Method for reducing thermal stress of interface of thermoelectric module

Abstract

The invention discloses a method for reducing thermal stress of a thermoelectric module interface. According to the method, a proper amount of negative thermal expansion material is compounded in the thermoelectric material, so that the thermal expansion behavior of the composite material is matched with that of a metallization layer material, and the thermoelectric module shows excellent thermal mechanical stability. The thermal expansion coefficient of the thermoelectric material is reduced through thermal expansion compensation of the negative thermal expansion material, the interface stress of the thermoelectric device is greatly reduced, and the cycling stability of the thermoelectric module is improved.

Description

Technical Field

[0001] The present invention belongs to the field of thermoelectric materials and relates to a method for reducing the interfacial thermal stress of a thermoelectric module. Background Art

[0002] A thermoelectric (TE) device can directly convert waste heat into useful electrical energy. The conversion efficiency (η) of a thermoelectric device depends to a large extent on the thermoelectric figure of merit (zT) and the quality of the internal connection of the thermoelectric device. Although considerable progress has been made in improving the performance of TE materials in the past two decades, establishing high-quality connections remains an ongoing challenge.

[0003] High-quality connections rely on the design of two key layers (i.e., the contact layer between the thermoelectric material and the metallization layer and the bonding layer between the metallization layer and the electrode). The ultimate goal is to minimize additional electrical and thermal resistance, release interfacial thermal stress, and improve the durability and stability of thermoelectric devices. In recent studies, low-temperature sintered nano-silver has been used to connect the electrodes and the metallization layer of thermoelectric modules, effectively avoiding welding thermal stress. By screening suitable metals or alloys through repeated trials, problems such as the bonding strength, interfacial resistance, thermal resistance, high-temperature performance, and chemical stability between the thermoelectric material and the metallization layer have been solved. However, most of these strategies cannot achieve a high degree of matching of the thermal expansion coefficients between the thermoelectric material and the metallization layer, and the risk of interfacial mechanical damage caused by excessive interfacial thermal stress is still very high.

[0004] Therefore, there is an urgent need to find a strategy that can design and adjust the thermal expansion of thermoelectric materials to achieve a high degree of matching of the thermal expansion coefficients between the thermoelectric materials and the metallization layer. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for reducing the interfacial thermal stress of a thermoelectric module.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] A method for reducing the interfacial thermal stress of a thermoelectric module, comprising the following steps:

[0008] (1) According to the formula (V 1 ·CTE 1 +V 2 ·CTE 2 ) / (V 1 +V 2 )=CTE 3 calculate the volume of the required negative thermal expansion material, where V 1 , V 2 are the volumes of the thermoelectric material and the negative thermal expansion (NTE) material respectively, and CTE 1 , CTE 2 and CTE3 are the thermal expansion coefficients of the thermoelectric material, the negative thermal expansion material, and the metallization layer, respectively. The negative thermal expansion material is added to the thermoelectric material in proportion, and the two are fully mixed;

[0009] (2) The mixture in step (1) is subjected to one-time spark plasma sintering to sinter into a bulk.

[0010] Further, in step (1), the thermal expansion coefficient of the thermoelectric material is higher than that of the metallization layer material.

[0011] Further, in step (1), the temperature range in which the negative thermal expansion material exhibits thermal shrinkage characteristics matches the temperature range in which the thermoelectric material operates.

[0012] Further, in step (1), the thermoelectric material includes but is not limited to PbTe-based thermoelectric materials.

[0013] Further, in step (1), the negative thermal expansion material includes but is not limited to ZrW 2 O 8 .

[0014] Further, in step (1), the thermoelectric material is PbTe 0.998 I 0.002 Sb 0.03 , and the negative thermal expansion material is ZrW 2 O 8 The two are fully mixed by physical grinding; in step (2), the sintering temperature is 550 °C, the heat preservation time is 10 min, and the sintering pressure is 40 Mpa.

[0015] Compared with the existing technology, the advantages of the present invention are as follows:

[0016] (1) For the first time, the negative thermal expansion material is introduced into the thermoelectric material to achieve adjustable thermal expansion of the thermoelectric material, which is accurately matched with the thermal expansion coefficient of the metallization layer, greatly reducing the interfacial thermal stress of the thermoelectric device and not affecting the thermoelectric performance of the thermoelectric material itself.

[0017] (2) There is no need to conduct a large number of screening experiments on thermoelectric interface materials, and the preparation process is simple and controllable, which is expected to guide other thermoelectric materials. Description of the Drawings

[0018] Figure 1 For PbTe prepared in Comparative Example 1 and Example 1 0.998 I 0.002 Sb 0.03 and PbTe 0.998 I 0.002 Sb 0.03 -5vol% ZrW 2 O 8Graph of the change in the thermoelectric figure of merit (zT) of the sample versus temperature (T).

[0019] Figure 2 For the PbTe prepared in Comparative Example 1 and Example 1 0.998 I 0.002 Sb 0.03 and PbTe 0.998 I 0.002 Sb 0.03 -5 vol% ZrW 2 O 8 samples and the curve of dL / Lo of the metallization layer Fe 0.75 Sb 0.25 versus temperature.

[0020] Figure 3 For the Fe prepared in Comparative Example 1 and Example 1 0.75 Sb 0.25 / PbTe 0.998 I 0.002 Sb 0.03 (a) and Fe 0.75 Sb 0.25 / PbTe 0.998 I 0.002 Sb 0.03 -5 vol% ZrW 2 O 8 (b) von Mises stress distribution obtained by finite element simulation of the joint. Detailed implementation manners

[0021] The present invention will be further described in detail below with reference to the embodiments and the drawings.

