Flexible self-supporting film and preparation method thereof

Abstract

The invention relates to the technical field of materials, in particular to a flexible self-supporting film and a preparation method thereof. The preparation method of the flexible self-supporting membrane comprises the following steps: reacting low-defect graphene, dopamine hydrochloride and a buffer solution to obtain graphene powder with polydopamine attached to the surface; grinding the graphene powder with the polydopamine attached on the surface, hydroxylated multi-walled carbon nanotubes and a solvent to obtain a grinding material; uniformly mixing the abrasive and a binder to obtain slurry; and coating a substrate with the slurry, and sequentially drying and stripping to obtain the flexible self-supporting film. The low-defect graphene is used as a main material, the polydopamine is synthesized on the surface of the low-defect graphene, and the hydroxylated multi-walled carbon nanotubes are added, so that the prepared flexible self-supporting film is uniform in thickness and relatively high in strength and flexibility.

Description

Technical Field

[0001] The invention relates to the technical field of materials, and in particular to a flexible self-supporting film and a preparation method thereof. Background Art

[0002] Graphene is a two-dimensional nanocarbon material with advantages including high specific surface area, good electrical conductivity, excellent mechanical strength, etc. Graphene's excellent electrical and thermal conductivity completely exceeds that of metals, and graphene has the advantages of high temperature resistance and corrosion resistance. This unique structure and properties give it broad application prospects in the fields of material science, flexible energy storage and electric heating.

[0003] At present, the preparation method of graphene film commonly used in the industry is mainly to form a film by vacuum filtration of graphene oxide dispersion, followed by high-temperature annealing and reduction. The conductivity of graphene oxide is poor, and after annealing or other repair techniques, its conductivity is also poor. Moreover, the graphene stacking problem is serious when preparing graphene film by vacuum filtration, resulting in a significant decrease in its specific surface area and performance. High-temperature annealing and reduction not only requires higher experimental conditions, but also during the high-temperature sintering process, the gas inside the graphene oxide film escapes, destroying the structure of the film itself. In the subsequent high-pressure pressing process, the closed pores are retained in the form of wrinkles, resulting in a poor orientation of the graphene film, and poor interlayer AB stacking, which seriously affects the further improvement of the performance of the graphene film. When the substrate of the graphene film is a polymer material or other material with a low temperature tolerance, the high-temperature annealing method has great limitations. High temperature may cause the structure of the substrate material to be destroyed, carbonized, or the bonding force between the substrate is weakened or ineffective.

[0004] In view of this, this invention is proposed. Summary of the invention

[0005] The first object of the present invention is to provide a method for preparing a flexible self-supporting film, thereby improving the strength and flexibility of the graphene film.

[0006] A second object of the present invention is to provide a flexible self-supporting film having excellent strength and flexibility.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] In a first aspect, the present invention provides a method for preparing a flexible self-supporting film, comprising the following steps:

[0009] reacting low-defect graphene, dopamine hydrochloride and a buffer solution to obtain graphene powder with polydopamine attached to the surface;

[0010] After grinding the graphene powder with polydopamine attached to its surface, hydroxylated multi-walled carbon nanotubes and a solvent, an abrasive is obtained; the abrasive and a binder are mixed evenly to obtain a slurry.

[0011] The slurry is coated on a substrate and, after drying and peeling in sequence, the flexible self-supporting film is obtained.

[0012] Further, the buffer solution includes tris(hydroxymethyl)aminomethane buffer solution.

[0013] And / or, the pH of the buffer solution is 8.5 - 10.

[0014] Further, the outer diameter of the hydroxylated multi-walled carbon nanotubes is 20 - 30 nm and the length is 10 - 30 μm.

[0015] Further, the solvent includes 1-methyl-2-pyrrolidone.

[0016] And / or, the binder includes polyvinylidene fluoride.

[0017] Further, the mass ratio of the low-defect graphene to the dopamine hydrochloride is (8 - 30):1.

[0018] Further, the mass ratio of the graphene powder with polydopamine attached to its surface to the hydroxylated multi-walled carbon nanotubes is (4 - 8):1.

[0019] Further, the ratio of the sum of the mass of the graphene powder with polydopamine attached to its surface and the mass of the hydroxylated multi-walled carbon nanotubes to the mass of the solvent is (0.6 - 1):10.

[0020] And / or, the mass ratio of the solute in the abrasive to the binder is (3 - 8):2.

