NiCoPBA@rGO electrode material, preparation method and application thereof

Abstract

The present application relates to supercapacitor electrode material technical field, specifically to NiCoPBA@rGO electrode material and its preparation method and application. The present application takes soluble nickel salt, sodium citrate, reduced graphene oxide and potassium hexacyanocobaltate as raw materials, first electrostatically adsorbs nickel ions of soluble nickel salt on reduced graphene oxide, then diffuses nickel ions of soluble nickel salt into potassium hexacyanocobaltate, embeds into potassium hexacyanocobaltate under the action of Oswald and completes partial substitution of cobalt ions, at the same time, nickel ions complete coordination reaction with cyanogen in potassium hexacyanocobaltate, finally prepare NiCoPBA@rGO electrode material with NiCoPBA attached on rGO sheet. The present application can obtain NiCoPBA@rGO electrode material at room temperature, and is not affected by pH and reaction temperature of solution, and overcomes technical defects existing in preparation of existing technology prussian blue derivative.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of supercapacitor electrode materials, and particularly relates to a NiCoPBA@rGO electrode material and a preparation method and application thereof. BACKGROUND

[0002] A supercapacitor is an electronic component that can store a large amount of electric charge. It has the advantages of high energy density, high power density and fast charging and discharging speed. Its working principle is to store electric charge by using the double-layer interface effect between the electrolyte and the electrode. When the ions in the electrolyte solution come into contact with the electrode surface, a layer of electric charge will be formed on it, and this layer of electric charge forms a double-layer interface with the ions in the electrolyte, thereby realizing the storage of electric 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 and wind energy fields. Supercapacitors are divided into flat type, cylindrical type and spiral type, among which the flat type is the most common structure because it has the advantages of simplicity, easy manufacturing and low cost. According to the working voltage of the supercapacitor, it is divided into two types: low-voltage supercapacitor and high-voltage supercapacitor. The working voltage of the low-voltage supercapacitor is generally below 2.5V, while the working voltage of the high-voltage supercapacitor can reach hundreds of volts, or even thousands of volts.

[0003] In a supercapacitor, electrode material is one of the key factors that determine its performance. In order to improve the performance of supercapacitors, it has always been a hot topic to constantly seek and develop new electrode materials. Among the new electrode materials, the excellent electrochemical performance of the Prussian blue analog (PBA) has attracted the attention of researchers. Prussian blue analog is a similar substance to Prussian blue, and there are many types. With different types and proportions of metals, the structure of the prepared Prussian blue analog is diverse. Prussian blue analog is a porous structure material, and its excellent charge transport performance makes it stand out among electrode materials, which makes it popular in the application of supercapacitors.

[0004] However, the existing technology of Prussian blue analog is greatly affected by the synthesis conditions, such as the pH of the solution and the reaction temperature, which makes it difficult to mass-produce Prussian blue analog, thereby affecting the application of Prussian blue analog. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a NiCoPBA@rGO electrode material and a preparation method and application thereof; the present application takes soluble nickel salt, sodium citrate, reduced graphene oxide and potassium hexacyanocobaltate as raw materials, first electrostatically adsorbs 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 ripening reaction mechanism and completes partial substitution of cobalt ions, at the same time, completes coordination reaction of the nickel ions and the cyanogen in the potassium hexacyanocobaltate, and finally prepares the NiCoPBA@rGO electrode material with the NiCoPBA attached to the rGO sheet layer. The method of the present application can obtain the NiCoPBA@rGO electrode material at normal temperature, is not affected by the pH of the solution and the reaction temperature, and overcomes the technical defects of the prior art in the preparation of the prussian blue derivative.

