Preparation method and application of ZnNiCoLDH / MXene composite material

Abstract

The invention belongs to the technical field of composite material preparation, and particularly relates to a preparation method and application of a ZnNiCoLDH / MXene composite material, ZnO is used as a conductive support frame, ZnO / ZIF-67 synthesized by adopting an oil bath method is used as a precursor, LDH is obtained through etching, then the LDH is compounded with an MXene material by adopting an electrostatic self-assembly method, and the ZnNiCoLDH / MXene composite material is obtained. The composite material is applied to preparation of a supercapacitor positive electrode, the obtained positive electrode material takes an MXene material as a conductive substrate, LDH nanosheets can be supported, agglomeration is prevented, exposure of active sites is increased, and the conductivity and the structural stability of the positive electrode material are improved; the LDH and the MXene material have a synergistic effect, the MXene material has high conductivity to promote electron transport, and the LDH can provide high pseudocapacitance, so that the electrochemical performance of the positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material preparation, and specifically relates to a preparation method and application of a ZnNiCoLDH / MXene composite material. Background Art

[0002] Supercapacitors, also known as electrochemical capacitors, are a new type of energy storage device between traditional capacitors and rechargeable batteries. They have the characteristics of rapid charging and discharging of capacitors and the energy storage characteristics of batteries. The core structure of supercapacitors is composed of high-specific surface area electrodes, electrolytes and diaphragms. They perform well in instantaneous high-power scenarios and are widely used in electric vehicle energy recovery, grid frequency modulation, backup power for smart devices and power supply in extreme environments. The electrode material of supercapacitors is a key factor affecting their performance. The positive electrode LDH material usually has a high theoretical specific capacity, but poor conductivity, large volume change and poor cycle stability.

[0003] MXene is a two-dimensional material and a research result of Drexel University in the United States. Unlike traditional batteries, this material provides more channels for the movement of ions, greatly increasing the speed of ion movement; MXene has also shown significant advantages in the field of supercapacitors. Its high conductivity and high specific surface area give the electrodes excellent charge transfer capabilities and high specific capacitance; the controllable surface functional groups enhance the interaction with the electrolyte and improve the contribution of pseudocapacitance; as a two-dimensional material, MXene has good conductivity but is easy to stack, resulting in a reduction in active sites and lower material performance. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a preparation method and application of a ZnNiCoLDH / MXene composite material. ZnO is used as a conductive support frame, and ZnO / ZIF-67 is synthesized as a precursor by an oil bath method. LDH is obtained by etching and then compounded with MXene by an electrostatic self-assembly method to obtain a ZnNiCoLDH / MXene composite material. The composite material is used in the preparation of a supercapacitor positive electrode.

