MECHANICAL ADVANTAGE IN LOW TEMPERATURE BOND TO A SUBSTRATE

IN A THERMOELECTRIC PACKAGE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims the benefit under 35 U.S.C. §1 19(e) of the earlier filing date of United States Provisional Patent Application No. 62/236,476, filed on October 2, 2015, and United States Provisional Patent Application No. 62/304,039, filed on March 4, 2016, the entire disclosures of which are hereby incorporated by reference.

BACKGROUND

[0002] Thermoelectric devices can convert heat energy into electrical energy. A thermoelectric device can comprise a hot junction, or hot side, a cold junction, or cold side, and one or more thermoelectric elements positioned between the hot junction and the cold junction. Oftentimes, the hot junction and the cold junction each comprise a plate, for example, positioned against and/or bonded to the opposite sides of the thermoelectric elements. The thermoelectric elements are comprised of thermoelectric materials, such as semiconductors, for example. When such thermoelectric devices are subjected to a temperature differential between their hot junction and cold junction, they can generate a voltage potential which is utilizable for any suitable purpose. Such thermoelectric devices are often referred to as Seebeck devices. Some thermoelectric devices can convert electrical energy to heat energy. When such thermoelectric devices are subjected to a voltage potential, they can generate a temperature differential between a first junction and a second junction. Such thermoelectric devices are often referred to as Peltier devices. In either event, the energy conversion efficiency of a thermoelectric device can be measured by its thermal power density, also known as its "thermoelectric figure of merit" ΖΓ, where ZT is equal to TS ² O/K and where 7 ^" is the temperature, S the Seebeck coefficient, a the electrical conductivity, and ( the thermal conductivity of the thermoelectric material utilized by the thermoelectric device.

1

PI-3951909 BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Various features of the embodiments described herein, together with advantages thereof, may be understood in accordance with the following description taken in conjunction with the accompanying drawings:

[0004] FIG. 1 is an exploded view of a thermoelectric system in accordance with at least one embodiment;

[0005] FIG. 2 is a plan view of a thermoelectric sub-assembly of the thermoelectric system of FIG. 1 illustrated with some components removed for the purpose of illustration;

[0006] FIG. 3 is a plan view of a thermoelectric sub-assembly in accordance with at least one embodiment illustrated with some components removed for the purpose of illustration;

[0007] FIG. 4 is a plan view of a thermoelectric sub-assembly in accordance with at least one embodiment illustrated with some components removed for the purpose of illustration;

[0008] FIG. 5 is a cross-sectional view of a portion of the sub-assembly of FIG. 3;

[0009] FIG. 6 is a cross-sectional view of a portion of the sub-assembly of FIG. 4;

[0010] FIG. 7 is a partial detail view of the portion of the sub-assembly of FIG. 5 illustrating the thermal resistance contribution of certain portions of the subassembly;

[0011] FIG. 8 is a partial detail view of the portion of the sub-assembly of FIG. 6 illustrating the thermal resistance contribution of certain portions of the subassembly;

[0012] FIG. 9 illustrates a method in accordance with at least one embodiment;

[0013] FIG. 10 illustrates a method step in accordance with at least one

embodiment; and

[0014] FIG. 1 1 is a chart illustrating certain process parameters for bonding thermoelectric elements to a substrate.

[0015] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate various embodiments of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. DETAILED DESCRIPTION

[0016] Thermoelectric systems generally comprise a hot side, a cold side, and a thermoelectric assembly positioned therebetween. The hot side of the

thermoelectric system often comprises a plate facing a heat source, i.e., a hot-side plate, and, similarly, the cold side often comprises a plate facing a heat sink, i.e., a cold-side plate. In use, heat flows through the thermoelectric assembly from the hot- side plate toward the cold-side plate which, in turn, generates electrical power within the thermoelectric assembly. In various instances, a thermoelectric system can be configured to harvest thermal energy from more than one heat source and/or discharge thermal energy to more than one heat sink. Moreover, a thermoelectric system can comprise more than one thermoelectric assembly configured to convert thermal energy to electrical energy.

[0017] A thermoelectric system, or thermoelectric generating unit (TGU), 100 is illustrated in FIG. 1 . The TGU 100 comprises a first cold-side plate 1 10, a hot-side heat exchanger 120, and a second cold-side plate 130. The TGU 100 further comprises a first thermoelectric assembly 160 and a second thermoelectric assembly 170. The first thermoelectric assembly 160 is positioned intermediate the first cold-side plate 1 10 and a first side 126 of the hot-side heat exchanger 120. The second thermoelectric assembly 170 is positioned intermediate the second cold-side plate 130 and a second side 127 of the hot-side heat exchanger 120. The TGU 100 also comprises lateral sides 125 positioned intermediate the first cold-side plate 1 10 and the second cold-side plate 130. The entire disclosure of International

Publication Number WO 2016/054333, entitled THERMOELECTRIC GENERATING UNIT AND METHODS OF MAKI NG AND USING SAME, which published on April 7, 2016, is incorporated by reference herein.

[0018] The TGU 100 further comprises a first insulation layer 150, a second insulation layer 180, and a plurality of fasteners 1 15. The first insulation layer 150 is positioned intermediate the first thermoelectric assembly 160 and the first cold-side plate 1 10. The second insulation layer 180 is positioned intermediate the second thermoelectric assembly 170 and the second cold-side plate 130. Fasteners 1 15 are positioned within apertures which extend through the first cold-side plate 1 10, the first insulation layer 150, the first thermoelectric assembly 160, the hot-side heat exchanger 120, the second thermoelectric assembly 170, the second insulation layer 180, and the second cold-side plate 130 and can clamp these components together such that satisfactory thermal contact between these components is maintained under a variety of operating conditions.

[0019] The hot-side heat exchanger 120 comprises a plurality of discrete channels 121 . Each channel 121 is configured to receive a fluid carrying waste heat such as, for example, exhaust from an engine. Each channel 121 comprises a fluidic inlet, a fluidic outlet 128, and a lumen that fluidically couples the fluidic inlet and the fluidic outlet 128. Each channel 121 is sealed from the other channels 121 and,

concurrently, sealed from the other internal portions of the TGU 100. The lumen is configured to efficiently extract heat from a fluid passing there through in the direction indicated by arrow 1 12, for example. In at least one instance, the channels 121 comprise fins disposed within and extending into the lumens defined therein. The fins can be arranged in a fin pack in the lumen and can comprise any suitable configuration, as described below.

[0020] Further to the above, any suitable arrangement, number, and density of fins within the channels 121 can be used. For instance, the density of the fins within the channels 121 can be at least 12 fins per inch, for example. In various instances, the channels 121 and/or the fins disposed therein are comprised of stainless steel, nickel plated copper, and/or stainless steel clad copper, for example. Such designs are configured to increase the contact area between the hot fluid and the sidewalls of the channels 121 which, as a result, increases the heat transfer between the hot fluid and the hot-side heat exchanger 120. Moreover, such designs are configured to disrupt the boundary layer of the fluid flowing through the channels 121 which also increases the heat transfer between the hot fluid and the hot-side heat exchanger 120.

[0021] In at least one instance, the hot-side heat exchanger 120 comprises a high efficiency hot-side heat exchanger. As used herein, a high efficiency hot-side heat exchanger is intended to mean a hot-side heat exchanger characterized by a thermal resistance of less than about 0.0015m ² K/W, for example. In at least one such instance, the thermal resistance of a hot-side heat exchanger is 0.00025 m ² K/W, for example. In various instances, the cold-side plates 1 10 and 130 comprise high efficiency cold-side heat exchangers. As used herein, a high efficiency cold-side heat exchanger is intended to mean a cold-side heat exchanger characterized by a thermal resistance of less than about 0.0001 m ² K/W, for example. [0022] The first cold-side plate 1 10 and the second cold-side plate 130 are flat, or at least substantially flat. As used herein, a substantially flat plate is intended to mean that the first and second major surfaces are substantially planar and parallel to one another. In at least one instance, a substantially flat plate is characterized by a flatness and planarity specification of about 0.010" or less across the major surfaces, for example. The cold-side plates 1 10 and 130 comprise a substantially flat slab of a thermally conductive material, such as a metal and/or a ceramic, for example.

Metals that are suitable for use in the first cold-side plate 1 10 and/or the second cold-side plate 130 can be selected from the group consisting of aluminum, copper, molybdenum, tungsten, copper-molybdenum alloy, stainless steel, nickel, and/or alloys of one or more of these materials, for example. Ceramics that are suitable for use in the first cold-side plate 1 10 and/or the second cold-side plate 130 can be selected from the group consisting of silicon carbide, aluminum nitride, alumina, silicon nitride and/or combinations thereof, for example. In at least one embodiment, one of the cold-side plates 1 10 and 130 is comprised of a metal and the other of the cold-side plates 1 10 and 130 is comprised of a ceramic, for example.

