A layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions and its application

Abstract

The present invention discloses a layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions and its application, which is a two-dimensional layered infinite structure, and the complex is composed of a mononuclear nickel ion and a bridging potassium ion to form a layered structure. Since the layers are connected by weak intermolecular interactions, the structure and volume of the complex will not be significantly affected during the charge or ion transmission or migration process. In addition, there are a large number of benzene rings, oxygen atoms, sulfur atoms and heterometallic ions of different valence states on the layered structure, which can store a large amount of charge. In particular, the tetracoordinated divalent nickel ion is a redox site with strong electrochemical activity, has strong commercial practicability, and can be applied to supercapacitor electrodes.

Description

Technical Field

[0001] The invention belongs to the technical field of supercapacitors, and in particular relates to a layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions, and a preparation method and application thereof. Background Art

[0002] With the excessive use of fuel, environmental pollution and energy difficulties are becoming more and more serious. The key to solving these urgent environmental problems is to develop clean new energy. In order to effectively utilize these energy sources, the demand for efficient energy storage systems is becoming more and more urgent. In these energy storage systems, lithium-ion batteries have high energy density compared to supercapacitors, but their power density is not high. Supercapacitors have high power density, good electrochemical reversibility and high cycle stability, and have great application prospects in portable electronic products, electric vehicles, and energy storage.

[0003] At present, the research on supercapacitor electrode materials mainly focuses on carbon-based electrode materials, conductive polymer electrode materials and transition metal compound electrode materials. Among them, skeleton complexes, as a functional material, have been applied in many fields due to their structural diversity, adjustable pore size (porosity, surface area, density), simple synthesis process and low cost. However, as electrode materials, the structure and volume of skeleton complexes will be significantly affected during the charge or ion transfer or migration process, thereby affecting the stability of the electrode material and limiting its application as supercapacitor electrode material.

[0004] The inventor team of this application has achieved some scientific research results in previous research, such as:

[0005] Chinese patent publication number CN112745510A: "A multilayer columnar functional complex containing nickel atom cluster structural units and sodium ions and its application";

[0006] Chinese patent publication number CN107221458B "Carbon-doped nickel oxide composite electrode material with nickel complex as precursor and preparation method thereof";

[0007] This application further innovates by halving the original nickel salt content and adding sodium salt. The use of mixed salts changes the coordination environment of nickel ions in the solution, changing the coordination mode of o-mercaptobenzoic acid, thereby obtaining a new structure of the complex. Compared with the team's previous results, this method provides the synthesis conditions for synthesizing a new structure of the complex, thereby deriving the new technical solution of this application. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions and its application.

[0009] To achieve the above-mentioned purpose, the technical solution of the present invention is the first aspect of the present invention, which provides a layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions.

[0010] The second aspect of the present invention provides a method for preparing the layered functional complex containing a tetracoordinated nickel ion structural unit and a potassium ion as described above, comprising the following steps:

[0011] ① Dissolve potassium hydroxide and / or alkaline potassium salt in ethanol;

[0012] ② Add o-mercaptobenzoic acid to the solution prepared in step ① to completely dissolve it;

[0013] ③ preparing a mixed solution of sodium ions and nickel ions, and dripping the mixed solution of sodium ions and nickel ions into the solution in step ②, wherein the ratio of sodium ions to nickel ions in the mixed solution of sodium ions and nickel ions is 1:15-20, and the molar ratio of total ions in the mixed solution of sodium ions and nickel ions to o-mercaptobenzoic acid is 1:2.6-5.4;

[0014] ④ Pour the solution of step ③ into a stainless steel reactor lined with polytetrafluoroethylene, and react at a temperature of 100-150°C for 3-5 days;

[0015] ⑤ After the reaction is completed, the reactor is cooled naturally to room temperature, and the obtained product is centrifugally washed with deionized water and anhydrous ethanol for multiple times, and dried to obtain a brown flaky product, which is the supercapacitor electrode material as claimed in claim 1.

[0016] Preferably, in step ③, the mixed solution of sodium ions and nickel ions is obtained by dissolving water-soluble sodium salt and nickel salt in ionized water, the water-soluble nickel salt is one or more of nickel nitrate hexahydrate, nickel acetate tetrahydrate, nickel sulfate hexahydrate, and nickel chloride hexahydrate, and the water-soluble sodium salt is one or more of sodium carbonate and sodium acetate.