[0005] To solve the above problems, the present invention provides a method for preparing a ZnNiCoLDH / MXene composite material, which is as follows: S1. Preparation of MXene suspension: LiF was dissolved in hydrochloric acid solution and magnetically stirred to obtain solution a. Titanium aluminum carbide was slowly added and stirred continuously in an oil bath to obtain solution b. The solution was centrifuged at 8000 rpm for 2 min. The supernatant liquid was removed to obtain a precipitate. The precipitate was dried and dissolved in ethanol solution. The solution was ultrasonically treated in an ice bath under argon flow for 1 h. The solution was centrifuged at 8000 rpm for 5 min. The supernatant liquid was collected to obtain a MXene suspension. Wherein, hydrochloric acid solution and ethanol solution refer to aqueous hydrochloric acid solution and aqueous ethanol solution; S2. Preparation of ZnO: (CH3COO)2Zn and cetyltrimethylammonium bromide were mixed, deionized water was added, and magnetic stirring was performed for 0.5 h to obtain solution c. Solid NaOH was added and magnetic stirring was continued for 2 h to obtain solution d. The mixture was centrifuged at 8000 rpm for 2 min, and the supernatant was removed to obtain a precipitate. The precipitate was washed and dried to obtain a white powdery substance, namely ZnO. S3. Preparation of ZnO / ZIF67: Dissolve 2-methylimidazole in N,N-dimethylformamide solution and stir magnetically until homogeneous to obtain solution e. Add Co(NO3)2·6H2O and the ZnO described in S2 and continue stirring magnetically until homogeneous to obtain solution f. Heat and stir in an oil bath to obtain solution g. Centrifuge at 5000-8000 rpm for 2-5 min, remove the supernatant, and obtain a precipitate. Wash and dry the precipitate to obtain a purple powder, namely ZnO / ZIF67. S4. Preparation of ZnNiCoLDH: Dissolve the ZnO / ZIF67 described in S3 in an ethanol solution and disperse it uniformly by ultrasonication to obtain solution h. Add Co(NO3)2·6H2O and Ni(NO3)2·6H2O to solution h in sequence, and stir until uniform. Then add hexamethylenetetramine and continue stirring until uniform to obtain solution j. Reflux at 80°C for 1 hour, cool to room temperature, and centrifuge at 5000-8000 rpm for 2-5 minutes. Remove the supernatant to obtain a precipitate, wash, and dry to obtain a blue-green powder, namely ZnNiCoLDH. S5. Dilute the MXene suspension described in S1 with deionized water to a concentration of 1 mg / mL to obtain solution k; take 40 mg of the ZnNiCoLDH described in S4 and dissolve it in 40 mL of deionized water, ultrasonically disperse it until uniform, and magnetically stir it for 1-2 hours to obtain solution l. Add solution k to solution 1 and magnetically stir it until uniform to obtain solution m. Centrifuge at 5000-8000 r / min for 2-5 minutes, remove the supernatant liquid, and obtain a precipitate. After washing and drying, a green powder is obtained, which is the ZnNiCoLDH / MXene composite material.

[0006] Preferably, the amount ratio of LiF, hydrochloric acid solution and titanium aluminum carbide described in S1 is 1g: 20mL: 1~3g; the oil bath conditions are: temperature 35~45°C, time 24~48h; drying temperature 50~60°C, time 24~28h; the amount of ethanol solution used is 50 mL / g.

[0007] Preferably, it is characterized in that the amount ratio of (CH3COO)2Zn, deionized water, hexadecyltrimethylammonium bromide and NaOH solid described in S2 is 1.5g: 60mL: 5.4g: 1g; the washing method is: washing with water and anhydrous ethanol 2 to 3 times respectively; the drying time is 12 to 24h, and the temperature is 60 to 70°C.

[0008] Preferably, it is characterized in that the amount ratio of ZnO, Co(NO3)2·6H2O, 2-methylimidazole and N,N-dimethylformamide solution described in S3 is 0.5g: 0.9g: 4g: 80~100 mL, the oil bath conditions are: temperature 60~70℃, time 8~12h; the washing method is: washing with N,N-dimethylformamide and anhydrous ethanol 2~3 times respectively; the drying time is 12~24h, and the temperature is 60~70℃.

[0009] Preferably, it is characterized in that the usage ratio of ZnO / ZIF67, ethanol solution, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, and hexamethylenetetramine described in S4 is 4mg: 5mL: 10mg: 10mg: 6~10mg; the ultrasonic dispersion time is 20~40 min; the washing method is: washing with anhydrous ethanol 2~3 times; the drying temperature is 60~70°C, and the time is 12~24h.

[0010] Preferably, it is characterized in that the mixing volume ratio of solution k and solution 1 described in S5 is 1:10~15; the washing method is: washing with deionized water and anhydrous ethanol respectively 2~3 times; the drying temperature is 60~70℃, and the time is 12~24h.

[0011] The ZnNiCoLDH / MXene composite material prepared by the technical solution of the present invention is applied to the preparation of supercapacitor positive electrode materials.

[0012] MXene materials have good conductivity and high mechanical strength, but their specific capacity is not as good as LDH. The combination of the two can complement each other's advantages and disadvantages; MXene materials, as a conductive substrate, can support LDH nanosheets, prevent agglomeration, and increase the exposure of active sites, which can improve the conductivity and structural stability of MXene materials; secondly, there is a synergistic effect between LDH and MXene materials, such as the high conductivity of MXene materials promotes electron transfer, and LDH provides high pseudocapacitance; in addition, the flexible structure of MXene materials can alleviate the volume expansion of LDH during charging and discharging, thereby extending the cycle life of the electrode.