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

[0007] The preparation method of the NiCoPBA@rGO electrode material comprises the following steps:

[0008] The soluble nickel salt, sodium citrate and reduced graphene oxide are mixed and dispersed in deionized water, the sodium citrate is used as a buffer agent for maintaining the pH of the solution stable, without the sodium citrate, the pH of the solution fluctuates greatly with the reaction, affecting the uniform formation of the NiCoPBA@rGO electrode material, the reduced graphene oxide (rGO) has a negative charge, and the nickel ions of the soluble nickel salt are electrostatically adsorbed on the reduced graphene oxide, to obtain a mixed solution;

[0009] The potassium hexacyanocobaltate is dissolved in deionized water to obtain a potassium hexacyanocobaltate solution;

[0010] Under stirring, the potassium hexacyanocobaltate solution is added dropwise into the mixed solution, at this time, the nickel ions of the soluble nickel salt replace part of the cobalt ions of the potassium hexacyanocobaltate, this reaction utilizes the Oswald ripening reaction mechanism, small nickel ion groups are converted into large nickel-cobalt cyanide ion coordination groups, part of the nickel ions are coordinated with the cyanogen in the potassium hexacyanocobaltate in the conversion process to complete the substitution process, and 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 the soluble nickel salt, the concentration of the sodium citrate and the mass ratio of the reduced graphene oxide are 0.5-1.5 mmol / L: 0.9 mmol / L: 0.01-0.02 g. The amount of the sodium citrate is determined according to the soluble nickel salt, and the sodium citrate is mainly used for maintaining the pH of the solution stable.

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

[0013] Preferably, the stirring time of the coordination reaction is greater than or equal to 10 minutes, and 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 in the mixed solution, deionized water is used for water washing to wash away the excess water-soluble ions, such as nickel ions and sodium ions, which do not participate in the coordination reaction.

[0015] Preferably, after water washing, drying is carried out under vacuum conditions, and vacuum drying ensures that the metal ions nickel and cobalt are not oxidized to form oxides.

[0016] The application also protects the NiCoPBA@rGO electrode material prepared by the above preparation method, and the NiCoPBA@rGO electrode material is a NiCo@rGO prussian blue derivative electrode material.

[0017] The application also protects a positive electrode material prepared from the NiCoPBA@rGO electrode material.

[0018] Preferably, the preparation method of the positive electrode material comprises the following steps:

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

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

[0021] The application also protects the application of the above positive electrode material in the preparation of a supercapacitor positive electrode material.

[0022] Compared with the prior art, the application has the beneficial effects that:

[0023] 1. This invention uses soluble nickel salt, sodium citrate, and reduced graphene oxide as raw materials, which are mixed in deionized water to obtain a mixed solution. rGO carries a negative charge and acts as an ion deposition site, allowing nickel ions from the soluble nickel salt to be electrostatically adsorbed onto the reduced graphene oxide. The mixed solution is then mixed with a potassium hexacyanocobaltate solution, allowing the nickel ions from the soluble nickel salt to diffuse into the potassium hexacyanocobaltate. Under Oswald reaction, these ions are inserted into the potassium hexacyanocobaltate, partially replacing the cobalt ions. Simultaneously, the nickel ions coordinate with the cyano groups in the potassium hexacyanocobaltate, achieving a chemical reaction at the nickel ion sites to form a Prussian blue-like derivative, thus producing the NiCoPBA@rGO electrode material. Compared with existing technologies, this invention can produce the Prussian blue-like derivative by stirring at room temperature, without requiring stringent pH conditions and reaction temperatures. Furthermore, the raw materials are readily available and inexpensive, the preparation method is simple, and it requires minimal equipment, making it suitable for large-scale mass production.

