Naphthalenetetracarboxylic Dianhydride@Reduced Graphene Oxide Composite Material, Preparation Method and Application

Abstract

The present invention belongs to the technical field of electrode materials for potassium ion batteries, and specifically relates to a naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material, a preparation method and an application. The preparation method of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material provided by the present invention uses naphthalene tetracarboxylic dianhydride and reduced graphene oxide as precursors, and through simple and efficient ultrasonic-assisted treatment and low-temperature thermal reduction, the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material is prepared. In the composite material, reduced graphene oxide and naphthalene tetracarboxylic dianhydride are tightly combined through π-π interactions. On the one hand, it can improve the conductivity of naphthalene tetracarboxylic dianhydride and reduce the solubility of naphthalene tetracarboxylic dianhydride in organic electrolytes; on the other hand, it can expose more active sites of naphthalene tetracarboxylic dianhydride and enhance the potassium ion storage capacity, and it is suitable for use as a positive electrode material for potassium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of potassium ion battery electrode materials, and particularly relates to a naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material, a preparation method and an application thereof. Background Art

[0002] In recent years, lithium ion batteries have been widely used in emerging fields such as electric vehicles due to their high energy density. However, with the continuous growth of the demand for large-scale energy storage devices, the global shortage and uneven distribution of lithium resources have led to an increase in the production cost of lithium ion batteries, which has also become a factor restricting their development. In comparison, potassium has rich reserves and similar electrochemical properties to lithium, and it has become a development trend to replace lithium ion batteries with potassium ion batteries.

[0003] The positive electrode of the battery plays a decisive role in the whole battery. Therefore, the preparation of high-performance positive electrode materials is particularly important for improving the overall performance of potassium ion batteries. Organic electrode materials have gradually attracted the attention of researchers due to their low price, recyclability and designability. However, when using organic substances as positive electrode materials, the main problems such as poor conductivity, easy dissolution in non-aqueous electrolytes and few active sites seriously affect the overall cycle stability and rate performance of the battery.

[0004] In order to improve the problems of poor conductivity and few exposed active sites of existing materials, the method of compounding organic substances and carbon materials is an effective way. The common carbon compounding methods in the prior art mainly focus on compounding organic substances with conductive materials. The conductive materials developed currently include carbon black, porous carbon, etc. The invention patent application with the application publication number of CN109267145A discloses a naphthalene tetracarboxylic dianhydride Zn-MOF crystal material, a preparation method and an application thereof. First, naphthalene tetracarboxylic acid is dissolved in a DMF / water mixed solution, then mixed with an aqueous solution of zinc nitrate, and then left standing and dried to obtain the naphthalene tetracarboxylic dianhydride in the Zn-MOF crystal material. Although the above prior art can improve the oxygen evolution electrocatalytic stability of the material to a certain extent, it does not involve the application of the material in potassium ion batteries and cannot achieve the improvement of the cycle and rate performance of potassium ion batteries. Summary of the Invention

[0005] Aiming at the above problems in the prior art, the purpose of the present invention is to provide a preparation method of a naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material, which has simple process, mild synthesis conditions, is suitable for large-scale batch production, and can endow the composite material with good cycle performance and rate performance.

[0006] The object of the present invention also lies in providing a naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material, which can improve the electrical conductivity of the composite material, alleviate the dissolution of naphthalene tetracarboxylic dianhydride during the electrochemical charge and discharge process, effectively improve the cycle stability and rate performance of the composite material, and is suitable for use as a potassium ion battery electrode material.

[0007] The present invention also provides an application of the above naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material.

[0008] In order to achieve the above object, the preparation method of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material of the present invention adopts the following technical solution:

[0009] A preparation method of a naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material comprises the following steps:

[0010] (1) Prepare a graphene oxide dispersion liquid, and then add naphthalene tetracarboxylic dianhydride into the graphene oxide dispersion liquid to obtain a naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid; in the naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is (1:4) to (2:1);

[0011] (2) Ultrasonically treat the naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid, then freeze-dry it, and then press the freeze-dried sponge-like substance into a round sheet to obtain a precursor;

[0012] (3) In an inert atmosphere, heat-treat the precursor at 300 - 400 °C, and cool it to obtain the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material.

[0013] The composite material preparation method of the present invention uses naphthalene tetracarboxylic dianhydride and graphene oxide as precursors, and through two simple and efficient steps of ultrasonic assistance and thermal reduction, the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material is prepared. The above preparation process is simple, the synthesis conditions are mild, expensive equipment does not need to be configured, it is suitable for large-scale batch production, and has good industrial application prospects.