[0023] In various instances, further to the above, the first thermoelectric assembly 160 and the second thermoelectric assembly 170 are part of an electrical circuit of the TGU 100. The thermoelectric assemblies 160 and 170 are electrically connected in series with one another. Alternatively, the thermoelectric assemblies 160 and 170 are electrically connected in parallel with one another. In either event, the electrical circuit of the TGU 100 further comprises an electrical connector comprising at least a first electrical terminal and a second electrical terminal. In use, the thermoelectric assemblies 160 and 170 create a voltage differential between the first electrical terminal and the second electrical terminal.

[0024] The thermoelectric assembly 160, further to the above, is comprised of a plurality of sub-assemblies, or cards, wherein each sub-assembly comprises a plurality of thermoelectric elements 190 mounted thereto. Similarly, referring to FIG. 2, the thermoelectric assembly 170 is comprised of a plurality of sub-assemblies, or cards, 170' wherein each sub-assembly 170' also comprises a plurality of

thermoelectric elements 190 mounted thereto. The sub-assemblies 170' are mounted to and supported by a printed circuit board (PCB) of the thermoelectric assembly 170. The thermoelectric assembly 170 comprises 80 sub-assemblies 170', for example; however, a thermoelectric assembly can comprise any suitable number of sub-assemblies 170'. The sub-assemblies 170' of the thermoelectric assembly 170 are electrically connected in series as part of an electrical circuit extending through the thermoelectric assembly 170. That said, the sub-assemblies 170' can be electrically connected in parallel and/or in series with one other in any suitable arrangement. It should also be appreciated that a sub-assembly 170' can be used by itself, i.e., without other sub-assemblies 170'.

[0025] Further to the above, each thermoelectric sub-assembly 170' comprises a substrate and a plurality of thermoelectric elements 190 mounted to the substrate. The substrate of each sub-assembly 170' can comprise a PCB and/or any suitable dielectric material. As described in greater detail below, the substrate comprises a trace circuit and the thermoelectric elements 190 are bonded to the trace circuit. Each sub-assembly 170' comprises 48 thermoelectric elements 190 mounted thereto; however, a thermoelectric sub-assembly can comprise any suitable number of thermoelectric elements 190. The thermoelectric elements 190 mounted to a subassembly 170' are electrically connected to each other in series. That said, the thermoelectric elements 190 mounted to a thermoelectric sub-assembly can be electrically connected in parallel and/or in series with one other in any suitable arrangement.

[0026] Further to the above, the thermoelectric elements 190 of each

thermoelectric sub-assembly 170' are arranged in a rectangular array of columns and rows between the second cold-side plate 130 and the second side 127 of the hot-side heat exchanger 120. That said, any suitable arrangement can be used.

[0027] Thermoelectric elements can comprise any suitable configuration. Each thermoelectric element 190 comprises two thermoelectric legs; however, a thermoelectric element can comprise one or more thermoelectric legs. Each thermoelectric leg comprises a thermoelectric material disposed between first and second conductive materials. A thermoelectric material can be selected from the group consisting of tetrahedrite, magnesium silicide (Mg ₂ Si), magnesium silicide stannide (Mg ₂ (SiSn)), silicon, silicon nanowire, bismuth telluride (Bi ₂ Te ₃ ), a skutterudite material, lead telluride (PbTe), TAGS (tellurium-antimony-germanium- silver alloys), a zinc antimonide, silicon-germanium (SiGe), a half-Heusler alloy, and combinations thereof, for example.

[0028] A thermoelectric leg can comprise a p-type thermoelectric material or a n- type thermoelectric material. A p-type thermoelectric material is comprised of at least one p-doped semiconductor material, for example. A n-type thermoelectric material is comprised of at least one n-doped semiconductor material, for example. Turning now to FIG. 2, each thermoelectric element 190 of the thermoelectric assemblies 160 and 170 comprises a n-type thermoelectric leg 194 and a p-type thermoelectric leg 196. In at least one such embodiment, the p-type thermoelectric legs 196 are larger than the n-type thermoelectric legs 194. In alternative

embodiments, the legs 196 are n-type thermoelectric legs and the legs 194 are p- type thermoelectric legs. In at least one instance, one or more of the n-type thermoelectric legs 194 are connected electrically in series and thermally in parallel with one or more of the p-type thermoelectric legs 196 so as to generate an electrical current responsive to a temperature differential across the thermoelectric assemblies 160 and 170.

[0029] Further to the above, the quantity of thermoelectric elements 190 in the first thermoelectric assembly 160 and the quantity of thermoelectric elements 190 in the second thermoelectric assembly 170 are the same. In at least one such instance, the first thermoelectric assembly 160 and the second thermoelectric assembly 170 have the same number of sub-assemblies, or cards (such as sub-assemblies 170'), wherein the sub-assemblies each have the same number of thermoelectric elements 190 mounted thereto. Moreover, the thermoelectric assemblies 160 and 170 each have an equal number of n-type legs 194 and p-type legs 196; however, other embodiments are envisioned in which the quantities of n-type legs 194 and p-type legs 196 in a thermoelectric assembly are different. The above being said, embodiments are envisioned in which the quantity of thermoelectric elements 190 in the first thermoelectric assembly 160 and the quantity of thermoelectric elements 190 in the second thermoelectric assembly 170 are different.

[0030] Further to the above, the fasteners 1 15 can extend through gaps defined between the thermoelectric elements 190 and/or gaps defined between the subassemblies, or cards, of the thermoelectric assemblies 160 and 170, for example. Also, further to the above, the fasteners 1 15 can be tightened to clamp the first cold- side plate 1 10, the first insulation layer 150, the first thermoelectric assembly 160, the hot-side heat exchanger 120, the second thermoelectric assembly 170, the second insulation layer 180, and the second cold-side plate 130 together such that the thermoelectric elements 190 are compressed against the hot-side heat exchanger 120 without interrupting the electrical connection between the thermoelectric elements 190 and/or between the sub-assemblies, or cards, of the thermoelectric assemblies 160 and 170.

[0031] A thermoelectric sub-assembly 170' of the thermoelectric assembly 170 is illustrated in FIG. 2. The thermoelectric sub-assembly 170' comprises a substrate 172 and a plurality of metal pads 192 mounted to the substrate 172. The metal pads 192 comprise direct bond copper (DBC) pads, for example, which are part of the electrical circuit of the thermoelectric sub-assembly 170'. In addition to or in lieu of the DBC pads, the metal pads 192 can comprise active metal brazing (AMB) pads, for example. The substrate 172 is comprised of a dielectric material and does not conduct current between the thermoelectric elements 190 and the metal pads 192. The thermoelectric legs 194 and 196 of the thermoelectric elements 190 are electrically and mechanically connected to the metal pads 192 through a bonding material.

[0032] In at least one instance, further to the above, the substrate 172 is comprised of alumina and the thermoelectric legs 194 and 196 are comprised of bismuth telluride (Bi ₂ Te ₃ ) blocks which are soldered to the metal pads 192, for example. In at least one instance, the substrate 172 is comprised of alumina and the thermoelectric legs 194 and 196 are comprised of tetrahedrite blocks which are soldered to the metal pads 192, for example. In either event, the solder may be any suitable solder, such as lead/tin eutectic solder, lead-free solders, and/or silver solders, for example. A reflow soldering process, for example, is utilized to bond the thermoelectric legs 194 and 196 to the metal pads 192. In at least one such instance, the thermoelectric sub-assembly 170' is positioned in a reflow oven which exposes the thermoelectric sub-assembly 170' to a temperature equal to or in excess of the reflow temperature of the solder. In addition to or in lieu of a reflow oven, an infrared lamp could be used, for example. In any event, the thermoelectric sub-assembly 170' is permitted to cool and/or is actively cooled after it has been removed from the reflow oven.

[0033] Further to the above, substrates comprising metal pads, such as metal pads 192, for example, are referred to as DBC and AMB substrates owing to the joining techniques used to attach the metal pads to the substrate. DBC and AMB substrates provide a desirable mechanical and electrical attachment for the thermoelectric devices 190 but can be expensive to manufacture given current manufacturing processes. Such manufacturing processes utilize high temperature vacuum processing, chemical etching, and additional metal plating, for example. Such manufacturing processes can also limit the thickness of the metal pads 192 that can be applied to the substrate 172, the size of the metal pads 192, and/or the spacing between the metal pads 192. In various instances, the high temperature processing may lead to high levels of built in mechanical stress within the metal pads 192 and/or the substrate 172 which, ultimately, can be detrimental to the reliability and efficiency of the thermoelectric sub-assembly 170'. In such instances, the thermal resistance of the thermoelectric sub-assembly 170' can increase when cracks develop during the operation of the TGU 100, thereby causing unwanted parasitic thermal resistances therein.

