ZnNiCo-LDH with hollow nanocage structure and preparation method and application thereof

Abstract

The application discloses a ZnNiCo-LDH with a hollow nanometer cage structure, and a ZIF-67 with a regular dodecahedron structure is synthesized by taking cobalt nitrate and 2-methyl imidazole as raw materials; a ZIF-67@NiCo-LDH with a core-shell structure is prepared by ZIF-67 and Ni(NO3)2.6H2O; and the ZnNiCo-LDH with the hollow nanometer cage structure can be obtained by the reaction of zinc chloride and the ZIF-67@NiCo-LDH. The preparation method comprises the following steps: 1, preparation of the ZIF-67 with the regular dodecahedron structure; 2, preparation of the ZIF-67@NiCo-LDH with the core-shell structure; and 3, preparation of the ZnNiCo-LDH with the hollow nanometer cage structure. As the application of the super capacitor, the specific capacitance is 1900-2000 F / g when charging and discharging in the range of 0-0.5 V and the discharge current density is 1 A / g; and the capacitance retention rate reaches 73% at 10 A / g relative to the capacitance at 1 A / g.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of supercapacitors, in particular to a ZnNiCo-LDH with a hollow nanocage structure and a preparation method and application thereof. BACKGROUND

[0002] According to the energy storage mechanism of the electrode material, the supercapacitor can be divided into two categories: double-layer supercapacitors EDLC and pseudo-capacitance supercapacitors. The double-layer supercapacitor mainly relies on the electrostatic action to form a double layer on the surface of the electrode and the electrolyte, and stores energy through physical electrostatic adsorption / desorption; and the pseudo-capacitance supercapacitor stores charges through the rapid oxidation-reduction reaction on the surface or near the electrode, and realizes a much higher specific capacitance than the double-layer capacitor.

[0003] Among them, the metal layered double hydroxide LDH in the pseudo-capacitance supercapacitor has the advantages of large interlayer spacing, highly adjustable composition, environmental friendliness and high theoretical specific capacity. The nickel-cobalt layered double hydroxide NiCo-LDH in the metal layered double hydroxide has a high theoretical specific capacitance, but has the problems of uneven morphology, serious agglomeration and poor conductivity, which leads to low capacitance or rapid decay in the charging and discharging process.

[0004] In view of the problems of poor stability and poor conductivity of the NiCo-LDH, the problems can be overcome by compounding with a conductive support such as graphene, carbon cloth and nickel foam;

[0005] In view of the problems of uneven morphology or serious agglomeration in the charging and discharging process, the problems can be solved by constructing a three-dimensional structure to reduce the accumulation of the sheet layer.

[0006] In view of the problems of low capacitance or decay, the problems can be solved by adjusting the micro-morphology of the composite material to provide more exposed active sites, so as to improve the electrochemical performance of the electrode material.

[0007] For example, prior art 1 (Slight Zinc Doping by an Ultrafast Electrodeposition Process Boosts the Cycling Performance of Layered Double Hydroxides for Ultralong-Life-Span Supercapacitors, ACS Applied Materials & Interfaces, 2021, 13(32): 38346-57. DOI: 10.1021 / acsami.1c10386) electrodeposits a polyaniline PANI nanolayer on carbon cloth CC, takes the polyaniline PANI nanolayer as an intermediate layer, and then electrodeposits NiCoZn-LDH on the PANI@CC. The Zn doping enhances the cycle structure stability of the NiCoZn-LDH, the PANI layer enhances the interface interaction between the LDH and the current collector, and by controlling the doping content of Zn ions at 2.9%, the composite electrode achieves the best performance, with a specific capacitance of 1749 F / g and an ultralong life, with a capacitance retention rate of 89% after 40,000 charge-discharge cycles. However, the technical problems existing in this technical solution mainly have two aspects: 1. The composite material with a two-dimensional structure leads to uneven deposition particle size; 2. Agglomeration occurs during the deposition process, resulting in a decrease in specific surface area and a decrease in active reaction sites, ultimately leading to a decrease in electrochemical performance.

