A thermoelectric device and a method for preparing the same

Abstract

The present invention discloses a thermoelectric device and a preparation method thereof. The thermoelectric device includes: a thermoelectric material matrix layer, and electrode layers attached to two surfaces of the matrix layer. Among them, the material of the electrode layer is a copper-magnesium-iron alloy. By using a copper-magnesium-iron alloy as the electrode material, the interfacial resistance between the electrode layer and the thermoelectric material matrix layer is reduced, and the shear strength is improved. The thermoelectric device provided by the present invention has a power density (ω max ) of 2.6 W / cm ‑2 at a temperature difference (ΔT) of 370 °C, and a conversion efficiency (η max ) of 8%.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic bulk thermoelectric devices, and in particular to a thermoelectric device and a preparation method thereof. Background Art

[0002] Thermoelectric (TE) devices can directly convert heat into electricity, showing great potential to power numerous sensors in the field of Internet of Things (IoT). Conversion efficiency (η) and power density (ω) are two key technical indicators for evaluating the performance of TE devices. In recent years, high η TE devices have been constructed using new TE materials such as PbTe, GeTe, SnSe, Cu2Se, AgSbTe2, Mg3Sb2, etc. However, achieving high ω is also essential for generating electricity to provide power for IoT sensors. The theoretical ω is mainly affected by the power factor (PF) of the TE material. Non-toxic, environmentally friendly, cost-effective and efficient Mg2(Si,Ge,Sn)-based TE materials have ultra-high PF in the medium and low temperature range (250-450℃), making them promising candidates for the IoT power generation market.

[0003] Compared with the basic research of emerging TE materials, the progress of TE device manufacturing has been very slow, mainly due to the technical challenges associated with device design and assembly. This has also resulted in the performance of Mg2(Si,Sn)-based TE devices not yet reaching the level predicted by theoretical models.

[0004] Therefore, the prior art needs to be further improved and enhanced. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a thermoelectric device and a method for preparing the same. The present invention adopts a copper-magnesium-iron alloy as the electrode material of the thermoelectric device, thereby reducing the interface resistance between the electrode layer and the thermoelectric material matrix layer and improving the shear strength, so that the obtained thermoelectric device has high power generation efficiency and high output power density.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, a thermoelectric device includes: a thermoelectric material matrix layer, and electrode layers attached to two surfaces of the thermoelectric material matrix layer, wherein the material of the electrode layers is a copper-magnesium-iron alloy.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0009] As a preferred technical solution, the thermoelectric device, wherein the composition of the copper-magnesium-iron alloy is Cu a Mgb Fe c , where a, b, and c are atomic ratios, a = 0.5 to 2.5; b = 0.5 to 1.5; c = 0.5 to 1.5.

[0010] As a preferred technical solution, the thermoelectric device, wherein the thermoelectric material is composed of Mg 2+x Sn 2-y- z A y B z , wherein A is Si, Ge or Sn, B is Sb or Bi, -0.2≤x≤0.3; x, y, z are atomic ratios, y=0~1.0; z=0~0.2.

[0011] As a preferred technical solution, in the thermoelectric device, the thickness of the electrode layer is 0.3-1.0 mm.

[0012] In a second aspect, a method for preparing the thermoelectric device described above, wherein the preparation method comprises:

[0013] The single elements of the electrode layer material are weighed and mixed according to the chemical formula ratio, and ground to obtain alloy powder;

[0014] The powder constituting the thermoelectric material matrix layer and the alloy powder are placed in a mold for spark plasma sintering to obtain the thermoelectric device.

[0015] As a preferred technical solution, in the method for preparing the thermoelectric device, the conditions for the plasma sintering include: sintering under an axial pressure of 30-60 MPa, a sintering temperature of 500-800° C., and a sintering time of 5-10 min.

[0016] As a preferred technical solution, the preparation method of the thermoelectric device, wherein the heating rate during the sintering process is 50-100°C min -1 .

[0017] As a preferred technical solution, in the method for preparing the thermoelectric device, the particle size of the alloy powder is 100-300 mesh.

[0018] As a preferred technical solution, the preparation method of the thermoelectric device, wherein the preparation method of the powder constituting the thermoelectric material matrix layer, comprises: placing the single elements of the thermoelectric material in a ball mill according to the chemical formula ratio, and ball milling for 1 to 20 hours in an inert gas atmosphere to obtain the powder of the thermoelectric material matrix layer.