[0034] Other technologies can be used to attach the thermoelectric legs 194 and 196 to the metal pads 192. In at least one instance, high temperature braze materials are used to attach the thermoelectric legs 194 and 196 to the metal pads 192. In this context, a high temperature braze material is exposed to temperatures in excess of 500°C to bond the thermoelectric materials of the legs 194, 196 to the metal pads 192. Such processes can expose the thermoelectric materials comprising the legs 194 and 196 to significant stresses owing to the higher processing temperature necessary to achieve the liquid phase of the high

temperature braze materials. Such stresses can create cracks within the

thermoelectric materials which can create electrical and/or thermal opens within the legs 194 and 196, for example. Moreover, such processes can often cause the thermoelectric materials to oxidize and/or sublimate. In addition, some materials are not stable at such high assembly temperatures.

[0035] Other methods for mechanically and electrically coupling the thermoelectric elements 190 to the substrate 172 are contemplated. For instance, individual metal foils can be brazed to the thermoelectric legs 194 and 196 in lieu of using the metal pads 192. Such individual metal foils, however, add cost to the assembly process. Moreover, such individual metal foils would require a mechanically-compliant, thermally-conductive dielectric material that is stable at temperatures up to 400°C in order to obtain efficient thermal coupling and electrical isolation between the thermoelectric elements 190 and their surroundings. It is believed that such a material is not currently available on the commercial market. In addition to or in lieu of the above, spring-loaded contacts can be mounted to the substrate 172 which are configured to engage the hot side of the thermoelectric legs 194 and 196 and electrically couple the legs 194 and 196 to the electrical circuit of the thermoelectric sub-assembly 170'. Spring-loaded contacts allow for low mechanical stress within the thermoelectric materials but currently suffer from high cost and complexity.

[0036] Turning now to FIGS. 3 and 5, a thermoelectric sub-assembly 270' comprises a hot-side substrate 272 and a plurality of metal pads 192 mounted to the substrate 272. Similar to the above, referring primarily to FIG. 5, a thermoelectric element 190 is mounted to each metal pad 192 via a bonding material 193. More specifically, the thermoelectric legs 194 and 196 of a thermoelectric element 190 are bonded to a metal pad 192 via the bonding material 193. The thermoelectric subassembly 270' further comprises a cold-side substrate 240 and one or more electrical connectors 242 mounted to the substrate 240. The cold-side substrate 240 is comprised of any suitable dielectric material, such as alumina, for example. In at least one instance, the electrical connectors 242 comprise metal pads, for example, but can comprise any suitable electrically-conductive material. Similar to the above, the thermoelectric legs 194 and 196 of the thermoelectric element 190 are bonded to the electrical connectors 242 via a bonding material 243.

[0037] When the thermoelectric sub-assembly 270' is exposed to a temperature gradient between the hot-side substrate 272 and the cold-side substrate 240, which is represented by heat vectors Q in FIG. 5, electrical current can flow through a circuit extending through the thermoelectric sub-assembly 270'. A portion of the electrical circuit is depicted in FIG. 5 which includes a first electrical connector 242, bonding material 243, a thermoelectric leg 196, bonding material 193, a metal pad 192, more bonding material 193, a thermoelectric leg 194, more bonding material 243, and a second electrical connector 242. As the reader should appreciate, this electrical circuit extends through a plurality of thermoelectric elements 190 mounted to the thermoelectric sub-assembly 270'. As the reader should also appreciate, the metal pads 192 and the connectors 242 create, in the aggregate, a significant thermal resistance between the hot-side substrate 272 and the cold-side substrate 240 and, additionally, a significant electrical resistance in the electrical circuit. Such resistances reduce the efficiency of a thermoelectric generating unit.

[0038] Further to the above, turning now to FIG. 7, the thermal resistance of the thermoelectric sub-assembly 270' increases from the hot-side substrate 272 to the cold-side substrate 240. The total thermal resistance R _T between the hot-side substrate 272 and the cold-side of the thermoelectric leg 196, for example, is equal to the sum of thermal resistance F of the hot-side substrate 272, the thermal resistance R ₂ of the metal pad 192, the contact resistance between the hot-side substrate 272 and the metal pad 192, the thermal resistance R ₃ of the bonding material 193, the contact resistance between the metal pad 192 and the bonding material 193, the thermal resistance R ₄ of the thermoelectric leg 196, and the contact resistance between the bonding material 193 and the thermoelectric leg 196.

[0039] As discussed above, the metal pads 192, which mechanically and electrically couple the thermoelectric elements 190 to the substrate 172, increase the thermal resistance of the thermoelectric system 170. Stated another way, the metal pads 192 reduce the total power output of the TGU 100 for a given temperature difference between the heat source passing through the hot-side heat exchanger 120 and the heat sink, or sinks, adjacent the cold-side plates 1 10 and 130.

Discussed below is a thermoelectric assembly that comprises an electrically- conductive bonding material that directly bonds thermoelectric elements to a dielectric substrate and eliminates the need for using metal pads on the substrate to electrically couple the thermoelectric elements to the electrical circuit of the thermoelectric assembly.

[0040] Turning now to FIGS. 4 and 6, a thermoelectric sub-assembly 370' comprises a hot-side substrate 372 and, in addition, an electrical circuit including a plurality of thermoelectric elements 190. Referring primarily to FIG. 4, the electrical circuit comprises, among other things, an array of bonding material zones 392 defined on the substrate 372. The thermoelectric legs 194 and 196 of each thermoelectric element 190 are mounted to the substrate 372 via a bonding material zone 392. Referring primarily to FIG. 6, the thermoelectric sub-assembly 370' further comprises a cold-side substrate 340 and bonding material zones 342 defined on the substrate 340. The thermoelectric legs 194 and 196 are mounted to the substrate 340 via bonding material zones 342.

[0041] When the thermoelectric sub-assembly 370' is exposed to a temperature gradient between the hot-side substrate 372 and the cold-side substrate 340, which is represented by heat vectors Q in FIG. 6, electrical current can flow through the circuit extending through the thermoelectric sub-assembly 370'. A portion of the electrical circuit is depicted in FIG. 6 which includes a first bonding material zone 342, a thermoelectric leg 196, a bonding material zone 392, a thermoelectric leg 194, and a second bonding material zone 342. As the reader should appreciate, this electrical circuit extends through a plurality of thermoelectric elements 190 mounted to the thermoelectric sub-assembly 370'.

[0042] Further to the above, turning now to FIG. 8, the thermal resistance of the thermoelectric sub-assembly 370' increases from the hot-side substrate 372 to the cold-side substrate 340. The total thermal resistance R _T between the hot-side substrate 372 and the cold-side of the thermoelectric leg 196, for example, is equal to the sum of the thermal resistance F of the hot-side substrate 372, the thermal resistance R ₃ of the bonding zone 392, the contact resistance between the hot-side substrate 372 and the bonding zone 392, the thermal resistance R ₄ of the

thermoelectric leg 196, and the contact resistance between the bonding zone 392 and the thermoelectric leg 196. Notably, the total thermal resistance R _T does not include the thermal resistance R2 of the metal pad 192 of FIG. 7, or the contact resistances between the metal pad 192 and the adjacent components, and, as a result, the total thermal resistance of the thermoelectric sub-assembly 370' is less than the total thermal resistance of the thermoelectric sub-assembly 270'. As such, a thermoelectric generating unit (TGU) employing the thermoelectric sub-assembly 370' can have a higher power output and higher efficiency than when employing the thermoelectric sub-assembly 270' for a given temperature differential across the TGU.

[0043] Further to the above, referring again to FIGS. 4 and 6, the bonding material zones 392 are part of a trace layer defined on the hot-side substrate 372. The trace layer can be applied to the substrate 372 in any suitable manner. In various instances, the trace layer is applied to the substrate 372 utilizing a screen, or stencil, printing process, for example. In at least one such instance, the substrate 372 is positioned in a printer and a stencil is aligned with and positioned over the substrate 372. The stencil comprises an array of apertures defined therein which corresponds to the array of bonding material zones 392 depicted in FIG. 4. A solder paste is then wiped across the stencil to deposit the solder paste onto the substrate 372 through the apertures in the stencil to create the bonding material zones 392. The stencil is then removed from the substrate 372.

