IMPROVED THERMOELECTRIC ELEMENT AND THERMOELECTRIC CONVERTER INCLUDING AT LEAST ONE SUCH ELEMENT

Abstract

A thermoelectric element, particularly for a thermoelectric converter, includes an assembly of constituent layers comprising a central layer made of p- or n-type thermoelectric material, then, in an assembly direction, and on each side of said central layer, an intermediate layer forming a diffusion barrier followed by a buffer layer made of composite metal material. The buffer layers are intended to be secured to metal electrodes, characterized in that the cumulative thickness of the two buffer layers is greater than or equal to 50% of the thickness of the central layer, and preferably greater than or equal to 100% of the thickness of the central layer and very preferably greater than or equal to 200% of the thickness of the central layer, and in that the constituent material of the buffer layers is an alloy of two metals chosen from the family: Ti.sub.xAg.sub.1-x, V.sub.xFe.sub.1-x, V.sub.xAg.sub.1-x, Ti.sub.xFe.sub.1-x, where 0<x<1.

Claims

1. A thermoelectric element for a thermoelectric converter including an assembly of constituent layers comprising a central layer of p- or n-type thermoelectric material, then, in an assembly direction, and on each side of said central layer, an intermediate layer forming a diffusion barrier followed by a buffer layer made of composite metal material, said buffer layers being intended to be secured to metal electrodes, wherein the cumulative thickness of the two buffer layers is greater than or equal to 50% of the thickness of the central layer, and preferably greater than or equal to 100% of the thickness of the central layer and very preferably greater than or equal to 200% of the thickness of the central layer, and in that the constituent material of the buffer layers is an alloy of two metals chosen from the family: Ti.sub.xAg.sub.1-x, V.sub.xFe.sub.1-x, V.sub.xAg.sub.1-x, Ti.sub.xFe.sub.1-x, where 0<x<1.

2. A thermoelectric element according to claim 1, wherein the central layer has a thickness of between 200 m and 2000 m.

3. A thermoelectric element according to claim 1, wherein the thickness of each buffer layer is between 500 m and 5000 m.

4. A thermoelectric element according to claim 1, wherein each intermediate layer has a thickness between 10 m and 200 m.

5. A thermoelectric element according to claim 1, wherein the thermoelectric element has, along a section transverse to the assembly direction, a surface area between 4 mm.sup.2 and 100 mm.sup.2.

6. A thermoelectric element according to claim 1, wherein the constituent material of the central layer is n- or p-type skutterudite.

7. A thermoelectric element according to claim 1, wherein the constituent material of the intermediate layers is chosen from the family of materials comprising nickel, titanium, chromium, tantalum, hafnium, niobium, zirconium, vanadium, yttrium, tungsten, tantalum nitride, indium oxide, copper silicide, tungsten nitride, titanium nitride.

8. A thermoelectric converter comprising two plates of ceramic material substantially parallel to each other and spaced apart from each other by an assembly of thermoelectric elements according to claim 1 and metal electrodes secured on the one hand to the facing surfaces of said plates according to a specific distribution, and on the other hand to the buffer layers via a layer of brazing material.

9. A thermoelectric converter according to claim 8, wherein the layer of brazing material disposed between the buffer layers and the metal electrodes contain aluminum in particular.

10. A thermoelectric converter according to claim 8, wherein the thickness of the layer of brazing material is equal to or less than the thickness of the buffer layers of composite metal material.

11. A thermoelectric converter according to claim 8, wherein the thickness of the layer of brazing material is between 50% and 200% of the thickness of the electrodes printed on the plates of ceramic material.

12. A thermoelectric converter according to claim 8, wherein the layer of brazing material covers at least a portion of the free surface of the metal electrode.

13. A thermoelectric converter according to claim 8, wherein the layer of brazing material extends around the buffer layer, forming a peripheral collar surrounding said buffer layer over a portion of the height of said buffer layer

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Other characteristics and advantages will be seen more clearly from the following description, provided with reference to the appended drawings, provided by way of non-limiting examples, in which:

[0042] FIG. 1 is a perspective view of an embodiment of a thermoelectric element, connected to electrodes,

[0043] FIG. 2 is a partial representation of another embodiment of a thermoelectric element, and

[0044] FIG. 3 is a perspective view, partially cut away, of an embodiment of a thermoelectric converter.

DETAILED DESCRIPTION

[0045] The structurally and functionally identical elements shown in several different figures are assigned the same numerical or alphanumerical reference.

[0046] FIG. 1 is a perspective view of an embodiment of a thermoelectric element (1). More precisely, FIG. 1 shows an assembly of two thermoelectric elements (1), assembled by means of an upper electrode (2a). Each of the thermoelectric elements (1) is also connected to a respective lower electrode (2b). The electrodes (2a) and (2b) are of metal type.

[0047] The thermoelectric element (1) includes an assembly of constituent layers comprising in particular a central layer (3a) or (3b). The central layer (3a) is for example made of an n-type thermoelectric material and the central layer (3b) is for example made of a p-type thermoelectric material. The central layers (3a) and (3b) are therefore preferably made respectively of n- and p-type skutterudite.

[0048] The thermoelectric element (1) also comprises in a longitudinal assembly direction A and on each side of the central layer (3a) and (3b) an intermediate layer (4) forming a diffusion barrier.

[0049] The purpose of the diffusion barrier is to prevent the diffusion of chemical elements from the thermoelectric material towards buffer layers (5) and vice versa, in this way the electrical, thermal and mechanical properties thereof can be preserved during operation of the thermoelectric converter.

[0050] The constituent material of the intermediate layers (4) is chosen from the family of materials comprising nickel, titanium, chromium, tantalum, hafnium, niobium, zirconium, vanadium, yttrium, tungsten, tantalum nitride, indium oxide, copper silicide, tungsten nitride and titanium nitride.

