NiCo-LDH / porous carbon composite material with expanded interlayer spacing as well as preparation method and application of NiCo-LDH / porous carbon composite material

Abstract

The invention discloses a NiCo-LDH / porous carbon composite material with expanded interlayer spacing as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing coal pitch serving as a carbon source with potassium hydroxide, combusting in an inert gas atmosphere, and performing acid pickling, suction filtration and drying to obtain a coal pitch-based porous carbon material; the preparation method comprises the following steps: uniformly dispersing a certain amount of porous carbon material in a mixed solution of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinylpyrrolidone (PVP) and ethylene diamine tetraacetic acid (EDTA-2Na), performing hydrothermal reaction, adding hydrazine hydrate (N2H4H2O), and performing hydrothermal reaction again to obtain the nickel-cobalt layered double hydroxide / porous carbon composite material (NiCo-LDH-PC) with expanded interlayer spacing. Compared with the prior art, the method has the advantages that the interlamellar spacing of NiCO-LDH is regulated and controlled, the interlamellar spacing is enlarged, and the NiCO-LDH has excellent electrochemical performance and cycling stability as an electrode material of a supercapacitor and a button cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode material preparation, and in particular relates to a method for preparing a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing. Background Art

[0002] As a specialized energy storage device, supercapacitors have attracted widespread attention due to their rapid charge and discharge, higher specific power than batteries, better specific capacity than traditional capacitors, and long-lasting cycling stability. However, because the charge transfer storage mechanism of supercapacitors is confined to the surface of the electrode material, their energy density, or capacitance, is lower than that of commercial batteries. Therefore, their energy density should be increased without compromising their power density.

[0003] Layered double hydroxides (LDHs), an emerging two-dimensional layered metal hydroxide material, are characterized by a structure consisting of a positively charged layered structure and charge-compensating anions located between the layers. This unique structure not only provides LDHs with a large surface area but also facilitates the rapid diffusion of ions and their rapid arrival at the surface. Nickel-cobalt layered double hydroxides (NiCo-LDHs) are widely used as supercapacitor electrode materials due to their high specific capacitance, excellent redox activity, and low preparation cost.

[0004] However, LDH is prone to problems such as agglomeration and dense stacking during the preparation process. The resulting small interlayer spacing limits the redox reaction process of LDHs, resulting in poor conductivity and increased volume during the charge and discharge process. Introducing macromolecules or anions between LDH layers to create a larger interlayer space can effectively promote ion diffusion, enhance reaction kinetics, and thus improve electrochemical performance. At the same time, compounding it with carbon-based materials can significantly enhance the overall conductivity of the material, alleviate the aggregation phenomenon of nanostructures, and further improve its electrochemical performance. Therefore, using porous carbon materials with excellent conductive properties as a substrate to achieve the growth of high-density NiCo-LDH nanostructures is crucial to achieving its theoretical specific capacitance and fully exerting the performance of electrode materials. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing, a preparation method thereof, and applications thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing, comprising the following steps:

[0007] S1, mixing coal tar powder with an alkaline activator, calcining under an inert gas atmosphere, acid washing, filtering and drying to obtain a porous carbon material;

[0008] S2, mixing the porous carbon material in S1, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinyl pyrrolidone (PVP), and ethylenediaminetetraacetic acid disodium (EDTA-2Na) solution, performing a hydrothermal reaction at a certain temperature, and cooling to room temperature to obtain a pink suspension;

[0009] S3, the suspension of S2 is uniformly mixed with a certain amount of hydrazine hydrate, and hydrothermally reacted again at a certain temperature, and cooled to room temperature to obtain a green suspension;

[0010] S4. The suspension of S3 is washed, filtered and dried to obtain a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing.

[0011] In a preferred embodiment of the present invention, in S1, the mass ratio of coal tar powder to alkaline activator is 1:2-4.

[0012] In a preferred embodiment of the present invention, in S1, the temperature is raised to 400-600°C at a heating rate of 2-10°C / min under an inert gas atmosphere and kept at this temperature for 1-3 hours.

[0013] In a preferred embodiment of the present invention, in S1, the alkaline activator is one of potassium hydroxide, zinc oxide or magnesium hydroxide.

[0014] In a preferred embodiment of the present invention, in S1, the calcined powder is washed in an acidic solution, then washed with water multiple times until the filtrate is neutral after filtration, and dried at 60-100°C for 6-18h to obtain a porous carbon material.

[0015] In a preferred embodiment of the present invention, in S2, the mass ratio of the porous carbon material, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinyl pyrrolidone, and disodium edetate is 10-70:872:873:1200:807, and 30-50 mL of water is added when configuring the aqueous solution.