[0044] Further to the above, the solder paste comprises a mixture of at least one solder and at least one flux. In various instances, the solder paste comprises any suitable electrically-conductive bonding material, such as an electrically-conductive adhesive, a metal solder, and/or a metal-metal bonding material, for example. The electrically-conductive bonding material may comprise one or more of a silver sinter, a lead-free solder, and a lead-containing solder, for example. In at least one instance, the electrically-conductive bonding material may comprise one or more of a solid-liquid interdiffusion material, for example. Such a solid liquid interdiffusion material can comprise one or more of a nickel-indium material, a nickel-tin material, and a copper-tin material, for example. In any event, the solder paste applied to the substrate has a thickness in the range of about 10 μιη-1000 μιη, for example. The thickness in which the solder paste is applied to the substrate is largely determined by the thickness of the stencil. For instance, if a 100 μιη thickness of the solder paste is desired on the substrate, then a stencil having a 100 μιη can be used. The above being said, any suitable thickness can be used.

[0045] After the solder paste has been applied to the substrate 372, the

thermoelectric legs 164 and 166 are placed in the solder paste. The solder paste comprises a tacky consistency which can, to a certain extent, hold the legs 164 and 166 in position. The substrate 372 and the legs 164 and 166 are then heated in a reflow oven which melts, or at least partially melts, the solder paste. As mentioned above, the solder paste comprises at least one flux therein. The flux comprises a rosin flux, but can include any suitable flux. The presence of a flux in the solder paste can create proper wetting of the solder between the substrate 372 and the legs 164 and 166. That said, the presence of a flux can drastically affect the final bond line thickness of the solder. Depending on the amount and density of the fluxes and solders that are used, the final bond line thickness can be half, or even less than half, of the printed solder thickness, for example. As a result, if a final bond line thickness of 10 μιη-1000 μιη is desired, then the solder paste may need to be printed within a thickness of 20 μιη-2000 μιη, for example.

[0046] Although a flux in the solder paste can be useful, further to the above, embodiments are envisioned in which the solder paste does not require or include a flux. In at least one such instance, a flux can be applied to the legs 164 and 166 before they are inserted into the solder paste. As a result, the final bond line thickness of the solder can be very close to the printed thickness of the solder paste.

[0047] After the substrate 372 and the legs 164 and 166 have been properly heated, they can be allowed to cool and/or actively cooled by one or more cooling systems. In either event, the legs 164 and 166 are mounted to the surface of the substrate 372 via the bonding material zones 392 as a result of the above. The cold- side substrate 340 can undergo a similar solder stencil printing process and can be placed on the thermoelectric legs 164 and 166 before the assembly is placed in the reflow oven, for example. In such instances, the cold-side substrate 340 and the hot-side substrate 372 can be bonded to the legs 164 and 166 at the same time. Alternatively, the cold-side substrate 340 can be bonded to the thermoelectric legs 164 and 166 after the hot-side substrate 372 has been bonded to the legs 164 and 166. In further alternative embodiments, the hot-side substrate 372 can be bonded to the thermoelectric legs 164 and 166 after the cold-side substrate 340 has been bonded to the legs 164 and 166.

[0048] The electrically-conductive bonding material that attaches the thermoelectric legs 164 and 166 to the hot-side substrate 372 has a coefficient of thermal expansion that is similar to the coefficient of thermal expansion of the material comprising the hot side substrate 372. Similarly, the electrically-conductive bonding material that attaches the thermoelectric legs 164 and 166 to the cold-side substrate 340 has a coefficient of thermal expansion that is similar to the coefficient of thermal expansion of the material comprising the cold side substrate 340. Such an arrangement can allow the thermoelectric sub-assembly 370' to expand and contract without generating significant stresses within the electrically-conductive bonding material and/or the thermoelectric material comprising the thermoelectric elements 190. As a result, the thermoelectric sub-assembly 370' is configured to operate within large thermal gradients. To be considered a "similar" coefficient of thermal expansion, in various instances, the electrically-conductive bonding material has a coefficient of thermal expansion that does not differ more than or less than the coefficients of thermal expansion of the material comprising the hot-side substrate 372, the material comprising the cold-side substrate 340, and the material comprising thermoelectric elements 190 by 10%, or by 20%, or by 30%.

[0049] Further to the above, the hot-side substrate 372 and the cold-side substrate 340 are comprised of one or more dielectric materials. In various instances, the dielectric material of the substrate 372 and/or substrate 340 comprises a ceramic material and/or a dielectric coating on a metal surface, for example. Such a dielectric coating may comprise one or more of alumina, zirconia, zirconia toughened alumina, silicon nitride, silicon carbide, and aluminum nitride, for example.

[0050] As discussed above, the thermoelectric legs 194 and 196 are comprised of at least one semiconductor material. In various instances, the semiconductor material of the thermoelectric legs 194 and 196 comprises tetrahedrite, or one or more of tetrahedrite and a silicide, or still further, one or more of tetrahedrite, a silicide, a skutterudite material, a half-Heusler alloy, lead telluride (PbTe), silicon- germanium (SiGe), a zinc antimonide, a magnesium silicide stannide (Mg ₂ (SiSn)) system solid solution, a magnesium silicide (Mg ₂ Si), a HMS (higher manganese silicide) (MnSi), and a bismuth chalcogenide material, for example.

[0051] A method 400 for preparing a thermoelectric system is illustrated in FIG. 9. The method 400 comprises the step 410 of printing an electrically-conductive bonding material onto a hot-side substrate, wherein the hot-side substrate comprises a thermally-conductive first dielectric material. The method 400 can also comprise the step of printing an electrically-conductive bonding material onto a cold-side substrate, wherein the cold-side substrate comprises a second dielectric material. The first dielectric material is different than the second dielectric material; however, in other embodiments, the first dielectric material and the second dielectric material are the same. These steps can be performed in any suitable order. The method 400 further comprises the step 420 of bonding a plurality of thermoelectric element pairs to the hot-side substrate directly through an electrically-conductive bonding material. When a cold-side substrate is also bonded to the thermoelectric element pairs, the order of bonding the thermoelectric elements to the hot-side substrate and the cold-side substrate can occur in any suitable order, or simultaneously. Each thermoelectric pair comprises a n-type doped semiconductor leg and a p-type doped semiconductor leg; however, other arrangements of thermoelectric legs are contemplated. After the thermoelectric system has been prepared, turning now to FIG. 10, the hot-side substrate is exposed to a heat source according to step 510 to generate electrical power within the thermoelectric system. Alternatively, the thermoelectric system can be used as a Peltier device to create a temperature difference when a voltage is applied thereto. In fact, any of the thermoelectric systems disclosed herein can be used as a Peltier device.

[0052] Further to the above, the electrically-conductive bonding material can be a fritted conductor, or glass-metal frit, that adheres to both the thermoelectric elements and the substrate. Fritted conductors are metal/glass mixtures designed for producing conductive traces on substrates. One such glass-metal frit is cermet silver conductor 599-E from Electro-Science Laboratories, Inc. in King of Prussia, PA, USA, for example. Fritted conductors can be simultaneously used to produce conductive traces on a substrate and mechanically join thermoelectric elements to the substrate. Fritted conductors may be optimized so they form joints between the thermoelectric elements and the substrates at low temperatures - as low as 200°C if a solder glass is used as the frit bonding material, for example. By forming the joint at a lower temperature than is common with braze materials, one can reduce the stress in the thermoelectric elements. A low-temperature electrically-conductive bonding material bonds thermoelectric elements to a substrate at a temperature below that which is used to bond thermoelectric elements to a substrate using braze materials.

[0053] Further to the above, a glass-metal frit can comprise glass powder and metal fillers. The glass powder can include one or more silicate glasses, for example. The metal fillers can include silver, palladium, platinum, gold, nickel, tungsten, silver/platinum, silver/gold, platinum/gold, and combinations thereof, for example. The glass-metal frit can also include at least one organic binder which can make a viscous paste with the glass powder and the metal fillers. In various instances, the viscosity of the glass-metal frit paste can be adjusted by using one or more solvents, for example. The glass-metal paste is applied to a hot-side substrate of a thermoelectric assembly using a screen printing process, although any suitable process can be used. The screen printing process allows the glass-metal frit paste to be selectively applied to a trace circuit on the hot-side substrate. Alternatively, the screen printing process can be used to create an entire trace circuit out of the glass- metal frit. A screen printing process can also be used to apply the glass-metal frit paste to a cold-side substrate.

[0054] To the extent that organic binders and/or solvents are used with the glass- metal frit, the organic binders and/or solvents can be removed, or at least

substantially removed, therefrom during a thermal conditioning process. The thermal conditioning process comprises heating the hot-side substrate in an oven, for example, after the glass-metal frit has been applied thereto. The thermal

conditioning process can include any suitable time and temperature profile. In at least one instance, the hot-side substrate is heated at a temperature of about 100- 200°C for about 5-10 minutes, for example, to diffuse the solvents. The temperature can then be increased to about 325-350°C for about 10-20 minutes, for example, to burn out the organic binders. The temperature can then be increased to about 400- 450°C for about 5-10 minutes, for example, to melt the glass and bond the glass- metal frit to the hot-side substrate. As a result of the above, the porosity of the glass-metal frit is reduced and forms a compact glass-metal material with few, if any, inclusions. In some instances, a compressive force or pressure can be applied to the glass-metal frit during the entire duration of the thermal conditioning process. Alternatively, the compressive force or pressure is applied to the glass-metal frit only during the glass melting stage of the thermal conditioning process, for example.

