A flexible thermoelectric composite film, preparation method and application thereof

Abstract

The present invention discloses a flexible thermoelectric composite film, a preparation method and its application. The preparation method comprises: (1) mixing tellurium antimony bismuth powder with a polymer solution to obtain a mixture, and ball milling the mixture under a protective atmosphere to obtain a thermoelectric composite slurry; (2) using polyimide as a substrate, tape-casting the thermoelectric composite slurry onto the substrate, and obtaining the flexible thermoelectric composite film after drying and discharge plasma annealing. In the present invention, the composite film after SPA treatment is transformed from a loose particle stacking structure to a composite structure with interconnected polymers, forming a large-area interconnected network structure, and the thermoelectric particles are embedded in the PVDF matrix. Such a structure is conducive to the conduction of electrons, thereby facilitating the improvement of electrical conductivity. The method adopted by the present invention greatly shortens the preparation process time, and the prepared organic / inorganic composite material has a high power factor.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible thermoelectric composite materials, and more specifically, relates to a flexible thermoelectric composite film, a preparation method and applications thereof. Background Art

[0002] There is currently a great deal of interest in developing low-cost, flexible, and efficient thermoelectric materials and devices to provide self-powered low-power micro-devices such as wireless sensors, wearable technology devices, and extreme weather clothing. Flexible thermoelectric materials with high thermoelectric performance at room temperature have been a focus of attention. The thermoelectric performance of thermoelectric materials can be evaluated using the dimensionless thermoelectric figure of merit, ZT, where ZT = S 2 σT / κ, σ is electrical conductivity, S is the Seebeck coefficient, T is the thermodynamic temperature, and κ is the thermal conductivity.

[0003] Traditional near-room-temperature inorganic thermoelectric materials, such as Bi2Te3 and MgAgSb, offer advantages such as diversity, maturity, and high thermoelectric performance. However, their brittleness, toxicity, scarcity, high price, and processing difficulties hinder their application in flexible devices. Organic polymers have attracted considerable attention due to their inherent low thermal conductivity and excellent flexibility. Organic / inorganic composite thermoelectric materials can leverage the advantages of each component through synergistic effects. As a result, organic / inorganic composite materials can exhibit good flexibility while maintaining high thermoelectric performance.

[0004] However, the current preparation process takes a long time, and the power factor of the prepared organic / inorganic composite material is low, which cannot meet the use requirements of thermoelectric films. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a flexible thermoelectric composite film, a preparation method and its application, the purpose of which is to optimize the preparation method, thereby solving the technical problems of long preparation process time and low power factor of organic / inorganic composite materials.

[0006] To achieve the above object, according to one aspect of the present invention, a method for preparing a flexible thermoelectric composite film is provided, comprising:

[0007] (1) mixing tellurium antimony bismuth powder with a polymer solution to obtain a mixture, and ball milling the mixture under a protective atmosphere to obtain a thermoelectric composite slurry;

[0008] (2) Using polyimide as a substrate, the thermoelectric composite slurry is tape-cast onto the substrate, and after drying and discharge plasma annealing treatment, the flexible thermoelectric composite film is obtained.

[0009] Preferably, the polymer solution comprises a polymer dissolved in an organic solvent, wherein the polymer is polyvinylidene fluoride with a molecular weight of 300,000-500,000, epoxy resin, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid or sorbitan oleate. Preferably, the polymer is polyvinylidene fluoride with a molecular weight of 300,000-500,000, and the organic solvent is N-methylpyrrolidone.

[0010] Preferably, the concentration of the polymer solution is 80-120 mg / mL.

[0011] Preferably, the tellurium antimony bismuth powder and the polymer solution in the mixture are mixed in a mass ratio of 80:20 to 95:5.

[0012] Preferably, the temperature of the discharge plasma annealing treatment is 300-340°C, the pressure of the discharge plasma annealing treatment is 5-20 MPa, and the time of the discharge plasma annealing treatment is 5-15 minutes. Preferably, the temperature of the discharge plasma annealing treatment is 340°C, the pressure of the discharge plasma annealing treatment is 12 MPa, and the time of the discharge plasma annealing treatment is 10 minutes.

[0013] Preferably, the drying is performed under vacuum at 40-65° C. for 8-12 hours.

[0014] Preferably, the mixture is ball-milled under a protective atmosphere, specifically: the mixture is mechanically ball-milled at a speed of 200-300 rpm for 2-3 hours under Ar atmosphere protection; the tellurium antimony bismuth powder is a powder that has been mechanically ball-milled for 2-4 hours and sieved with 200 mesh.