[0008] In order to obtain a three-dimensional structure, prior art 2 (Structure-Engineered Core-Shell Ni-Co-O / NiCo-LDH Nanospheres as High-Performance Supercapacitor Electrodes, Coatings, 2023, 13: 353. DOI: 10.3390 / coatings13020353) constructs a kind of chestnut-like core-shell composite material named Ni-Co-O / NiCo-LDH as an electrode material through a self-template method, Ni-Co-O improves the conductivity of the composite material, and NiCo-LDH provides a higher specific capacitance, and the structure is uniform, with a specific capacitance of 1434 F / g at a current density of 1 A / g. The technical solution has the technical problem of low specific capacitance, which cannot meet the application requirements. The reason is that although the technical solution successfully synthesizes a three-dimensional chestnut-like core-shell structure, by adjusting the morphology, the problem of agglomeration is avoided, but the chestnut-like core-shell structure has a small specific surface area due to its own structural characteristics, so it cannot effectively improve the specific capacitance performance.

[0009] To further improve the specific surface area, the prior art 3 (Microwave-assisted synthesis of NiCo-LDH / graphene nanoscrolls composite for supercapacitor, Carbon, 2022, 190:57-67. DOI:10.1016 / j.carbon.2021.12.097) vertically anchors the petal-shaped NiCo-LDH nanosheet on the three-dimensional interconnected graphene nanoscroll (GNS) skeleton by a microwave-assisted method to form an array core-shell heterostructure graphene nanoscroll composite, which avoids the stacking of the layered structure, provides more active sites, and the NiCo-LDH@GNS electrode has a specific capacitance of 1470 F / g at a current density of 1 A / g, a capacitance retention rate of 73% at a current density of 10 A / g, and a cycle life of 81.6% after 1000 cycles. The technical problem existing in this technical solution is that the petal-shaped structure itself has poor structural stability, which leads to shedding and collapse during the cycle process, and the disappearance of active sites, and ultimately leads to poor cycle stability.

[0010] Therefore, based on the above prior art, it can be known that controlling the micro-morphology and structure of the material and forming a three-dimensional structure electrode material can avoid the stacking of the sheet structure and provide a large specific surface area, but the current electrode material has the problem that in order to improve the specific surface area, the cycle stability is poor or in order to ensure the cycle stability, the specific surface area is sacrificed, that is, the specific surface area and cycle stability cannot be compatible. SUMMARY

[0011] The purpose of the present application is to provide a hollow nanocage structure ZnNiCo-LDH and its preparation method and application.

[0012] The present application solves the above problems by using the following method in view of the technical problems existing in the prior art:

[0013] 1. The core-shell structure of cobalt-nickel double metal hydroxide is used as a precursor, then different amounts of zinc chloride are added to the ZIF-67@NiCo-LDH solution, stirred at room temperature for 2h, the zinc chloride reacts with the ZIF-67@NiCo-LDH to form a hollow nanocage structure ZnNiCo-LDH to improve the electrochemical performance;

[0014] 2. A simple room temperature stirring is used to construct a three-dimensional structure to avoid the stacking of the two-dimensional sheet structure.

[0015] 3. The hollow nanocage structure provides a large specific surface area and rich active sites, thereby having a high specific capacitance.

[0016] To achieve the above object of the application, the technical scheme adopted by the application is:

[0017] A ZnNiCo-LDH with a hollow nanocage structure is prepared by first synthesizing ZIF-67 from cobalt nitrate and 2-methylimidazole, then preparing ZIF-67@NiCo-LDH from ZIF-67 and Ni(NO3)2, and finally reacting ZIF-67@NiCo-LDH with zinc chloride to obtain the ZnNiCo-LDH with a hollow nanocage structure, which is referred to as ZnNiCo-LDH;

[0018] The micro-morphology of the ZIF-67 is a regular dodecahedron structure with a smooth surface.