[0024] 2. This invention, through rational design, regulates the morphology, structure, and chemical composition of Prussian blue-like derivative materials. In terms of morphology and structure, the NiCoPBA@rGO electrode material prepared using the method of this invention possesses a stable porous framework structure with high porosity and a lamellar / layered distribution, resulting in a high specific surface area and abundant active sites. In terms of chemical composition, NiCoPBA is stably electrostatically adsorbed onto rGO. NiCoPBA is a Prussian blue-like MOF material, and its multi-metal coordination structure provides ample sites for ion insertion and extraction. Furthermore, the porous structure facilitates ion transport, improving reaction efficiency and thus increasing the supercapacitor capacity. This results in a NiCoPBA@rGO electrode material with high charge-discharge specific capacity and high power density, effectively solving the problem of low specific capacity and power density in existing supercapacitors, thereby enabling the NiCoPBA@rGO electrode material to fully utilize its superior performance in supercapacitors. Attached Figure Description

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

[0026] Figure 2 The image shows the XRD pattern of NiCoPBA@rGO-0.02 from Example 2.

[0027] Figure 3 In the figures, (a) is the cyclic voltammetry test diagram of NiCoPBA in Comparative Example 1, and (b) is the cyclic voltammetry test diagram of NiCoPBA@rGO-0.01 in Example 1.

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

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

[0030] Figure 6 The figure is the rate test figure of NiCoPBA@rGO-0.03 of Comparative Example 2.

[0031] Figure 7 The figure is the AC impedance figure 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 application are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application. The experimental methods described in the embodiments of the present application are conventional methods unless otherwise specified.

[0033] In view of the excellent performance of the Prussian blue analogues and the technical defects of the existing preparation methods of the Prussian blue analogues, the present application provides a new preparation method of the Prussian blue analogues and a NiCoPBA@rGO electrode material. Compared with the existing preparation methods of the Prussian blue analogues, the preparation method of the present application overcomes the limitations of pH and reaction temperature, so that the NiCoPBA@rGO electrode material can be produced industrially. In addition, the NiCoPBA@rGO electrode material obtained by the method of the present application has excellent electrochemical performance, high specific capacity and power density, and can be used as a supercapacitor positive electrode material.

[0034] The application also conducts a comparison and research on the amount of raw materials used, and the research shows that the amount of reduced graphene oxide will affect the performance of the NiCoPBA@rGO electrode material, and an appropriate amount of reduced graphene oxide will have a beneficial 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 part of the performance of the NiCoPBA@rGO electrode material. Under the experimental conditions, when the mass of the reduced graphene oxide is 0.01 g, the comprehensive performance is the best. When the mass of the reduced graphene oxide increases to 0.02 g, the energy storage efficiency decreases, and the conduction capacity also decreases. When the mass of the reduced graphene oxide reaches 0.03 g, the transmission performance is the best, but the energy storage efficiency is greatly reduced. If large-scale industrial production is carried out, the data provided by the application can be calculated and produced in proportion.

[0035] The technical solutions of the application are explained and described below by using examples and comparative examples, as follows:

[0036] Example 1

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

[0038] S1, adding nickel nitrate, sodium citrate and 0.01 g of reduced graphene oxide (rGO) into 25 mL of deionized water and mixing uniformly 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] Potassium hexacyanocobaltate is added to 25 mL of deionized water and dissolved to obtain a potassium hexacyanocobaltate solution, and the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.4 mmol / L;

[0040] S2, under the action of stirring, the potassium hexacyanocobaltate solution is added dropwise into the mixed solution, and stirring is continued for 10 min, and then centrifugal treatment is carried out, the product is collected, washed with deionized water for several times, and finally dried at 60°C in a vacuum environment for 24 h to obtain the NiCoPBA@rGO electrode material, which is recorded as NiCoPBA@rGO-0.01.

[0041] Example 2

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

[0043] S1, add nickel nitrate, sodium citrate and 0.02 g of reduced graphene oxide (rGO) into 25 mL of deionized water, and mix uniformly to obtain a mixed solution, 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 into 25 mL of deionized water and dissolve to obtain a potassium hexacyanocobaltate solution, the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.4 mmol / L;

[0045] S2, under the action of stirring, drop the potassium hexacyanocobaltate solution into the mixed solution, continue to stir for 10 min, then perform centrifugal treatment, collect the product, wash with deionized water for multiple times, and finally dry at 60°C in a vacuum environment for 24 h to prepare a NiCoPBA@rGO electrode material, denoted as NiCoPBA@rGO-0.02.

