohydride, continue magnetic stirring, and obtain solution A;

[0036] S2, after centrifuging the solution A obtained in S1 at a speed of 8000 r / min for 2 minutes, washing the obtained solid matter, and drying it at a temperature of 60° C. for 24 hours, the obtained black powder is named NiFe-LDH; the washing method is: washing with deionized water for 3 times, and then washing with anhydrous ethanol for 3 times;

[0037] S3, 2.91 g of cobalt nitrate was mixed with 250 mL of methanol, and magnetic stirring was performed at a speed of 400 r / min for 30 min to obtain solution B;

[0038] S4, 3.28 g of 2-methylimidazole was mixed with 250 mL of methanol, and the mixture was magnetically stirred at a speed of 400 r / min for 30 min to obtain a solution C, and the solution C was transferred to the solution B obtained in S3, and the mixture was magnetically stirred at a speed of 400 r / min for 30 min to obtain a solution D;

[0039] S5, aging the solution D obtained in S4 for 36 hours, then centrifuging at a speed of 8000 r / min for 2 minutes, washing the obtained solid matter, and drying at a temperature of 60° C. for 24 hours to obtain a purple powder, named ZIF-67; the washing method is: washing with methanol for 3 times, and then washing with anhydrous ethanol for 3 times;

[0040] S6, dispersing 10 mg of NiFe-LDH obtained in S2 in 25 mL of anhydrous ethanol, then adding 900 mg of nickel nitrate, stirring at a speed of 400 r / min for 30 min, to obtain solution E;

[0041] S7, dispersing 200 mg of ZIF-67 obtained in S5 in 100 mL of anhydrous ethanol to obtain solution F, transferring the solution F to solution E obtained in S6, reacting for 3 h with magnetic stirring, and then centrifuging at a speed of 8000 r / min for 2 min, washing the obtained solid with anhydrous ethanol for 6 times, and drying at a temperature of 60° C. for 24 h to obtain a green powder, named NiFe-LDH@CoNi-LDH;

[0042] S8. Immerse 50 mg of the NiFe-LDH@CoNi-LDH obtained in S7 into an aqueous sodium borohydride solution containing sodium hydroxide and stir. After the reaction is completed, centrifuge the solution. Wash the solid and dry it at 60°C for 24 hours to obtain a dark green powder, which is an oxygen vacancy-rich NiFe-LDH@CoNi-LDH composite material (Ov-NiFe-LDH@CoNi-LDH composite material). The aqueous sodium borohydride solution containing sodium hydroxide contains 378.3 mg of sodium borohydride, 200 mg of sodium hydroxide and 20 mL of deionized water. This step produces oxygen vacancies, forming a dodecahedral morphology with surface-loaded spheres and single-crystal surface defects.

[0043] This embodiment also provides an application of the Ov-NiFe-LDH@CoNi-LDH composite material prepared by the above method, and the Ov-NiFe-LDH@CoNi-LDH composite material is applied in the positive electrode of a supercapacitor.

[0044] The alkaline etching method selected in this embodiment is simple, and ZIF-67 is etched by introducing nickel nitrate hydrolysis to produce protons, and NiFe-LDH is anchored therein, forming a very unique dodecahedral morphology of surface-loaded spheres, and the structure uses ZIF-67 as a self-template to effectively suppress the self-aggregation effect of NiFe-LDH nanoparticles, and this special load structure is not easy to collapse or agglomerate during the charge and discharge cycle, and is more stable. The subsequent sodium borohydride-assisted reduction strategy successfully introduced oxygen defects, and these oxygen vacancies not only increased the exposure of the active sites of the material, but also promoted charge transfer, thereby achieving efficient redox reactions. Therefore, the material has excellent electrochemical properties such as high specific capacitance, high rate performance and good cycle stability, and can be widely used in the field of supercapacitor positive electrode materials.

[0045] Figure 1This is the XRD pattern of Ov-NiFe-LDH@CoNi-LDH prepared in this embodiment and the corresponding standard card. As shown in the figure, the diffraction peaks of Ov-NiFe-LDH@CoNi-LDHs at 2θ=11.6°, 23.3°, 34.9°, 60.9°, 62.3°, etc. can be attributed to the characteristic diffraction peaks of crystal planes such as (003), (006), (012), (110), and (113). These peaks are all characteristic diffraction peaks of NiCo-LDH, which shows that the material prepared in this embodiment is a PBA@CoNi-LDH-CQDs composite material.

