Skutterudite thermoelectric device and preparation method thereof

Abstract

The skutterudite thermoelectric device comprises an electrode layer, a brazing layer, a barrier layer, an adhesion layer and a skutterudite thermoelectric material layer, the electrode layer is made of a molybdenum-copper alloy material, the barrier layer is made of a tungsten material, the molybdenum-copper electrode layer and the tungsten barrier layer are in brazed connection, and the adhesion layer is made of an adhesion layer. The tungsten barrier layer and the skutterudite thermoelectric material layer are connected through an adhesion layer. According to the design scheme of the interface structure of the high-stability thermoelectric device provided by the invention, the problem of device failure caused by disconnection of the copper electrode in the service period is solved, and the performance and efficiency of the skutterudite thermoelectric device are greatly improved.

Description

Technical Field

[0001] This invention belongs to the technical field of cobaltite thermoelectric devices, specifically relating to a cobaltite thermoelectric device employing a tungsten barrier layer and its preparation method. Background Technology

[0002] Radioisotope thermoelectric batteries (RTBs) possess advantages such as long lifespan, high reliability, maintenance-free operation, and strong adaptability, making them potentially valuable in important fields such as military defense, aerospace, polar exploration, biomedicine, and the electronics industry. Thermoelectric devices are the key components for converting thermal energy into electrical energy, and the interface stability of these devices is a crucial factor determining the reliability and lifespan of the device and even the entire thermoelectric battery. Cobaltite thermoelectric devices are currently a relatively mature mid-temperature thermoelectric device system. During device operation, the commonly used copper electrodes react with volatilized antimony, causing corrosion and circuit breakage, leading to device failure. Furthermore, existing cobaltite thermoelectric devices commonly use barrier layers such as TiAl, Fe-based, and Co-based barrier layers. These barrier layers react significantly with the cobaltite element at high temperatures, resulting in reduced thermoelectric efficiency. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a cobaltite thermoelectric device with a tungsten barrier layer and its preparation method, thereby improving the interface stability of the cobaltite thermoelectric device.

[0004] To achieve the above objectives, a specific embodiment of the present invention provides a cobaltite thermoelectric device, comprising an electrode layer, a brazing layer, a barrier layer, an adhesive layer, and a cobaltite thermoelectric material layer. The electrode layer is made of a molybdenum-copper alloy, the barrier layer is made of tungsten, the molybdenum-copper electrode layer and the tungsten barrier layer are brazed together, and the tungsten barrier layer and the cobaltite thermoelectric material layer are connected by an adhesive layer.

[0005] Furthermore, in a specific embodiment, in the cobaltite thermoelectric device described above, the adhesive layer is made of titanium or a mixture of titanium and cobalt.

[0006] Furthermore, in a specific embodiment, in the cobaltite thermoelectric device described above, the tungsten barrier layer, the adhesive layer, and the cobaltite thermoelectric material layer are connected by a high-temperature sintering method.

[0007] Furthermore, in a specific embodiment, the cobaltite thermoelectric device described above, wherein the tungsten barrier layer is made of tungsten foil, the adhesive layer is made of titanium powder or a mixture of titanium powder and cobalt powder, and the cobaltite thermoelectric material is made of cobaltite powder, which are interconnected by high-temperature sintering.

[0008] Furthermore, in a specific embodiment, in the cobaltite thermoelectric device described above, the brazing layer is a silver-copper brazing layer or a copper-tin brazing layer.

[0009] Furthermore, in a specific embodiment, the cobaltite thermoelectric device as described above, wherein the cobaltite thermoelectric material layer includes p-type cobaltite thermoelectric material and n-type cobaltite thermoelectric material.

[0010] In a specific embodiment, the present invention further provides a method for preparing the above-mentioned cobaltite thermoelectric device, comprising the following steps:

[0011] (1) A tungsten barrier sheet with an adhesion layer was prepared by hot pressing sintering process;

[0012] (2) The tungsten barrier layer with the adhesion layer is connected to the cobaltite thermoelectric material by spark plasma sintering process;

[0013] (3) The molybdenum copper electrode layer and the tungsten barrier layer are welded together by brazing process.