[0019] The micro-morphology of the ZIF-67@NiCo-LDH is a core-shell structure.

[0020] The micro-morphology of the ZnNiCo-LDH is a hollow nanocage structure.

[0021] A preparation method of a ZnNiCo-LDH with a hollow nanocage structure, comprising the following steps:

[0022] Step 1: Preparation of ZIF-67 with a regular dodecahedron structure, first, 2-methylimidazole is weighed and dissolved in methanol to obtain solution A, at the same time, Co(NO3)2·6H2O solid is weighed and dissolved in methanol to obtain solution B, then solution B is poured into solution A for mixing, finally, centrifugation is performed under certain conditions, and the obtained product is washed with methanol and then vacuum dried under certain conditions to obtain ZIF-67.

[0023] In the step 1, the mass ratio of 2-methylimidazole to Co(NO3)2·6H2O is (3-4):1.

[0024] In the step 1, the mixing condition is uniform stirring at room temperature for 30-60 min, followed by standing for 18-24 h.

[0025] In the step 1, the centrifugation condition is a centrifugal speed of 8000 rpm and a centrifugation time of 5 min; and the drying condition is a drying temperature of 60-80℃ and a drying time of 12-24 h.

[0026] Step 2, preparation of ZIF-67@NiCo-LDH with core-shell structure, first, ZIF-67 obtained in step 1 is weighed and dissolved in ethanol to obtain solution C, at the same time, nickel nitrate hexahydrate is weighed and dissolved in ethanol to obtain solution D, then, solution D is quickly poured into solution C for mixing, finally, centrifugation is carried out under certain conditions, and the obtained product is washed with methanol and vacuum dried under certain conditions, so that ZIF-67@NiCo-LDH with core-shell structure is obtained;

[0027] In step 2, the mass ratio of ZIF-67 to nickel nitrate hexahydrate is 1:(2-3);

[0028] In step 2, the mixing condition is that the uniform stirring is carried out at room temperature for 90-120 min;

[0029] In step 2, the centrifugation condition is that the centrifugal speed is 5000 rpm and the centrifugation time is 5 min; and the drying condition is that the drying temperature is 60-80 DEG C and the drying time is 12-24 h;

[0030] Step 3, preparation of ZnNiCo-LDH with hollow nanocage structure, zinc chloride and ZIF-67@NiCo-LDH meet a certain mass ratio, the product ZIF-67@NiCo-LDH obtained in step 2 is dissolved in methanol to obtain solution E, then, zinc chloride is dissolved in solution E under room temperature and stirring is carried out, finally, the obtained product is washed by suction filtration and vacuum dried under certain conditions, so that ZnNiCo-LDH with hollow nanocage structure is obtained;

[0031] In step 3, the mass ratio of zinc chloride to ZIF-67@NiCo-LDH is (6-8):1; and the drying condition is that the drying temperature is 60-80 DEG C and the drying time is 12-24 h.

[0032] The application of ZnNiCo-LDH with hollow nanocage structure as a supercapacitor is that the charge and discharge are carried out in the range of 0-0.5V, and the specific capacitance is 1900-2000 F / g when the discharge current density is 1 A / g;

[0033] The capacitance retention rate of 10 A / g relative to that of 1 A / g reaches 73%.

[0034] The technical effect of the application is detected by XRD, EDS, SEM, GCD, CV and EIS, and the results are as follows:

[0035] According to XRD and EDS tests, ZIF-67 is successfully prepared in step 1; NiCo-LDH is grown on the surface of ZIF-67 in step 2, that is, ZIF-67@NiCo-LDH is successfully prepared; after adding zinc chloride in step 3, ZIF-67 reacts with zinc chloride and disappears, and the phenomenon that the characteristic peaks of NiCo-LDH appear to move to a low diffraction angle indicates that, due to the addition of Zn element, Zn atoms replace part of Ni atoms and Co atoms, and change the original lattice spacing. The EDS test is supplemented to prove that ZnNiCo-LDH-7 contains not only Ni and Co elements, but also Zn element; and the positions of the three elements overlap, which proves that Zn atoms are successfully doped into ZIF-67@NiCo-LDH to form ZnNiCo-LDH.