[0016] In a preferred embodiment of the present invention, in S3, the suspension of S2 is uniformly mixed with 2-4 mL of hydrazine hydrate and hydroheated again.

[0017] In a preferred embodiment of the present invention, in S4, the green suspension in S3 is washed several times with anhydrous ethanol and water, respectively, and vacuum dried at 60-80°C for 6-18h.

[0018] The present invention provides a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing, based on the above-mentioned preparation method: the composite material is used as an electrode material for supercapacitors and button batteries.

[0019] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0020] (1) The present invention provides a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing. The porous carbon material is prepared by mixing coal tar powder as a carbon source with potassium hydroxide and calcining. NiCo-LDH / porous carbon composite materials with different loadings are prepared by a hydrothermal method using a specific amount of porous carbon added. The porous carbon has a rich pore structure and a large specific surface area, which is conducive to the adsorption of metal ions, thereby uniformly loading the metal hydroxide on the porous carbon surface, solving the problem of agglomeration, and improving the structural stability of the composite material. At the same time, the porous carbon material has a certain degree of graphitization, which improves the electrical conductivity of the composite material and solves the problem of low electrical conductivity of the composite material.

[0021] (2) The present invention expands the interlayer spacing of NiCo-LDH by introducing EDTA-2Na (disodium ethylenediaminetetraacetic acid). EDTA-2Na dissolves in aqueous solution to form EDTA 2+ ions, during the initial hydrothermal process at 120℃, EDTA 2+ The ions are inserted into the nickel cobalt hydroxide layer to maintain a large initial stable interlayer spacing. Subsequently, during the secondary hydrothermal process at 120 ° C, hydrazine hydrate is introduced to adjust the pH of the solution to alkaline, so that EDTA 2+ Converted to EDTA 4+ At the same time, under the strong complexing effect of EDTA-2Na, the electrostatic attraction between the sheets is reduced, the interlayer spacing is expanded, and the effective transmission of electrolyte ions and electrons between the composite material sheets is ensured, thereby enhancing the electrochemical performance.

[0022] (3) The NiCo-LDH@PC-40 prepared in the present invention can maintain a high specific capacitance at different current densities, which is 1767F / g at a current density of 0.5A / g. It can be used as an electrode material for supercapacitors and button batteries, and can enable energy storage devices to have excellent electrochemical performance and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 is a flow chart of the NiCo-LDH / porous carbon composite material of Example 1 of the present invention;

[0025] Figure 21 is a scanning electron microscope (SEM) image of the materials prepared in Example 1, Example 6, and Example 7 of the present invention;

[0026] Figure 3 TEM images of the materials prepared in Example 1 and Example 7 of the present invention;

[0027] Figure 4 1 is an X-ray diffraction (XRD) pattern of the materials prepared in Example 1, Example 6, and Example 7 of the present invention;

[0028] Figure 5 This is a high-resolution transmission electron microscope interlayer spacing measurement image of the double metal hydroxide / porous carbon composite material prepared in Example 1 and Example 6 of the present invention;

[0029] Figure 6 1 is a cyclic voltammetry (CV) curve of the NiCo-LDH@PC-40 working electrode three-electrode system at different scan rates in the 0-0.5 V voltage window in Example 8 of the present invention;

[0030] Figure 7 3. The constant current charge and discharge (GCD) diagram of the NiCo-LDH@PC-40 working electrode three-electrode system at different current densities in the 0-0.5 V voltage window in Example 8 of the present invention;

[0031] Figure 8 The cyclic voltammetry (CV) curves of the three-electrode system of the NiCo-LDH@PC composite working electrode at five different loadings in Example 8 of the present invention were obtained in a voltage window of 0-0.5 V at a scan rate of 5 mV / s;

[0032] Figure 9 This is a galvanostatic charge-discharge (GCD) graph of the NiCo-LDH@PC composite working electrode three-electrode system at five different loadings in Example 8 of the present invention obtained in a 0-0.5 V voltage window at a current density of 0.5 A / g;

[0033] Figure 10 This is a rate performance diagram of the NiCo-LDH@PC composite working electrode three-electrode system at five different loading amounts in Example 8 of the present invention in the 0-0.5V voltage window;

[0034] Figure 11 This is a rate performance diagram of the three-electrode system of the NiCo-FDH@PC-40 composite working electrode in Example 8 of the present invention in the 0-0.5V voltage window;

[0035] Figure 12 is a rate performance graph of the button-type asymmetric supercapacitor prepared in Example 9 of the present invention;

[0036] Figure 13 is a Lagung plot comparing the energy density of the button-type asymmetric supercapacitor prepared in Example 9 of the present invention with the energy density of the supercapacitor prepared by the prior art;

[0037] Figure 14 3 is a comparison chart of the electrochemical cycling stability of the button-type asymmetric supercapacitor prepared in Example 9 of the present invention and the button-type symmetric supercapacitor prepared using the porous carbon material in the same manner as in Example 9. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Unless otherwise stated, when describing numerical ranges herein, the endpoint values ​​are included. When two or more preferred or exemplary numerical values ​​or numerical ranges are given, it goes without saying that all ranges formed by combining different numerical values ​​or endpoints are also included in the scope of the present invention.

