A method for preparing a honeycomb-like multi-layer graphene foam anode material and its application

Abstract

The present invention provides a method for preparing a honeycomb-like multi-layer graphene foam anode material and its application. The method includes graphite pre-oxidation treatment, preparation of multi-layer graphene oxide foam, and preparation method of self-crosslinked honeycomb-like multi-layer graphene foam to obtain the honeycomb-like multi-layer graphene foam anode material. Compared with traditional graphene materials, the number of layers of the honeycomb-like multi-layer graphene foam provided by the present invention is controlled between 10 and 30 layers, which is much higher than the number of layers of graphene. At the same time, the above anode material has a honeycomb-like morphology and combines the energy storage characteristics of both graphene and graphite, so that it can obtain a high energy density during the process of sodium storage and potassium storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials, and particularly relates to a method for preparing a honeycomb-like multi-layer graphene foam anode material and its application. Background Art

[0002] Due to its large specific surface area and the advantage of having fewer layers, graphene materials tend to exhibit capacitive characteristics in the energy storage mechanism. However, this energy storage characteristic is not conducive to obtaining a high energy density during the process of sodium storage and potassium storage in the electrode. Moreover, due to the large specific surface area of graphene materials, the surface energy of the materials is relatively high, which makes it difficult to use pure graphene materials as the anode in the electrode preparation process. This is mainly because the fewer the number of graphene layers (≤5 layers), the higher the difficulty of the preparation process.

[0003] In recent years, most of the three-dimensional graphene materials disclosed in the prior art are prepared by the template method or chemical vapor deposition method. These preparation methods have the disadvantages of high equipment requirements, high cost, and low preparation efficiency. For example, CN107507967A discloses a graphene battery anode composite material, which is obtained by sequentially coating carbon and silicon carbide on the surface of graphene. The above technical solution sequentially coats carbon and silicon carbide on the surface of graphene, making the graphene battery anode composite material have characteristics such as high capacity and high cycle stability. However, this composite material does not improve the performance of graphene itself, but only improves the specific capacity of the composite material by compounding with a high specific capacity silicon-based material.

[0004] Therefore, in this field, there is an urgent need to develop a graphene material with a high specific capacity, which not only has a small specific surface energy but also can be compatible with the existing electrode preparation process. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a honeycomb-like multi-layer graphene foam anode material and its application. The present invention provides a method for graphite pre-oxidation treatment, preparation of multi-layer graphene oxide foam, and preparation of self-crosslinked honeycomb-like multi-layer graphene foam, so as to obtain an anode material with a high energy density.

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted:

[0007] In the first aspect, the present invention provides a method for preparing a honeycomb-like multi-layer graphene foam anode material, and the method includes the following steps:

[0008] (1) Mix potassium persulfate, phosphorus pentoxide, and concentrated sulfuric acid, and then add flake graphite. After the reaction, pre-oxidized graphite is obtained;

[0009] (2) Mix the pre-oxidized graphite, sodium nitrate, and concentrated sulfuric acid obtained in step (1), cool, and then dropwise add concentrated sulfuric acid. Add potassium permanganate in batches, and after the reaction, perform a cooling treatment to obtain a precursor solution;

[0010] (3) Add deionized water to the precursor solution obtained in step (2) in batches. After the reaction, add hydrogen peroxide, and then add deionized water for dilution and cooling treatment to obtain a coolant. The coolant undergoes post-treatment to obtain multi-layer graphene oxide-like foam;

[0011] (4) Mix the multi-layer graphene oxide-like foam, cross-linking agent, and solvent obtained in step (3), then add sodium citrate pentahydrate and stir. After the reaction, obtain a cross-linked material. Wash the cross-linked material to obtain a dispersion, and perform ultrasonic treatment and freeze-drying on the dispersion to obtain the honeycomb multi-layer graphene-like foam anode material.

[0012] First, the present invention uses a method for pre-oxidizing graphite, preparing multi-layer graphene oxide-like foam, and preparing self-cross-linked honeycomb multi-layer graphene-like foam to obtain a honeycomb multi-layer graphene-like foam anode material. Compared with traditional graphene materials, the number of layers of the honeycomb multi-layer graphene-like foam provided by the present invention is controlled between 10 and 30 layers, which is much higher than that of graphene. At the same time, the above anode material has a honeycomb morphology and combines the energy storage characteristics of both graphene and graphite, so that it can obtain a high energy density during the process of storing sodium and potassium.

[0013] Secondly, the preparation method provided by the present invention endows the anode material with special structural characteristics, greatly reducing the specific surface energy of the material itself, and thus better compatible with the existing pole piece manufacturing process. Compared with traditional graphene materials, the honeycomb multi-layer graphene-like foam anode material has lower requirements for the preparation process, greatly reducing the manufacturing cost.