[0055] In various instances, further to the above, the glass-metal frit forms electrically-conductive pads on the hot-side substrate. Thermoelectric legs can be bonded to the electrically-conductive pads during a second heating process using a glass-metal frit having the same composition as the glass-metal frit used to form the electrically-conductive pads. Alternatively, a glass-metal frit can be used to bond the thermoelectric legs to the electrically-conductive pads having a different composition than the glass-metal frit used to form the electrically-conductive pads. In either event, the second heating process can comprise any suitable time and temperature profile. In various instances, the time and temperature profile of the second heating process is the same as the thermal conditioning process discussed above. In other instances, the time and temperature profile of the second heating process is different than the thermal conditioning process discussed above. In at least one such instance, the glass-metal frit pads are cured at approximately 450°C and the thermoelectric elements are bonded to the glass-metal frit pads at approximately 350-400°C, for example. Bonding the thermoelectric elements at a lower

temperature than the pad curing temperature improves the stability of the

components in some instances.

[0056] In other embodiments, further to the above, the thermoelectric legs are positioned in the glass-metal frit on the hot-side substrate before the hot-side substrate is positioned in the oven to perform the thermal conditioning process discussed above. In such instances, the solvents and/or organic binders, if used, can be heated out of the glass-metal frit while the thermoelectric legs are positioned in the glass-metal frit. Moreover, the glass particles of the glass-metal frit can be melted while the thermoelectric legs are positioned in the glass-metal frit. In such instances, the glass-metal frit can form a bond with the hot-side substrate and the thermoelectric legs at the same time. In some instances, a compressive force or pressure can be applied to the thermoelectric elements to hold the thermoelectric elements against the hot-side substrate during the entire duration of the thermal conditioning process. Alternatively, the compressive force or pressure is applied to the thermoelectric elements only during the glass melting stage of the thermal conditioning process, for example.

[0057] Alternatively, further to the above, electrically-conductive pads comprising a glass-metal frit can be formed on the hot-side substrate and, in addition, on the ends of the thermoelectric legs before the thermoelectric legs are bonded to the hot-side substrate. In such instances, the glass-metal frit used to form the electrically- conductive pads on the thermoelectric legs has the same composition as the glass- metal frit used to form the electrically-conductive pads on the hot-side substrate. However, the glass-metal frit used to form the electrically-conductive pads on the thermoelectric legs can have a different composition than the glass-metal frit used to form the electrically-conductive pads on the hot-side substrate. Moreover, the glass- metal frit used to form the electrically-conductive pads of the thermoelectric legs and the hot-side substrate has the same composition as the glass-metal frit used to bond the electrically-conductive pads of the thermoelectric legs to the electrically- conductive pads of the hot-side substrate. However, the glass-metal frit used to form the electrically-conductive pads can have a different composition than the glass- metal frit used to bond the electrically-conductive pads of the thermoelectric legs to the electrically-conductive pads of the hot-side substrate.

[0058] In various instances, a first pad can be formed from one type of fritted conductor to attach a first end of a thermoelectric leg to a first substrate and a second pad can be formed from another type of fritted conductor to attach a second end of the thermoelectric leg to a second substrate. In other instances, one type of fritted conductor can be used to attach both ends of a thermoelectric leg to first and second substrates.

[0059] The low joining temperature and bonding nature of fritted conductors provides an additional benefit in that many different substrate materials can be used to further reduce stress in the thermoelectric leg. In various instances, a thick metal substrate, such as stainless steel, nickel, and/or aluminum, for example, can be used that has a closely-matched coefficient of thermal expansion (CTE) to the

thermoelectric material. The thick metal substrate can be finished with a dielectric material via a plasma spray process, a cold spray process, an anodization process, and/or an enameling process, for example. The thermoelectric elements could then be joined to the substrate using the fritted conductor. This embodiment allows the direct integration of the thermoelectric materials onto, for example, the stainless steel surface of a heat exchanger which could dramatically reduce the cost and improve the performance of a thermoelectric device by eliminating the need for a separate alumina substrate, providing lower mechanical stress than bonding to a ceramic substrate, and/or reducing the thermal resistance between the heat source and the thermoelectric material.

[0060] In various instances, further to the above, a glass-metal frit includes at least one glass frit and at least one metal. In at least one instance, the metal comprises a powder which is mixed with the glass frit. A glass-metal frit can also include at least one reactive metal oxide. In certain embodiments, a glass frit can be mixed with a reactive metal oxide to form a glass-reactive-metal-oxide frit. In various

embodiments, an electrical circuit defined on a substrate can be comprised of a material including a glass frit and at least one reactive metal oxide. In at least one such embodiment, portions of the electrical circuit can be comprised of a material including a glass frit and at least one metal. Although several of the examples provided herein are discussed in connection with a glass-metal frit, the reader should appreciate that such examples can be adapted for use with any of the compositions mentioned herein.

[0061] Further to the above, the maximum efficiency in which a thermoelectric material can convert heat energy into electricity can be computed using the following equation:

The first term in the equation is known as the Carnot efficiency. Generally, the greater the temperature difference across the thermoelectric material, the higher the efficiency. So, when designing a thermoelectric couple for operation, it is often desirable to be able to operate the thermoelectric material in the largest temperature gradient possible.

[0062] To achieve the maximum temperature difference, the cold side temperature is pushed as low as possible while the hot side temperature is pushed as high as possible. A problem can occur as the hot side temperature approaches the point where the thermoelectric material deteriorates, i.e., oxidizes, sublimates, and/or cracks, for example. This problem is further exacerbated when a rigid bond is desired between the thermoelectric material and an electrical connector on a substrate, for instance. Another problem occurs as the hot side temperature approaches the melting temperature of a solder, and/or another bonding material, which mechanically and/or electrically attaches the thermoelectric material to the electrical connector. In such instances, the bonding material may reflow causing a non-rigid joint. When this bonding material reflows, there is a risk of "pump out", i.e., the bonding material being squeezed out of the joint between the thermoelectric material and the electrical connector, particularly during thermal cycling where thermal expansion and contraction can cause a pumping motion.

Reflowing of the bonding material can also create a highly-resistive intermetallic formation which can degrade the joint resistance and robustness.

[0063] Using a braze to make the bond between the thermoelectric material and the electrical connector can allow the bond to withstand high temperature operation. Brazes usually reflow at temperatures greater than 600°C. Many thermoelectric materials, however, can not withstand the brazing temperatures above 600°C. There are a few brazes that will reflow at temperatures between 400°C and 600°C, but not many. The brazes that will reflow at temperatures between 400°C and 600°C , further to the above, happen be difficult to use, expensive, or not readily available. Thermoelectric materials, such as tetrahedrite, for example, may deteriorate during assembly if assembled with these brazes.

[0064] It is also advantageous, as can be seen in the above-provided equation, to be able to operate the thermoelectric material where the average ZT of the material is high. Many thermoelectric materials, such as lead telluride (PbTe), a skutterudite material, magnesium silicide (Mg ₂ Si), manganese silicide (MnSi), TAGS (tellurium-antimony- germanium-silver alloys), half-Heusler alloys, and/or tetrahedrite, for example, have, however, their highest ZT at or near the point where they start to deteriorate.

[0065] Lower temperature bonding enables effective bonding below the deterioration point of the thermoelectric material. It also has structural and stress benefits. One of the largest concerns in thermoelectric package design is thermal expansion mismatch between the components of a thermoelectric assembly. The large temperature gradients across a TGU, often exceeding 400°C, that are desired over a short length of material, such as 0.5mm to 10mm, for example, can lead to extreme thermal expansion mismatch. The hot side of the thermoelectric assembly expands so much more than the cold side that the package tears itself apart. This can be improved through the use of different materials on the hot and cold sides of the package, but is difficult to fully control.

[0066] There is also more localized stress between the thermoelectric material and the electrical connector. One of the highest points of stress can be created during assembly. If the thermoelectric material is brazed at temperatures in excess of 600°C and cooled down to ambient temperature, for example, the zero point, or freeze point, occurs when the braze resolidifies. Any change in temperature from this freeze point can create thermal stress within a joint if the two materials that are being joined have considerably different coefficients of thermal expansion (CTEs). Copper is often a desirable material to be used as a shunt because of its high electrical and thermal conductivity. Copper has a considerably different CTE, i.e., approximately 16-25 μιη/ιη' in a temperature range between 0-1000°C, than many thermoelectric materials which have a CTE of approximately 10-15 μιη/ιτι' over the same temperature range. This difference can build up to tens or hundreds of microns depending on the size of the joint and the temperature difference. Such an expansion difference stresses the joint and can often cause joint failure and/or a failure in one or both materials being joined.

