Composite thermoelectric flexible film, and preparation method and application thereof

Abstract

This invention belongs to the field of thermoelectric materials technology, specifically relating to a composite thermoelectric flexible film, its preparation method, and its application. The invention provides a composite thermoelectric flexible film comprising a flexible substrate and a thermoelectric functional film loaded on the surface of the flexible substrate. The thermoelectric functional film includes a carbon nanotube film and Bi₂Se₃ nanosheets attached to the carbon nanotube film; the carbon nanotube film is a network structure formed by freely distributed carbon nanotubes; the flexible substrate is a porous organic film. The composite thermoelectric flexible film provided by this invention combines Bi₂Se₃ nanosheets and carbon nanotubes. The thin film formed by the carbon nanotubes significantly improves the conductivity of the composite thermoelectric flexible film. Simultaneously, the network structure of the carbon nanotubes can effectively counteract the stress and strain caused by external forces, enhancing the deformability of the film material, which is beneficial for realizing the application of the composite thermoelectric flexible film provided by this invention in the field of flexible electronics.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, specifically relating to a composite thermoelectric flexible film, its preparation method, and its application. Background Technology

[0002] Thermoelectric materials possess significant advantages among various energy materials, enabling direct conversion between thermal and electrical energy through the movement of charge carriers within the material. This makes them invaluable in thermoelectric power generation and thermoelectric refrigeration. Devices based on thermoelectric materials exhibit advantages such as small size, fast response, absence of mechanical rotating parts, cleanliness, and ease of maintenance, thus attracting widespread attention.

[0003] The performance of thermoelectric materials / devices is typically evaluated using the dimensionless thermoelectric figure of merit ZT, where Z represents the overall thermal and electrical properties of the thermoelectric material, and T represents the absolute temperature of the environment in which the material is used; ZT = S 2 σT / κ, where S is the Seebeck coefficient of the material, σ is the electrical conductivity, and κ is the thermal conductivity of the material. 2 σ is the power factor.

[0004] (Bi,Sb)₂(Se,Te)₃ thermoelectric materials exhibit excellent thermoelectric properties near room temperature and are among the earliest and most mature thermoelectric materials studied. It is a compound semiconductor composed of group V and VI elements, with an operating temperature range of 300–450 K and a band gap of 0.15 eV. It is a typical narrow band gap semiconductor material with a hexahedral layered structure. Each layer contains the same type of atoms, arranged in a Te(II)-Bi-Te(I)-Bi-Te(II) atomic configuration. Three such five-atom layers form a hexagonal unit cell, and the layers interact through van der Waals forces. Bi₂Te₃, Sb₂Te₃, and Bi₂Se₃ have the same crystal structure and can form pseudo-binary continuous solid solutions across the entire composition range.

[0005] Compared to bulk materials, thin film materials possess numerous advantages in electromagnetic, optoelectronic, and thermoelectric properties, such as outstanding individual performance, large controllability range, fast response speed, and miniaturization, demonstrating high research and application value. In recent years, reports on flexible thermoelectric thin film materials have proliferated, making it a hot research topic. Bi2Te3-based flexible thermoelectric thin films are particularly promising, showing excellent application potential in the field of flexible microelectronics and serving as a key focus in flexible thermoelectric materials and applications research. Due to the inherent brittleness of inorganic Bi2Te3-based materials, they are typically combined with organic materials to improve their deformability; however, the addition of organic materials usually reduces the electrical conductivity of the composite material, limiting its practical application. Summary of the Invention

[0006] The purpose of this invention is to provide a composite thermoelectric flexible film, its preparation method and application. The composite thermoelectric flexible film provided by this invention not only has high conductivity, but also has the characteristics of buffering stress and strain, which is conducive to the application of the material in the field of flexible electronics.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a composite thermoelectric flexible membrane, comprising a flexible substrate and a thermoelectric functional membrane loaded on the surface of the flexible substrate; the thermoelectric functional membrane comprises a carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane; the carbon nanotube membrane is a network structure formed by the free distribution of carbon nanotubes; the flexible substrate is a porous organic membrane.

[0009] Preferably, the carbon nanotube is a single-walled carbon nanotube; the diameter of the single-walled carbon nanotube is 0.75–3 nm; and the length of the single-walled carbon nanotube is 5–50 μm.

[0010] This invention provides a method for preparing the composite thermoelectric flexible film described in the above technical solution, comprising the following steps:

[0011] Carbon nanotubes are dispersed in an alcohol solvent to form a carbon nanotube alcohol dispersion.