[0014] Moreover, in the composite material prepared by the above method of the present invention, there is a strong π-π interaction between the reduced graphene oxide and naphthalene tetracarboxylic dianhydride. On the one hand, it can improve the electrical conductivity of naphthalene tetracarboxylic dianhydride and reduce the solubility of naphthalene tetracarboxylic dianhydride in the organic electrolyte; on the other hand, it can expose more active sites of naphthalene tetracarboxylic dianhydride, which is beneficial to the improvement of capacity. In addition, the material prepared by the above process of the present invention has a self-supporting film structure, can be directly used as a self-supporting electrode material, and after being used as a self-supporting electrode, the use of an electron-insulating binder is avoided, and there is no complex slurry preparation process.

[0015] Therefore, when the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material prepared by the present invention is used as the cathode material of the potassium ion battery, it can effectively improve the cycle stability and rate performance of the battery on the basis of simplifying the process operation, and greatly meet the use requirements of the electrode material of the potassium ion battery.

[0016] Regarding the graphene oxide used in step (1), the present invention does not impose special restrictions. It can be conventional graphene oxide in the art, which can be obtained through conventional commercial channels or prepared by itself. When preparing by itself, natural flake graphite can be used to prepare according to the improved Hummer's method.

[0017] For the convenience of addition and to promote the uniform dispersion of graphene oxide, preferably, in step (1), the graphene oxide dispersion is obtained by adding graphene oxide to water and dispersing it by ultrasonic treatment.

[0018] Preferably, in step (1), in the graphene oxide dispersion, the concentration of graphene oxide is 1.0 - 5.0 mg / mL.

[0019] In step (1), the dosage and addition method of naphthalene tetracarboxylic dianhydride will affect the morphology and structure of the product, thereby affecting the use performance of the composite material, and the dosage of naphthalene tetracarboxylic dianhydride needs to be matched with the dosage of graphene oxide. To optimize the morphology, structure and properties of the composite material and improve the rate and cycle performance of the material. To achieve the best improvement effect of the material structure and performance, the following typical ratio can be adopted: in the naphthalene tetracarboxylic dianhydride / graphene oxide mixed solution, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is 2:3.

[0020] Based on the consideration of promoting the structural uniformity of the composite material and the preparation effect of the composite material, preferably, in step (2), the time of the ultrasonic treatment is 1 - 5 h, and the ultrasonic frequency is 40 KHz - 100 KHz.

[0021] The purpose of freeze-drying is to fully remove the moisture in the naphthalene tetracarboxylic dianhydride / graphene oxide mixed solution. Preferably, in step (2), the temperature of the freeze-drying is -40°C to -20°C, and the time of the freeze-drying is 12 - 24 h.

[0022] Furthermore, the freeze-dried sponge-like substance can be pressed into a round sheet by a conventional method in the art, such as first pressing the freeze-dried sponge-like substance into a film and then punching it into a round sheet with a punching machine. Preferably, in step (2), the diameter of the round sheet is 10 - 15 mm, and the thickness is 30 - 50 μm.

[0023] Through heat treatment at a specific temperature, the graphene oxide part in the precursor can be reduced to obtain reduced graphene oxide with effectively controlled reduction degree, and the morphology and structure of the obtained composite material can be optimized. Further, in order to ensure the cycle performance of the composite material while taking into account the heat treatment efficiency and cost, in step (3), the time of the heat treatment is 120-180 min.

[0024] The naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material of the present invention is prepared by the preparation method as described above.

[0025] The present invention also provides the application of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material as described above, specifically the application in potassium ion batteries.

[0026] Further preferably, the application is the application of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material as the positive electrode material of a potassium ion battery.

[0027] The naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material obtained by the above preparation method of the present invention has good electronic conductivity and potassium ion storage ability. Based on the above characteristics, when it is used as the electrode material of a potassium ion battery, it can exhibit good electrochemical cycle stability and rate performance, greatly meeting the use requirements of the positive electrode material of a potassium ion battery. Description of the Drawings

[0028] Figure 1 XRD pattern of the reduced graphene oxide material prepared for Comparative Example 1;

[0029] Figure 2 XRD pattern of the naphthalene tetracarboxylic dianhydride material prepared for Comparative Example 2;

[0030] Figure 3 XRD pattern of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material prepared in Example 1 of the present invention;