[0040] These and other aspects, features and advantages of the present invention will become apparent to those skilled in the art through the detailed description below. In this context, any feature or any embodiment from one aspect of the present invention may be used in any other aspect of the present invention. Furthermore, it is self-evident that the embodiments herein included are intended to describe and illustrate the present invention, not to limit the present invention, and in particular, the present invention is not limited to these embodiments.

[0041] The following will be combined Figure 1 An exemplary embodiment of a method for forming a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to the present invention is described. Figure 1 The embodiments shown in FIG. 1 are merely illustrative, and the embodiments of the present invention are not limited thereto.

[0042] Specifically, the following steps are included:

[0043] S1, mixing coal tar powder with an alkaline activator, calcining under an inert gas atmosphere, acid washing, filtering and drying to obtain a porous carbon material;

[0044] S2, mixing the porous carbon material in S1, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinyl pyrrolidone (PVP), and ethylenediaminetetraacetic acid disodium (EDTA-2Na) solution, performing a hydrothermal reaction at a certain temperature, and cooling to room temperature to obtain a pink suspension;

[0045] S3, the suspension of S2 is uniformly mixed with a certain amount of hydrazine hydrate, and hydrothermally reacted again at a certain temperature, and cooled to room temperature to obtain a green suspension;

[0046] S4. The suspension of S3 is washed, filtered and dried to obtain a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing.

[0047] In step S1 of the present invention, the mass ratio of coal tar powder to alkaline activator is 1:2-4.

[0048] The coal tar powder in the present invention is coal tar from Zaozhuang, Shandong, which is obtained by distilling and extracting coal tar. The coal tar powder is black and is used as an experimental raw material after grinding and drying. The particle size range of the coal tar powder in the present invention is preferably 40-200 mesh, and more preferably 100-120 mesh.

[0049] The alkaline activator is one of potassium hydroxide, zinc oxide or magnesium hydroxide, preferably potassium hydroxide. In one or more embodiments, the purity of potassium hydroxide is 80-100%, more preferably 90-95%.

[0050] In one or more embodiments, coal tar pitch powder is mixed with potassium hydroxide and then heated to 400-600°C at a rate of 2-10°C / min under an inert gas atmosphere for 1-3 hours. At high temperatures, KOH etches the porous carbon surface, forming a hierarchical pore structure with coexisting micropores and mesopores, while retaining a certain degree of graphitization, resulting in a certain degree of conductivity, making it suitable as a carbon substrate for negative electrode materials.

[0051] The inert gas may be helium, neon, or argon. The calcination temperature is preferably 400-600°C, more preferably 490-510°C, for example, about 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, or a range defined by any two of the above values.

[0052] In one or more embodiments, the holding time is preferably 1-3 hours, more preferably 1.5-2.5 hours, for example, about 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or a range defined by any two of the above values.

[0053] In one or more embodiments, the calcined powder is washed in an acidic solution. The acidic solution can be one of hydrochloric acid, nitric acid, or sulfuric acid, preferably hydrochloric acid, with a concentration of 0.1-6 mol / L, more preferably 1-1.5 mol / L. The washing time is preferably 12-36 hours, more preferably 20-24 hours.

[0054] In one or more embodiments, the calcined powder is washed with an acidic solution and then washed with water until the filtrate is neutral (pH=7).

[0055] In one or more embodiments, the washed porous carbon material is dried at 60-100° C. for 6-18 hours to accelerate water evaporation, and the porous carbon material is obtained after complete drying.

[0056] In step S2 of the present invention, the porous carbon material, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinyl pyrrolidone, and disodium edetate are prepared in a mass ratio of 10-70:872:873:1200:807, and 30-50 mL of water is added when the aqueous solution is prepared.