[0021] Further, it includes at least one of the following features (1) to (3);

[0022] (1) The reaction time is 8 - 10 h;

[0023] (2) The grinding includes ball milling, the rotation speed of the ball milling is 250 - 350 rpm, and the time is 4 - 8 h;

[0024] (3) The coating thickness is 400 - 600 μm.

[0025] In a second aspect, the present invention provides a flexible self-supporting film prepared by using the preparation method of the flexible self-supporting film as described above.

[0026] Further, the thickness of the flexible self-supporting film is 25 - 40 μm.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] The preparation method of the flexible self-supporting film provided by the present invention uses low-defect graphene as the main material, eliminating the high-temperature treatment and the step of repairing graphene defects required for graphene oxide, and can effectively improve the electrical conductivity and thermal conductivity of the flexible self-supporting film; by synthesizing polydopamine on the surface of low-defect graphene, the dispersibility is improved, effectively reducing the agglomeration of graphene itself and reducing the disordered stacking of graphene; adding hydroxylated multi-walled carbon nanotubes not only maintains the high electrical conductivity of the material, but also provides stress buffering and improves the flexibility of the material; at the same time, the hydroxyl groups in the hydroxylated multi-walled carbon nanotubes can react with the amino groups introduced by polydopamine to generate a strong binding force; thus, the prepared flexible self-supporting film has a uniform thickness, high strength and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a scanning electron microscope plan view of the flexible self-supporting film prepared in Example 1 of the present invention.

[0031] Figure 2 It is a scanning electron microscope cross-sectional view of the flexible self-supporting film prepared in Example 1 of the present invention.

[0032] Figure 3 It is a picture of the flexibility of the flexible self-supporting film prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Conditions not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0034] The flexible self-supporting film and its preparation method in the embodiments of the present invention will be specifically described below.

[0035] In some embodiments of the present invention, a method for preparing a flexible self-supporting film is provided, comprising the following steps:

[0036] React low-defect graphene, dopamine hydrochloride and a buffer solution to obtain graphene powder with polydopamine attached to its surface;

[0037] After grinding the graphene powder with polydopamine attached to its surface, hydroxylated multi-walled carbon nanotubes and a solvent, an abrasive is obtained; mix the abrasive and a binder to obtain a slurry;

[0038] Coat the slurry on a substrate, and after drying and peeling in sequence, a flexible self-supporting film is obtained.

[0039] In the method for preparing the flexible self-supporting film of the present invention, low-defect graphene, dopamine hydrochloride and a buffer solution are mixed. Under alkaline conditions, polydopamine is synthesized on the surface of the low-defect graphene to obtain graphene powder with polydopamine attached to its surface; after grinding the graphene powder with polydopamine attached to its surface, hydroxylated multi-walled carbon nanotubes and a solvent, an abrasive is obtained; then a binder is added to obtain a slurry; coat the slurry on a substrate, and after drying, a film is formed on the surface of the substrate, and after peeling the film from the substrate, a flexible self-supporting film is obtained.

[0040] The present invention uses low-defect graphene as the main material, and polydopamine is used to improve the dispersibility of the material and reduce the disordered accumulation of graphene; hydroxylated multi-walled carbon nanotubes have the advantages of large aspect ratio, high strength, good toughness, low density, etc. Adding hydroxylated multi-walled carbon nanotubes not only maintains the high conductivity of the material, but also provides stress buffering and improves the flexibility of the material; at the same time, the hydroxyl groups in the hydroxylated multi-walled carbon nanotubes can react with the amino groups introduced by polydopamine to generate a strong binding force.

[0041] In the method for preparing the flexible self-supporting film of the present invention, graphene is the main material. Graphene is a two-dimensional material with a larger specific surface area and a more uniform surface distribution; hydroxylated multi-walled carbon nanotubes play an auxiliary improvement role.

[0042] In the preparation process of traditional graphene films, graphene oxide is annealed at high temperature; in the high-temperature annealing step, the oxygen-containing functional groups on the graphene oxide decompose into gases and are released, generating vacancies or structural defects on the graphene sheets, which have an adverse impact on the size and performance of the material, and the cost required in the high-temperature annealing reduction process is relatively high, and the preparation process is cumbersome; reducing graphene oxide can achieve fewer layer numbers, but a large number of oxidation functional groups and lattice defects are introduced into its two-dimensional crystal structure, resulting in poor conductivity, low tensile strength and insufficient flexibility. The present invention uses low-defect graphene, eliminating the high-temperature treatment and the step of repairing graphene defects required for graphene oxide, and can also effectively improve the conductivity and thermal conductivity of the flexible self-supporting film.