[0014] Finally, the multi-layer graphene oxide-like foam undergoes self-cross-linking in the presence of a cross-linking agent, that is, self-assembly of graphene materials can be achieved under liquid-phase conditions, and a three-dimensional honeycomb-like graphene material can be obtained without a template. The above method has low requirements for equipment, low cost, and high preparation efficiency.

[0015] Preferably, the mass ratio of potassium persulfate, phosphorus pentoxide, and flake graphite in step (1) is 1:1:(0.5 - 2.0), for example, it can be 1:1:0.5, 1:1:0.8, 1:1:1, 1:1:1.2, 1:1:1.5, 1:1:1.8, 1:1:2.0.

[0016] In the present invention, by adjusting the mass ratio of potassium persulfate, phosphorus pentoxide, and flake graphite, the degree of graphitization is different.

[0017] Preferably, the concentrated sulfuric acid described in step (1) needs to be added slowly.

[0018] Preferably, the mixing described in step (1) is carried out under stirring.

[0019] Preferably, the temperature of the reaction described in step (1) is 80 °C and the time is 4 h.

[0020] Preferably, after the reaction described in step (1), it also includes adding deionized water for dilution and washing and drying treatments.

[0021] Preferably, the mass ratio of the pre-oxidized graphite, sodium nitrate and potassium permanganate described in step (2) is (1 - 3):5:15, and for example, it can be 1:5:15, 1.2:5:15, 1.5:5:15, 1.8:5:15, 2:5:15, 2.2:5:15, 2.5:5:15, 2.8:5:15, 3:5:15.

[0022] In the present invention, by adjusting the mass ratio of the pre-oxidized graphite, sodium nitrate and potassium permanganate, different numbers of graphene layers can be obtained within the regulated ratio range.

[0023] Preferably, the mixing described in step (2) is carried out under stirring.

[0024] Preferably, it is cooled to 5 °C in step (2).

[0025] In the present invention, the cooling treatment described in step (2) includes but is not limited to ice bath treatment.

[0026] Preferably, the dropping rate of the concentrated sulfuric acid described in step (2) is 3 - 7 mL / min, and for example, it can be 3 mL / min, 4 mL / min, 5 mL / min, 6 mL / min, 7 mL / min.

[0027] Preferably, the number of times of adding potassium permanganate in batches in step (2) is three times.

[0028] Preferably, the time interval for adding potassium permanganate in batches in step (2) is 20 min.

[0029] Preferably, the reaction time in step (2) is 70 min.

[0030] Preferably, the cooling treatment in step (2) is to carry out a water bath reaction at 35 °C for 2 h.

[0031] Preferably, the number of times of adding deionized water in batches in step (3) is 20 times.

[0032] Preferably, the dropping rate of the deionized water added in batches in step (3) is 10-40 mL / min, for example, it can be 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min.

[0033] In the present invention, the self-heating reaction is achieved by controlling the dropping rate of deionized water.

[0034] Preferably, the temperature of the reaction in step (3) is 150-250 °C, for example, it can be 150 °C, 180 °C, 200 °C, 220 °C, 250 °C.

[0035] It should be noted that in step (3), hydrogen peroxide is added when the reaction solution turns dark yellow, and the solution turns bright yellow rapidly after adding hydrogen peroxide.

[0036] Preferably, it is cooled to room temperature in step (3).

[0037] Preferably, the post-treatment in step (3) includes sequentially performing static settlement, filtration, washing, and freeze-drying on the coolant.

[0038] Preferably, the temperature of the static settlement is room temperature and the time is 12 h.

[0039] Preferably, the washing is carried out 2-3 times with hydrochloric acid with a mass fraction of 5%, and then washed with deionized water until the pH is 5-7.

[0040] Preferably, the concentration of the solution for freeze-drying is 1.0-1.5 mg / mL, for example, it can be 1.0 mg / mL, 1.1 mg / mL, 1.2 mg / mL, 1.3 mg / mL, 1.4 mg / mL, 1.5 mg / mL.

[0041] Preferably, the mass ratio of the multi-layer graphene oxide foam to the cross-linking agent in step (4) is 1:(0.5-2.0), for example, it can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2.0.

[0042] Preferably, the cross-linking agent in step (4) includes polyvinylpyrrolidone or sodium dodecylsulfonate.

[0043] Preferably, the solvent in step (4) is deionized water.

[0044] Preferably, the mixing in step (4) is carried out under ultrasonic dispersion.

[0045] Preferably, the mass ratio of the multi-layer graphene oxide-like foam and sodium citrate pentahydrate in step (4) is 1:(10-20), for example, it can be 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20.

