A porous flexible self-supporting carbon paper modified by a MOF and a preparation method thereof

Abstract

The application discloses a MOF modified porous flexible self-supporting carbon paper and a preparation method thereof and a negative electrode material. The preparation method comprises the following steps: completely immersing a paper towel in a dimethyl imidazole solution, adding a cobalt nitrate aqueous solution to the dimethyl imidazole solution, and mixing and reacting the two solutions; sequentially performing first annealing treatment and second annealing treatment on a product obtained through the reaction to obtain a cobalt-containing carbon material; sequentially performing an acid pickling process and hydrothermal treatment in an acidic system on the cobalt-containing carbon material, and then performing third pressure annealing treatment to obtain the MOF modified porous flexible self-supporting carbon paper; and the heat treatment temperatures of the first annealing treatment, the second annealing treatment and the third pressure annealing treatment are sequentially increased. The preparation method is reasonable in design, convenient in operation, simple in reaction process, environment-friendly and low in cost, and does not need large equipment and harsh conditions. Through gradient heat treatment, the microstructure of the material is controlled, and the controllable synthesis of the hard carbon material is effectively realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery preparation, and relates to a MOF modified porous flexible self-supporting carbon paper and a preparation method thereof. BACKGROUND

[0002] In recent years, sodium ion batteries are considered to be the most promising energy storage system that can replace or partially replace lithium ion batteries, and the successful commercial application thereof can significantly alleviate the problem of lithium resource shortage. At present, hard carbon (HC) anode material is the most suitable material for practical application, and has the advantages of low cost, high stability and good conductivity. However, the rate performance of hard carbon is poor, and the initial coulombic efficiency is also unsatisfactory, so it is particularly important to improve the rate performance and ICE of hard carbon for sodium storage by changing experimental conditions and other means to regulate the microstructure of the material. Researchers improve the sodium storage capacity and rate performance of hard carbon by means of heteroatom doping and increasing defects, but these methods basically reduce the low-voltage platform capacity of hard carbon negative material and reduce the ICE. On the contrary, some researchers improve the ICE by reducing the defects and porosity of hard carbon, but this method cannot improve the rate performance. SUMMARY

[0003] In view of the problems in the prior art, the application provides a MOF modified porous flexible self-supporting carbon paper and a preparation method thereof, so as to effectively solve the technical problem that the ICE and rate performance of hard carbon cannot be improved simultaneously in the prior art.

[0004] The application is realized by the following technical scheme:

[0005] A preparation method of a MOF modified porous flexible self-supporting carbon paper, comprising the following steps:

[0006] S1: completely immerse a paper towel in a dimethyl imidazole solution, then add a cobalt nitrate aqueous solution and mix to react, and then sequentially perform first annealing treatment and second annealing treatment on the obtained product to obtain a cobalt-containing carbon material;

[0007] S2: sequentially perform an acid pickling process and hydrothermal treatment in an acidic system on the cobalt-containing carbon material, and then perform third pressure annealing treatment to obtain the MOF modified porous flexible self-supporting carbon paper; the heat treatment temperatures of the first annealing treatment, the second annealing treatment and the third pressure annealing treatment are sequentially increased.

[0008] Preferably, in step S1, the molar ratio of the dimethyl imidazole to the cobalt nitrate is (4-32):1.

[0009] Preferably, in step S1, the heat treatment temperature of the first annealing treatment is 400-600 DEG C.

[0010] Preferably, in step S1, the heat treatment temperature of the second annealing treatment is 700-1100℃.

[0011] Preferably, in step S2, the acid pickling process is performed on the cobalt-containing carbon material by using hydrochloric acid or sulfuric acid.

[0012] Preferably, in step S2, the hydrothermal treatment in the acid system is specifically: adding nitric acid into the dried product after acid pickling, and then hydrothermally treating at 60-80℃ for 12-24h.

[0013] Preferably, in step S2, the heat treatment temperature of the third pressure annealing treatment is 1200-1500℃.

[0014] A MOF-modified porous flexible self-supporting carbon paper is prepared by the above method.

[0015] A negative electrode material comprises the MOF-modified porous flexible self-supporting carbon paper.

[0016] A sodium ion battery comprises the negative electrode material, and the sodium ion battery has a capacity retention rate of 80%-95% and a first coulombic efficiency of 30%-90% after 500 cycles at a current density of 50mAg -1

[0017] Compared with the prior art, the present application has the following beneficial technical effects:

[0018] ​The application relates to a preparation method of a MOF modified porous flexible self-supporting carbon paper, which comprises the following steps: mixing a paper towel with dimethyl imidazole and a cobalt nitrate aqueous solution, synthesizing a flexible self-supporting precursor material, and sequentially performing three times of heat annealing treatment with gradually increased temperature to realize the microstructure regulation of the porous flexible self-supporting carbon paper material. The first annealing treatment preliminarily regulates the microstructure of the carbon material. In the second annealing treatment, the structural order of the carbon material is improved, the defect quantity is continuously reduced, and the graphite sheet thickness is increased with the gradual increase of the temperature in the annealing process, which is beneficial to the embedding and disembedding process of sodium ions between the graphite layers when the hard carbon material is used as a negative electrode material of a sodium ion battery, and the electrochemical performance is effectively improved. In the preparation method, the samples after the twice annealing treatment are subjected to an acid washing process and an acid system hydrothermal treatment, so that the impurities and metal cobalt in the porous carbon material can be effectively removed. The metal cobalt on the surface of the porous carbon material is removed in the acid washing process, and the metal cobalt in the hard carbon material is effectively removed in the acid system hydrothermal treatment, so that the metal cobalt in the porous carbon material is completely removed through the two steps, because the metal cobalt does not provide an energy storage site, and the existence of the metal cobalt will affect the electrochemical performance. Subsequently, the third pressure heat treatment is performed to further improve the crystallinity and the sodium storage property of the material. The pressure heat treatment can make the electrochemical performance of the material better. Meanwhile, the porous flexible self-supporting hard carbon paper composed of free interwoven micrometer bands can effectively improve the pore structure in the material, and the free interwoven micrometer bands also provide more ion transmission paths, so that the specific surface area and the transmission path diversity of the material ensure the embedding and disembedding process of ions when the material is used as a negative electrode material of a battery, and the sodium storage performance is effectively improved. The preparation method is reasonable in design, convenient in operation, simple in reaction process, environment-friendly, low in cost, and does not need large-scale equipment and harsh conditions. The microstructure of the material is regulated through the gradient heat treatment, and the controllable synthesis of the hard carbon material is effectively realized.

[0019] Further, in the step S1, the molar ratio of the dimethyl imidazole to the cobalt nitrate is (4-32):1, and the microstructure of the MOF material can be effectively regulated.

[0020] Further, the heat treatment temperature of the first annealing treatment is 400-600 DEG C, and the microstructure of the carbon material can be effectively regulated.

[0021] Further, the heat treatment temperature of the second annealing treatment is 700-1100 DEG C, and the crystallinity of the carbon material can be effectively improved.

[0022] Further, in the step S2, the cobalt-containing carbon material is subjected to an acid washing process by using hydrochloric acid or sulfuric acid, and the cobalt metal in the material can be effectively removed.

[0023] Further, the heat treatment temperature of the third pressure annealing treatment is 1200-1500 DEG C, which can further improve the crystallinity of the carbon material, so as to improve the electrochemical performance thereof. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0025] Figure 1 is a flowchart of the preparation method of a MOF modified porous flexible self-supporting carbon paper in the present application;

[0026] Figure 2 is a scanning electron micrograph (SEM) of the MOF modified porous flexible self-supporting carbon paper prepared in Example 1 of the present application;

[0027] Figure 3 is a Raman spectrum (Raman) of the MOF modified porous flexible self-supporting carbon paper prepared in Examples 1-3 of the present application;

[0028] Figure 4 is the rate graph of the MOF modified porous flexible self-supporting carbon paper prepared in Examples 1-6 of the present application in a sodium ion battery;

[0029] Figure 5 is the charge-discharge curve of the MOF modified porous flexible self-supporting carbon paper prepared in Example 1 of the present application in a sodium ion battery;

[0030] Figure 6 is the transmission electron micrograph (TEM) of the MOF modified porous flexible self-supporting carbon paper prepared in Example 1 of the present application after discharging in a sodium ion battery. DETAILED DESCRIPTION

[0031] In order for those skilled in the art to understand the characteristics and effects of the present application, the following will make a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have the usual meanings understood by those skilled in the art of the present application, and in case of conflict, the definition in the specification shall prevail.

[0032] Theories or mechanisms described and disclosed herein, whether correct or wrong, should not limit the scope of the present application in any way, i.e. the content of the present application can be implemented without being limited by any particular theory or mechanism.

[0033] Herein, all features defined by a numerical range or a percentage range, such as numerical values, amounts, contents and concentrations, are for the sake of brevity and convenience only. Accordingly, the description of a numerical range or a percentage range should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0034] Herein, unless otherwise specifically stated, "comprise", "include", "contain", "have" or similar terms, encompass both "consist of" and "consist essentially of", for example, "A comprises a" encompasses both "A comprises a and others" and "A comprises only a".

[0035] Herein, for the sake of brevity, all possible combinations of the various technical features in the various embodiments or examples are not described. Therefore, the various technical features in the various embodiments or examples can be combined with each other as long as there is no contradiction, and all possible combinations should be considered as falling within the scope of the present specification.

[0036] As shown in FIG. 1, a method for preparing a MOF-modified porous flexible self-supporting carbon paper comprises the following steps: Figure 1

[0037] S1: completely immerse a paper towel in dimethylimidazole, then mix with a cobalt nitrate hexahydrate aqueous solution and ultrasonically react for 1 min, after the reaction is completed, stand for 2 h, then rinse the surface of the sample with deionized water, treat the sample at 60°C for 12 h to completely dry it, and sequentially subject the dried sample to a first annealing treatment and a second annealing treatment to obtain a cobalt-containing carbon material. The molar ratio of dimethylimidazole to cobalt nitrate hexahydrate is (4-32):1.

[0038] The specific process of the first annealing treatment in step S1 is as follows: after the dried precipitate is heated to 400-600°C at a rate of 2°C / min under an Ar atmosphere, it is kept at this temperature for 4 h, and then naturally cooled to room temperature. The annealing treatment in the present application is all carried out under an Ar atmosphere, which can effectively ensure the stability and safety of the experiment.

[0039] The specific process of the second annealing treatment is as follows: after the product after the first annealing treatment is heated to 700-1100°C at a rate of 2-5°C / min under an Ar atmosphere, it is kept at this temperature for 4 h, then cooled to 200-600°C at a rate of 2°C / min, and then naturally cooled to room temperature.