[0019] Beneficial effect: Compared with the prior art, the thermoelectric device provided by the present invention has a power density (ω max) is 2.6 W cm -2 , conversion efficiency (η max ) is 8%. In addition, the ω of the four-leg module device combined with p-type commercial Bi2Te3 at ΔT of 270℃ max 1.3W cm -2 , η max The ratio of the pn-type Mg2Sn-based thermoelectric device to the pn-type Mg2Sn-based thermoelectric device is 5.4%, which is equivalent to the pn-type commercial Bi2Te3-based device. The invention provides the n-type Mg2Sn-based thermoelectric device with the best comprehensive performance in the industry and improves the practicality of the Mg2Sn-based thermoelectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the preparation process of the Mg2(Si,Ge,Sn) based device in the present invention;

[0021] Figure 2 is the performance of the Mg2(Si,Ge,Sn) based device in the present invention: where (a) is the ω dependent on ΔT max , (b) is the ΔT-dependent η max , (c) is the variation of ΔR / R0 with the number of cycles at high current density at ambient temperature, and (d) is the variation of output power (P) and η with the number of cycles at 200-400°C;

[0022] Figure 3 Cu2MgFe / Mg2Sn in the present invention 1.75 Ge 0.25 Contact interface stability: Contact resistivity ρ at 400℃ c and (b) shear strength σ s ;

[0023] Figure 4 Cu2MgFe / Mg2Sn in the present invention 1.75 Ge 0.25 Contact interface stability: 400℃ aging timeσ s Changes in RMS with time;

[0024] Figure 5 Cu2MgFe / Mg2Sn 0.75 Ge 0.25 Contact interface microstructure and reliability evaluation, including (a) high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image and corresponding EDS spectrum before in-situ heating, (b) TEM image of the white rectangular area in (a) at different heating temperatures after in-situ heating, (c) high-resolution transmission electron microscopy (HRTEM) image and fast Fourier transform (FFT) spectrum of the contact interface in the yellow rectangular area in the range of 300-450°C;

[0025] Figure 6 It is a two-dimensional distribution diagram of the maximum output power and conversion efficiency of related thermoelectric devices. DETAILED DESCRIPTION

[0026] The present invention provides a thermoelectric device and a method for preparing the same. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, but does not exclude the presence or addition of one or more other features.

[0028] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as herein.

[0029] The thermoelectric device and the preparation method thereof provided by the present invention are further explained and illustrated by means of specific preparation examples.

[0030] Example 1

[0031] Thermoelectric material: Mg 2.06 Sn 1.728 Ge 0.25 Sb 0.022 The powder was obtained by high-energy ball milling for 8 hours under argon protection and placed in a glove box for later use. Electrode: Cu2FeMg was obtained by high-energy ball milling for 1 hour under argon protection and placed in a glove box for later use. 2.06 Sn 1.728 Ge 0.25 Sb 0.022 The powder and Cu2FeMg powder were placed in a mold and sintered for 5 min at 500 °C under an axial pressure of 30 MPa. Mg 2.06 Sn 1.728 Ge 0.25 Sb 0.022 / Cu2FeMg thermoelectric devices.

[0032] Example 2

[0033] Thermoelectric material: Mg1.8 Sn 1.455 Ge 0.5 Sb 0.045 The powder was obtained by high-energy ball milling for 10 hours under argon protection and placed in a glove box for later use. Electrode: Cu 0.5 Fe 0.5 Mg 0.5 The powder was milled under high energy for 1 hour under argon protection and placed in a glove box for later use. 1.8 Sn 1.455 Ge 0.5 Sb 0.045 Powder and Cu 0.5 Fe 0.5 Mg 0.5 The powder was placed in a mold and sintered for 7 min at 600 °C under an axial pressure of 40 MPa. Mg 1.8 Sn 1.455 Ge 0.5 Sb 0.045 / Cu 0.5 Fe 0.5 Mg 0.5 Thermoelectric devices.

[0034] Example 3

[0035] Thermoelectric material: Mg 2.1 Sn 1.3 Ge 0.6 Sb 0.1 The powder was obtained by high-energy ball milling for 8 hours under argon protection and placed in a glove box for later use. Electrode: CuFeMg was obtained by high-energy ball milling for 5 hours under argon protection and placed in a glove box for later use. Mg 2.1 Sn 1.3 Ge 0.6 Sb 0.1 The powder and CuFeMg powder were placed in a mold and sintered for 8 min at 700 °C under an axial pressure of 50 MPa. 2.1 Sn 1.3 Ge 0.6 Sb 0.1 / CuFeMg thermoelectric devices.

[0036] Example 4

[0037] Thermoelectric material: Mg 2.15 Sn 1.15 Ge 0.7 Sb 0.15 The powder was obtained by high-energy ball milling for 8 hours under argon protection and placed in a glove box for standby use. Electrode: Cu 1.5 Fe 0.5 Mg 0.8 The powder was milled under high energy for 1 hour under argon protection and placed in a glove box for later use.2.15 Sn 1.15 Ge 0.7 Sb 0.15 Powder and Cu 1.5 Fe 0.5 Mg 0.8 The powder was placed in a mold and sintered for 5 min at 700 °C under an axial pressure of 30 MPa. Mg 2.15 Sn 1.15 Ge 0.7 Sb 0.15 / Cu 1.5 Fe 0.5 Mg 0.8 Thermoelectric devices.