[0046] Preferably, the temperature of the reaction in step (4) is 90 °C and the time is 5-20 h, for example, it can be 5 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h.

[0047] Preferably, the power of the ultrasonic wave in step (4) is 800-1500 W, for example, it can be 800 W, 900 W, 1000 W, 1100 W, 1200 W, 1300 W, 1400 W, 1500 W.

[0048] Preferably, the time of the ultrasonic wave in step (4) is 5-15 h, for example, it can be 5 h, 8 h, 10 h, 12 h, 15 h.

[0049] In a second aspect, the present invention provides a honeycomb multi-layer graphene-like foam anode material, and the honeycomb multi-layer graphene-like foam anode material is prepared according to the method for preparing a honeycomb multi-layer graphene-like foam anode material described in the first aspect.

[0050] In a third aspect, the present invention provides a negative electrode sheet, and the negative electrode sheet includes a current collector and a negative electrode active material layer provided on the surface of the current collector.

[0051] Preferably, the negative electrode active material layer includes the honeycomb multi-layer graphene-like foam anode material described in the second aspect.

[0052] In a fourth aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, and the negative electrode sheet is the negative electrode sheet described in the third aspect.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The present invention uses a method for graphite pre-oxidation treatment, preparation of multi-layer graphene oxide-like foam, and preparation of self-crosslinked honeycomb multi-layer graphene-like foam to obtain a honeycomb multi-layer graphene-like foam anode material. Compared with traditional graphene materials, the number of layers of the honeycomb multi-layer graphene-like foam provided by the present invention is controlled between 10 and 30 layers, which is much higher than the number of layers of graphene. At the same time, the above anode material has a honeycomb morphology and combines the energy storage characteristics of both graphene and graphite, so that it can obtain a high energy density during the process of sodium storage and potassium storage.

[0055] The preparation method provided by the present invention endows the anode material with special structural features, significantly reducing the specific surface energy of the material itself, and thus better compatible with the existing anode sheet manufacturing processes. Compared with traditional graphene materials, the honeycomb-like multi-layer graphene foam anode material has lower requirements for the preparation process, greatly reducing the manufacturing cost.

[0056] In addition, the multi-layer graphene oxide foam undergoes self-crosslinking in the presence of a crosslinking agent, that is, self-assembly of the graphene material can be achieved under liquid-phase conditions, and a three-dimensional honeycomb-like graphene material can be obtained without a template. The above method has low requirements for equipment, low cost, and high preparation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a schematic flow chart of the synthesis method for the graphite pre-oxidation treatment provided in Example 1.

[0058] Figure 2 is a schematic flow chart of the synthesis method for the multi-layer graphene oxide foam provided in Example 1.

[0059] Figure 3 is a schematic flow chart of the synthesis method for the self-crosslinked honeycomb-like multi-layer graphene foam provided in Example 1.

[0060] Figure 4 is an SEM image of the honeycomb-like multi-layer graphene foam anode material provided in Example 1, with a scale bar of 100 μm.

[0061] Figure 5 is an XRD pattern of the honeycomb-like multi-layer graphene foam anode material provided in Example 1.

[0062] Figure 6 is a graph showing the rate performance and cycling performance of sodium storage of the honeycomb-like multi-layer graphene foam anode material provided in Application Example 1.

[0063] Figure 7 is a graph showing the rate performance and cycling performance of potassium storage of the honeycomb-like multi-layer graphene foam anode material provided in Application Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] The technical solution of the present invention will be further described below by combining the accompanying drawings and specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0065] Example 1

[0066] This example provides a honeycomb-like multi-layer graphene foam anode material and its preparation method, which includes the following steps, as Figures 1 - 3 shown:

[0067] (1) Mix potassium persulfate and phosphorus pentoxide, slowly add 30 mL of concentrated sulfuric acid, and stir magnetically for 10 min. Then slowly add flake graphite. The mass ratio of potassium persulfate, phosphorus pentoxide, and flake graphite is 1:1:1.2. After reacting at 80 °C for 4 h, add 500 mL of deionized water for dilution, washing, and drying to obtain pre-oxidized graphite;

[0068] (2) Mix the pre-oxidized graphite obtained in step (1) with sodium nitrate, slowly add 50 mL of concentrated sulfuric acid, and stir magnetically until evenly mixed. After the temperature of the reaction solution cools to 5 °C, add concentrated sulfuric acid dropwise at a rate of 5 mL / min. Start timing the reaction after the addition of concentrated sulfuric acid is complete. Add potassium permanganate in three batches, with a time interval of 20 min between the batches. After the reaction ends in 70 min, transfer it to a water bath at 35 °C and react for 2 h. The mass ratio of pre-oxidized graphite, sodium nitrate, and potassium permanganate is 2:5:15 to obtain a precursor solution;