[0040] S2: sequentially subject the above cobalt-containing carbon material to an acid pickling process and an acidic system hydrothermal treatment, after water system drying treatment, then carry out a third pressure heat treatment to obtain the MOF-modified porous flexible self-supporting carbon paper in the present application;

[0041] ​The pickling process is specifically using 20wt% hydrochloric acid or 20wt% sulfuric acid for pickling, washing to neutral after pickling, and treating in a blast drying oven at 60 DEG C for 12h to completely dry the product;

[0042] The acid system hydrothermal treatment process is specifically adding nitric acid to the pickled and dried product, wherein the nitric acid is analytical pure concentrated nitric acid with a mass fraction of 65%, then hydrothermally treating at 60-80 DEG C for 12-24h, washing to neutral, and treating in a blast drying oven at 60 DEG C for 12h until completely dry.

[0043] The third pressure annealing treatment in step S2 is specifically as follows: placing the dried sample in a graphite plate, applying pressure, heating to 1200-1500 DEG C at a rate of 2 DEG C / min in an Ar atmosphere, holding for 1h, then cooling to 200-600 DEG C at a rate of 2 DEG C / min, and finally naturally cooling to room temperature to obtain the MOF modified porous flexible self-supporting carbon paper.

[0044] The MOF modified porous flexible self-supporting carbon paper prepared by the preparation method of the application comprises free interwoven micrometer strips and abundant porous structures.

[0045] The porous flexible self-supporting carbon paper in the application is used as a negative electrode material of a sodium ion battery, wherein the sodium ion battery has a capacity retention rate of 80-95% and a first coulombic efficiency of 30-90% after 500 cycles at a current density of 50mAg -1 . -1 The MOF modified hard carbon in the application achieves high ICE and excellent rate performance. In addition, the flexible self-supporting electrode material is prepared, the addition of a binder and a conductive agent is avoided, and the ICE of the hard carbon for sodium storage can be further improved. A commercial paper towel is selected as a flexible precursor, the paper towel is first modified by MOF, a three-step annealing process is performed, and pressure is applied to prepare a porous flexible self-supporting hard carbon paper composed of self-interwoven micrometer strips, i.e., PHCP. The prepared PHCP has an ICE of 85%, and can provide reversible capacities of 294.2 and 159.5mAh g -1 at current densities of 25 and 500mAg -1 , respectively.

[0046] The preparation method of the application synthesizes the porous flexible self-supporting carbon paper by a simple method. The method has a simple reaction process, does not require large equipment and harsh conditions, is environmentally friendly and low in cost. The structure of the material is regulated by a simple method, parameters such as the amount of a drug and temperature are controlled, the special structure of the porous flexible self-supporting carbon paper is fully utilized, and excellent sodium storage characteristics are achieved.

[0047] The porous flexible self-supporting carbon paper prepared according to the preparation method has a large specific surface area, free interwoven micrometer strips, a high exposed active site, sufficient open areas and a convenient electron transmission path. The hard carbon material prepared by taking the metal organic framework compound as a precursor has a hierarchical porous structure, provides abundant active sites for storing potassium or sodium, shortens the diffusion migration path of sodium ions and further improves the sodium storage capacity. By adjusting the carbonization temperature of the precursor, the microstructure can be controlled. With the increase of the annealing carbonization temperature, the order degree of the material is increased, the number of defects is continuously reduced and the thickness of the graphite sheet is increased, which is beneficial to the embedding and disembedding process of sodium ions between the graphite layers, increases the platform capacity of the battery and the porous flexible self-supporting carbon paper has good electrochemical performance when applied to a sodium battery.

[0048] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application but not to limit the scope of the application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope defined by the appended claims of the application.

[0049] The following examples use the conventional instruments and equipment in the art. The experimental methods in the following examples are not specified, and are usually carried out according to the conventional conditions or the conditions recommended by the manufacturers. The following examples use various raw materials, unless otherwise specified, and the conventional commercially available products are used, and the specifications are conventional specifications in the art. In the specification of the application and the following examples, unless otherwise specified, “%” means weight percent, “parts” means weight parts, and the ratio means weight ratio.

[0050] Example 1

[0051] A preparation method of a MOF modified porous flexible self-supporting carbon paper, comprising the following steps:

[0052] Step one: completely immerse a commercial paper towel in a 0.4 mol / L dimethyl imidazole aqueous solution, then add a 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and then stand for 2 h; wash the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven for drying at 60℃ for 12 h to obtain a MOF modified flexible precursor;

[0053] Step two: heat the obtained flexible precursor to 450℃ / min at a heating rate of 2℃ / min under an Ar atmosphere, keep for 4 h, and then naturally reduce to room temperature; then heat to 1100℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a carbon material containing cobalt metal;

[0054] Step 3: Treat the obtained cobalt-containing carbon material with 20% hydrochloric acid, wash with water until neutral, and then dry in a forced-air drying oven at 60℃ for 12h; add concentrated nitric acid to the hydrochloric acid-treated sample, hydrothermally treat at 80℃ for 12h, wash with water until neutral, and dry in a forced-air drying oven at 60℃ for 12h to obtain self-supporting carbon paper.