[0012] The carbon nanotube alcohol dispersion, alcohol-soluble inorganic bismuth salt, and alcohol-soluble alkali metal selenite are mixed and subjected to a redox reaction to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets.

[0013] After alcohol precipitation, the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets is separated into solid and liquid phases using a porous organic membrane. A carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane are formed on the surface of the porous organic membrane to obtain an initial composite thermoelectric flexible membrane.

[0014] The initial composite thermoelectric flexible film is hot-pressed to obtain the composite thermoelectric flexible film.

[0015] Preferably, the alcohol-soluble inorganic bismuth salt is bismuth nitrate, and the alkali metal selenite is sodium selenite; the molar ratio of the alcohol-soluble inorganic bismuth salt to the alcohol-soluble alkali metal selenite is 1:1.5.

[0016] Preferably, the temperature of the redox reaction is 240–280°C; and the holding time of the redox reaction is 5–10 h.

[0017] Preferably, the alcohol solvent is ethylene glycol; the mass ratio of the carbon nanotube to the volume of the alcohol solvent is (0.01-0.05) mg:(30-50) mL.

[0018] Preferably, the hot pressing temperature is 150–250°C; the hot pressing pressure is 5–20 MPa; and the hot pressing holding time is 20–60 min.

[0019] Preferably, the alcohol precipitation yields Bi2Se3 nanosheets and carbon nanotube precipitates; the alcohol precipitation further includes ultrasonic washing of the Bi2Se3 nanosheets and carbon nanotube precipitates to obtain a washing solution of purified Bi2Se3 nanosheets and carbon nanotube precipitates; the solvent for ultrasonic washing is ethanol, the number of ultrasonic washings is 3 to 5, and the time for each ultrasonic washing is 15 to 30 minutes.

[0020] Preferably, before hot pressing, the initial composite thermoelectric flexible film is dried; the drying temperature is 50-80°C, and the drying time is 12-24 hours.

[0021] This invention provides the application of the composite thermoelectric flexible film described in the above technical solution or the composite thermoelectric flexible film prepared by the preparation method described in the above technical solution in flexible electronic materials.

[0022] This invention provides a composite thermoelectric flexible film, comprising a flexible substrate and a thermoelectric functional film loaded on the surface of the flexible substrate; the thermoelectric functional film includes a carbon nanotube film and Bi₂Se₃ nanosheets attached to the carbon nanotube film; the carbon nanotube film is a network structure formed by freely distributed carbon nanotubes; the flexible substrate is a porous organic film. The composite thermoelectric flexible film provided by this invention combines thermoelectric Bi₂Se₃ nanosheets and a carbon nanotube film. The thin film formed by the carbon nanotubes significantly improves the conductivity of the composite thermoelectric flexible film, while the network structure of the carbon nanotubes can effectively counteract the stress and strain caused by external forces, enhancing the deformability of the film material, which is beneficial for realizing the application of the composite thermoelectric flexible film provided by this invention in the field of flexible electronics.

[0023] Furthermore, in this invention, the composite thermoelectric flexible membrane further includes a porous organic membrane, with the carbon nanotube membrane located on the surface of the porous organic membrane. The composite thermoelectric flexible membrane provided by this invention further includes a porous organic membrane, thereby improving the self-supporting performance of the composite thermoelectric flexible membrane.

[0024] This invention provides a method for preparing the composite thermoelectric flexible film described in the above technical solution, comprising the following steps: dispersing carbon nanotubes in an alcohol solvent to form a carbon nanotube alcohol dispersion; mixing the carbon nanotube alcohol dispersion, an alcohol-soluble inorganic bismuth salt, and an alcohol-soluble alkali metal selenite, and subjecting them to a redox reaction to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets; precipitating the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets with alcohol and then performing solid-liquid separation using a porous organic membrane to form a carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane on the surface of the porous organic membrane, thereby obtaining an initial composite thermoelectric flexible film; and hot-pressing the initial composite thermoelectric flexible film to obtain the composite thermoelectric flexible film. This invention employs a chemical solution method to generate Bi₂Se₃ nanosheets in situ through a uniformly dispersed carbon nanotube alcohol dispersion. The Bi₂Se₃ nanosheets nucleate and grow on the nanotube surface, attaching to the carbon nanotubes. After alcohol precipitation, solid-liquid separation is performed using a porous organic membrane, resulting in a network structure formed by the carbon nanotubes while the Bi₂Se₃ nanosheets remain attached. Finally, a dense composite thermoelectric flexible membrane is obtained through hot pressing. Compared to current methods that typically synthesize Bi₂Te₃-based thin films using vacuum deposition equipment, which limits the thickness and planar dimensions of the film material and is relatively expensive, the preparation method provided by this invention enables the preparation of large-area, highly dense membrane materials. It is simple to operate, safe, reliable, and easily industrialized. Attached Figure Description

[0025] Figure 1 The curve shows the change in conductivity of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 1 as a function of temperature.