[0057] In step S2, the porous carbon material is mixed with four other compounds for a hydrothermal reaction. The goal is to uniformly grow nickel-cobalt double hydroxide nanostructures (NiCo-LDH) on the surface of the porous carbon material through a chemical reaction. These layered structures form a composite material with the porous carbon material. Polyvinylpyrrolidone acts as a binder to make the layered structure grow more firmly. Disodium ethylenediaminetetraacetic acid acts as a spreading agent and complexing agent, making the layered structure more uniform and increasing the interlayer spacing.

[0058] In one or more embodiments, the mass ratio of porous carbon material, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinylpyrrolidone, and disodium edetate is preferably 1-100:872:873:1200:807, more preferably 10-70:872:873:1200:807, for example, about 10:872:873:1200:807, 20:872:873:1200:807, 30:872:873:1200:807, 40:872:873:1200:807, 50:872:873:1200:807, 60:872:873:1200:807, 70:872:873:1200:807 or a range defined by any two of the above values.

[0059] In one or more embodiments, the hydrothermal reaction temperature is 100-150°C, more preferably 100-120°C.

[0060] In one or more embodiments, the hydrothermal reaction time is 6-12 hours, more preferably 8-10 hours.

[0061] In step S3 of the present invention, the pink suspension in S2 is uniformly mixed with a certain amount of hydrazine hydrate, and a hydrothermal reaction is performed again at a certain temperature.

[0062] In step S3, the pink suspension in S2 is uniformly mixed with a certain amount of hydrazine hydrate. The purpose is to adjust the pH value of the solution to alkaline by hydrazine hydrate, on the one hand, to promote the reaction and precipitation of double metal hydroxide and its attachment to the porous carbon, and on the other hand, to dissolve EDTA-2Na in the aqueous solution to form EDTA 2+ Ions converted to EDTA 4+ , EDTA 4+ Inserted between the layers, it reduces the electrostatic attraction between the layers, thereby expanding the interlayer spacing. 4+ The ion expansion occurs at high temperature, so the interlamellar spacing is expanded again by hydrothermal treatment.

[0063] In one or more embodiments, the amount of hydrazine hydrate added is preferably 1-5 mL, more preferably 2-4 mL.

[0064] In one or more embodiments, the hydrothermal reaction temperature is 100-150°C, more preferably 100-120°C.

[0065] In one or more embodiments, the hydrothermal reaction time is 6-12 hours, more preferably 8-10 hours.

[0066] In step S4 of the present invention, the green suspension in S3 is washed several times with anhydrous ethanol and water, and then vacuum-dried at 60-80° C. for 6-18 hours.

[0067] In step S4, the green suspension in S3 is washed several times with anhydrous ethanol and water respectively, the purpose of which is to wash away the polyvinyl pyrrolidone and EDTA-2Na residues on the surface of the composite material, while ensuring that the by-products of the reaction or the unreacted raw materials are removed, thereby improving the purity of the composite material.

[0068] In one or more embodiments, the drying temperature is preferably 50-100°C, more preferably 70-80°C.

[0069] In one or more embodiments, the drying time is preferably 6-24 hours, more preferably 8-12 hours.

[0070] The embodiments of the present invention will be described in detail below with reference to the examples. However, the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0071] Example 1

[0072] This embodiment provides a method for preparing a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing, comprising the following steps:

[0073] (1) 2 g of coal tar powder and 6 g of potassium hydroxide were placed in a mortar and ground thoroughly, and then placed in a horizontal tube furnace. The temperature was raised to 500° C. at 5° C. / min under a nitrogen atmosphere and maintained for 2 h to obtain a calcined product; the calcined product was placed in a mortar and ground thoroughly, and the calcined powder was placed in a 1 mol / L hydrochloric acid solution and stirred for 24 h. The filtrate was filtered and washed with deionized water until the pH of the filtrate was 7, and then dried in a blast drying oven at 80° C. for 12 h to obtain a porous carbon material;

[0074] (2) 40 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate and 1.2 g of polyvinylpyrrolidone were placed in 47 mL of water and stirred for 1 h to dissolve them so as to uniformly disperse them to form a mixed suspension; the mixed solution was transferred to a 100 mL Teflon high-pressure hydrothermal reactor and heated at 120 ° C for 10 h. After cooling to room temperature, a pink suspension was obtained;

[0075] (3) Add 3 mL of hydrazine hydrate to the obtained pink suspension and stir for 1.5 h. Then, place it in a hydrothermal kettle and heat it at 120 °C for 10 h to obtain a green suspension.

[0076] (4) The obtained green suspension was washed three times with anhydrous ethanol and deionized water respectively, and dried in a vacuum at 80 °C for 12 h to obtain a NiCo-LDH / porous carbon composite material, namely NiCo-LDH@PC-40.