[0055] Step 4: The self-supporting carbon paper is heated to 1400℃ / min at a heating rate of 2℃ / min under Ar atmosphere, held at that temperature for 1h, then cooled to 200℃ / min at a heating rate of 5℃ / min, and finally allowed to cool naturally to room temperature to obtain MOF-modified porous flexible self-supporting carbon paper.

[0056] The transmission electron microscope (TEM) image of a MOF-modified porous flexible self-supporting carbon paper prepared in this embodiment is as follows: Figure 2 As shown, from Figure 2 It can be seen that the material has a porous structure in its micron bands. This porous structure increases the contact area with the electrolyte, increases the number of reactive sites, and is beneficial to the reaction. Meanwhile, Figure 3 The Raman spectrum of this material is obtained from... Figure 3 It can be seen that the carbon material exhibits two characteristic peaks, namely the D peak at 1346 cm⁻¹ and the G peak at 1598 cm⁻¹. Both TEM and Raman results indicate that the porous flexible self-supporting carbon paper was successfully prepared.

[0057] The MOF-modified porous flexible self-supporting carbon paper prepared in this embodiment was applied to a sodium-ion battery, and its electrochemical performance was tested. The rate performance test of the sodium-ion battery is shown in [link to relevant documentation]. Figure 4 As can be seen from the figure, sodium-ion batteries exhibit good rate performance at different current densities. Meanwhile, from... Figure 5 It can be seen that at 25mAg -1 At a current density of 253 mAh g, it has 253 mAh g. -1 The specific capacity is high, and the initial coulombic efficiency is 85%. In summary, this porous flexible self-supporting carbon paper exhibits good electrochemical performance in sodium-ion batteries.

[0058] Figure 6 The image shows a TEM image of the MOF-modified porous flexible self-supporting carbon paper prepared in this embodiment after discharge in a sodium-ion battery. It can be seen that sodium ions are adsorbed / embedded in the carbon material, which still maintains a stable porous structure, which is beneficial to its good cycle stability.

[0059] Example 2

[0060] A method for preparing MOF-modified porous flexible self-supporting carbon paper includes the following steps:

[0061] Step one: immerse the paper towel completely in 0.4 mol / L dimethyl imidazole aqueous solution, then add 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and then stand for 2 h; rinse the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven at 60℃ for 12 h to obtain a MOF-modified flexible precursor;

[0062] Step two: first heat the obtained flexible precursor to 450℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 4 h, and then naturally reduce to room temperature; then heat to 1100℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a cobalt metal-containing carbon material;

[0063] Step three: treat the obtained cobalt metal-containing carbon material with 20% hydrochloric acid, wash with water to neutral, and then dry in a blast drying oven at 60℃ for 12 h; after hydrochloric acid treatment, add concentrated nitric acid to the sample, hydrothermal treatment at 80℃ for 12 h, then wash with water to neutral, and dry in a blast drying oven at 60℃ for 12 h to obtain a self-supporting carbon paper.

[0064] Step four: first heat the self-supporting carbon paper to 1200℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 1 h, then reduce to 200℃ / min at a heating rate of 5℃ / min, and finally naturally reduce to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0065] Example 3

[0066] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0067] Step one: immerse the commercial paper towel completely in 0.4 mol / L dimethyl imidazole aqueous solution, then add 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and then stand for 2 h; rinse the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven at 60℃ for 12 h to obtain a MOF-modified flexible precursor;

[0068] Step two: first heat the obtained flexible precursor to 450℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 4 h, and then naturally reduce to room temperature; then heat to 1100℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a cobalt metal-containing carbon material;

[0069] Step three: the obtained cobalt metal-containing carbon material is treated with 20% hydrochloric acid, washed with water to neutral, and then dried in a blast drying oven at 60°C for 12h; the sample after hydrochloric acid treatment is added to concentrated nitric acid, hydrothermally treated at 80°C for 12h, washed with water to neutral, and dried in a blast drying oven at 60°C for 12h to obtain a self-supporting carbon paper.

[0070] Step four: the self-supporting carbon paper is first heated to 1300°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 1h, then cooled to 200°C / min at a cooling rate of 5°C / min, and finally naturally cooled to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0071] Example 4

[0072] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0073] Step one: a commercial paper towel is completely immersed in a 0.4mol / L dimethyl imidazole aqueous solution, then a 0.025mol / L cobalt nitrate hexahydrate aqueous solution is added, ultrasonic treatment is performed for 1min to obtain a uniform solution, and the solution is left to stand for 2h; the surface of the sample obtained after standing is washed clean with deionized water, and the sample is placed in a blast drying oven and dried at 60°C for 12h to obtain a MOF-modified flexible precursor;

[0074] Step two: the obtained flexible precursor is first heated to 450°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 4h, and naturally cooled to room temperature; then heated to 1100°C / min at a heating rate of 2°C / min, kept for 4h, cooled to 600°C / min at a cooling rate of 2°C / min, and finally naturally cooled to room temperature to obtain a cobalt metal-containing carbon material;

[0075] Step three: the obtained cobalt metal-containing carbon material is treated with 20% hydrochloric acid, washed with water to neutral, and then dried in a blast drying oven at 60°C for 12h; the sample after hydrochloric acid treatment is added to concentrated nitric acid, hydrothermally treated at 80°C for 12h, washed with water to neutral, and dried in a blast drying oven at 60°C for 12h to obtain a self-supporting carbon paper.