[0022] Comparative Example 1

[0023] 3.0 g of PbTe 0.998 I 0.002 Sb 0.03 powder was sintered by plasma at 823 K under a pressure of 40 MPa for 10 min. The bulk was cut into a disc with a diameter of 10 mm and a thickness of 1 ± 0.2 mm by a diamond wire cutting machine for the measurement of the thermal diffusivity. The bulk was cut vertically twice to form a column with a length of 3 ± 0.3 mm, a width of 2 ± 0.5 mm, and a height of 9 ± 0.5 mm for the measurement of the electrical conductivity and the Seebeck coefficient and the calculation of the thermoelectric figure of merit zT.

[0024] 4.0 g of PbTe 0.998 I 0.002 Sb 0.03The powder was sintered by plasma at 823 K under a pressure of 40 MPa for 10 min. The bulk was cut vertically 4 times by a diamond wire saw into cylinders with a length of 4.0 mm, a width of 4.0 mm, and a height greater than 4.0 mm for the measurement of the coefficient of thermal expansion. Under the heating condition of 273 - 773 K (the volume of the bulk was 3.0×3.0×7.0 mm 3 , Fe 0.75 Sb 0.25 with a thickness of 250 μm), the von Mises stress distribution was obtained through finite element simulation.

[0025] Example 1

[0026] 2.92 g of PbTe 0.998 I 0.002 Sb 0.03 and 0.08 g of ZrW 2 O 8 powders were added to a mortar, and then 5 ml of absolute ethanol was added. The two were uniformly dispersed by manual grinding. Then the mixture was dried in vacuum at 40 °C for 12 h. When preparing the bulk material, the mixed powder was sintered by plasma at 823 K under a pressure of 40 MPa for 10 min. The bulk was cut horizontally once by a diamond wire saw into discs with a diameter of 10 mm and a thickness of 1 ± 0.2 mm for the measurement of the thermal diffusivity. The bulk was cut vertically twice into cylinders with a length of 3 ± 0.3 mm, a width of 2 ± 0.5 mm, and a height of 9 ± 0.5 mm for the measurement of the conductivity and Seebeck coefficient and the calculation of the thermoelectric figure of merit zT. As Figure 1 shown, the thermoelectric performance of the composite material was improved.

[0027] 4 g of PbTe 0.998 I 0.002 Sb 0.03 and 0.11 g of ZrW 2 O 8 powders were added to a mortar, and then 5 ml of absolute ethanol was added. The two were uniformly dispersed by manual grinding. Then the mixture was dried in vacuum at 40 °C for 12 h. When preparing the bulk material, the mixed powder was sintered by plasma at 823 K under a pressure of 40 MPa for 10 min. The bulk was cut vertically 4 times by a diamond wire saw into cylinders with a length of 4.0 mm, a width of 4.0 mm, and a height greater than 4.0 mm for the measurement of the coefficient of thermal expansion. As Figure 2 shown, the dL / Lo of the composite material and that of Fe 0.75 Sb 0.25 achieved better matching. Under the heating condition of 273 - 773 K (the volume was 3.0×3.0×7.0 mm 3 , Fe 0.75 Sb 0.25(with a thickness of 250 μm), the von Mises stress distribution was obtained through finite element simulation. As Figure 3 shown, the maximum von Mises stress of the composite material decreased to 49.208 MPa. Finally, it was determined that PbTe 0.998 I 0.002 Sb 0.03 -x vol% ZrW 2 O 8 , with x = 5 being the best, which can not only ensure that the thermoelectric performance is not affected, but also ensure that the thermal expansion coefficient of the thermoelectric material is highly matched with the thermoelectric contact material.

Claims

1. A method for reducing thermal stress at the interface of a thermoelectric module, characterized in that: The following steps are involved: (1) Calculate the volume of the required negative thermal expansion material according to the formula (V1·CTE1 + V2·CTE2) / (V1+V2) = CTE3, where V1 and V2 are the volumes of the thermoelectric material and the negative thermal expansion material, respectively, and CTE1, CTE2 and CTE3 are the thermal expansion coefficients of the thermoelectric material, the negative thermal expansion material and the metallization layer, respectively. Add the negative thermal expansion material to the thermoelectric material in proportion and mix the two thoroughly. (2) The mixture in step (1) is subjected to a spark plasma sintering to form a block.

2. The method according to claim 1, characterized in that In step (1), the thermal expansion coefficient of the thermoelectric material is higher than the thermal expansion coefficient of the metallization layer material.

3. The method according to claim 1, characterized in that In step (1), the temperature range in which the negative thermal expansion material exhibits thermal contraction characteristics matches the temperature range in which the thermoelectric material operates.

4. The method according to claim 1, characterized in that In step (1), the thermoelectric material is a PbTe-based thermoelectric material.

5. The method according to claim 1, characterized in that In step (1), the negative thermal expansion material is ZrW2O8.

6. The method according to claim 1, characterized in that In step (1), the thermoelectric material is PbTe 0.998 I 0.002 Sb 0.03 The negative thermal expansion material is ZrW2O8 and the two are fully mixed by physical grinding; in step (2), the sintering temperature is 550 °C, the holding time is 10 min, and the sintering pressure is 40 Mpa.

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