[0013] The technical solution of the present invention improves the stacking structure of MXene materials through the electrostatic self-assembly method and optimizes the cyclic stability of MXene materials; the prepared ZnNiCoLDH / MXene composite material has high conductivity and can promote electron transmission, solving the stacking problem of MXene materials.

[0014] The prepared ZnNiCoLDH / MXene composite material is applied to the preparation of supercapacitor positive electrode materials. First, MXene material, as a conductive substrate, can support LDH nanosheets, prevent agglomeration, and increase the exposure of active sites; this improves the conductivity and structural stability of the positive electrode material; secondly, there is a synergistic effect between LDH and MXene materials, such as the high conductivity of MXene material promotes electron transport, and LDH provides high pseudocapacitance, which improves the electrochemical performance of the positive electrode material.

[0015] Compared with the prior art, the present invention has the following advantages: 1. The technical solution of the present invention uses a heating reflux method to form a ZIF framework with flower-shaped ZnO as the substrate and coordinate with ZIF to form a uniformly dispersed ZIF framework. ZnO@ZIF67 is prepared as a precursor by a one-step oil bath heating method, which can accurately guide the growth of LDH to form a high specific surface area, porous or hierarchical structure, significantly increasing the exposure of active sites of MXene materials and improving their ion transport efficiency. Zinc, nickel, and cobalt optimize the electronic structure of LDH through electronic coupling and enhance redox activity. ZnNiCoLDH composite materials are formed by metal salt etching. The electrostatic self-assembly method is used to achieve the composite of MXene materials, giving MXene materials the advantages of high specific surface area and fast ion / electron transport channels, thereby improving the electrochemical energy storage and mechanical stability of MXene materials. 2. The ZnNiCoLDH / MXene composite material prepared by the technical solution of the present invention has the superior performance of high specific capacity. It is applied to the preparation of supercapacitor positive electrode materials. The resulting ZnNiCoLDH / MXene composite electrode forms an LDH nanosheet array through a metal ion-assisted etching strategy, which is evenly distributed on the MXene material substrate, solving the stacking problem of the MXene material and improving its electrochemical performance. At the same time, it improves and improves the specific capacity and rate response performance of the electrode material, so that the supercapacitor has high energy density and ultra-long service life; 3. Compared with the prior art, the ZnNiCoLDH / MXene composite material prepared by the technical solution of the present invention improves the performance of the MXene material, so that the MXene material has the advantages of inhibiting interlayer stacking, enhancing interfacial conductivity and chemical stability. The ZnNiCoLDH / MXene composite material is applied to the preparation of supercapacitor positive electrode materials, which improves the energy storage performance of the capacitor and extends the cycle life of the capacitor.

[0016] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD pattern of the ZnNiCoLDH / MXene composite material prepared in Example 1 of the present invention; Figure 2 The electrode material prepared from the ZnNiCoLDH / MXene composite material prepared in Example 1 of the present invention was subjected to a voltage range of 0-0.5 V and a scan rate of 10 mV·s -1 , 20mV·s -1 、30mV·s -1 , 50mV·s -1 and 70mV·s -1 Cyclic voltammogram below; Figure 3 This is a graph showing the relationship between time and voltage when the ZnNiCoLDH / MXene composite material prepared in Example 1 of the present invention is charged and discharged by applying a constant current. DETAILED DESCRIPTION