[0077] Example 2

[0078] The only difference between this embodiment and Example 1 is that: in step (2) of Example 1, 10 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate and 1.2 g of polyvinylpyrrolidone were placed in 47 mL of water and stirred for 1 hour, and then subjected to secondary hydrothermal treatment to obtain a composite material, namely NiCo-LDH@PC-10.

[0079] Example 3

[0080] The only difference between this embodiment and Example 1 is that: in step (2) of Example 1, 30 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate and 1.2 g of polyvinylpyrrolidone were placed in 47 mL of water and stirred for 1 hour, and then subjected to secondary hydrothermal treatment to obtain a composite material, namely NiCo-LDH@PC-30.

[0081] Example 4

[0082] The only difference between this embodiment and Example 1 is that: in step (2) of Example 1, 50 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate and 1.2 g of polyvinylpyrrolidone were placed in 47 mL of water and stirred for 1 hour, and then subjected to secondary hydrothermal treatment to obtain a composite material, namely NiCo-LDH@PC-50.

[0083] Example 5

[0084] The only difference between this embodiment and Example 1 is that: in step (2) of Example 1, 70 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate and 1.2 g of polyvinylpyrrolidone were placed in 47 mL of water and stirred for 1 hour, and then subjected to secondary hydrothermal treatment to obtain a composite material, namely NiCo-LDH@PC-70.

[0085] Example 6

[0086] The only difference between this embodiment and Example 1 is that: in step (2) of Example 1, 40 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate and 1.2 g of polyvinyl pyrrolidone were placed in 47 mL of water and stirred for 1 hour, and then subjected to secondary hydrothermal treatment to obtain a composite material, namely NiCo-FDH@PC-40.

[0087] Example 7

[0088] The only difference between this embodiment and Example 1 is that in step (2) of Example 1, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate, and 1.2 g of polyvinylpyrrolidone were placed in 47 mL of water and stirred for 1 h, and then subjected to secondary hydrothermal treatment to obtain a metal compound, namely NiCo-LDH.

[0089] Example 8

[0090] This embodiment provides a method for preparing a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing, comprising the following steps:

[0091] (1) 2 g of coal tar powder and 6 g of potassium hydroxide were placed in a mortar and ground thoroughly, and then placed in a horizontal tube furnace. The temperature was raised to 500° C. at 5° C. / min under a nitrogen atmosphere and maintained for 2 h to obtain a calcined product; the calcined product was placed in a mortar and ground thoroughly, and the calcined powder was placed in a 1 mol / L hydrochloric acid solution and stirred for 24 h. The filtrate was filtered and washed with deionized water until the pH of the filtrate was 7, and then dried in a blast drying oven at 80° C. for 12 h to obtain a porous carbon material;

[0092] (2) 40 mg of porous carbon material, 0.8731 g of cobalt nitrate hexahydrate, 0.8724 g of nickel nitrate hexahydrate, 0.8069 g of disodium ethylenediaminetetraacetate, 1.2 g of polyvinylpyrrolidone and 3 mL of hydrazine hydrate were placed in 47 mL of water and stirred for 1 h to dissolve them so as to uniformly disperse them to form a mixed suspension; the mixed solution was transferred to a 100 mL Teflon high-pressure hydrothermal reactor and heated at 120 ° C for 10 h. After cooling to room temperature, a green suspension was obtained;

[0093] (3) The obtained green suspension was washed three times with anhydrous ethanol and deionized water respectively, and dried under vacuum at 80°C for 12 h to obtain a NiCo-LDH / porous carbon composite material, namely NiCo-LDH-PC-40.

[0094] The composite material obtained by the hydrothermal reaction in this embodiment contains green double metal hydroxide and black porous carbon material, indicating that the prepared double metal hydroxide is not loaded on the porous carbon material. During the suction filtration and washing process in step (3) of this embodiment, it was found that the green double metal hydroxide precipitate and the black porous carbon were separated, and there was no green embellishment on the black porous carbon. At the same time, preliminary electrochemical performance tests did not observe energy storage performance, and the discharge time did not reach the minimum range of the instrument test. Therefore, it is speculated that this embodiment was not successfully loaded.

[0095] Example 9

[0096] The only difference between this embodiment and embodiment 1 is that the porous carbon material in step (2) is replaced with commercial activated carbon (CAC), and a NiCo-LDH / composite material, namely NiCo-LDH@CAC, is finally prepared. The prepared NiCo-LDH@CAC was subjected to preliminary charge and discharge tests and found that its performance did not reach the lowest range of the instrument test and had almost no energy storage performance. It is preliminarily speculated that the reason is that asphalt is rich in polycyclic aromatic hydrocarbons and forms a hierarchical pore structure during the activation process, while the preparation method of CAC is unknown and may contain some impurities. There are relatively few active sites during the hydrothermal reaction, resulting in incomplete loading or loading failure.