[0014] Furthermore, in a specific embodiment, the preparation method of the cobaltite thermoelectric device as described above, step (1) specifically includes:

[0015] (1-1) Add tungsten material and titanium material or titanium / cobalt mixture into graphite mold in sequence and press them together;

[0016] (1-2) The graphite mold is placed in a vacuum hot press furnace for hot pressing and sintering;

[0017] (1-3) Take out the prepared tungsten barrier sheet with the adhesion layer and polish the surface graphite clean.

[0018] Furthermore, in step (1-1), the tungsten material is tungsten foil, the titanium material is titanium powder, and the titanium / cobalt mixture is a mixture of titanium powder and cobalt powder.

[0019] Furthermore, in a specific embodiment, in the preparation method of the cobaltite thermoelectric device as described above, in step (2), a tungsten barrier sheet with an adhesion layer is placed into a graphite mold, cobaltite powder is added on it, and after compaction, it is placed in an SPS sintering furnace for spark plasma sintering.

[0020] The beneficial effects of this invention are as follows: The cobaltite thermoelectric device provided by this invention uses tungsten as the barrier layer material, which not only blocks the diffusion of antimony but also possesses low thermal conductivity and high electrical conductivity. Furthermore, its low reactivity with antimony prevents the reduction in device efficiency caused by thermoelectric material poisoning. Through the combined design of the tungsten barrier layer and the molybdenum-copper electrode, the infinite miscibility of tungsten and molybdenum provides better mechanical properties, greatly improving the stability of the interface between the thermoelectric device electrode and the barrier layer. The titanium in the adhesion layer enhances the connection between the tungsten barrier layer and the cobaltite material. Simultaneously, the elastic deformation of titanium and the particle slippage generated during heating can alleviate stress, improve its mechanical strength, and enhance device stability. The high-stability thermoelectric device interface structure design provided by this invention solves the problem of device failure caused by open circuits in the copper electrode during service. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of the cobaltite thermoelectric device in a specific embodiment of the present invention;

[0023] Figure 2 This is a graph showing the change in interface resistance of the composite barrier layer after 7 days of aging at 550°C in a specific embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the interface reaction of the composite barrier layer after aging at 550°C for 7 days in a specific embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the interface resistance change of the TiAl barrier layer after aging at 550°C for 5 days in a comparative example of the present invention.

[0026] Figure 5 This is a schematic diagram of the interfacial reaction of the TiAl barrier layer after aging at 550°C for 5 days in a comparative example of the present invention.

[0027] Figure 6 This is a schematic diagram of the interface resistance change of the FeCrCo barrier layer after aging at 550°C for 5 days in a comparative example of the present invention.

[0028] Figure 7 This is a schematic diagram of the interfacial reaction of the FeCrCo barrier layer aged at 550°C for 5 days in a comparative example of the present invention.

[0029] Figure 8This is a schematic diagram of the interfacial reaction of the Co-based barrier layer after aging at 550°C for 7 days in a comparative example of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0032] The terms “comprising”, “including”, etc., as used herein indicate the presence of the steps, features, operations, or components, but do not preclude the addition of one or more other steps, features, operations, or components.

[0033] To address the problem of electrode open circuits caused by the reaction between copper electrodes and volatile antimony during the service of cobaltite thermoelectric devices, this invention provides an interface structure design scheme for cobaltite thermoelectric devices and a corresponding fabrication method for cobaltite thermoelectric devices, thereby expanding application avenues for improving the interface stability of cobaltite thermoelectric devices.

[0034] like Figure 1 As shown, the present invention provides a cobaltite thermoelectric device, comprising an electrode layer, a brazing layer, a barrier layer, an adhesive layer, and a cobaltite thermoelectric material layer. The electrode layer is made of a molybdenum-copper alloy, the barrier layer is made of tungsten, the molybdenum-copper electrode layer and the tungsten barrier layer are brazed together, and the tungsten barrier layer and the cobaltite thermoelectric material layer are connected by an adhesive layer.

