NiCoPBA (at) rGO electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of supercapacitor electrode materials, in particular to a NiCoPBA (at) rGO electrode material and a preparation method and application thereof. Soluble nickel salt, sodium citrate, reduced graphene oxide and potassium hexacyanocobaltate are used as raw materials, nickel ions of the soluble nickel salt are electrostatically adsorbed on the reduced graphene oxide, and then the nickel ions of the soluble nickel salt are diffused into the potassium hexacyanocobaltate; under the action of Ostwald, the nickel ions are embedded into potassium hexacyanocobaltate and partial substitution of the cobalt ions is completed, at the same time, the coordination reaction of the nickel ions and cyano groups in the potassium hexacyanocobaltate is completed, and finally the NiCoPBA (at) rGO electrode material with NiCoPBA attached to the rGO sheet layer is prepared. According to the method disclosed by the invention, the NiCoPBAatrGO electrode material can be obtained at normal temperature and is not influenced by the pH value of a solution and the reaction temperature, and the technical defects existing in the preparation of prussian blue derivatives in the prior art are overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of supercapacitor electrode materials, and specifically relates to NiCoPBA@rGO electrode materials and preparation methods and applications thereof. Background Art

[0002] A supercapacitor is an electronic component that can store a large amount of charge. It has the advantages of high energy density, high power density and fast charging and discharging speed. Its operating principle is to use the interfacial double layer effect between the electrolyte and the electrode to store charge. When the ions in the electrolyte solution contact the electrode surface, a layer of charge is formed on it. This layer of charge forms a double layer interface with the ions in the electrolyte, thereby realizing the storage of charge. It can complete charging and discharging in a short time and can work at high power, so it is widely used in electric vehicles, solar energy and wind energy. Supercapacitors are divided into flat plate type, cylindrical type and spiral type. Among them, the flat plate type is the most common structure because it has the advantages of simplicity, easy manufacturing and low cost. According to the working voltage of supercapacitors, they are divided into low-voltage supercapacitors and high-voltage supercapacitors. The working voltage of low-voltage supercapacitors is generally below 2.5V, while the working voltage of high-voltage supercapacitors can reach hundreds of volts or even thousands of volts.

[0003] In supercapacitors, electrode materials are one of the key factors that determine their performance. In order to improve the performance of supercapacitors, the continuous search for and development of new electrode materials has always been a hot topic. Among the new electrode materials, the excellent electrochemical properties of Prussian blue derivatives (PBA) have brought them into the field of vision of researchers. Prussian blue is an analogue of Prussian blue, and there are many types. With the different types and proportions of metals, the structures of the prepared Prussian blue derivatives are diverse. Prussian blue derivatives are a porous structure material, and their excellent charge transfer performance makes them stand out among electrode materials, which makes their application in supercapacitors very popular.

[0004] However, the Prussian blue derivatives in the prior art are greatly affected by the synthesis conditions, such as the pH of the solution and the reaction temperature, which results in the inability to prepare the Prussian blue derivatives on a large scale, thereby affecting the application of the Prussian blue derivatives. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned prior art, the present invention provides a NiCoPBA@rGO electrode material and a preparation method and application thereof; the present invention uses a soluble nickel salt, sodium citrate, reduced graphene oxide and potassium hexacyanocobaltate as raw materials, first electrostatically adsorbs the nickel ions of the soluble nickel salt on the reduced graphene oxide, then diffuses the nickel ions of the soluble nickel salt into the potassium hexacyanocobaltate, embeds into the potassium hexacyanocobaltate under the Oswald effect and completes partial substitution of the cobalt ions, and at the same time, the nickel ions complete a coordination reaction with the cyano group in the potassium hexacyanocobaltate, and finally prepares a NiCoPBA@rGO electrode material in which NiCoPBA is attached to the rGO sheet. The method of the present invention can obtain the NiCoPBA@rGO electrode material at room temperature, and is not affected by the pH and reaction temperature of the solution, overcoming the technical defects of the preparation of Prussian blue derivatives in the prior art.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The preparation method of NiCoPBA@rGO electrode material is characterized by comprising the following steps:

[0008] Soluble nickel salt, sodium citrate and reduced graphene oxide are mixed and dispersed in deionized water. Sodium citrate is a buffer for maintaining the pH stability of the solution. Without sodium citrate, the pH value of the solution fluctuates greatly as the reaction proceeds, affecting the uniform formation of the NiCoPBA@rGO electrode material. Reduced graphene oxide (rGO) is negatively charged, and nickel ions of the soluble nickel salt are electrostatically adsorbed on the reduced graphene oxide to obtain a mixed solution.