[0076] Step four: the self-supporting carbon paper is first heated to 1300°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 1h, then cooled to 200°C / min at a cooling rate of 5°C / min, and finally naturally cooled to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0077] Example 5

[0078] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0079] Step one: immerse the commercial paper towel completely in 0.4 mol / L dimethyl imidazole aqueous solution, then add 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and stand for 2 h; rinse the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven at 60℃ for 12 h to obtain a MOF-modified flexible precursor;

[0080] Step two: first heat the obtained flexible precursor to 600℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 4 h, and naturally reduce to room temperature; then heat to 900℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a cobalt metal-containing carbon material.

[0081] Step three: treat the obtained cobalt metal-containing carbon material with 20% hydrochloric acid, wash with water to neutral, and then dry in a blast drying oven at 60℃ for 12 h; after hydrochloric acid treatment, add concentrated nitric acid, hydrothermal treatment at 80℃ for 12 h, then wash with water to neutral, and dry in a blast drying oven at 60℃ for 12 h to obtain a self-supporting carbon paper.

[0082] Step four: first heat the self-supporting carbon paper to 1200℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 1 h, then reduce to 200℃ / min at a heating rate of 5℃ / min, and finally naturally reduce to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0083] Example 6

[0084] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0085] Step one: immerse the commercial paper towel completely in 0.4 mol / L dimethyl imidazole aqueous solution, then add 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and stand for 2 h; rinse the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven at 60℃ for 12 h to obtain a MOF-modified flexible precursor;

[0086] Step two: first heat the obtained flexible precursor to 600℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 4 h, and naturally reduce to room temperature; then heat to 900℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a cobalt metal-containing carbon material;

[0087] Step three: the obtained cobalt metal-containing carbon material was treated with 20% hydrochloric acid, washed with water to neutral, and then dried in a blast drying oven at 60°C for 12h; the sample after hydrochloric acid treatment was added to concentrated nitric acid, hydrothermally treated at 80°C for 12h, washed with water to neutral, and dried in a blast drying oven at 60°C for 12h to obtain a self-supporting carbon paper.

[0088] Step four: the self-supporting carbon paper was first heated to 1300°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 1h, then cooled to 200°C / min at a cooling rate of 5°C / min, and finally naturally cooled to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0089] Example 7

[0090] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0091] Step one: a commercial paper towel was completely immersed in a 0.4mol / L dimethyl imidazole aqueous solution, followed by the addition of a 0.025mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic treatment for 1min to obtain a uniform solution, and standing for 2h; the surface of the sample obtained after standing was washed clean with deionized water, and it was placed in a blast drying oven at 60°C for 12h to obtain a MOF-modified flexible precursor.

[0092] Step two: the obtained flexible precursor was first heated to 500°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 4h, and naturally cooled to room temperature; then heated to 900°C / min at a heating rate of 2°C / min, kept for 4h, cooled to 600°C / min at a cooling rate of 2°C / min, and finally naturally cooled to room temperature to obtain a cobalt metal-containing carbon material.

[0093] Step three: the obtained cobalt metal-containing carbon material was treated with 20% hydrochloric acid, washed with water to neutral, and then dried in a blast drying oven at 60°C for 12h; the sample after hydrochloric acid treatment was added to concentrated nitric acid, hydrothermally treated at 80°C for 12h, washed with water to neutral, and dried in a blast drying oven at 60°C for 12h to obtain a self-supporting carbon paper.

[0094] Step four: the self-supporting carbon paper was first heated to 1500°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 1h, then cooled to 200°C / min at a cooling rate of 5°C / min, and finally naturally cooled to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0095] Example 8

[0096] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0097] Step one: immerse the commercial paper towel completely in 0.4 mol / L dimethyl imidazole aqueous solution, then add 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and stand for 2 h; rinse the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven at 60℃ for 12 h to obtain a MOF-modified flexible precursor;

[0098] Step two: first heat the obtained flexible precursor to 600℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 4 h, and naturally reduce to room temperature; then heat to 1000℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a cobalt metal-containing carbon material;

[0099] Step three: treat the obtained cobalt metal-containing carbon material with 20% hydrochloric acid, wash with water to neutral, and then dry in a blast drying oven at 60℃ for 12 h; after hydrochloric acid treatment, add concentrated nitric acid, hydrothermal treatment at 80℃ for 12 h, then wash with water to neutral, and dry in a blast drying oven at 60℃ for 12 h to obtain a self-supporting carbon paper.

[0100] Step four: first heat the self-supporting carbon paper to 1300℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 1 h, then reduce to 200℃ / min at a heating rate of 5℃ / min, and finally naturally reduce to room temperature to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0101] Example 9

[0102] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0103] Step one: immerse the commercial paper towel completely in 0.4 mol / L dimethyl imidazole aqueous solution, then add 0.025 mol / L cobalt nitrate hexahydrate aqueous solution, ultrasonic for 1 min to obtain a uniform solution, and stand for 2 h; rinse the surface of the sample obtained after standing with deionized water, and place it in a blast drying oven at 60℃ for 12 h to obtain a MOF-modified flexible precursor;

[0104] Step two: first heat the obtained flexible precursor to 600℃ / min at a heating rate of 2℃ / min under Ar atmosphere, keep for 4 h, and naturally reduce to room temperature; then heat to 1000℃ / min at a heating rate of 2℃ / min, keep for 4 h, and then reduce to 600℃ / min at a heating rate of 2℃ / min, and finally naturally reduce to room temperature to obtain a cobalt metal-containing carbon material;

[0105] Step three: the obtained cobalt-containing carbon material is treated with 20% hydrochloric acid, washed with water until neutral, and then dried in a blast drying oven at 60°C for 12h; the sample after hydrochloric acid treatment is added with concentrated nitric acid, hydrothermally treated at 80°C for 12h, then washed with water until neutral, dried in a blast drying oven at 60°C for 12h, to obtain a self-supporting carbon paper.