[0026] Figure 2 This is a curve showing the Seebeck coefficient of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 2 as a function of temperature.

[0027] Figure 3 The curve of the power factor of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 3 as a function of temperature is shown.

[0028] Figure 4 This is a surface morphology image of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 3. Detailed Implementation

[0029] This invention provides a composite thermoelectric flexible membrane, comprising a flexible substrate and a thermoelectric functional membrane loaded on the surface of the flexible substrate; the thermoelectric functional membrane comprises a carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane; the carbon nanotube membrane is a network structure formed by the free distribution of carbon nanotubes; the flexible substrate is a porous organic membrane.

[0030] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0031] The composite thermoelectric flexible membrane provided by the present invention includes a flexible substrate; the flexible substrate is a porous organic membrane.

[0032] In this invention, the porous organic membrane is preferably a porous polytetrafluoroethylene membrane.

[0033] In this invention, the pore size of the porous organic membrane is preferably 2 μm.

[0034] The composite thermoelectric flexible film provided by the present invention includes a thermoelectric functional film loaded on the surface of the flexible substrate; the thermoelectric functional film includes a carbon nanotube film, which is a network structure formed by the free distribution of carbon nanotubes.

[0035] In this invention, the carbon nanotubes are preferably single-walled carbon nanotubes (SWCNTs).

[0036] In this invention, the diameter of the single-walled carbon nanotube is preferably 0.75 to 3 nm.

[0037] In this invention, the length of the single-walled carbon nanotube is preferably 5 to 50 μm, more preferably 5.5 to 20 μm.

[0038] The composite thermoelectric flexible film provided by the present invention includes a thermoelectric functional film loaded on the surface of the flexible substrate; the thermoelectric functional film includes Bi2Se3 nanosheets attached to the carbon nanotube film.

[0039] In this invention, the planar size of the Bi2Se3 nanosheets is preferably 500-800 nm.

[0040] The composite thermoelectric flexible film provided by this invention has the characteristics of large area and high conductivity. The addition of carbon nanotubes can not only improve the conductivity of the composite film material, but also buffer stress and strain, which is conducive to the application of the material in the field of flexible electronics.

[0041] This invention provides a method for preparing the composite thermoelectric flexible film described in the above technical solution, comprising the following steps:

[0042] Carbon nanotubes are dispersed in an alcohol solvent to form a carbon nanotube alcohol dispersion.

[0043] The carbon nanotube alcohol dispersion, alcohol-soluble inorganic bismuth salt, and alcohol-soluble alkali metal selenite are mixed and subjected to a redox reaction to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets.

[0044] After alcohol precipitation, the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets is separated into solid and liquid phases using a porous organic membrane. A carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane are formed on the surface of the porous organic membrane to obtain an initial composite thermoelectric flexible membrane.

[0045] The initial composite thermoelectric flexible film is hot-pressed to obtain the composite thermoelectric flexible film.

[0046] This invention disperses carbon nanotubes in an alcohol solvent to form a carbon nanotube alcohol dispersion.

[0047] In this invention, the alcohol solvent is preferably ethylene glycol.

[0048] In this invention, the preferred ratio of the mass of the carbon nanotube to the volume of the alcohol solvent is (0.01-0.05) mg:(30-50) mL.

[0049] In this invention, the dispersion is preferably carried out under stirring conditions, and there are no special requirements for the specific implementation process of the stirring.

[0050] After forming the carbon nanotube alcohol dispersion, the present invention mixes the carbon nanotube alcohol dispersion, alcohol-soluble inorganic bismuth salt, and alkali metal selenite to undergo a redox reaction to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets.

[0051] In this invention, the alcohol-soluble inorganic bismuth salt is preferably bismuth nitrate.

[0052] In this invention, the alcohol-soluble alkali metal selenite is preferably sodium selenite.

[0053] In this invention, the molar ratio of the alcohol-soluble inorganic bismuth salt to the alcohol-soluble alkali metal selenite is preferably 1:1.5.