[0069] (3) Add 500 mL of deionized water to the precursor solution obtained in step (2) in 20 batches, with a dropping rate of 25 mL / min. React at 200 °C and stir while it is hot to make the reaction continue. When the solution turns dark yellow, add 30 mL of hydrogen peroxide, and at this time the solution quickly turns bright yellow from dark yellow. Then add 400 mL of deionized water for dilution and transfer it to a cool water constant temperature pot and continue stirring to cool it to room temperature. Let the coolant stand at room temperature for 12 h to make it layer and precipitate. Filter off the supernatant, then wash it three times with 5% hydrochloric acid by mass, and then wash it with deionized water until the pH is 6. Finally, freeze-dry the deionized water dispersion of graphene oxide with a concentration of 1.2 mg / mL to obtain multi-layer graphene oxide-like foam;

[0070] (4) Ultrasonically disperse the multi-layer graphene oxide-like foam, polyvinylpyrrolidone-K30 cross-linking agent, and deionized water obtained in step (3) for 2 h. The mass ratio of multi-layer graphene oxide-like foam to the cross-linking agent is 1:1.2. Then add sodium citrate dihydrate and stir. The mass ratio of multi-layer graphene oxide-like foam to sodium citrate dihydrate is 1:15. After reacting in an oil bath at 90 °C for 12 h, obtain a cross-linked material. Wash the cross-linked material three times with deionized water to obtain a dispersion, and ultrasonically disperse the dispersion at a power of 1100 W for 10 h and then freeze-dry it to obtain a honeycomb-like multi-layer graphene foam anode material.

[0071] Figure 4 It shows that the prepared honeycomb-like multi-layer graphene foam anode material has a honeycomb structure, Figure 5 It shows that the honeycomb-like multi-layer graphene foam anode material obtained in Example 1 has a pure phase structure.

[0072] Example 2

[0073] This example provides a honeycomb-like multi-layer graphene foam anode material and its preparation method, which includes the following steps:

[0074] (1) Mix potassium persulfate and phosphorus pentoxide, slowly add 30 mL of concentrated sulfuric acid, and stir magnetically for 10 min. Then slowly add flake graphite, where the mass ratio of potassium persulfate, phosphorus pentoxide, and flake graphite is 1:1:0.8. After reacting at 80 °C for 4 h, add 500 mL of deionized water for dilution, washing, and drying to obtain pre-oxidized graphite;

[0075] (2) Mix the pre-oxidized graphite obtained in step (1) with sodium nitrate, slowly add 50 mL of concentrated sulfuric acid, and stir magnetically until evenly mixed. After the temperature of the reaction solution cools to 5 °C, add concentrated sulfuric acid dropwise at a rate of 4 mL / min. After the addition of concentrated sulfuric acid is complete, start timing the reaction, and add potassium permanganate in three batches with a time interval of 20 min between each batch. After 70 min, transfer the reaction mixture to a water bath at 35 °C and react for 2 h. The mass ratio of pre-oxidized graphite, sodium nitrate, and potassium permanganate is 1.5:5:15 to obtain a precursor solution;

[0076] (3) Add 500 mL of deionized water to the precursor solution obtained in step (2) in 20 batches at a dropping rate of 15 mL / min. React at 180 °C and stir while it is hot to make the reaction continue. When the solution turns dark yellow, add 30 mL of hydrogen peroxide, and at this time the solution quickly turns bright yellow from dark yellow. Then add 400 mL of deionized water for dilution and transfer to a constant-temperature cool water bath and continue stirring to cool it to room temperature. Let the coolant stand at room temperature for 12 h to form a layered precipitate, filter off the supernatant, then wash it three times with 5% hydrochloric acid by mass fraction, then wash it with deionized water until the pH is 6, and finally freeze-dry the deionized water dispersion of graphene oxide with a concentration of 1.1 mg / mL to obtain multi-layer graphene oxide foam;

[0077] (4) Ultrasonically disperse the multi-layer graphene oxide foam, polyvinylpyrrolidone-K30 cross-linking agent, and deionized water obtained in step (3) for 2 h, where the mass ratio of multi-layer graphene oxide foam to the cross-linking agent is 1:0.8. Then add sodium citrate dihydrate and stir, where the mass ratio of multi-layer graphene oxide foam to sodium citrate dihydrate is 1:12. React in an oil bath at 90 °C for 10 h to obtain a cross-linked material. Wash the cross-linked material three times with deionized water to obtain a dispersion, and ultrasonically disperse the dispersion at a power of 900 W for 8 h and then freeze-dry it to obtain a honeycomb-like multi-layer graphene foam anode material.