[0046] Figure 2 This is a scanning electron microscope image of Ov-NiFe-LDH@CoNi-LDH prepared in this embodiment (the large image is the main view, and the inset in the upper right corner is the side view). It can be seen from the scanning electron microscope image that the material retains the dodecahedral morphology while assembling the NiFe-LDH nanoparticles to form a unique anchoring structure. In the process of introducing oxygen vacancies, the crystal plane is selectively etched to form a dodecahedral morphology with surface-loaded spheres and single-crystal surface defects. This structure increases the contact area with the electrolyte, thereby improving the electrochemical performance of the material.

[0047] Figure 3 The cyclic voltammetry curves (CV curves) of Ov-NiFe-LDH@CoNi-LDH prepared in this embodiment at different scan rates. It can be seen from the CV curve that there are obvious redox peaks, which can prove that the material is a typical pseudocapacitive material. In addition, as the scan rate increases, the peak current of the redox peak increases significantly, indicating that the redox rate on the electrode is accelerated; at the same time, the overall shape of the curve does not change much, and the corresponding redox peak remains good, indicating that the polarization phenomenon of the electrode is not obvious.

[0048] Figure 4 The constant current charge and discharge diagram of Ov-NiFe-LDH@CoNi-LDH prepared in this example at different current densities. -1 The specific capacitances at different current densities are 1417.6, 1299.2, 1209.6, 1104.0, and 928.0 F·g -1 , indicating that the material has a high specific capacitance. And the current density is 10A·g -1 The specific capacitance can still maintain 1A·g -1 The initial specific capacitance at a current density of 65.5% also indicates that the material has excellent rate performance.

[0049] Figure 5 This is the cycle performance diagram of Ov-NiFe-LDH@CoNi-LDH prepared in this example.

[0050] After 5000 cycles, the specific capacitance of Ov-NiFe-LDH@CoNi-LDH can still maintain the initial

[0051] 82.7%, indicating that the material has good cycle stability.

[0052] The Ov-NiFe-LDH@CoNi-LDH structure prepared in this embodiment retains the unique dodecahedral morphology of the core ZIF-67 material. Through a clever etching method, nickel nitrate hydrolysis is introduced to produce protons to etch ZIF-67. At the same time, NiFe-LDH nanoparticles are assembled. The subsequent sodium borohydride-assisted reduction strategy successfully prepares the oxygen-deficient Ov-NiFe-LDH@CoNi-LDH composite material. The prepared electrode material has high specific capacitance, good rate performance, and stable cycle performance, which has practical guiding significance for the preparation of positive electrode materials for supercapacitors.

[0053] Example 2

[0054] The preparation method of the oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material of this embodiment is as follows:

[0055] S1. Mix 297.5 mg of nickel sulfate, 314.7 mg of ferrous sulfate and 20 mL of deionized water, stir magnetically at a speed of 600 r / min for 10 min, then slowly add 1200 mg of sodium hydroxide solution, adjust the pH to 6.5, then quickly add 1200 mg of sodium borohydride, continue magnetic stirring, and obtain solution A;

[0056] S2, after centrifuging the solution A obtained in S1 at a speed of 5000 r / min for 5 minutes, washing the obtained solid matter, and drying it at a temperature of 70° C. for 12 hours, the obtained black powder is named NiFe-LDH; the washing method is: washing with deionized water for 4 times, and then washing with anhydrous ethanol for 4 times;

[0057] S3, 2.91 g of cobalt nitrate was mixed with 250 mL of methanol, and magnetic stirring was performed at a speed of 600 r / min for 10 min to obtain solution B;

[0058] S4, 3.28 g of 2-methylimidazole was mixed with 250 mL of methanol, and the mixture was magnetically stirred at a speed of 600 r / min for 10 min to obtain a solution C, and the solution C was transferred to the solution B obtained in S3, and the mixture was magnetically stirred at a speed of 600 r / min for 10 min to obtain a solution D;

[0059] S5, aging the solution D obtained in S4 for 12 hours, then centrifuging at a speed of 5000 r / min for 5 minutes, washing the obtained solid matter, and drying it at a temperature of 70° C. for 12 hours to obtain a purple powder named ZIF-67; the washing method is: washing with methanol 4 times, and then washing with anhydrous ethanol 4 times;

[0060] S6, dispersing 10 mg of NiFe-LDH obtained in S2 in 25 mL of anhydrous ethanol, then adding 900 mg of nickel nitrate, stirring at a rotation speed of 600 r / min for 10 min, to obtain solution E;