[0097] The morphology of the materials prepared in Example 1, Example 6 and Example 7 was characterized and analyzed. Figure 2 As shown, Figure 2 (ad) shows the SEM images of NiCo-LDH@PC-40 (Example 1). Figure 2 (eh) shows the SEM image of NiCo-FDH@PC-40 (Example 6), Figure 2 (il) shows a scanning electron microscope (SEM) image of NiCo-LDH (Example 7). As can be seen from the SEM image, for the NiCo-LDH@PC-40 composite material, after secondary hydrothermal treatment, it can be observed that layered double hydroxides grow uniformly on the surface of the porous carbon material. The layered structure of NiCo-FDH@PC-40 shows severe stacking, and the active components agglomerate into a dense structure, which cannot provide sufficient active sites. Since NiCo-LDH does not introduce porous carbon materials, it also shows obvious agglomeration phenomenon, resulting in poor electron transport ability, which in turn affects the electrochemical performance.

[0098] like Figure 3 As shown, Figure 3 (ae) are transmission electron microscope (TEM) images of NiCo-LDH (Example 7). Figure 3 (fj) is the transmission electron microscope TEM image of NiCo-LDH@PC-40 (Example 1), Figure 3 (k) is the EDS element distribution diagram of NiCo-LDH@PC-40 (Example 1). TEM images also further prove that the layered double hydroxide is uniformly loaded on the porous carbon material. Figure 3 In the high-resolution TEM image (i), lattice fringes of 0.19 nm and 0.23 nm can be clearly observed, which correspond to the lattice fringes of Co(CO3) and Co(CO3) respectively. 0.5 The (340) crystal plane of (OH)·0.11H2O coincides with the (191) crystal plane of Ni2CO3(OH)2·H2O. The EDS elemental distribution diagram shows the distribution of C, N, O, Ni, and Co. Ni and Co are evenly distributed in the NiCo-LDH@PC-40 material, indicating that porous carbon materials as a support can effectively promote the uniform growth of NiCo-LDH. It also indicates that the secondary hydrothermal preparation of NiCo-LDH / porous carbon composites is successful.

[0099] like Figure 4The figures shown are X-ray diffraction XRD patterns of NiCo-LDH@PC-40 (Example 1), NiCo-FDH@PC-40 (Example 6) and NiCo-LDH (Example 7). NiCo-LDH@PC-40 (Example 1) has a certain shift in the (003) peak position, and the peak shape is relatively sharp, indicating that the interlayer spacing has been effectively regulated under the action of EDTA-2Na, and the interlayer spacing has become larger, making the lamellar structure more relaxed. The Bragg equation was used to calculate the (003) crystal plane interlayer spacing d of NiCo-LDH@PC-40 (Example 1): The (001) interlayer spacing d of NiCo-FDH@PC-40 (Example 6) is Therefore, the interlayer spacing of the composite material was expanded by nearly 71.83% by introducing EDTA-2Na.

[0100] like Figure 5 As shown, Figure 5 (a) is a high-resolution transmission electron microscope interlayer spacing measurement image of NiCo-FDH@PC-40 (Example 6), Figure 5 (b) is a high-resolution transmission electron microscopy interlayer spacing measurement image of NiCo-LDH@PC-40 (Example 1). The small figures in the two figures are the calculation results of the molecular dynamics diameter of potassium ions and hydroxide ions in the electrolyte potassium hydroxide. Through measurement, the average interlayer spacing of NiCo-FDH@PC-40 (Example 6) is 0.429nm, and the average interlayer spacing of NiCo-LDH@PC-40 (Example 1) is 0.735nm. The average interlayer spacing has increased by 71.33%, which is 2.3% larger than that of NiCo-LDH@PC-40 (Example 1). Figure 4 The expanded interlayer spacing is sufficient for the smooth insertion and extraction of electrolyte KOH ions, which enhances the electron transfer rate, conductivity, and electrochemical performance.

[0101] Example 10

[0102] This example is to verify the performance of the layered double hydroxide porous carbon composite material prepared in Examples 1 to 6 when used as an electrode material.

[0103] Specifically include:

[0104] This example uses a slurry coating process to prepare an electrode. 0.08g of the layered double hydroxide porous carbon composite material prepared in Examples 1 to 6 was thoroughly mixed with 0.01g of polytetrafluoroethylene powder and 0.01g of acetylene black, 1mL of anhydrous ethanol was added, and ultrasonic dispersion was performed for 15 minutes. The mixture was evenly applied to a 1cm*1cm nickel foam and pressurized at 10MPa. The stamped nickel foam was placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain 6 different double hydroxide porous carbon composite electrodes.