[0078] Example 3

[0079] This embodiment provides a honeycomb-like multi-layer graphene foam anode material and a preparation method thereof, which includes the following steps:

[0080] (1) Mix potassium persulfate and phosphorus pentoxide, slowly add 30 mL of concentrated sulfuric acid and stir magnetically for 10 min, then slowly add flake graphite. The mass ratio of potassium persulfate, phosphorus pentoxide and flake graphite is 1:1:1.6. After reacting at 80 °C for 4 h, add 500 mL of deionized water for dilution, washing and drying to obtain pre-oxidized graphite;

[0081] (2) Mix the pre-oxidized graphite obtained in step (1) with sodium nitrate, slowly add 50 mL of concentrated sulfuric acid, stir magnetically to mix evenly. After the temperature of the reaction solution cools to 5 °C, add concentrated sulfuric acid dropwise at a rate of 6 mL / min. After the addition of concentrated sulfuric acid is completed, start timing the reaction, add potassium permanganate in three batches, and the time interval between the batches of adding potassium permanganate is 20 min. After the reaction ends in 70 min, transfer it to a water bath at 35 °C for 2 h. The mass ratio of pre-oxidized graphite, sodium nitrate and potassium permanganate is 2.5:5:15 to obtain a precursor solution;

[0082] (3) Add 500 mL of deionized water to the precursor solution obtained in step (2) in 20 batches, and the dropping rate of adding deionized water is 35 mL / min. React at 220 °C and stir while it is hot to make the reaction continue. When the solution turns dark yellow, add 30 mL of hydrogen peroxide, and at this time the solution quickly turns bright yellow from dark yellow. Then add 400 mL of deionized water for dilution and transfer it to a constant temperature water bath at room temperature and continue stirring to cool it to room temperature. The coolant is allowed to stand at room temperature for 12 h to form a layered precipitate. Filter off the supernatant, then wash it 3 times with 5% hydrochloric acid by mass fraction, then wash it with deionized water until the pH is 6. Finally, freeze-dry the deionized water dispersion of graphene oxide with a concentration of 1.4 mg / mL to obtain multi-layer graphene oxide foam;

[0083] (4) Ultrasonically disperse the multi-layer graphene oxide foam, polyvinylpyrrolidone-K30 cross-linking agent and deionized water obtained in step (3) for 2 h. The mass ratio of the multi-layer graphene oxide foam to the cross-linking agent is 1:1.8. Then add sodium citrate dihydrate and stir. The mass ratio of the multi-layer graphene oxide foam to sodium citrate dihydrate is 1:18. After an oil bath reaction at 90 °C for 16 h, a cross-linked material is obtained. Wash the cross-linked material 3 times with deionized water to obtain a dispersion, and ultrasonically disperse the dispersion at a power of 1200 W for 12 h and then freeze-dry it to obtain a honeycomb-like multi-layer graphene foam anode material.

[0084] Example 4

[0085] This embodiment provides a honeycomb-like multi-layer graphene foam anode material and a preparation method thereof, which includes the following steps:

[0086] (1) Mix potassium persulfate and phosphorus pentoxide, slowly add 30 mL of concentrated sulfuric acid, and stir magnetically for 10 min. Then slowly add flake graphite. The mass ratio of potassium persulfate, phosphorus pentoxide, and flake graphite is 1:1:0.5. After reacting at 80 °C for 4 h, add 500 mL of deionized water for dilution, washing, and drying to obtain pre-oxidized graphite;

[0087] (2) Mix the pre-oxidized graphite obtained in step (1) with sodium nitrate, slowly add 50 mL of concentrated sulfuric acid, and stir magnetically until evenly mixed. After the temperature of the reaction solution cools to 5 °C, add concentrated sulfuric acid dropwise at a rate of 3 mL / min. After the addition of concentrated sulfuric acid is completed, start timing the reaction, and add potassium permanganate in three batches. The time interval between the batches of adding potassium permanganate is 20 min. After the reaction ends in 70 min, transfer it to a water bath at 35 °C for reaction for 2 h. The mass ratio of pre-oxidized graphite, sodium nitrate, and potassium permanganate is 1:5:15 to obtain a precursor solution;

[0088] (3) Add 500 mL of deionized water to the precursor solution obtained in step (2) in 20 batches at a dropping rate of 10 mL / min. React at 150 °C and stir while it is hot to make the reaction continue. When the solution turns dark yellow, add 30 mL of hydrogen peroxide, and at this time the solution quickly turns bright yellow from dark yellow. Then add 400 mL of deionized water for dilution and transfer it to a constant temperature water bath at room temperature and continue stirring to cool it to room temperature. The coolant is allowed to stand at room temperature for 12 h to form a layered precipitate. Filter off the supernatant, then wash it three times with 5% hydrochloric acid by mass fraction, then wash it with deionized water until the pH is 6. Finally, freeze-dry the deionized water dispersion of graphene oxide with a concentration of 1.0 mg / mL to obtain multi-layer graphene oxide foam;