[0043] By synthesizing polydopamine on the surface of low-defect graphene, the present invention effectively reduces the agglomeration of graphene itself, enables better dispersion of the slurry, and the prepared flexible self-supporting film has a uniform thickness, high strength and flexibility.

[0044] The film-forming method of the present invention is simple to prepare, low in cost, and easy to achieve large-area preparation, so it has a broader application prospect. For example, it has potential application value in the fields of flexible electronics, wearable devices, energy storage, etc.

[0045] In some embodiments of the present invention, the preparation method of low-defect graphene refers to the method for preparing graphene in the patent with the application number CN108622887A.

[0046] In some embodiments of the present invention, the buffer solution includes tris(hydroxymethyl)aminomethane buffer solution; the pH of the buffer solution is 8.5 to 10; typically but not restrictively, for example, the pH of the buffer solution can be 8.5, 9, 9.5, 10 or the range value composed of any two of them; preferably 8.5.

[0047] In some embodiments of the present invention, the preparation method of tris(hydroxymethyl)aminomethane buffer solution includes: stirring tris(hydroxymethyl)aminomethane and deionized water evenly, adding hydrochloric acid until the pH is 8.5 to 10 to obtain tris(hydroxymethyl)aminomethane buffer solution (Tris buffer solution).

[0048] In some embodiments of the present invention, the outer diameter of the hydroxylated multi-walled carbon nanotubes is 20 to 30 nm, and the length is 10 to 30 μm.

[0049] In some embodiments of the present invention, the solvent includes 1-methyl-2-pyrrolidone.

[0050] In some embodiments of the present invention, the binder includes polyvinylidene fluoride; using polyvinylidene fluoride as the connecting phase to form a film improves the performance of the material.

[0051] In some embodiments of the present invention, the mass ratio of low-defect graphene to dopamine hydrochloride is (8 to 30):1; typically but not restrictively, for example, the mass ratio of low-defect graphene to dopamine hydrochloride can be 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, 22:1, 24:1, 26:1, 28:1, 30:1 or the range value composed of any two of them; preferably 15:1.

[0052] The interaction between a small amount of polydopamine generated from dopamine hydrochloride and low-defect graphene can improve the mechanical strength of the membrane. If the amount of dopamine hydrochloride used is too small, the amount of polydopamine is small and the effect is not obvious. If the amount of dopamine hydrochloride used is too large, the amount of polydopamine is large and the strength of the graphene membrane will decrease because the strength of low-defect graphene itself is relatively high, and the decrease in the proportion of low-defect graphene will lead to a decrease in the strength of the membrane.

[0053] In some embodiments of the present invention, the mass ratio of graphene powder with polydopamine attached to the surface and hydroxylated multi-walled carbon nanotubes is (4-8):1; typically but not restrictively, for example, the mass ratio of graphene powder with polydopamine attached to the surface and hydroxylated multi-walled carbon nanotubes can be 4:1, 5:1, 6:1, 7:1, 8:1 or a range value composed of any two of them; preferably 6:1.

[0054] In some embodiments of the present invention, the ratio of the sum of the mass of graphene powder with polydopamine attached to the surface and hydroxylated multi-walled carbon nanotubes to the mass of the solvent is (0.6-1):10; typically but not restrictively, for example, the ratio of the sum of the mass of graphene powder with polydopamine attached to the surface and hydroxylated multi-walled carbon nanotubes to the mass of the solvent can be 0.6:10, 0.7:10, 0.8:10, 0.9:10, 1:10 or a range value composed of any two of them; preferably 0.8:10.

[0055] In some embodiments of the present invention, the mass ratio of the solute (graphene powder with polydopamine attached to the surface and hydroxylated multi-walled carbon nanotubes) in the abrasive to the binder is (3-8):2; typically but not restrictively, for example, the mass ratio of the solute in the abrasive to the binder can be 3:2, 4:2, 5:2, 6:2, 7:2, 8:2 or a range value composed of any two of them; preferably 7:3.

[0056] In some embodiments of the present invention, the reaction time is 8-10 h; typically but not restrictively, for example, the reaction time can be 8 h, 8.5 h, 9 h, 9.5 h, 10 h or a range value composed of any two of them; during the reaction process, under alkaline conditions, polydopamine is synthesized on the surface of low-defect graphene.

[0057] In some embodiments of the present invention, after the reaction, water is removed by drying to obtain graphene powder with polydopamine attached to the surface.