[0036] According to SEM and TEM tests, the SEM test results prove that the particle size of the polyhedron increases due to the successful doping of Zn atoms, and the surface layer nanosheet shows obvious refinement phenomenon. The TEM test results show that ZIF-67@NiCo-LDH with core-shell structure is generated by the reaction of nickel nitrate and ZIF-67; with the addition of zinc chloride, ZIF-67 continues to react, which eventually leads to the disappearance of the core and forms a hollow nanocage structure of ZnNiCo-LDH-7.

[0037] According to GCD, CV and EIS electrochemical tests, it is proved that the specific capacitance of the hollow nanocage structure formed by doping Zn ions is increased by 86%; ZnNiCo-LDH has the battery-type electrochemical behavior of redox-type electrode material, and the test results also show that ZnNiCo-LDH has good rate performance and small equivalent series resistance.

[0038] Therefore, the ZnNiCo-LDH electrode material with a hollow nanocage structure of the present application has the following advantages over the prior art:

[0039] 1. The precursor ZIF-67 is prepared by a room temperature stirring synthesis method, and the nickel-cobalt layered hydroxide ZIF-67@NiCo-LDH with a core-shell structure is prepared, the original structure, specific surface area and porosity of ZIF-67 are well maintained and improved to some extent, and the conductivity is improved;

[0040] 2. Zn ions are doped into ZIF-67@NiCo-LDH by a room temperature stirring synthesis method to prepare a ZnNiCo-LDH electrode material with a hollow nanocage structure, and after adding zinc chloride, the reaction between zinc chloride and ZIF-67@NiCo-LDH continues, which makes the ZIF-67 core disappear and the ZnNiCo-LDH become a hollow nanocage structure, providing more active sites for more electroactive parts to participate in the Faraday redox reaction.

[0041] 3. The preparation method adopts a room temperature stirring method, the process is simple and easy to operate, the hollow nanocage structure prevents the accumulation of lamellar and provides a larger specific surface area, and the electrochemical performance of the synthesized material in the supercapacitor is better.

[0042] Therefore, the application has better capacitance performance compared with the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is an XRD graph of ZIF-67 in Example 1;

[0044] Figure 2 It is an XRD graph of ZIF-67@NiCo-LDH and ZnNiCo-LDH in Example 1;

[0045] Figure 3 It is an EDS graph of ZnNiCo-LDH-7 in Example 1;

[0046] Figure 4 It is an SEM graph of ZIF-67 in Example 1;

[0047] Figure 5 It is an SEM graph of ZIF-67@NiCo-LDH in Example 1;

[0048] Figure 6 It is an SEM graph of ZnNiCo-LDH-7 in Example 1;

[0049] Figure 7 It is a TEM graph of ZIF-67@NiCo-LDH in Example 1;

[0050] Figure 8 It is a TEM graph of ZnNiCo-LDH-7 in Example 1;

[0051] Figure 9 It is a GCD graph of ZIF-67@NiCo-LDH in Example 1;

[0052] Figure 10 It is a GCD graph of ZnNiCo-LDH-7 in Example 1;

[0053] Figure 11 It is a CV graph of ZnNiCo-LDH-7 in Example 1;

[0054] Figure 12 It is a graph of the specific capacitance and current density of ZnNiCo-LDH-7 in Example 1;

[0055] Figure 13 It is an AC impedance graph in Example 1, Comparative Example 1 and Comparative Example 2;

[0056] Figure 14 GCD plot of Comparative Example ZnNiCo-LDH-6;

[0057] Figure 15 GCD plot of Comparative Example ZnNiCo-LDH-8. DETAILED DESCRIPTION

[0058] The present application is further described in detail by way of examples with reference to the accompanying drawings.