[0054] In this invention, the temperature of the redox reaction is preferably 240–280°C, more preferably 245–275°C.

[0055] In this invention, the holding time for the redox reaction is preferably 5 to 10 hours, more preferably 5.5 to 9 hours.

[0056] In this invention, after the oxidation reaction, the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets is preferably cooled to room temperature.

[0057] After obtaining a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets, the present invention performs solid-liquid separation by alcohol precipitation of the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets and then using a porous organic membrane. A carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane are formed on the surface of the porous organic membrane to obtain an initial composite thermoelectric flexible membrane.

[0058] In this invention, the preferred method for alcohol precipitation is to mix the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets with isopropanol.

[0059] The present invention does not have special requirements on the amount of isopropanol used, as long as it is sufficient to completely precipitate Bi2Se3 nanosheets and carbon nanotubes.

[0060] In this invention, the alcohol precipitation yields Bi2Se3 nanosheets and carbon nanotube precipitates; preferably, after the alcohol precipitation, the invention further includes ultrasonic washing of the Bi2Se3 nanosheets and carbon nanotube precipitates to obtain a washing solution of purified Bi2Se3 nanosheets and carbon nanotube precipitates; the solvent for ultrasonic washing is ethanol, the number of ultrasonic washings is 3 to 5, and the time for each ultrasonic washing is 15 to 30 minutes.

[0061] In this invention, the alcohol precipitation directly yields an alcohol precipitate containing Bi₂Se₃ nanosheets and carbon nanotubes. Preferably, the alcohol precipitate containing Bi₂Se₃ nanosheets and carbon nanotubes is centrifuged to obtain the Bi₂Se₃ nanosheets and carbon nanotubes precipitate. Specifically, the centrifugation speed is preferably 3000 r / min, and the centrifugation time is preferably 5 min.

[0062] The present invention does not have any special requirements on the amount of ethanol used in each ultrasonic cleaning; it is sufficient to immerse the Bi2Se3 nanosheets and carbon nanotube precipitate.

[0063] In this invention, the ultrasonic time during the first ultrasonic washing is preferably 30 minutes.

[0064] In this invention, the ultrasonic time for the remaining ultrasonic washing is preferably 15 to 30 minutes.

[0065] In this invention, for two consecutive ultrasonic washes, centrifugation is preferably used to remove the washing solvent from the previous ultrasonic wash.

[0066] In this invention, when the washing liquid of the purified Bi₂Se₃ nanosheets and carbon nanotube precipitates is used for solid-liquid separation using a porous organic membrane, the solid-liquid separation is preferably performed by vacuum filtration. In this invention, the vacuum degree of the vacuum filtration is preferably -0.1 × 10⁻⁶. 5 ~-0.4×10 5 Pa.

[0067] In this invention, the initial composite thermoelectric flexible film preferably comprises a porous organic film, a carbon nanotube film, and Bi2Se3 nanosheets attached to the carbon nanotube film.

[0068] After obtaining the initial composite thermoelectric flexible film, the present invention hot-presses the initial composite thermoelectric flexible film to obtain the composite thermoelectric flexible film.

[0069] In this invention, after obtaining the initial composite thermoelectric flexible film and before performing the hot pressing, the invention preferably further includes drying the initial composite thermoelectric flexible film; the drying temperature is preferably 50-80°C, more preferably 55-75°C; the drying holding time is preferably 12-24h, more preferably 13-23h.

[0070] In this invention, the temperature of the hot pressing is preferably 150-250°C, more preferably 160-240°C; the pressure of the hot pressing is preferably 5-20 MPa, more preferably 8-15 MPa; and the holding time of the hot pressing is preferably 20-60 min, more preferably 25-50 min.

[0071] The preparation method provided by this invention preferably uses ethylene glycol with uniformly dispersed SWCNTs as a precursor solution. Bi(NO3)3 and Na2SeO3 preferably undergo a redox reaction at high temperature to generate Bi2Se3 nanosheets, which adhere to the SWCNTs, forming a suspension of Bi2Se3 nanosheets and SWCNTs. A large-area composite flexible film material is preferably obtained by vacuum filtration and then dried. Then, the Bi2Se3 nanosheets and SWCNTs composite thermoelectric film material is preferably hot-pressed using a hot-pressing device. The hot-pressing temperature is preferably 150–250°C, and the hot-pressing time is preferably 20–60 min, resulting in a dense composite film material. The hot-pressed Bi2Se3 / SWCNTs composite film material exhibits high conductivity, which is beneficial for promoting its industrial application.