[0018] Example 1 This embodiment discloses a method for preparing a ZnNiCoLDH / MXene composite material, which specifically includes the following steps: S1. Preparation of MXene suspension: 1 g of LiF was dissolved in 20 mL of hydrochloric acid solution and stirred magnetically to obtain solution a. 1 g of titanium aluminum carbide was slowly added with continuous stirring. The mixture was reacted in an oil bath at 35°C for 48 h to obtain solution b. The obtained solution b was centrifuged at 8000 r / min for 2 min, and the supernatant was removed to obtain a precipitate. The precipitate was dried at 50°C for 28 h and dissolved in ethanol at a dosage of 50 mL / g. The precipitate was ultrasonically treated in an ice bath under argon flow for 1 h. The precipitate was centrifuged at 8000 r / min for 5 min, and the supernatant was collected to obtain a MXene suspension. S2. Preparation of ZnO: 1.5 g of (CH3COO)2Zn was mixed with 5.4 g of hexadecyltrimethylammonium bromide, 60 mL of deionized water was added, and magnetic stirring was performed for 0.5 h to obtain solution c. 1 g of solid NaOH was then added, and magnetic stirring was continued for 2 h to obtain solution d. Solution d was centrifuged at 8000 rpm for 2 min, and the supernatant liquid was removed to obtain a precipitate. The precipitate was washed twice with water and twice with anhydrous ethanol, respectively, and dried at 60°C for 24 h to obtain a white powdery substance, namely ZnO. S3. Preparation of ZnO / ZIF67: Dissolve 4 g of 2-methylimidazole in 80 mL of N,N-dimethylformamide solution and stir magnetically until uniform to obtain solution e. Add 0.9 g of Co(NO3)2·6H2O and 0.5 g of ZnO described in S2 and continue stirring magnetically until uniform to obtain solution f. Heat and stir in an oil bath at 60°C for 12 h to obtain solution g. Centrifuge solution g at 5000 rpm for 5 min, remove the supernatant and obtain a precipitate. Wash the precipitate twice with N,N-dimethylformamide and anhydrous ethanol, respectively, and dry at 60°C for 24 h to obtain a purple powder, namely ZnO / ZIF67. S4. Preparation of ZnNiCoLDH: 4 mg of ZnO / ZIF67 described in S3 was dissolved in 5 mL of ethanol solution and ultrasonically dispersed for 20 min to obtain solution h. 10 mg of Co(NO3)2·6H2O and 10 mg of Ni(NO3)2·6H2O were added to solution h in sequence, and stirred until uniform. 6 mg of hexamethylenetetramine was added and stirred until uniform to obtain solution j. The obtained solution j was refluxed at 80°C for 1 h, cooled to room temperature, and centrifuged at 5000 r / min for 5 min. The supernatant liquid was removed to obtain a precipitate, which was washed twice with anhydrous ethanol and dried at 60°C for 24 h to obtain a blue-green powder, namely ZnNiCoLDH. S5. Dilute the MXene suspension described in S1 with deionized water to a concentration of 1 mg / mL to obtain solution k; take 40 mg of ZnNiCoLDH described in S4 and dissolve it in 40 mL of deionized water, ultrasonically disperse it for 1 hour, and magnetically stir it for 2 hours to obtain solution l; mix solution k and solution l in a volume ratio of 1:10, and magnetically stir them until uniform to obtain solution m, and then centrifuge solution m at 5000 r / min for 5 minutes, remove the upper liquid, and obtain a precipitate. Wash it twice with deionized water and anhydrous ethanol respectively, and dry it at 60°C for 24 hours to obtain a green powder, which is the ZnNiCoLDH / MXene composite material.

[0019] The ZnNiCoLDH / MXene composite material prepared in Example 1 was applied to the preparation of a supercapacitor positive electrode material. In the prepared positive electrode material, MXene was used as a conductive substrate to support LDH nanosheets, prevent agglomeration, and increase the exposure of active sites; the conductivity and structural stability of the positive electrode material were improved; there was a synergistic effect between LDH and MXene materials, the high conductivity of MXene material promoted electron transport, and LDH provided high pseudocapacitance, thereby improving the electrochemical performance of the positive electrode material.