[0031] Figure 4 SEM image of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material prepared in Example 2 of the present invention;

[0032] Figure 5 SEM image of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material prepared in Example 3 of the present invention;

[0033] Figure 6 SEM image of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material prepared in Example 4 of the present invention;

[0034] Figure 7 Electrochemical rate performance of the naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material prepared in Example 1 of the present invention as the positive electrode material of a potassium ion battery;

[0035] Figure 8 Electrochemical rate performance of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite prepared in Example 2 of the present invention as a cathode material for potassium ion batteries;

[0036] Figure 9 Electrochemical rate performance of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite prepared in Example 3 of the present invention as a cathode material for potassium ion batteries;

[0037] Figure 10 Electrochemical rate performance of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite prepared in Example 4 of the present invention as a cathode material for potassium ion batteries;

[0038] Figure 11 Electrochemical rate performance of the reduced graphene oxide material prepared in Comparative Example 1 as a cathode material for potassium ion batteries;

[0039] Figure 12 Electrochemical rate performance of the naphthalene tetracarboxylic dianhydride material prepared in Comparative Example 2 as a cathode material for potassium ion batteries. Detailed implementation manners

[0040] The technical solutions of the present invention will be further described below in conjunction with the detailed implementation manners. However, those skilled in the art should understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0041] In the following examples, unless otherwise specified, the raw materials involved are all conventional commercially available products. Among them, naphthalene tetracarboxylic dianhydride is called 1,4,5,8-naphthalene tetracarboxylic dianhydride and is purchased from Macklin Reagent Company.

[0042] In the following examples, the graphene oxide used is prepared by the improved Hummer's method from natural flake graphite. The specific preparation process is as follows: a) Weigh 2.0 g of flake graphite (325 mesh) and 1.0 g of sodium nitrate and add them to 45 mL of concentrated sulfuric acid, and stir evenly in an ice-water bath; b) Slowly add 6.0 g of potassium permanganate solid to obtain a dark green mixture, and ensure that the temperature of the reaction mixture does not exceed 10 °C during the addition of potassium permanganate; c) After the addition of potassium permanganate is completed, stir the solution in a water bath at 35 °C for 30 min, and then gradually add 100 mL of H2O drop by drop; d) After the addition of H2O is completed, place the mixture in a water bath at 110 °C and react for 30 min; e) After the reaction is completed, pour in 15 mL of H2O2, and the color of the mixture becomes golden yellow at this time; f) Finally, wash with 5% hydrochloric acid, and then dialyze. When the graphene oxide solution is weakly acidic, its concentration is calibrated by the differential method.

[0043] Example 1

[0044] The naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material of this embodiment is prepared by a method comprising the following steps:

[0045] 1) Mix 5 mL of graphene oxide solution (with a concentration of 4 mg / mL) with 5 mL of deionized water, and ultrasonically disperse for 30 min to obtain a graphene oxide dispersion; in the graphene oxide dispersion, the concentration of graphene oxide is 2 mg / mL;

[0046] Add 10 mg of naphthalene tetracarboxylic dianhydride powder to the graphene oxide dispersion to obtain a naphthalene tetracarboxylic dianhydride / graphene oxide mixture; in the naphthalene tetracarboxylic dianhydride / graphene oxide mixture, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is 2:1;

[0047] 2) Place the naphthalene tetracarboxylic dianhydride / graphene oxide mixture obtained in step 1) in an ultrasonic cleaner and perform ultrasonic treatment (60 KHz, 3 h); after ultrasonic treatment, pour the mixed solution into a crystallization dish and perform freeze-drying (-40 °C, 12 h), press the freeze-dried sponge-like substance into a film, and use a punching machine to punch out a disc with a diameter of 12 mm and a thickness of 50 μm to obtain a precursor;

[0048] 3) Heat-treat the precursor in an argon atmosphere at 300 °C for 180 min, and then cool to obtain the product.

