Thermoelectric generators -- US6620994

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United States Patent

US006620994B2

(2) (10) Patent No.: US 6,620,994 B2
Rossi (45) Date of Patent: Sep. 16, 2003
(54) THERMOELECTRIC GENERATORS 4,929,282 A * 5/1990 Brun et al. 136/239
4,999,576 A 3/1991 Levinson . 324/142
75) I tor: Andi Rossi, Bedford, NH (US
(75) Inventor malrea HOSS, Heron’, (Us) (List continued on next page.)
(73) Assignee: Nnws). Technologies, Inc., Bedford, FOREIGN PATENT DOCUMENTS
WO WO 00/59047 10/2000
(*) Notice: Subject to any disclaimer, the term of this wo WO 01/69657 A2 — 9/2001
patent is extended or adjusted under 35
U.S.C. 154(b) by 0 days. OTHER PUBLICATIONS
“Evaluate & Demostrate Broad Applications For Thermo-
(21) Appl. No.: 09/971,280 electric Devices for DOE’s Office of Fossil Energy” DOE
Contract No. DE~-AM26-99FT40465, Product, Program
22 : > ,
(22) Filed: Oct. 4, 2001 and Project Engineering and Analysis (P3EA) Task 51304
(65) Prior Publication Data submitted to: US Dept. of Energy, National Energy Tech-
nology Laboratory by: Concurrent Technologies Nov. 21,
US 2002/0046762 Al Apr. 25, 2002 2001.
Related U.S. Application Data “Evaluate & Demonstrate Broad Applications for Thermo-
electric Devices for DOE’s Office of Industrial Technolo-
(63) Continuation of application No. 09/679,041, filed on Oct. 4, 848" DOE Contract No. DE~AM26-99F'T40465, Product,
2000, now abandoned Program and Project Engineering and Analysis (P3EA) Task
(60) Provisional application No. 60/312,617, filed on Aug. 15, 50517B submitted to: US Dept of Energy, National Energy
Zn01, and provisional application No. 60/158,530, filed on Technology Laboratory by: Concurrent Technologies Cor-
ct. 8, . poration (CTC), Energy and Environmental Efficiency Man-
(51) Int. Cl.’ . . HOLL 35/34; HOLL 35/16; agement, Inc. (E3M, Inc.) and Leonardo Technologies, Inc.
HO1L 35/20 (LTT) Nov. 27, 2001.
(52) US. Ch ee 136/201; 136/238; 136/239; . . .
136/240; 136/241 Primary Examiner—Patrick Ryan
(58) Field of Search 136/200, 201 Assistant Examiner—Thomas H. Parsons
136/236.1, 238, 239 240, 241 (74) Attorney, Agent, or Firm—Grossman, Tucker,
pee ee Perreault & Pfleger, PLLC
(56) References Cited (57) ABSTRACT
U.S. PATENT DOCUMENTS A thermoelectric module including a couple formed between
3,095,330 A 6/1963 Epstein et al. two bismuth telluride thermoelectrodes. The first thermo-
3,136,134 A 6/1964 Smith ..... electrode is doped with palladium, selenium, or a combina-
3,182,391 A * 5/1965 Charland et al. tion of the two. The second thermoelectrode is doped with
3,248,777 A 5/1966 Stoll ... antimony, gold, or a combination of the two. Multiple
34 1,858 A 6/1969 Dingwall thermoelectric modules may be used in series and parallel to
38 Front a sions Patheabers 6 achieve the desired voltage and current outputs.
4,292,579 A 9/1981 Constant .
4,463,214 A 7/1984 Lowther . 136/208 17 Claims, 3 Drawing Sheets

10
24
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18 16 7 20
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US 6,620,994 B2

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U.S. PATENT DOCUMENTS 6,147,293 A * 11/2000 Tauchi et al. . 136/236.1
“ 6,222,242 BL 4/2001 Konishi et al. 257/467
5,108,515 A * 4/1992 136/201 6,225,548 BL 5/2001 Sakakibara et al. . 136/201
Seale ante Ben 6,226,994 BL 5/2001 Yamada et al. . 62/37
5,419,780 A oios anos 6,233,944 BL 5/2001 Yamada et al. - 62/3.7
5502067 A 1/1997 320/15 6,269,645 B1 8/2001 Yamaguchi 60/653
5,763,293 A 6/1998 Yamashita et al. 438/55 Ce BE conor wus etal 136/201
5.856.210 A 1/1999 | 438/55 6,274,803 B1 8/2001 Yos! ioka et al. 136/201
So2l087 A 7/1999 62/32 6,288,321 B1 9/2001 Fleurial et al. 136/205
6,002,081 A 12/1999 136/203
6,103,967 A 8/2000 136/201 * cited by examiner