[0009] dissolving potassium hexacyanocobaltate in deionized water to obtain a potassium hexacyanocobaltate solution;

[0010] Under stirring conditions, potassium hexacyanocobaltate solution is added dropwise to the mixed solution. At this time, the nickel ions of the soluble nickel salt replace part of the cobalt ions in potassium hexacyanocobaltate. This reaction utilizes the Oswald ripening reaction mechanism, and the small nickel ion group is transformed into a large nickel cobalt cyano ion coordination group. During the transformation process, part of the nickel ions coordinate with the cyano group in potassium hexacyanocobaltate to complete the substitution process. After the reaction is completed, the solvent is separated to obtain the NiCoPBA@rGO electrode material.

[0011] Preferably, in the mixed solution, the concentration of soluble nickel salt, the concentration of sodium citrate and the mass ratio of reduced graphene oxide are 0.5-1.5mmol / L:0.9mmol / L:0.01-0.02g. The amount of sodium citrate is determined according to the soluble nickel salt, and sodium citrate is mainly used to maintain the pH stability of the solution.

[0012] Preferably, the molar ratio of the soluble nickel salt to potassium hexacyanocobaltate is 1-3:1. Due to partial substitution, the molar ratio of the two is 1-3:1.

[0013] Preferably, the stirring time of the coordination reaction is ≥10 min. If large-scale production is carried out, the stirring time is adjusted according to the amount of raw materials.

[0014] Preferably, after separating the solvent from the mixed solution, deionized water is used for washing to remove excess water-soluble ions that do not participate in the coordination reaction, such as nickel ions and sodium ions.

[0015] Preferably, the precipitate is dried under vacuum conditions after washing, and vacuum drying ensures that the metal ions nickel and cobalt are not oxidized by air to form oxides.

[0016] The present invention also protects the NiCoPBA@rGO electrode material prepared by the above preparation method, and the NiCoPBA@rGO electrode material is a NiCo@rGO-type Prussian blue derivative electrode material.

[0017] The present invention also protects the positive electrode material prepared by the NiCoPBA@rGO electrode material.

[0018] Preferably, the method for preparing the positive electrode material comprises the following steps:

[0019] The NiCoPBA@rGO electrode material, the conductive agent and the binder are mixed, ethanol is added to obtain a slurry, the slurry is evenly coated on the current collector, and the positive electrode material is obtained after drying and pressing;

[0020] Among them, the mass ratio of NiCoPBA@rGO electrode material, conductive agent and binder is 0.75-0.85:0.1-0.15:0.1-0.15.

[0021] The present invention also protects the use of the above positive electrode material in preparing the positive electrode material of super capacitor.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses soluble nickel salt, sodium citrate and reduced graphene oxide as raw materials, mixes them in deionized water to obtain a mixed solution, rGO is negatively charged, and it serves as an ion deposition site, so that the nickel ions of the soluble nickel salt are electrostatically adsorbed on the reduced graphene oxide, and then the mixed solution is mixed with a potassium hexacyanocobaltate solution, and the nickel ions of the soluble nickel salt diffuse into the potassium hexacyanocobaltate, and are embedded in the potassium hexacyanocobaltate under the action of Oswald and complete the partial replacement of the cobalt ions. At the same time, the nickel ions complete the coordination reaction with the cyano group in the potassium hexacyanocobaltate, and a chemical reaction is carried out at the nickel ion site to form a Prussian blue derivative, and the NiCoPBA@rGO electrode material is prepared. Compared with the prior art, the present invention can prepare a Prussian blue derivative by stirring at room temperature, without harsh pH conditions and reaction temperature, and the raw materials are easily available, low-priced, and the preparation method is simple, without excessive equipment, and is suitable for large-scale batch production.