[0020] Figure 1 The XRD pattern of the ZnNiCoLDH / MXene composite material prepared in Example 1 and the corresponding standard card are shown in the figure. As shown in the figure, the diffraction peak of the ZnNiCoLDH / MXene composite material at 2θ=8.2° can be attributed to the diffraction peak of the (002) crystal plane, which is the characteristic diffraction peak of the MXene material; the diffraction peaks at 2θ=23.1°, 33.5°, 59.9°, etc. can be attributed to the characteristic diffraction peaks of the (006), (101), (110) crystal planes, which are all characteristic diffraction peaks of Ni-LDH; at the same time, the diffraction peaks at 2θ=26.2°, 33.6°, 59.7° can be attributed to (111), (200), (320) Characteristic diffraction peaks of the isocrystalline plane are all characteristic diffraction peaks of ZnCo-LDH. It can be seen that the ZnNiCoLDH / MXene material prepared in this embodiment contains MXene, Ni-LDH, and ZnCo-LDH materials, that is, the ZnNiCoLDH / MXene material is composited by MXene, Ni-LDH, and ZnCo-LDH materials.

[0021] Figure 2 The ZnNiCoLDH / MXene composite material prepared in Example 1 was used in the preparation of the electrode material for the positive electrode of the supercapacitor. The cyclic voltammetry curves (CV curves) of the prepared electrode material at different scan rates were as follows: the voltage range was 0-0.5 V, and the scan rate was 10 mV·s -1、 20mV·s-1 、30mV·s -1 , 50mV·s -1 and 70mV·s -1 ; It can be seen from the CV curve that the prepared electrode material has obvious oxidation-reduction peaks, which shows that the ZnNiCoLDH / MXene composite material is a typical pseudocapacitive material. From the curve in the figure, it can be seen that there are paired oxidation-reduction peaks, which shows that the ZnO@NiCo-LDH composite material has the characteristics of a pseudocapacitive material; and as the scan rate increases, the peak current of the redox peak increases significantly, indicating that the redox rate on the electrode material is accelerated; the faster the redox rate, the better the synergistic optimization performance of the electrode material interface charge transfer and ion diffusion.

[0022] Figure 3 The constant current charge-discharge diagram of the ZnNiCoLDH / MXene composite material prepared in Example 1 at different current densities; the specific capacitance can be calculated using the formula C = mΔV / IΔt; Where, C = mΔV / IΔt m represents: the mass of the material involved in the electrode test (g); ΔV represents: potential window size (V); I represents: the required current (A); Δt represents the time required for the voltage to drop to 0 (s); As can be seen from the figure, as the composite material is charged and discharged, the constant current charge and discharge curve first rises and then falls. It can be concluded that the capacitance of the material is mainly caused by the Faradaic redox reaction, indicating that the electrode material is a pseudocapacitive material; Among them, at 1, 2, 3, 5, and 10 A∙g -1 Under different current densities, the specific capacitance values are calculated to be 1406 F∙g -1 、1385 F∙g -1 、1350 F∙g -1 、1303 F∙g -1 、1137 F∙g -1 , indicating that the prepared ZnNiCoLDH / MXene composite material has a higher specific capacitance; when the current density is 10A∙g -1 When the specific capacitance of the composite material can be maintained at 10A∙g -1 The initial specific capacitance at this current density is 80.8%, which indicates that the prepared ZnNiCoLDH / MXene composite material has good rate performance.