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U.S. Patent Sep. 16, 2003 Sheet 1 of 3 US 6,620,994 B2

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U.S. Patent Sep. 16, 2003 Sheet 3 of 3 US 6,620,994 B2

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US 6,620,994 B2

1
THERMOELECTRIC GENERATORS

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S.
patent application Ser. No. 09/679,041, filed on Oct. 4, 2000,
now abandoned, which claims the benefit of U.S. provi-
sional application Ser. No. 60/158,530 filed Oct. 8, 1999,
now abandoned, and claims priority to U.S. provisional
application Ser. No. 60/312,617, filed Aug. 15, 2001. The
teachings of both applications are incorporated herein by
reference.

FIELD OF THE INVENTION

The present invention relates to the thermoelectric gen-
eration of electricity.

BACKGROUND OF THE INVENTION

There are three principle thermoelectric phenomena: the
Seebeck effect, the Peltier effect, and the Thomson effect.
Advantageous thermoelectric generation is based on the
interacting relationships of these effects. The Seebeck effect
is the production of an electrical potential occurring when
two different conducting materials are joined to form a
closed circuit with junctions at different temperatures. The
Peltier effect relates to the absorption of heat occurring when
an electric current passes through a junction of two different
conductors. The third thermoelectric principle, the Thomson
effect, is the reversible evolution of heat that occurs when an
electric current passes through a homogeneous conductor
having a temperature gradient about its length.

The Seebeck effect is the phenomenon directly related to
thermoelectric generation. According to the Seebeck effect,
thermoelectric generation occurs in a circuit containing at
least two dissimilar materials having one junction at a first
temperature and a second junction at a second different
temperature. The dissimilar materials giving rise to thermo-
electric generation in accordance with the Seebeck effect are
generally n-type and p-type semiconductors.

While these thermoelectric principles have been known
for more than a century, the extreme high cost of generating
even a small amount of electricity has prevented any wide-
spread use of these thermoelectric effects for power genera-
tion. In fact, previously the Seebeck effect has been
employed almost exclusively for thermocouples. Thermo-
couples in accordance with the Seebeck effect allow tem-
perature measurement based upon a current induced in
couples of metals, such as PT-Rh or Fe-Constantan.
However, these couples cannot be advantageously used to
generate electricity.

SUMMARY OF THE INVENTION

A thermoelectric generator consistent with the invention
includes a couple of bismuth telluride thermoelectrodes,
wherein one thermoelectrode is doped with either palladium
(Pd) or selenium (Se), and the other thermoelectrode of the
couple is doped with either antimony (Sb) or gold
Accordingly, the thermoelectric generator consistent with
the present invention achieves highly efficient thermoelec-
tric conversion.

A method for producing thermoelectrodes consistent with
the invention herein is provided wherein the individual
constituent metals are first purified. Following purification
the constituent metals of cach thermoelectrode are combined
in precise stoichiometric ratios to produce stock salts.
Finally, the stock salts are subjected to a sliding electrical

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resistance whereby the stock salts experience directional
fusion. The directional fusion process produces an oriented
crystalline structure in the final salts.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are set forth in
the following description as shown in the drawings,
wherein:

FIG. 1 schematically illustrates an exemplary thermoelec-
tric module consistent with the present invention;

FIG. 2 schematically illustrates an exemplary thermoelec-
tric cell consistent with the present invention, comprising a
plurality of thermoelectric modules as shown in FIG. 1; and

FIG. 3 illustrates a first exemplary apparatus employing,
the thermoelectric modules consistent with the present
invention.

DETAILED DESCRIPTION OF THE
INVENTION

Referring to FIG. 1, the basic element of an exemplary
thermoelectric pile consistent with the present invention is
an individual thermoelectric module, shown at 10. The
individual thermoelectric module 10 consistent with the
present invention comprises a couple of thermoelectrodes 12
and 14, i.c., a junction formed between two semiconductor,
termed thermoelectrodes. Each couple comprises a positive
thermoelectrode 12 and a negative thermoelectrode 14,
wherein the two thermoelectrodes are electrically coupled in
a manner suitable to provide good continuity over the
service temperature range of the element 10. In the exem-
plary embodiment illustrated in FIG. 1, the positive ther-
moelectrode 12 and the negative thermoelectrode 14 may be
physically and electrically coupled via an aluminum
connector, or strap, 16 soldered to the respective interfaces
18 and 20 of cach of the two thermoelectrodes 12 and 14. An
exemplary solder compound which may advantageously be
employed comprises 60% tin-40% lead. Finally, the exem-
plary thermoelectric module 10 is completed by sandwich-
ing the assembled positive and negative thermoelectrodes 12
and 14 between two thin sheets of alumina 22 and 24,
thereby providing the thermoelectric module 10 in the form
of a wafer or chip.