[0059] Example 1

[0060] A method for preparing a hollow nanocage structure ZnNiCo-LDH, comprising the following steps:

[0061] Step 1, preparation of ZIF-67 with a regular dodecahedron structure, first, 3.28g of 2-methylimidazole was weighed and dissolved in 250mL of methanol to obtain solution A, at the same time, 2.91g of Co(NO3)2·6H2O solid was weighed and dissolved in 250mL of methanol to obtain solution B, then, under room temperature conditions, solution B was poured into solution A and stirred at a uniform speed for 30min for mixing, then, it was left to stand for 24h, finally, it was centrifuged under the conditions of a centrifugal speed of 8000rpm and a centrifugal time of 5min, and the obtained product was washed with methanol for 4 times, then, it was vacuum dried under the conditions of a drying temperature of 80℃ and a drying time of 8h, thus ZIF-67 was obtained;

[0062] Step 2, preparation of ZIF-67@NiCo-LDH with a core-shell structure, first, 0.2g of ZIF-67 obtained in step 1 was weighed and dissolved in 100mL of ethanol to obtain solution C, at the same time, 0.45g of nickel nitrate hexahydrate was weighed and dissolved in 25mL of ethanol to obtain solution D, then, under room temperature conditions, solution D was quickly poured into solution C and stirred at a uniform speed for 90min for mixing, finally, it was centrifuged under the conditions of a centrifugal speed of 5000rpm and a centrifugal time of 5min, and the obtained product was washed with methanol for 4 times, then, it was vacuum dried under the conditions of a drying temperature of 60℃ and a drying time of 12h, thus ZIF-67@NiCo-LDH with a core-shell structure was obtained;

[0063] Step 3, preparation of ZnNiCo-LDH with hollow nanocage structure, with the mass ratio of zinc chloride to ZIF-67@NiCo-LDH being 7:1, 50 mg of the product ZIF-67@NiCo-LDH obtained in step 2 was dissolved in 30 mL of methanol to obtain solution E, then 350 mg of zinc chloride was dissolved in the solution E and stirred at room temperature, finally, the obtained product was vacuum dried after washing by suction filtration, under the conditions of a drying temperature of 60°C and a drying time of 12 h, to obtain ZnNiCo-LDH with hollow nanocage structure, and the ZnNiCo-LDH obtained in specific embodiment 1 was named as ZnNiCo-LDH-7.

[0064] In order to prove the composition and reaction process of ZnNiCo-LDH, XRD tests were performed on ZIF-67 obtained in step 1, ZIF-67@NiCo-LDH obtained in step 2 and ZnNiCo-LDH-7 obtained in step 3, respectively.

[0065] The XRD test result of ZIF-67 is shown in Figure 1 , the characteristic peaks of ZIF-67 are the same as the standard peaks of ZIF-67, and the test result shows that ZIF-67 is successfully prepared in step 1;

[0066] The XRD test result of ZIF-67@NiCo-LDH is shown in Figure 2 , which contains the characteristic peaks of ZIF-67 and NiCo-LDH, and the test result shows that NiCo-LDH is successfully grown on the surface of ZIF-67 in step 2, that is, ZIF-67@NiCo-LDH is successfully prepared;

[0067] The XRD test result of ZnNiCo-LDH-7 is shown in Figure 2 , ZnNiCo-LDH-7 does not have the characteristic peaks of ZIF-67, and the characteristic peaks of NiCo-LDH appear to move to low diffraction angle, and the test result shows that ZIF-67 reacts with zinc chloride and disappears after the addition of zinc chloride in step 3, and the phenomenon that the characteristic peaks of NiCo-LDH appear to move to low diffraction angle shows that, due to the addition of Zn element, Zn atoms replace part of Ni atoms and Co atoms, changing the original lattice spacing.

[0068] The above conclusion can be supplemented by EDS test, and the EDS test result of ZnNiCo-LDH-7 is shown in Figure 3 , ZnNiCo-LDH-7 not only contains Ni element and Co element, but also contains Zn element; and the positions of the three elements overlap, which proves that Zn atoms are successfully doped into ZIF-67@NiCo-LDH to form ZnNiCo-LDH-7.