[0046] Example 3

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

[0048] S1, add nickel nitrate, sodium citrate and 0.01 g of reduced graphene oxide (rGO) into 25 mL of deionized water, and mix uniformly to obtain a mixed solution, 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 into 25 mL of deionized water and dissolve to obtain a potassium hexacyanocobaltate solution, the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution is 0.5 mmol / L;

[0050] S2, under the action of stirring, drop the potassium hexacyanocobaltate solution into the mixed solution, continue to stir for 10 min, then perform centrifugal treatment, collect the product, wash with deionized water for multiple times, and finally dry at 60°C in a vacuum environment for 24 h to prepare a NiCoPBA@rGO electrode material.

[0051] Example 4

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

[0053] S1, add nickel nitrate, sodium citrate and 0.01 g of reduced graphene oxide (rGO) into 25 mL of deionized water, and mix uniformly to obtain a mixed solution, 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;

[0054] Potassium hexacyanocobaltate was added into 25 mL deionized water and dissolved to obtain a potassium hexacyanocobaltate solution, and the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution was 0.5 mmol / L;

[0055] S2, under the action of stirring, the potassium hexacyanocobaltate solution was added dropwise into the mixed solution, and stirring was continued for 10 min, and then centrifugal treatment was carried out, the product was collected, washed with deionized water for multiple times, and finally dried at 60°C in a vacuum environment for 24 h to prepare a NiCoPBA@rGO electrode material.

[0056] Comparative Example 1

[0057] The preparation method of the NiCo prussian blue analogue electrode material was the same as the preparation steps of Example 1, except that the mass of rGO was replaced by 0 g instead of 0.01 g, that is, no rGO was added, and included the following steps:

[0058] S1, nickel nitrate and sodium citrate were added into 25 mL deionized water and mixed uniformly to obtain a mixed solution, and the concentration of nickel nitrate in the mixed solution was 0.6 mmol / L, and the concentration of sodium citrate was 0.9 mmol / L;

[0059] Potassium hexacyanocobaltate was added into 25 mL deionized water and dissolved to obtain a potassium hexacyanocobaltate solution, and the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution was 0.4 mmol / L;

[0060] S2, under the action of stirring, the potassium hexacyanocobaltate solution was added dropwise into the mixed solution, and stirring was continued for 10 min, and then centrifugal treatment was carried out, the product was collected, washed with deionized water for multiple times, and finally dried at 60°C in a vacuum environment for 24 h to prepare a NiCo prussian blue analogue electrode material, denoted as NiCoPBA.

[0061] Comparative Example 2

[0062] The preparation method of the NiCoPBA@rGO electrode material was the same as the preparation steps of Example 1, except that the mass of rGO was replaced by 0.03 g instead of 0.01 g, and included the following steps:

[0063] S1, nickel nitrate, sodium citrate and 0.03 g of reduced graphene oxide (rGO) were added into 25 mL deionized water and mixed uniformly to obtain a mixed solution, and the concentration of nickel nitrate in the mixed solution was 0.6 mmol / L, and the concentration of sodium citrate was 0.9 mmol / L;

[0064] Potassium hexacyanocobaltate was added into 25 mL deionized water and dissolved to obtain a potassium hexacyanocobaltate solution, and the concentration of potassium hexacyanocobaltate in the potassium hexacyanocobaltate solution was 0.4 mmol / L;

[0065] S2, under the action of stirring, the potassium hexacyanocobaltate solution is dropped into the mixed solution, and stirring is continued for 10 min, and then centrifugal treatment is carried out, the product is collected, washed with deionized water for several times, and finally dried at 60 DEG C in a vacuum environment for 24 h, to obtain the NiCoPBA@rGO electrode material, recorded as NiCoPBA@rGO-0.03.