[0049] Example 2

[0050] The naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material of this embodiment is prepared by a method comprising the following steps:

[0051] 1) Mix 5 mL of graphene oxide solution (with a concentration of 4 mg / mL) with 5 mL of deionized water, and ultrasonically disperse for 30 min to obtain a graphene oxide dispersion; in the graphene oxide dispersion, the concentration of graphene oxide is 2 mg / mL;

[0052] Add 30 mg of naphthalene tetracarboxylic dianhydride powder to the graphene oxide dispersion to obtain a naphthalene tetracarboxylic dianhydride / graphene oxide mixture; in the naphthalene tetracarboxylic dianhydride / graphene oxide mixture, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is 2:3;

[0053] 2) Place the naphthalene tetracarboxylic dianhydride / graphene oxide mixture obtained in step 1) in an ultrasonic cleaner and perform ultrasonic treatment (40 KHz, 3 h); after ultrasonic treatment, pour the mixed solution into a crystallization dish and perform freeze-drying (-40 °C, 12 h), press the freeze-dried sponge-like substance into a film, and use a punching machine to punch out a disc with a diameter of 12 mm and a thickness of 50 μm to obtain a precursor;

[0054] 3) Heat-treat the precursor in an argon atmosphere at 300 °C for 180 min, and then cool to obtain the product.

[0055] Example 3

[0056] The naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material of this example is prepared by a method including the following steps:

[0057] 1) Mix 5 mL of graphene oxide solution (concentration 4 mg / mL) with 5 mL of deionized water, and ultrasonically disperse for 30 min to obtain a graphene oxide dispersion; in the graphene oxide dispersion, the concentration of graphene oxide is 2 mg / mL;

[0058] Add 60 mg of naphthalene tetracarboxylic dianhydride powder to the graphene oxide dispersion to obtain a naphthalene tetracarboxylic dianhydride / graphene oxide mixture; in the naphthalene tetracarboxylic dianhydride / graphene oxide mixture, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is 1:3;

[0059] 2) Place the naphthalene tetracarboxylic dianhydride / graphene oxide mixture obtained in step 1) in an ultrasonic cleaner and perform ultrasonic treatment (40 KHz, 3 h); after ultrasonic treatment, pour the mixed solution into a crystallization dish and perform freeze-drying (-20 °C, 24 h), press the freeze-dried spongy material into a film, and use a punching machine to punch out a disc with a diameter of 12 mm and a thickness of 50 μm to obtain a precursor;

[0060] 3) Heat-treat the precursor in an argon atmosphere at 300 °C for 180 min, and then cool to obtain the product.

[0061] Example 4

[0062] The naphthalene tetracarboxylic dianhydride @ reduced graphene oxide composite material of this example is prepared by a method including the following steps:

[0063] 1) Mix 5 mL of graphene oxide solution (concentration 4 mg / mL) with 5 mL of deionized water, and ultrasonically disperse for 30 min to obtain a graphene oxide dispersion; in the graphene oxide dispersion, the concentration of graphene oxide is 2 mg / mL;

[0064] Add 80 mg of naphthalene tetracarboxylic dianhydride powder to the graphene oxide dispersion to obtain a naphthalene tetracarboxylic dianhydride / graphene oxide mixture; in the naphthalene tetracarboxylic dianhydride / graphene oxide mixture, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is 1:4;

[0065] 2) Place the naphthalene tetracarboxylic dianhydride / graphene oxide mixture obtained in step 1) in an ultrasonic cleaner and perform ultrasonic treatment (80 KHz, 2 h); after ultrasonic treatment, pour the mixed solution into a crystallization dish and perform freeze-drying (-30 °C, 12 h), press the freeze-dried spongy material into a film, and use a punching machine to punch out a disc with a diameter of 12 mm and a thickness of 50 μm to obtain a precursor;

[0066] 3) The precursor is heat-treated in an argon atmosphere at 300 °C for 180 min, and then cooled to obtain the product.

[0067] Comparative Example 1

[0068] This comparative example is a single reduced graphene oxide material. The difference in its preparation method from that of Example 1 lies in that: in step 1), naphthalenetetracarboxylic dianhydride is not added to the reaction raw materials, and an equal amount of deionized water is used instead, and the other steps are the same as those in Example 1.

[0069] Comparative Example 2

[0070] This comparative example is a single naphthalenetetracarboxylic dianhydride material. The difference in its preparation method from that of Example 1 lies in that: in step 1), graphene oxide is not contained in the reaction raw materials, and an equal amount of deionized water is used instead.

[0071] Test Example 1 X-ray diffraction (XRD) analysis

[0072] In this test example, XRD analysis was performed on the naphthalenetetracarboxylic dianhydride@reduced graphene oxide composite material of Example 1 and the single materials of Comparative Examples 1-2. The scanning angle was 10-70°, and waveform images were obtained through scanning. The results are as Figures 1 to 3 shown.

[0073] From Figure 1 the XRD pattern of, it can be seen that the reduced graphene oxide material sample of Comparative Example 1 has a diffraction peak at 24°, corresponding to the (002) crystal plane.