[0015] Preferably, the step (2) specifically includes: introducing the thermoelectric composite slurry into a casting production line, using polyimide as a substrate, controlling the film thickness by a scraper, and then performing drying and discharge plasma annealing treatment on the production line to continuously obtain the flexible thermoelectric composite film.

[0016] According to another aspect of the present invention, a flexible thermoelectric composite film is provided.

[0017] According to another aspect of the present invention, there is provided an application of a flexible thermoelectric composite film in a flexible thermoelectric power generation device or a thermoelectric cooling device, such as a single-arm thermoelectric generator.

[0018] In general, the above technical solutions conceived by the present invention can achieve at least the following beneficial effects compared with the prior art.

[0019] (1) The composite membrane of the present invention undergoes SPA treatment, transforming from a loosely packed particle structure to a composite structure with interconnected polymers. This dramatic transformation is due to the high temperature and high pressure SPA post-treatment environment (e.g., preferably 340°C and 12 MPa in the present invention). Under these conditions, the tellurium, antimony, and bismuth particles can be immersed in the molten PVDF matrix, forming a dense composite structure. This structure facilitates electron conduction, thereby improving electrical conductivity. The preparation process employed by the present invention significantly shortens the processing time, and the resulting organic / inorganic composite material exhibits a high power factor.

[0020] (2) The present invention uses an organic solvent such as PVDF as a polymer solution to form a large-area interconnected structure, better connecting the thermoelectric nanopowders together and compensating for the conductivity. After the SPA annealing treatment, the pores on the film surface are significantly reduced. This is because under high temperature, the greater pressure makes the Bi 0.5 Sb 1.5 Te3 particles can be immersed in the molten PVDF matrix, forming a dense composite structure, which to a certain extent inhibits the generation or expansion of surface cracks. On the other hand, the PVDF in the composite film crosses each other and plays an important role in supporting the BST particles.

[0021] (3) The present invention adopts a casting production line preparation method, which can achieve large-scale production, ensure consistency and reliability in the production process, and improve production efficiency.

[0022] (4) The process used in the present invention is simple, highly controllable and has good performance, such as Bi 0.5 Sb 1.5 Flexible Bi prepared by Te3 powder and PVDF / NMP solution with a mass ratio of 85:15 0.5 Sb 1.5 The Te3 / PVDF thermoelectric composite film has a smooth surface and a dense internal composite structure. The electrical conductivity reaches 38.85S / cm and the power factor reaches 200.6μWm -1 K -2 , and after 1000 bending cycles, the conductivity of the composite film only decreased by 7.7%. The highest ZT value calculated based on the theoretical thermal conductivity is about 0.27. 0.5 Sb 1.5 Te3 mass percentage, the composite film will show higher electrical properties. 95wt.%Bi 0.5 Sb 1.5 The composite film with Te3 content achieved a conductivity of up to 122.0S / cm and a conductivity of 711.9μWm -1 K -2 The highest power factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic flow chart of a method for preparing a flexible thermoelectric composite film provided by the present invention;

[0024] Figure 2 (a1), (a2), and (a3) ​​are the flexible Bi prepared in Example 1 of the present invention. 0.5 Sb 1.5 Digital photos of Te3 / PVDF thermoelectric composite film at different viewing angles;

[0025] Figure 3 (a) and (b) are the flexible Bi prepared in Example 1 of the present invention. 0.5 Sb 1.5 Digital photos of the bending test of Te3 / PVDF thermoelectric composite film at different viewing angles;

[0026] Figure 4 The flexible Bi prepared in Example 1 of the present invention 0.5 Sb 1.5 Conductivity loss of Te3 / PVDF thermoelectric composite film under different bending times;

[0027] Figure 5 It is different 0.5 Sb 1.5 XRD test pattern of Te3 powder and PVDF / NMP solution at the mass ratio of 340℃SPA10min;

[0028] Figure 6 The flexible Bi prepared in Example 1 of the present invention 0.5 Sb 1.5 Cross-sectional scanning electron microscope (SEM) image of Te3 / PVDF thermoelectric composite film;

[0029] Figure 7 (a) is different Bi 0.5 Sb 1.5 The change diagram of Seebeck coefficient and conductivity under the mass ratio of Te3 powder and PVDF / NMP solution, Figure 7 (b) is different Bi 0.5 Sb 1.5 The change of power factor under the mass ratio of Te3 powder and PVDF / NMP solution;

[0030] Figure 8 (a) Ordinary annealing process, surface morphology of the film after annealing at 300℃ for 3h, Figure 8 (b) is the surface morphology of the film after annealing at 300°C for 5 minutes in the SPA annealing process of the present invention;