[0023] Example 2 This embodiment discloses a method for preparing a ZnNiCoLDH / MXene composite material, which specifically includes the following steps: S1. Preparation of MXene suspension: 1 g of LiF was dissolved in 20 mL of hydrochloric acid solution and stirred magnetically to obtain solution a. 3 g of titanium aluminum carbide was slowly added with continuous stirring. The mixture was reacted in an oil bath at 45°C for 24 h to obtain solution b. The obtained solution b was centrifuged at 8000 r / min for 2 min, and the supernatant was removed to obtain a precipitate. The precipitate was dried at 60°C for 24 h and dissolved in ethanol at a dosage of 50 mL / g. The precipitate was ultrasonically treated in an ice bath under argon flow for 1 h. The precipitate was centrifuged at 8000 r / min for 5 min, and the supernatant was collected to obtain a MXene suspension. S2. Preparation of ZnO: 1.5 g of (CH3COO)2Zn was mixed with 5.4 g of hexadecyltrimethylammonium bromide, 60 mL of deionized water was added, and magnetic stirring was performed for 0.5 h to obtain solution c. 1 g of solid NaOH was then added, and magnetic stirring was continued for 2 h to obtain solution d. Solution d was centrifuged at 8000 rpm for 2 min, and the supernatant liquid was removed to obtain a precipitate. The precipitate was washed three times with water and three times with anhydrous ethanol, respectively, and dried at 70°C for 12 h to obtain a white powdery substance, namely ZnO. S3. Preparation of ZnO / ZIF67: Dissolve 4 g of 2-methylimidazole in 100 mL of N,N-dimethylformamide solution and stir magnetically until uniform to obtain solution e. Add 0.9 g of Co(NO3)2·6H2O and 0.5 g of ZnO described in S2 and continue stirring magnetically until uniform to obtain solution f. Heat and stir in an oil bath at 70°C for 8 h to obtain solution g. Centrifuge solution g at 8000 rpm for 2 min, remove the supernatant liquid and obtain a precipitate. Wash the precipitate three times with N,N-dimethylformamide and anhydrous ethanol, respectively, and dry at 70°C for 12 h to obtain a purple powder, namely ZnO / ZIF67. S4. Preparation of ZnNiCoLDH: 4 mg of the ZnO / ZIF67 described in S3 was dissolved in 5 mL of ethanol solution and ultrasonically dispersed for 20 min to obtain solution h. 10 mg of Co(NO3)2·6H2O and 10 mg of Ni(NO3)2·6H2O were added to solution h in sequence, and stirred until uniform. 10 mg of hexamethylenetetramine was added and stirred until uniform to obtain solution j. The obtained solution j was refluxed at 80°C for 1 h, cooled to room temperature, and centrifuged at 8000 r / min for 2 min. The supernatant liquid was removed to obtain a precipitate, which was washed three times with anhydrous ethanol and dried at 70°C for 12 h to obtain a blue-green powder, namely ZnNiCoLDH. S5. Dilute the MXene suspension described in S1 with deionized water to a concentration of 1 mg / mL to obtain solution k; take 40 mg of ZnNiCoLDH described in S4 and dissolve it in 40 mL of deionized water, ultrasonically disperse it for 1 hour, and magnetically stir it for 2 hours to obtain solution l; mix solution k and solution l in a volume ratio of 1:15, and magnetically stir them until uniform to obtain solution m. Then centrifuge solution m at 8000 r / min for 2 minutes, remove the upper liquid, and obtain a precipitate. Wash it with deionized water and anhydrous ethanol three times respectively, and dry it at 70°C for 12 hours to obtain a green powder, which is the ZnNiCoLDH / MXene composite material.

[0024] The ZnNiCoLDH / MXene composite material prepared in Example 2 was applied to the preparation of a positive electrode material for a supercapacitor. The prepared positive electrode material had the advantages of high conductivity and long service life.