[0074] From Figure 2 the XRD pattern of, it can be seen that the naphthalenetetracarboxylic dianhydride material sample of Comparative Example 2 shows strong diffraction peaks at 12.28°, 23.61°, and 27.64°, indicating a high π-π stacking between naphthalenetetracarboxylic dianhydride molecules.

[0075] From Figure 3 the XRD pattern of, it can be seen that similarly, the four diffraction peaks of naphthalenetetracarboxylic dianhydride also exist in the naphthalenetetracarboxylic dianhydride@reduced graphene oxide sample of Example 1, but their intensities are weaker than those of naphthalenetetracarboxylic dianhydride. This is mainly because after the naphthalenetetracarboxylic dianhydride is compounded with the reduced graphene oxide, the crystallinity of the naphthalenetetracarboxylic dianhydride attached to the surface of the reduced graphene oxide decreases. It should be noted that the diffraction peak of the reduced graphene oxide disappears in the naphthalenetetracarboxylic dianhydride@reduced graphene oxide sample, mainly because the diffraction peak of the naphthalenetetracarboxylic dianhydride is stronger and masks the weak diffraction peak of the reduced graphene oxide.

[0076] Test Example 2 Scanning electron microscope (SEM) analysis

[0077] In this test example, the cross-sectional morphology of the naphthalenetetracarboxylic dianhydride@reduced graphene oxide composite materials prepared in Examples 2-4 was analyzed by a scanning electron microscope. The SEM images are as Figures 4 to 6as shown

[0078] It can be seen from Figures 4 to 6 that as the ratio of naphthalene tetracarboxylic dianhydride to graphene oxide changes, the number of naphthalene tetracarboxylic dianhydride in the reduced graphene oxide interlayer also changes, and the layered structure of the film changes significantly.

[0079] Test Example 3 Electrochemical Cycling Rate Stability Test

[0080] The methods and parameters for measuring electrochemical properties are as follows: In order to test the potassium ion storage performance of the prepared samples, potassium ion button half-cells were assembled, and the assembly of the button cells was completed in a glove box filled with argon. Before assembling the button cells, the battery case and the separator should be placed in an oven to remove the moisture adsorbed on the surface. Among them, the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite films of Examples 1-4 and the reduced graphene oxide material of Comparative Example 1 were weighed and directly used as the positive electrode plates. The oxide layer on the surface of the potassium block should be cut off before rolling it into a thin sheet. The positive electrode plate of Comparative Example 2 was prepared by the traditional coating method. Specifically, a certain mass of polyvinylidene fluoride was dissolved in 1,3-N-methylpyrrolidone, and then naphthalene tetracarboxylic dianhydride and Ketjenblack (mass ratio of polyvinylidene fluoride: Ketjenblack: naphthalene tetracarboxylic dianhydride is 2:3:5) were added, and stirred at room temperature for 8 h; then, the prepared slurry was coated on the aluminum foil, the coating thickness was 20 μm, and it was placed in an oven at 80 °C overnight for drying; finally, the dried aluminum foil was punched into a circular electrode plate with a diameter of 12 mm to be used as the positive electrode plate.

[0081] The assembly order of the half-cell: positive electrode case, electrode plate, electrolyte, separator, electrolyte, potassium sheet, gasket, spring piece, negative electrode case, sealing and pressing. The electrolyte is 1.0 M potassium bis(fluorosulfonyl)imide (KFSI), and the solvent is ethylene carbonate / diethyl carbonate EC / DEC (volume ratio 1:1).

[0082] The rate performance test was carried out on a Blue Electric Battery Tester. The battery was tested for discharge-charge at different current densities (25, 50, 100, 200, 300, 500 mA / g). Finally, when the current density returned from a large value to a small value (50 mA / g), if the capacity could be restored, it indicated that the material had good rate performance. The voltage window for the rate performance test was 0.01-3 V. The experimental results are as Figures 7 to 12 shown

[0083] Among them, Figures 7 to 10 are the electrochemical rate performances of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite materials prepared in Examples 1-4 of the present invention as the positive electrode materials for potassium ion batteries; Figure 11 is the electrochemical rate performance of the reduced graphene oxide material prepared in Comparative Example 1 as the positive electrode material for potassium ion batteries; Figure 12The electrochemical rate performance of the naphthalene tetracarboxylic dianhydride material prepared in Comparative Example 2 as a cathode material for potassium ion batteries.