[0031] Figure 9Where (a) is the mass ratio Bi 0.5 Sb 1.5 Te3:PVDF / NMP=85:15 flexible Bi 0.5 Sb 1.5 The change of Seebeck coefficient and conductivity of Te3 / PVDF thermoelectric composite film with annealing process, Figure 9 (b) is the mass ratio Bi 0.5 Sb 1.5 Te3:PVDF / NMP=85:15 flexible Bi 0.5 Sb 1.5 Curve showing the variation of power factor of Te3 / PVDF thermoelectric composite film with annealing process. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0033] Polyvinylidene fluoride (PVDF) is a commonly used polymer electrolyte material. In addition to having good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance, and radiation resistance, it also has special properties such as piezoelectricity, dielectricity, and thermoelectricity. This type of material and its advantages such as flexibility, low density, low impedance, and high voltage constant have attracted worldwide attention and are widely used in the fields of petrochemicals, electronics, and fluorocarbon coatings. In order to compensate for the conductivity of the polymer, the organic / inorganic composite material provided by the present invention relies on Bi 0.5 Sb 1.5 The conductive network formed by the Te3 thermoelectric powder filler improves electrical performance. Discharge plasma annealing (SPA) treatment further enhances thermoelectric performance. The film, after discharge plasma annealing (SPA), achieves a smooth surface and a dense internal composite structure, significantly improving the microstructure and performance.

[0034] In this invention, spark plasma annealing (SPA) specifically refers to simulating the spark plasma annealing process using spark plasma sintering (SPS) equipment. The sample is placed in the SPS equipment and annealed at a specific temperature and pressure. This can improve the thermoelectric properties of composite films and shorten the cycle time for large-scale industrial production. High-current, low-voltage square-wave pulses can achieve rapid densification at lower temperatures.

[0035] Example 1

[0036] This embodiment provides a method for preparing a flexible thermoelectric composite film and a flexible thermoelectric composite film prepared by the method. Specifically, the preparation method includes the following steps:

[0037] (1) Change Bi 0.5 Sb 1.5 After the Te3 ingot was crushed and ground, it was placed in a stainless steel ball mill and mechanically ball milled for 3 h under Ar atmosphere. It was then sieved through a 200-mesh standard sieve to complete the powder making process.

[0038] (2) PVDF was mixed with N-methylpyrrolidone (NMP) solvent and mechanically stirred until PVDF was completely dissolved to obtain a 100 mg / mL PVDF / NMP solution; the molecular weight of PVDF was 400,000, and the concentration of the PVDF and N-methylpyrrolidone mixture was 100 mg / mL;

[0039] (3) Bi 0.5 Sb 1.5 Te3 powder and PVDF / NMP solution were mixed at a mass ratio of 85:15 and then planetary ball milled at 300 rpm for 3 h under Ar atmosphere to obtain a uniformly dispersed thermoelectric composite slurry;

[0040] (4) The composite slurry was introduced into the casting production line, with polyimide as the substrate, and the film thickness was controlled by a scraper. It was then vacuum dried at 50°C for 10 hours on the production line, and then subjected to discharge plasma annealing at 340°C and 12 MPa for 10 minutes to obtain a flexible Bi with a thickness of 17.6 μm. 0.5 Sb 1.5 Te3 / PVDF thermoelectric composite film;

[0041] The preparation process is as follows Figure 1 shown.

[0042] Prepared flexible Bi 0.5 Sb 1.5 Digital photos of Te3 / PVDF thermoelectric composite films, such as Figure 2 As shown in (a1)-(a3), the surface is flat and uniform, bendable, and has good flexibility; Figure 3 (a)-(b) are bending test diagrams with a bending radius of 6 mm; the flexible Bi prepared in this embodiment 0.5 Sb 1.5 The conductivity loss of Te3 / PVDF thermoelectric composite film under different bending times was tested, such as Figure 4 As shown in Figure 2, the conductivity of the composite film only decreased by 7.7% after 1000 repeated bending cycles. Figure 5 As shown, it is a flexible Bi 0.5Sb 1.5 The XRD pattern of Te3 / PVDF thermoelectric composite film, and the Seebeck coefficient, conductivity and power factor of the flexible thermoelectric composite film prepared in this embodiment were tested. 0.5 Sb 1.5 The conductivity of Te3 / PVDF thermoelectric composite film reaches 38.85S / cm, and the power factor reaches 200.6μWm -1 K -2 .