[0105] The prepared six double metal hydroxide porous carbon composite materials were used as working electrodes, platinum electrode as counter electrode, and Hg / HgO electrode as reference electrode to form a three-electrode system in 6 mol / L potassium hydroxide aqueous solution for electrochemical performance testing.

[0106] like Figure 6 The figure shows the cyclic voltammetry (CV) curves of the NiCo-LDH@PC-40 working electrode three-electrode system at different scan rates in the voltage window of 0-0.5 V. As the scan rate increases, the redox peaks are clear and well-symmetrical, indicating that the composite material has high pseudocapacitive behavior and excellent electrochemical reaction reversibility.

[0107] like Figure 7 Figure 2 shows galvanostatic charge-discharge (GCD) plots of a three-electrode system with a NiCo-LDH@PC-40 working electrode at various current densities within the 0-0.5V voltage window. At a low current density of 0.5A / g, the NiCo-LDH@PC-40 composite exhibits a long discharge time and high specific capacitance, further demonstrating its excellent energy storage capacity. While the discharge time decreases with increasing current density, the voltage plateau remains stable, demonstrating the material's high electrochemical stability and excellent rate capability.

[0108] like Figure 8 Figure 2 shows cyclic voltammetry (CV) curves for a three-electrode system of NiCo-LDH@PC composite materials (Examples 1-5) with five different loadings, obtained in a 0-0.5V voltage window at a scan rate of 5mV / s. NiCo-LDH@PC-40 exhibits the largest curve area, indicating the highest specific capacitance and the greatest pseudocapacitive charge storage capacity. Furthermore, the symmetrical redox peaks are prominent, demonstrating good charge-discharge reversibility and pseudocapacitive performance.

[0109] like Figure 9 As shown, the constant current charge-discharge (GCD) diagram of the working electrode three-electrode system of NiCo-LDH@PC composite materials (Examples 1-5) with five different loadings was obtained at a current density of 0.5A / g in the 0-0.5V voltage window. NiCo-LDH@PC-40 showed the longest discharge time, further confirming its superior electrochemical performance. Figure 8 The results are consistent.

[0110] like Figure 10Figure 2 shows the rate performance of the three-electrode system of the NiCo-LDH@PC composite materials (Examples 1-5) with five different loadings in the 0-0.5 V voltage window. The specific capacitance of NiCo-LDH@PC-40 is highest at various current densities (0.5 A / g, 1 A / g, 2 A / g, 5 A / g, and 10 A / g), reaching a high of 1767 F / g at 0.5 A / g and 1220 F / g at 10 A / g, with a capacitance retention of 69.04%.

[0111] It is worth noting that under the action of hydrazine hydrate, NiCo-LDH was successfully loaded on the surface of porous carbon material through secondary hydrothermal treatment, and Ni and Co showed Ni 2+ / Ni 3+ and Co 2+ / Co 3+ The valence state transition is crucial to improving electrochemical performance, especially Co 3+ and Ni 3+ The increase in helps to improve the pseudocapacitive contribution, thereby enhancing the charge storage capacity of the material.

[0112] like Figure 11 As shown, it shows the rate performance diagram of the three-electrode system of the NiCo-FDH@PC-40 composite material (Example 6) working electrode in the 0-0.5V voltage window. The specific capacitance of NiCo-FDH@PC-40 is obviously too low, eventually exceeding the instrument measurement range, and finally maintaining at 20F / g. This may be because the NiCo-FDH structure with too small interlayer spacing leads to poor ion passage, which limits the charge and discharge process of the material at high rates, thereby affecting the overall electrochemical performance.

[0113] It should be noted that under the action of EDTA-2Na, EDTA 2+ With EDTA 4+ Ions are embedded in the NiCo-LDH interlayers, expanding the interlayer spacing and enabling rapid insertion and removal of electrolyte potassium hydroxide ions, enhancing the conductivity of the composite material and improving its electrochemical performance. However, the excessively small interlayer spacing of NiCo-FDH@PC-40 (Example 6) is insufficient for efficient charge transfer between potassium and hydroxide ions, resulting in decreased electrochemical performance.