[0051] The constituent materials of the intermediate layers (4) are advantageously chosen to adapt to the nature of the central layer (3a) or (3b), namely the n- or p-type thermoelectric material. With skutterudites, several of the metals previously cited have led to very positive results.

[0052] Each intermediate layer (4) is followed by a buffer layer (5) of composite metal material. The buffer layers (5) are intended to be secured to the metal electrodes (2a) or (2b). Said secure fastening is preferably achieved by means of a layer of brazing material (6) containing in particular aluminum. The significant thickness of the buffer layers (5) makes it possible to use a larger quantity of brazing material compared to that of the known state of the art, without risking a short-circuit.

[0053] Moreover, it is advantageous that the brazing material (6) overflows onto the buffer layer (5) in order to improve its electrical performance.

[0054] The constituent material of the buffer layers (5) is preferably a composite of two metals chosen from the family of pairs of metals comprising silver and titanium, iron and vanadium, silver and vanadium and iron and titanium. The proportions of the two constituent materials of the buffer layer (5) are specified as follows, with x being an atomic fraction falling strictly between 0 and 1, i.e. with 0<x<1. The constituent composite material of the buffer layers (5) is thus a composite of two metals chosen from the family: TixAg1x, VxFe1x, Vx Ag1x, TixFe1x.

[0055] Each buffer layer (5) is connected to the metal electrodes by the layer of brazing material (6).

[0056] The layer of brazing material (6), as illustrated in FIG. 2, connecting each buffer layer (5) to the electrodes (2a, 2b), is also spread over all of the free surfaces and over the full length of the electrodes (2a, 2b) printed on the plates (8, 9) of ceramic material, in order to reduce the electrical resistance thereof. The brazing material (6) also covers the buffer layers (5).

[0057] The thickness of the layer of brazing material (6) in this case is typically equal to or less than the thickness of the composite buffer layers (5) and is between 50% and 200% of the thickness of the electrodes (2a, 2b) printed on the plates (8, 9) of ceramic material.

[0058] The material of the layer of brazing material (6) is therefore advantageously spread over the free surface of the metal electrode (2a, 2b) in order to cover at least part or all of the surface thereof that is not covered by the buffer layer (5).

[0059] Advantageously, the layer of brazing material (6), illustrated for example in FIG. 2, also extends around the buffer layer (5) forming a peripheral collar (6a) surrounding said buffer layer (5) over a portion of the height thereof.

[0060] Different possible proportions can advantageously be adapted to the n- or p-type thermoelectric material of the central layer (3a) or (3b). In the case of TixAg1x, the value of x is 0.86 for the n-type thermoelectric element and 0.57 for the p-type.

[0061] Advantageously, the cumulative thickness of the two buffer layers (5) of a thermoelectric element (1) is greater than or equal to 50% of the thickness of the central layer (3a) or (3b).

[0062] According to another preferred embodiment, said cumulative thickness is greater than or equal to 100% of the thickness of the central layer (3a) or (3b).

[0063] According to another particularly preferred embodiment, said cumulative thickness is greater than or equal to 200% of the thickness of said central layer (3a) or (3b).

[0064] For example, the central layer (3a) or (3b) has a thickness of between 200 m and 2000 m.

[0065] The thickness of each buffer layer (5) is between 500 m and 5000 m.

[0066] The thickness of each intermediate layer (3) is preferably between 10 m and 200 m.

[0067] A thermoelectric element (1) advantageously has, along a section transverse to the assembly direction A, a surface area between 4 mm2 and 100 mm2.

[0068] FIG. 3 is a perspective view, partially cut away, of an embodiment of a thermoelectric converter (7), incorporating the thermoelectric elements (1). The thermoelectric converter (7) comprises two plates of ceramic material (8) and (9) that are substantially parallel to each other and spaced apart from each other by an assembly of thermoelectric elements (1).

[0069] The metal electrodes (2a) and (2b) are respectively secured onto two facing surfaces of said plates (8) and (9) of ceramic material.

[0070] The distribution and attachment of the electrodes (2a) and (2b) on the respective plates (8) and (9) of ceramic material is achieved according to known technologies, so as to enable the assembly of said plates (8) and (9) with the thermoelectric elements (1).

[0071] For example, two assemblies of twelve thermoelectric elements (1), six n-type and six p-type, were produced and the electrical power thereof was measured. Each thermoelectric element comprises buffer layers (5) of TixAg1-x, a diffusion layer of Ni and a thermoelectric layer as follows: skutterudite In0.4Co4Sb12 for the n-type, and skutterudite Ce0.9Fe3.5Co0.5Sb12 for the p-type. The respective thicknesses of said layers were 1000 m, 10 m and 500 m for the first assembly and 1000 m, 10 m and 1000 m for the second. The transverse surface area of each thermoelectric element was about 2.5 mm2.5 mm, corresponding to 6.25 mm2 for the first and 2 mm2 mm, corresponding to 4 mm2 for the second.

[0072] Subject to a temperature difference of 500 K, the measured electrical power was 3.1 W, corresponding to a power density of 4.1 W.Math.cm2 for the first and 3.6 W, corresponding to a power density of 7.5 W.Math.cm-2 for the second.

[0073] These achieved power densities are quite remarkable compared to the values of the prior art, which at best are on the order of 1 W.Math.cm-2, especially taking into account the small quantity of thermoelectric material used.

[0074] It is evident that this description is not limited to the examples explicitly described, but also comprises other embodiments and/or implementations. Thus, a described technical characteristic can be replaced by an equivalent technical characteristic without going beyond the scope of the present disclosure.