Consistent with the present invention, the positive then-
noelectrode 12 and the negative thermoelectrode 14 may
each comprise bismuth telluride. The relative thermoelectric
polarity of each of the thermoelectrodes may be controlled
by the incorporation of a dopant. According to the exem-
plary embodiment consistent with the present invention the
positive thermoelectrode 12 may be formed by doping the
bismuth telluride electrode with antimony (Sb) or gold (Au).
The negative thermoelectrode 14 may be formed by doping
bismuth telluride with palladium (Pd) or selenium (Se).
Because bismuth telluride ejects electrons along the con-
ductive orbitals when heated as the thermoelectric couple 10
is heated on one side, the electrons migrate from the positive
thermoelectrode 12 to the negative thermoelectrode 14,
therein producing a current.

Performance of the thermoelectric modules 10 consistent
with the present invention may be optimized by employing,
the semiconductors, i.e., the thermoelectrodes 12 and 14, in
the form of salts bound in regular and equal crystals.
Reaching this configuration requires that the constituent
ingredients first be refined to an extremely high state of
purity. Subsequent to refining, the positive and negative salts
must be formed. Finally, the crystals of the respective
positive and negative salts must be oriented.

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US 6,620,994 B2

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In order to obtain the optimum performance, it is prefer-
able to obtain a 99.99% purity level in individual constituent
metals. This level of purity requires a multi-step refinement
process. In the refinement process a 99.5% purity in the
constituent metals, bismuth, tellurium, antimony, and
selenium, may be achieved. The metals may be placed in
individual crucibles and fused in a vacuum environment.
The fused metals may then be placed in individual quartz
ampoules and a sliding electric resistance may be induced
therethrough, thereby inducing a directional fusion. The
walls of the quartz ampoules may be coated with activated
carbon which will absorb impurities and act as a lubricant
for the subsequent extraction of the purified bars. The
directional fusion may be carried out at a speed of between
about 5-25 mm per hour, thereby extracting the impurities
and oxygen from the metals.

After the constituent metals have been purified, the salts
may be produced by mixing and fusing the metals in exact
stoichiometric ratios while under vacuum. To produce the
exemplary positive salt bismuth, tellurium, and antimony
may be combined in a crucible in a 2:3:3 stoichiometric
ratio. Correspondingly, the negative salt may be formed by
combining bismuth, tellurium and selenium in a crucible in
a 2:3:3 stoichiometric ratio. The crucible may be agitated
during the fusion process to provide adequate mixing of the
metals.

After the metals have been mixed and fused, the crystals
of the salts are aligned to allow the electrons freed during the
thermoelectric generation to move with a minimum of
resistance through the crystalline structure. The alignment of
the crystals may be accomplished by directional fusion of
each of the salts. As during refinement of the metals, each of
the fused salts is transferred to a quartz ampoule containing
activated carbon lined walls. The directional fusion of the
salts may be carried out at a rate of 2-3 mm per hour. During
experimentation, the power consumption for producing salts
having oriented crystal structures is approximately 30 kW
per kilogram of salt.

Following the orientation of the crystal structures of the
salts, the salts are extracted from the quartz ampoules and
sliced into wafers. The cutting of the salt bars may be carried
out by employing laser cutting. During the cutting operation,
respect should be given to the direction of the directional
fusion, i.¢., the orientation of the crystals. The positive and
negative salt wafers are finally assembled, soldered, and
sandwiched between alumina wafers as described previ-
ously. It should be appreciated that all of the above described
refinement, orientation, and assembly operations may
advantageously be automated, therein minimizing human
error and involvement.

Experimental performance evaluations have been con-
ducted on the exemplary embodiment discussed above. A
thermoelectric module 10 having a positive thermoelectrode
12 and a negative thermoelectrode 14 each dimensioned 5
mmx5 mmx1 mm thick will perform as follows:

ratio watts/surface area=10 W/em*

ratio of weight/watts=1 g/W

ratio of weight/surface area=10 g/cm*

Accordingly, a module 10 weighing 1 kg and having a
surface area of 10 cmx10 cm can generate 1 kW of electric
power.