[0072] This invention provides the application of the composite thermoelectric flexible film described in the above technical solution or the composite thermoelectric flexible film prepared by the preparation method described in the above technical solution in flexible electronic materials.

[0073] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0074] Example 1

[0075] (1) Weigh 30 mL of ethylene glycol and place it in a container. Add 0.01 mg of SWCNTs and stir until a uniformly dispersed single-walled carbon nanotube alcohol dispersion is formed.

[0076] (2) Weigh 1 mmol Bi(NO3)3 and 1.5 mmol Na2SeO3 in an inert atmosphere and place them in the container of step (1) and mix them with the carbon nanotube alcohol dispersion. React at 240°C for 5 h to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets. Cool to room temperature.

[0077] (3) Isopropanol was added to the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets in step (2) for alcohol precipitation, and centrifugation was performed to obtain precipitates of Bi2Se3 nanosheets and single-walled carbon nanotubes (SWCNTs).

[0078] (4) Disperse the Bi2Se3 nanosheets and SWCNTs precipitate obtained in step (3) in ethanol, wash with sonication for 30 min, and centrifuge to obtain the precipitate;

[0079] (5) Repeat the ethanol washing in step (4) 3 times, disperse the Bi2Se3 nanosheets and SWCNTs precipitate obtained by centrifugation in ethanol again, sonicate for 15 min, and obtain the washing solution of purified Bi2Se3 nanosheets and SWCNTs precipitate.

[0080] (6) The washing solution of the purified Bi2Se3 nanosheets and SWCNTs precipitate obtained in step (5) above is vacuum filtered using a porous polytetrafluoroethylene membrane (pore size of 2 μm) to obtain a Bi2Se3 / SWCNTs composite membrane formed on the surface of the porous polytetrafluoroethylene membrane, thus obtaining an initial composite thermoelectric flexible membrane; the initial composite thermoelectric flexible membrane includes the porous polytetrafluoroethylene membrane and the Bi2Se3 / SWCNTs composite membrane formed on the surface; then the initial composite thermoelectric flexible membrane is dried at 60°C for 12 h;

[0081] (7) The initial composite thermoelectric flexible film dried in step (6) above is hot-pressed at a temperature of 150°C for 20 minutes to obtain a dense large-area composite thermoelectric flexible film.

[0082] Comparative Example 1

[0083] (1) Weigh 30 mL of ethylene glycol and place it in a container;

[0084] (2) Weigh 1 mmol Bi(NO3)3 and 1.5 mmol Na2SeO3 in an inert atmosphere and place them in the container of step (1) and mix them with ethylene glycol. React at 240°C for 5 h to obtain an ethylene glycol dispersion containing Bi2Se3 nanosheets. Cool to room temperature.

[0085] (3) Isopropanol was added to the ethylene glycol dispersion containing Bi2Se3 nanosheets in step (2) for alcohol precipitation, and the precipitate of Bi2Se3 nanosheets was obtained by centrifugation.

[0086] (4) Disperse the Bi2Se3 nanosheet precipitate obtained in step (3) in ethanol, ultrasonically wash for 30 min, and centrifuge to obtain the precipitate;

[0087] (5) Repeat the ethanol washing in step (4) 3 times, disperse the Bi2Se3 nanosheet precipitate obtained by centrifugation in ethanol again, sonicate for 15 min, and obtain the washing solution of purified Bi2Se3 nanosheet precipitate.

[0088] (6) The washing solution of the purified Bi2Se3 nanosheet precipitate obtained in step (5) above is vacuum filtered using a porous polytetrafluoroethylene membrane (pore size of 2 μm) to obtain a Bi2Se3 nanosheet membrane formed on the surface of the porous polytetrafluoroethylene membrane, thus obtaining an initial composite thermoelectric flexible membrane; the initial composite thermoelectric flexible membrane includes a porous polytetrafluoroethylene membrane and a Bi2Se nanosheet membrane formed on the surface; then the initial composite thermoelectric flexible membrane is dried at 60°C for 12 h;

[0089] (7) The initial composite thermoelectric flexible film dried in step (6) above is hot-pressed at a temperature of 150°C for 20 minutes to obtain the composite thermoelectric film.

[0090] Example 2

[0091] (1) Weigh 40 mL of ethylene glycol and place it in a container. Add 0.03 mg of SWCNTs and stir until a uniformly dispersed single-walled carbon nanotube alcohol dispersion is formed.