[0017] The third aspect of the present invention provides the use of the layered functional complex containing tetracoordinated nickel ion structural units and potassium ions as described above as a supercapacitor electrode material.

[0018] A fourth aspect of the present invention provides a supercapacitor electrode material, which uses the layered functional complex containing tetracoordinated nickel ion structural units and potassium ions as described above as at least a part of the electrode material.

[0019] The fifth aspect of the present invention provides a method for preparing a supercapacitor electrode as described above, comprising the following steps: coating a slurry of electrode material on a current collector and drying to obtain a supercapacitor electrode material; the slurry of the electrode material comprises a layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions, a conductive agent, and a binder as described above.

[0020] The conductive agent may specifically be a conductive agent raw material commonly used for supercapacitor electrodes, such as carbon black, acetylene black, Ketjen black, Super-P, etc. An embodiment of the present invention uses acetylene black as the conductive agent.

[0021] The binder may specifically be a binder raw material commonly used for supercapacitor electrodes, such as polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide and various copolymers. In one embodiment of the present invention, polytetrafluoroethylene is used as the binder.

[0022] The current collector is a material that is conductive and does not cause chemical changes in the supercapacitor, such as stainless steel mesh, copper mesh, aluminum foil, carbon cloth, nickel foam, etc. One embodiment of the present invention uses nickel foam as the current collector.

[0023] The beneficial effects of the present invention are as follows: The present invention provides a layered functional complex containing a tetracoordinated nickel ion building block and a potassium ion, which is a two-dimensional layered infinite structure, and the complex is composed of a mononuclear nickel ion and a bridging potassium ion to form a layered structure. Since the layers are connected by weak intermolecular interactions, the structure and volume of the complex will not be significantly affected during the charge or ion transmission or migration process. In addition, there are a large number of benzene rings, oxygen atoms, sulfur atoms and heterometallic ions of different valence states on the layered structure, which can store a large amount of charge. In particular, the tetracoordinated divalent nickel ion is a redox site with strong electrochemical activity and has strong commercial practicality.

[0024] The complex [Ni 2+ K + (Hmba) - (mba) 2- ] n (mba o-mercaptobenzoic acid divalent anion) is prepared into an electrode sheet of a three-electrode system, and a high specific capacitance of 496F / g is obtained at a current density of 1A / g, which can provide strong commercial practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0026] Figure 1 This is a single crystal analysis diagram of the coordination unit of the tetracoordinated Ni-functional complex prepared in Example 1 of the present invention;

[0027] Figure 2 A schematic diagram of the layered structure of the tetracoordinated Ni-functional complex prepared in Example 1 of the present invention;

[0028] Figure 3 The X-ray diffraction pattern of the tetracoordinated Ni-functional complex prepared in Example 1 of the present invention;

[0029] Figure 4 This is a thermogravimetric curve of the tetracoordinated Ni-functional complex prepared in Example 1 of the present invention;

[0030] Figure 5 This is a scanning electron microscope image of the tetracoordinated Ni-functional complex prepared in Example 1 of the present invention, wherein (a), (b) and (c) represent the view scales of 10 μm, 5 μm and 4 μm, respectively;

[0031] Figure 6 The cyclic voltammetry curves of the tetracoordinated Ni-functional complex prepared in Example 3 of the present invention at different scan rates in a three-electrode system;

[0032] Figure 7 This is a constant current charge-discharge curve of the four-coordinated Ni-functional complex prepared in Example 3 of the present invention in a three-electrode system;

[0033] Figure 8 This is a graph showing the specific capacitance of the tetracoordinated Ni-functional complex prepared in Example 3 of the present invention in a three-electrode system;

[0034] Fig. 9 This is an AC impedance curve of the four-coordinated Ni-functional complex prepared in Example 3 of the present invention in a three-electrode system. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] The raw materials used in the following examples and test examples are as follows:

[0037] The raw materials are shown in Table 1 below:

[0038] Table 1 Main reagents

[0039]

[0040] Example 1: Preparation of a layered functional complex containing a tetracoordinated nickel ion building block and a potassium ion:

[0041] ① Pour potassium hydroxide (0.003 mol, 0.1683 g) into 10 ml of anhydrous ethanol, and then ultrasonicate it in an ultrasonic cleaner for a period of time until the potassium hydroxide is completely dissolved in the anhydrous ethanol. Potassium hydroxide can be replaced by alkaline potassium salts such as potassium carbonate.