[0024] 2. The present invention regulates the morphology, structure and chemical composition of Prussian blue derivative materials through reasonable design. In terms of morphology and structure, the NiCoPBA@rGO electrode material prepared by the method of the present invention has a stable structure of a porous skeleton, a large porosity and a flaky layered distribution, a high specific surface area, and abundant active sites; in terms of chemical composition, NiCoPBA is stably electrostatically adsorbed on rGO. NiCoPBA is a Prussian blue-like MOF material. The multi-metal coordination structure of NiCoPBA provides sufficient sites for ion insertion and extraction. In addition, the porous structure is easy for ion transmission, which improves the reaction efficiency, thereby increasing the capacity of the supercapacitor, so that the obtained NiCoPBA@rGO electrode material has a high charge and discharge specific capacity and a high power density, which effectively solves the problem of low specific capacity and power density of existing supercapacitors, thereby realizing that the NiCoPBA@rGO electrode material can give full play to its excellent performance in supercapacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 SEM scans of NiCoPBA@rGO-0.02 of Example 2 at low magnification (a) and high magnification (b).

[0026] Figure 2 This is the XRD pattern of NiCoPBA@rGO-0.02 of Example 2.

[0027] Figure 3 In the figure, (a) is the cyclic voltammetry test graph of NiCoPBA of comparative example 1, and (b) is the cyclic voltammetry test graph of NiCoPBA@rGO-0.01 of example 1.

[0028] Figure 4In the figure, (a) is the cyclic voltammetry test graph of NiCoPBA@rGO-0.02 of Example 2, and (b) is the cyclic voltammetry test graph of NiCoPBA@rGO-0.03 of Comparative Example 2.

[0029] Figure 5 In the figure, (a) is the NiCoPBA@rGO-0.01 rate test diagram of Example 1, and (b) is the NiCoPBA@rGO-0.02 rate test diagram of Example 2.

[0030] Figure 6 This is the rate test diagram of NiCoPBA@rGO-0.03 of comparative example 2.

[0031] Figure 7 These are the AC impedance diagrams of NiCoPBA@rGO-0.01 of Example 1, NiCoPBA@rGO-0.02 of Example 2, NiCoPBA of Comparative Example 1, and NiCoPBA@rGO-0.03 of Comparative Example 2. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0033] Taking into account the excellent performance of Prussian blue-like derivatives and the technical defects of the prior art preparation method of Prussian blue-like derivatives, the present invention provides a new preparation method of Prussian blue-like derivatives and NiCoPBA@rGO electrode material. Compared with the prior art preparation method of Prussian blue-like derivatives, the preparation method of the present invention overcomes the limitations on pH and reaction temperature, so that the NiCoPBA@rGO electrode material can be industrially produced; in addition, the NiCoPBA@rGO electrode material obtained by the method of the present invention has excellent electrochemical properties, high specific capacity and power density, and can be used as a supercapacitor positive electrode material.

[0034] The present invention also compares and studies the amount of raw materials used. The study shows that the amount of reduced graphene oxide will affect the performance of the NiCoPBA@rGO electrode material. An appropriate amount of reduced graphene oxide will have a favorable effect on the performance of the NiCoPBA@rGO electrode material, but an excessive amount of reduced graphene oxide will also have an adverse effect on some of the performances of the NiCoPBA@rGO electrode material. Under experimental conditions, when the mass of reduced graphene oxide is 0.01g, the comprehensive performance is the best. When the mass of reduced graphene oxide increases to 0.02g, the energy storage efficiency is reduced, and a decrease in conductivity occurs. When the mass of reduced graphene oxide reaches 0.03g, the nuclear transfer performance is the best, but the energy storage efficiency is greatly reduced. If industrial large-scale production is carried out, it can be calculated and produced in proportion to the data provided by the present invention.