[0061] S7, dispersing 200 mg of ZIF-67 obtained in S5 in 100 mL of anhydrous ethanol to obtain solution F, transferring the solution F to solution E obtained in S6, reacting for 1 h with magnetic stirring, and then centrifuging at a speed of 5000 r / min for 5 min, washing the obtained solid with anhydrous ethanol for 7 times, and drying at a temperature of 70° C. for 12 h to obtain a green powder, named NiFe-LDH@CoNi-LDH;

[0062] S8. Immerse 50 mg of NiFe-LDH@CoNi-LDH obtained in S7 into an aqueous solution of sodium borohydride containing sodium hydroxide and stir. After the reaction is completed, centrifuge the mixture. Wash the solid and dry it at 70°C for 12 hours to obtain a dark green powder, which is an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material (Ov-NiFe-LDH@CoNi-LDH composite material). The aqueous solution of sodium borohydride containing sodium hydroxide contains 378.3 mg of sodium borohydride, 200 mg of sodium hydroxide and 20 mL of deionized water.

[0063] This embodiment also provides an application of the Ov-NiFe-LDH@CoNi-LDH composite material prepared by the above method, and the Ov-NiFe-LDH@CoNi-LDH composite material is applied in the positive electrode of a supercapacitor.

[0064] The Ov-NiFe-LDH@CoNi-LDH composite material prepared in this example has a high -1 The best performance is 1307.2F·g -1 Excellent specific capacitance, and at 10A·g -1 The capacitance retention rate is 55.1%, showing excellent rate performance. After 5000 cycles, the capacitance retention rate is still 70.5%.

[0065] Comparative Example 1

[0066] The preparation method of the NiFe-LDH@CoNi-LDH composite material (material without oxygen vacancies) of this comparative example is:

[0067] S1. Mix 297.5 mg of nickel sulfate, 314.7 mg of ferrous sulfate and 20 mL of deionized water, stir magnetically at a speed of 600 r / min for 10 min, then slowly add 1200 mg of sodium hydroxide solution, adjust the pH to 6.5, then quickly add 1200 mg of sodium borohydride, continue magnetic stirring, and obtain solution A;

[0068] S2, after centrifuging the solution A obtained in S1 at a speed of 5000 r / min for 5 minutes, washing the obtained solid matter, and drying it at a temperature of 70° C. for 12 hours, the obtained black powder is named NiFe-LDH; the washing method is: washing with deionized water for 4 times, and then washing with anhydrous ethanol for 4 times;

[0069] S3, 2.91 g of cobalt nitrate was mixed with 250 mL of methanol, and magnetic stirring was performed at a speed of 600 r / min for 10 min to obtain solution B;

[0070] S4, 3.28 g of 2-methylimidazole was mixed with 250 mL of methanol, and the mixture was magnetically stirred at a speed of 600 r / min for 10 min to obtain a solution C, and the solution C was transferred to the solution B obtained in S3, and the mixture was magnetically stirred at a speed of 600 r / min for 10 min to obtain a solution D;

[0071] S5, aging the solution D obtained in S4 for 12 hours, then centrifuging at a speed of 5000 r / min for 5 minutes, washing the obtained solid matter, and drying it at a temperature of 60° C. to 70° C. for 12 hours to obtain a purple powder, named ZIF-67; the washing method is: washing with methanol 4 times, and then washing with anhydrous ethanol 4 times;

[0072] S6, dispersing 10 mg of NiFe-LDH obtained in S2 in 25 mL of anhydrous ethanol, then adding 900 mg of nickel nitrate, stirring at a speed of 600 r / min for 10 min, to obtain solution E;

[0073] S7. Disperse 200 mg of ZIF-67 obtained in S5 in 100 mL of anhydrous ethanol to obtain solution F. Transfer the solution F to solution E obtained in S6, react for 1 h with magnetic stirring, and then centrifuge for 5 min at a speed of 5000 r / min. Wash the obtained solid with anhydrous ethanol for 7 times and dry it at 70°C for 12 h to obtain a green powder named NiFe-LDH@CoNi-LDH. The NiFe-LDH@CoNi-LDH is a material without oxygen vacancies, and its morphology is as follows: the surface-loaded spheres are complete dodecahedrons, which are used in the positive electrode of supercapacitors. At 1 A·g -1 At a current density of 1228.6F·g -1 , 10A·g -1 The capacitance retention rate is 61.2% at 1000 cycles and 50.3% after 5000 cycles.