[0058] In some embodiments of the present invention, the grinding includes ball milling, the rotation speed of the ball milling is 250-350 rpm, and the time is 4-8 h; preferably, the rotation speed of the ball milling is 300 rpm and the time is 6 h.

[0059] In some embodiments of the present invention, the substrate includes a glass plate.

[0060] In some embodiments of the present invention, the coating thickness is 400 - 600 μm; typically but not restrictively, for example, the coating thickness can be 400 μm, 450 μm, 500 μm, 550 μm, 600 μm or a range value composed of any two of them; preferably, the coating thickness is 500 μm.

[0061] In some embodiments of the present invention, the coating method includes: knife coating.

[0062] The present invention is adapted to all film-forming means of the slurry; among them, by using the knife coating method, a large-area self-supporting film can be prepared, which is suitable for industrial production.

[0063] In some embodiments of the present invention, drying includes vacuum drying; preferably, the drying temperature is 40 - 70 °C, and the drying time is 8 - 12 h; more preferably, the drying temperature is 60 °C, and the drying time is 10 h.

[0064] In some embodiments of the present invention, peeling includes: immersing the dried substrate coated with the slurry in deionized water, and manually peeling after 0.5 h; preferably, after peeling, it is dried.

[0065] In some embodiments of the present invention, a flexible self-supporting film is also provided, which is prepared by using the above-mentioned preparation method of the flexible self-supporting film.

[0066] In some embodiments of the present invention, the thickness of the flexible self-supporting film is 25 - 40 μm; typically but not restrictively, for example, the thickness of the flexible self-supporting film can be 25 μm, 30 μm, 35 μm, 40 μm or a range value composed of any two of them.

[0067] In some embodiments of the present invention, the tensile strength of the flexible self-supporting film is 65 - 75 MPa.

[0068] Example 1

[0069] The preparation method of the flexible self-supporting film provided in this example includes the following steps:

[0070] Stir 0.605 g of tris(hydroxymethyl)aminomethane and 490 ml of deionized water evenly, add hydrochloric acid until pH = 8.5 to obtain a Tris buffer solution;

[0071] Add 6 g of low-defect graphene into 500 ml of the Tris buffer solution, stir for 1 h until evenly dispersed; then add 0.4 g of dopamine hydrochloride, stir for 0.5 h and then sonicate for 1 h, and then stir for 8 h. Under alkaline conditions, polydopamine is synthesized on the surface of graphene; dry in an oven for 24 h to remove deionized water to obtain graphene powder with polydopamine attached to the surface;

[0072] Add 2.4 g of the graphene powder with polydopamine attached to its surface and 0.3 g of hydroxylated multi-walled carbon nanotubes (outer diameter 20 - 30 nm, length 10 - 30 μm) into a ball milling jar, add 32 g of 1-methyl-2-pyrrolidone, and ball mill at 300 rpm for 6 h to obtain a ball milled material;

[0073] Mix 25 g of the ball milled material with 0.83 g of polyvinylidene fluoride and stir for 8 h until evenly mixed to obtain a slurry;

[0074] Evenly coat the above slurry on a glass plate to form a continuous film with a coating thickness of 500 μm; put the glass plate coated with the slurry into a vacuum oven and dry at 60 °C for 10 h; after drying, soak it in deionized water, manually separate it after 0.5 h, and after drying, a flexible self-supporting film can be obtained with a thickness of 23 μm.

[0075] Example 2

[0076] The preparation method of the flexible self-supporting film provided in this example includes the following steps:

[0077] Add 2.4 g of the graphene powder with polydopamine attached to its surface in Example 1 and 0.4 g of hydroxylated multi-walled carbon nanotubes (outer diameter 20 - 30 nm, length 10 - 30 μm) into a ball milling jar, add 35 g of 1-methyl-2-pyrrolidone, and ball mill at 250 rpm for 8 h to obtain a ball milled material;

[0078] Mix 25 g of the ball milled material with 0.8 g of polyvinylidene fluoride and stir for 8 h until evenly mixed to obtain a slurry;

[0079] Evenly coat the above slurry on a glass plate to form a continuous film with a coating thickness of 400 μm; put the glass plate coated with the slurry into a vacuum oven and dry at 70 °C for 8 h; after drying, soak it in deionized water, manually separate it after 0.5 h, and after drying, a flexible self-supporting film can be obtained with a thickness of 25 μm.