[0106] Step four: the self-supporting carbon paper is first heated to 1500°C / min at a heating rate of 2°C / min under an Ar atmosphere, kept for 1h, then cooled to 200°C / min at a cooling rate of 5°C / min, and finally naturally cooled to room temperature, to obtain a MOF-modified porous flexible self-supporting carbon paper.

[0107] Example 10

[0108] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0109] S1: the paper towel is completely immersed in dimethyl imidazole, and then mixed with a cobalt nitrate hexahydrate aqueous solution for ultrasonic reaction for 1min; after the reaction is completed, the sample is washed with deionized water after standing for 2h, and then dried at 60°C for 12h; the dried sample is sequentially subjected to first annealing treatment and second annealing treatment, to obtain a cobalt-containing carbon material. The molar ratio of dimethyl imidazole to cobalt nitrate hexahydrate is 4:1.

[0110] The specific process of the first annealing treatment is as follows: the dried precipitate is heated to 400°C at a heating rate of 2°C / min under an Ar atmosphere, kept for 4h, and then naturally cooled to room temperature. Then, the product after the first annealing treatment is heated to 700°C at a heating rate of 2°C / min under an Ar atmosphere, kept for 4h, then cooled to 200°C at a cooling rate of 2°C / min, and then naturally cooled to room temperature, to complete the second annealing treatment.

[0111] S2: the above cobalt-containing carbon material is subjected to acid washing in 20% hydrochloric acid, washed with water until neutral, and then dried at 60°C in a blast drying oven for 12h until completely dry; then, 65% nitric acid is added to the dried product after acid washing, and then hydrothermally treated at 60°C for 12h, then washed with water until neutral, and dried at 60°C in a blast drying oven for 12h until completely dry. The sample after hydrothermal drying in nitric acid is placed in a graphite plate and subjected to pressure, heated to 1200°C at a heating rate of 2°C / min under an Ar atmosphere, kept for 1h, then cooled to 200°C at a cooling rate of 2°C / min, and finally naturally cooled to room temperature to obtain the MOF-modified porous flexible self-supporting carbon paper.

[0112] The porous flexible self-supporting carbon paper in this example is used as a negative electrode material of a sodium ion battery, wherein the sodium ion battery has an initial discharge capacity of 400mAh / g at a current density of 50mAg -1The capacity retention rate is 80% and the initial coulombic efficiency is 30% after 500 cycles at a current density of 50 mAg

[0113] Example 11

[0114] A preparation method of a MOF modified porous flexible self-supporting carbon paper, comprising the following steps:

[0115] S1: The paper towel is completely immersed in dimethyl imidazole, and then mixed with a cobalt nitrate hexahydrate aqueous solution for ultrasonic reaction for 1 min. After the reaction is completed, the sample surface is washed with deionized water after standing for 2 h. The sample is treated at 60 DEG C for 12 h to completely dry. The dried sample is sequentially subjected to first annealing treatment and second annealing treatment to obtain a cobalt-containing carbon material. The molar ratio of dimethyl imidazole to cobalt nitrate hexahydrate is 8:1.

[0116] The specific process of the first annealing treatment is as follows: the dried precipitate is heated to 450 DEG C at a rate of 2 DEG C / min under Ar atmosphere, and then naturally cooled to room temperature. Then, the product after the first annealing treatment is heated to 700 DEG C at a rate of 2 DEG C / min under Ar atmosphere, and then cooled to 200 DEG C at a rate of 2 DEG C / min, and then naturally cooled to room temperature to complete the second annealing treatment.

[0117] S2: The above cobalt-containing carbon material is subjected to acid pickling in 20% sulfuric acid by mass fraction, and then washed to neutral after acid pickling, and treated at 60 DEG C in a blast drying oven for 12 h to completely dry. Then, 65% nitric acid by mass fraction is added to the dried product after acid pickling, and then hydrothermally treated at 65 DEG C for 18 h, and then washed to neutral, and treated at 60 DEG C in a blast drying oven for 12 h until completely dry. The sample after hydrothermal drying in nitric acid is placed in a graphite plate and subjected to pressure, and then heated to 1260 DEG C at a rate of 2 DEG C / min under Ar atmosphere, and then kept for 1 h, and then cooled to 270 DEG C at a rate of 2 DEG C / min, and finally naturally cooled to room temperature to obtain the MOF modified porous flexible self-supporting carbon paper.

[0118] The porous flexible self-supporting carbon paper in the embodiment is used as a negative electrode material of a sodium ion battery, wherein the sodium ion battery has a capacity retention rate of 82.5% and an initial coulombic efficiency of 40.6% after 500 cycles at a current density of 50 mAg -1

[0119] Example 12

[0120] A preparation method of a MOF modified porous flexible self-supporting carbon paper, comprising the following steps:

[0121] ​S1: The paper towel is completely immersed in dimethylimidazole, and then mixed with a cobalt nitrate hexahydrate aqueous solution for ultrasonic reaction for 1 min. After the reaction is completed, the sample surface is washed with deionized water after standing for 2 h. The sample is treated at 60℃ for 12 h to completely dry it. The dried sample is sequentially subjected to a first annealing treatment and a second annealing treatment to obtain a cobalt-containing carbon material. The molar ratio of dimethylimidazole to cobalt nitrate hexahydrate is 10:1.