[0074] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material, characterized in that: The method is: S1. Mix nickel sulfate, ferrous sulfate and deionized water and stir them magnetically, then add sodium hydroxide solution, adjust the pH to 6.5, then add sodium borohydride, and continue stirring magnetically to obtain solution A; S2, after centrifuging the solution A obtained in S1, washing and drying the obtained solid matter, the obtained black powder is named NiFe-LDH; S3, mixing cobalt nitrate and methanol, and performing magnetic stirring to obtain solution B; S4, mixing 2-methylimidazole and methanol, and stirring magnetically to obtain solution C, transferring the solution C to solution B obtained in S3, and stirring magnetically to obtain solution D; S5, aging the solution D obtained in S4, and then centrifuging it, washing and drying the obtained solid matter to obtain a purple powder, named ZIF-67; S6, dispersing the NiFe-LDH obtained in S2 in anhydrous ethanol, then adding nickel nitrate, and stirring to obtain a solution E; S7, dispersing the ZIF-67 obtained in S5 in anhydrous ethanol to obtain a solution F, transferring the solution F to the solution E obtained in S6, reacting by magnetic stirring, and then centrifuging, washing and drying the obtained solid to obtain a green powder, named NiFe-LDH@CoNi-LDH; S8. Immerse the NiFe-LDH@CoNi-LDH obtained in S7 into an aqueous solution of sodium borohydride containing sodium hydroxide and stir. After the reaction is completed, centrifuge the solution. Wash and dry the solid to obtain a dark green powder, which is the oxygen vacancy-NiFe-LDH@CoNi-LDH composite material.

2. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The usage ratio of nickel sulfate, ferrous sulfate, sodium borohydride and deionized water in S1 is 297.5 mg: 314.7 mg: 1200 mg: 20 mL; the magnetic stirring time is 10 min to 60 min, and the rotation speed is 400 r / min to 600 r / min.

3. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The centrifugal speed in S2 is 5000r / min~8000r / min, and the centrifugal time is 2min~5min; the washing method is: washing with deionized water for 3~4 times, and then washing with anhydrous ethanol for 3~4 times; the drying temperature is 60℃~70℃, and the drying time is 12h~24h.

4. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The amount ratio of cobalt nitrate and methanol in S3 is 2.91 g:250 mL; the magnetic stirring time is 10 min to 30 min, and the rotation speed is 400 r / min to 600 r / min.

5. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The usage ratio of 2-methylimidazole and methanol in S4 is 3.28 g:250 mL; the magnetic stirring time is 10 min to 30 min, and the rotation speed is 400 r / min to 600 r / min.

6. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The aging time in S5 is 12h to 36h, the centrifugal speed is 5000r / min to 8000r / min, and the centrifugal time is 2min to 5min; the washing method is: washing with methanol for 3 to 4 times, and then washing with anhydrous ethanol for 3 to 4 times; the drying temperature is 60℃ to 70℃, and the drying time is 12h to 24h.

7. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The dosage ratio of NiFe-LDH, nickel nitrate and anhydrous ethanol in S6 is 10 mg:900 mg:25 mL; the stirring time is 10 min to 30 min, and the rotation speed is 400 r / min to 600 r / min.

8. The method for preparing an oxygen vacancy-rich NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The dosage ratio of ZIF-67 and anhydrous ethanol in S7 is 200 mg:100 mL; the stirring time is 1 h to 3 h, the centrifugal speed is 5000 r / min to 8000 r / min, and the centrifugal time is 2 min to 5 min; the washing method is: washing with anhydrous ethanol 6 to 7 times; the drying temperature is 60°C to 70°C, and the drying time is 12 h to 24 h.

9. The method for preparing an oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material according to claim 1, characterized in that: The amount ratio of sodium borohydride, sodium hydroxide and deionized water in the sodium borohydride aqueous solution containing sodium hydroxide in S8 is 378.3 mg: 200 mg: 20 mL; the stirring time is 0.5 h to 1.5 h, and the rotation speed is 400 r / min to 600 r / min; the centrifugal speed is 5000 r / min to 8000 r / min, and the centrifugal time is 2 min to 5 min; the washing method is: after washing with methanol for 3 to 4 times, washing with anhydrous ethanol for 3 to 4 times; the drying temperature is 60°C to 70°C, and the drying time is 12 h to 24 h.

10. An application of the oxygen-rich vacancy-NiFe-LDH@CoNi-LDH composite material prepared by the method according to any one of claims 1 to 9, characterized in that: The oxygen vacancy-rich NiFe-LDH@CoNi-LDH composite material is used in the positive electrode of supercapacitors; at 1A·g -1 The specific capacitance is 1307.2F·g at a current density of -1 ~1417.6F·g -1 , after 5000 cycles, the capacitance retention rate is 70.5% to 82.7%.

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