[0042] ② Add o-mercaptobenzoic acid (0.003 mol, 0.4626 g) to solution ① and stir on a constant temperature magnetic stirrer until it is completely dissolved.

[0043] ③ Completely dissolve nickel sulfate hexahydrate (0.00071 mol, 0.1877 g) and sodium carbonate decahydrate (0.000035 mol, 0.0102 g) in 5 ml of deionized water, then slowly drip the solution into the above solution with a dropper, and continue stirring for half an hour. The nickel raw material can also be common nickel salts such as nickel sulfate hexahydrate and nickel nitrate hexahydrate, and the sodium raw material can also be anhydrous sodium acetate.

[0044] ④ Pour the stirred solution into a 30 ml polytetrafluoroethylene-lined stainless steel reactor and react at 120°C in an electric blast drying oven for 4 days.

[0045] ⑤ After the reaction is completed, wait for the reactor to cool naturally to room temperature, then centrifuge and wash the obtained product with deionized water and anhydrous ethanol for multiple times, and finally dry it in an electric heated blast drying oven at 90°C to obtain a brown layered product, named Ni-functional complex.

[0046] Example 2: Preparation of a layered functional complex containing a tetracoordinated nickel ion building block and a potassium ion:

[0047] ① Pour potassium hydroxide (0.003 mol, 0.1683 g) into 10 ml of anhydrous ethanol, and then ultrasonicate it in an ultrasonic cleaner for a period of time until the potassium hydroxide is completely dissolved in the anhydrous ethanol.

[0048] ② Add o-mercaptobenzoic acid (0.003 mol, 0.4626 g) to solution ① and stir on a constant temperature magnetic stirrer until it is completely dissolved.

[0049] ③ Completely dissolve nickel sulfate hexahydrate (0.00070 mol, 0.1877 g) and anhydrous sodium acetate (0.000046 mol, 0.00384 g) in 5 ml of deionized water, then slowly add the solution into the above solution with a dropper and continue stirring for half an hour.

[0050] ④ Pour the stirred solution into a 30 ml polytetrafluoroethylene-lined stainless steel reactor and react at 120°C in an electric blast drying oven for 4 days.

[0051] ⑤ After the reaction is completed, wait for the reactor to cool naturally to room temperature, then centrifuge and wash the obtained product with deionized water and anhydrous ethanol for multiple times, and finally dry it in an electric heated blast drying oven at 90°C to obtain a brown layered product, named Ni-functional complex.

[0052] Example 3: Preparation of a layered functional complex containing a tetracoordinated nickel ion building block and a potassium ion:

[0053] ① Pour potassium hydroxide (0.003 mol, 0.1683 g) into 10 ml of anhydrous ethanol, and then ultrasonicate it in an ultrasonic cleaner for a period of time until the potassium hydroxide is completely dissolved in the anhydrous ethanol.

[0054] ② Add o-mercaptobenzoic acid (0.003 mol, 0.4626 g) to solution ① and stir on a constant temperature magnetic stirrer until it is completely dissolved.

[0055] ③ Completely dissolve nickel chloride hexahydrate (0.00071 mol, 0.1697 g) and anhydrous sodium acetate (0.000035 mol, 0.00287 g) in 5 ml of deionized water, then slowly add the solution into the above solution with a dropper and continue stirring for half an hour.

[0056] ④ Pour the stirred solution into a 30 ml polytetrafluoroethylene-lined stainless steel reactor and react at 120°C in an electric blast drying oven for 4 days.

[0057] ⑤ After the reaction is completed, wait for the reactor to cool naturally to room temperature, then centrifuge and wash the obtained product with deionized water and anhydrous ethanol for multiple times, and finally dry it in an electric heated blast drying oven at 90°C to obtain a brown layered product, named Ni-functional complex.

[0058] Test Example 1: Crystal structure analysis

[0059] like Figure 1As shown, the complex consists of a tetracoordinated mononuclear divalent nickel structural unit (upper side) and a bridging potassium ion (lower side). The mononuclear nickel ion is chelated and coordinated by a monovalent o-mercaptobenzoic acid anion and a divalent o-mercaptobenzoic acid anion through a carboxyl oxygen and a mercaptosulfur, respectively, to form a tetracoordinated mononuclear divalent nickel structural unit. Among them, the carboxyl group of the monovalent o-mercaptobenzoic acid anion is not deprotonated. The carbonyl oxygen on the carboxyl group of the monovalent o-mercaptobenzoic acid anion and the two oxygens on the carboxyl group of the divalent o-mercaptobenzoic acid anion simultaneously bridge the K1 ion, forming a coordination unit of the Ni-functional complex.