[0038] Example 5

[0039] Thermoelectric material: Mg 2.2 Sn 1.045 Ge 0.8 Sb 0.155 The powder was obtained by high-energy ball milling for 18 hours under argon protection and placed in a glove box for later use. Electrode: Cu2Fe 1.5 Mg 1.5 The powder was milled under high energy ball milling for 15 hours under argon protection and placed in a glove box for later use. 2.2 Sn 1.045 Ge 0.8 Sb 0.155 Powder and Cu2Fe 1.5 Mg 1.5 The powder was placed in a mold and sintered at 800°C for 10 min under an axial pressure of 60 MPa to obtain Mg 2.2 Sn 1.045 Ge 0.8 Sb 0.155 / Cu2Fe 1.5 Mg 1.5 Thermoelectric devices.

[0040] Example 6

[0041] Thermoelectric material: Mg 2.3 Sn 0.8 ikB 0.2 The powder was obtained by high-energy ball milling for 20 hours under argon protection and placed in a glove box for later use. Electrode: Cu 2.5 Fe 1.5 Mg 1.5 The powder was milled under high energy ball milling for 20 hours under argon protection and placed in a glove box for later use. 2.3 Sn 0.8 oeLh 0.2 Powder and Cu 2.5 Fe 1.5Mg 1.5 The powder was placed in a mold and sintered at 800°C for 10 min under an axial pressure of 60 MPa to obtain Mg 2.3 Sn 0.8 oeLh 0.2 / Cu 2.5 Fe 1.5 Mg 1.5 Thermoelectric devices.

[0042] Comparative Example 1

[0043] Thermoelectric material: commercial full pn Bi2Te3 (bulk purchased from Guangdong Fuxin Technology Co., Ltd., Guangdong Fuxin Technology Co.,), electrode: Ni (the company brings its own electroplated Ni electrode), Bi2Te3 thermoelectric device is prepared according to the technical scheme mentioned in the patent of this invention. The sintering conditions of this part are 500℃, 5min, 50MPa.

[0044] Comparative Example 2

[0045] Thermoelectric material: Mg 2.05 Si 0.98 Bi 0.02 , electrode: Mg 50 Si 15 Ni 50 Reference: Journal of Alloys and Compounds 926(2022)166888. Test conditions: hot end 400C, cold end 25 degrees, power density less than 0.5Wcm -2 The sintering conditions were 600°C, 5 min, and 30 MPa.

[0046] Comparative Example 3

[0047] Thermoelectric material: Mg2Si 0.3 Sn 0.7 , electrode: Cu, reference: Materials Science and Engineering B 272 (2021) 115338. The test conditions are 300°C at the hot end, 30°C at the cold end, and a power density of 0.52 W cm -2 .

[0048] Comparative Example 4

[0049] Thermoelectric material: Mg 2.06 Si 0.3 Sn 0.665 Bi 0.035, electrode: Cu, reference: Adv. Eng. Mater. 2023, 25, 2200776. Test conditions are hot end 400C, cold end 25 degrees, power density 0.9W cm -2 .

[0050] like Figure 1 As shown, the device preparation process includes sintering composite, cutting and assembly welding.

[0051] like Figure 2 As shown, the present invention uses Cu2MgFe as an electrode to prepare a single-leg n-type Mg 2.06 Sn 1.728 Ge 0.25 Sb 0.022 TE device, assembled with p-type Bi2Te3 module Mg 2.06 Sn 1.728 Ge 0.25 Sb 0.022 TE devices. A high ω max (2.6W cm -2 ) and η max (8%) Figure 2 a and b in the figure). At 8A cm -2 The electrical stability was evaluated at high current density, and thermal shock tests were performed to evaluate the thermal stability ( Figure 2 c and d in ). From Figure 2 It can be clearly seen in a that the maximum values ​​of ω for the single-leg and module TE devices are approximately 2.6 and 1.3 W cm, respectively. -2 The temperature change of thermal shock test is as follows Figure 2 The yellow curve in middle d shows that the cold end temperature is fixed during the test, and the hot end oscillates between 200-400 degrees. Figure 6 As shown, through the two-dimensional distribution diagram of the maximum output power and conversion efficiency of relevant thermoelectric devices, it is found that the device prepared by the present invention has the highest power density compared with other thermoelectric materials (MgAgSb, PBTe, SKD.Mg3Sb2) and the same type of thermoelectric materials (Mg2SiGeSn).