FIG. 2 schematically illustrates an exemplary thermoelec-
tric generation cell 100, herein also referred to as a chip,
consistent with the present invention. The chip 100 is shown
comprising three individual thermoelectric modules 10a,
106, 10c, corresponding to the thermoelectric module illus-

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trated in FIG. 1, however the number of individual modules
is widely variable. Accordingly, the chip comprises three
positive thermoelectrodes 102a—c and three negative ther-
moelectrodes 104a-c. As illustrated, the positive thermo-
electrodes 102a—c and the negative thermoelectrodes
104a-c are connected in electrical series by aluminum straps
106a-e. Finally, the chip 100 is completed by providing an
two alumina wafers 108 and 110, one to either side of the
thermoelectric generation cell 100.

Many alternate embodiments consistent with the present
invention may be derived from the above described chip
100. The number of individual modules may be varied
according to specific needs, and the positive thermoelec-
trodes 102 and the negative thermoelectrodes 104 may be
configured in other than a planar and linear arrangement. It
is only required that the modules be connected in electrical
series and thermal parallel. Accordingly, while aluminum
straps 106 are preferred, any conductive material will per-
form this function, including, but not limited to, copper, iron
alloys, tin, gold, etc. Similarly, the alumina layers may be
replaced by various material. It is preferred that the outer
layers provide high thermal conductivity, but it is only
necessary that they be electrically insulating. Accordingly,
the alumina layers may be replaced with glass, mineral
products, polymeric materials, etc. These and other varia-
tions will become more apparent from the following work-
ing examples consistent with the present invention.

A first exemplary method for employing the thermoelec-
tric generation cell is illustrated in FIG. 3. According to this
application, a plurality of thermoelectric chips 100a—e are
arranged spaced apart and in parallel to one another within
a container 101, whereby the chips 100a-—e act as partitions
within the container 101. The spaces between the chips
100c-e are alternately in communication with either a
heating medium supplied by manifold 111, or a cooling
medium supplied from manifold 113. Exemplary heating
mediums may include heated water, steam, or heated oil,
while the cooling medium is preferably chilled water, air, or
refrigerant. Accordingly, when the heating and cooling
mediums are caused to flow through the spaces between the
chips 100a—e, the requisite temperature gradient is estab-
lished to drive the thermoelectric generation.

In the above described example, the heating medium may
include the exhaust coolant from an industrial application or
an internal combustion engine. Many industrial processes
generate a great deal of heat that must be taken away be
coolants. The coolants that become heated during the cool-
ing cycle are then typically either exhausted into the
environment, such as a water way, or are recycle and
rechilled for further use. As an intervening step before
exhaust or recycling the coolant may be run through an
apparatus consistent with FIG. 3 whereby the extracted
thermal energy may be put to the beneficial use of generating
electricity.

The thermoelectric generator consistent with the present
invention may similarly be utilized in any application where
waste heat is generated. For example, a thermoelectric
generator may be applied to the exhaust manifold of an
engine, such as an automobile engine. The thermal energy
for the thermoelectric generator is supplied by the hot
exhaust gas, while a heat sink in the air stream of the moving
vehicle may be employed on the “cold side” of the generator.

Similarly, the thermoelectric couples may be attached to
the compressor of a refrigeration unit. The thermoelectric
modules may be applied to a sheet of ZENITE, a liquid
crystal polymer produced by DuPont, which is a good
thermal conductor and electrical insulator. The cold side of

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US 6,620,994 B2

5

the thermocouples may be cooled by providing them with a
heat sink which is in the air stream of the refrigerator’s
cooling fan.

Thermoelectric generation may also be driven by a ther-
mochemical reaction. An exemplary such reaction is based
on the strong affinity of palladium for deuterium during the
electrolysis reaction of deuterium oxide. The thermoelectric
generator may be configured such that the positive pole of
the thermoelectric generator is connected to a platinum
anode and the negative pole of the thermoelectric generator
is connected to a palladium cathode. The two electrodes are
immersed in a bath of deuterium oxide contained within a
glass heat exchanger. The heat exchanger is thermally
coupled to the hot side of the thermoelectric generator. Once
the reaction has been initiated using an external power
source, sufficient heat will be evolved to sustain the reaction
using the thermoelectric generator. The cold side of the
thermoelectric generator may be cooled by means such as a
heat sink and a fan or fluid forced convention, as by cooling,
water.