[0092] (2) Weigh 1 mmol Bi(NO3)3 and 1.5 mmol Na2SeO3 in an inert atmosphere and place them in the container of step (1) and mix them with the carbon nanotube alcohol dispersion. React at 260°C for 8 h to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets. Cool to room temperature.

[0093] (3) Isopropanol was added to the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets in step (2) for alcohol precipitation, and centrifugation was performed to obtain precipitates of Bi2Se3 nanosheets and single-walled carbon nanotubes (SWCNTs).

[0094] (4) Disperse the Bi2Se3 nanosheets and SWCNTs precipitate obtained in step (3) in ethanol, wash with sonication for 30 min, and centrifuge to obtain the precipitate;

[0095] (5) Repeat the ethanol washing in step (4) 3 times, disperse the Bi2Se3 nanosheets and SWCNTs precipitate obtained by centrifugation in ethanol again, sonicate for 20 min, and obtain the washing solution of purified Bi2Se3 nanosheets and SWCNTs precipitate.

[0096] (6) The washing solution of the purified Bi2Se3 nanosheets and SWCNTs precipitate obtained in step (5) above is vacuum filtered using a porous polytetrafluoroethylene membrane (pore size of 2 μm) to obtain a Bi2Se3 / SWCNTs composite membrane formed on the surface of the porous polytetrafluoroethylene membrane, thus obtaining an initial composite thermoelectric flexible membrane; the initial composite thermoelectric flexible membrane includes the porous polytetrafluoroethylene membrane and the Bi2Se3 / SWCNTs composite membrane formed on the surface; then the initial composite thermoelectric flexible membrane is dried at 70°C for 15 h;

[0097] (7) The initial composite thermoelectric flexible film dried in step (6) above is hot-pressed at a temperature of 180°C for 30 minutes to obtain a dense large-area composite thermoelectric flexible film.

[0098] Comparative Example 2

[0099] (1) Weigh 40 mL of ethylene glycol and place it in a container;

[0100] (2) Weigh 1 mmol Bi(NO3)3 and 1.5 mmol Na2SeO3 in an inert atmosphere and place them in the container of step (1) and mix with ethylene glycol. React at 260°C for 8 h to obtain an ethylene glycol dispersion containing Bi2Se3 nanosheets. Cool to room temperature.

[0101] (3) Isopropanol was added to the ethylene glycol dispersion containing Bi2Se3 nanosheets in step (2) for alcohol precipitation, and the precipitate of Bi2Se3 nanosheets was obtained by centrifugation.

[0102] (4) Disperse the Bi2Se3 nanosheet precipitate obtained in step (3) in ethanol, ultrasonically wash for 30 min, and centrifuge to obtain the precipitate;

[0103] (5) Repeat the ethanol washing in step (4) 3 times, disperse the Bi2Se3 nanosheet precipitate obtained by centrifugation in ethanol again, sonicate for 20 min, and obtain the washing solution of purified Bi2Se3 nanosheet precipitate.

[0104] (6) The washing solution of the purified Bi2Se3 nanosheet precipitate obtained in step (5) above is vacuum filtered using a porous polytetrafluoroethylene membrane (pore size of 2 μm) to obtain a Bi2Se3 nanosheet membrane formed on the surface of the porous polytetrafluoroethylene membrane, thus obtaining an initial composite thermoelectric flexible membrane; the initial composite thermoelectric flexible membrane includes a porous polytetrafluoroethylene membrane and a Bi2Se nanosheet membrane formed on the surface; then the initial composite thermoelectric flexible membrane is dried at 70°C for 15 h;

[0105] (7) The initial composite thermoelectric flexible film dried in step (6) above is hot-pressed at a temperature of 180°C for 30 minutes to obtain the composite thermoelectric film.

[0106] Example 3

[0107] (1) Weigh 50 mL of ethylene glycol and place it in a container. Add 0.04 mg of SWCNTs and stir until a uniformly dispersed single-walled carbon nanotube alcohol dispersion is formed.

[0108] (2) Weigh 1 mmol Bi(NO3)3 and 1.5 mmol Na2SeO3 in an inert atmosphere and place them in the container of step (1) and mix them with the carbon nanotube alcohol dispersion. React at 260°C for 10 h to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets. Cool to room temperature.

[0109] (3) Isopropanol was added to the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets in step (2) for alcohol precipitation, and centrifugation was performed to obtain precipitates of Bi2Se3 nanosheets and single-walled carbon nanotubes (SWCNTs).