[0035] The technical solution of the present invention is explained below using embodiments and comparative examples, as shown below:

[0036] Example 1

[0037] The preparation method of NiCoPBA@rGO electrode material comprises the following steps:

[0038] S1. Add nickel nitrate, sodium citrate and 0.01 g of reduced graphene oxide (rGO) to 25 mL of deionized water and mix well to obtain a mixed solution, wherein the concentration of nickel nitrate in the mixed solution is 0.6 mmol / L and the concentration of sodium citrate is 0.9 mmol / L;

[0039] Add potassium hexacyanocobaltate to 25 mL of deionized water and dissolve it to obtain a potassium hexacyanocobaltate solution, wherein the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.4 mmol / L;

[0040] S2. Under stirring, potassium hexacyanocobaltate solution was dropped into the mixed solution, and stirring was continued for 10 minutes. Then centrifugation was performed, the product was collected, washed with deionized water for multiple times, and finally dried at 60°C in a vacuum environment for 24 hours to obtain NiCoPBA@rGO electrode material, recorded as NiCoPBA@rGO-0.01.

[0041] Example 2

[0042] The preparation method of NiCoPBA@rGO electrode material is the same as the preparation steps of Example 1, except that the mass of rGO is replaced from 0.01 g to 0.02 g, and includes the following steps:

[0043] S1. Add nickel nitrate, sodium citrate and 0.02 g of reduced graphene oxide (rGO) to 25 mL of deionized water and mix well to obtain a mixed solution, wherein the concentration of nickel nitrate in the mixed solution is 0.6 mmol / L and the concentration of sodium citrate is 0.9 mmol / L;

[0044] Add potassium hexacyanocobaltate to 25 mL of deionized water and dissolve it to obtain a potassium hexacyanocobaltate solution, wherein the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.4 mmol / L;

[0045] S2. Under stirring, potassium hexacyanocobaltate solution was dropped into the mixed solution, and stirring was continued for 10 minutes. Then centrifugation was performed, the product was collected, washed with deionized water for multiple times, and finally dried at 60°C in a vacuum environment for 24 hours to obtain NiCoPBA@rGO electrode material, recorded as NiCoPBA@rGO-0.02.

[0046] Example 3

[0047] The preparation method of NiCoPBA@rGO electrode material comprises the following steps:

[0048] S1. Add nickel nitrate, sodium citrate and 0.01 g of reduced graphene oxide (rGO) to 25 mL of deionized water and mix well to obtain a mixed solution, wherein the concentration of nickel nitrate in the mixed solution is 0.5 mmol / L and the concentration of sodium citrate is 0.9 mmol / L;

[0049] Add potassium hexacyanocobaltate to 25 mL of deionized water and dissolve it to obtain a potassium hexacyanocobaltate solution, wherein the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.5 mmol / L;

[0050] S2. Under stirring, potassium hexacyanocobaltate solution was dropped into the mixed solution, and stirring was continued for 10 minutes. Then centrifugation was performed, the product was collected, washed with deionized water for multiple times, and finally dried under a vacuum environment at 60°C for 24 hours to obtain NiCoPBA@rGO electrode material.

[0051] Example 4

[0052] The preparation method of NiCoPBA@rGO electrode material comprises the following steps:

[0053] S1. Add nickel nitrate, sodium citrate and 0.01 g of reduced graphene oxide (rGO) to 25 mL of deionized water and mix well to obtain a mixed solution, wherein the concentration of nickel nitrate in the mixed solution is 1.5 mmol / L and the concentration of sodium citrate is 0.9 mmol / L;

[0054] Add potassium hexacyanocobaltate to 25 mL of deionized water and dissolve it to obtain a potassium hexacyanocobaltate solution, wherein the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.5 mmol / L;

[0055] S2. Under stirring, potassium hexacyanocobaltate solution was dropped into the mixed solution, and stirring was continued for 10 minutes. Then centrifugation was performed, the product was collected, washed with deionized water for multiple times, and finally dried under a vacuum environment at 60°C for 24 hours to obtain NiCoPBA@rGO electrode material.

[0056] Comparative Example 1

[0057] The preparation method of the NiCo-based Prussian blue electrode material is the same as the preparation steps of Example 1, except that the mass of rGO is replaced from 0.01 g to 0 g, that is, rGO is not added, and includes the following steps:

[0058] S1. Add nickel nitrate and sodium citrate to 25 mL of deionized water and mix well to obtain a mixed solution, wherein the concentration of nickel nitrate in the mixed solution is 0.6 mmol / L and the concentration of sodium citrate is 0.9 mmol / L;

[0059] Add potassium hexacyanocobaltate to 25 mL of deionized water and dissolve it to obtain a potassium hexacyanocobaltate solution, wherein the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.4 mmol / L;

[0060] S2. Under stirring, potassium hexacyanocobaltate solution was dripped into the mixed solution, and stirring was continued for 10 minutes, followed by centrifugation, collecting the product, washing it with deionized water for multiple times, and finally drying it under a vacuum environment at 60°C for 24 hours to obtain a NiCo-type Prussian blue electrode material, recorded as NiCoPBA.