As a final exemplary application of the present invention,
spent nuclear fuel rods may be used as the source of thermal
energy, thereby fully utilizing the available energy in the fuel
rod before it is discarded. The thermoelectric generators may
be applied directly to the fuel rods using steel straps.
Cooling of the “cold” side of the thermoelectric generator
may be accomplished by providing the cold side with a heat
sink and submerging the fuel rod in a cooling pool.
Alternately, cooling may be accomplished by providing a
circulating coolant in contact with the cold side of the
thermoelectric generator.

The individual thermoelectric modules consistent with the
present invention may be arranged electrically in series
and/or in parallel to achieve the desired voltage and current
output. Furthermore, any of the above embodiments consis-
tent with the present invention may advantageously incor-
porate an inverter capable of providing an alternating current
electrical output from the direct current produced by the
thermoelectric generator. Additionally, it will be appreciated
that batteries, or other electrical storage devices, may also be
employed in conjunction with the invention herein.

It will be appreciated that the exemplary embodiment
described and depicted in the accompanying drawings
herein is for illustrative purposes only, and should not be
interpreted as a limitation. It is obvious that many other
embodiments, which will be readily apparent to those skilled
in the art, may be made without departing materially from
the spirit and scope of the invention as defined in the
appended claims.

What is claimed is:

1. A method of producing a thermoelectrode comprising:

forming a salt by combining purified bismuth and purified
tellurium with at least one of selenium, palladium,
antimony, and gold in a 2:3:3 stoichiometric ratio;

directionally fusing the salt to produce an oriented erys-
talline structure in the salt.

2. The method according to claim 1 wherein the step of
forming the salt comprises directionally fusing the bismuth,
tellurium and at least one of selenium, palladium, antimony,
and gold individually at a rate of between about 5-25 mm
per hour.

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3. The method according to claim 2 wherein the step of
directionally fusing comprises applying a sliding resistance
to the bismuth, tellurium and at least one of selenium,
palladium, antimony, and gold.

4. The method according to claim 1 wherein the step of
directionally fusing the salt to produce the oriented crystal-
line structure comprises directionally fusing the salt at a rate
of between about 2-3 mm per hour.

5. The method according to claim 1 wherein the step of
directionally fusing the salt comprises applying a sliding
resistance to the salt.

6. A method of producing a thermoelectrode comprising:

forming a salt by combining bismuth and tellurium with
at least one of selenium, palladium, antimony, and gold;
and

producing an oriented crystalline structure in said salt;

wherein said oriented crystalline structure is produced by

directionally fusing said salt.

7. The method according to claim 6 wherein said salt is
formed by directionally fusing said bismuth, tellurium and at
least one of selenium, palladium, antimony, and gold indi-
vidually at a rate of between about 5-25 mm per hour.

8. The method according to claim 7 wherein said direc-
tionally fusing said salt comprises applying a sliding resis-
tance to said bismuth, tellurium and at least one of selenium,
palladium, antimony, and gold.

9. The method according to claim 6 wherein said direc-
tionally fusing said salt comprises directionally fusing said
salt at a rate of between about 2-3 mm per hour.

10. The method according to claim 6 wherein said direc-
tionally fusing said salt comprises applying a sliding resis-
tance to said salt.

11. The method according to claim 6, wherein said
bismuth and said tellurium are purified.

12. Amethod of producing a thermoelectrode comprising:

forming a salt by combining bismuth and tellurium with

at least one of selenium, palladium, antimony, and gold;
and

producing an oriented crystalline structure in said salt;

wherein said bismuth and tellurium are combined with

said at least one of selenium, palladium, antimony, and
gold in a 2:3:3 stoichiometric ratio.

13. The method according to claim 12 wherein said salt is
formed by directionally fusing said bismuth, tellurium and at
least one of selenium, palladium, antimony, and gold indi-
vidually at a rate of between about 5-25 mm per hour.

14. The method according to claim 13 wherein said
directionally fusing said salt comprises applying a sliding
resistance to said bismuth, tellurium and at least on of
selenium, palladium, antimony, and gold.

15. The method according to claim 12 wherein said
directionally fusing said salt comprises directionally fusing
said salt at a rate of between about 2—3 mm per hour.

16. The method according to claim 12 wherein said
directionally fusing said salt comprises applying a sliding
resistance to said salt.

17. The method according to claim 12, wherein said
bismuth and said tellurium are purified.

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