[0066] The NiCoPBA@rGO electrode material with high specific capacity and high power density is prepared in the embodiments 1-4 of the present application, and the following takes the NiCoPBA@rGO-0.01 of embodiment 1 and the NiCoPBA@rGO-0.02 of embodiment 2 as examples for research, and the NiCoPBA of comparative example 1 and the NiCoPBA@rGO-0.03 of comparative example 2 are compared and researched, and the specific research method and results are shown as follows:

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

[0068] In order to understand the morphology and structure of the sample, the present application carries out electron microscope scanning on the NiCoPBA@rGO-0.02 sample of embodiment 2. Figure 1 (a) is the low magnification appearance of NiCoPBA@rGO-0.02 under the scanning electron microscope, and the NiCoPBA@rGO-0.02 nanoparticles are clearly seen to be distributed in a sheet-like layer, so that the NiCoPBA@rGO-0.02 has a higher specific surface area, and has more reaction sites. Figure 1 (b) is the high magnification appearance of NiCoPBA@rGO-0.02 under the scanning electron microscope, and the NiCoPBA@rGO-0.02 surface can be seen to have some wavy protrusions, which further increases the specific surface area, so that it has a more favorable reaction condition, and its energy storage performance is further improved, and also provides a reference for the subsequent chemical test.

[0069] II. XRD test:

[0070] In order to better characterize the structure of the sample, the present application carries out XRD test on the NiCoPBA@rGO-0.02, Figure 2XRD pattern of NiCoPBA@rGO-0.02, the XRD results show that NiCoPBA@rGO-0.02 appears obvious diffraction peaks, and the number of miscellaneous peaks is less, indicating that the crystallinity of NiCoPBA@rGO-0.02 is better, which is consistent with the FCC face-centered cubic structure of the general metal-organic framework structure of Prussian blue type. In addition, the diffraction peaks of NiCoPBA@rGO-0.02 can correspond to the standard card Co3(CO3(CN)6)2(PDF#22-0215), which further proves the successful preparation of NiCoPBA@rGO-0.02.

[0071] III. Cyclic voltammetry test:

[0072] Cyclic voltammetry (CV) is widely used in the field of electrochemical analysis to study the electrochemical reaction on the electrode surface and the characteristics of the electroactive material. The core principle of CV test is to apply voltage on the electrode and gradually change its size, record and measure the current through the electrode, so as to obtain the electrochemical response of the electrode surface.

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

[0074] Preparation of working electrode: 0.5g of binder polytetrafluoroethylene was weighed into a 50mL beaker, anhydrous ethanol was added, and the beaker was placed in an ultrasonic cleaner. After mixing evenly, 80mg 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 was added, and the mixture was ultrasonically mixed until uniform. Then 15mg of conductive agent acetylene black was added and ultrasonically mixed until uniform. The slurry was obtained by placing the mixture in a water bath at 80°C.

[0075] A 1cm x 1cm foam nickel was taken, and the slurry was evenly applied on the foam nickel. Then the foam nickel was placed in an oven at 80°C and dried for 1h to obtain an electrode sheet. The electrode sheet was placed in a powder tablet machine and pressed into a 2mm thick sheet under a pressure of 2MPa to obtain a working electrode.

[0076] Figure 3 (a) is the cyclic voltammetry test diagram of NiCoPBA of Comparative Example 1 at a scan rate of 5mV / s, 8mV / s and 10mV / s, Figure 3(b) is the cyclic voltammetry test diagram of NiCoPBA@rGO-0.01 of Example 1 at a scan rate of 5 mV / s, 8 mV / s and 10 mV / s. As can be seen from the two CV curves, there are obvious redox peaks in both samples, and as the scan rate increases, the CV curve shows an amplification trend. This is because at the same voltage, a faster scan rate results in a higher current value of the working electrode, thereby increasing the closed area of the CV curve. Figure 3 The redox peaks of (a) are unstable at different scan rates, Figure 3 The redox peaks of (b) are more stable, so the stability of reduced graphene oxide on NiCoPBA is good.