[0080] Example 3

[0081] The preparation method of the flexible self-supporting film provided in this example includes the following steps:

[0082] Add 2.4 g of the graphene powder with polydopamine attached to its surface in Example 1 and 0.6 g of hydroxylated multi-walled carbon nanotubes (outer diameter 20 - 30 nm, length 10 - 30 μm) into a ball milling jar, add 38 g of 1-methyl-2-pyrrolidone, and ball mill at 350 rpm for 4 h to obtain a ball milled material;

[0083] After mixing 25 g of ball-milled abrasive with 0.78 g of polyvinylidene fluoride and stirring for 8 h until evenly mixed, a slurry is obtained;

[0084] The above slurry is evenly coated on a glass plate to form a continuous film with a coating thickness of 600 μm; the glass plate coated with the slurry is placed in a vacuum oven and dried at 50 °C for 11 h; after drying, it is soaked in deionized water, manually detached after 0.5 h, and a flexible self-supporting film with a thickness of 22 μm can be obtained after drying.

[0085] Example 4

[0086] The preparation method of the flexible self-supporting film provided in this example includes the following steps:

[0087] 0.605 g of tris(hydroxymethyl)aminomethane and 490 ml of deionized water are stirred evenly, and hydrochloric acid is added until pH = 8.5 to obtain a Tris buffer solution;

[0088] 6 g of low-defect graphene is added to 500 ml of the Tris buffer solution and stirred for 1 h until evenly dispersed; then 0.75 g of hydrochloric acid dopamine is added, stirred for 0.5 h, sonicated for 1 h, and then stirred for 8 h. Under alkaline conditions, polydopamine is synthesized on the surface of graphene; dried in an oven for 24 h to remove deionized water, and graphene powder with polydopamine attached to the surface is obtained;

[0089] 2.4 g of the above graphene powder with polydopamine attached to the surface and 0.3 g of hydroxylated multi-walled carbon nanotubes (outer diameter 20 - 30 nm, length 10 - 30 μm) are added to a ball mill, 30 g of 1-methyl-2-pyrrolidone is added, and ball milled at 250 rpm for 7 h to obtain a ball-milled abrasive;

[0090] After mixing 25 g of the ball-milled abrasive with 0.8 g of polyvinylidene fluoride and stirring for 8 h until evenly mixed, a slurry is obtained; the slurry is evenly coated on a glass plate to form a continuous film with a coating thickness of 450 μm; the glass plate coated with the slurry is placed in a vacuum oven and dried at 40 °C for 12 h; after drying, it is soaked in deionized water, manually detached after 0.5 h, and a flexible self-supporting film with a thickness of 25 μm can be obtained after drying.

[0091] Comparative Example 1

[0092] The preparation method of the flexible self-supporting film provided in this comparative example includes the following steps:

[0093] 2.4 g of the graphene powder with polydopamine attached to the surface in Example 1 and 0.3 g of multi-walled carbon nanotubes (ordinary multi-walled carbon nanotubes, with the same outer diameter and length as the hydroxylated multi-walled carbon nanotubes in Example 1) are added to a ball mill, 30 g of 1-methyl-2-pyrrolidone is added, and ball milled at 350 rpm for 5 h to obtain a ball-milled abrasive;

[0094] 25 g of ball mill material was mixed with 0.8 g of polyvinylidene fluoride, and stirred for 8 h until the mixture was uniform to obtain a slurry;

[0095] The above slurry is evenly coated on a glass plate to form a continuous film with a coating thickness of 550 μm; the glass plate coated with the slurry is placed in a vacuum oven and dried at 55°C for 9 hours; after drying, it is immersed in deionized water and manually removed after 0.5 hours. After drying, a flexible self-supporting film with a thickness of 30 μm can be obtained.

[0096] Comparative Example 2

[0097] The method for preparing the flexible self-supporting film provided in this comparative example comprises the following steps:

[0098] 2.4 g of low-defect graphene and 0.3 g of hydroxylated multi-walled carbon nanotubes (outer diameter of 20-30 nm, length of 10-30 μm) were added to a ball mill, and 32 g of 1-methyl-2-pyrrolidone was added, and ball milling was performed at 275 rpm for 5 h to obtain a ball mill material;

[0099] 25 g of ball mill material was mixed with 0.83 g of polyvinylidene fluoride, and stirred for 8 h until the mixture was uniform to obtain a slurry;

[0100] The above slurry is evenly coated on a glass plate to form a continuous film with a coating thickness of 500 μm; the glass plate coated with the slurry is placed in a vacuum oven and dried at 65°C for 9 hours; after drying, it is immersed in deionized water and manually removed after 0.5 hours. After drying, a flexible self-supporting film with a thickness of 27 μm can be obtained.