[0052] In the present invention, due to Mg 2.06 Sn 1.728 Ge 0.25 Sb 0.022 The high power factor (PF) and the selection of Cu2MgFe as electrodes, low interfacial contact resistance and high shear strength make the resulting thermoelectric device have high ω max .like Figure 3 and Figure 4 As shown, the low interface resistivity of 1.6 μΩ cm was obtained. 2, shear strength 15MPa, and the rate of change of these two values ​​over time is the smallest (fitting slope), indicating that its stability is the best. (By fitting ρ c and σ s The two growth constants k are calculated from the curves of RMS and time. ρc and k σs , quantitatively evaluate the performance stability. Cu2MgFe / Mg2Sn 0.75 Ge 0.25 k of the contact interface ρc and k σs The values ​​are 1.1×10 -3 μΩcm 2 s 1 / 2 and 2.3×10 -3 MPa s 1 / 2 (like Figure 5 a and b), which is lower than the interfaces between TEcM and Cu, Al, 304SS and Mg2SiNi3 / TEcM.

[0053] like Figure 5 As shown, Figure 5 Figure a shows a well-bonded Cu2MgFe / Mg2Sn 0.75 Ge 0.25 The interface has no microcracks, few Kirkendall voids, and little diffusion between elements. The apparent diffusion depth of element Sn is only a few hundred nanometers. Figure 5 b is Cu2MgFe / Mg2Sn 0.75 Ge 0.25 The HRTEM images of the interface below 200 °C show the stability of the well-bonded contact interface.

[0054] like Figure 5 As shown in Figure 5c, during the heating process, HRTEM and FFT did not show any such changes, indicating that Cu2MgFe / Mg2Sn 0.75 Ge 0.25 No phase transition occurs near the interface (in which periodic contrast differences such as moiré fringes can be produced due to lattice mismatch caused by slight displacements of atoms at the interface).

[0055] The thermoelectric device prepared by the present invention successfully achieved a maximum η value of 8% when the temperature difference (ΔT) reached 370°C. h ), the dual-couple module also achieved the maximum η value (5.4%), which is comparable to that of commercial Bi2Te3TE devices. -2 ), the stable device internal resistance (Rin) value even after 1000 cycles also proves the electrical stability of the device (e.g. Figure 2 In addition, the robustness of the thermoelectric device after five thermal shock cycles from 200 to 400 °C confirmed the thermal stability of the device (e.g. Figure 2 d) in.

[0056] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A thermoelectric device, comprising: A thermoelectric material matrix layer, and electrode layers attached to two surfaces of the thermoelectric material matrix layer, wherein the material of the electrode layer is a copper-magnesium-iron alloy; the composition of the copper-magnesium-iron alloy is Cu a Mg b Fe c , where a, b, and c are atomic ratios, a = 0.5 to 2.5; b = 0.5 to 1.5; c = 0.5 to 1.5; The composition of the thermoelectric material is Mg 2+x Sn 2-y-z A y B z , wherein A is Si, Ge or Sn, B is Sb or Bi, -0.2≤x≤0.3; x, y, z are atomic ratios, y=0~1.0; z=0~0.2; The composition of the copper-magnesium-iron alloy is Cu2MgFe; the composition of the thermoelectric material is Mg 2.06 Sn 1.728 Ge 0.25 Sb 0.022 ; The power density of a single thermoelectric device is 2.6 W cm at a temperature difference of 370 °C. -2 , the conversion efficiency is 8%.

2. The thermoelectric device according to claim 1, characterized in that The thickness of the electrode layer is 0.3-1.0 mm.

3. A method for preparing a thermoelectric device according to any one of claims 1 to 2, characterized in that: include: The single elements of the electrode layer material are weighed and mixed according to the chemical formula ratio, and ground to obtain alloy powder; The powder constituting the thermoelectric material matrix layer and the alloy powder are placed in a mold for spark plasma sintering to obtain the thermoelectric device.

4. The method for preparing a thermoelectric device according to claim 3, characterized in that: The plasma sintering conditions include: sintering under an axial pressure of 30-60 MPa, a sintering temperature of 500-800° C., and a sintering time of 5-10 min.

5. The method for preparing a thermoelectric device according to claim 4, characterized in that: The heating rate during sintering is 50-100℃min -1 .

6. The method for preparing a thermoelectric device according to claim 3, characterized in that: The particle size of the alloy powder is 100-300 meshes.

7. The method for preparing a thermoelectric device according to claim 3, characterized in that: The preparation method of powder constituting a thermoelectric material matrix layer comprises: placing each element in the thermoelectric material in a ball mill according to a chemical formula ratio, and ball milling for 1 to 20 hours in an inert gas atmosphere to obtain powder of the thermoelectric material matrix layer.

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