[0060] The two oxygens on the carboxyl group of the divalent o-mercaptobenzoic acid anion in the coordination unit simultaneously bridge the K ion in another adjacent coordination unit. At the same time, the sulfur on the thiol group of the monovalent o-mercaptobenzoic acid anion and the divalent o-mercaptobenzoic acid anion in the coordination unit simultaneously bridges the K ion in the other coordination unit. Similarly, the K1 ion is also bridged by the two oxygens on the carboxyl group of the divalent o-mercaptobenzoic acid anion in the adjacent coordination unit and the sulfur on the thiol group of the monovalent o-mercaptobenzoic acid anion and the divalent o-mercaptobenzoic acid anion in the two coordination units below, forming a nine-coordination mode. In this way, one potassium ion bridges four four-coordinated mononuclear divalent nickel structural units, extending infinitely in two dimensions to form a structure like Figure 2 The two-dimensional layered structure shown.

[0061] Experimental Example 2: X-ray diffraction phase analysis (XRD)

[0062] The Ni-functional complex of the electrode material synthesized in Example 1 was analyzed by X-ray diffraction. Figure 3 As shown. XRD spectrum ( Figure 3 The peaks in the above are similar to those in the single crystal data ( Figure 3 Next) C 14 The peaks are consistent with those simulated by H9KNiO4S2. Figure 3 It can also be seen that the diffraction peak is sharp and no other peaks are observed, indicating that the synthesized sample is pure phase.

[0063] Test Example 3: Thermal Stability Analysis (TGA)

[0064] The thermal stability of the synthesized Ni-functional complex of electrode material was analyzed by thermogravimetric analysis. Figure 4 It can be seen that when the temperature is between 25℃ and 150℃, the mass loss of the complex is about 1.2%, which is mainly caused by the release of free water molecules in the complex; there are two main decomposition stages at the temperature between 120℃ and 500℃. In the first stage, the temperature rises from 150℃ to 300℃, and the mass of the complex slowly decreases, with a loss of about 4.6%, which represents the Ni 2+The coordinated hydroxide ions are released; the second stage is at 300-360°C, the rapid decrease in sample weight (~24.3%) indicates the decomposition of organic ligands, indicating the rapid collapse of the structure; the third stage is at 360-500°C, Ni is oxidized, and due to the carbonization of organic ligands, the structure collapses into the main phase of NiO with some residues (such as C and S). When the temperature is higher than 500°C, the mass of the sample decreases slowly, which is due to the release of gases formed by the oxidation of residues such as C and S formed after the carbonization of ligands.

[0065] Test Example 4: Scanning Electron Microscope (SEM)

[0066] The macroscopic morphology of the synthesized Ni-functional complex of electrode material was characterized and analyzed by scanning electron microscopy. Figure 5 As shown in a, b and c, the Ni-functional complex in the figure is stacked by layers of different shapes and sizes, with a relatively smooth surface and a large specific surface area.

[0067] Example 2: Electrode preparation of supercapacitor three-electrode system

[0068] ① The Ni-functional complex prepared in Example 1 was used as an electrode material, and was added into a mortar with acetylene black and polytetrafluoroethylene in a mass ratio of 8:1:1, and ground to mix them thoroughly until a paste was formed to obtain an electrode active substance.

[0069] ②Evenly coat the ground electrode active material on the nickel foam. The mass of the coated electrode active material is about 2 mg and the coating area is 1 cm 2 , and then dried at 90°C for more than 1 h, and pressed at a pressure of 2 MPa to obtain an electrode sheet.

[0070] ③ Soak the electrode sheet obtained in ② in 6M KOH electrolyte for more than 10 hours to obtain the electrode sheet to be tested in the three-electrode system.

[0071] Experimental Example 4: Cyclic Voltammetry (CV)

[0072] The electrode sheet prepared in Example 2 was tested using an electrochemical workstation CHI760E at 5 mV s -1 , 10 mV s -1 , 20mV s -1 and 30mV s -1 The results are as follows: Figure 6 The figure shows a cyclic voltammetry curve with a pseudocapacitive characteristic redox peak, indicating that the redox reaction on the surface of the electrode material is reversible. As the scan rate increases, the redox peak gradually polarizes and shifts, indicating that the Faraday reaction may be controlled by the ion diffusion process.