[0122] The specific process of the first annealing treatment is as follows: the dried precipitate is heated to 510℃ at a rate of 2℃ / min under an Ar atmosphere, and then kept at 510℃ for 4 h. Then, the temperature is naturally reduced to room temperature. Then, the product after the first annealing treatment is heated to 790℃ at a rate of 2℃ / min under an Ar atmosphere, and then kept at 790℃ for 4 h. Then, the temperature is reduced to 460℃ at a rate of 2℃ / min, and then naturally reduced to room temperature to complete the second annealing treatment.

[0123] S2: The above cobalt-containing carbon material is subjected to acid pickling in 20% hydrochloric acid by mass fraction. After acid pickling, it is washed to neutral, and then treated at 60℃ in a blast drying oven for 12 h to completely dry it. Then, 65% nitric acid by mass fraction is added to the dried product after acid pickling, and then hydrothermally treated at 75℃ for 20 h. Then, it is washed to neutral, and then treated at 60℃ in a blast drying oven for 12 h until completely dry. The sample after hydrothermal drying in nitric acid is placed in a graphite plate and subjected to pressure. It is heated to 1350℃ at a rate of 2℃ / min under an Ar atmosphere, and then kept at 1350℃ for 1 h. Then, the temperature is reduced to 350℃ at a rate of 2℃ / min, and then naturally reduced to room temperature to obtain the MOF-modified porous flexible self-supporting carbon paper.

[0124] The porous flexible self-supporting carbon paper in this embodiment is used as a negative electrode material of a sodium ion battery. The sodium ion battery has a capacity retention rate of 85% and a first coulombic efficiency of 51% after 500 cycles at a current density of 50 mAg -1

[0125] Example 13

[0126] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0127] S1: The paper towel is completely immersed in dimethylimidazole, and then mixed with a cobalt nitrate hexahydrate aqueous solution for ultrasonic reaction for 1 min. After the reaction is completed, the sample surface is washed with deionized water after standing for 2 h. The sample is treated at 60℃ for 12 h to completely dry it. The dried sample is sequentially subjected to a first annealing treatment and a second annealing treatment to obtain a cobalt-containing carbon material. The molar ratio of dimethylimidazole to cobalt nitrate hexahydrate is 15.5:1.

[0128] ​The specific process of the first annealing treatment is: the dried precipitate is heated to 550℃ at a rate of 2℃ / min under Ar atmosphere, and kept for 4h, and then naturally cooled to room temperature. Then, the product after the first annealing treatment is heated to 870℃ at a rate of 2℃ / min under Ar atmosphere, kept for 4h, and then cooled to 500℃ at a rate of 2℃ / min, and then naturally cooled to room temperature, to complete the second annealing treatment.

[0129] S2: The above cobalt-containing carbon material is subjected to acid washing in 20% hydrochloric acid by mass fraction, washed with water to neutral after acid washing, and treated at 60℃ in a blast drying oven for 12h to completely dry; then, 65% nitric acid by mass fraction is added to the dried product after acid washing, and then hydrothermally treated at 80℃ for 22h, and then washed with water to neutral, treated at 60℃ in a blast drying oven for 12h until completely dry. The sample after hydrothermal drying in nitric acid is placed in a graphite plate to apply pressure, heated to 1450℃ at a rate of 2℃ / min under Ar atmosphere, kept for 1h, and then cooled to 450℃ at a rate of 2℃ / min, and finally naturally cooled to room temperature to obtain the MOF-modified porous flexible self-supporting carbon paper.

[0130] The porous flexible self-supporting carbon paper in the embodiment is used as the negative electrode material of a sodium ion battery, wherein the sodium ion battery has a capacity retention rate of 90% and a first coulombic efficiency of 66% after 500 cycles at a current density of 50mAg -1

[0131] Embodiment 14

[0132] A method for preparing a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0133] S1: The paper towel is completely immersed in dimethylimidazole, and then mixed with a cobalt nitrate hexahydrate aqueous solution to ultrasonically react for 1min. After the reaction, the sample is washed with deionized water after standing for 2h, and then treated at 60℃ for 12h to completely dry. The dried sample is sequentially subjected to the first annealing treatment and the second annealing treatment to obtain a cobalt-containing carbon material. The molar ratio of dimethylimidazole to cobalt nitrate hexahydrate is 26:1.

[0134] The specific process of the first annealing treatment is: the dried precipitate is heated to 550℃ at a rate of 2℃ / min under Ar atmosphere, and kept for 4h, and then naturally cooled to room temperature. Then, the product after the first annealing treatment is heated to 870℃ at a rate of 2℃ / min under Ar atmosphere, kept for 4h, and then cooled to 500℃ at a rate of 2℃ / min, and then naturally cooled to room temperature, to complete the second annealing treatment.