[0089] (4) Ultrasonically disperse the multi-layer graphene oxide foam, polyvinylpyrrolidone-K30 cross-linking agent, and deionized water obtained in step (3) for 2 h. The mass ratio of multi-layer graphene oxide foam to the cross-linking agent is 1:0.5. Then add sodium citrate dihydrate and stir. The mass ratio of multi-layer graphene oxide foam to sodium citrate dihydrate is 1:10. After reacting in an oil bath at 90 °C for 5 h, a cross-linked material is obtained. Wash the cross-linked material three times with deionized water to obtain a dispersion, and ultrasonically disperse the dispersion at a power of 800 W for 15 h and then freeze-dry it to obtain a honeycomb-like multi-layer graphene foam anode material.

[0090] Example 5

[0091] This embodiment provides a honeycomb-like multi-layer graphene foam anode material and a preparation method thereof, which includes the following steps:

[0092] (1) Mix potassium persulfate and phosphorus pentoxide, slowly add 30 mL of concentrated sulfuric acid, and stir magnetically for 10 min. Then slowly add flake graphite, where the mass ratio of potassium persulfate, phosphorus pentoxide, and flake graphite is 1:1:2.0. After reacting at 80 °C for 4 h, add 500 mL of deionized water for dilution, washing, and drying to obtain pre-oxidized graphite.

[0093] (2) Mix the pre-oxidized graphite obtained in step (1) with sodium nitrate, slowly add 50 mL of concentrated sulfuric acid, and stir magnetically until evenly mixed. After the temperature of the reaction solution cools to 5 °C, add concentrated sulfuric acid dropwise at a rate of 7 mL / min. After the addition of concentrated sulfuric acid is completed, start timing the reaction, add potassium permanganate in three batches, with a time interval of 20 min between the batches of adding potassium permanganate. After the reaction ends in 70 min, transfer it to a water bath at 35 °C for 2 h. The mass ratio of pre-oxidized graphite, sodium nitrate, and potassium permanganate is 3:5:15 to obtain a precursor solution.

[0094] (3) Add 500 mL of deionized water to the precursor solution obtained in step (2) in 20 batches, with a dropping rate of 40 mL / min. React at 250 °C and stir while it is hot to make the reaction continue. When the solution turns dark yellow, add 30 mL of hydrogen peroxide, and at this time the solution quickly turns bright yellow from dark yellow. Then add 400 mL of deionized water for dilution and transfer it to a constant temperature water bath at room temperature and continue stirring to cool it to room temperature. The coolant is allowed to stand at room temperature for 12 h to make it layer and precipitate. Filter off the supernatant, then wash it three times with 5% hydrochloric acid by mass, and then wash it with deionized water until the pH is 6. Finally, freeze-dry the deionized water dispersion of graphene oxide with a concentration of 1.5 mg / mL to obtain multi-layer graphene oxide foam.

[0095] (4) Ultrasonically disperse the multi-layer graphene oxide foam obtained in step (3), polyvinylpyrrolidone-K30 cross-linking agent, and deionized water for 2 h, where the mass ratio of multi-layer graphene oxide foam and cross-linking agent is 1:2.0. Then add sodium citrate dihydrate and stir, where the mass ratio of multi-layer graphene oxide foam and sodium citrate dihydrate is 1:20. After reacting in an oil bath at 90 °C for 20 h, obtain a cross-linked material. Wash the cross-linked material three times with deionized water to obtain a dispersion, and ultrasonically treat the dispersion at a power of 1500 W for 5 h and then freeze-dry it to obtain a honeycomb-like multi-layer graphene foam anode material.

[0096] Example 6

[0097] The difference between this example and Example 1 is that in step (2), the mass ratio of pre-oxidized graphite, sodium nitrate, and potassium permanganate is 0.5:5:15, and the others are the same as in Example 1.

[0098] Example 7

[0099] The difference between this example and Example 1 is that in step (2), the mass ratio of pre-oxidized graphite, sodium nitrate, and potassium permanganate is 6:5:15, and the others are the same as in Example 1.

[0100] Example 8

[0101] The difference between this example and Example 1 is that in step (2), the dropping rate of concentrated sulfuric acid is 1 mL / min, and the others are the same as in Example 1.

[0102] Example 9

[0103] The difference between this example and Example 1 is that in step (2), the dropping rate of concentrated sulfuric acid is 10 mL / min, and the others are the same as in Example 1.