[0061] Comparative Example 2

[0062] The preparation method of NiCoPBA@rGO electrode material is the same as the preparation steps of Example 1, except that the mass of rGO is replaced from 0.01 g to 0.03 g, and includes the following steps:

[0063] S1. Add nickel nitrate, sodium citrate and 0.03 g of reduced graphene oxide (rGO) to 25 mL of deionized water and mix well to obtain a mixed solution, wherein the concentration of nickel nitrate in the mixed solution is 0.6 mmol / L and the concentration of sodium citrate is 0.9 mmol / L;

[0064] Add potassium hexacyanocobaltate to 25 mL of deionized water and dissolve it to obtain a potassium hexacyanocobaltate solution, wherein the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.4 mmol / L;

[0065] S2. Under stirring, potassium hexacyanocobaltate solution was dropped into the mixed solution, and stirring was continued for 10 minutes. Then centrifugation was performed, the product was collected, washed with deionized water for multiple times, and finally dried at 60°C in a vacuum environment for 24 hours to obtain NiCoPBA@rGO electrode material, recorded as NiCoPBA@rGO-0.03.

[0066] Examples 1 to 4 of the present invention all prepared NiCoPBA@rGO electrode materials with high specific capacity and high power density. The following is a study using NiCoPBA@rGO-0.01 of Example 1 and NiCoPBA@rGO-0.02 of Example 2 as examples, and a comparative study with NiCoPBA of Comparative Example 1 and NiCoPBA@rGO-0.03 of Comparative Example 2. The specific research methods and results are as follows:

[0067] 1. Scanning electron microscope test (SEM):

[0068] In order to understand the morphological characteristics and structure of the sample, the present invention performed electron microscope scanning on the NiCoPBA@rGO-0.02 sample of Example 2. Figure 1 (a) is the low-magnification appearance of NiCoPBA@rGO-0.02 under a scanning electron microscope. In the figure, it can be clearly seen that the NiCoPBA@rGO-0.02 nanoparticles are distributed in flaky layers, which gives NiCoPBA@rGO-0.02 a higher specific surface area and more reaction sites. Figure 1 (b) is the high-magnification appearance of NiCoPBA@rGO-0.02 under a scanning electron microscope. In the figure, it can be seen that there are some wavy protrusions on the surface of NiCoPBA@rGO-0.02, which further increases its specific surface area, provides better reaction conditions, further improves its energy storage performance, and provides a reference for subsequent chemical tests.

[0069] 2. XRD test:

[0070] In order to better characterize the structure of the sample, the present invention conducted XRD test on NiCoPBA@rGO-0.02. Figure 2The XRD spectrum of NiCoPBA@rGO-0.02 shows that NiCoPBA@rGO-0.02 has obvious diffraction peaks and fewer impurity peaks, indicating that NiCoPBA@rGO-0.02 has good crystallinity and conforms to the Prussian blue-like FCC face-centered cubic structure in the general metal organic framework structure. In addition, the diffraction peaks of NiCoPBA@rGO-0.02 can correspond to the standard card Co3(CO3(CN)6)2(PDF#22-0215), further proving the successful preparation of NiCoPBA@rGO-0.02.

[0071] 3. Cyclic voltammetry test:

[0072] Cyclic Voltammetry (CV) is widely used in the field of electrochemical analysis to study the electrochemical reactions on the electrode surface and the characteristics of electroactive substances. The core principle of CV testing is to apply voltage to the electrode and gradually change its magnitude, record and measure the current passing through the electrode, and thus obtain the electrochemical response of the electrode surface.