[0035] In some specific embodiments, the adhesive layer is made of titanium or a mixture of titanium and cobalt. Since the coefficient of thermal expansion of tungsten does not match that of cobaltite thermoelectric materials, stress concentration may occur during service. Titanium, being a highly reactive metal, can enhance the connection between the tungsten barrier layer and the cobaltite thermoelectric material layer through a titanium-containing adhesive layer. Furthermore, doping the titanium material with an appropriate amount of cobalt can significantly reduce the thickness of the adhesive layer while maintaining connection stability.

[0036] In some specific embodiments, the tungsten barrier layer, adhesive layer, and cobaltite thermoelectric material layer are connected by high-temperature sintering. Specifically, the tungsten barrier layer can be made of tungsten foil, and the adhesive layer can be made of titanium powder or a mixture of titanium and cobalt powder. The thickness of each layer is calculated using software according to the specific design requirements of the thermoelectric device, and the layers are sequentially added to a graphite mold and pressed together. A tungsten barrier layer sheet with an adhesive layer is then formed by vacuum hot pressing sintering. The prepared tungsten barrier layer sheet is then connected to the cobaltite powder in a graphite mold using a spark plasma sintering process.

[0037] Cobaltite thermoelectric materials include p-type cobaltite thermoelectric materials and n-type cobaltite thermoelectric materials. P-type cobaltite thermoelectric elements or n-type cobaltite thermoelectric elements can be prepared by sintering p-type cobaltite powder (such as Fe4Sb12-based material) or n-type cobaltite powder (such as CoSb3-based material) with tungsten barrier layers through a spark plasma sintering process.

[0038] In some specific embodiments, the cobaltite thermoelectric element (containing a tungsten barrier layer) made by high-temperature sintering is connected to the molybdenum copper electrode by brazing, for example, by using silver-copper solder or copper-tin solder to form the brazing layer.

[0039] In this invention, the electrode layer of the cobaltite thermoelectric device is changed from a copper electrode to a molybdenum-copper electrode, which has lower reactivity with antimony. This prevents the problem of electrode disconnection and device failure caused by reactive corrosion. The molybdenum-copper electrode can typically withstand 5-10 times more thermal cycles than a pure copper electrode. The molybdenum-copper electrode material retains a low interfacial resistivity even after high-temperature aging, reducing Joule heat loss during current flow. In contrast, copper electrodes experience a sharp increase in interfacial resistivity due to corrosion cracking after high-temperature aging. Furthermore, the thermal expansion coefficient of the molybdenum-copper electrode (7-9 × 10⁻⁶) is significantly lower. -6 The coefficient of thermal expansion ( / K) is similar to that of cobaltite, while the coefficient of thermal expansion of copper electrodes is 18×10⁻⁶. -6 The difference between the / K) and cobaltite materials is significant. Therefore, the interface stability of the molybdenum-copper electrode combined with the cobaltite thermoelectric material is higher.

[0040] This invention selects tungsten as the barrier layer material, which not only blocks the diffusion of antimony but also possesses low thermal conductivity and high electrical conductivity. Furthermore, its low reactivity with antimony prevents the reduction in device efficiency caused by thermoelectric material poisoning. Through the combined design of the tungsten barrier layer and the molybdenum-copper electrode, the infinite miscibility of tungsten and molybdenum provides excellent mechanical properties, significantly improving the stability of the interface between the thermoelectric device electrode and the barrier layer. Since the thermal expansion coefficient of tungsten does not match that of cobaltite, stress concentration may occur during service. Using titanium, a highly reactive metal, as the adhesion layer enhances the connection between the tungsten barrier layer and the cobaltite material. Simultaneously, the elastic deformation of titanium and the particle slippage generated during heating can alleviate stress, improve mechanical strength, and enhance device stability.

[0041] This invention further provides a method for preparing the above-mentioned cobaltite thermoelectric device, comprising the following steps:

[0042] (1) A tungsten barrier sheet with an adhesion layer was prepared by hot pressing sintering process;

[0043] (2) The tungsten barrier layer with the adhesion layer is connected to the cobaltite thermoelectric material by spark plasma sintering process;

[0044] (3) The molybdenum copper electrode layer and the tungsten barrier layer are welded together by brazing process.