[0104] Example 10

[0105] The difference between this example and Example 1 is that in step (3), the dropping rate of deionized water added in batches is 5 mL / min, and the others are the same as in Example 1.

[0106] Example 11

[0107] The difference between this example and Example 1 is that in step (3), the dropping rate of deionized water added in batches is 50 mL / min, and the others are the same as in Example 1.

[0108] Example 12

[0109] The difference between this example and Example 1 is that in step (4), the mass ratio of multi-layer graphene oxide foam and polyvinylpyrrolidone-K30 cross-linking agent is 1:0.1, and the others are the same as in Example 1.

[0110] Example 13

[0111] The difference between this example and Example 1 is that in step (4), the mass ratio of multi-layer graphene oxide foam and polyvinylpyrrolidone-K30 cross-linking agent is 1:4, and the others are the same as in Example 1.

[0112] Example 14

[0113] The difference between this example and Example 1 is that in step (4), the mass ratio of multi-layer graphene oxide foam and sodium citrate pentahydrate is 1:5, and the others are the same as in Example 1.

[0114] Example 15

[0115] The difference between this example and Example 1 is that in step (4), the mass ratio of the multi-layer graphene oxide-like foam to sodium citrate pentahydrate is 1:25, and the others are the same as those in Example 1.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that step (4) is not carried out, and the others are the same as those in Example 1.

[0118] Comparative Example 2

[0119] This comparative example provides a graphene material.

[0120] Application Examples 1 to 15 and Comparative Application Examples 1 to 2

[0121] The honeycomb multi-layer graphene-like foam anode materials provided by Examples 1 to 15 and Comparative Examples 1 to 2 were used to prepare sodium ion batteries:

[0122] Preparation of the negative electrode sheet: The above-mentioned negative electrode material, super carbon, and carboxymethyl cellulose were mixed and ground for 20 min according to a mass ratio of 8:1:1, and deionized water was added to adjust the slurry to obtain a uniform electrode slurry. Then, the slurry was evenly coated on a copper foil using a coater and vacuum dried at 80 °C for 12 h to obtain a pole piece. The prepared pole piece was rolled, punched, and assembled into a button-type half cell for testing;

[0123] Preparation of the sodium ion battery: The prepared active material electrode sheet was used as the working electrode, a high-purity sodium sheet was used as the counter electrode, and the electrolyte was 1 mol L -1 NaPF6 + DMC (volume ratio 1:1) solution, and a Celgard 2325 separator was used. The assembly was carried out in a glove box under a protective atmosphere of high-purity argon with a water and oxygen content of less than 0.1 ppm, and sealed using an MSK-110 type manual hydraulic sealer. Finally, the battery was removed from the glove box and left to stand for 20 h.

[0124] Test conditions

[0125] The sodium ion batteries provided by Application Examples 1 to 15 and Comparative Application Examples 1 to 2 were subjected to performance tests, and the test methods were as follows:

[0126] (1) Morphology test: Test using a scanning electron microscope;

[0127] (2) Structure test: Test using an X-ray diffractometer;

[0128] (3) Rate performance: At 25 °C, with an electrochemical window of 0.01 V - 1.5 V, test its capacity retention rate at a rate of 1C;

[0129] (4) Cycle performance: At 25 °C, with an electrochemical window of 0.01 V - 1.5 V, test its capacity retention rate after 10,000 cycles at a rate of 1C.

[0130] The test results are shown in Table 1:

[0131] Table 1

[0132]

[0133]

[0134] As can be seen from the data in Table 1, the present invention uses a method of graphite pre-oxidation treatment, preparation of multi-layer graphene oxide-like foam, and preparation of self-crosslinked honeycomb multi-layer graphene-like foam to obtain a honeycomb multi-layer graphene-like foam anode material. Compared with traditional graphene materials, Figures 6 - 7 it shows that the number of layers of the honeycomb multi-layer graphene-like foam provided by the present invention is controlled between 10 and 30 layers, which is much higher than the number of layers of graphene. At the same time, the above anode material has a honeycomb morphology and combines the energy storage characteristics of both graphene and graphite, so that it can obtain a high energy density during the process of sodium storage and potassium storage.