[0073] Construction of the three-electrode system: A saturated calomel electrode is used as the reference electrode, a carbon electrode is used as the counter electrode, and a working electrode is used to form a three-electrode system. One end of the reference electrode, the counter electrode, and the working electrode are immersed in a 6 mol / L KOH solution for 24 hours, and the other ends are electrically connected to the electrochemical workstation. During the test, the potential on the working electrode will change with time, stimulating the electrochemical reaction on the electrode surface.

[0074] Preparation of the working electrode: Weigh 0.5 g of binder polytetrafluoroethylene and put it into a 50 mL beaker, add anhydrous ethanol, place the beaker in an ultrasonic cleaner, and add 80 mg of NiCoPBA@rGO-0.01 of Example 1, NiCoPBA@rGO-0.02 of Example 2, NiCoPBA of Comparative Example 1 or NiCoPBA@rGO-0.03 of Comparative Example 2 after mixing evenly. After ultrasonic mixing evenly, add 15 mg of conductive agent acetylene black. After ultrasonic mixing evenly, place it in a water bath at 80°C to obtain a slurry.

[0075] Take 1cm×1cm nickel foam, then evenly spread the slurry on the nickel foam, and then put it into an oven at 80℃ for 1h to obtain an electrode sheet. Place the electrode sheet in a powder tablet press and press it into a 2mm thick sheet at a pressure of 2MPa to obtain a working electrode.

[0076] Figure 3 (a) is a cyclic voltammetry test diagram of NiCoPBA of comparative example 1 at scan rates of 5 mV / s, 8 mV / s, and 10 mV / s, Figure 3(b) is the cyclic voltammetry test diagram of NiCoPBA@rGO-0.01 at scan rates of 5mV / s, 8mV / s, and 10mV / s in Example 1. It can be seen from the two CV curves that both samples have obvious redox peaks, and as the scan rate increases, the CV curves tend to amplify. This is because at the same voltage, a faster scan rate causes the working electrode to produce a higher current value, thereby increasing the closed area of ​​the CV curve. Figure 3 The redox peak of (a) is unstable at different scan rates. Figure 3 The redox peak of (b) is more stable, which shows that reduced graphene oxide has a good effect on the stability of NiCoPBA.

[0077] According to the cyclic voltammetry test results at scan rates of 5mV / s, 8mV / s and 10mV / s, Figure 4 (a) shows the test spectrum of NiCoPBA@rGO-0.02 of Example 2, Figure 4 (b) shows the NiCoPBA@rGO-0.03 test spectrum of Comparative Example 2. By comparing these two sets of cyclic voltammetry data, it can be clearly seen that all samples show significant redox peaks, and the redox peak of NiCoPBA@rGO-0.02 has shifted, and NiCoPBA@rGO-0.03 has lost half at 5mV / s. It can be seen that too much reduced graphene oxide will cause the reduced graphene oxide to agglomerate with each other, and the deposition sites of nickel ions will become less, which will affect the performance of the NiCoPBA@rGO electrode material.

[0078] 4. Ratio test:

[0079] Rate testing is a test method used to evaluate battery performance. It simulates the performance of the battery under different operating conditions by applying different current loads to the battery. Rate testing is usually used to evaluate the performance indicators of battery capacity, energy density, power density and cycle life. During the test, the battery is charged and discharged, and the battery voltage, current and temperature parameters are recorded at the same time.

[0080] Figure 5 (a) is the rate test diagram of NiCoPBA@rGO-0.01 after 50 cycles. It can be seen from the figure that the charge and discharge efficiency of NiCoPBA@rGO-0.01 is as high as 98%. Figure 5 (b) is the rate test diagram of NiCoPBA@rGO-0.02 after 50 cycles, and its charge and discharge efficiency decreases slightly. Figure 5 (a) It can be seen that when the mass of reduced graphene oxide is 0.01g, the charge and discharge performance is the best, the storage capacity is the largest, and its coulomb efficiency reaches more than 98%, with a good capacity retention rate; Figure 5 (b) has a poor charge-discharge specific capacity, indicating that its charge-discharge performance is poor and the charge-discharge coulombic efficiency is relatively unstable. From the above analysis, it can be seen that with the increase of reduced graphene oxide content, the charge-discharge specific capacity of NiCoPBA@rGO becomes smaller and smaller, indicating that excessive reduced graphene oxide will cause the performance of NiCoPBA@rGO to decline.