[0045] In some specific embodiments, the fabrication method of the cobaltite thermoelectric device as described above includes step (1):

[0046] (1-1) Add tungsten foil and titanium powder (or a mixture of titanium powder / cobalt powder) into the graphite mold in sequence and press them together;

[0047] (1-2) Place the graphite mold into a vacuum hot press furnace and perform hot pressing and sintering according to the set process parameters;

[0048] (1-3) Take out the prepared tungsten barrier sheet with the adhesion layer and polish the surface graphite clean.

[0049] In some specific embodiments, in the preparation method of the cobaltite thermoelectric device as described above, in step (2), a tungsten barrier sheet with an adhesion layer is placed into a graphite mold, cobaltite powder (p-type cobaltite powder or n-type cobaltite powder) is added on it, and after compaction, it is placed in an SPS sintering furnace for spark plasma sintering to obtain the desired p-type cobaltite thermoelectric element or n-type cobaltite thermoelectric element.

[0050] The cobaltite thermoelectric device of the present invention and its performance are described in detail below through specific embodiments and comparative examples.

[0051] Example

[0052] The cobaltite thermoelectric device provided in this embodiment is fabricated according to the following process:

[0053] (1) Calculate the thickness of each layer of material using software according to the specific design requirements of the thermoelectric device, and add the mixture of tungsten foil and titanium / cobalt powder into the graphite mold in sequence and press it.

[0054] In this embodiment, the thickness of the tungsten foil is 0.1-0.2 mm, the titanium powder added is 0.2-0.3 mm, and the cobalt powder added is 0.3-0.4 mm.

[0055] (2) The graphite mold is placed in a vacuum hot press furnace for hot pressing and sintering, and the barrier layer is successfully fired.

[0056] In the hot pressing sintering process, the furnace temperature is raised to 750℃ and the pressure is raised to 80MPa in 0.5 hours, and then held at this temperature and pressure for 1.5 hours.

[0057] (3) Take out the prepared barrier sheet and grind the surface graphite clean to obtain a clean and usable barrier sheet.

[0058] (4) The polished barrier layer is placed into a graphite mold, and cobaltite powder is added on it according to the design requirements. After compaction, it is placed in an SPS sintering furnace for spark plasma sintering to obtain a cobaltite thermoelectric element.

[0059] In the spark plasma sintering process, the temperature is raised to 650°C for 15 minutes under a pressure of 70MPa, held at this temperature and pressure for 20 minutes, then cooled to 200°C for 20 minutes, and then allowed to cool naturally to room temperature.

[0060] (5) The molybdenum copper electrode is welded to the tungsten barrier layer of the cobaltite thermoelectric element by brazing.

[0061] The cobaltite thermoelectric device prepared by the above process in this embodiment includes a molybdenum-copper electrode layer, a silver-copper brazing layer, a tungsten barrier layer, a titanium / cobalt adhesion layer, and a cobaltite thermoelectric material layer. For cobaltite thermoelectric devices, the barrier layer performance is typically measured by interfacial resistivity and the thickness of the reaction layer; lower interfacial resistivity and thinner reaction layer result in better barrier layer performance. Figure 2 , Figure 3 As shown, the composite barrier layer formed by tungsten and titanium / cobalt materials in this embodiment achieves an interfacial resistivity of 3.78 μΩ•cm after 7 days of thermal aging at 550°C. 2 The thickness of the interface reaction layer is 16 μm.

[0062] Comparative example

[0063] The following section compares and analyzes the performance of barrier layers, taking the commonly used TiAl, Fe-based, and Co-based barrier layers in cobaltite thermoelectric devices as examples.

[0064] The interface resistance change of the TiAl barrier layer is as follows: Figure 4 As shown, the interface response is as follows: Figure 5 As shown, the interfacial resistivity reached 5.34 μΩ•cm after aging at 550℃ for 5 days. 2 Meanwhile, the thickness of the interface reaction layer reaches 20 μm. Compared with the TiAl barrier layer, the composite barrier layer in this embodiment of the invention exhibits lower resistivity and a thinner interface reaction layer thickness over a longer aging time.