[0073] Test Example 5: Constant Current Charge and Discharge Test Analysis (GCD)

[0074] Figure 7 The constant current charge and discharge curves at different current densities show that at a current density of 1A / g, the discharge time is the longest, indicating the highest capacitance performance. As the current density increases, the discharge time gradually decreases, which may be due to the lack of ideal redox activity at high current density.

[0075] Test Example 6: Specific Capacitance Analysis

[0076] From the constant current charge and discharge curve, the specific capacitance of the electrode material can be calculated according to the following formula 1: Figure 8 shown.

[0077]

[0078] In the formula, Cm(F g-1) is the mass specific capacity of the material, I(A) is the charge and discharge current, Δt(s) is the discharge time, m(g) is the mass of the active material, and ΔV(V) is the charge and discharge voltage window.

[0079] Depend on Figure 8 It can be clearly seen that when the current density is 1, 2, 3, 5, 8, 10, 15, and 20 A / g, the specific capacitance is 496, 442.8, 414.2, 377.2, 333.4, 306.4, 276, and 236.8 F / g, respectively, and the capacitance retention rate is 48%.

[0080] Test Example 7: Electrochemical Impedance Spectroscopy (EIS)

[0081] The material was activated for half an hour using a constant current charge-discharge test method using an electrochemical workstation. After the electrochemical system was stable, the material was activated at an open circuit voltage in the frequency range of 10 -2 Hz~10 5 Hz conducted an AC impedance test on the three-electrode system of the supercapacitor, and the results were as follows Fig. 9 As shown in the figure, it can be seen that the AC impedance curve of the electrode material can be divided into two parts: high-frequency region and low-frequency region. By fitting the impedance spectrum, the solution impedance of the three-electrode system is 1.2Ω and the electron transfer impedance is 1.9Ω.

[0082] Although the invention has been described with reference to several specific embodiments, it should be understood that the invention is not limited to the specific embodiments disclosed. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A layered functional complex containing a tetracoordinated nickel ion structural unit and a potassium ion, characterized in that: It consists of a mononuclear four-coordinated divalent nickel ion and a bridging potassium ion to form a layered structure, and the layers are connected by weak intermolecular interactions; The preparation method of the complex comprises the following steps: ① Dissolve potassium hydroxide and / or alkaline potassium salt in ethanol; ② Add o-mercaptobenzoic acid to the solution prepared in step ① to completely dissolve it; ③ preparing a mixed solution of sodium ions and nickel ions, and dripping the mixed solution of sodium ions and nickel ions into the solution in step ②, wherein the ratio of sodium ions to nickel ions in the mixed solution of sodium ions and nickel ions is 1:15-20, and the molar ratio of total ions in the mixed solution of sodium ions and nickel ions to o-mercaptobenzoic acid is 1:2.6-5.4; ④ Pour the solution in step ③ into a reaction kettle and react at a temperature of 100-150°C for 3-5 days; ⑤ After the reaction is completed, the reactor is cooled naturally to room temperature, and the obtained product is centrifuged and washed to obtain a brown flaky product, which is the layered functional complex containing a tetracoordinated nickel ion structural unit and a potassium ion; In the step ③, the mixed solution of sodium ions and nickel ions is obtained by dissolving water-soluble sodium salt and nickel salt in deionized water, the water-soluble nickel salt is one or more of nickel nitrate hexahydrate, nickel acetate tetrahydrate, nickel sulfate hexahydrate, and nickel chloride hexahydrate, and the water-soluble sodium salt is one or more of sodium carbonate decahydrate and anhydrous sodium acetate.

2. A use of the layered functional complex containing a tetracoordinated nickel ion structural unit and potassium ions as claimed in claim 1 as a supercapacitor electrode material.

3. A supercapacitor electrode material, characterized in that: The electrode material is composed of the layered functional complex containing tetracoordinated nickel ion structural units and potassium ions as claimed in claim 1 as at least one part.

4. A method for preparing a supercapacitor electrode material, characterized in that: The slurry of the electrode material is coated on the current collector and dried to obtain the supercapacitor electrode material; the slurry of the electrode material comprises the layered functional complex containing the tetracoordinated nickel ion structural unit and the potassium ion as claimed in claim 1, a conductive agent, and an adhesive.

5. A supercapacitor, characterized in that: Comprising the supercapacitor electrode material as claimed in claim 3.

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