[0114] Example 11

[0115] In this example, the NiCo-LDH@PC-40 composite material electrode prepared according to Example 1 in Example 8 was used as the positive electrode, and the electrode prepared by the porous carbon material according to the electrode preparation method in Example 6 was used as the negative electrode. The two electrode sheets were placed in a CR2032 battery case, an aqueous diaphragm was placed in the middle of the electrode sheet, and 2 drops of 6 mol / L potassium hydroxide solution were added to the diaphragm. The battery was pressed and packaged at 10 MPa using a button battery sealing machine. After standing for 6 hours, an asymmetric supercapacitor was obtained, and constant current charge and discharge tests, cyclic voltammetry tests, and cycle performance tests were performed in the 0-1.5 V voltage window.

[0116] like Figure 12 The figure shows the rate performance of the button-type asymmetric supercapacitor prepared in this example. At a current density of 0.5 A / g, the specific capacitance reaches 109 F / g, and at a current density of 10 A / g, the specific capacitance is 54 F / g, with a specific capacitance retention rate of 49.54%, demonstrating its excellent specific capacitance and rate performance.

[0117] like Figure 13 The figure shows a comparison of the energy density of the button-type asymmetric supercapacitor prepared in this example with that of a supercapacitor prepared using the prior art. When the energy density is 375 W / kg, the energy density is 34.06 Wh / kg, which is higher than that of the supercapacitor prepared in the literature.

[0118] like Figure 14 As shown, a comparison chart of the electrochemical cycle stability of the button-type asymmetric supercapacitor prepared in this embodiment and the button-type symmetric supercapacitor prepared by the porous carbon material prepared in Example 1 using the same method as this embodiment is shown. After the asymmetric supercapacitor was subjected to 12,000 charge and discharge cycles at a current density of 5 A / g, the capacitance retention rate of the button-type asymmetric supercapacitor was 86.96%, and the coulombic efficiency was maintained at 100%, indicating its good cycle stability. This is because the divalent and trivalent coexistence of Ni and Co can reversibly change the valence state during the charge and discharge redox reaction. At the same time, the expanded interlayer spacing makes the electron transfer in the valence state transition faster and more efficient, thereby giving the material better cycle stability. However, since the symmetric supercapacitor has no load of active components, the pore structure gradually collapses during the electrochemical cycle reaction, resulting in a low electron adsorption and desorption efficiency, which reduces the electrochemical performance.

[0119] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing, characterized in that: The following steps are involved: S1, mixing coal tar powder with an alkaline activator, calcining under an inert gas atmosphere, acid washing, filtering and drying to obtain a porous carbon material; S2, mixing the porous carbon material in S1, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinyl pyrrolidone, and disodium ethylenediaminetetraacetic acid solution, performing a hydrothermal reaction at a certain temperature, and cooling to room temperature to obtain a pink suspension; S3, the suspension of S2 is uniformly mixed with a certain amount of hydrazine hydrate, and hydrothermally reacted again at a certain temperature, and cooled to room temperature to obtain a green suspension; S4. The suspension of S3 is washed, filtered and dried to obtain a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing.

2. The method for preparing a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to claim 1, characterized in that: In the S1, the mass ratio of coal tar powder to alkaline activator is 1:2-4.

3. The method for preparing a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to claim 1, characterized in that: In the S1, the temperature is raised to 400-600° C. at a heating rate of 2-10° C. / min under an inert gas atmosphere and kept at that temperature for 1-3 hours.

4. The method for preparing a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to claim 1, characterized in that: In the step S1, the alkaline activator is one of potassium hydroxide, zinc oxide or magnesium hydroxide.

5. The method for preparing a NiCo-LDH / porous carbon composite material with an enlarged interlayer spacing according to claim 1, characterized in that: In the S1, the calcined powder is placed in an acidic solution for washing, and then washed with water for multiple times until the filtrate is neutral after filtration, and then dried at a temperature of 60-100° C. for 6-18 hours to obtain a porous carbon material.

6. The method for preparing a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to claim 1, characterized in that: In S2, the mass ratio of the porous carbon material, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, polyvinyl pyrrolidone, and disodium edetate is 10-70:872:873:1200:807, and 30-50 mL of water is added when preparing an aqueous solution.

7. The method for preparing a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to claim 1, characterized in that: In the S3, the suspension of S2 is uniformly mixed with 2-4 mL of hydrazine hydrate and hydroheated again.

8. The method for preparing a NiCo-LDH / porous carbon composite material with an expanded interlayer spacing according to claim 1, characterized in that: In the step S4, the green suspension in S3 is washed several times with anhydrous ethanol and water, respectively, and vacuum-dried at 60-80°C for 6-18 hours. 9 . The NiCo-LDH / porous carbon composite material with enlarged interlayer spacing prepared by the preparation method according to claim 1 .

10. Use of the NiCo-LDH / porous carbon composite material according to claim 9 as a negative electrode material.

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