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

[0078] Four, rate test:

[0079] Rate test is a test method for evaluating the performance of a battery. It simulates the performance of a battery under different working conditions by applying different current loads on the battery. Rate test is commonly 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 voltage, current and temperature parameters of the battery are recorded.

[0080] Figure 5 (a) is the rate test diagram of NiCoPBA@rGO-0.01 after 50 cycles. As can be seen from the figure, 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) shows that when the mass of reduced graphene oxide is 0.01 g, the charge and discharge performance is the best and the storage capacity is the largest, and the coulombic efficiency is more than 98%, with good capacity retention rate; whileFigure 5 The charge-discharge specific capacity of (b) is poor, indicating that its charge-discharge performance is poor, and the charge-discharge coulombic efficiency is less stable. From the above analysis, it can be seen that the charge-discharge specific capacity of NiCoPBA@rGO decreases with the increase of the content of reduced graphene oxide, indicating that excessive reduced graphene oxide can cause the performance of NiCoPBA@rGO to decrease.

[0081] Figure 6 The figure of rate test after 50 cycles of NiCoPBA@rGO-0.03 of Comparative Example 2. It can be seen from the figure that the charge-discharge efficiency of NiCoPBA@rGO-0.03 is the worst among the four samples, and the charge-discharge specific capacity is the smallest, which further verifies the above guess. Figure 6 It can be seen that when the mass of reduced graphene oxide continues to increase, its charge-discharge efficiency will continue to decrease, further verifying the above guess.

[0082] V. AC impedance test:

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

[0084] Figure 7 The AC impedance diagram of NiCoPBA@rGO-0.01, NiCoPBA@rGO-0.02, NiCoPBA@rGO-0.03 and NiCoPBA reflects the charge transfer performance and interface charge transfer resistance of NiCoPBA@rGO and NiCoPBA. The radius of the arc provides information about the rate of electrode surface reaction, and the radius of the arc is proportional to the rate of 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 0.03 g, the curvature radius 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 transmission performance, and when the mass of reduced graphene oxide is 0.02 g, the radius is the largest, and the slope is the smallest, the transmission performance is poor.

[0085] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A method for preparing NiCoPBA@rGO electrode material, characterized in that, Includes the following steps: Soluble nickel salt, sodium citrate, and reduced graphene oxide are mixed and dispersed in deionized water. Sodium citrate maintains pH stability, and nickel ions from the soluble nickel salt are electrostatically adsorbed onto the reduced graphene oxide to obtain a mixed solution. In the mixture, the molar 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. Potassium hexacyanocobaltate was dissolved in deionized water to obtain a potassium hexacyanocobaltate solution; Under stirring conditions, potassium hexacyanocobaltate solution was added dropwise to the mixture. At this time, nickel ions from the soluble nickel salt replaced some of the cobalt ions in potassium hexacyanocobaltate, and the nickel ions underwent a coordination reaction with the cyano groups in potassium hexacyanocobaltate. After the reaction was completed, the solvent was 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 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 for the coordination reaction is ≥10 min.

4. The method for preparing the NiCoPBA@rGO electrode material according to claim 1, characterized in that, After solvent separation, the mixture is washed with deionized water.

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 1-5, characterized in that, The NiCoPBA@rGO electrode material is a Prussian blue derivative electrode material based on NiCo@rGO.

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

8. A method for preparing the cathode material according to claim 7, characterized in that, Includes the following steps: NiCoPBA@rGO electrode material, conductive agent and binder are mixed, and ethanol is added to obtain a slurry. The slurry is uniformly coated on the current collector, and after drying and pressing, the positive electrode material is obtained. 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. The application of the cathode material according to claim 7 in the preparation of cathode materials for supercapacitors.

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