[0135] The applicant declares that the present invention uses the above embodiments to illustrate the process method of the present invention, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent substitution of the raw materials selected by the present invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a honeycomb-like multi-layer graphene foam anode material, characterized in that, The method comprises the following steps: (1) Mix potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid, and then add flake graphite. After the reaction, pre-oxidized graphite is obtained; (2) Mix the pre-oxidized graphite obtained in step (1), sodium nitrate and concentrated sulfuric acid, cool it, and then dropwise add concentrated sulfuric acid. Potassium permanganate is added in batches. After the reaction, it is cooled to obtain a precursor solution; (3) Add deionized water to the precursor solution obtained in step (2) in batches. After the reaction, hydrogen peroxide is added, and then deionized water is added for dilution and cooling to obtain a coolant. The coolant is post-treated to obtain a multi-layer graphene oxide-like foam; (4) Mix the multi-layer graphene oxide-like foam obtained in step (3), a cross-linking agent and a solvent, and then add sodium citrate pentahydrate and stir. After the reaction, a cross-linked material is obtained. The cross-linked material is washed to obtain a dispersion, and the dispersion is ultrasonicated and freeze-dried to obtain the honeycomb-like multi-layer graphene foam anode material.

2. The method according to claim 1, wherein In step (1), the mass ratio of potassium persulfate, phosphorus pentoxide and flake graphite is 1:1:(0.5 - 2.0).

3. The method according to claim 1, wherein In step (1), the concentrated sulfuric acid needs to be added slowly.

4. The method according to claim 1, wherein In step (1), the mixing is carried out under stirring.

5. The method according to claim 1, wherein In step (1), the temperature of the reaction is 80 °C and the time is 4 h.

6. The method according to claim 1, characterized in that, After the reaction in step (1), it also includes adding deionized water for dilution and washing and drying treatment.

7. The method according to claim 1, wherein In step (2), the mass ratio of pre-oxidized graphite, sodium nitrate and potassium permanganate is (1 - 3):5:

15.

8. The method according to claim 1, wherein In step (2), the mixing is carried out under stirring.

9. The method according to claim 1, characterized in that In step (2), the cooling is to cool to 5 °C.

10. The method according to claim 1, wherein In step (2), the dropping rate of the concentrated sulfuric acid is 3 - 7 mL / min.

11. The method according to claim 1, characterized in that, In step (2), the number of times of adding potassium permanganate in batches is three times.

12. The method according to claim 1, wherein In step (2), the time interval between adding potassium permanganate in batches is 20 min.

13. The method according to claim 1, wherein In step (2), the reaction time is 70 min.

14. The method according to claim 1, wherein In step (2), the cooling treatment is to carry out a water bath reaction at 35 °C for 2 h.

15. The method according to claim 1, characterized in that, In step (3), the number of times of adding deionized water in batches is 20 times.

16. The method according to claim 1, wherein In step (3), the dropping rate of adding deionized water in batches is 10 - 40 mL / min.

17. The method according to claim 1, wherein In step (3), the reaction temperature is 150 - 250 °C.

18. The method according to claim 1, wherein In step (3), the cooling treatment is to cool to room temperature.

19. The method according to claim 1, characterized in that In step (3), the post-treatment includes successively carrying out static settling, filtration, washing and freeze-drying treatment on the coolant.

20. The method according to claim 19, wherein The temperature of the static settling is room temperature and the time is 12 h.

21. The method according to claim 19, wherein The washing includes washing 2 - 3 times with hydrochloric acid with a mass fraction of 5%, and then washing with deionized water until the pH is 5 - 7.

22. The method according to claim 19, wherein The concentration of the solution for freeze-drying is 1.0 - 1.5 mg / mL.

23. The method according to claim 1, wherein In step (4), the mass ratio of the multi-layer graphene oxide-like foam and the cross-linking agent is 1:(0.5 - 2.0).

24. The method according to claim 1, characterized in that In step (4), the cross-linking agent includes polyvinylpyrrolidone or sodium dodecyl sulfate.

25. The method according to claim 1, characterized in that, In step (4), the solvent is deionized water.

26. The method according to claim 1, characterized in that, In step (4), the mixing is carried out under ultrasonic dispersion.

27. The method according to claim 1, characterized in that The mass ratio of the multi-layer graphene oxide-like foam and sodium citrate pentahydrate described in step (4) is 1:(10-20).

28. The method according to claim 1, characterized in that The temperature of the reaction described in step (4) is 90 °C, and the time is 5-20 h.

29. The method according to claim 1, wherein The power of the ultrasonic wave described in step (4) is 800-1500 W.

30. The method according to claim 1, wherein The time of the ultrasonic wave described in step (4) is 5-15 h.

31. A honeycomb-like multi-layer graphene foam anode material, characterized in that, The honeycomb-like multi-layer graphene foam anode material is prepared according to the method for preparing the honeycomb-like multi-layer graphene foam anode material described in any one of claims 1-30.

32. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active material layer provided on the surface of the current collector.

33. The negative electrode sheet according to claim 32, wherein The negative electrode active material layer includes the honeycomb-like multi-layer graphene foam anode material described in claim 31.

34. A lithium-ion battery, characterized in that, The lithium ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, and the negative electrode sheet is the negative electrode sheet described in claim 32 or 33.

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