[0101] Test example

[0102] The SEM plan view and SEM cross-sectional view of the flexible self-supporting film prepared in Example 1 are as follows: Figure 1 and Figure 2 shown.

[0103] The flexibility of the flexible self-supporting film prepared in Example 1 is as follows Figure 3 shown.

[0104] from Figure 1 It can be seen that the hydroxylated multi-walled carbon nanotubes are distributed relatively evenly on the flexible self-supporting film, which indicates that the hydroxylated multi-walled carbon nanotubes are well dispersed during the preparation process, with a part of them occupying the low-defect graphene sheets and the other part becoming the connecting medium between the low-defect graphene sheets; this structure can effectively improve the tensile strength of the flexible self-supporting film.

[0105] from Figure 2It can be seen that the flexible self-supporting film prepared by ball milling and scraping coating has a very uniform thickness and a dense structure, which is also the key to maintaining the mechanical properties of the film. Such a film with uniform thickness and high strength is more conducive to large-scale industrial preparation.

[0106] From Figure 3 It can be seen that the flexible self-supporting film has very good flexibility and can be easily folded into a thousand paper cranes; simple bending will not cause any impact on the film; after being folded multiple times, only creases appear on the surface of the flexible self-supporting film, and the film still remains intact without any damage.

[0107] Tensile strength tests were carried out on the flexible self-supporting films of Examples 1-4 and Comparative Examples 1-2, and the results are shown in Table 1.

[0108] Tensile strength test: When a tensile force is applied to a material, the material will undergo tensile deformation. When the material reaches its maximum load-bearing capacity, failure will occur. The maximum tensile force limit applied during the test is 50 N, and the film is cut into a rectangle of 4 cm × 8 cm for each test.

[0109] Table 1

[0110] Thickness / μm <![CDATA[Cross-sectional area / mm 2 > Maximum force / N Tensile strength / MPa Example 1 23 0.575 39.84 69.29 Example 2 25 0.625 46.84 74.95 Example 3 22 0.550 39.88 72.49 Example 4 25 0.625 42.84 68.55 Comparative example 1 30 0.750 38.40 51.55 Comparative example 2 27 0.675 36.43 53.98

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a flexible self-supporting film, characterized in that: The following steps are involved: reacting low-defect graphene, dopamine hydrochloride and a buffer solution to obtain graphene powder with polydopamine attached to the surface; Grinding the graphene powder with polydopamine attached to the surface, hydroxylated multi-walled carbon nanotubes and a solvent to obtain a grinding material; and mixing the grinding material and a binder to obtain a slurry; The slurry is coated on a substrate, and then dried and peeled off in sequence to obtain the flexible self-supporting film.

2. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The buffer solution includes tris(hydroxymethyl)aminomethane buffer solution; And / or, the pH of the buffer solution is 8.5-10.

3. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The hydroxylated multi-walled carbon nanotube has an outer diameter of 20 to 30 nm and a length of 10 to 30 μm.

4. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The solvent includes 1-methyl-2-pyrrolidone; And / or, the binder includes polyvinylidene fluoride.

5. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The mass ratio of the low-defect graphene to the dopamine hydrochloride is (8-30):

1.

6. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The mass ratio of the graphene powder with polydopamine attached to the surface to the hydroxylated multi-walled carbon nanotube is (4-8):

1.

7. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The ratio of the sum of the mass of the graphene powder with polydopamine attached to the surface and the hydroxylated multi-walled carbon nanotube to the mass of the solvent is (0.6-1):10; And / or, the mass ratio of the solute in the abrasive to the binder is (3-8):

2.

8. The method for preparing a flexible self-supporting film according to claim 1, characterized in that: The method comprises at least one of the following features (1) to (3); (1) The reaction time is 8 to 10 hours; (2) The grinding includes ball milling, the rotation speed of the ball mill is 250 to 350 rpm, and the time is 4 to 8 hours; (3) The coating has a thickness of 400 to 600 μm.

9. A flexible self-supporting film, characterized in that: The flexible self-supporting film is prepared by the method for preparing the flexible self-supporting film according to any one of claims 1 to 8.

10. The flexible self-supporting film according to claim 9, characterized in that: The thickness of the flexible self-supporting film is 25-40 μm.

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