[0069] In order to prove the micro-morphology of ZnNiCo-LDH-7 and the change in the reaction process, the SEM tests are respectively conducted on ZIF-67, ZIF-67@NiCo-LDH and ZnNiCo-LDH-7.

[0070] The SEM test result of ZIF-67 is shown in the figure Figure 4 , which is a polyhedral structure with a smooth surface and a particle size of 1 μm;

[0071] The SEM test result of ZIF-67@NiCo-LDH is shown in the figure Figure 5 , the basic micro-morphology of ZIF-67@NiCo-LDH is consistent with that of ZIF-67, which is a polyhedral structure, and the specific micro-morphology is a polyhedral structure with a surface coated with a layered nanosheet, and the particle size is 1.01 μm. It can be known from the foregoing XRD test result that the layered nanosheet is NiCo-LDH.

[0072] The SEM test result of ZnNiCo-LDH-7 is shown in the figure Figure 6 , the basic micro-morphology of ZnNiCo-LDH-7 is consistent with that of ZIF-67@NiCo-LDH, which is a polyhedral structure with a surface coated with a layered nanosheet, and the particle size is 1.035 μm. The test result shows that due to the successful doping of Zn atoms, the particle size of the polyhedron increases, and the surface layered nanosheet shows an obvious refinement phenomenon.

[0073] In order to further prove the change of the internal morphology of ZnNiCo-LDH-7, that is, to prove the regulation of zinc chloride on the micro-morphology, the TEM tests are respectively conducted on ZIF-67@NiCo-LDH and ZnNiCo-LDH-7.

[0074] The TEM test result of ZIF-67@NiCo-LDH is shown in the figure Figure 7 , ZIF-67@NiCo-LDH is a core-shell structure, in which ZIF-67 is a core structure and NiCo-LDH is a shell structure;

[0075] The TEM test result of ZnNiCo-LDH-7 is shown in the figure Figure 8 , ZnNiCo-LDH-7 is a hollow nanocage structure, that is, only the shell structure of NiCo-LDH is retained, and the core structure of ZIF-67 disappears.

[0076] The TEM test result shows that the reaction of nickel nitrate and ZIF-67 generates ZIF-67@NiCo-LDH with a core-shell structure; with the addition of zinc chloride, ZIF-67 continues to react, which eventually leads to the disappearance of the core and forms a hollow nanocage structure of ZnNiCo-LDH-7.

[0077] The electrochemical test adopts a three-electrode system, taking the material to be tested as the working electrode, taking the oxidized mercury electrode as the reference electrode, taking the platinum electrode as the counter electrode, and taking the 6M KOH solution as the electrolyte. The specific preparation method of the working electrode is as follows: 0.008g of ZnNiCo-LDH-7, 0.001g of acetylene black, 0.001g of polytetrafluoroethylene powder and an appropriate amount of ethanol are mixed and ground in a mass ratio of 8:1:1; after grinding, drying is carried out under an infrared lamp to obtain a dry sample; finally, the dry sample is placed on a 2cm×4cm foam nickel current collector, the foam nickel is folded, and the foam nickel is pressed at a pressure of 5kPa to obtain a supercapacitor electrode, i.e. the working electrode.

[0078] The electrochemical test results are as follows:

[0079] In order to prove the specific capacitance performance of ZnNiCo-LDH-7, constant current charge-discharge GCD test is carried out on ZIF-67@NiCo-LDH and ZnNiCo-LDH-7.

[0080] The GCD test results of ZIF-67@NiCo-LDH are as shown in Figure 9 , in the range of 0-0.5V, the discharge time is 512s and the specific capacitance is 1025F / g when the current density is 1A / g;

[0081] The GCD test results of ZnNiCo-LDH-7 are as shown in Figure 10 , ZnNiCo-LDH-7 is charged and discharged in the range of 0-0.5V, the discharge time is 954s and the specific capacitance is 1908F / g when the current density is 1A / g.