[0135] ​S2: The above-mentioned cobalt-containing carbon material is subjected to acid washing in 20% sulfuric acid by mass fraction, washed with water to neutral after acid washing, and treated at 60 DEG C in a blast drying oven for 12h to completely dry it; then, 65% nitric acid by mass fraction is added to the product after acid washing and drying, and then hydrothermally treated at 80 DEG C for 24h, then washed with water to neutral, treated at 60 DEG C in a blast drying oven for 12h until completely dry. The sample after hydrothermal drying in nitric acid is placed in a graphite plate to apply pressure, heated to 1480 DEG C at 2 DEG C / min under Ar atmosphere, kept for 1h, then cooled to 550 DEG C at 2 DEG C / min, and finally naturally cooled to room temperature to obtain the MOF-modified porous flexible self-supporting carbon paper.

[0136] The porous flexible self-supporting carbon paper in the embodiment is used as a negative electrode material of a sodium ion battery, wherein the sodium ion battery has a capacity retention rate of 92.3% and a first coulombic efficiency of 78.5% after 500 cycles at a current density of 50mAg -1

[0137] Embodiment 15

[0138] A preparation method of a MOF-modified porous flexible self-supporting carbon paper, comprising the following steps:

[0139] S1: The paper towel is completely immersed in dimethylimidazole, and then mixed with a cobalt nitrate hexahydrate aqueous solution to ultrasonically react for 1min. After the reaction, the sample is washed with deionized water after standing for 2h, and then treated at 60 DEG C for 12h to completely dry it. The dried sample is sequentially subjected to first annealing treatment and second annealing treatment to obtain a cobalt-containing carbon material. The molar ratio of dimethylimidazole to cobalt nitrate hexahydrate is 32:1.

[0140] The specific process of the first annealing treatment is as follows: the dried precipitate is heated to 600 DEG C at 2 DEG C / min under Ar atmosphere, kept for 4h, and then naturally cooled to room temperature. Then, the product after the first annealing treatment is heated to 1100 DEG C at 2 DEG C / min under Ar atmosphere, kept for 4h, cooled to 600 DEG C at 2 DEG C / min, and then naturally cooled to room temperature to complete the second annealing treatment.

[0141] ​S2: The above cobalt-containing carbon material is subjected to acid washing in 20% sulfuric acid by mass fraction, washed to neutral after acid washing, and treated at 60°C in a blast drying oven for 12 h to completely dry it; then, 65% nitric acid by mass fraction is added to the product after acid washing and drying, then hydrothermally treated at 80°C for 24 h, then washed to neutral, treated at 60°C in a blast drying oven for 12 h until completely dry. The sample after hydrothermal drying in nitric acid is placed in a graphite plate to apply pressure, heated to 1500°C at 2°C / min under an Ar atmosphere, kept for 1 h, then cooled to 600°C at 2°C / min, and finally naturally cooled to room temperature to obtain the MOF-modified porous flexible self-supporting carbon paper.

[0142] The porous flexible self-supporting carbon paper in the embodiment is used as a negative electrode material of a sodium ion battery, wherein the sodium ion battery has a capacity retention rate of 95% and a first coulombic efficiency of 90% after 500 cycles at a current density of 50 mAg -1

[0143] The above only describes the preferred embodiments of the present application, and it should be noted that those of ordinary skill in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, and although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.​

Claims

1. A method for preparing a MOF-modified porous flexible self-supporting carbon paper, characterized in that, The method comprises the following steps: S1: the paper towel is completely immersed in a dimethyl imidazole solution, and a cobalt nitrate aqueous solution is added to mix and react with the dimethyl imidazole, the obtained product is sequentially subjected to a first annealing treatment and a second annealing treatment, and a cobalt-containing carbon material is obtained; S2: the cobalt-containing carbon material is sequentially subjected to an acid pickling process and a hydrothermal treatment in an acidic system, and then a third pressure annealing treatment is performed, and the MOF modified porous flexible self-supporting carbon paper is obtained; the heat treatment temperatures of the first annealing treatment, the second annealing treatment and the third pressure annealing treatment are sequentially increased; In step S1, the heat treatment temperature of the first annealing treatment is 400-600 DEG C; In step S1, the heat treatment temperature of the second annealing treatment is 700-1100 DEG C; In step S2, the heat treatment temperature of the third pressure annealing treatment is 1200-1500 DEG C; In step S1, the molar ratio of dimethyl imidazole to cobalt nitrate is (4-32):

1.

2. The method for preparing MOF-modified porous flexible self-supporting carbon paper according to claim 1, characterized in that, In step S2, hydrochloric acid or sulfuric acid is used for the acid pickling process of the cobalt-containing carbon material.

3. The method for preparing MOF-modified porous flexible self-supporting carbon paper according to claim 1, characterized in that, In step S2, the hydrothermal treatment in an acidic system is specifically as follows: nitric acid is added to the product after acid pickling and drying, and the hydrothermal treatment is performed at 60-80 DEG C for 12-24 h.

4. A MOF-modified porous flexible self-supporting carbon paper, characterized in that, The MOF modified porous flexible self-supporting carbon paper is prepared by the method of any one of claims 1-3.

5. A negative electrode material, characterized by, The MOF modified porous flexible self-supporting carbon paper of claim 4.

6. A sodium-ion battery, characterized by, The sodium-ion battery comprising the negative electrode material described in claim 5 has a capacity retention rate of 80% to 95% and a first coulombic efficiency of 30% to 90% after 500 cycles at a current density of 50 mA g -1 .

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