[0067] Using a lower temperature bonding method provides a more advantageous "freeze" point to help manage a thermal expansion mismatch within a thermoelectric system. Instead of having to withstand the expansion mismatch from 600°C to ambient temperature during the assembly, in such instances, the joint would only have to experience the expansion mismatch from about 200- 300°C to the ambient

temperature, for example. In various embodiments, the low temperature bonding material connection between the thermoelectric material and the electrical connectors is made using silver sinter or nano-silver bonding, for example. Such a bonding material provides a higher modulus and more flexible joint than many solders or brazes. It also provides higher electrical and thermal conductivity at the joint between the

thermoelectric material and the electrical connectors than many solders or brazes. As a result, a thermoelectric system utilizing such bonding materials can be used in environments having large temperature gradients.

[0068] As discussed above, thermoelectric materials can deteriorate when exposed to elevated temperatures. Among other things, the thermoelectric materials can oxidize, sublimate, and/or crack. Provided herein are certain embodiments in which the thermoelectric material is bonded to an electrical connector bonding below the deterioration point of the thermoelectric material.

[0069] Further to the above, a silver sinter can be used as an electrically-conductive bonding material. In various instances, the silver sinter comprises a paste. The paste comprises powdered silver and, in certain instances, other powdered metals. The powdered silver and other powdered metals can be mixed using a vibration mixing process, for example. The paste can also comprise at least one flux. The paste can be applied to a substrate using a stencil printing process, such as the processes described above, for example. In at least one instance, the stencil is approximately 75 μιη thick which can produce a trace layer of silver sinter on the substrate which is approximately 75 μιη thick, for example. Notably, the final bond line thickness of the silver sinter may be less than the thickness of the printed paste after the substrate is exposed to a reflow process, for example. Depending on the amount and density of the flux present in the paste, the final bond line thickness may be approximately half, or less than half, than the thickness of the printed paste. In at least one instance, the approximately 75 μιη thick printed paste will result in an approximately 30 μιη final bond line thickness after the reflow process, for example.

[0070] Further to the above, the reflow process may utilize any suitable time and temperature parameters, although a chart depicting one exemplary embodiment is provided in FIG. 1 1 . The temperature profile illustrated in FIG. 1 1 comprises an approximately 30 minute ramp up from an ambient temperature to 230°C followed by an approximately 90 minute hold at 230°C. Thereafter, the temperature profile comprises an approximately 30 minute ramp down to the ambient temperature. In various instances, the substrate may require additional time outside of the reflow oven for it to cool to the ambient temperature. In any event, the reflow process of FIG. 1 1 is performed at atmospheric pressure, or at least substantially atmospheric pressure; however, a pressurized atmosphere can be used during the bonding process. Similar to the above, a silver sinter reflow process can be used to bond substrates to both the hot and cold sides of the thermoelectric legs at the same time or at different times.

[0071] In various instances, the components of a thermoelectric assembly are cleaned before they are assembled. In at least one instance, the substrate of a thermoelectric assembly is plasma cleaned before the silver sinter paste is applied to the substrate, for example.

[0072] In one embodiment, the silver sinter, or other bonding material, can be used with a silver metallization layer. In another embodiment, the silver sinter, or other bonding material, can be used with a gold metallization layer. In another embodiment, the silver sinter, or other bonding material, can be used with a nickel or molybdenum metallization layer. In one embodiment, the thermoelectric material that is being bonded is tetrahedrite. In another embodiment, the thermoelectric material comprises a skutterudite material, a half-Heusler alloy, lead telluride (PbTe), silicon-germanium (SiGe), a zinc antimonide, magnesium silicide stannide (Mg ₂ SiSn), magnesium silicide (Mg ₂ Si), manganese silicide (MnSi), TAGS (tellurium-antimony-germanium-silver alloys), and/or bismuth telluride (Bi ₂ Te ₃ ), for example. In another embodiment, the electrical and thermal connection between the thermoelectric material and the connectors is made using transient liquid phase (TLP) bonding. TLP can include copper, nickel, silver, gold with either indium and/or lead, and/or combinations thereof, for example. In another embodiment, the electrical and thermal connection between the thermoelectric material and the connectors is made using nano-copper bonding, for example.

[0073] In addition to or in lieu of the above, any of the bonding materials described herein can be used to bond and/or create portions of the thermoelectric circuit on a substrate. In at least one such instance, the thermoelectric circuit comprises shunts to conduct the current flowing through the thermoelectric circuit. The bonding materials described herein can be used to bond such shunts to a substrate.

[0074] The embodiments disclosed herein provide tremendous flexibility in the substrate and bond materials that can be used to retain a simple, low-cost package that exhibits low stress in the thermoelectric elements - and thereby high reliability - in high temperature, i.e., greater than 300°C, environments, for example.

[0075] The thermoelectric systems disclosed herein can be adapted for use with automotive systems. Certain automotive systems comprise a propulsion system including an internal combustion engine which generates exhaust heat. One or more of the thermoelectric systems disclosed herein can be adapted to reclaim that exhaust heat. In at least one instance, a thermoelectric system is mounted to and/or downstream of a catalytic converter which treats the exhaust stream from the internal combustion engine. The thermoelectric system can be mounted within the catalytic converter and/or to an exterior housing of the catalytic converter, for example. In certain instances, the thermoelectric system can be embedded within the exterior housing of the catalytic converter. In various instances, a voltage potential generated by a catalytic converter thermoelectric system can be used to power one or more sensor systems configured to evaluate the exhaust passing through the catalytic converter, for example. [0076] Further to the above, heat generated by an internal combustion engine is often discharged to the surrounding environment through an air-cooled heat exchanger via a fluidic thermodynamic circuit. One or more of the thermoelectric systems disclosed herein can be adapted to reclaim that discharged heat. In at least one instance, a thermoelectric system is mounted to a heat exchanger, or radiator, of the fluidic thermodynamic circuit which cools the fluid flowing through the circuit. In various instances, a voltage potential generated by a radiator thermoelectric system can be used to power one or more sensor systems configured to evaluate the fluid passing through the radiator, for example. In various instances, a thermoelectric system can be mounted to any suitable portion of the fluidic thermodynamic circuit and/or mounted directly to the block of the internal combustion engine, for example. In at least one instance, further to the above, a thermoelectric system can be mounted to an exhaust manifold which connects the exhaust system to the engine block, for example.

[0077] The entire disclosures of the following patents are incorporated by reference herein:

- U.S. Patent No. 8,603,940, entitled AUTOMOBI LE EXHAUST GAS CATALYTIC CONVERTER, which issued on December 10, 2013;

- U.S. Patent No. 8,650,864, entitled COMBINATION LIQUID-COOLED EXHAUST MANIFOLD ASSEMBLY AND CATALYTIC CONVERTER ASSEMBLY FOR A MARINE ENGINE, which issued on February 18, 2014;

- U.S. Patent No. 8,544,257, entitled ELECTRICALLY STIMULATED CATALYTIC CONVERTER APPARATUS, AND METHOD OF USING SAME, which issued on October 1 , 2013;

- U.S. Patent No. 7,858,052, entitled CATALYTIC CONVERTER OPTIMIZATION, which issued on December 28, 2010;

- U.S. Patent No. 7,767,622, entitled CATALYTIC CONVERTER WITH IMPROVED START-UP BEHAVIOR, which issued on August 3, 2010;

- U.S. Patent No. 7,051 ,522, entitled THERMOELECTRIC CATALYTIC

CONVERTER TEMPERATURE CONTROL, which issued on May 30, 2006;

- U.S. Patent No. 9,276, 188, entitled THERMOELECTRIC-BASED POWER

GENERATION SYSTEMS AND METHODS, which issued on March 1 , 2016;

- U.S. Patent No. 9,006,556, entitled THERMOELECTRIC POWER GENERATOR FOR VARIABLE THERMAL POWER SOURCE, which issued on April 14, 2015; - U.S. Patent No. 8,646,261 , entitled THERMOELECTRIC GENERATORS

INCORPORATING PHASE-CHANGE MATERIALS FOR WASTE HEAT

RECOVERY FROM ENGINE EXHAUST, which issued on February 1 1 , 2014;

- U.S. Patent No. 6,986,247, entitled THERMOELECTRIC CATALYTIC POWER GENERATOR WITH PREHEAT, which issued on January 17, 2006; and

- U.S. Patent No. 4,029,472, entitled THERMOELECTRIC EXHAUST GAS

SENSOR, which issued on June 14, 1977.