[0081] Figure 6 This is the rate test diagram of NiCoPBA@rGO-0.03 of comparative example 2 after 50 cycles. Figure 6 It can be seen that when the mass of reduced graphene oxide continues to increase, its charging and discharging efficiency will continue to decrease, which further verifies the above hypothesis.

[0082] 5. AC impedance test:

[0083] AC impedance testing is a test method used to study the resistance and capacitance properties of a material. It determines the resistance and capacitance of a material by applying an AC voltage to the material and measuring the current through the material. AC impedance testing is commonly used to study the performance of batteries, supercapacitors, sensors, semiconductors and other electronic materials. It can provide information about the material's conductivity, dielectric constant, charge storage capacity and interface resistance.

[0084] Figure 7 The AC impedance diagrams of NiCoPBA@rGO-0.01, NiCoPBA@rGO-0.02, NiCoPBA@rGO-0.03 and NiCoPBA reflect the charge transfer performance of NiCoPBA@rGO and NiCoPBA and the size of the interfacial charge transfer resistance. The radius of the arc provides information about the rate of the electrode surface reaction, and the radius of the arc is proportional to the rate of the electrochemical reaction occurring on the surface of NiCoPBA@rGO and NiCoPBA. As can be seen from the figure, when the mass of reduced graphene oxide reaches 0.03g, the radius of curvature of the curve is the smallest, and the slope of the curve in the low-frequency region is the largest, indicating that it has very good nuclear transfer performance. When the mass of reduced graphene oxide is 0.02g, the radius is the largest, the slope is the smallest, and the nuclear transfer performance is poor.

[0085] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing NiCoPBA@rGO electrode material, characterized in that: The following steps are involved: A soluble nickel salt, sodium citrate and reduced graphene oxide are mixed and dispersed in deionized water, wherein the sodium citrate maintains pH stability, and nickel ions of the soluble nickel salt are electrostatically adsorbed on the reduced graphene oxide to obtain a mixed solution; In the mixed solution, the concentration ratio of soluble nickel salt to sodium citrate is 0.5-1.5:0.9; the mass ratio of sodium citrate to reduced graphene oxide is 0.23:0.01-0.02; dissolving potassium hexacyanocobaltate in deionized water to obtain a potassium hexacyanocobaltate solution; Under stirring conditions, a potassium hexacyanocobaltate solution is added dropwise to the mixed solution. At this time, the nickel ions of the soluble nickel salt replace part of the cobalt ions in the potassium hexacyanocobaltate, and the nickel ions react with the cyano group in the potassium hexacyanocobaltate. After the reaction, the solvent is separated to obtain the NiCoPBA@rGO electrode material.

2. The method for preparing the NiCoPBA@rGO electrode material according to claim 1, characterized in that: The molar ratio of the soluble nickel salt to potassium hexacyanocobaltate is 1-3:

1.

3. The method for preparing the NiCoPBA@rGO electrode material according to claim 1, characterized in that: The stirring time of the coordination reaction is ≥10min.

4. The method for preparing the NiCoPBA@rGO electrode material according to claim 1, characterized in that: After the solvent is separated, deionized water is used for washing.

5. The method for preparing the NiCoPBA@rGO electrode material according to claim 1, characterized in that: After washing with water, it was dried under vacuum conditions.

6. A NiCoPBA@rGO electrode material prepared by the preparation method according to any one of claims 1 to 5, characterized in that: NiCoPBA@rGO electrode material is a NiCo@rGO-type Prussian blue derivative electrode material.

7. A positive electrode material prepared using the NiCoPBA@rGO electrode material according to claim 6.

8. A method for preparing the positive electrode material according to claim 7, characterized in that: The steps include: The NiCoPBA@rGO electrode material, the conductive agent and the binder are mixed, ethanol is added to obtain a slurry, the slurry is evenly coated on the current collector, and the positive electrode material is obtained after drying and pressing; Among them, the mass ratio of NiCoPBA@rGO electrode material, conductive agent and binder is 0.75-0.85:0.1-0.15:0.1-0.

15.

9. Use of the positive electrode material according to claim 7 in preparing a positive electrode material for a supercapacitor.

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