[0084] It can be seen from Figures 7 to 10 that as the content of naphthalene tetracarboxylic dianhydride increases continuously, the cyclic stability of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material as a self-supporting electrode first increases and then decreases. This is because the surface area of the interaction between the surface of graphene oxide and naphthalene tetracarboxylic dianhydride molecules through π-π interaction is certain. When the content of naphthalene tetracarboxylic dianhydride increases, the excessive naphthalene tetracarboxylic dianhydride is more likely to dissolve in the electrolyte. Among them, the test results show that when the current density increases to the maximum current density of 500 mA / g, the capacities of the battery materials corresponding to Examples 1-4 are 35, 73, 31, and 25 mAh / g respectively. Among them, the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material of Example 2 has the best rate performance, and the capacity recovery rate is high after multiple cycles, and the cyclic performance is good.

[0085] It can be seen from Figure 11 that when no naphthalene tetracarboxylic dianhydride is added, the reduced graphene oxide material of Comparative Example 1 shows low capacity and rate performance at each current density. The reason may be that the π-π interaction causes the stacking of reduced graphene oxide sheets, resulting in a reduction in the ion-accessible area and a decrease in the ion transport efficiency.

[0086] It can be seen from Figure 12 that when graphene oxide is not added during the material preparation process, the synthesized naphthalene tetracarboxylic dianhydride material of Comparative Example 2 shows a sharp attenuation of capacity during the potassium ion storage performance test as the current density gradually increases. This may be due to the dissolution of naphthalene tetracarboxylic dianhydride causing irreversible attenuation of capacity.

[0087] In summary, it can be seen that the present invention uses naphthalene tetracarboxylic dianhydride and reduced graphene oxide as precursors, and through simple and efficient ultrasonic-assisted treatment and low-temperature thermal reduction, a naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material is prepared. In the composite material, reduced graphene oxide and naphthalene tetracarboxylic dianhydride are tightly combined through π-π interaction. On the one hand, it can improve the conductivity of naphthalene tetracarboxylic dianhydride and reduce the solubility of naphthalene tetracarboxylic dianhydride in the organic electrolyte; on the other hand, it can expose more active sites of naphthalene tetracarboxylic dianhydride, enhance the potassium ion storage ability, effectively improve the rate performance and cyclic performance of the battery material, and is suitable for use as an electrode material for potassium ion batteries.

Claims

1. A preparation method of a naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material, characterized in that It includes the following steps: (1) Prepare a graphene oxide dispersion liquid, and then add naphthalene tetracarboxylic dianhydride to the graphene oxide dispersion liquid to obtain a naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid; in the naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is (1∶4)~(2∶1); (2) Ultrasonically treat the naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid, then freeze-dry it, and then stamp the freeze-dried sponge-like substance into circular wafers to obtain a precursor; (3) In an inert atmosphere, heat-treat the precursor at 300~400 °C, and then cool it to obtain a naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material; the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material is used as a cathode material for the battery.

2. The preparation method of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to claim 1, characterized in that, In step (1), the graphene oxide dispersion liquid is obtained by adding graphene oxide to water and performing ultrasonic dispersion.

3. The preparation method of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to claim 1, characterized in that, In step (1), in the graphene oxide dispersion liquid, the concentration of graphene oxide is 1.0~5.0 mg / mL.

4. The preparation method of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to claim 1, characterized in that, In step (1), in the naphthalene tetracarboxylic dianhydride / graphene oxide mixed liquid, the mass ratio of graphene oxide to naphthalene tetracarboxylic dianhydride is 2:

3.

5. The preparation method of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to any one of claims 1 to 4, characterized in that, In step (2), the time of the ultrasonic treatment is 1~5 h, and the ultrasonic frequency is 40 KHz~100 KHz; the temperature of the freeze-drying is -40 °C~-20 °C, and the time of the freeze-drying is 12~24 h.

6. The preparation method of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to any one of claims 1 to 4, characterized in that In step (2), the diameter of the circular wafer is 10~15 mm, and the thickness is 30~50 μm.

7. The preparation method of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to any one of claims 1 to 4, characterized in that, In step (3), the time of the heat treatment is 120~180 min.

8. A naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material prepared by the preparation method according to any one of claims 1~7.

9. Use of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to claim 8, characterized in that, Application in a potassium ion battery.

10. Use of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material according to claim 9, characterized in that, The application is the application of the naphthalene tetracarboxylic dianhydride@reduced graphene oxide composite material as a cathode material for a potassium ion battery.

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