[0078] Certain automotive systems, further to the above, comprise a propulsion system including an electric motor powered by one or more batteries. In use, the batteries can generate a significant amount of thermal energy owing to high power demands from the electric motor. Similarly, the electric motor can generate a significant amount of thermal energy during use. Such thermal energy can be harvested and reclaimed by one or more of the thermoelectric systems disclosed herein. In various instances, a battery comprises one or more battery cells positioned within an outer housing. The battery cells comprise lithium-ion battery cells, for example. In use, the heat generated by the battery cells radiates through the outer housing of the battery. In certain instances, the thermoelectric elements of a thermoelectric system are mounted to the outer housing of the battery. In various instances, the thermoelectric elements of a thermoelectric system are positioned intermediate two battery cells.

[0079] In addition to or in lieu of the above, a thermoelectric system disclosed herein can be used to cool a battery, for example. In such instances, the

thermoelectric system is operated as a Peltier device. In at least one such instance, the thermoelectric elements of the thermoelectric system are positioned on, at, and/or near the hottest portions of the battery, for example, to prevent, or at least reduce the possibility of the battery entering into a thermal runaway condition.

[0080] The entire disclosures of the following patents are incorporated by reference herein:

- U.S. Patent No. 7,781 ,097, entitled CELL THERMAL RUNAWAY PROPAGATION RESISTANCE USING AN INTERNAL LAYER OF INTUMESCENT MATERIAL, which issued on August 24, 2010;

- U.S. Patent No. 7,763,381 , entitled CELL THERMAL RUNAWAY PROPAGATION RESISTANCE USING DUAL INTUMESCENT MATERIAL LAYERS, which issued on July 27, 2010; - U.S. Patent No. 7,736,799, entitled METHOD AND APPARATUS FOR

MAINTAINING CELL WALL INTEGRITY DURING THERMAL RUNAWAY USING AN OUTER LAYER OF INTUMESCENT MATERIAL, which issued on June 15, 2010;

- U.S. Patent No. 8, 168,315, entitled METHOD FOR DETECTING BATTERY THERMAL EVENTS VIA BATTERY PACK ISOLATION MONITORING, which issued on May 1 , 2012;

- U.S. Patent No. 8, 154,256, entitled BATTERY THERMAL EVENT DETECTION SYSTEM USING AN ELECTRICAL CONDUCTOR WITH A THERMALLY INTERRUPTIBLE INSULATOR, which issued on April 10, 2012;

- U.S. Patent No. 8, 153,290, entitled HEAT DISSIPATION FOR LARGE BATTERY PACKS, which issued on April 10, 2012;

- U.S. Patent No. 8, 1 17,857, entitled INTELLIGENT TEMPERATURE CONTROL SYSTEM FOR EXTENDING BATTERY PACK LIFE, which issued on February 21 , 2012;

- U.S. Patent No. 8,082,743 , entitled BATTERY PACK TEMPERATURE

OPTIMIZATION CONTROL SYSTEM, which issued on December 27, 201 1 ;

- U.S. Patent No. 8,092,081 , entitled BATTERY THERMAL EVENT DETECTION SYSTEM USING AN OPTICAL FIBER, which issued on January 10, 2012;

- U.S. Patent No. 8,059,007, entitled BATTERY THERMAL EVENT DETECTION SYSTEM USING A THERMALLY INTERRUPTIBLE ELECTRICAL CONDUCTOR, which issued on November 15, 201 1 ;

- U.S. Patent No. 7,940,028, entitled THERMAL ENERGY TRANSFER SYSTEM FOR A POWER SOURCE UTILIZING BOTH METAL-AIR AND NON-METAL-AIR BATTERY PACKS, which issued on May 10, 201 1 ;

- U.S. Patent No. 7,939, 192, entitled EARLY DETECTION OF BATTERY CELL THERMAL EVENT, which issued on May 10, 201 1 ;

- U.S. Patent No. 7,820,319, entitled CELL THERMAL RUNAWAY PROPAGATION RESISTANT BATTERY PACK, which issued on October 26, 2010;

- U.S. Patent No. 7,789, 176, entitled ELECTRIC VEHICLE THERMAL

MANAGEMENT SYSTEM, which issued on September 7, 2010;

- U.S. Patent No. 8, 178,227, entitled METHOD FOR DETECTING BATTERY THERMAL EVENTS VIA BATTERY PACK ISOLATION RESISTANCE MONITORI NG, which issued on May 15, 2012; - U.S. Patent No. 8, 168,315, entitled METHOD FOR DETECTING BATTERY THERMAL EVENTS VIA BATTERY PACK ISOLATION MONITORING, which issued on May 1 , 2012;

- U.S. Patent No. 7,890,218, entitled CENTRALIZED MULTI-ZONE COOLING FOR INCREASED BATTERY EFFICIENCY, which issued on February 15, 201 1 ;

- U.S. Patent No. 8,481 , 191 , entitled RIGID CELL SEPARATOR FOR MINIMIZING THERMAL RUNAWAY PROPAGATION WITHI N A BATTERY PACK, which issued on July 9, 2013;

- U.S. Patent No. 8,402,776, entitled THERMAL MANAGEMENT SYSTEM WITH DUAL MODE COOLANT LOOPS, which issued on March 26, 2013;

- U.S. Patent No. 8,367,233, entitled BATTERY PACK ENCLOSURE WITH

CONTROLLED THERMAL RUNAWAY RELEASE SYSTEM, which issued on February 5, 2013;

- U.S. Patent No. 8,313,850, entitled METHOD FOR DETECTING BATTERY THERMAL EVENTS VIA BATTERY PACK PRESSURE MONITORING, which issued on November 20, 2012;

- U.S. Patent No. 8,263,250, entitled LIQUID COOLING MANIFOLD WITH MULTIFUNCTION THERMAL INTERFACE, which issued on September 1 1 , 2012;

- U.S. Patent No. 8,541 , 127, entitled OVERMOLDED THERMAL INTERFACE FOR USE WITH A BATTERY COOLING SYSTEM, which issued on September 24, 2013;

- U.S. Patent No. 8,968,949, entitled METHOD OF WITHDRAWING HEAT FROM A BATTERY PACK, which issued on March 3, 2015;

- U.S. Patent No. 8,907,594, entitled COOLING SYSTEMS AND METHODS, which issued on December 9, 2014;

- U.S. Patent No. 8,906,541 , entitled BATTERY MODULE WITH INTEGRATED THERMAL MANAGEMENT SYSTEM, which issued on December 9, 2014;

- U.S. Patent No. 8,899,492, entitled METHOD OF CONTROLLING SYSTEM TEMPERATURE TO EXTEND BATTERY PACK LIFE, which issued on December 2, 2014;

- U.S. Patent No. 8,875,828, entitled VEHICLE BATTERY PACK THERMAL

BARRIER, which issued on November 4, 2014;

- U.S. Patent No. 8,758,924, entitled EXTRUDED AND RIBBED THERMAL

INTERFACE FOR USE WITH A BATTERY COOLI NG SYSTEM, which issued on June 24, 2014; - U.S. Patent No. 9,093,726, entitled ACTIVE THERMAL RUNAWAY MITIGATION SYSTEM FOR USE WITHIN A BATTERY PACK, which issued on July 28, 2015; and

- U.S. Patent No. 9,030,063, entitled THERMAL MANAGEMENT SYSTEM FOR USE WITH AN INTEGRATED MOTOR ASSEMBLY, which issued on May 12, 2015.

[0081] The entire disclosures of the following patents are incorporated by reference herein:

- U.S. Patent No. 9,306, 143, entitled HIGH EFFICIENCY THERMOELECTRIC GENERATION, which issued on April 5, 2016;

- U.S. Patent No. 9,293,680, entitled CARTRIDGE-BASED THERMOELECTRIC SYSTEMS, which issued on March 22, 2016; and

- U.S. Patent No. 9,276, 188, entitled THERMOELECTRIC-BASED POWER

GENERATION SYSTEMS AND METHODS, which issued on March 1 , 2016.

[0082] The entire disclosures of the following patent applications are incorporated by reference herein:

- U.S. Patent Application Publication No. 2014/0190185, entitled SYSTEM AND METHOD FOR PREVENTING OVERHEATING OR EXCESSIVE BACKPRESSURE IN THERMOELECTRIC SYSTEMS, which published on July 10, 2014;

- U.S. Patent Application Publication No. 2013/0276849, entitled TEG-POWERED COOLING CIRCUIT FOR THERMOELECTRIC GENERATOR, which published on October 24, 2013; and

- U.S. Patent Application Publication No. 2013/0255739, entitled PASSIVELY COOLED THERMOELECTRIC GENERATOR CARTRIDGE, which published on October 3, 2013.