[0065] The interfacial resistance change of the FeCrCo barrier layer is as follows: Figure 6 As shown, the interface response is as follows: Figure 7 As shown, the interfacial resistivity reached 10.75 μΩ•cm after aging at 550℃ for 5 days. 2 Meanwhile, the thickness of the interface reaction layer reaches 40 μm. Compared with the FeCrCo barrier layer, the composite barrier layer in this embodiment of the invention exhibits lower resistivity and a thinner interface reaction layer thickness over a longer aging time.

[0066] The interface reaction of the Co-based barrier layer after 7 days of aging at 550℃ is as follows: Figure 8 As shown, the CoNiCr barrier layer reached a thickness of 24.3 μm after aging at 550℃ for 7 days, and the CoNiW barrier layer reached a thickness of 39.8 μm after aging at 550℃ for 7 days. Compared with the two Co-based barrier layers, the composite barrier layer in this embodiment of the invention has a thinner interface reaction layer thickness under the same aging time, and the reaction with scocite is weaker.

[0067] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. Thus, the invention also intends to include such variations and adaptations if they fall within the scope of the claims and their equivalents.

[0068] The above embodiments are merely illustrative examples of the present invention. The present invention may also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of protection of the present invention should be defined by the claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A cobaltite thermoelectric device, characterized in that, It includes an electrode layer, a brazing layer, a barrier layer, an adhesive layer, and a cobaltite thermoelectric material layer. The electrode layer is made of copper-molybdenum alloy, the barrier layer is made of tungsten, the copper-molybdenum electrode layer and the tungsten barrier layer are brazed together, and the tungsten barrier layer and the cobaltite thermoelectric material layer are connected by an adhesive layer.

2. The cobaltite thermoelectric device as described in claim 1, characterized in that, The adhesive layer is made of titanium or a mixture of titanium and cobalt.

3. The cobaltite thermoelectric device as described in claim 1, characterized in that, The tungsten barrier layer, adhesive layer, and cobaltite thermoelectric material layer are connected by high-temperature sintering.

4. The cobaltite thermoelectric device as described in claim 3, characterized in that, The tungsten barrier layer is made of tungsten foil, the adhesion layer is made of titanium powder or a mixture of titanium powder and cobalt powder, and the cobaltite thermoelectric material is made of cobaltite powder, which are connected to each other by high-temperature sintering.

5. The cobaltite thermoelectric device as described in claim 1, characterized in that, The brazing layer is a silver-copper brazing layer or a copper-tin brazing layer.

6. The cobaltite thermoelectric device as described in claim 1, characterized in that, The cobaltite thermoelectric material layer includes p-type cobaltite thermoelectric material and n-type cobaltite thermoelectric material.

7. A method for preparing a cobaltite thermoelectric device according to any one of claims 1-6, characterized in that, Includes the following steps: (1) A tungsten barrier sheet with an adhesion layer was prepared by hot pressing sintering process; (2) The tungsten barrier sheet with the adhesion layer is connected to the cobaltite thermoelectric material by a discharge plasma sintering process; (3) The copper-molybdenum electrode layer and the tungsten barrier layer are welded together by brazing process.

8. The method for preparing the cobaltite thermoelectric device as described in claim 7, characterized in that, Step (1) specifically includes: (1-1) Add tungsten material and titanium material or titanium / cobalt mixture into graphite mold in sequence and press them together; (1-2) The graphite mold is placed in a vacuum hot press furnace for hot pressing and sintering; (1-3) Take out the prepared tungsten barrier sheet with the adhesion layer and polish the surface graphite clean.

9. The method for preparing the cobaltite thermoelectric device as described in claim 8, characterized in that, In step (1-1), tungsten material is tungsten foil, titanium material is titanium powder, and titanium / cobalt mixed material is a mixture of titanium powder and cobalt powder.

10. The method for preparing the cobaltite thermoelectric device as described in claim 7, characterized in that, In step (2), a tungsten barrier sheet with an adhesion layer is placed into a graphite mold, cobaltite powder is added on it, it is compacted and then placed in an SPS sintering furnace for discharge plasma sintering.

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