[0025] Example 3 This embodiment discloses a method for preparing a ZnNiCoLDH / MXene composite material, which specifically includes the following steps: S1. Preparation of MXene suspension: 1 g of LiF was dissolved in 20 mL of hydrochloric acid solution and stirred magnetically to obtain solution a. 2 g of titanium aluminum carbide was slowly added with continuous stirring. The mixture was reacted in an oil bath at 40°C for 35 h to obtain solution b. The obtained solution b was centrifuged at 8000 r / min for 2 min, and the supernatant was removed to obtain a precipitate. The precipitate was dried at 55°C for 26 h and dissolved in ethanol at a dosage of 50 mL / g. The precipitate was ultrasonically treated in an ice bath under argon flow for 1 h. The precipitate was centrifuged at 8000 r / min for 5 min, and the supernatant was collected to obtain a MXene suspension. S2. Preparation of ZnO: 1.5 g of (CH3COO)2Zn was mixed with 5.4 g of hexadecyltrimethylammonium bromide, 60 mL of deionized water was added, and magnetic stirring was performed for 0.5 h to obtain solution c. 1 g of solid NaOH was then added, and magnetic stirring was continued for 2 h to obtain solution d. Solution d was centrifuged at 8000 rpm for 2 min, and the supernatant liquid was removed to obtain a precipitate. The precipitate was washed three times with water and three times with anhydrous ethanol, and dried at 65°C for 18 h to obtain a white powdery substance, namely ZnO. S3. Preparation of ZnO / ZIF67: Dissolve 4 g of 2-methylimidazole in 90 mL of N,N-dimethylformamide solution and stir magnetically until uniform to obtain solution e. Add 0.9 g of Co(NO3)2·6H2O and 0.5 g of ZnO described in S2 and continue stirring magnetically until uniform to obtain solution f. Heat and stir in an oil bath at 65°C for 10 h to obtain solution g. Centrifuge solution g at 8000 rpm for 2 min, remove the supernatant and obtain a precipitate. Wash the precipitate three times with N,N-dimethylformamide and anhydrous ethanol, respectively, and dry at 65°C for 18 h to obtain a purple powder, namely ZnO / ZIF67. S4. Preparation of ZnNiCoLDH: 4 mg of ZnO / ZIF67 described in S3 was dissolved in 5 mL of ethanol solution and ultrasonically dispersed for 20 min to obtain solution h. 10 mg of ZnO and 10 mg of Ni(NO3)2·6H2O were added to solution h in sequence, and stirred until uniform. 8 mg of hexamethylenetetramine was added and stirred until uniform to obtain solution j. The obtained solution j was refluxed at 80°C for 1 h, cooled to room temperature, and centrifuged at 8000 r / min for 2 min. The supernatant was removed to obtain a precipitate, which was washed with anhydrous ethanol three times and dried at 65°C for 20 h to obtain a blue-green powder, namely ZnNiCoLDH. S5. Dilute the MXene suspension described in S1 with deionized water to a concentration of 1 mg / mL to obtain solution k; take 40 mg of ZnNiCoLDH described in S4 and dissolve it in 40 mL of deionized water, ultrasonically disperse it for 1 hour, and magnetically stir it for 2 hours to obtain solution l; mix solution k and solution l in a volume ratio of 1:12, and magnetically stir them until uniform to obtain solution m. Then centrifuge solution m at 8000 r / min for 2 minutes, remove the upper liquid, and obtain a precipitate. Wash it with deionized water and anhydrous ethanol three times respectively, and dry it at 65°C for 20 hours to obtain a green powder, which is the ZnNiCoLDH / MXene composite material.

[0026] The ZnNiCoLDH / MXene composite material prepared in Example 3 was applied to the preparation of a supercapacitor positive electrode material to prepare the obtained positive electrode material, which solved the problems of easy stacking of MXene and few active sites, and improved the performance of the positive electrode material.