[0082] The GCD test results show that the specific capacitance of the hollow nanocage structure formed by doping Zn ions is significantly improved by 86%.

[0083] In order to prove the electrochemical behavior of ZnNiCo-LDH-7, CV test is carried out. The test results are as shown in Figure 11 , when the scanning rate is 5mv / s, obvious redox peaks appear. The test results show that ZnNiCo-LDH-7 has a battery-type electrochemical behavior of redox-type electrode material, and the test results also show that ZnNiCo-LDH-7 has good rate performance.

[0084] In order to further quantify the rate performance of ZnNiCo-LDH-7, the specific capacitance performance test of ZnNiCo-LDH-7 electrode material under different current densities is carried out. The test results are as shown in Figure 12As shown, the specific capacitance of ZnNiCo-LDH-7 was 1392 F / g at a current density of 10 A / g; the specific capacitance retention rate at 10 A / g relative to that at 1 A / g was 73%. The test results show that ZnNiCo-LDH-7 has good rate performance.

[0085] In order to prove the electron transfer resistance performance of ZnNiCo-LDH-7, an alternating current impedance EIS test was performed, and in order to perform comparative analysis, a ZIF-67@NiCo-LDH was also subjected to an alternating current impedance EIS test. The test results are as follows Figure 13 As shown,

[0086] The equivalent series resistance Rs value of ZIF-67@NiCo-LDH was 0.32 Ω, and the charge transfer resistance Rct value was 0.82 Ω;

[0087] The equivalent series resistance Rs value of ZnNiCo-LDH-7 was 0.28 Ω, and the charge transfer resistance Rct value was 0.73 Ω.

[0088] The test results show that the equivalent series resistance and the charge transfer resistance of ZnNiCo-LDH-7 are both smaller than those of ZIF-67@NiCo-LDH, indicating that due to the addition of zinc ions, the charge transfer rate of the electrode material is higher, which is more conducive to electrochemical reaction, so the specific capacitance is improved.

[0089] In order to prove the influence of the amount of zinc chloride incorporated on ZIF-67@NiCo-LDH, a comparative example 1 and a comparative example 2 are provided, i.e. ZnNiCo-LDH with a mass ratio of zinc chloride to ZIF-67@NiCo-LDH of 6:1 and 8:1 respectively.

[0090] Comparative example 1

[0091] A method for preparing a hollow nanocage structure ZnNiCo-LDH-6, the steps not specifically described are the same as those in example 1, the difference is that the mass ratio of zinc chloride added in step 3 to ZIF-67@NiCo-LDH is 6:1, and the ZnNiCo-LDH obtained in comparative example 1 is named as ZnNiCo-LDH-6.

[0092] The GCD test results of ZnNiCo-LDH-6 are as follows Figure 14 As shown, the discharge time was 667 s and the specific capacitance was 1334 F / g at a current density of 1 A / g when charging and discharging in the range of 0-0.5 V; compared with ZnNiCo-LDH-7 obtained in example 1, the discharge time was 954 s, i.e. the electrochemical performance was weaker than that of ZnNiCo-LDH-7.

[0093] The test results of ZnNiCo-LDH-6 are as followsFigure 13 As shown, the equivalent series resistance Rs value of ZnNiCo-LDH-6 is calculated to be 0.32 Ω, and the charge transfer resistance Rct value is 0.88 Ω.

[0094] Comparative Example 2

[0095] A method for preparing ZnNiCo-LDH-8 with a hollow nanocage structure, the steps not specifically described are the same as those in Example 1, the difference is that the mass ratio of zinc chloride added in step 3 to ZIF-67@NiCo-LDH is 8:1, and the ZnNiCo-LDH obtained in Comparative Example 2 is named ZnNiCo-LDH-8.