[0083] The Applicant of the present application also owns the patents and patent applications identified below, the entire disclosures of which are incorporated by reference herein:

- U.S. Patent Application Serial No.1 1/645,236, entitled METHODS OF

FABRICATING NANOSTRUCTURES AND NANOWIRES AND DEVICES FABRICATED THEREFROM, now U.S. Patent No. 7,834,264;

- U.S. Patent Application Serial No. 12/487,893, entitled IMPROVED MECHANICAL STRENGTH & THERMOELECTRIC PERFORMANCE IN METAL CHALCOGENIDE MQ (M=GE,SN,PB AND Q=S, SE, TE) BASED COMPOSITIONS, now U.S. Patent No. 8,277,677; - U.S. Patent Application Serial No. 12/882,580, entitled THERMOELECTRICS COMPOSITIONS COMPRISING NANOSCALE INCLUSIONS IN A CHALCOGENIDE MATRIX, now U.S. Patent No. 8,778,214;

- U.S. Patent Application Serial No. 12/943, 134, entitled UNI WAFER

THERMOELECTRIC MODULES, now U.S. Patent Application Publication No. 201 1 /01 14146;

- U.S. Patent Application Serial No. 13/299, 179, entitled ARRAYS OF LONG NANOSTRUCTURES IN SEMICONDUCTOR MATERIALS AND METHODS THEREOF, now U.S. Patent No. 9,240,328;

- U.S. Patent Application Serial No. 13/308,945, entitled LOW THERMAL

CONDUCTIVITY MATRICES WITH EMBEDDED NANOSTRUCTURES AND METHODS THEREOF, now U.S. Patent No. 8,736,01 1 ;

- U.S. Patent Application Serial No. 13/331 ,768, entitled ARRAYS OF FILLED NANOSTRUCTURES WITH PROTRUDING SEGMENTS AND METHODS THEREOF, now U.S. Patent Application Publication No. 2012/0152295;

- U.S. Patent Application Serial No. 13/364, 176, entitled ELECTRODE

STRUCTURES FOR ARRAYS OF NANOSTRUCTURES AND METHODS THEREOF, now U.S. Patent Application Publication No. 2012/0247527;

- U.S. Patent Application Serial No. 13/749,470, entitled MODULAR

THERMOELECTRIC UNITS FOR HEAT RECOVERY SYSTEMS AND METHODS THEREOF, now U.S. Patent No. 9,318,682;

- U.S. Patent Application Serial No. 13/760,977, entitled BULK NANOHOLE STRUCTURES FOR THERMOELECTRIC DEVICES AND METHODS FOR MAKING THE SAME, now U.S. Patent Application Publication No. 2013/0175654;

- U.S. Patent Application Serial No. 13/786,090, entitled BULK NANO-RIBBON AND/OR NANO-POROUS STRUCTURES FOR THERMOELECTRIC DEVICES AND METHODS FOR MAKING THE SAME, now U.S. Patent No. 9,051 , 175;

- U.S. Patent Application Serial No. 13/947,400, entitled METHOD AND

STRUCTURE FOR THERMOELECTRIC UNICOUPLE ASSEMBLY, now U.S. Patent No. 9,257,627;

- U.S. Patent Application Serial No. 14/053,452, entitled STRUCTURES AND METHODS FOR MULTI-LEG PACKAGE THERMOELECTRIC DEVICES, now U.S. Patent Application Publication No. 2014/0182644; - U.S. Patent Application Serial No. 14/059,362, entitled NANOSTRUCTURED THERMOELECTRIC ELEMENTS AND METHODS OF MAKING THE SAME, now U.S. Patent No. 9,082,930;

- U.S. Patent Application Serial No. 14/062,803, entitled BULK-SIZE

NANOSTRUCTURED MATERIALS AND METHODS FOR MAKING THE SAME BY SINTERING NANOWIRES, now U.S. Patent Application Publication No.

2014/01 16491 ;

- U.S. Patent Application Serial No. 14/297,444, entitled SILICON-BASED

THERMOELECTRIC MATERIALS INCLUDING ISOELECTRONIC IMPURITIES, THERMOELECTRIC DEVICES BASED ON SUCH MATERIALS, AND METHODS OF MAKING AND USING SAME, now U.S. Patent Application Publication No.

2014/0360546;

- U.S. Patent Application Serial No. 14/469,404, entitled THERMOELECTRIC DEVICES HAVING REDUCED THERMAL STRESS AND CONTACT RESISTANCE, AND METHODS OF FORMING AND USING THE SAME, now U.S. Patent No.

9,065,017;

- U.S. Patent Application Serial No. 14/679,837, entitled FLEXIBLE LEAD FRAME FOR MULTI-LEG PACKAGE ASSEMBLY, now U.S. Patent Application Publication No. 2015/0287901 ;

- U.S. Patent Application Serial No. 14/682,471 , entitled ULTRA-LONG SILICON NANOSTRUCTURES, AND METHODS OF FORMING AND TRANSFERRING THE SAME, now U.S. Patent Application Publication No. 2016/0035829;

- U.S. Patent Application Serial No. 14/686,641 , entitled MODULAR

THERMOELECTRIC UNITS FOR HEAT RECOVERY SYSTEMS AND METHODS THEREOF, now U.S. Patent Application Publication No. 2015/0287902;

- U.S. Patent Application Serial No. 14/823,738, entitled TIN SELENIDE SINGLE CRYSTALS FOR THERMOELECTRIC APPLICATIONS, now U.S. Patent

Application Publication No. 2016/0049568;

- U.S. Patent Application Serial No. 14/872,681 , entitled THERMOELECTRIC GENERATING UNIT AND METHODS OF MAKING AND USING SAME;

- U.S. Patent Application Serial No. 14/872,898, entitled THERMOELECTRIC GENERATORS FOR RECOVERING WASTE HEAT FROM ENGI NE EXHAUST, AND METHODS OF MAKING AND USING SAME, now U.S. Patent Application Publication No. 2016/0099398; - U.S. Patent Application Serial No. 14/971 ,337, entitled ELECTRICAL AND

THERMAL CONTACTS FOR BULK TETRAHEDRITE MATERIAL, AND METHODS OF MAKING THE SAME, now U.S. Patent Application Publication No.

2016/0190420; and

- International Application Patent No. PCT/US2015/053434, entitled

THERMOELECTRIC GENERATING UNIT AND METHODS OF MAKING AND USING SAME, now WO Publication No. 2016/054333.

[0084] Although various devices have been described herein in connection with certain embodiments, modifications and variations to those embodiments may be implemented. Also, where materials are disclosed for certain components, other materials may be used. Furthermore, according to various embodiments, a single component may be replaced by multiple components, and multiple components may be replaced by a single component, to perform a given function or functions. The foregoing description and following claims are intended to cover all such

modifications and variations.

[0085] Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. Well- known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. The reader will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and illustrative. Variations and changes thereto may be made without departing from the scope of the claims.

[0086] The terms "comprise" (and any form of comprise, such as "comprises" and "comprising"), "have" (and any form of have, such as "has" and "having"), "include" (and any form of include, such as "includes" and "including") and "contain" (and any form of contain, such as "contains" and "containing") are open-ended linking verbs. As a result, a thermoelectric system, device, or apparatus that "comprises," "has," "includes" or "contains" one or more elements possesses those one or more elements, but is not limited to possessing only those one or more elements.

Likewise, an element of a system, device, or apparatus that "comprises," "has," "includes" or "contains" one or more features possesses those one or more features, but is not limited to possessing only those one or more features. [0087] It is to be understood that certain descriptions of the embodiments described herein have been simplified to illustrate only those elements, features, and aspects that are relevant to a clear understanding of the disclosed embodiments, while eliminating, for purposes of clarity, other elements, features, and aspects. Persons having ordinary skill in the art, upon considering the present description of the disclosed embodiments, will recognize that other elements and/or features may be desirable in a particular implementation or application of the disclosed

embodiments. However, because such other elements and/or features may be readily ascertained and implemented by persons having ordinary skill in the art upon considering the present description of the disclosed embodiments, and are therefore not necessary for a complete understanding of the disclosed embodiments, a description of such elements and/or features is not provided herein. As such, it is to be understood that the description set forth herein is merely exemplary and illustrative of the disclosed embodiments and is not intended to limit the scope of the claims.

[0088] Also, any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited herein is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicants reserve the right to amend the present disclosure, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein.

[0089] The grammatical articles "one", "a", "an", and "the", as used herein, are intended to include "at least one" or "one or more", unless otherwise indicated. Thus, the articles are used herein to refer to one or more than one (i.e., to at least one) of the grammatical objects of the article. By way of example, "a component" means one or more components, and thus, possibly, more than one component is contemplated and may be employed or used in an implementation of the described embodiments.

[0090] Any patent, publication, or other disclosure material that is said to be incorporated, in whole or in part, by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.

[0091] The present disclosure includes descriptions of various embodiments. It is to be understood that all embodiments described herein are exemplary, illustrative, and non-limiting.