[0027] The above description 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 variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a ZnNiCoLDH / MXene composite material, characterized in that: The method is as follows: S1. Preparation of MXene suspension: LiF was dissolved in hydrochloric acid solution and magnetically stirred to obtain solution a. Titanium aluminum carbide was slowly added and stirred continuously in an oil bath to obtain solution b. The solution was centrifuged at 8000 rpm for 2 min. The supernatant liquid was removed to obtain a precipitate. The precipitate was dried and dissolved in ethanol solution. The solution was ultrasonically treated in an ice bath under argon flow for 1 h. The solution was centrifuged at 8000 rpm for 5 min. The supernatant liquid was collected to obtain a MXene suspension. S2. Preparation of ZnO: (CH3COO)2Zn and cetyltrimethylammonium bromide were mixed, deionized water was added, and magnetic stirring was performed for 0.5 h to obtain solution c. Solid NaOH was added and magnetic stirring was continued for 2 h to obtain solution d. The mixture was centrifuged at 8000 rpm for 2 min, and the supernatant was removed to obtain a precipitate. The precipitate was washed and dried to obtain a white powdery substance, namely ZnO. S3. Preparation of ZnO / ZIF67: Dissolve 2-methylimidazole in N,N-dimethylformamide solution and stir magnetically until homogeneous to obtain solution e. Add Co(NO3)2·6H2O and the ZnO described in S2 and continue stirring magnetically until homogeneous to obtain solution f. Heat and stir in an oil bath to obtain solution g. Centrifuge at 5000-8000 rpm for 2-5 min, remove the supernatant, and obtain a precipitate. Wash and dry the precipitate to obtain a purple powder, namely ZnO / ZIF67. S4. Preparation of ZnNiCoLDH: Dissolve the ZnO / ZIF67 described in S3 in an ethanol solution and disperse it uniformly by ultrasonication to obtain solution h. Add Co(NO3)2·6H2O and Ni(NO3)2·6H2O to solution h in sequence, and stir until uniform. Then add hexamethylenetetramine and continue stirring until uniform to obtain solution j. Reflux at 80°C for 1 hour, cool to room temperature, and centrifuge at 5000-8000 r / min for 2-5 minutes. Remove the supernatant to obtain a precipitate, wash, and dry to obtain a blue-green powder, namely ZnNiCoLDH. S5. Dilute the MXene suspension described in S1 with deionized water to a concentration of 1 mg / mL to obtain solution k; take 40 mg of the ZnNiCoLDH described in S4 and dissolve it in 40 mL of deionized water, ultrasonically disperse it until uniform, and magnetically stir it for 1-2 hours to obtain solution l. Add solution k to solution 1 and magnetically stir it until uniform to obtain solution m. Centrifuge at 5000-8000 r / min for 2-5 minutes, remove the supernatant liquid, and obtain a precipitate. After washing and drying, a green powder is obtained, which is the ZnNiCoLDH / MXene composite material.

2. The method for preparing the ZnNiCoLDH / MXene composite material according to claim 1, characterized in that: The amount ratio of LiF, hydrochloric acid solution and titanium aluminum carbide described in S1 is 1g: 20mL: 1-3g; the oil bath conditions are: temperature 35-45°C, time 24-48h; the drying temperature is 50-60°C, time 24-28h; the amount of ethanol solution used is 50 mL / g.

3. The method for preparing the ZnNiCoLDH / MXene composite material according to claim 1, characterized in that: The amount ratio of (CH3COO)2Zn, deionized water, hexadecyltrimethylammonium bromide and NaOH solid described in S2 is 1.5g:60mL:5.4g:1g; the washing method is: washing with water and anhydrous ethanol respectively 2 to 3 times; the drying time is 12 to 24 hours, and the temperature is 60 to 70°C.

4. The method for preparing the ZnNiCoLDH / MXene composite material according to claim 1, wherein: The dosage ratio of ZnO, Co(NO3)2·6H2O, 2-methylimidazole, and N,N-dimethylformamide solution described in S3 is 0.5g: 0.9g: 4g: 80~100 mL, and the oil bath conditions are: temperature 60~70℃, time 8~12h; the washing method is: washing with N,N-dimethylformamide and anhydrous ethanol respectively 2~3 times; the drying time is 12~24h, and the temperature is 60~70℃.

5. The method for preparing the ZnNiCoLDH / MXene composite material according to claim 1, characterized in that: The usage ratio of ZnO / ZIF67, ethanol solution, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, and hexamethylenetetramine described in S4 is 4 mg:5 mL: 10 mg: 10 mg: 6~10 mg; the ultrasonic dispersion time is 20~40 min; the washing method is: washing with anhydrous ethanol 2~3 times; the drying temperature is 60~70℃, and the time is 12~24 h.

6. The method for preparing the ZnNiCoLDH / MXene composite material according to claim 1, characterized in that: The mixed volume ratio of solution k and solution l described in S5 is 1:10~15; the washing method is: washing with deionized water and anhydrous ethanol respectively 2~3 times; the drying temperature is 60~70℃, and the time is 12~24h.

7. An application of a ZnNiCoLDH / MXene composite material, characterized by: The ZnNiCoLDH / MXene composite material prepared by the method according to any one of claims 1 to 6 is applied to the preparation of a supercapacitor positive electrode material.

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