[0096] The GCD test results of ZnNiCo-LDH-8 are as shown in Figure 15 As shown, the charge and discharge were carried out in the range of 0-0.5V, and the discharge time was 794s and the specific capacitance was 1588F / g when the current density was 1A / g. Compared with ZnNiCo-LDH-7 obtained in Example 1, the discharge time was 954s, i.e., the electrochemical performance was weaker than that of ZnNiCo-LDH-7.

[0097] The test results of ZnNiCo-LDH-8 show that the equivalent series resistance Rs value of ZnNiCo-LDH-8 is calculated to be 0.28 Ω, and the charge transfer resistance Rct value is 0.71 Ω.

[0098] The AC impedance test results of Example 1, Comparative Example 1 and Comparative Example 2 can prove that as the amount of added Zn ions increases, the charge transfer resistance becomes smaller, which is beneficial to accelerate the charge transfer, but too much Zn ions will lead to a decrease in specific capacitance, therefore, ZnNiCo-LDH-7 is most suitable for supercapacitor electrode materials.

Claims

1. A method for preparing ZnNiCo-LDH with hollow nanocage structure, characterized by It comprises the following steps: Step 1, preparation of ZIF-67 with regular dodecahedron structure, first, 2-methylimidazole is weighed and dissolved in methanol to obtain solution A, at the same time, Co(NO3)2·6H2O solid is weighed and dissolved in methanol to obtain solution B, then solution B is poured into solution A for mixing, finally, centrifugation is carried out under certain conditions, and the obtained product is washed with methanol and then vacuum dried under certain conditions, so that ZIF-67 is obtained; In step 1, the mass ratio of 2-methylimidazole to Co(NO3)2·6H2O is (3-4):1; In step 1, the mixing condition is that the solution is stirred at room temperature for 30-60 min, and then left to stand for 18-24 h; In step 1, the centrifugation condition is that the centrifugal speed is 8000 rpm and the centrifugation time is 5 min; the drying condition is that the drying temperature is 60-80℃ and the drying time is 12-24 h; Step 2, preparation of ZIF-67@NiCo-LDH with core-shell structure, first, ZIF-67 obtained in step 1 is dissolved in ethanol to obtain solution C, at the same time, nickel nitrate hexahydrate is dissolved in ethanol to obtain solution D, then solution D is quickly poured into solution C for mixing, finally, centrifugation is carried out under certain conditions, and the obtained product is washed with methanol and then vacuum dried under certain conditions, so that ZIF-67@NiCo-LDH with core-shell structure is obtained; In step 2, the mass ratio of ZIF-67 to nickel nitrate hexahydrate is 1:(2-3); In step 2, the mixing condition is that the solution is stirred at room temperature for 90-120 min; In step 2, the centrifugation condition is that the centrifugal speed is 5000 rpm and the centrifugation time is 5 min; the drying condition is that the drying temperature is 60-80℃ and the drying time is 12-24 h; Step 3, preparation of ZnNiCo-LDH with hollow nanocage structure, zinc chloride and ZIF-67@NiCo-LDH are mixed in a certain mass ratio, ZIF-67@NiCo-LDH obtained in step 2 is dissolved in methanol to obtain solution E, then zinc chloride is dissolved in solution E and stirred at room temperature, finally, the obtained product is washed by suction filtration and then vacuum dried under certain conditions, so that ZnNiCo-LDH with hollow nanocage structure is obtained; In step 3, the mass ratio of zinc chloride to ZIF-67@NiCo-LDH is (6-8):1; the drying condition is that the drying temperature is 60-80℃ and the drying time is 12-24 h.

2. The method of claim 1, wherein: The obtained ZnNiCo-LDH with hollow nanocage structure is applied as a supercapacitor, and the specific capacitance is 1900-2000 F / g at a discharge current density of 1 A / g in the range of 0-0.5 V.

3. The method of claim 1, wherein: The obtained ZnNiCo-LDH with hollow nanocage structure is applied as a supercapacitor, and the capacitance retention rate at 10 A / g relative to that at 1 A / g reaches 73%.

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