[0110] (4) Disperse the Bi2Se3 nanosheets and SWCNTs precipitate obtained in step (3) in ethanol, wash with sonication for 30 min, and centrifuge to obtain the precipitate;

[0111] (5) Repeat the ethanol washing in step (4) 3 times, disperse the Bi2Se3 nanosheets and SWCNTs precipitate obtained by centrifugation in ethanol again, sonicate for 25 min, and obtain the washing solution of purified Bi2Se3 nanosheets and SWCNTs precipitate.

[0112] (6) The washing solution of the purified Bi2Se3 nanosheets and SWCNTs precipitate obtained in step (5) above is vacuum filtered using a porous polytetrafluoroethylene membrane (pore size of 2 μm) to obtain a Bi2Se3 / SWCNTs composite membrane formed on the surface of the porous polytetrafluoroethylene membrane, thus obtaining an initial composite thermoelectric flexible membrane; the initial composite thermoelectric flexible membrane includes the porous polytetrafluoroethylene membrane and the Bi2Se3 / SWCNTs composite membrane formed on the surface; then the initial composite thermoelectric flexible membrane is dried at 80℃ for 20 h;

[0113] (7) The initial composite thermoelectric flexible film dried in step (6) above is hot-pressed at a temperature of 230°C for 50 minutes to obtain a dense, large-area composite thermoelectric flexible film. Electron micrographs are shown below. Figure 4 As shown, by Figure 4 It can be concluded that the single-walled carbon nanotube membrane is a network structure formed by the free distribution of single-walled carbon nanotubes, and Bi2Se3 nanosheets are attached to the single-walled carbon nanotube membrane.

[0114] Comparative Example 3

[0115] (1) Weigh 50 mL of ethylene glycol and place it in a container;

[0116] (2) Weigh 1 mmol Bi(NO3)3 and 1.5 mmol Na2SeO3 in an inert atmosphere and place them in the container of step (1) and mix them with ethylene glycol. React at 260°C for 10 h to obtain an ethylene glycol dispersion containing Bi2Se3 nanosheets. Cool to room temperature.

[0117] (3) Isopropanol was added to the ethylene glycol dispersion containing Bi2Se3 nanosheets in step (2) for alcohol precipitation, and the precipitate of Bi2Se3 nanosheets was obtained by centrifugation.

[0118] (4) Disperse the Bi2Se3 nanosheet precipitate obtained in step (3) in ethanol, ultrasonically wash for 30 min, and centrifuge to obtain the precipitate;

[0119] (5) Repeat the ethanol washing in step (4) 3 times, disperse the Bi2Se3 nanosheet precipitate obtained by centrifugation in ethanol again, sonicate for 25 min, and obtain the washing solution of purified Bi2Se3 nanosheet precipitate.

[0120] (6) The washing solution of the purified Bi2Se3 nanosheet precipitate obtained in step (5) above is vacuum filtered using a porous polytetrafluoroethylene membrane (pore size of 2 μm) to obtain a Bi2Se3 nanosheet membrane formed on the surface of the porous polytetrafluoroethylene membrane, thus obtaining an initial composite thermoelectric flexible membrane; the initial composite thermoelectric flexible membrane includes a porous polytetrafluoroethylene membrane and a Bi2Se nanosheet membrane formed on the surface; then the initial composite thermoelectric flexible membrane is dried at 80°C for 20 h;

[0121] (7) The initial composite thermoelectric flexible film dried in step (6) above is hot-pressed at a temperature of 230°C for 50 minutes to obtain the composite thermoelectric film.

[0122] Test case

[0123] The electrical properties of the composite thermoelectric film products prepared in Examples 1-3 and Comparative Examples 1-3 were tested. Figure 1This is a curve showing the change in conductivity of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 1 as a function of temperature. Figure 1 In this context, "Bi2Se3 / SWCNTscompositefilms" refers to the product prepared in Example 1. Figure 1 In this context, "Bi2Se3films" represents the product prepared in Comparative Example 1. Figure 2 This is a curve showing the Seebeck coefficient of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 2 as a function of temperature. Figure 2 In this context, "Bi2Se3 / SWCNTscompositefilms" refers to the product prepared in Example 2. Figure 2 In this context, "Bi2Se3films" represents the product prepared in Comparative Example 2. Figure 3 The curve of the power factor of the Bi2Se3 / SWCNTs composite thermoelectric flexible film material prepared in Example 3 as a function of temperature is shown. Figure 3 In this context, "Bi2Se3 / SWCNTscompositefilms" refers to the product prepared in Example 3. Figure 3 In this context, "Bi2Se3 films" represents the product prepared in Comparative Example 3. (The text appears to be incomplete and contains several typographical errors. A more accurate translation would require the full context.) Figures 1-3 It can be concluded that, compared with the thermoelectric film products prepared in Comparative Examples 1 to 3, the thermoelectric film products prepared in Examples 1 to 3 of the present invention have significantly improved conductivity.