[0043] See also Figure 6 , which shows a cross-sectional image of the composite film provided in this example after SPA annealing (340°C / 10 min), demonstrating that PVDF forms a large-area interconnected network structure within the composite material. Compared to the original, unannealed film, the SPA-treated composite film transforms from a loosely packed particle structure to a composite structure with interconnected polymers. Under high temperature and high pressure, BST particles can be immersed in the molten PVDF matrix, forming a dense composite structure.

[0044] Examples 2-5

[0045] The difference between Example 2-5 and Example 1 is that in step (3), Bi 0.5 Sb 1.5 The mass ratios of Te3 powder and PVDF / NMP solution are different. See Table 1 for details.

[0046] Table 1 Bi with different ratios 0.5 Sb 1.5 Te3 / PVDF thermoelectric composite film performance table

[0047]

[0048]

[0049] From Table 1 and Figure 7 As can be seen from (a) and (b), as Bi 0.5 Sb 1.5 With the increase of Te3 powder, the conductivity and power factor of the composite film increased linearly, but the flexibility gradually deteriorated.

[0050] In addition, from Figure 5 The XRD patterns show that after discharge plasma annealing at 340°C for 10 minutes, all film samples with BST weight contents between 80% and 95% exhibit the same BST peak. Due to the inherently low intensity of the PVDF peak and the low weight content of PVDF in the composite material, the PVDF peak was not detected in the XRD patterns.

[0051] The difference between Examples 6-8 and Example 1 is that the temperature and time of the discharge plasma annealing treatment in step (4) are different. The difference between Comparative Example 1 and Example 1 is that the discharge plasma annealing treatment is not used in step (4), but a conventional annealing treatment is used. The conventional annealing treatment specifically comprises placing the composite material in a high-temperature furnace, annealing it in an argon atmosphere at 300°C for 3 hours, and then removing it. See Table 2 for details.

[0052] Table 2 Bi with different annealing treatments 0.5 Sb 1.5 Te3 / PVDF thermoelectric composite film performance table

[0053]

[0054] See also Figure 9 As can be seen in Figures (a) and (b) and Table 2, conventional annealing is time-consuming and produces thermoelectric composite films with significantly lower conductivity and power factors than the thermoelectric composite films obtained using the discharge plasma annealing method described in this application. Increasing the discharge plasma annealing temperature or treatment time improves the sample's conductivity, and thus its power factor.

[0055] See also Figure 8 As shown in (a) and (b), after the SPA post-treatment of the present invention, the BST particles can be immersed in the molten PVDF matrix under high temperature and high pressure, forming a dense composite structure. This structure facilitates electron conduction, thereby improving electrical conductivity. Conventional annealing processes, on the other hand, result in a composite film with a loose, packed structure of particles.

[0056] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a flexible thermoelectric composite film, characterized in that: include: (1) mixing tellurium antimony bismuth powder with a polymer solution to obtain a mixture, and ball-milling the mixture under a protective atmosphere to obtain a thermoelectric composite slurry; the polymer solution comprises a polymer dissolved in an organic solvent, the polymer being polyvinylidene fluoride having a molecular weight of 300,000-500,000; the concentration of the polymer solution is 80-120 mg / mL; the tellurium antimony bismuth powder and the polymer solution in the mixture are mixed in a mass ratio of 90:10-95:5; (2) Using polyimide as a substrate, the thermoelectric composite slurry is cast on the substrate, and after drying and discharge plasma annealing treatment, the flexible thermoelectric composite film is obtained; the temperature of the discharge plasma annealing treatment is 300-340°C, and the pressure of the discharge plasma annealing treatment is 5-20MPa.

2. The preparation method according to claim 1, wherein The organic solvent is N-methylpyrrolidone.

3. The preparation method according to claim 1 or 2, wherein The discharge plasma annealing treatment lasts for 5 to 15 minutes.

4. The preparation method according to claim 1 or 2, wherein The drying is specifically performed by vacuum drying at 40-65° C. for 8-12 h.

5. The preparation method according to claim 1 or 2, wherein The mixture is ball milled under a protective atmosphere, specifically: the mixture is mechanically ball milled at a speed of 200-300 rpm for 2-3 hours under Ar atmosphere protection; the tellurium antimony bismuth powder is a powder that has been mechanically ball milled for 2-4 hours and sieved with 200 mesh.

6. The preparation method according to claim 1 or 2, wherein The step (2) specifically includes: using polyimide as a substrate, and controlling the film thickness by a scraper during the process of tape casting the flexible thermoelectric composite film.

7. A flexible thermoelectric composite film prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the flexible thermoelectric composite film according to claim 7 in a flexible thermoelectric power generation device or a thermoelectric refrigeration device.

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