[0124] The Bi₂Se₃ / SWCNTs composite thermoelectric flexible membrane provided by this invention features a large area and high conductivity. The addition of single-walled carbon nanotubes significantly improves the conductivity of the composite material, while the network structure of the carbon nanotubes can counteract stress and strain caused by external forces, enhancing the deformability of the membrane material. The Bi₂Se₃ / SWCNTs composite material is tightly bonded to the filter membrane through filtration and hot-pressing processes, further improving the material's flexibility. Moreover, by controlling the size of the porous organic membrane, large-area fabrication of the membrane material can be achieved.

[0125] This invention provides a method for preparing the aforementioned large-area, highly conductive Bi₂Se₃ / SWCNTs composite thermoelectric flexible film material. The method employs a chemical solution method to prepare Bi₂Se₃ nanosheets through a redox reaction in ethylene glycol containing uniformly dispersed single-walled carbon nanotubes. The nanosheets adhere to the carbon nanotubes, forming a composite material. Then, a large-area, dense Bi₂Se₃ / SWCNTs composite flexible film material is prepared using vacuum filtration and hot pressing. The method is simple, safe, reliable, and easily industrialized.

[0126] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite thermoelectric flexible film, characterized by, The method comprises the following steps: dispersing carbon nanotubes in an alcohol solvent to form a carbon nanotube alcohol dispersion; mixing the carbon nanotube alcohol dispersion, bismuth nitrate and sodium selenite to generate a redox reaction to obtain a carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets, wherein the molar ratio of the bismuth nitrate to the sodium selenite is 1:1.5, the temperature of the redox reaction is 240-280℃, and the holding time of the redox reaction is 5-10h; after alcohol precipitation of the carbon nanotube alcohol dispersion containing Bi2Se3 nanosheets, performing solid-liquid separation using a porous organic membrane to form a carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane on the surface of the porous organic membrane, thereby obtaining an initial composite thermoelectric flexible film; performing hot pressing on the initial composite thermoelectric flexible film to obtain the composite thermoelectric flexible film.

2. The production method according to claim 1, characterized by, The carbon nanotubes are single-walled carbon nanotubes, the diameter of the single-walled carbon nanotubes is 0.75-3nm, and the length of the single-walled carbon nanotubes is 5-50μm.

3. The preparation method according to claim 1, characterized in that, The alcohol solvent is ethylene glycol, and the mass of the carbon nanotubes to the volume of the alcohol solvent is (0.01-0.05)mg:(30-50)mL.

4. The method of claim 1, wherein, The temperature of the hot pressing is 150-250℃, the pressure of the hot pressing is 5-20MPa, and the holding time of the hot pressing is 20-60min.

5. The preparation method according to claim 1, characterized in that, The alcohol precipitation obtains Bi2Se3 nanosheets and carbon nanotube precipitates, and after the alcohol precipitation, the Bi2Se3 nanosheets and carbon nanotube precipitates are further subjected to ultrasonic washing to obtain a washing liquid of purified Bi2Se3 nanosheets and carbon nanotube precipitates, the solvent for the ultrasonic washing is ethanol, the number of times of the ultrasonic washing is 3-5, and the time of each ultrasonic washing is 15-30min.

6. The method of claim 1, wherein, Before the hot pressing, the initial composite thermoelectric flexible film is further dried, the temperature of the drying is 50-80℃, and the holding time of the drying is 12-24h.

7. The composite thermoelectric flexible film prepared by the method according to any one of claims 1 to 6, characterized in that, The composite thermoelectric flexible film comprises a flexible substrate and a thermoelectric functional film loaded on the surface of the flexible substrate, the thermoelectric functional film comprises a carbon nanotube membrane and Bi2Se3 nanosheets attached to the carbon nanotube membrane, the carbon nanotube membrane is a network structure formed by free distribution of carbon nanotubes, and the flexible substrate is a porous organic membrane.

8. Application of the composite thermoelectric flexible film of claim 7 in flexible electronic materials.

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